JP7836201B2 - Honeycomb structure - Google Patents

Description

This invention relates to a honeycomb structure.

To purify harmful substances contained in the exhaust gas emitted from the engine, an exhaust gas purification device is installed in the exhaust pipe path, which is equipped with a honeycomb substrate supporting a catalyst capable of purifying exhaust gases.
To improve the efficiency of exhaust gas purification systems in purifying harmful substances, it is necessary to maintain the internal temperature of the exhaust gas purification system at a temperature suitable for catalyst activation (hereinafter also referred to as the catalyst activation temperature).

Patent Document 1 discloses an exhaust gas purification device that collects soot contained in the exhaust gas of a diesel engine to purify the exhaust gas. In the exhaust gas purification device described in Patent Document 1, multiple filters (also called honeycomb segments) are arranged adjacent to each other. Between the honeycomb segments, electric heating wires are placed to act as heat sources for burning the soot accumulated inside the filters.

Japanese Patent Application Publication No. 7-54643

The heating wires, positioned between the honeycomb segments, are joined to electrode terminals by means of welding or other methods, and then connected to an external power source via the electrode terminals.
When using heating elements in parallel, external power is supplied by, for example, connecting each electrode terminal connected to the heating element with an inter-electrode component (also called a connector), and then connecting the inter-electrode component to an external power source. With this configuration, it is not necessary to supply power to each heating element and each electrode terminal individually from an external source.

Examples of inter-electrode members include metal plates of uniform thickness that are curved according to the position of the electrode terminals. However, when such metal plates are used as inter-electrode members, the amount of heat generated increases in the area closer to the power source, leading to a problem of reduced heat uniformity in the honeycomb structure.

This temperature rise is due to resistive heating in the inter-electrode material, and therefore its contribution to the temperature rise of the honeycomb structure is small compared to the heat generated by the heating element. Therefore, by increasing the volume of the inter-electrode material to reduce resistance and thus heat generation, the temperature difference can be reduced, improving the uniformity of the honeycomb structure.

However, increasing the volume of the inter-electrode component to reduce the temperature difference leads to a problem: the weight of the inter-electrode component becomes too large, making it more susceptible to electrode terminal detachment and honeycomb segment damage due to vibration and shock.

This invention was made to solve the above-mentioned problems, and its objective is to provide a honeycomb structure that can achieve both improved heat uniformity and suppression of damage to the honeycomb segments.

In other words, the honeycomb structure of the present invention comprises a honeycomb assembly formed by combining multiple honeycomb segments having partitions that divide a large number of cells via an adhesive layer; a heating unit disposed inside the adhesive layer and consisting of a heating wire and first and second electrode terminals connected to both ends of the heating wire; a first power supply terminal connected to a power source; a first connection portion connecting all of the first electrode terminals and the first power supply terminal in a single line; a second power supply terminal connected to a power source; and a second connection portion connecting all of the second electrode terminals and the second power supply terminal in a single line. The honeycomb structure is characterized in that multiple heating units are connected in parallel by the first and second connection portions, and the cross-sectional areas of the first and second connection portions decrease as they are further from the first and second power supply terminals, respectively.

In this specification, when the first electrode terminal and the second electrode terminal are not distinguished, they are simply referred to as electrode terminals. Similarly, when the first connection part and the second connection part are not distinguished, they are simply referred to as connection parts, and when the first power supply terminal and the second power supply terminal are not distinguished, they are simply referred to as power supply terminals.

In the honeycomb structure of the present invention, the first connection portion that connects all the first electrode terminals and the first power supply terminal is configured such that its cross-sectional area decreases as the distance from the first power supply terminal increases. The same applies to the second connection portion, which connects all the second electrode terminals and the second electrode terminal is configured such that its cross-sectional area decreases as the distance from the second power supply terminal increases.
In this configuration, the decrease in the cross-sectional area of the connection point at a position far from the power supply terminal, where the current flowing is small, increases the electrical resistance and reduces variations in heat generation. Furthermore, the decrease in the volume of the connection point at a position far from the power supply terminal reduces the volumetric heat capacity. For these two reasons, the temperature rise of the connection point is equalized regardless of the distance from the power supply terminal, eliminating areas that generate abnormal heat.
Therefore, the uniformity of heat distribution in the honeycomb structure can be improved.
Furthermore, by reducing the cross-sectional area of the connection points in areas far from the power supply terminals, the weight of the connection points is reduced. As a result, the load on the electrode terminals due to vibrations and shocks when mounted in a vehicle can be reduced, and damage to the honeycomb structure can be suppressed.

