U.S. patent application number 12/448947 was filed with the patent office on 2010-04-01 for exhaust purification system for internal combustion engine.
This patent application is currently assigned to Toyota Jidosha Kabushiki Kaisha. Invention is credited to Mikio Inoue, Akinori Morishima.
Application Number | 20100077736 12/448947 |
Document ID | / |
Family ID | 39636078 |
Filed Date | 2010-04-01 |
United States Patent
Application |
20100077736 |
Kind Code |
A1 |
Morishima; Akinori ; et
al. |
April 1, 2010 |
EXHAUST PURIFICATION SYSTEM FOR INTERNAL COMBUSTION ENGINE
Abstract
In a treatment for regenerating the purification capability of
an exhaust emission control system, a technique for improving
exhaust emission more positively is provided by supplying a
reducing agent to the exhaust emission control system and allowing
part of exhaust to bypass the exhaust emission control system. When
an addition synchronous bypass control is carried out in which an
reducing agent is added when an NSR is subject to NOx reduction
treatment and the volume of exhaust passing through a bypass pipe
out of exhaust passing an exhaust pipe is increased to thereby
decrease the volume of exhaust passing through the NSR, a judgment
is made (S106) as to which is larger a reduction in volume of Nox
exhausted (S105) due to an increase in conversion efficiency of the
NSR as the result of the addition synchronous bypass control
carried out or an increase in volume of Nox exhausted (S103) due to
an increase in exhaust passing through the bypass pipe. When a
reduction in volume of NOx exhausted due to an increase in
conversion efficiency of the NSR is judged to be larger than an
increase in volume of Nox exhausted due to an increase in exhaust
passing through the bypass pipe, the addition synchronous bypass
control is executed (107).
Inventors: |
Morishima; Akinori;
(Susono-shi, JP) ; Inoue; Mikio; (Susono-shi,
JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
Toyota Jidosha Kabushiki
Kaisha
Toyota-shi
JP
|
Family ID: |
39636078 |
Appl. No.: |
12/448947 |
Filed: |
January 21, 2008 |
PCT Filed: |
January 21, 2008 |
PCT NO: |
PCT/JP2008/051136 |
371 Date: |
July 16, 2009 |
Current U.S.
Class: |
60/288 ;
60/295 |
Current CPC
Class: |
F01N 2410/04 20130101;
Y02A 50/20 20180101; F01N 2610/02 20130101; B01D 2258/012 20130101;
Y02T 10/12 20130101; F01N 13/009 20140601; B01D 2255/91 20130101;
F01N 9/00 20130101; B01D 53/9477 20130101; F01N 2570/14 20130101;
Y02T 10/47 20130101; Y02T 10/24 20130101; B01D 53/9459 20130101;
B01D 2251/208 20130101; B01D 53/9409 20130101; F01N 3/0814
20130101; Y02A 50/2344 20180101; Y02T 10/40 20130101; F01N 3/0842
20130101; F01N 3/0878 20130101; F01N 2410/12 20130101; B01D 53/9495
20130101; F01N 3/0253 20130101 |
Class at
Publication: |
60/288 ;
60/295 |
International
Class: |
F01N 3/031 20060101
F01N003/031; F01N 3/035 20060101 F01N003/035 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 19, 2007 |
JP |
2007-009813 |
Dec 13, 2007 |
JP |
2007-322119 |
Claims
1.-6. (canceled)
7. An exhaust purification system for an internal combustion engine
comprising: an exhaust purification device provided in an exhaust
passage of said internal combustion engine, for purifying exhaust
gas passing through said exhaust passage; a bypass passage
branching from said exhaust passage on an upstream side of said
exhaust purification device and merging into said exhaust passage
on a downstream side of said exhaust purification device, for
causing said exhaust gas passing through said exhaust passage to
bypass said exhaust purification device; reducer supply device for
supplying a reducer to said exhaust gas passing through said
exhaust passage on the upstream side of said exhaust purification
device; and regeneration device for performing a regeneration
treatment for regenerating purification performance of said exhaust
purification device, when an amount of a purification substance
accumulated in said exhaust purification device becomes equal to or
larger than a predetermined value, said regeneration treatment
being a treatment for regenerating the purification performance of
said exhaust purification device by supplying said reducer from
said reducer supply device to said exhaust gas to introduce said
reducer into said exhaust purification device, regeneration exhaust
flow rate control device for executing regeneration exhaust flow
rate control when said regeneration device performs said
regeneration treatment, said regeneration exhaust flow rate control
being a control operation in which, of said exhaust gas passing
through said exhaust passage, an amount of exhaust gas passing
through said bypass passage is increased and an amount of exhaust
gas passing through said exhaust purification device is reduced;
and purification substance amount determination device for
determining the magnitude relation between the following two values
which are obtained when said regeneration exhaust flow rate control
is executed during execution of said regeneration treatment: the
decrease in the amount of said purification substance discharged
from said exhaust purification device due to the increase in the
rate of purification by said exhaust purification device; and the
increase in the amount of said purification substance discharged
from said bypass passage due to the increase in said exhaust gas
passing through said bypass passage, wherein said regeneration
exhaust flow rate control is executed when said purification
substance amount determination device determines that the decrease
in the amount of said purification substance discharged from said
exhaust purification device due to the increase in the rate of
purification by said exhaust purification device is larger than the
increase in the amount of said purification substance discharged
from said bypass passage due to the increase in said exhaust gas
passing through said bypass passage.
8. The exhaust purification system for an internal combustion
engine according to claim 7, wherein said purification substance
amount determining device determines the magnitude relation between
the following two values which are obtained in a period from start
of supplying said reducer in said regeneration treatment to start
of supplying said reducer in a next regeneration treatment: the
decrease in the amount of said purification substance discharged
from said exhaust purification device due to the increase in the
rate of purification by said exhaust purification device; and the
increase in the amount of said purification substance discharged
from said bypass passage due to the increase in said exhaust gas
passing through said bypass passage.
9. An exhaust purification system for an internal combustion engine
comprising: a storage-reduction type NOx catalyst provided in an
exhaust passage of said internal combustion engine, for purifying
exhaust gas passing through said exhaust passage; a bypass passage
branching from said exhaust passage on an upstream side of said
storage-reduction type NOx catalyst and merging into said exhaust
passage on a downstream side of said storage-reduction type NOx
catalyst, for causing said exhaust gas passing through said exhaust
passage to bypass said storage-reduction type NOx catalyst; reducer
supply device for supplying a reducer to said exhaust gas passing
through said exhaust passage on the upstream side of said
storage-reduction type NOx catalyst; and regeneration device for
performing a regeneration treatment for regenerating purification
performance of said storage-reduction type NOx catalyst, when an
amount of NOx accumulated in said storage-reduction type NOx
catalyst becomes equal to or larger than a predetermined value,
said regeneration treatment being a treatment for regenerating the
purification performance of said storage-reduction type NOx
catalyst by supplying said reducer from said reducer supply device
to said exhaust gas to introduce said reducer into said
storage-reduction type NOx catalyst; and regeneration exhaust flow
rate control device for executing regeneration exhaust flow rate
control when said regeneration device performs said regeneration
treatment, said regeneration exhaust flow rate control being a
control operation in which, of said exhaust gas passing through
said exhaust passage, an amount of exhaust gas passing through said
bypass passage is increased and an amount of exhaust gas passing
through said storage-reduction type NOx catalyst is reduced, and an
oxidation catalyst that has an oxidation ability and is provided in
said exhaust passage on a downstream side of a merging portion of
said exhaust passage and said bypass passage, wherein whether said
regeneration exhaust flow rate control is executed or not is
determined based on the following three values which are obtained
when said regeneration exhaust flow rate control is executed during
execution of said regeneration treatment: a decrease in an amount
of NOx discharged from said storage-reduction type NOx catalyst due
to an increase in the rate of purification by said
storage-reduction type NOx catalyst; an increase in an amount of
NOx discharged from said bypass passage due to an increase in said
exhaust gas passing through said bypass passage; and an increase in
an amount of NOx through oxidation of NH3 discharged from said
storage-reduction type NOx catalyst by said oxidation catalyst.
