U.S. patent application number 13/981319 was filed with the patent office on 2014-10-23 for exhaust gas heating method.
The applicant listed for this patent is Mikio Inoue, Kenichi Tsujimoto. Invention is credited to Mikio Inoue, Kenichi Tsujimoto.
Application Number | 20140311124 13/981319 |
Document ID | / |
Family ID | 48745026 |
Filed Date | 2014-10-23 |
United States Patent
Application |
20140311124 |
Kind Code |
A1 |
Tsujimoto; Kenichi ; et
al. |
October 23, 2014 |
EXHAUST GAS HEATING METHOD
Abstract
A method according to the present invention of heating exhaust
gas to be introduced into an exhaust gas purifying device from an
internal combustion engine by heating and igniting fuel supplied
into an exhaust passage from a fuel supply valve includes the steps
of determining a necessity for supplying fuel into the exhaust
passage, setting an amount of fuel to be supplied into the exhaust
passage from the fuel supply valve, the amount being set when it is
judged in the determining step that fuel needs to be supplied into
the exhaust passage, checking an operating state of the engine, and
controlling an air-fuel ratio of exhaust gas such that the air-fuel
ratio falls within an area where amounts of both smoke and HC to be
generated in the exhaust gas are low in the operating state of the
engine checked in the checking step.
Inventors: |
Tsujimoto; Kenichi;
(Mishima-shi, JP) ; Inoue; Mikio; (Susono-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Tsujimoto; Kenichi
Inoue; Mikio |
Mishima-shi
Susono-shi |
|
JP
JP |
|
|
Family ID: |
48745026 |
Appl. No.: |
13/981319 |
Filed: |
January 4, 2012 |
PCT Filed: |
January 4, 2012 |
PCT NO: |
PCT/JP2012/000006 |
371 Date: |
July 24, 2013 |
Current U.S.
Class: |
60/274 |
Current CPC
Class: |
F02D 41/029 20130101;
F01N 3/035 20130101; F02B 37/00 20130101; F01N 9/002 20130101; F01N
3/0253 20130101; F01N 3/208 20130101; F01N 13/0097 20140603; F01N
2900/08 20130101; F01N 2240/14 20130101; F01N 2900/0408 20130101;
F01N 2900/1402 20130101; F01N 2610/03 20130101; F01N 3/0231
20130101; F02D 2250/38 20130101; F01N 3/0256 20130101; Y02T 10/47
20130101; F01N 2900/1404 20130101; F01N 2430/06 20130101; Y02T
10/40 20130101 |
Class at
Publication: |
60/274 |
International
Class: |
F01N 3/20 20060101
F01N003/20 |
Claims
1.-8. (canceled)
9. A method of heating exhaust gas to be introduced into an exhaust
gas purifying device from an internal combustion engine by
supplying fuel into an exhaust passage from a fuel supply valve
disposed upstream of the exhaust gas purifying device in an exhaust
pipe upstream, and then by heating and igniting the fuel supplied
into the exhaust passage, the method comprising steps of:
determining a necessity for supplying fuel into the exhaust
passage; setting an amount of fuel to be supplied into the exhaust
passage from the fuel supply valve, the amount being set when it is
judged in the determining step that fuel needs to be supplied into
the exhaust passage; checking an operating state of the internal
combustion engine; and controlling an air-fuel ratio of exhaust gas
to be released into the exhaust passage from a combustion chamber
of the internal combustion engine such that the air-fuel ratio
falls within an area where amounts of both smoke and HC to be
generated in the exhaust gas flowing through the exhaust passage
are low in the operating state of the internal combustion engine
checked in the checking step.
10. The method as claimed in claim 9, wherein the controlling step
includes at least one of steps of: setting an amount of fuel to be
injected into the combustion chamber of the internal combustion
engine from a fuel injection valve such that an amount of oxygen to
be released into the exhaust passage from the combustion chamber of
the internal combustion engine is reduced; setting an opening
degree of a throttle valve; and setting an opening degree of an EGR
control valve.
11. The method as claimed in claim 10, wherein the step of setting
the fuel supply amount includes a step of correcting the fuel
supply amount set in the step of setting the fuel supply amount by
reducing the fuel supply amount in accordance with the fuel
injection amount set in the step of setting the fuel injection
amount.
12. The method as claimed in claim 10, wherein the controlling step
includes the step of setting the fuel injection amount, the
checking step includes a step of obtaining a temperature of the
exhaust gas, and the method further comprising a step of correcting
the fuel injection amount set in the step of setting the fuel
injection amount in accordance with the temperature of the exhaust
gas obtained in the step of obtaining the temperature of the
exhaust gas.
13. The method as claimed in claim 12, wherein in the step of
correcting the fuel injection amount, the fuel injection amount set
in the step of the fuel injection amount is corrected by increasing
the fuel injection amount during an operating state in which the
temperature of the exhaust gas is high, while the fuel injection
amount set in the step of setting the fuel injection amount is
corrected by reducing the fuel injection amount during an operating
state in which the temperature of the exhaust gas is low.
14. The method as claimed in claim 10, wherein the controlling step
includes the step of setting the fuel injection amount, the
checking step includes a step of obtaining an air-fuel ratio of the
exhaust gas to be released into the exhaust passage from the
combustion chamber of the internal combustion engine, and the
method further comprising a step of correcting the fuel injection
amount set in the step of setting the fuel injection amount in
accordance with the air-fuel ratio of the exhaust gas obtained in
the step of obtaining the air-fuel ratio of the exhaust gas.
15. The method as claimed in claim 14, wherein in the step of
correcting the fuel injection amount, the fuel injection amount set
in the step of setting the fuel injection amount is corrected by
increasing the fuel injection amount when the air-fuel ratio of the
exhaust gas is within a lean region, while the fuel injection
amount set in the step of setting the fuel injection amount is
corrected by reducing the fuel injection amount when the air-fuel
ratio of the exhaust gas is within a rich region.
16. The method as claimed in claim 9, wherein the exhaust gas
purifying device includes a DPF, and the step of setting the fuel
injection amount includes a step of correcting the fuel injection
amount set in the step of setting the fuel injection amount by
reducing the fuel injection amount when it is judged that fuel
needs to be supplied into the exhaust passage in the determining
step during a regeneration process of the DPF.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a national phase application of
International Application No. PCT/JP2012/000006, filed Jan. 4,
2012, the content of which is incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to a method of heating exhaust
gas to be introduced into an exhaust gas purifying device by
supplying fuel into an exhaust passage from a fuel supply valve
disposed upstream of the exhaust gas purifying device in an exhaust
pipe, and then by heating and igniting the fuel.
