U.S. patent application number 09/846354 was filed with the patent office on 2001-08-23 for control system for an internal combustion engine.
This patent application is currently assigned to Toyota Jidosha Kabushiki Kaisha. Invention is credited to Katoh, Kenji, Tanahashi, Toshio, Tanaka, Hiroshi.
Application Number | 20010015193 09/846354 |
Document ID | / |
Family ID | 26515862 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010015193 |
Kind Code |
A1 |
Tanaka, Hiroshi ; et
al. |
August 23, 2001 |
Control system for an internal combustion engine
Abstract
A control system for an internal combustion engine comprising a
direct cylinder fuel injection valve for directly injecting the
fuel into a cylinder of an internal combustion engine. The main
fuel that burns in the cylinder is injected in the latter half of
the compression stroke of the cylinder, and the secondary fuel
which is the ineffective fuel that does not burn in the cylinder is
injected in the latter half of the exhaust stroke, the main fuel
and the secondary fuel being injected toward a cavity formed in the
top surface of the piston. The main fuel that is injected is
deflected by the cavity to form a charge of a combustible air-fuel
ratio mixture around the spark plug. When the secondary fuel is
injected, the exhaust valve is opening, and the fuel that is
deflected is all discharged out of the cylinder through the exhaust
port. Therefore, the ineffective fuel supplied by the secondary
fuel injection does not remain in the cylinder, and the output
torque does not change in the combustion of the next cycle.
Inventors: |
Tanaka, Hiroshi;
(Susono-shi, JP) ; Tanahashi, Toshio; (Susono-shi,
JP) ; Katoh, Kenji; (Shizuoka-ken, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. Box 19928
Alexandria
VA
22320
US
|
Assignee: |
Toyota Jidosha Kabushiki
Kaisha
|
Family ID: |
26515862 |
Appl. No.: |
09/846354 |
Filed: |
May 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09846354 |
May 2, 2001 |
|
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09356453 |
Jul 19, 1999 |
|
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Current U.S.
Class: |
123/300 ;
123/568.21 |
Current CPC
Class: |
F02D 2041/389 20130101;
F02M 45/02 20130101; F02D 41/1443 20130101; Y02T 10/40 20130101;
F01N 13/011 20140603; F02D 41/1456 20130101; F02D 41/3029 20130101;
F02D 41/006 20130101; F02D 41/0065 20130101; F02D 41/0275 20130101;
F01N 3/0842 20130101; Y02T 10/44 20130101; F02D 41/405 20130101;
F01N 13/009 20140601; F02D 41/0055 20130101; Y02T 10/47 20130101;
F01N 2610/03 20130101 |
Class at
Publication: |
123/300 ;
123/568.21 |
International
Class: |
F02B 003/00; F02M
025/07; F02B 047/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 22, 1998 |
JP |
10-206775 |
Oct 6, 1998 |
JP |
10-284368 |
Claims
1. A control system for an internal combustion engine comprising: a
direct cylinder fuel injection valve for directly injecting the
fuel into a cylinder of an internal combustion engine; and a fuel
injection control means which executes a main fuel injection to
inject the fuel that burns in the cylinder by controlling said
direct cylinder fuel injection valve, and further executes, as
required, a secondary fuel injection to inject the fuel that does
not burn in the cylinder during the expansion stroke or the exhaust
stroke after the main fuel injection; wherein when the secondary
fuel injection is being executed, said fuel injection control means
controls the secondary fuel injection based on the engine operating
conditions in such a manner that the fuel supplied by the secondary
fuel injection is discharged out of the cylinder before the end of
the exhaust stroke.
2. A control system for an internal combustion engine according to
claim 1, wherein said internal combustion engine is equipped with a
variable valve timing means for varying the valve timing of the
engine, and said fuel injection control means controls the
secondary fuel injection in accordance with a change in the valve
timing of the engine.
3. A control system for an internal combustion engine according to
claim 1, wherein said fuel injection control means controls the
secondary fuel injection in such a manner that the fuel supplied by
the secondary fuel injection rides on the flow of the exhaust gas
that is formed in the cylinder in the exhaust stroke heading toward
the exhaust port.
4. A control system for an internal combustion engine comprising: a
direct cylinder fuel injection valve for directly injecting the
fuel into a cylinder of an internal combustion engine; and a fuel
injection control means which executes a main fuel injection to
inject the fuel that burns in the cylinder by controlling said
direct cylinder fuel injection valve, and executes, as required, a
secondary fuel injection to inject the fuel that does not burn in
the cylinder during the expansion stroke or the exhaust stroke
after the main fuel injection; wherein said fuel injection control
means advances the timing for injecting the secondary fuel with an
increase in the amount of the fuel injected by the secondary fuel
injection.
5. A control system for an internal combustion engine comprising: a
direct cylinder fuel injection valve for directly injecting the
fuel into a cylinder of an internal combustion engine; a fuel
injection control means which executes a main fuel injection to
inject the fuel that burns in the cylinder by controlling said
direct cylinder fuel injection valve, and executes, as required, a
secondary fuel injection to inject the fuel that does not burn in
the cylinder during the expansion stroke or the exhaust stroke
after the main fuel injection; and a deflecting means for
deflecting the flow of the fuel supplied by the secondary fuel
injection toward the exhaust port of the cylinder.
6. A control system for an internal combustion engine according to
claim 5, wherein said deflecting means has a cavity formed in the
top surface of the piston, so that the flow of fuel supplied by the
secondary fuel injection is deflected toward said exhaust port
along the surface of said cavity.
7. A control system for an internal combustion engine according to
claim 5, wherein said deflecting means is equipped with an
injection direction control means for changing the direction of
fuel injected from the injection valve toward the exhaust port when
the secondary fuel is injected.
8. A control system for an internal combustion engine comprising: a
direct cylinder fuel injection valve for directly injecting the
fuel into a cylinder of an internal combustion engine; and a fuel
injection control means which executes a main fuel injection to
inject the fuel that burns in the cylinder by controlling said
direct cylinder fuel injection valve, and executes, as required, a
secondary fuel injection to inject the fuel that does not burn in
the cylinder during the expansion stroke or the exhaust stroke
after the main fuel injection; wherein said fuel injection control
means sets the pressure of the secondary fuel injection at a value
lower than the pressure of the main fuel injection.
9. A control system for an internal combustion engine comprising: a
direct cylinder fuel injection valve for directly injecting the
fuel into a cylinder of an internal combustion engine; and a fuel
injection control means which executes a main fuel injection to
inject the fuel that burns in the cylinder by controlling said
direct cylinder fuel injection valve, and executes, as required, a
secondary fuel injection to inject the fuel that does not burn in
the cylinder during the expansion stroke or the exhaust stroke
after the main fuel injection; wherein said fuel injection control
means calculates the amount of fuel remaining in the cylinder,
which is part of the fuel supplied by the preceding secondary fuel
injection, and corrects the amount of said main fuel injection
based on said remaining amount of fuel.
10. A control system for an internal combustion engine comprising:
a direct cylinder fuel injection valve for directly injecting the
fuel into a cylinder of an internal combustion engine; and a fuel
injection control means which executes a main fuel injection to
inject the fuel that burns in the cylinder by controlling said
direct cylinder fuel injection valve, and executes, as required, a
secondary fuel injection to inject the fuel that does not burn in
the cylinder during the expansion stroke or the exhaust stroke
after the main fuel injection; wherein said fuel injection control
means, as required, executes said main fuel injection two times by
dividing it into a first main fuel injection for forming a uniform
air-fuel mixture in the cylinder and a second main fuel injection
for forming a charge of a combustible air-fuel ratio mixture in the
cylinder, and, when said secondary fuel injection is executed,
calculates the amount of fuel remaining in the cylinder, which is
part of the fuel supplied by the preceding secondary fuel
injection, and corrects the amount of said first main fuel
injection based on the remaining amount of fuel.
11. A control system for an internal combustion engine comprising:
an ineffective fuel-supply means for supplying ineffective fuel
that does not burn in the combustion chamber of an internal
combustion engine; an EGR means for recirculating the exhaust gas
from the engine into the combustion chamber of the engine; and an
EGR limiting means for limiting the exhaust gas recirculated by
said EGR means when the ineffective fuel is being supplied to the
engine by said ineffective fuel supply means.
12. A control system for an internal combustion engine according to
claim 11, wherein said EGR means is equipped with an exhaust gas
recirculation passage for connecting the exhaust passage of the
engine to the intake passage of the engine and an EGR valve for
adjusting the flow rate of the exhaust gas flowing through said
exhaust gas recirculation passage, and said EGR limiting means
limits the recirculation of said exhaust gas by controlling the
opening degree of said EGR valve.
13. A control system for an internal combustion engine according to
claim 11, wherein said internal combustion engine is equipped with
a variable valve timing device for varying the open-close timings
of the intake valves and the exhaust valves of the cylinders, and
said EGR limiting means controls said variable valve timing means
to change the open-close timings of the intake valves or the
exhaust valves to limit the recirculation of the exhaust gas.
14. A control system for an internal combustion engine comprising:
an ineffective fuel-supply means for supplying ineffective fuel
that does not burn in the combustion chamber of an internal
combustion engine; an EGR means for recirculating the exhaust gas
from the engine into the combustion chamber of the engine; and an
ineffective fuel limiting means for limiting the supply of the
ineffective fuel by said ineffective fuel-supply means when the
exhaust gas is recirculated by said EGR means.
15. A control system for an internal combustion engine according to
claim 14, wherein said ineffective fuel limiting means limits the
ineffective fuel supplied by said ineffective fuel supply means
when the flow rate of the exhaust gas recirculated by said EGR
means is larger than a predetermined amount.
16. An internal combustion engine comprising: a main fuel-supply
means for supplying, into said engine, the fuel that burns in the
combustion chamber based on the operating conditions of the
internal combustion engine; an ineffective fuel-supply means for
supplying, into said engine, the ineffective fuel that does not
burn in the combustion chamber of the engine; an EGR means for
recirculating the exhaust gas of the engine into the combustion
chamber of the engine; and a correction means for estimating the
amount of the ineffective fuel in the exhaust gas recirculated by
said EGR means to correct the amount of fuel supplied to the engine
by said main fuel-supply means based on the estimated amount.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a control system for an
internal combustion engine. More specifically, the invention
relates to a control system for an internal combustion engine, for
supplying ineffective fuel which does not burn in the combustion
chamber.
[0003] 2. Description of the Related Art
[0004] There has been known a technology for adjusting the air-fuel
ratio of the exhaust gas from an engine independently of the engine
operating air-fuel ratio (combustion air-fuel ratio in the
combustion chamber) by supplying, to the engine, ineffective fuel
that does not contribute to the combustion in the combustion
chamber. For example, a NO.sub.x occluding and reducing catalyst is
disposed in the exhaust passage of the engine which operates at a
lean air-fuel ratio, the NO.sub.x occluding and reducing catalyst
absorbing NO.sub.x in the exhaust gas when the air-fuel ratio of
the exhaust gas flowing in is lean, and releasing and purifying by
reduction the absorbed NO.sub.x when the air-fuel ratio in the
exhaust gas becomes rich. In this case, the air-fuel ratio of the
exhaust gas flowing into the NO.sub.x occluding and reducing
catalyst must be set to be rich at regular intervals and the
NO.sub.x must be released from the NO.sub.x occluding and reducing
catalyst, so that the NO.sub.x occluding and reducing catalyst will
not be saturated with NO.sub.x when the engine is operated at a
lean air-fuel ratio. In such a case, a change in the engine
operating air-fuel ratio from the lean side to the rich side
increases the engine output torque; i.e., a change in the air-fuel
ratio changes the torque. Upon supplying ineffective fuel that does
not contribute to the combustion in the engine combustion chamber,
i.e., that does not burn in the engine combustion chamber,
therefore, it becomes possible to advantageously change only the
air-fuel ratio of the exhaust gas independently from the engine
operating air-fuel ratio. In an engine having direct cylinder fuel
injection valves for directly injecting the fuel into the
cylinders, the ineffective fuel can be supplied into the cylinders
by secondary fuel injection in the expansion stroke or in the
exhaust stroke of the cylinders. In an engine having exhaust port
fuel injection valves for injecting the fuel into the exhaust port
of the engine, further, the ineffective fuel can be supplied into
the exhaust ports by the exhaust port fuel injection.
[0005] The fuel injected into the cylinder during the expansion
stroke or the exhaust stroke or the fuel injected into the exhaust
port of the cylinder is vaporized without being burned and is
discharged together with the exhaust gas. That is, the ineffective
fuel that is supplied does not contribute to the combustion in the
engine, but the amount of the unburned HC component in the exhaust
gas from the engine increases by an amount of the ineffective fuel
that is supplied to establish a rich air-fuel ratio. By supplying
the ineffective fuel to the engine, therefore, it is possible to
change the air-fuel ratio only in the exhaust gas from the engine
without affecting the engine operating air-fuel ratio.
[0006] A device for supplying the ineffective fuel of this type has
been disclosed in, for example, Japanese Unexamined Patent
Publication (Kokai) No. 6-212961.
[0007] According to the device of this publication, a NO.sub.x
occluding and reducing catalyst is disposed in the exhaust passage
of a diesel engine to absorb the NO.sub.x in the exhaust gas when
the air-fuel ratio of the exhaust gas flowing in is lean and to
release the NO.sub.x when the oxygen concentration has decreased in
the exhaust gas that is flowing in. Under normal condition, the
main fuel is injected into the cylinder near the compressive top
dead center of the cylinder of the engine and, when the NO.sub.x is
to be released from the NO.sub.x occluding and reducing catalyst,
the secondary fuel is injected during the expansion stroke or the
exhaust stroke of the engine in addition to injecting the main
fuel. The fuel injected into the cylinder during the expansion or
exhaust stroke does not contribute to the combustion in the
cylinder, i.e., does not burn in the cylinder and is exposed to the
burned gas of a high temperature in the cylinder. Therefore,
hydrocarbons having large molecular weights in the fuel are
decomposed into hydrocarbons having small molecular weights.
Besides, the fuel supplied by the secondary fuel injection does not
contribute to the combustion but is simply discharged from
cylinders together with the exhaust gas. By supplying the
ineffective fuel to the engine, therefore, it is made possible to
inject the fuel in a relatively large amount for establishing a
rich air-fuel ratio in the exhaust gas without increasing the
pressure of an explosion in the cylinder even in a diesel engine.
