U.S. patent application number 13/218862 was filed with the patent office on 2012-03-01 for exhaust gas purification apparatus.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Masanori HATTA, Kazuhiro ITOH, Atsushi KIDOKORO, Noriyoshi TAKAHASHI.
Application Number | 20120047882 13/218862 |
Document ID | / |
Family ID | 44658646 |
Filed Date | 2012-03-01 |
United States Patent
Application |
20120047882 |
Kind Code |
A1 |
KIDOKORO; Atsushi ; et
al. |
March 1, 2012 |
EXHAUST GAS PURIFICATION APPARATUS
Abstract
An adhesion preventing member 21 formed in a substantially
circular-cylindrical shape is provided in an exhaust pipe 2. Urea
water injected from an injection nozzle 6 is introduced into an
inner peripheral side of the adhesion preventing member 21 through
an opening portion 21a, and hence adhesion of the urea water to an
inner peripheral surface 2a of the exhaust pipe 2 is inhibited. In
the adhesion preventing member 21, there are provided five
dispersion members 22 each having a plurality of through-holes 22a
and urea water is dispersed in the exhaust pipe 2 by flowing
through through-holes 22a. The adhesion preventing member 21 and
the dispersion members 22 are arranged at a part spaced apart from
the inner peripheral surface 2a of the exhaust pipe 2, that is, at
a part which is heated to high temperature in the exhaust pipe
2.
Inventors: |
KIDOKORO; Atsushi; (Aichi,
JP) ; HATTA; Masanori; (Aichi, JP) ;
TAKAHASHI; Noriyoshi; (Aichi, JP) ; ITOH;
Kazuhiro; (Mishima-shi, JP) |
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
KABUSHIKI KAISHA TOYOTA JIDOSHOKKI
Kariya-shi
JP
|
Family ID: |
44658646 |
Appl. No.: |
13/218862 |
Filed: |
August 26, 2011 |
Current U.S.
Class: |
60/301 |
Current CPC
Class: |
F01N 3/103 20130101;
F01N 2560/026 20130101; F01N 3/2066 20130101; F01N 2610/02
20130101; F01N 2570/18 20130101; F01N 2560/14 20130101; Y02T 10/24
20130101; F01N 13/009 20140601; Y02T 10/12 20130101; F01N 13/008
20130101; F01N 2610/102 20130101; F01N 3/021 20130101 |
Class at
Publication: |
60/301 |
International
Class: |
F01N 3/28 20060101
F01N003/28 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 27, 2010 |
JP |
2010-190329 |
Claims
1. An exhaust gas purification apparatus, comprising: an exhaust
pipe in which an exhaust gas discharged from an internal combustion
engine flows; urea-water addition means for injecting urea water
into the exhaust pipe; and a reduction catalyst for purifying
nitrogen oxides contained in the exhaust gas by using ammonia
generated from the urea water as a reducing agent, wherein the
exhaust pipe comprises therein at least one of: a plate-like
adhesion preventing member extending along a flow direction of the
exhaust gas; and a plate-like dispersion member extending along the
flow direction of the exhaust gas and provided with a plurality of
through-holes through which the urea water injected from the
urea-water addition means is flowable, and wherein the adhesion
preventing member and the dispersion member are arranged at a part
that faces the urea-water addition means and is heated to high
temperature in the exhaust pipe.
2. An exhaust gas purification apparatus according to claim 1,
comprising the adhesion preventing member, wherein the adhesion
preventing member is formed of a substantially cylindrical member,
and includes a urea-water introducing portion for introducing the
urea water injected from the urea-water addition means into an
inner peripheral side of the adhesion preventing member.
3. An exhaust gas purification apparatus according to claim 1,
wherein the urea-water addition means injects the urea water into a
fan shape substantially flat in a direction substantially
perpendicular to the flow direction of the exhaust gas.
4. An exhaust gas purification apparatus according to claim 1,
further comprising a NO.sub.x sensor for detecting concentration of
the nitrogen oxides contained in the exhaust gas on an upstream
side of the reduction catalyst, wherein the NO.sub.x sensor is
arranged at a part separated from the urea-water addition means by
the adhesion preventing member.
