Reduction of acoustic waves with minimum back pressure
65-dBA-traffic noise -> chance of having a heart attack + 20%
In the exhaust system emission control is particularly important apart from noise reduction. In addition exhaust gases are safely to be derived and the efficiency of the engine to be as little as possible obstructed. Recently it even plays a role with the crash behavior. To avoid that the last silencer under the trunk disturbs the crash absorbing in case of a rear collision, it can be mounted in the center tunnel together with the catalyst. For the noise behavior itself the following long pipe is even more favorable. If the spare wheels disappears from the trunk, this can become even large. For the noise behavior importantly is double-walled pipe with fleece pad.
Something relatively new is the overlapping of sound waves using loudspeakers which are insensitive to exhaust gas. These speakers must be able to endure temperatures of up to 500°C. In particularly large volume engines they weigh only around half as much as a normal exhaust system. Because the exhaust is not blocked, and the flow of the gasses is not hindered, a higher efficiency, particularly for utility vehicles, can be attained in two ways. All in all, there is a second effect of the speaker in the exhaust system. From the drivers seat in motor cars, by pushing a button one can select the exhaust sound, e.g., a good natured diesel could be made to sound like a Ferrari.
As one can see in the above picture, the first, and in fact, very effective noise damping is made possible solely by providing the exhaust gas with more space. Unscientifically expressed, one could say that the sound waves simply get lost. In fact, within this container, still other measures are possible. One can combat noise as in the following first three principles, by producing a suitable counter-noise or, as in the fourth, through damping.
Resonance effect In the resonance absorber the acoustic waves are reflected several times. Certain frequencies (vibration areas) of this resonances are purposefully absorbed.
Reflection effect With the reflection absorber the pipes are arrangedout of alignment. The chambers are differently large, and the exhaust gas stream is turned back several times.
Absorption effect With the absorption absorber the chambers are differently large and contain filling material (e.g. mineral wool).
Interference effect In the interference absorber the exhaust gas stream is divided and led after differently long ways again together. Differently pronounced acoustic waves absorb each other.
Mixture of the effects In practice several effects in a muffler housing are realised.
In the meantime exhaust system completely in one piece from stainless steel are manufactured. For the case of the replacement there are pre-defined interfaces, between which then sections can be replaced. 01/09