U.S. patent application number 12/203784 was filed with the patent office on 2009-03-26 for exhaust emission purification system for internal combustion engine.
This patent application is currently assigned to HONDA MOTOR CO., LTD.. Invention is credited to Fumihiro MONDORI, Hiroshi OHNO.
Application Number | 20090077948 12/203784 |
Document ID | / |
Family ID | 39970950 |
Filed Date | 2009-03-26 |
United States Patent
Application |
20090077948 |
Kind Code |
A1 |
MONDORI; Fumihiro ; et
al. |
March 26, 2009 |
EXHAUST EMISSION PURIFICATION SYSTEM FOR INTERNAL COMBUSTION
ENGINE
Abstract
An exhaust emission purification system for an internal
combustion engine, which can appropriately recover the cleanup
performance of a NOx purification device that is disposed on the
downstream side of a SOx absorbent is disclosed. The exhaust
emission purification system is provided with a SOx trap 13, which
is provided on an upstream side of a NOx purification device 17,
and a SOx desorption temperature of the SOx trap 13 being higher
than that of the NOx purification device 17; a sulfur purge
determination portion 21 that determines whether to execute a
sulfur purge, on the basis of the SOx concentration detected by a
SOx sensor 16; a sulfur purge execution portion 22 that changes the
exhaust gas into a high temperature reducing atmosphere, in cases
where a sulfur purge determination portion 21 determines to execute
a sulfur purge of the NOx purification device 17.
Inventors: |
MONDORI; Fumihiro;
(Wako-shi, JP) ; OHNO; Hiroshi; (Wako-shi,
JP) |
Correspondence
Address: |
ARENT FOX LLP
1050 CONNECTICUT AVENUE, N.W., SUITE 400
WASHINGTON
DC
20036
US
|
Assignee: |
HONDA MOTOR CO., LTD.
Tokyo
JP
|
Family ID: |
39970950 |
Appl. No.: |
12/203784 |
Filed: |
September 3, 2008 |
Current U.S.
Class: |
60/285 ; 60/295;
60/299 |
Current CPC
Class: |
Y02T 10/22 20130101;
Y02T 10/40 20130101; F01N 9/00 20130101; Y02T 10/12 20130101; Y02T
10/47 20130101; F01N 13/009 20140601; F01N 2560/027 20130101; F01N
3/085 20130101; F01N 3/0842 20130101; F01N 2240/25 20130101; F01N
3/2073 20130101; F01N 2560/026 20130101; F01N 3/0885 20130101; F01N
2560/025 20130101 |
Class at
Publication: |
60/285 ; 60/295;
60/299 |
International
Class: |
F01N 9/00 20060101
F01N009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 26, 2007 |
JP |
2007-248904 |
Claims
1. An exhaust emission purification system for an internal
combustion engine, comprising: a NOx absorbent catalyst disposed in
an exhaust passage of the internal combustion engine, the absorbent
absorbing NOx in exhaust gas; a SOx absorbent disposed in an
upstream side of the NOx absorbent catalyst in the exhaust passage,
the absorbent absorbing SOx in the exhaust gas, and a SOx
desorption temperature of the absorbent being higher than that of
the NOx absorbent catalyst; a SOx concentration detecting means for
detecting SOx concentration in the exhaust gas that circulates
between the SOx absorbent and the NOx absorbent catalyst in the
exhaust passage; a regeneration determination means for determining
whether to execute a regeneration process for the NOx absorbent
catalyst so as to desorb SOx that has been absorbed to the NOx
absorbent catalyst, on the basis of the SOx concentration detected
by the SOx concentration detecting means; and a regeneration
execution means for changing the exhaust gas into a high
temperature reducing atmosphere in cases where the regeneration
determination means determines to execute the regeneration process
for the NOx absorbent catalyst.
2. The exhaust emission purification system for an internal
combustion engine according to claim 1, wherein the SOx absorbent
does not substantially comprise precious metals.
3. The exhaust emission purification system for an internal
combustion engine according to claim 1, wherein a substrate of the
SOx absorbent does not substantially comprise silica.
4. The exhaust emission purification system for an internal
combustion engine according to claim 1, wherein the NOx absorbent
catalyst is a catalyst which generates ammonia and absorbs the
generated ammonia when the air-fuel ratio of the exhaust gas is
rich, and which reduces NOx to elements thereof with the absorbed
ammonia when the air-fuel ratio of the exhaust gas is lean.
5. The exhaust emission purification system for an internal
combustion engine according to claim 4, wherein a three-way
catalyst is disposed in an upstream side of the SOx absorbent in
the exhaust passage.
6. An exhaust emission purification system for an internal
combustion engine, comprising: a NOx absorbent catalyst disposed in
an exhaust passage of the internal combustion engine, the absorbent
absorbing NOx in exhaust gas; a SOx absorbent disposed in an
upstream side of the NOx absorbent catalyst in the exhaust passage,
the absorbent absorbing SOx in the exhaust gas, and a SOx
desorption temperature of the absorbent being higher than that of
the NOx absorbent catalyst; a NOx concentration detecting means for
detecting NOx concentration in the exhaust gas that circulates in a
downstream side of the NOx absorbent catalyst in the exhaust
passage; a regeneration determination means for determining whether
to execute a regeneration process for the NOx absorbent catalyst so
as to desorb SOx that has been absorbed to the NOx absorbent
catalyst, on the basis of the NOx concentration detected by the NOx
concentration detecting means; and a regeneration execution means
for changing the exhaust gas into a high temperature reducing
atmosphere in cases where the regeneration determination means
determines to execute the regeneration process for the NOx
absorbent catalyst.
7. The exhaust emission purification system for an internal
combustion engine according to claim 6, wherein the SOx absorbent
does not substantially comprise precious metals.
8. The exhaust emission purification system for an internal
combustion engine according to claim 6, wherein a substrate of the
SOx absorbent does not substantially comprise silica.
