U.S. patent application number 11/489518 was filed with the patent office on 2006-11-09 for exhaust gas purifying filter with reinforced peripheral area and method for manufacturing the same.
This patent application is currently assigned to DENSO CORPORATION. Invention is credited to Mikio Ishihara, Mamoru Nishimura.
Application Number | 20060249888 11/489518 |
Document ID | / |
Family ID | 32044689 |
Filed Date | 2006-11-09 |
United States Patent
Application |
20060249888 |
Kind Code |
A1 |
Ishihara; Mikio ; et
al. |
November 9, 2006 |
Exhaust gas purifying filter with reinforced peripheral area and
method for manufacturing the same
Abstract
An exhaust gas purifying filter having a high strength and an
excellent efficiency of exhaust gas purification and a method for
manufacturing the same are provided. An exhaust gas purifying
filter 1 comprises a ceramic honeycomb structure 2 having a
surrounding wall 21, partition walls 22 provided in a honeycomb
pattern within the surrounding wall 21, and a plurality of cells 23
partitioned by the partition walls 22 and penetrating through end
faces 241, 242. If a virtual line 3 is drawn on the end faces 241,
242 of the structure 2 by continuously connecting points at a
distance of 1.0 to 3.0 times the cell pitch in the direction toward
the center from an inner surface 211 of the surrounding wall 21,
not less than 90% of a peripheral area 25 outside the virtual line
3 is blocked with plug material 4.
Inventors: |
Ishihara; Mikio;
(Kariya-city, JP) ; Nishimura; Mamoru;
(Nagoya-city, JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
DENSO CORPORATION
|
Family ID: |
32044689 |
Appl. No.: |
11/489518 |
Filed: |
July 20, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10681133 |
Oct 9, 2003 |
7101601 |
|
|
11489518 |
Jul 20, 2006 |
|
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Current U.S.
Class: |
264/630 |
Current CPC
Class: |
B01D 46/2429 20130101;
B28B 11/007 20130101; F01N 3/0222 20130101; Y02T 10/12 20130101;
Y10T 428/24149 20150115; B01D 46/2474 20130101; Y10T 428/24793
20150115; Y10T 428/24157 20150115; C04B 2111/00793 20130101; C04B
38/0006 20130101; Y10T 428/24777 20150115; B01D 46/2459 20130101;
B01D 46/2451 20130101; B01D 2046/2433 20130101; B28B 11/006
20130101; B01D 46/2455 20130101; Y10T 428/131 20150115; Y10T
428/24744 20150115; B01D 46/2466 20130101; F01N 2330/06 20130101;
Y02T 10/20 20130101; C04B 38/0006 20130101; C04B 35/195 20130101;
C04B 38/0009 20130101 |
Class at
Publication: |
264/630 |
International
Class: |
C04B 33/32 20060101
C04B033/32; C04B 35/64 20060101 C04B035/64; B28B 1/00 20060101
B28B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 15, 2002 |
JP |
2002-300828 |
Sep 8, 2003 |
JP |
2003-315831 |
Claims
1. A method for manufacturing an exhaust gas purifying filter
comprising: a forming process for forming a ceramic honeycomb
structure having a surrounding wall, partition walls provided in a
honeycomb pattern within the surrounding wall, and a plurality of
cells partitioned by the partition walls and, at the same time,
penetrating through from one end face of the ceramic honeycomb
structure to the other; a masking process for pasting mask tapes to
the entire end faces of the ceramic honeycomb structure; a drilling
process in which a virtual line is drawn by continuously connecting
points at a distance of 1.0 to 3.0 times the pitch of the cells in
the direction toward the center from the inner surface of the
surrounding wall, and at least the mask tape pasted to the openings
of the cells through which the virtual line passes and the openings
of the cells outside the virtual line is drilled; and a plugging
process in which not less than 90% of the peripheral area outside
the virtual line is blocked with plug material after dipping the
end faces into the plug material paste and forming the plug
material in the openings of the cells other than those blocked with
the mask tape.
2. A method for manufacturing an exhaust gas purifying filter, as
set forth in claim 1, wherein as for part of the mask tape pasted
to the openings of the cells within the virtual line, the part of
the mask tape pasted to one of two neighboring openings of the
cells is drilled in the drilling process.
3. A method for manufacturing an exhaust gas purifying filter
comprising: a forming process for forming a ceramic honeycomb
structure having a surrounding wall, partition walls provided in a
honeycomb pattern within the surrounding wall, and a plurality of
cells partitioned by the partition walls and, at the same time,
penetrating through from one end face of the ceramic honeycomb
structure to the other; a masking process in which a virtual line
is drawn on the end face of the ceramic honeycomb structure by
continuously connecting points at a distance of 1.0 to 3.0 times
the pitch of the cells in the direction toward the center from the
inner surface of the surrounding wall and a mask tape is pasted to
the central area within the virtual line; and a plugging process in
which not less than 90% of the peripheral area outside the virtual
line is blocked with plug material after dipping the end faces into
the plug material paste and forming the plug material in the
openings of the cells other than those blocked with the mask
tape.
4. A method for manufacturing an exhaust gas purifying filter, as
set forth in claim 3, wherein the drilling process is carried out
for drilling at least the mask tape covering the openings of the
cells through which the virtual line passes after the making
process and before the plugging process.
5. A method for manufacturing an exhaust gas purifying filter
comprising: a forming process for forming a ceramic honeycomb
structure having a surrounding wall, partition walls provided in a
honeycomb structure within the surrounding wall, and a plurality of
cells partitioned by the partition walls and, at the same time,
penetrating through from one end face of the ceramic honeycomb
structure to the other; a masking process for pasting mask tapes to
the entire end faces of the ceramic honeycomb structure; a cutting
process in which a virtual line is drawn on the end face by
continuously connecting points at a distance of 1.0 to 3.0 times
the pitch of the cells in the direction toward the center from the
inner surface of the surrounding wall, and the mask tape pasted to
the peripheral area outside the virtual line is cut and removed;
and a plugging process in which not less than 90% of the peripheral
area outside the virtual line is blocked with plug material after
dipping the end faces into the plug material paste and forming the
plug material in the openings of the cells other than those blocked
with the mask tape.
