Curso Cat Fan System STMG

Service TrainingMay 2003

TECHNICAL PRESENTATION

MACHINE HYDRAULIC FAN SYSTEMSELECTRONICALLY CONTROLLED

NOTES

Fan Systems - 2 - Reference06/01/03

TABLE OF CONTENTS

INTRODUCTION ........................................................................................................................5

M300C DEMAND FAN SYSTEM ..............................................................................................6Fixed Displacement Pump ......................................................................................................6

WHEEL LOADER FAN DRIVE SYSTEMS ............................................................................14924G/924Gz and 928G/IT28G Fan Drive System - Fixed Displacement Pump..................14938G Series II Hydrualic Fan System - Variable Displacement Pump ................................20950G - 980G Series On Demand Fan - Variable Displacement Pump .................................29992G Wheel Loader Fan Drive System - Variable Displacement Pump..............................34

OFF-HIGHWAY TRUCK HYDRAULIC FAN SYSTEMS ......................................................41797B Off Highway Truck - Variable Displacement Pump ...................................................41793C Sound Reduction Truck - Variable Displacement Pump/Twin Motors .......................57

COLOR CODES.........................................................................................................................79


NOTES


INTRODUCTION

To improve machine cooling system and overall machine performance, Caterpillar hasdeveloped electronically controlled hydraulic fan systems.

These systems are controlled by a Electronic Control Module (ECM). The ECM will typicallyuse the engine coolant temperature and hydraulic oil temperature to determine the required fanspeed. Additional inputs may also be monitored for some machine applications.

The ECM controls a a proportional solenoid that modulates the fan speed. The proportionalsolenoid is used to control the pump flow to the motor. This may done using bypass valves orchanging the signal to the pump.

This presentation provides information on representative electronically controlled hydraulic fansystems. The first systems covered use fixed displacement-type pumps. Later systems discussthe use of variable displacement pumps.

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MACHINE HYDRAULIC FMACHINE HYDRAULIC FANANSYSTEMSSYSTEMS

ELECTRONICALLELECTRONICALLY CONTROLLEDY CONTROLLED

© 2003 Caterpillar Inc.

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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 fandrive pump is a single-section gear pump.


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


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


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The one-piece radiator group consists of the radiator (1) and the oil cooler (2). The radiator andoil cooler cannot be replaced individually.

The demand fan (3) is driven by the fan drive pump. Fan speed is controlled by the MachineECM.

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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The fan drive pump directs oil to the fan motor, the flow control valve, and the cooling fansolenoid valve.

The fan pump and the fan motor have the same displacement. If full fan drive pump flow weredirected through the motor, the fan would turn at engine speed. The flow control valve andcooling fan solenoid valve is used to reduce the fan speed. Oil flowing through the solenoidvalve controls the amount of oil that is bypassed around the motor through the flow controlvalve.

The cooling fan solenoid valve is a proportional solenoid valve that is controlled by the MachineECM. Fan speed decreases as the current to the solenoid increases because the amount of oilbypassing the fan motor increases as the current increases. The solenoid valve allows thegreatest amount of oil to bypass when the hydraulic oil temperature is less than 60°C (140°F ) orthe 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 controlmaximum fan speed.

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FAN DRIVEPUMP

COOLING FANSOLENOID VALVE

FLOW CONTROLVALVE

BACKPRESSURE VALVE

MAIN CONTROLVALVE GROUP

MOTOR

RADIATORAND

HYDRAULICOIL COOLER

GROUP

DEMAND FAN DRIVE SYSTEM

The fan is controlled by a proportional solenoid that modulates the fan speed. The MachineECM uses the engine coolant temperature and hydraulic oil temperature to determine the fanspeed.

The Machine ECM has two fan speed maps. One determines the fans speed for the currentengine coolant temperature and the other determines the fan speed for the current hydraulic oiltemperature. The Machine ECM compares the two fan speed values and commands the demandfan to the higher of the two speeds. The fan speed output is not changed unless the new speeddemand is more than 2% different than the currently-commanded speed. This prevents speedfluctuation.

The fan speed will be set to maximum if the hydraulic oil temperature sensor is faulted or thecoolant temperature is unavailable or unknown. The fan speed is set to maximum (minimumcurrent) if the limp home switch is activated.

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COOLANT AND OILTEMP INCREASE CURRENT

DECREASES

SOLENOID VALVEBYPASSES LESS OIL FAN SPEED

INCREASES

CURRENT TO FAN SOLENOID


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

The demand fan system on M300C Excavators does not require calibration. The coolant and oiltemperatures 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 isallowed to bypass the demand fan motor. The fan speed decreases because of the reducedavailability of oil to the demand fan motor.

Likewise, if the fan speed is too slow, the coolant and oil temperatures will increase. As thetemperatures increase, the Machine ECM will decrease the current to the demand fan solenoidso that less oil is allowed to bypass the demand fan motor. This causes the fan speed to increase.

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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 ECMallows 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) worktogether with the Machine ECM to regulate oil flow in the brake and fan systems.


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3

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The Machine ECM will send the required signal to the demand fan solenoid valve in order toprovide the proper fan speed for the cooling system. The Machine ECM will monitor thefollowing 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, thatbypasses some of the supply oil to the fan to the cooler. The maximum fan speed is controlledby the fan control solenoid valve. Maximum fan speed occurs when the fan control solenoidvalve is de-energized. Most of the pump flow is now directed through the fan motor.


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At the rated engine rpm, the fan speed is maintained at a minimum of 600 rpm. The maximumfan speed of approximately 1625 rpm is controlled by the solenoid valve in the fan circuit. Thereturn oil from the fan motor is directed through the oil cooler and filter to the tank. Both thecooler and the filter are equipped with bypass valves.

