Abstract:
An exhaust gas treatment device ( 1 ), for an exhaust system ( 1 ) of an internal combustion engine, includes a housing ( 2 ), providing an exhaust path ( 3 ), an injector ( 4 ) arranged on the housing ( 2 ) for introducing a reduction agent into an exhaust gas flow following the exhaust gas path ( 3 ), and a mixer ( 7 ) arranged in the housing ( 2 ). The mixer ( 7 ) includes a shell ( 8 ), which encloses a mixer cross section ( 10 ) through which the exhaust gas flow can flow. The mixer ( 7 ) includes multiple guide blades ( 11 ), which on a shell inside project from the shell ( 8 ) and project into the mixer cross section ( 10 ). A simplified producibility is obtained with the mixer ( 7 ) including multiple straps ( 13 ), on a shell outside ( 14 ), which project from the shell ( 8 ) and project into a strap opening ( 16 ) formed on the housing ( 2 ) and penetrate a housing wall ( 15 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. §119 of German Patent Application 10 2014 222 296.6 filed Oct. 31, 2014, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to an exhaust gas treatment device for an exhaust system of an internal combustion engine, which can be arranged for example in a motor vehicle. 
     BACKGROUND OF THE INVENTION 
     For aftertreatment of exhaust gases of an internal combustion engine it can be required to introduce a liquid reactant into the exhaust gas flow. It can be required, for example, to introduce water or fuel into the exhaust gas flow. However, so-called SCR-systems, SCR standing for “selective catalytic reduction”, are of particular interest. With such an SCR system, attempts are made with the help of a reduction agent to reduce harmful nitrogen oxides contained in the exhaust gas to harmless nitrogen. A possible reduction agent in this case is ammonia. This is generally introduced into the exhaust gas flow in the form of a watery urea solution. Through thermolysis and hydrolysis, an efficient mixture of ammonia and carbon dioxide is created from this, which makes it possible in conjunction with an SCR-catalytic converter, to convert nitrogen oxides into nitrogen and water. In order for the respectively desired reaction to take place as efficiently as possible, extensive evaporation of the introduced liquid reactant and as homogeneous as possible a mixing-through of the reactant with the exhaust gas flow is required. For this purpose, stationary mixers are employed which are installed in a housing of the exhaust gas treatment device, specifically with respect to the exhaust gas flow downstream of an injector for introducing the reduction agent. 
     Since the exhaust gases of an internal combustion engine, depending on the operating state, can reach relatively high temperatures, efficient fixing of the mixer in the housing is required. Furthermore, exhaust gas treatment devices are products which are produced within the scope of large series. To this end, the construction of the exhaust gas treatment device has to be realizable as cost-effectively as possible. 
     SUMMARY OF THE INVENTION 
     The present invention deals with the problem of providing an improved embodiment for an exhaust gas treatment device of the type mentioned above, which is characterized in particular through cost-effective producibility. The aim at the same time is efficient and durable fixing of the mixer in the housing. 
     According to the invention an exhaust gas treatment device for an exhaust system of an internal combustion engine is provided. The device comprises a housing defining an exhaust gas path, an injector arranged on the housing for introducing a reduction agent into an exhaust gas flow following the exhaust gas path and a mixer arranged in the housing for mixing-through the reactant with the exhaust gas flow. The mixer comprises a shell (outer wall), which encloses a mixer cross section through which the exhaust gas flow can flow and comprises multiple guide blades, which on a shell inside project from the shell and project into the mixer cross section. The mixer further comprises multiple straps (or flanges), which on a shell outside project from the shell and in each case project into a strap opening formed on the housing and penetrate a housing wall of the housing. The mixer is a shaped single sheet metal part comprised of a single sheet metal piece, in which the shell, the guide blades and the straps are formed by the single sheet metal piece. 
