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SERVICE TRAINING TECHNICAL PRESENTATION
994F WHEEL LOADER INTRODUCTION
Service Training Meeting Guide (STMG)
994F WHEEL LOADER -
INTRODUCTION
MEETING GUIDE XXXX
SLIDES AND
SCRIPT AUDIENCE Service personnel who understand the principles of machine systems operation, diagnostic equipment, and testing and adjusting procedures.
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 994D Wheel Loader.
OBJECTIVES After learning the information in this presentation, the serviceman will be able to: 1. locate and identify the major com ponents in the engi ne, power train, implement, steering, and brake systems; 2. explain the operation of each compo nent in the power trai n, implement, steering, and brake systems; and 3. trace the flow of oil through the power train, implement, steering, and brake systems.
REFERENCES 994F Wheel Loader Specalog XXXXX 994F Wheel Loader Service Manual RENR2500 994F Wheel Loader Parts Book SEBP2793 Video "994F Wheel Loader - Introduction" SEVN4643 TIM "994 Wheel Loader - Power Train" SEGV2596 TIM "994 Wheel Loader - Implement Hydraulic, Air, and Lube Systems" SEGV2601 TIM "994 Wheel Loader - Steering and Brake Systems" SEGV2602 TIM "992G Wheel Loader - Steering and Brake Systems " SERV2632-01 Estimated Time: 1 Hour Illustrations: 32 Handouts: 4 Form: SERV7104-05 Date: 04/04 © 2004 Caterpillar Inc.
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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 Schematics......................................................................87 Implement Oil Cooling System ......................................................................................90 Autolube System.............................................................................................................91 STEERING HYDRAULIC SYSTEM..................................................................................93 Steering System Components ........................................................................................93 Steering Hydraulic System Schematics .......................................................................100 STEERING AND BRAKE OIL COOLING SYSTEM .....................................................107 BRAKE HYDRAULIC SYSTEM .....................................................................................108 Brake System Schematic ..............................................................................................108 Brake Component Locations .......................................................................................110 CONCLUSION...................................................................................................................114 SLIDE LIST........................................................................................................................115 HANDOUTS.......................................................................................................................117
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994F WHEEL LOADER INTRODUCTION
© 2005 Caterpillar Inc.
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INTRODUCTION
This presentation discusses the component locations and systems operation of the 994F Wheel Loader. Basic engine and machine component locations will be discussed. Also, the power train, the implement hydraulics, the steering, and the braking system’s component location and operation will be covered. The 994F is the largest wheel loader in the Caterpillar product line. The loading capacity is matched with the 785 Off-Highway Truck (Standard Machine), the 789 Off-highway Trucks (High Lift) and 793 Off-highway Truck (Super High Lift). The new 994F Super High Lift can be equipped with a 35.9 cubic meter (47 cubic yard) coal application bucket. The 994F operating weight is approximately 160,200 Kg (429, 300 lbs) for a Standard Machine, 160,800 Kg (430,900 lbs) for the High Lift, and 174,300 Kg (467,000 lbs) for the Super High Lift. The serial number prefix for the 994F Wheel Loader is 442.
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Component Location
This illustration shows the basic component locations on the 994F. The component locations on the 994F are basically the same as the 994D but are restated in this presentation as a reminder. Power for the 994F is supplied by the 3516B High Displacement (HD) engine. The engine is connected to the rear pump drive with a spring coupling. Power flows from the rear pump drive to the torque converter, to the input drive shaft, and through the input transfer gear to the transmission. Power from the transmission flows through the output transfer gears to the drive shafts, to the bevel gears in the differentials, and then to the double reduction final drives. The 994F also has an auxiliary drive shaft that turns the front pump drive. The front pump drive is located in the Non Engine End Frame (NEEF). The secondary steering pump is splined to the output transfer gears. The secondary steering pump is ground driven.
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Similarities and Differences
This illustration compares the basic features of the 994F to the previous 994D. The chart illustrates if the features are different, similar, or the same. The major systems on the 994F are similiar to the 994D. The machine appearance and the implement hydraulic system are basically the same as the 994D with the addition of a variable displacement piston pump in tandem with the center fixed displacement piston pump on the front pump drive. The main relief pressure have been increased from 30360 kPa (4700 psi) on the 994D to 32775 kPa (4750 psi) on the 994F. Access to the implement pump case drain filters and the transmission and torque converter filters has improved from the previous version of the 994D. The 994F is installed with a lift linkage position sensor supporting in the cab control of the variable lift kickouts. Also, the 994F is equipped with remote pressure taps for the various hydraulic systems.
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The 994F is equipped with a 3516B HD EUI as compared to the 3516B EUI in the 994D. The new engine delivers 1,436 horse power, an increase of 14%. The 994F features new turbocharges, high-capacity air filters, and dual 80-amp alternators. The dual alternators promote faster engine response and increase fuel efficiency. The 994F has both starter and transmission lockout switches and engine shutoff switch at ground level for easy access. Also, the 994F has the option of installing the Caterpillar Oil Renewal System (ORS) which offers a means to reduce oil changes and increased machine availability. The power train difference between the 994D and 994F is the removal of the free wheel stator and the torque converter outlet relief valve. The 994F power train is now equipped with two added air-to-oil coolers in order to increase cooling of the power train system. The 994F has a fully modulated impeller clutch torque converter with flexibility of reducing rimpull using the left brake pedal. The pedal fully modulates the rimpull through the range of 100% to 25%. Also, the 994F power train has remote pressure taps installed. The braking system on the 994F has increased increased circuit pressure and now features split control system. The operator station on the 994F now has a new and larger cab with an approximate 75dBa sound level. A new Caterpillar seat with state of the art suspension is installed. Also, the cab has a trainer sear with a padded seat and back. The new cab has 50% more glass area increasing visibilty. The 994F retains the steering and transmission integrated control (STIC) power train which enables the operator to use small movements of a single hand to steer the machine and make direction/gear changes. The 994F is equipped with the latest Vital Information Management System (VIMS) that is similiar to the 994D. The maintenance items on the 994F are similar to the 994D. The major changes in the maintenance are access to the filters on the 994F. NOTE: For more information on the VIMS refer to the VIMS Service Manual RENR6318
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ENGINE
This view shows the right side of the engine which can be accessed from the left side of the machine. Components which can be seen are: - Turbocharger (1) - Coolant regulator housing (2) - Engine oil cooler (3) - Fuel Filter (4) - Alternator (5) - Transmission cooler (coolant-to-oil) (6) - Engine speed timing sensor (7) - Crankcase pressure sensor (8)
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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 throttle lock switches, the throttle lock enabled indicator, the right brake pedal switch, the ether start control solenoid, and the ground level shutdown switch.
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Input Components: 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. Oil level switch - The oil level switch (lower) is a float type switch mounted in the side of the engine oil sump. The Engine ECM monitors the engine oil level switch to alert the operator when the oil level is low. Coolant flow switch - 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. Exhaust temperature sensors -The exhaust temperature sensors have an analog to digital converter that provides a Pulse Width Modulated (PWM) signal. Cooling fan speed sensor, permanent timing calibration sensor - These speed sensors are passive speed sensors that provide a signal similar to a sine wave that varies in amplitude and frequency as speed increases. The permanent timing calibration sensor monitors the speed and position of the flywheel. Jacket water temperature sensor, aftercooler coolant temperature sensor - These temperature sensors are analog temperature sensors that provide a voltage signal to the Engine ECM. Crankcase, atmospheric, turbocharger outlet, filtered and unfiltered oil, left and right turbocharger inlet pressure sensors - These sensors are analog sensors that provide a voltage signal to the Engine ECM. The voltage varies to a level that corresponds with a calibrated pressure. The Engine ECM calibrates the pressure sensors to the atmospheric pressure when the key switch is moved to ON position for 3 seconds without the engine running.
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This illustration shows the machine controls that are located at the rear of the machine. The following is a list of the ground level components: - Ground level shutdown (1) - Hood lamp (2) - Ground level stair lamp (3) - VIMS key switch (4) - VIMS serial download port (5) - Hour meter (6) - Start lockout indicator (7) - Transmission lockout LED (8) - Transmission lockout switch (9) - Start lockout switch (10) - Locks (11)
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Turbocharger Inlet Pressure Sensor
This illustration shows the left turbocharger inlet pressure sensor (2) and right turbocharger inlet pressure sensor (3). The illustration shows the sensors on the turbochargers (1) that are installed on the front of the engine (located toward the rear of the machine). These analog sensors read the pressrue in the turbo inlets and send a corresponding voltage signal to the engine ECM. The left turbocharger inlet pressure sensor (2) and the right turbocharger inlet pressure sensor (3) communicates with the Engine ECM. Also shown are the inlet tubes (4).
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This illustration shows the two engine oil level switches. Both switches are normally open when installed for this application. Level switch (3) communicates with the Engine ECM. This switch opens the circuit when the oil level is below the neccessary level. Level switch (2) communicates with the VIMS module. The level switch signals that oil should be added to the engine. If the machine is equipped with the optional Oil Renewal System, the level switch (2) will disable the Oil Renewal System when the oil level is below the switch. Also shown is the engine oil filler tube (1).
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This illustration show the right side turbo inlet exhaust temperature sensor (1). The engine is also equipped with a turbo inlet exhaust temperature sensor on the left side (not shown). The sensors communicate with the Engine ECM.
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The illustration that is above shows the location of the Engine ECM (2) and the atmospheric pressure sensor (1). The engine ECM is an ADEMIII is equipped two 70 pin connectors. The Engine ECM (2) is mounted on the engine on the right side of the machine. The engine ECM is accessed from under the machine. The Engine ECM makes decisions based on control program information in memory, switch inputs, analog input signals and sensor input signals. The Engine ECM responds to machine control decisions by sending a signal voltage to the appropriate circuit which creates an action. For example, as the operator depresses the throttle pedal. The Engine ECM interprets the input signal from the throttle pedal position sensor, evaluates the engine status and sends a signal to the injectors to increase fuel. The Engine 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.
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The Engine 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 Engine ECM receives signals from the speed timing sensors, oil level switch, coolant flow switch, exhaust temperature sensors, coolant temperatures sensors, engine pressure sensors, and the current engine operating status. The Engine ECM interprets signals and determines the appropriate output signals to the engine. Different conditions of the inputs affect the output conditions. The Engine 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 Engine ECM has built-in diagnostic capabilities. As the Engine ECM detects fault conditions that are developed by the engine, it logs the faults in memory and displays them on theused VIMS. The faults fault codes can be accessed using the ET service tool. VIMS software can be to view logged byalso the VIMS. INSTRUCTOR NOTE: Engine ECM faults displayed on the VIMS relating to the Engine ECM will have a Module Identifier (MID) of "36." For more information, refer to the Service Manual module "Engine, Systems Operation Testing and Adjusting" (Form RENR2211).
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This is a partial view of the front right side of the engine. The illustration is showing the location of the following components on the right front side of the engine: Components which can be seen are: - Primary fuel filter (1) - Alternator (2) - Air conditioning compressor (3) - Engine oil cooler (4) - Fuel transfer pump (5) - Coolant flow switch (6) - Coolant pump for water jacket (7)
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This illustration shows the left side of the engine near the front. This side of the engine can be accessed by the right side of the machine. The illustration show the following components: - Secondary fuel filters (1) - Electric fuel priming pump and switch (2) - Fuel differential pressure switch (3) - Oil pressure sensor filtered (4) - SOS fluid sampling oil port (engine oil) (5) - Engine oil dipstick (6) - Oil pressure sensor unfiltered (behind the secondary fuel filters) (7) - Engine oil filters (8)
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Fuel System Fuel is pulled from the tank through a fuel heater, if equipped, and through the primary fuel filter by the fuel transfer pump. Fuel flows from the transfer pump through the Engine ECM to the secondary fuel filters. Fuel flows from the fuel filter base through the fuel injectors in the cylinder heads. Return fuel from the injectors flows through the fuel pressure regulator before returning through the fuel heater to the fuel tank. Engine oil flows from the engine block through an oil filter to the engine oil renewal system manifold. A small amount of oil flows from the engine oil renewal system manifold into the return side of the fuel pressure regulator. The engine oil returns to the fuel tank with the return fuel. The engine oil mixes with the fuel in the tank and flows with the fuel to the injectors to be burned.
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Engine Oil System The engine oil pump draws oil from the oil pan through a screen. The engine also has a scavenge pump at the rear of the engine to transfer oil from the rear of the oil pan to the main sump. Oil flows from the pump through an engine oil cooler bypass valve to the engine oil cooler. The bypass valve for the engine oil cooler permits oil flow to the system during cold starts when the oil is thick or if the cooler is plugged. Oil flows from the engine oil cooler to the oil filters. The oil flows through the filters and enters the engine cylinder block to clean, cool and lubricate the internal components and the turbochargers. Some trucks are equipped with an optional engine oil renewal system. Engine oil flows from the engine block through an oil filter to an engine oil renewal system manifold. A small amount of oil flows from the engine oil renewal system manifold into the return side of the fuel pressure regulator. The engine oil returns to the fuel tank with the return fuel
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This illustration shows the left side of the 3516B HD engine which can be accessed from the right side of the machine Components that can be seen include: - Left side alternator (1) - SOS port for the Coolant (2) - Secondary fuel filters (3) - Engine oil filters (4) - Air compressor (5) - Separate Circuit After Cooler (SCAC) water pump (6) - Engine oil fill tube (7)
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Throttle Lock Circuit
The Throttle Lock feature is very similar to a cruise control system used on automotive and truck applications. The main difference is that this system uses engine speed as its reference instead of vehicle speed. Therefore, engine speed is maintained, unlike other applications which control ground speed. The Throttle Lock control is within the ECM. The other components are: - Throttle Lock Enable Switch - Set/Deceleration Switch - Resume/Acceleration Switch - Right Brake Pedal Switch - Throttle Lock lamp does not communicate with the engine ECM. The Throttle Lock Lamp ON/OFF is controlled by the Throttle Lock Enable Switch.
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The throttle lock enable switch (1) is located in the dash. The throttle lock switches that are mounted in the cab to the right of the operator's seat are the set/decelerate (2) and the resume/accelerate switch (3). Also shown are button (4) for the horn and control levers (5)
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The Throttle Lock lamp (1) is lit when the Throttle Lock Switch is in the enable position. Depressing the right brake pedal (2) will cause the desired engine speed to return to low idle. An invalid brake switch signal will also cause the desired engine speed to return to low idle. The throttle pedal (3) is used select the desired engine speed
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The 994F derates for the 3516B HD Engine are as follows: - Exhaust Temperature Derate - Altitude Compensation Derate - Air Inlet Restriction Derate
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Exhaust Temperature Derate: The engine power will be derated when the turbine inlet temperatures reach a critical level that may cause engine damage. The Engine ECM measures the turbo inlet temperatures using the signals from the left and right exhaust temperature sensors.
In the illustration above, 0% engine derate equates to a temperature of 750º C (1382º F) or below with 15 seconds as the trigger for the derate. When the highest of the right or left turbine inlet temperatures goes above 750º C (1382º F) for 15 seconds, the torque map is reduced by 2%. If the measured temperature does not return to below 750º C (1382º F) within 15 second interval, the torque map will be reduced by 2%. This will continue in 2% steps with each step lasting 15 seconds until the temperature drops below 750º C or the maximum derate of 20% is reached. The last derate level reached will remain active until the engine is powered down. If the condition reoccurs and the Engine ECM has not been powered down, the fuel will be limited in the same manner starting from the previous derate level. If a failure is detected in either the left or right exhaust temperature sensor circuits, the Engine ECM will default to the maximum derate value of 20%. An exhaust temperature derate occurrence will log an Engine Event in the Engine ECM that requires a Level 3 password to clear.
