Investigation on crack failure of helical gear system of the gearbox in wind turbine: Mesh stiffness calculation and vibration characteristics recognition

When cracks are initiated in a helical gear pair, the mesh stiffness and vibration response of the gear pair will be affected. Unlike previous studies on gear crack, in which only the transverse gear stiffnesses are calculated due to gear crack, or purely uniformly distributed gear crack are modelled, however, in the current study, an improved model is proposed for the calculation of mesh stiffness of helical gear system due to gear crack, in which the gear tooth stiffness, and gear foundation stiffness in both transverse and axial direction have been comprehensively considered. Two typical cracking cases, namely, the addendum extended crack and end face extended crack have been investigated. Furthermore, the analytical mesh stiffness calculation results are validated with the simulated results that obtained from finite-element method, both results show acceptable coincidence. Based on the proposed method, the dynamic model of the cracked helical gear system has been established to analyze the vibration response of the system with the propagation of gear cracks. The obtained results indicate that cracks in gear could cause substantial mesh stiffness reduction. The vibration response in time-domain experience sudden change when the cracked gear tooth is engaged in mesh, and the spectrum shows that the side frequency components become more abundant with higher amplitude under more severe crack conditions. The findings in our study have wide applications in vibration-based fault diagnosis of helical gear systems.