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| Illustration 1 | g06031290 |
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Left Propel Hydraulic System in Neutral (1) Forward solenoid (2) Reverse solenoid (3) Metering spool (4) Forward multifunction valve (5) Pressure limiter (6) Main relief valve (7) Makeup valve (8) Right track tension manifold (9) Inlet check valve (10) Relief valve (11) Needle valve (12) To return manifold (13) Right track tension cylinder (14) Final drive (15) From auxiliary hydraulic system (16) Parking brake cylinder (17) Servo piston (18) Left propel pump (19) To cooler bypass manifold port "A" (20) From hydraulic tank suction return filter (21) Charge pump (22) Charge relief valve (23) Reverse multifunction valve (24) Left propel motor (25) Flushing relief valve (26) Flushing spool (27) Shuttle valve (28) Speed valve (29) From auxiliary manifold port "FDS" (30) Servo piston (31) To port "E" of cooler bypass manifold (32) Motor output shaft | |
Note: The right and left propel hydraulic circuits operate in the same manner. However, the plumbing between the pump and motor differs between the left circuit and the right circuit. Port "A" of the left propel pump is connected to port "B" of the left propel motor. Port "A" of the right propel pump is connected to port "A" of the right propel motor. Port "B" of the left pump is connected to port "A" of the left motor. Port "B" of the right pump is connected to port "B" of the right motor. The following generic circuit description can be used to discuss either circuit. The left propel hydraulic circuit is shown in the above illustration.
When the engine is running, left propel pump (18) and charge pump (21) rotate. The charge pump draws oil from the tank through the combined suction and return filter (20). Internal passages distribute output oil from the charge pump to the following components:
- Charge relief valve (22)
- Forward solenoid (1)
- Reverse solenoid (2)
- Metering spool (3)
- Multifunction valves (4) and (23)
When the propel lever is in the NEUTRAL position, forward solenoid (1) reverse solenoid (2) 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 (17) and the pump case drain. The pump swashplate then moves to minimum angle.
Charge oil that enters multifunction valves (4) and (23) seats the check valves and acts against makeup valves (7). Since left propel pump (18) rotates while the engine is running, normal leakage occurs in the left propel circuit. When pressure in the left propel circuit falls below charge pressure, the makeup valves open and the left propel circuit fills with charge oil.
When the charge pressure in a circuit increases to
Charge oil also flows out port "M3" of the propel pump. This oil flows to port "P" of right track tension manifold (8). Inside the track tension manifold, charge oil opens inlet check valve (9) and splits into three branches. One branch delivers charge oil to relief valve (10). The second branch delivers oil to needle valve (11), and the third branch directs charge oil out port "CYL" of the manifold.
Under normal operating conditions, needle valve (11) is closed, and oil flows into the head end of right track tension cylinder (13). Charge pressure provides the force that maintains track tension. If the track encounters an external force that compresses the track tension cylinder, inlet check valve (9) prevents high-pressure oil from entering the charge circuit. In this case, relief valve (10) directs displaced oil from the track tension cylinder out port "T" of the track tension manifold.
The auxiliary hydraulic system controls the oil flow to and from parking brake cylinder (16) and speed valve (28). When the parking brake status is set to "engaged", 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 mode 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 | g06031304 |
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Left Propel Hydraulic System in Forward Pave (1) Forward solenoid (2) Reverse solenoid (3) Metering spool (4) Forward multifunction valve (5) Pressure limiter (6) Main relief valve (7) Makeup valve (8) Right track tension manifold (9) Inlet check valve (10) Relief valve (11) Needle valve (12) To return manifold (13) Right track tension cylinder (14) Final drive (15) From auxiliary hydraulic system (16) Parking brake cylinder (17) Servo piston (18) Left propel pump (19) To cooler bypass manifold port "A" (20) From hydraulic tank suction return filter (21) Charge pump (22) Charge relief valve (23) Reverse multifunction valve (24) Left propel motor (25) Flushing relief valve (26) Flushing spool (27) Shuttle valve (28) Speed valve (29) From auxiliary manifold port "FDS" (30) Servo piston (31) To port "E" of cooler bypass manifold (32) Motor output shaft | |
When the machine is traveling forward, forward solenoid (1) 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 (1). 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 (17). The charge oil shifts the servo piston to shift, changing the angle of the swashplate in propel pump (18). Then, the pump generates flow in the forward circuit.
Forward circuit oil flows to forward multifunction valve (4) and flows to the forward side of propel motor (24). Forward circuit oil in the forward multifunction valve closes makeup valve (7). Forward circuit oil also acts against pressure limiter (5) and main relief valve (6). If the pressure differential between the forward circuit and charge circuit reaches
Inside propel motor (24), forward oil flows to the following locations:
- Flushing spool (22)
- Shuttle valve (27)
- Forward side of the rotating group in the propel motor
Oil in the forward circuit causes propel motor (24) 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 (26)
- reverse multifunction valve (23)
- the reverse side of propel pump (18).