The makeup valve prevents cavitation in the fan motor. During a quick deceleration, the flow ofoil to the fan motor can stop. The makeup valve will open. This allows oil to flow from theoutlet side of the fan motor to the inlet side of the fan motor.


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The optional reversing hydraulic fan system has a reversing solenoid controlled by the machineECM. When the top of the reversing fan switch (not shown) is depressed, the fan reversingsolenoid is energized in order to reverse the fan for 10 seconds. Supply oil from the pump isdirected to the other side of the fan motor, while the other side of the fan motor is open to thecooler circuit.

When the bottom of the reversing fan switch is depressed, the fan reversing solenoid isenergized in order to reverse the fan for 10 seconds. This will repeat every 30 minutes until thereversing fan switch is returned to the center position.

The crossover relief valve prevents cavitation in the fan motor. During a quick deceleration, theflow of oil to fan motor can stop. The crossover relief valve will open. This allows oil to flowfrom the outlet side of the fan motor to the inlet side of the fan motor.


REVERSING HYDRAULIC FAN SYSTEM

COOLER

BYPASS

FILTER

CROSSOVERRELIEF AND MAKEUP

REVERSINGSOLENOID VALVE

FAN CONTROLSOLENOID VALVE

FLOWCONTROL

MAKEUPVALVE

PUMPGROUP

REVERSINGSOLENOID VALVE

FAN CONTROLSOLENOID VALVE

FANMOTOR

FLOWCONTROL

MAKEUPVALVE

PUMPGROUP

FANMOTORFORWARD

REVERSE

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The reversing fan allows debris to be cleared from the grills without leaving the cab. Thereversing demand cooling fan has three modes of operation. The operator selects the fan modeusing 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 theMachine ECM to direct flow to the motor or divert flow away from the motor to control the fanspeed.

Minimum and maximum fan speeds can be calibrated through ET.


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


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938G Series II Hydrualic Fan System - Variable Displacement Pump

The cooling system is a hydraulically driven fan that is controlled by a demand fan controlsystem. The demand fan system controls the fan speed in order to provide the required amountof cooling air. This will maintain key system temperatures.

During heavy machine usage or high ambient temperatures, the demand fan system will increasethe fan speed to the maximum. During light usage and lower ambient temperature, the demandfan 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 thatcan vary the volume of hydraulic oil to the fan motor. The volume of oil that is produced by thehydraulic fan pump is controlled by the pressure and flow compensator valve.


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The pressure and flow compensator valve which controls the pump flow is mounted belowhydraulic fan pump. The pressure and flow compensator valve contains a flow control spooland a pressure cutoff spool. The flow control spool will control the minimum fan speed and upto the maximum fan speed. The pressure cutoff spool will control the maximum fan speed. Thepressure cutoff spool also controls the maximum pressure of the hydraulic fan pump. Thesettings 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 foursensors monitor the engine air inlet temperature, the coolant temperature, the hydraulic oiltemperature, and the transmission oil. The Engine ECM interprets the data from the foursensors. 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 fansolenoid valve in order to increase the fan speed. If one of the temperatures is less than thetarget temperature, the Engine ECM will send a signal to the fan solenoid valve in order todecrease the fan speed. If all of the temperatures are below the target temperatures, the EngineECM will send a signal to the fan solenoid valve in order to decrease the fan speed which willresult in minimum fan speed.

The solenoid valve sends a signal to the pressure and flow compensator valve on the pistonpump. The piston pump will adjust the output for the flow demand.


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

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If the temperature at one of the sensors increases, the Engine ECM sends a proportionalreduction in current to the solenoid valve. The solenoid valve will start to shift to allow some ofthe supply pressure to flow to the flow control spool to act as a pressure signal. The flow controlspool starts to shift to the left. A proportional amount of oil that is behind the actuator pistonwill flow back to the hydraulic tank. As the pressure behind the actuator piston begins todecrease, the actuator bias spring will increase the swashplate angle. The pump output flow willincrease resulting in the fan speed to increase.

As the machine temperatures continue to increase the ECM will continue to reduce the currentsent to the solenoid valve. The solenoid will continue to shift to increase the hydraulic signal tothe flow control spool. The control spool will shift more to the left to continue to drain oil in theactuator piston to the tank. The pump swashplate angle moves more toward maximumswashplate angle and the pump flow continues to increase, resulting in higher fan speeds.

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If the current from the ECM to the solenoid is at the minimum, the solenoid valve will send themaximum hydraulic pressure signal to the flow control spool to shift it fully to the left whichwill drain oil from the actuator piston to tank. Pump output flow will increase due the to pumpswashplate moving toward maximum angle.

As the rpm of the hydraulic fan motor approaches the maximum speed, the pressure of the pumpdischarge oil also increases. The increase in pressure of the pump discharge oil will work on theleft of both the flow compensator spool and the pressure cutoff spool. The flow compensatorwill stay to the left. The cutoff spool will start to shift to the right to allow some of the pumpsupply 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 andfrom the actuator piston to pump to maintain or limit the maximum fan speed. The adjustmentof 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, thecutoff spool would destroke the pump to minimum angle to produce minimum flow.


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The hydraulic fan pump is a variable displacement piston pump. The axial piston type pump isused to supply oil flow to the hydraulic fan motor. The movement of the piston assembly in thehydraulic fan pump draws oil from the hydraulic tank. The oil is pressurized in the hydraulic fanpump. The high pressure oil flows from the hydraulic fan pump to the hydraulic fan motor inorder to rotate the fan.

