Abstract:
A static mixer ( 12 ) for an exhaust system ( 7 ) for mixing a reducing agents with an exhaust gas flow ( 8 ). The static mixer ( 12 ) has a plurality of guide blades ( 14 ) for deflecting the exhaust gas flow ( 8 ). A reduced flow resistance is obtained when at least one of the guide blades ( 14 ) has a perforation ( 25 ) through which the exhaust gas flow ( 8 ) can flow.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119 of German Patent DE 10 2014 213 746.2 filed Jul. 15, 2014, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention pertains to a static mixer for an exhaust system for mixing a reducing agent with an exhaust gas flow. The present invention also pertains to an exhaust system equipped with such a mixer. 
       BACKGROUND OF THE INVENTION 
       [0003]    In exhaust systems of internal combustion engines there is in certain applications the need to introduce a reducing agent into the exhaust gas flow. For example, a fuel can be introduced into the exhaust gas flow upstream of an oxidation catalytic converter in order to increase the heat of the exhaust gas flow due to a reaction of the fuel in the oxidation catalytic converter, for example, in order to heat up a particle filter that is arranged downstream to its regeneration temperature. It is likewise common in SCR systems to introduce an aqueous urea solution upstream of an SCR catalytic converter into the exhaust gas flow, whereby SCR denotes Selective Catalytic Reaction. The aqueous urea solution can be converted by means of thermolysis and hydrolysis into ammonia and carbon dioxide, which makes a conversion of nitrogen oxides into nitrogen and water possible in the SCR catalytic converter. 
         [0004]    In order to optimize the respective reaction, which shall be brought about with the reducing agent introduced, it is of high importance to mix the introduced reducing agent with the exhaust gas flow as homogeneously as possible. Frequently, the reducing agent is introduced in liquid form into the exhaust gas flow, such that it is also necessary to evaporate the reducing agent as completely as possible. A static mixer mentioned in the introduction, which brings about an intense mixing of exhaust gas and reducing agent, is used for this purpose. 
         [0005]    A static mixer, which has a plurality of guide blades for deflecting the exhaust gas flow, is known from EP 1 985 356 A2. For this purpose, the guide blades project into the exhaust gas flow and are set towards the exhaust gas flow in order to be able to bring about the respective deflection of the exhaust gas flow. As a result of this, the guide blades at the same time form impact areas for the reducing agent introduced in liquid form. Due to the impact of the guide blades with the exhaust gas flow, these guide blades have a relatively high temperature, such that the guide blades at the same time are used as evaporation surfaces for reducing agent deposited thereon. 
         [0006]    An as large as possible impact surface, on the one hand, and an as intensive as possible deflection of the flow, on the other hand, result each in an increased flow resistance of the mixer. The flow resistance of the mixer brings about a rise in pressure in the exhaust system upstream of the mixer, which reduces the efficiency of an internal combustion engine equipped with the exhaust system or increases its fuel consumption. 
       SUMMARY OF THE INVENTION 
       [0007]    An object of the present invention is to provide an improved embodiment for a static mixer of the type mentioned above or for an exhaust system equipped therewith, which is characterized especially by a comparatively low flow resistance, while at the same time a sufficient mixing and especially a sufficient evaporation can be achieved. 
         [0008]    According to the invention, a static mixer is provided comprising a plurality of guide blades for deflecting the exhaust gas flow. At least one of the guide blades comprises a perforation through which the exhaust gas flows. 
         [0009]    According to another aspect of the invention, an exhaust system is provided for an internal combustion engine. The exhaust system comprises an injector for introducing a liquid reducing agent into an exhaust gas flow and at least one static mixer arranged downstream of the injector with regard to the exhaust gas flow. The static mixer comprises a plurality of guide blades for deflecting the exhaust gas flow. At least one of the guide blades comprises a perforation through which the exhaust gas flows. 
         [0010]    The present invention is based on the general idea of equipping at least one of the guide blades, and preferably all guide blades, each with a perforation, through which the exhaust gas, i.e., a part of the exhaust gas flow, can flow. It has been shown that such a perforation can significantly reduce the flow resistance of the mixer, whereby at the same time turbulence is sufficiently generated by the perforation to bring about the desired intensive mixing. 
