U.S. patent application number 15/549137 was filed with the patent office on 2018-01-25 for exhaust gas purification system for internal combustion engine, internal combustion engine, and exhaust gas purification method for internal combustion engine.
The applicant listed for this patent is ISUZU MOTORS LIMITED. Invention is credited to Daiji NAGAOKA, Teruo NAKADA, Takayuki SAKAMOTO.
Application Number | 20180023435 15/549137 |
Document ID | / |
Family ID | 56564083 |
Filed Date | 2018-01-25 |
United States Patent
Application |
20180023435 |
Kind Code |
A1 |
NAGAOKA; Daiji ; et
al. |
January 25, 2018 |
EXHAUST GAS PURIFICATION SYSTEM FOR INTERNAL COMBUSTION ENGINE,
INTERNAL COMBUSTION ENGINE, AND EXHAUST GAS PURIFICATION METHOD FOR
INTERNAL COMBUSTION ENGINE
Abstract
An exhaust gas purification system for an internal combustion
engine includes an oxidation catalyst device on an upstream side in
an exhaust passage of an internal combustion engine and a lean NOx
trap catalyst device on a downstream side, a controller which
controls the exhaust gas purification system is configured to, when
a temperature-rising control of an exhaust gas in a regeneration
control is performed to recover a purification ability of the
exhaust gas purification system, perform a control that changes a
measurement position of a control temperature which is a control
amount of a feedback control in the temperature-rising control,
according to an excess air ratio or an oxygen concentration of the
exhaust gas passing through the exhaust passage.
Inventors: |
NAGAOKA; Daiji;
(Kamakura-shi, Kanagawa, JP) ; NAKADA; Teruo;
(Yokohama-shi, Kanagawa, JP) ; SAKAMOTO; Takayuki;
(Fujisawa-shi, Kanagawa, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ISUZU MOTORS LIMITED |
Tokyo |
|
JP |
|
|
Family ID: |
56564083 |
Appl. No.: |
15/549137 |
Filed: |
February 1, 2016 |
PCT Filed: |
February 1, 2016 |
PCT NO: |
PCT/JP2016/052905 |
371 Date: |
August 4, 2017 |
Current U.S.
Class: |
60/299 |
Current CPC
Class: |
F01N 2900/1404 20130101;
F02D 41/028 20130101; F01N 2560/06 20130101; F01N 3/0871 20130101;
F02D 2200/0802 20130101; F02D 41/024 20130101; Y02T 10/47 20130101;
F01N 11/00 20130101; F02D 41/029 20130101; F01N 3/0814 20130101;
F01N 9/00 20130101; F02D 41/1441 20130101; F02D 41/0275 20130101;
F01N 3/08 20130101; F01N 2560/025 20130101; F01N 2560/14 20130101;
F01N 2260/04 20130101; F01N 3/0885 20130101; F01N 2900/1402
20130101; F01N 2900/1602 20130101; Y02T 10/40 20130101; F01N 3/0842
20130101; F01N 3/106 20130101; Y02T 10/12 20130101; Y02T 10/24
20130101; F01N 11/002 20130101; F01N 13/009 20140601; F01N 3/103
20130101 |
International
Class: |
F01N 3/08 20060101
F01N003/08; F01N 3/10 20060101 F01N003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 6, 2015 |
JP |
2015-022016 |
Claims
1. An exhaust gas purification system for an internal combustion
engine, which includes an oxidation catalyst device on an upstream
side in an exhaust passage of an internal combustion engine and a
lean NOx trap catalyst device on a downstream side, wherein a
controller which controls the exhaust gas purification system is
configured to, when a temperature-rising control of an exhaust gas
in a regeneration control is performed to recover a purification
ability of the exhaust gas purification system, perform a control
that changes a measurement position of a control temperature which
is a control amount of a feedback control in the temperature-rising
control, according to an excess air ratio or an oxygen
concentration of the exhaust gas passing through the exhaust
passage.
2. The exhaust gas purification system for the internal combustion
engine according to claim 1, the exhaust gas purification system
comprising: a first temperature sensor which measures a first
temperature relating to a temperature of the oxidation catalyst
device; and a second temperature sensor which measures a second
temperature relating to a temperature of the lean NOx trap catalyst
device, wherein the controller is configured to, when the
temperature-rising control of the exhaust gas in the regeneration
control is performed to recover the purification ability of the
exhaust gas purification system, perform a control such that the
control temperature is set as the first temperature when the excess
air ratio or the oxygen concentration of the exhaust gas passing
through the exhaust passage is higher than an upper limit threshold
set in advance, and the control temperature is set as the second
temperature when the excess air ratio or the oxygen concentration
of the exhaust gas passing through the exhaust passage is lower
than a lower limit threshold set in advance.