6. A method for manufacturing an exhaust gas purifying filter, as
set forth in claim 5, wherein a drilling process is carried out for
drilling at least the mask tape covering the openings of the cells
through which the virtual line passes after the cutting process and
the before the plugging process.
7. A method for manufacturing an exhaust gas purifying filter
comprising: a forming process for forming a ceramic honeycomb
structure having a surrounding wall, partition walls arranged in a
honeycomb pattern within the surrounding wall, and a plurality of
cells partitioned by the partition walls and, at the same time,
penetrating through from one end of the ceramic honeycomb structure
to the other; a masking process for pasting mask tapes to the
entire end faces of the ceramic honeycomb structure; a cutting
process in which a virtual line is drawn on the end face by
continuously connecting points at a distance of 1.0 to 3.0 times
the pitch of cells in the direction toward the center from the
inner surface of the surrounding wall, and the mask tape is cut
along the partition walls of the cells through which the virtual
line passes and, at the same time, the mask tape outside the
virtual line is removed; and a plugging process in which not less
than 90% of the peripheral area outside the virtual line is blocked
with plug material after dipping the end faces into the plug
material paste and forming the plug material in the openings of the
cells other than those blocked with the mask tape.
8. A method for manufacturing an exhaust gas purifying filter, as
set forth in claim 3, wherein as for the mask tape pasted to the
openings of the cells within the virtual line, the mask tape pasted
to one of two neighboring openings of the cells is drilled after
the masking process and before the plugging process.
9. A method for manufacturing an exhaust gas purifying filter, as
set forth in claim 5, wherein as for the mask tape pasted to the
openings of the cells within the virtual line, the mask tape pasted
to one of two neighboring openings of the cells is drilled after
the masking process and before the plugging process.
10. A method for manufacturing an exhaust gas purifying filter, as
set forth in claim 7, wherein as for the mask tape pasted to the
openings of the cells within the virtual line, the mask tape pasted
to one of two neighboring openings of the cells is drilled after
the masking process and before the plugging process.
11. A method for manufacturing an exhaust gas purifying filter, as
set forth in claim 1, wherein the virtual line is a line drawn by
continuously connecting points at a distance of 1.0 to 2.0 times
the pitch of the cells in the direction toward the center from the
inner surface of the surrounding wall.
12. A method for manufacturing an exhaust gas purifying filter, as
set forth in claim 1, wherein the partition wall has a thickness of
0.25 to 0.40 mm.
13. A method for manufacturing an exhaust gas purifying filter, as
set forth in claim 3, wherein the virtual line is a line drawn by
continuously connecting points at a distance of 1.0 to 2.0 times
the pitch of the cells in the direction toward the center from the
inner surface of the surrounding wall.
14. A method for manufacturing an exhaust gas purifying filter, as
set forth in claim 3, wherein the partition wall has a thickness of
0.25 to 0.40 mm.
15. A method for manufacturing an exhaust gas purifying filter, as
set forth in claim 5, wherein the virtual line is a line drawn by
continuously connecting points at a distance of 1.0 to 2.0 times
the pitch of the cells in the direction toward the center from the
inner surface of the surrounding wall.
Description
[0001] This application is a division of application Ser. No.
10/681,133 filed Oct. 9, 2003, the entire contents of which is
hereby incorporated by reference in this application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an exhaust gas purifying
filter for purifying an exhaust gas, by collecting particulates
from the exhaust gas of an internal combustion engine, and a method
for manufacturing the same.
[0004] 2. Description of the Related Art
[0005] Conventionally, an exhaust gas purifying filter having a
ceramic honeycomb structure acts as an exhaust gas purifying
filter, for purifying an exhaust gas, by collecting particulates
from the exhaust gas of an internal combustion engine.
[0006] The ceramic honeycomb structure comprises a surrounding
wall, partition walls provided in a honeycomb pattern within the
surrounding wall, and a plurality of cells partitioned by the
partition walls and, at the same time, penetrating through from one
end face of the ceramic honeycomb structure to the other.
[0007] In order to improve the efficiency of purification of the
exhaust gas purifying filter, it is desired to make the partition
walls thinner and to increase the porosity in the surrounding wall
and the partition walls. However, if the partition wall is made
thinner and the porosity is increased, the mechanical strength of
the ceramic honeycomb structure is reduced. Therefore, a problem
arises that the end portions of the ceramic honeycomb structure
become more likely to fracture when catalysts are provided, when
the structure is attached to an internal combustion engine, or the
like.
[0008] In order to solve this problem, a ceramic honeycomb
structure, whose cells in the vicinity of the peripheral portion
are filled with plug material, has been proposed (for example,
refer to Patent References 1 and 2).
[0009] [Patent Reference 1]
[0010] Japanese Examined Patent Publication (Kokoku) No.
63-12658
[0011] [Patent Reference 2]
[0012] Japanese Unexamined Patent Publication (Kokai) No.
7-246341
[0013] However, no definition is given as to the range of the
peripheral area to be filled with the plug material in the
conventional ceramic honeycomb structure. If the range of the
peripheral area to be filled with the plug material is too large, a
problem arises that the exhaust gas filtration area decreases and,
at the same time, the pressure loss increases. On the other hand,
if the peripheral area to be filled with the plug material is too
small, it is not possible to secure a sufficient strength of the
ceramic honeycomb structure.
