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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ignition control apparatus for an
internal combustion engine. More particularly, it relates to an ignition
control apparatus provided with a plurality of ignition timing data maps
which are selected in accordance with changes in the operating condition
of the engine.
2. Description of the Related Art
An internal combustion engine as applied to an automobile and provided with
an electric control system, such as a micro-computer system adapted for
effective control of the engine, is well known in the art.
Such a system is used to control various operating parameters of the
internal combustion engine, for example, ignition timing in a spark
ignition type engine, in which the control apparatus controls the optimum
value of the ignition timing in accordance with engine operating
parameters, such as engine speed and engine load.
Known in the prior art is an electric control system for an internal
combustion engine wherein the air-fuel ratio of the air-fuel mixture to be
introduced into the engine combustion chambers is controlled to a
theoretical value. This system utilizes ignition timing data maps, and an
ignition timing is calculated by a map in accordance with the engine load
and the engine speed.
Recently, due to improvements made to sensor devices and control devices, a
system has been proposed wherein the air-fuel mixture is controlled in the
area leaner than that providing the theoretical air-fuel ratio, to save
fuel consumption. Such a control of the air-fuel mixture is referred to
hereinafter as "lean A/F control". In such lean A/F control, the
combustion is controlled in the lean area under a stable running condition
of the engine. When the engine is required to provide a high output, the
combustion is also controlled in an area corresponding to the theoretical
air-fuel ratio and sometimes in the area which is richer than the area
corresponding to the theoretical air-fuel ratio. In this system, the
air-fuel ratio is therefore widely varied in accordance with the
conditions of the engine, which makes it difficult to obtain an optimum
ignition timing calculated by a single map. The ignition timing calculated
by a single map can, of course, be arithmetically corrected in accordance
with the operating condition of the engine. The correction is, however,
insufficient to attain optimum control of the ignition timing in every
area of the engine, and thus a deterioration occurs in the drivability,
knocking is caused, and the fuel consumption efficiency becomes degraded.
This difficulty is worsened if the engine is provided with a swirl control
system for attaining a stable combustion with lean A/F control, since
selection of the ignition timing in this case becomes very complex.
This difficulty is more or less encountered also when the air-fuel ratio is
controlled to the stoichiometric value.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an apparatus for
controlling the ignition timing in such a manner that it is suitably
carried out in accordance with any change in the engine operating
conditions.
According to the present invention, an apparatus is provided for
controlling an ignition timing in a spark ignition internal combustion
engine, which apparatus comprises: means for storing a plurality of
ignition timing data maps, these maps having a respective order of
priority which is determined in accordance with engine requirements
related to the ignition timing; means for detecting a plurality of engine
parameters related to at least one engine operating condition; means for
judging whether the parameters detected by the detecting means meet the
engine requirement; means for selecting a map which has the highest order
of priority from the maps judged by the judging means so that the detected
parameters are matched to the engine requirement; means for calculating an
ignition timing from the map selected by the selecting means; and means
for controlling the ignition in such a manner that ignition occurs at the
calculated ignition timing.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention may be more fully understood from the description of
the preferred embodiment of the invention set forth below, together with
the accompanying drawings, in which:
FIG. 1 is a cross-sectional view of an entire engine, with a block diagram
of a control circuit;
FIG. 2 is a cross-sectional side view of the cylinder head;
FIG. 3 is a cross-sectional plan view of the cylinder head;
FIG. 4 is a schematically illustrated perspective view of the engine;
FIG. 5 is a plan view, partly in cross-section, of a portion of the
cylinder head;
FIG. 6 is a diagram illustrating the operation of the idle switch Idle,
lean switch LS, and fully open switch VL of the throttle sensor;
FIG. 7 shows a relationship between the air-fuel ratio and the output
current of the lean sensor;
FIG. 8 is a flow chart showing the operation of the swirl control valve
(SCV);
FIGS. 9 to 12 respectively show a routine for controlling flags used in the
routines for controlling the air-fuel ratio and ignition timing;
FIGS. 13, 14, 14A, 14B and 15 show flow charts for explaining the
