U.S. patent application number 12/312785 was filed with the patent office on 2010-02-18 for exhaust purification device of compression ignition type internal combustion engine.
Invention is credited to Kazuhiro Itoh, Takekazu Itoh, Tomihisa Oda, Yutaka Tanai, Shunsuke Toshioka.
Application Number | 20100037596 12/312785 |
Document ID | / |
Family ID | 39765983 |
Filed Date | 2010-02-18 |
United States Patent
Application |
20100037596 |
Kind Code |
A1 |
Toshioka; Shunsuke ; et
al. |
February 18, 2010 |
EXHAUST PURIFICATION DEVICE OF COMPRESSION IGNITION TYPE INTERNAL
COMBUSTION ENGINE
Abstract
In an internal combustion engine, an NO.sub.x selective reducing
catalyst (15) is arranged in an engine exhaust passage and an
oxidation catalyst (12) is arranged in the engine exhaust passage
upstream of the NO.sub.x selective reducing catalyst (15). At the
time of engine startup, HC is fed from a HC feed valve (28) to the
oxidation catalyst (12), thereby raising the temperature of the
NO.sub.x selective reducing catalyst(15) by the heat of the
oxidation reaction of HC. At this time, the temperature of the
NO.sub.x selective reducing catalyst (15) is raised to a HC
desorption range where HC is desorbed from the NO.sub.x selective
reducing catalyst (15).
Inventors: |
Toshioka; Shunsuke;
(Susono-shi, JP) ; Oda; Tomihisa; (Numazu-shi,
JP) ; Itoh; Takekazu; (Toyota-shi, JP) ; Itoh;
Kazuhiro; (Mishima-shi, JP) ; Tanai; Yutaka;
(Susono-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Family ID: |
39765983 |
Appl. No.: |
12/312785 |
Filed: |
March 18, 2008 |
PCT Filed: |
March 18, 2008 |
PCT NO: |
PCT/JP2008/055615 |
371 Date: |
May 27, 2009 |
Current U.S.
Class: |
60/286 ;
60/301 |
Current CPC
Class: |
F01N 2610/02 20130101;
B01D 2255/1021 20130101; Y02T 10/12 20130101; B01D 2258/012
20130101; F01N 3/0814 20130101; B01D 53/9477 20130101; B01D 53/96
20130101; F01N 2610/03 20130101; F01N 3/2033 20130101; Y02T 10/40
20130101; B01D 2251/2067 20130101; F01N 9/00 20130101; B01D 2251/21
20130101; F01N 13/009 20140601; B01D 2255/50 20130101; F01N 2560/06
20130101; Y02T 10/47 20130101; B01D 53/9495 20130101; B01D
2255/20738 20130101; F01N 3/2066 20130101; Y02T 10/24 20130101;
Y02T 10/26 20130101; B01D 53/9418 20130101; F01N 2560/14 20130101;
F01N 3/106 20130101 |
Class at
Publication: |
60/286 ;
60/301 |
International
Class: |
F01N 9/00 20060101
F01N009/00; F01N 3/10 20060101 F01N003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 19, 2007 |
JP |
2007-070020 |
Claims
1-4. (canceled)
5. An exhaust purification device of a compression ignition type
internal combustion engine arranging an NO.sub.x selective reducing
catalyst in an engine exhaust passage, arranging an oxidation
catalyst in the engine exhaust passage upstream of the NO.sub.x
selective reducing catalyst, feeding urea to the NO.sub.x selective
reducing catalyst, and using an ammonia produced from the urea to
selectively reduce NO.sub.x contained in an exhaust gas, wherein HC
is fed into the oxidation catalyst at the time of engine startup to
raise a temperature of the NO.sub.x selective reducing catalyst
with a heat of oxidation reaction of HC, and at this time, the
temperature of the NO.sub.x selective reducing catalyst is
increased to a HC desorption temperature range where HC is desorbed
from the NO.sub.x selective reducing catalyst, an amount of HC
deposited at the NO.sub.x selective reducing catalyst being
calculated, and the feed of HC being stopped when a calculated HC
amount becomes less than a predetermined set value.
6. The exhaust purification device of the compression ignition type
internal combustion engine as claimed in claim 5, wherein at the
time of raising the temperature of the NO.sub.x selective reducing
catalyst, the temperature of the NO.sub.x selective reducing
catalyst is increased to a range within 350.degree. C. to
650.degree. C.
