Patent ID: 6976830

Claim:
A variable displacement pump comprising: a cam ring carried swingably between plates on both sides; a first fluid pressure chamber formed in one of the swing directions of the cam ring; a second fluid pressure chamber provided in the other swing direction of the cam ring; urging means for urging the cam ring toward the first fluid pressure chamber, disposed on a side of the second fluid pressure chamber; a rotor eccentrically disposed within the cam ring and having a plurality of vanes on an outer circumference thereof; a metering orifice disposed part way along a discharge passage of a pressure fluid discharged from a pump; and a control valve activated by a pressure difference between upstream and downstream sides of the metering orifice, wherein a fluid pressure in at least one of the first and second fluid pressure chambers is controlled by activation of the control valve to swing the cam ring; wherein the first fluid pressure chamber is connected to the control valve to control a fluid pressure in the first fluid pressure chamber; the second fluid pressure chamber is shut off from the control valve and is always connected to a pump suction side; and wherein an internal pressure of the cam ring is applied in the one of the swing directions of the cam ring; and wherein the second fluid pressure chamber is always shut off from the control valve.