Active and passive measures to reduce the noise pollution of combustion engines

In recent years comfort has become an important factor when evaluating the performance of modern automobiles. One important aspect that has negative ramifications on the perception of the quality is the generated noise, which mainly contributes to the disturbing noise level of urban regions. Therefore, an important goal in current research is the attenuation of the noise level of car engines. The paper at hand presents two main approaches, an active and a passive one, to reduce the noise radiation of combustion engines, which is the main noise source of automobiles. In the active approach thin piezoelectric wafers are attached to the structure as sensors and actuators. With an appropriate controller the structural vibrations are reduced, which result in an attenuation of the sound pressure in the environment. The passive approach utilizes a full engine encapsulation, which is also designed to reduce the sound radiation of the engine. By encapsulating the motor the oil temperature can be increased such resulting in decreased fuel consumptions.