FR2942435A1 - Multilayer structure for e.g. panel of car, has airtight zone covering entirety of cavity with exception of chosen place such that cavity resonates at given resonance frequency considered from its chosen length and location of chosen place - Google Patents

Abstract

The structure (SM) has a connection layer (CL) intercalated between a support element (P) and a mass layer (CM). An airtight zone (FE) covers entirety of a cavity (CV) e.g. L-shaped cavity, with the exception of a chosen place of the cavity such that the cavity resonates at given resonance frequency considered from chosen length and location of the chosen place. The chosen place is situated above an end (E1) of the cavity such that the cavity constitutes a quarter-wave type resonant cavity.

Description

The invention relates to the sound insulation (or soundproofing) of certain parts of vehicles, possibly motor vehicles. As known to those skilled in the art, in order to sound isolate (or soundproof) parts of a vehicle, possibly automotive, it is possible to join multilayer structures to elements of Zo support of this vehicle, such as panels (apron, awning, door, floor or roof, for example). These multilayer structures comprise a mass layer (sometimes called a heavy mass) and a tie layer (sometimes called a spring layer) intended to be interposed between a support member and the mass layer. The tie layer (or spring layer) is a layer containing a lot of air. It may for example be made of fibrous material (such as for example cotton felt or glass felt) or foam (such as polyurethane (or PU).) The mass layer (or heavy mass) is generally produced. in a material capable of damping the vibrations and / or of absorbing a part of the sound waves, in particular those which strike it (possibly after at least one reflection), It may for example be made of bituminous material or of elastomer or copolymer (e.g., EPDM (Ethylene Propylene Diene Monomer) loaded with barite.) Once the multilayer structure is secured to a support member, they constitute an assembly that can be modeled by first and second masses coupled by a spring. The first mass is the support element, the second mass is the mass layer and the spring is the bonding layer (hence its name on the spring layer). then has a resonance frequency f0 that can be calculated. This type of assembly provides quality soundproofing, except (at least) in a small frequency band that is substantially centered on the resonance frequency. Indeed, when one observes the curve of evolution of the sound attenuation (in dB) as a function of the frequency (Hz) of this set, one realizes that this curve increases monotonically with the frequency, except in at least one zone which is located at the resonance frequency f0 and in which it decreases very strongly before increasing again very strongly. In order to improve the quality of the soundproofing in the aforementioned small frequency band, it is possible to define at least one cavity in the support element or in the connection layer. Unfortunately, this solution, which is described in particular in patent documents FR 2516034 and FR 2903054, insufficiently improves the quality of the soundproofing. The object of the invention is to improve the situation, and more precisely to improve the quality of the soundproofing compared to the solutions of the prior art using a multilayer structure.

It proposes for this purpose a multilayer structure, intended to be secured to a support element of a vehicle (possibly automotive) and comprising a ground layer and a bonding layer intended to be interposed between the support element and the layer of mass, the multilayer structure or the support member comprising at least one cavity of length (or extension) selected, and the multilayer structure and the support member being intended to constitute an assembly having a given resonance frequency. This multilayer structure is characterized by the fact that it comprises an airtight zone which covers at least the entire cavity except for a chosen location of the latter so that this cavity resonates at the frequency resonance given its chosen length and the location of the chosen location. The multilayer structure according to the invention may comprise other characteristics that can be taken separately or in combination, and 3o in particular: the location chosen may be located above one end of the cavity so that it constitutes a resonant cavity of the so-called quarter wave type (or λ / 4); in a variant, the chosen place may be situated above a central part of the cavity so that it constitutes a resonant cavity of the so-called half wave (or λ / 2) type; the cavity may be chosen from (at least) a rectilinear cavity, an L-shaped cavity, a spiral-shaped cavity and a resonant Helmholtz cavity; when the cavity is defined in the support element, the airtight zone can be defined either by an air-tight layer interposed between the support element and the connecting layer, and provided with a through hole above the selected location, or at least a portion of the tie layer, the portion thereof being then adapted to be substantially airtight and having a hole above the chosen place; in the last alternative, the tie layer may comprise a first substantially airtight sub-layer in which the hole, which is then a through hole, is defined, and a second sub-layer interposed between the first sub-layer and the mass layer; in a variant, the cavity may be defined in the bonding layer; the connecting layer may then comprise a first substantially airtight sub-layer and in which the cavity is defined, a second airtight sub-layer defining the air-tight zone and provided with a through hole above the chosen location, and a third sub-layer interposed between the second sub-layer and the ground layer; The tie layer may comprise a fourth sub-layer intended to be interposed between the support element and the first sub-layer. The invention also proposes a support element intended to form part of a vehicle, possibly an automobile, and comprising a multilayer structure 3o of the type of that presented above. Such a support member may for example be a vehicle panel.

