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| Illustration 1 | g03816708 |
Propel System Hydraulic Schematic (1) Relief valve (2) Flushing spool (3) Axle motor (4) Relief valve (5) Flushing spool (6) Drum motor (7) Parking brake (8) Charge pressure tap (9) Charge filter (10) From steering pump (11) Neutral start switch (12) Reverse combination valve (13) Forward combination valve (14) Axle rotating group (15) Bypass valve (16) Interlock solenoid (17) Charge relief valve (18) Drum rotating group (19) Forward combination valve (20) Reverse combination valve (21) Test manifold (22) Hydraulic tank (23) Filter bypass valve (24) Return filter (25) Suction strainer (26) From port "T" vibratory manifold (27) To steer/vibe pumps (28) Oil cooler (29) S·O·S tap (30) Charge filter bypass valve | |
The above illustration shows the propel system operating under the following conditions:
- The propel lever is in the NEUTRAL position.
- The parking brake switch is in the ON position.
The propel system consists of a hydrostatic-drive circuit for axle propulsion and a hydrostatic drive circuit for drum propel. Each closed-loop circuit has rotating group (14) and (18). Each circuit also has drive motor (3) and (6).
Displacement of the rotating groups in the propel pump is mechanically controlled. When the propel lever is in the NEUTRAL position, swashplate in rotating group (14) and (18) is at zero angle. In this case, neither rotating group produces flow to axle motor (3) or drum motor (6) .
Steering pump (10) provides charge oil to the propel system when the engine is running. Charge oil from charge filter (9) flows to port "E" of the propel pump. Inside the propel pump, charge oil flows to interlock solenoid (16) and to charge relief valve (17) .
When the parking brake switch is in the ON position, interlock solenoid (16) is not energized. This solenoid prevents charge oil from reaching the pump control spools and from reaching parking brake (7) piston cavity. Under these conditions, the brake piston cavity and both sides of the servo pistons are open to the pump case drain. The servo pistons hold swashplates in rotating group (14) and (18) at zero angle. The springs that act against the brake piston engage the disks of the parking brake.
As long as interlock solenoid (16) is not energized, the swashplate in rotating group (14) and (18) remains in the zero angle position. These conditions are maintained, regardless of the position of the propel lever.
Charge pressure acts on the charge relief valve. When charge pressure reaches 2500 ± 200 kPa (363 ± 29 psi), oil pressure overcomes the spring force, and charge relief valve (17) opens. This action directs charge pump flow into the case drain.
Charge pressure acts against the makeup valves in each combination valve (12), (13), (19) and (20). 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.
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 spool (2) and (5) in each propel motor (3) and (6) is in the center position. These spools prevent flushing oil from flowing into the case drains of the motors.
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| Illustration 2 | g03816714 |
Propel System Hydraulic Schematic (1) Relief valve (2) Flushing spool (3) Axle motor (4) Relief valve (5) Flushing spool (6) Drum motor (7) Parking brake (8) Charge pressure tap (9) Charge filter (10) From steering pump (11) Neutral start switch (12) Reverse combination valve (13) Forward combination valve (13) Forward combination valve (14) Axle rotating group (15) Bypass valve (16) Interlock solenoid (17) Charge relief valve (18) Drum rotating group (19) Forward combination valve (20) Reverse combination valve (21) Test manifold (22) Hydraulic tank (23) Filter bypass valve (24) Return filter (25) Suction strainer (26) From vibratory manifold port "T" (27) To steer/vibe pumps (28) Oil cooler (29) S·O·S tap (30) Charge filter bypass valve | |
The above illustration shows the propel system operating under the following conditions:
- The parking brake switch is in the OFF position.
- The machine is traveling in the forward direction.
When the parking brake switch is in the OFF position, interlock solenoid (16) is energized. In this case, the interlock valve shifts, and charge oil is directed to the parking brake (7) piston cavity. The charge pressure overcomes the spring force in the piston, and the parking brake is released. Charge oil is also sent to the direction control spools in rotating group (14) and (18) .
When the propel lever is moved into the forward range, the direction control spools shift. In this case, charge oil is directed into the forward side of the servo pistons. The pressure in the forward side of the servo pistons causes the pump servos to move. This movement changes the angle of the swashplate in rotating groups (14) and (18). The farther the propel lever is moved forward, the greater the swashplate angle increases. This increase in swashplate angel causes a greater oil flow from the propel pump.
Supply oil from axle rotating group (14) flows to the following locations:
- Forward combination valve (13)
- Port "MA" of test manifold (21)
- The forward side of axle motor (3)
- The forward side of flushing spool (2)
The pressure differential between the forward and reverse sides of axle motor (3) causes the motor to turn.