3. The exhaust gas purification system for the internal combustion
engine according to claim 2, wherein the controller is configured
to, when the temperature-rising control of the exhaust gas in the
regeneration control is performed to recover the purification
ability of the exhaust gas purification system, perform a control
such that a weight coefficient is set to be changed according to
the excess air ratio or the oxygen concentration of the exhaust gas
passing through the exhaust passage, and the control temperature is
set to a weighted average value of the first temperature and the
second temperature obtained using the weight coefficient, when the
excess air ratio or the oxygen concentration of the exhaust gas
passing through the exhaust passage is equal to or less than the
upper limit threshold and equal to or more than the lower limit
threshold.
4. An internal combustion engine comprising: the exhaust gas
purification system for the internal combustion engine according to
claim 1.
5. An exhaust gas purification method for an internal combustion
engine having an exhaust gas purification system for the internal
combustion engine, which includes an oxidation catalyst device on
an upstream side and a lean NOx trap catalyst device on a
downstream side in an exhaust passage of the internal combustion
engine, the method comprising: changing, when a temperature-rising
control of an exhaust gas in a regeneration control is performed to
recover a purification ability of the exhaust gas purification
system, a measurement position of a control temperature which is a
control amount of a feedback control in the temperature-rising
control, according to an excess air ratio or an oxygen
concentration of the exhaust gas passing through the exhaust
passage.
Description
TECHNICAL FIELD
[0001] The present invention relates to an exhaust gas purification
system for an internal combustion engine, an internal combustion
engine, and an exhaust gas purification method for the internal
combustion engine which can avoid a lack of temperature increment
of each catalyst device, an overshooting at the time of increasing
a temperature, heat degradation of a catalyst, erosion of the
catalyst so as to perform the regeneration processing reliably when
each catalyst device including an exhaust gas purification device
of the internal combustion engine performs regeneration
processing.
BACKGROUND ART
[0002] Generally, an exhaust gas purification system is used which
includes an exhaust gas purification device which has catalyst
devices such as an oxidation catalyst, a device (DOC), a
particulate collection device (CSF, SCRF, and the like), a
selective reduction catalyst (SCR) device, and a lean NOx trap
catalyst device (LNT) to purify purification object components such
as hydrocarbon (HC), carbon monoxide (CO), particulate substance
(PM), and nitrogen oxide (NOx) included in exhaust gases of the
internal combustion engine such as a diesel engine.
[0003] In the exhaust gas purification system, a temperature-rising
control of the exhaust gas is regularly performed for the release
and the reduction (NOx regeneration) of NOx stored in the lean NOx
trap catalyst device, the combustion-removal (PM regeneration) of
the particulate substance collected in the particulate collection
device, the removal (sulfur purge) of the sulfur component
accumulated in various catalyst devices such as an oxidation
catalyst device or the lean NOx trap catalyst device, and the
like.
[0004] In the related art, at the time of the temperature-rising
control of the exhaust gas, a detection temperature of an exhaust
gas temperature sensor provided in the vicinity of any one catalyst
device in the catalyst devices, and the estimation temperature of
any one catalyst device obtained by following methods are set as a
control temperature which is a control value of a feedback control
with respect to a target temperature of the exhaust gas in the
temperature-rising control. In the case of some catalyst devices,
normally, in view of responsiveness, the temperature relating to
the catalyst device in which the heat generation amount by the
combustion of unburned hydrocarbon (HC) supplied to increase a
temperature is largest is used as the control temperature
steadily.
[0005] With respect thereto, as described, for example, in Japanese
Unexamined Patent Application Publication No. 2013-174203, an
exhaust gas purification device is proposed which includes a
selective reduction catalyst, a particulate filter which is
arranged on the exhaust gas upstream side from the selective
reduction catalyst and in which an oxidation catalyst layer is
formed to further collect the particulate in the exhaust gas, a
liquid injection nozzle through which the hydrocarbon based liquid
can be injected toward the particulate filter, and a liquid feeding
unit which supplies the liquid to the liquid injection nozzle. In
the exhaust gas purification device which purifies the exhaust gas
of the engine, the temperature of the exhaust gas relating to the
particulate filter is detected using a temperature sensor, and the
liquid feeding unit is controlled on the basis of a detection
output of the temperature sensor.