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Altitude Compensation Derate: The Engine ECM derates engine power according to operating altitude in order to reduce exhaust temperatures. The engine ECM calculates the operating altitude of the machine based on the signal received from the atmospheric pressure sensor.
The Engine ECM derates the engine power approximately 3% per 305 m (1000 ft) when the machine is operated above 3050 m (10,000 ft). The maximum altitude derate for the engine is 24% at 5180m (17,000 ft). Altitude compensation derate does not log an event in the Engine ECM.
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Air Inlet Restriction Derate: The Engine ECM derates engine power when the air inlet or filter becomes plugged and restricts air available for combustion resulting in elevated exhaust temperatures. The above illustration shows the engine derates in relation to the air inlet restriction.
The Engine ECM determines inlet air restriction by subtracting the turbocharger inlet air pressure that is measured by the turbocharger inlet air pressure sensors from the atmospheric air pressure. The Engine ECM derates the power by 1% when the inlet air restriction reaches 6.5kPa (25 inches of water). The engine will default to a maximum derate of 20% if the Engine ECM detects a fault in the circuits for the left or right turbocharger inlet pressure sensors or the atmospheric pressure sensor. An air inlet restriction event will be logged in the Engine ECM when the engine starts derating. A password is not required to clear an air inlet restriction event. NOTE: Multiple engine derate percentages can add up and result in a total engine power derate greater than 20%.
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COOLING SYSTEM
This illustration shows the flow of the engine coolant through the radiator, the engine, the oil coolers, and the Separate Circuit After Cooler (SCAC) coolant through the after coolers. The 994F has been updated with Next Generation Modular Radiator (NGMR) cores for the engine coolant and the SCAC. Hot engine coolant from the engine enters the half of the bottom tank that is closest to the rear of the machine. The coolant flows up through the dual pass radiator cores, then down through the same cores and enters the half of the bottom tank nearest the engine after it has been cooled. The main coolant pump draws the cooled engine coolant from the radiator, or the regulator housing when the regulators are in bypass, and sends it through the engine oil cooler, the brake oil cooler, the power train oil cooler, and then into the engine block. The engine coolant flows through the engine coolant passages and exits the engine block through the regulator housing.
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The engine coolant regulators open and allow the engine coolant to bypass the engine radiators and flow to the main coolant pump inlet when the engine is cold. The regulators close and direct engine coolant to the radiator when the engine reaches operating temperature. The engine coolant regulators and radiator bypass circuit allow coolant flow through the engine and coolers when the engine is below operating temperature. The auxiliary coolant pump pulls the coldest coolant from the SCAC radiator cores and sends it to the aftercoolers. The coolant flows through the aftercoolers in series and then returns to the SCAC radiator cores. The SCAC radiator cores are NGMR radiator cores. The hot coolant enters the split bottom tank and flows up through the tube in the dual pass radiator cores nearest the back of the machine. The coolant then flows down through the same cores to the half of the bottom tank nearest the engine after it has been cooled. The brake oil cooler has not changed and is mounted below the engine on the inside of the left rear frame rail. The brake oil cooler is an oil to water cooler and cools the oil from the brake cooling circuit not the brake application hydraulic oil.
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Radiator Group
The illustration shows the radiator cores that are used to cool the engine. The Next Generation Modular Radiator cores are divided into two groups. Each core has nine fins per inch with two pass coolant travel. The five cores (1) on the left make up the Separate Circuit Aftercooler (SCAC) Radiator. The SCAC cools the front and rear aftercoolers. The thirteen cores (2) on the right side are used to cool the engine. Also, included in the radiator group are the engine oil cooler, the brake oil cooler, and the power train oil coolers that are not shown in the illustration. These coolers are located between the cooling cores and the fan blade.
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Air Start System
This illustration shows the location of the engine air start components on or near the the rear frame. Components that can be seen include: - Air dryer (1) - Air horns (2) - Air start tank (3) - Air horn solenoids (4) - Air compressor (5) - Air start motor (6) - Air start solenoid (7) - Air relay (8) - Gauge (service fill) (9) - Socket (service fill) (10)
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This illustration shows the air engine starter (1) and the air starter solenid valve (2). This photo shows the air engine starter from under the machine on the right side. The air engine starter solenoid valve receives starting current from the Power Train ECM (not shown).
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Air Start System
This illustration shows the air start tank charged with air pressure and the solenoids deenergized. The engine air start system supplies the required amount of air to turn the air start motor and will in turn start the engine. At initial start up, the air start tank is bled down, or through leakage the air tank will need to be charged. The socket that is located in the service fill area is used to provide the required air to pressurize the tank. The air from the socket flows around the air dryer and into the air tank. At this time, the air in the tank will charge the line going to the relay valve. Also, air flows to the air horn solenoids, the gauge, the air start solenoid, and to the unloading valve on the air compessor. When the air compressor has fully charged the tank and the lines, the unloading valve will signal the air compressor to stop. The pressures switch communicates with contact J1-13 on the VIMS module. If the pressure on the unloading line (between the air tank and the air compressor) decreases, the unloading valve will signal the compressor to resume supplying air for the air tank. At this time, no air pressure is directed to the air start motor or to the air horns.
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Air Start System
This illustration shows the air start tank charged with air pressure and the air start solenoid energized. When the engine start switch is turned to the ON position, a signal is sent to the Power Train ECM. Then, the Power Train ECM sends a voltage signal to the coil on the air start solenoid to open and allow air to pass through the solenoid valve. The air will flow through the air solenoid valve and flow to the air start motor. The pinnion (not shown) will move into the fly wheel. Then, the air flows to the relay valve to signal the relay valve to open and allow air to flow directly from the tank to the air start motor. When the engine is started, release the key and the Power Train ECM will de-energize the air start solenoid valve. Also, the Power Train ECM will de-energize the air start solenoid valve when the ECM gets a signal that the engine is rotating at least 400 rpm for 10 seconds.
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The air start system is equipped with a socket (2) in the service fill bay to charge the air start tank for an initial startup or in the case of a air leak. The service bay is equipped with a gauge (1) for checking the air pressure in the air start tank.
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There are several parameters that are monitored to determine if it is appropriate to inject oil. If any of these are not true then operation of the ORS strategy is halted until all conditions are met or the ECM power is recycled. The parameters that are monitored are as follows: - Engine Speed – must be greater than 1100 rpm. If engine speed exceeds 1100 rpm, oil will be injected at the end of the 5 minute sampling period. - Engine must be running for 5 minutes - Coolant Temperature – must be between 63°C and 107°C before ORS start up - Coolant Temperature sensor fault check (open or short to ground) - Oil pressure sensor fault check (open or short to ground) - Oil pressure Event check (active or inactive) - Fuel Level must be equal or greater than 10% - Fuel Level sender fault from VIMS - Engine Oil Level Status The following callouts are locations of the components for the Oil Renewal System. - Renewal tank (1) - Metering valve (2) - Service fill (3)
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Oil Renewal System (ORS)
The Oil Renewal System (ORS) is intended to increase the time between oil changes without shortening the life of the engine. Also, the system will decrease the amount of oil to be disposed of. The ORS removes used engine oil from the engine sump and meter that oil into the fuel return line. The used oil wil be consumed by the engine during the normal process of combustion. Normal Oil Analysis will determine whether the engine oil should be changed. The Oil Renewal System is an integrated system that requires the installation of additional iron. The Engine ECM monitors fuel rate for 5 minutes to determine an approximate fuel usage. For the next 5 minutes, oil is injected from the crankcase into the engine’s fuel return line based on the amount of fuel that is burnt. The target concentration for this operation is approximately 0.5% oil to fuel. When the fuel tank is filled, the oil concentration will be below target. When the fuel tank is low, the oil concentration will be above target. It should be noted that the monitoring of fuel usage and the injection of oil would be taking place simultaneously with the corresponding oil injection lagging by 5 minutes.
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The Oil Renewal System is filled at the service fill that is located on the right side of the engine end frame (EEF) near the articulation hitch. The tank filler (1) is used in order to fill the renewal tank (not shown). LED (2) will light when the upper level switch in the renewal tank (not shown) is activated. Access the tank filler by openning the cover over the service fill (The illustration show the cover removed).
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The renewal tank holds oil that will eventually be metered into the engine sump. The tank is equipped with two level switches. The upper level switch (2) is used to illuminate the blue LED that is in the service fill. The lower level switch (3) communicates with the VIMS module giving a signal that the renewal tank is empty. VIMS does display a warning saying ORS OIL LVL LO but does not ins truct the operator to take any action.
NOTE: The Oil Renewal System will not be shut down until the upper level switch for the engine oil sump shows a low level event.
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The metering valve draws oil from the engine oil sump and sends that oil to to the fuel return line and eventually to the fuel tank. At the same time, the engine oil sump is back filled with new oil from the renewal tank.
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Variable Clutch Fan Control
The variable clutch fan control is use to meet the changing cooling requirements, thus reducing the horsepower that is used to drive the fan in cooler ambients or light duty cycle work conditions. The Rockford fan controls and limits fan speed by proportally modulating engine oil pressure to the clutch. The speed of the fan will increase or decrease to compensate for a temperature change through feedback from the temperature sensors. The Engine ECM receives feedback from three sensors: the hydraulic oil temperature sensor, coolant temperarture sensor, and the aftercooler temperature sensor. Each sensor has a target temperature programmed into the ECM. When one or more of the sensors read a temperture above the key target temperature, the ECM will send a signal voltage to the solenoid valve to increase the flow of engine oil through the valve resulting in an increase in pressure to the variable clutch. At the same time, the speed sensor within the clutch assembly will monitor the speed of the fan and send feedback to the Engine ECM that the fan is rotating at the necessary speed.
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The following is a list of components in the variable clutch fan control. - Fan clutch (1) - Control valve (2) - Engine oil pressure supply port (3) - Return to the engine sump port (4)
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POWER TRAIN Power Flow
Power from the diesel engine is sent from the flywheel through the spring coupling to the rear pump drive. The rear pump drive is splined to the torque converter. Other components (not shown on this illustration) that are driven by the rear pump drive are: the two steering pumps, the brake actuation pump, the brake cooling pump, and the steering cooling pump. Two universal joints and the input drive shaft connect the torque converter to the transmission input transfer gear. The input transfer gear is splined to the transmission input shaft. The transmission output shaft is splined to the output transfer gear. Power from the output transfer gear is sent through the front drive shaft and it’s respective pinion, bevel gear, differential carrier, and axles to the front final drives and similarly to the rear final drives.
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Power Train Electrical System
This illustration of the Power Train Electrical System shows the components which provide input signals to the Power Train ECM. Based on the input signals, the Power Train ECM energizes the appropriate transmission control valve solenoids for speed and directional clutch engagement. The Power Train ECM also energizes the starter relay when starting the machine and the back-up alarm when the operator selects a reverse gear. When required, the Power Train ECM energizes the impeller clutch control valve solenoid, the lockup clutch control valve solenoid, and the reduced rimpull indicator lamp. The CAT Data Link connects the Power Train ECM to the Engine ECM. The data link also connects the ECMs to the Vital Information Management System (VIMS) and electronic service tools such as Caterpillar Electronic Technician (ET).
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Power Train ECM Inputs: STIC: Combines control of the vehicle steering system and the transmission shifting system in a single input device. Key Start switch: Provides a signal to the Power Train ECM when the operator wants to start the engine. The STIC directional switch must be in the NEUTRAL position before the Power Train ECM will permit engine starting. Reduced rimpull selection switch: When enabled by the reduced rimpull enable switch, this rotary switch determines the maximum rimpull torque. Park brake pressure switch: Monitors the park brake hydraulic pressure and the Power Train ECM can determine when pressure is applied to release the park brake. Parking Brake Position Switch: Provides an input the Power Train ECM to signal whether the parking brake is engaged or disengaged. Lockup clutch enable switch: When in the ON position, enables the lockup clutch to ENGAGE when the machine operating conditions are correct. The lockup clutch enable lamp is turned on by electrical contacts in the switch whenever the lockup clutch is enabled.. Steering and transmission lock switch: When in the LOCK position, causes the Power Train ECM to shift the transmission to NEUTRAL. Torque converter pedal position sensor: Signals the position of the torque converter pedal to the Power Train ECM. The Power Train ECM uses the position information to vary torque to the drive train through the impeller clutch. The actual value of torque reduction is determined
by a combination of different input signals. Torque converter speed sensor: Provides a signal the Power Train ECM uses to determine the output speed and direction of the torque converter. Transmission speed sensors: Provides a signal the Power Train ECM uses to determine the output speed of the transmission. Impeller clutch pressure sensor: Provides a pulse width modulated signal the Power Train ECM uses to determine the impeller clutch hydraulic pressure. Bumper Transmission Lockout Switch: Provides a ground level input the Power Train ECM that will neutralize the transmission until the switch is moved to the UNLOCK position. Engine Speed Sensor: A magnetic switch input that provides the engine speed to the Power Train ECM. Auto Lube Pressure Sensor: Provides a signal the Power Train ECM to determine the status of the pressure disengage the
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Power Train ECM Outputs: Air Start Solenoid: The Power Train ECM energizes the air start solenoid valve when the appropriate conditions to start the machine have been met. Reduced rimpull indicator lamp: The Power Train ECM illuminates the reduced rimpull indicator lamp when the appropriate machine operating conditions are met and the Power Train ECM is providing reduced rimpull. Clutch solenoids: The solenoids control oil flow to the speed and directional control spools. Impeller clutch solenoid: The Power Train ECM energizes the impeller clutch modulating valve in order to control hydraulic pressure to the impeller clutch. Lockup clutch solenoid: The Power Train ECM energizes the lockup clutch modulating valve in order to control pressure to the lockup clutch when the correct machine conditions have been met. Back-up alarm relay: The Power Train ECM energizes the back-up alarm when the operator selects the REVERSE direction with the STIC. The backup alarm relay energizes the two backup alarms. Auto Lube Solenoid: The energizes the auto lube solenoid for the next lube cycle. Bumper Transmission Lockout LED: The Power Train ECM illuminates the bumper transmission lockout LED when the bumper transmission lockout switch is in the LOCKED position.
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Power Train Electronic Control Module (ECM)
The Power Train ECM (1) is located on the left side of the machine under the door on the platform (cover must be removed). The Power Train ECM makes decisions based on control program information in memory and switch and sensor input signals. 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 using the STIC. The Power Train ECM interprets the input signals from the STIC, evaluates the current machine operating status and energizes the appropriate solenoid 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.
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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 and the operation of the impeller clutch and lockup clutch. The Power Train ECM interprets signals from the STIC, the torque converter pedal position sensor, the lockup clutch enable switch, and the current machine operating status to determine the appropriate output signals to the systems. Different conditions of the inputs affect the output conditions. These conditions will be discussed later. 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 faultVIMS. conditions thecodes powercan train system, it logs using the faults in memory and displays them on can the The in fault also be accessed the ET service tool. VIMS software be used to view faults logged by the VIMS. INSTRUCTOR NOTE: Power Train ECM faults displayed on the VIMS relating to the Power Train ECM will have a Module Identifier (MID) of "81." For additional information, refer to the Service Manual module "994F Wheel Loader Power Train, Troubleshooting, Testing and Adjusting" (Form RENR6306).
