Acoustic panel

Abstract

The invention relates to an improved acoustic panel (1) comprising cells (2) having at least two chambers (11, 12) arranged in series along an axis (X2) extending along the thickness (E1) of the panel and separated from one another by a diaphragm (10). Preferably, each of the cells is produced by folding a single sheet on itself.

Description

Description Title of the invention: Acoustic panel

[0001] The present invention relates to the field of acoustic panels, in particular intended for soundproofing engines.

[0002] Such a panel must be able to attenuate frequencies between 500 and 3000 Hertz. It must also be able to withstand temperatures between -55°C and 135°C, resist many chemicals and corrosion in a humid and hot environment. In addition, it must be able to be made with a single or double curvature.

[0003] Also, such a panel must be able to be produced at sustained industrial frequencies.

[0004] Such panels are known in particular from document FR 3 098 143 and from document WO 2021 / 260286.

[0005] An aim of the invention is to provide an acoustic panel meeting the above requirements.

[0006] According to a first object of the invention, a cell for an acoustic panel extends along a cell axis and comprises at least two chambers arranged in series along this axis and a diaphragm substantially transverse to this axis which separates the two chambers from each other.

[0007] Advantageously, such a cell is formed from a single sheet folded back on itself. The sheet may comprise a first row of folds to form sides of a first chamber among the two chambers, a second row of folds to form the diaphragm, and a third row of folds to form the second chamber, the second row of folds being separated from each of the other rows by a respective transverse fold, the folds of the second row forming a pattern suitable for forming said diaphragm by folding the sheet back on itself. The pattern of the second row is preferably of the “Kresling” type or of the “Chicken wire tessellation” type.

[0008] The cell preferably has a polygonal cross-section, preferably forming a regular hexagon. The chambers may have different heights, these heights being measured axially.

[0009] Preferably, the diaphragm forms a diaphragm opening which connects the two chambers to each other.

[0010] According to a second object of the invention, an acoustic panel comprises several cells according to the invention, arranged side by side and whose axis extends substantially in a local direction of the thickness of the panel. Such a panel preferably comprises an acoustic wall for bonding a free edge of a first chamber of each of the cells, the wall comprising perforations for communicating the interior of the chamber with an external environment of the panel. Also, the panel may comprise a covering wall for bonding a free edge of another chamber axially opposite the first of each of the cells, the edge comprising cutouts forming, with the wall, drains. Brief description of the figures

[0011] Embodiments and variants will be described below, by way of non-limiting examples, with reference to the appended drawings in which:

[0012] [Fig. 1] is a schematic view, in elevation, in exploded perspective according to its thickness, of an acoustic panel according to the invention;

[0013] [Fig. 2] is an isolated, schematic, sectional and elevational view of a cell of a first type present on the panel of Figure 1, according to the section plane ll-ll indicated in Figure 3;

[0014] [Fig. 3] is an axial and perspective view of the cell of Figure 2, along direction II indicated in Figure 2;

[0015] [Fig. 4] is a view from below and in perspective, of a cell similar to the cell of Fig. 3;

[0016] [Fig. 5] is a developed view of a sheet for the production of the cell of figures 2 to 4;

[0017] [Fig. 6] is a schematic view, in elevation and in perspective of an acoustic panel of a group of three cells according to the invention assembled on a cladding wall;

[0018] [Fig. 7] is an axial schematic view of a group of three cells according to the invention assembled together by a coupling;

[0019] [Fig. 8] is a schematic view in elevation and perspective of the group of Figure 7, thus harnessed.

[0020] [Fig. 9] is a schematic perspective view of the coupling of Figures 7 and 8; and,

[0021] [Fig. 10] is a schematic view illustrating several inserts which can be used to fill a cell according to the invention, each insert being represented both in perspective and in axial view. Detailed description

[0022] In this description, in particular the terms "top", "bottom", "upper" and "lower", "horizontal" and "vertical" and other terms of the same type may be arbitrarily used in this description and generally refer to the positions illustrated in the figures.