[0006] However, in a zone-coat and the like in which a plurality of
catalyst devices or the catalyst layers are coated for each part in
separate colors, a place (catalyst device) in which the heat
generation amount is largest in the exhaust passage may be
different according to an operating condition of the engine. For
example, in the case of a system which is configured by the
oxidation catalyst device, the lean NOx trap catalyst device, and
the particulate collection device, when an excess air ratio .lamda.
in the exhaust gas is high, and the concentration of the oxygen is
high, the most hydrocarbon is combusted by the oxidation catalyst
device on the upstream side to generate beat. For this reason, in
the lean NOx trap catalyst device or the particulate collection
device on the downstream side, the temperature of each catalyst
device is increased not by the generation of the combustion heat of
the hydrocarbon, but by the heat transmission of the exhaust gas of
which the temperature is increased by the oxidation catalyst
device.
[0007] On the other hand, in a case where the excess air ratio of
the exhaust gas is low and the concentration of the oxygen is low
such as the sulfur purge (S purge: sulfur purge) control or rich
combustion of NOx regeneration, the combustion of the hydrocarbon
is caused using the oxygen adsorbed in the lean NOx trap catalyst
device or the oxygen generated by NOx reduction, and thus the
generation amount of the combustion heat of the hydrocarbon in the
lean NOx trap catalyst device is larger than that in the oxidation
catalyst device.
[0008] Similarly, in the case of the exhaust gas purification
system configured by a plurality of catalyst devices in
combination, a place in which the generation amount of the fuel
heat is largest is changed according to the operating condition of
the engine. Therefore, as in the related art, when the control
temperature at the time of the temperature-rising control is fixed
to a temperature relating to a specified catalyst device such as
the catalyst device in which the heat generation amount due to the
combustion of the hydrocarbon is largest, an insufficient
temperature increment, an overshooting at the time of increasing a
temperature, erosion, and the like may be occur according to the
operating condition of the engine in another catalyst device other
than the specified catalyst device.
CITATION LIST
Patent Literature
[0009] [Patent Literature i]: Japanese Unexamined Patent
Application Publication No. 2013-174203
SUMMARY OF THE INVENTION
Technical Problem
[0010] The present inventor found, through tests, such a relation
between the change of the catalyst device in which a heat
generation amount is largest in an exhaust passage and an increased
degree of temperature is high and the oxygen concentration of the
exhaust gas when the operating condition of the engine is changed.
For example, a phenomenon is found in which at the time of the PM
regeneration processing or the high load of the engine in which the
excess air ratio in the exhaust gas is high and the oxygen
concentration is high, the heat generation amount of the oxidation
catalyst device is large, and on the other hand, at the time of the
sulfur purge control or the low load of the engine in which the
excess air ratio in the exhaust gas is low, and the oxygen
concentration is low, the heat generation amount of the lean NOx
trap catalyst device is large.
[0011] From this point, it is acknowledged that in order to prevent
that the insufficient temperature increment, the overshooting at
the time of increasing a temperature, the erosion, and the like
occur at the time of the temperature-rising control in the catalyst
device, when the temperature-rising control is performed more
optimally in response to the operating condition of the engine,
preferably, a position of the control temperature in the feedback
control, in other words, the catalyst device relating to the
control temperature to be the target temperature is selected and
changed in consideration of the oxygen concentration of the exhaust
gas. That is, preferably, the catalyst device relating to the
control temperature, in other words, a position where the control
temperature is measured is changed on the basis of the oxygen
concentration of the exhaust gas.
[0012] More specifically, following knowledge is obtained. When the
excess air ratio or the oxygen concentration is high, the control
temperature relating to the temperature of the former oxidation
catalyst device may be adopted, and when the excess air ratio or
the oxygen concentration is low, the control temperature relating
to the temperature of the lean NOx trap catalyst device may be
adopted. In addition, in order to avoid a drastic change of the
control in association with the switch of the control temperature,
preferably, the measurement temperature relating to the temperature
of the former oxidation catalyst device and the measurement
temperature relating to the temperature of the lean NOx trap
catalyst device are weighted (target temperature ratio), the weight
is gradually changed according to the excess air ratio or the
oxygen concentration, the control temperature is calculated on the
basis of a weighted average thereof, and the temperature-rising
control is performed at the feedback control such that the control
temperature becomes the target temperature.
