JP2001096115A - Exhaust gas cleaning apparatus and honeycomb filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the sealing state of through-holes due to a sealing material and to prevent the generation of a crack in the sealing material. SOLUTION: A casing 18 is provided on the exhaust side of a diesel engine 12 and a honeycomb filter 22 for removing particlates in exhaust gas is housed in the casing. A large number of through-holes 25 demarcated by cell walls are formed to the honeycomb filter 22 and the end parts of the through-holes 25 are sealed with a sealing material 31. The the central part of the sealing material 31 is made thinner than the peripheral edge part thereof and the difference between the thickness of the central part of the sealing material 31 and that of the peripheral edge part thereof is set to 0.3-1.0 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus and a honeycomb filter used in the apparatus.

[0002]

2. Description of the Related Art The number of automobiles has increased exponentially since the turn of the century, and the amount of exhaust gas emitted from internal combustion engines of automobiles has been increasing rapidly.
In particular, various substances contained in exhaust gas emitted from a diesel engine cause pollution, and are now seriously affecting the world environment. Also, recently, research results have reported that soot (diesel particulate) in exhaust gas sometimes causes allergic disorders and a decrease in sperm count. In other words, taking measures to remove diesel particulates in exhaust gas is considered to be an urgent task for humanity.

Under such circumstances, various types of exhaust gas purifying devices have been proposed. In a general exhaust gas purifying apparatus, a casing is provided on an exhaust pipe connected to an exhaust manifold of an engine, and a honeycomb filter made of a ceramic sintered body is provided therein. In such a honeycomb filter, a plurality of through-holes are defined by lattice-shaped cell walls. The ends of the through holes are sealed in a checkered pattern with a sealing material.

Here, a conventional method for manufacturing a honeycomb filter will be briefly described. First, a honeycomb formed body is manufactured, and a ceramic sealing paste is prepared. Next, a flexible sealing film is adhered to the entire end face of the honeycomb formed body. In this state, the end surface on the film sticking side is dipped in a sealing paste. Then, the paste flows in through the paste introduction hole provided in the sealing film, and the paste is dried to form a sealing material. Therefore, the end of the through hole is sealed by the sealing material. Thereafter, when the honeycomb formed body is fired, the honeycomb formed body and the sealing material are sintered together,
A honeycomb filter having a large number of cells can be obtained.

[0005]

By the way, immediately after the filling of the sealing paste, the outer end surface of the portion to be the sealing material is usually flat. However, if baking is performed after this, sinks occur due to volatilization or decomposition of the solvent and the like in the sealing paste. Therefore, despite the work being done before firing,
The central portion of the outer end surface of the sealing material is greatly recessed, and a recess is formed there. As a result, there is a problem that a gap is easily formed between the sealing material and the inner wall surface of the through hole, and the sealing material is easily dropped. At the same time, there has been a problem that cracks occur in the sealing material.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to make it possible to improve the sealing state of a through hole by a sealing material and to prevent cracks from occurring in the sealing material. An object of the present invention is to provide an exhaust gas purification device and a honeycomb filter.

[0007]

According to a first aspect of the present invention, there is provided a casing provided on an exhaust side of an internal combustion engine, and a casing accommodated in the casing and having an exhaust gas. And a honeycomb filter that removes the contained particulate matter. The honeycomb filter includes:
In an exhaust gas purifying apparatus having a plurality of through holes defined by cell walls, and an end of each through hole is sealed with a sealing material, a thickness of a peripheral portion of the sealing material that contacts the cell wall. The thickness is set in the range of 1.0 to 6.0 mm, the center of the sealing material is thinner than the peripheral portion, and the difference between the thickness of the central portion of the sealing material and the thickness of the peripheral portion is 0. .3 to 1.0
The gist is that the distance is set in the range of mm.

According to a second aspect of the present invention, in the exhaust gas purifying apparatus according to the first aspect, the gist is that the outer end surface of the sealing material is depressed in a hemispherical concave shape. Claim 3
In the invention described in (1), in the exhaust gas purifying apparatus according to the first or second aspect, the gist is that the sealing material is formed using the same material as the honeycomb filter.

