Honeycomb structure body

A honeycomb structure body has a cylindrical outer peripheral wall, partition walls and cells. The cells are surrounded by the partition walls. In a radial cross section of the honeycomb structure body, the cells is divided into cell density sections having different cell densities formed from a central section to the outer peripheral wall. A boundary wall is formed between two cell density sections. Each cell density section has boundary cells and interior cells. The boundary cells are in contact with the boundary wall. The interior cells are not in contact with the boundary wall. In the radial cross section of the honeycomb structure body, an inscribed circle of each of the boundary cells has a diameter of not less than 0.5 mm. Further, an inscribed circle of an interior cell adjacent to the boundary cell also has a diameter of not less than 0.5 mm.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to and claims priority from Japanese Patent Applications No. 2014-63095 filed on Mar. 26, 2014, and No. 2014-243691 filed on Dec. 2, 2014 the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to honeycomb structure bodies having a structure in which the honeycomb structure body has partition walls to form a plurality of cells, and a radial cross section of the honeycomb structure body, perpendicular to an axial direction along which the cells are formed, is divided into a plurality of cell density sections having different cell densities, and the cells belong to respective cell density sections.

2. Description of the Related Art

There have been known and widely used honeycomb structure bodies as a catalyst supporter, in which catalyst is supported. A honeycomb structure body is mounted to an exhaust gas pipe connected to an internal combustion engine such as a diesel engine and purifies exhaust gas emitted from the internal combustion engine. For example, such a honeycomb structure body has an outer peripheral wall of a cylindrical shape, and partition walls arranged in a lattice shape in the inside of the outer peripheral wall. In particular, the partition walls are formed and arranged in a lattice shape to form a plurality of cells along an axial direction of the honeycomb structure body. Each of the cells is surrounded by the partition walls. The cells are formed along an axial direction of the honeycomb structure body.

The honeycomb structure body having such a structure is mounted to the exhaust gas pipe connected to an internal combustion engine. Through the exhaust gas pipe, exhaust gas emitted from the internal combustion engine is discharged outside. Because exhaust gas has a high temperature, the catalyst supported in the honeycomb structure body is activated by heat energy of the exhaust gas and the activated honeycomb structure body at a high temperature purifies the exhaust gas when the exhaust gas is passing through the inside of the cells in the honeycomb structure body.

The recent vehicle emission control is becoming stricter year by year in view of environmental protection, and there is also strong demand to decrease carbon dioxide contained in exhaust gas emitted from internal combustion engines such as diesel engines and more improve fuel efficiency of motor vehicles. It is very important to eliminate particulate matter such as black smoke contained in exhaust gas emitted from diesel engines in view of recent vehicle emissions control which intends to reduce motor vehicle emissions, etc. In order to solve and satisfy the above recent requirement, many motor vehicles are equipped with a diesel particulate filter. The diesel particulate filter equipped with a honeycomb structure body is mounted on an exhaust gas pipe through which exhaust gas emitted from a diesel engine is discharged to the outside of the motor vehicle. The diesel particulate filter purifies such exhaust gas. For this reason, this increases an amount of the noble metal used as catalyst in the honeycomb structure body. In order to avoid price risk of the noble metal and resource procurement risk, it is required to reduce a total amount of the noble metal used in the honeycomb structure body. Accordingly, there is a strong demand for a honeycomb structure body to have an excellent purification capability of exhaust gas.

For example, a patent document, Japanese patent laid open publication No. 2013-173133 has disclosed a honeycomb structure body having a conventional structure in which a plurality of cell density sections having different cell densities is formed in a radial direction of the honeycomb structure body. This radial direction is perpendicular to an axial direction of the honeycomb structure body. The cell density sections are formed from a central section to the outer peripheral section in a radial cross section. Because the outer peripheral section has a low flowing speed of exhaust gas as compared with a flowing speed of the exhaust gas in the central section, a cell density is gradually reduced from the central section to the outer peripheral section in the honeycomb structure body disclosed in the patent document, Japanese patent laid open publication No. 2013-173133. This structure makes it possible to have a uniform flowing speed of exhaust gas in the honeycomb structure body, and promote an effective use of catalyst supported in the honeycomb structure body. The honeycomb structure body having the structure previously described improves the exhaust gas purification capability.

Still further, a boundary section is further formed between the cell density sections having different cell densities in the honeycomb structure body disclosed in the patent document, Japanese patent laid open publication No. 2013-173133. Because the boundary section has boundary cells having a specific structure, it is possible to reduce a pressure loss of the honeycomb structure body and increase the exhaust gas purification capability.

However, the boundary section formed between the adjacent cell density sections having different cell densities in the honeycomb structure body previously described has an insufficient strength around the boundary section, and there is a possible drawback of the honeycomb structure body easily breaking due to external stress. Furthermore, the honeycomb structure body is generally produced by firing a honeycomb mold body having a honeycomb structure. The boundary section formed between the cell density sections in the honeycomb structure body non-uniformly shrinks during a drying step and a firing step in the manufacturing process of producing honeycomb structure bodies. For this reason, it is difficult to produce a honeycomb structure body having a correct roundness. This reduces a productivity of honeycomb structure bodies having a correct roundness.

That is, it is possible to increase the strength of the honeycomb structure body when a boundary wall section is formed between two cell density sections having different cell densities, and reduce influence of outside stress applied to the honeycomb structure body. However, because small sized cells having a small cross section are formed near the boundary wall section, catalyst clogging (in which a cell is clogged with catalyst) occurs in the small sized cells when catalyst is supported in the honeycomb structure body during the manufacturing process of producing honeycomb structure bodies. As a result, such small sized cells having a small cross section formed adjacent to the boundary wall section are clogged with catalyst. This increases a pressure loss of the honeycomb structure body. In addition, the formation of catalyst-clogged cells causes a reduction in exhaust gas flow in some sections which support catalyst and are clogged by catalyst. This is a waste of catalyst because catalyst is used in the unnecessary sections in the honeycomb structure body.

SUMMARY

It is therefore desired to provide a honeycomb structure body having a structure of an excellent strength capable of preventing occurrence of catalyst clogging in cells and reducing a pressure loss of the honeycomb structure body.

An exemplary embodiment of the present invention provides a honeycomb structure body having an improved structure comprised of an outer peripheral wall, partition walls, and a plurality of cells. The outer peripheral wall has a cylindrical shape. The partition walls are formed in the inside of the outer peripheral wall and arranged in a lattice shape. Each of the cells is surrounded by the partition walls. In a cross section in a radial direction of the honeycomb structure body, which is perpendicular to an axial direction of the honeycomb structure body, the cells are divided into a plurality of cell density sections arranged from a central section to the outer peripheral wall. In particular, the cell density sections have different cell densities. A boundary wall is formed between two cell density sections which are adjacent to each other. Each of the cell density sections is comprised of boundary cells and interior cells. The boundary cells are in contact with the boundary wall. The interior cells are not in contact with the boundary wall and surrounded by the partition walls. In the cross section along the radial direction (i.e. in a radial cross section), which is perpendicular to the axial direction of the honeycomb structure body, an inscribed circle of each of the boundary cells has a diameter of not less than 0.5 mm.

The honeycomb structure body according to the present invention has a plurality of the cell density sections formed in a radial direction which is perpendicular to an axial direction of the honeycomb structure body. That is, the cell density sections are formed in a radial cross section and arranged from the central point to the outer peripheral wall. For example, the honeycomb structure body has two cell density sections, a first cell density section and a second cell density section having different cell densities. The boundary wall is formed between the first cell density section and the second cell density section. This structure makes it possible to have a uniform gas flow distribution of exhaust gas in a radial cross section of the honeycomb structure body. Such exhaust gas is emitted from an internal combustion engine to outside through the honeycomb structure body. The exhaust gas is introduced into the inside of the honeycomb structure body and is flowing through the cells of the honeycomb structure body at a uniform flow distribution of exhaust gas. Further, the honeycomb structure body of a cylindrical shape has the boundary wall which is formed between the first cell density section and the second cell density section. This structure increases the mechanical strength of the honeycomb structure body. It is therefore possible to prevent generation of defects in the honeycomb structure body and avoid the honeycomb structure body from being broken during a manufacturing process or when the products of the honeycomb structure body are conveyed. Still further, this structure makes it possible to prevent deterioration of the roundness of a honeycomb mold body during the manufacturing process. This provides an excellent productivity of the honeycomb structure body.

Further, each of the cell density sections has the boundary cells and the interior cells. The boundary cells are in contact with the boundary wall. The interior cells are not in contact with the boundary wall and are surrounded by the partition walls. In a radial cross section of the honeycomb structure body, an inscribed circle of each of the boundary cells has a diameter of not less than 0.5 mm. This structure increases a size of the boundary cell and prevents occurrence of catalyst clogging in the boundary cells when catalyst is supported by the boundary cells and the interior cells of the honeycomb structure body during the manufacturing process. Further, this structure makes it possible to decrease a pressure loss because of avoiding occurrence of catalyst clogging.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, various embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the various embodiments, like reference characters or numerals designate like or equivalent component parts throughout the several diagrams.

A description will be given of a honeycomb structure body according to the present invention.

A honeycomb structure body according to an exemplary embodiment of the present invention has a plurality of cell density sections having different cell densities arranged in a radial direction from a central section to an outer peripheral wall. That is, the honeycomb structure body is divided into a plurality of the cell density sections having different cell densities in a radial direction from the central section to the outer peripheral wall. The cells are arranged in a same cell density in each of the cell density sections. Further, the two cell density sections which are arranged adjacent to each other have different cell densities. The cell density is changed stepwise in a radial direction.

