The behaviour of lubricated EHD contacts subjected to vibrations

X Zhang,R P Glovnea

doi:10.1088/1757-899x/174/1/012036

Abstract

Machine components containing contacts working in elastohydrodynamic (EHD) conditions are often subjected to vibrations. These may be originated from the mechanism or machine the contact is part of, the surrounding environment and within the contact itself. The influence of vibrations upon the behaviour of elastohydrodynamic films has been studied experimentally in a number of papers, but a comprehensive study of the effect of the parameters of the oscillatory motion upon the film thickness has not been carried out yet. In this study the authors evaluate the effect of the frequency of the oscillatory motion upon the EHD film thickness. Optical interferometry is used to measure lubricant film thickness in a ball-on-flat disc arrangement. A high – speed camera records the interferometric images for later analysis and conversion into film thickness maps. The disc runs at a constant angular velocity while the ball is driven by the traction forces developed in the EHD film. In steady state conditions, this would ensure pure rolling conditions, however in the present investigation the ball is subjected to harmonic vibrations in a direction perpendicular to the plane of the film. The contact under study is lubricated by basic oils and the temperature is kept at a constant value of 60°C. The aim of this paper is to understand how vibrations influence the lubricant film formation.

Highlights

The elastohydrodynamic (EHD) regime occurs in lubricated non – conformal contacting surfaces, where, apart from the hydrodynamic action of convergent geometry, the elastic deformation of the surfaces and the increase of lubricant’s viscosity with pressure govern the formation of the film
The tests were carried out at entrainment speeds with values between 0.1 m/s to 0.5 m/s it was found that because of the too large film thickness obtained at the larger speeds, data obtained at those conditions was not usable
This paper shows the results of an experimental investigation into the behaviour of elastohydrodynamic films subjected to harmonic, forced vibrations

Summary

Introduction

The elastohydrodynamic (EHD) regime occurs in lubricated non – conformal contacting surfaces, where, apart from the hydrodynamic action of convergent geometry, the elastic deformation of the surfaces and the increase of lubricant’s viscosity with pressure govern the formation of the film. Many experimental [1 – 7] and numerical [8 – 11] studies have been carried out during the past six decades or so, which allowed the evaluation of the contribution of various parameters upon the behaviour of the lubricant film. This is valid for steady state conditions where the geometry of surfaces and various parameters are constant during the operation of the machine component full steady state conditions are almost never encountered in practice. Classic examples of non – steady state or transient EHD conditions are cams and gears mechanisms, where rapid changes of geometry and load take place. Many aspects of transient EHD have been approached such as elastic rebound and cyclic squeeze of a sphere on a flat surface [12 – 14], variation of geometry including artificially

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Results

Conclusion