FR3040678A1 - STRUCTURING FLOOR OF A MOTOR VEHICLE AND METHOD OF MANUFACTURING THE SAME - Google Patents

Abstract

This structuring floor comprises: - a rigid shim (16) having a density of less than 50 kg / m3; - a foam decoupling layer (18) in contact with the shim (16) on at least one upper surface (28) of the shim (16); a porous stiffening layer (20) disposed on the decoupling layer (18). The thickness of the stiffening layer (20) is greater than 10 mm, in particular between 15 mm and 20 mm, the floor (10) comprising an intermediate layer (22) sealed with a mass per unit area of less than 500 g / m2, arranged between the decoupling layer (18) and the stiffening layer (20).

Description

Structuring floor of a motor vehicle and method of manufacturing the same

The present invention relates to a structuring floor of a motor vehicle, comprising: - a rigid block having a density of less than 50 kg / m3; a foam decoupling layer in contact with the shim on at least one upper surface of the shim; a porous stiffening layer disposed on the decoupling layer.

Such a floor is intended to be arranged in the space between the sheet metal of the bottom of the body and the passenger compartment of a motor vehicle. The floor is intended to support a relatively flat-shaped aspect layer, for example a carpet, based on the non-planar structure of the bottom.

To meet the constraints of motor vehicles, such a floor must be both lightweight, inexpensive and have good acoustic properties.

In known solutions, described for example in US 5483028, EP 1527954 or EP 2626249, the floor comprises a lower elastic decoupling layer placed in contact with the sheet and a rigid shim, the shim having a support wall of the diaper layer. appearance and support pads on the lower layer. A porous and elastic upper layer is advantageously disposed between the support wall and the appearance layer.

In another solution, a lightweight composite such as a self-supporting double-shelled glass / polypropylene compressed nonwoven is used with thick air blades in which porous materials are positioned. Absorbent material is optionally disposed below the carpet.

In addition to its mechanical support properties, such a floor thus forms a set of soundproofing that can partially solve the acoustic problems that arise in a passenger compartment of a motor vehicle in the vicinity of noise sources such as a motor, the contact of pneumatic with a road, etc.

Within the meaning of the present invention, a soundproofing assembly provides "insulation" when it prevents the entry of medium and high frequency acoustic waves into the soundproof space, essentially by reflection of the waves towards the noise sources or the outside of the soundproofed space.

A soundproofing package operates by "sound absorption" (in the medium and high frequency range) when the energy of the acoustic waves dissipates in an absorbent material.

An efficient soundproofing system must work both by ensuring good insulation and absorption. To characterize the performance of such a set, we use the NR noise reduction index concept which takes into account the two notions of isolation and absorption. This index can be calculated by the following equation: NR (dB) = TL-10log (S / A) where TL is the sound attenuation index (hereinafter weakening index) reflecting the insulation. The higher this index, the better the insulation A is the equivalent absorption surface. The higher A is, the better the absorption.

The floors of the aforementioned type generally have insufficient acoustic properties, in particular with regard to their mass and the space occupied in the vehicle, since they cover the bottom sheet metal. These floors do not take advantage of the large space available between this sheet and the cabin.

In particular, these floors generally have a fairly low absorption at medium frequencies, especially in the ranges between 300 Hz and 900 Hz.

An object of the invention is therefore to provide a structuring floor, suitable for being placed on the bottom of the body of a motor vehicle, which has a weight and a low cost, and which nevertheless has significantly improved acoustic properties, especially in medium frequency absorption. For this purpose, the subject of the invention is a floor of the aforementioned type, characterized in that the thickness of the stiffening layer is greater than 10 mm, in particular between 15 mm and 20 mm, the floor comprising a tight intermediate layer. with a mass per unit area of less than 500 g / m2, disposed between the decoupling layer and the stiffening layer.

