Transient Effects in the Lubrication of Hertzian Contacts

Abstract

Analysis of the lubrication of mechanisms such as gears, roller bearings and cams shows that their contacts involve a squeeze effect when they operate. The classical approach, however, is to limit investigations to steady state conditions. The aim of our work is to estimate the validity of this hypothesis. First, we shall examine the behaviour of contacts with rigid surfaces and we shall compare the results with the Martin theory. The straightforwardness of the derivation of the Reynolds equation allows us to study the effect thoroughly. The squeeze effect contributes to damp down the variations of the external parameters, such as load or speed. Secondly, this result is confirmed in elasto-hydrodynamic theory. In this case the exact calculation is too complicated and we have used the Grubin's approximation. Finally, an experimental study will confirm the theoretical results and will show a phenomenon which has a thermal origin.