10. The exhaust purification system for an internal combustion
engine according to claim 9, further comprising said exhaust
purification system further comprises NOx amount determining device
for determining the magnitude relation between the following two
values which are obtained when said regeneration exhaust flow rate
control is executed during execution of said regeneration
treatment: the decrease in the amount of NOx discharged from said
storage-reduction type NOx catalyst due to the increase in the rate
of purification by said storage-reduction type NOx catalyst; and a
sum of the increase in the amount of NOx discharged from said
bypass passage due to the increase in said exhaust gas passing
through said bypass passage and the increase in the amount of NOx
through oxidation of NH3 discharged from said storage-reduction
type NOx catalyst by said oxidation catalyst, wherein said
regeneration exhaust flow rate control is executed when said NOx
amount determining device determines that the decrease in the
amount of NOx discharged from said storage-reduction type NOx
catalyst due to the increase in the rate of purification by said
storage-reduction type NOx catalyst is larger than the sum of the
increase in the amount of NOx discharged from said bypass passage
due to the increase in said exhaust gas passing through said bypass
passage and the increase in the amount of NOx through oxidation of
NH3 discharged from said storage-reduction type NOx catalyst by
said oxidation catalyst.
11. The exhaust purification system for an internal combustion
engine according to claim 10, wherein said NOx amount determination
device determines the magnitude relation between the following two
values which are obtained in a period from start of supplying said
reducer in said regeneration treatment to start of supplying said
reducer in a next regeneration treatment: the decrease in the
amount of NOx discharged from said storage-reduction type NOx
catalyst due to the increase in the rate of purification by said
storage-reduction type NOx catalyst; and the sum of the increase in
the amount of NOx discharged from said bypass passage due to the
increase in said exhaust gas passing through said bypass passage
and the increase in the amount of NOx through oxidation of NH3
discharged from said storage-reduction type NOx catalyst by said
oxidation catalyst.
Description
TECHNICAL FIELD
[0001] The present invention relates to an exhaust purification
system for an internal combustion engine.
BACKGROUND ART
[0002] Exhaust gas of an internal combustion engine contains
harmful substances such as NOx. It is known that a NOx catalyst for
purifying NOx in the exhaust gas may be provided in an exhaust
system of the internal combustion engine to reduce discharge of
these harmful substances. In this technique, when a
storage-reduction type NOx catalyst is provided, for example, the
purification performance decreases as the amount of stored NOx
increases. Therefore, a reducer is supplied to the
storage-reduction type NOx catalyst by executing rich spike control
to reduce and release the NOx stored in the catalyst (hereinafter,
referred to as a "NOx reduction treatment").
[0003] Exhaust gas from an internal combustion engine also contains
particulate matter (PM) having carbon as a main component. In a
known technique for preventing emission of the particulate matter
into the atmosphere, a particulate filter (hereafter, referred to
as a "filter") is provided in the exhaust system of the internal
combustion engine to trap the particulate matter.
[0004] In this filter, as the accumulated amount of trapped
particulate matter increases, the filter becomes clogged, causing
an increase in back pressure on the exhaust gas and a decrease in
the engine performance. Therefore, the temperature of the filter is
raised to remove the trapped particulate matter through oxidation
(hereafter, referred to as a "PM regeneration treatment"). In this
case as well, a fuel as a reducer may be supplied to the filter in
order to raise the temperature of the filter.
[0005] In a proposed technique, when the NOx reduction treatment
for a NOx catalyst and the PM regeneration treatment for a filter
(especially a filter carrying a NOx catalyst thereon) are
performed, a reducer is supplied, and at the same time, a part of
the exhaust gas is caused to bypass an exhaust purification device,
such as the NOx catalyst and the filter, to reduce the flow rate of
the exhaust gas passing through the exhaust purification device.
According to this technique, the reducer can be prevented from
being oxidized by a large amount of exhaust gas before reaching the
exhaust purification device, and sufficient time can be ensured for
the reducer to react in the exhaust purification device. As a
result, the efficiency of regenerating the purification performance
of the exhaust purification device can be improved.
[0006] In relation to this technique of the exhaust purification
system, a technique is disclosed in, for example, Japanese Patent
Application Publication No. JPA-2002-349236. That is, a NOx
storage-reduction catalyst is provided in an exhaust pipe of an
engine, and a liquid injection nozzle capable of injecting a
reducer is provided in the exhaust pipe on the exhaust gas upstream
side of the NOx storage-reduction catalyst. Moreover, a particulate
filter functioning as an oxidation catalyst is provided in the
exhaust pipe on the exhaust gas downstream side of the NOx
storage-reduction catalyst. Moreover, a bypass pipe is connected to
the exhaust pipe so that the exhaust gas bypasses the NOx
storage-reduction catalyst. An exhaust gas regulation valve
switches so that the exhaust gas flows into either the NOx
storage-reduction catalyst or the bypass pipe. Injection of the
reducer and the degree of opening of the exhaust gas regulation
valve are controlled based on a detection output of a temperature
sensor for detecting the temperature of the exhaust gas in the
exhaust pipe on the exhaust gas upstream side of the NOx
storage-reduction catalyst.
[0007] In this technique, when the exhaust gas temperature is lower
than a predetermined value, injection of the reducer is turned off,
and the exhaust gas regulation valve is regulated so that the
exhaust gas flows into the NOx storage-reduction catalyst and does
not flow into the bypass pipe. As a result, NOx in the exhaust gas
is stored in the catalyst, and HC in the exhaust gas is oxidized by
an oxidation function of a noble metal carried by the catalyst.
When the exhaust gas temperature is equal to or higher than the
predetermined value, the exhaust gas regulation valve is regulated
so that a major part of the exhaust gas flows into the bypass pipe
and a part of the exhaust gas flows into the catalyst, and at the
same time, the reducer is injected from the liquid injection
nozzle. As a result, the excess air ratio of the exhaust gas at the
catalyst inlet is reduced, and NOx stored in the catalyst reacts
with the HC and the like, and are released from the catalyst as
N.sub.2, CO.sub.2, and H.sub.2O. Moreover, a part of HC and the
like generated by injection of the reducer passes through the
catalyst and are trapped by the filter. While the reducer is being
injected, a major part of the exhaust gas flows into the bypass
pipe and the exhaust gas having a high excess air ratio flows into
the filter. Therefore, HC and the like thus trapped by the filter
are oxidized and burnt by an oxidation function of an active metal
carried by the filter.
[0008] According to this technique, the discharge amount of NOx and
particulates contained in the exhaust gas can be reduced with high
efficiency, and the reducer injected from the liquid injection
nozzle into the exhaust pipe can be prevented from being discharged
into the atmosphere in a vaporized state.
[0009] An engine exhaust purification device disclosed in Japanese
Patent Application Publication No. JP-A-2000-265827 includes an
exhaust purifying catalyst provided right below an exhaust
manifold, a bypass passage for bypassing the exhaust purifying
catalyst, a sensor for detecting the temperature of exhaust gas,
and an exhaust control valve for limiting entry of the exhaust gas
into the exhaust purifying catalyst. When conditions for raising
the temperature of the exhaust purifying catalyst are satisfied, a
controller reduces the limitation by the exhaust control valve to
increase the amount of exhaust gas to be introduced into the
exhaust purifying catalyst. As a result, the catalyst temperature
is raised without degrading running performance and fuel
consumption.
