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| Illustration 1 | g00586122 |
Location of fan drive pump (1) Fan drive pump (2) Pump drive (3) Displacement solenoid (4) High pressure cutoff valve (5) Current adjustment screw (6) Pressure and flow compensator valve (7) Stop screw (minimum angle) | |
The fan drive pump (1) is located at the front bottom section of the pump drive (2). The fan drive pump (1) is a variable displacement piston pump. The Brake/Cooling ECM controls the flow of oil from the fan drive pump by energizing the displacement solenoid (3) .
The Brake/Cooling ECM will analyze the sensor inputs for the temperatures, the status of the brakes and the ground speed. The Brake/Cooling ECM will send 0 to 680 milliampere to the solenoid. At 0 milliampere, the pump is at the maximum displacement and the fan speed is at maximum speed. At 680 milliampere, the pump is at the minimum displacement and the fan speed is at minimum speed.
The displacement solenoid (3) moves a spool in the pressure and flow compensator valve (6) in order to control the flow of pump output pressure to the actuator piston (minimum angle). The actuator piston (minimum angle) will move the swashplate to the position of minimum flow. The current adjustment screw (5) controls the minimum current that is required to start destroking the pump.
The high pressure cutoff valve (4) controls the maximum pressure in the fan drive system. The high pressure cutoff valve controls the system pressure by controlling the flow of pump output pressure to the actuator piston (minimum angle). When the system pressure is at the maximum, the high pressure cutoff valve (4) will send oil to the actuator piston (minimum angle). The actuator piston (minimum angle) will move the swashplate to the position of minimum flow.
The stop screw (minimum angle) (7) is located near the pressure and flow compensator valve (6). The stop screw (maximum angle) is located on the other side of the pump.
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| Illustration 2 | g00760021 |
Sectional view of the fan drive pump (3) Displacement solenoid (6) Pressure and flow compensator valve (7) Stop screw (minimum angle) (8) Swashplate (9) Piston (10) Spring (11) Actuator piston (maximum angle) (12) Drive shaft (13) Stop screw (maximum angle) (14) Rotary (15) Actuator piston (minimum angle) (16) Impeller (charge pump) | |
Oil flows from the pump through a makeup valve to the fan motor. Fan speed is controlled by controlling the flow from the pump to the fan motor.
Oil from the hydraulic tank enters the pump in the port below the impeller (16). The charge pump keeps the fan drive pump full of oil.
The large spring (10) around the actuator piston (11) holds the swashplate (8) at the maximum angle. Pump output pressure is always present on the right side of the actuator piston (11). Pump output pressure also helps to hold the swashplate (8) at the maximum angle. When the swashplate (8) is at the maximum angle, the pump output is at the maximum flow. The fan speed is at maximum speed. This is the position of the pump when the displacement solenoid (3) receives 0 milliampere from the Brake/Cooling ECM. When the displacement solenoid (3) is receiving 0 to 680 milliampere from the Brake/Cooling ECM, the displacement solenoid (3) will move a spool in the pressure and flow compensator valve (6). The spool allows pump output pressure to flow to the actuator piston (15) .
The actuator piston (15) has a larger diameter than the actuator piston (11). The actuator piston (15) moves the swashplate (8) toward the position of minimum flow. The swashplate angle, pump flow and fan speed will modulate with the amount of current at the displacement solenoid (3). When the swashplate (8) is at the minimum angle, the pump output is at the minimum flow and the fan speed is at minimum speed. This is the position of the pump when the displacement solenoid receives 680 milliampere from the Brake/Cooling ECM.
Before the swashplate (8) contacts the stop screw (7), the actuator piston (15) will open a small drain port to the tank. This will stop the movement of the swashplate (8). Draining the oil from the actuator piston will prevent the swashplate (8) from contacting the stop screw (7) repeatedly. Repeated contact between the swashplate and the stop screw can be noisy and the contact may cause damage to the pump.
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| Illustration 3 | g00754072 |
5YW1-229 (1) Fan drive pump (17) Oil filter (case drain) | |
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| Illustration 4 | g00716169 |
5YW230-UP (17) Oil filter (case drain) | |
Oil that leaks past the pistons into the pump housing provides lubrication for the rotating components. This oil leakage is referred to as case drain oil. Case drain oil flows through the case drain port and a oil filter (17) to the hydraulic tank.
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| Illustration 5 | g00760022 |
(3) Displacement solenoid (4) High pressure cutoff valve (5) Current adjustment screw (11) Actuator piston (maximum angle) (15) Actuator piston (minimum angle) (18) Oil from pump supply (19) Oil to actuator piston (minimum angle) (20) Oil to drain | |
The charge pump pulls oil from the hydraulic tank which keeps the fan drive pump full of oil. Oil flows from the pump to the high pressure cutoff valve (4), the displacement valve (3) and actuator piston (11) .
The pump output oil and the spring around the actuator piston (11) holds the swashplate (8) at the maximum angle. This is the position of the pump when the displacement solenoid (3) receives 0 milliampere from the Brake/Cooling ECM and the pump output pressure is low.
When the displacement solenoid (3) is receiving 0 to 680 milliampere from the Brake/Cooling ECM, the displacement solenoid (3) moves the valve spool to the left. The spool allows pump output pressure to flow to the actuator piston (15). The actuator piston (15) has a larger diameter than the actuator piston (11). The actuator piston (15) moves the swashplate (8) toward the position of minimum flow.
The current adjustment screw (5) controls the spring pressure in the displacement valve (3). The current adjustment screw (5) changes the minimum current that is required to start destroking the pump.
The high pressure cutoff valve (4) controls the maximum pressure in the fan drive system. The high pressure cutoff valve (4) controls the flow of pump output pressure to the actuator piston (15). When system pressure is at the maximum, the high pressure cutoff valve (4) sends oil to the actuator piston (15). The actuator piston (15) moves the swashplate (8) to the position of minimum flow.