The engine ECM adjusts pump output by varying the amount of signal current that is sent to the solenoid on the pump control valve. Maximum signal current is a command for minimum calibrated fan speed and the pump output pressure will be a lower value. Minimum signal current is a command for maximum calibrated fan speed and the pump output will be a higher value. No signal current will produce the maximum mechanical pump pressure and a high fan speed will be the result.
| |
| Illustration 1 | g02444546 |
|
Fan Pump and Control Valve (Maximum Speed) (1) Actuator piston (2) Swashplate (3) Bias spring (4) Drive shaft (5) Fan pump (6) Piston and barrel assembly (7) Case drain passage (8) Output to fan motor (9) Pin (10) Plunger (11) Spring (12) Solenoid (13) Adjustment screw (14) Spring (15) Orifice (16) Signal passage (17) Pump control spool (18) Pressure control spool (19) Adjustment screw (20) Pump control valve (BB) Cutaway section (CC) Component surface (FF) Activated components (GG) Tank pressure (JJ) High pressure | |
When maximum fan speed is required, the engine ECM sends minimum signal current to solenoid (12). Plunger (10) blocks signal passage (16). The force of spring (14) plus the signal pressure holds pump control spool (17) downward.
When pump control spool (17) is held downward, the passage to actuator piston (1) is open to the case drain. The force of bias spring (3) moves swashplate (2) toward the maximum angle.
The pistons travel in and out of the barrel at increasing distances which increase flow and fan motor speed. Fan speed continues to increase until the resistance from the fan drive motor creates enough pressure for the force exerted on pressure control spool (18) to exceed the force from spring (11) or swash plate (2) reaches the maximum angle.
Pressure control spool (18) limits the maximum pressure of the oil that flows to the fan motor through output (8). If the output pressure overcomes spring (11), the pressure control spool moves upward. High-pressure oil is allowed to flow to actuator piston (1). The pump destrokes.
| |
| Illustration 2 | g02444716 |
|
Fan Pump and Control Valve (Minimum Fan Speed) (1) Actuator piston (2) Swashplate (3) Bias spring (4) Drive shaft (5) Fan pump (6) Piston and barrel assembly (7) Case drain passage (8) Output to fan motor (9) Pin (10) Plunger (11) Spring (12) Solenoid (13) Adjustment screw (14) Spring (15) Orifice (16) Signal passage (17) Pump control spool (18) Pressure control spool (19) Adjustment screw (20) Pump control valve (BB) Cutaway section (CC) Component surface (FF) Activated components (GG) Tank pressure (KK) First pressure reduction (LL) Second pressure reduction | |
When the engine is first started or when the machine is working in a cold climate, the required fan speed for cooling is low. Maximum signal current is sent to solenoid (12).
When a slower fan speed is required, the engine ECM increases the signal current to solenoid (12). Pin (9) pushes plunger (10) downward against spring (11). When the plunger moves downward, signal passage (16) is opened to the case drain. The pressure at the top of pump control spool (17) lowers. The pressure at the bottom of the pump control spool overcomes the force of spring (14). The spool shifts upward which allows pressurized oil to flow to actuator piston (1).
When oil flows into actuator piston (1), the force of bias spring (3) is overcome. Swashplate (2) moves toward the minimum angle until equilibrium is reached between the pressure in the actuator piston and the force of the bias spring.
The pistons travel in and out of the barrel for a shorter distance. The cylinders fill to a smaller amount. A decreased amount of oil flows through output (8) to the fan motor. The decreased amount of oil flow to the fan motor causes the fan to rotate at a slower speed.
Components of the Fan Pump and Control Valve
Actuator Piston (1) - When the pressure of the oil increases behind the actuator piston, the piston overcomes the force of bias spring (3). When bias spring (3) is compressed, the angle of swashplate (2) is reduced.
Swashplate (2) - The angle of the swashplate controls the displacement of the pump. When the swashplate is at a maximum angle, the pistons move the maximum volume of oil in and out of the rotating barrel.
Bias Spring (3) - When oil acts on actuator piston (1), the angle of swashplate (2) is decreased. When there is no oil pressure at the actuator piston, the bias spring holds the swashplate at the maximum angle.
Drive Shaft (4) - The rotation of the pump is clockwise when the pump is viewed from the drive end. The piston and barrel assembly (6) is splined to the drive shaft. The piston and barrel assembly rotate when the drive shaft rotates.
Piston and Barrel Assembly (6) - The barrel contains nine pistons. The piston and barrel assembly rotate whenever the engine is running. The pistons move oil into the barrel and out of the barrel.
Case Drain Passage (7) - When solenoid (12) is de-energized, the oil at the top of actuator piston (1) flows around pressure control spool (18) and pump control spool (17). The oil then travels through case drain passage (7) to the hydraulic oil tank.
Output to Fan Motor (8) - When the piston and barrel rotate, pressurized oil flows to the fan motor from the output to the fan motor.
Pin (9) - This pin is part of solenoid (12). When the solenoid is energized, the pin pushes plunger (10).
Plunger (10) - Pin (9) pushes plunger (10) downward when solenoid (12) is energized.
Spring (11) - This spring reacts against pressure control spool (18) in response to plunger (10) moving downward.
Solenoid (12) - The solenoid receives input current from the engine ECM. When the solenoid receives maximum input current, pin (9) moves plunger (10) downward to the maximum distance. When minimum current is sent to the solenoid, spring (11) pushes plunger (10) fully upward.
Adjustment Screw (13) - The adjustment screw is used to either increase or decrease the spring pressure against pump control spool (17). Adjusting the screw modifies the low-pressure standby of the pump.
Spring (14) - This spring and the load sensing signal pushes pump control spool (17) downward. When some of the oil from the load sensing signal is allowed to flow around plunger (10), the pressure on the other side of the pump control spool becomes greater than the sum of the force of the spring and the pressure from the load sensing signal. The pump control spool moves upward.
Orifice (15) - This orifice allows some of the oil from the pump output to flow through pump control spool (17). This oil then flows through signal passage (16).
Signal Passage (16) - The signal passage allows oil to drain from the top side of pump control spool (17) to case drain passage (7). Draining the oil allows the pump control spool to move upward.
Pump Control Spool (17) - The load sensing signal and spring (14) apply pressure on the top of the pump control spool. Pump output pressure acts on the bottom of the pump control spool. The pump control spool shifts upward in order to allow oil to flow to actuator piston (1).
Pressure Control Spool (18) - The pressure control spool limits the maximum pressure of the output oil to the fan motor. When pump output pressure is high enough to overcome the force of spring (11), the pressure control spool moves upward. High-pressure oil flows to actuator piston (1). The angle of the swashplate is reduced and the pump destrokes.
Adjustment Screw (19) - This adjustment screw is used to adjust the tension on spring (11). Increased tension on the spring causes plunger (10) to move less when the plunger is pushed by pin (9). Adjusting the screw modifies the high-pressure cutoff of the pump.