5. An exhaust gas purification apparatus according to claim 1,
comprising both the adhesion preventing member and the dispersion
member, wherein the dispersion member is arranged between the
urea-water addition means and the adhesion preventing member.
6. An exhaust gas purification apparatus according to claim 1,
comprising a plurality of the dispersion members.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an exhaust gas purification
apparatus, and more particularly, to a structure for purifying
nitrogen oxides contained in the exhaust gas of a diesel
engine.
[0003] 2. Description of the Related Art
[0004] As an example of an exhaust gas purification apparatus for
purifying nitrogen oxides (NO.sub.x) contained in the exhaust gas
of a diesel engine, there is a urea selective catalytic reduction
system (urea SCR system). For example, as described in Japanese
Patent Application Laid-open No. 2003-301737, the urea SCR system
comprises an SCR catalyst provided in an exhaust pipe and a
urea-water addition device for injecting urea water into the
exhaust pipe on an upstream side of the SCR catalyst. The SCR
catalyst uses ammonia (NH.sub.3), generated from urea water added
to the exhaust gas, as a reducing agent so as to react NO.sub.x
contained in the exhaust gas, and NO.sub.x is reduced to harmless
nitrogen (N.sub.2) and water (H.sub.2O).
[0005] In general, in the urea SCR system as described in Japanese
Patent Application Laid-open No. 2003-301737, ammonia is generated
by the hydrolysis of the urea water through the use of heat of the
exhaust gas. Here, for example, immediately after start-up of an
engine, the temperature of the exhaust pipe is lower than the
temperature of the exhaust gas because the outer peripheral surface
thereof is cooled by the outside air. In such a state, when the
urea water injected from the urea-water addition device adheres to
an inner peripheral surface of the exhaust pipe, the hydrolysis
does not occur. As a result, because the moisture in the urea water
is vaporized and urea remains, the residual urea may be deposited
on the inner peripheral surface of the exhaust pipe. In such a
case, the deposited urea does not reach the SCR catalyst.
Therefore, original required amount of ammonia is not supplied to
the SCR catalyst, and hence it is necessary to increase the amount
of urea water added.
[0006] Meanwhile, when the temperature of the exhaust pipe becomes
higher after elapse of a predetermined time period from the
start-up of the engine, ammonia is generated from urea deposited on
the inner peripheral surface of the exhaust pipe by the heat of the
exhaust pipe. Because a large part of the ammonia thus generated
becomes surplus, the ammonia passes through the SCR catalyst
without being reacted, and so-called ammonia slip occurs. That is,
the urea SCR system described in Japanese Patent Application
Laid-open No. 2003-301737 has difficulty in efficiently using the
urea water added to the exhaust gas.
SUMMARY OF THE INVENTION
[0007] The present invention has been made to solve such problems,
and it is therefore an object of the present invention to provide
an exhaust gas purification apparatus in which urea water injected
into an exhaust pipe is used with improved efficiency.
[0008] An exhaust gas purification apparatus according to the
present invention comprises: an exhaust pipe in which an exhaust
gas from an internal combustion engine flows; urea-water addition
means for injecting urea water into the exhaust pipe; and a
reduction catalyst for purifying nitrogen oxides contained in the
exhaust gas by using ammonia generated from the urea water as a
reducing agent, in which the exhaust pipe comprises therein at
least one of: a plate-like adhesion preventing member extending
along a flow direction of the exhaust gas; and a plate-like
dispersion member extending along the flow direction of the exhaust
gas and provided with a plurality of through-holes through which
the urea water injected from the urea-water addition means is
flowable, and in which the adhesion preventing member and the
dispersion member are arranged at a part that faces the urea-water
addition means and is heated to high temperature in the exhaust
pipe.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] In the accompanying drawings:
[0010] FIG. 1 is a schematic view of a structure of an exhaust gas
purification apparatus according to a first embodiment of the
present invention;
[0011] FIG. 2 is a schematic sectional side view of the structure
of the exhaust gas purification apparatus according to the first
embodiment;
[0012] FIG. 3 is a sectional view taken along III-III of FIG.
