Curso Cat Fan System STMG

Service Training May 2003

TECHNICAL PRESENTATION

MACHINE HYDRAULIC FAN SYSTEMS ELECTRONICALLY CONTROLLED

Fan Systems 06/01/03

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NOTES

Reference


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Reference

TABLE OF CONTENTS INTRODUCTION ........................................................................................................................5 M300C DEMAND FAN SYSTEM ..............................................................................................6 Fixed Displacement Pump ......................................................................................................6 WHEEL LOADER FAN DRIVE SYSTEMS ............................................................................14 924G/924Gz and 928G/IT28G Fan Drive System - Fixed Displacement Pump..................14 938G Series II Hydrualic Fan System - Variable Displacement Pump ................................20 950G - 980G Series On Demand Fan - Variable Displacement Pump .................................29 992G Wheel Loader Fan Drive System - Variable Displacement Pump ..............................34 OFF-HIGHWAY TRUCK HYDRAULIC FAN SYSTEMS ......................................................41 797B Off Highway Truck - Variable Displacement Pump ...................................................41 793C Sound Reduction Truck - Variable Displacement Pump/Twin Motors .......................57 COLOR CODES.........................................................................................................................79


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NOTES

Reference


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Reference

MACHINE HYDRAULIC FAN SYSTEMS ELECTRONICALLY CONTROLLED

© 2003 Caterpillar Inc.

1

INTRODUCTION To improve machine cooling system and overall machine performance, Caterpillar has developed electronically controlled hydraulic fan systems. These systems are controlled by a Electronic Control Module (ECM). The ECM will typically use the engine coolant temperature and hydraulic oil temperature to determine the required fan speed. Additional inputs may also be monitored for some machine applications. The ECM controls a a proportional solenoid that modulates the fan speed. The proportional solenoid is used to control the pump flow to the motor. This may done using bypass valves or changing the signal to the pump. This presentation provides information on representative electronically controlled hydraulic fan systems. The first systems covered use fixed displacement-type pumps. Later systems discuss the use of variable displacement pumps.


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Reference

2

M300C DEMAND FAN SYSTEM Fixed Displacement Pump The demand fan system is used to cool the engine coolant and the hydraulic oil. The drive pump (arrow) for the demand fan is mounted to the rear of the swing pump. The fan drive pump is a single-section gear pump.


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Reference

3

The demand fan motor is protected by an inline filter (arrow) on the line coming from the fan drive pump. The filter should be replaced every 2000 hours or one year.


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Reference

4

A pressure tap (arrow) is provided on the left side of the machine for checking fan drive pump pressure. This tap can be used to diagnose a failed fan drive pump.


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3

Reference

1

2

5

The one-piece radiator group consists of the radiator (1) and the oil cooler (2). The radiator and oil cooler cannot be replaced individually. The demand fan (3) is driven by the fan drive pump. Fan speed is controlled by the Machine ECM. Normal maximum fan speed is approxiamately 1300 rpm for the M316C, M318C and M322C. The normal fan speed for the M313C and M315C is approximately 1600 rpm.


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Reference

DEMAND FAN DRIVE SYSTEM BACK PRESSURE VALVE

MAIN CONTROL VALVE GROUP COOLING FAN SOLENOID VALVE

RADIATOR AND HYDRAULIC OIL COOLER GROUP

MOTOR

FAN DRIVE PUMP

FLOW CONTROL VALVE

6

The fan drive pump directs oil to the fan motor, the flow control valve, and the cooling fan solenoid valve. The fan pump and the fan motor have the same displacement. If full fan drive pump flow were directed through the motor, the fan would turn at engine speed. The flow control valve and cooling fan solenoid valve is used to reduce the fan speed. Oil flowing through the solenoid valve controls the amount of oil that is bypassed around the motor through the flow control valve. The cooling fan solenoid valve is a proportional solenoid valve that is controlled by the Machine ECM. Fan speed decreases as the current to the solenoid increases because the amount of oil bypassing the fan motor increases as the current increases. The solenoid valve allows the greatest amount of oil to bypass when the hydraulic oil temperature is less than 60°C (140°F ) or the engine coolant temperature is less than 80°C (176°F). In the case of an electrical failure, the flow control valve acts as a relief valve to control maximum fan speed.


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Reference

M300C HYDRAULIC DEMAND FAN MACHINE ECM CAN J1939 FAN SOLENOID ENGINE ECM

HYDRAULIC OIL TEMPERATURE SENSOR

ENGINE COOLANT TEMPERATURE SENSOR

7 The fan is controlled by a proportional solenoid that modulates the fan speed. The Machine ECM uses the engine coolant temperature and hydraulic oil temperature to determine the fan speed. The Machine ECM has two fan speed maps. One determines the fans speed for the current engine coolant temperature and the other determines the fan speed for the current hydraulic oil temperature. The Machine ECM compares the two fan speed values and commands the demand fan to the higher of the two speeds. The fan speed output is not changed unless the new speed demand is more than 2% different than the currently-commanded speed. This prevents speed fluctuation. The fan speed will be set to maximum if the hydraulic oil temperature sensor is faulted or the coolant temperature is unavailable or unknown. The fan speed is set to maximum (minimum current) if the limp home switch is activated.


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Reference

CURRENT TO FAN SOLENOID COOLANT AND OIL TEMP INCREASE

CURRENT DECREASES

SOLENOID VALVE BYPASSES LESS OIL

FAN SPEED INCREASES

8

The fan speed decreases as current to the solenoid increases. The commanded current supplied to the solenoid will be determined based on the calculated total fan speed demand and engine speed. The Machine ECM will continue to send the solenoid's last valid current setting for two seconds after the key switch is placed in the OFF position.


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Reference

M300C DEMAND FAN SELF-CALIBRATION CONDITION

Fan speed is too fast.

CONDITION Fan speed is too slow.

EFFECT Coolant and oil temperature decrease.

EFFECT Coolant and oil temperature increase.

RESULT Machine ECM decreases fan speed.

RESULT Machine ECM increases fan speed.

9 The demand fan system on M300C Excavators does not require calibration. The coolant and oil temperatures will decrease fi the fan speed is too fast. As a result of the decreasing temperature, the Machine ECM will increase the current to the demand fan solenoid so that more oil is allowed to bypass the demand fan motor. The fan speed decreases because of the reduced availability of oil to the demand fan motor. Likewise, if the fan speed is too slow, the coolant and oil temperatures will increase. As the temperatures increase, the Machine ECM will decrease the current to the demand fan solenoid so that less oil is allowed to bypass the demand fan motor. This causes the fan speed to increase.


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Reference

3

2

1

10

WHEEL LOADER FAN DRIVE SYSTEMS 924G/924Gz and 928G/IT28G Fan Drive System - Fixed Displacement Pump Flow from the fan drive and brake pump (1) is controlled by the Machine ECM. The ECM allows flow to the fan after sensor input indicates that the brake accumulators are charged. The brake charging solenoid valve (2) and the brake system pressure sensor switch (3) work together with the Machine ECM to regulate oil flow in the brake and fan systems.


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Reference

HYDRAULIC FAN SYSTEM FAN FLOW CONTROL

COOLER

FAN MOTOR

PUMP GROUP

MAKEUP VALVE

BYPASS FILTER

FAN CONTROL SOLENOID VALVE

ENGINE COOLANT TEMPERATURE SENSOR HYDRAULIC OIL TEMPERATURE SENSOR

TRANSMISSION OIL TEMPERATURE SENSOR

MACHINE ECM

AIR INLET TEMPERATURE SENSOR

11 The Machine ECM will send the required signal to the demand fan solenoid valve in order to provide the proper fan speed for the cooling system. The Machine ECM will monitor the following parameters in order to provide the proper fan speed: - coolant temperature - hydraulic oil temperature - transmission oil temperature - air inlet temperature The solenoid valve controls the fan drive speed by controlling the flow control valve, that bypasses some of the supply oil to the fan to the cooler. The maximum fan speed is controlled by the fan control solenoid valve. Maximum fan speed occurs when the fan control solenoid valve is de-energized. Most of the pump flow is now directed through the fan motor.

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Reference

At the rated engine rpm, the fan speed is maintained at a minimum of 600 rpm. The maximum fan speed of approximately 1625 rpm is controlled by the solenoid valve in the fan circuit. The return oil from the fan motor is directed through the oil cooler and filter to the tank. Both the cooler and the filter are equipped with bypass valves. The makeup valve prevents cavitation in the fan motor. During a quick deceleration, the flow of oil to the fan motor can stop. The makeup valve will open. This allows oil to flow from the outlet side of the fan motor to the inlet side of the fan motor.


