HYDRAULIC TRANSMISSION DEVICE

A hydraulic transmission device operable to translate hydraulic energy into mechanical energy and vice versa. The device has a housing 14 having a close end portion and an open end portion in the longitudinal direction. The housing supports therein a drive shaft 11, a retainer 12, and a cylinder block 13 which have an integral structure. A recess is formed at a substantially central location of the end surface of the cylinder block 13 that is on the side of an open end of the housing, and a cover 15 closing the open end of the housing has a protruding portion 15A which extends through a port plate 23 to be engaged with the recess of the cylinder block through a bearing 17. A plurality of pistons are disposed in the cylinder block and are kept in tight engagement with a swash plate fixed to the closed end portion of the housing at a constant tilt angle. The device acts as either a swash plate type axial piston pump or motor of this type as the drive shaft rotates.