2;
[0013] FIG. 4 is a schematic sectional side view of a structure of
an exhaust gas purification apparatus according to a second
embodiment of the present invention;
[0014] FIG. 5 is a schematic sectional side view of a structure of
an exhaust gas purification apparatus according to a third
embodiment of the present invention; and
[0015] FIG. 6 is a schematic sectional side view of a structure of
an exhaust gas purification apparatus according to a fourth
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] In the following, description is made of embodiments of the
present invention with reference to the accompanying drawings.
First Embodiment
[0017] FIG. 1 is a schematic view of a structure of a diesel engine
provided with an exhaust gas purification apparatus according to
the first embodiment. An exhaust pipe 2 is connected to a diesel
engine 1 as an internal combustion engine. An exhaust gas
discharged from the diesel engine 1 into the exhaust pipe 2 flows
in a direction indicated by an arrow A, that is, from the side of
the diesel engine 1 as an upstream side. Midway in the exhaust pipe
2, there is provided an oxidation catalyst 3 for oxidizing carbon
monoxide (CO), hydrocarbons (HC) and the like contained in the
exhaust gas. On a downstream side of the oxidation catalyst 3,
there is provided a filter 4 for collecting particulate matter (PM)
contained in the exhaust gas. Further, on a downstream side of the
filter 4, there is provided an SCR catalyst 5 as a reduction
catalyst for purifying nitrogen oxides (NO.sub.x) contained in the
exhaust gas.
[0018] The SCR catalyst 5 is a catalyst for purifying NO.sub.x by
using ammonia (NH.sub.3), generated from urea water added to the
exhaust gas, as a reducing agent. Between the filter 4 and the SCR
catalyst 5, there is provided an injection nozzle 6 as a urea-water
addition means for injecting the urea water into the exhaust pipe
2. A urea-water tank 8 is connected to the injection nozzle 6
through intermediation of a connecting pipe 7, and the urea water
is stored in the urea-water tank 8. Further, midway in the
connecting pipe 7, there is provided a urea-water supply system 9
for supplying the urea water in the urea-water tank 8 to the
injection nozzle 6. The urea-water supply system 9 is electrically
connected to an ECU 10 for controlling operations of the diesel
engine 1 and the exhaust gas purification apparatus. In response to
signals output from the ECU 10 to the urea-water supply system 9,
the amount and timing of urea water injection from the injection
nozzle 6 are controlled.
[0019] On a downstream side of the SCR catalyst 5, there is
provided a slip catalyst 11 for removing unreacted ammonia which
passes through the SCR catalyst 5, for example, when an excess
amount of ammonia relative to an amount of NO.sub.x contained in
the exhaust gas is generated. A muffler (not shown) is connected to
a downstream side of the slip catalyst 11, and the exhaust gas
which passes through the slip catalyst 11 is discharged into the
air after exhaust noise is reduced in the muffler. Further, on an
upstream side and the downstream side of the SCR catalyst 5, there
are provided an upstream NO.sub.x sensor 12 and a downstream
NO.sub.x sensor 13 respectively. The upstream NO.sub.x sensor 12
and the downstream NO.sub.x sensor 13 are sensors for detecting the
concentration of NO.sub.x contained in the exhaust gas, and are
electrically connected to the ECU 10. The ECU 10 controls the
amount of urea water injection from the injection nozzle 6 based on
the amount of NO.sub.x detected by these NO.sub.x sensors.
[0020] Here, detailed description is made of the structure around
the injection nozzle 6 with reference to FIGS. 2 and 3. Note that,
for the sake of convenience in description, upper and lower
directions in the exhaust gas purification apparatus are defined by
arrows illustrated in FIGS. 2 and 3. As illustrated in FIG. 2, the
injection nozzle 6 injects urea water F, indicated by dashed lines,
downwardly in a direction substantially perpendicular to the
exhaust gas flow direction indicated by the arrow A. In the exhaust
pipe 2, at a part facing the injection nozzle 6, that is, at a part
to which the urea water F is injected from the injection nozzle 6,
there is provided an adhesion preventing member 21 which is a
substantially circular-cylindrical member extending along the
exhaust gas flow direction, and five dispersion members 22 which
are flat-plate like members extending along the exhaust gas flow
direction.
