Improved Performance of a Baffle-less Automotive Muffler Using Piezoelectric Materials

Piezoelectric materials have been used in the past to reduce noise and vibration in several different applications, but the use of these materials to enhance noise reduction for automotive exhaust systems is a new application of this technology. The work detailed herein shows how an inductive shunt circuit may be used to improve the noise reduction performance of a baffle-less automotive muffler system. The absence of interior baffles in the muffler minimizes backpressure and improves fuel efficiency of the upstream engine system. We designed and built a prototype system utilizing an IM7/bismaleimide composite for the muffler body, stainless steel end caps and PZT 5A piezo-ceramic for the passive/adaptive element. By matching the acoustic resonance of the cavity inside the muffler with that of the structure surrounding it, a fully coupled system was achieved. The mechanical impedance of the muffler shell was then matched to the electrical impedance of a piezoelectric strain device which served as energy converter (mechanical to electrical). The electrical energy could then be dissipated through an inductive shunt tuned for the appropriate structural resonance of the shell. An optimization of the parameters was performed so that the radiated noise at an acoustic resonance could be reduced. Vibration and acoustic tests were performed to confirm the analytical predictions, and reduction of both vibration and noise was achieved with this design at the target frequency. A narrowband acoustic reduction of 5 dB was achieved in the laboratory. While our muffler system is effective in a narrow range around the target frequency, broadband acoustic control can be achieved through the use of multiple tuned segments.