Oil from the hydraulic tank flows into the pump head through the pump inlet. The oil then flowsfrom the pump inlet through inlet passages in the valve plate. When the drive shaft rotates, theopenings of the cylinder barrel move toward the inlet passages of the valve plate. The angle ofthe swashplate determines the amount of oil that is pushed out of each cylinder barrel. Theswashplate can be at any angle between the minimum angle and the maximum angle. Pistonassemblies move in and out of the cylinder barrel. The in and out movement of the pistonassemblies allows oil to be drawn in to and pushed out of the cylinder barrel. The swashplateangle is controlled by the actuator piston. The movement of the actuator piston is regulated byoil 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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When the engine is started and all temperatures are very low, the Engine ECM sends themaximum current to the solenoid valve. Signal oil to the flow control spool is open to thehydraulic tank through the solenoid valve. Supply pressure from the pump shifts the flowcontrol spool up. Supply oil is directed to the actuator piston to destroke the pump. The pumpswashplate is at reduced angle. The pump produces low flow resulting in minimum fan speed.

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

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If the current from the Engine ECM to the solenoid is at the minimum, the solenoid valve willsend the maximum hydraulic pressure signal to the flow control spool to shift it fully downwhich will drain oil from the actuator piston to tank. Pump output flow will increase due to thepump swashplate moving toward maximum angle.

As the rpm of the hydraulic fan motor approaches the maximum speed, the pressure of the pumpsupply oil also increases. The increase in pressure of the pump supply oil will work on thebottom of the flow control spool and pressure cutoff spool. The flow control spool will staydown due to the signal oil from the solenoid valve and the margin spring. The cutoff spool willstart to shift up to allow some of the pump supply oil to flow to the actuator piston to slightlydestroke the pump to reduce pump flow.

Once the desired fan speed is reached, the pressure cutoff spool will meter the supply oil to andfrom the actuator piston to maintain or limit the maximum fan speed. The adjustment of thecutoff spool can be adjusted for any maximum flow.

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DEMAND FAN

950G - 980G Series II On Demand Fan - Variable Displacement Pump

The 950G -908G Series II Electronically controlled fan system is virtually the same as the938G/IT38G system. The above views show the on demand fan components on the 3126Bengine in the 950G/962G Series II (top right view), 3176C/3196 engine in the 966G/972G SeriesII (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), whichprovides oil flow to the cooling fan motor (not shown). The Engine ECM controls the fan speedbased on temperature sensor inputs from the engine coolant, inlet air manifold, transmission oiland 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 tothe tank causing the pump to DESTROKE. In this position, flow from the pump to the fanmotor is reduced which results in slower fan speed.

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This schematic shows the fan drive hydraulic system.

The solenoid valve controls the signal oil to the flow control spool for the fan pump. Varyingthe current to the proportional solenoid valve changes the hydraulic signal to vary the oil flow tothe fan motor to increase or decrease the fan speeds. The solenoid valve is essentially a variableorifice 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 controlvalve is diverted to the tank. The flow control spool moves to the right. Supply oil flowsthrough the pump control spools to the pump actuator to destroke the pump to achieve LOWPRESSURE STANDBY. This pressure is controlled by the flow control spool spring. The fanmotor rotates at minimum rpm.

When the solenoid is DE-ENERGIZED, more flow through the orifice in the solenoid valve isdirected to the flow control spool causing the fan pump to UPSTROKE to increase the fanspeed.


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When system pressure increases to the setting of the pressure cutoff spool the spool shifts to theright to destroke the pump in order to maintain the maximum fan speed. Maximum fan speed isbased 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, forexample, the engine is shut off or a rapid deceleration of the engine.

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The Engine ECM receives input signals from the engine coolant temperature sensor, intakemanifold air temperature sensor and transmission lubrication oil temperature sensor.

Hydraulic oil temperature sensor signals are sent to the Caterpillar Monitoring System maindisplay 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 thevariable speed fan solenoid valve.

NOTE: The variable speed fan control feature can be enabled or disabled using the ETService Tool. The variable speed fan default setting is enabled.


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


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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 EngineECM. 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 steeringand 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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Fan Drive System Components

The fan drive pump (1) is a variable displacement piston pump. The pump is mounted to theright 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), theelectro-hydraulic proportional valve (5), the proportional valve solenoid (6), the proportionalvalve drain tube (7), the proportional valve signal hose (8), the margin spool adjustment (9), thecompensator valve (10), the pressure compensator valve adjustment (11), the signal pressure tap(12), and the system pressure tap (13).

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

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The fan drive motor (1) is located at the rear of the machine in front of the engine radiatorassembly.

Also shown are the motor intake hose (2), the motor outlet hose (3), the case drain hose (4), andthe case drain filter (5).

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When the engine is running, the fan drive pump pulls oil from the implement hydraulic tank andsends oil flow to the fan motor. The fan motor turns the cooling fan. Oil from the fan motorflows through the implement hydraulic cooler to the implement hydraulic tank.

The cooling fan sends air flow through the engine radiator, the implement hydraulic cooler, thesteering 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 proportionalvalve.

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), theproportional valve closes the passage for signal oil flow to the tank. The signal oil flowsthrough the two orifices to the pump compensator valve. The signal oil causes the compensatorvalve to upstroke the pump.


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The Engine ECM receives input signals from the engine coolant temperature sensor, the steeringhydraulic tank temperature sensor, the implement hydraulic tank temperature sensor, and the airconditioner on/off switch. The Engine ECM analyzes the signals and energizes the electro-hydraulic proportional valve when needed.

