BLOCK 1073785 - Caterpillar

Illustration 1 g06266641
Fan Drive Hydraulic System
(1) Makeup valve
(2) Passage to charge filter
(3) Fan solenoid
(4) Steering pump
(5) Passage to steering control unit
(6) Fan motor
(7) Control spool
(8) Orifice
(9) Charge pump
(10) Suction strainer
(11) Hydraulic tankWhen the engine is operating, charge pump (9) and steering pump (4) draw oil from hydraulic tank (11) through suction strainer (10). Supply from the charge pump is sent to fan motor (6).Inside fan motor (6) supply oil splits into four branches. One branch flows to the gears of the fan motor. The second branch seats makeup valve (1). The third branch flows to control spool (7). The fourth branch flows through orifice (8) and to fan solenoid (3). Supply oil acts on one side of the control spool. The oil downstream from the orifice acts on the opposite side of the control spool with a spring.Fan solenoid (3) and control spool (7) determine the amount of supply oil that flows through fan motor (6). If the fan solenoid is not energized, the fan solenoid blocks supply oil. In this case, the pressure on either side of orifice (8) is equal. When no oil is flowing across the orifice, the spring closes the passage across the control spool. Under these conditions, full supply flow is directed through the fan motor, and the fan operates at the highest speed.Note: During normal operation, fan solenoid (3) will always be energized to some degree.When fan solenoid (3) is energized, some pump supply oil flows across the spool of the fan solenoid. The amount of oil that flows across the solenoid depends on the magnetic field created by the fan solenoid. As the signal strength to the solenoid increases, the magnetic field increases, and the flow across the spool of the solenoid increases.Flow across fan solenoid (3) causes oil to flow through orifice (8). Oil flow through the orifice results in a lower pressure on the downstream side of the orifice. In this case, the pressure differential on either side of control spool (7) allows the spool to shift. This shift allows additional pump supply oil to bypass the fan motor. The speed of the fan motor depends on the position of the fan solenoid and the position of the control spool.