METHOD FOR PRODUCING AN ACOUSTIC PROTECTION SCREEN FOR A MOTOR VEHICLE ENGINE AND SCREEN OBTAINED USING SUCH A METHOD

Abstract

A method for producing an acoustic protection screen for a motor vehicle engine, comprising providing a reflective metal thermal protection sheet having a plurality of micro perforations, providing a batt of fibres containing a thermosetting resin, superposing the metal thermal protection sheet and the batt in a first thermocompression mould, compressing the batt by binding the fibres together, in order to form a thermal insulation layer, and combining the metal thermal protection sheet with the layer using the thermosetting resin, placing the thermal protection shell against an upper wall of a second mould, the wall being provided with out-gassing vents, the sheet facing toward the wall, injecting into the second mould an air-porous polyurethane foam precursor mixture, the lower wall of the second mould being free of any fluid-tight coating, after the foam has expanded, demoulding the screen obtained, in which screen the foam forms a support overmoulding the layer.

Claims

1. A method for producing an acoustic protection screen for a motor vehicle engine, said method comprising the steps: providing a reflective metal thermal protection sheet, said metal thermal protection sheet being provided with a plurality of micro perforations, providing a batt of fibres containing a thermosetting resin, superposing said metal thermal protection sheet and said batt in a first thermocompression mould, compressing said batt by binding said fibres together, in order to form a thermal insulation layer, and combining said metal thermal protection sheet with said layer using said thermosetting resin, obtaining a thermal protection shell comprising said thermal insulation layer and said metal thermal protection sheet, placing said thermal protection shell against an upper wall of a second mould, said wall being provided with out-gassing vents, said sheet facing toward said wall, injecting into said second mould an air-porous polyurethane foam precursor mixture, the lower wall of said second mould being free of any fluid-tight coating, after the foam has expanded, demoulding the screen obtained, in which screen the foam forms a support overmoulding said layer.

2. The method according to claim 1, wherein the surface density of the micro-perforations is between 400,000 and 600,000 micro-perforations per m.sup.2.

3. An acoustic protection screen for a motor vehicle engine obtained by a method according to claim 1, said screen comprising, arranged successively one on the other: a reflective metal sheet made of aluminium for thermal protection, said reflective metal sheet being provided with a plurality of micro perforations, the surface density of the micro-perforations being between 400,000 and 600,000 micro-perforations per m.sup.2, a thermal insulation layer bonded together by a thermosetting binder, a support with a porous polyurethane foam base allowing for the acoustic absorption of the noise coming from said engine, said support overmoulding said layer in such a way that the foam coats the surface fibres of said layer, the outer face of said support being free of any fluid-tight coating in such a way that said foam can absorb the noise coming from said engine.

4. The screen according to claim 3, wherein the support has a resistance to the passing of air of between 1000 and 1500 N.Math.s.Math.m.sup.3.

5. The screen according to claim 4, wherein the foam of the support has a density of between 0.22 and 0.28, and in particular between 0.23 and 0.27.

6. The screen according to claim 5, wherein the insulation layer has a thermal conductivity of between 0.055 and 0.061 W.Math.m.sup.1.Math.K.sup.1 at 200 C., and in particular of between 0.057 and 0.059 W.Math.m.sup.1.Math.K.sup.1.

7. The screen according to claim 6, wherein the insulation layer has a resistance to the passing of air less than 4000 N.Math.s.Math.m.sup.3.

8. The screen according to claim 7, wherein the insulation layer has a thickness of between 3 and 8 mm.

9. The screen according to claim 8, wherein the insulation layer has a surface density of between 600 and 1000 g/m.sup.2.

10. The screen according to claim 9, wherein a first portion of the support is free of any thermal protection and/or a second portion of said support is protected only by the insulation layer, a third portion of said support, intended to be the most exposed, being protected by said insulation layer and by the metal sheet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Other particularities and advantages of the invention shall appear in the following description, given in reference to the attached figures, wherein:

[0029] FIG. 1 is a partial cross-section diagrammatical view if a screen in the process of manufacture, according to an embodiment, before the demoulding thereof,

[0030] FIG. 2 is a partial cross-section diagrammatical view of a screen according to a particular embodiment.

