Honeycomb structure

Abstract

To provide a honeycomb structure which consists of a plurality of honeycomb segments combined, and the whole of which can be efficiently heated.SOLUTION: The honeycomb structure consists of a plurality of honeycomb segments combined and having partition walls to section and form a number of cells, and has a first end face into which gas flows, and a second end face out of which the gas flow. Catalysts are supported on the respective honeycomb segments, and heating wires are arranged between the adjacent honeycomb segments. In the longitudinal direction, which is a direction where the cells extend, a range shorter than 80% of the length in the longitudinal direction of the honeycomb structure from the first end face of the honeycomb structure is a heating wire arrangement region where the heating wires are arranged. A range being at least 20% of the length in the longitudinal direction of the honeycomb structure from the second end face of the honeycomb structure is a heating wire non-arrangement region where the heating wires are not arranged.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a honeycomb structure.

Background Art

[0002] In order to purify harmful substances contained in the exhaust gas discharged from an engine, an exhaust gas purification device including a honeycomb substrate carrying a catalyst capable of purifying exhaust gas is provided in the exhaust pipe path. In order to increase the purification efficiency of harmful substances by the exhaust gas purification device, it is necessary to maintain the temperature inside the exhaust gas purification device at a temperature suitable for catalyst activation (hereinafter, also referred to as the catalyst activation temperature).

[0003] Patent Document 1 discloses a configuration including a cylindrical honeycomb substrate having a heating part disposed so as to surround the outer peripheral part of a honeycomb part as a honeycomb catalyst body capable of maintaining a necessary temperature even when the temperature of the exhaust gas discharged from an engine decreases.

[0004] Patent Document 2 discloses a filter that collects soot contained in the exhaust gas of a diesel engine and purifies the exhaust gas. In this filter, in order to burn the soot deposited inside the filter, a heating wire as a heating body is disposed between adjacent filters.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the configuration disclosed in Patent Document 1, the heat-generating portion is arranged to surround the outer periphery of the honeycomb portion. In this case, the temperature in the center of the honeycomb substrate does not rise sufficiently, which can result in insufficient catalytic activity.

[0007] In the configuration disclosed in Patent Document 2, heating wires are arranged between adjacent filters, but the heating wires are arranged across the entire outer surface of the filter (see Figure 1 in Patent Document 2). The filters on which the heating wires are arranged are then combined with an adhesive to form an exhaust gas purification device consisting of multiple filters. This configuration had problems such as reduced adhesion between adjacent filters, which could cause damage to the exhaust gas purification system consisting of multiple filters, and increased deterioration of the heating elements.

[0008] Furthermore, when the filter is heated by an electric heating element, the heat moves from the exhaust gas inlet end face to the exhaust gas outlet end face due to the flow of exhaust gas. As a result, the heat generated by the electric heating element placed near the exhaust gas outlet end face does not contribute to the temperature rise of the filter and immediately flows out from the exhaust gas outlet end face of the filter. Consequently, the filter disclosed in Patent Document 2 has a configuration that is inefficient in terms of thermal performance.

[0009] The present invention was made to solve the above problems, and aims to provide a honeycomb structure in which a plurality of honeycomb segments are combined, and in which the entire honeycomb structure can be heated efficiently. [Means for solving the problem]

[0010] The honeycomb structure of the present invention is made up of a plurality of honeycomb segments having partitions that divide a large number of cells, and is a honeycomb structure having a first end face through which gas flows and a second end face through which gas flows, wherein a catalyst is supported on the honeycomb segments, and electric heating wires are arranged between adjacent honeycomb segments, and in the longitudinal direction in which the cells extend, the range from the first end face of the honeycomb structure to less than 80% of the longitudinal length of the honeycomb structure is an electric heating wire arrangement region in which the electric heating wires are arranged, and the range from the second end face of the honeycomb structure to at least 20% of the longitudinal length of the honeycomb structure is an electric heating wire non-arrangement region in which the electric heating wires are not arranged.

