Customers may be impressed with the fuel economy provided by either a four-cylinder or a diesel engine, but they may not be bowled over by the acoustic properties. To reduce — or in some cases, improve — the noises made by engines, BMW is working with a series of acoustic systems, including one it calls Active Sound Design.
First tested on a MINI Cooper and now applied to a European-spec 635d diesel, ASD is quite similar to the noise-canceling system found on the 2010 Chevrolet Equinox. An electro-acoustic system, ASD utilizes microphones and the vehicle’s sound system to alter the engine’s sound characteristics. The system can either increase the sound of the engine during hard acceleration, or can produce frequencies that help cancel noise.
In this instance, BMW engineers have primarily tuned the ASD system to eliminate the coarse “knocking” noise emitted by the diesel mill in favor of a sporty sound akin to its typical gasoline-powered engines. Engineers have configured the system to provide a mild burble at half-throttle, and a loud roar during full-throttle blasts.
In addition to the active system, BMW engineers have refined traditional noise abatement designs in what it dubs Intelligent Acoustics. New lightweight materials — like thermoplastics — replace heavier sound deadening materials, and can be incorporated directly into the vehicle’s subframe, feasibly reducing mass. Further noise reduction can be improved through the engine’s design itself. The strategic placement of thin metal ribs on the crankcase, for instance, helps reduce disturbing engine noises.
These designs allow BMW to explore lighter, more fuel-efficient engines typically deemed unfit for luxury vehicles because of their sound characteristics. BMW is already applying Intelligent Acoustics throughout its portfolio, but it has not indicated when ASD will be applied to a production vehicle.