 |
Claims  |
|
|
What is claimed is:
1. Apparatus for controlling the amount of exhaust gases to be recirculated
from an exhaust passage of an internal combustion engine to an intake
passage of the same, comprising:
(a) means for detecting various engine parameters;
(b) gas sensor means for detecting the concentration of an exhaust gas in
said exhaust passage;
(c) means for forcibly interrupting exhaust gas recirculation when said
engine is under air/fuel ratio feedback control and exhaust gas
recirculation is being performed; and
(d) computing means for computing a value representing a desired amount of
exhaust to be recirculated using engine parameters and for:
(1) producing a correction factor using an output signal from said gas
sensor means;
(2) obtaining a first mean value of a first plurality of feedback
correction factor values during feedback control of air/fuel ratio and
during exhaust gas recirculation control;
(3) interrupting exhaust gas recirculation during air/fuel ratio feedback
control;
(4) obtaining a second mean value of a second plurality of feedback
correction factor values when exhaust gas recirculation is being
interrupted;
(5) resuming exhaust gas recirculation when said second mean value is
obtained;
(6) detecting a difference between said first mean value and said second
mean value; and
(7) correcting said value using said difference.
2. A method of accurately estimating the amount of exhaust actually
recirculated from an exhaust passage of an internal combustion engine to
an intake passage of said engine equipped with air/fuel ratio feedback
control apparatus, comprising the steps of:
(a) deriving a first variable using an output signal from a gas sensor used
for measuring concentration of a gas in said exhaust passage, when
air/fuel ratio feedback control and exhaust gas recirculation are both
being performed, said first variable being a mean value of a plurality of
feedback correction factor values;
(b) forcibly interrupting the exhaust gas recirculation;
(c) deriving a second variable using the output signal from said gas sensor
when air/fuel ratio feedback control is being performed but exhaust gas
recirculation is interrupted, said second variable being a mean value of a
plurality of feedback correction factor values;
(d) resuming exhaust gas recirculation when said second variable is
obtained;
(e) calculating the difference between said first and second variables; and
(f) obtaining the amount of exhaust gas recirculated using said difference.
3. A method of accurately estimating the amount of exhaust gases actually
recirculated from an exhaust passage of an internal combustion engine to
an intake passage of said engine equipped with air/fuel ratio feedback
control apparatus, comprising the steps of:
(a) deriving a first variable using an output signal from a gas sensor used
for measuring a concentration of a gas in said exhaust passage, when
air/fuel ratio feedback control and exhaust gas recirculation are both
being performed, said first variable being a mean value of a plurality of
feedback correction factor values, said step of deriving said first
variable including:
(1) detecting a plurality of values of said first variable when stepwisely
changing;
(2) computing a mean value of said plurality of values;
(3) cancelling at least one value which is deviated from said mean value by
a predetermined amount; and
(4) finally obtaining a mean value of said plurality of values, which
plurality equals a predetermined value;
(b) forcibly interrputing the exhaust gas recirculation;
(c) deriving a second variable using the output signal from said gas sensor
when air/fuel ratio feedback control is being performed but exhaust gas
recirculation is interrupted, said second variable being a mean value of a
plurality of feedback correction factor values, said step of deriving said
first variable including:
(1) detecting a plurality of values of said second variable when stepwisely
changing;
(2) computing a mean value of said plurality of values;
(3) cancelling at least one value which is deviated from said mean value by
a predetermined amount; and
(4) finally obtaining a mean value of said plurality of values, which
plurality equals a predetermined value;
(d) resuming exhaust gas recirculation when said second variable is
obtained;
(e) calculating the difference between said first and second variables; and
(f) obtaining the amount of exhaust gas recirculated using said difference.