[0021] As illustrated in FIG. 3, the adhesion preventing member 21
is formed into the substantially circular-cylindrical shape by
curving a plate-like member along an inner peripheral surface 2a of
the exhaust pipe 2, and has an opening portion 21a, which extends
along an axial direction, on a side facing the injection nozzle 6.
The urea water F injected from the injection nozzle 6 is introduced
into an inner peripheral side of the adhesion preventing member 21
through the opening portion 21a, and therefore inhibits the urea
water F from adhering to the inner peripheral surface 2a of the
exhaust pipe 2. Here, the opening portion 21a constitutes a
urea-water introducing portion of the adhesion preventing member
21. Note that, the injection nozzle 6 injects the urea water F into
a fan shape substantially flat in a direction perpendicular to the
exhaust-gas flow direction indicated by the arrow A. Thus, in
comparison with a case where the same amount of urea water is
conically injected, more urea water is dispersed in a narrower
range, and hence the urea water can be efficiently added to the
exhaust gas.
[0022] The adhesion preventing member 21 is formed to have an outer
diameter smaller than an inner diameter of the exhaust pipe 2, and
is arranged so that an outer peripheral surface 21b of the adhesion
preventing member 21 is spaced apart from the inner peripheral
surface 2a of the exhaust pipe 2. Thus, when flowing through the
inside of the exhaust pipe 2, the exhaust gas passes through an
outer peripheral side and an inner peripheral side of the adhesion
preventing member 21. Here, although the exhaust pipe 2 is heated
by the exhaust gas flowing therein, an outer peripheral surface 2b
of the exhaust pipe 2 is cooled by the outside air. Thus, for
example, immediately after start-up of the diesel engine 1 (refer
to FIG. 1), the temperature of the exhaust pipe 2 is lower than the
temperature of the exhaust gas. The adhesion preventing member 21
is arranged at a part which is heated to high temperature in the
exhaust pipe 2, that is, at a part spaced apart from the inner
peripheral surface 2a of the exhaust pipe 2. Thus, the adhesion
preventing member 21 is rapidly heated by the exhaust gas passing
through the outer peripheral side and the inner peripheral side
thereof without being influenced by the temperature of the exhaust
pipe 2. Further, the adhesion preventing member 21 is shorter than
the exhaust pipe 2 in the exhaust gas flow direction, and hence
smaller in heat capacity. Thus, the adhesion preventing member 21
is more easily heated by the exhaust gas. Note that, a plurality of
protruding portions 2c project from the inner peripheral surface 2a
of the exhaust pipe 2, and the adhesion preventing member 21 is
retained in the exhaust pipe 2 through fixation of both end
portions thereof in the axial direction with respect to the
protruding portions 2c by welding or the like.
[0023] The five dispersion members 22 are flat-plate like members
arrayed along the upper and lower directions in the adhesion
preventing member 21, and are arranged so as to be perpendicular to
the upper and lower directions and so that clearances S are formed
between the dispersion members 22 adjacent to each other. As
described above, the adhesion preventing member 21 is arranged at
the part which is heated to high temperature in the exhaust pipe 2,
that is, at the part spaced apart from the inner peripheral surface
2a of the exhaust pipe 2. Thus, the dispersion members 22 provided
in the adhesion preventing member 21 are also arranged at the part
which is heated to high temperature in the exhaust pipe 2. Further,
this part is near the center of the exhaust pipe 2, and hence the
temperature at this part becomes higher. Thus, each of the
dispersion members 22 is rapidly heated by the exhaust gas passing
through upper surface sides and lower surface sides thereof without
being influenced by the temperature of the exhaust pipe 2. Further,
each of the dispersion members 22 has a plurality of through-holes
22a which pass therethrough in the upper and lower directions. A
part of the urea water F, which reaches the upper surface side of a
dispersion member 22, is blocked by colliding against the
dispersion member 22, and a residual part of the urea water F flows
through the through-holes 22a. Thus, when the amount of urea water
F which passes through the through-holes 22a is reduced, for
example, by 20% with respect to each dispersion member 22, the urea
water F is dispersed in the exhaust pipe 2, and hence the urea
water can be uniformly added to the exhaust gas.