[0014] Therefore, it is difficult to obtain an exhaust gas
purifying filter having a high strength and an excellent efficiency
of purification only by filling the vicinity of the peripheral
portion with plug material.
SUMMARY OF THE INVENTION
[0015] The present invention has been developed with the
above-problem being taken into consideration and the object is to
provide an exhaust gas purifying filter having a high strength and
an excellent efficiency of exhaust gas purification and a method
for manufacturing the same.
[0016] An exhaust gas purifying filter according to a first aspect
of the present invention has a ceramic honeycomb structure
comprising: a surrounding wall; partition walls provided in a
honeycomb pattern within the surrounding wall; and a plurality of
cells partitioned by the partition walls and, at the same time,
penetrating through from one end face of the ceramic honeycomb
structure to the other. If a virtual line is drawn on the both end
faces of the ceramic honeycomb structure by continuously connecting
points at a distance of 1.0 to 3.0 times the pitch of the cells
(cell pitch) in the direction toward the center from the inner
surface of the surrounding wall, not less than 90% of the
peripheral area outside the virtual line is blocked with plug
material.
[0017] Next, the operation/working-effect of the present invention
is described.
[0018] In the ceramic honeycomb structure, as described above, not
less than 90% of the peripheral area of both end faces is blocked
with plug material.
[0019] Therefore, the peripheral portions of both end faces of the
above-mentioned ceramic honeycomb structure are reinforced.
Moreover, as the above-mentioned virtual line is drawn by
continuously connecting points at a distance of not less than 1.0
times the cell pitch in the direction toward the center from the
inner surface of the surrounding wall, the width of the peripheral
area to be plugged with the plug material is not less than 1.0
times the cell pitch. Because of this, sufficient strength of the
ceramic honeycomb structure can be secured. Due to this, it is
possible to prevent a fracture from occurring when the exhaust gas
purifying filter is manufactured, handled, and so forth.
[0020] Moreover, as the above-mentioned virtual line is drawn by
continuously connecting points at a distance of not more than 3.0
times the cell pitch in the direction toward the center from the
inner surface of the surrounding wall, the width of the peripheral
area to be plugged with the plug material is not more than 3.0
times the cell pitch. Because of this, in the exhaust gas purifying
filter, the area of the peripheral area through which an exhaust
gas cannot pass can be reduced sufficiently. Due to this, it is
possible to secure the exhaust gas filtration area and, at the same
time, to suppress the pressure loss in the exhaust gas. Therefore,
it is possible to obtain an exhaust gas purifying filter having an
excellent efficiency of purification.
[0021] As described above, according to the present invention, it
is possible to obtain an exhaust gas purifying filter having a high
strength and an excellent efficiency of exhaust gas
purification.
[0022] A method for manufacturing an exhaust gas purifying filter
according to a second aspect of the present invention comprises: a
forming process for forming a ceramic honeycomb structure having a
surrounding wall, partition walls provided in a honeycomb pattern
within the surrounding wall, and a plurality of cells partitioned
by the partition walls and, at the same time, penetrating through
from one end face of the ceramic honeycomb structure to the other;
a masking process for pasting mask tapes to the entire end faces of
the ceramic honeycomb structure; a drilling process in which a
virtual line is drawn by continuously connecting points at a
distance of 1.0 to 3.0 times the pitch of the cells (cell pitch) in
the direction toward the center from the inner surface of the
surrounding wall and at least the mask tape pasted to the openings
of the cells through which the virtual line passes and the openings
of the cells outside the virtual line is drilled; and a plugging
process in which not less than 90% of the peripheral area outside
the virtual line is blocked with plug material after dipping the
end faces into the plug material paste and forming the plug
material in the openings of the cells other than those blocked with
the mask tape.
[0023] According to the present manufacturing method, it is
possible to form plug material in the peripheral area of the
ceramic honeycomb structure both easily and securely.
[0024] Therefore, according to the second aspect of the present
invention described above, it is possible to easily and surely
manufacture an exhaust gas purifying filter having a high strength
and an excellent efficiency of exhaust gas purification.
[0025] A method for manufacturing an exhaust gas purifying filter
according to a third aspect of the present invention comprises: a
forming process for forming a ceramic honeycomb structure having a
surrounding wall, partition walls provided in a honeycomb pattern
within the surrounding wall, and a plurality of cells partitioned
by the partition walls and, at the same time, penetrating through
from one end face of the ceramic honeycomb structure to the other;
a masking process in which a virtual line is drawn on the end face
of the ceramic honeycomb structure by continuously connecting
points at a distance of 1.0 to 3.0 times the pitch of the cells
(cell pitch) in the direction toward the center from the inner
surface of the surrounding wall and a mask tape is pasted to the
central area within the virtual line; and a plugging process in
which not less than 90% of the peripheral area outside the virtual
line is blocked with plug material after dipping the end faces into
the plug material paste and forming the plug material in the
openings of the cells other than those blocked with the mask
tape.
[0026] According to the present manufacturing method, it is
possible to form plug material in the peripheral area without
drilling the mask tape in the peripheral area because the mask tape
is not pasted to the peripheral area. Therefore, the number of
man-hours can be reduced and it is possible to easily manufacture
an exhaust gas purifying filter and, at the same time, reduce the
manufacturing cost.
[0027] A method for manufacturing an exhaust gas purifying filter
according to a fourth aspect of the present invention comprises: a
forming process for forming a ceramic honeycomb structure having a
surrounding wall, partition walls provided in a honeycomb pattern
within the surrounding wall, and a plurality of cells partitioned
by the partition walls and, at the same time, penetrating through
from one end face of the ceramic honeycomb structure to the other;
a masking process for pasting mask tapes to the entire end faces of
the ceramic honeycomb structure; a cutting process in which a
virtual line is drawn on the end face by continuously connecting
points at a distance of 1.0 to 3.0 times the pitch of the cells
(cell pitch) in the direction toward the center from the inner
surface of the surrounding wall, and the mask tape pasted to the
peripheral area outside the virtual line is cut and removed; and a
plugging process in which not less than 90% of the peripheral area
outside the virtual line is blocked with plug material after
dipping the end faces into the plug material paste and forming the
plug material in the openings of the cells other than those blocked
with the mask tape.
