US Patent 7455507 Structure for preventing cavitation erosion of oil pump

A side face of a pump gear is formed into a stepped face such that an annular region extending radially from a diameter which is smaller than a dedendum circle diameter of the pump gear and larger than the outer diameter of a pump gear bearing to the addendum circle diameter of the pump gear is recessed by a certain depth to increase the side gap in the recessed annular region. Therefore, the side gap in the recessed annular region is larger than a side gap in a region between the diameter smaller than the dedendum circle diameter of the pump gear and larger than the outer diameter of the pump gear bearing to the outer diameter of the pump gear bearing.