In the honeycomb structure of the present invention, it is preferable that the cross-sectional area of the first connection portion and the cross-sectional area of the second connection portion decrease in stages according to the distance from the first power supply terminal and the second power supply terminal.
If the cross-sectional areas of the first and second connection points decrease in stages according to the distance from the first and second power supply terminals, it becomes easier to match the resistance values of the parts where the current flowing through the connection points is the same, and thus easier to control the temperature rise.

In the honeycomb structure of the present invention, it is preferable that the angle between the first power supply terminal, the center of gravity of the honeycomb assembly, and the second power supply terminal is 30 to 90° when viewed in plan from the longitudinal direction of the honeycomb structure.
The above configuration contributes to miniaturizing the entire exhaust gas purification system, including the power supply.

In the honeycomb structure of the present invention, it is preferable that the cross-sectional area of the first connection portion at the position furthest from the first power supply terminal is 15 to 35% of the cross-sectional area of the first connection portion at the position closest to the first power supply terminal, and the cross-sectional area of the second connection portion at the position furthest from the second power supply terminal is 15 to 35% of the cross-sectional area of the second connection portion at the position closest to the second power supply terminal.
With the above configuration, the difference in temperature rise between the connection point closest to the power supply terminal and the connection point further away can be further reduced, thereby suppressing abnormal heat generation in certain areas.

In the honeycomb structure of the present invention, it is preferable to have three or more of the above-mentioned heating units.
When a heating unit has three or more components, abnormal heat generation is likely to occur in certain areas if a connection point with a constant cross-sectional area is used. A honeycomb structure having such a configuration is suitable for application of the present invention.

In an end view of the honeycomb structure of the present invention, 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.
This configuration helps to suppress localized heat generation. Furthermore, since no heating wires are positioned in the direction perpendicular to the first direction, the adhesive strength between honeycomb segments by the adhesive layer can be increased.

Figure 1 is a schematic perspective view showing an example of a honeycomb assembly that constitutes the honeycomb structure of the present invention. Figure 2 is a cross-sectional view of the honeycomb segment perpendicular to its longitudinal direction. Figure 3 is a partial cross-sectional view of an example of a honeycomb structure using the honeycomb aggregate shown in Figure 1. Figure 4 is an end view of the honeycomb structure shown in Figure 3, viewed from the first end face side. Figure 5 is a magnified view of a portion of Figure 4. Figure 6 is an end view of another example of the honeycomb structure of the present invention, viewed from the first end face side. Figure 7 is an image taken with a thermographic camera showing the heating of the first end face of the honeycomb structure according to Example 1.

(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 comprises a honeycomb assembly formed by combining a plurality of honeycomb segments having partition walls that partition a plurality of cells via an adhesive layer; a heating unit disposed inside the adhesive layer and consisting of a heating wire and first electrode terminals and second electrode terminals connected to both ends of the heating wire; a first power supply terminal connected to a power source; a first connection part that connects all of the first electrode terminals and the first power supply terminal in a single line; a second power supply terminal connected to a power source and a second connection part that connects all of the second electrode terminals and the second power supply terminal in a single line; wherein a plurality of the heating units are connected in parallel by the first connection part and the second connection part, and the cross-sectional areas of the first connection part and the second connection part are smaller the further they are from the first power supply terminal and the second power supply terminal, respectively.

Figure 1 is a schematic perspective view showing an example of a honeycomb assembly that constitutes the honeycomb structure of the present invention.
The honeycomb assembly 100 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. Each honeycomb segment 20 has a first end face 101 through which gas flows in and a second end face 102 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 101.

