U.S. patent application number 14/886679 was filed with the patent office on 2016-02-11 for exhaust gas purifying filter, system and regenerating gasoline particulate filter, and method thereof.
The applicant listed for this patent is Hyundai Motor Company, Kia Motors Corporation. Invention is credited to Jin Woo Choung, Chibum In.
Application Number | 20160040569 14/886679 |
Document ID | / |
Family ID | 47990864 |
Filed Date | 2016-02-11 |
United States Patent
Application |
20160040569 |
Kind Code |
A1 |
In; Chibum ; et al. |
February 11, 2016 |
EXHAUST GAS PURIFYING FILTER, SYSTEM AND REGENERATING GASOLINE
PARTICULATE FILTER, AND METHOD THEREOF
Abstract
An exhaust gas purifying filter, a system for regenerating a
particulate filter, and a method therefore are disclosed. An
exhaust gas purifying filter may include: an ammonia storage
catalyst unit adapted to absorb ammonia contained in the exhaust
gas when a temperature of the ammonia storage catalyst unit is
lower than a predetermined temperature, release the absorbed
ammonia when the temperature of the ammonia storage catalyst unit
is higher than or equal to the predetermined temperature, and
generate nitrogen oxide from the released ammonia; and a
particulate filter adapted to trap particulate matter contained in
the exhaust gas and regenerate the trapped particulate matter by
using the nitrogen oxide generated from the ammonia storage
catalyst unit.
Inventors: |
In; Chibum; (Yongin-
Gyeonggi-Do, KR) ; Choung; Jin Woo; (Suwon,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hyundai Motor Company
Kia Motors Corporation |
Seoul
Seoul |
|
KR
KR |
|
|
Family ID: |
47990864 |
Appl. No.: |
14/886679 |
Filed: |
October 19, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13534823 |
Jun 27, 2012 |
|
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14886679 |
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Current U.S.
Class: |
60/274 |
Current CPC
Class: |
Y02T 10/22 20130101;
Y02T 10/12 20130101; F01N 3/0814 20130101; F02D 41/029 20130101;
F01N 13/0097 20140603; F01N 2570/18 20130101; F01N 2430/06
20130101; F01N 2370/04 20130101; F01N 3/0231 20130101; F01N 3/2073
20130101; F01N 3/101 20130101 |
International
Class: |
F01N 3/023 20060101
F01N003/023; F01N 3/08 20060101 F01N003/08 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 13, 2011 |
KR |
10-2011-0104662 |
Claims
1.-8. (canceled)
9. A method for regenerating a particulate filter that comprises an
ammonia storage catalyst unit adapted to absorb or release ammonia
contained in exhaust gas depending on a temperature of the ammonia
storage catalyst unit, and a particulate filter adapted to trap
particulate matter contained in the exhaust gas, the method
comprising: absorbing ammonia contained in the exhaust gas;
comparing a pressure difference of the particulate filter to a
predetermined pressure difference; creating a lean atmosphere when
the pressure difference of the particulate filter is larger than or
equal to the predetermined pressure difference; releasing the
ammonia from the ammonia storage catalyst unit; generating nitrogen
oxide from the released ammonia; and regenerating the particulate
filter using the generated nitrogen oxide.
10. The method of claim 9, wherein the step of generating the
nitrogen oxide is performed by creating a lean atmosphere depending
on the temperature of the ammonia storage catalyst unit.
11. The method of claim 9, wherein a ratio of the ammonia in the
exhaust gas is raised by creating a rich atmosphere when the
ammonia is absorbed.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to and the benefit of
Korean Patent Application No. 10-2011-0104662 filed in the Korean
Intellectual Property Office on Oct. 13, 2011, the entire contents
of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] (a) Field of the Invention
[0003] The present invention relates to an exhaust gas purifying
filter, a system for regenerating a particulate filter, and a
method thereof. More particularly, the present invention relates to
an exhaust gas purifying filter, and a system and a method for
regenerating a particulate filter of a gasoline engine.