According to the device of the above-mentioned publication, when
the secondary fuel is injected, the exhaust gas having a rich
air-fuel ratio, containing a large amount of hydrocarbons of low
molecular weights which are highly active, flows into the NO.sub.x
occluding and reducing catalyst in the exhaust passage. When the
secondary fuel is injected, therefore, the NO.sub.x that has been
absorbed is released from the NO.sub.x occluding and reducing
catalyst and is purified by reduction with hydrocarbons in the
exhaust gas.
[0008] In an engine which effects the secondary fuel injection as
done by the device of the above-mentioned publication, however, the
fuel supplied by the secondary fuel injection is not completely
exhausted during the exhaust stroke but often remains in the
cylinder. When the fuel of the secondary fuel injection partly
remains in the cylinder, this remaining fuel burns in the cylinder
in addition to the fuel supplied by the main fuel injection at the
time when the main fuel is injected next time. Accordingly, an
amount of fuel burnt in the engine increases, whereby an increased
torque is produced by the combustion. This causes a change in the
output torque of the engine.
[0009] When the ineffective fuel is supplied to the engine by the
exhaust port fuel injection without relying upon the secondary fuel
injection, on the other hand, the fuel does not remain in the
cylinder. In an engine equipped with an exhaust gas recirculation
(EGR) device, however, the similar problem may occur when the
exhaust port fuel injection is effected.
[0010] There has been generally known an exhaust gas recirculation
(EGR) device in which the exhaust gas from the engine is partly
recirculated into the combustion chamber of an internal combustion
engine to lower the combustion temperature in the combustion
chamber in order to decrease the amount of NO.sub.x (nitrogen
oxides) formed by the combustion. The exhaust gas recirculation
system includes an external EGR system in which an exhaust passage
of the engine is connected to an intake passage of the engine
through an EGR passage, and the amount of the exhaust gas to be
recirculated is adjusted by a flow rate adjusting valve (EGR valve)
provided in the EGR passage, and an internal EGR system by which
the amount of blow back of the burned gas in the combustion chamber
caused by the overlapping of valve is adjusted by changing the
open-close timings of the intake valve and the exhaust valve of the
engine.
[0011] When the ineffective fuel is supplied to the engine that
utilizes the EGR (exhaust gas recirculation) as described above,
there a problem occurs not only when the ineffective fuel is
supplied by the secondary fuel injection but also when the
ineffective fuel is supplied by the exhaust port injection.
[0012] That is, when the ineffective fuel is supplied as described
above, the exhaust gas from the engine contains unburned fuel in
relatively large amounts. When the exhaust gas is directly
recirculated by the EGR device into the combustion chamber of the
engine, part of the ineffective fuel that should not burn in the
combustion chamber is recirculated into the combustion chamber and
burns therein. When the ineffective fuel is supplied while the EGR
is being performed, therefore, the fuel is supplied in an excess
amount into the engine and the combustion air-fuel ratio becomes
excessively rich, whereby the combustion in the combustion chamber
becomes unstable or the output torque of the engine increases due
to the combustion of excess fuel.
SUMMARY OF THE INVENTION
[0013] In view of the problems in the related art as set forth
above, the object of the present invention is to provide a control
system for an internal combustion engine capable of preventing the
combustion from becoming unstable and preventing a change in the
output torque caused by the residual fuel or recirculation of the
fuel in the combustion chamber, when the fuel is supplied to the
engine as ineffective fuel.
[0014] The object as set forth above is achieved by a control
system for an internal combustion engine according to the present
invention, comprising:
[0015] a direct cylinder fuel injection valve for directly
injecting the fuel into a cylinder of an internal combustion
engine; and
[0016] a fuel injection control means which executes a main fuel
injection to inject the fuel that burns in the cylinder by
controlling the direct cylinder fuel injection valve, and further
executes, as required, a secondary fuel injection to inject the
fuel that does not burn in the cylinder during the expansion stroke
or the exhaust stroke after the main fuel injection; wherein
[0017] when the secondary fuel injection is being executed, the
fuel injection control means controls the secondary fuel injection
based on the engine operating conditions in such a manner that the
fuel supplied by the secondary fuel injection is exhausted out of
the cylinder before the end of the exhaust stroke.
[0018] According to this aspect of the invention, the fuel
injection control means controls the secondary fuel injection based
on the engine operating conditions such as valve timing, rotational
speed, etc., and changes, for example, the amount of fuel
injection, injection timing, etc., so that the fuel supplied by the
secondary fuel injection is all discharged out of the cylinder
before the end of the exhaust stroke, i.e., before the exhaust
valve is closed. Thus, there remains no fuel in the cylinder, and
the engine output torque does not change even when the secondary
fuel is injected.
[0019] According to another aspect of the present invention, there
is provided a control system for an internal combustion engine
comprising:
[0020] a direct cylinder fuel injection valve for directly
injecting the fuel into a cylinder of an internal combustion
engine; and
[0021] a fuel injection control means which executes a main fuel
injection to inject the fuel that burns in the cylinder by
controlling the direct cylinder fuel injection valve, and executes,
as required, a secondary fuel injection to inject the fuel that
does not burn in the cylinder during the expansion stroke or the
exhaust stroke after the main fuel injection; wherein
[0022] the fuel injection control means advances the timing for
injecting the secondary fuel with an increase in the amount of the
fuel injected by the secondary fuel injection.
[0023] According to this aspect of the invention, the fuel
injection control means advances the timing for injecting the
secondary fuel with an increase in the amount of the secondary fuel
injection. Therefore, even when the amount of the secondary fuel
injection is large, a sufficient period of time is maintained
before the exhaust valve is closed, and the injected fuel does not
remain in the cylinder. Accordingly, the engine output torque does
not change even when the secondary fuel is injected.
[0024] According to a further aspect of the present invention,
there is provided a control system for an internal combustion
engine comprising:
[0025] a direct cylinder fuel injection valve for directly
injecting the fuel into a cylinder of an internal combustion
engine;
[0026] a fuel injection control means which executes a main fuel
injection to inject the fuel that burns in the cylinder by
controlling the direct cylinder fuel injection valve, and executes,
as required, a secondary fuel injection to inject the fuel that
does not burn in the cylinder during the expansion stroke or the
exhaust stroke after the main fuel injection; and
[0027] a deflecting means for deflecting the flow of the fuel
supplied by the secondary fuel injection toward the exhaust port of
the cylinder.
[0028] According to this aspect of the invention, the deflecting
means deflects the fuel supplied by the secondary fuel injection
toward the exhaust port. Therefore, the whole amount of the fuel
supplied by the secondary fuel injection is discharged from the
exhaust port and does not remain in the cylinder. Therefore, the
engine output torque does not change even when the secondary fuel
is injected.
[0029] According to a further aspect of the present invention,
there is provided a control system for an internal combustion
engine comprising:
[0030] a direct cylinder fuel injection valve for directly
injecting the fuel into a cylinder of an internal combustion
engine; and
[0031] a fuel injection control means which executes a main fuel
injection to inject the fuel that burns in the cylinder by
controlling the direct cylinder fuel injection valve, and executes,
as required, a secondary fuel injection to inject the fuel that
does not burn in the cylinder during the expansion stroke or the
exhaust stroke after the main fuel injection; wherein
[0032] the fuel injection control means sets the pressure of the
secondary fuel injection to be lower than the pressure of the main
fuel injection.
[0033] According to this aspect of the invention, the fuel
injection control means sets the pressure of the secondary fuel
injection to be lower than the pressure of the main fuel injection.
Therefore, the fuel supplied by the secondary fuel injection does
not collide with the cylinder wall or the piston to adhere thereon,
and is discharged together with the exhaust gas from the cylinder.
Therefore, no fuel remains in the cylinder, and the engine output
torque does not change even when the secondary fuel is
injected.
[0034] According to a further aspect of the present invention,
there is provided a control system for an internal combustion
engine comprising:
[0035] a direct cylinder fuel injection valve for directly
injecting the fuel into a cylinder of an internal combustion
engine; and
[0036] a fuel injection control means which executes a main fuel
injection to inject the fuel that burns in the cylinder by
controlling the direct cylinder fuel injection valve, and executes,
as required, a secondary fuel injection to inject the fuel that
does not burn in the cylinder during the expansion stroke or the
exhaust stroke after the main fuel injection; wherein
[0037] the fuel injection control means calculates the amount of
fuel remaining in the cylinder, which is part of the fuel supplied
by the preceding secondary fuel injection, and corrects the amount
of the main fuel injection based on the remaining amount of
fuel.
[0038] According to this aspect of the present invention, the fuel
injection control means calculates the amount of fuel remaining in
the cylinder due to the preceding secondary fuel injection, and
corrects the amount of the main fuel injection depending upon the
remaining amount of fuel. This correction is effected by, for
example, decreasing the amount of the main fuel injection by an
amount corresponding to the remaining amount of fuel. Therefore,
the amount of fuel that contributes to the combustion at the time
when the main fuel is injected is maintained at a target amount.
Therefore, the engine output torque does not change even when the
fuel remains in the cylinder due to the secondary fuel
injection.
[0039] According to a further aspect of the present invention,
there is provided a control system for an internal combustion
engine comprising:
[0040] a direct cylinder fuel injection valve for directly
injecting the fuel into a cylinder of an internal combustion
engine; and
[0041] a fuel injection control means which executes a main fuel
injection to inject the fuel that burns in the cylinder by
controlling the direct cylinder fuel injection valve, and executes,
as required, a secondary fuel injection to inject the fuel that
does not burn in the cylinder during the expansion stroke or the
exhaust stroke after the main fuel injection; wherein
[0042] the fuel injection control means, as required, executes the
main fuel injection two times by dividing it into a first main fuel
injection for forming a uniform air-fuel mixture in the cylinder
and a second main fuel injection for forming a charge of a
combustible air-fuel ratio mixture in the cylinder, and, when the
secondary fuel injection is executed, the fuel injection means
calculates the amount of fuel remaining in the cylinder, which is
part of the fuel supplied by the preceding secondary fuel
injection, and corrects the amount of the first main fuel injection
based on the remaining amount of fuel.
[0043] According to this aspect of the present invention, the fuel
injection control means, as required, executes the main fuel
injection twice and, in this case, corrects the amount of the first
main fuel injection based on the amount of fuel remaining in the
cylinder due to the secondary fuel injection. This correction is
effected by, for example, decreasing the amount of the first fuel
injection by an amount corresponding to the remaining amount of
fuel. The first main fuel injection is for forming a uniform
mixture in the cylinder whereas the second main fuel injection is
for forming a stratified charge of the mixture. On the other hand,
the fuel remaining in the cylinder forms a uniform mixture in the
cylinder. When the amount of the first main fuel injection is
normally set, therefore, the air-fuel ratio of the formed uniform
mixture becomes more rich than the target value. According to the
present invention, therefore, the amount of the first main fuel
injection is corrected based on the remaining amount of fuel, so
that the air-fuel ratio of the uniform mixture formed in the
cylinder is maintained at the target value.
[0044] According to a further aspect of the present invention,
there is provided a control system for an internal combustion
engine comprising:
[0045] an ineffective fuel supply means for supplying ineffective
fuel that does not burn in the combustion chamber of an internal
combustion engine;
[0046] an EGR means for recirculating the exhaust gas from the
engine into the combustion chamber of the engine; and
[0047] an EGR limiting means for limiting the exhaust gas
recirculated by the EGR means when the ineffective fuel is being
supplied to the engine by the ineffective fuel supply means.
[0048] According to this aspect of the present invention, the EGR
is limited by the EGR limiting means when the ineffective fuel is
being supplied. Therefore, the ineffective fuel is recirculated in
a decreased amount into the combustion chamber of the engine
together with the recirculated exhaust gas, making it possible to
prevent the combustion in the combustion chamber from becoming
unstable and to prevent a change in the output torque. Here, "limit
the recirculation of exhaust gas" includes both the case where the
exhaust gas is recirculated in a decreased amount and the case
where the recirculation of the exhaust gas is completely
interrupted.
[0049] According to a further aspect of the present invention,
there is provided a control system for an internal combustion
engine comprising:
[0050] an ineffective fuel supply means for supplying ineffective
fuel that does not burn in the combustion chamber of an internal
combustion engine;
[0051] an EGR means for recirculating the exhaust gas from the
engine into the combustion chamber of the engine; and
[0052] an ineffective fuel limiting means for limiting the supply
of the ineffective fuel by the ineffective fuel supply means when
the exhaust gas is recirculated by the EGR means.
[0053] According to this aspect of the present invention, the
supply of the ineffective fuel is limited by the ineffective fuel
limiting means when the EGR is executed. Therefore, the ineffective
fuel is recirculated into the combustion chamber of the engine
together with the recirculated exhaust gas. Here, "limit the supply
of the ineffective fuel" includes both the case where the
ineffective fuel is supplied in a decreased amount and the case
where the supply of the ineffective fuel is completely
interrupted.
[0054] According to a further aspect of the present invention,
there is provided a control system for an internal combustion
engine comprising:
[0055] a main fuel supply means for supplying, into the engine, the
fuel that burns in the combustion chamber based on the operating
conditions of the internal combustion engine;
[0056] an ineffective fuel supply means for supplying, into the
engine, the ineffective fuel that does not burn in the combustion
chamber of the engine;
[0057] an EGR means for recirculating the exhaust gas of the engine
into the combustion chamber of the engine; and
[0058] a correction means for estimating the amount of the
ineffective fuel in the exhaust gas recirculated by the EGR means
to correct the amount of fuel supplied to the engine by the main
fuel supply means based on the estimated amount.
[0059] According to this aspect of the present invention, the
amount of the main fuel is corrected depending upon the amount of
the ineffective fuel that recirculates into the combustion chamber
together with the exhaust gas. Therefore, the fuel is supplied in a
proper amount into the combustion chamber based on the engine
operating conditions irrespective of the recirculating amount of
the ineffective fuel, preventing the combustion in the combustion
chamber from losing stability and preventing a change in the output
torque.