[0024] Further, the upstream NO.sub.x sensor 12 on the upstream
side of the SCR catalyst 5 is provided at a part corresponding to
the outer peripheral side of the adhesion preventing member 21, and
is separated from the injection nozzle 6 by the adhesion preventing
member 21. That is, the adhesion preventing member 21 inhibits
adhesion of the urea water F injected from the injection nozzle 6
to the upstream NO.sub.x sensor 12. Here, in general, NO.sub.x
sensors for detecting the concentration of NO.sub.x contained in
the exhaust gas include fine ceramics such as zirconia as a
material thereof. Further, the NO.sub.x sensor is exposed to the
exhaust gas flowing in the exhaust pipe 2, and hence operates under
high temperatures, for example, of from 600.degree. C. to
1,000.degree. C. If the urea water adheres to the NO.sub.x sensor
operated under such high temperatures, so-called thermal shock,
where abrupt temperature change occurs, is applied, and hence
breakage such as cracking may occur.
[0025] In order to prevent such breakage, a NO.sub.x sensor is
normally provided a predetermined distance upstream of the
injection nozzle 6 so as to prevent adhesion of the urea water F.
However, the upstream NO.sub.x sensor 12 of the present invention
is separated from the injection nozzle 6 by the adhesion preventing
member 21, and hence does not suffer breakage owing to adhesion of
the urea water F. Thus, the upstream NO.sub.x sensor 12 can be
arranged near the injection nozzle 6. As a result, the distance
between the filter 4 and the SCR catalyst 5 (refer to FIG. 1) can
be reduced for the purpose of downsizing the apparatus. Further,
decreases in exhaust gas temperature before the exhaust gas reaches
the SCR catalyst 5 can be inhibited, and hence NO.sub.x can be
efficiently purified by the SCR catalyst 5.
[0026] Next, description is made of operation of the exhaust gas
purification apparatus according to the first embodiment of the
present invention.
[0027] As illustrated in FIG. 1, when the operation of the diesel
engine 1 is started, the exhaust gas discharged into the exhaust
pipe 2 flows in the direction indicated by the arrow A, and
sequentially passes through the oxidation catalyst 3 and the filter
4. Carbon monoxide (CO), hydrocarbons (HC) and the like contained
in the exhaust gas are oxidized while passing through the oxidation
catalyst 3, and the particulate matter contained in the exhaust gas
is removed while passing through the filter 4. Further, when the
operation of the diesel engine 1 is started, the ECU 10 outputs
signals to the urea-water supply system 9 so as to start injection
of the urea water by the injection nozzle 6, and urea water is
added to the exhaust gas passing through the filter 4. The urea
water thus added is subjected to hydrolysis by the heat of the
exhaust gas, with the result that ammonia is generated.
[0028] Here, as illustrated in FIG. 2, the substantially
circular-cylindrical adhesion preventing member 21 and the five
dispersion members 22 are provided at the part facing the injection
nozzle 6, and the urea water F injected from the injection nozzle 6
is introduced into the inner peripheral side of the adhesion
preventing member 21 through the opening portion 21a of the
adhesion preventing member 21. Thus, in this state, the adhesion
preventing member 21 inhibits adhesion of the urea water F to the
inner peripheral surface 2a of the exhaust pipe 2. Further, the
adhesion preventing member 21 is arranged at the part where the
outer peripheral surface 21b thereof is spaced apart from the inner
peripheral surface 2a of the exhaust pipe 2, that is, at the part
which is heated to high temperature in the exhaust pipe 2. Thus,
the adhesion preventing member 21 is heated by the exhaust gas
without being influenced by the temperature of the exhaust pipe 2.
Therefore, even if the temperature of the exhaust pipe 2 is lower
than the temperature of the exhaust gas such as immediately after
the start-up of the diesel engine 1, hydrolysis of the urea water
adhering to the adhesion preventing member 21 is not hindered.
Thus, ammonia is generated from a large part of the urea water
added to the exhaust gas.
