A simple and accurate method to calculate transient EHL film thickness in machine components undergoing operation cycles

This paper presents a new method to calculate EHL film thicknesses for contacts operating in transient conditions. The method approximates the EHL pressure distribution by its corresponding Hertz distribution. The transient Reynolds equation is simplified to a partial differential equation governing wave propagation of the film thickness from the inlet to the outlet of the Hertz contact region. The film thickness at the Hertz inlet is calculated by the Dowson-Toyoda formula in which the parameters are determined by the current operating conditions. These modeling techniques greatly enhance the robustness and computational efficiency of the method. A wide range of practical EHL problems can be solved, and film thicknesses for a full cycle of machine operation can be calculated on a PC in a few seconds of CPU time. The accuracy of the method is evaluated by comparing its results with those obtained by a full transient EHL model. The comparison is fairly favorable for a wide range of operating conditions with large variations of load and speed parameters and with a frequency of variation up to 1000 cycles per second. This method of transient film thickness calculations can be easily implemented into design programs for EHL machine elements. It also establishes a platform upon which other design calculations and analyses can be performed such as asperity contacts, temperature and traction.