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| Illustration 1 | g06266352 |
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Propel Hydraulic Schematic NEUTRAL (1) Forward combination valve (2) Propel pump (3) Reverse solenoid (4) Forward solenoid (5) Interlock valve (6) Charge relief valve (7) Forward solenoid (8) Reverse solenoid (9) Reverse combination valve (10) Charge filter (11) Parking brake (12) Right rear propulsion motor (13) Right front propulsion motor (14) Parking brake (15) Front balance valve (16) Left front propulsion motor (17) Parking brake (18) Reverse combination valve (19) Pump rotating group (20) Servo piston (21) Return manifold (22) Oil cooler (23) Servo piston (24) Pump rotating group (25) Manual brake release pump (26) Two-speed valve (26) Rear propulsion motor (27) Forward combination valve (28) Parking brake (29) Left rear propulsion motor (30) Rear balance valve (31) From fan motor (32) Rear flushing valve (33) Front flushing valve | |
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 a hydrostatic-drive circuit. This closed-loop circuit contains pump rotating group (19) and (24) in propulsion pump (2). The propel circuit also consists of four motors; two front propulsion motors (13) and (16) and two rear propulsion motors (12) and (29).
Displacement of propel rotating group (19) and (24) is electronically controlled. The machine ECM calculates the desired speed and energizes the appropriate pump control solenoid to move the machine at the desired speed. When the propel lever is in the NEUTRAL position, the swashplate in the rotating groups is at zero angle. The swashplate is also at zero angle if the machine ECM has disabled the propel system. In either of these cases, the rotating groups do not produce flow.
The charge pump provides hydraulic oil to drive the fan system. Oil from fan motor (31) flows through charge filter (10) to provide charge oil to the propel system when the engine is running. Charge oil from the charge filter flows to port"E" of propulsion pump (2). Charge oil also flows to two-speed valve (26). Inside the propulsion hydraulic pump, charge oil flows to interlock valve (5).
Charge pressure acts on charge relief valve (6). When the differential pressure between pump supply and case pressure reaches
When the parking brake switch is in the ON position or the machine ECM has disabled the propel system, the interlock solenoid 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 each servo piston (20) and (23) are open to the pump case. The servo pistons hold swashplate in rotating group (19) and (24) at zero angle. The springs that are acting against the brake pistons engage front parking brakes (14) and (17) and rear parking brakes (11) and (28).
As long as interlock solenoid (5) is not energized, swashplate in rotating group (19) and (24) remains in the zero angle position. In this case, charge pressure is blocked at the interlock valve and the servo chambers of the pumps are vented to the pump case. These conditions are maintained, regardless of the position of the propel lever.
Charge pressure acts against the makeup valves in each combination valve. If the pressure in either the forward loop or the reverse loop falls below charge pressure, the makeup valves open. In this case, charge oil flows into the loop.
Pressure in the forward circuit can be measured at the pressure tap in port "MB" and "MB"of propulsion pump (2). Reverse pressure can be measured at the pressure tap in port "MA" and "MC" of the pump.
When the machine is not moving, the pressure in the forward circuit is equal to the pressure in the reverse circuit. In this case, the flushing spools in flushing valves (32) and (33) are in the center position. The spool prevents flushing oil from flowing into the case drain of the motors.
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| Illustration 2 | g06266357 |
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Hydraulic Schematic FORWARD (1) Forward combination valve (2) Propel pump (3) Reverse solenoid (4) Forward solenoid (5) Interlock valve (6) Charge relief valve (7) Forward solenoid (8) Reverse solenoid (9) Reverse combination valve (10) Charge filter (11) Parking brake (12) Right rear propulsion motor (13) Right front propulsion motor (14) Parking brake (15) Front balance valve (16) Left front propulsion motor (17) Parking brake (18) Reverse combination valve (19) Pump rotating group (20) Servo piston (21) Return manifold (22) Oil cooler (23) Servo piston (24) Pump rotating group (25) Manual brake release pump (26) Two-speed valve (26) Rear propulsion motor (27) Forward combination valve (28) Parking brake (29) Left rear motor (30) Rear balance valve (31) From fan motor (32) Rear flushing valve (33) Front flushing valve | |
The above illustration shows the propel hydraulic system under the following conditions:
- The parking brake switch is in the OFF position.
- The propel mode is set to low.
- The propel lever is in the forward range with the operator station facing the front of the machine.
- The propel lever is in the reverse range with the operator station facing the rear of the machine.
Charge oil flows to forward combination valves (1) and (27), reverse combination valve (9) and (18) and interlock valve (5). With the parking brake switch in the OFF position, the interlock valve directs charge oil into the piston cavity of the parking brakes. The charge pressure in the brake piston cavities overcomes the spring force, and the parking brakes release. At the same time, charge oil is also routed to propulsion pump (2) control spools.
When the propel mode is set to low, the two-speed valve (26) is not energized. In this case, the shift spools in front propulsion motors (13) and (16) are open to the return side of the propel loop. In this case, the front propulsion motors operate at low speed and full torque.