[0010] However, when the exhaust gas is caused to bypass the
exhaust purification device in treatments of regenerating
purification performance, such as a NOx reduction treatment and a
PM regeneration treatment, the efficiency of regenerating the
purification performance of the exhaust purification device can be
increased as described above, and improvement of the rate of
purification can be expected. However, a purification substance in
the exhaust gas which has bypassed the exhaust purification device
may be discharged without passing through the exhaust purification
device, which may degrade emission.
[0011] It is an object of the present invention to provide a
technique of more reliably improving exhaust gas emission by
supplying a reducer to an exhaust purification device and causing a
part of the exhaust gas to bypass the exhaust purification device
in a treatment of regenerating the purification performance of the
exhaust purification device.
DISCLOSURE OF THE INVENTION
[0012] In order to achieve the above object, the present invention
has been made on the premise that regeneration exhaust flow rate
control is executed when a treatment of regenerating purification
performance of an exhaust purification device is performed. In the
regeneration exhaust flow rate control, a reducer is supplied and,
of the exhaust gas passing through an exhaust passage, the amount
of exhaust gas passing through a bypass passage is increased, and
the amount of exhaust gas passing through the exhaust purification
device is reduced. The largest feature of the present invention is
that whether the regeneration exhaust flow rate control is executed
or not is determined based on the following two values which are
obtained when the regeneration exhaust flow rate control is
executed: a decrease in an amount of a purification substance
discharged from the exhaust purification device due to an increase
in a rate of purification by the exhaust purification device; and
an increase in an amount of the purification substance discharged
from the bypass passage due to an increase in the exhaust gas
passing through the bypass passage.
[0013] More specifically, an exhaust purification system for an
internal combustion engine according to the present invention is
characterized by including:
[0014] an exhaust purification device provided in an exhaust
passage of the internal combustion engine, for purifying exhaust
gas passing through the exhaust passage;
[0015] a bypass passage branching from the exhaust passage on an
upstream side of the exhaust purification device and merging into
the exhaust passage on a downstream side of the exhaust
purification device, for causing the exhaust gas passing through
the exhaust passage to bypass the exhaust purification device;
[0016] reducer supply means for supplying a reducer to the exhaust
gas passing through the exhaust passage on the upstream side of the
exhaust purification device; and
[0017] regeneration means for performing a regeneration treatment
for regenerating purification performance of the exhaust
purification device, when an amount of a purification substance
accumulated in the exhaust purification device becomes equal to or
larger than a predetermined value, the regeneration treatment being
a treatment for regenerating the purification performance of the
exhaust purification device by supplying the reducer from the
reducer supply means to the exhaust gas to introduce the reducer
into the exhaust purification device; and
[0018] regeneration exhaust flow rate control means for executing
regeneration exhaust flow rate control when the regeneration means
performs the regeneration treatment, the regeneration exhaust flow
rate control being a control operation in which, of the exhaust gas
passing through the exhaust passage, an amount of exhaust gas
passing through the bypass passage is increased and an amount of
exhaust gas passing through the exhaust purification device is
reduced, wherein
[0019] whether the regeneration exhaust flow rate control is
executed or not is determined based on the following two values
which are obtained when the regeneration exhaust flow rate control
is executed during execution of the regeneration treatment: a
decrease in an amount of the purification substance discharged from
the exhaust purification device due to an increase in a rate of
purification by the exhaust purification device; and an increase in
an amount of the purification substance discharged from the bypass
passage due to an increase in the exhaust gas passing through the
bypass passage.
[0020] According to this structure, it is possible to determine
whether the regeneration exhaust flow rate control is executed or
not in view of both of the following two values which are obtained
when the regeneration exhaust flow rate control is executed: the
decrease in the amount of the purification substance discharged
from the exhaust purification device due to the increase in the
rate of purification by the exhaust purification device; and the
increase in the amount of the purification substance discharged
from the bypass passage due to the increase in the exhaust gas
passing through the bypass passage. More specifically, the
regeneration exhaust flow rate control can be executed only when it
is determined that the amount of the purification substance
discharged to the downstream side of the merging portion of the
exhaust passage and the bypass passage becomes smaller than that in
the case where the regeneration exhaust flow rate control is not
executed. Accordingly, exhaust emission can be more reliably
improved by the regeneration exhaust flow rate control.
[0021] Note that the term "purification substance" in the above
description collectively refers to substances which are contained
in the exhaust gas from an internal combustion engine, such as NOx
and particulate matter, and which should be purified by the exhaust
purification device. Moreover, the expression "regenerates the
purification performance of the exhaust purification device when
the amount of the purification substance becomes equal to or larger
than the predetermined value means that a NOx reduction treatment,
a PM regeneration treatment, and the like are performed when NOx
storage performance of a storage-reduction type NOx catalyst has
significantly degraded as a result of an excessive amount of NOx
stored in the storage-reduction type NOx catalyst, or when increase
in the back pressure by the filter becomes significant as a result
of an excessive amount of particulate matter accumulated on the
filter.
[0022] The present invention has been made on the premise that the
regeneration exhaust flow rate control is executed when the
treatment of regenerating the purification performance of the
exhaust purification device is performed. In the regeneration
exhaust flow rate control, the reducer is supplied and, of the
exhaust gas passing through the exhaust passage, the amount of
exhaust gas passing through the bypass passage is increased, and
the amount of exhaust gas passing through the exhaust purification
device is reduced.
[0023] The exhaust purification system of the present invention is
characterized in that the magnitude relation is determined between
the following two values which are obtained when the regeneration
exhaust flow rate control is executed: the decrease in the amount
of the purification substance discharged from the exhaust
purification device due to the increase in the rate of purification
by the exhaust purification device; and the increase in the amount
of the purification substance discharged from the bypass passage
due to the increase in the exhaust gas passing through the bypass
passage. The regeneration exhaust flow rate control is executed
when it is determined that the decrease in the amount of the
purification substance discharged from the exhaust purification
device due to the increase in the rate of purification by the
exhaust purification device is larger than the increase in the
amount of the purification substance discharged from the bypass
passage due to the increase in the exhaust gas passing through the
bypass passage.
[0024] More specifically, the exhaust purification system for an
internal combustion engine according to the present invention is
characterized by further including
[0025] purification substance amount determination means for
determining the magnitude relation between the following two values
which are obtained when the regeneration exhaust flow rate control
is executed during execution of the regeneration treatment: the
decrease in the amount of the purification substance discharged
from the exhaust purification device due to the increase in the
rate of purification by the exhaust purification device; and the
increase in the amount of the purification substance discharged
from the bypass passage due to the increase in the exhaust gas
passing through the bypass passage, wherein
[0026] the regeneration exhaust flow rate control is executed when
the purification substance amount determination means determines
that the decrease in the amount of the purification substance
discharged from the exhaust purification device due to the increase
in the rate of purification by the exhaust purification device is
larger than the increase in the amount of the purification
substance discharged from the bypass passage due to the increase in
the exhaust gas passing through the bypass passage.
