Patent Publication Number: US-2009235623-A1

Title: Device for depolluting exhaust gases of a thermal engine

Description:
The present invention relates to a device for depolluting exhaust gases of a thermal engine of the type comprising an outer casing, the casing comprising first and second successive tubular portions containing, respectively, a first and a second depollution element which are mounted successively in the passage, the first portion comprising a female end in which a male end of the second portion is fitted. 
     A device of this type is used in particular for the depollution of motor vehicle diesel engines. In this case, it generally comprises, arranged in the same casing, a catalytic purification element and a particulate filter. 
     The catalytic purification element is suitable for processing polluting emissions in the gaseous phase, whilst the particulate filter is suitable for retaining the particles of soot discharged by the engine. 
     In the devices for petrol engines, a plurality of catalytic purification elements are arranged in the same casing. 
     It is known to form the depollution device in two portions which each comprise a tubular portion, inside which a depollution element is arranged. The two portions are fitted one inside the other and are retained in a fixedly joined state by means of a flange or hoop-like member. A device of this type is described, for example, in the patent applications FR-2 821 117 and FR-2 839 533. 
     The production of depollution devices of this type is relatively complex since it requires the use of means which allow correct axial positioning of the two portions before the joining device is positioned. 
     The object of the invention is to provide a device for depolluting exhaust gases which can be readily produced and can therefore have a low cost. 
     To this end, the invention relates to a device for depolluting exhaust gases of the above-mentioned type, characterised in that the male end has, at the end thereof, an axial stop surface which is in abutment against the first depollution element contained in the first portion. 
     According to specific embodiments, the device comprises one or more of the following features:
         the axial stop surface is defined by an inner collar which is provided at the end of the male end;   the inner diameter of the inner collar is less than the cross-section of the face opposite the first depollution element;   the first portion comprises, opposite the female end relative to the first depollution element, a peripheral shoulder on which the first depollution element is supported axially;   the first depollution element comprises a substrate and a wedge which is interposed between the axial stop surface and the substrate;   the second depollution element is in axial abutment against the inner collar;   the female and male ends which are fitted one inside the other are welded to each other by means of a peripheral weld seam; and   the female and male ends which are fitted one inside the other are connected to each other by means of a hoop-like collar in which associated profiles of the female and male ends are fitted.       

    
    
     
       The invention will be better understood from a reading of the following description, given purely by way of example and with reference to the drawings, in which: 
         FIG. 1  is a longitudinal section of the depollution device according to the invention; 
         FIG. 2  is a longitudinal section of the depollution device before two successive portions are assembled; and 
         FIG. 3  is a partial longitudinal section of the coupling of two successive portions according to another embodiment. 
     
    
    