4. Apparatus for controlling air-fuel mixture to be supplied to an internal
combustion engine having an intake passage, an exhaust passage, and an
exhaust gas recirculation passage for recirculating exhaust gases in said
exhaust passage to said intake passage therethrough, said apparatus
comprising:
(a) means for detecting intake and rotational conditions of said engine;
(b) means for controlling an amount of fuel to be supplied to said engine
along with air for combustion therein in accordance with said detected
intake and rotational conditions;
(c) means for detecting an exhaust composition in said exhaust passage;
(d) means for determining a correction factor using the detected exhaust
composition when said engine is under a predetermined feedback control;
(e) means for correcting said amount of fuel using said correction factor;
(f) means for controlling an amount of exhaust to be recirculated through
said recirculation passage in accordance with said detected intake and
rotational conditions;
(g) means for detecting a difference between a first correction factor
value detected when the operation of said recirculation control means is
enabled, and a second correction factor value detected when the operation
of said recirculation control means is disabled during a period where said
engine is in said predetermined feedback control condition, the difference
detecting means including:
(1) first averaging means for averaging a first plurality of said
correction factor values detected when an output signal from said exhaust
composition detecting means stepwisely changes during a period where the
operation of said recirculation control means is enabled;
(2) second averaging means for averaging a second plurality of correction
factor values detected when said output signal from said exhaust
composition detecting means stepwisely changes during a period where the
operation of said recirculation control means is disabled; and
(3) subtracting means for subtracting a second mean value obtained by said
second averaging means from a first mean value obtained by said first
averaging means;
(h) means for enabling the operation of said first averaging means each
time the operation of said recirculation control means is enabled;
(i) means for disabling the operation of said recirculation control means
each time said first correction factor values are averaged by said first
averaging means; and
(j) means for correcting said air-fuel mixture in accordance with said
detected difference between correction factor values, the mixture
correcting means having recirculation correcting means for correcting said
amount of recirculated exhaust in accordance with the detected difference.
5. Apparatus for controlling an air-fuel mixture to be supplied to an
internal combustion engine having an intake passage, an exhaust passage,
and an exhaust gas recirculation passage for recirculating exhaust gases
in said exhaust passage to said intake passage therethrough, said
apparatus comprising:
(a) means for detecting intake and rotational conditions of said engine;
(b) means for controlling an amount of fuel to be supplied to said engine
with air for combustion therein in accordance with said detected intake
and rotational conditions;
(c) means for detecting exhaust composition in said exhaust passage;
(d) means for correcting said amount of fuel by a correction factor
determined by the detected exhaust composition when said engine is under a
predetermined feedback control;
(e) means for controlling an amount of exhaust to be recirculated through
said recirculation passage in accordance with said detected intake and
rotational conditions;
(f) means for detecting a difference between correction factor values
respectively detected when the operation of said recirculation control
means is enabled and disabled during a period when said engine is in said
predetermined feedback control condition, the difference detecting means
having:
(1) first averaging means for averaging a first plurality of correction
factor values detected when an output signal from said exhaust composition
detecting means stepwisely changes during a period where the operation of
said recirculation control means is enabled;
(2) second averaging means for averaging a second plurality of correction
factor values detected when said output signal from said exhaust
composition detecting means stepwisely changes during a period where the
operation of said recirculation control means is disabled; and
(3) subtracting means for subtracting a mean value obtained by said second
averaging means from another mean value obtained by said first averaging
means;
(g) means for enabling the operation of said first averaging means each
time said engine is under said predetermined feedback control;
(h) means for disabling the operation of said recirculation control means
each time said first correction factor values are averaged by said first
averaging means; and
(i) means for correcting said air-fuel mixture in accordance with said
detected difference between correction factor values, said mixture
correcting means having recirculation correcting means for correcting said
amount of recirculated exhaust in accordance with the detected difference.