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

The thickness of the partition walls is preferably uniform. Specifically, the thickness of the partition walls is preferably less than 0.30 mm. Furthermore, it is preferable that it be 0.05 mm or more.

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.

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

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

The shape of the honeycomb structure is not particularly limited; it is not limited to a cylindrical shape, but can also be a prismatic, elliptical, oblong, or chamfered prismatic shape (for example, a triangular prismatic shape with rounded chamfers).

When 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.

The longitudinal length of the honeycomb structure is preferably 150 mm or less, and more preferably 50 mm or more.

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) reaches the honeycomb segment 20, the exhaust gas flows into the cell 21 from the first end face 101 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, harmful gas components such as CO, HC, and _NOx in the exhaust gas are purified by the catalyst 23 supported on the partition wall 22. Finally, the exhaust gas flows out of the cell 21 at the second end face 102 of the honeycomb segment 20.

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, as well as zeolites, titania, vanadium oxide, etc. The zeolite may be a CHA-type 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, toxic exhaust gases such as CO, HC, and _NOx can be effectively purified.
In particular, it is preferable to use a honeycomb structure as an SCR catalyst that reduces NOx using zeolite as a catalyst.

Figure 3 is a partial cross-sectional view of an example of a honeycomb structure using the honeycomb aggregate shown in Figure 1.
In the honeycomb assembly 100 that constitutes the honeycomb structure 1, the honeycomb segments 20 are arranged in a grid pattern 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.
A heating unit 50 is positioned between adjacent honeycomb segments 20.
The heating unit 50 consists of heating wires 51, 52, and 53, and electrode terminals 40 provided at both ends of the heating wires.
The electrode terminals 40 protrude from the first end face 101. The heating elements 51, 52, and 53 are arranged inside the adhesive layer 30.
The heating unit may have one or more heating elements.

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 in the form of a wire, its diameter is not particularly limited, but is preferably 0.1 to 1 mm. When the heating element is in the form of a plate, its thickness is not limited, but is preferably 0.1 to 0.5 mm, and its width is preferably 1 to 10 mm.

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.

Electrode terminals 40 are connected to both ends of the heating wires 51, 52, and 53, and the electrode terminals 40 protrude from the first end face 101, allowing power to be supplied from the electrode terminals 40 to the heating wires 51, 52, and 53 to generate heat. The electrode terminals 40 are plate-shaped and are joined to the heating wires 51, 52, and 53.
The electrode terminals 40 are connected to each other by a connecting portion 60 that connects the electrode terminals.

In the heating unit 50 shown in Figure 3, multiple heating wires (51, 52, 53) are connected in parallel. Electrode terminals 40 are connected to both ends of each heating wire.
If the heating unit consists of multiple insulated wires connected in parallel, even if one of the heating wires breaks, the entire heating unit will not break, thus minimizing the reduction in heating performance.

The honeycomb structure of the present invention preferably has three or more heating units.
When a heating unit has three or more components, abnormal heat generation is likely to occur in certain areas if a connection point with a constant cross-sectional area is used. A honeycomb structure having such a configuration is suitable for application of the present invention.

The electrode terminal 40 has a first electrode terminal 41 and a second electrode terminal 42.
In other words, one end of each heating element (51, 52, 53) is connected to the first electrode terminal 41, and the other end is connected to the second electrode terminal 42.
The first electrode terminal 41 and the second electrode terminal 42, which constitute the same heating unit 50, are positioned at one end and the other end of the adhesive layer 30 extending in the first direction.
Therefore, all heating elements are arranged in the same direction along the first direction.

The honeycomb assembly 100 constituting the honeycomb structure 1 has six adhesive layers 30 extending in a first direction, and a first electrode terminal 41 and a second electrode terminal 42 are arranged at both ends of each adhesive layer 30.
Therefore, the number of heating units is equal to the number of adhesive layers 30 extending along the first direction. In other words, the honeycomb structure shown in Figure 3 has six heating units.

The first electrode terminal 41 and the second electrode terminal 42, which constitute the heating unit 50, are each connected to different power supply terminals 70 (71 or 72).
In other words, the first electrode terminal 41 is connected to the first power supply terminal 71, and the second electrode terminal 42 is connected to the second power supply terminal 72.

