FR2925579A1 - Exhaust element e.g. catalyst, for e.g. petrol engine of motor vehicle, has web comprising layers containing respective fibers, where part of fibers in one of layers cooperates with material of another layer and forms assembling unit - Google Patents

Abstract

The element has a canning web (4) maintaining an active exhaust gas treating element with respect to an envelope. The web has fibrous layers (5, 5') containing respective fibers (6, 6') and assembled by an assembling unit (7). The layers (5) are formed by a non woven material. A part (6A) of the fibers (6) cooperates with the material of the layer (5') and forms the unit. The fibers are selected from refractory ceramic fibers, bisoluble fibers, glass fibers, silica fibers or polycrystalline fibers. The web includes heat insulation material formed by vermiculite particles or glass/silica beads. An independent claim is also included for a method for fabricating a web for maintaining an active element with respect to an envelope of an exhaust element.

Description

The invention relates to an exhaust element for a gas exhaust line of a motor vehicle with a combustion engine. This invention relates to the field of the automotive industry and, more particularly, that of the manufacture of equipment to ensure the escape of gases from the combustion of a fuel within an internal combustion engine. Such equipment is in the form of an exhaust line connected to this engine and having a plurality of exhaust elements, succeeding each other along this exhaust line in accordance with the direction of flow of the gases in question. its breast, and connected to each other by exhaust tubes. In this regard, it will be observed that such an exhaust element may, in fact, be constituted by a catalyst or by a particulate filter. In the usual way, such an exhaust element comprises, on the one hand, an envelope in the form of a tube or an assembly of two half-shells.

On the other hand, this exhaust element comprises an active gas treatment element, in particular in the form of a substrate, and implanted inside the envelope. This exhaust element also has a so-called canning web, designed to maintain the active element relative to the envelope. In fact, such a sheet may be of the intumescent type and contain particles (more particularly vermiculite) having the property of expanding with temperature. However, such a sheet has the disadvantage of ensuring limited maintenance at low temperatures (200 to 400 ° C) and at high temperature (above 850 °). Such a sheet may, again, be made based on long ceramic fibers which have good low and high temperature resilience properties but whose cost is particularly high.

In order to overcome these drawbacks, it has been imagined multilayer plies constituted by a superposition of layers including, in particular, a first layer containing long ceramic fibers and a second layer containing an intumescent material as well as fibers of a different nature. . In this regard, it will be observed that, to ensure the cohesion of such a sheet, these layers are, in fact, assembled by means of an adhesive (usually organic type) which allows for a chemical type of assembly but which generates, however, new disadvantages. Thus and under the effect of temperature, this glue no longer ensures the assembly of these layers that dissociate. The sheet thus presents a risk of delamination jeopardizing the maintenance of the active gas treatment element so that, at the outlet of the exhaust element, at least part of the exhaust gas is not treated. In addition, the heat causes combustion of this glue generating combustion products that are often toxic and can lead to poisoning of the lambda probe used to control the effectiveness of the catalyst. The present invention is intended to overcome the disadvantages of devices of the state of the art. For this purpose, the invention relates to an exhaust element for the gas exhaust line of a motor vehicle with a combustion engine and comprising, on the one hand, a casing, on the other hand, an active element for the treatment of exhaust gas disposed inside this casing and, secondly, a web for holding the active element relative to the casing, this holding web being at least constituted by a superposition of at least two layers containing fibers and assembled by means of assembly means. Such an exhaust element is characterized in that at least one of the fibrous layers of the holding ply consists of a nonwoven material containing fibers, part of which, on the one hand, cooperates with the material of at least one other layer containing fibers and, on the other hand, constitutes the assembly means of these two layers. Another feature of the invention consists in that the two layers consist of a nonwoven material containing fibers and that part of the fibers of each layer, on the one hand, cooperates with the material of the other layer and on the other hand, constitutes the assembly means of these two layers. Yet another characteristic relates to the fact that, on the one hand, a layer is constituted by a woven material containing fibers and, on the other hand, the other layer is constituted by a nonwoven material containing fibers, a part of which constitutes the assembly means and cooperates by hooking with the fibers of the layer of woven material.