[0023] Figure 1 illustrates very schematically and partially an acoustic panel 1 according to the invention. Such an acoustic panel is intended to attenuate or muffle a sound produced by a transmitter in a first environment E1 to protect a second environment E2 from it. Such a transmitter is not shown in the figures; it may be an engine, for example an aircraft engine, an orchestra or any other sound transmitter.

[0024] In the illustrated example, the panel comprises a layer 200 of cells 2 functioning as sound traps; the layer 200 of cells is sandwiched between two walls 3, 4. A first wall 3 among these walls, hereinafter referred to as the “sound wall”, is intended to be positioned between the sound emitter and the layer of cells. A second wall, hereinafter referred to as the “cladding”, is then arranged beyond the layer of cells relative to the emitter. Each cell 2 extends between the walls, substantially along a direction DE locally perpendicular to the walls substantially along a local thickness of the panel 1.

[0025] Each wall comprises a structural sheet 5, that is to say which helps to give a shape and stiffness to the panel, and an adhesive film 6 which ensures the cohesion of the wall with the layer of cells. The soundproof wall 3 comprises perforations 8, formed both in the sheet and the film, in a corresponding manner so that these perforations 8 put into fluidic and vibratory communication an interior N of each cell with the first environment E1 in which the transmitter is located. The cladding does not comprise perforations.

[0026] In Figure 1, three cells are illustrated. Of course, a panel usually comprises very many cells, for example several hundred or several thousand cells. Here, each of the cells is of a different type; one is of a first type 21, another of a second type 22, and the third of a third type 23.

[0027] We will now describe the cell of the first type 21, with reference to the figures 2 to 5. In Figure 1, the walls 3, 4 are partially represented. The cell 2 extends substantially around an axis X2 parallel to the local direction DE of the thickness E1 of the panel 1.

[0028] In this first type 21, the cell comprises two chambers 11, 12 separated from each other by a diaphragm 10. In the example illustrated, a first chamber 11, among the two, has a height H11 greater than the height H12 of the second chamber 12. The diaphragm 10 has a height H10. Thus, the height H2 of the cell 2 is equal to the sum H11 +H12+H10 of these heights. The total thickness of the panel E1 =H2+E3+E4 further includes the respective thicknesses E3, E4 of the walls 3, 4.

[0029] As particularly illustrated in Figure 3, the cell 2 has a regular hexagonal cross-section. A free edge 15 of the first chamber, opposite the diaphragm 10, forms an opening closed by the sound-absorbing wall 3. A free edge 16 of the second chamber forms an opening closed by the covering 4.

[0030] The diaphragm 10 has an opening 18, which fluidly connects the chambers 11, 12 to each other. In axial view, the opening 18 of the diaphragm 10 is itself hexagonal.

[0031] In the example illustrated in the figures, each cell 2 is made from a sheet folded back on itself. Such a sheet 25, suitable for forming a cell of the first type 21 is illustrated in Figure 5, flat.

[0032] The sheet comprises a multitude of folds defining three rows. A first transverse fold PA separates a first row R1 from a second row R2; a second transverse fold PA separates a second row R2 from a third row R3.

[0033] The first row R1 is formed of first rectangles separated from each other by first vertical folds PV of length H1 1; each of the first rectangles corresponds to one of the six sides 26 of the first chamber 1 1. In the same way, the third row is formed of second rectangles separated from each other by second vertical folds PV of length H12; each of the rectangles corresponds to one of the six sides 26 of the second chamber 12.

[0034] The second row comprises folds A, B and C, forming a pattern of the type known as the "Kresling pattern". This pattern is formed of non-rectangular parallelepipeds of which two opposite horizontal sides A, of length LA, together form the horizontal folds PA; The other two sides are formed by first bias folds B, of length LB, parallel to each other and connecting the horizontal folds PA to each other. The pattern further comprises diagonal folds C, of ​​length LC, each extending along the large diagonal of each of the non-rectangular parallelepipeds.

