Abstract:
A method for producing an exhaust-gas aftertreatment device ( 2 ) inserts a monolith ( 8 ) in a housing ( 4 ), assembled from a circumferentially enclosed jacket ( 5 ) and two end funnels. The monolith ( 8 ) is axially inserted into the jacket ( 5 ) with a circumferentially enclosing support mat ( 9 ). The funnels ( 6 ) are connected to the jacket ( 5 ) via an axial connecting section ( 10 ) shaped complementary to the cross-section of the jacket ( 5 ), such that each connecting section ( 10 ) and an axial end section ( 25 ) of the support mat ( 9 ) axially overlap. The jacket ( 5 ), including the connecting sections ( 10 ) of the funnels ( 6 ) from a starting cross-section ( 13 ) to an end cross-section ( 15 ). This produces a predetermined radial preload in the support mat ( 9 ) in a support area ( 16 ) extending from the one connecting section ( 10 ) to the other connecting section ( 10 ) to retain the monolith ( 8 ) in the jacket ( 5 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a United States National Phase Application of International Application PCT/EP2013/059783 filed May 13, 2013 and claims the benefit of priority under 35 U.S.C. §119 of German Patent Application 10 2012 208 449.5 filed May 21, 2012, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a method for producing an exhaust gas aftertreatment device. The invention additionally relates to an exhaust gas aftertreatment device for an exhaust system of an internal combustion engine, which can be arranged in particular in a motor vehicle. 
       BACKGROUND OF THE INVENTION 
       [0003]    Exhaust gas aftertreatment devices, such as for example catalytic converters and particles filters, can comprise at least one monolith for the exhaust gas aftertreatment, which is retained in a housing with the help of a bearing mat enclosing the monolith in the circumferential direction. Such monoliths can be produced comparatively cost-effectively from ceramic materials. Ceramic materials are characterized by high temperature resistance. However, ceramic materials are comparatively brittle and have a thermal expansion coefficient which significantly differs from the thermal expansion coefficients of metals, which are usually employed for producing the housing. The bearing mat thus serves to protect the monolith from voltage peaks. On the other hand, the bearing mat has to be deformable elastically reversibly in order to be able to offset thermally-induced expansion effects. Furthermore, the bearing mat can also dampen vibrations and oscillations in order to thereby reduce the loading of the monolith. A further problem when using ceramic monoliths is production-related. While the metallic housing can be produced with comparatively close shape tolerances, the shape tolerances for producing ceramic monoliths are significantly greater. The bearing mats, too, can have geometries or densities which vary, in particular from lot to lot. In order to be able to fix the respective monolith with sufficient strength in the housing with the help of the respective bearing mat, a predetermined preload force however has to be realized with which the bearing mat can be pressed into a ring gap, which radially materializes between the monolith and a jacket of the housing. If compression is too weak, the monolith can axially move relative to the housing during operation. Furthermore, the aggressive hot exhaust gases during the operation of the exhaust gas aftertreatment device can attack and destabilize the bearing mat. If by contrast the compression is too severe, the bearing mat can no longer elastically absorb the thermal expansion effects, as a result of which the lifespan of the mounting or the retaining of the monolith in the housing is likewise greatly impaired. Additionally, the permissible stresses can then be exceeded on the monolith as a result of which the risk of damaging the monolith also arises. To sort this problem it is usual to individually adapt the housing with respect to its dimensions to the respective monolith in order to provide a desired gap width radially between the monolith and the jacket of the housing. The predetermined radial gap width then leads to a predetermined radial compression of the bearing mat in the assembled state, so that the bearing mat can optimally fulfill its functions. 