[0013] The present invention has been made in consideration of the
above situation, and an object thereof is to provide an exhaust gas
purification system for an internal combustion engine, an internal
combustion engine, and an exhaust gas purification method for the
internal combustion engine in which during the temperature-rising
control of the exhaust gas for recovering an exhaust gas
purification ability of the catalyst device, a lack of temperature
increment of catalyst devices, an overshooting at the time of
increasing a temperature, heat degradation of a catalyst, and
erosion of the catalyst can be avoided using the exhaust gas
purification system for the internal combustion engine which
includes an oxidation catalyst device on an upstream side and a
lean NOx trap catalyst device on a downstream side in an exhaust
passage of the internal combustion engine, thereby performing a
regeneration processing reliably.
Solution to Problem
[0014] In an exhaust gas purification system for an internal
combustion engine of the present invention to achieve the
above-described object, an exhaust gas purification system for an
internal combustion engine includes an oxidation catalyst device on
an upstream side in an exhaust passage of an internal combustion
engine and a lean NOx trap catalyst device on a downstream side,
and a controller which controls the exhaust gas purification system
is configured to, when a temperature-rising control of an exhaust
gas in a regeneration control is performed to recover a
purification ability of the exhaust gas purification system,
perform a control that changes a measurement position of a control
temperature which is a control amount of a feedback control in the
temperature-rising control, according to an excess air ratio or an
oxygen concentration of the exhaust gas passing through the exhaust
passage.
[0015] With this configuration, at the time of the
temperature-rising control of the exhaust gas for performing
regeneration processing on the catalyst devices included in the
exhaust gas purification device, the measurement position of the
control temperature which is the control amount of the feedback
control in the temperature-rising control, that is, the control
temperature to be a target temperature is changed and set in
consideration of the oxygen concentration of the exhaust gas, and
more specifically, the control temperature is set to the
temperature relating to the catalyst device in which the heat
generation amount is largest at that time in the exhaust gas
purification system and the temperature is increased most, whereby
the temperature-rising control of the exhaust gas can be optimized.
Therefore, the lack of temperature increment of each of the
catalyst devices, the overshooting at the time of increasing a
temperature, the heat degradation of the catalyst, and the erosion
of the catalyst can be avoided so that the regeneration processing
can be performed reliably.
[0016] Further, the above-described exhaust gas purification system
for the internal combustion engine further includes: a first
temperature sensor which measures a first temperature relating to a
temperature of the oxidation catalyst device; and a second
temperature sensor which measures a second temperature relating to
a temperature of the lean NOx trap catalyst device, and the
controller is configured to, when the temperature-rising control of
the exhaust gas in the regeneration control is performed to recover
the purification ability of the exhaust gas purification system,
perform a control such that the control temperature is set as the
first temperature when the excess air ratio or the oxygen
concentration of the exhaust gas passing through the exhaust
passage is higher than an upper limit threshold set in advance, and
the control temperature is set as the second temperature when the
excess air ratio or the oxygen concentration of the exhaust gas
passing through the exhaust passage is lower than a lower limit
threshold set in advance, thereby obtaining following effect.
[0017] That is, when the heat generation amount of the oxidation
catalyst device is larger than that of the lean NOx trap catalyst
device, the excess air ratio and the oxygen concentration of the
exhaust gas is higher than the upper limit threshold set in
advance. Thus, the first temperature relating to the oxidation
catalyst device is set as the control temperature, so that the
temperature-rising control can be performed at the temperature of
the oxidation catalyst device. In addition, when the heat
generation amount of the lean NOx trap catalyst device is larger
than that of the oxidation catalyst device, the excess air ratio
and the oxygen concentration of the exhaust gas is lower than the
lower limit threshold set in advance. Thus, the second temperature
relating to the lean NOx trap catalyst device is set as the control
temperature, so that the temperature-rising control can be
performed at the temperature of the lean NOx trap catalyst device.
Therefore, the temperature-rising control of the exhaust gas can be
optimized with the relatively simple control.
[0018] In the above-described exhaust gas purification system for
the internal combustion engine, when the temperature-rising control
of the exhaust gas in the regeneration control is performed to
recover the purification ability of the exhaust gas purification
system, when the excess air ratio or the oxygen concentration of
the exhaust gas passing through the exhaust passage is equal to or
less than the upper limit threshold and equal to or more than the
lower limit threshold, the controller performs a control to set the
weight coefficient to be changed according to the excess air ratio
or the oxygen concentration of the exhaust gas passing through the
exhaust passage, and to set the control temperature to a weighted
average value of the first temperature and the second temperature
using the weight coefficient. Therefore, the temperature-rising
control can be performed while a drastic change due to the switch
of the control temperature with respect to the change of the excess
air ratio or the oxygen concentration is avoided.