[0028] According to the present manufacturing method, it is easy to
paste mask tapes to the end faces of the ceramic honeycomb
structure because an exact positional alignment of the mask tape is
not necessary. Therefore, according to the fourth aspect of the
present invention described above, it is possible to easily
manufacture an exhaust gas purifying filter having a high strength
and an excellent efficiency of exhaust gas purification.
[0029] A method for manufacturing an exhaust gas purifying filter
according to a fifth aspect of the present invention comprises: a
forming process for forming a ceramic honeycomb structure having a
surrounding wall, partition walls arranged in a honeycomb pattern
within the surrounding wall, and a plurality of cells partitioned
by the partition walls and, at the same time, penetrating through
from one end face of the ceramic honeycomb structure to the other;
a masking process for pasting mask tapes to the entire end faces of
the ceramic honeycomb structure; a cutting process in which a
virtual line is drawn on the end face by continuously connecting
points at a distance of 1.0 to 3.0 times the pitch of the cells
(cell pitch) in the direction toward the center from the inner
surface of the surrounding wall, and the mask tape is cut along the
partition walls of the cells through which the virtual line passes
and, at the same time, the mask tape outside the virtual line is
removed; and a plugging process in which not less than 90% of the
peripheral area outside the virtual line is blocked with plug
material after dipping the end faces into the plug material paste
and forming the plug material in the openings of the cells other
than those blocked with the mask tape.
[0030] According to the present manufacturing method, by removing
even the mask tape that covers the specified cells through which
the virtual line passes, it is possible to open the entire openings
of the specified cells. Therefore, it is possible to form the plug
material in the entire openings of the specified cells through
which the virtual line passes.
[0031] Moreover, it is not necessary to drill the mask tape in the
openings of the cells through which the virtual line passes.
[0032] Therefore, according to the fifth aspect of the present
invention, it is possible to easily manufacture an exhaust gas
purifying filter having a high strength and an excellent efficiency
of exhaust gas purification.
[0033] In the first aspect of the present invention described
above, the cell pitch is defined by the following expression (1) 1
pitch=25.4/(number of meshes).sup.1/2 (1) where, the number of
meshes is the number of cells within a square with the side of 25.4
mm.
[0034] Therefore, if the cell has a square section, the length of 1
pitch is equal to the length of one side of the cell plus the
thickness of the partition wall.
[0035] Moreover, the percentage 90% of the peripheral area to be
blocked with the plug material is on the basis of the total area of
the openings of the cells contained in the peripheral area.
[0036] It is also possible to block a partial area or the whole
area of the opening of each cell, through which the virtual line
passes, with the plug material.
[0037] It makes the manufacturing process more simple to block a
partial area of the opening of each cell with the plug material.
When the whole area of the opening of each cell is blocked with the
plug material, an exhaust gas purifying filter having a higher
strength can be obtained.
[0038] It is possible to use a ceramic honeycomb structure having
the surrounding wall and the partition walls with a porosity of not
less than 50%.
[0039] In this case, the exhaust gas filtration area and the
catalyst carrying area are increased and it is possible to obtain
an exhaust gas purifying filter having a high efficiency of
purification.
[0040] When the porosity is less than 50%, it is likely that the
efficiency of exhaust gas purification cannot be improved
sufficiently.
[0041] It is preferable for the surrounding wall to have a
thickness of 0.2 to 0.8 mm.
[0042] In this case, it is possible to secure the strength and the
efficiency of exhaust gas purification of the exhaust gas purifying
filter.
[0043] When the thickness is less than 0.2 mm, it is likely that a
sufficient strength of the exhaust gas purifying filter cannot be
secured. On the other hand, when the thickness exceeds 0.8 mm, it
is likely that the exhaust gas filtration area is decreased and, at
the same time, the pressure loss is increased, therefore, a
sufficient efficiency of exhaust gas purification cannot be
secured.
[0044] It is preferable that the ceramic honeycomb structure is
made of cordierite.
[0045] In this case, it is possible to form a ceramic honeycomb
structure having a surrounding wall and partition walls with a
desired porosity both easily and inexpensively.
[0046] The exhaust gas purifying filter may be used for a diesel
engine and purifies the exhaust gas discharged from the diesel
engine and there may mixedly exist both openings of the cells
provided with the plug material and those of the cells not provided
with the plug material in such a way that they are arranged
alternately in the central area within the virtual line on the end
face of the ceramic honeycomb structure.
[0047] In this case, it is possible to provide an exhaust gas
purifying filter for a diesel engine having a high strength and an
excellent efficiency of exhaust gas purification.
[0048] It is preferable that the virtual line is a line drawn by
continuously connecting points at a distance of 1.0 to 2.0 times
the cell pitch in the direction toward the center from the inner
surface of the surrounding wall.
[0049] In this case, it is possible to maintain a sufficient
strength of the ceramic honeycomb structure and, at the same time,
to obtain an exhaust gas purifying filter having an excellent
efficiency of purification (refer to the seventh embodiment).
[0050] It is preferable that the partition wall has a thickness of
0.25 to 0.40 mm.
[0051] In this case, it is possible to collect abundant
particulates from an exhaust gas and, at the same time, to reduce
the pressure loss of the exhaust gas. Therefore, it is possible to
obtain an exhaust gas purifying filter having a more excellent
purification efficiency.