         [0004]    Adapting the housing to the dimensions of the respective monolith can take place prior to inserting the monolith with the bearing mat in the jacket of the housing, so-called pre-sizing. Pre-sizing can be realized on the one hand in that a selection of housings with varying dimensions is kept in stock so that dependent on the respective monolith a housing that is suitable with respect to its dimensions can be installed. On the other hand it is possible to keep only one housing side in stock, which is matched to the largest monolith within the tolerance range. Since this standard housing is then too large, for most of the monoliths, a cross-sectional reduction has to be carried out before inserting the monolith in the jacket of the housing, which is possible with the help of suitable tools. During pre-sizing, introducing the monolith with the bearing mat in the housing is comparatively complex since during the axial insertion comparatively large shearing forces act on the bearing mat, as a result of which damages to the bearing mat can occur. 
         [0005]    Alternatively to pre-sizing, a so-called post-sizing can also be carried out, during which the monolith is axially introduced with the bearing mat into a comparatively large-dimensioned jacket of a standard housing and with which subsequently, i.e. with the monolith inserted in the jacket and enveloped by the bearing mat, a cross-sectional reduction is carried out in order to individually adapt the dimensions of the jacket or of the housing to the dimensions of the respective monolith. The cross-sectional reduction for adapting the dimensions of the housing to the individual dimensions of the respective monolith can also be called “calibrating” of the housing, namely both during pre-sizing and also during post-sizing. 
         [0006]    The housing usually consists of said material, which encloses the respective monolith with the bearing mat in the circumferential direction, and two funnels which are arranged at the face end of the jacket. Usually, the jacket and the two funnels are separate components so that the housing has to be assembled by attaching the two funnels to the jacket. Accordingly, at least one of the funnels has to be attached to the jacket after the inserting of the monolith. Usually, the respective funnel with a cylindrical connecting section can be plugged with the cylindrical jacket; either the funnel with its connecting section is plugged onto the jacket or into the jacket. Practically, jacket and funnel are fastened to one another by means of a closed circumferential weld seam in the circumferential direction. 
         [0007]    Since the jacket through the calibrating can have varying cross sections, further problems for attaching the funnels arise since standard funnels are too large as a rule and weld seams are comparatively unstable for offsetting these dimensions. For reducing these problems it is possible in principle to also calibrate the funnels so that calibrated funnels can then be plugged with the calibrated jacket. Through this measure, a radial play between the respective face-end region of the jacket and the connecting section of the respective funnel overlapping said jacket can be reduced. Thus, the required weld seams can be configured smaller, which favors their strength. 
         [0008]    In modern exhaust systems, in particular with smaller motor vehicles, there is frequently the desire to construct the respective exhaust gas aftertreatment device as compact as possible in the axial direction. This can be achieved in that within the housing the axial spacing between the monolith and the funnels is selected as small as possible. A further reduction of the dimensions can only be achieved in that the respective plugging region, in which the jacket and the respective funnel are plugged into one another, axially overlaps with an axial end region of the monolith. Because of this, new problems are created however since with plugged-in funnel the respective connecting section of the funnel then axially enters the ring gap between monolith and jacket, which impairs the installation space that is available for the bearing mat. With plugged-on funnel, however, an axial region of the jacket, in which the required calibrating can be carried out, is reduced. There is thus the risk altogether that the bearing mat can no longer optimally fulfill its retaining function. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention deals with the problem of providing an improved embodiment for an exhaust gas aftertreatment device of the type mentioned at the outset or for an associated production method which is characterized in particular in that an axially compact design with adequate retaining function of the bearing mat can be realized. 
