FR3078299A1 - ACOUSTIC ABSORPTION PIECE FOR MOTOR VEHICLE AND ASSOCIATED MANUFACTURING METHOD - Google Patents

Abstract

The present invention relates to a sound absorption part (10) for a motor vehicle, formed of a first expanded plastic material (12), said part comprising a base (14) defining an internal cavity. The piece further comprises a cover (18) and a hinge (20) hinging said cover to the base; the cover being adapted to assemble with said base in a closed configuration of said part. The base, the lid and the hinge are integrally formed, said hinge (20) being formed of a flexible band of the first expanded plastics material (12); the first expanded plastic material has a first density at the base (14) and a second density, greater than the first density, at the hinge.

Description

Sound absorption part for motor vehicle and associated manufacturing process

The present invention relates to a sound absorption part for a motor vehicle, formed of a first expanded plastic material, said part comprising a base defining an internal cavity, said base comprising at least first and second walls facing each other. .

It is known, for example from document EP1693255, to equip motor vehicles with sound absorption elements made of expanded plastic material. It is also known, for example from document FR3026080, to equip a structure for a motor vehicle, such as a vehicle floor, with compartments containing an acoustic insulation material.

The volume of the sound absorption elements represents an additional weight for the vehicle. However, it is necessary that the material of said elements has a density greater than a certain threshold, for questions of mechanical constraints and acoustic performance.

The object of the present invention is to provide a piece of sound absorption of reduced weight, while retaining sufficient rigidity and good acoustic performance.

To this end, the invention relates to an acoustic absorption piece of the aforementioned type, further comprising a cover and a hinge hinging said cover to the first wall of the base; the cover being able to be assembled with the second wall in a closed configuration of said part. The base, the cover and the hinge are formed in one piece, said hinge being formed from a flexible strip of the first expanded plastic material. Said first expanded plastic material has a first density at the base and a second density, greater than the first density, at the hinge.

According to other advantageous aspects of the invention, the sound absorption part comprises one or more of the following characteristics, taken in isolation or in any technically possible combination:

- The first expanded plastic material comprises a thermoplastic polymer, preferably chosen from polyethylenes, polypropylenes and polystyrenes;

- The part is configured so that, in the closed configuration, the internal cavity forms a volume closed by the cover;

- The part is configured so that the base defines two internal cavities, said part further comprising two covers, each of said covers being hinged to the base by a separate hinge.

The invention also relates to a structure for a motor vehicle, comprising: at least one sound absorption part as described above, in the closed configuration; and a second plastic material, molded onto said at least one part. Advantageously, the second plastic material (204) comprises a polyurethane.

The invention further relates to a method of manufacturing an acoustic absorption part as described above, said method comprising the following steps: supply of a mold comprising first and second movable parts one relative to the other between an open configuration and a closed configuration, the first part comprising a strip forming an upper edge, the second part comprising a movable drawer, said drawer comprising a lower surface; provision, in the mold in open configuration, of particles of first plastic material capable of expanding under a high temperature and / or pressure; placement of the mold in closed configuration, a first air gap separating the upper edge of the slide and the lower surface of the movable drawer; and applying a high temperature and / or pressure in the mold. Said step of applying a high temperature and / or pressure comprises: a first phase, corresponding to the first air gap between the slide and the movable drawer, allowing at least partial expansion of the first plastic material; then a displacement of said drawer in the direction of the strip to a second gap lower than the first gap; then a second phase corresponding to said second air gap between the strip and the movable drawer; said displacement of the drawer in the direction of the strip leading to densify the first at least partially expanded plastic material, disposed between said drawer and said strip.

According to other advantageous aspects of the invention, the method comprises one or more of the following characteristics, taken in isolation or in any technically possible combination:

- The upper edge of the strip is formed by the intersection of two side panels, said side panels forming a non-zero angle and less than 20 °, said angle preferably being between 6 ° and 10 °;

- The strip is removable from the rest of the first part of the mold;

- The movable drawer is configured so that its movement towards the strip results in densifying part of the first at least partially expanded plastic material, disposed on either side of the strip.