9. The exhaust emission purification system for an internal
combustion engine according to claim 6, wherein the NOx absorbent
catalyst is a catalyst which generates ammonia and absorbs the
generated ammonia when the air-fuel ratio of the exhaust gas is
rich, and which reduces NOx to elements thereof with the absorbed
ammonia when the air-fuel ratio of the exhaust gas is lean.
10. The exhaust emission purification system for an internal
combustion engine according to claim 9, wherein a three-way
catalyst is disposed in an upstream side of the SOx absorbent in
the exhaust passage.
11. An exhaust emission purification system for an internal
combustion engine, comprising: a NOx absorbent catalyst disposed in
an exhaust passage of the internal combustion engine, the absorbent
absorbing NOx in exhaust gas; a SOx absorbent disposed in an
upstream side of the NOx absorbent catalyst in the exhaust passage,
the absorbent absorbing SOx in the exhaust gas, and a SOx
desorption temperature of the absorbent being higher than that of
the NOx absorbent catalyst; an air-fuel ratio detecting means for
detecting an air-fuel ratio in the exhaust gas that circulates in a
downstream side of the NOx absorbent catalyst in the exhaust
passage; a regeneration determination means for determining whether
to execute a regeneration process for the NOx absorbent catalyst so
as to desorb SOx that has been absorbed to the NOx absorbent
catalyst, on the basis of the air-fuel ratio detected by the
air-fuel ratio detecting means; and a regeneration execution means
for changing the exhaust gas into a high temperature reducing
atmosphere in cases where the regeneration determination means
determines to execute the regeneration process for the NOx
absorbent catalyst.
12. The exhaust emission purification system for an internal
combustion engine according to claim 11, wherein the SOx absorbent
does not substantially comprise precious metals.
13. The exhaust emission purification system for an internal
combustion engine according to claim 11, wherein a substrate of the
SOx absorbent does not substantially comprise silica.
14. The exhaust emission purification system for an internal
combustion engine according to claim 11, wherein the NOx absorbent
catalyst is a catalyst which generates ammonia and absorbs the
generated ammonia when the air-fuel ratio of the exhaust gas is
rich, and which reduces NOx to elements thereof with the absorbed
ammonia when the air-fuel ratio of the exhaust gas is lean.
15. The exhaust emission purification system for an internal
combustion engine according to claim 14, wherein a three-way
catalyst is disposed in an upstream side of the SOx absorbent in
the exhaust passage.
Description
[0001] This application is based on and claims the benefit of
priority from Japanese Patent Application No. 2007-248904, filed on
26 Sep. 2007, the content of which is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an exhaust emission
purification system for an internal combustion engine. More
particularly, the present invention relates to an exhaust emission
purification system for an internal combustion engine, which is
provided with a NOx absorbent catalyst for absorbing NOx in exhaust
gas.
[0004] 2. Related Art
[0005] A technique for reducing the amount of emission of NOx
(nitrogen oxide) is conventionally known, in which a NOx
purification device is provided for an exhaust system of an
internal combustion engine, thereby absorbing NOx in exhaust gas.
On the other hand, in exhaust gas exhausted from the internal
combustion engine, SOx (sulfur oxide) is included in addition to
NOx, SOx being generated by oxidation of sulfur contained in fuel
and engine oil. When such SOx in exhaust gas is absorbed by the NOx
purification device, the cleanup performance of the NOx
purification device is deteriorated.
[0006] For this reason, an exhaust emission purification system has
been conventionally proposed, in which a SOx absorbent for
absorbing SOx is provided on the upstream side of a NOx
purification device, thereby reducing the amount of SOx which flows
into the NOx purification device (see Japanese Unexamined Patent
Application, First Publication No. 2006-329018). However, when, for
example, absorption performance of the SOx absorbent is
deteriorated due to aging deterioration and the like, SOx leaks
from the SOx absorbent. As a result, SOx is absorbed to the NOx
purification device provided on the downstream side of the SOx
absorbent. For this reason, in cases where the cleanup performance
of the NOx purification device may be deteriorated, or has been
deteriorated, it is preferable to appropriately recover the cleanup
performance.
[0007] Accordingly, for example, Japanese Unexamined Patent
Application, First Publication No. 2006-138223 discloses an exhaust
emission purification system, in which extra SOx absorbent is held
in advance, and when it is presumed that the SOx retention capacity
by the main SOx absorbent is deteriorated, SOx absorbent is newly
supplied. This prevents the deterioration of the performance of the
NOx purification device due to absorption of SOx onto the NOx
purification device.
SUMMARY OF THE INVENTION
[0008] However, in the exhaust emission purification system as
described above, it is necessary to newly provide a holding means
for holding SOx absorbent in order to newly supply SOx, and a
supplying means for supplying SOx absorbent held by this holding
means. Accordingly, it is understood that the holding means and the
supplying means increase the size of the device and increase the
cost.
[0009] Moreover, it is conceivable to provide SOx absorbent with
high capacity, in addition to this exhaust emission purification
system. However, in order to improve capacity of the SOx absorbent,
it is required to increase the size of a substrate that supports
the SOx absorbent. Accordingly, it is understood that the size of
the device is increased and the manufacturing cost is increased in
this case as well.
[0010] The present invention has been made in consideration of the
above. It is an object of the present invention to provide an
exhaust emission purification system for an internal combustion
engine, which can appropriately recover the cleanup performance of
the NOx purification device that is provided on the downstream side
of SOx absorbent, without increasing the size and cost of the
device.