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Reference

REVERSING HYDRAULIC FAN SYSTEM FORWARD

CROSSOVER FAN MOTOR RELIEF AND MAKEUP

REVERSING SOLENOID VALVE

FLOW CONTROL PUMP GROUP

COOLER

BYPASS FILTER

REVERSE

FAN MOTOR

MAKEUP VALVE


REVERSING SOLENOID VALVE

FLOW CONTROL PUMP GROUP

MAKEUP VALVE


12 The optional reversing hydraulic fan system has a reversing solenoid controlled by the machine ECM. When the top of the reversing fan switch (not shown) is depressed, the fan reversing solenoid is energized in order to reverse the fan for 10 seconds. Supply oil from the pump is directed to the other side of the fan motor, while the other side of the fan motor is open to the cooler circuit. When the bottom of the reversing fan switch is depressed, the fan reversing solenoid is energized in order to reverse the fan for 10 seconds. This will repeat every 30 minutes until the reversing fan switch is returned to the center position. The crossover relief valve prevents cavitation in the fan motor. During a quick deceleration, the flow of oil to fan motor can stop. The crossover relief valve will open. This allows oil to flow from the outlet side of the fan motor to the inlet side of the fan motor.


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Reference

2

1

13

The reversing fan allows debris to be cleared from the grills without leaving the cab. The reversing demand cooling fan has three modes of operation. The operator selects the fan mode using the reversing fan switch and the Machine ECM controls the fan motor (1) from this input. The demand flow solenoid valve (2) and a flow control valve use the information from the Machine ECM to direct flow to the motor or divert flow away from the motor to control the fan speed. Minimum and maximum fan speeds can be calibrated through ET.


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Reference

2

14

The reversing fan function switch has three positions. The switch locks in the middle and bottom positions but the top position is momentary. The fan will function as a single direction variable speed fan when the switch is in the center position. When the top of the switch (2) is depressed, the fan will reverse for 10 seconds. If the bottom of the switch is pressed, the fan will reverse for 10 seconds and repeat this every 20 minutes until the switch is returned to the center position.


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Reference

HYDRAULIC FAN SYSTEM

SOLENOID VALVE

FAN MOTOR

OIL BYPASS COOLER VALVE


FAN

POWER TRAIN ECM FLOW CONTROL SPOOL PRESSURE PRESSURE AND FLOW CUTOFF COMPENSATOR VALVE SPOOL

CAT DATA LINK

ENGINE ECM FAN ACTUATOR PISTON PUMP


COOLANT TEMPERATURE SENSOR


18 938G Series II Hydrualic Fan System - Variable Displacement Pump The cooling system is a hydraulically driven fan that is controlled by a demand fan control system. The demand fan system controls the fan speed in order to provide the required amount of cooling air. This will maintain key system temperatures. During heavy machine usage or high ambient temperatures, the demand fan system will increase the fan speed to the maximum. During light usage and lower ambient temperature, the demand fan system will maintain a lower fan speed. This can result in lower horsepower requirements. The demand fan controls the speed of the hydraulic fan through the use of a piston pump that can vary the volume of hydraulic oil to the fan motor. The volume of oil that is produced by the hydraulic fan pump is controlled by the pressure and flow compensator valve.

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Reference

The pressure and flow compensator valve which controls the pump flow is mounted below hydraulic fan pump. The pressure and flow compensator valve contains a flow control spool and a pressure cutoff spool. The flow control spool will control the minimum fan speed and up to the maximum fan speed. The pressure cutoff spool will control the maximum fan speed. The pressure cutoff spool also controls the maximum pressure of the hydraulic fan pump. The settings of both spools for the pressure and flow control valve can be adjusted. The Engine ECM receives inputs from four sensors that are installed on the machine. The four sensors monitor the engine air inlet temperature, the coolant temperature, the hydraulic oil temperature, and the transmission oil. The Engine ECM interprets the data from the four sensors. The logic for the demand fan is compared against a set of target temperatures. If one temperature exceeds the target temperature, the Engine ECM will send a signal to the fan solenoid valve in order to increase the fan speed. If one of the temperatures is less than the target temperature, the Engine ECM will send a signal to the fan solenoid valve in order to decrease the fan speed. If all of the temperatures are below the target temperatures, the Engine ECM will send a signal to the fan solenoid valve in order to decrease the fan speed which will result in minimum fan speed. The solenoid valve sends a signal to the pressure and flow compensator valve on the piston pump. The piston pump will adjust the output for the flow demand.


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Reference

HYDRAULIC FAN SYSTEM MINIMUM FAN SPEED

BYPASS VALVE

SOLENOID VALVE

FAN MOTOR OIL COOLER

FAN


PRESSURE AND FLOW COMPENSATOR VALVE

POWER TRAIN ECM

FLOW CONTROL SPOOL CAT DATA LINK

PRESSURE CUTOFF SPOOL

FAN PUMP

ENGINE ECM ACTUATOR PISTON




19 When the engine is started and all temperatures are very low, the Engine ECM sends the maximum current to the solenoid valve. Signal oil to the flow control spool is open to the hydraulic tank through the solenoid valve. Supply pressure from the pump, shifts the flow control spool to the right. Supply oil is directed to the actuator piston to destroke the pump. The pump swashplate is at minimum angle. The pump produces minimum flow resulting in minimum fan speed.


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Reference

HYDRAULIC FAN SYSTEM MAXIMUM FAN SPEED

BYPASS VALVE

SOLENOID VALVE

FAN MOTOR OIL COOLER

FAN


PRESSURE AND FLOW COMPENSATOR VALVE

POWER TRAIN ECM

FLOW CONTROL SPOOL CAT DATA LINK


FAN PUMP

ENGINE ECM ACTUATOR PISTON




20 If the temperature at one of the sensors increases, the Engine ECM sends a proportional reduction in current to the solenoid valve. The solenoid valve will start to shift to allow some of the supply pressure to flow to the flow control spool to act as a pressure signal. The flow control spool starts to shift to the left. A proportional amount of oil that is behind the actuator piston will flow back to the hydraulic tank. As the pressure behind the actuator piston begins to decrease, the actuator bias spring will increase the swashplate angle. The pump output flow will increase resulting in the fan speed to increase. As the machine temperatures continue to increase the ECM will continue to reduce the current sent to the solenoid valve. The solenoid will continue to shift to increase the hydraulic signal to the flow control spool. The control spool will shift more to the left to continue to drain oil in the actuator piston to the tank. The pump swashplate angle moves more toward maximum swashplate angle and the pump flow continues to increase, resulting in higher fan speeds.

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Reference

If the current from the ECM to the solenoid is at the minimum, the solenoid valve will send the maximum hydraulic pressure signal to the flow control spool to shift it fully to the left which will drain oil from the actuator piston to tank. Pump output flow will increase due the to pump swashplate moving toward maximum angle. As the rpm of the hydraulic fan motor approaches the maximum speed, the pressure of the pump discharge oil also increases. The increase in pressure of the pump discharge oil will work on the left of both the flow compensator spool and the pressure cutoff spool. The flow compensator will stay to the left. The cutoff spool will start to shift to the right to allow some of the pump supply oil to flow to the actuator piston to slightly destroke the pump to reduce pump flow. Once the desired fan speed is reached, the pressure cutoff spool will meter the supply oil to and from the actuator piston to pump to maintain or limit the maximum fan speed. The adjustment of the cutoff spool can be adjusted for any maximum flow. The cutoff spool is similar to a relief valve. If for some reason the motor would lock up, the cutoff spool would destroke the pump to minimum angle to produce minimum flow.


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Reference

FAN PUMP ENGINE OFF

MARGIN SPRING

ACTUATOR PISTON

FROM PUMP

BIAS SPRING

SOLENOID VALVE ORIFICE ORIFICES

SHAFT

PISTON AND SWASHPLATE BARREL ASSEMBLY

TO FAN MOTOR

ENGINE ECM FLOW CONTROL SPOOL


21 The hydraulic fan pump is a variable displacement piston pump. The axial piston type pump is used to supply oil flow to the hydraulic fan motor. The movement of the piston assembly in the hydraulic fan pump draws oil from the hydraulic tank. The oil is pressurized in the hydraulic fan pump. The high pressure oil flows from the hydraulic fan pump to the hydraulic fan motor in order to rotate the fan. Oil from the hydraulic tank flows into the pump head through the pump inlet. The oil then flows from the pump inlet through inlet passages in the valve plate. When the drive shaft rotates, the openings of the cylinder barrel move toward the inlet passages of the valve plate. The angle of the swashplate determines the amount of oil that is pushed out of each cylinder barrel. The swashplate can be at any angle between the minimum angle and the maximum angle. Piston assemblies move in and out of the cylinder barrel. The in and out movement of the piston assemblies allows oil to be drawn in to and pushed out of the cylinder barrel. The swashplate angle is controlled by the actuator piston. The movement of the actuator piston is regulated by oil pressure from pressure and flow compensator valve. When the engine is off, the bias spring holds the swashplate at the maximum angle.


