The effects of laser surface texture applied to internal combustion engine journal bearing shells - An experimental study

We present an experimental study into the impact of surface texturing on crank shaft bearing friction. This was achieved by applying a series of laser-etched patterns to the surface of shell components and comparing friction measurements - obtained using a journal bearing test rig - to those of a non-texture reference. Tests were performed under a range of applied loads, speeds and lubricant viscosities in order to simulate the operating conditions encountered in an engine. Three texture configurations were assessed with varying dimple density and area coverage. The lubricant film temperature was also measured in order to remove shear heating effects and deduce accurate friction values. The bearing shell with a texture pattern applied to the whole of its circumference showed substantial reduction in friction (approximately 18%) when compared with the non-textured reference. This reduction in friction increases as the film thickness increases (i.e.: moving right on the Stribeck curve) and is most pronounced under full film hydrodynamic conditions. Friction reductions of up to 13% were observed using bearing shells that were only textured outside the loaded region. This is attributed to a reduction in shear rate due to an increased gap without alteration of the pressure generation and is important since this texture configuration maintains its effectiveness, even after the heavily loaded region becomes worn. These reported hydrodynamic friction reductions have practical implications for automotive bearings.