Method of controlling fuel in an engine

A quantity of fuel supplied to an engine so as to allow the air-fuel ratio of a gas mixture to be a target air-fuel ratio is subjected to a feedback correction based on an air-fuel ratio sensor. At the time of the feedback correction, a learning correction is also conducted on the basis of a learning value that is calculated in accordance with a feedback correction value. When the learning value to be used for the learning correction is altered, the feedback correction value is initialized. An initialized feedback correction value is an addition of the feedback correction value before the alteration to a deviation of the respective learning values before and after the alteration of the learning values.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a fuel control apparatus for an engine 
and, more particularly, to a fuel control apparatus adapted to carry out a 
control by learning, in addition to a feedback control. 
2. Description of the Prior Art 
In an engine, particularly an internal combustion engine for vehicles, an 
air-fuel ratio is frequently controlled according to an output from an 
air-fuel ratio sensor such as an O.sub.2 sensor, that is, a fuel amount 
supplied to the engine is frequently controlled (or corrected) so that the 
air-fuel ratio of a mixture gas become a target value. 
This feedback control has a problem in the responsiveness of the control. 
Thus, control by learning or a learning control, in addition to the 
feedback control, has been recently proposed. In Japanese Patent 
Application Laid Open No. 59335/1983, the feedback correction is conducted 
using a feedback correction value that is obtained in accordance with an 
output from an O.sub.2 sensor for detecting the oxygen concentration 
(air-fuel ratio) in exhaust gas. A learning value is calculated according 
to the feedback correction value and the learning value is stored in 
memory means having, for example, a plurality of learning zones divided at 
every predetermined vehicle speed. At a certain vehicle speed while 
conducting a sort of prospect control by the learning correction in 
accordance with the learning value stored in the learning zone of the 
memory means, corresponding to the vehicle speed, the feedback control as 
described hereinabove is carried out. Accordingly, an amount of correction 
by the feedback control (feedback correction value) can be reduced by the 
amount of the prospect control with the learning value, thus leading to a 
higher responsiveness of the control. 
In particular, according as an increase in the number of learnings as the 
same driving state is continued for a long period of time, the amount of 
correction by the feedback correction can be extremely reduced. Also such 
a learning control may absorb the individual difference of engines, in 
particular, the individual difference of fuel injection valves, which 
affects the setting of supplying the fuel amount to a great extent or the 
individual difference of sensors for detecting the amount of intake air. 
However, in the conventional learning control, a problem arises in the 
control response in instances where a learning value used for the learning 
correction is altered, leading to a lack in the control accuracy of an 
air-fuel ratio. More specifically, if the memory means for storing the 
learning value has a plurality of learning zones divided at every 
predetermined vehicle speed as described hereinabove, it is common that 
the learning values stored in two learning zones are different when one 
learning zone is altered to the other learning zone. Accordingly, if the 
learning value altered is used immediately after the alteration of the 
learning zone the control is caused to deviate because the feedback 
correction value is set on the basis of the learning value before 
alteration. Accordingly when the learning value to be used for the 
learning correction is altered, the feedback correction value was 
heretofore set to a value that is not attributable to any learning value, 
i.e., initialized to "zero". With such an intialization of the feedback 
correction value, it requires a considerable amount of time until the 
air-fuel ratio is stabilized to the target air-fuel ratio after the 
learning zone is changed. 
The delay of the control caused by the alteration of the learning value as 
described above occurs not only in the case of altering the learning zone 
but in the case of renewing the learning value, i.e., in the case of 
updating to the optimum learning value. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a fuel 
control apparatus for an engine wherein, in instances where a fuel amount 
supplied to the engine is subjected to a feedback control according to an 
air-fuel ratio sensor and and a learning correction is achieved by using a 
learning value calculated on the basis of the feedback correction value, 
the control responsiveness is enhanced when the learning value used for 
the learning correction is altered. 
It is another object of the present invention to provide a fuel control 
apparatus for an engine wherein, in instances where the feedback 
correction and the learning correction are carried out in the same manner 
as the above object, the responsiveness of the control is enhanced during 
a course of the shift of learning zones, where memory means for storing 
the learning value is divided into a plurality of learning zones in 
response to the driving states of the engine. 
It is a further object of the present invention to provide a fuel control 
apparatus for an engine wherein, in instances where the feedback 
correction and the learning correction are carried out in the same manner 
as the above first object, the responsiveness of the control at the time 
of updating the learning value is enhanced where the learning value stored 
in the memory means is updated. 
