Sound-absorbing apparatus of a motor vehicle body

Abstract

The sound-absorbing apparatus 2 for application to a motor vehicle body 1 comprises at least two layers, a first layer 8 and a second layer 9. The first layer 8 comprises passage openings 10 , wher

Description

The invention relates to a sound-absorbing apparatus of a motor vehicle body. Sound-absorbing measures of a motor vehicle body are known, wherein a liner of an interior or a trunk of the motor vehicle body having a textile in the form of a carpet already comprises a sound absorption mechanism. A flexible sound insulation nonwoven for an interior of vehicles made from natural materials such as hemp, jute, or cork can be found in the disclosure document DE 199 54 779 A1 as a sound-absorbing apparatus. This nonwoven is provided with a perforated paper layer on its outer surfaces. An adhesive or a binder is formed between the nonwoven and the foil. The disclosure document DE 10 2019 118 591 A1 describes a sound insulation element consisting of a plurality of layers. An upper layer is a perforated, textile cover layer made from natural materials such as grass, nettles, or flax. Under the latter is a cell layer consisting of wood material, paper, or cardboard. The bottommost layer is a terminal layer made from materials such as grass, wood, or paperboard. Pores of the cover layer and absorbent layers are designed so as to provide certain acoustic properties. The disclosure publication DE 20 2004 018 241 U1 describes a sound insulation panel for vehicle interiors consisting of a carrier panel made of wood or wood fibers. A perforated cover layer is applied to the carrier panel and is formed from a woodbased material. The cover layer, comprising a coating and an adhesive layer, has holes in the coating and the adhesive layer, which can be different in shape and size. The holes can be formed regularly or irregularly in the cover layer. They are aligned with one another in the coating and the adhesive layer and have substantially equal cross sections. The carrier panel comprises channels that are formed so as to penetrate the carrier panel from one side to the other side. The sides each have grooves into which the channels open. In particular, a portion of the holes of the cover layer is connected to one of the grooves or channels. The disclosure document EP 2 871 638 A1 discloses a sound insulation panel for vehicles, consisting of a perforated layer and a non-perforated layer. At least the non-perforated layer is made of natural materials, for example wood wool. The disclosure document JP 2001065077 A describes a sound insulation panel composed of an apertured wood panel and a plywood cover panel. The apertured wood panel serves as a sound absorber, and the cover panel serves for stabilizing and protecting the apertured wood panel. The two panels are fixedly connected together so as to form a stable and effective sound insulation panel. The disclosure document DE 2004 011 287 A1 describes a sound insulation mat consisting of a plurality of layers. One of these layers is a cotton sponge. A further layer is an apertured carrier layer, which can be made of cotton or gypsum cardboard. The disclosure document DE 44 13 009 A1 describes a sound-insulating panelling part, which consists of an apertured front wall and an unapertured back wall. The present invention seeks to provide an improved sound-absorbing apparatus of a motor vehicle body. According to an aspect of the invention there is provided a sound-absorbing apparatus of a motor vehicle body having the features of claim 1. Advantageous embodiments, including preferable and non-trivial further developments of the invention, are specified in the respective dependent claims. A sound-absorbing apparatus of a motor vehicle body consists of at least two layers, a first layer and a second layer. The first layer comprises passage openings for the permeability of sound waves, wherein the passage openings are configured so as to permeate the first layer entirely over its first thickness. The second layer is arranged adjacent to the first layer. According to an aspect of the present invention, the passage openings are configured so as to be permeable to sound waves at selected frequencies, and the second layer is designed with the aid of its material properties for absorbing the sound waves, wherein at least the second layer is made from a sustainable material. The advantage of aspects of the invention can be seen in that effective noise reduction in a body interior can be achieved while using sustainable materials with the aid of the sound-absorbing apparatus, because the sound-absorbing apparatus is designed according to a principle of a Helmholtz resonator. That is to say, the first layer serves as a partial barrier, which only allows certain frequencies to pass through it, and the second layer acts as an absorber, in which the sound waves are purposefully brought to energy absorption with the aid of structural properties of the material used. To effectively reduce noise, the first layer is arranged facing an outer surface of the motor vehicle body and the second layer is positioned facing a body interior of the motor vehicle body or vice versa. That is to say, the arrangement in which the first layer faces the body interior and the second layer faces the outer surface can also be expedient, because the sound waves can also reproduce in the body interior, but can also be weakened with the aid of this arrangement. An alignment of the frequencies to be allowed through the first layer is carried out in a simple manner with the aid of corresponding cross-sections and shapes of the passage openings. That is to say, in other words, frequencies for absorption in the second layer are filtered through the passage openings, depending on the crosssections