A connecting portion 60 (61 or 62) is used to connect the power supply terminal 70 and the electrode terminal 40.
The first electrode terminal 41 and the first power supply terminal 71 are connected in a single unit by the first connection part 61.
The second electrode terminal 42 and the second power supply terminal 72 are connected in a single unit by the second connection part 62.
This results in the six heating units being connected in parallel.

As shown in Figure 3, the second power supply terminal 72 and all of the second electrode terminals 42 (42A, 42B, 42C, 42D, 42E, 42F) are connected in a single unit by the second connection part 62 (62A, 62B, 62C, 46D, 62E, 62F).
The first power supply terminal 71 and all of the first electrode terminals 41 are also connected in a single unit by the first connection part 61.

The shape of the connection part is not particularly limited, as long as it can connect all the electrode terminals and power supply terminals to be connected in a single unit. Furthermore, the connection part may be composed of two or more parts combined together.
The connecting parts are preferably made of metal.

Examples of connection points include metal plates curved to match the position of the electrode terminals to be connected. Multiple metal plates may be stacked on top of each other, or the metal plates may have different thicknesses and heights.
When the connecting section is made up of multiple stacked metal plates, the cross-sectional area can be easily adjusted, as described later, by adjusting the thickness, height, and number of stacked metal plates.

Figure 4 is an end view of the honeycomb structure shown in Figure 3, viewed from the first end face side.
As shown in Figure 4, the first power supply terminal 71 and all of the first electrode terminals 41 (41A, 41B, 41C, 41D, 41E, 42F) are also connected in a single unit by the first connection part 61.

The positions of the first and second power supply terminals are not particularly limited, but it is preferable to arrange them such that the angle between the first power supply terminal, the center of gravity of the honeycomb assembly, and the second power supply terminal is 30 to 90°.
In the honeycomb structure shown in Figure 4, the angle between the first power supply terminal 71, the centroid g of the honeycomb assembly, and the second power supply terminal 72 is 45°.

The cross-sectional area of the connection point will be explained using Figure 5. Figure 5 is a partially enlarged view of Figure 4.
As shown in Figure 5, the first connection sections 61A to 61F connect the first power supply terminal 71 to the first electrode terminals 41A to 41F in a single unit. Note that the first connection section 61A is at a different height from the other first connection sections 61B to 61F. In Figures 4 and 5, the parts with different heights (first connection sections 61A and 62A) are shown with dashed lines.

The part of the first connection part 61 furthest from the first power supply terminal 71 is the part that connects the first electrode terminal 41E and the first electrode terminal 41F (first connection part 61F). The cross-sectional area of the first connection part 61F is the cross-sectional area when the first connection part 61F is cut at the position indicated by the line F-F in Figure 4, and is, for example, the area indicated by S _F.

Next, the second furthest part from the first power supply terminal 71 is the part of the first connection part 61 that connects the first electrode terminal 41E and the first electrode terminal 41D (first connection part 61E). The cross-sectional area of the first connection part 61E is the cross-sectional area when the first connection part 61E is cut at the position indicated by the line E-E in Figure 4, and is, for example, the area indicated by _SE (where _SE > S _F ).

Next, the third furthest part from the first power supply terminal 71 is the part of the first connection part 61 that connects the first electrode terminal 41D and the first electrode terminal 41C (first connection part 61D). The cross-sectional area of the first connection part 61D is the cross-sectional area when the first connection part 61D is cut at the position indicated by the line D-D in Figure 4, and is, for example, the area indicated by S _D (where S _D > S _E ).

Next, the fourth furthest part from the first power supply terminal 71 is the part of the first connection part 61 that connects the first electrode terminal 41C and the first electrode terminal 41B (first connection part 61C). The cross-sectional area of the first connection part 61C is the cross-sectional area when the first connection part 61C is cut at the position indicated by the line C-C in Figure 4, and is, for example, the area indicated by S _C (where S _C > S _D ).

