EP0806030B1 - l/4-SOUND ABSORBER - Google Patents

Description

The invention relates to a sound absorber according to the preamble of claim 1 and in particular a sound absorber for vehicles made of several tubular resonators, preferably with different lengths.

It is the aspiration of the modern automotive industry that reduce noise generated by vehicles or to eliminate entirely. For sound absorption today essential mats made of fiber insulation or open-pore Foams used around or in the noise sources immediate surroundings. The usage such open-pore sound absorbers in the engine compartment, such as. described in DE-34'28'157, but proves to be problematic because of this with oil, water, dust and others Contaminants contaminate and thus in their acoustic The effect wears off quickly.

It is therefore, for example, with DE-40'11'705, DE-42'41'518 or DE-43'05'281 has already been proposed, one Oil and water resistant arrangement from a variety of Helmholtz resonators to be provided. These known arrangements consist of box-shaped hollow bodies, which a Have a hole or neck. The volume of the hollow body determine together with the dimension of the hole or neck the resonance frequency of the absorber. These known arrangements are essentially for a frequency range designed from 1 to 2 kHz and can on the hood, in Wheel arch or be mounted on the floor pan.

In addition, these arrangements are undesirably demanding Space, i.e. can not with limited space be used.

In the practical use of this type of absorber, the walls of the box-shaped hollow body must be lightweight, ie very thin. However, these thin-walled hollow bodies tend to deform due to the fluctuations in sound pressure and thus limit the quality factor of the resonator. Since the quality factor significantly influences the efficiency of the absorbers, the lightweight design also means that the acoustic effectiveness of these absorbers must always be reduced.
The acoustic effectiveness of these absorbers is fundamentally limited because the number of sound-absorbing openings is limited by the geometric expansion of the individual hollow bodies. These hollow bodies typically have a base area of 15x15mm ² to 60x60mm ² , with a construction height of 5 to 25mm and a hole diameter of 4 to 11mm. This makes it clear that these Helmholtz resonators can only couple to a limited extent to the disturbing sound field, since, when used across the board, the sound-absorbing opening area, which is proportional to the quality factor Q, can only be a maximum of 2.5% to 4% of the total sound area.
In addition, when installing the helmet wood absorbers described on a vehicle floor pan, the openings are directed upwards and can therefore easily fill the cavities with moisture and dirt, which in turn impairs sound absorption.

An insulating part is also known from DE-39'13'347, which has a multiplicity of cell-like cavities arranged closely next to one another, which are open on one side. With this insulating part, the energy of the impinging sound field is essentially irregular
Reflections, absorption in the material and interference effects dissipated.
These insulating parts are also only suitable to a limited extent for use in automobile construction, in particular because they are easily soiled and wear out quickly due to their lack of inherent stability.

GB-2'090'334 describes a damping device to dampen the generated in a nozzle drive aerodynamic vibrations, in which one Variety of tubular resonators is used. The Length of these tubular resonators is dimensioned so that this is a quarter of the wavelength of this Corresponds to vibrations. This can result in a partial cancellation the pressure fluctuations in the mouth area of this Resonators are generated. In the in this patent proposed damping device, however, will not note that the to the individual resonator openings mutually influence interaction zones, and in particular the intended effect from the proposed one Arrangement can be canceled.

It is therefore an object of the present invention To create sound absorbers that are known for the disadvantages Absorber overcomes and in particular a space-saving To create sound absorbers that have improved sound absorption which, even with a lightweight Construction and effective in a highly polluting environment remains.

According to the invention, this object is achieved by a sound absorber solved with the features of claim 1, i.e. With a sound absorber made up of several tubular resonators, preferably with different lengths, the at least one sound opening to a sound reflecting one Adjacent area. The tubular resonators can any position to the sound reflecting surface in particular, the resonators can also rest on this surface.

