Patent Publication Number: US-2005115070-A1

Title: Metal carrier

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is based upon and claims the benefit of priorities from Japanese Patent Applications No. 2003-399384 filed on Nov. 28, 2003 and No. 2004-195606 filed on Jul. 1, 2004; the entire contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      The present invention relates to a metal carrier for catalytic converter provided in an exhaust system of an internal combustion engine and the like.  
      An exhaust system for an internal combustion engine or the like is provided with a catalytic converter which cleans emissions. This kind of catalytic converter generally uses metal carrier having metal sheet such as Fe—Cr—Al based ferrite stainless foil as the catalytic converter.  
      To produce a metal carrier of this kind, metal sheet corrugated plates and metal sheet flat plates are alternately stacked on one another. These stacked plates are wound many times, forming a core having a honeycomb structure. The structure has a circular cross section and the like. A lower-corrugated plate having lower corrugation height than that of the corrugated plate may be used as the flat plate. Then, a brazing foil material is wound around an outer periphery of the core, it is press-fitted into a metal outer cylinder, and this is heated in a vacuum. With this heating operation, crests of the corrugated plate and the flat plate are joined to each other using diffusion joining, and the outer cylinder and the core are brazed to each other.  
      Catalyst such as platinum is added to the core, diffusers are welded to both ends of the outer cylinder, thereby forming a catalytic converter. In the catalyst-adding processing, wash coat solution containing catalyst is poured into the core, and a thin membrane containing the catalyst is formed on the surface of the core. See Japanese Patent Applications Laid-open Nos. 2000-61317 and No. 2003-334456.  
     SUMMARY OF THE INVENTION  
      The metal carrier has a joint portion between the corrugated plate and the flat plate (or low-corrugated plate) The joint portion has a fillet (catalyst residue) produced from the wash coat solution under surface tension. This fillet is determined by the plate material, air (atmosphere), the surface tension of the solution and the like. The fillet is formed such as to draw an arc, and has large thickness. This prevents catalyst contained in the fillet from exhibiting the original performance, and the catalyst is waste.  
      It is an object of the present invention to reduce the fillet produced in a joint between a flat plate or a corrugated plate forming a core, reducing an amount of waste catalyst.  
      It is another object of the invention to enhance the cleaning performance.  
      The first aspect of the invention provides the following metal carrier. The metal carrier Includes a core having a thinned film containing a metal catalyst. The core includes a first metal sheet corrugated and having a crest with a first radius. The core includes a second metal sheet flattened or corrugated smaller in corrugation height than the first metal sheet. The first and second metal sheets are stacked on each other and are wound up. The crest and second metal sheet are joined to each other, having a joint therebetween. A fillet of the catalyst is formed between the joint, the first metal sheet, and the second metal sheet, having an arced surface of a second radius extending between the first and second metal sheets. The first radius is set substantially equal to the second radius.  
      The first radius may be an inner radius of the crest.  
      The first radius may be 1.0 to 1.2 times of the second radius.  
      The second aspect of the invention provides the following metal carrier. The metal carrier includes a core having a thinned film containing a metal catalyst.  
      The core includes a first metal sheet corrugated and having a crest of a first radius. The core includes a second metal sheet flattened or corrugated smaller in corrugation height than the first metal sheet. The first and second metal sheets are stacked on each other and are wound up. The crest and second metal sheet are joined to each other, having a joint therebetween. A fillet of the catalyst is formed between the Joint, the first metal sheet, and the second metal sheet, having an arced surface of a second average radius extending between the first and second metal sheets. The first radius is set to the second average radius with a standard deviation (a) or more. The first metal sheet has a vertical wall set to be substantially normal to the second metal sheet.  
      The first metal sheet may have a corrugation height between a crest and a trough thereof and a corrugation pitch between neighboring crests.  
      The corrugation height may be greater than the corrugation pitch. 
    
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS  
       FIG. 1  is an illustrative view of a method of producing a metal carrier according to a first embodiment;  
       FIG. 2  is a perspective view of the metal carrier of the first embodiment;  
       FIG. 3  is an elevation view illustrating the benefit of the first embodiment;  
       FIG. 4  is a partial sectional view of a metal carrier of a comparative example;  
       FIG. 5  is a partial sectional view of a metal carrier according to a second embodiment;  
       FIGS. 6A and 5B  are illustrative views of a concrete. design example according to the second embodiment; and  
       FIGS. 7A and 7B  are illustrative views of catalyst-reduction effects obtained by a substantially normal corrugated foil vertical wall. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Embodiments of the present invention will be described with reference to the drawings.  