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The STIC (1) is bolted to the seat at the front of the left armrest. The transmission directional control switch (2) is a three position rocker switch that the operator uses to select NEUTRAL, FORWARD, or REVERSE. The transmission speed upshift switch (3) and the transmission speed downshift switch (4) are momentary contact switches that the operator uses to select the desired speed. When the operator selects REVERSE by depressing the top of the directional control switch, the Power Train ECM energizes the reverse directional solenoid. The Power Train ECM also activates the back-up alarm. When the operator selects FORWARD by depressing the bottom of the directional control switch, the Power Train ECM energizes the forward directional solenoid. When the operator selects NEUTRAL by placing the directional control switch in the center position, the Power Train ECM de-energizes both the forward and the reverse directional solenoids. After two seconds, the Power Train ECM energizes speed solenoid No. 3 and the transmission is in NEUTRAL until the operator selects a different gear. When the operator presses the upshift switch, the Power Train ECM energizes the appropriate speed clutch solenoid to select the next higher gear, and the transmission upshifts. When the operator presses the downshift switch, the Power Train ECM energizes the appropriate speed clutch solenoid to select the next lower gear, and the transmission downshifts. The switches must be released and pressed again to continue shifting. If the operator presses and holds the upshift or the downshift switch, the transmission will shift once and remain in that speed until the switch is released and pressed again.
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When the steering and transmission lock lever (5) is moved to the LOCK position (not shown), the STIC is held in the center position and steering is disabled. In the LOCK position, the steering lock lever depresses the steering and transmission lock switch (not visible). The steering and transmission lock switch signals the Power Train ECM to shift the transmission to NEUTRAL. When the steering and transmission lock lever is moved to the UNLOCK position, the steering and transmission functions are enabled. The power train portion of the STIC sends input signals to the Power Train ECM. Certain machine operating conditions will override the operator desired function of the STIC. If the directional switch is in the FORWARD or REVERSE position when the steering and transmission lock lever is moved to the UNLOCK position, the Power Train ECM will not shift from NEUTRAL. The directional switch must first be moved to the NEUTRAL position, then to the direction desired before the Power Train ECM will engage a directional clutch. Also shown, is the push/pull parking brake control (6).
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Reduced Rimpull Selection Switch
The Power Train ECM reduces rimpull by increasing the current to the impeller clutch solenoid, which reduces the hydraulic pressure to the impeller clutch and allows slippage between the impeller and the torque converter housing. By additionally decreasing the impeller clutch pressure, the impeller will slip more resulting in lower torque to the power train. The resulting additional engine horsepower can be used for the implements. The reduced rimpull selection switch (1) has four positions. Each position corresponds to a maximum allowable percentage of maximum rimpull. The default values for each position are indicated as follows: Maximum Rimpull (2)
85% Rimpull (3)
70% Rimpull (4)
55% Rimpull (5)
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The operator turns the key start switch (1) clockwise to signal the Power Train ECM to start the engine. The key start switch supplies a signal of +Battery to the Power Train ECM. The Power Train ECM energizes the air start solenoid and the air start solenoid supplies air to the starting motor and begin engine cranking. In order to start the engine, the following conditions must be met before the Power Train ECM will energize the air start solenoid: 1. The key switch is turned to the start position. 2. The transmission directional control switch is in neutr al. 3. The system voltage is below +32 Volts. 4. Engine prelube is complete (if equipped). If the machine is equipped with the optional engine prelubrication the Power Train ECM will request prelubrication status from the Engine ECM via the datalink. If the Engine ECM determines the need for prelubrication, the Engine ECM will perform the prelubrication function and signal the Power Train ECM when prelubrication has been completed.
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The Power Train ECM monitors the position of the torque converter pedal (1) with the torque converter pedal position sensor (2) located behind the panel at the pivot for the pedal. As the operator depresses the pedal, the Power Train ECM increases the current to the impeller clutch solenoid and reduces the hydraulic pressure to the impeller clutch. The rimpull will decrease with pedal travel from the reduced maximum setting to the minimum setting. When the operator releases the left pedal, the rimpull will return to the maximum percentage as set by the reduced rimpull selector switch (not shown). When the maximum allowable percentage is in the lower values, the total change of rimpull from maximum to minimum is decreased. This condition results in a more gradual change of rimpull over the travel of the torque converter pedal. If the machine is not in FIRST GEAR, the impeller clutch pressure will remain at the maximum level until the transmission is shifted into FIRST GEAR. The torque converter pedal functions similarly when the maximum rimpull selector switch is in the maximum position, except the maximum allowable percentage is now 100%. NOTE: An increase in current to the impeller clutch solenoid from the Power Train ECM results in a decrease in pressure to the impeller clutch. INSTRUCTOR NOTE: To change the setting for each position of the reduced rimpull selection switch, refer to the Service Manual module "994F Wheel Loader Power Train, Troubleshooting, Testing and Adjusting" (Form RENR6306).
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The impeller clutch modulating valve (1) is located on the left side of the torque converter housing (3). The Power Train ECM (not shown) monitors the status of the impeller clutch solenoid and can determine certain faults that may affect operation of the impeller clutch. These faults include: a short to +Battery, a short to ground, an open circuit, or the impeller clutch not responding properly. The Power Train ECM receives a signal from the impeller clutch pressure sensor (5) to monitor the impeller clutch pressure. The Power Train ECM can compare the control of the impeller clutch solenoid with the response of the impeller clutch pressure to determine if the impeller clutch is responding properly.
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When a fault is detected, controlled throttle shifting is used. When a directional shift is made above 1100 rpm, the Power Train ECM will request a desired engine speed of 1100 rpm from the Engine ECM for 1.9 seconds if shifting into forward and a desired engine speed of 1100 rpm for 2.5 seconds if shifting into reverse. This feature helps decrease the energies absorbed in the transmission. When the Power Train ECM detects a fault in the impeller clutch solenoid circuit, a fault will be displayed on the VIMS message center (not shown). The torque converter pedal position sensor (not shown) and the impeller clutch solenoid must be calibrated through the VIMS to ensure proper operation. Also shown are the lockup clutch solenoid (2) and the lockup clutch valve. The lockup clutch solenoid and lockup clutch valve look similar to the impeller clutch solenoid and impeller clutch valve but are different and should not be interchanged. The lockup clutch solenoid is mounted on the lockup clutch valve. The lockup clutch modulating valve is located on the left side of the torque converter housing between the impeller clutch solenoid valve and the torque converter housing. The Power Train ECM energizes the solenoid for the lockup clutch in order to allow oil to flow to the lockup clutch. The pressure increases in the lockup clutch, causing it to engage and the machine operates in DIRECT DRIVE. The solenoid for the lockup clutch is a proportional solenoid and is energized by a modulated signal from the Power Train ECM. The Power Train ECM varies the amount of current to control the amount of oil flow through the lockup clutch valve to the lockup clutch. The Power Train ECM receives a signal from the torque converter output speed sensor (4). The speed sensor is mounted on the front of the torque converter housing above the output shaft. The signal is a fixed voltage level, patterned waveform which the Power Train ECM uses to determine the speed and direction of the torque converter output. If the machine is allowed to roll backwards on an incline when a forward gear is selected the toque converter output can turn in reverse . This condition is called reverse turbine and can result in high temperatures inside the torque converter. If the Power Train ECM determines the output of the torque converter is turning in the reverse direction greater than 500 rpm, the Power Train ECM will ignore the left pedal position input and increase the impeller clutch pressure to prevent this condition. The Power Train ECM will also override the reduced rimpull setting if necessary to try to eliminate the reverse turbine. The Power Train ECM monitors the temperature (6) of oil exiting the torque converter with the torque converter outlet oil temperature sensor (1) which is mounted on the front right of the torque converter housing, just above the torque converter outlet relief valve. INSTRUCTOR NOTE: An increase in current to the lockup clutch solenoid from the Power Train ECM results in an increase in pressure to the lockup clutch.
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The lockup clutch enable switch (1) is located on the right side panel in the cab. When the switch is in the ON (closed) position and the proper conditions have been met, the Power Train ECM will engage the lockup clutch in order to improve the efficiency of the power train. The Power Train ECM first sends a signal to the lockup clutch modulating valve to enengage the lockup clutch to a Hold Level for .75 seconds to allow time for the clutch to fill. Then, the current is ramped up to full ON in .65 seconds. During normal operation, the Power Train ECM will ENERGIZE the torque converter lockup clutch solenoid based on the following conditions: 1. Lockup clutch enable switch state: ON (closed). 2. Torque converter output speed: When the torque converter output speed is greater than 1125 ± 50 rpm. 3. Time in g ear: The transmission must be in the present speed and direction for at least two seconds. 4. Time since lockup clutch solenoid was de-energized: At least four seconds must have passed since the Power Train ECM de-energized the lockup clutch solenoid. 5. Left pedal and right brake pedal status: Both pedals must be fully released.
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Torque Converter Components
The torque converter is installed on the rear pump drive. - Impeller clutch modulating valve (2) - Lockup clutch modulating valve (3) Impeller clutch pressure is monitored by the Power Train ECM via the impeller clutch pressure sensor (5). The lockup clutch pressure and the impeller clutch pressure is measured at the pressure tap panel along with the respective clutches. The torque converter output speed and direction is monitored by the Power Train ECM via the torque converter output speed sensor (4) mounted near the torque converter output shaft (6). The torque converter output speed sensor sends a signal to the Power Train ECM. The temperature of the torque converter output oil is monitored by the torque converter output sensor (1). The torque converter output temperature sensor sends a pulse width modulated signal to the VIMS control module.
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This illustration show the transmission pump that is mounted on the torque converter housing below the output shaft on the rear pump drive. The transmission pump has two sections. The front section (1) supplies oil to the torque converter. The rear section nearest to the torque converter housing (2) supplies oil to the priority valve, then the lockup clutch modulating valve, the impeller clutch modulating valve, and the transmission control valve.
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Transmission Oil Filters
The upper illustrations shows the location of the power train filters (1) in the rear frame of the machine. The transmision filters can be accessed by raising the door on the platform that is behind the cab. Also shown are the torque converter housing (2) and the transmission (3). The lower illustration shows both filters. The filter on the left filters oil that is flowing to the priority valve (not shown). The filter on the right filters oil that is flowing to the torque converter. Both filters are equipped with fluid sampling ports (S O S) (4).
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Torque Converter
The Illustration shows a sectional view of the torque converter. The major components include the rotating housing, the impeller, the turbine, the non free wheel stator, the impeller clutch, and the lockup clutch. The rotating housing is splined to the engine flywheel and turns with the flywheel. When the impeller clutch port is pressurized, the impeller is connected to the rotating housing through the impeller clutchengagement. The clutch discs are splined to the impeller. The clutch plates are splined to the rotating housing. Pressure oil at the clutch piston will engage the discs and plates. The impeller rotates with the housing. The turbine is splined to the output shaft. In torque converter drive, the turbine is turned by oil from the impeller. In direct drive, the lockup clutch port is pressurized. The lockup clutch connects the turbine to the rotating housing. The lockup clutch discs are splined to the turbine. The lockup clutch plates are splined to the rotating housing. Pressure oil moves the clutch piston to engage the discs and plates. When the clutch is engaged, the turbine, the housing, the impeller, and the output shaft rotate as a unit at engine rpm.
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The input transfer gear (not shown) and the basic transmission remains unchanged. The planetary power shift transmission (1) has three FORWARD and three REVERSE speeds. Electronic solenoids located in the hydraulic control valve (2) shift the transmission. The solenoids are actuated by the Power Train Electronic Control Module (ECM) located in the electronics bay at the rear of the cab. The transmission output speed sensor (3) monitors the transmission output shaft. The signal is sent to the Power Train ECM. The transmission output speed signal indicates when the clutches have engaged. The two transmission oil screens located in the front of the output transfer gear housing can be accessed by removing the covers (4). Also shown here are the secondary steering pump and diverter valve (5) and the output shaft (6) for the rear drive shaft. The oil sump for the transmission pump (not shown) is located in the bottom of the output transfer gear case (7).
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This illustration is a sectional view of the impeller clutch solenoid valve. When the impeller clutch solenoid is DE-ENERGIZED, the spring moves the pin assembly against the ball. The ball blocks the pump flow through the orifice to drain. The oil pressure increases at the left end of the valve spool and moves the valve spool to the right against the spring. The valve spool blocks the passage between the impeller clutch and drain and opens the passage between the impeller clutch and the pump. Pump oil flows past the valve spool to the impeller clutch. When the impeller clutch solenoid is ENERGIZED, the solenoid moves the pin assembly against the spring and away from the ball. Pump oil flows through the center of the valve spool, through the orifice and past the ball to drain. The valve spring moves the valve spool to the left. The valve spool blocks the passage between the impeller clutch and the pump and opens the passage between the impeller clutch and drain. Pump flow to the impeller clutch is blocked. The oil in the impeller clutch flows past the valve spool to drain.
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This illustration is a sectional view of the lockup clutch solenoid valve. When the lockup clutch solenoid is DE-ENERGIZED, the force that held the pin assembly against the ball is removed. The pump oil flows through the orifice and past the ball to drain. The spring moves the valve spool to the left. The valve spool opens the passage between the lockup clutch and drain and blocks the passage between the lockup clutch and the pump. Pump flow to the lockup clutch is blocked. The oil in the lockup clutch flows past the valve spool to drain. When the lockup clutch solenoid is ENERGIZED, the solenoid moves the pin assembly against the ball. The ball blocks pump oil flow through the orifice to drain. The oil pressure increases at the left end of the valve spool and moves the valve spool to the right against the spring. The valve spool blocks the passage between the lockup clutch and drain and opens the passage between the lockup clutch and the pump. Pump oil flows past the valve spool to the lockup clutch.
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56 Tansmisison Hydraulic Control Valve Modulating relief valve: Limits the maximum clutch pressure. First and third speed selection spool: Directs oil flow to the No. 5 and No. 3 clutches. Load piston: Works with the modulation relief valve to control the rate of pressure increase in the clutches. Second speed selector spool: Directs oil flow to the No. 4 clutch. Pressure differential valve: Controls speed and directional clutch sequencing. Directional selection spool: Directs oil to the FORWARD and REVERSE directional clutches. Converter inlet ratio valve: Limits the pressure to the torque converter. Passage to Clutch No. 1: Passage to the port to energize clutch No. 1 (Reverse). Passage to Clutch No. 2: Passage to the port to energize clutch No. 2 (Forward). Passage to Clutch No. 3: Passage to the port to energize clutch No. 3. (Third Speed) Passage to Clutch No. 4: Passage to the port to energize clutch No. 4. (Second Speed) Passage to Clutch No. 5: Passage to the port to energize clutch No. 5 (First Speed).
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Transmission Hydraulic Control Valve
The transmission hydraulic control valve is shown with the transmission shifted to the NEUTRAL position. Supply oil from the transmission filter is directed to either the solenoid valve manifolds (not shown) or at the top of the modulating relief valve. The pressure of the supply oil overrides the check valve (at the inlet). Oil flows through the passage (red) around the modulating valve through the ball check valve and fills the slug chamber (red). The pressure in the slug chamber will override the spring and the modulating valve will move downward. As the modulating valve moves downward, oil will flow around the modulating valve to the cavity (orange). The oil will flow through the passag (orange) to the port for the torque converter inlet (not shown). The supply oil flows through the flow control orifice to the chamber for the 1st and 3rd speed selector spool and the chamber for the 2nd speed spool (in neutral, the speed selector spool will be shifted ordertotothe direct flow toofthe clutch No. 3). and Also, oil flows the passagein(red) slugoil chamber thepassage converter ratio valve thethe center of thethrough pressure differential valve. Oil that is flowing from the center of the differential valve through the orifice is directed below the load piston.
