Experimental Study of Lubrication Film Formation in Multiple Contacts Device Under Starved Conditions

Some machine elements such as gears, rolling bearings, cams and traction drives operate under starved lubrication conditions where the average lubricant film thickness is considerably less than under fully flooded conditions. These parts must operate correctly, often over prolonged periods with sufficient performance. One of the most important parameters determining the performance and life of machine parts is a lubrication film thickness, which is generated within elastohydrodynamic lubricated (EHL) non-conformal contacts. The film thickness in this regime is often time dependent and its value is governed by lubricant supply. If loss outstrips supply this leads to very thin films, which can no longer fulfill their role of separating the surfaces, and thus component failure can result. To achieve optimum bearing performance and component life, it is obviously desirable to be able to predict when starvation will occur. Today the film thickness and pressure in EHL can be predicted using numerical models also in the case of starvation. Although it is very essential to solve the starved EHL problems very little work aimed at comparing experiment and theory has been done. Especially in the case where the starved lubrication model requires as input the inlet layer thickness. This is crucial if the validity of numerical models is to be properly established. This paper is focused on the study of starved lubrication conditions on lubrication film formation. A new optical test rig with multiple EHL contacts was developed for experimental study of lubrication film formation.