374D Excavator Hydraulic System Fan Pump (Hydraulic and Radiator Cooling) Caterpillar

Fan pump (3) drives the separate cooling system. The fan pump is a variable displacement piston pump. The fan pump is mechanically connected to the swing pump and the pilot pump and the pump is mechanically driven by the engine. The oil delivery from the fan pump flows to the fan motor in order to cool the hydraulic oil in the hydraulic oil cooler, the engine coolant in the radiator, and the air conditioner condenser.

Hydraulic oil is drawn into the fan pump through suction hose (1) at the rear of the pump. High-pressure oil to the fan motor flows through delivery line (4) at the front of the pump. Case drain oil from the fan pump is directed to the case drain filters through the case drain line (5). Case drain line (5) is located behind the pump delivery port.

As the oil temperature or the coolant temperature varies, an electrical signal is sent from the machine ECM to proportional reducing valve. The proportional reducing valve on control valve (2) directs pressure for control of the fan pump swashplate. The operation of control valve (2) causes the output flow of the cooling pump to increase or to decrease. The rotational speed of the fan motor is varied accordingly to the output flow of the fan pump.

Cooling Fan Operation

Maximum Fan Speed

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Illustration 2	g02162220
Fan system at maximum fan speed (1) Hydraulic oil temperature sensor (2) Intake manifold air temperature sensor (3) Engine coolant temperature sensor (4) Engine ECM (5) Machine ECM (6) Makeup valve (7) Fan motor (8) Return filter (9) Proportional fan pump control solenoid (10) Orifice (11) Orifice (12) Passage (13) Pump flow control spool (14) Orifice (15) Large actuator piston (16) Small actuator piston (17) Fan pump (18) Swashplate

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Illustration 3	g02162221
Fan system at maximum fan speed (9) Proportional fan pump control solenoid (10) Orifice (11) Orifice (12) Passage (13) Pump flow control spool (14) Orifice (15) Large actuator piston (16) Small actuator piston (18) Swashplate (19) PWM signal (20) Springs (21) Spring (22) Pressure control spool (23) Bias spring (24) Piston and barrel assembly

The hydraulic cooling fan is part of the hydraulic system and is controlled by the Machine ECM (5). The intake manifold air temperature sensor (2) and the coolant temperature sensor (3) are inputs into the Engine ECM (4). Engine ECM (4) shares this temperature information with the Machine ECM (5) through the Cat Data Link. The Machine ECM also receives information from the hydraulic oil temperature sensor (1). Machine ECM (4) software evaluates these three temperature sensor inputs for controlling the fan.

A target speed for the cooling fan is assigned for each engine speed based on the output of the various temperature sensors. The Machine ECM (5) sends a PWM signal to the proportional fan pump control solenoid (6) to regulate the oil flow from the pump. The pump oil flow is directed to the fan motor (9) to cause rotation of the motor and attached fan blade. This rotation will pull air through the radiator and cooler cores.

When the solenoid is ENERGIZED with minimum signal (19), the pressure control spool (22) is only moved slightly. This downward spool movement blocks most of the pump output oil in the pump flow control spool (13) spring chamber from draining to tank through the case drain passage. This action also causes the pump flow control spool spring chamber to become pressurized. In this condition, the force of springs (20) at the top of pump flow control spool (13) and the pressure of the oil, is greater than the oil pressure at the bottom of pump flow control spool (13).

This will cause the pump flow control spool (13) to be held DOWN and block pump output oil from entering signal passage (12) to the large actuator piston (15) in the pump. The large actuator piston (15) is open to case drain around both the pump pressure control spool (13) and the pump flow control spool (22). Small actuator piston (16) and bias spring (23) to keep the pump UPSTROKED. With the pump in the UPSTROKED condition, maximum oil flow is sent to fan motor (17), resulting in maximum fan speed.

Makeup valve (6) for fan motor (7) is used to prevent cavitation when the machine is shut down and flow from the fan pump stops. The momentum of the fan blade will continue to rotate the fan motor, which can cause the fan motor to cavitate without the makeup valve.

Minimum Fan Speed

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Illustration 4	g02163595
Fan system at minimum fan speed (1) Hydraulic oil temperature sensor (2) Intake manifold air temperature sensor (3) Engine coolant temperature sensor (4) Engine ECM (5) Machine ECM (6) Makeup valve (7) Fan motor (8) Return filter (9) Proportional fan pump control solenoid (10) Orifice (11) Orifice (12) Passage (13) Pump flow control spool (14) Orifice (15) Large actuator piston (16) Small actuator piston (17) Fan pump (18) Swashplate

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Illustration 5	g02163596
Fan system at minimum fan speed (9) Proportional fan pump control solenoid (10) Orifice (11) Orifice (12) Passage (13) Pump flow control spool (14) Orifice (15) Large actuator piston (16) Small actuator piston (18) Swashplate (19) PWM signal (20) Springs (21) Spring (22) Pressure control spool (23) Bias spring (24) Piston and barrel assembly

Machine ECM (5) sends the MAXIMUM PWM signal (19) to energize proportional fan pump control solenoid (9) to reduce pump oil flow. This signal causes the solenoid to push pressure control spool (22) DOWN. This movement will compress spring (21) and unseat the valve to allow oil to drain to tank through the case drain passage. Oil is also drained from the spring chamber above pump flow control spool (13). These two pressure chambers are connected through internal passages in the control valve body. This condition creates a pressure drop across orifice (14) at the top of pump flow control spool (13). The pump output pressure at the bottom of flow control spool (13) is now greater than the combined forces of springs (20) and the reduced pressure in the spring chamber above the pump flow control spool (13). The pump output pressure pushes pump flow control spool (13) UP. This action closes the case drain passage from large actuator and allows pump supply oil to flow through the signal passage (12) to large actuator piston (15) .

The flow of oil to the large actuator (15) causes an increase in pressure at the large actuator piston. The large actuator (15) overcomes the combined forces of bias spring (23) and small actuator (16) to move the swashplate toward minimum angle. The decrease in pump flow to fan motor (7) causes the fan speed to decrease.