An automobile’s exhaust system is becoming more and more critical to its success in the marketplace. Most important, the sound produced by the vehicle serves to a considerable degree as the signature of the brand. For example, an auto enthusiast can recognize the approach of a Bentley or Ferrari with his or her eyes closed. Purchasers of lower-priced vehicles may not be quite so finicky but they still expect to hear a certain sound when they start up the engine. Meanwhile, automotive original equipment manufacturers (OEM) are being forced by government regulations to reduce the levels of noise emitted from the tailpipe. Automakers are also hoping to reduce the back pressure of exhaust systems in order to achieve improvements in fuel economy.
It’s becoming increasingly difficult to meet these often conflicting goals using conventional passive exhaust system technology which relies upon the use of perforated tubes and chambers to filter out acoustic waves. Automotive original equipment manufacturers (OEMs) are looking at active exhaust systems as a way to address these issues. Active exhaust systems use a loudspeaker driven by a microprocessor to cancel out unwanted sound generated by the engine as well as to produce more desirable sounds. A key advantage of active exhaust systems is that they can be controlled by software to adjust the output of the loudspeaker to deliver just the right sound under a wide range of different operating conditions.
“Actran has enabled Tenneco to develop a process for electroacoustic simulation of an active exhaust system including the loudspeaker and housing that correlates very well with physical experiments,” said Nicolas Driot, Senior Core Science Engineer for Tenneco. “We are now using simulation to develop our next generation active exhaust system. Simulation will make it possible to evaluate the performance of many alternative design concepts in a minimal amount of time without the expense of building physical prototypes. This should make it possible to improve the performance of the exhaust system beyond what can be achieved with the traditional process where only a few different design alternatives can normally be evaluated. Simulation will also make it possible to bring new products to market faster.”