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| Illustration 1 | g02174947 |
(1) Fan drive motor (piston motor) (2) Cooler bypass valve (3) Hydraulic oil cooler (4) Fan drive pump (piston pump) (5) Pump compensator valve (6) Hydraulic oil tank (7) Check valve | |
The main components of the fan hydraulic system are fan drive motor (1) and fan drive pump (4) .
Fan drive pump (4) draws oil from hydraulic oil tank (6). Fan drive pump (4) sends oil to fan drive motor (1). The amount of oil that is sent to the motor by the pump is regulated by the engine ECM. The engine ECM adjusts the current to pump compensator valve (5). The pump compensator valve controls the amount of oil that is sent to fan drive motor (1). When more oil is sent to fan drive motor (1), the fan turns faster.
The oil from the outlet side of the fan drive motor flows through hydraulic oil cooler (3). The oil from the hydraulic oil cooler combines with the oil from the case drain of the fan drive pump. The combined oil then returns to hydraulic oil tank (6) .
When the hydraulic oil is cold, the oil from the outlet side of fan drive motor (1) will bypass hydraulic oil cooler (3) through cooler bypass valve (2). After the hydraulic oil warms, the oil will flow through the hydraulic oil cooler in order to keep the oil at a predetermined temperature.
Operation of the Fan Hydraulic System
The hydraulic fan pump is controlled by the engine ECM. The discharge flow and pressure from the hydraulic fan pump determines the rpm of the fan drive motor.
The engine ECM considers the following inputs in controlling the discharge pressure from the hydraulic fan drive pump:
- Hydraulic oil temperature sensor
- Inlet manifold temperature sensor
- Engine coolant temperature sensor
- Engine speed
The engine ECM monitors the temperature inputs. The engine ECM provides a signal to the solenoid for the fan pump. When the solenoid receives minimum current and the engine is running at HIGH IDLE, maximum flow is sent to the fan motor. This maximum flow will cause the fan motor to rotate at the maximum speed. Also, this pressure will be observed if the solenoid is not working.
In cooler weather, the engine ECM may utilize an engine software strategy that is called "Cool Engine Elevated Idle Strategy" when the following conditions are met:
- The coolant temperature is less than 70 °C (158 °F).
- The parking brake is set to the ON position.
- The transmission is set to the NEUTRAL position.
- The throttle switch is set to the LOW IDLE position.
When the conditions that are listed above are met, the engine ECM will automatically increase engine speed up to 1000 rpm in order to increase coolant temperature. When any one of the four conditions are not met, the "Cool Engine Elevated Idle Strategy" is ignored.