Tire-road noise

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The tire-road noise is one of the main components of the exterior noise of motor vehicles . It is significantly involved in the generation of road traffic noise.

Meaning of the tire-road noise

The tire-road noise has steadily increased in importance since the 1970s, as the drive noise has been significantly reduced since then. In passenger cars , the drive noise usually only dominates in first and sometimes in second gear when driving at a constant speed. The drive noise also predominates when accelerating. In most driving situations in urban areas and almost all driving situations outside of town, the tire / road noise dominates. Only at high motorway speeds does aerodynamic noise become the loudest component.

Mechanisms for the development of tire-road noise

Different mechanisms contribute to the generation of noise when the tire rolls on the road surface. Both structure-borne noise and airborne noise sources are involved in the generation of tire-road noise. The causes and radiation conditions are very complex and depend on the combination of tire and road surface. The most important mechanisms that lead to sound radiation from freely rolling tires are:

  • Airpumping and
  • Tire vibrations

Air pumping

As Airpumping (-Geräusch) a component of the tire-road noise is denoted by Luftverdrängungs- -ansaugeffekte and in the region of the tire contact area is generated. The compression of the tire tread in the tire inlet (when a tread zone begins to contact the road surface) and the covering of the road structure by the tread blocks of the tire leads to the air being pressed out there. In contrast, the air flows back into the contact zone in the tire outlet when the tread areas begin to lift off the road again.

Air pumping is responsible for the aeroacoustic component of the tire-road noise and - depending on the tire-road combination - is one of its main causes in addition to carcass and profile vibrations. Air pumping noises are more pronounced the less rough and the less porous a road surface is. The speed and the amount of flowing air determine the volume, the shape of the channels provides the sound and the pitch .

Tire vibrations

Simulation of a rolling tire on a drum test stand, representation of the structural amplitude (IBNM, Leibniz University Hannover)

When the tire rolls on the road, the tire is excited to radial and tangential vibrations due to the roughness of the tread profile and the road surface . Airborne noise is generated by these tire vibrations. The sound is mainly emitted in the immediate vicinity of the mountainous area. The radiation characteristics of the tire are of particular importance. The wedge-shaped funnels formed by the road and tire surface in the inlet and outlet areas lead to a significant increase in the sound radiation in the direction of the opening funnel.

The vibration excitations of the tire, which can be determined by measuring the acceleration on tread blocks, are primarily caused by impulsive processes:

  • Impact effect
The flattening of the tire in the contact area with the roadway is of central importance for the impact of the profile elements. As a result, when the tire is rolling, tread elements hit the roadway at the entry point and are briefly accelerated radially at over 1000 m / s². The amount of acceleration increases with the square of the speed; 5000 m / s² can already be achieved at 100 km / h.
When a tire rolls, sliding movements occur in the contact area when the actually two-dimensionally curved tread is pressed into the contact plane. The result is small sliding movements of profile elements on the road surface. These stick-slip effects also lead to structure-borne noise excitations in the tire structure.
  • Tunnel vibrations
The profile elements are tensioned in the contact zone when the two-dimensionally curved tread is pressed into the contact plane. The remaining shear stresses are discharged in the run-out area of ​​the tire by pulsed "snapping out" of the tread elements lifting off the roadway. This leads to lug vibrations, which in turn are transmitted to the carcass . This phenomenon is particularly pronounced on slippery roads, where good contact between the tire and the road leads to high tangential frictional forces in the contact area.

Influencing variables on the tire-road noise

The noise components generated by the different creation mechanisms depend on numerous influencing factors. Vehicle speed, tread structure and road conditions have the greatest influence on the overall level and the spectral composition of the noise generated by the tire-road combination. The cumulative level of the rolling noise and sound intensity generated by the tire-road contact generally increase with the power of the second power of the speed, whereas the sound intensity of the noises caused by the airflow increases with the 6th power of the driving speed.

Influence of the roadway

The type of road surface has the greatest influence on tire-road noise. It is known from investigations that different road surfaces when measured under otherwise constant conditions can lead to differences in tire-road noise of up to 10 dB (A). Largest grain sizes of 5 to 8 mm have proven to be acoustically beneficial for both asphalt and concrete ceilings. Open -pored asphalt pavements are particularly quiet .

Influence of the tire

In all efforts to take measures aimed at reducing tire noise, it should not be forgotten that the tire must primarily meet driving safety requirements, such as driving stability, cornering behavior, behavior with regard to aquaplaning (slippery water), durability, wear resistance, etc. For a number of parameters, a reduction in tire / road noise leads to a loss in driving safety. As noise measurements on the one hand and sliding coefficient measurements on the other hand have shown for various tire-road combinations, however, "quiet" tire-road combinations can also have good driving dynamics properties, even on wet roads. Since October 1999 there has also been the first tire manufacturer to award one of its products the Blue Angel for low-noise and fuel-saving tires.

The noise emanating from a tire is largely determined by its mechanical and structural properties; it increases z. B. with the tire hardness clearly. A larger tire width also tends to lead to an increase in tire-road noise; the prevailing tendency to use wide tires therefore leads to a significant increase in tire noise. Furthermore, a favorable profile design is of great importance. In the middle of the tire, where no drainage capacity is required, longitudinal profiles are beneficial. In order to avoid tonal components in the noise, irregular profile divisions are generally used.

