Abstract: A new design renovation for pitch curve by transforming non-circular gear to high precision segmented circular gear is put forward, which controls the approaching error and the length error of arc to be very small and simplifies the designing and processing problems of non-circular gear to be resolved as the circular gear after the pitch curve of the non-circular gear replaced by arcs. In the basis of conducting out a kind of pitch curve formulation of non-circular low-speed heavy torque hydraulic motor, this renovation processed the arc approximation toward pitch curve and obtained an extremely high precision of arc enclose and approximaiton.

Key words: Approaching, Arc, Error, Non-circular gear, Pitch curve