[0011] In the honeycomb structure of the present invention, a heating wire arrangement area is provided within a predetermined range from a first end face into which gas flows, and a heating wire non-arrangement area is provided within a predetermined range from a second end face out which gas flows. The heat generated in the heating wire arrangement region near the first end face moves towards the second end face of the honeycomb structure along the gas flow. Therefore, the entire honeycomb structure can be heated even if heating wires are not placed in the region near the second end face. The region near the second end face is a region without heating wires, and unlike the arrangement of heating wires in Patent Document 2, the generation of heat that does not contribute to the temperature rise of the honeycomb structure is prevented. Furthermore, since the heating element is placed between the honeycomb segments, unlike the configuration in Patent Document 1, the temperature can be sufficiently raised even in the center of the honeycomb structure. Based on the above, the configuration of the present invention allows for efficient heating of the entire honeycomb structure.

[0012] In the honeycomb structure of the present invention, it is preferable that the honeycomb segments are assembled via an adhesive layer, and that the heating wire is arranged inside the adhesive layer.

[0013] When honeycomb segments are assembled via an adhesive layer, only adhesive is present in areas where heating wires are not present. Therefore, the adhesive strength between honeycomb segments due to the adhesive layer is high in areas where heating wires are not present, which can suppress damage to the honeycomb structure and prevent deterioration of the heating wires between honeycomb segments.

[0014] In the honeycomb structure of the present invention, when viewed from the end face of the honeycomb structure, the honeycomb segments are arranged in a grid pattern vertically and horizontally, and it is preferable that all of the heating wires are arranged in the same direction along a first direction, which is either the vertical or horizontal direction of the grid. With such a configuration, localized heat generation can be suppressed. Furthermore, since no heating wires are arranged in a direction perpendicular to the first direction, the adhesive strength between the honeycomb segments by the adhesive layer can be increased.

[0015] Furthermore, in the end face view of the honeycomb structure, with the direction perpendicular to the first direction as the second direction, it is preferable that the length of the heating element placement area from the first end face is longer as the distance from the center of the honeycomb structure along the second direction is greater for the position where the heating element is placed.

[0016] With this configuration, the entire honeycomb structure can be efficiently heated both at the central part of the honeycomb structure where the gas flow rate is high and heat transfer by the gas is large, and at the outer periphery of the honeycomb structure where the gas flow rate is slow and heat transfer by the gas is small.

[0017] In the honeycomb structure of the present invention, between adjacent honeycomb segments, a first set of heating wires in which a plurality of heating wires are connected in parallel is arranged. In a plan view of the honeycomb structure, between adjacent honeycomb segments at a position different from the position where the first set of heating wires is arranged, a second set of heating wires different from the first set of heating wires in which a plurality of heating wires are connected in parallel is arranged. It is preferable that the first set of heating wires and the second set of heating wires are connected in parallel.

[0018] When the heating wires and the set of heating wires are connected in parallel, even if a part of the heating wire is disconnected, the entire circuit constituted by the heating wires provided in the honeycomb structure will not be disconnected, so that a decrease in heating performance can be minimized.

[0019] In the honeycomb structure of the present invention, it is preferable that the length of the honeycomb structure in the longitudinal direction is 150 mm or less.

[0020] In the honeycomb structure of the present invention, the honeycomb structure has a cylindrical shape, and it is preferable that the ratio (length / diameter) of the length of the honeycomb structure in the longitudinal direction to the diameter of the end face of the honeycomb structure is 0.8 or less.

Brief Description of the Drawings

[0021] [Figure 1] FIG. 1 is a perspective view schematically showing an example of the honeycomb structure of the present invention. [Figure 2] FIG. 2 is a cross-sectional view in a direction perpendicular to the longitudinal direction of the honeycomb segment. [Figure 3] FIG. 3 is a partial cross-sectional view of the honeycomb structure shown in FIG. 1. [Figure 4] FIG. 4 is a plan view of the honeycomb structure shown in FIG. 1 as viewed from the first end face side. [Figure 5A] FIG. 5A is a cross-sectional view schematically showing an example of a heating wire arrangement region and a non-heating wire arrangement region in a cross section of the honeycomb structure. [Figure 5B]Figure 5B is a schematic cross-sectional view showing examples of areas with and without heating wires in a honeycomb structure. [Figure 5C] Figure 5C is a schematic cross-sectional view showing examples of areas with and without heating wires in a honeycomb structure. [Figure 6A] Figure 6A is a schematic cross-sectional view showing another example of a region with and without heating wires in a cross-section of a honeycomb structure. [Figure 6B] Figure 6B is a schematic cross-sectional view showing another example of a region with and without heating wires in a cross-section of a honeycomb structure. [Figure 6C] Figure 6C is a schematic cross-sectional view illustrating another example of a region with and without heating wires in a cross-section of a honeycomb structure. [Figure 7] Figure 7 is an explanatory diagram illustrating the arrangement of the heating wires.