[0035] A free longitudinal edge of the first row R1, parallel to the horizontal folds PA, forms the free edge 15 of the first chamber. A free longitudinal edge of the third row R3, parallel to the horizontal folds PA, forms the free edge 16 of the second chamber.

[0036] The second row R2, because it is of a Kresling pattern, is able to fold back on itself so that once thus folded it forms the diaphragm. Because it is made up of several superimposed folds, the diaphragm maintains between the two chambers 11, 12 a spacing of a height H10; thus, the chambers are not stuck together; they can vibrate independently of each other.

[0037] The dimensions of the opening 18 of the diaphragm and its thickness H10 depend on the ratio of the dimensions LA, LB, LC of the folds A, B and C of the second row R2.

[0038] Typically, for LB = 2 x LA, the diaphragm can be completely closed, i.e. its aperture18 has a zero cross-section. To obtain the desired cross-section opening, for example, with a section close to that of a corresponding perforation 8, such a diaphragm can be punched. When shaping the cell, the diaphragm can also be folded around a rod serving as a template; it is also possible to play on a more or less large folding of the diaphragm on itself, that is to say, on its height H10.

[0039] Cutouts D16 in the free edge 16 of the second chamber form, with the cladding 4, drains 27. This arrangement is particularly visible in figures 2 and 6. Such drains are useful for circulating fluids, in particular condensation fluids likely to form in the panel 1.

[0040] If the cell of the first type 21 previously described comprises two chambers 11, 12 separated by a diaphragm 10, the cells of the second type and the third type comprise a third chamber 13 separated from the second by a second diaphragm 10. In the second type 22, the second chamber is high, while the first and third are of reduced height. In the third type 23, the first and second chambers are of an intermediate height, while the third is of reduced height.

[0041] Of course, other types of cells can be used. For example, cells with only one chamber, or more than three chambers can be used.

[0042] It appears, for a given larger transverse dimension of the cell, that is to say the diameter D of the circle circumscribed to the hexagonal section of the cell, the frequency band of the sound which is absorbed varies with the height H, H1 1 , H12 of the chamber. Thus, the same cell comprising several chambers of different heights can absorb as many frequency bands as different heights. Also, a panel comprising a suitable layout of cells of different types can absorb a very wide frequency band composed of the narrower frequency bands absorbed by the different chambers which compose this panel. Furthermore, a panel can be designed to absorb different frequencies at different locations on the panel; this is particularly useful for a panel used in the fairing of an aircraft engine where the frequencies emitted vary from the front to the rear of the engine.

[0043] Thus, with a diameter D = 35 millimeters, for the following different heights H: if H = 25 mm, a chamber absorbs frequencies close to 500 Hz if H = 15 mm, a chamber absorbs frequencies close to 700 Hz if H = 7 mm, a chamber absorbs frequencies close to 1000 Hz; if H = 3 mm a chamber absorbs frequencies close to 1500 Hz; and, if H = 1 mm a chamber absorbs frequencies close to 2500 Hz.

[0044] Preferably the diameter D is greater than 27 millimeters, preferably between 32 and 40 millimeters.

[0045] Typically, the cells may be formed from sheets 25 of aramid paper, for example known under the brand name Nomex®, in thicknesses between 0.13 millimeters and 0.58 millimeters. An impregnation is then advantageously carried out, after shaping the cells.

[0046] Figures 1 to 6 illustrate cells juxtaposed with each other, which can be glued together.

[0047] Figures 7 to 9 illustrate another embodiment in which the cells 2 are kept at a distance from each other by a coupling 30. The coupling forms cells 32, each of which can receive a corresponding cell 2. In the example illustrated, the coupling only comprises two cells; of course, in an industrial reality, a coupling advantageously comprises several hundred or several thousand cells.

[0048] Here, the coupling 31 is intended to maintain two sides 26 of two neighboring cells opposite each other at a distance D30. The coupling has a constant height H30. In the figures, the height H30 is significantly less than the height H2 of the cells 2. A coupling may also be provided having a height close to or equal to that of the cells.

[0049] Such a coupling is useful, for example, to compensate for angular offsets between different chambers 11, 12 of the same cell 2 around its axis X2. It also makes it possible to produce panels with curved walls with single or double curvature.

