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Claims  |
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What is claimed is:
1. A control system for an internal combustion engine having at least one
combustion chamber, an intake passage having an inner surface, and intake
parameter changing means for changing an intake parameter within said
intake passage, comprising:
operating condition detecting means for detecting operating conditions of
said engine;
adherent fuel amount estimating means for estimating an amount of adherent
fuel adhering to said inner surface of said intake passage;
carried-off fuel amount estimating means for estimating an amount of
carried-off fuel evaporated from fuel adhering to said inner surface of
said intake passage and carried into said combustion chamber;
supply fuel amount determining means for determining an amount of supply
fuel to be supplied to said engine, based upon operating conditions of
said engine detected by said operating condition detecting means, said
adherent fuel amount estimated by said adherent fuel amount estimating
means, and said carried-off fuel amount estimated by said carried-off fuel
amount estimating means;
fuel supply means for supplying said supply fuel amount determined by said
supply fuel amount determining means onto said intake passage; and
estimated fuel amount correcting means for correcting said adherent fuel
amount estimated by said adherent fuel amount estimating means, and said
carried-off fuel amount estimated by said carried-off fuel amount
estimating means, in response to said intake parameter changed by said
intake parameter changing means.
2. A control system as claimed in claim 1, wherein said engine has a fuel
tank, a canister for adsorbing evaporative fuel generated from said fuel
tank, and a purging passage connecting between said canister and said
intake passage, said intake parameter being an amount of said evaporative
fuel supplied to said intake passage from said canister via said purging
passage.
3. A control system as claimed in claim 1, wherein said engine has at least
one intake valve, at least one exhaust valve, and valve operating means
for changing a valve operating characteristic of at least one of said
intake valve and said exhaust valve, said intake parameter being said
valve operating characteristic of said at least one of said intake valve
and said exhaust valve;
4. A control system as claimed in claim 1, wherein said engine has fuel
injection means having an injection port, and auxiliary air supply means
for supplying auxiliary air to said fuel injection means at a zone in the
vicinity of said injection port, said intake parameter being an amount of
said auxiliary air.
5. In a control system for an internal combustion engine having at least
one combustion chamber, an intake passage having an inner surface, a fuel
tank, a canister for adsorbing evaporative fuel generated from said fuel
tank, and a purging passage connecting between said canister and said
intake passage, said control system including supply fuel amount
calculating means for calculating an amount of supply fuel to be supplied
to said engine, based upon operating conditions of said engine;
adherent fuel amount estimating means for estimating an amount of adherent
fuel adhering to said inner surface of said intake passage, carried-off
fuel amount estimating means for estimating an amount of carried-off fuel
amount evaporated from fuel adhering to said inner surface of said intake
passage and carried into said combustion chamber, supply fuel amount
correction means for correcting said supply fuel amount calculated by said
supply fuel amount calculating means, in response to said adherent fuel
amount estimated by said adherent fuel amount estimating means and said
carried-off fuel amount estimated by said carried-off fuel amount
estimating means, and fuel supply means for supplying said supply fuel
amount corrected by said supply fuel amount correcting means into said
intake passage,
the improvement comprising:
(1) evaporative fuel amount detecting means for detecting an amount of
evaporative fuel supplied to said intake passage via said purging passage;
and
(2) estimated fuel amount correcting means for correcting said adherent
fuel amount estimated by said adherent fuel amount estimating means and
said carried-off fuel amount estimated by said carried-off fuel amount
estimating means, in response to said evaporative fuel amount detected by
said evaporative fuel amount detecting means.
6. A control system as claimed in claim 5, wherein said estimated fuel
amount correcting means corrects said adherent fuel amount and said
carried-off fuel amount in response to concentration of hydrocarbon in
said evaporative fuel supplied to said intake passage via said purging
passage and a flow rate of said evaporative fuel.