Next, the fifth furthest part from the first power supply terminal 71 is the part of the first connection part 61 that connects the first electrode terminal 41B and the first electrode terminal 41A (first connection part 61B). The cross-sectional area of the first connection part 61B is the cross-sectional area when the first connection part 61B is cut at the position indicated by the line B-B in Figure 4, and is, for example, the area indicated by S _B (where S _B > S _C ).

Finally, the sixth furthest part from the first power supply terminal 71 (i.e., the part closest to the first power supply terminal 71) is the part connecting the first power supply terminal 71 and the first electrode terminal 41A (the first connection part 61A). The cross-sectional area of the first connection part 61A is, for example, the area shown by S _A (where S _A > S _B ).

The cross-sectional area of the first connection portion 61 changes in a stepwise manner, starting from the one furthest from the first power supply terminal 71 (i.e., in the order of the first connection portions 61F, 61E, 61D, 61C, 61B, and 61A), in the order of S _F , S _E , S _D , S _C , S _B , and S _A. The relationship between the magnitudes of the cross-sectional areas satisfies S _F < S _E < S _D < S _C < S _B < S _A.
In other words, the further away the connection point is from the first power supply terminal 71, the smaller the cross-sectional area of the connection point becomes in stages.

Furthermore, the first connection part 61A, which connects the first power supply terminal 71 and the first electrode terminal 41A, has a different height from the other first connection parts (61B to 61E).
Therefore, in the first connection sections 61B to 61E, the relative sizes of the cross-sectional areas are calculated based on the relative sizes of the total thickness of the metal plates. However, when comparing with the first connection section 61A, it is necessary to consider not only the thickness of the metal plates but also their height.

In this specification, "cross-sectional area of the connection" means the cross-sectional area of the connection in a direction perpendicular to the direction in which current is presumed to flow through the connection.
The above cross-sectional area is the cross-sectional area measured at the point where the cross-sectional area of each first connection is smallest.

Although not shown in Figure 5, the relative sizes of the cross-sectional areas of the second connection points 62 (62A, 62B, 62C, 62D, 62E, 62F) that connect the second electrode terminal 42 and the second power supply terminal 72 are the same as those of the first connection point 61.

As shown in Figures 4 and 5, if the cross-sectional areas of the first connection portion 61 and the second connection portion 62 decrease as they move further away from the first power supply terminal 71 and the second power supply terminal 72, respectively, the decrease in the cross-sectional area of the connection portion at positions far from the power supply terminals where the current is small increases the electrical resistance and reduces the variation in heat generation. Furthermore, the decrease in the volume of the connection portion at positions far from the power supply terminals reduces the volumetric heat capacity.
For the two reasons mentioned above, the temperature rise at the connection point is equalized regardless of the distance from the power supply terminal, eliminating areas that overheat abnormally. This improves the uniformity of the honeycomb structure. In addition, because the cross-sectional area of the connection point is reduced in areas farther from the power supply terminal, the weight of the connection point is reduced. This reduces the load on the electrode terminals due to vibrations and shocks when mounted in a vehicle, thereby suppressing damage to the honeycomb structure.

The honeycomb structure of the present invention having the above configuration can, for example, reduce the amount of heat generated at the first connection portion 61A to about twice the amount of heat generated at the first connection portion 61F.
If the above configuration is not adopted, for example, if the first connecting parts 61A, 61B, 61C, 61D, 61E, and 61F are made of metal plates of the same thickness (cross-sectional area), the amount of heat generated at the first connecting part 61A will be approximately 47 times the amount of heat generated at the first connecting part 61F.
Compared to honeycomb structures with such configurations, the honeycomb structure of the present invention can suppress abnormal heat generation because the temperature rise at the connection points is equalized.