There are methods of changing stepwise a cell density of the cell density sections formed in a radial direction from the central section to the outer peripheral wall in the honeycomb structure body. For example, one method changes a cell pitch between adjacent cells, and another method changes a shape of the cells. The cells have a polygonal, for example, a triangle shape, a rectangular shape, a pentagonal shape, a hexagonal shape, etc. It is preferable for each cell formed in the honeycomb structure body to have a rectangular shape from the point of view of mechanical strength.

When the cells are formed in a polygonal shape on a cross section in a radial direction (or on a radial cross section) of the honeycomb structure body, it is preferable that a corner section, at which two polygonal shaped cells are arranged adjacently to each other, has a rounded shape, and a radial of curvature of the corner section is not less than 0.03 mm. This structure makes it possible to more increase mechanical strength of the honeycomb structure body. In addition, it is therefore possible to improve reliability of the honeycomb structure body as commercial products. From the same point of view, it is preferable for a corner section of the cell to have a radius of curvature of not less than 0.05 mm, and more preferable to have a radius of curvature of not less than 0.1 mm, and most preferable to have a radius of curvature of not less than 0.15 mm.

An inscribed circle of a boundary cell is a virtual circle which is in contact with at least three partition walls (three sides) of the boundary cell, i.e. which form the boundary cell. When not less than two inscribed circles are present in the boundary cell, the inscribed circle having a maximum diameter is determined as the inscribed circle of the boundary cell. In the structure of the honeycomb structure body according to the present invention, the inscribed circle of each of the boundary cells has a diameter of not less than 0.5 mm. In the structure of the honeycomb structure body according to the present invention, it is sufficient for a minimum diameter of the inscribed circle of the boundary cell to be not less than 0.5 mm. There is a concrete method of producing the honeycomb structure body having the structure previously described in which the diameter of the inscribed circle of the boundary cell is not less than the predetermined value, i.e. not less than 0.5 mm. For example, as will be explained later in detail, a common use partition wall arranged between the boundary cell and an interior cell which is adjacent to the boundary cell is moved, i.e. relocated toward a predetermined direction, or such an interior cell is eliminated.

It is possible to adjust a diameter of an inscribed circle of each of usual interior cells, excepting the boundary cells and adjacent interior cells which are arranged next to the boundary cells, to be within a range of 0.5 mm to 1.6 mm. When considered from the viewpoint of reducing a pressure loss and increasing mechanical strength of a honeycomb structure body, it is preferable for an inscribed circle of each usual interior cell to have a diameter within a range of 0.9 mm to 1.6 mm. A diameter of the inscribed circle of each of the usual interior cells and the boundary cells is defined by the same manner previously described.

A cell density of the cells arranged in the honeycomb structure body is defined by the number of cells per unit area. Specifically, when the unit cell area is defined as an area surrounded by intermediate lines (for example, such intermediate lines are virtual lines. A rectangular shaped cell is surrounded by four partition walls, the intermediate line runs through a central point in a thickness direction of each partition wall. The unit cell area is an area surrounded by the four intermediate lines when the cell is a rectangular shape), it is possible to obtain the number of cells per unit area by using the calculated unit cell area. The obtained number indicates the cell density. In particular, such a calculation of the cell density uses the usual interior cells, does not use any boundary cells, adjacent interior cells and adjacent exterior cells. That is, the boundary cells are in contact with the boundary wall having a cylindrical shape formed between two cell density sections having different cell densities, which are adjacent to each other through the boundary wall. Each of the adjacent interior cells has partition walls which are shifted in position as compared with the partition walls of the usual interior cells. The adjacent exterior cells are in contact with the outer peripheral wall having a cylindrical shape.

As previously described, the cell density is calculated on the basis of the cells having a circular shaped cross section in a radial direction and the cells having a rectangular shaped cross section in a radial direction.

It is possible that the honeycomb structure body according to the present invention have a monolithic structure. In addition, it is also possible that the honeycomb structure body is made of a plurality of segments assembled together. It is preferable for the honeycomb structure body to have a monolithic structure. This can eliminate connection sections when the segments are assembled together in the latter case, and further reduce a whole pressure loss of the honeycomb structure body in addition to a pressure loss obtained by the improved structure of the honeycomb structure body according to the present invention.

The honeycomb structure body according to the present invention is made of ceramic raw material, for example, cordierite, SiC, aluminum titanate, etc.

For example, the honeycomb structure body according to the present invention is used as a catalyst converter, etc. The catalyst converter is capable of purifying exhaust gas emitted from an internal combustion engine. Catalyst is supported on the partition walls of the cells in the honeycomb structure body. For example, the honeycomb structure body according to the present invention has a porosity within a range of 10% to 70%. The honeycomb structure body according to the present invention has an average pore size of not less than 2 μm, for example. Further, the honeycomb structure body according to the present invention has the partition walls having a thickness within a range of 40 μm to 160 μm. Still further, the honeycomb structure body according to the present invention has the boundary wall having a thickness within a range of 0.04 mm to 0.4 mm.

It is acceptable that a central point of the outer peripheral wall having a cylindrical shape is conformed to or differs from a central point of the boundary wall having a cylindrical shape. That is, it is acceptable that a central point of a cell density section formed in the interior of the boundary wall differs from a central point of a radial cross section in the honeycomb structure body according to the present invention.

First Exemplary Embodiment

A description will be given of various test samples according to exemplary embodiment of the honeycomb structure body and comparative examples.

The first exemplary embodiment prepared test samples E1to E6as the honeycomb structure body according to the first exemplary embodiment and comparative examples C1to C5, and evaluated these samples.

A description will now be given of the test samples E1to E6according to the first exemplary embodiment.

FIG. 1is a perspective view showing an overall honeycomb structure body1according to the first exemplary embodiment.FIG. 2is a view showing a partial cross section in a radial direction of the honeycomb structure body (test samples E1to E6) according to the first exemplary embodiment shown inFIG. 1.

As shown inFIG. 1andFIG. 2, the honeycomb structure body1is made of ceramics and has an outer peripheral wall10having a cylindrical shape, partition walls11arranged in a lattice shape in the interior section of the outer peripheral wall10and a plurality of cells2. Each of the cells3is surrounded by the partition walls11. In a cross section in a radial direction (i.e., in a radial cross section) which is perpendicular to an axial direction X of the honeycomb structure body1, a plurality of cell density sections12is formed. That is, the cell density sections12have different cell densities and are formed in a radial direction Y from a central section O to the outer peripheral wall10. A boundary wall14is formed between the cell density sections12(a first ell density section and a second cell density section) which are adjacent to each other through the boundary wall14. The cells2are composed of boundary cells21and interior cells22(or usual interior cells). Each of the boundary cells is in contact with the boundary wall14. None of the interior cells22are in contact with the boundary wall14, and they are surrounded by the partition walls11.

FIG. 3is a view showing an enlarged partial cross section in a radial direction of the honeycomb structure body1(test samples E1to E6) according to the first exemplary embodiment shown inFIG. 1.

As shown inFIG. 2andFIG. 3, in a cross section in the axial direction X of the honeycomb structure body1, the boundary cell21has an inscribed circle210having a diameter D of not less than 0.5 mm.

In the structure of the honeycomb structure body1according to the first exemplary embodiment, at least one of the boundary cells21is formed by connection cells211. Each of the connection cells211is formed by connecting two cells2which are arranged adjacent to each other.

A description will now be given of the honeycomb structure body1according to the first exemplary embodiment in detail.

The honeycomb structure body1according to the first exemplary embodiment is used as a catalyst carrier capable of supporting catalyst. The catalyst carrier purifies exhaust gas emitted from internal combustion engines such as diesel engines.

As shown inFIG. 1andFIG. 2, the honeycomb structure body1has a plurality of the partition walls11, a plurality of the cells2, and the outer peripheral wall10having a cylindrical shape. The partition walls11are arranged in a rectangular lattice shape. Each of the cells2is surrounded by the partition walls11. The outer peripheral wall10has a cylindrical shape and surrounds the outer peripheral surface of the honeycomb structure body1.

A radial cross section of each of the cells2has a rectangular shape including a square shape. Each of the cells2is formed to extend along the axial direction X of the honeycomb structure body1. The honeycomb structure body1is made of cordierite and has a monolithic structure. The honeycomb structure body1has a diameter of 103 mm and a total length of 105 mm, for example.

As shown inFIG. 2, two cell density sections12, i.e. a first cell density section121and a second cell density section122, are formed in a radial cross section Y which is perpendicular to the axial direction X of the honeycomb structure body1. The first cell density section121and the second cell density section122have different cell densities. The cells in each of the first cell density section121and the second cell density section122are formed with a same cell density. In particular, the cells arranged in the second cell density section122have a second cell density which is lower than a first cell density of the cells arranged in the first cell density section121. Table 1 shows the cell density of each of the first cell density section121and the cell density of the second cell density section122in each of the samples. Table 1 will be described later in detail.

As shown inFIG. 2, the first cell density section121contains the central point O of the honeycomb structure body1and is arranged in the innermost area of the honeycomb structure body1. On the other hand, the second cell density section122is arranged in the outermost section which contains the outer peripheral wall10of the honeycomb structure body1. That is, the second cell density section122is arranged in the outermost section of the cell density section12. Each of the partition walls11in the first cell density section121and the second cell density section122has a thickness of 0.09 mm (90 μm).

As shown inFIG. 1andFIG. 2, the honeycomb structure body1has the boundary wall14by which the honeycomb structure body1is divided into the first cell density section121and the second cell density section122in a radial cross section in a radial direction Y which is perpendicular to the axial direction X. The boundary wall14has a cylindrical shape. In the structure of the honeycomb structure body1according to the first exemplary embodiment, the boundary wall14has a thickness of 0.2 mm.

