U.S. patent application number 12/530842 was filed with the patent office on 2010-06-03 for exhaust gas purification device for internal combustion engine.
Invention is credited to Hirohito Hirata, Masaya Ibe, Masaya Kamada, Hiroyuki Matsubara.
Application Number | 20100132337 12/530842 |
Document ID | / |
Family ID | 39842480 |
Filed Date | 2010-06-03 |
United States Patent
Application |
20100132337 |
Kind Code |
A1 |
Hirata; Hirohito ; et
al. |
June 3, 2010 |
EXHAUST GAS PURIFICATION DEVICE FOR INTERNAL COMBUSTION ENGINE
Abstract
This invention is intended to ensure that an exhaust gas
purification device with an NOx storage reduction catalyst and a
particulate filter is able to fully utilize an original NOx storage
capability of the NOx storage reduction catalyst. For this end, in
addition to the filter 40 disposed upstream relative to the NOx
storage reduction catalyst 22, the purification device includes a
fuel supply element 42 for supplying a fuel so that the fuel is
mixed with exhaust gas that flows into the filter, and an ozone
feeder 30 for supplying ozone so that the ozone is mixed with
exhaust gas that flows into the NOx storage reduction catalyst at a
downstream position relative to the filter 40.
Inventors: |
Hirata; Hirohito;
(Shizuoka-ken, JP) ; Ibe; Masaya; (Shizuoka-ken,
JP) ; Matsubara; Hiroyuki; (Aichi-ken, JP) ;
Kamada; Masaya; (Aichi-ken, JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
39842480 |
Appl. No.: |
12/530842 |
Filed: |
March 11, 2008 |
PCT Filed: |
March 11, 2008 |
PCT NO: |
PCT/JP2008/054379 |
371 Date: |
January 14, 2010 |
Current U.S.
Class: |
60/286 ; 60/295;
60/297; 60/301; 60/303 |
Current CPC
Class: |
F01N 13/009 20140601;
F01N 3/0871 20130101; B01D 46/42 20130101; B01D 2251/104 20130101;
B01D 2255/2042 20130101; B01D 2258/012 20130101; F01N 2610/03
20130101; B01D 2279/30 20130101; B01D 53/9445 20130101; Y02T 10/12
20130101; B01D 2251/208 20130101; F01N 3/0253 20130101; F01N
2560/14 20130101; F01N 2560/026 20130101; F01N 2560/025 20130101;
F01N 3/0814 20130101; Y02T 10/22 20130101; B01D 2255/1021 20130101;
B01D 2255/91 20130101; F01N 2240/38 20130101; F01N 2900/1614
20130101; F01N 3/0842 20130101; F01N 2560/08 20130101; F01N 2610/00
20130101 |
Class at
Publication: |
60/286 ; 60/297;
60/301; 60/303; 60/295 |
International
Class: |
F01N 9/00 20060101
F01N009/00; F01N 3/035 20060101 F01N003/035; F01N 3/10 20060101
F01N003/10; F01N 3/023 20060101 F01N003/023 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 12, 2007 |
JP |
2007-062160 |
Claims
1.-8. (canceled)
9. An exhaust gas purification device for an internal combustion
engine, comprising: an NOx storage reduction catalyst disposed on
an exhaust passage of the internal combustion engine; a filter
disposed upstream relative to the NOx storage reduction catalyst,
the filter being used to capture particulates contained in exhaust
gas; means for supplying a fuel such that the fuel will be mixed
with the exhaust gas flowing into the filter; and means for
supplying ozone downstream with respect to the filter such that the
ozone will be mixed with the exhaust gas flowing into the NOx
storage reduction catalyst.
10. The exhaust gas purification device for the internal combustion
engine according to claim 9, further comprising: second means for
supplying the fuel downstream with respect to the filter such that
the fuel will be mixed with the exhaust gas flowing into the NOx
storage reduction catalyst.
11. The exhaust gas purification device for the internal combustion
engine according to claim 9, wherein the fuel supply means is
adapted to: during regeneration of the filter, execute fuel supply
while controlling a supply quantity of the fuel such that an
air-fuel ratio of the exhaust gas flowing into the filter will be
lean; and after the regeneration of the filter, continue a
predetermined period of fuel supply while controlling the supply
quantity of the fuel such that the air-fuel ratio of the exhaust
gas flowing into the filter will be rich.
12. The exhaust gas purification device for the internal combustion
engine according to claim 10, wherein: during regeneration of the
filter, the fuel supply means executes fuel supply while
controlling a supply quantity of the fuel such that an air-fuel
ratio of the exhaust gas flowing into the filter will be lean; and
during the execution of fuel supply by the fuel supply means, the
second means for supplying the fuel executes a predetermined period
of fuel supply while controlling a supply quantity of the fuel such
that the air-fuel ratio of the exhaust gas flowing into the NOx
storage reduction catalyst will be rich.
13. The exhaust gas purification device for the internal combustion
engine according to claim 9, wherein the fuel supply means executes
fuel supply during the execution of ozone supply by the ozone
supply means.
14. The exhaust gas purification device for the internal combustion
engine according to claim 9, wherein the fuel supply means executes
fuel supply during the stoppage of ozone supply by the ozone supply
means.
15. The exhaust gas purification device for the internal combustion
engine according to claim 14, wherein the fuel supply means
executes fuel supply while controlling a supply quantity of the
fuel such that an air-fuel ratio of the exhaust gas will be
rich.
16. The exhaust gas purification device for the internal combustion
engine according to claim 9, further comprising: means for
measuring a differential pressure between an inlet and outlet of
the filter during the execution of ozone supply by the ozone supply
means, wherein the fuel supply means executes fuel supply on the
basis of the measuring result of the differential pressure by the
differential pressure measuring means.