BACKGROUND ART
[0003] In recent years, coping with strict emission standards set
on internal combustion engines has lead to a necessity for
facilitating the activation of an exhaust gas purifying device at
the start of its internal combustion engine, maintaining its active
state during the operation of the internal combustion engine, and
so on. In this respect, Japanese Patent Laid-Open No. 2010-084710
and the like have proposed internal combustion engines in which an
exhaust gas heating device is installed upstream of an exhaust gas
purifying device in an exhaust passage. This exhaust gas heating
device generates heating gas within exhaust gas and supplies this
generated heating gas into the exhaust gas purifying device given
at the downstream side to thereby facilitate the activation of the
exhaust gas purifying device and maintain its active state. To do
so, the exhaust gas heating device generally includes a fuel supply
valve which adds fuel into the exhaust passage, and an igniter such
as a glow plug which heats and ignites the fuel to generate heating
gas. Meanwhile, in the conventional exhaust gas heating device
disclosed in Japanese Patent Laid-Open No. 2010-084710, the igniter
is disposed in proximity to the fuel supply valve. Hence, the fuel
supplied into the exhaust passage from the fuel supply valve and
the exhaust gas may fail to be mixed sufficiently, leading to
incomplete combustion of the ignited fuel in some cases. To solve
this, Japanese Patent Laid-Open No. 2010-084710 proposes an idea
that a receiving plate which receives the fuel injected from the
fuel supply valve and scatters that fuel inside the exhaust passage
is installed in the exhaust passage.
CITATION LIST
Patent Literature
[0004] PTL 1: Japanese Patent Laid-Open No. 2010-084710
SUMMARY OF INVENTION
Technical Problem
[0005] The fuel addition into the exhaust passage differs from the
fuel injection into the combustion chamber of the engine in that
the injection pressure of the fuel tends to be low and the pressure
and temperature thereof tend to be absolutely low as well. This
retards the fuel's vaporization and causes residual droplets of the
fuel within the exhaust gas. Thus, the fuel supplied into the
exhaust passage may fail to be well combusted depending upon the
operating state of the internal combustion engine, which in turn
leads to a possibility of generating a large amount of smoke (or
soot). For example, when the exhaust gas flowing through the
exhaust passage has a high oxygen concentration or a high exhaust
gas temperature, the combustion rate of the fuel during ignition by
the igniter tends to increase, thus generating a large amount of
smoke. Consequently, unburned fuel flows to the downstream side as
it is, resulting in the unburned fuel adhering to a catalytic
converter forming part of the exhaust gas purifying device and the
fuel passing therethrough, thereby possibly generating white
smoke.
[0006] In the conventional exhaust gas heating device disclosed in
Japanese Patent Laid-Open No. 2010-084710, the igniter is disposed
in proximity to the fuel supply valve, and hence the fuel supplied
into the exhaust passage from the fuel supply valve and the exhaust
gas may fail to be mixed sufficiently, leading to incomplete
combustion of the ignited fuel in some cases. This in turn causes
the generation of a large amount of smoke and clogging of the
catalytic converter forming part of the exhaust gas purifying
device, which is troublesome. As a result, there arises a problem
that the catalytic converter needs to undergo frequent regeneration
processes, deteriorating the fuel efficiency due to the consumption
of fuel for the frequent regeneration processes.
[0007] An object of the present invention is to provide a method
capable of always suppressing the generation of smoke and HC to a
small amount when fuel is supplied into an exhaust passage from a
fuel supply valve disposed upstream of an exhaust gas purifying
device in an exhaust pipe, and then by heating and igniting the
fuel to heat exhaust gas to be introduced into the exhaust gas
purifying device.
Solution to Problem
[0008] A method according to the present invention of heating
exhaust gas to be introduced into an exhaust gas purifying device
from an internal combustion engine by supplying fuel into an
exhaust passage from a fuel supply valve disposed upstream of the
exhaust gas purifying device in an exhaust pipe upstream, and then
by heating and igniting the fuel supplied into the exhaust passage,
comprises the steps of determining a necessity for supplying fuel
into the exhaust passage, setting an amount of fuel to be supplied
into the exhaust passage from the fuel supply valve, the amount
being set when it is judged in the determining step that fuel needs
to be supplied into the exhaust passage, checking an operating
state of the internal combustion engine, and controlling an
air-fuel ratio of exhaust gas to be released into the exhaust
passage from a combustion chamber of the internal combustion engine
such that the air-fuel ratio falls within an area where amounts of
both smoke and HC to be generated in the exhaust gas flowing
through the exhaust passage are low in the operating state of the
internal combustion engine checked in the checking step.
[0009] The combustion state of the fuel in the exhaust gas heating
device varies among a state where the combustion is good, a state
where smoke is easily generated, and a state where unburned fuel
easily remain, depending upon the operating state of the internal
combustion engine. When the exhaust gas heating device of the
present invention is used to heat the exhaust gas, the amount of
the fuel to be injected into the combustion chamber of the internal
combustion engine from the fuel injection valve is controlled
according, for example, to states such as the temperature of the
exhaust gas, the exhaust flow rate, and the oxygen concentration of
the exhaust gas so as to reduce the amount of the oxygen to be
released into the exhaust passage from the combustion chamber of
the internal combustion engine. Accordingly, the operating state is
set such that it is difficult for smoke and unburned fuel to be
contained in the exhaust gas flowing downstream of the exhaust gas
heating device in the exhaust passage, thereby allowing the
maintenance of a good combustion state for the fuel to be supplied
into the exhaust passage.
[0010] In the exhaust gas heating method according to the present
invention, the controlling step may include at least one of the
steps of setting an amount of fuel to be injected into the
combustion chamber of the internal combustion engine from a fuel
injection valve such that an amount of oxygen to be released into
the exhaust passage from the combustion chamber of the internal
combustion engine is reduced, setting an opening degree of a
throttle valve, and setting an opening degree of an EGR control
valve. Here, it is effective that the step of setting the fuel
supply amount include a step of correcting the fuel supply amount
set in the step of setting the fuel supply amount by reducing the
fuel supply amount in accordance with the fuel injection amount set
in the step of setting the fuel injection amount.
[0011] The controlling step may include the step of setting the
fuel injection amount, the checking step may include a step of
obtaining a temperature of the exhaust gas, and the exhaust gas
heating method may further include a step of correcting the fuel
injection amount set in the step of setting the fuel injection
amount in accordance with the temperature of the exhaust gas
obtained in the step of obtaining the temperature of the exhaust
gas. Here it is effective that, in the step of correcting the fuel
injection amount, the fuel injection amount set in the step of
setting the fuel injection amount be corrected by increasing the
fuel injection amount during an operating state in which the
temperature of the exhaust gas is high, while the fuel injection
amount set in the step of setting the fuel injection amount is
corrected by reducing the fuel injection amount during an operating
state in which the temperature of the exhaust gas is low.