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Reference

FAN PUMP

MINIMUM FAN SPEED

BIAS SPRING

PASSAGE

MARGIN SPRING

ACTUATOR PISTON

FROM PUMP SOLENOID VALVE

ORIFICE ORIFICES

TO FAN MOTOR

SWASHPLATE

ENGINE ECM FLOW CONTROL SPOOL PRESSURE CUTOFF SPOOL

22 When the engine is started and all temperatures are very low, the Engine ECM sends the maximum current to the solenoid valve. Signal oil to the flow control spool is open to the hydraulic tank through the solenoid valve. Supply pressure from the pump shifts the flow control spool up. Supply oil is directed to the actuator piston to destroke the pump. The pump swashplate is at reduced angle. The pump produces low flow resulting in minimum fan speed.


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Reference

FAN PUMP

CONSTANT SPEED MARGIN SPRING

FROM PUMP

ACTUATOR PISTON BIAS SPRING

SOLENOID VALVE

ORIFICE

ORIFICES

ENGINE ECM TO FAN MOTOR

SWASHPLATE

FLOW CONTROL SPOOL


23 As the pump output flow increases (upstroke condition) or decreases (destroke condition) to meet the system demand, the forces acting above and below the margin spool will equalize and the margin spool will move to a metering position. The system stabilizes. The swashplate is held at a relatively constant angle to maintain the required flow and fan speed.


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Reference

FAN PUMP

MAXIMUM SPEED MARGIN SPRING

ACTUATOR PISTON

FROM PUMP SOLENOID VALVE

BIAS SPRING ORIFICE ORIFICES

ENGINE ECM TO FAN MOTOR

SWASHPLATE

FLOW CONTROL SPOOL PRESSURE CUTOFF SPOOL

24 If the current from the Engine ECM to the solenoid is at the minimum, the solenoid valve will send the maximum hydraulic pressure signal to the flow control spool to shift it fully down which will drain oil from the actuator piston to tank. Pump output flow will increase due to the pump swashplate moving toward maximum angle. As the rpm of the hydraulic fan motor approaches the maximum speed, the pressure of the pump supply oil also increases. The increase in pressure of the pump supply oil will work on the bottom of the flow control spool and pressure cutoff spool. The flow control spool will stay down due to the signal oil from the solenoid valve and the margin spring. The cutoff spool will start to shift up to allow some of the pump supply oil to flow to the actuator piston to slightly destroke the pump to reduce pump flow. Once the desired fan speed is reached, the pressure cutoff spool will meter the supply oil to and from the actuator piston to maintain or limit the maximum fan speed. The adjustment of the cutoff spool can be adjusted for any maximum flow.


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Reference

1

DEMAND FAN

4

3 2

2

3

2

1

1 4

3

4

15

950G - 980G Series II On Demand Fan - Variable Displacement Pump The 950G -908G Series II Electronically controlled fan system is virtually the same as the 938G/IT38G system. The above views show the on demand fan components on the 3126B engine in the 950G/962G Series II (top right view), 3176C/3196 engine in the 966G/972G Series II (lower left view), and the 3406E engine in the 980G Series II (lower right view). The 950G-980G Series II Wheel Loaders use an electronically controlled fan pump (1), which provides oil flow to the cooling fan motor (not shown). The Engine ECM controls the fan speed based on temperature sensor inputs from the engine coolant, inlet air manifold, transmission oil and the hydraulic oil. The fan pump compensator valve (2) senses pump supply pressure through the signal line (3). When the solenoid valve (4) is ENERGIZED by the Engine ECM, signal pressure is directed to the tank causing the pump to DESTROKE. In this position, flow from the pump to the fan motor is reduced which results in slower fan speed.


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Reference

FAN DRIVE SYSTEM

LOW PRESSURE STANDBY

OIL COOLER

FAN MOTOR FAN

FROM BRAKE CHARGING VALVE

SOLENOID VALVE PUMP COMPENSATOR VALVE

FLOW CONTROL SPOOL PRESSURE CUTOFF SPOOL

FAN PUMP

MIN ANGLE

16 This schematic shows the fan drive hydraulic system. The solenoid valve controls the signal oil to the flow control spool for the fan pump. Varying the current to the proportional solenoid valve changes the hydraulic signal to vary the oil flow to the fan motor to increase or decrease the fan speeds. The solenoid valve is essentially a variable orifice used to control the rate of flow to the flow control valve. When the solenoid valve is fully ENERGIZED (as shown), signal pressure to the flow control valve is diverted to the tank. The flow control spool moves to the right. Supply oil flows through the pump control spools to the pump actuator to destroke the pump to achieve LOW PRESSURE STANDBY. This pressure is controlled by the flow control spool spring. The fan motor rotates at minimum rpm. When the solenoid is DE-ENERGIZED, more flow through the orifice in the solenoid valve is directed to the flow control spool causing the fan pump to UPSTROKE to increase the fan speed.

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Reference

When system pressure increases to the setting of the pressure cutoff spool the spool shifts to the right to destroke the pump in order to maintain the maximum fan speed. Maximum fan speed is based on the spring adjustment of the pressure cutoff spool. In most conditions the system operates somewhere between these two extremes. The makeup valve in the fan motor is used to prevent the motor from cavitating when, for example, the engine is shut off or a rapid deceleration of the engine.


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ENGINE ECM

ON DEMAND FAN CIRCUIT MAIN DISPLAY MODULE 10

GN 18 GY 18

A B C

18

COOLANT TEMPERATURE SIGNAL

32

CAT DATA LINK

24 +8V SENSOR SUPPLY

J2

ANALOG TEMPERATURE SENSOR COMMON

INTAKE AIR TEMPERATURE

HYD TEMP SENSOR

Reference

BU 18 PK 18

35

3

+V GROUND SIGNAL

TRANSMISSION LUBE OIL TEMP SENSOR

26


VARIABLE SPEED FAN CONTROL

43

VARIABLE SPEED FAN CONTROL

51

OR 18 BK 18 WH 18

SIGNAL GROUND

ENGINE COOLANT TEMPERATURE SENSOR BU 18 PK 18

1 2

SIGNAL GROUND

INTAKE MANIFOLD AIR TEMPERATURE SENSOR

J1 ANALOG SENSOR RETURN

1 2

YL 18 PU 18

1 2

SIGNAL GROUND

TRANSMISSION LUBRICATION OIL TEMPERATURE SENSOR

YL 18 BR 18

1 2 VARIABLE SPEED FAN SOLENOID

16 The Engine ECM receives input signals from the engine coolant temperature sensor, intake manifold air temperature sensor and transmission lubrication oil temperature sensor. Hydraulic oil temperature sensor signals are sent to the Caterpillar Monitoring System main display module and transmitted over the Cat Data Link to the Engine ECM. The Engine ECM processes the input signals and sends corresponding output signals to the variable speed fan solenoid valve. NOTE: The variable speed fan control feature can be enabled or disabled using the ET Service Tool. The variable speed fan default setting is enabled.


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Reference

17 Using the engine calibration pull down menu in Electronic Technician (ET)the "Engine Fan Control" can be turned ON or OFF. The "Engine Reversing Fan Feature" may be ENABLED or DISABLED.


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Reference

FAN DRIVE SYSTEM ENGINE OFF

OIL COOLER BYPASS VALVE

IMPLEMENT HYDRAULIC OIL COOLER

COOLING FAN

BYPASS SWITCH

FAN MOTOR

MAKEUP VALVE ELECTRO-HYDRAULIC PROPORTIONAL VALVE

PRESSURE SWITCH

CASE DRAIN FILTERS FAN DRIVE PUMP

FROM IMPLEMENT CASE DRAIN FILTER

COMPENSATOR VALVE

BYPASS SWITCH

25 992G Wheel Loader Fan Drive System - Variable Displacement Pump Shown is a schematic of the fan drive system. The fan drive system is controlled by the Engine ECM. Components of the fan drive system are: Hydraulic tank: Reservoir for the hydraulic oil supply. Fan drive pump: Pulls oil from the tank and supplies oil to the fan drive motor. Electro-hydraulic proportional valve: Controls the signal to the pump. Compensator valve: Controls fan speed by controlling pump flow. Fan motor: Works with the fan drive pump to turn the fan. Makeup valve: Prevents cavitation of the fan drive motor. Cooling fan: Circulates air through the radiator, the hydraulic system oil cooler, the steering and brake systems oil cooler, the brake and axle oil cooler, and the air conditioner condenser. Implement hydraulic oil cooler: Cools the oil used in the fan drive and hydraulic systems. Oil cooler bypass valve: Allows cold oil to bypass the cooler, normally at engine start-up.


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13

3

1

Reference

4 5

9

6 8

10 11

2

7 12

26

Fan Drive System Components The fan drive pump (1) is a variable displacement piston pump. The pump is mounted to the right front of the pump drive housing (2) opposite the variable displacement implement pump (not shown). Other components of the fan drive pump are the outlet tube (3), the signal pressure outlet (4), the electro-hydraulic proportional valve (5), the proportional valve solenoid (6), the proportional valve drain tube (7), the proportional valve signal hose (8), the margin spool adjustment (9), the compensator valve (10), the pressure compensator valve adjustment (11), the signal pressure tap (12), and the system pressure tap (13).


