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| Illustration 1 | g06008916 |
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Right Propel Hydraulic System in Neutral (1) Forward solenoid (2) Reverse solenoid (3) Metering spool (4) To front-wheel assist motor (right) port "F" (5) Forward multifunction valve (6) Pressure limiter (7) Main relief valve (8) Makeup valve (9) Final drive (10) From auxiliary hydraulic system (11) Parking brake cylinder (12) Servo piston (13) Right propel pump (14) To cooler bypass manifold port (15) From hydraulic tank suction return filter (16) Charge pump (17) Charge relief valve (18) Reverse multifunction valve (19) To propel pump (left) port "M2" (20) To propel pump (left) port (21) Right propel motor (22) Flushing relief valve (23) Flushing spool (24) Shuttle valve (25) Speed valve (26) From auxiliary manifold port "FDS" (27) Servo piston (28) To cooler bypass manifold port (29) Motor output shaft | |
When the engine is running, right propel pump (13) and charge pump (16) rotate. The charge pump draws oil from the tank through the combined suction and return filter (15). Internal passages distribute output oil from the charge pump to the following components:
- Charge relief valve (17)
- Forward solenoid (1)
- Reverse solenoid (2)
- Metering spool (3)
- Multifunction valves (5) and (18)
Note: If the machine is equipped with a front-wheel assist system, charge oil is also sent to cases of the front-wheel assist motors.
When the propel lever is in the NEUTRAL position, forward solenoid (1) and reverse solenoid (2) are not energized. Also, if the transmission ECM has disabled the propel system, these solenoids are not energized. Under these conditions, both ends of metering spool (3) are open to the case drain, and the center envelope of the spool is active. The metering spool blocks charge oil. The spool also opens a passage between servo piston (12) and the pump case drain. The pump swashplate then moves to minimum angle.
Charge oil that enters multifunction valves (5) and (18) seats the check valves and acts against makeup valves (8). Since right propel pump (13) rotates while the engine is running, normal leakage occurs in the right propel circuit. When pressure in the right propulsion circuit falls below charge pressure, the makeup valves open and the right propel circuit fills with charge oil.
When the charge pressure in a circuit increases to
The auxiliary hydraulic system controls the oil flow to and from parking brake cylinder (11) and speed valve (25). When the parking brake switch is in the ON position, the parking brake solenoid on the auxiliary manifold is not energized. Therefore, supply oil cannot flow to the parking brake cylinders, and the parking brakes are engaged. When the propel status is set to pave or maneuver, the shift solenoid on the auxiliary manifold is not energized. Therefore, supply oil cannot flow to the speed valve.
Note: For additional information about hydraulic control of the parking brake and shift solenoids, refer to the auxiliary hydraulic system.
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| Illustration 2 | g06008904 |
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Left Propel Hydraulic System in Neutral (1) Reverse solenoid (2) Forward solenoid (3) Metering spool (4) To front-wheel assist motor (left) port "F" (5) Reverse multifunction valve (6) Pressure limiter (7) Main relief valve (8) Makeup valve (9) Final drive (10) From auxiliary hydraulic system (11) Parking brake cylinder (12) Servo piston (13) Left propel pump (14) To cooler bypass manifold port "A" (15) From hydraulic tank suction return filter (16) Charge pump (17) Charge relief valve (18) Forward multifunction valve (19) To propel pump (right) port (20) To propel pump (right) port "M1" (21) Left propel motor (22) Flushing relief valve (23) Flushing spool (24) Shuttle valve (25) Speed valve (26) From auxiliary manifold port "FDS" (27) Servo piston (28) To cooler bypass manifold port (29) Motor output shaft | |
The left propel hydraulic system is similar to the right propel hydraulic system.
However, the left and right pumps have some minor differences. Forward solenoid (2) and reverse solenoid (1) are flipped between the left and right pumps. This change makes port "A" of the left pump the reverse supply port and port "B" the forward port.