It is still further object of the present invention to provide a fuel 
control apparatus for an engine wherein, in instances, where the feedback 
correction and the learning correction are carried out in the same manner 
as the above first object, the responsiveness of the control is enhanced 
at the times of both shifting the learning zone and updating the learning 
value in the identical learning zone, where the learning value stored in 
the memory is divided into a plurality of learning zones or areas in 
response to the driving state of the engine and the learning value stored 
in the learning zone is updated. 
It is still another object of the present invention to provide a fuel 
control apparatus for an engine wherein, in instances where the feedback 
correction and the learning correction are achieved in the same manner as 
the first object, the air-fuel ratio can be more precisely controlled. 
For achieving the above first object, a first aspect of the present 
invention provides a fuel control apparatus for an engine which is 
fundamentally constituted as claimed in claim 1. With such an arrangement, 
when the learning value to be used for the learning correction is altered, 
the learning value after the alteration is effectively used as it is to 
set the feedback correction value immediately after the alteration as the 
optimum value corresponding to the learning value after the alteration, 
thereby enhancing the responsiveness of the control. 
The above second to fourth objects according to the present invention are 
achieved by considering the times of both shifting the learning zone and 
updating the learning value to be the time of altering the learning value 
as claimed in claim 1. 
The above fifth object according to the present invention is achieved by 
reducing the feedback correction value obtainable on the basis of an 
air-fuel ratio sensor as the number of alterations, that is, the number of 
learnings increases, with the prerequisite that the learning value is 
altered. More particularly, the feedback correction value is calculated as 
the value based on a deviation between an output signal from an air-fuel 
ratio sensor and a reference signal corresponding to a target air-fuel 
ratio. If the deviation is the same as the number of alterations 
increases, the calculated feedback correction value is decreased. With 
this arrangement, variations in the air-fuel ratio near the target 
air-fuel ratio is extremely reduced. In other words, the convergent width 
converged to the target air-fuel ratio is reduced so that the air-fuel 
ratio is more precisely controlled. 
An air-fuel ratio sensor used in the present invention may include an 
O.sub.2 sensor which operates in ON or OFF at a stoichiometric air-fuel 
ratio as a boundary if the feedback control is conducted in the 
stoichiometric air-fuel ratio. If the feedback control is carried out in a 
wide range of air-fuel ratios, for example, in a stoichiometric air-fuel 
ratio or in an air-fuel ratio representing a gas mixture leaner than the 
stoichiometric air-fuel ratio, a so-called lean sensor which may supply a 
signal substantially proportional to the air-fuel ratio may be used as an 
air-fuel ratio sensor. As fuel supply means for supplying fuel to the 
engine may be used a so-called feedback type carburetor, but it is 
preferable to use a fuel injection value capable of more accurately 
regulating a quantity of the supply fuel. In this case, the fuel injection 
amount from the fuel injection valve may be regulated by controlling a 
pulse width of its drive pulse (e.g., a duty control). 
In instances where memory means for storing the learning values is used in 
which a plurality of learning zones are divided in response to the driving 
states of the engine, parameters for the driving state of the engine may 
contain the most fundamental engine load and the engine speed or number of 
engine revolutions. As the setting or altering of the target air-fuel 
ratio, a warming-up correction or acceleration correction may be 
frequently employed, these factors may be included. In addition, suitable 
factors such as vehicle speed may be employed as parameters in the driving 
state of the engine. 
The learning value is calculated according to a plurality of feedback 
correction values different from each other at calculating timings. In 
this case, it is preferable to set a new feedback correction value so as 
to be given more weight than old feedback correction values. When a 
learning value is calculated in accordance with a plurality of feedback 
correction values at different calculating timings, the learning values 
can be calculated at the stage that the predetermined number of correction 
values is stored while all feedback correction values sampled are stored. 
When the number of stored feedback correction values increases, a memory 
capacity is rendered extremely large. To this end, a temporary learning 
value according to one feedback correction value is calculated with 
reference to the calculation formula of a preset learning value and 
stored, and the stored temporary learning value is corrected (added) in 
accordance with a feedback correction value sampled thereafter. By making 
this arrangement, it is enough to store only one temporary learning value 
even if the number of feedback correction values increases. 
The above and other objects, features and advantages of the present 
invention will be apparent from the description of preferred embodiments 
which will be hereinafter described in detail with reference to the 
accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described in more detail by way of a 
preferred embodiment with reference to the accompanying drawings. 
FIG. 1 illustrates one embodiment according to the present invention. 
