Experimental study on point contact EHL under non-steady-state speed impacts

Abstract To investigate the variation patterns of lubricating film thickness in rolling bearings under non-steady-state conditions, research was conducted on a laboratory-built test rig. Based on PLC control of motor speed, oil film thickness was measured from start-up to stop under variable speed conditions to reveal its formation patterns. During initial start-up, oil film thickness increases rapidly; the greater the acceleration is, the faster the central film thickness grows. Introducing an abrupt acceleration change during the acceleration phase revealed that the central film thickness undergoes a transient oscillation period at the instant of change, whereas a sudden change during deceleration results in a smooth transition. Before reaching the target speed and stabilizing, the central film thickness fluctuates, exhibiting a lead-out phase before returning to a stable thickness. This lead-out phase increases with higher acceleration. These findings provide crucial insights into lubricant film behavior under non-steady-state conditions and offer a basis for lubrication design under such conditions.