Dynamic characteristics of planetary gear transmission system with sun gear failure

Planetary gear transmission system has the advantages of stable operation, high bearing capacity and high transmission ratio, so it has a wide range of applications in the field of wind turbine, aviation and agricultural machinery. Planetary gear transmission system is complex and needs high manufacturing accuracy. In the meshing process, the system is subject to internal and external double excitation. Therefore, in the high-speed operation state, it is easy to cause failure and reduce the reliability of the equipment. Due to the complexity of planetary gear structure, fault factors have a great impact on its overall performance, which makes the fault diagnosis and prevention of planetary gear more difficult. Therefore, it is of great significance to study the dynamic characteristics of planetary gears with fault factors.

Many scholars at home and abroad have conducted in-depth research on planetary gear transmission system. Samuel and pines use multi-sensor to extract the vibration signal of planetary gear transmission system, and use continuous wavelet transform to analyze the extracted vibration signal. It is proved that the separated planetary gear fault is easy to be detected, and the correctness of the new method is verified. Zhang et al transformed the dynamic equation into matrix form to calculate the natural frequency and mode shape, and studied the influence of stiffness on different modes by comparing the lumped mass method and the finite element method. Ericson and Parker considered the radial and tangential load of the planetary bearing, calculated the bearing stiffness in two directions, and introduced it into the model to study the influence of the load on the natural frequencies of the planetary gear in the process of rotation. Considering the influence of phase difference between meshing parts, Lei Yaguo et al. Established a new dynamic model of planetary gear transmission system and studied its fault response characteristics. Most of the existing researches focus on the single fault, but few on the influence of the dynamic process from crack to broken tooth on the planetary gear transmission system.

Considering the contact stress of tooth surface, a planetary gear transmission system with sun gear fault factor is established by adding torsion spring to introduce the bending stress of tooth surface. The dynamic process from cracking to root fracture is simulated by changing the stiffness of torsion spring, and the influence of typical faults on the dynamic characteristics of transmission system is analyzed.

Based on Hertz contact theory, a planetary transmission system model with fault factors is established. The dynamic characteristics of the sun gear during the process from crack generation to tooth breaking are analyzed

The results show that: (1) the crack depth is deeper, the torsional spring stiffness is reduced, and the impact of meshing force is increased with the occurrence of the crack until the tooth is broken.

(2) when the sun wheel cracks, the floating track of the sun wheel expands gradually with the deepening of the crack; The amplitude of the meshing force between the planetary gear and the inner ring gear increases slightly when passing through the cracked tooth.

(3) when the sun gear is broken, the meshing frequency is larger than that without fault, a large number of sidebands appear in the low-frequency region, and the floating trajectory of the sun gear deviates greatly at the meshing position; The amplitude of meshing force between planetary gear and inner gear ring is large.

(4) with the increase of speed and load, the amplitude of three fault conditions increases, and the influence of load is slightly greater than that of speed.

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