U.S. patent application number 10/504987 was filed with the patent office on 2005-06-02 for exhaust emission control device and casing structure of the control device.
This patent application is currently assigned to IBIDEN CO. LTD. Invention is credited to Kojima, Masaaki.
Application Number | 20050115224 10/504987 |
Document ID | / |
Family ID | 29422261 |
Filed Date | 2005-06-02 |
United States Patent
Application |
20050115224 |
Kind Code |
A1 |
Kojima, Masaaki |
June 2, 2005 |
Exhaust emission control device and casing structure of the control
device
Abstract
An exhaust gas purifying device includes a tubular casing
arranged in exhaust passages of an internal combustion engine. A
filter is held in the casing. The filter collects and burns
particulates contained in the exhaust gas discharged by the
internal combustion engine. The casing has a double structure
including an inner case supporting an outer peripheral surface of
the filter and an outer case arranged around the inner case. The
inner and outer cases are spaced from each other with a clearance
defined between the cases.
Inventors: |
Kojima, Masaaki; (Gifu,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
IBIDEN CO. LTD
GIFU
JP
|
Family ID: |
29422261 |
Appl. No.: |
10/504987 |
Filed: |
August 19, 2004 |
PCT Filed: |
February 21, 2002 |
PCT NO: |
PCT/JP02/01557 |
Current U.S.
Class: |
60/282 ; 60/295;
60/297 |
Current CPC
Class: |
F01N 2260/08 20130101;
F01N 2260/10 20130101; F01N 3/0211 20130101; Y02T 10/12 20130101;
F01N 13/14 20130101; F01N 3/027 20130101; F01N 3/022 20130101; F01N
3/0222 20130101; F01N 3/025 20130101; Y02T 10/20 20130101 |
Class at
Publication: |
060/282 ;
060/297; 060/295 |
International
Class: |
F01N 003/00 |
Claims
1. An exhaust gas purifying device for use with an engine having an
exhaust passage, the exhaust gas purifying device comprising: a
tubular casing disposed in the exhaust passage of the engine and a
filter accommodated in the casing for collecting, burning, and
removing particulates contained in the exhaust gas discharged by
the engine, the casing having a multiple case structure including
an inner case supporting an outer peripheral surface of the filter
and at least one outer case arranged around the inner case, with
the inner and outer cases being spaced from each other with and a
clearance defined between the inner and outer cases.
2. An exhaust gas purifying device for use with an engine having an
exhaust passage, the exhaust as purifying device comprising: a
tubular casing disposed in the exhaust passage of the engine and a
filter accommodated in the casing for collecting, burning, and
removing particulates contained in the exhaust gas discharged by
the engine, the casing having a double case structure including an
inner case supporting an outer peripheral surface of the filter and
an outer case arranged around the inner case, with the inner and
outer cases being spaced from each other and a clearance defined
between the inner and outer cases.
3. The exhaust gas purifying device according to claim 1, further
comprising a fluid blocking member formed at an upstream end
portion of the inner case for blocking communication between a
space including an upstream end surface of the filter and the
clearance.
4. The exhaust gas purifying device according to claim 1, further
comprising a support piece provided at an upstream side of the
inner case.
5. The exhaust gas purifying device according to claim 3, further
comprising a fluid blocking member provided at a downstream side of
the inner case and between the inner case and the outer case for
blocking communication between a space including a downstream end
surface of the filter and the clearance.
6. The exhaust gas purifying device according to claim 3, wherein
the fluid blocking member is a flange projecting from an outer
peripheral surface of an end of the inner case, and the flange is
secured to an outermost component of the outer case in an
attachable or detachable manner.
7. The exhaust gas purifying device according to claim 1, further
comprising a heater for regenerating the filter disposed at an
upstream position with respect to the filter, and a porous heat
reflector arranged at a further upstream position with respect to
the heater.
8. A casing structure for an exhaust gas purifying device having a
filter for use with an engine, the casing structure comprising: a
multiple case structure including an inner case supporting an outer
peripheral surface of the filter for collecting, burning, and
removing particulates contained in the exhaust gas discharged by
the engine and at least one outer case arranged around the inner
case, the casing structure including inner and outer cases spaced
from each other with a clearance defined between the inner and
outer cases.
9. The exhaust gas purifying device according to claim 1, wherein
the filter is a ceramic filter.
10. The exhaust gas purifying device according to claim 1, wherein
the filter is a sintered honeycomb body formed of porous silicon
carbide.