Also, port "L1" of the left pump is connected to the cooler bypass manifold, and port "L2" contains the case drain pressure tap. The charge pump on the left pump supplies oil to the left front-wheel assist motors.
Port "A" of left propel motor (21) is the reverse port, and port "B" is the forward port.
Note: Since the right and left propel hydraulic circuits operate in the same manner, the following generic circuit descriptions can be used to discuss either circuit. The left propel hydraulic circuit is shown in the following illustrations.
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| Illustration 3 | g06008901 |
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Left Propel Hydraulic System in Forward Pave (1) Reverse solenoid (2) Forward solenoid (3) Metering spool (4) To front-wheel assist motor (left) port "F" (5) Reverse multifunction valve (6) Pressure limiter (7) Main relief valve (8) Makeup valve (9) Final drive (10) From auxiliary hydraulic system (11) Parking brake cylinder (12) Servo piston (13) Left propel pump (14) To cooler bypass manifold port "A" (15) From hydraulic tank suction return filter (16) Charge pump (17) Charge relief valve (18) Forward multifunction valve (19) To propel pump (right) port (20) To propel pump (right) port "M1" (21) Left propel motor (22) Flushing relief valve (23) Flushing spool (24) Shuttle valve (25) Speed valve (26) From auxiliary manifold port "FDS" (27) Servo piston (28) To cooler bypass manifold port "F" (29) Motor output shaft | |
When the machine is traveling forward, forward solenoid (2) is energized. The transmission ECM analyzes the input signals to determine the magnitude of the output signal that is sent to the forward solenoid.
Charge pressure flows across forward solenoid (2). This pressure acts against metering spool (3). The metering spool moves, and charge oil is metered across the spool to the forward chamber of servo piston (12). The charge oil shifts the servo piston to shift, changing the angle of the swashplate in propel pump (13). Then, the pump generates flow in the forward circuit.
Forward circuit oil flows to forward multifunction valve (18) and flows to the forward side of propel motor (21). Forward circuit oil in the forward multifunction valve closes the makeup valve. Forward circuit oil also acts against the pressure limiter and the main relief valve. If the pressure differential between the forward circuit and case drain pressure reaches
Inside propel motor (21), forward oil flows to the following locations:
- Flushing spool (23)
- Shuttle valve (24)
- Forward side of the rotating group in the propel motor
Oil in the forward circuit causes propel motor (21) to turn. After the motor turns, the pressure of the forward circuit oil is reduced. Oil at a reduced pressure then enters the reverse circuit. Reverse circuit oil flows to the following locations: flushing spool (23), reverse multifunction valve (5), the reverse side of propel pump (13). The drive circuit is then complete.
Since reverse circuit oil is at a lower pressure than forward circuit oil, forward circuit oil causes flushing spool (23) to shift. Shuttle valve (24) also shifts. The shift of the flushing spool allows oil from the reverse circuit to act on flushing relief valve (22). When the pressure (gauge) that acts against the flushing valve is greater than the setting of the flushing relief valve, the flushing relief valve opens. When the flushing relief valve is open, a maximum of
- Makeup valve (8) in reverse multifunction valve (5)
- Main relief valve (7) in the reverse multifunction valve
- Pressure limiter valve (6) in the reverse multifunction valve
As flushing spool (23) removes oil from the reverse circuit, the pressure in the reverse circuit decreases. When the pressure in the reverse circuit is less than the pressure in the charge circuit, charge pressure unseats makeup valve (8). Then, flow from charge pump (16) enters the reverse circuit. This action allows cool, filtered oil from the charge circuit to flush the propel circuit.
When the parking brake is off, the transmission ECM energizes the brake solenoid. Oil from auxiliary system (10) is allowed to flow into parking brake cylinder (11). The pressure in the parking brake cylinder overcomes the spring forces, and the parking brake releases.