If a sound wave front falls on a sound reflecting one Surface, a sound pressure maximum forms directly this area. This maximum sound pressure level arises from the Superimposition of the incident and reflected wave this place. In the arrangement according to the invention the mouth of a tube, directly to one sound reflecting surface. So the incident runs Sound wave into the tube is on the tube The end reflects and runs back to the mouth opening. Sound waves whose wavelength is 4 times the length of the Tubes appear at the mouth opening a phase shift of half a wavelength. This leads to destructive interference with that in the mouth area of the tube reflected wave the same Wavelength because the standing wave generated in the tube is yours Sound pressure minimum at the mouth opening, while the wave reflected in the mouth area has its maximum sound pressure there having. This will be in the mouth area creates a strong sound pressure gradient, which is locally too high Air flow speeds and thus to the desired one Dissipation of acoustic energy contributes.

From this understanding it is clear that the λ / 4 tubes can be arranged in any direction and also not necessarily a straight line must have. Likewise, the cross section of these tubes have any shape. It is for the Expert, the length of the tubes of the chosen shapes and Adapt resonance frequencies. Simply that However, those skilled in the art have shapes that are essentially the same Select cross-sectional area.

The formation of areas in which destructive interference takes place is essential for the effective functioning of the present invention. These areas are called interaction zones A _w below, the extent of which can be related to the respective sound opening area A _o and the quality factor Q. It turns out that the ratio between the area of the interaction zone A _w and the sound opening area A _{o is} proportional to the quality factor Q. Q = k A w A O

It is therefore the aim of the embodiments according to the invention to ensure that the individual interaction zones are distributed as widely as possible and at the same time do not substantially overlap, since such an overlap reduces the above-mentioned sound pressure gradient and thus reduces the dissipating local air flows. In order to achieve an acoustically effective arrangement of the interaction zones A _w that is as extensive as possible, the openings of the tubular resonators are preferably distributed over the corner points of an imaginary network of isosceles triangles.
If sound absorption over a wide frequency range is desired, several groups of differently tuned tube absorbers can be interleaved. Likewise, the combination of the λ / 4 absorbers according to the invention with conventional absorbers can be quite useful for certain applications.

The individual are in the preferred field of application tubular resonators on a sound field in the area tuned from 1 - 2 kHz, i.e. have a quarter wavelength appropriate length of approx. 80 - 40 mm. In standing waves can form in these λ / 4 resonators, compared to that reflected in the mouth area Wavefront of the same wavelength out of phase by λ / 2 are and interfere destructively with it. To a vehicle-specific Effectively absorb noise spectrum the λ / 4 absorber according to the invention has at least a group of tubular resonators of different Length on. It doesn't matter whether the sound openings are on the front or on the jacket side are.

In a preferred embodiment, the individual Resonators distributed on a surface. The effectiveness the mechanism shown also largely depends on the sound reflecting property of the cavity educational material. Soft and compliant materials lead to losses in reflection and impair the above absorption mechanism. It is therefore understood that only for the resonators according to the invention airtight, smooth and reverberant, i.e. good sound reflecting Materials come into question.

In a special embodiment, the λ / 4 resonators formed from a sheet or plastic film. By the arrangement of the resonators in groups can do this Tile-like attached to the vehicle and aligned in this way that there is any contamination by water or cannot catch oil, i.e. flow out again directly can. The assembly of these according to the invention Sound absorbers can be made using known means. By the application of the reverberant absorbers becomes vibrations and vibration-prone vehicle parts stiffened and steamed.

In another embodiment, the cavities are direct into a reverberant matrix, preferably into a lightweight one Plastic, metal or ceramic matrix molded.

The advantages of the device according to the invention are Expert immediately apparent and are particularly in the creation of a specifically tunable and lightweight Absorbers with a low overall height. In addition, use this absorber in heavily polluting environments, is not sensitive to moisture and can be manufacture inexpensively. A particular advantage these properties during vehicle assembly. Here can use this sound absorber together with the vehicle chassis be immersed in a dye bath without soiling it and without being damaged.