[0022] (Detailed description of the invention) [Honeycomb structure] The honeycomb structure of the present invention will now be described. The honeycomb structure of the present invention is made up of a plurality of honeycomb segments having partitions that divide a large number of cells, and is a honeycomb structure having a first end face through which gas flows and a second end face through which gas flows, wherein a catalyst is supported on the honeycomb segments, and electric heating wires are arranged between adjacent honeycomb segments, and in the longitudinal direction in which the cells extend, the range from the first end face of the honeycomb structure to less than 80% of the longitudinal length of the honeycomb structure is an electric heating wire arrangement region in which the electric heating wires are arranged, and the range from the second end face of the honeycomb structure to at least 20% of the longitudinal length of the honeycomb structure is an electric heating wire non-arrangement region in which the electric heating wires are not arranged.

[0023] Figure 1 is a schematic perspective view showing an example of the honeycomb structure of the present invention. The honeycomb structure 1 shown in Figure 1 is made up of multiple honeycomb segments 20, each having a partition wall 22 that divides a large number of cells 21, and has a first end face 11 through which gas flows in and a second end face 12 through which gas flows out. The direction in which the cells 21 of the honeycomb segment 20 extend is defined as the longitudinal direction (the direction indicated by the double-headed arrow L in Figure 1). Multiple honeycomb segments are joined together via an adhesive layer 30. Furthermore, the electrode terminal 40 protrudes from the first end face 11.

[0024] The materials used to make up the honeycomb segments (partitions) should preferably have high thermal conductivity, such as SiC or Si-impregnated SiC.

[0025] The thickness of the partition walls is preferably uniform. Specifically, the thickness of the partition walls is preferably less than 0.30 mm, and preferably 0.05 mm or more.

[0026] The shape of the cell is not limited to a rectangular prism; examples include triangular prisms, hexagonal prisms, and so on. The shapes of the cells may differ, but it is preferable that they are all the same. That is, it is preferable that the size of the cells surrounded by partitions is the same in a cross section perpendicular to the longitudinal direction of the honeycomb segment.

[0027] The porosity of the septum should preferably be 50% or less. If the porosity of the bulkhead is 50% or less, it is possible to achieve both high mechanical strength and exhaust gas purification performance.

[0028] If the porosity of the partition wall exceeds 50%, the porosity becomes too high, which reduces the mechanical properties of the honeycomb segment, making the honeycomb structure more susceptible to cracks and fractures during use.

[0029] The shape of the honeycomb structure is not particularly limited and is not limited to a cylindrical shape; examples include prismatic, elliptical, oblong, and chamfered prismatic shapes (for example, chamfered triangular prismatic shapes).

[0030] When the shape of the honeycomb structure is cylindrical, it is preferable that the ratio of the length of the honeycomb structure in the longitudinal direction to the diameter of the end face of the honeycomb structure (length / diameter) is 0.8 or less.

[0031] The length of the honeycomb structure in the longitudinal direction is preferably 150 mm or less, and preferably 50 mm or more.

[0032] Figure 2 is a cross-sectional view of the honeycomb segment perpendicular to its longitudinal direction. When exhaust gas emitted from the internal combustion engine (shown by arrow G in Figure 2, indicating the flow of exhaust gas) reaches the honeycomb segment 20, the exhaust gas flows into the cell 21 from the first end face 11 of the honeycomb segment 20. Furthermore, the exhaust gas passes through the cell 21 while in contact with the catalyst 23 supported on the partition wall 22. At this time, CO, HC, NO in the exhaust gas X These harmful gas components are purified by the catalyst 23 supported on the partition wall 22. The exhaust gas then flows out of the cell 21 at the second end face 12 of the honeycomb segment 20.

[0033] The catalyst 23 is not particularly limited as long as it can treat the exhaust gas, but examples include catalysts made of precious metals such as platinum, palladium, and rhodium, and zeolites. The zeolite may be CHA zeolite, and the zeolite may be ion-exchanged with Cu or the like. These catalysts may be used individually or in combination of two or more types. When these catalysts are supported, CO, HC, NO X It can effectively purify toxic exhaust gases such as those mentioned above. In particular, it is preferable to use a honeycomb structure as an SCR catalyst that reduces NOx using zeolite as a catalyst.

