Patent ID: 7588429

Claim:
An oil pump rotor assembly comprising: an inner rotor formed with n external teeth where n is a natural number; and an outer rotor formed with (n+1) internal teeth for engaging with the external teeth; and a casing having a suction port for drawing fluid and a discharge port for discharging fluid, wherein the fluid is conveyed by drawing and discharging fluid by volume change of cells formed between tooth surfaces of the inner and outer rotors during relative rotation between the inner and outer rotors engaging each other, wherein each of the tooth profiles of the inner rotor is formed such that the profile of a tooth tip thereof is formed using an epicycloid curve which is generated by rolling a first circumscribed-rolling circle Di along a base circle bi without slippage, and the profile of a tooth space thereof is formed using a hypocycloid curve which is generated by rolling an inscribed-rolling circle di along the base circle bi without slippage, wherein each of the tooth profiles of the outer rotor is formed such that the profile of a tooth space thereof is formed using an epicycloid curve which is generated by rolling a second circumscribed-rolling circle Do along a base circle bo without slippage, and the profile of a tooth tip thereof is formed using a hypocycloid curve which is generated by rolling a second inscribed-rolling circle do along the base circle bo without slippage, and wherein the inner and outer rotors are constructed to satisfy the following relations: φ bi=n ·(φ Di+φdi ), φ bo =( n+ 1)·(φ Do+φdo ), φ Di+φdi= 2 e , or φ Do+φdo= 2 e φDo>φDi, φdi>φdo, and (φ Di+φdi )<(φ Do+φdo ), where φbi is the diameter of the base circle bi of the inner rotor, φDi is the diameter of the first circumscribed-rolling circle Di of the inner rotor, φdi is the diameter of the first inscribed-rolling circle di of the inner rotor, φbo is the diameter of the base circle bo of the outer rotor, φDo is the diameter of the second circumscribed-rolling circle Do of the outer rotor, φdo is the diameter of the second inscribed-rolling circle do of the outer rotor, and e is the eccentric distance between the inner and outer rotors.