     The invention is based on the general idea of equipping the mixer with multiple straps, which project from a shell of the mixer towards the outside and thereby engage in strap openings which are formed in a housing wall of the housing engaging about the mixer. During the production of the exhaust gas treatment device, the straps on the mixer side make possible simple positioning of the mixer in the housing in that the straps engage in the associated strap openings in a positively joined manner. Because of this it is possible in particular to at least temporarily fix the mixer on the housing via the straps engaging in the strap openings, so that final fixing can be carried out at a later time. Up to then, the handling of the housing with inserted mixer is simplified and in particular the further completion or production of the exhaust gas treatment device. 
     Furthermore, it is of special interest that the mixer is designed as a shaped sheet metal part which is characterized in that the mixer is produced by forming from a single sheet metal piece which comprises the shell, guide blades projecting there from and the aforementioned straps, wherein the forming can obviously be preceded by cutting processes and punching processes. Such a unitary shaped sheet metal part can be produced particularly cost-effectively, handle easily and inserted in the housing. By integrating the straps on this shaped sheet metal part, additional separate fastening means for fixing the mixer in the housing can be omitted. 
     In detail, the mixer comprises said shell which encloses a mixer cross section through which an exhaust gas flow can flow. During the operation of the exhaust system, the exhaust gas flow follows an exhaust gas path which passes through the housing of the exhaust gas treatment device. The aforementioned guide blades project from the shell on a shell inside and project into the mixer cross section. The guide blades can generate swirling of the exhaust gas flow through their geometrical shape and through their blade angle with respect to the exhaust gas flow, which is advantageous for intensive mixing-through between reactant and exhaust gas. 
     According to an advantageous embodiment, the straps in each case can be fastened to the housing from the outside by means of a welded connection, wherein the respective welded connection closes off the associated strap opening. By providing the welded connections on a wall outside of the housing wall facing away from the mixer, the previously mentioned final fixing of the mixer in the housing can also be performed with closed housing, which substantially simplifies the production of the exhaust gas treatment device. By using a welded connection, the strap openings, at the same time, can be additionally closed off sufficiently gas-tight in order to avoid undesirable leakages in the region of the strap openings. 
     In another embodiment, the mixer, on its shell outside, can be radially supported via supporting zones on a wall inside of the housing wall, wherein the supporting zones are arranged distributed in the circumferential direction of the shell and spaced from one another. As a consequence, an air gap is formed radially between the shell outside and the wall inside outside the strap and outside the supporting zones which acts as thermal insulation between mixer and housing. With the help of the supporting zones which are distributed in the circumferential direction and spaced from one another, only a local contacting that is limited to few places thus takes place between mixer and housing or between shell and housing wall, which on the one hand makes possible larger manufacturing tolerances and on the other hand reduces a heat transfer between mixer and housing through heat conduction to few, small singular places. In the air gap, by contrast, a heat transfer takes place only through heat radiation, which corresponds to efficient thermal insulation. A radially measured gap width of the air gap in this case can be smaller than a wall thickness of the shell and/or a wall thickness of the housing wall in the region of the mixer. 
     According to an advantageous further development, the supporting zones can be formed by elevations, which, through forming, are integrally shaped only on the housing wall. Alternatively, an embodiment is also possible, in which the supporting zones are formed by elevations, which are integrally shaped by forming only on the shell. Likewise, mixed forms may be provided in which the supporting zones are formed by elevations, which are integrally shaped by forming both on the housing wall and also on the shell. Preferred, however, is a configuration, in which the elevations are integrated in the housing wall. 
     Particularly preferably in this case is a further development, in which the supporting zones in each case are formed in the region of the straps. In other words, the respective strap and the associated strap opening in this case are formed within such a supporting zone. By placing the supporting zone and the plug connections between the straps and the strap openings together, the number of contact places between shell and housing wall can be reduced, which improves the thermal insulation of the mixer relative to the housing. 
     In principle, however, any embodiment may be provided in which the supporting zones and the straps are formed separately and are spaced from one another in the circumferential direction of the shell. 
     According to another advantageous embodiment, the housing can be configured in a two-shelled manner at least in a housing section containing the mixer such that the shell outside extends in a first circumferential section along a first housing shell and along a second circumferential section along a second housing shell. The two-shelled configuration of the housing simplifies the installation of the mixer in the housing. In particular, the mixer can thus be inserted in the housing shell while the other housing shell can then be subsequently attached. In particular in the case that the mixer comprises a shell running around closed in the circumferential direction, axially inserting the mixer in a closed housing can prove difficult because of the straps which radially project to the outside. Through the shell design, the housing can now be opened for inserting the mixer. Furthermore, the two-shelled design makes possible a housing geometry which deviates from a conventional cylindrical design. 