When the Engine ECM energizes the electro-hydraulic proportional valve, the proportionalvalve opens the passage for signal oil flow to the tank. The size of the opening is proportional tothe signal from the Engine ECM. Signal oil flows through the open passage to the tank. Thiscondition 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 pumpflow 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 of375 ± 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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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 fanmotor 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 fandrive motor turning faster than the fan drive pump can supply oil. The oil pressure at the fanmotor inlet becomes lower than the oil pressure at the fan motor outlet. The higher outletpressure opens the makeup valve and allows oil from the motor outlet to flow to the inlet. Thecombination of oil flow through the makeup valve and the pump oil flow prevents cavitation ofthe fan motor.

When pump output matches the fan speed, the motor inlet oil pressure increases above the motoroutlet oil pressure. The higher inlet pressure closes the makeup valve.


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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 tothe fixed displacement motor shown in the center of the fan. The hydraulic motor turns the fanblades.

Fan speed is controlled by the Brake/Cooling ECM. Fan speed varies depending on many inputsbut 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 makeupvalve 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 motoroutlet oil pressure. The higher inlet pressure closes the makeup valve.



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 to200 rpm to reduce the load on the pump drive.

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


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As shown in the chart above for fan speed control temperature limits, if the sensor temperaturesare all below the lower limits, the fan control is turned off and fan speed could be as low as 0rpm. If the temperatures are between the sensor lower and upper limits, fan speed will modulateby sensor priority to a fan speed curve that has been pre-set for each sensor. If any of the sensortemperatures are above the upper limits, fan speed will be set to the limits shown in the topchart.

After being programmed (flashed), the Brake/Cooling ECM needs to know what fanarrangement is installed on the machine. Because of the changes to the fan iron, there are threedifferent 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 from96 to 106 inch fan, change fan control solenoid, . . .). In addition to these cases, if you replacethe 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.


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Shown is the 797B fan drive hydraulic system. Oil flows from the fan drive pump through amakeup valve to the fan drive motor. Oil flows from the motor through the makeup valve andthe 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 themass of the fan. The makeup valve allows oil to flow from the return side of the circuit to thesupply 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 theamount of flow from the fan drive pump. The fan drive pump is a variable displacement piston-type 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 thesteering/fan drive tank.


Steering supply oil flows from the steering solenoid and relief valve manifold to a pressurereducing valve. The pressure reducing valve reduces the steering pressure to a signal pressure of6200 kPa (900 psi). Excess steering oil flows from the reducing valve back through the steeringsolenoid and relief valve manifold to tank. The reduced signal oil flows to the to the fan drivepump and the brake cooling drive pump.

The fan drive pump and the brake cooling drive pump use the signal oil pressure to destroke thepumps to minimum flow at start-up and during cold temperatures.

36

Shown is closer view of the 797B fan drive motor. Oil flows from the fan drive pump through amakeup valve to the fan drive motor. Oil flows from the motor through the makeup valve andthe 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 theamount of flow from the fan drive pump. The fan drive pump is a variable displacement piston-type 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 thesteering/fan drive tank.

The fan speed sensor (2) provides an input signal to the Brake/Cooling ECM. TheBrake/Cooling ECM uses this input to maintain the fan speed between 0 and 525 rpm.


1

2

37

Shown is a sectional view of the fixed displacement, bent-axis fan drive motor. The motor isrotated by flow from the fan drive pump. Oil flows through the supply port and the port plateand pushes the pistons out of the barrel. The pistons force the barrel and the output shaft torotate. The output shaft turns the planetary drive group and the fan. As the barrel rotates andthe pistons return, oil flows from the pistons through the port plate, the return port and a makeupvalve to the steering/fan drive tank.

Oil that leaks past the pistons into the motor housing provides lubrication for the rotating motorcomponents. This oil leakage is referred to as case drain oil. Case drain oil flows through thecase 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. TheBrake/Cooling ECM uses this input to maintain the fan speed between 0 and 525 rpm.


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The fan drive pump (1) is part of a double piston pump group. The steering pump (2) is theother part of the pump group. The pump group is mounted on the front of the pump drive. Thepump drive is located on the inside of the right frame rail near the torque converter. A chargingpump is located between the steering pump and the fan drive pump and is used to keep thepumps supplied with oil.

The fan drive pump is a variable displacement piston-type pump. The Brake/Cooling ECMcontrols 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 andsends between 0 and 680 milliamps to the solenoid. The displacement solenoid moves a spoolin the pressure and flow compensator valve (4) to control the flow of pump output pressure tothe minimum angle actuator piston.

The minimum angle actuator piston moves the swashplate to the minimum flow position. Thecurrent adjustment screw (5) controls the minimum current required to start destroking thepump. Do not adjust the current adjustment screw in chassis. This adjustment should only bedone on a hydraulic test stand.


1

2

3

4 5

6

7

8

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 theminimum or maximum angle stop screws in chassis. This adjustment should only be done on ahydraulic test stand.

A reducing valve provides a signal pressure through the hose (8) and a shuttle valve to the fandrive pump and the brake cooling drive pump.


39

Shown is a sectional view of the 797B fan drive pump. The fan drive pump is part of a doublepiston pump group. The steering pump is the other part of the pump group. The pumps arevariable displacement piston-type pumps. Oil flows from the fan drive pump through a makeupvalve to the fan motor. Fan speed is controlled by controlling the flow from the pump to the fanmotor. Oil from the steering/fan drive tank enters the pump group in the port below the chargepump impeller. The charge pump keeps the two pumps full of oil.

