Abstract:
A mixing element ( 1 ) for a mixing device in an exhaust gas-conducting pipe ( 8 ) of an exhaust system of a combustion engine provides advantageous intermixing of the exhaust gas with an additive and an advantageous temperature distribution within the exhaust gas-additive mixture. The mixing element ( 1 ) includes at least four vanes ( 2 ) and a connecting section ( 3 ), The vanes ( 2 ) are angled off from the connecting section ( 3 ). Two vanes ( 2 ) which, with respect to a longitudinal axis ( 5 ) of the connecting section ( 3 ), are directly adjacent or two vanes ( 2 ) which are located directly opposite, with respect to the longitudinal axis ( 5 ) of the connecting section ( 3 ), are angled off towards different sides ( 4′, 4″ ) of the connecting section ( 3 ). The mixing element ( 1 ) as well as the connecting section ( 3 ) and the associated vanes ( 2 ) are embodied as shaped sheet metal part.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119 of German Patent Application DE 10 2011 075 252.8 filed May 4, 2011, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a mixing element for a mixing device in an exhaust gas-conducting pipe of a combustion engine, in particular of a motor vehicle. The invention furthermore relates to a mixing device for an exhaust system of a combustion engine with at least one such mixing element. 
       BACKGROUND OF THE INVENTION 
       [0003]    Mixing elements are frequently used components in exhaust systems for combustion engines. They are used, in particular with combustion engines of motor vehicles, in order to guarantee a homogeneous thermal and chemical distribution within an exhaust gas flow of the exhaust system. In particular, mixing elements play a fundamental role in the admixing of ammonia-containing additives, such as for example urea or “Adblue” to the exhaust gas. These additives are used in particular for the so-called selective catalytic reduction (SCR) of the exhaust gas, during which harmful nitric oxides are usually converted into nitrogen. Naturally, local concentrations and the local temperature play a decisive role for such reactions. It is therefore of great importance to guarantee a homogenous distribution of the additive and a homogeneous temperature distribution within the exhaust gas additive mixture, in order to have the mentioned reduction reactions in particular take place in a controlled and effective manner. This is usually ensured through mixing elements in the exhaust system. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention deals with the problem of providing an improved or at least alternative embodiment for a mixing element of the type mentioned at the outset, which in particular fulfils the demanded mixing demands and is simple to produce. 
         [0005]    The present invention is based on the general idea of providing at least four vanes with a mixing element of the mentioned type, which are coupled by a connecting section. Here, the connecting section has two sides, which are formed by the surfaces of the connecting section facing away from each other. The invention now utilises the realisation that adjacent vanes, which are located in different space halves separated by the connecting section, achieve an improved mixing of an exhaust gas and an additive and/or an improved temperature distribution within the exhaust gas-additive mixture. Thus, through this arrangement of the vanes, a distribution which in particular is even, i.e. homogeneous, of an additive within the exhaust gas, and/or an improved thermal distribution, i.e. a homogeneous temperature within the exhaust gas-additive mixture is achieved. The invention furthermore utilises the realisation that the production of such a mixing element as shaped sheet metal part is possible, by means of which a particularly favourable production is achieved. 
         [0006]    In accordance with the inventive idea, a mixing element comprises four vanes, which are coupled together by a connecting section. Here, the connecting section has two sides, which are defined by the surfaces of the connecting section. The connecting section furthermore comprises a longitudinal axis, which because of the extension of the connecting section is defined corresponding to the direction with the greatest extension. The four vanes are now arranged in such a manner, that two vanes which are directly adjacent with respect to the longitudinal axis of the mixing element, are angled off towards different sides of the connecting section. Furthermore, two vanes which are located directly opposite each other with respect to the longitudinal axis of the mixing element, are angled off towards different sides of the connecting section. Furthermore, the mixing element is embodied as shaped sheet metal part, in particular through cutting and bending processes. 
         [0007]    In an advantageous embodiment, the mixing element is produced from a single continuous sheet metal piece. Here, the production comprises in particular a cutting process and a forming process. The production of the mixing element from a single sheet metal part results in a particularly cost-effective production. The use of sheet metal as material of the mixing element furthermore ensures that the mixing element achieves a long lifespan even with corresponding thermal loading. 