The boundary cells21are in contact with the boundary wall14. Each of the boundary cells21is surrounded by the partition walls11and the boundary wall14. On the other hand, each of the usual interior cells2(interior cells22) has a predetermined shape (for example, as a rectangle shape in the first exemplary embodiment) and is surrounded by the partition walls11only. In other words, as shown inFIG. 3, the usual interior cell2(or interior cell22) is different in shape from the boundary cell21.

As shown inFIG. 2andFIG. 3, each of the boundary cells21in each of the first cell density section121and the second cell density section122is formed by a connection cell211. The connection cell211is formed by combining at least two cells2which are arranged adjacently to each other. Because the boundary cell21is formed by the connection cell211, the boundary cell21has an inscribed circle210having a diameter D of not less than 0.5 mm.

A description will now be given of the structure of the connection cell211with reference toFIG. 4.

FIG. 4is a view showing an enlarged partial cross section in a radial direction of the honeycomb structure body (test samples E1to E6) according to the first exemplary embodiment shown inFIG. 1in which a virtual partition wall is considered in a boundary cell21as a connection cell211.

As previously described, the connection cell211is comprised of not less than two cells connected together. A virtual partition wall11A can be considered (which is designated by the dotted lines shown inFIG. 4). The virtual partition wall11A is present before two cells are combined to form the connection cell211as the boundary cell21. This virtual partition wall11A is a partition wall present between two cells before the two cells of a predetermined shape are combined in each of the cell density sections121and122. As shown inFIG. 4, when the virtual partition wall11A is present, a virtual interior cell22A (a perfect cell) having a rectangle shape surrounded by the virtual partition wall11A and other partition walls11and a virtual boundary cell21A (an imperfect cell) surrounded by the boundary wall14, the virtual partition wall11A and another partition wall11. The imperfect cell21A has a cross sectional area which is smaller in radial cross section than a cross sectional area of the perfect cell22(22A). That is, the formation of such boundary cells having a small size reduces the entire mechanical strength of the honeycomb structure body.

As shown inFIG. 4, the connection cell211is formed by combining the two cells, i.e. the imperfect cell21A and the perfect cell22A, in which the virtual partition wall11A has been eliminated. In a concrete example, the connection cells211are formed by using a metal die having slit grooves to be used for forming the connection cells211during the production of the honeycomb structure body1. In more detail, a metal die is used, in which no slit grove is formed to make a virtual partition wall11A which is virtually present between the virtual partition wall (imperfect cell)21A and a virtual interior cell (perfect cell)22A. It is thereby possible to produce the honeycomb structure body1having the boundary cells21and the connection cells211by using the metal die having the structure previously described.

The explanation previously disclosed shows the connection cell having the structure in which the imperfect cell21A and the perfect cell22A are arranged adjacently and connected together. However, the concept of the present invention is not limited by this. It is acceptable to connect the imperfect cell21A with another imperfect cell, or another perfect cell, or both an imperfect cell and a perfect cell. Further,FIG. 3clearly shows the structure of the honeycomb structure body1as an actual honeycomb structure body3not having any virtual imperfect cell21A and virtual perfect cell22A, i.e. from which the virtual imperfect cell21A and the virtual perfect cell22A have been eliminated.

FIG. 5is a view showing a partial cross section in a radial direction of a honeycomb structure body7as a comparative samples C1used in the first exemplary embodiment.FIG. 6is a view showing an enlarged partial cross section in a radial direction of the honeycomb structure body7shown inFIG. 5. As shown inFIG. 5andFIG. 6, the honeycomb structure body7as the comparative example C1has imperfect cells as boundary cells21without any connection cell.

The first exemplary embodiment produced the test samples E1to E6and the comparative examples C4and C5having a different cell connection pattern. The test samples E1to E6and the comparative examples C4and C5have the boundary cells21having a different size. The boundary cell21in each of the test samples E1to E6is the connection cell211.

As shown inFIG. 3, it is possible to calculate the size of the boundary cell21on the basis of the diameter D of the inscribed circle210of the boundary cell21in a radial cross section of each of the test samples E1to E6, and the comparative examples C4and C5. In particular, the inscribed circle210of the boundary cell21has a maximum diameter in contact with at least three sides of the boundary cell21.

Table 1 shows the minimum diameter D of the inscribed circle in the entire inscribed circles of the boundary cells21in each of the test samples E1to E6and the comparative samples C4and C5.

Further, as shown inFIG. 3, the honeycomb structure body1according to the first exemplary embodiment (test samples E1to E6and the comparative examples C4and C5) has the boundary cells21. Each of the boundary cells21has a round corner section218which is adjacent to the boundary wall14. That is, the round corner section210in the boundary cell21is formed by the boundary wall14and the partition wall11. The round corner section218has a round shape. The first exemplary embodiment produced a plurality of the honeycomb structure bodies1(test samples E1to E6and the comparative samples C4and C5), each of which has the corner section218having a different radius of curvature. Table 1 shows the radius of curvature of the corner section218in each of the test samples E1to E6and the comparative samples C4and C5. As previously described, the honeycomb structure body1according to the first exemplary embodiment (test samples E1to E6, and comparative examples C4and C5) has the interior cells22(perfect cells), a radial cross section of which has a rectangle shape. The corner section29of each of the cells2containing those interior cells22has a round shape. The corner sections29of the cells2, excepting the corner sections218of the boundary cells21arranged adjacently the boundary wall14, has a radius of curvature of 0.03 mm.

A description will now be given of the honeycomb structure body7(comparative examples C1, C2and C3).

As shown inFIG. 5andFIG. 6, the test sample C1is a honeycomb structure body7which does not have any connection cell to be used as the boundary cell21. That is, because the test sample C1does not have any connection cell, each of the boundary cells21adjacent to the boundary wall14in the test sample C1is comprised of an imperfect cell. Each of the boundary cells21has an imperfect shape, and a cross sectional area of which in a radial direction is smaller than a cross sectional area of the interior cell (as a perfect cell)22. As shown inFIG. 6, the comparative sample C1has the cells, each of which has an inscribed circle having a diameter D of less than 0.5 mm. Other components of the comparative sample C1are the same as those of the test samples E1to E6.

FIG. 7is a view showing a partial cross section in a radial direction of a honeycomb structure body8(comparative sample C2) used in the first exemplary embodiment.

As shown inFIG. 7, the comparative sample C2does not have any boundary wall or any connection cell. That is, the honeycomb structure body8as the comparative sample C2does not have any boundary wall formed between the first cell density section121and the second cell density section122in each of the test samples E1to E6. Further, the honeycomb structure body8as the comparative sample C2does not have any connection cell which is formed by combining at least two cells arranged adjacently to each other. Other components of the comparative sample C2are the same as those of each of the test samples E1to E6.

FIG. 8is a view showing a partial cross section in a radial direction of a honeycomb structure body9(comparative sample C3) used in the first exemplary embodiment.

As shown inFIG. 8, the honeycomb structure body9has a boundary section94instead of having the connection cells and the boundary wall. The boundary section94has a conventional structure, for example, disclosed in Japanese patent laid open publication No. 2013-173133.

Specifically, as shown inFIG. 8, the honeycomb structure body9has the boundary section94formed between the first cell density section121and the second cell density section122. The boundary section94has a plurality of boundary cells942having a polygonal shape, which is different in shape from the cells2(or the interior cells22) formed in the first and second cell density sections121and122. Each of the boundary cells942is surrounded by boundary partition walls941, each of which connects the partition wall11of the first cell density section121with the partition walls11of the second cell density section122. Further, each of boundary cells in at least some of the boundary cell942is surrounded by other boundary walls941.

The honeycomb structure body9as the comparative sample C3has a structure which satisfies a relationship of φ1/φ2>=1.25, where φ1 indicates an average hydraulic diameter of the boundary cells942formed in the boundary section94, and φ2 indicates an average hydraulic diameter of the cells2formed in the first cell density section121formed directly inside of the boundary section94.

The boundary section94formed in the honeycomb structure body9has an octagonal shape in a radial cross section of the honeycomb structure body9. The boundary section94has the boundary partition walls941and the boundary cells942. The boundary section94connects the partition wall11formed in the cell density section12(as the first cell density section121) with the partition wall11formed in the cell density section12(as the second cell density section122).

The boundary cells942are surrounded by the partition walls11in the cell density sections12such as the first cell density section121and the second cell density section122formed at both sides of the boundary walls941and the boundary section94. In addition, the boundary cells942have a shape which is different from the shape of the cells2formed in the cell density sections12(as the first cell density section121and the second cell density section122) formed at both sides of the boundary section94.

The honeycomb structure body9has the boundary cells942having a pentagonal shape. The boundary walls941are formed to connect grid points911of the partition walls11arranged in a lattice shape of the cell density sections12(as the first cell density section121and the second cell density section122) formed at both sides of the boundary section94. Other components of the comparative sample C3are the same as those of the test samples E1to E6.

The same components between the comparative samples C1, C2and C3and the test samples E1to E6are designated by the same reference numbers and characters. The explanation of these same components is omitted for brevity.

A description will now be given of the method of producing the honeycomb structure bodies (test samples E1to E6and comparative samples C1to C5).

