Development of an active muffler system for reducing exhaust noise and flow restriction in a heavy vehicle

In this paper an application of an active muffler system is presented for r educing exhaust noise of a heavy vehicle. The signal-to-noise ratio associa ted with the process of estimating the transfer function of a secondary pat h was improved using conventional inverse modeling combined with an adaptiv e line enhancer as a control strategy. The simplified passive muffler using two-duct perforated elements was combined with the active muffler system i nstead of a conventional passive exhaust system to reduce exhaust noise and flow restriction simultaneously. In experiments to estimate the transfer f unction of a secondary path, the estimates using the inverse modeling metho d alone show many errors at the dominant frequencies of primary noise. Resu lts obtained using the proposed algorithm correspond well to the actual tra nsfer function as estimated without the primary noise. Control experiments with the proposed active muffler system have been implemented for stationar y and driving states, respectively. Compared to the conventional passive mu ffler, the experimental results showed that the proposed active muffler cou ld reduce the backpressure up to 60% as well as the overall sound pressure level below about 2200 rpm. (C) 1999 Institute of Noise Control Engineering , [S0736-2501(99)00302-1].