Study On The Factors Affecting The Lubrication Performances Of A Piston Skirt-liner Pair

With increasingly strict emission regulation and stringent energy situation, theautomobile engine industry is facing severe challenges. It’s very important problemsto be solved in engine’s field recently and in the future as well to further improve thefuel economy and reduce the emission of an internal combustion engine. A pistonskirt-liner friction pair, as one of the most important friction pairs, works in the worstoperation conditions, whose friction power loss significantly affects the total enginefriction power loss, thus influences engine’s fuel economy. The influence laws obtainedthrough systematical investigation on the factors that affect the lubrication performancesof the piston skirt-liner pair can guide the design of the piston skirt and selection of theliner clearance to achieve good lubricating properties.First, the theory model of piston motion coupled with hydrodynamic lubrication ofthe piston skirt was established considering the roughness of the surface and microasperity contact. The parameters, which influence the performance of the piston skirtlubrication and the piston secondary motion including the length of the piston skirt, theoffset of piston pin and the clearance between piston and cylinder, was researched. Theresults show that large clearance between piston and cylinder, negative offset of pistonpin and short piston skirt can improve the lubrication of the piston skirt.Secondly, the effects of liner and piston elastic deformation on piston secondarymotion and piston skirt lubrication characteristics were analyzed based on the AVLEXCITE POWER UNITE and finite element modal reduction method. The results showthat elastic deformation of the piston and the liner has a great influence on thelubrication performances of the piston skirt. When considering the elastic deformationof the piston, the minimum oil film thickness of piston skirt becomes less, and peak oilfilm pressure and total friction power loss gets lower, respectively.Finally, an analysis model of piston dynamics coupled to hydrodynamic lubricationof piston skirt is proposed considering the effects of skirt topography, surface wavinessand roughness, thermal and elastic deformation of piston and liner. The weight analysisof the structural parameters on the skirt lubrication performances is discussed bycombining the model and the orthogonal experimental design method.The results indicate that the greatest influencing factor on minimum oil film thickness isthe profile height at the bottom of the skirt, and location at maximum of the profile height lays least influence on minimum oil film thickness. Meanwhile, the main factorsaffecting the peak oil film pressure are the four profile variables which have closeinfluence weight. Radial clearance has least influence on peak oil film pressure. Theorder of importance for the average friction loss is the profile height at the bottom of theskirt, the radial clearance, the profile height at the top of the skirt, the cross-sectionovality of the skirt and the location at maximum of the profile height.