FR2974595A1 - BENDING ENVELOPE OF AN EXHAUST GAS POST-TREATMENT ASSEMBLY OF A COMBUSTION ENGINE HAVING TWO HALF-SHELLS - Google Patents

Abstract

The invention relates to a casing for an aftertreatment assembly of the exhaust gases of a combustion engine, having: a first straight leg (1) capable of receiving a first monolith for treating the exhaust gases; - A second branch (2) right able to accommodate a second monolith of exhaust gas treatment; - A fluidic connection (3) bent between the first and the second branch; characterized in that at least part of the casing, forming one of the branches (1, 2) and the connection (3), is constituted by the assembly of a first half-shell (C1) and of a second half-shell (C2).

Description

The invention relates to the field of means for the treatment of exhaust gas pollutants of combustion engines. The invention relates to the field of means for treating exhaust gas pollutants of combustion engines. combustion. Polluting emissions of combustion engines fitted to motor vehicles are regulated by increasingly stringent standards. Regulated pollutants are - depending on the combustion engine technology considered - carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NOx), and particulates. It is known to employ a number of pollution control means in the exhaust line of combustion engines to limit the emissions of regulated pollutants. For example, an oxidation catalyst allows the treatment of carbon monoxide, unburned hydrocarbons, and under certain conditions nitrogen oxides; a particulate filter can be used for the treatment of soot particles. [0004] Specific means are also known for the treatment of nitrogen oxides or NOx, such as NOx traps or so-called SCR catalysts for "selective catalytic reduction". The latter technology consists of reducing NOx by introducing a reducing agent (or a precursor of such a reducing agent) into the exhaust gas. In the remainder of the present document, a "reducing agent" will generally be used to designate a reducing agent or a reducing agent precursor. The reducing agent generated makes it possible to reduce the nitrogen oxides by reaction in an SCR catalyst, that is to say a substrate carrying a catalytic impregnation able to promote the reduction of NOx by the reducing agent. These devices are generally designated by the term "after-treatment" means of the exhaust gases. In a motor vehicle having the most common architecture, that is to say with a motor in a volume under the hood at the front of the vehicle, the various post-processing devices are generally located under the floor of the vehicle , in a "tunnel" formed by this floor (we talk about an equivalent arrangement "under the box"), or distributed partly in the engine compartment (under hood volume) which houses the oxidation catalyst and partly under box, where are the other devices (SCR catalyst, particulate filter, etc.). However, it is known from the French patent application filed under the number FR 1050453 the advantage of positioning a maximum of exhaust aftertreatment devices in the space under the bonnet. Indeed, in addition to saving space in the underbody space of the vehicle, such a positioning of the catalysts (oxidation and / or SCR) and / or the particle filter can bring them as close as possible to the engine output , and therefore to take advantage of favorable thermal conditions including their rise in temperature and their activation (passage above a temperature necessary for good treatment efficiency). Thus, such a positioning generates a virtuous cycle in the design of the exhaust gas treatment assembly: the elements of the after-treatment device, being disposed near the outlet of the combustion chambers of the engine (under hood and not underbody), enjoy thermal conditions favorable to optimal operation, which allows to reduce the size to obtain the same processing efficiency, compared to an implanted device underbody. It thus gains even more compactness, and in addition, reducing the size of the pollution control elements, it decreases the thermal inertia which accelerates even more their rise in temperature. In order to optimize the functionality and implementation in the space under the engine hood of a compact exhaust gas treatment system, it has been proposed by the applicant through the French patent application filed under the numbers FR1151374 and FR1153159 (unpublished applications to date) compact exhaust gas treatment assemblies grouping according to a "U" or "L" architecture respectively an oxidation catalyst, an SCR catalyst, and a filter with particles. The implementation of these architectures, however, generally requires the constitution of envelopes or "cannings" bent complex, intended to accommodate different monoliths (or breads) of gas treatment (oxidation catalyst, SCR catalyst, particulate filter or single monolith having the functions of particle filter and SCR catalyst). According to a traditional embodiment, to produce such bent envelopes, tubular sections are formed respectively adapted to each