[0052] When the thickness of the partition wall is less than 0.25
mm, the particulates are likely to escape through the partition
wall and there is the possibility that the particulate collection
efficiency decreases. On the other hand, when the thickness of the
partition wall exceeds 0.40 mm, there is the possibility that the
pressure loss of the exhaust gas increases (refer to the eighth
embodiment).
Seventh Embodiment
[0053] In the present embodiment, as shown in FIG. 18, a
relationship between the width of the peripheral area blocked with
plug material and the rate of rise in pressure loss, and between
that and the depth of fracture, of the exhaust gas purifying filter
is assessed.
[0054] In other words, test samples, including those whose widths
of the peripheral area to be plugged are one cell pitch, two cell
pitches, three cell pitches and four cell pitches, respectively,
and one whose peripheral area is not plugged, are prepared.
[0055] Next, in the second aspect of the present invention, it is
possible to carry out the masking process, the drilling process and
the plugging process for both end faces of the ceramic honeycomb
structure, respectively.
[0056] In the drilling process, as for the mask tape pasted to the
openings of the cells within the virtual line, it is also possible
to drill the mask tape pasted to one of two neighboring openings of
the cells.
[0057] In this case, there mixedly exist both openings of the cells
provided with the plug material and those of the cells not provided
with the plug material in such a way that they are arranged
alternately in the central area within the virtual line on the end
face of the ceramic honeycomb structure. As a result, it is
possible to obtain an exhaust gas purifying filter for a diesel
engine having a high strength and an excellent efficiency of
exhaust gas purification.
[0058] Next, in the third aspect of the present invention, it is
preferable to carry out the drilling process for drilling at least
the mask tape that covers the openings of the cells through which
the virtual line passes after the masking process and before the
plugging process.
[0059] In this case, it is possible to form the plug material even
in all of the openings of the cells through which the virtual line
passes. Therefore, it is possible to obtain an exhaust gas
purifying filter having a higher strength.
[0060] In the fourth aspect of the present invention, it is
preferable to carry out the drilling process for drilling at least
the mask tape that covers the openings of the cells through which
the virtual line passes after the cutting process and before the
plugging process.
[0061] In this case, it is possible to form the plug material even
in all of the openings of the cells through which the virtual line
passes. Therefore, it is possible to obtain an exhaust gas
purifying filter having a higher strength.
[0062] In the third aspect or the fourth aspect of the present
invention, as for the mask tape pasted to the openings of the cells
within the virtual line, it is possible to drill the mask tape
pasted to one of two neighboring openings of the cells after the
masking process and before the plugging process.
[0063] In this case, there mixedly exist both openings of the cells
provided with the plug material and those of the cells not provided
with the plug material in such a way that they are arranged
alternately in the central area within the virtual line on the end
face of the ceramic honeycomb structure. As a result, it is
possible to obtain an exhaust gas purifying filter for a diesel
engine having a high strength and an excellent efficiency of
exhaust gas purification.
[0064] The present invention may be more fully understood from the
description of the preferred embodiments of the invention set forth
below, together with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0065] In the drawings:
[0066] FIG. 1 is a front view of an exhaust gas purifying filter in
a first embodiment of the present invention.
[0067] FIG. 2 is a perspective view of the exhaust gas purifying
filter in the first embodiment.
[0068] FIG. 3 is a sectional view of the exhaust gas purifying
filter in the direction in which a cell penetrates through in the
first embodiment.
[0069] FIG. 4 is a front view of the opening of a cell in the first
embodiment.
[0070] FIG. 5 is an explanatory perspective view that illustrates a
state in which a mask tape is pasted to a ceramic honeycomb
structure in the first embodiment.
[0071] FIG. 6 is an explanatory perspective view that illustrates
how the position of the mask tape to be drilled is detected in the
first embodiment.
[0072] FIG. 7 is an explanatory perspective view that illustrates
how the mask tape pasted to the ceramic honeycomb structure is
drilled, in the first embodiment.
[0073] FIG. 8 is an explanatory sectional view that illustrates a
state in which the end face of the ceramic honeycomb structure is
dipped into the slurry of plug material, in the first
embodiment.
[0074] FIG. 9 is an explanatory sectional view that illustrates a
state after dipping, in the first embodiment.
[0075] FIG. 10 is an explanatory sectional view that illustrates a
state in which the other end face of the ceramic honeycomb
structure is dipped into the slurry of the plug material, in the
first embodiment.
[0076] FIG. 11 is an explanatory sectional view that illustrates a
state after both end faces of the ceramic honeycomb structure are
dipped, in the first embodiment.
[0077] FIG. 12 is a front view of a ceramic honeycomb structure to
whose end face a mask tape is pasted in a second embodiment of the
present invention.
[0078] FIG. 13 is an explanatory view that illustrates a state in
which the mask tape is drilled in the second embodiment of the
present invention.
[0079] FIG. 14 is a front view of an exhaust gas purifying filter
in a third embodiment of the present invention.
[0080] FIG. 15 is an explanatory view that illustrates a state in
which a mask tape pasted to the end face of a ceramic honeycomb
structure is cut in a fifth embodiment of the present
invention.
[0081] FIG. 16 is an explanatory view of a fracture test method in
a sixth embodiment of the present invention.
[0082] FIG. 17 is a graph that shows the test results in the sixth
embodiment.
[0083] FIG. 18 is a graph that shows the measurement results in the
seventh embodiment.
[0084] FIG. 19 is a graph that shows the measurement results in the
eighth embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
[0085] The exhaust gas purifying filter and the method for
manufacturing the same according to the present invention are
described below by using FIG. 1 to FIG. 11.
