 |
Description  |
|
|
BACKGROUND OF THE INVENTION
This invention relates to a method of controlling the operating amount of
an operation control means for an internal combustion engine, and more
particularly to a method of this kind which is adapted to correct a
desired or target value of the operating amount of such operation control
means in a simple and inexpensive manner responsive to the temperature of
intake air being supplied to the engine for improvement of the
driveability of the engine over all operating regions of the engine
inclusive of low load operating regions such as an idling region.
A method has been proposed, e.g. by Japanese Provisional Patent
Publications (Kokai) Nos. 58-88436 and 53-8434, which determines a basic
operating amount of operation control means for controlling the operation
of the engine, such as a basic fuel injection amount to be supplied to the
engine by a fuel supply quantity control system, a basic value of spark
ignition timing to be controlled by an ignition timing control system, and
a basic recirculation amount of exhaust gases to be controlled by an
exhaust gas recirculation control system, in dependence on values of
engine operating parameters indicative of loaded conditions of the engine,
such as absolute pressure in the intake pipe of the engine and engine
rotational speed, and corrects the basic operating amount thus determined
in response to the temperature of intake air being supplied to the engine,
to thereby set a desired operating amount for the operation control means
with accuracy.
However, while the engine is operating in a low load condition such as at
idle, the intake pipe absolute pressure has a reduced rate of change
relative to the lapse of time with respect to a rate of change in the
engine rotational speed relative to the lapse of time. Therefore,
according to the above proposed method of determining operating amounts of
the operation control means in dependence on the intake pipe absolute
pressure and the engine rotational speed (generally called "the speed
density method", and hereinafter merely referred to as "the SD method"),
it is difficult to set with accuracy an operating amount such as a fuel
supply quantity in accordance with the state of condition of the engine,
thus causing hunting of the engine rotation, during operation of the
engine in such a low load condition. In view of the foregoing, a method
(hereinafter merely called "the KMe method") has been proposed, e.g. by
Japanese Patent Publication No. 52-6414, which is based upon the
recognition that the quantity of intake air passing the throttle valve is
not dependent upon either of pressure PBA in the intake pipe downstream of
the throttle valve and pressure of the exhaust gases while the engine is
operating in a particular low load condition wherein the ratio PBA/PA' of
intake pipe pressure PBA downstream of the throttle valve to intake pipe
pressure PA' upstream of the throttle valve is below a critical pressure
ratio (=0.528) at which the intake air forms a sonic flow, and accordingly
the quantity of intake air can be determined solely in dependence on the
valve opening of the throttle valve, if the intake pipe pressure PA'
upstream of the throttle valve remains constant. Therefore, this proposed
method detects the valve opening of the throttle valve alone to thereby
detect the quantity of intake air with accuracy while the engine is
operating in the above-mentioned particular low load condition, and then
sets an operating amount such as a fuel injection quantity on the basis of
the detected value of the intake air quantity.
Also a value of an operating amount determined by the above KMe method
requires correction responsive to a change in the intake air temperature
in a manner proper to the KMe method different from a manner of correction
applied to the SD method. That is, while according to the SD method the
detection of the intake air temperature should desirably be made at a
location as close to the intake valve as possible, such detection
according to the KMe method has to be made at a location immediately
upstream of the throttle valve, because the flow rate of intake air in
gravity or weight intrinsically varies in response to a change in the
temperature of intake air immediately upstream of the throttle valve.
However, if both the SD method and the KMe method are employed for
correcting an operating amount in response to the intake air temperature
in a selective manner dependent upon loaded conditions of the engine, to
provide two separate intake air temperature sensors for respective
exclusive use for these methods will render the control system complicate
in structure and result in an increased manufacturing cost.
SUMMARY OF THE INVENTION
It is the object of the invention to provide a method of controlling the
operating amount of an operation control means for controlling an internal
combustion engine, which employs both of the SD method and the KMe method
for determining the operating amount, and is capable of correcting the
values of operating amounts determined by these methods in response to the
intake air temperature, in respective appropriate manners to these
methods, so as to set the operating amount with accuracy throughout the
whole operating region of the engine inclusive of low load conditions of
the engine such as an idling condition, thereby contributing to
improvement of the driveability of the engine.