After turning the axle motor (3), oil at a reduced pressure flows to the following locations:
- The reverse side of flushing spool (2)
- Port "MB" of test manifold (21)
- Reverse combination valve (12)
- The reverse side of axle rotating group (14)
Supply oil from drum rotating group (18) flows to the following locations:
- Forward combination valve (19)
- Port "MC" of test manifold (21)
- The forward side of flushing spool (5)
- The forward side of drum motor (6)
The pressure differential between the forward and reverse sides of drum motor (6) causes the motor to turn.
After turning the drum motor (6), oil at a reduced pressure flows to the following locations:
- The reverse side of flushing spool (5)
- Port "MD" of test manifold (21)
- The reverse side of drum rotating group (18)
- Reverse combination valve (20)
The orifices in test manifold (21) modulate large pressure differences by allowing oil to transfer between the axle and drum drive circuits. In effect, the balance orifices act as a "hydraulic differential". In the event of potential spin-out, pressures will develop independently in each loop. As long as loop pressures remain below relief pressure setpoints, drive speed will remain fairly equal between the axle and drum.
Inside each rotating group (14) and (18), supply oil acts against the relief valve in the corresponding forward combination valve (13) and (19). The relief section of the combination valve limits the pressure in the circuit to 35 500 ± 1500 kPa (5149 ± 218 psi). The makeup section of the valves allows charge oil to flow into the low-pressure circuit. The charge oil replenishes the oil lost to internal leakage and loop flushing.
As long as pressure in the forward circuit is greater than charge pressure, the makeup valve in forward combination valve (13) and (19) remain seated. As long as the supply pressure is less than relief pressure, the corresponding relief valves remain closed.
If pressure in either of the reverse loops falls below charge pressure, the makeup valve in the corresponding combination valve 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 axle motor (3) and the drum motor (6). In each motor, forward circuit oil acts against one side of the flushing spool (2) or (5). Reverse circuit oil acts against the opposite side of each flushing spool. In both motors, the higher-pressure oil moves the flushing spool. This movement allows reverse circuit oil to flow across the spool to flushing relief valve (1) or (4).
Any time the pressure in either reverse circuit is greater than the setting of flushing relief valve (1) or (4), the corresponding valve opens. In this case, oil from the reverse circuit flows through an orifice and into the respective motor case drain line.
The pressure setting for flushing relief valve (1) and (4) is less than the pressure setting of charge relief valve (17). This fact ensures that oil is sent through the motor case drain 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 that flow through the flushing orifice does not cause charge pressure to fall below brake release requirement.
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| Illustration 3 | g03816716 |
Propel System Hydraulic Schematic (1) Relief valve (2) Flushing spool (3) Axle motor (4) Relief valve (5) Flushing spool (6) Drum motor (7) Parking brake (8) Charge pressure tap (9) Charge filter (10) From steering pump (11) Neutral start switch (12) Reverse combination valve (13) Forward combination valve (14) Axle rotating group (15) Bypass valve (16) Interlock solenoid (17) Charge relief valve (18) Drum rotating group (19) Forward combination valve (20) Reverse combination valve (21) Test manifold (22) Hydraulic tank (23) Filter bypass valve (24) Return filter (25) Suction strainer (26) From vibratory manifold port "T" (27) To steer/vibe pumps (28) Oil cooler (29) S·O·S tap (30) Charge filter bypass valve | |
The above illustration shows the propel system operating under the following conditions:
- The parking brake switch is in the OFF position.
- The machine is traveling in the reverse direction.
When the propel lever is moved into the reverse range, the direction control spools shift. In this case, charge oil is directed into the reverse side of the servo pistons. The pressure in the reverse side of the servo pistons causes the pump servos to move. This movement changes the angle of the swashplate in rotating group (14) and (18). The farther the propel lever is moved to the rear, the greater the swashplate angle increases. This increase in swashplate angle causes a greater oil flow from the propel pump.
Supply oil from axle rotating group (14) flows to the following locations:
- Reverse combination valve (12)
- Port "MB" of manifold (21)
- The reverse side of flushing spool (2)
- The reverse side of axle motor (3)
The pressure differential between the reverse and forward sides of axle motor (3) causes the motor to turn.
After turning the axle motor (3), oil at a reduced pressure flows to the following locations:
- The forward side of flushing spool (2)
- Port "MA" of test manifold (21)
- The forward side of axle rotating group (14)
- Forward combination valve (13)
Supply oil from drum rotating group (18) flows to the following locations:
- Reverse combination valve (20)
- Port "MD" of test manifold (21)
- The reverse side of flushing spool (5)
- The reverse side of drum motor (6)
The pressure differential between the reverse and forward sides of drum motor (6) causes the motor to turn.
After turning the drum motor (6), oil at a reduced pressure flows to the following locations:
- The forward side of flushing spool (5)
- Port "MC" of test manifold (21)
- Forward combination valve (19)
- The forward side of drum rotating group (18)