Abstract:
A device for removing pollutants from exhaust gases of a combustion engine, includes a longitudinal outer casing ( 23 ) defining a passage through which the exhaust gases flow, and first and second pollution-removal members ( 18, 20 ) mounted in series in the passage. The device includes a holding sleeve ( 38 ) holding the first pollution-removal member ( 18 ) in place and interposed between the first pollution-removal member ( 18 ) and the outer casing ( 23 ) and running longitudinally at least over most of the length of the first pollution-removal member ( 18 ), the holding sleeve ( 38 ) being guided in the external casing ( 23 ) and forming, between the first and second pollution-removal members ( 18, 20 ) a longitudinal thrust surface ( 40 ) against which the first pollution-removal member ( 18 ) bears.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates in general to a device for removing pollution from the exhaust gases of a heat engine. 
     To be more precise, the invention relates to a device for removing pollution from the exhaust gases of a heat engine, of the type comprising a longitudinal outer casing defining a passage for the flow of the exhaust gases, and first and second pollution-removal members mounted in series in the passage. 
     Such a device is used in particular for removing pollution from diesel engines of motor vehicles. In that case it normally comprises, located in the same casing, a catalytic purification member and a particle filter. The catalytic purification member is suitable for treating the polluting emissions in gaseous phase, while the particle filter is suitable for retaining the soot particles emitted by the engine and optionally for fixing the gaseous pollutants. 
     In devices for petrol engines, several catalytic purification members are located in the same casing. 
     In some cases, one of the two pollution-removal members may have a small thickness compared with its diameter. Such a pollution-removal member is difficult to position inside the casing. In particular, it is difficult to obtain a situation where the upstream and downstream faces of the pollution-removal member are in an orientation perpendicular to the longitudinal axis of the casing. 
     SUMMARY OF THE INVENTION 
     In this context, the object of the invention is to propose a device for removing pollution from exhaust gases, in which device the positioning of a pollution-removal member of small thickness is facilitated. 
     To that end, the invention relates to a device for removing pollution from exhaust gases of the above-mentioned type, characterised in that it comprises a sleeve for holding the first pollution-removal member, which sleeve is interposed between the first pollution-removal member and the outer casing and extends longitudinally at least over most of the length of the first pollution-removal member, the holding sleeve being guided in the outer casing and forming between the first and second pollution-removal members a surface for longitudinal abutment against which the first pollution-removal member bears. 
     The device may also have one or more of the following features, considered individually or in any technically possible combination:
         the outer casing comprises a cylindrical wall in which the first and second pollution-removal members are placed, and a divergent portion rigidly secured to the cylindrical wall;   the holding sleeve forms two surfaces for longitudinal abutment, one on each side of the first pollution-removal member, the first pollution-removal member bearing against the two abutment surfaces;   the divergent portion forms a peripheral shoulder on the opposite side to the second pollution-removal member relative to the first pollution-removal member, the first pollution-removal member bearing longitudinally against the peripheral shoulder and against the abutment surface;   the cylindrical wall and the divergent portion of the outer casing comprise respective free edges which face each other and which are welded to each other and to the holding sleeve;   the divergent portion forms a female end in which a male end of the cylindrical wall is engaged;   the cylindrical wall forms a female end in which a male end of the divergent portion is engaged, a peripheral edge of the holding sleeve being gripped between the male and female ends and welded to the male and female ends;   the holding sleeve is a piece of open rolled sheet-metal;   the holding sleeve is a piece of rolled sheet-metal having two parallel edges secured rigidly to each other; and   the first pollution-removal member has a longitudinal thickness smaller than half its largest dimension in a transverse plane.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the invention will emerge from the description thereof given hereinafter by way of non-limiting example with reference to the appended Figures, of which: 
         FIG. 1  is a longitudinal half-section through a pollution-removal device according to a first embodiment of the invention; 
         FIG. 2  is a longitudinal section through a portion of a pollution-removal device according to a second embodiment of the invention; and 
         FIGS. 3 and 4  are views similar to that of  FIG. 2  for two other embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The pollution-removal device  10  shown in  FIG. 1  comprises a generally cylindrical exhaust silencer  12  having, at one end, an inlet  14  and, at its other end, an outlet  16 . A catalytic purification member  18  and a particle filter  20  which are separated by a free transition space  22  are located in succession from the inlet to the outlet inside the silencer  12 . 