6. Apparatus for controlling an air-fuel mixture to be supplied to an
internal combustion engine having an intake passage, an exhaust passage,
and an exhaust gas recirculation passage for recirculating exhaust gases
in said exhaust passage to said intake passage therethrough, said
apparatus comprising:
(a) means for detecting intake and rotational conditions of said engine;
(b) means for controlling an amount of fuel to be supplied to said engine
with air for combustion therein in accordance with said detected intake
and rotational conditions;
(c) means for detecting an exhaust composition in said exhaust passage;
(d) means for correcting said amount of fuel by a correction factor
determined by the detected exhaust composition when said engine is under a
predetermined feedback control;
(e) means for controlling an amount of exhaust to be recirculated through
said recirculation passage in accordance with said detected intake and
rotational conditions;
(f) means for detecting a difference between correction factor values
respectively detected when the operation of said recirculation control
means is enabled and disabled during a period where said engine is in said
predetermined feedback control condition, the difference detecting means
having:
(1) first averaging means for averaging a first plurality of correction
factor values detected when an output signal from said exhaust composition
detecting means stepwisely changes during a period where the operation of
said recirculation control means is enabled;
(2) second averaging means for averaging a second plurality of correction
factor values detected when said output signal from said exhaust
composition detecting means stepwisely changes during a period where the
operation of said recirculation control means is disabled; and
(3) subtracting means for subtracting a mean value obtained by said second
averaging means from another mean value obtained by said first averaging
means;
(g) means for enabling the operation of said first averaging means each
time the operation of said recirculation control means is enabled;
(h) means for disabling the operation of said recirculation control means
each time said first correction factor values are averaged by said first
averaging means; and
(i) means for correcting said air-fuel mixture in accordance with said
detected difference between correction factor values, the mixture
correcting means having fuel correcting means for correcting the amount of
fuel in accordance with the detected difference.
7. Apparatus for controlling air-fuel mixture to be supplied to an internal
combustion engine having an intake passage, an exhaust passage, and an
exhaust gas recirculation passage for recirculating exhaust gases in said
exhaust passage to said intake passage therethrough, said apparatus
comprising:
(a) means for detecting intake and rotational conditions of said engine;
(b) means for controlling an amount of fuel to be supplied to said engine
with air for combustion therein in accordance with said detected intake
and rotational conditions;
(c) means for detecting exhaust composition in said exhaust passage;
(d) means for correcting said amount of fuel by a correction factor
determined by the detected exhaust composition when said engine is under a
predetermined feedback control;
(e) means for controlling an amount of exhaust to be recirculated through
said recirculation passage in accordance with said detected intake and
rotational conditions;
(f) means for detecting a difference between correction factor values
respectively detected when the operation of said recirculation control
means is enabled and disabled during a period where said engine is in said
predetermined feedback control condition, the difference detecting means
having:
(1) first averaging means for averaging a first plurality of correction
factor values detected when an output signal from said exhaust composition
detecting means stepwisely changes during a period where the operation of
said recirculation control means is enabled;
(2) second averaging means for averaging a second plurality of correction
factor values detected when said output signal from said exhaust
composition detecting means stepwisely changes during a period where the
operation of said recirculation control means is disabled; and
(3) subtracting means for subtracting a mean value obtained by said second
averaging means from another mean value obtained by said first averaging
means;
(g) means for enabling the operation of said first averaging means each
time said engine is under said predetermined feedback control;
(h) means for disabling the operation of said recirculation control means
each time said first correction factor values are averaged by said first
averaging means; and
(i) means for correcting said air-fuel mixture in accordance with said
detected difference between correction factor values, the mixture
correcting means having fuel correcting means for correcting the amount of
fuel in accordance with the detected difference.
8. An apparatus for accurately estimating the amount of exhaust gases
actually recirculated from an exhaust passage of an internal combustion
engine to an intake passage of said engine equipped with air/fuel ratio
feedback control apparatus, comprising:
(a) first means for deriving a first variable using an output signal from a
gas sensor used for measuring a concentration of a gas in said exhaust
passage, when air/fuel ratio feedback control and exhaust gas
recirculation are both being performed, said first variable being a mean
value of a plurality of feedback correction factor values, said first
deriving means also for:
(1) detecting a plurality of values of said first variable when stepwisely
changing;
(2) computing a mean value of said plurality of values;
(3) cancelling at least one value which is deviated from said mean value by
a predetermined amount; and
(4) finally obtaining a mean value of said plurality of values, which
plurality equals a predetermined value;
(b) means for forcibly interrupting the exhaust gas recirculation;
(c) second means for deriving a second variable using the output signal
from said gas sensor when air/fuel ratio feedback control is being
performed but exhaust gas recirculation is interrupted, said second
variable being a mean value of a plurality of feedback correction factor
values, said second deriving means also for:
(1) detecting a plurality of values of said second variable when stepwisely
changing;
(2) computing a mean value of said plurality of values;
(3) cancelling at least one value which is deviated from said mean value by
a predetermined amount; and
(4) finally obtaining a mean value of said plurality of values whose number
equals a predetermined value;
(d) means for resuming exhaust gas recirculation when said second variable
is obtained;
(e) means for calculating the difference between said first and second
variables; and
(f) means for obtaining the amount of exhaust gas recirculated using said
difference.