Other characteristics and advantages of the invention will become apparent upon examination of the following detailed description, and the accompanying drawings, in which: FIG. 1 schematically illustrates, in a cross-sectional view, a first assembly consisting of a support element secured to a first embodiment of a multilayer structure according to the invention; - Figure 2 schematically illustrates, in a view from above, a first embodiment of a resonant cavity that can be defined in a set according to the invention; FIG. 3 schematically illustrates, in a view from above, a second embodiment of a resonant cavity that can be defined in an assembly according to the invention; FIG. 4 schematically illustrates, in a view from above, a third embodiment of resonant cavity can be defined in an assembly according to the invention, - Figure 5 schematically illustrates in a view of the d Essus, a fourth embodiment of resonant cavity that can be defined in an assembly according to the invention, - Figure 6 schematically illustrates, in a cross-sectional view, a second assembly consisting of a support element secured to a second example embodiment of a multilayer structure according to the invention, - Figure 7 schematically illustrates, in a cross-sectional view, a third assembly consisting of a support member secured to a third embodiment of a multilayer structure according to the l and Figure 8 schematically illustrates, in a cross-sectional view, a fourth assembly consisting of a support member secured to a fourth embodiment of a multilayer structure according to the invention. The attached drawings may not only serve to complete the invention, but also contribute to its definition, if any. The object of the invention is to propose a multilayer structure (SM) intended to be secured to a support element (P) of a vehicle (possibly an automobile) in order to constitute an assembly offering quality soundproofing. In the following, we consider, by way of non-limiting example, that the vehicle is automotive type, such as a car, a commercial vehicle, a bus or a truck. But, the invention is not limited to this type of vehicle. It concerns indeed any type of vehicle, and especially those that can travel on land or navigation. Furthermore, it is considered in the following, by way of non-limiting example, that the support member (P) is a car panel, such as an apron (intended to be located on the side of the passenger compartment) , an awning, a door, a floor or a roof. But, the invention is not limited to this type of support element. Thus, it also relates to vehicle hoods or tailgates. Note that a support element (P), here a panel, can be made of any type of material, including sheet metal, aluminum or plastic or synthetic material.

As illustrated without limitation in FIG. 1, a multilayer structure SM, according to the invention, comprises a layer of mass (or heavy mass) CM solidarized with a bonding layer (or spring layer) CL. The CM mass layer is for example made of a material which is capable of damping the vibrations and / or of absorbing a part of the sound waves, in particular those which strike it (possibly after at least one reflection). This CM mass layer may for example be made of bituminous material or elastomer or copolymer (for example EPDM loaded baryte). For example, it may for example be the outer part (facing the interior of the passenger compartment) of a floor mat or a lining. The connecting layer CL is intended to be interposed between a support element P and the associated ground layer CM. It may for example be made of fibrous material (s), such as for example cotton felt or glass felt, and / or foam (s), such as polyurethane (or PU). It will be noted that once the multilayer structure SM is formed and then secured to a support element P, they constitute an assembly (P, SM) of one of the types illustrated in FIGS. 1 and 6 to 8. We also call here together a support element P equipped with a multilayer structure SM. Such a set then has a given resonance frequency f0. This set (P, SM) comprises at least one cavity CV of length (or extension) chosen. In the non-limiting embodiments illustrated in FIGS. 1, 6 and 7, the cavity CV is defined in the support element P (for example by stamping or by molding). On the other hand, in the nonlimiting embodiment illustrated in FIG. 8, the cavity CV is defined in the connection layer CL.

