REFINEMENTS OF A PRODUCTION MUFFLER TO MEET THE DEFINED EXHAUST NOISE TARGET

For the development of exhaust system, using the available production muffler is a preferred means to reduce the manufacturing cost. However, in order to meet the specific designed NVH target, the muffler modification and refinement process is unavoidable. This paper presents a case study of the exhaust noise development, and the specific emphasis is placed on the trouble-shooting process, muffler design modification and experimental NVH verifications. The first modification of production muffler was the proportional size reduction due to the package concern. Out of different size reductions, the one with relative lowest exhaust noise was chosen, but it can not meet the target below 2500 rpm. Further order analysis shows that the 6th and 8th orders are the dominant components below 3000 rpm and they both correspond to the single noise frequency of 256 Hz. To solve the problem, an individual Helmholtz resonator was designed and verified at first. Then the original built-in resonator inside the muffler was tuned to the optimum dimensions to account for the Helmholtz effect. It was verified that 5 to 10 dB(A) improvement of the 6th and 8th order exhaust noise at major concerned speeds for the final muffler version. It is shown that the final muffler version can fully satisfy the target of exhaust noise as well as the targets of pass-by and stationary noise, and raises no engineering concern. The trouble-shooting methodology and muffler design rules employed in this case study can serve as a useful reference for the related field. (A) For the covering abstract see ITRD E113232.