Analytically evaluating the profile shift on the mesh stiffness and dynamic load of cracked spur gears

Abstract

Profile shift is a powerful tool for increasing the gear tooth thickness and enhancing bending fatigue strength. However, it is one-sided to only improve the bending fatigue life of positive profile-shifted spur gear by strengthening the gear tooth body. Furthermore, the current research has not revealed the effect of profile shift on the dynamic load of the gear system with tooth root crack. Therefore, this paper establishes a novel analytical model. Based on the revised tooth shape, the model considers bending, shear, axial compressive, contact Hertzian, and fillet foundation potential energies. The results show that the negative profile shift is more sensitive to the root mean square value (RMS) of time-varying meshing stiffness (TVMS) than the positive. The negative profile-shifted gear provides high TVMS due to the high contact ratio under the health state. In comparison, it loses more TVMS with the crack propagation. Moreover, the positive profile-shifted gear has a lower effective meshing force and vibration intensity value in crack propagation than the negative. Overall, the positive profile shift can increase gear tooth life because it thickens the gear tooth and simultaneously decreases the dynamic load.