Variable displacement pump

A variable displacement pump comprising:

• a rotor driven by an internal combustion engine;
• a plurality of vanes fitted into an outer periphery of the rotor to be retractable and extendable in a radial direction of the rotor;
• a cam ring configured to accommodate therein the rotor and the vanes and configured to define a plurality of working chambers in cooperation with an outer peripheral surface of the rotor and two axially opposed sidewalls facing respective side faces of the cam ring, and further configured to change an eccentricity of a geometric center of the cam ring to an axis of rotation of the rotor by a displacement of the cam ring relative to the rotor;
• a housing configured to accommodate therein the cam ring and having an inlet portion and a discharge portion formed in at least one of the two axially opposed sidewalls, the inlet portion being configured to open into the working chambers whose volumes increase during rotation of the rotor in an eccentric state of the geometric center of the cam ring to the axis of rotation of the rotor, and the discharge portion being configured to open into the working chambers whose volumes decrease during rotation of the rotor in the eccentric state of the geometric center of the cam ring to the axis of rotation of the rotor;
• a first coil spring configured to be always kept in abutted-engagement with the cam ring to force the cam ring by a first spring load in a first direction that the eccentricity of the geometric center of the cam ring to the axis of rotation of the rotor increases;
• a second coil spring configured to be kept out of contact with the cam ring, while being held in a compressed state, when the eccentricity of the geometric center of the cam ring is less than the predetermined eccentricity, and further configured to force the cam ring by a second spring load, produced by the second coil spring, which second coil spring is brought into abutted-engagement with the cam ring, and less than the first spring load, in a second direction that the eccentricity of the geometric center of the cam ring to the axis of rotation of the rotor decreases, when the eccentricity of the geometric center of the cam ring is greater than or equal to a predetermined eccentricity;
• and
• a control oil chamber configured to move the cam ring against the first spring load of the first coil spring by a discharge pressure introduced into the control oil chamber.

A variable displacement pump comprising:

• a rotor driven by an internal combustion engine;
• a pump structural member configured to change a volume of each of a plurality of working chambers by rotation of the rotor, so as to introduce oil through an inlet portion into the working chambers and to discharge the oil through discharge portion;
• a variable mechanism configured to variably adjust the volumes of the working chambers, which chambers open into the discharge portion, by a displacement of a movable member, caused by a discharge pressure of the oil discharged from the discharge portion;
• a first biasing member configured to force the movable member by a first force in a first direction that a rate of change of the volume of each of the working chambers increases;
• a second biasing member configured to force the movable member by a second force less than the first force in a second direction that a rate of change of the volume decreases, under a state where the movable member has been displaced to a position that the rate of change of the volume is greater than or equal to a predetermined value, and further configured to be held in a specified preload state without any application of the second force to the movable member, under a state where the movable member has been displaced to a position that the rate of change of the volume is less than the predetermined value;
• and
• a control oil chamber configured to move the movable member against the first force of the first biasing member by a discharge pressure introduced into the control oil chamber.