9. Apparatus for controlling air-fuel mixture to be supplied to an internal
combustion engine having an intake passage, an exhaust passage, and an
exhaust gas recirculation passage for recirculating exhaust gases in said
exhaust passage to said intake passage therethrough, said apparatus
comprising:
(a) means for detecting intake and rotational conditions of said engine;
(b) means for controlling an amount of fuel to be supplied to said engine
with air for combustion therein in accordance with said detected intake
and rotational conditions;
(c) means for detecting an exhaust composition of said exhaust gas in said
exhaust passage;
(d) means for determining a correction factor which is determined from
detected exhaust composition when said engine is under a predetermined
feedback control;
(e) means for correcting said amount of fuel using said correction factor;
(f) means for controlling an amount of exhaust to be recirculated through
said recirculation passage in accordance with said detected intake and
rotational conditions;
(g) first averaging means for obtaining a first mean value of a first
plurality of said correction factor values during feedback control of
air/fuel ratio and during exhaust gas recirculation control;
(h) means for prohibiting exhaust gas recirculation during air/fuel ratio
feedback control;
(i) second averaging means for obtaining a second mean value of a second
plurality of said correction factor values when exhaust gas recirculation
is being prohibited;
(j) means for resuming exhaust gas recirculation when said mean value of
said second feedback correction factor values is obtained;
(k) means for determining a difference between said mean value of said
first feedback correction factor values and said means value of said
second feedback correction factor values; and
(l) means for correcting said air-fuel mixture in accordance with said
detected difference between said first and second correction factor
values.
10. Apparatus as claimed in claim 9, wherein said first averaging means is
also for obtaining said first mean value when an output signal from said
exhaust composition detecting means stepwisely changes during a period
where the operation of said recirculation control means is enabled; and
said second averaging means is also for obtaining said second mean value
when said output signal from said exhaust composition detecting means
stepwisely changes during a period where the operation of said
recirculation control means is disabled;
the difference detecting means including subtracting means for subtracting
said second mean value obtained by said second averaging means from said
first mean value obtained by said first averaging means.
11. Apparatus as claimed in claim 9, wherein said mixture correcting means
(1) comprises recirculation correcting means for correcting said amount of
recirculated exhaust in accordance with the detected difference.
12. Apparatus as claimed in claim 1, wherein said first averaging means is
also for obtaining said first mean value when an output signal from said
exhaust composition detecting means stepwisely changes during a period
where the operation of said recirculation control means is enabled; and
said second averaging means is also for obtaining said second mean value
when said output signal from said exhaust composition detecting means
stepwisely changes during a period where the operation of said
recirculation control means is disabled;
the difference detecting means including subtracting means for subtracting
said second mean value obtained by said second averaging means from said
first mean value obtained by said first averaging means. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
BACKGROUND OF THE INVENTION
This invention relates generally to control of an internal combustion
engine equipped with exhaust gas recirculation system, and more
specifically to apparatus for controlling the amount of recirculated
exhaust gasses and air/fuel ratio of an air/fuel mixture supplied to an
internal combustion engine.
Exhaust gas recirculation, which is known as EGR, is used for reducing the
concentration of nitrogen oxides (NOx) included in exhaust gasses from an
internal combustion engine. Conventionally, to ensure the accuracy of the
EGR control, a valve is controlled electronically in order to control the
amount of recirculated exhaust gasses.