7. The exhaust purification device of the compression ignition type
internal combustion engine as claimed in claim 5, wherein there is
a convergence temperature at which the temperature of the NO.sub.x
selective reducing catalyst ultimately converges when an idling
operation is continued during warm-up operation and wherein the
temperature of the NO.sub.x selective reducing catalyst at the time
of raising the temperature of the NO.sub.x selective reducing
catalyst is increased to a temperature at least 100.degree. C.
higher than the convergence temperature.
Description
TECHNICAL FIELD
[0001] The present invention relates to an exhaust purification
device of a compression ignition type internal combustion
engine.
BACKGROUND ART
[0002] Known in the art is an internal combustion engine arranging
an NO.sub.x selective reducing catalyst in an engine exhaust
passage, arranging an oxidation catalyst in the engine exhaust
passage upstream of the NO.sub.x selective reducing catalyst,
feeding urea to the NO.sub.x selective reducing catalyst, and using
the ammonia produced from the urea to selectively reduce the
NO.sub.x contained in the exhaust gas (for example, see Japanese
Patent Publication (A) No. 2005-23921). In this internal combustion
engine, the NO.sub.x selective reducing catalyst adsorbs ammonia
and the adsorbed ammonia reacts with the NO.sub.x contained in the
exhaust gas whereby the NO.sub.x is reduced.
[0003] In this internal combustion engine, however, when HC is fed
into the oxidation catalyst at engine startup and the heat of
oxidation reaction of the HC raises the temperature of the NO.sub.x
selective reducing catalyst, if a large amount of HC is fed to warm
up the NO.sub.x selective reducing catalyst early, HC unable to be
completely oxidized in the oxidation catalyst will flow into the
NO.sub.x selective reducing catalyst and deposit on the NO.sub.x
selective reducing catalyst. In this regard, the problem arises
that if HC deposits on the NO.sub.x selective reducing catalyst,
the NO.sub.x selective reducing catalyst will become unable to
adsorb ammonia and thereby the NO.sub.x purification rate will
fall.
[0004] As opposed to this, if reducing the amount of HC so as to
keep HC from adhering to the NO.sub.x selective reducing catalyst,
that is, to prevent the NO.sub.x selective reducing catalyst from
being poisoned by HC, time will be needed for the NO.sub.x
selective reducing catalyst to rise and therefore, in this case as
well, the problem arises that the NO.sub.x purification rate will
fall.
DISCLOSURE OF THE INVENTION
[0005] An object of the present invention is to provide an exhaust
purification device of a compression ignition type internal
combustion engine capable of obtaining a good NO.sub.x purification
rate at engine startup.
[0006] According to the present invention, there is provided an
exhaust purification device of a compression ignition type internal
combustion engine arranging an NO.sub.x selective reducing catalyst
in an engine exhaust passage, arranging an oxidation catalyst in
the engine exhaust passage upstream of the NO.sub.x selective
reducing catalyst, feeding urea to the NO.sub.x selective reducing
catalyst, and using an ammonia produced from the urea to
selectively reduce NO.sub.x contained in the exhaust gas, wherein
HC is fed to the oxidation catalyst at the time of engine startup
to raise a temperature of the NO.sub.x selective reducing catalyst
with a heat of oxidation reaction of HC, and at this time, the
temperature of the NO.sub.x selective reducing catalyst is
increased to a HC desorption temperature range where HC is desorbed
from the NO.sub.x selective reducing catalyst.
[0007] Increasing the temperature of the NO.sub.x selective
reducing catalyst to the HC desorption temperature range eliminates
the HC poisoning of the NO.sub.x selective reducing catalyst and
thereby gives a good NO.sub.x purification rate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is an overview of a compression ignition type
internal combustion engine,
[0009] FIG. 2 is an overview showing another embodiment of the
compression ignition type internal combustion engine,
[0010] FIG. 3 is a view showing an oxidation rate and desorption
rate,
[0011] FIG. 4 is a time chart showing warm-up control, and
[0012] FIG. 5 is a flow chart for performing the warm-up
control.
BEST MODE FOR CARRYING OUT THE INVENTION
[0013] FIG. 1 shows an overview of a compression ignition type
internal combustion engine.
