U.S. patent application number 12/525092 was filed with the patent office on 2010-02-25 for exhaust gas purifying apparatus for internal combustion engine.
Invention is credited to Takaaki Itou, Keisuke Sano, Kazuhiro Wakao.
Application Number | 20100043410 12/525092 |
Document ID | / |
Family ID | 39674040 |
Filed Date | 2010-02-25 |
United States Patent
Application |
20100043410 |
Kind Code |
A1 |
Wakao; Kazuhiro ; et
al. |
February 25, 2010 |
EXHAUST GAS PURIFYING APPARATUS FOR INTERNAL COMBUSTION ENGINE
Abstract
An object of the present invention, in an internal combustion
engine equipped with a moisture adsorbent and a NOx adsorbent in
series in order from the upstream side of an exhaust passage, is to
provide an exhaust gas purifying apparatus for the internal
combustion engine which can successfully prevent an adsorption
capability of NOx from being inhibited by moisture and is capable
of maintaining the NOx adsorption capability of the NOx adsorbent
adequately. A main exhaust passage 14 through which exhaust gas
exhausted from an internal combustion engine 10 flows is provided.
A bypass passage 20 bypassing the main exhaust passage 14 is
provided. A moisture adsorbent 24 and a NOx adsorbent 28 are
provided in the bypass passage 20 in series in order from a side
closer to the upstream connecting portion 20a. A switching valve 22
is controlled to prevent the exhaust gas from flowing into the NOx
adsorbent 28 when it is judged that the desorption of the moisture
from the moisture adsorbent 24 is started.
Inventors: |
Wakao; Kazuhiro;
(Shizuoka-ken, JP) ; Itou; Takaaki; (Shizuoka-ken,
JP) ; Sano; Keisuke; (Shizuoka-ken, JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
39674040 |
Appl. No.: |
12/525092 |
Filed: |
January 30, 2008 |
PCT Filed: |
January 30, 2008 |
PCT NO: |
PCT/JP2008/051407 |
371 Date: |
July 30, 2009 |
Current U.S.
Class: |
60/287 |
Current CPC
Class: |
F01N 3/0842 20130101;
F01N 2570/22 20130101; F02M 26/15 20160201; F01N 13/0097 20140603;
F01N 3/0878 20130101; F01N 13/009 20140601 |
Class at
Publication: |
60/287 |
International
Class: |
F01N 3/08 20060101
F01N003/08 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 1, 2007 |
JP |
2007-023443 |
Claims
1. An exhaust gas purifying apparatus for an internal combustion
engine, the apparatus comprising: a main exhaust passage through
which exhaust gas exhausted from the internal combustion engine
flows; a bypass passage branching off from the main exhaust passage
at an upstream connecting portion connected to the main exhaust
passage while merging again with the main exhaust passage at a
downstream connecting portion provided downstream of the upstream
connecting portion; flow path switching means that is capable of
switching a flow target into which the exhaust gas flows between
the main exhaust passage and the bypass passage; a moisture
adsorbent that is disposed in the bypass passage and has a function
of adsorbing moisture; a NOx adsorbent that is disposed in the
bypass passage at a downstream side of the moisture adsorbent as
for an exhaust gas flow in a state where the moisture adsorbent
adsorbs the moisture and has a function of adsorbing NOx; moisture
desorption judgment means for judging whether desorption of the
moisture from the moisture adsorbent is started; and flow path
control means for controlling the flow path switching means to
prevent the exhaust gas from flowing into the NOx adsorbent when it
is judged that the desorption of the moisture from the moisture
adsorbent is started.
2. The exhaust gas purifying apparatus for the internal combustion
engine according to claim 1, wherein the moisture desorption
judgment means judges whether the desorption of the moisture is
started on the basis of a temperature of the moisture
adsorbent.
