Abstract:
An exhaust gas purification system, in particular for motor vehicles, having at least one catalyst body ( 6 ) which is arranged in a housing ( 1 ) and which has an in particular honeycomb-like metal matrix ( 8 ) as a substratefor the active catalyst material and a jacket ( 10 ), also made of metal, surrounding the matrix ( 8 ) and attached thereto in particular by soldering, via which the catalyst body ( 6 ) is fixedly connected, in particular welded, to the housing ( 1 ), wherein the catalyst body ( 6 ) is only fixedly connected to the housing ( 1 ) at one point ( 16 ), in particular at its downstream end region

Description:
The present invention relates to an exhaust gas purification system, in particular for motor vehicles, having at least one catalyst body which is arranged in a housing and which has an in particular honeycomb-like metal matrix as a substrate for the active catalyst material and a jacket, also made of metal, surrounding the matrix and attached thereto in particular by soldering, via which the catalyst body is fixedly connected, in particular welded, to the housing. 
     The metal jacket around the matrix is required in such exhaust gas purification systems as the matrix with the active catalyst material is not of stable shape alone. In particular with underhood metal catalysts, the problem can arise that stresses occur between the jacket and the matrix, by means of which the matrix can detach from the jacket. These stresses occur due to the thermal stress and the uneven heating of jacket and matrix. 
     It is the object of the invention to provide an exhaust gas purification system of the kind first named which is improved in this respect over known exhaust gas purification systems. In particular, the stresses between the jacket and the matrix of the catalyst body and so the risk of detachment of the two from one another should be reduced. 
     This object is satisfied in that the catalyst body is only fixedly connected to the housing at one point, in particular at its downstream end region. 
     As a result of the fixed connection of the catalyst body to the housing at only one point, it is achieved that the jacket can expand with the matrix. As a result of the connection at only one side, the jacket is supported in the housing in a floating-like manner and can follow the thermal expansion movement of the matrix which heats up faster due to the direct contact with the exhaust gas. Stresses between the jacket and the matrix of the catalyst body are thereby reduced. This counters the detachment of the matrix from the jacket. 
     The jacket of the catalyst body is preferably surrounded by a gas space in communication with the exhaust gas flow, but not itself flowed through. The contact between the exhaust gas and the jacket of the catalyst body is improved by this design so that the jacket heats up faster. The thus reduced temperature differences between the jacket and the matrix result in a further reduction in stresses. 
     In accordance with a preferred embodiment of the invention, the catalyst body is arranged inside an inner pipe fixedly connected to the housing and, in turn, fixedly connected to the inner pipe. As a result, the jacket has no support function, with the exception of the matrix, and can thus be made with a reduced thickness. The thickness of the jacket can, for example, be reduced from 1.5 mm to approximately 1 mm or lower. To allow the thickness of the jacket to be reduced even further, a welded ring can be provided which grips round the jacket in the fastening region. 
     In accordance with a further embodiment of the invention, the inner pipe is spaced from the housing to form an insulation gap. The outside temperature of the exhaust gas purification system can be reduced and the heating up of the catalyst body accelerated in this way in a manner known as such. 
     In accordance with a further embodiment of the invention, the catalyst body is spaced from the inner pipe to form the gas space. The gas space to cause exhaust gas to flow over the jacket of the catalyst body is provided in a constructionally simple manner in this way. 
     The gas space is closed in particular at its downstream end, and its upstream end is in communication with the exhaust gas flow. The exhaust gas is thus led directly into the gas space so that the fast warming up of the jacket is ensured in an especially good manner. 
     In accordance with a special embodiment of the invention, the inner pipe is designed as a prolongation of an inlet pipe piece or an outlet pipe piece provided in the housing. A separate inner pipe can thus be saved and the directing of the exhaust gas is especially easy. 
     In accordance with a further embodiment of the invention, the inner pipe protrudes over the catalyst body at least at one side. It can thus be used advantageously in this way for communication with an adjacent exhaust gas directing element. 
     In accordance with another embodiment of the invention, the jacket is connected to the housing or the inner pipe via an intermediate pipe piece. This allows a welded joint to be made from the outside between the jacket of the catalyst body and the housing or the inner pipe. The matrix of the catalyst body is thus protected against welding splashes. 
     It is particularly preferred if the intermediate pipe piece engages into the inner pipe and is connected to the jacket with one end and protrudes over the associated end of the inner pipe and is connected to the inner pipe with the other end. A welded joint can thus also be made from the outside between the inner pipe and the intermediate pipe piece so that the matrix is again also protected from welding splashes. 