An additional feature is that the cooperation of the fibers of a layer constituting the assembly means with the fibers of another layer is made by needling. According to another characteristic, the holding ply further comprises at least one intumescent material and / or at least one thermal insulation material interposed between two layers, containing fibers, and assembled via said assembly means. An additional feature is that the assembly means are grouped together by bundles of fibers and / or portions of fibers, spaced apart from each other, preferably regularly or arranged in accordance with a matrix. The invention also relates to an exhaust element consisting, as the case may be, of a catalyst or a particulate filter. In addition, the invention relates to an exhaust line comprising such an exhaust element. Finally, the invention relates to a method of manufacturing a web for maintaining an active element for treating the exhaust gases with respect to an envelope of such a gas exhaust element that comprises a line exhaust gas of a motor vehicle with a combustion engine. This method consists in producing, on the one hand, a superposition of at least two layers each consisting of a material containing fibers and, on the other hand, an assembly of at least two of these layers. This method is characterized in that the assembly of two fibrous layers is achieved by ensuring the cooperation of a portion of the fibers of at least one layer formed by a nonwoven material with the material of the other layer.

An additional feature of this process consists in introducing at least one intumescent material, at least partly consisting of vermiculite, and / or at least one material of at least two fibrous layers of the web. thermal insulation, in particular at least partly constituted by air, vermiculite particles, glass beads and / or silica beads. The advantages of the present invention consist in that the assembly of the layers of a holding ply is carried out using the material used in the actual composition of the layers of this ply. This advantageously makes it possible to avoid resorting to an additional element (glue layer) requiring an additional step for its installation. This also makes it possible to avoid the use of an external material (organic glue) liable to undergo damage. On the contrary and advantageously, the assembly of the layers of the holding ply is ensured by making use of the constituent material of these layers, this material being specifically chosen so as not to undergo any degradation under the normal conditions of use of the element. exhaust which allows, advantageously, the realization of a perennial assembly. The assembly of the layers of a holding ply is made mechanically and by hooking, or even entanglement, fibers of a layer with the fibers of another layer, which advantageously makes it possible to reinforce the connection between these layers. two layers and improve the shear strength between these layers. Another advantageous feature is that it is possible to interpose, between two fibrous layers assembled, at least one intumescent material and / or at least one thermal insulation material. In this regard, it will be observed that such a material is introduced between two fibrous layers by injection. Advantageously, such an injection is facilitated by an implantation of the assembly means in the form of regularly spaced beams. Another advantage is that such a material can be implanted or introduced between two fibrous layers without requiring its attachment because its maintenance, within the web, is ensured by the assembly of the fibrous layers of the latter. Another advantage is that the presence of an insulating-type material makes it possible to use a fibrous layer, oriented toward the envelope or in contact therewith, and containing fibers whose thermal insulation performance may be lower than in the absence of such an insulating material. This allows, advantageously, to use, for such a fibrous layer, lower quality fibers and, therefore, lower cost. Other objects and advantages of the present invention will become apparent from the following description relating to embodiments which are given by way of indicative and non-limiting examples. The understanding of this description will be facilitated with reference to the accompanying drawings in which: - Figure 1 is a schematic and sectional view of an exhaust element according to the invention; - Figure 2 is a schematic sectional view of a holding web according to a first embodiment of the invention; - Figure 3 is a similar view to the previous corresponding to a holding web according to a second embodiment of the invention. The present invention relates to the field of the automotive industry and, more particularly, that of the manufacture of equipment to ensure the escape of gases from the combustion of a fuel within an internal combustion engine. Such equipment is in the form of an exhaust line connected to this engine, more particularly through a connection means that includes this exhaust line and which is usually constituted by a collector or the like . This exhaust line comprises, again, a plurality of exhaust elements 1, succeeding each other along this exhaust line in accordance with the direction of the flow of the gases in it, and connected to each other by tubes of 'exhaust. In this regard, it will be observed that such an exhaust element 1 may, in fact, be constituted by a catalyst, a particulate filter, a silencer or other. In the usual manner and as can be seen in FIG. 1, such an escapement element 1 comprises, on the one hand, an envelope 2 in the form of a tube (for example of the crimped rolled, flow-wrapped or other type) or of an assembly of two half-shells. On the other hand, this exhaust element 1 comprises, implanted inside said casing 2, an active element 3 of gas treatment. Such an active element 3 is usually in the form of a substrate designed to provide a treatment of the exhaust gas, or even particles contained in these gases. In this regard, it will be observed that such a substrate may consist of a catalyst, a particulate filter or a silencer to ensure a treatment consisting, respectively, in a chemical, physical or sound depollution of these gases.