3. An exhaust gas purifying apparatus for an internal combustion
engine, comprising: a main exhaust passage through which exhaust
gas exhausted from the internal combustion engine flows; a bypass
passage branching off from the main exhaust passage at an upstream
connecting portion connected to the main exhaust passage while
merging again with the main exhaust passage at a downstream
connecting portion provided downstream of the upstream connecting
portion; a flow path switching device that is capable of switching
a flow target into which the exhaust gas flows between the main
exhaust passage and the bypass passage; a moisture adsorbent that
is disposed in the bypass passage and has a function of adsorbing
moisture; a NOx adsorbent that is disposed in the bypass passage at
a downstream side of the moisture adsorbent as for an exhaust gas
flow in a state where the moisture adsorbent adsorbs the moisture
and has a function of adsorbing NOx; a moisture desorption judgment
device for judging whether desorption of the moisture from the
moisture adsorbent is started; and a flow path control device for
controlling the flow path switching device to prevent the exhaust
gas from flowing into the NOx adsorbent when it is judged that the
desorption of the moisture from the moisture adsorbent is started.
Description
TECHNICAL FIELD
[0001] The present invention relates to an exhaust gas purifying
apparatus for an internal combustion engine, and more particularly
to an exhaust gas purifying apparatus including an adsorbent that
is placed downstream of a catalyst in an exhaust passage for
adsorbing unpurified components that cannot be purified by the
catalyst.
BACKGROUND ART
[0002] A related technique for purifying ventilation gas exhausted
from a road tunnel by adsorbing and removing NOx using a dry
processing with a zeolitic adsorbent has been disclosed in the
past, for example, by Patent Document 1. In the conventional
technique, a silica-gel series dehumidifying agent (moisture
adsorbent) is disposed to adsorb moisture contained in the
ventilation gas.
[Patent Document 1] Japanese Laid-open Patent Application
Publication No. Hei 1-155934
[Patent Document 2] Japanese Laid-open Patent Application
Publication No. 2002-138820
DISCLOSURE OF INVENTION
Problem to be Solved by the Invention
[0003] An exhaust passage of an internal combustion engine includes
a catalyst for purifying exhaust gas. However, at the cold start
when the temperature of the catalyst is low, the exhaust gas
containing NOx may be exhausted outward until the catalyst is
warmed and activated. The exhaust gas contains a large amount of
moisture which is generated by the combustion of fuel.
Consequently, as is the case with the conventional technique, it is
conceivable to dispose a moisture adsorbent for adsorbing the
moisture that harms a NOx adsorption capability of a NOx adsorbent
at an upstream side of the exhaust gas flow in the exhaust passage
of the internal combustion engine, and to dispose the NOx adsorbent
downstream of the moisture adsorbent.
[0004] As described above, in the configuration equipped with the
moisture adsorbent and the NOx adsorbent in the exhaust passage, if
an adsorbing amount of the moisture in the moisture adsorbent has
reached to a saturation point, or if an amount of moisture that
exceeds the moisture adsorbing capability of the moisture adsorbent
flows into the moisture adsorbent, the moisture that cannot be
adsorbed by the moisture adsorbent flows into the NOx adsorbent
disposed downstream thereof. When the moisture flows into the NOx
adsorbent, the NOx adsorption by the NOx adsorbent is largely
obstructed. Consequently, the desorption of NOx that is adsorbed in
the NOx adsorbent is likely to occur.
[0005] The present invention has been made to solve the above
problem. It is an object of the present invention, in an internal
combustion engine equipped with a moisture adsorbent and a NOx
adsorbent in series in order from the upstream side of an exhaust
passage, to provide an exhaust gas purifying apparatus for the
internal combustion engine which can successfully prevent an
adsorption capability of NOx from being harmed by moisture and is
capable of maintaining the NOx adsorption capability of the NOx
adsorbent adequately.
Means for Solving the Problem
[0006] A first aspect of the present invention is an exhaust gas
purifying apparatus for an internal combustion engine, the
apparatus comprising:
[0007] a main exhaust passage through which exhaust gas exhausted
from the internal combustion engine flows;
[0008] a bypass passage branching off from the main exhaust passage
at an upstream connecting portion connected to the main exhaust
passage while merging again with the main exhaust passage at a
downstream connecting portion provided downstream of the upstream
connecting portion;
[0009] flow path switching means that is capable of switching a
flow target into which the exhaust gas flows between the main
exhaust passage and the bypass passage;
[0010] a moisture adsorbent that is disposed in the bypass passage
and has a function of adsorbing moisture;
[0011] a NOx adsorbent that is disposed in the bypass passage at a
downstream side of the moisture adsorbent as for an exhaust gas
flow in a state where the moisture adsorbent adsorbs the moisture
and has a function of adsorbing NOx;
[0012] moisture desorption judgment means for judging whether
desorption of the moisture from the moisture adsorbent is started;
and
[0013] flow path control means for controlling the flow path
switching means to prevent the exhaust gas from flowing into the
NOx adsorbent when it is judged that the desorption of the moisture
from the moisture adsorbent is started.