The invention will be better understood on reading the description which follows, given solely by way of nonlimiting example and made with reference to the drawings in which:

- Figures 1 and 2 are sectional views of a sound absorption part according to a first embodiment of the invention, respectively in a first and in a second configuration;

- Figures 3 and 4 are sectional views of a sound absorption part according to a second embodiment of the invention, respectively in a first and in a second configuration;

- Figure 5 is a sectional view of a structure for a motor vehicle comprising a sound absorption part as shown in Figures 1 and 2;

- Figure 6 is a schematic sectional view of a device for manufacturing the sound absorption part of Figures 1 and 2, during a first step of a manufacturing process according to one embodiment of the invention; and

- Figures 7 and 8 are detailed views of the device of Figure 6, respectively according to a second and a third step of the manufacturing process.

Figures 1-2 and 3-4 respectively represent a first 10 and a second 110 sound absorption parts, respectively according to a first and according to a second embodiment of the invention.

In the following description, the parts 10 and 110 will be described simultaneously, the similar elements of the two parts being designated by the same reference numbers.

The part 10, 110 is formed from a first expanded plastic material 12 and comprises: a base 14, 114 defining at least one internal cavity 16, 116, 117; at least one cover 18, 118, 119; and at least one hinge 20, 120, 122.

Preferably, the first expanded plastic material 12 comprises a thermoplastic polymer, more preferably chosen from polyethylenes, polypropylenes and polystyrenes

In each of the first and second embodiments, the base 14, 114 has a lower surface 26 and an upper surface 28, preferably substantially planar and parallel. In the following description, an orthonormal base (X, Y, Z) is considered, the lower 26 and upper 28 surfaces being arranged in planes (X, Y).

In the first embodiment of Figures 1 and 2, the base 14 has a bottom 30 defining the lower surface 26. Said bottom 30 has a substantially rectangular outline whose edges extend in the directions X and Y. The base 14 has further four side walls 32, 34, 36 substantially planar, each of said side walls extending in the direction Z from an edge of the bottom. More specifically, the base 14 comprises a first 32 and a second 34 side walls arranged along planes (Y, Z) and a third and a fourth side walls 36 arranged along planes (X, Z).

An upper end of the side walls 32, 34, 36 is formed by the upper surface 28. The internal cavity 16 defined by the bottom 30 and the side walls 32, 34, 36 has a substantially parallelepiped shape.

In the second embodiment of Figures 3 and 4, the base 114 has walls 132, 134, 136 substantially planar and parallel to the direction Y, said walls extending obliquely between the lower 26 and upper 28 surfaces to form a profile substantially sinusoidal. More specifically, the base 114 comprises a first series of walls 132, 134 and a second series of walls 136. Each series comprises one or more walls, the walls of the same series being parallel to each other. Each wall 132, 134, 136 has an oblique section in a plane (X, Z), the walls of the first and second series being inclined relative to each other by an angle a. For example, in the embodiment of Figures 3 and 4, the angle a is about 60 ° and the base 114 has a section substantially forming an alignment of equilateral triangles.

The base 114 is formed by a succession of alternating walls of the first 132, 134 and of the second 136 series, said alternating walls being fixed to each other at the level of the lower surface 26 and / or of the upper surface 28. Preferably, a first 132 and a second 134 walls, forming the ends along X of the base 114, belong to the first series and are parallel to each other.

The number of alternating walls 132, 134, 136 is in particular chosen according to the length along X desired for the base 114.

The base 114 defines a first internal cavity 116, open upwards, and a second internal cavity 117, open downwards. Each of the first 116 and second 117 internal cavities has the shape of one or more prisms aligned along X, each prism extending along Y.

The at least one cover 18, 118, 120 of the part 10, 110 has a substantially flat assembly surface 38, intended to come into contact with the base 14, 114 in a closed configuration of said part 10, 110.