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 (26) to shift. Shuttle valve (27) also shifts. The shift of the flushing spool allows oil from the reverse circuit to act on flushing relief valve (25). 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
Inside the propel pump, reverse circuit oil acts against the following:
- Makeup valve in reverse multifunction valve (23)
- Main relief valve in the reverse multifunction valve
- Pressure limiter valve in the reverse multifunction valve
As flushing spool (26) 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 the makeup valve. Then, flow from charge pump (21) 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 (15) is allowed to flow into parking brake cylinder (16). 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 (29) is open to the hydraulic tank. When this passage is open to tank, the spring on speed valve (28) forces the valve to block pump supply pressure. In this case, the speed valve opens the head end of servo piston (30) 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 (24) operates at maximum displacement. Under these conditions, the machine operates in the pave-speed range.
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| Illustration 3 | g06031320 |
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Propel Hydraulic System Reverse Travel (1) Forward solenoid (2) Reverse solenoid (3) Metering spool (4) Forward multifunction valve (5) Pressure limiter (6) Main relief valve (7) Makeup valve (8) Right track tension manifold (9) Inlet check valve (10) Relief valve (11) Needle valve (12) To return manifold (13) Right track tension cylinder (14) Final drive (15) From auxiliary hydraulic system (16) Parking brake cylinder (17) Servo piston (18) Left propel pump (19) To cooler bypass manifold port "A" (20) From hydraulic tank suction return filter (21) Charge pump (22) Charge relief valve (23) Reverse multifunction valve (24) Left propel motor (25) Flushing relief valve (26) Flushing spool (27) Shuttle valve (28) Speed valve (29) From auxiliary manifold port "FDS" (30) Servo piston (31) To port "E" of cooler bypass manifold (32) Motor output shaft | |
When the machine is traveling in reverse, reverse solenoid (2) 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 (2) 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 (17). The charge oil causes the servo piston to shift. This shift changes the angle of the swashplate in propel pump (18), and the pump generates flow in the reverse circuit.
While the machine is traveling in reverse, the following occurs:
- Reverse multifunction valve (23) limits system pressure.
- Oil from the forward circuit flows through flushing spool (26).
- Makeup valve (7), in forward multifunction valve (4), 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 (15) and (29) is directed into parking brake cylinder (16) and to speed valve (28), 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 (30). 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 4 | g06031203 |
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Hydraulic Schematic for Parking Brake and Shift Control (33) Auxiliary manifold (34) Parking brake valve (35) Pressure reducing valve (36) Shift valve (37) Left speed valve (38) Right speed valve (39) Brake pressure switch (40) Brake release manifold (41) Needle valve (42) From cooler bypass manifold (43) Hand pump (44) From mainframe extend manifold (45) From auxiliary pump (46) To return filter (47) To screed lift circuit and mainframe extend manifold (48) Left brake cylinder (49) Right brake cylinder | |
When the engine is operating, the auxiliary pump provides oil to auxiliary manifold (33). Inside the auxiliary manifold, supply oil flows to pressure reducing valve (35).
Downstream from pressure reducing valve (35), oil divides into four branches. One branch acts against the pressure reducing valve, in opposition to a spring. The spring maintains the pressure in the lines downstream from the valve at
When the propel mode is set to "pave", the shift solenoid is not energized. In this case, reduced-supply oil is blocked at shift valve (36). The pilot port of each speed valve (37) and (38) is open to return filter (46). These conditions allow the machine to operate in pave and maneuver.
When the parking brake status is set to "engaged" and/or the other brake engagement parameters are met, the parking brake solenoid is not energized. Under these conditions, reduced-supply oil is blocked at parking brake valve (34). In this case, a passage opens that allows return oil from brake cylinders (48) and (49) to flow into the line to return filter (46). These conditions allow the springs in the brake cylinders to engage the parking brakes.
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| Illustration 5 | g06031292 |
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Hydraulic Schematic for Parking Brake and Shift Control (33) Auxiliary manifold (34) Parking brake valve (35) Pressure reducing valve (36) Shift valve (37) Left speed valve (38) Right speed valve (39) Brake pressure switch (40) Brake release manifold (41) Needle valve (42) From cooler bypass manifold (43) Hand pump (44) From mainframe extend manifold (45) From auxiliary pump (46) To return filter (47) To screed lift circuit and mainframe extend manifold (48) Left brake cylinder (49) Right brake cylinder | |
When the propel mode is set to "travel", the shift solenoid is energized. Reduced pressure oil flows across shift valve (36) to left speed valve (37) and right speed valve (38). These conditions allow the machine to operate in the travel speed range.
When the parking brake status is set to "disengaged" and all other brake release parameters are met, the parking brake solenoid is energized. Under these conditions, reduced pressure oil flows across parking brake valve (34) to brake release manifold (40). When needle valve (41) is open, supply oil flows out of the brake release manifold. This oil flows to right brake cylinder (49) and to left brake cylinder (48).
Note: When needle valve (41) in brake release manifold (40) is closed, hand pump (43) can be used to manually release the parking brakes.