When the propel system is in the pave mode, the shift solenoid is not energized. In this case, the passage to port "FDS" of auxiliary manifold (26) is open to the hydraulic tank. When this passage is open to tank, the spring on speed valve (25) forces the valve to block pump supply pressure. In this case, the speed valve opens the head end of servo piston (27) to the motor case drain. Since the rod end of the servo piston is pressurized and the head end is open to case drain, propel motor (21) operates at maximum displacement. Under these conditions, the machine operates in the pave-speed.
The forward and reverse circuits of the right and left propel systems are connected by balance lines (19) and (20). An orifice is installed in each balance line. One orifice is installed port "M2" of the left propel pump. One orifice is installed in port "M2" of the right propel pump (refer to the illustration for the right pump and motor).
These balance lines allow makeup oil to transfer between the right and left propel circuits. This oil transfer ensures that the pressure in the forward and the reverse circuits of the right and left propel systems is equal.
Oil transfer between the two systems is necessary when the machine is turning. Oil transfer is also necessary to compensate for differences in underfoot conditions and to compensate for differences in internal leakage in the circuits. The pressure in the forward and reverse circuits can be measured at the taps that are installed in the balance lines.
Note: The balance lines must be removed to isolate each pump when the pumps are being tested.
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| Illustration 4 | g06008868 |
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Propel Hydraulic System Reverse Travel (1) Reverse solenoid (2) Forward solenoid (3) Metering spool (4) To front-wheel assist motor (left) port (5) Reverse multifunction valve (6) Pressure limiter (7) Main relief valve (8) Makeup valve (9) Final drive (10) From auxiliary hydraulic system (11) Parking brake cylinder (12) Servo piston (13) Left propel pump (14) To cooler bypass manifold port "A" (15) From hydraulic tank suction return filter (16) Charge pump (17) Charge relief valve (18) Forward multifunction valve (19) To propel pump (right) port "M2" (20) To propel pump (right) port "M1" (21) Left propel motor (22) Flushing relief valve (23) Flushing spool (24) Shuttle valve (25) Speed valve (26) From auxiliary manifold port "FDS" (27) Servo piston (28) To cooler bypass manifold port (29) Motor output shaft | |
When the machine is traveling in reverse, reverse solenoid (1) is energized. The transmission ECM analyzes the input signals to determine the magnitude of the output signal that is sent to the reverse solenoid.
Charge pressure flows across reverse solenoid (1) and acts against metering spool (3). The metering spool moves, and charge oil is metered across the spool to the reverse chamber of servo piston (12). The charge oil causes the servo piston to shift. This shift changes the angle of the swashplate in propel pump (13), and the pump generates flow in the reverse circuit.
While the machine is traveling in reverse, the following occurs:
- Reverse multifunction valve (5) limits system pressure.
- Oil from the forward circuit flows through flushing spool (23).
- The makeup valve, in forward multifunction valve (18), allows charge oil to flow into the forward circuit.
When the propel system is in the travel mode and the parking brake is off, the transmission ECM energizes the shift and brake solenoids. Oil from auxiliary system (10) and (26) is directed into parking brake cylinder (11) and speed valve (25), respectively. The pressure in parking brake cylinder overcomes the spring force. These conditions cause the parking brakes to release. The pressure acting against the speed valve causes the valve to shift. This shift opens a passage for reverse circuit oil to flow into the head end of servo piston (27).Since the effective area of the head end of the servo piston is greater than the effective area of the rod end, the piston extends. Under these conditions, the propel motor operates at minimum displacement, and the machine operates in the travel-speed range.
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| Illustration 5 | g06008945 |
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Front-wheel Assist System Freewheel (1) Freewheel check valve (2) Freewheel control spool (3) Front-wheel assist manifold (4) Flow divider (5) Flow divider (6) Minimum pressure valve (7) Front-wheel assist solenoid (8) To return manifold port (9) Left rear motor (10) Right rear motor (11) Left front motor (12) Right front motor (13) From right propel charge pump (14) To return manifold port "B" (15) From left propel charge pump (16) To case manifold port "D" (17) Actuator piston (18) From hydraulic tank port "3" (19) Bias spring (20) Front-wheel assist pump (21) Flow compensator (22) Pressure compensator | |
When the engine is operating, the propel charge pumps and front-wheel assist pump (20) generate flow. Flow from charge pumps (13) and (15) is directed into the case drain of front-wheel assist motors (9), (10), (11), (12).