[0029] Further, the dispersion members 22 provided in the adhesion
preventing member 21 each block a part of the injected urea water
F, and the residual parts thereof flow through to the lower
dispersion member 22. That is, the urea water F is uniformly
dispersed by the dispersion members 22 in the exhaust pipe 2, and
hence ammonia generated from the urea water F is uniformly supplied
to the SCR catalyst 5 (refer to FIG. 1). Note that, the dispersion
members 22 are provided in the adhesion preventing member 21, and
heated by the exhaust gas as well as the adhesion preventing member
21. Thus, the hydrolysis of the urea water adhering to the
dispersion members 22 is not hindered, and ammonia is generated
from a large part of the urea water. Therefore, the moisture of the
urea water adhering to the adhesion preventing member 21 and the
dispersion members 22 does not evaporate and urea does not remain.
As a result, efficiency in the use of the urea water F injected by
the injection nozzle 6 is improved.
[0030] When ammonia generated from the urea water F is supplied as
described above, the SCR catalyst 5 uses ammonia as a reducing
agent so as to reduce NO.sub.x contained in the exhaust gas to
harmless nitrogen (N.sub.2) and water (H.sub.2O). If the exhaust
gas passing through the SCR catalyst 5 contains surplus ammonia,
ammonia is removed by the slip catalyst 11. The exhaust gas passing
through the slip catalyst 11 is, after noise is reduced in the
muffler (not shown), discharged into the air. Further, the upstream
NO.sub.x sensor 12 and the downstream NO.sub.x sensor always detect
the concentration of NO.sub.x on the upstream side and the
downstream side of the SCR catalyst 5 respectively. The ECU 10
controls the amount of injection of the urea water F from the
injection nozzle 6 based on the concentration of NO.sub.x detected
by these NO.sub.x sensors.
[0031] As described above, because the adhesion preventing member
21 and the dispersion members 22 are provided at the part facing
the injection nozzle 6, adhesion of the urea water F to the inner
peripheral surface of the exhaust pipe 2 is inhibited. The adhesion
preventing member 21 and the dispersion members 22 are arranged at
the part which is heated to high temperature in the exhaust pipe 2,
that is, at the part spaced apart from the inner peripheral surface
2a of the exhaust pipe 2, and hence ammonia is not hindered from
being generated from the urea water adhering to these members. That
is, an amount of urea deposited in the exhaust pipe 2 is reduced,
and a large part of the injected urea water is used for
purification of NO.sub.x. Further, the adhesion preventing member
21 and the dispersion members 22 are members extending parallel to
the exhaust gas flow direction, and hence NO.sub.x can be purified
without an increase in pressure loss of the exhaust gas. Thus,
efficiency in the use of urea water can be improved in an exhaust
gas purification apparatus in which the urea water is injected into
the exhaust pipe 2.
[0032] Further, the adhesion preventing member 21 is formed into a
substantially circular-cylindrical shape having the opening portion
21a so that the urea water F is introduced into the inner
peripheral side of the adhesion preventing member 21 through the
opening portion 21a. Thus, the adhesion of the urea water to the
inner peripheral surface 2a of the exhaust pipe 2 can be further
inhibited.
[0033] Still further, the injection nozzle 6 injects the urea water
into a fan shape substantially flat in the direction substantially
perpendicular to the exhaust gas flow direction. Thus, the urea
water can be efficiently added to the exhaust gas flowing in the
exhaust pipe 2. Further, the apparatus can be downsized in the
exhaust gas flow direction.
[0034] The upstream NO.sub.x sensor 12 is arranged at the part
separated from the injection nozzle 6 by the adhesion preventing
member 21, and hence the upstream NO.sub.x sensor 12 can be
arranged near the injection nozzle 6. As a result, the exhaust pipe
2 on the upstream side of the SCR catalyst 5 is shortened, and the
entire apparatus is downsized. Thus, mountability to vehicles is
enhanced, and the amount of decrease of the exhaust gas temperature
before the exhaust gas reaches the SCR catalyst 5 can be inhibited,
and hence NO.sub.x can be purified with improved efficiency by the
SCR catalyst 5.
[0035] Further, the exhaust gas purification apparatus is provided
with the adhesion preventing member 21 and the plurality of
dispersion members 22. Thus, the urea water is dispersed by the
dispersion members 22, and adhesion of the urea water to the
exhaust pipe 2 is inhibited by the adhesion preventing member.
Therefore, ammonia is generated with improved efficiency, and
efficiency in the use of the urea water is further improved.