According to particular embodiments, the floor according to the invention comprises one or more of the following characteristics, taken alone or in any combination technically possible: the shim is made of expanded foam, in particular expanded foam of polystyrene and / or polyolefin; the intermediate layer is produced by penetration of the decoupling layer into the stiffening layer; the wedge is embedded in the decoupling layer; the thickness of the decoupling layer above the shim is greater than 5 mm, the thickness of the decoupling layer below the shim being greater than 5 mm; the wedge comprises a base and studs projecting downwards from the base; the stiffening layer has a density greater than 50 kg / m 3, in particular between 80 kg / m 3 and 140 kg / m 3; - The stiffening layer has a flexural stiffness greater than 0.01 Nm, especially between 0.5 Nm and 1.5 Nm; the stiffening layer has a tortuosity greater than 1.5, in particular between 1.8 and 2.5; the floor comprises an upper layer chosen from a carpet, a filmed carpet, advantageously having a backing layer formed by a nonwoven, or else an optionally resistive textile. The invention also relates to a method for manufacturing a structural floor of a motor vehicle comprising the following steps: - supply of a shim having a density of less than 50 kg / m3 and a stiffening layer, the thickness the stiffening layer being greater than 10 mm, in particular between 15 mm and 20 mm, - forming a decoupling layer, in contact with the shim on at least a portion of an upper surface of the shim; - Provision between the decoupling layer and the stiffening layer of a sealed intermediate layer of basis weight less than 500 g / m2.

The floor according to the invention comprises one or more of the following characteristics, taken in isolation or in any technically possible combination: the sealed intermediate layer is formed by penetration of the material forming the decoupling layer into the stiffening layer. The invention will be better understood on reading the description which follows, given solely by way of example, and with reference to the appended drawings, in which: FIG. 1 is a diagrammatic view, taken in section following a vertical plane, a first structuring floor according to the invention; - Figure 2 is a view similar to Figure 1, a second structuring floor according to the invention; FIG. 3 is a view of the absorption curves as a function of frequency for the first floor according to the invention and for the second floor according to the invention, in comparison with floors of the state of the art; FIG. 4 is a view of the curves of sound reduction index as a function of frequency for the first floor according to the invention and for the second floor according to the invention, in comparison with floors of the state of the technical; FIG. 5 is a view of the noise reduction index curves as a function of frequency for the first floor according to the invention and for the second floor according to the invention, in comparison with floors of the state of the art. ; - Figure 6 is a view similar to Figure 1 of a third floor according to the invention; - Figure 7 is a view similar to Figure 3, for the third floor according to the invention; - Figure 8 is a view similar to Figure 4, for the third floor according to the invention; and - Figure 9 is a view similar to Figure 5, for the third floor according to the invention.

In all that follows, the orientations are generally the usual orientations of a motor vehicle. The terms "above", "below", "below", "below", "above" and "below" are relative to the reference surface of the motor vehicle, relative to the reference surface of the motor vehicle. of which is disposed the soundproofing unit. The term "inferior" is thus understood to be the closest to the surface and the term "superior" to be the farthest from that surface.

A first structural floor 10 according to the invention is illustrated in Figure 1. The floor 10 is intended to be interposed between a bottom plate 12 of the body of a motor vehicle and the passenger compartment 14 of the motor vehicle.

With reference to FIG. 1, the floor 10 comprises a rigid shim 16, a porous elastic lower layer 18, arranged in contact with the bottom plate 12, the decoupling layer 18 receiving the shim 16.

The floor 10 further comprises, according to the invention, a porous stiffening layer 20 disposed on the decoupling layer 18 and an impervious intermediate layer 22 interposed between the decoupling layer 18 and the stiffening layer 20.

In this example, the floor 10 further comprises a layer 24 of appearance, disposed above the stiffening layer 20.

The rigid wedge 16 is here a solid wedge made from foam, in particular from closed foam, lightweight because of its low density and expanded. It advantageously has an internal porosity, for example between 0.1 and 0.5, but is devoid of internal macroscopic cavities, minimum dimension greater than 1 mm.

The foam is for example a polystyrene fly, in particular an expanded polystyrene foam or a polyolefin foam, in particular an expanded polypropylene foam.

The rigid block 16 has a low density, for example less than 50 kg / m3, especially between 20 kg / m3 and 40 kg / m3.

The Young's modulus of the shim 16 is advantageously greater than 3 Mega Pa.

The wedge 16 has a maximum thickness adapted to adapt to the thickness available between the passenger compartment 14 and the sheet 12.

This thickness is here greater than the thickness of the stiffening layer 20. In particular, this thickness is greater than 30 mm, in particular between 40 mm and 80 mm.