[0034] Figure 3 is a partial cross-sectional view of the honeycomb structure shown in Figure 1. Figure 3 schematically shows the region in the honeycomb structure where the heating wires are placed. A heating element 50 is placed between adjacent honeycomb segments 20. Electrode terminals 40 are provided at both ends of the heating element 50, and the electrode terminals 40 protrude from the first end face 11.

[0035] The heating element 50 is positioned in the longitudinal direction of the honeycomb segment 20 within a predetermined range from the first end face 11 of the honeycomb structure 1. The area where the heating element is positioned is called the heating element placement area. In Figure 3, this is the area indicated by the double arrow B. The heating element placement area extends from the first end face of the honeycomb structure to less than 80% of the length of the honeycomb structure in the longitudinal direction.

[0036] On the other hand, the heating element 50 is not positioned within a predetermined range from the second end face 12 of the honeycomb structure 1 in the longitudinal direction of the honeycomb segment 20. The area where the heating element is not positioned is defined as the heating element non-positioned area. In Figure 3, this is the area indicated by the double arrow C. The area where heating wires are not installed extends from the second end face of the honeycomb structure to at least 20% of the longitudinal length of the honeycomb structure.

[0037] To rephrase the arrangement of heating wire placement areas and heating wire non-placement areas, the area from the second end face of the honeycomb structure to 20% of the length of the honeycomb structure in the longitudinal direction is always a heating wire non-placement area. Furthermore, a predetermined area extending from the first end face of the honeycomb structure (up to a maximum of less than 80% of the length of the honeycomb structure in the longitudinal direction from the first end face) becomes the heating element placement area.

[0038] Here, a region without heating wires may be provided, starting from the first end face of the honeycomb structure and extending to a predetermined position along the longitudinal length of the honeycomb structure. In this case, the starting point of the heating wire region will be a position slightly away from the first end face of the honeycomb structure. In this case, a region without heating wires may be provided in an area extending from the first end face of the honeycomb structure to a region of 0% to 10% of the longitudinal length of the honeycomb structure.

[0039] A preferred range for the ratio of heating element areas to areas without heating elements is heating element areas:heating element areas

[0040] Thus, in the honeycomb structure of the present invention, a heating wire arrangement area is provided within a predetermined range from the first end face into which gas flows, and a heating wire non-arrangement area is provided within a predetermined range from the second end face out which gas flows. The heat generated in the heating wire arrangement region near the first end face moves towards the second end face of the honeycomb structure along the gas flow. Therefore, the entire honeycomb structure can be heated even if heating wires are not placed in the region near the second end face. The region near the second end face is a region without heating wires, and unlike the arrangement of heating wires in Patent Document 2, the generation of heat that does not contribute to the temperature rise of the honeycomb structure is prevented. Furthermore, since the heating element is placed between the honeycomb segments, unlike the configuration in Patent Document 1, the temperature can be sufficiently raised even in the center of the honeycomb structure. Based on the above, the configuration of the present invention allows for efficient heating of the entire honeycomb structure.

[0041] The heating element 50 is positioned inside the adhesive layer 30. When honeycomb segments are assembled via an adhesive layer, only adhesive is present in areas where heating wires are not present. Therefore, the adhesive strength between honeycomb segments due to the adhesive layer is high in areas where heating wires are not present, which can suppress damage to the honeycomb structure and prevent deterioration of the heating wires between honeycomb segments.

[0042] Nickel-chromium alloy, nickel-chromium-iron alloy, chromium-iron-aluminum alloy, etc., can be used as materials for the heating element. Furthermore, the heating element can be used in either a wire or plate form. When the heating element is linear, its diameter is not particularly limited, but is preferably 0.1 to 1 mm. When the heating element is plate-shaped, its thickness is not limited, but is preferably 0.1 to 0.5 mm, and its width is preferably 1 to 10 mm.

[0043] The adhesive layer is formed by applying and drying an adhesive paste containing an inorganic binder and inorganic particles. The adhesive layer may further contain inorganic fibers and / or whiskers. Furthermore, the thickness of the adhesive layer is preferably 0.5 to 3 mm.

[0044] Electrode terminals 40 are connected to both ends of the heating element 50, and the electrode terminals 40 protrude from the first end face 11. Power can be supplied from the electrode terminals 40 to the heating element 50 to generate heat. The electrode terminals 40 are plate-shaped and welded to the heating element 50. The electrode terminals 40 are connected to each other by wiring 60 that connects the electrode terminals.

