Honeycomb unit and catalytic converter
The honeycomb unit's optimized geometric configurations and material properties enhance catalyst activation and purification performance during cold starts by minimizing burr ignition, achieving efficient catalyst activation and improved structural durability.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- NIPPON STEEL CHEM & MATERIAL CO LTD
- Filing Date
- 2024-12-06
- Publication Date
- 2026-06-18
AI Technical Summary
Existing catalytic converters struggle to achieve high purification performance during cold starts due to the limitations of burr ignition effects, and there is a need for improved structures that can activate catalysts more effectively at low temperatures.
A honeycomb unit is designed with specific geometric configurations and material properties, including hole arrangements and foil thicknesses, to enhance catalyst activation without relying on burr ignition, ensuring π × d1 × n × ε ≥ 50 and cross-sectional area ratios of the hole edge foil are optimized.
The design significantly improves catalyst activation and purification performance during cold starts, while maintaining structural durability, by ensuring sufficient volume and porosity of the pore edge foil, and reducing heat capacity.
Smart Images
Figure 2026099611000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a catalytic converter, and particularly to a honeycomb unit for supporting a catalyst used in a catalytic converter for purifying exhaust gas of an internal combustion engine such as an automobile.
Background Art
[0002] As an exhaust gas purification device for an internal combustion engine such as an automobile, a catalytic converter is used in which a catalyst is supported on a honeycomb unit formed by fitting a honeycomb body made of the same heat-resistant alloy into an outer cylinder made of the same alloy.
[0003] In recent years, emission regulations on harmful substances such as carbon monoxide, hydrocarbons, and nitrogen oxides contained in exhaust gas of automobiles and the like have become extremely strict. Regarding these harmful substances, the emission amount at cold start immediately after engine startup in the measurement mode of the exhaust gas measurement test occupies a quite large proportion of the total emission amount. Therefore, in order to suppress the emission of harmful substances at cold start, a technique for reducing the heat capacity of the catalytic converter is required to activate the catalyst earlier.
[0004] Here, as the honeycomb body constituting the catalytic converter, a laminated structure of a metal flat foil with a thickness of about 50 μm and a corrugated foil obtained by corrugating the flat foil, or a structure obtained by winding a strip-shaped flat foil and a corrugated foil in a spiral shape by overlapping them is used. By perforating the flat foil and / or the corrugated foil constituting the honeycomb body, the heat capacity of the catalytic converter can be reduced.
[0005] Furthermore, the burrs (so-called flashing) that are naturally formed by the perforation process applied to flat foil and / or corrugated foil have a small heat capacity and their temperature rises easily when exhaust gas is introduced, thus acting as a kindling to initiate the catalytic reaction (hereinafter, this effect will also be referred to as the kindling effect). For this reason, this kindling effect is sometimes used for the early activation of catalysts. For example, Patent Document 1 discloses a catalytic converter that induces the kindling effect and early activation of a catalyst by controlling the average height of the burrs of multiple holes formed in the flat foil and corrugated foil of a honeycomb structure to 0.1 μm or more and 30 μm or less, and by setting the average hole diameter and opening ratio of the multiple holes within a predetermined range. [Prior art documents] [Patent Documents]
[0006] [Patent Document 1] Patent No. 6975306 [Overview of the project] [Problems that the invention aims to solve]
[0007] The inventors then conducted further studies on the structure of the honeycomb. As a result, they devised a honeycomb structure that further improves the purification performance during cold starts without using the ignition effect of burrs as described in Patent Document 1. [Means for solving the problem]
[0008] To solve the above problems, the present invention provides a honeycomb unit comprising (1) a honeycomb body formed by alternately laminating flat foils and corrugated foils of metal, and an outer cylinder positioned to surround the outer circumferential surface of the honeycomb body, wherein a plurality of holes are formed in the flat foils and the corrugated foils, and the foil located in the region from the edge of the hole to a distance corresponding to half the thickness of the flat foils and the corrugated foils toward the radially outward direction of the hole is called the hole edge foil, and the hole edge foil of the flat foils and the corrugated foils If the foil portion excluding the hole edge is defined as the matrix foil, then the hole edge foil exists only on the foil thickness center side of the first reference plane extending along the back surface of the matrix foil in which the hole edge foil is located and the second reference plane extending along the front surface of the matrix foil, and the diameter of the hole is π, the hole diameter is d1 (mm), the distance between the centers of adjacent holes is d2 (mm), the foil thickness of the flat foil and the corrugated foil is t (μm), and the area of the flat foil and the corrugated foil is 1 square inch (645.16 mm). 2 A honeycomb unit characterized by satisfying the following equation, where n is the number of holes per unit and ε is the porosity. π × d1 × n × ε ≥ 50 (d2-d1)×t / 50≧0.07