[0019] The internal combustion engine of the present invention to
achieve the above-described object includes the above-described
exhaust gas purification system for the internal combustion engine,
so as to make the same operational effect as that of the
above-described exhaust gas purification system for the internal
combustion engine.
[0020] In an exhaust gas purification method for the internal
combustion engine of the present invention to achieve the
above-described object, an exhaust gas purification method for an
internal combustion engine having an exhaust gas purification
system for the internal combustion engine, which includes an
oxidation catalyst device on an upstream side and a lean NOx trap
catalyst device on a downstream side in an exhaust passage of the
internal combustion engine, the method includes: changing, when a
temperature-rising control of an exhaust gas in a regeneration
control is performed to recover a purification ability of the
exhaust gas purification system, a measurement position of a
control temperature which is a control amount of a feedback control
in the temperature-rising control, according to an excess air ratio
or an oxygen concentration of the exhaust gas passing through the
exhaust passage, thereby it is possible to make the same
operational effect as that of above-described the exhaust gas
purification system for the internal combustion engine.
Advantageous Effects of the Invention
[0021] According to the exhaust gas purification system for the
internal combustion engine, the internal combustion engine, and the
exhaust gas purification method for the internal combustion engine
in the present invention, at time of the temperature-rising control
of the exhaust gas for performing the regeneration processing on
the catalyst devices included in the exhaust gas purification
device, the measurement position of the control temperature which
is the control amount of the feedback control in the
temperature-rising control, that is, the control temperature to be
a target temperature is changed and set in consideration of the
oxygen concentration of the exhaust gas, and more specifically, the
control temperature is set to the temperature relating to the
catalyst device in which the heat generation amount is largest at
that time in the exhaust gas purification system and the
temperature is increased most, thereby optimizing the
temperature-rising control of the exhaust gas. Therefore, it is
possible to avoid a lack of temperature increment of each of the
catalyst devices, an overshooting at the time of increasing a
temperature, heat degradation of the catalyst, and erosion of the
catalyst, and it is possible to perform the regeneration processing
reliably.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a view schematically illustrating a configuration
of an internal combustion engine which includes an exhaust gas
purification system for an internal combustion engine of an
embodiment according to the present invention.
[0023] FIG. 2 is a view schematically illustrating a relation
between a weight coefficient which is a weight ratio of a first
temperature to a second temperature and an excess air ratio of the
exhaust gas.
DESCRIPTION OF EMBODIMENTS
[0024] Hereinafter, an exhaust gas purification system for an
internal combustion engine, an internal combustion engine, and an
exhaust gas purification method for the internal combustion engine
in the embodiment according to the present invention will be
described with reference to the drawings. Incidentally, the
internal combustion engine of the embodiment according to the
present invention includes an exhaust gas purification system for
an internal combustion engine of the embodiment according to the
present invention, so as to make the same operational effect as an
operational effect made by the exhaust gas purification system for
the internal combustion engine (to be described later).
[0025] First, an internal combustion engine (hereinafter, engine)
10 and an exhaust gas purification system 20 of the internal
combustion engine of the embodiment according to the present
invention will be described with reference to FIG. 1. The engine 10
are provided with a fuel injection device 11, an intake valve 12,
and an exhaust valve 13 facing a cylinder 10a, and further with an
intake passage 14 communicating with the intake valve 12, an
exhaust passage 15 communicating with the exhaust valve 13, and an
EGR passage 16.
[0026] The intake passage 14 is provided with an air cleaner 17, a
compressor 18b of a turbocharger (turbo type supercharger) 18, an
intercooler 19a, and an intake throttle valve 19b in order from the
upstream side. Further, the exhaust passage 15 is provided with a
turbine 18a of the turbocharger 18 and an exhaust gas purification
device 21 in order from the upstream side. In addition, the EGR
passage 16 is provided by connecting the intake passage 14 on the
downstream from the compressor 18b with the exhaust passage 15 on
the upstream from the turbine 18a. The EGR passage 16 is provided
with an EGR cooler 16a, an EGR valve 16b in order from the upstream
side.