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Reference

27

The case drain filter for the fan drive pump (arrow) is located in the pump bay, above the fan drive pump. The case drain filter removes contaminants from the case drain oil before the oil enters the hydraulic tank.


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Reference

2 1 3

4

5

28

The fan drive motor (1) is located at the rear of the machine in front of the engine radiator assembly. Also shown are the motor intake hose (2), the motor outlet hose (3), the case drain hose (4), and the case drain filter (5).


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Reference

FAN DRIVE SYSTEM

SOLENOID DE-ENERGIZED / MAX SPEED



COOLING FAN

BYPASS SWITCH

FAN MOTOR


PRESSURE SWITCH



COMPENSATOR VALVE

BYPASS SWITCH

29 When the engine is running, the fan drive pump pulls oil from the implement hydraulic tank and sends oil flow to the fan motor. The fan motor turns the cooling fan. Oil from the fan motor flows through the implement hydraulic cooler to the implement hydraulic tank. The cooling fan sends air flow through the engine radiator, the implement hydraulic cooler, the steering and brake oil cooler, the front and rear axle coolers, and the air conditioner condenser. The fan drive pump also sends oil flow through the screen to the electro-hydraulic proportional valve. The electro-hydraulic proportional valve controls the signal oil to the pump compensator valve. When the Engine ECM de-energizes the electro-hydraulic proportional valve (as shown), the proportional valve closes the passage for signal oil flow to the tank. The signal oil flows through the two orifices to the pump compensator valve. The signal oil causes the compensator valve to upstroke the pump.


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Reference

FAN DRIVE SYSTEM

SOLENOID ENERGIZED / REDUCED SPEED



COOLING FAN

BYPASS SWITCH

FAN MOTOR


PRESSURE SWITCH



COMPENSATOR VALVE

BYPASS SWITCH

30 The Engine ECM receives input signals from the engine coolant temperature sensor, the steering hydraulic tank temperature sensor, the implement hydraulic tank temperature sensor, and the air conditioner on/off switch. The Engine ECM analyzes the signals and energizes the electrohydraulic proportional valve when needed. When the Engine ECM energizes the electro-hydraulic proportional valve, the proportional valve opens the passage for signal oil flow to the tank. The size of the opening is proportional to the signal from the Engine ECM. Signal oil flows through the open passage to the tank. This condition decreases the signal pressure at the compensator valve and destrokes the pump. Destroking the pump decreases pump flow and decreases the fan speed. Decreasing the pump flow also decreases the horsepower needed to turn the pump. When the engine is operating below 88°C (190°F), the fan will operate at a minimum speed of 375 ± 50 rpm. Above 98°C (208°F), the fan will operate at a maximum speed of 885 rpm. When the air conditioner is ON, the fan will operate at a minimum speed of 621 rpm. If an electrical system failure occurs, the fan goes to maximum (100%) speed.


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Reference

FAN DRIVE SYSTEM

RAPID ENGINE DECELERATION



COOLING FAN

BYPASS SWITCH

FAN MOTOR


PRESSURE SWITCH

CASE DRAIN FILTER FAN DRIVE PUMP


COMPENSATOR VALVE

BYPASS SWITCH

31 In this illustration, the fan motor is being driven by the cooling fan. During normal operation, oil pressure at the fan motor inlet is higher than oil pressure at the fan motor outlet. The higher inlet pressure seats the makeup valve. When the engine is decelerated rapidly from HIGH IDLE, the inertia of the fan keeps the fan drive motor turning faster than the fan drive pump can supply oil. The oil pressure at the fan motor inlet becomes lower than the oil pressure at the fan motor outlet. The higher outlet pressure opens the makeup valve and allows oil from the motor outlet to flow to the inlet. The combination of oil flow through the makeup valve and the pump oil flow prevents cavitation of the fan motor. When pump output matches the fan speed, the motor inlet oil pressure increases above the motor outlet oil pressure. The higher inlet pressure closes the makeup valve.


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Reference

32

OFF-HIGHWAY TRUCK HYDRAULIC FAN SYSTEMS 797B Off Highway Truck - Variable Displacement Pump The fan is hydraulically driven. A variable displacement piston-type pump provides oil flow to the fixed displacement motor shown in the center of the fan. The hydraulic motor turns the fan blades. Fan speed is controlled by the Brake/Cooling ECM. Fan speed varies depending on many inputs but the maximum fan speed will be: - 475 rpm--when not braking or retarding (going uphill) - 525 rpm--when braking or retarding (going down hill) The minimum fan speed will be 0 rpm; generally when all temperatures are cold.the makeup valve and the pump oil flow prevents cavitation of the fan motor. When pump output matches the fan speed, the motor inlet oil pressure increases above the motor outlet oil pressure. The higher inlet pressure closes the makeup valve.

Î


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Reference

The inputs that determine fan speed are: - Jacket water coolant temperature - Aftercooler coolant temperature - Transmission lube temperature - Brake oil temperature - Torque converter outlet temperature - Brake status - Ground speed - Hoist system status output When the hoist system is in the RAISE or LOWER position, the desired fan speed is reduced to 200 rpm to reduce the load on the pump drive.


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Reference

FAN SPEED CONTROL LIMITS (RPM) ENGINE SPEED

NON-RETARDING FAN SPEED LIMIT

RETARDING FAN SPEED LIMIT

1250 OR LESS 1300 1450 1500 1600 1700 1750 OR MORE

339 353 394 407 434 461 475

525 525 525 525 525 525 525

33 Shown above are the fan speed limits based on the temperature sensor inputs, ground speed, and retarding/braking input.


- 44 -

Reference

ENGINE FAN CONTROL--NON-RETARDING OR RETARDING BELOW 4 MPH AFTERCOOLER TEMPERATURE

JACKET WATER TRANS LUBE TEMPERATURE TEMPERATURE

° C (° F)

TC OUT TEMPERATURE

BRAKE TEMPERATURE

FAN CONTROL

PRIORITY 1

2

3

4

5

< 65 (150)

< 88 (190)

< 88 (190)

< 88 (190)

< 102 (215)

OFF

< 65 (150)

< 99 (210) > 88 (190)

< 96 (205) > 88 (190)

< 102 (215) > 88 (190)

< 107 (225) > 102 (215)

MODULATE BY PRIORITY

> 65 (150)

> 99 (210)

> 96 (205)

> 102 (215)

> 107 (225)

LIMIT CHART

NOTE: DURING RETARDING/BRAKING 4 MPH AND ABOVE, FAN SPEED SET TO LIMIT CHART

34 As shown in the chart above for fan speed control temperature limits, if the sensor temperatures are all below the lower limits, the fan control is turned off and fan speed could be as low as 0 rpm. If the temperatures are between the sensor lower and upper limits, fan speed will modulate by sensor priority to a fan speed curve that has been pre-set for each sensor. If any of the sensor temperatures are above the upper limits, fan speed will be set to the limits shown in the top chart. After being programmed (flashed), the Brake/Cooling ECM needs to know what fan arrangement is installed on the machine. Because of the changes to the fan iron, there are three different configurations that the Brake/Cooling ECM has to support. They are listed below: - 2438.4 mm ( 96 inch) fan with planetary drive - 2692.4 mm (106 inch) fan with planetary drive - 2692.4 mm (106 inch) fan with motor only You must flash the software on the machine whenever the fan iron is updated (e.g. change from 96 to 106 inch fan, change fan control solenoid, . . .). In addition to these cases, if you replace the ECM, or flash an earlier version of software on the machine (e.g. 156-1394-10 or earlier), you will have to re-calibrate the machine.


- 45 -

Reference

797B FAN DRIVE HYDRAULIC SYSTEM FAN DRIVE MOTOR (1)

PUMP DRIVE (3) FAN MAKEUP VALVE (2)

FAN DRIVE PUMP (4) STEERING SOLENOID AND RELIEF VALVE (6) PRESSURE REDUCING VALVE (5)

OIL FILTER (STEERING AND FAN DRIVE) (7)

OIL COOLER STEERING AND FAN DRIVE (8)

BRAKE COOLING DRIVE PUMP

OIL FILTER (CASE DRAIN) (9)

HYDRAULIC TANK (10)

35 Shown is the 797B fan drive hydraulic system. Oil flows from the fan drive pump through a makeup valve to the fan drive motor. Oil flows from the motor through the makeup valve and the steering/fan drive oil filters and cooler and returns to the steering/fan drive tank. If supply oil to the fan stops suddenly, the fan and motor may continue to rotate because of the mass of the fan. The makeup valve allows oil to flow from the return side of the circuit to the supply side to prevent a vacuum in the supply lines. The fan drive motor is a fixed displacement motor, therefore, the fan speed is determined by the amount of flow from the fan drive pump. The fan drive pump is a variable displacement pistontype pump that is controlled by the Brake/Cooling ECM. Case drain oil flows from the fan drive motor and pump through a case drain oil filter to the steering/fan drive tank.

