Patent ID: 7344361

Claim:
Variable-capacity vane pump for pumping a medium from an aspiration zone to a delivery zone, said vane pump comprising a body comprising a cavity, in which a mobile ring can move, inside which a hub is located which is rotatable around a fixed axis and equipped with vanes which during rotation are supported against the inner face of the mobile ring, displacing means for moving the mobile ring as a function of a control pressure between a position centered on the axis of rotation of the hub and a predefined extreme eccentric position with respect to the axis of rotation of the hub, wherein the displacing means of the mobile ring comprise a control recess provided in the wall of the cavity of the body, and a projection formed on the outer face of the mobile ring and having lateral sides designed to slide inside the control recess of the cavity of the body so as to form a control chamber in which the control pressure is applied, and a guiding organ to guide the mobile ring in the cavity of the body, wherein the guiding organ is formed by walls placed on the outer surface of the mobile ring on another side of the mobile ring with respect to the projection, parallel to each other and parallel to the lateral sides of the projection, these walls being designed to slide in a corresponding guiding recess provided in the wall of the cavity of the body, wherein a first portion of the external surface of the ring between the projection and the guiding organ on a side of the aspiration zone is subjected to a pressure existing in the aspiration zone, and a second portion of the external surface of the ring between the projection and the guiding organ on a side of the delivery zone is subjected to a pressure existing in the delivery zone, and wherein a surface area of the second portion is smaller than a surface area of the first portion.