Predictions of friction and temperature at marine cam-tappet interface based on mixed lubrication analysis with real surface roughness

Abstract

The working conditions of cam-tappet pairs in marine diesel engines are directly influenced by the engine output power, the operational speed, the temperature, as well as the components surface micro-morphology, etc., which cause the cam-tappet pairs work in the mixed lubrication state, thus the interfacial friction, pressure and temperature rise are vital to engine performance, efficiency, and durability. An interfacial friction–temperature prediction model for the cam-tappet pairs, considering the effects of transient working conditions and the real surface roughness, is developed in the present study, based on the theories of the transient mixed EHL and the heat transfer under the condition of a fast moving heat source. The numerical results of surface temperature rise are compared with those from the Blok formula, and a good agreement is found. The obtained results show that the presence of 3D roughness may lead to a decrease in the lubricant film thickness, and the surface temperature rise of tappet may exceed 700 K, which is close to the material scuffing temperature, causing the surface failure due to scuffing and wear. If increasing the cam speed and base circle radius within certain range, it may lead to the increment of film thickness and reduction of surface temperature rise, thus the lubrication effectiveness is increased. In addition, using cast aluminum bronze may significantly reduce the surface temperature rise and improve the interfacial characteristics.