         [0011]    In the present context, a perforation is defined as any interruption of a structure of the guide blade that is otherwise closed or impermeable to exhaust gas. Thus, openings, through holes, tiltings and the like are perforations. 
         [0012]    The perforation of the respective guide blade may in this case have a plurality of passage openings which are each arranged within a lateral outer contour of the respective guide blade according to a preferred embodiment. Thus, the respective guide blade has an outer contour which is not compromised by the passage openings. In this way, the flow-guiding function of the respective guide blades is only comparatively slightly compromised by the perforation. 
         [0013]    According to an advantageous variant, the passage openings may have a round or an angular cross section. Likewise, the passage openings may have a punctiform or else an oblong cross section. Passage openings with oblong cross section may be linear or single-curved or multi-curved. 
         [0014]    In another advantageous variant, the passage openings may each have an oblong cross section and be arranged parallel to each other and next to each other along a blade length measured from a blade footing to a blade tip of the respective guide blade. In such an embodiment, a low flow resistance can be shown for the respective guide blade with sufficient or improved mixing effect. 
         [0015]    According to a variant, the passage openings may be arranged with their oblong cross sections sloped toward the blade length and sloped toward a blade width measured from a leading edge to a discharge edge of the respective guide blade. By means of this measure, the mixing effect can, in addition, be affected and optimized. 
         [0016]    According to another embodiment, the perforation may have at least one or a plurality of passage openings, which are open on the side at a discharge edge or at a leading edge of the respective guide blade. In this embodiment, these passage openings open on the side have an effect on a lateral outer contour of the respective guide blade. For example, targeted flow separations and swirl may be generated thereby, which may have advantageous effects on an intensive mixing. All the passage openings of the perforation are preferably open on the side at the discharge edge or at the leading edge. However, an embodiment, in which the perforation has at least one open passage opening on the outer contour of the guide blade and at least one passage opening lying completely within the outer contour, is also generally conceivable. 
         [0017]    In a variant which assumes that a plurality of passage openings open on the side are provided, the passage openings open on the side may be oblong and be sloped towards a blade length of the guide blade as well as towards a blade width of the guide blade. As before, the blade length extends from a blade footing up to a blade tip, while the blade width extends from the leading edge to the discharge edge. 
         [0018]    In another variant, the passage openings open on the side of the leading edge may be sloped with regard to the blade length opposed to the passage openings of the discharge edge. As a result of this, the flow-conducting action of the guide blades can be optimized with regard to an improved mixing. 
         [0019]    In an alternative embodiment the perforation in at least one of the guide blades may be formed from a single passage opening. Such a singular passage opening is advantageously dimensioned larger in terms of its flow cross section than the individual passage openings of the perforations explained above, which are formed by a plurality of passage openings. Accordingly, such a perforation has a reduced flow resistance. 
         [0020]    This singular passage opening may be arranged within a lateral outer contour of the respective guide blade in one variant. In other words, an embodiment, in which the passage opening does not have an effect on the outer contour of the guide blade, is preferred here as well. It can essentially extend from a blade footing up to a blade tip as well. Further, the passage opening may have a pointed design, whereby the tip of the passage opening can then be arranged in the area of the blade tip. As an alternative, the passage opening may also be provided with a constant width. 
         [0021]    Basically, it is likewise possible to develop the singular passage opening open on the side on a blade tip of the respective guide blade. If this singular passage opening open on one side is, in addition, designed as oblong, quasi a division of the guide blade in the area of the passage opening can thus be achieved. Such a passage opening, open in the area of the blade tip, may lead to an especially low flow resistance in the area of the respective guide blade. 
         [0022]    In another advantageous embodiment the respective guide blade may have a single- or multi-curved course along its blade length. While the guide blades usually have a linear design, it is suggested here now to equip the respective guide blade with a curved course with regard to its central longitudinal axis. The central longitudinal axis of the respective guide blade extends thereby from the blade footing to the blade tip approximately in the center with regard to the blade width. A single-curved guide blade then has a sickle-shaped design. A twice-curved guide blade then has an S-shaped design. In addition or as an alternative, the respective guide blade may have a twisting with regard to its central longitudinal axis, which leads to a varying pitch angle along the blade length. 