[0027] In other words, an exhaust purification system for an
internal combustion engine according to the present invention is
characterized by including:
[0028] an exhaust purification device provided in an exhaust
passage of the internal combustion engine, for purifying exhaust
gas passing through the exhaust passage;
[0029] a bypass passage branching from the exhaust passage on an
upstream side of the exhaust purification device and merging into
the exhaust passage on a downstream side of the exhaust
purification device, for causing the exhaust gas passing through
the exhaust passage to bypass the exhaust purification device;
[0030] reducer supply means for supplying a reducer to the exhaust
gas passing through the exhaust passage on the upstream side of a
bifurcating portion of the exhaust passage to the bypass
passage;
[0031] regeneration means for performing a regeneration treatment
for regenerating purification performance of the exhaust
purification device, when an amount of a purification substance
accumulated in the exhaust purification device becomes equal to or
larger than a predetermined value, the regeneration treatment being
a treatment for regenerating the purification performance of the
exhaust purification device by supplying the reducer from the
reducer supply means to the exhaust gas to introduce the reducer
into the exhaust purification device;
[0032] regeneration exhaust flow rate control means for executing
regeneration exhaust flow rate control when the regeneration means
performs the regeneration treatment, the regeneration exhaust flow
rate control being a control operation in which, of the exhaust gas
passing through the exhaust passage, an amount of exhaust gas
passing through the bypass passage is increased and an amount of
exhaust gas passing through the exhaust purification device is
reduced; and
[0033] purification substance amount determination means for
determining the magnitude relation between the following two values
which are obtained when the regeneration exhaust flow rate control
is executed during execution of the regeneration treatment: a
decrease in an amount of the purification substance discharged from
the exhaust purification device due to an increase in a rate of
purification by the exhaust purification device with and an
increase in an amount of the purification substance discharged from
the bypass passage due to an increase in the exhaust gas passing
through the bypass passage, wherein
[0034] the regeneration exhaust flow rate control is executed when
the purification substance amount determination means determines
that the decrease in the amount of the purification substance
discharged from the exhaust purification device due to the increase
in the rate of purification by the exhaust purification device is
larger than the increase in the amount of the purification
substance discharged from the bypass passage due to the increase in
the exhaust gas passing through the bypass passage.
[0035] According to this structure, in the case where the
regeneration exhaust flow rate control is executed, it is possible
to execute the regeneration exhaust flow rate control only when the
total amount of the purification substance discharged to the
downstream side of the merging portion of the exhaust passage and
the bypass passage (the difference between the decrease in the
amount of the purification substance discharged from the exhaust
purification device due to the increase in the rate of purification
by the exhaust purification device and the increase in the amount
of the purification substance discharged from the bypass passage
due to the increase in the exhaust gas passing through the bypass
passage) becomes smaller, compared to the case where the
regeneration exhaust flow rate control is not executed.
Accordingly, exhaust emission can be more reliably improved by the
regeneration exhaust flow rate control.
[0036] According to the present invention, the purification
substance amount determining means may determine the magnitude
relation between the following two values which are obtained in a
period from start of supplying the reducer in the regeneration
treatment to start of supplying the reducer in a next regeneration
treatment: the decrease in the amount of the discharged
purification substance due to the increase in the rate of
purification by the exhaust purification device; and the increase
in the amount of the discharged purification substance due to the
increase in the exhaust gas passing through the bypass passage.
[0037] In the case where the regeneration exhaust flow rate control
is executed in the regeneration treatment, the regeneration exhaust
flow rate control is executed in a period in which the reducer is
supplied from the reducer supply means. In this case, the increase
in the discharged purification substance due to the increase in the
exhaust gas passing through the bypass passage occurs in a period
in which the regeneration exhaust flow rate control is executed. On
the other hand, the purification performance of the exhaust
purification device is regenerated in the period in which the
regeneration exhaust flow rate control is executed. Therefore, the
amount of the discharged purification substance is reduced
thereafter due to improvement in the rate of purification in a
period until the purification substance is accumulated in the
exhaust purification device. A similar change is repeated from the
supply of the reducer in the next regeneration treatment as a
starting point.
[0038] Accordingly, it is appropriate that whether the regeneration
exhaust flow rate control is executed or not in each regeneration
treatment is determined based on the magnitude relation between the
following two values in a period from the start of supplying the
reducer in the regeneration treatment to the start of supplying the
reducer in the next regeneration treatment: the decrease in the
amount of the discharged purification substance due to the increase
in the rate of purification by the exhaust purification device; and
the increase in the amount of the discharged purification substance
due to the increase in the exhaust gas passing through the bypass
passage.
[0039] Therefore, in the present invention, the magnitude relation
is determined between the following two values in the period from
the start of supplying the reducer in the regeneration treatment to
the start of supplying the reducer in the next regeneration
treatment: the decrease in the amount of the discharged
purification substance due to the increase in the rate of
purification by the exhaust purification device; and the increase
in the amount of the discharged purification substance due to the
increase in the exhaust gas passing through the bypass passage.
[0040] According to this structure, it is possible to determine
whether the regeneration exhaust flow rate control is executed or
not based on the total amount of the purification substance
discharged in the whole period of each regeneration treatment.
Therefore, exhaust emission can be more reliably improved by the
regeneration exhaust flow rate control.
[0041] In the present invention, the exhaust purification device
may be a storage-reduction type NOx catalyst,
[0042] the exhaust purification system may further include an
oxidation catalyst that has an oxidation ability and is provided in
the exhaust passage on a downstream side of a merging portion of
the exhaust passage and the bypass passage, and
[0043] whether the regeneration exhaust flow rate control is
executed or not may be determined based on the following three
values which are obtained when the regeneration exhaust flow rate
control is executed during execution of the regeneration treatment:
a decrease in an amount of NOx discharged from the exhaust
purification device due to an increase in the rate of purification
by the exhaust purification device; an increase in an amount of NOx
discharged from the bypass passage due to an increase in the
exhaust gas passing through the bypass passage; and an increase in
an amount of NOx through oxidation of NH.sub.3 discharged from the
exhaust purification device by the oxidation catalyst.
[0044] Here, a case in which the exhaust purification device of the
internal combustion engine is a storage-reduction type NOx catalyst
is considered. In this case, in the regeneration treatment, NOx
stored (including absorption and adsorption) in the
storage-reduction type NOx catalyst, and NOx which is newly
discharged from the internal combustion engine during the
regeneration treatment are reduced for the most part, but are
partially converted into NH.sub.3 and discharged from the
storage-reduction type NOx. A part of the NH.sub.3 may be oxidized
back to NOx in the oxidation catalyst located downstream. In this
case, NOx thus generated may reduce the overall rate of
purification of NOx in an exhaust system of the internal combustion
engine.
[0045] In view of this, in the present invention, it is possible to
determine whether the regeneration exhaust flow rate control is
executed or not in view of all of the following values which are
obtained when the regeneration exhaust flow rate control is
executed: the decrease in the amount of NOx discharged from the
exhaust purification device due to the increase in the rate of
purification by the exhaust purification device; the increase in
the amount of NOx discharged from the bypass passage due to the
increase in the exhaust gas passing through the bypass passage; and
the increase in the amount of NOx through oxidation of NH.sub.3
discharged from the exhaust purification device by the oxidation
catalyst. More specifically, the regeneration exhaust flow rate
control can be executed only when it is determined that the amount
of NOx discharged to the downstream side of the oxidation catalyst
is reduced compared to the case where the regeneration exhaust flow
rate control is not executed. Accordingly, exhaust emission can be
more reliably improved by the regeneration exhaust flow rate
control.
[0046] Moreover, in the present invention, the exhaust purification
system may further include NOx amount determining means for
determining the magnitude relation between the following two values
which are obtained when the regeneration exhaust flow rate control
is executed during execution of the regeneration treatment: the
decrease in the amount of NOx discharged from the exhaust
purification device due to the increase in the rate of purification
by the exhaust purification device; and a sum of the increase in
the amount of NOx discharged from the bypass passage due to the
increase in the exhaust gas passing through the bypass passage and
the increase in the amount of NOx through oxidation of NH.sub.3
discharged from the exhaust purification device by the oxidation
catalyst, and
[0047] the regeneration exhaust flow rate control may be executed
when the NOx amount determining means determines that the decrease
in the amount of NOx discharged from the exhaust purification
device due to the increase in the rate of purification by the
exhaust purification device is larger than the sum of the increase
in the amount of NOx discharged from the bypass passage due to the
increase in the exhaust gas passing through the bypass passage and
the increase in the amount of NOx through oxidation of NH.sub.3
discharged from the exhaust purification device by the oxidation
catalyst.
