ACOUSTIC AND THERMAL SHIELD FOR A MOTOR VEHICLE

Abstract

The invention relates to a shield comprising: a thermo-compressed porous three-dimensional shell based on glass fibers, the fibers being joined together by a binding agent. The shield includes a foam-based inner spring layer, and additionally has the following features: the foam layer is produced by reaction injection molding (RIM), the layer overmolding the shell. The shell has a porosity arranged in order to enable the foam to penetrate a fraction of the thickness of the shell, so as to create a leaktight skin the binding agent is based on polypropylene. The shell comprises between 45 and 55% by weight of glass fibers.

Claims

1. An acoustic and thermal shield for a motor vehicle, the shield comprising: a thermo-compressed porous three-dimensional shell based on glass fibers, the fibers being joined together by a binding agent, a foam-based inner spring layer made of elastically compressible polyurethane, the shield further comprising: spring layer produced by reaction injection molding, the layer overmolding the shell, the shell having a porosity arranged to enable the foam to penetrate a fraction of the thickness of the shell, to create a leaktight skin, such that the shield: is acoustically insulating according to a mass-spring principle, the shield additionally having acoustic absorption properties conferred by the fraction of thickness of the shell not penetrated by the foam and remaining porous, has the rigidity thereof increased by the reinforcement by the fibers coated by the foam, the shield having: the binding agent based on polypropylene, and the shell comprises between 45 and 55% by weight of glass fibers.

2. The shield according to claim 1, wherein the skin has a thickness of between 0.3 and 1 mm.

3. The shield according to claim 1, wherein the shell is provided, on at least one of the faces thereof, with a non-woven protective layer.

4. The shield according to claim 1, wherein the binding agent is produced by polypropylene particles, to ensure a binding of the fibers to one another by a multiplicity of binding points.

5. A mounting comprising a shield according to claim 1, comprising the shield and a component to be protected, the component being delimited by a wall, the visible face of the spring layer being shaped to substantially mold the shape of the wall, to make it possible for an optimisation of the acoustic and thermal insulation.

6. A method for producing a shield according to claim 4, wherein the method comprises the following steps: producing a mixture of glass fibers and polypropylene particles, the percentage by weight of the fibers with respect to the total weight of the fibers and particles being between 45 and 55%, the mixture being dispersed in a liquid matrix, producing, with the mixture dispersed in the matrix, a continuously unwound fibrous ply, passing said ply into a furnace to evaporate the matrix and to achieve the fusion of the particles, to have a dry ply, producing a calendaring of the dry ply to compress it and to connect the fibers to one another by the polypropylene once cooled forming a binding agent, producing, from a blank of the compressed ply, by compression between two walls of a hot compression mold, a thermo-compressed porous three-dimensional shell based on the glass fibers, the fibers being joined together by the polypropylene, arranging the shell against a wall of a reaction injection mold, the visible face of the shell being arranged towards the wall, injecting on the shell, within the molding cavity defined by the mold, a precursory foam mixture made of elastically compressible polyurethane, after expansion of the foam, demolding the shield obtained.

7. The method according to claim 6, wherein the shell is obtained from a dry ply having a surface mass of between 500 and 800 g/m.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0038] Other particularities and advantages of the invention will appear in the following description, made in reference to the attached FIGURE which is a schematic cross-sectional view of a mounting of a shield, according to an embodiment, on a component to be protected.

DETAILED DESCRIPTION

[0039] In reference to the FIGURE, an acoustic and thermal shield 1 for a motor vehicle is described, the shield comprising: [0040] a thermo-compressed porous three-dimensional shell 2 based on glass fibers, the fibers being joined together by a binding agent, [0041] a foam-based inner spring layer 3in particular made of polyurethaneelastically compressible,

[0042] the shield additionally having the following features: [0043] the layer is produced by reaction injection molding (RIM), the layer overmolding the shell, [0044] the shell has a porosity arranged in order to enable the foam to penetrate a fraction 4 of the thickness of the shell, so as to create a leaktight skin 5, such that the shield: [0045] is acoustically insulating according to a mass-spring principle, the shield additionally having acoustic absorption properties conferred by the fraction of thickness of the shell not penetrated by the foam and remaining porous, [0046] has the rigidity thereof increased by the reinforcement brought by the fibers coated by the foam, [0047] the binding agent is based on polypropylene, [0048] the shell 2 comprises between 45 and 55% by weight of glass fibers.

