Abstract:
A catalytic purification device including a substrate permeable to exhaust gases, is optionally impregnated with catalytic materials, and is provided with an upstream face and an opposing downstream face; and an envelope containing the permeable substrate and defining an enclosure provided with an inlet line and an outlet line, between which the permeable substrate is arranged, the upstream face of the permeable substrate projecting along the extension of the inlet line, and the axis of the inlet line defining, with the upstream face ( 14 A), an angle smaller than 20°. The envelope includes a deflector arranged at the outlet of the inlet line, the deflector being inclined towards the upstream face and used to orient the exhaust gases escaping from the inlet line towards the permeable substrate. The envelope also includes elements for creating turbulence in the flow along the upstream face.

Description:
BACKGROUND OF THE INVENTION 
     Currently, exhaust lines for motor vehicles are provided with pollution control means and in particular devices for purification of exhaust gases, such as catalytic converters or particulate filters. These purification devices comprise, in a casing, a substrate which is permeable to exhaust gases, and which is optionally impregnated with catalytic substances which facilitate the conversion reaction of some polluting substances which are contained in exhaust gases. 
     Purification devices are commonly received in housings which are provided below the floor of the vehicle or in the engine compartment thereof. This housing sometimes has a small height and/or volume, with the result that it is complex to arrange the purification device at that location. 
     The substrates included in these purification elements are generally cylindrical having a circular cross-section. The length of the substrate measured between the upstream and downstream faces is often very much greater than the diameter of the upstream and downstream faces. In the case of a purification element which is placed below the floor, the substrate is arranged with the length thereof arranged horizontally so that the height of the cavity which receives the catalytic purification device must be greater than the diameter of the upstream and downstream faces of the substrate. In order to allow a purification element to be placed in a cavity having a small height, it was envisaged to use catalytic substrates which have a very small length and in contrast have very extensive upstream and downstream faces. The length is referred to as the thickness and these substrates are referred to as “pancakes” since they have a shape which is similar to a disc. 
     These substrates are arranged with their thickness very slightly inclined relative to the vertical. In order to allow the gases to flow, the inlet channel and the outlet channel of the catalytic purification device open with a slight incident angle practically tangentially relative to the upstream and downstream faces of the filter. 
     This type of catalytic purification device has low levels of efficiency in terms of pollution control, in particular owing to the unfavourable ratio between the small thickness of the filter and the large extent of the upstream and downstream faces, which limits the contact between the catalytic materials and the exhaust gases. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide a purification device for exhaust gases in which the inlet and outlet channels extend almost tangentially relative to the upstream and downstream faces of the substrate but which allows optimised use of the surface of the substrate by the gases. 
     To this end, the invention relates to a purification device of the above-mentioned type, characterised in that the casing comprises, at the outlet of the inlet channel, a deflector which is inclined towards the upstream face and which is capable of directing the exhaust gases from the inlet channel towards the permeable substrate. 
     According to specific embodiments, the purification device comprises one or more of the following features: 
     the deflector extends opposite the front half of the upstream face of the permeable substrate arranged at the side of the inlet channel; 
     the casing comprises a shell which covers the upstream face of the substrate and delimits therewith a chamber in the continuation of the inlet channel, and the deflector is formed by a deformation of the shell which delimits, towards the inner side of the chamber, a face which is inclined towards the permeable substrate; 
     the deflector extends over the main part of the width of the substrate, the width extending transversely relative to the direction of the inlet channel; 
     the deflector is curved in the plane of the upstream face of the permeable substrate, the centre of curvature of the deflector being arranged opposite the inlet channel relative to the deflector; 
     the deflector extends from the inlet channel between a bottom portion which is remote from the upstream face of the permeable substrate and a top portion which is close to the upstream face, and the casing comprises, from the top portion, a level which extends along the upstream face of the permeable substrate towards the rear end of the upstream face; 
     the level has, in the direction from the deflector towards the rear end of the upstream face, means which are capable of creating turbulences in the flow along the upstream face; 
     the means which are capable of creating turbulences in the flow along the upstream face comprise a succession of transverse faces; and 
     the thickness of the porous substrate measured between the upstream face and downstream face is less than half of the largest dimension of the upstream face of the permeable substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       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: 
         FIGS. 1 and 2  are a longitudinal section and top section, respectively, of a first embodiment of a purification device according to the invention; 
         FIGS. 3 and 4  are views which are identical to those of  FIGS. 1 and 2  of a production variant of the purification device of  FIGS. 1 and 2 ; and 
         FIGS. 5 and 6  are views which are identical to those of  FIGS. 1 and 2  of another production variant of the purification device according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The purification device  10  illustrated in  FIGS. 1 and 2  is intended to be fitted in an exhaust line of a motor vehicle which is equipped with a thermal engine. The purification device  10  comprises a casing  12  which delimits a closed space in which a substrate  14  is arranged. The casing  12  delimits an inlet  16  for admitting the exhaust gases and an outlet  18  for discharging the exhaust gases, between which the substrate  14  is arranged. 