Î


- 46 -

Reference

Steering supply oil flows from the steering solenoid and relief valve manifold to a pressure reducing valve. The pressure reducing valve reduces the steering pressure to a signal pressure of 6200 kPa (900 psi). Excess steering oil flows from the reducing valve back through the steering solenoid and relief valve manifold to tank. The reduced signal oil flows to the to the fan drive pump and the brake cooling drive pump. The fan drive pump and the brake cooling drive pump use the signal oil pressure to destroke the pumps to minimum flow at start-up and during cold temperatures.


- 47 -

Reference

1 2

36

Shown is closer view of the 797B fan drive motor. Oil flows from the fan drive pump through a makeup valve to the fan drive motor. Oil flows from the motor through the makeup valve and the steering/fan drive oil filter and returns to the steering/fan drive tank. The fan drive motor is a fixed displacement motor, therefore, the fan speed is determined by the amount of flow from the fan drive pump. The fan drive pump is a variable displacement pistontype pump that is controlled by the Brake/Cooling ECM. Case drain oil flows from the fan drive motor through hose (1) and a case drain filter to the steering/fan drive tank. The fan speed sensor (2) provides an input signal to the Brake/Cooling ECM. The Brake/Cooling ECM uses this input to maintain the fan speed between 0 and 525 rpm.


- 48 -

SPEED SENSOR

Reference

797B FAN MOTOR

PISTON OUTPUT SHAFT

BARREL

RETURN PORT

CASE DRAIN PORT PORT PLATE

SUPPLY PORT

37 Shown is a sectional view of the fixed displacement, bent-axis fan drive motor. The motor is rotated by flow from the fan drive pump. Oil flows through the supply port and the port plate and pushes the pistons out of the barrel. The pistons force the barrel and the output shaft to rotate. The output shaft turns the planetary drive group and the fan. As the barrel rotates and the pistons return, oil flows from the pistons through the port plate, the return port and a makeup valve to the steering/fan drive tank. Oil that leaks past the pistons into the motor housing provides lubrication for the rotating motor components. This oil leakage is referred to as case drain oil. Case drain oil flows through the case drain port and a case drain oil filter to the steering/fan drive tank. The fan drive motor speed sensor provides an input signal to the Brake/Cooling ECM. The Brake/Cooling ECM uses this input to maintain the fan speed between 0 and 525 rpm.


- 49 -

Reference

6 3

8

2

1

7

5

4

38

The fan drive pump (1) is part of a double piston pump group. The steering pump (2) is the other part of the pump group. The pump group is mounted on the front of the pump drive. The pump drive is located on the inside of the right frame rail near the torque converter. A charging pump is located between the steering pump and the fan drive pump and is used to keep the pumps supplied with oil. The fan drive pump is a variable displacement piston-type pump. The Brake/Cooling ECM controls the flow of oil from the fan drive pump by energizing the displacement solenoid (3). The Brake/Cooling ECM analyzes the temperatures, brake status, and ground speed inputs and sends between 0 and 680 milliamps to the solenoid. The displacement solenoid moves a spool in the pressure and flow compensator valve (4) to control the flow of pump output pressure to the minimum angle actuator piston. The minimum angle actuator piston moves the swashplate to the minimum flow position. The current adjustment screw (5) controls the minimum current required to start destroking the pump. Do not adjust the current adjustment screw in chassis. This adjustment should only be done on a hydraulic test stand.

Î


- 50 -

Reference

The high pressure cut-off valve (6) controls the maximum pressure in the fan drive system. The minimum angle stop screw (7) is located near the pressure and flow compensator valve. The maximum angle stop screw is located on the other side of the pump. Do not adjust the minimum or maximum angle stop screws in chassis. This adjustment should only be done on a hydraulic test stand. A reducing valve provides a signal pressure through the hose (8) and a shuttle valve to the fan drive pump and the brake cooling drive pump.


- 51 -

FAN DRIVE PUMP

STEERING PUMP PRESSURE AND FLOW COMPENSATOR

MINIMUM ANGLE STOP SWASHPLATE

Reference

MAXIMUM ANGLE ACTUATOR PISTON

PISTON

DRIVE SHAFT

MAXIMUM ANGLE STOP

ROTARY GROUP

CHARGE PUMP IMPELLER

MINIMUM ANGLE ACTUATOR PISTON

39 Shown is a sectional view of the 797B fan drive pump. The fan drive pump is part of a double piston pump group. The steering pump is the other part of the pump group. The pumps are variable displacement piston-type pumps. Oil flows from the fan drive pump through a makeup valve to the fan motor. Fan speed is controlled by controlling the flow from the pump to the fan motor. Oil from the steering/fan drive tank enters the pump group in the port below the charge pump impeller. The charge pump keeps the two pumps full of oil. The large spring around the maximum angle actuator piston holds the swashplate at maximum angle. Pump output pressure is always present on the right side of the fan drive pump maximum angle actuator piston and also helps to hold the swashplate at maximum angle. When the swashplate is at maximum angle, pump output is at maximum flow and fan speed is at maximum. This is the position of the pump when the displacement solenoid receives 0 milliamps from the Brake/Cooling ECM.

Î


- 52 -

Reference

When the displacement solenoid is receiving between 0 and 680 milliamps from the Brake/Cooling ECM, the displacement solenoid moves a spool in the pressure and flow compensator valve. The spool allows pump output pressure to flow to the minimum angle actuator piston. At 0 milliamps the pump is at maximum displacement and the fan speed is at maximum. At 680 milliamps the pump is at minimum displacement and the fan speed is at minimum. The coil resistance through the solenoid is approximately 24 ohms. At zero pressure, the actuator piston spring will hold the pump at maximum angle. The fan drive pump needs the signal pressure so that the displacement solenoid can position the fan drive pump at minimum angle at start-up and during cold temperatures. Without the signal pressure the pump could not stay at minimum angle to provide zero fan speed at start-up and during cold temperatures. The minimum angle actuator piston has a larger diameter than the maximum angle actuator piston. The minimum angle actuator piston moves the swashplate toward the minimum flow position. The swashplate angle, pump flow, and fan speed will modulate with the amount of current at the displacement solenoid. When the swashplate is at minimum angle, pump output is at minimum flow and fan speed is at minimum. This is the position of the pump when the displacement solenoid receives 680 milliamps from the Brake/Cooling ECM. Before the swashplate contacts the minimum angle stop, the minimum angle actuator piston will open a small drain port to tank and stop the movement of the swashplate. Draining the minimum angle actuator piston oil will prevent the swashplate from contacting the minimum angle stop repeatedly which can be noisy and may cause damage to the pump. Oil that leaks past the pistons into the pump housing provides lubrication for the rotating components. This oil leakage is referred to as case drain oil. Case drain oil flows through the case drain port and a case drain oil filter to the steering/fan drive tank.


PUMP SUPPLY

- 53 -

TO MINIMUM ANGLE ACTUATOR PISTON

DRAIN

Reference

STEERING PUMP CONTROL

HIGH PRESSURE CUT-OFF

FAN DRIVE PUMP CONTROL

TO STEERING SOLENOID AND BACK-UP RELIEF VALVE

TO FAN DRIVE MOTOR

FROM REDUCING VALVE

HIGH PRESSURE CUT-OFF DISPLACEMENT SOLENOID AND VALVE MAXIMUM ANGLE ACTUATOR PISTON

CURRENT ADJUSTMENT

DRAIN


PUMP SUPPLY


CASE DRAIN

DISPLACEMENT SOLENOID AND VALVE

CHARGE PUMP

40 Shown is the pressure and flow compensator valve for the 797B fan drive pump. The charge pump pulls oil from the steering/fan drive tank and keeps the steering and fan drive pumps full of oil. Oil flows from the pump to the high pressure cut-off valve, the displacement valve and the maximum angle actuator piston. The pump output oil and the spring around the maximum angle actuator piston holds the swashplate at maximum angle. This is the position of the pump when the displacement solenoid receives 0 milliamps from the Brake/Cooling ECM and pump output pressure is low. When the displacement solenoid is receiving between 0 and 680 milliamps from the Brake/Cooling ECM, the displacement solenoid moves the valve spool to the left. The spool allows pump output pressure to flow to the minimum angle actuator piston. The minimum angle actuator piston has a larger diameter than the maximum angle actuator piston. The minimum angle actuator piston moves the swashplate toward the minimum flow position.