The large spring around the maximum angle actuator piston holds the swashplate at maximumangle. Pump output pressure is always present on the right side of the fan drive pump maximumangle actuator piston and also helps to hold the swashplate at maximum angle. When theswashplate is at maximum angle, pump output is at maximum flow and fan speed is atmaximum. This is the position of the pump when the displacement solenoid receives 0milliamps from the Brake/Cooling ECM.


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When the displacement solenoid is receiving between 0 and 680 milliamps from theBrake/Cooling ECM, the displacement solenoid moves a spool in the pressure and flowcompensator valve. The spool allows pump output pressure to flow to the minimum angleactuator piston. At 0 milliamps the pump is at maximum displacement and the fan speed is atmaximum. At 680 milliamps the pump is at minimum displacement and the fan speed is atminimum. 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 fandrive pump needs the signal pressure so that the displacement solenoid can position the fandrive pump at minimum angle at start-up and during cold temperatures. Without the signalpressure the pump could not stay at minimum angle to provide zero fan speed at start-up andduring cold temperatures.

The minimum angle actuator piston has a larger diameter than the maximum angle actuatorpiston. The minimum angle actuator piston moves the swashplate toward the minimum flowposition. The swashplate angle, pump flow, and fan speed will modulate with the amount ofcurrent at the displacement solenoid. When the swashplate is at minimum angle, pump output isat minimum flow and fan speed is at minimum. This is the position of the pump when thedisplacement solenoid receives 680 milliamps from the Brake/Cooling ECM.

Before the swashplate contacts the minimum angle stop, the minimum angle actuator piston willopen a small drain port to tank and stop the movement of the swashplate. Draining theminimum angle actuator piston oil will prevent the swashplate from contacting the minimumangle 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 rotatingcomponents. This oil leakage is referred to as case drain oil. Case drain oil flows through thecase drain port and a case drain oil filter to the steering/fan drive tank.


40

Shown is the pressure and flow compensator valve for the 797B fan drive pump. The chargepump pulls oil from the steering/fan drive tank and keeps the steering and fan drive pumps fullof oil. Oil flows from the pump to the high pressure cut-off valve, the displacement valve andthe maximum angle actuator piston.

The pump output oil and the spring around the maximum angle actuator piston holds theswashplate at maximum angle. This is the position of the pump when the displacement solenoidreceives 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 theBrake/Cooling ECM, the displacement solenoid moves the valve spool to the left. The spoolallows pump output pressure to flow to the minimum angle actuator piston. The minimum angleactuator piston has a larger diameter than the maximum angle actuator piston. The minimumangle actuator piston moves the swashplate toward the minimum flow position.


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The current adjustment screw controls the spring pressure in the displacement valve andchanges the minimum current required to start destroking the pump. Do not adjust the currentadjustment 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. Thehigh pressure cut-off valve controls the flow of pump output pressure to the minimum angleactuator piston. When system pressure is at maximum, the high pressure cut-off valve sends oilto 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 drivepump solenoid is disconnected and the engine is run at high idle, the fan would overspeed if thehigh pressure cut-off valve setting is too high. A fan overspeed occurs at approximately 541rpm.

When accelerating from LOW IDLE to HIGH IDLE, the fan drive pressure will spike to startthe 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 tooverride the hydraulic fan speed to 525 rpm, raise the engine speed to HIGH IDLE, and recordthe pump pressure and fan speeds. We now know what pressure is required to rotate the fan at525 rpm at the current altitude. For example, at our current altitude, it required approximately16675 kPa (2420 psi) to rotate the fan at 525 rpm. Pump cut-off pressure should be set aminimum 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 portand disconnect the fan drive pump solenoid. Start the engine and run at LOW IDLE. The pumpwill destroke and operate at minimum flow and maximum pressure (High Pressure Cut-off).Adjust the high pressure cut-off to the specification.


41

Steering oil flows through the hose (1) to the pressure reducing valve (2). The pressure reducingvalve reduces the steering pressure to a signal pressure of 6200 kPa (900 psi). Excess steeringoil flows to tank through hose (3). The reduced signal oil flows through hose (4) to the to thefan 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 thepumps to minimum flow at start-up and during cold temperatures.


1

2

3

4

42

Shown is the fan drive makeup valve (1). The makeup valve is located behind the lower rightsection of the radiator. Supply oil flows from the fan drive pump through the makeup valve tothe 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 fanmotor when the fan operation stops.

If supply oil to the fan stops suddenly, the fan and motor may continue to rotate because of themass of the fan. Continued rotation of the fan motor would create a vacuum in the supply circuitbetween the fan drive pump and motor. The makeup valve allows oil to flow from the returnside 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 supplypressure should be between 0 to 24115 kPa (0 to 3500 psi) at sea level. Pump supply pressure isadjusted at the high pressure cut-off valve mounted on the fan drive pump. The pressure willvary depending on the desired fan speed set by the Brake/Cooling ECM.


12

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 fandrive pump through a makeup valve to the fan drive motors. Oil flows from the motors throughthe 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 rotatebecause of the mass of the fans. The makeup valve allows oil to flow from the return side of thecircuit 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 bythe amount of flow from the fan drive pump. The fan drive pump is a variable displacementpiston-type pump that is controlled by the Brake ECM. Case drain oil flows from the fan drivemotors and the fan drive pump through a case drain oil filter and a case drain screen to the fandrive tank.


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Shown is the twin radiator module. The fans are hydraulically driven. A variable displacementpiston-type pump provides oil flow to the fixed displacement motors shown in the center of thefans. The hydraulic motors turn the fan blades.

The left fan rotates counter-clockwise and the right fan rotates clockwise. The fans rotate inopposite directions to obtain the best airflow.

