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Dependence of Mixed Lubrication on Asperity Height Distribution~Application to Piston Rings
Technical Paper
2006-05-0204
Sector:
Language:
English
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, another 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.