Variable displacement oil pump

摘要

Variable displacement oil pump includes a: rotor; vanes; cam ring; housing; biasing member biasing the cam ring in a direction enlarging an eccentricity between centers of the rotor and inner circumferential surface of the cam ring; a contact surface to contact with a cam ring outer circumferential surface via a biasing force applied to the cam ring by the biasing member; a control chamber separately formed by the contact surface and a swing fulcrum of the cam ring on a cam ring outer circumference when the contact surface contacts the cam ring outer circumferential surface, and causing the cam ring to swing against the biasing force of the biasing member by a pressure from a discharge portion to the control chamber; and a choking portion formed on the outer circumferential surface of the cam ring to maintain a pressure of the control chamber even when the cam ring swings.