Dynamic characteristics of helical gears under sliding friction with spalling defect

The change of friction force on both sides of the pitch plane and the change of contact stiffness induced by tooth spalling defect cause the change of the dynamic characteristics of helical gears. However, there is no good solution for the modeling and calculation of the internal excitation in helical gears with spalling defect to reveal the change of the dynamic characteristics. In this study, the calculation methods of friction excitations and contact stiffness are proposed based on the time-varying length of contact line in helical gears. By considering the change of the mesh position and the loss of length of contact line induced by tooth spalling defect, the time-varying friction force is obtained by subtracting the length of spalling defect at the mesh position from the length of the normal contact line, and the time-varying contact stiffness is obtained by Hertz contact algorithm. A six-degree-of-freedom analytical helical gear pair model is developed by incorporating the time-varying sliding friction and mesh stiffness based on the changes of friction force and mesh stiffness. Dynamic characteristics are simulated via helical gear pair examples with spalling defects. The results show that the oscillations of the dynamic responses become more significant at both the beginning and the end of the spalling area, especially with the growth of the spalling size. The developed analytical model provides a new method for the study of excitation characteristics in helical gears with tooth spalling defect.