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Movement of the load piston in the upwards direction, begins the modulating cycle. The oil in the upper cavity of the differential valve shifts the valve downward against the spring. When the supply oil pressure is at approximately 380 kPa (55 psi) the force that is developed by the oil flow to the center of the differential valve moves the differential valve downward and overrides the spring. Oil can flow around the differential valve and flow through passage (red/white) to cavity (P2). When the pressure at P2 reaches the 380 kPa (55 psi) differential, the differential valve shift upwards in order to block around the differential valve. The oil pressure at P2 will always be approximately 380 kPa (55 psi) less than the pressure at P1. The differential pressure between P1 and P2 will make sure that the speed clutch will always engage before the direction clutch. With a directional shift out of neutral, the directional selector spool will be shifted in either direction and oil in cavity (P2) will be directed to one of the two directional clutches (not shown).
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This illustration is a sectional view that is showing the transmission planetary group. The planatary group is equipped with two directional and three speed clutches. In this sectional view of the transmision, the input shaft and the input sun gear ar shown in red with the output shaft and the output sun gears shown in blue. The ring gears are shown in green. The planetary carriers are shown in brown while the planetary gears and shafts are shown in orange. The clutch discs, clutch plates, pistons, springs, and bearings are shown in yellow. Stationary components are shown in gray. Speed
EngagedClutches
First/Forward
No.2andNo.5
Second/Forward
No. 2 and No. 4
Third/Forward
No.2andNo.3
Neutral
No. 3
First/Reverse
No.1andNo.5
Second/Reverse
No. 1 and No. 4
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Power Train Hydraulic System
This illustration shows the components and the oil flow for the power train hydraulic system in Neutral. In this schematic, the engine is running and the transmission in neutral. With the transmission direction switch in the NEUTRAL position, the Power Train ECM energizes the No. 3 clutch solenoid. The Power Train ECM also de-energizes the lockup clutch solenoid. The transmission pump (a two section gear pump) draws oil from the sump (located in the bottom of the transmission transfer case) through three magnetic screens that are located in the sump by the transmission pump. Oil from the left section of the transmission pump flows through the transmission filter (red) to the priority valve. From the right side of the priority valve, oil flows to the lockup clutch modulating valve and to the impeller clutch modulating valve. During a shift, the priority valve maintains 2205 kPa (320 psi) oil pressure to the lockup clutch modulating valve and impeller clutch modulating valve. When the transmission is in neutral, the lockup clutch is disengaged. Also, the solenoid for the impeller clutch is de-energized and the impeller clutch is engaged.
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When the transmission pump supply pressure increases above the priority valve setting, the priority valve opens and sends oil flow to the manifold for clutch solenoid valves No. 2 and 3, the manifold for clutch solenoid valves No. 1, 5 and 4, and the inlet passage for the selector and pressure control valves. The oil at the clutch solenoid valve manifolds becomes the pilot oil for the transmission speed and directional selector spools. When the No. 3 clutch solenoid is ENERGIZED, the No. 3 solenoid valve sends pilot oil to the upper of the firstspring and third spool. pilot oil pressureOil overcomes force of the end selector valve andspeed movesselector the spool fromThe its center position. from the the inlet passage flows through the orifice, past the speed selector spool, and into the No. 3 speed clutch. When directional solenoids No. 1 and 2 are DE-ENERGIZED, pilot oil is blocked at the directional solenoid valves. The directional clutch selector spool spring centers the spool. Oil flow between the direction selector spool and the the directional clutches is blocked. When the oil requirements of the selector and pressure control valve have been satisfied, the remaining power train pump oil flows to the torque converter. Oil from right side of the transmission pump is directed to the torque converter filter. Oil flows from the filter and joins with the oil from the selector and pressure control valve. The combined oil flows to the inlet of the torque converter. Flow continues through the torque converter to either the sump or the power train coolers. Then the oil flows to various lube points in the transmission lubrication circuit. When the transmission is in NEUTRAL, the Power Train ECM disengages the optional lockup clutch. The turbine is disconnected from the rotating housing. No power is transmitted from the housing through the turbine. INSTRUCTOR NOTE: Operation of the modulating relief valve, the torque converter inlet ratio valve, and the pressure differential valve is the same as explained in STMG 421 "966D Wheel Loader Part 2--Power Train" (Form SERV1421).
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In this illustration, the engine is running and the transmission is in 1st speed forward in torque converter drive. Flow from the transmission pump is directed through the transmission filter to the priority valve, the impeller clutch solenoid valve, and the lockup clutch solenoid valve. The priority valve maintains a minimum oil pressure to the impeller clutch solenoid valve and the lockup clutch solenoid valve during transmission shifts. When the transmission pump supply pressure increases above the spring setting of the priority valve, the priority valve opens and oil is directed to the speed manifold and the direction manifold. Also, pump supply oil is directed past the orifice to the inlet port for the 1st and 3rd speed selector spool and the inlet port for the 2nd speed selector spool. When the operator moves the directional switch and upshift or downshift switch to the 1st speed forward position, the Power Train ECM energizes the impeller clutch solenoid (the impeller solenoid willThen, be energized then de-energized). The and solenoid the lockup clutch is clutch also de-energized. the No. and 5 solenoid is energized first No. 2for solenoid will be energized next.
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When the No. 5 solenoid is ENERGIZED, oil pressure is directed to the lower end of the 1st and 3rd speed selector spool. The force of the oil pressure overcomes the force of the speed selector spool spring, the spool shifts upwards and No. 5 clutch is engaged. The No. 2 solenoid is ENERGIZED, pilot oil is directed to the upper end of the directional selection spool. The oil pressure overcomes the force of the selector spool spring and the spool shifts downward.The No. 2 clutch will be engaged. When the oil requirements of the selector and pressure control valve have been satisfied, the remaining oil combines with the oil from the transmission pump (orange). The combined oil flows to the torque converter. Flow continues through the torque converter through the power train coolers to the transmission lubrication circuit. When the transmission is in NEUTRAL, the Power Train ECM pressurizes the impeller clutch in response to the engine speed. When the engine speed is less than 1100 rpm, the impeller clutch pressure is maintained at a holding pressure of 550 ± 207 kPa (80 ± 30 psi). When the engine rpm increases from 1100 to 1300 rpm, the Power Train ECM increases the impeller clutch pressure from 550 ± 207 kPa (80 ± 30 psi) to 2580 ± 207 kPa (375 ± 30 psi) for one second. The Power Train ECM then reduces the impeller clutch pressure to 2274 ± 207 kPa (330 ± 30 psi). The impeller clutch pressure remains at 2274 ± 207 kPa (330 ± 30 psi) for all engine speeds above 1300 rpm. The torque converter housing and impeller rotate at engine speed. When the engine rpm decreases from 1300 to 1100 rpm, the Power Train ECM decreases the impeller clutch pressure from 2274 ± 207 kPa (330 ± 30 psi) to 550 ± 207 kPa (80 ± 30 psi). The impeller clutch pressure remains at a holding pressure of 550 ± 207 kPa (80 ± 30 psi) for all engine speeds below 1100 rpm. The low pressure allows the impeller clutch to remain filled without engaging. The torque converter housing rotates with the engine while the torque converter impeller is only partially engaged without transmitting torque. NOTE: The impeller clutch pressure is reduced because the pressure to the impeller clutch is reduced after the first second (1/60 of a minute) of engagement to extend the life of the seals and pistons in the impeller clutch. This can be demonstrated by connecting a pressure gauge to the impeller clutch pressure tap and viewing the gauge during a directional shift. Caterpillar Electronic Technician (ET) can also be used to view the impeller clutch pressure and the impeller clutch solenoid valve current during a directional shift.
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When the transmissionis shifted from FIRST SPEED FORWARD to SECOND SPEED FORWARD (speed shift), the Power Train ECM de-energizes the No. 5 clutch solenoid, and energizes the No. 4 clutch solenoid. The Power Train ECM also continues to de-energize the impeller clutch solenoid and the lockup clutch solenoid. When de-energized, the No. 5 clutch solenoid valve interrupts the flow of pilot oil to the speed selector spool and directs the pilot oil to the sump. When energized, the No. 4 clutch solenoid valve sends oil to the end of the 2nd speed selector spool. The force of the oil pressure overcomes the force of the selector valve spring and moves the spool from its center position. Oil from the inlet passage flows through the orifice, into the No. 4 speed clutch. The empty No. 4 clutch causes the pressure at P1 and P2 to be less than 375 kPa (55 psi). The decrease in P1 oil pressure allows the pressure differential valve spring to move the differential valve up. When the differential valve moves up, the differential valve opens a passage for oil in the differential valve spring chamber and the load piston cavity to flow to drain. The transmission control valve then repeats the fill and modulation cycle. During a speed shift, the Power Train ECM maintains maximum pressure in the impeller clutch. The transmission directional clutch picks up the load after a dirction shift.
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When the transmission is shifted from First Speed Forward to Second Speed Reverse (directional shift), the Power Train ECM de-energizes clutch solenoids No. 2 and 5 and energizes clutch solenoids No. 1 and 4. The ECM also energizes the impeller clutch solenoid and de-energizes the lockup clutch solenoid. When the Power Train ECM de-energizes the No. 2 clutch solenoid, the No. 2 clutch solenoid valve blocks the pilot oil flow and sends the pilot oil at the end of the selector spool to drain. The force of the selector valve spring moves the spool to its center position. When the selector spool moves to the center position, oil in the No. 2 clutch flows to the sump. When the Power Train ECM energizes the No.1 clutch solenoid, the No. 1 clutch solenoid valve sends pilot oil to the lower end of the directional selector spool. The force of the oil pressure overcomes the force of the selector valve spring and shifts the spool from its center position. Directional clutch oil flows from the pressure differential valve, past the directional selector spool, and into the REVERSE clutch (No. 1).
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When the Power Train ECM de-energizes the No. 5 clutch solenoid, the No. 5 clutch solenoid valve blocks the flow of pilot oil and sends the pilot oil at the end of the 1st and 3rd selector spool to the sump. The selector spool moves to the center position, oil in the No. 5 clutch flows to the sump. When the ECM energizes the No. 4 clutch solenoid, the No. 4 clutch solenoid valve sends pilot oil to the right side of the 2nd speed selector spool. The force of the oil pressure overcomes the force of the selector spool spring and moves the spool from its center position. Oil from the inlet passage flows through the orifice, past the 1st and 3rd speed selector spool, past the 2nd speed selector spool, and into the No. 4 speed clutch. As the empty No. 1 and 4 clutches fill, they cause the P1 and P2 pressures to decrease to less than 375 kPa (55 psi) momentarily. The momentary decrease in P1 oil pressure allows the differential valve spring to move the differential valve up. When the differential valve moves up, the differential valve opens a passage for oil in the differential valve spring chamber and the load piston cavity to flow to drain. The transmission control valve then repeats the fill and modulation cycle. During a directional shift, the Power Train ECM reduces the pressure in the impeller clutch allowing the impeller clutch to slip. The ECM monitors the torque converter output speed sensor and the transmission output speed sensor to determine when the transmission clutches are engaged. When the transmission clutches are engaged, the ECM engages the impeller clutch in the torque converter. The torque converter absorbs the energy of a directional shift.
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When the machine is operating in torque converter drive, six conditions must be present before the Power Train ECM will energize the solenoid for the lockup clutch and shift the torque converter to direct drive. 1. The transmission is in second or third gear. 2. The lockup clutch enable switch is in the ON position. 3. The torque converter output speed is above 1375 ± 50 rpm. 4. The machine has been in the prese nt speed and direction for more than two seconds. 5. Neither brake pedal is depressed. 6. The lockup clutch has been released by the Power T rain ECM for at least fo ur seconds.
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When the solenoid for the lockup is energized, the lockup clutch modulating valve opens. The transmission pump oil flows past the lockup clutch modulating valve and fills the lockup clutch. The lockup clutch engages and connects the turbine to the rotating housing. In DIRECT DRIVE, both the impeller clutch and the lockup clutch are engaged. The torque converter rotating housing, the impeller, and the turbine turn as a unit. When the solenoid for the lockup is energized, the lockup clutch modulating valve opens. The transmission pump oil flows past the lockup clutch modulating valve and fills the lockup clutch. The lockup clutch engages and connects the turbine to the rotating housing.
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The 994F Wheel Loader is equipped with two oil-to-coolant coolers (1) and two oil-to-air coolers (2 and 3). The oil-to-coolant coolers are located on the left side of the engine. These two coolers use engine coolant to cool the transmission oil as the oil passes through the coolers. In line with the transmission oil flow through the two oil-to-coolant, an orifice is installed to divide the flow of oil between the oil-to-coolant and two oil-to-air coolers. Approximately two thirds of the torque converter outlet oil flow through the oil-to-coolant coolers. The two oil-to-air coolers are located in the cooler package at the rear of the machine. Cooler (3) has an orifice (not shown) that divides the other one-third of the transmission oil in half. One half of the oil flows through cooler (2) and one half of the torque converter oil flows through cooler (3). The oil from the coolers flow back to the transmission and lubricate the transmission bearings before returning to the transmission sump.
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The Power Train ECM shifts the transmission by energizing the solenoid valves that are located in the transmission control valve group on top of the transmission. Two solenoid valves are used to control Reverse (1) or Forward (2) directional shifts and three solenoid valves are used to control speed shifts: First (5), Second (4), and Third (3). The solenoid valves are two-position, three-way solenoid valves. The solenoid valves are normally open to drain. When energized, the solenoid valve spool moves to direct pressure oil to one end of the transmission control valve spool. The transmission control valve spool then directs oil to the appropriate clutch. The solenoids are operated by 12VDC max. The Power Train ECM first energizes the solenoids with 12VDC for one second and then decreases the voltage to approximately 8.25VDC for the remainder of the time that the solenoid is energized. The decreased voltage level is enough to keep pressure oil to the control valve spool to maintain position while extending the service life of the solenoid.
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Auto Lube System
The auto lube system (arrow) is located on the left side in the platform. Access the auto lube system by lifting the door panel as shown in the upper illustration. The auto lube sensor (2) is located on the top plate of the tank. The sensor is a 5 kHz sensor that communicates with the Power Train ECM. The auto lube solenoid (1) is an output of the Power Train ECM. The ECM sends a current to the solenoid to cycle the auto lube pump (3). Also shown, is the auto lube tank (4).
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This illustration shows the lubrication points on the rear frame (EEF) of the machine. The auto lube pump and tank assembly (1) is located on the left side of the machine in the platform. The previous illustration shows the components of the auto lube pump. Also shown is the engine fan system and pulley (2). The following is a list of the lube points on the EEF. - Fan drive shaft bearing - Pulley (support group alternator) - Rear trunnion (rear axle) (Qty 2) - Front trunnion (rear axle) (Qty 2) - Head end of the steering cylinders (Qty 2) - Lower bearing articulation hitch Hose (3) supplies auto lubrication to the components on the loader frame (NEEF).
Note: The upper drive shaft bearing is not an auto lube point. This point is greased manually by the operator.
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This illustration shows the locaton of the auto lube points on the pulley shaft and the fan drive shaft.