[0011] The present invention provides an exhaust emission
purification system for an internal combustion engine (1),
including: a NOx absorbent catalyst (17) disposed in an exhaust
passage (4) of the internal combustion engine, the absorbent
absorbing NOx in exhaust gas; a SOx absorbent (13) disposed in an
upstream side of the NOx absorbent catalyst in the exhaust passage,
the absorbent absorbing SOx in the exhaust gas, and a SOx
desorption temperature of the absorbent being higher than that of
the NOx absorbent catalyst; a SOx concentration detecting means
(16) for detecting SOx concentration in the exhaust gas that
circulates between the SOx absorbent and the NOx absorbent catalyst
in the exhaust passage; a regeneration determination means (21) for
determining whether to execute a regeneration process for the NOx
absorbent catalyst so as to desorb SOx that has been absorbed to
the NOx absorbent catalyst, on the basis of the SOx concentration
detected by the SOx concentration detecting means; and a
regeneration execution means (22) for changing the exhaust gas into
a high temperature reducing atmosphere in cases where the
regeneration determination means determines to execute the
regeneration process for the NOx absorbent catalyst.
[0012] With this configuration, for example, when the SOx
absorption performance of the SOx absorbent is deteriorated due to
aging degradation and the like, thereby leaking SOx from the SOx
absorbent, the SOx concentration on the downstream side of the SOx
absorbent of the exhaust passage is increased. The increase of the
SOx concentration is detected by the SOx concentration detecting
means for detecting the SOx concentration in the section between
the SOx absorbent and the NOx absorbent catalyst. On the basis of
the detection of the SOx concentration, it is determined whether to
execute a regeneration process of the NOx absorbent catalyst. When
it is determined to execute a regeneration process, the exhaust gas
is changed into a high temperature reducing atmosphere, thereby
desorbing SOx that has been absorbed to the NOx absorbent catalyst.
This makes it possible to recover the NOx cleanup performance of
the NOx absorbent catalyst, even in cases where the SOx absorption
performance of the SOx absorbent is deteriorated.
[0013] Moreover, since the SOx desorption temperature of the SOx
absorbent used here is higher than the desorption temperature of
the NOx absorbent catalyst, SOx is not desorbed from the SOx
absorbent, even if the exhaust gas is changed into the high
temperature reducing atmosphere in the regeneration process.
Therefore, it is not necessary to newly provide a passage and the
like for bypassing the NOx absorbent catalyst in order to prevent
the deterioration of the cleanup performance of the NOx absorbent
catalyst. In this way, newly providing the SOx concentration
detecting means, the regeneration determination means, and the
regeneration execution means, suffices in order to appropriately
recover the cleanup performance of the NOx absorbent catalyst.
Accordingly, the size of the device is not increased, and the
manufacturing cost is not increased either. Moreover, when the
exhaust gas is changed into a high temperature reducing atmosphere
in the regeneration process, for example, a post injection is
carried out. According to the present invention, it is determined
whether to execute a regeneration process on the basis of the SOx
concentration detected by the SOx concentration detecting means.
This makes it possible to minimize the number of regeneration
processes to be executed. Accordingly, it is possible to minimize
the consumption of a fuel required for execution of regeneration
processes and to minimize the thermal degradation of the catalyst
provided to the exhaust passage.
[0014] The present invention further provides an exhaust emission
purification system for an internal combustion engine, including: a
NOx absorbent catalyst disposed in an exhaust passage of the
internal combustion engine, the absorbent absorbing NOx in exhaust
gas; a SOx absorbent disposed in an upstream side of the NOx
absorbent catalyst in the exhaust passage, the absorbent absorbing
SOx in the exhaust gas, and a SOx desorption temperature of the
absorbent being higher than that of the NOx absorbent catalyst; a
NOx concentration detecting means (16A) for detecting NOx
concentration in the exhaust gas that circulates in a downstream
side of the NOx absorbent catalyst in the exhaust passage; a
regeneration determination means (21A) for determining whether to
execute a regeneration process for the NOx absorbent catalyst so as
to desorb SOx that has been absorbed to the NOx absorbent catalyst,
on the basis of the NOx concentration detected by the NOx
concentration detecting means; and a regeneration execution means
(22A) for changing the exhaust gas into a high temperature reducing
atmosphere in cases where the regeneration determination means
determines to execute the regeneration process for the NOx
absorbent catalyst.
[0015] With this configuration, for example, the SOx absorption
performance of the SOx absorbent is deteriorated due to aging
degradation and the like, SOx leaks from the SOx absorbent. As a
result, SOx is absorbed to the NOx absorbent catalyst provided on
the downstream side of the SOx absorbent, and the cleanup
performance of the NOx absorbent catalyst begins to deteriorate.
When the cleanup performance of the NOx absorbent catalyst is
deteriorated, the NOx concentration in the downstream side of the
NOx absorbent catalyst is increased as compared to the normal
state. Then the NOx concentration detecting means detects the NOx
concentration in the downstream side of the NOx absorbent catalyst.
On the basis of the detection of the NOx concentration, it is
determined whether to execute a regeneration process of the NOx
absorbent catalyst. When it is determined to execute the
regeneration process, the exhaust gas is changed into a high
temperature reducing atmosphere, thereby desorbing SOx that has
been absorbed to the NOx absorbent catalyst. This makes it possible
to recover the NOx cleanup performance of the NOx absorbent
catalyst, even in cases where the SOx absorption performance of the
SOx absorbent is deteriorated.
[0016] Moreover, since the SOx desorption temperature of the SOx
absorbent used here is higher than the desorption temperature of
the NOx absorbent catalyst, SOx is not desorbed from the SOx
absorbent, even if the exhaust gas is changed into the high
temperature reducing atmosphere in the regeneration process.
Therefore, it is not necessary to newly provide a passage and the
like for bypassing the NOx absorbent catalyst in order to prevent
the deterioration of the cleanup performance of the NOx absorbent
catalyst. In this way, newly providing the NOx concentration
detecting means, the generation determination means, and the
regeneration execution means, suffices in order to appropriately
recover the cleanup performance of the NOx absorbent catalyst.
Accordingly, the size of the device is not increased, and the
manufacturing cost is not increased either. Moreover, when the
exhaust gas is changed into a high temperature reducing atmosphere
in the regeneration process, for example, a post injection is
carried out. According to the present invention, it is determined
whether to execute a regeneration process on the basis of the NOx
concentration detected by the NOx concentration detecting means.
