Abstract: A differential hydraulic motor comprises a swash plate joined to an output shaft, and a cylinder block joined to an input shaft. A change-over valve is provided which changes over according to the relative rotation of the output shaft and input shaft, and leads a different fluid pressure to pistons housed in the cylinder block according to whether these pistons are extending or contracting. A rotary distributor is provided which connects a high pressure port and low pressure port in a casing to the change-over valve even when the cylinder block is rotating. This rotary distributor comprises a port block which is free to slide in the casing. Pressure from the high pressure port acts on a piston formed on an end face of the port block so as to push the port block against a sliding surface of a cover block joined to the cylinder block.

Abstract: A combined mode hydrostatic transmission comprises a differential hydraulic motor and a variable capacity hydraulic pump for supplying this motor with pressurized oil. The differential hydraulic motor comprises a swash plate connected to an output shaft and a cylinder block joined to an input shaft. Further provided are a brake which selectively brakes the rotation of the cylinder block and a clutch which selectively interrupts the input rotation to the cylinder block. When the brake is operated and fluid is supplied from the variable capacity hydraulic pump with the clutch disengaged, the differential hydraulic motor functions in a HST mode. When the brake is released, the clutch is connected and fluid is supplied from the variable capacity hydraulic pump, the differential hydraulic motor functions in a HMT mode.