[0014] A second aspect of the present invention is the exhaust gas
purifying apparatus for the internal combustion engine according to
the first aspect of the present invention,
[0015] wherein the moisture desorption judgment means judges
whether the desorption of the moisture is started on the basis of a
temperature of the moisture adsorbent.
ADVANTAGES OF THE INVENTION
[0016] According to the first aspect of the present invention, an
adsorbing operation of NOx by the NOx adsorbent is terminated when
it is judged that the desorption of the moisture from the moisture
adsorbent is started so that the desorption of NOx due to the
moisture is suppressed.
[0017] According to the second aspect of the present invention, it
is possible to certainly terminate the adsorption of NOx before NOx
starts to desorb from the NOx adsorbent by estimating inflow of the
moisture to the NOx adsorbent on the basis of not the temperature
of the NOx adsorbent but the temperature of the moisture adsorbent
placed upstream thereof so that the judgment concerning the
switching of the switching valve is performed more rapidly.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 is a diagram explaining a configuration of an
internal combustion engine system having an exhaust gas purifying
apparatus according to a first embodiment of the present
invention.
[0019] FIG. 2 is a diagram explaining an operation of the system
according to the first embodiment of the present invention.
[0020] FIG. 3 is a timing chart for showing how a control to
terminate the adsorbing operation of NOx is performed according to
the first embodiment of the present invention.
[0021] FIG. 4 is a flowchart illustrating a routine that is
executed in the first embodiment of the present invention.
[0022] FIG. 5 is a timing chart for showing how a control to
terminate the adsorbing operation of NOx is performed according to
the second embodiment of the present invention.
[0023] FIG. 6 is a flowchart illustrating a routine that is
executed in the second embodiment of the present invention.
DESCRIPTION OF SYMBOLS
[0024] 10 internal combustion engine [0025] 12 intake passage
[0026] 14 main exhaust passage [0027] 16 front stage catalyst
[0028] 18 rear stage catalyst [0029] 20 bypass passage [0030] 20a
upstream connecting portion [0031] 20b downstream connecting
portion [0032] 22 switching valve [0033] 24 moisture adsorbent
[0034] 28 NOx adsorbent [0035] 30 return passage [0036] 32 purge
control valve [0037] 40 Electronic Control Unit (ECU)
BEST MODE FOR CARRYING OUT THE INVENTION
First Embodiment
Description of System Configuration
[0038] FIG. 1 is a diagram explaining a configuration of an
internal combustion engine system having an exhaust gas purifying
apparatus according to a first embodiment of the present invention.
The internal combustion engine 10 shown in FIG. 1 includes an
intake passage 12 for taking air into a cylinder, and an exhaust
passage through which exhaust gas exhausted from the cylinder
flows.
[0039] The exhaust passage of the present embodiment includes a
main exhaust passage 14 for exhausting the exhaust gas from the
cylinder, and a bypass passage 20 described later. In the main
exhaust passage 14, a front stage catalyst (SC) 16 and rear stage
catalyst (UF) 18 that can purify the exhaust gas is placed in
series in order from the upstream side.
[0040] The system of the present embodiment has the bypass passage
20 as a passage bypassing the main exhaust passage 14. The bypass
passage 20 is configured to branch off from the main exhaust
passage 14 at an upstream connecting portion 20a placed downstream
of the rear stage catalyst 18, and merge again with the main
exhaust passage 14 at a downstream connecting portion 20b placed
downstream of the upstream connecting portion 20a. The upstream
connecting portion 20a is provided with a switching valve 22 for
switching a flow target into which the exhaust gas flows between
the main exhaust passage 14 and the bypass passage 20. The opening
and closing of the switching valve 22 is controlled by controlling
an engine intake vacuum pressure, which acts on a negative pressure
diaphragm 22a, with an electromagnetic valve (not shown).