The decoupling layer 18 has an upper portion 26 disposed on an upper surface 28 of the shim 16 and, in this example, a lower portion 30, interposed between a lower surface 32 of the shim 16 and the sheet 12. The shim 16 is thus embedded in the decoupling layer 18, between the upper part 26 and the lower part 30.

The decoupling layer 18 is made based on an elastic porous foam or else viscoelastic

This foam is advantageously open cell. It is for example made of polyurethane. This foam is advantageously injected.

The decoupling layer 18 is porous and has a porosity adapted to present a resistivity to the passage of air advantageously between 10000 Nm 4.s and 90000 Nm "4.s including between 25 000 Nm" 4.s and 35 000 Nm "4.s.

Resistance to the passage of air or its resistivity is measured by the method described in the thesis "Measurements of parameters characterizing a porous medium.Experimental study of the acoustic behavior of foams at low frequencies.", Michel HENRY, defended on October 3, 1997 at the University of Le Mans.

The density of the decoupling layer 18 is between 30 kg / m 3 and 70 kg / m 3 and in particular between 45 kg / m 3 and 55 kg / m 3. The thickness of the upper portion 26 of the decoupling layer 18, taken perpendicular to the surface 12, is advantageously between 5 mm and 30 mm, for example between 10 mm and 20 mm.

Similarly, the thickness of the lower portion 30 of the decoupling layer 18 taken perpendicular to the surface 12 is advantageously between 5 mm and 30 mm, for example between 10 mm and 20 mm.

To present spring properties, the decoupling layer 18 advantageously has an elastic modulus greater than 5000 Pa. This modulus is advantageously between 5000 Pa and 60 000 Pa, in particular between 10 000 Pa and 20 000 Pa.

The porous stiffening layer 20 is made of foam, in particular an injected foam or an open-celled foam. It is for example made of polyurethane.

In a variant, the foam also contains recycled material, as defined above, and / or mineral filler and / or 'bio-polyol'. The thickness of the porous stiffening layer 20 is greater than 10 mm and is for example between 10 mm and 30 mm, and is in particular between 15 mm and 20 mm.

The porous stiffening layer 20 is dense. The density of the porous stiffening layer 20 is strictly greater than that of the decoupling layer 18. This density is strictly greater than 50 kg / m 3 and is advantageously between 80 kg / m 3 and 140 kg / m 3.

The porosity of this layer 20 is chosen so that the resistivity at the passage of the air is greater than 40 000 N.m'4.s, advantageously between 100 000 Nm "4.s and 200 000 N.m'4. s, especially between 150 000 Nm "4.s and 200 000 N.m'4.s.

According to the invention, the porous stiffening layer 20 is stiff. It has a flexural stiffness B, reduced to a unit width, greater than 0.01 N.m, especially between 0.01 N.m and 10 N.m. This flexural stiffness B is for example greater than 0.1 Nm, and is in particular between 0.1 N.m and 1 N.m.

Flexural stiffness B may also be greater than 1.5 Nm, especially greater than 3 N.m. It can be between 1.5 Nm and 2.5 N.m.

Flexural stiffness B is calculated by the equation: B = E.h3 / 12, where h is the thickness of layer 20, and E is its Young's modulus.

The Young's modulus or modulus of elasticity is measured for example by the method described in the article: C. Langlois, R. Panneton, and N. Atalla, "Polynomial relations for quasistatic mechanical characterization of isotropy poroelastic materials," . Acoust. Soc. Am. 110, 3032-3040 (2001).

Advantageously, the porous stiffening layer 20 is tortuous. It has a tortuosity ainf greater than 1.5, and especially between 1.8 and 2.5.

The tortuosity is measured by determining the slope of the curve representing the variation of the square of the refractive index for the acoustic wavelength used as a function of the inverse of the square root of the frequency. In practice, tortuosity is related to the shape of the circulation paths in a porous material. A method of measuring tortuosity is described, for example, in paragraph 4.2.2 of the article "Characterization of Porous Materials", SAPEM 2005 Conference, pages 167 to 180.

The intermediate layer 22 is impervious to the passage of air. By "airtightness" is meant that its resistance to the passage of air is too high to be measured by the method mentioned above.