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This illustration shows the lubrication points on the loader frame (NEEF) of the machine. The loader arms and the draw bar lube points are not shown in this illustration and will be shown in the following illustration. The following is a list of the lube points on the EEF. - Tilt cylinder head end pins (Qty 2) - Steering cylinder rod end pins (Qty 2) - Lift cylinder head end pins (Qty 2) - Upper bearing articulation hitch Divider block (1) supplies auto lubrication to the left side of the lift linkage and divider block (2) supplies auto lubrication to the right side of the lift linkage.
Note: The lower drive shaft bearing is not an auto lube point. This point is greased manually by the operator.
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The illustration shows the auto lubrication points for the lift and tilt linkage. The following is a list of the lube points on the lift linkage and tilt linkage. - A-Pins for upper end of the lift arms (Qty 2) - B-Pins for the lower end of the lift arms (Qty 2) - C-Pins link assembly to the bucket (Qty 2) - D-Pins lever assembly to the link assembly (Qty 2) - E-Pins lever assemlby to the rod end of the tilt cylinder (Qty 2) - K-Pins for the rod end of the lift cylinder (qty 2) - Center pins for the lever assembly to the lift linkage (qty 2)
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The power train hydraulic system is equipped with remote pressure taps. The remote pressure taps are located in the service bay, behind the cab. The remote pressure taps are: Rear brake pressure (1) Front brake pressure (2) Brake cooling pump pressure (3) Front brake accumulator pressure (4) Rear brake accumulator pressure (5) Implement pilot pressure (6) Implement cooling pump pressure (7) Left steering pump pressure (8) Right steering pump pressure (9) Steering cooling pump pressure (10) Speed clutch pressure (11) Directional clutch pressure (12) Torque converter inlet pressure (13) Torque converter outlet pressure (14) Transmission lube pressure (15) Impeller clutch control pressure (16) Lock-up clutch control pressure (17) Transmission fluid sampling port (SOS) (18)
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Implement Hydraulic System
The 994F Wheel Loader implement hydraulic system consists of two basic systems with an additional common cooling system. The systems are divided in the following color codes: Orange
Pilot hydraulic system
Red
Main hydraulic system
Green
Common cooling system for the Implement hydraulic oil
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Implement Electronic Control System
This diagram of the Implement Electronic Control System shows the components which provide input signals to the Implement ECM and output signals from the Implement ECM. The Implement Electronic Control Module (ECM) receives input signals from the various sensors and switches on the machine. The Implement ECM processes the input signals, makes decisions, and provides a corresponding signal voltages to the proportional solenoid valves and detent coils. 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. Also, the Implement ECM provides a means of calibrating the mechanical 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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The input components to the Implement ECM are: 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. Kickout set switch: Sends the raise and lower kickout position to the Implement ECM Tilt kickout switch: Sends a signal to the Implement ECM to de-energize the tilt detent coil at the exact set position. Implement pump pressure sensor: Sends the implement pump pressure to the Implement ECM as a pulse width modulated signal. The output components which receive signals from the PowerTrain ECM are: Variable Pump Solenoid Valve: This solenoid valve is an output from the Implement ECM that controls the signal flow from the implement pump. The solenoid valve controls the upstroke and destroke of the variable piston pump Lower kickout cushion solenoid: This proportional solenoid valve is an output from the Implement ECM. The lower solenoid directs pilot oil through an orfice to the lower end of the lift stems. Raise stop solenoid: This proportional solenoid valve is an output from the Implement ECM. Blocks pilot oil flow to the raise end of the lift stems.
Raise kickout coil is an electromagnetic component that retains the lift control lever in detent the fullcoil: raiseThe position. Lower kickout detent coil: The coil is an electromagnetic component that retains the lift control lever in the full lower position. Tilt kickout detent coil: The coil is an electromagnetic component that retains the tilt control lever in the full tilt back position.
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The upper illustration shows the lift linkage position sensor (1). Lift linkage position sensor is located on the right side of the loader frame. The sensor sends a PWM signal to the Implement ECM reflecting the position of the lift linkage. NOTE: To calibrate the lift linkage position sensor,refer to the Service Manual module "994F Wheel Loader Hydraulic System, Troubleshooting, Testing and Adjusting Position Sensor (Lift Linkage - (Calibrate)" (Form RENR6323).
The lower illustration shows the tilt kickout switch (2). The tilt kickout switch is located on the right side tilt cylinder. The switch sends a signal to the Implement ECM to de-energize the tilt detent coil (not shown) as the magnet (3) passes under the switch. Normally, the magnet is adjusted to position the bucket at the proper dig angle.
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The upper illustration shows the implement pump pressure sensor (1). The pressure sensor is located on the right side inside the loader frame. Access the pressure sensor from under the front frame. The sensor sends the pressure through a PWM signal to the Implement ECM. The lower illustration shows the raise/lower kickout set switch (2) on the panel inside the cab. The switch sends the Implement ECM the position to set the kickout for the raise position and the lower cushion
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The above illustration shows the location of the variable pump solenoid valve (1) in the NEEF (2). The lower illustration shows the variable pump solenoid valve (1). The valve controls the signal pressure for the variable displacement piston pump (center section). When the solenoid is de-energized , the valve is closed and the pressure in the signal line instructs the pump to go to maximum flow. When the conditions are met to activate Dig Trigger, the Implement ECM sends current to the solenoid valve. The solenoid is energized and the solenoid valve shifts to the OPEN position. The signal oil goes tank pressure and the variable pump will be instructed to go to standby. Also shown are the check valve (3) and the selector and pressure control valve (4)
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The upper illustration shows the location of the raise stop solenoid valve and the lower kickout cushion solenoid valve (1) in releation to the transmission control valve (2). The lower kickout cushion solenoid valve (3) controls the flow of pilot oil from the pilot control valve to the main control valves. When the solenoid is de-energized, the pilot oil free flows through the valve. When the solenoid is energized by a signal from the Implement ECM, the flow orifice of pilot(5). oil through the will valvecause is blocked. The pilot oil flows around theend solenoid valve through The orifice a drop in pilot pressure to the lower of the lift stem. The lift stems in the main control valves (not shown) will decrease the flow of supply oil to the rod end of the lift cylinder.
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When the lift cylinders approach the raise stop at approximately 20 mm ( 0.8 inch) away from full extension, the Implement ECM sends a voltage signal to the raise stop solenoid valve to block pilot oil to the raise end of the lift stem. The lift stem will shift to the CENTER position block supply oil to the head end of the lift cylinders.
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The above illustration shows the location of the pumps on the 994F front pump drive. The implement system has three fixed displacement piston pumps (1) and one variable displacement piston pump (2). The implement oil cooling pump (3), the implement pilot pump (4), and the front pump drive lubrication pump (5) are fixed displacement gear pumps.
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Front Pump Drive Lubrication System
The front pump drive system is located in the loader frame (NEEF). The front pump drive lubrication system lubricates the bearings and gears and filters the oil in the front pump drive. Access the front pump drive (1) from the articulation hitch area.
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Front Pump Drive System
The oil is drawn from the front pump drive (1) by the front drive lubrication pump (4) and is sent through the filter (3). The oil from the filter is sent to the divider block (2) and the oil is directed to the individual bearing and gear lubrication points in the front pump drive. The oil filter group consists of the filter base and filter, the SOS fluid sampling port (7), filter bypass switch (5), and the temperature sensor (6). The front pump drive oil filter bypass switch and the front pump drive oil temperature sensor communicate with the VIMS module.
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Pilot System
This illustration shows a block diagram of the pilot hydraulic system. In this illustration, the engine is running and the control levers are in the HOLD position. The pilot system is a closed center design. Oil is drawn from the implement hydraulic tank by the pilot pump. Pump oil is directed through the pilot filter group and is divided into two directions. One pathe flows to the the pilot relief valve and the other path flows to the selector valves . The pilot hydraulic system will constantly operate at the relief valve setting. When the pilot pump pressure reaches the relief valve setting, the relief valve opens. Oil over the relief valve flows to the implement oil cooler (not shown) before returning to the hydraulic tank. The pilot oil flows over an opened check valve 2 to the pilot control valves. Check valve 2 blocks oil from returning back to the pump. The pilot oil will be blocked at the pilot control valves until either the tilt or lift control lever is moved. Check valve 1 is installed between the pilot line and the selector and pressure control valve in order to block the pilot oil from flowing to the selector and pressure control valve. Pilot oil from the filter is also directed to the selector valves for the lift and tilt pilot lines. When the control levers are in the HOLD position, the pressure at each end of the selector valves is equal.
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The selector valves will be in the CENTER position. Pilot oil flows through the selector valves and through the orifices. The selector valve is used in order to circulate a small amount of warm pilot oil from the pilot pump into the pilot lines when the pilot control valve controls aren't being used to help out with cold weather conditions. As soon as the operator moves either control lever, in either direction, the valve shifts and blocks the flow to the pilot lines. It's called a thermal purge because it "purges" warm pilot oil into the pilot system. In the HOLD position, the pilot oil flows back through the tank port on the pilot control valve to the hydraulic tank. The selector and pressure control valve is used in the pilot system to control the pilot pressure that is provided when the lift cylinders are extended and there is pressure in the head end of the lift cylinders. The selector valve blocks the flow of oil through the selector valve when the pilot oil pressure provided by the pilot pump is greater than the pressure at the output end of the selector valve. In the event that the engine is not running and the lift cylinders are extended, the oil at the output of the selector valve will be greater than the pilot oil and check valve 1 will unseat. The oil from the head end of the lift cylinders flows through the selector valve, over the check valve 1, and flow to the pilot control valve. The pilot system will have sufficient pilot oil to lower the lift linkage.
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In the event the engine is not running and the bucket is raised and must be lowered, the pilot system will use oil pressure in the head end of the lift cylinders for the necessary pilot pressure. Oil in the head end of the lift cylinders (blue) flows to the selector and pressure control valve. The pilot oil will open check valve 1 and flow the the pilot control valves. Pilot oil will flow to check valve 2 and be blocked. When the oil pressure in the head end of the lift cylinders goes above the adjusted pressure of the selector valve, the valve will shift and the excess oil pressure will be directed to tank. The selector and pressure control valve reduces the pressure and makes the low pressure oil available for emergency use in the pilot system. When the lift control lever is moved in the lower direction, the reduced pilot oil will flow from the lift control valve through the lower kickout cushion solenoid valve to the lower ends of the lift stems (not shown) in the main control valve.
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The implement hydraulic system is made up of the following components. The illustration shows the location of the components in the NEEF Pilot Filter Group (1) Non-Engine-End-Frame (2) Pilot pump (gear) (3) Selector and pressure reducing valve (4) Float sequence valve (5) Pilot relief valve (6) Selector valve (thermal bypass) (7) Selector valve (thermal bypass) (8)
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The upper illustration shows the pilot filter group that is located in the NEEF (1). The pilot filter group is equipped with a filter (3) that is rated at 33 micron and a pressure switch (2). The pressure switch communicates with the VIMS module relaying that the pilot oil is below the required pressure. The lower illustration shows the location of the pilot components the Selector and pressure control valve (6), check valve (7), check valve (8), float sequence valve (9), pilot relief valve (10), and selector valves (thermal purge) (11 and 12). Also shown are the implement hydraulic tank (4) and the variable pump solenoid valve (5)
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Pilot Control Valve The pilot control is located in the cab to the right of the operator's seat. The control consists of the tilt control lever (2), the lift control lever (3) and the implement lever lock (1). When the implement lever lock is in the forward position, the control levers are unlocked. When the lever lock is pulled back, the control levers are locked. The pilot control valve is also equipped with detent coils (not shown). The detent coils will hold the lift control lever in full RAISE and full LOWER and the tilt control lever in the full TILT BACK positions until the linkage has reached the set kickout position.
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Tilt Pilot Control Valve
This illustration shows a sectional view of the tilt pilot control valve in the HOLD position. When the engine is running and the control lever is in the HOLD position, pilot oil from the pilot pump enters the pilot control valve and is blocked by the dump and tilt back metering stems. At the same time, a path for any pilot oil in the system to flow back to the hydraulic tank through pilot control valve. The lift pilot control valve operates the same way as the tilt pilot control valve. The tilt pilot control valve is equipped with a detent coil for the tilt back function only. When the tilt control lever is pulled to the full travel, the retainer will engage the detent coil. The detent coil will hold the retainer until the current to the detent coil is interupted. The lift pilot control valve is equipped with a detent coil for both raise and lower functions as shown in the next illustration.
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Lift Pilot Control Valve
This illustration shows a sectional view of the lift pilot control valve in the RAISE position. In the RAISE position, the pilot oil (orange) from the pilot pump enters the control valve. When the When the operator moves the lift control lever into the raise direction, the pivot plate is rotated and the upper plunger, the upper retainer, lower plunger, metering spring, the lower retainer and the metering stem moves downward. As the metering stem moves downward, the port holes in the stem pass over the oil passage from the pilot pump. Pilot oil flows from the passage through the center of the metering stem to the end of the lift stem in the main control valve (not shown). At the same time, the metering stem spring is adding an upward force against the upper edge of the metering stem. Return oil from the main control valve throug the lowermetering stem, the center of the metering stem and to the tank port. The objective of the metering stem is to allow movement of the stem in the main control valve proportionally with the movement of the pilot control lever. The metering stem and the metering spring function as a pressure reducing valve and control the pilot oil pressure at the end of the main control valve stem. As the metering stem moves downward, pilot oil flows through the orifice, the center of the metering stem and out to the main control valve.
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The flow of pilot oil is blocked at the main control valve stem causing the pilot pressure to increase. The pressure increase overcomes the centering spring for the main control valve stem and shifts the stem. Then, supply oil is directed to the actuator. The pressure increase is also sensed against the lower end of the metering stem. When the pressure increase overcomes the applied force, the metering stem moves up and compresses the metering spring. The upward movement restricts the flow of pilot through the orifice in the metering stem. Restricting the pilot oil flow controls the signal pressure at the stem of the main control valve . The metering spring therefore adjusts the pressure at the main control valve stem in proprtion to the movement of the pilot control lever. When the lift control lever is moved to full travel and the detent coil is energized, the upper retainer (raise) will be held in position by electromagnetic force of the detent coil. The detent coil will be energized until the position sensor (not shown) recognizes the kickout position. The lever can be removed from a detent position manually. When the operator moves the lift control lever to the full LOWER position, the lower side of the pilot control valve will operated similiar to the raise side and the float detent coil will hold the control valve in the FLOAT position.
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Implement Hydraulic System The implement hydraulic system is equipped with three fixed displacement piston pumps and one variable displacement piston pump. The three fixed displacement pumps draw oil from the implement hydraulic tank. The supply oil is directed through the high pressure screens and the individual relief valves. The individual relief valves limits the supply oil pressure that is flowing to the left and right control valves. This illustration shows the main control valve with no signal pressure from the pilot control valve (not shown). The oil that is between the main control valve and both ends of the lift and tilt cylinders is blocked. Each individual piston pump is equipped with its own case drain filter. Oil flow from the three fixed displacement pumps operate the lift and tilt cylinders. Oil flow is metered to the cylinders by the main control valve stems. The oil flow around the stems is controlled by the movement of the stems in the valve through the pressure that is applied to the ends of the stems. The operator controls the pilot oil flow and pressure that shifts the stems. Also, movement of the valve stems opens a passage for the oil in the opposite end of the cylinders to return to tank.