monolith, or at most forming each of the branches of the bent envelope, then assembled by welding or brazing different sections. The inlet divergence of the casing and convergent outlet of the casing are also reported and welded to the sections, and the connection is also reported between each of the branches of the bent envelope. Such an envelope constitution is problematic because it requires a number of important steps to obtain the complete envelope. As part of the constitution of a U-shaped envelope, this represents 6 different parts to assemble, in 5 welding positions. Similarly, this envelope constitution is complex to implement because it requires precise positioning of the various elements before welding. Furthermore, depending on the geometry of the envelope, the bend may form an area of mechanical weakness and / or concentration of stress (for example due to the expansion of the envelope when it heats up or cooled) favorable for cracking or breaking. Finally, the various welds peripheral to the envelope are areas of high rigidity, which is particularly problematic when it is desired to crush the envelope in case of frontal impact of the vehicle equipped with a set of post-processing implanted in the under-hood space, and in particular between an engine face and an apron separating the under hood space of the passenger compartment of the vehicle. The invention aims to solve one or more of the above problems evoked by the adoption of an envelope of optimized constitution. More specifically, the invention relates to a casing for post-treatment exhaust gas assembly of a combustion engine, having: - a first straight leg (1) adapted to receive a first monolith of treatment of exhaust gas ; - A second branch (2) right able to accommodate a second monolith of exhaust gas treatment; - A fluidic connection (3) bent between the first and the second branch; wherein a portion (at least) of the envelope forming one of the branches and the elbow is formed by the assembly of a first half-shell and a second half-shell. In the preferred embodiment of the invention, the angled connector has at its inlet the section of the outlet of the first branch (that is to say a section adapted to receive the monolith or gas treatment it is intended to accommodate), and at its output the same section as at the entrance of the second branch (that is to say a section adapted to the reception of the monoliths or gas treatment that it is meant to welcome). Preferably, the envelope is constituted by the assembly of the first half-shell and the second half-shell. The envelope is then constituted in its entirety by the assembly of the first half-shell and the second half-shell. Preferably, the first branch (1) comprises an input divergent (11), and the second branch (2) comprises an output convergent (21). The diverging and possibly converging, according to the variant of the invention in question, are also formed directly by the assembly of the half-shells. Preferably, the first half-shell and the second half-shell are each made of a single stamped metal sheet. This is the solution that allows to limit as much as possible the operations required to obtain an envelope according to the invention, and subsequently an exhaust gas treatment assembly involving such an envelope. Nevertheless, depending on the depths of stamping to obtain, it may be necessary or economically advantageous to form each half-shell by assembling several stamped sheets. In the invention, it may for example be a substantially U-shaped envelope. The elbow joint can then form a single elbow, or present two elbows linked by a cross section. It may also be an envelope substantially shaped "L". Preferably, the first branch and the second branch are connected by a reinforcement inside the angle formed between the first branch and the second branch. This limits the risk of cracking or rupture of the envelope at the elbow or bends of the connection, which are areas of stress concentration. In the variants of the invention in which each half-shell consists of a single stamped metal sheet the reinforcement is preferably formed by the metal sheet constituting one of the half-shells or by each of the metal sheets forming the half-shells. shells. This is both the simplest way of obtaining the reinforcement, but also the one that allows the best cohesion between the reinforcement and the branches (since it is formed integrally with the half-shells). reinforcement can alternatively be reported to the envelope. If the envelope is substantially U-shaped, the reinforcement preferentially fills the gap between the two branches of the "U" formed by the envelope. If the envelope is substantially in the shape of "L" the reinforcement is preferably triangular. Preferably, the reinforcement is bonded over the entire length of the shorter of the two branches. This gives it, associated with a sufficient link length to the other branch, maximum efficiency. The invention also relates to an exhaust gas treatment assembly of a combustion engine comprising an envelope