In such a conventional EGR system, the amount of recirculated exhaust
gasses is estimated by detecting an opening degree of an EGR valve. When
using such an EGR system for a long period of time, dirty particles, such
as carbon and unburnt substances, are attached to the inner surfaces of
the EGR valve and EGR passage. Therefore, the relationship between the
opening degree of the EGR valve and the amount of recirculated gasses is
disturbed raising a problem that the initial object of estimating the
recirculation is not achieved. One approach for solving this problem is to
measure the amount of recirculated gasses so as to control the same. One
example of a conventional arrangement according to such approach is a
technique of estimating the amount of EGR by ascertainining the amount of
fresh air with an airflow meter being provided to an intake manifold so as
to measure the amount of fresh air even during EGR operation. This
technique is disclosed in Japanese patent provisional publication No.
57-44760. Another example is a technique of estimating the amount of fresh
air using total intake amount of an internal combustion engine and a
sensor provided to an EGR valve. This is disclosed in Japanese patent
provisional publication No. 57-83641.
Such conventional techniques, however, only estimate the amount of fresh
air or the amount of EGR by detecting one of them where their measuring
system is provided centering around the intake pipe of the internal
combustion engine. Therefore, true state of air-fuel mixing within the
combustion chambers of the internal combustion engine cannot be detected.
As a result, air/fuel ratio control carried out through computation of
fuel injection amount for obtaining optimal air/fuel ratio is apt to
suffer from errors. Furthermore, the above-mentioned first convetional
technique requires an airflow meter which introduces resistance to airflow
within the intake system. In addition, since the above-mentioned second
conventional technique employs a sensor installed in the EGR valve, the
sensor is apt to suffer from deterioration due to dirty particles in the
exhaust gasses, while there arises a problem relating to maintenance of
the sensor. For these reasons, conventional EGR systems are desired to be
improved.
SUMMARY OF THE INVENTION
The present invention has been developed in order to remove the
above-described drawbacks inherent to the conventional EGR systems.
It is, therefore, an object of the present invention to provide a new and
useful apparatus for controlling EGR and air/fuel ratio for an internal
combustion engine.
According to a feature of the present invention the amount of recirculated
exhausted gasses is accurately detected so as to operate an internal
combustion engine under an optimal operating condition all the time. To
this end a correction factor derived from oxygen sensor output, which is
used for air/fuel ratio control, is monitored so as to obtain a difference
of a correction factor value resulted from engine operation with EGR and
another correction factor value resulted from engine operation without
EGR. This difference is obtained by forcibly interrupting EGR operation.
Once the amount of recirculated exhaust is accurately estimated, the EGR
control and/or air/fuel ratio control are performed with compensation for
possible error due to secular change in EGR system.
BRIEF DESCRIPTION OF THE DRAWINGS
The object and features of the present invention will become more readily
apparent from the following detailed description of the preferred
embodiments taken in conjunction with the accompanying drawings in which:
FIG. 1 is a schematic view of an internal combustion engine equipped with
EGR system according to the present invention;
FIG. 2 is a block diagram of an electronic control unit used in the system
of FIG. 1;
FIG. 3 is a flowchart showing an operational program of a microcomputer
used in the electronic control unit of FIG. 2, which flowchart corresponds
to a first embodiment of the present invention;
FIG. 4 is a diagram showing the relationship between oxygen sensor output
and air/fuel ratio correction factor both used in the processing by the
microcomputer of FIG. 2;
FIG. 5 is a flowchart showing another operational program of the
microcomputer showing a second embodiment of the present invention;
FIG. 6 is a flowchart showing another operational program of the
microcomputer showing a third embodiment of the present invention; and
FIG. 7 is a flowchart showing another operational program of the
microcomputer showing a fourth embodiment of the present invention.
The same or corresponding elements and parts are designated at like
reference numerals throughout the drawings.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIG. 1, a schematic view of an internal combustion engine
equipped with an EGR system according to the present invention is shown.
An internal combustion engine 10 is equipped with an intake pipe 12 and an
exhaust pipe 14, and the operating state of the engine 10 is detected by
various sensors all the time. An electronic control unit 50 controls the
internal combustion engine 10 using detection results from the various
sensors as will be described in detail hereinlater.
