Plastic deformation mechanism of hypoid gears

Hypoid gears are used as the final reduction gear of vehicles to transmit and change direction torque. Plastic deformation of a hypoid gear tooth flank occurs when a load exceeding the yield stress acts on the tooth surface. This study analyzed the plastic deformation mechanism of hypoid gears. First, the relationship between plastic deformation and these stresses was identified by finite element analysis of approximated tooth contact. The results of this analysis found that local plastic deformation of the tooth flank is caused by internal stress under line of contact. The local plastic deformation expands to all the tooth section by movement of the line of contact. Particularly, the lines of contact near heel side contribute to the plastic deformation more than the other lines. Second, a plastic deformation index which was defined for simulation of the plastic deformation consists of three elements: 1) yield stress considering the hardness distribution of a case-hardened gear, 2) internal stress under the line of contact considering contact load by tooth contact analysis calculated by two cylinders Herzian contact model, and 3) correction coefficients both tooth profile direction and tooth trace direction at the contact point. The correlation between the plastic deformation index and plastic deformation was confirmed by a deformation test.