controlling of the air-fuel ratio;
FIG. 16 is a timing chart illustrating the map selection operation
according to the present invention;
FIG. 17 shows a relationship between NE and KLEANNE;
FIG. 18 shows a relationship between PM and KLEANPM;
FIG. 19 shows a relationship between KLEAN and a signal from the lean
sensor, IR;
FIG. 20 shows a relationship between PM and KLEAN at a fixed engine speed,
with the various minimum values of KLEAN selected in accordance with
engine parameters;
FIG. 21 shows an arrangement of the various maps in the ROM addresses;
FIGS. 22 to 24 are flow charts for explaining the ignition timing control
routine;
FIG. 25 shows relationships between ignition timing and engine output
torque before and after the engine has warmed-up;
FIG. 26 shows similar relationships when closed loop control is carried out
and open loop control is carried out;
FIGS. 27a-27d show timing charts of the ignition timing control operation;
and
FIG. 28, 28A and 28B show a flow chart for explaining the calculating of
the ignition timing from the selected map in the second embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIGS. 1 through 4, reference numeral 1 designates an engine
body, 2 a cylinder block, 3 a piston reciprocally movable in the cylinder
block 2, and 4 a cylinder head fixed to the cylinder block 2; 5 designates
a combustion chamber, 6 a spark plug arranged in the combustion chamber 5,
7 an intake valve, and 8 a helically-shaped intake port; 9 designates an
exhaust valve, and 10 an exhaust port. A downwardly projecting separating
wall 11 is formed on the upper wall 12 of the intake port 8, and a space
is formed between the lower face of the separating wall 11 and the bottom
wall of the intake port 8. This separating wall 11 passes the side of the
valve stem 7a and extends along the axis of the intake port 8. An inlet
passage portion A, a helical portion B, and a bypass passage 13 are formed
in the intake port 8 by the separating wall 11. The inlet passage portion
A is tangentially connected to the helical portion B, and the bypass
passage 13 is branched from the inlet passage portion A and connected to
the helix terminating portion C of the helical portion B. As illustrated
in FIG. 3, the transverse width of the inlet passage portion A formed
between the side wall 14 of the intake port 8 and the separating wall 11
decreases toward the helical portion B, and a narrow passage portion 15 is
formed between the cylindrical side wall 16 of the helical portion B and
the separating wall 11. A swirl control valve 17 is arranged in the bypass
passage 13. This swirl control valve 17 includes a thin walled valve body
18 and a valve shaft 19, the valve shaft 19 being rotatably supported by a
valve holder 20 fixed to the cylinder head 4. As illustrated in FIG. 2, an
arm 21 is fixed to the upper end of the valve shaft 19.
As illustrated in FIG. 1, the intake port 8 is connected to a surge tank 22
via a branch pipe 23, and a fuel injector 24 is arranged in the branch
pipe 23. This fuel injector 24 is connected to the fuel pump (not shown)
driven by the engine. The surge tank 22 is connected to the outside air
via an intake air duct 25 and an air filter element 26, and a throttle
valve 27 actuated in response to the depression of the accelerator pedal
(not shown) is arranged in the intake air duct 26. A throttle sensor 28 is
connected to the valve shaft 27a of the throttle valve 27. The throttle
sensor 28 is provided with an idle switch Idle, lean switch LS, and fully
open switch VL, as shown in FIG. 6. The idle switch Idle is made ON when
the degree of opening of the throttle valve 27 is lower than a
predetermined degree, for example, 1.5 degrees. The lean switch LS is made
ON when the degree of opening of the throttle valve 27 exceeds a
predetermined degree, for example, 25 degrees. The fully open switch VL is
made ON when the degree of opening of the throttle valve 27 exceeds a
further predetermined degree, for example, 50 degrees. These switches
Idle, LS, and VL are connected to a control unit 50.
A vacuum sensor 29 is attached to the surge tank 22 and produces an output
voltage proportional to the absolute pressure produced in the surge tank
22. This vacuum sensor 29 is connected to the electronic control unit 50.
As illustrated in FIGS. 1 and 5, the arm 21 of the swirl control valve 17
is connected to a control rod 30 of an actuator 31 via a connecting rod 32
and a link member 33. The actuator 31 includes a vacuum chamber 34 and an
atmospheric pressure chamber 35, which chambers are separated by a
diaphragm 36. The control rod 30 is connected to the diaphragm 36, and a
compression spring 37 for biasing the diaphragm is arranged in the vacuum
chamber 34. The vacuum chamber 34 is connected to the surge tank 22 via a
conduit 38. A solenoid valve 39, which can be opened to the outside air,
is arranged in the conduit 38 and, in addition, a check valve 40 which
permits only the outflow of air from the vacuum chamber 34 to the surge
tank 22 is arranged in the conduit 22. The solenoid valve 39 is connected
to the electronic control unit 50 and is controlled in response to signals
output by the electronic control unit 50.