[0048] According to this structure, in the case where the
regeneration exhaust flow rate control is executed, it is possible
to execute the regeneration exhaust flow rate control only when the
total amount of NOx discharged to the downstream side of the
oxidation catalyst (the total of the decrease in the amount of NOx
discharged from the exhaust purification device due to the increase
in the rate of purification by the exhaust purification device and
the sum of the increase in the amount of NOx discharged from the
bypass passage due to the increase in the exhaust gas passing
through the bypass passage and the increase in the amount of NOx
through oxidation of NH.sub.3 discharged from the exhaust
purification device by the oxidation catalyst) becomes smaller,
compared to the case where the regeneration exhaust flow rate
control is not executed. Accordingly, exhaust emission can be more
reliably improved by the regeneration exhaust flow rate
control.
[0049] Moreover, in the present invention, the NOx amount
determination means may determine the magnitude relation between
the following two values which are obtained in a period from start
of supplying the reducer in the regeneration treatment (in this
case, a NOx reduction treatment) to start of supplying the reducer
in a next regeneration treatment: the decrease in the amount of NOx
discharged from the exhaust purification device due to the increase
in the rate of purification by the exhaust purification device; and
the sum of the increase in the amount of NOx discharged from the
bypass passage due to the increase in the exhaust gas passing
through the bypass passage and the increase in the amount of NOx
through oxidation of NH.sub.3 discharged from the exhaust
purification device by the oxidation catalyst.
[0050] As described above, it is herein appropriate that whether
the regeneration exhaust flow rate control is executed or not in
each regeneration treatment is determined based on the magnitude
relation between the following two values in a period from the
start of supplying the reducer in the regeneration treatment to the
start of supplying the reducer in the next regeneration treatment:
the decrease in the amount of discharged NOx due to the increase in
the rate of purification by the exhaust purification device; and
the sum of the increase in the amount of NOx discharged from the
bypass passage due to the increase in the exhaust gas passing
through the bypass passage and the increase in the amount of NOx
through oxidation of NH.sub.3 discharged from the exhaust
purification device by the oxidation catalyst.
[0051] Therefore, in the present invention, the magnitude
relationship is determined between the following two values in the
period from the start of supplying the reducer in the regeneration
treatment to the start of supplying the reducer in the next
regeneration treatment: the decrease in the amount of NOx
discharged from the exhaust purification device due to the increase
in the rate of purification by the exhaust purification device and
the sum of the increase in the amount of NOx discharged from the
bypass passage due to the increase in the exhaust gas passing
through the bypass passage and the increase in the amount of NOx
through oxidation of NH.sub.3 discharged from the exhaust
purification device by the oxidation catalyst.
[0052] According to this structure as well, it is possible to
determine whether the regeneration exhaust flow rate control is
executed or not based on the total amount of NOx discharged in the
whole period of each regeneration treatment. Therefore, exhaust
emission can be more reliably improved by the regeneration exhaust
flow rate control.
[0053] Note that means for solving the problems in the present
invention may be used in combination as far as possible.
BRIEF DESCRIPTION OF THE DRAWINGS
[0054] FIG. 1 is a diagram showing a schematic structure of an
internal combustion engine according to a first embodiment of the
present invention, and an exhaust system and a control system
thereof.
[0055] FIG. 2 is an example of a timing chart showing the timing of
adding fuel and the timing of opening and closing a switch valve
according to an embodiment of the present invention.
[0056] FIG. 3 is a flowchart showing an addition-synchronous bypass
control execution determination routine according to the first
embodiment of the present invention.
[0057] FIG. 4 is a diagram showing a schematic structure of an
internal combustion engine according to a second embodiment of the
present invention, and an exhaust system and a control system
thereof.
[0058] FIG. 5 is a flowchart showing an addition-synchronous bypass
control execution determination routine 2 according to the second
embodiment of the present invention.
BEST MODES FOR CARRYING OUT THE INVENTION
[0059] Hereinafter, best modes for carrying out the present
invention will be described in detail by using examples, with
reference to the accompanying drawings.
First Embodiment
[0060] FIG. 1 is a diagram showing a schematic structure of an
internal combustion engine according to the present embodiment, and
an exhaust system and a control system thereof. An internal
combustion engine 1 shown in FIG. 1 is a diesel engine. Note that
the interior of the internal combustion engine 1 and an intake
system thereof are omitted in FIG. 1.
[0061] In FIG. 1, an exhaust pipe 5 is connected to the internal
combustion engine 1 as an exhaust passage through which exhaust gas
flows after being discharged from the internal combustion engine 1.
The exhaust pipe 5 is connected downstream to a muffler (not
shown). A storage-reduction type NOx catalyst (hereinafter,
abbreviated as "NSR") 10 for purifying NOx contained in the exhaust
gas is provided in the exhaust pipe 5. A filter 11 for trapping
particulate matter contained in the exhaust gas is provided on the
downstream side of the NSR 10 in the exhaust pipe 5. Note that an
oxidation catalyst CCo having an oxidation ability may be added to
the NSR 10.
[0062] A bypass pipe 6 serving as a bypass passage branches off
from the exhaust pipe 5 in a bifurcating portion 5a upstream of the
NSR 10. A switch valve 15 for switching to allow or block the flow
of the exhaust gas from the internal combustion engine 1 into the
bypass pipe 6 is provided in the bypass pipe 6. The bypass pipe 6
merges into the exhaust pipe 5 at a position between the NSR 10 and
the filter 11.
[0063] By operating the switch valve 15 to cause the exhaust gas
from the internal combustion engine 1 to pass directly through the
exhaust pipe 5, the exhaust gas is enabled to pass through both the
NSR 10 and the filter 11. Similarly, by allowing the exhaust gas
from the internal combustion engine 1 to pass through the bypass
pipe 6, the exhaust gas is enabled to bypass the NSR 10 and to pass
only through the filter 11.
[0064] Note that a fuel addition valve 14 for adding fuel serving
as a reducer to the exhaust gas during a NOx reduction treatment or
a SOx poisoning regeneration treatment of the NSR 10, and during a
PM regeneration treatment of the filter 11 is provided on the
upstream side of the NSR 10 in the exhaust pipe 5. The NSR 10
described above functions as an exhaust purification device in the
present embodiment. The fuel addition valve 14 functions as reducer
supply means.
[0065] An electronic control unit (ECU) 20 for controlling the
internal combustion engine 1 and the exhaust system thereof is also
provided for the internal combustion engine 1 and the exhaust
system which are structured as described above. The ECU 20 is a
unit for not only controlling the operational state of the internal
combustion engine 1 and the like according to the operating
conditions of the internal combustion engine 1 and requests from a
driver, but also performing control relating to an exhaust
purification system including the NSR 10 and the filter 11 for the
internal combustion engine 1.
[0066] Sensors relating to control of the operational state of the
internal combustion engine 1, such as an airflow meter, a crank
position sensor, and an accelerator position sensor, which are not
shown in the drawing, are connected to the ECU 20 via electric
wirings, and output signals from these sensors are applied to the
ECU 20. Meanwhile, a fuel injection valve (not shown) and the like
in the internal combustion engine 1 are connected to the ECU 20 via
electric wiring, while the switch valve 15, the fuel addition valve
14, and the like of the present embodiment are connected to the ECU
20 via electric wiring so that these valves and the like are
controlled by the ECU 20.