     In accordance with a further embodiment of the invention, which is also claimed independently, the jacket protrudes over the matrix at least at one side. A welded joint to fasten the catalyst body to the housing can thereby advantageously be provided in a region in which no matrix is present, The risk of destroying the matrix during the welding process can thereby be reduced. In addition, the intermediate pipe piece can advantageously engage into the protruding section of the jacket. 
     In a special embodiment of the invention, two catalyst bodies are arranged behind one another and at least the front catalyst body is fixedly connected to the housing only at one point. It has been found that it can be sufficient for only the front catalyst body to be supported in a floating manner, as the temperature stress of the rear catalyst body and so the stresses occurring there are much lower due to the gas dynamics and the flow distribution. If only the front catalyst body is supported in a floating manner, the exhaust gas purification system can be simplified in construction. 
     In accordance with embodiments of the invention, the inner pipe, the intermediate pipe piece or the jacket of the front catalyst body can be led to the rear catalyst body and be connected to the jacket of the rear catalyst body for the flow communication between the front catalyst body and the rear catalyst body. It is preferred if the inner pipe, the intermediate pipe piece or the jacket of the front catalyst engage into a protruding section of the jacket of the rear catalyst body. A welded joint can thereby also be introduced at a region in which no matrix is present and thereby the risk of the matrix being destroyed by the welding process can be reduced. 
     The jacket and the matrix and, preferably, also the welded joints between the jacket and the housing, the inner pipe and/or the intermediate pipe piece and/or between the jacket of the first catalyst body and the jacket of the second catalyst body are preferably made of the same material. The thermal expansion values of the different elements can thereby be matched to one another and so stresses reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention are shown in the drawing and described below. There are shown, in each case in schematic representation: 
         FIG. 1  a longitudinal section through a first variant of the exhaust gas purification system in accordance with the invention; 
         FIG. 2  a longitudinal section through a second variant of the exhaust gas purification system in accordance with the invention, and 
         FIG. 3  a longitudinal section through a third variant of the exhaust gas purification system in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The exhaust gas purification system shown in  FIG. 1  comprises a housing  1 , in particular formed from two half-shells, having an exhaust gas inlet aperture  2  and an exhaust gas outlet aperture  3 . The exhaust gas inlet aperture  2  is formed by an inlet funnel  4 ; the exhaust gas outlet aperture  3  by an outlet funnel  5 . 
     Two catalyst bodies  6  and  7 , namely a pre-catalyst  6  and a main catalyst  7 , are arranged behind one another in the housing  1  in the direction of flow  1 . The catalyst bodies  6  and  7  each comprise a metal matrix  8 ,  9  formed like a honeycomb as the substrate for the catalyst material and a jacket  10 ,  11 , also made of metal, preferably of the same metal as the matrix, enclosing the matrix  8 ,  9 . 
     The catalyst body  6  is arranged in a tubular section  12  which connects to the inlet funnel  4  and is made as one piece therewith, The tubular section  12  is spaced from the housing  1  so that an insulation gap  13  is formed between the tubular section  12  and the housing  1 . As can be seen, the insulation gap  13  is open towards the outer space via apertures  14 . 
     The jacket  10  of the catalyst body  6  protrudes over the matrix  8  at its downstream end. The jacket  10  and the tubular section  12  of the inlet funnel  4  contact one another in this section protruding over the matrix  8 . The jacket  10  is connected tightly and fixedly to the tubular section  12  via a peripheral welded joint  16 . The welded joint preferably consists of the same material as the jacket  10  and the matrix  8 . 
     The remaining part of the jacket  10 , in contrast, is spaced from the tubular section  12  of the inlet funnel  4 . This is achieved by the tubular section  12  having a diameter enlarged with respect to the section  15  in this region. In this way, a gas space  17  is created between the jacket  10  of the catalyst body  6  and the tubular section  12  of the inlet funnel  4 , said gas space  17  being closed at is downstream end. The upstream end of the gas space  17 , however, is in communication with the inside of the inlet funnel  4 , and so with the exhaust flow, via an annular aperture  18 . The upstream end of the catalyst body  6  is furthermore supported with respect to the tubular section  12  by a plurality of spacers  19  which are arranged spread over the periphery of the catalyst body  6  and which can preferably be burned off in the operation of the exhaust gas purification system. The assembly of the catalyst body  6  is made easier m this way. However, the spacers  19  can also be omitted. Furthermore, it is possible to provide one or more wire cushions enclosing the jacket  10  in full or in part instead of the spacers  19 . 
