The friction directly affected by lubrication conditions is an inevitable non-smooth factor in the surface contact of gears. And the continuous consumption of tooth surface materials, caused by friction and pulse forces in the gear meshing process, easily results in a wear fault. This paper conducts a study on the dynamic behaviors of gear wear for a wind turbine gearbox considering various lubrication states. The tooth friction force for dry friction, mixed lubrication and elastohydrodynamic lubrication is calculated according to the Coulomb law of friction. The wear of the first-stage fixed-axis gear pair is simulated by varying the comprehensive transmission error magnitude, and the time-varying meshing stiffness of fixed-axis and planetary gears is calculated using the potential energy method. The torsional dynamic model of the gearbox is established by taking into account the tooth surface friction, transmission error, stiffness, damping and backlash. The dynamic wear characteristics in different friction states are analyzed through the displacement bifurcation diagram, phase portrait and Poincare section, and the frequency domain results are compared with the experimental data. The results show that in different friction states, the quasi-periodic interval is in advance and becomes larger with the increment of wear, and the largest displacement amplitude in chaotic motion increases. The wear makes the chaotic motion appear early in dry friction state and delay in mixed and elastohydrodynamic lubrication states. The research provides significant guidance for diagnosing and monitoring the wear fault of gear transmission systems.