and shapes of the passage openings. Further effective sound reduction is possible by forming the second layer from a porous material, because the porous material has a preferred and therefore high and effective dissipation of the sound energy, or a preferred reduction of the vibrations. Preferably, sustainable materials are wood or also wood fibers or cork or a foam. For example, cork is a good sound absorber, because it has numerous small air pockets, as well as a foam, which assist in dissipating the sound energy. The passage opening of the first layer can be an actively created and / or material-inherent passage opening. In particular, in the case of the material-inherent passage opening, the possibility of providing an inexpensive sound-absorbing apparatus is given, because method steps for producing the passage openings are omitted. To the extent that the actively created passage opening is to be realised, it can be simply and thus inexpensively achieved with the aid of a chipping method. Advantageously, a third layer is formed, which is arranged adjacent to the second layer and facing away from the first layer. The advantageously porous second layer, which faces the body interior for the realization of an effective noise reduction, is thus covered with the aid of the third layer opposite the body interior. To the extent that the third layer is designed in the form of a supporting layer, in particular a supporting panel, a dual-mass oscillator is advantageously realised, so that structural vibrations of the first layer are eliminated via the second layer or at least reduced to a structural vibration of the third layer. That is to say, the first layer and the third layer can vibrate at different frequencies, wherein the sound emission from the third layer into the body interior is further reduced. For further effective sound reduction, a second thickness of the second layer is many times greater than the first thickness of the first layer, so that the energy reduction of the sound waves is as large as possible in the second layer. In particular, the second thickness is designed to form as large a volume of the body interior as possible. The motor vehicle body has laminarly designed body elements, for example doors or a roof, which can comprise the sound-absorbing apparatus even before its assembly in a frame of the motor vehicle body, wherein they are configured as a hybrid component, and the sound-absorbing apparatus is at least partially enclosed by a frame and / or a structural element of the corresponding body element, thus the motor vehicle body. Additional advantages, features, and details of the invention arise from the following description of preferred exemplary embodiments, as well as with reference to the drawings. The features and feature combinations specified hereinabove in the description, as well as the features and feature combinations mentioned hereinafter in the description of the drawings and / or shown alone in the drawings, can be used not only in the respectively specified combination, but also in other combinations, or on their own, without departing from the scope of the invention. Identical or functionally identical elements are assigned identical reference signs. The figures show: Fig. 1 in a schematic diagram, a section of a motor vehicle body with a sound-absorbing apparatus according to an embodiment of the invention and its principle of action, and Fig. 2 in a schematic diagram, the sound-absorbing apparatus according to an embodiment of the invention with a schematic representation of its function. In Fig. 1, a schematic diagram shows a section of a motor vehicle body 1 with a sound-absorbing apparatus 2 according to an embodiment of the invention. The motor vehicle body 1 has an outer surface 3, which is configured so as to delineate a body interior 4 from an environment 5. The environment 5 has sound sources 6 whose sound waves 7 strike the motor vehicle body 1. The motor vehicle body 1 is associated with an electric vehicle, but could also be associated with a motor vehicle having an internal combustion engine or with a hybrid drive. In particular, in electric vehicles in which fewer low frequencies with higher noise amplitudes can cover or mask high-frequency noises due to a lack of an internal combustion engine, interference noises can be perceived much more easily, so that the use of the sound-absorbing apparatus 2 according to the invention is preferred here. The sound source 6 generates an airborne sound which, when it strikes the outer surface 3, can cause vibrations and thus induce a body sound in the motor vehicle body 1. The vibrations associated with the body sound are emitted into the body interior 4 and are typically perceived as disruptive therein. For example, large surfaces of the motor vehicle body 1, such as side surfaces, door surfaces, or the loading floor in a trunk of the motor vehicle body 1, are particularly critical, because they can stimulate many molecules in the body interior 4 and in the trunk, respectively, to begin vibrating and thus to cause high sound pressures or amplitudes. The motor vehicle body 1 preferably comprises the sound-absorbing apparatus 1 directly adjacent to the outer surface 3 and is constructed according to a principle of action of a Helmholtz resonator. It comprises a first layer 8 and a second layer 9. The principle of a Helmholtz resonator is that the sound waves 7 can pass through a first space, in the present exemplary embodiment the first layer 8, in order to penetrate from the first space into a second space, in the present exemplary embodiment the second layer 9, so as to be reflected therein in multiple ways and times. They thus preferably remain in the second space, wherein the sound power can be reduced by energy dissipation. The two layers 8, 9 are