[0012] The controlling step may include the step of setting the
fuel injection amount, the checking step may include a step of
obtaining an air-fuel ratio of the exhaust gas to be released into
the exhaust passage from the combustion chamber of the internal
combustion engine, and the exhaust gas heating method may further
comprise a step of correcting the fuel injection amount set in the
step of setting the fuel injection amount in accordance with the
air-fuel ratio of the exhaust gas obtained in the step of obtaining
the air-fuel ratio of the exhaust gas. Here, it is effective that
in the step of correcting the fuel injection amount, the fuel
injection amount set in the step of setting the fuel injection
amount be corrected by increasing the fuel injection amount when
the air-fuel ratio of the exhaust gas is within a lean region,
while the fuel injection amount set in the step of setting the fuel
injection amount is corrected by reducing the fuel injection amount
when the air-fuel ratio of the exhaust gas is within a rich
region.
[0013] Preferably, the exhaust gas purifying device includes a DPF
(Diesel Particulate Filter), and the step of setting the fuel
injection amount includes a step of correcting the fuel injection
amount set in the step of setting the fuel injection amount by
reducing the fuel injection amount when it is judged that fuel
needs to be supplied into the exhaust passage in the determining
step during a regeneration process of the DPF.
Advantageous Effects of Invention
[0014] The flow rate of the exhaust gas flowing through the exhaust
passage largely varies depending upon the operating state of the
internal combustion engine. Thus, it is extremely difficult to
perform accurate control on the combustion of the fuel supplied
into the exhaust passage from the fuel supply valve without being
affected by such variations in the flow rate of the exhaust gas.
However, the present invention controls the air-fuel ratio of the
exhaust gas which is released into the exhaust passage from the
combustion chamber of the internal combustion engine when the fuel
is supplied into the exhaust passage. Thus, the air-fuel ratio can
fall within an area where the amounts of smoke and HC to be
generated are both low. For example, when the exhaust gas heating
device heats the exhaust gas in a state where the fuel injection
into the combustion chamber of the internal combustion engine is
stopped, such as during deceleration of the vehicle, fuel is
supplied into the combustion chamber of the internal combustion
engine without combustion and is mixed with the exhaust gas. This
lowers the oxygen concentration of the exhaust gas, thereby making
it possible to suppress the generation of smoke.
[0015] When the controlling step includes at least one of the steps
of setting the fuel injection amount, setting the throttle valve
opening degree, and setting the EGR control valve opening degree,
the air-fuel ratio of the exhaust gas to be released into the
exhaust passage from the combustion chamber of the internal
combustion engine can be controlled rapidly and accurately.
[0016] When the fuel supply amount set in the step of setting the
fuel supply amount is corrected by reducing it in accordance with
the fuel injection amount set in the step of setting the fuel
injection amount, the release of unburned fuel can further be
suppressed.
[0017] Similarly, the release of unburned fuel can further be
suppressed as well when the fuel injection amount set in the step
of setting the fuel injection amount is corrected according to the
exhaust gas temperature obtained in the step of obtaining the
exhaust gas temperature. Specifically, the fuel injection amount is
corrected by increasing it during an operating state in which the
exhaust gas temperature is high, while the fuel injection amount
set in the step of setting the fuel injection amount is corrected
by reducing it during an operating state in which the exhaust gas
temperature is low. In this way, the generation of smoke can be
suppressed together with the suppression of unburned fuel.
[0018] When the exhaust gas heating method further includes the
step of correcting the fuel injection amount set in the step of
setting the fuel injection amount in accordance with the air-fuel
ratio of the exhaust gas obtained in the step of obtaining the
air-fuel ratio of the exhaust gas, an increase in the amount of
unburned fuel can further be suppressed. Specifically, the fuel
injection amount is corrected by increasing it in a case where the
air-fuel ratio of the exhaust gas is within a lean region, while
the fuel injection amount is corrected by reducing it in a case
where the air-fuel ratio of the exhaust gas is within a rich
region. In this way, the generation of smoke can be suppressed
together with the suppression of unburned fuel.
[0019] When the exhaust gas purifying device includes a DPF, and
the set fuel supply amount is corrected by reducing it in a case
where fuel is supplied into the exhaust passage during a
regeneration process of the DPF, the fuel consumption can be
suppressed. Moreover, since the DPF is in the regeneration process,
smoke generated can be removed through oxidation thereof.
Furthermore, the burnability of PM (Particulate Matter) can be
enhanced along with an increase in the oxygen concentration of the
exhaust gas flowing into the DPF.
BRIEF DESCRIPTION OF DRAWINGS
[0020] FIG. 1 is a conceptual diagram of an embodiment of an engine
system which is capable of implementing an exhaust gas heating
method of the present invention;
[0021] FIG. 2 is a control block diagram of a main part of the
embodiment shown in FIG. 1;
[0022] FIG. 3 is a graph schematically showing the relationship
between the amount of fuel injected into a cylinder and the amounts
of smoke and HC generated;
[0023] FIG. 4 is a graph schematically showing the relationship
between the exhaust gas temperature and an area to be selected for
a target air-fuel ratio;
[0024] FIG. 5 is a graph schematically showing the relationships
between the exhaust gas temperature and oxygen concentration, and
an area involving the generation of a large amount of smoke, an
area involving the generation of a large amount of HC, and a
preferable combustion area;
[0025] FIG. 6 is a graph schematically showing the relationships
between the exhaust gas temperature and air-fuel ratio, and an area
involving the generation of a large amount of smoke and a
preferable combustion area;
[0026] FIG. 7 is graph schematically showing the relationships
between the intake flow rate and air-fuel ratio, and an area
involving the generation of a large amount of smoke and a
preferable combustion area;
[0027] FIG. 8 is a flowchart showing a procedure related to fuel
addition control of the embodiment;
[0028] FIG. 9 is a flowchart showing a specific procedure in a
fuel-injection-amount setting step in FIG. 8;
[0029] FIG. 10 is a flowchart showing a specific procedure in a
fuel-addition-amount setting step in FIG. 8; and
[0030] FIG. 11 is a flowchart showing a specific procedure in an
injection-amount air-fuel ratio correcting step in FIG. 8.
DESCRIPTION OF EMBODIMENTS
[0031] An embodiment of a compression-ignition internal combustion
engine capable of implementing an exhaust gas heating method of the
present invention will be described in detail with reference to
FIGS. 1 to 11. Note that the present invention is not limited to
this embodiment, and its configuration can be changed freely
according to the specifications, characteristics, and the like
required.
[0032] FIG. 1 schematically shows a main part of an engine system
of this embodiment, and FIG. 2 shows a control block thereof. It is
to be noted that a valve gear and the like for air intake and
exhaust to and from an engine 10 are omitted in FIG. 1 for
simplicity and convenience.
