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| Illustration 1 | g00635225 |
Hydraulic Schematic for the Propel System (1) Left propel motor (2) Right propel charge filter (3) Right electrical displacement control (EDC) (4) Right propel motor (5) Right flushing valve (6) Multifunction valves in right propel pump (7) Right propel pump (8) Case drain filter (9) Front return manifold (10) Suction manifold (11) Oil cooler bypass valve (12) Oil cooler (13) Hydraulic tank (14) Suction filter for the left propel pump (15) Suction filter for the right propel pump (16) Left propel pump (17) Left propel charge filter (18) Left electrical displacement control (EDC) (19) Multifunction valves in the left propel pump (20) Left flushing valve | |
When the engine is running, propel pumps (7) and (16) are rotating. The charge pumps in each propel pump provide charge oil for the propel system. Oil flows from hydraulic tank (13) to each charge pump. The oil flows from the charge pump through propel charge filters (2) and (17). In neutral, charge oil pressure is maintained by the charge relief valves and inside each propel pump.
Charge oil is used as makeup oil for the following functions: pump leakage, motor leakage, cooling for the pumps and motors and control oil for moving the pump swashplate.
Both pressure control pilot valves in the electrical displacement controls (3) and (18) are connected to the propel electronic control module. The pressure control pilot valve converts an electrical input signal to a hydraulic input signal in order to operate a servo valve that is spring centered. In neutral, the PCP valve places each EDC in the center position. Charge oil is blocked at the EDC. With equal pressure to either side of the swashplate control piston, the swashplates stay in neutral and there is no oil flow from the propel pumps. Charge oil goes through the check valves in the multifunction valves (6) and (19) and to the closed loop lines.
Charge oil also goes to both sides of the flushing valves (5) and (20) and the charge oil positions the flushing valves in the center. This blocks oil flow to the motor charge relief valves.
The direction of the swashplate angle of propel pumps (7) and (16) determines the direction of the machine travel (forward or reverse). When the system is in forward, propel pump (7) routes high pressure oil to the loop line for multifunction valve (6) and to propel motor (4). The high pressure oil acts against the pistons inside the propel motors in order to cause the output shafts to rotate.
High pressure oil causes flushing valves (5) and (20) to shift upward. When the flushing valves shift upward, the flushing valve blocks high pressure oil from entering the charge relief valve. The flushing valve opens the passage in order for low pressure oil in the loop line to enter the charge relief valve. Oil from the charge pump enters the low pressure loop line through the check valve in the multifunction valve. The charge pump is a fixed displacement pump. Excess oil flow that is not needed to makeup oil for leakage must flow through the charge relief valve. The oil flows from the charge relief valve through the motor case drain line and the return oil filter in hydraulic tank (13) .
Low pressure return oil from propel motor (4) flows back to propel pump (7) through the loop line. This completes the closed circuit. Low pressure return oil from propel motor (1) flows back to propel pump (16) through loop line. This completes the closed circuit.
When the system is in reverse, propel pump (7) pumps high pressure oil to the loop line for multifunction valve (6) and to propel motor (4). Propel pump (16) pumps high pressure oil to the loop line for multifunction valve (19) and to propel motor (1). The high pressure oil acts against the pistons inside the propel motors in order to cause the output shafts to rotate.
High pressure oil causes flushing valve (5) to shift downward. When the flushing valve shifts downward, the flushing valve blocks high pressure oil from the charge relief valve. The flushing valve opens the passage for low pressure oil to the charge relief valve. Oil from the charge pump enters low pressure loop line through the check valve in the multifunction valve. The oil flows from the charge relief valve to the return circuit and hydraulic tank (13) .
Low pressure return oil from propel motor (4) flows back to propel pump (7) through the loop line. This completes the closed circuit.
Multifunction valves (6) and (19) perform the following four functions: high pressure relief valve, system loop bypass, charge system check valve and system pressure limiter. System pressure is limited to approximately 2345 kPa (340 psi) below the main relief valve setting by the pressure limiter of the multifunction valve. When the system pressure reaches the pressure limiter setting, the pressure limiter routes oil to the servo valve. This causes the propel pump to destroke. The destroking of the pump reduces the pump output flow. This reduces the system pressure.
The multifunction valves within each propel pump are identical and interchangeable. In each propel pump, one multifunction valve controls the system when the machine is in forward operation. In each propel pump, the other multifunction valve controls the system when the machine is in reverse operation.
When the machine is in forward or reverse, the charge system pressure is lowered by the motor charge relief valve and the orifice. This causes the system pressure to be less than the pump charge relief setting in NEUTRAL.
The flushing valves provide a route for some of the hot hydraulic oil in order to return the oil to the hydraulic tank. In this way, cooler oil from the hydraulic tank is always introduced into the system.
The motor case drain line returns the oil to the propel pump. All the case drain oil from the propel pump is returned to the hydraulic tank.
If the machine becomes disabled due to an electrical failure, the manual override controls on the operator station can be used to move the machine. The manual override controls send a current to the pressure control pilot valve in order to electronically stroke the pump. This allows the machine to safely move to a proper area for repairs.