The method of producing a honeycomb structure body prepares ceramic raw material composed of kaolin, fused silica, aluminum hydroxide, alumina, carbon particles, etc. so that cordierite as the ceramic raw material has a chemical composition of SiO2within a range of 45 to 55 weight %, Al2O3within a range of 33 to 42 weight %, and MgO within a range of 12 to 18 weight %. The method adds water, binder, etc. having a predetermined amount to the prepared cordierite as raw material to make a mixture. The mixture is mixed to make the mixed ceramic raw material.

The method extrudes the mixed ceramic raw material by using an extrusion metal die to produce a honeycomb structure molded body. The extrusion metal die has a cross section having a pattern of slit grooves which correspond to a cell arrangement formed by the partition walls arranged in the honeycomb structure body.

The method dries the honeycomb structure molded body by using microwaves. The method cuts the dried honeycomb structure body to a plurality of parts having a desired length. After this, the method fires the honeycomb structure body having the desired length at a maximum temperature (for example, within a range of 1390° C. to 1430° C.). The production of the honeycomb structure body is thereby completed.

A description will now be given of evaluation results of the honeycomb structure bodies (test samples E1to E6and comparative examples C1to C5) in occurrence of catalyst clogging in cells, pressure loss and isostatic strength.

In order to detect occurrence of catalyst clogging in each of the honeycomb structure bodies, it was detected whether or not cells were formed at a boundary section between cell density sections having different cell densities when catalyst was supported in each of the honeycomb structural bodies. The state of catalyst clogging indicates that opening end surface of each cell is completely clogged with catalyst.

It is possible to use catalyst composed of γ-alumina, oxygen storage material and at least one of platinum (Pt), Rhodium (Rh) and Palladium (Pd) as a three-way catalyst, There are ceria, etc. as the oxygen storage material.

After slurry containing catalyst was poured into the inside of the cells, the honeycomb structural body was fired to support the catalyst in the honeycomb structural body. The number of catalyst-clogged cells in each of the honeycomb structural bodies (test samples E1to E6, comparative samples C1to C3) was detected. When the number of catalyst-clogged cells becomes not less than 100, the evaluation result indicates “D”. When within 20 to 99, the evaluation result indicates “C”. Further, when within 1 to 19, the evaluation result indicates “B”. When the number of catalyst-clogged cells is zero, the evaluation result indicates “A”. Table 1 shows the evaluation result in occurrence of catalyst clogging of each of the test samples E1to E6and comparative samples C1to C3.

The evaluation of isostatic strength, i.e. isostatic breaking strength of each of the test samples E1to E6and comparative samples C1to C5was performed on the basis of an isostatic breaking strength test defined by standard M505-87 of JASO (Japanese Automotive Standards Organization). Specifically, the sample as the honeycomb structural body was set in a cylinder casing made of rubber and sealed with a cover made of aluminum. The isostatic pressing of each sample was performed in water to detect a load when the honeycomb structural body as each sample was broken and to calculate the isostatic breaking strength on the basis of the detected load.

The isostatic breaking strength of each of the test samples E1to E6and the comparative samples C1to C5was detected by the method previously described. Table 1 shows a ratio of the detected isostatic breaking strength of each sample to the isostatic breaking strength of the comparative sample C1.

A pressure loss of each of the honeycomb structural bodies (test samples E1to E6and comparative samples C1to C5) was detected by a pressure loss detection apparatus. The test samples E1to E6and the comparative samples C1to C5supported catalyst therein.

FIG. 9is a view showing a pressure loss detection apparatus6for detecting a pressure loss of each of the test samples E1to E6and the comparative samples C1to C3used in the first exemplary embodiment.

Specifically, as shown inFIG. 9, each sample as the honeycomb structure body1,7,8,9was mounted on the pressure loss detection apparatus6. The pressure loss of each sample was detected when an air blower (not shown) was used, i.e. sucked air A1in the pressure loss detection apparatus6in which each sample was arranged. This produces a negative pressure in the inside of the pressure loss detection apparatus6, and a predetermined amount of introduced air A2was introduced into the inside of the honeycomb structural body1,7,8,9arranged in the pressure loss detection apparatus6. It was adjusted that the introduced new air A2had 6 m3/minutes introduced in the inside of each sample. A pressure sensor61arranged in the inside of the pressure loss detection apparatus6detected a pressure of inside air. A difference between atmospheric pressure and the pressure of inside air detected by the pressure sensor61was calculated in order to obtain a pressure loss of each sample.

Table 1 shows a ratio of the detected pressure loss of each sample to the pressure loss of the comparative sample C1.

That is, Table 1 shows the detected parameters of each of the test samples E1to E6and the comparative samples C1to C5:

(a1) Cell density (×104cells/m2) of first cell density section;

(a2) Cell density (×104cells/m2) of second cell density section;

(a3) Presence of boundary cell;

(a4) Presence of connection cell

(a5) Minimum diameter D (mm) of inscribed circle in boundary cell (formed by connection cell);

(a6) Radius of curvature (mm) of corner section of boundary cell arranged adjacent to boundary wall;

(a7) Evaluation result in catalyst clogging in cell;

The honeycomb structural body1(test samples E1to E6and comparative samples C4and C5) has the connection cells211as the boundary cells21which are in contact with the boundary wall14. That is, as can be clearly understood from the results shown in Table 1, the structure of the honeycomb structural body1shown inFIG. 1,FIG. 2andFIG. 3(as test samples E1to E6and comparative samples C4and C5) can suppress occurrence of catalyst clogging in cells, i.e. generation of catalyst-clogged cells such as the boundary cells21, and reduce its pressure loss (or have a low pressure loss) when compared with the comparative sample C1without having any connection cell in contact with the boundary wall. Furthermore, the honeycomb structural body1(test samples E1to E6and comparative samples C4and C5) has an increased mechanical strength because of having the boundary wall14when compared with mechanical strength of the comparative samples C2and C3which have no boundary wall.

As previously explained, the honeycomb structural body1(test samples E1to E6and comparative samples C3and C5) has an increased mechanical strength because of having the boundary wall14having a cylindrical shape formed between the cell density sections12. That is, the cell density sections12are adjacent to each other through the boundary wall. This structure having the boundary wall makes it possible to prevent the honeycomb structural body1from being broken, etc. the structure of the honeycomb structural body1shown inFIG. 1toFIG. 3makes it possible to prevent deterioration of a roundness during the manufacturing of the honeycomb structural body1. This makes it possible to provide a high productivity of producing the honeycomb structural body. Still further, the honeycomb structural body1has a plurality of the cell density sections12having different cell densities formed from the central point O to the outer peripheral wall10in the radial direction Y, which is a radial cross section perpendicular to the axial direction X of the honeycomb structural body1. This structure makes it possible to allow uniform distribution of a flowing speed of exhaust gas in a radial cross section of the honeycomb structural body1.

Each of the boundary cells21in contact with the boundary wall14in the honeycomb structural body1is comprised of the connection cells211(seeFIG. 2toFIG. 4) which are formed by combining a plurality of the cells. This structure makes it possible to avoid generation of small sized cells (imperfect cells), which occurs catalyst clogging in the boundary cell21formed adjacently the boundary wall14(like the comparative sample C1shown inFIG. 5andFIG. 6). It is accordingly possible for the structure of the honeycomb structural body1to prevent occurrence of catalyst clogging in the boundary cells21and have a reduced pressure loss.

In addition, as can be understood from the results shown in Table 1, no catalyst clogging occurs in cells, i.e. no catalyst-clogged cell has observed in a radial cross section perpendicular to the axial direction X of the honeycomb structural body1(test samples E1to E6) having the boundary cells21, a diameter of an inscribed circle210of each boundary cell21is not less than 0.5 mm. That is, catalyst clogging does not occur in any cell formed in the honeycomb structural body1(test samples E1to E6). Accordingly, as previously described, the boundary cell21is formed by combining adjacent two cells to form the connection cell211having a large size. It is possible to prevent generation of catalyst clogging in the cells, i.e. catalyst-clogged cells when the inscribed circle210of the boundary cell211has a diameter of not less than 0.5 mm.

Form the viewpoint of reducing the pressure loss of the honeycomb structural body, it is preferable for the inscribed circle210of the boundary cell21to have a diameter of not less than 0.7 mm, more preferable to have a diameter of not less than 0.9 mm.

On the other hand, from the point of view of increasing mechanical strength, it is preferable for the inscribed circle210of the boundary cell21to have a diameter of not more than 1 mm, more preferable to have a diameter of not more than 0.75 mm.

It is possible to form each boundary cell21by using the connection cell211only, or some of the boundary cells21by using the connection cell211. That is, it is possible that each of boundary cells in at least some of the boundary cells21is formed by using the connection cell211, and each of the boundary cells21in the remaining part is formed by using the usual interior cell22. It is possible to avoid occurrence of catalyst clogging when the inscribed circle210of the boundary cell21has a diameter D of not less than 0.5 mm in spite of using the connection cell211.

Like the inscribed circle210of the boundary cell21previously described, when an inscribed circle (not shown) of the interior cell22is considered in the honeycomb structure body according to the first exemplary embodiment and the second and third exemplary embodiments (which will be explained later), the inscribed circle of the interior cell22in each of the cell density sections121and122has a diameter of not less than 0.5 mm.

As can be understood from the results shown in Table 1, like the structure of each of the test samples E1to E6according to the first exemplary embodiment previously described, when the corner section218which is in contact adjacently with the boundary wall14in the boundary cell21has a radius of curvature of not less than 0.05 mm, this structure makes it possible to increase the mechanical strength of the honeycomb structure body1. It is preferable for the corner section218to have a radius of curvature of not less than 0.15 mm, and more preferable to have a radius of curvature of not less than 0.25 mm.