[0033] The engine 10 of this embodiment is an internal combustion
engine of a compression ignition type which causes spontaneous
ignition of diesel oil, serving as fuel, by injecting the diesel
oil from a fuel injection valve 11 directly into a combustion
chamber 10a being in a compressed state.
[0034] An ECU (Electronic Control Unit) 13 controls the amount of
fuel to be supplied into the combustion chamber 10a from the fuel
injection valve 11 (hereinafter, referred to as the fuel injection
amount) and the timing of the injection on the basis of the
vehicle's operating state including the amount of the driver's
depression of an accelerator pedal 12. An accelerator opening
sensor 14 detects this amount of depression of the accelerator
pedal 12 (hereinafter, referred to as the accelerator opening
degree) GA and outputs the detected information to the ECU 13.
[0035] In this embodiment, two injection modes are set for the fuel
injection into the combustion chamber 10a from the fuel injection
valve 11. Specifically, one is an engine driving mode in which fuel
is subjected to compression ignition and combusted inside the
combustion chamber 10a to obtain an output of the engine 10. The
other is an exhaust gas heating mode in which injected fuel is not
ignited inside the combustion chamber 10a but is flowed as it is
into a later-described exhaust passage 23a. FIG. 3 schematically
shows the relationship between the fuel injection amount and the
amounts of smoke and unburned HC in the exhaust gas in the exhaust
gas heating mode. As is obvious from FIG. 3, there is a tendency
that the generated smoke increases as the fuel injection amount
decreases, and conversely the amount of unburned HC increases as
the fuel injection amount increases. Thus, the smoke and HC can
both be suppressed to a small amount by setting the fuel injection
amount within an appropriate smoke/HC reduction range given in FIG.
3.
[0036] In this embodiment, when a fuel injection process is needed
during the exhaust gas heating mode, the fuel injection amount is
set to F.sub.M which is situated substantially at the center of the
smoke/HC reduction range. However, when a PM burning rate V.sub.B
is higher than a rate V.sub.D of PM deposition onto a DPF 26b of a
later-described exhaust gas purifying device 26 during a
regeneration process of the DPF 26b, smoke will be processed in the
DPF 26b even if a large amount of smoke is generated. Thus, in this
case, the fuel injection amount is corrected by reducing it by
.DELTA.F.sub.M so as to suppress unnecessary fuel consumption and
also suppress the generation of unburned HC.
[0037] Moreover, the amounts of smoke and unburned HC to be
generated vary when an exhaust gas temperature T.sub.E is too low
or too high. Thus, the fuel injection amount is further corrected
according to the exhaust gas temperature T.sub.E. More
specifically, when the exhaust gas temperature T.sub.E is below a
preset first threshold temperature T.sub.L, the amount of smoke to
be generated is highly likely to decrease, and therefore the fuel
injection amount is corrected by reducing it by .DELTA.F.sub.T,
thereby suppressing an increase in the amount of unburned HC to be
generated. On the other hand, when the exhaust gas temperature
T.sub.E is higher than a preset second threshold temperature
T.sub.M, the amount of smoke to be generated is highly likely to
increase, and therefore the fuel injection amount is corrected by
increasing it by .DELTA.F.sub.T, thereby suppressing an increase in
the amount of smoke to be generated.
[0038] Likewise, in this embodiment, the amounts of smoke and
unburned HC to be generated vary also when an actual air-fuel ratio
R.sub.N differs greatly from a target air-fuel ratio R.sub.T by,
for example, .+-..DELTA.R. Thus, the fuel injection amount is
further corrected according to the air-fuel ratio R.sub.N. More
specifically, when the air-fuel ratio R.sub.N is leaner by .DELTA.R
than the target air-fuel ratio R.sub.T, smoke is easily generated,
and therefore the fuel injection amount is corrected by increasing
it by .DELTA.F.sub.R. On the other hand, when the air-fuel ratio
R.sub.N is richer by .DELTA.R than the target air-fuel ratio
R.sub.T, unburned HC is easily generated, and therefore the fuel
injection amount is corrected by reducing it by .DELTA.F.sub.R.
[0039] Note that instead of the fuel-injection-amount correcting
processes described above or in addition to the
fuel-injection-amount correcting processes, at least one of the air
intake amount and the EGR amount may be controlled. In this way
too, a similar advantageous effect can be achieved.
[0040] The ECU 13 includes an operating status determining section
13a, a fuel injection setting section 13b, a fuel injection valve
driving section 13c, a PM deposition rate calculating section 13d,
and a PM burning rate calculating section 13e. The operating status
determining section 13a checks the operating state of the vehicle
on the basis of information from the accelerator opening sensor 14,
later-described various sensors, and the like. The fuel injection
setting section 13b sets the amount of fuel to be injected from the
fuel injection valve 11 and the timing of the injection on the
basis of the result of the determination by the operating status
determining section 13a. Note that the fuel injection setting
section 13b basically sets the fuel injection amount to F.sub.M
when the exhaust gas heating mode is selected. The fuel injection
valve driving section 13c controls the actuation of the fuel
injection valve 11 such that fuel is injected from the fuel
injection valve 11 by the amount and at the timing set by the fuel
injection setting section 13b. The PM deposition rate calculating
section 13d calculates the PM deposition rate V.sub.D during the
DPF regeneration process, and the PM burning rate calculating
section 13e calculates the PM burning rate V.sub.B during the DPF
regeneration process. These calculations are performed by use of
well-known methods.
[0041] In a cylinder head 15 forming therein an intake port 15a and
an exhaust port 15b each in communication with the combustion
chamber 10a, the unillustrated valve gear is installed which
includes an intake valve 16a and an exhaust valve 16b which open
and close the intake port 15a and the exhaust port 15b,
respectively. The aforementioned fuel injection valve 11 is
installed in this cylinder head 15 as well.
[0042] In an intake pipe 17 joined to the cylinder head 15 in
communication with the intake port 15a and defining an intake
passage 17a together with the intake port 15a, a throttle valve 19
is installed with which to adjust the opening degree of the intake
passage 17a with a throttle actuator 18.
[0043] The aforementioned ECU 13 further includes a throttle
opening setting section 13f and an actuator driving section 13g.
The throttle opening setting section 13f sets the opening degree of
the throttle valve 19 on the basis of the result of the checking by
the aforementioned operating status determining section 13a. The
actuator driving section 13g controls the actuation of the throttle
actuator 18 such that the throttle valve 19 is set at the opening
degree set by the throttle opening setting section 13f.
[0044] In a cylinder block 21 in which a piston 20a reciprocates, a
crank angle sensor 22 is mounted which detects the rotational phase
of a crankshaft 20c, i.e. the crank angle and outputs it to the ECU
13. The piston 20a is joined to the crankshaft 20c through a
connecting rod 20b.
