The Modeling And Application Of Coupled Dynamics And Tribology Of Piston Assembly

Nowadays,people pay attention to the characteristic of moving components,for example,piston assemblies,not only in view of traditional Dynaimcs,but also in coupled way of consideration on dynamic motion and lubrication,friction and wear since the coupled characteristics have strong influence on the performance of engines such as,reliability,econominal efficiency,and vibration and noise.Piston assembliy is one of the most important moving components in internal combustion engines,therefore,it isvery meaningful to develop a medel for the coupled prediction on Dynamics and Tribology of piston assembly.The modeling of coupled Dynamics and Tribology of piston assembly,including skirt and ring pack,and the measurement of oil film thickness of piston ring running face as well as skirt were studied in this thesis.The coupled model was deduced according to the equation of force and moment balance of piston and Average Reynolds Equation for lubrication analysis.The effect of asperities on lubrication was introduced in the Average Reynolds Equation in forms of some factors.The equations were solved with the program coded in Fortran language with the algorithm of Finite Difference Method and the model was successful to predict the performance of piston assemblies,including oil film thickness,lubricant oil pressure distribution,piston lateral motion,tilting,fluttering and twist of rings,blow-by,lubricant oil consumption and power loss of components as well.The design of a reciprocating machine was also included in this thesis and a series test runs for ring-liner pair was conducted on it so that the friction coefficient of dry sliding measured was used as friction coefficient between asperities in the model of Dynamics.A system for measurement of lubricant oil film thickness was designed with Laser Induced Fluorescence in this thesis.The laser in 532nm wavelength was chosen as excitation and a special fluorescence dye was selected according to its higher efficiency of fluorescence light emission.A tiny amount dye was mixed in the lubricant oil of the engine and the fluorescence signal was calibrated in a certain concentration on a specially designed gage.The measurement of oil film thickness was conducted on a motored diesel engine with glass window in the cylinders in order to verify the validity of the model to study the distribution of oil film around the piston assemblies.According to the test results,the designed measurement system could give the reasonable curve and clearly describe the structure of piston assemblies and the distribution of oil film.Combined with the distribution of oil film around the piston assemblies,the modeling for thermal conduction for piston assemblies and cylinder liner was accomplished with the assumption of equivalent thermal resistance on oil film thickness in order to study the interactive between the piston performance under thermal load and that of coupled Dynamics and Tribology.Results of Lubrication analysis and themo-mechanical analysis showed that the oil film around ring pack had small effect on cooling of piston and the viscosity of oil played important role on piston motion.Moreover,the profile of piston skirt changed remarkably under thermal load and position of maximum radius would move upward slightly so that the second motion of piston under steady working condition would differ from that under cold condition.The sensibility of structuralcharacteristic on piston assemblies was conducted with the consideration of power loss and blow-by through top ring as the optimization goal and the structural parameters were ranked according to the importance of effect on the power loss and blow-by.At last,the optimization of skirt profile for a real design case was conducted acoording to the conclusion from sensibility analysis.