Patent ID: 9714657
Date: 2017-07-25
CPC Classifications: B62D,F04C

Claim:
1. A variable displacement vane pump for supplying a hydraulic fluid to a power steering system of a vehicle, comprising: a pump housing having a pump element accommodating portion in an interior of the pump housing; a drive shaft which is supported rotatably in the pump housing; a rotor which is accommodated in the pump element accommodating portion, which has a plurality of slits which are formed to be aligned in a circumferential direction and which is driven to rotate by the drive shaft; vanes which are provided so as to be extendable from and retractable into the slits; a cam ring which is provided movably in the pump element accommodating portion and which defines a plurality of pump chambers together with the rotor and the vanes; a suction port which is provided in the pump housing and which opens to an area where some of the plurality of pump chambers increase gradually displacements of the pump chambers as the rotor rotates; a discharge port which is provided in the pump housing and which opens to an area where the others of the plurality of pump chambers decrease gradually displacements of the pump chambers as the rotor rotates; a suction line which is provided in the pump housing and which supplies a hydraulic fluid which is reserved in a reservoir tank to the suction port; a discharge line which is provided in the pump housing and which supplies the hydraulic fluid which is discharged from the discharge port to an exterior of the pump housing; a first fluid pressure chamber and a second fluid pressure chamber which constitute a pair of spaces which are formed between the cam ring and the pump element accommodating portion, the first fluid pressure chamber being formed on a side where a volume of the pump chambers decreases when the cam ring moves in a direction in which an eccentricity of the cam ring relative to the rotor increases, the second fluid pressure chamber being formed on a side where a volume of the pump chambers increases when the cam ring moves in the direction in which the eccentricity of the cam ring relative to the rotor increases; a metering orifice which is provided in the discharge line; a control valve accommodating portion which is provided in the pump housing and which is formed so as to communicate with the first fluid pressure chamber via a cam control pressure induction line; a high pressure induction line which connects the discharge port with the control valve accommodating portion; a valve body which is provided movably in the control valve accommodating portion; a first land portion which is, assuming that the valve body moves in an axial direction, provided at a one side of the valve body in the axial direction to restrict a flow of hydraulic fluid in a gap between the control valve accommodating portion and the valve body; a second land portion which is provided to the other side of the valve body in the axial direction with respect to the first land portion to restrict the flow of hydraulic fluid in the gap between the control valve accommodating portion and the valve body; a small-diameter portion which is formed smaller in diameter than the first land portion and the second land portion so that a space is formed between the control valve accommodating portion and the valve body in an area between the first land portion and the second land portion in the axial direction; three spaces which are formed in the control valve accommodating portion, the three spaces including a high pressure chamber which is provided at the one side of the valve body in the axial direction and to which a hydraulic fluid existing upstream of the metering orifice is supplied by way of the high pressure induction line which is provided at an axial side of the first land portion in the axial direction, a middle pressure chamber which is provided at the other side of the valve body in the axial direction and to which a hydraulic fluid existing downstream of the metering orifice is supplied, and a low pressure chamber which is provided between the first land portion and the second land portion, which constitutes a space defined between the control valve accommodating portion and the small-diameter portion and which communicates with the suction line; a biasing member which is provided in the control valve accommodating portion and which biases the valve body in the one side in the axial direction; a control valve which controls variably a communication amount by which the cam control pressure induction line communicates with the high pressure chamber and a communication amount by which the cam control pressure induction line communicates with the low pressure chamber as the valve body moves to thereby control a pressure in the first fluid pressure chamber and an eccentricity of the cam ring; and a bypass line which is formed so as not only to cause a hydraulic fluid in any one of the high pressure chamber, the high pressure induction line and the discharge line which lies in an area which is upstream of the metering orifice to flow directly to either of the suction line side or the discharge line which lies in an area which is downstream of the metering orifice by performing a bypass but also to increase a bypass flow rate as a pressure in the hydraulic fluid existing downstream of the metering orifice increases as the power steering system is activated to operate and which is configured to decrease a difference in pressure between the high pressure chamber and the middle pressure chamber by increasing the bypass flow rate, to increase the communication amount of the cam control pressure induction line with the low pressure chamber by moving the valve body to the one side in the axial direction as the pressure difference decreases, and to increase the eccentricity of the cam ring by decreasing the pressure in the first fluid pressure chamber.