| 主权项 |
1. A variable displacement oil pump for supplying oil to at least sliding sections of an internal combustion engine, comprising:
a pump element including a rotor rotationally driven by the internal combustion engine, and a plurality of vanes disposed at an outer peripheral section of the rotor to be projectable from and retractable in the outer peripheral section; 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; side walls disposed respectively on axially opposite sides of the cam ring to define a plurality of hydraulic fluid chambers each of which is defined by the rotor and the adjacent vanes; a housing for accommodating the cam ring thereinside and including a discharge section opened through at least one of the side walls to a discharge region in which volumes of the hydraulic fluid chambers decrease along a rotational direction of the rotor, and a suction section opened through at least one of the side walls to a suction region in which volumes of the hydraulic chambers increase along the rotational direction 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; a first pressure chamber defined by an inner peripheral surface of the housing, and the outer peripheral section and the swinging movement fulcrum of the cam ring having a first pressure receiving surface, and directly connected to the discharge section via an open valve-less path, a discharge pressure being introduced into the first pressure chamber 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 inner peripheral surface of the housing, and the outer peripheral section and the swinging movement fulcrum of the cam ring having a second pressure receiving surface, the discharge pressure being introduced into the second pressure chamber to allow 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; and a control device for changeover controlling supply of the discharge pressure to the second pressure chamber, wherein the first pressure receiving surface is set larger in pressure receiving area than the second pressure receiving surface, wherein a part of each of the first and second pressure chambers is disposed overlapping with the discharge region in a radial direction of the rotor, and wherein the first and second pressure chambers are disposed nearer to the swinging movement fulcrum than to the axis of the rotor. |
