| 主权项 |
1. A variable displacement oil pump comprising:
a rotor rotationally driven; a plurality of vanes provided in an outer circumference portion of the rotor to be projectable from and retractable into the rotor; a cam ring which receives the rotor and the vanes therein to form a plurality of pump chambers, and which is moved so as to vary an eccentric amount of a center of an inner circumference surface of the cam ring with respect to a center of a rotation of the rotor; a suction portion opened in pump chambers of the plurality of pump chambers whose volumes are increased in accordance with the rotation of the rotor; a discharge portion opened in pump chambers of the plurality of pump chambers whose volumes are decreased in accordance with the rotation of the rotor; an urging member arranged to urge the cam ring in a direction in which the eccentric amount of the cam ring is increased with respect to the center of the rotation of the rotor; a first control hydraulic chamber which is arranged to receive a hydraulic fluid discharged from the discharge portion, and thereby to apply, to the cam ring, a force to eccentrically move the cam ring in a direction in which the eccentric amount of the cam ring is decreased against an urging force of the urging member; a second control hydraulic chamber which is arranged to receive the hydraulic fluid, and thereby to apply, to the cam ring, a force to eccentrically move the cam ring in a direction in which the eccentric amount of the cam ring is increased by cooperating with the urging force of the urging member; a switching mechanism to which the hydraulic fluid discharged from the discharge portion is introduced, and which is arranged to switch a state in which the introduced hydraulic fluid is introduced to a connection passage connected to the second control hydraulic chamber, and a state in which the hydraulic fluid is discharged from the second control hydraulic chamber through the connection passage; and a control mechanism to which the hydraulic fluid discharged from the discharge portion is introduced, which is arranged to be actuated before the eccentric amount of the cam ring becomes minimum, and which is arranged to disconnect the discharge portion and the first control hydraulic chamber when a discharge pressure of the hydraulic fluid discharged from the discharge portion is smaller than a first discharge pressure, to introduce the introduced hydraulic fluid to an introduction passage connected to the first control hydraulic chamber when the discharge pressure is greater than the first hydraulic pressure, to connect the switching mechanism and the second control hydraulic chamber when the discharge pressure is smaller than a second hydraulic pressure which is greater than the first discharge pressure, and to connect the connection passage to a discharge passage arranged to discharge the hydraulic fluid within the second control hydraulic chamber when the discharge pressure is greater than the second discharge pressure. |