Fig. 1a-d

erfindungsgemässe Anordnungen zwischen einem röhrchenförmigen Absorber und einer schallreflektierenden Fläche;

Fig. 2

wabenförmige Ausführungsform der erfindungsgemässen Vorrichtung;

Fig. 3a,b

flächige Ausführungsform der erfindungsgemässen Vorrichtung;

Fig. 4a,b

ziegelartige Ausführungsformen der erfindungsgemässen Vorrichtung;

Fig. 5

bevorzugte Verteilung unterschiedlich langer Resonatoren.

Die Figuren 1a bis 1d zeigen die grundsätzliche Anordnung der Resonatoren in Bezug auf die schallreflektierende Fläche A. In Figur la steht der λ/4-Resonator senkrecht zur schallreflektierenden Fläche A. Dabei liegt seine Mündungsöffnung A_o in dieser Fläche A. Es lässt sich experimentell nachweisen, dass die Schallabsorption in dem Masse nachlässt, in dem die Mündungsöffnung A_o die schallreflektierende Fläche A überragt. Erfindungsgemäss kann der Resonator 3 aber auch schräg oder dachziegelartig zur schallreflektierenden Fläche A stehen. Damit kann die Baudicke des gesamten Resonators reduziert werden. Diese Anordnung bietet sich insbesondere wegen deren einfachen Herstellungsweise an und eignet sich für die Verwendung als modulartiger Bausatz. Die Länge der einzelnen Resonatoren 3 und deren Durchmesser kann den gewünschten Absorptionseigenschaften in einfacher Weise angepasst werden. Eine bevorzugte Anordnung ist in Figur lc ersichtlich. Hier liegen die Resonatoren 3 parallel auf der schallreflektierenden Fläche A. Diese Anordnung funktioniert erfindungsgemäss, d.h. erzeugt im Bereich A_w lokal eine starke Luftströmung. Die in Figur ld dargestellte Anordnung entspricht derjenigen aus Figur lc, ist in der Praxis jedoch einfacher herzustellen. Dabei kann, wie in Figur lc dargestellt, die Schallöffnung A_o des Resonators 3 an dessen Stirnseite liegen oder kann, wie in Figur ld gezeigt, im Mantel des röhrchenförmigen Resonators 3 angebracht sein. Es versteht sich, dass die Querschnittfläche des Resonators 3 jede beliebige Form aufweisen kann und insbesondere die Resonatoren 3 selbst nicht notwendigerweise einen geradlinigen Verlauf haben müssen, sondern auch mit einem gekrümmten Verlauf ausgebildet sein können.The invention is to be explained in more detail below with the aid of exemplary embodiments and with the aid of the figures. Show:

1a-d

Arrangements according to the invention between a tubular absorber and a sound-reflecting surface;

Fig. 2

honeycomb-shaped embodiment of the device according to the invention;

3a, b

Flat embodiment of the device according to the invention;

4a, b

brick-like embodiments of the device according to the invention;

Fig. 5

preferred distribution of resonators of different lengths.

FIGS. 1a to 1d show the basic arrangement of the resonators in relation to the sound-reflecting surface A. In FIG. 1a, the λ / 4 resonator is perpendicular to the sound-reflecting surface A. Its mouth opening A _{o is located} in this surface A. It can be experimented demonstrate that the sound absorption decreases to the extent that the mouth opening A _o projects beyond the sound-reflecting surface A. According to the invention, the resonator 3 can also be inclined or in the manner of a roof tile in relation to the sound-reflecting surface A. This allows the overall thickness of the entire resonator to be reduced. This arrangement lends itself particularly to its simple method of manufacture and is suitable for use as a modular kit. The length of the individual resonators 3 and their diameter can be adapted to the desired absorption properties in a simple manner. A preferred arrangement is shown in Figure lc. Here, the resonators 3 lie parallel on the sound-reflecting surface A. This arrangement works according to the invention, ie locally generates a strong air flow in the region A _w . The arrangement shown in FIG. 1d corresponds to that from FIG. 1c, but is easier to manufacture in practice. In this case, as shown in FIG. 1c, the sound opening A _{o of} the resonator 3 can be located on its end face or, as shown in FIG. 1d, can be provided in the jacket of the tubular resonator 3. It goes without saying that the cross-sectional area of the resonator 3 can have any shape and in particular the resonators 3 themselves do not necessarily have to have a straight course, but can also be designed with a curved course.