[0009] (2) Let π be the value of pi, d1 be the diameter of the hole, and 1 square inch (645.16 mm) be the area of the flat foil and the corrugated foil. 2 The honeycomb unit according to (1), characterized in that it satisfies the following equation when the number of holes per ) is n (pieces) and the porosity is ε. π × d1 × n × ε ≥ 400
[0010] (3) The honeycomb unit according to (1) or (2), characterized in that the following formula is satisfied when the distance between the centers of adjacent holes is d2 (mm), the diameter of the holes is d1 (mm), and the thickness of the flat foil and the corrugated foil is t (μm). (d2-d1)×t / 50≧0.2
[0011] (4) The honeycomb unit according to (1) or (2), wherein, in the matrix foil, two virtual surfaces are arranged at a distance of t / 2 in the radial direction of the hole and penetrate the matrix foil in the thickness direction, enclosing the outer circumference of the hole, and these two virtual surfaces are designated as the first virtual surface and the second virtual surface, and the cross-sectional area in a cross-sectional view obtained by cutting the hole edge foil in the thickness direction is 95% or less of the area of the rectangle enclosed by the back surface of the matrix foil, the front surface of the matrix foil, the first virtual surface and the second virtual surface in that cross-sectional view.
[0012] (5) The honeycomb unit according to (3), wherein, in the matrix foil, two virtual surfaces are arranged at a distance of t / 2 in the radial direction of the hole and penetrate the matrix foil in the thickness direction, enclosing the outer circumference of the hole, and these two virtual surfaces are designated as the first virtual surface and the second virtual surface, and the cross-sectional area of the hole edge foil when cut in the thickness direction is 95% or less of the area of the rectangle enclosed by the back surface of the matrix foil, the front surface of the matrix foil, the first virtual surface and the second virtual surface in the cross-sectional view.
[0013] (6) A catalytic converter comprising a catalyst supported on a honeycomb unit as described in (1) or (2).
[0014] (7) A catalytic converter comprising a catalyst supported on the honeycomb unit described in (3).
[0015] (8) A catalytic converter comprising a catalyst supported on the honeycomb unit described in (4).
[0016] (9) A catalytic converter comprising a catalyst supported on the honeycomb unit described in (5). [Effects of the Invention]
[0017] According to the present invention, the purification performance during a cold start can be further improved without using the ignition effect of a burr. [Brief explanation of the drawing]
[0018] [Figure 1] It is a perspective view of the honeycomb unit 1. [Figure 2] It is a developed view of a part of the flat foil 2. [Figure 3] It is an enlarged view of the region A surrounded by the broken line in FIG. 2. [Figure 4] (a) It is an enlarged view of the region B surrounded by the dashed-dotted line in FIG. 2, and (b) it is a cross-sectional view obtained by cutting the region B in the thickness direction of the flat foil 2 along the diameter of the hole 8. [Figure 5] It is a cross-sectional view in the thickness direction corresponding to FIG. 4(b) immediately after the flat foil 2 has been perforated. [Figure 6] It is an example of a brush used to thin the foil near the edge of the hole 8. [Figure 7] It is a plan view when the thinning treatment by the brush 100 is performed on the flat foil 2.
Embodiments for Carrying Out the Invention
[0019] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view of the honeycomb unit 1. The honeycomb unit 1 includes a honeycomb body 4 formed by alternately laminating flat foils 2 and corrugated foils 3, and an outer cylinder 5 surrounding the outer peripheral surface of the honeycomb body 4. By supporting a catalyst on the honeycomb body 4 of the honeycomb unit 1, a catalytic converter can be obtained. In the present embodiment, the honeycomb body 4 is formed by winding the flat foil 2 and the corrugated foil 3, but it is not limited to this configuration, and the honeycomb body 4 may be a laminate in which the flat foil 2 and the corrugated foil 3 are alternately stacked. A plurality of holes 8 (described later) penetrating in the thickness direction are formed in the flat foil 2 and the corrugated foil 3, respectively.