When the machine ECM determines that the machine should be moving forward, ECM energizes forward solenoid (4) and (7). In this case, the solenoid directs charge oil into the forward side of servo piston (20) and (23). The pressure in the forward side of the servo pistons cause the pump servos to move. This movement changes the angle of the swashplate in pump rotating group (19) and (24). The stronger the signal to the solenoids, the greater the swashplate angle, and therefore, the greater the oil flow from propulsion pump (2).
Supply oil from pump rotating group (19) flows to the following locations:
- Forward combination valve (1)
- Port "MD" on propulsion pump (2)
- Port "D" of front balance valve (15)
- Port "1" of flushing valve (33)
Front balance valve (15) directs forward supply oil from pump rotating group (19) to the following locations:
- The forward side of right front propulsion motor (13)
- The forward side of left front propulsion motor (16)
At the same time, supply oil from pump rotating group (24) flows to the following locations:
- Port "MB" on propulsion pump (2)
- Reverse combination valve (7)
- Port "B" of rear balance valve (30)
- Port "2" of flushing valve (32)
Rear balance valve (30) directs forward supply oil from pump rotating group (24) to the following locations:
- The forward side of right rear propulsion motor (12)
- The forward side of left rear propulsion motor (29)
The pressure differential between the forward and reverse sides of the front and rear propulsion motors causes the motors to turn. After turning the motors, oil at a reduced pressure flows to the following locations:
- The reverse side of rotating group (19) and (24)
- Port "MA" and port "MC" on propulsion pump (2)
Inside propulsion pump (2), forward supply oil from the rotating groups acts against the relief valve in forward combination valve (1) and (27). As long as the pressure in the forward circuit is greater than charge pressure, the makeup valve in the combination valves remains seated. As long as the supply pressure is less than relief pressure, the relief valve in the combination valves remains closed.
If pressure in the reverse loop falls below charge pressure, the makeup valve in reverse combination valves (9) and (18) 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 valves close.
Loop flushing occurs in front propulsion motors (13) and (16) and rear propulsion motors (12) and (29). In each motor, forward circuit oil acts against one side of the respective flushing spools. Reverse circuit oil acts against the opposite side of each flushing spool. In this case, the higher-pressure oil moves the flushing spools. This movement allows reverse circuit oil to flow across the spool to the flushing relief valve. An orifice restricts the flushing flow rate.
The pressure setting of flushing relief valves is less than the pressure setting of charge relief valve (6). This fact ensures that oil is sent through the motor case drains under normal operating conditions. The flushing relief valve will stop flushing flow if the charge pressure is less than the setting of the flushing relief valve. This fact ensures flow through the flushing orifice does not cause charge pressure to decrease below brake release requirement.
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| Illustration 3 | g06266360 |
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Hydraulic Schematic REVERSE, HIGH-SPEED (1) Forward combination valve (2) Propel pump (3) Reverse solenoid (4) Forward solenoid (5) Interlock valve (6) Charge relief valve (7) Forward solenoid (8) Reverse solenoid (9) Reverse combination valve (10) Charge filter (11) Parking brake (12) Right rear propulsion motor (13) Right front propulsion motor (14) Parking brake (15) Front balance valve (16) Left front propulsion motor (17) Parking brake (18) Reverse combination valve (19) Pump rotating group (20) Servo piston (21) Return manifold (22) Oil cooler (23) Servo piston (24) Pump rotating group (25) Manual brake release pump (26) Two-speed valve (26) Rear propulsion motor (27) Forward combination valve (28) Parking brake (29) Left rear propulsion motor (30) Rear balance valve (31) From fan motor (32) Rear flushing valve (33) Front flushing valve | |
The above illustration shows the propel hydraulic system in the following conditions:
- The parking brake switch in the OFF position
- The propel mode set to high
- The propel lever is in the reverse range with the operator station facing the front of the machine.
- The propel lever is in the forward range with the operator station facing the rear of the machine.
During reverse operation, pump rotating groups (19) directs supply oil to the following locations:
- Port "MC" on propulsion pump (2)
- Port "B" of front balance valve (15)
- Reverse combination valve (18)
- Port "2" of flushing valve (33)
Front balance valve (15) directs forward supply oil from pump rotating group (19) to the following locations:
- The reverse side of right front propulsion motor (13)
- The reverse side of left front propulsion motor (16)
At the same time, supply oil from pump rotating group (24) flows to the following locations:
- Port "MA" on propulsion pump (2)
- Reverse combination valve (9)
- Port "D" of rear balance valve (30)
- Port "1" of flushing valve (32)
Rear balance valve (30) directs forward supply oil from pump rotating group (24) to the following locations:
- The reverse side of right rear propulsion motor (12)
- The reverse side of left rear propulsion motor (29)
The motors rotate, and reduced-pressure oil returns to the rotating groups through port "B" and "D" on propulsion pump (2). The relief valve in reverse combination valve (9) and (18) limits the maximum pressure in the reverse circuit. The makeup valve in forward combination valve (1) and (27) allows charge oil to enter the forward circuit to replenish oil lost to loop flushing.
When the propel mode is set to high, the two-speed valve (26) is energized and the valve shifts. The position of the two-speed valve allows charge oil to act on the shift spool in front propulsion motor (13) and (16). In this case, the motors operate at high speed but with less torque.