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| Illustration 1 | g03640139 |
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Typical of 914M, 918M, 920K (1) Hydrostatic pump (2) Hydrostatic motor (de-clutching) (3) Hydrostatic motor (constant drive) (4) Transmission (5) Hydraulic oil filter (6) Clutch (8) Charge pump | |
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| Illustration 2 | g03589722 |
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Typical of 910M (1) Hydrostatic pump (2) Hydrostatic motor (de-clutching) (3) Hydrostatic motor (constant drive) (4) Transmission (5) Hydraulic oil filter (6) Clutch (8) Charge pump | |
The hydrostatic system contains the following components:
- hydrostatic pump (1)
- hydrostatic motors (2) and (3)
- transmission (4)
- hydraulic oil filter (5)
- clutch (6)
- charge pump (8)
- hydrostatic drive pressure sensor (9)
The hydrostatic pump (1) supplies oil to hydrostatic motors (2) and (3). The hydrostatic motors (2) and (3) are mounted to the transmission (4). The front drive shaft and rear drive shaft connect the transmission to the axles.
Charge pump (8) provides control oil to transmission (4). Charge pump (8) provides oil to the hydrostatic system and pilot oil to the implement system through hydraulic oil filter (5).
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| Illustration 3 | g03589825 |
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(1) Hydrostatic piston pump
(2) Hydrostatic piston motor (de-clutching motor) (3) Hydrostatic piston motor (constant drive motor) (4) Transmission (5) Hydraulic oil filter (6) Clutch (8) Charge pump (9) Hydrostatic drive pressure sensor (10) Charge pressure relief valve (11) Cross over relief makeup check vale (12) Cross over relief makeup check vale (13) Hydrostatic drive interlock solenoid valve (14) Proportional pump control valves (forward) (15) Proportional pump control valves (reverse) (16) Pump actuator (17) Motor control solenoid valve (18) Transmission clutch solenoid (19) Transmission clutch valve (20) Motor flushing valve (21) Hydraulic oil cooler (22) Hydraulic oil cooler bypass | |
When the machine is started and in the NEUTRAL position, hydrostatic pump (1) has no displacement until a direction of travel is selected.
Cross Over Relief (COR)/makeup check (11) and (12) protect the hydrostatic system by limiting the pressure spikes in the drive loop. The check valves in the crossover relief COR/makeup valves (11) and (12) open and supply oil to the drive loop. The check valves in the COR/makeup valves (11) and (12) also supply oil to the flushing valve. The COR/makeup valves (11) and (12) supply make oil that is flushed by the flushing valves. The COR/makeup valves (11) and (12) make any oil lost through internal leakage. Charge relief valve (10) limits the charge pressure.
Charge pump (8) sends oil through hydraulic oil filter (5) and then to various components of the hydrostatic drive system. Oil flows from hydraulic oil filter (5) to the interlock valve manifold. Oil in the hydrostatic pump control valve manifold flows to the charge relief valve and to the cross over relief/makeup valves. Within the interlock manifold is the hydrostatic interlock solenoid valve (13). The hydrostatic interlock solenoid valve (13), when energized, allows oil to hydrostatic pump control valves (14) and (15). The hydrostatic interlock solenoid valve (13) is powered on when the machine is running and the parking brake is disengaged. The charge oil pressure is set by charge pressure relief valve (10) in the pump. Charge oil is supplied to hydrostatic pump control valves (14) and (15). Hydrostatic pump control valves (14) and (15) controls the flow of oil to the actuator cylinder (16) of hydrostatic drive pump (1). Charge oil is also supplied to hydrostatic motors (2) and (3) for bearing lube.
Hydrostatic System Forward Drive
The three position Forward, Neutral, and Reverse (FNR) switch on the joystick allows the operator to select the direction of travel. The left pedal position and right (accelerator) pedal position are monitored by the ECM. The following information describes machine functions when selecting FORWARD with the FNR switch after start-up.
As the operator depresses the accelerator pedal, an increasing PWM signal is sent to hydrostatic pump control valve (14) to increase machine speed. When the pump nears maximum displacement, the ECM increases PWM signal to motor solenoid (17) to further increase speed. When
Left pedal input of 1% to 50% cuts back the hydrostatic drive as the following information describes. When slowing the machine, the inching command is applied directly to pump and both motors .When only motor (3) is engaged, the inching command is applied to the pump and motor (3) only. When motor (2) is clutched in, the ECM reduces the PWM signal to proportional solenoid (17) to increase motor (2) displacement. PWM signal to hydrostatic pump control valves (14) is reduced to zero as the left pedal reaches 50%. Reducing PWM signal to hydrostatic pump control valve (14) further reduces machine speed, slowing the machine to a stop. Left pedal travel of greater than 50% mechanically applies the hydromechanical service brake by actuating the hydraulic service brake valve.
Pump And Motor Flushing In The NEUTRAL Position
While the machine is in the NEUTRAL position, flushing valve (20) is closed, not allowing oil to pass. The charge pump (8) supplies oil to the drive loop through the COR/makeup valves. Case drain oil flows through hydrostatic motors (2) and (3) to the hydraulic oil tank.
Drive Loop Flushing In The FORWARD Or REVERSE Direction
The oil pressure difference from the high and low-pressure sides will shift the flushing valve spools . When flushing valves (20) shift, oil flows from the flushing valves to the case drain of piston motor (1). From the case drain, oil flows through hydraulic oil cooler (21) and to the tank.