Referring first to FIG. 1, an engine body 1 of 4-cycle reciprocating type 
is provided with a piston 2 telescoped therein to form a combustion 
chamber 4. An intake port 6 and an exhaust port 8 are perforated in the 
combustion chamber 4, an intake valve 10 is disposed in the intake port 6. 
and an exhaust valve 12 is disposed in the exhaust port 8. 
The piston 2 is connected through a connecting rod 14 to an output shaft 
16. As the piston 2 reciprocates, the output shaft 16 is rotatably driven, 
and the intake valve 10 and the exhaust valve 12 are opened and closed at 
the known timing in synchronization with the rotation of the output shaft 
16. 
An intake air passage 18 connecting to the intake port 6 is disposed from 
the upstream side to the downstream sequentially with an air cleaner 20, 
an intake air temperature sensor 21 for detecting an intake gas 
temperature, an air flowmeter 22 for measuring a quantity of the intake 
air, a throttle valve 24 for controlling a quantity of the intake air, and 
a fuel injection valve 26 for supplying fuel into the intake air passage 
18. An exhaust gas passage 28 connecting to the exhaust port 8 is disposed 
with an O.sub.2 sensor 30 as well as a catalyzer and a silencer, omitted 
in the drawing. An ignition plug 31 is also provided. 
Intake air purified by the air cleaner 20 is mixed with fuel injected from 
the fuel injection valve 26, and the resulting gas mixture is filled in 
the combustion chamber 4. Combustion gas in the combustion chamber 4 is 
exhausted through the exhaust gas passage 28. The fuel injected from the 
fuel injection valve 26 is vaporized and atomized with assist air from an 
assist air passage 27. 
The fuel injection valve 26 is connected to a fuel tank 34 through a fuel 
supply conduit 32 that in turn is arranged with a fuel pump 36 and a fuel 
filter 38. When the pump 36 is driven, fuel in the fuel tank 34 is fed 
under pressure to the fuel injection valve 26, and excessive fuel is 
returned to the fuel tank 34 through a return conduit 40. A fuel pressure 
regulator 42 is disposed in the return conduit 40, thereby supplying fuel 
having a predetermined pressure difference from the internal pressure of 
the intake air passage 18 to the fuel injection valve 26. The quantity of 
fuel injection from the fuel injection valve 26 is regulated by 
controlling the valve open time of the fuel injection valve 26 by means of 
a pulse width of a drive output signal from a control unit 44 (in a duty 
control). 
The control unit 44 is supplied with a feedback signal from the O.sub.2 
sensor 30, an intake air temperature signal from the intake air 
temperature sensor 21, an intake air amount signal from the air flowmeter 
22, an engine speed signal from an engine speed sensor 46 and a voltage 
signal from a battery 48. The control unit 44 controls the air-fuel (A/F), 
that is, the quantity of fuel injection to be injected from the fuel 
injection valve 26, on the basis of each of the signals supplied. 
The control unit 44 is comprised of a digital or analog computer and more 
particularly a microcomputer. The control unit 44 comprises conventional 
parts such as a CPU, an ROM, an RAM, a CLOCK and an input/output 
interfaces. Further, the control unit 44 is also provided with A/D 
converters in response to the output signals of the respective sensors and 
drive circuit for the fuel injection valve 26. Since the above-mentioned 
arrangement utilizing the microcomputer is heretofore known in general, 
the detailed description will be omitted. 
The control by the control unit 44 will be generally described. The 
operating state of an engine is divided, for example, as shown in FIG. 5, 
into an idle range, a deceleration range, a feedback range and a high load 
range in accordance with the engine speed and the load. The control unit 
44 controls the air-fuel ratio in response to the respective range of the 
operating state of the engine. A broken line in FIG. 5 is a no-load line. 
More specifically, a basic fuel injection amount (a basic fuel injection 
time .tau.EI; corresponding to a stoichiometric air-fuel ratio (=14.7) and 
an oxygen excessive rate .lambda.=1) is determined in accordance with the 
intake air amount and the engine speed. A final fuel injection amount 
(fuel injection time T) is calculated by making various corrections on the 
basic fuel injection amount, and a drive pulse signal having a pulse width 
corresponding to this injection amount is supplied to the fuel injection 
valve 26. The air-fuel ratios in the respective ranges in FIG. 5 is, for 
example, "14.7" in the feedback range, "15" in the idle range, "13" in the 
high load range, and the fuel is cut (by half or in full) in the 
deceleration range. An open loop control (prospect control) is conducted 
in the ranges other than the feedback range. 