Incidentally, at the normal operation of the internal combustion
engine 10, by controlling the switching valve 22 to block the
bypass passage 20, the exhaust gas passes through the main exhaust
passage 14 without passing through the bypass passage 20 and is
then released into the atmosphere.
[0041] The middle of the bypass passage 20 is provided with two
adsorbents. More specifically, a moisture adsorbent 24 having a
function of adsorbing moisture contained in the exhaust gas is
installed at an upstream side of the main exhaust passage 14, that
is, at a side closer to the upstream connecting portion 20a.
Zeolitic materials, for example, can be used as such moisture
adsorbent 24. Into the moisture adsorbent 24, a temperature sensor
26 is integrated to detect a temperature of the moisture adsorbent
24.
[0042] In addition, in the bypass passage 20, a NOx adsorbent 28
having a function of adsorbing NOx, which is an unpurified
component contained in the exhaust gas, is installed at a
downstream side of the moisture adsorbent 24, that is, at a side
farther to the upstream connecting portion 20a. Zeolitic materials
which support iron Fe, for example, can be used as such NOx
adsorbent 28.
[0043] A part between the upstream connecting portion 20a and
moisture adsorbent 24 in the bypass passage 20 communicates with a
return passage 30. A purge control valve 32 is provided in the
middle of the return passage 30. The remaining end of the return
passage 30 communicates with the intake passage 12. Incidentally, a
connection point of the return passage 30 is not limited to the
intake passage 12. A passage upstream of the rear stage catalyst
18, for instance, an upstream portion of the front stage catalyst
16 in the main exhaust passage 14, may be used as the connection
point.
[0044] The system of the present embodiment includes an electronic
control unit (ECU) 40. A water temperature sensor 42 for detecting
a temperature of engine cooling water is connected to the ECU 40,
as well as various sensors for controlling the internal combustion
engine 10 and the above temperature sensor 26. In addition, various
actuators such as the switching valve 22 and the purge control
valve 32 mentioned above are connected to the ECU 40.
[Operation of First Embodiment]
[0045] FIG. 2 is a diagram explaining an operation of the system
according to the first embodiment of the present invention.
(Adsorbing Operation)
[0046] First, with reference to FIG. 2(A), an operation for causing
the above adsorbents 24, 28 to adsorb NOx and the moisture
contained in the exhaust gas exhausted from the cylinder at the
cold start of the internal combustion engine 10 will be
described.
[0047] As shown in FIG. 2(A), the adsorbing operation is started in
a state where the switching valve 22 blocks the main exhaust
passage 14 at the cold start of the internal combustion engine 10.
In addition, the purge control valve 32 is controlled to become a
closed condition under the adsorbing operation.
[0048] In the state mentioned above, all of the exhaust gas
exhausted from the internal combustion engine 10 is supplied from
the main exhaust passage 14 into the bypass passage 20. The exhaust
gas supplied into the bypass passage 20 passes through the moisture
adsorbent 24 and the NOx adsorbent 28 in sequence and is then
returned to the main exhaust passage 14 and is then released into
the atmosphere.
[0049] If the amount of exhaust gas that exceeds the adsorption
capability of the NOx adsorbent 28 is supplied to the NOx adsorbent
24, NOx adsorbed once by the NOx adsorbent 24 is desorbed and
exhaust emission is caused to deteriorate. Therefore, the adsorbing
operation needs to be terminated at an appropriate timing before
the desorption of NOx from the NOx adsorbent 28 starts. A setting
of the timing to terminate such adsorbing operation of NOx is a
feature portion of the present embodiment and will be described
later with reference to FIG. 3. In addition, if such a timing to
terminate the adsorbing operation has come, the switching valve 22
is controlled to become a state where the bypass passage 20 is
blocked.
[0050] According to the adsorbing operation described above, the
moisture contained in the exhaust gas is adsorbed by the moisture
adsorbent 24 and removed. Furthermore, NOx contained in the exhaust
gas is adsorbed by the NOx adsorbent 28 and removed. This can
prevent NOx from being released into the atmosphere at the cold
start when the front stage catalyst 16 has not yet been
activated.