When the vacuum chamber 34 of the actuator 31 is connected to the surge
tank 22 via the solenoid valve 39, vacuum acts in the vacuum chamber 34.
At this time, the check valve 40 opens only when the level of vacuum in
the surge tank 22 is higher than that of the vacuum in the vacuum chamber
34. Consequently, the level of vacuum in the vacuum chamber 34 is
maintained at the maximum vacuum produced in the surge tank 22. When the
level of vacuum in the vacuum chamber 34 exceeds a predetermined level,
the diaphragm 36 moves toward the vacuum chamber 34 and, as a result, the
swirl control valve 17 closes the bypass passage 13, as illustrated in
FIG. 3. At this time, air introduced into the inlet passage portion A of
the intake port 8 flows into the helical portion B, as illustrated by the
arrow K in FIGS. 3 and 4. Then, since the inlet passage portion A is
formed in such a manner that the transverse width thereof decreases toward
the helical portion B, as mentioned above, the velocity of the air is
increased. The air then flows along the cylindrical side wall 16 of the
helical portion B, and thus a strong swirl motion is created.
When the vacuum chamber 34 of the actuator 31 is opened to the outside air
via the solenoid valve 39, the diaphragm 36 is moved toward the
atmospheric pressure chamber 35 by the spring force of the compression
spring 37. As a result, the swirl control valve 17 opens the bypass
passage 13. Consequently, at this time, part of the air flows into the
helical portion B via the bypass passage 13 having a small flow
resistance. This part of the air comes into head-on collision with the air
stream swirling along the cylindrical side wall 16 of the helical portion
B, and thus the swirl motion is weakened. As mentioned above, when the
swirl control valve 17 is open to the maximum extent, the swirl motion is
weakened and, in addition, the flow area of the intake port 8 is
increased. As a result, a high volumetric efficiency can be obtained.
Referring to FIG. 1, an exhaust manifold 41 is connected to the exhaust
port 10 (FIG. 3), and a catalytic converter 42 containing a catalyzer
therein is connected to the exhaust manifold 41. Hydrocarbons (HC),
carbon-monoxide (CO), and nitrogen-oxides (NOx) are purified in the
catalytic converter 42. A lean sensor 43 is arranged in the exhaust
manifold 41 and connected to the electronic control unit 50. The lean
sensor 43 produces an output current proportional to the oxygen
concentration in the exhaust gas, as illustrated in FIG. 7. In FIG. 7, the
ordinate indicates the output current I of the lean sensor 43, and the
abscissa indicates the air-fuel ratio (A/F). The construction and the
operation of the lean sensor 43 is known (for example, Japanese Unexamined
Patent Publication (Kokai) No. 58-143108) and, therefore, a description of
the construction and the operation of the lean sensor 43 is omitted.
As illustrated in FIG. 1, the engine 1 is equipped with a distributor 44
having a rotor 45 driven by the engine 1. The distributor 44 is connected
to the electronic control unit 50 via an ignition coil 46 and an igniter
47. The electronic control unit 50 produces an ignition signal (FIG.
27(d)). This ignition signal is fed into the igniter 47 and the primary
current of the ignition coil 46 is then controlled by the ignition signal.
The high voltage produced in the ignition coil 46 is applied to the spark
plug 6 of each cylinder via the distributor 44, and thus the spark plug 6
produces a spark at a time determined by the ignition signal. A pair of
crank angle sensors 48, 49 are arranged in the distributor 44 and
connected to the electronic control unit 50. The crank angle sensor 48
produces an output pulse every time the crank shaft of the engine 1
rotates by 30 degrees, and the crank angle sensor 49 produces an output
pulse every time the crankshaft of the engine 1 rotates by 720 degrees.
An engine cooling water temperature sensor 70 is mounted to the cylinder
block 2 and produces an output voltage proportional to the temperature of
the cooling water in a water jacket in the engine. The temperature sensor
70 is connected to the control unit 50.
An outside air temperature sensor 71 is arranged in the intake system near
the air cleaner 26, for producing an output voltage proportional to the
temperature of the air. The sensor 71 is connected to the control unit 50.
