Patent Publication Number: US-2020300144-A1

Title: Substrate for an exhaust gas treatment unit

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. § 119 of German Application 10 2019 107 386.3, filed Mar. 22, 2019, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention pertains to a substrate for an exhaust gas treatment unit, especially for an exhaust system of an internal combustion engine, as well as to an exhaust gas treatment unit configured with such a substrate. 
     TECHNICAL BACKGROUND 
     Exhaust gas treatment units, for example, catalytic converters in exhaust systems of internal combustion engines in vehicles, are generally composed of a substrate, which has a substrate body which is coated with a material that is suitable for the treatment of exhaust gas, for example, with a catalyst material. A plurality of cells extending in the longitudinal direction of the substrate are formed in the substrate body, which is made, for example, of ceramic material, wherein the exhaust gas to be treated can flow through each such cell essentially in the substrate longitudinal direction and thus provides a flow duct for the exhaust gas to be treated. A very large surface, around which exhaust gas can flow and in the area of which an exhaust gas treatment can take place, for example, by interacting with catalytically active material to reduce the pollutants contained in the exhaust gas, is provided in this manner. 
     Such substrates are generally accommodated in a housing with a tubular circumferential wall. For a stable holding of the substrates in such a circumferential wall, the substrates are wrapped with fiber mats, which are compressed when the substrates are pressed into the tubular circumferential wall and then have a holding effect, hold this substrate in a stable manner at the circumferential wall between a respective circumferential wall and the outer circumference of a substrate accommodated there. 
     SUMMARY 
     An object of the present invention is to provide a substrate for an exhaust gas treatment unit, and in particular for an exhaust system of an internal combustion engine, which substrate has an increased strength against loads exerted onto same from outside. 
     According to the present invention, this object is accomplished by a substrate for an exhaust gas treatment unit, especially for an exhaust system of an internal combustion engine, comprising a substrate body elongated in the substrate longitudinal direction, wherein the substrate body is flattened (has a less round or a flattened, round, or an elliptical outer circumferential contour or has a cylindrical shape with one smaller radial dimension) in a flattening direction essentially at right angles to the substrate longitudinal direction, wherein a plurality of cells, which extend essentially in the substrate longitudinal direction and provide flow ducts, are formed in the substrate body, wherein the cells are defined by cell walls, which extend essentially in the substrate longitudinal direction, and the cell walls are bent (extend and are disposed) at an angle in relation to the flattening direction. 
     Substrates, which are, above all, flattened, i.e., configured, for example, with an elliptical outer contour, exhibit the tendency to extend in the direction of the flattening direction in case of a pressure load from the radially outward direction in relation to the substrate longitudinal direction. A better load distribution in case of a load from the radially outward direction is achieved by the bending at an angle of the cell walls in relation to the flattening direction, i.e., the arrangement such that the cell walls extend neither parallel nor at right angles to the flattening direction, as a result of which the risk of formation of cracks in the substrate body due to locally excessively high surface pressure is markedly reduced. 
     For a configuration that is stable and nevertheless suitable for absorbing high loads from the outside, it is proposed that first cell walls, which are arranged parallel to one another and at spaced locations from one another, and second cell walls, which are arranged parallel to one another and at spaced locations from one another, be provided, wherein the first cell walls are disposed at an angle in relation to the second cell walls such that the cells are each defined by two first cell walls and by two second cell walls, which means in an especially preferred embodiment that the cells are only defined each by two first cell walls parallel to one another and two second cell walls parallel to one another, i.e., by a total of four cell walls. In this case, the first cell walls may be disposed at an angle of about 90° in relation to the second cell walls for an especially uniform load distribution. 
     For a homogeneous structure in the interior of the substrate body, it is proposed that the mutual spacing from one another of directly adjacent first cell walls correspond essentially to the mutual spacing from one another of directly adjacent second cell walls. 
     Cells lines may be formed with cells adjacent to one another in the substrate body, wherein the cells of a cell line are defined by the two identical first cell walls or by the two identical second cell walls. This means that the first or second cell walls defining the cells of particular cell lines run essentially without interruption along all cells associated with a particular cell line and may extend, for example, from an area adjoining an outer circumferential area of the substrate body up to an area adjoining an opposite outer circumferential area of the substrate body. 