17. An exhaust gas purification device for an internal combustion
engine, comprising: an NOx storage reduction catalyst disposed on
an exhaust passage of the internal combustion engine; a filter
disposed upstream relative to the NOx storage reduction catalyst,
the filter being used to capture particulates contained in exhaust
gas; a fuel injector supplying a fuel such that the fuel will be
mixed with the exhaust gas flowing into the filter; and an ozone
feeder supplying ozone downstream with respect to the filter such
that the ozone will be mixed with the exhaust gas flowing into the
NOx storage reduction catalyst.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to exhaust gas
purification devices for internal combustion engines, and more
particularly, to an exhaust gas purification device including an
NOx storage reduction catalyst and a particulate filter.
BACKGROUND ART
[0002] As disclosed in the patent documents listed below, exhaust
gas purification devices with a filter and an NOx storage reduction
catalyst arranged in that order from upstream toward downstream on
the exhaust passages in internal combustion engines, especially,
diesel engines, are traditionally known (the NOx storage reduction
catalyst is hereinafter referred to as the NSR catalyst). In these
purification devices, the particulates contained in exhaust gas can
be captured with the filter. Additionally, NOx whose purification
becomes insufficient under a lean atmosphere can be captured with
the NSR catalyst.
[0003] In the above exhaust gas purification devices, a process for
removing the captured particulates from the filter (hereinafter,
this process is referred to as the regeneration of the filter) is
needed to prevent increases in exhaust resistance due to filter
clogging. A known way to remove particulates from such a filter is
by adding fuel to exhaust gas upstream relative to the filter and
increasing the temperature of the exhaust gas flowing into the
filter. Enhancing the temperature of the exhaust gas allows the
particulates to be burned by utilizing the heat.
[0004] The above exhaust gas purification devices also require a
process for removing stored NOx from the NSR catalyst (hereinafter,
this process is referred to as the regeneration of the NSR
catalyst). A known way to remove stored NOx from an NSR catalyst is
by adding fuel to exhaust gas upstream relative to the NSR catalyst
and making rich the air-fuel ratio of the exhaust gas flowing into
the NSR catalyst. Making the exhaust gas rich in air-fuel ratio
allows the stored NOx to be reduced and purified by means of the HC
or CO contained in the exhaust gas. The reduction of the stored NOx
by the HC or the CO is a reaction occurring when the NSR catalyst
is sufficiently warmed. Accordingly, not all chemical potentials of
the fuel added to the exhaust gas during the regeneration of the
NSR catalyst will be used to reduce the stored NOx. Instead, one
portion or a large portion of the chemical potential will be used
to heat the NSR catalyst.
[0005] Patent Document 1: JP-A-2002-89240
[0006] Patent Document 2: JP-A-2005-538295
[0007] Patent Document 3: JP-A-2006-522272
[0008] Patent Document 4: JP-A-2000-297633
[0009] Patent Document 5: JP-A-2002-188432
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0010] Neither the fuel consumed during the regeneration of the
filter, nor the fuel consumed during the regeneration of the NSR
catalyst contributes to enhancing the output energy of the internal
combustion engine. The fuel efficiency of the internal combustion
engine, therefore, can be correspondingly improved if the fuel
consumption can be reduced. One method of achieving this is by
utilizing the heat generated by the regeneration of the filter for
regenerating the NSR catalyst. During the regeneration of the
filter, the combustion of the added fuel generates heat and at the
same time, the combustion of particulates also generates heat. If
such heat is used to warm the NSR catalyst, only the amount of fuel
consumed to chemically reduce stored NOx will be required as the
fuel consumption for the regeneration of the NSR catalyst.
[0011] In fact, however, there is a significant gap between the
period at which the regeneration of the filter is executed, and the
period at which the regeneration of the NSR catalyst is executed.
The regenerating period of the NSR catalyst, compared with that of
the filter, is extremely short and the heat generated during the
regeneration of the filter has substantially no chance of being
used for regenerating the NSR catalyst. To extend the regenerating
period of the NSR catalyst, there is a need to make the NSR
catalyst store NOx in greater quantities. The original NOx-storing
capability of the NSR catalyst, however, is not fully utilized in
conventional exhaust gas purification devices. If the original
NOx-storing capability of the NSR catalyst can be fully utilized,
this will allow the regenerating period of the NSR catalyst to be
brought close to that of the filter. The heat generated during the
regeneration of the filter will be consequently useable to
regenerate the NSR catalyst.
[0012] The present invention has been made for solving the above
problem, and an object of the invention is to provide an exhaust
gas purification device including an NOx storage reduction catalyst
and a particulate filter, in the purification device of which, the
NOx storage reduction catalyst can fully utilize its original
capability to store NOx.
Means for Solving the Problem
[0013] In order to attain the object described above, a first
aspect of the present invention is an exhaust gas purification
device for an internal combustion engine, comprising:
[0014] an NOx storage reduction catalyst disposed on an exhaust
passage of the internal combustion engine;
[0015] a filter disposed upstream relative to the NOx storage
reduction catalyst, the filter being used to capture particulates
contained in exhaust gas;
[0016] means for supplying a fuel such that the fuel will be mixed
with the exhaust gas flowing into the filter; and
[0017] means for supplying ozone downstream with respect to the
filter such that the ozone will be mixed with the exhaust gas
flowing into the NOx storage reduction catalyst.
[0018] A second aspect of the present invention is the exhaust gas
purification device for the internal combustion engine according to
the first aspect of the present invention, further comprising:
[0019] second means for supplying the fuel downstream with respect
to the filter such that the fuel will be mixed with the exhaust gas
flowing into the NOx storage reduction catalyst.
[0020] A third aspect of the present invention is the exhaust gas
purification device for the internal combustion engine according to
the first aspect of the present invention, wherein the fuel supply
means is adapted to:
[0021] during regeneration of the filter, execute fuel supply while
controlling a supply quantity of the fuel such that an air-fuel
ratio of the exhaust gas flowing into the filter will be lean;
and
[0022] after the regeneration of the filter, continue a
predetermined period of fuel supply while controlling the supply
quantity of the fuel such that the air-fuel ratio of the exhaust
gas flowing into the filter will be rich.