Fan speed is controlled by the Brake ECM. Fan speed varies depending on jacket watertemperature, aftercooler temperature, brake temperature, and the air conditioning status. Themaximum fan speed is 625 rpm.

The minimum fan speed will be approximately 100 rpm when all temperatures are cold and theair conditioning is OFF. The fan will never actually stop because there is always a small amountof 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

45

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


ENGINE FAN CONTROL °C (°F)

JACKET WATERTEMPERATURE

AFTERCOOLERTEMPERATURE

BRAKETEMPERATURE

FANCONTROL

< 88 (190) < 78 (172) < 102 (215) BASE TEMPOFF

> 88 (190)< 98 (208)

> 98 (208)

> 78 (172)< 88 (190)

> 88 (190)

> 102 (215)< 107 (225)

> 107 (225)

MODULATE TOTEMP CHART

MAXIMUM

46

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


DESIRED ENGINE FAN SPEEDS

COOLANTTEMPERATURE

ABOVEBASE TEMP

ENGINE RPM

700 1200 1750 1950

1°C (1.8°F)

2°C (3.6°F)

3°C (5.4°F)

4°C (7.2°F)

5°C (9°F)

0

0

0

0

0

0

0 0

150 150

150

6°C (10.8°F)

7°C (12.6°F)

8°C (14.4°F)

9°C (16.2°F)

10°C (18°F)

BRAKETEMPERATURE

ABOVEBASE TEMP

.5°C (1°F)

1°C (2°F)

1.5°C (3°F)

2°C (4°F)

2.5°C (5°F)

3°C (6°F)

3.5°C (7°F)

4°C (8°F)

4.5°C (9°F)

5°C (10°F)

186 208

171 249 277

1920 280 312

150 235 342 381

162 277 405 451

186 320 466 520

208 363 529 589

224 384 560 624

47


Shown is closer view of a fan drive motor (1) and the makeup valve (2). Oil flows from the fandrive pump through the makeup valve to the fan drive motors. Oil flows from the motorsthrough the makeup valve, the fan drive oil cooler, and the fan drive oil filter and returns to thefan drive tank.

The fan drive motor is a fixed displacement motor, therefore, the fan speed is determined by theamount 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 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 LEFTFan Speed Sensor is identified as Eng Cool Fan #1 and the RIGHT Fan Speed Sensor isidentified as Eng Cool Fan #2. The Brake ECM uses the inputs to determine the fan speed andadjusts 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 loggedin the Brake ECM. The Brake ECM sends the signal to the VIMS, which informs the operatorof the fan speed error.

NOTE: Fan speed is not accurate below 100 rpm.

1

2

3


FAN MOTOR

OUTPUTSHAFT

BARREL

PISTON

PORT PLATE

CASE DRAINPORT

RETURN PORT

SUPPLY PORT

SPEEDSENSOR

48

Shown is a sectional view of the fixed displacement, bent-axis fan drive motor. The motor isrotated by flow from the fan drive pump. Oil flows through the supply port and the port plateand pushes the pistons out of the barrel. The pistons force the barrel and the output shaft torotate. The output shaft turns the fan. As the barrel rotates and the pistons return, oil flows fromthe 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 motorcomponents. This oil leakage is referred to as case drain oil. Case drain oil flows through thecase 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 ECMuses this input to maintain the desired fan speed. There are 67 teeth on the plate that the speedsensor uses to determine the motor speed

49


Shown is the front of the 793C XQ truck engine with the radiator assembly removed. The fandrive hydraulic tank (1), the fan drive pump (2), and the fan drive case drain filter (3) can beseen.

A fan drive oil temperature sensor (4) is installed in the hydraulic tank and provides an inputsignal to the Brake ECM. The Brake ECM sends the signal to the VIMS, which informs theoperator of the fan drive system oil temperature. If the fan drive system temperature increasesabove 107°C (225°F), the Brake ECM will log an oil temperature too high event.

2

4

1

3

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 oiland the engine stopped. The level should again be checked with warm oil and the enginerunning.

When filling the hydraulic tank after an oil change, fill the tank with oil to the FULL COLDmark on the sight gauge. Turn on the engine manual shutdown switch so the engine will notstart. Crank the engine for approximately 15 seconds. The oil level will decrease as oil fills thefan drive hydraulic system. Add more oil to the tank to raise the oil level to the FULL COLDmark. Crank the engine for an additional 15 seconds. Repeat this step as required until the oillevel 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 andmotors before starting the engine.

Turn off the engine manual shutdown switch and start the engine. Warm the hydraulic oil. Addmore 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. Changethe oil every 2000 hours. If Scheduled Oil Sampling (S•O•S) is used, the oil change interval canmaybe be extended to 4000 hours.

5

4

1

2

3


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 every500 hours. A bypass valve is located in the filter housing. The oil filter bypass valve will openif 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 pressurerelease button on the breather (4) to release any pressure from the tank. Inspect the hydraulictank breather for plugging.

The fan drive pump and motors case drain filter (5) is located above the fan drive hydraulictank. The case drain oil filter should be changed every 500 hours. An oil filter bypass switch islocated on the oil filter base. If the filter restriction exceeds 140 kPa (20 psi), the oil filterbypass switch provides an input signal to the Brake ECM. The Brake ECM sends the signal tothe VIMS, which informs the operator that the filter is restricted. A bypass valve is also locatedon the case drain oil filter base. The case drain oil filter bypass valve will open if the oil filterrestriction is greater than 170 kPa (25 psi).