11. The exhaust gas purifying device according to claim 1, wherein
the filter is an integral body formed by bundling a plurality of
prism-shaped sintered honeycomb bodies formed of porous silicon
carbide and binding the bundled bodies with an adhesive agent.
12. A casing structure for an exhaust gas purifying device having a
filter for use with an engine the casing structure comprising: a
multiple case structure including an inner case supporting an outer
peripheral surface of the filter for collecting, burning, and
removing particulates contained in the exhaust gas discharged by an
engine, at least one outer case arranged around the inner case, and
a heating means accommodating case accommodating a heating means
for regenerating the filter arranged at an upstream side of the
outer case, with the inner and outer cases spaced from each other
and a clearance defined between the inner and outer cases.
13. The exhaust gas purifying device according to claim 2, further
comprising a fluid blocking member formed at an upstream end
portion of the inner case for blocking communication between a
space including an upstream end surface of the filter and the
clearance.
14. The exhaust gas purifying device according to claim 2, further
comprising a support piece is provided at an upstream side of the
inner case.
15. The exhaust gas purifying device according to claim 3, further
comprising a support piece is provided at an upstream side of the
inner case.
16. The exhaust gas purifying device according to claim 3, further
comprising a fluid blocking member provided at a downstream side of
the inner case and between the inner case and the outer case for
blocking communication between a space including a downstream end
surface of the filter and the clearance.
17. The exhaust gas purifying device according to claim 16, wherein
the fluid blocking member is a flange projecting from an outer
peripheral surface of an end of the inner case, and the flange is
secured to an outermost component of the outer case in an
attachable or detachable manner.
18. The exhaust gas purifying device according to claim 5, wherein
the fluid blocking member is a flange projecting from an outer
peripheral surface of an end of the inner case, and the flange is
secured to an outermost component of the outer case in an
attachable or detachable manner.
19. The exhaust gas purifying device according to claim 2, further
comprising a heater for regenerating the filter disposed at an
upstream position with respect to the filter, and a porous heat
reflector arranged at a further upstream position with respect to
the heater.
20. The exhaust gas purifying device according to claim 3, further
comprising a heater for regenerating the filter disposed at an
upstream position with respect to the filter, and a porous heat
reflector arranged at a further upstream position with respect to
the heater.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to exhaust gas purifying
devices for purifying exhaust gas discharged by internal combustion
engines including diesel engines and casing structures for the
devices.
BACKGROUND OF THE INVENTION
[0002] Conventionally, a number of exhaust gas purifying devices
have been proposed. The devices are configured by accommodating a
ceramic honeycomb filter for purifying exhaust gas in a metal
tubular casing, which is disposed in an exhaust passage of a diesel
engine. As the filter is used for a relatively long time, the
filter collects soot (diesel particulates) from the exhaust gas.
The soot is deposited in the filter and gradually increases the
engine load. If this is the case, the filter is heated to the
ignition temperature of the soot (600 to 630 degrees Celsius) by a
heating means such as a heater or burner. The soot is thus burned
and removed such that the filter is regenerated.
[0003] However, conventional exhaust gas purifying devices have the
following problems.
[0004] That is, when the filter is heated by the heating means, the
heat is transmitted to a different component (for example, the
casing) that is held in contact with the filter. The heat thus
escapes to the exterior of the filter, hampering the heating of the
filter. This increases the energy needed to heat the filter to the
soot ignition temperature and raises costs. Further, if an electric
heater is used as the heating means, an increased electric load is
applied to the battery, which accelerates the battery
consumption.
[0005] In addition, a temperature difference is caused between the
middle portion of the filter and an outer peripheral portion of the
filter. Therefore, if the honeycomb filter is formed of, for
example, porous silicon carbide, an increased thermal stress is
generated in the filter. In this case, the filter has a tendency to
crack, which is damaging to the filter. Moreover, in conventional
devices, replacement of the filter is complicated, making it
difficult to maintain the devices.
[0006] The present invention is for solving the above problems.
Accordingly, it is an objective of the invention to provide an
exhaust gas purifying device that saves costs by decreasing energy
loss and suppressing damage to the filter, as well as a casing
structure for the device.
DISCLOSURE OF THE INVENTION
[0007] To solve the above problems, the gist of a first embodiment
of the present invention is an exhaust gas purifying device
comprising a tubular casing disposed in an exhaust passage of an
internal combustion engine and a filter accommodated in the casing
for collecting, burning, and removing particulates contained in the
exhaust gas discharged by the internal combustion engine. The
device is characterized in that the casing has a multiple case
structure including an inner case supporting an outer peripheral
surface of the filter and at least one outer case arranged around
the inner case, and that the inner and outer cases are spaced from
each other with a clearance defined between the cases.
