WO2019053343A1

WO2019053343A1 - Assembly comprising a thin-walled exhaust line and a stiffening structure, and vehicle equipped with such an assembly

Info

Publication number: WO2019053343A1
Application number: PCT/FR2017/052430
Authority: WO
Inventors: Jean Lagier; Xavier Bartolo; Frédéric Greber; Frédéric BLANCO-SOTELO
Original assignee: Faurecia Systemes D'echappement
Priority date: 2017-09-12
Filing date: 2017-09-12
Publication date: 2019-03-21

Abstract

The assembly (1) comprises: – an exhaust line (3) comprising an upstream part (7) fixed rigidly to a powertrain (9), and a downstream part (11) fixed directly or indirectly to the bodyshell (13) of a vehicle, the upstream and downstream parts (7, 11) being coupled together by an uncoupler (15), the downstream part (11) having a determined developed length, the downstream part (11) having an external wall (28) made of a metallic material of a thickness smaller than 0.3 mm over at least 50% of the developed length thereof; – a stiffening structure (5) extending over at least 50% of the developed length of the downstream part (11), the downstream part (11) being fixed to the stiffening structure (5).

Description

Assembly comprising a thin-walled exhaust line and a stiffening structure, vehicle equipped with such a set

The invention generally relates to reducing the mass of vehicle exhaust lines.

All motor vehicle manufacturers are currently seeking to reduce the mass of their vehicles, in order to reduce fuel consumption and C0 ₂ emissions. They therefore ask the equipment manufacturers to reduce the weight of each system of the vehicle.

For the exhaust lines, the reduction in weight was achieved in the past by decreasing the wall thickness of the exhaust gas ducts and the main components of the line. Currently, it is envisaged to use sheets with a thickness of 0.8 mm for the ducts, and a thickness of 0.6 mm for the silencers.

It is difficult to fall below these thicknesses, because this would induce extremely troublesome side effects:

- Increase of the noise transmitted through the walls, especially on the volumes of the silent type. Indeed, the wall thickness becomes too thin to absorb the sounds transmitted through the material.

- Reduced resistance to mechanical stresses from the engine or resulting from the movement of the vehicle on the road. The material is too thin to absorb or withstand such stresses.

- Resistance to corrosion: because of the thinness of the walls, corrosion can quickly cause holes in the components of the exhaust line.

- Damage during the handling of the exhaust line: the components of the line are too fragile to be handled by hand.

In this context, the invention aims to provide an exhaust line whose weight is reduced drastically, and that allows to solve all or part of the technical problems mentioned above.

To this end, the invention relates to an assembly comprising:

an exhaust line comprising an upstream portion rigidly attached to a powertrain and a downstream part fixed directly or indirectly to the body of a vehicle, the upstream and downstream parts being connected to each other by a decoupler, the downstream portion having a determined developed length, the downstream portion having an outer wall of a metal material less than 0.3 mm thick over at least 50% of its developed length; a stiffening structure extending over at least 50% of the developed length of the downstream part, the downstream part being fixed to the stiffening structure.

The use of a metal material with a thickness of less than 0.3 mm over a large part of the downstream part of the exhaust line makes it possible to drastically reduce the mass of the exhaust line.

The stiffening structure allows conveniently moving the exhaust line before it is attached to the vehicle. It also conveniently fixes the exhaust line on the vehicle. Indeed, it is the stiffening structure itself which is attached to the vehicle and not the exhaust line.

The set may also have one or more of the following characteristics, considered individually or in any technically feasible combination:

the downstream part comprises treatment members, exhaust gases and exhaust gas circulation conduits fluidly connected to the treatment members, the circulation ducts having a determined cumulative length, the circulation ducts having an external wall; in a metallic material of thickness less than 0.3 mm on at least 50% of the cumulative length;

the downstream part comprises a layer of thermal and / or acoustic insulation, covering the outer wall for at least 50% of the developed length;