[0045] Based on the information from this crank angle sensor 22,
the operating status determining section 13a of the ECU 13 checks
the rotational phase of the crankshaft 20c and the engine speed as
well as the travel speed of the vehicle and the like on a real-time
basis.
[0046] Installed in the engine 10 are an EGR system 24, a exhaust
turbocharger 25, the exhaust gas purifying device 26, and an
exhaust gas heating device 27. The EGR system 24 introduces part of
the exhaust gas, flowing inside the exhaust passage 23a, back into
the intake passage 17a.
[0047] The EGR system 24 for primarily reducing nitrogen oxides in
the exhaust gas includes an EGR pipe 28 which defines an EGR
passage 28a and an EGR control valve 29 which is provided to this
EGR pipe 28 to control the flow rate of the exhaust gas flowing
through the EGR passage 28a. The EGR pipe 28 is in communication at
one end with an exhaust pipe 23 defining the exhaust passage 23a
together with the exhaust port 15b, and is in communication at the
other end with a portion of the intake passage 17a between the
intake port 15a and a surge tank 17b disposed downstream of the
above-mentioned throttle valve 19.
[0048] In this embodiment, when the operating status determining
section 13a of the ECU 13 determines that the vehicle equipped with
the engine 10 is within a preset EGR operation region, the EGR
amount setting section 13h of the ECU 13 sets the opening degree of
the EGR control valve 29 in accordance with the operating state of
the vehicle of that moment. The EGR valve driving section 13i of
the ECU 13 controls the EGR control valve 29 at the opening degree
set by the EGR amount setting section 13h. Besides the above case,
the EGR valve driving section 13i basically drives the EGR control
valve 29 such that the EGR control valve 29 shifts to a closed
state to close the EGR passage 28a.
[0049] The exhaust turbocharger (hereinafter, simply referred to as
the supercharger) 25 utilizes the kinetic energy of the exhaust gas
flowing through the exhaust passage 23a to supercharge the
combustion chamber 10a, thereby enhancing the air charging
efficiency. The main part of the supercharger 25 of this embodiment
is formed of an intake turbine 25a and an exhaust turbine 25b which
rotates together with this intake turbine 25a. The intake turbine
25a is installed in an intermediate portion of the intake pipe 17
which is located upstream of the throttle valve 19. The exhaust
turbine 25b is installed in an intermediate portion of the exhaust
pipe 23 joined to the cylinder head 15 in communication with the
exhaust port 15b. In this embodiment, an intercooler 25c is
installed in an intermediate portion of the intake passage 17a
between the intake turbine 25a and the surge tank 17b so as to
lower the temperature of the intake air heated by heat transfer
from the exhaust turbine 25b side through the intake turbine
25a.
[0050] An air flow meter 30 is provided upstream of the intake
turbine 25a of the supercharger 25 in the intake pipe 17 and
detects the flow rate of the intake air flowing through the intake
passage 17a of this portion and outputs it to the ECU 13. Note that
the one end of the EGR pipe 28 mentioned above is connected to a
portion of the exhaust pipe 23 upstream of the exhaust turbine
25b.
[0051] The exhaust gas purifying device 26 for detoxifying toxic
substances generated by the combustion of an air-fuel mixture in
the combustion chamber 10a is installed in a portion of the exhaust
pipe 23 defining a portion of the exhaust passage 23a downstream of
the exhaust turbine 25b of the supercharger 25. The exhaust gas
purifying device 26 of this embodiment includes an oxidation
catalytic converter 26a and the DPF (Diesel Particulate Filter) 26b
both being well known. Note that NOX (Nitrogen Oxides) catalytic
converter or the like may further be included.
[0052] In this exhaust gas purifying device 26, a catalyst
temperature sensor 31 is installed which detects a temperature
T.sub.C thereof (hereinafter, referred to as the catalyst
temperature) and outputs it to the ECU 13. Moreover, an exhaust gas
temperature sensor 32 is mounted upstream of the exhaust gas
purifying device 26 and downstream of the exhaust gas heating
device 27 in the exhaust pipe 23. This exhaust gas temperature
sensor 32 detects a temperature T.sub.E of the exhaust gas flowing
through a portion of the exhaust passage 23a immediately before the
exhaust gas purifying device 26 and outputs the detected
information to the ECU 13.
[0053] Based on the information from the catalyst temperature
sensor 31 and the exhaust gas temperature sensor 32, the ECU 13 of
this embodiment determines the necessity for actuating the exhaust
gas heating device 27, i.e. whether or not fuel needs to be
supplied. The ECU 13 determines that fuel needs to be supplied
normally when the catalyst temperature T.sub.C is or is expected to
be lower than a reference being the lowest possible temperature for
the oxidation catalyst 26a to maintain its active state. However,
some other conventionally well-known determining method can be
employed optionally.
[0054] The exhaust gas heating device 27, the actuation of which is
controlled based on the operating state of the vehicle and the
state of the exhaust gas purifying device 26, is configured to heat
the exhaust gas to be introduced into the exhaust gas purifying
device 26 from the engine 10 to thereby rapidly activate the
exhaust gas purifying device 26 and maintain its active state. The
exhaust gas heating device 27 of this embodiment includes a fuel
supply valve 27a and a glow plug 27b.
[0055] The fuel supply valve 27a for supplying fuel to activate the
exhaust gas purifying device 26 or to maintain its active state is
mounted to the exhaust pipe 23 in such a way as to face a portion
of the exhaust passage 23a located downstream of the exhaust
turbine 25b of the supercharger 25 but upstream of the exhaust gas
purifying device 26. When the exhaust gas purifying device 26 comes
in need of heating, or activation, fuel is supplied from this fuel
supply valve 27a into the exhaust passage 23a by actuating the
exhaust gas heating device 27 basically in a low-load operating
state. The glow plug 27b for igniting the fuel supplied from the
fuel supply valve 27a into the exhaust passage 23a has a heating
portion on its tip side disposed downstream of the fuel supply
valve 27a in the exhaust passage 23a. The fuel from the fuel supply
valve 27a is supplied toward this heating portion. The glow plug
27b is connected to an unillustrated on-vehicle power supply
through an unillustrated switch whose ON and OFF are controlled by
the ECU 13. A glow plug driving section 13m of the ECU 13 switches
the ON and OFF of the actuation of the glow plug 27b on the basis
of information on the drive of the fuel supply valve 27a from a
fuel supply valve driving section 13l.
[0056] The ECU 13 further includes a target air-fuel ratio setting
section 13j, a fuel supply setting section 13k, and the fuel supply
valve driving section 13l.