[0008] The gist of a second embodiment is an exhaust gas purifying
device comprising a tubular casing disposed in an exhaust passage
of an internal combustion engine and a filter accommodated in the
casing for collecting, burning, and removing particulates contained
in the exhaust gas discharged by the internal combustion engine.
The device is characterized in that the casing has a double
structure including an inner case supporting an outer peripheral
surface of the filter and an outer case arranged around the inner
case, and that the inner and outer cases are spaced from each other
with a clearance defined between the cases.
[0009] It is desirable that a fluid blocking member is provided at
an upstream end portion of the inner case for blocking
communication between a space including an upstream end surface of
the filter and the clearance.
[0010] A fluid blocking member may be provided at a downstream side
of the inner case and between the inner case and the outer case for
blocking communication between a space including a downstream end
surface of the filter and the clearance.
[0011] The fluid blocking member may be a flange projecting from an
outer peripheral surface of an end of the inner case. The flange
may be secured to an outermost component of the outer case in an
attachable or detachable manner.
[0012] A heater for regenerating the filter may be disposed at an
upstream position with respect to the filter. Further, a porous
heat reflector may be arranged at a further upstream position with
respect to the heater.
[0013] The gist of a third embodiment is a casing structure of an
exhaust gas purifying device having a multiple structure including
an inner case supporting an outer peripheral surface of a filter
for collecting, burning, and removing particulates contained in the
exhaust gas discharged by an internal combustion engine and at
least one outer case arranged around the inner case. The casing
structure is characterized in that the inner and outer cases are
spaced from each other with a clearance defined between the
cases.
[0014] In each of the above-described embodiments, the outer
peripheral surface of the filter is held in contact with the inner
case. However, the clearance is defined between the inner case and
the outer case. Therefore, in other words, a heat insulating air
layer is ensured between the inner and outer cases. The heat
transmission from the inner case to the outer case is thus
hampered. This prevents the heat from escaping to the exterior of
the filter such that the temperature of the filter is efficiently
raised. That is, the exhaust gas purifying device reduces energy
loss and thus saves costs. Further, since the heat is prevented
from escaping from the outer peripheral portion of the filter, the
temperature difference between the middle portion and the outer
peripheral portion of the filter hardly occurs. As a result, a
relatively large thermal stress, which leads to cracks damaging the
filter, is avoided.
[0015] If the fluid blocking member is provided at the upstream end
portion of the inner case, communication between the space
including the upstream end surface of the filter and the clearance
is blocked. Therefore, a relatively hot exhaust gas does not flow
into the clearance in which the heat insulating air layer is
formed. This structure reduces heat energy loss caused by heat
transmission from the exhaust gas to the outer case. The costs are
thus further saved. Further, the exhaust gas does not bypass the
filter or reach the downstream side of the filter without being
purified. The purifying efficiency is thus prevented from being
lowered.
[0016] If the fluid blocking member is provided at the downstream
end portion of the inner case, communication between the space
including the downstream end surface of the filter and the
clearance is blocked. This structure further reduces the heat
energy loss caused by the heat transmission from the exhaust gas to
the outer case. The costs are thus further saved.
[0017] If the fluid blocking member is configured by the flange,
the flange serves also as a portion to which the inner case is
secured. This avoids an increase in the number of the parts and
complication of the structure. Further, the filter may be removed
from the outer case in a state accommodated in the inner case. The
replacement of the filter thus becomes relatively easy, as compared
to a conventional case. As a result, maintenance is
facilitated.
[0018] If a heater for regenerating the filter and heat reflector
are provided, the heat of the heater is reflected by the heat
reflector. The heat energy loss of the heater is thus decreased,
and the filter is heated efficiently. Further, since the heat
reflector is porous, the flow of the exhaust gas to the filter is
not hampered.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a schematic view showing an example of an exhaust
gas purifying device according to a first embodiment of the present
invention;
[0020] FIG. 2 is a cross-sectional view showing the exhaust gas
purifying device of FIG. 1;
[0021] FIG. 3 is an exploded perspective view showing a casing
structure of the exhaust gas purifying device of FIG. 1;
[0022] FIG. 4 is an end view showing a filter employed in the
exhaust gas purifying device of FIG. 1;
[0023] FIG. 5 is a cross-sectional view showing a portion of the
filter;
[0024] FIG. 6 is a cross-sectional view showing an exhaust gas
purifying device of a second embodiment;
[0025] FIG. 7 is a cross-sectional view showing an exhaust gas
purifying device of a third embodiment;
[0026] FIG. 8 is a cross-sectional view showing an exhaust gas
purifying device of a fourth embodiment; and
[0027] FIG. 9 is a cross-sectional view showing an exhaust gas
purifying device of a fifth embodiment.
