JPH07269398A - Air-fuel ratio controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To restrain the vibration level of a vehicle body and prevent the resonance of air-fuel ratio change and a drive system by calculating an air-fuel ratio correction control coefficient so that the change period of an air-fuel ratio may approach a target period, preventing overlapping with a frequency zone where the change frequency of the air-fuel ratio becomes problematic. CONSTITUTION:The operation state of an engine is detected, and a fuel amount to be fed to the engine is calculated according to the detected operation state, and the air-fuel ratio of the engine is detected by feeding the calculated fuel amount, and it is decided whether the detected air-fuel ratio is rich or lean in regard to a target air-fuel ratio (a-e). By means of (j, f) devices by which on the basis of an outcome thus decided, an air-fuel ratio correction control coefficient to be made up of a proportional control portion and an integral control portion is added/subtracted to/from an air-fuel ratio correction coefficient, and on the basis of the calculated air-fuel ratio correction coefficient, the fuel amount is corrected, and the return control of the air-fuel ratio is carried out, the change period of the air-fuel ratio is detected, and compared with a target period, and means (g, h, i) to calculate the air-fuel ratio correction control coefficient so as to approach the target period are also equipped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an air-fuel ratio control system for an internal combustion engine.

[0002]

2. Description of the Related Art An air-fuel ratio control device provided in an automobile engine or the like has an air-fuel ratio correction control coefficient composed of a proportional control component and an integral control component based on the detected actual air-fuel ratio. The amount of fuel is corrected by addition and subtraction to bring the air-fuel ratio close to the target air-fuel ratio.

By the way, such feedback control for the air-fuel ratio has a certain time delay due to the response speed of the sensor for detecting the air-fuel ratio, the control speed, etc., so that the actual air-fuel ratio is periodically on the rich side. It changes to the lean side, and along with this, the engine output also changes periodically. When the fluctuating frequency substantially matches the natural frequency at the gear shift position of the engine drive system, the vibration level of the vehicle body increases.

As a countermeasure against this, Japanese Patent Laid-Open No. 64-36941
The one disclosed in Japanese Patent Publication detects the fluctuation frequency of the air-fuel ratio resulting from the feedback control of the air-fuel ratio, and the detected fluctuation frequency substantially matches the natural frequency at the gear shift position of the engine drive system. In this case, the control coefficient that is added to or subtracted from the air-fuel ratio correction coefficient is changed from a value that is normally used to another predetermined value, and the fluctuating frequency of the air-fuel ratio caused by feedback control is changed to prevent air-fuel ratio fluctuation and drive system resonance. It is like this.

[0005]

However, in such a conventional air-fuel ratio control device for an internal combustion engine, the fluctuation cycle of the air-fuel ratio generated by changing the control coefficient that is added to or subtracted from the air-fuel ratio correction coefficient is changed. The change width varies depending on the cycle before changing the control coefficient and the operating state, and the fluctuation cycle after changing the control coefficient is unnecessarily long and deteriorates the controllability, or conversely, the fluctuation cycle is too short, There is a problem that the frequency band is sensitive to human vibration of about several Hz.

It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine, which focuses on the above-mentioned problems and makes the fluctuation cycle of the air-fuel ratio close to a target value according to the operating state.

[0007]

The invention according to claim 1 is
As shown in FIG. 8, means a for detecting the operating state of the engine
A means b for calculating the amount of fuel supplied to the engine in accordance with the detected operating state, a means c for supplying the calculated amount of fuel, a means d for detecting the air-fuel ratio of the engine, Means for determining whether the air-fuel ratio is rich or lean with respect to the target air-fuel ratio, and based on the result of the determination, an air-fuel ratio correction coefficient that is composed of proportional control portion and integral control portion In an air-fuel ratio control device for an internal combustion engine, which comprises means j for adding and subtracting a control coefficient, and means f for correcting the fuel amount based on the calculated air-fuel ratio correction coefficient and performing feedback control of the air-fuel ratio, Means g for detecting the fluctuation cycle of the air-fuel ratio,
Means h for comparing the detected fluctuation cycle of the air-fuel ratio with the target cycle; and means i for calculating the air-fuel ratio correction control coefficient so that the fluctuation cycle of the air-fuel ratio approaches the target cycle based on the compared results. , Is provided.