(Purging Operation)
[0051] FIG. 2(B) is a diagram explaining a purging operation
according to the present embodiment. As shown in FIG. 2(B), the
purging operation according to the present embodiment is performed
by using a method which flows NOx adsorbed by the NOx adsorbent 28
back into the intake passage via the return passage 30.
[0052] As shown in FIG. 2(B), the purging operation is started by
opening the purge control valve 32, at a time when a predetermined
purge start timing has come, for example, the front stage catalyst
16 has been activated, in a state where the switching valve 22 is
controlled to block the bypass passage 20. According to such
purging operation, part of the exhaust gas exhausted from the
cylinder is supplied from the main exhaust passage 14 into the
bypass passage 20 via the downstream connecting portion 20b, by
using a vacuum being generated in the intake passage 12 of the
internal combustion engine 10.
[0053] As a result, the exhaust gas relatively heated after the
start is supplied to the adsorbent 28 or the like. Accordingly, NOx
is desorbed from the NOx adsorbent 28 and purged to the intake
passage 12 via the return passage 30. NOx returned to the intake
passage 12 is burned again and then purified by the active catalyst
16 or the like.
[Feature Portions of the First Embodiment]
[0054] In the present embodiment, the moisture adsorbent 24 is
disposed upstream of the NOx adsorbent 28 at the adsorbing
operation as shown in FIG. 2. By such a layout, the moisture is
preliminarily removed by the moisture adsorbent 24 at the upstream
of the NOx adsorbent 28. This can allow a dried exhaust gas to
supply to the NOx adsorbent 28 and can highly maintain the NOx
adsorbing performance of the NOx adsorbent 28.
[0055] At the adsorbing operation, however, if an adsorbing amount
of moisture in the moisture adsorbent 24 has reached to a
saturation point, or if an amount of moisture that exceeds the
moisture adsorbing capability of the moisture adsorbent 24 flows
into the moisture adsorbent 24, the moisture that cannot be
adsorbed by the moisture adsorbent 24 flows into the NOx adsorbent
28 disposed downstream thereof. When the moisture flows into the
NOx adsorbent 28, the NOx adsorption capability of the NOx
adsorbent 28 is largely harmed. Consequently, the desorption of NOx
that is adsorbed by the NOx adsorbent 28 is likely to occur.
[0056] The present embodiment controls the switching valve to block
the inlet of the bypass passage 20 and terminates the adsorbing
operation of NOx, at a time when it is judged that the desorption
of the moisture from the moisture adsorbent 24 which is installed
upstream of the NOx adsorbent is started. More specifically, when
performing the adsorbing operation, the present embodiment judges a
time when the desorption of the moisture from the moisture
adsorbent 24 is started by judging whether a temperature of the
moisture adsorbent 24 detected by the temperature sensor 26 has
become equal to or higher than a predetermined value.
[0057] FIG. 3 is a timing chart for showing how a control to
terminate the adsorbing operation of NOx is performed according to
the first embodiment of the present invention. As shown in FIG. 3,
when the moisture adsorbent 24 adsorbs the moisture by introducing
the exhaust gas including the moisture, the temperature of the
moisture adsorbent 24 increases due to the adsorption heat.
However, when the moisture adsorbent 24 adsorbs the moisture larger
than a certain amount, it cannot adsorb any more moisture.
Therefore, the moisture flows into the NOx adsorbent 28.
[0058] A predetermined value T1 shown in FIG. 3 concerning the
moisture adsorbent 24 is a value used to judge a time when a
certain amount of moisture which coincides with such an amount that
the desorption of the moisture from the moisture adsorbent 24 is
started is adsorbed by the moisture adsorbent 24. The present
embodiment, at a time when the temperature of the moisture
adsorbent 24 has reached the predetermined value T1, changes
positions of the switching valve 22 so that a state where the
bypass passage 20 is opened (a state of "with adsorption" shown in
FIG. 3) varies to a state where the bypass passage 20 is closed (a
state of "without adsorption" shown in FIG. 3).
[0059] FIG. 4 is a flowchart illustrating a routine that the ECU 40
executes in order to implement the adsorbing operation and purging
operation according to the present embodiment. The routine shown in
FIG. 4 is started immediately after the internal combustion engine
10 is started.
