Analysis of vibration and load-sharing characteristics of two-stage planetary gear transmission system with cracks

To reveal the influence of cracks on the dynamic characteristics of a two-stage planetary gear transmission system (TSPGTS), a nonlinear dynamic model with 30-DOF in bending and torsion was constructed, taking into account parameters of different crack degrees (depth, angle, length), as well as factors such as error, time-varying meshing stiffness (TVMS), and damping. In the model, the TVMS model of components with cracks was established using the potential energy method. By incorporating the crack factor into the model, time domain, frequency domain, phase diagram, and Poincare diagram characterizing the dynamic load characteristics were obtained, as well as the curve of dynamic load-sharing characteristics changing with cracks. The influence of different crack degrees on the displacement vibration and dynamic load characteristics of the system was analyzed, and vibration testing experiments were conducted on the system with planetary gear cracks. The results indicate that when the gear contains cracks, it will lead to a decrease in the stiffness of the system, when cracks appear on the II-stage planetary gear, the system will experience impact components with intervals of the rotation period of the II-stage planetary gear, and obvious sidebands will appear near the meshing frequency doubling. These situations will become more pronounced as the degree of cracks intensifies. As the degree of cracks in the II-stage planetary gear increases, the dynamic load-sharing characteristics of the TSPGTS will first improve and then deteriorate, and as the degree of cracks increases, the external and internal dynamic load coefficients continue to increase. Through experiments, the influence of normal gears and cracked gears on system vibration changes was compared and analyzed, and the theoretical results were in good agreement with experimental results, verifying the correctness of the theoretical model. This provides a theoretical basis for fault diagnosis and reliability research of the system.