Analysis Of Piston Secondary Motion And Research On Squeezing Effect Of Surface Topography

The piston-cylinder system of an internal combustion engine is taken as the main researchobject in this paper. The characteristics of secondary motion and mixed lubrication of piston skirt isstudied in working condition. By applied surface texture technology to tribological analysis of pistonskirt, friction characteristics and secondary motion trajectory of dimple textured piston skirt isresearched through calculation and comparison. The tribological experiment on modelingpiston-cylinder friction pair is designed, and the validity of the theoretical analysis is verifiedindirectly. The effects of different type surface topography on characteristics of squeeze film ofpiston skirt are studied. The aim is to provide a set of quantitative design guidelines for tribologicaldesign of piston assembly.The thermal and the mechanical deformation of piston skirt are calculated by three-dimensionalFEM analysis. The thermomechanical deformations data of piston skirt corresponding to the crankangle are obtained. The results provide good foundation for the further analyses of piston skirtlubrication.A mathematical model for piston skirts in mixed lubrication is developed. It takes into accountthe effects of the topography of the skirt, surface waviness and roughness, thermal and mechanicaldeformation of both piston skirts and cylinder bore. The entire piston secondary motion trajectory,minimum film thickness, total friction forces of cold state and working condition are compared.The effects of the cross and the longitudinal piston skirt profile on mixed lubricating characters ofpiston skirt are analyzed during working condition and the optimum topography design scheme ofpiston skirt is proposed. By simulating design process of piston, the effects of design parameters onpiston secondary motion and friction are studied, such as piston skirt length, wrist pin offset, radialclearance between piston and cylinder bore, radial reduction of piston skirt, et al. The design criteriaof some piston structure parameters are proposed.Combined with surface texture technology, the Reynolds equation and the kinetic equation ofthe piston, the lubrication analysis model for piston skirt with micro-pits is presented. The effects ofdimple depth over diameter ratio, diameter and area density on the piston secondary motion andfriction characteristics are evaluated and compared. The best texture surface modeling parameters ofpiston skirt is discussed.A tribological experiment is designed for modeling piston-cylinder friction pair. The actualanti-friction effect of piston skirt with different micro-pits on piston-cylinder friction pair is studied.The experimental results show that the friction coefficient of piston skirt can be effectively reduced by treating piston skirt surface with micro-dimples. The validity of the theoretical analysis is verifiedindirectly.Squeezing effect of surface topography is studied. A fluid-solid coupling analysis model isestablished for squeeze film between cylinder and piston skirt considering surface topography.Coupling Euler Lagrange algorithm is employed to simulate extrusion process of lubrication oilbetween piston skirt and cylinder. The comprehensive effects of dimple diameter, depth overdiameter ratio and area density on squeeze film are investigated. Comparing the changing conditionof squeeze film bearing capacity of different surface topography, structure parameters of micro-pitsfor piston skirt which lead to maximum carrying capacity of squeeze film is obtained.