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| Illustration 1 | g00781081 |
(1) Hydrostatic pump. (2) Charge pump. | |
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| Illustration 2 | g00503482 |
(3) Hydraulic oil filters. | |
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| Illustration 3 | g00510144 |
(4) Variable displacement motors. (5) Hydrostatic drive box. (6) Drive shaft. | |
The hydrostatic system contains a hydrostatic pump (1), a charge pump (2), hydraulic oil filters (3), two variable displacement motors (4), a hydrostatic drive box (5), a rear axle, a drive shaft (6), and a front axle.
The hydrostatic pump supplies oil to the variable displacement motors (4). Variable displacement motors (4) are mounted to the hydrostatic drive box (5). The hydrostatic drive box (5) is connected to the rear axle. The rear axle is connected with a drive shaft (6) to the front axle.
Hydrostatic System in Neutral
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| Illustration 4 | g00816253 |
Hydrostatic System in NEUTRAL for (S/N: 9WM1-12981WN1-898) (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. | |
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| Illustration 5 | g00811694 |
Hydrostatic System in NEUTRAL for (S/N: 9WM1299-UP1WN899-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 (9WM1-12981WN1-898) (2) Brake valve (9WM1299-UP1WN899-UP) (3) Large variable displacement motor (4) Oil line from the oil cooler to the motor case (5) Oil returns to tank (6) Small variable displacement motor (7) Small variable displacement motor gp (8) Shuttle valve (9) Motor displacement control (10) Actuator for the motor (11) "M1"Test port for the motor (12) Pin (13) Charge relief valve (14) Crossover relief valve for Forward (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) Speed sensing valve (28) Test port for charge pressure (29) Oil line to the implement pilot system (30) Crossover relief valve for Reverse (31) Test port for pressure in the pump case (32) Motor Signal Control Valve (33) Test port for the high pressure oil of the drive loop (34) POR valve (35) Flushing valve (36) Actuator for the motor (37) "M2" test port for the motor (38) Motor displacement control (39) Large variable displacement motor group (40) "MS" Signal pressure for the motor (41) Pin (42) Shutoff Valve for pilot signal (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), which then flows to speed sensing valve (27) .
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 (27) converts some of the charge oil to signal oil (DD). The signal oil (DD) controls the hydrostatic pump (24) and the hydrostatic motor (6). Most of the oil in speed sensing valve (27) flows to crossover relief valve (14) and (30), charge relief valve (13), implement pilot system (29), and motor signal control valve (32) .
The crossover relief valve (14) and crossover relief valve (30) 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 (14) and crossover relief valve (30) open in order to direct charge oil to hydrostatic pump (24), small variable displacement motor (3), large variable displacement motor (6), flushing valve (35), and shuttle valve (8). Charge relief valve (13) limits the maximum hydrostatic system pressure, when the machine is in NEUTRAL. When the hydrostatic system is completely charged, charge relief valve (13) opens. Most of the charge oil flows to the pump case and to the hydraulic tank.
Charge oil also flows to both motor displacement controls (9) and (38), to both actuators for the motors (10) and (36), and through the resolver in the POR valve (34). The hydrostatic motors are at the maximum displacement.
When the accelerator is depressed, speed sensing valve (27) creates signal oil. The signal oil flows to POR valve (34) and Forward/Neutral/Reverse valve (18). The signal oil also flows to the valve for the creeper speed (1) and valve (2). The creeper speed control is an option.
In NEUTRAL, signal oil (DD) is blocked at the Forward/Neutral/Reverse valve (18). Without signal oil pressure to the actuator for the hydrostatic pump (19), the pump will remain in NEUTRAL and no oil flow will be produced. The pump actuator (19) is held in the center position by springs.
The inching valve (2) allows hydrostatic braking before the service brakes are applied. The inching valve provides an inching operation that allows low machine speed with high engine speed. This allows high implement pump flow for faster implement speed.
For (S/N: 9WM1-12981WN1-898), the inching valve is connected to the master cylinder by a linkage. For (S/N: 9WM1299-UP1WN899-UP), the inching valve is incorporated into the brake valve. The service brakes will begin to apply a moment before the hydrostatic drive is completely neutralized. As the service brake pedal is depressed, the inching valve allows most of the signal oil to flow to the tank. In the FAST speed mode, the reduced flow of signal oil causes both of the motors to upstroke. The reduced flow of signal oil causes the pump to destroke.
