Technology explained - sound actuators: When it has to sound good

G Good driving behavior and low fuel consumption are important, but the sound of the engine is just as important for many drivers. In models like the Porsche 911 or a Ferrari, the characteristic engine sound is even part of the vehicle's DNA. But many efforts and regulations to save fuel, especially so-called downsizing, are at the expense of the soundscape. Although robust three-cylinder engines are now a pleasure for one or the other ear, four-cylinder and supercharged diesel engines hardly arouse emotions. Some manufacturers therefore help with special sound actuators. The active sound technology from Eberspächer, for example, can modify the engine sound so that a diesel sounds like a classy V8 petrol engine.

For this purpose, a control unit uses defined algorithms to calculate which frequency ranges are amplified or covered. On the one hand, it takes into account engine electronics data such as speed and load. On the other hand, a sensor records the sound pressure level in order to improve the sound again if necessary. In addition, the selected driving mode influences whether the car sounds sporty and powerful or comfortable and discreet. The signal reaches the sound actuator via a power amplifier stage, in which a special loudspeaker generates the desired soundscape. The actuator is usually located near the tailpipe and is connected to the exhaust system via a connecting pipe.

Attenuation by counter-noise

Nach The same principle can be used to achieve the opposite goal: soundproofing. The Active Silence System reduces the engine noise with targeted counter-noise. This works in a similar way to headphones, which block out disturbing ambient noise. Turbo gasoline engines in particular would benefit, as they get louder when driving at low revs and usually need large and heavy mufflers. With the sound actuator system, on the other hand, rear silencers can be omitted and central silencers can be made smaller. That saves around 30 percent weight.

The developers of actuators installed close to the engine, which could dispense with the entire exhaust system, expect even more potential in terms of lightweight construction. The challenges currently lie in the limited installation space and the high temperatures near the engine. While the Active Silence technology is still waiting for series use, the Active Sound System has been available in various models since 2011, including the VW Golf GTD and Audi A6.

You ask, we answer

What's the pointactually the braking energy recovery in the combustion engine - does the engine braking power even matter?

Alyson Geier from Obrigheim (Palatinate)

The term brake energy recovery is a bit misleading. In the internal combustion engine, the generator, often referred to as an alternator, generates the electricity for the on-board network. While it used to run continuously, today it is usually only active in overrun mode. Speak when the driver takes off the gas or brakes. In other driving situations, it does not load the engine, which should save up to four percent fuel according to the manufacturer.

Annette Napp, technology editor