 | |
| Illustration 1 | g00500971 |
Piston Motor (Typical Illustration) (1) Drive shaft. (2) Motor case. (3) Port for flushing. (4) Retainer. (5) Piston. (6) Stop for the minimum displacement. (7) Head. (8) Lens control. (9) Stop for the Maximum displacement. (10) Spring. (11) Barrel. (12) Pivot pin. | |
The hydrostatic motor is bidirectional. The motor has a displacement that is variable. The motor has 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 signal pressure, a hose for the oil supply of the motor bearing, and a hose for the case drain.
Drive shaft (1), retainer (4), pistons (5) and barrel (11) rotate. Motor case (2), head (7) and lens control (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 lens control. This also creates a high pressure seal between the barrel and the head.
Lens control (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 lens control (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 retainer (4). Seven pistons (5) are held by barrel (11). The barrel rotates around pivot 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 lens control (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.
 | |
| Illustration 2 | g00529302 |
Schematic of the Variable Displacement Motor (13) Flushing valve. (14) Motor displacement control. (15) Motor speed selection solenoid valve. (16) Reverse solenoid valve. (17) Actuator for the motor. (18) Variable displacement motor. | |
 | |
| Illustration 3 | g00501168 |
(14) Motor displacement control. (15) Motor speed selection solenoid valve. (16) Reverse solenoid valve. (18) Variable displacement motor. | |
The motor displacement control (14) senses the signal from the speed sensing valve. The valve compares the signal pressure with the high pressure oil of the drive loop in order to control the actuator for the motor (17). When the FAST speed mode is selected and the accelerator is depressed, the signal 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.
When the SLOW speed mode is selected, the motor speed selection solenoid valve (15) is energized. Signal oil is blocked from reaching the motor displacement control. The motor is upstroked and the motor is at the maximum displacement. In this mode, the speed of the machine is reduced in order to improve the performance of loading.
When the reverse solenoid valve (16) is energized, the valve sends the pressure into the drive loop for reverse to the motor displacement control (14). In the FORWARD position, the reverse solenoid (16) is de-energized. The pressure for the forward drive loop goes to the motor displacement control (14) .
The inching valve 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 (PIN: 7ZM1-5998ZM1-499), the inching valve is connected to the master cylinder by a linkage. For (PIN: 7ZM600-UP8ZM500-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 some signal oil to flow to the tank. In the FAST speed mode, this causes the motor to upstroke and this causes the pump to destroke.
The flushing valve (13) 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.