Elastohydrodynamic lubrication: A lubricant industry perspective

Abstract

The twin challenges facing the automotive and lubricants industries as we approach the millennium are: how to reduce the levels of gaseous emissions and how to achieve increased durability. Improved durability is necessary in order to maintain low levels of emissions. The lubricant has an important part to play in both the improvement in durability by way of improved wear and in the reduction of emissions and conservation of non-renewable energy resources by way of the reduction of friction levels in engines. Examples are shown of how the application of electrohydrodynamic lubrication (EHL) equations permit the calculation of the oil film distribution between cam and follower contacts as a function of cam angle, cam speed and oil viscosity. The results are compared to post-engine test cam wear patterns. The position with of maximum wear can thus be predicted and critical operating conditions identified. The development of optical methods for studying EHL behaviour and simple, reliable, methods for measuring traction under EHL conditions represents a major advance and allows the development of lubricants that offer high levels of wear protection together with high levels of fuel efficiency. This paper shows the importance of selection of both base oils and additive packages to achieve these ends. The relationships between ambient pressure viscosity, pressure coefficient of viscosity, EHL film thicknesses and EHL traction coefficients are discussed. The use of such data in the prediction of fuel economy performance in industry engine tests is also discussed.