Patent ID: 8613610
Filing Date: 2013-12-24
Classification: F04C

Abstract:
1. 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 biasing member configured to force the cam ring by a first force 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 biasing member configured to force the cam ring by a second force less than the first force 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 further configured to be held in a specified preload state without any application of the second force to the cam ring, when the eccentricity of the geometric center of the cam ring is less than the predetermined eccentricity; and a control oil chamber configured to move the cam ring against the first force of the first biasing member by a discharge pressure introduced into the control oil chamber.