arranged adjacent one another, wherein the first layer 8 is arranged facing the environment 5, and the second layer 9 faces away from the environment 5 while facing towards the body interior 4. It should be noted that in this context, any space delineated by the motor vehicle body 1 is to be considered a body interior 4, such as a trunk of the motor vehicle body 1 or a load compartment of the motor vehicle body 1. The first layer 8 has passage openings 10 that completely penetrate the first layer 8 in its first thickness D1 and adjoin the second layer 9 which has a second thickness D2. The sound waves 7 emitted from the environment 5 enter the passage openings 10 and are directed into the second layer 9 starting from the passage openings 10, in which they undergo energy degradation due to their material properties. In other words, by way of a reduction of a sound power of the sound waves 7 caused with the aid of the material properties of the second layer 9, an energy degradation of the sound waves 7 is caused. Or, in other words, the second layer 9 is designed with the aid of its material properties for absorbing the sound waves 7. The first layer 8 is configured so as to be permeable to sound waves 7 at selected frequencies and comprises the passage openings 10 having different shapes and / or different effective passage opening cross-sections. Thus, sound waves 7 having different frequencies can pass through the first layer 8 and penetrate into the second layer 9. Or, in other words, the passage openings 10 are formed with the aid of corresponding, in particular effective, opening cross-sections and shapes of the passage openings 10 so as to allow the selected frequencies to pass through the first layer 8. As illustrated in Fig. 2, a portion of the sound waves 7 are reflected on the first layer 8, in particular webs 11 enclosing the passage openings 10. The second layer 9, which is designed with the aid of its material properties for the absorption of the sound waves 7, is formed from a porous material. Here, a porous material is understood to mean a material having cavities and can be designed in the form of an open-porous or closed-porous material. Its porosity can be ordered or disordered. As a material, for example, a braid, a porous cork, in particular a high-porous cork, various foams made of, for example, wood fibers or lignin, wood wool, and the like, can be used. The material is a so-called sustainable material. Thus, with the aid of the second layer 9 realised from sustainable material, a significant reduction, possibly also elimination, of the sound waves 7 can be realised. The first layer 8, which is plate-shaped, is made of a supporting and stable material. That is to say, it is not elastic, and it is designed in the form of a plywood panel, veneer liner structures, flax panels, or extremely hard foams, for example. Depending on the material of the first layer 8, the passage openings 10 can be actively created, for example, in a chipping manner by drilling or milling. They can also already be inherent in the material, for example, branch holes in the wood, wherein a branch section typically formed in the first layer 8 has fallen out of its receiving space. Cracks in the material, for example, screed cracks, could also form the passage openings 10. Likewise, a combination of the actively created passage openings 10 and the material-inherent passage openings 10 is contemplated. A third layer 12 of the sound-absorbing apparatus 2 according to the invention can be formed adjacent to the second layer 9. That is to say, the third layer 12 is arranged adjacent to the second layer 9, facing away from the first layer 8. Or, in other words, the second layer 9 is arranged between the first layer 8 and the third layer 12. This third layer 12 can be designed in the form of a supporting panel, wherein the advantage is that the second layer 9, being designed porously, delineates the body interior 4 against the second layer 9. The first layer 8 has a first thickness D1, which is many times smaller in relation to a second thickness D2 of the second layer 9, at least three times. The layers 8, 9, 12 are in particular laminarly formed. The sound-absorbing apparatus 2 according to the invention is thus designed in the form of an at least dual-mass oscillator, which is decoupled in its sub-regions. That is to say, structural vibrations originating from the first layer 8 do not result in direct vibrational excitation of the third layer 12, because between both layers 8, 12, the second layer 9 consisting of the energy-absorbing material is formed. This further means that the first layer 8, which is designed in the form of a rigid panel, and the third layer 12, which is also configured in the form of a rigid panel, are decoupled and can vibrate at different frequencies. In an exemplary embodiment not shown in further detail, the sound-absorbing apparatus 2 is enclosed by a frame of the motor vehicle body 1, for example in the form of a profile, in particular an aluminum profile, and is thus part of an overall component of the motor vehicle body 1. Or, the sound-absorbing apparatus 2 is covered with a structural component of the motor vehicle body 1 on its end faces and additionally advantageously comprises the frame. That is to say, the sound-absorbing apparatus 2, in conjunction with a further component of the motor vehicle body 1, which is formed in peripheral regions of the sound-absorbing apparatus 2 or on its end faces, and is made of, for example, a sheet metal or plastic, can realise a hybrid component of the motor vehicle body 1. List of reference signs Motor vehicle body Sound-absorbing apparatus Outer surface Body interior Environment Sound source Sound wave First layer Second layer Passage opening Web Third layer First thickness Second thickness