This makes it possible to minimize the number of regeneration
processes to be executed. Accordingly, it is possible to minimize
the consumption of fuel required for execution of regeneration
processes and to minimize the thermal degradation of the catalyst
provided to the exhaust passage.
[0017] The present invention further provides an exhaust emission
purification system for an internal combustion engine, including: a
NOx absorbent catalyst disposed in an exhaust passage of the
internal combustion engine, the absorbent absorbing NOx in exhaust
gas; a SOx absorbent disposed in an upstream side of the NOx
absorbent catalyst in the exhaust passage, the absorbent absorbing
SOx in the exhaust gas, and a SOx desorption temperature of the
absorbent being higher than that of the NOx absorbent catalyst; an
air-fuel ratio detecting means (16B) for detecting an air-fuel
ratio in the exhaust gas that circulates in a downstream side of
the NOx absorbent catalyst in the exhaust passage; a regeneration
determination means (21B) for determining whether to execute a
regeneration process for the NOx absorbent catalyst so as to desorb
SOx that has been absorbed to the NOx absorbent catalyst, on the
basis of the air-fuel ratio detected by the air-fuel ratio
detecting means; and a regeneration execution means (22B) for
changing the exhaust gas into a high temperature reducing
atmosphere in cases where the regeneration determination means
determines to execute the regeneration process for the NOx
absorbent catalyst.
[0018] With this configuration, for example, the SOx absorption
performance of the SOx absorbent is deteriorated due to aging
degradation and the like, SOx leaks from the SOx absorbent. As a
result, SOx is absorbed to the NOx absorbent catalyst provided on
the downstream side of the SOx absorbent, and the cleanup
performance of the NOx absorbent catalyst begins to deteriorate.
When the cleanup performance of the NOx absorbent catalyst is
deteriorated, the air-fuel ratio of the NOx absorbent catalyst on
the downstream side of the NOx absorbent catalyst becomes different
from that in the normal state. Then, the air-fuel ratio detecting
means detects the air-fuel ratio of the NOx absorbent catalyst on
the downstream side. On the basis of the air-fuel ratio, it is
determined whether to execute a regeneration process of the NOx
absorbent catalyst. When it is determined to execute the
regeneration process, the exhaust gas is changed into a high
temperature reducing atmosphere, thereby desorbing SOx that has
been absorbed to the NOx absorbent catalyst. This makes it possible
to recover the NOx cleanup performance of the NOx absorbent
catalyst, even in cases where the SOx absorption performance of the
SOx absorbent is deteriorated.
[0019] Moreover, since the SOx desorption temperature of the SOx
absorbent used here is higher than the desorption temperature of
the NOx absorbent catalyst, SOx is not desorbed from the SOx
absorbent, even if the exhaust gas is changed into the high
temperature reduction atmosphere in the regeneration process.
Therefore, it is not necessary to newly provide a passage and the
like for bypassing the NOx absorbent catalyst in order to prevent
the deterioration of the cleanup performance of the NOx absorbent
catalyst. In this way, newly providing the air-fuel ratio detecting
means, the recycling determining means, and the recycling executing
means, suffices in order to appropriately recover the cleanup
performance of the NOx absorbent catalyst. Accordingly, the size of
the device is not increased, and the manufacturing cost is not
increased either. Moreover, when the exhaust gas is changed into a
high temperature reducing atmosphere in the regeneration process,
for example, a post injection is carried out. According to the
present invention, it is determined whether to execute a
regeneration process on the basis of the air-fuel ratio detected by
the air-fuel ratio detecting means. This makes it possible to
minimize the number of regeneration processes to be executed.
Accordingly, it is possible to minimize the consumption of fuel
required for execution of regeneration processes and to minimize
the thermal degradation of the catalyst provided to the exhaust
passage.
[0020] Preferably, the SOx absorbent does not substantially
comprise precious metals.
[0021] With this configuration, the SOx absorbent does not
substantially include precious metals. This makes it possible to
further increase the SOx desorption temperature of the SOx
absorbent. This prevents SOx from being desorbed from the SOx
absorbent even if, for example, the exhaust gas is changed into a
high temperature reducing atmosphere, thereby making it possible to
prevent deterioration of the NOx absorbent catalyst, which is
provided on the downstream side, due to absorption of SOx.
[0022] Preferably, a substrate of the SOx absorbent does not
substantially comprise silica.
[0023] With this configuration, the substrate that supports the SOx
absorbent does not substantially include silica. This prevents
reaction of silica and alkali. This makes it possible to use a SOx
absorbent of which the alkalinity is high and which SOx desorption
temperature is high. This makes it possible to prevent
deterioration of the NOx absorbent catalyst, which is provided on
the downstream side of the SOx absorbent, due to absorption of
SOx.
[0024] Preferably, the NOx absorbent catalyst is a catalyst which
generates ammonia and absorbs the generated ammonia when the
air-fuel ratio of the exhaust gas is rich, and which reduces NOx to
elements thereof with the absorbed ammonia when the air-fuel ratio
of the exhaust gas is lean.
[0025] With this configuration, the catalyst, which is used as the
catalyst of the NOx absorbent catalyst, generates ammonia when the
air-fuel ratio is rich, and reduces NOx to its elements when the
air-fuel ratio is lean. This makes it possible to lower the SOx
desorption temperature of the NOx absorbent catalyst. Accordingly,
it is possible to further increase the temperature difference
between the SOx desorption temperature of the SOx absorbent and the
SOx desorption temperature of the NOx absorbent catalyst. This
makes it possible to more securely prevent SOx from being desorbed
from the SOx absorbent at the time of desorbing SOx that has been
absorbed to the NOx absorbent catalyst.
[0026] Preferably, a three-way catalyst is disposed in an upstream
side of the SOx absorbent in the exhaust passage.