7. In a control system for an internal combustion engine having at least
one combustion chamber, an intake passage having an inner surface, at
least one intake valve, at least one exhaust valve, and valve operating
means for changing a valve operating characteristic of at least one of
said intake valve and said exhaust valve, said control system including
supply fuel amount calculating means for calculating an amount of fuel to
be supplied to said engine, based upon operating conditions of said
engine, adherent fuel amount estimating means for estimating an amount of
adherent fuel adhering to said inner surface of said intake passage,
carried-off fuel amount estimating means for estimating an amount of
carried-off fuel evaporated from fuel adhering to said inner surface of
said intake passage and carried into said combustion chamber, supply fuel
amount correcting means for correcting said supply fuel amount calculated
by said supply fuel amount calculating means, based upon said adherent
fuel amount estimated by said adherent fuel amount estimating means and
said carried-off fuel amount estimated by said carried-off fuel amount
estimating means, and fuel supply means for supply said supply fuel amount
corrected by said fuel amount correcting means into said intake passage,
the improvement comprising:
estimated fuel amount correcting means for correcting said adherent fuel
amount estimated by said adherent fuel amount estimating means and said
carried-off fuel amount estimated by said carried-off fuel amount
estimating means, in response to said valve operating characteristic of
said at least one said intake valve and said exhaust valve.
8. A control system as claimed in claim 7, wherein said valve operating
characteristic includes a low speed valve timing suitable for operation of
said engine in a lower rotational speed region of said engine, and a high
speed valve timing suitable for operation of said engine in a higher
rotational speed region of said engine, said adherent fuel amount and said
carried-off fuel amount being each corrected to different values between
when said low speed valve timing is selected and when said high speed
valve timing is selected.
9. In a control system for an internal combustion engine having at least
one combustion chamber, and an intake passage, including supply fuel
amount calculating means for calculating an amount of supply fuel amount
calculating means for calculating an amount of fuel to be supplied to said
engine, based upon operating conditions of said engine, adherent fuel
amount estimating means for estimating an amount of adherent fuel adhering
to said inner surface of said intake passage, carried-off fuel amount
estimating means for estimating an amount of carried-off fuel evaporated
from fuel adhering to said inner surface of said intake passage and
carried into said combustion chamber, supply fuel amount correcting means
for correcting said supply fuel amount calculated by said supply fuel
amount calculating means, based upon said adherent fuel amount estimated
by said adherent fuel amount estimating means and said carried-off fuel
amount estimated by said carried-off fuel amount estimating means, fuel
injection means for injecting said supply fuel amount corrected by said
supply fuel amount correcting means into said intake passage, said fuel
injection means having an injection port, and auxiliary air supply means
for supplying auxiliary air to said fuel injection means at a zone in the
vicinity of said injection port,
the improvement comprising:
estimated fuel amount correcting means for correcting said adherent fuel
amount estimated by said adherent fuel amount estimating means and said
carried-off fuel amount estimated by said carried-off fuel amount
estimating means, in response to an amount of said auxiliary air supplied
by said auxiliary air supply means.
10. A control system as claimed in claim 9, wherein said fuel injection
means has heating means for heating fuel injected by said fuel injection
means, said estimated fuel amount correcting means correcting said
adherent fuel amount and said carried-off fuel amount, based upon an
amount of heating calory generated by said heating means. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a control system for internal combustion engines,
and more particularly to a control system which controls the supply of
fuel injected into an intake pipe in a manner compensating for a fuel
amount adhering to the inner surface of the intake pipe.
2. Prior Art
In conventional internal combustion engines of the type that fuel is
injected into an intake pipe, there is a problem that some of injected
fuel adheres to the inner surface of the intake pipe, so that a required
amount of fuel cannot be drawn into the combustion chamber. To solve this
problem, there has been proposed a fuel supply control method which
estimates a fuel amount which is to adhere to the inner surface of the
intake pipe and one which is to be drawn into the combustion chamber by
evaporation from the fuel adhering to the intake pipe, and determines a
fuel injection amount in dependence on the estimated fuel amounts
(Japanese Provisional Patent Publication (Kokai) No. 61-126337).
On the other hand, conventionally, evaporative fuel emission control
systems have been widely used in internal combustion engines, which
operate to prevent evaporative fuel from being emitted from a fuel tank
into the atmosphere, by temporarily storing evaporative fuel from the fuel
tank in a canister, and purging same into the intake system of the engine.
Purging of evaporative fuel into the intake system causes fluctuations in
the air-fuel ratio of a mixture supplied to the combustion chamber. To
prevent such fluctuations in the air-fuel ratio or a deviation thereof
from a desired value due to purging of evaporative fuel, it has also been
proposed to estimate an amount of evaporative fuel to be purged, and
determine a fuel injection amount based on the estimated evaporative fuel
amount (Japanese Provisioned Patent Publications (Kokai) Nos. 1-148043 and
2-27167).