DETAILED DESCRIPTION

[0031] In reference to the figures, a method for producing an acoustic protection screen 1 for a motor vehicle engine is described, said method comprising the following steps: [0032] providing a reflective metal sheet 4in particular made of aluminiumfor thermal protection, said sheet being provided with a plurality of micro perforations 19, [0033] providing a batt of fibres containing a thermosetting resin, in particular phenolic, [0034] superposing said sheet and said batt in a first thermocompression mould, in such a way as to compress said batt by binding said fibres together, in order to form a thermal insulation layer 5, and so as to combine said sheet with said layer using said resin, so as to obtain a thermal protection shell comprising said layer and said sheet, [0035] placing said shell against the upper wall 10 of a second mould, said wall being provided with out-gassing vents 11, said sheet facing toward said wall, [0036] injecting into said second mould an air-porous polyurethane foam precursor mixture, the lower wall 12 of said second mould being free of any fluid-tight coating, [0037] after the foam has expanded, unmoulding the screen 1 obtained, wherein the foam forms a support 2 overmoulding said layer.

[0038] According to an embodiment, the surface density of the micro-perforations 19 is between 400,000 and 600,000 micro-perforations per m.sup.2.

[0039] An acoustic protection screen 1 for a motor vehicle engine obtained using such a method is now described, said screen comprising, arranged successively one on the other: [0040] a reflective metal sheet 4in particular made of aluminiumfor thermal protection, said sheet being provided with a plurality of micro perforations 19, the surface density of the micro-perforations being in particular between 400,000 and 600,000 micro-perforations per m.sup.2, [0041] a thermal insulation layer 5 of fibres bonded together by a thermosetting binder, [0042] a support 2 with a porous polyurethane foam base that allows for the acoustic absorption of the noise coming from said engine, said support overmoulding said layer in such a way that the foam coats the surface fibres of said layer, the outer face 18 of said supporti.e. the face opposite the one receiving said layerbeing free of any fluid-tight coating in such a way that said foam can absorb the noise coming from said engine.

[0043] It is specified here that the coating of the surface fibres of the insulation layer 5 by the foam is the consequence of the method such as implemented, wherein the foam precursor mixture coats said fibres during the expansion of the foam.

[0044] The foam once polymerised thus provides the coating observed for the surface fibres described hereinabove.

[0045] According to an embodiment not shown, the outer face 18 of the support 2 can be coated with a porous coating layer, for example of the non-woven type, said porous layer not obstructing the penetration of the sound waves within the foam of said support in order to be absorbed therein.

[0046] According to an embodiment, the support 2 has a resistance to the passing of air between 1000 and 1500 N.Math.s.Math.m.sup.3, which allows it to correctly absorb the sound waves coming from the engine.

[0047] The fibres used are in particular mineral fibresfor example glass, silica or rockchosen according to the expected characteristics of thermal conductivity.

[0048] According to an embodiment, the foam of the support 2 has a density between 0.22 and 0.28, and in particular between 0.23 and 0.27.

[0049] According to an embodiment, the insulation layer 5 has a thermal conductivity between 0.055 and 0.061 W.Math.m.sup.1.Math.K.sup.1 at 200 C., and in particular between 0.057 and 0.059 W.Math.m.sup.1.Math.K.sup.1.

[0050] According to an embodiment, the insulation layer 5 has a resistance to the passing of air less than 4000 N.Math.s.Math.m.sup.3.

[0051] According to an embodiment, the insulation layer 5 has a thickness between 3 and 8 mm.

[0052] According to an embodiment, the insulation layer 5 has a surface density between 600 and 1000 g/m.sup.2.

[0053] According to an embodiment, the fibres of the insulation layer 5 are bonded together by a phenolic resin.

[0054] According to an embodiment, the metal sheet 4 has a thickness between 50 and 150 microns, and in particular between 70 and 100 microns, an equally low thickness that contributes to lightening the screen 1.

[0055] According to the particular embodiment shown in FIG. 2, the insulation layer 5 partially covers the support 2.

[0056] According to an alternative not shown, the insulation layer 5 could cover the entire support 2.

[0057] According to this same embodiment, the sheet 4 partially covers the insulation layer 5.

[0058] It is as such possible to arrange a screen 1 of which a first portion 15 of the support 2 is free of any thermal protection and/orhere and, in the embodiment showna second portion 16 of said support is protected only by the insulation layer 5, a third portion 17 of said support, intended to be the most exposed, being protected by said insulation layer and by the metal sheet 4.