         [0010]    The invention is based on the general idea of producing the exhaust gas aftertreatment device according to the post-sizing principle and to perform calibrating with funnels plugged with the jacket, wherein the funnels in their connecting sections are axially plugged with the jacket so far that the respective connecting section of the respective funnel axially overlaps an axial end section of the bearing mat. During calibrating, the jacket is then calibrated over its entire axial length including its end regions with which the funnels are plugged, i.e. subjected to a cross-sectional reduction. The cross-sectional reduction is thus carried out both in the connecting sections, in which a two-layered configuration of coaxially arranged funnel and jacket is present, and also in a bearing region, which axially extends from the one connecting section as far as to the other connecting section and in which a single-layered configuration is present, which is only formed by the jacket. Through the joint calibrating of jacket and plugged funnel logistics are simplified since only a standard size for the jacket and the funnels has to be kept in stock. At the same time, a radial gap between the connecting section of the respective funnel and the end section of the jacket running coaxially thereto is eliminated through the joint calibrating so that funnel and jacket are plugged into one another radially free of play. Because of this, realizing an adequately strong weld seam is simplified, since the latter does not have to bridge a radial gap at any point. It has been shown, furthermore, that the axial overlap of the respective connecting section with the bearing mat is less disadvantageous than expected. In particular, sealing of the bearing mat with respect to the exhaust gas is not impaired. Altogether, an extremely short or compact design for the exhaust gas aftertreatment device can be realized on the respective axial face end in the axial direction through the axial overlap of the respective connecting section of the respective funnel with an axial end region of the bearing mat and thus also of the jacket and of the monolith. 
         [0011]    According to an advantageous embodiment, calibrating can be carried out so that the cross-sectional reduction is identical in size in the bearing region and in the connecting sections. This means that the jacket including the end regions with the plugged connecting sections of the funnels over its entire axial length has a constant outer cross section after calibrating. Because of this, the calibrating operation is particularly simple. In particular, a conventional calibrating tool can be used for this purpose. Since in the face-end sections of the jacket through the plugged connecting sections of the funnels a double wall is present, increased radial compression of the bearing mat results with this configuration in the region of the axial overlap with the bearing mat. In particular, the bearing mat is compressed more strongly by the wall thickness of the wall sections in the connecting sections, at least in particular when the bearing mat in turn has a constant wall thickness in the axial direction. 
         [0012]    According to an advantageous further development it can now be provided to configure the bearing mat in the respective overlap region with a reduced wall thickness and/or with a reduced density. In particular, the bearing mat can have an annular step or an axial groove in the respective overlap region which with respect to its geometry can be matched to the wall thickness of the respective connecting section. In this way, a largely homogeneous compression can be realized over the entire axial extension of the bearing mat even when in the overlap regions the radial gap is smaller than in the bearing region. 
         [0013]    In another embodiment, calibrating by contrast can be carried out so that the cross-sectional reduction in the bearing region is greater than in the connecting sections. This means that following the calibrating the outer cross section of the jacket is constant over the entire axial length of the bearing region and in the end regions plugged with the connecting vessels of the funnels is greater than in the bearing region, i.e. is stepped or comprises a step. In other words, the wall doubling in the overlap regions is taken into account, as a result of which it is possible in particular to realize a largely constant gap width for the radial gap over the entire axial length of the bearing mat. Thus, a homogeneous compression of the bearing mat over the entire axial length can be realized. This applies in particular when the cross-sectional reduction in the bearing region is greater by the wall thickness of the respective connecting section than in the respective connecting section. 
         [0014]    In order to realize such a cross-sectional reduction which is inhomogeneous along the jacket, a special calibrating tool is advantageous which has a pushing contour shaped complementarily to the outer contour of the jacket for applying pressure forces reducing the cross section of the jacket. This calibrating tool accordingly is configured so that its pushing contour in the region of the connecting sections comprises a step each which represents a setback. Preferentially, the dimension of the step in radial direction is matched to the wall thickness of the respective connecting section. The inhomogeneous cross-sectional reduction in the finished housing leads to an outer cross section which is greater in the overlap regions than in the bearing region. 
         [0015]    According to an advantageous embodiment, the funnels are axially fixed in the calibrating tool relative to the jacket in order to avoid axial yielding of the funnels during calibrating. Additionally or alternatively it can be provided to fasten the funnels to the jacket after the assembly and prior to the calibrating. Such fastening can for example be realized by means of one or multiple spot welds or by means of a (temporary) weld seam. Thereby, the funnels can also be fixed to the jacket for the calibrating. 