This exhaust element 1 furthermore comprises a ply 4, usually called a canning ply, and designed to maintain the active element 3 with respect to the casing 2.

As can be seen in the appended figures, such a holding ply 4 is constituted by a superposition of at least two layers 5, 5 'each containing fibers 6, 6' and assembled by means of assembly means 7. According to the invention, at least one of the layers (5, 5 ') of this holding ply 4 consists of a non-woven material containing fibers 6, a part 6A of which, on the one hand, cooperates with the material of at least one other layer 5 'also containing fibers 6' and, on the other hand, constitutes the means 7 for assembling these two layers (5, 5 ').

FIG. 2 shows a first embodiment corresponding to a holding ply 4 comprising: a layer 5 constituted by a nonwoven material and containing fibers 6 (nonwoven); a layer 5 'constituted by a woven material and containing fibers 6' (at least a part of which, all, is woven). In such a case, the assembly means 7 are constituted by a portion 6A of the fibers 6, on the one hand, which contains the fibrous layer 5 constituted by a nonwoven material and, on the other hand, which cooperates with the fibers 6 'of the fibrous layer 5' constituted by a woven material. In this regard and as visible in this same Figure 2, such cooperation is provided by attachment of the fibers 6A of the nonwoven layer 5 with the fibers 6 'of the woven layer 5'. FIG. 3 shows a preferred embodiment of the invention corresponding to a holding ply 4 comprising two layers (5, 5 ') each constituted by a nonwoven material and containing fibers (6, 6'). ). In such a case, the assembly means 7 of these two layers (5; 5 ') are constituted by a portion (6A; 6'A) of the fibers (6; 6') of each layer (5; 5 '). ) which cooperates with the material of the other layer (5 '; 5). In this respect and as can be seen in FIG. 3, this cooperation is ensured by entanglement and / or by attachment of the fibers (6A, 6'A) of a layer (5; 5 ') with the fibers (6'A, 6'). 6A, 6) of the other layer (5 '; 5). According to another characteristic of the present invention, the cooperation of the fibers (6A; 6'A) of a layer (5; 5 ') constituting the assembly means 7 with the fibers (6'A, 6'; 6A, 6) of another layer (5 '; 5) is made by needling, regardless of the fibrous material (woven or non-woven) of this other layer (5', 5). As mentioned above, such a holding ply 4 may comprise a layer 5 constituted by a fibrous material of the nonwoven type. In this connection, it will be observed that, in such a case, the fibers 6 contained in such a layer 5 of nonwoven material consist of polycrystalline fibers, refractory ceramic fibers or biosoluble fibers.

