| Piston is one of the key parts of internal combustion engine,and it has important influence on the performance of internal combustion engine.About 25% of the total mechanical loss is produced from the friction pair of piston skirt and cylinder liner.Owing to piston located for a long time in the working condition of high temperature,pressure,and load,skirt surface are suffered from different degrees of wear,and it will cause the problem of pollutant emissions and scuffing when it is serious.Piston secondary motion will causes the striking on cylinder liner,which brings about vibration and noise.Therefore,in order to meet the practical needs of high efficiency,low emission and low noise,it is of great practical significance to reduce piston skirt friction wear and piston striking energy through the study of piston secondary motion.In this paper,the piston assembly of certain diesel engine is took as research object.Through the combination of numerical simulation and experimental verification,the study of piston friction wear and striking energy is carried out through the CAE method of numerical simulation,and the multi-objective optimization of the structural parameters of piston skirt profile is also carried out.The research conclusions and main content of this article are summarized as follows:(1)A dynamic model of the piston secondary motion is established,which considers the surface roughness,the heat and elastic deformation of piston and cylinder liner based on the temperature field experiment of piston and cylinder liner.Experiment of piston wear is carried out,and its results show that the calculation results have good consistent with the actual test result.Its accuracy of the model is proved.(2)The influence of prototype piston structural parameters on skirt friction wear and striking energy is studied ueing the single variable method in the rated condition.When cylinder clearance is near 90 ?m,the friction power loss of skirt is the lowest,and the cylinder clearance has a great influence on the piston striking energy.When the cylinder clearance is increased from 70 ?m to 190 ?m,maximum wear load of the skirt is gradually decreased from 75.408 MW/m2 to 32.482 MW/m2,and the reduced amplitude was about 56.9%.When the piston pin offset is near 0.9 mm,friction power loss of skirt is the lowest.With the piston pin offset increases from 0 mm to 1.8 mm,the piston maximum striking energy gradually decreases firstly from 2.157 mJ to 0.755 mJ,and then increases to 2.349 mJ.The maximum wear load of skirt increases slightly,but the wear area changes greatly.The friction power loss of skirt is lowest when the top clearance of skirt is near 96 ?m.As skirt top clearance is increased gradually from 56?m to 176?m,the piston maximum striking energy is increased from 1.202 mJ to 5.109 mJ,increased by about 3.3 times.The skirt maximum wear load is decreased from 60.53 MW/m2 to 41.278 MW/m2,reduced by about 31.8%.The wear serious areas of thrust surface and anti-thrust surface move downward.The bump point of skirt profile is closer to skirt top and the greater of skirt friction power loss.The bump point of skirt profile is increased from 10 mm to 40 mm,piston maximum striking energy is decreased from the 2.311 mJ 0.758 mJ,reduced by 67.2%,the maximum wear load of skirt is gradually increased from 28.334 MW/m2 to 141.67 MW/m2,increased by about 4 times,and areas of the largest wear load are moved upward.(3)Structure design of piston skirt profile is optimized in the rated condition.The optimal solution set of piston skirt profile design were obtained through optimal Latin hypercube sampling,sample calculation,fitting of response surface and "NSAGII" genetic algorithm.Two schemes are selected for comparison with the performance of original machine,and final scheme of piston skirt profile design is gained.In the rated condition,friction loss of piston skirt is reduced by 18.17%,and piston maximum striking energy is reduced by 7.88%. |
PDF Full Text Request