JP2013094721A - Honeycomb structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a honeycomb structure capable of being enhanced in heat shock resistance while ensuring air permeability.SOLUTION: The columnar honeycomb structure 10 extending along a center axis CL includes a first end surface 10a and a second end surface 10b mutually opposed in the extending direction of the center axis CL, and partition walls 10c forming a plurality of first flow channels Ra and a plurality of second flow channels Rb. The first flow channels Ra are opened on the side of the first end surface 10a and sealed on the side of the second end surface 10b while the second flow channels Rb are sealed on the side of the first end surface 10a and opened on the second end surface 10b. The opening ratio of the first end surface 10a is larger than that of the second end surface 10b and a high strength region F containing at least one second flow channel Rb2 is formed to the second end surface 10b and all of the second flow channels Rb2 not contained in the high strength region F are large in the minimum radius of curvature of the cross-sectional shape orthogonal to the center axis CL as compared with the second flow channels Rb1 not contained in the high strength region F.

Description

  The present invention relates to a honeycomb structure used as a filter for purifying gas.

  A honeycomb structure is widely used as a filter for purifying exhaust gas from an internal combustion engine, such as a diesel particulate filter (DPF) (see, for example, Patent Document 1). Since the soot removed from the exhaust gas accumulates on the honeycomb structure, it is necessary to regenerate the filter by burning the soot at regular intervals. In order to burn the soot, it is only necessary to supply a large amount of combustion exhaust gas at a high temperature to ignite the soot and burn out the soot.

  Since the honeycomb structure may be damaged by the combustion heat of the soot during filter regeneration, the honeycomb structure is required to have high thermal shock resistance. Patent Document 1 describes a honeycomb structure having a structure in which a plurality of segment portions are joined at a connecting portion, and having improved thermal shock resistance by adjusting the strength of the connecting portion.

JP 2009-202143 A

  By the way, when the present inventors conducted experiments on the honeycomb structure, a plurality of radial cracks were generated on the gas downstream end face of the honeycomb structure in the thermal shock resistance test, and these cracks expanded under more severe conditions. As a result, it was found that they were connected to each other and eventually formed an annular crack. For this reason, it is necessary to take measures to avoid deterioration in filter performance due to the occurrence of cracks.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a honeycomb structure capable of improving thermal shock resistance while ensuring air permeability.

  In order to solve the above-mentioned problem, the present invention is a columnar honeycomb structure extending along the central axis, the first end surface and the second end surface facing each other in the extending direction of the central axis, and the center A plurality of first flow paths extending along the axis and a partition wall forming a plurality of second flow paths, wherein the first flow path is opened on the first end face side and the second end face side is sealed The second flow path is sealed at the first end face side and opened at the second end face side, and the opening ratio of the first end face is larger than the opening ratio of the second end face. A high-strength region including at least one second flow path is formed on the end surface, and all the second flow paths included in the high-strength region are centered compared to the second flow path not included in the high-strength region. The minimum radius of curvature of the cross-sectional shape perpendicular to the axis is large.

  According to the honeycomb structure, since the stress concentration on the opening on the second end face can be reduced as the minimum curvature radius of the cross-sectional shape (opening shape) of the second flow path is increased, generation of cracks in the high-strength region is prevented. Can be suppressed. Moreover, in the above honeycomb structure, the second flow path not included in the high-strength region has a cross-sectional shape with a small minimum radius of curvature, so that the second cross-sectional shape of all the second flow paths is the same as that of the second case. The second flow path can be efficiently arranged on the end face, and the opening area per unit area of the filter can be increased to ensure sufficient air permeability. Therefore, according to the honeycomb structure, it is possible to improve the thermal shock resistance by suppressing the generation of cracks while sufficiently ensuring the air permeability.

The high-strength region may include a plurality of second flow paths.
In this case, generation of cracks can be suppressed in a wider area.

The high-strength region may be formed in an annular shape surrounding the central axis.
In this case, it is possible to effectively suppress the occurrence of an annular crack that appears on the second end face due to thermal shock.

The high-strength region may be formed so as to extend along a direction orthogonal to the central axis.
In this case, the occurrence of radial cracks appearing on the second end face due to thermal shock can be effectively suppressed.

A plurality of the high-intensity regions may be formed radially about the central axis.
In this case, it is possible to more effectively suppress the occurrence of radial cracks that appear on the second end face due to thermal shock.