In the air-fuel ratio control apparatus for an internal combustion engine according to a second aspect, in the invention according to the first aspect, the target cycle of the air-fuel ratio fluctuation is set to be longer during steady operation of the engine than during transient operation.

According to a third aspect of the present invention, in the air-fuel ratio control system for an internal combustion engine according to the first or second aspect of the invention, the integral control amount of the air-fuel ratio correction control coefficient is added or subtracted to correct the fuel amount. Then, feedback control of the air-fuel ratio is performed.

An air-fuel ratio control system for an internal combustion engine according to a fourth aspect is the invention according to any one of the first to third aspects,
The integral control amount of the air-fuel ratio correction control coefficient refers to different basic values during steady operation and transient operation, and learns the feedback control result of the integral control in both operating states, and this learned value is next time. Refer to when controlling.

[0011]

[Function] Based on the detected actual air-fuel ratio, the air-fuel ratio correction coefficient is added to or subtracted from the air-fuel ratio correction coefficient, which is composed of proportional control portion and integral control portion, to correct the fuel amount, and the air-fuel ratio is set to the target air-fuel ratio. Approach to. Feedback control for such air-fuel ratio is
There is a certain time delay due to the influence of the response speed of the sensor that detects the air-fuel ratio, or the control speed, etc., so the actual air-fuel ratio changes periodically between the rich side and the lean side, and the engine output also changes accordingly. Fluctuate.

The air-fuel ratio control apparatus for an internal combustion engine according to claim 1 calculates the air-fuel ratio correction control coefficient so that the fluctuation cycle of the air-fuel ratio approaches the target cycle, so that the fluctuation frequency of the air-fuel ratio becomes a problem frequency. Try not to overlap the band.

In the air-fuel ratio control apparatus for an internal combustion engine according to a second aspect of the present invention, the target cycle of the air-fuel ratio fluctuation is set to be longer during the steady operation of the engine than during the transient operation, so that the air-fuel ratio is fed back during the transient operation. It is possible to prevent the control responsiveness from being impaired, and prevent the fluctuation frequency of the air-fuel ratio from overlapping the vibration frequency band in question from the transient operation to the steady operation.

That is, during steady operation, the change in the basic fuel injection amount required under the operating conditions is small and the air-fuel ratio is less likely to deviate than during transient operation. Therefore, the response speeds of air-fuel ratio feedback control are compared. It becomes possible to set the frequency of the air-fuel ratio fluctuation to a lower frequency side than the frequency band in which the problem occurs by delaying the delay.

On the other hand, during the transient operation, the change in the basic fuel injection amount required under the operating conditions is large, and the air-fuel ratio is likely to shift. Therefore, it is necessary to increase the response speed of the air-fuel ratio feedback control.

An air-fuel ratio control apparatus for an internal combustion engine according to a third aspect of the present invention corrects the fuel amount by adding and subtracting the integral control amount of the air-fuel ratio correction control coefficient, and performs feedback control of the air-fuel ratio.
The fluctuation range of the air-fuel ratio can be suppressed to be small, and the feedback control response of the air-fuel ratio can be improved.

The air-fuel ratio control apparatus for an internal combustion engine according to claim 4 refers to different basic values during steady operation and during transient operation,
In addition, by learning the feedback control result for the integral control in both operating states and referring to this learned value at the time of the next control, when the operating state changes between the steady operating region and the transient operating region, The control response immediately after the start of control can be improved.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, the engine 1 includes an intake valve 2
Intake air (air mixture) is sucked into the cylinder 4 from the intake port 3 as the engine is opened, and the intake air is compressed by the piston 5 and ignited and burned by the spark plug 6, and the exhaust valve 7 is opened. The exhaust gas is exhausted to the exhaust passage 9 through the exhaust port 8 and these steps are continuously repeated.

An injector 14 for injecting fuel into the intake port 3 and a throttle valve 11 for restricting intake air in association with an accelerator pedal are provided in the middle of the intake passage 20, and an air flow detecting an intake air amount is provided upstream thereof. A meter 10 is provided.

A three-way catalyst 21 is installed in the middle of the exhaust passage 9 to oxidize HC and CO in the exhaust gas and NOx.
Reduce.

