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| Illustration 1 | g00503435 |
(1) Hydrostatic pump. (2) Charge pump. | |
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| Illustration 2 | g00503482 |
(3) Hydraulic oil filters. | |
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| Illustration 3 | g00503437 |
(4) Hydrostatic drive box. (5) Variable displacement motor. (6) Drive shaft. | |
The hydrostatic system contains a hydrostatic pump (1), a charge pump (2), hydraulic oil filters (3), a variable displacement motor (5), a hydrostatic drive box (4), a rear axle, a drive shaft (6), and a front axle.
The hydrostatic pump supplies oil to variable displacement motor (5). Variable displacement motor (5) is mounted to hydrostatic drive box (4). Hydrostatic drive box (4) is connected to the rear axle. The rear axle is connected with drive shaft (6) to the front axle.
Hydrostatic System in Neutral
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| Illustration 4 | g00504418 |
Hydrostatic System in NEUTRAL for (PIN: 7ZM1-5998ZM1-499) (AA) High pressure oil of the drive loop. (BB) Low pressure oil of the drive loop. (CC) Charge oil pressure. (DD) Signal oil pressure. (EE) Return oil to the tank. The callouts are defined after the NEUTRAL schematics. | |
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| Illustration 5 | g00504419 |
Hydrostatic system in NEUTRAL for (PIN: 7ZM600-UP8ZM500-UP) (AA) High pressure oil of the drive loop. (BB) Low pressure oil of the drive loop. (CC) Charge oil pressure. (DD) Signal oil pressure. (EE) Return oil to the tank. The callouts are defined on the next page. (1) Valve for the creeper speed (2) Inching valve (7ZM1-5998ZM1-499) (2) Brake valve (7ZM600-UP8ZM500-UP) (3) Oil returns to tank (4) Oil line from the oil cooler to the motor case (5) Variable displacement motor (6) Variable displacement motor group (7) Reverse solenoid (8) Test port for the motor (9) Actuator for the motor (10) POR valve (11) Charge relief valve (12) Oil line from the housing of the hydrostatic pump to the hydraulic tank (13) Crossover relief valve for Forward (14) Speed sensing valve (15) Hydraulic oil filter (16) Hydraulic oil filter bypass valve (17) Scheduled oil sampling valve (18) Forward/Neutral/Reverse valve (19) Actuator for the hydrostatic pump (20) Hydraulic oil line from the hydraulic tank (21) Brake and steering pump (22) Implement pump (23) Charge pump (24) Hydrostatic pump (25) Hydrostatic pump group (26) "PS"Test port for pump signal pressure (27) Test port for charge pressure (28) Oil line to the implement pilot system (29) Crossover relief valve for Reverse (30) Test port for pressure in the pump case (31) Test port for the high pressure oil of the drive loop (32) Flushing valve (33) Motor displacement control (34) Solenoid for the speed control (AA) High pressure oil of the drive loop (BB) Low pressure oil of the drive loop (CC) Charge oil pressure (DD) Signal oil pressure (EE) Return to tank oil | |
The charge pump (23) charges the system and the charge pump provides makeup oil, when the machine is started and the machine is in NEUTRAL. The charge pump sends oil through hydraulic oil filter (15). The oil then flows to speed sensing valve (14) .
The hydraulic oil filter (15) contains filter bypass valve (16). If the filter is plugged, the bypass valve opens and the switch closes. An indicator light turns ON in the operator compartment. When the oil is cold, the bypass valve opens and the indicator light turns ON temporarily.
The speed sensing valve (14) converts some of the charge oil to signal oil. The signal oil controls the hydrostatic pump (24) and the variable displacement motor (5). Most of the oil in speed sensing valve (14) flows to crossover relief valve (13) and (29), charge relief valve (11), and implement pilot system (28).
The crossover relief valve (13) and crossover relief valve (29) protect the system by maintaining a minimum pressure or by reducing the pressure spikes in the drive loop. When the machine is started, crossover relief valve (13) and crossover relief valve (29) open in order to direct charge oil to hydrostatic pump (24), variable displacement motor (5), flushing valve (32) and reverse solenoid (7). Charge relief valve (11) limits the maximum hydrostatic system pressure, when the machine is in NEUTRAL. When the hydrostatic system is completely charged, charge relief valve (11) opens. Most of the charge oil flows to the pump case and to the hydraulic tank.
In NEUTRAL, reverse solenoid (7) directs pressure oil to the forward drive loop, to motor displacement control (33), and to the actuator for the motor (9) .