     According to an advantageous further development, at least one such supporting zone each can be formed in the region of the first housing shell and in the region of the second housing shell. Accordingly, the mixer is supported both on the first housing shell as well as on the second housing shell via such supporting zones. 
     According to another further development, at least one such strap opening each can be formed on the first housing shell and on the second housing shell. Through this design it is achieved that the mixer is fixed both on the first housing shell and also on the second housing shell. 
     Practically, the mixer cross section can be flat so that a width of the mixer is greater than a height of the mixer. In particular, the mixer is at least twice as wide as high. The width and the height in this case are measured perpendicularly to one another and perpendicularly to a longitudinal direction, which is defined by the through-flow direction of the mixer or by the flow direction of the exhaust gas flow. 
     Practically, the guide blades can run straight and parallel to one another. In particular in connection with a flat cross section, an efficient flow guiding effect for the guide blades is obtained with such parallel guide blades. In the case of a flat shell cross section, the straight guide blades extend parallel to the height direction. Here, at least one guide blade row is formed on the shell, in the case of which the guide blades are arranged next to one another in the width direction of the shell cross section. 
     A particularly simple producibility of the mixer is ensured by a design in which the guide blades in each case are connected in a fixed manner to the shell at one end, while they are arranged in a free-standing manner on the other end. Thus, the guide blades project from the shell and project into the mixer cross section in a free-standing manner. Here, thermal expansion effects cannot create any stresses whatsoever of the guide blades within the mixer. Relative movements of the guide blades relative to the shell cannot create any noises either. 
     Particularly advantageous is an embodiment, in which the shell on an inflow-sided or outflow-sided mixer side comprises a first circumferential section and a second circumferential section, which are located opposite one another. This is true in particular for a design with flat mixer cross section. The circumferential sections that are located opposite one another then extend each along the width direction and lie opposite one another in the height direction. Practically it can now be provided that the first circumferential section comprises first guide blades which project from the first circumferential section in the direction of the second circumferential section. Thus, a first guide blade row is formed on the first circumferential section, in the case of which the first guide blades are arranged next to one another in the width direction. Furthermore, the second circumferential section comprises second guide blades, which project from the second circumferential section in the direction of the first circumferential section. Thus, the second circumferential section has a second guide blade row, in which the second guide blades are arranged next to one another in the width direction. Particularly advantageous now is an embodiment, which the first guide blades are arranged in the flow direction of the exhaust gas flow offset from the second guide blades. In this way, the guide blades of the one guide blade row are subjected to earlier inflow during the operation of the exhaust system than the guide blades of the other guide blade row. Because of this it is possible, in particular, to arrange a larger number of guide blades on the respective mixer side, since both the first circumferential section and also the second circumferential section can be utilized for this purpose. In addition it is likewise possible to arrange the first guide blades and the second guide blades with different blade angles, in particular, the first guide blades can be set at an angle opposite to the second guide blades. Because of this, the mixing-through can be substantially improved. In addition to this it is particularly easily possible through this design to take into account specific flow geometries, which form within the exhaust gas path in the region of the mixer in order to optimize the mixing-through of reactant and exhaust gas flow. To this end it can be required to arrange the first guide blades and/or the second guide blades only over a part of the height of the mixer cross section, for example the first guide blades can each extend over 50% to 75% of the height of the mixer cross section, while the second guide blades extend between 25% and 50% of the height of the mixer cross section. In particular, the first guide blades can have a greater height than the second guide blades. Likewise an embodiment may be provided in which the mixer both on its inflow side and also on its outflow side comprises to guide blade rows each, which can be arranged offset from one another in the flow direction of the exhaust gas. 
     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. 