BEST MODE FOR CARRYING OUT THE INVENTION
[0028] An exhaust gas purifying device 1 according to a first
embodiment of the present invention will hereafter be described
with reference to FIGS. 1 to 5.
[0029] As illustrated in FIG. 1, the exhaust gas purifying device 1
purifies exhaust gas discharged by a diesel engine 2, which serves
as an internal combustion engine. The diesel engine 2 includes a
plurality of non-illustrated cylinders. A branch 4 of a metal
exhaust manifold 3 is coupled to each of the cylinders. The
branches 4 are connected to a manifold body 5. Thus, the exhaust
gas sent from each of the cylinders is concentrated at one
point.
[0030] A first exhaust pipe 6 and a second exhaust pipe 7, which
are formed of metal, are disposed at a downstream side of the
exhaust manifold 3. An upstream end of the first exhaust pipe 6 is
coupled to the manifold body 5. The exhaust gas purifying device 1
is located between the first exhaust pipe 6 and the second exhaust
pipe 7.
[0031] With reference to FIG. 2, the exhaust gas purifying device 1
includes a cylindrical casing 21. An exhaust gas purifying filter
13 is accommodated in the casing 21. The filter 13 will hereafter
be explained.
[0032] Since the filter 13 is used for removing diesel
particulates, the filter 13 is called also as a diesel particulate
filter (DPF). The filter 13 of the first embodiment, as shown in
FIGS. 4 and 5, is formed by bundling a plurality of sintered
honeycomb bodies F as one body. The sintered honeycomb bodies F
located in the middle portion of the filter 13 are shaped as square
rods. A plurality of sintered honeycomb bodies F that are shaped
differently, or unlike the square rods, are arranged around the
honeycomb bodies F that are shaped as the square rods. Accordingly,
the filter 13 as a whole is shaped as a cylinder.
[0033] In the first embodiment, each of the sintered honeycomb
bodies F is formed from a sintered body of porous silicon carbide
(SiC), which is a type of sintered ceramic body. However, other
than the sintered body of silicon carbide, a sintered body of
silicon nitride or sialon or alumina or cordierite may be selected.
A plurality of through holes 11, each of which has a substantially
square cross-sectional shape, are formed in each of the sintered
honeycomb bodies F and are arranged regularly in an axial
direction. The through holes 11 are spaced from one another by cell
walls 12. An opening of each through hole 11 is sealed by a plug 14
(in this embodiment, a sintered body of porous silicon carbide) at
one of end surfaces 13a, 13b. Each of the end surfaces 13a, 13b as
a whole thus presents a diced pattern. As a result, a number of
cells each having a square cross-sectional shape are formed in each
sintered honeycomb body F. Approximately half of the cells open at
the upstream end surface 13a, while the remaining cells open at the
downstream end surface 13b.
[0034] As shown in FIGS. 4 and 5, the sintered honeycomb bodies F
are bound together by an adhesive 15 at the outer peripheral
surfaces. The adhesive 15 serves to compensate thermal expansion of
the sintered honeycomb bodies F. In other words, the adhesive 15
prevents cracks from being caused by thermal stress. In the first
embodiment, a heat resistant ceramic adhesive in which ceramic
fibers are dispersed is used as the adhesive 15. It is preferred
that silicon carbide powders, in addition to the ceramic fibers,
are dispersed in the adhesive 15.
[0035] With reference to FIGS. 2 and 3, the casing 21, which
accommodates the filter 13, is configured by a plurality of metal
tubular members. More specifically, in the first embodiment, three
members including a heater case 22, an inner case 23, and an outer
case 24 (all formed of SUS304) configure the casing 21. The heater
case 22, serving as a heating means accommodating case, forms a
portion of a heater unit. The inner case 23 forms a portion of a
filter unit.
[0036] The heater case 22 defines a sealed space for preventing
exhaust gas from entering the heater case 22. The heater case 22
thus provides a heat insulating effect. A mat-shaped heat
insulating material 8, the main component of which is ceramic
fibers, is packed in the space of the heater case 22. This improves
the heat insulating effect.