         [0016]    After the calibrating, the funnels are each preferentially fastened to the jacket by at least one closed circumferential (final) weld seam. Since the funnels where jointly calibrated with the jacket, the funnels are plugged with the jacket radially free of place as a result of which the respective weld seam can be realized comparatively small. Because of this, the respective weld seam is provided with a particularly high fatigue strength. 
         [0017]    According to a further development of the method it can be provided that prior to assembling the housing the at least one monolith and/or the at least one bearing mat are measured in order to determine parameters required for the calibrating. Calibrating is then carried out dependent on the previously determined parameters. Such parameters are usually the cross-sectional geometry of the monolith and the thickness and/or density of the bearing mat. 
         [0018]    An exhaust gas aftertreatment device according to the invention is thus characterized in that the jacket together with the plugged connecting sections has been reduced through forming from an initial cross section to a final cross section in such a manner that the jacket and the funnels are plugged into one another radially free of play. A cross-sectional reduction through forming can be substantiated in the structure of the jacket and of the funnel. It can likewise be substantiated with the help of microstructures, which develop during forming on the contact surfaces of funnel and jacket, that jacket and funnel were jointly formed. 
         [0019]    Particularly advantageous is a further development, in which the jacket and the connecting sections of the funnels are radially preloaded against one another. Such radial preload can be achieved in that during the forming for the cross-sectional reduction the respective component located radially inside is more strongly deformed within the plug region. Since any plastic forming is also accompanied by an elastic forming, the relaxing of the formed components that occur after the forming can result in that the component located inside can theoretically relax more strongly than the component located outside, but is practically prevented from doing so by the component located outside, as a result of which the desired radial preload between the jacket and the respective connecting section is created. 
         [0020]    According to another embodiment, the jacket can comprise a step on at least an axial end region, in which the respective connecting section of the bearing mat overlaps. Such a configuration is obtained through the inhomogeneous cross-sectional reduction described above. 
         [0021]    Alternatively, an embodiment is also conceivable, in which the bearing mat is radially more strongly compressed in the respective overlap region at least in an axial end region of the jacket than in a bearing region extending from the one connecting section to the other connecting section. Such a constellation can result in particular when the homogeneous cross-sectional reduction described above is carried out. 
         [0022]    Practically, both end regions comprise such a step or the bearing mat is more greatly compressed in both overlap regions than in the bearing region. In principle, however, a combined design is also conceivable in which in the one end region a step is present while in the other end region stronger compression is provided. 
         [0023]    The invention additionally relates to a calibrating tool for calibrating a housing of such an exhaust gas aftertreatment device. Such a calibrating tool accordingly is characterized by a pushing contour for applying pressure forces reducing the cross section of the jacket, wherein this pushing contour in the region of the connecting sections has a step each, which in particular takes into account the wall thickness of the respective connecting section. 
         [0024]    The geometry of the monolith and the cross section of the jacket are of no consequence to the method, to the exhaust gas aftertreatment device and to the calibrating tool. Usual are above all round cross sections, for example with circular, oval or elliptical geometry. Alternatively, however, angular cross sections are also employed for example with a rectangular, hexagonal or triangular geometry. It is clear that the angular cross sections can be embodied suitably rounded in their corners. 
         [0025]    It is to be understood that the features mentioned above and still to be explained in the following cannot only be used in the respective combination stated but also in other combinations or by themselves without leaving the scope of the present invention. 