[0057] The target air-fuel ratio setting section 13j sets the
target air-fuel ratio R.sub.T of the exhaust gas which flows into
the exhaust gas purifying device 26 when the exhaust gas is to be
heated in an exhaust gas heating process. In this embodiment, an
air-fuel ratio allowing efficient fuel combustion in the exhaust
gas heating process, i.e. the target air-fuel ratio RT is set based
on the exhaust gas temperature T.sub.E detected by the exhaust gas
temperature sensor 32 and the oxygen concentration of the exhaust
gas flowing into the exhaust gas heating device 27 from the
combustion chamber 10a. FIG. 4 schematically shows the relationship
between the exhaust gas temperature T.sub.E and the air-fuel ratio.
FIGS. 5 to 7 schematically show the relationships between the
intake flow rate, air-fuel ratio, oxygen concentration and exhaust
gas temperature T.sub.E and regions allowing efficient fuel
combustion in the exhaust gas heating process (hereinafter,
referred to as the preferable combustion regions for convenience).
Note that while the oxygen concentration is calculated by the
operating status determining section 13a of the ECU, a well-known
O.sub.2 sensor may be installed upstream of the exhaust gas heating
device 27 in the exhaust passage 23a. The preferable combustion
region is a region enclosed by a dashed line in each of FIGS. 5 to
7. By the target air-fuel ratio setting section 13j, a single value
of the target air-fuel ratio R.sub.T is set to such a value as to
fall within each of these regions enclosed by the dashed line.
[0058] The fuel supply setting section 13k sets the amount of fuel
to be supplied into the exhaust passage 23a from the fuel supply
valve 27a. More specifically, based on the difference between a
target catalyst temperature T.sub.T and the catalyst temperature
T.sub.C detected by the catalyst temperature sensor 31, the fuel
supply setting section 13k calculates the amount of fuel to be
supplied into the exhaust passage 23a in the exhaust gas heating
process for heating the exhaust gas, i.e. a target fuel supply
amount F.sub.T. In general, selected as the target catalyst
temperature T.sub.T is the lowest possible temperature for the
oxidation catalyst 26a to be in an active state. The fuel supply
setting section 13k also sets an amount F.sub.U of fuel to be
supplied into the exhaust passage 23a in a single current
application to the fuel supply valve 27a (hereinafter, referred to
as the unit supply amount), as well as the cycle of the current
application (hereinafter, referred to as the supply cycle) t.sub.P.
The unit supply amount F.sub.U is set based on an exhaust flow rate
which is based on the information from the air flowmeter 30.
Basically, the larger the exhaust flow rate is, the larger the unit
supply amount F.sub.U is set. The supply cycle t.sub.P is set such
that adding the set unit supply amount F.sub.U of fuel into the
exhaust passage 23a results in the aforementioned target air-fuel
ratio R.sub.T.
[0059] Note that in a case where the fuel addition from the fuel
supply valve 27a and the fuel injection from the fuel injection
valve 11 are to be performed simultaneously, at least one of the
target fuel supply amount F.sub.T and the unit supply amount
F.sub.U is corrected by reducing it in accordance with the amount
of the fuel to be injected from the fuel injection valve 27a.
Moreover, in a case where the actual air-fuel ratio R.sub.N differs
from the target air-fuel ratio R.sub.T, air-fuel ratio control is
performed to make the actual air-fuel ratio R.sub.N match the
target air-fuel ratio R.sub.T, and at least one the fuel injection
amount, the air intake amount, and the EGR amount is corrected if
necessary.
[0060] The fuel supply valve driving section 13l controls the
actuation of the fuel supply valve 27a such that fuel is supplied
into the exhaust passage 23a by the unit supply amount at the
supply cycle set by the fuel supply setting section 13k.
[0061] In this embodiment, the operating status determining section
13a calculates the air-fuel ratio R.sub.N of the exhaust gas
immediately before flowing into the exhaust gas purifying device 26
on the basis of the air intake amount detected by the air flow
meter 30, the fuel injection amount of the fuel injection valve 11,
and the fuel supply amount of the fuel supply valve 27a.
Alternatively, an air-fuel ratio sensor can be disposed downstream
of the exhaust gas heating device 27 and upstream of the exhaust
gas purifying device 26 in the exhaust passage 23a, and the
air-fuel ratio R.sub.N can be detected by use of a detection signal
from the air-fuel ratio sensor.
[0062] As described, by introducing exhaust gas containing unburned
fuel into the exhaust gas heating device 27, it is possible to
minimize the concentration of the oxygen contained in the exhaust
gas sent out to the exhaust gas heating device 27 from the
combustion chamber 10a of the engine 10, and thereby to reduce the
amount of smoke to be generated.
[0063] The ECU 13 of this embodiment is a well-known one-chip
microprocessor and includes a CPU, a ROM, a RAM, a nonvolatile
memory, an I/O interface, and the like which are connected to each
other by an unillustrated data bus. This ECU 13 performs
predetermined arithmetic processing on the basis of the detection
signals from the above-mentioned sensors 14, 22, 31, and 32, air
flow meter 30, and the like so that the engine 10 can operate
smoothly. Moreover, the ECU 13 controls the actuations of the fuel
injection valve 11, the throttle valve 19, the EGR control valve
29, the fuel supply valve 27a, the glow plug 27b, and the like in
accordance with a preset program.
[0064] Accordingly, the intake air supplied into the combustion
chamber 10a through the intake passage 17a form an air-fuel mixture
together with the fuel injected into the combustion chamber 10a
from the fuel injection valve 11. Then, normally, the air-fuel
mixture undergoes spontaneous ignition and combustion immediately
before the piston 20a reaches top dead center of the compression
stroke. The resultant exhaust gas generated passes through the
exhaust gas purifying device 26 and is released in a detoxified
state into the atmosphere through the exhaust pipe 23.
[0065] Meanwhile, the exhaust gas heating process of the present
invention is performed while the engine 10 is in operation, in
accordance with the state of the exhaust gas purifying device 26.
Using the flowcharts in FIGS. 8 to 11, a procedure for actuating
the exhaust gas heating device 27 in this embodiment will be
described. First, in step S11, it is determined whether or not fuel
needs to be supplied. If it is judged in this step that fuel needs
to be supplied, that is, the exhaust gas purifying device 26 needs
to be activated, the procedure proceeds to step S12, where it is
judged whether or not the current operating state is within an area
involving the generation of a large amount of smoke. If it is
judged in this step that the current operating state is within the
generation area of a large amount of smoke, that is, it is
desirable to inject fuel into the combustion chamber 10a from the
fuel injection valve 11, the procedure proceeds to step S13, where
a fuel injection amount setting process is performed.