The cross-sectional shape perpendicular to the central axis of all the second flow paths included in the high-strength region is circular or elliptical, and the cross-sectional shape perpendicular to the central axis of the second flow path not included in the high-strength region is Polygon shape may be sufficient.
According to the honeycomb structure, since the occurrence of cracks can be suppressed in a high-strength region where the cross-sectional shape of the second flow path is a circular shape or an elliptical shape, it is possible to further improve the thermal shock resistance. . Moreover, in the honeycomb structure, the second flow path is formed in a region other than the high-strength region by making the cross-sectional shape of the second flow channel not included in the high-strength region into a polygonal shape having a minimum curvature radius compared to the circular shape. Can be arranged efficiently, and the opening area per unit area of the filter can be increased to ensure sufficient air permeability.

  According to the present invention, it is possible to improve thermal shock resistance while ensuring air permeability.

1 is a perspective view showing a honeycomb structure according to a first embodiment. It is an enlarged view showing a part of a cross section perpendicular to the central axis of the honeycomb structure. (A) is an enlarged view showing a part of the first end face of the honeycomb structure. (B) is an enlarged view showing a part of the second end face of the honeycomb structure. It is an enlarged view showing a part of a cross section along the central axis of the honeycomb structure. It is a whole view which shows the 2nd end surface of a honeycomb structure. It is the elements on larger scale of FIG. (A) It is a figure which shows the cross-sectional shape of the 2nd flow path which is not contained in a high intensity | strength area | region. (B) It is a figure which shows the cross-sectional shape of the 2nd flow path contained in a high intensity | strength area | region. FIG. 6 is an overall view showing a second end face of a honeycomb structure according to a second embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
As shown in FIG. 1, the honeycomb structure 10 according to the first embodiment is attached to a DPF [Diesel Particulate Filter] or the like, and is a cylindrical structure used as a filter for purifying exhaust gas from an internal combustion engine. Is the body. The columnar honeycomb structure 10 extends along the central axis CL. Hereinafter, the extending direction of the central axis CL is referred to as a central axis direction.

  The honeycomb structure 10 includes a first end face 10a and a second end face 10b that face each other in the central axis direction, and a plurality of first flow paths Ra and a plurality of second flow paths Rb that extend along the central axis CL. And a partition wall 10c.

  The honeycomb structure 10 is made of a porous ceramic material (for example, an average pore diameter of 20 μm or less). Examples of the ceramic material used for the honeycomb structure 10 include alumina, silica, mullite, cordierite, glass, oxides such as aluminum titanate, silicon carbide, silicon nitride, and metal. The aluminum titanate can further contain magnesium and / or silicon.

  Such a honeycomb structure 10 can be obtained by firing the green molded body (unfired molded body) as the ceramic material described above and performing a predetermined sealing process on each of the flow paths Ra and Rb. A green molded object contains the inorganic compound source powder which is a ceramic raw material, organic binders, such as methylcellulose, and the additive added as needed.

  For example, in the case of a green molded body of aluminum titanate, the inorganic compound source powder includes an aluminum source powder such as α-alumina powder, and a titanium source powder such as anatase-type or rutile-type titania powder. Further, magnesium source powder such as magnesia powder and magnesia spinel powder, and / or silicon source powder such as silicon oxide powder and glass frit can be included.

  Examples of the organic binder include celluloses such as methylcellulose, carboxymethylcellulose, hydroxyalkylmethylcellulose, and sodium carboxymethylcellulose; alcohols such as polyvinyl alcohol; and lignin sulfonate.

  Examples of the additive include a pore-forming agent, a lubricant, a plasticizer, a dispersant, and a solvent.

  Examples of the pore-forming agent include carbon materials such as graphite; resins such as polyethylene, polypropylene and polymethyl methacrylate; plant materials such as starch, nut shells, walnut shells and corn; ice; and dry ice.

  Lubricants and plasticizers include alcohols such as glycerin; higher fatty acids such as caprylic acid, lauric acid, palmitic acid, arachidic acid, oleic acid and stearic acid; stearic acid metal salts such as Al stearate, polyoxyalkylene alkyl And ether (POAAE).

  Examples of the dispersant include inorganic acids such as nitric acid, hydrochloric acid and sulfuric acid; organic acids such as oxalic acid, citric acid, acetic acid, malic acid and lactic acid; alcohols such as methanol, ethanol and propanol; ammonium polycarboxylate Surfactant etc. are mentioned.