[0067] The ECU 20 includes a CPU, a ROM, a RAM, and the like.
Programs for executing various controls relating to the internal
combustion engine 1 and maps storing data are stored in the ROM. An
addition-synchronous bypass control execution determination routine
according to the present embodiment, which will be described below,
is one of the programs stored in the ROM in the ECU 20.
[0068] Hereinafter, a case in which a NOx reduction treatment of
the NSR 10 is performed in the above structure will be considered.
In this case, fuel serving as a reducer is added from the fuel
addition valve 14. The switch valve 15 is opened during a period in
which the fuel is added, so that a part of the exhaust gas passes
through the bypass pipe 6. This reduces the amount of exhaust gas
flowing into the NSR 10 (reduces the space velocity (SV)), whereby
the fuel added from the fuel addition valve 15 can be prevented
from being consumed for oxidation before reaching the NSR 10.
Moreover, this can assure enough time for the fuel which has
reached the NSR 10 to complete a reduction reaction in the NSR 10,
whereby the NOx reduction efficiency can be improved (hereinafter,
this control will be referred to as "addition-synchronous bypass
control"). FIG. 2 is a timing chart relating to fuel addition from
the fuel addition valve 14 and switching of the switch valve 15 in
the NOx reduction treatment. Note that the addition-synchronous
bypass control functions as regeneration exhaust flow rate control,
and the ECU 20 for executing the addition-synchronous bypass
control and the switch valve 15 function as regeneration exhaust
flow rate control means. The ECU 20 also functions as regeneration
means in the present embodiment.
[0069] When the addition-synchronous bypass control is executed,
however, the exhaust gas flows through the bypass pipe 6 to the
downstream side without flowing through the NSR 10 during a period
in which the switch valve 15 is open. Therefore, the amount of NOx
which is discharged without being purified increases. Depending on
the conditions such as an interval of the NOx reduction treatment,
an increase in the amount of discharged NOx from the bypass pipe 6
becomes larger than a decrease in the amount of discharged NOx due
to improvement in the rate of purification by the NSR 10, whereby
the total emission may degrade.
[0070] In other words, for example, although the valve open time of
the switch valve 15 by the addition-synchronous bypass control is
fixed, the interval of the NOx reduction treatment may
significantly vary depending on the amount of NOx stored in the NSR
10 and the amount of NOx discharged from the internal combustion
engine 1. In this case, the magnitude relation between a decrease
in the amount of discharged NOx due to improvement in the rate of
purification by the NSR 10 and an increase in the amount of
discharged NOx from the bypass pipe 6 may change.
[0071] The above amounts of discharged NOx may be compared in
advance by adjustment in a steady state. In this method, however,
it is sometimes difficult to adapt to a change in interval in an
actual transient state.
[0072] In view of the above, in the present embodiment, a decrease
in the amount of discharged NOx due to improvement in the rate of
purification by the NSR 10 and an increase in the amount of
discharged NOx from the bypass pipe 6 are compared with each other
regarding an interval of the NOx reduction treatment. The
addition-synchronous bypass control is executed only when it is
determined that the decrease in the amount of discharged NOx due to
improvement in the rate of purification by the NSR 10 is larger
than the increase in the amount of discharged NOx from the bypass
pipe 6.
[0073] FIG. 3 shows a flowchart of the addition-synchronous bypass
control execution determination routine of the present embodiment.
This routine is a program stored in the ROM in the ECU 20, and is a
routine which is executed every predetermined period by the ECU 20
during execution of the NOx reduction treatment.
[0074] When this routine is executed, in S101, the amount of NOx
(g/s) discharged from the internal combustion engine 1 per unit
time is derived from a current engine speed and a current fuel
injection amount. More specifically, the amount of NOx (g/s)
discharged from the internal combustion engine 1 per unit time is
derived by reading the amount of NOx discharged per unit time,
which corresponds to the current engine speed and the current fuel
injection amount, from a map storing the relation between the
engine speed and the fuel injection amount and the amount of NOx
discharged from the internal combustion engine 1 per unit time. The
routine proceeds to S102 after the process of S101 is
completed.
[0075] In S102, the flow division ratio of the exhaust gas into the
bypass pipe 6, which is controlled by the switch valve 15, is
derived based on a current intake air amount. More specifically,
the flow division ratio of the exhaust gas into the bypass pipe 6
is derived by reading the value of the flow division ratio
corresponding to the current intake air amount from a map storing
the relation between the intake air amount and a control target
value of the flow division ratio in the addition-synchronous bypass
control. The routine proceeds to S103 after the process of S102 is
completed.
[0076] In S103, an increase in the amount of NOx discharged through
the bypass pipe 6 while the switch valve 15 is open is calculated.
More specifically, the increase in the amount of NOx is calculated
by multiplying the amount of NOx (g/s) discharged from the internal
combustion engine 1 per unit time which has been derived in S101,
by the valve open time (s) of the switch valve 15, and the flow
division ratio derived in S102. The routine proceeds to S104 after
the process of S103 is completed.
[0077] In S104, an increase in the rate of purification of NOx by
the addition-synchronous bypass control (decreased SV) is derived
from a current bed temperature of the NSR 10 and the current intake
air amount. More specifically, the increase in the rate of
purification of NOx is derived by reading the value of the increase
in the rate of purification of NOx, which corresponds to the
current bed temperature of the NSR 10 and the current intake air
amount, from a map storing the relation between the bed temperature
of the NSR 10 and the intake air amount and the increase in the
rate of purification of NOx. The routine proceeds to S105 after the
process of S104 is completed.
[0078] In S105, a decrease in the amount of NOx discharged from the
NSR 10 by the addition-synchronous bypass control is calculated.
More specifically, the decrease in NOx discharged from the NSR 10
is calculated by multiplying a NOx reduction interval (s), by the
amount of NOx (g/s) discharged from the internal combustion engine
1 per unit time and the increase in the rate of purification of NOx
due to the decreased SV. The routine proceeds to S106 after the
process of S105 is completed.
[0079] In S106, the amount of NOx discharged through the bypass
pipe 6 while the switch valve 15 is open, which has been calculated
in S103, is compared with the decrease in the amount of NOx
discharged from the NSR 10 by the addition-synchronous bypass
control, which has been calculated in S105. If it is determined
that the decrease in the amount of discharged NOx by the
addition-synchronous bypass control is larger than the amount of
NOx discharged through the bypass pipe 6 while the switch valve 15
is open, the routine proceeds to S107. On the other hand, the
routine is terminated once if it is determined that the amount of
NOx discharged through the bypass pipe 6 while the switch valve 15
is open is equal to or larger than the decrease in the amount of
discharged NOx by the addition-synchronous bypass control.
[0080] In S107, the addition-synchronous bypass control is
executed. The routine is terminated once after the process of S107
is completed.
[0081] As described above, in this routine, the amount of NOx
discharged through the bypass pipe 6 while the switch valve 15 is
open (which can also be referred to as the "increase in the amount
of discharged NOx") is compared with the decrease in the amount of
NOx discharged from the NSR 10 by the addition-synchronous bypass
control, which has been calculated in S105. The
addition-synchronous bypass control is executed only when the
decrease in the amount of NOx discharged from the NSR 10 by the
addition-synchronous bypass control is larger. Accordingly, the
addition-synchronous bypass control can be executed only when it is
determined that the total emission is improved by performing the
addition-synchronous bypass control. The effect of improving
emission can therefore be reliably obtained.
[0082] Note that, in the above description, the ECU 20 for
performing the processes of S101 through S106 functions as
purification substance amount determining means in the present
embodiment.