[0020] Metal foils made of heat-resistant alloys can be used for the flat foil 2 and corrugated foil 3. The thickness of the metal foil is preferably 20 μm to 100 μm. The width of the metal foil is preferably 10 mm to 500 mm. The size of the metal foil can be appropriately changed depending on the application of the catalytic converter. The corrugated foil 3 can be manufactured by corrugating the flat foil 2 (for example, by corrugating). The cell density of the honeycomb body 4 is preferably 100 to 600 cells per square inch.
[0021] Here, the most preferable heat-resistant alloy used as the flat foil 2 and corrugated foil 3 is a ferritic stainless steel (in other words, Fe-20Cr-5Al alloy) consisting of Cr: 20% by mass, Al: 5% by mass, and the remainder being Fe and unavoidable impurities. However, the heat-resistant alloy applicable to the present invention is not limited to the aforementioned ferritic stainless steel, and a wide range of heat-resistant stainless steels containing Al in their alloy composition can be used. That is, the metal foil typically used in the honeycomb body 4 contains 15-25% by mass of Cr and 2-8% by mass of Al, and Fe-18Cr-3Al alloy and Fe-20Cr-8Al alloy can also be used as heat-resistant alloys.
[0022] For the outer cylinder 5, a ferritic stainless steel containing 13% to 20% by mass of Cr, such as SUS436L, SUS430, or EN standard 1.4509, can be used. However, it is not limited to ferritic stainless steel; austenitic stainless steel such as SUS315J1 can also be used. The thickness of the outer cylinder 5 is preferably set to 0.5 mm to 3 mm, more preferably to 1 mm to 2 mm.
[0023] The flat foil 2 and corrugated foil 3 that make up the honeycomb body 4, or the honeycomb body 4 and the outer cylinder 5, are joined using methods such as brazing or mechanical methods such as crimping. When joining by brazing, a heat-resistant Ni-based brazing material (e.g., BNi-5) is used, the brazing material is placed at the intended joining location, and vacuum heat treatment is performed. By joining in this manner, the honeycomb unit 1 is manufactured.
[0024] A catalytic converter is manufactured by supporting a catalyst on the honeycomb unit 1. The catalyst can be supported on the metal foil of the honeycomb body 4 by applying a predetermined wash coat liquid to the surface of the metal foil, drying it, and firing it. For example, the wash coat liquid can be a slurry made by stirring powders of γ-alumina, lanthanum oxide, zirconium oxide, and cerium oxide in an aqueous solution of palladium nitrate.
[0025] The catalytic converter manufactured in this manner is installed in the exhaust pipe of a vehicle (not shown) such that exhaust gas flows in from the axial inlet end 1A and is discharged from the outlet end 1B. When the exhaust gas flowing into the catalytic converter comes into contact with the supported catalyst, CO, hydrocarbons, NO contained in the exhaust gas are released. X The emissions are rendered harmless, and clean gases can be discharged outside the vehicle. Vehicles equipped with catalytic converters include motorcycles, automobiles, and off-road vehicles.
[0026] Figure 2 is an unfolded view of a portion of the flat foil 2. In Figure 2, the X-axis direction corresponds to the exhaust gas conduction direction in the honeycomb body 4 (i.e., the axial direction of the honeycomb body 4), and the Y-axis direction is perpendicular to the X-axis and corresponds to the longitudinal direction of the flat foil 2.
[0027] The holes 8 can be formed in a staggered pattern along the X-axis in the region of the flat foil 2 excluding the gas inlet end region T in the exhaust gas conduction direction. Here, "staggered pattern" means that the next row of holes 8 is arranged on an imaginary line extending in the X-axis direction, passing through the intermediate position of adjacent holes 8 in the Y-axis direction, and this arrangement is continuous in the Y-axis direction. Note that the arrangement of the holes 8 is not limited to a staggered arrangement along the X-axis direction; for example, a matrix arrangement in which the holes 8 are arranged linearly along the X-axis and Y-axis directions is also possible.
[0028] The gas inlet end region T of the honeycomb body 4 is susceptible to damage from the pulsating flow of exhaust gas. Forming holes 8 therein would weaken the structure and potentially reduce the lifespan of the honeycomb unit 1. Therefore, it is preferable not to provide holes 8 in the gas inlet end region T. The range of the gas inlet end region T is preferably 5 mm from the gas inlet end S (corresponding to the inlet end 1A in Figure 1). However, if the effect of the pulsating flow of exhaust gas is small, it is not necessary to provide the gas inlet end region T.
