SERVXXXX November 2005
GLOBAL SERVICE LEARNING TECHNICAL PRESENTATION
966H AND 972H WHEEL LOADERS
Service Training Meeting Guide (STMG)
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TABLE OF CONTENTS TABLE OF CONTENTS INTRODUCTION ..................................................................................................................5 Similarities and Differences .............................................................................................6 Component Location.........................................................................................................9 ENGINE................................................................................................................................13 Electrical Block Diagram ...............................................................................................16 COOLING SYSTEM............................................................................................................22 POWER TRAIN ...................................................................................................................27 Power Flow .....................................................................................................................27 Transmission Hydraulic System .....................................................................................32 Power Train Electrical System .......................................................................................51 Component Locations and Functions .............................................................................54 IMPLEMENT HYDRAULIC SYSTEM..............................................................................71 Pilot System ....................................................................................................................73 Main Hydraulic System ..................................................................................................79 Implement Hydraulic System Schematic .......................................................................87 Implement Oil Cooling System ......................................................................................90 Autolube System.............................................................................................................91 STEERING HYDRAULIC SYSTEM..................................................................................93 Steering System Components ........................................................................................93 Steering Hydraulic System Schematic ........................................................................100 STEERING AND BRAKE ................................................................................................107 BRAKE HYDRAULIC SYSTEM .....................................................................................108 Brake System Schematic ..............................................................................................108 Brake Component Locations .......................................................................................110 CONCLUSION...................................................................................................................114 SLIDE LIST........................................................................................................................115 HANDOUTS.......................................................................................................................117
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966H AND 972H WHEEL LOADERS AUDIENCE Level II - Service personnel who understands the principles of machine system operation, diagnostic equipment, and procedures for testing and adjusting.
CONTENT This presentation describes the location of the basic components on the engine, and the operation of the power train, implement, steering, and brake systems for the 966H and 972H Wheel Loader. This presentation may be used for self-paced and self-directed training.
OBJECTIVES After learning the information in this presentation, the technician will be able to: 1. Locate and identify the major components in the C11 and C13 ACERT™ engine, power train, implement, steering, and brake systems; 2. Explain the operation of each component in the power train, implement, steering, and brake systems. 3. Trace the flow of oil through the power train, implement, steering, and brake systems..
REFERENCES "966H Wheel Loader Specalog "972H Wheel Loader Specalog "966H and 972H Wheel Loader Service Manual 966H Wheel Loader Parts Book” 972H Wheel Loader Parts Book” NPI Vol. 9, No. 1 "966H and 972H Wheel Loader TIM "966G Series II Wheel Loader Power Train" TIM "966G Series II Wheel Loader Hydraulic System"
Estimated Time: 1 Hour Illustrations: 32 Handouts: 4 Form: SERVXXXX Date: 11/05 © 2005 Caterpillar Inc.
AEHQ5657 AEHQ5658 RENR8840 SEBP3743 SEBP3744 SERV7109 SERV2739 SERV2740
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966H AND 972H II WHEEL LOADERS
© 2005 Caterpillar Inc.
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INTRODUCTION This presentation discusses the component locations and systems operation of the 966H and 972H Wheel Loader. Basic engine and machine component operation will be discussed. The new C11 and the C13 ACERT™ engines, the power train, proportional priority, pressure compensated implement hydraulics, the steering, and braking system operation will be covered. The 966H and 972H are medium wheel loaders in the Caterpillar product line. The serial number prefix for the 966H is A6D Aurora built (A6G Gosselies, A6J Sagami) and the serial number for the 972H Wheel Loader is A7D Aurora built (A7G Gosselies, A7J Sagami). The 966H operating weight is approximately 23,100 Kg (51,000 lbs) and the 972H operating weight is approximately 25,000 Kg (55,400 lbs). The color codes used for hydraulic oil throughout this presentation are: Red
- System or high pressure
Red and White Stripes
- First reduced pressure
Orange
- Pilot pressure
Blue
- Blocked oil
Green
- Tank or return oil
Yellow
- Active component
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2 Component Location This illustration shows the basic component locations on the 966H and 972H. The component locations on the 966H and 972H are basically the same as in the G series II Wheel Loaders. Power for the 966H is supplied by the C11 ACERT™ and the power for the 972H is supplied by the C13 ACERT™ engine. Power flows from the engine to the torque converter, to the Electronic Clutch Pressure Controlled (ECPC) transmission, through the output transfer gear to front and rear drive shafts. From the drive shafts, to the bevel gears in the differentials, and through the axles. The wheel loader is equipped with a steering pump, steering valve and steering cylinders. Also, the machine is equipped with electrohydraulic implement control with a variable displacement implement piston pump supplying oil to the 3PC hydraulic valve located in the loader frame. The machine may be equipped with an optional electric secondary steering pump that is installed inside the rear frame. The wheel loader is equipped with an on demand hydraulic fan system and brake system that share a common variable displacement piston pump and accumulator charging valve. The oil uses a priority valve with the brake system having priority over the hydraulic fan system. The brake system includes the front and rear service brakes and hydraulically released parking brake.
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3 IMPLEMENT ELECTROHYDRAULIC SYSTEM The "H" Series Medium Wheel Loader is equipped with a Proportional Priority, Pressure Compensated (3PC) implement electrohydraulic system. The 3PC electrohydraulic system will sense a demand for a flow change and the implement pump will upstroke or destroke in order to provide the demanded flow. The following components make up the 3PC electrohydraulic system. - Implement Electronic Control Module (ECM) - Lift and tilt position sensor - Implement pump - 3PC electrohydraulic control valve - Lift and tilt cylinders - Ride control accumulator - Implement control levers - Hydraulic tank (hydraulic tank is common to all the hydraulic systems)
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4 Implement Electronic Control System This diagram of the Implement Electronic Control System shows the components which provide input and output signals to the Implement ECM The Implement Electronic Control Module (ECM) receives input signals from the various sensors and switches on the machine, processes the input signals, makes decisions, and provides a corresponding signal voltage to the proportional solenoid valves. The Implement ECM stores information from the calibrations, machine settings and operational functions. The Implement ECM monitors diagnostic conditions and reports events to the Cat Monitoring System or to Cat Electronic Technician (ET). Also, the Implement ECM provides a means of calibrating the electrohydraulic components for optimal operation. The Implement ECM shares operational data with the other ECMs and the Cat Monitoring System through the Cat data link.
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+24 Volts: Unswitched power supplied to the Power Train ECM from the battery. Location code enable (grounded): The location code enable is a grounded input signal to the Implement ECM that enables the location code detection feature to become active. Location code 4 (grounded) : The location code pin number 4 is a grounded input signal that establishes the ECM is dedicated to the Implement operation. The output components which receive signals from the Implement ECM are: Pilot solenoid valve: This ON/OFF solenoid valve is an output from the Implement ECM. This valve opens the flow of pilot oil to the pilot valves. Raise solenoid valve: This proportional solenoid valve is an output from the Implement ECM. This solenoid valve sends a proportional amount of pilot oil to the raise end of the lift stem depending on the amount of current applied to the solenoid. Lower solenoid valve: This proportional solenoid valve is an output from the Implement ECM. This solenoid valve sends a proportional amount of pilot oil to the lower end of the lift stem depending on the amount of current applied to the solenoid. Dump solenoid valve: This proportional solenoid valve is an output from the Implement ECM. This solenoid valve sends a proportional amount of pilot oil to the dump end of the tilt stem depending on the amount of current applied to the solenoid. Tilt back solenoid valve: This proportional solenoid valve is an output from the Implement ECM. This solenoid valve sends a proportional amount of pilot oil to the tilt back end of the tilt stem depending on the amount of current applied to the solenoid.. Auxiliary HE solenoid valve: This proportional solenoid valve is an output from the Implement ECM. This solenoid valve sends a proportional amount of pilot oil to the head end of the auxiliary stem depending on the amount of current applied to the solenoid. Auxiliary RE solenoid valve: This proportional solenoid valve is an output from the Implement ECM. This solenoid valve sends a proportional amount of pilot oil to the rod end of the auxiliary stem depending on the amount of current applied to the solenoid. Low fuel pressure indicator: This indicator is illuminated when the fuel pressure is reported low from the engine ECM over CAT datalink. Lower anti drift solenoid valve: This ON/OFF solenoid valve is a current output from the Implement ECM. The solenoid valve drains oil from the anti drift valve allowing the poppet to unseat and lift cylinder head end oil to flow through the valve.
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The input components to the Implement ECM are: Key switch ON: Input to the Implement ECM signaling the ECM to power ON. Lift linkage position sensor: Sends a PWM signal to the implement ECM communicating the position of the lift linkage in relation to the loader frame. Tilt linkage position sensor: Sends a PWM signal to the implement ECM communicating the position of the tilt linkage in relation to the lift linkage. Lift lever position sensor: Sends a PWM signal to the implement ECM communicating the angle of the lift lever position sensor away from the calibrated HOLD position. Tilt lever position sensor: Sends a PWM signal to the implement ECM communicating the angle of the tilt lever position sensor away from the calibrated HOLD position. Auxiliary lever position sensor: Sends a PWM signal to the implement ECM communicating the angle of the auxiliary function lever position sensor away from the calibrated HOLD position. Kickout set switch lift/tilt: Sends an input to the Implement ECM to recognize the desired raise/lower/tilt back kickout position. Autodig trigger switch: Sends an input signal to the Implement ECM when the operator has pressed the switch to indicate that the loading cycle should begin. Autodig select mode switch: Sends an input signal to the Implement ECM to signal if autodig should be off or in which mode it should operate (auto, operator trigger or record). Autodig dig mode switch: Sends an input signal to the Implement ECM to recognize what type of operation is currently desired due to the type of material that is being handled. Autodig kickout set switch: Sends an input signal to the Implement ECM to set the current position of the lift arms to be the position where autodig stops after a completed autodig cycle. Lift head end hydraulic pressure sensor: Measures the pressure of the head end of the lift cylinder to determine operation of autodig. Fine modulation switch: Sends an input signal to the Implement ECM to reduce the amount of current to the raise solenoid valve. Hydraulic lockout switch: Sends an input signal to the Implement ECM to not energize the pilot solenoid valve to protect from inadvertent movement of the lift arms.. Auxiliary continuous flow switch: Sends an input signal to the Implement ECM keep the auxiliary function output to the solenoid valve at the current that was being commanded at the time of the switch being depressed. This mode can be exited by depressing the switch again or moving the auxiliary lever.
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Dump anti drift solenoid valve: This ON/OFF solenoid valve is a current output from the Implement ECM. The solenoid valve drains oil from the anti drift valve allowing the poppet to unseat and tilt cylinder head end oil to flow through the valve. Autodig operator trigger mode indicator: This indicator is illuminated when the Implement ECM recognizes that autodig operator trigger mode is activated. Autodig Auto Trigger mode indicator: This indicator is illuminated when the Implement ECM recognizes that autodig auto trigger mode is activated. Autodig audible indicator: This audible indicator beeps when the Implement ECM recognizes that a different autodig mode have beeen activated and to confirm a setting or to warn about failed autodig operations.
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The upper illustration shows the lift linkage position sensor (1). The lift linkage position sensor is located on the right side of the loader frame. The lower illustration shows the location of the tilt linkage position sensor (2). The lift linkage position sensor is located on the right side of the lift linkage. The tilt linkage position sensor shaft is attached to the tilt lever pin reflecting the rotation of the tilt linkage compared to the lift linkage. NOTE: In order to calibrate the lift or tilt linkage position sensors, refer to the Service Manual module “966H and 972H Wheel Loaders Electrohydraulic System, troubleshooting ,testing and Adjusting - Position Sensor for the Lift and Tilt Linkage (Electronic Technician) - Calibrate or Position Sensor for the Lift and Tilt Linkage (Operator Monitor) - Calibrate” (Form RENR 8858)
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Implement Control Levers The implement control levers send a pulse with modulated signal to the Implement ECM with the position of the control lever. In the HOLD position, the sensor in each lever sends a 50% duty cycle. The movement of each lever in the forward or reverse direction will increase the duty cycle to 90% or decrease to 10% depending to the direction that the lever is moved. The "H" Series machines are a self-contained single axis lever equipped with a single sensor and no mechanical or electrical detents. The frequency of the sensor is 500Hz. The self contained single axis lever is equipped with "Soft detents". With "Soft detents" the control levers are no longer held in place mechanically. The detents are software controlled within the Implement ECM. When the control lever is moved in either direction into a area of movement with a slight resistance and the lever is released within 1 second, the actuator will continue to move until the software controlled kickout is reached. When the control lever is moved in either direction and the lever is not released within 1 second, the actuator will continue to move under lever control. During troubleshooting of a control lever or joystick, always move the control lever both fast and slow through lever movement. The duty cycle for the control lever can be viewed through Caterpillar ET. The following are the functions of the control levers: Tilt control lever (1), Lift control lever (2), and Auxiliary control lever (3).
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9 Fine Modulation allows the operator to reduce the lever sensitivity for the first 2/3 of lever travel (adjustable range) to provide better control of the linkage for smaller movements. The last 1/3 of lever travel increases to maximum modulation current to provide full flow to the cylinder. The fine modulation value can be adjusted independently for the lift and tilt levers using the configuration screen in the ET Service Tool. The fine modulation default setting is 59 percent of the normal lever modulation current. The fine modulation feature can be turned ON and OFF using the fine modulation switch in the cab on the right side armrest.
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The kickout set switch (1) is an input to the Implement ECM. The kickout set switch is a momentary three position rocker switch located on the operator panel. The kickout set switch is used to set the kickout positions for the raise and lower kickout. When the switch is pushed, the ECM records the current position of the lift arm. The ECM uses the recorded position for the raise kickout position or the lower kickout position. If the upper position of the kickout set switch is depressed and the lift arm is above midway, the kickout will be set for raising the lift arm. If the upper position of the kickout set switch is depressed and the lift arm is midway below halfway, the lower kickout will be set. If the lower position of the kickout set switch is depressed the rotation of the tilt back will be set.
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The two switches that are located to the right of the operator’s seat control functions of the implement hydraulic system. The hydraulic lockout switch (1) sends an input to the Implement ECM to shift the hydraulic lockout solenoid valve to the OPEN position. The fine modulation switch (2) is an input to the Implement ECM. The fine modulation switch allows the operator to request a lower ramp up current relative to the standard lever curves during the first two-thirds of control lever movement. In the final one-third of the control lever travel, the commanded current is the same as the standard control lever curve.
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11 Autodig Control Arrangement Autodig automatically controls the implement system cycles. At the same time Autodig limits the tire slippage by keeping the front tires loaded. There are three modes that Autodig can operate in: Automatic Pile Detection Mode, Operator Triggered Mode, and Record Mode. The Autodig operation mode switch (2) activates Autodig when the top of the switch is pressed and deactivates Autodig when the bottom of the switch is pressed. When Autodig is ON, the spring-loaded switch is held in the center position. Pressing the top of the switch will allow the operator to toggle between the three operating modes. Autodig is disabled by default when the key start switch is turned ON. The automatic pile detection mode indicator (5), operator triggered mode indicator (6), and the record mode indicator (7) flash ON and OFF to indicate the mode that is currently active.
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The Autodig horn also indicates which mode is active by beeping once in the automatic pile detection mode, twice in the operator triggered mode, and three times in the record mode. The Autodig horn also sounds to indicate when Autodig begins and ends a bucket loading cycle. The Autodig kickout position set switch (3) is used to set the lift cylinder kickout position when Autodig is activated. The Autodig dig mode switch (1) is a 10 position rotary switch which provides a range of dig modes from the lightest material in position 1, to heavier or larger material in position 9. Position 10 on the Autodig dig mode switch is used for the record/playback position. By default, position 10 is identical to position 9 until the operator has recorded a bucket loading cycle. Autodig will downshift the transmission to an appropriate gear for loading, based on the position of the autodig material selector switch. In positions 1 or 2 (light material), the transmission will downshift only to 2nd gear. The machine will load in 1st gear if already in that gear when bucket loading starts. With the Autodig material selector switch in positions 3 through 9, the transmission will automatically downshift to 1st gear upon pile entry, regardless of the position of the autoshift selector switch if the machine is in 2nd or 3rd gear. Automatic pile detection mode automatically controls bucket loading. When loading is complete, the bucket and linkage return to the Autodig kickout position. The operator triggered mode is used if the operator wants to control the loading cycle. In the operator triggered mode, Autodig is activated when the operator presses the trigger switch (4) to indicate when the pile has been contacted. After the trigger switch is pressed, the system automatically loads the bucket and returns the bucket and linkage to the Autodig kickout position. Record mode allows the operator to record the bucket loading cycle and replay the cycle if the preprogrammed modes are not acceptable. Autodig records all lever movements while loading the bucket. The lever movements are stored in the record/playback position of the Autodig selector switch.
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12 The following conditions are required to properly load the bucket with Autodig: - Autodig is ON - Lift linkage is less than 2 feet off the ground - Bucket angle is less than 10 degrees from level - Machine speed is greater than 0.7 kph and less than 12.3 kph - Transmission is in 1st, 2nd or 3rd gear FORWARD - No directional changes in last 2.0 seconds - No gear changes in last 0.5 second - Neutralizer is not active, and has not been active for the last 0.5 second - Lift and tilt levers are centered
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13 IMPLEMENT HYDRAULIC SYSTEM Implement Hydraulic System - Hold The "H" series Medium Wheel Loaders are now equipped with a Proportional Priority, Pressure Compensated (3PC) implement hydraulic system. The 3PC hydraulic system is load sensing with a signal duplication valve, signal relief valve, pressure compensator valves, pressure differential relief valve, pressure reducing valve and a resolver network. Also, the 3PC valve has anti-drift solenoid valves for the lift and tilt functions. The implement control valve is a closed center valve. The 3PC hydraulic system will sense a demand for a change in flow and the implement pump will upstroke or destroke to provide the flow. The machine may also be equipped with an optional auxiliary function. The auxiliary section is installed between the ride control valve and the cover manifold.
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When the engine is started and the implement control levers are in the HOLD position, the implement pump supplies standby oil flow to the 3PC valve group. The oil flows into the inlet manifold and is divided into two paths. The supply path for the implements flows through the inlet manifold into the tilt section where the flow path is divided again. One path flows to the tilt stem and is blocked. The second path flows to the lift control section, to the ride control section, to the optional auxiliary section, and to the cover manifold. Within the cover manifold, the oil flows to both the pilot pressure reducing valve (PRV) and the differential pressure relief valve. The differential pressure relief valve maintains a difference between the load sensing pressure and the pump supply oil pressure of 3000 kPa (435 psi). When all of the control valves are in the HOLD position, the implement pump is at low pressure standby. The differential pressure relief valve maintains the minimum pressure for low pressure standby. The standby pressure is directed to the pilot pressure reducing valve (PRV), and the pilot pressure reducing valve provides a regulated pilot oil pressure to activate the control valves as needed. The pilot oil flows from the PRV through the check valve to the pilot accumulator and the hydraulic lockout solenoid valve. If the wheel loader is equipped with the optional Command Control Steering (CCS), the oil flow will be shared by the implement pilot system and the steering pilot system. The hydraulic lockout solenoid valve is in the CLOSED position until the hydraulic lockout switch in the cab is activated. When the solenoid valve is energized, the solenoid valve opens and pilot oil flows to the various implement function solenoid valves. The second path of oil in the inlet manifold flows through the screen to the signal duplication valve. The signal duplication valve uses highest work port pressure in the resolver network to supply an identical pressure to the pump control valve. When all implement control valves are in the HOLD position, there is no load sensing signal in the resolver network. With no load sensing pressure present, the implement pump supplies low pressure standby.
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15 Implement Hydraulic System - DUMP When the tilt lever is moved to the DUMP position, the Implement ECM energizes the dump proportional solenoid and the tilt anti-drift valve. As the control valve initially shifts to the left, and there is pressure in the rod end of the tilt cylinder, the pressure goes around the control spool to the bridge passage. The pressure in the bridge passage goes to the resolver network and to the signal duplication valve to upstroke the implement pump. The pressure also goes to the spring chamber in the center of the pressure compensator valve. The lower half of the pressure compensator valve shifts down to block the oil flow from the bridge passage to the feeder passage. As the tilt control spool continues shifting to the left, pump supply oil flow around the center land on the control spool to the feeder passage. Oil pressure in the feeder passage lift the pressure compensator valve up. Pump flow goes the through the opening in the lower end of the compensator valve to the bridge passage. From the bridge passage the pump flow goes around the right end of the control spool into the work port to the rod end of the tilt cylinder. Return oil from the head end of the tilt cylinder flow around the tilt anti-drift valve and the left end of the control spool to the tank port.
