A vibration model for fault diagnosis of planetary gearboxes with localized planet bearing defects

摘要

Fault diagnosis of localized bearing defects of planetary gear system is studied in this paper. A gear-bearing coupling dynamics model of planetary gear trains is established based on a nonlinear bearing dynamics model with two degrees of freedom and a bending-torsion coupling dynamics model of planetary gear trains. Both the Hertzian contact between rolling elements and raceways, bearing clearance, gear backlash, time-varying mesh stiffness, and gravity excitation are taken into account in the model. The localized defects in both inner and outer raceways are modeled as half sinusoidal waves. Then, the theoretical model is solved numerically and the vibrational responses are obtained. Through time domain analysis and envelope analysis, the fault characteristic frequencies of inner/outer raceway defects are obtained. It is shown that the fault frequencies are greatly modulated by the rotation frequencies of the planet and carrier. When a defect occurs on the inner raceway, the modulation frequency is the rotational frequency of the carrier. For the defect on the outer raceway, the modulation frequency changes into the difference between the rotational frequencies of the planet and carrier. The influence of the defect depth, defect width and defect location on the vibration characteristics of the system is analyzed. The simulation results are verified by a test of bearing defects on a certain planetary gear train.