Another characteristic is that such a holding ply 4 may comprise a layer 5 constituted by a fibrous material, as the case may be, of woven or non-woven type. In such a case, the fibers 6 contained in such a layer 5 of woven material or nonwoven material are constituted by refractory ceramic fibers, biosoluble fibers, glass fibers or silica fibers. As mentioned above, the exhaust element 1 comprises, on the one hand, a casing 2, on the other hand, an active element 3 for treating gases and, on the other hand, a sheet of maintaining 4 interposed between this envelope 2 and this active element 3. In this regard, it will be observed that this holding ply 4 comprises, then, on the one hand, an inner layer in contact with the active element 3 and, on the other hand, part, an outer layer in contact with the envelope 2.

According to the invention, said inner layer is then made of a nonwoven material while said outer layer is made, as the case may be, of a woven material or, preferably, a nonwoven material.

In this regard and according to an additional feature of the present invention, at least the inner layer (which comprises the holding ply 4 and which is in contact with the active element 3) is made of a non-woven material containing polycrystalline fibers. , refractory ceramic fibers or biosoluble fibers. In such a case and according to a preferred embodiment of the invention, this inner layer as well as the outer layer (which comprises the holding ply 4 and which is in contact with the envelope 2) are both realized. a nonwoven material containing polycrystalline fibers, refractory ceramic fibers or biosoluble fibers. According to another characteristic of the invention, this outer layer (which comprises the holding ply 4 and which is in contact with the casing 2) can be made, as the case may be, of a woven or non-woven material containing fibers refractory ceramics, biosoluble fibers, glass fibers or silica fibers. Also and according to a particularly advantageous embodiment of the invention, on the one hand, the inner layer is made of a nonwoven material containing polycrystalline fibers, refractory ceramic fibers or biosoluble fibers and on the other hand the outer layer is made, as the case may be, of a woven or non-woven material containing refractory ceramic fibers, biosoluble fibers, glass fibers or silica fibers. As mentioned above, the holding ply 4 is at least constituted by a superposition of at least two layers 5, 5 'fibrous. However, according to an additional feature of the present invention, such a holding ply 4 may, again, comprise at least one intumescent material and / or at least one thermal insulation material interposed between two layers (5, 5 ') containing fibers (6, 6 '), these fibrous layers (5, 5') being joined together (5, 5 ') by means of said joining means 7.

This or these materials are, in fact, an intermediate layer 8 interposed between two fibrous layers (5, 5 '). In this regard, it will be observed that such a material can be of the intumescent type and is at least partly constituted by vermiculite or the like.

When such a material is of thermal insulation type, it is then at least partly constituted by air, vermiculite particles, glass beads and / or silica beads. In this regard, it will be observed that the implantation, between two fibrous layers (5, 5 '), of a thermal insulation material advantageously makes it possible to use a fibrous layer, oriented towards the envelope 2 or in contact with the latter 2, and containing fibers 6 whose thermal insulation performance may be lower than those 6 which would be necessary in the case of a holding ply 4 without an intermediate insulation layer 8. Another feature of the invention consists in that the assembly means 7 are grouped together by bundles 9 of fibers (6, 6 ') and / or portions (6A; 6'A) of fibers (6, 6'). as shown in FIGS. 2 and 3. Such bundles 9 extend substantially perpendicular to the fibrous layers (5, 5 ') and are spaced from each other, preferably in a regular manner. In fact and according to a preferred embodiment, these bundles 9 of fibers (6, 6 ') are arranged in accordance with a matrix, in particular square or rectangular. In this regard, it will be observed that these bundles 9 of fibers (6, 6 ') or portions of fibers (6, 6') have, between them, an interval allowing the injection of a material (intumescent and / or thermal insulation) between, on the one hand, the fibrous layers (5, 5 ') and, on the other hand, the bundles 9.

As mentioned above, the present invention also relates to an exhaust element 1 comprising an envelope 2, an active element 3 and a holding ply 4 having the characteristics described above.