A control unit 13 for controlling the amount of fuel injected from the injector 14 is provided. The control unit 13 includes an intake air amount Q detected by the air flow meter 10, a throttle opening TVO detected by the throttle position sensor 12, an engine speed N detected by the engine speed sensor 22, and a cooling water temperature sensor. The coolant temperature TW detected in 23 is input, and the basic fuel injection amount Tp is calculated according to the operating state.

An O ₂ sensor 15 is installed in the exhaust passage 9. The control unit 13 has an O ₂ sensor 15
Input the output VO ₂ according to the oxygen concentration in the exhaust gas detected at, and feedback control the fuel injection amount so that the air-fuel mixture becomes the stoichiometric air-fuel ratio, and maximize the conversion efficiency in the three-way catalyst 21. To maintain.

The control unit 13 contains a clock 16 and a counter 17 for detecting the air-fuel ratio fluctuation period.

The flow chart of FIG. 2 shows a program for air-fuel ratio feedback control executed in the control unit 13, which is executed at regular intervals.

First, in step S1, engine speed N, throttle opening TVO, cooling water temperature TW, intake air amount Q
Read in.

In step S2, the basic fuel injection amount Tp is calculated based on these detected values.

In step S3, it is determined whether or not the current operating condition is within the preset air-fuel ratio feedback control region,
If it is within the region, the process proceeds to step S4, and if it is outside the region, the process proceeds to step S20 to set the air-fuel ratio correction coefficient α to 100%, and then proceeds to step S21, and the flag Flag is set.
V is reset, and the basic fuel injection amount Tp of this time is stored in BTp in step S11.

In step S4, the O ₂ sensor output VO ₂ is read, and in step S5 VO ₂ is compared with a predetermined value VSL to determine whether the air-fuel ratio of the exhaust gas is rich or lean.

When VO ₂ is judged to be leaner than the predetermined value VSL, the routine proceeds to step S6, where the flag FlagVO
Referring to, the lean air-fuel ratio when the exhaust air-fuel ratio is inverted from rich to lean is detected. When this reversal is detected, the process proceeds to step S7, and the air-fuel ratio correction control coefficient to be described later is calculated.

At the lean reversal, the routine proceeds to step S8, where the proportional control amount Pl at the time of the rich reversal is set based on a map preset according to the engine speed N and the basic fuel injection amount Tp.
Is searched for, and the proportional control amount Pl is added to the air-fuel ratio correction coefficient α in step S9.

If it is not lean inversion, step S12
To the lean-time integral control component I of the air-fuel ratio correction control coefficient I.
1 is read, and the routine proceeds to step S13, where the air-fuel ratio correction coefficient α
Is added to the integral control component Il.

After the air-fuel ratio correction coefficient α is determined in this way, the routine proceeds to step S10, the rich / lean determination result of this time is stored in the flag FlagVO, and the basic fuel injection amount Tp of this time is BTp at step S11. Store in.

On the other hand, when VO ₂ is richer than the predetermined value VSL, the routine proceeds to step S14, where the flag Fl is set.
With reference to ugVO, a rich inversion time when the exhaust air-fuel ratio is inverted from lean to rich is detected.

At the time of rich inversion, the process proceeds to step S15,
The proportional control amount P at the time of lean reversal based on a map preset according to the engine speed N and the basic fuel injection amount Tp
r is searched, and the routine proceeds to step S16, where the air-fuel ratio correction coefficient α
This proportional control amount Pr is subtracted from.

If it is not during the rich inversion, step S18
To the rich-time integral control component I of the air-fuel ratio correction control coefficient I.
r is read, and the routine proceeds to step S19, where the air-fuel ratio correction coefficient α
This integral control component Ir is subtracted from.

After the air-fuel ratio correction coefficient α is determined in this way, the lean / rich determination result of this time is stored in the flag FlagVO in step S17, and step S11
Then, the basic fuel injection amount Tp of this time is stored in BTp.

The control unit 13 calculates the fuel injection amount by the following equation based on the air-fuel ratio correction coefficient α calculated in the above routine.

Fuel injection amount = Tp × various correction coefficients × α + voltage correction amount (1) As shown in FIG. 4, when the air-fuel ratio is on the rich side, O
_{2 When} the output of the sensor 15 becomes larger than the slice level corresponding to the theoretical air-fuel ratio, the air-fuel ratio correction coefficient α is first stepped down by the proportional control amount Pr and then the integral control amount I
It is controlled so that the air-fuel ratio is made thinner by gradually lowering it with the inclination of r. In this way, when the air-fuel ratio becomes lean, when the output of the O ₂ sensor 15 becomes smaller than the slice level, the air-fuel ratio correction coefficient α is first lowered stepwise by the proportional control amount Pl, and then the slope of the integral control amount Il is increased. Is controlled to gradually increase the air-fuel ratio. By repeating this control, the actual air-fuel ratio can be maintained near the stoichiometric air-fuel ratio.