In the first embodiment of Figures 1 and 2, the cover 18 has a ceiling 40 and four side panels 42, 44, 46, substantially planar and of substantially rectangular outline. In the closed configuration of Figure 2, the edges of the ceiling 40 extend in the directions X and Y and each of the side panels 42, 44, 46 extends in the direction Z from an edge of the ceiling. One end of the side panels 42, 44, 46, opposite the ceiling 40, is formed by the assembly surface 38.

In the closed configuration, a first 42 and a second 44 side panels are arranged along the planes (Y, Z), respectively of the first 32 and the second side walls of the base 14; a third and a fourth side panels 46 are arranged along the planes (X, Z) of the third and fourth side walls 23 of the base

14.

More specifically, in the first embodiment, the cover 18 of the part 10 has a shape substantially identical to that of the base 14. In the open configuration of FIG. 1, the bottom 30 and the ceiling 40 rest on the same plane (X, Y) and the base 14 and the cover 18 are substantially the image of one another with respect to a plane of symmetry (Y, Z) passing through the hinge 20.

According to a variant not shown of the first embodiment of Figures 1 and 2, the cover 18 has the shape of a substantially planar plate.

In the second embodiment of Figures 3 and 4, the part 110 comprises a first 118 and a second 119 covers, substantially identical. Each cover 118, 119 has the shape of a substantially flat plate, of substantially rectangular outline. In the closed configuration of FIG. 4, the edges of each cover 118, 119 extend in the directions X and Y.

The at least one hinge 20, 120, 122 of the part 10, 110 articulates the or each cover 18, 118, 119 with the base 14, 114. More precisely, in the embodiments shown, each hinge 20, 120, 122 forms a pivot connection around an axis substantially parallel to Y. The or each cover 18, 118, 119 can thus be reversibly moved relative to the base 14, 114 between the open and closed configurations. The shape of the hinge 20, 120, 122 will be described later.

In the first embodiment of Figures 1 and 2, the hinge 20 connects the first side wall 32 of the base 14 to the first side panel 42 of the cover 18. In the closed configuration of Figure 2, the assembly surface 38 of said cover 18 is in contact with the upper surface 28 of base 14, thus forming a closed volume 48 which includes the internal cavity 16.

In the second embodiment of Figures 3 and 4, the part 110 has a first 120 and a second 122 hinges, respectively articulating the first

118 and the second 119 cover with the first wall 132 and with the second wall 134 of the base 114. The first 120 and second 122 hinges are arranged at, respectively, the upper surface 28 and the lower surface 26 of the base 114. In the closed configuration of FIG. 4, the assembly surface 38 of each of the first 118 and second 119 covers is in contact, respectively, with said upper surface 28 and said lower surface 26. In the closed configuration of the FIG. 4, the first 118 and second 119 covers thus define a closed section, respectively at the first 116 and at the second 117 cavities.

According to one embodiment, the part 110 also comprises side walls (not shown) which, in the closed configuration of FIG. 4, close the first 116 and second 117 cavities according to Y. These side walls can be attached, or else be formed in one piece with the base 114 and / or with the first 118 and / or the second 119 cover.

In the open configuration of FIG. 3, the first 118 and second 119 covers are deployed on either side of the base 114 along X. Several pieces 110 of identical shape can thus be stacked along Z, the bases 114 interlocking one inside the other, which saves space for the storage and transport of said parts 110.

The hinge 20, 120, 122 of the part 10, 110 will now be described in more detail. The hinge 20, 120, 122 consists of a flexible strip of the first expanded plastic material 12, said strip extending along Y between two lateral edges forming a junction, respectively with the base 14, 114 and with the cover 18, 118 , 119 correspondent. The hinge 20, 120, 122 is formed integrally with the base 14, 114 and the cover 18, 118, 119 corresponding.

As will be detailed later, the first expanded plastic material 12 of the part 10, 110 has a first density d! at the base 14, 114 and a second density d ₂ , greater than the first density d ₁₅ at the hinge 20, 120, 122.

