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| Illustration 1 | g01943487 |
Hydraulic Schematic NEUTRAL, BRAKE ENGAGED (1) Rear right parking brake (2) Traction control valve (3) Makeup valve (4) From vibratory motors (5) From vibratory pump (6) Rear right propel motor (7) Throttle spool (8) Relief valve (9) Manual brake release pump (10) Charge filter (11) Filter bypass valve (12) From fan motor (13) Thermal bypass valve (14) Rear left parking brake (15) Rear left propel motor (16) Traction control valve (17) Throttle spool (18) Makeup valve (19) Relief valve (20) Shunt valve (21) Flushing relief valve (22) Front right parking brake (23) Front right propel motor (24) Traction control valve (25) Makeup valve (26) Throttle spool (27) Relief valve (28) Propel pump (29) Forward combination valve (30) Directional control valve (31) Servo piston (32) Brake valve (33) Front left parking brake (34) Front left propel motor (35) Traction control valve (36) Front flow divider (37) Throttle spool (38) Makeup valve (39) Relief valve (40) Reverse combination valve (41) POR valve | |
When the engine is running, the propel pump and the charge pump (not shown) rotate. The charge pump draws oil from the hydraulic tank and directs charge oil to the propel pump via the fan motor and the charge filter. Internal passages distribute charge oil to the forward and reverse combination valves, the brake valve, the POR valve, and the directional control valve. External lines distribute charge oil to the shunt valve and to the drum motor brakes.
When the propel lever is in the NEUTRAL position or the machine ECM has disabled the propel system, the directional control valve is not energized. Under these conditions, the center envelope of the directional control valve is active, and both ends of the servo piston are open to the pump case drain. The pump swashplate then moves to zero angle.
Charge oil that enters the combination valves seats the check valves and acts against the makeup valves. Since the propel pump rotates while the engine is running, normal leakage occurs in the propel circuit. When pressure in the propel circuit falls below charge pressure, the makeup valves open and the propel circuit fills with charge oil.
When charge pressure increases to the relief setting, the charge relief valve in the vibratory pump opens. This action directs charge oil into the case drain of the vibratory pump. An orifice in the charge line controls the flow of charge oil into the case of the propel pump.
When the parking brake switch is in the ON position, the parking brake solenoid is de-energized. Under these conditions, charge oil is blocked at the solenoid, and the brake piston cavities are open to the tank. This allows the springs which are acting against the brake pistons to press the disks and plates together to engage the parking brakes.
When the parking brake switch is in the ON position, the propel shunt solenoid is de-energized. Under these conditions, the shunt valve is open, and the control pressure to the directional control valve is open to the tank. Under these conditions, both ends of the servo piston are open to the pump case drain. The pump swashplate then moves to a minimum angle.
When the oil is cold, the majority of the oil flows directly to the tank through port "R" of the thermal bypass manifold. When the hydraulic oil temperature reaches 54 °C (129 °F), the thermal bypass valve begins to close the passage to port "R" of the manifold. When the oil temperature reaches 66 °C (151 °F), the bypass spool is fully closed. In this case, the passage to port "R" of the manifold is fully closed, and all the oil flow is sent through port "TC" of the manifold to the oil cooler.
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| Illustration 2 | g01943515 |
Hydraulic Schematic FORWARD, BRAKE RELEASED (1) Rear right parking brake (2) Traction control valve (3) Makeup valve (4) From vibratory motors (5) From vibratory pump (6) Rear right propel motor (7) Throttle spool (8) Relief valve (9) Manual brake release pump (10) Charge filter (11) Filter bypass valve (12) From fan motor (13) Thermal bypass valve (14) Rear left parking brake (15) Rear left propel motor (16) Traction control valve (17) Throttle spool (18) Makeup valve (19) Relief valve (20) Shunt valve (21) Flushing relief valve (22) Front right parking brake (23) Front right propel motor (24) Traction control valve (25) Makeup valve (26) Throttle spool (27) Relief valve (28) Propel pump (29) Forward combination valve (30) Directional control valve (31) Servo piston (32) Brake valve (33) Front left parking brake (34) Front left propel motor (35) Traction control valve (36) Front flow divider (37) Throttle spool (38) Makeup valve (39) Relief valve (40) Reverse combination valve (41) POR valve | |
When the machine is traveling forward, the forward solenoid is energized. The condition of the forward solenoid is determined by the duty cycle of the signal that is sent from the side console ECM. The side console ECM analyzes the input signals in order to determine the magnitude of the output signal which is sent to the forward solenoid.