[0027] As needed, new air A guided from the atmosphere is fed to
the cylinder (cylinder) 10a through the intake valve 12 in
association with the exhaust gas (EGR gas) Ge flowing in the intake
passage 14 from the EGR passage 16. In addition, the exhaust gas G
generated in the cylinder 10a flows out to the exhaust passage 15
through the exhaust valve 13. Some of the exhaust gas G flows to
the EGR passage 16 as the EGR gas Ge. The remaining exhaust gas Ga
(=G-Ge) flows in the exhaust gas purification device 21 through the
turbine 18a, and after being purified, is released as the purified
exhaust gas Gc into the atmosphere through a muffler (not
illustrated) and a tail pipe (not illustrated).
[0028] In the configuration of FIG. 1, the exhaust gas purification
device 21 of the exhaust gas purification system 20 includes
catalyst devices such as an oxidation catalyst (DOC) device 22, a
particulate collection device (CSF) 23, a lean NOx trap catalyst
device (LNT) 24, and a subsequent-stage oxidation catalyst (DOC)
device 25. Incidentally, the catalyst devices may be provided in
the exhaust gas purification device 20 in the reverse order to the
arrangement order of the particulate collection device 23 and the
lean NOx trap catalyst device 24, that is, in order of the
oxidation catalyst device 22, the lean NOx trap catalyst device 24,
the particulate collection device 23, and the subsequent-stage
oxidation catalyst device 25.
[0029] The fuel injection device 26 which injects the unburned fuel
into the exhaust passage 15 is arranged in the exhaust passage 15
on the upstream side of the oxidation catalyst device 22. The
unburned fuel is injected into the exhaust passage 15 at the time
of the temperature-rising control of the exhaust gas such as a NOx
regeneration control on the lean NOx trap catalyst device 24, a
sulfur purge control on the oxidation catalyst device 22 and the
lean NOx trap catalyst device 24, and a PM regeneration control on
the particulate collection device 23. By the injection, the
hydrocarbon which is an unburned fuel is oxidized by the oxidation
catalyst device 22 and the like, and by oxidation heat, the
temperature of the exhaust gas Ga is increased. When the
temperature of the exhaust gas Ga is increased or the temperature
of the hydrocarbon is increased by the combustion in the catalyst
devices 22, 23, and 24, the temperature of the lean NOx trap
catalyst device 24 is increased to a temperature range of the
release and the reduction of the occlusion NOx, the temperature of
the particulate collection device 23 is increased such a
temperature range that can realize the PM combustion, or the
temperatures of the oxidation catalyst device 22 and the lean NOx
trap catalyst device 24 are increased to such a temperature range
that can realize desulfurization. In this manner, the exhaust gas
purification ability of the catalyst devices 22, 23, and 24 are
recovered.
[0030] The first temperature sensor 31 which detects the
temperature TDOC of the exhaust gas Ga flowing in the oxidation
catalyst device 22 is arranged in the exhaust passage 15 on the
upstream side (inlet side) of the oxidation catalyst device 22. In
addition, the second temperature sensor 32 which detects a
temperature TLNT of the exhaust gas Ga flowing in the lean NOx trap
catalyst device 24 is arranged in the exhaust passage 15 on the
upstream side of the lean NOx trap catalyst device 24. In addition,
the third temperature sensor 33 which detects the temperature TCSF
of the exhaust gas Ga flowing out from the oxidation catalyst
device 22 to flow in the particulate collection device 23 is
arranged in the exhaust passage IS between the oxidation catalyst
device 22 and the particulate collection device 23.
[0031] A .lamda.-sensor 34 which measures the excess air ratio
.lamda. of the exhaust gas Ga or an oxygen concentration Co or an
oxygen concentration sensor (not illustrated) is arranged on the
downstream side of the exhaust gas purification device 20. The
.lamda.-sensor or the oxygen concentration sensor may be arranged
on the upstream side of the exhaust gas purification device 20, or
may be arranged in an exhaust manifold.
[0032] Herein, the temperature TDOC detected by the first
temperature sensor 31 is set as a first temperature T1 relating to
the oxidation catalyst device 22. The temperature TLNT detected by
the second temperature sensor 32 is set as a second temperature T2
relating to the lean NOx trap catalyst device 24. The temperature
TCSF detected by the third temperature sensor 33 is set as a third
temperature T3 relating to the particulate collection device
23.