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Implement Hydraulic System In the illustration, the graphic shows the machine in dig trigger mode. The machine is in first speed forward, the ground speed is less than 6.8 kmh (4.25 mph), and the B-Pin is above the horizontal line of the A-Pin. The three fixed displacement piston pumps and one variable displacement piston pump are supplying the oil flow to the implement hydraulic system. The four pumps draw oil from the implement hydraulic tank. The supply oil is directed through the high pressure screens and the individual relief valves. The individual relief valves limits the supply oil pressure that is flowing to the left and right control valves. This illustration shows the main control valve with a raise signal from the pilot control valve (not shown). Also, each individual piston pump is equipped with its own case drain filter. An increased oil flow will be directed to the head end of the lift cylinders until the lift stop solenoid valve is energized and pilot oil to the end of the lift stem in the main control valve is blocked or the operator releases the lift control lever.
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The implement hydraulic system is built into the Non-Engine-end-Frame (1). The following components are shown in the NEEF: case drain filters and bypass switches (2), the implement pumps and pump drive (3), the high pressure screen groups and relief valves (5, 6, 7, 9), and the hydraulic tank (4). High pressure screen (7) filters supply oil for the left side fixed displacement pump. High pressure screen (9) filters supply oil for the right side fixed piston pump. High pressure screen (5) filters supply oil for the variable displacement pump (section of the tandem pump). High pressure screen (6) filters supply oil for the center fixed displacement pump (section of the tandem pump). The main control valve is made up of two valve sections. The right control valve (8) and the left control valve (10).
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The implement hydraulic system is equipped with four case drain filters with bypass switches. These filter groups filter the case drain oil from the four implement pumps. The following filter and bypass switch are in line with the following pump. Filter (2) and bypass switch (1) are in line with the left side fixed displacment pump. Filter (4) and bypass switch (3) are in line with the center fixed displacment pump. Filter (6) and bypass switch (5) are in line with the variable displacment pump. Filter (8) and bypass switch (7) are in line with the right side fixed displacment pump.
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High pressure screen (2) is a 200 micron filter that is between the implement pump and the relief valve group (3). Each individual implement pump is equipped with it own high pressure screen and relief valve. The relief valve pressure is adjusted by rotating the adjustment screw (1). The factory pressure setting for the relief valves is approximately 32800 kPa (4760 psi). The relief valve is also equipped with a check valve (not shown) with free flow out of the valve.
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This illustration shows the front pump drive (2) and implement pumps removed from the NonEngine-Engine Frame. The right fixed pump (1) and left fixed pump (3) are installed on each side of the tandem pump (4). The tandem pump is a combination of a fixed piston pump (nearest to the pump drive) and a variable displacement piston pump. The variable displacement piston pump is equipped with a pump control valve (5) that controls the upstroking and de-stroking of the pump when the machine requirements are met.
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The 994F Wheel Loader is now equipped with a new center pump on the front pump drive. The new pump is a two section piston type pump. The tandem pump is equipped with an impeller pump (charge) that draws oil from the implement hydraulic tank (not shown) and directs oil to the inlet cavities of each pump section. The pump section that is located next to the pump drive is a fixed displacement piston pump. This section will continuously supply oil to the main control valve when the engine is running. The displacement for the fixed pump is predetermined by the locking bolts that retain the swashplate at the fixed angle. The other pump section is a variable displacement piston pump. This section will supply either minimum flow or maximum flow to the main control valve depending on the signal pressure at the pump control valve. The pump control valve will control the output of the variable pump using pump pressure to shift either the flow control spool (not shown) and the pressure compensator spool (not shown). In this illustration showing minimum flow, oil pressure is directed to the large piston and the force against the piston moves the piston rod and the swashplate against the stop. At the same time, the spring and the pressure that is behind the small piston will be overridden. Small piston will allow the swashplate to rotate against the stop. The pump will supply sufficient oil pressure to lubricate the pump and supply instantaneous response to a request for maximum flow.
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The signal for the control of the upstroke and destroke of the variable displacement piston pump is through a voltage signal from the Implement ECM to the solenoid valve (not shown) for variable displacement piston pump. The solenoid valve relieves or retains the oil pressure in the signal line to the pump control valve. In this illustration, the signal oil pressure is releived to tank pressure. When the oil at the signal line goes to tank pressure, oil pressure at the right end of the flow compensator spool decreases. The spring force on the right side of the flow compensator spool is overridden by the force that is developed by the system pressure on the left side of the spool. The spool shifts to the right. System pressure is allowed to flow over the flow compensator spool to the large actuator piston. The increased pressure in the large actuator piston overcomes the combined force of the small actuator and bias spring and moves the swashplate to a reduced angle. As pump decreases, pressure also decreases. When supply pressure and equalsflow the sum of the supply oil pressure at the right end of the flowthe compensator spool decreases and spring force, the flow compensator spool moves to a metering position and the system stabilizes.
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The fixed displacement pump supplies oil to the main control valve continuously when the engine is running. The displacement for the fixed pump is predetermined by the stops that retain the swashplate at the fixed angle. The pump section on the right is a variable displacement piston pump. This section will supply either minimum flow or maximum flow to the main control valve depending on the signal pressure at the pump control valve. In this illustration, the pump is showing maximum oil flow. The oil pressure that is behind the large piston is relieved to tank. At the same time, the spring and the pressure that is behind the small piston will override the large piston and the small piston will rotate the swashplate against the lock stop. The variable pump will upstroke to maximum flow. The pump will continue to provide maximum flow until the pressure at the signal pressure at the pump control valve changes.
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The signal for the control of the upstroke and destroke of the variable displacement piston pump is through a voltage signal from the Implement ECM to the solenoid valve (not shown) for variable displacement piston pump. The solenoid valve relieves or retains the oil pressure in the signal line to the pump control valve. In this illustration, the signal oil pressure is retained at system pressure. When the oil at the signal line increases to system pressure, oil pressure at the right end of the flow compensator spool is increased. The combination of the spring force and the system pressure on the right side of the flow compensator spool overrides by the force that is developed by the system pressure on the left side of the spool. The flow compensator spool shifts to the left. Oil at the large actuator piston is allowed to flow over the flow compensator spool and the pressure compensator spool. The large actuator piston is at tank pressure. The force of the bias spring and the system pressure on the small piston enables the small piston to override the large piston and the swashplate will move to maximum angle. The pump will upstroke and add an oil source to the main control valve to increase the cycle time of the raise function and the dump cycle time if the following conditions are met. The machine is in first speed forward, the ground speed is below 4.25 mph, and the B-Pin is above the horizontal line of the A-Pin.
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This illustration shows the components in the right side implement control valve. The control valve is accessed from the articulation hitch. The following is a list of the components. - Inlet port for the right fixed displacement implement pump (1) - Tilt rod end port (2) - Tilt load check valve(3) - Check valve (4) - Tilt head end port (5) - Check valve (6) - Lift rod end port (7) - Lift head end port (8) - Check valve (9) - Makeup and vent valve (10) - Lift load check valve (11) - Hydraulic tank port (12)
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This illustration shows the back side of the right implement control valve. Port (1) is the inlet connection for the center variable displacement piston pump.
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The 994F Wheel Loader main control valve is made up of two control sections, the right control section and the left control section. The above illustration shows the right side control valve in the float position including the makeup and vent valve. The makeup and vent valve is shown in both the makeup and float operation. In the makeup operation, the pressure in the hydraulic tank exceeds the pressure in the rod end of the lift cylinder. Lowering the bucket faster than the pump can fill the rod end of the lift cylinder the piston displacement causes a vacuum in the rod end of the lift cylnders. The makeup valve allows oil from the tank line to flow into the rod end of the lift cylinders and fill the void. In the float operation, the makeup and vent valve allows the oil that is holding the vent valve against the seat to flow through the float sequence valve (not shown) to the hydraulic tank. The small orifices in the base of the vent valve (in the left control vent valve) restrict oil flow to th chamber that is behind the valve. With the oil flowing from behind the vent valve faster thatn the oil flowing in, the pressure difference between the oil around the vent valve and the oil behind the vent valve increases enough to lift the vent valve off its seat. When the vent valve moves off the seat, the oil from the implemnt pumps flow past the vent valve to the hydraulic tank. Both ends of the lift cylinders are open to the hydraulic tank allowing the bucket to float along the contour of the ground.
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In the float operation, the makeup and vent valve allows the oil that is holding the vent valve against the seat to flow through the float sequence valve (not shown) to the hydraulic tank. The pressure of the supply oil that is flowing to the rod end of the lift cylinders acts against the vent valve and the force overrides the spring and the valve opens. When the vent valve shifts to the OPEN position and the supply oil flows to the hydraulic tank. At that time, both ends of the lift cylinders will be open to the tank. This will allow the bucket to follow the contour of the ground.
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This illustration shows the components in the left side implement control valve. The control valve is accessed from the articulation hitch. The following is a list of the components. - Inlet port for the left fixed displacement implement pump (1) - Check valve (2) - Lift head end drain port (3) - Tilt load check valve (4) - Relief and makeup valve (5) - Tilt head end port (6) - Tilt rod end port (7) - Relief and makeup valve (8) - Lift rod end port Check valve (9) - Lift head end port (10) - Makeup and vent valve (11) - Relief and makeup valve (12) - Lift load check valve (13) - Hydraulic tank port (14)
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This illustration shows the back side of the left implement control valve. Port (1) is the inlet connection for the center fixed displacement piston pump.
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The 994F Wheel Loader main control valve is made up of two control sections, the right control section and the left control section. The above illustration shows the left side control valve in the float position including the makeup and vent valve. The makeup and vent valve is shown in both the makeup and float operation. In the makeup operation, the pressure in the hydraulic tank side of the vent valve exceeds the pressure in the rod end of the lift cylinder. Lowering the bucket faster than the pump can fill the rod end of the lift cylinder the piston displacement causes a vacuum in the rod end of the lift cylnders. The vent valve on the left control valve is equipped with an orifice. The makeup valve allows oil from the tank line to flow into the rod end of the lift cylinders and fill the void. In the float operation, the makeup and vent valve allows the oil that is holding the vent valve against the seat to flow through the float sequence valve (not shown) to the hydraulic tank. The small orifices in the base of the vent valve restrict oil flow to the chamber that is behind the valve. With the oil flowing from behind the vent valve faster than the oil flowing in, the pressure difference between the oil around the vent valve and the oil behind the vent valve increases enough to lift the vent valve off its seat. When the vent valve moves off the seat, the oil from the implemnt pumps flow past the vent valve to the hydraulic tank. Both ends of the lift cylinders are open to the hydraulic tank allowing the bucket to float along the contour of the ground.
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The left control valve on the 994F Wheel Loader is now equipped with an auxiliary stem that uses pilot oil pressure from the lower pilot valve to control when the stem will be shifted. When the lower pilot oil reaches reaches the required pressure, the force that is developed by the pilot oil pressure will override the springs on the right side of the auxiliary stem. The auxiliary stem will start to shift to the right. Return oil from the head end of the lift cylinders will be allowed to flow around the auxiliary stem through the passage in the valve to the hydraulic tank. This will increase the lower cycle time by approximately 10%.
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Implement Hydraulic System Schematic HOLD
This schematic shows the hydraulic flow with the control levers in the HOLD position. When the engine is running, pilot oil that flows from the pilot pump through the pilot relief valve and is blocked at the pilot control valve. At the same time, oil from the pilot pump flows through the tilt selector valve and lift selector valve. With no signal pressure at either end of the selector valves, the selector valves are in the CENTER position. The pilot oil that is flowing out of the selector valves pass through orifices. Then, the oil flows back through the pilot control valves to the hydraulic tank. The two fixed displacement piston pumps draw oil from the hydraulic tank. The pumps direct oil through high pressure screens, over the individual relief valves and supply hydraulic oil to the main control valve. The open center valve directs the supply oil through the main control valve to the hydraulic tank. Also, the tandem pump draws oil from the hydraulic tank. The fixed displacement pump draws oil from the hydraulic tank and directs supply oil to the main control valve. With the B-Pin below the horizontal level of the A-Pin, the variable displacement pump will be at zero flow.
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This illustration shows the hydraulic oil flow with the variable displacement piston pump destroked. When the lift control lever is in the RAISE position, pilot oil is directed through lift stop solenoid valve to the raise ends of the individual lift stems in the main control valve. Also, the pilot oil pressure to the right side of the lift selector valve increases, the lift selector valve shifts to the left. The flow of pilot oil through the lift selector valve is blocked. All the pilot oil is directed to the ends of the raise end of the lift stems. The force of the oil pressure on the lift stems cause the spools to move against the centering springs. The lift stems shift to the RAISE position. At this time, the lift stems direct supply oil flow to the head end of the lift cylinders. When the lift linkage position sensor communicate that the lift cylinders are at approximately 70 mm (2.75 inch) from the end of stroke, the Implement ECM energizes the raise stop solenoid valve and the flow of pilot oil to the end of the lift stems is blocked. The lift stems will shift back to the CENTER position. The supply oil to the lift cylinders will be blocked.
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This illustration shows the hydraulic oil flow when the control lever is moved to the RAISE position and the variable displacement piston pump upstroked. When the pilot control lever is in the RAISE position, pilot oil is directed through lift stop solenoid valve to the raise ends of the lift stems. Also, the pilot oil that is flowing to the lift selector increases in pressure, the lift selector valve shifts to the left. The flow of pilot oil through the lift selector valve is blocked. All the pilot oil is directed to the raise end of the lift stems. The force of the oil pressure on the lift stems push the lift stems to move against the centering springs to the RAISE position. The lift stems send supply oil flow to the head end of the lift cylinders. When the lift arms raise to the B-Pin over the horizontal line of the A-Pin, 1st speed forward for at least 2.0 seconds, and ground speed is less than 6.8 kilometers/hr (4.25 mph), the implement ECM sends a signal to energize the variable pump solenoid valve. Pump control oil is relieved to tank. The variable displacement piston pump will upstroke. When the lift cylinders are at approximately 70 mm (2.75 inch) from the end of stroke, the Implement ECM energizes the raise stop solenoid valve and the flow of pilot oil to the end of the lift stems is blocked. The lift stems will shift to the CENTER position. The supply oil to the head end of the lift cylinders will be blocked.
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The supply oil to the head end of the lift cylinders will be blocked.This illustration shows the hydraulic flow when the lift control lever is moved to the LOWER position and the pilot pressure is greater than 900 kPa (130 psi). When the lift control lever is in the LOWER position, pilot oil is directed to the lower end of the lift stems. Also, the pilot oil that is flowing to the lift selector increases in pressure, the lift selector valve shifts to the right. The flow of pilot oil through the lift selector valve is blocked. All the pilot oil is directed to the lower end of the lift stems. The lift stems shift and the lift stems open passages for oil flow from the implement pumps, through the load check valves, the lift control spools and the rod end of the lift cylinders to lower the bucket. The position of the lift stem also opens a passage for the oil in the head end of the lift cylinders to flow to the implement hydraulic tank. When the pilot pressure is greater than 900 kPa (130 psi) pilot oil pressure, the lower sequence stem starts to shift to the right. Oil in the head end of the lift cylinder is allowed to flow through the sequence stem, through the main control valve and return to the implement hydraulic tank. This will increase the cycle time for lowering the lift linkage. The lower circuit is equipped with a lower kickout cushion solenoid valve. When the lift linkage is lowered to a predetermined position that is set by the lower kickout, the solenoid valve is energized by the Implement ECM. The solenoid valve shifts and blocks the flow of pilot oil through the valve.
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All the pilot oil flows through the orifice causing a pressure drop at the lower end of the lift stems. The drop in the lower pilot pressure will allow the lower stems to shift toward the HOLD position for one second, and reducing the flow of system oil to the rod end of the lift cylinders. This cushions the the lift cylinders as the bucket nears the set kickout position.
