Pressure regulating variable displacement vane pump

A variable displacement vane oil pump for an internal combustion engine comprising:

• a housing having a peripheral wall, a cover, an oil inlet, and a pressurized oil outlet;
• a rotor rotatable in the housing on a fixed axis, the rotor having a plurality of slide vanes internally engaging a cam ring to define pumping chambers;
• the cam ring being pivotally connected to the housing wall by a pivot and pivotable to vary the displacement of the pumping chambers;
• a control chamber defined internally by the housing wall, the cam ring, and a first seal disposed between the housing wall and the cam ring;
• a control orifice disposed between the control chamber and the pressurized oil outlet for communicating engine oil to the control chamber;
• a dump chamber adjacent the control chamber and defined by the housing wall, the cam ring, the first seal, and a second seal;
• a dump orifice defined by an intersection of a first groove in the cam ring and a first groove in the housing cover for communicating engine oil between the control chamber and the dump chamber;
• a vent chamber adjacent the dump chamber and defined by the housing wall, the cam ring, and the second seal, the vent chamber being generally at atmospheric pressure;
• a vent orifice defined by an intersection of a second groove in the cam ring and a second groove in the housing cover connecting the dump chamber and the vent chamber for venting the dump chamber;
• wherein pivotal movement of the cam ring in the housing varies the position of the first cam ring groove relative to the first housing cover groove and the second cam ring groove relative to the second housing cover groove, causing the dump orifice and the vent orifice to open and close.