According to the invention, the multilayer structure SM comprises an airtight zone FE (or CL) which is intended to cover at least the entire cavity CV except for a selected location El of the latter CV. . This location E1 is chosen so that the cavity CV resonates substantially at the given resonance frequency f0 of the set (P, SM), especially in view of its chosen length (or extension) and the location of said chosen location E1 . Here, an airtight zone is understood to mean an area that hardly lets sound waves pass. The cavity CV and at least the part of the airtight zone FE (or CL) which covers the cavity CV thus constitute what is called a resonant cavity or a resonator. Thanks to this resonance of the resonant cavity at a resonant frequency f0 which is substantially equal to the resonance frequency of the assembly (P, SM), the sound insulation weakness present in this assembly (P, SM) is considerably reduced. ) in the small frequency band which is substantially centered on its own resonant frequency. It is important to note that a set (P, SM) may have several (at least two) CV cavities. In this case, the cavities CV do not necessarily have the same orientation. As is not illustrated in FIGS. 2 to 5, the cavity CV can take many forms. Thus, in the example of Figure 2, it has (seen from above) a substantially rectangular shape. In the example of Figure 3, it has (seen from above) an L shape. In the example of Figure 4, it has (seen from above) a spiral shape. In the example of Figure 5, it has (seen from above) a shape called Helmholtz (square or rectangle with the center of one of its four sides a small square or rectangular extension). It will be noted that the cavity CV is a three-dimensional and non-two-dimensional element. As indicated above, the length (or extension) of the cavity CV and the chosen location E1 of the cavity CV, which is not covered by the airtight zone FE (or CL), constitute two other adjustment parameters of the resonance frequency f0 of the resonant cavity. In fact, these two parameters are partially related. Indeed, if the chosen location El is an end of the cavity CV, then the latter (CV) constitutes with the airtight zone FE (or CL) a resonant cavity of the so-called quarter wave type (or / 4, À being equal to the length (or extension) of the cavity CV (that is to say the distance separating its two opposite ends E1 and E2) This situation is that illustrated in FIGS. (The chosen location El is indeed one of the two opposite ends of the cavity CV).

If the chosen location E1 is a central part of the cavity CV, then the latter (CV) forms with the airtight zone FE (or CL) a resonant cavity of the so-called half wave type (or A / 2). By way of example, to obtain a resonant cavity having a resonance frequency f0 of about 340 Hz, the chosen length of the cavity CV must be equal to about 250 mm if the chosen location El is located at one of its opposite ends (case A / 4). It will be noted that the resonance frequencies of the sets (P, SM) are generally between about 200 Hz and 1 kHz, and more frequently between about 300 Hz and 700 Hz. More precise information on the sizing and possible shapes of the reasoning cavities are included in the document by JM Mason and FJ Fahy, The use of acoustically tuned resonators to improve the sound transmission loss of double-panel partitions, Journal of Sound and Vibration, p.367-379, 124 (2), 1988. The part of the airtight zone FE (or CL) which does not cover the chosen place E1 of the cavity CV can be a hole TT, possibly passing through. The location where this hole TT is defined may vary depending on the embodiment considered. In the first exemplary embodiment illustrated in FIG. 1, the cavity CV is defined in the support element P, and the airtight zone FE is defined by a layer FE of the multilayer structure SM. This layer FE is airtight, intended to be interposed between the support element P and the CL bonding layer (to which it is secured during the formation of the multilayer structure SM), and provided with a hole This layer FE is for example in the form of an airtight film, for example a very thin film of plastic material (for example polyethylene). This film can be secured to the CL bonding layer by any means known to those skilled in the art, including bonding, heat sealing or thermoforming. In this first exemplary embodiment, the multilayer structure SM thus consists of the airtight layer FE, the bonding layer CL and the mass layer CM, the bonding layer CL being interposed between the airtight layer FE air and the CM mass layer. It is important to note that the airtight layer FE is not required to extend, as illustrated, over the entire surface of the underside of the CL bond layer. What is needed is that it extends over a surface that must at least completely cover the cavity CV (except its chosen location El). In the second exemplary embodiment illustrated in FIG. 6, the cavity CV is also defined in the support element P, and the airtight zone 8 FE is defined by the connecting layer CL. The latter is adapted (at least at its portion which must completely cover the cavity CV) so as to be substantially airtight. This can for example be done by compressing (very) strongly the material in which it (CL) is made. In this case, the CL bonding layer is intended to be interposed between the support element P and the CM mass layer (to which it is secured during the formation of the multilayer structure SM), and provided with a hole crossing TT above the chosen location El.

