The Structural Optimization Design Of Automobile Muffler Based On A Acoustic Transfer Matrix Method

In today's society,noise pollution has seriously affected people's life in many aspects,so the noise control has become urgent to guarantee people's life essential quality.As the main contribution to the vehicle noise,the engine noise is an important factor for the vehicle NVH performance.Means to get high NVH performance of a car can mainly be divided into the: control of the noise source and control of the noise transmission.But the noise source control is closely dependent on the engine performance,so it is too cumbersome and difficult to realize.Hence,controlling the sound transmission is the widely used way to reduce the noise.And the main measure is to install the engine exhaust muffler.Study on the development of muffler with good performance will bring great application value to improve the vehicle NVH performance.At present,the main indicator to evaluate an automobile muffler's sound performance is the transmission loss,which is calculated by on the import and export pressure of the muffle.Due to its simplicity,this method is practical and widely used in the muffler design.The common muffler design methods include finite element method and transfer matrix method.It is worth pointing out that,the last one is based on a one dimensional model of muffler,so its calculation and analysis are simple.However,it only obtains high calculation accuracy in low frequency range.Meanwhile,the calculation accuracy of the former method is high in full band since it generally adapts two-dimensional or three-dimensional calculation model.But repeated geometric modeling is needed when the parametric discuss is carried out by this method.In this paper,based on the Helmholtz equation for the acoustic pressure,and applying the transfer matrix method and finite element method,optimization and design of the parameters of the main and auxiliary muffler for an exhaust system are carried out according to the characteristics of the vehicle engine exhaust noise.Firstly,a simplified numerical model is established for a vehicle exhaust system by using three-dimensional modeling software Catia.Then,because the effect of the higher-order wave can be neglected in the low frequency range as the diameter of the muffler is greater than half of the wavelength of the highest frequency sound,the high-order sound waves are treated as the plane wave.The first-order differential matrix equation of the sound pressure and sound velocity is established by the one-dimensional analytical method,and the transmission loss formula of the muffler is deduced and calculated by the precise integration method.Based on the formulas,the Matlab program are made to calculate the muffler performance.The results are compared with the finite element method,which has proved the effectiveness of the analytical method.Finally,using the characteristic of the analytical method that it need not repeated model,structure parameters,the procedure of optimizing the internal structure parameters for the muffler of a vehicle is programmed.Through the comparison between the program calculation results and the simulation results,the optimal structure parameters of the muffler are determined.The designed muffler can meet the influence factors of the acoustic performance,and the NVH performance of the vehicle can be improved.