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| Illustration 1 | g03863253 |
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(1) Reversing solenoid
(2) Pressure reducing solenoid (3) Pressure override valve (4) Crossover relief and makeup valves | |
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| Illustration 2 | g03863437 |
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(5) Charge oil inlet line
(6) Closed loop line to the fan motor (7) Closed loop line to the fan motor (8) Case drain and flushing flow outlet line | |
The hydraulic fan pump is a bidirectional variable displacement axial piston pump. The displacement of the pump and the direction of oil flow is controlled by the engine ECM.
The fan hydraulic pump has the following components:
POR valve (3) - When the pressure of the oil in the drive loop exceeds the pressure setting of the POR valve, the pressure will cause the pump to destroke.
Crossover relief and makeup valves (4) - The crossover relief valves relieve high-pressure spikes in the fan loop. Each valve also contains a makeup valve. The makeup valve allows charge oil to replenish the closed fan loop.
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| Illustration 3 | g03863486 |
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(9) Spring
(10) Passage from the actuator piston (11) Passage to pump case (12) Passage from the drive loop (13) Passage from the drive loop (14) Slug (15) Chamber (16) Piston (17) Valve | |
The POR valve limits the maximum pressure in both sides of the closed drive loop. When the valve opens, the valve drains oil from the actuator piston in the fan pump. As the actuator piston is drained, the centering springs in the actuator piston move the swashplate in order to reduce pump output.
Slug (14) serves as a resolver. Oil from the high-pressure side of the closed loop enters the POR valve through either passage (12) or passage (13). Slug (14) is moved left if the high pressure is in passage (13). Slug (14) is moved right if the high pressure is in passage (10). The high-pressure oil is sent to chamber (15).
When the pressure in chamber (15) is high enough to overcome spring (9), piston (16) and valve (17) move to the left against spring (9). The valve connects passage (10) to passage (11). The oil from the actuator piston is then allowed to drain to the pump case.
The pressure setting of the POR valve is adjustable.
Crossover Relief and Makeup Valve
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| Illustration 4 | g03863509 |
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(18) Passage from the drive loop
(19) Passage to charge the circuit (20) Spring (21) Spring (22) Valve (23) Chamber (24) Valve | |
A crossover relief and makeup valve is placed in each side of the closed drive loop. The crossover relief valves are designed to remove high-pressure spikes in the drive loops. Some charge oil is lost in the closed drive loop from leakage and flushing. The makeup valves allow charge oil to replenish the low-pressure side of the drive loop.
Oil from the drive loop enters the valve through passage (18). The oil flows into chamber (21). Valve (22) is held closed by spring (21).
The pressure of the oil in chamber (23) acts against valve (22). The force of spring (21) keeps valve (22) closed until oil pressure in the drive loop reaches the relief pressure.
When the force of the pressure of the oil in chamber (23) against valve (22) becomes greater than the force of spring (21), valve (22) opens to the right. The oil in chamber (23) flows around valve (22) to the drain.
When the pressure drops in chamber (23), only the force of spring (20) is acting against valve (24). The high pressure on the left side of valve (24) is greater than the force of spring (20). Valve (24) opens to the right. Oil from the drive loop can now go through passage (19) into the charge circuit.
The valve also acts as a makeup valve for the closed drive loop. When the pressure of the low-pressure side of the closed loop drops below charge pressure, charge oil in passage (19) opens valve (24). Oil from the charge circuit flows into the low-pressure side of the drive loop through passage (18). When the pressure in passage (18) and chamber (23) reaches charge pressure, the force of spring (20) closes valve (24).