     The exhaust silencer  12  comprises a longitudinal outer casing  23  delimiting a passage for the flow of the exhaust gases through which passage the catalytic purification member  18  and the particle filter  20  are put in position. 
     The catalytic purification member  18  comprises, for example, a gas-permeable structure  19  covered with catalytic metals promoting the oxidation of the combustion gases and/or the reduction of the nitrogen oxides. 
     The particle filter  20  comprises a filtration material formed by a monolithic structure  21  of ceramics or of silicon carbide having a porosity sufficient to permit the passage of the exhaust gases. However, as known per se, the diameter of the pores is selected to be sufficiently small to ensure that the particles, and especially the soot particles, are retained on the upstream face of the filter. The particle filter may also be produced from a ceramic foam, cordierite or silicon carbide. It may also be in the form of a cartridge filter or a sintered metal filter. 
     The particle filter used here comprises, for example, a set of parallel ducts divided into a first group of inlet ducts and a second group of outlet ducts. The inlet and outlet ducts are in an alternating arrangement. 
     The inlet ducts open into the upstream section of the particle filter and are closed off in the region of the downstream section of the particle filter. 
     In contrast, the outlet ducts are closed off at the upstream section of the particle filter and open into the downstream section thereof. 
     In its linear portion, the outer casing  23  is formed by a cylindrical wall  24  having a substantially constant cross-section. 
     The outer casing  23  also comprises a divergent portion  26  connecting an inlet tube  28  to the cylindrical wall  24 . The tube  28  defines the inlet  14 . Likewise, at its rear end, the cylindrical wall  24  is extended by a convergent portion  30  terminating in an outlet tube  32  delimiting the outlet  16 . 
     In operation, the exhaust gases flow longitudinally first through the catalytic purification member  18  and then through the particle filter  20 . 
     In the text below, the terms upstream and downstream will be considered in relation to the normal direction of flow of the exhaust gases. 
     The pollution-removal device  10  comprises a cylindrical sleeve  38  inside which the catalytic purification member  18  is accommodated in its entirety. 
     The sleeve  38  comprises a longitudinal ring  39  and a reentrant collar  40  formed at the downstream longitudinal end of the ring  39 . The collar  40  forms a surface for longitudinal abutment against which the catalytic pollution-removal member  18  bears. 
     In addition to the gas-permeable structure  19 , the catalytic purification member  18  comprises a shim  50  interposed between the periphery of the downstream face of the structure  19  and the collar  40 . This shim extends along the lateral wall of the structure  19 . 
     The shim  50  is formed by an annular seal having in cross-section the general shape of an L, one branch of which bears on the collar  40  and the other branch of which bears on the ring  39  of the sleeve  38 . 
     A shim  52 , identical to the shim  50 , is engaged at the periphery of the upstream face of the structure  19  and it, too, extends partially along the lateral surface of the structure. The branch of the shim covering, at its periphery, the upstream surface forms a seat for bearing against the divergent portion  26 . The branch covering the lateral surface of the structure  19  bears on the ring  39 . The divergent portion  26  has a peripheral edge  54  for securing to the cylindrical wall  24 , forming a U-shaped turned-back portion. This edge  54  has a central portion  56  having an orientation substantially perpendicular to the longitudinal direction and forming a peripheral shoulder against which the catalytic purification member  18  bears. 
     The branch of the shim  52  covering the periphery of the upstream face of the structure  19  bears against the shoulder  56 . 
     The edge  54  also comprises a cylindrical free portion  58  which has a longitudinal orientation and which extends the shoulder  56  away from the catalytic purification member  18 . The cylindrical portion  58  forms a male end engaged in a female end formed by the upstream peripheral edge  60  of the cylindrical wall  24 . 
     The sleeve  38  is engaged by its upstream end  61  between the cylindrical portion  58  and the peripheral edge  60 . A single peripheral weld  62  fixedly joins the sleeve  38 , the edge  60  and the cylindrical portion  58 . 