[0037] Each of the inner case 23 and the outer case 24 has a
cylindrical shape. The inner case 23, which is accommodated in the
outer case 22, is smaller than the outer case 24 (the longitudinal
dimension and the diameter of the inner case 23 are smaller than
those of the outer case 24). Therefore, when the cases are
assembled, a clearance C1 having a constant dimension is defined
between the outer peripheral surface of the inner case 23 and the
inner peripheral surface of the outer case 24, which is arranged
around the inner case 23. In the first embodiment, the dimension of
the clearance C1 is approximately 1 to 5 millimeters. A flange 25
of the inner case 23 serves also as a fluid blocking member that
blocks communication between the space including the upstream end
surface 13a of the filter 13 and the clearance C1.
[0038] The flange 25 projects from the outer peripheral surface of
an upstream end portion of the inner case 23. In the same manner, a
flange 26 projects from the outer peripheral surface of an upstream
end portion of the outer case 24. The flanges 25, 26 are designed
to define equal outer diameters. A plurality of bolt holes 28 are
formed in the flange 25 and are spaced from adjacent ones at
certain intervals. In the same manner, a plurality of bolt holes 29
are formed in the flange 26 and are spaced from adjacent ones at
certain intervals. Attachment bolts 27 are passed through the bolt
holes 28, 29. The bolt holes 29 of the flange 25 are located at
positions corresponding to the bolt holes 28 of the flange 26. In
the same manner, a plurality of bolt holes 31 are formed in a
downstream end surface of the heater case 22 at positions
corresponding to the bolt holes 28, 29. Thus, if the bolts 27 are
passed through the corresponding bolt holes 28, 29, 31 and fastened
as such, the cases 22, 23, 24 are fixed to each other to form one
body, or the casing 21. If the bolts 27 are removed from the bolt
holes 28, 29, 31, the casing 21 is separated into three parts. In
other words, it may be understood that the flange 25 of the inner
case 23 is secured to the flange 26 of the outer case 24 in an
attachable or detachable manner.
[0039] The mat-shaped heat insulating material 17 containing
ceramic fibers is wrapped around the filter 13. In this state, the
filter 13 is held in the inner case 23. That is, the inner case 23
supports the outer peripheral surface of the filter 13 through the
heat insulating material 17. A filter support 30 projects from the
inner peripheral surface of the downstream end of the inner case 23
and extends along the entire circumference. The filter support 30
is abutted by an outer peripheral portion of the downstream end
surface 13b of the filter 13. This structure prevents the filter 13
from falling from the inner case 23 to the downstream side.
[0040] A support piece 30a is attached to the inner peripheral
surface of the upstream end portion of the inner case 23 and
extends along the entire circumference. The support piece 30a is
abutted by an outer peripheral portion of the upstream end surface
13a of the filter 13. This structure prevents the filter 13 from
falling from the inner case 23 to the upstream side. Further, the
heat insulating material 17 is prevented from being displaced. A
plurality of support pieces 30a may be deployed as spaced from
adjacent ones at predetermined angular intervals.
[0041] A coupling portion 32 projects from a middle portion of the,
upstream end surface of the heater case 22 and is coupled with a
downstream end of the first exhaust pipe 6. Further, a coupling
portion 33 projects from a middle portion of the downstream end
surface of the outer case 24 and is coupled with an upstream end of
the second exhaust pipe 7.
[0042] As illustrated in FIGS. 1 and 2, the heater case 22, a
component of the casing 21, accommodates a heater 34 and a
temperature detector 35. The heater 34 serves as an electric
heating means for regenerating the filter and is located at an
upstream position with respect to the filter 13. In the first
embodiment, an AC heater is used as the heater 34. The heater 34 is
formed by winding a cable spirally. More specifically, the cable
includes a conductive core of a nichrome wire covered by a sheath
of magnesia, which presents improved insulating performance.
[0043] The heater 34 is opposed to the upstream end surface 13a of
the filter 13 and is spaced from the upstream end surface 13a at a
certain interval. Two end portions 34a of the heater 34 extend
through an outer peripheral portion of the heater case 22 to the
exterior of the casing 21. The core projecting from each of the end
portions 34a of the heater 34 is electrically connected to a
connector through a glass tube. The connector, as shown in FIG. 1,
is electrically connected to a driver circuit of a control unit U1
controlling the regenerating operation of the filter 13. Thus, when
necessary, the control unit U1 operates to supply power to the
heater 34 from an external power source B1. This enables the heater
34 to generate heat from the entire portion such that the
temperature rises to 800 to 900 degrees Celsius.
