Predicting Shell Vibration and Implosion Issues in Automotive Muffler Design

The muffler shell of an automotive exhaust system can cause significant NVH (noise/vibration/harshness) issues like shell vibration and radiated noise, buzzing, rattling, and implosion problems. Due to the complex relationship between the dynamic behavior of the muffler shell and many parameters like engine operating temperature, curvature of the shell, material density, shell thickness and baffle spacing, the NVH engineers have experienced difficulties identifying the root cause of problems and solutions to them. By considering all design parameters, a theoretical study on shell vibration has been conducted to investigate applicability of an analytical technique to predict and solve the NVH issues of an automotive muffler. We have identified the most promising shell vibration theories by comparing the solutions with the results from modal test and finite element analysis. Utilizing those theories, an analytical model to predict the natural frequencies and mode shape for muffler shells of circular and non-circular cross section has been developed. Case studies are presented to demonstrate that theoretical approach for circular and non-circular cylindrical shell can be applied efficiently to predict and solve shell vibration, radiated noie, and implosion issues.