Downstream from front-wheel assist motors (9), (10), (11), (12), case drain oil is combined. The combined oil is directed into port "CD2" of the front-wheel assist manifold (3). This oil flows to freewheel control spool (2) and to freewheel check valve (1).
Supply oil from the front-wheel assist pump flows to the pump compensator valve and out port "B" of the pump. From port "B", oil flows to port "P" of the front-wheel assist manifold (3). This oil is available at minimum pressure valve (6).
Inside the compensator valve, supply oil acts against pressure compensator spool (22) and flow compensator spool (21). Supply oil also flows through an orifice. Downstream from the orifice, the oil divides into two branches. The oil in one branch acts against the flow compensator spool with a spring. Oil in the other branch flows out port "X" of the pump compensator valve to the front-wheel assist manifold (3).The oil pressure at port "X" provides the signal pressure for the pump compensator valve.
Inside front-wheel assist manifold (3), signal oil divides into three branches. One branch flows to front-wheel assist solenoid (7). Oil in the second branch acts against minimum pressure valve (6) in opposition to a spring. Oil in the third branch acts against freewheel control spool (2) in opposition to a spring.
The pressure at port "X" of front-wheel assist pump (20) is controlled by front-wheel assist solenoid (7). When the front-wheel assist system is not operating, the front-wheel assist solenoid is not energized. In this case, oil in the signal passage to port "X" is open to return line (8). This opening creates a pressure drop across the orifice in the pump compensator valve. The pressure acting against flow compensator spool (21), with the spring, causes the front-wheel assist pump to operate at low-pressure standby.
Note: For additional information about pump operation, refer to the propel pump description, above.
At low-pressure standby, minimum pressure valve (6) in front-wheel assist manifold (3) remains closed. When this valve is closed, the valve spool blocks the supply oil entering port "P" of the front-wheel assist manifold. In this case, pump supply oil is not directed to the front-wheel assist motors.
When the front-wheel assist system is not operating, freewheel control spool (2) in front-wheel assist manifold (3) is closed. In this case, freewheel check valve (1) maintains a back pressure of
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| Illustration 6 | g06008959 |
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Front-wheel Assist System Forward (1) Freewheel check valve (2) Freewheel control spool (3) Front-wheel assist manifold (4) Flow divider (5) Flow divider (6) Minimum pressure valve (7) Front-wheel assist solenoid (8) To return manifold port (9) Left rear motor (10) Right rear motor (11) Left front motor (12) Right front motor (13) From right propel charge pump (14) To return manifold port (15) From left propel charge pump (16) To case manifold port (17) Actuator piston (18) From hydraulic tank port "3" (19) Bias spring (20) Front-wheel assist pump (21) Flow compensator (22) Pressure compensator | |
When the front-wheel assist system is operating, front-wheel assist solenoid (7) is energized. This solenoid is a proportional solenoid. The transmission ECM determines the output signal that is sent to the solenoid, and the relay driver module generates the output signal.
As the output signals to front-wheel assist solenoid (7) increases, the solenoid begins to close the return passage for the signal oil. This action increases the oil pressure that acts against with the spring against flow compensator (21). The increased force on flow compensator spool moves the spool, and the pressure in actuator piston (17) is reduced. This pressure reduction allows bias spring (19) to increase the angle of the swashplate, and the pump produces more flow.
When the pressure in the signal line increases to approximately
When the pressure in the signal line increases to approximately
One flow divider (4) equally splits the flow between left rear motor (9) and right front motor (12). Second flow divider (5) equally splits the flow between right rear motor (10) and left front motor (11). A balance line orifice, downstream from each flow divider, equalizes the pressure in the lines to each set of front-wheel assist motors.