Further, conventionally internal combustion engines are known, in which
operating characteristics of intake valves and exhaust valves, i.e., valve
timing (valve opening/closing timing and/or valve lift) are changeable,
(e.g. Japanese Provisional Patent Publication (Kokai) No. 2-50285).
Furthermore, a fuel injection system is known, in which air (so-called
assist-air) is supplied to the fuel injection valves through ports
provided in the vicinity thereof to promote atomization of fuel injected
from the fuel injection valves (e.g. Japanese Provisional Patent
Publication (Kokoku) No. 55-9555).
The above proposed or known systems or methods are intended to solve their
respective problems alone. However, in actuality, unless all the problems
are solved at the same time, the air-fuel ratio of a mixture supplied to
an internal combustion engine cannot be accurately controlled to a desired
value. In any event, at least the problem of adherence of fuel to the
inner surface of the intake pipe has to be taken into consideration in
solving the problems mentioned above. However, a mere combination of two
or more of the above-mentioned systems or methods cannot lead to
successful control of the air-fuel ratio.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a control system for an
internal combustion engine, which is capable of accurately controlling the
air-fuel ratio of a mixture supplied to combustion chambers of the engine,
by taking into consideration the amount of fuel adhering to the inner
surface of the intake pipe as well as an intake pipe parameter within the
intake passage.
A further object of the invention is to provide a control system for an
internal combustion engine, which is capable of accurately controlling the
air-fuel ratio, by taking into consideration the amount of fuel adhering
to the inner surface of the intake pipe as well as the valve timing of
intake valves and/or the exhaust valves thereof.
Another object of the injection is to provide a control system which is
capable of accurately controlling the air-fuel ratio, by taking into
consideration the amount of fuel adhering to the inner surface of the
intake pipe as well as the amount of evaporative fuel purged.
Still another object of the invention is to accurately control the air-fuel
ratio in dependence on the amount of fuel adhering to the intake pipe
inner surface as well as the amount of auxiliary air (assist air) supplied
to the fuel injection valves.
To attain the first-mentioned object, the present invention provides a
control system for an internal combustion engine having at least one
combustion chamber, an intake passage having an inner surface, and intake
parameter changing means for changing an intake parameter within the
intake passage, comprising:
operating condition detecting means for detecting operating conditions of
the engine;
adherent fuel amount estimating means for estimating an amount of adherent
fuel adhering to the inner surface of the intake passage;
carried-off fuel amount estimating means for estimating an amount of
carried-off fuel evaporated from fuel adhering to the inner surface of the
intake passage and carried into the combustion chamber;
supply fuel amount determining means for determining an amount of supply
fuel to be supplied to the engine, based upon operating conditions of the
engine detected by the operating condition detecting means, the adherent
fuel amount estimated by the adherent fuel amount estimating means, and
the carried-off fuel amount estimated by the carried-off fuel amount
estimating means;
fuel supply means for supplying the supply fuel amount determined by the
supply fuel amount determining means into the intake passage; and
estimated fuel amount correcting means for correcting the adherent fuel
amount estimated by the adherent fuel amount estimating means, and the
carried-off fuel amount estimated by the carried-off fuel amount
estimating means, in response to the intake parameter changed by the
intake parameter changing means.
To attain the second object, the present invention provides a control
system for an internal combustion engine having at least one combustion
chamber, an intake passage having an inner surface, a fuel tank, a
canister for adsorbing evaporative fuel generated from the fuel tank, and
a purging passage connecting between the canister and the intake passage,
the control system including supply fuel amount calculating means for
calculating an amount of supply fuel to be supplied to the engine, based
upon operating conditions of the engine;
adherent fuel amount estimating means for estimating an amount of adherent
fuel adhering to the inner surface of the intake passage, carried-off fuel
amount estimating means for estimating an amount of carried-off fuel
amount evaporated from fuel adhering to the inner surface of the intake
passage and carried into the combustion chamber, supply fuel amount
correction means for correcting the supply fuel amount calculated by the
supply fuel amount calculating means, in response to the adherent fuel
amount estimated by the adherent fuel amount estimating means and the
carried-off fuel amount estimated by the carried-off fuel amount
estimating means, and fuel supply means for supplying the supply fuel
amount corrected by the supply fuel amount correcting means into the
intake passage,
the system being characterized by an improvement comprising:
(1) evaporative fuel amount detecting means for detecting an amount of
evaporative fuel supplied to the intake passage via the purging passage;
and
(2) estimated fuel amount correcting means for correcting the adherent fuel
amount estimated by the adherent fuel amount estimating means and the
carried-off fuel amount estimated by the carried-off fuel amount
estimating means, in response to the evaporative fuel amount detected by
the evaporative fuel amount detecting means.