  Examples of the solvent include alcohols such as methanol, ethanol, butanol, and propanol; glycols such as propylene glycol, polypropylene glycol, and ethylene glycol; and water.

  FIG. 2 is an enlarged view showing a part of a cross section along the central axis CL of FIG. As shown in FIG. 2, either one of the first end face 10 a side and the second end face 10 b side is sealed in the flow paths Ra and Rb of the honeycomb structure 10. Specifically, the first flow path Ra is opened on the first end face 10 a side, and the second end face 10 b side is sealed by the sealing material 11. In addition, the second flow path Rb is opened on the second end face 10 b side, and the first end face 10 a side is sealed by the sealing material 12.

  As the material of the sealing materials 11 and 12, the same material as that of the green molded body described above may be used, or a different material may be used. Moreover, you may use the material which does not allow the exhaust gas of an internal combustion engine to pass through as the material of the sealing materials 11 and 12. FIG.

  The honeycomb structure 10 includes partition walls 10c that form a plurality of first flow paths Ra and a plurality of second flow paths Rb. In other words, the individual channels Ra and Rb are separated by the partition wall 10c. The partition wall 10c extends along the central axis CL from the first end surface 10a to the second end surface 10b.

  The honeycomb structure 10 shown in FIG. 2 is disposed on the exhaust gas flow path of the internal combustion engine with the first end face 10a as the gas upstream side (internal combustion engine side) and the second end face 10b as the gas downstream side. The main flow of exhaust gas passing through the honeycomb structure 10 is indicated by an arrow G.

  As indicated by the arrow G, the exhaust gas of the internal combustion engine first flows into the flow path Ra from the opening on the first end face 10a side. The gas that has flowed into the channel Ra passes through the partition wall 10c and flows into the channel Rb because the second end face 10b side of the channel Ra is sealed. When the gas passes through the partition wall 10c, soot or the like in the gas is captured. The gas that has flowed into the flow path Rb flows out of the honeycomb structure 10 through the opening on the second end face 10b side. As a result, the purified gas is discharged from the second end face 10 b side of the honeycomb structure 10.

  Next, the cross-sectional shapes of the first channel Ra and the second channel Rb will be described. FIG. 3 is an enlarged view showing a part of a cross section perpendicular to the central axis CL of the honeycomb structure 10. 4A is an enlarged view showing a part of the first end face 10a of the honeycomb structure 10, and FIG. 4B is an enlarged view showing a part of the second end face 10b.

  As shown in FIGS. 3 and 4, the cross section perpendicular to the central axis CL of the honeycomb structure 10 has a lattice structure in which the flow paths Ra and Rb are partitioned by partition walls 10c. The shape of such a honeycomb structure 10 is made by extrusion integral molding except for the sealing materials 11 and 12, and the cross-sectional shapes of the flow paths Ra and Rb are not deformed in the middle and are kept at a constant shape. It extends in the axial direction.

  As the cross-sectional shapes of the first flow path Ra and the second flow path Rb, regular hexagonal shapes and regular hexagonal shapes (for example, a long side having the same length as one side of a cross section of adjacent regular hexagonal flow paths, and A hexagonal shape having a short side shorter than the long side) and a circular shape. That is, the honeycomb structure 10 includes an asymmetric cell structure (asymmetric lattice structure) having flow paths having different cross-sectional shapes.

  Specifically, the first channel Ra has a regular hexagonal cross-sectional shape. On the other hand, the second flow path Rb is divided into two flow paths Rb1 and Rb2 according to the cross-sectional shape. The channel Rb1 has a regular hexagonal cross-sectional shape, and the channel Rb2 has a circular cross-sectional shape. The flow path Rb2 is not shown in FIGS.

  In a cross section perpendicular to the central axis CL of the honeycomb structure 10, the first flow channel Ra having a regular hexagonal cross section is disposed so as to surround the flow channel Rb1 having a regular hexagonal cross sectional shape. With such an arrangement, in the honeycomb structure 10, the first flow path Ra is formed in a larger number than the second flow path Rb. For this reason, the opening ratio in the first end face 10a (the ratio of the opening area of the first flow path Ra in the entire area of the first end face 10a) is the opening ratio in the second end face 10b (the entire second end face 10b). The ratio of the opening area of the second flow path Rb in area) is larger. The honeycomb structure 10 is disposed on the exhaust gas flow path with the first end face 10a facing the gas upstream side. By setting the first end surface 10a having a large opening ratio on the gas upstream side, the exhaust gas can easily flow into the honeycomb structure 10, so that the pressure loss of the exhaust gas in the honeycomb structure 10 can be reduced.