The present invention provides a method of controlling an operating amount
of an operation control means for controlling the operation of an internal
combustion engine. The operating amount of the operation control means is
controlled in a first arithmetic manner to a first desired value
determined on the basis of a first operating operating parameter of the
engine when the engine is operating in a predetermined operating
condition, while it is controlled in a second arithmetic manner to a
second desired value determined on the basis of a second operating
parameter of the engine when the engine is operating in a condition other
than the above predetermined operating condition.
The method according to the invention is characterized by comprising the
following steps:
(1) detecting the temperature of intake air being supplied to the engine;
(2) when the engine is operating in the above predetermined operating
condition, determining a first correction value appropriate to the first
arithmetic manner, as a function of the detected value of the intake air
temperature, correcting the first desired value of operating amount by the
use of the determined first correction value, and controlling the
operating amount of the operation control means to the corrected first
desired value; and
(3) when the engine is operating in a condition other than the above
predetermined operating condition, determining a second correction value
appropriate to the second arithmetic manner, as a function of the detected
value of the intake air temperature, correcting the second desired value
of operating amount by the use of the determined second correction value,
and controlling the operating amount of the operation control means to the
corrected second desired value.
Preferably, the engine has an intake passage, and an intake air quantity
control means arranged in the intake passage for adjusting the opening
area of the intake passage, and wherein the first operating parameter of
the engine is the opening area of the intake passage which is adjusted by
the intake air quantity control means, while the second operating
parameter of the engine is pressure in the intake passage at a location
downstream of the intake air quantity control means.
Further, preferably, the first correction value is set to a value as a
function of the temperature of intake air upstream of the intake air
quantity control means, whereas the second correction value is set to a
value as a function of the temperature of intake air downstream of the
intake air quantity control means. Preferably, the detection of intake air
temperature in the step (1) is effected at one of an upstream side of the
intake air quantity control means and a downstream side thereof.
Preferably, the aforesaid predetermined operating condition of the engine
is a low load condition of the engine. Also preferably, the aforesaid
operation control means is a fuel supply quantity control means, wherein
the aforesaid operating amount is a quantity of fuel being supplied to the
engine by the fuel supply quantity control means.
The above and other objects, features, and advantages of the invention will
be more apparent from the ensuing detailed description taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of the whole arrangement of a fuel injection
control system for an internal combustion engine, to which is applied the
method according to the present invention;
FIG. 2 is a block diagram of the interior construction of an electronic
control unit (ECU) appearing in FIG. 1;
FIG. 3 is a flowchart showing a manner of calculating the valve opening
period TOUT for the fuel injection valves;
FIG. 4 is a flowchart showing a manner of determining whether or not the
engine is operating in a predetermined operating condition; and
FIG. 5 is a flowchart showing a manner of calculating an intake air
temperature-dependent correction coefficient KTA.
DETAILED DESCRIPTION
The invention will now be described in detail with reference to the
drawings showing an embodiment thereof.
As an example for correcting in dependence on intake air temperature an
operating amount of an operation control means for an internal combustion
engine, e.g. the fuel supply quantity, which is determined by the SD
method, a method has been disclosed in U.S. Pat. No. 4,465,051, which
multiplies a basic fuel injection period Ti determined as a function of
intake passage absolute pressure and engine rotational speed by the
following correction coefficient KTA1:
##EQU1##
where TA represents the temperature (.degree.C.) of intake air flowing in
the intake pipe, and TA0 a calibration variable, which is set e.g. at
50.degree. C., respectively. CTAMAP represents a calibration coefficient
having its value set at a constant value (e.g. 1.26.times.10.sup.-3) in
dependence upon the operating characteristics of the engine. In the above
equation, since the value of CTAMAP(TA-TA0) is smaller than 1, the
coefficient KTA1 can be approximately determined by the following
equation:
KTA1=1-CTAMAP(TA-TA0) (1)
When the ratio (PBA/PA') of intake pipe pressure PBA downstream of the
throttling portion such as a throttle valve to intake pipe pressure PA'
upstream of the throttling portion is smaller than the critical pressure
ratio (=0.528), intake air passing the throttling portion forms a sonic
flow. The flow rate Ga(g/sec) of intake air can be expressed as follows:
##EQU2##
where A represents the equivalent opening area (mm.sup.2) of the
throttling portion such as the throttle valve, C a correction coefficient
having its value determined by the configuration, etc. of the throttling
portion, PA atmospheric pressure (PA=PA', mmHg), .kappa. the ratio of
specific heat of air, R the gas constant of air, TAF the temperature
(.degree.C.) of intake air immediately upstream of the throttling portion,
and g the gravitational acceleration (m/sec.sup.2), respectively.