         [0026]    Preferred exemplary embodiments of the invention are shown in the drawing and are explained in more detail in the following description, wherein same reference characters relate to same or similar or functionally same components. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    In the drawings: 
           [0028]      FIG. 1  is a highly simplified schematic representation of an exhaust system in the region of an exhaust gas aftertreatment device; 
           [0029]      FIG. 2  is an expanded representation of the exhaust gas aftertreatment device; 
           [0030]      FIG. 3   a  is an end view of a monolith with bearing mat; 
           [0031]      FIG. 3   b  is a lateral view of a monolith with bearing mat; 
           [0032]      FIG. 4  is an expanded representation of the exhaust gas aftertreatment device during the assembly; 
           [0033]      FIG. 5  is a lateral view of the assembled exhaust gas aftertreatment device; 
           [0034]      FIG. 6   a  is a highly simplified longitudinal sectional view of the exhaust gas aftertreatment device in the region of a funnel before calibrating; 
           [0035]      FIG. 6   b  is a highly simplified longitudinal sectional view of the exhaust gas aftertreatment device in the region of a funnel after calibrating; 
           [0036]      FIG. 7   a  is a highly simplified longitudinal sectional view of the exhaust gas aftertreatment device in the region of a funnel before calibrating, according to another embodiment; 
           [0037]      FIG. 7   b  is a highly simplified longitudinal sectional view of the exhaust gas aftertreatment device in the region of a funnel after calibrating, according to the another embodiment of  FIG. 7   a;    
           [0038]      FIG. 8   a  is a highly simplified longitudinal sectional view of the exhaust gas aftertreatment device in the region of a funnel before calibrating, according to another embodiment; 
           [0039]      FIG. 8   b  is a highly simplified longitudinal sectional view of the exhaust gas aftertreatment device in the region of a funnel after calibrating, according to the another embodiment of  FIG. 8   a;    
           [0040]      FIG. 9   a  is a highly simplified longitudinal sectional view of the exhaust gas aftertreatment device in the region of a funnel before calibrating, according to another embodiment; 
           [0041]      FIG. 9   b  is a highly simplified longitudinal sectional view of the exhaust gas aftertreatment device in the region of a funnel after calibrating, according to the another embodiment of  FIG. 9   a;    
           [0042]      FIG. 10  is a longitudinal sectional view of the exhaust gas aftertreatment device in an axial end region, without funnel, with a special embodiment of the jacket; 
           [0043]      FIG. 11  is a longitudinal sectional view showing a further embodiment of the jacket; 
           [0044]      FIG. 12  is a longitudinal sectional view showing a further embodiment of the jacket; 
           [0045]      FIG. 13  is a sectional view showing an embodiment with a double-walled funnel; and 
           [0046]      FIG. 14  is a sectional view showing another embodiment with a double-walled funnel. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0047]    Referring to the drawings, according to  FIG. 1 , an exhaust system  1  for discharging exhaust gases of an internal combustion engine which is not shown here, which can be arranged in particular in a motor vehicle, comprises at least one exhaust gas aftertreatment device  2 , which is incorporated in an exhaust line  3  of the exhaust system  1 . The exhaust gas aftertreatment device  2  comprises a housing  4 , which comprises a jacket  5  and two face-end funnels  6 . The exhaust gas aftertreatment device  2  comprises a housing  4 , which comprises a jacket  5  and two face-end funnels  6 . Accordingly, the jacket  5  is closed in a circumferential direction, which relates to a longitudinal direction or axial direction  7  of the housing  4 . In the half sections of  FIGS. 6 to 10 , the longitudinal axis  7  simultaneously represents a longitudinal center axis in which a symmetry plane is located. 
         [0048]    As is evident from the  FIGS. 2 to 4 , the jacket  5  and the funnels  6  form separate components which have to be assembled to form the housing  4 . The housing  4  serves for accommodating at least one monolith  8  and at least one bearing mat  9 , which in the assembled state encloses the monolith  8  in the circumferential direction. 
         [0049]    In  FIG. 2 , the monolith  8  is perpendicularly turned relative to the housing  5  which is evident by the two longitudinal axes  7  running at 90° to one another. The bearing mat  9  is represented in the unrolled initial state. The respective funnel  6  has a connecting section  10  facing the jacket  5 , which is formed complementarily to the jacket  5  in such a manner that the respective funnel  6  can be plugged with the jacket  5 . In particular, the jacket  5  has a cylindrical cross section. Complementarily thereto, the connecting sections  10  then also have such a cylindrical cross section each. The funnels  6  can be plugged into the respective face end axial end region  11  of the jacket  5 , which is shown in the embodiments of  FIGS. 8 and 9 , or plugged onto the jacket  5 , which is shown in the versions of the  FIGS. 6 and 7 . A mixed design is also conceivable, in which the one funnel  6  is plugged into the jacket  5  while the other funnel  6  is plugged onto the jacket  5 . 