According to the fourth aspect of the invention, the first to third aspects are provided.
In the exhaust gas purifying apparatus according to any one of the above, the gist is that the honeycomb filter and the sealing material are porous silicon carbide sintered bodies.

[0010] In the honeycomb filter according to the fifth aspect of the present invention, there is provided a honeycomb filter having a through hole defined by a plurality of cell walls, and an end of the through hole is sealed by a sealing material. , The thickness of the peripheral portion in contact with the cell wall is set in the range of 1.0 to 6.0 mm, the central portion of the sealing material is thinner than the peripheral portion, and the thickness of the central portion of the sealing material is The point is that the difference between the height and the thickness of the peripheral portion is set in the range of 0.3 to 1.0 mm.

Hereinafter, the "action" of the present invention will be described. According to the first and fifth aspects of the present invention, the difference between the thickness of the central part of the sealing material and the thickness of the peripheral part thereof is 0.3 to 1.0.
mm. Therefore, the sealing state of the through hole by the sealing material can be improved, and cracks can be prevented from being generated in the sealing material. That is, in order to make the difference in thickness less than 0.3 mm, unless the viscosity of the molding material of the sealing material is extremely reduced, a failure that the sealing material protrudes from the adjacent cell wall is caused. If the difference in thickness exceeds 1.0 mm, stress concentrates on the interface between the cell wall and the sealing material or on the center of the sealing material. For this reason, it causes cracks to occur in the sealing material.

According to the second aspect of the present invention, since the outer end surface of the sealing material is depressed in a hemispherical concave shape, it is possible to disperse the stress applied to the central portion of the sealing material. For this reason, generation of cracks in the sealing material can be further prevented.

According to the third aspect of the present invention, since the sealing material is formed using the same type of material as the honeycomb filter, the thermal expansion coefficient of the sealing material is similar to that of the honeycomb filter. Therefore, thermal stress is less likely to occur, and peeling of the sealing material from the honeycomb filter can be prevented.

According to the fourth aspect of the present invention, the honeycomb filter and the sealing material made of the silicon carbide sintered body have excellent heat resistance. The filter and the encapsulant do not deteriorate or burn out. Therefore, efficient exhaust gas purification can be performed over a long period of time.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings. As shown in FIG. 1, the exhaust gas purification device 11 is a device for purifying exhaust gas discharged from a diesel engine 12 as an internal combustion engine. The diesel engine 12 includes a plurality of cylinders (not shown), and each of the cylinders is connected to a branch portion 14 of an exhaust manifold 13 made of a metal material. Each branch 14 is connected to one manifold body 15. Therefore, the exhaust gas discharged from each cylinder is concentrated at one place.

Downstream of the exhaust manifold 13, a first exhaust pipe 16 and a second exhaust pipe 17 made of a metal material are provided. The upstream end of the first exhaust pipe 16 is connected to the manifold body 15. Between the first exhaust pipe 16 and the second exhaust pipe 17, a cylindrical casing 18 also made of a metal material is arranged. The upstream end of the casing 18 is connected to the downstream end of the first exhaust pipe 16, and the downstream end of the casing 18 is connected to the upstream end of the second exhaust pipe 17. It can also be grasped that the casing 18 is provided on the way of the exhaust pipes 16 and 17. As a result, the internal regions of the first exhaust pipe 16, the casing 18, and the second exhaust pipe 17 communicate with each other, and exhaust gas flows therein.

The casing 18 is formed so that the portion other than both ends thereof has a larger diameter than the exhaust pipes 16 and 17. Therefore, the internal region of the casing 18 is
It is wider than the internal areas 6 and 17. A honeycomb filter 22 is accommodated in the casing 18,
Between those outer peripheral surfaces and the inner peripheral surface of the casing 18,
Insulating material layers 23 are respectively provided. Insulation layer 23
Is a mat-like material including a ceramic fiber, and has a thickness of several mm to several tens mm.

