A3 Hydraulic Fan Drive System

170-1

A3 Hydraulic Fan Drive System

Table of Contents

Table of Contents ........................................ 1Safety ........................................................... 2Warnings and Cautions .............................. 2Introduction................................................. 2Hydraulic Fan Drive Components.............. 2Description of Operation............................. 2Reservoir...................................................... 3Hydraulic Pump .......................................... 3Priority Flow Divider .................................. 3Fan Motor Bypass ....................................... 4Pilot Control Circuit ................................... 4Charge Air Override Control Valve........... 5Thermovalve................................................ 5Port T........................................................... 5Hydraulic Oil Cooler................................... 6Description of Major Modules.................... 6Hydraulic Reservoir.................................... 6Hydraulic Pump .......................................... 6Priority Oil Flow Divider Valve.................. 7Hydraulic Fan Motor .................................. 7Fan Motor Control Valve............................ 7Pilot Control System Port (RPT) ................ 7Hydraulic Oil Cooler................................... 8Engine Coolant Thermovalve ..................... 8Charge Air Override Control Valve........... 8Charge Air Temperature Sensor (Kysor) .. 8Cooling Fan Temperature Switch............... 9Oil Reservoir TemperatureWarning Light............................................. 9Hydraulic Fan Drive Troubleshooting ....... 9Abbreviations .............................................. 9A-Check Engine Coolant Level................... 14B-Check Hydraulic Oil Level...................... 14C-Check for Air in the Hydraulic Oil......... 14D-Check De-Energize the Charge AirOverride Solenoid (CAOS) ......................... 14E-Check the Condition of the Fan blade .... 14F-Check the Fan Motor for Free Rotation. 14G-Check Radiator for ExternalContamination............................................. 14H-Check Radiator and ChargeAir Baffles.................................................... 15

I-Check Hydraulic Fan Circuit Pressure....15J-Check Fan Speed ......................................15K-Check the Hydraulic System...................16

List of Figures ..............................................1Figure 1System Oil Flow Diagram..........3Figure 1.1Fan Motor Control Valves.......4Figure 1.2Pilot Operating Circuit ............5Figure 2Oil Reservoir..............................6Figure 3Hydraulic Pump .........................6Figure 4Oil Flow Divider Valve..............7Figure 5Hydraulic Fan Motor..................7Figure 6Fan Motor Control Valve ...........7Figure 7Pilot Control System Ports .........7Figure 8Hydraulic Oil Cooler..................8Figure 9Engine Coolant Thermovalve.....8Figure 10Charge Air Override SolenoidRelief Valve................................................8Figure 11Charge Air Temperature...........8Figure 12Cooling Fan TemperatureSwitch ........................................................9Figure 13Oil Reservoir TemperatureWarning Light ............................................9

List of Tables................................................1Table 1Fan Speed Vs Engine Speed ........19Table 2Hydraulic Cooling SystemPerformance A3RE) ..................................20

List of Charts ...............................................1Chart 1Troubleshooting ..........................11

List of Schematics ........................................ 1Schematics 1Hayden Hydraulic Oil CoolingCircuit ........................................................12

List of Graph................................................ 1Graph 1Fan Speed Vs Engine Speed(Cummins ISB A3RE) ................................18

7DEOH RI &RQWHQWV

A3 Hydraulic Fan Drive System

170-2

SafetyThe purpose of this safety summary is to ensure thesafety and health of personnel and the protection ofequipment.

All users of this publication shall read, understand,and apply this safety summary when performingmaintenance and operating procedures.

WARNINGS and CautionsAll users of this publication shall read, andunderstand, all WARNINGS and Cautions.

WARNINGS REFER TO A PROCEDUREOR PRACTICE, THAT, IF NOT

CORRECTLY OBSERVED, COULDRESULT IN INJURY OR DEATH.

Cautions refer to a procedure or practice,that, if not correctly observed, could result in

damage to or destruction of equipment.

IntroductionThe All American rear engine bus uses a hydraulicfan drive. The hydraulic fan drive creates airflowthrough the engine-cooling radiator and the chargeair cooler.

Hydraulic Fan Drive Components1. Hydraulic Reservoir

2. Hydraulic Pump

3. Priority Oil Flow Divider Valve

4. Fan Motor

5. Fan Motor Control Valve

6. Pilot Control System

7. Hydraulic Oil Cooler

Description of OperationThe fan drive system responds to coolingrequirements by monitoring engine coolanttemperature and charge air temperature.