[0004] (b) Description of the Related Art
[0005] In general, a gasoline direct injection (GDI) technology
involves direct injection of fuel into a combustion chamber as
opposed to injection into an intake pipe. The technology has been
developed so as to improve fuel consumption efficiency and
performance of an internal combustion engine.
[0006] Since the air/fuel ratio is low (rich atmosphere) around a
spark plug, an engine generally is operated in a lean fuel
condition. However, this presents a problem in a gasoline direct
injection engine (GDI) which generates a large amount of
particulate matter (PM) during an incomplete combustion period
increment in a combustion chamber. Accordingly, a particulate
filter is mounted in a vehicle with a gasoline direct injection
engine (GDI).
[0007] However, if such a vehicle operates at a low speed for a
long time, it is difficult to passively regenerate particulate
matter (PM) in the particulate filter because the temperature and
oxygen concentration in the particulate filter are low.
[0008] In a conventional art, various devices for supplying oxygen
to a particulate filter have been developed in an attempt to
resolve such problems. In particular, regeneration of the
particulate filter has been performed such that the particle matter
(PM) trapped in the particulate filter is oxidized and eliminated
by supplying additional air to the front end of the particulate
filter mounted on an exhaust pipe.
[0009] Although the additional air is supplied to the front end of
the particulate filter, a high temperature is required for
oxidizing PM trapped in the particulate filter with oxygen.
However, in the particulate filter of a gasoline engine, it is
difficult to secure a temperature at which the particle matter (PM)
and the oxygen can sufficiently react.
[0010] The above information disclosed in this Background section
is only for enhancement of understanding of the background of the
invention and therefore it may contain information that does not
form the prior art that is already known in this country to a
person of ordinary skill in the art.
SUMMARY OF THE INVENTION
[0011] The present invention has been made in an effort to provide
an exhaust gas purifying filter, and a system and a method for
regenerating a particulate filter having advantages of sufficiently
oxidizing particulate matter in a particulate filter of a gasoline
engine.
[0012] In addition, the present invention has been made in an
effort to provide an exhaust gas purifying filter, and a system and
a method for regenerating a particulate filter having further
advantages of oxidizing the particulate matter in the particulate
filter of a gasoline engine at a lower temperature than typically
required.
[0013] According to one aspect, the present invention provides an
exhaust gas purifying filter that includes: an ammonia storage
catalyst unit adapted to absorb ammonia contained in the exhaust
gas when a temperature of the ammonia storage catalyst unit is
lower than a predetermined temperature, release the absorbed
ammonia when the temperature of the ammonia storage catalyst unit
is higher than or equal to the predetermined temperature, and
generate nitrogen oxide from the released ammonia; and a
particulate filter adapted to trap particulate matter contained in
the exhaust gas and regenerate the trapped particulate matter by
using the nitrogen oxide generated by the ammonia storage catalyst
unit.
[0014] According to various embodiments, the ammonia storage
catalyst unit may further include a three-way catalyst layer.
[0015] According to various embodiments, the ammonia storage
catalyst unit may include zeolite or an ammonia absorptive
material.
[0016] According to another aspect of the present invention, a
system is provided for regenerating a particulate filter, wherein
the system may be mounted on an exhaust pipe of a gasoline engine.
According to various embodiments, the system may include: a
three-way catalyst device mounted on the exhaust pipe connected to
the gasoline engine, the three-way catalyst device adapted to
oxidize or reduce an exhaust gas exhausted from the gasoline
engine; an ammonia storage catalyst unit mounted on the exhaust
pipe downstream of the three-way catalyst device, wherein the
ammonia storage catalyst unit is adapted to absorb ammonia
generated in the three-way catalyst when a temperature of the
ammonia storage catalyst unit is lower than a predetermined
temperature, release the absorbed ammonia when the temperature of
the ammonia storage catalyst unit is higher than or equal to the
predetermined temperature, and generate nitrogen oxide from the
released ammonia; a particulate filter mounted proximal to the
ammonia storage catalyst unit, and adapted to trap particulate
matter contained in the exhaust gas and regenerate the trapped
particulate matter by using the nitrogen oxide generated from the
ammonia storage catalyst unit; and a control portion adapted to
control an air-fuel ratio of an air-fuel mixture flowing into the
gasoline engine, wherein the control portion is further adapted to
create a lean atmosphere when a pressure difference of the
particulate filter is larger than or equal to a predetermined
pressure difference. In particular, when used herein, creating a
lean atmosphere refers to creating an atmosphere in which the
air/fuel ratio is high (as opposed to a rich atmosphere in which
the air/fuel ratio is low).
