Dynamic contact stiffness of transient mixed lubrication induced by periodic load and speed

Abstract Currently, the lubricated interface contact stiffness of driving system is regard as steady-state without considering the effect of load and speed fluctuation. However, the multi-directional mechanical vibration of driving system is universal and inevitable in the practical engineering, which is accompanied by noteworthy normal load fluctuation and tangential speed fluctuation. It is of great significance to predict and understand the dynamic contact stiffness evolution for the design and dynamic simulation of transmission mechanism. While the research on the dynamic contact stiffness in transient mixed lubrication caused by fluctuation load and speed hasn't been reported yet. In this manuscript, a comprehensive study about the lubricated dynamic contact stiffness in point contact and spiral bevel gears (SBG) under periodic fluctuation load and velocity was performed. The results emerge some unusual and unprecedented characteristics. There is an obvious hysteresis loop of load-displacement when the phase of the coupled periodic load and velocity is 90° or 270°. And the hysteresis loop expands as speed fluctuation amplitude rises. The dynamic contact stiffness of SBG is sensitive to load and speed fluctuation especially in the stable engagement period. In addition, due to the competitive relationship between dynamic load and contact area/ radius, the reversals of positive and negative stiffness would occur at certain fluctuation amplitudes, which can lead to extremely low (even zero) stiffness or extremely high stiffness.