[0014] Referring to FIG. 1, 1 indicates an engine body, 2 a
combustion chamber of a cylinder, 3 an electronic control type fuel
injector for injecting fuel into each combustion chamber 2, 4 an
intake manifold, and 5 an exhaust manifold. The intake manifold 4
is connected through an intake duct 6 to the outlet of a compressor
7a of an exhaust turbocharger 7, while the inlet of the compressor
7a is connected through an intake air amount detector 8 to an air
cleaner 9. Inside the intake duct 6, a throttle valve 10 driven by
a step motor is arranged. Further, around the intake duct 6, a
cooling device 11 for cooling the intake air flowing through the
inside of the intake duct 6 is arranged. In the embodiment shown in
FIG. 1, the engine cooling water is guided to the cooling device 11
where the engine cooling water cools the intake air.
[0015] On the other hand, the exhaust manifold 5 is connected to
the inlet of an exhaust turbine 7b of the exhaust turbocharger 7,
while the outlet of the exhaust turbine 7b is connected to the
inlet of an oxidation catalyst 12. Downstream of the oxidation
catalyst 12, a particulate filter 13 is arranged adjacent to the
oxidation catalyst 12 for collecting particulate matter contained
in the exhaust gas, while the outlet of this particulate filter 13
is connected through an exhaust pipe 14 to the inlet of an NO.sub.x
selective reducing catalyst 15. The outlet of this NO.sub.x
selective reducing catalyst 15 is connected to an oxidation
catalyst 16.
[0016] Inside an exhaust pipe 14 upstream of the NO.sub.x selective
reducing catalyst 15, an aqueous urea solution feed valve 17 is
arranged. This aqueous urea solution feed valve 17 is connected
through a feed pipe 18 and a feed pump 19 to an aqueous urea
solution tank 20. The aqueous urea solution stored inside the
aqueous urea solution tank 20 is injected by the feed pump 19 into
the exhaust gas flowing within the exhaust pipe 14 from the aqueous
urea solution feed valve 17, while the ammonia
((NH.sub.2).sub.2CO+H.sub.2O.sub.2NH.sub.3+CO.sub.2) generated from
urea causes the NO.sub.x contained in the exhaust gas to be reduced
in the NO.sub.x selective reducing catalyst 15.
[0017] The exhaust manifold 5 and the intake manifold 4 are
connected to each other through an exhaust gas recirculation
(hereinafter referred to as the "EGR") passage 21. Inside the EGR
passage 21 is arranged an electronic control type EGR control valve
22. Further, around the EGR passage 21 is arranged a cooling device
23 for cooling the EGR gas flowing through the inside of the EGR
passage 21. In the embodiment shown in FIG. 1, the engine cooling
water is guided through the cooling device 23, where the engine
cooling water is used to cool the EGR gas. On the other hand, each
fuel injector 3 is connected through a fuel feed pipe 24 to a
common rail 25. This common rail 25 is connected through an
electronically controlled variable discharge fuel pump 26 to a fuel
tank 27. The fuel stored in the fuel tank 27 is fed by the fuel
pump 26 into the common rail 25, and the fuel fed to the inside of
the common rail 25 is fed through each fuel pipe 24 to the fuel
injectors 3. Furthermore, an HC feed valve 28 for feeding
hydrocarbons, i.e., HC into the exhaust manifold 5 is arranged in
the exhaust manifold 5. In the embodiment shown in FIG. 1, this HC
is comprised of diesel oil.
[0018] An electronic control unit 30 is comprised of a digital
computer provided with a ROM (read only memory) 32, RAM (random
access memory) 33, CPU (microprocessor) 34, input port 35, and
output port 36 all connected to each other by a bi-directional bus
31. A temperature sensor 45 for detecting the bed temperature of
the oxidation catalyst 12 is attached to the oxidation catalyst 12,
and a temperature sensor 46 for detecting the bed temperature of
the NO.sub.x selective reducing catalyst 15 is attached to the
NO.sub.x selective reducing catalyst 15. The output signals of
these temperature sensors 45 and 46 and intake air amount detector
8 are input through corresponding AD converters 37 into the input
port 35.
[0019] On the other hand, the accelerator pedal 40 has a load
sensor 41 generating an output voltage proportional to the amount
of depression L of the accelerator pedal 40 connected to it. The
output voltage of the load sensor 41 is input through a
corresponding AD converter 37 to the input port 35. Further, the
input port 35 has a crank angle sensor 42 generating an output
pulse each time the crank shaft rotates by for example 15.degree.