Figure 2 shows a simple embodiment of the inventive Sound absorber under supervision. A group of Resonators 10 are designed as straight hollow bodies that either front 13 or bottom 15 a sound opening exhibit. The honeycomb base 12 allows a comprehensive coating. With this approx. 100 mm broad embodiment, the individual resonators 10 a length of 43 mm to 84 mm, i.e. are on frequencies tuned between 1 and 2 kHz. This λ / 4 absorber can be made of hard and smooth plastic, for example manufacture or form from sheet metal foils.

Figure 3a shows a box-shaped embodiment an extruded plastic molding 16. The cross section of the individual resonators 10 is approximately rectangular here. The sound-effective orifices 17 are on the jacket side appropriate. In this embodiment, the end walls 18 of the resonators 10 shifted in the desired manner become. This allows a targeted optimization of the acoustic Absorption effectiveness. It goes without saying that too these λ / 4 absorbers can be arranged in several layers can.

In Figure 3b an embodiment is shown at which essentially consists of two molded parts 7, 9 are constructed. A first molded part 7 is preferably made of aluminum and points in parallel mutually extending ribs 8. This molding 7 can directly from aluminum foam or from an aluminum sheet be shaped. The ribs 8 of this molded part 7 are with a second molded part 9, in particular a film or a sheet, preferably made of aluminum, covered and together form the hollow body 6 according to the invention Openings 5 can be punched out of the second molded part 9 his. Easily after merging the two molded parts 7, 9 partial areas of the second molded part 9 pressed into the hollow body 6 such that resonator openings 5 arise and at the same time, between each Resonators 6 end walls 4 are formed. The end walls 4 can also be molded directly into the first molded part 7 his. Such an embodiment can be adapt easily to the desired contours and is therefore inexpensive. It is understood that through that Molding of ribs and end walls in the first molded part 7, this maintains a high degree of mechanical rigidity and the desired one even with relatively thin material acoustic sound hardness can be achieved.

FIG. 4a shows a further modular embodiment of the λ / 4 absorber according to the invention. This consists of block-like Components 25 in which the tubular Resonators 27 are. These can be drilled out later or with an appropriate injection molding process directly be shaped. In a preferred form, the Cavities of the resonators 27 parallel to the block geometry and these blocks 25 become like tiles during assembly placed on top of each other and fixed. It is understood that the optimal dimensioning of the tubular resonators 23 lies in the area of professional skill. As well can be used for the production of these λ / 4 absorber blocks reverberant materials are used. So come for the time being only light-weight for the vehicle construction Materials such as hard plastics, open or closed-pore Foams, especially aluminum foam, coated Papers or foils, especially aluminum foils in Consideration. For other applications, e.g. in the building or Road construction, can of course be the usual there Materials are used so long on a smooth and respected hard surface within the resonators becomes.

In a variant of this embodiment according to FIG. 4b the resonators 27 run obliquely to the block geometry. The angular position of the individual can of course Resonators are different from each other.

FIG. 5 shows a schematic illustration of the distribution of the resonators of different lengths. The sound openings 21, 22, 23, 24 of the individual resonators each lie on the node of a network which is essentially spanned by isosceles triangles. It is clear from FIG. 5 that, in this configuration, the interaction zone A _{w of} the λ / 4 absorbers applied for a specific wavelength does not substantially overlap and an area-wide arrangement of the wavelength-dependent interaction zones A _{w is} achieved.

