PM620, PM622, PM820, PM822 and PM825 Cold Planer Machine System Caterpillar

Illustration 1	g06259835
Fan System Hydraulic Schematic (1) Fan pump (2) Direction control valve (3) Speed control valve (4) Oil temperature sensor (5) Case drain E (6) Case drain C (7) Case drain B (8) Case drain A (9) Thermal bypass manifold (10) Case drain T1 (11) Servo piston (12) Reverse makeup and relief valve (13) Forward makeup and relief valve (14) From charge manifold (15) POR valve (16) Fan motor (17) Flushing spool (18) Flushing relief valve (19) Hydraulic oil cooler (20) Hydraulic tank

When the engine is running, fan pump (1) rotates. The fan pump receives charge oil from charge manifold (14) at port"G1". Inside the pump, charge oil flows to the following:

• Direction control valve (2)

• Speed control valve (3)

• Servo piston (11)

• Reverse makeup and relief valve (12)

• Forward makeup and relief valve (13)

• Pressure Override Valve (POR) valve (15)

Direction control valve (2) is not utilized in this application. Therefore, the valve remains in the default position and directs charge oil to the forward chamber of servo piston (11). The charge oil causes the servo piston to shift, changing the angle of the swashplate in the fan pump (1). This action causes the pump to generate flow in the forward circuit.

The charge pressure maintained on servo piston (11) acts against an opposing spring. The balance of charge pressure and spring force determines swashplate angle and the output of fan pump (1). Speed control valve (3) meters the charge pressure in the servo circuit. Therefore, the speed control valve controls the swashplate angle of the fan pump.

Speed control valve (3) is controlled by the speed control solenoid. This valve is closed when the solenoid is not energized. As the signal increases to the solenoid, the valve opens proportionally to a set value. As the speed control valve opens, a portion of charge pressure is used as pilot pressure for POR valve (15).

When speed control valve (3) is closed, full charge pressure acts on servo piston (11). In this case, maximum output of the pump is generated, and fan motor (16) runs at maximum speed. As the speed control valve opens, a corresponding reduction in charge pressure reduces the servo piston pressure. Therefore, the output of the pump is proportional to the signal of the speed control solenoid.

Note: During engine start-up, speed control valve (3) is fully energized. In this case, the output of fan pump (1) is minimized. This action reduces the parasitic load on the engine for ease of starting.

The pilot pressure and a spring act to control speed control valve (3) against the set value of the solenoid signal. When no signal is applied to the solenoid, the pilot pressure is purged to tank pressure. As the speed control valve opens, pilot pressure increases.

POR valve (15) has a dual function purpose. First, the valve acts as a progressive control for the pump servo circuit. Second, the valve limits maximum working pressure. To control the pump servo circuit, the POR valve control spool shifts proportionate to the combined pilot pressure and system pressure in the high-pressure circuit. This action controls pressure in the servo control circuit.

As the POR valve opens, a portion of servo piston pressure is purged into the case of fan pump (1). In this case, the servo piston moves the swashplate toward the minimum output position, and the fan operates at less speed.

Therefore, the signal sent to the speed control solenoid indirectly controls the position of the spool in POR valve (15). This pump control system allows fan pump (1) to operate more smoothly, and also allows the pump to compensate for varying operating conditions.

POR valve (15) also functions to limit the maximum working pressure in the forward high-pressure circuit of the fan system. If the forward circuit reaches 30000 1000 kPa (4351 145 psi), the POR valve opens to reduce the servo control pressure. This action causes the servo piston to move the swashplate toward the minimum output position. The POR valve modulates the control pressure to keep the high-pressure circuit working pressure at this value until the load drops in the system.

Makeup and relief valves (12) and (13) inside fan pump (1) consist of a makeup check valve and a relief valve. The makeup valve allows charge oil to fill the fan circuit when pressure in the reverse circuit falls below charge pressure. The makeup valve also replenishes the system for normal leakage that occurs in the fan circuit. The relief valve protects the forward circuit during operation of the fan system. If the high-pressure circuit exceeds 32500 1000 kPa (4713 145 psi), the relief valve opens. This action directs high-pressure oil into the charge circuit and the reverse circuit.

Note: The high-pressure relief function of the forward makeup and relief valve (13) cannot divert full pump flow into the low-pressure circuit. However, this valve reduces pressure in the circuit faster than the relief section of the POR valve. Therefore, the relief section of the makeup and relief valve removes pressure peaks in the system. The relief section of the POR valve serves as the main relief for the high-pressure circuit.

When the fan is operating, high-pressure oil is directed out port"A" of fan pump (1). This oil flow is plumbed to port"B" of fan motor (16). The pressure in the forward circuit is measured at port"MA" of the fan pump.

Inside fan motor (16), high-pressure oil in the forward circuit rotates the motor. This oil also acts on one end of flushing spool (17). After turning the motor, the pressure of the circuit oil is reduced. Oil at a reduced pressure then flows to the opposite end of the flushing spool before returning to fan pump (1). The fan circuit is then complete.

The high-pressure circuit oil acting on flushing spool (17) causes the spool to shift. This shift allows return oil from the circuit to act on the flushing relief valve (18). When the return pressure is greater than the setting of the flushing relief valve, the flushing relief valve opens. When the flushing relief valve opens, a portion of oil flows from the return circuit into the motor case drain for lubrication and cooling purposes. Flushing oil from the motor case drain flows to port"E" of thermal bypass manifold (9).

Thermal bypass manifold (9) receives case drain oil from other various systems. Refer to the current hydraulic schematic for details of case drain port connections (5), (6), (7), (8), and (10).

During normal operation, thermal bypass manifold (9) controls hydraulic oil flow to hydraulic oil cooler (19). The bypass manifold contains a combination relief check valve and bypass spool.

If oil flow through hydraulic oil cooler (19) becomes blocked, the relief check valve in thermal bypass manifold (9) protects the cooling circuit. The valve limits return pressure to 200 kPa (29 psi).

The bypass spool of thermal bypass manifold (9) senses hydraulic oil temperature. When the oil is cold, the spool is open, and oil flow bypasses hydraulic oil cooler (19). When the oil temperature reaches 45 °C (113 °F), the bypass spool begins to close. In this case, a portion of oil is directed to the oil cooler. When the oil temperature reaches 55 °C (131 °F), the bypass spool is closed. In this case, all oil flow is directed to the hydraulic oil cooler.