     The first cell walls and the second cell walls may form a grid-like (grid or grid-shaped) cell wall structure. Further, the first cell walls and the second cell walls are preferably essentially unbent for a structure that is stable per se, wherein the cells preferably further have an essentially rectangular, preferably square cross-sectional contour. Further, a very good load distribution in case of impact from the outside can be achieved, when the cell walls are disposed at an angle in a range from 40° to 50°, preferably at about 45°, in relation to the flattening direction. 
     To provide a symmetrical, yet flattened outer circumferential contour of the substrate, it is proposed that the substrate body be configured with an essentially mirror-symmetrical outer circumferential contour in relation to a first longitudinal central plane, which is extended in the flattening direction and in the substrate longitudinal direction, or/and that the substrate body be configured with an essentially mirror-symmetrical outer circumferential contour in relation to a second longitudinal central plane, which is extended at right angles to the flattening direction and in the substrate longitudinal direction. 
     Peak loads in corners or edge areas can be avoided when the substrate body has a flattened, round, preferably essentially elliptical outer circumferential contour. Further, the substrate body has an essentially cylindrical configuration preferably in relation to the substrate longitudinal direction for a simple insertion of the substrate into a tubular housing. 
     For a configuration that is thermally stable and resistant to environmental effects, it is proposed that the substrate body be made of ceramic material. Further, the cell walls may be coated with exhaust gas treatment material, preferably with catalyst material for an efficient exhaust gas treatment. 
     The present invention further pertains to an exhaust gas treatment unit, especially for an exhaust system of an internal combustion engine, comprising a housing with a tubular circumferential wall, which encloses a housing interior, and at least one substrate with the configuration according to the present invention, which substrate is arranged in the interior. 
     For a stable holding that is nevertheless simple to establish, it is proposed that at least one substrate, preferably each substrate, which is arranged in the interior, be enclosed by at least one layer of support material in a manner supporting the substrate in relation to the circumferential wall. 
     The circumferential wall may also be flattened in the flattening direction in adaptation to the design of a substrate configured according to the present invention. In particular, the circumferential wall may have a flattened, round, preferably essentially elliptical outer circumferential contour. 
     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: 
       The only FIGURE is a cross-sectional view of an exhaust gas treatment unit with a substrate accommodated in a tubular housing. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to the drawings, an exhaust gas treatment unit, for example, a catalytic converter unit, for an exhaust system of an internal combustion engine in a vehicle is generally designated by  10  in  FIG. 1 . The exhaust gas treatment unit  10  comprises a tubular housing  12  with a longitudinal central axis L at right angles to the drawing plane of  FIG. 1 . The housing  12  comprises a circumferential wall  14 , which is made, for example, of sheet metal material and which is flattened in a flattening direction A and thus has a flattened, round, for example, elliptical outer circumferential contour in the example shown. 
     A substrate generally designated by  16  is arranged in the interior of the housing  12 , which interior is enclosed by the circumferential wall  14 . The substrate  16  has a substrate body  18 , which is made, for example, of ceramic material. A plurality of cells  24 , which are defined by first cell walls  20  and by second cell walls  22 , which extend in a substrate longitudinal direction S, which corresponds essentially to the direction of extension in the longitudinal central axis L in the example shown, are formed in the substrate body  18 . The first cell walls  20  and the second cell walls  22  are disposed at an angle in relation to the flattening direction A and have an angle of about 45° to this flattening direction in the example shown. In this case, in the view of  FIG. 1 , the first cell walls  20  extend obliquely from the left bottom to the right top or vice versa, while the second cell walls  22  extend obliquely from the right bottom to the left top or vice versa. Since both the first cell walls  20  and the second cell walls  22  are disposed at an angle of about 45° in relation to the flattening direction, the first cell walls  20  and the second cell walls  22  are approximately at right angles to one another. Since, furthermore, the first cell walls  20  and also the second cell walls  22  extend each essentially without interruption between two outer circumferential areas of the substrate body  18 , a grid-shaped structure of the cell walls  20 ,  22  is obtained, in which the cells  24  defined by two first cell walls  20  directly adjacent to one another and two second cell walls  22  directly adjacent to one another have a rectangular cross-sectional contour. Since, furthermore, the mutual spacing of all first cell walls  20  directly adjacent to one another corresponds in an especially preferred embodiment essentially to the mutual spacing of all second cell walls  22  directly adjacent to one another, the cells  24  have a square cross-sectional contour as well. 