It is understood that from the description of the mode of operation, many different embodiments and fields of application are considered by the person skilled in the art. Reducing vehicle noise to the outside is an important task for which the specialist arranges sound absorbers in the immediate vicinity of the sound-generating units, in particular around the engine and the transmission. The highest and therefore most disturbing sound pressures are generated by these units in the frequency range of 1-2 kHz. If a value of 340 m / s is used for the sound propagation speed, this results in λ / 4 resonators with a length of 85-42.5 mm. Resonator groups in this length range and with a cross-sectional area of 0.25 to 2 cm ² can be produced inexpensively by deforming a plastic or metal foil in such a way that semi-tubular depressions are formed and this shaped foil is mounted or mounted against a carrier layer or carrier plate. is stuck on. Such shaped resonators are also sound-hard when using thin foils because of the inherent rigidity of curved surfaces and have a high quality factor as resonators.

Another important area of application in the field of Vehicle acoustics consist of reducing the in the vehicle cell generated internal noise. For this purpose, the Resonators resp. the above with tubular Lower the foils onto the inner surface of the Walls or the roof of e.g. panel vans are glued. The λ / 4 resonator foils have an additional stiffening effect and with a suitable choice of the adhesive also produce one vibration damping effect.

Form a special technical problem in vehicle construction Cavities caused by the special structure of the chassis arise. In particular, the cavities in doors special attention between sheet metal and cladding be given as a gift. The inventive method can also be used in this area λ / 4 absorber film on both the door panel and can also be applied to the door trim. When gluing with the door panel can turn from the stiffening and vibration-damping effect can be benefited.

The absorbers according to the invention are, their conception accordingly, primarily suitable for applications in which the disturbing and absorbable noise in one limited frequency range occurs. Generate in particular Gear or timing belt, which at constant Speed running, fan blower, electric motors or propeller motors in aircraft, Noise sources with a precisely defined narrow frequency range.

The use of the absorbers according to the invention soundproof walls, such as those on the side of Motorways are set up, should only be mentioned here in passing become. To do this, the embodiments would include the extruded sheet or the modular bricks particularly suitable. An analogous use of the inventive Absorber is also used for sound absorbing linings conceivable from traffic tunnels. It is understood that the Use of the absorber according to the invention not on the Vehicle area should be restricted. That's how it is Can also be used in swimming pools, sports halls or factories conceivable as wall or ceiling cladding.

Claims (10)

1. Sound absorber comprising several tubular resonators (10) having at least one sound aperture (13), and with a sound-reflecting surface (A), whereby the sound apertures (13) are adjacent to the sound-reflecting surface (A),
   characterized in that, for forming areas in which a destructive interference can occur between a wave reflected off the sound-reflecting surface (A) and a wave being phase-shifted in the tubular-resonator (10), the respective sound apertures (13) are spaced from each other at least by the radius of the corresponding interaction region (A_w), that is they do not substantially overlap the interaction regions (A_w), and that these interaction zones (A_w) are distributed so as to cover the largest surface possible of the sound reflecting surface (A).
2. Sound absorber according to claim 1, characterized in that the tubular resonators (1) are of different lengths.
3. Sound absorber according to claim 1 or 2, characterized in that the sound apertures are located in the end surface of the tubular resonators.
4. Sound absorber according to claim 1 or 2, characterized in that the sound apertures are located in the lateral surface of the tubular resonators.
5. Sound absorber according to any of claims 1 to 4, characterized in that the sound apertures are of different sizes.
6. Sound absorber according to any of claims 1 to 5, characterized in that the resonators (10) in the mounted state are open at the bottom.
7. Sound absorber according to any of claims 1 to 6, characterized in that the resonators are arranged parallel to the surface (A).
8. Sound absorber according to any of claims 1 to 7, characterized in that the resonators are formed in an acoustically hard matrix (16, 25) or in acoustically hard shaped parts (7, 9).
9. Sound absorber according to claim 8, characterized in that the acoustically hard matrix or each of the shaped parts consists of plastic or a light metal.
10. Sound absorber according to any of claims 1 to 9, characterized in that at least the inside of the tubular resonators (19) has a smooth surface.

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