     The two shims  50 ,  52  define an axial clearance between the shoulder  56  and the upstream face of the substrate  19  which is of the order of 5.5 mm while the radial clearance defined between the lateral surfaces opposite the substrate  19  and the sleeve  38  is of the order of 3.5 mm. 
     These two shims are formed by a metal lattice of the type ACS LSP 5600 supplied by the company ACS. Only the upstream shim  52  is associated with a heat-expandable material of the vermiculite type which provides a seal against the exhaust gases. 
     The substrate  21  of the particle filter bears via its upstream face on the collar  40  with the interposition of a shim  64  formed by an annular seal having an L-shaped cross-section, one branch of which is interposed between the collar  40  and the periphery of the upstream face of the substrate  21  and the other wing of which extends between the lateral wall of the substrate and the cylindrical wall  24 . 
     The widened end of the convergent portion  30  is inserted into the downstream end of the wall  24 . For that purpose, it has a generally cylindrical outer rim  72  suitable for fitting against the inner surface of the wall  24 . The convergent portion  30  bears against the substrate  21  of the particle filter with the interposition of a shim  74  formed by a seal identical to the shim  64 . A peripheral weld  75  fixedly joins the rim  72  and the wall  24 . 
     The shims  64  and  74  define an axial clearance of the order of 5 mm and a radial clearance of the order of 3.5 mm. 
     The shims are, for example, of the type LSP-5600.45 supplied by the company ACS. They differ from the shims  50  and  52  inasmuch as they are denser in order better to absorb the stresses of the particle filter  20 . 
     Furthermore, the substrate  21  is surrounded in its linear portion by a holding mat  76  interposed between the substrate and the inner surface of the portion  40 . This mat is formed, for example, by ISOMAT AV 3280 g/m 2  supplied by the company Unifrax. 
     The catalytic purification member  18  has a small longitudinal length compared with its transverse dimensions. Thus, the longitudinal length of the substrate  19  is smaller than 0.5 times its largest dimension in a transverse direction. Preferably, the longitudinal length of the substrate  19  is from 0.2 to 0.4 times its largest dimension in a transverse direction and is, for example, 0.3 times that largest dimension. The substrate  19  typically has a cylindrical shape, so that its largest dimension in a transverse direction corresponds to its diameter. 
     In a variant, the catalytic purification member  18  may comprise a peripheral holding mat around the substrate  19 , between the shims  50  and  52 . 
     The sleeve  38  is typically a piece of rolled sheet-metal. This piece of sheet-metal is curved, at one of its longitudinal ends, or at its two longitudinal ends, in such a manner as to form the reentrant collar(s). 
     The sleeve  38  may remain open, in which case the two parallel longitudinal edges of the piece of rolled sheet-metal are not secured to each other and remain free. The sleeve may also be closed, in which case the two longitudinal parallel edges of the piece of rolled sheet-metal are secured rigidly to each other. The two edges may be secured to each other by weld spots, or by form-fitting, for example by means of a dovetail device or a tenon and mortise device. The two longitudinal edges may be separate or may cover each other, totally or partially. In this latter case, one of the longitudinal edges comprises a circumferential tongue covering the other edge. 
     In a variant, the sleeve  38  may be produced from a piece of thin sheet-metal having a thickness of less than 1 mm, preferably from 0.2 to 0.6 mm. This thickness is, for example, 0.4 mm. 
     For assembly, the catalytic purification member  18  is first of all engaged inside the sleeve  38 , the shims  50  and  52  being interposed between the substrate  19  and the sleeve  38 . This operation can be carried out, for example, by the substrate supplier or, otherwise, in the workshop for mounting the exhaust silencer. 
     The substrate  21  of the particle filter is then engaged with the two shims  64 ,  74  in the cylindrical wall  24 . The convergent portion  30  is inserted into the wall  24  from the downstream end and the weld  75  for securing the wall  24  to the convergent portion  30  is produced. The assembly formed by the sleeve  38  and the catalytic purification member  18  is then fitted into the cylindrical wall  24  via the upstream side. This assembly is pushed in until it abuts the shim  64  via the collar  40 . Owing to the fact that the sleeve  38  has a cylindrical shape with an outside diameter corresponding nominally to the inside diameter of the upstream portion of the wall  24 , it is guided when it is put in place in the cylindrical wall  24 . As a result, the positioning of the sleeve  38 , and therefore of the purification member  18 , is very precise. In particular, the orientation of the upstream and downstream faces of the substrate  19  is absolutely perpendicular to the longitudinal direction. 