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16 Pressure Compensator Valve - HOLD Position When the control spool is in the HOLD position, the load check spool and the pressure compensator valve are held down by the spring force on top of the load sense spool. Pump supply oil in the supply passage is blocked by the control spool. No supply oil from the supply passage flows to the feeder passage. Therefore, no load sensing pressure is directed to the implement pump control valve. The implement pump is destroked.
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14 Tilt Control Valve - HOLD With the tilt control valve in the HOLD position, the springs on each end of the control spool keep the spool centered. The control spool blocks the flow of pump supply oil to the pressure compensator valve. The bridge passage is open to tank through the internal passage in the control spool and there is no oil flow to the resolver valve. With no oil flow to the resolver network, there is no signal to the signal duplication valve and the signal pressure to the pump control valve is matching the oil pressure in the resolver network. The implement pump is supplying low pressure standby.
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17 Load Check Operation This illustration shows the pressure compensator and load check valve in the load check operation. When the control spool is initially shifted to the left, work port pressure from the rod end of the cylinder (if any) flows around the right end of the control spool into the bridge passage. The pressure goes through the holes between the pressure compensator valve and the load check spool. The pressure moves the pressure compensator spool down and the load check spool up. With the pressure compensator valve shifted down, no pressure can go from the bridge passage to the feeder passage. The pressure compensator valve serves as a load check valve to hold the load up to prevent it from dropping. The pressure in the bridge passage is directed through the resolver network to the signal duplication valve. The signal duplication valve generates a load sensing signal pressure equal to the work port pressure. The load sensing signal pressure is directed to the top of the spring chamber on top of the load sense spool. The load sensing signal pressure is also directed to the pump control valve to upstroke the pump.
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15 Pressure Compensator Operation Three compensators are shown in various states in this illustration. The pressure compensator valve for valve "A" is in HOLD. The circuit with the highest work port pressure keeps the resolver valve closed. The circuit with the highest work port pressure regulates the oil flow through all activated control valves. The highest work port pressure is directed through the ball resolver network to the pump control valve as the load sensing pressure When a high pressure circuit is activated as shown for valve "C", the control spool is shifted and pump supply oil enters the feeder passage below the pressure compensator valve. Pressure increases and the pressure compensator valve moves up. When the valve moves up, supply oil enters the bridged passage of the control valve. Supply oil in the bridged passage enters the signal network sending the work port pressure to the signal duplication valve.
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The work port oil pressure goes to the signal duplication valve. The signal duplication valve is a shock absorber. The valve uses work port pressure signal and the pump system pressure signal to generate a stabilized load sensing signal which is sent to the pump control valve. The pump control valve directs a pressure signal to the actuator piston to UPSTROKE the pump. The increased flow lifts the pressure compensator spool up. The flow goes through the bridge passage, around the control spool and out to the work port. The signal oil also flows to the chamber above the compensator. The signal oil on the top of the pressure compensator valve works against the forces working below the pressure compensator. When the forces are in balance, the supply oil is metered through the crossdrilled holes in the pressure compensator to provide work port oil. The pressure of the signal oil is limited by the signal relief valve. When more than one circuit is activated at the same time, the highest work port pressure is directed to the signal duplication valve. The signal duplication valve sends the signal oil to the chamber at the top of all pressure compensators valves. With the same circuit pressure working on all pressure compensators, the pressure differential across all shifted control stems is the same, as shown in the illustration for the pressure compensator for valve "C" and for valve "B." The pressure differential across the control stems will be the same value whether the pump can supply the flow demand for all activated circuits or not. For example, if the margin pressure is 2100 kPa (300 psi) the pressure differential between the pump supply passage and the feeder passage is approximately 2100 kPa (300 psi) regardless of what the circuit pressure is. With multiple valves activated, the individual circuit pressures will vary. When the pump cannot meet the flow needs of all activated circuits, the pressure compensators will move down to proportion the pump flow in relation to the amount of control spool travel and pressure for each circuit. The pressure differential will be less than described in the example, but the pressure differential will be the same for all spools. Valve "B" pressure compensator shows what occurs when an additional circuit is activated with a lower circuit pressure than the first activated valve. The pressure compensator valve will respond to changes in the circuit pressure by opening and closing off the passage between the feeder passage and the bridged passage to maintain a constant flow rate for a given control stem displacement. As the compensator opens and closes, the pressure differential across the compensator will vary in order to maintain a constant flow rate to the implement. The pressure differential across the main control spool is the same for all activated main control spools.
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The load signal from the valve "C" pressure compensator is directed to the top of the valve "B" pressure compensator valve with the lower circuit pressure. When the control spool is moved, pressure oil in the feeder passage moves the pressure compensator valve up. The pressure compensator valve does not move up enough to open the resolver valve to the signal network due to the higher forces working on the resolver valve. The pressure compensator valve will respond to changes in the circuit pressure by opening and closing off the passage between the feeder passage and the bridged passage to maintain a constant flow rate for a given control spool displacement. As the compensator opens and closes, the pressure differential across the compensator will vary in order to maintain a constant flow rate to the implement, while the pressure differential across the main control spool is the same for all activated main control spools.
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18 Pressure Compensator Operation When the control spool is shifted farther to the left, the pump supply oil in the supply passage is directed around the center land of the control spool to the feeder passage. When pressure in the feeder passage increases to more than the pressure on top of the load sense spool plus the spring force, the pressure compensator valve and the load sense spool shift up. Pump flow in the feeder passage goes through the orifices in the bottom of the pressure compensator valve to the bridge passage. From the bridge passage the flow goes around the control spool to the passage to the rod end of the cylinder. The tilt anti-drift valve is activated to allowing flow from the head end of the cylinder to be directed around the left end of the control spool to the tank return passage. During a stall condition, the signal limiter valve in the load sensing signal valve and the margin spool maintains pump discharge pressure approximately 2100 kPa (300 psi) higher than the work port pressure. The pressure compensator valve can direct full pump flow to the bridge passage if demand for flow is great enough.
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19 Implement Hydraulic System - Dump When the tilt control lever is moved into the DUMP position, a load sensing signal pressure equal to work port pressure is directed to the resolver network. The signal oil goes through the resolver to the top of the signal duplication valve. The signal duplication valve shifts down. Pump flow goes through the signal duplication valve to the bottom of the duplication valve and the orifice. The duplication valve and the orifice stabilizes the load sensing signal pressure to the pump control, the spring chamber on each compensator valve, and to the pressure differential relief valve. The load sensing pressure acting on the bottom of the pressure differential relief valve, the pressure setting is increased. The pilot pressure reducing valve limits maximum pilot pressure to 3450 ± 170 kPa (500 ± 25 psi). The implement pump oil flows through the cover manifold, regulated pilot oil is directed to the various implement function solenoid valves. The load sensing signal moves the pump load sensing spool in the pump control valve to up stroke the pump. The signal circuit is also equipped with a choke check valve. The valve will allow free flow to the pump control valve. Also, the choke check valve will slow the signal flow return back to the hydraulic tank.
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With the control lever moved to DUMP direction, current proportional to the movement of the control lever is directed to the coil on the dump pilot solenoid valve. The solenoid valve sends a proportional amount of pilot oil to the dump end of the tilt stem. The tilt spool begins to shift upward. The lower end of the tilt spool is active. Supply oil flowing through the inlet manifold is directed around the lands of the tilt spool to the load check valve. The check valve unseats. Supply oil flows to the tilt pressure compensator valve. The oil flow through the compensator valve is blocked. As the pressure at the top of the compensator valve increases, the oil pressure shifts the compensator spool downward. The supply oil flows through the compensator valve and back around the tilt spool to the rod end of the tilt cylinder. The supply oil is directed to rod end of the tilt cylinder. Also, as the tilt lever is moved, the solenoid for the tilt anti-drift valve is energized. The oil from the head end of the tilt cylinder flows around the load check valve, through the tilt spool and back to tank. Oil directed to the rod end of the tilt cylinder through the bridge passage is also directed to the tilt ball resolver in the resolver network. The work port pressure increases the pressure in the resolver network, the resolver ball shifts and blocks oil from any other resolvers in the network. The oil at the tilt ball resolver is directed to the top of the signal duplication valve. The dump operation is also equipped with a makeup and line relief valve. The line relief valve regulates the pressure spikes caused by outside forces acting on the work tool. This allows the pressure spike to return to the hydraulic tank. This will prevent high pressure from damaging any components in the work tool or actuator. The line relief valve acts like a makeup valve, when the pump can not supply the amount of oil needed to fill the void in the cylinder. When the negative pressure occurs in the tilt cylinder, the valves moves off the seat and tank oil flows around the valve to fill the void in the cylinder. NOTE: The pilot line used on the optional Command Control Steering has been removed form the illustration.
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20 Implement Hydraulic System - Raise When the lift control lever is moved to the RAISE position, the lift lever position sensor sends a proportional electronic signal to the Implement ECM. The Implement ECM sends a corresponding proportional signal to the raise pilot solenoid valve. The Implement ECM also sends a fixed signal to the lift anti-drift valve. A proportional amount of pilot oil is directed from the raise pilot solenoid valve to the top of the lift spool. The lift spool shifts downward. Initially, as the lift spool begins to shift, any work port pressure will enter the control valve and is directed around the spool to the feeder passage. The work port oil pressure goes through the holes in the pressure compensator valve to the area between the compensator valve and the load check spool. The oil pressure helps the spring force hold the pressure compensator valve down to function as a load check valve. As the control spool shifts down, supply oil flows through the throttling slots into the supply passage. The pressure compensator valve will move up to the load check spool as the pump discharge pressure increases above the the work port pressure. The pump system oil pressure flows through the orifices in the pressure compensator valve to the feeder passage, around the lift anti-drift valve, and to the head end of the lift cylinder.
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The pressure at the work port begin to increase which increases the pressure in the lift resolver network. The ball resolver moves downward and oil flows through the resolver network to the top of the signal duplication valve. The signal duplication valve shifts and sends a matching resolver network pressure out of the duplication valve over the choke check valve to the pump control valve. The implement pump upstrokes to supply the flow demand. Also, matching oil from the signal duplication valve flows to the pressure compensator valve working on the bottom of the compensator valve. As the pressure changes in the head end of the lift cylinders, the pressure compensator valve opens and closes to maintain a constant flow for a given control spool displacement. If the machine is equipped with the optional ride control, the balance valve solenoid will be energized, allowing oil on the right side of the balance valve to go to the hydraulic tank. As the pressure in the head end of the lift cylinders increases to raise, the oil pressure on the left side of the balance valve will force the balance valve to shift to the right. Supply oil flows over the check valve, through the balance valve to the ride control accumulator, charging the accumulator. With ride control not active, the head end solenoid valve is de-energized and the accumulator charge oil will block the flow of oil between the head end of the lift cylinders and the accumulator. NOTE: The pilot line used on the optional Command Control Steering has been removed form the illustration.
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21 Implement Hydraulic System - Float When the lift lever is moved to the FLOAT position, the lift lever position sensor sends a proportional electronic signal to the Implement ECM. The Implement ECM sends a corresponding proportional electronic signal to the lower/float pilot solenoid valve. The Implement ECM also sends a fixed electronic signal to the lift load check valve. Pilot oil flows from the lower/float pilot solenoid valve to the bottom of the lift spool and the lift spool shift up fully. System oil pressure is blocked. Also, oil flow through the pressure compensator loop is blocked. Oil from the head end and rod end of the lift cylinders along with the oil to the resolver network is open to tank. In the FLOAT position, the pilot oil also flows to the resolver valve in the ride control control section, through the resolver network to the signal duplication valve. A matching signal (pilot pressure) is directed to the pump control valve from the signal duplication valve. The pump is upstroked to meet the demand required by the pilot pressure.
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As the machine moves, the lift cylinders move up and down with the contour of the ground. The check valve allows oil to flow to the lift cylinders when the pressure in the lift cylinders drops below tank pressure.
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22 Implement Hydraulic System - Tilt Back And Raise When the lift control lever is moved to the RAISE position and the tilt control lever is moved to the TILT BACK position, the lift lever position sensor and tilt lever position sensor sends an individual proportional electronic signal to the Implement ECM. The Implement ECM sends a corresponding proportional signal to the raise pilot solenoid valve and the tilt back pilot solenoid valve. The Implement ECM also sends a fixed signal to the lift and tilt anti-drift valve. A proportional amount of pilot oil is directed from the raise pilot solenoid valve to the top of the lift spool and a proportional amount of pilot oil is directed from the tilt back pilot solenoid valve to the top of the tilt spool. The lift spool shifts downward. Initially, as the lift spool begins to shift, any work port pressure will enter the control valve and is directed around the spool to the feeder passage. The work port oil pressure goes through the orifices in the pressure compensator valve in between the compensator valve and the load check spool. The oil pressure helps the spring force hold the pressure compensator valve down. Identically, as the tilt spool begins to shift, any work port pressure will enter the control valve and is directed around the spool to the feeder passage.
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The work port oil pressure goes through the holes in the pressure compensator valve to the area between the compensator valve and the load check spool. The oil pressure helps the spring force hold the pressure compensator valve down to function as a load check valve. As the cylinders start to move, the pressure at the work ports increase which increases the pressure in the resolver network. The ball resolver with the highest work port pressure moves seats and blocks oil flow back through the resolver network. The highest work port pressure flows through the resolver network to the top of the signal duplication valve. The signal duplication valve shifts and sends the matching resolver network pressure out of the duplication valve over the choke check valve to the pump control valve. The implement pump recognizes a demand for increased oil flow and the pump upstrokes to supply the flow demand. Also, matching oil from the signal duplication valve flows to the pressure compensator valve working on the bottom of the load check spool. As the pressure changes in the head end of the lift cylinders, the pressure compensator valve opens and closes to maintain a constant flow for a given control spool displacement. If the machine is equipped with the optional ride control, the balance valve solenoid will be energized, allowing oil on the right side of the balance valve to go to the hydraulic tank. As the pressure in the head end of the lift cylinders begins to raise, the oil pressure on the left side of the balance valve will force the balance valve to shift to the right. Supply oil flows over the check valve, through the balance valve to the ride control accumulator, charging the accumulator. With ride control not active, the head end solenoid valve is de-energized and the accumulator charge oil will block the flow of oil between the head end of the lift cylinders and the accumulator. NOTE: The pilot line used on the optional Command Control Steering has been removed from the illustration.
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23 Implement Hydraulic System - RIDE CONTROL AUTO When the ride control system is in AUTO and the machine reaches the configured ride control ground speed, the ride control balance solenoid valve is de-energized by the Power Train ECM. After the ride control equalization time has expired, the Power Train ECM energizes both the ride control accumulator solenoid valve and the ride control rod end solenoid valve. The head end solenoid valve connects the head end of the lift cylinders to the ride control accumulator. The ride control accumulator dampens the motion of the lift arms which makes the machine more stable. The rod end solenoid valve allows oil from the tank passage to flow into the rod ends of the lift cylinders when the lift cylinders move down. When the machine is in ride control AUTO, the control levers are in the HOLD position, and the ground speed is more than the 9.7 km/h (6 mph), the control spools are in the HOLD position blocking all oil flow through the implement control valve to the cylinders. The resolver network is at tank pressure and the pump is at low pressure standby.
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When the ground speed reaches the ECM configured value of 9.7 km/h (6 mph), the balance solenoid valve will be de-energized and the balance spool will move in the direction needed to equalize the pressures on each end of the balance spool. During the balancing operation, when the pressure at the right side of the balance spool is lowest, the spool shifts to the right and the implement pump supplies oil flow to equalize the pressure on both ends of the spool. During the balancing operation, when the pressure at the left side of the balance spool is lowest, the spool shifts to the left and the pressure in the oil pressure in the accumulator flows to tank until the pressures on both ends of the spool are equal. The Power Train ECM limits the time to equalize to one second (default). Then, the ECM energizes the balance solenoid valve. The oil pressure on the right end of the balance spool flows through the orifice to the hydraulic tank. The balance spool shifts to the right. Oil in the accumulator is trapped at the check valve. After the one second balancing time, the rod end solenoid and the head end solenoid valves are energized. The oil pressure that holds the check valves locked is released to tank. The oil in the head end of the lift cylinders flows to the ride control accumulator. The accumulator cushions the forward and backward pitching motions of the machine. At a ground speed below the ECM configured value of 9.7 km/h (6 mph), the rod end solenoid and the head end solenoid valves are de-energized. The check valves close and the spring force and the oil pressure hold the check valves closed. NOTE: The one second balance default time can be reconfigured in Caterpillar Electronic Technician (ET).
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24 Ride Control Valve - Auto/Travel Below 9.7 km/h (6 mph) The main control valve is equipped with the optional ride control section to dampen the ride during machine travel. This illustration shows a sectional view of the ride control section of the main control valve with the ride control system in AUTO, the bucket off the ground, and the travel speed below 9.7 km/h (6 mph). With the head end solenoid valve de-energized, the oil between the head end of the lift cylinders and the ride control valve is blocked. With the rod end solenoid valve de-energized, the oil between the rod end of the lift cylinders and the valve is also blocked. When the balance valve solenoid is energized, oil flow is blocked from the accumulator port to the left side of the balance spool. The blocked oil on the right side of the balance valve is above the tank pressure on the left side of the balance spool. The balance spool shifts to the left and oil in the accumulator port flows back through the balance spool and is blocked by the check valve. The check valve blocks all oil and any spikes from flowing back to the implement pump and causing damage to the pump. The relief valve limits pressure in the accumulator port to 34,500 kPa (5000 psi).
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25 Ride Control Valve - Auto/Travel More Than 9.7 km/h (6 mph) This illustration is a sectional view of the ride control section with the ride control system in AUTO, the bucket off the ground, and the travel speed more than 9.7 km/h (6 mph). The balance valve solenoid is de-energized by the Power Train ECM. Oil pressure from the accumulator port flows around the solenoid valve to the left side of the balance valve. The balance valve will equalize the pressure between the head end of the lift cylinders and the accumulator port. Oil flow around the balance valve is blocked. The default time for equalization in the Power Train ECM is one second. After the one second equalization time, the balance solenoid is energized. The oil on the right side of the balance spool flows through the orifice and the hydraulic tank. The balance spool shifts to the right and the oil between the head end of the lift cylinder and the accumulator is blocked in the system by the check valve. After the one second of equalization time, the head end solenoid valve and the rod end solenoid valve are energized. An oil passage is opened between the rod end of the lift cylinders and the tank port. The head end solenoid valve allows the oil blocked by the check valve is allowed to flow to the hydraulic tank. The check valve opens and oil flows between the head end of the lift cylinders and the accumulator.
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The head end solenoid valve and the rod end solenoid valve stay in energized until either the ride control switch is moved to the OFF position or the machine ground speed falls below 9.7 km/h (6 mph).
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26 This illustration is a transparent view of the ride control valve section. This view shows the location of the following components that are installed on the exterior and the interior of the section. - Head end solenoid valve (1) - Rod end solenoid valve (2) - Pilot pressure reducing valve (3) - Balance solenoid valve (4) - Balance valve (5) - Ball resolver (6) - Check valve (7) - Ride control relief valve (8)
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27 This illustration shows the location of the ride control accumulator (2) within the loader frame (1). Testing and adjusting, and service to the accumulator is completed at the articulation hitch. The charge medium for the accumulator is dry nitrogen. Also shown is the location of the implement control valve (3).
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Implement Pump and Pump Control Valve The Implement hydraulic pump for the 966H and 972H wheel loaders is a variable displacement piston type pump. The implement pump is installed on the accessory drive from the torque converter housing. The following is a list of components on the implement pump. - Load sensing port (1)
- Maximum angle adjustment (5)
- Case drain port (2)
- Pump control valve (6)
- Pump inlet (3)
- Pump outlet (7)
- Set screw (4)
- Load sensing adjustment screw (8)
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30 Pump Control Valve - Engine OFF This illustration shows the pump control group components with the engine OFF. The swashplate pin connects the actuator piston is connected to the pump swashplate (not shown). The bias spring moves the actuator piston and the pump swashplate to maximum angle. The pump control valve group consists of a load sensing spool assembly, which consists of a load sensing spool and a load sensing sleeve. The load sensing spool is moved up or down by different signal pressures pushing on the piston on each end of the spool. The pump system pressure piston receives an internal signal pressure equal to pump system pressure. The load sensing piston receives a load sensing signal from the implement hydraulic control valve, which is equal to the highest work pressure. The signal relief valve (located in the implement control valve) limits the maximum load sensing signal to the load sensing piston. Pump system pressure is directed through the orifice on the right side of the control valve group to the spring chamber in the upstroke end of the actuator piston and the center lands of the load sensing piston.