according to the invention, and at least one exhaust treatment monolith in the first branch of the engine. casing and at least one exhaust treatment monolith in the second leg of the casing, wherein the treatment monoliths are selected from: an oxidation catalyst; a selective catalytic reduction catalyst of nitrogen oxides; a particle filter; a particulate filter carrying selective catalytic reduction impregnation of nitrogen oxides. In one embodiment of such an assembly in which the monoliths are straight cylindrical, of revolution or not, the joint plane of the half-shells at the first branch, respectively the second branch, is preferably confused with a plane of symmetry of the monolith or monoliths contained in the first branch, respectively the second branch. This allows easy placement of monoliths in the envelope. Finally, the invention relates to a motor vehicle comprising a combustion engine installed in a space under the front hood of the vehicle, and an exhaust gas treatment assembly according to the invention, for the treatment of exhaust gases. said combustion engine, wherein the exhaust gas treatment assembly is disposed in the space under the hood of the vehicle, between the engine and an apron separating the space under the hood of a passenger compartment of the vehicle. This configuration takes advantage particularly of the advantages of the invention offered in case of impact before the equipped vehicle, as will be detailed later in this document. The invention is described in more detail below and with reference to the figures schematically showing the system in its preferred embodiment. Figure 1 schematically shows in three dimensions an exhaust gas treatment assembly having a casing "U" made according to the state of the prior art. Figure 2 shows schematically in three dimensions an exhaust gas treatment assembly having a casing "U" made according to one embodiment of the invention. Figure 3 shows schematically in an exploded view an exhaust gas treatment assembly having a casing "U" made according to one embodiment of the invention. Figure 4 shows schematically in an exploded view an exhaust gas treatment assembly having a casing "U" made according to another embodiment of the invention. Figure 5 shows schematically in three dimensions an exhaust gas treatment assembly having a casing "U" made according to one embodiment of the invention having a reinforcement. Figure 6 shows a 3-dimensional exhaust gas treatment assembly having a bent envelope made according to an embodiment of the invention having a reinforcement. Figure 7 schematically shows the areas of high rigidity on an exhaust gas treatment assembly according to the state of the art on the one hand, and according to one embodiment of the invention on the other hand . Figure 1 shows schematically in three dimensions an exhaust gas treatment assembly having a casing "U" made according to the state of the prior art. Such an assembly has an envelope or "canning", comprising a first rectilinear branch 1 and a second rectilinear branch 2. The first branch 1 and the second branch 2 are intended to accommodate breads or monoliths of gas treatment. Straight prismatic exhaust, generally cylindrical. The monoliths may especially be: an oxidation catalyst, for the treatment of unburned hydrocarbons (HC) and carbon monoxide (CO); a catalyst for selective catalytic reduction of nitrogen oxides, for the treatment of nitrogen oxides (NOx); a particulate filter for trapping and optionally the oxidation of the soot particles; a particulate filter carrying selective catalytic reduction impregnation of the nitrogen oxides, thus combining the functions of particulate filter and selective catalytic reduction catalyst of nitrogen oxides. Typically, the first branch 1 may contain an oxidation catalyst, and the second branch 2 may contain a particulate filter carrying a selective catalytic reduction impregnation of nitrogen oxides. The first branch comprises a diverging input 11. [0041] The second branch comprises a convergent output 21. The latter may comprise, as in the example here shown, a side exit. The first and the second branch are connected by a fluidic coupling 3, forming a first elbow 31 and a second elbow 32 to give the assembly a U-shape. [0043] As envisaged in the state of the technique, the divergent 11 is welded to a first section 12 of tube, by a first peripheral weld P1, to form the first branch 1. The first branch 1 is welded by a second peripheral weld P2 connection 3. [ 0045] The connector 3 is welded to the second branch 2 by a third peripheral weld P3. The second branch 2 comprises in the example shown here a second section 22 of tube, welded by a fourth peripheral seal P4 to a third tube section 23. Thus, the second section 22 can accommodate a gearbox mixer SCR, and the third section is adapted to accommodate an SCR catalyst. The third section of tube 23 is welded to the convergent by a fifth peripheral weld P5. The constitution of such a set of post-processing is complex, and requires many welding