Abstract:Elastohydrodynamic lubrication(EHL)model of spur gears under oscillation conditions was established.The problem of coordinate system inconformity caused by variation of rotate direction was solved. Considering timevariant effect,EHL analysis of the spur gears with sine law swing was carried out.Results show that there are evident fluctuations in centre film pressure,centre film thickness,minimum film thickness and maximum film pressure under oscillation conditions,moreover,they all reach the minimums nearby the transient that rotate direction varies.Oscillation frequency has obvious influence on film pressure and film thickness.Amplitude of variation of centre film pressure and maximum film pressure, centre film thickness and minimum film thickness are obvious under high frequency oscillation conditions,and their values are greater than those under low frequency oscillation conditions.The phenomenon of a surge and collapse in the centre film pressure and maximum film pressure under oscillation conditions,especially under high frequency oscillation conditions,which causes a remarkable increase in cycle frequency of meshing teeth surface stress and may lead to teeth contact failure.Therefore,high frequency oscillation should be avoided.