In the aforementioned equation, the ratio of the flow rate Ga0 of intake
air assumed when the temperature of air upstream of the throttling portion
is equal to a reference temperature TAF0, to the flow rate Ga of intake
air at a given temperature TAF can be given by the following equation:
##EQU3##
If the quantity of fuel being supplied to the engine is varied at a rate
equal to the above ratio of flow rate of intake air, the resulting
air/fuel ratio is maintained at a constant value. Therefore, the flow rate
Gf of fuel can be determined from the flow rate Gf0 of same at the
reference temperature TAF0, as expressed by the following equation:
##EQU4##
Here, the intake air temperature-dependent correction coefficient KTA2
value can be expressed as follows:
##EQU5##
Therefore, the correction coefficient KTA2 value can be approximated by the
following equation:
##EQU6##
Thus, the above correction coefficient KTA2 value is determined as a
function of the temperature TAF of intake air upstream of the throttling
portion. It has been experimentally ascertained that the functional
relationship between the intake air temperature TAF upstream of the
throttling portion and the intake air temperature TA downstream of same is
approximated by the following equation, when the engine is in an idling
condition:
TAF=a.times.TA+b (4)
where a and b represent constants. Taking the relationship of
TAF0=a.times.TA0+b into consideration, the equation (3) can be expressed
as follows, by substituting the equation (4) into the equation (3):
##EQU7##
Therefore, by multiplying a value of the fuel flow rate determined by the
KMe method at the reference intake air temperature by a value of the
correction coefficient KTA2 determined by the equation (5), it is possible
to obtain a proper value of the fuel flow rate required to be supplied to
the engine at the actual intake air temperature TA.
FIG. 1 schematically illustrates the whole arrangement of a fuel injection
control system for internal combustion engines, to which is applied the
method according to the invention. In the figure, reference numeral 1
designates an internal combustion engine which may be a four-cylinder
type. Connected to the engine 1 are an intake pipe 3 with its air intake
end provided with an air cleaner 2 and an exhaust pipe 4. Arranged in the
intake pipe 3 is a throttle valve 9, and an air passage 8 opens at one end
8a into the intake pipe 3 at a downstream side of the throttle valve 9 and
communicates with the atmosphere through the other end. The air passage 8
has an air cleaner 7 provided at the other end opening in the atmosphere.
Arranged across the air passage 8 is a supplementary air quantity control
valve (hereinafter merely called "the control valve") 6 which is a
normally closed type electromagnetic valve comprising a solenoid 6a and a
valve body 6b disposed to open the air passage 8 when the solenoid 6a is
energized, the solenoid 6a being electrically connected to an electronic
control unit (hereinafter abbreviated as "the ECU") 5.
Fuel injection valves 10 are projected into the intake pipe 3 at a location
between the engine 1 and the open end 8a of the air passage 8, and
connected to a fuel pump, not shown, and also electrically connected to
the ECU 5.
A throttle valve opening (.theta.TH) sensor 17 is connected to the throttle
valve 9, while an intake air temperature (TA) sensor 11 and an intake pipe
absolute pressure (PBA) sensor 12 are mounted in the intake pipe 3 at
locations downstream of the open end 8a of the air passage 8. Further, the
main body of the engine 1 is provided with an engine cooling water
temperature (TW) sensor 13 and an engine rotational speed (Ne) sensor 14.
These sensors are electrically connected to the ECU 5. Reference numeral
15 represents electrical devices such as headlights, a brake lamp, an
electric motor for driving a radiator cooling fan. One terminal of each of
these electrical devices 15 is electrically connected to the ECU 5 by way
of a switch 16, while another terminal thereof is electrically connected
to a battery 19. Reference numeral 18 designates a sensor for sensing
another engine operating parameter, for instance, an atmospheric pressure
sensor, also electrically connected to the ECU 5.