The first expanded plastic material 12 of the part 10, 110 has a third density d ₃ at the cover 18, 118, 119 corresponding to the hinge 20, 120, 122. According to one embodiment, the third density d ₃ of the cover is substantially equal to the first density d! of the base 14, 114. According to another embodiment, the third density d ₃ of the cover is greater than the first density d! of the base 14, 114, and preferably between said first density d! and the second density d ₂ of the hinge 20, 120, 122.

Preferably, a thickness of the hinge 20, 120, 122 is much less than an average thickness of the base 14, 114. The thickness of said base 14,

114 gives it rigidity, compared to the flexibility of the hinge 20, 120, 122.

By way of example, in the first embodiment of Figures 1 and 2, the hinge 20 has an average thickness of 0.5 mm and the base 14 has an average thickness of 15 mm.

FIG. 5 represents a structure 200 for a motor vehicle, such as a vehicle floor, similar to the floor described in document FR3026080. The structure 200 comprises a body 202 formed from a second plastic material 204, said body defining at least one compartment 206 for sound absorption. Said sound absorption compartment 206 contains a sound absorption part 10 in the closed configuration, as shown in FIG. 2.

In the embodiment shown, the structure 200 comprises several compartments 206 for sound absorption, each of said compartments containing an identical part 10.

Preferably, the second plastic material 204 is expanded. Preferably, the second plastic material 204 comprises a polyurethane.

A method of manufacturing the part 10 of FIGS. 1 and 2 will now be described, with the support of FIGS. 6 to 8.

FIG. 6 represents a schematic view, in section, of a device 300 for manufacturing the part 10. The manufacturing device 300 comprises a mold 302, said mold comprising a first 304 and a second 306 elements, displaceable one by compared to each other.

The first element 304, or female element of the mold 302, has an imprint corresponding to the external surface of the part 10 in the closed configuration of FIG. 2. The second element 306, or male element of the mold 302, has an imprint corresponding to the walls of the internal volume 48 of the part 10 in the closed configuration of FIG. 2.

We consider an orthonormal base (X ', Y', Z ') associated with the female element 304 of the mold 302. In the following description, we consider that the male element 306 is movable in vertical translation, either according to the direction Z ', relative to the female element 304.

The imprint of each of the female 304 and male 306 elements comprises two substantially identical portions, corresponding respectively to the base 14 and to the cover 18 previously described. It is considered that said two substantially identical portions of each imprint are aligned in the direction X ’, the section plane of FIGS. 6 to 8 being a plane (X’, Y ’).

More particularly, the imprint of the female element 304 comprises two substantially identical flat parts 308, corresponding respectively to the surfaces of the bottom 30 and of the ceiling 40 previously described. The imprint of the male element 306 comprises two similar flat parts 310.

The female element 304 comprises a strip 312 extending in a substantially rectilinear fashion along Y ’. The strip 312, more particularly visible in FIGS. 7 and 8, comprises two substantially planar side panels 314 which meet at an upper edge 316. The side panels 314 correspond to the respective imprints of the first side wall 32 and the first side panel 42 previously described.

Preferably, a section of the strip 312 has a substantially triangular shape, each side panel 314 forming with the vertical Z ’a non-zero angle β. The angle β is less than 10 °, and more preferably between 3 ° and 5 °.

Likewise, the previously described flat parts 308, 310 of the mold cavities 302 are inclined at an angle β relative to the horizontal.

The edge 316 corresponds to the imprint of the hinge 20. Said edge 316 has a narrow width 318 along X ′, for example of the order of 2 to 4 mm. Preferably, the strip 312 is removable relative to the flat parts 308 of the female element 304 of the mold, so that it can be changed in the event of wear or breakage.

The imprint of the male element 306 comprises two flats 320, substantially facing each other, corresponding respectively to the first side wall 32 and to the first side panel 42 previously described. Each flat is inclined by the angle β relative to the vertical. Each flat 320 is extended upwards by a flat, substantially vertical slide 322.