As shown in FIGS. 2 and 3, the honeycomb filter 22 is made of a ceramic sintered body (specifically, a porous silicon carbide sintered body). As a sintered body other than silicon carbide, for example, a sintered body such as silicon nitride, alumina, cordierite, and mullite can be selected. The entirety of the honeycomb filter 22 is formed in a columnar shape and a honeycomb shape.

In the honeycomb filter 22, a plurality of through-holes 25 having a substantially square cross section are formed regularly along the axial direction. The opening of each through-hole 25 is sealed by a sealing material 31 on one end face 22a, 22b side, and the end faces 22a, 22b as a whole have a checkered pattern. The sealing material 31 is formed using the same material as the honeycomb filter 22. That is, the sealing material 31
Is made of a porous silicon carbide sintered body. As a sintered body other than silicon carbide, for example, a sintered body such as silicon nitride, alumina, cordierite, and mullite can be selected.

As a result, a large number of cells are formed in the honeycomb filter 22. Of the many cells, about half of the cells are opened at the upstream end face 22a by the sealing material 31, and the remaining cells are opened at the downstream end face 22b. On the inner wall 27 of the cell, an oxidation catalyst comprising a platinum group element, another metal element, an oxide thereof and the like is carried. In this embodiment, the average pore diameter is 14
μm, porosity is 40%, wall thickness of inner wall 3 is 0.3 mm, cell size is 1.5 × 1.5 mm, cell opening area (opening area of through hole 25) is 2.25 mm ² , cell pitch Is set to 1.8 mm.

The sealing material 31 which is a main part of the present embodiment will be described. As shown in FIGS. 4A and 4B, the outer end surface of the sealing material 31 is depressed in a hemispherical concave shape, and is buried in the end surfaces 22a and 22b of the honeycomb filter 22. In short, the central portion 31a of the sealing material 31 is thinner than its peripheral edge 31b, that is, the portion in contact with the cell wall 27.

In terms of specific numerical values of each part of the sealing material 31, the thickness T1 of the peripheral portion 31b of the sealing material 31 is 1.0 to 1.0.
It is set in the range of 6.0 mm. The thickness T2 of the central portion 31a of the sealing material 31 is set in a range of 0.7 to 5.0 mm. Therefore, the difference ΔT between the thickness of the central portion 31a of the sealing material 31 and the thickness of the peripheral portion 31b is 0.3 to 1.0.
mm. In other words, the sealing material 3
The ratio of the thickness T1 of the peripheral portion 31b to the thickness T2 of the central portion 31a is set to 0.7 to 5.0.

Here, the reason why the difference between the thickness of the central portion 31a of the sealing material 31 and the thickness of the peripheral portion 31b is set as described above is as follows. In order to make the thickness difference ΔT less than 0.3 mm, the viscosity of the molding material of the sealing material 31 must be extremely small. If the viscosity is reduced, the sealing material 31 can move from the adjacent cell wall 27 to the through hole 25.
This causes a defect of protruding through the opening. If the thickness difference ΔT exceeds 1.0 mm, the interface between the cell wall 27 and the sealing material 31 or the central portion 31 of the sealing material 31
Stress concentrates on a. For this reason, cracks may occur in the sealing material 31.

Next, a method of manufacturing the sealing material 31 will be described. [Raw Material Adjustment Step] In the present embodiment, the ceramic raw material slurry used in the extrusion molding step and the sealing paste used in the end face sealing step were prepared in advance.