[0029] Here, the open area ratio will be explained with reference to Figure 3. Figure 3 is an enlarged view of the area A enclosed by the dashed line in Figure 2. Referring to Figure 3, a triangle is drawn with the centroid of three adjacent holes 8 (in this embodiment, the center C of hole 8) as its vertex, and the area of this triangle is defined as the total area, and the area of the part where the triangle and the holes 8 overlap is defined as the hole area. In this case, the open area ratio is calculated as the "ratio of the hole area to the total area". Furthermore, even if the arrangement of the holes 8 is not a staggered arrangement along the X-axis direction as shown in Figure 2 (for example, the matrix arrangement described above), the open area ratio can be calculated according to the above definition.
[0030] Figure 4 shows (a) an enlarged view of region B enclosed by the dashed line in Figure 2, and (b) a cross-sectional view of region B cut along the diameter of the hole 8 in the thickness direction of the flat foil 2. In the present invention, the foil (hereinafter referred to as the hole edge foil 21) located in the region of the flat foil 2 from the edge of the hole 8 to a distance corresponding to half the foil thickness t (t / 2) of the flat foil 2, extending radially outward from the hole 8, exists only on the foil thickness center side than the first reference plane D1 extending along the back surface of the foil excluding the hole edge foil 21 (hereinafter referred to as the matrix foil 22) and the second reference plane D2 extending along the surface of the matrix foil 22. With this configuration, the heat capacity of the hole edge foil 21 is smaller than that of the matrix foil 22, so the hole edge foil 21 heats up easily, and therefore the catalyst is activated early in that region. The activation of the catalyst in the pore-edge foil 21 generates reaction heat from the catalytic reaction, which is then conducted to the matrix foil 22, allowing the matrix foil 22 to be heated up quickly, and the catalyst supported on the matrix foil 22 to be activated quickly as well. In other words, by providing the pore-edge foil 21 described above, it is possible to improve the purification performance during cold starts in the catalytic converter.
[0031] To improve the purification performance during cold starts, it is necessary to ensure a certain volume of the pore edge foil 21 in the entire catalytic converter. Here, by increasing the number of pores per predetermined area and / or setting a larger porosity, the total length of the edges of the pores 8 in the catalytic converter increases, thus increasing the volume of the pore edge foil 21 in the entire catalytic converter. Also, by increasing the diameter of the pores 8, the length of the edge of each pore 8 in the catalytic converter increases, thus increasing the volume of the pore edge foil 21 in the entire catalytic converter. In view of these points, the inventors conducted diligent studies and concluded that pi is π, the diameter of the pores 8 is d1 (mm), and 1 square inch (645.16 mm) in the flat foil 2 and corrugated foil 3... 2 We found that catalytic converters that satisfy the following equation, where n is the number of pores per ) and ε is the porosity, exhibit improved purification performance during cold starts. π × d1 × n × ε ≥ 50
[0032] Furthermore, we found that the purification performance during a cold start is further improved when each of the above parameters satisfies the following equation. π × d1 × n × ε ≥ 400
[0033] However, if the diameter of pore 8 is smaller than 0.2 mm, there is a risk that pore 8 may become blocked by the wash coat when the catalyst is supported on the foil. Therefore, it is preferable that the diameter of pore 8 be 0.2 mm or larger.
[0034] When the distance between the centers of adjacent holes 8 is d2 (mm), d2, d1, and foil thickness t (μm) must satisfy the following equation. (d2-d1)×t / 50≧0.07 If (d2-d1)×t / 50 < 0.07, it is not possible to secure a sufficient volume of foil between adjacent holes 8, making inter-hole cracks more likely to occur and preventing sufficient structural durability of the honeycomb structure. Therefore, it is necessary to set (d2-d1)×t / 50 ≥ 0.07.
[0035] Furthermore, it is preferable that the following equation is satisfied. (d2-d1)×t / 50≧0.2 According to the above configuration, a sufficient volume of foil can be secured between adjacent holes 8, making it less likely for cracks to occur between holes and thus ensuring greater structural durability of the honeycomb body.