In this regard, it should be noted that such an exhaust element 1 may then consist of a pollution control element comprising an active element 3 for treating the exhaust gas constituted by a catalyst. In such a case and for a fuel-driven thermal engine, the holding ply 4 of the active element 3 comprises, on the one hand, an (internal) layer consisting of a non-woven material, in contact with the catalyst, and containing refractory polycrystalline or ceramic fibers and, on the other hand, an (outer) layer consisting of a nonwoven material, in contact with the casing 2, and containing biosoluble fibers or silica. However, and in the case of a diesel engine fueled, such a holding ply 4 of the active element 3 may comprise, on the one hand, an (internal) layer consisting of a nonwoven material, in contact with the catalyst, and containing polycrystalline fibers, refractory ceramics or even biosoluble and, secondly, an (outer) layer consisting of a nonwoven material, in contact with the casing 2, and containing biosoluble fibers, silica, or even glass. Said exhaust element 1 may, again, be constituted by a pollution control element comprising an active element 3 for treating exhaust gases constituted by a particulate filter.

In such a case and for a fuel-driven thermal engine, the holding ply 4 of the active element 3 comprises, on the one hand, an (internal) layer consisting of a non-woven material, in contact with the particulate filter. and containing refractory polycrystalline or ceramic fibers and, on the other hand, an (outer) layer consisting of a nonwoven material, in contact with the casing 2, and containing biosoluble fibers or silica. However, and in the case of a diesel engine fueled, such a holding ply 4 of the active element 3 may comprise, on the one hand, an (internal) layer consisting of a nonwoven material, in contact with the particulate filter, and containing polycrystalline fibers, refractory ceramics, biosoluble or silica and, secondly, an (outer) layer consisting of a nonwoven material, in contact with the casing 2, and containing polycrystalline fibers, Refractory ceramics, biosoluble, silica, or glass. As mentioned above, the invention also relates to a gas exhaust line of a motor vehicle with a combustion engine comprising, on the one hand, a connecting means (collector) of this exhaust line. to the engine and, on the other hand, at least one exhaust element 1. In this regard, it will be observed that such an exhaust line may comprise an exhaust element 1 positioned near the connecting means and constituted, more particularly, by a catalyst. In such a case, the holding ply 4 of the active gas treatment element 3 comprises, on the one hand, an (internal) layer consisting of a nonwoven material, in contact with the active element 3, and containing refractory polycrystalline or ceramic fibers (or even biosoluble fibers for a motor fueled with gas oil) and, on the other hand, a layer constituted by a nonwoven material, in contact with the casing 2, and containing biosoluble fibers or silica (or even glass fibers for a motor fueled with gas oil). However, such an exhaust line may also include an exhaust element 1 positioned at a distance from the connecting means along this exhaust line. Such positioning corresponds, more particularly, to an implantation of such an exhaust element 1 under the floor of the vehicle.

In such a case, the holding ply 4 of the active gas treatment element 3 comprises, on the one hand, an (internal) layer consisting of a nonwoven material, in contact with the active element, and containing biosoluble fibers or silica and, secondly, a layer (outer), in contact with the casing 2, consisting of a woven material or (and preferably) non-woven and containing silica or glass fibers. The invention also relates to a method of manufacturing such a holding ply 4. In a manner known per se, this method consists in producing, on the one hand, a superposition of at least two layers (5, 5). ') each consisting of a fiber-containing material (6, 6') and, on the other hand, an assembly of at least two of these layers (5, 5 '). According to the invention, this method consists, then, in that the assembly of two fibrous layers (5, 5 ') is achieved by ensuring the cooperation of a portion (6A, 6'A) of the fibers (6; at least one layer (5; 5 ') of non-woven material with the material of the other layer (5'; 5). In fact and according to the first embodiment described above, the assembly of a layer 5 constituted by a nonwoven material with a layer 5 'constituted by a woven material is achieved by ensuring a fastening of a portion 6A of fibers 6 of the layer 5 of nonwoven material with part of the fibers 6 'of the layer 5' of woven material, preferably by needling. However, and according to a preferred embodiment of the invention consisting in assembling two layers (5, 5 ') each consisting of a nonwoven material containing fibers (6, 6'), the assembly of these two layers (5, 5 ') is achieved by entangling and / or catching a portion (6A, 6'A) of the fibers (6, 6') of a layer (5, 5 ') with a portion ( 6'A, 6', 6A, 6) of the fibers (6 ', 6) of the other layer (5', 5), preferably by needling.