When the propel lever is moved into the FORWARD range, the ECM sends an output signal to the forward solenoid. The forward solenoid causes the direction control spool to shift, allowing charge oil to enter the forward pump servo cavity.
The charge pressure in the pump servo cavity overcomes the force of the springs, and the servo piston moves. Movement of the servo piston causes the angle of the swashplate to change, and the pump begins to produce flow. The farther the propel lever is moved, the greater the signal to the forward solenoid. As the signal increases, the direction control spool shifts closer to the maximum position, increasing the angle of the swashplate, and therefore, increasing the oil flow from the propel pump.
Supply oil flows to the forward combination valve, the pressure override relief valve, the flushing spool, and through the flow dividers to the forward side of the propel motors. The pressure differential between the forward and reverse sides of the propel motors causes the motors to turn. After turning the propel motors, oil at a reduced pressure flows back through the flow dividers to the reverse side of the propel pump in order to complete the drive circuit.
If pressure in the reverse circuit falls below charge pressure, the check valve in the combination valve opens, causing charge oil to flow into the reverse circuit. If the pressure in the reverse circuit rises above charge pressure, the check valve closes.
Supply oil which flows into the combination valve in the pump acts against the high pressure relief section of the valve. Supply oil which flows into the pressure override relief valve in the pump moves the shuttle valve and acts on the relief section of the pressure override relief valve.
The relief section of the pressure override relief valve is set at 40000 ± 2000 kPa (5802 ± 290 psi), and the main relief valve is set at 42500 ± 2000 kPa (6164 ± 290 psi). As the pressure increases in the system, the pressure reaches the pressure override relief setting first. When the relief section of the pressure override relief valve is open, the control pressure in the servo piston chamber decreases, and the pump destrokes. This action requires a finite amount of time.
If the pressure in the system reaches 42500 ± 2000 kPa (6164 ± 290 psi) before the pump destrokes, the main relief valve opens. The main relief valve is a fast acting valve. When the main relief valve is open, oil from the high pressure circuit is directed into the low pressure circuit through the makeup valve in the low pressure circuit. The main relief valve quickly limits the pressure while the pressure override relief valve has time in order to destroke the pump.
Action of the pressure override relief valve maintains the swashplate at an angle that will maintain 40000 ± 2000 kPa (5802 ± 290 psi) in the high pressure side of the loop. If the motors are not rotating, the pump swashplate angle will be near zero. In this case, little heat is being generated.
Loop flushing occurs through the flushing relief valve. At the flushing spool, forward circuit oil acts against one side of the spool, and reverse circuit oil acts against the other side. When the forward circuit pressure is higher than the reverse circuit pressure, forward circuit oil causes the flushing spool to shift, allowing reverse circuit oil to flow across the spool and to the flushing relief valve. When the pressure in the reverse circuit is greater than 1700 kPa (247 psi), the flushing relief valve opens, and approximately 11.4 L/min (3.0 US gpm) of oil is removed from the low pressure loop in order to cool and clean the propel circuit. Additional loop flushing occurs through a 1.4 mm (0.055 inch) orifice in the pump. This orifice allows 4 L/min (1.0 US gpm) of oil to flow from the charge circuit into the pump case.
When the parking brake solenoid is energized, the brake solenoid directs charge oil into the piston cavities of the front and rear parking brakes. The charge pressure in the piston cavities overcomes the spring force, and the parking brakes release.
When the parking brake switch is in the OFF position and the side console ECM does not register a level three fault, the propel shunt solenoid is energized. Under these conditions, the shunt valve is closed, and the control pressure to the directional control valve is provided by charge oil pressure. Under these conditions, the pressures in the ends of the servo piston are determined by the position of the direction control valve.