[0086] As shown in FIG. 1 to FIG. 3, an exhaust gas purifying
filter 1 has a ceramic honeycomb structure 2 comprising a
surrounding wall 21, partition walls 22 arranged in a honeycomb
pattern within the surrounding wall 21, and a plurality of cells 23
partitioned by the partition walls 22 and, at the same time,
penetrating through both end faces 241 and 242.
[0087] On both end faces 241 and 242 of the ceramic honeycomb
structure 2, if a virtual line 3 is drawn by continuously
connecting points at a distance of 1.0 to 3.0 times the cell pitch
in the direction toward the center from an inner surface 211 of the
surrounding wall 21, not less than 90% of a peripheral area 25
outside the virtual line 3 are blocked with plug material 4, as
shown in FIG. 1.
[0088] The definition of the cell pitch is defined by the
above-mentioned expression (1), and in the present embodiment, as
shown in FIG. 4, as the section of the cell 23 is square the length
of a pitch is equal to the length a of a side of the cell 23 plus
the thickness b of the partition wall 22.
[0089] In concrete terms, the length a of the side of the cell 23
described above is 1.07 to 1.27 mm, and the thickness b of the
partition wall 22 is 0.25 to 0.35 mm. Therefore, the pitch is 1.32
to 1.62 mm.
[0090] The surrounding wall 21 has a thickness of 0.2 to 0.8 mm.
The plug material 4 is plugged into an opening 231 of the cell 23
to a depth of 1 to 6 mm from the end faces 241 and 242.
[0091] The above-mentioned ceramic honeycomb structure 2 has the
surrounding wall 21 and the partition walls 22 with a porosity of
not less than 50%.
[0092] Moreover, the ceramic honeycomb structure 2 is made of
cordierite. The plug material 4 is also made of cordierite.
[0093] The exhaust gas purifying filter 1 is one for a diesel
engine for purifying an exhaust gas discharged from a diesel
engine. As shown in FIG. 1 and FIG. 3, in a central area 26 within
the above-mentioned virtual line 3 on the end faces 241 and 242 of
the ceramic honeycomb structure 2, the openings 231 of the cells 23
provided with the plug material 4 and the openings 231 of the cells
23 not provided with the plug material 4 mixedly exist in such a
way that they are arranged alternately.
[0094] In other words, as shown in FIG. 3, the cell 23 in the
central area 26 has totally two openings 231 at its ends and one of
the two openings 231 is blocked with the plug material 4 in such a
way that the openings of two neighboring cells 23 in which the plug
material 4 is formed are opposite to each other.
[0095] Next, the method for manufacturing the exhaust gas purifying
filter 1 in the present embodiment is described below.
[0096] First a forming process is carried out for forming the
ceramic honeycomb structure 2 having the surrounding wall 21, the
partition walls 22 and the plurality of cells 23.
[0097] Next, a masking process is carried out for pasting a mask
tape 5 to the entire end face 241 of the ceramic honeycomb
structure 2, as shown in FIG. 5.
[0098] Then, as shown in FIG. 7, the mask tape 5 pasted to the
openings of the cells 23 through which the above-mentioned virtual
line 3 (FIG. 1) passes and the openings of the cells 23 outside the
virtual line 3 is drilled. At this time, a drilling process is
carried out for drilling the mask tape 5 on the openings 231 of the
cells 23 in the central area 26 in a checkerboard pattern.
[0099] After this, as shown in FIG. 8, the end face 241 is dipped
into plug material paste 41 and, as shown in FIG. 9, a plugging
process is carried out for forming the plug material 4 in the
openings 231 of the cells 23 other than those blocked with the mask
tape 5.
[0100] Moreover, as shown in FIG. 10 and FIG. 11, the plug material
4 is formed also on the other end face 242 of the ceramic honeycomb
structure 2.
[0101] In this way, as shown in FIG. 1, not less than 90% of the
peripheral area 25 outside the virtual line 3 on both end faces 241
and 242 of the ceramic honeycomb structure 2 is blocked with the
plug material 4.
[0102] Before holes are drilled in the mask tape, the image of the
end face 241 (242) of the ceramic honeycomb structure 2 is captured
by using a camera 51 and the positions to be drilled are detected
by processing the image, as shown in FIG. 6. Then, the mask tape 5
is drilled by using a laser 52, as shown in FIG. 7.
[0103] As described above, after the plug material 4 is formed in
the openings 231 of the fixed cells 23, the exhaust gas purifying
filter 1, is obtained by baking the ceramic honeycomb structure
2.
[0104] Moreover, it is possible for the partition walls 23 of the
exhaust gas purifying filter 1 to carry catalysts.
[0105] Next, the operation/working-effect of the present embodiment
is described below.
[0106] As described above, not less than 90% of the peripheral area
25 on the end faces 241 and 242 of the ceramic honeycomb structure
2 is blocked with the plug material 4.
[0107] Therefore, the peripheral portion, that is, the corner
portion, of both the end faces 241 and 242 of the ceramic honeycomb
structure 2 is reinforced. Moreover, as the above-mentioned virtual
line 3 is drawn by continuously connecting points at a distance of
more than 1.0 times the cell pitch in the direction toward the
center from the inner surface 211 of the surrounding wall 21, the
width of the peripheral area 25 to be plugged with the plug
material 4 is not less than 1.0 times the cell pitch. Therefore, it
is possible to secure the sufficient strength of the ceramic
honeycomb structure 2. Due to this, it is possible to prevent a
fracture from occurring when the exhaust gas purifying filter 1 is
manufactured, handled, and so forth.
