Variable displacement pump

A variable displacement pump comprising:

• a rotor fixed to a pump shaft inserted into a pump casing so as to be rotationally driven, and structured such that a plurality of vanes are accommodated in grooves so as to be movable in a radial direction;
• an outer case fitted to a fitting hole within a pump casing;
• a cam ring supported by an oscillation supporting point provided in an inner peripheral surface of the outer case so as to freely oscillate and displace, forming a pump chamber with respect to an outer peripheral portion of the rotor, and forming first and second fluid pressure chambers with respect to the outer case;
• a discharge flow rate control apparatus introducing a pressure in an upstream side of a main throttle provided in a pump discharge side passage to the first fluid pressure chamber, and introducing a pressure in a downstream side of the main throttle to the second fluid pressure chamber;
• and
• the discharge flow rate control apparatus having a switch valve apparatus which is actuated on the basis of a pressure difference between the upstream and downstream sides of the main throttle, and controls a supply fluid pressure to the first fluid pressure chamber in correspondence to a discharge flow rate of a pressure fluid from the pump chamber,
• wherein an outer peripheral surface of the cam ring approximately in an opposite side to the portion of the cam ring supported by the oscillation supporting point with respect to the pump shaft is formed as a convex surface portion holding a seal member brought into slidable contact with an inner peripheral surface of the outer case, and
• wherein the inner peripheral surface of the outer case with which the seal member held to the convex surface portion of the cam ring is brought into slidable contact is formed as a circular arc surface around the oscillation supporting point;
• and
• wherein a circular arc shaped inner peripheral surface with which the seal member is brought into slidable contact, in the inner peripheral surface of the outer case is formed as a concave surface portion which is formed in a concave shape with respect to both side inner peripheral surfaces pinching the circular arc shaped inner peripheral surface from both sides in a circumferential direction.