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| Illustration 1 | g00552526 |
(1) Shaft housing. (2) Rotor housing. (3) Rotor. (4) Piston assembly. (5) Brake housing. (6) Clutch pack. (7) Brake piston. (8) Belleville washer. (9) Roller bearing. (10) Roller bearing. (11) Shaft. | |
There are two hydrostatic piston motors on each machine. The hydrostatic piston motors are of a radial piston type with a rotating shaft. The hydrostatic piston motors consists of three sections. These sections are the shaft housing (1), the rotor housing (2) and the brake housing (5). Rotor (3) is connected to shaft (11) by splines. Clutch pack (6) is engaged by brake piston (7) and the belleville washer (8) when there is no hydraulic pressure. When there is hydraulic pressure, the pressure forces brake piston (7) against the belleville washer (8). This allows clutch pack (6) to disengage.
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| Illustration 2 | g00599077 |
The oil starts in the tank. Oil flows from the tank to the gear pump. The oil flows from the gear pump to the fan motor.
On the 228 Skid Steer Loader, the oil flows from the fan drive motor to the hydraulic oil filter. From the hydraulic oil filter, the oil flows to the speed sensing valve. The speed sensing valve is located in the piston pump (hydrostatic). The oil flows from the speed sensing valve to the charge relief valve. The oil flows from the charge relief valve to the piston pump (hydrostatic). From the piston pump (hydrostatic), the oil flows to the piston motors.
On the 248 Skid Steer Loader, the oil flows from the fan drive motor to the pressure switch for the engine cut off circuit. From the pressure switch for the engine cut off circuit, the oil flows to the hydraulic oil filter. Then, the oil flows to the speed sensing valve that is located in the piston pump (hydrostatic). From the speed sensing valve, the oil flows to the charge relief valve. From the charge relief valve, the oil flows to the piston pump (hydrostatic). From the piston pump (hydrostatic), the oil flows to the piston motors.
The hydraulic oil from the piston pump (hydrostatic) flows through ports (A) and (B). One port will be high pressure and the other port will be low pressure. The high pressure port is determined by the desired direction of rotation. For this explanation of the motor, port (A) is considered to be the high pressure port.
Hydraulic oil flows through the axial bore of port A and into the annular passage (D). Hydraulic oil then flows through the exposed ports (E). The exposed ports (E) are below the piston assemblies. As the pressure increases, the piston is forced outward. As the piston is forced outward, the piston rollers roll on the inner diameter of the cam.
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| Illustration 3 | g00599046 |
As the pistons move along the inner diameter of the cam, the pistons turn the rotor. The rotor turns the shaft. The rotor is connected to the shaft by splines. Illustration 3 shows the rotational motion of the pistons as the pistons rotate about the shaft.
As the rotor turns, the previously exposed ports are covered and previously covered ports are exposed. The fully extended piston assembly next passes over an exposed port.
The piston rollers, which follow the inner diameter of the rotor, force the piston assembly toward the shaft. This is due to the shape of the inner diameter of the rotor. The hydraulic oil is forced through the exposed port by the inward motion of the piston assembly. The hydraulic oil then returns to an annular passage (D) which then directs the oil through an axial bore and out of port (B) .
Port (C) is a case drain for oil that leaks by the piston assemblies and for the flushing valve. The flushing valve uses the oil in order to cool the motor. The flushing valve also uses the oil in order to flush harmful particles from the motor.
Oil for the flushing valve flows from the low pressure side of the drive loop. The oil pressure in the forward drive cavity increases. The pressure increase shifts the spool toward the reverse drive cavity. Oil from the reverse drive cavity flows through the center passage. The oil pressure in the center passage opens the relief poppet. The oil flows through port (C) to the return manifold and the oil is routed through the oil cooler. Then, the oil returns to the tank.
The oil pressure in the reverse drive cavity increases. The pressure increase shifts the spool toward the forward drive cavity. From the forward drive cavity, oil flows through the center passage. The oil pressure in the center passage opens the relief poppet. The oil flows through port (C) to the return manifold and the oil is routed through the oil cooler. Then, the oil returns to the tank.