Preferably, the estimated fuel amount correcting means corrects the
adherent fuel amount and the carried-off fuel amount in response to
concentration of hydrocarbon in the evaporative fuel supplied to the
intake passage via the purging passage and a flow rate of the evaporative
fuel.
To attain the third object, the prevent invention provides a control system
for an internal combustion engine having at least one combustion chamber,
an intake passage having an inner surface, at least one intake valve, at
least one exhaust valve, and valve operating means for changing a valve
operating characteristic of at least one of the intake valve and the
exhaust valve, the control system including supply fuel amount calculating
means for calculating an amount of fuel to be supplied to the engine,
based upon operating conditions of the engine, adherent fuel amount
estimating means for estimating an amount of adherent fuel adhering to the
inner surface of the intake passage, carried-off fuel amount estimating
means for estimating an amount of caried-off fuel evaporated from fuel
adhering to the inner surface of the intake passage and carried into the
combustion chamber, supply fuel amount correcting means for correcting the
supply fuel amount calculated by the supply fuel amount calculating means,
based upon the adherent fuel amount estimated by the adherent fuel amount
estimating means and the carried-off fuel amount estimated by the
carried-off fuel amount estimating means, and fuel supply means for
supplying the supply fuel amount corrected by the fuel amount correcting
means into the intake passage,
the system being characterized by an improvement comprising:
estimated fuel amount correcting means for correcting the adherent fuel
amount estimated by the adherent fuel amount estimating means and the
carried-off fuel amount estimated by the carried-off fuel amount
estimating means, in response to the valve operating characteristic of the
at least one the intake valve and the exhaust valve.
Preferably, the valve operating characteristic includes a low speed valve
timing suitable for operation of the engine in a lower rotational speed
region of the engine, and a high speed valve timing suitable for operation
of the engine in a higher rotational speed region of the engine, the
adherent fuel amount and the carried-off fuel amount being each corrected
to different values between when the low speed valve timing is selected
and when the high speed valve timing is selected.
To attain the fourth object, the present invention provides a control
system for an internal combustion engine having at least one combustion
chamber, and an intake passage, including supply fuel amount calculating
means for calculating an amount of supply fuel amount calculating means
for calculating an amount of fuel to be supplied to the engine, based upon
operating conditions of the engine, adherent fuel amount estimating means
for estimating an amount of adherent fuel adhering to the inner surface of
the intake passage, carried-off fuel amount estimating means for
estimating an amount of carried-off fuel evaporated from fuel adhering to
the inner surface of the intake passage and carried into the combustion
chamber, supply fuel amount correcting means for correcting the supply
fuel amount calculated by the supply fuel amount calculating means, based
upon the adherent fuel amount estimated by the adherent fuel amount
estimating means and the carried-off fuel amount estimated by the
carried-off fuel amount estimating means, fuel injection means for
injecting the supply fuel amount corrected by the supply fuel amount
correcting means into the intake passage, the fuel injection means having
an injection port, and auxiliary air supply means for supplying auxiliary
air to the fuel injection means at a zone in the vicinity of the injection
port,
the system being characterized by an improvement comprising:
estimated fuel amount correcting means for correcting the adherent fuel
amount estimated by the adherent fuel amount estimating means and the
carried-off fuel amount estimated by the carried-off fuel amount
estimating means, in response to an amount of the auxiliary air supplied
by the auxiliary air supply means.
Preferably, the fuel injection means has heating means for heating fuel
injected by the fuel injection means, the estimated fuel amount correcting
means correcting the adherent fuel amount and the carried-off fuel amount,
based upon an amount of heating calory generated by the heating means.