      With reference to  FIG. 1 , a metal carrier  10 A includes a corrugated plate  1 A as a first metal sheet and a flat sheet  2  as a second metal sheet of a thinned metal plate in a band-shape. The corrugated plate  1 A and the flat plate  2  are composed with Al of around 5%, Cu of around 20%, in addition, minute amount of metal Mn, Mo and the like, and the remains of Fe. The thickness of plate  1 A or  2  is 20 to 50 μm. The corrugated plate  1 A and the flat plate  2  are alternately stacked on one another, forming a layered product. The layered product is wound many times, forming a core  3  having a honeycomb structure. The honeycomb structure has a circular cross section for example. A brazing foil material wound around the outer periphery of the core  3 . This is press-fitted into a metal outer cylinder  4  as shown in  FIG. 2  and heated in a vacuum. With this heating operation, the corrugated plate  1 A and the flat plate  2  are joined to each other using diffusion joining, and the outer cylinder  4  and the core  3  are brazed to each other for joint.  
      Wash coat solution containing catalyst such as platinum is poured into the core  3 , forming a thin membrane containing the catalyst on the surface of the core  3 . The catalyst contains a main component of alumina (Al 2 O 3 ) with another minute amount of cerium oxide (CeO 2 ) or barium oxide or the like, which contains Pt, Pd, or Rh. Diffusers (not shown) are welded to both ends of the outer cylinder  4 , forming a catalytic converter.  
      With reference to  FIG. 3 , the corrugated plate  1 A has thickness of 30 μm, corrugation height H 1  of 2.0 mm, and corrugation pitch P 1  of 1.6 mm. The corrugation height is a distance between the trough and the crest of a corrugation. The corrugation pitch is a distance between neighboring crests or between neighboring troughs of a corrugation. The corrugated plate  1 A has crests  1   a,    1   b,  and  1   c  whose radii R 1 , R 2 , and R 3  are 0.2 mm, 0.3 mm and 0.4 mm, respectively. The cross section areas of fillets  5   a,    5   b,  and  5   c  are  55 ,  65 , and  90 , respectively. These numeric values are comparative values when a cross section area of a fillet  103  of a comparative example shown in  FIG. 4  is set to 100. The corrugated plate  101  is interposed between two flat plates  102 . The corrugated plate  101  has corrugation height H 2  of 1.2 mm, pitch P 2  of 2.56 mm, and crest radius R 4  of 0.55 mm.  
      Each of the fillets  5   a,    5   b,  and  5   c  has radius r 1  of 0.25 mm. A crest la having radius R 1  of 0.2 mm produces a catalyst residue inside the crest  1   a.    
      The crest  1   a  having radius R 4  of 0.4 mm does not produce a catalyst residue inside of the crest  1   a.  The fillet  5   c  is greater in area than the fillet  5   a  having the radius R 1  of 0.2 mm.  
      The crest  1   b  having radius R 2  of 0.3 mm produces little catalyst residue inside the crest  1   b.  The fillet  5   b  is smaller in area than the fillet  5   c  in correspondence with radius R 3 , and greater than the fillet  5   a.  The crest  1   b  reduces a total amount of waste catalyst as compared with the crests  5   a  and  5   c  of radius R 1  and R 3 .  
      The radii R 1 , R 2 , and R 3  are outer radii of the crests  1   a,    1   b,  and  1   c,  respectively. The inner radii of the crests  1   a,    1   b,  and  1   c  are smaller than the radii R 1 , R 2 , and R 3 . The inner radius of the crest la having the radius R 2  is 0.27 mm (=0.3 mm−0.03 mm) , which is substantially equal to the radius r 1  of the arc, or arced surface, of the fillet  5   b.    
      As this manner, the determination of inner radius of the crest  1   a  as a reference eliminates the influence due to the thickness of the corrugated plate  1 , reducing the amount of the catalyst residue with higher accuracy.  
      The inner radius of the crest  1   a  may not be completely equal to the radius r 1 . The inner radius is 0.8 to 1.2 times of the radius r 1 . The inner radius may be 1.0 to 1.2 times of the radius r 1 .  
      In the above embodiment, the stacked corrugated plates, flat plates, and metal carrier  10 A are described. The flat plate  2  may be replaced by a lower-corrugated plate with a lower corrugation height. The lower-corrugated plate and the corrugated plate  1  may be stacked on each other to form the core, which obtains the identical benefit.  
     Second Embodiment  
      With reference to  FIG. 5 , a metal carrier  10 B of a second embodiment will be described. The basic structure of the metal carrier  10 B is identical with that of the metal carrier  10 A in the first embodiment. Corrugated plate  1 B and flat plate  2  of band-shaped thinned metal plates are alternately stacked on one another, forming a layered product. The layered product is wound many times, forming a core  3  having a honeycomb structure. This honeycomb structure has a rectangular cross section. Brazing foil material is wound around the outer periphery of the core  3  (see  FIG. 1 ). This is press-fitted into a metal outer cylinder  4  and heated in a vacuum. With this heating operation, the corrugated plate  1 B and the flat plate  2  are joined to each other using diffusion joining, and the outer cylinder  4  and the core  3  are brazed to each other for joint (see  FIG. 2 ).  