operations. In the invention, and as shown for a particular embodiment in Figure 2 (according to an external view in 3 dimensions) and in Figure 3 (in a 3-dimensional exploded view), the envelope of an exhaust gas aftertreatment assembly consists of a first half-shell C1 and a second half-shell C2, the first half-shell C1 and the second half-shell C2. Each shell may consist of a single stamped metal sheet. However, without departing from the scope of the invention, provide a first nozzle 4 attached to the inlet of the diverging 11, and a cannula 5 and a second nozzle 6 reported at the outlet of the diverging. In the assembly shown here, an oxidation catalyst 7, a mixer 8 and a FAP / SCR monolith 9, that is to say a particle filter carrying a selective catalytic reduction impregnation of the nitrogen oxides. It will be noted that according to other embodiments of the invention, the mixing function of the gearbox SCR may be favored by the geometry of the coupling 3, or even completely made in the coupling 3, either by adding a mixer or by constitution of a mixer by the geometry of the connector (which may for example comprise a boss generating turbulence in the flow of exhaust gas to ensure a mixture of SCR gear). Figure 4 shows an embodiment of the invention similar, with the difference that the oxidation catalyst has an oval cylindrical shape (elliptical section and not revolution). Preferably, the plane of connection, or joint plane, of the shells is adapted to be confused with a plane of symmetry of each of the monoliths or gas treatment devices. Thus, in the example shown in FIG. 4, the welding plane at the level of the first branch 1 is slightly inclined with respect to the weld plane at the level of the second branch 2, so as to correspond to the plane of symmetry of the bread cylindrical oval that the first branch is intended to receive. This allows easy installation of the monoliths in the envelope, because none of the half-shells has an "undercut" shape that would oppose the installation of monoliths. Figures 5 and 6 show two envelopes according to the invention, according to two different embodiments. In Figure 5, the casing is substantially U-shaped, while in Figure 6, the casing has any bent shape. These embodiments have in common the presence of a reinforcement R within the angle formed between the first branch and the second branch. In the examples shown here, the reinforcement R connects the first branch 1 to the second branch 2, and is bound over the entire length of the shortest branch of the two, namely here the first branch 1. The reinforcement is, in the examples presented, formed directly by the metal sheet constituting each half-shell. It could, in another embodiment, be reported. The reinforcement is intended to protect the envelope from its rupture in the bent zone, which constitutes a stress concentration zone. In the example shown in Figure 5, the reinforcement completely fills the space between the two branches of the "U", thus preventing their spacing relative to each other. In the example shown in FIG. 6, the reinforcement is of substantially triangular shape, and avoids any angle variation between the two branches, and in particular the opening of the angle that they form relative to each other. to the other. In addition to great ease of implementation, because it is possible to assemble the two shell at a single welding station, the invention has another major advantage that is illustrated in Figure 7. Figure 7 schematically presents a comparison between the zones of high rigidity (linked to a localized stack of sheet metal and to their welding), on an envelope made according to the state of the prior art (left figure), and on a shell conforming to a mode embodiment of the invention (right figure). These areas of high rigidity oppose the crushing of the envelope. Areas of high rigidity are shown in strong lines in Figure 7. In an envelope constituted according to the state of the prior art, its stiffness zones are peripheral to the branches of the envelope. The side faces of the envelope therefore have areas of high rigidity. This is particularly problematic in an automotive application, particularly if the exhaust gas treatment assembly is positioned in a space under the front hood of the vehicle, between the engine and the passenger compartment of the vehicle. Areas of high rigidity must then be taken into account in the context of the scenarios in the event of a frontal impact of the equipped vehicle, which implies positioning them adequately (which is problematic in an environment that is otherwise highly constrained) and / or reinforce the apron separating the under-hood space of the passenger compartment of the vehicle facing these areas of high rigidity. In the invention, depending on the variant considered, the high rigidity area is only the sidewalk of welding, which is in direct vis-à-vis neither the engine block nor the deck. The post-treatment assembly obtained by assembling two half-shells does not therefore have a local area of high