Î


- 54 -

Reference

The current adjustment screw controls the spring pressure in the displacement valve and changes the minimum current required to start destroking the pump. Do not adjust the current adjustment screw in chassis. This adjustment should only be done on a hydraulic test stand. The high pressure cut-off valve controls the maximum pressure in the fan drive system. The high pressure cut-off valve controls the flow of pump output pressure to the minimum angle actuator piston. When system pressure is at maximum, the high pressure cut-off valve sends oil to the minimum angle actuator piston and moves the swashplate to the minimum flow position. The high pressure cut-off valve setting must be set lower at higher altitudes. At 3142 Meters (10300 ft.) it only requires 15158 kPa (2200 psi) to maintain 525 rpm fan speed. If the fan drive pump solenoid is disconnected and the engine is run at high idle, the fan would overspeed if the high pressure cut-off valve setting is too high. A fan overspeed occurs at approximately 541 rpm. When accelerating from LOW IDLE to HIGH IDLE, the fan drive pressure will spike to start the fan rotation. The spike pressure may be the pump high pressure cut-off setting. To determine the correct high pressure cut-off setting at altitudes above sea level, use ET to override the hydraulic fan speed to 525 rpm, raise the engine speed to HIGH IDLE, and record the pump pressure and fan speeds. We now know what pressure is required to rotate the fan at 525 rpm at the current altitude. For example, at our current altitude, it required approximately 16675 kPa (2420 psi) to rotate the fan at 525 rpm. Pump cut-off pressure should be set a minimum of 2070 kPa (300 psi) above the pressure required to maintain the maximum fan speed (525 rpm) with the solenoid unplugged. This will vary with the elevation above sea level. So, at this altitude we should set the pump cut-off pressure to a minimum of 18740 kPa (2720 psi). To adjust the pump high pressure cut-off setting, install a blocker plate in the pump outlet port and disconnect the fan drive pump solenoid. Start the engine and run at LOW IDLE. The pump will destroke and operate at minimum flow and maximum pressure (High Pressure Cut-off). Adjust the high pressure cut-off to the specification.


- 55 -

Reference

2 3

1

4

41

Steering oil flows through the hose (1) to the pressure reducing valve (2). The pressure reducing valve reduces the steering pressure to a signal pressure of 6200 kPa (900 psi). Excess steering oil flows to tank through hose (3). The reduced signal oil flows through hose (4) to the to the fan drive pump and the brake cooling drive pump. The fan drive pump and the brake cooling drive pump use the signal oil pressure to destroke the pumps to minimum flow at start-up and during cold temperatures.


- 56 -

Reference

1

2

42

Shown is the fan drive makeup valve (1). The makeup valve is located behind the lower right section of the radiator. Supply oil flows from the fan drive pump through the makeup valve to the fan drive motor. Return oil also flows from the fan drive motor through the makeup valve. Return oil from the fan motor is used as makeup oil to prevent a vacuum condition in the fan motor when the fan operation stops. If supply oil to the fan stops suddenly, the fan and motor may continue to rotate because of the mass of the fan. Continued rotation of the fan motor would create a vacuum in the supply circuit between the fan drive pump and motor. The makeup valve allows oil to flow from the return side of the circuit to the supply side and prevents a vacuum. The fan drive pressure tap (2) is used to measure fan drive pump pressure. Pump supply pressure should be between 0 to 24115 kPa (0 to 3500 psi) at sea level. Pump supply pressure is adjusted at the high pressure cut-off valve mounted on the fan drive pump. The pressure will vary depending on the desired fan speed set by the Brake/Cooling ECM.


- 57 -

Reference

DUAL FAN DRIVE HYDRAULIC SYSTEM MAKEUP VALVE FAN DRIVE MOTORS

CASE DRAIN FILTER

OIL COOLER CAT 3 5 1 6 ENGINE FAN DRIVE PUMP FAN TANK

43 793C Sound Reduction Truck - Variable Displacement Pump/Twin Motors Shown is the 793C Sound Reduction Truck fan drive hydraulic system. Oil flows from the fan drive pump through a makeup valve to the fan drive motors. Oil flows from the motors through the makeup valve, the fan drive oil cooler, and the fan drive oil filter to the fan drive tank. If supply oil to the fan motors stops suddenly, the fans and motors may continue to rotate because of the mass of the fans. The makeup valve allows oil to flow from the return side of the circuit to the supply side and prevents a vacuum in the supply lines. The fan drive motors are fixed displacement motors, therefore, the fan speeds are determined by the amount of flow from the fan drive pump. The fan drive pump is a variable displacement piston-type pump that is controlled by the Brake ECM. Case drain oil flows from the fan drive motors and the fan drive pump through a case drain oil filter and a case drain screen to the fan drive tank.


- 58 -

Reference

44

Shown is the twin radiator module. The fans are hydraulically driven. A variable displacement piston-type pump provides oil flow to the fixed displacement motors shown in the center of the fans. The hydraulic motors turn the fan blades. The left fan rotates counter-clockwise and the right fan rotates clockwise. The fans rotate in opposite directions to obtain the best airflow. Fan speed is controlled by the Brake ECM. Fan speed varies depending on jacket water temperature, aftercooler temperature, brake temperature, and the air conditioning status. The maximum fan speed is 625 rpm. The minimum fan speed will be approximately 100 rpm when all temperatures are cold and the air conditioning is OFF. The fan will never actually stop because there is always a small amount of flow from the fan drive pump when it is fully destroked. The inputs that determine fan speed are: - Jacket water coolant temperature - Aftercooler coolant temperature - Brake oil temperature - Air Conditioning status

Î


- 59 -

Reference

ENGINE FAN CONTROL °C (°F) JACKET WATER TEMPERATURE

AFTERCOOLER TEMPERATURE

BRAKE TEMPERATURE

FAN CONTROL

< 88 (190)

< 78 (172)

< 102 (215)

BASE TEMP OFF

> 88 (190) < 98 (208)

> 78 (172) < 88 (190)

> 102 (215) < 107 (225)

MODULATE TO TEMP CHART

> 98 (208)

> 88 (190)

> 107 (225)

MAXIMUM

45 When the Air Conditioner is ON, the fan speed is set to follow the 10°C (18°F) coolant temperature override shown in the chart below. Shown above are the fan speed limits based on the temperature sensor inputs.


- 60 -

Reference

ENGINE RPM

BRAKE TEMPERATURE ABOVE BASE TEMP

COOLANT TEMPERATURE ABOVE BASE TEMP

700

1°C (1.8°F)

0

0

0

0

.5°C (1°F)

2°C (3.6°F)

0

0

150

150

1°C (2°F)

3°C (5.4°F)

0

150

186

208

1.5°C (3°F)

4°C (7.2°F)

0

171

249

277

2°C (4°F)

5°C (9°F)

0

192

280

312

2.5°C (5°F)

6°C (10.8°F)

150

235

342

381

3°C (6°F)

7°C (12.6°F)

162

277

405

451

3.5°C (7°F)

8°C (14.4°F)

186

320

466

520

4°C (8°F)

9°C (16.2°F)

208

363

529

589

4.5°C (9°F)

10°C (18°F)

224

384

560

624

5°C (10°F)

1200

1750

1950

DESIRED ENGINE FAN SPEEDS

46 As shown in the chart above for fan speed temperature limits, if the sensor temperatures are all below the lower base temperature limits, the fan control is turned off and fan speed could be as low as 100 rpm. If the temperatures are between the sensor lower and upper limits, fan speed will modulate according to the fan speed chart shown below. If any of the sensor temperatures are above the upper limits, fan speed will be set to the maximum.


- 61 -

Reference

2

1

3

47

Shown is closer view of a fan drive motor (1) and the makeup valve (2). Oil flows from the fan drive pump through the makeup valve to the fan drive motors. Oil flows from the motors through the makeup valve, the fan drive oil cooler, and the fan drive oil filter and returns to the fan drive tank. The fan drive motor is a fixed displacement motor, therefore, the fan speed is determined by the amount of flow from the fan drive pump. The fan drive pump is a variable displacement pistontype pump that is controlled by the Brake ECM. Case drain oil flows from the fan drive motors through a case drain filter to the fan drive tank. The fan speed sensors (3) provide input signals to the Brake ECM. In VIMS and ET, the LEFT Fan Speed Sensor is identified as Eng Cool Fan #1 and the RIGHT Fan Speed Sensor is identified as Eng Cool Fan #2. The Brake ECM uses the inputs to determine the fan speed and adjusts the current to the fan drive pump solenoid to maintain the desired fan speed. If the difference between the fan speeds is greater than 50 rpm, a fan speed event will be logged in the Brake ECM. The Brake ECM sends the signal to the VIMS, which informs the operator of the fan speed error. NOTE: Fan speed is not accurate below 100 rpm.