Charge oil (CC) also flows through the ball resolver in POR valve (10) .
When the accelerator is depressed, speed sensing valve (14) creates signal oil (DD). The signal oil (DD) flows to POR valve (10) and Forward/Neutral/Reverse valve (18). The signal oil also flows to the valve for the speed control (34), the valve for the creeper speed (1), and inching valve (2). The creeper speed control is an option.
If the solenoid for the speed control (34) is not energized, signal oil (DD) flows to the motor displacement control (33) and to the actuator for the motor (10). If the solenoid for the speed control (34) is energized, the signal oil (DD) is blocked and the motor stays at the maximum displacement.
In NEUTRAL, the charge oil (CC) is blocked at the Forward/Neutral/Reverse valve (18). There is no oil pressure in the actuator for the hydrostatic pump (19). Therefore, the pump remains in neutral and no oil flow is produced.
Hydrostatic System in Forward
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| Illustration 6 | g00504420 |
Hydrostatic System in FORWARD and FAST speed mode for (PIN: 7ZM1-5998ZM1-499) (AA) High pressure oil of the drive loop. (BB) Low pressure oil of the drive loop. (CC) Charge oil pressure. (DD) Signal oil pressure. (EE) Return oil to the tank. The callouts are defined after the FORWARD schematics. | |
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| Illustration 7 | g00504421 |
Hydrostatic system in FORWARD and FAST speed mode for (PIN: 7ZM600-UP8ZM500-UP) (AA) High pressure oil of the drive loop. (BB) Low pressure oil of the drive loop. (CC) Charge oil pressure. (DD) Signal oil pressure. (EE) Return oil to the tank. The callouts are defined on the next page. (1) Valve for the creeper speed (2) Inching valve (7ZM1-5998ZM1-499) (2) Brake valve (7ZM600-UP8ZM500-UP) (3) Oil returns to tank (4) Oil line from the oil cooler to the motor case (5) Variable displacement motor (6) Variable displacement motor group (7) Reverse solenoid (8) Test port for the motor (9) Actuator for the motor (10) POR valve (11) Charge relief valve (12) Oil line from the housing of the hydrostatic pump to the hydraulic tank (13) Crossover relief valve for Forward (14) Speed sensing valve (15) Hydraulic oil filter (16) Hydraulic oil filter bypass valve (17) Scheduled oil sampling valve (18) Forward/Neutral/Reverse valve (19) Actuator for the hydrostatic pump (20) Hydraulic oil line from the hydraulic tank (21) Brake and steering pump (22) Implement pump (23) Charge pump (24) Hydrostatic pump (25) Hydrostatic pump group (26) "PS"Test port for pump signal pressure (27) Test port for charge pressure (28) Oil line to the implement pilot system (29) Crossover relief valve for Reverse (30) Test port for pressure in the pump case (31) Test port for the high pressure oil of the drive loop (32) Flushing valve (33) Motor displacement control (34) Solenoid for the speed control (AA) High pressure oil of the drive loop (BB) Low pressure oil of the drive loop (CC) Charge oil pressure (DD) Signal oil pressure (EE) Return to tank oil | |
When the operator moves the transmission control lever to the FORWARD position, an electrical signal is sent to the forward solenoid of Forward/Neutral/Reverse valve (18). When the forward solenoid is energized, signal oil from speed sensing valve (14) flows to the left end of the pump actuator (19). The pump actuator (19) is held in the center position by springs. Because the signal pressure is too low, the pump will not upstroke and the machine will not move.
As the operator depresses the accelerator pedal, the engine speed increases causing the signal pressure to increase. The increase of pressure causes the pump to upstroke. As the pump upstrokes, the speed of the machine increases.
As the engine speed continues to increase, the signal pressure from speed sensing valve (14) also increases. The increase in signal pressure will move motor displacement control (33). This allows the high pressure oil of the drive loop (AA) to flow to the actuator for the motor (9) in order to destroke the motor. Destroking the motor causes the motor to rotate faster. When the motor is fully destroked, the pump is fully upstroked and the engine is at maximum rpm. The machine speed is maximum.
Motor displacement control (33) continually balances the signal pressure and the drive pressures. The pressure must be continually balanced in order to prevent the engine lugging.
After the motor is at the maximum displacement, any resistance to the rotation of the motor increases the drive pressure. When the pressure of the drive loop reaches the POR valve (10), the signal pressure will begin to drain to the hydraulic tank. As the signal pressure decreases, the pump swashplate destrokes. This causes the pump flow to decrease and this causes the motor displacement to increase. The speed of the machine is reduced.