By the way, such feedback control with respect to the air-fuel ratio has a certain time delay due to the influence of the response speed of the O ₂ sensor 15, the control speed of the control unit 13, etc., so that the actual air-fuel ratio is periodically on the rich side. Then, the engine output changes periodically with the change to lean side. The fluctuating frequency varies depending on the engine operating condition and the like, but generally has a value close to a frequency band of about several Hz, which is sensitive to human vibration.

To cope with this, as shown in FIG. 5, the fluctuation frequency of the air-fuel ratio does not overlap the frequency band sensitive to human vibration, and the natural vibrations at the shift positions A, B and C of the drive system. The target cycle which does not overlap with the number is set, the control unit 13 detects the fluctuation cycle of the air-fuel ratio, and the values of the integrated control components Ir and Il of the air-fuel ratio correction control coefficient are detected so that the detected fluctuation cycle approaches the target cycle. To calculate.

The flow chart of FIG. 3 shows a program for calculating the air-fuel ratio control coefficient, which is executed in the control unit 13 for feedback control of the fluctuation cycle of the air-fuel ratio.

First, in step A1, the timer counter value COUNT driven by the clock is read.

Then, in step A2, the difference DCOUNT between the counter value COUNT read this time and the counter value BCOUNT read last time is calculated as the fluctuation cycle of the air-fuel ratio, and the counter value read this time is calculated in step A3. COUN
Store T in the counter value BCOUNT.

Then, in step A4, the step S
The difference between the previous Tp stored in 11, that is, BTp and the current Tp is obtained, and it is determined whether or not the absolute value is in a transient operation of a predetermined value TPTRJ or more.

When it is determined in step A4 that the engine is in the transient operation of the predetermined value TPTRJ or more, the process proceeds to step A5, and the target cycle TCOUNT of the air-fuel ratio fluctuation is set to the target cycle TCOUNTT of the transient.

Then, the process proceeds to step A6 and the FlagT
By referring to RJ, if it is determined that the vehicle was in the transient operation state last time, the process proceeds to step A7.

In step A7, the engine speed N
And a map M of the integral control portions Ir and Il of the air-fuel ratio correction control coefficient assigned to the lattice consisting of the basic fuel injection amount Tp and
Read 1.

In step A8, the integral control component Ir,
It is determined whether or not Il is within a predetermined control range, and the integral control components Ir and Il are prevented from becoming excessively large or small as a result of this control.

If it is determined in step A8 that the integral control components Ir and Il are within the predetermined range, the process proceeds to step A9, in which the actual exhaust air-fuel ratio fluctuation period DCOUNT and the target period TCOUNT are compared to determine DCOUNT. If it is larger, the process proceeds to step A10 and the integral control components Ir, I
A predetermined amount dI is added to l, and in the opposite case, the process proceeds to step A13, where the predetermined amount dI is subtracted from the integral control parts Ir and Il.

Then, the process proceeds to step A11, and the integral control components Ir and Il of the calculation result are written in the equal portions of the map M1. Lastly, in step A12, the fact that the current time is the transient operation state is recorded in FlagTRJ, and the process proceeds to step S8.

On the other hand, when it is determined in step A6 that the transient operation state is not the last time, the map M is set at this stage.
1 is a map M1CS of the integrated control components Ir and Il in the steady state.
Since T and its cycle control result have been stored, the process proceeds to step A14, where it is stored in the map M1CST.
Then, the process proceeds to step A15 to read the map M1TRJ of the integral control components Ir and Il during transient into the map M1. Thus, the integral control components Ir and Il can be changed with good responsiveness immediately after the transition to the transient operation state.

In step A14, when the data is stored, the weighted average of the original MICST value and the period control result MI value is stored in the map MICST to learn the data. By starting the control with this value as the initial value at the time of the next control, it becomes possible to enhance the controllability immediately after the start of the control.

