Patent ID: 8794124

Claim:
An axial hydraulic pump or motor comprising: a cylinder block having a plurality of cylinder bores formed around a rotation shaft, configured to slide on a valve plate with a high pressure side port and a low pressure side port; a plurality of cylinder ports of the plurality of cylinder bores; a swash plate having an inclination for controlling a reciprocating amount of a piston inside each cylinder bore; a plurality of communication holes which are formed in the cylinder block and are directed from the cylinder bores toward the valve plate, the plurality of communication holes being provided correspondingly to the plurality of cylinder ports, respectively; a top dead center side communication port which is formed in the valve plate and is formed in a top dead center side confining region as a region between an end of a valve plate suction port and an end of a valve plate discharge port at a top dead center side; a bottom dead center side communication port which is formed in the valve plate and is formed in a bottom dead center side confining region as an another region between the end of the valve plate suction port and the end of the valve plate discharge port at a bottom dead center side; and a residual pressure regenerating circuit for connecting the top dead center side communication port to the bottom dead center side communication port, the top dead center side communication port communicating to one of the plurality of communication holes in response to rotation of the rotation shaft, and the bottom dead center side communication port communicating to another one of the plurality of communication holes in response to rotation of the rotation shaft, wherein the bottom dead center side communication port is provided at the bottom dead center side with a predetermined angular difference with respect to the position of the top dead center side communication port at the rotation advancing direction side of the cylinder block in relation to the line connecting the rotation shaft center.