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| Illustration 1 | g00647636 |
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Hydraulic Schematic for the Propel System (1) Control piston. (2) Axle propulsion motor. (3) Return line. (4) Parking brakes. (5) Shift valve. (6) Line from fan motor. (7) Line from steering metering pump. (8) Propel charge filter. (9) Shift spools. (10) Drum drive motor. (11) Flushing valves. (12) Reverse return lines. (13) Charge oil line. (14) Manual displacement control valves. (15) Servo valves. (16) Brake interlock valve. (17) Pressure override relief valve. (18) Drum propel pump. (19) Charge relief valve. (20) Charge check valves. (21) Charge check valves. (22) Forward multifunction valves. (23) Reverse multifunction valves. (24) Balance lines. (25) Axle propulsion pump. (26) Oil cooler. (27) Hydraulic oil tank. (28) Thermal bypass valve. (29) Return manifold. | |
Parking Brake On Neutral Position
When you run the engine, the propel pumps (18) and (25) are turning. The secondary oil flow from the fan motor (6) and steering metering pump (7) provides charge oil for the propel pumps. The maximum charge oil pressure in neutral is controlled by the two charge relief valves (19) in the propel pumps. The charge relief valve for the axle is set higher than the charge relief valve for the drum. The relief valve for the axle should not operate.
The charge oil provides makeup oil and charge pressure for the following functions:
- Replenish the propel pump and the motor leakage.
- cooling for the propel pump and motor
- moving the servo piston for the propel pump
- releasing the parking brakes.
- shift the motor displacement for high speed and low speed.
In neutral, the manual displacement control valves (14) are in the center position. The charge oil is blocked. The charge oil is blocked to the manual displacement control valve. The control lines that go to the pump servo valves (15) are open to the tank. There is equal pressure on both sides of the swashplates creating a neutral position. The propel pumps will be at zero displacement.
When the parking brake is applied, the interlock solenoids (16) for the brakes (4) are not energized. In this position, the springs in the parking brakes are applied. The charge oil that goes to the manual displacement valves is directed back to the tank. In this condition, the machine will not move even if the propel lever is moved.
Low Speed in the Forward Drive Position
Forward movement of the propel control lever mechanically moves the directional control valve that is on the axle propel pump. The directional control valve on the axle propel pump is mechanically connected to the directional control valve on the drum propel pump. The mechanical connection allows the two propel pumps to be synchronized when the propel control lever is moved. This movement causes charge oil to flow through the bottom of the servo valves (15). The result is an increase in the angle of the swashplate of the propel pumps (18) and (25). High-pressure oil flows from the propel pumps and the oil goes to each of the propel motors (2) and (10). Low-pressure oil exits the motors and the oil returns to the propel pumps through return lines (3).
Charge check valve (20) closes when high-pressure oil is pumped through the high-pressure side of the closed loop. Charge check valve (21) opens to allow oil from the charge circuit to enter the return side of the closed loop. Opening the check valve compensates for internal leakage and the flushing valves (11) within the circuit.
High-pressure oil moves the shuttle valve spool that is inside flushing valves (11). Hot low-pressure oil flows from the flushing valves to the return manifold (29) and the thermal bypass valve (28) creating a cooling effect. This allows fresh charge oil to enter the low-pressure side of the closed loop through charge check valves (20).
POR valves (17) sense the pressure in the high-pressure side of the closed loop. When the pressure in the line reaches
Multifunction valves (22) and (23) protect the system from sudden high-pressure spikes. When the system pressure reaches
Oil from the case of the propel pumps and the propel motors flows to the return manifold. Then, the oil is directed to the thermal bypass valve (28) and the oil flows to the oil cooler (26) or the hydraulic oil tank (27).
When the speed selector switch on the control console is in the LOW SPEED position, shift valve (5) is not energized. In the LOW SPEED position, the shift spools (9) in each propel motor are open to the tank. Each propel motor is at the maximum displacement position.
High Speed in the Reverse Drive Position
Rearward movement of the propel control lever mechanically moves the directional control valve that is for the axle propel pump. The directional control valve on the axle propel pump is mechanically connected to the directional control valve on the drum propel pump. The mechanical connection allows the two propel pumps to be synchronized when the propel control lever is moved. This movement causes charge oil to flow through the bottom of the servo valves (15). The result is an increase in the angle of the swashplate of the propel pumps (18) and (25).High-pressure oil flows from the propel pumps and the oil goes to each of the propel motors (2) and (10). Low-pressure oil exits the motors and the oil returns to the propel pumps through return lines (12).
Charge check valve (21) closes when high-pressure oil is pumped through the high-pressure side of the closed loop. Charge check valve (20) opens to allow oil from the charge circuit to enter the return side of the closed loop. This compensates for internal leakage and the flushing valves within the circuit.
High-pressure oil moves the shuttle valve spool that is inside flushing valve (28). Hot low-pressure oil flows from the flushing valves (11) to the return manifold (29) and the thermal bypass valve (28) creating a cooling effect. This allows fresh charge oil to enter the low-pressure side of the closed loop through charge check valves (21).
POR valves (17) sense the pressure in the high-pressure side of the closed loop. When the pressure in the line reaches
Multifunction valves (22) and (23) protect the system from sudden high-pressure spikes. When the system pressure reaches
Oil from the case of the propel pumps and the propel motors flows to the return manifold. Then, the oil is directed to the thermal bypass valve (28) and the oil flows to the oil cooler (26) or the hydraulic oil tank (27).
When the speed selector switch on the control console is in the HIGH SPEED position, shift valve (5) is energized. In this position, the shift spools (9) in each propel motor are open to charge pressure. Each propel motor is at the minimum displacement position.