     The depollution device  10 , illustrated in  FIG. 1 , comprises an exhaust chamber  12  which is generally cylindrical and which has, at one end, an inlet  14  and, at the other end thereof, an outlet  16 . A catalytic purification element  18  and a particulate filter  20  which are separated by a free transition space  22  are arranged successively from the inlet to the outlet inside the chamber  12 . 
     The exhaust chamber  12  comprises an outer casing  23  which delimits a passage for circulation of exhaust gases through which the catalytic purification element  18  and the particulate filter  20  are arranged. 
     The catalytic purification element  18  comprises, for example, a gas-permeable structure  19  which is coated with catalytic metals which promote the oxidation of combustion gases and/or the reduction of nitrogen oxides. 
     The particulate filter  20  comprises a filtration material which is constituted by a monolithic structure  21  of ceramic material or silicon carbide and which has sufficient porosity to allow the passage of exhaust gases. However, as known per se, the diameter of the pores is selected to be sufficiently small to ensure that particles are retained, and in particular particles of soot, on the upstream face of the filter. The particulate filter can also be produced from a ceramic foam, cordierite or silicon carbide. It may also be constituted by a cartridge filter or a filter of sintered metal. 
     The particulate filter used in this instance comprises, for example, an assembly of parallel channels which are divided into a first group of inlet channels and a second group of outlet channels. The inlet and outlet channels are arranged in a zig-zag arrangement. 
     The inlet channels open in the upstream cross-section of the particulate filter and are blocked in the region of the downstream cross-section of the particulate filter. 
     Conversely, the outlet channels are blocked in the upstream cross-section of the particulate filter and open in the downstream cross-section thereof. 
     In the current portion thereof, the outer casing  23  is formed by a cylindrical wall  24  having a substantially constant cross-section. 
     At the inlet end thereof, the chamber comprises a divergent portion  26  which connects an inlet pipe  28  to the cylindrical wall  24 . In the same manner, at the rear end thereof, the cylindrical wall  24  is extended by a convergent portion  30  which terminates in an outlet pipe  32  which delimits the outlet  16 . 
     During operation, the exhaust gases first flow through the catalytic purification element  18  then through the particulate filter  20 . 
     The casing  23  is delimited, in the example in question, by two successive tubular portions  38 ,  40  which are coupled to each other and which contain, respectively, the catalytic purification element  18  and the particulate filter  20 . Each portion is formed by a rolled hoop whose two longitudinal edges are connected to each other along a longitudinal connection which is formed by means of welding or crimping. 
     The upstream portion  38 , when viewed in the normal flow direction of the gas, has, at the downstream end thereof, a widened female end  42  in which there is axially engaged the upstream end of the portion  40  which forms a male end designated  44 . 
     The portion  38  has, at the upstream end thereof, a recessed collar  46  which forms, at the inner side, a shoulder  48  for abutment against the catalytic purification element  18 . 
     The catalytic purification element  18  comprises, in addition to the gas permeable structure  19 , a wedge  50  (an element for blocking in position) which is interposed between the periphery of the upstream face of the structure  50  and the shoulder  48 . This wedge extends along the lateral wall of the structure  19 . 
     The wedge  50  is formed by an annular joint which generally has, in cross-section, an L-shape, of which one branch is supported on the shoulder  48  and the other branch is supported on the lateral surface of the structure  19 . 
     A wedge  52 , which is identical to the wedge  50 , is engaged at the periphery of the downstream face of the structure  19  and also extends partially along the lateral surface of the structure. The branch of the wedge which overlaps, at the periphery thereof, the downstream surface, forms a support seat for the end of the male end  44  of the second portion  40 . 
     The two wedges  50 ,  52  define an axial clearance between the shoulder  48  and the upstream face of the substrate  19  which is in the order of 5.5 mm whilst the radial clearance defined between the lateral surfaces opposite the substrate  19  and the portion  38  is in the order of 3.5 mm. 
     These two wedges are formed by a metal trellis of the type ACS LSP 5600 supplied by the company ACS. Only the upstream wedge  50  is associated with a heat-expandable material of the vermiculite type which allows sealing with respect to the exhaust gases. 
     Beyond the wedge  52 , the portion  38  has a widened portion  54  which forms the female end  42 . 
     The second portion  40  has, at the end of the male end  44 , a recessed peripheral collar  56  which delimits internally a shoulder  58  for supporting the particulate filter  20 . The collar  56  has, at the inner side, a cross-section which is less than the periphery cross-section of the downstream face of the porous structure  19 , in order to be supported thereon by means of the wedge  52 , forming a stop. 
     The substrate  21  of the particulate filter is supported with the upstream face thereof on the shoulder  58  with a wedge  60  being interposed which is formed by an annular joint which has an L-shaped cross-section, one branch of which is interposed between the shoulder  58  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 lateral wall of the second portion  40 . 
     The connection between the first and second portions  38 ,  40  is provided by a peripheral weld seam  70  which is formed at the end of the female end  42  against the lateral wall  40  of the second portion. 
     The first and second portions  38 ,  40  are connected by being fitted to the divergent portion  26  and the convergent portion  30 , respectively. 
     More precisely, the divergent portion  26  has, at the periphery thereof having the largest diameter, a widened end in which the upstream end of the first portion  38  is fitted, the collar  46  being supported on the shoulder of the divergent portion  46  formed by the widened end. 
     The widened end of the convergent portion  30  is fitted at the inner side of the downstream end of the second portion  40 . To this end, it has a generally cylindrical outer edge  72  which is capable of pressing against the inner surface of the wall  40 . The convergent portion  30  presses against the substrate  21  of the particulate filter with a wedge  74  being interposed which is formed by a joint which is identical to the wedge  60 . 