         [0023]    In another advantageous embodiment, the mixer may have a cylindrical pipe body, which encloses a flow cross section through which the exhaust gas flow can flow in the circumferential direction and from which the guide blades project inwards. In this type of construction, the guide blades may be especially arranged detached radially inwards in the area of their blade tips. Furthermore, the guide blades may be arranged in a contactless manner relative to each other. 
         [0024]    Especially advantageous is a variant, in which the pipe body with all guide blades is produced from a single sheet metal body by means of shaping. As a result of this, the mixer can be produced at a comparatively low cost by means of punching and shaping processes. 
         [0025]    In another advantageous embodiment, the perforation may have at least one passage opening with an opening edge, which is detached along its entire circulation. Such a detached opening edge may be produced by a punching process in an especially simple manner in case of a guide blade designed as a sheet metal body. Preferably, the circulation is completely closed, when the respective passage opening is arranged within the outer contour of the guide blade. If, on the other hand, the passage opening is designed open on the side on the outer contour of the guide blade, the circulation of the opening edge on the outer contour is interrupted. 
         [0026]    Advantageously, all passage openings of the respective guide blade are equipped with such a detached opening edge. 
         [0027]    In another embodiment, the perforation may have at least one passage opening with an opening edge, which is connected with a tilting device (angled feature) along a circulation section. The tilting device may at least partly cover the associated passage opening. In addition or as an alternative, the tilting device may be sloped towards an area of the guide blade adjacent thereto. In addition or as an alternative, the tilting device may be arranged at least partly offset towards an area of the guide blade adjacent thereto. The arrangement of the tilting device is thereby preferred, such that the tilting device at least partly covers the passage opening and accordingly brings about a flow deflection of an exhaust gas flow passing through the passage opening. Such a tilting device at the opening edge of the passage opening improves the mixing action of the guide blade. At the same time, the flow resistance can be reduced by the flow deflection with the tilting device. 
         [0028]    The tilting device is advantageously formed integrally in one piece with the respective guide blade. The respective tilting device can especially advantageously be an area of the respective guide blade that is free-cut and tilted for producing the respective passage opening. Thus, the respective guide blade can be equipped in an especially simple manner with the passage openings and tilting devices adjacent thereto. 
         [0029]    According to an advantageous variant, provisions may be made for at least one such tilting device to have a central area and two lateral areas, whereby the central area extends essentially parallel to the respective guide blade and is connected with the respective guide blade via the two lateral areas. As a result of this, an especially efficient covering of the respective passage opening is obtained. 
         [0030]    Further, according to another variant, provisions may be made for at least one such tilting device to be designed as a wing, which is connected only on one side with the respective guide blade and is otherwise arranged detached to the respective guide blade. Such a wing acts as a flow-guiding element, such that the flow of the respective passage opening can be especially favorably affected by means of such a wing. 
         [0031]    In addition, provisions may advantageously be made for at least one such tilting device to be formed by a step, which is spaced apart in a blade longitudinal direction from a (different) step formed in the respective guide blade. The respective step may be produced by means of bending the guide blade twice, preferably by approx. 90°, transversely to its longitudinal direction. 
         [0032]    It is clear that the different variants mentioned above for the perforation—insofar as useful—can be achieved at at least one single guide blade or in case of various guide blades of the same mixer, i.e., especially passage openings of different sizes and/or geometries and/or with or without tilting devices. 
         [0033]    The mixer presented here is heated exclusively by the exhaust gas flow during the operation of the exhaust system, such that it operates free from external energy with regard to its evaporation action. 
         [0034]    In an exhaust system according to the present invention, which is suitable for discharging combustion waste gases in an internal combustion engine, an injector is provided for introducing a liquid reducing agent into the exhaust gas flow, whereby, in addition, at least one mixer of the type described above is arranged downstream of this injector with regard to the exhaust gas flow. The exhaust system may, furthermore, have an SCR catalytic converter downstream of the mixer or an oxidation catalytic converter downstream of the mixer. 
         [0035]    Further important features and advantages of the present invention appear from the subclaims, from the drawings and from the associated description of the figures based on the drawings. 
         [0036]    It is apparent that the features mentioned above and those still to be explained below can be used not only in the respective given combination, but also in other combinations or alone, without going beyond the scope of the present invention. 