[0017] According to various embodiments, the control portion is
adapted to create a rich atmosphere when a concentration of the
ammonia is lower than or equal to a predetermined
concentration.
[0018] According to various embodiments, the control portion is
adapted to create a lean atmosphere depending on the temperature of
the ammonia storage catalyst unit when the pressure difference of
the particulate filter is larger than or equal to the predetermined
pressure difference.
[0019] According to various embodiments, the ammonia storage
catalyst unit further includes a three-way catalyst layer.
[0020] According to various embodiments, the ammonia storage
catalyst unit includes zeolite or an ammonia absorptive
material.
[0021] According to another aspect of the present invention, a
system for regenerating a particulate filter is provided which can
be applied to the present methods for regenerating a particulate
filter. According to various embodiments, the method may include:
absorbing the ammonia contained in the exhaust gas; comparing a
pressure difference of the particulate filter to a predetermined
pressure difference; creating a lean atmosphere when the pressure
difference of the particulate filter is larger than or equal to the
predetermined pressure difference; releasing the ammonia from the
ammonia storage catalyst unit; generating nitrogen oxide from the
released ammonia; and regenerating the particulate filter using the
generated nitrogen oxide.
[0022] According to various embodiments, generating the nitrogen
oxide is performed by creating a lean atmosphere depending on the
temperature of the ammonia storage catalyst unit.
[0023] According to various embodiments, a ratio of the ammonia in
the exhaust gas is raised by creating a rich atmosphere when the
ammonia is absorbed.
[0024] It is understood that the term "vehicle" or "vehicular" or
other similar term as used herein is inclusive of motor vehicles in
general such as passenger automobiles including sports utility
vehicles (SUV), buses, trucks, various commercial vehicles,
watercraft including a variety of boats and ships, aircraft, and
the like, and includes hybrid vehicles, electric vehicles, plug-in
hybrid electric vehicles, hydrogen-powered vehicles and other
alternative fuel vehicles (e.g., fuels derived from resources other
than petroleum). As referred to herein, a hybrid vehicle is a
vehicle that has two or more sources of power, for example both
gasoline-powered and electric-powered vehicles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 and FIG. 2 are schematic diagrams of a system for
purifying an exhaust gas according to an exemplary embodiment of
the present invention.
[0026] FIG. 3 is a graph showing an absorption ratio of ammonia
according to temperature change.
[0027] FIG. 4 is a flowchart of a method for purifying exhaust gas
according to an exemplary embodiment of the present invention.
[0028] FIG. 5 is a graph showing a combustion ratio according to
temperature change of particulate matter.
TABLE-US-00001 [0029]<Description of Symbols> 1: system for
regenerating particulate filter 10: gasoline engine 11: cylinder
13: injector 15: intake manifold 17: exhaust manifold 19: exhaust
pipe 20: three-way catalyst device 32: ammonia storage catalyst
unit 33: ammonia storage layer 34: three-way catalyst layer 35:
particulate filter 36: temperature sensor 38: differential pressure
sensor 40: control portion
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0030] An exemplary embodiment of the present invention will
hereinafter be described in detail with reference to the
accompanying drawings.
[0031] FIG. 1 and FIG. 2 are schematic diagrams of a system for
purifying exhaust gas according to an exemplary embodiment of the
present invention, and FIG. 3 is a graph showing an absorption
ratio of ammonia according to temperature change.