In Figures 4 and 5, the first connection portion 61 is constructed by stacking multiple metal plates of different thicknesses. The thickness and height of each metal plate, as well as the number of plates stacked, differ between each electrode terminal.
For example, the first connecting portion 61F is made of a single thin metal plate, while the first connecting portion 61E is made by stacking two metal plates that make up the first connecting portion 61F.
Furthermore, a portion of the first connecting portion 61D is constructed by laminating a metal plate that constitutes the first connecting portion 61F with a metal plate that is thicker than the metal plate that constitutes the first connecting portion 61F. The other portion of the first connecting portion 61D and the first connecting portion 61C are constructed by laminating two metal plates that are thicker than the metal plate that constitutes the first connecting portion 61F. The first connecting portion 61B is constructed by laminating a metal plate that constitutes the first connecting portion C with a metal plate that is thicker than the metal plate that constitutes the first connecting portion 61C. In addition, the height of the metal plate that constitutes the first connecting portion 61A is twice that of the metal plates that constitute the other first connecting portions 61B to 61F.

The thickness of each metal plate constituting the first connection portion 61F is thinner than the thickness of the thicker metal plate constituting the first connection portion 61D. Furthermore, the thickness of the thicker metal plate constituting the first connection portion 61D is thinner than the thickness of the thicker metal plate constituting the first connection portion 61B.

The cross-sectional areas of the first and second connection parts may decrease gradually (discontinuously) or continuously depending on the distance from the first and second power supply terminals.
The connection points shown in Figures 3 to 5 all have a cross-sectional area that decreases in stages according to the distance from the first power supply terminal and the second power supply terminal.

Preferably, the cross-sectional area of the first connection portion at the position furthest from the first power supply terminal is 15 to 35% of the cross-sectional area of the first connection portion at the position closest to the first power supply terminal.
Furthermore, it is preferable that the cross-sectional area of the second connection portion at the position furthest from the second power supply terminal is 15 to 35% of the cross-sectional area of the second connection portion at the position closest to the second power supply terminal.

The first power supply terminal and the second power supply terminal are terminals for supplying current to the heating element through the first connection and the second connection, respectively.
The shapes of the first power supply terminal and the second power supply terminal are not particularly limited.
The materials constituting the first power supply terminal and the second power supply terminal are not particularly limited, but may be the same as, or different from, the materials constituting the first connection part and the second connection part.

Figure 6 is an end view of another example of the honeycomb structure of the present invention, viewed from the first end face side.
Figure 6 can also be described as an example in which the first power supply terminal 73 and the second power supply terminal 74 are arranged such that the angle between the first power supply terminal 73, the centroid g of the honeycomb assembly, and the second power supply terminal 74 is 180°.

As shown in Figure 6, the cross-sectional areas of the first connection portion 63 and the second connection portion 64 decrease as they move further away from the first power supply terminal 73 and the second power supply terminal 74, respectively.

The first connection section 63 connects the first power supply terminal 73 and the first electrode terminals 43A to 43F in a single unit.
The portion of the first connection portion 63 furthest from the first power supply terminal 73 is the portion connecting the first electrode terminal 43A and the first electrode terminal 43B (first connection portion 63A), and the portion connecting the first electrode terminal 43E and the first electrode terminal 43F (first connection portion 63E). The cross-sectional areas of the first connection portion 63A and the first connection portion 63E are the areas indicated by S _A2 and S _E2 , respectively.

Next, the portion of the first connection portion 63 closest to the first power supply terminal 73 is the portion connecting the first electrode terminal 43B and the first electrode terminal 43C (first connection portion 63B), and the portion connecting the first electrode terminal 43D and the first electrode terminal 43E (first connection portion 63D). The cross-sectional areas of the first connection portion 63B and the first connection portion 63D are the areas indicated by S _B2 and S _D2 , respectively (where S _B2 > S _A2 and S _D2 > S _E2 ).

Finally, the third furthest part from the first power supply terminal 73 (i.e., the part closest to the first power supply terminal 73) is the part connecting the first electrode terminal 43C, the first power supply terminal 73, and the first electrode terminal 43D (the first connection part 63C). The cross-sectional area of the first connection part 63C is, for example, the area shown by S _C2 (where S _C2 > S _B2 and S _C2 > S _D2 ).

From the above, the cross-sectional areas of the first connection parts 63 are such that, in order from the one furthest from the first power supply terminal 73 (i.e., the first connection parts 63E and 63A, the first connection parts 63D and 63B, and the first connection part 63C), S _F2 = S _A2 < S _D2 = S _B2 < S _C2 . However, if the conditions S _F2 < S _D2 < S _C2 and S _A2 < S _B2 < S _C2 are met, then S _F2 ≠ S _A2 and S _D2 ≠ S _B2 .