[0036] Still further, the dispersion members 22 are retained by the
adhesion preventing member 21. Thus, in comparison with a structure
in which the dispersion members 22 are retained directly on the
inner peripheral surface 2a of the exhaust pipe 2, the dispersion
members 22 are less liable to be influenced by the temperature of
the exhaust pipe 2, and more easily heated by the exhaust gas.
Second Embodiment
[0037] Next, description is made of the exhaust gas purification
apparatus according to a second embodiment of the present
invention.
[0038] While the exhaust gas purification apparatus according to
the first embodiment includes the substantially
circular-cylindrical adhesion preventing member and the flat-plate
like dispersion members, the exhaust gas purification apparatus
according to the second embodiment includes only a flat-plate like
adhesion preventing member. Note that, in the embodiments described
below, the same or similar components are denoted by the same
reference symbols as those in FIGS. 1 to 4, and hence detailed
description thereof is omitted.
[0039] As illustrated in FIG. 4, in the exhaust pipe 2, there is
provided a flat-plate like adhesion preventing member 31 extending
along the exhaust gas flow direction, which is fixed to the inner
peripheral surface 2a of the exhaust pipe 2 by welding or the like.
The adhesion preventing member 31 is arranged at a part facing the
injection nozzle 6 in the exhaust pipe 2, that is, at a part to
which the urea water F is injected from the injection nozzle 6 so
as to pass through the central portion of the exhaust pipe 2. Thus,
the urea water F injected from the injection nozzle 6 collides
against the adhesion preventing member 31. Further, an upper
surface 31a and a lower surface 31b of the adhesion preventing
member 31 are spaced apart from the inner peripheral surface 2a of
the exhaust pipe 2, and hence the adhesion preventing member 31 is
arranged at a part which is heated to high temperature in the
exhaust pipe 2. Other structural details are similar to those in
the first embodiment.
[0040] As described above, even when only the flat-plate like
adhesion preventing member 31 is used, the urea water F is
inhibited from adhering to the inner peripheral surface 2a of the
exhaust pipe 2. Thus, similarly to the first embodiment, urea can
be inhibited from being deposited on the inner peripheral surface
2a of the exhaust pipe 2.
Third Embodiment
[0041] Next, description is made of an exhaust gas purification
apparatus according to a third embodiment of the present
invention.
[0042] Unlike the exhaust gas purification apparatus according to
the second embodiment, the exhaust gas purification apparatus
according to the third embodiment further includes the flat-plate
like dispersion members in the first embodiment. As illustrated in
FIG. 5, at the part facing the injection nozzle 6 in the exhaust
pipe 2, there are provided an adhesion preventing member 41 and
five dispersion members 42, each of which is a flat-plate like
member. Each of the dispersion members 42 has a plurality of
through-holes 42a similar to the through-holes 22a of the
dispersion members 22 in the first embodiment, and allows the urea
water F injected from the injection nozzle 6 to sequentially pass
through from an upper side to a lower side. Further, the adhesion
preventing member 41 is provided below the dispersion members 42 so
as to inhibit the urea water F, which passes through the lowermost
dispersion member 42, from adhering to the inner peripheral surface
2a of the exhaust pipe 2. Other structural details are similar to
those in the first embodiment.
[0043] As described above, even when the adhesion preventing member
41 and the dispersion members 42, each of which has a flat-plate
like shape, are used, similarly to the first embodiment, the urea
water F is inhibited from adhering to the inner peripheral surface
2a of the exhaust pipe 2, and the dispersion members 42 disperse
the urea water F. Thus, efficiency in the use of the urea water can
be improved.
Fourth Embodiment
[0044] Next, description is made of an exhaust gas purification
apparatus according to a fourth embodiment of the present
invention.
[0045] While the adhesion preventing member in the exhaust gas
purification apparatus according to the first embodiment is
arranged in a linear exhaust pipe 2, the adhesion preventing member
in the exhaust gas purification apparatus according to the fourth
embodiment is arranged in an exhaust pipe having a bent portion as
described below. As illustrated in FIG. 6, an exhaust pipe 52 of
the exhaust gas purification apparatus according to the fourth
embodiment includes an upstream straight portion 52a connected to
the filter 4 in the first embodiment (refer to FIG. 1), and a
downstream straight portion 52b connected to the SCR catalyst 5
(refer to FIG. 1). The upstream straight portion 52a and the
downstream straight portion 52b are connected to each other through
intermediation of a bent portion 52c. Thus, in the exhaust pipe 52,
an exhaust gas flowing straight in the upstream straight portion
52a as indicated by an arrow B1 is turned at the bent portion 52c
as indicated by an arrow B2, and then flows straight in the
downstream straight portion in a direction indicated by an arrow
B3.