[0033] Incidentally, the average value of the temperatures detected
by the temperature sensors before and after the oxidation catalyst
device 22 may be set as the first temperature T1. The average value
of the temperatures detected by the temperature sensors before and
after the lean NOx trap catalyst device 24 may be set as the second
temperature T2. In addition, the average value of the temperatures
detected by the temperature sensors before and after the
particulate collection device 23 may be set as the third
temperature. Further, instead of the exhaust gas temperatures on
the upstream side of the catalyst devices 22, 23, and 24, the
exhaust gas temperatures on the respective downstream sides may be
used.
[0034] A controller 40 is provided which controls the exhaust gas
purification system 20 of the internal combustion engine of the
present invention. Normally, the controller 40 is configured to be
embedded in an engine control unit (ECU) which controls the whole
operating condition of the engine 10, but may be configured
separately.
[0035] In the exhaust gas purification system 20 of the internal
combustion engine of the embodiment according to the present
invention, when the temperature-rising control of the exhaust gas
Ga in the regeneration control is performed for recovering the
purification ability of the exhaust gas purification system 20, the
controller 40 which controls the exhaust gas purification system 20
performs a control to change the measurement position of the
control temperature Tc which is the control amount of the feedback
control in the temperature-rising control, according to the excess
air ratio .lamda. or the oxygen concentration Co of the exhaust gas
G passing through the exhaust passage 15.
[0036] With the configuration, at the time of the
temperature-rising control of the exhaust gas Ga for the
regeneration processing to recover the purification ability of the
catalyst devices 22 to 25 included in the exhaust gas purification
device 20, the amount of the unburned fuel (hydrocarbon) injected
by the fuel injection device 26 is adjusted such that the control
temperature Tc becomes a target temperature Tm set according to
each regeneration processing. The measurement position of the
control temperature Tc is changed according to the excess air ratio
.lamda. or the oxygen concentration Co of the exhaust gas Ga. More
specifically, the measurement position is changed to the
measurement temperature which reflects best the temperature (any
one of T1, T2, and T3) of the catalyst device (any one of 22, 23,
and 24) in which the heat generation amount is largest at that time
in the exhaust passage and the temperature is increased most.
[0037] That is, when the temperature-rising control of the exhaust
gas Ga in the regeneration control is performed for recovering the
purification ability of the exhaust gas purification system 20, the
controller 40 performs a control such that the control temperature
Tc is set as the first temperature T1 when the excess air ratio
.lamda. or the oxygen concentration Co of the exhaust gas Ga
passing through the exhaust passage 15 is higher than an upper
limit threshold A1 set in advance, and the control temperature Tc
is set as the second temperature T2 when the excess air ratio
.lamda. or the oxygen concentration Co is lower than a lower limit
threshold A2 set in advance. Incidentally, the upper limit
threshold A1 and the lower limit threshold A2 are set in advance by
the experiments and the like, and are stored in the controller 40.
In addition, when the control is simplified, the upper limit
threshold A1 and the lower limit threshold A2 may be set the same
as each other, and in this case, the first temperature T1 and the
second temperature T2 preferably become the substantially same
value.
[0038] In this manner, when the heat generation amount of the
oxidation catalyst device 22 is larger than that of the lean NOx
trap catalyst device 24, the excess air ratio .lamda. and the
oxygen concentration Co of the exhaust gas Ga is larger than the
upper limit threshold A1. Thus, the first temperature T1 relating
to the oxidation catalyst device 22 is set as the control
temperature Tc, and the temperature-rising control can be performed
at the first temperature T1 of the oxidation catalyst device 22. In
addition, when the heat generation amount of the lean NOx trap
catalyst device 24 is larger than that of the oxidation catalyst
device 22, the excess air ratio .lamda. and the oxygen
concentration Co of the exhaust gas Ga is lower than the lower
limit threshold A2 set in advance. Thus, the second temperature T2
relating to the lean NOx trap catalyst device 24 is set as the
control temperature Tc, and the temperature-rising control can be
performed at the second temperature T2 of the lean NOx trap
catalyst device 24. Therefore, the temperature-rising control of
the exhaust gas Ga can be optimized with the relatively simple
control.
[0039] When the temperature-rising control of the exhaust gas Ga in
the regeneration control is performed to recover the purification
ability of the exhaust gas purification system 20, when the excess
air ratio .lamda. or the oxygen concentration Co of the exhaust gas
Ga passing through the exhaust passage 15 is equal to or less than
the upper limit threshold A1 and equal to or more than the lower
limit threshold A2, the controller 40 performs a control to set a
weight coefficient .alpha. to be changed according to the excess
air ratio .lamda. or the oxygen concentration Co, and to set the
control temperature Tc to a weighted average value T12 of the first
temperature T1 and the second temperature T2 using the weight
coefficient .alpha.. In this manner, the temperature-rising control
can be performed while a drastic change due to the switch of the
control temperature Tc with respect to the change of the excess air
ratio .lamda. or the oxygen concentration Co is avoided.
