Effect of tooth microgeometry profile modification on the efficiency of planetary hub gears

Planetary hub systems offer desired speed and torque variation with a lighter, compact and coaxial construction than the traditional gear trains. Frictional losses are one of the main concerns. Generated friction between the mating teeth flanks of vehicular planetary hubs under varying load-speed conditions is one of the main sources of power loss. Modification of gear tooth geometry as well as controlling the surface topography are the remedial actions to reduce friction and hence the power loss. The paper studies the effect of tooth crowning and tip relief upon system efficiency. It includes an analytical elastohydrodynamic analysis of elliptical point contact of crowned spur gear teeth, also including the effect of direct contact of asperities on the opposing surfaces. Tooth contact analysis (TCA) is performed to obtain contact footprint shape as well as contact kinematics and load distribution. A parametric study is carried out with the expounded model to observe the effect of gear crowning and tip relief with different levels of gear surface finish upon planetary hubs’ power loss.