The electronic control unit 50, to which power is supplied by a regulator
72 operated by engine key switch 73, is constructed as a digital computer
and includes a central processing unit (CPU) 51 carrying out the
arithmetic and logic processing, a random-access memory (RAM) 52, a
read-only memory (ROM) 53 storing a predetermined control program and
arithmetic constant therein, an input/output (I/O) port 54, and an
analog-digital (A/D) converter 55 incorporating a multiplexer. The CPU 51,
the RAM 52, the ROM 53, the I/O port 54, and the A/D converter 55 are
interconnected to each other via a bidirectional bus 56. The idle switch
Idle, lean switch VL, and fully open switch VL of the throttle sensor 28
are connected to the I/O port 54, and signals output by the throttle
sensor 28 are input to the I/O port 54. The vacuum sensor 29 is connected
to the A/D converter 55, and the output signal of the vacuum sensor 29 is
input to the A/D converter 55. The lean sensor 43 is connected to the A/D
converter 55 via a current-voltage converting circuit 57 of the electronic
control unit 50. The output current of the lean sensor 43 is converted to
corresponding voltage in the current-voltage converting circuit 57, and
the voltage thus converted is then input to the A/D converter 55. The
water temperature sensor 70 is connected to the A/D converter 55 and the
signal output from the temperature sensor 70 is input to the A/D converter
55. The air temperature sensor 71 is connected to the A/D converter 55,
and the signal output from the sensor 71 is input to the A/D converter 55.
In the A/D converter 55, the output voltage of the vacuum sensor 29, the
output voltage of the current-voltage converting circuit 57, the output
voltage of the water temperature sensor 70, or the output voltage of the
air temperature sensor 71 is selectively converted to a corresponding
binary code in response to the indication signal issued form the CPU 51.
The binary code thus obtained, that is, data representing the absolute
pressure PM in the surge tank 22, data corresponding the output current
LNSR of the lean sensor 42, data indicating the water temperature THW, and
data indicating the air temperature TA are stored in the RAM 52.
The crank angle sensors 48 and 49 are connected to the I/O port 54, and the
output pulses of the crank angle sensors 48 and 49 are input to the I/O
port 54. These output pulses are then input to the CPU 51 and, for
example, the engine speed NE is calculated by measuring the number of
output pulses which the crank angle sensor 48 produces per unit time. The
thus-calculated engine speed NE is stored in the RAM 52.
The fuel injector 24 and the solenoid valve 39 are connected to the I/O
port 54 via corresponding drive circuits 58 and 59, and the igniter 47 is
connected to the I/O port 54. An injection signal is fed into the fuel
injector 24 from the CPU 51 via the I/O port 54 and the drive circuit 58.
The solenoid of the fuel injector 24 is energized for a time period
determined by the injection signal, and thus fuel is intermittently
injected from the fuel injector 24 into the intake port 8. A swirl control
drive signal is fed into the solenoid valve 39 from the CPU 51 via the I/O
port 54 and the drive circuit 59. The solenoid valve 39 is energized for a
time period determined by the swirl control drive signal. As mentioned
previously, the ignition signal is fed into the ignitor 47 from the CPU 51
via the I/O port 54.
In the engine according to the present invention, various kinds of air-fuel
mixture are supplied to the engine in accordance with the engine
requirements. Roughly speaking, when the engine is operating at a high
load, the air-fuel mixture of an approximately stoichiometric air-fuel
ratio or smaller is fed into the engine cylinders. When the engine is
operating at a low load, the lean air-fuel mixture is fed into the engine
cylinders, although the air-fuel ratio is determined by the position of
the throttle valve 27. That is, when the throttle opening is large, a
relatively lean air-fuel mixture (air-fuel ratio is, for example,
18:1-19:1) is fed into the cylinders. Contrary to this, when the throttle
opening is small, an extremely lean air-fuel mixture (air-fuel ratio is,
for example, 22:1) is fed into the cylinders. In addition, when the
air-fuel mixture of an approximately stoichiometric air-fuel ratio is fed
into the cylinders, the swirl control valve 17 is opened to the maximum
extent and, when the lean air-fuel mixture is fed into the cylinders, the
swirl control valve 17 is closed. If the swirl control valve 17 is closed,
a strong swirl motion is created in the combustion chamber 5 and, as a
result, the burning velocity is increased. Consequently, at this time,
even if the lean air-fuel mixture is fed into the cylinders, stable
combustion can be obtained. The above-mentioned operation is a basic
operation.