Another feature mentioned above is that the holding ply 4 further comprises at least one intumescent material and / or at least one thermal insulation material interposed between two layers (5, 5 ') containing fibers. and assembled by means of said assembly means 7. In this regard, it will be observed that the presence of such a material (intumescent and / or thermal insulation) is ensured during a step of the manufacturing process of the holding ply 4 consisting in introducing (preferably by injection) between at least two fibrous layers (5, 5 ') of the ply 4: - at least one intumescent material, in particular at least partly constituted by vermiculite; at least one thermal insulation material, in particular at least partly constituted by air, vermiculite particles, glass beads and / or silica beads. As mentioned above, the assembly means 7 consist of fibers (6, 6 ') and / or portions (6A; 6'A) of fibers (6, 6') grouped together in bundles 9. These bundles 9 are spaced from each other, preferably regularly, or arranged in accordance with a matrix. In this regard, it will be observed that these bundles 9 of fibers (6, 6 ') or portions of fibers (6, 6') have, then, between them, an interval allowing, advantageously, the injection of a material (intumescent and / or thermal insulation) between the fibrous layers (5, 5 ') and the bundles 9.

Claims (18)

An exhaust element (1) for the exhaust gas line of a motor vehicle with a combustion engine and comprising, on the one hand, an envelope (2), on the other hand, an active element (3) of treatment of the exhaust gases disposed inside this envelope (2) and, secondly, a web (4) for maintaining the active element (3) relative to the envelope (2) , said holding ply (4) being at least constituted by a superposition of at least two layers (5; 5 ') containing fibers (6; 6') and assembled by means of assembly means (7), characterized in that at least one of the fibrous layers (5; 5 ') of the holding ply (4) consists of a non-woven material containing fibers (6; 6') of which a portion (6A; 6 'A), on the one hand, cooperates with the material of at least one other layer (5'; 5) containing fibers (6 '; 6) and, on the other hand, constitutes the connecting means (7); ) of these two layers (5; 5 '). 2. Exhaust element (1) according to claim 1, characterized in that the two layers (5; 5 ') are constituted by a nonwoven material containing fibers (6; 6') and a part (6A, 6'A) fibers (6; 6 ') of each layer (5; 5'), on the one hand, cooperates with the material of the other layer (5 '; 5) and, on the other hand on the other hand, constitutes the assembly means (7) of these two layers (5; 5 '). 3. Exhaust element (1) according to claim 2, characterized in that the cooperation of the fibers (6A; 6A ') of a layer (5; 5') with the material of another layer (5 '). 5) is made by entangling and / or hooking the fibers (6A; 6'A) of a layer (5; 5 ') with the fibers (6'A, 6'; 6A, 6) of the other layer (5 ', 5). 4. Exhaust element (1) according to claim 1, characterized in that on the one hand, a layer (5 ') is formed by a woven material containing fibers (6') and, on the other hand, the other layer (5) consists of a non-woven material containing fibers (6), part of which (6A) constitutes the assembly means (7) and cooperates by engagement with the fibers (6 ') of the layer ( 5 ') of woven material. 5. Exhaust element (1) according to any one of the preceding claims, characterized in that the cooperation of the fibers (6A; 6'A) of a layer (5; 5 ') constituting the assembly means (7) with the fibers (6'A, 6 '; 6A, 6) of another layer (5 '; 5) is made by needling. 6. Exhaust element (1) according to any one of the preceding claims, characterized in that the fibers (6; 6 ') contained in a layer (5) of woven material or a layer (5; 5') nonwoven material are refractory ceramic fibers, biosoluble fibers, glass fibers or silica fibers. 7. Exhaust element (1) according to any one of claims 1 to 5, characterized in that the fibers (6; 6 ') contained in a layer (5; 5') of nonwoven material are constituted by polycrystalline fibers, refractory ceramic fibers or biosoluble fibers. 