         [0037]    Preferred exemplary embodiments of the present invention are shown in the drawings and are explained in detail in the following description, whereby identical reference numbers refer to identical or similar or functionally identical 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 
         [0038]      FIG. 1  is a circuit-diagram-like schematic diagram of an internal combustion engine with an exhaust system, which contains a static mixer; 
           [0039]      FIG. 2  is an isometric view of the mixer; 
           [0040]      FIG. 3  is an axial view of the mixer; 
           [0041]      FIG. 4  is a layout of the mixer; 
           [0042]      FIG. 5  is a simplified view of a guide blade of the mixer in one of various embodiments; 
           [0043]      FIG. 6  is a simplified view of a guide blade of the mixer in another of various embodiments; 
           [0044]      FIG. 7  is a simplified view of a guide blade of the mixer in another of various embodiments; 
           [0045]      FIG. 8  is a simplified view of a guide blade of the mixer in another of various embodiments; 
           [0046]      FIG. 9  is a simplified view of a guide blade of the mixer in another of various embodiments; 
           [0047]      FIG. 10  is a simplified view of a guide blade of the mixer in another of various embodiments; 
           [0048]      FIG. 11  is a simplified view of a guide blade of the mixer in another of various embodiments; 
           [0049]      FIG. 12  is a simplified view of a guide blade of the mixer in another of various embodiments; 
           [0050]      FIG. 13  is a simplified view of a guide blade of the mixer in another of various embodiments; 
           [0051]      FIG. 14  is a simplified view of a guide blade of the mixer in one of various embodiments and partly with associated sectional view or variant A; 
           [0052]      FIG. 15  is a simplified view of a guide blade of the mixer in another of various embodiments and partly with associated sectional views or variants A, B and C; 
           [0053]      FIG. 16  is a simplified view of a guide blade of the mixer in another of various embodiments; 
           [0054]      FIG. 17A  is a simplified view of another embodiment of a guide blade of the mixer; 
           [0055]      FIG. 17B  is a simplified view of another embodiment of a guide blade of the mixer; 
           [0056]      FIG. 17C  is a simplified view of another embodiment of a guide blade of the mixer; 
           [0057]      FIG. 17D  is a simplified view of another embodiment of a guide blade of the mixer; 
           [0058]      FIG. 18  is a simplified view of a guide blade of the mixer in another of various embodiments; 
           [0059]      FIG. 19  is a simplified view of a guide blade of the mixer in another of various embodiments and partly with associated sectional views or variants A and B; and 
           [0060]      FIG. 20  is an isometric view of a guide blade of the mixer from  FIG. 19  in the area of a perforation. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0061]    Referring to the drawings, according to  FIG. 1 , an internal combustion engine  1  comprises an engine block  2  which contains a combustion chamber  4  each in a plurality of cylinders  3 . Pistons, which are not shown here, are arranged with adjustable stroke in the cylinders  3 , such that the internal combustion engine  1  is a piston engine. A fresh air feed unit  5  is provided for supplying the combustion chambers  4  with fresh air. A corresponding fresh air flow  6  is indicated by an arrow. In order to be able to discharge combustion gases from the combustion chambers  4 , the internal combustion engine is, in addition, equipped with an exhaust system  7 . An exhaust gas flow  8  is indicated by an arrow. In the example of  FIG. 1 , the exhaust system  7  is equipped with an SCR system  9 , which has an injector for introducing a liquid reducing agent into the exhaust gas flow  8 , an SCR catalytic converter  11  for reducing nitrogen oxides with the aid of the previously injected reducing agent as well as a static mixer  12 . With regard to the flow direction of the exhaust gas flow  8 , the SCR catalytic converter  11  is arranged downstream of the injector  10 . Further, the mixer  12 , with regard to the direction of flow of the exhaust gas flow  8 , is arranged downstream of the injector  10  and upstream of the SCR catalytic converter  11 . The exhaust system  7  has an exhaust line  13 , into which the above-mentioned components of the SCR system  9  are integrated. 
         [0062]    According to  FIGS. 2 and 3 , the mixer  2  has a plurality of guide blades  14  which are each used for deflecting the exhaust gas flow  8 . In the preferred example shown the mixer  12  has, moreover, a cylindrical pipe body  15 , which encloses a flow cross section  16 , through which the exhaust gas flow  8  can flow, in the circumferential direction  17 . The circumferential direction  17  is in reference to a central longitudinal axis  18  of the pipe body  15  or of the mixer  12 . The guide blades  14  project from the pipe body  15  inwards, i.e., in the direction of the central longitudinal axis  18 . Thereby, the direction of extension of the respective guide blade  14  has at least one radial component. Further, this direction of extension may optionally also have an axial component. 
