Patent ID: 7503757

Claim:
An oil pump comprising: a housing including a rotor receiving portion at an inner side; an inner rotor accommodated in the rotor receiving portion formed at the housing, the inner rotor including a plurality of outer teeth sequentially arranged at an outer peripheral side and integrally rotating about a first rotational center with a drive shaft; an outer rotor accommodated in the rotor receiving portion and including a plurality of inner teeth sequentially arranged at an inner peripheral side, the outer rotor rotating about a second rotational center eccentric relative to the first rotational center by a predetermined amount in relation to rotations of the inner rotor in such a manner that the inner teeth and the outer teeth engage with each other; and a restriction portion restricting an operating range of the outer rotor in a direction perpendicular to an eccentric direction that is defined by a line connecting the first rotational center and the second rotational center, wherein a shape of the rotor receiving portion is defined in such a manner that facing portions of an inner surface of the rotor receiving portion in the direction perpendicular to the eccentric direction are each constituted by a straight line while facing portions of the inner surface of the rotor receiving portion in the eccentric direction are each constituted by an arc.