In this second embodiment, the multilayer structure SM is constituted by the CL bond layer and the CM ground layer. It is important to note that the CL bond layer is not necessarily airtight everywhere. What is required is that it has an airtight portion which extends over a surface which must at least completely cover the cavity CV except its orifice located at the chosen location E1. The through hole TT can be made by ablation of material, for example by perforation or cutting. This second multilayer structure is not optimal in terms of soundproofing. This results in particular from the fact that the resonant cavity communicates here with the ground layer CM and not with a portion of the CL bond layer which should be filled with air. It is possible to substantially improve this second embodiment by breaking down its CL link layer into two sub-layers CL1 and CL2, as shown in Figure 7. The third embodiment illustrated in Figure 7 strongly resembles the second example embodiment which is illustrated in FIG. 6. What differentiates it is the fact that the connecting layer CL comprises a first sub-layer CL1, which is substantially airtight (at least at the level of its part which must completely cover the cavity CV) and in which is defined the through hole TT above the chosen location El, and a second sub-layer CL2, which is interposed between the first sub-layer CL1 and the ground layer CM .

The airtight zone is thus defined here by the first sub-layer CL1. The latter (CL1) is for example derived from a standard type of bonding layer (for example of fibrous material or of PU type foam) which is then adapted (at least at its part which must completely cover the cavity CV ) so as to be substantially airtight. This can for example be done by compressing (very) strongly the material in which it (CL1) is made. In this case, the first sub-layer CL1 is intended to be interposed between the support element P and the second sub-layer CL2 (which is a standard type of bonding layer (and therefore filled with air) and to which it is secured during the constitution of the multilayer structure SM). The first CL1 and second CL2 underlays can be secured to one another by any means known to those skilled in the art, including bonding, heat sealing or thermoforming.

In the fourth exemplary embodiment illustrated in FIG. 8, the cavity CV and the airtight zone FE are defined in the bonding layer CL of the multilayer structure SM. To do this, the bonding layer CL comprises at least a first sub-layer CL1, in which is defined the cavity CV, a second sub-layer FE which is airtight and in which is defined the through hole TT at above the chosen location El, and a third sub-layer CL3, which is interposed between the second sub-layer FE and the ground layer CM. The second sub-layer FE is thus interposed between the first CL1 and third CL3 sub-layers and secured to the latter during the constitution of the multilayer structure SM. Furthermore, the second sub-layer FE is for example in the form of an airtight film, for example a very thin plastic film (for example polyethylene). This film can be secured to the first CL1 and third CL3 underlays by any means known to those skilled in the art, and in particular by gluing, heat sealing or thermoforming. In this fourth embodiment, the multilayer structure SM is constituted by the connecting layer CL (itself consisting of the first CL1, second FE and third CL3 sub-layers) and the ground layer CM, the CL bond layer. being interposed between the support element P and the ground layer CM. Moreover, and as illustrated, the connection layer CL may optionally comprise a fourth sub-layer CL4 intended to be interposed between the support element P and the first sub-layer CL1. The different sub-layers CLi (i = 1 to 4) may not all have the same densities and / or absorption characteristics so as to improve the overall acoustic behavior of the multilayer structure SM.