         [0063]    Advantageously, this pipe body is produced integrally with the guide blades  14  from a single sheet metal body  19 , namely by means of shaping, such that the mixer  12  is ultimately a single shaped sheet metal part. A layout of the sheet metal body  19  or of the mixer  12  is shown in  FIG. 4 . The sheet metal body  19  has a jacket section  20 , which forms the pipe body  15  in the shaped state. The guide blades  14  project from this jacket section  20 . In the layout of  FIG. 4 , the individual guide blades  14  are already free-cut, whereby individual sections are designated with  21 . The sections  21  pass over at the jacket section  20  into round holes  22  to avoid a tear formation at this passing over. 
         [0064]    In order to produce the mixer  12  from the planar sheet metal body  19  in  FIG. 4 , the blades  14  are each bent over a bending edge  23  and the jacket section  20  is bent over the central longitudinal axis  18  of the mixer  12  in the circumferential direction  17 . Thereby, the longitudinal ends  24  of the jacket section  20  may form a butt joint at the pipe body  15  in the circumferential direction  17  and be fastened to each other. 
         [0065]    As can be inferred from  FIGS. 2 through 4 , the guide blades  14  in the example shown of the mixer  12  are exclusively designed on a leading side of the pipe body  15 . For orientation, the exhaust gas flow  8  is indicated by a flow arrow. Likewise, an embodiment is conceivable, in which all guide blades  14  are arranged on a discharge side of the pipe body  15 . Further, it is conceivable to provide such guide blades  14  at the pipe body  15  both on the leading side and on the discharge side each. The use of two mixers  12 , which are arranged one behind the other in the direction of flow of the exhaust gas flow  8 , is also conceivable. 
         [0066]    As can be inferred from  FIGS. 2 through 4 , at least one of the guide blades  14  is equipped with a perforation  25 . The perforation  25  is thereby configured, such that the perforation  25  traverses the otherwise closed guide blade  14 , such that the exhaust gas flow  8  or partial flows of the exhaust gas flow  8  can flow through the guide blade  14  through the respective perforation  25 . Even though not all guide blades  14  are equipped with such a perforation  25  in the examples of  FIGS. 2 through 4 , an embodiment is, however, preferred, in which all of the guide blades  14  have such a perforation  25 . Even though various perforations  25  are provided in the individual guide blades  14  in  FIGS. 2 through 4 , an embodiment is preferred, in which the perforated blades  14  have an identical perforation  25  each. 
         [0067]    Various embodiments of such a perforation  25  are explained in detail below based on  FIGS. 5 through 20 . For example, the respective perforation  25  may have a plurality of passage openings  26 , which are arranged within a lateral outer contour  27  of the respective guide blade  14 .  FIGS. 5 through 10 ,  15  and  18  show embodiments, in which all passage openings  26  of the perforation  25  are arranged within the outer contour  27  of the guide blade  14 . In the embodiment shown in  FIG. 5 , all passage openings  26  are equipped with a round and punctiform cross section. In particular, the passage openings  26  show each a round cross section. 
         [0068]    In the embodiment shown in  FIG. 6 , the passage openings  26  are designed as oblong and linear. Further, they extend parallel to each other. Furthermore, the parallel arranged passage openings  26  are arranged next to each other along a blade length  28 . The blade length  28  is thereby measured from a blade footing  29  up to a blade tip  30 . In a mixer according to the embodiment shown in  FIGS. 2 through 4 , the blade footing is arranged at the pipe body  15 , while the blade tip  30  is arranged detached in the area of the central longitudinal axis  18 . 
         [0069]    The embodiment shown in  FIG. 7  corresponds to the embodiment shown in  FIG. 6 , providing that the passage openings  26  have different cross sections. On the other hand,  FIG. 8  shows an embodiment, in which the oblong passage openings  26  have an angular, in this case parallelogram-like cross section. Further, the passage openings  26  are arranged sloped with regard to their oblong cross section towards the blade length  28  as well as towards a blade width  31 . The blade width  31  is thereby measured from a leading edge  32  up to a discharge edge  33  of the respective guide blade  14 . By contrast, the oblong passage openings  26  in the examples of  FIGS. 6 and 7  are aligned parallel to the blade width  31 . 
