Numerical Investigation And Application Of Three-Dimensional Lubrication Performance In Piston Ring Pack

In this paper, a three-dimensional hydrodynamic lubrication analysis and an elastohydrodynamic lubrication analysis have been developed to predict the lubrication performances of piston ring and cylinder liner contact. At the same time, a three- dimensional FEM model has been presented to simulate the heat transfer in the piston assembly-lubrication film-cylinder liner coupled system. A gasoline engine, CUB100, is adopted as the model engine in the research.The study of piston ring lubrication has remained a very active area in internal combustion engines (ICE), but almost all previous models were based on the assumption that piston ring and cylinder liner were axisymmetric. Along the direction of circumference, the differences in the lubrication performances of piston ring were neglected. In the current work, a three-dimensional lubrication model has been presented to analyze the performance characteristics of piston ring.In the paper, the three-dimensional HL model is based on the average Reynolds equation, asperity contact approach and Reynolds boundary conditions. For a more realistic simulation, the factors that have effects on the lubrication performances of piston ring are considered, such as surface roughness, rupture location, blowby through the piston ring pack, the nonaxisymmetric in the circumferential direction of cylinder liner and the effects of temperature and pressure on the density and viscosity of oil. The equation has been solved cyclically using the finite difference method. The oil film thickness, pressure, friction force and friction heat are determined. The lubrication performances of piston ring are analyzed and compared in the conditions of different geometrical characteristics of piston ring, the asperity of surface, the viscosity of oil and the distortion in the circumferential direction of cylinder liner.Around the top dead center firing (TDCF), the total surface elastic distortion of piston ring and cylinder liner significantly increases, which is due to the higher oil film pressure. This greatly affects the lubrication performances of piston ring. In the paper, a three- dimensional EHL model has been built, which coupled the three-dimensional HL equation and surface elastic distortion equation of lubrication surfaces. The lubrication performances of piston ring in EHL have been compared with that in HL. The EHL lubrication performances of piston ring pack are also discussed in the paper.Based on the above lubrication analysis of piston ring, the study of heat transfer in the components of combustion chamber in ICE has been carried out. In the paper, the oil film is treated as a radial thermal resistance and the heat transfer relation between the piston assembly and cylinder liner has been built up. The coupled boundary elements on the boundary surfaces of piston assembly and cylinder liner are regularly arranged and in the same size, which can fill the requirement of coupled heat transfer calculation. The three-dimensional transient heat transfer model of piston assembly-oil film-cylinder liner coupled system is built up and a FEM program is developed. The oil film thickness and friction heat of piston ring pack obtained in the lubrication analysis are input into the program. The heat transfer in ICE has been analyzed under the firing and motoring conditions. The results in the simulation are correlated well with the test results, which denotes that the heat transfer model is reliable and robust.The major conclusions that maybe be drown from the results are listed below: the factors have significant effects on the lubrication performances of piston ring, such as surface roughness, viscosity of oil, the geometrical characteristics of piston ring and the nonaxisymmetric in the circumferential direction of piston ring. The lubricant film pressure is varied around the circumferential direction of piston ring, which is due to the deformation of the cylinder liner. The gas pressure in combustion chamber and inter-ring has a significant effect on the lubrication performances o...