rigidity on its lateral faces (faces respectively defined by the bottom of each shell), which are able to be intrusive with respect to each other. the passenger compartment of the vehicle. Thus, the invention provides a post-treatment assembly according to a simple method, in which: the two half-shells 1, 2 are made by stamping (and possibly assembly of stamped parts); winding sheets are wrapped around the loaves 7, 9 (monoliths) and the gas treatment; the loaves 7, 9 and any other devices (for example the mixer 8, the first nozzle 4) are deposited in the first half-shell 1; we close the assembly with the second half-shell 2; or weld the two shells together. It is then possible to complete the envelope thus obtained by adding a cannula 5 at the output of the output convergent 21, cannula provided with the second endpiece 6. [0064] An industrial installation for the implementation of the invention can therefore present: 2 stamping stations for half-shells. - 1 welding station to assemble the assembly and possibly 1 welding station of the outlet pipe on the exit cone [0065] For comparison a manufacturing facility of a conventional casing comprises (at least) 10 positions: - 3 stamping stations, for the entry and exit cones, the elbow obtained in the form of a connection cup; 2 enveloping stations for breads; 5 welding stations to assemble the assembly; and possibly 1 welding station of the outlet pipe on the outlet cone It is also possible in the context of the invention to form by assembling two half-shells only one of the two branches of the casing and the fluidic connection. The advantages of the invention will then be obtained to a lesser extent, namely: a method of obtaining simpler than a traditional method, but nevertheless more complex in welding, but easier to stamp, than if the two branches are made by half-shells, an absence of area of high rigidity only on the lateral faces of one of the branches.

Claims (11)

CLAIMS: 1. Envelope for exhaust aftertreatment assembly of a combustion engine, having: - a first leg (1) right adapted to accommodate a first monolith exhaust gas treatment; - A second branch (2) right able to accommodate a second monolith of exhaust gas treatment; - A fluidic connection (3) bent between the first and the second branch; characterized in that at least part of the envelope forming one of the branches (1, 2) and the joint (3) bent is formed by the assembly of a first half-shell (Cl) and a second half-shell (C2). 2. Envelope according to claim 1, characterized in that it is constituted by the assembly of the first half-shell and the second half-shell. An envelope according to claim 1 or claim 2, wherein the first limb (1) further comprises an input divergent (11), and the second limb (2) has an output convergent (21). 4. Envelope according to one of claims 1 to 3, wherein the first half-shell (Cl) and the second half-shell (C2) each consist of a single stamped metal sheet. 5. Envelope according to any one of the preceding claims, wherein the first leg (1) and the second leg (2) are connected by a reinforcement (R) within the angle formed between the first leg (1). ) and the second branch (2). 6. Envelope according to claim 5, each half-shell (C1, C2) consisting of a single stamped metal sheet, wherein the reinforcement (R) is constituted by the metal sheet constituting one of the half-shells (C1, C2). ) or by each of the metal sheets forming the half-shells (C1, C2). 7. Envelope according to claim 5, wherein the reinforcement (R) is attached to the envelope. 8. Envelope according to one of claims 5 to 7, wherein the reinforcement (R) is bonded over the entire length of the shorter of the two branches (1,2). 9. An exhaust gas treatment assembly of a combustion engine comprising an envelope according to any one of the preceding claims and at least one exhaust treatment monolith in the first branch of the envelope and at least one an exhaust gas treatment monolith in the second branch of the casing, wherein the treatment monoliths are selected from: an oxidation catalyst (7); a selective catalytic reduction catalyst of nitrogen oxides; a particle filter; a particulate filter having selective catalytic reduction impregnation of the nitrogen oxides (9). 10. The assembly of claim 9, whose monoliths (7,9) are straight cylindrical, of revolution or not, wherein the joint plane of the half-shells (C1, C2) at the first branch (1), respectively the second branch (2) is coincident with a plane of symmetry of the monolith (s) (7,9) contained in the first branch (1), respectively the second branch (2). 11. A motor vehicle having a combustion engine installed in a space under the front hood of the vehicle, and an exhaust gas treatment assembly according to claim 9 or claim 10, for the treatment of the exhaust gases of said combustion engine. , characterized in that the exhaust gas treatment assembly is disposed in the space under the hood of the vehicle, between the engine and an apron separating the space under the hood of a passenger compartment of the vehicle.