Analysis And Optimization Of Piston Second Order Motion And Skirt Lubrication Characteristics

As the main part of power transmission in the internal combustion engine,the working condition of the piston has an important influence on the comprehensive performance of the internal combustion engine.Based on a small gasoline engine with a displacement of 0.25 L,this paper analyzes the second-order motion and skirt lubrication characteristics of pistons by constructing piston dynamics model and skirt fluid dynamic lubrication model,and provides theoretical guidance for piston optimization.In order to improve the comprehensive performance of the engine and improve the wear of piston skirts,the influence law of piston line,cylinder gap,piston pin bias and crankshaft bias on piston friction and knock characteristics is studied,and the optimal matching study of piston line,cylinder gap,piston pin bias and crankshaft bias is carried out by using the response surface method,and the validity of the optimization results is verified by the engine bench test,which provides reference and guidance for the optimization design of pistons.The main research content of this paper is:1.The radial stiffness of the piston is solved by using finite element analysis software,the radial stiffness characteristics of the piston are obtained,and the radial stiffness matrix file of the piston is written.The temperature field of piston and cylinder liner is solved,and the thermal deformation caused by piston and cylinder liner is analyzed,and the amount of deformation is superimposed with the external pattern data of piston and cylinder liner.2.Build a piston dynamic model and a skirt hydrodynamic lubrication model considering the thermal deformation and elastic deformation of piston and cylinder liner.The engine was tested on the bench,the friction loss power of the engine was measured by the back drag method,and then the simulation model was calibrated to verify its accuracy.3.Analyze the general rule of the second-order motion of the piston,the piston striking characteristic,the piston friction characteristic,the piston joint contact force,the minimum oil film thickness,oil film distribution,the skirt oil film pressure and the rough contact pressure.It provides guidance for the multi-objective optimization of piston group design parameters.4.Starting with many factors caused by piston knocking and friction,the influence factors are studied and analyzed one by one,and the influence law is drawn.A method of optimizing the key influence parameters of piston friction and slap characteristics by using response surface model is proposed.To improve piston friction and slap characteristics,the multi-objective optimization model is established by taking piston profile,cylinder clearance,piston pin offset and crankshaft offset as optimization design variables,and taking the minimum value of kinetic energy peak value and the minimum friction loss as optimization objectives.The optimization results show that the optimized design parameter matching can reduce the friction loss of piston group by 9.13% and the maximum knock energy by 29.20%under the maximum torque condition of the studied engine.Finally,the bench test is carried out in the optimized prototype.The test results show that the engine power and torque averagely increase by 2.37% and 2.54% respectively,the mechanical efficiency increases by2.06% on average,the fuel consumption rate decreases by 1.19% on average.The wear condition of the piston was improved after optimization.