The relative sizes of the cross-sectional areas of the second connection points 64 (64A, 64B, 64C, 64D, 64E), which connect the second electrode terminal 44 and the second power supply terminal 74, are the same as those for the first connection point 63.

As shown in Figure 6, if the cross-sectional areas of the first connection part 63 and the second connection part 64 decrease as they move further away from the first power supply terminal 73 and the second power supply terminal 74, respectively, the decrease in the cross-sectional area of the connection part at positions far from the power supply terminals where the current is small increases the electrical resistance and reduces the variation in heat generation. Furthermore, the decrease in the volume of the connection part at positions far from the power supply terminals reduces the volumetric heat capacity.
For the two reasons mentioned above, the temperature rise at the connection point is equalized regardless of the distance from the power supply terminal, eliminating areas that overheat abnormally. This improves the uniformity of the honeycomb structure. In addition, because the cross-sectional area of the connection point is reduced in areas farther from the power supply terminal, the weight of the connection point is reduced. This reduces the load on the electrode terminals due to vibrations and shocks when mounted in a vehicle, thereby suppressing damage to the honeycomb structure.

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.

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 adhesive 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 becomes the first end face in the honeycomb structure.

After applying more adhesive paste to 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 assembly, 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 assembly.

Each electrode terminal exposed on the first end face of the honeycomb assembly is connected to either the first or second connection. Specifically, the first connection is connected so that the first power supply terminal is connected to all of the first electrode terminals in a single unit.
At this time, the cross-sectional area of the first connection part is adjusted so that the cross-sectional area of the first connection part decreases as the distance from the first power supply terminal increases.
Similar to the first connection, the second connection is connected so that the second power supply terminal and all the second electrode terminals are connected in one continuous line, and the cross-sectional area of the second connection is adjusted so that the cross-sectional area of the second connection decreases as the distance from the second power supply terminal increases.

The method for adjusting the cross-sectional area of the connection is not particularly limited, but for example, changes in the thickness of the metal plate, changes in the height of the metal plate, and changes in the number of layers of metal plate may be combined as needed.
Through the above process, a honeycomb structure can be manufactured.

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.

(Example 1)
A honeycomb structure according to Example 1 was fabricated so that the electrode terminals, power supply terminals, and connection parts were in the positions and shapes shown in Figures 3 and 4. SiC was used as the material for the honeycomb segments.
The diameter of the honeycomb aggregate constituting the created honeycomb structure was 266.7 mm, and the length in the longitudinal direction was 101.6 mm. The positions and shapes of the electrode terminals (first electrode terminal and second electrode terminal), power supply terminals (first power supply terminal and second power supply terminal), and connection parts (first connection part and second connection part) were as shown in Figures 3 to 5. Specifically, the cross-sectional areas of the connection parts, in order from the furthest from the power supply terminal (first connection part 61F and second connection part 62F), were S _F = 9 ^mm² , S _E = 18 ^mm² , S _D = 27 ^mm² , S _C = 36 ^mm² , S _B = 45 ^mm² , and S _A = 54 ^mm² . The metal plate constituting the connection part closest to the power supply terminal had a height twice that of the other metal plates.
Stainless steel was used as the material for the electrode terminals and connection parts.

(Comparative Example 1)
The honeycomb structure according to Comparative Example 1 was created using the same procedure as in Example 1, except that the number and thickness of the stacked metal plates forming the first and second connection parts were adjusted so that the cross-sectional area of the connection parts was 9 ^mm² in all parts.

(Heating test)
A DC current of 48V and 208A was applied between the two power supply terminals of the honeycomb structure according to Example 1 and Comparative Example 1, and the temperature of the first end face of the honeycomb structure after 90 seconds was captured using a thermographic camera. Figure 7 is an image captured by a thermographic camera showing the heating of the first end face of the honeycomb structure according to Example 1.