[0060] In the routine shown in FIG. 4, step 100 is first performed
to judge whether the temperature of the engine cooling water is
equal to or lower than a predefined temperature. As a result, if
the judgment result indicates that the temperature of the engine
cooling water is higher than the predefined temperature, that is,
if it can be judged that the engine warm-up has been completed, the
current processing cycle immediately terminates.
[0061] If, on the other hand, the judgment result obtained in step
100 indicates the temperature of the engine cooling water is equal
to or lower than the predefined temperature, that is, if it can be
judged that the engine is in a cold start condition, step 102 is
performed to open the switching valve 22 and close the purge
control valve 32. The switching valve 22 at the normal operation
blocks the inlet of the bypass passage 20. However, if it can be
judged that the engine is in the cold start condition, step 102 is
performed so that the main exhaust passage 14 may communicate with
the bypass passage 20. Thus, the adsorbing operation is
started.
[0062] Next, step 104 is performed to judge whether the temperature
of the moisture adsorbent 24 has reached a predetermined value T1.
Incidentally, the temperature of the moisture adsorbent 24 is
directly measured by the temperature sensor 26 here. But, an
alternative method that estimate the temperature of the moisture
adsorbent 24 based on the anterior and posterior exhaust gas
temperatures of the moisture adsorbent 24 may be used.
[0063] If the judgment result obtained in step 104 indicates that
the temperature of the moisture adsorbent 24 has reached the
predetermined value T1, that is, if it can be judged that the
moisture adsorbent 24 is in a state where the desorption of the
moisture is started, step 106 is performed to close the switching
valve 22 in order to block the bypass passage 20. Thus, the
adsorbing operation of NOx is ended.
[0064] Next, step 108 is performed to judge whether the start
timing of the purging operation has come. More specifically, step
108 performs a judgment based on whether the catalyst 16 or the
like is in an active state, a judgment based on whether the
temperature of the exhaust gas supplied to the bypass passage 20 is
within a temperature range suitable for performing the purging
operation, and a judgment based on whether the internal combustion
engine 10 is in a stable operating state that can perform the
purging operation without an adverse effect.
[0065] If the judgment result obtained in step 108 indicates that
the start timing of the purging operation has come, step 110 is
performed to open the purge control valve 32. Next, the purge
amount judgment is performed in step 112. More specifically, it is
judged whether the current purge amount has reached a predefined
amount. The current purge amount can be estimated on the basis of
the relation between the temperature of the purge gas, and the
elapsed time after the purge control valve 32 is opened in step 110
described above.
[0066] If the judgment result obtained in step 112 indicates that
the purge amount has reached the predefined amount, step 114 is
performed to close the purge control valve 32. Thus, the purging
operation is ended.
[0067] According to the routine that has been described above with
reference to FIG. 4, the switching valve 22 is operated when the
temperature of the moisture adsorbent 24 has reached the
predetermined value T1, (that is, on the basis of the estimation
results of the adsorption capability of the NOx adsorbent 28 using
the temperature of the moisture adsorbent 24). This makes it
possible to terminate the adsorbing operation of NOx when the
desorption of the moisture from the moisture adsorbent 24 starts.
According to such a control, it is possible to terminate the
adsorption operation of NOx, immediately before the moisture flows
into the NOx adsorbent 28, that is, before NOx adsorbed by the NOx
adsorbent 28 is desorbed due to the moisture. Therefore, the NOX
adsorption capability of the NOx adsorbent 28 can be utilized at a
maximum.
[0068] In addition, the routine described above can certainly
terminate the adsorption of NOx before NOx starts to desorb from
the NOx adsorbent 28 by estimating the inflow of the moisture to
the NOx adsorbent 28 based on not the temperature of the NOx
adsorbent 28 but the temperature of the moisture adsorbent 24
placed upstream thereof so that the judgment concerning the
switching of the switching valve 22 is performed more rapidly.
[0069] Incidentally, in the first embodiment, which has been
described above, the switching valve 22, the return passage 30, and
the purge control valve 32 correspond to the "flow path switching
means" according to the first aspect of the present invention. In
addition, the "moisture desorption judgment means" according to the
first aspect of the present invention is implemented when the ECU
40 performs step 104; and the "flow path control means" according
to the first aspect of the present invention is implemented when
the ECU 40 performs step 106.
