Active Cancellation of Exhaust Noise over Broad RPM Range with Simultaneous Exhaust Sound Enhancement

Demands for engines to operate at low-frequency firing order are increasing in the automotive market. This requirement is driven by consumer and regulatory demand for vehicles which are more efficient in the use of fuel. As a result, engine and transmission technologies have been developed which permit operation of engines with fewer cylinders at increasingly low RPM's. The resulting low frequency exhaust noise is more difficult to attenuate than in vehicles in years past. At the same time, vehicles often have less packaging space for mufflers, when larger volume would otherwise be needed to attenuate at lower frequencies. A further challenge is the demand for increasingly refined performance sounds from the exhaust systems of premium cars despite the technical obstacles involved in even maintaining sound quality. Finally, legally permissible sound levels are decreasing in some markets. These market and regulatory demands require new solutions. Technology has been demonstrated using an ANC system. The system uses the operating principle of ANC, using a feed-forward control mechanism. This system has now been demonstrated to attenuate multiple firing orders by sound cancellation down to 1000 RPM on a 4 cylinder gasoline turbocharged engine. It has also been demonstrated to simultaneously attenuate undesirable orders and accentuate desirable orders. This has been demonstrated in a vehicle with a 4 cylinder TC engine and also in a V8 application operating in 4 cylinder mode, where such desired engine order sounds could not be expected typically.