Active noise-cancellation system for automotive mufflers

Abstract

In an active control noise-cancelling muffler system, a substantially complete acoustic and mechanical decoupling of the noise-cancelling signal pipe from the gas exhaust pipe is achieved. The noise-cancelling signal delivery pipe is physically isolated and separate from the gas exhaust pipe, and is mounted separately. The outlet end of both pipes are essentially coplanar. Using pressure sensors on the tubes, the system also accurately and continuously electronically replicates the mixing of the exhaust noise and the noise-cancelling acoustic energy that goes on in the space immediately beyond the two outlets. This electronic signal is a useful alternative for a direct measure of the resultant two acoustic waves when they mix in the space beyond the tube outlets, and allows the system to continuously estimate the degree of success of noise cancellation without having to measure it directly when impractical. The system uses measures of pressure and temperature of the two tubes to continuously adjust a transducer drive signal that drives the sum of the pressures at the two tube outlets toward zero. An advantageous algorithm for the control process is identified.