     Preferred exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein same reference numbers 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 
       In the drawings: 
         FIG. 1  is a schematic lateral view of an exhaust gas treatment device; 
         FIG. 2  is a schematic view of the exhaust gas treatment device corresponding to view direction II in  FIG. 1 ; 
         FIG. 3  is a schematic sectional view of the exhaust gas treatment device corresponding to section lines III in  FIG. 2 ; 
         FIG. 4  is a schematic enlarged view of a detail IV from  FIG. 3 ; 
         FIG. 5  is a schematic view of the exhaust gas treatment device according to view direction V in  FIG. 1 ; 
         FIG. 6  is a schematic sectional view of the exhaust gas treatment device according to section lines VI in  FIG. 5 ; 
         FIG. 7  is a schematic enlarged detail VII from  FIG. 6 ; 
         FIG. 8  is a schematic view as in  FIG. 2 , however showing another embodiment; 
         FIG. 9  is a schematic sectional view corresponding to section lines IX in  FIG. 8 ; 
         FIG. 10  is a schematic enlarged detail X from  FIG. 9 ; 
         FIG. 11  is a schematic view as in  FIG. 5 , however showing the other embodiment; 
         FIG. 12  is a schematic sectional view corresponding to section lines XII from  FIG. 11 ; 
         FIG. 13  is a schematic enlarged detail XIII from  FIG. 12 ; 
         FIG. 14  is a schematic front view of a mixer; 
         FIG. 15  is a schematic lateral view of the mixer corresponding to view direction XV in  FIG. 14 ; 
         FIG. 16  is a schematic lateral view of the mixer corresponding to view direction XVI in  FIG. 14 ; 
         FIG. 17  is a schematic sectional view of the mixer corresponding to section lines XVII in  FIG. 16 ; 
         FIG. 18  is a schematic enlarged detail XVIII from  FIG. 17 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, according to  FIG. 1 , an exhaust gas treatment device  1 , which is only partly shown here, which is provided for use in an exhaust system of an internal combustion engine, comprises a housing  2  which is likewise only partly shown, through which leads an exhaust gas path  3  indicated by arrows. The exhaust gas treatment device  1  additionally comprises an injector  4 , which is arranged on the housing  2 , and with which a reactant can be introduced into an exhaust gas flow, which during the operation of the exhaust system follows the exhaust gas path  3 . According to a preferred embodiment, the exhaust gas treatment device  1  is an SCR-system, with which with the help of the injector  4 , watery urea solution can be sprayed into the exhaust gas flow. In the housing  2 , an SCR-catalytic converter  5  is then arranged in the exhaust gas path  3  downstream of the injector  4 , which makes possible reducing nitrogen oxides to nitrogen and water by means of ammonia and carbon dioxide. In the housing  2 , a static mixer  7  is additionally arranged in a mixing region  6  indicated by a brace, which is evident in the sectional views of  FIGS. 3, 4, 6, 7, 9, 10, 12, 13  and in the views of the  FIGS. 14 to 18 . The mixer  7  serves for mixing-through the reactant with the exhaust gas flow. To this end, the mixer  7  is arranged in the exhaust gas path  3  downstream of the injector  4  and upstream of the SCR-catalytic converter  5 . 
     As is evident in particular from the views of  FIGS. 14 to 18 , the mixer  7  comprises a shell  8 , which in a circumferential direction  9  encloses a mixer cross section  10  through which an exhaust gas flow can flow. Furthermore, the mixer  7  comprises multiple guide blades  11 , which on a shell inside  12  project from the shell  8  and project into the mixer cross section  10 . As is evident in particular from the detail views of the  FIGS. 4, 7, 10, 13 and 18 , the mixer  7  additionally comprises multiple straps  13  which in each case project on a shell outside  14  from the shell  8  to the outside. Complementarily to the straps  13 , strap openings  16  are formed in a housing wall  15  of the housing  2 , wherein each strap  13  projects into such a strap opening  16 . In this case, a separate strap opening  16  is provided for each strap  13 . The straps  13  engaging in the strap openings  16  bring about fixing of the mixer  7  in the housing  2 . This fixing in this case is effected by way of a positive connection. Final fixing of the mixer  7  in the housing  2  in this case can be effected by means of welded connections  17 , with which the respective strap  13  is fastened to the housing wall  15  on a housing outside  18  namely practically in such a manner that in the process the associated strap opening  16  is closed off at the same time. In particular, the respective welded connection  17  can be formed as a weld seam which surrounds the respective strap  13  along the strap opening  16  in a closed manner. Instead of a surrounding weld seam, a pendulum seam can also be provided, which runs over and beyond the respective strap opening  16 . 