[0040] The weight coefficient .alpha. can be determined such that,
for example, T12=T1.times..alpha.+T2.times.(1-.alpha.), or
T12=(T1.times..alpha.+T2)/(1+.alpha.). The weight coefficient
.alpha. is set in advance by the experiments and the like with
respect to the excess air ratio .lamda., and is stored in the
controller 40. In FIG. 2, the weight coefficient .alpha. is set to
be increased as the excess air ratio .lamda. is smaller, and to be
decreased as the excess air ratio .lamda. is larger. Incidentally,
in FIG. 2, a correlation between the excess air ratio .lamda. and
the weight coefficient .alpha. is a linear relation falling
downward to the right. However, the linear relation of FIG. 2 is
illustrated as an example, and a curvilinear relation convex to a
lower left side or a curvilinear relation convex to an upper right
side may be adopted.
[0041] Incidentally, on the basis of the oxygen concentration
.lamda. of the exhaust gas Ga, in a case where the number of the
temperatures of the catalyst device as a maximum heat generation
amount is three or more, for example, in the case of TDOC, TLNT,
and TCSF, the number of the weight coefficient is increased, and a
temperature as the control temperature Tc is obtained as a weighted
average. For example, the weight coefficients .alpha. and .beta.
are set in advance with respect to the oxygen concentration .lamda.
of the exhaust gas Ga, and the control temperature Tc is set such
that
Tc=TDOC.times..alpha.+.times.TLNT.times..beta.+TCSF.times.(1-.alpha.-.bet-
a.).
[0042] Next, the exhaust gas purification method for the internal
combustion engine of the embodiment according to the present
invention will be described. This method is an exhaust gas
purification method for the internal combustion engine in the
above-described exhaust gas purification system 20 of the internal
combustion engine. In the method, when the temperature-rising
control of the exhaust gas Ga in the regeneration control is
performed to recover the purification ability of the exhaust gas
purification system 20, the measurement position of the control
temperature Tc which is the control amount of the feedback control
in the temperature-rising control is changed according to the
excess air ratio .lamda. or the oxygen concentration Co of the
exhaust gas Ga passing through the exhaust passage 15.
[0043] According to the exhaust gas purification system 20 of the
internal combustion engine, the internal combustion engine 10, and
the exhaust gas purification method for the internal combustion
engine which are described above, at time of the temperature-rising
control of the exhaust gas Ga for performing the regeneration
processing on the catalyst devices 22, 23, and 24 included in the
exhaust gas purification device 21, the measurement position of the
control temperature Tc which is the control amount of the feedback
control in the temperature-rising control, that is, the control
temperature Tc to be the target temperature Tm is changed and set
in consideration of the excess air ratio .lamda. or the oxygen
concentration Co of the exhaust gas Ga. and more specifically, the
control temperature Tc is set to the temperatures T1, T2, and T3
relating to the catalyst devices 22, 23, and 24 in which the heat
generation amount is largest at that time in the exhaust gas
purification system 20 and the temperature is increased most,
thereby optimizing the temperature-rising control of the exhaust
gas Ga. Therefore, it is possible to avoid a lack of temperature
increment of each of the catalyst devices 22, 23, and 24, an
overshooting at the time of increasing a temperature, heat
degradation of the catalyst, and erosion of the catalyst, and it is
possible to perform the regeneration processing reliably.
REFERENCE SIGNS LIST
[0044] 10 engine (internal combustion engine) [0045] 11 fuel
injection device [0046] 15 exhaust passage [0047] 20 exhaust gas
purification system [0048] 21 exhaust gas purification device
[0049] 22 oxidation catalyst (DOC) device [0050] 23 particulate
collection device [0051] 24 selective reduction catalyst (SCR)
device [0052] 25 subsequent-stage oxidation catalyst (DOC) device
[0053] 26 fuel injection device [0054] 31 first temperature sensor
[0055] 32 second temperature sensor [0056] 33 third temperature
sensor [0057] 34 .lamda.-sensor [0058] 40 controller [0059] A new
air [0060] G generated exhaust gas [0061] Ga exhaust gas passing
through exhaust gas purification device [0062] Gc purified exhaust
gas [0063] Ge EGR gas
* * * * *