[0032] Referring to FIG. 1 and FIG. 2, a system 1 for regenerating
a particulate filter according to an exemplary embodiment of the
present invention includes a gasoline engine 10, a three-way
catalyst device 20, an ammonia storage catalyst unit 32, a
particulate filter 35, and a control portion 40.
[0033] The gasoline engine 10 is an internal combustion engine
using gasoline as a fuel, and burns fuel and air so as to convert
chemical energy into mechanical energy. The gasoline engine 10
includes a plurality of cylinders 11 into which the fuel and the
air flow, and an ignition device (not shown) for igniting the fuel
and the air flowing into the cylinders 11. The gasoline engine 10
is connected to an intake manifold 15 so as to receive the air in
the cylinders 11, and is connected to an exhaust manifold 17 such
that exhaust gas generated in a combustion process is gathered in
the exhaust manifold 17 and is exhausted to the exterior through an
exhaust pipe 19. As further shown, an injector 13 can be mounted at
the cylinders 11 so as to inject the fuel into the cylinders
11.
[0034] The three-way catalyst device 20 is mounted on the exhaust
pipe 19, and is adapted to oxidize or reduce the exhaust gas
exhausted from the gasoline engine 10. Generally, the three-way
catalyst device 20 converts toxic chemicals (CO, HC, and NO.sub.X)
in the exhaust gas into harmless gases (CO.sub.2, H.sub.2O,
N.sub.2, and O.sub.2) by way of an oxidation-reduction
reaction.
[0035] The three-way catalyst device 20 is a catalytic converter
that stimulates the oxidation-reduction reaction, and generally
includes a suitable catalyst, such as, for example, a combination
of platinum (Pt), palladium (Pd), and rhodium (Rh). The platinum
catalyst and the palladium catalyst stimulate the oxidation
reaction to reduce carbon monoxide (CO) and hydrocarbon (HC), and
the rhodium catalyst stimulates the reduction reaction to reduce
nitrogen oxide (NO.sub.X). If the air-fuel ratio is lean (i.e., air
is rich as compared to fuel), the oxidation reaction for reducing
carbon monoxide (CO) and hydrocarbon (HC) occurs actively in the
three-way catalyst device 20 such that production ratios of water
(H.sub.2O) and carbon dioxide (CO.sub.2) are increased. On the
other and, if the air-fuel ratio is rich (i.e., air is lean as
compared to fuel), the reduction reaction for reducing nitrogen
oxide (NO.sub.x) actively occurs such that a production ratio of
nitrogen N.sub.2 is increased.
[0036] As shown in FIGS. 1 and 2, the ammonia storage catalyst unit
32 is mounted on the exhaust pipe 19 downstream of the three-way
catalyst device 20. The ammonia storage catalyst unit 32 can, for
example, be mounted in the proximity of the particulate filter 35,
or can be mounted in the particulate filter 35. As shown in FIG. 1
and FIG. 2, the ammonia storage catalyst unit 32 and the
particulate filter 35 can be provided in a common space.
[0037] The ammonia storage catalyst unit 32 is adapted to absorb
and release ammonia (NH.sub.3). As described above, if an excessive
amount of fuel is supplied, ammonia (NH.sub.3) is produced by
reducing nitrogen oxide (NO.sub.X) in the three-way catalyst device
20. Therefore, the ammonia storage catalyst unit 32 is adapted to
mainly absorb and release ammonia (NH.sub.3) produced in the
three-way catalyst device 20.
[0038] In the present system, an absorption ratio and a release
ratio of ammonia (NH.sub.3) in the ammonia storage catalyst unit 32
vary according to temperature. That is, the lower the temperature
is, the higher the absorption ratio of ammonia (NH.sub.3) in the
ammonia storage catalyst unit 32. On the contrary, the higher the
temperature is, the higher the release ratio of ammonia (NH.sub.3)
in the ammonia storage catalyst unit 32. Therefore, as shown in
FIG. 3, ammonia (NH.sub.3) produced in the three-way catalyst
device 20 is mainly absorbed below a certain temperature of the
ammonia storage catalyst unit 32 and is mainly released at a
temperature higher than or equal to the certain temperature of the
ammonia storage catalyst unit 32. According to an exemplary
embodiment, the certain temperature may be, but is not limited to,
about 350.degree. C. Of course, this certain temperature can vary
and can be, for example, about 300.degree. C., about 310.degree.
