Effect of high-pressure rheology of lubricants upon entrapped oil film behaviour at halting elastohydrodynamic lubrication

Abstract

The steady-state elastohydrodynamic lubrication (EHL) is now quite well understood both computationally and experimentally. However, many practical machine elements such as rolling element bearings and traction continuously variable transmission (CVT) operate often under the halting of machine, the suspension of long time and start of machine. It is often in such operating condition that breakdown of lubrication films occurs, which eventually gives rise to fail of the lubricated surfaces. This paper describes an experimental study of EHL film thickness at halting of operation and a change by the time of an entrapped film thickness. The film thickness is investigated with some different type of lubricating oil, which a phase diagram is known by high-pressure density measurements. The results demonstrate an entrapped oil film thickness at EHL halting is dependant on αηa, where α is the pressure-viscosity coefficient, η is the dynamic viscosity, a is the deceleration, and squeeze out time of entrapped oil film is dependant on a phase diagram parameter TVE - T, where TVE is the viscoelastic solid transition temperature at Hertzian pressure, and T is the oil temperature.