SEGMENT GP-SPROCKET 4782936 - Caterpillar

Hydraulic Fan Drive
Illustration 1 g00903515
Lines for the hydraulic fan system
(1) Line to the fan motor from the fan speed control valve
(2) Return line to the hydraulic tank
(3) Signal line
(4) Line from the pump to the fan speed control valve
(5) Test port for the hydraulic fan
(6) Fan speed control valve
Illustration 2 g01000502
(6) Fan Speed Control Valve
(7) Pressure and Flow Compensator Valve
(8) Fan Drive Pump
(9) Oil Pressure Sensor for the Fan
(10) Makeup Valve
(11) Fan Drive Motor The fan drive system consists of a fan drive pump (8), fan speed control valve (6), and a fan drive motor (11). Motor (11) is a fixed displacement motor and pump (8) is a variable displacement pump.Oil flows from pump (8) to motor (11). The output oil from motor (11) flows back to the hydraulic tank. In machines that are equipped with all wheel drive, the oil returns to the tank through the return circuit for the all wheel drive.Makeup valve (10) for motor (11) allows the fan to stop gradually when the engine is stopped. Makeup valve (10) prevents motor (11) from cavitating when the engine is stopped. When pump (8) stops producing flow, makeup valve (10) will allow oil to enter the inlet of motor (11).The fan speed depends on the volume of oil that is supplied by pump (8). The displacement of pump (8) is changed by fan speed control valve (6). The fan speed control valve receives a variable current from the engine electronic control module (ECM) that changes the output of pump (8). The engine ECM receives information from the engine coolant temperature sensor, the inlet air temperature sensor, and the oil pressure sensor (9) for the fan. In machines that are equipped with all wheel drive, the engine ECM also receives information from the hydraulic oil temperature sensor.When the current to fan speed control valve (6) is at the maximum, pump (8) is at minimum output. If fan speed control valve (6) fails or there is another problem in the electrical circuit for the fan drive system, pump (8) will produce maximum output.The maximum pressure in the fan drive system is controlled by the setting of pressure compensator valve (7).