- The downstream part is fixed to the stiffening structure by fasteners, the insulating layer being interposed between the fasteners and the outer wall;

the metallic material is a stainless steel or a titanium alloy;

the downstream part comprises an upstream end connected by the decoupler to the upstream part, the upstream end being rigidly fixed to the stiffening structure by a fastening sized to take up the weight of the upstream end and the tilting forces of the power unit ;

- The downstream portion extends in a predetermined plane and comprises at least one exhaust gas flow conduit, connected to the stiffening structure by a rigid connection in a direction substantially perpendicular to said determined plane, but allowing a displacement in said determined plan;

the downstream part comprises at least two exhaust gas treatment elements and an exhaust gas circulation duct fluidly connecting the two treatment elements to each other, an additional decoupler being inserted between the two organs treatment along the circulation duct;

the stiffening structure is below the exhaust line; the stiffening structure is a plate;

the plate has at least one ventilation opening;

the stiffening structure consists of more than 80% by volume of composite material;

- The stiffening structure further supports son or pipe connecting probes, sensors and / or organs together or with a vehicle.

According to a second aspect, the invention relates to a vehicle comprising a body and an assembly having the above characteristics, the stiffening structure being fixed to the body.

Furthermore, the vehicle may be such that the body defines a tunnel open downwards in which extends the exhaust line, the stiffening structure being a plate closing the tunnel.

Other features and advantages of the invention will emerge from the detailed description given below, for information only and in no way limitative, with reference to the appended figures among which:

- Figure 1 is a simplified schematic representation, seen from below, a vehicle equipped with the assembly of the invention, the stiffening structure is not shown to reveal the exhaust line;

- Figures 2 and 3 are top and side views of an assembly according to the invention, only the downstream portion of the exhaust line being shown;

- Figure 4 is a simplified sectional representation of all of Figures 2 and 3 mounted in the vehicle tunnel;

- Figures 5 to 8 schematically illustrate different assembly modes of components of the exhaust line;

- Figures 9 to 1 1 illustrate different embodiments of the stiffening structure of the assembly of the invention;

- Figures 12 to 16 illustrate various means for limiting heat transfer from the exhaust line to its environment; and

- Figures 17 to 19 illustrate various means for limiting the noise transmitted through the components of the exhaust line.

The invention relates to an assembly 1 comprising, as illustrated in Figures 1 to 3, an exhaust line 3 and a stiffening structure 5 (see Figures 2 and 3).

The exhaust line 3 comprises, in a conventional manner, an upstream portion 7 rigidly attached to a power unit 9, and a downstream portion 1 1 fixed directly or indirectly to the body 13 of the vehicle (Figure 1). The upstream and downstream parts 7, 1 1 are connected to each other by a decoupler 15.

The upstream and downstream parts 7, 1 1 are frequently designated respectively by the terms hot part and cold part.

The upstream portion 7 typically comprises a manifold 17 which captures the exhaust gases exiting the combustion chambers of the power unit 9, and a plurality of processing members such as a turbocharger 19, or gas purification members. exhaust 21.

The decoupler 15 connects a downstream end 23 of the upstream portion 7 to an upstream end 25 of the downstream portion 1 January.

In a known manner, it makes it possible to absorb part of the vibrations transmitted between the upstream part 7 and the downstream part 1 1 of the exhaust line 3, and to absorb part of the thermal expansion and movements of the line exhaust 3.

The invention is based on the observation that, in a conventional exhaust line, all the functions of the downstream part of the exhaust line are provided by the same components.

The downstream part 1 1 performs the following two main functions:

driving the exhaust gas emitted by the engine to the cannulas 27 for release into the atmosphere;

- reduce the noise emitted by the exhaust gases.

The downstream part 1 1 of the exhaust line 3 also provides the following secondary functions:

managing the heat emitted by the exhaust line 3 towards the other components of the vehicle;

- manage the noise transmitted through the walls;

- withstand mechanical stresses from the motor or external sources;

resist the thermal expansion of the exhaust line 3;

- Allow the handling of the exhaust line 3 during its entire life cycle.

According to the invention, these different functions are provided by different members, which are specially designed to minimize the total weight of the assembly 1.

