Failure of steel helical gear used for automotive transmission

Abstract

The advantage of helical gear that can operate silently, on parallel and nonparallel shafts at high capacity has been great such that helical gears are used in almost all car transmission systems. As such, study on two major failures of helical gears which are due to bending and contact stresses is critical. In this research, modelling of a helical gear that is used in a 5-speed transmission car system has been conducted using finite element method. Bending and pitting stress analysis have been conducted on this helical gear that was modelled in 3D involute form. The obtained results of maximum bending and contact stresses have been compared to analytical results obtained using the American Gear Manufacturing Association (AGMA) formulations. The results of the FEM modelling and the AGMA formulations have been found to be in good agreement. Furthermore, parametric studies have been conducted on the effects of face width and helical angle of the gears on the bending and pitting stresses. It is observed that the increase of face width of the gear will decrease the maximum bending stress while the increase of the helical angle will increase the pitting stress in a non-linear fashion for both cases.