     First cell lines, which are illustrated by a line L 1  in  FIG. 1 , are formed by cells  24  adjacent to one another or following one another in the direction of the line L 1  between the first cell walls  20 , which are parallel to one another and are disposed at an angle in relation to the flattening direction A. Equally, second cells lines, which are illustrated by a line L 2  in  FIG. 1 , are formed by cells  24  adjacent to one another or following one another in the direction of the line L 2  between the second cell walls  22 , which are parallel to one another and are disposed at an angle in relation to the flattening direction A. All cells  24  in a particular first cell line L 1  are defined by the two identical first cell walls  20  and all cells  24  in a particular second cell line L 2  are defined by the two identical second cell walls  22 . 
     The substrate  16  has a flattened, round, for example, elliptical outer circumferential contour of the circumferential wall  14  in adaptation to the cross-sectional contour of the circumferential wall  14 . In this case, the substrate  16  has an especially mirror-symmetrical outer circumferential contour, which is symmetrical to a first longitudinal central plane that extends essentially in the flattening direction A and in the direction of the longitudinal central axis L. This first longitudinal central plane E 1  intersects the substrate  16  in the two areas  26  with maximum radius of curvature of the outer circumferential contour, which areas are diametrically opposed to each other. The substrate  16  has an especially mirror-symmetrical configuration, which is also symmetrical to a second longitudinal central plane E 2 , which is at right angles to the first longitudinal central plane E 1  and also contains the longitudinal central axis L. The second longitudinal central plane E 2  intersects the outer circumference of the substrate  16  in areas  28  with minimal radius of curvature of the outer circumferential contour of the substrate  16 , which areas  28  are diametrically opposed to each other. 
     When the substrate  16  is inserted into the housing  12  or into the circumferential wall  14  of same, at first the substrate  16  is wrapped with at least one layer of support material  30 , for example, fiber mat or the like. The thus wrapped substrate  16  is then inserted into the housing  12 , for example, via an insertion funnel. In this case, the layer of support material  30  is compressed, so that the substrate  16  is held by the compressed layer of support material  30  in a defined position in the interior of the housing  12 . In the course of this insertion motion, the greatest surface pressure is exerted onto the substrate  16  in transition areas  32  between the areas  28  with minimal radius of curvature and the areas  26  with maximum radius of curvature. Since the cell walls  20 ,  22  extend at an angle of about 45° in relation to the flattening direction A, one of the two types of cell walls  20 ,  22  each extends in each of the transition areas  32 , in which the outer circumferential contour of the substrate  16  has an average radius of curvature, approximately at right angles to the force F acting from outside on the substrate  16  in these areas. The result is that the forces acting on the substrate  16  in these high-load areas can be absorbed in the respective cell walls  20 ,  22  which extend approximately in the force introduction direction, without a significant deformation of the substrate  16  being generated, since the substrate  16  also essentially has its maximum stiffness in the direction of the force introduction. The risk that damage, for example, cracks in the substrate body  18  is brought about by such loads is thus reduced significantly. 
     Finally, it should be pointed out that when the the substrate body  18  is used in a catalytic converter unit, the substrate body  18  can be coated with catalytically active material on its cell walls  20 ,  22  defining the cells  24 . The exhaust gas flowing through the cells  24  can thus interact with the catalytic material in the area of a comparatively large surface in the interior of the substrate body  18  for carrying out the catalytic reaction, so that such a catalytic converter may be effective, for example, as an oxidation catalytic converter or as a SCR catalytic converter. 
     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.