[0045] The heating element 50 shown in Figure 3 is a composite heating element in which multiple heating elements (51, 52, 53) are connected in parallel. Electrode terminals 40 are connected to both ends of each heating element. If the heating elements are in a bundled configuration, even if one of the multiple heating elements breaks, the entire bundle will not break, thus minimizing the reduction in heating performance.

[0046] Figure 4 is an end view of the honeycomb structure shown in Figure 1, viewed from the first end face side. In the end view of the honeycomb structure 1 shown in Figure 4, the honeycomb segments 20 are arranged in a grid pattern both vertically and horizontally. One direction of this grid pattern is designated as the first direction, and the direction perpendicular to the first direction is designated as the second direction. In Figure 4, the horizontal direction is considered the first direction, and the vertical direction is considered the second direction.

[0047] All heating elements 50 are arranged in the same direction along the first direction. In Figure 4, the adhesive layer 30a along the first direction where the heating wire is located is shown with dark hatching, and the adhesive layer 30b along the second direction where the heating wire is not located is shown with light hatching. This configuration helps to suppress localized heat generation. Furthermore, since no heating wires are positioned in the second direction perpendicular to the first direction, the adhesive strength between honeycomb segments due to the adhesive layer can be increased.

[0048] As shown in Figure 4, the heating wires arranged in the adhesive layer 30a along the first direction are each in the form of a heating wire assembly. These heating wire assemblies are connected to each other in parallel. I will explain this in detail. The heating element arranged in the adhesive layer 30a1 oriented in a first direction between the honeycomb segments is referred to as the first heating element 50a1. Between adjacent honeycomb segments at a position different from the position where the first heating element 50a1 is placed, there is another adhesive layer 30a2 aligned with the first direction. The heating element placed in the adhesive layer 30a2 is referred to as the second heating element 50a2. The first heating element 50a1 and the second heating element 50a2 are connected in parallel by wiring 60 that connects the electrode terminals. Figure 4 shows six adhesive layers 30a aligned in the first direction, with a heating element arranged in each adhesive layer 30a. The six heating elements are connected in parallel by wiring 60.

[0049] When the heating elements are connected in parallel, even if some of the heating elements break, the entire circuit formed by the heating elements in the honeycomb structure will not break, thus minimizing the reduction in heating performance.

[0050] In the honeycomb structure of the present invention, the further the distance along the second direction from the center of the honeycomb structure from the position where the heating wires are arranged, the longer the longitudinal length of the heating wire arrangement area from the first end face is. This will be described with reference to the drawings.

[0051] FIG. 5A, FIG. 5B, and FIG. 5C are cross-sectional views schematically showing examples of a region where heating wires are arranged and a region where heating wires are not arranged in a cross-section of a honeycomb structure. FIG. 5A shows a cross-section at the center of the honeycomb structure, FIG. 5B shows a cross-section at a position away from the center of the honeycomb structure along a second direction, and FIG. 5C shows a cross-section at a position further away from the center of the honeycomb structure along the second direction. The cross-section shown in FIG. 5A is the cross-section indicated by line D-D in FIG. 4, the cross-section shown in FIG. 5B is the cross-section indicated by line E-E in FIG. 4, and the cross-section shown in FIG. 5C is the cross-section indicated by line F-F in FIG. 4.

[0052] In the cross-section at the center of the honeycomb structure shown in FIG. 5A, the region where heating wires are arranged is the region indicated by double-headed arrow B1. In the cross-section at a position away from the center of the honeycomb structure shown in FIG. 5B, the region where heating wires are arranged is the region indicated by double-headed arrow B2. In the cross-section at a position further away from the center of the honeycomb structure shown in FIG. 5C, the region where heating wires are arranged is the region indicated by double-headed arrow B3. The relationship between the lengths of these regions where heating wires are arranged is B1 < B2 < B3, and it can be said that the longer the distance along the second direction from the center of the honeycomb structure, the longer the longitudinal length of the region where heating wires are arranged from the first end face. With such a configuration, the entire honeycomb structure can be efficiently heated both at a position close to the center of the honeycomb structure where the gas flow rate is high and the heat transfer by the gas is large, and at a position close to the outer periphery of the honeycomb structure where the gas flow rate is low and the heat transfer by the gas is small.