BRIEF DESCRIPTION OF THE DRAWINGS
[0060] The present invention will be better understood from the
description as set forth hereinafter with reference to the
accompanying drawings in which:
[0061] FIG. 1 is a diagram schematically illustrating the general
construction of an embodiment when the present invention is applied
to an internal combustion engine for automobiles;
[0062] FIG. 2 is a vertical sectional view of a cylinder for
illustrating a first embodiment of the present invention;
[0063] FIG. 3 is a flow chart illustrating the operation for
controlling the secondary fuel injection according to the first
embodiment;
[0064] FIG. 4 is a vertical sectional view of a cylinder for
illustrating a second embodiment of the present invention;
[0065] FIG. 5 is a flow chart illustrating the operation for
controlling the secondary fuel injection according to the second
embodiment;
[0066] FIG. 6 is a diagram similar to FIG. 4 and illustrates a
modified example of the second embodiment;
[0067] FIG. 7 is a diagram illustrating a method of calculating the
remaining amount of fuel according to a third embodiment of the
present invention;
[0068] FIG. 8 is a flow chart illustrating the operation for
controlling the main fuel injection according to the third
embodiment;
[0069] FIG. 9 is a diagram schematically illustrating the general
construction of an embodiment when the present invention is applied
to an internal combustion engine that executes the external EGR for
automobiles;
[0070] FIG. 10 is a flow chart illustrating the secondary fuel
injection operation according to a fourth embodiment of the present
invention;
[0071] FIG. 11 is a diagram schematically illustrating the general
construction of an embodiment when the present invention is applied
to an internal combustion engine that executes the internal EGR for
automobiles;
[0072] FIG. 12 is a diagram illustrating valve timings of the
engine of FIG. 11;
[0073] FIG. 13 is a flow chart illustrating the secondary fuel
injection operation according to a sixth embodiment of the present
invention;
[0074] FIG. 14 is a flow chart illustrating the secondary fuel
injection operation according to the sixth embodiment of the
present invention but is different from that of FIG. 13;
[0075] FIG. 15 is a flow chart illustrating the secondary fuel
injection operation according to a seventh embodiment of the
present invention;
[0076] FIG. 16 is a diagram illustrating a method of calculating
the amount of unburned fuel recirculated into the combustion
chamber; and
[0077] FIG. 17 is a flow chart illustrating the operation for
correcting the amount of main fuel injection according to an eighth
embodiment of the present invention using the method of FIG.
16.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0078] Hereinafter, embodiments of the control system according to
the present invention will be explained with reference to the
attached drawings.
[0079] FIG. 1 is a view schematically illustrating the constitution
of an embodiment in which a fuel injection device of the present
invention is applied to an internal combustion engine for an
automobile.
[0080] In FIG. 1, reference numeral 1 denotes an internal
combustion engine for an automobile. In this embodiment, the engine
1 is a four-cylinder gasoline engine having four cylinders #1 to #4
which are equipped with fuel injection valves 111 to 114 for
directly injecting fuel into the cylinders. As will be described
later, the internal combustion engine 1 of this embodiment is a
lean-burn engine that can be operated at an air-fuel ratio higher
(more lean) than the stoichiometric air-fuel ratio.
[0081] In this embodiment, further, the cylinders #1 to #4 are
grouped into two groups of cylinders each group including two
cylinders so that the ignition timings will not take place
consecutively (in the embodiment of FIG. 1, for example, the order
of igniting the cylinders is 1-3-4-2, the cylinders #1 and #4
constituting one group of cylinders, and the cylinders #2 and #3
constituting another group of cylinders). The exhaust port of each
cylinder is connected to an exhaust manifold of each group of
cylinders, and is connected to an exhaust passage of each group of
cylinders. In FIG. 1, reference numeral 21a denotes an exhaust
manifold for connecting exhaust ports of the group of the cylinders
#1 and #4 to an independent exhaust passage 2a, and reference
numeral 21b denotes an exhaust manifold for connecting exhaust
ports of the group of the cylinders #2 and #4 to an independent
exhaust passage 2b. In this embodiment, start catalysts
(hereinafter referred to as "SCs") 5a and 5b comprising a three-way
catalyst are arranged in the independent exhaust passages 2a and
2b. The independent exhaust passages 2a and 2b meet together in a
common exhaust passage 2 on the downstream side of the SCs.
[0082] An NO.sub.x occluding and reducing catalyst 7 that will be
described later is arranged in the common exhaust passage 2. In
FIG. 1, reference numerals 29a and 29b denote air-fuel ratio
sensors arranged on the upstream side of the start catalysts 5a and
5b of the independent exhaust passages 2a and 2b, and reference
numeral 31 denotes an air-fuel ratio sensor arranged at an outlet
of the NO.sub.x occluding and reducing catalyst 7 in the exhaust
passage 2. The air-fuel ratio sensors 29a, 29b and 31 are so-called
linear air-fuel ratio sensors that produce voltage signals
corresponding to the air-fuel ratio of the exhaust gas over a wide
range of air-fuel ratios.
[0083] In FIG. 1, further, intake ports of the cylinders #1 to #4
of the engine 1 are connected to a surge tank 10a through the
intake manifold 10b, the surge tank 10a being connected to a common
intake passage 10. In this embodiment, further, a throttle valve 15
is installed in the intake passage 10. The throttle valve 15 in
this embodiment is a so-called electronically controlled throttle
valve which is driven by an actuator 15a of a suitable form such as
a step motor to define a degree of opening based on a control
signal from an ECU 30 that will be described later. In FIG. 1,
further, reference numeral 15b denotes a throttle valve
opening-degree sensor (throttle sensor) for detecting the opening
degree of the throttle valve 15.
[0084] In this embodiment, the direct cylinder fuel injection
valves 111 to 114 are separately connected to a reservoir (common
rail) 110 to inject the fuel of a high pressure in the common rail
110 into the cylinders. In FIG. 1, reference numeral 130 denotes a
fuel pump comprising a high-pressure pump such as plunger pump. The
fuel pump 130 supplies a high pressure fuel to the common rail 110
at a timing just after the fuel is injected by the fuel injection
valves (111 to 114).
[0085] In FIG. 1, reference numeral 200 denotes a variable valve
timing device for varying the valve timings of the engine 1. In
this embodiment, the variable valve timing device 200 may be any
known type provided it is capable of changing the valve timings of
the engine based on an instruction signal from an ECU 30 that will
be described later, and may be either one which changes the
open-close timings only of the intake valves and/or the exhaust
valves, or one which changes the valve lift in addition to the
open-close timings. The valve timings may be changed either
continuously or stepwisely.
[0086] In FIG. 1, reference numeral 30 denotes the ECU (engine
control unit) for controlling the engine 1. The ECU 30 comprises a
widely known microcomputer having RAM, ROM and CPU that are
connected together through a bidirectional bus, and executes basic
control operations such as controlling the main fuel injection and
the ignition timings. In this embodiment, the ECU 30 further works
to change the combustion in the cylinder into a rich air-fuel ratio
during a regenerating operation of the NO.sub.x occluding and
reducing catalyst that will be described later, and controls the
secondary fuel injection by injecting the secondary fuel during the
expansion or exhaust stroke of each cylinder to change the air-fuel
ratio of the exhaust gas flowing into the NO.sub.x occluding and
reducing catalyst to a rich air-fuel ratio within a short period of
time.
[0087] The input port of the ECU 30 receives signals from the
air-fuel ratio sensors 29a and 29b representing the exhaust gas
air-fuel ratios at the inlet of the start catalysts 5a and 5b, a
signal from the air-fuel ratio sensor 31 representing an exhaust
gas air-fuel ratio at the outlet of the NO.sub.x occluding and
reducing catalyst 7, a signal corresponding to the intake air
pressure of the engine from an intake-air-pressure sensor 37
provided in the surge tank 10a, and a signal from the accelerator
opening-degree sensor 33 representing the amount of the accelerator
pedal depressed by the driver (accelerator opening degree), and a
pulse signal from a rotational speed sensor 35 disposed near the
crankshaft (not shown) of the engine after every predetermined
rotational angle of the engine crankshaft. The ECU 30 calculates
the rotational angle of the crankshaft from the pulse signal, and
calculates the rotational speed of the engine from the frequency of
the pulse signals. Further, the input port of the ECU 30 receives a
signal from a fuel pressure sensor 120 arranged in the common rail
110 representing the fuel pressure in the common rail 110, and a
signal from the throttle valve opening-degree sensor 15b
representing the opening degree of the throttle valve 15.
[0088] In order to control the amounts of fuel injection into the
cylinders and to control the fuel injection timings, further, the
output port of the ECU 30 is connected to fuel injection valves 111
to 114 of the cylinders through a fuel injection circuit (not
shown), and is further connected to the actuator 15b of the
throttle valve 15 through a drive circuit (not shown) to control
the opening degree of the throttle valve 15.
[0089] In addition to the above-mentioned control operations, the
ECU 30 controls by feedback the rate of the fuel supplied by the
fuel pump 130 based on the signal representing the fuel pressure in
the common rail 110 input from the fuel pressure sensor 120, so
that the fuel pressure in the common rail is adjusted to a target
value. The fuel is supplied from the fuel pump 130 to the common
rail 110 at a timing just after the fuel is injected by the fuel
injection valves 111 to 114.
[0090] The output port of the ECU 30 is connected to the variable
valve timing device 200 through a drive circuit (not shown) to
control the valve timings of the engine 1 based on the engine load
conditions (degree of accelerator opening, engine rotational
speed).
[0091] In this embodiment, the main fuel injection of the engine 1,
i.e., the injection of fuel for combustion in the cylinder, is
controlled in the following five modes based upon the loads exerted
on the engine:
[0092] {circle over (1)}. A lean air-fuel ratio stratified charge
combustion (fuel is injected in the compression stroke).
[0093] {circle over (2)}. A lean air-fuel ratio uniform
mixture/stratified charge combustion (fuel is injected in the
suction stroke and in the compression stroke).
[0094] {circle over (3)}. A lean air-fuel ratio uniform
mixture/stratified charge combustion (fuel is injected in the
suction stroke).
[0095] {circle over (4)}. A stoichiometric air-fuel ratio uniform
mixture combustion (fuel is injected in the suction stroke).
[0096] {circle over (5)}. A rich air-fuel ratio uniform mixture
combustion (fuel is injected in the suction stroke).
[0097] That is, the lean air-fuel ratio stratified charge
combustion {circle over (1)} is carried out in the light-load
operating region of the engine 1. In this state, the fuel is
injected into the cylinders only one time in the latter half of the
compression stroke in each cylinder, and the injected fuel forms a
charge of a combustible mixture near the spark plug in the
cylinder. In this operating state, further, the amount of fuel
injected is very small, and the air-fuel ratio in the cylinder as a
whole becomes from about 25 to about 30.
[0098] As the load increases from the above-mentioned state {circle
over (1)} to enter into the low-load operation region, there takes
place the above-mentioned lean air-fuel ratio uniform
mixture/stratified charge combustion {circle over (2)}. The amount
of fuel injected into the cylinder increases with an increase in
the load exerted on the engine. In the above-mentioned stratified
charge combustion {circle over (1)}, the fuel is injected in the
latter half of the compression stroke, whereby the injection time
is limited and limitation is imposed on the amount of fuel for
forming the stratified charge. In this load region, therefore, the
fuel is injected in advance in the former half of the suction
stroke in an amount to compensate for the shortage of the fuel
injected in the latter half of the compression stroke, thereby to
supply the fuel in a target amount into the cylinder. The fuel
injected into the cylinder in the former half of the suction stroke
forms a very lean and uniform mixture before being ignited. In the
latter half of the compression stroke, the fuel is further injected
into this very lean and uniform mixture in order to form the charge
of an ignitable and combustible mixture near the spark plug. At the
time of ignition, this combustible mixture charge starts burning,
and the flame propagates to the surrounding lean mixture charge, so
that the combustion takes place stably. In this state, the amount
of fuel injected in the suction stroke and in the compression
stroke is larger than that of the mode {circle over (1)} , but the
air-fuel ratio as a whole is still lean (e.g., air-fuel ratio of
about 20 to about 30).
[0099] When the load on the engine further increases, the engine 1
is operated in the lean air-fuel ratio uniform mixture combustion
{circle over (3)}. In this state, the fuel is injected only one
time in the former half of the suction stroke, and the amount of
the injected fuel becomes larger than that of the mode {circle over
(2)}. The uniform air-fuel mixture formed in the cylinder in this
state has a lean air-fuel ratio (e.g., air-fuel ratio of from about
15 to about 25) relatively close to the stoichiometric air-fuel
ratio.
[0100] As the load on the engine further increases to enter into
the high-load operation region of the engine, the amount of fuel
becomes larger than that of the mode {circle over (3)}, and the
engine is operated in the stoichiometric air-fuel ratio uniform
mixture operation {circle over (4)}. In this state, a uniform
mixture of the stoichiometric air-fuel ratio is formed in the
cylinder, and the engine output increases. When the load on the
engine further increases to enter into the full-load operation of
the engine, the amount of fuel injection is further increased in
excess of that of the mode {circle over (4)}, and the engine is
operated in the rich air-fuel ratio uniform mixture operation
{circle over (5)}. In this state, the uniform mixture formed in the
cylinder becomes a rich air-fuel ratio (e.g., air-fuel ratio of
from about 12 to about 14).
[0101] In this embodiment, optimum operation modes {circle over
(1)} to {circle over (5)} have been empirically set based upon the
degree of accelerator opening (amount of the accelerator pedal
depressed by the driver) and the rotational speed of the engine,
and a map using the degree of accelerator opening and the engine
rotational speed is stored in the ROM of the ECU 30. When the
engine 1 is in operation, the ECU 30 determines which one of the
above-mentioned operation modes {circle over (1)} to {circle over
(5)} be selected based on the degree of accelerator opening
detected by the accelerator opening-degree sensor 37 and the
rotational speed of the engine, and determines the amount of fuel
injection, timing for fuel injection, the number of times of
injection and the degree of throttle valve opening based on each of
the modes.
[0102] When the any one of the modes {circle over (1)} to {circle
over (3)} (lean air-fuel ratio combustion) is selected, the ECU 30
determines the amount of fuel injection from the degree of
accelerator opening and the rotational speed of the engine based on
a map that has been prepared in advance for each of the modes
{circle over (1)} to {circle over (2)}. When the mode {circle over
(4)} or {circle over (5)} (stoichiometric air-fuel ratio or rich
air-fuel ratio uniform mixture combustion) is selected, the ECU 30
sets the amount of fuel injection based on the intake air pressure
detected by the intake air pressure sensor 37 and the rotational
speed of the engine by using a map that has been prepared in
advance for each of the modes {circle over (4)} and {circle over
(5)}.