[0049] According to an embodiment, the skin 5 has a thickness of between 0.3 and 1 mm.

[0050] The shell 2 can itself typically have a thickness of between 2 and 3 mm.

[0051] In a non-represented manner, it can be provided that the shell 2 is provided, on at least one of the faces thereof, with a non-woven protective layer.

[0052] The presence of such a layer makes it possible to bring a protection to production operators faced with the risks of cuts by the glass fibers contained in the shell 2.

[0053] Such a protective layer in particular has a surface mass of between 15 and 120 g/m.sup.2 and in particular a resistance to the passage of air of between 50 and 180N.s.m.sup.3.

[0054] With such features, a protective layer arranged towards the spring layer 3 does not substantially interfere with the penetration of a fraction 4 of the thickness of the shell 2 by the foam, to form the skin 5.

[0055] According to a non-represented embodiment, the outer facei.e. that opposite the spring layer 3of the shell 2 is covered by a coating layer, for example based on fabric.

[0056] According to an embodiment, the binding agent is produced by polypropylene particles, so as to ensure a binding of fibers to one another according to a multiplicity of binding points, as will be explained later.

[0057] Now, a mounting of such a shield 1 is described, the mounting comprising the shield and a component 6 to be protected, the componentfor example in the form of an oil housing or a gearboxbeing delimited by a wall 7, in particular made of sheet metal, the visible face 8 of the spring layer 3 being shaped so as to mold substantially the shape of the wall, so as to make it possible for an optimisation of the acoustic and thermal insulation.

[0058] Finally, a method for producing such a shield 1 is described, the method comprising the successive following steps: [0059] producing a mixture of glass fibers and polypropylene particles, the percentage by weight of the fibers with respect to the total weight of the fibers and particles being between 45 and 55%, the mixture being dispersed in a liquid matrix, [0060] producing, with the mixture dispersed in the matrix, a continuously unwound fibrous ply, [0061] making the ply pass into a furnace so as to evaporate the matrix and to achieve the fusion of the particles, in order to have a dry ply, [0062] producing a calendaring of the dry ply so as to compress it and to connect the fibers to one another by the polypropylene once cooled forming a binding agent, [0063] producing, from a blank of the compressed ply, by compression between two walls of a hot compression mold, a thermo-compressed porous three-dimensional shell 2 based on the glass fibers, the fibers being joined together by the polypropylene, [0064] arranging the shell against a wall of a reaction injection mold (RIM), the visible face 9 of the shell being arranged towards the wall, [0065] injecting on the shell, within the molding cavity defined by the mold, a precursory foam mixturein particular made of polyurethaneelastically compressible, [0066] after expansion of the foam, demolding the shield 1 obtained.

[0067] Such a method falls under an embodiment by paper, in reference to the dispersion of the fibre/particle mixture in a liquid matrix which is then removed.

[0068] The interest in such a process, compared with another manner of proceeding consisting of achieving a co-needling of glass fibers with polypropylene fibers configured to form a binding agent after the fusion thereof, is to make it possible for a binding of the fibers to one another according to a multiplicity of binding points.

[0069] This results in the formation of a dry ply, and subsequently a shell 2, having a higher rigidity than if it was obtained by the above-mentioned process involving a co-needling.

[0070] In this manner, the rigidification of the shield 1 brought by partial penetration of foam in the shell 2 is improved, knowing that the shield however retains a sufficient flexibility to be able to be mounted or provided with cuts without it resulting in a deterioration.

[0071] According to an embodiment, the shell 2 is obtained from a dry ply having a surface mass of between 500 and 800 g/m.sup.2, knowing that, in the prior art, it is possible to start from a ply having a surface mass of around 1000 g/m.sup.2 or more.

[0072] In a non-represented manner, it can be provided that the ply is calendared with at least one non-woven protective layer, such as described above, arranged on at least one of the faces thereof.