[0066] Specifically, in step S131 in FIG. 9, the fuel injection
amount is set to F. Then, in step S132, it is determined whether or
not the DPF 26b is in a regeneration process. If it is judged in
this step that the DPF 26b is in a regeneration process, the
procedure proceeds to step S133, where it is determined whether or
not the PM burning rate V.sub.B is equal to or greater than the PM
deposition rate V.sub.D. If it is judged in this step that the PM
burning rate V.sub.B is equal to or greater than the PM deposition
rate V.sub.D, that is, PM is decreasing due to the regeneration
process of the DPF 26b, the procedure proceeds to step S134. There,
the fuel injection amount F.sub.M set in the step S131 is corrected
by reducing it by .DELTA.F.sub.M, thus suppressing an increase in
the amount of unburned HC to be generated.
[0067] Thereafter, in step S135, it is determined whether or not
the exhaust gas temperature T.sub.E is equal to or higher than the
first threshold temperature T.sub.L but is equal to or lower than
the second threshold temperature T.sub.H. If it is judged in this
step that the exhaust gas temperature T.sub.E is equal to or higher
than the first threshold temperature T.sub.L but is equal to or
lower than the second threshold temperature T.sub.H, that is, the
exhaust gas temperature T.sub.E is not too lower or too high, this
subroutine for setting the fuel injection amount is terminated, and
the procedure proceeds to step S14 in the main flowchart shown in
FIG. 8. On the other hand, if it is judged in the step S135 that
the exhaust gas temperature T.sub.E is not equal to or higher than
the first threshold temperature T.sub.L or not equal to or lower
than the second threshold temperature T.sub.M, the procedure
proceeds to step S136. This time, it is determined whether or not
the exhaust gas temperature T.sub.E is higher than the second
threshold temperature T.sub.H. If it is judged in this step that
the exhaust gas temperature T.sub.E is higher than the second
threshold temperature T.sub.H, that is, the amount of smoke to be
generated will be greater than initially expected, then, in step
S137, the fuel injection amount F.sub.M set in the step S131 is
corrected by increasing it by .DELTA.F.sub.T. On the other hand, if
it is judged in the step S136 that the exhaust gas temperature
T.sub.E is not higher than the second threshold temperature
T.sub.H, that is, the exhaust gas temperature T.sub.E is lower than
the first threshold temperature T.sub.L and therefore the amount of
smoke to be generated will be less than initially expected, the
procedure proceeds to step S138. There, the fuel injection amount
F.sub.M set in the step S131 is corrected by reducing it by
.DELTA.F.sub.T, thus suppressing an increase in the amount of
unburned HC to be generated.
[0068] When the exhaust gas temperature T.sub.E is not equal to or
higher than first threshold temperature T.sub.1, or not equal to or
lower than second threshold temperature T.sub.H, the fuel injection
amount F.sub.M set in the step S131 is corrected in the step S137
or S138 as described above, and then the fuel injection amount
setting process in FIG. 9 is terminated. Thereafter, the procedure
proceeds to the step S14 in FIG. 8.
[0069] In the step S14, it is determined whether or not the
accelerator opening degree .theta..sub.A is 0. If it is judged in
this step that the accelerator opening degree .theta..sub.A is 0,
that is, the vehicle is decelerating or idling and no fuel is being
injected into the combustion chamber 10a from the fuel injection
valve 11, the procedure proceeds to step S15. In this step,
injection of fuel from the fuel injection valve 11 into the
combustion chamber 10a is started. The fuel is released to the
exhaust passage 23a without being combusted inside the combustion
chamber 10a, thereby lowering the oxygen concentration of the
exhaust gas. As described, in this embodiment, fuel is injected
into the combustion chamber 10a from the fuel injection valve 11
only when the vehicle is decelerating or idling. This makes it
possible to minimize an awkward feel the driver experiences due to
torque fluctuations of the engine 10. After step S15, it is
determined in step S16 whether or not a flag is set. At first, a
flag is not set, and the procedure therefore proceeds to step S17,
where a timer is caused to count up, and it is determined in step
S18 whether or not a count value C.sub.N of the timer is equal to
or greater than a target count value C.sub.T. Subsequently, the
procedure returns to the step S11 from the step S18 and the
above-mentioned processes are basically repeated until the count
value C.sub.N of the timer reaches the target count value
C.sub.T.
[0070] When it is eventually judged in the step S18 that the count
value C.sub.N of the timer is equal to or great than the target
count value C.sub.T, that is, the exhaust gas containing the fuel
injected from the fuel injection valve 11 has reached the exhaust
gas heating device 27, the procedure proceeds to step S19, where a
flag is set. Then, the procedure proceeds to step S20, where a fuel
addition amount setting process is performed.
[0071] Meanwhile, in the step S12 mentioned earlier, if it is
judged that the current operating state is not within the
generation area of a large amount of smoke, that is, it is not
necessary to inject fuel into the combustion chamber 10a, the
procedure proceeds to step S21, where it is determined whether or
not the current operating state is within an operating area
involving the generation of a large amount of unburned HC. If it is
judged in this step that the current operating state is within the
generation area of a large amount of unburned HC, the procedure
proceeds to the step S134 in FIG. 9, where the fuel injection
amount F.sub.M set in the step S131 is corrected by reducing it by
.DELTA.F.sub.M, thus suppressing the generation of unburned HC.
Moreover, if it is judged in the step S21 that the current
operating state is not within the generation area of a large amount
of unburned HC, that is, it is not necessary to inject fuel into
the combustion chamber 10a from the fuel injection valve 11, the
procedure proceeds directly to the step S20. Note that the
procedure proceeds to the step S20 also when it is determined in
the step S16 that a flag is set, that is, the exhaust gas
containing the fuel injected from the fuel injection valve 11 has
reached the exhaust gas heating device 27.
[0072] In a subroutine for setting the fuel supply amount in the
step S20 shown in FIG. 10, first, in step S201, the target fuel
supply amount F.sub.T is set according to the difference between
the catalyst temperature T.sub.C and the target catalyst
temperature T.sub.T. Then, in step S202, the target air-fuel ratio
R.sub.T is set. Thereafter, in step S203, the unit supply amount
F.sub.U is calculated. Subsequently, in step S204, the supply cycle
t.sub.P is set according to the unit supply amount F.sub.U and the
target air-fuel ratio R.sub.T, and then the fuel-addition-amount
setting process is terminated. The procedure then proceeds to step
S22 in the main flowchart shown in FIG. 8.
[0073] In this step S22, fuel is supplied into the exhaust passage
23a from the fuel supply valve 27a. The fuel is ignited and
combusted by use of the ignition means, and the resultant hot
exhaust gas is introduced into the exhaust gas purifying device 26.
In this case, fuel is also injected into the combustion chamber 10a
from the fuel injection valve 11 as needed so as to suppress the
generation of both smoke and HC to a small amount. Accordingly,
harmful effects of the smoke and HC on the exhaust gas purifying
device 26 can be minimized. Thereafter, in step S23, it is
determined whether or not a flag is set. If it is judged in this
step that a flag is set, that is, fuel is also injected into the
combustion chamber 10a from the fuel injection valve 11, the
procedure proceeds to step S24, where an injection-amount air-fuel
ratio correcting process is performed.