[0053] For example, when the longitudinal length of the honeycomb structure is 125 mm, B1 can be set as the region from 10 to 69 mm from the first end face of the honeycomb structure, B2 can be set as the region from 10 to 75 mm from the first end face of the honeycomb structure, and B3 can be set as the region from 10 to 98 mm from the first end face of the honeycomb structure. Furthermore, when the longitudinal length of the honeycomb structure is 150 mm, B1 can be defined as the region from 10 to 72 mm from the first end face of the honeycomb structure, B2 as the region from 10 to 102 mm from the first end face of the honeycomb structure, and B3 as the region from 10 to 120 mm from the first end face of the honeycomb structure. Thus, when the lengths of the heating wire arrangement areas differ, even at the location where the longest heating wire arrangement area is formed, at least 20% of the length of the honeycomb structure from the second end face will be a heating wire-free area where no heating wires are placed.

[0054] Furthermore, a second direction may be defined as a direction perpendicular to the first direction, and the longitudinal length of the heating element placement area from the first end face may be the same regardless of the distance along the second direction from the center of the honeycomb structure.

[0055] Figures 6A, 6B, and 6C are schematic cross-sectional views illustrating another example of a region with and without heating wires in a cross-section of a honeycomb structure. Figure 6A shows a cross-section at the center of the honeycomb structure, Figure 6B shows a cross-section at a location away from the center of the honeycomb structure along the second direction, and Figure 6C shows a cross-section at a location even further away from the center of the honeycomb structure along the second direction. The cross-section shown in Figure 6A is the cross-section indicated by line DD in Figure 4, the cross-section shown in Figure 6B is the cross-section indicated by line EE in Figure 4, and the cross-section shown in Figure 6C is the cross-section indicated by line FF in Figure 4.

[0056] In the cross-section of the honeycomb structure shown in Figure 6A, the area where the heating wires are arranged is indicated by the double-headed arrow B4. In the cross-section of the honeycomb structure shown in Figure 6B, located away from the center, the area where the heating wires are arranged is indicated by the double-headed arrow B5. In the cross-section of the honeycomb structure shown in Figure 6C, located further away from the center, the heating element area is indicated by the double-headed arrow B6. The relationship between the lengths of these heating wire arrangement regions is B4=B5=B6, which means that the longitudinal length of the heating wire arrangement region from the first end face is the same regardless of the distance along the second direction from the center of the honeycomb structure.

[0057] An example of a method for manufacturing the honeycomb structure of the present invention will be described. The above-mentioned honeycomb structure can be manufactured, for example, by fabricating honeycomb segments made of ceramic using a known manufacturing method, and then bonding the honeycomb segments together via an adhesive layer. When forming the adhesive layer on the side surface of the honeycomb segment, a heating wire is placed between the honeycomb segment, and electrode terminals are connected to the ends of the heating wire so that the electrode terminals protrude from the first end face of the honeycomb structure.

[0058] When bonding the honeycomb segments, multiple honeycomb segments are arranged so that a surface parallel to the first direction in the honeycomb structure is exposed, an adhesive paste is applied to form the bonding layer, and a heating wire is placed on top of the adhesive paste. Furthermore, multiple heating wires are connected in parallel to form a heating wire assembly, and the electrode terminals are exposed from the direction that will become the first end face in the honeycomb structure. Furthermore, the heating wires should not be placed within 20% of the length of the honeycomb structure from the position that will become the second end face of the honeycomb structure.

[0059] After applying more adhesive paste onto the heating element, arrange the honeycomb segments on top of the adhesive paste. This process is repeated to combine the honeycomb segments and form a honeycomb assembly. By heating the honeycomb aggregate, the adhesive paste is heated and solidified to form an adhesive layer, thereby creating a honeycomb structure. The honeycomb aggregate may be processed on its outer surface to achieve the desired shape, or the outer surface may be coated with a paste similar to adhesive paste after processing. Electrode terminals are exposed at the first end face of the honeycomb structure. Connect the electrode terminals so that the heating elements are connected in parallel. Through the above process, a honeycomb structure can be manufactured.