[0083] The above embodiment was described with respect to the case
where the exhaust purification device is the NSR 10. However, the
exhaust purification device may be a DPNR in which a
storage-reduction type NOx catalyst is carried by a filter, or a
selective-reduction type NOx catalyst. In the case where the
exhaust purification device is the DPNR, the present invention may
be applied to PM regeneration of the DPNR. The present invention
may also be applicable to an exhaust purification system using a
liquid other than fuel, for example, a urea solution, as a reducer.
A method for supplying fuel to the exhaust purification device is
not limited to addition of the fuel from the fuel addition valve
14, but may be implemented by, for example, auxiliary injection in
the internal combustion engine 1.
[0084] Moreover, in the above embodiment, the addition-synchronous
bypass control is executed by switching the switch valve 15 between
an open state and a closed state. However, the degree of opening of
the switch valve 15 may be continuously varied to appropriately
adjust the amount of exhaust gas passing through the bypass pipe 6
and the amount of exhaust gas passing through the NSR 10, of the
exhaust gas passing through the exhaust pipe 5. Instead of using
the switch valve 15, the addition-synchronous bypass control may be
executed by using a three-way valve provided in the bifurcating
portion 5a.
[0085] In the addition-synchronous bypass control execution
determination routine described above, the amount of NOx discharged
through the bypass pipe 6 while the switch valve 15 is open and the
decrease in the amount of discharged NOx due to improvement in the
rate of purification by the NSR 10 are compared with each other for
the regeneration treatment (NOx reduction) interval. However, the
period for comparison is not limited to the NOx reduction interval.
For example, after the addition-synchronous bypass control is
completed, the rate of purification by the NSR gradually decreases
as NOx is stored in the NSR 10. Therefore, comparison may be
performed for a period in which significant decrease in the amount
of discharged NOx due to improvement in the rate of purification by
the NSR 10 is actually expected. Moreover, regarding a plurality of
NOx reduction intervals, a mean value of the amounts of NOx
discharged through the bypass pipe 6 while the switch valve 15 is
open may be compared with a mean value of the decreases in the
amount of discharged NOx due to improvement in the rate of
purification by the NSR 10.
[0086] In S101 to S105 of the addition-synchronous bypass control
execution determination routine described above, the method for
calculating the amount of NOx discharged through the bypass pipe 6
while the switch valve 15 is open and the decrease in the amount of
NOx discharged from the NSR 10 by the addition-synchronous bypass
control is not specifically limited to the method described in the
present embodiment. The above calculation method may be modified as
appropriate if there is any method capable of calculating these
values more accurately.
[0087] In the above embodiment, in S106 of the addition-synchronous
bypass control execution determination routine, the amount of NOx
discharged through the bypass pipe 6 while the switch valve 15 is
open, which has been calculated in S103, is compared with the
decrease in the amount of NOx discharged from the NSR 10 by the
addition-synchronous bypass control, which has been calculated in
S105. The addition-synchronous bypass control is executed only when
it is determined that the decrease in the amount of NOx discharged
from the NSR 10 by the addition-synchronous bypass control is
larger than the amount of NOx discharged through the bypass pipe 6
while the switch valve 15 is open.
[0088] However, the method for determining whether the
addition-synchronous bypass control is executed or not based on the
amount of NOx discharged through the bypass pipe 6 while the switch
valve 15 is open and the decrease in the amount of NOx discharged
from the NSR 10 by the addition-synchronous bypass control is not
limited to this. For example, in the case where there is a
difference in calculation accuracy between the amount of NOx
discharged through the bypass pipe 6 while the switch valve 15 is
open, which has been calculated in S103, and the decrease in the
amount of NOx discharged from the NSR 10 by the
addition-synchronous bypass control, which has been calculated in
S105, the above method for determining whether the
addition-synchronous bypass control is executed or not may be
modified as appropriate by, for example, multiplying one of the
above two values by a weighting coefficient.
[0089] In other words, the addition-synchronous bypass control may
be executed when it is determined that the total emission is
substantially improved in view of the following two factors: the
amount of NOx discharged through the bypass pipe 6 while the switch
valve 15 is open; and the decrease in the amount of NOx discharged
from the NSR 10 by the addition-synchronous bypass control.
Second Embodiment
[0090] Hereinafter, a second embodiment of the present invention
will be described. The second embodiment will be described with
respect to an example in which the NSR and an oxidation catalyst
are provided in the exhaust system of the internal combustion
engine. In this example, in addition to a decrease in the amount of
discharged NOx due to improvement in the rate of purification by
the NSR 10 and an increase in the amount of NOx discharged from the
bypass pipe 6, an increase in the amount of NOx through oxidation
of NH.sub.3 discharged from the NSR in a NOx reduction treatment by
the oxidation catalyst, is considered to determine whether
addition-synchronous bypass control is executed or not.
[0091] FIG. 4 shows a schematic structure of an internal combustion
engine according to the present embodiment, and an exhaust system
and a control system thereof. In the present embodiment, a fuel
addition valve 24 is provided in an exhaust pipe 5 on the
downstream side of a bifurcating portion 5a to a bypass pipe 6 in
the exhaust pipe 5. An oxidation catalyst 21 is also provided on
the downstream side of a merging portion at which the bypass pipe 6
merges with the exhaust pipe 5, and that is located on the
downstream side of an NSR 10 in the exhaust pipe 5. The structure
is otherwise the same as that shown in FIG. 1. Therefore, in the
following description, the same components as those shown in FIG. 1
will be denoted by the same reference numerals and characters, and
description thereof will be omitted. Moreover, in the present
embodiment as well, a NOx reduction treatment is performed
according to the timing chart of FIG. 2.
[0092] A case in which addition-synchronous bypass control is
executed in this structure to carry out the NOx reduction treatment
of the NSR 10 is considered. In this case, NOx stored in the NSR 10
and NOx discharged from the internal combustion engine 1 are
reduced for the most part in the NSR 10 by fuel addition from the
fuel addition valve 24, but are partially discharged from the NSR
10 as NH.sub.3.
[0093] NH.sub.3 discharged from the NSR 10 may be oxidized back to
NOx in the oxidation catalyst 21. In this case, NOx thus generated
may be discharged from the oxidation catalyst 21, which may reduce
the rate of purification of NOx as a result.
[0094] In view of this, in the present embodiment, a decrease in
the amount of discharged NOx due to improvement in the rate of
purification by the NSR 10 and the sum of an increase in the amount
of NOx discharged from the bypass pipe 6 and an increase in the
amount of NOx through oxidation of NH.sub.3 discharged from the NSR
10 by the oxidation catalyst 21 are compared with each other for an
interval of the NOx reduction treatment. The addition-synchronous
bypass control is executed only when it is determined that the
decrease in the amount of discharged NOx due to improvement in the
rate of purification by the NSR 10 is larger than the sum of the
increase in the amount of NOx discharged from the bypass pipe 6 and
the increase in the amount of NOx through oxidation of NH.sub.3
discharged from the NSR 10 by the oxidation catalyst 21.
[0095] FIG. 5 is a flowchart showing an addition-synchronous bypass
control execution determination routine 2 of the present
embodiment. This routine is a program stored in the ROM in the ECU
20, and is a routine which is executed every predetermined period
by the ECU 20 while the NOx reduction treatment is performed. Since
the processes of S101 to S105 in this routine are the same as those
of the addition-synchronous bypass control execution determination
routine shown in FIG. 3, description thereof will be omitted.
[0096] In S201 of this routine, the amount of NH.sub.3 discharged
from the NSR 10 in a NOx reduction (regeneration treatment)
interval shown in FIG. 2 is derived from the sum of the amount of
NOx discharged from the internal combustion engine 1 in the NOx
reduction interval and the amount of NOx stored in the NSR 10, and
an estimated value of an air-fuel ratio in the addition-synchronous
bypass control.