     The wedges  60  and  74  define an axial clearance in the order of 5 mm and a radial clearance in the order of 3.5 mm. 
     The wedges are, for example, of the type LSP-5600.45 from the company ACS. They differ from the wedges  50  and  52  in that they are more dense in order to better absorb the forces of the particulate filter  20 . 
     Furthermore, the substrate  21  is surrounded in the current portion thereof by a retention sheet  76  which is interposed between the substrate and the inner surface of the portion  40 . This sheet is formed, for example, from ISOMAT AV 3280 g/m 2  from the company Unifrax. 
     For assembly, and as illustrated in  FIG. 2 , the catalytic purification element is first engaged inside the first portion  48 , the wedges  50  and  52  being interposed between the substrate  19  and the first portion  38 . 
     In the same manner, the substrate  21  of the particulate filter is engaged with the two wedges  60 ,  74  in the second portion  40 . The substrate is held in abutment against the shoulder  58  by the convergent portion  30  which is fitted in the second portion  40  from the rear end. In this manner, the substrate  21  is held secure between the shoulder  58  and the edge of the convergent portion  30 . The substrate  21  is held with a compression force of 4000N imposed by the convergent portion  30 . 
     The male end  44  of the second portion is fitted in the female end  42  of the first portion until the collar  56  which forms a stop comes into abutment against the wedge  52  in order to ensure axial locking of the substrate  19  of the catalytic purification element, this substrate being retained between the shoulder  48  and the stop  56  which is formed by the inner collar which is provided at the end of the male end  44 . The fitting force compressing the catalytic purification element  18  between the two support surfaces is controlled and is adjusted in accordance with the forces. This force is preferably between 1500 and 5000 N and is, for example, in the order of 2000 N. 
     It should be understood that, in a depollution device of this type, the substrate  19  of the catalytic purification element is retained axially only by fitting the male end  44  which is provided with the collar  56  in the female end  42 . In the same manner, the abutment of the male end of the second portion against the substrate  19  and via the substrate  19  against the shoulder  48  allows axial positioning of the first and second portions  38 ,  40  relative to each other. 
     In this manner, with an arrangement of this type, the collar  56  allows both locking of the substrate  19  and correct positioning of the first and second portions, which ensures a lower production cost of the depollution device. 
     In the embodiment envisaged above, the collar  56  also provides a stop function for the substrate  21  of the particulate filter. 
     In the embodiment of  FIG. 3 , elements which are identical or similar to those of the first embodiment have been given the same reference numerals. 
     The second portion  40  is equipped, at the end of the male end, as above, with an inner collar  56 . However, the substrate  21  of the particulate filter is not in abutment against the collar  56  but is retained axially inside the second portion  40  by the intermediate sheet  76  which is interposed between the lateral surface of the substrate  21  and the lateral wall of the second portion  40 . 
     Furthermore, and in order to allow releasable fixing of the first and second portions  38 ,  40 , in particular in order to clean the upstream face of the particulate filter, the first and second portions are connected by means of a removable collar  80  which surrounds a curved end edge  82  formed at the end of the female end  44  and a strip  84  which is fixedly joined to the outer surface of the portion  40 , the edge  82  being pressed against the strip  84  and both being retained inside the V-shaped profile of the collar  80 . 
     In the embodiment envisaged, the strip  84  is formed by an curved hoop which has a flat portion  86  which is extended with a portion  88  having a V-shaped cross-section which has two flanks which are inclined relative to each other by 90° and which forms the strip itself. The hoop is connected to the outer surface of the second portion  40  by means of a weld seam  90 . 
     Also in this embodiment, the axial positioning of the first and second portions, and the locking in position of the substrate  19  are provided by the inner collar  56 . Furthermore, the locking of the collar  80  retains the depollution element  18  by means of compression, in so far as the collar  80  surrounds the substrate  19 . 
     According to another embodiment, more than two portions are fitted successively. Each of them has a female end at the downstream end thereof, viewed in the flow direction, and a male end at the upstream end thereof, the male end of a portion being fitted in the female end of the adjacent portion. 
     In order to provide sealing with respect to gases at the periphery of the purification element  18 , it is possible to provide a heat-expandable sheet between the wedges  50  and  52 . If the depollution element  18  has a length less than 40 mm, it is no longer possible to position a sheet and it becomes necessary to use wedges alone to provide sealing with respect to gases. 
     The device of the invention is particularly suitable for those cases in which a short ceramic is used. A ceramic is said to be short when the length/diameter ratio is less than 0.5. 
     Advantageously, the wedges  50 ,  52  which are positioned at each corner of the depollution element  18  allow the element to be retained securely fixed to the inner side of the portion  38  whilst providing sealing between the body of the portion  38  and the substrate  19 . 
     When the depollution element  18  has a length/diameter ratio of less than 0.5, a maintenance sheet, that is to say, a material which surrounds the circumference of the element  18 , cannot be used in order to retain the depollution element in the portion  38  owing, on the one hand, to the small contact surface-area between the lateral surface of the depollution element and the surface of the portion  38  and, on the other hand, the strong vibrations to which the device is subjected during operation. The small surface-area is linked to the shortness of the depollution element  18 . 
     Advantageously, the collar  56  is short and extends only in an axial direction towards the inner side of the portion  38 . This collar is in abutment against a face of the wedge  52  in order to ensure that the wedge is held in position.