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| Illustration 1 | g01950290 |
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Piston motor (1) Drive shaft (2) Motor case (3) Port (4) Retainer (5) Speed sensor (6) Piston (7) Minimum displacement screw (8) Solenoid (9) Pivot pin (10) Ring gear (11) Spring (12) Barrel (13) Maximum displacement screw (14) Control lens (15) Flushing relief valve (16) Displacement control valve | |
The piston motors convert hydraulic power into mechanical power. The piston motors are mounted to the brakes that are located on the rear frame. The piston motors are infinitely variable and the speeds of the piston motors are controlled by the motor displacement servo valve in the head. For additional information regarding the operation of the displacement control valve, refer to Systems Operation, "Servo Valve - (Motor Displacement)".
The following components rotate within the piston motor:
- Drive shaft (1)
- Retainer (4)
- Pistons (6)
- Barrel (12)
The following components do not rotate with the piston motor:
- Motor case (2)
- Head
- Control lens (14)
Spring (11) pushes barrel (12) against control lens (14) in order to ensure a high pressure seal between barrel (12) and control lens (14) and between control lens (14) and the head.
Control lens (14) has two oil 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 to the control slot in control lens (14). Oil in the control slot flows into the cylinders of barrel (12) that are over the control slot.
The spherical piston heads are held in the sockets in the drive shaft (1) by retainer (4). Seven pistons (6) are held by barrel (12). Barrel (12) rotates around pivot pin (9) which is at an angle to the axis of drive shaft (1). As a result of the bent axis relationship between the barrel and the shaft, the seven pistons move in and out of the cylinders as pressure oil enters the cylinders and pressure oil leaves the cylinders. This movement forces the pistons, the barrel and the drive shaft to rotate.
While the pistons, the barrel and the drive shaft continue to rotate, piston (6) reaches the fully retracted position. At the same time, the cylinder begins to overlap the control slot in control lens (14) on the low pressure side of the loop. At this point, the piston starts to move back into barrel (12). As piston (6) moves back into barrel (12), piston (6) pushes oil out of the cylinder through the control slot to the low pressure side of the loop.
The motor bearings receive oil for lubrication and for cooling from the fan pump. The oil flows from the fan pump to an orifice in the hydraulic block through port (3) to the motor bearings. The remainder of the internal components are lubricated by this oil and by normal leakage from pistons (6) and from barrel (12).
Speed sensor (5) sends two signals back to the ECM as the teeth of ring gear (10) rotate past speed sensor (5). The signals that are produced by speed sensor (5) determine the speed of the motor and the direction of the motor.