C. connected to it. On the other hand, the output port 36 is
connected through corresponding drive circuits 38 to the fuel
injectors 3, throttle valve 10 drive step motor, aqueous urea
solution feed valve 17, feed pump 19, EGR control valve 22, fuel
pump 26, and HC feed valve 28.
[0020] The oxidation catalyst 12, for example, carries a precious
metal catalyst such as platinum. This oxidation catalyst 12
performs the action of converting the NO contained in the exhaust
gas to NO.sub.2 and the action of oxidizing the HC contained in the
exhaust gas. That is, NO.sub.2 has stronger oxidation properties
than NO. Therefore, if NO is converted to NO.sub.2, the oxidation
reaction of the particulate matter trapped on the particulate
filter 13 is promoted. Further, the reduction action by the ammonia
at the NO.sub.x selective reducing catalyst 15 is promoted. On the
other hand, at the NO.sub.x selective reducing catalyst 15, as
explained above, if HC is deposited, the adsorption amount of the
ammonia will decrease, therefore the NO.sub.x purification rate
will fall. Accordingly, by using the oxidation catalyst 12 to
oxidize the HC, the deposition of HC at the NO.sub.x selective
reducing catalyst 15, that is, the HC poisoning of the NO.sub.x
selective reducing catalyst 15, is avoided.
[0021] As the particulate filter 13, a particulate filter not
carrying a catalyst may be used. For example, a particulate filter
carrying, for example, a precious metal catalyst such as platinum
may be used. On the other hand, the NOX selective reducing catalyst
15 is comprised of an ammonia adsorption type Fe zeolite having a
high NO.sub.x purification rate at low temperatures. Further, the
oxidation catalyst 16 carries, for example, a precious metal
catalyst comprised of platinum, and this oxidation catalyst 16
performs an action of oxidizing ammonia leaked from the NO.sub.x
selective reducing catalyst 15.
[0022] FIG. 2 shows another embodiment of the compression ignition
type internal combustion engine. In this embodiment, the
particulate filter 13 is arranged downstream of the oxidation
catalyst 16, accordingly, in this embodiment, the outlet of the
oxidation catalyst 12 is coupled through the exhaust pipe 14 to the
inlet of the NO.sub.x selective reducing catalyst 15.
[0023] If the NO.sub.x selective reducing catalyst 15 does not rise
in temperature a certain degree, the selective reduction action of
NO.sub.x will not be performed, that is, the catalyst will not be
activated. Accordingly, it is necessary to activate the NO.sub.x
selective reducing catalyst 15 as soon as possible at engine
startup. Here, in the present invention, HC is fed to the oxidation
catalyst 12 at the time of engine startup so as to raise the
temperature of the NO.sub.x selective reducing catalyst 15 with the
heat of oxidation reaction of HC. The feed of the HC may be
performed, for example, by injecting fuel into the combustion
chamber 2 during the exhaust stroke or by feeding HC into the
engine exhaust passage. In the embodiments shown in FIG. 1 and FIG.
2, the HC is fed by injecting diesel fuel from the HC feed valve
28.
[0024] However, it is not necessarily possible to oxidize all of
the HC fed in the oxidation catalyst 12 at the time of engine
startup. This will be explained while referring to FIG. 3(A). FIG.
3(A) shows the relation between the bed temperature T.sub.0 of the
oxidation catalyst 12 and the oxidation rate M.sub.0(g/sec) of the
HC, that is, the amount of HC able to be oxidized per unit
time.
[0025] As is clear from FIG. 3(A), when the bed temperature T.sub.0
of the oxidation catalyst 12 is approximately 200.degree. C. or
below, that is, when the oxidation catalyst 12 is not activated,
the oxidation rate M.sub.0 is zero. Accordingly, the HC flowing
into the oxidation catalyst 12 at this time will slip the oxidation
catalyst 12. On the other hand, upon activation of the oxidation
catalyst 12, when the amount of HC flowing into the oxidation
catalyst 12 per unit time is lower than the oxidation rate M.sub.0
determined from the bed temperature T.sub.0 of the oxidation
catalyst 12, all of the inflowing HC is oxidized in the oxidation
catalyst 12, and when the amount of HC flowing into the oxidation
catalyst 12 per unit time is greater than the oxidation rate
M.sub.0 determined from the bed temperature of the oxidation
catalyst 12, the amount by which the HC exceeds the oxidation rate
M.sub.0 will slip the oxidation catalyst 12.