[0103] When the mode {circle over (4)} (stoichiometric air-fuel
ratio uniform mixture combustion) is selected, the ECU 30 controls
the air-fuel ratio by correcting the amount of fuel injection
calculated above by feedback based on the outputs of the air-fuel
ratio sensors 29a and 29b, so that the air-fuel ratio of the
exhaust gas emitted by the engine becomes the stoichiometric
air-fuel ratio.
[0104] The start catalysts (SCs) 5a and 5b are constituted as a
three-way catalyst by using a honeycomb-shaped substrate of
cordierite or the like, forming a thin coating of alumina on the
surface of the substrate, and carrying a novel metal catalyst
component such as platinum Pt, palladium Pd or rhodium Rh on the
alumina layer. The three-way catalyst highly efficiently removes
the three components, i.e., HC, CO and NO.sub.x near the
stoichiometric air-fuel ratio. The three-way catalyst exhibits a
decreased ability for reducing NO.sub.x when the air-fuel ratio of
the exhaust gas flowing in becomes higher than the stoichiometric
air ratio. When the engine 1 is operating at a lean air-fuel ratio,
therefore, the three-way catalyst is not capable of removing
NO.sub.x in the exhaust gas to a sufficient degree.
[0105] In this embodiment, the start catalysts (SCs) 5a and 5b
chiefly work to purify the exhaust gas of when the engine 1 is
operating at a rich air-fuel ratio immediately after the cold
starting and to purity the exhaust gas of when the engine 1 is
operating at the stoichiometric air-fuel ratio under normal
operating condition. Therefore, the start catalysts (SCs) 5a and 5b
are disposed in the exhaust passages 2a and 2b at positions close
to the engine 1 and have a relatively small capacity to decrease
their heat capacity, so that they can be heated to their activated
temperature within a short period of time after the start of the
engine to start their catalytic activity.
[0106] Next, described below is the NO.sub.x occluding and reducing
catalyst 7 according to this embodiment. The NO.sub.x occluding and
reducing catalyst 7 according to this embodiment uses alumina as a
substrate to carry at least one component selected from the alkali
metals such as potassium K, sodium Na, lithium Li and cesium Cs,
alkaline earth elements such as barium Ba and calcium Ca, and rare
earth elements such as lanthanum La, cerium Ce and yttrium Y, as
well as a noble metal such as platinum Pt. The NO.sub.x occluding
and reducing catalyst exhibits the action of absorbing and
releasing NO.sub.x, i.e., absorbs NO.sub.x (nitrogen oxides) in the
exhaust gas in the form of nitric acid ions NO.sub.3.sup.- when the
air-fuel ratio of the exhaust gas flowing in is lean, and releases
the absorbed NO.sub.x when the air-fuel ratio of the exhaust gas
flowing in becomes smaller than the stoichiometric air-fuel ratio
(rich air-fuel ratio).
[0107] The mechanism for absorbing and releasing NO.sub.x will be
described next with reference to the case of using platinum Pt and
barium Ba. The same mechanism, however, is created even when other
noble metals, alkali metals, alkaline earth elements and rare earth
elements are used.
[0108] When the concentration of oxygen increases in the exhaust
gas that is flowing in (i.e., when the air-fuel ratio of the
exhaust gas turns into a lean air-fuel ratio), oxygen adheres in
the form of O.sub.2.sup.31 or O.sup.2- onto platinum Pt, whereby
NO.sub.x in the exhaust gas reacts with O.sub.2.sup.- or O.sup.2-
on platinum Pt thereby to form NO.sub.2. NO.sub.2 in the exhaust
gas and NO.sub.2 thus formed are further oxidized on platinum Pt,
absorbed by the absorbing agent in which they are bonded to barium
oxide BaO and are diffused in the form of nitric acid ions
NO.sub.3.sup.-in the absorbing agent. In a lean atmosphere,
therefore, NO.sub.x in the exhaust gas is absorbed in the form of
nitrates by the NO.sub.x absorbing agent.
[0109] When the concentration of oxygen greatly decreases in the
exhaust gas that is flowing in (i.e., when the air-fuel ratio of
the exhaust gas becomes smaller (more rich) than the stoichiometric
air-fuel ratio), NO.sub.2 forms in a decreased amount on platinum
Pt, and the reaction proceeds in the reverse direction permitting
nitric acid ions NO.sub.3.sup.31 in the absorbing agent to be
released in the form of NO.sub.2 from the absorbing agent. In this
case, the reducing components such as CO and the like and the
components such as HC, CO.sub.2 and the like in the exhaust gas
work to reduce NO.sub.2 on platinum Pt.
[0110] In this embodiment, the engine 1 is normally operated at a
lean air-fuel ratio in most of the load regions except the
high-load operation, and the NO.sub.x occluding and reducing
catalyst absorbs NO.sub.x in the exhaust gas that flows in. When
the engine 1 is operated at a rich air-fuel ratio, the NO.sub.x
occluding and reducing catalyst 7 releases and purifies the
absorbed NO.sub.x by reduction. When the NO.sub.x is absorbed in
increased amounts by the NO.sub.x occluding and reducing catalyst 7
during the operation at a lean air-fuel ratio, therefore, a
rich-spike operation is carried out to change the air-fuel ratio of
the engine from a lean air-fuel ratio to a rich air-fuel ratio for
a short period of time in order to release NO.sub.x from the
NO.sub.x occluding and reducing catalyst and to purify NO.sub.x by
reduction (to regenerate the NO.sub.x occluding and reducing
catalyst).
[0111] However, it has been known that when the rich-spike
operation is effected for the engine 1, the unpurified NO.sub.x is
released from the NO.sub.x occluding and reducing catalyst
immediately after the lean air-fuel ratio is changed over to the
rich air-fuel ratio. This is attributed to the components HC and CO
becoming in short supply in the exhaust gas when the engine is
changed from the lean air-fuel ratio operation over to the rich
air-fuel ratio operation. That is, the air-fuel ratio in the
exhaust gas continuously changes when it is changed from the lean
side over to the rich side. At this moment, though the air-fuel
ratio may be rich, the degree of richness is not very high, and a
region where the amount of the HC and CO in the exhaust gas is
relatively small must be passed through. In this region where the
HC and CO components are in short supply in the exhaust gas,
therefore, it is not considered that the NO.sub.x released from the
NO.sub.x occluding and reducing catalyst is all reduced.
[0112] In this embodiment, therefore, when the NO.sub.x is to be
released from the NO.sub.x occluding and reducing catalyst, the
secondary fuel is injected during the expansion or the exhaust
stroke after the main fuel injection in order to quickly change the
air-fuel ratio of the exhaust gas to a considerably rich air-fuel
ratio, so that the unpurified NO.sub.x will not be released from
the NO.sub.x occluding and reducing catalyst. After the main fuel
injected into the cylinder has burned, the fuel is injected in the
expansion or the exhaust stroke and remains unburned and comes in
contact with the burned gas of a high temperature, and is vaporized
to form hydrocarbons of low molecular weights. Besides, the fuel
supplied by the secondary fuel injection does not contribute to the
combustion in the cylinder. Therefore, even when the fuel is
supplied in a relatively large amount by the secondary fuel
injection, the output torque of the engine does not increase. When
the secondary fuel is injected when the NO.sub.x is to be released
from the NO.sub.x occluding and reducing catalyst, therefore, the
air-fuel ratio of the exhaust gas can be quickly changed down to a
low value without causing a change in the output torque of the
engine. It is therefore possible to supply the exhaust gas having a
high rich degree to the NO.sub.x occluding and reducing catalyst
without passing through a region of intermediate air-fuel ratios.
This prevents the release of unpurified NO.sub.x from the NO.sub.x
occluding and reducing catalyst in the early period of the NO.sub.x
releasing action. The NO.sub.x may be released from the NO.sub.x
occluding and reducing catalyst relying on the secondary fuel
injection only or by effecting the secondary fuel injection at the
initial period only of the rich-spike operation at the time of
conducting the normal rich-spike operation by increasing the amount
of main fuel injection thereby to quickly change the air-fuel ratio
of the exhaust gas to a rich air-fuel ratio.
[0113] However, when the fuel supplied by the secondary fuel
injection partly remains in the cylinder, there may occur a change
in the output torque of the engine. As described above, the ECU 30
calculates the required amount of fuel based on the engine load
conditions (degree of accelerator opening, rotational speed) and
supplies the fuel into the cylinder by the main fuel injection.
When the fuel due to the secondary fuel injection remains in the
cylinders, therefore, this remaining fuel burns in the cylinders in
addition to the fuel supplied by the main fuel injection of the
next cycle; i.e., the output torque of the engine increases due to
the combustion of the fuel of an amount larger than the required
amount, and the torque changes.
[0114] According to the present invention, this problem is solved
by the below-mentioned two methods.
[0115] (A) The fuel supplied by the secondary fuel injection is all
discharged out of the cylinder during the exhaust stroke (while the
exhaust valve is opening), so that no fuel is left.
[0116] (B) When the fuel remains, the amount of injecting the main
fuel in the next time is corrected (decreased) by the remaining
amount of fuel, so that the amount of fuel that contributes to the
combustion comes into agreement with a target amount of main fuel
injection.
[0117] Described below are the embodiments of when these methods
are employed.
[0118] (1) First Embodiment
[0119] In this embodiment, the fuel supplied by the secondary fuel
injection is all discharged out of the cylinder during the exhaust
stroke, in order to prevent a change in the output torque of the
engine caused by the secondary fuel injection.
[0120] In FIG. 2, reference numeral 10 denotes a cylinder
combustion chamber, 11 denotes a piston, 13 denotes an intake port,
13a denotes an intake valve, 15 denotes an exhaust port, and 15a
denotes an exhaust valve. Further, reference numeral 111 denotes a
direct cylinder fuel injection valve, and 17 denotes a spark plug
provided at a central portion in the cylinder head. In this
embodiment, a recessed piston cavity 11a is formed in the top
surface of the piston 11. The cavity 11a works to concentrate the
fuel injected from the fuel injection valve 111 in the latter half
of the compression stroke during the operation at a lean air-fuel
ratio, to the vicinity of the spark plug 17 to form a charge of a
mixture of a combustible air-fuel ratio near the plug 17. That is,
in the main fuel injection for the above-mentioned {circle over
(1)} lean air-fuel ratio stratified charge combustion (fuel is
injected in the compression stroke) and {circle over (2)} lean
air-fuel ratio uniform mixture/stratified charge combustion (fuel
is injected in the suction stroke and in the compression stroke),
the fuel having a relatively strong piercing force (having a high
injection pressure) is injected from the direct cylinder fuel
injection valve 111 toward the piston cavity 11a at a moment when
the piston arrives at a sufficiently elevated position in the
latter half of the compression stroke.
[0121] At this moment, the injected fuel arrives at the surface of
the piston cavity 11a and flows along the curved surface of the
cavity 11a. The cavity 11a has a side surface 11b having a
relatively small radius of curvature on the side remote from the
fuel injection valve 111, so that the fuel flowing along the
surface of the cavity 11a is deflected toward the vicinity of the
spark plug 17. Accordingly, the fuel injected from the fuel
injection valve 111 forms a stratified charge near the spark plug
17.
[0122] In this embodiment, all the fuel supplied by the secondary
fuel injection is discharged through the exhaust port 15 by
utilizing the piston cavity 11a. That is, in this embodiment, the
timing for injecting the fuel is set at a point delayed by 360
degrees in terms of the crank angle behind the timing for injecting
the main fuel. When the secondary fuel is injected, therefore, the
piston 11 is assuming the same position as when the main fuel is
injected (hereinafter referred to as "fuel injection in the
compression stroke") for forming the stratified charge of the
mixture. Accordingly, the fuel supplied by the secondary fuel
injection is deflected along the curved surface 11b in the same
manner as the main fuel injection and flows toward the vicinity of
the spark plug 17 (i.e., toward the exhaust port 13). Here, the
exhaust valve 15a is opening in the latter half of the exhaust
stroke, and the deflected secondary fuel does not form a stratified
charge about the spark plug 17 as designated at F in FIG. 2, and is
all discharged out of the cylinder through the exhaust port 15.
Therefore, the secondary fuel does not remain in the cylinder.
Here, the injected fuel comes in contact with the surface of the
piston cavity 11a. However, the piston which is in operation is
heated at a high temperature, and the fuel that comes in contact
with the surface of the cavity 11a is readily vaporized, and does
not adhere or remain on the surface of the cavity 11a.
[0123] In order to discharge all fuel supplied by the secondary
fuel injection out of the cylinder, the fuel must have been
entirely discharged through the exhaust port 15 before the intake
valve 13a starts opening in the exhaust stroke. If the fuel remains
in the cylinder during a period in which both the exhaust valve 15a
and the intake valve 13a are opening (valve overlapping period),
the fuel partly flows in a reverse direction toward the intake port
and flows again into the cylinder in the next suction stroke; i.e.,
the secondary fuel may partly remain in the cylinder. The engine 1
of this embodiment is equipped with a variable valve timing device
200, and the valve timing varies based on the engine load
conditions. According to this embodiment, therefore, the intake
valve opening timing is read when the secondary fuel injection is
executed, and the amount of the secondary fuel injection is changed
relying on the intake valve opening timing, so that the fuel
supplied by the secondary fuel injection will not reversely flow
toward the intake port and will not remain in the cylinder.
[0124] FIG. 3 is a flow chart illustrating the operation for
controlling the fuel injection according to the embodiment. This
operation is conducted by a routine executed by the ECU 30 at every
predetermined crankshaft rotation angle.
[0125] When the operation starts in FIG. 3, it is judged at a step
301 whether the secondary fuel injection is requested. In this
embodiment, the amount of NO.sub.x absorbed by the NO.sub.x
occluding and reducing catalyst 7 is estimated based on the engine
operating conditions by using a routine (not shown) that is
separately executed. When the absorbed amount of NO.sub.x has
reached a predetermined value, the secondary fuel injection (rich
spike) is requested. Instead of estimating the absorbed amount of
NO.sub.x it may be so presumed that the amount of NO.sub.x absorbed
by the NO.sub.x occluding and reducing catalyst has reached a
predetermined value when a predetermined period of time has lapsed
from the last execution of the NO.sub.x releasing operation or when
the integrated value of the number of revolutions of the engine has
reached a predetermined value from the last execution of the
NO.sub.x releasing operation of the previous time, and the
secondary fuel injection may be requested.