         [0008]    A further embodiment of the mixing element comprises six vanes. Here, it is likewise true for the vanes of this embodiment that two vanes which are directly adjacent with respect to the longitudinal axis of the mixing element are angled off towards different sides of the connecting section. Two vanes, which with respect to the longitudinal axis of the mixing element are located directly opposite, are likewise angled off towards different sides of the connecting section. As already mentioned, this embodiment can be configured as shaped sheet metal part. In particular, the embodiment can also be produced from a single continuous sheet metal piece, in particular through cutting processes and forming processes. 
         [0009]    The number of the vanes of a mixing element is governed, according to the laws of fluid dynamics, that a straight number should be preferentially selected. However, mixing elements with an uneven number of vanes likewise belong to the scope of this invention. 
         [0010]    According to a further advantageous embodiment, the mixing element at least partially contacts a pipe section associated with the mixing element. To this end, at least one of the vanes of the mixing element has an outer contour at a vane edge located on the outside associated with this vane, which is moulded complementarily to an inner contour of the pipe section associated with the respective vane, wherein the outer contour of the vane edge is moulded in such a manner that the associated vane, with the mixing element inserted in the pipe, contacts the pipe with the vane edge. In particular, this serves the purpose of being able to attach the mixing element in a suitable pipe section in a simple and retaining manner. The contact in this case can be both concentrated as well as linear. Through the lower heat transfer between mixing element and pipe section, a concentrated contact with the pipe section has a heat transfer that is different from that of a linear contact, during which the heat transfer between mixing element and pipe section is greater. Here, the exact embodiment of the contact can be adapted to the respective requirements. 
         [0011]    According to a further embodiment, the connecting section comprises a sweep with respect to the longitudinal axis of the mixing element, which extends transversely to the longitudinal axis of the connecting element. For example, the longitudinal axis of the mixing element in the installed state extends parallel to the main flow direction of the exhaust gas. The longitudinal direction of the connecting section then extends transversely to the main flow direction of the exhaust gas. The sweep is then orientated in the main flow direction or opposite the main flow direction. Such a sweep leads to a corresponding change of the vane orientations. Because of this, a better mixing-through of the exhaust gas-additive mixture is achieved in particular through the generating of an additional swirl. 
         [0012]    It is pointed out that the vanes and the connecting section can have any shape and size. Here, reference is made in particular to vanes having an elliptical shape of their outer edge. If the vanes each have a pointed shape of the associated vane edges, this results in an improved mixing-through of the additive with the exhaust gas in particular in the case of liquid additives, since the drops of the additive are reduced in size on the pointed vane edges. 
         [0013]    With an advantageous further development, at least one mixing element according to the invention is integrated in a mixing device for an exhaust system of a combustion engine, in particular of a motor vehicle. Here, the mixing element is arranged in an exhaust gas-conducting pipe of the mixing device or of the exhaust system. Thus, the mixing device ensures an improved mixing-through of the exhaust gas-additive mixture and/or an improved, i.e. homogeneous temperature distribution within the exhaust gas-additive mixture. 
         [0014]    With a further embodiment, the mixing device comprises an envelope, which envelopes at least one mixing element. Here, the envelope is such that at least one of the vanes of the mixing element has an outer contour on an associated vane edge located on the outside, which contacts this envelope. Here, both concentrated as well as linear contacts serve the objective. Thus, a hold of the mixing element in the envelope is ensured in particular. It is to be understood that with this embodiment a contact between the mentioned vane edge and a pipe section associated with the mixing element is not possible. 
         [0015]    In a further embodiment, the envelope can be inserted in a pipe section associated with the envelope. Furthermore, the envelope can contact this pipe section, wherein the contact can be concentrated or linear. With this arrangement, the exhaust gas preferably flows through the envelope. Here, in particular in the case of a concentrated contact between envelope and the pipe section associated with the envelope, a thermal insulation in particular between envelope or mixing element and pipe section is ensured. 