The intermediate layer 22 has a thickness less than that of the porous stiffening layer 20, advantageously a thickness less than 50% of the thickness of the porous stiffening layer 20.

The intermediate layer 22 furthermore has a thickness less than 10% of the thickness of the upper part 26 of the decoupling layer 18. The thickness of the intermediate layer 22 is, for example, less than 2 mm, and especially between 0 , 5 mm and 1.5 mm.

The weight per unit area of the intermediate layer 22 is greater than 50 g / m 2 and is especially greater than 150 g / m 2, advantageously greater than 200 g / m 2. This weight per unit area is in particular between 200 g / m2 and 400 g / m2.

The weight per unit area of the intermediate layer 22 is in any case less than 500 g / m 2, to be less than that of a conventional heavy mass layer. The layer 22 does not play the role of heavy mass.

The intermediate layer 22 is assembled under the porous stiffening layer 20.

The Young's modulus of the intermediate layer 22 is thus equal to or greater than that of the stiffening layer 20 and thus contributes to the bending stiffness of the absorbent layer.

Advantageously, the intermediate layer 22 is formed by a mixture of the foam forming the upper part 26 of the decoupling layer 18 and the porous material forming the porous stiffening layer 20. The sealing of the intermediate layer 22 is obtained by filling the pore or interstices formed in the porous stiffening layer 20 by means of the foaming material injected during the production of the upper part 26 of the decoupling layer 18. The thickness of the intermediate layer 22 thus depends on the porosity of the porous decoupling layer 20, and the pressure applied during the injection of the foam forming the upper part 26 of the decoupling layer 18.

In a variant, the intermediate layer 22 is formed by a sealed film coated on the porous layer 20, of the plastisol type. A plastisol is formed by the dispersion of a thermoplastic resin in a plasticizer. By heating this mixture the plasticizer and polymer molecules interlock forming a flexible and waterproof coating. The most common plastisols are based on PVC (polyvinyl chloride)

In another variant, the sealed intermediate layer 22 is formed by extruding a film of thermoplastic material on the porous decoupling layer 20 to form a sealing layer with a mass of less than 500 g / m 2.

In yet another variant, the impermeable intermediate layer 22 is formed by melting a dispersed material, for example a pulverulent material, previously dispersed on a surface of the porous stiffening layer 20.

Alternatively, the intermediate layer 22 may be a light film of a weight less than 150 g / m 2 of the same type as those used to prevent penetration of the foam, provided that it adheres perfectly to the stiffening layer 20.

The appearance layer 24 is for example formed of a carpet, a carpet or a nonwoven. It is intended to be visible in the passenger compartment 14 of the motor vehicle. It is preferably laid without being fixed on the stiffening layer 20, in order to avoid the continuity of the stresses. It is devoid of heavy mass layer.

The carpet is for example filmed, or advantageously has a backing layer formed by a nonwoven fabric or an optionally resistive textile.

The nonwoven or the resistive textile is a material having a resistance to the passage of controlled air (for example, a light weight felt, a preferably calendered textile, etc.).

In this case, it has a surface density of between 20 g / m 2 and 200 g / m 2, advantageously 100 g / m 2.

This material is then porous to advantageously have a specific resistance to the passage of low air of between 200 N.m'3.s and 2000 Nm "3.s, for example between 500 N.m3, .s and 1200 N .m'3.s.

In order to manufacture the floor 10, the pre-fabricated stiffening layer 16 and shim 16 are provided and are introduced into a production mold.

A foaming material intended to form the decoupling layer 18 is then injected into the mold on the one hand, between the upper surface 28 of the shim 16 and the stiffening layer 20, and on the other hand, between the lower surface 32 of the wedge 16 and the wall of the mold.

The upper part 26 of the decoupling layer 18 is formed by expansion and hardening of the foaming material. The foaming material also penetrates partially into the stiffening layer 20 to form the tight intermediate layer 22.

The acoustic properties of the structuring floor 10 according to the invention are illustrated with reference to FIGS. 3 to 5 which respectively represent the absorption a, the sound reduction index TL, and the noise reduction index NR as a function of the frequency F for the floor 10 (curves 50) in comparison with floors of the state of the art.

