Design and manufacturing of a novel high contact ratio internal gear with a circular arc contact path

Abstract

A new internal gear drive with a high contact ratio (HCR) is presented in this paper. In the new gear drive, the number of teeth working at the same time has reached 7, which is usually only less than 2 in the traditional involute gear drive. The bearing capacity of the new gear is improved significantly. To obtain a high contact ratio, the addendum tooth profiles of the pinion and internal gear are deduced by a given path of contact based on gear meshing theory and the dedendum tooth profile is designed as the envelope to the family of addendum tooth profile of the mating gear. The mathematical models, including the equation of the path of contact, the equations of addendum and dedendum tooth profiles and the equation of modification, are established. An example drive in the three-dimensional (3D) model is presented. The characteristics, such as contact ratio, sliding ratio, induced curvature, and the contact and bending stress are evaluated. The results confirm that the novel internal gear drive has a higher contact ratio and lower sliding coefficient, and the contact and bending stresses are reduced in comparison with the involute gear drive. Furthermore, a prototype is produced, which illustrate the feasibility of manufacturing.