[0027] With this configuration, a three-way catalyst is provided on
the upstream side of the SOx absorbent. This makes it possible to
clean up NOx with this three-way catalyst, even in cases where the
exhaust gas is changed into a high temperature reducing atmosphere
at the time of desorbing SOx from the NOx absorbent catalyst.
Particularly here, if the catalyst as described above, which is
used as the catalyst for the NOx absorbent catalyst, generates
ammonia when the air-fuel ratio is rich, and converts NOx into
nitrogen when the air-fuel ratio is lean, the NOx cleanup
efficiency under the high temperature reducing atmosphere is
decreased. Accordingly, it is possible to compensate for the
deterioration of the NOx cleanup efficiency under the high
temperature reducing atmosphere by providing such a three-way
catalyst.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a diagram showing a configuration of an internal
combustion engine and its control unit according to a first
embodiment of the present invention;
[0029] FIG. 2 is a diagram showing a configuration of an internal
combustion engine and its control unit according to a second
embodiment of the present invention; and
[0030] FIG. 3 is a diagram showing a configuration of an internal
combustion engine and its control unit according to a third
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment
[0031] A first embodiment of the present invention is described
with reference to an attached drawing. FIG.1 is a diagram showing a
configuration of an internal combustion engine and its control
unit, which are provided with an exhaust emission purification
system according to the first embodiment of the present invention.
An internal combustion engine 1 (hereinafter merely referred to as
an engine) is a diesel engine that directly injects fuel into each
cylinder. Fuel injectors are provided to the respective cylinders.
An electronic control unit 20 (hereinafter referred to as ECU) is
electrically connected these fuel injectors. The ECU 20 controls a
valve-opening time and a valve-closing time of the fuel
injectors.
[0032] The engine 1 is provided with an intake pipe 2 through which
intake air circulates, and an exhaust pipe 4 through which exhaust
gas circulates. The intake pipe 2 is connected to intake ports of
the respective cylinders of the engine 1. The exhaust pipe 4 is
connected to exhaust ports of the respective cylinders of the
engine 1.
[0033] An intercooler for cooling pressurized air and a throttle
valve for controlling intake air volume are provided in the intake
pipe 2. The throttle valve is connected through an actuator to the
ECU 20, and its valve opening degree is electromagnetically
controlled by the ECU 20.
[0034] As for the exhaust pipe 4, in the section which extends from
the exhaust ports of the engine 1 and is located immediately under
the engine 1, there are provided a subjacent catalytic converter
11, a SOx trap 13, and a particulate trap device 15 (hereinafter
referred to as "DPF" (Diesel Particulate Filter)) in this order
from the upstream side. On the other hand, in the section which is
located in the downstream side of the DPF 15 and is located under
the floor, a NOx purification device 17 is provided.
[0035] The subjacent catalytic converter 11 has a three-way
catalyst, and cleans up the exhaust gas by reaction of this
catalyst and the exhaust gas. More specifically, the subjacent
catalytic converter 11 has the three-way catalyst that is made by
causing an alumina (Al.sub.2O.sub.3) substrate to support precious
metals such as platinum (Pt), palladium (Pd), rhodium (Rh) and the
like acting as a catalyst, and adding thereto ceria with NOx
adsorptivity. By using such a three-way catalyst while lean, NOx is
trapped and hydrocarbon (HC) is oxidized into carbon monoxide (CO).
On the other hand, while rich, NOx is released, and cleaned up by
reduction into nitrogen (N.sub.2). This makes it possible to reduce
the amount of NOx emissions.
[0036] The SOx trap 13 absorbs SOx in exhaust gas, and is formed by
supporting SOx trap materials to a porous substrate, the SOx trap
materials having a higher desorption temperature of SOx than that
of the catalyst of the NOx purification device 17 to be described
later. More specifically, it is desirable that the substrate of the
SOx trap materials does not substantially include silica, is
configured mainly with, for example, alumina particles and alumina
fibers, and is configured as a honeycomb of 400 g/L and 400
cells/square inch.
[0037] More specifically, this SOx trap 13 is made by impregnating
the aforementioned porous substrate into a mixed solution, and
calcining the substrate in an atmosphere at 600 degrees Celsius for
one hour. The mixed solution is composed of potassium nitrate of
alkali metal compound and calcium nitrate tetrahydrate of alkaline
earth compound, which are converted into potassium weight and
calcium weight of 45 g/L, respectively. Moreover, it is desirable
that the SOx trap materials do not substantially include precious
metals.
[0038] When the exhaust gas passes through minute pores of the
filter wall, the DPF 15 accumulates soot as particulates on the
surface of the filter wall and in the pores of the filter wall,
thereby capturing the soot, the main component of the soot being
carbon in the exhaust gas. As the construction material of the
filter wall, for example, ceramics such as silicon carbide (SiC) as
well as porous metals are used.
[0039] When the soot is captured to the capacity of the
soot-capturing ability (i.e. accumulation limit) of the DPF 15, the
exhaust pressure increases. Accordingly, it is required to
regenerate the DPF by burning the soot as appropriate. This DPF
regeneration is performed by post-injection to increase the
temperature of the exhaust gas to the combustion temperature of the
soot.
[0040] The NOx purification device 17 is provided with platinum
(Pt) acting as a catalyst supported on an alumina (Al.sub.2O.sub.3)
substrate, ceria having a NOx adsorption capability, and a zeolite
having a function to hold ammonia (NH.sub.3) in the exhaust gas as
an ammonium ion (NH.sub.4.sup.+).
[0041] It is preferable that the SOx desorption temperature of this
NOx purification device 17 be lower than the SOx desorption
temperature of the abovementioned SOx trap 13. More specifically,
it is desirable that the temperature difference of the SOx
desorption temperatures between the NOx purification device 17 and
the SOx trap 13 be not less than 200 degrees Celsius.