[0074] In a subroutine for correcting the injection amount and the
air-fuel ratio shown in FIG. 11, first, in step S241, it is
determined whether or not the current air-fuel ratio R.sub.N is
within a predetermined region with respect to the target air-fuel
ratio R.sub.T. If it is judged in this step that the current
air-fuel ratio R.sub.N is within the predetermined region with
respect to the target air-fuel ratio R.sub.T, that is, it is not
necessary to correct the current air-fuel ratio, the injection
amount air fuel ratio correcting process in FIG. 11 is terminated.
The procedure then proceeds to step S25 in FIG. 8. On the other
hand, if it is judged in the step S241 that the current air-fuel
ratio R.sub.N is outside the predetermined region with respect to
the target air-fuel ratio R.sub.T, the procedure proceeds to step
S242, where it is determined whether or not the current air-fuel
ratio R.sub.N is greater than the target air-fuel ratio R.sub.T by
.DELTA.R or greater. If it is judged in this step that the current
air-fuel ratio R.sub.N is greater than the target air-fuel ratio
R.sub.T by .DELTA.R or greater, that is, the air-fuel ratio is so
lean that smoke is easily generated, then in step S243, the fuel
injection amount set in the step S13 is corrected by increasing it
by .DELTA.F.sub.R. If it is judged in the step S242 that the
current air-fuel ratio R.sub.N is not greater than the target
air-fuel ratio R.sub.T by .DELTA.R, that is, the air-fuel ratio is
so rich that HC is easily generated, then in step S244, the fuel
injection amount F.sub.M set in the step S13 is corrected by
reducing it by .DELTA.F.sub.R.
[0075] The procedure proceeds to step S25 once the current air-fuel
ratio R.sub.N is controlled to fall within the predetermined region
with respect to the target air-fuel ratio R.sub.T by correcting the
fuel injection amount of the fuel injection valve 11 in accordance
with the difference between the current air-fuel ratio R.sub.N and
the target air-fuel ratio R.sub.T as described above.
[0076] Meanwhile, in the step S23 mentioned earlier, if it is
judged that the a flag is not set, that is, fuel is not injected
from the fuel injection valve 11, the procedure also proceeds to
the step S25, where it is determined whether or not the catalyst
temperature T.sub.C has become equal to or higher than the target
catalyst temperature T.sub.T. If it is judged in this step that the
catalyst temperature T.sub.C is lower than the target catalyst
temperature T.sub.T, that is, it is necessary to continue heating
the exhaust gas, the procedure returns to the step S11 and the
above mentioned processes are repeated. On the other hand, if it is
judged that the catalyst temperature T.sub.C is equal to or higher
than the target catalyst temperature T.sub.T, that is, the exhaust
gas purifying device 26 has shifted to an active state and the
heating is no longer necessary, the procedure proceeds to step S26.
Then, the exhaust gas heating process is terminated, and the count
value C.sub.N of the timer is reset to 0, and thereafter the
procedure returns to the initial step S11. Moreover, the procedure
proceeds to the step S26 also when the accelerator opening degree
.theta..sub.A is not 0 in the step S14, that is, the driver is
depressing the accelerator pedal 12 in the step S14. This is
because the driver's depression of the accelerator pedal 12 starts
the combustion of fuel inside the combustion chamber 10a and thus
raises the exhaust gas temperature T.sub.E, thereby eliminating the
need for performing the exhaust gas heating process. Similarly,
when it is judged in the step S11 mentioned earlier that fuel does
not need to be injected, the procedure also proceeds to step S26,
where the exhaust gas heating process is terminated and the count
value C.sub.N of the timer is reset to 0.
[0077] It is to be noted that the present invention shall be
construed solely from the matters described in the claims thereof,
and the foregoing embodiment includes not only the matters
described above but any changes and corrections encompassed by the
concept of the present invention. In other words, all the matters
in the foregoing embodiment are not to limit the present invention,
but include any configurations which may not be directly related to
the present invention and can be changed optionally depending upon
the application, purpose, and the like.
REFERENCE SIGNS LIST
[0078] 10 engine [0079] 10a combustion chamber [0080] 11 fuel
injection valve [0081] 12 accelerator pedal [0082] 13 ECU [0083]
13a operating status determining section [0084] 13b fuel injection
setting section [0085] 13c fuel injection valve driving section
[0086] 13d PM deposition rate calculating section [0087] 13e PM
burning rate calculating section [0088] 13f throttle opening
setting section [0089] 13g actuator driving section [0090] 13h EGR
amount setting section [0091] 13i EGR valve driving section [0092]
13j target air-fuel ratio setting section [0093] 13k fuel supply
setting section [0094] 13l fuel supply valve driving section [0095]
13m glow plug driving section [0096] 14 accelerator opening sensor
[0097] 15 cylinder head [0098] 15a intake port [0099] 15b exhaust
port [0100] 16a intake valve [0101] 16b exhaust valve [0102] 17
intake pipe [0103] 17a intake passage [0104] 17b surge tank [0105]
18 throttle actuator [0106] 19 throttle valve [0107] 20a piston
[0108] 20b connecting rod [0109] 20c crankshaft [0110] 21 cylinder
block [0111] 33 crank angle sensor [0112] 23 exhaust pipe [0113]
23a exhaust passage [0114] 24 EGR system [0115] 25 exhaust
turbocharger [0116] 25a intake turbine [0117] 25b exhaust turbine
[0118] 25c intercooler [0119] 26 exhaust gas purifying device
[0120] 26a oxidation catalytic converter [0121] 26b DPF [0122] 27
exhaust gas heating device [0123] 27a fuel supply valve [0124] 27b
glow plug [0125] 28 EGR pipe [0126] 28a EGR passage [0127] 29 EGR
control valve [0128] 30 air flow meter [0129] 31 catalyst
temperature sensor [0130] 32 exhaust gas temperature sensor [0131]
.theta..sub.A accelerator opening degree [0132] C.sub.N count value
of timer [0133] C.sub.T target count value [0134] F.sub.M fuel
injection amount [0135] F.sub.T target fuel supply amount [0136]
F.sub.U unit supply amount [0137] .DELTA.F.sub.M fuel-injection
correcting amount [0138] T.sub.C catalyst temperature [0139]
T.sub.E exhaust gas temperature [0140] T.sub.H second threshold
temperature [0141] T.sub.L first threshold temperature [0142]
T.sub.T target catalyst temperature [0143] R.sub.N actual air-fuel
ratio [0144] R.sub.T target air-fuel ratio [0145] V.sub.B PM
burning rate [0146] V.sub.D PM deposition rate [0147] t.sub.P
supply cycle
* * * * *