The planetary gear system has the advantages of a large transmission ratio and high transmission efficiency, and is widely used in various mechanical systems. Complicated working conditions and harsh working environments often cause gear failures. The floating set of the sun gear gives rise to the changes in the pressure angle, overlap ratio, and meshing phase during the operation, which makes the vibration signal complex. To reveal the generation mechanism of fault signal, an evaluation model of time-varying meshing stiffness for both internal gear and external gear with tooth tip chipping fault is proposed in this paper. At the same time, considering the time-varying meshing characteristics caused by the sun gear floating set, a new dynamic model of planetary gear system is established. Based on this model, the dynamic response laws of the system with internal and external gear failures are analyzed respectively and the influence laws of the failure severity on the response are discussed in the meantime. By comparing with the health system, the dynamic characteristics and modulation laws of the faulty system under different working conditions are analyzed. This study can provide a reference for the fault diagnosis of the planetary gear transmission system.

planetary gear system; time-varying meshing stiffness; tooth tip chipping fault; dynamic response; modulation