Variable capacity pump having a variable metering orifice for biasing

Abstract

A variable capacity pump includes a rotor, a plurality of vanes, a cam ring, a spring, a variable orifice, first and second fluid pressure chambers, and first and second openings. The spring biases the cam ring to a position where a volume of the pump chamber of a portion ranging from a pump suction region to a pump discharge region becomes maximum. The variable metering orifice is formed midway along a discharge passage of a pressure fluid discharged from the pump chamber. The first and second fluid pressure chambers are formed between the outer circumferential portion of the cam ring and the inner circumferential surface of the pump body to be divided in a biasing direction of the cam ring, and swing the cam ring upon introduction of input and output fluid pressures of the metering orifice thereto. The first and second openings respectively open to the pump suction region and the pump discharge region of the pump chamber to have opening areas that are changed by a swing of the cam ring. At least the second opening is formed in a range where a portion thereof opposing the first fluid pressure chamber is wider than a portion thereof opposing the second fluid pressure chamber.