- 62 -

Reference

SPEED SENSOR

FAN MOTOR CASE DRAIN PORT

OUTPUT SHAFT

PISTON

BARREL

PORT PLATE

RETURN PORT SUPPLY PORT

48 Shown is a sectional view of the fixed displacement, bent-axis fan drive motor. The motor is rotated by flow from the fan drive pump. Oil flows through the supply port and the port plate and pushes the pistons out of the barrel. The pistons force the barrel and the output shaft to rotate. The output shaft turns the fan. As the barrel rotates and the pistons return, oil flows from the pistons through the port plate, the return port, and a makeup valve to the fan drive tank. Oil that leaks past the pistons into the motor housing provides lubrication for the rotating motor components. This oil leakage is referred to as case drain oil. Case drain oil flows through the case drain port and a case drain oil filter to the fan drive tank. The fan drive motor speed sensor provides an input signal to the Brake ECM. The Brake ECM uses this input to maintain the desired fan speed. There are 67 teeth on the plate that the speed sensor uses to determine the motor speed


- 63 -

Reference

3

1

4 2

49

Shown is the front of the 793C XQ truck engine with the radiator assembly removed. The fan drive hydraulic tank (1), the fan drive pump (2), and the fan drive case drain filter (3) can be seen. A fan drive oil temperature sensor (4) is installed in the hydraulic tank and provides an input signal to the Brake ECM. The Brake ECM sends the signal to the VIMS, which informs the operator of the fan drive system oil temperature. If the fan drive system temperature increases above 107°C (225°F), the Brake ECM will log an oil temperature too high event.


- 64 -

Reference

5 3

4 1 2

50

Shown is the fan drive hydraulic tank (1) located on the frame near the right front of the engine. The oil level is checked at the sight gauge (2). The oil level should first be checked with cold oil and the engine stopped. The level should again be checked with warm oil and the engine running. When filling the hydraulic tank after an oil change, fill the tank with oil to the FULL COLD mark on the sight gauge. Turn on the engine manual shutdown switch so the engine will not start. Crank the engine for approximately 15 seconds. The oil level will decrease as oil fills the fan drive hydraulic system. Add more oil to the tank to raise the oil level to the FULL COLD mark. Crank the engine for an additional 15 seconds. Repeat this step as required until the oil level stabilizes at the FULL COLD mark. Ensure that the pump and motor cases are filled with oil and bleed the air out of the pump and motors before starting the engine. Turn off the engine manual shutdown switch and start the engine. Warm the hydraulic oil. Add more oil to the tank as required to raise the oil level to the FULL WARM mark. Use 30W Transmission Drive Train Oil (TDTO) oil in the fan drive hydraulic system. Change the oil every 2000 hours. If Scheduled Oil Sampling (S•O•S) is used, the oil change interval can maybe be extended to 4000 hours.

Î


- 65 -

Reference

Fan drive hydraulic system oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (not shown) located in the case drain oil filter base. The fan drive return oil filter (3) is located in the tank. The oil filter should be changed every 500 hours. A bypass valve is located in the filter housing. The oil filter bypass valve will open if the oil filter restriction is greater than 170 kPa (25 psi). Before removing the cap to add oil to the fan drive hydraulic system, depress the pressure release button on the breather (4) to release any pressure from the tank. Inspect the hydraulic tank breather for plugging. The fan drive pump and motors case drain filter (5) is located above the fan drive hydraulic tank. The case drain oil filter should be changed every 500 hours. An oil filter bypass switch is located on the oil filter base. If the filter restriction exceeds 140 kPa (20 psi), the oil filter bypass switch provides an input signal to the Brake ECM. The Brake ECM sends the signal to the VIMS, which informs the operator that the filter is restricted. A bypass valve is also located on the case drain oil filter base. The case drain oil filter bypass valve will open if the oil filter restriction is greater than 170 kPa (25 psi).

NOTICE Failure to correctly fill the hydraulic tank and the pump and motor cases after an oil change may cause component damage.


- 66 -

6

Reference

2

3

5

4 1

51

Shown is the fan drive pump located at the front of the engine. The fan drive pump is a variable displacement piston-type pump. The Brake ECM controls the flow of oil from the fan drive pump by energizing the displacement solenoid (1). The Brake ECM analyzes the temperatures and the air conditioning status and sends between 0 and 640 milliamps to the solenoid. Between 0 to 220 milliamps, the pump is at maximum displacement and the fan speed is at maximum. Between 600 to 640 milliamps, the pump is at minimum displacement and the fan speed is at minimum. The coil resistance through the solenoid is approximately 24 ohms. The displacement solenoid moves a spool in the pressure and flow compensator valve (2) to control the flow of pump output pressure to the minimum angle actuator piston. The minimum angle actuator piston moves the swashplate to the minimum flow position. The current adjustment screw (3) controls the minimum current required to start destroking the pump. The present setting is 220 milliamps. Do not adjust the current adjustment screw in chassis. This adjustment should only be done on a hydraulic test stand.

Î


- 67 -

Reference

The high pressure cut-off valve (4) controls the maximum pressure in the fan drive system. The high pressure cut-off valve controls maximum pressure by controlling the flow of pump output pressure to the minimum angle actuator piston. When system pressure is at maximum, the high pressure cut-off valve sends oil to the minimum angle actuator piston and moves the swashplate to destroke the pump only enough to maintain that maximum pressure. In the fan drive system, it does not go to minimum stroke because the fans are still turning. The pump will only destroke a small percentage in order to hold the high pressure. At sea level the high pressure cut-off valve setting is 27000 ± 345 kPa (3920 ± 50 psi). The high pressure cut-off valve setting must be set lower at higher altitudes. If the fan drive pump solenoid is disconnected and the engine is run at high idle, the fan speed would be too high if the high pressure cut-off valve setting is too high. The fan drive pressure tap (5) is used to measure fan drive pump pressure. The minimum angle stop screw (6) is located near the pressure and flow compensator valve. The maximum angle stop screw is located on the other side of the pump. Do not adjust the minimum or maximum angle stop screws in chassis. This adjustment should only be done on a hydraulic test stand. Pump cut-off pressure should be set at least 2070 kPa (300 psi) greater than the pressure required to maintain the maximum fan speed (625 rpm) with the fan drive pump solenoid unplugged. This will vary with the elevation above sea level. When accelerating from LOW IDLE to HIGH IDLE, the fan drive pressure will spike to start the fan rotation. The spike pressure may be the pump high pressure cut-off setting. When at low idle and you are requesting maximum fan speed, the pump will be at maximum stroke. When you go to high idle, the pump will remain at full stroke until the 625 rpm maximum fan speed is exceeded. After 625 rpm is exceeded, the control will start stroking the pump back to the proper displacement for this fan speed. This will take several seconds and fan speed may exceed 700 rpm. The pump/motor combination may result in fan speeds as high as 775 rpm if the pump cut-off pressure is set high enough. To determine the correct high pressure cut-off setting at altitudes above sea level, use ET to override the hydraulic fan speed to 625 rpm, raise the engine speed to HIGH IDLE, and record the pump pressure and fan speeds. We now know what pressure is required to rotate the fans at 625 rpm at the current altitude. For example, at our current altitude, it required approximately 16675 kPa (2420 psi) to rotate the fans at 625 rpm. Pump cut-off pressure should be set a minimum of 2070 kPa (300 psi) above the pressure required to maintain the maximum fan speed (625 rpm) with the solenoid unplugged. This will vary with the elevation above sea level. So, at this altitude we should set the pump cut-off pressure to a minimum of 18740 kPa (2720 psi).

Î


- 68 -

Reference

FAN DRIVE PUMP MINIMUM ANGLE STOP

PRESSURE AND FLOW COMPENSATOR PISTON


SWASHPLATE

DRIVE SHAFT

CHARGE PUMP IMPELLER

MAXIMUM ANGLE STOP

ROTARY GROUP


52 Shown is a sectional view of the fan drive pump. The pump is a variable displacement pistontype pump. Oil flows from the pump through a makeup valve to the fan motor. Fan speed is controlled by controlling the flow from the pump to the fan motor. Oil from the fan drive tank enters the pump in the port below the charge pump impeller. The charge pump keeps the fan drive pump full of oil. The large spring around the maximum angle actuator piston holds the swashplate at maximum angle. Pump output pressure is always present on the right side of the maximum angle actuator piston and also helps to hold the swashplate at maximum angle. When the swashplate is at maximum angle, pump output is at maximum flow and fan speed is at maximum. This is the position of the pump when the displacement solenoid receives between 0 to 220 milliamps from the Brake ECM.

Î


- 69 -

Reference

When the displacement solenoid is receiving between 220 and 640 milliamps from the Brake ECM, the displacement solenoid moves a spool in the pressure and flow compensator valve. The spool allows pump output pressure to flow to the minimum angle actuator piston. The minimum angle actuator piston has a larger diameter than the maximum angle actuator piston. The minimum angle actuator piston moves the swashplate toward the minimum flow position. The swashplate angle, pump flow, and fan speed will modulate with the amount of current at the displacement solenoid. When the swashplate is at minimum angle, pump output is at minimum flow and fan speed is at minimum. This is the position of the pump when the displacement solenoid receives between 600 to 640 milliamps from the Brake ECM. Before the swashplate contacts the minimum angle stop, the minimum angle actuator piston will open a small drain port to tank and stop the movement of the swashplate. Draining the minimum angle actuator piston oil will prevent the swashplate from contacting the minimum angle stop repeatedly which can be noisy and may cause damage to the pump. Oil that leaks past the pistons into the pump housing provides lubrication for the rotating components. This oil leakage is referred to as case drain oil. Case drain oil flows through the case drain port and a case drain oil filter to the fan drive tank.