As shown inFIG. 2, in the structure of the honeycomb structure body1according to the first exemplary embodiment, the cells2formed in the first cell density section121are arranged in a first direction which is different from a second direction of the cells2arranged in the second cell density section122. Specifically, the cells2in the second cell density section122are inclined to the cells2in the first cell density section121by 45 degrees. The concept of the present invention is not limited by this structure.

FIG. 10is a view showing a partial cross section in a radial direction of the honeycomb structure body according to the first exemplary embodiment in which the cells2formed in the first cell density section121and the cells2formed in the second cell density section122are inclined in the same direction, where the first cell density sections121and the second cell density section122have different cell densities.

That is, it is acceptable for the cells2in the first cell density section121and the cells2in the second cell density section122to have a same slope of an optional degree. For example, the cells2in the first cell density section121and the cells2in the second cell density section122are the same slope, i.e. are inclined by the same degrees, as shown inFIG. 10(which will be explained later in detail).

FIG. 11is a view showing a partial cross section in a radial direction of the honeycomb structure body according to the first exemplary embodiment in which the cells2formed in the first cell density section121are inclined by a degree of less than 45 degrees to the cells2formed in the second cell density section122, where the first cell density sections121and the second cell density section122have different cell densities.

That is, it is acceptable for the honeycomb structure body to have a structure in which the cells2formed in the first cell density section121are inclined by a degree of less than 45 degrees to the cells2formed in the second cell density section122, as shown inFIG. 11(which will be explained later in detail).

From the point of view of obtaining and maintaining an adequately mechanical strength of the honeycomb structure body1, it is preferable that the cells2in the first cell density section121are inclined by 45 degrees to the cells2in the second cell density section122.

The first exemplary embodiment shows the structure of the honeycomb structure body1having the first cell density section121and the second cell density section122. However, the concept of the present invention is not limited by this. For example, it is possible for the honeycomb structure body to have not less than three cell density sections having different cell densities. In the structure having not less than three cell density sections, it can be considered that the cell density of each of the cell density sections is decreased from the central point O to the outer peripheral wall along a radial direction of the honeycomb structure body.

As previously described in detail, the first exemplary embodiment can provide the honeycomb structure body1(test samples E1to E6) having an improved structure and excellent functions capable of preventing occurrence of catalyst clogging and reducing a pressure loss.

Second Exemplary Embodiment

A description will be given of the honeycomb structure body according to the second exemplary embodiment.

The honeycomb structure body according to the second exemplary embodiment (test samples E7to E10, and comparative samples C6to C9) has the first and second cell density sections having different cell densities.

In particular, the first cell density section in the honeycomb structure body (test samples E7to E10, and comparative samples C6to C9) according to the second exemplary embodiment is different in cell density from the first cell density section of the honeycomb structure body according to the first exemplary embodiment (test samples E1to E6, and comparative samples C1to C5). Further, the second cell density section in the honeycomb structure body (test samples E7to E10, and comparative samples C6to C9) according to the second exemplary embodiment is different in cell density from the second cell density section of the honeycomb structure body (test samples E1to E6, and comparative samples C1to C5) according to the first exemplary embodiment.

The second exemplary embodiment produced the honeycomb structure body (the test samples E7to E10and the comparative samples C6and C9) by the same method performed by the first exemplary embodiment previously described.

Other components of the honeycomb structure body according to the second exemplary embodiment are the same as those of the honeycomb structure body previously described. Accordingly, the explanation of the same components is omitted here for brevity.

Similar to Table 1, as previously described, Table 2 shows the detected parameters of each of the test samples E7to E10and the comparative samples C6to C9:

(a1) Cell density (×104cells/m2) of first cell density section;

(a2) Cell density (×104cells/m2) of second cell density section;

(a3) Presence of boundary cell;

(a4) Presence of connection cell

(a5) Minimum diameter D (mm) of inscribed circle in boundary cell (formed by connection cell);

(a6) Radius of curvature (mm) of corner section of boundary cell arranged adjacent to boundary wall;

(a7) Evaluation result in catalyst clogging in cell;

As can be understood from the results shown in Table 2, the honeycomb structure body (test samples E7to E10), like the honeycomb structure body (test samples E1to E6), has an increased mechanical strength, prevents occurrence of catalyst clogging, and reduces its pressure loss when compared in these properties with the comparative samples C6to C9. In other words, the honeycomb structure body (test samples E7to E10) according to the second exemplary embodiment has the same effects as the honeycomb structure body (test samples E1to E6) according to the first exemplary embodiment.

Third Exemplary Embodiment

A description will be given of the honeycomb structure body according to the third exemplary embodiment.

The honeycomb structure body according to the second exemplary embodiment (test samples E11to E14, and comparative samples C10to C13) has two cell density sections, each having a different cell density. In particular, the first cell density section in the honeycomb structure body according to the third exemplary embodiment (test samples E11to E14, and comparative samples C10to C13) is different in cell density from the first cell density section of the honeycomb structure body according to the first and second exemplary embodiment previously described. Further, the second cell density section in the honeycomb structure body according to the third exemplary embodiment (test samples E11to E14, and comparative samples C10to C13) is different in cell density from the second cell density section of the honeycomb structure body according to the first and second exemplary embodiment previously described.

The third exemplary embodiment produced the honeycomb structure body (test samples E11to E14, and comparative samples C10and C13) by the same method performed by the first exemplary embodiment previously described.

Other components of the honeycomb structure body according to the third exemplary embodiment are the same structure as the honeycomb structure body previously explained. Accordingly, the explanation of the same components is omitted here for brevity.

Similar to Table 1 and Table 2, as previously described, Table 3 shows the detected parameters of each of the test samples E11to E14and the comparative samples C10to C13:

(a1) Cell density (×104cells/m2) of first cell density section;

(a2) Cell density (×104cells/m2) of second cell density section;

(a3) Presence of boundary cell;

(a4) Presence of connection cell

(a5) Minimum diameter D (mm) of inscribed circle in boundary cell (formed by connection cell);

(a6) Radius of curvature (mm) of corner section of boundary cell arranged adjacent to boundary wall;

(a7) Evaluation result in catalyst clogging in cell;

As can be shown in Table 3 and clearly understood from the results shown in Table 3, the honeycomb structure body (test samples E11to E14) according to the third exemplary embodiment, like the honeycomb structure body (the test samples E1to E6), has an increased mechanical strength, prevents occurrence of catalyst clogging in the cells, in particular in the boundary cells, and reduces its pressure loss when compared in these properties with the comparative samples C10to C13. In other words, the honeycomb structure body (test samples E11to E14) according to the third exemplary embodiment has the same effects as the honeycomb structure body (test samples E1to E6) according to the first exemplary embodiment.

Fourth Exemplary Embodiment

A description will be given of the honeycomb structure body according to the fourth exemplary embodiment with reference toFIG. 12,FIG. 13and Table 4.

FIG. 12is a view showing a partial cross section in a radial direction of a honeycomb structure body (test sample E15) according to the fourth exemplary embodiment having reinforced partition walls115of a large thickness.FIG. 13is a view showing an enlarged partial cross section in a radial direction of the honeycomb structure body (test sample E15) having the reinforced partition walls115of a large thickness according to the fourth exemplary embodiment shown inFIG. 12.

Specifically, as shown inFIG. 12andFIG. 13, in the structure of the honeycomb structure body (test sample E15) according to the fourth exemplary embodiment, the partition wall115extending to and in contact with the boundary wall14has a thickness T2which is larger than a thickness T1of the partition wall11forming the interior cell122. The partition wall115having the thickness T2will be referred to as the “reinforced partition wall115”.

Other components of the honeycomb structure body (test sample E15) according to the fourth exemplary embodiment are the same of those of the honeycomb structure body previously explained. Accordingly, the explanation of the same components is omitted here for brevity. The honeycomb structure body (test sample E15) has the connection cells211, like the structure of each of the honeycomb structure bodies (test samples E1to E6).

It is possible to produce the test sample E15by the same method of producing the honeycomb structure body (test samples E1to E6according to the first exemplary embodiment) using a metal die having a specific structure in which slit grooves of the metal die corresponding to the reinforced partition walls115have a specific width which is wider than a width of the partition walls11. Each of the partition walls11, other than the reinforced partition walls115, in the test sample E15has the same width of the partition walls in the honeycomb structure body (test samples E1to E6) according to the first exemplary embodiment previously described. Other components of the test sample E15according to the fourth exemplary embodiment are the same as those of the test samples E1to E6according to the first exemplary embodiment. The same components between the test sample E15and the test samples E1to E6are designated by the same reference numbers and characters. The explanation of these same components is omitted for brevity.

The fourth exemplary embodiment produced the test sample E16which has no reinforced partition walls115. Other components of the test sample E16are the same as those of the test sample E15.

Further, the fourth exemplary embodiment evaluated occurrence of catalyst clogging in the boundary cells21of the test sample E15and the test sample E16by using the same method of the first exemplary embodiment previously described. Table 4 shows the evaluation results of the test sample E15and the test sample E16regarding an isostatic strength ratio and a pressure loss ratio to the comparative sample C1.