[0042] When the amount of adsorbed ammonia in the NOx purification
device 17 is decreased, the NOx cleanup performance is
deteriorated. Accordingly, the reducing agent is supplied to the
NOx purification device 17 in order to appropriately reduce NOx to
elements thereof (this supply of the reducing agent is hereinafter
referred to as "reduction"). In this reduction, the reducing agent
is supplied to the NOx purification device 17, by increasing the
fuel level injected by the fuel injectors, and by decreasing the
intake air volume by the throttle valve, thereby causing the
air-fuel ratio of the fuel/air mixture in the combustion chamber to
be richer than the theoretic mixture ratio. That is to say, the
air-fuel ratio is made richer, as a result of which the
concentration of the reducing agent in the exhaust gas that flows
into the NOx purification device 17 becomes higher than the oxygen
concentration, thereby carrying out the reduction.
[0043] The cleanup of NOx in this NOx purification device 17 is
described. At first, the air-fuel ratio of the fuel/air mixture
burning in the engine 1 is set to be leaner than the theoretic
mixture ratio, thereby carrying out the so-called lean burn
operation. As a result, the concentration of the reducing agent in
the exhaust gas that flows into the NOx purification device 17 is
made lower than the oxygen concentration. As a result, carbon
monoxide (CO) and oxygen (O.sub.2) in the exhaust gas react with
each other by an action of the catalyst, and are adsorbed as
NO.sub.2 to ceria. Moreover, oxygen that has not been reacted with
carbon monoxide (CO) is also adsorbed to ceria.
[0044] Next, when reduction is carried out in which the
concentration of the reducing agent in the exhaust gas is higher
than the oxygen concentration, carbon monoxide (CO) in the exhaust
gas reacts with water (H.sub.2O) to generate carbon dioxide
(CO.sub.2) and hydrogen (H.sub.2), and hydrocarbon (HC) in the
exhaust gas reacts with water to generate carbon monoxide (CO) and
carbon dioxide (CO.sub.2) as well as hydrogen. Furthermore, NOx
included in the exhaust gas, NOx (NO, NO.sub.2) adsorbed to ceria
(and to platinum), and the generated hydrogen react by action of
the catalyst to generate ammonia (NH.sub.3) and water. Moreover,
thus generated ammonia is adsorbed in the form of the ammonium ion
(NH.sub.4.sup.+) to zeolite.
[0045] Next, when a lean burn operation is performed in which the
air-fuel ratio is set to be leaner than the theoretic mixture
ratio, and the concentration of the reducing agent in the exhaust
gas that flows into the NOx purification device 17 is set to be
lower than the oxygen concentration, NOx is adsorbed to ceria. In
addition, in a state where ammonium ion is adsorbed to zeolite, NOx
and oxygen in the exhaust gas react with ammonia to generate
nitrogen (N.sub.2) and water.
[0046] In this way, with the NOx purification device 17, ammonia
that is generated while supplying the reducing agent is adsorbed to
zeolite, and the adsorbed ammonia reacts with NOx during the lean
burn operation. Accordingly, it is possible to efficiently clean up
NOx.
[0047] The desorption of SOx absorbed to this NOx purification
device 17 is described. When the SOx absorption performance of the
SOx trap 13 is deteriorated due to aging degradation and the like,
SOx leaks from the SOx trap 13. When this SOx is absorbed to the
NOx purification device 17, the NOx cleanup performance of the NOx
purification device 17 is deteriorated. Accordingly, it is
necessary to perform regeneration (hereinafter referred to as
"sulfur purge") of the NOx purification device 17 in order to
desorb SOx that has been absorbed to the NOx purification device
17. This sulfur purge is performed by carrying out the
post-injection control, and by increasing the temperature of the
exhaust gas to the SOx desorption temperature of the NOx
purification device 17. In this post-injection control, in addition
to normal injection in the compression stroke, a post-injection is
performed by the fuel injector in the subsequent combustion stroke
and the exhaust stroke.
[0048] Volumes of the subjacent catalytic converter 11, the SOx
trap 13, the DPF 15, and the NOx purification device 17 as
described above are determined by considering, for example, the
cleanup performance for HC, CO and the NOx in the exhaust gas, the
collection efficiency for the particulates, the absorption quantity
of SOx, the pressure loss of the exhaust pipe 4, and the like. More
specifically, for example, the volumes of the subjacent catalytic
converter 11, the SOx trap 13, the DPF 15 and the NOx purification
device 17 are 0.7 L, 1.4 L, 2.1 L and 2.0 L, respectively.
[0049] Moreover, as for the exhaust pipe 4, a SOx sensor 16 as a
SOx concentration detecting means is provided between the DPF 15
and the NOx purification device 17. This SOx sensor 16 detects the
SOx concentration in the exhaust gas that circulates between the
SOx trap 13 and the NOx purification device 17, and supplies a
detection signal, which is substantially proportionate to the
detected SOx concentration, to the ECU 20.
[0050] The ECU 20 is provided with an input circuit and a central
processing unit (hereinafter referred to as "CPU"). The input
circuit has functions for shaping the input signal wave forms from
various sensors, correcting voltage levels to predetermined levels,
converting analog signal values into digital signal values, and
performing the like. In addition, the ECU 20 is provided with a
storage circuit for storing various operation programs executed
inside the CPU and the results thereof and the like, and an output
circuit for outputting a control signal to the fuel injector of the
engine 1 and the like.
[0051] Moreover, the ECU 20 is provided with a plurality of control
blocks that function with a hardware configuration including the
input circuit, the CPU, the storage circuit, the output circuit and
the like. More specifically, the ECU 20 is provided with a sulfur
purge determination portion 21 as a regeneration determination
means and a sulfur purge execution portion 22 as a regeneration
execution means.
[0052] The sulfur purge determination portion 21 determines whether
to execute a sulfur purge on the basis of the SOx concentration
detected by the SOx sensor 16. More specifically, the sulfur purge
determination portion 21 estimates an amount of SOx that has been
absorbed to the NOx purification device 17 on the basis of the
history of the SOx concentration detected by the SOx sensor 16, and
determines whether to execute a sulfur purge of the NOx
purification device 17 on the basis of this estimation.