The floor 10 has a shim 16 made of expanded polystyrene, with a density equal to 25 kg / m3 and a thickness of 60 mm.

The decoupling layer 18 is made of polyurethane foam. It comprises a resistivity at the passage of air equal to 32 000 Nm "4.s and a density equal to 50 kg / m3 .The thickness of the upper part 26 and the thickness of the lower part 30 are respectively equal. at 10 mm and 15 mm ..

The stiffening layer 20 has an air flow resistivity substantially equal to 180,000 Nm "4.s, a tortuosity equal to 2.8, and a density equal to 90 kg / m3. equal to 500,000 Pa against 1,500,000 Pa for layer 22.

In comparison, the acoustic behavior of a first floor of the state of the art comprising a polypropylene wedge with hollow cones with a thickness of 80 mm, a 10 mm felt decoupling layer, and a top foam of 10 mm thick is illustrated by the curve 52.

The acoustic behavior of a second floor of the state of the art, comprising a double-shell compressed glass / polypropylene nonwoven composite layer of thickness equal to 6 mm with thick air blades, of thickness equal to 74 mm, and a decoupling layer of felt 20 mm thick is illustrated by the curve 54.

The acoustic behavior of a third floor of the state of the art, formed by a 20 mm felt layer, and a heavy mass layer of 3 kg / m 2 (spring mass system) is illustrated by curve 56.

With reference to FIGS. 1 to 3, the structuring floor 10 according to the invention surprisingly has improved absorption over a wide frequency band compared to the floors of the state of the art.

The structuring floor 10 according to the invention also has a much better insulation than the floors of the state of the art, in particular better than conventional mass-spring systems, for a comparable overall mass per unit area (of the order of 4 kg / m2 in the examples given). In particular, the insulation and noise reduction index are better from 10dB to 15dB above 1000Hz up to 10 000 Hz, which greatly impacts the acoustic comfort by improving the intelligibility in the cabin.

The high thickness of the stiff, stiff, resistive and tortuous stiffening layer increases the coupling with the leaktight intermediate layer 22 to improve the sound attenuation index, and to reach slopes of 18 dB / octave while maintaining high absorption. broadband, adjustable from about 125 Hz to about 10 000 Hz.

The average absorption coefficient of the passenger compartment 14 is thus improved, which reduces the noise at the ear point and offsets the insulation losses related to the lightening of the floor 10.

The stiffening layer 20 further improves the lift of the structural floor 10, and easily fills thicknesses of 50 mm up to 150 mm, thanks to the clever use of 16 full but nevertheless light shims.

A second structural floor 60 according to the invention is illustrated in FIG. 2. Unlike the floor 10 of FIG. 1, the shim 16 has a base 62 of substantially constant thickness and studs 64 projecting downwards from from the base 62.

The base 62 defines the upper surface 28 of the shim 16. It has a thickness of, for example, between 10 mm and 50 mm, in particular between 20 mm and 30 mm.

The base 62 has a lower surface 66 from which the studs 64 project.

The studs 64 are here of frustoconical shape. They have a height greater than 10 mm, and especially between 20 mm and 50 mm, in particular between 25 mm and 40 mm.

The lower part 30 of the decoupling layer 18 matches the shape of the pads 64, and the lower surface 66 of the base 62 between the pads 64. Thus, the region 68 of the lower part 30 disposed opposite each pad 64 s Applies to the sheet 12. Conversely, the region 70 of the lower portion 30 disposed below the lower surface 66 away from the pads 64 extends away from the sheet 12, defining a free space 72 above the sheet 12. The free space 70 is advantageously available for the passage of functional lines of the vehicle, for example electric cables.

The second floor 60 according to the invention is therefore still lighter than the first floor 10 and allows a weight reduction of about 15%.

The acoustic behavior of the second floor 60 according to the invention is also similar to that of the first floor, as illustrated by the curves 74 in FIGS. 3 to 5.

A third structural floor 80 according to the invention is illustrated in FIG. 6. The third floor 80 differs from the first floor 10 in that the thickness of the shim 16 is substantially equal to or less than that of the stiffening layer 20. thickness is for example between 10 mm and 20 mm.

The acoustic behavior of the third structural floor 80 according to the invention is illustrated by FIGS. 7 to 9 by the curves 82.