     As is evident in particular from the  FIGS. 14 to 17 , the mixer  7  is preferentially configured as a shaped sheet metal part  19 , which is formed by a single sheet metal piece  20 , which comprises the shell  8 , the guide blades  11  and the straps  13 . In a starting state, the sheet metal piece  20  is flat. The guide blades  11  and the straps  13  are cut clear, for example by a punching process or a cutting process. Following this, the guide blades  11  and the straps  13  are angled relative to the remaining sheet metal piece  20 . The remaining region of the sheet metal piece  20  thereby forms the shell  8 , which by bending over in the circumferential direction  9  is preferably bent over so far that its longitudinal ends from a joint  21 . 
     Practically, the mixer  7  on its shell outside  14  is radially supported on a wall inside  23  of the housing wall  15  via supporting zones  22 . In this case, multiple such supporting zones  22  are provided, which are arranged distributed in the circumferential direction  9  of the shell  8  and spaced from one another. With the help of these supporting zones  22  it is achieved that the mixer  7  only supports itself on the housing  2  only locally via these supporting zones  22 . In particular, the mixer  7  because of this does not have any physical contact with the housing  2  outside these supporting zones  22  and outside the plug connections, which in each case are formed by a strap  13  inserted in the associated strap opening  16 . Accordingly, an air gap  24  is formed radially between the shell outside  14  and the wall inside  23  outside the straps  13  and outside the supporting zones  22 . With the help of this air gap  24 , an air gap insulation between mixer  7  and housing  2  is created. 
     The supporting zones  22  are formed by elevations  25 , which in the case of the embodiments shown here are each integrally shaped on the housing wall  15  by forming. Accordingly, the elevations  25  project from the housing  2  or from the housing wall  15  to the inside in the direction of the mixer  7 . In the embodiments shown in the  FIGS. 1 to 7 , the supporting zones  22  are positioned spaced from the straps  13  in the circumferential direction  9 , in the view of  FIG. 2 , a supporting zone  22  is arranged in the circumferential direction  9  between two adjacent straps  13 . In the view of  FIG. 5 , by contrast, a strap  13  is arranged in the circumferential direction  9  between two adjacent supporting zones  22 . 
     In contrast with this, the  FIGS. 8 to 13  show an embodiment, in which the supporting zones  22  are each formed in the region of the straps  13 . In this case, the respective strap opening  16  is located within the respective supporting zone  22 . Accordingly, the respective strap  16  is also arranged within the respective supporting zone  22 . In the view of  FIG. 8 , two supporting zones  22  are evident, in which, in each case, the interaction between strap  13  and strap opening  16  takes place centrally. In contrast with this, only one supporting zone  22  is evident in the view of  FIG. 11 , in which the respective strap  13  engages in the associated strap opening  16 . 
     As is evident in particular from the  FIGS. 3, 6, 9 and 12 , the housing  2 , in the housing section  26  shown here, which contains the mixer  7 , is configured in a two-shelled manner so that a first shell  27  and a second shell  28  are provided, which are inserted into one another or attached to one another. In the shown example, a substantially flat connection zone  29  is provided, in which the two housing shells  27 ,  28  are attached to one another. 
     The mixer  7  is installed in the two-shelled housing section  26  so that a first circumferential section  30  of the shell  8  extends along the first housing shell  27 , while a second circumferential section  31  of the shell  8  extends along the second housing shell  28 . In the examples shown here, the first circumferential section  30  comprises two straps  13 , and the first housing shell  27  comprises the two associated strap openings  16 . The second circumferential section  31  by contrast comprises only a single strap  13 . The second housing shell  28  comprises the strap opening  16  fitting the same. Both on the first housing shell  27  and also on the second housing shell  28 , the elevations  25  in the mixer region  6  are shaped by a stamping process or the like in order to form the contact zones  22 . 