[0023] A fourth aspect of the present invention is the exhaust gas
purification device for the internal combustion engine according to
the second aspect of the present invention, wherein:
[0024] during regeneration of the filter, the fuel supply means
executes fuel supply while controlling a supply quantity of the
fuel such that an air-fuel ratio of the exhaust gas flowing into
the filter will be lean; and
[0025] during the execution of fuel supply by the fuel supply
means, the second means for supplying the fuel executes a
predetermined period of fuel supply while controlling a supply
quantity of the fuel such that the air-fuel ratio of the exhaust
gas flowing into the NOx storage reduction catalyst will be
rich.
EFFECTS OF THE INVENTION
[0026] According to the first aspect of the present invention,
supplying ozone such that the ozone will be mixed with the exhaust
gas flowing into the NOx storage reduction catalyst allows
accelerated oxidation of any NOx substances contained in the
exhaust gas, and hence, accelerated storage of the NOx into the NOx
storage reduction catalyst. In particular, if the amount of ozone
to be supplied is controlled for a molar quantity of the ozone in
the exhaust gas to be larger than a molar quantity of NO, nitrogen
oxides of an order higher than that of NO.sub.2, such as NO.sub.2
and N.sub.2O.sub.5, can be generated. The same also applies to
HNO.sub.3 if moisture is present. Generating the above nitrogen
oxides of a higher order enables the NOx storage reduction catalyst
to further accelerate its internal NOx storage reaction.
[0027] It is possible, by accelerating the storage of NOx in the
NOx storage reduction catalyst, to make the catalyst store a
greater amount of NOx, and thus to extend a regenerating period of
the NOx storage reduction catalyst. If the regenerating period of
the NOx storage reduction catalyst is extended, heat that is
generated during regeneration of the filter will have more chances
to be utilized for the regeneration of the NOx storage reduction
catalyst. Consumption of the fuel required for the regeneration of
the NOx storage reduction catalyst and that of the filter, can be
consequently suppressed, which allows the internal combustion
engine to be improved in fuel efficiency.
[0028] According to the second aspect of the present invention, the
fuel can be supplied to the NOx storage reduction catalyst without
being passed through the filter. The fuel can also be
simultaneously supplied in divided form to two sections, namely, an
upstream side of the filter and that of the NOx storage reduction
catalyst. In this way, the fuel can be supplied in any one or more
of selectable plural forms to make more effective use of the
fuel.
[0029] According to the third aspect of the present invention, the
filter can be regenerated and at the same time, the heat generated
during the regeneration of the filter can be used to warm the NOx
storage reduction catalyst. After the regeneration of the filter,
the NOx storage reduction catalyst can be regenerated efficiently
by supplying the exhaust gas of a rich air-fuel ratio to the NOx
storage reduction catalyst that has been warmed to high enough a
temperature.
[0030] According to the fourth aspect of the present invention, the
filter can be regenerated and at the same time, the heat generated
during the regeneration of the filter can be used to warm the NOx
storage reduction catalyst. Additionally, a lean atmosphere in the
filter and a rich atmosphere in the NOx storage reduction catalyst
can both be created at the same time by supplying the fuel in
divided form to two different sections. This makes the regeneration
of the NOx storage reduction catalyst simultaneously achievable
with that of the filter, thus making more effective use of the heat
generated during the regeneration of the filter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a diagram illustrating an exhaust gas purification
device configuration in a first embodiment of the present
invention.
[0032] FIG. 2 is a flowchart representing a routine executed in the
first embodiment of the present invention.
[0033] FIG. 3 is a diagram illustrating an exhaust gas purification
device configuration in a second embodiment of the present
invention.
[0034] FIG. 4 is a flowchart representing a routine executed in the
second embodiment of the present invention.
[0035] 10 engine [0036] 12 exhaust passage [0037] 20 catalytic
converter [0038] 22 NOx storage reduction catalyst [0039] 30 ozone
feeder [0040] 32 gas injection port [0041] 40 DPF [0042] 42, 44
fuel injector [0043] 50 controller [0044] 52 differential pressure
sensor [0045] 54, 58 air-fuel ratio sensor [0046] 56 NOx sensor
BEST MODE FOR CARRYING OUT THE INVENTION
First Embodiment
Exhaust Gas Purification Device Configuration in a First
Embodiment
[0047] The present invention is suitable for an internal combustion
engine which is placed in lean-burn operation, especially, a diesel
engine. In the present embodiment, the invention is applied to a
diesel engine. FIG. 1 is a diagram illustrating an exhaust gas
purification device configuration in a first embodiment of the
invention. The exhaust gas purification device configuration in the
first embodiment is described below using FIG. 1.
[0048] As shown in FIG. 1, the exhaust gas purification device of
the first embodiment includes a diesel particulate filter
(hereinafter, referred to as DPF) 40 and a catalytic converter 20,
in an exhaust passage 12 of a diesel engine (hereinafter, referred
to simply as engine) 10. The catalytic converter 20 is disposed
downstream relative to the DPF 40. In such a configuration, exhaust
gas from the engine 10 first have any particulates removed by the
DPF 40, and then have any NOx, HC, and CO substances purified by
the catalytic converter 20 before the exhaust gas are released to
the atmosphere.
[0049] A fuel injector 42 is installed near an inlet of the DPF 40
on the exhaust passage 12, and the same fuel as used for operating
the engine 10 is injected from the fuel injector 42.
[0050] An NOx storage reduction catalyst (hereinafter, referred to
as NSR catalyst) 22 is accommodated in the catalytic converter 20.
A noble metal such as platinum Pt, and BaCO.sub.3 are supported on
a ceramic support to constitute the NSR catalyst 22, with Pt
functioning as an active site that simultaneously activates an
oxidation reaction of CO, HC and a reducing reaction of NOx, and
BaCO.sub.3 functioning as an NOx-retaining substance to occlude the
NOx contained in the exhaust gas in the form of a nitrate. More
specifically, NOx is occluded as Ba(NO.sub.3).sub.2 in BaCO.sub.3.