[0046] In the exhaust pipe 52 structured as described above, at a
part positioned on an extension of the direction indicated by the
arrow B1, that is, at a part positioned on an extension of a flow
line of the exhaust gas flowing in the upstream straight portion
52a, there is provided a plate-like adhesion preventing member 51
bent with the same curvature as that of the bent portion 52c .
Further, at an inner peripheral side of the bent portion 52c, the
injection nozzle 6 is provided at a part facing the adhesion
preventing member 51 so that the urea water F injected from the
injection nozzle 6 collides against the adhesion preventing member
51. Here, the adhesion preventing member 51 is provided so as to be
spaced apart from an inner peripheral surface 52d of the exhaust
pipe 52. Thus, when the exhaust gas flows in the bent portion 52c
of the exhaust pipe 52, it flows through the side of a front
surface 51a and the side of a rear surface 51b of the adhesion
preventing member 51.
[0047] Further, a part on an outer peripheral side of the bent
portion 52c of the exhaust pipe 52, that is, a part provided with
the adhesion preventing member 51, is a part against which the
exhaust gas flowing in the upstream straight portion 52a of the
exhaust pipe 52 collides. Thus, in the exhaust pipe 52, this part
is a part which is heated to high temperature by the exhaust gas.
Therefore, the adhesion preventing member 51 is heated by the
exhaust gas. As a result, the adhesion preventing member 51
inhibits adhesion of the urea water injected from the injection
nozzle 6 to the inner peripheral surface 52d of the exhaust pipe
52. Further, because the adhesion preventing member 51 is heated by
the exhaust gas, ammonia is generated without hindrance of
hydrolysis.
[0048] As described above, in the bent portion 52c of the exhaust
pipe 52, the part positioned on the extension of the flow line of
the exhaust gas flowing in the upstream straight portion 52a is
also heated to high temperature. Thus, even when the adhesion
preventing member 51 is arranged at such a part, efficiency in the
use of the urea water can be improved.
[0049] In the first embodiment, although the adhesion preventing
member is formed of a substantially circular-cylindrical member,
the shape of the adhesion preventing member is not limited thereto.
As long as the adhesion preventing member is capable of inhibiting
the urea water injected from the injection nozzle from adhering to
the inner peripheral surface of the exhaust pipe, other shapes such
as a cylindrical member having a polygonal cross-section may be
employed. Further, in the first embodiment, the opening portion
extending along the axial direction of the adhesion preventing
member constitutes the urea-water introducing portion.
Alternatively, for example, the adhesion preventing member may be
formed of a member having a perfect circular-cylindrical shape,
and, such as a rectangular or circular hole may be formed at the
part facing the injection nozzle so as to be used as the urea-water
introducing portion.
[0050] In the third embodiment, although the injection nozzle, the
adhesion preventing member, the dispersion members and the NO.sub.x
sensor are provided in the exhaust pipe, the arrangement position
of those components is not limited thereto. For example, as
illustrated in FIG. 1, the SCR catalyst 5 generally includes a
hollow tapered cone 5a connected to the exhaust pipe 2, and the
injection nozzle, the adhesion preventing member, the dispersion
members, and the NO.sub.x sensor may be provided to the cone
5a.
[0051] Further, in the above-mentioned embodiments, although the
ECU 10 controls the amount of urea water injected from the
injection nozzle 6 based on the amount of NO.sub.x detected by the
NO.sub.x sensors 12 and 13, the ECU 10 may control the urea water
addition amount based on the concentration of NO.sub.x estimated
from engine conditions.
[0052] Still further, although each of the dispersion members 22 in
the first embodiment and the adhesion preventing members and the
dispersion members in the second and third embodiments has a flat
surface shape, a cylindrical shape or a corrugated shape may also
be employed.
* * * * *