         [0050]    For the assembly of the exhaust gas aftertreatment device  1  or for assembling and filling the housing  4 , the respective monolith  8  according to the  FIGS. 3   a  and  3   b  is initially provided with the respective bearing mat  9  so that the bearing mat  9  encloses the monolith  8  in the circumferential direction. A corresponding circumferential butt joint of the bearing mat  9  is marked with  12  in  FIG. 3   a . Following this, the monolith  8  is axially plugged into the jacket  5  together with the bearing mat  9 . Following this, the funnels  6  are plugged onto the jacket  5 , which is hinted in  FIG. 4 . Following this, the state of the housing  4  shown in  FIG. 5  is present, in which the jacket  5  has an initial outer cross section  13 . Following this, calibrating of the housing  4  is carried out which is explained in more detail in the following with the help of the  FIGS. 6 to 9 . 
         [0051]    According to the  FIGS. 6 to 9 , the respective funnel  6  with its connecting section  10  is plugged onto the jacket  5  or plugged into the jacket  5  so that the respective connecting section  10  and an axial end section  14  of the bearing mat  9  axially overlap. Thus, the housing  4  and thus the exhaust gas aftertreatment device  2  is an extremely short construction in the axial direction  7 . 
         [0052]    During calibrating, the jacket  5  including the end regions  11 , in which the connecting sections  10  of the funnels  6  are located, is now reduced starting out from the initial cross section  13  to a final cross section  15  in such a manner that at least in a bearing region  16  a predetermined preload for retaining the monolith  8  in the jacket  5  is created in the bearing mat  9 . The bearing region  16  axially extends from the one connecting section  10  of the one funnel  6  as far as to the other connecting section  10  of the other funnel  6 , i.e. between the end sections  11 . 
         [0053]    In the embodiments of the  FIGS. 6 and 8 , calibrating is effected in such a manner that the cross-sectional reduction in the bearing region  6  and in the connecting regions  14  is approximately identical in size. As a consequence, a constant outer cross section, namely the final cross section  15  is obtained over the entire axial length of the jacket  5  including the connecting sections  10 . Since in the end sections  11  a wall thickness  17  of the respective connecting section  10  is added to a wall thickness  18  of the jacket  5 , a correspondingly greater radial compression is obtained in the overlap region  14  of the bearing mat  9 . In other words, with this procedure the bearing mat  9  in the overlap region  14  with the respective connecting section  10  is more strongly compressed than in the bearing region  16 . 
         [0054]    In the  FIGS. 6   a  and  8   a , a calibrating tool  19  is hinted which comprises a pushing contour  20 . This pushing contour  20  is formed complementarily to the upper contour of the jacket  5  and serves for applying pressure forces reducing the cross section of the jacket  5 . 
         [0055]    In the embodiments of the  FIGS. 7 and 9 , calibrating is effected in such a manner that the cross-sectional reduction in the bearing region is greater than in the connecting sections  10 . To this end, the previously mentioned calibrating tool  19  can have a step  21  in its pushing contour  20  in the region of the respective connecting section  10  which is practically dimensioned approximately identical in size as wall thickness  17  of the connecting section  10  in radial direction. During the forming, an inhomogeneous outer contour profile such as is evident for example in  FIGS. 7   b  and  9   b  is then obtained. In these cases, the housing  4  then has a step  22  on the respective axial end region  11  of the jacket  5  which in the plugged-on version according to  FIG. 7   b  is formed through the connecting section  10  of the respective funnel  6  and which in the plugged-in version according to  FIG. 9   b  is formed by a cranked end region  11  of the jacket  5 . 
