Patent ID: 8038417

Claim:
An electric pump unit comprising: an electric motor; an internal gear pump having an inner rotor and an outer rotor, the internal gear pump being driven by the electric motor to draw and discharge fluid; arcuate ports arranged in correspondence with a discharge side and a suction side of the internal gear pump; and a relief valve having a spool received in a valve hole that allows communication between the arcuate ports, the communication between the arcuate ports being selectively permitted and prohibited by changing an opening degree of the relief valve in correspondence with movement of the spool in the valve hole, wherein, when a fluid pressure at the discharge side of the internal gear pump becomes greater than or equal to a predetermined value, the spool of the relief valve moves across an inner arc of one of the arcuate ports that corresponds to the suction side of the internal gear pump and from a position at which the spool prohibits the communication between the arcuate ports to a position at which the spool permits the communication between the arcuate ports, thereby causing a backflow of fluid from the discharge side to the suction side of the internal gear pump, and wherein the opening degree of the relief valve increases in accordance with a downward convex curve as the spool moves away from the position at which the spool prohibits the communication between the arcuate ports.