The stored Ba(NO.sub.3).sub.2 is reduced and decomposed primarily
under a rich state of the exhaust gas. The NOx-retaining substance,
however, not only occludes NOx, but may also adsorb NOx. For this
reason, the "retaining" action of the NOx-retaining substance
connotes "adsorbing" the NOx as well as "occluding" the NOx.
[0051] A gas injection port 32 is provided at an upstream side of
the NSR catalyst 22 within the catalytic converter 20. The gas
injection port 32 is connected to an ozone feeder 30. The ozone
feeder 30 contains an ozonizer that creates ozone by use of air
obtained from an air suction port 34. Further detailed description
of the ozonizer is omitted herein since various techniques
concerning its configuration and functionality are already known.
The ozone feeder 30 supplies internally created ozone from the gas
injection port 32 to the inside of the catalytic converter 20.
Inside the catalytic converter 20, the ozone supplied from the
ozone feeder 30 gets mixed with the exhaust gas flowing in through
the exhaust passage 12, and then the mixed gas flows into the NSR
catalyst 22.
[0052] The exhaust gas purification device of the present
embodiment includes a plurality of sensors for obtaining
information on states of the purification device. More
specifically, the DPF 40 has a differential pressure sensor 52 that
outputs a signal commensurate with a differential pressure between
an inlet and outlet of the DPF. An air-fuel ratio sensor 54 that
outputs a signal commensurate with an air-fuel ratio of the exhaust
gas is mounted near the outlet of the DPF 40 on the exhaust passage
12. Also, an NOx sensor 56 that detects NOx is mounted near an
outlet of the catalytic converter 20 on the exhaust passage 12.
[0053] The exhaust gas purification device of the present
embodiment also includes a controller 50 that controls operation of
the purification device. The above-described ozone feeder 30 and
fuel injector 42 are connected to an output section of the
controller 50. The above-described sensors 52, 54, 56 are connected
to an input section of the controller 50. Information on operating
parameters and operating states of the engine 10 is also input to
the input section of the controller 50. Upon receiving the various
input information, the controller 50 controls the ozone feeder 30
and the fuel injector 42 in accordance with a predetermined control
program.
Exhaust Gas Purification Device Operation in the First
Embodiment
[0054] Next, the operation of the exhaust gas purification device
of the present embodiment will be described.
(Ozone-Aided NOx Storage into the NSR Catalyst)
[0055] Compared with HC and CO, a large amount of NOx is contained
in the exhaust gas from the engine 10 during lean-burn operation
thereof. According to the configuration shown in FIG. 1, the NOx
contained in the exhaust gas can be stored using the NSR catalyst
22. As described below, the present embodiment utilizes ozone to
improve the NSR catalyst 22 in NOx storage capability.
[0056] During lean-burn operation in the present embodiment, the
engine 10 activates the ozone feeder 30 to supply ozone to the
catalytic converter 20. It is known that when ozone is added to
exhaust gas, the NOx contained in the exhaust gas will be oxidized
by a gas-phase reaction. More specifically, the NOx and the ozone
will react upon each other to develop the reactions shown in
reaction formulae (1) to (3) that follow. Reaction formula (3) is
shown only with an arrow that indicates a rightward reaction, but
such a leftward reaction as enclosed in brackets below can also
occur.
NO+O.sub.3.fwdarw.NO.sub.2+O.sub.2 (1)
NO.sub.2+O.sub.3.fwdarw.NO.sub.3+O.sub.2 (2)
NO.sub.2+NO.sub.3.fwdarw.N.sub.2O.sub.5(NO.sub.2+NO.sub.3.rarw.N.sub.2O.-
sub.5) (3)
[0057] After the oxidation of the NOx, the NOx-retaining substance
occludes the resulting nitrogen oxides of a high order (or
HNO.sub.3 generated by reactions of these nitrogen oxides with
water). The NOx occlusion occurring with the NOx-retaining
substance is thus achieved. For instance, when converted into a
nitrate such as Ba(NO.sub.3).sub.2, NO.sub.3 is occluded by an NOx
occluding material. As shown in above reaction formulae (1) to (3),
therefore, when ozone is added to exhaust gas, the high-order
nitrogen oxides that the NOx-retaining substance easily occludes
can be created efficiently. That is to say, the NOx storage
capability of the NSR catalyst 22 can be enhanced.
[0058] To obtain an NOx storage reaction more efficiently, it is
desirable that the NOx in the exhaust gas be converted into
higher-order nitrogen oxides containing larger amounts of NO.sub.3,
N.sub.2O.sub.5, and/or the like. In the present embodiment,
therefore, the quantity of ozone to be supplied is controlled so
that a molar ratio of the ozone to NO is greater than 1 in a
mixture of the exhaust gas and the ozone. The control of the ozone
supply quantity is conducted by the controller 50. On the basis of
the information relating to an engine speed, fuel injection
quantity, and other operating parameters of the engine 10, the
controller 50 estimates and calculates the quantity of NO in the
exhaust gas and controls the ozone feeder 30 to supply an
appropriate quantity of ozone according to the estimated quantity
of NO.
[0059] Under a state with a molar ratio of the ozone equal to or
less than 1 to the NO contained in the mixed gas, although the
reaction in reaction formula (1) generates NO.sub.2, the reaction
in reaction formula (2) or (3) does not lead to generating NO.sub.3
or N.sub.2O.sub.5. If the molar ratio of the ozone to the NO
contained in the mixed gas is increased above 1, however, this
makes it possible to supply an enough amount of ozone for oxidizing
the NO into NO.sub.3 and N.sub.2O.sub.5. Consequently, a total
quantity of high-order nitrogen oxides contained in the exhaust gas
can be increased reliably and the NOx can be stored more
effectively.
[0060] Alternatively, the quantity of ozone to be supplied is
preferably controlled to obtain a molar ratio of at least 2 of the
ozone to the NO in the mixed gas. This alternative method allows a
large portion of the NO to be oxidized into NO.sub.3 and
N.sub.2O.sub.5, and the quantity of NOx storage into the NSR
catalyst 22 to be increased remarkably.
