Exhaust System Design for Sound Quality

The exhaust system is one of the major P/T systems for sound quality tuning. The many varieties in exhaust pipe routing and the flexibility in muffler design make it possible to design an exhaust system to deliver tailpipe sound for specific sound quality requirements. It is essential that the tailpipe sound be balanced with other P/T sound to yield the overall sound targets. The primary contribution of an exhaust system is the firing and sub-firing orders. The typical tailpipe sound target contains banded targets for “good” orders as well as “do-not-exceed” targets for the rest. Every order target needs to be met in order to yield the right tailpipe sound. In most cases, the pipe routing and the muffler volumes of mufflers are dictated by package constraints, however, the internal design of muffler with a given volume can create quite different tailpipe sounds. Usually a particular muffler design is able to bring down the excess levels of certain un-wanted orders, but very often it also causes the deficiency of some of the good orders. Numerous design iterations are required to meet all the order targets. This is a costly and time-consuming process if it purely relies on prototype hardware testing. This paper presents a systematic target cascading strategy and a CAE driven design process to design an exhaust system for sound quality. The CAE analysis is extensively used to understand the impact of major design features and identify the optimal combination of these features. Correlation between test and CAE simulation results is also included to illustrate the interpretation of the gap between the target and analysis results, which is used to determine the design direction for subsequent design iterations.