NOTICE

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


51


Shown is the fan drive pump located at the front of the engine. The fan drive pump is a variabledisplacement piston-type pump. The Brake ECM controls the flow of oil from the fan drivepump 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 maximumdisplacement and the fan speed is at maximum. Between 600 to 640 milliamps, the pump is atminimum 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) tocontrol the flow of pump output pressure to the minimum angle actuator piston. The minimumangle actuator piston moves the swashplate to the minimum flow position. The currentadjustment screw (3) controls the minimum current required to start destroking the pump. Thepresent setting is 220 milliamps. Do not adjust the current adjustment screw in chassis. Thisadjustment should only be done on a hydraulic test stand.

1

4326

5


The high pressure cut-off valve (4) controls the maximum pressure in the fan drive system. Thehigh pressure cut-off valve controls maximum pressure by controlling the flow of pump outputpressure to the minimum angle actuator piston. When system pressure is at maximum, the highpressure cut-off valve sends oil to the minimum angle actuator piston and moves the swashplateto 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 onlydestroke a small percentage in order to hold the high pressure. At sea level the high pressurecut-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 drivepump solenoid is disconnected and the engine is run at high idle, the fan speed would be toohigh 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 theminimum or maximum angle stop screws in chassis. This adjustment should only be done on ahydraulic test stand.

Pump cut-off pressure should be set at least 2070 kPa (300 psi) greater than the pressurerequired to maintain the maximum fan speed (625 rpm) with the fan drive pump solenoidunplugged. This will vary with the elevation above sea level.

When accelerating from LOW IDLE to HIGH IDLE, the fan drive pressure will spike to startthe fan rotation. The spike pressure may be the pump high pressure cut-off setting. When atlow 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 fanspeed is exceeded. After 625 rpm is exceeded, the control will start stroking the pump back tothe proper displacement for this fan speed. This will take several seconds and fan speed mayexceed 700 rpm. The pump/motor combination may result in fan speeds as high as 775 rpm ifthe pump cut-off pressure is set high enough.

To determine the correct high pressure cut-off setting at altitudes above sea level, use ET tooverride the hydraulic fan speed to 625 rpm, raise the engine speed to HIGH IDLE, and recordthe pump pressure and fan speeds. We now know what pressure is required to rotate the fans at625 rpm at the current altitude. For example, at our current altitude, it required approximately16675 kPa (2420 psi) to rotate the fans at 625 rpm. Pump cut-off pressure should be set aminimum 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).



PRESSURE AND FLOWCOMPENSATOR

MINIMUMANGLE STOP

DRIVE SHAFT

SWASHPLATE

MAXIMUMANGLE STOP

ROTARYGROUP

CHARGEPUMP

IMPELLER

MINIMUM ANGLEACTUATOR PISTON

MAXIMUMANGLE

ACTUATORPISTON

PISTON

FAN DRIVE PUMP

52

Shown is a sectional view of the fan drive pump. The pump is a variable displacement piston-type pump. Oil flows from the pump through a makeup valve to the fan motor. Fan speed iscontrolled 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. Thecharge pump keeps the fan drive pump full of oil.

The large spring around the maximum angle actuator piston holds the swashplate at maximumangle. Pump output pressure is always present on the right side of the maximum angle actuatorpiston and also helps to hold the swashplate at maximum angle. When the swashplate is atmaximum angle, pump output is at maximum flow and fan speed is at maximum. This is theposition of the pump when the displacement solenoid receives between 0 to 220 milliamps fromthe Brake ECM.


When the displacement solenoid is receiving between 220 and 640 milliamps from the BrakeECM, 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 actuatorpiston. The minimum angle actuator piston moves the swashplate toward the minimum flowposition. The swashplate angle, pump flow, and fan speed will modulate with the amount ofcurrent at the displacement solenoid. When the swashplate is at minimum angle, pump output isat minimum flow and fan speed is at minimum. This is the position of the pump when thedisplacement solenoid receives between 600 to 640 milliamps from the Brake ECM.

Before the swashplate contacts the minimum angle stop, the minimum angle actuator piston willopen a small drain port to tank and stop the movement of the swashplate. Draining theminimum angle actuator piston oil will prevent the swashplate from contacting the minimumangle 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 rotatingcomponents. This oil leakage is referred to as case drain oil. Case drain oil flows through thecase drain port and a case drain oil filter to the fan drive tank.



FAN DRIVE PUMP CONTROL

PUMPSUPPLY

DRAIN

TO MINIMUM ANGLEACTUATOR PISTON

HIGH PRESSURECUT-OFF

CURRENTADJUSTMENT

HIGH PRESSURECUT-OFF

DISPLACEMENTSOLENOID AND

VALVE

MINIMUM ANGLEACTUATOR PISTON

MAXIMUMANGLE

ACTUATORPISTON

PUMPSUPPLY

DRAIN

TO MINIMUM ANGLEACTUATOR PISTON

DISPLACEMENTSOLENOID AND

VALVE

TO FANMOTORS

CASEDRAIN

53

Shown is the pressure and flow compensator valve for the fan drive pump. The charge pumppulls oil from the fan drive tank and keeps the fan drive pump full of oil. Oil flows from thepump to the high pressure cut-off valve, the displacement valve, and the maximum angleactuator piston.

The pump output oil and the spring around the maximum angle actuator piston holds theswashplate at maximum angle. This is the position of the pump when the displacement solenoidreceives 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 BrakeECM, the displacement solenoid moves the valve spool to the left. The spool allows pumpoutput pressure to flow to the minimum angle actuator piston. The minimum angle actuatorpiston has a larger diameter than the maximum angle actuator piston. The minimum angleactuator piston moves the swashplate toward the minimum flow position.