On the other hand, in step A4, the basic fuel injection amount T
When it is determined that the change in p is in the steady operation which is smaller than the predetermined value TPTRJ, the process proceeds to step A16, and the target cycle TCOUNT of the air-fuel ratio fluctuation is set to the target cycle TCO in the steady state.
Determined by UNTC.

Then, the process proceeds to step A17, where the flag is set.
By referring to TRJ, when it is determined that the steady operation state was also last time, the process proceeds to step A18.

In step A18, the map M1 of the integral control parts Ir and Il of the air-fuel ratio correction control coefficient assigned to the grid consisting of the engine speed N and the basic fuel injection amount Tp is read.

In step A19, the integral control component I
It is determined whether r and Il are within a predetermined control range,
As a result of this control, the integral control components Ir and Il are prevented from becoming too large or too small.

At step A19, integral control components Ir and Il
If it is determined that is within a predetermined range, step A2
0, the actual exhaust air-fuel ratio variation cycle DCOUNT is compared with the target cycle TCOUNT. If DCOUNT is larger, the process proceeds to step A21, where the integral control component I
A predetermined amount dI is added to r and Il, and in the opposite case, step A2
Proceeding to step 2, the predetermined amount dI is subtracted from the integral control parts Ir and Il.

Subsequently, the process proceeds to step A22, and the integral control components Ir and Il of the calculation result are written in the equal portions of the map M1. Finally, in step A23, the fact that this time is in the transient operation state is recorded in FlagTRJ, and the process proceeds to step S8.

On the other hand, if it is determined in step A17 that the previous steady-state operation was not performed, then at this stage, the map M1 has a map M1T of integral control parts Ir and Il at the time of transition.
Since the RJ and the cycle control result thereof are stored, the process proceeds to step A25 and the map M1TR is set.
After storing in J, the process proceeds to step A26, and the map M1CST of the transient integration control parts Ir and Il is read into the map M1. As a result, the integral control components Ir and Il can be changed with good responsiveness immediately after shifting to the steady operation state.

As shown in FIG. 5, the target fluctuation cycle TCOUNT of the air-fuel ratio fluctuation is set to be longer during steady operation than during transient operation, thereby impairing the feedback control response of the air-fuel ratio during transient operation. While preventing, it is possible to prevent the fluctuation frequency of the air-fuel ratio from overlapping the vibration frequency band in which people are concerned.

That is, during steady operation, the change in the basic fuel injection amount Tp required under the operating conditions is small and the air-fuel ratio is less likely to deviate than during transient operation. By making it relatively slow, it becomes possible to shift the air-fuel ratio fluctuation frequency to a lower frequency side than the frequency band that humans care about.

On the other hand, during the transient operation, the change in the basic fuel injection amount Tp required under the operating conditions is large, and the air-fuel ratio is likely to shift. Therefore, it is necessary to increase the response speed of the air-fuel ratio feedback control.

Further, the fluctuation range of the air-fuel ratio can be suppressed to a small level by performing the feedback control of the air-fuel ratio by adding and subtracting the integral control parts Ir and Il of the air-fuel ratio correction control coefficient to correct the fuel amount.

FIG. 6 shows a change characteristic of the air-fuel ratio when the proportional control components Pr and Pl of the air-fuel ratio correction control coefficient are added and subtracted to correct the fuel amount. In this case, the air-fuel ratio correction coefficient α takes a value far from 100%, and an overshoot occurs in which the air-fuel ratio changes rapidly.

FIG. 7 shows a change characteristic of the air-fuel ratio in the case of correcting the fuel amount by adding and subtracting the integral control parts Ir and Il of the air-fuel ratio correction control coefficient. In this case, the air-fuel ratio correction coefficient α takes a value close to 100%, and the fluctuation range of the air-fuel ratio can be suppressed to be small.

[0067]

As described above, according to the first aspect of the invention, in the air-fuel ratio control device for an internal combustion engine that performs feedback control of the air-fuel ratio, means for detecting the fluctuation cycle of the air-fuel ratio and the detected air-fuel ratio. Means for comparing the fluctuation cycle of and the target cycle,
Based on the result of comparison, a means for calculating the air-fuel ratio correction control coefficient so that the air-fuel ratio fluctuation cycle approaches the target cycle is provided, so that the air-fuel ratio fluctuation frequency does not overlap the frequency band in question. As a result, it is possible to reduce the vibration felt by the occupant of the vehicle.