[0126] When the secondary fuel injection is not requested at the
step 301, the operation immediately ends without executing the
steps 303 through 321, and the secondary fuel is not injected. When
the secondary fuel injection is requested at the step 301, on the
other hand, the step 303 is executed to calculate a target value
qinjex of the amount of the secondary fuel injection. At the step
303, the secondary fuel injection amount qinjex necessary for
obtaining a desired air-fuel ratio is calculated from the amount of
the air Q taken in by the cylinder per a revolution of the engine 1
and from the amount of main fuel injection. In this embodiment, the
rotational speed N of the engine, load (degree of accelerator
opening) ACCP, and the amount of the air Q taken in by the cylinder
per a revolution of the engine are measured in advance under
various operating conditions to find a relationship among Q, N and
ACCP. Based on these measured results, the values of the amount of
the air Q taken in by the cylinder were stored in the ROM of the
ECU 30 in the form of a numerical value table using N and ACCP as
parameters. Likewise, the amounts of main fuel injection were
stored in the ROM of the ECU 30 as a numerical value table of N and
ACCP. At the step 303, therefore, the amount of the air Q taken in
and the amount of main fuel injection are calculated from these
numerical tables using the present load conditions (N, ACCP),
thereby to calculate the secondary fuel injection amount qinjex
necessary for bringing the air-fuel ratio of the exhaust gas to a
target value.
[0127] The secondary fuel injection amount qinjex (milliliters)
that is calculated is then converted at a step 305 into a fuel
injection time (fuel injection valve opening time) tauex
(milliseconds) by using a fuel pressure in the common rail 110 and
a characteristic value of the direct cylinder fuel injection
valve.
[0128] At a step 307, the intake valve opening timing (crank angle)
IO currently set by the variable valve timing device 200 is read
and at a step 309, a maximum secondary fuel injection time (guard
value) tauexmax that can now be permitted is calculated.
[0129] In this embodiment as described above, the fuel supplied by
the secondary fuel injection from the fuel injection valve must all
be discharged out of the cylinder before the intake valve opens. In
this embodiment, further, the timing for injecting the secondary
fuel has been fixed (delayed by 360 degrees behind the injection
timing in the compression stroke). In order to discharge all the
injected fuel out of the cylinder before the intake valve opens,
therefore, a maximum amount of fuel injection must be limited. At
the step 309, the time t.sub.1 (milliseconds) is calculated from
the start of fuel injection to the opening of intake valve by using
the present rotational speed N of the engine and a difference
between the intake valve opening crank angle IO read at the step
307 and the secondary fuel injection start crank angle ainjc +360
(ainjc is a timing for injecting the main fuel in the compression
stroke). In order for the fuel injected in the last stage of the
secondary fuel injection to be discharged through the exhaust port,
further, a time t.sub.2 is required for the fuel to move from the
fuel injection valve to the exhaust port. Here, t.sub.2 is
determined by the pressure in the common rail 110. In this
embodiment, therefore, the fuel may remain in the cylinder unless
the injection of fuel from the fuel injection valve is finished
within a time (t.sub.1 - t.sub.2) after the start of the fuel
injection. At the step 309, therefore, the times t.sub.1 and
t.sub.2 are calculated by using the intake valve opening crank
angle IO, rotational speed N of the engine and fuel pressure in the
common rail, and a maximum fuel injection time tauexmax is
calculated as tauexmax =t.sub.1- t.sub.2.
[0130] Then, at steps 311 to 317, the target secondary fuel
injection time tauex set at the step 305 is limited by a maximum
value tauexmax and a minimum value taumin thereby to set a value
tauex to lie within a range taumin .ltoreq.tauex .ltoreq.tauexmax.
The minimum value tauemin is a minimum controllable valve opening
time of the fuel injection valve 111 and is a characteristic value
of the fuel injection valve 111.
[0131] At a step 319, the secondary fuel injection start timing
ainjex is set to be ainjex=ainjc +360 and at a step 321, ainjex and
tauex are set to a fuel injection circuit (not shown). Then, the
secondary fuel injection starts at a crank angle ainjex and
continues for a time tauex.
[0132] According to this embodiment as described above, the fuel
supplied by the secondary fuel injection is deflected toward the
exhaust port 13 by utilizing the piston cavity 11a, and the amount
of fuel injection is controlled based on the engine load conditions
and the valve timing, so that the fuel supplied by the secondary
fuel injection is all discharged out of the cylinder during the
exhaust stroke.
[0133] In the embodiment of FIG. 2, the flow of fuel supplied by
the secondary fuel injection is deflected toward the exhaust port
by the cavity 11a formed in the top surface of the piston. However,
the flow of fuel may be deflected toward the exhaust port by using
other means.
[0134] For example, the fuel injection valve may be constituted as
an air assist valve that injects the compressed air together with
the fuel, and the compressed air may be injected toward the exhaust
port only at the time of the secondary fuel injection, so that the
injected fuel is deflected toward the exhaust port while being
assisted by the air.
[0135] When the fuel injection valve is so constructed as to change
the direction of injection depending on the main fuel injection and
the secondary fuel injection, the direction of fuel injection may
be changed toward the exhaust port or toward the deflecting flow
that is headed to the exhaust port at the time when the secondary
fuel is injected.
[0136] In the embodiment of FIG. 2, the main fuel injection and the
secondary fuel injection are effected using the same fuel injection
valve. It is, however, also allowable to provide an auxiliary fuel
injection valve exclusively for the secondary fuel injection
separately from the fuel injection valve for main fuel injection,
and the direction of injection of the auxiliary fuel injection
valve may be set being pointed to the exhaust port.
[0137] Instead of the piston cavity, there may be provided a
deflecting plate that protrudes into the cylinder at the time of
the secondary fuel injection only, and the flow of fuel supplied by
the secondary fuel injection may be brought into collision with the
deflecting plate so as to be headed toward the exhaust port.
[0138] (2) Second Embodiment
[0139] Next, a second embodiment of the invention will be
described. In this embodiment also, the fuel supplied by the
secondary fuel injection is all discharged out of the cylinder
during the exhaust stroke to prevent a change in the output torque
of the engine caused by the secondary fuel injection, as in the
above-mentioned first embodiment.
[0140] FIG. 4 is a sectional view of the cylinder of the engine 1
and is similar to FIG. 2. In FIG. 4, reference numerals same as
those of FIG. 2 denote the elements same as those of FIG. 2.
[0141] In this embodiment, the secondary fuel injection is effected
at an early timing in the exhaust stroke in which the piston is
located at a position close to the bottom dead center, and the
pressure for the secondary fuel injection (common rail pressure) is
set to be lower than the pressure for the main fuel injection. At
an early timing in the exhaust stroke, the burned gas is produced a
high pressure in the cylinder, and a relatively strong exhaust flow
is produced in the cylinder and moves toward the exhaust port as
indicated by arrows in FIG. 4. If the secondary fuel is injected
with a relatively low pressure at this early timing, then, the
injected fuel does not arrive at the cylinder wall or the piston
piercing through the exhaust flow in the cylinder but rides on the
exhaust flow near the center of the cylinder and is conveyed to the
exhaust port as designated at F in FIG. 4. Accordingly, the
injected fuel does not adhere to the cylinder wall, piston or
cylinder head; i.e., the fuel supplied by the secondary fuel
injection is all discharged out of the cylinder during the exhaust
stroke and does not remain in the cylinder.
[0142] In the above-mentioned embodiment, the amount of secondary
fuel injection is controlled based on the engine operating
conditions (load conditions) and the valve timings in order to
discharge all fuel supplied by the secondary fuel injection out of
the cylinder before the intake valve is opened. In this embodiment,
however, the timing of the secondary fuel injection plays an
important role. That is, as the fuel injection timing is delayed,
the fuel that is injected may partly flow reversely toward the
intake port. When the fuel injection timing is too early, on the
other hand, the injected fuel is diffused in the cylinder and may
not all be discharged out of the cylinder riding on the exhaust
flow. Next, described below is the operation for controlling the
fuel injection timing according to this embodiment.
[0143] FIG. 5 is a flow chart illustrating the operation for
controlling the fuel injection according to the embodiment. This
operation is conducted by a routine executed by the ECU 30 at every
predetermined crankshaft rotation angle.
[0144] When the operation starts in FIG. 5, it is judged at a step
501 whether the secondary fuel injection is requested. At a step
503, a target value qinjex of the secondary fuel injection amount
is calculated and at a step 505, the injection time tauex is
calculated from the target injection amount qinjex. The target
injection amount qinjex at the step 503 and the injection time
tauex at the step 505 are calculated by the same methods as those
of the steps 303 and 305 in FIG. 3. In this embodiment, however,
the pressure in the common rail 110 for the secondary fuel
injection is controlled to be smaller than the pressure for the
main fuel injection. Even when the target injection amount qinjex
is the same as the case of FIG. 3, therefore, the injection time
tauex becomes longer than that of the case of FIG. 3.
[0145] After qinjex and tauex are calculated in this embodiment,
the present intake valve opening timing (crank angle) IO and the
exhaust valve opening timing (crank angle) EO are read at a step
507, and, at a step 509, a flying time t.sub.2 of the fuel from
when it is injected from the fuel injection valve 111 until it is
discharged through the exhaust port is calculated as
t.sub.2=.alpha.+.beta.. Here, .alpha. is the time required by the
fuel from when it is injected through the fuel injection valve 1112
until when it arrives at the central portion of the cylinder, and
varies in proportion to the pressure in the common rail 110 (fuel
injection pressure), and .beta. is the time required by the fuel
from when it has arrived at the central portion until when it is
discharged through the exhaust port riding on the exhaust flow, and
varies in proportion to the rotational speed N of the engine.
[0146] After the flying time t.sub.2 is calculated at the step 509,
a maximum value (guard value) tauexmax of the secondary fuel
injection time is calculated at a step 511 as tauexmax=t.sub.3 -
t.sub.2.
[0147] Here, t.sub.3 is the time from when the exhaust valve is
opened until when the intake valve is opened, and is calculated by
using the valve opening timings IO, EO of the intake and exhaust
valves read at the step 507 and by using the rotational speed N of
the engine. That is, tauexmax is an injection time corresponding to
a maximum fuel injection amount that can be all discharged out of
the cylinder without reversely flowing into the intake port when
the secondary fuel is injected simultaneously with the opening of
the discharge valve.
[0148] After tauexmax is calculated at the step 511, the target
injection time tauex calculated at the step 505 is limited at the
steps 513 to 517 by the maximum value tauexmax and the minimum
value taumin. At a step 521, the secondary fuel injection start
timing ainjex is calculated based on the intake valve opening
timing IO, rotational speed N of the engine and the value of tauex
after being limited. That is, the secondary fuel injection starts
before the intake valve starts opening by the amount of time (tauex
+t.sub.2), i.e., starts at a timing at which the fuel injected at
the end of the secondary fuel injection can be discharged through
the exhaust port just before the intake valve opens. That is, in
this embodiment, the secondary fuel injection timing is advanced
with an increase in the amount of the secondary fuel injection.
Therefore, the fuel supplied by the secondary fuel injection all
arrives at the exhaust port before the intake valve opens, and is
also prevented from diffusing in the cylinder, caused by the
secondary fuel injection timing being too early.
[0149] In the above-mentioned second embodiment, the direction of
fuel injection by the direct cylinder fuel injection valve 111 is
the same as that of the embodiment of FIG. 2. As shown in FIG. 6,
however, the direct cylinder fuel injection valve may be provided
being directed downward at the central portion of the cylinder
head. At the time of the secondary fuel injection, the fuel is
injected with a low pressure toward the central portion of the
cylinder, which is more effective for preventing the fuel from
remaining in the cylinder.
[0150] (3) Third Embodiment
[0151] Described below is a third embodiment of the present
invention. In this embodiment, the amount of main fuel injection is
corrected based on a prerequisite that the fuel supplied by the
secondary fuel injection partly remains in the cylinder. That is,
in this embodiment, the amount of fuel remaining in the cylinder
due to the secondary fuel injection is calculated from the engine
operating conditions, and the amount of main fuel injection in the
next time is decreased by the remaining amount of fuel. Thus, the
amount of fuel that contributes to the combustion in the cylinder
due to the main fuel injection comes into correct agreement with
the target amount of main fuel injection. Even when the fuel
remains due to the secondary fuel injection, therefore, the change
in the output torque of the engine does not occur.
[0152] First, described below is the method of calculating the
remaining amount of fuel due to the secondary fuel injection
according to this embodiment.
[0153] FIG. 7 is a graph illustrating a relationship between the
output torque of the engine (ordinate) and the amount of main fuel
injection (abscissa) of when the engine is operated at a
predetermined rotational speed. In FIG. 7, a curve I represents a
relationship between the output torque and the amount of main fuel
injection when the main fuel only is injected without injecting the
secondary fuel, and a curve II represents a relationship between
the output torque and the amount of main fuel injection when the
secondary fuel is injected in addition to the main fuel injection.
As described earlier, the amount of the secondary fuel injection
has been determined in a manner that the air-fuel ratio of the
exhaust gas becomes a target air-fuel ratio in their respective
cases, and is determined based on the load on the engine (main fuel
injection) and the rotational speed. In this case, further, the
timing for the secondary fuel injection may be set by any one of
the above-mentioned methods or may be fixed to a predetermined
suitable crank angle.
[0154] As described earlier, when the fuel due to the secondary
fuel injection does not remain in the cylinder, the output torque
of the engine remains the same irrespective of whether the
secondary fuel is injected. When the fuel remains in the cylinder
due to the secondary fuel injection, however, the output torque of
the engine increases by an amount corresponding to the amount of
the remaining fuel (curve II in FIG. 7).
[0155] It is now presumed that the output torque has increased with
a given amount of main fuel injection due to the injection of the
secondary fuel as represented by a in FIG. 7. It is further
presumed that the amount of increase in the output torque is equal
to an increase in the amount of main fuel injection by an amount
represented by b in FIG. 7. In this case, the increase in the
output torque is caused by the combustion of the fuel remaining in
the cylinder due to the secondary fuel injection. Therefore, the
amount of the remaining fuel will become equal to the amount of
main fuel injection necessary for increasing the output torque,
i.e., will become equal to the amount of fuel denoted by b in FIG.