     The substrate  14  is formed from a material which is preferably porous and permeable to exhaust gases. The substrate is optionally impregnated with catalytic materials. The substrate is formed, for example, from cordierite or silicon carbide, but it is conceivable to use a metal type substrate. Impregnating catalytic materials are, for example, those which are commonly used in 3-way catalysers, in oxidation catalysers or any other type of catalyser which can be used in an automotive application. 
     The substrate  14  has an upstream face  14 A which is directed towards the inlet  16  and a downstream face  14 B which is directed towards the outlet  18 . The upstream and downstream faces extend parallel with each other and together delimit the thickness e of the substrate. The substrate is generally cylindrical, the bottom thereof being formed by either the upstream or downstream face. In the example given, these faces have a generally oblong shape with two parallel longitudinal walls  14 C which are connected at the ends thereof by means of convex end walls  14 D. 
     Advantageously, the thickness e of the substrate, that is to say, the distance which separates the upstream and the downstream faces, is less than half of the maximum dimension of the upstream face or the downstream face of the substrate. The dimensions (length and width) of the substrate are between 150 and 300 mm. 
     In particular, the thickness e is preferably between 20 and 60 mm. It is 40 mm in the example in question. The length of the filter is 320 mm and the width thereof is 150 mm. 
     The casing  12  delimits, between the inlet  16  and the outlet  18 , a chamber  20  in which the substrate  14  is arranged. The casing is formed by two half-shells  22 A and  22 B which are assembled along a central longitudinal weld seam  24 . 
     The two half-shells  22 A,  22 B together delimit a case  26  in which the substrate  14  is accommodated and a divergent portion  28  and convergent portion  30  which open in the case  26  and at the end of which the inlet  16  and outlet  18  are formed, respectively. These inlets and outlets are delimited by cylindrical channels  32 ,  34  which allow a tube of the exhaust line to be connected, in particular by means of welding. 
     The axes X 1 -X 1  and X 2 -X 2  of the channels  32 ,  34 , respectively, extend parallel with each other and are offset along the height of the purification device by a small distance D of between 10 and 30 mm. 
     In the casing  26 , the substrate  14  is inclined relative to the directions X 1 -X 1  and X 2 -X 2  of the inlet and outlet channels so that the centre plane thereof, which is parallel with the upstream face  14 A and downstream face  14 B, defines, with the axes of the channels  32 ,  34 , a non-zero angle which is less than 20° and in particular equal to 6°. 
     The upstream face  14 A and downstream face  14 B, respectively, extend in the continuation of the channels  32 ,  34 . Each half-shell comprises a lateral wall  42 ,  44  which is capable of conforming to the shape of a convex end wall  14 D of the catalytic substrate  14 . 
     A peripheral sealing joint  46  is interposed between the catalytic substrate  14  and the peripheral wall of the case  26 . In particular, this joint is interposed between the lateral walls  42 ,  44  and the end walls  14 D of the catalytic substrate  14 . 
     The longitudinal walls  14 C of the substrate press on longitudinal walls of the case which are delimited, in the case of one half, by one of the half-shells and, in the case of the other half, by the other half-shell, the connection plane extending substantially along a diagonal line relative to the lateral faces of the case. 
     The divergent portion  28  and convergent portion  30  are connected at their wide end to the case  26 , at right-angles to the end walls  42 ,  44 , along a passage P having a small height. This passage has a height which is substantially equal to half of the diameter of the channels  32  and  34 . It extends over the entire width of the substrate  14  as illustrated in  FIG. 2 . The passage cross-section P is at least equivalent to two times the cross-section of the channels  32  and  34 . 
     Each channel  32 ,  34  is extended along the divergent portion  28  and convergent portion  30  in the continuation of the lateral walls  42 ,  44  with a ramp  52 ,  54  which is connected to the edges of the lateral walls  42 ,  44  at the bottom of the passage P. 
     Furthermore, along the other face thereof, the divergent portion  28  and the convergent portion  30  are each delimited by a main solid face  58 ,  60  which widens from the inlet or the outlet and which extends parallel with the axes X 1 -X 1  and X 2 -X 2 . 
     The passage P has a surface-area which corresponds to the projected surface-area of the corresponding face  14 A,  14 B of the substrate over the transverse section of the channel  34 . 
     In this manner, the upper edge of the passage P opposite the lateral wall  42  extends substantially in the region of the opposite end of the upstream face  14 A of the substrate. 
     According to the invention, a deflector  70  extends in the continuation of the inlet channel  32 . This deflector  70  is inclined towards the upstream face  14 A of the substrate  14  and is capable of directing the exhaust gases from the inlet channel  32  towards the substrate. This deflector  70  is arranged immediately downstream of the passage P and extends in the front half of the upstream face  14 A of the substrate arranged at the side of the inlet channel  32 . 
     Advantageously, the deflector  70  is provided in the first  20  percent of the upstream face  14 A close to the inlet channel  32 . 
     The deflector  70  is formed by a deformation of the upper shell  22 A which delimits a ramp  72  whose bottom portion  74  extends in the region of connection to the planar main face  58 . 