The current adjustment screw controls the spring pressure in the displacement valve andchanges the minimum current required to start destroking the pump. The present setting is 220milliamps. NOTE: Do not adjust the current adjustment screw in chassis. This adjustmentshould only be done on a hydraulic test stand.

The high pressure cut-off valve controls the maximum pressure in the fan drive system. Thehigh pressure cut-off valve controls the flow of pump output pressure to the minimum angleactuator piston. When system pressure is at maximum, the high pressure cut-off valve sends oilto 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 drivepump solenoid is disconnected and the engine is run at high idle, the fan speed would be toohigh if the high pressure cut-off valve setting is too high.


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


FAN SPEED VERSUS PUMP SOLENOID CURRENT

00

100200300400500600700800

100 200 300 400 500 600 700 800PUMP SOLENOID CURRENT (mA)

LOW IDLE FAN SPEED HIGH IDLE FAN SPEED

FAN

SPE

ED (R

PM)

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Shown is the fan drive makeup valve (arrow). The makeup valve is located between the two fandrive motors. Supply oil flows from the fan drive pump, through the makeup valve, to the fandrive motors. Return oil also flows from the fan drive motor through the makeup valve. Returnoil from the fan motor is used as makeup oil to prevent a vacuum condition in the fan motorswhen the fan operation stops.

If supply oil to the fan stops suddenly, the fans and motors may continue to rotate because of themass of the fans. Continued rotation of the fan motors would create a vacuum in the supplycircuit between the fan drive pump and motors. The makeup valve allows oil to flow from thereturn side of the circuit to the supply side and prevents a vacuum.

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Shown is the fan drive hydraulic system oil cooler (arrow). Return oil flows from the fan drivemotors, through the makeup valve, to the fan drive oil cooler. Return oil flows from the fandrive oil cooler, through the return filter, to the hydraulic tank. A bypass valve is located on theoil 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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When running tests on the 793C XQ hydraulic fan drive system, ET can be used to observe realtime status of the parameters that control the hydraulic fan drive system. Shown is a statusscreen 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 truckhas the Electronically Controlled Fan Drive System installed, the value of this parameter willchange 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 drivepump solenoid. At 0 milliamps the pump is at maximum displacement and the fan drive pumpflow is at maximum. If the value displayed is 0.640 Amps, the ECM is sending 640 milliampsof current to the fan drive pump solenoid. At 640 milliamps the pump is at minimumdisplacement and the fan drive pump flow is at minimum.


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


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When "Change" has been selected to override the "Desired Engine Cooling Fan SpeedOverride," 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 speedscan 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 duringthe override test unless a second laptop with ET is connected to the truck. If the overrideparameter screen is left by selecting another ET screen, the override parameter test is turned off.


PROPORTIONAL(SERVO) SOLENOID

TCSENGAGED LAMP TCS SELECTOR SOLENOID

LEFT AND RIGHT

ARC SUPPLYSOLENOID

RIGHT WHEEL SPEED SENSOR

INPUT COMPONENTS

OUTPUT COMPONENTS

ENGINE OUTPUTSPEED SENSOR

TRANSMISSION/CHASSIS ECMENGINE ECMSERVICE TOOL

CAT DATA LINK

ARC CONTROLSOLENOID

LEFT WHEEL SPEED SENSOR

ARC ON/OFFSWITCH

ON INPUT

OFF INPUT

RETARDERENGAGED LAMPAUTO RETARDER

PRESSURE SWITCH

RETARDERPRESSURE SWITCH

TCS TESTSWITCH

ARC

TCS

ARC

TCS

SHIFT LEVERSWITCH

ACTUAL GEARSWITCH

PARKING/SECONDARYBRAKE SWITCH

TRANSMISSION OUTPUTSPEED SENSOR

SERVICE/RETARDERBRAKE SWITCH

THROTTLESENSORENGINE

SPEED/TIMINGSENSOR

VIMSBRAKE OVERSTROKE

SWITCH

DIFFERENTIALOIL LEVEL

DIFFERENTIALFILTER

PARKING BRAKE FILTER

DIFFERENTIAL FAN RELAY

DIFFERENTIAL OILTEMP SENSOR

BRAKE AIR PRESSURE

DIFFERENTIALPRESSURE

FRONT BRAKEFILTER SWITCH

ECM LOCATIONCODE

FAN DRIVECASE DRAIN FILTER

LEFT FAN SPEED SENSOR

RIGHT FAN SPEED SENSOR

FAN DRIVE OILTEMP SENSOR

FAN DRIVE PUMPSOLENOID

BRAKE ELECTRONIC CONTROL SYSTEM

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The earlier 793C trucks use the Brake Electronic Control Module (ECM) for controlling theAutomatic Retarder Control (ARC), the Traction Control System (TCS), the Rear Axle Coolingstatus, Filter Bypass status, Brake Overstroke status, and Brake Air Pressure status. On the793C 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 theBrake 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


Dark Gray - Cutaway section

Light Gray - Surface color

Red - High pressure oil

Red/White Stripes - 1st pressure reduction

Red Crosshatch - 2nd reduction in pressure

Pink - 3rd reduction in pressure

Red/Pink Stripes - Secondary source oil pressure

Orange - Pilot, signal or Torque Converter oil

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

Green - Tank, sump, or return oil Blue - Trapped oil

Brown - Lubricating oil

Purple - Pnuematic pressure

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

White - Atmosphere ORAir (no pressure)

Yellow - Moving or activated components

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

Black - Mechanical connection. Seal

Green/White Stripes -Scavenge Oil or Hydraulic Void

HYDRAULIC SCHEMATIC COLOR CODE

COLOR CODES

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

Curso Cat Fan System STMG

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