The system then provides a modulated fan speed tomeet cooling requirements for each system, seeFigure 1System Oil Flow Diagram.

A hydraulic fan motor directly drives the engine-cooling fan. Modulated fan speed will depend onthe amount of oil flowing through the fan motor.The oil flow is measured in gallons per (GPM)minute, low oil flow results in low fan speeds. Asoil flow increases fan speeds increases. Oil flowthrough the fan motor will depend on three mainareas of the hydraulic fan drive system.

1. Pump Speed

2. The amount of oil allowed to bypass the Fanmotor

3. Fan Circuit Relief Valve

A pump creates oil flow necessary to operate thehydraulic fan drive system. The pump is a positivedisplacement gear type pump.

As engine Revolution Per Minute (RPM) increasesproportionally, oil flow increases. As engine, RPMdecreases proportionally oil flow decreases.

The amount of oil allowed to bypass the fan motor iscontrolled by the fan motor bypass valve. The valveis located in the fan motor control valve, which isintegrated into the fan motor housing.

The fan motor bypass valve is controlled by thehydraulic pilot operated circuit. The hydraulic pilotcircuit is in turn controlled by a charge air overridevalve and a thermovalve.

The charge air override sensor and the thermovalvemonitors charge air temperature and engine coolanttemperature. As charge air and engine coolanttemperature increase, the charge air overridesolenoid valve and thermovalve respond to controloil flow through the pilot circuit.

A3 Hydraulic Fan Drive System

170-3

With the engine at full speed and at maximumoperating temperature, the following conditionsexist.

1. The pump would deliver maximum oil flow tothe fan motor control valve.

2. The fan motor bypass valve would allowminimum oil to bypass the fan motor. Thiswould result in maximum pressure developing inthe fan drive circuit.

3. The fan circuit relief valve would open limitingthe system pressure.

4. This would allow oil to bypass the fan motor.Pressure relief at the fan motor allows thepressure relief valve to control maximum fanspeed under those conditions.

ReservoirA 12-quart reservoir provides a supply of clean airfree oil to the pump. The reservoir is vented anduses a dipstick and sight glass for monitoring oillevel. The reservoir has an internal filter that filtersreturn oil flow from the fan and the steering circuit.

Hydraulic PumpThe single stage hydraulic pump provides oil flowfor the fan drive circuit and the power steeringcircuit. This is done by a priority flow divider valveintegrated into the back of the pump housing.

Priority Flow DividerThe flow divider valve prioritizes the steering circuitby providing 4.3-GPM flow to the steering circuitregardless of oil flow available for the fan drivecircuit.

With proper operation of the flow divider valve,both systems function as if they have dedicatedpumps.

Figure 1System Oil Flow Diagram

A3 Hydraulic Fan Drive System

170-4

A steering circuit pressure relief valve is integratedinto the flow divider housing. The valve limitspressure in the steering circuit only and has no effecton the fan circuit.

Oil flow required for the fan drive circuit isapproximately 4.3 GPM depending on engine speed.Oil will flow to the fan motor control valve.

Fan Motor BypassThe fan motor control valve has a fan motor bypassvalve to modulate fan speed and a pressure reliefvalve to limit fan circuit pressure.

When the fan motor bypass valve is in the fullbypass position most of the oil will bypass the fanmotor.

Oil flow bypassing the fan motor flows through anintegral passage in the fan motor control valvehousing.

The fan will be in an off mode, with the engine,operating below 185 degrees Fahrenheit. In the offmode, the fan will rotate at a very low RPMregardless of engine speed. As the engine RPM,increases there should not be a noticeable increase infan RPM.

When the fan motor bypass valve is in full closedposition all fan circuit oil flow will be directedthorough the fan motor. The fan will be in a fullrun mode with the engine at maximum operatingtemperature and full engine speed.

As vehicle, operating conditions change the load onthe engine changes. This will affect the engineoperating temperature. To compensate for varyingcooling needs the bypass valve is designed andcontrolled to allow varying amounts of oil to bypassthe fan motor.

This will result in a modulated (variable) fan speedof approximately 320-RPM at low operatingte