     The ramp  72  extends over the entire width of the upstream face  14 A. It has a curved shape whose centre of curvature is arranged at the side opposite the inlet channel  32  relative to the ramp  72 . This ramp defines, with the centre plane of the case parallel with the inlet channel  32 , an angle of between 20° and 50°, preferably substantially equal to 30°. 
     The ramp  72  extends in the direction of the upstream face  14 A of the substrate from the edge  74  which forms a bottom portion to an edge  76  which forms a top portion. The distance from the edge  76  to the upstream face  14 A is between 15 and 5 mm and is preferably substantially equal to 10 mm. 
     Beyond the edge  76  of the top portion, the wall which delimits the half-shell  22 A forms a smooth level  78  which extends substantially parallel with the upstream face  14 A as far as the lateral end wall  44  in order to form a lamellar space  80 . In the example in question, the level  78  is formed by a planar surface. This converges progressively towards the rear portion of the upstream face  14 A in the direction of the end wall  44  so that the distance which separates the level  78  from the upstream face  14 A is between 3 and 8 mm and in particular equal to 5 mm in the region of the rear portion of the upstream face  14 A. 
     The half-shell  22 B has the main face  60  which extends from the outlet channel  34  as far as the edge of the front end wall  42 . In this manner, an outlet chamber  84  which has a cross-section which increases progressively towards the channel  34  is delimited between the main wall  60  and the downstream face  14 B of the catalytic substrate. 
     With a purification device of this type, it is conceivable for the exhaust gases which penetrate into the casing  12  from the inlet channel  32  to be distributed over the entire cross-section of the passage P, flowing in the divergent portion  28 . The ramp  52  guides the flow which arrives in the lower half of the channel  32  to the upper half of the divergent portion  38 . The flow which is channeled in this manner, as soon as it enters the case  26 , comes into contact with the deflector  70  and is thus deflected towards the front portion of the upstream face  14 A. In this manner, a significant proportion of the exhaust gases penetrates into the substrate from this front portion of the upstream face  14 A. The remaining exhaust gases flow between the level  78  and the remainder of the upstream face, being rolled in the circulation layer delimited between the level  78  and the upstream face  14 A. In this manner, the other exhaust gases penetrate into the substrate progressively over the entire extent of the upstream face  14 A. The decreasing cross-section of the lamellar space  80  promotes the penetration of the exhaust gases through the substrate  14 . 
     It should be appreciated that, with a deflector of this type, the gases are restricted from first coming into contact with the front portion of the upstream face  14 A of the substrate, thus allowing a distribution of the gas stream which is advantageous for better use of the useful surface-area of the upstream face of the porous substrate. 
     On the other hand, in the absence of a deflector of this type, the gases which arrive tangentially relative to the upstream face  14 A penetrate firstly into the rear portion of the upstream face of the substrate and, in doing so, use only a small portion of the useful surface of this upstream face. 
       FIGS. 3 and 4 , on the one hand, and  FIGS. 5 and 6  illustrate production variants. In these alternative embodiments, elements which are identical or similar to those of the embodiment of  FIGS. 1 to 2  are given the same reference numerals. 
     In the embodiment of  FIGS. 3 and 4 , the level  78  is provided, from the edge  76  of the top portion of the deflector, with a succession of transverse channels  102 ,  104 ,  106  which open in the lamellar space  80  opposite the upstream face  14 A of the catalytic substrate. These channels have a cross-section which becomes progressively smaller from the front end to the rear end of the upstream face  14 A. They extend over the main part of the width of the upstream face  14 A. They are formed by a deformation of the wall which forms the half-shell  22 A. 
     These channels have, for example, a semi-circular cross-section and have a diameter of between 10 and 40 mm. 
     They form faces which are capable of creating a turbulence in the gas stream which flows in the lamellar space  80  which promotes the deflection of the gas stream towards the upstream face  14 A of the catalytic substrate at right-angles to each channel. 
     In the embodiment of  FIGS. 5 and 6 , the planar main face  58  extends beyond the deflector  70  opposite the upstream face  14 A via a planar surface which is designated  129 . This is connected to the edge  76  of the top portion of the deflector by means of a curved member  132 . 
     Furthermore, ribs  134 ,  136 ,  138  which are directed towards the upstream face  14 A are formed in the planar face  129 . These ribs extend along the main part of the width of the porous substrate. They delimit, together and with the deflector  70 , transverse channels  142 ,  144 ,  146 ,  148  which allow the gas stream to flow over the entire surface-area of the upstream face  14 A. The ribs  134 ,  136 ,  138  have, for example, a semi-circular cross-section and form means for creating turbulence in the gas stream which is formed downstream of the deflector  70 . As above, these means for forming turbulence promote the penetration of the exhaust gases through the front portion of the upstream face  14 A before the gases reach the rear portion thereof. 
     Of course, the means for forming turbulences may have forms which are different from that of the transverse ribs and may be constituted by localised deformations of the level  78 , for example, in the form of “bowls” which have a small diameter and depth as they extend towards the rear portion of the upstream face  14 A.