SPACER 0773108 - Caterpillar

Illustration 1 g03727531
Schematic of fan drive system (1) Hydraulic oil cooler (2) Fan hydraulic pump (3) Fan (4) Fan speed sensor (5) Fan motor (6) Flow control spool (7) Solenoid valve (8) Actuator piston (9) Hydraulic oil tank (10) Hydraulic oil temperature sensorFan hydraulic pump (2) is a variable displacement piston pump. In the hydraulic fan system, the demand for more fan speed through an increase of oil flow is supplied by fan hydraulic pump (2). The discharge pressure of fan hydraulic pump (2) is controlled by solenoid valve (7). When solenoid valve (7) receives a change in current from the engine electronic control module (ECM), signal pressure to fan hydraulic pump (2) will change accordingly. As signal pressure changes, the displacement will change in order to maintain the pump pressure above the signal pressure. The engine ECM receives information from temperature sensors for the engine coolant and hydraulic oil.When the current to solenoid valve (7) is at the maximum, the fan pump is at minimum output. If the fan speed solenoid fails or there is another problem in the electrical circuit for the hydraulic fan system, the fan pump will advance to high-pressure cutoff. Then, the pump will produce maximum output. The maximum output that is provided by fan hydraulic pump (2) is controlled by the adjustment of flow control spool (6). This spool is in the pump control valve.Fan motor (2) is a fixed displacement gear motor.When the engine is started and if all temperatures for the sensors are below the key target temperatures the engine ECM will send the maximum current to solenoid valve (7). Signal oil to the flow control spool is open to the hydraulic tank through the solenoid valve (7). Supply oil is directed to actuator piston (8) in order to destroke the pump. The angle of the pump swashplate is at a minimum. Fan hydraulic pump (2) will produce a minimum flow.As one of the temperatures of the three sensors increases above the key target temperature, the engine ECM sends a proportional reduction in current to solenoid valve (7). Solenoid valve (7) will start to shift. This action will allow some of the supply oil to flow to control spool (6). Flow control spool (6) starts to shift. A proportional amount of oil will flow back to the hydraulic tank. As the pressure behind actuator piston (8) begins to decrease, the actuator spring will increase the swashplate angle. The pump output flow will increase. The fan speed will increase.As the temperatures of the machine continue to increase, the engine ECM will continue to reduce the current that is sent to solenoid valve (7). Solenoid valve (7) will continue to shift causing an increase of the hydraulic signal to flow control spool (6). Flow control spool (6) will continue to drain oil that is behind actuator piston (8). The swashplate moves more toward a maximum angle and the pump flow continues to increase. The fan speed continues to increase.Once the cutoff pressure is