[0053] In cases where the sulfur purge determination portion 21
determines to execute a sulfur purge of the NOx purification device
17, the sulfur purge execution portion 22 executes a post injection
control, in which the temperature of the exhaust gas flowing into
the NOx purification device 17 is changed into a high temperature
reducing atmosphere, the temperature of which is higher than the
SOx desorption temperature of the NOx purification device 17,
thereby executing the sulfur purge of the NOx purification
device.
[0054] As described in detail above, for example, in the present
embodiment, when the SOx absorption performance of the SOx trap 13
is deteriorated due to aging degradation and the like, thereby
leaking SOx from the SOx trap 13, the SOx concentration in the
downstream side of the SOx trap 13 of the exhaust pipe 4 is
increased. The increase of the SOx concentration is detected by the
SOx sensor 16 that detects the SOx concentration in the section
between the SOx trap 13 and the NOx purification device 17. On the
basis of the detection of the SOx concentration, it is determined
whether to execute a sulfur purge of the NOx purification device
17. When it is determined to execute a sulfur purge, the exhaust
gas is changed into a high temperature reduction atmosphere,
thereby desorbing SOx that has been absorbed to the NOx
purification device 17. This makes it possible to recover the NOx
cleanup performance of the NOx purification device 17, even in
cases where the SOx absorption performance of the SOx trap 13 is
deteriorated. Moreover, since the SOx desorption temperature of the
SOx trap 13 used here is higher than the desorption temperature of
the NOx purification device 17, SOx is not desorbed from the SOx
trap 13 even if the exhaust gas is changed into the high
temperature reducing atmosphere during the sulfur purge. Therefore,
it is not necessary to newly provide a passage and the like for
bypassing the NOx purification device 17 in order to prevent
deterioration of the cleanup performance of the NOx purification
device 17. In this way, newly providing the SOx sensor 16, the
sulfur purge determination portion 21, and the sulfur purge
execution portion 22, suffices in order to appropriately recover
the cleanup performance of the NOx purification device 17.
Accordingly, the size of the device is not increased, and the
manufacturing cost is not increased either. Moreover, when the
exhaust gas is changed into a high temperature reduction atmosphere
in the sulfur purge, for example, a post injection is carried out.
According to the present embodiment, it is determined whether to
execute a sulfur purge on the basis of the SOx concentration
detected by the SOx sensor 16. This makes it possible to minimize
the number of sulfur purges to be executed. Accordingly, it is
possible to minimize the consumption of fuel required for execution
of sulfur purges and to minimize the thermal degradation of the
catalyst provided to the exhaust pipe 4.
[0055] Moreover, the SOx trap materials used for the SOx trap 13 do
not substantially include precious metals. This makes it possible
to further increase the SOx desorption temperature of the SOx trap
13. This prevents SOx from being desorbed from the SOx trap 13 even
if, for example, the exhaust gas is changed into a high temperature
reducing atmosphere, thereby making it possible to prevent
deterioration of the NOx purification device 17, which is provided
in the downstream side, due to absorption of SOx.
[0056] Moreover, the substrate that supports the SOx trap materials
used for the SOx trap 13 does not substantially include silica.
This prevents reaction of silica and alkali. This makes it possible
to use SOx trap materials of which the alkalinity is high and the
SOx desorption temperature is high. This makes it possible to
prevent deterioration of the NOx purification device 17, which is
provided on the downstream side of the SOx trap 13, due to
absorption of SOx.
[0057] Moreover, the catalyst, which is used as the catalyst of the
NOx purification device 17, generates ammonia when the air-fuel
ratio is rich, and reduces NOx to elements thereof when the
air-fuel ratio is lean. This makes it possible to lower the SOx
desorption temperature of the NOx purification device 17.
Accordingly, it is possible to further increase the temperature
difference between the SOx desorption temperature of the SOx trap
13 and the SOx desorption temperature of the NOx purification
device 17. This makes it possible to more securely prevent SOx from
being desorbed from the SOx trap 13 at the time of desorbing SOx
that has been absorbed to the NOx purification device 17.
[0058] Moreover, the subjacent catalytic converter 11 having a
three-way catalyst is provided on the upstream side of the SOx trap
13. This makes it possible to clean up NOx with this three-way
catalyst, even in cases where the exhaust gas is changed into a
high temperature reducing atmosphere at the time of desorbing SOx
from the NOx purification device 17. Particularly here, if the
catalyst as described above, which is used as the catalyst for the
NOx purification device 17, generates ammonia when the air-fuel
ratio is rich, and converts NOx into nitrogen when the air-fuel
ratio is lean, the NOx cleanup efficiency under the high
temperature reduction atmosphere is decreased. Accordingly, it is
possible to compensate for the deterioration of the NOx cleanup
efficiency under the high temperature reducing atmosphere by
providing such a three-way catalyst.
Second Embodiment
[0059] A second embodiment of the present invention is described
with reference to an attached drawing. In describing the second
embodiment as follows, constituent features that are the same as
those of the first embodiment are assigned the same reference
symbols, and descriptions thereof is omitted or simplified. FIG. 2
is a diagram showing a configuration of an internal combustion
engine and its control unit, which are provided with an exhaust
emission purification system according to the second embodiment of
the present invention. In the present embodiment, a NOx sensor 16A
is provided in place of the SOx sensor 16 of the exhaust emission
purification system according to the first embodiment.
[0060] As for the exhaust pipe 4, a NOx sensor 16A as a NOx
concentration detecting means is provided on the downstream side of
the NOx purification device 17. This NOx sensor 16A detects the NOx
concentration in the exhaust gas that circulates on the downstream
side of the NOx purification device 17, and supplies a detection
signal, which is substantially proportionate to the detected NOx
concentration, to an ECU 20A.
