Calculation of Tooth Bending Strength and Surface Durability of High Transverse Contact Ratio Spur and Helical Gear Drives

Calculation methods of spur and helical gear drives with a transverse contact ratio higher than 2, accurate enough for preliminary designs or standardization purposes, are not available in technical literature. If the load is assumed to be uniformly distributed along the line of contact, simple equations given by the linear theory of elasticity and the Hertzian contact model are not in good agreement with experimental results. However, these simple equations may work quite accurately with a more realistic model of load distribution accounting the changing rigidity of the pair of teeth along the path of contact. In this paper a nonuniform model of load distribution along the line of contact, obtained from the minimum elastic potential criterion, has been considered for stress calculation of spur and helical gear drives with transverse contact ratio between 2 and 2.5. The determinant load conditions have been calculated and the nominal contact stress and the nominal tooth-root stress have been computed.