[0044] With reference to FIG. 2, a punching plate 38 serving as a
porous heat reflector is disposed at an upstream position with
respect to the heater 34. The punching plate 38 is a disk-shaped
plate member and is formed of stainless steel (SUS304) in the first
embodiment. The outer periphery of the punching plate 38 is bonded
with the inner peripheral surface of the heater case 22 through,
for example, welding. The punching plate 38 is thus secured to the
heater case 22. Further, the heater 34 is fixed to the punching
plate 38 by a fixing tool 37.
[0045] A number of through holes 38a extend through the punching
plate 38. The through holes 38a are arranged regularly to cover
substantially the entire area of the punching plate 38. Therefore,
after being discharged from the first exhaust pipe 6, exhaust gas
passes through the through holes 38a to reach the filter 13.
Further, the punching plate 38 reflects the heat generated by the
heater 34, preventing the heat from being released to the exterior.
In other words, the heat reflected by the punching plate 38 is
supplied to the filter 13 as radiation heat. The filter 13 is thus
efficiently heated.
[0046] A ceramic foam reflector 39 serving as another porous heat
reflector is disposed at the downstream side of the filter 13, as
illustrated in FIG. 2. In the first embodiment, the ceramic foam
reflector 39 is supported by a heat reflector support 40, which
projects from the inner peripheral surface of the outer case 24 and
extends along the entire circumference. The ceramic foam reflector
39 is a porous body formed of aluminum nitride or the like and
presents fluid permeability and heat insulating properties.
Therefore, like the upstream side of the filter 13, a heat
insulating effect is ensured at the downstream side of the filter
13.
[0047] With reference to FIG. 2, the temperature detector 35 is
deployed in the vicinity of the heater 34. The temperature detector
35 is a rod-shaped body, and a temperature detecting portion 35a is
formed at a distal end of the temperature detector 35. The
temperature detector 35 of this embodiment includes a sheath
thermocouple covered by a protecting pipe formed of stainless steel
or the like. The temperature detecting portion 35a is exposed from
a distal end of the covered sheath thermocouple. The temperature
detecting portion 35a is placed in the space defined by the cable
spirally wound in the heater 34. The temperature detector 35 is
electrically connected to the control unit U1.
[0048] The operation of the exhaust gas purifying device 1
configured as described above will hereafter be explained.
[0049] The casing 21 accommodating the filter 13 is deployed in the
exhaust gas passage, or between the first exhaust pipe 6 and the
second exhaust pipe 7. In this state, if the engine 2 is started,
exhaust gas is sent to the interior of the casing 21. That is,
after being discharged from the first exhaust pipe 6, the exhaust
gas flows first into the cells opening at the upstream end surface
13a of the filter 13. The gas then permeates the cell walls 12 and
reaches the adjacent cells, which open at the downstream end
surface 13b of the filter 13. Further, through the openings of the
cells, the exhaust gas is discharged from the downstream end
surface 13b of the filter 13.
[0050] However, the soot contained in the exhaust gas is not
permitted to permeate the cell walls 12 and is trapped in the
cells. As a result, the exhaust gas is purified before being
discharged from the downstream end surface 13b of the filter 13.
The purified gas further flows in the second exhaust pipe 7 and is
eventually released to the atmosphere. Afterwards, the heater 34 is
powered to heat the filter 13 and supporting air is supplied such
that the soot is burned and removed. More specifically, the soot in
the vicinity of the upstream end surface 13a of the filter 13
starts to burn. Burning of the soot is gradually spread to the
downstream end surface 13b. By maintaining the soot burning for a
certain time period, the filter 13 is regenerated.
[0051] Accordingly, the first embodiment has the following
effects.
[0052] (1) The casing 21 of the first embodiment has a double
structure formed by the inner case 23 and the outer case 24. The
inner case 23 supports the outer peripheral surface of the filter
13. The outer case 24 is arranged around the inner case 23.
Further, the cases 23, 24 are spaced from each other at an interval
corresponding to the clearance C1.
[0053] Although the outer peripheral surface of the filter 13 is
held in contact with the inner case 23, the clearance C1 is ensured
between the inner case 23 and the outer case 24. In other words, a
heat insulating air layer is formed between the cases 23, 24. The
heat insulting air layer presents relatively low heat conductivity
as compared to metal and hampers the heat transmission from the
inner case 23 to the outer case 24. Further, air convection does
not occur readily in the clearance C1. This structure stops heat
from escaping to the exterior of the filter 13. The temperature of
the filter 13 is thus efficiently raised. In other words, the
exhaust gas purifying device 1 has decreased energy loss and thus
saves costs. In addition, since the heat energy applied to the
filter 13 is also decreased, the power supplied to the heater 34 is
reduced and the time required for regenerating the filter 13 is
shortened.