As shown in Figure 7, in the honeycomb structure according to Embodiment 1, the temperature of the eight connection points near the power supply terminal (corresponding to the first connection points 61A to 61D and the second connection points 62A to 62D in Figures 3 and 4) is almost the same, and it can be confirmed that only the connection points near the power supply terminal are not overheating abnormally.
Furthermore, the amount of heat generated at the connection point closest to the power supply terminal (corresponding to the first connection point 61A and the second connection point 62A of the honeycomb structure shown in Figures 3 and 4) was approximately twice the amount of heat generated at the connection point furthest from the power supply terminal (corresponding to the first connection point 61F and the second connection point 62F of the honeycomb structure shown in Figures 3 and 4).

In the honeycomb structure according to Comparative Example 1, the heat generated at the connection point closest to the power supply terminal (corresponding to the first connection point 61A and the second connection point 62A of the honeycomb structure shown in Figures 3 and 4) was approximately 47 times greater than the heat generated at the connection point furthest from the power supply terminal (corresponding to the first connection point 61F and the second connection point 62F of the honeycomb structure shown in Figures 3 to 5).

1 Honeycomb structure 20 Honeycomb segment 21 Cell 22 Partition wall 23 Catalyst 30 Adhesive layer 40 Electrode terminals 41, 41A, 41B, 41C, 41D, 41E, 41F, 43, 43A, 43B, 43C, 43D, 43E, 43F First electrode terminals 42, 42A, 42B, 42C, 42D, 42E, 42F, 44, 44A, 44B, 44C, 44D, 44E, 44F Second electrode terminal 50 Heating unit 51, 52, 53 Heating wire 60 Connection part 61, 61A, 61B, 61C, 61D, 61E, 61F, 63, 63A, 63B, 63C, 63D, 63E First connection parts 62, 62A, 62B, 62C, 62D, 62E, 62F, 64, 64A, 64B, 64C, 64D, 64E Second connection part 70 Power supply terminals 71, 73 First power supply terminals 72, 74 Second power supply terminal 100 Honeycomb assembly 101 First end face 102 Second end face S _A , S _B , S _C , S _D , S _E , S _F , S _A2 , S _B2 , S _C2 , S _D2 , S _E2 Cross-sectional area of connection part

Claims (6)

A honeycomb assembly is formed by combining multiple honeycomb segments, each having a partition wall that divides a large number of cells, via an adhesive layer.
A heating unit is disposed inside the adhesive layer and comprises a heating wire and a first electrode terminal and a second electrode terminal connected to both ends of the heating wire.
A first power supply terminal connected to the power supply,
A first connection section that connects all of the first electrode terminals and the first power supply terminal in a single unit,
A second power supply terminal connected to the power supply,
A honeycomb structure comprising a second connection portion that connects all of the second electrode terminals and the second power supply terminals in a single unit,
Multiple heating units are connected in parallel by the first connection and the second connection.
A honeycomb structure characterized in that the cross-sectional areas of the first connection portion and the second connection portion are smaller the further they are from the first power supply terminal and the second power supply terminal, respectively. The honeycomb structure according to claim 1, wherein the cross-sectional area of the first connection portion and the cross-sectional area of the second connection portion decrease in stages according to the distance from the first power supply terminal and the second power supply terminal. The honeycomb structure according to claim 1 or 2, wherein, when viewed from the longitudinal direction of the honeycomb structure in a plan view, the angle between the first power supply terminal, the center of gravity of the honeycomb assembly, and the second power supply terminal is 30 to 90°. The cross-sectional area of the first connection portion at the position furthest from the first power supply terminal is 15 to 35% of the cross-sectional area of the first connection portion at the position closest to the first power supply terminal.
The honeycomb structure according to any one of claims 1 to 3, wherein the cross-sectional area of the second connection portion at the position furthest from the second power supply terminal is 15 to 35% of the cross-sectional area of the second connection portion at the position closest to the second power supply terminal. The honeycomb structure according to any one of claims 1 to 4, comprising three or more of the aforementioned heating units. The honeycomb structure according to any one of claims 1 to 5, wherein, 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 the vertical or horizontal direction of the grid.