C., about 320.degree. C., about 330.degree. C., about 340.degree.
C., about 360.degree. C., about 370.degree. C., about 380.degree.
C., etc.
[0039] The ammonia storage catalyst unit 32 can use various
absorptive materials. According to an exemplary embodiment, one of
the absorptive materials may be zeolite.
[0040] As shown in FIG. 2, the ammonia storage catalyst unit 32 can
include, in addition to the ammonia storage layer 33, a three-way
catalyst layer 34. According to an embodiment, one of the ammonia
storage layer 33 or the three-way catalyst layer 34 is provided on
the other (i.e. the three-way catalyst layer 34 or the ammonia
storage layer 33 respectively) in the ammonia storage catalyst unit
32. In particular, according to one embodiment the three-way
catalyst layer 34 is disposed on the ammonia storage layer 33, but
such disposition of the three-way catalyst layer 34 and the ammonia
storage layer 33 are not limited as such.
[0041] As shown in FIGS. 1 and 2, the three-way catalyst layer 34
and the three-way catalyst device 20 are provided separated from
each other. According to preferred embodiments, the three-way
catalyst layer 34, like the three-way catalyst device 20, is
adapted to oxidize or reduce exhaust gas. Thus, for example, if the
fuel is supplied excessively (i.e., air-fuel ratio is rich), the
three-way catalyst layer 34 produces ammonia (NH.sub.3) by reducing
nitrogen oxide (NO.sub.x) which is not reduced in the three-way
catalyst device 20. Therefore, an ammonia (NH.sub.3) ratio in the
exhaust gas passing to the ammonia storage layer 33 is increased.
Also, if oxygen (O.sub.2) is supplied excessively (i.e., air-fuel
ratio is lean), then the three-way catalyst layer 34 increases the
production ratio of nitrogen oxide (NO.sub.x), particularly
nitrogen dioxide (NO.sub.2), particularly by stimulating the
oxidation reaction of ammonia (NH.sub.3) released from the ammonia
storage layer 33.
[0042] As shown in FIGS. 1 and 2, the particulate filter 35 is
mounted downstream in the proximity of the ammonia storage catalyst
unit 32, and is adapted to trap particulate matter (PM) in the
exhaust gas. The particulate matter (PM) mainly comprises
hydrocarbon that is called soot, a soluble organic fraction, and so
on. The particulate filter 35 is adapted to trap the particulate
matter (PM). According to a preferred embodiment, the particulate
filter 35 has a honeycomb structure.
[0043] However, if the particulate matter (PM) becomes trapped in
the particulate filter 35, the flow of the exhaust gas may be
interrupted. Therefore, the particulate filter 35 is configured to
perform a regeneration process to oxidize and eliminate the
particulate matter (PM). In particular, if particulate matter (PM)
of more than a certain amount is trapped in the particulate filter
35, then a pressure difference is created in the particulate filter
35. A pressure sensor 38 is configured and arranged to measure this
pressure difference. If the pressure difference measured by the
differential pressure sensor 38 is higher than or equal to a
predetermined pressure difference, then the particulate filter 35
performs a regeneration process.
[0044] The particulate filter 35 is adapted to regenerate the
particulate matter (PM) using the nitrogen oxide (NO.sub.x),
particularly nitrogen dioxide (NO.sub.2), which is generated by
oxidizing the ammonia (NH.sub.3) released from the ammonia storage
catalyst unit 32. That is, the particulate matter (PM) is oxidized
and eliminated by an oxidation reaction with the nitrogen oxide
(NO.sub.x), particularly nitrogen dioxide (NO.sub.2).
[0045] As shown in FIGS. 1 and 2, a control portion 40 is provided
which is adapted to control an air-fuel ratio of an air-fuel
mixture flowing into the gasoline engine 10. In particular, the
control portion 40 is adapted to control the fuel amount and the
air amount flowing into the gasoline engine 10 so as to control the
oxygen (O.sub.2) ratio in the exhaust gas.