[0108] Moreover, as the virtual line 3 is drawn by continuously
connecting points at a distance of not more than 3.0 times the cell
pitch in the direction toward the center from the inner surface 211
of the surrounding wall 21, the width of the peripheral area 25 to
be plugged with the plug material 4 is not more than 3.0 times the
cell pitch. Therefore, it is possible to sufficiently reduce the
area in the peripheral area 25 which cannot pass an exhaust gas in
the exhaust gas purifying filter 1. Due to this, it is possible to
secure the exhaust gas filtration area and, at the same time, to
suppress the pressure loss of exhaust gas. As a result, the exhaust
gas purifying filter 1 having an excellent efficiency of
purification can be obtained.
[0109] As the ceramic honeycomb structure 2 has the surrounding
wall 21 and the partition walls 22 with a porosity of not less than
50%, the exhaust gas purifying filter 1 having an excellent
efficiency of purification can be obtained.
[0110] In this case, if the peripheral area 25 is not provided with
the plug material 4, a fracture is likely to occur because the
strength of the ceramic honeycomb structure 2 is insufficient.
Therefore, the strength of the ceramic honeycomb structure 2 is
increased by forming the plug material 4 in the peripheral area 25,
as described above, and the strength of the exhaust gas purifying
filter 1 can be increased as a result.
[0111] As the surrounding wall 21 has a thickness of 0.2 to 0.8 mm,
it is possible to secure the strength and the efficiency of exhaust
gas purification of the exhaust gas purifying filter 1.
[0112] Moreover, as the ceramic honeycomb structure 2 is made of
cordierite, it is possible to form the ceramic honeycomb structure
2 having the surrounding wall 21 and the partition walls 22 with a
desired porosity both easily and inexpensively.
[0113] As described above, according to the present embodiment, it
is possible to obtain an exhaust gas purifying filter having a high
strength and an excellent efficiency of exhaust gas
purification.
Second Embodiment
[0114] In the present embodiment, the exhaust gas purifying filter
1 is manufactured by a method different from that in the first
embodiment, as shown in FIG. 12 and FIG. 13.
[0115] In other words, on the end face 241 (242) of the ceramic
honeycomb structure 2 shown in the first embodiment, the mask tape
5 is pasted to the central area 26 within the virtual line 3, as
shown in FIG. 12.
[0116] Therefore, the mask tape 5 has a shape whose outline
coincides with the virtual line 3.
[0117] Then, before the plugging process, as shown in FIG. 13, the
drilling process is carried out for drilling the mask tape 5 which
covers the openings 231 of the cells 23 through which the virtual
line 3 passes. In this drilling process, the mask tape 5 in the
central area 26 within the virtual line 3 is also drilled in a
checkerboard pattern. In FIG. 13, reference number 55 denotes the
drilled parts.
[0118] Others are the same as the first embodiment.
[0119] According to the present manufacturing method, it is
possible to form the plug material 4 in the peripheral area 25
without drilling the mask tape 5 in the peripheral area 25 because
the mask tape 5 is not pasted to the peripheral area 25. Therefore,
the number of man-hours for the drilling process can be reduced and
it is possible to easily manufacture the exhaust gas purifying
filter 1 and, at the same time, to reduce the manufacturing
cost.
[0120] Others are the same as the first embodiment.
Third Embodiment
[0121] In the present embodiment, the plug material 4 is partly
formed in the cells 3 through which the virtual line 3 passes in
the exhaust gas purifying filter 1, as shown in FIG. 14.
[0122] In other words, the forming process and the masking process
are first carried out as in the second embodiment (refer to FIG.
12). Then, the cells 23 through which the virtual line 3 passes are
not drilled in the drilling process.
[0123] Others are the same as the second embodiment.
[0124] Due to this, the plug material 4 is formed as a partial plug
in the cells 3 through which the virtual line 3 passes, as shown in
FIG. 14. In this case, it is possible to reduce the number of
man-hours for the drilling process by further reducing the number
of positions to be drilled.
[0125] Others have the same operation/working-effect as that in the
second embodiment.
Fourth Embodiment
[0126] In the present embodiment, the mask tape 5 is pasted to the
entire end face 241 (242) of the ceramic honeycomb structure 2 in
the masking process, and then a cutting process is carried out for
cutting the mask tape 5 along the virtual line 3.
[0127] After the cutting process, the exhaust gas purifying filter
1 is manufactured by the same method as that in the second or third
embodiment.
[0128] A laser, for example, is used to cut the mask tape 5.
[0129] Others are the same as the first embodiment.
[0130] According to the present manufacturing method, when the mask
tape 5 is pasted to the end faces 241 and 242 of the ceramic
honeycomb structure 2, pasting is easy because no exact positional
alignment of the mask tape 5 is required. Therefore, it is possible
to easily manufacture an exhaust gas purifying filter having a high
strength and an excellent efficiency of exhaust gas
purification.
[0131] Others have the same operation/working-effect as that in the
first embodiment.
Fifth Embodiment
[0132] In the present embodiment, the mask tape 5 is pasted to the
entire end face 241 (242) of the ceramic honeycomb structure 2 in
the masking process, and in the cutting process, the mask tape 5 is
cut along the partition walls 22 of the cells 23 through which the
virtual line 3 passes and, at the same time, the mask tape 5
outside the partition walls 22 is removed, as shown in FIG. 15.
[0133] Therefore, the cutting line forms a closed curve which
encloses the maximum area which can be drawn along the partition
walls 22 within the virtual line 3.
[0134] Then, the exhaust gas purifying filter 1 is manufactured by
the same method as in the first embodiment.
[0135] A laser, for example, is used to cut the mask tape 5.
[0136] Others are the same as the first embodiment.
[0137] According to the present manufacturing method, it is
possible to open the whole of the openings 231 of the specified
cells 23, through which the virtual line 23 passes, by removing the
mask tape 5 which covers the specified cells 23. Therefore, it is
possible to form the plug material 4 in all of the openings 231 of
the cells 23 through which the virtual line 3 passes.