         [0070]      FIG. 9  now shows an embodiment, in which a plurality of oblong passage openings  26  are arranged one behind the other in the direction of the blade width  31 , which passage openings  26  are arranged in this case, in addition, offset to each other in the direction of the blade length  28 . Further, the passage openings  26  are arranged next to each other along the blade length  28 , as well as aligned parallel to each other and parallel to the blade width  31 . In the perforation  25  shown in  FIG. 9 , the passage openings  26  have markedly smaller cross sections through which flow is possible than in the embodiments of  FIGS. 5 through 8 . 
         [0071]      FIG. 10  shows an embodiment, in which the passage openings  26  have an oblong cross section and thereby are single-curved. Regardless of the geometry and number of the passage openings  26 ,  FIG. 10  shows, in addition, an embodiment, in which the respective guide blade  14  has a twice-curved course along its blade length  28 . As a result of this, the guide blade  14  has an S-shaped course with regard to its blade length  28 . 
         [0072]    In the embodiments shown in  FIGS. 11 and 16 , the respective perforation  15  has a plurality of passage openings  26 , which are open on the side on the leading edge  32  or on the discharge edge  33  of the respective guide blade  14 . As a result of this, the passage openings  26  have an effect on the lateral outer contour  27  of the guide blade  1 . In the example of  FIG. 14 , all passage openings  26  of the perforation  25  are designed as open on the side. Further, all passage openings  26  are oblong in this case and provided with a rectangular cross section. In addition, the passage openings  26  arranged on the leading edge  32  are each arranged parallel to each other and next to each other with regard to the blade length  28 . The passage openings  26  provided on the discharge edge  33  are also arranged parallel to each other and next to each other in the blade length  28 . Furthermore, the passage openings  26  shown are aligned sloped both towards the blade length  28 , i.e., towards the blade width  31 . In addition, provisions are thereby made, in addition, for the passage openings  26  of the leading edge  32  to be sloped with regard to the blade length  28  opposed to the passage openings  26  of the discharge edge  33 . In particular, the passage openings  26  are arranged in a mirror-symmetrical manner with regard to a central longitudinal axis of the respective guide blade  14 , as a result of which the perforation  25  shows a sweepback and the guide blade  14  has a fishbone-like shape. The sweepback of the perforation  25  is aligned toward the blade tip  30  for this. 
         [0073]    On the other hand, only a single passage opening  26  open on the side is provided on the leading edge  32  and on the discharge edge  33  each in  FIG. 16 . 
         [0074]    While the examples of  FIGS. 5 through 11 ,  15 ,  17  and  18  each show perforations  25 , which have a plurality of passage openings  26 ,  FIGS. 12 through 14  and  19 ,  20  show an embodiment each, in which the perforation  25  has only a single passage opening  26  each. At least in the examples of  FIGS. 12 through 14 , this passage opening  26  is provided with an oblong cross section, which is aligned parallel to the blade length  28 . Furthermore, the respective passage opening  26  extends over an essential longitudinal section of the respective guide blade  14 . In these examples, the respective passage opening  26  extends over at least 75% of the blade length  28 . In the example of  FIG. 12 , the passage opening  26  has a rectangular cross section, while a triangular cross section is provided in the embodiment shown in  FIG. 13 . A rectangular cross section is provided again in  FIG. 14 . In  FIGS. 12 and 14 , the passage opening  26  has a constant cross section along the blade length  28 , while in  FIG. 13  the cross section decreases in the direction toward the blade tip  30 . In the examples of  FIGS. 12 through 14  and  19 ,  20 , the passage opening  26  remains within the lateral outer contour  27  of the associated guide blade  14 . In another embodiment, the passage opening  26  may, on the other hand, be so arranged and/or so dimensioned that it is open on the side at the blade tip  30 , as a result of which the guide blade  14  is quasi divided in the area of this passage opening  26 . 