[0046] The control portion 40 receives the pressure difference
value measured by the differential pressure sensor 38, compares the
measured pressure difference value with a predetermined pressure
difference value, and determines whether the particulate filter 35
will be regenerated. If the pressure difference of the particulate
filter 35 is larger than or equal to the predetermined pressure
difference, then the control portion 40 is adapted to create a lean
atmosphere. In particular, the control portion 40 is adapted to
increase the oxygen (O.sub.2) ratio in the exhaust gas so as to
oxidize and eliminate the particulate matter (PM), mainly carbon
(C) particles, from the particulate filter 35. According to an
exemplary embodiment, the control portion 40 is adapted to control
the injector 13 and can, for example, stop the supply of fuel into
the cylinder 11 so as to increase the oxygen (O.sub.2) ratio in the
exhaust gas.
[0047] Further, the present system is configured such that when
controlling the air-fuel ratio to be lean for regeneration of the
particulate filter 35, the control portion 40 is adapted to further
control the air-fuel ratio depending to the temperature of the
ammonia storage catalyst unit 32 as measured by a temperature
sensor 36. In particular, after determining whether the particulate
filter 35 will be regenerated, the control portion 40 is adapted to
control the air-fuel ratio by comparing the temperature measured in
the temperature sensor 36 with a releasable temperature (e.g.,
about 350.degree. C.) in the ammonia storage catalyst unit 32. This
releasable temperature is a temperature at which the ammonia
(NH.sub.3) can be released in the ammonia storage catalyst unit 32.
For example, if the temperature measured in the temperature sensor
36 is lower than the releasable temperature in the ammonia storage
catalyst unit 32, then the control portion 40 is adapted to
increase the oxygen (O.sub.2) ratio in the exhaust gas so as to
increase the measured temperature to the releasable temperature of
the ammonia storage catalyst unit 32.
[0048] The control portion 40 is further adapted to control the
ammonia (NH.sub.3) ratio in the exhaust gas. For example, the
control portion 40 can receive the ammonia (NH.sub.3) concentration
value as measured by an ammonia concentration measure sensor (not
shown), and compare the measured ammonia (NH.sub.3) concentration
with a predetermined concentration. If the measured ammonia
(NH.sub.3) concentration is lower than the predetermined
concentration, then the control portion 40 can be adapted to create
a rich atmosphere. In particular, the control portion 40 is adapted
to control the injector 13 and supply the fuel in an excessive
amount to the cylinder 11 so as to increase the ammonia (NH.sub.3)
ratio in the exhaust gas.
[0049] The control portion 40 can further be configured to
calculate the ammonia (NH.sub.3) ratio in the exhaust gas depending
on parameters (e.g., an engine operation condition, an exhaust gas
temperature, an air-fuel ratio, a degradation amount of the
catalyst, and so an), and the control portion 40 can include a map
table in which the ammonia (NH.sub.3) ratio according to the
parameters is stored in advance.
[0050] FIG. 4 is a flowchart showing a method for purifying exhaust
gas according to an exemplary embodiment of the present
invention.
[0051] Referring to FIG. 4, a regenerating method using the system
1 as shown in FIGS. 1 and 2 will be described in detail.
[0052] Referring to FIG. 4, the system 1 for regenerating the
particulate filter is operated while the engine operates beginning
at step S100. If the gasoline engine 10 is operated and the fuel is
supplied excessively into the gasoline engine 10 (step S110) (i.e.