[0054] (2) The casing structure of the first embodiment prevents
heat from escaping from the outer peripheral portion of the filter
13. Thus, a temperature difference is hardly caused between the
middle portion of the filter 13 and the outer peripheral portion of
the filter 13. This avoids generation of relatively large thermal
stress, which leads to cracks damaging the filter 13. Therefore,
the exhaust gas purifying device 1 presents improved strength and
has relatively high reliability.
[0055] (3) Since the casing structure of the first embodiment stops
heat from escaping from the outer peripheral portion of the filter
13, the temperature of the outer peripheral surface of the outer
case 24 is reliably lowered. Therefore, the components attached to
the outer surface of the outer case 24 and those disposed around
the outer case 24, for example, do not necessarily have to have
high heat resisting performance, as compared to conventional
counterparts.
[0056] (4) In the casing structure of the first embodiment, the
flange 25 serving as the fluid blocking member, which is formed at
the upstream end portion of the inner case 23, blocks communication
between the space including the upstream end surface of the filter
13 and the clearance C1. Thus, relatively hot exhaust gas does not
flow into the clearance C1 in which the heat insulating air layer
is located. This prevents the heat from the exhaust gas from being
transmitted to the outer case 24, reducing the heat energy loss
otherwise caused by such heat transmission. The costs are thus
further saved. In addition, the exhaust gas does not bypass the
filter 13 or reach the downstream side without being purified. This
structure prevents the purifying efficiency from being lowered.
[0057] (5) In the casing structure of the first embodiment, the
flange 25 serving as the fluid blocking member also functions as a
portion to which the inner case 23 is fixed. This structure avoids
an increase in the number of the parts and complication of the
configuration.
[0058] Further, this structure allows the filter 13 to be removed
from the outer case 24 in a state accommodated in the inner case
23. It is thus possible to easily replace the filter 13, as
compared to a conventional case. Also, a major portion of the
downstream end surface 13b of the filter 13 is exposed from the
inner case 23. This makes it relatively easy to clean ashes after
the filter 13 is removed from the casing 21. In this manner, the
casing structure of this embodiment facilitates the
maintenance.
[0059] (6) In the casing structure of the first embodiment, the
punching plate 38 serving as the heat reflector reflects the heat
of the heater 34. Further, the heat of the filter 13, which is
heated by the heater 34, is reflected by the ceramic foam reflector
39 also serving as the heat reflector. The heat energy loss of the
heater 34 is thus decreased such that the filter 13 is efficiently
heated. This structure contributes to shortening of the time
required for regenerating the filter 13. In addition, since the
heat reflectors are porous, the exhaust gas flow to and from the
filter 13 is not hampered.
[0060] (7) In the first embodiment, the outer peripheral portion of
the upstream end surface 13a of the filter 13 is held in contact
with the filter support piece 30a formed at the upstream end
portion of the inner case 23. This structure prevents the heat
insulating material 17 from being corroded. Further, when the
filter 13 is removed from the casing 21 and is washed in water for
cleaning ashes, the heat insulating material 17 is stopped from
being displaced.
[0061] Other embodiments of the present invention will hereafter be
described.
[0062] In a second embodiment illustrated in FIG. 6, a flange 41
projects from the outer peripheral surface of the downstream end
portion of the inner case 23 and extends along the entire
circumference. In this embodiment, the flange 41 serving as a fluid
blocking member blocks communication between the space including
the downstream end surface 13b of the filter 13 and the clearance
C1. This structure further reduces the heat energy loss caused by
the heat transmission from the exhaust gas to the outer case 24, as
compared to the first embodiment. This effect is brought about by
the fact that a heat insulating air layer more preferable than that
of the first embodiment is formed in the clearance C1. Therefore,
costs are further saved. In addition, the filter 13 is further
securely fixed as long as the outer periphery of the flange 41 is
held in contact with the inner peripheral surface of the outer case
24, as shown in FIG. 6.
[0063] Further, it is desirable that a clearance is defined between
the flange 41 and the inner peripheral surface of the outer case
24. The clearance makes it possible to remove the inner case 23
smoothly from the outer case 24, even if the dimensions of the
inner case 23 are changed due to thermal expansion.
