Abstract
The mixed lubrication phenomenon is becoming a key issue for reliable and low friction engine design. This fact can be explained by several reasons: the increase of the engine torques at low speed has generated very low oil film thicknesses in lubricated devices, for the last ten years car manufacturers have decreased the viscosity of the oil in order to reduce friction, an other reason lays on the oil temperatures on lubricated components that have increased along with the specific power increase,.
From a global point of view, the physical mechanisms of the mixed lubrication are explained in order to show the strong link between mixed lubrication and the reliability.
From a local point of view, the way to model the contacts between antagonist surfaces responsible of the mixed lubrication is detailed. Commonly, a Gaussian type of distribution is used for asperity summit distribution. However, this kind of distribution has a significant influence on the load generated by direct contact, on the friction and heat generated. In order to show the importance of the asperity summit distribution, at the transition between hydrodynamic and mixed lubrication, one example of modelling is provided. This example refers to piston ring lubrication. This paper leads to the conclusion that in spite of the effort required to introduce contact models in mixed lubrication, it does represent an important contribution for reliability analysis.
Keywords:mixed lubrication, contact pressure, reliability, Abbott curve, roughness parameters.