Research On Impact Noise And Lubrication Of Diesel Engine Piston Assembly Considering Thermal-mechanical Coupling Loadsand Optimization Design

Energy and environment are two main research subjects with the development ofthe automotive engine industry in the21st century, among which engine noise andemission have been a challenging problem and drawn universal attention. Impactnoise caused by piston is one of the main compositions of mechanical noise, whilepiston rings are the primary source of oil consumption and the entrance of cylinderwhere oil burns. Therefore, this dissertation studied mechanisms of impact noise andoil consumpution of a new domestic diesel engine piston assembly consideringthermal-mechanical coupling loads, and proposed an optimization design schemevarified by simulations and bench tests.In the research of impact noise and low noise optimization design, coupledthermal-mechanical analysis of piston assembly were carried out firstly. Thedistribusions of piston stress and deformation under heat and mechanical loads wereobtained. By considering the effects of coupled loads, the dynamic model ofpiston-connecting rod-crank mechanism was much closer to actual working condition.Secondly, the piston impact force was calculated by dynamic mechanical analysis.Then the finite element model of the whole engine was developed and revised usingmodal tests. Under the impact force, dynamic responses of the engine were calculated,and impact noise was obtained by using the boundary element method. Finally, a BPneural network was used to optimize the piston impact noise. The results showed thatboth impact force and noise decreased significantly. In the validation of optimaldesign, bench tests were carried out before and after the optimization and the resultsshowed that the impact force and noise of the optimized piston greatly reduced.For the studies of piston ring-cylinder liner lubricating property, oil consumption,and low oil consumption piston optimization design, a2D control equation of pistonring-liner lubrication was established considering the cavitation effect. The massconservation principle of control volume was applied to solve the equation. And theoil film pressure distribution including cavitation regions and density distributionwere calculated. In addition, cavitation effects on the minimum oil film thickness andfriction were analyzed. Secondly, four types (evaporation from liner wall，throw-offabove the top ring，oil blow through the top ring end gap，and oil scraping of piston top land edge) of oil consumption in cylinder were modeled and calculated. Influencesof main parameters of piston rings on oil consumption were analyzed. Then in orderto reduce the oil consumption, piston rings were optimally designed by neuralnetworks. The computation results showed that the oil consumption in cylinderdecreased. Finally, oil consumptions before and after the optimizations were testedand the results showed that the optimized piston rings significantly reduced the oilconsumption.