[0026] The HC slipping the oxidation catalyst 12 will flow into the
NO.sub.x selective reducing catalyst 15 and deposit on the NO.sub.x
selective reducing catalyst 15. However, this deposited HC may be
desorbed from the NO.sub.x selective reducing catalyst 15 by
raising the temperature of the NO.sub.x selective reducing catalyst
15. This will be explained while referring to FIG. 3(B).
[0027] FIG. 3(B) shows the relation between the bed temperature Tn
of the NO.sub.x selective reducing catalyst 15 and the desorption
rate Md(g/sec) of the HC, that is, the amount of HC desorbed from
the NO.sub.x selective reducing catalyst 15 per unit time. As shown
in FIG. 3(B), when the bed temperature Tn of the NO.sub.x selective
reducing catalyst 15 exceeds approximately 350.degree. C., the
desorption rate Md rises. In FIG. 3(B), the approximately
350.degree. C. indicated by TF becomes the desorption start
temperature. Accordingly, by raising the bed temperature Tn of the
NO.sub.x selective reducing catalyst 15 to the desorption start
temperature TF or above, HC can be desorbed from the NO.sub.x
selective reducing catalyst 15.
[0028] To raise the temperature of the NO.sub.x selective reducing
catalyst 15 early, a large amount of HC may be fed from the HC feed
valve 28. However, if feeding a large amount of HC, HC will slip
the oxidation catalyst 12 and the NO.sub.x selective reducing
catalyst 15 will be poisoned by HC. However, if raising the
temperature of the NO.sub.x selective reducing catalyst 15 to an HC
desorption temperature range greater than the desorption start
temperature TF, HC poisoning can be eliminated. Accordingly, in the
present invention, the temperature of the NO.sub.x selective
reducing catalyst 15 at the time of engine startup will be raised
to the HC desorption temperature range where HC is desorbed from
the NO.sub.x selective reducing catalyst 15.
[0029] Next, the warm-up control of the NO.sub.x selective reducing
catalyst 15 according to the present invention will be explained
while referring to FIG. 4.
[0030] When the engine is started up, a large amount of unburned HC
will be exhausted from the combustion chamber 2. Accordingly, as
shown in FIG. 4, the amount G.sub.0 of HC exhausted from the
combustion chamber 2 at the time of engine startup will temporarily
become high. Normally, the oxidation catalyst 12 is not activated
at this time, so this exhaust HC slips the oxidation catalyst 12.
This slipped HC is deposited on the NO.sub.x selective reducing
catalyst 15. Accordingly, as is clear from FIG. 4, the slipped HC
amount W is added to the NO.sub.x HC deposition amount .SIGMA.HC of
the selective reducing catalyst 15.
[0031] Next, when the bed temperature T.sub.0 of the oxidation
catalyst 12 exceeds the activation temperature TX, HC feed from the
HC feed valve 28 will begin. Fluctuation in the HC feed amount is
indicated as G.sub.I. That is, the HC feed amount G.sub.I is
reduced little by little so that the bed temperature T.sub.0 of the
oxidation catalyst 12 approaches the target temperature smoothly.
The HC feed amount G.sub.I is large, so a large amount of HC will
slip the oxidation catalyst 12, but the more the bed temperature
T.sub.0 of the oxidation catalyst 12 rises, the more the HC amount
oxidized in the oxidation catalyst 12, so, as shown in FIG. 4, the
slipped HC amount W will gradually decrease along with the elapse
of time.
[0032] On the other hand, as the NO.sub.x selective reducing
catalyst 15 is heated by the exhaust gas raised in temperature in
the oxidation catalyst 12, so, as shown by the solid line in FIG.
4, its temperature will rise slower than the oxidation catalyst 12.
When the bed temperature Tn of the NO.sub.x selective reducing
catalyst 15 is lower than the desorption start temperature TF, the
slipped HC amount W will be added to the HC deposition amount
.SIGMA.HC, whereby the deposition amount .SIGMA.HC will gradually
increase. However, when the bed temperature Tn of the NO.sub.x
selective reducing catalyst 15 exceeds the desorption start
temperature TF, the desorption action of the HC from the NO.sub.x
selective reducing catalyst 15 will begin, whereby the HC
deposition amount .SIGMA.HC will gradually decrease.