[0036] In the matrix foil 22, two virtual surfaces are formed at a distance of t / 2 in the radial direction of the hole 8, penetrating the matrix foil 22 in the thickness direction and surrounding the outer circumference of the hole 8. These are designated as F1 (corresponding to the "first virtual surface" in claim 4) and F2 (corresponding to the "second virtual surface" described in claim 4). That is, as shown in Figure 4(a), F1 and F2 are formed concentrically with the hole 8 in a plan view of the matrix foil 22. In this case, as shown in Figure 4(b), if the thickness of the flat foil 2 is t, then in a cross-sectional view of the flat foil 2 in the thickness direction, the cross-sectional area of the hole edge foil 21 is the area of the rectangle P enclosed by the back surface of the matrix foil 22, the front surface of the matrix foil 22, and the virtual surfaces F1 and F2 (t2 It is smaller than ( / 2). Area of rectangle P (t 2 The ratio of the cross-sectional area of the hole edge foil 21 to (hereinafter also referred to as the cross-sectional area ratio W of the hole edge foil 21) is preferably 95% or less, more preferably 90% or less, and most preferably 85% or less. With this configuration, the heat capacity of the hole edge foil 21 can be made smaller, and thus the purification performance during cold start in the catalytic converter can be further improved.
[0037] For example, one hole 8 can be randomly selected, and multiple (e.g., four) cross-sectional views can be obtained by cutting the flat foil 2 in the thickness direction along the diameter of the selected hole 8. The average value of the ratio of the cross-sectional area of the foil 21 at the edge of the hole in each of the obtained cross-sectional views can be taken as the ratio of the cross-sectional area of the foil 21 at the edge of the hole. Alternatively, 100 holes 8 can be randomly selected, and the average value of the ratio of the cross-sectional area of the foil 21 at any cross-section of each hole 8 can be taken as the ratio of the cross-sectional area of the foil 21 at the edge of the hole. Furthermore, 100 holes 8 can be randomly selected, and multiple (e.g., four) cross-sectional views can be obtained by cutting the flat foil 2 in the thickness direction along the diameter of each selected hole 8. The average value (first average value) of the ratio of the cross-sectional area of the foil 21 at the edge of the hole in each of the obtained cross-sectional views (first average value) can be obtained for each hole 8, and the second average value obtained by averaging this first average value over the 100 randomly selected holes can be taken as the ratio of the cross-sectional area of the foil 21 at the edge of the hole.
[0038] A method for achieving the shape of the hole edge foil 21 will be explained with reference to Figure 5. Figure 5 is a cross-sectional view in the thickness direction corresponding to Figure 4(b) immediately after the flat foil 2 has been punched. Referring to Figure 5, when holes are punched in the foil using a punching press or the like, burrs 9 are formed on the edge of the hole 8, as shown in Figure 5, and protrude beyond the second reference plane D2. By polishing the area near the edge of the hole 8 on the side where the burrs 9 protrude using a metal brush or the like, the foil near the edge of the hole 8 can be thinned, thereby forming the hole edge foil 21. Note that the foil 10 near the edge of the hole 8 on the side opposite to the side where the burrs 9 protrude is located on the foil thickness center side of the first reference plane D1 when the holes are punched, so polishing is not particularly necessary for the foil 10. However, by performing a polishing process, the foil near the edge of the hole 8 can be further thinned, and the cross-sectional area ratio W of the hole edge foil 21 can be made smaller, thereby further improving the purification performance during cold start in the catalytic converter.
[0039] For example, a brush 100 with the shape shown in Figure 6 is used as a metal brush to thin the foil near the edge of the hole 8. Figure 6 is an example of a brush used to thin the foil near the edge of the hole 8. Referring to Figure 6, the brush 100 comprises a shaft portion 110 and a brush portion 120. By rotating the brush portion 120 around the shaft portion 110 as the central axis and moving the brush 100 itself, thinning can be performed by the brush portion 120.
