Study On Dynamic And Tribological Performances Of Piston System Considering The Cylinder Vibration And Piston-Pin Axial Movement

As the consumption of resources and increasing demand for emissions reduction,the engine, as the most widely used machinery, is developed towards the direction of high efficiency, high speed and high power. However, some problems, such as the lubrication failure, excessive wear and fatigue damage, frequently appeared during the working process of the engine have become the main influencing factors restricting the development of engine technologies. The piston–cylinder liner system is the core part of the engine, whose performance impacts directly on the working stability, security and economy of itself. In order to further improve the performance of the engine, especially for its operating reliability, and high efficiency of power transmission, the piston–cylinder liner system must have good dynamic performance and tribological performance.The present research is supported by the start–up fund of the Ministry of education for overseas returnees(Education Department with NO.[2011] 1568) and the project of Chongqing City Board of Education(KJ08A11). The coupling dynamic and tribological performances of the piston–cylinder liner system are studied with the consideration of the vibration of the cylinder liner and the axial motion of the piston–pin. The main research contents are as follows:Firstly, the analysis models of secondary motion of the engine’s piston, vibration of the cylinder liner and hydrodynamic lubrication of the piston skirt are established in the present thesis, in which the influences of surface roughness, elastic deformation and micro asperity contact have been considered fully. On this basis, a numerical calculation program is developed by the author to solve these models using the Broyden algorithm.By solving these models, the response of the cylinder liner vibration, piston secondary motion track, piston skirt film thickness and the friction power consumption can be obtained. The numerical results show that both transverse speed of the piston and oil film thickness fluctuate, and the friction power consumption of the piston skirt increases,if the cylinder liner vibration is considered.On the basis of the above work, influences of engine working conditions and cylinder liner vibration parameters such as stiffness, damping and mass on secondary motion of the piston, vibration of the cylinder liner and lubrication performance of the piston skirt are studied. The numerical results show that the cylinder liner vibration,piston secondary motion and oil film thickness for the piston skirt fluctuate most severely in the power stroke at different engine rotational speeds, and the fluctuation weakens with the increment of the stiffness, damping and mass.Finally, a 3D analysis model of the piston is established with the consideration of the piston–pin axial motion. At the same time, the dynamic model of cylinder liner is improved and the expression for the oil film thickness is revised. Based on the established models, the performance of piston–pin axial motion is solved and the influences of engine rotational speed, piston pin eccentricity, lubricant viscosity and connecting rod length–crank radius ratio on the piston skirt lubrication performance are also studied. The results show that the displacement of the piston–pin axial motion can reach below to several microns, which pertains to the same order of magnitude with the film thickness. Besides, the piston pin axial motion will lead to the oil film pressure distribute asymmetrically along the direction of bearing angle and will also lead to a deccline in the average oil film thickness and rise in the friction power consumption due to increasing probability of the contact between the piston skirt and cylinder liner.