The above and other objects, features, and advantages of the invention will
be more apparent from the following detailed description taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing the whole arrangement of a fuel supply
control system for an internal combustion engine, according to a first
embodiment of the invention;
FIG. 2 is a flowchart of a program for calculating a fuel injection period
Tout;
FIG. 3 is a flowchart of a program for calculating an intake pipe-adherent
fuel amount TWP(N);
FIGS. 4(a), (b), and (c) show tables for calculating correction
coefficients for correcting a direct supply ratio A and a carry-off ratio
B;
FIG. 5 is a block diagram showing the whole arrangement of a fuel supply
control system for an internal combustion engine, according to a second
embodiment of the invention;
FIG. 6 is a flowchart of a program for calculating the fuel injection
period Tout, according to the second embodiment;
FIGS. 7(a) and (b) show tables for calculating correction coefficients for
correcting the direct supply ratio A and the carry-off ratio B, according
to the second embodiment;
FIG. 8 is a block diagram showing the whole arrangement of a fuel supply
control system for an internal combustion engine, according to a third
embodiment of the invention;
FIG. 9 is a cross-sectional view of an oil hydraulic valve driving unit
provided in an engine in FIG. 8;
FIG. 10 is a graph useful in explaining operating characteristics (valve
timing) of an intake valve in the engine in FIG. 8;
FIG. 11 is a flowchart of a program for calculating the fuel injection
period Tout, according to the third embodiment;
FIGS. 12(a) and (b) show tables for use in calculating the direct supply
ratio A and the carry-off ratio B;
FIGS. 13(a) and (b) show tables for calculating correction coefficients
dependent upon the direct supply ratio A and the carry-off ratio B;
FIG. 14 is a block diagram showing the whole arrangement of a fuel supply
control system for an internal combustion engine, according to a fourth
embodiment of the invention;
FIG. 15 is a cross-sectional view of essential parts of a fuel injection
valve provided in the system of FIG. 14;
FIG. 16 is a flowchart of a program for calculating the fuel injection
period Tout, according to the fourth embodiment;
FIGS. 17(a) and (b) show tables for calculating correction coefficients for
correcting the direct supply ratio A and the carry-off ratio B;
FIG. 18 is a graph showing the relationship between engine coolant
temperature TW and heater supply power PH;
FIG. 19 is a graph showing transient characteristics of the air-fuel ratio
A/F; and
FIG. 20 is a block diagram showing a variation of an assist-air supply
system employed in the fourth embodiment.
DETAILED DESCRIPTION
The invention will now be described in detail with reference to the
drawings showing embodiments thereof.
Referring first to FIG. 1, there is illustrated the whole arrangement of a
fuel supply control system of an internal combustion engine, according to
a first embodiment of the invention. In the figure, reference numeral 1
designates an internal combustion engine for automotive vehicles. The
engine is a four-cylinder type, for instance. Connected to the cylinder
block of the engine 1 is an intake pipe 2 across which is arranged a
throttle body 3 accommodating a throttle valve 301 therein. A throttle
valve opening (.theta..sub.TH) sensor 4 is connected to the throttle valve
301 for generating an electric signal indicative of the sensed throttle
valve opening and supplying same to an electronic control unit
(hereinafter called "the ECU") 5.
Fuel injection valves 6, only one of which is shown, are inserted into the
interior of the intake pipe 2 at locations intermediate between the
cylinder block of the engine 1 and the throttle valve 301 and slightly
upstream of respective intake valves, not shown. The fuel injection valves
6 are connected to a fuel tank 8 via a fuel pump 7, and electrically
connected to the ECU 5 to have their valve opening periods controlled by
signals therefrom.
On the other hand, an intake pipe absolute pressure (PBA) sensor 10 is
provided in communication with the interior of the intake pipe 2 via a
conduit 9 at a location immediately downstream of the throttle valve 301
for supplying an electric signal indicative of the sensed absolute
pressure within the intake pipe 2 to the ECU 5.
An engine coolant temperature (TW) sensor 11 is mounted in the cylinder
block of the engine 1, for supplying an electric signal indicative of the
sensed engine coolant temperature TW to the ECU 5. An engine rotational
speed (NE) sensor 12 is arranged in facing relation to a camshaft or a
crankshaft of the engine 1, not shown. The engine rotational speed sensor
12 generates a pulse as a TDC signal pulse at each of predetermined crank
angles whenever the crankshaft rotates through 180 degrees, the pulse
being supplied to the ECU 5.
An O.sub.2 sensor 13 as an exhaust gas ingredient concentration sensor is
mounted in an exhaust pipe 14 connected to the cylinder block of the
engine 1, for sensing the concentration of oxygen present in exhaust gases
emitted from the engine 1 and supplying an electric signal indicative of
the detected value of the oxygen concentration to the ECU 5.