A summary of the control in the feedback range will be described 
hereinbelow. In the feedback range, a feedback correction according to the 
feedback signal from the O.sub.2 sensor 30 and a learning correction are 
conducted in the basic fuel injection amount (basic fuel injection time 
.tau.EI). In other words, a plurality of learning zones finely divided 
according to the engine speed and the basic fuel injection time .tau.EI 
corresponding to the engine load are set in the feedback range, and the 
learning values calculated in accordance with the feedback correction 
value is stored in the respective learning zones of the memory (FIG. 6). 
The feedback correction value is determined in accordance with a 
predetermined control gain value (P.I value), and the control gain value 
(P.I value) and the learning value are altered at every number of 
learnings. 
The fuel injection amount (fuel injection time T) in the feedback range is 
calculated according to the following equation: 
EQU T=.tau.EI.times.C.sub.AIR .times.(1+C.sub.FB +C.sub.LC)+.tau.BAT (1) 
where .tau.EI: basic fuel injection time 
C.sub.AIR : Intake air temperature correction value 
C.sub.FB : Feedback correction value 
C.sub.LC : Learning correction value 
.tau.BAT: Reactive injection time (Battery voltage correction) 
The control gain value (P.I) in the feedback correction value (C.sub.FB) is 
altered according to the following equations: 
EQU C.sub.FB =F (P.I) 
EQU P=K.times.P.sub.0 
EQU I=K.times.I.sub.0 
where P.sub.0 : skip width initial value 
I.sub.0 : Integrating rate initial value 
K: Coefficient 
The coefficient K is set smaller, as shown in FIG. 4, as the number of 
learnings (the number of alterations) C.sub.LC increases. From this, the 
control gain value (P.I value) is set a small value as the number of 
learnings C.sub.LC advances 
The learning value C.sub.LC is altered in every number of learnings 
according to the following equation from the maximum value C.sub.FB MAX 
and the minimum value C.sub.FB MIN of the feedback correction value 
C.sub.FB sampled at every zone n=1, n=2, . . . (for example, at every zone 
of 8 msec.) as shown in FIG. 3 at every learning time according to the 
following equation. In the following equation, "j" means the sequential 
number of alterations of the learning value, and "i" means the value 
reduced in the sampling number as the value of "i" is smaller. 
##EQU1## 
When the learning value is altered according to the above, the feedback 
correction value CFB is also altered or initialized on the basis of the 
following equation: 
##EQU2## 
From the above equation, as the number of learnings C.sub.LC advances, the 
learning value C.sub.LC is sequentially optimized, and the responsiveness 
of the feedback control is gradually improved. When the learning value is 
altered, for example, in the learning zone .alpha. of FIG. 6 the deviation 
.DELTA.x of the learning value before and after the alteration is 
calculated from the equation (2), 
##EQU3## 
The .DELTA.x is an correction amount of the feedback correction value when 
the learning value is altered. The relationship between each of the 
learning values C.sub.LCj, C.sub.LCj+1, C.sub.FBj and C.sub.FB j+1 and the 
.DELTA.x before and after the learning value is altered as shown in FIG. 
7. As readily understood from FIG. 7, the feedback correction value 
C.sub.FBj+1 is optimized in response to the alteration of the learning 
value immediately after the learning value is altered, leading to 
improvements in the responsiveness of the control, and, as a result, in 
accuracy in the control of the resultant air-fuel ratio. 
When one learning zone is shifted to other learning zone, e.g., when the 
learning zone .beta. is shifted to the learning zone .gamma. as in FIG. 6, 
the initial value C.sub.FB0 of the feedback correction is initialized 
according to the following equation: 
EQU C.sub.FB0 =C.sub.FBk+1 +(C.sub.LCk+1 -C.sub.LCk+2) (4) 
where 
C.sub.FBk+1 : the feedback correction value immediately before the learning 
zone is shifted 
C.sub.LCk+1 : the learning value before the shift (e.g., stored value of 
the learning zone .beta.) 
C.sub.LCk+2 : the learning value after the shift (e.g., stored value of the 
learning zone .gamma.) 
The deviation .DELTA.y of the learning value before and after the shift of 
the learning zone is as evident from the above equation (4) 
EQU .DELTA.y=C.sub.LCk+1 -C.sub.LCk+2 
The initial value C.sub.FB0 of the feedback correction value initialized 
immediately after the learning zone is shifted is a value corrected by the 
amount .DELTA.y from the feedback correction value C.sub.FBk+1 before the 
shifting (FIG. 8). 
The control by the control unit 44 as described hereinabove will be further 
described with reference to flowcharts in FIG. 9 and FIG. 10. In FIG. 9, 
the sampling of the feedback correction value C.sub.FB is conducted by 
means of an interrupt. The countup of the number of learnings C.sub.LC is 
executed in every alteration of the learning value with the prerequisite 
that the learning value is in the identical learning zone. 