[0060] Furthermore, it is preferable to immerse the manufactured honeycomb structure in a slurry containing the catalyst and dry it to support the catalyst on the partition walls of the honeycomb structure. [Examples]

[0061] (Example 1) 52.8% by weight of coarse silicon carbide powder having an average particle size of 22 μm and 22.6% by weight of fine silicon carbide powder having an average particle size of 0.5 μm were mixed. To the resulting mixture, 4.6% by weight of an organic binder (methylcellulose), 0.8% by weight of a lubricant (Unilube, manufactured by NOF Corporation), 1.3% by weight of glycerin, 2.8% by weight of oleic acid, and 15.1% by weight of water were added and kneaded to obtain a raw material composition. After that, a molding process was carried out by extrusion molding using a mold to obtain a honeycomb molded body.

[0062] Next, the honeycomb molded body was dried using a microwave dryer to produce a dried honeycomb molded body. Next, the dried honeycomb molded body was degreased at 400°C, and then fired at 2200°C for 3 hours under atmospheric pressure and an argon atmosphere. This allowed us to create a honeycomb segment in the shape of a rectangular prism. The honeycomb segment had dimensions of 36 mm square x 150 mm in length, a partition thickness of 7 mil (0.18 mm), a cell shape of rectangular prism, a cell density of 300 cpsi, a partition porosity of 38%, and an average pore diameter of 11 μm.

[0063] A heat-resistant adhesive paste was prepared containing 31% by weight of ceramic fibers with an average fiber length of 20 μm, 37% by weight of silicon carbide particles with an average particle size of 0.5 μm, 16% by weight of silica sol, and 16% by weight of water.

[0064] A heating element (wire-shaped, 0.6 mm in diameter) made of Fe-Cr-Al (chromium-iron-aluminum alloy) was prepared. Honeycomb segments were arranged, adhesive paste was applied, heating wires were placed in position, more adhesive paste was applied on top of the heating wires, and another honeycomb segment was arranged.

[0065] By repeating this process, honeycomb segments were combined to obtain a honeycomb assembly. The honeycomb structure has 7 vertical and 7 horizontal segments (without corners, 45 segments total).

[0066] The arrangement of the heating wires was as shown in Tables 1, 2, and 3 for the positions in the cross-sectional views of lines DD (position D), EE (position E), and FF (position F) in Figure 4, respectively. The arrangement is symmetrical vertically in Figure 4, with two positions at D, two at E, and two at F. Three heating wires were used at positions D and E, and two at position F. Multiple heating wires placed at each position were connected in parallel to form a heating wire assembly. Furthermore, the heating elements were connected in parallel.

[0067] Each table shows the pitch, length, number of parallel heating elements, distance from the first end face, and distance between heating elements. Figure 7 is an explanatory diagram illustrating the arrangement of the heating wires. The pitch of the heating wires is the distance between adjacent peaks of the meander-shaped heating wires, and is the length indicated by the double-headed arrow P. The length of the heating element is the height of the peaks (depth of the valleys) of the meander-shaped heating element, and is the length indicated by the double-headed arrow N. The distance from the first end face is the distance from the first end face to the nearest heating element, and is the length indicated by the double-headed arrow Q. The distance between heating elements is the distance between adjacent heating elements, and is the length indicated by the double-headed arrow K. The length of the placement area from the first end face can be calculated as follows: [Distance from the first end face + Length of the heating wire × Number of heating wires + Distance between heating wires × (Number of heating wires - 1)]. The length of the non-placed area from the second end face is calculated as [length of the honeycomb structure in the longitudinal direction - length of the placed area from the first end face].

[0068] Furthermore, the honeycomb aggregate was heated to 120°C to dry and solidify the adhesive paste, forming an adhesive layer and creating a prismatic honeycomb structure. Next, the outer perimeter of the prismatic honeycomb structure was cut using a diamond cutter, and the same paste as the adhesive paste was applied to the outer perimeter and dried to obtain a roughly cylindrical honeycomb structure with a diameter of 266.7 mm.

[0069] Next, the honeycomb structure was immersed in a slurry containing CHA zeolite (SSZ-13) with an average particle size of 2 μm, which had been ion-exchanged with Cu ions. The slurry was then dried at 120°C and heat-treated at 450°C to support 150 g / L of zeolite as an SCR catalyst on the honeycomb structure.

[0070] (Examples 2-4, Comparative Example 1) A honeycomb structure was obtained in the same manner as in Example 1, except that the arrangement of the heating wires was changed as shown in Tables 1-3.

