Patent ID: 7207783

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 halfway on 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 a discharge opening for discharging a pressure fluid from a pump chamber is disposed on one of the plates for carrying the cam ring; wherein a first seal ring surrounding a drive shaft for driving the rotor and a second seal ring on an outer circumference of the first seal ring, surrounding a wider region than a region where the discharge opening is disposed are provided on a rear face of the other plate; and wherein an inlet passage for introducing a discharge pressure is formed in an area between the first and second seal rings.