Vibration Characteristics Analysis And Optimization Of A Passenger Car Exhaust System

With the continuous progress and innovation of automotive technology, consumers’ demand of serviceability is increasingly improved. Especially, people pay much more attention to the NVH performance. Exhaust system is an important part of a car, and directly connected to the engine and the body(or frame). When it’s working, the violent vibration will make a great influence to the NVH performance of the car. So it is most significant for engineering application to analyze the vibration characteristics of an exhaust system.Automobile exhaust system composed of multiple components, and the structure shape is complex, so it’s difficult to analyze and describe it with simple theoretical model. On premise of not breaking the structure features, simplified the geometric model, and built FEM of the exhaust model with HyperWorks. Free modal analysis was carried out on the exhaust system, including computational modal analysis and experiment modal analysis. By analyzing the conformance of the test result, it’s feasible to verify the accuracy of the FEM. The suspension points could be preliminary determined with the average driving degree of freedom displacement(ADDOFD) based on the free modal analysis.By means of the static analysis and constraint modal analysis, achieved the load distribution of suspension points and modal parameters(frequency and vibration mode). Frequency response analysis was completed to calculate the force transmitted from the rubber lugs to the body. Based on above analysis, it is easy to point out the problems that modal frequency was too closed to the idle excitation frequency and transmitted force was more than 6N were needed to be optimized.Sensitivity analysis of some parts of the exhaust system was performed to study the influence to the exhaust system vibration characteristics when parameters(thickness of pipe, stiffness of rubber lugs, etc.) changed. Based on orthogonal test, when getting the transmitted force of lugs and modal frequency of the exhaust with different parameters, the optimal combination of parameters could be decided by data processing. Then the exhaust system got the best vibration characteristic, and which was that the modal frequency was far away from the idle excitation frequency, and the transmitted force was less than 4N.In this article, the research of some vehicle exhaust system vibration characteristics was valuable to engineering application and practices guidance. For the development of a new vehicle exhaust system, it is cost saving and helpful to cut down the period of design.