Multi-objective Robust Design Of Powertrain Mounting System

The main function of the powertrain mounting system is to reduce the vibration of the powertrain to transfer to the body.The evaluation criteria of the ride comfort of the powertrain mounting system include two aspects.On the one hand,the relationship between the natural frequency and the excitation frequency of the mounting system is adjusted so as to reduce the coupling between the modes in all directions of the whole system and the channel of vibration energy transmission;on the other hand,the isolation capability of the mounting system should be considered from the measured vibration of the mounting system.Designers usually use the vehicle test method in the later stage of mounting design.Vibration isolation performance evaluation.In practice,the decoupling rate may meet the design requirements,but the actual isolation performance can not meet the isolation requirements,so the mounting system needs to analyze its isolation performance from multiple evaluation angles.At the same time,the parameters of rubber mount stiffness are uncertain,and the robustness of the mount system should be taken into account in the optimization design of the mount system.In view of this,this study is mainly carried out from the following aspects:(1)Based on the 6-DOF decoupling,natural frequency allocation and mounting force transfer rate of the mounting system,the applicability and analysis process of the above three evaluation indexes are analyzed.From the analysis results,it is concluded that the limitations caused by considering different evaluation indexes as optimization objectives alone lead to the situation that the optimization effect is not obvious.In order to avoid this situation,a vibration isolation performance evaluation strategy of mounting system is proposed,which can take into account both decoupling rate and transmission rate.It lays a foundation for the establishment of multi-objective optimization objective function.(2)The test principle,method and test bench construction process of the parameters needed for modeling are introduced in detail,including the mass of power assembly,the position of mass center,inertia parameters and static stiffness of rubber mount.Then a6-DOF simulation model of powertrain mounting system is established based on Lagrange equation.In order to verify the accuracy of the MATLAB model,hammering modal test method and Adams modal analysis are used to verify the modal frequency of the model.Then the power train excitation of electric bus is analyzed,and the power train excitationunder different driving conditions is calculated.The vibration isolation performance of the mounting system is calculated by the simulation model.The results show that the vibration isolation performance of the mounting system is poor.(3)Aiming at the problem of insufficient vibration isolation performance of mounting system,the optimal design variables and constraints of mounting system are defined in this paper.The 6-DOF decoupling rate and the weighted dynamic reaction of the system are taken as optimization objectives.The multi-objective optimization solution set is obtained by using the NSGA-II genetic algorithm.The optimized parto solution set is weighted by using the linear weighting method,and the mounting system is obtained.The solution is determined by multi-objective optimization.The natural frequency,energy decoupling rate and weighted dynamic reaction index after multi-objective optimization are compared with those before optimization and those considering energy decoupling method separately.The results show that the multi-objective optimization method has certain advantages.(4)Considering that the fluctuation of stiffness parameters brings insufficient robustness to the system,based on the 6Sigma robust design theory,the sum of weighted dynamic reaction and the mean value of 6-DOF decoupling rate and 6-fold standard deviation is selected as the optimization objective function.According to the constraints of multi-objective optimization of the mounts system,the genetic algorithm is used to optimize the stability of the mounts stiffness parameters.Monte Carlo validation analysis of the results of multi-objective optimization and robust optimization shows that the robustness of the system is improved by 30.34% after robust optimization,and robust optimization achieves good results.(5)According to the optimization parameters obtained by the above research,the vehicle mounting system was modified.Road tests were carried out under 10 km/h,20 km/h,30 km/h and 40 km/h driving conditions respectively.From the test results,the vibration isolation performance of the mounting system was significantly improved,and the effectiveness of the multi-objective robust optimization method was verified.The innovation of the subject:(1)An evaluation strategy for vibration isolation performance of mounts system with both decoupling rate and transmission rate is proposed to ensure that the optimization results obtained by multi-objective optimization can take into account both decoupling rate and vibration transmission rate of mounts system.(2)Combining multi-objective optimization with robust design,the rubber mounting stiffness is optimized robustly,which avoids the problem of insufficient robustness ofmounting system.