Variable displacement pump

A variable displacement pump comprising:

• a rotor fixed to a pump shaft inserted to 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;
• a cam ring fitted to a fitting hole within a pump casing so as to be movable and displaceable, forming a pump chamber with respect to an outer peripheral portion of the rotor, and forming first and second hydraulic chambers with respect to the pump casing;
• 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 hydraulic chamber, and introducing a pressure in a downstream side of the main throttle to the second hydraulic 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 hydraulic chamber in correspondence to a discharge flow rate of the pressurized fluid from the pump chamber,
• wherein a suction port open to a suction region of the pump chamber is provided in an end surface of a side plate or a cover fixed to the pump casing so as to close a side portion of the cam ring,
• wherein a first groove always connected to the second hydraulic chamber is provided in a slide surface of the cam ring facing to the end surface of the side plate or the cover,
• wherein a second groove always connected to the suction port is provided in the end surface of the side plate or the cover, and
• wherein when the cam ring is moved to a moving end side in which a volumetric capacity of the pump chamber is reduced, the first groove and the second groove are connected, and the second hydraulic chamber is connectable to the suction port by the grooves.