  Next, the high strength region F included in the honeycomb structure 10 will be described. FIG. 5 is an overall view showing the second end face 10b, and FIG. 6 is a partially enlarged view of FIG. As shown in FIGS. 5 and 6, in the honeycomb structure 10, a high-strength region F on a ring is formed on the second end face 10 b. The high-strength region F is formed so as to surround the central axis CL.

  In addition, on the second end face 10b of the honeycomb structure 10, a plurality of open second flow paths Rb are formed at predetermined intervals. On the second end face 10b, the plurality of second flow paths Rb are separated from each other across the sealing material 11 (first flow path Ra) and the partition wall 10c.

  The high-strength region F includes only the flow path Rb2 having a circular cross-sectional shape (opening shape) in the second flow path Rb. In other words, the second flow paths Rb included in the high-strength region F are all flow paths Rb2. The high-strength region F also includes a sealing material 11 and a partition wall 10c that seal the first flow path Ra. On the other hand, all the second flow paths Rb not included in the high-strength region F are flow paths Rb1 having a regular hexagonal cross-sectional shape.

  Next, the minimum curvature radius of the cross-sectional shape of the second flow path Rb (the cross-sectional shape perpendicular to the central axis CL) will be described. The minimum curvature radius of the cross-sectional shape means the smallest one of the curvature radii of the curves (curves that protrude outward) forming the cross-sectional shape.

  FIG. 7A is a diagram illustrating a cross-sectional shape of the flow path Rb1 that is not included in the high-strength region F. FIG. As shown in FIG. 7A, the flow path Rb1 has a regular hexagonal cross-sectional shape with rounded corners. Such rounded corners of the cross-sectional shape are caused by the forming conditions of the honeycomb structure 10. That is, in practice, the cross-sectional shapes of the flow paths Ra and Rb are not formed only from a complete straight line, and the corners of the cross-sectional shape are usually rounded. In addition, in order to reduce stress concentration, the cross-sectional roundness may be intentionally provided.

  The minimum radius of curvature in the cross-sectional shape of the flow path Rb1 is indicated by an arrow r1. It is assumed that the minimum radius of curvature at each corner of the regular hexagon in FIG.

  Here, FIG. 7B is a diagram illustrating a cross-sectional shape of the flow path Rb2 included in the high-strength region F. As shown in FIG. 7B, the flow path Rb2 has a circular cross-sectional shape with a radius r2. The minimum radius of curvature of the cross-sectional shape of the flow path Rb2 is equal to r2.

  As shown in FIGS. 7A and 7B, the minimum curvature radius r1 of the cross-sectional shape of the flow path Rb1 is smaller than the minimum curvature radius r2 of the cross-sectional shape of the flow path Rb2. In other words, the minimum curvature radius r2 of the cross-sectional shape of the flow path Rb2 included in the high-strength region F is larger than the minimum curvature radius r1 of the cross-sectional shape of the flow path Rb1 not included in the high-strength region F.

  According to the honeycomb structure 10 according to the first embodiment described above, the stress concentration on the opening on the second end face 10b is increased as the minimum curvature radius of the cross-sectional shape (opening shape) of the second flow path Rb is increased. Since it can reduce, generation | occurrence | production of a crack can be suppressed in the high intensity | strength area | region F which has flow path Rb2 with a large minimum curvature radius of a cross-sectional shape. Moreover, in the honeycomb structure 10, the flow path Rb1 that is not included in the high-strength region F has a regular hexagonal cross-sectional shape with a small minimum radius of curvature, so that all the second flow paths Rb have the same cross-sectional shape. In comparison, the second flow path Rb can be efficiently arranged on the second end face 10b, and the opening area per unit area of the filter can be increased to ensure sufficient air permeability. Therefore, according to the honeycomb structure 10, it is possible to improve the thermal shock resistance by suppressing the generation of cracks while ensuring sufficient air permeability.

  In the honeycomb structure 10, the high-strength region F is formed in an annular shape surrounding the central axis CL, thereby effectively suppressing the occurrence of an annular crack that appears on the second end face 10b due to thermal shock. it can.