The operation of the fuel injection control system constructed as above
will now be described.
The ECU 5 is supplied with signals indicative of operating parameter values
of the engine from the throttle valve opening sensor 17, the intake air
temperature sensor 11, the intake pipe absolute pressure sensor 12, the
engine cooling water temperature sensor 13, the engine rotational speed
sensor 14, and the another engine parameter sensor 18. The ECU 5 operates
on these engine operating parameter signals and signals indicative of
electrical loads from the electrical devices 15 to determine whether or
not the engine is operating in an operating condition requiring the supply
of supplementary air to the engine, and set a desired idling speed value.
When the engine is determined to be operating in such supplementary
air-supplying condition, the ECU 5 determines the quantity of
supplementary air to be supplied to the engine in response to the
difference between the set desired idling speed value and the actual
engine rotational speed, so as to make the same difference zero, and
thereby calculates a value of the valve opening duty DOUT ratio for the
control valve 6 to drive the same valve with the calculated duty ratio.
The solenoid 6a of the control valve 6 is energized for a valve opening
period of time corresponding to the calculated valve opening duty ratio
DOUT to open the valve body 6b to open the air passage 8 so that a
required quantity of air determined by the valve opening period of the
valve 6 is supplied to the engine 1 through the air passage 8 and the
intake pipe 3.
If the valve opening period for the control valve 6 is set to a larger
value so as to increase the supplementary air quantity, an increased
quantity of the mixture is supplied to the engine 1 to thereby increase
its output so that the engine rotational speed increases. On the contrary,
if the valve opening period is set to a smaller value, it results in a
reduced mixture quantity and accordingly a decrease in the engine
rotational speed. By controlling the supplemtary air quantity, that is,
the valve opening period for the control valve 6 in this manner, the
engine rotational speed can be maintained at the desired idling speed
value during idling operation of the engine.
On the other hand, the ECU 5 also operates on values of the aforementioned
various engine operating parameter signals and in synchronism with
generation of pulses of a TDC signal indicative of top-dead-center
positions of the engine cylinders, which may be supplied from the engine
rotational speed sensor 14, to calculate the fuel injection period TOUT
for the fuel injection valves 10 by the use of the following equation:
TOUT=Ti.times.K1+K2 (6)
where Ti represents a basic fuel injection period, which is determined
according to the aforementioned SD method or the KMe method, selected
depending upon whether or not the engine is operating in an operating
region wherein a predetermined idling condition is fulfilled, as
hereinafter described in detail.
In the above equation, K1 and K2 represent correction coefficients or
correction variables which are calculated on the basis of values of engine
operating parameter signals supplied from the aforementioned various
sensors such as the engine cooling water temperature (TW) sensor 13, the
throttle valve opening (.theta.TH) sensor 17, and the intake air
temperature (TA) sensor 11. For instance, the correction coefficient K1 is
calculated by the use of the following equation:
K1=KTA.times.KTW.times.KWOT (7)
where KTA represents an intake air temperature-dependent correction
coefficient, described in detail hereinafter, and KTW represents a
coefficient for increasing the fuel supply quantity, which has its value
determined in dependence on the engine cooling water temperature TW sensed
by the engine cooling water temperature (TW) sensor 13, and KWOT a
mixture-enriching coefficient applicable at wide-open-throttle operation
of the engine and having a constant value, respectively.
The ECU 5 supplies the fuel injection valves 10 with driving signals
corresponding to the fuel injection period TOUT calculated as above, to
open the same valves.
FIG. 2 shows a circuit configuration within the ECU 5 in FIG. 1. An output
signal from the engine speed (Ne) sensor 14 is applied to a waveform
shaper 501, wherein it has its pulse waveform shaped, and supplied to a
central processing unit (hereinafter called "the CPU") 503, as the TDC
signal, as well as to an Me value counter 502. The Me value counter 502
counts the interval of time between a preceding pulse of the TDC signal
and a present pulse of same, inputted thereto from the Ne sensor 14, and
therefore its counted value Me is proportional to the reciprocal of the
actual engine speed Ne. The Me value counter 502 supplies the counted
value Me to the CPU 503 via a data bus 510.