7. In this embodiment, therefore, when an increase in the output
torque due to the secondary fuel injection is as denoted by a in
FIG. 7, the remaining amount of fuel is estimated presuming that
the amount represented by b in FIG. 7 is equal to the amount of
fuel remaining in the cylinder.
[0156] According to this embodiment, curves corresponding to those
of FIG. 7 are prepared in advance through experiment for every
combination of the rotational speeds of the engine and the fuel
injection modes {circle over (1)} to {circle over (5)} described
below, and the amount of the remaining fuel (b in FIG. 7) is
calculated in each of the main fuel injection amounts. The amounts
of the remaining fuel b are prepared in the form of a numerical
value table using the engine rotational speed N and the main fuel
injection amount (qinj=qinjei+qinjec) as parameters for each of the
fuel injection modes, and are stored in the ROM of the ECU 30. When
the engine is in operation, the ECU 30 calculates the amount of
fuel remaining in the cylinder when the secondary fuel is injected
based on the engine rotational speed N and the main fuel injection
amount qinj. Here, qinjei is the amount of the first main fuel
injection during the suction stroke, qinjec is the amount of the
second main fuel injection in the compression stroke, and qinj is
the sum of the two.
[0157] In this embodiment, the engine 1 is also operated in the
below-mentioned five kinds of fuel injection modes.
[0158] {circle over (1)} A lean air-fuel ratio stratified charge
combustion (fuel is injected in the compression stroke).
[0159] {circle over (2)} A lean air-fuel ratio uniform
mixture/stratified charge combustion (fuel is injected in the
suction stroke and in the compression stroke).
[0160] {circle over (3)} A lean air-fuel ratio uniform
mixture/stratified charge combustion (fuel is injected in the
suction stroke).
[0161] {circle over (4)} A stoichiometric air-fuel ratio uniform
mixture combustion (fuel is injected in the suction stroke).
[0162] {circle over (5)} A rich air-fuel ratio uniform mixture
combustion (fuel is injected in the suction stroke).
[0163] In this embodiment, when the mode {circle over (2)} (fuel is
injected in the suction stroke and in the compression stroke) is
selected, the correction is effected by decreasing the amount of
fuel injection in the suction stroke by the remaining amount of
fuel. The remaining fuel diffuses in the cylinder to become part of
the uniform mixture and, hence, directly affects the air-fuel ratio
of the uniform mixture formed in the cylinder. In order to prevent
this, the amount of the fuel injection in the suction stroke for
forming the uniform mixture is decreased by the remaining amount of
fuel, so that the air-fuel ratio of the uniform mixture actually
formed is maintained at a target value.
[0164] FIG. 8 is a flow chart illustrating the operation for
controlling the main fuel injection according to the embodiment.
This operation is executed at every predetermined crankshaft
rotation angle of the engine.
[0165] In FIG. 8, when the operation starts, the engine load
(degree of accelerator opening) ACCP and the rotational speed N are
read at a step 801. At steps 803, 811 and 823, it is determined
which of the fuel injection modes {circle over (1)} to {circle over
(4)} shall be employed based on the degree of accelerator opening
ACCP and the rotational speed N.
[0166] At the step 803, it is determined from ACCP and N whether
one of the fuel injection mode of {circle over (3)} lean air-fuel
ratio uniform mixture combustion (fuel is injected in the suction
stroke), {circle over (4)} stoichiometric air-fuel ratio uniform
mixture combustion (fuel is injected in the suction stroke), or
{circle over (5)} rich air-fuel ratio uniform mixture combustion
(fuel is injected in the suction stroke) is employed. When the mode
{circle over (3)} or {circle over (4)}, {circle over (5)} is
employed, the suction stroke fuel injection amount qinjei is
calculated at the step 805 based on ACCP and N from the numerical
value table that has been stored in advance in the ROM of ECU 30.
At a step 807, the compression stroke fuel injection amount qinjec
is set to 0.
[0167] Then, at a step 809, the sum qinj of qinjei and qinjec is
calculated, and the amount b of fuel remaining in the cylinder when
the secondary fuel is injected is calculated from the relationship
of FIG. 7 in the fuel injection mode {circle over (3)} or {circle
over (4)} based on the rotational speed N and the amount of main
fuel injection qinj. At a step 817, it is judged whether the
secondary fuel injection is now requested. When the secondary fuel
injection is requested, the operation proceeds to a step 819 where
the suction stroke fuel injection amount qinjei is decreased by the
remaining amount b of fuel and at a step 821, the suction stroke
fuel injection amount qinjei after corrected and the compression
stroke fuel injection amount qinjec (quinjec=0 in this case) are
set to the fuel injection circuit before terminating the operation.
When the secondary fuel is injected, therefore, the amount of main
fuel is decreased by an amount equal to the remaining amount b of
fuel. Even when the secondary fuel is injected, therefore, the
output torque of the engine is prevented from changing.
[0168] When none of the fuel injection mode {circle over (3)},
{circle over (4)} or {circle over (5)} is employed at the step 803,
the routine proceeds to a step 811 where it is judged whether one
of the fuel injection mode {circle over (2)} (lean air-fuel ratio
uniform mixture/stratified charge combustion (fuel is injected in
the suction stroke and in the compression stroke)) is employed.
When the mode {circle over (2)} is employed, the suction stroke
fuel injection amount qinjei and the compression stroke fuel
injection amount qinjec are calculated at a step 813 from the
numerical value table stored in advance in the ROM of ECU 30 based
on ACCP and N. At a step 815, the remaining amount b of fuel due to
the secondary fuel injection is calculated from the relationship of
FIG. 7 in the mode {circle over (2)}, and the operations of the
step 817 and subsequent steps are carried out. In this case, also
the suction stroke fuel injection amount qinjei only is decreased
by the remaining amount b of fuel, but the compression stroke fuel
injection amount qinjec is not corrected.
[0169] When none of the fuel injection modes {circle over (2)} to
{circle over (5)} is employed at the steps 803 and 801, then, the
fuel injection mode {circle over (1)} (lean air-fuel ratio
stratified charge combustion (fuel is injected in the compression
stroke)) is employed. In this case, the compression stroke fuel
injection amount qinjec is calculated based on ACC and N at a step
823, and the suction stroke fuel injection amount qinjei is set to
0. In this case, also the remaining amount b of fuel due to the
secondary fuel injection is calculated at the step 827 from the
relationship of FIG. 7 in the mode {circle over (1)}, and it is
judged at a step 829 whether the secondary fuel injection is
requested. When the secondary fuel injection is requested at the
step 829, the compression stroke fuel injection amount qinjec is
decreased by the amount of the remaining fuel b at a step 831, and
the operation of the step 821 is executed.
[0170] According to this embodiment as described above, the amount
of main fuel injection is corrected based upon the remaining amount
of fuel due to the secondary fuel injection, and the output torque
of the engine is not changed by the secondary fuel injection. In
effecting the correction in the mode {circle over (3)} (fuel is
injected in the suction stroke and in the compression stroke),
further, the suction stroke fuel injection amount only is
corrected, so that the air-fuel ratio of the uniform air-fuel ratio
mixture is brought into agreement with the target value.
[0171] In this embodiment, the correction is effected for each
cycle by using a relationship between the amount of main fuel
injection and the amount of fuel remaining in the cylinder, that is
found in advance through experiment. It is, however, also allowable
to detect a change in the output torque of the engine (change
represented by a in FIG. 7) caused by the fuel remaining in the
cylinder from a change in the rotational speed of the engine or
from a change in the combustion pressure in the cylinder, and
calculate the amount b for correcting the amount of main fuel
injection from the relationship of FIG. 7 based on the amount of
change in the torque. In this case, the amount of main fuel
injection is corrected in a cycle next of the cycle in which the
change in the torque was detected.
[0172] The foregoing embodiments have dealt with the engine which
changes over the fuel injection mode based on the engine operating
conditions. However, it needs not be pointed out that the present
invention can also be applied to the engine in which the fuel
injection mode is fixed to the suction stroke fuel injection or the
compression stroke fuel injection or to both of them (injected
twice), as a matter of course.
[0173] Further, the foregoing embodiments have dealt with the case
where the NO.sub.x occluding and reducing catalyst was disposed in
the exhaust passage. However, it needs not be pointed out that the
invention is in no way limited thereto only but can be applied to
any case where the secondary fuel is injected. For example, when a
selectively reducing catalyst is disposed in the exhaust passage to
reduce the NO.sub.x by selectively reacting HC in the exhaust gas
(or HC adsorbed by the catalyst) with NO.sub.x under the conditions
of a lean air-fuel ratio, it is required to supply HC to the
selectively reducing catalyst. The present invention can be applied
even to the case where the HC is supplied to the selectively
reducing catalyst by the secondary fuel injection.
[0174] (4) Fourth Embodiment
[0175] Next, described below is a fourth embodiment of the present
invention.
[0176] FIG. 9 schematically illustrates the constitution of this
embodiment and is similar to FIG. 1. In FIG. 9, reference numerals
same as those of FIG. 1 denote the same elements.
[0177] The embodiment of FIG. 9 is different from the embodiment of
FIG. 1 with respect to the provision of an exhaust gas
recirculation device for recirculating part of the exhaust gas of
the engine into the engine intake air system. Though not indicated
in FIG. 9, the engine 1 in this embodiment, too, is equipped with
the common rail 110, throttle valve 15, etc. like in the embodiment
of FIG. 1.
[0178] In this embodiment as shown in FIG. 9, the upstream side of
the SC 5b of the exhaust passage 2b of the cylinders #2 and #3 is
connected to the surge tank 10a of the engine intake passage 10
through an EGR passage 43. Further, an EGR valve 41 comprising a
flow rate control valve is provided in the EGR passage 43 to
control the flow rate of the exhaust gas recirculating from the
exhaust passage 2b to the intake passage 10 through the EGR
passage. The EGR valve 41 is equipped with an actuator 41a of a
suitable form such as step motor, negative-pressure actuator, etc.
that operates in response to a control signal from the ECU 30, and
determines its opening degree based on the control signal from the
ECU 30.
[0179] In this embodiment, too, the ECU 30 changes the fuel
injection mode of the direct cylinder injection valves 111 to 114
in the same manner as in the embodiment of FIG. 1, and operates the
engine in any one of the below-mentioned five modes based on the
engine operating conditions.
[0180] {circle over (1)} A lean air-fuel ratio stratified charge
combustion (fuel is injected in the compression stroke).
[0181] {circle over (2)} A lean air-fuel ratio uniform
mixture/stratified charge combustion (fuel is injected in the
suction stroke and in the compression stroke).
[0182] {circle over (3)} A lean air-fuel ratio uniform
mixture/stratified charge combustion (fuel is injected in the
suction stroke).
[0183] {circle over (4)} A stoichiometric air-fuel ratio uniform
mixture combustion (fuel is injected in the suction stroke).
[0184] {circle over (5)} A rich air-fuel ratio uniform mixture
combustion (fuel is injected in the suction stroke).
[0185] In this embodiment, further, the ECU 30 controls the EGR
valve 41 to recirculate part of the exhaust gas into the intake
passage 10 from the exhaust passage 2b based on the engine
operating conditions. In other words, this embodiment executes the
external EGR. In order to control the amount of EGR, the output
port of the ECU 30 is connected to the actuator 41a of the EGR
valve through a drive circuit (not shown) to control the opening
degree of the EGR valve 41.
[0186] In this embodiment, too, the ECU 30, as required, executes
the secondary fuel injection from the direct cylinder fuel
injection valves 111 to 114 into the respective cylinders during
the expansion stroke or the exhaust stroke while the engine is in
operation, in order to change the air-fuel ratio of the exhaust gas
from the engine independently of the engine operating air-fuel
ratio.
[0187] In this embodiment, as the amount of NO.sub.x absorbed by
the NO.sub.x occluding and reducing catalyst 7 increases during the
operation at a lean air-fuel ratio, the ineffective fuel that does
not burn in the cylinder is supplied to the engine so that the
exhaust gas from the engine becomes a rich air-fuel ratio, thereby
to release NO.sub.x from the NO.sub.x occluding and reducing
catalyst and to purify the NO.sub.x by reduction (to regenerate the
NO.sub.x occluding and reducing catalyst).
[0188] In this embodiment, the ECU 30 increases or decreases the
value of an NO.sub.x counter in order to estimate the amount of NOX
absorbed and held by the NO.sub.x occluding and reducing catalyst
7. The amount of NO.sub.x absorbed by the NO.sub.x occluding and
reducing catalyst 7 per a unit time varies in proportion to the
amount of NO.sub.x in the exhaust gas flowing into the NO.sub.x
occluding and reducing catalyst per a unit time, i.e., varies in
proportion to the amount of NO.sub.x generated by the engine 1 per
a unit time. On the other hand, the amount of NO.sub.x generated by
the engine per a unit time is determined by the amount of fuel fed
to the engine, air-fuel ratio, flow rate of the exhaust gas, etc.
When the operation conditions of the engine are determined,
therefore, it is possible to know the amount of NO.sub.x absorbed
by the NO.sub.x occluding and reducing catalyst. According to this
embodiment, the engine operating conditions (degree of accelerator
opening, engine rotational speed, amount of the air taken in,
intake air pressure, air-fuel ratio, amount of feeding fuel, etc.)
are changed to measure the amount of NO.sub.x generated by the
engine per a unit time, and the amount of NO.sub.x absorbed by the
NO.sub.x occluding and reducing catalyst 7 per a unit time is
stored in the ROM of ECU 30 in the form of a numerical value table
using, for example, load on the engine (amount of fuel injection)
and the engine rotational speed as parameters. The ECU 30
calculates the amount of NO.sub.x absorbed by the NO.sub.x
occluding and reducing catalyst per a unit time after every
predetermined period of time (after every unit time) by using the
load on the engine (amount of fuel injection) and the engine
rotational speed, and increases the value of the NO.sub.x counter
by the amount of NO.sub.x absorbed. Therefore, the value of the
NO.sub.x counter always indicates the amount of NO.sub.x absorbed
by the NO.sub.x occluding and reducing catalyst 7. When the value
of the NO.sub.x counter exceeds a predetermined value while the
engine is in operation at a lean air-fuel ratio, the ECU 30
supplies to the engine the fuel that does not burn in the
combustion chamber to change the air-fuel ratio of the exhaust gas
of the engine over to a rich air-fuel ratio. Therefore, the exhaust
gas having a rich air-fuel ratio flows into the NO.sub.x occluding
and reducing catalyst irrespective of the engine operating air-fuel
ratio. Therefore, the absorbed NO.sub.x is released from the
NO.sub.x occluding and reducing catalyst and is purified by
reduction. The time for maintaining the exhaust gas air-fuel ratio
rich by supplying the ineffective fuel is experimentally determined
based upon the kind and volume of the NO.sub.x occluding and
reducing catalyst. The value of the NO.sub.x counter is reset to 0
after the NO.sub.x is released from the NO.sub.x occluding and
reducing catalyst and is purified by reduction upon supplying the
ineffective fuel. Upon supplying the ineffective fuel based on the
amount of NO.sub.x absorbed by the NO.sub.x occluding and reducing
catalyst 7 as described above, the NO.sub.x occluding and reducing
catalyst 7 is properly regenerated and is not saturated with the
absorbed NO.sub.x.
