Transmission Loss Analysis And Optimization Of Automobile Exhaust Muffler

Nowadays, automobile industry is developing rapidly. The requirement of automobile comfort also becomes more and more high. With the development of large displacement and high speed automobile, exhaust noise is becoming more and more influential in vehicle noise and comfort levels. Therefore, it is necessary to take a study on exhaust noise in order to strengthen the muffler performance, improve automobile ride comfort and reduce automobile noise pollution.Conventional theoretical research methods mainly include:boundary element method, finite element method, multi-dimensional numerical analysis method, transfer matrix method and so on.Transfer matrix method exists in the one-dimensional space. It’s convenient but limited to the range of applicable frequencies. Finite element and boundary element method belong to the frequency category. Although these two have good adaptability, but the calculation is slow. Multi-dimensional numerical analysis method calculation results are more accurate, but the speed of operation is slower. This paper, based on a muffler of heavy car, apply the acoustic finite element analysis method to study the muffler transmission loss, Through simulation we obtain transmission loss curves. Then through comprehensive analysis of the curves we can get optimal structural parameters of exhaust muffler.The main contents are:simplifying the three-dimensional model of the muffler, enveloping the model to form an acoustic tetrahedral mesh, analyzing the transmission loss by the finite element method, optimizing the internal structure of the muffler to improve the acoustic performance. There are a large number of perforations on the inlet and outlet pipes of the muffler. The existence of these perforations is unfavorable to form an acoustic tetrahedral mesh. We use the transfer admittance relationship to substitute these perforations to solve this problem. We set acoustic tetrahedral mesh only to envelope the area where air flow through. We rotate a two-dimensional surface mesh to obtain a three-dimensional body stretch mesh. Setting boundary conditions to obtain transmission loss curves.Then we change the size of perforations on the perforated plate, the internal volume of the chamber and the position of main flow channel to explore the impact of these structural parameters to transmission loss. On the basis of analysis results, we take a comprehensive consideration on previous experience, the actual processing difficulty and cost factors in order to obtain the optimum parameters. Then we can update the model parameters of the muffler and analysis again. The results show transmission loss has effectively improved and we achieved very satisfactory results. Finally, on the basis of acoustic analysis, respectively analyze acoustic and structure modal of the optimized muffler. We do this process to provide a theoretical basis in order to avoid resonance on the muffler natural frequency and improve noise performance of the exhaust muffler on the same time.