         [0016]    The envelope is optionally equipped with a flange radially arranged on the envelope. Because of this, different exhaust gas-conducting pipe sections, in particular, can be coupled. As flange, reference is made in particular to a beaded gasket, which additionally results in a sealing of the construction. 
         [0017]    If an envelope with at least one mixing element is located in a pipe section, this pipe section with a further embodiment can have a changed size and/or a changed shape compared to a pipe section without envelope or mixing element. This embodiment, in particular, serves the purpose of making available, through a suitable change of the size or shape of the pipe section with envelope or mixing element, a same cross section conducting exhaust gas in this pipe section. 
         [0018]    If a mixing device has a plurality of mixing elements, these mixing elements can be arranged one after the other. Here, an arrangement of the mixing elements is preferred for example, wherein the mixing elements in particular overlap one another axially or are arranged partially within one another. 
         [0019]    It is pointed out that the mixing elements are preferentially arranged in such a manner that their longitudinal axis is arranged parallel to a main flow direction of the exhaust gas-conducting pipe. Embodiments, wherein the longitudinal axes of the individual mixing elements are substantially arranged parallel to the main flow direction are also advantageous. 
         [0020]    Here respectively two vanes of such a mixing element can be arranged offset transversely to one another along the main flow direction. In addition, embodiments are advantageous in which opposite vanes of the mixing element along the main flow direction are angled in the main flow direction on different sides of the connecting section. This means that the surfaces of the vanes, in particular on the upflow side, are flowed against substantially frontally by the exhaust gas, in order to achieve an intensified mixing-through or respectively swirling of the exhaust gas. 
         [0021]    If the individual mixing elements have a sweep of their connecting section, this sweep is preferentially designed in such manner that it is positive or negative with respect to the main flow direction. 
         [0022]    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 of by themselves without leaving the scope of the present invention. 
         [0023]    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 refer to same or similar of 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 
         [0024]      FIG. 1  is a lateral view of a mixing element according to the invention; 
           [0025]      FIG. 2  is a perspective view showing an embodiment of the mixing element; 
           [0026]      FIG. 3  is a perspective view showing another embodiment of the mixing element; 
           [0027]      FIG. 4  is a perspective view of a mixing device; 
           [0028]      FIG. 5  is a longitudinal sectional view through the mixing device showing one of different embodiments; 
           [0029]      FIG. 6  is a longitudinal sectional view through the mixing device showing another of different embodiments; and 
           [0030]      FIG. 7  is a longitudinal sectional view through the mixing device showing another of different embodiments. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    Referring to the drawings in particular, according to  FIGS. 1 to 7 , a mixing element  1  comprises at least four vanes  2 , which are coupled to one another through a connecting section  3 . As is shown in  FIG. 1  and  FIG. 5  to  FIG. 7 , the connecting section  3  furthermore has two sides  4 ′,  4 ″, which are facing away from each other. According to the spatial position of the mixing element  1  reflected in  FIG. 1  and  FIG. 5  to  FIG. 7 , the two sides  4 ′,  4 ″ can also be described as top  4 ′ and bottom  4 ″. 
         [0032]    The mixing element  1  shown in  FIG. 1  comprises four vanes  2 , which are connected to one another through the connecting section  3 . Here, both the vanes  2  as well as the connecting section  3  have a plane flat shape. However, curved shapes of the vanes are also conceivable. Furthermore, all vanes  2  have the same size. The vanes  2  are now angled off from the connecting section  3  in such a manner that with respect to a longitudinal axis  5  (see  FIGS. 2 to 4 ) of directly adjacent vanes it is true that one of the vanes  2  is angled off towards a side  4 ′ of the connecting section  3  and the other vane  2  is angled off towards the other side  4 ″ of the connecting section  3 . The same applies to vanes  2  directly located opposite with respect to the longitudinal axis  5 , i.e. that one of these vanes  2  is angled off towards a side  4 ′ of the connecting section  3  and the other vane  2  is angled off towards the other side  4 ″ of the connecting section  3 . Here, all vanes  2  have the same angle to the respective sides  4 ′,  4 ″ of the connecting section  3  to which they are angled off. 