[0050] With reference to Figure 10, five different inserts that can be used with a cell 2 according to the invention will now be described, for example of the first type 21 previously described. A first row illustrates perspective views of each of the five inserts. A second row illustrates axial views of these same inserts.

[0051] A first insert 41 is provided to close the opening 18 of a diaphragm, except in that it comprises an axial cylindrical air passage 48, of section substantially equal to that of the corresponding perforation 8; this passage 48 makes it possible to match two neighboring chambers. The insert 41 is made of a solid material, for example foam or cork, and of constant thickness E41.

[0052] A second insert 42 differs from the first in that it is made of a rigid plastic and comprises recesses 51, separated by ribs, which make it possible to lighten this insert 42.

[0053] A third insert 43 differs from the second insert 42 in that it is designed to fit into a chamber and does not have an air passage.

[0054] A fourth insert 44 has the shape of a hexagonal ring; it is designed to fit into a chamber, against the sides 26 of this chamber.

[0055] The fifth insert 45 differs from the second insert 42 in that it is designed to fit into a chamber and does not have an air passage.

[0056] Of course, the invention is not limited to the examples just described. On the contrary, the invention is defined by the claims which follow.

[0057] It will indeed appear to those skilled in the art that various modifications can be made to the embodiments described above, in light of the teaching which has just been disclosed to them.

[0058] Thus, other folding patterns can be used to form a diaphragm. For example, a pattern known as "chicken wire tessellation" can be used.

[0059] Instead of a hexagonal section, a cell can be made on the basis of a polygon, preferably regular, comprising a number of sides other than six, for example it can comprise eight.

[0060] A coupling may be provided, not to isolate individual cells, but groups of cells. For example, a cell of such a coupling may be provided to receive a group of three cells glued together.

[0061] A panel made according to the invention is particularly advantageous. It is easy to industrialize. In addition, it can absorb a wider spectrum of frequencies with a reduced mass compared to prior art panels.

Claims

Claims

1. Cell (2) for an acoustic panel (1), characterized in that it extends along a cell axis (X2) and comprises at least two chambers (11, 12) arranged in series along said axis and a diaphragm (10) substantially transverse to said axis which separates said two chambers from each other.

2. Cell according to claim 1, characterized in that it is formed from a single sheet (25) folded back on itself.

3. Cell according to claim 2, characterized in that the sheet comprises a first row (R1) of folds to form sides (26) of a first chamber (11) among the two chambers, a second row of folds (R2) to form the diaphragm, and a third row of folds (R3) to form the second chamber (12), the second row of folds being separated from each of the other rows by a respective transverse fold (PA), the folds (A, B, C) of said second row forming a pattern adapted to form said diaphragm by folding the sheet back on itself.

4. Cell according to claim 3, characterized in that the pattern of the second row is of the “Kresling” type or of the “Chicken wire tessellation” type.

5. Cell according to one of claims 1 to 4, characterized in that it has a polygonal cross-section preferably forming a regular hexagon.

6. Cell according to one of claims 1 to 5, characterized in that the chambers have different heights (H11, H12), said heights being measured axially.

7. Cell according to one of claims 1 to 6, characterized in that the diaphragm forms a diaphragm opening (18) which connects the two chambers to each other.

8. Acoustic panel (1), characterized in that it comprises several cells according to one of the preceding claims arranged side by side and whose axis extends substantially in a local direction (DE) of the thickness of said panel.

9. Acoustic panel (1) according to claim 8, characterized in that it comprises an acoustic wall (3) for gluing thereto a free edge (15) of a first chamber (11) of each of the cells, said wall comprising perforations (8) for communicating the interior of said chamber with an external environment (E1) of said panel.

10. Acoustic panel (1) according to claim 9, characterized in that it comprises a covering wall (4) for gluing thereto a free edge (16) of another chamber (12) axially opposite the first of each of the cells, said edge (16) comprising cutouts (D16) forming, with said wall (4), drains (27).

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