Firstly, the downstream part 1 1 of the exhaust line 3 is provided with an outer wall 28 of a metal material with a thickness of less than 0.3 mm, over at least 50% of its developed length. The length developed corresponds to the length of the downstream part 1 1 when one follows it from its upstream end 25 to the cannula or tubes 27. When the downstream part 1 1 has several sections arranged in parallel, the lengths are added developed parallel sections. In the example of FIG. 1, the exhaust line 3 comprises two downstream end sections 29 arranged in parallel, ranging from the silencer 31 to the cannulas 27. For the calculation of the developed length of the downstream part 1 1, add up the developed lengths of the two sections 29.

In other words, the developed length of the downstream part 1 1 corresponds to the total length that would have the downstream part 1 1 if all its components were straightened to adopt a rectilinear shape, and if all the components placed in parallel were placed end to end in the extension of each other.

The outer wall 28 considered here is the outermost exhaust gastight wall of the component. When the component is double-walled, with an inner wall and an outer wall, the outer wall is considered here. When the component comprises a layer of thermally insulating material or acoustically insulating, this layer is not considered as the outer wall.

Preferably, the downstream portion 1 1 has an outer wall 28 with a thickness of less than 0.3 mm over at least 70%, more preferably 90% of its developed length.

Typically, the downstream portion 1 1 comprises exhaust gas treatment members, and exhaust gas flow conduits fluidly connected to the treatment members.

The processing members are, for example, silencers such as silencers 31 and 33 shown in FIG. As a variant, they comprise, in addition to or instead of silencers 31, 33, a heat exchanger, an energy recuperator, one or more exhaust gas purifying members or any other suitable organ.

The circulation ducts are in any number. They are arranged in series or in parallel. Some ducts, such as the upstream end portion 25, fluidly connect the decoupler 15 to an exhaust treatment unit, which is the silencer 33 in the example of FIG. Other ducts, here the downstream end sections 29, fluidly connect a treatment member to the cannulas 27, this treatment member being the silencer 31 in the example of FIG.

Still other conduits, such as the conduit 35, fluidly connect the treatment members to each other. Advantageously, an additional decoupler 36 is inserted along the conduit 35 connecting the two processing members 31, 33 to one another. This additional decoupler 36 is of any suitable type and makes it possible to absorb the thermal expansions of the downstream part 1 1.

Advantageously, the circulation ducts have an outer wall 28 of metal material with a thickness of less than 0.3 mm, over at least 50% of their accumulated developed length.

Preferably, the conduits have an outer wall 28 made of a metallic material having a thickness of less than 0.3 mm over at least 70% of their accumulated developed length, more preferably at least 90%.

Typically, the elbows 37 of the ducts have a thickness greater than 0.3 mm, and the rectilinear portions of the ducts have a thickness of less than 0.3 mm.

The outer wall 28 is preferably less than 0.2 mm thick, and even more preferably less than 0.1 mm thick, for all the components of the downstream part 1 1.

The metallic material is preferably a stainless steel or a titanium alloy.

For example, the metallic material is an alloy of grades 1 .4404 or 1 .4571.

Due to the fineness of the material used to form the various components of the downstream part 1 1, it is not possible to use for the assembly of the various components to each other, or for the manufacture of each component individually, conventional welding processes such as TIG or MAG processes.

These methods are generally used for:

- weld to one another the two edges of a welded rolled sheet;

- Securing to one another different elements of the same component, for example two half-shells, or end cups with a tubular wall;

- Solder to each other ducts and exhaust gas treatment members.

In the exhaust line 3 of the invention, the assemblies mentioned above are made by one or the other of the following methods:

welding with a laser welding head 34 (FIG. 5);

- chemical assembly, for example by glue lines 38 (Figure 6);

brazing (FIG. 7);

- stapling (Figure 8);

- fitting. These different assembly methods are well adapted to walls made of an extremely thin material.

In the invention, the exhaust line 3 provides the two main functions mentioned above, namely to drive the exhaust gases to the cannulas 27, and reduce the noise produced by the exhaust gas. In addition, the choice of material makes it possible to limit corrosion.

The stiffening structure 5 extends over at least 50% of the developed length of the downstream portion 11, preferably at least 75% and more preferably at least 90% of the developed length.

