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| Illustration 1 | g00500971 |
Piston Motor (Typical Illustration) (1) Drive shaft (2) Motor housing (3) Port for flushing (4) Retaining plate (5) Piston (6) Stop for the minimum displacement (7) Head (8) Control plate (9) Stop for the maximum displacement (10) Spring (11) Barrel (12) Center pin | |
The hydrostatic motors are bidirectional. The motors have a displacement that is variable. The motors have a bent axis. The motor and the actuator convert the hydraulic power into mechanical power. The power is transferred into a hydrostatic drive box that is mounted to the rear axle. Power is also sent to the front axle by a drive shaft.
The actuator piston controls the motor displacement by changing the angle of the rotating group relative to the output shaft. As the stroke of the pistons increases, the stroke creates a higher torque and a lower speed. As the stroke of the pistons decreases, the stroke creates a lower torque and a higher speed.
There are five hoses that are connected to the motor. There are two hoses for the high pressure oil of the drive loop. There is a hose for the speed sensing pressure, a hose for the oil supply of the motor bearing, and a hose for the case drain.
Drive shaft (1), retaining plate (4), pistons (5) and barrel (11) rotate. Motor housing (2), head (7) and control plate (8) do not rotate. Spring (10) pushes barrel (11) against lens control (8) in order to make a high pressure seal between the barrel and the control plate. This also creates a high pressure seal between the barrel and the head.
Control plate (8) has two control slots. One control slot is for the high pressure loop. The other control slot is for the low pressure loop.
When the high pressure oil is at the high pressure loop port, oil from the port flows through the control slot in control plate (8). Oil in the control slot flows into the cylinders of barrel (11) that are over the control slot.
The spherical piston heads are held in the sockets in drive shaft (1) by retaining plate (4). Seven pistons (5) are held by barrel (11). The barrel rotates around center pin (12), which is at an angle to the axis of drive shaft (1). As pressure oil enters the cylinders and pressure oil exits the cylinders, the seven pistons move in the cylinders and out of the cylinders. This rotates the pistons, the barrel and the drive shaft.
As the pistons, the barrel and the drive shaft continue to rotate, the piston reaches the top center (fully retracted position). At the same time, the cylinder begins to overlap the control slot in control plate (8) on the low pressure side of the loop. At this point, the piston starts to move down. This pushes oil out of the cylinder through the control slot to the low pressure loop.
The motor bearings receive lubrication from port (3) and cooling oil from port (3). The remaining internal components are lubricated by oil leakage from the pistons and barrel.
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| Illustration 2 | g01045687 |
(13) Overspeed valve (14) Flushing valve (15) Large variable displacement motor (16) Actuator for the motor (17) Motor displacement control for the large motor (18) FORWARD speed sensing oil line (19) REVERSE speed sensing oil line (20) Shuttle valve (21) Motor displacement control for the small motor (22) Actuator for the motor (23) Small variable displacement motor (24) Drive loop (25) Throttle pin (26) Charge oil line | |
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| Illustration 3 | g01045786 |
(15) Large variable displacement motor. (17) Motor displacement control for the large motor. (18) FORWARD speed sensing oil line. (19) REVERSE speed sensing oil line. (21) Motor displacement control for the small motor. (23) Small variable displacement motor. (26) Charge oil from the overspeed valve. | |
Small variable displacement motor (23) has a motor displacement control (21). When a direction is selected, the pump control valve sends speed sensing oil from the speed sensing valve to the pump actuator. The speed sensing oil also flows through the actuator to the shuttle valve (20) in the small motor. The shuttle valve shifts in order to send the speed sensing oil to the right side of the motor displacement control. The oil pressure works against the oil pressure of the drive loop and spring on the left side of the motor displacement control.
The motor displacement control (21) compares the speed sensing pressure with the high pressure oil of the drive loop in order to control the actuator for the motor (22). When the accelerator is depressed, the speed sensing pressure increases and the motor destrokes. If the machine goes up an incline then the drive pressure increases and the motor upstrokes. This causes the machine speed to decrease and this causes the torque to increase.
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| Illustration 4 | g01045825 |
Overspeed valve (13) The overspeed valve is located on the left side of the machine. | |
Large variable displacement motor (15) has a motor displacement control. The motor displacement control (17) receives charge pressure from overspeed valve (13). The motor displacement control (17) determines the position of the actuator for the motor (16) from the charge pressure from overspeed valve (13). The electronic control module (ECM) determines the amount of spool movement of overspeed valve (13). This will vary the charge pressure to the motor displacement control (17). The ECM monitors the engine speed and the drive shaft speed. The ECM then uses these inputs in order to determine the position of the actuator piston.
When the SLOW speed mode is selected, the ECM de-energizes overspeed valve (13). If overspeed valve (13) is not energized, the large variable displacement motor (15) remains at the maximum displacement position. In this mode, the speed of the machine is reduced in order to improve the performance of loading.
When the direction control lever is moved to the FORWARD position, the pump sends speed sensing oil to speed sensing oil line (18). The speed sensing oil causes the shuttle valve (20) to shift to the left. Then, shuttle valve (20) will direct speed sensing oil to the actuator for the motor (22) .
When the direction control lever is moved to the REVERSE position, the pump sends speed sensing oil from the pump control valve and the pump actuator to speed sensing oil line (19). The speed sensing oil causes the shuttle valve (20) to shift to the right. Speed sensing oil is directed to the actuator for the motor (22). The shuttle (20) senses the position of the pump control valve.
The flushing valve (14) continuously drains some oil from the low pressure side of the drive loop. The oil then drains through the motor to the case drain. The action purges heat, debris and air from the drive loop. The flushing valve (14) also limits the maximum pressure in the low pressure drive loop.
The throttle pin (25) is part of the head group of each motor. Different slots are on the end of each throttle pin. The throttle pin controls the time for stroking the pump. The throttle pins restrict the flow of oil to the actuator piston of the motor. The throttle pins control the acceleration or deceleration of the machine. The throttle pins are self-cleaning because flow direction occurs in both directions. If the throttle pin is assembled incorrectly, testing the machine will reveal abnormal deceleration. The throttle pin of the large motor has one slot. The throttle pin of the small motor has two slots.