In addition to the basic operation of the control of the air-fuel ratio,
the lean air-fuel mixture is corrected in accordance with various
operating conditions. For example, when the engine is cold, the lean
air-fuel mixture is corrected so that its highest value is lower than that
of the very lean air-fuel mixture. This means that the very lean air-fuel
mixture is usually supplied to the engine without correction after the
engine has warmed-up. However, when the feedback control of the air-fuel
ratio is stopped due to a particular engine operating condition, the very
lean air-fuel mixture is also corrected so that its highest air-fuel ratio
is lower than that of the extremely lean air-fuel mixture.
FIG. 8 illustrates the processing routine for controlling the swirl control
valve 17. This routine is processed by sequential interruptions executed
at predetermined time intervals. Referring to FIG. 8, initially, at step
100, it is judged whether the engine is in one of the predetermined states
in which the swirl control valve 17 should be opened. These predetermined
states are as follows.
(1) when the engine speed is higher than 2800 rpm
(2) when the throttle valve 27 is open to the maximum extent
(3) when the starting operation of the engine is carried out
When at least one of the above states (1), (2), and (3) is satisfied, the
routine goes to step 101. At step 101, the solenoid valve 39 is energized,
and the vacuum chamber 34 of the actuator 31 opened to the outside air. As
a result, the swirl control valve (SCV) 17 is opened to the maximum
extent. When the engine is not in a predetermined state in which the swirl
control valve 17 should be opened, the routine goes to step 102 where it
is judged whether a flag XSCVF is 1. At a following point 103 it is judged
whether a flag XVLCN is 1. When the flag XSCVF or XVLCN is 1, the routine
goes to the above-mentioned step 101 to open the SCV 17. The meaning of
the flags will be described later. When both the flags are 0, then the
routine goes to step 104 and the solenoid valve 39 is de-energized. As a
result, the vacuum chamber 34 of the actuator 31 is connected to the surge
tank 22 and the swirl control valve (SCV) 17 is closed.
FIG. 9 illustrates the processing routine for setting the flag XSCVF. At
point 200 it is judged whether the absolute pressure PM is decreasing.
When the pressure PM is increasing the routine goes to point 201, where it
is judged whether PM exceeds a predetermined fixed level PM1. If the
result of the judgement at the point 201 is "yes", the routine flows to
point 202, where it is judged whether a predetermined time .DELTA.t has
elapsed from the beginning of the decrease in PM. When the predetermined
time .DELTA.t has elapsed, the routine goes to point 203 where the flag
XSCVF is set (See FIG. 16(f)). As will be easily seen, the flag is adapted
to detect the leakage of air into the vacuum chamber 34 via the check
valve 40 for decreasing the pressure in the vacuum chamber 34 to a level
sufficient to open the SCV 17.
When the PM is decreasing, the routine flows from point 200 to point 204.
At point 204 it is judged whether the PM exceeds a predetermined level
PM2. If the result is "yes", the routine flows to point 205 where the flag
XSCVF is reset (0).
FIGS. 10 to 12 are routines for controlling other flags used in routines
for controlling the air-fuel ratio and ignition timing. In FIG. 10, at
point 210, it is judged whether the throttle fully open switch VL is ON.
When the degree of opening of the throttle valve 27 is larger than 50
degrees, the throttle fully open switch VL is made ON (FIG. 6). In this
case, the flag XVLCN is set to 1 at point 211. See FIG. 16 (h). A
predetermined pressure drop P' is attained after the switch VL is made
OFF. When the pressure drop P' is not yet attained, the flag XVLCN is
maintained at 1. When the pressure drop P' is attained, the routine goes
to point 213, where the flag XVLCN is reset (0).
In FIG. 11, at point 220, it is judged whether the lean switch LS is ON.
When the degree of opening TH of the throttle valve 27 is larger than 25
degrees, the lean switch LS is made ON as shown in FIG. 6. The program
then proceeds to point 221 to set the flag XLSCN. See FIG. 16 (g). When
the degree of opening of the throttle valve becomes smaller than 25
degrees, the switch LS is made OFF, and the program proceeds to point 222
where it is judged whether the absolute pressure PM is decreased for P as
shown in FIG. 16(b). When the absolute pressure PM is not decreased for P
after the lean switch LS is made OFF, the flag XLSCN is maintained at 1 at
point 221. When the pressure PM has attained the drop for P, the program
then proceeds to point 223 where the flag XLSCN is reset to 0 as shown in
FIG. 16(g).