[0040] Here, by creating irregularities on the surface of the foil and increasing the surface roughness Ra of the foil, the adhesion of the catalyst to the flat foil 2 can be improved by the anchoring effect. However, if the thinning treatment with the brush 100 is performed on each hole 8 individually, the brush 100 mainly contacts the foil 21 at the edge of the holes, and therefore the surface roughness of the foil cannot be sufficiently increased. Therefore, the inventors came up with the idea of designing the brush 100 to an appropriate size that can perform thinning treatment on multiple holes 8 simultaneously, as shown in Figure 7. Figure 7 is a plan view when the thinning treatment with the brush 100 is performed on the flat foil 2. With this configuration, the brush 100 contacts not only the foil 21 at the edge of each hole 8 but also the surface of the foil (matrix foil 22) located between adjacent holes 8, so that the thinning treatment of the foil 21 at the edge of the holes and the adjustment of the surface roughness of the flat foil 2 can be performed simultaneously. For example, the brush 100 can be designed to surround multiple adjacent holes 8 in a plan view. Furthermore, the anchoring effect can be enhanced more effectively if the irregularities formed on the surface of the foil are arranged in random directions rather than aligned in a predetermined direction. For example, when irregularities are formed on the surface of the foil by rolling, the shape of the irregularities in the direction perpendicular to the rolling direction is generally the same, so the anchoring effect cannot be fully realized. Therefore, in order to further improve the adhesion of the catalyst to the flat foil 2, it is preferable to design the brush 100 so as to increase the surface roughness Ra of the flat foil 2 and to make the direction of the irregularities formed on the surface of the foil random. In particular, it is preferable that the brush 100 be designed so as to make the surface roughness Ra of the flat foil 2 0.1 μm or more and to make the direction of the irregularities formed on the surface of the foil random.
[0041] The foil thickness of the flat foil 2, the diameter of the holes 8, the porosity ratio, and the cell density can be appropriately set according to the application of the catalytic converter.
[0042] The corrugated foil 3 is manufactured by applying a corrugation process (for example, corrugation) to the flat foil 2 that has undergone the perforation and thinning processes described above. Therefore, the corrugated foil 3 has the same structure as the flat foil 2 described above.
[0043] (Examples) The present invention will be described in detail with reference to examples. <Examples 1-81, Comparative Examples 1-21> First, two 50 μm thick flat foils made of ferritic stainless steel foil (Fe-20Cr-5Al alloy) with a width of 100 mm were punched in a staggered pattern using a punching press to form circular holes (corresponding to hole 8 in the above embodiment) with predetermined diameters as shown in Table 1, so as to achieve a predetermined porosity ratio. At this time, the holes were formed in positions that avoided the area from the edge to 5 mm in the short direction of the flat foil (corresponding to the gas inlet side edge area T in the above embodiment). The definition of porosity ratio has been described above, so an explanation is omitted.
[0044] Next, the edges of the holes on the side with protruding burrs on the two perforated flat foils were polished with a metal brush to thin them down. As a result, as shown in Figure 4(b), the foil at the edge of the hole was polished so that it existed only on the foil thickness center side, relative to the first reference plane extending along the back surface of the matrix foil and the second reference plane extending along the front surface of the matrix foil. The degree of polishing was controlled so that the average value of the cross-sectional area ratio of the foil at the edge of the hole in any cross-section of each hole when 100 holes were randomly selected (corresponding to the cross-sectional area ratio W of the foil at the edge of the hole 21 in the above embodiment) fell within one of the following ranges: 93-95% (Pattern A), 88-90% (Pattern B), or 83-85% (Pattern C). In all patterns, the Ra value was 0.1 μm or greater.
[0045] Next, a honeycomb structure was manufactured by winding together one of two thinned flat foils (corresponding to flat foil 2 in the above embodiment) and a corrugated foil formed by corrugating the other flat foil (corresponding to corrugated foil 3 in the above embodiment). The outer diameter of the honeycomb structure was 77 mm, the length was 100 mm, and the cell density was 62 cells per square centimeter (400 cells per square inch).
[0046] Next, the manufactured honeycomb structure was inserted into an outer cylinder made of SUS436L with an outer diameter of 80 mm, a thickness of 1.5 mm, and a length of 100 mm. Powdered brazing material (BNi-5 (see JIS Z3265)) was applied in advance to the areas where the corrugated foil and flat foil were to be joined, and foil brazing material (BNi-5a (AWS standard)) was placed on the outer surface of the honeycomb structure corresponding to the areas where the honeycomb structure and the outer cylinder were to be joined.
[0047] Subsequently, the honeycomb structure inserted into the outer cylinder was heat-treated at 1200°C under a vacuum atmosphere. This process joined the flat and corrugated foils constituting the honeycomb structure to each other by brazing, and the honeycomb structure and the outer cylinder were also joined by brazing to manufacture the honeycomb unit.
