Driving noise
The driving noise is a limit value that vehicles that are to be approved for use on public roads must not exceed .
Germany
Details are determined in Germany by Section 49 of the StVZO . In Germany, two noise limit values are noted in the registration document of a homologated motor vehicle, namely the stationary noise and the driving noise. Only compliance with the driving noise is required by law. In the course of time, the maximum value permitted for new vehicles has already been lowered several times. Older vehicles only have to comply with the limit value valid at the time of their first registration ( grandfathering ) .
Mechanisms of origin
Tire-road noise
The most important mechanism for generating noise from road traffic is tire-road noise . The roughness of the road surface and the tire profile cause the tread lugs and the carcass to vibrate and emit airborne sound. In addition, air in the tire contact is displaced in the inlet and sucked in again in the outlet. This creates aerodynamic noises (so-called air pumping ). Tire-road noises are dominant over a wide speed range (from around 30–50 km / h, depending on the gear selected). They are particularly noticeable on natural stone pavement with a rough surface and wide joints and on trucks. In passenger cars, the introduction of radial tires (steel belt tires), which are more durable and safer, but also significantly louder than bias tires, has increased the noise level drastically since the 1950s. The trend towards wider and wider tires contributes to an increase in tire noise to a small extent.
Drive noises
Drive noises are caused by the operation of the engine, transmission and drive train of a motor vehicle as well as their auxiliary units and attachments. In the internal combustion engine, noises are generated by combustion pressures, pressure fluctuations in the intake and exhaust systems and mechanical forces in the valve and crank mechanism. In the case of electric drives, they arise from electromagnetic forces, in the bearings and from switching operations.
Drive noises are transmitted as airborne and structure-borne noise to the interior and exterior of the vehicle and dominate - depending on the vehicle class and type of drive - at low speeds and high engine power, such as when starting off.
Aerodynamic noises
At high speeds, noise-generating air turbulences are created on the body and on attachments. They are examined in aeroacoustic wind tunnels . At motorway speeds and “quiet” tire-road combinations, the aerodynamic sound sources can clearly dominate.
Other noises
Acoustic signals such as horns, bells, sirens and the like are necessary to ensure road safety. Therefore, they cannot be completely avoided. Furthermore, noises are caused by audio playback systems or by slamming doors and hoods.
Standing noise
The driving noise is comparatively difficult to measure. That is why a value is also given for the stationary noise. It serves as a point of reference in order to quickly and easily gain information during traffic checks as to whether the checked vehicle complies with the specifications or has possibly been manipulated. If the stationary noise measurement detects a significant deviation from the value specified in the vehicle documents, there is suspicion of manipulation of the engine or the exhaust system, for example, and the authorities can, for example, order an (expensive) driving noise measurement. For vintage cars built before 1980, the police must add 26 dB to the entered value if there is no letter after the dB number in the letter. For younger vehicles with a P after the dB information in the letter, only 5 dB tolerance is added. Vehicles built before 1954 are not subject to any precisely defined restrictions; The general rule of § 1 StVO applied that no "nuisance" was allowed. In addition, the "general state of the art" had to be observed in the design of the vehicles.
Measurement method for driving noise measurement
The measurement procedure to be used for cars is now regulated uniformly across the EU . The corresponding regulations are named in § 49 StVZO. Put simply, the vehicle must drive past the measuring device at a certain distance at three quarters of the nominal speed (but max. 50 km / h) and be fully accelerated in the process. Depending on the transmission , the measurement is carried out in second gear (four-speed transmission) or in third gear (transmission with more than four gears). Today, the pure sound pressure (Phon) is no longer measured, but in dB (decibels) with the inclusion of a weighting filter ("A"), which takes into account the frequency dependence of the sensitivity of the human ear. A comparison of "Phon" and "dBA" is therefore only possible to a limited extent. Motorcycles accelerate fully in second and third gear from 50 km / h. The measured values give the average driving noise. For bikes with no more than 4 gears, measurements are only taken in second gear.
Effects on Practice
The driving noise depends not only on the "actual volume" of a vehicle, but also on the power curve of its engine and on the gear ratio, as a result of the prescribed, complicated measuring process that is supposed to simulate a real acceleration process. This fact opens up certain constructive "back doors" to circumvent the noise reduction actually intended by the legislature.
If a new, lower limit is issued that a vehicle type that was still eligible for approval in the previous year exceeded, the manufacturer could, for example, extend the transmission ratio of its drive so that the engine only achieves lower speeds during the measurement, at which the vehicle emits less noise. In practice, however, most drivers will not stay in the "low-noise" high gear in a corresponding driving situation, but will shift down in order to achieve the desired acceleration - and release as much noise as before the tightening. In this case, the only tangible result would be higher fuel consumption, because the vehicle with too long a gear ratio is increasingly driven in the lower gears.
With more modern motorcycles, on the other hand, the manufacturer sometimes electronically regulates the engine output in the corresponding gears and the speed range of the driving noise measurement.
In quite a few luxury-class cars and almost all sports cars, the driving noise in the narrow area encompassed by the driving noise measurement is increasingly attenuated by mechanical flaps in the exhaust and thus kept within limit values. Since these flaps are open in all other driving states (other gears and speeds), the vehicle is actually much louder during normal driving than the official information on the driving noise suggests.
See also
literature
- Heribert Braun, Heribert Konitzer, Walter Kretschmann: StVZO - Road Traffic Licensing Regulations . Kirschbaum Verlag, Bonn. Loose-leaf edition (texts, comments), ISBN 978-3-7812-1537-5 .
- Richard van Basshuysen, Fred Schäfer: Handbook internal combustion engine . Siemens-VDO, Vieweg + Teubner Verlag, p. 946 f.
- Gert Thöle: fold-out in Motorrad issue 25/2008 p. 64
Web links
Individual evidence
- ↑ Ulf Sandberg and Jerzy A. Ejsmont: Tire / Road Noise Reference Book . Informex, Kisa (Sweden), 2002, ISBN 91-631-2610-9
- ↑ Heinz Steven: Potential for reducing road traffic noise . Noise Congress 2000, Mannheim, 25. – 26. September 2000, full text (PDF) ( Memento of the original from January 24, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ^ Helfer, M .: Aeroacoustics . In: WH Hucho: Aerodynamics of the automobile - fluid mechanics, heat engineering, driving dynamics, comfort . Vieweg, Wiesbaden 2005, ISBN 3-528-33114-3
- ↑ Directive 84/372 / EEC (PDF)