The respective output signals from the throttle valve opening (.theta.TH)
sensor 17, the intake pipe absolute pressure (PBA) sensor 12, the engine
cooling water temperature (TW) sensor 13, the intake air temperature (TA)
sensor 11, etc., appearing in FIG. 1 have their voltage levels shifted to
a predetermined voltage level by a level shifter unit 504 and successively
applied to an analog-to-digital converter 506 through a multiplexer 505.
The analog-to-digital converter 506 successively converts into digital
signals analog output voltages from the aforementioned various sensors,
and the resulting digital signals are supplied to the CPU 503 via the data
bus 510.
On-off state signals supplied from the switches 16 of the electrical
devices 15 in FIG. 1 are supplied to another level shifter unit 512
wherein the signals have their voltage levels shifted to a predetermined
voltage level, and the level shifted signals are processed by a data input
circuit 513 and applied to the CPU 503 through the data bus 510.
Further connected to the CPU 503 via the data bus 510 are a read-only
memory (hereinafter called "the ROM") 507, a random access memory
(hereinafter called "the RAM") 508 and driving circuits 509 and 511. The
RAM 508 temporarily stores various calculated values from the CPU 503,
while the ROM 507 stores a control program executed within the CPU 503,
etc.
The CPU 503 operates in accordance with the control program stored in the
ROM 507 to determine operating conditions of the engine on the basis of
the engine operating parameter signals, as well as electrically loaded
conditions of the engine on the basis of the on-off signals from the
electrical devices 15, to calculate the valve opening duty ratio DOUT for
the control valve 6 to a value corresponding to the determined loaded
condition of the engine.
The CPU 503 supplies the driving circuit 511 with a control signal
corresponding to the calculated valve opening duty ratio DOUT for the
control valve 6, and then the driving circuit 511 operates on the control
signal to apply a driving signal to the control valve 6 to drive same. The
CPU 503 also operates on the various engine operating parmeter signals to
calculate the valve opening period TOUT for the fuel injection valves 10,
and supplies the driving circuit 509 with a control signal corresponding
to the calculated valve opening period to cause same to apply driving
signals to the fuel injection valves 10 to drive same.
FIG. 3 shows a manner of calculating the valve opening period TOUT for the
fuel injection valves 10. First, in the step 1 of FIG. 3, it is determined
whether or not is fulfilled a condition for applying the KMe method to
calculation of the basic value Ti of the valve opening period 10
(hereinafter this condition will be called "the idle mode"). This
determination as to fulfillment of the idle mode may be made by
determining whether or not the engine is operating in a predetermined
operating region as shown in the flowchart of FIG. 4, for instance. That
is, in the step 1a of FIG. 4, it is determined whether or not the engine
rotational speed Ne is lower than a predetermined value NIDL (e.g. 1,000
rpm). If the answer is negative or no, the program jumps to step 1d
wherein a decision is rendered that the idle mode is not fulfilled. If the
answer to the question at step 1a, the program proceeds to step 1b wherein
it is determined whether or not the intake pipe absolute pressure PBA is
lower than a predetermined reference value PBAC. The reference value PBAC
is set at such a value as to determine whether or not the ratio of intake
pipe absolute pressure PBA downstream of the throttle valve 9 to intake
pipe absolute pressure PA' upstream of the throttle valve 9 is smaller
than the critical pressure ratio (=0.528) at which the flow of intake air
passing the throttle valve 9 forms a sonic flow. If the answer to the
question of step 1b is negative or no, the fulfilment of the idle mode is
negated at step 1d, while if the answer is affirmative, the program
proceeds to step 1c to make a determination as to whether or not the valve
opening .theta.TH of the throttle valve 9 is smaller than a predetermined
value .theta.IDLH. That is, at a transition in engine operation from an
idling condition with the throttle valve 9 in its substantially closed
position to an accelerating condition with the throttle valve 9 rapidly
opened, if this accelerating condition is detected solely from changes in
the engine rotational speed and the intake pipe absolute pressure, there
will occur a detection lag mainly due to the response lag of the absolute
pressure sensor 12. Therefore, the throttle valve opening .theta.TH is
employed to detect such accelerating condition. When such accelerating
condition is detected by the throttle valve opening sensor 17, the SD
method, hereinafter referred to, is applied to calculation of a proper
accelerating increased fuel quantity for supply to the engine. If the
answer to the question of step 1c is negative, it is decided that the idle
mode is not then fulfilled. If all the answers to the questions of steps
1a through 1c are found affirmative at the same time, the program proceeds
to step 1e to decide that the engine is operating in the idle mode.