That is, Table 4 shows the detected parameters of each of the test sample E15, the test sample E16and the comparative sample C1:

(a1) Cell density (×104cells/m2) of first cell density section;

(a2) Cell density (×104cells/m2) of second cell density section;

(a4) Presence of connection cell

(a5) Minimum diameter D (mm) of inscribed circle in boundary cell (formed by connection cell);

(a6) Radius of curvature (mm) of corner section of boundary cell arranged adjacent to boundary wall;

(a7) Evaluation result in catalyst clogging in cell;

As can be shown in Table 4 and clearly understood from the results shown in Table 4, the test sample E15and the test sample E16according to the fourth exemplary embodiment are the same evaluation results in catalyst clogging and pressure loss of the test samples E1to E6according to the first exemplary embodiment. That is, the test samples E15and E16have the connection cells211as the boundary cells21, in which an inscribed circle of the boundary cell21has not less than 0.5 mm, can suppress occurrence of catalyst clogging in cells and reduce its pressure loss when compared with the comparative sample C1having the boundary cell, a diameter of an inscribed circle of which is less than 0.5 mm. In addition, the test sample E15having the reinforced partition walls115having an increased width extending to the boundary wall14has an increased mechanical strength which is larger than that of the test sample E16without any reinforced partition wall. As a result, it is preferable for the honeycomb structure body to have the reinforced partition walls having an increased width which extends to the boundary wall14.

Fifth Exemplary Embodiment

A description will be given of the honeycomb structure body according to the fifth exemplary embodiment with reference toFIG. 14toFIG. 19and Table 5.

FIG. 14is a view showing a partial cross section in a radial direction of the honeycomb structure body (test sample E17) according to the fifth exemplary embodiment having relocated partition walls112.FIG. 15is a view showing an enlarged partial cross section in a radial direction of the honeycomb structure body (test sample E17), shown inFIG. 14.

As previously described in detail, the first to fourth exemplary embodiments explain the honeycomb structure body having the boundary cells having an increased size and a diameter of an inscribed circle of each boundary cell becomes not less than the predetermined value (0.5 mm).

On the other hand, the fifth exemplary embodiment shows the honeycomb structure body having the relocated partition walls112. That is, the common use partition wall111formed between the boundary cell21and the interior cell221which is arranged adjacently to the boundary cell21is relocated, i.e. moved to increase the overall size (or overall area) of the boundary cell21. This makes it possible to increase a diameter of an inscribed cell210of the boundary cell21having an increased size.

As shown inFIG. 14andFIG. 15, in each of the cell density sections121and122in the honeycomb structure body, there is a common use partition wall111formed between the boundary cell21and an adjacent interior cell221. This adjacent interior cell221is arranged in the radial direction adjacently to the boundary cell21. In each of the common use partition walls111as at least some of the common use partition walls111, the relocated partition wall112is formed at a position, which is apart in location from (or offset from) the boundary wall14by a predetermined length. That is, the relocated partition wall112is formed to be offset from a virtual partition wall11A designated by the dotted line shown inFIG. 15. The virtual partition wall11A is formed in the same arrangement pattern of the interior cell22formed in the area having the same cell density in each of the cell density sections121and122in the honeycomb structure body. This makes it possible to increase the diameter D of the inscribed circle210of the boundary cell21having the relocated partition wall112.FIG. 15shows the virtual partition wall11A which is designated by the dotted line and not formed in an actual honeycomb structure body.

In particular, the relocated partition wall112is formed at the same position of the virtual partition wall11A shown inFIG. 4previously described, as well as inFIG. 21andFIG. 23according to a sixth exemplary embodiment which will be explained later.

As shown inFIG. 14, the partition walls11having a rectangle shape are arranged so that each of the cell density sections121and122in the honeycomb structure body has a predetermined cell density. That is, in each of the cell density sections121and122in the honeycomb structure body, a large part of the partition walls11are formed in a predetermined lattice pattern. In addition to this arrangement of the partition walls11, the honeycomb structure body according to the fifth exemplary embodiment has the relocated partition walls112formed in a specific lattice pattern different from the predetermined lattice pattern of the partition walls11. As clearly shown inFIG. 15, each of the relocated partition walls112is formed at the location of the virtual partition wall11A if the relocated partition wall112is formed in the predetermined lattice pattern like the partition walls11. However, if the relocated partition wall112is formed at the location of the virtual partition wall11A, the boundary cell21has a reduced size or area and a diameter D of the inscribed circle of the boundary cell21is reduced, for example, less than 0.5 mm.

In the structure of the honeycomb structure body according to the fifth exemplary embodiment, each of common use partition walls in at least some of the common use partition walls111is relocated as the relocated partition walls112which are apart in location from (or offset from) the boundary wall14. This makes it possible to increase an overall size of each boundary cell21, as shown inFIG. 14andFIG. 15.

Specifically, in each of the cell density sections121and122in the honeycomb structure body, the common use partition wall111is formed at a relocated position in each of the boundary cells21so as to be offset from the boundary wall14, where the common use partition wall111has a reduced size when the common use partition wall111is formed in the predetermined lattice pattern.

The formation of the relocated partition wall112reduces an overall size of the adjacent interior cell221which is formed adjacent to the boundary cell21, On the other hand, the overall size of the boundary cell21can be reduced.

When the boundary cell21has an inscribed circle having a diameter of less than the predetermined value (for example, 0.5 mm) if the virtual partition wall11A is formed in each of the boundary cells21, it is possible for the boundary cell21to have an inscribed circle having a diameter D of not less than the predetermined value by replacing the common use partition wall111with the relocated partition wall112, i.e. by moving the common use partition wall111to the location of the relocated partition wall112which is offset from the boundary wall14.

It is possible to enlarge the size of each of the boundary cells21without reducing the size of the adjacent interior cell221by adjusting the location of forming the relocated partition wall112. Specifically, it is possible for the adjacent interior cell221to have an inscribed circle220having a diameter D1of not less than 0.5 mm and for the boundary cell21to have an inscribed circle210having a diameter D1of not less than 0.5 mm. This structure of the honeycomb structure body makes it possible to prevent occurrence of catalyst clogging in the adjacent interior cells221in addition to the boundary cells21.

Still further, it is possible for each of all of the boundary cells21to have an inscribed circle having a diameter D of not less than the predetermined value (for example, less than 0.5 mm) by combining the formation of the relocated partition wall112with the formation of the connection cell211, like the honeycomb structure body according to the first to fourth exemplary embodiment previously described which forms a part of the boundary cell21by using the connection cell211. For example,FIG. 14andFIG. 15show an example of forming the relocated partition wall112to which the common use partition wall111has relocated and further forming the connection cell211by eliminating the common use partition wall111. This makes it possible to easily increase the diameter D of the inscribed circle210of the boundary cell21to be not less than 0.5 mm, and further to easily increase the diameter of the inscribed circle220of the adjacent interior cell221to be not less than 0.5 mm, for example.

Still further, it is possible to increase the size of the boundary cell to be not less than a predetermined value by forming the relocated partition wall112without using any connection cell211. The relocated partition wall112is formed without using any connection cell211by adjusting a formation pattern of the partition walls11in each of the cell density sections121and122.

Other components of the honeycomb structure body according to the fifth exemplary embodiment are the same as those of the honeycomb structure body according to the first exemplary embodiment previously described. Accordingly, the explanation of the same components is omitted here for brevity.

The fifth exemplary embodiment produced two types of honeycomb structure bodies (test sample E17and comparative sample C14), each of which had the boundary cell21and the inscribed circle210of the boundary cell21had an increased diameter D.

The test sample E17is a honeycomb structure body having the boundary cells21, each of the boundary cells21has the inscribed circle210having the diameter D of not less than 0.5 mm (minimum value is 0.5 mm). On the other hand, the comparative sample C14is a honeycomb structure body having the boundary cells21, each of the boundary cells21has the inscribed circle210having the diameter D of not less than 0.4 mm (minimum value is 0.4 mm).

FIG. 16is a view showing a partial cross section in a radial direction of the honeycomb structure body (test sample E18) according to the fifth exemplary embodiment having the relocated partition walls112of a large thickness extending to the boundary wall14.FIG. 17is a view showing an enlarged partial cross section in a radial direction of the honeycomb structure body according to the fifth exemplary embodiment having the relocated partition walls112of a large thickness extending to the boundary wall14shown inFIG. 6.

The fifth exemplary embodiment further produced a honeycomb structure body (test sample E18), which had the reinforced partition walls115, like the fourth exemplary embodiment previously described. Like the structure of the test sample E17, the test sample E18had the relocated partition walls112in order to increase the diameter D of the inscribed circle210of the boundary cell21to be not less than 0.5 mm. Still further, like the structure of the test sample E15used in the fourth exemplary embodiment, the test sample E18had the reinforced partition walls115extending to the boundary wall14.

The fifth exemplary embodiment further produced honeycomb structure bodies (test sample E19, comparative sample C15, test sample E20and comparative sample C16) having the first cell density section and the second cell density section which are different in cell density from those of the test sample E17and the comparative sample C14. In particular, the test sample E19and the test sample E20had the same structure as the test sample E17excepting the cell density of the first cell density section and the second cell density section. On the other hand, the comparative sample C15and the comparative sample C16had the same structure as the comparative sample C14excepting the cell density of the first cell density section and the second cell density section.

Table 5 shows various parameters and evaluation results of the test samples E17to E20, and the comparative samples C14to C16as follows:

(a1) Cell density (×104cells/m2) of first cell density section;

(a2) Cell density (×104cells/m2) of second cell density section;

(a11) Presence of relocated partition walls;

(a5) Minimum diameter D (mm) of inscribed circle of boundary cell;

(a6) Radius of Curvature (mm) of corner section of boundary cell adjacently and in contact with boundary wall;

(a10) Ratio T2/T1, where T1indicates thickness of partition wall11and T2indicates thickness of partition wall115extending to boundary wall14;

(a7) Evaluation result in catalyst clogging in cell; and

It had been adjusted so that in the test samples E17to E20having the relocated partition walls112and the boundary cells21, the diameter D of the inscribed circle210of the boundary cell21was not less than 0.5 mm, and the inscribed circle220of the adjacent interior cell221had the diameter D1of not less than 0.5 mm (which are omitted from Table 5).