[0097] More specifically, the total amount of NOx is derived from a
product of the amount of NOx (g/s) discharged from the internal
combustion engine 1 per unit time which is derived in S101 and the
time of the NOx reduction interval, and the amount of NOx stored in
the NSR 10 which is estimated from the history of the operational
state of the internal combustion engine 1. The amount of NH.sub.3
discharged from the NSR 10 in the NOx reduction interval is derived
by reading the amount of NH.sub.3 corresponding to the current
total amount of NOx and the estimated air-fuel ratio, from a map
storing the relation among the total amount of NOx, the air-fuel
ratio estimated based on the amount of fuel added from the fuel
addition valve 24 to the exhaust gas and the intake air amount, and
the amount of NH.sub.3 discharged from the NSR 10 in the NOx
reduction interval. Note that, at this time, a part of the amount
of NOx discharged from the internal combustion engine 1 in the NOx
reduction (regeneration treatment) interval passes through the
bypass pipe 6 and is not introduced into the NSR 10. This value is
ignored as an error in the present embodiment. The routine proceeds
to S202 after the process of S201 is completed.
[0098] In S202, the conversion ratio of NH.sub.3 discharged from
the NSR 10 into NOx in the oxidation catalyst 21 is derived from
the bed temperature of the oxidation catalyst 21. More
specifically, the conversion ratio is derived by reading the value
of the conversion ratio corresponding to a current bed temperature
of the oxidation catalyst 21 from a map storing the relation
between the bed temperature of the oxidation catalyst 21 and the
conversion ratio. Note that the bed temperature of the oxidation
catalyst 21 may be obtained by detecting the temperature of the
exhaust gas discharged from the oxidation catalyst by an exhaust
temperature sensor (not-shown). The bed temperature of the
oxidation catalyst 21 may alternatively be estimated from the
operational state of the internal combustion engine 1. The routine
proceeds to S203 after the process of S202 is completed.
[0099] In S203, the amount of NOx generated through oxidation of
NH.sub.3 discharged from the NSR 10 by the oxidation catalyst 21 is
calculated. More specifically, the amount of NOx generated through
oxidation of NH.sub.3 discharged from the NSR 10 in the NOx
reduction interval by the oxidation catalyst 21 is calculated by
multiplying the amount of NH.sub.3 discharged from the NSR 10 in
the NOx reduction interval, which has been derived in S201, by the
conversion ratio into the NOx derived in S202. The routine proceeds
to S204 after the process of S203 is completed.
[0100] In S204, the sum of the amount of NOx discharged through the
bypass pipe 6 while the switch valve 15 is open, which has been
calculated in S103, and the amount of NOx generated through
oxidation of NH.sub.3 discharged from the NSR 10 in the NOx
reduction interval by the oxidation catalyst 21, which has been
calculated in S203, is compared with the decrease in the amount of
NOx discharged from the NSR 10 by the addition-synchronous bypass
control, which has been calculated in S105. The routine proceeds to
S107 if it is determined that the decrease in the amount of NOx
discharged from the NSR 10 by the addition-synchronous bypass
control is larger than the sum of the amount of NOx discharged
through the bypass pipe 6 while the switch valve 15 is open and the
amount of NOx generated through oxidation of NH.sub.3 discharged
from the NSR 10 in the NOx reduction interval by the oxidation
catalyst 21. On the other hand, the routine is terminated once if
it is determined that the total amount of NOx is equal to or larger
than the decrease in the amount of NOx discharged from the NSR 10
by the addition-synchronous bypass control.
[0101] As described above, in this routine, the sum of the amount
of NOx discharged through the bypass pipe 6 while the switch valve
15 is open and the amount of NOx generated through oxidation of
NH.sub.3 discharged from the NSR 10 in the NOx reduction interval
by the oxidation catalyst 21 which has been calculated in S203 is
compared with the decrease in the amount of NOx discharged from the
NSR 10 by the addition-synchronous bypass control. The
addition-synchronous bypass control is executed only when the
decrease in the amount of NOx discharged from the NSR 10 by the
addition-synchronous bypass control is larger than the total amount
of NOx. Accordingly, the addition-synchronous bypass control can be
executed only when it is determined that the total emission is
improved by executing the addition-synchronous bypass control.
Therefore, the effect of improving emission can be more reliably
obtained.
[0102] Note that, in the present embodiment, the ECU 20 for
performing the processes of S101 through S204 functions as NOx
amount determining means in the present embodiment.
[0103] Moreover, in the addition-synchronous bypass control
execution determination routine 2 described above, the sum of the
amount of NOx discharged through the bypass pipe 6 while the switch
valve 15 is open and the amount of NOx generated through oxidation
of NH.sub.3 discharged from the NSR 10 in the NOx reduction
interval by the oxidation catalyst 21 is compared with the decrease
in the amount of discharged NOx due to improvement in the rate of
purification by the NSR 10 for the NOx reduction interval. However,
the period for comparison is not limited to the NOx reduction
interval. For example, regarding a plurality of NOx reduction
intervals, a mean value of the sums of the amount of NOx discharged
through the bypass pipe 6 while the switch valve 15 is open and the
amount of NOx generated through oxidation of NH.sub.3 discharged
from the NSR 10 in the NOx reduction interval by the oxidation
catalyst 21 may be compared with a mean value of the decreases in
the amount of discharged NOx due to improvement in the rate of
purification by the NSR 10.
[0104] In S201 to S203 of the addition-synchronous bypass control
execution determination routine 2 described above, the method for
calculating the amount of NOx generated through oxidation of
NH.sub.3 discharged from the NSR 10 in the NOx reduction interval
by the oxidation catalyst 21 is not specifically limited to the
method described in the present embodiment. The above calculation
method may be modified as appropriate if there is any method
capable of calculating the value more accurately.
[0105] In S204 of the addition-synchronous bypass control execution
determination routine 2, the sum of the amount of discharged NOx
calculated in S103 and the amount of generated NOx calculated in
S203 is compared with the decrease in the amount of discharged NOx
calculated in S105. The addition-synchronous bypass control is
executed only when it is determined that the decrease in the amount
of discharged NOx calculated in S105 is larger than the sum of the
amount of discharged NOx calculated in S103 and the amount of
generated NOx calculated in S203.
[0106] However, the method for determining whether the
addition-synchronous bypass control is executed or not based on the
amount of NOx discharged through the bypass pipe 6 while the switch
valve 15 is open, the decrease in the amount of NOx discharged from
the NSR 10 by the addition-synchronous bypass control, and the
amount of NOx generated through oxidation of NH.sub.3 discharged
from the NSR 10 by the oxidation catalyst 21 is not limited to
this. For example, in the case where there is a difference in
calculation accuracy among the amount of discharged NOx calculated
in S103, the decrease in the amount of discharged NOx calculated in
S105, and the amount of generated NOx calculated in S203, the above
method for determining whether the addition-synchronous bypass
control is executed or not may be modified as appropriate by, for
example, multiplying any of the above three values by a weighting
coefficient.
[0107] In other words, the addition-synchronous bypass control may
be executed when it is determined that the total emission is
substantially improved in view of the following three factors: the
amount of NOx discharged through the bypass pipe 6 while the switch
valve 15 is open; the amount of NOx generated through oxidation of
NH.sub.3 discharged from the NSR 10 by the oxidation catalyst 21;
and the decrease in the amount of NOx discharged from the NSR 10 by
the addition-synchronous bypass control.
INDUSTRIAL APPLICABILITY
[0108] According to the present invention, in a treatment of
regenerating the purification performance of an exhaust
purification device, a reducer is supplied to the exhaust
purification device and a part of the exhaust gas is caused to
bypass the exhaust purification device, whereby exhaust emission
can be more reliably improved.
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