Abstract: Contact characteristics of the tooth surfaces of spherical gears are investigated. After building the equations of tooth surfaces and the meshing model of a spherical gear pair, tooth contact analysis of spherical gear pairs is performed through simulation. The tooth contact form of meshing spherical gears is a point contact between convexity and saddle surfaces. The contact ellipses of the meshing tooth surfaces are studied, and the orientations and dimensions of contact ellipses are obtained. Then the movement rule of contact ellipses is gained for spherical gear pairs which mesh in any plane that passes through their polar axes: the contact ellipse is relatively small on tooth base and tooth tip, so then the contact stress is large; the contact ellipse is relatively large on tooth middle part, so then the contact stress is small. The above conclusions are useful to further investigations in transmission theory and practical application of spherical gear pairs.

Key words: spherical gear pair, ring-involute tooth surface, contact analysis, point contact, contact ellipse