Influence of frictional excitations on the diagnostic features of helical gears under different operating conditions

Gradual wear of gear tooth occurs inevitably over a long period of service life, which results in not only degraded transmission performances but also increases noise and vibration due to variations of frictional excitation. For helical gear, tremendous investigations on meshing stiffness and tooth surface impact have been conducted, but time-varying frictional excitation is less considered due to the complicated lubrication mechanism and time-varying contact mesh line length. Frictional excitation is affected by not only lubricant viscosity, sliding velocity and rolling velocity, but also the variation of specific load due to the time-varying contact mesh line length. To achieve high accuracy and reliability of monitoring gear conditions. This study focuses on the influence of viscosity and overlap ratios on vibration characteristics of helical gear by numerical analysis and experimental studies. The experimental results of viscosity tests show that in the frequency range of 4000-4300 Hz, the amplitudes of vibration signal increase gradually with the decrease in lubricant viscosities. For analysis of overlap ratio tests, the amplitudes of vibration signals of 44% overlap ratio are higher than the other three ratios because the total contact ratio is approximate to an integer.