Claims

1. A sound-absorbing apparatus of a motor vehicle body, wherein the apparatus comprises at least two layers, a first layer and a second layer, wherein the first layer comprises passage openings for the permeability of sound waves, wherein the passage openings are formed so as to completely penetrate the first layer over its first thickness, and wherein the second layer is formed adjacent to the first layer, whereinthe passage openings are configured so as to be permeable to sound waves at selected frequencies, and the second layer is designed with the aid of its material properties for absorbing the sound waves, and wherein at least the second layer is made from a sustainable material.

2. The sound-absorbing apparatus according to claim 1, whereinthe first layer faces an outer surface of the motor vehicle body and the second layer is arranged facing a body interior of the motor vehicle body, or vice versa.

3. The sound-absorbing apparatus according to claim 1 or 2, whereinthe passage openings are designed with the aid of corresponding crosssections and shapes of the passage openings so as to allow the selected frequencies to pass through the first layer.

4. The sound-absorbing apparatus according to any one of the preceding claims, whereinthe second layer consists of a porous material.

5. The sound-absorbing apparatus according to claim 4, whereinthe sustainable and porous material is wood or cork or a foam.

6. The sound-absorbing apparatus according to any one of the preceding claims, whereinthe passage opening is an actively created and / or material-inherent passage opening.

7. The sound-absorbing apparatus according to claim 5, whereinthe actively created passage opening is realised with the aid of a chipping method.

8. The sound-absorbing apparatus according to any one of the preceding claims, whereina third layer is formed, which is arranged adjacent to the second layer while facing away from the first layer.

9. The sound-absorbing apparatus according to any one of the preceding claims, whereina second thickness of the second layer is many times greater than the first thickness of the first layer.

10. The sound-absorbing apparatus according to any one of the preceding claims, whereinthe sound-absorbing apparatus is at least partially enclosed by a frame and / or a structural element of the motor vehicle body.T +44(0)30 0300 2000A

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