As the ceramic raw material slurry, a mixture obtained by mixing a predetermined amount of an organic binder and water with silicon carbide powder and kneading the mixture was used. As the sealing paste, a mixture obtained by mixing and kneading an organic binder, a lubricant, a plasticizer, and water with silicon carbide powder was used. Further, the viscosity of the sealing paste is in the range of 10,000 to 70000 mPa · S. This is because one of the major factors for keeping the difference ΔT between the thickness of the central portion 31a of the sealing material 31 and the thickness of the peripheral portion 31b within the above-described range (0.3 to 1.0 mm). is there. [Extrusion Forming Step] A honeycomb formed body having a cross-sectional shape was continuously formed by extruding a ceramic raw material slurry using an extruder. The extruded honeycomb formed body was cut into equal lengths using a cutter (not shown). [End face sealing step] As shown in FIGS. 5 and 6, a flexible sealing film 44 made of paper or resin is attached to the entire end face of the obtained honeycomb formed body 41, and A hole to be the paste introduction hole 44a is formed. In this state, the end face side of the film sticking side was dipped in the sealing paste 43. Then, the paste 43 was filled through the paste introduction hole 44a provided in the sealing film 44. As a result, the opening of the through hole 45 was sealed. After that, a paste drying step, a repair step of the sealing material 31, a film peeling step,
After performing the hole correcting step and the like, the honeycomb formed body 41 is fired. [Firing Step] After drying in advance, main firing was performed at a predetermined temperature for a predetermined time, and the honeycomb formed body 41 and the sealing material 31 were completely sintered. As a result, a honeycomb filter 22 having many cells was obtained.

Next, the function of trapping particles by the exhaust gas purifying apparatus 11 will be briefly described. As shown by an arrow in FIG. 1, exhaust gas is supplied to the honeycomb filter 22 housed in the casing 18 from the upstream end face 22 a side. Exhaust gas from the diesel engine 12 first flows into a cell that opens at the upstream end face 22a. Next, the exhaust gas passes through the cell wall 27 and reaches the inside of the cell adjacent thereto, that is, the cell opened at the downstream end face 22b. And
The exhaust gas passes through the honeycomb filter 2 through the opening of the cell.
2 flows out from the downstream end face 22b.

However, the particulates contained in the exhaust gas cannot pass through the cell wall 27 and are trapped there. As a result, the purified exhaust gas is discharged from the downstream end face 22b of the honeycomb filter 22. The purified exhaust gas further passes through the second exhaust pipe 17 and is finally released to the atmosphere. Since the honeycomb filter 22 removes particulates as described above, it is also called a diesel particulate filter (DPF). When the internal temperature of the honeycomb filter 22 reaches a predetermined temperature, the trapped fine particles are ignited by the action of the catalyst and burn.

The exhaust gas purifying apparatus 11 of the present embodiment
In this case, no heating means such as a burner or a heater for regeneration processing is provided on the upstream end face of the honeycomb filter 22. That is, the device 11 employs a spontaneous ignition system. Therefore, the collected diesel particulates are burned only by the heat of the exhaust gas.

Therefore, according to the present embodiment, the following effects can be obtained. (1) The honeycomb filter 22 has a plurality of through-holes 25 defined by cell walls 27, and an end of each through-hole 25 is sealed with a sealing material 31. The thickness of the peripheral portion 31b of the sealing material 31 that contacts the cell wall 27 is 1.0 to
It is set in the range of 6.0 mm. The difference ΔT between the thickness T2 of the central portion 31a of the sealing material 31 and the thickness T1 of the peripheral portion 31b is set in the range of 0.3 to 1.0 mm. Since the thickness difference ΔT between the two portions 31a and 31b of the sealing material 31 is not less than 0.3 mm, the viscosity of the sealing paste 43 for forming the sealing material 31 does not need to be extremely reduced. As a result, the sealing paste 43 does not protrude from the adjacent cell wall 27, and the sealing state of each through hole 25 does not become uneven. Therefore, the honeycomb filter 22
It is possible to reliably prevent defective products from appearing in the manufacture of the. In addition, since the difference ΔT in thickness between the two portions 31a and 31b of the sealing material 31 does not exceed 1.0 mm, the difference between the interface between the sealing material 31 and the cell wall 27 and the central portion 31a of the sealing material 31 is reduced. Almost no stress is concentrated at the location. As a result,
Cracks can be prevented from occurring in the sealing material 31. Further, since there is no possibility that a gap is formed between the sealing material 31 and the cell wall 27, it is possible to prevent the sealing material 31 from falling off.

(2) Since the outer end surface of the sealing material 31 is depressed in a hemispherical concave shape, the stress applied to the central portion 31a of the sealing material 31 can be dispersed. For this reason, cracks can be more reliably prevented from being generated in the sealing material 31.