- 70 -

Reference

FAN DRIVE PUMP CONTROL TO FAN MOTORS

TO MINIMUM ANGLE ACTUATOR PISTON DRAIN

PUMP SUPPLY

CASE DRAIN




CURRENT ADJUSTMENT

DRAIN


PUMP SUPPLY




53 Shown is the pressure and flow compensator valve for the fan drive pump. The charge pump pulls oil from the fan drive tank and keeps the fan drive pump full of oil. Oil flows from the pump to the high pressure cut-off valve, the displacement valve, and the maximum angle actuator piston. The pump output oil and the spring around the maximum angle actuator piston holds the swashplate at maximum angle. This is the position of the pump when the displacement solenoid receives 0 to 220 milliamps from the Brake ECM and pump output pressure is low. When the displacement solenoid is receiving between 220 to 640 milliamps from the Brake ECM, the displacement solenoid moves the valve spool to the left. The spool allows pump output pressure to flow to the minimum angle actuator piston. The minimum angle actuator piston has a larger diameter than the maximum angle actuator piston. The minimum angle actuator piston moves the swashplate toward the minimum flow position.

Î


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Reference

The current adjustment screw controls the spring pressure in the displacement valve and changes the minimum current required to start destroking the pump. The present setting is 220 milliamps. NOTE: Do not adjust the current adjustment screw in chassis. This adjustment should only be done on a hydraulic test stand. The high pressure cut-off valve controls the maximum pressure in the fan drive system. The high pressure cut-off valve controls the flow of pump output pressure to the minimum angle actuator piston. When system pressure is at maximum, the high pressure cut-off valve sends oil to the minimum angle actuator piston and moves the swashplate to the minimum flow position. At sea level the high pressure cut-off valve setting is 27000 ± 345 kPa (3920 ± 50 psi). The high pressure cut-off valve setting must be set lower at higher altitudes. If the fan drive pump solenoid is disconnected and the engine is run at high idle, the fan speed would be too high if the high pressure cut-off valve setting is too high.


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Reference

FAN SPEED VERSUS PUMP SOLENOID CURRENT

FAN SPEED (RPM)

800 700 600 500 400 300 200 100 0 0

100

200

300

400

500

600

700

800

PUMP SOLENOID CURRENT (mA) LOW IDLE FAN SPEED

HIGH IDLE FAN SPEED

54 This graph shows the relationship between fan speed and pump solenoid current. As the current to the solenoid increases the fan speed is reduced.


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Reference

55

Shown is the fan drive makeup valve (arrow). The makeup valve is located between the two fan drive motors. Supply oil flows from the fan drive pump, through the makeup valve, to the fan drive motors. Return oil also flows from the fan drive motor through the makeup valve. Return oil from the fan motor is used as makeup oil to prevent a vacuum condition in the fan motors when the fan operation stops. If supply oil to the fan stops suddenly, the fans and motors may continue to rotate because of the mass of the fans. Continued rotation of the fan motors would create a vacuum in the supply circuit between the fan drive pump and motors. The makeup valve allows oil to flow from the return side of the circuit to the supply side and prevents a vacuum.


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Reference

56

Shown is the fan drive hydraulic system oil cooler (arrow). Return oil flows from the fan drive motors, through the makeup valve, to the fan drive oil cooler. Return oil flows from the fan drive oil cooler, through the return filter, to the hydraulic tank. A bypass valve is located on the oil cooler. The oil cooler bypass valve will open if the oil cooler restriction is greater than 170 kPa (25 psi). The fan drive hydraulic oil is cooled by the jacket water cooling system.


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Reference

57 When running tests on the 793C XQ hydraulic fan drive system, ET can be used to observe real time status of the parameters that control the hydraulic fan drive system. Shown is a status screen group that was created to observe most of the hydraulic fan drive system parameters. One of the parameters shown on the screen is "Engine Cooling Fan Solenoid Current." If a truck has the Electronically Controlled Fan Drive System installed, the value of this parameter will change from 0 to 0.640 Amps, which represents a current between 0 to 640 milliamps. If the value displayed is 0 Amps, the ECM is sending 0 milliamps of current to the fan drive pump solenoid. At 0 milliamps the pump is at maximum displacement and the fan drive pump flow is at maximum. If the value displayed is 0.640 Amps, the ECM is sending 640 milliamps of current to the fan drive pump solenoid. At 640 milliamps the pump is at minimum displacement and the fan drive pump flow is at minimum.


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Reference

58 ET can be used to override the fan speed to test the hydraulic fan drive system. To override the fan speed, select "Diagnostics" from the ET pull-down menu and then select "Override Parameters." The "Desired Engine Cooling Fan Speed Override" parameter will be shown. Highlight the parameter and select "Change" (see next slide).


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Reference

59 When "Change" has been selected to override the "Desired Engine Cooling Fan Speed Override," the new value can be entered in the screen shown. After the new value is entered, select "OK" and the fan speed should change to the value entered. The left and right fan speeds can be observed using the VIMS Message Center or a laptop with VIMSpc installed. The real time status of the hydraulic fan drive parameters can not be observed with ET during the override test unless a second laptop with ET is connected to the truck. If the override parameter screen is left by selecting another ET screen, the override parameter test is turned off.


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Reference

BRAKE ELECTRONIC CONTROL SYSTEM

INPUT COMPONENTS ECM LOCATION CODE

FRONT BRAKE FILTER SWITCH

CAT DATA LINK SERVICE TOOL ENGINE ECM

PARKING BRAKE FILTER

TRANSMISSION/CHASSIS ECM

BRAKE OVERSTROKE SWITCH

VIMS BRAKE AIR PRESSURE

SHIFT LEVER SWITCH ACTUAL GEAR SWITCH

LEFT FAN SPEED SENSOR RIGHT FAN SPEED SENSOR FAN DRIVE CASE DRAIN FILTER DIFFERENTIAL FILTER

PARKING/SECONDARY BRAKE SWITCH

FAN DRIVE OIL TEMP SENSOR

OFF INPUT ARC ON/OFF SWITCH

TCS

ENGINE SPEED/TIMING SENSOR

SERVICE/RETARDER BRAKE SWITCH

FAN DRIVE PUMP SOLENOID

DIFFERENTIAL OIL LEVEL

ON INPUT

TRANSMISSION OUTPUT SPEED SENSOR

OUTPUT COMPONENTS DIFFERENTIAL OIL TEMP SENSOR

DIFFERENTIAL PRESSURE

ARC

THROTTLE SENSOR

DIFFERENTIAL FAN RELAY

ARC SUPPLY SOLENOID

ENGINE OUTPUT SPEED SENSOR

ARC

ARC CONTROL SOLENOID

RETARDER PRESSURE SWITCH AUTO RETARDER PRESSURE SWITCH

RETARDER ENGAGED LAMP TCS ENGAGED LAMP

TCS TEST SWITCH LEFT WHEEL SPEED SENSOR

TCS TCS SELECTOR SOLENOID LEFT AND RIGHT

PROPORTIONAL (SERVO) SOLENOID

RIGHT WHEEL SPEED SENSOR

60 The earlier 793C trucks use the Brake Electronic Control Module (ECM) for controlling the Automatic Retarder Control (ARC), the Traction Control System (TCS), the Rear Axle Cooling status, Filter Bypass status, Brake Overstroke status, and Brake Air Pressure status. On the 793C XQ Truck, the Brake ECM is also used to control the Dual Fan Hydraulic Drive System. In order to control the Dual Fan Hydraulic System, four inputs and one output were added to the Brake ECM. The new Brake ECM Inputs are: - Left Fan Speed - Right Fan Speed - Fan Drive Case Drain Filter Bypass - Fan Drive Oil Temperature The new Brake ECM Output is: - Fan Drive Pump Solenoid


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Reference

HYDRAULIC SCHEMATIC COLOR CODE Black - Mechanical connection. Seal

Red - High pressure oil

Dark Gray - Cutaway section

Red/White Stripes - 1st pressure reduction

Light Gray - Surface color

Red Crosshatch - 2nd reduction in pressure

White - Atmosphere OR Air (no pressure)

Pink - 3rd reduction in pressure

Purple - Pnuematic pressure

Red/Pink Stripes - Secondary source oil pressure

Yellow - Moving or activated components

Orange - Pilot, signal or Torque Converter oil

Cat Yellow - (restricted usage) Identification of components within a moving group

Orange/White Stripes Reduced pilot, signal or TC oil pressure

Brown - Lubricating oil

Orange Crosshatch - 2nd reduction in pilot, signal or TC oil pressure.

Green - Tank, sump, or return oil

Blue - Trapped oil

Green/White Stripes Scavenge Oil or Hydraulic Void

COLOR CODES This color palette is used throughout this document in ISO schematics.

Curso Cat Fan System STMG

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