An evaporative fuel emission control system is arranged between the fuel
tank 8 and the intake pipe 2. More specifically, a conduit line (purging
passage) 24 extends from an upper space inn the fuel tank 8 which has an
enclosed body and opens into interior of a canister 23 having an adsorbent
231. A two-way valve 22 is arranged across the conduit line 21. A purging
passage 24 extends from the canister 23 and opens into the interior of the
intake pipe 2 at a location of the throttle valve 3. Arranged across the
purging passage 24 are a purge control valve 25, which is a linear control
valve (EPCV) having a solenoid for actuating a valve element thereof, a
flowmeter 26 which detects a flow rate VP of an air-fuel mixture
containing evaporative fuel, flowing through the purge passage 24
(hereinafter referred to as "purging flow rate"), and a HC (hydrocarbon)
concentration sensor 27 for sensing the concentration of HC in the
air-fuel mixture. The solenoid of the purge control valve 25 is
electrically connected to the ECU 5 to be controlled by a control signal
therefrom to linearly vary its valve opening.
Evaporative fuel or gas (hereinafter merely referred to as "evaporative
fuel") generated within the fuel tank 8 forcibly opens a positive pressure
valve, not shown, of the two-way valve 22 when the pressure of the
evaporative fuel reaches a predetermined level, to flow through the valve
22 into the canister 23, where the evaporative fuel is adsorbed by the
adsorbent 231 in the canister and thus stored therein. The purge control
valve 25 is a so-called on-off control type solenoid valve, which has its
valve opening linearly variable in response to the duty ratio of a control
signal from the ECU 5, i.e. the ratio between the valve opening period and
the valve closing period. Thus, the purge control valve 25 is opened to a
valve opening corresponding to the duty ratio of the control signal from
the ECU 5, whereby evaporative fuel temporarily stored in the canister 23
flows therefrom together with fresh air introduced through an outside
air-introducing port 232 of the canister 23 at the flow rate determined by
the valve opening of the purge control valve 25, through the purging
passage 24 into the intake pipe 2 to be supplied to the cylinders. When
the fuel tank 8 is cooled due to low ambient temperature etc. so that
negative pressure increases within the fuel tank 8, a negative pressure
valve, not shown, of the two-way valve 22 is opened to return evaporative
gas temporarily stored in the canister 23 into the fuel tank 8. In the
above described manner, the evaporative fuel generated within the fuel
tank 8 is prevented from being emitted into the atmosphere.
The ECU 5 comprises an input circuit having the functions of shaping the
waveforms of input signals from various sensors, shifting the voltage
levels of sensor output signals to a predetermined level, converting
analog signals from analog-output sensors to digital signals, and so
forth, a central processing unit (hereinafter called "the CPU") which
executes programs for controlling the fuel injection valves 6 and the
purge control valve 25, etc., memory means storing maps and tables,
referred to hereinafter, and various operational programs which are
executed in the CPU and for storing results of calculations therefrom,
etc., and an output circuit which outputs control or driving signals to
the fuel injection valves 6 and the purge control valves 25.
The CPU operates in response to the above-mentioned signals from the
sensors to determine operating conditions in which the engine 1 is
operating, such as an air-fuel ratio feedback control region in which the
fuel supply is controlled in response to the detected oxygen concentration
in the exhaust gases, and open-loop control regions, and calculates, based
upon the determined operating conditions, the valve opening period or fuel
injection period Tout over which the fuel injection valves 6 are to be
opened, by the use of the program of FIG. 2 in synchronism with inputting
of TDC signal pulses to the ECU 5.
The CPU supplies via the output circuit the driving signals based upon the
fuel injection period Tout determined as above to the fuel injection
valves 6 to open same over the fuel injection period Tout. The fuel
injection period Tout is proportional to the fuel injection amount, and
therefore will be hereinafter referred to as the fuel injection amount.
FIG. 2 shows the program for calculating the fuel injection amount Tout.
This program is executed upon generation of each TDC signal pulse and in
synchronism therewith.