if the air-fuel ratio is rich), then the reduction reaction of the
nitrogen oxide (NOx) is stimulated in the three-way catalyst device
20 and the ammonia (NH.sub.3) is produced at step S120. Typically,
in an initial operation region and at a high load region, the fuel
is supplied excessively for protecting the exhaust manifold 17 and
the catalyst of the three-way catalyst device 20. Also, if the
ammonia (NH.sub.3) concentration as measured by the ammonia
concentration measure sensor (not shown) or as calculated by the
control portion 40 is lower than the predetermined concentration,
then the control portion 40 is adapted to control the injector 13
so as to supply the fuel excessively. The ammonia NH.sub.3 of the
exhaust gas exhausted in the three-way catalyst device 20 is then
absorbed in the ammonia storage catalyst unit 32 at step S130. As
described above, the ammonia (NH.sub.3) is absorbed below the
certain temperature, (e.g., about 350.degree. C.) in the ammonia
storage catalyst unit 32. Because the temperature of the exhaust
gas is not higher than the releasable temperature during a normal
operating mode of the gasoline engine 10, a majority of the ammonia
(NH.sub.3) is absorbed in the ammonia storage catalyst unit 32.
[0053] The differential pressure sensor 38 measures the pressure
difference of the particulate filter 35 during the normal operating
mode of the gasoline engine 10 at step S140, and transmits the
measured pressure difference to the control portion 40.
[0054] Then, the control portion 40 determines whether the pressure
difference of the particulate filter 35 is larger than or equal to
the predetermined pressure difference at step S150. If the pressure
difference of the particulate filter 35 is larger than or equal to
the predetermined pressure difference, the control portion 40 is
adapted to control the air-fuel ratio in the gasoline engine 10 to
be lean at step S160. Since the oxygen (O.sub.2) ratio in the
exhaust gas exhausted from the gasoline engine 10 is increased, the
oxidation reaction in the three-way catalyst device 20 is
stimulated, thereby increasing the temperature of the exhaust gas
by the generated oxidation heat. Therefore, if the increased
temperature of the exhaust gas is higher than or equal to the
certain temperature (e.g., about 350.degree. C.), then ammonia
(NH.sub.3) is released from the ammonia storage layer 33 of the
ammonia storage catalyst unit 32 at step S170. Next, the released
ammonia (NH.sub.3) is oxidized such that the nitrogen oxide
(NO.sub.x), particularly nitrogen dioxide (NO.sub.2), is generated
at step S180. Then the particulate matter (PM) in the particulate
filter 35 is oxidized and eliminated by the nitrogen oxide (NOx),
particularly nitrogen dioxide (NO.sub.2), at step S190. That is,
the particulate filter 35 is regenerated.
[0055] Generally, the particulate filter 35 is adapted to oxidize
and eliminate the particulate matter (PM) using oxygen (O.sub.2)
gas, but the system 1 for regenerating the particulate filter may
also be adapted to oxidize and eliminate the particulate matter
(PM) using nitrogen dioxide (NO.sub.2).
[0056] FIG. 5 is a graph for showing a combustion ratio according
to temperature change of particulate matter.
[0057] Referring to FIG. 5, an ambient temperature must be higher
than or equal to about 400.degree. C. at a minimum for oxidizing
(i.e., burning) the particulate matter (PM) (e.g. soot) trapped in
the particulate filter with oxygen (O.sub.2) gas. However, as
shown, nitrogen dioxide (NO.sub.2) can oxidize (i.e., burn) the
particulate matter (PM) below 400.degree. C.
[0058] Therefore, the system 1 for regenerating the particulate
filter is adapted to increase nitrogen dioxide (NO.sub.2) flowing
into the particulate filter 35 such that the particulate matter
(PM) is oxidized and eliminated by the nitrogen dioxide (NO.sub.2)
at a lower temperature when the particulate filter 35 is to be
regenerated.
[0059] As described above, the particulate matter (PM) in the
particulate filter 35 of the gasoline engine may be sufficiently
oxidized according to exemplary embodiments of the present
invention.
[0060] Also, the particulate matter (PM) in the particulate filter
35 of the gasoline engine may be oxidized at a temperature lower
than typically required.
[0061] While this invention has been described in connection with
what is presently considered to be practical exemplary embodiments,
it is to be understood that the invention is not limited to the
disclosed embodiments. On the contrary, it is intended to cover
various modifications and equivalent arrangements included within
the spirit and scope of the appended claims.
* * * * *