An oil pump emits less noise by properly forming the profiles of teeth of an inner rotor and an outer rotor thereof which engage each other, whereby decreasing sliding resistance and rattle between the tooth surfaces of the rotors. The rotors of the oil pump are formed so the inner rotor having “n” teeth is formed such that the tooth tip profile and tooth space profile thereof are formed using cycloid curves which are formed by rolling a first circumscribed-rolling circle and a first inscribed-rolling circle along a base circle, respectively, and the outer rotor having “n+1” teeth is formed such that the tooth tip profile and tooth space profile thereof are formed using cycloid curves which are formed by rolling a second circumscribed-rolling circle and a second inscribed-rolling circle along a base circle, respectively, and in such a manner that the following equations are satisfied: øBo=øBi; øDo=øDi·(n+1)/n+t·(n+1)/(n+2); and øAo=øAi+t/(n+2).
1. An oil pump rotor assembly comprising:
an inner rotor having “n” external teeth; and
an outer rotor having (n+1) internal teeth which are engageable with the external teeth,
wherein each of the tooth profiles of the inner rotor is formed such that the tip profile thereof is formed using an epicycloid curve which is formed by rolling a first circumscribed-rolling circle along a base circle without slip, and the tooth space profile thereof is formed using a hypocycloid curve which is formed by rolling a first inscribed-rolling circle along the base circle without slip, and each of the tooth profiles of the outer rotor is formed such that the tooth space profile thereof is formed using an epicycloid curve which is formed by rolling a second circumscribed-rolling circle along a base circle without slip, and the tip profile thereof is formed using a hypocycloid curve which is formed by rolling a second inscribed-rolling circle along the base circle without slip, and
wherein the inner rotor and the outer rotor are formed such that the following equations are satisfied:
ø B=øBi;
ø Do=øDi ·( n+ 1)/ n+t ·( n+ 1)/( n+ 2); and
øi Ao=øAi+t/( n+ 2),
where øDi is the diameter of the base circle of the inner rotor, øAi is the diameter of the first circumscribed-rolling circle, øBi is the diameter of the first inscribed-rolling circle, øDo is the diameter of the base circle of the outer rotor, øAo is the diameter of the second circumscribed-rolling circle, øBo is the diameter of the second inscribed-rolling circle, and t (≠0) is gap between the tooth tip of the inner rotor and the tooth tip of the outer rotor.
2. An oil pump rotor assembly according to claim 1 , wherein the inner rotor and the outer rotor are formed such that the following inequalities are satisfied:
0.03 mm≦ t≦ 0.25 mm (mm: millimeter).
3. An oil pump rotor assembly comprising:
an inner rotor having “n” external teeth; and
an outer rotor having (n+1) internal teeth which are engageable with the external teeth,
wherein each of the tooth profiles of the inner rotor is formed such that the tip profile thereof is formed using an epicycloid curve which is formed by rolling a first circumscribed-rolling circle along a base circle without slip, and the tooth space profile thereof is formed using a hypocycloid curve which is formed by rolling a first inscribed-rolling circle along the base circle without slip, and each of the tooth profiles of the outer rotor is formed such that the tooth space profile thereof is formed using an epicycloid curve which is formed by rolling a second circumscribed-rolling circle along a base circle without slip, and the tip profile thereof is formed using a hypocycloid curve which is formed by rolling a second inscribed-rolling circle along the base circle without slip, and
wherein the inner rotor and the outer rotor are formed such that the following equations are satisfied:
ø Ao=øAi;
ø Do=øDi ·( n+ 1)/ n+t ·( n+ 1)/( n+ 2); and
ø Bo=øBi+t /( n+ 2),
where øDi is the diameter of the base circle of the inner rotor, øAi is the diameter of the first circumscribed-rolling circle, øBi is the diameter of the first inscribed-rolling circle, øDo is the diameter of the base circle of the outer rotor, øAo is the diameter of the second circumscribed-rolling circle, øBo is the diameter of the second inscribed-rolling circle, and t (≠0) is gap between the tooth tip of the inner rotor and the tooth tip of the outer rotor.
4. An oil pump rotor assembly according to claim 3 , wherein the inner rotor and the outer rotor are formed such that the following inequalities are satisfied:
0.03 mm≦ t≦ 0.25 mm (mm: millimeter).