Patent ID: 8287255

Claim:
A variable displacement rotary pump comprising: a main pump unit having a first discharge port; an auxiliary pump unit having a second discharge port; a discharge passage in communication with the first discharge port and the second discharge port, wherein fluid in the first discharge port and fluid in the second discharge port join together in the discharge passage and are then discharged from the discharge passage; a bypass passage in communication with the second discharge port; a suction passage in communication with the bypass passage; a check valve disposed in the discharge passage for preventing the fluid in the first discharge port from flowing into the bypass passage, wherein the check valve is operated by pressure of the second discharge port; a control valve having a valve member for opening and closing the bypass passage, wherein when the valve member opens the bypass passage and the check valve closes the discharge passage, flow rate of the fluid that is discharged from the discharge passage is reduced, wherein the valve member has a cylindrical end portion that is movable into the bypass passage; and a throttle passage provided in the bypass passage or the control valve for regulating flow of the fluid in early phase of operation of the control valve to open the bypass passage, wherein the throttle passage is a clearance formed between an outer circumferential surface of the cylindrical end portion of the valve member and an inner peripheral surface of the bypass passage, and wherein a length of the throttle passage is set in accordance with a moving speed of the check valve so that a flow rate of fluid flowing into the bypass passage is restricted until the check valve fully closes the discharge passage.