Still further, like the first exemplary embodiment, the fifth exemplary embodiment evaluated each of the test samples E17to E20, and the comparative samples C14to C16regarding the isostatic strength ratio, the catalyst clogging and the pressure loss ratio. Table 5 shows these evaluation results. Further, Table 5 shows the evaluation results and various parameter of the comparative samples C1used in the first exemplary embodiment, the comparative samples C6used in the second exemplary embodiment, and the comparative samples C10used in the third exemplary embodiment.

That is, as can be clearly understood from the results shown in Table 5, the structure of each of the test samples E17to E20, in which the relocated partition walls112are formed and each of the boundary cells21has its inscribed circle having a diameter of not less than 0.5 mm, can suppress reduction of the mechanical strength, occurrence of catalyst clogging in the boundary cells, and reduce its pressure loss.

Even if having a relocated partition walls112as the honeycomb structure body according to the fifth exemplary embodiment, it is possible for a honeycomb structure body to increase its mechanical strength by forming the reinforced partition walls115, like the structure of forming the connection cells in the honeycomb structure body according to the fourth exemplary embodiment.

Further, the fifth exemplary embodiment evaluated the test samples and the comparative samples in optimum thickness ratio T2/T1. Specifically, the thickness of the partition wall115extending to the boundary wall14was changed in each of the samples. Other components of these samples are the same of these of the test sample E17. The fifth exemplary embodiment detected a ratio of the isostatic strength of each of the samples to the isostatic strength of the comparative sample C1. The fifth exemplary embodiment detected a relationship between the ratio T2/T1in thickness (thickness ratio T2/T1) and the isostatic strength.FIG. 18shows the detected relationship.

FIG. 18is a view explaining a relationship between the thickness ratio T2/T1of partition walls and the isostatic strength ratio of the honeycomb structure body according to the fifth exemplary embodiment.

The fifth exemplary embodiment detected a rate of generating molding fault in the test samples and the comparative samples. These samples have the partition walls115having a different thickness and each of the partition walls115is formed to extend to the boundary wall14. Specifically, fifth exemplary embodiment detected the number Naof defects of adjacent interior cells221which are arranged adjacent to the boundary cells21and the total number Nbof the adjacent interior cells221in each of the test samples and the comparative samples. A molding defect was detected on the basis of occurrence of a broken partition wall in the adjacent interior cell and presence of a zigzag pattern in the partition walls11. When such defects (broken parts and zigzag patterns) were generated in the partition walls forming each of the adjacent interior cells221, the number of defects is one.

The fifth exemplary embodiment calculated the generation rate of defect in each sample on the basis of the following equation:
Generation rate of detect=100×Na/Nb.
The fifth exemplary embodiment obtained a relationship between the thickness ratio T2/T1of the partition walls and the calculated generation rate of detect.

FIG. 19is a view explaining a relationship between the thickness ratio T2/T1of the partition walls11and a generation ratio of molding defect in each sample.

The reason why a molding defect is detected on the basis of the condition of the partition walls11of the adjacent interior cells221is as follows:

When a thickness of the partition wall115extending to the boundary wall14is increased, raw material is easily fed to the slit grooves corresponding to the partition walls115(reinforced partition walls) during a molding step in the manufacturing of the honeycomb structure body. As a result, this introduces fluctuation of feeding raw material to slit grooves corresponding to the partition walls of the adjacent interior cells221formed near the partition walls115(reinforced partition walls), and such defects (broken partition walls and zigzag pattern) easily occur.

Further, it can be understood from the result shown inFIG. 18that it is preferable for the honeycomb structure body to have the thickness ratio T2/T1of the partition walls11of not less than 1.52. This structure makes it possible to obtain excellent mechanical strength which is equal to or more the mechanical strength of the comparative sample C1even if the size of the boundary cell is increased to an optimum size which can prevent occurrence of catalyst clogging in the cells having a small size such as the boundary cells. Further, it can be recognized that the honeycomb structure body has the same tendency regarding the thickness ratio T2/T1when having the connection cells, as explained in the fourth exemplary embodiment, and having the inclined partition walls as will be explained later in the sixth exemplary embodiment.

Still further, it can be understood from the result shown inFIG. 19that it is preferable for the honeycomb structure body to have the thickness ratio T2/T1of the partition walls11of not more than 2.5. This structure makes it possible to prevent generation of molding defect in the honeycomb structure body. Further, it can be recognized that the honeycomb structure body has the same tendency regarding the thickness ratio T2/T1when having the connection cells, as explained in the fourth exemplary embodiment, and having the inclined partition walls as will be explained later in the sixth exemplary embodiment.

As previously described in detail, according to the fifth exemplary embodiment, it can be understood to increase the diameter D (mm) of the inscribed circle210of the boundary cell21by forming the relocated partition walls112(seeFIG. 14toFIG. 17). It is possible to produce the honeycomb structure body having an excellent mechanical strength and capable of preventing occurrence of catalyst clogging in cells having a small size such as the boundary cells21and reducing its pressure loss when the diameter D of the inscribe circle210of the boundary cell21is not less than 0.5 mm.

Sixth Exemplary Embodiment

A description will be given of the honeycomb structure body according to the sixth exemplary embodiment with reference toFIG. 20toFIG. 27and Table 6. The sixth exemplary embodiment produced the honeycomb structure body having inclined partition walls113instead of specific common use partition walls in a group which is in at least some of the common use partition walls. The inclined partition wall to be replaced with the specific common use partition wall is formed between the boundary cell111and the adjacent interior cell221. The inclined partition wall113is inclined to the partition wall11which is usually formed.

FIG. 20is a view showing a partial cross section in a radial direction of the honeycomb structure body having the inclined partition walls113connected to the partition walls11according to the sixth exemplary embodiment.FIG. 21is a view showing an enlarged partial cross section in a radial direction of the honeycomb structure body having the inclined partition walls113connected to the partition walls11according to the sixth exemplary embodiment shown inFIG. 20.

That is, as shown inFIG. 20andFIG. 21, the honeycomb structure body according to the sixth exemplary embodiment has the inclined partition walls113instead of the specific common use partition walls in at least some of the common use partition walls. Each inclined partition wall113is inclined to the partition wall11by a predetermined angle. The formation of the inclined partition wall113makes it possible to increase a diameter D of an inscribed circle210of the boundary cell21surrounded by the inclined partition wall113, the partition wall11and the boundary wall14.

A description will now be given of the structure of the honeycomb structure body according to the sixth exemplary embodiment in detail.

In the honeycomb structure body according to the sixth exemplary embodiment shown inFIG. 20, most of the partition walls11are arranged in the predetermined lattice pattern in each of the cell density sections121and122, like the partition walls11in the honeycomb structure body according to the fifth exemplary embodiment.

The honeycomb structure body according to the sixth exemplary embodiment further has the inclined partition wall113arranged in a pattern which is different from the predetermined lattice pattern to arrange the partition walls11which are usually used.

A virtual partition wall11A will be considered. That is, as shown inFIG. 21, the virtual partition wall11A is designated by the dotted lines. The virtual partition wall11A is replaced with the inclined partition wall113which is inclined to the virtual partition wall11A (as the usually-used partition wall11) by a predetermined angle. However, if the boundary cell21is formed by using the virtual partition wall11A, the size of the boundary cell21has a reduced size (or reduced area) when compared with the size of the boundary cell21having the inclined partition wall113which is replaced with the virtual partition wall11A. For example, when using the virtual partition wall11A, the boundary cell21has an inscribed circle having a diameter of less than 0.5 mm because the size of the boundary cell21is reduced by the formation of the virtual partition wall11A. On the other hand, the use of the inclined partition wall113instead of the virtual partition wall11A can increase the size (or area) of the boundary cell21.

In the structure of the honeycomb structure body according to the sixth exemplary embodiment, the specific common use partition walls in at least some of the common use partition walls111are replaced with the inclined partition walls113in order to increase the size (i.e. area) of each of the boundary cells21(seeFIG. 20andFIG. 21). Specifically, in a case where the size of each of specific boundary cells21is reduced when the partition walls11(i.e. virtual partition walls11A) are formed in the predetermined lattice pattern in each of the cell density sections111and122having the same cell density of the interior cells22, the common use partition wall111forming the specific boundary cell21is replaced with the inclined partition walls113in order to increase the size of the specific boundary cell21. The inclined partition wall113is inclined to the virtual partition wall11A by the predetermined angle previously explained.

The formation of the inclined partition wall113instead of the specific common use partition walls makes it possible to increase the size of each of the boundary cells21. Furthermore, it is possible to increase the size of the boundary cell21without reducing the size of the adjacent interior cell221more than necessary by adjusting an inclined angle of the inclined partition wall113to the virtual partition wall11A.

Because the inclined partition wall113is inclined to the partition wall11by a relatively low angle, as shown inFIG. 20andFIG. 21, the inclined partition wall113is in contact directly with the partition wall11, not in contact with the boundary wall14. In this structure shown inFIG. 21, the boundary cell21is formed to be connected directly to the boundary wall14. On the other hand, the adjacent interior cell211is formed apart in location from or offset from the boundary wall14side when viewed from the inclined partition wall113. That is, the adjacent interior cell211is arranged adjacent to the boundary cell21and formed at the opposite side of the boundary wall14side when viewed from the inclined partition wall113shown inFIG. 21.

On the other hand, when the inclined angle of the inclined partition wall113to the virtual partition wall11A is increased, the inclined partition wall113finally becomes in contact directly with the boundary wall14, as shown inFIG. 22andFIG. 23.