The downstream part 1 1 is fixed to the stiffening structure 5.

The stiffening structure 5 is typically placed below the exhaust line 3. In other words, it is interposed between the exhaust line 3 and the running surface of the vehicle.

According to a first exemplary embodiment, illustrated in FIGS. 2 to 4, the stiffening structure 5 is a plate.

Advantageously, it consists of more than 80% by volume of a composite material. As a variant, the stiffening structure 5 is not made of a composite material but is made of a metallic material, for example of the same type as the components of the downstream part 1 1 of the exhaust line 3, or else light alloy such as an aluminum alloy or magnesium.

The use of a plate 5 is particularly advantageous because it reduces the C _x of the vehicle, as described below.

The plate 5 has any suitable shape. Typically, its shape is chosen so that, seen in projection in a direction perpendicular to the running surface of the vehicle, the exhaust line 3 is located entirely at the right of the plate 5, without any part projecting laterally beyond the plate 5 except possibly cannulas 27.

The plate 5 is typically a solid plate.

The plate 5 preferably has openings to allow heat removal, as described below. Alternatively, it is without opening.

According to another variant embodiment, the plate 5 is made in the form of a lattice of metal wires 39, as illustrated in FIG. 9.

According to another variant embodiment, the stiffening structure 5 is not in the form of a plate but in the form of an external skeleton. he then typically comprises bars or tubes, of metal or composite material, such as the bars 41 shown in Figure 10, rigidly fixed to each other.

The bars 41 are arranged such that the exhaust line 3 can be fixed to the skeleton.

According to yet another alternative embodiment, the stiffening structure 5 has the shape of a box 43, receiving internally the exhaust line 3 (Figure 1 1). The box 43 is made of any suitable material: composite material, metallic material, wire mesh, etc.

It should be noted that the stiffening structure 5 may comprise a shield 44, to protect the exhaust line 3 external aggressions. This shield is for example fixed on one face of the stiffening structure 5 facing the running surface, as illustrated in FIG. 4. It is particularly useful when the stiffening structure 5 does not constitute a solid surface, protecting the line Escape 3 pebbles or any other projectiles that may come from the running surface.

The shield 44 is for example of a flexible material, for example a woven or non-woven material, a natural or artificial rubber, a resin or a special paint such as the blazon.

Alternatively, the shield 44 is a rigid material, for example stainless steel or composite material.

The upstream end 25 of the downstream part 1 1 is rigidly fixed to the stiffening structure 5 by a fastener 45, sized to take up the weight of the upstream end 25 and the tilting forces of the heat engine (FIGS. 2 and 3). .

Thus, the attachment 45 makes it possible to isolate the downstream part 1 1 from the mechanical stresses transmitted from the power unit 9 via the upstream part 7 of the exhaust line 3.

The attachment 45 is rigid, and leaves no degree of freedom at the upstream end 25 with respect to the stiffening structure 5.

In an exemplary embodiment, the upstream end 25 is a pipe inclined with respect to the stiffening structure 5. It extends from a point 47 connected to the decoupler 15 to a bend 49, the bend 49 being extended by a duct section 51 which is for example connected to the muffler 33. The point 47 is relatively more distant from the stiffening structure 5 than the bend 49.

The processing members of the downstream part 1 1 are rigidly fixed to the stiffening structure 5, without possible degree of freedom. In the example shown, they are fixed by straps 53. In a variant, the treatment members are rigidly attached to the stiffening structure 5 in a given direction, this determined direction being typically substantially perpendicular to the stiffening structure 5. On the other hand, a slight movement is possible in the plane perpendicular to the determined direction.

The ducts 29, 35, connecting to each other the components of the downstream part 1 1, with the exception of the upstream end 25, are connected to the stiffening structure 5 by the links 55. These links are of one different type of fastener 45.

The connection of each circulation duct to the stiffening structure 5 is rigid in the determined direction, but allows a displacement of the duct in the plane perpendicular to the determined direction.

Thus, the links 55 make it possible to manage the thermal expansion of the circulation ducts.