[0061] A sulfur purge determination portion 21A determines whether
to execute a sulfur purge on the basis of the NOx concentration
detected by the NOx sensor 16A. It is assumed here that, when SOx
is absorbed to the NOx purification device 17, the NOx cleanup
performance of the NOx purification device 17 is deteriorated
depending on the absorbed amount thereof. The sulfur purge
determination portion 21A estimates the deterioration of the NOx
cleanup performance of the NOx purification device 17 on the basis
of the NOx concentration detected by the NOx sensor 16A, thereby
indirectly estimating an amount of SOx that has been absorbed to
the NOx purification device 17. Based on this estimation, the
sulfur purge determination portion 21A determines whether to
execute a sulfur purge of the NOx purification device 17.
[0062] In cases where the sulfur purge determination portion 21A
determines to execute a sulfur purge of the NOx purification device
17, a sulfur purge execution portion 22A executes a post injection
control, whereby the temperature of the exhaust gas flowing into
the NOx purification device 17 is changed into a high temperature
reducing atmosphere, the temperature of which is higher than the
SOx desorption temperature of the NOx purification device 17,
thereby executing the sulfur purge of the NOx purification device
17.
[0063] As described in detail above, the exhaust emission
purification system of the present embodiment achieves an effect
similar to that of the exhaust emission purification system of the
first embodiment.
Third Embodiment
[0064] A third embodiment of the present invention is described
with reference to an attached drawing. In describing the third
embodiment as follows, constituent features that are the same as
those of the first embodiment are assigned with the same reference
symbols, and descriptions thereof are omitted or simplified. FIG.3
is a diagram showing a configuration of an internal combustion
engine and its control unit, which are provided with an exhaust
emission purification system according to the third embodiment of
the present invention. In the present embodiment, an air-fuel ratio
sensor (hereinafter referred to as "LAF sensors") 16B is provided
in place of the SOx sensor 16 of the exhaust emission purification
system according to the first embodiment.
[0065] As for the exhaust pipe 4, the LAF sensor 16B as an air-fuel
ratio detecting means is provided on the downstream side of the NOx
purification device 17. This LAF sensor 16B detects the oxygen
concentration in the exhaust gas that circulates on the downstream
side of the NOx purification device 17, and supplies a detection
signal, which is substantially proportionate to the detected oxygen
concentration, to the ECU 20A.
[0066] The sulfur purge determination portion 21B determines
whether to execute a sulfur purge on the basis of the oxygen
concentration detected by the LAF sensor 16B. More specifically,
for example, at the time of increasing/decreasing the air-fuel
ratio of the fuel/air mixture, the sulfur purge determination
portion 21B monitors the response of the air-fuel ratio on the
downstream side of NOx purification device 17 by the LAF sensor
16B, thereby estimating the deterioration of the NOx cleanup
performance of the NOx purification device 17, and indirectly
estimating an amount of SOx that has been absorbed to the NOx
purification device 17. Based on this estimation, the sulfur purge
determination portion 21B determines whether to execute a sulfur
purge of the NOx purification device 17.
[0067] In cases where the sulfur purge determination portion 21B
determines to execute a sulfur purge of the NOx purification device
17, a sulfur purge execution portion 22B executes a post injection
control, whereby the temperature of the exhaust gas flowing into
the NOx purification device 17 is changed into a high temperature
reducing atmosphere, the temperature of which is higher than the
SOx desorption temperature of the NOx purification device 17,
thereby executing the sulfur purge of the NOx purification device
17.
[0068] As described in detail above, the exhaust emission
purification system of the present embodiment achieves an effect
similar to that of the exhaust emission purification system of the
first embodiment.
[0069] It should be noted that the present invention is not limited
to the aforementioned embodiments, and that various modifications
are possible. For example, in the aforementioned embodiments, the
subjacent catalytic converter 11, the SOx trap 13, the DPF 15, and
the NOx purification device 17 are provided to the exhaust pipe 4
in this order from the upstream side. However, there is no
limitation thereto as long as the SOx trap is provided on the
upstream side of the NOx purification device, and the order may be
different form the order in the embodiments. For example, the order
from the upstream side may be the subjacent catalytic converter,
the SOx trap, the NOx purification device, and the DPF, or may be
the subjacent catalytic converter, the DPF, the SOx trap, and the
NOx purification device.
[0070] Moreover, in the aforementioned embodiments, the subjacent
catalytic converter 11, the SOx trap 13 and the DPF 15 are provided
in the section located immediately after the engine, and the NOx
purification device is provided in the section located under the
floor, but there is no limitation thereto. For example, the
subjacent catalytic converter, the SOx trap, the DPF and the NOx
purification device may be provided in the section immediately
after the engine, or the subjacent catalytic converter and the SOx
trap may be provided immediately after the engine, while the DPF
and the NOx purification device may be provided under the
floor.
[0071] Moreover, the SOx sensor 16, the NOx sensor 16A and the
air-fuel ratio sensor 16B are provided in the first to third
embodiments, respectively; however, there is no limitation thereto,
and any of the sensors may be combined. For example, in the second
embodiment, only the NOx sensor is provided. In such a case,
however, if the air-fuel ratio of the fuel/air mixture is
increased/decreased for example, the NOx concentration in the
exhaust gas that is exhausted from the NOx purification device also
fluctuates, thereby making it difficult to estimate the cleanup
performance of the NOx purification device. Thus, for example, the
NOx sensor and the air-fuel ratio sensor are used in combination,
thereby making it possible to estimate the cleanup performance with
high accuracy.
[0072] Moreover, in the aforementioned embodiments, alumina is used
as a main material of the substrate of the SOx trap 13. However, an
alumina titanium series may be used as a main material of the
substrate of the SOx trap.
[0073] Furthermore, it is also possible to apply the present
invention to an exhaust emission purification system for an engine
and the like for ship propulsion such as an outboard engine that
has its crankshaft in the vertical direction.
* * * * *