Mbined Evaluation And Orthogonal Optimization Of Design Parameters For Muffler

Exhaust noise takes the biggest part in noise generated by the car. Research of exhaust noise means much to improvement of people’s living environment. There are two main exhaust noise research methods, one is based on one-dimensional aerodynamic theory, the other is based on linear acoustic theory. When based on one-dimensional aerodynamic theory, it takes a long simulation time only with a limited precision, especially in the high frequency region. When based on linear acoustic theory, the acoustic source is at the junction of engine and acoustic loads. The acoustic characteristic of the source can be extracted and the acoustic performance of the muffler can be calculated. Exhaust noise can be predicted by combining the acoustic characteristic of the source and the acoustic performance of the muffler. Four-load least squares method put forward by Boden, actually a curve fitting method, is commonly used in acoustic characteristic extraction with a high accuracy.The thesis studied how to extract characteristic of exhaust noise source basing on four-load least squares method. The impact of acoustic loads difference on noise source precision was studied, leading to the conclusion that the more difference of the loads, the more precision of the source. Taking the rapidity of transfer matrix method into account, the transfer matrixes of automobile noise eliminating components commonly used in engineering practice were deduced. The impact of hole diameter, perforated tube thickness, perforated tube diameter, and insertion length of intake and exhaust pipe on the transmission loss was studied. Particularly, Orthogonal Optimization Method was introduced to optimal design of muffler, guiding the determination of best parameters. By predicting and optimal design for acoustic performance of an exhaust muffler, it was found that appropriate reducing of the perforated tube thickness, perforated pipe diameter, the intake and exhaust pipe insertion length, and appropriate increasing of the hole diameter can all effectively improve the transmission loss of the exhaust muffler. With the decreasing order of effecting sensitivity on average transmission loss of the above five parameters, perforated tube diameter ranks the first,hole diameter ranks the second, perforated tube thickness ranks the third, and insertion length of intake and exhaust pipe the last with similar sensitivity. And eventually engine bench test shows the simulation results match well with the experimental ones.Nowadays, domestic scholars research much for a single parameter’s impact on transmission loss of the muffler, but multiple parameters’impact on transmission loss is less rare. This thesis using Orthogonal Optimization Method to investigate the best combined parameters possesses a certain prospective,providing some guidance to actual muffler design.