Patent ID: 8684702
Filing Date: 2014-04-01
Classification: F04C

Abstract:
1. A variable displacement oil pump for supplying oil at least to sliding sections of an internal combustion engine, comprising: a pump element including a rotor configured to be rotationally driven by the internal combustion engine, and a plurality of vanes disposed at an outer peripheral section of the rotor; a cam ring having an inner peripheral section for accommodating the pump element thereinside, and an outer peripheral section having a swinging movement fulcrum, the cam ring being swingingly movable around the swinging movement fulcrum to change an eccentricity amount of the cam ring relative to an axis of the rotor; a biasing member for biasing the cam ring in a direction to increase the eccentricity amount of the cam ring relative to the axis of the rotor; the first pressure chamber having a first pressure receiving surface on the outer peripheral section of the cam ring, and directly connected to the discharge section via an open valve-less path, to constantly receive a discharge pressure of the pumped oil fed into the first pressure chamber from the discharge section, to allow the discharge pressure to be applied through the first pressure receiving surface to the cam ring to oppose to a biasing force of the biasing member so as to provide the cam ring with a swinging force in a direction to decrease the eccentricity amount of the cam ring; a second pressure chamber defined by the outer peripheral section of the cam ring and the housing, and having a second pressure receiving surface on the outer peripheral section of the cam ring, where introduction of the same discharge pressure that is introduced into the first pressure chamber causes the discharge pressure to be applied through the second pressure receiving surface to the cam ring to assist the biasing force of the biasing member so as to provide the cam ring with a swinging force in a direction to increase the eccentricity amount of the cam ring, the second pressure receiving surface being set smaller in pressure receiving area than the first pressure receiving surface; and a hydraulic switch for changeover controlling supply of the discharge pressure to the second pressure chamber, based on an energizing current.