Hydrostatic System in Reverse
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| Illustration 8 | g00504422 |
Hydrostatic System in REVERSE and FAST speed mode for (PIN: 7ZM1-5998ZM1-499) (AA) High pressure oil of the drive loop. (BB) Low pressure oil of the drive loop. (CC) Charge oil pressure. (DD) Signal oil pressure. (EE) Return oil to the tank. The callouts are defined after the REVERSE schematics. | |
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| Illustration 9 | g00504443 |
Hydrostatic system in REVERSE and FAST speed mode for (PIN: 7ZM600-UP8ZM500-UP) (AA) High pressure oil of the drive loop. (BB) Low pressure oil of the drive loop. (CC) Charge oil pressure. (DD) Signal oil pressure. (EE) Return oil to the tank. The callouts are defined on the next page. (1) Valve for the creeper speed (2) Inching valve (7ZM1-5998ZM1-499) (2) Brake valve (7ZM600-UP8ZM500-UP) (3) Oil returns to tank (4) Oil line from the oil cooler to the motor case (5) Variable displacement motor (6) Variable displacement motor group (7) Reverse solenoid (8) Test port for the motor (9) Actuator for the motor (10) POR valve (11) Charge relief valve (12) Oil line from the housing of the hydrostatic pump to the hydraulic tank (13) Crossover relief valve for Forward (14) Speed sensing valve (15) Hydraulic oil filter (16) Hydraulic oil filter bypass valve (17) Scheduled oil sampling valve (18) Forward/Neutral/Reverse valve (19) Actuator for the hydrostatic pump (20) Hydraulic oil line from the hydraulic tank (21) Brake and steering pump (22) Implement pump (23) Charge pump (24) Hydrostatic pump (25) Hydrostatic pump group (26) "PS"Test port for pump signal pressure (27) Test port for charge pressure (28) Oil line to the implement pilot system (29) Crossover relief valve for Reverse (30) Test port for pressure in the pump case (31) Test port for the high pressure oil of the drive loop (32) Flushing valve (33) Motor displacement control (34) Solenoid for the speed control (AA) High pressure oil of the drive loop (BB) Low pressure oil of the drive loop (CC) Charge oil pressure (DD) Signal oil pressure (EE) Return to tank oil | |
When the operator moves the transmission control lever to the REVERSE position, an electrical signal is sent to the reverse solenoid of Forward/Neutral/Reverse valve (18). When the reverse solenoid is energized, signal oil from speed sensing valve (14) flows to the right end of pump actuator (19). The pump actuator (19) is held in the center position by springs. Because the signal pressure is too low, the pump will not upstroke and the machine will not move.
When the machine is in REVERSE, reverse solenoid (7) on variable displacement motor group (6) is energized. Oil from the reverse side of the drive loop flows to motor displacement control (33) and to the actuator for the motor (9) .
As the operator depresses the accelerator pedal, the engine speed increases. This causes the signal pressure that is created by the speed sensing valve (14) to increase. The increase in signal pressure causes the hydrostatic pump (24) to upstroke and the increase in signal pressure causes the pump flow to increase. An increase in pump flow will cause variable displacement motor (5) to turn faster. As the motor turns faster, the speed of the machine increases.
As the engine speed continues to increase, the signal pressure from the speed sensing valve also increases. The increase in signal pressure will move the motor displacement control (33) downward. This allows the high pressure oil of the drive loop (AA) to flow to the actuator of the motor to destroke the motor. Destroking the motor causes the motor to rotate faster. When the motor is fully destroked, the pump is fully upstroked and the engine is at maximum rpm. The machine speed is maximum.
Any resistance to the rotation of the motor increases the pressure of the drive loop. This pressure acts on the bottom of the motor displacement control (33). The motor displacement control (33) moves upward. Oil in the actuator for the motor (9) flows to the hydraulic tank. The actuator for the motor (9) will move downward. This causes the motor displacement to increase and this causes machine speed to decrease.
Motor displacement control (33) continually balances the signal pressure and the drive pressures. The pressures must be continually balanced in order to prevent the engine lugging.
When the motor is at the maximum displacement, any further resistance to the rotation of the motor will increase the pressure of the drive loop more. When the pressure of the drive loop reaches the POR valve (10), the signal pressure will begin draining to the hydraulic tank. As the signal pressure decreases, the pump swashplate destrokes. This causes the pump flow to decrease and this causes the motor displacement to increase. The speed of the machine is reduced.