Influence of the operating conditions

When driving on wet roads (closed film of water) the tire / road noise is considerably higher than on dry roads. The noise primarily arises in the run-in of the tire contact patch and is primarily related to the water displacement, whereby the amount of water to be displaced or the speed at which the water is displaced from the area of ​​the tire contact patch influences the noise emission. Water particles experience high acceleration here for a short time, which causes the characteristic hissing and splashing noise in the high frequency range.

Another factor influencing the tire-road noise is the driving speed. The sound intensity increases with the third to fourth power of the driving speed or by 9 to 12 dB (A) per doubling of speed. This also means that the influence of an absolute change in speed is great, especially at low speeds. Reducing the speed is therefore the most effective way of reducing traffic noise .

In the case of high-performance commercial vehicles in particular, the torque acting on the drive wheels has also proven to be a significant influencing variable on tire / road noise. The reason for the increasing influence of the driving force is the increasing engine power of trucks in recent years. In the case of cars, too, the drive-related tire-road noise should not be underestimated. The resulting high tensile forces inevitably cause greater slip between the tire and the road surface and greater tension in the tread blocks. This also leads to higher levels of tire-road noise. In the case of trucks with traction tires, this level increase under the effect of pulling force can be up to 20 dB (A) compared with freely rolling wheels.

Comparison of various influencing factors

It is by no means the case that the same tire is always the quietest on all roads. In fact, the ranking changes depending on the road surface. Ultimately, the decisive factor is not the tire or the road surface, but the respective combination of both. The road surface has the greatest influence on tire-road noise (around 10 dB (A)). Even without taking special drain coverings into account, the bandwidth is still 6 dB (A). In contrast, the possibilities that the tire offers due to its construction and tread design are rather limited. The bandwidth for a fixed tire size is around 3 dB. Even if the tire width is also varied in addition to the design, the tire-side influence does not yet come into the range of the possible road influence. The vehicle model itself has only a minor influence when rolling without a drive due to the different design of wheel houses and underbody.

Speed ​​above which the tire-road noise predominates

  • Passenger car from the years 1985–1995, 30–35 km / h, when accelerating 45–50 km / h
  • Cars from 1996, 15-25 km / h, when accelerating 30-45 km / h
  • Trucks from 1985–1995, 40–50 km / h, when accelerating 50–55 km / h
  • Trucks from 1996, 30–35 km / h, accelerates 45–50 km / h

Measurement of tire-road noise

State-of-the-art near-field noise measurement trailer with towing vehicle and warning markings ( Müller-BBM )

Two different methods are used to measure tire-road noise: the far-field method and the near-field method.

Near field method, CPX measurement
The near field measurement method is used either in connection with special noise measurement trailers or drum test stands. The trailer measurement method can be used on public roads that are underneath traffic as well as on test tracks. Here, the rolling noise of one or two freely rolling tires in the immediate vicinity of the tire is recorded in a trailer. The near-field measurement method can also be used on the drum test bench in the laboratory.
Far field method
Pass-by measurement on the test site of the FKFS , Stuttgart
With the far-field method, the sound pressure level is measured at a distance of 7.5 m from the center of the lane and 1.2 m above the road surface when test vehicles roll past on the roadway to be examined, whereby the vehicles of members of the measurement team are measured at defined, constant speeds and certain types of tires are driven.

With these methods, the influence of different road surfaces on the tire-road noise can be determined when using a collective of tires. A differentiation between existing tire collectives on a given road surface is also possible.

literature

  • M. Helfer, G. Haug, E.-J. Horch: Influence of the tractive force on the tire-road noise. In: B. Breuer (Ed.): 2nd Darmstädter Tire Colloquium, October 16, 1998. (= progress reports VDI. Series 12, No. 362). VDI-Verlag, Düsseldorf 1998, ISBN 3-18-336212-0 .
  • T. Beckenbauer: Influence of the road surface texture on the tire-road noise. Report on the research and development project 03.293 / 1995 / MRB of the Federal Ministry of Transport, Building and Housing. Federal Ministry of Transport, Building and Housing, Road Construction and Road Traffic Department, Bonn 2002, ISBN 3-934458-79-3 .
  • G. Haug, U. Essers: Influences of the tensile force on the tire-road noise of heavy commercial vehicles. In: Automobiltechnische Zeitschrift. 99, No. 5, 1997, pp. 266-269.

See also

Web links

Individual evidence

  1. ↑ http://dipbt.bundestag.de/dip21/btd/15/032/1503290.pdf
  2. ↑ http://www.umweltaktion.de/pics/medien/1_1164277796/2006-11-17_15_Laermschutzkonferenz_Saemann_Manuskript.pdf
  3. ↑ a b Peter Zeller: Handbook vehicle acoustics. ISBN 978-3-834-89322-2 , p. 159 ( limited preview in Google book search).
  4. ↑ a b c d http://www.umweltbundesamt.at/umweltsituation/laerm/laermschutz/massn_strasse/reifenlaerm/