(DPF Regeneration and NSR Catalyst Regeneration)
[0061] The regeneration of the DPF 40 is a process for preventing
increases in exhaust resistance due to clogging of the DPF 40, and
this process is executed upon detection of the clogging of the DPF
40 by the differential pressure sensor 52. More specifically,
combustion heat of the fuel injected from the fuel injector 42
heats the DPF 40. Particulates that the DPF 40 has captured are
burned by the heating of the DPF, and removed therefrom. Since
oxygen is needed to burn the particulates, an injection quantity of
the fuel from the fuel injector 42 is controlled so that the
exhaust gas flowing into the DPF 40 will be a lean air-fuel
ratio.
[0062] The regeneration of the NSR catalyst 22 is a process for
recovering the NOx storage capability of the NSR catalyst 22 by
removing stored NOx from the NSR catalyst 22. More specifically,
the NSR catalyst 22 is heated and the air-fuel ratio of the exhaust
gas flowing thereinto is temporarily enhanced for a rich air-fuel
ratio. The stored NOx within the NSR catalyst 22 is reduced by the
HC and CO contained in the exhaust gas, and then removed from the
NSR catalyst 22. The air-fuel ratio of the exhaust gas flowing into
the NSR catalyst 22 can be adjusted according to the particular
fuel injection quantity of the fuel injector 42.
[0063] Heat that has been generated during the regeneration of the
DPF 40 can be utilized to regenerate the NSR catalyst 22. During
the regeneration of the DPF 40, combustion of the fuel injected
from the fuel injector 42 generates heat and at the same time, the
combustion of the particulates also generates heat. Much of the
fuel injected from the fuel injector 42 can be used for the
reduction of the stored NOx if such heat is utilized to heat the
NSR catalyst 22.
[0064] To ensure that the heat generated during the regeneration of
the DPF 40 is utilized to regenerate the NSR catalyst 22, it is
preferable that a regenerating period of the NSR catalyst 22 be as
long as possible. This is because the DPF 40 is of an extremely
long regenerating period. As described above, the exhaust gas
purification device of the present embodiment allows the NOx
storage quantity of the NSR catalyst 22 to be increased by
utilizing ozone, and thus the regenerating period of the NSR
catalyst 22 to be extended.
(More Specific Processing by the Controller)
[0065] Hereunder, more specific processing that the controller 50
conducts will be described using FIG. 2. FIG. 2 is a flowchart
representing a routine executed by the controller 50 in the present
embodiment. The above-described addition of ozone and regeneration
of the DPF 40 and NSR catalyst 22 are both executed in accordance
with the routine shown in FIG. 2.
[0066] In first step S100 of the routine shown in FIG. 2, ozone is
created from air by the ozone feeder 30 and then the ozone is added
to exhaust gas. A gas-phase reaction with the ozone in the
catalytic converter 20 accelerates the oxidation of the NOx in the
exhaust gas, and hence, storage of the NOx into the NSR catalyst
22.
[0067] Whether the clogging of the DPF 40 is detected by the
differential pressure sensor 52 is judged in step S102. If the
clogging of the DPF 40 is detected, process control advances to
step S104 to execute the regeneration of the DPF 40.
[0068] In step S104, fuel injection from the fuel injector 42 is
executed and fuel is added to the exhaust gas flowing into the DPF
40. The fuel injection quantity of the fuel injector 42 is
controlled so that the exhaust gas flowing into the DPF 40 will be
a lean air-fuel ratio. An output signal from the air-fuel ratio
sensor 54 is fed back during the control of the fuel injection
quantity. The fuel that has been injected from the fuel injector 42
is burned upon reacting with the oxygen in the exhaust gas, and the
resulting heat creates a high-temperature atmosphere in the DPF 40.
Thus, the particulates on the DPF 40 are burned upon reacting with
excess oxygen present in the exhaust gas, and are progressively
removed from the DPF 40.
[0069] Whether the clogging of the DPF 40 is detected by the
differential pressure sensor 52 is re-judged in step S106. Process
step S104 is continued if the clogging of the DPF 40 is re-detected
or still remains detected. Conversely if the clogged state of the
DPF 40 is cleared, the regeneration thereof terminates and process
control advances to step S108 to execute the regeneration of the
NSR catalyst 22.
[0070] In step S108, the creation of ozone by the ozone feeder 30
is stopped and the addition of the ozone to the exhaust gas is also
stopped.
[0071] In next step S110, fuel injection from the fuel injector 42
is continued and fuel is added to the exhaust gas flowing into the
DPF 40. A fuel injection quantity of the fuel injector 42 at this
time is controlled so that the exhaust gas flowing into the DPF 40
will be a rich air-fuel ratio. An output signal from the air-fuel
ratio sensor 54 is fed back during the control of the fuel
injection quantity. The NOx stored within the NSR catalyst 22 is
reduced by the HC and CO contained in the exhaust gas, and then
removed from the NSR catalyst 22 progressively.
[0072] During the regeneration of the DPF 40, the heat generated by
the combustion of the added fuel and stored particulates raises a
temperature of the exhaust gas flowing into the catalytic converter
20. The high-temperature exhaust gas then warm the NSR catalyst 22
and the catalyst temperature upon completion of the regeneration of
the DPF 40 rises to, or nearly to, a temperature level required for
the regeneration thereof. Therefore, the amount of fuel consumed to
heat the NSR catalyst 22 for the regeneration thereof is saved and
much of the fuel injected from the fuel injector 42 can be used to
reduce the stored NOx.
[0073] Fuel addition for regenerating the NSR catalyst 22 is
executed only for a required regenerating period calculated from
the NOx storage quantity existing immediately before the
regeneration. The NOx storage quantity can be estimated and
calculated from counts of a cumulative operating period and/or
cumulative traveling distance from a previous regenerating process
for the NSR catalyst 22. After elapse of the required regenerating
period, process control proceeds to step S112 to stop the addition
of fuel from the fuel injector 42. This completes the regeneration
of the DPF 40 and then completes that of the NSR catalyst 22 as
well.