[0033] Next, when the HC deposition amount .SIGMA.HC is less than
the set value HCX, the feed of HC is stopped. That is, in this
embodiment, the HC amount deposited on the NO.sub.x selective
reducing catalyst 15 is calculated and the feed of HC is stopped
when the calculated HC amount .SIGMA.HC becomes less than the
predetermined set value HCX.
[0034] Note that, the maximum temperature limit which the bed
temperature T.sub.0 of the NO.sub.x selective reducing catalyst 15
can be raised to, when considering heat deterioration, becomes
approximately 650.degree.. Accordingly, in the embodiment of the
present invention, the temperature of the NO.sub.x selective
reducing catalyst 15 at the time of engine startup is increased
within the range of 350.degree. C. to 650.degree. C.
[0035] On the other hand, the change of the bed temperature Tn of
the NO.sub.x selective reducing catalyst 15 shown by the broken
line in FIG. 4 shows the change at the time of conventional
temperature raising control. In the internal combustion engine,
when idling operation is continued during the warm-up operation,
there is a convergence temperature T.sub.f which the temperature of
the NO.sub.x selective reducing catalyst 15 ultimately converges
to. This convergence temperature T.sub.f is approximately
200.degree. C. to 250.degree. C. In a conventional temperature
raising control, the bed temperature Tn of the NO.sub.x selective
reducing catalyst 15, as shown by the broken line, is changed to
smoothly increase towards the convergence temperature T.sub.f.
[0036] As opposed to this, in the present invention, it is learned
that the bed temperature Tn of the NO.sub.x selective reducing
catalyst 15 at the time of engine startup is raised to a
temperature of 350.degree. C. at least 100.degree. C. higher than
the convergence temperature T.sub.f.
[0037] Next, the warm-up control routine shown in FIG. 5 will be
explained. Note that this control routine is executed by
interruption every constant time period.
[0038] Referring to FIG. 5, first, at step 50, the exhaust HC
amount G.sub.0 is calculated. The exhaust HC amount G.sub.0
changing based on the operation state of the engine is stored in
advance in the ROM 32. Next, at step 51, it is judged whether the
bed temperature T.sub.0 of the oxidation catalyst 12 exceeds the
activation temperature TX. When T.sub.0.ltoreq.TF, the routine
proceeds to step 52, where the slipped amount W is made the exhaust
HC amount G.sub.0, then the routine proceeds to step 59.
[0039] As opposed to this, when T.sub.0>TX, the routine proceeds
to step 53, where the HC feed amount G.sub.I is calculated. Next,
at step 54, feed control for the HC from the HC feed valve 28 is
performed. Next, at step 55, the oxidation rate M.sub.0, as shown
in FIG. 3(A), is calculated based on the bed temperature T.sub.0 of
the oxidation catalyst 12. Next, at step 56, it is judged whether
the oxidation rate M.sub.0 is larger than the sum (G.sub.0+G.sub.1)
of the exhaust HC amount G.sub.0 and the fed HC amount G.sub.1.
When M.sub.0.gtoreq.G.sub.0+G.sub.1, the routine proceeds to step
57, where the slipped amount W is made 0, then the routine proceeds
to step 59. As opposed to this, when the
M.sub.0<G.sub.0+G.sub.1, the routine proceeds to step 58, where
the slipped amount is made G.sub.0+G.sub.1-M.sub.0, then the
routine proceeds to step 59.
[0040] At step 59, the desorption rate Md shown in FIG. 3(B) is
calculated based on the bed temperature Tn of the NO.sub.x
selective reducing catalyst 15. Next, at step 60, the slipped
amount W is added to the HC deposition amount .SIGMA.HC and the
desorption rate Md is subtracted from the HC deposition amount
.SIGMA.HC to calculate the HC deposition amount .SIGMA.HC. Next, at
step 61, it is judged whether the HC deposition amount .SIGMA.HC is
still decreasing. When it is still decreasing, the routine proceeds
to step 62, where it is judged whether the HC deposition amount
.SIGMA.HC has become lower than the set value HCX. When
.SIGMA.HC<HCX, the routine proceeds to step 63, where the feed
of HC is stopped.
LIST OF REFERENCES
[0041] 4 . . . intake manifold [0042] 5 . . . exhaust manifold
[0043] 7 . . . exhaust turbocharger [0044] 12, 16 . . . oxidation
catalyst [0045] 13 . . . particulate filter [0046] 15 . . . NOX
selective reducing catalyst [0047] 17 . . . aqueous urea feed valve
[0048] 28 . . . HC feed valve
* * * * *