Patent ID: 7128542

Claim:
A hydraulic pump of the variable capacity type, comprising: a cam ring movable in a radial direction within a housing, a rotor mounted within the housing for rotation in the cam ring and supporting a plurality of circumferentially spaced vanes movable in a radial direction and slidably engaged with an internal surface of the cam ring, suction and discharge ports formed in the housing or a stationary member fixed in place in the housing and an orifice provided in a discharge passage communicating the discharge port to an outlet port, first and second action chambers formed on an outer circumference of the cam ring and opposed to each other in a movement direction of the cam ring, wherein the cam ring is resiliently biased toward the first action chamber to maximize an eccentric amount relative to the rotor, a differential pressure control valve axially slidably disposed in a valve bore in the housing to control each pressure in the first and second action chambers, and means for providing that spring forces acting on both sides of the differential pressure control valve have more than one value for a single position in said valve bore of said differential pressure control valve.