(3) The sealing material 31 is made of the honeycomb filter 2
2 are formed using the same type of material. Therefore, the sealing material 31 can be approximated to the thermal expansion coefficient of the honeycomb filter 22. As a result, thermal stress is less likely to occur, and peeling of the sealing material 31 from the honeycomb filter 22 can be prevented.

(4) Honeycomb filter 22 and sealing material 3
Since 1 is a porous silicon carbide sintered body, heat resistance can be improved. Therefore, even if the honeycomb filter 22 and the sealing material 31 are disposed in a place where the temperature tends to be high, the honeycomb filter 22 and the sealing material 31 do not deteriorate or burn out.
Therefore, efficient exhaust gas purification can be performed over a long period of time.

The embodiment of the present invention may be modified as follows. -The specific numerical value of each part of the sealing material 31 may be changed as follows. The thickness T1 of the peripheral portion 31b of the sealing material 31 is
It is set in the range of 3.0 to 5.0 mm. The thickness T2 of the central portion 31a of the sealing material 31 is set in a range of 1.0 to 4.0 mm. The difference ΔT between the thickness of the central portion 31a of the sealing material 31 and the thickness of the peripheral portion 31b is 1.0 to 2.0 m.
Set within the range of m.

As shown in FIG. 7, a plurality of honeycomb filter pieces F1 and F2 prepared in advance are bonded with an adhesive to form a honeycomb filter 22.
May be configured. More specifically, in the center of the honeycomb filter 22, a plurality of rectangular honeycomb filter pieces F1 are arranged. The outer dimensions of each honeycomb filter piece F1 are 33 × 33 × 150 here.
mm. Around each honeycomb filter small piece F1, a non-rectangular prism shaped honeycomb filter small piece F
2 are arranged. As a whole, a cylindrical honeycomb filter 22 is formed. Note that an adhesive made of ceramics is used. With this configuration, it is possible to prevent the occurrence of cracks due to the stress caused by the temperature gradient due to heating, and to increase the thermal shock resistance. Therefore, it is particularly effective when the size of the honeycomb filter 22 is increased.

The diesel particulates may not be burned only by the heat of the exhaust gas, but may be burned by heating means such as a burner or a heater. In this case, as shown in FIG. 1, it is preferable that the heating means 19 be disposed upstream of the honeycomb filter 22.

The heat insulating material layer 23 is not limited to a material mainly made of ceramic fibers, but may be a material mainly made of a metal wire or the like. If the exhaust gas having a sufficiently high temperature is supplied to the honeycomb filter 22, the heat insulating layer 23 may be omitted.

As a material for forming the honeycomb filter 22, a material other than the ceramic sintered body, for example, a metal or an alloy can be selected. Next, in addition to the technical ideas described in the claims, technical ideas grasped by the above-described embodiments are listed below together with their effects.

(1) In an exhaust gas purifying apparatus provided with a honeycomb filter having a plurality of through holes defined by cell walls, and an end of each through hole is sealed by a sealing material. A thickness of a peripheral portion of the material contacting the cell wall is set in a range of 1.0 to 6.0 mm; a central portion of the sealing material is thinner than a peripheral portion contacting the cell wall; An exhaust gas purifying apparatus, wherein a ratio of a thickness of a peripheral portion to a thickness of a central portion of the material is set in a range of 0.7 to 5.0. According to this configuration, the same effect as the first aspect is obtained.

(2) In any one of claims 1 to 5, (1), the cross-sectional area of the through hole is 1.50 to 3.00 mm.
An exhaust gas purification device, which is set to ² . (3) The exhaust gas purifying apparatus according to any one of claims 1 to 5, (1), and (2), wherein a heat insulating material layer mainly composed of ceramic fibers is provided on an outer peripheral surface of the honeycomb filter. With this configuration, it becomes difficult for heat to escape from the outer peripheral portion of the honeycomb filter to the casing side,
Less heat loss. Therefore, the occurrence of partial unburned residue in the honeycomb filter can be more reliably avoided.