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The adjustment screw at the top of the actuator piston is used to the adjust maximum angle of the swashplate. The set screw at the top of the load sensing spool is used to hold the load sensing sleeve in position. The adjustment screw at the bottom of the load sensing spool is used to adjust the load sensing margin pressure for the pump. The spring at the bottom of the load sensing spool is the margin pressure spring.
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31 Pump Control Valve - Standby When the engine is started, pump flow goes to the closed center control valves in the implement control valve group. The flow is blocked in the implement control valve. Pressure in the system increases, and the pump system pressure is directed to the top end of the actuator piston. Pump system pressure on top of the pump system pressure piston moves the piston and load sensing spool down against the force of the margin spring. The spool moves down until the upper opening of the spool opens a path around the load sensing spool to drain. The opening to drain must open sufficient to provide a pressure differential across the orifice. With reduced pressure on the lower end and full pressure on the top of the actuator piston, the actuator piston moves the swashplate pin toward minimum angle. In STANDBY, the pump is delivering minimum flow to compensate for leakage in the pump, for leakage in the implement control valve, and for the operation of the pump control valve.
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32 Pump Control Group - Upstroke When the control lever or levers are moved to activate one or more implements, a load sensing signal, equal to the highest work port pressure, is directed to the lower end of the load sensing piston. The combined forces of the load sensing piston and the margin spring push the load sensing spool up until the center land on the load sensing spool closes the drain passage. The upward movement of the load sensing spool continues until the lower opening of the spool opens a path to the two metering ports. Pump system oil flows through the lower opening of the load sensing spool to the spring chamber of the actuator piston. The combined force on the the larger diameter of the actuator piston and the spring pushes the actuator piston and the swashplate pin up, increasing the swashplate angle to increase pump flow.
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33 Pump Control Valve - Constant Flow Demand When the flow demand is met, the force developed by the pump system pressure on top of the pump system pressure piston is equal to the force developed by the load sensing signal on the load sensing piston plus margin spring. When the forces are equal, the pump flow is constant and the load sensing spool is in the CENTER position. The pump flow remains constant until a change in the flow demand occurs.
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34 Pump Control Valve - Maximum System Pressure This illustration shows the pump control valve with the load sense pressure at signal relief with one function activated. When the work port pressure increases to the setting of the signal relief valve, the valve opens to limit the signal pressure to the bottom of the load sensing piston. Pump system pressure will increase to overcome the combination of forces on the bottom of the load sensing piston. The load sensing spool moves down to open the actuator piston spring cavity to drain. The pump system pressure moves the actuator piston and swashplate pin towards minimum angle. The pump destrokes to minimum flow.
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35 Pump Control Valve - Maximum System Pressure With Added Flow Demand This illustration shows the pump control valve with the load sense pressure at signal relief. When an additional function is activated, the pump system pressure slightly decreases. With less pressure on top of the pump system pressure piston, the force on the bottom of the load sensing piston moves the load sensing spool up. The load sensing spool restricts the flow through the upper opening to drain. The increased pressure on the larger area of the actuator piston plus the bias spring pushes the actuator piston up. The pump upstrokes to meet the added flow demand.
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36 Implement Valve This illustration shows a side view of the implement control valve out of the loader Frame. The following components can be seen in this view: Pilot accumulator (1)
Pilot pressure reducing valve (8)
Ride control balance solenoid valve (2)
Balance valve (ride control) (9)
Rod end solenoid valve (ride control) (3)
Lower pilot valve housing (10)
Tilt Back Line Relief valve (4)
Lower solenoid valve (11)
Tilt Anti-drift valve (5)
Tilt back pilot valve housing (12)
Signal relief valve (6)
Tilt back solenoid valve (13)
Signal duplication valve (7)
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37 Differential Pressure Relief Valve During normal working conditions, the pressure difference between the pump delivery pressure and the load sensing signal pressure is maintained at 1960 kPa (285 psi) or less. When the load sensing signal pressure reaches its maximum pressure based on the signal relief valve, the maximum pressure setting from pump delivery pressure is limited to 2950 kPa (430 psi) higher than the load sensing signal pressure. When the machine movement is stopped, the main control valve returns to the NEUTRAL position. At this time, the load signal pressure from the implement circuit is blocked from the pump regulator. Since the pumps have not destroked, the pump delivery pressure flowing into the pressure differential relief valve increases. The pressure difference between the pump delivery pressure and the load signal pressure also increases. If the differential pressure exceeds 2950 kPa (430 psi) the load sensing signal differential pressure relief valve opens, and pump delivery pressure is immediately drained into the return passages and the oil returns to the hydraulic tank. The differential pressure relief valve will maintain the 2950 kPa (430 psi) difference between pump delivery pressure and the load sensing signal pressure.
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38 Pressure Reducing Valve The pressure reducing valve regulates the oil pressure in the pilot system. The pilot oil from the implement pump flows into the valve through the holes in the spool, to the center of the spool. Then, the regulated oil flows out of the left end of the reducing valve to the pilot accumulator. Also, the pilot oil flows through the orifice into the left spring cavity. The force of the oil pressure acting on the ball is not sufficient to override the force of the right spring. The right spring holds the ball on the seat. When the oil pressure flowing into the valve is below 3445 kPa (500 psi), the spool blocks the flow of any pilot oil to the hydraulic tank. NOTE: For adjustment procedures for the pressure reducing valve, refer to the Service Manual module (RENR8858) Troubleshooting Testing and Adjusting 966H and 972H Wheel Loaders Electrohydraulic System. Pilot Pressure to the Main Control Valve - Check.
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39 Pressure Reducing Valve - Above The Adjusted Pressure As the oil pressure from the implement pump increases, the reducing valve will regulate the pressure in the pilot system. The following steps occur to regulate the oil to the adjusted pressure. The pilot oil flows into the center of the spool through the holes in the spool to the pilot accumulator and the hydraulic lockout solenoid. When the solenoid valve is energized and one or more of the control levers are moved, the pressure in the pilot system will increase above the adjusted pressure of the reducing valve. The oil flow through the orifice into the spring cavity. The oil pressure rises above the adjusted setting and and the force of the oil pressure overrides the force of the spring. The ball and retainer is moved off the seat. The oil in the spring cavity to the right is allowed to flow to the hydraulic tank. The force of the oil pressure is greater than the force of the left spring allows the spool to override the spring. The spool moves and blocks the oil supply from implement pump. The spool shifts to the right to allow the groove in the spool to clear the hydraulic tank passage. Enough oil flows from the pilot system through the passage regulating the pressure to the adjusted setting.
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If the pilot oil pressure can not be correctly adjusted, check the for proper operation in the differential pressure relief valve and the load sense signal to the differential pressure relief valve is correct.
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Load Sense Pressure Tap The access to the load sense pressure tap is on the right side of the machine at the articulation hitch. This pressure tap is used to measure the load sense pressure between the pump control valve and the signal duplication valve.
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41 The following components are located on the implement control valve: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
Head end solenoid valve (ride control) Hydraulic lockout valve Margin relief valve Lift anti-drift valve Dump line relief valve (rod end) Dump pilot valve housing Dump solenoid valve Raise Solenoid valve Raise pilot valve housing Ride control relief valve Pilot check valve
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42 The following components can be seen from the left rear of the control valve: - Tilt pressure compensator valve (1) - Lift pressure compensator valve (2) - Head end solenoid valve (ride control) (3)
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This illustration shows a transparent view of the inlet manifold on the implement control valve. The signal relief valve (1) limits the signal pressure to the load sensing spool which controls the maximum pump system pressure. Signal duplication valve (3) duplicates the true load signal received from the work port. Orifice (2) is used to stabilize the duplicated load sensing signal that is being directed to the tops of the pressure compensator spools and the load sensing spool in the pump control valve. Implement control valve return to the hydraulic tank (4). Implement control valve inlet (5)
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45 Signal Duplication Valve The work port pressure pushes on the right end of the signal duplication valve spool pushing it to the left. When the spool shifts left, a passage allowing pump delivery pressure to enter the outer chamber is opened. At the same time, the drain passage to the hydraulic tank is closed. Pump delivery pressure enters the center passage of the signal duplication valve spool through an orifice and pump delivery pressure pressurizes the center passage of the signal duplication valve. The pressurization of the center passage creates the duplicated work port pressure. The duplicated work port pressure on the left end of the signal duplication valve spool moves the spool to the right. When the signal duplication valve spool moves to the right, the passage for pump delivery pressure partially closes and the drain passage partially opens. The duplicated work port pressure on the left end of the signal duplication valve spool is reduced. True load signal pressure on the right end moves the signal duplication valve spool to the left until the work port pressure and the duplicated work port pressure is equal. The duplicated work port pressure is sent from the left end of the signal duplication valve spool into the load sensing signal network.
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46 Signal Relief Valve - Below The Adjusted Pressure Setting When the machine is under a load condition, the signal relief valve operates in the following manner. From the signal duplication valve, the duplicated load sensing signal flows through the orifice in two directions. One direction flows to the pressure compensator valve in each control valve section. The second path flows as a load sensing signal to the signal relief valve, through the choke check valve, and to the pump control valve. In the signal relief valve, load sensing signal oil enters the signal relief valve on the left end. The spring force being greater than the force of the load sensing signal the poppet is held against the seat. No signal oil is allowed to flow to the hydraulic tank.
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47 Signal Relief Valve - Above The Adjusted Pressure Setting When the force of the load sensing oil at the left end of the signal relief valve is above the force of the spring, the poppet moves off the seat, and a small amount of oil drains through the passage to the hydraulic tank. The signal relief valve functions like a signal relief valve. As a result, the load sensing signal is maintained at the adjusted pressure setting of the signal relief valve.
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48 Line Relief - Closed When the control valves for the cylinders are in the NEUTRAL position, spring force on the poppet and the inner and outer springs to the right of the piston keep the spool moved to the left in the closed position. The line relief valves limits the circuit pressure to the adjusted pressure setting. The pressure between the cylinder and the main control valve pressurizes the line relief valve. The pressure oil flows in the center passage of the spool into the inner spring and outer spring chamber. During normal conditions, the oil pressure is lower than the line relief valve pressure setting and the valve remains in the CLOSED position by the force of the spring on the poppet. The oil pressure in the inner spring chamber and the passage to the cylinder are equal. The surface area of the right side of the spool is larger than the area on the left side of the spool.
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With the oil pressure equal on both sides of the spool, the spring force of the inner spring and outer spring assist in keeping the spool seated. Therefore, the force on the right side is greater than the force on the left side and the spool remains seated to the left. The pressure oil does not flow to the return passages and to the hydraulic tank.
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49 When the high oil pressure in the passage between the main control valve and the cylinder exceeds the line relief valve setting, the line relief valve overcomes the force of the spring on the poppet. The reduced pressurized oil in the spring chamber flows into the poppet chamber and the low pressure oil from there flows into the return passages within the valve and returns to the hydraulic tank. At the same time, the high pressure oil in the passage to the cylinder pushes the spool to the right overcoming the force of the inner spring and outer spring until the piston come in contact with the left end of the valve. At this time, the high pressure oil also flows through the opening in the seat to the return passages and back to the hydraulic tank. When the high pressure oil in the passage between the cylinder and the main control valve reach the specified pressure setting of the line relief valve, the spring force on the poppet moves the poppet to the left seating the poppet. With the poppet seated, the oil pressure in the spring chamber will raise to be equal to that of the main passage. With the oil pressure in the spring chamber equal to that of the main passage pressure, the spring force of the inner spring and outer spring will move the spool to the left blocking the oil flow through the opening in the seat.
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50 When oil from one end of the cylinder is discharged through the line relief valve, a vacuum condition is created on the opposite end of the cylinder. Makeup oil is needed to prevent the vacuum condition in the cylinder. Also, during the operation of the machine in certain conditions, it is possible to create a vacuum condition on one end of the cylinder. When the vacuum condition occurs on the end of the cylinder, that vacuum also occurs in the spring chamber of the line relief valve. At this point, the return oil is now at a higher pressure than the oil in the passage between the cylinder and the main control valve. When this occurs, the higher pressure return oil flows through the return passage into the poppet chamber. The return oil pressure works with the spring acting on the poppet, keeping it seated to the left. Simultaneously, the return oil pushes on the shoulder area of the sleeve pushing it to the right. When the sleeve moves to the right, the spool also moves to the right. However, as the sleeve moves to the right, a passage opens between the return passage to the hydraulic tank and to the passage to the cylinder. Return oil flows from the return passage into the main passage in order to remove the vacuum condition in the cylinder.
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51 This illustration shows the lift section of the implement control valve with the lift body section in transparent. The following is a list of components that are in the interior of the valve. Pressure compensator valve (1) Load check spool (2) Load check spool spring (3) Check valve (ride control) (4) Lift anti-drift valve (5) Lower solenoid valve (6) Lift resolver valve (7) Lift stem (8) Raise solenoid valve (9)
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52 POWER TRAIN This illustration shows the major components in the power train. Power from the engine flows to a 360 mm (14.5 inch) diameter torque converter. The torque converter output shaft is splined to the input shaft of the electronically controlled power shift transmission. The transmission output shaft is splined to the output transfer gear. The output transfer gear transmits power from the transmission to the front and rear drive shafts. Power from the transmission output shaft flows through the front drive shaft and the parking brake to the front pinion, bevel gear, differential and axles to the final drives. Power from the transmission output shaft also flows through the rear universal joint group to the rear pinion, bevel gear, differential and axles to the final drives. Power train movements and operations are controlled through the Power Train ECM.
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The Power Train Electronic Control Module (ECM) is the central component in the electronic control system. The ECM is located at the right rear of the cab. The rear panel must be removed for access to the ECM. The Power Train ECM will be located behind the operator’s seat and have the connectors horizontal to each other. The ECM makes decisions based on switch-type and sensor input signals and memory information. Input signals to the ECM come from the operator's station, the machine, and the transmission. The operator's station input components consist of direction and shift switches, the neutralizer and neutralizer override switches, the park brake switch, the key start switch, and the Auto/Manual select switch. Optional switch inputs are the ride control switch and the secondary steer test switch. The machine input components are the engine speed sensor, the primary steering pressure switch, the optional secondary steering pressure switch and the Caterpillar Monitoring System message center module. The transmission input components are the transmission oil temperature sensor, the torque converter output speed sensor, and the two transmission output speed sensors. The ECM communicates with other electronic control modules, such as the Caterpillar Monitoring System, the Engine Electronic Control Module (ECM) and the Electrohydraulic Electronic Control Module (ECM), through the Cat Data Link. The Cat Data Link allows the transmission ECM to receive and send information. The power train and the implement use the same A4M1 Electronic Control Module (ECM). To enable the ECM for power train functions, contact (J1-27) is grounded. Contact (J1-32) is grounded in order to enable the ECM.
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The Power Train ECM responds to machine control decisions by sending a signal to the appropriate circuit which initiates an action. For example, the operator selects an upshift with the shift lever. The Power Train ECM interprets the input signals from the shift lever, evaluates the current machine operating status and energizes the appropriate modulating valve. The Power Train ECM receives three different types of input signals: 1. Switch input: Provides the signal line to battery, ground, or open. 2. PWM input: Provides the signal line with a square wave of a specific frequency and a varying positive duty cycle. 3. Speed signal: Provides the signal line with either a repeating, fixed voltage level pattern signal or a sine wave of varying level and frequency. The Power Train ECM has three types of output drivers: 1. ON/OFF driver: Provides the output device with a signal level of +Battery voltage (ON) or less than one Volt (OFF). 2. PWM solenoid driver: Provides the output device with a square wave of fixed frequency and a varying positive duty cycle. 3. Controlled current output driver: The ECM will energize the solenoid with 1.25 amps for approximately one half second and then decrease the level to 0.8 amps for the duration of the on time. The initial higher amperage gives the actuator rapid response and the decreased level is sufficient to hold the solenoid in the correct position. An added benefit is an increase in the life of the solenoid. The Power Train ECM controls the transmission speed and directional clutches. The Power Train ECM interprets signals from the shift lever to signal the transmission to perform the following options: Upshift, Downshift, Forward Neutral, and Reverse. The Power Train ECM communicates through the CAT Data Link. The CAT Data Link allows high speed proprietary serial communications over a twisted pair of wires. The CAT Data Link allows different systems on the machine to communicate with each other and also with service tools such as Caterpillar Electronic Technician (ET). The Power Train ECM has built-in diagnostic capabilities. As the Power Train ECM detects fault conditions in the power train system, it logs the faults in memory and displays them through the Caterpillar Monitoring System.
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54 Power Train Electrical System This illustration shows the input components which provide power or signals to the Power Train ECM. Power Train ECM Inputs: Shift lever (Forward, Neutral, Reverse and Gear): Combines control of the transmission shifting to a single input device. The shift lever can be pushed forward, backward, or placed in the middle position for machine direction. The lever is rotated in order to change the speeds of the transmission..This is the standard control for shifting that comes with the Hand Metering Unit (HMU) steering. Direction Switch (Forward, Neutral, Reverse, Upshift, and Downshift): Combines control of the transmission shifting with a single input device. The 3 position switch controls direction and the 2 thumb-switches controls upshift and downshift. This is the control for shifting that comes with the Command Control Steering (CCS). Key Start switch: Provides a signal to the Power Train ECM when the operator wants to start the engine. The direction switch/shift lever must be in the NEUTRAL position before the Power Train ECM will permit engine starting.
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Variable Shift Control: The variable shift control switch is an input of the power train ECM. The switch allows the selection of a range of shifting points in the Power Train ECM for each speed. The switch has three inputs to the power train ECM. Transmission output speed sensors: These sensors measures the transmission output speed in the range of 25 to 3000 rpm. By looking at the difference in phase in between these 2 sensors, direction can be told. Torque converter output speed sensor: Measures the torque converter speed in the range of 25 to 3000 rpm. Auto/manual gear selector switch (HMU): Signals the Power Train ECM which shift mode the operator wants to operate on a standard machine. The operator can select between manual shifting or automatic shifting in the range of gears 4 to 2 or in the range of gears 4 to 1. Maximum gear, if lower gear than 4 is desired, will be determined by the shift lever position. Auto/manual gear selector switch (CCS option): Signals the Power Train ECM which shift mode the operator wants to operate on a machine with the optional Command Control Steering. The operator can select between manual shifting and automatic shifting with maximum gear of 4, 3 or 2 and also a 4 to 1 range shifting mode. Primary steering pressure switch: Sends a signals the Power Train ECM if the primary steering system loses steering oil flow. Secondary steering pressure switch: It tells the ECM if the secondary steering pump is correctly building up pressure. When the pump is running and we still do not see pressure a warning indicator is lit. It is mostly used as feedback for the startup test and the manual switch test to ensure that the system is working properly. Left pedal position sensor: Signals the position of the torque converter pedal to the Power Train ECM. The position of the pedal is being used to downshift the transmission and neutralize the transmission during operation. Both the downshift and neutralization function of the pedal can be disabled and hence the pedal would function as a brake pedal only Parking brake pressure switch: Provides a signal the Power Train ECM when the park brake is engaged or disengaged. Ride control switch (ON/OFF/AUTO): Signals the Power Train ECM which mode the operator wants to operate. The operator should never operate in ON mode since this is the service mode.
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Transmission neutralizer disable Switch: Provides an input to the Power Train ECM that will disable the the left pedal neutralization of the transmission. Transmission oil temperature sensor: Provides an input to the Power Train ECM with the temperature of the transmission oil. Implement pod downshift switch: The downshift switch provides an input to the Power Train ECM to downshift the transmission. This switch is only used on a HMU steering machine. Engine speed tach signal: The engine speed is sent over a single wire to the Power Train ECM from the Engine ECM. Location code enable (grounded): The location code enable is a grounded input signal to the Power Train ECM that enables the location code detection feature to become active. Location code 2 (grounded) : The location code pin number 2 is a grounded input signal that establishes the ECM is dedicated to the Power Train operation. CAN Data Link (J1939): The Power Train ECM receives engine speed over the CAN Data Link.