      Wash coat solution containing catalyst such as platinum is poured into the core  3 . This forms a thin membrane containing the catalyst on the surface of the core  3 . Diffusers (not shown) are welded to both ends of the outer cylinder  4 , forming a catalytic converter.  
      With reference to  FIG. 5 , the corrugated plate  1 B has crests  1   d  each having radius R 5 . Each of the crests  1   d  has a fillet  5   d.  The arc of the fillet  5   d  is set equal to or greater than average radius r 2 +σ (σ: standard deviation). The corrugated plate  1 B has a corrugated foil vertical wall  1   e.  The vertical wall  1   e  is set to be substantially normal (for example 88°, preferably 90°) relative to the flat plate  2 .  
      In  FIGS. 6A and 6B , a concrete design example of the second embodiment using the wash coat solution will be described. The fillet  5   d  has the arc having average value of 0.264 mm and radius r 2  having standard deviation of 0.024. Here, in order to reduce the production probability of filling of a catalyst into the crests  1   d,  radius R 5  of the crest  1   d  is set to the average value +2.33σ of the radius r 2  of the arc of the fillet  5   d,  e.g., to 0.32 mm for example. In the design example shown in  FIG. 6A , the density of a corrugated plate  1  is 600 cells, and its corrugation height H 3  is 1.91 mm. Corrugation pitch P 3  is 1.28 mm which is two times of the radius R 5 . With this, the height H 3  of the corrugated plate is greater than the corrugation pitch P 3  thereof. In  FIG. 6B , the corrugation pitch P 4  is 1.28 mm. The corrugation height H 4  is 1.35 mm. The corrugation pitch P 4  and the corrugation height H 4  are substantially equal to each other.  
      Like the first embodiment, the corrugated plate  1 B produces little catalyst residue Inside of the crest  1   d.  For example, as shown in  FIGS. 6A and 6B , radius R 5  of 0.32 mm does not produce the catalyst residue with a probability of 99%. The fillet  5   d  is smaller in area than the fillet  5   c  (see  FIG. 3 ) with the radius R 3  of 0.4 mm, which reduces the total amount of waste catalyst.  
      The corrugated vertical wall  1   e  of the corrugated plate  1 B is substantially normal to the flat plate  2 . With reference to  FIGS. 7A and 7B , the following describes a catalyst reducing effect obtained by the substantially normal corrugated vertical wall  1   e.    FIG. 7A  shows a corrugated plate  101  of a comparative example with respect to  FIG. 4 , and radius r of an arc of a fillet  103  is in contact with a straight line of the corrugated plate. The fillet  103  is formed in a range surrounded by contact points Rfa, Rfb, and Rla. In  FIG. 7B , the substantially normal corrugated vertical wall  1   b  allows an arc of a fillet  5  with radius r 2  and the circle of the crest  1   a  of the corrugated plate  1 B with radius R 5  to be in contact with each other. Geometrically, the area of the fillet  5   d  is smaller than that of the fillet  5  shown in  FIG. 7A .  
      As described above, the radius R 5  of the crest  1   d  of the corrugated plate  1 B is slightly greater than the radius r 2  of the arc of the fillet  5 . The corrugated plate  1 B has a corrugation-shape having a substantially normal corrugated vertical wall  1   d.  This configuration minimizes the waste catalyst, reducing the production costs.  
      While the standard deviation is 2.33 in this embodiment, in order to obtain the benefit of this embodiment, the standard deviation may be at least  1   a.    
      Specifically as shown in  FIG. 6A , the relationship between the corrugation height H 3  and the corrugation pitch P 3  is H 3 /P 3 =1.5. This relationship reduces the representative length (equivalent diameter) which controls the coefficient of heat transfer by the current corrugated plate. The reduction promotes heating of the carrier, which shortens period from start of an engine to activation of the catalyst. This relation enhances the cleaning performance in a cold region. This effect enhances the cleaning performance also in the corrugation shape of the first embodiment by increasing the value of H 1 /P 1 . The embodiment with the substantially normal corrugated vertical wall  1   e  has the maximum H 3 /P 3  value. This corrugation shape achieves the best cleaning performance.  
      As shown in  FIG. 6B , in the relation of corrugation height H 4 &gt;corrugation pitch P 4 , H 4 :P 4  is set to about 1:1. This relationship slightly reduces the cleaning performance in a cold region, while increases call density. This enhances the cleaning performance as a whole. Where a carrier with a corrugation height H 3  of 1.91 mm has 600 cells in  FIG. 6A , a carrier with a corrugation height H 4  of 1.35 mm has 900 cells in  FIG. 6B .  
      As described above, this embodiment provides products with a high cleaning performance and the reduced cost overall.  
      In this embodiment, the corrugated plate and the flat plate are stacked on each other. The flat plate may be replaced by a lower-corrugated plate that is lower in corrugation height than the corrugated plate. The lower-corrugated plate is stacked on the corrugated plate, forming the core, which provides the identical benefit.  
      Although the Invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings. The scope of the invention is defined with reference to the following claims.