The intake pipe 12 is provided for supplying the engine 10 with fresh air
and recirculated exhausted gasses. To one end of the intake pipe 12 is
attached an air filter 16 for cleaning intake air, and a throttle valve 18
is provided within the intake pipe 12 for contolling the intake fresh air
quantity. The throttle valve 18 is associated with a throttle opening
degree sensor 20 supplying the electronic control unit 50 with throttle
opening degree information.
The exhaust gas recirculation from the exhaust pipe 14 to the intake pipe
12 is carried out via an EGR tube 24 in which an EGR control device 22 is
provided. The EGR control device 22 comprises a control valve of the
diaphragm type and is arranged such that a diaphragm 22C thereof drives a
control valve 22D having a valve head against a force of cylindrical
spring in accordance with pressure fed via a control conduit 22A so that
the amount of exhaust gasses flowing through the EGR tube 24 is
controlled. Thus the control valve 22D moves up and down in the drawing,
where the reciprocal movement of the control valve 22D is detected by an
EGR valve lift sensor 22B built in the EGR control device 22. The EGR
valve lift sensor 22B is of the linear solenoid type, producing an output
signal indicative of the position of the control valve 22D. The control
conduit 22A communicates via two passages 80 and 82 with the intake pipe
12 at a portion upstream the throttle valve 18 and downstream the same.
More specifically, the passage 80, which is referred to as an upstream
passage, is provided between the control conduit 22A and the intake pipe
12 at a portion upstream the throttle valve with an electromagnetic valve
26, while the other passage 82, which is referred to as a downstream
passage, is provided between the control conduit 22A and the intake pipe
12 at a portion downstream the throttle valve with an electromagnetic
valve 28. The portion upstream the throttle valve 18 where the upstream
passage 80 is connected exhibits a pressure substantially the same as
atmospheric pressure, while the portion downstream the throttle valve 18
where the downstream passage 82 is connected exhibits a large negative
pressure. With this arrangement, when the electromagnetic valve 26 is
energized to open, pressure substantially equal to atmospheric pressue is
sent via the passage 26 to the control conduit 22A. As a result, the
diaphragm 22C is lowered by the force of the cylindrical spring causing
the valve head of the control valve 22D to be in contact with an
associated valve seat closing the EGR tube 24. Therefore, exhaust gasses
are prevented from being recirculated. On the other hand, when the other
electromagnetic valve 28 is energized to open, the diaphragm 22C moves
upwardly against the force of the cylindrical spring. As a result, the
valve head of the control valve 22D is lifted up, allowing exhaust gas
recirculation via the EGR tube 24. An intake pressure sensor 30 is
provided to detect the negative pressure at a portion downstream the
throttle valve 18 to detect the pressure of fresh air and recirculated
exhaust gasses within the intake pipe 12. An output signal from the intake
pressure sensor 30 is fed to the electronic control unit 50. The reference
32 is a fuel injection valve through which fuel is sprayed into air taken
into each cylinder of the engine 10. The reference 34 is a distributor of
an ignition system of the engine 10, and the reference 36 is a rotational
angle sensor associated with the distributor 34 for detecting the
rotational speed of the engine crankshaft. The reference 38 is a coolant
temperature sensor for detecting the temperature of engine coolant, and
the reference 40 is an oxygen sensor for detecting the concentration of
oxygen within the exhaust gasses in the exhaust pipe 14.
FIG. 2 is a block diagram of an electrical system associated with the EGR
system according to the present invention. The electronic control unit 50
comprises a microcomputer 52, an input processing portion 54 including an
A/D converter (not shown), and three drive circuits 56, 58 and 60. The
input processing portion 54 also comprises buffers and waveform shaping
circuits so as to receive various signals from the sensors 20, 22B, 30,
36, 38 and 40 and send corresponding information in the form of digital
signals to the microcomputer 52 having memories (not shown). The
microcomputer 52 is arranged to operate in accordance with a program
stored in its memory using various information from the above-mentioned
sensors so as to output instruction signals to the drive circuits 56, 58
and 60 by which the engine 10 is optimally controlled. More specifically,
the fuel injection valve 32 is controlled to inject a desired amount of
fuel to obtain a desired air/fuel ratio, while the electromagnetic valves
26 and 28 are respectively controlled to adjust the amount of recirculated
exhaust gasses.