Second Embodiment
[0070] Next, a second embodiment of the present invention will now
be described with reference to FIGS. 5 and 6.
[0071] The system according to the present embodiment is
implemented by adopting the hardware configuration shown in FIG. 1
and by allowing the ECU 40 to execute a routine shown in FIG. 6
described below instead of the routine shown in FIG. 4.
[Feature Portions of the Second Embodiment]
[0072] FIG. 5 is a timing chart for showing how a control to
terminate the adsorbing operation of NOx is performed according to
the second embodiment of the present invention.
[0073] The first embodiment described above judges the start timing
of the moisture desorption from the moisture adsorbent 24 by
judging whether the temperature of the moisture adsorbent 24 at the
adsorbing operation has reached the predetermined value T1. In
contrast, the present embodiment judges the start timing of the
moisture desorption from the moisture adsorbent 24 by judging
whether a temperature-elevation degree of the moisture adsorbent 24
at the adsorbing operation has become smaller than a predetermined
value X1.
[0074] As described above, when the moisture is adsorbed by the
moisture adsorbent 24, the temperature of the moisture adsorbent 24
increases due to the adsorption heat. On the other hand, when the
adsorbed moisture desorbs from the moisture adsorbent 24, the
temperature of the moisture adsorbent decreases due to the
desorption heat. Consequently, if the desorption amount is larger
than the adsorption amount as the inflow amount of moisture to the
moisture adsorbent 24 increases, the temperature-elevation degree
of the moisture adsorbent 24 decreases.
[0075] The predetermined value X1 shown in FIG. 5 concerning the
temperature-elevation degree of the moisture adsorbent 24 is a
value used to judge a time when a certain amount of moisture which
coincides with such an amount that the desorption of the moisture
from the moisture adsorbent 24 is started is adsorbed by the
moisture adsorbent 24.
[0076] The present embodiment, at a time when the
temperature-elevation degree of the moisture adsorbent 24 has
become smaller than the predetermined value X1, changes positions
of the switching valve 22 so that a state where the bypass passage
20 is opened (a state of "with adsorption" shown in FIG. 5) varies
to a state where the bypass passage 20 is closed (a state of
"without adsorption" shown in FIG. 5).
[0077] FIG. 6 is a flowchart illustrating a routine that the ECU 40
executes in order to implement the adsorbing operation and purging
operation according to the present embodiment. The routine shown in
FIG. 6 is started immediately after the internal combustion engine
10 is started. In addition, as regards the steps in FIG. 6 that are
the same as those in FIG. 4 according to the first embodiment,
their description is omitted or abridged with the same reference
numerals assigned.
[0078] As shown in FIG. 6, the adsorbing operation is started by
performing step 102 to open the switching valve 22 after the cold
start of the internal combustion engine 10. Then, step 200 is
performed to judge whether the temperature-elevation degree of the
moisture adsorbent 24 has become smaller than the predetermined
value X1.
[0079] As a result, if the temperature-elevation degree of the
moisture adsorbent 24 has become smaller than the predetermined
value X1, that is, if it can be judged that the moisture adsorbent
24 is in a state where the desorption of the moisture is started,
step 106 is performed to close the switching valve 22 in order to
block the bypass passage 20. Thus, the adsorbing operation of NOx
is ended.
[0080] After that, steps 108 to 114 of the routine shown in FIG. 6
are sequentially performed. Because these processes are the same as
those in the routine shown in FIG. 4, their detailed description is
omitted here.
[0081] According to the routine that has been described above with
reference to FIG. 6, the switching valve 22 is operated when the
temperature-elevation degree of the moisture adsorbent 24 has
become smaller than the predetermined value X1. This makes it
possible to terminate the adsorbing operation of NOx when the
desorption of the moisture from the moisture adsorbent 24 starts.
According to such a control, it is possible to terminate the
adsorption operation of NOx, immediately before the moisture flows
into the NOx adsorbent 28, that is, before NOx adsorbed by the NOx
adsorbent 28 is desorbed due to the moisture. Therefore, the NOX
adsorption capability of the NOx adsorbent 28 can be utilized at a
maximum.
* * * * *