     As is evident in particular from the  FIGS. 14 to 17 , the mixer cross section  10  is practically flat so that a width  32  of the mixer  7  is greater than a height  33  of the mixer  7 . In this case, the inner dimensions are drawn in  FIG. 14 . The same then applies also to the outer dimensions. In the example, the width  32  is at least twice the size as the height  33 . 
     Furthermore, all guide blades  11  are configured as straight guide blades  11  in this case, which are each orientated parallel to the height direction. Accordingly, all guide blades  11  run parallel to one another. Furthermore, the guide blades  11  in each case project into the mixer cross section  10  in a free-standing manner. They consequently have free ends which do not have any contact with the shell  8 . 
     In the case of the mixer  7  introduced in this case, a total of four guide blade rows  34  are formed, namely a first guide blade row  34   1 , a second guide blade row  34   2 , a third guide blade row  34   3  and a fourth guide blade row  34   4 . In  FIG. 15 , a flow direction  35  of the exhaust gas flow is indicated by an arrow. On the inflow sided mixer side  36  and on the outflow-sided mixer side  37 , the shell  8  comprises a first circumferential section  30  and a second circumferential section  31  each, which with the flat mixer cross section  10  are located opposite one another. The first circumferential section  30  of the inflow-sided mixer side  36 , which can also be called inflow side  36  or inlet side  36 , comprises guide blades  11 , which from the first circumferential section  30  project in the direction of the second circumferential section  31  and which in the example form the fourth guide blade row  34   4 . On the inflow-sided mixer side  36 , which can also be called inflow side  36  or inlet side  36 , the second circumferential section  31  comprises guide blades  11 , which project from the second circumferential section  31  in the direction of the first circumferential section  30 . These guide blades  11  in the example form the third guide blade row  34   3 . On the outflow-sided mixer side  27 , which can also be called outflow side  37  or outlet side  37 , the first circumferential section  30  comprises guide blades  11 , which project from the first circumferential section  30  in the direction of the second circumferential section  31 , and which in the example form the second guide blade row  34   2 . Finally, on its outflow-sided mixer side  37  on the second circumferential section  31 , the shell  8  comprises guide blades  11  which project from the second circumferential section  31  in the direction of the first circumferential section  30  and which in the example form the first guide blade row  34   1 . 
     On the respective mixer side  36 ,  37 , the guide blades  11  of the first circumferential section  30  are arranged offset in the flow direction  35  relative to the guide blades  11  of the second circumferential section  31 . Accordingly, the exhaust gas flow consecutively flows about or flows through the four guide blades rows  34  shown in this case. The two guide blade rows  34   3  and  34   4  of the inflow-sided mixer side  36  each extend over the entire height  33  of the mixer  7 . In this case, the guide blades  11  of the third guide blade row  34   3  and the guide blades  11  of the fourth guide blade row  34   4  are set at an angle opposite to the exhaust gas flow. 
     Opposite blade angles are also provided in the case of the two guide blade rows  34   1  and  34   2  of the outflow-sided mixer side  37 . There it is additionally provided that the guide blades of the first guide blade row  34   1  and of the second guide blade row  34   1  are designed differently in size. In particular it is evident that the guide blades  11  of the first guide blade row  34   1  and of the second guide blade row  34   1  each do not extend over the entire height  33  of the mixer  7 . It is rather evident from the  FIGS. 14 and 17  that a guide blade  11  each of the first guide blade row  34   1  and a guide blade  11  each of the second guide blade row  34   2  jointly reach the height  33  of the mixer  7 . In particular, a separating plane  38  is evident, which is located between the two circumferential sections  30 ,  31 . The guide blades  11  of the first guide blade row  34   1  extend from the second circumferential section  31  only as far as to the separating plane  38 . The guide blades  11  of the second guide blade row  34   2  by contrast extend from the first circumferential section  30  only as far as to the separating plane  38 . 
     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.