     The downstream end of the tubular section  12  of the inlet funnel  4  protrudes over the catalyst body  6  and is flared in diameter to form an intermediate funnel  20  in the exhaust gas flow direction I. The intermediate funnel  20  engages to fit into a protruding section  21  of the jacket  11  of the second catalyst body  7  and is tightly connected thereto by a peripheral weld  22 . The jacket  11  also shows a protrusion  23  at its downstream end into which the outlet funnel  5  engages to fit, The outlet funnel  5  is tightly connected to the protruding section  23  of the jacket  11  via a peripheral weld  24 . The jacket  11  of the second catalyst body  7  thus has a supporting function, while the jacket  10  of the first catalyst body  6  has no supporting function, with the exception of the matrix  8 . The supporting function is rather taken over by the tubular section  12  of the inlet funnel  4 , The welded joints  22  and  24  also preferably consist of the same material as the jacket  11  and the matrix  9 . 
     The matrix  8  and the matrix  9  are in each case soldered to the jacket  10  and the jacket  11  respectively. The soldering can be provided practically over the whole region of the matrix  8  by the arrangement of the weld  16  of the catalyst body  6  in the region of the protrusion  15  of the jacket  10 . A soldering is preferred in particular in the upstream end region of the matrix  8 . The soldering can also be provided in the catalyst body  7  approximately over the whole matrix  9  as the welded joints  22  and  24  of the jacket  11  are also provided in protruding sections  21 ,  23  of the jacket  11 . However, the soldering is provided in particular in the middle region of the matrix  9  due to the welding of the jacket  11  on both sides. 
     The exhaust gas purification system shown in  FIG. 2  largely agrees with the exhaust gas purification system of FIG.  1 . The main difference is that here the catalyst body  6  is in communication with the tubular section  12  of the inlet funnel  4  via a separate intermediate pipe piece  25 . The intermediate pipe piece  25 , which is formed as an intermediate funnel due to the flaring of its diameter in the direction of exhaust gas flow I, engages with its upstream end into the protruding section  15  of the jacket  10  and contacts this from the inside. The welded joint  26  between the jacket  10  of the catalyst body  6  and the intermediate pipe piece  25  can thereby be provided on the outside of the jacket  10  and the intermediate pipe piece  25  so that the matrix  8  is protected against weld splashing during the making of the welded joint  26 . 
     The downstream end of the intermediate pipe piece  25  contacts the tubular section  12  of the inlet funnel  4  from the inside, but protrudes over its downstream end. A welded joint  27  can thereby also be made from the outside between the intermediate pipe piece  25  and the tubular section  12  of the inlet funnel  4 . The protruding section  28  of the intermediate pipe piece  25  now engages to fit into the protruding section  21  of the jacket  11  of the second catalyst body  7  and is tightly connected thereto via a welded joint  22 . In all other respects, the two exhaust gas purification systems are in agreement with one another. 
     The variant of  FIG. 3  is also largely in agreement with the two variants described above. The difference is substantially that in the variant of  FIG. 3 , the jacket  10  of the first catalyst body  6  is extended up to the second catalyst body  7  and its extended section  15  engages into the protruding section  21  of the jacket  11  of the second catalyst body  7 . The flow communication is now effected only by the jacket  10  of the first catalyst body. This achieves a further simplification in construction. Another difference between the variant of FIG.  3  and the two previously described variants is that in the variant of  FIG. 3 , no spacers are present between the catalyst body  6  and the tubular section  12 . 
     The risk of detachment of the matrix  8  from the jacket  10  of the catalyst body  6  is reduced by the embodiment in accordance with the invention of the exhaust gas purification system. This is achieved in a simple constructive manner by the catalyst body  6  being supported in a floating manner in the tubular section  12  of the inlet funnel  4  and being fixedly connected to said tubular section only at one side. Despite the different heating-up, the jacket  10  can thereby expand with the matrix  8  so that the stresses occurring between the jacket  10  and the matrix  8  are reduced. A further reduction in the stresses results from the fact that the jacket  10  is flowed over by exhaust gas via the gas space  17  so that its warming up is less behind that of the matrix  8 . This can also be promoted by the thickness of the jacket  10  being reduced as much as possible, for example to 1 mm. This is made possibly by the jacket  10  exercising no supporting function, with the exception of the matrix  8 . 
     Reference Numeral List 
     
         
           1  Housing 
           2  Inlet aperture 
           3  Outlet aperture 
           4  Inlet funnel 
           5  Outlet funnel 
           6  First catalyst body 
           7  Second catalyst body 
           8  Matrix of  6   
           9  Matrix of  7   
           10  Jacket of  6   
           11  Jacket of  7   
           12  Tubular section 
           13  Insulation gap 
           14  Aperture 
           15  Section of  10   
           16  Weld 
           17  Gas space 
           18  Annular aperture 
           19  Spacer 
           20  Intermediate funnel 
           21  Section of  11   
           22  Weld 
           23  Section of  11   
           24  Weld 
           25  Intermediate pipe piece 
           26  Weld 
           27  Weld 
           28  Section of  25   
         I exhaust gas flow direction