The floor 80 illustrated in this figure has a shim 16 made of expanded polystyrene, with a density equal to 25 kg / m3 and a thickness of 14 mm.

The decoupling layer 18 is made of polyurethane foam. It has a resistivity at the passage of the air equal to 32 000 N.m'4.s and a density equal to 50 kg / m3. The thickness of the upper portion 26 and the thickness of the lower portion 30 are respectively equal to 10 mm and 15 mm.

The stiffening layer 20 has an air flow resistivity substantially equal to 180,000 Nm "4.s, a tortuosity equal to 2.8, and a density equal to 90 kg / m3. The layer 22 has a Young's modulus of 1,500,000 Pa.

In comparison, the acoustic behavior of a floor of the state of the art comprising a polypropylene wedge with hollow cones of thickness equal to 35 mm, a decoupling layer made of felt of 10 mm, and an upper foam of 10 mm. mm thick is illustrated by curve 84.

As previously, the floor 80 according to the invention has a broadband absorption, greater than the absorption of the floor of the state of the art over almost the entire frequency range, and significantly improved insulation, with a weakening index of the order of 18 dB / octave.

This combination of beneficial acoustic properties is obtained in a surprising manner with a reduced weight per unit area of about 6% compared to the floor of the state of the art.

Claims (12)

1. - structuring floor (10; 60; 80) of a motor vehicle, comprising: - a rigid block (16) having a density of less than 50 kg / m3; - a foam decoupling layer (18) in contact with the shim (16) on at least one upper surface (28) of the shim (16); a porous stiffening layer (20) disposed on the decoupling layer (18); characterized in that the thickness of the stiffening layer (20) is greater than 10 mm, in particular between 15 mm and 20 mm, the floor (10; 60; 80) comprising an intermediate layer (22) waterproof of mass per unit area less than 500 g / m2, disposed between the decoupling layer (18) and the stiffening layer (20). 2. - Floor (10; 60; 80) according to claim 1, wherein the shim (16) is made of expanded foam, especially expanded foam of polystyrene and / or polyolefin. 3. - Floor (10; 60; 80) according to any one of the preceding claims, wherein the intermediate layer (22) is formed by penetration of the decoupling layer (18) in the stiffening layer (20). 4. - Floor (10; 60; 80) according to any one of the preceding claims, wherein the shim (16) is embedded in the decoupling layer (18). 5. - Floor (10; 60; 80) according to claim 4, wherein the thickness of the decoupling layer (18) above the wedge (16) is greater than 5 mm, the thickness of the layer decoupling device (18) below the shim (16) being greater than 5 mm. The floor (60) of any preceding claim, wherein the shim (16) comprises a base (62) and studs (64) projecting downwardly from the base (62). 7. - Floor (10; 60; 80) according to any one of the preceding claims, wherein the stiffening layer (20) has a density greater than 50 kg / m3, especially between 80 kg / m3 and 140 kg / m3. 8. - Floor (10; 60; 80) according to any one of the preceding claims, wherein the stiffening layer (20) has a flexural rigidity greater than 0.01 Nm, in particular between 0.5 Nm and 1 , 5 Nm 9. - Floor (10; 60; 80) according to any one of the preceding claims, wherein the stiffening layer (20) has a tortuosity greater than 1.5, especially between 1.8 and 2.5. 10. Floor (10; 60; 80) according to any one of the preceding claims, comprising an upper layer (24) selected from a carpet, a filmed carpet, advantageously having a backing layer formed by a nonwoven, or a possibly resistive textile. 11. A method for manufacturing a motor vehicle structuring floor (10; 60; 80) comprising the following steps: providing a shim (16) having a density of less than 50 kg / m 3 and a layer of stiffening (20), the thickness of the stiffening layer (20) being greater than 10 mm, in particular between 15 mm and 20 mm, - forming a decoupling layer (18), in contact with the wedge (16 ) on at least a portion of an upper surface (28) of the shim (16); - Arrangement between the decoupling layer (18) and the stiffening layer (20) of an intermediate layer (22) sealed with a mass per unit area of less than 500 g / m2. 12. - The method of claim 11, wherein the sealed intermediate layer (22) is formed by penetration of the material forming the decoupling layer (18) in the stiffening layer (20).