In the air-fuel ratio control device for an internal combustion engine according to a second aspect, in the invention according to the first aspect, the target cycle of the air-fuel ratio fluctuation is set to be longer during transient operation of the engine than during transient operation. It is possible to prevent the fluctuation frequency of the air-fuel ratio from overlapping the vibration frequency band in question from the transient operation to the steady operation without deteriorating the feedback control response of the air-fuel ratio at the time.

According to a third aspect of the present invention, in the air-fuel ratio control apparatus for an internal combustion engine according to the first or second aspect of the invention, the amount of integral control of the air-fuel ratio correction control coefficient is added or subtracted to correct the fuel amount. However, since the feedback control of the air-fuel ratio is performed, the fluctuation range of the air-fuel ratio can be suppressed to be small and the responsiveness of the feedback control of the air-fuel ratio can be improved.

An air-fuel ratio control device for an internal combustion engine according to a fourth aspect is the invention according to any one of the first to third aspects,
The integral control amount of the air-fuel ratio correction control coefficient refers to different basic values during steady operation and transient operation, and learns the feedback control result of the integral control in both operating states, and this learned value is next time. Since the configuration is referred to during control, when the operating state changes between the steady operating region and the transient operating region, the control responsiveness immediately after the start of control in each operating region can be improved.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart for similarly performing feedback control of the air-fuel ratio.

FIG. 3 is a flowchart for similarly calculating an air-fuel ratio correction control coefficient.

FIG. 4 is a timing chart showing an example of controlling the air-fuel ratio.

FIG. 5 is a diagram showing a setting example of an air-fuel ratio fluctuation frequency.

FIG. 6 is a timing chart showing an example of controlling the air-fuel ratio.

FIG. 7 is a timing chart showing an example of controlling the air-fuel ratio.

FIG. 8 is a claim correspondence diagram showing the invention according to claim 1;

[Explanation of symbols]

1 engine 2 intake valve 3 intake passage 4 cylinder 5 piston 7 exhaust valve 8 exhaust passage 10 air flow meter 11 throttle valve 12 throttle position sensor 13 control unit 14 injector 15 O ₂ sensor 16 clock 17 counter 22 engine rotation sensor 23 cooling water temperature sensor a operating state detection means b basic fuel injection amount calculation means c fuel supply means d air-fuel ratio detection means e air-fuel ratio determination means f air-fuel ratio correction means g air-fuel ratio variation cycle detection means h air-fuel ratio variation cycle determination cycle i air-fuel ratio correction control Coefficient calculation means j Air-fuel ratio correction coefficient calculation means

Claims (4)

[Claims] 1. A means for detecting an operating state of an engine, a means for calculating an amount of fuel supplied to the engine according to the detected operating state, a means for supplying the calculated amount of fuel, and an empty space of the engine. A means for detecting the fuel ratio, a means for judging whether the detected air-fuel ratio is rich or lean with respect to the target air-fuel ratio, and a proportional control component for the air-fuel ratio correction coefficient based on the judged result. An internal combustion engine comprising: means for adding / subtracting an air-fuel ratio correction control coefficient composed of integral control parts; means for correcting the fuel amount based on the calculated air-fuel ratio correction coefficient and performing feedback control of the air-fuel ratio. In the air-fuel ratio control device, the means for detecting the fluctuation cycle of the air-fuel ratio, the means for comparing the fluctuation cycle of the detected air-fuel ratio with the target cycle, and the fluctuation cycle of the air-fuel ratio based on the result of the comparison. Air-fuel ratio correction control section to approach the target cycle An air-fuel ratio control device for an internal combustion engine, comprising: a means for calculating the number. 2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the target cycle of the air-fuel ratio fluctuation is set longer during steady operation of the engine than during transient operation. 3. The internal combustion engine according to claim 1, wherein feedback control of the air-fuel ratio is performed by adding and subtracting an integral control amount of the air-fuel ratio correction control coefficient to correct the fuel amount. Air-fuel ratio control system for engines. 4. The integral control portion of the air-fuel ratio correction control coefficient is:
2. A different basic value is referred to during steady operation and during transient operation, the feedback control result for integral control in both operating states is learned, and this learned value is referred to in the next control. 4. The air-fuel ratio control device for an internal combustion engine according to any one of 1 to 3.