         [0033]    The embodiment of the mixing element  1  shown in  FIG. 2  shows four vanes  2 , which are connected to one another through the connecting section  3 . Here, the connecting section  3  has an elongated flat shape, wherein its longitudinal axis  5  runs along the long side. This mixing element  1  is produced from a single continuous work piece, preferentially of sheet metal, in particular through cutting and forming. Here, the sheet metal piece has a flat and round shape prior to the forming. Because of this, all vanes  2  have a straight inner edge which are directed towards the inside of the mixing element  1  and at a vane tip meet a round outer edge of the vane  2 . The respective vanes  2  which are directly adjacent with respect to the longitudinal axis  5  of the connecting section  3  are angled off in such a manner that one of these vanes  2  is angled off towards a side  4 ′ of the connecting section  3  and the other vane  2  is angled off towards the other side  4 ″. The vanes  2 , which are directly adjacent with respect to the longitudinal axis  5 , are also angled off in such a manner that one of the vanes  2  is angled off towards a side  4 ′ of the connecting section  3  and the other vane  2  towards the other side  4 ″ of the connecting section  3 . 
         [0034]    An embodiment of the mixing element  1  having six vanes  2  is shown in  FIG. 3 . This mixing element  1 , too, can be formed of a single continuous flat and round sheet metal piece. Since the vanes  2  are arranged along the longitudinal sides of the connecting section  3 , the outer vanes  2  have straight inner edges, which in a pointed transition meet rounded outer edges of the respective vane  2 . The, on the respective long sides of the connecting piece  3 , middle vanes  2  each have two straight inner edges, which end on vane tips in round outer contours of these vanes  2 . The vanes  2  which with respect to the longitudinal axis  5  of the connecting section  3  are directly adjacent are angled off in such a manner that one of these vanes  2  is angled off towards a side  4 ′ of the connecting section  3  and the other vane  2  is angled off towards the other side  4 ″. The vanes  2 , which with respect to the longitudinal axis  5  are directly adjacent, are angled off in such a manner that one of the vanes  2  is angled off towards a side  4 ′ of the connecting section  3  and the other vane  2  towards the other side  4 ″ of the connecting section  3 . 
         [0035]      FIG. 4  shows two identical mixing elements  1  of a mixing device  6 . The mixing elements  1  in this case have a sweep with respect to the longitudinal axis  7  of the respective mixing element  1  and are arranged in such a manner that they partially overlap one another radially. The mixing elements  1  furthermore comprise four vanes  2  each. For the vanes  2  of the respective mixing elements  1  it is true, in this case, that vanes  2  which with respect to the respective longitudinal axis  5  are directly adjacent, are each angled off towards a side  4 ′,  4 ″ of the connecting piece  3 . The same applies to two vanes  2  located directly opposite with respect to the longitudinal axis  5 . The vanes  2  of both mixing elements  1  show straight inner edges, which in a tip meet rounded outer edges of the associated vane  2 . The mixing elements  1  are arranged in a pipe  8  (the pipe  8  is indicated as a line for reasons of representation), wherein the outer edges of the vanes  2  partially contact the pipe  8 . 
         [0036]    The mixing element  1  of a mixing device  6  shown in  FIG. 5  comprises four vanes  2 , which with respect to a longitudinal axis  5  of the connecting section  3  are angled off towards different sides  4 ′,  4 ″ of the connecting section  3 . Here, it is also true that two vanes  2  which with respect to the longitudinal axis  5  are located directly opposite or two vanes  2  which with respect to the longitudinal axis  5  are directly adjacent, are angled off towards different sides  4 ′ and  4 ″ of the connecting section  3 . In the case of the mixing device  6  shown here, the vanes  2  of the mixing element  1  through their outside edges contact an envelope  9  enveloping them. In the process, the mixing element  1  partially fills the envelope  9  axially and in the middle. Furthermore, the envelope  9  is embodied in such a manner that it contacts a pipe  8  associated with this envelope  9  in a linear manner. Here, the envelope  9  contacts the pipe  8  only in a region, in which the mixing element  1  is not located, as a result of which in the region, in which the mixing element  1  is located, a gap between the envelope  9  and the pipe  8  is created. The envelope  9 , furthermore, is axially shorter than the pipe  8 , so that the envelope  9  only partially fills the pipe  8 . The envelope  9  and the mixing element  1  are now arranged in such a manner that the longitudinal axis  7  of the mixing element  1  is arranged parallel to a main flow direction  10  of the exhaust gas of the exhaust gas-conducting pipe  8  symbolised by arrows. Here respectively two vanes  2  of the respective mixing element  1  are arranged offset transversely to one another along the main flow direction  10 , whilst opposite vanes  2  along the main flow direction  10  are angled in the main flow direction  10  on different sides  4 ′,  4 ″ of the connecting section  3 . Therefore, the respective vane stands “in the way” of the onflowing exhaust gas with a substantial surface, so that an intensive swirling or respectively through-mixing of the exhaust gas is brought about. 