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Engine Start Switch and Diagnostic Service Tool Connector The engine start switch (1) signals the Power Train ECM that the operator wants to start the engine. The ECM determines if the transmission directional switch (not shown) is in the NEUTRAL position. When the directional switch is in the NEUTRAL position and the key start switch (1) is turned to the START position, the ECM energizes the starter relay. The diagnostic service tool connector (2) for a laptop computer using Caterpillar Electronic Technician (ET) are on the front panel on the right side. A laptop computer with ET can be used for calibrating, checking and clearing fault codes, and monitoring system inputs and outputs for troubleshooting the transmission system. Also shown are the the hazard switch (3), and the 12 Volt adapter socket (4).
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Transmission Shift Lever This is a picture of the standard type of transmission shift lever control group that is found on the 966H/972H Wheel Loaders. This control group is found on machines with conventional (HMU) steering systems. The shift lever is mounted on the left side of the steering column. The operator moves the shift lever forward to travel in the FORWARD direction or toward the rear to travel in the REVERSE direction. FIRST through FOURTH speeds are selected by rotating the shift lever. When the transmission is in the Manual mode, the Power Train ECM allows the shift lever to control the transmission. The transmission ECM shifts the transmission to the exact gear and direction shown on the shift lever. When the transmission is in the Automatic mode, the shift lever selection is the maximum gear the transmission will obtain. The transmission ECM will automatically select the correct speed clutches (SECOND, THIRD or FOURTH) based on the engine and transmission output speeds.
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Transmission Shift Control This illustration shows the transmission shift control for the optional Command Control Steering (CCS). The directional control switch (1), and the upshift/downshift switch (2) are mounted on the left side of the half moon shaped steering wheel. The directional control switch is a three position switch with which the operator selects either FORWARD (toggle forward), NEUTRAL (center position), or REVERSE (toggle backward) directions. The switch position the operator selects closes (grounds) that contact while the remaining two contacts stay open. Closing a switch contact sends a signal to the Power Train ECM indicating the direction selected by the operator. The upshift switch/downshift switch are identical in construction and operation. When the operator wants to manually shift to a higher or lower gear, the upshift switch or downshift switch is pressed. Each switch has two input connections at the Power Train ECM. When the switches are not activated, one connection is closed (grounded) and the other connection is open. When the operator pushes the upshift or downshift switch, the selected switch momentarily reverses connections to signal the Power Train ECM to change the desired speed.
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This illustration shows the location of the ride control ON/OFF/AUTO switch (1). The ride control switch has three positions. In the center position, ride control is disabled. In the UP position (as shown) the ride control switch is in the AUTO position. With the switch in AUTO, the ride control system will be enabled when the machine is traveling at least 9.5 km/h (6.0 mph). The SERVICE position (as shown on the switch) is used for service to the ride control system, and the ride control system is always ON. The transmission neutralization disable switch (2) is used to disable the neutralization of the left brake pedal. By pressing the upper section of the switch will activate the override. When the neutralization is disabled, the left brake pedal will not neutralize the transmission, but will downshift the transmission and apply the service braks. The switch is a momentary switch. Heated mirror switch (3) enables the heated mirror relay that is located behind the operator seat below the Power Train ECM. If the machine is equipped with the optional secondary steering, there will be a secondary steering test switch (4) mounted in the blocked position on the panel. When the switch is depressed it feeds a ground signal to a relay and also to a switch input on the Power Train ECM. The relay turns on the secondary steering pump, motor, which builds up pressure in the steering hydraulic lines. The Power Train ECM is monitoring the pressure of the secondary steering pressure switch to ensure the pressure has increased to an acceptable level while the pump is running.
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If the switch is depressed and the pressure is not increased to the acceptable level within 3 seconds, the secondary steering warning indicator will be illuminated to indicate that the secondary steering system is not functioning properly.
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The 966H and 972H Wheel Loaders are equipped with a variable shift control switch (1). The Power Train (ECM) uses the position of the variable shift control switch and the engine speed in order to determine the autoshift points for the transmission. The variable shift control switch has three inputs to the power train electronic control module (ECM). The Auto/manual gear selector switch (2) sends a signal to the Power Train ECM to control shifting mode in auto. The Power Train (ECM) will shift the transmission automatically. The power train ECM evaluates the input that is sent from the engine speed sensor, the transmission speed sensors, the torque converter output speed sensor, and the left brake pedal position sensor in order to regulate transmission shifts. The automatic mode of operation is represented by two numbers that are separated by a dash. The first number indicates the speed of the transmission when the transmission is placed into gear. The second number indicates the highest speed of the transmission when the machine is travelling. The switch shown is for HMU steering. For example, place the autoshift control switch into the 2-4 position. The machine will automatically shift into second gear when the transmission is placed into gear. The transmission will automatically upshift into fourth gear as the machine accelerates. The Power Train ECM does not allow an upshift to a speed that is higher than the speed that is selected with transmission direction and speed control lever. An automatic downshift from second speed to first speed occurs only if the autoshift switch is in the 1-4 position.
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This illustration shows the panel with the optional Command Control Steering. The Auto/manual gear selector switch sends a signal to the Power Train ECM to control shifting mode in auto. In the MANUAL position, the operator is responsible for upshifting and downshift the transmission. The Power Train ECM automatically shifts the transmission if the autoshift switch is in one of the four AUTO positions and the left brake pedal must be released. The Power Train ECM evaluates the inputs that are sent from the engine speed sensor, transmission speed sensors, the torque converter output speed sensor, and the left brake pedal position sensor in order to regulate transmission shifts. When the machine is operating in "AUTO" mode, the transmission speed selector switch can be used in order to downshift the transmission. This switch is normally used to downshift from second speed to first speed in order to load the bucket. The transmission will remain in the downshifted gear for three seconds after the switch is released. Then, automatic shifting will resume. If the transmission is downshifted to first speed, the machine remains there until there is a direction change or a manual upshift. For example, place the autoshift switch into position “3”. The machine will automatically shift into second gear when the transmission is placed into gear. The transmission will automatically upshift into third speed when the machine accelerates. An automatic downshift from second speed to first speed occurs only if the autoshift switch is in the 1-4 position. The Power Train ECM does not allow automatic an upshift to a speed that is higher than the speed that is selected with the auto/manual switch. The autoshift switch is used to select the top speed for the transmission when the transmission is in the AUTO mode. There are four modes of automatic operation: 4 position, 3 position, 2 position and 1-4 position.
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61 The Power Train ECM receives inputs from three speed sensors on the transmission. The sensors are: - No. 1 (leading) output speed sensor (1) - No. 2 (trailing) output speed sensor (2) - Torque converter output speed sensor (3) The output speed sensors (1 and 2) are positioned out of phase with each other. The Power Train ECM uses the phasing of the input data to determine the direction of rotation of the intermediate and output gears. The torque converter output speed sensor measures torque converter output speed in the range of 25 to 3000 rpm. The Power Train ECM has no direct feed back information to determine if clutch engagement and disengagement is completed. The Power Train ECM uses the speed sensor information, including the engine speed sensor data, to measure expected clutch slippage and planetary speeds to ensure the transmission is shifting according to the application program stored in the ECM memory. The speed sensor information is also used by the Power Train ECM to set and adjust transmission shift points.
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Transmission Oil Temperature Sensor The transmission oil temperature sensor (1) is a two-wire passive temperature sensor that is located on the left side of the machine. The sensor is an input to the Power Train ECM. The oil temperature sensor information is used to adjust transmission clutch fill times. The transmission oil temperature sensor information is also sent by the Power Train ECM to the Caterpillar Monitoring System over the Cat Data Link.
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Left Brake Pedal Position Sensor The left brake pedal position sensor is located in the cab as part of the left brake pedal. The position sensor (left brake pedal) sends an input to the Power Train ECM. The sensor continuously generates a 500 Hz PWM signal. The duty cycle varies in proportion to the position of the left brake pedal position sensor. The left pedal position sends a change in the input signal to the power train ECM. The ECM measures the duty cycle in order to determine the position of the pedal to downshift and neutralize the transmission.
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Implement Pod Downshift Switch And Remote F-N-R Switch The downshift switch (1) is located on the implement pod. If the machine is equipped with a joystick, the downshift switch will be located on the joystick handle. When the Power Train ECM is operating in the Manual Mode, depressing the downshift switch will cause a downshift from SECOND speed to FIRST speed. In the Manual mode, the downshift switch will not shift from FOURTH to THIRD speed or from THIRD to SECOND speed. The transmission will remain in FIRST speed until one of the following conditions occurs: 1.
A directional shift is made.
2.
The shift lever is moved to NEUTRAL before selecting a speed.
3.
The shift lever is turned to FIRST speed and then to another speed.
When operating in the Automatic mode, depressing the downshift switch causes the Power Train ECM to downshift the transmission at a higher than normal ground speed. Pressing and immediately releasing the downshift switch causes the Power Train ECM to immediately downshift the transmission one speed range. A downshift will occur only if the machine speed and engine speed will not result in an engine overspeed. Automatic shifting is disabled for five seconds after the downshift switch is pressed. After five seconds, automatic shifting, based on speed sensor inputs, is reactivated. The remote FNR switch (2) is only installed on the machines that are equipped with the standard HMU steering.
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Parking Brake Pressure Switch The parking brake pressure switch (1) is a normally closed switch with the parking brake engaged. When the parking brake is engaged, the parking brake indicator light (3) will be illuminated. When the parking brake knob is pushed to the IN position, the parking brake valve (2) will direct oil pressure to the parking brake release cylinder. The switch state will change the parking brake indicator light will not be illuminated and the Power Train ECM will receive a signal that the parking brake is dis-engaged.
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68 Based on the input signals, the Power Train ECM energizes the appropriate transmission control modulating valve for speed and directional clutch engagement. The Power Train ECM also energizes the key start relay when starting the machine and the back-up alarm when the operator select a reverse gear. The Cat Data Link connect the Power Train ECM to the other machine ECMs. The data link also connects the ECM to the Caterpillar Monitoring System and electronic service tools such as Caterpillar Electronic Technician (ET). Power Train ECM Outputs: Key start relay: The Power Train ECM energizes the key start relay when the appropriate conditions are met to start the engine. The ECM controls the current between the key start switch and the key start relay. Transmission oil filter bypass indicator LED: The Power Train ECM illuminates the indicator LED when the oil is bypassing the transmission filter. Low fuel level warning indicator LED: The Power Train ECM illuminates the indicator LED when the fuel level in the tank is below 10% of total fuel tank volume as read by the fuel level sensor (input to EMS-III communicated over Cat Data Link).
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Ride Control ON indicator LED: The Power Train ECM illuminates the indicator LED when ride control is active. Either in AUTO mode when driving above the configured ground speed or when in ON mode. Clutch solenoid: The solenoid control the oil flow through the respective speed and directional modulating valves. Secondary steering intermediate relay: The Power Train ECM energizes the relay when the loss of steering pressure is detected by the Power Train ECM. The ECM energizes the relay and power is supplied to the secondary steering pump. Back-up alarm: The Power Train ECM energizes the back-up alarm when the operator selects the REVERSE direction. The backup alarm is located .on the rear bumper. Heated mirror relay: The Power Train ECM energizes the relay to send current to the coil to warm the mirror. CAN-J1939 signal between machine ECMs: Signals sent between the machine ECMs and product Link on the faster CAN datalink. Ride Control Solenoid valve 1 (RE): The Power Train ECM energizes the solenoid valve that controls the opening of the anti-drift valve allowing flow between the rod end of the lift cylinders and tank. Ride Control Solenoid valve 3 (HE): The Power Train ECM energizes the solenoid valve that controls the opening of the anti-drift valve allowing flow between the accumulator and the head end of the lift cylinders. Ride Control Solenoid valve 2 (Balance): At engine start up, the Power Train ECM energizes the solenoid valve 2. When the Power Train ECM recognizes the ground speed in AUTO reaches the default configured speed value in the Power Train ECM, the ECM de-energizes the solenoid 2 for a default time designated through Caterpillar ET configuration. The pressure between the head end of the lift cylinders and the accumulator are balanced. Then the Power Train ECM energizes the1 and 3 ride control solenoids. +8 Volts: Regulated power supply providing 8 VDC that is used in order to power the digital sensors.
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Warning Panel - Left Side The illustration shows the warning panel on the left side of the dash panel. These indicators are driven outputs of the Power Train ECM. The transmission oil filter bypass (1) is located on the top right hand side. This alarm is illuminated when the transmission oil filter is bypassing due to a plugged filter requiring a change. The transmission neutralizer disabled indicator (2) is located in the center of the panel. This indicator is illuminated when the transmission neutralized is disabled. The low fuel level warning indicator (3) is located in the center row on the right side. This indicator is illuminated when the fuel level is below 10% of the total fuel tank volume. The ride control SERVICE indicator (4) is located in the bottom row on left side. This indicator is illuminated when the ride control switch is placed in the SERVICE position. The ride control AUTO indicator (5) is located in the bottom row, center. This indicator is illuminated when the ride control switch is placed in the AUTO position.
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71 Implement Control Valve - With Ride Control The ride control system is an option on the 966H and the 972H Wheel Loaders. The optional ride control system provides a means for dampening the bucket forces which produce a pitching motion as the machine travels over rough terrain. The operation of ride control is initiated by the switch input to the Power Train ECM with outputs to the solenoid valves on the implement control valve (1). On the implement control valve, there are two solenoid valves that controls oil flow over the anti-drift valves and one solenoid valve controlling the shifting of the balance valve. Energizing solenoid valve (2) provides a path of oil between the head end of the lift cylinders and the ride control accumulator. Energizing solenoid valve (3) allows the balance spool to shift as the solenoid valve provides a path for the oil on the end of the balance spool to flow to the hydraulic tank passage. Energizing solenoid valve (4) drains the oil pressure off the antidrift valve enabling the valve to raise and allow oil to flow between the rod end of the lift cylinders and the hydraulic tank. The optional ride control is enabled through the Machine Configuration screen with Caterpillar Electronic Technician (ET). When ride control system is in SERVICE/AUTO, the respective LED is illuminated on the machine status display.
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Backup Alarm The backup alarm is located on the right hand side of the machine inside the access door. the alarm sounds when the transmission directional switch is placed in the REVERSE position.
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Secondary Steering Intermediate Relay The secondary steering intermediate relay (1) is an output of the Power Train ECM. When the steering oil pressure at the primary pressure switch goes below the value of the switch, a signal is sent to the Power Train ECM and the ECM sends current to intermediate relay to energize the secondary steering pump motor.
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Engine Start Relay The engine start relay (2) is located in the left side service center (1). The engine start relay is energized by the Power Train ECM when all the engine starting requirements are met. When the relay is energized, battery voltage flow through the relay to the starter solenoid
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75 Transmission Hydraulic System - Neutral This illustration shows the transmission hydraulic system with the engine running and the transmission shift lever in the NEUTRAL position. When the engine is running, flow from the pump is sent through the filter to the six transmission solenoid valves. Pump flow is also sent to the transmission relief valve. The transmission relief valve limits the transmission oil pressure to the modulating valves. When NEUTRAL is selected, the Power Train ECM energizes the No.3 solenoid . The modulating valve controls the flow of oil to the No. 3 clutch. When the No. 3 solenoid is energized, the electromagnetic force moves the pin against the ball. The ball moves to the right against the seat. The oil flow through the center of the valve spool is blocked. The oil pressure increases at the left end of the valve spool and the valve spool moves to the right against the spring. Oil flow is directed to the ports for clutch 3. From the main relief valve, oil flows to the torque converter and the torque converter inlet relief valve. The torque converter inlet relief valve limits the oil pressure to the torque converter. When oil pressure to the torque converter exceeds 900 ± 70 kPa (130 ± 10 psi), the inlet relief valve opens and sends the excess oil pressure to drain.
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Oil in the torque converter flows out of the torque converter through the torque converter outlet relief valve. The outlet relief valve maintains the pressure in the torque converter at a minimum of 415 ± 135 kPa (60 ± 20 psi) at torque converter stall rpm. From the torque converter outlet relief valve, the oil flows through the transmission oil cooler and on to the transmission for cooling and lubrication of the bearings and planetary.
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76 This illustration shows the transmission hydraulic system with the engine running and the transmission shift lever in the FORWARD position and the speed selector in FIRST SPEED. When the engine is running, flow from the pump is sent through the filter to the six transmission solenoid valves. Pump flow is also sent to the transmission relief valve. The transmission relief valve limits the transmission oil pressure to the modulating valves. When FIRST SPEED FORWARD is selected, the Power Train ECM energizes the No. 2 solenoid and the No. 6 solenoid. The modulating valve controls the flow of oil to the No. 2 and No. 6 clutches. When the No. 2 and No. 6 solenoids are energized, the electromagnetic force moves the armature against the ball. The ball moves to the right against the seat. The oil flow through the center of the valve spool to is blocked. The oil pressure increases at the left end of the valve spool and the valve spool moves to the right against the spring. Oil flow is directed to the ports for clutch 2 and clutch 6. From the main relief valve, oil flows to the torque converter and the torque converter inlet relief valve. The torque converter inlet relief valve limits the oil pressure to the torque converter. When oil pressure to the torque converter exceeds 900 ± 70 kPa (130 ± 10 psi), the inlet relief valve opens and sends the excess oil pressure to drain.
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Oil in the torque converter flows out of the torque converter through the torque converter outlet relief valve. The outlet relief valve maintains the pressure in the torque converter at a minimum of 415 ± 135 kPa (60 ± 20 psi) at torque converter stall rpm. From the torque converter outlet relief valve, the oil flows through the transmission oil cooler and on to the transmission for cooling and lubrication of the bearings and planetary.
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77 This illustration shows the transmission hydraulic system with the engine running and the transmission shift lever in the FORWARD position and the speed selector in SECOND SPEED. When the engine is running, flow from the pump is sent through the filter to the six transmission solenoid valves. Pump flow is also sent to the transmission relief valve. The transmission relief valve limits the transmission oil pressure to the modulating valves. When FIRST SPEED FORWARD is selected, the Power Train ECM energizes the No. 2 solenoid and the No. 5 solenoid. The modulating valve controls the flow of oil to the No. 2 and No. 5 clutches. When the No. 2 and No. 5 solenoids are energized, the electromagnetic force moves the armature against the ball. The ball moves to the right against the seat. The oil flow through the center of the valve spool to is blocked. The oil pressure increases at the left end of the valve spool and the valve spool moves to the right against the spring. Oil flow is directed to the ports for clutch 2 and clutch 5. From the main relief valve, oil flows to the torque converter and the torque converter inlet relief valve. The torque converter inlet relief valve limits the oil pressure to the torque converter. When oil pressure to the torque converter exceeds 900 ± 70 kPa (130 ± 10 psi), the inlet relief valve opens and sends the excess oil pressure to drain.
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Oil in the torque converter flows out of the torque converter through the torque converter outlet relief valve. The outlet relief valve maintains the pressure in the torque converter at a minimum of 415 ± 135 kPa (60 ± 20 psi) at torque converter stall rpm. From the torque converter outlet relief valve, the oil flows through the transmission oil cooler and on to the transmission for cooling and lubrication of the bearings and plan
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78 This illustration shows the transmission hydraulic system with the engine running and the transmission shift lever in the REVERSE position and the speed selector in SECOND SPEED. When the engine is running, flow from the pump is sent through the filter to the six transmission solenoid valves. Pump flow is also sent to the transmission relief valve. The transmission relief valve limits the transmission oil pressure to the modulating valves. When FIRST SPEED FORWARD is selected, the Power Train ECM energizes the No. 1 solenoid and the No. 5 solenoid. The modulating valve controls the flow of oil to the No. 1 and No. 5 clutches. When the No. 1 and No. 5 solenoids are energized, the electromagnetic force moves the armature against the ball. The ball moves to the right against the seat. The oil flow through the center of the valve spool to is blocked. The oil pressure increases at the left end of the valve spool and the valve spool moves to the right against the spring. Oil flow is directed to the ports for clutch 1 and clutch 5. From the main relief valve, oil flows to the torque converter and the torque converter inlet relief valve. The torque converter inlet relief valve limits the oil pressure to the torque converter. When oil pressure to the torque converter exceeds 900 ± 70 kPa (130 ± 10 psi), the inlet relief valve opens and sends the excess oil pressure to drain.