[Second Embodiment]
The honeycomb structure 20 according to the second embodiment is different from the honeycomb structure 10 according to the first embodiment in the shape of the high-strength region.

  FIG. 8 is an overall view showing the second end face 20b of the honeycomb structure 20 according to the second embodiment. As shown in FIG. 8, the honeycomb structure 20 according to the second embodiment has a plurality of oval high strength regions H. The high-strength region H is formed so as to extend in a direction orthogonal to the central axis CL at a position separated from the central axis CL by a predetermined distance. Six high-strength regions H are formed around the central axis CL at intervals of 60 °, and are located radially about the central axis CL.

  All the second flow paths Rb included in the high-strength region H are Rb2 whose cross-sectional shape (opening shape) is circular. On the other hand, all the second flow paths Rb not included in the high-strength region H are Rb1 having a regular hexagonal cross-sectional shape.

  According to the honeycomb structure 20 according to the second embodiment described above, as in the honeycomb structure 10 according to the first embodiment, the occurrence of cracks in the high-strength region H while ensuring sufficient air permeability. By suppressing the thermal shock resistance, it is possible to improve the thermal shock resistance. In addition, in the honeycomb structure 20, since the high-strength regions H are located radially on the second end face 20b, generation of radial cracks appearing on the second end face 20b due to thermal shock is effectively suppressed. Can do.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to said each embodiment. For example, the high-strength region does not necessarily need to include a plurality of second flow paths, and may include only one second flow path. Further, the shape of the high-strength region is not limited to an annular shape or a radial shape, and various shapes can be adopted. The shape, position, size, and the like of such a high-strength region can be appropriately set according to, for example, a region where cracks are likely to occur on the second end face of various honeycomb structures.

  Further, the cross-sectional shapes of the flow paths Ra and Rb are not limited to those described above. For example, the shapes of the flow paths Ra and Rb may be a hexagonal shape or other polygonal shapes, as well as a circular shape or an elliptical shape. If the cross-sectional shapes of both the flow path Rb1 and the flow path Rb2 are perfectly circular, the size of the minimum curvature radius of the cross-sectional shape is proportional to the size of the cross-sectional area. That is, the cross-sectional shape of the flow path Rb1 not included in the high-strength region F may be a small circular shape, and the flow path Rb2 included in the high-strength region F may be a large circular shape. Further, the honeycomb structures 10 and 20 do not necessarily have to be made by extrusion integral molding, and may be made by a segment structure.

  DESCRIPTION OF SYMBOLS 10, 20 ... Honeycomb structure 10a, 20a ... 1st end surface 10b, 20b ... 2nd end surface 10c, 20c ... Partition 11 ... Sealing material 12 ... Sealing material CL ... Center axis Ra ... 1st flow path Rb ... 2nd Channel Rb1 ... Second channel (regular hexagonal shape) Rb2 ... Second channel (circular shape) F, H ... High strength region

Claims (6)

A columnar honeycomb structure extending along the central axis,
A first end surface and a second end surface facing each other in the extending direction of the central axis;
Partition walls forming a plurality of first flow paths and a plurality of second flow paths extending along the central axis,
The first flow path is open on the first end face side and sealed on the second end face side,
The second flow path has the first end face side sealed, and the second end face side opened.
The opening ratio of the first end face is larger than the opening ratio of the second end face,
A high-strength region including at least one second flow path is formed on the second end surface,
All the second flow paths included in the high-strength region have a honeycomb structure having a larger minimum curvature radius in a cross-sectional shape perpendicular to the central axis than the second flow paths not included in the high-strength region. .   The honeycomb structure according to claim 1, wherein the high-strength region includes a plurality of the second flow paths.   The honeycomb structure according to claim 2, wherein the high-strength region is formed in an annular shape surrounding the central axis.   The honeycomb structure according to claim 2, wherein the high-strength region is formed so as to extend along a direction orthogonal to the central axis.   The honeycomb structure according to claim 4, wherein a plurality of the high-strength regions are radially formed around the central axis.   The cross-sectional shape perpendicular to the central axis of all the second flow paths included in the high-strength region is circular or elliptical, and the central axis of the second flow path not included in the high-strength region is The honeycomb structure according to any one of claims 1 to 5, wherein the vertical cross-sectional shape is a polygonal shape.

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