Robustness-based Research On The Vibration Isolation Performance Of Automotive Powertrain Mounting System

With the continuous improvement of living standards and automotive technology,consumers are demanding higher and higher comfort of passenger compartment.The performance of NVH(Noise,Vibration,Harshness)is the main factor that determines the comfort of passenger compartment.The poor performance of NVH may even endanger the physical and mental health of passengers and pollute the urban traffic environment.As one of the main vibration and noise sources of automobile,engine will cause body vibration,passenger compartment structural noise and radiated noise.Powertrain mounting system is the key to attenuate the transmission of powertrain vibration to the body,and its vibration isolation performance is one of the determinants of passenger compartment comfort.In this thesis,the vibration isolation performance of the first and second stages of the mounting system is studied.Considering the uncertainty of design variables caused by manufacturing and assembly errors,the robust design is applied to the vibration isolation performance of the mounting system,which meets the design principles and reduces the fluctuation of the vibration isolation performance.This thesis takes a passenger car mounting system as an example to carry out research.The specific research contents are as follows:(1)The engine vibration characteristics and basic vibration isolation theory were analyzed,and the design principles of mounting system vibration isolation were defined,including natural frequencies design principle,energy decoupling rate design principle and vibration transmissibility design principle,and the common robust methods are expounded.(2)The low-frequency vibration isolation performance design(the first stage)of the mounting system was accomplished by matching mounting stiffness to achieve the optimal design of natural frequencies and energy decoupling rate.In this stage,a 6DOFs dynamic model of the mounting system was established,and natural frequencies and energy decoupling rate were optimized based on the model.The constraints were the reasonable distribution of natural frequencies of each order and the minimum requirement of energy decoupling rate,and the design objective was the maximum energy decoupling rate.Considering the uncertainty of mounting stiffness,the 6? constraint boundary was introduced into the optimization mathematical model,and the natural frequencies and energy decoupling rate were designed robustly.(3)The medium and high frequency vibration isolation performance design(the second stage)of the mounting system was completed by matching the passive side dynamic stiffness to achieve the optimal design of vibration transmissibility.In view of the insufficiency of the vibration transmissibility of right mount,the relationship between the passive side dynamic stiffness and the vibration transmissibility of mounting system was analyzed in this stage,and the feasibility of adjusting the passive side dynamic stiffness to enhance the vibration transmissibility was illustrated,and a finite element analysis model of the vibration transmissibility of mounting system was established.In order to improve the calculation efficiency,an approximate model was used to instead of the finite element analysis model.Because of the multi-objective of the vibration transmissibility optimization,the multi-objective algorithm NSGA-II was used to optimize the vibration transmissibility,and robust design was carried out in the process of optimization.Finally,the optimal target values of the passive side dynamic stiffness of right mount were obtained.(4)In order to make the passive side dynamic stiffness of right mount reach the set optimal target values,the passive side dynamic stiffness of right mount was strengthened,and the optimized passive side dynamic stiffness reached the target values.At the same time,the vibration isolation test of the optimized right mount was carried out.The test results showed that the vibration transmissibility of right mount met the design principle,and the vibration and noise of the passenger compartment were reduced to varying degrees.The problem of insufficient vibration isolation performance of right mount was solved.