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| Illustration 1 | g03271236 |
Propel Hydraulic Schematic NEUTRAL (1) Front right propel motor (2) Parking brake (3) Flushing spool (4) Flushing relief valve (5) Forward solenoid "1" (6) Interlock valve (7) Forward solenoid "2" (8) Rear right propel motor (9) Parking brake (10) Flushing spool (11) Flushing relief valve (12) Reverse solenoid "1" (13) Propel pump (14) Forward combination valve (15) Reverse combination valve (16) Parking brake (17) Front left propel motor (18) Flushing spool (19) Flushing relief valve (20) Pump rotating group (21) Servo piston (22) Charge relief valve (23) Servo piston (24) Pump rotating group (25) Parking brake (26) Rear left propel motor (27) Flushing spool (28) Flushing relief valve (29) Manual brake release pump (30) Forward combination valve (31) Oil cooler (32) Return manifold (33) Reverse combination valve (34) Reverse solenoid "2" (35) From fan motor (36) Charge filter | |
The above illustration shows the propel hydraulic system under the following conditions:
- The propel lever is in the NEUTRAL position.
- The parking brake switch is in the ON position.
The propel circuit consists of two hydrostatic drive circuits. One circuit drives the front right propel motor and the rear left propel motor. The second circuit drives the front left propel motor and the rear right propel motor. Each closed loop circuit has a rotating group inside the single pump. Each circuit also has two motors.
The fan system provides charge oil to the propel system when the engine is running. Charge oil from front charge filter (36) flows to port "E" of propel pump (13). Inside the propel pump, charge oil flows to interlock valve (6) and to charge relief valve (22).
Charge pressure acts on charge relief valve (22). When charge pressure reaches 3000 ± 300 kPa (435 ± 45 psi), the oil pressure overcomes the spring force and the charge relief valve opens. This action directs charge pump flow into the case drain.
Charge pressure acts against the makeup valves in each combination valve (14), (15), (30), and (33). If the pressure in either side of either loop falls below charge pressure, the corresponding makeup valve opens. In this case, charge oil flows into the loop.
When the parking brake switch is in the ON position or the machine ECM number one has disabled the propel system, solenoid in interlock valve (6) is not energized. This solenoid prevents charge oil from reaching the pump control solenoids and from reaching the parking brake piston cavities. Under these conditions, the brake piston cavities and both sides of servo pistons (21) and (23) are open to the pump case. The servo piston holds the swashplate in the rotating group at zero angle. The springs that are acting against the brake pistons engage the parking brakes.
Since the pressure in each loop is equal when the propel system is not operating, flushing spool (3), (10), (18), and (27) in each propel motor is in the center position. In this case, the spool prevents flushing oil from flowing into the case drains of the motors.
Pressure in the forward circuits can be measured at the pressure tap in port "MB" and the pressure tap in port "MD" of the propel pump. Reverse pressures can be measured at the pressure tap in port "MA" and the pressure tap in port "MC" of the propel pump.
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| Illustration 2 | g03271237 |
Hydraulic Schematic FORWARD (1) Front right propel motor (2) Parking brake (3) Flushing spool (4) Flushing relief valve (5) Forward solenoid "1" (6) Interlock valve (7) Forward solenoid "2" (8) Rear right propel motor (9) Parking brake (10) Flushing spool (11) Flushing relief valve (12) Reverse solenoid "1" (13) Propel pump (14) Forward combination valve (15) Reverse combination valve (16) Parking brake (17) Front left propel motor (18) Flushing spool (19) Flushing relief valve (20) Pump rotating group (21) Servo piston (22) Charge relief valve (23) Servo piston (24) Pump rotating group (25) Parking brake (26) Rear left propel motor (27) Flushing spool (28) Flushing relief valve (29) Manual brake release pump (30) Forward combination valve (31) Oil cooler (32) Return manifold (33) Reverse combination valve (34) Reverse solenoid "2" (35) From fan motor (36) Charge filter | |
The above illustration shows the propel hydraulic system under the following conditions:
- The parking brake switch is in the OFF position.
- The propel lever is in the FORWARD range with the operator station facing the front of the machine or the propel lever is in the REVERSE range with the operator station facing the rear of the machine.
Interlock valve (6) is energized when the machine ECM number one determines that the parking brake should be released. When this solenoid operated valve is energized, charge oil is available at pump control solenoids (5), (7), (12), and (34).
Displacement of rotating groups (20) and (24) in the pump is electronically controlled. The machine ECM number one calculates the desired speed and energizes the appropriate pump control solenoid in order to move the machine at the desired speed. When the propel lever is in the FORWARD position, forward solenoid "1" (5) and forward solenoid "2" (7) are energized. Each forward solenoid causes the corresponding direction control spool to shift, allowing charge oil to act against the servo pistons. The pressure in the servo piston causes the pump servo to move. This movement changes the angle of the swashplate in the corresponding rotating group. The stronger the signal to the solenoid, the greater the swashplate angle, and therefore, the greater the oil flow out of the corresponding section of the propel pump.
As a swashplate moves, the feedback linkage tends to move the pump solenoid spool back to neutral through an internal feedback spring. This action prevents the servo piston from tilting the swashplate too far.
Supply oil from rotating groups (20) and (24) flows to the following locations:
- Forward combination valve (14)
- Forward combination valve (30)
- Port "A" of front right propel motor (1)
- Port "B" of rear left propel motor (26)
- Port "A" of rear right propel motor (8)
- Port "B" of front left propel motor (17)
The pressure differential between the two sides of each propel motor causes the motor to turn. After turning each motor, oil at a reduced pressure flows back to return loop of propel pump (13) .
Inside propel pump (13), supply oil from rotating groups (20) and (24) acts against the relief valve in forward combination valve (14) and (30). As long as the supply pressure is greater than charge pressure, the makeup valve in the combination valve remains seated. As long as the supply pressure is less than relief pressure, the relief valve in the combination valve remains closed.
If pressure in the return side of either loop falls below charge pressure, the makeup valve in corresponding reverse combination valves (15) or (33) opens. In this case, charge oil flows into the low-pressure side of the loop. When pressure in the low-pressure side of the loop rises above charge pressure, the makeup valve closes.
Loop flushing occurs in each propel motor. In the motor, oil in the high-pressure side of the circuit acts against one side of the flushing spool. Oil in the low-pressure side of the circuit acts against the opposite side of the flushing spool. The higher pressure oil moves the flushing spool. This movement allows oil from the low-pressure side of the circuit to flow across the spool to the flushing relief valve.
Any time the pressure in the low-pressure side of the circuit is greater than the setting of the flushing relief valve, the flushing relief valve opens. In this case, oil from the low-pressure circuit flows through an orifice and into the motor case drain line.
The pressure setting of the flushing relief valve is less than the pressure setting of charge relief valve (22). This fact ensures that oil is sent through the motor case drain under normal operating conditions. The flushing relief valve will stop flow if the charge pressure is less than the setting of the flushing relief valve. This fact ensures that flow through the flushing orifice does not cause charge pressure to decrease to the point at which charge pressure becomes less than the brake release requirement in the propel hydraulic circuit.