The male element 306 further comprises a drawer 324 extending in a substantially rectilinear fashion along Y ’. The drawer 324 is able to slide vertically between the two slides 322.

The drawer 324 has a lower surface 326, a central part 327 of which corresponds to the imprint of the hinge 20. Preferably, lateral parts 328 of said lower surface 326 correspond to ends of the first side wall 32 and of the first panel lateral 42 previously described.

The manufacturing device 300 further comprises means (not shown) for injecting water vapor inside the mold 302, as well as means (not shown) for heating and pressurizing the interior of said mold.

In a first step in the process for manufacturing the part 10, the mold 302 is in an open configuration as shown in FIG. 6, the male element 306 being separated from the female element 304.

The first step of the method includes the provision, in the imprint of the female element 304, of granules 330 comprising of the first plastic material 12. Preferably, the granules 330 also comprise at least one foaming agent allowing the first plastic material 12 expand under high temperature and / or pressure.

The granules 330 are for example analogous to the granules described in the document EP1693255.

In a second step of the method, the male element 306 is brought closer along Z ′ to the female element 304 so as to place the mold 302 in an initial closed configuration, as shown in FIG. 7. In said initial closed configuration, a first air gap 332, measured along Z ', separates the upper edge 316 of the strip 312 and the lower surface 326 of the drawer 324.

In a third step of the process, a high temperature and pressure are applied in the mold 302, so as to allow the expansion of the first plastic material 12 of the granules 330. Preferably, said third step first comprises the injection of water vapor inside the mold 302, between the female 304 and male 306 elements.

Said third step comprises a first phase, during which the first air gap 332 is maintained between the strip 312 and the drawer 324. This first phase allows at least partial expansion of the first plastic material 12 of the granules 330, and in particular the formation of foam 334 between the edge 316 of said strip 312 and the lower surface 326 of said drawer 324.

Said third step then comprises a displacement along Z 'of the drawer 324 in the direction of the strip 312, to a second air gap 336 lower than the first air gap 332. Such a movement of the drawer 324 has the effect of compacting the foam 334 which s is formed between the drawer and the strip, leading to a densified zone 338 of first expanded plastic material 12.

Said third step then comprises a second phase of application of the high temperature and pressure, during which the second air gap 336 is maintained between the strip 312 and the drawer 324. This second phase makes it possible to complete the expansion of the first plastic material 12.

For example, the first air gap 332 is in the order of 15 mm and the second air gap 336 is in the order of 0.5 mm.

The mold is then brought back to ambient temperature and pressure, which allows the first plastic material 12 to solidify.

The part 10 previously described, in the open configuration, is thus obtained. The hinge 20 is formed by the part of the densified zone 338 lying between the edge 316 of the strip 312 and the central part 327 of the lower surface 326 of the drawer 324.

At a distance from the hinge 20, the base 14 of the part 10 obtained has the first density di of the first plastic material 12; the hinge 20 has the second density d ₂ .

In general, the densified zone 338 corresponds at least to the hinge 20 of the part 10. Preferably, as in the embodiment shown, the densified zone 338 also extends over the ends of the first side wall 32 and of the first side panel 42 previously described, which strengthens the mechanical connection of the hinge 20 with the base 14 and the cover 18.

According to an embodiment not shown, the manufacturing process also makes it possible to compact the foam 334 at the level of the cover of the part, so as to make it more resistant to mechanical stresses. This compaction is carried out using a mobile drawer similar to drawer 324. According to another embodiment not shown, the cover is reinforced by the formation of a groove in the mold, and not by compacting the foam.

A manufacturing process as described above makes it possible to obtain a hollow part 10, 110, therefore lighter, while retaining good mechanical and acoustic properties. The presence of the hinge (s) 20, 120, 122 makes it possible to form the part 10, 110 in a single piece and not in several elements, which simplifies the manufacturing process. Furthermore, the second embodiment of FIGS. 3 and 4 saves space during storage / transport in the open configuration.