FIG. 22is a view showing a partial cross section in a radial direction of the honeycomb structure body having another inclined partition wall which is in contact directly with, i.e. connected to the boundary wall14according to the sixth exemplary embodiment. FIG.23is a view showing an enlarged partial cross section in a radial direction of the honeycomb structure body having the inclined partition wall connected to the boundary wall14shown inFIG. 22.

As shown inFIG. 22andFIG. 23, the inclined partition wall113is in contact with the boundary wall14. In this structure, the boundary cell21is divided into two sections (i.e. into two boundary cells21) by the inclined partition wall113.

As previously described in detail, the common use partition wall111is inclined to form the inclined partition wall113in each of specific boundary cells21, where an inscribed circle210of which has a diameter D of less than the predetermined value (for example, 0.5 mm) when the virtual partition wall11A is formed. This makes it possible for the boundary cell21to have its inscribed circle of not less than the predetermined value (0.5 mm). This structure makes it possible to prevent occurrence of catalyst clogging of the boundary cells21.

Further, it is possible for the honeycomb structure body to have the adjacent interior cell211, a diameter D1of which becomes not less than 0.5 mm by forming the inclined partition wall113. In this structure makes it possible to prevent occurrence of catalyst clogging in the adjacent interior cells211in addition to the boundary cells21.

It is possible for all of the boundary cells21to have the inscribed circle, a diameter D of which becomes not less than the predetermined value by combining the formation of the connection cells211instead of using some of the boundary cells21, like the first to fourth exemplary embodiments previously described, and the formation of the inclined partition wall113disclosed in the sixth exemplary embodiment.

For example,FIG. 20toFIG. 23show the honeycomb structure body showing a structure in which the connection cells211are formed instead of using the common use partition walls111in addition to the inclined partition walls113obtained by inclining the common use partition walls111. It is also possible to increase the size of the boundary cell21which is larger than the predetermined size by forming the inclined partition walls113without using the connection cells211. This structure can be obtained by adjusting the formation pattern of the partition walls11in each of the cell density sections121and122.

Further, it is possible for the honeycomb structure body to have a combination of the inclined partition walls113used in the sixth exemplary embodiment and the relocated partition walls112used in the fifth exemplary embodiment (which are omitted from the drawings).

Other components of the honeycomb structure body according to the sixth exemplary embodiment are the same as those of the honeycomb structure body according to the first exemplary embodiment. Accordingly, the explanation of the same components is omitted here for brevity.

The sixth exemplary embodiment produced a test sample E21and a test sample E22having the inclined partition walls113to increase the diameter D of the inscribed circle of the boundary cell21.

As shown inFIG. 20andFIG. 21, the test sample E21has the inclined partition walls113having a relatively small inclined angle. That is, the inclined partition wall113is in contact with the partition wall11without being in contact with the boundary wall14.

On the other hand, shown inFIG. 22andFIG. 23, the test sample E22has the inclined partition walls113having a relatively large inclined angle. That is, the inclined partition wall113is in contact directly with the boundary wall14.

Still further, the sixth exemplary embodiment produced honeycomb structure bodies as a test sample E23and a test sample E24having the reinforced partition walls115shown inFIG. 24toFIG. 27, like the structure of the honeycomb structure body according to the fourth exemplary embodiment.

FIG. 24is a view showing a partial cross section in a radial direction of a honeycomb structure body (test sample E23) having the inclined partition walls113connected to the partition walls11and the reinforced partition walls115having a large thickness extending to the boundary wall14according to the sixth exemplary embodiment.FIG. 25is a view showing an enlarged partial cross section in a radial direction of a honeycomb structure body (test sample E24) having the inclined partition walls which are in contact with the boundary wall14, like the structure of the test sample E22, and the reinforced partition walls115having a large thickness extending to the boundary wall14according to the sixth exemplary embodiment.

FIG. 26is a view showing a partial cross section in a radial direction of the honeycomb structure body having the inclined partition walls113having a large thickness, which are reinforced, connected directly to the boundary wall14and the reinforced partition walls115having a large thickness extending to the boundary wall14according to the sixth exemplary embodiment.FIG. 27is a view showing an enlarged partial cross section in a radial direction of the honeycomb structure body having the inclined partition walls113having a large thickness connected directly to the boundary wall14and the reinforced partition walls113having a large thickness extending to the boundary wall14, shown inFIG. 26.

Further, the sixth exemplary embodiment produced honeycomb structure bodies as test samples E25to E28having the first cell density section and the second cell density section having a cell density which is different from a cell density of each of the first and second cell density sections of the test sample E21and the test sample E22. The test samples E25and E27have the same structure as the test sample E21except for the cell density of each of the first and second cell density sections. The test samples E26and E28have the same structure as the test sample E22except for the cell density of each of the first and second cell density sections.

Table 6 shows the parameters and evaluation results of the test samples E17to E20, and the comparative samples C14to C16as follows:

(a1) Cell density (×104cells/m2) of first cell density section;

(a2) Cell density (×104cells/m2) of second cell density section;

(a12) Presence of inclined partition walls

(a13) Presence of connection node between inclined partition wall and boundary wall;

(a5) Minimum diameter D (mm) of inscribed circle of boundary cell;

(a6) Radius of Curvature (mm) of corner section of boundary cell adjacently and in contact with boundary wall;

(a10) Ratio T2/T1, where T1indicates thickness of partition wall11and T2indicates thickness of partition wall115extending to boundary wall14;

(a7) Evaluation result in catalyst clogging in cell; and

It had been adjusted that in the test samples E21to E28having the inclined partition walls113and the boundary cells21, the diameter D of the inscribed circle210of the boundary cell21was not less than 0.5 mm, and the inscribed circle220of the adjacent interior cell221had the diameter D1of not less than 0.5 mm (which are omitted from table 6). Still further, like the first exemplary embodiment, the sixth exemplary embodiment evaluated each of the test samples E21to E28regarding the isostatic strength ratio, the catalyst clogging and the pressure loss ratio. Table 6 shows these evaluation results. Further, Table 6 shows the evaluation results and various parameter of the comparative samples C1used in the first exemplary embodiment, the comparative samples C6used in the second exemplary embodiment, and the comparative samples C10used in the third exemplary embodiment.

As can be understood from the results shown in Table 6, the structure of the honeycomb structure body as each of the test samples E21to E28(shown inFIG. 20toFIG. 27), in which the inclined partition walls113are formed and each of the boundary cells21has its inscribed circle having a diameter of not less than 0.5 mm, can suppress reduction of the mechanical strength, occurrence of catalyst clogging in the boundary cells, and reduce its pressure loss.

In addition to the structure of the honeycomb structure body according to the sixth exemplary embodiment having the inclined partition walls113, it is possible to further add the reinforced partition walls115, like the structure of the honeycomb structure body according to the fourth exemplary embodiment having the connection cells211and the structure of the honeycomb structure body according to the fifth exemplary embodiment having the relocated partition walls112. This structure makes it possible to increase the mechanical strength of the honeycomb structure body.

As previously explained in detail, according to the sixth exemplary embodiment, the formation of the inclined partition walls113makes it possible to increase or expand the diameter D of the inscribed circle210of the boundary cell21. This structure makes it possible to provide the honeycomb structure body having a high mechanical strength and capable of preventing occurrence of catalyst clogging in cells having a small size such as the boundary cells21, or generation of catalyst-clogged cells, and reducing its pressure loss.

Seventh Exemplary Embodiment

A description will be given of the honeycomb structure body according to the seventh exemplary embodiment with reference toFIG. 28. Similar to the honeycomb structure body according to each of the first to sixth exemplary embodiments previously described, it can be understood to prevent occurrence of catalyst clogging in the boundary cells21, i.e., generation of catalyst-clogged cells by forming the connection cells211, the relocated partition walls112or inclined partition walls113in order to increase a diameter D of an inscribed circle of each boundary cell21.

The seventh exemplary embodiment evaluates a relationship between a diameter D of an inscribed circle of each boundary cell and a generation rate of catalyst clogging in boundary cells.

FIG. 28is a view explaining the relationship between a diameter D of an inscribed circle of each boundary cell and a generation rate of catalyst clogging in the boundary cells in honeycomb structure bodies having a different diameter D.

Like the method of detecting occurrence of catalyst clogging in cells used in the first exemplary embodiment, the generation rate of catalyst clogging in boundary cells was obtained by counting the number of catalyst-clogged cells to the total number of boundary cells.

As can be understood from the results shown inFIG. 28, the catalyst clogging occurs in the boundary cell when the diameter D of its inscribed circle of the boundary cell becomes less than 0.5 mm. On the other hand, no catalyst clogging occurs in the boundary cell when the diameter D of an inscribed circle of the boundary cell is not less than 0.5 mm. That is, it is possible to prevent generation of catalyst clogging in the boundary cells when an inscribed circle of each boundary cell has a diameter of not less than 0.5 mm.

The honeycomb structure body having the connection cells211, relocated partition walls112or the inclined partition walls113are the same relationship, as shown inFIG. 28, between the diameter D of the inscribed circle of each boundary cell and the generation rate of catalyst clogging in the boundary cells. Further, the adjacent interior cells, previously explained in the fifth exemplary embodiment and the sixth exemplary embodiment, have the same relationship, shown inFIG. 28, between the diameter D of the inscribed circle of each adjacent interior cell and the generation rate of catalyst clogging in the adjacent interior cells. That is, it is possible to prevent occurrence of catalyst clogging in adjacent interior cells when an inscribed circle of the adjacent interior cell has a diameter D1of not less than 0.5 mm.