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Oil in the torque converter flows out of the torque converter through the torque converter outlet relief valve. The outlet relief valve maintains the pressure in the torque converter at a minimum of 415 ± 135 kPa (60 ± 20 psi) at torque converter stall rpm. From the torque converter outlet relief valve, the oil flows through the transmission oil cooler and on to the transmission for cooling and lubrication of the bearings and plan
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79 Transmission Modulating Valve - No Commanded Signal In this illustration, the transmission modulating valve is shown with no current signal applied to the solenoid. The Power Train ECM controls the rate of oil flow through the transmission modulating valves to the clutches by changing the signal current strength to the solenoid. With no current signal applied to the solenoid, the transmission modulating valve is DE-ENERGIZED and oil flow to the clutch is blocked. The transmission modulating valves are located on the transmission case. Pump oil flows into the valve body around the valve spool and into a drilled passage in the center of the valve spool. The oil flows through the drilled passage and orifice to the left side of the valve spool to a drain orifice. Since there is no force acting on the pin assembly to hold the ball against the drain orifice, the oil flows through the spool and the drain orifice past the ball to the tank. The spring located on the right side of the spool in this view holds the valve valve spool to the left. The valve spool opens the passage between the clutch passage and the tank passage and blocks the passage between the clutch passage and the pump supply port. Oil flow to the clutch is blocked. Oil from the clutch drains to the tank preventing clutch engagement.
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80 Transmission Modulating Valve - Commanded Signal Below Maximum In this illustration, the modulating valve is shown with a signal to the solenoid that is below the maximum current. Clutch engagement begins when the Power Train ECM sends an initial current signal to ENERGIZE solenoid. The amount of commanded current signal is proportional to the desired pressure that is applied to the clutch during each stage of the engagement and disengagement cycle. The start of clutch engagement begins when the current signal to the solenoid creates a magnetic field around the pin. The magnetic force moves the pin against the ball in proportion to the strength of the current signal from the Power Train ECM. The position of the ball against the orifice begins to block the drain passage of the oil flow from the left side of the valve spool to the tank. This partial restriction causes the pressure at the left end of the valve spool to increase. The oil pressure moves the valve spool to the right against the spring. As the pressure on the right side of the valve spool overrides the force of the spring, the valve spool shifts to the right. The valve spool movement starts to open a passage on the right end of the valve spool for pump supply oil to fill the clutch. Oil also begins to fill the spring chamber on the right end of the spool.
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In the initial clutch filling stage, the Power Train ECM commands a high current pulse to quickly move the valve spool to start filling the clutch. During this short period of time, the clutch piston moves to remove the clearances between the clutch discs and plates to minimize the amount of time required to fill the clutch. The ECM then reduces the current signal which reduces the pressure setting of the proportional solenoid valve. The change in current signal reduces the flow of oil to the clutch. The point where the clutch plates and discs start to touch is called TOUCH-UP. Once TOUCH-UP is obtained, the Power Train ECM begins a controlled increase of the current signal to start the MODULATION cycle. The increase in the current signal causes the ball and pin to further restrict oil through the drain orifice to tank causing a controlled movement of the spool to the right. The spool movement allows the pressure in the clutch to increase. During the MODULATION cycle, the valve spool working with the variable commanded current signal from the Power Train ECM acts as a variable pressure reducing valve. The sequence of partial engagement is called desired slippage. The desired slippage is controlled by the application program stored in the Power Train ECM.
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81 Transmission Modulating Valve - Commanded Signal At Maximum In this illustration, the modulating valve is shown with a maximum current signal commanded to the solenoid. When the modulation cycle stops, the Power Train ECM sends the maximum specified current signal to fully engage the clutch. The constant current signal pushes the pin firmly against the ball in the solenoid valve. The pin force against the ball blocks more oil from flowing through the drain orifice. This restriction causes an increase in pressure on the left side of the valve spool. The valve spool moves to the right to allow pump flow to fully engage the clutch. In a short period of time, maximum pressure is felt at both ends to the proportional solenoid valve spool. This pressure along with the spring force on the right end of the spool cause the valve spool to move to the left until the forces on the right end and the left end of the valve spool are balanced. The valve spool movement to the left (balanced) position reduces the flow of oil to the engaged clutch. The Power Train ECM sends a constant maximum specified current signal to the solenoid to maintain the desired clutch pressure.
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The different maximum specified pressures for each clutch is caused by different maximum current signals being sent by the Power Train ECM to each individual modulating valve. The different maximum signal causes a difference in the force pushing the pin against the ball to block leakage through the drain orifice in each solenoid valve. The different rate of leakage through the spool drain orifice provide different balance positions for the proportional solenoid valve spool. Changing the valve spool position changes the flow of oil to the clutch and the resulting maximum clutch pressure. The operation of the proportional solenoid to control the engaging and releasing of clutches is not a simple on and off cycle. The Power Train ECM varies the strength of the current signal through a programmed cycle to control movement of the valve spool.
The actual Power Train ECM current cycle and transmission calibration will be discussed later in this presentation.
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6 Transmission Modulating Valve - Solenoids This illustration shows a view of the transmission modulating valves. The six modulating valves on the top of the transmission are located over the respective planetary they control. The solenoid valves provide electronically controlled pressure modulation. The transmission shifting function is controlled by the Power Train Electronic Control Module (ECM). The Power Train ECM and the transmission modulating valves provide modulation to each individual clutch. Also shown is the transmission main relief valve (7)
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The main Power Train ECM output is the pulse width modulated current signal that is sent to the six transmission modulating valves. The Power Train ECM analyzes the input signals and memory information and activates current drivers within the ECM. The current drivers send electrical pulse width current to energize the modulating valves that are located on the transmission clutch housing. The varying signal strength sent to each proportional solenoid valve by the Power Train ECM controls the rate of oil flow and the rate of pressure modulation of each clutch. In turn, the solenoid provide electronically controlled clutch filling and pressure modulation. The following Tables shows which solenoid is energized for the desired speed and direction: Forward First speed Forward Solenoid
2 and 6
Second speed Forward Solenoid
2 and 5
Third speed Forward Solenoid
2 and 4
Fourth speed Forward Solenoid
2 and 3
Reverse First speed Reverse Solenoid
1 and 6
Second speed Reverse Solenoid
1 and 5
Fourth speed Reverse Solenoid
1 and 3
Third speed Reverse Solenoid
1 and 4
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Transmission Relief Valve Shown is the transmission hydraulic main relief valve (1) located on the left side of the machine on the torque converter housing (2). The transmission main relief valve operates as both a pressure relief valve and a priority flow control valve. The main relief valve regulates the supply oil pressure to the six transmission proportional solenoid valves by limiting the supply oil pressure to 2785 ± 70 kPa (404 ± 20 psi) at high idle. The main relief valve also insures the solenoid valves have an adequate oil supply before the torque converter and oil coolers receive oil flow. The torque converter inlet relief valve is located behind the transmission main relief valve. The relief valve must be removed to gain access to the torque converter inlet relief valve. The torque converter inlet relief valve limits torque converter inlet oil pressure to a maximum of 900 ± 70 kPa (130 ± 10 psi).
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85 This illustration shows the major components of the torque converter. The rotating housing is shown in red. The rotating housing has a direct mechanical connection to the engine flywheel. The turbine and the output shaft are shown in blue, and are mechanically connected. The free wheel stator and the carrier are shown in green. The impeller is shown in pink. The bearings are shown in yellow. The impeller is bolted to the rotating housing and rotate at engine speed. Charge oil from the torque converter inlet relief valve enters the inlet passage in the carrier and fills the torque converter. The torque converter outlet relief, which is connected to the outlet passage, maintains the minimum pressure in the torque converter. As the impeller rotates, it directs oil against the turbine blades, causing the turbine to rotate. Turbine rotation causes the output shaft to rotate. During NO LOAD conditions, the output shaft rotates at nearly the same speed as the engine flywheel. As load is applied, the output shaft slows down. A decrease in output shaft speed causes the rpm of the turbine to decrease. As the output shaft speed is decreased, the output torque from the torque converter increases. When the output shaft is stalled, the torque converter is applying maximum torque to the output shaft.
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The torque converter is equipped with a freewheel stator. The stator, which is mounted to the torque converter outer housing is stationery. When a load is applied, the output shaft slows down. When the turbine is turning slower than the impeller, the stator redirects the oil from the turbine and increases the pressure on the turbine. The increase in pressure on the turbine tends to increase the torque output from the torque converter. When the output shaft is turning at near the same speed as the impeller, the stator freewheels backwards to reduce the drag and turbulence inside the torque converter. The stator freewheels in light load applications and multiplies torque in heavy load applications.
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Shown is the torque converter outlet relief valve (1) located on the right side of the transmission and below the torque converter housing (2). The torque converter outlet relief valve controls the pressure inside the torque converter by maintaining a minimum pressure of 415 ± 140 kPa (60 ± 20 psi) at torque converter stall rpm.
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This illustration shows the service center on the right side of the machine below the platform. In the service center is the transmission oil filter (1), the power train fluid sampling port (2) , and the transmission oil filter bypass switch (3). The transmission oil filter bypass switch reports to the Caterpillar Monitoring System sending a warning when the transmission oil filter needs to be serviced.
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This illustration shows the message center for the Caterpillar Monitoring System. When the Caterpillar Monitoring System is in the Service Mode (Mode 3), the Message Center shows the fault codes. The fault codes consist of the Module Identifier (MID) followed by the Component Identifier (CID) and Failure Mode Identifier (FMI). The MID tells which electronic control module diagnosed the fault. An MID of 081 means the fault was diagnosed in the Power Train ECM. MID's are listed on the machine Electrical Schematic in the Service Manual. The CID tells which component is faulty. For example, CID 623 means the fault was diagnosed in the transmission directional switch. The FMI tells the type of failure. For example, an FMI of 05 means the failure is an open circuit or current value is below normal.
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Variable Shift Control The 966H and the 972H Wheel Loaders feature Variable Shift Control on electrohydraulic machines. Variable Shift Control allows the transmission to shift at lower engine speeds. The variable shift control switch (arrow) is a three-position switch (POWER, MID, ECONOMY) that will change the shift points stored in the Power Train ECM. When the switch is rotated to the ECONOMY position (clockwise) the switch sends a signal to the Power Train ECM to shift the transmission at a lower engine rpm for increased fuel economy. When the switch is rotated to the POWER position (counterclockwise), the transmission shifts when the engine reaches 2100 rpm.
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91 Integrated Brake System The 966H and the 972H Wheel Loaders are equipped with the Integrated Brake System (IBS) allowing the operator to downshift the transmissio, neutralize the transmission, and apply the service brakes using the left brake pedal. The left service brake pedal (1) is attached to a PWM rotary position sensor (2) and a mechanical linkage (not shown). The position sensor continuously monitors the left brake pedal position. The position sensor sends an input signal to the Power Train ECM indicating left brake pedal position. The mechanical linkage is connected to the brake control valve (not shown) located below the cab. The right service brake pedal (not shown) is also connected to the brake control valve independent of the left brake pedal. NOTE: The amount of brake pedal travel can be displayed on the ET Service Tool screen or the Caterpillar Monitoring System main display module. Pedal travel is displayed as a percentage (%) in ET and by counts (ct.) on the Caterpillar Monitoring System. Three percent of brake pedal travel is about 2 ct. or 1°, and 100 percent of pedal travel is about 66 counts or 33°.
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92 Left Brake Pedal Actions This view shows the actions that occur as the brake pedal is depressed. In approximately the first nine percent of brake pedal travel (dead band), no braking or downshift occurs. Brake pedal travel between the pedal dead band and the calibrated initial brake pressure point is the Initial Mode. In the Initial Mode, the transmission downshifts, but the service brakes are not engaged and the transmission is not neutralized. The Integrated Brake System is in the Normal Mode when the left brake pedal is further depressed between the calibrated initial brake pressure point and the maximum pedal travel. In the Normal Mode, the transmission downshifts and the service brakes are engaged. When the left pedal is depressed in the Initial and Normal Modes, and if the transmission is in third or fourth gear, the transmission will downshift one gear at a time until second gear is reached. Each downshift will occur when the transmission output speed decreases to the shift point of the current transmission speed.
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In the Normal Mode, when the brake pedal reaches the neutralization set point and the transmission neutralizer is active, the Power Train ECM will DE-ENERGIZE the direction clutch solenoid to neutralize the transmission when the following conditions exist: or -
The auto/manual selector switch is NOT in the 1-4 position The transmission is in 2nd gear The ground speed is 6.5 mph The auto/manual selector switch is in the 1-4 position The transmission is in 1st gear The ground speed is 4.5 mph
If the left brake pedal is raised 2° above the Neutralization Set Point, the the transmission will re-engage. If the auto/manual switch setting is "2," the re-engage/re-neutralize cycle continues by raising the brake pedal 2° above Neutralization Set Point then pressing the brake back down to Neutralization Set Point if the operator does not allow the brake pedal to rise to the dead band. However, if the auto/manual switch setting is not "2," the re-neutralization point may not be the Neutralization Set Point, but a pedal position below the Neutralization Set Point at which neutralization occurred in the previous cycle. Generally, brake pedal travel overshoots the Neutralization Set Point. Each time brake travel overshoots the Neutralization Set Point, the point of re-neutralization moves down to the point of overshoot. In normal conditions, the best gear for loading trucks is 2nd, or "Second Auto." The operator pushes the bucket into the pile, and then manually shifts the transmission down to FORWARD 1. When the bucket is full, the operator changes the direction of the machine to REVERSE. In SECOND AUTO, the transmission automatically reverses in REVERSE 2, instead of REVERSE 1. The auto/manual selector switch sets parameters in the ECM that influence the Integrated Brake System. On a machines equipped with the optional Command Control Steering (CCS), the switch has 5 positions: 1-4, 2, 3, 4, and MANUAL. The switch position for the smoothest neutralization during truck loading in normal applications is 2. Smoothest means high engine speed with the following limitations: unacceptable jerkiness during slowdown, unacceptable engine overspeed during slowdown, and unacceptable transmission overspeed during slowdown. On machines equipped with the standard Hand Metering Unit HMU steering, the auto/manual selector switch has 3 positions: 1-4, 2-4, and MANUAL. With the speed selector on the steering column in the 2 position, the ideal auto/manual selector switch position for the smoothest neutralization during truck loading in normal applications is 2-4.
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93 Speed Limiter The Speed Limiter feature limits machine ground speed to 20 km/h (12 mph) on 966H-972H Wheel Loaders. The speed limiter software in the Power Train ECM monitors the machine engine speed, ground speed, and acceleration. The Power Train ECM receives the ground speed signal from the transmission output speed sensors and the engine speed signal directly from the Engine ECM. The Power Train ECM calculates machine acceleration from the speed sensor data. The Power Train ECM processes the input signals and sends a requested engine speed signal to the Engine ECM via the Cat Data Link, which controls the engine speed.
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94 This illustration shows the location of the components for the standard HMU steering system for the 966H and the 972H Wheel Loaders. The following is a list of the components: - Hydraulic tank - Steering pump - Steering control valve - Secondary steering diverter valve - Hand Metering Unit - Neutralizer valves - Secondary steering pump and motor - Steering cylinders -Orifices
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95 This diagram shows the components and oil flow for the 966H/972H the standard steering system. The primary steering system is made up of two basic circuits: main circuit and pilot circuit. The steering system includes a third circuit if the 966H/972H is equipped with the optional secondary steering system The main steering circuit consists of the steering pump, the steering control valve, the steering cylinders, the hydraulic oil tank. The variable displacement piston steering pump draws oil from the tank and sends flow to the steering control valve. The steering pilot circuit consists of the metering pump, a check valve and two neutralizer valves. The supply oil is ported through an orifice in the steering control valve that supplies pilot oil to the steering pilot circuit. When the steering wheel is moved to the left or right, the metering pump sends pilot oil through the respective neutralizer valve to the selector spool and directional stem in the steering control valve. The pilot oil moves the directional spool and directs pump supply oil to the steering cylinders.
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This diagram shows the system in the HOLD position. The steering supply oil to the steering cylinders is blocked. The optional secondary steering system consists of the secondary steering pump/electric motor and the secondary steering valve. The secondary steering diverter valve contains two check valves, the primary steering pressure switch, and the secondary steering pressure switch. Also, the secondary steering system includes an intermediate relay to run the electric motor. The relay receives current from the Power Train ECM to enable the relay. When the relay is engaged, battery voltage flows to the electric motor.
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96 The following are components of the standard Hand Metering Unit (HMU) Steering System - Hydraulic tank (1) -Hand Metering Unit (2) - Steering pump (3) - Neutralizer valves (4) -Orifices (5) - Steering control valve (6) - Steering cylinders (7)
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97 Steering Pump The steering pump (2) for the 966H and 972H Wheel Loader is a Variable displacement piston pump. The steering pump is equipped with a pump control valve (3). The pump control valve is equipped with both the flow compensator valve (4) and the high pressure cutoff valve (5). Also shown is the implement pump (1).
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98 Steering Pump with the Engine OFF This Illustration shows a sectional view of the steering pump and pump control valve. The major components are shown. When the engine is OFF, the bias spring holds the swashplate at maximum angle. Also, the spring force on the flow compensator and the pressure compensator spools pushes both the spools down against the plugs.
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99 Low Pressure Standby This illustration shows the steering pump in LOW PRESSURE STANDBY. When there is no demand for steering system oil, the pump goes to LOW PRESSURE STANDBY. At that position, the pump produces a sufficient amount flow to compensate for internal leakage and maintain sufficient pressure to ensure instantaneous response when the signal from the HMU commands steering oil flow. At STANDBY, no load sensing pressure signal is detected at the flow compensator spool. Pump supply oil pushes the flow compensator spool up, system pressure is then directed into the large actuator piston. The large actuator piston moves the swashplate towards minimum angle until the cross-drilled hole in the large actuator piston opens to case drain. At this point, the pressure inside the piston decreases and the pump stops destroking. The pump will supply enough flow to maintain the standby pressure and to compensate for internal leakage. NOTE: LOW PRESSURE STANDBY is more than margin pressure because of the higher back pressure the blocked oil at the closed center valves creates when all of the control valves are in NEUTRAL. The pump supply oil pushes the margin spool up to further compresses the margin spring. More supply oil goes to the large actuator piston and flows through the cross-drilled hole in the stem to the pump case.
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100 Pump Upstroke When a demand for increased oil flow in the steering system occurs, a load sensing signal is sent to the pump control valve. The load sensing signal is equal to the steering system pressure. The load sensing signal is directed to the spring chamber of the flow compensator spool. The spring force plus the load sensing signal from the HMU shifts the flow compensator spool downward. The flow compensator spool blocks oil between the pump discharge and the large actuator. The oil in the large actuator piston flows around the pressure compensator spool and the flow compensator spool to case drain. Pump system pressure plus spring force on the small actuator piston moves the pump swashplate toward maximum angle to increase pump flow. As pump flow increases, system pressure will also increase. When system pressure increases to 2400 kPa (350 psi) more than the load sensing signal from the control valve, the flow compensator spool starts to move upward. The center land on the margin spool reaches a balance point where flow is metered to and from the large actuator piston. At this point, flow from the pump remains constant until there is a change in the load sensing signal pressure from the control valve.
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101 Pump Destroke This illustration shows the pump and pump control valve in the DESTROKE position. When demand for oil flow in the steering system is decreased, the signal from the HMU is decreased allowing the flow compensator spool to move upward. Oil is allowed to flow around the flow compensator spool and into the large actuator. The large actuator moves to the right and forces the swashplate toward a minimum angle.
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102 High Pressure Stall This Illustration shows the pump and pump control valve at HIGH PRESSURE STALL. When steering system pressure reaches the pressure setting of the pressure compensator, the force on the bottom of the cutoff spool will shift the cutoff spool upward. System pressure is then directed into the large actuator piston. The large actuator piston moves the swashplate towards minimum angle until the cross-drilled hole in the large actuator piston opens to case drain. When system pressure decreases to less than the pressure setting of the pressure compensator, spring force pushes the cutoff spool down and the margin spool again controls flow from the pump.