[0048] Subsequently, a wash coat solution containing ceria-zirconia-lantana-alumina as the main component and 1.25 g of palladium per 100 g was passed through the honeycomb body of the manufactured honeycomb unit. After removing the excess wash coat solution, it was dried at 180°C for 1 hour, followed by firing at 500°C for 2 hours to produce a honeycomb unit (catalytic converter) with a supported catalyst. The corrugated foil and flat foil of this catalytic converter were supported with a wash coat layer at a rate of 200 g / L per unit volume of the honeycomb body after drying, and palladium was supported at a rate of 2.5 g / L.
[0049] As a reference example corresponding to Example 1, a catalytic converter was fabricated under the same specifications and conditions as Example 1, except that the thinning treatment was not performed. Similarly, reference examples corresponding to the other examples and comparative examples were prepared. The average height of the burrs in each reference example was 10 μm.
[0050] <Examples 82-162, Comparative Examples 22-42> In Examples 82-162, Comparative Examples 22-42, and their corresponding reference examples, catalytic converters were manufactured in the same manner as in Examples 1-81, Comparative Examples 1-21, and their corresponding reference examples, except that the foil thickness was changed to 30 μm.
[0051] <Method for evaluating purification performance during cold start> A model gas (a mixed gas consisting of carbon monoxide: 5000 ppm, propylene: 500 ppm, nitric oxide: 500 ppm, oxygen: 4500 ppm, carbon dioxide: 14%, water vapor: 10%, with the remainder being nitrogen) heated to 300°C at a rate of 500 liters per minute under standard conditions was passed through a catalytic converter at room temperature, and the time required for the propylene concentration to decrease by 50% (hereinafter referred to as the 50% purification time) was measured.
[0052] Then, the purification performance during a cold start was evaluated based on the ratio of the 50% purification time of Examples 1-174 and Comparative Examples 1-30 to the 50% purification time of the corresponding standard example (50% purification time ratio). For example, in Example 1, the purification performance during a cold start was evaluated based on the 50% purification time ratio of Example 1 to the corresponding standard example. If the 50% purification time ratio was 95% or less, it was evaluated as "○" indicating improved purification performance during a cold start; if it was 90% or less, it was evaluated as "◎" indicating further improvement in purification performance during a cold start; and if it was 85% or less, it was evaluated as "◎◎" indicating even greater improvement in purification performance during a cold start. Furthermore, for cases where the 50% purification time ratio exceeded 95%, it was evaluated as "×" indicating insufficient improvement in purification performance during a cold start.
[0053] <Method for evaluating structural durability> Structural durability was evaluated by conducting heating and cooling cycle tests on an engine bench. The test apparatus and catalytic converter were connected by welding via a cone. A 400cc single-cylinder gasoline engine was used.
[0054] A temperature pattern was selected for the cooling cycle, which involves varying the inlet temperature of the gas flowing into the catalytic converter between 900°C and a temperature below 100°C. Specifically, one cooling cycle consisted of a heating step where the engine was run for 5 minutes from a stopped state to raise the inlet gas temperature to 900°C in approximately 30 seconds, a holding step to maintain the temperature at 900°C, and a cooling step where the engine was stopped and room temperature air was supplied for 5 minutes to cool the gas down to 100°C in approximately 60 seconds, followed by a cooling step where room temperature air was continuously supplied.
[0055] After repeating this cooling-heating cycle 1000 times, the honeycomb structure of the catalytic converter was observed, and the ratio of the number of pores with cracks to the total number of pores (crack ratio) was examined. Those with a crack ratio of 80% or more were evaluated as having insufficient structural durability and received a "×" rating. On the other hand, those with a crack ratio between 40% and 80% were evaluated as having sufficient structural durability and received a "〇" rating. Furthermore, those with a crack ratio of less than 40% were evaluated as having even more sufficient structural durability and received a "◎" rating.
[0056] Tables 1 to 4 show the structure and evaluation results of the catalytic converters in each example and comparative example. From Tables 1 to 4, it was found that in catalytic converters where the pore edge foil exists only on the foil thickness center side of the first reference plane extending along the back surface of the matrix foil and the second reference plane extending along the front surface of the matrix foil, and where π×d1×n×ε≧50 is satisfied, the evaluation of the purification performance during cold start was "○" or higher, indicating that sufficient purification performance during cold start can be obtained. Furthermore, it was found that the purification performance improves even further if the cross-sectional area ratio of the pore edge foil is 90% or less, and even more if the cross-sectional area ratio of the pore edge foil is 85% or less. It was also found that the purification performance improves even further in catalytic converters where π×d1×n×ε≧400 is satisfied.