(4) The honeycomb filter according to any one of (1) to (5), (1) to (3), wherein the outer peripheral surfaces of a plurality of honeycomb filter small pieces made of a porous ceramic sintered body are bonded to each other with a ceramic. An exhaust gas purifying apparatus constituted by adhering using an agent and integrating the respective honeycomb filter pieces. According to this configuration, it is possible to prevent the occurrence of cracks due to the stress caused by the temperature gradient due to heating, and to increase the resistance to thermal shock.

(5) The exhaust gas purifying apparatus according to (4), wherein the ceramic adhesive contains ceramic fibers and silicon carbide powder. With this configuration, since the ceramic adhesive contains ceramic fibers and silicon carbide powder, it not only has excellent heat resistance, but also has a coefficient of thermal expansion similar to that of a honeycomb filter made of a porous silicon carbide sintered body. I have. Therefore, the use of the ceramic adhesive contributes to prevention of breakage of the unit due to application of a large back pressure of the exhaust gas.

(6) The exhaust gas purifying apparatus according to any one of claims 1 to 3 and (1) to (5), wherein a heater for heating the honeycomb filter is provided upstream of the honeycomb filter.

[0043]

As described above in detail, according to the first and fifth aspects of the present invention, it is possible to improve the sealing state of the through hole by the sealing material and to prevent the crack from being generated in the sealing material. Can be prevented.

According to the second aspect of the present invention, the occurrence of cracks in the sealing material can be further prevented. According to the third aspect of the present invention, since thermal stress is less likely to be generated in the sealing material, it is possible to prevent the sealing material from peeling off from the honeycomb filter.

According to the fourth aspect of the present invention, exhaust gas can be efficiently purified over a long period of time.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an exhaust gas purification device according to an embodiment.

FIG. 2 is a sectional view showing a state in which a filter is accommodated in a casing.

FIG. 3 is a side view of the filter.

4A is an enlarged side view of the filter, and FIG. 4B is an enlarged front sectional view of the filter.

FIG. 5 is a schematic cross-sectional view for explaining a method of sealing a honeycomb filter.

FIG. 6 is a schematic cross-sectional view of a honeycomb filter for describing a sealing method following FIG. 5;

FIG. 7 is a side view of a filter according to another embodiment.

[Explanation of symbols]

12 ... diesel engine (internal combustion engine), 18 ... casing, 22 ... honeycomb filter, 25 ... through hole, 27 ...
Cell wall, 31: sealing material, T1: thickness of peripheral portion of sealing material,
T2: thickness at the center of the sealing material, ΔT: difference in thickness.

Claims (5)

[Claims] 1. A casing provided on an exhaust side of an internal combustion engine, and a honeycomb filter housed in the casing and removing particulates contained in exhaust gas, wherein the honeycomb filter is partitioned by cell walls. In the exhaust gas purifying apparatus having a plurality of through holes formed and the end of each through hole is sealed with a sealing material, the thickness of a peripheral portion of the sealing material which is in contact with the cell wall is set to 1. The thickness is set in the range of 0 to 6.0 mm, the central portion of the sealing material is thinner than the peripheral portion, and the difference between the thickness of the central portion and the thickness of the peripheral portion of the sealing material is 0.3 to 1 An exhaust gas purifying device characterized by being set in a range of 0.0 mm. 2. The exhaust gas purifying apparatus according to claim 1, wherein an outer end surface of the sealing material is depressed in a hemispherical concave shape. 3. The exhaust gas purifying apparatus according to claim 1, wherein the sealing material is formed using the same material as the honeycomb filter. 4. The method according to claim 1, wherein the honeycomb filter and the sealing material are porous silicon carbide sintered bodies.
3. The exhaust gas purifying device according to any one of the items 3. 5. A honeycomb filter having a through-hole defined by a plurality of cell walls, and an end of the through-hole sealed with a sealing material, wherein a peripheral edge of the sealing material contacting the cell wall. The thickness of the portion is set in the range of 1.0 to 6.0 mm, the central portion of the sealing material is thinner than the peripheral portion, and the thickness of the central portion of the sealing material and the thickness of the peripheral portion are different. A honeycomb filter, wherein the difference is set in a range of 0.3 to 1.0 mm.