FIG. 3 is a flowchart showing an EGR control routine among various control
routines. With this routine a valve-opening duration Tp of the fuel
injection valve 32, which defines the amount of fuel supplied to the
engine 10, and the amount of recirculated exhaust gasses are determined,
while the amount of recirculated exhaust gasses is also corrected by this
routine. Since this routine should be carried out frequently in accordance
with the operating state of the engine, this routine is arranged to be
executed at an interval corresponding to a given number of rotations of
the engine 10 or at a given interval using a timer built in the
microcomputer 52. The EGR control routine will be described in detail
hereinafter.
When the EGR control routine of FIG. 3 is started, a step 100 is executed
for reading outputs from the intake pipe pressure sensor 30 and from the
rotational angle sensor 36 so as to detect intake pipe pressure PM and
rotational speed NE of the engine 10.
In a subsequent step 110, an optimum amount of fuel to be supplied to the
engine 10 is calculated in the form of a basic fuel injection duration Tp
of the fuel injection valve 32 using the above two detected data PM and
NE. To calculate Tp, actual computation using a formula including the data
PM and NE may be operated or a two-dimensional map may be used, so that a
corresponding T.sub.p is picked up from the map prepared in advance by
storing data in the memory using PM and NE as two variables.
In a step 120, an amount of recirculated exhaust gasses, which is indicated
at EGR1, is obtained using the above-mentioned two data PM and NE in the
same manner as one of the above-mentioned two methods. This exhaust gas
recirculation amount EGR1 is a value which corresponds to the output from
the EGR valve lift sensor 22B, and represents an opening degree of the
control valve 22D of the EGR control device 22 which is necessary for
recirculating an optimum amount of exhaust gasses using two variables PM
and NE.
In a step 130, the basic fuel injection duration Tp is corrected. There are
various modes of engine operations during which engine output is
maximized, starting characteristic is improved and so on, and therefore,
engine operation cannot be simply determined by the intake pipe pressure
PM and the engine speed NE during these periods. The basic fuel injection
duration Tp only shows a basic value of fuel injection duration, and this
basic value undergoes various corrections effected by the electronic
control unit 50 using the results of detection from various sensors, so
that the basic fuel injection duration Tp is corrected to a value most
suitable for the present operating state of the engine 10.
The above-mentioned various corrections include a correction for increasing
the amount of fuel to be injected into the engine 10 to increase output
when it is detected such that the throttle valve 18 is largely opened by
the throttle opening sensor 20, another correction for effecting air/fuel
ratio feedback control to cause the engine to operate with a specific
air/fuel ratio using a correction factor in accordance with an output
signal from the oxygen sensor 40 under a given condition, and so on. The
above-mentioned air/fuel ratio feedback control per se is well known in
the art, and will be described briefly since it has a close relationship
with the following processings.
In the air/fuel ratio feedback control, the engine 10 is operated with a
specific mixing ratio between fuel and oxygen, which mixing ratio is
selected through an overall decision relating to fuel consumption, engine
output, harmful components emission or the like in a steady operating
state after the engine 10 is warmed up. The air/fuel mixing ratio is
detected using the oxygen sensor 40.
The oxygen sensor 40 is arranged to output a lean signal when air/fuel
ratio is higher than a desired value, i.e. when amount of fuel is less,
and a rich signal when air/fuel ratio is lower than the desired value,
through continuous detection of oxygen concentration in exhaust gasses in
the exhaust pipe 14. The electronic control unit 50 receiving the output
from the oxygen sensor 40 performs feedback control so as to continually
maintain the above-mentioned specific air/fuel ratio by lengthening the
basic fuel injection duration Tp when the lean signal is present, and by
shortening the same when the rich signal is present.
FIG. 4 shows the output from the oxygen sensor 40 (see upper waveform) and
the variation of a correction factor (see lower waveform) used in the
electronic control unit 50 which operates using the output from the oxygen
sensor 40. As shown, the output from the oxygen sensor 40 is a binary
signal assuming either a rich state level (high level) and a lean state
level (low level), and the correction factor varies by a predetermined
amount instantaneously in response to a rising or falling edge "a" of the
waveform of the output from the oxygen sensor 40. More specifically, the
correction factor stepwisely changes in the presence of rising or falling
edge "a" and further changes linearly over a period between the rising and
falling edges "a" so that the air/fuel ratio feedback control is performed
proportionally and integrally.
