Hydraulic pump-motor and method of preventing pulsation of hydraulic pump-motor

A method of preventing pulsation of a hydraulic pump-motor for increasing inner pressure of a cylinder bore shifting from a low-pressure suction side to a high-pressure discharge side of a valve plate in an axial hydraulic pump-motor, wherein bottom dead center is defined as mid-point between the low-pressure suction side and the high-pressure suction side of the valve plate in an area in which the cylinder bore transitions from low to high pressure, the axial hydraulic pump-motor having a cylinder block having a plurality of cylinder bores formed about a rotational axis slides relative to the valve plate having a high-pressure side port and a low-pressure side port to control an amount of reciprocation of a piston in each cylinder bore by tilt of a swash plate, comprising:

• a first pressure-increasing step for transmitting high pressure in a first cylinder bore of the plurality of cylinder bores on the high-pressure discharge side of the valve plate of top dead center freed from communication with the high-pressure side port to a second cylinder bore of the plurality of cylinder bores on the low-pressure suction side of the valve plate of the bottom dead center freed from communication with the low-pressure side port after the cylinder bore is freed from the communication with the low-pressure side port;
• a second pressure-increasing step for transmitting high pressure of the high-pressure side port to the second cylinder bore on a side of the bottom dead center through an oil passage for allowing the high-pressure side port and the second cylinder bore to only temporarily communicate with each other after the first pressure-increasing step and before the second cylinder bore begins communication with the high-pressure side port;
• and
• a third pressure-increasing step for transmitting the high pressure of the high-pressure side port to the second cylinder bore by communicating between the cylinder bore on the high-pressure discharge side of the valve plate and the high-pressure side port in a time period after the second pressure-increasing step until before the cylinder bore communicates with the high-pressure side port.

An axial hydraulic pump-motor in which a cylinder block having a plurality of cylinder bores formed about a rotational axis slides relative to a valve plate having a kidney-shaped high-pressure side port and a kidney-shaped low-pressure side port to control an amount of reciprocation of a piston in each cylinder bore by tilt of a swash plate, wherein:

• the cylinder bores rotate counterclockwise with respect to the valve plate;
• a first central location between the side ports where the cylinder bores pass from high-pressure to low-pressure is top dead center;
• a second central location between the side ports where the cylinder bores pass from low-pressure to high-pressure is bottom dead center;
• the cylinder bores and side ports are sized and configured such that each cylinder bore is not in communication with either side port approaching and passing away from the dead centers;
• the valve plate defines an oil passage port near the bottom dead center on the high-pressure side;
• each bore defines a radially inward notch groove that aligns with the oil passage port as the cylinder bores rotate;
• the valve plate defines a residual pressure loss recovery port near the top dead center on the high-pressure side;
• the valve plate defines a residual loss regeneration port near the bottom dead center on the low-pressure side;
• each bore defines a residual pressure loss port that aligns with the residual pressure loss recovery port and the residual loss regeneration port as the cylinder bores rotate, the pump-motor comprising:
• an oil passage for allowing the high-pressure side port and each cylinder bore to temporarily communicate for a time when the notch groove aligns with the oil passage port in a time period of passing through the bottom dead center after each cylinder bore is freed from communication with the low-pressure side port until each cylinder bore communicates with the high-pressure side port, wherein the oil passage has a length capable of transmitting high pressure in the oil passage to the cylinder bore at the time of communication, and of restoring pressure in the oil passage to a pressure of the high-pressure side port before communication with a next cylinder bore during a time of non-communication;
• and
• a residual pressure loss regeneration circuit extending between the residual pressure loss recovery port and the residual pressure loss regeneration port to transmit pressure in one of the cylinder bore on a side of a top dead center when the residual pressure loss recovery port aligns with the residual pressure loss port of such cylinder bore so that the cylinder bore is freed from communication with the high-pressure side port to another cylinder bore on a side of a bottom dead center when the residual loss regeneration port aligns with the residual pressure loss port of said another cylinder bore so that the another cylinder bore is freed from communication with the low-pressure side port in a time period after the cylinder bore is freed from the communication with the low-pressure side port until the notch groove of said another cylinder bore aligns with the oil passage port to establish the oil passage.