Variable displacement pump

A variable displacement pump comprising:

• a rotationally driven rotor;
• a plurality of vanes provided in an outer periphery of the rotor and arranged to be moved in a radially inward direction and to be moved in a radially outward direction;
• a cam ring in an inside of which the rotor and the vanes are housed, in an inner part of which a plurality of pump chambers are formed, and configured to be moved to vary an eccentricity of the cam ring with respect to a rotary center of the rotor;
• a housing including:
• a suction section formed on at least one side surface of the cam ring and opened to one of the pump chambers whose volume is increased when the cam ring is eccentrically moved toward one direction with respect to the rotary center of the rotor;
• and
• a discharge section opened to one of the pump chambers whose volume is decreased when the cam ring is eccentrically moved toward another direction with respect to the rotary center of the rotor;
• a biasing member configured to bias the cam ring in a state in which a spring load is given to the biasing member such that the eccentricity of the cam ring with respect to the rotary center of the rotor becomes large;
• a first control oil chamber configured to move the cam ring toward the other direction against a biasing force of the biasing member when a discharge pressure is introduced into the first control oil chamber;
• a second control oil chamber configured to act a hydraulic pressure upon the cam ring by cooperating with the biasing force of the biasing member when hydraulic oil is introduced into the second control oil chamber;
• a switching mechanism configured to switch between one state in which hydraulic oil is introduced from the discharge section to the second control oil chamber via an aperture to another state in which hydraulic oil within the second control oil chamber is exhausted;
• and
• a control mechanism including:
• a valve body having an introduction port to which the discharge pressure is introduced, a first control port communicated with the first control oil chamber, a second control port communicated with the second control oil chamber, and a drain port communicated with a drain passage;
• a spool valve slidably disposed within the valve body to control a communication state of each of the ports;
• and a control spring which biases the spool valve with a biasing force smaller than that of the biasing member,
• wherein the spool valve receives the discharge pressure to slide within the valve body against a biasing force of the control spring, at an initial position at which the spool valve is biased by, the control spring to move maximally, a communication state between the introduction port and the second control port and another port than the introduction port and second control port is limited and a first state in which the first control port and the drain port are communicated with each other occurs, and, when the discharge pressure is increased, the second control port is communicated with the drain port and a second state in which the introduction port and the first control port are communicated with each other occurs.

A variable displacement pump comprising:

• a pump constituent body configured to rotationally be driven to vary volumes of a plurality of hydraulic oil chambers to discharge oil introduced from a suction section through a discharge section;
• a variable mechanism configured to modify volume variation quantities of the hydraulic oil chambers opened to the discharge section according to movement of a movable member;
• a biasing member configured to bias the movable member in a, state in which a spring load is given to the movable member in a direction toward which the volume variation quantity of one of the hydraulic chambers opened to the discharge section becomes large;
• a first control oil chamber into which the discharge pressure is introduced to impart a force in a direction against a biasing force of the biasing member to the variable mechanism;
• a second control oil chamber into which hydraulic oil is introduced to act a force in the same direction as the biasing force of the biasing member upon the variable mechanism;
• a switching mechanism configured to switch between one state in which hydraulic oil that has a decreased pressure relative to the discharge pressure is introduced from the discharge section to the second control oil chamber and another state in which hydraulic oil within the second control oil chamber is exhausted;
• and
• a control mechanism configured to exhaust hydraulic oil within the second control oil chamber as the discharge pressure becomes larger and to adjust the pressure within the second control oil chamber in a pressure decrease direction when the switching mechanism introduces hydraulic oil whose pressure is decreased relative to the discharge pressure to the second control oil chamber during a high revolution of the pump.