The shutoff valve for the pilot signal (42) is used to block the signal oil to the brake valve on (S/N: 9WM1299-UP1WN899-UP) for testing purposes only.
Hydrostatic System in Forward for the Fast Mode
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| Illustration 6 | g00816260 |
Hydrostatic System in FORWARD and FAST speed mode for (S/N: 9WM1-12981WN1-898) (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. | |
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| Illustration 7 | g00811742 |
Hydrostatic System in FORWARD and FAST speed mode for (S/N: 9WM1299-UP1WN899-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 (9WM1-12981WN1-898) (2) Brake Valve (9WM1299-UP1WN899-UP) (3) Large variable displacement motor (4) Oil line from the oil cooler to the motor case (5) Oil returns to tank (6) Small variable displacement motor (7) Small variable displacement motor gp (8) Shuttle valve (9) Motor displacement control (10) Actuator for the motor (11) "M1"Test port for the motor (12) Pin (13) Charge relief valve (14) Crossover relief valve for Forward (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) Speed sensing valve (28) Test port for charge pressure (29) Oil line to the implement pilot control valve (30) Crossover relief valve for Reverse (31) Test port for pressure in the pump case (32) motor signal control valve (33) Test port for the high pressure oil of the drive loop (34) POR valve (35) Flushing valve (36) Actuator for the motor (37) "M2" test port for the motor (38) Motor displacement control (39) Large variable displacement motor gp (40) "MS" Signal pressure for the motor (41) Pin (42) Shutoff valve for pilot signal (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 (27) flows to the left end of the pump actuator (19) and to shuttle valve (8). The pump actuator (19) is held in the center position by springs.
The signal pressure will cause the shuttle valve (8) to shift upward. The movement of the shuttle valve (8) allows the signal pressure to reach motor displacement control (9). Because the signal pressure is too low, the pump will not upstroke and the machine will not move.
Motor signal control valve (32) is energized by the electronic control module, when a certain ground speed is reached. Charge oil (CC) will flow through the motor signal control valve (32). Charge oil (CC) will begin to destroke large variable displacement motor (3) .
As the accelerator pedal is depressed, the engine speed increases. The signal pressure (DD) that is created by the speed sensing valve (27) also increases. The increase in signal pressure (DD) will cause the hydrostatic pump (24) to upstroke. Pump flow from the hydrostatic pump (24) also increases. The increased pump flow causes both variable displacement motors (3) and (6) to turn faster and the machine speed increases. As the engine speed continues to increase, both motors will begin to destroke at the same time but at different rates.
Each motor reacts differently to increasing ground speed and increasing signal pressure. Each motor will be explained separately.
Small Variable Displacement Motor
As the engine speed continues to increase, the signal pressure from the speed sensing valve (27) also increases. Eventually, the signal pressure moves motor displacement control (9) downward. This allows high pressure oil of the drive loop (AA) to flow to the actuator for the motor (10) in order to destroke the motor (6). As the motor displacement decreases, the motor speed increases. When the motor is at the minimum displacement, the machine is at the maximum speed.
Any resistance to the rotation of the motor increases the drive pressure. The high pressure oil of the drive loop (AA) acts on the bottom of the motor displacement control (9). The motor displacement control (9) moves upward. This allows the oil in the actuator for the motor (10) to flow to the hydraulic tank. The actuator for the motor (10) moves down causing an increase in the motor displacement. This reduces the machine speed.
The motor displacement control (9) continuously balances the signal pressure (DD) and the high pressure oil of the drive loop (AA). This prevents an excessive amount of engine lugging.
After the motors are at the maximum displacement, any further resistance to the rotation of the motor increases the drive pressure. When the drive pressure reaches the setting for the POR valve (34), the signal pressure begins to drain to the hydraulic tank. The decrease in the signal pressure destrokes the pump swashplate. This causes the pump flow to decrease. The speed of the machine is reduced.
Large Variable Displacement Motor
The electronic control module receives an input from the engine speed and an input from the drive shaft speed in order to regulate the motor signal control valve (32). The motor signal control valve (32) meters the charge oil to motor displacement control (38) in order to vary the motor displacement.
As the ground speed increases, the motor signal control valve (32) begins to send a variable hydraulic signal to the motor displacement control (38). The motor displacement control (38) begins to move down. High pressure oil of the drive loop (AA) flows to the bottom end of the actuator for the motor (36), which destrokes the motor.
