Abstract: The elastohydrodynamic lubrication (EHL) of an involute spur gear is studied by considering the transient effect, thermal effect and the tooth surface longitudinal roughness. The load is first assumed to be carried by either two pairs of gear teeth or by only one pair, this transition is modeled as a step variation of the load by simplifying the experimental load spectrum. A full numerical solution to the problem of the time-dependent thermal line contact EHL with single asperities of an involute spur gear is obtained by using the multi-grid method for pressure, the multi-integration method for deformation and the column scanning method for temperature rise. The variation of the oil film thickness, pressure distribution and the temperature rise along the line the action between the contact teeth is discussed. Numerical results reveal that the existence of single asperities on the tooth surface can lead pressure and temperature to change drastically and film thickness to become thin in the vicinity of the asperities. The influences of the single asperities on the pressure, the film thickness and the temperature rise are investigated. The gear teeth surface longitudinal roughness has tiny influence on the friction coefficient. The maximum friction coefficient and the highest film temperature all occur in the vicinity of the pitch point.

Key words: Involute spur gear, Micro-elastohydrodynamic lubrication(EHL), Single asperity, Thermal EHL, Transient solution