[0071] [Table 1]

[0072] [Table 2]

[0073] [Table 3]

[0074] (Measurement of NOx purification rate) An exhaust gas purification device equipped with a honeycomb structure was connected to a 15L HD engine, and ammonia was injected into the honeycomb structure to adsorb the ammonia. The honeycomb structure was heated by supplying power to the heating element with an output of 10kW and an applied voltage of 48V, and operation in WHTC mode was started 90 seconds after the voltage was applied. Ammonia injection will continue when the exhaust gas temperature is 180°C or higher. Two minutes after the start of operation, the NOx concentration N0 before the exhaust gas flowed through the honeycomb structure and the NOx concentration N1 after the exhaust gas passed through the honeycomb structure were measured, and the NOx purification rate of the honeycomb structure was measured for 3 minutes using the following formula. NOx purification rate (%) = [(N0-N1) / N0] × 100 The results of the NOx purification rate measurements obtained above are shown in Table 4.

[0075] [Table 4]

[0076] The results shown in Table 4 indicate that when the non-placement area from the second end face exceeds 20%, the NOx purification rate increases. Comparing Examples 2 and 4, where the range of the non-placement area at the position where the placement area is maximized is the same, Example 4, which has a longer longitudinal length of the placement area at position F, which is farther away from the center of the honeycomb structure along the second direction, showed a higher NOx purification rate. On the other hand, in Comparative Example 1, since there was no region without heating wires, the heating efficiency was inferior and the NOx purification rate was low. [Explanation of Symbols]

[0077] 1. Honeycomb structure 11 First end face 12 Second end face 20 Honeycomb Segments 21 cells 22 Bulkhead 23 Catalyst 30 Adhesive layer 30a, 30a1, 30a2 Adhesive layers aligned with the first direction 30b Adhesive layer along the second direction 40 electrode terminal 50 Heating wire (assembled heating wire) 50a1 First set of heating elements 50a2 Second set of heating wires 51, 52, 53 heating wire 60 Wiring connecting electrode terminals

Claims

1. A honeycomb structure comprising a plurality of honeycomb segments having partition walls that divide a large number of cells, having a first end face through which gas flows and a second end face through which gas flows out, The honeycomb segment is supported with a catalyst. A heating element is placed between adjacent honeycomb segments. In the longitudinal direction in which the cell extends, the area extending from the first end face of the honeycomb structure to 80% or less of the length of the honeycomb structure in the longitudinal direction is the heating wire arrangement area in which the heating wires are arranged. From the second end face of the honeycomb structure, at least 20% of the length of the honeycomb structure is a region where no heating wires are placed, and The honeycomb structure is characterized in that, in an end view of the honeycomb structure, the honeycomb segments are arranged in a grid pattern vertically and horizontally, and all of the heating wires are arranged in the same direction along a first direction which is either vertical or horizontal in the grid pattern.

2. In the end view of the honeycomb structure, the direction perpendicular to the first direction is defined as the second direction. The honeycomb structure according to claim 1, wherein the greater the distance along the second direction from the center of the honeycomb structure to the position where the heating wire is arranged, the longer the longitudinal length of the heating wire arrangement area from the first end face.

3. A honeycomb structure comprising a plurality of honeycomb segments having partition walls that divide a large number of cells, having a first end face through which gas flows and a second end face through which gas flows out, The honeycomb segment is supported with a catalyst. A heating element is placed between adjacent honeycomb segments. In the longitudinal direction in which the cell extends, the area extending from the first end face of the honeycomb structure to 80% or less of the length of the honeycomb structure in the longitudinal direction is the heating wire arrangement area in which the heating wires are arranged. From the second end face of the honeycomb structure, at least 20% of the length of the honeycomb structure is a region where no heating wires are placed, and Between adjacent honeycomb segments, a first heating element is arranged, in which multiple heating wires are connected in parallel. In an end view of the honeycomb structure, a second set of heating wires, different from the first set of heating wires, is arranged between adjacent honeycomb segments at a position different from the position where the first set of heating wires is arranged, with multiple heating wires connected in parallel. A honeycomb structure characterized in that the first heating element and the second heating element are connected in parallel.

4. The honeycomb structure according to any one of claims 1 to 3, wherein the length of the honeycomb structure in the longitudinal direction is 150 mm or less.

5. The honeycomb structure according to any one of claims 1 to 4, wherein the honeycomb structure is cylindrical in shape, and the ratio of the length in the longitudinal direction of the honeycomb structure to the diameter of the end face of the honeycomb structure (length / diameter) is 0.8 or less.

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