Prediction And Optimization Of Vibration Performance Of China-? Diesel Engine Coupled With Various Excitations

With the continuous improvement of internal combustion engine performance parameters,people pay more and more attention to the internal combustion engine NVH problem.Structural noise is the main source of internal combustion engine noise,and is closely related to the internal combustion engine vibration performance.So engine vibration performance improvement has a very high practical significance.This paper takes a five-state diesel engine as research object,and discuss from the excitation,vibration response and structural optimization these three aspects.First,this paper analyzes the second-order motion of the piston in the cylinder bore,and calculate the influence of thermal stress and mechanical deformation on cylinder line and piston profile,so that the secondary motion calculation of piston is more accurate.The maximum lateral force on the main thrust side is 6887.78 N and5667.33 N under the thermo-mechanical coupling and cold condition respectively.The maximum piston strike kinetic energy is equal to 29.77N·mm under the thermo-mechanical coupling condition and 37.10N·mm in the cold state.The main thrust side FEMP was 0.35 bar and 0.47 bar,and the anti-thrust side FMEP was 0.17 bar and 0.28 bar.It can be seen that the frictional loss increases obviously when the coupling deformation of the cylinder bore is considered.Secondly,based on the discrete mass method,the valve motion characteristics of the engine valve train and the impact load of the valve seat are analyzed.The model of valve dynamic calculation was established by using Excite Timing Drive.By calculating the spring lift and force on spring,the flutter and flyout phenomena were determined,and the spring force was calculated as the load of the subsequent calculation model.At the same time this paper calculate the valve seat force,and use FFT analysis to find that valve seating force showed a strong order.Thirdly,establish the finite element model of the whole engine,with the coupling pairs between the different parts,then analyze the vibration response of the whole machine.In this process,select a number of points as observation points,and compared with the test results.The results show that the accuracy of the vibration response of the whole engine is influenced by the impact force,especially in the high frequency.The whole vibration calculation results are close to the measured values,which satisfies the analytical requirements.Finally,the piston and cylinder head cover are optimized.In the optimization of the piston,the piston pin offset,the cylinder gap and the bump height are taken as theoptimization parameters and the striking kinetic energy is taken as optimization target.The optimization use BP neural network,and take 58 groups for raw data training,and 6 groups for test.Finally,the optimal result is satisfied.Then,in this chapter,the dynamic characteristics of cylinder head cover are analyzed by modal analysis theory,and the natural frequencies and vibration modes of cylinder head cover are obtained.The results of topological optimization can be used as an important reference to improve the vibration performance of cylinder head cover.