         [0056]    The respective step  21  of the calibrating tool  19  practically takes into account the wall thickness  17  of the connecting section  17  in such a manner that after the calibrating a substantially homogeneous radial compression is obtained within the bearing mat  9  along the entire axial length of the bearing mat  9 . Evidently with the embodiments of the  FIGS. 7   b  and  9   b , a radial gap  23  is identical in size over the entire axial length of the monolith  8 , wherein said radial gap  23  is present radially between the monolith  8  and the jacket  5 . The bearing mat  9  is compressed in this radial gap  23 . It is remarkable that in the embodiments of  FIGS. 7   b  and  9   b  the radial gap  23  in the bearing region  16  is approximately identical in size as in the respective overlap region  14 . 
         [0057]    Following the calibrating, the respective funnel  6  can be fastened on the jacket  5  by at least one closed circumferential weld seam  24 . 
         [0058]      FIG. 10  shows an embodiment in which the bearing mat  9  comprises an annular step  26  in its axial end region  25 . The annular step  26  can for example simplify the axial plugging-in of the connecting section  10  in the end section  11  of the jacket  5  shown in  FIG. 9   a . In principle, such a stepped embodiment is also suitable for the version with plugged-on funnel  6 , since through the stepped configuration of the bearing mat  9  the radial compression in its end section  25  can be reduced even when according to  FIG. 6   b  or according to  FIG. 8   b  the radial gap  23  following calibrating is smaller in the overlap region  14  than in the bearing region  16 . In the embodiment shown in  FIG. 10 , the step  26  is molded radially outside in the end region  25  of the bearing mat  9 . Thus, this embodiment is particularly suitable for a plugged-in funnel  6  according to the  FIGS. 9   a  and  9   b . Alternatively, the step  26  can also be molded on the bearing mat  9  radially inside. Conceivable is also a version with two steps  26 , wherein the one annular step is then arranged radially outside while the other annular step is then arranged radially inside. 
         [0059]      FIG. 11  shows an embodiment of the bearing mat  9 , in which instead of such a step  26 , an axial open groove  27  is worked into the end region  25  of the bearing mat  9  in order to reduce the radial compression. While in the embodiments of  FIGS. 10 and 11  the bearing mat  9  altogether has a homogeneous density,  FIG. 12  shows an embodiment in which in the end region  25  a reduced density is realized. The reduced density provided in the subsequent overlap region  14  is specifically matched to the density of the bearing region  16  which is higher relative thereto in such a manner that after the forming in the bearing region  16  and in the overlap region  14  substantially the same preload forces can be realized although the compression in the overlap region  14  is stronger by the wall thickness  17  of the connecting section  10 . 
         [0060]    Although in the  FIGS. 6 to 9  the respective funnel  6  is represented as a single-walled funnel  6 , a two-walled funnel  6  can also be provided according to the  FIGS. 13 and 14 . The respective two-walled funnel  6  then has an outer funnel  26  and an inner funnel  32  which is arranged concentrically therein. The outer funnel  26  comprises the connecting section  10  for plugging on or plugging in on the jacket  5 . The inner funnel  32  is radially spaced from the outer funnel  26  at least in the respective conical region of the funnel  6  in order to thus form a ring gap  28 , which leads to a ring gap insulation or air gap insulation. According to  FIG. 13 , a thermally insulating insulation material  29  can be arranged in the ring gap  28 . 
         [0061]    In the embodiment shown in  FIG. 13 , the inner funnel  32  is equipped with a radially projecting collar  30  on its end facing the monolith  8 , which is practically dimensioned so that this ring-shaped collar  30  after the calibrating covers the ring space  23  on an axial face end of the bearing mat  9 , thus protecting it from the direct exposure to hot exhaust gas. In contrast with this,  FIG. 14  shows an embodiment in which the end of the inner funnel  32  facing the monolith  8  comprises an axially projecting collar  31 , which after calibrating dips into the ring space  23  in order to largely close off the same. In this way, efficient protection of the bearing mat  9  from exhaust gas can likewise be achieved. 
         [0062]    While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.