At a step S1, a direct supply ratio A and a carry-off ratio B are
calculated. The direct supply rate A is defined as a ratio of a fuel
amount directly or immediately drawn into a combustion chamber to the
whole fuel amount injected in a cycle, the direct supply ratio including a
fuel amount carried off the inner surface of the intake pipe 2 by
evaporation etc., in the same cycle. The carry-off ratio B is defined as a
ratio of a fuel amount carried off the inner surface of the intake pipe 2
by evaporation etc. and drawn into the combustion chamber in the present
cycle to the whole fuel amount which adhered to the inner surface of the
intake pipe 2 in the last or immediately preceding cycle. The direct
supply ratio A and the carry-off ratio B are read, respectively, from an A
map and a B map set in accordance with coolant temperature TW and intake
pipe absolute pressure PBA, in response to the detected TW and PBA values.
The direct supply ratio A and the carry-off ratio B may be calculated by
interpolation, if required.
At the next step S2, first, second and third correction coefficients KA1 to
KA3 and KB1 to KB3, which correct the direct supply ratio A and the
carry-off ratio B, are calculated. The first correction coefficients KA1
and KB1 are determined in response to the HC concentration .beta. detected
by the HC concentration sensor 27, as shown in FIG. 4(a). The second
correction coefficients KA2 and KB2 are determined in response to the
purging flow rate VP detected by the flowmeter 26, as shown in FIG. 4(b).
Therefore, (KA1.times.KA2) and (KB1.times.KB2) assume values representing
(.beta..times.VP), i.e., an amount of evaporative fuel flowing through the
purging passage 24. According to FIG. 4(a), as the HC concentration .beta.
increases, the first correction coefficients KA1 and KB1 are increased.
This is because, when the evaporative fuel amount which is supplied to the
intake pipe 2 increases, the direct supply ratio A and the carry-off ratio
B apparently increase. The setting of the second correction coefficients
KA2 and KB2 in FIG. 4(b) is based upon a similar ground.
The third correction coefficients KA3 and KB3 are determined in response to
the engine rotational speed NE, as shown in FIG. 4(c). Specifically,
according to FIG. 4(c), the correction coefficient KA3 for correcting the
direct supply ratio A is set such that it increases as the engine
rotational speed NE increases. The third correction coefficient KB3 for
correcting the carry-off ratio B is set likewise.
The reason why the third correction coefficients KA3 and KB3 are thus
increased as the engine rotational speed NE increases is that the direct
supply ratio A and the carry-off ratio B apparently increase as the intake
air flow speed in the intake pipe increases with an increase in the engine
rotational speed NE.
Next, at a step S3, corrected values Ae and Be of the direct supply ratio
and the carry-off ratio are calculated by the use of the following
equations (1) and (2). Further, (1-Ae) and (1-Be) are calculated at a step
S4, followed by the program proceeding to a step S5:
Ae=A.times.KA1.times.KA2.times.KA3 (1)
Be=B.times.KB1.times.KB2.times.KB3 (2)
where the values Ae, (1-Ae) and (1-Be) thus calculated are stored into a
RAM of the ECU 5 for use in a program shown in FIG. 3, which will be
described hereinafter.
At a step S5, it is determined whether or not the engine is being started.
If the answer is affirmative (YES), the fuel injection amount Tout is
calculated based upon a basic fuel amount Ti for use at the start of the
engine, and then the program is terminated. If the answer to the question
of the step S5 is negative (NO), i.e., if the engine is not being started,
a required fuel amount TCYL(N) for each cylinder, which does not include
an additive correction term Ttotal, referred to hereinafter, is calculated
by the use of the following equation (3), at a step S6:
Tcyl(N)=TiM.times.Ktotal (N) (3)
where (N) represents a number allotted to the cylinder for which the
required fuel amount Tcyl is calculated. TiM represents a basic fuel
amount to be applied when the engine is under normal operating conditions
(other than the starting condition) and is calculated in response to the
rotational speed NE and the intake pipe absolute pressure PBA. Ktotal(N)
represents the product of all correction coefficients (e.g. a coolant
temperature-dependent correction coefficient KTW and a leaning correction
coefficient KLS) which are calculated based upon engine operating
parameter signals from various sensors excluding an air-fuel ratio
correction coefficient KO2 which is calculated based on an output signal
from the O.sub.2 sensor 18.