When the motor reaches a specified speed, the large variable displacement motor (3) will stay at the minimum displacement. Any additional increase in machine speed is caused by destroking the small variable motor (6) .
If the machine exceeds the maximum speed, the electronic module causes the motor signal control valve to reduce the charge pressure oil to the motor displacement control (38). This causes the actuator for the motor to upstroke and this causes a decrease in the machine speed.
Hydrostatic System in Forward for the Slow Mode
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| Illustration 8 | g00816255 |
Hydrostatic System in FORWARD and SLOW speed mode for (S/N: 9WM1-12981WN1-898) (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. | |
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| Illustration 9 | g00811747 |
Hydrostatic System in FORWARD and Slow speed mode for (S/N: 9WM1299-UP1WN899-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 (9WM1-12981WN1-898) (2) Brake Valve (9WM1299-UP1WN899-UP) (3) Large variable displacement motor (4) Oil line from the oil cooler to the motor case (5) Oil returns to tank (6) Small variable displacement motor (7) Small variable displacement motor gp (8) Shuttle valve (9) Motor displacement control (10) Actuator for the motor (11) "M1"Test port for the motor (12) Pin (13) Charge relief valve (14) Crossover relief valve for Forward (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) Speed sensing valve (28) Test port for charge pressure (29) Oil line to the implement pilot control valve (30) Crossover relief valve for Reverse (31) Test port for pressure in the pump case (32) motor signal control valve (33) Test port for the high pressure oil of the drive loop (34) POR valve (35) Flushing valve (36) Actuator for the motor (37) "M2" test port for the motor (38) Motor displacement control (39) Large variable displacement motor gp (40) "MS" Signal pressure for the motor (41) Pin (42) Shutoff valve for the pilot signal (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 hydrostatic system in the slow mode differs with the fast mode. In the slow mode, the control valve for motor displacement signal line does not energize. The large motor will not destroke. The large motor remains destroked in order to limit the speed of the machine. The motor displacement control in the motor moves.
Hydrostatic System in Reverse
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| Illustration 10 | g00816257 |
Hydrostatic System in REVERSE and FAST speed mode for (S/N: 9WM1-12981WN1-898) (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. | |
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| Illustration 11 | g00811910 |
(1) Valve for the creeper speed (2) Inching valve (9WM1-12981WN1-898) (2) Brake valve (9WM1299-UP1WN899-UP) (3) Large variable displacement motor (4) Oil line from the oil cooler to the motor case (5) Oil returns to tank (6) Small variable displacement motor (7) Small variable displacement motor gp (8) Shuttle valve (9) Motor displacement control (10) Actuator for the motor (11) "M1"Test port for the motor (12) Pin (13) Charge relief valve (14) Crossover relief valve for Forward (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) Speed sensing valve (28) Test port for charge pressure (29) Oil line to the implement pilot control valve (30) Crossover relief valve for Reverse (31) Test port for pressure in the pump case (32) motor signal control valve (33) Test port for the high pressure oil of the drive loop (34) POR valve (35) Flushing valve (36) Actuator for the motor (37) "M2" test port for the motor (38) Motor displacement control (39) Large variable displacement motor gp (40) "MS" Signal pressure for the motor (41) Pin (42) Shutoff valve for the pilot signal (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 (27) flows to the right end of the pump actuator (19). The pump actuator (19) is held in the center position by springs.
The signal pressure also flows to the shuttle valve (8). The shuttle valve (8) shifts downward. The downward movement allows the signal pressure to reach motor displacement control (9). Because the signal pressure is too low, the pump will not upstroke and the machine will not move.
The motor signal control valve (32) is energized by the electronic control module, when a certain ground speed is reached. Charge oil (CC) will flow through the motor signal control valve (32). Charge oil (CC) will begin to destroke large variable displacement motor (3) .
As the accelerator pedal is depressed, the engine speed increases. The signal pressure (DD) that is created by the speed sensing valve (27) also increases. The increase in signal pressure (DD) will cause the hydrostatic pump (24) to upstroke. The high pressure oil of the drive loop (AA) is sent to the opposite side of the drive loop. This causes the motors to rotate in the opposite direction. This causes the pump flow to increase and this causes the motor displacement to decrease. Both variable displacement motors (3) and (6) turn faster and the machine speed is increased. As the engine speed continues to increase, both motors will begin to destroke at the same time but at different rates.
The motors rotate in the opposite direction, when the machine is in REVERSE. The motors operate the same way, when the machine is in REVERSE and in FORWARD.