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| Illustration 3 | g01943586 |
Hydraulic Schematic REVERSE, BRAKE RELEASED (1) Rear right parking brake (2) Traction control valve (3) Makeup valve (4) From vibratory motors (5) From vibratory pump (6) Rear right propel motor (7) Throttle spool (8) Relief valve (9) Manual brake release pump (10) Charge filter (11) Filter bypass valve (12) From fan motor (13) Thermal bypass valve (14) Rear left parking brake (15) Rear left propel motor (16) Traction control valve (17) Throttle spool (18) Makeup valve (19) Relief valve (20) Shunt valve (21) Flushing relief valve (22) Front right parking brake (23) Front right propel motor (24) Traction control valve (25) Makeup valve (26) Throttle spool (27) Relief valve (28) Propel pump (29) Forward combination valve (30) Directional control valve (31) Servo piston (32) Brake valve (33) Front left parking brake (34) Front left propel motor (35) Traction control valve (36) Front flow divider (37) Throttle spool (38) Makeup valve (39) Relief valve (40) Reverse combination valve (41) POR valve | |
When the machine is traveling in reverse, the reverse solenoid is energized. The condition of the reverse solenoid is determined by the duty cycle of the signal that is sent from the side console ECM. The side console ECM analyzes the input signals to determine the magnitude of the output signal which it then sends to the reverse solenoid.
When the propel lever is moved into the REVERSE range, the ECM sends an output signal to the reverse solenoid. The reverse solenoid causes the direction control spool to shift, allowing charge oil to enter the reverse pump servo cavity.
The charge pressure in the pump servo cavity overcomes the force of the springs, and the servo piston moves. Movement of the servo piston causes the angle of the swashplate to change, and the pump begins to produce flow. The farther the propel lever is moved, the greater the signal to the reverse solenoid. As the signal increases, the direction control spool shifts closer to the maximum position, increasing the angle of the swashplate, and therefore, increasing the oil flow from the propel pump.
Supply oil flows to the reverse combination valve, the pressure override relief valve, the flushing spool, and through the propel motors and then into the flow divider valves. The pressure differential between the forward and reverse sides of the propel motors causes the motors to turn. After turning the propel motors, oil at a reduced pressure flows back through the flow dividers to the forward side of the propel pump in order to complete the drive circuit.
If pressure in the forward circuit falls below charge pressure, the check valve in the combination valve opens, causing charge oil to flow into the forward circuit. If the pressure in the forward circuit rises above charge pressure, the check valve closes.
Supply oil which flows into the combination valve in the pump acts against the high pressure relief section of the valve. Supply oil which flows into the pressure override relief valve in the pump moves the shuttle valve and acts on the relief section of the pressure override relief valve.
The relief section of the pressure override relief valve is set at 40000 ± 2000 kPa (5802 ± 290 psi), and the main relief valve is set at 42500 ± 2000 kPa (6164 ± 290 psi). As the pressure increases in the system, the pressure reaches the pressure override relief setting first. When the relief section of the pressure override relief valve is open, the control pressure in the servo piston chamber decreases, and the pump destrokes. This action requires a finite amount of time.
If the pressure in the system reaches 42500 ± 2000 kPa (6164 ± 290 psi) before the pump destrokes, the main relief valve opens. The main relief valve is a fast acting valve. When the main relief valve is open, oil from the high pressure circuit is directed into the low pressure circuit through the makeup valve in the low pressure circuit. The main relief valve quickly limits the pressure while the pressure override relief valve has time in order to destroke the pump.
Action of the pressure override relief valve maintains the swashplate at an angle that will maintain 40000 ± 2000 kPa (5802 ± 290 psi) in the high pressure side of the loop. If the motors are not rotating, the pump swashplate angle will be near zero. In this case, little heat is being generated.
Loop flushing occurs through the flushing relief valve. At the flushing spool, forward circuit oil acts against one side of the spool, and reverse circuit oil acts against the other side. Reverse circuit oil causes the flushing spool to shift, allowing forward circuit oil to flow across the spool and to the flushing relief valve. When the pressure in the forward circuit is greater than 1700 kPa (247 psi), the flushing relief valve opens, and 11.4 L/min (3.0 US gpm) of oil is removed from the low pressure loop in order to cool and clean the propel circuit. Additional loop flushing occurs through a 1.4 mm (0.055 inch) orifice in the pump. This orifice allows 4 L/min (1.0 US gpm) of oil to flow from the charge circuit into the pump case.