In step P1, signals from each of the sensors 21, 22 and 46 except the 
O.sub.2 sensor 30 and the battery voltage are read out. In step P2, the 
intake air temperature correction coefficient CAIR is calculated in 
accordance with the intake air temperature, and the voltage correction 
value (reactive injection time) .tau.BAT is calculated according to the 
battery voltage. In step P3, the basic fuel injection amount (time) 
.tau.EI is calculated in accordance with the intake air amount and the 
engine speed. And the zone correction coefficient K is set to 1. The basic 
fuel injection amount .tau.EI here corresponds to the stoichiometric 
air-fuel ratio (.lambda.=1). 
In step P4, it is decided whether the current engine operating state 
satisfies a feedback condition or not. This decision is fundamentally 
conducted by referring to the map in FIG. 5. In fact, the conditions that 
the o.sub.2 sensor is active (a predetermined temperature or higher) are 
additionally considered. If the feedback conditions are not satisfied in 
the decision of step P4, the control flow is shifted to step P5. In step 
P5, the zone correction coefficient K is set to become the air-fuel ratio 
(FIG. 5) corresponding to the current operating state of the engine. Then, 
the feedback correction value C.sub.FB is set to "0" because the feedback 
correction is not executed at this time, and the 
learning correction value C.sub.LC is set to "0" because the learning 
correction is not conducted as well. 
After step P6, the control flow is shifted to step P7, and the final fuel 
injection time T is calculated according to the equation indicated in step 
P7 (where the C.sub.FB and the C.sub.LC are both "0"). Then, in step P8, 
when a predetermined fuel injection time is obtained, the final fuel 
injection time T calculated in step P7 is output in step P9 (fuel 
injection). 
When the feedback conditions are decided to be satisfied in step P4, the 
control flow is shifted to step P10, and the air-fuel ratio from the 
O.sub.2 sensor 30 is read out. In step P11, the feedback correction value 
C.sub.FB is calculated according to the signal from the O.sub.2 sensor 30 
as already described above. 
After the step P11, it is decided, in step P12, whether the conditions for 
executing the learning correction is satisfied or not. This decision is 
made by observing whether a predetermined time, more specifically, 2 
seconds, is elapsed or not from the start of the feedback correction when 
the number of samplings of the feedback correction value C.sub.FB that 
become the bases of calculating the learning value becomes a predetermined 
value or larger. In step P12, if it is decided that the conditions of the 
learning correction are not satisfied, the learning correction value 
C.sub.LC is set to "0" in step P13. Then, the processes after step P7 are 
conducted. 
If the conditions of the learning correction is decided to be satisfied in 
step P12, the control flow is shifted to step P14, and the current 
learning zone is decided. Then, in step P15, it is decided whether the 
current learning zone is the same as the previous learning zone or not. If 
it is decided, in step P15, that the current learning zone is the same as 
the previous learning zone, it is decided in step P16, whether the 
learning zone is altered or not. This decision is made by observing 
whether 2 seconds are elapsed or not from the previous learning 
alteration. In step P16, when it is decided that the learning value is not 
altered, the learning correction value C.sub.LC is set, in step P17, to 
the learning value C.sub.LC1 stored in the corresponding learning zone by 
referring to the map in FIG. 6. Then, the processes after step P7 are 
conducted. 
If it is decided, in step P16, that the learning value is altered, the 
control flow is shifted to step P18, and the learning value C.sub.LC is 
calculated according to the previous equation (2). And the feedback 
correction value C.sub.FB is calculated according to the previous equation 
(3). In step P19, the learning value is altered or updated as the value 
calculated in step P18, and the feedback correction value C.sub.FB is 
altered or initialized. Thereafter, the processes after step P7 are 
conducted. 
If it is decided in step P15 that the learning zone is not the same as the 
previous zone, i.e., when the learning zone is shifted, the learning 
correction value C.sub.LC is set, in step P20, according to the learning 
value C.sub.LC2 stored in a new learning zone after shifting. In step P20, 
the feedback correction value C.sub.FB is also calculated according to the 
previous equation (4). Then in step P21, the feedback correction value 
C.sub.FB is altered or initialized to the value calculated in step P20. 
While, in the above-described embodiments, a description has been made of 
the case where the present invention is embodied as described above, it is 
to be understood that the present invention is not limited to the 
particular embodiments. Various other changes, modifications and 
variations may be made within the spirit and scope of the present 
invention in a range as claimed in claim 1 with reference to the 
description of the embodiments and the accompanying drawings.