[0064] In a third embodiment illustrated in FIG. 7, the casing 21
includes an additional outer case 42, other than the outer case 24.
The casing 21 thus has a triple structure. The additional outer
case 42 is arranged between the outer case 24 and the inner case
23. This structure has two clearances C1, each of which serves as a
heat insulating air layer. Further, a flange 43 projects from the
outer peripheral surface of the upstream end portion of the outer
case 42. The flange 43 is deployed as clamped between the flanges
25, 26.
[0065] In a fourth embodiment illustrated in FIG. 8, a flange 41a
serving as a fluid blocking member projects from the inner
peripheral surface of the outer case 24. The flange 41a is engaged
with the filter support 30 of the inner case 23. The communication
between the space including the downstream end surface 13b of the
filter 13 and the clearance C1 is blocked by the flange 41a. This
structure further reduces the heat energy loss caused by the heat
transmission from the exhaust gas to the outer case 24, as compared
to a comparative example (which will be described later).
[0066] Also, the fourth embodiment is not provided with the
punching plate 38 such that the configuration becomes simple.
[0067] In a fifth embodiment illustrated in FIG. 9, the support
piece 30a, which is otherwise formed at the upstream end portion of
the inner case 23, is not provided, as is clear from comparison
with the first embodiment. The fifth embodiment thus has the
operational effects of the first embodiment, except for that of the
support piece 30a.
[0068] The exhaust gas purifying devices of the illustrated
embodiments were subjected to an operational test. One cycle of the
test was defined by sending exhaust gas to each of the devices,
heating the filter by the heater, and supplying supporting air for
burning the soot. The test included ten cycles. The test results
are shown in Table 1. The longitudinal dimension of the filter 13
was 150 millimeters.
1TABLE 1 Up- Down- Temperature Insulator stream stream Support
Punching Difference Corrosion Embodiment Drawing Blocker Blocker
Structure Piece Plate (C. .degree.) Crack Size 1 Formed None Double
Formed Formed 30 None 0 2 Formed Formed Double Formed Formed 20
None 0 3 Formed None Triple Formed Formed 26 None 0 4 Formed Formed
Double Formed None 40 None 0 5 Formed None Double None Formed 30
None 15 Comparative -- None None Single None None 150 Detected
15
[0069] In Table 1, the temperature difference indicates the
temperature difference between the middle portion and the outer
peripheral portion of the filter 13. The insulator corrosion size
indicates the size of the portion of the heat insulating material
lost due to corrosion in the test. Detection of cracks was
conducted visually after the test was completed. A purifying device
prepared as the comparative example did not include any of the
inner case, the upstream blocking member, the downstream blocking
member, the support piece, and the punching plate. This purifying
device was also subjected to the operational test.
[0070] As indicated clearly in Table 1, in the comparative example,
the temperature difference between the middle portion and the outer
peripheral portion of the filter was enlarged, causing cracks. In
contrast, the temperature difference was relatively small in the
first to fifth embodiments. Therefore, no crack was detected, and
the durability was improved.
[0071] Further, as is clear from comparison among the comparative
example, the first embodiment, and the fifth embodiment, the
support piece 30a operated efficiently for preventing the heat
insulating material from being corroded.
[0072] The present invention is not restricted to the illustrated
embodiments but may be embodied in the following forms.
[0073] In the illustrated embodiments, the punching plate 38 and
the ceramic foam reflector 39 are employed as the porous heat
reflectors. However, the heat reflectors are not limited to those
of the embodiments but may be, for example, a body formed of metal
meshes or ceramic fibers.
[0074] The ceramic foam reflector 39, which is provided at the
downstream side of the filter 13, may be replaced by the punching
plate 38. Further, the ceramic foam reflector 39 may be omitted. In
this manner, the number of the components of the exhaust gas
purifying device 1 is decreased.
[0075] The heater 34 does not necessarily have to be an AC heater
but may be, for example, a DC heater. Further, the electric heating
means such as the electric heater may be replaced by a non-electric
heating means such as a burner.
[0076] The fluid blocking member does not necessarily have to be
the flange 25, which projects from the outer peripheral surface of
the end of the inner case 23. The fluid blocking member may be a
different structure provided separately from the inner case 23.
[0077] The flange 25 may be fixed to the outer case 24, which is
the outermost layer, through, for example, welding, such that the
flange 25 is prohibited from being attached to or detached from the
outer case 24.
* * * * *