Elastohydrodynamic Lubrication

The development of the theory of elastohydrodynamic lubrication - and the understanding of the complex phenomena involved - was one of the major advances in tribology in the twentieth century. The revelation of the existence of a hitherto unsuspected lubricating film revolutionized this science, explaining the remarkable efficiency of lubrication in Hertzian contacts.

Elastohydrodynamic lubrication (EHD) occurs in contacts subject to punching (non-conforming surfaces), with very high local pressures, mainly in bearings, gears and cam devices. EHD theory can be used to calculate the thickness of the oil film in Hertzian contacts, which in turn can be used to predict mechanism life.

In these highly loaded contacts, local elastic deformation of the facing surfaces modifies the geometry of the parts in the vicinity of the contact. The hydrodynamic equilibrium is then governed not only by the Reynolds equation, but also by the piezoviscosity of the oil and by Hertz theory, enabling films of sufficient thickness to be generated to separate the parts and limit their friction and wear. This is a very important field for its practical applications: EHD theory now makes it possible to rationally design bearings, gears and cam devices, optimizing contact geometry and operating conditions to maximize oil film thickness.

However, there are two phenomena that contribute to reducing lubricant film thickness, both of which are localized at the contact entrance: thermal effects and feed conditions. Current models propose corrective factors that reflect the reduction in lubricant film thickness caused by these two phenomena.

This article presents the development of this theory and its advances up to the early 2010s.