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This illustration shows the hydraulic oil flow when the lift control lever is moved to the FLOAT position. When the lift control lever is in the FLOAT position, pilot oil is directed to the lower end of the lift stems. The force that is developed by the pilot oil pressure causes the lift stems to move against the centering springs to the FLOAT position. The lift stems open passages for supply oil flow from the implement pumps, to flow to the rod end of the lift cylinders. With the lift control lever is in the FLOAT position, the oil pressure in the pilot line develops a force on the spool in the sequence valve. The sequence valve shifts, and allows the oil in the spring cavity for the makeup and vent valve to flow through the sequence valve and back to the hydraulic tank. The makeup and vent valve shifts to allow oil that is directed to the rod end of the lift cylinder to flow to the hydraulic tank. When the makeup and vent valves move off their seats, oil intended of the rod end of the lift cylinders flows past the makeup valves to the tank. At thisthe time, both ends theposition lift cylinders theopens tank allowing along ground. Also,ofthe of the are lift open stem to also a passagethe forbucket the oil to in float the head end of the lift cylinders to flow to the implement hydraulic tank. The detent coil will hold the lift control lever in the FLOAT position until the lever is moved from the FLOAT position or the current to the detent coil is interuppted.
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This illustration shows the hydraulic flow when the tilt control lever is moved to the DUMP position and the variable displacement piston pump upstroked. When the tilt control lever is in the DUMP position, pilot oil is directed to the dump end of the tilt stems. Also, Pilot oil is flowing to the tilt selector valve.. As the pilot pressure at the tilt selector valve increases, the tilt selector valve shifts to the right. The flow of pilot oil through the tilt selector valve is blocked. All the pilot oil is directed to the dump end of the tilt stems. The force of the oil pressure on the tilt stems cause the stems to move against the centering springs to the DUMP position. The tilt stems send supply oil flow to the rod end of the tilt cylinders. The dump circuit is equipped with makeup valve. As the speed of the bucket rotating around the B-Pin increases, the effect of gravity on the bucket changes the force from the rod end of the tilt cylinder to the head end. The implement pumps are not able to supply the required oil. There will The be void in the pressure rod end of cylinder. the dump will decrease. increased onthe thetilt lower side ofThe the pressure make up in valve will becircuit greater than the pressure on the upper side. The poppet will come off the seat and return oil from the head end of the tilt cylinder flows into the rod end to fill the void.
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Implement Hydraulic Oil Cooling System
The upper illustration shows the components of the implement hydraulic oil cooing system in the loader frame (NEEF). In the system, the implement oil cooling gear pump (1) on the front pump drive (2) draws hydraulic oil from the hydraulic tank (4) and directs the oil to check valve (3). Also, the tank oil from the pilot relief valve (5) is directed to the check valve (3). The combined oil flows out of the check valve to the implement oil filter (7), and through the implement oil cooler (1) in the lower illustration (EEF) and then back to the hydraulic tank (4) in the NEEF. Also shown is the hydraulic tank (9) for the brake oil cooler system and the main control valve (6). The filter group is equipped with a bypass switch (8) that communicates with the VIMS module.
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Implement Hydraulic Oil Cooling System
The upper illustration shows the filter group. In the filter group is the filter (1) and the filter bypass switch (3). Also shown are the steering and brake hydraulic tank (2) and the brake cooler tank (4). The filter bypass switch communicates with the VIMS module. The lower illustration shows the location of the implement hydraulic oil cooler (5) within the radiator package (6).
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The upper illustration shows the location of the diagnostic ports for the loader frame (NEEF). The lower illustration shows the location for the following pressure taps. - Parking brake pressure (1)
- Center fixed displacement pump(2)
- Left fixed displacement pump (3)
- Center variable displacement pump (4)
- Right fixed displacement pump (5)
- Lift head end pressure (6)
- Tilt head end pressure (7) - Tilt rod end pressure (9)
- Lift rod end pressure (8)
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STEERING HYDRAULIC SYSTEM Steering System Components
This illustration shows the components in the steering hydraulic system on the 994F Wheel Loader. The color codes for the components in the steering hydraulic system are: Orange-
Steering pilot system
Red
Main steering system
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Green -
Steering cooling system
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This illustration shows the location of the pumps on the 994F rear pump drive as viewed from above. The pump locations are the same as the 994D. The service brake cooling pump (1) and the steering and brake oil cooling pump (3) are fixed displacement gear pumps. The steering hydraulic oil pumps (2) and the brake application oil pump (4) are variable displacement piston pumps.
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The Steering System The steering system is made up of the following components that are located on the rear frame (1). - Neutralizers and quad check valves (2) - High pressure screens (3) - Steering Valves (control and reducing) (4) - Case drain filters (5) - Steering and brake hydraulic tank (6) - Right steering cylinder (7) - Left steering cylinder (8) - Steering pumps (9)
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The steering neutralizers and quad check valve is located at the articulation hitch between the cab and frame (EEF) (1). The bracket for the strikers (2) and (5) are attached to the loader frame (NEEF). The neutralizer valve is normally open between the pilot control valve (not shown) and the quad check valve. Pilot oil is allowed to flow through the neutralizer valve when the operator moves the pilot valve to articulate the machine. When the adjusted striker makes contact with the neutralizer, the valve will block pilot oil through the neutralizer valve. The machine will stop articulating. In a right turn, neutralizer (3) will contact striker (2). In a left turn, neutralizer (6) will contact striker (5). Quad check valve (4) is between the neutralizer valves and the ends of the stem in the steering control valve (not shown). The quad check valve has two check valves for each pilot line. One check valve is free flow through and the second is will block pilot oil flow to the steering control valve. When pilot oil is directed to the steering control valve, the pilot oil flows through the free flow check valve. When the pilot control valve is returned to the HOLD position, the free flow check valve will seat and block pilot oil between the check valve and the steering control valve. The stem in the steering control valve will be held in the articulated position until the pilot control valve is moved in either direction. The second check valve will allow the trapped pilot oil to flow back to the pilot control valve when the valve is moved to the opposite direction (the opposite direction).
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This illustration shows a sectional view of the neutralizer valve. During a less than maximum turn, oil from the steering control lever flows through the neutralizer valve to the steering control valve. When the striker comes in contact with the neutralizer valve spool, the valve stem shifts and oil flow to the steering control valve is blocked. Pilot oil at the steering control valve flows back through the orifice and center passage in the spool valve to drain. The centering spring centers the steering control valve and stops the machine from turning.
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The upper illustration shows the case drain filters that are located in the pump bay. The lower illustration show the high pressure screens. Access to the filters and screens is gained through the doors in the platform behind the cab. The steering hydraulic system is equipped with two case drain filters (1) and (3). They filter the oil that is in the steering pump case that will flow back to the steering hydraulic tank. Each filter is equipped with a bypass switch (2) and (4). The switch will send a signal to the VIMS module if one of the filters becomes plugged. High pressure screens (5, 6) strain the system oil that is flowing from the steering pumps to the inlet port on the steering control valve.
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This illustration shows the location of the following components of the steering hydaulic system that are located on the inside of the right frame. Access these components through the door that is behind the cab in the platform. Steering control valve (4) sends system oil supplied by the two steering pumps to the steering cylinders (not shown) when a pilot oil signals the valve to shift. The steering control valve also sends a signal to the margin spool in each pump control valve on the steering pumps. Selector and pressure reducing valve 1 (6) reduces oil that is supplied by the steering pump to the unloading valve in the steering control valve. Orifice (3) meters the reduced oil that flows to the pressure switch (5). The pressure switch sends a signal to the VIMS module if the primary steering pressure is lost. Adapter (2) is equipped with an orifice and that restricts the flow of steering pump oil to tank in order build up pressure behind the orifice to shift the diverter spool in the secondary steering valve. Also, the orifice opens a free path to discharge the oil between the reducing valve and the diverter valve to drain in case of a loss of steering pump oil. Selector and pressure reducing valve 2 (1) reduces the pressure of the steering oil pressure to the pilot pressure level. Then, that oil is directed to the pilot control valve.
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Shown is a schematic and sectional view of the steering pump and pump control valve. The pump has two actuator pistons which work together to continually adjust the angle of the swashplate. The small actuator piston that that is assisted by the bias spring is used to upstroke the pump. The large actuator piston is used to destroke the pump. The pump control valve consists of a flow compensator (margin) spool and a pressure compensator (cutoff) spool. The valve keeps the pump flow and pressure at a level needed to fulfill the demands of the steering system. The margin compensator spring maintains the pump supply pressure at 2100 ± 105 kPa (305 ± 15 psi) above the signal pressure. The pressure compensator spring limits the system pressure to 29000 ± 350 kPa (4200 ± 50 psi). When the engine is OFF, the bias spring in the small actuator piston moves the swashplate to maximum angle.
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At machine start-up, the small actuator spring holds the swashplate at maximum angle. When the steering control valve is in the HOLD position, pump flow is blocked at the steering control valve and no signal pressure is generated. As the pump produces flow, the system pressure begins to increase. This pressure is felt at the lower end of both the flow compensator spool and the pressure compensator spool. The flow compensator spool moves up against spring force and permits system oil to go to the large actuator piston. The oil pressure at the large actuator piston overcomes the combined force of the bias spring and system oil pressure at the small actuator piston. The large actuator piston moves the swashplate to the LOW PRESSURE STANDBY position. In LOW PRESSURE STANDBY, the pump produces enough flow to compensate for system leakage at sufficient pressure to provide instantaneous response when the steering control valve is moved.
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When the load on the steering system decreases, signal oil pressure at the right end of the flow compensator valve decreases. This decreased pressure causes the force (flow compensator valve spring plus signal oil pressure) at the right end of the flow compensator spool to decrease below the pump supply pressure at the left end of the spool. The decreased pressure at the right end of the flow compensator spool causes the spool to shift and allows more flow to the large actuator causing the pressure in the large actuator piston to increase. The increased pressure in the large actuator piston overcomes the combined force of the small actuator and bias spring and moves the swashplate to a reduced angle. As pump flow decreases, supply pressure also decreases. When the supply pressure decreases and equals the sum of the oil pressure at the right end of the flow compensator spool and spring force, the flow compensator spool moves to a metering position and the system stabilizes.
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During a turn, signal pressure at the steering control valve increases. This increased pressure causes the force (flow compensator valve spring plus signal oil pressure) at the right end of the flow compensator spool to become greater than the pump supply pressure at the left end of the spool. The increased pressure at the right end of the flow compensator spool causes the spool to shift left. The spool reduces or blocks pump output oil flow to the large actuator piston, and opens a passage to drain. Reducing or blocking oil flow to the large actuator piston reduces or eliminates the pressure acting against the large actuator piston. When the pressure in the large actuator piston decreases, the bias spring and small actuator piston move the swashplate to an increased angle causing the pump to UPSTROKE.
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The pressure compensator spool limits the maximum system pressure for any given pump displacement. The pressure compensator spool is held in the left position during normal operation by spring force. When steering hydraulic system pressure is at maximum, pump supply pressure increases and the pressure compensator spool moves right against spring force. The pressure cutoff spool blocks oil in the large actuator piston from returning to the tank and allows supply oil to go 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 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 relief valve in the steering hydraulic system. Maximum system pressure is adjusted by turning the pressure compensator adjustment screw.
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Steering Pilot Valve
The steering pilot valve (2) for the steering system is mounted below the STIC (1) on the left side of the operator's seat. When the steering pilot valve is moved side to side, the valve directs pilot oil through the neutralizer valves (not shown) to one of the ends of the directional control valve stem in the steering valve body (not shown). The STIC lock lever (3) is shown in the LOCKED position. At this time, the STIC will not not move. Push the STIC lock lever forward to the UNLOCK position in order to shift the steering pilot valve.
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This illustration shows the major components in the steering pilot valve. The steering pilot valve directs pilot oil to both ends of the stem in the steering control valve. With the engine running and the control lever in the HOLD position, pilot oil enters the pilot oil passage and is blocked by the pilot stems. Any return pilot oil in the lines that is between the steering control valve and the steering pilot valve will be vented to the drain passage through the center of the metering stems.
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When the handle for the steering pilot valve is moved to the left, the cam follower linkage pushes the left port plunger downward against the regulating spring. The force of the regulating spring is greater than the return spring so the pilot stem moves downward. At the same time, the return spring adds an upward force against the pilot stem to stabilize the movement. When the hole through the pilot stem moves over the port from the pilot oil passage, the pilot oil flows through the center of the pilot stem. Then, the pilot oil flows through the orifice to the quad check valve and then to the end of the stem in the steering control valve. As the handle is moved further to the left more pilot oil is allowed to flow through the pilot stem. The pilot oil that is directed to the end of the stem will build up pressure and override the force of the centering spring in the steering control valve (not shown) in order to move the stem. The pressure will build up a force in the center of the pilot stem. The combination of the return spring and in that push the regulating spring. The flow between the hole theforce pilotwill stem andupward the pilotagainst oil passage will be blocked. The oil pilot stem will act like a reducing valve. As more articulation speed is required, the regulating spring force pushing down must be increased by more handle movement. As the stem in the steering control valve is shifted, return pilot oil will be directed through the orfice in the right port, through the center of the pilot stem.
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The force that is developed by the pressure of the return oil will override the regulating spring. The pilot stem will move upward far enough to allow the return oil to flow out of the drain passage.
NOTE: The shims that were previously used to change the adjudtment of the capsules at the base of the valve have been removed. Also, the adjustment procedure has been changed. To adjust the capsules, loosen the bolts that hold the steering control valve and raise the bracket. Then, rotate the capsules to the desired amount, lower the bracket over the capsules and tighten the bolts. The recommended amount of movement of the steering lever in both directions before the machine starts to turn is 15 ± 3 mm (0.59 ± 0.120 inch).
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This sectional view of the steering control valve identifies the various components. The control valve is in the HOLD position. When system oil from the steering pumps enters the steering control valve, the oil is blocked by the control stem. The oil flows through the hole in the relief valve and into the spring cavity. The pressue in the spring cavity will be equal to the pressure at the inlet of the control valve. The relief valve will block any oil flow between the inlet of the control valve and the tank port. The function of the control stem is to direct oil to the respective ends of the steering cylinders when making a turn. When in the steering control valve is in the HOLD position, the oil between the steering cylinders and the control valve will be blocked. System oil flow entering the steering valve is blocked by the control stem.
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This sectional view shows the steering control valve with the control stem shifted for a left turn. When the steering control lever is moved to the left, pilot oil is directed to the left turn pilot cavity. Then, the control stem is shifted to the left. System oil from the inlet of the valve flows around the control stem to the head end of the right cylinder and the rod end of the left cylinder. Also, the system oil flows to the ball resolver. The ball shifts to the and system oil flow around the ball resolver to the steering control valve in each steering pump. Continual movement of the steering control lever sends pilot oil to keep the steering control spool in the open position. Steering pump oil flow is blocked at the cylinders. The pressure in the spring chamber will increase over the relief valve setting. The force that is developed by pressure in the spring chamber exceeding the spring force on the poppet. The poppet will unseat. The force of the oil pressue in the spring cavity and the spring force will drop below the pressure at the valve inlet. The relief valve will shift to the right and all allow the extra pressure to flow out of the tank port. When the pressures are equalized, the poppet will seat and the the relief valve shifts to the left and stops all flow to the tank. When an external force acts on the wheels when the control stem is in the HOLD position, a hydraulic spike is induced in the steering system. At this time the pressure at the crossover relief valve will open and allow the higher pressure to flow to the steering cylinder that is not being controlled.