When the parking brake switch is in the OFF position and the side console ECM does not register a level three fault, the propel shunt solenoid is energized. Under these conditions, the shunt valve is closed, and the control pressure to the directional control valve is provided by charge oil pressure. Under these conditions, the pressures in the ends of the servo piston are determined by the position of the direction control valve.
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| Illustration 4 | g01943595 |
Flow Divider Valve With Equal Traction (FORWARD) (22) Right parking brake (23) Right propel motor (24) Traction control valve (25) Makeup valve (26) Throttle spool (27) Relief valve (33) Left parking brake (34) Left propel motor (35) Traction control valve (36) Front flow divider (37) Throttle spool (38) Makeup valve (39) Relief valve (42) From manual brake release pump (43) To thermal bypass valve (44) From propel pump (Fa) (45) To propel pump (B) (46) To tank return (47) From propel pump (A) | |
Note: The front flow divider and the rear flow divider are identical. These valves operate in the same manner. The following circuit description can be used to discuss either flow divider. The front flow divider is shown in the illustration.
When the propel system is operating, charge oil is used to release the parking brakes. Inside the flow divider valve, charge oil flows to both traction control spools. When the underfoot conditions are equal under both front drums, the traction control solenoids are de-energized. In this case, the traction control valves block charge oil.
When the propel system is operating, supply oil enters port "P" of the flow divider. Internal passages direct supply flow to the throttle spools. With equal traction conditions under both drums, the throttle control spools are not active. In this case, pump supply oil flows out port "A" of the flow divider and out port "B" of the flow divider without restriction. This oil flows to the forward sides of the propel motors. After turning the propel motors, oil at a reduced pressure flows back to the reverse side of the propel pump.
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| Illustration 5 | g01943632 |
Flow Divider Valve Forward Operation With Right Drum Spin (22) Right parking brake (23) Right propel motor (24) Traction control valve (25) Makeup valve (26) Throttle spool (27) Relief valve (33) Left parking brake (34) Left propel motor (35) Traction control valve (36) Front flow divider (37) Throttle spool (38) Makeup valve (39) Relief valve (42) From manual brake release pump (43) To thermal bypass valve (44) From propel pump (Fa) (45) To propel pump (B) (46) To tank return (47) From propel pump (A) | |
When the machine electronic control system determines that the right drum is spinning faster than the left drum, the system energizes the right traction control solenoid. This solenoid is a proportional solenoid. The amount the solenoid moves is proportional to the speed difference between the drums.
When the traction control valve is energized, charge oil is metered to the throttle spool, and the throttle spool shifts. This shift restricts the flow to the right motor, and supply oil is forced to the other drum motors.
The makeup valves in the flow divider help to prevent cavitation in the drum motors when the machine is coming to a stop or when the throttle valve reduces flow to a drum motor faster than the motor can respond.
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| Illustration 6 | g01943646 |
Flow Divider Valve Reverse Operation With Right Drum Spin (22) Right parking brake (23) Right propel motor (24) Traction control valve (25) Makeup valve (26) Throttle spool (27) Relief valve (33) Left parking brake (34) Left propel motor (35) Traction control valve (36) Front flow divider (37) Throttle spool (38) Makeup valve (39) Relief valve (42) From manual brake release pump (43) To thermal bypass valve (44) From propel pump (Fa) (45) To propel pump (B) (46) To tank return (47) From propel pump (A) | |
When the machine is operating in the reverse direction, supply oil from the reverse side of the propel pump is directed to the reverse sides of the propel motors. Oil flows through the motors and is directed to the flow divider valve.
If the right drum is spinning faster than the left drum, the machine electronic control system energizes the right traction control valve. This action causes the throttle spool to shift, creating a restriction in the return line from the right motor. The back pressure slows the right motor and forces more oil through the other drum motors.
If the pressure in the right propel circuit reaches the relief setting, the relief valve opens, and oil is directed to the throttle spool and an orifice. The throttle spool shifts against the force of the metered charge oil. This shift opens the restriction in the return line from the right motor, and the pressure in the system reduces.