A method of manufacturing the structure 200 of FIG. 5 will now be described. The part 10 obtained by the above method is placed in the closed configuration of FIG. 2, by folding the hinge 20 to bring the cover 18 into contact with the base 14. Optionally, the internal cavity 16 is previously filled an acoustic insulation material, such as a recycled felt, a fibrous soundproofing or an acoustic nonwoven. Alternatively, the closed volume 48 is left empty.

Several similar pieces 10, in closed configuration, are then placed in a mold, then the second plastic material 204, such as a polyurethane foam, is overmolded on said pieces 10 to form the body 202 previously described.

Claims (10)

1. - Part (10, 110) for sound absorption for a motor vehicle, formed from a first expanded plastic material (12), said part comprising a base (14, 114) defining an internal cavity (16, 116, 117) , said base comprising at least a first (32, 132) and a second (34, 134) facing walls; said part being characterized in that: - It further comprises a cover (18, 118, 119) and a hinge (20, 120, 122) hinging said cover to the first wall of the base (14, 114); the cover being able to be assembled with the second wall in a closed configuration of said part; - The base, the cover and the hinge are formed in a single piece, said hinge (20, 120, 122) being formed of a flexible strip of the first expanded plastic material (12); and - The first expanded plastic material has a first density (d0 at the base (14, 114) and a second density (d ₂ ), greater than the first density, at the hinge. 2. - Part according to claim 1, wherein the first expanded plastic material (12) comprises a thermoplastic polymer, preferably chosen from polyethylenes, polypropylenes and polystyrenes. 3. - Part (10) according to claim 1 or claim 2, configured so that, in the closed configuration, the internal cavity (16) forms a volume (48) closed by the cover (18). 4. - Part (110) according to claim 1 or claim 2, configured so that the base (114) defines two internal cavities (116, 117), said part further comprising two covers (118, 119), each of said covers being hinged at the base by a separate hinge (120, 122). 5. - Structure (200) for a motor vehicle, comprising: at least one part (10) for sound absorption according to one of the preceding claims, in the closed configuration; and a second plastic material (202, 204), molded onto said at least one part. 6. - Structure according to claim 5, wherein the second plastic material (204) comprises a polyurethane. 7. - Method for manufacturing a sound absorption part (10) according to one of the preceding claims, said method comprising the following steps: - Supply of a mold (302) comprising a first (304) and a second (306) parts movable relative to each other between an open configuration and a closed configuration, the first part comprising a strip (312) forming an upper edge (316), the second part comprising a movable drawer (324), said drawer comprising a lower surface (326); - provision, in the open configuration mold, of particles (330) of first plastic material (12) capable of expanding under a high temperature and / or pressure; - placement of the mold in closed configuration, a first air gap (332) separating the upper edge (316) of the strip and the lower surface (326) of the movable drawer; and - application of a high temperature and / or pressure in the mold; said step of applying a temperature and / or a high pressure comprising: a first phase, corresponding to the first air gap between the slide and the movable drawer, allowing at least partial expansion of the first plastic material (12); then a displacement of said drawer in the direction of the strip to a second air gap (336) lower than the first air gap; then a second phase corresponding to said second air gap between the strip and the movable drawer; said displacement of the drawer in the direction of the strip leading to densify (338) the first at least partially expanded plastic material, disposed between said drawer and said strip. 8. - Method according to claim 7, wherein the upper edge (316) of the strip (312) is formed by the intersection of two side panels (314), said side panels forming a non-zero angle (2β) and less than 20 °, said angle preferably being between 6 ° and 10 °. 9. - Method according to claim 7 or claim 8, wherein the strip (312) is removable from the rest (308) of the first part (304) of the mold. 10. - Method according to one of the preceding claims, wherein the movable drawer (324) is configured (328) so that its movement towards the strip leads to densify (338) a portion of the first plastic material (12) at least partially expanded, disposed on either side of the strip (312).