     Finally, the divergent portion  26  is inserted into the upstream peripheral edge  60  of the wall  24 . The shoulder  56  bears against the purification member  18 . The member  18  is thus urged against the collar  40 , the latter in turn urging the particle filter  20  against the convergent portion  30 . Thus, the particle filter  20  is kept clamped between the collar  40  and the rim of the convergent portion  30 . The substrate  21  is held with a compressive force of 4000 N imposed by the convergent portion  30  and the divergent portion  26 . 
     The compression of the catalytic purification member  18  between the shoulder  56  and the collar  40  is monitored and adjusted in accordance with the stresses by altering the insertion force applied to the divergent portion  26 . This force is preferably from 1500 to 5000 N and is, for example, of the order of 2000 N. 
     Several other embodiments of the invention will now be described. Elements identical to those of the first embodiment, or playing the same role, are denoted by the same references. 
     A second embodiment of the invention is shown in  FIG. 2 . Only the differences relative to the first embodiment will be described below. 
     As shown in  FIG. 2 , the substrate  19  is not accommodated completely inside the sleeve  38  but the latter nevertheless extends over most of the longitudinal length of the catalytic purification member  18 . The upstream face of the substrate  19  is located slightly outside the upstream end  61  of the sleeve. 
     In addition, the peripheral edge  54  of the divergent portion no longer forms a U-shaped turned-back portion. The edge  54  still has a central portion  56  of transverse orientation forming a peripheral shoulder against which the catalytic purification member  18  bears. The portion  56  extends longitudinally to the cylindrical wall  24  via a cylindrical free portion  78  of longitudinal orientation. The cylindrical portion  78  forms a female end into which a male end formed by the upstream peripheral edge  60  of the cylindrical wall  24  is inserted. A peripheral weld  80  fixedly joins the portion  78  and the edge  60 . 
     In the second embodiment, the sleeve  38  is welded neither to the cylindrical wall  24  nor to the divergent portion  26 . 
     A shoulder  82  is formed in the cylindrical wall  24 , substantially at right-angles to the free transition space  22 . The shoulder  82  forms, inside the wall  24 , a peripheral surface for the longitudinal bearing of the sleeve  38 . 
     The assembly of the exhaust silencer  12  is effected in accordance with the procedure below. 
     As before, the catalytic purification member  18  is first of all engaged inside the sleeve  38 , the shims  50  and  52  being interposed between the substrate  19  and the sleeve  38 . This assembly is then engaged in the cylindrical wall  24  via the upstream side until the sleeve  38  abuts the shoulder  82  of the cylindrical wall  24 . Subsequently, the cylindrical wall  24  is inserted into the peripheral edge  54  for securing the divergent portion. The compression of the catalytic purification member  18  between the shoulder  56 , on the one hand, and the collar  40 , which itself bears on the shoulder  82 , on the other hand, is monitored and adjusted in accordance with the stresses. The weld  80  for fixedly joining the cylindrical wall  24  and the divergent portion  26  is then produced. 
     Finally, the particle filter  20  is fitted in the cylindrical wall  24  via the downstream side, and the convergent portion  30  is inserted into the wall  24  from the downstream end. The compression of the particle filter  20  is adjusted by the force used to fit the convergent portion  30 . Finally, the weld  75  for securing the wall  24  to the convergent portion  30  is produced. 
     As before, the sleeve  38  is guided during its insertion into the cylindrical wall  24  owing to the fact that the outside diameter of the sleeve  38  corresponds to the inside diameter of the upstream portion of the cylindrical wall. The catalytic purification member  18  is thus positioned and oriented with precision. 
     In a variant, the particle filter does not comprise a shim  64  and does not bear on the collar  40 . Owing to the fact that the sleeve  38  bears against the shoulder  82 , this shim is not indispensable. 
     A third embodiment will now be described with reference to  FIG. 3 . 