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Steering Hydraulic System
When the engine is running and the steering system is in HOLD, pilot oil from the right pump is blocked at the steering control valve spool. Oil from the left and right steering pumps flows through the respective check valves to the steering control valve. The control valve spool blocks oil flow to the steering cylinders and no signal pressure is generated. System pressure is sensed at the margin spool, the pressure compensator spool, and the small actuator piston (rod end symbol) of each pump . As system pressure increases, the margin spool moves against the spring force and opens a passage for pump oil to flow to the large actuator piston (head end symbol). The pressure in the large actuator piston overcomes the combined force of the actuator spring and the pressure in the small piston and moves the swashplate to the LOW PRESSURE STANDBY position. In LOW PRESSURE STANDBY, the pump produces adequate flow to compensate for system leakage and sufficient pressure to provide for instantaneous response when the steering control valve is moved. The pilot steering system receives system oil from the output of the steering pumps. System oil flows from the steering pumps to the selector and pressure reducing valve 2. The valve reduces the system pressure to pilot pressure and pilot oil flows to the steering pilot valve.
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When the operator moves the STIC to the right, pilot oil flows through the pilot control valve and the right neutralizer valve to the right side of the steering control spool. Pilot oil pressure moves the steering control spool to the right. System oil from the steering pumps flows through the check valves and the high pressure screens. Then, the system oil flows around the control spool to the steering cylinders. As pressure increases in the steering cylinders, the pressure (signal pressure) is sensed in the margin valve spring chamber at each pump. The signal pressure combines with the force of the margin spool spring and moves the margin spool down. The margin spool restricts the flow of oil to the large actuator piston (head end). The spring and pressure in the small actuator piston overcome the pressure in the large piston to move the swashplate toward maximum angle. The increase in swashplate angle increases pump oil flow. The increase in oil flow through the control spool orifice increases the system pressure. The system pressure is sensed at the margin spool. The increased pressure moves the margin spool against the combined forces of the spring and signal pressure and sends oil to the large actuator piston. The actuator piston moves the swashplate to a reduced angle that produces flow relative to the position of the control spool.
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When making a FULL RIGHT TURN, the right striker (not shown) cont acts the right neutralizer valve. Oil flow from the pilot control valve to the steering control valve is blocked by the movement of the neutralizer valve. The steering control spool returns to the center position. Flow to the steering cylinders is blocked and the machine stops turning. The steering pumps return to the LOW PRESSURE STANDBY position. The neutralizer valves prevent the machine front frame from contacting the machine rear frame when turning FULL RIGHT or FULL LEFT. Refer to the Service Manual for the correct procedue for any adjustments to the steering system.
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The illustration shows the 994F steering system when the Secondary Steering System is active. The bi-directional secondary steering pump is splined to the output transfer gears and turns whenever the machine is rolling. The diverter valve directs oil from the tank to the input side of the pump and the oil from the output side of the pump to the main steering system depending on if the machine is rolling FORWARD or REVERSE. The secondary steering relief valve limits the maximum pressure in the secondary steering system. The unloader spool senses the pressure in the primary steering system from the pressure and selector valve 1. If there is steering system pressue, the unloader spool directs secondary steering oil to the hydraulic tank. When the machine is rolling with the engine not running, the main steering pumps are not providing flow to the steering system. The main steering pump output is blocked and the pressure is zero. The pressure that is acting on the top of the unloader valve is relieved. Spring force moves the unloader spool up and blocks the flow of secondary steering oil to tank. The pressure unseats the check valve and directs secondary steering oil into the main steering system. The check valves on the output of the main steering pumps seat and block the oil from entering the pumps.
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The secondary steering oil flows to the steering control valve and the selector and pressure reducing valve. The selector and pressure reducing valve reduces the secondary steering pressure to a pilot level. The steering pilot control valve can use that oil in order to shift the spool in the steering control valve. The steering warning switch senses the main steering system pressure after the selector and pressure control valve. The steering warning switch is monitored by VIMS. When the main system pressure drops, the switch opens. The VIMS alerts the operator with a Level 3 warning that the main steering system pressure is low.
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The above illustration shows the location of the pumps on the 994F rear pump drive. The pump locations are the same as the 994D. The service brake cooling pump (1) and the steering and brake oil cooling pump (3) are fixed displacement gear pumps. The steering hydraulic oil pumps (2) and the brake application oil pump (4) are variable displacement piston pumps.
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STEERING AND BRAKE OIL COOLING SYSTEM
Shown is a block diagram of the steering and brake hydraulic oil cooling system. The gear pump draws oil from the steering and brake hydraulic tank. Pump oil flows past the fluid sampling valve, through the filter, through the three oil cooler cores, and back to the steering and brake hydraulic tank. The cooler bypass valve allows pump oil to bypass the coolers at machine start-up or when the oil is cold. The cooler bypass valve is set to open at approximately 345 kPa (50 psi).
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Steering And Brake Hydraulic Oil Cooling System
This illustration shows the location in the Engine-End-Frame of the components that are used to cool the steering and brake hydraulic oil. In the cooling system, oil is drawn from the steering/brake hydraulic tank (1) by the gear pump (4). The oil is directed through the filter group (2) and then through the steering/brake oil cooler (radiator group) (3) and back to the hydraulic tank. Also shown are the left steering cylinder (5) and the torque converter housing (6).
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The upper illustration shows the components that are in the area of the rear pump drive. The gear pump (1) and the fluid sampling port (2) are located on the rear pump drive towards the rear of the machine. The filter group is located on the right side of the machine next to the steering and brake oil tank. Installed on the filter is the bypass switch (4). Steering oil cooler filter bypass switch cmmunicates with the VIMS module. Also shown is the implement hydraulic oil cooler filter. In the lower illustration, the steering and brake oil cooler (5) is located in the radiator group at the rear of the machine.
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This illustrations shows the brake component locations on the 994F Wheel Loader. The axle components are retained from the 994D Wheel Loader. The service brakes now feature an increased circuit pressure and a split control system.
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Brake System Components
This illustration shows a schematic of the brake system with the engine not running and the pumps not rotating. The brake system component functions are: Brake pump: The brake pump is a variable displacement piston pump with a pressure compensated pump control valve. The pump draws oil from the steering and brake hydraulic oil tank and sends supply oil to through the check valves to the accumulators. Check valves: Allows oil flow in one direction between the brake pump and the accumulators. Brake accumulators: When the engine is running, the front and rear brake accumulators supply oil within a controlled pressure range to the brake valve and to the parking brake valve. If the engine stops running, the accumulators provide an emergency oil supply to provide braking. Service brake valve: Controls the flow of brake oil to the front and rear service brakes. Parking brake valve: Controls the engagement and disengagement of the parking brake.
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Parking brake: Prevents the machine from moving when parked. Parking brake pressure switch: The pressure switch sends a signal to the Power Train ECM if a low pressure event occurs at in the parking brake circuit. Brake low pressure warning switches: The pressure switch sends a signal to the VIMS module if a low pressure event occurs at either brake accumulator.
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BRAKE SYSTEM Brake System Schematic
Shown is a schematic of the service brake system, the parking brake system, and the brake cooling system. In the illustration, the parking brake is disengaged and the service brakes are not engaged.
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Brake System Schematic
Shown is a schematic is the service brake system, the parking brake system, and the brake cooling system. In the illustration, the service brakes are engaged and the parking brake is disengaged.
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Hydraulic Brake System Control
The hydraulic brake system control consists of the following components: Steering and brake hydaulic tank (1) Service brake control valve (2) Parking brake control valve (3) Brake pump (4) Brake accumulators (5) Also shown for location of the brake components are the left side steering cylinder (6) and the EEF (7).
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This illustration shows the service brake valve (3) and the parking brake control valve (4). The service brake control is attached below the cab frame at the articulation hitch. The parking brake valve group is located one EEF at the articulation hitch. Installed on the parking brake control valve group is the parking brake interlock switch (7) and the parking brake pressure switch (5). These two switches communicate with the Power Train ECM. Service brake low pressure switches (1) and (2) are installed in the brake lines between the service brake control valve and the brake accumulators (not shown). Front brake pressure switch (2) and the rear brake pressure switch (1) communicate a drop in pressure to the VIMS module. Also, hose (8) is connected to the rear service brakes in the EEF (not shown), hose (9) is connected to the front service brakes in the NEEF (not shown), and hose (6) is connected to the parking brake in the NEEF (not shown).
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This illustration shows the service brake valve operation with the right service brake pedal applied and also not applied. When the operator depresses either brake pedal (right view), the upper spring moves the two brake spools down. The brake spools close the passages to the tank and open the passages from the two accumulators. The oil from the rear accumulator flows through the upper brake spool to ENGAGE the rear service brakes and to fill the chamber between the upper brake spool and the lower brake spool. The oil from the front brake accumulator flows through the lower brake spool to ENGAGE the front service brakes and to fill the chamber at the bottom of the lower spool. The pressure at the bottom of the lower brake spool and the force of the spring move the lower brake spool up against the pressure in the chamber between the upper brake spool and the lower brake spool. The pressure in the chamber between the upper brake spool and the lower brake spool moves the upper brake spool up against the force on the brake pedal. The force at the bottom of each brake spool balances that brake spool against the force at the top of the brake spool. Each brake spool acts as a pressure reducing valve to limit the pressure in the brakes proportionally to the force at the top of the respective brake spool.
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When the brake pedal is RELEASED (left view), the oil passages from the accumulators to the brakes are closed, and the passages from the brakes to the tank are opened. Oil in the rear and front service brakes flows through the respective brake spools to the tank. Spring force at the bottom of the lower brake spool moves the brake spools up.
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This illustration shows the service brake accumulators and the check valves. Accumulator (2) and check valve (4) is in the circuit for the front service brakes. Accumulator (1) and check valve (6) is in the circuit for the rear service brakes. The accumulators are piston type that is charged with dry nitrogen. The charge pressure for the accumulators at 160 °C (70 °F) is 5520 ± 280 kPa (800 ± 40 psi). Also, hose (5) is the supply line that is feeding the two accumulators. The hose is installed between the brake pump (not shown) and the divider block (5).
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This illustration shows the location of the brake pump (4) and the check valve (9) on the rear pump drive (6). The brake pump is a pressure compensated piston pump that is adjusted to supply 16000 ± 345 kPa (2300 ± 50 psi) pressure. The check valve has a cracking pressure of 448 ± 55 kPa (65 ± 8 psi). Also shown is the steering and brake hydraulic tank (1) and brake cooling tank (5). Installed on the steering and brake hydraulic tank are the temperature sensor (3) and the liquid level switch (2) (the liquid level switch is located on the opposite side of the tank). Temperature sensor for the steering and brake hydraulic oil (3) reports to J2-54 on the VIMS module. Liquid level switch (2) for the oil in the steering and brake hydraulic tank reports to the VIMS module. Also shown are the steering and brake oil cooling pump (8) and the hose (7) that is connected to the dividing block for the brake accumulators (not shown).
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Brake Pump
Shown in this illustration are the main components of the brake pump. The components are: - Pump control valve - Control piston - Spring - Swashplate - Piston assembly - Barrel - Drive shaft When pressure in the brake system is less than 16000 ± 345 kPa (2300 ± 50 psi), the spring keeps the swashplate at maximum angle. The pump piston stroke is longest and pump displacement is maximum. A small amount of pressure oil from the outlet passage flows to the pressure compensator. A spool in the pressure compensator blocks the flow of oil to the control
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This illustration shows the main components and the operation of the pump control valve. The components are: - Adjustment bolt - Locknut - Spring - Pressure compensator pool The left illustration shows the operation of the pressure compensator valve when the brake system pressure is less than 16000 ± 345 kPa (2300 ± 50 psi). Pump output oil flows around the right land of the pressure compensator spool and into the chamber at the right end of the spool. When the brake system pressure increases to 16000 ± 345 kPa (2300 ± 50 psi), the pressure of the oil in the chamber is high enough to move the spool against the spring. Movement of the spool permits oil to flow past the spool to the control piston in the pump.
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When the brake system pressure reaches 16000 ± 345 kPa (2300 ± 50 psi), oil from the pump control valve fills the chamber in the control piston. As the brake system pressure increases above 16000 ± 345 kPa (2300 ± 50 psi), the oil pressure from the pump control valve moves the control piston against the control spring. This movement decreases the angle of the swashplate, the stroke of the pistons, and the displacement of the pump. The amount of oil per pump revolution is decreased to the amount needed to maintain the system pressure at 16000 ± 345 kPa (2300 ± 50 psi).
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This illustration shows the brake pads and spacers being assembled into the final drive.
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Parking Brake
This illustration shows the location of the parking valve group (1) with the parking brake pressure switch (2) and the parking brake position switch (3). The parking brake valve group is located under the cab on the top of the Engine-End-Frame at the articulation hitch. The parking brake is spring applied with hydraulic pressure release. The parking brake pressure switch sends a signal to the Power Train ECM that the oil pressure is high enough to disengage the parking brake. The parking brake position switch sends a input to the Power Train ECM giving the On/Off position of the parking brake control
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The parking brake assembly (2) is located at the articulation hitch on the loader frame (1). The parking brake is spring activated and hydraulic oil pressure released through cylinders (3). The cylinders are equipped with air purge screws (4).
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The front axle (1) and the rear axle (3) are equipped with temperature sensors. The pressure sensor (2) and the pressure sensor (4) report the temperature of the respective axles to the VIMS module through a PWM signal. The VIMS module interputs the information and reports a warning if necessary to the operator panel.
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Brake Oil Cooler System
The hydraulic brake system control consists of the following components: Brake oil cooler tank (1) Brake cooler pump (2) Brake oil cooler (3) Engine-End-Frame (4) Also shown is the transmission (5).
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Brake Oil Cooler System
This illustration shows the line routing through the Non-Engine-End-Frame The brake oil cooler system in the NEEF consists of two hoses that are connected to the front axle (not shown). Hose (5) directs flow to the divider block (not shown) on the front axle. Hose (4) is the return line to the brake oil cooler tank that is located in the Engine-End-Frame. Also shown is the implement hydraulic oil tank (1) and the front pump drive (2) on the loader frame (3).
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The screens (2) for the front service brakes are mounted to the front axle housing. Each screen has a check valve (1) not shown to prevent oil from flowing in the reverse direction. The brake cooling screens are canister type screens with replaceable 500 micron elements.
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This view shows the screen (arrow) for the right rear wheel brake cooling circuit. It is mounted to the axle housing between the axle housing and the trunion. The rear brake cooling screens are also equipped with check valves (not shown) to prevent the oil from flowing in the wrong direction. The rear brake cooling screens are also canister type screens with replaceable 500 micron elements.
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This illustration shows the screen (arrow) for the rear left wheel brake cooling circuit. It is mounted to the axle housing between the axle housing and the trunion. The rear brake cooling screens are also equipped with check valves (not shown) to prevent the oil from flowing in the wrong direction.
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176
The 994F Wheel Loader can be equipped with an optional rear vision camera. The camera that is mounted on the rear of the machine gives the operator a look at what is behind the machine. The upper illustration shows the location of the rear vision camera at the rear of the EEF. The operator can view what is behind the machine through the display in the cab (shown in the lower illustration).
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Hydraulic Schematic Color Code
The table above shows the color code for hydraulic schematics and cross-sectional views that are shown in this presentation.
