Optimum Time Step in a Transient EHL Contact

Transient effects in Elasto-Hydrodynamically Lubricated contacts have been studied for the last 15 years. The most complex transient EHL contact is likely to be the cam-tappet contact, because load, speed and contact radius vary with time. In such contacts the film thickness is very small and a high precision is required. As a consequence these calculations can be very time consuming and the turn around time is too long for the codes to be useful in an industrial design situation. In this paper a dynamic time step selection procedure is presented which leads to large reductions in the necessary computing time at negligable loss of accuracy. At each point in time the time step is determined by a comparison of the magnitude of the squeeze term and the wedge term in the Reynolds equation. By comparing results obtained with a fixed small time step, and with the new variable time step algorithm it is shown that the small time steps are only needed in a very short period of the cycle.