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| Illustration 1 | g06130891 |
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Propulsion Hydraulic Schematic NEUTRAL, LOW SPEED, PARKING BRAKE ON (1) Propulsion pump (2) Axle reverse combination valve (3) Axle forward solenoid (4) Axle reverse solenoid (5) Servo piston (6) Sequence valve solenoid (7) From charge filter (8) Servo piston (9) Drum reverse solenoid (10) Drum forward solenoid (11) Drum forward combination valve (12) Test manifold (13) Axle brakes (14) Servo piston (15) Axle forward combination valve (16) Axle shift spool (17) Flushing relief valve (18) Flushing spool (19) Axle rotating group (20) Charge relief valve (21) Shift solenoid (22) From vibratory pump (23) Return manifold (24) Drum rotating group (25) Drum reverse combination valve (26) Flushing spool (27) Flushing relief valve (28) Servo piston (29) Drum shift spool (30) Drum motor (31) Drum speed sensor (32) Parking brake (33) Axle speed sensor (34) Axle motor (35) Shuttle valve (36) Oil cooler (37) Relief valve (38) Thermal bypass valve (39) From vibratory motor (40) Temperature sensor (41) Shuttle valve | |
The above illustration shows the propulsion hydraulic system under the following conditions:
- The propulsion lever is in the NEUTRAL position.
- The parking brake switch is in the ON position.
- The propulsion mode is set to low.
The propulsion circuit consists of a hydrostatic-drive circuit for axle propulsion and a hydrostatic drive circuit for drum propulsion. Each closed-loop circuit has a rotating group inside a single pump. Each circuit also has a motor.
Displacement of the rotating groups in the pump is electronically controlled. The machine ECM calculates the desired speed and energizes the appropriate pump control solenoids to move the machine at the desired speed. When the propulsion lever is in the NEUTRAL position, the swashplate in each rotating group is at zero angle. The swashplate is also at zero angle if the machine ECM has disabled the propulsion system. In either of these cases, neither rotating group produces flow.
The steering system and fan system provide charge oil to the propulsion system (and the vibratory system) when the engine is running. Charge oil from the charge filter flows to port"E" of propulsion pump (1). Charge oil also flows to port"P" of shift valve (21). Inside the propulsion pump, charge oil flows to sequence valve (6) and to charge relief valve (20).
When the parking brake switch is in the ON position or the machine ECM has disabled the propulsion system, solenoid in sequence 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 (5) and (8) are open to the pump case. The servo pistons hold the swashplates in each rotating group at zero angle. The springs that are acting against the brake pistons engage axle brakes (13) and drum brake (32).
As long as solenoid in sequence valve (6) is not energized, the swashplate in each rotating group remains in the zero angle position. In this case, charge pressure is blocked at the sequence valve and the servo chambers of the pumps are vented to the pump case. These conditions are maintained, regardless of the position of the propulsion lever.
Charge pressure acts on charge relief valve (20). When charge pressure reaches
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.
The pressure in the forward circuit is equal to the pressure in the reverse circuit when the machine is not moving. In this case, flushing spool (18) and (26) in each propulsion motor is in the center position. In this case, the spool prevents flushing oil from flowing into the case drains of the motors.
The forward circuits of the axle and drum propulsion systems are connected through an orifice in test manifold (12). The reverse circuits of the axle and drum propulsion systems are also connected by an orifice in the test manifold. Each orifice restricts oil flow between the axle circuit and the drum circuit. The orifices prevent all flow from the drum circuit to flow to the axle circuit if the tires begin to spin. The orifices also prevent all flow from the axle circuit to flow to the drum circuit if the drum begins to spin.
The balance orifices allow oil to transfer between the drum and axle propulsion circuits. This oil transfer modulates the pressure difference in the hydrostatic drive circuits of the drum and axle propulsion systems. Oil transfer between the two systems is necessary to compensate for the following situations:
- Differences in underfoot conditions
- Differences in speeds between the drum and the wheels during turns
- Differences in rolling radii between the drum and the tires
Pressure in the axle forward circuit can be measured at the pressure tap in port"AF" of the test manifold. Pressure in the drum forward circuit can be measured at the pressure tap in port"DF" of the test manifold. Drum reverse pressure can be measured at the pressure tap in port"DR" of the test manifold. Axle reverse pressure can be measured at the pressure tap in port"AR" of the test manifold.
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| Illustration 2 | g06130892 |
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Hydraulic Schematic "FORWARD, LOW SPEED, PARKING BRAKE OFF" (1) Propulsion pump (2) Axle reverse combination valve (3) Axle forward solenoid "C1" (4) Axle reverse solenoid "C2" (5) Servo piston (6) Sequence valve solenoid (7) Port"E" (charge inlet) (8) Servo piston (9) Drum reverse solenoid "C2" (10) Drum forward solenoid "C1" (11) Drum forward combination valve (12) Test manifold (13) Axle brakes (optional) (14) Servo piston (15) Axle forward combination valve (16) Shift spool (17) Flushing relief valve (18) Flushing spool (19) Axle rotating group (20) Charge relief valve (21) Shift solenoid (22) Port"P" (charge inlet) (23) Return manifold (24) Drum rotating group (25) Drum reverse combination valve (26) Flushing spool (27) Flushing relief valve (28) Servo piston (29) Shift spool (30) Drum motor (31) Drum speed sensor (32) Parking brake (33) Axle speed sensor (34) Axle motor (35) Shuttle valve (36) Oil cooler (37) Relief valve (38) Thermal bypass valve (39) Passage from vibratory motor case (40) Temperature sensor (41) Shuttle valve | |
The above illustration shows the propulsion hydraulic system under the following conditions:
- The parking brake switch in the OFF position
- The propulsion mode is set to low
- The machine traveling forward
Charge oil to charge relief valve (20), to the combination valves, and to sequence valve solenoid (6). With the parking brake switch in the OFF position, the sequence valve solenoid directs charge oil into the piston cavities of parking brakes (32) and axle brakes (13), if equipped. The charge pressure in the parking brake piston cavities overcomes the spring force, and the parking brakes release.