Such bonds are of any suitable type, including pads formed directly by the plate 5 such as for example a protrusion.

Thus, the stiffening structure 5 and the connections of the various components of the downstream part 1 1 to the stiffening structure 5 allow the exhaust line 3 to withstand the stresses from the engine or created by the rolling of the vehicle. They also make it possible to manage the thermal expansion of the exhaust line 3.

In order to limit heat transfers by conduction between the downstream part 1 1 of the exhaust line 3 and the stiffening structure 5, the connections 55 between the downstream part 1 1 and the stiffening member 5 advantageously comprise dedicated devices: fins , layers of thermally insulating material, etc.

These links 55 preferably also include devices for limiting the transmission of vibrations between the exhaust line 3 and the stiffening structure 5, for example springs or a layer of thermal insulating material.

The exhaust line 3 comprises means making it possible to reduce the skin temperature of the downstream part 1 1, and thus to limit the radiative and convective thermal transfers towards the other components of the vehicle and the stiffening structure 5.

For example, the downstream portion 1 1 comprises for this purpose a layer of a thermal insulator 57, covering the outer wall 28 over at least 50% of the developed length of the downstream portion 1 January. Preferably, the thermal insulation layer 57 covers the outer wall 28 over at least 75% of the developed length, more preferably on at least 90% of the developed length. Typically, the thermal insulation layer 57 covers the entire periphery of the outer wall 28 (see Figure 12). The thermal insulation layer 57 is made of a fibrous or microporous material. The fibrous material is for example silica fibers, keviar or ceramic. Preferably, it is made of silica fibers.

According to an alternative embodiment, the thermal insulating material is a paint

61, deposited on the outer wall 28 (see Figure 13). This paint contains for example gold particles, or a ceramic material.

According to yet another alternative embodiment, the downstream portion 1 1 is double skin, with an inner wall 63 in addition to the outer wall 28. The inner wall 63 and the outer wall 28 are separated from each other by an air gap 65, which can be filled with a thermally insulating material if necessary.

As shown in Figures 1, 4, 15 and 16, the box 13 defines a tunnel 67, open downwards, that is to say towards the running surface of the vehicle. At least a part of the exhaust line 3, and more particularly of the downstream part 1 1 of the exhaust line 3, is housed inside the tunnel 67.

Advantageously, the stiffening structure 5 is a plate arranged to close the tunnel 67 downwards, that is to say towards the running surface of the vehicle. In this case, so as to facilitate the lowering of the surface temperature of the exhaust line 3, the stiffening structure 5 preferably comprises ventilation openings 69 forming air intakes, so as to ensure a flow of air. inside the tunnel 67 (Figure 15).

The air intakes 69 may also be formed in the stiffening structure 5 when the exhaust line 3 is not arranged in the tunnel 67.

Alternatively, or in addition, the assembly 1 comprises one or more fans 71, arranged to create a flow of air in contact with the exhaust line 3 (Figure 16). This is particularly advantageous when the exhaust line 3 is housed in the tunnel 67.

The forced circulation of air can be started continuously or only in special situations, such as for example when the vehicle is stopped at toll or in slow motion extended when the vehicle stops, etc.

The assembly of the invention also advantageously comprises an acoustic insulation layer 73, covering the outer wall 28 over at least 50% of the developed length of the downstream portion 1 1 of the exhaust line 3 (Figure 17). Preferably, the acoustic insulating layer 73 covers at least 75% of the developed length, more preferably at least 90% of the developed length. This layer 73 allows reduce the noise passing through the outer wall 28. As seen in Figure 17, the layer of acoustic insulating material 73 extends over the entire periphery of the outer wall 28.

The layer 73 is made of a fibrous or microporous material. For example, this material is identical to that for achieving thermal insulation, a single layer of this material providing both thermal insulation and sound insulation.

Alternatively, the downstream portion 1 1 is double skin, with an inner wall 75 doubling the outer wall 28 (Figure 18). An acoustic insulating material 77 is disposed in the interstice separating the inner 75 and outer walls 28. This material is for example glass wool.