It is important to note, as illustrated, that the second airtight sub-layer FE is not required to extend over the entire surface of the first CL1 and third CL3 sub-layers. What is needed is that it extends over a surface that must at least completely cover the cavity CV (except its chosen location El).

The first CL1, second FE and third CL3 sub-layers, as well as the possible fourth CL4 sub-layer can be joined to each other by any means known to those skilled in the art, including bonding, heat-sealing or thermoforming.

Claims (14)

REVENDICATIONS1. Multilayer structure (SM) for a support element (P) of a vehicle, said structure (SM) comprising a ground layer (CM) and a bonding layer (CL) intended to be interposed between said support element (P) ) and said ground layer (CM), said structure (SM) or said support member (P) comprising at least one cavity (CV) of selected length, and said multilayer structure (SM) and said support member (P) being intended to constitute an assembly having a given resonant frequency (f0), characterized in that it comprises an airtight zone (FE; CL) intended to cover at least the entirety of said cavity (CV) at the exception of a chosen location (El) of the latter (CV) so that said cavity (CV) resonates at said given resonance frequency (f0), given its chosen length and the location of said chosen location (El). 2. Structure according to claim 1, characterized in that said chosen location (El) is located above one end (El) of said cavity (CV) so that it constitutes a resonant cavity of said type quarter 'wave. 3. Structure according to claim 1, characterized in that said chosen location (El) is located above a central portion of said cavity (CV) so that it constitutes a resonant cavity of said half wave type. 4. Structure according to one of claims 1 to 3, characterized in that said cavity (CV) is selected from a group comprising at least one rectilinear cavity, an L-shaped cavity, a spiral-shaped cavity and a cavity resonant Helmholtz. 5. Structure according to one of claims 1 to 4, characterized in that said cavity is defined in said support layer (P). 6. Structure according to claim 5, characterized in that said airtight zone (FE) is defined by a layer (FE) airtight, intended to be interposed between said support member (P) and said connecting layer (CL), and provided with a through hole (TT) above said chosen location (El). 7. Structure according to claim 5, characterized in that said airtight zone (CL) is defined by at least part of said bonding layer (CL), said part of the latter (CL) being adapted so to be substantially airtight and comprising a hole (TT) above said selected location (El). 8. Structure according to claim 7, characterized in that said connecting layer (CL) comprises a first sub-layer (CL1) substantially airtight and in which said hole (TT) is defined, which is through, and a second sub-layer (CL2) interposed between said 1 o first sub-layer (CL1) and said ground layer (CM). 9. Structure according to one of claims 1 to 4, characterized in that said cavity (CV) is defined in said connecting layer (CL). 10. Structure according to claim 9, characterized in that said connecting layer (CL) comprises a first sub-layer (CL1) substantially airtight in which said cavity (CV) is defined, a second underlayer (FE) airtight, defining said airtight zone (FE) and provided with a through hole (TT) above said chosen location (El), and a third sub-layer (CL3) interposed between said second sublayer (CL1) and said ground layer (CM). 20 11. Structure according to claim 10, characterized in that said connecting layer (CL) comprises a fourth sub-layer (CL4) intended to be interposed between said support member (P) and said first sub-layer (CL1). 12. Support element (P) for a vehicle, characterized in that it comprises a multilayer structure (SM) according to one of claims 1 to 11. 13. Support element according to claim 12, characterized in that it constitutes a vehicle panel. 14. Use of the multilayer structure (SM) according to one of claims 1 to 11 and the support element (P) according to one of claims 12 and 13 in a motor vehicle.