[0074] During above successive processing, the NSR catalyst 22 is
regenerated timely according to a progress of the regeneration of
the DPF 40, but there may be a need to regenerate the NSR catalyst
22 before the DPF 40 requires regeneration. If the clogging of the
DPF 40 is not detected in step S102, control is transferred to step
S114 for a next judgment. Whether NOx is detected by the NOx sensor
56 is judged in step S114. If no NOx is detected, control is
returned to the judgment in step S102. Subsequently, either step
S102 or S114 is repeated until a positive judgment has been
conducted therein.
[0075] The NOx detected by the NOx sensor 56 is that which has not
been stored into the NSR catalyst 22. Upon saturation of the
quantity of NOx storage in the NSR catalyst 22, non-stored NOx
flows out in the downstream direction. After the saturation, if NOx
is detected by the NOx sensor 56, control proceeds to step S116, in
which step, the regeneration of the NSR catalyst 22 is then
executed.
[0076] In step S116, the creation of ozone by the ozone feeder 30
is stopped and the addition of the ozone to the exhaust gas is also
stopped.
[0077] In next step S118, fuel injection from the fuel injector 42
is executed and fuel is added to the exhaust gas flowing into the
DPF 40. The fuel injection quantity of the fuel injector 42 is
controlled so that the exhaust gas flowing into the DPF 40 will be
a rich air-fuel ratio. An output signal from the air-fuel ratio
sensor 54 is fed back during the control of the fuel injection
quantity. The fuel that has been injected from the fuel injector 42
is burned upon reacting with the oxygen in the exhaust gas, and the
resulting heat warms the exhaust gas. In addition, excess fuel is
left intact in the exhaust gas, passes through the DPF 40, and
flows into the NSR catalyst 22. When the high-temperature exhaust
gas of a rich air-fuel ratio flows into the NSR catalyst 22, the
NOx stored therein is reduced by the HC and CO contained in the
exhaust gas, and is progressively removed from the NSR catalyst
22.
[0078] Fuel addition for the regeneration of the NSR catalyst 22 is
executed only for the required regenerating period calculated from
the NOx storage quantity existing immediately before the
regeneration. The NOx storage quantity can be estimated and
calculated from counts of the cumulative operating period and/or
cumulative traveling distance from the previous regenerating
process for the NSR catalyst 22. After elapse of the required
regenerating period, process control proceeds to step S120 to stop
the addition of fuel from the fuel injector 42. This completes the
regeneration of the NSR catalyst 22.
Effects of the Exhaust Gas Purification Device in the First
Embodiment
[0079] As described above, supply of ozone to the inside of the
catalytic converter 20 by the ozone feeder 30 during lean-burn
operation of the engine 10 allows the oxidation of the NOx in the
exhaust gas to be accelerated and thus the quantity of NOx storage
into the NSR catalyst 22 to be increased. An increase in the
quantity of NOx storage into the NSR catalyst 22 extends the
regenerating period thereof, with a result that the heat generated
during the regeneration of the DPF 40 will have more chances to be
utilized for the regeneration of the NSR catalyst 22. The exhaust
gas purification device of the present embodiment, therefore, can
suppress consumption of the fuel required for the regeneration of
the NSR catalyst 22 and DPF 40, and thereby improve fuel efficiency
of the engine 10.
Second Embodiment
Exhaust Gas Purification Device Configuration in a Second
Embodiment
[0080] FIG. 3 is a diagram illustrating an exhaust gas purification
device configuration in a second embodiment of the invention. The
exhaust gas purification device configuration in the present
embodiment is described below using FIG. 3. In FIG. 3, sections and
components common to those of the exhaust gas purification device
according to the first embodiment are each assigned the same
reference number. In addition, except when necessary, description
of the common sections and components is omitted, with descriptive
focus placed only upon configurational differences relative to the
first embodiment.
[0081] As shown in FIG. 3, in addition to the fuel injector 42
disposed near the inlet of the DPF 40, the exhaust gas purification
device of the present embodiment has a fuel injector 44 between the
DFP 40 and catalytic converter 20 on the exhaust passage 12. The
fuel injector 44, as with the fuel injector 42, injects the same
fuel as used for operating the engine 10.
[0082] In addition to the air-fuel ratio sensor 54 disposed near
the outlet of the DPF 40, the exhaust gas purification device of
the present embodiment further has an air-fuel ratio sensor 58
disposed downstream relative to the fuel injector 44, near an inlet
of the catalytic converter 20, the air-fuel ratio sensor 58 being
adapted to output a signal according to a particular air-fuel ratio
of exhaust gas. The fuel injector 44 is installed between the two
air-fuel ratio sensors 54, 58.
[0083] In the present embodiment, the ozone feeder 30 and the two
fuel injectors 42 and 44 are connected to the output section of the
controller 50. Also, the plurality of sensors 52, 54, 56 and 58,
including the above-described air-fuel ratio sensor 58, are
connected to the input section of the controller 50. In addition,
information on operating parameters and operating states of the
engine 10 is input to the input section of the controller 50. Upon
receiving the various input information, the controller 50 controls
the ozone feeder 30 and the fuel injectors 42 and 44 in accordance
with the predetermined control program.
Exhaust Gas Purification Device Operation in the Second
Embodiment
[0084] Next, operation of the exhaust gas purification device of
the present embodiment will be described. Except when necessary,
description of the device operation common to that of the first
embodiment is omitted, with descriptive focus placed only upon
operational differences relative to the first embodiment.
(DPF Regeneration and NSR Catalyst Regeneration)
[0085] One of the operational differences between the present
embodiment and the first embodiment exists in that the DPF 40 and
the NSR catalyst 22 are simultaneously regenerated in the present
embodiment. As described in the first embodiment, regenerating the
DPF 40 requires adding fuel while ensuring a lean air-fuel ratio
state of the exhaust gas flowing into the DPF 40. Regenerating the
NSR catalyst 22, on the other hand, requires ensuring a rich
air-fuel ratio state of the exhaust gas flowing into the NSR
catalyst 22. In the device configuration of the first embodiment,
since it has been impossible to make the device satisfy the above
two requirements at the same time, the regeneration of the NSR
catalyst 22 has been conducted following completion of that of the
DPF 40.