At a step S7, the required fuel amount TCYL(N) calculated above is
corrected by applying a purging correction variable Tpurge to the
following equation (4). The purging correction variable Tpurge represents
a fuel injection period corresponding to an evaporative fuel amount
calculated based upon outputs from the flowmeter 26 and the HC sensor 27:
Tcyl(N)=Tcyl(N)-Tpurge (4)
At a step S8, a combustion chamber supply fuel amount TNET, which should be
supplied to the corresponding combustion chamber in the present injection
cycle, is calculated by the use of the following equation (5):
TNET=Tcyl(N)+Ttotal-Be.times.TWP(N) (5)
where Ttotal is the sum of all additive correction terms (e.g. an
acceleration fuel-increasing correction term TACC), which is calculated
based on engine operating parameter signals from various sensors. The
value Ttotal does not include an ineffective time correction term TV,
refered to later. TWP(N) represents an intake pipe-adherent fuel amount
(estimated value), which is calculated by the program of FIG. 3.
(Be.times.TWP(N)) corresponds to an amount of fuel, which is evaporated
from fuel adhering to the inner surface of the intake pipe 2 and carried
into the combustion chamber. A fuel amount corresponding to the fuel
amount carried off the intake pipe inner surface need not be injected,
and, therefore, is to be subtracted from the value Tcyl(N) in the equation
(5).
At a step S9, it is determined whether or not the value TNET calculated by
the equation (5) is larger than a value of 0. If the answer is negative
(NO), i.e., if TNET.ltoreq.0, the fuel injection amount Tout is set to 0,
followed by terminating the program. If the answer at the step S9 is
affirmative (YES), i.e., if TNET>0, the TOUT value is calculated by the
use of the following equation (6):
Tout=TNET(N)/Ae.times.KO2+TV (6)
where KO2 is the aforementioned air fuel ratio correction coefficient
calculated in response to the output from the O.sub.2 sensor 18. TV is the
ineffective time correction term.
Thus, a fuel amount corresponding to TNET(N).times.KO2+Be.times.TWP(N) is
supplied to the combustion chamber by opening the fuel injection valve 6
over the time period Tout calculated by the equation (6).
FIG. 3 shows the program for calculating the intake pipe-adherent fuel
amount TWP(N), which is executed upon generation of each crank angle pulse
which is generated whenever the crankshaft rotates through a predetermined
angle (e.g. 30 degrees).
At a step S21, it is determined whether or not the present loop of
execution of this program falls within a time period after the start of
the calculation of the fuel injection amount Tout and before the fuel
injection is completed (hereinafter referred to as the injection control
period). If the answer is affirmative (YES), a first flag FCTWP(N) is set
to a value of 0 at a step S32, followed by terminating the program. If the
answer at the step S21 is negative (NO), i.e., if the present loop is not
within the injection control period, it is determined at a step S22
whether or not the first flag FCTWP(N) is equal to 1. If the answer is
affirmative (YES), that is, if FCTWP(N)=1, the program jumps to a step
S31, whereas if the answer is negative (NO), i.e., if FCTWP(N)=0, it is
determined at a step S23 whether or not the engine is under fuel cut (the
fuel supply is interrupted).
If the engine is not under fuel cut, the intake pipe-adherent fuel amount
TWP(N) is calculated at a step S24 by the use of the following equation
(7), then a second flag FTWPR(N) is set to a value of 0, and the first
flag FCTWP(N) is set to a value of 1 at steps S30 and S31, followed by
terminating the program:
TWP(N)=(1-Be).times.TWP(N)(n-1)+(1-Ae).times.(Tout(N)-TV) (7)
where TWP(N) (n-1) represents a value of TWP(N) obtained on the last
occasion, and Tout(N) an updated or new value of the fuel injection amount
Tout which has been calculated by the program of FIG. 2. The first term on
the right side corresponds to a fuel amount remaining on the inner surface
of the intake pipe 2 without being carried into the combustion chamber,
out of the fuel previously adhering to the inner surface of the intake
pipe 2, and the second term on the right side corresponds to a fuel amount
newly adhering to the inner surface of the intake pipe 2 out of newly
injected fuel.
If the answer at the step S23 is affirmative (YES), i.e., if the engine is
under fuel out, it is determined at a step S25 whether or not the second
flag FTWPR(N) has been set to a value of 1. If the answer is affirmative
(YES), i.e., if FTWPR(N)=1, the program jumps to the step S31. If the
answer is negative (NO), i.e., if FTWPR(N)=0, the adherent fuel amount
TWP(N) is calculated by the use of the following equation (8) at a step
S26, and then the program proceeds to a step S27:
TWP(N)=(1-Be).times.TWP(N)(n-1) (8)
The equation (8) is identical with the equation (1), except that the second
term on the right side is omitted. The reason for the omission is that is
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