     This third embodiment is very similar to the second embodiment except for the following points. 
     As shown in  FIG. 3 , the upstream peripheral edge  60  of the cylindrical wall  24  is not inserted into the cylindrical free portion  78  of the divergent portion. Instead, the cylindrical free portion  78  and the edge  60  have the same diameter and are located at a small distance from and opposite each other. 
     They are both placed on an outer face of the sleeve  38 . A single continuous weld bead  84  fixedly joins the edge  60  to the cylindrical free portion  78 . The weld bead  84  also fixedly joins the edge  60  and the portion  78  to the sleeve  38 . 
     The assembly of the exhaust silencer is effected in accordance with the same procedure as for the second embodiment. 
     A fourth embodiment will now be described with reference to  FIG. 4 . 
     This fourth embodiment is similar to the third, except for the following differences. 
     As shown in  FIG. 4 , the sleeve  38  forms, one on each side of the catalytic purification member  18 , reentrant collars  86  and  88 , forming surfaces for longitudinal abutment against which the catalytic purification member  18  bears. The branch of the seal  52  covering the periphery of the upstream face of the substrate  19  bears against the collar  88 . Likewise, the branch of the seal  50  covering the periphery of the downstream face of the substrate  19  bears against the collar  86 . 
     The collar  88  is located longitudinally at a distance from the shoulder  56  formed on the divergent portion  26 . Likewise, the collar  86  is located longitudinally at a distance from the shoulder  82  formed in the cylindrical wall  24 . 
     As in the third embodiment, the weld bead  84  fixedly joins the cylindrical portion  78  of the edge  54  to the peripheral edge  60 , and fixedly joins the portion  78  and the edge  60  to the sleeve  38 . 
     The assembly of the exhaust silencer is effected in accordance with the following procedure. 
     The catalytic purification member  18  is first of all arranged inside the sleeve  38 . The shims  50  and  52  are interposed between the substrate  19  and the sleeve  38 . The compression of the catalytic purification member is adjusted during the mounting operation by adjusting the spacing between the collars  86  and  88  by any suitable means. The particle filter  20  is then fitted inside the cylindrical wall  24 , and the convergent portion  30  is inserted into the wall  24  from the downstream end. The weld  75  for securing the wall  24  to the portion  30  is then produced. 
     The assembly formed by the sleeve  38  and the catalytic purification member  18  is then fitted in the cylindrical wall  24  via the upstream side. The compression of the particle filter  20  is adjusted by altering the force used to fit the assembly. The assembly sleeve  38 /member  18  is kept in place by producing a few weld spots between the peripheral edge  60  of the cylindrical wall  24  and the sleeve  38 . The divergent portion  26  is then fitted around the sleeve  38 , and the continuous weld bead  84  is produced with a view to securing the wall  24 , the divergent portion  26  and the sleeve  38  to one another. 
     Thus, in the fourth embodiment, the substrate  19  of the catalytic purification member is compressed by the collars  86  and  88  of the sleeve  38 . In the first three embodiments, the substrate  19  is compressed by the collar  40  of the sleeve co-operating for this purpose with the shoulder  56 . 
     The invention has been described in the case where the catalytic purification member  18  has a small length compared with its transverse dimensions. However, it is possible for it not to be the catalytic purification member  18  which has a small length but, rather, the particle filter  20 . In that case, it is the particle filter  20  which is accommodated in the sleeve  38 . Furthermore, it is also possible for the catalytic purification member  18  and the particle filter  20  both to have simultaneously a small longitudinal length compared with their transverse dimensions. In that case, the two pollution-removal members are each located inside a sleeve  38  accommodated in the cylindrical wall  24 . 
     It will be appreciated that the use of an inner sleeve facilitates the positioning and orientation of the catalytic purification member  18  without having too adverse an effect on the amount of material used. 
     For, owing to the fact that the member  18  is short longitudinally, the sleeve  38 , too, is longitudinally short. It is therefore inexpensive in terms of material. 
     In addition, a single weld bead enables the sleeve  38  to be secured to the wall  24  and to the divergent portion  26 , and the wall  24  to be secured to the portion  26 . This also helps to reduce the cost of the pollution-removal device.