Centered trochoid

Abstract: The present invention relates to an oil pump rotor provided with an inner rotor 10 to which n (n is a natural number) outer teeth 11 are formed, an outer rotor 20 to which n+1 inner teeth 21 are formed which engage with each of the outer teeth 11, and a casing 30 in which an intake port 31 for taking up fluid and an expulsion port 32 for expelling fluid are formed, wherein: the outer teeth of inner rotor are formed by alternately combining an epicycloid curve and a hypocycloid curve, the epicycloid curve being generated as an orbit of the point on a circle which rolls along the outside of the base circle without slipping, and the hypocycloid curve being generated as an orbit of a point on a circle which rolls along the inside of the base circle without slipping; the alternately combined curve being generated under the following condition, where E is the diameter of the circle which rolls along the outside of the base circle, and H is the diameter of the circle which rolls along the inside of the base circle: 05≦H/E≦08