         [0075]    In the embodiments of  FIGS. 5 through 13 , the passage openings  26  are each equipped with an opening edge  34 , which is detached along is entire circumferential extent (circulation). In the embodiments of  FIGS. 5 through 10 ,  12  and  13 , in which the passage openings  26  are arranged within the outer contour  27 , the respective circulation of the opening edge  24  is closed, while the circulation in the embodiment shown in  FIG. 11 , in which the passage openings  26  are open on the side at the outer contour  27 , is interrupted in each case by the opening on the side of the respective passage openings  26 . 
         [0076]    In the embodiments of  FIGS. 14 through 20 , the perforation  25  may have at least one passage opening  26 , whose opening edge  34  is connected with a tilting device  35  along a circulation section. In the embodiments of  FIGS. 16 through 18 , this tilting device  35  is arranged sloped towards an area of the respective guide blade  14  adjacent thereto. Thereby, the respective tilting device  35  brings about a covering of at least one part of the respective passage opening  26 . In  FIGS. 16 through 18  in the rectangular passage opening  26 , three consecutive, linear circulation sections each form a free opening edge  34 , while the remaining fourth, linear circulation section is then connected with the tilting device  35 , as a result of which the respective tilting device  35  forms a wing  36 . The tilting device  35  advantageously forms a free-cut and tilted area of the guide blade  14  in the creation of the respective passage opening  26 . Thus, the respective tilting device  35  is formed integrally in one piece with the guide blade  14 . 
         [0077]    In  FIGS. 14 through 20 , provisions are made for the perforation  25  to have at least one passage opening  26  with an opening edge  34 , which is connected with a tilting device  35  along at least one circulation section, which tilting device  35  at least partly covers the associated passage opening  26  and/or is arranged sloped and/or offset towards an area of the guide blade  14  adjacent thereto. 
         [0078]    In  FIGS. 14 and 15 , provisions are made for at least one such tilting device  35  to have a central area  36  and two lateral areas  37 , whereby the central area  36  extends essentially parallel to the respective guide blade  14  and is connected via the two lateral areas  37  with the respective guide blade  14 . 
         [0079]    On the other hand, in  FIGS. 17 and 18 , provisions are made for at least one such tilting device  35  to be designed as a wing  36 , which is characterized in that it is connected only on one side with the respective guide blade  14 , while it is otherwise arranged detached to the respective guide blade  14 . These wings  36  may thereby be integrated into the outer contour  27  as in  FIG. 16 , such that their passage openings  26  are open on the side. Likewise, a distance to the outer contour  27  may be maintained in another embodiment. Two different geometries for the wings  36  are shown in  FIG. 16 .  FIG. 17  shows other variants A, B, C and D for the geometric shape of such wings  36 . Thus,  FIG. 17A  shows a wing  36  with a linear profile.  FIG. 17B  shows a wing  36  with a concave bent profile in the tilting direction.  FIG. 17C  shows a wing  36  with a convex bent profile in the tilting direction.  FIG. 17D  shows, on the other hand, a wing  36  with an aerodynamically shaped profile, especially a drop profile. 
         [0080]      FIG. 18  shows, in an exemplary manner, an embodiment, in which the formation of the perforation  25  by means of a plurality of various passage openings  26  with tilting devices  35  (left half in  FIG. 18 ) and without tilting devices  35  (right half in  FIG. 18 ), which differ from each other, moreover, by different geometries and cross sections. 
         [0081]      FIGS. 19 and 20  show another embodiment for a special perforation  25 , in which the guide blade  14  is equipped with a step  38 , which is formed by means of two bending edges  39 . In the area of the perforation  25  are provided two other bending edges  40 , which are arranged offset to the above-mentioned bending edges  39  in a blade longitudinal direction  42 , which runs parallel to the blade length  28  and in which the guide blade  14  is bent in the opposite direction. Accordingly, the tilting device also forms a step  41 , which is arranged offset in the blade longitudinal direction  42  to the step  38  of the guide blade  14 . As a result of this, two open cross sections, spaced apart from one another, which make possible a lateral inflow and lateral outflow of the exhaust gas, are formed in a blade transverse direction  43 , which extends parallel to the blade width  31 . 
         [0082]    Even though in the preferred embodiment shown here the mixer is designed as a shaped sheet metal part, it may also be designed as a cast part or a sintered part in another embodiment. The respective perforation  25  is then advantageously worked in later. 
         [0083]    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.