[0138] Moreover, it is not necessary to drill the openings 231 of
the cells 23 through which the virtual line 3 passes.
[0139] Therefore, according to the present embodiment, it is
possible to easily manufacture an exhaust gas purifying filter
having a high strength and an excellent efficiency of exhaust gas
purification.
[0140] Others have the same operation/working-effect as that in the
first embodiment.
Sixth Embodiment
[0141] In the present embodiment, the exhaust gas purifying filter
according to the present invention is tested to examine how it
fractures, as shown in FIGS. 16 and 17.
[0142] The exhaust gas purifying filter of the present invention,
that is, the exhaust gas purifying filter in whose peripheral area
plug material is formed, is referred to as test sample 1.
[0143] A ceramic honeycomb structure similar to that used in test
sample 1, in whose peripheral area plug material is not formed, is
referred to as test sample 2.
[0144] A monolith 3 mil product having a relatively low porosity is
referred to as test sample 3.
[0145] Various pieces of data for each test sample are shown in
table 1. TABLE-US-00001 TABLE 1 Test sample 1 Test sample 2 Test
sample 3 Plug material in the In Non-existent Non-existent
peripheral area existence Dimensions 129 .times. 50 mm 129 .times.
50 mm 129 .times. 50 mm (diameter .times. height) Thickness in 0.6
mm 0.6 mm 0.6 mm surrounding wall Thickness in 0.3 mm 0.3 mm 0.09
mm partition wall Number of cells 300 meshes 300 meshes 600 meshes
Material Cordierite Cordierite Cordierite Porosity 65% 65% 35%
[0146] In the test, each ceramic honeycomb structure 61 is mounted
on a support base 62 in a state in which the direction T in which
the cell penetrates through the honeycomb structure 61 is tilted
with respect to the vertical direction S so that the angle between
T and S is 45 degrees, as shown in FIG. 16.
[0147] Then, a cylindrical lead weight 63 having a base diameter of
20 mm and a height of 30 mm and weighing 100 g is dropped freely
from 30 cm above to a corner portion 611 of the ceramic honeycomb
structure 61.
[0148] The weight 63 is dropped through a cylindrical guide 64
provided in the vertical direction.
[0149] In this way, the depth of the fracture which occurs at the
corner portion 611 of each ceramic honeycomb structure 61 is
measured. This test is conducted five times for each test
sample.
[0150] The results of the test are shown in FIG. 17. The values
shown in the figure are the average of the results of the test
conducted five times.
[0151] As obvious from FIG. 17, test sample 1 according to the
present invention exhibits a depth of a fracture considerably less
than that of test sample 2 in whose peripheral area no plug
material is provided.
[0152] Although test sample 1 has a porosity of as large as 65%,
the depth of a fracture thereof is substantially the same as that
of the monolithic test sample 3 whose porosity is as low as
35%.
[0153] From these results, it is concluded that, according to the
present invention, it is possible to obtain an exhaust gas
purifying filter which can sufficiently prevent the occurrence of a
fracture and which is excellent in strength.
[0154] The rate of rise in pressure loss is a quantity based on the
pressure loss of a test sample whose peripheral area is not
plugged. The pressure loss is a value obtained as a difference in
pressure between that at one end and that at the other of the
exhaust gas purifying filter when air at room temperature flows
through the exhaust gas purifying filter at a rate of 5
m.sup.3/min. The pressure loss in the eighth embodiment, to be
described later, is also a value obtained in this manner.
[0155] The depth of fracture is measured by the fracture testing
method described in the sixth embodiment. In FIG. 18, the rate of
rise in pressure loss is denoted by while circles and the depth of
fracture is denoted by black circles.
[0156] As shown in FIG. 18, the rate of rise in pressure loss
remarkably increases for the test samples having the peripheral
area whose width to be plugged is two cell pitches or wider. When
the width of the peripheral area to be plugged reaches four cell
pitches, the rate of rise in pressure loss increases further,
exceeding 40%.
[0157] As for the fracture, it is possible to reduce the depth of
fracture by plugging the peripheral area corresponding to a width
of one cell pitch, compared to that not being plugged. Moreover, it
is possible to further reduce the depth of fracture by plugging the
peripheral area corresponding to a width of two cell pitches.
[0158] From these results, it is found that the width of the
peripheral area to be plugged needs to be one to three cell pitches
and, preferably, one to two cell pitches.
Eighth Embodiment
[0159] In the present embodiment, as shown in FIG. 19, a
relationship between the thickness of the partition wall of the
ceramic honeycomb structure and the collection efficiency of
particulates in an exhaust gas, and between that and the pressure
loss, is assessed.
[0160] In other words, an exhaust gas containing particulates flows
through each exhaust gas purifying filter at a rate of 2
m.sup.3/min. Then, the mass M1 of the exhaust gas purifying filter
before the exhaust gas flows, and the mass M2 of that after the
exhaust gas flows are measured respectively and, at the same time,
the mass N of the particulates that have passed through the exhaust
gas purifying filter is measured. Based on the mass M1, M2 and N,
the collection efficiency P of particulates is calculated from the
formula: P=(M2-M1)/(M2-M1+N)
[0161] In FIG. 19, the collection efficiency is denoted by black
circles and the pressure loss is denoted by white circles.
[0162] As shown in FIG. 19, it is possible to sufficiently increase
the collection efficiency by setting the thickness of the partition
wall to 0.25 mm or more. However, if the thickness of the partition
wall exceeds 0.40 mm, the pressure loss increases extremely.
[0163] From these results, it is found that the thickness of the
partition wall is preferably 0.25 to 0.40 mm.
[0164] While the invention has been described by reference to
specific embodiments chosen for the purposes of illustration, it
should be apparent that numerous modifications could be made
thereto by those skilled in the art without departing from the
basic concept and scope of the invention.
* * * * *