[0086] In contrast to the first embodiment, the exhaust gas
purification device configuration in the second embodiment makes it
possible to supply fuel to the NSR catalyst 22 without passing the
fuel through the DPF 40. Fuel can also be supplied in divided form
to two sections at the same time, that is, an upstream side of the
DPF 40 and that of the NSR catalyst 22. In the present embodiment,
therefore, the fuel injection quantities of the fuel injectors 42
and 44 are controlled, as appropriate, to supply the exhaust gas of
a rich air-fuel ratio to the NSR catalyst 22 while supplying the
exhaust gas of a lean air-fuel ratio to the DPF 40. Thus, the DPF
40 and the NSR catalyst 22 can be regenerated simultaneously.
(More Specific Processing by the Controller)
[0087] Hereunder, more specific processing that the controller 50
conducts will be described using FIG. 4. FIG. 4 is a flowchart
representing the routine executed by the controller 50 in the
present embodiment. The above-described addition of ozone and
regeneration of the DPF 40 and NSR catalyst 22 are both executed in
accordance with the routine shown in FIG. 4.
[0088] In first step S200 of the routine shown in FIG. 4, ozone is
created from air by the ozone feeder 30 and then the ozone is added
to exhaust gas. A gas-phase reaction with the ozone in the
catalytic converter 20 accelerates the oxidation of the NOx in the
exhaust gas, and hence, storage of the NOx into the NSR catalyst
22.
[0089] Whether the clogging of the DPF 40 is detected by the
differential pressure sensor 52 is judged in step S202. If the
clogging of the DPF 40 is detected, process control advances to
step S204, in which step, the creation of ozone by the ozone feeder
30 is then stopped and the addition of the ozone to the exhaust gas
is also stopped. Process control further advances to step S206 to
execute the regeneration of the DPF 40.
[0090] In step S206, fuel injection from the fuel injector 42 is
executed and fuel is added to the exhaust gas flowing into the DPF
40. A fuel injection quantity of the fuel injector 42 is controlled
so that the exhaust gas flowing into the DPF 40 will be of a lean
air-fuel ratio. An output signal from the air-fuel ratio sensor 54
is fed back during the control of the fuel injection quantity. The
fuel that has been injected from the fuel injector 42 is burned
upon reacting with the oxygen in the exhaust gas, and the resulting
heat creates a high-temperature atmosphere in the DPF 40. Thus,
particulates present on the DPF 40 are burned upon reacting with
excess oxygen present in the exhaust gas, and are progressively
removed from the DPF 40.
[0091] Whether the regenerating process for the NSR catalyst 22 is
necessary is judged in next step S208. This judgment is based upon
the quantity of NOx stored at up to a current point of time. The
NOx storage quantity can be estimated and calculated from counts of
the cumulative operating period and/or cumulative traveling
distance from the previous regenerating process for the NSR
catalyst 22. If the estimated quantity of NOx storage is in excess
of a predetermined reference level, the regenerating process for
the NSR catalyst 22 is judged to be necessary. In this case,
control is transferred to step S210, in which, the regeneration of
the NSR catalyst 22 is executed simultaneously with that of the DPF
40.
[0092] In step S210, fuel injection by the fuel injector 44 is also
executed downstream relative to the DPF 40, and fuel is added to
the exhaust gas flowing into the NSR catalyst 22. A fuel injection
quantity of the fuel injector 44 is controlled so that the exhaust
gas flowing into the NSR catalyst 22 will be a rich air-fuel ratio.
A large amount of fuel does not need to be injected from the fuel
injector 44 at this time since fuel addition by the fuel injector
42 is also continued at the upstream side of the DPF 40. An output
signal from the air-fuel ratio sensor 58 is fed back during the
control of the fuel injection quantity of the fuel injector 44. The
NOx stored within the NSR catalyst 22 is reduced by the HC and CO
contained in the exhaust gas, and is progressively removed from the
NSR catalyst 22.
[0093] During the regeneration of the DPF 40, the exhaust gas that
have passed through the DPF 40 are heated to a high temperature by
the combustion of the added fuel and that of the particulates.
Since the heat of the high-temperature exhaust gas can be used
during the regeneration of the NSR catalyst 22, there is no need to
burn new fuel for heating the NSR catalyst 22, or even if new fuel
needs burning, it is enough just to burn a slight amount of fuel.
Much of the fuel injected from the fuel injector 44, therefore, can
be used to reduce stored NOx.
[0094] Fuel addition by the fuel injector 44 for the regeneration
of the NSR catalyst 22 is executed only for the required
regenerating period calculated from the NOx storage quantity
existing immediately before the regeneration. The NOx storage
quantity can be estimated and calculated from counts of the
cumulative operating period and/or cumulative traveling distance
from the previous regenerating process for the NSR catalyst 22.
After elapse of the required regenerating period, process control
proceeds to step S212, in which step, the addition of fuel by the
fuel injector 44 is then stopped. This completes the regeneration
of the NSR catalyst 22.
[0095] Completion of the regeneration of the NSR catalyst 22 is
followed by a re-judgment in step S214. Whether the clogging of the
DPF 40 is detected by the differential pressure sensor 52 is
re-judged in step S214. Process step S206 is continued if the
clogging of the DPF 40 is re-detected or still remains detected.
After the regeneration of the NSR catalyst 22, it is judged in step
S208 that the regenerating process is unnecessary. Process steps
S210 and S212 are therefore skipped and the judgment in step S214
follows.
[0096] If, in step S214, the clogged state of the DPF 40 is judged
to be cleared, process control advances to step S216. In step S216,
the addition of fuel at the upstream side of the DPF 40 by the fuel
injector 42 is stopped. This completes the regeneration of the DPF
40.