When the propulsion mode is set to low, solenoid in shift valve (21) is not energized. In this case, propulsion motors (30) and (34) operate with the swashplates at the maximum displacement angle.
When the machine ECM determines that the machine should be moving forward, the ECM energizes axle forward solenoid"C1" (3) and drum forward solenoid"C1" (10). In this case, the solenoids direct charge oil into the forward side of servo pistons (5) and (8). 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 each 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 the propulsion 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 axle rotating group (19) flows to the following locations:
- Port"A" on the forward side of axle motor (34)
- Forward combination valve (15)
- Port"AF" of test manifold (12)
The pressure differential between the forward and reverse sides of axle motor (34) causes the motor to turn. After turning the axle motor, oil at a reduced pressure flows to the following locations:
- Flushing spool (18) in the axle motor
- The reverse side of axle rotating group (19)
- Port"AR" of test manifold (12)
Supply oil from drum rotating group (24) flows to the following locations:
- Port"A" on the forward side of drum motor (30)
- Forward combination valve (11)
- Port"DF" of test manifold (12)
Drum motor (30) turns. Reduced pressure oil flows to drum motor flushing spool (26), back to the reverse side of drum rotating group (24), and to port"DR" of test manifold (12).
The orifices in test manifold (12) 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 setpoints, drive speed will remain fairly equal between the axle and drum.
Inside propulsion pump (1), forward supply oil from each rotating group acts against the relief valve in corresponding forward combination valve (2) and (11). As long as the pressure in the forward circuit 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 either reverse loop 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 (34) and drum motor (30). In each motor, forward circuit oil acts against one side of the flushing spool. 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 the flushing relief valve.
Any time the pressure in either reverse circuit is greater than the setting of the flushing relief valve, the corresponding flushing relief valve opens. In this case, oil from the reverse 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 the charge relief valve. 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 decrease to the point at which charge pressure becomes less than the brake release requirement.
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| Illustration 3 | g06130894 |
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Hydraulic Schematic REVERSE, HIGH SPEED, PARKING BRAKE OFF (1) Propulsion pump (2) Axle reverse combination valve (3) Axle forward solenoid "C1" (4) Axle reverse solenoid "C2" (5) Servo piston (6) Sequence valve solenoid (7) Port"E" (charge inlet) (8) Servo piston (9) Drum reverse solenoid "C2" (10) Drum forward solenoid "C1" (11) Drum forward combination valve (12) Test manifold (13) Axle brakes (optional) (14) Servo piston (15) Axle forward combination valve (16) Shift spool (17) Flushing relief valve (18) Flushing spool (19) Axle rotating group (20) Charge relief valve (21) Shift solenoid (22) Port"P" (charge inlet) (23) Return manifold (24) Drum rotating group (25) Drum reverse combination valve (26) Flushing spool (27) Flushing relief valve (28) Servo piston (29) Shift spool (30) Drum motor (31) Drum speed sensor (32) Parking brake (33) Axle speed sensor (34) Axle motor (35) Shuttle valve (36) Oil cooler (37) Relief valve (38) Thermal bypass valve (39) Passage from vibratory motor case (40) Temperature sensor (41) Shuttle valve | |
The above illustration shows the propulsion hydraulic system in the following conditions:
- The parking brake switch in the OFF position
- The propulsion mode set to high
- The machine traveling in reverse
During reverse operation, axle rotating group (19) directs oil out port"B" of propulsion pump (1). This oil flows to the reverse side of axle motor (34) and to port"MB" of test manifold (12). The axle motor rotates, and reduced-pressure oil returns to the axle rotating group through port"A" of the propulsion pump. Flushing spool (18) and flushing relief valve (17) direct oil from the forward side of the axle circuit to the case drain of the axle motor. The relief valve in reverse combination valve (2) limits the maximum pressure in the axle reverse circuit. The makeup valve in forward combination valve (15) allows charge oil to enter the forward circuit to replenish oil lost to loop flushing.
During reverse operation, drum rotating group (24) directs oil out port"D" of propulsion pump (1). This oil flows to the reverse side of drum motor (30) and to port"MD" of test manifold (12). The drum motor rotates, and reduced-pressure oil returns to the drum rotating group through port"C" of the propulsion pump. Flushing spool (26) and flushing relief valve (27) direct oil from the forward side of the drum circuit to the case drain of the drum motor. The relief valve in reverse combination valve (25) limits the maximum pressure in the drum reverse circuit. The makeup valve in forward combination valve (11) allows charge oil to enter the forward circuit to replenish oil lost to loop flushing and leakage.
When the propulsion mode is set to high, solenoid in shift valve (21) is energized. The position of the shift solenoid allows charge oil to act on shift spool (16) in axle motor (34) and on shift spool (29) in drum motor (30). The shift spools in each motor moves, and oil is directed from the reverse circuit into the high side of the servo piston chambers. The oil pressure causes the servo piston to shift. This shift causes the rotating group in the drum motor to move against the minimum displacement adjustment screw.