Patent ID: 9243632
Filing Date: 2016-01-26
CPC Classification: F04C

Claim Text:
1. A variable displacement oil pump comprising: a rotor configured to be rotationally driven; a plurality of vanes movable out from and into an outer circumferential portion of the rotor; a cam ring separately forming a plurality of working-oil rooms by receiving the rotor and the plurality of vanes in an inner circumferential space of the cam ring, wherein the cam ring is configured to move to vary an eccentricity between a rotation center of the rotor and a center of an inner circumferential surface of the cam ring and thereby to vary a variation rate of volume of each of the plurality of working-oil rooms which is produced when the rotor rotates; a lateral wall provided on at least one of lateral portions of the cam ring, wherein the lateral wall includes a suction portion open to the working-oil room whose volume is increasing when the rotor is rotating under a state where the cam ring is eccentric, and a discharge portion open to the working-oil room whose volume is decreasing when the rotor is rotating under the state where the cam ring is eccentric; a first control oil chamber configured to apply a first biasing force to the cam ring in a direction that reduces the eccentricity between the rotation center of the rotor and the center of the inner circumferential surface of the cam ring, by oil discharged and introduced from the discharge portion into the first control oil chamber; a second control oil chamber configured to apply a second biasing force to the cam ring in a direction that enlarges the eccentricity between the rotation center of the rotor and the center of the inner circumferential surface of the cam ring, by oil discharged and introduced from the discharge portion into the second control oil chamber, wherein the second biasing force is smaller than the first biasing force; a biasing mechanism configured to apply a third biasing force to the cam ring in the direction that enlarges the eccentricity between the rotation center of the rotor and the center of the inner circumferential surface of the cam ring under a state where the biasing mechanism is given a set load, wherein the biasing mechanism is configured to increase the third biasing force discontinuously in a stepwise manner when the eccentricity between the rotation center of the rotor and the center of the inner circumferential surface of the cam ring becomes lower than or equal to a predetermined amount; and a changeover mechanism wherein the changeover mechanism changes from the first position of the valving element to the second position of the valving element, when the discharge pressure becomes higher than or equal to a pressure level at which the cam ring can move against the set load of the biasing mechanism, and is lower than or equal to a pressure level at which the third biasing force of the biasing mechanism is increased in the stepwise manner.