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103 Steering Control Valve Shown is the steering control valve (1). This valve is mounted above the transmission between the operator's station and the engine. This illustration shows the location of the following components: - Right neutralizer valve (1) - Left neutralizer valve (2) - Right return to tank orifice(3) - Left return to tank orifice (4) - Steering control valve (5) - Crossover relief valve (6) - Pump backup relief valve (7) - System pressure port (8) - Return flow port (9)
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104 Operation Shown in this illustration is the operation of the steering control valve in the NO TURN position. The directional spool is held in the center position by centering springs and blocks supply oil from the steering pump. Pump standby pressure is felt on the relief valve and is directed to the HMU through a orifice. The steering cylinders are connected to the valve through the right and left turn ports and are held in position by oil blocked in the passages when steering wheel movement stops. Oil pressure in the right and left turn ports is felt on the cross line relief valve. Makeup valves are connected to the right and left steer ports and are normally seated by spring force. In negative steering situations (such as when the steering cylinders are moved by shock loading on the wheels), the pressure generated in the steering cylinders is felt in the right and left steer ports. If the pressure is higher than the setting of the cross line relief valve, the valve will open and unload oil flow to the opposite passage, which is at a lower pressure. The makeup valves prevent cavitation of the cylinder by allowing oil to be drawn from tank port . This illustration does not represent a true cross section of the valve. Components are shown out of position for clarity.
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105 When the steering wheel is turned counterclockwise to make a LEFT TURN, pilot oil from the HMU enters the valve through the left turn pilot port. The pilot spool shifts to the left and oil flows through the pilot passage to end of the directional stem. The directional spool shifts to the left against the force of the spring and the metering orifices are aligned with the pilot passage. The metering orifices permit the pilot pressure to open the pilot load check valve. Oil displaced from the left end of the directional stem flows through the pilot passages to the chamber on the right end of the directional stem. As the directional spool moves to the left, the pump passage is connected to the cylinder port and pump oil flows into the head end of the right steering cylinder and the rod end of the left steering cylinder. Oil from the rod end of the right cylinder and the head end of the left cylinder flows into the valve through the opposite cylinder port and returns to the hydraulic tank.
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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Steering cylinder pressure is now transmitted through the open pilot load check valve and through the pilot passages to the HMU load sensing port. The HMU load sensing port is connected to the control section of the steering pump. The pump control valve adjusts the pump flow to the output required by the steering system. The distance that the directional spool shifts and, therefore, the speed at which the machine turns depends on how fast the steering wheel is turned and the rpm of the engine. The orifice limits the oil supply to the HMU and controls the maximum speed at which the steering wheel can be turned. As the maximum speed is reached, the pilot oil pressure between the HMU and the directional stem will decrease. The pump output will decrease slightly as the sensing line signal pressure decreases. As pump pressure and signal pressure decrease, a heavier feel at the steering wheel will slow steering wheel rotation. When the steering wheel rotation is stopped, the HMU returns to the spring centered position and the pilot oil flow to the steering directional valve is cut off. Steering cylinder pressure closes the pilot load check valve and the centering spring moves the directional stem toward the center position to hold the steering cylinders in position. Pilot oil in the chamber on the right end of the directional spool is displaced through orifices and pilot passages to the chamber on the left end of the directional stem.
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106 Steering Neutralizer Valves The steering neuralizers are a plunger type valve. The neutralizer valve is used to block the pilot oil that is flowing from the HMU to both the pilot control stem and the main steering control stem. As the machine is articulating to the left and the neutralizer valve (1) meets striker (2), the the pusher will move inward and block the pilot oil flow to the steering control valve. The left articulation will stop. As the machine is articulating to the right and the neutralizer valve (3) meets striker (4), the the pusher will move inward and block the pilot oil flow to the steering control valve. The right articulation will stop.
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107 Steering Neutralizer Valve This illustration show s sectional view of the neutralizer valve. During a less that maximum turn, oil from the HMU flows through the valve to the pilot end of the stem in the steering control valve. When the striker comes in contact with the neutralizer valve, the valve spool shifts and oil flow to the steering control valve is blocked. Steering pilot oil flows back through the orifice in center passage in the spool to drain. The centering springs in the steering control valve and stops the machine from articulating. The machine will continue to command a turn until the steering wheel is turned in the opposite direction.
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Steering System Schematic When the engine is running and the steering system is in HOLD, oil is drawn from the hydraulic tank by the steering pump. The oil flows past the secondary steering diverter valve to the back-up relief valve and the directional spool in the steering control valve. Also, the oil flows through the flow control orifice to the hand metering unit. At this time, the oil is blocked from flowing through the HMU. With the HMU in the center position, a small amount of oil then flows through the orifice and back to the hydraulic tank. The HMU and the steering pump are connected by a signal line. A sense of change in the signal pressure at the HMU will send a reflected change in signal pressure to the pump control valve demanding a change in the output flow of the steering pump. If the pressure of the signal oil is decreases, the steering pump will destroke. If the pressure of the signal oil is increases, the steering pump will upstroke. In the HOLD position, the flow of pressure oil from the steering pump to the steering cylinders is blocked at the directional stem in the steering control valve. In the HOLD condition, there is no signal pressure sensed at the compensator valve on the steering pump. The steering pump goes to the LOW PRESSURE STANDBY position.
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In LOW PRESSURE STANDBY, the pump supplies an adequate amount of flow to compensate for any system leakage and to maintain sufficient system pressure to provide instantaneous response when the steering wheel is turned.
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109 GRADUAL LEFT TURN During a GRADUAL LEFT TURN with the engine running, the steering pump sends supply oil past the secondary steering diverter valve to the steering control valve and the hand metering unit. When the steering wheel is turned counterclockwise to make a LEFT TURN, pilot oil from the hand metering unit flows past the left neutralizer valve to the steering control valve to the selector spool. The selector spool shifts down, and oil flows to the end of the directional stem. The directional stem shifts down against the force of the centering spring. When the directional spool moves down, main steering pump oil flows through the directional stem to the rod end of the left steering cylinder and the head end of the right steering cylinder. At the same time that oil flows into the two steering cylinders, return oil flows from the head end of the left steering cylinder and the rod end of the right steering cylinder through the directional spool and back to the hydraulic tank. The machine articulates to the left for a left turn.
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110 Full Left Turn - Steering Neutralized During a FULL LEFT TURN with the engine running, the left striker contacts the left neutralizer valve. The neutralizer valve moves to the closed position, and oil flow from the hand metering unit to the steering control valve is blocked at the left neutralizer valve. The steering selector spool and the steering directional spool return to the center position. Flow to the steering cylinders is blocked at the directional spool in the steering control valve, and the machine stops turning. The neutralizer valves prevent the machine loader frame from contacting the machine rear frame when articulating fully to the right or left.
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111 If the steering pump or the engine fails, the primary pressure switch will sense the low pressure in the steering system. The primary steering pressure switch closes and sends a signal to the monitoring system which causes a Category 3 Warning to occur. After a one second delay, the Power Train ECM energizes the intermediate relay for the secondary steering pump and electric motor actuates. At the same time, the secondary steering indicator on the monitoring system display illuminates. The secondary steering pump draws oil from the hydraulic tank. The oil then flows to the secondary steering valve, which causes the check valve in the hydraulic line from the steering pump to close and the check valve in the hydraulic line from the secondary steering pump to open. The closed check valve prevents pressure oil from flowing to the steering pump. Oil from the secondary steering pump flows past the secondary steering valve to the steering control valve and hand metering unit. Pilot oil from the hand metering unit flows past the left neutralizer valve and moves the steering selector spool. The oil then flows through the steering selector spool and moves the directional spool, allowing the secondary steering oil to flow to the rod end of the left steering cylinder and to the head end of the right steering cylinder. Secondary steering provides a method to steer the machine to a safe location if a failure occurs in the primary steering pump or in the engine.
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112 Secondary Steering This illustration shows the location of the secondary steering components in the rear frame (1). If the steering pump or the engine fails, the primary pressure switch will sense the low pressure in the steering system. The primary steering pressure switch closes and sends a signal to the monitoring system which causes a Category 3 Warning to occur. After a one second delay, the transmission electronic control module energizes the intermediate relay (4) for the secondary steering pump and electric motor actuates. At the same time, the secondary steering indicator on the monitoring system display turns ON. The secondary steering pump (3) draws oil from the hydraulic tank. The oil then flows to the secondary steering diverter valve (2), which causes the check valve in the hydraulic line from the steering pump to close and the check valve in the hydraulic line from the secondary steering pump to open. The closed check valve prevents pressure oil from flowing to the steering pump. Oil from the secondary steering pump flows past the secondary steering valve to the steering control valve (5) and metering pump.
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Pilot oil from the metering pump flows past the left neutralizer valve and moves the steering selector spool. The oil then flows through the steering selector spool and moves the directional spool, allowing the pressure oil from the secondary steering pump to flow to the rod end of the left steering cylinder and to the head end of the right steering cylinder. NOTE: The secondary steering pump does not produce the same amount of flow as the main steering system pump. Secondary steering operations are reduced compared to normal operation. Secondary steering provides a method to steer the machine to a safe location if a failure occurs in the primary steering system or in the engine.
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113 The secondary steering diverter (1) valve directs oil from the secondary steering pump to the steering control valve when the primary pressure switch (3) senses a loss of oil pressure in the primary steering system and the drive shaft speed is greater than 50 mph. The primary pressure switch sends a signal to the Power Train ECM and the ECM enables the secondary steering pump motor. When the engine is running and the steering pump is supplying oil to the steering system, oil flows into the diverter valve through line (6), oil flows over check valve (5) through line (8) to the steering control valve (not shown). At this time, the oil pressure in the primary steering system holds check valve (4) against the seat. When the primary steering pressure switch senses a loss of oil pressure in the primary system, the secondary system is initiated. At this time, the primary pressure switch is closed and illuminates the primary steering warning LED. Oil flows into the diverter valve through line (7), over check valve (4) and out to the steering control valve through line (8). At this time, check valve (5) is seated. When the Power Train ECM enables the secondary steering pump motor, the secondary pressure switch (2) measures the oil pressure in the secondary steering system and sends a signal to illuminate the secondary steering warning LED.
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114 This illustration shows the location of the components for the optional CCS steering system for the 966H and the 972H Wheel Loaders. The hydraulic tank is common to all hydraulic systems on the machine. INSTRUCTOR NOTE: The color codes used for hydraulic oil throughout this presentation are: Red
- System or high pressure
Red and White Stripes
- Reduced pressure
Orange
- Pilot pressure
Blue
- Blocked oil
Green
- Tank or return oil
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115 This diagram shows the components and oil flow for the 966H/972H Command Control Steering system. The primary steering system is made up of two basic circuits: main circuit and pilot circuit. The steering system includes a third circuit if the 966H/972H is equipped with the optional secondary steering system. The main steering circuit consists of the steering pump, the steering control valve, the steering cylinders, the backup relief valve, and the hydraulic oil tank. The variable displacement piston steering pump draws oil (green) from the tank and sends flow (red) to the steering control valve.
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The steering pilot circuit consists of the the steering pilot control valve, the steering quad check valve, the screened orifice manifold and two neutralizer valves. The pilot system supply oil comes from the implement control valve. When the steering wheel is moved to the left or right, the steering pilot control valve supplies oil through the quad check valves and the respective neutralizer valve to the end of the respective directional spool in the steering control valve. The directional spool directs pump supply oil to the steering cylinders. This diagram shows the system in the HOLD position. The oil (blue) to the steering cylinders is blocked. The optional secondary steering system (not shown) consists of the secondary steering pump and motor and the secondary steering valve. The secondary steering valve contains two check valves, the primary steering pressure switch, and the secondary steering pressure switch.
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116 This graphic shows the position of the quad check valve during a left turn. Oil flows from the steering pilot control valve through one side of the quad check valve. The quad check valve consists of four check valves in two sets of two valves each. In each set of two valves, one check valve has a higher cracking pressure than the other valve. One set of check valves are for left turns and the other set of check valves are for right turns. The purpose of the steering quad check valve is to provide an alternative path for pilot oil returning from the non-activated side of the main control valve spool. The normal path for this oil returning to the tank is through the screened orifice manifold (not shown). The check valves with the lower setting prevent return oil from the non-activated spool end to flow through the quad check valve back to the steering pilot valve and to the tank. If the normal path for return pilot oil is blocked in the screened orifice manifold, the return oil will unseat the check valves with the higher setting and allow the oil to return through the steering pilot valve to the tank.
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Steering Pilot Valve The Command Control Steering (CCS) pilot control valve (1) is identical to the valve used on the "G" Series II machines. The steering pilot control valve consists of the directional control valve section and the pressure regulating valve section. Also shown is the pilot oil in pressure tap (2) and the pilot lines (3) to the steering control valve In the Command Control System (CCS) on the "H" Series machines, the pilot oil flows to the pilot control valve through hose (4) that is connected to the implement control valve in the front frame.
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6 7 Located in the front frame is drive shaft (1) for the pilot control valve. This shaft is connected to the input shaft on one end with the other end connected to the steering wheel shaft. Also shown in the upper illustration is the neutral pilot pressure tap (2) located remotely on the loader frame right side. Neutral pilot pressure is the oil pressure in the directional control valve section of the pilot valve in the NO TURN position. The lower illustration shows the screen group (7). The screen group includes the screens (5) and the orifices (6). Attached to the tees are the right pressure tap (3) and left pressure tap (4). The pressure taps are for measuring the output pressure to each end of the spool in the steering control valve. The tubing that is connected to the screen group is a drain to the hydraulic tank. The neutralizer valves (not shown) operate identical to the standard HMU neutralizer valves.
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Steering Pilot Valve - No Turn This illustration shows the components in the steering pilot valve. When input shaft that is connected to the steering wheel is in the NO TURN position, the flow of pilot oil through the steering pilot valve is blocked by the pressure regulating valve.
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Steering Pilot Valve - Right Turn When the steering wheel is turned to the right, the steering wheel causes rotation of the steering column, the steering shaft, the input shaft, the cam and the directional control valve. The cam moves the plunger against the spring and the pressure regulating valve spool. Pilot oil from the pump flows between the pressure regulating valve spool and the valve body, which function as an orifice. As the regulating valve moves down, the size of the orifice increases. The larger orifice creates a smaller pressure drop which increases the pressure of the pilot oil to the directional control valve. Also, the pilot oil flows through the orifice in the pressure regulating valve. The force of the pilot oil pressure between the piston and the regulating valve pushes up the regulating valve against the spring. The flow of the pilot oil is proportional to the downward movement pressure regulating valve spool. The pilot pressure controls the steering speed. Increasing the flow of pilot oil between the body and the pressure regulating valve will increase the steering cycle time.
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As the steering wheel is rotated, the directional control valve also rotates. This movement allows pilot oil from the pressure regulating valve to flow through the directional control valve port through the quad check valve to the neutralizer valve and the steering control valve directional spool. When the pilot pressure moves the steering control valve directional spool to the RIGHT TURN position, the steering control valve directs main pump oil to the head end of the left steering cylinder and the rod end of the right steering cylinder. The machine articulates to the right. When the steering wheel is returned to the CENTER position, the flow of pilot oil to the steering control valve directional spool is blocked. The centering spring in the steering control valve moves the directional spool to the neutral position and the machine stops articulating. NOTE: The machine turning speed depends on the rotational position of the steering wheel. The farther the steering wheel is turned, the faster the machine will turn. The turning speed of the machine does not depend on how fast the steering wheel is turned.
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123 This illustration shows the optional Command Control Steering system in a LEFT TURN. When the operator turns the steering wheel to the left, torque is transmitted through the steering column and the steering shaft to the steering pilot valve input shaft. The pilot valve located in the loader frame directs pilot oil through the quad check valve, through the neutralizer, to the directional spool in the steering control valve. Turning the steering wheel to a greater angle from the neutral position increases the flow of pilot oil to the directional spool in the steering control valve. Increased flow of pilot oil to the steering control valve moves the directional spool further from the neutral (blocking) position and allows greater flow of steering pump oil to the steering cylinders. When the pilot oil shifts the directional spool to the LEFT TURN position, steering pump oil is sent to the to the head end of the right steering cylinder and the rod end of the left steering cylinder. The machine articulates to the left for a left turn. The pressure in the steering cylinders is also sent to the shuttle valve. The cylinder pressure moves the shuttle valve up and becomes the signal pressure to the steering pump control valve. The signal pressure is sensed in the margin spool spring chamber of the control valve. The signal pressure combines with the force of the margin spring and causes the pump to UPSTROKE.
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The supply oil from the steering pump flows over the backup relief valve. If the pressure exceeds 23500 kPa (3400 psi), the backup relief valve opens and excess oil flows to the hydraulic tank. Also, the steering control valve is equipped with a pressure reducing valve. The reducing valve will supply pilot oil to the steering pilot valve if the pilot oil supply is lost. The steering control valve also is equipped with a crossover relief valve. In case of a pressure spike above 25600 kPa (3700 psi) as the machine is articulating, the crossover relief valve will open and send the excessive oil pressure to the hydraulic tank. When the machine fully articulates, the striker mounted on the loader frame contacts the neutralizer valve mounted on the rear frame. This action stops the flow of pilot oil from the pilot valve to the directional spool. The directional spool shifts to the CENTER position and the steering oil to the cylinders is blocked. Also, when the steering wheel is returned to the CENTER position, the flow of pilot oil to the directional spool is blocked. The centering spring in the steering control valve returns the directional spool to the neutral position, and the machine stops turning. The pilot valve is mounted on the front frame while the steering wheel and shaft are mounted on the rear frame. As the machine begins to turn, the shaft for the steering pilot valve begins to rotate back to the neutral position. As the shaft rotates closer to the neutral position, the turning speed of the machine is reduced due to lower pilot pressure to the steering control valve directional spool. However, the machine will continue to turn until the steering wheel returns to the center position. As long as the pilot directional valve is rotated from the neutral position and the neutralizer valves are not closed, pilot oil will flow to the steering control valve directional spool. NOTE: The machine turning speed depends on the rotational position of the steering wheel. The farther the steering wheel is turned, the faster the machine will turn. The turning speed of the machine does not depend on how fast the steering wheel is rotated.
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124
BRAKE AND HYDRAULIC FAN SYSTEM COMPONENTS Shown are the brake and hydraulic fan system components on the 966H and 972H Wheel Loaders. The brake system and the hydraulic fan system share the same pump. The hydraulic tank is common to both the brake system and the hydraulic fan system. The brake system components are: - Accumulator charging valve and hydraulic fan system solenoid valve - Brake accumulators - Service brake valve - Front and rear service brakes - Parking brake valve - Parking brake - Brake and hydraulic fan system pump - Service brake pedal
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The hydraulic fan system components are: - Accumulator charging valve and hydraulic fan system solenoid valve - Hydraulic fan motor - Hydraulic oil cooler - Engine Electronic Control Module (ECM) - Brake and hydraulic fan system pump
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125 Brake And Hydraulic Fan System - Cut In And Minimum Fan Speed This illustration shows the brake system and hydraulic fan system schematic. In the schematic, the accumulator charge pressure has dropped below 117 bar (1700 psi). The cut in valve is shifted to the left The pump draws oil from the hydraulic tank and directs the flow of oil to the accumulator charging valve and solenoid valve. The charge pressure for the brake accumulators is below 117 bar (1700 psi), the cut in valve is shifted to the left, and the system oil flows to the resolver valve. The resolver valve allows the higher of the two pressures between the signal from the fan solenoid and from the cut in valve to flow to the flow control spool of the pump control valve. In this instance the oil from the cut in valve is at a higher pressure. The flow control spool controls the displacement of the brake and fan pump. At this time, the pump will upstroke. Also, oil also flows to the lower port on the priority valve which shifts the priority valve upward and partially blocks the flow of oil to the fan motor. Oil also flows past the screen, the check valve and orifice to the inverse shuttle valve. The oil flowing into the inverse shuttle valve continues until both the accumulators are charged. The inverse shuttle valve maintains equal pressure between both brake accumulators. The system is also equipped with a relief valve to limit the brake system pressure to 207 bar (3000 psi).
