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This paper established the system dynamics model for two kinds of tooth cracks of different depths of the sun gear and inner gear ring to study the influence mechanism of crack failure on the tooth root strain of the planetary gear transmission system. Combined with the finite element model of the inner gear ring, the tooth root strain of the ring was solved. Experiments verified the correctness of the solution method. The root strain under the crack fault of the sun gear and the tooth crack fault of the inner gear ring is analyzed, and the following conclusions are drawn: Periodic fault impact occurs in the strain signal of the tooth root of the inner gear ring during the crack fault of the sun gear root. The fault can be extracted by the fast spectral kurtosis method (FSK), and the fault components are used to determine whether the sun gear cracks. The Lempel–Ziv index showed a tendency to increase gradually during the process of solar wheel crack deepening, which could be used as the damage index of crack depth. The results can provide a basis and reference for fault diagnosis. [ABSTRACT FROM AUTHOR]

Purpose: This work presents an analysis method for the vibration and stress characteristics of the ring gear. Methods: First, the dynamic model of planetary gear sets is established to extract the meshing force of meshing element. The model is then combined with the load tooth contact analysis (LTCA) method to determine the load relationship between teeth. The dynamic characteristics of the ring gear are calculated using the modal superposition method and Newmark β time integration method, and the effectiveness of the calculation method is verified by comparing with the experimental results. Finally, the vibration and stress characteristics of the thin-walled ring gear are analyzed. Results and Conclusion: The amplitude and stress of ring gear vibration increase obviously at resonance speed. Because of the flexibility of the thin-walled ring gear, the compressive stress of the tooth root at the meshing position is obviously smaller than the tensile stress caused by the concave deformation. Due to the influence of external convex deformation, the stress on the outside of the gear ring at the meshing position is more concentrated than the tooth root position. [ABSTRACT FROM AUTHOR]

Based on the planetary gear transmission system considering the coupling effects of friction and elastohydrodynamic lubrication, a torsional dynamic model considering friction, oil film, time-varying meshing stiffness, meshing damping, and gear backlash is established. The Runge–Kutta numerical method is used to solve the vibration equation of the system. The bifurcation diagram and largest Lyapunov exponent are used to analyze the dynamic characteristics of the system under different bifurcation parameters such as the excitation frequency, lubricant viscosity, sun–planet backlash, and planet–ring backlash. The numerical results demonstrate that with the increase of excitation frequency, the system exhibits rich nonlinear dynamic characteristics such as short-period motion, long-period motion, and chaotic motion. With the increase of lubricant viscosity, the chaotic motion of the system is suppressed at low excitation frequency and the periodic motion of the system increases at high excitation frequency. With the increase of sun–planet backlash, the chaotic motion of the system increases at low excitation frequency, and the bifurcation characteristics become complicated at high excitation frequency and enters chaotic motion in advance. With the increase of ring–planet backlash, the system delays into chaotic motion at low excitation frequency and bifurcates from single-period motion to multi-period motion in advance at high excitation frequency. [ABSTRACT FROM AUTHOR]

• Similarity relationship of load sharing coefficient of gear system is derived. • The sensitivity of load sharing coefficient to different machining errors is calculated. • The method of comprehensive tangential error similarity is proposed. • Correctness of the modification methods of position error distortion are verified. The uneven load distribution among planetary gears will aggravate the vibration of the system, thus reducing the bearing capacity of the planetary gear transmission system (PGTS) and shortening the service life of the system. It is an effective method to predict and study the load sharing performance of the prototype through the scale model of PGTS. According to similarity theory, the similarity ratio of load sharing coefficient (LSC) of the dynamic model and LSC of the physical experiment model is derived. The LSC of PGTS is predicted and verified under different working conditions and structural flexibility. Based on the comprehensive tangential error similarity, the modified load method and the modified similarity ratio method are established to deal with position error distortion on planetary gear. Then, the dynamic model is used to verify the feasibility of the modification method. A scale model of PGTS is designed according to the similarity theory, and mechanical power closed test bench is established for the scale model. Finally, the load sharing performance of prototype PGTS is predicted through physical experiments under similar working conditions. [Display omitted] [ABSTRACT FROM AUTHOR]