The above-described operation is of normal fuel injection amount control,
and further processing is carried out in this routine as will be described
hereinafter.
In a step 140, it is checked whether the above mentioned air/fuel ratio
feedback control is carried out in the various corrections executed in the
step 130. The air/fuel ratio feedback control is carried out for obtaining
most suitable air/fuel ratio for steady operating state of the engine 10.
Therefore, air/fuel ratio feedback control is interrupted during
engine-starting period and heavy-load operating period, and air/fuel ratio
is controlled to be suitable for such transient periods respectively.
Processings following the step 140 are all carried out only when air/fuel
ratio feedback control is being effected. In other words, a step 150 is
executed when the determination in the step 140 resulted in YES. When the
determination in the step 140 results in NO, namely when it is determined
that the air/fuel ratio feedback control is being interrupted, the
processing of the present routine is terminated.
The step 150 is provided for determining whether exhaust gas recirculation
is being carried out or not. More specifically, exhaust gas recirculation
is effected under limited conditions since it suffers from the decrease in
engine output as described in the above. Therefore, it is determined
whether exhaust gas recirculation is being carried out or not using the
output from the EGR valve lift sensor 22B. When it is detected that
exhaust gas recirculation is being carried out, a step 160 is then
executed. On the other hand, a step 200 is executed when no recirculation
is made.
In the step 160, which is executed only when the air/fuel ratio feedback
control and EGR control are both being effected, the correction factor
shown in FIG. 4 is monitored such that correction factor values Bn
(wherein n is 0, 1, 2, 3 . . . ) are detected at points where the
correction factor varies stepwisely. These points where stepwise changes
are made will be referred to as varying points hereinafter. Then in a
following step 165, the value Bn of the correction factor at each varying
point is stored in a sequence so as to calculate a mean value thereof. In
a following step 170, it is determined whether the number of values of Bn
used for obtaining the mean value has reached a predetermined number such
as 4. A mean value of such a predetermined number of values of Bn is
expressed in terms of A1, and therefore, the step 170 is executed to see
if such a mean value A1 is present or not. When such a mean value A1 is
present, a step 180 is executed to set a flag EGRF to logic "1".
As the routine of FIG. 3 is executed a number of times so that the
predetermined number, such as four, of the varying points Bn (for example
from B1 to B4) are detected, then the determination in the step 170 turns
to YES because the mean value A1 of the predetermined number of Bn is
first obtained. To ensure the reliability of the mean value A1, the
predetermined number of Bn are processed as follows. The difference
between each measured value Bn and the mean value A1 is first computed and
when one or more of the respective measured values of Bn, such as B0 to
B3, are very far from the mean value A1, such deviated value or values are
erased and it is regarded that the mean value A1 has not been calculated.
In the example shown in FIG. 5, since the value of B0 is deviated from the
mean value A1 for a period T1 by more than a predetermined value, B0 is
erased. Then the operational flow does not proceed to a next step 180 but
the above-mentioned steps from 100 to 170 are repeatedly executed until a
subsequent varying point B4 is detected. From the above it will be
understood that the step 180 is exeucted only when the internal combustion
engine 10 continuously stably operates so that a predetermined number of
varying points, such as B1 to B4 over the period T2 in FIG. 4, repeatedly
appear with substantially the same varying pattern.
The step 180 is provided to set the flag EGRF to logic "1" for interrupting
exhaust gas recirculation. More specifically, this flag EGRF is used to
command EGR interruption for forcibly interrupting EGR. Since the step 180
is executed only when the engine 10 operates stably as described in the
above, EGR interruption is made only during such stable engine operation.
All the processings carried out after the determination in the step 150
that EGR is being carried out are terminated when the step 180 is
completed.
Turning back to the step 150, when it is determined that EGR is not being
carried out steps 200 to 260 are executed. In step 200, it is checked | | |