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126 Brake And Hydraulic Fan System - Minimum Fan Speed At Cut Out This illustration shows the brake system and hydraulic fan system schematic. In the schematic, the accumulators are charged and the parking brake is disengaged. In the system, the pump draws oil from the hydraulic tank and directs the flow of oil to the accumulator charging valve and solenoid valve. This system is designed for the brake system to have priority over the hydraulic fan system. The supply oil has charged the accumulators to 145 bar (2100 psi). The cut out valve momentarily dropped downward to exhaust the oil from the right side of the cut in valve to tank. The cut in valve shifts to the right. The oil that was directed through the resolver valve as a signal to the pump control valve drops to tank level. The resolver valve shifts and the oil from the fan solenoid valve is directed to the pump control valve.
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The amount of oil that is flowing into the hydraulic motor is determined by the solenoid valve which feeds pressure back to the pump control valve through the load sense line. When the brake accumulators are charged (as shown) the pressure from the pump overrides the force of the priority valve spring. The priority valve opens and the supply oil is directed to the hydraulic motor. If all the key target temperatures are below the default values of the particular sensors, the fan pump will supply sufficient oil flow to rotate the hydraulic motor at minimum fan speed. The minimum fan speed is calibrated through Caterpillar Electronic Technician (ET).
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127 Brake and Hydraulic Fan System - Max Fan Speed At Cut Out In this illustration, the brake accumulators are charged and there is no demand for oil from the brake system. In the system, the pump draws oil from the hydraulic tank and directs the flow of oil to the accumulator charging valve and solenoid valve. With no demand by the brake system for oil, the hydraulic fan system has priority. The amount of oil that is flowing into the hydraulic motor is determined by the solenoid valve which feeds pressure back to the pump control valve through the load sense line. When the brake accumulators are charged the pressure supplied by the pump overrides the force of the priority valve spring. The priority valve opens and the supply oil is directed to the hydraulic motor. As one or more of the key target temperatures rise above the default values of the particular sensors, the current to the solenoid valve decreases. The solenoid valve shifts upward proportionally to the drop in current. The increase in oil flowing through the solenoid valve will increase the force on the flow control spool. The flow control spool shifts proportionally to the left and oil from behind the large actuator is allowed to flow to the hydraulic tank. The pump will upstroke, increase the fan speed, and move more air through the radiator group. The fan pump can supply sufficient oil flow to rotate the hydraulic motor to the maximum fan speed. The maximum fan speed is calibrated through Caterpillar Electronic Technician (ET).
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128
In the hydraulic fan system, the speed of the fan and the output of the hydraulic fan pump is directly controlled by the Engine ECM through the hydraulic fan solenoid valve. The Engine ECM interprets signals from the three sensors on the machine. Then, the Engine ECM sends a proportional current to the hydraulic fan solenoid valve. The following sensors report directly to the Engine ECM. Air intake temperature Engine coolant The sensor for the air intake temperature is a passive sensor that is used to measure temperature. The sensor sends an analog signal to the Engine ECM. The analog signal will increase in voltage as the temperature of the air increases. The engine coolant temperature sensor is a passive sensor that is used to measure the temperatures of liquids. The sensor sends an analog signal to the Engine ECM. The analog signal will increase in voltage as the temperature of the engine coolant increases. The hydraulic oil temperature sensor is used for the measurement of liquid temperatures. The sensor sends an analog output to the Monitoring System ECM. The analog signal will increase in voltage as the temperature of the oil increases.
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When the engine is started, the hydraulic fan pump will be controlled to run at minimum fan speed. The following conditions must be met, in order to run the fan system at minimum fan speed. The air intake temperature is below 49 °C (120 °F). The hydraulic oil temperature is below 90 °C (195 °F). The engine coolant temperature is below 89 °C (192 °F). As one or more of the sensors reads a temperature that is above the key target temperature, Engine ECM interprets a demand for additional cooling. Engine ECM starts sending a reduced amount of current from the Engine ECM to the solenoid valve. The solenoid valve will move proportionally, in the de-energized direction. The fan pump will upstroke. The minimum speed of the fan and the maximum speed are stored in the Engine ECM. The set limits for speed of the hydraulic fan can be changed through Caterpillar Electronic Technician. For additional information regarding the calibration of the hydraulic fan system, refer to the Testing and Adjusting, "Hydraulic Fan System - Test and Adjust".
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129 The Engine ECM receives input signals from the engine coolant temperature sensor, and intake manifold air temperature sensor. Hydraulic oil temperature sensor signals are sent to the Caterpillar Monitoring System main display module and transmitted over the Cat Data Link to the Engine ECM. The Engine ECM processes the input signals and sends corresponding output signals to the variable speed fan solenoid valve. NOTE: The variable speed fan control feature can be enabled, disabled, and calibrated using the ET Service Tool. The variable speed fan default setting is enabled.
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The coolant temperature sensor (1) is installed in the jacket water and located on the front of the engine and the rear of the machine. The sensor sends an input to the Engine ECM (3) with the temperature of the engine coolant. The air intake temperature sensor (2) is located in the air intake manifold on the left side of the machine. The sensor also sends an input to the Engine ECM (3) with the temperature of the air in the air intake manifold.
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The hydraulic oil temperature sender (1) is located on the bottom of the hydraulic tank (2) behind the cab. The sender sends an input to the Engine ECM (not shown) with the temperature of the hydraulic oil. The hydraulic fan solenoid (3) is installed on the accumulator charging valve and solenoid valve (4). The solenoid valve is an output from the Engine ECM. The valve controls the signal oil to the pump control valve.
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The Brake and Hydraulic fan Pump The brake and hydraulic fan pump is located on the right side of the machine. The pump is installed on the engine and is driven by the gear train in the front cover. The pump is a variable displacement piston pump that is upstroked when the demand for more oil flow is commanded by the pump control valve. Located on the engine is the accumulator charging valve and fan solenoid. The valve is also located on the same side of the engine as the pump. Also, installed on the engine is the Engine ECM. The Engine ECM is an A4E4 with a 120 pin connector and a 70 pin connector. The Engine ECM reads key target temperatures and sends current to the solenoid valve on the accumulator charging valve and fan solenoid. These temperatures will determine the amount of oil sent to the fan motor in order to cool the machine components.
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135 When the engine is OFF, the bias spring holds the swashplate at maximum angle. When the engine is started, the pump drive shaft starts to rotate. Oil is drawn into the piston bore from the pump inlet. As the pistons and barrel assembly rotate, the oil is forced out the pump discharge.
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136 Brake And Hydraulic Fan Pump - Low Pressure Standby When no flow is demanded, no signal pressure is generated. Flow generated by the pump creates "low pressure standby." The pump produces sufficient flow to compensate for system leakage at low pressure standby to provide instantaneous response when flow is requested. At machine start-up, the bias spring holds the swashplate at maximum angle. As the pump produces flow, system pressure begins to increase because the flow is blocked in the system. This pressure is felt under both the flow compensator spool and the pressure compensator spool. The flow compensator spool moves up against the margin spring and permits system oil to flow around the pressure compensator spool to the large actuator piston. As pressure in the large actuator piston increases, the large actuator piston overcomes the force of the bias spring and the pressure in the small actuator piston and moves the swashplate to a reduced angle. The large actuator piston will move to the right until the cross-drilled passage in the stem is uncovered. Oil in the large actuator piston can then drain to the pump case. At this minimum angle, the pump will produce sufficient flow to make up for system leakage.
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NOTE: Low pressure standby is usually higher than margin pressure. This characteristic is due to the oil flow being blocked by the closed centered control valves when all the valves are in HOLD. The blocked pump supply oil pushes the margin spool up and compresses the margin spool spring more when the pump is at low pressure standby than during a constant flow condition (which will be discussed later in detail).
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137 Brake And Hydraulic Fan Pump - Upstroke When the demand for flow is increased, a signal pressure equal to the work port pressure is sent to the margin spring chamber. This signal pressure increases the force (margin spring plus signal pressure) at the top of the flow compensator spool to become higher than the supply pressure at the bottom of the spool. The spool then moves down, blocks oil to the large actuator and opens a passage to drain. Pressure at the large actuator piston is reduced or eliminated, which allows the bias spring and small piston to move the swashplate to an increased angle. The pump will upstroke to produce the required increase in flow.
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138 As pump flow increases, pump supply pressure also increases. When the pump supply pressure increases and equals the sum of the signal pressure plus the margin spring pressure, the flow compensator spool moves to a metering position and the system becomes stabilized.
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139 When less flow is needed, the pump is destroked. To destroke the pump, the force at the bottom of the flow compensator spool becomes higher than at the top. The flow compensator spool then moves up directing more pressure and flow to the large actuator piston. The large actuator piston then overcomes the combined force of the small actuator and bias spring and moves the swashplate to a reduced angle. The pump will now supply less flow.
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140 The pressure compensator spool is in parallel with the flow compensator spool. The pressure compensator limits the maximum system pressure for any given pump displacement. The spool is forced down during normal operation by the pressure compensator spring. During a stall condition or when system pressure is maximum, signal pressure is equal to pump supply pressure. The combination of the signal pressure and the margin spring force moves the margin spool down. This movement of the margin spool normally opens a passage in the pump control valve for the oil in the large actuator piston to drain and causes the pump to upstroke. However, since the supply pressure is high enough, the pressure cutoff spool is forced up against the spring. This movement of the pressure compensator spool directs pump system pressure to the large actuator piston. The increase in pressure allows the large actuator piston to overcome the combined force of the small actuator piston and bias spring to destroke the pump. The pump is now at minimum flow and pump supply pressure is at maximum. This feature eliminates the need for a main system relief valve in this brake and hydraulic fan system. Maximum system pressure is adjusted by turning the adjustment screw for the pressure compensator spool.
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Accumulator Charge Valve and Hydraulic Fan Solenoid The accumulator charge valve and hydraulic fan solenoid is a priority valve. The operation of the valve determines the oil flow for the hydraulic fan system and the braking system. The amount of flow going to the fan motor is, determined by a solenoid valve, which feeds pressure back to the load sense line to the pump control valve. A priority valve in the fan drive portion determines whether or not to send flow to the fan. Whenever the brake accumulators are adequately charged, the priority valve will be open, allowing full flow to the fan. However, when brake accumulator pressure is low, the priority valve will be shut off by the brake charge cut-in valve, forcing all flow to the brake charge section of the block. The brake charge section of the block will send the flow to the brake accumulators to charge them. The two halves are separate by a brake charge check valve, intended to hold the oil pressure within the brake charge section of the block.
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The following components are located on the fan control and brake accumulator charging valve: - Signal line to the fan and brake pump (1) - Fan solenoid valve, an electronic output of the Engine ECM which controls the speed of the cooling fan (2) - Relief valve, limits the maximum pressure in the brake system (3) - Cut-in valve, maintains minimum brake accumulator pressure (4) - Return hose to the hydraulic tank (5) - Cut-out valve, maintains maximum brake accumulator pressure (6) - Brake pressure switch, warns the operator when brake accumulator pressure is low (7) - Inverse shuttle valve, maintains equal charge pressure in both accumulators (8) - Accumulator ports (9) - Pump inlet port (10) - Fan motor outlet port (11) - Priority valve, blocks flow to the fan motor when the brake accumulators are charging (12)
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Service Brake Valve This illustration shows the service brake valve. The service brake valve is located under the cab at the articulation hitch. Pressure tap (2) is for the front brakes and pressure tap (3) is for the rear brakes.
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143 This illustration shows the brake system with the parking brake dis-engaged. The parking brake actuator is spring applied and hydraulically released. When the operator pushes the parking brake knob inward, the parking brake valve is shifted mechanically downward allowing brake oil to flow to the parking brake actuator. The springs are compressed and the lever moves the arm downward releasing the parking brake. At this time, the parking brake pressure switch sends a signal to the Power Train ECM informing the ECM that the parking brake is disengaged and the transmission can be shifted to FORWARD or REVERSE. The Power Train ECM communicates to the Monitoring System over the Cat Data Link that the parking brake is released.
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144 This illustration shows the brake system with the engine running and the parking brake disengaged. The parking brake actuator is spring applied and hydraulically released. When the operator pushes the parking brake knob inward, the parking brake valve is shifted mechanically downward allowing brake oil to flow to the parking brake actuator. The springs are compressed and the lever moves the arm downward releasing the parking brake. At this time, the parking brake pressure switch sends a signal to the Power Train ECM informing the ECM that the parking brake is dis-engaged and the transmission can be shifted to FORWARD or REVERSE. Also shown in this illustration, is the service brakes applied. The right brake pedal is depressed and the service brake valve shifts downward and the charged brake oil is directed to the service brakes.
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145 CATERPILLAR MONITORING SYSTEM This illustration shows the the relationship of the Caterpillar Monitoring System to the other ECMs on the "H" Series Wheel Loaders. Information displayed on the Caterpillar Monitoring System is sent to the main display module from input components in the monitoring system. Information is also received by the monitoring system from the Power Train ECM, Engine ECM, and Implement ECM over the CAT Data Link. The "H" Series Wheel Loaders use a programmable Caterpillar Monitoring System main display module, which enables installation of updated software that may include future control system features.
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Fuel Level Sender The fuel level sender is located on the top of the fuel tank at the rear of the machine. The sender can be accessed by raising the engine hood. The sender measures the depth of fuel in the tank. The fuel level sender has an internal resistance between 28 and 250 Ohms and is connected to pin 9 and the Cat Monitoring System ECM. The quad gauge displays the fuel level. Note: The fuel level sender can be service separately from the float assembly.
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Hydraulic Oil Temperature Sensor The hydraulic oil temperature sensor is located in the lower end of the hydraulic tank. The sensor is a passive temperature sensor with a thermistor at the tip. The voltage output will decrease as the temperature increases in the tank. The signal from the sensor is connected to pin 10 on the Cat Monitoring System ECM.
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148 Service Brake Pressure Switch The service brake pressure switch (1) is located on the right side of the machine below the Engine ECM (2) and next to the engine oil pan (3). The pressure type switch contacts are normally open. When the engine is running, the switch contacts make as the brake accumulator oil pressure increases to approximately 8270 kpa (1200 psi). If the brake pressure decreases to approximately 6890 kPa (1000 psi), the contacts will open the ground path for pin 20 on the Cat Monitoring System ECM. The brake oil pressure alert will begin flashing on the main display module.
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Axle Oil Temperature Sensors The above illustrations show the location of the axle oil temperature sensors. Sensor (1) is located in the front differential. Sensor (2) is located in the rear differential. The sensors are passive temperature sensor with a thermistor at the tip. The voltage output of the sensor will decrease as the oil temperature in the respective differentials increases. The front axle temperature sensor is connected to pin 8 on the Cat Monitoring System ECM. The rear axle temperature sensor is connected to pin 38 on the Cat Monitoring System ECM.
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Filter Bypass Switches In The Right Side Service Bay These illustrations show the locations of the power train filter pressure bypass switch (2) and the hydraulic oil filter bypass switch (7) in the service bay. The power train filter bypass switch (2) is a pressure differential switch which will give a Level 3 Warning when the filter is bypassing. The Cat Monitoring System will announce the warning when the transmission oil temperature is at normal operating temperature. The hydraulic oil filter bypass switch (7) is located on the filter base (1) base. The switch signals for illumination when the pressure is above 138 kPa (20 psi).
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Hydraulic oil SOS port (4) (Blue) is located on the filter base (1) and the power train SOS port (6) (Purple) is located on the power train filter base (3). Also shown is the brake accumulators (5)
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Torque Converter Outlet Temperature Sensor The torque converter outlet temperature sensor (1) is a passive sensor that sends an input temperature signal to Cat Monitoring System ECM. The monitoring system interprets the temperature signal and moves the needle for the transmission oil temperature indicator (3) to reflect the oil temperature. Also shown is the Engine ECM (2).
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Electrical System The indicator (1) for the electrical system will illuminate when there is a malfunction in the electrical system. The system voltage is too high for normal machine operation or the system voltage is too low for normal machine operation. If the electrical loads are high with low engine speed, then increase output from the alternator. If the alert indicator for the electrical system turns off within one minute, the electrical system is operating normally. Overloading may occur during periods of low engine speeds. Revise the operating cycle in order to avoid overloading the electrical system. Overloading the electrical system could result in discharging the batteries.
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If this procedure does not cause the alert indicator to turn off, stop the machine and investigate the cause of the fault. The fault may be caused by an alternator belt that is loose or broken. Also, the batteries may be faulty. If the indicator remains on near normal operating speeds and with light electrical loads, stop the machine and investigate the cause of the fault. The fault may be caused by an alternator belt that is loose or broken. Also, the batteries or the alternator may be faulty. The electrical indicator is connected to the "R" (3) contact on the alternator (2).
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Action Alarm The action alarm (1) is an output of the Cat Monitoring System (pin 4). When the action alarm is audible, the machine needs immediate attention. A safe machine shutdown is required. The main display module will sound the action alarm whenever a warning category 3 problem exists. An alarm for a warning category 3 is a pulsating sound. The alarm for a warning category 2S is a continuous tone. The action alarm does not operate when the engine is stopped. The main display module uses functions in order to determine when the engine is running. The following functions are examples: engine oil pressure, alternator output and engine speed. If necessary, the action alarm SOUNDS when the main display module decides that the engine is running. The action alarm is located behind the operator’s seat next to the implement ECM (2).
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Fuel Pressure Indicator The fuel pressure indicator is located on the left side of the dash panel. This light indicator illuminates if the fuel pressure is extremely low. If this alert indicator flashes during operation, the primary fuel filter is bypassing.
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Engine Tachometer Tachometer located on the front dash panel shows an analog display of the engine speed in both rpm and km/h. The engine speed is determined by the information sent to the Cat Monitoring System module over the Cat Data Link from the Engine ECM. The crankshaft speed timing sensor and the camshaft speed timing sensor initiate the input signals to the Engine ECM. The Cat Monitoring System also sends the Module Clock signal and the Data signal to the tachometer module.
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The C11 ACERT™ and C13 ACERT™ engines utilize the A4 Electronic Control Module (ECM) engine control and is equipped with an Air-to-Air Aftercooler (ATTAC) intake air cooling system. The C11 engine is rated at 175 kW (235 net horsepower). The C13 engine is rated at 198 kW (265 horsepower). The C11 and C13 engines are electronically configured to provide constant net horsepower through the operating ranges. Constant net horsepower automatically compensates for any parasitic loads, allowing the operator to maintain a constant level of productivity The Engine ECM utilizes the Advanced Diesel Engine Management (ADEM IV) to control the fuel injector solenoid and to monitor fuel injection. The fuel is delivered is through a Mechanical Electric Unit Injection (MEUI) system. ACERT™ Technology provides an advanced electronic control, a precision fuel delivery, and refined air management. The C11 engine is an in-line six-cylinder arrangement with a displacement of 11.1 L. The C13 engine is also an-inline six-cylinder arrangement with a displacement of 12.5 L. The C11 ACERT™ and C13 ACERT™ engines meet US Environmental Protection Agency (EPA) Tier III Emission Regulations for North America and Stage III a European Emission Regulations. NOTE: For additional information in troubleshooting the engine, refer to the Service Manual module Troubleshooting "C11 and C13 Engines for Caterpillar Built Machines (RENR9318).
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161 Engine Electrical Block Diagram This block diagram of the engine electrical system shows the components that are mounted on the engine which provide input signals to and receive output signals from the Engine Electronic Control Module (ECM). Based on the input signals, the Engine ECM energizes the injector solenoid valves to control fuel delivery to the engine, and the cooling fan proportional solenoid valve to adjust pressure to the cooling fan clutch. The two machine interface connectors provide electrical connections from the engine to the machine including the Cat Data Link. Some of the components connected to the Engine ECM through the machine interface connectors are: the throttle pedal position sensor, the right brake pedal switch, the ether start control solenoid, and the ground level shutdown switch.