[0189] As described above, the ineffective fuel is supplied by the
two methods, i.e., a method which injects the secondary fuel from
the direct cylinder fuel injection valve into the cylinder in the
expansion stroke or the exhaust stroke of the cylinder, and a
method which injects the fuel into the exhaust port. In this
embodiment having the direct cylinder fuel injection valves 111 to
114, the ineffective fuel is supplied to the engine by the
secondary fuel injection. The present invention, however, can be
similarly applied even to the engine equipped with exhaust port
fuel injection valves and in which the ineffective fuel is supplied
by the exhaust port fuel injection.
[0190] When the ineffective fuel is supplied to the engine by the
secondary fuel injection (or exhaust port fuel injection) as
described above, the exhaust gas of the engine contains relatively
large amounts of unburned fuel supplied as the ineffective fuel.
When the ineffective fuel is supplied while the EGR is being
executed, therefore, the exhaust gas containing relatively large
amounts of unburned fuel is recirculated into the intake passage 10
through the EGR passage 43, and the unburned fuel is supplied into
the combustion chamber in the cylinder and is burned in the
combustion chamber. As described above, however, the amount of fuel
injection into the engine (hereinafter referred to as the amount of
main fuel injection to make a distinction over the ineffective
fuel) is controlled to an optimum value by the ECU 30 based on the
engine operating conditions. When the unburned fuel supplied into
the combustion chamber together with the recirculated exhaust gas
burns, therefore, the amount of fuel supplied into the engine
becomes excessive, and the air-fuel ratio becomes too rich causing
the combustion to become unstable, or the rich combustion air-fuel
ratio causes the engine to produce an increased output, resulting
in a change in the engine output torque.
[0191] When the secondary fuel is injected according to this
embodiment, therefore, the EGR is limited to solve the
above-mentioned problem. That is, the EGR is limited (e.g.,
interrupted), whereby no exhaust gas containing the unburned fuel
recirculates into the combustion chamber of the engine. Therefore,
the combustion air-fuel ratio in the combustion chamber varies in
proportion to the amount of main fuel injection, and the air-fuel
ratio is prevented from becoming more rich than an optimum
value.
[0192] FIG. 10 is a flow chart illustrating the operation of the
secondary fuel injection according to the embodiment. This
operation is conducted by a routine executed by the ECU 30 at every
predetermined interval (e.g., at every predetermined crankshaft
rotation angle).
[0193] When the operation starts in FIG. 10, it is judged at a step
1001 whether the secondary fuel injection is now requested. In this
embodiment, the ECU 30 requests the secondary fuel injection for a
predetermined period of time only when the value of the NO.sub.x
counter CNOX of the NO.sub.x occluding and reducing catalyst 7
becomes larger than a predetermined value.
[0194] When the secondary fuel injection is requested at the step
1001, the degree of accelerator opening ACCP, the engine rotational
speed NE and the engine intake air pressure PM are read at a step
1003 and where the present operation mode ({circle over (1)} to
{circle over (5)}) is judged from ACCP and NE. Further, the present
main fuel injection amount qINJ of the engine is calculated from
the numerical value table prepared for each of the operation modes
based on ACCP and NE (modes {circle over (1)} to {circle over (3)})
or based on PM and NE (modes {circle over (4)} and {circle over
(5)}).
[0195] At a step 1007, the EGR is interrupted. In this embodiment,
the EGR is interrupted by fully closing the EGR valve 41. At a step
1009, it is judged whether the EGR is interrupted by the above
operation (i.e., whether the EGR valve 41 is fully closed). Steps
1011 and 1013 are not executed until the EGR is interrupted.
[0196] When the EGR is interrupted at the step 1009, the secondary
fuel injection amount q.sub.EX is calculated at the step 1011. The
secondary fuel injection amount q.sub.EX is calculated based on the
main fuel injection amount q.sub.INJ and the engine operating
air-fuel ratio so that the air-fuel ratio of the exhaust gas
flowing into the NO.sub.x occluding and reducing catalyst 7 becomes
a predetermined rich air-fuel ratio. At the step 1013, the
secondary fuel is injected into all cylinders in the expansion
stroke or in the exhaust stroke. When the secondary fuel injection
is not requested at the step 1001, the operation immediately
terminates without injecting the secondary fuel. In this case, the
EGR that is being effected is allowed to continue.
[0197] In this embodiment, the EGR is interrupted when the
secondary fuel is injected, to prevent the unburned fuel from
recirculating into the engine combustion chamber and to prevent the
combustion from losing stability and the output torque from
changing. In this embodiment, the EGR is completely interrupted
when the secondary fuel is injected. In the actual operation,
however, problems do not occur even if the unburned fuel is
recirculated into the combustion chamber to some extent unless the
combustion becomes unstable and the output torque changes.
Therefore, a maximum EGR amount may be found in advance through
experiment that does not cause problem even if the EGR is executed
with the secondary fuel being injected, and the EGR amount may be
decreased to a value not larger than the above maximum value when
the secondary fuel is injected.
[0198] (5) Fifth Embodiment
[0199] The fourth embodiment has dealt with the case of the
external EGR system. However, the same control operation can be
applied to the case of the internal EGR system, too.
[0200] FIG. 11 is a diagram schematically illustrating the
constitution of a fifth embodiment of the present invention using
the internal EGR system. In FIG. 11, reference numerals the same as
those of FIGS. 1 and 9 denote elements similar to those of FIGS. 1
and 9.
[0201] The embodiment of FIG. 11 is provided with neither the EGR
passage 43 nor the EGR valve 41 of FIG. 9. Instead, the internal
EGR is controlled by using a variable valve timing device 200 for
varying the valve timings of the engine 1. In this embodiment, any
known variable valve timing device 200 can be used provided it is
capable of varying the valve timings of the engine 1 based on
control signals from the ECU 30. For example, there can be used any
one for varying the open-close timings of the intake valves and/or
the exhaust valves, or for varying the open-close timings as well
as the valve lift. The valve timings may be varied either
continuously or stepwisely.
[0202] FIG. 12 is a diagram illustrating the valve timings of the
engine 1. FIG. 12 schematically illustrates general open-close
timings of an intake valve and an exhaust valve, and where the
open-close timings of the intake valve are changed by an equal
amount. In FIG. 12, TDC is the top dead center of the piston, BDC
is the bottom dead center, IO and IC are the valve-opening timing
and the valve-closing timing of the intake valve, and EO and EC are
the valve-opening timing and the valve-closing timing of the
exhaust valve. As shown in FIG. 12, the intake valve is opened
before the top dead center (TDC) in the exhaust stroke and is
closed after the bottom dead center (BDC) in the suction stroke.
The exhaust valve is opened before the bottom dead center (BDC) in
the explosion stroke and is closed after the top dead center (TDC)
in the exhaust stroke. In the exhaust stroke as shown in FIG. 12,
the valve timing has been so set that the intake valve is opened
(IO) before the exhaust valve is closed (EC) and, hence, there
exists a period in which both the intake valve and the exhaust
valve are opened (OL in FIG. 12). In this embodiment, the length
(angle) of the period OL is called valve overlapping amount. In
this embodiment, as will be described later, the intake valve
timing (valve-opening timing) can be adjusted from a timing
represented by IO.sub.0 (most delayed timing) to a timing
represented by IO.sub.1 (most advanced timing) shown in FIG. 12. In
this embodiment, further, the crankshaft rotation angle from the
most delayed valve timing position (IO.sub.0) to the present
position (IO) is defined to be a valve timing value VT. In this
embodiment as will be understood from FIG. 12, the timing for
closing the exhaust valve is fixed and, hence, the valve timing
value VT and the valve overlapping amount OL correspond to each
other in a 1:1 manner.
[0203] In general, the time in which the intake valve remains
opened during the exhaust stroke increases with an increase in the
valve overlapping amount OL of the intake and exhaust valves (with
an increase in the intake valve timing VT). Therefore, the burned
gas (exhaust gas) after the combustion in the cylinder flows
reversely into the intake port through the intake valve that is
opened, and is recirculated again into the cylinder during the
suction stroke. Therefore, the amount of exhaust gas (amount of EGR
gas) recirculated into the engine combustion chamber increases with
an increase in the valve overlapping amount OL. According to this
embodiment, therefore, the ECU 30 adjusts the amount of the exhaust
gas recirculating into the engine combustion chamber by controlling
the intake valve timing VT (i.e., valve overlapping amount OL)
instead of controlling the opening degree of the EGR valve 41 of
FIG. 9.
[0204] When the secondary fuel is injected into the cylinders
during the expansion stroke or the exhaust stroke, the ineffective
fuel that is injected partly flows reversely into the intake port
together with the burned gas during the overlapping period and
recirculates into the combustion chamber during the suction stroke,
causing the same problem as that of the external EGR. In this case,
therefore, the ECU 30 interrupts the EGR (sets the overlapping
amount OL to 0) when the secondary fuel is being injected, so that
the combustion will not lose stability and the output torque will
not be changed by the recirculation of the unburned fuel.
[0205] The operation in this case is the same as that of the flow
chart of FIG. 10. However, the operation for interrupting the EGR
at the step 1007 is executed by delaying the intake valve timing VT
and by setting the valve overlapping amount to be 0.
[0206] In this case, too, the EGR amount may be decreased to such a
degree that no problem occurs in practice when the secondary fuel
is injected, instead of interrupting the EGR.
[0207] (6) Sixth Embodiment
[0208] Described below is a sixth embodiment of the present
invention.
[0209] In the fourth and fifth embodiments, the EGR is interrupted
when the secondary fuel is injected. In the embodiment described
below, however, the injection of secondary fuel is inhibited when
the EGR is executed. Since no secondary fuel is injected when the
EGR is executed, no unburned fuel is contained in the exhaust gas
recirculated into the engine combustion chamber. Similar to the
above-mentioned embodiments, therefore, a problem caused by the
recirculation of the unburned fuel into the combustion chamber does
not occur.
[0210] FIG. 13 is a flow chart illustrating the operation of the
secondary fuel injection when the secondary fuel injection is
inhibited at the time of executing the EGR in the engine of the
external EGR system of FIG. 9. This operation is conducted by a
routine executed by the ECU 30 at predetermined interval (e.g., at
predetermined crankshaft rotation angle).
[0211] In the engine 1 of FIG. 9, the EGR passage 43 is connected
to the exhaust passage 2b of the cylinders #2 and #3 of the engine.
When the EGR is executed, therefore, the secondary fuel injection
may be inhibited for the cylinders #2 and #3 to prevent the
unburned fuel from being mixed into the recirculating exhaust gas.
In this operation, therefore, the secondary fuel is not injected
into the cylinders #2 and #3 when the EGR is executed, and the
secondary fuel is injected into the cylinders #1 and #4 only.
[0212] When the operation starts in FIG. 13, it is judged at a step
1301 whether the secondary fuel injection is now requested. When
the secondary fuel injection is requested, the degree of
accelerator opening ACCP, the engine rotational speed NE and the
engine intake air pressure PM are read at a next step 1303 the
present main fuel injection amount q.sub.INJ is calculated.
Operations at steps 1301 to 1305 are the same as operations of the
steps 1001 to 1005 of FIG. 10.
[0213] Next, it is judged at a step 1307 whether the EGR is now
being effected. When the EGR is effected, the amount Q.sub.EX of
recirculating exhaust gas is calculated at a step 1309 based on the
main fuel injection amount q.sub.INJ and the rotational speed NE.
Then, at a step 1311, the secondary fuel injection amount q.sub.EX
is calculated based on the EGR amount Q.sub.EX and the main fuel
injection amount q.sub.INJ. In this embodiment, the secondary fuel
injection amount q.sub.EX is set in advance based on the main fuel
injection amount q.sub.INJ and the amount Q.sub.EX of recirculating
exhaust gas, so that the air-fuel ratio of the exhaust gas flowing
into the NO.sub.x occluding and reducing catalyst 7 becomes a
predetermined rich air-fuel ratio. When the EGR is effected,
however, no secondary fuel is injected to the cylinders #2 and #3.
Therefore, the air-fuel ratio of the exhaust gas flowing into the
NO.sub.x occluding and reducing catalyst 7 must be maintained at a
predetermined rich air-fuel ratio by injecting the secondary fuel
into the cylinders #1 and #4 only. In this embodiment, the
secondary fuel injection amount q.sub.EX is set previously based on
the main fuel injection amount q.sub.INJ and the amount Q.sub.EX of
circulating exhaust gas (based on combustion air-fuel ratio in the
cylinder determined by q.sub.EX and Q.sub.EX) for the case where
the secondary fuel is injected into the cylinders #1 and #4 only,
and is stored as a numerical value table using q.sub.INJ and
Q.sub.EX as parameters in the ROM of the ECU 30. At a step 1311,
therefore, the secondary fuel injection amount q.sub.EX is
calculated from q.sub.INJ and Q.sub.EX based on the numerical value
table. At a step 1313, the secondary fuel is injected in the
expansion stroke or in the exhaust stroke of the cylinders #1 and
#4.
