Research on elastohydrodynamic lubrication of a crankshaft bearing with a rough surface considering crankshaft deformation

Abstract

Journal misalignment in bearings caused by crankshaft deformation under load exists generally in internal combustion engines. When serious journal misalignment takes place, the minimum oil-film thickness of bearings is greatly reduced and the maximum oil-film pressure of the bearings increases markedly. Therefore, it is necessary to consider the surface roughness and deformation of bearing surface when analysing the hydrodynamic lubrication characteristics of a misaligned bearing. In this paper, the elastohydrodynamic lubrication properties of crankshaft bearings considering crankshaft deformation under load and the surface roughness for a four-cylinder internal combustion engine were studied. The lubrications of the crankshaft bearings were analysed by the dynamic method. The deformation of the bush surface under the oil-film pressure was calculated by the deformation matrix method. The results show that, when crankshaft deformation is considered, the surface roughness has a marked effect on the orbits of the crankshaft bearings, but deformation of the bearing surface scarcely affects the orbits of the crankshaft bearings. When the surface roughness of a bearing is considered, the maximum oil-film pressure of crankshaft bearings obviously increases, the minimum oil-film thickness decreases markedly, and the end flowrate changes little in most of the engine cycle. When elastic deformation of the bearing surface is considered, the maximum oil-film pressure of bearings decreases to a different extent: elastic deformation of the bearing surface affects the end flowrate, the frictional coefficient of the journal, and the minimum oil-film thickness very little.