[0057] If the value of (d2-d1)×t / 50 was less than 0.07, the durability evaluation was "×". On the other hand, if the value of (d2-d1)×t / 50 was 0.07 or more and less than 0.2, the durability evaluation was "〇". Furthermore, if the value of (d2-d1)×t / 50 was 0.2 or more, the durability evaluation was "◎". In other words, it was found that sufficient durability was obtained when the value of (d2-d1)×t / 50 was 0.07 or more, and particularly good durability was obtained when the value of (d2-d1)×t / 50 was 0.2 or more.
[0058] [Table 1] [Table 2] [Table 3] [Table 4] [Explanation of Symbols]
[0059] 1 Honeycomb Unit 2 Flat foil 3 wave foil 4 Honeycomb 5. Outer cylinder 8 holes 21 Hole edge foil 22 Matrix Foil
Claims
1. A honeycomb unit comprising a honeycomb body formed by alternately laminating flat metal foils and corrugated metal foils, and an outer cylinder positioned to surround the outer surface of the honeycomb body, Multiple holes are formed in the flat foil and the corrugated foil. If we define the foil located in the region from the edge of the hole to a distance corresponding to half the thickness of the flat foil and the corrugated foil, extending radially outward from the edge of the hole, as the hole edge foil, and the portion of the flat foil and the corrugated foil excluding the hole edge foil as the matrix foil, then, The hole edge foil exists only on the foil thickness center side of the first reference plane extending along the back surface of the matrix foil in which the hole edge foil is located, and the second reference plane extending along the front surface of the matrix foil. π is the value of pi, d1 (mm) is the diameter of the hole, d2 (mm) is the distance between the centers of adjacent holes, t (μm) is the thickness of the flat foil and the corrugated foil, and 1 square inch (645.16 mm) of the flat foil and the corrugated foil. ２ A honeycomb unit characterized by satisfying the following equation, where n is the number of holes per unit and ε is the porosity. π × d¹ × n × ε ≥ 50 (d2-d1)×t / 50≧0.07
2. π represents pi, d1 (mm) represents the diameter of the hole, and 1 square inch (645.16 mm) represents the area of the flat foil and the corrugated foil. ２ The honeycomb unit according to claim 1, characterized in that it satisfies the following equation when the number of holes per ) is n (pieces) and the porosity is ε. π × d¹ × n × ε ≥ 400
3. The honeycomb unit according to claim 1 or 2, characterized in that it satisfies the following formula when the distance between the centers of adjacent holes is d2 (mm), the diameter of the holes is d1 (mm), and the thickness of the flat foil and the corrugated foil is t (μm). (d2-d1)×t / 50≧0.2
4. In the matrix foil, if two virtual surfaces are arranged at a distance of t / 2 in the radial direction of the hole and penetrate the matrix foil in the thickness direction, enclosing the outer circumference of the hole, then these two virtual surfaces are designated as the first virtual surface and the second virtual surface, respectively. The honeycomb unit according to claim 1 or 2, characterized in that the cross-sectional area of the hole edge foil when cut in the thickness direction is 95% or less of the area of the rectangle enclosed by the back surface of the matrix foil, the front surface of the matrix foil, the first virtual surface, and the second virtual surface in the cross-sectional view.
5. In the matrix foil, if two virtual surfaces are arranged at a distance of t / 2 in the radial direction of the hole and penetrate the matrix foil in the thickness direction, enclosing the outer circumference of the hole, then these two virtual surfaces are designated as the first virtual surface and the second virtual surface, respectively. The honeycomb unit according to claim 3, characterized in that the cross-sectional area of the hole edge foil when cut in the thickness direction is 95% or less of the area of the rectangle enclosed by the back surface of the matrix foil, the front surface of the matrix foil, the first virtual surface, and the second virtual surface in the cross-sectional view.
6. A catalytic converter comprising a catalyst supported on a honeycomb unit according to claim 1 or 2.
7. A catalytic converter comprising a catalyst supported on a honeycomb unit as described in claim 3.
8. A catalytic converter comprising a catalyst supported on a honeycomb unit as described in claim 4.
9. A catalytic converter comprising a catalyst supported on a honeycomb unit as described in claim 5.