Because of the limited applying scope of the internal gear drive with zero-tooth-difference

less attention was paid to the kinematic and dynamic features of this mechanism. In 1998

the author of this paper applied it in the submerged-motor-driven progressing cavity pumping system as a coupling to connect the output shaft of reducer and the rotor of pump. The relative motion feature of rotor and stator of the pump requires that the output shaft axis do eccentric motion around the input one of coupling with an eccentricitye

therefore

the meshing teeth number in the mechanism is fewer compared with that generally used in engineering. Furthermore

the sliding motion takes place between the gear-tooth profiles. For such reasons

the problems such as strength

efficiency and vibration must be taken into account. As a premier basic work

the tooth profile engaging process was analyzed deeply in this paper. Altogether 16 kinds of relationships between classifications and attributes were established. At last

the analytical method to determine the starting and ending contact points of tooth profiles

in both polar and rectangular coordinate system

was given.