Referring again to FIG. 3, if the determination at step 1 provides a
negative answer, the SD method is employed to determine the basic fuel
injection period value Ti at step 2. According to the SD method, a basic
fuel injection period value Ti is selected from among a plurality of
predetermined values stored in the ROM 507 within the ECU 5, which
corresponds to a combination of detected values of intake pipe absolute
pressure PBA and engine rotational speed Ne. The basic fuel injection
period value Ti thus determined is applied to the aforegiven equation (6)
together with the intake air temperature-dependent correction coefficient
KTA forming part of the correction coefficients K1, to calculate the final
fuel injection period TOUT, at step 4.
If the answer to the question of step 1 is affirmative, the program
proceeds to step 3 to employ the KMe method for calculation of the basic
fuel injection period Ti.
The basic fuel injection period Ti according to the KMe method is
determined by the following equation:
Ti=K(A).times.Me (8)
where K(A) represents the equivalent opening area of the throttling portion
in the intake passage, which is determined by the sum of the valve opening
areas of the throttle valve 9 and the control valve 6. The valve opening
areas of these valves 9, 6 may be obtained, respectively, from a value of
the output signal from the throttle valve opening sensor 17 and a value of
the valve opening duty ratio for the control valve 6 calculated by the CPU
503. In the equation (8), Me represents a time interval of generation of
pulses of the TDC signal which is measured by the Me counter 502 in FIG.
2. The reason why the basic fuel injection period Ti can be determined by
the use of the equation (8) above is as follows: The quantity of intake
air passing the throttling portion of the intake passage per unit time is
given solely as a function of the equivalent opening area of the
throttling portion provided that the atmospheric pressure PA and the
intake air temperature TAF remain constant, as endorsed by the equation
(2). Further, the quantity of intake air sucked into an engine cylinder
per suction stroke is proportional to the reciprocal of the engine rpm Ne,
and accordingly to the Me value.
The basic fuel injection period value Ti thus determined is applied to the
equation (6) to calculate the final fuel injection period TOUT, at step 4.
FIG. 5 shows a manner of calculating the intake air temperature-dependent
correction coefficient KTA as part of the correction coefficients K1,
appearing in the equation (7).
It is first determined in step 1 of FIG. 5 whether or not the engine is
operating in the idle mode, as in step 1 of FIG. 3. If the answer is
negative, the program proceeds to step 2 wherein the intake air
temperature-dependent correction coefficient KTA1 is calculated by the use
of the equation (1), to be applied to correction of the basic fuel
injection period Ti determined according to the SD method. The coefficient
KTA1 value thus determined is applied as the correction coefficient KTA to
the equations (7) and (6), at step 3. If the answer to the question of
step 1 is affirmative, the program proceeds to step 4 wherein the intake
air temperature-dependent correction coefficient KTA2 is calculated by the
use of the equation (5), to be applied to correction of the basic fuel
injection period Ti determined according to the KMe method. The
coefficient KTA2 value thus determined is applied as the correction
coefficient KTA to the equations (7) and (6), at step 5.
The method according to the invention is not limited to control of the fuel
supply quantity in a fuel supply control system for internal combustion
engines as in the foregoing embodiment, but it may be applied to control
of an operating amount of any operation control means for controlling the
operation of an internal combustion engine, insofar as the operating
amount is determined by the use of a parameter indicative of the intake
air quantity. For instance, the method according to the invention may be
applied to control of an operating amount of an ignition timing control
system, and an exhaust gas recirculation control system.
* * * * *
|
|
 |
|
 |
Description |
|