[0097] During above successive processing, the NSR catalyst 22 is
regenerated simultaneously with the regeneration of the DPF 40, but
there may be a need to regenerate the NSR catalyst 22 before the
DPF 40 requires regeneration. If the clogging of the DPF 40 is not
detected in step S202, control is transferred to step S218 for a
next judgment. Whether NOx is detected by the NOx sensor 56 is
judged in step S218. If no NOx is detected, control is returned to
the judgment in step S202. Subsequently, either step S202 or S218
is repeated until a positive judgment has been conducted
therein.
[0098] If NOx is detected by the NOx sensor 56, control proceeds to
step S220, in which step, the regeneration of the NSR catalyst 22
is then executed. In step S220, the creation of ozone by the ozone
feeder 30 is stopped and the addition of the ozone to the exhaust
gas is also stopped.
[0099] In next step S222, fuel injection from the fuel injector 44
at the downstream side of the DPF 40 is executed and fuel is added
to the exhaust gas flowing into the NSR catalyst 22. The fuel
injection quantity of the fuel injector 44 is controlled so that
the exhaust gas flowing into the NSR catalyst 22 will be a rich
air-fuel ratio. An output signal from the air-fuel ratio sensor 58
is fed back during the control of the fuel injection quantity. The
fuel that has been injected from the fuel injector 44 is burned
upon reacting with the oxygen in the exhaust gas, and the resulting
heat warms the exhaust gas. In addition, excess fuel is left intact
in the exhaust gas and flows into the NSR catalyst 22. When the
high-temperature exhaust gas of a rich air-fuel ratio flows into
the NSR catalyst 22, the NOx stored therein is reduced by the HC
and CO contained in the exhaust gas, and is progressively removed
from the NSR catalyst 22.
[0100] Fuel addition for the regeneration of the NSR catalyst 22 is
executed only for the required regenerating period calculated from
the NOx storage quantity existing immediately before the
regeneration. The NOx storage quantity can be estimated and
calculated from counts of the cumulative operating period and/or
cumulative traveling distance from the previous regeneration of the
NSR catalyst 22. After elapse of the required regenerating period,
process control proceeds to step S224 to stop the addition of fuel
from the fuel injector 44. This completes the regeneration of the
NSR catalyst 22.
Effects of the Exhaust Gas Purification Device in the Second
Embodiment
[0101] As described above, the exhaust gas purification device of
the present embodiment can regenerate the DPF 40 and at the same
time, heat the NSR catalyst 22 using the heat generated during the
regeneration of the DPF 40. Additionally, the creation of a lean
atmosphere in the DPF 40 and that of a rich atmosphere in the NSR
catalyst 22 can be achieved by supplying fuel in divided forms to
the upstream and downstream sides of the DPF 40. Thus, the NSR
catalyst 22 can be regenerated at the same time the DPF 40 is
regenerated, and the heat generated during the regeneration of the
DPF 40 can be used more effectively.
Others
[0102] While embodiments of the present invention have been
described above, the invention is not limited to the embodiments
and may be modified without departing from the spirit and scope of
the invention. For example, the invention may be modified as
follows:
[0103] Although the configuration shown in FIG. 1 or 3 includes the
gas injection port 32 in the catalytic converter 20, ozone may be
supplied to a position other than the gas injection port. If ozone
can be reliably added to the exhaust gas flowing into the NSR
catalyst, the ozone may be supplied upstream relative to the
catalytic converter, on the exhaust passage.
[0104] In addition, although BaCO.sub.3 is used as an NOx-retaining
substance in the NSR catalyst of the above embodiments, the kind of
material used for the NOx-retaining substance is not limited to
BaCO.sub.3. That is to say, an alkaline metal such as Na, K, Cs, or
Rb, an alkaline earth metal such as Ba, Ca, or Sr, or a rare-earth
element such as Y, Ce, La, or Pr may be used according to
particular needs. Furthermore, the kind of material used for the
active site of the NSR catalyst is not limited to Pt and a
noble-metal material such as Rh or Pd may be used according to
particular needs.
[0105] In terms of functionality, the NSR catalyst can be broken
down into a "catalyst" and an "NOx-retaining material". In the NSR
catalyst, the noble metal that is the active site, and a support
that supports the noble metal are equivalent to the "catalyst", and
the NOx-retaining substance and a support that supports the
NOx-retaining substance are equivalent to the "NOx-retaining
material". The "catalyst" and the "NOx-retaining material" do not
always need to be an integrated structure and may be independent
structures. The "NOx storage reduction catalyst" pertaining to the
present invention is not necessarily an integrated structure of the
"catalyst" and the "NOx-retaining material", and includes the
"catalyst" and the "NOx-retaining material" in the form of
independent structures.
[0106] More specifically, in a support arrangement with two
independent supports, one of the supports may be used to form the
"catalyst" by supporting only a noble metal that is the active
site, and the other support may be used to form the "NOx-retaining
material" by supporting only the NOx-retaining substance. In such a
support arrangement, however, the "catalyst" is desirably provided
downstream with respect to the "NOx-retaining material" so that the
"catalyst" can process the NOx released from the "NOx-retaining
material". Alternatively, although one common support may be used,
the noble metal that is the active site, and the NOx-retaining
substance may be supported in divided different areas on the common
support. For example, the support may be adapted to support the
substances separately from each other on the upstream and
downstream sides thereof, or upper-layer and lower-layer sides
thereof.
[0107] In addition, during the regeneration of the NSR catalyst 22
in the above-described embodiments, the addition of ozone is
stopped (steps S108 and S116 of the routine shown in FIG. 2, or
steps S204 and S220 of the routine shown in FIG. 4), but under
certain conditions, the addition of ozone is anticipated to modify
fuel composition. Under specific conditions, therefore, adding fuel
under a coexisting state of ozone may enhance a stored-NOx reducing
effect, and if this is the case, the addition of ozone may be
continued.
[0108] While, in the above embodiments, the present invention is
applied to a diesel engine, the kind of internal combustion engine
to which the invention can be applied is not limited to diesel
engines. If the invention is applied to the internal combustion
engines, including gasoline lean-burn engines, that emit
NOx-containing exhaust gases, the advantages described above can be
obtained from the application of the invention.
* * * * *