         [0037]      FIG. 6  and  FIG. 7  each show a mixing device  6 , each of which comprises two pipe sections  8 ′ and  8 ″. Furthermore, both mixing devices  6  each comprise a mixing element  1 , wherein two vanes which are directly adjacent or located directly opposite with respect to the longitudinal axis  5  of the associated mixing element  1  are each angled off towards different sides  4 ′ and  4 ″ of the associated connecting section  3 . The respective mixing elements  1  are attached in the respective mixing devices  6  in such a manner that their longitudinal axis  7  runs parallel to the main flow direction  10 . Furthermore, the respective mixing elements  1  of the mixing devices  6  are arranged in an envelope  9  and in the process partially fill this envelope  9  axially. The envelope  9  of the mixing devices  6  is designed in such a manner that on one of its sides which corresponds to the left side of the spatial position shown in  FIGS. 6 and 7 , it linearly contacts one of the pipe sections  8 ′ in a region in which the mixing element  1  is not located and with its ends facing away from the mixing element  1  is angled off from this pipe section  8 ′. On the other side, i.e. on the right side of the envelope  9 , the envelope  9  linearly contacts the pipe section  8 ′ in a region in which the mixing element  1  is not located. Thus, in the region in which the mixing element  1  is located, a gap is created between the envelope  9  and the pipe section  8 ′. Here, the envelope  9  protrudes over the pipe section  8 ′ axially towards the other pipe section  8 ″. The pipe sections  8 ′ and  8 ″ each have two flanges  11 ′ and  11 ″, which are arranged radially to the associated pipe section  8 ′,  8 ″. Here, the flanges  11 ′ of the pipe section  8 ′ are facing the other pipe section  8 ″ and the flanges  11 ″ of the pipe section  8 ″ are facing the pipe section  8 ″ in such a manner that in each case one of the flanges  11 ′ of the pipe section  8 ′ is located opposite one of the flanges  11 ″ of the pipe section  8 ″. The sleeve  9  furthermore comprises two flanges  12 , each of which are arranged radially to the envelope  9  and are located between the flanges  11 ′ and  11 ″ of the pipe sections  8 ′ and  8 ″. The flanges  12  of the envelope  9  in this case show the form of a beaded gasket. In particular, these embodiments serve for a simplified assembly of a mixing device  6 . 
         [0038]    The pipe section  8 ′ shown in  FIG. 7 , with which the envelope  9  is directly contacted, additionally comprises a variation of the shape and size. Here, the radius of the pipe section  8 ′ in the region in which the envelope  9  or the mixing element is located, is larger than the radius of the other pipe section  8 ″. On the side of the pipe section  8 ′ facing away from the other pipe section  8 ″, i.e. along the main flow direction  10 , the pipe section  8 ′ tapers in a region in which the envelope  9  or the mixing element  1  is not located. Here, the pipe section  8 ′ tapers so far until its radius corresponds to the radius of the other pipe section  8 ″. In particular, this serves for the purpose of making available an adapted cross section of the pipe section  8 ′ for the exhaust gas in a region in which the mixing element  1  and/or envelope  9  is/are located, as in a region in which no mixing element  1  and/or envelope  9  is/are present. 
         [0039]    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.