Dynamics modeling of faulty planetary gearboxes by time-varying mesh stiffness excitation of spherical overlapping pittings

Planetary gearboxes are the key components of various rotating machineries, so it is of great significance to analyze their dynamic characteristics under the local gear faults for assuring the high reliability and service performance of equipment. Pitting is the most typical gear fault, and it can be approximately treated as part of a sphere. When multiple pittings are randomly distributed, they probably overlap, the effect of overlapping pittings on mesh stiffness is more complex. Additionally, sliding friction is another important factor affecting mesh stiffness. It follows that a new time-varying mesh stiffness model considering time-varying friction is established to characterize the spherical overlapping pittings. In particular, considering that the cross-section shapes of overlapping pittings are irregular, a piecewise integration method is proposed for calculating multiple tooth meshing contact lines. Then a multi-degree-of-freedom nonlinear fault dynamics model of planetary gearbox is built based on time-varying meshing force, time-varying friction force, and inertial force. Via different degrees of pittings at different locations, the simulation results validate the positive roles of the proposed time-varying mesh stiffness model and time-varying friction excitation in the dynamic responses of planetary gearboxes. Finally, the experiments on faulty planetary gearboxes are performed, and the comparative results verify the superiority of the proposed model over the existing models.