According to another alternative embodiment, the noise passing through the wall is reduced by using straps 53 or metal sheets arranged around the exhaust gas treatment members, as illustrated in FIGS. 2 and 3. Such a technical solution is described in the patent applications filed under the numbers EP 15305593.4 or EP 16180891 .0.

According to yet another variant embodiment, shown in FIG. 19, the noise passing through the wall is reduced by placing masses 79 on the outer wall 28. The weight of each mass, and its position, is determined by calculation and / or by tests.

It should be noted that, advantageously, the thermal insulation layer 57 and / or acoustic layer 73 is interposed between the fastening members to the stiffening structure 5 and the outer wall 28. This is particularly the case when the fasteners are straps 53 of the type used to fix the exhaust gas treatment members. This makes it possible to thermally and acoustically decouple the exhaust line 3 from the stiffening structure 5.

According to another advantageous variant, the stiffening structure 5 supports wires 81 or pipes 82 connecting probes, sensors and / or members to each other or to the vehicle (FIG. 2). The wires 81 transmit a power electric current, or a signal. The pipes 82 are designed to transport a fluid, for example to a heat exchanger integrated in the exhaust line 3.

As indicated above, the assembly 1 described above is intended to be integrated in a vehicle, typically a motor vehicle such as a car or a truck.

In this case, the stiffening structure 5 is rigidly fixed to the body 13, and more precisely to the floor of the vehicle. In particular, the downstream part 1 1 of the exhaust line 3 is not fixed directly to the body 13 of the vehicle. It is fixed to the body 13 of the vehicle only through the stiffening structure 5.

This greatly facilitates the mounting of the exhaust line 3 on board the vehicle.

The stiffening structure 5 is fixed to the body 13 by any means: welding, fasteners such as screws, clips, rivets, etc.

As indicated above, the body 13 defines the tunnel 67, and the exhaust line 3 is at least partially housed inside the tunnel 67.

The downstream part 1 1 of the exhaust line 3 is at least partially housed inside the tunnel 67, with the possible exception of the exhaust cannulas 27 and the silencer 31.

Advantageously, the stiffening structure 5 is then in the form of a plate closing the tunnel 67 to the running surface. The stiffening structure 5 advantageously closes the tunnel 67 over its entire length. It can for this purpose extend under the upstream part 7 of the exhaust line 3.

A detailed embodiment will now be described.

In this example, the downstream portion 1 1 of the exhaust line 3 is made almost entirely of a stainless steel of 1.4571 1 (316ΤΊ). The outer wall 28 is of a thickness of substantially 0.2 mm. The various structures forming the components of the downstream part 1 1 are assembled by gluing, and these components are assembled to each other also by gluing. The downstream part 1 1 of the exhaust line 3 comprises two silencers 31, 33 and the additional decoupler 36 interposed between the two silencers 31, 33, along the circulation duct 35 fluidly connecting the two silencers 31, 33 one to the other.

The downstream part 1 1 of the exhaust line 3, excluding thermal / acoustic insulation, has a mass in this case of about 3.5 kg, whereas the downstream part of an equivalent exhaust line of a design conventional has a weight of about 16.5 kg.

The stiffening structure 5 is a plate made of a composite material. The composite material is preferably made of glass fibers, and is made for example in the form of SMC (Sheet Molding Component), or in the form of braided glass fibers. As a variant, the composite material is made of carbon fibers, and is made for example in the form of SMC (Sheet Molding Component), or in the form of carbon fibers. braided. According to another variant, the composite material is keviar fibers. More preferably, the stiffening structure 5 is made of SMC type glass fibers.

This plate 5 has air intakes, making it possible to create a stream of air in contact with the exhaust line 3.

This plate is rigidly fixed on the floor of the vehicle, and closes the tunnel

67.

The stiffening structure 5 and the fasteners of the downstream part 1 1 to the stiffening structure 5 have a mass of about 4 kg.

The assembly 1 also comprises a layer of a thermal and acoustic insulation material, silica fibers, ceramic or keviar, preferably silica fibers. This extends over the entire length of the downstream part 1 1, and over the entire periphery of the components. It weighs about 2 kg.

