When the planetary gear transmission system operates under extreme conditions such as poor lubrication, it is prone to tooth surface pitting faults, which seriously affects the transmission accuracy and the service life. In order to ensure reliable operation of the system, it is necessary to deeply explore the dynamic characteristics of the system under pitting failure. In this paper, a nonlinear dynamic model of planetary gear transmission system coupling with multiple excitation factors is established by considering the time-varying meshing stiffness, time-varying friction, transmission error and backlash under pitting fault. The fourth-order Runge-Kutta numerical integration method is used to solve the vibration differential equation of the system, and the vibration characteristics of the system under different rotational speeds and pitting faults are analyzed by means of time domain diagram, phase plane diagram, spectrum diagram, wavelet time-frequency diagram, three-dimension spectrum diagram and bifurcation diagram. The results show that the system exhibits rich nonlinear dynamic behaviors at different rotational speeds, including periodic motion, multi-periodic motion and chaotic motion; that the pitting fault of the gear tooth causes a sudden change in the vibration displacement of the system and reduces the stability of the system by changing the time-varying meshing stiffness; and that, with the increase of rotational speed, the amplitude of system vibration caused by the pitting fault also increases. Finally, the accuracy of the proposed model and calculation method is verified by building a dynamic characteristic test bench of planetary gear transmission system. This paper reveals the intrinsic relationship between pitting fault and system dynamic characteristics, and provides references for the fault diagnosis and condition monitoring of planetary gear transmission system.

To enhance the transmission stability during vehicle gearbox operation, this paper analyzed the nonlinear vibration characteristics of the Ravigneaux planetary gear transmission system in the transmission, and established a dynamic model of the Ravigneaux planetary gear transmission system including a variety of nonlinear factors. The model comprehensively considers nonlinear factors such as time-varying meshing stiffness, time-varying meshing damping, comprehensive transmission error, dynamic meshing force and time-varying friction force. Based on Newton’s second law, the nonlinear dynamic differential equations of the system were derived, and the Runge-Kutta numerical integration method was used to iteratively solve the differential equations of the system to obtain the dynamic response characteristics of the system under different external excitation frequencies. To investigate the impact of different excitation frequencies on the vibration displacement of the front and rear sun gear pairs, this study constructed time history diagrams, frequency spectra, phase portraits, and Poincare maps. The analysis shows that the vibration displacement evolution law of the two gear pairs is consistent. In order to further reveal the evolution law of the nonlinear response of the system, the bifurcation diagram and the spatial waterfall diagram were used to analyze the influence of the external excitation frequency on the nonlinear behavior of the system and reveal its evolution process. The results show that vibration displacement of the dual gear pairs undergoes a nonlinear evolution path along with variations in external excitation frequency: transitioning from chaotic motion through period-doubling bifurcation, and ultimately converging to periodic motion. By reasonably adjusting the external excitation frequency, unsteady vibrations can be effectively suppressed throughout the system, transient impact loads reduced, thereby enhancing operational stability and extending gear transmission service life. This research provides both theoretical foundations and engineering references for designing and optimizing high-performance, highly-reliable transmissions for new energy vehicles.