FIG. 12 is a routine for controlling a feedback flag FB. At point 230 it is
judged whether the engine is in a condition in which the closed loop
feedback control of the air-fuel ratio is carried out. When the engine is
under the following conditions, the feedback control is stopped.
(1) when the engine is under acceleration
(2) when the engine is in an idling condition
(3) when the engine is warming up
(4) when the engine is under deceleration
(5) when the engine is starting
(6) when the lean sensor is not activated
When any one of the above mentioned conditions is realized, the engine does
not require the feedback control and the program then proceeds to point
232 to reset the feedback flag FB to 0. When any one of the
above-mentioned conditions is not realized, then the program proceeds to
point 231 where the feedback flag FB is set for allowing the feedback
control of the air-fuel ratio to proceed.
FIG. 13 illustrates a processing routine for calculating the pulse width
TAU of the injection signal. This routine is executed in a main routine
every time the crankshaft rotates by a predetermined angle, for example,
180 degrees. Referring to FIG. 11, at step 300, the basic pulse width TP
of the injection signal is obtained from the engine speed NE and the
absolute pressure PM. Data indicating the relationship among the basic
pulse width TP, the engine speed NE, and the absolute pressure PM is
stored in the ROM 53 in the form of a data table. Thus, at step 300, the
basic pulse width TP is obtained from the data stored in the ROM 53. Then,
at step 301, the actual pulse width TAU of the injection signal is
calculated from the following equation by using the basic pulse width TP,
the air-fuel ratio feedback correction coefficient FAF, the lean
correction coefficient KLEAN, and other correction coefficients .alpha.
and .beta..
TAU=TP.multidot.FAF.multidot.KLEAN .alpha.+.alpha.
FAF is a correction coefficient used for carrying out the closed loop
control of the air-fuel ratio. FAF is calculated in the processing routine
illustrated in FIG. 15. When open loop control of the air-fuel ratio is
carried out, FAF is maintained at 1.0.
KLEAN is a correction coefficient used for changing the desired air-fuel
ratio to an air-fuel ratio which is on the lean side of the stoichiometric
air-fuel ratio. KLEAN is calculated in the processing routine illustrated
in FIG. 14. When the desired air-fuel ratio is the stoichiometric air-fuel
ratio, KLEAN is maintained at 1.0.
At step 302, the actual pulse width TAU is stored in the RAM 52. In the
main routine processed by sequential interruptions executed every
predetermined crank angle, the injection start time and the injection stop
time are obtained from the actual pulse width TAU, and the injection
signal is output to the I/O port 54 between the injection start time and
the injection stop time. As a result, fuel is injected from the fuel
injector 24.
FIG. 14 illustrates a processing routine for calculating the lean
correction coefficient KLEAN and the feedback correction coefficient FAF.
This routine is executed when the processing routine illustrated in FIG.
14 is carried out in the main routine. Referring to FIG. 14, initially, at
point 398, it is determined whether the fully open switch VL of the
throttle sensor 28 is made ON. At the following point 399, it is judged
whether the flag XSCVF is 1, and at point 400 it is judged whether flag
XVLCN is 1. When the VL switch is made ON, the flag XSCVF is 1, or the
flag XVLCN is 1, then the routine flows to point 401 where 1.0 is moved to
KLEAN. This means that the air-fuel ratio is maintained at the
stoichiometric ratio. At point 402, 1.0 is moved to FAF. This means that
the closed loop feedback control of the air-fuel ratio is not carried out.
When the throttle fully open switch VL is OFF and the flags XSCVF and XVLCN
are equal to 0, the swirl control valve 17 is closed or ready to be
closed, and the routine flows to point 404 where KLEAN is obtained from
the engine speed NE and the absolute pressure PM. That is, data indicating
the relationship between KLEANNE and the engine speed NE as illustrated in
FIG. 17 is stored in the ROM 53, and data indicating the relationship
between KLEANPM and the absolute pressure PM as illustrated in FIG. 18 is
stored in the ROM 53. At this step 404, KLEANNE is multiplied by KLEANPM,
and thus KLEAN (=KLEANNE.multidot.KLEANPM) | | |
