Researches On The Vibration Reduction Design And Optimization Of An Automotive Exhaust System Based On Vibration Modes

The exhaust system is one of the main components that affect the NVH performance of a vehicle.It withstands vibration shocks from the powertrain and transmits them to the underbody through hooks and lifting lugs,and thus affecting the comfort of the vehicle.In this paper,the vibration reduction design and optimization research of a exhaust system are carried out from vibration isolation and vibration absorption based on vibration mode theory and finite element method.The finite element model including exhaust system,powertrain,engine mount and underbody is first established,then the free mode and constrained mode of the exhaust system are simulated,and the theoretical result is verified by testing result.Based on the average driving degree of freedom displacement method,the position of the suspension point of the exhaust system is optimized.In the research of vibration isolation,based on the above finite element model,the vibration isolation rate of the exhaust system is analyzed and designed.The vibration isolation performance of the lifting lug is improved by increasing the structural rigidity of the passive hook.Based on the response surface method,the minimum values of dynamic supporting force is taken as the optimization target to optimize the dynamic stiffness of lifting ears,with the requirements of static deformations and static loads of lifting ears are taken considered,the dynamic support forces of lifting lugs are reduced.In the research of vibration absorption,based on the design theory of dynamic vibration absorber,the dynamic vibration absorber is designed for the free state of the exhaust system.The result shows that the vibration absorption effect is significant at the corresponding modal frequency point.The influence of the installation position of different vibration absorbers on the vibration absorption effect is studied for the restraint state of the exhaust system.The result shows that the vibration absorber installed at the antinode of the constrained mode shape has better vibration absorption effect and in high frequency the effect is better.Finally,based on the genetic algorithm,with the goal of the minimum vibration energy of the exhaust system,the quality,stiffness and damping of the dynamic vibration absorber are optimized.With a set of optimized dynamic vibration absorbers,the vibration energy and vibration peaks of the exhaust system passive hooks are reduced.