Fixing the stiffening structure 5 to the vehicle adds a weight of approximately

0.5 kg.

In total, the downstream portion 1 1 of the exhaust line 3 represents a weight of about 10 kg.

By comparison, for an exhaust line of conventional design, the downstream part represents a weight of 16.5 kg, to which is added a heat shield with a weight of 2 kg, and attachments to the vehicle with a weight about 1.5 kg, for a total of about 20 kg.

Thus, the invention makes it possible to reduce the weight of the downstream part 1 1 of the exhaust line 3 by a factor of 2.

Claims

1. - Set (1) comprising:

an exhaust line (3) comprising an upstream part (7) fixed rigidly to a power unit (9) and a downstream part (1 1) fixed directly or indirectly to the body (13) of a vehicle, the parts upstream and downstream (7, 1 1) being connected to each other by a decoupler (15), the downstream part (1 1) having a determined developed length, the downstream part (1 1) having an outer wall ( 28) of a metal material of thickness less than 0.3 mm over at least 50% of its developed length;

- A stiffening structure (5) extending over at least 50% of the developed length of the downstream portion (1 1), the downstream portion (1 1) being fixed to the stiffening structure (5).

2. - The assembly of claim 1, wherein the downstream portion (1 1) comprises treatment members (31, 33), exhaust gas and ducts (25, 29, 35) of the gas circulation. exhaust fluidically connected to the treatment members (31, 33), the circulation ducts (25, 29, 35) having a determined cumulative length, the circulation ducts (25, 29, 35) having an outer wall (28) in one metal material with a thickness of less than 0.3 mm on at least 50% of the cumulative length.

3. - assembly according to claim 1 or 2, wherein the downstream portion (1 1) comprises a layer of thermal insulation (57) and / or acoustic (73), covering the outer wall (28) on at least 50% developed length.

4. - The assembly of claim 3, wherein the downstream portion (1 1) is fixed to the stiffening structure (5) by fasteners (53), the insulating layer (57, 73) being interposed between the fasteners (53) and the outer wall (28).

An assembly according to any one of the preceding claims, wherein the metallic material is a stainless steel or a titanium alloy.

6. An assembly according to any one of the preceding claims, wherein the downstream part (1 1) comprises an upstream end (25) connected by the decoupler (15) to the upstream part (7), the upstream end (25). ) being rigidly fixed to the stiffening structure (5) by a fastener (45) sized to take up the weight of the upstream end (25) and tilting forces of the powertrain (9).

7. - The assembly of claim 6, wherein the downstream portion (1 1) extends in a predetermined plane and comprises at least one exhaust gas flow duct (29, 35), related to the stiffening structure (5) by a rigid link (55) in a direction substantially perpendicular to said determined plane, but allowing movement in said determined plane.

8. - An assembly according to any one of the preceding claims, wherein the downstream portion (1 1) comprises at least two exhaust gas treatment members (31, 33) and a conduit (35) for circulating the exhaust gases. exhaust system fluidly connecting the two treatment members (31, 33) to one another, an additional decoupler (36) being interposed between the two treatment members (31, 33) along the circulation duct (35) .

9. - An assembly according to any one of the preceding claims, wherein the stiffening structure (5) is below the exhaust line (3).

10. - An assembly according to any one of the preceding claims, wherein the stiffening structure (5) is a plate.

1 1. - The assembly of claim 10, wherein the plate (5) has at least one opening (69) ventilation.

12. An assembly according to any one of the preceding claims, wherein the stiffening structure (5) consists of more than 80% by volume of composite material.

13. - An assembly according to any one of the preceding claims, wherein the stiffening structure (5) further supports son (81) or pipes (82) connecting probes, sensors and / or organs together or with a vehicle.

14. - Vehicle comprising a box (13) and an assembly (1) according to any one of the preceding claims, the stiffening structure (5) being fixed to the body (13).

15. - Vehicle according to claim 14, wherein the box (13) defines a tunnel (67) open downwards in which extends the exhaust line (3), the stiffening structure (5) being a plate closing the tunnel (67).