[0214] When the EGR is not being effected at the step 1307, the
operation proceeds to a step 1315 where the secondary fuel
injection amount q.sub.EX is calculated. Here, since the EGR is not
being effected, the secondary fuel is injected into all cylinders,
and the secondary fuel injection amount q.sub.EX is calculated
based on the main fuel injection amount q.sub.INJ and the engine
operating air-fuel ratio like at the step 1011 in FIG. 10. At a
step 1317, the secondary fuel is injected into all cylinders
inclusive of the cylinders #2 and #3 in the expansion stroke or in
the exhaust stroke. When the secondary fuel injection is not
requested at the step 1301, the secondary fuel is not injected, and
the operation is immediately terminated.
[0215] When the EGR is being executed as described above, the
secondary fuel injection is inhibited to completely prevent the
unburned fuel from being mixed into the engine combustion chamber.
In this embodiment, the secondary fuel injection is completely
inhibited when the EGR is being effected. However, in the actual
operation, problems do not occur even if the unburned fuel enters
into the combustion chambers provided the amount of the unburned
fuel is small enough so that it does not cause the combustion to
lose stability or does not cause a change in the torque. Therefore,
a maximum secondary fuel injection amount may be set in advance
through experiment in such a manner that it does not cause the
combustion to lose stability or does not cause a change in the
torque when the EGR is being effected, and the secondary fuel
injection amount for the cylinders #2 and #3 may be decreased to a
value smaller than the maximum amount when the EGR is effected.
[0216] FIG. 14 is a flow chart for explaining the operation of the
secondary fuel injection when the secondary fuel injection is
inhibited in the engine of the internal EGR system of FIG. 11 while
the EGR is being effected. This operation is conducted by a routine
executed by the ECU 30 at every predetermined interval (e.g., at
every predetermined crankshaft rotation angle).
[0217] When the operation starts in FIG. 14, it is judged at steps
1401 to 1405 whether the secondary fuel injection is requested
(step 1401), and ACCP, NE and PM are read (1403), and the main fuel
injection amount q.sub.INJ is calculated (step 1405). Operations of
the steps 1401 to 1405 are the same as those of the steps 1301 to
1305 in FIG. 13. At a step 1407, it is judged whether the EGR is
now being effected based on the engine valve overlapping amount OL.
When OL=0 (no overlapping), the internal EGR is not now being
effected, and the operation proceeds to a step 1409 where the
secondary fuel injection amount q.sub.EX is calculated. At a step
1411, the secondary fuel is injected into all cylinders in the
expansion stroke or in the exhaust stroke. Operations at the steps
1409 and 1411 are the same as those of the steps 1315 and 1317 of
FIG. 13. In this embodiment, on the other hand, when the EGR is
being effected at the step 1407, the secondary fuel is injected
into none of the cylinders. That is, the secondary fuel injection
is inhibited for all cylinders, and the unburned fuel is prevented
from recirculating into the combustion chambers.
[0218] In this embodiment, too, the secondary fuel may be injected
but in such a small amount that does not cause any problem instead
of inhibiting the secondary fuel from being injected into the
cylinders while the EGR is being effected.
[0219] (7) Seventh Embodiment
[0220] Next, described below is a further embodiment of the present
invention. In the embodiments of FIGS. 13 and 14, the secondary
fuel injection is limited while the EGR is being effected to
prevent the unburned fuel from being recirculated into the
combustion chambers. However, in the internal EGR system of FIG.
11, in particular, limitation of the secondary fuel injection makes
it quite difficult to release NO.sub.x from the NO.sub.x occluding
and reducing catalyst 7. When the secondary fuel injection is
limited whenever the EGR is effected, therefore, the frequency of
the operation for releasing NO.sub.x from the NO.sub.x occluding
and reducing catalyst decreases, and the NO.sub.x occluding and
reducing catalyst tends to be saturated with the NO.sub.x which it
has absorbed. In an embodiment that will be described below,
therefore, when the amount of recirculating exhaust gas while the
EGR is being effected is larger than a predetermined value, the
secondary fuel injection is inhibited even when the secondary fuel
injection is requested like in the embodiment of FIG. 14. When the
amount of recirculating exhaust gas is smaller than the
predetermined value, however, contrary to the above-mentioned
operation, the secondary fuel is injected while interrupting the
EGR. When the EGR is interrupted, the amount of NO.sub.x emitted
from the engine increases. However, the amount of NO.sub.x emission
does not greatly increase even when the EGR is interrupted when the
amount of recirculating exhaust gas before the EGR is interrupted
is relatively small. When the amount of recirculating exhaust gas
is relatively small, therefore, it becomes advantageous, as a
whole, to increase the frequency for releasing NO.sub.x by
injecting the secondary fuel while interrupting the EGR. In this
embodiment, since the engine equipped with the internal EGR system
is used as shown in FIG. 11, the secondary fuel injection is
inhibited when the amount of recirculating exhaust gas by the EGR
is larger than a predetermined value but, conversely, the secondary
fuel is injected while interrupting the EGR when the amount of
recirculating exhaust gas is smaller than the predetermined value.
This makes it possible to prevent the combustion from losing
stability and the engine output torque from changing, due to by the
recirculation of the unburned fuel into the combustion chambers,
while maintaining a high frequency for executing the operation for
releasing NO.sub.x from the NO.sub.x occluding and reducing
catalyst.
[0221] FIG. 15 is a flow chart illustrating the operation of the
secondary fuel injection according to the embodiment. This
operation is conducted by a routine executed by the ECU 30 at every
predetermined interval (e.g., at every predetermined crankshaft
rotation angle).
[0222] In the operation of FIG. 15, it is judged at a step 1501
whether the secondary fuel injection is now being requested. At
steps 1503 and 1505, the main fuel injection amount q.sub.INJ is
calculated based on ACCP, NE and PM. The operations at the steps
1501 to 1505 are the same as those of the steps 1001 to 1005 of
FIG. 10.
[0223] After the main fuel injection amount q.sub.INJ is calculated
at the step 1505, it is judged at a step 1507, based on the valve
overlapping amount OL, whether the amount of recirculating exhaust
gas due to EGR is now larger than the predetermined amount. As
described earlier, the amount of exhaust gas recirculating into the
combustion chamber due to EGR increases with an increase in the
valve overlapping amount OL. In this embodiment, therefore, when
the valve overlapping amount OL is larger than a predetermined
value a, it is so judged that the amount of the recirculating
exhaust gas due to EGR is now larger than the predetermined
value.
[0224] When the secondary fuel injection is not requested at the
step 1501 and when the valve overlapping amount OL is larger than
the predetermined value .alpha. at the step 1507, the operation
readily ends without executing the operations of a step 1509 and of
subsequent steps. That is, when the exhaust gas is recirculated in
large amounts into the combustion chamber, the secondary fuel is
not injected even when the secondary fuel injection is
requested.
[0225] On the other hand, when the valve overlapping amount OL is
smaller than a at the step 1505, i.e., when the exhaust gas is
recirculated in small amounts by the EGR, the operation proceeds to
the step 1509 to execute the interruption operation (i.e., to
accomplish OL=0 by delaying the intake valve timing VT). After the
interruption of EGR is confirmed at a step 1511, i.e., when OL=0 is
established, the secondary fuel injection amount q.sub.EX is
calculated at a step 1513, and, at a step 1515, the secondary fuel
is injected into all cylinders in the expansion stroke or in the
exhaust stroke. Operations of the steps 1513 and 1515 are the same
as those of the steps 1011 and 1013 of FIG. 10.
[0226] When the valve overlapping amount OL is larger than the
predetermined value .alpha., therefore, the secondary fuel
injection is inhibited and the EGR continues. When the valve
overlapping amount OL is smaller than the predetermined value
.alpha., the EGR is interrupted and the secondary fuel is injected.
Therefore, the frequency for injecting the secondary fuel increases
(frequency for releasing NO.sub.x from the NO.sub.x occluding and
reducing catalyst increases), and the NO.sub.x occluding and
reducing catalyst is prevented from being saturated.
[0227] (8) Eighth Embodiment
[0228] Described below is a still further embodiment of the present
invention.
[0229] In the above-mentioned fourth to seventh embodiments, the
secondary fuel injection is limited when the EGR is being effected,
or the EGR is limited when the secondary fuel is being injected.
When the secondary fuel injection is limited, however, the
frequency for executing the operation for releasing NO.sub.x from
the NO.sub.x occluding and reducing catalyst may decrease, and the
efficiency for purifying the exhaust gas may drop due to the
saturation of the NO.sub.x occluding and reducing catalyst. When
the EGR is limited, further, the amount of NO.sub.x emitted from
the engine increases. It is therefore desired to effect both the
EGR and the secondary fuel injection simultaneously without
limitation, if it is possible.
[0230] When the ineffective fuel is supplied while the EGR is being
effected, a problem occurs, since the unburned fuel is recirculated
into the combustion chamber together with the recirculating exhaust
gas, in that excess fuel is supplied to the combustion chamber.
Therefore, if the fuel is not supplied in excess amounts into the
combustion chamber, the problem does not occur even if the
ineffective fuel is supplied while the EGR is being effected. In
the embodiment described below, therefore, the amount of unburned
fuel recirculated into the combustion chamber is estimated when the
ineffective fuel is supplied while the EGR is being effected, and
the amount of the main fuel injection is decreased relative to the
target value by the amount of the unburned fuel. Even when the
unburned fuel recirculates, therefore, the sum of the amount of
fuel supplied to the engine combustion chamber is maintained to be
the same as the target value of the main fuel injection amount, and
the fuel is not supplied in excess amounts. When the EGR is being
effected, therefore, the secondary fuel is injected without being
limited, preventing the combustion from losing stability and
preventing a change in the output torque.
[0231] Prior to describing the operation for correcting the main
fuel injection amount according to this embodiment, mentioned below
first is a method of calculating the amount of unburned fuel
recirculating into the combustion chamber due to the supply of
ineffective fuel at the time when the EGR is being effected in the
embodiment. In this embodiment, the amount of recirculating of the
unburned fuel by the supply of ineffective fuel at the time of
effecting the EGR is calculated based on the method which is nearly
the same as the one described with reference to FIG. 7.
[0232] FIG. 16 is a graph showing a relationship between the
cylinder output torque (ordinate) of when the engine is operated at
a predetermined rotational speed and the amount of the main fuel
injection (abscissa). In FIG. 16, a curve I represents a
relationship between the output torque and the amount of main fuel
injection of when the EGR is being effected, and a curve II
represents a relationship between the output torque and the amount
of main fuel injection of when the ineffective fuel is supplied
(secondary fuel in this case) while the EGR is being effected. As
described earlier, the amount of the secondary fuel has been set to
be the one required for bringing the air-fuel ratio of the exhaust
gas to the target air-fuel ratio for each of the cases, and is
determined from the engine load (main fuel injection) and the
rotational speed. Similarly, the amount of recirculating the
exhaust gas by the EGR is determined from the engine load and the
rotational speed.
[0233] If the unburned fuel does not recirculate by the secondary
fuel injection into the combustion chamber, the cylinder output
torque remains the same irrespective of the secondary fuel
injection. However, when the unburned fuel recirculates due to the
secondary fuel injection, the cylinder output torque increases at
the time when the secondary fuel is injected by an amount
corresponding to the amount of the unburned fuel that is
recirculated (curve II in FIG. 16).
[0234] In this embodiment, when the output torque is increased by
the amount a shown in FIG. 16 with a given main fuel injection
amount due to the secondary fuel injection while the EGR is being
executed, the recirculating amount of the unburned fuel is
estimated by presuming that an increase in the amount of the main
fuel injection (amount b in FIG. 16) necessary for increasing the
output torque by the amount a when the EGR is being effected
without the secondary fuel injection, is equal to the amount of the
unburned fuel recirculating into the combustion chamber due to the
secondary fuel injection.
[0235] That is, in this embodiment, curves corresponding to FIG. 16
are prepared, in advance, through experiment for every combination
of the engine rotational speeds and the above-mentioned engine
operating modes {circle over (1)} to {circle over (5)}, in order to
calculate the recirculating amount of the unburned fuel (b in FIG.
16) in their respective main fuel injection amounts when the EGR is
being effected. The values of unburned fuel amounts b are prepared
as a numerical value table using the engine rotational speed NE and
the main fuel injection amount q.sub.INJ as parameters for each of
the operating modes, and are stored in the ROM of the ECU 30. When
the engine is in operation, the ECU calculates the amount b of the
unburned fuel recirculating into the combustion chamber when the
EGR is being effected based on the engine rotational speed NE and
the main fuel injection amount q.sub.INJ.
[0236] FIG. 17 is a flow chart illustrating the operation for
correcting the amount of main fuel injection according to the
embodiment. This operation is executed at every predetermined crank
rotation angle of the engine.
[0237] When the operation starts in FIG. 17, the engine load
(degree of accelerator opening) ACCP and the rotational speed NE
are read at a step 1701, and the main fuel injection amount
q.sub.INJ is calculated at a step 1703. Operations of the steps
1701 and 1703 are the same as those of the steps 1003 and 1005 of
FIG. 10.
[0238] Next, it is judged at a step 1705 whether the secondary fuel
is now being injected and at a step 1707, it is judged whether the
EGR is being effected. When both the secondary fuel injection and
the EGR are now being effected, the unburned fuel recirculates into
the combustion chamber due to the secondary fuel injection. At a
step 1709, therefore, the amount b of unburned fuel that
recirculates into the combustion chamber when the secondary fuel is
injected is calculated from the above-mentioned numerical value
table prepared for each of the operating modes based on the
relationship of FIG. 16, by using the main fuel injection amount
q.sub.INJ calculated at the step 1703. Then, at a step 1711, the
main fuel injection amount q.sub.IDJ calculated at the step 1703 is
decreased by the recirculating amount b of the unburned fuel.
[0239] When either the secondary fuel injection or the EGR has not
been effected at the steps 1705 and 1707, it is not probable that
the unburned fuel recirculates into the combustion chamber.
Therefore, the corrections are not effected at the steps 1709 and
1711, and the operation ends.
[0240] According to this embodiment, since the secondary fuel is
injected without being limited even when the EGR is being effected,
both an increase in the amount of NO.sub.x emitted by the engine
and a decrease in the frequency for executing the operation for
releasing NO.sub.x from the NO.sub.x occluding and reducing
catalyst can be prevented.
[0241] According to the present invention as described above, the
combustion in the engine does not lose stability and the output
torque does not change even when the ineffective fuel, which does
not burn in the combustion chamber but is discharged together with
the exhaust gas, is supplied to the engine.
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