Patent ID: 9534596
Date: 2017-01-03
CPC Classifications: F04B,F04C

Claim:
1. A variable displacement pump comprising: a rotor disposed to be driven to rotate about a rotation axis; a plurality of vanes disposed on an outer peripheral portion of the rotor so as to be moveable to project from the rotor and retreat into the rotor; a cam ring accommodating the rotor and the plurality of vanes in an inner peripheral side thereof, the cam ring cooperating with the rotor and the plurality of vanes to define a plurality of working fluid chambers, the cam ring being moveable to vary an eccentric amount of a central axis thereof with respect to the rotation axis of the rotor such that a volume of each of the working fluid chambers is increased and decreased during rotation of the rotor, end walls disposed at opposite axial ends of the cam ring, respectively, at least one of the end walls comprising a suction portion and a discharge portion, the suction portion being opened to the working fluid chambers that are increased in volume by and according to rotation of the rotor, the discharge portion being opened to the working fluid chambers that are decreased in volume by and according to rotation of the rotor, a biasing mechanism comprising two biasing members disposed with preloads, respectively, the biasing mechanism being constructed to bias the cam ring in a direction in which the eccentric amount is increased in accordance with a biasing force generated by the two biasing members, the biasing mechanism being constructed such that the biasing force becomes discontinuous when the eccentric amount is a predetermined amount, a first control fluid chamber into which a working fluid discharged from the discharge portion is introduced, the first control fluid chamber serving to apply an urging force to the cam ring in accordance with an inside pressure thereof in a direction in which the eccentric amount is reduced against the biasing force of the biasing mechanism, a second control fluid chamber into which the working fluid discharged from the discharge portion is introduced through an orifice, the second control fluid chamber cooperating with the biasing mechanism to apply an urging force to the cam ring in accordance with an inside pressure thereof in the direction in which the eccentric amount is increased, and a control mechanism serving to control movement of the cam ring, the control mechanism comprising a valve body, a spool slidably accommodated in a side of one axial end of the valve body and a control spring accommodated in a side of the other axial end of the valve body, the valve body comprising an introduction port disposed at the one axial end of the valve body, the introduction port serving to introduce the working fluid discharged into the valve body, a first control port communicated with the first control fluid chamber, a second control port communicated with the second control fluid chamber and a drain port communicated with a low fluid pressure portion, the spool carrying out changeover of fluid communication between the introduction port, the first control port, the second control port and the drain port corresponding to a position of the spool in an axial direction of the valve body with respect to the valve body, the control spring biasing the spool toward the one axial end of the valve body with a biasing force smaller than the biasing force of the biasing mechanism, wherein the control mechanism is shiftable between a first state, a second state and a third state, when fluid pressure introduced into the introduction port is a first changeover fluid pressure or less, the control mechanism is in the first state, in which fluid communication between the introduction port and the remaining ports is restrained, fluid communication between the first control port and the drain port is allowed, and fluid communication between the second control port and the drain port is restrained, when the fluid pressure introduced into the introduction port is higher than the first changeover fluid pressure and is a second changeover fluid pressure or less, the control mechanism is in the second state, in which the fluid communication between the introduction port and the first control port is allowed, the fluid communication between the first control port and the drain port is restrained, and the fluid communication between the second control port and the drain port is restrained, and when the fluid pressure introduced into the introduction port exceeds the second changeover fluid pressure, the control mechanism is in the third state, in which the fluid communication between the introduction port and the first control port is allowed, the fluid communication between the first control port and the drain port is restrained, and the fluid communication between the second control port and the drain port is allowed.