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Input Components: Camshaft speed timing sensor - The speed timing sensor sends a fixed voltage level, signal to the Engine ECM in order to determine the engine speed, direction, and timing. Crankshaft speed timing sensor - The speed timing sensor sends a fixed voltage level, signal to the Engine ECM in order to determine the engine speed, direction, and timing. Atmospheric pressure sensor - This sensor is an input to the Engine ECM and is used as a reference for air filter restriction. Also, the sensor is used to supply information to the Engine ECM during operation at high altitudes. Turbo inlet pressure sensor - This sensor is an input to the Engine ECM to supply information about the air restriction before the turbocharger. Intake manifold temperature sensor - This sensor supplies air temperature data at the air intake manifold to the Engine ECM.. Fuel pressure differential switch - This switch relays information to ECM that the fuel pressure at the output of the filter base is restricted in comparison to the inlet pressure. Engine coolant temperature sensor - The coolant flow switch mounts in the coolant passage near the engine coolant pump. When the coolant is flowing past the switch the paddle moves and closes the switch contacts. The Engine ECM alerts the operator when there is no coolant flow while the engine is running. Fuel temperature sensor - This sensor relays data to the Engine ECM about the fuel temperature. Engine oil pressure sensor - This sensor is an input to the Engine ECM to supply information warning for low oil pressure, engine derates for low oil pressure, or a logged event read by ET. Throttle pedal position sensor - This sensor relays the position of the throttle to the Engine ECM in order to increase or decrease the fuel supply to the injector. Auto reversing fan switch - The switch is an operator input to the Engine ECM. The operator can manually enable the reversing solenoid valve and change the direction of oil flow through the hydraulic fan motor . Key switch ON (+B) - The key switch on sends + voltage to the electrical system. Ground level shutdown switch - This switch will disable the engine start or shutdown the engine from ground level. Intake manifold pressure sensor - This sensor is an input to the Engine ECM to supply information about the air pressure into the intake manifold.
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Output Components: +5 Volt - Regulated supply voltage for the sensor inputs to the Engine ECM. Throttle sensor voltage - Voltage supply for the throttle position sensor. Analog sensor voltage - Analog voltage for the turbo inlet pressure sensor. Either ON solenoid valve - Solenoid valve used to apply ether in order to start the engine in cold weather. Auto reversing solenoid valve - This solenoid valve is used in order to reverse the oil flow oil through the hydraulic fan motor.. Demand fan solenoid valve - Proportional solenoid valve that controls the signal pressure to the brake and fan pump in order to meet the varying cooling requirements of the machine. Air filter restriction indicator - This indicator illuminates in case of a restriction in the inlet air system. Ether On indicator - This indicator illuminates when the ether solenoid valve is initiated.
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162 Engine Right Side This view shows the right side of the engine accessed from the right side of the machine. Components which can be seen are: - Alternator (1) - Electric fuel priming pump (2) - Secondary fuel filter (3) - Air inlet (4) - Fuel transfer pump (5) - Hydraulic fan pump (6) - Brake accumulator charging valve (7) - Engine ECM (8) - Cam speed sensor and Atmospheric pressure sensor
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163 Engine Left Side This view shows the left side of the engine accessed from the left side of the machine. Components which can be seen are: - Air inlet (with turbo inlet pressure sensor) (1) - Turbocharger (waste gated) (2) - Coolant regulator housing (3) - Transmission cooler (coolant-to-oil) (4) - Engine coolant pump (5) - Engine oil cooler (coolant-to-oil) (6) - Engine starter (7) - Engine oil filter (8)
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Crankshaft Speed Timing Sensor The crankshaft speed timing sensor (1) is located in the front of the engine at the rear of the machine. The crankshaft sensor is the primary speed sensor reporting to the Engine ECM with the engine speed and position of the crankshaft. The speed sensor detects the reference for engine speed and timing from a unique pattern on the respective gear. Normally the crankshaft speed timing sensor identifies the timing during starting and determines when the N0. 1 cylinder is at the top of the stroke. When the timing is established, the crankshaft timing sensor is used to relay the engine speed and the camshaft sensor is ignored. If the engine is running and the signal from the crankshaft is lost, a slight change in performance is noticed during change over to the camshaft sensor.
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If the signal from the crankshaft speed timing sensor is lost or intermittent, normally a CID 0190 FMI 08 Engine Speed Abnormal will be logged and can be viewed through Caterpillar ET. Also, the engine speed is also shared with the Power Train ECM and Implement ECM. Also shown is the hydraulic fan pump (2).
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The atmospheric pressure sensor (1) is located on the right side of the machine on the engine. The Engine ECM uses the sensor as a reference for air filter restriction, and derating the engine under certain parameters. All pressure sensors in the system measure absolute pressure and, therefore, require the atmospheric pressure sensor to calculate gauge pressures. The atmospheric pressure sensor is one of the many sensor that require a regulated 5.0 VDC for the sensor supply voltage. The atmospheric pressure sensor outputs a variable DC voltage signal. The Camshaft speed timing sensor (2) is located below the atmospheric pressure sensor. Under normal operation, the camshaft speed timing sensor determines the No. 1 compression timing prior to the engine starting. If the camshaft sensor is lost, a CID 342 MID 08 Secondary engine Speed signal abnormal and the crankshaft sensor will time the engine with an extended starting period and run rough until the Engine ECM determines the proper firing order using the crankshaft sensor only. In the case that the signal from both engine speed sensors are lost, the engine will not start. During a running condition, the engine will shutdown. The sensor serves as a backup for the crankshaft speed timing sensor. If the crankshaft speed timing sensor fails, the camshaft speed timing sensor allows for continuous operation.
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167 Engine Speed/Timing Calibration Port The speed/timing calibration port is located on the right side of the machine. The Engine ECM (1) has the ability to calibrate the mechanical differences between the Top Center (TC) of the crankshaft and the timing gear on the camshaft. A magnetic transducer signals the TC of the crankshaft to the ECM when the notch (2) on a counterweight passes by the transducer (not shown). The speed/timing sensor signals the TC of the timing gear to the Engine ECM. Any offset between the TC of the crankshaft and the TC of the timing gear is stored into the memory of the Engine ECM. Remove plug (3) in order to install the timing probe. NOTE: For additional information in troubleshooting the engine, refer to the Service Manual module Troubleshooting "C11 and C13 Engines for Caterpillar Built Machines" (RENR9318) "Engine Speed/Timing Sensor - Calibrate.
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168 FUEL SYSTEM Fuel is drawn from the fuel tank through the primary fuel filter and water separator by a geartype fuel transfer pump. The fuel transfer pump then directs the fuel through the secondary fuel filter. The fuel then flows to the cylinder head. The fuel enters the cylinder head and flows into the fuel gallery, where it is made available to each of the six MEUI fuel injectors. Any excess fuel not injected leaves the cylinder head and flows back to the secondary fuel filter base where it flows past the fuel pressure regulator. The fuel pressure regulator is a check valve that is installed in the secondary fuel filter base. The fuel pressure regulator maintains fuel system pressure between the fuel transfer pump and the fuel pressure regulator. From the fuel pressure regulator, the excess fuel flow returns to the fuel tank. The ratio of fuel used for combustion and fuel returned to tank is approximately 3:1 (i.e. four times the volume required for combustion is supplied to the system for combustion and injector cooling purposes).
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A pressure differential switch is installed in the secondary fuel filter base and will alert the operator of a fuel filter restriction. The pressure differential switch compares the filter inlet pressure to the filter outlet pressure. When the difference in the inlet and outlet pressures causes the switch to activate, the Engine ECM will signal the Implement ECM to warn the operator the fuel flow is probably restricted. A fuel temperature sensor is installed in the secondary fuel filter base and will signal the Engine ECM of a high fuel temperature. The effect of high fuel temperature is an engine derate. The fuel system will derate to 12.5% at 91 °C (196 °F) percent to a maximum derate of 25%. A fuel pressure sensor is installed in the secondary fuel filter base and will signal the Engine ECM of a high fuel pressure. If the fuel pressure exceeds a pressure of 758 kPa (110 psi) the Engine ECM will log a E096 code. In the case of a logged high fuel pressure Event, check the Fuel System's Components - Inspect the fuel transfer pump pressure relief valve that is in the body of fuel transfer pump. Check for damage to the spring or to the valve assembly. - Verify that the pressure regulating valve in the fuel manifold is operating correctly. Check for damage or for dirt in the valve assembly. - Check the return line from the fuel filter base to the fuel tank for damage or collapse.
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Fuel Transfer Pump The fuel transfer pump is a gear pump that is located near the balancer at the front of the engine and the rear of the machine. The fuel transfer pump is driven by the front gear train. Fuel is drawn through the primary fuel filter and water separator by the fuel transfer pump and is directed to the secondary fuel filter. The fuel transfer pump incorporates a check valve. The check valve allows fuel to flow around the gears of the pump when the fuel system is primed. A relief valve (not shown) is also installed in the fuel transfer pump. The relief valve limits the maximum fuel pressure in the fuel system.
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170 Power Derate The illustration above defines the power derate in relation to the rated torque map and the default torque map. The power derate is a percentage reduction from the rated power at a given engine speed toward the default map at the same rpm. Power is unchanged until the requested power exceeds the derated level. The maximum power during a derate is calculated as: Maximum Power Output = Rated Power - (Rated Power - Default Power) * Derate Percentage For example, if the engine has a maximum rated power of 500 hp and a 100 hp default torque map with a 50% derate, the engine will have 300 hp output power. If 250 hp was needed, then the operator will not notice any change. If however, 400 hp was needed, there would be only 300 hp available due to derates. 300 hp = 500 hp - (500 hp - 100 hp) X 50% (.50)
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Fuel Filter Sensors The fuel system is equipped with two filters, a primary fuel filter/water separator (1) and a secondary filter (2). The primary fuel filter is located on the right side of the machine. the primary filter contains a water separator which removes water from the fuel. Water in a high pressure fuel system can cause premature failure of the injector due to corrosion and lack of lubrication. Water should be drained from the water separator daily, using the drain valve that is located at the bottom of the filter.
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The electric fuel priming pump (4) is integrated into the primary fuel filter base. The priming pump is activated by toggling the fuel priming pump switch (3). The fuel priming pump is used to fill the fuel filters with fuel after they have been replaced. The priming pump will purge the air from the entire fuel system. To activate the fuel priming pump, the key start switch must be in the OFF position. The fuel system is equipped with a secondary high efficiency fuel filter. The fuel regulator (5) is integrated into the secondary fuel filter base. The fuel pressure regulator regulates the pressure Also, installed on the base is a fuel pressure differential switch (7), a fuel pressure sensor (6) and and a fuel temperature sensor (8).
High fuel pressure sensor is an indicator of a fuel return or a pressure control problem. Excessively high pressure in the fuel system can cause problems for the injector. A pressure differential switch is installed in the secondary fuel filter base and will alert the operator of a fuel filter restriction. The pressure differential switch compares the filter inlet pressure to the filter outlet pressure. When the difference in the inlet and outlet pressures causes the switch to activate, the Engine ECM will signal the Implement ECM to warn the operator the fuel flow is probably restricted. A fuel temperature sensor is installed in the secondary fuel filter base and will signal the Engine ECM of a high fuel temperature. The effect of high fuel temperature is an engine derate. The fuel system will derate to 12.5% at 91 °C (196 °F) percent to a maximum derate of 25%. A fuel pressure sensor is installed in the secondary fuel filter base and will signal the Engine ECM of a high fuel pressure. If the fuel pressure exceeds a pressure of 758 kPa (110 psi) the Engine ECM will log a E096 code. In the case of a logged high fuel pressure Event, check the Fuel System's Components - Inspect the fuel transfer pump pressure relief valve that is in the body of fuel transfer pump. Check for damage to the spring or to the valve assembly. - Verify that the pressure regulating valve in the fuel manifold is operating correctly. Check for damage or for dirt in the valve assembly. - Check the return line from the fuel filter base to the fuel tank for damage or collapse.
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173 FUEL TEMPERATURE DERATE This illustration shows the graph for the warning and derates map for the fuel temperature. When the fuel temperature exceeds 90° C (194° F), the Engine ECM will activate a Level 1 Warning. Also, the graph shows, as the fuel temperature increases to 91.0 °C (196° F) a Level 2 Warning will be initiated by the Engine ECM. At the same time, the engine will derate to 12.5%. If the fuel temperature exceeds 92° C (198° F), the engine will be derated to 25%. A fuel temperature sensor open circuit will derate the engine to 12.5%. Excessive fuel temperature will cause injector wear.
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174 High Fuel Filter Restriction Derates When the differential pressure switch recognizes a fuel pressure of 103 kPa (15 psi) for 3 minutes, the Engine ECM will initiate a Level 1 Warning. When the differential pressure switch recognizes 15 psi across the filter for 4 hours, the Engine ECM will initiate a Level 2 Warning. With the Level 2 Warning initiated a 17.5 % derate is applied to the engine. After 1 second, the Engine ECM will initiate a second derate of 17.5%. The total derate will be 35%. This feature will be disabled when the fuel temperature is below 30° C (86 ° F)
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Engine Inlet Air System In the engine inlet air system, the air enters the compressor section of the turbocharger (4) through the air cleaner (2). The compressor directs the air through the ATAAC (3), the air intake manifold, and to the cylinder head. Exhaust exits the cylinder head to the turbine housing. From the turbine housing, the turbine wheel directs the exhaust out of the turbo and out through the muffler (1).
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177 The C11 and C13 ACERT™ engines are equipped with a waste gate turbocharger which provides higher boost over a wide range, improving engine response and peak torque, as well as outstanding low-end performance. All of the exhaust gases go from the exhaust manifold through the turbocharger. The exhaust gases enter the turbocharger and drives the turbine wheel. The exhaust exit the turbocharger through turbine wheel outlet (2) to the muffler. The turbine wheel is connected by a shaft to the compressor wheel, the turbine wheel rotates the compressor wheel at very high speeds. The rotation of the compressor wheel pulls clean air through the compressor housing air inlet (1). The compressor wheel blades force air into the cylinder head to the inlet valves. The increased amount of forced air enables the engine is able to burn more fuel producing increased power. The engine can operate under low boost conditions. During a lower boost condition, the canister closes the wastegate, allowing the turbocharger to operate at maximum performance. Under high boost conditions, the wastegate opens. The open wastegate allows exhaust gases to bypass the turbine side of the turbocharger. The rpm of the turbocharger is limited by bypassing a portion of the exhaust gases around the turbine wheel of the turbocharger. NOTE: The wastegate calibration is preset at the factory.
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Turbo Inlet Pressure Sensor The turbocharger inlet pressure sensor is located in the tube that is between the air filter group and the inlet to the compressor housing of the turbocharger. The turbocharger inlet pressure sensor measures restriction of air flow through the air filters and the inlet to the turbocharger. Restriction of the air flow to the turbocharger will initiate a warning and engine derate.
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180 Engine Oil Pressure Sensor The engine oil pressure sensor (1) is located on the left side of the engine and the right side of the machine near the Engine ECM (2). The sensor monitors the pressure of the engine oil. The engine oil pressure sensor is one of the many sensors that require a regulated 5.0 VDC for the sensor supply voltage. The sensor outputs a variable DC voltage signal. The Engine ECM will use the information supplied oil pressure sensor to output warning levels to the Caterpillar Monitoring System and engine derates.
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181 LOW OIL PRESSURE This illustration shows a graph with the two different warning levels for low oil pressure. When the oil pressure is below (154 kPag @ 1600 rpm) the blue line, the cat monitoring system will enable the low oil pressure Level 1 Warning. Change machine operation or perform maintenance to the system. When the oil pressure is below (104 kPag @ 1600 rpm) the red line, the cat monitoring system will enable the low oil pressure Level 3 Warning. The operator should immediately perform a safe engine shutdown. Also, with the Level 3 Warning, the Engine ECM initiates a 35% engine derate. If the signal between the Engine ECM and the oil pressure sensor is lost or disabled, the Engine ECM will initiate a low engine oil pressure Level 1 Warning.
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179 Air Inlet Restriction Derate The turbo inlet pressure sensor measures the restriction of the air inlet that is flowing to the inlet of the compressor housing of the turbocharger. When the pressure difference between the turbo inlet pressure sensor and the atmospheric sensor read a difference of 9.0 KPa, the Engine ECM will derate the engine approximately 2%. The Engine ECM will then derate the engine 2% more for every 1 kPa difference up to 10%. Typically the atmospheric pressure sensor is 100 Kpa at sea level. As the air restriction increases, the difference will increase. The first derate will occur when the difference is approximately (100 kpa minus 91 kpa.= 9 kpa). If the air inlet restriction is 92.5 kPa (a pressure that is between 7.5 kPa and 9 kPa) for 10 seconds, the Engine ECM will initiate a Level 1 Warning. If the air restriction goes to the point that the turbo inlet pressure sensor sees a difference of 91.0 kPa (a pressure that is 9.0 KPa) for 10 seconds, then the Level 2 Warning will occur then the engine will going into the air inlet restriction derate.
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182 Engine Coolant Temperature Sensor The coolant temperature sensor is installed at the right front corner of the engine, above the jacket water pump. The coolant temperature sensor monitors the temperature of the fluid in the coolant system. The coolant sensor information sent to the Engine ECM is used for Warning Levels that are sent to the Caterpillar Monitoring System and engine derates.
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Intake Manifold Sensors The upper illustration shows the intake manifold air pressure sensor (1), and the intake manifold air temperature sensor. The intake manifold air pressure sensor (1) is used to monitor intake manifold pressure. The intake manifold air temperature sensor (2) is used to monitor the air temperature flowing into the intake manifold. The Engine ECM also uses the temperature sensor as one of the key target temperatures to control the fan speed in the hydraulic fan system and as an input to the Engine ECM for the virtual exhaust temperature derate. Also shown is the Engine ECM (3) and intake manifold (4).
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186 Intake Manifold Air Temperature Sensor Derate The intake manifold air temperature sensor measures the temperature of the air that is flowing to the intake manifold. The sensor is used to initiate warning levels and engine derates After the engine is running for at least 3 minutes and if the intake manifold air temperature goes above 82° C (180° F), the Engine ECM will initiate a Level 1 Warning. After the engine is running for at least 3 minutes and if the intake manifold air temperature goes above 86° C (187° F), the Engine ECM will initiate a Level 2 Warning. With the Level 2 Warning, the Engine ECM signals the engine to initiate a 3% derate. This derate will have a 20% upper limit.
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183 High Coolant Temperature Derate The coolant temperature sensor measures the temperature of the coolant. When the temperature of the coolant exceeds 110° C (230° F), the Engine ECM will initiate a Level 1 Warning. When the temperature of the coolant exceeds 111° C (231° F), the Engine ECM will initiate a Level 2 Warning. At 111° C (231° F) the Engine ECM will initiate a 25% derate. Refer to the Illustration for the remainder of the high engine coolant temperature derates. At 100% derate, the engine available power will be approximately 50%.
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187 Virtual Exhaust Temperature Derate An engine derate can occur due to a estimated (virtual) high exhaust gas temperature. The Engine ECM monitors barometric pressure, intake manifold temperature, and engine speed to estimate exhaust gas temperature. Certain conditions (high altitude, high ambient temperatures, high load and full accelerator pedal throttle, barometric pressure, intake manifold temperature, and engine speed) are monitored to determine if the engine derate should be enabled. The Engine ECM determines a maximum fuel delivery percentage to maintain safe maximum power output under load. This calculation is new to the off-road Tier III engines and is used in place of the previous altitude compensation derate strategy. This event is to inform the mechanic that a derate has occurred because of operating conditions. Generally, this is normal and requires no service action. The Engine ECM will process all derate inputs in the highest derate priority selector. The most critical derate condition input will be used to adjust fuel system delivery limiting engine power to a safe level for the conditions in which the product is being operated, thereby prevent elevated exhaust temperatures.
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The virtual exhaust temperature derate will log a 194 event code. The derate will enable a Level 1 Warning and eventually a Level 2 Warning. The level of the warning will depend on the conditions that are sent to the Engine ECM. The following conditions must be met in order to initiate a virtual exhaust temperature derate. -.No CID 168 01 FMI (low battery voltage to the Engine ECM) are active. - No active intake manifold pressure sensor faults. - No active atmospheric pressure (barometric) sensor faults - No +5 V sensor voltage codes active. - The virtual exhaust temp derate must be the highest derate. - More fuel is being requested than the virtual exhaust temp derate will allow. This derate is triggered by the information inferred by the Engine ECM, rather than an individual sensor as with the previous single derate strategies. If you think this derate is possibly being imposed incorrectly check for event codes on high intake manifold temperature and correct those first. Also, make sure the aftercooler is unobstructed. For additional information about troubleshooting, refer to the troubleshooting for the particular engine that is being serviced.
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CONCLUSION This presentation has provided information on the machine systems for the 966H Wheel Loader that is equipped with a C11 ACERT Engine and the 972H Wheel Loader equipped with a C13 ACERT Engine. Understanding the information and features accessible using Cat ET can make troubleshooting, diagnosis, and testing easier and more accurate. Always use the latest Service Information to ensure that the most current specifications and test procedures are used.