8. Exhaust element (1) according to any one of the preceding claims, characterized in that the holding ply (4) comprises, on the one hand, an inner layer in contact with the active element (3) and made of a nonwoven material and, on the other hand, an outer layer in contact with the wrapper (2) and made, as the case may be, of a woven material or, preferably, a nonwoven material . 9. Exhaust element (1) according to claim 8, characterized in that at least the inner layer, which comprises the holding ply (4) and which is in contact with the active element (3), is made of a nonwoven material containing polycrystalline fibers, refractory ceramic fibers or biosoluble fibers. 10. Exhaust element (1) according to any one of claims 8 or 9, characterized in that the outer layer, which comprises the holding ply (4) and which is in contact with the casing (2) is made, as the case may be, of a woven or non-woven material containing refractory ceramic fibers, biosoluble fibers, glass fibers or silica fibers. 11. Exhaust element (1) according to any one of the preceding claims, characterized in that the holding ply (4) further comprises at least one intumescent material and / or at least one thermal insulation material. interposed between two layers (5; 5 '), containing fibers (6; 6'), and assembled through said connecting means (7). 12. Exhaust element (1) according to claim 11, characterized in that the intumescent material is at least partly constituted by vermiculite or the like. 13. Exhaust element (1) according to claim 11, characterized in that the thermal insulation material is at least partly constituted by air, vermiculite particles, glass beads and / or silica beads. 14. Exhaust element (1) according to any one of the preceding claims, characterized in that the assembly means (7) are grouped together by bundles (16) of fibers (6; 6 ') and / or portions (6A, 6'A) of fibers (6; 6 '), spaced from one another, preferably regularly, or arranged in accordance with a matrix. 15. A method of manufacturing a web (4) for maintaining an active element (3) for treating the exhaust gases with respect to an envelope (2) of an exhaust element (1) of the gases comprising a gas exhaust line of a motor vehicle with a heat engine, which method consists in producing, on the one hand, a superposition of at least two layers (5; 5 ') each consisting of a material containing fibers (6; 6 ') and, on the other hand, an assembly of at least two of these layers (5; 5'), characterized in that the assembly of two layers (5; 5 ') fibrous is made by ensuring the cooperation of a portion (6A; 6'A) of the fibers (6; 6 ') of at least one layer (5; 5') constituted by a nonwoven material with the material of the other layer (5 ', 5). 16. Manufacturing method according to claim 15, characterized in that the assembly of two layers (5; 5 ') each constituted by a nonwoven material containing fibers (6; 6') is produced by ensuring entanglement and / or attachment of a portion (6A, 6'A) of the fibers (6; 6 ') of a layer (5; 5') with a portion (6'A, 6 '; 6A, 6a) ) fibers (6 '; 6) of the other layer (5'; 5), preferably by needling. 17. The manufacturing method according to claim 15, characterized in that the assembly of a layer (5) constituted by a nonwoven material with a layer (5 ') constituted by a woven material is achieved by ensuring a hooking a portion (6A) of the fibers (6) of the layer (5) of nonwoven material with a portion of the fibers (6 ') of the layer (5') of woven material, preferably by needling. 18. Manufacturing process according to any one of claims 15 to 17, characterized in that at least two fibrous layers (5; 5 ') of the ply (4) are introduced with at least one intumescent material. , in particular at least partly constituted by vermiculite, and / or at least one thermal insulation material, in particular at least partly constituted by air, vermiculite particles, glass beads and / or balls of silica.