JPS618438A - Method of controlling air-fuel ratio of internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the air-fuel ratio from being enriched when the control of increment of fuel is carried out instead of the feed-back control of air-fuel ratio, by carrying out the feed-back control of air fuel ratio for every predetermined time to learn deviations in air-fuel ratio due to variations in the density of intake-air. CONSTITUTION:During operation of an engine, an electronic control circuit 8 determines whether the demand which requires the control of increment of fuel is present or not in accordance with the turn-on or turn-off of a power switch 12, and if the demand is not present, feed-back control is carried out such that the amount of fuel injection from a fuel injection valve 2 is compensated in accordance with the output of an O2 sensor 4. On the contrary, if the demand is present, the control of increment of fuel is carried out while the above-mentioned feed-back control is creased. In this stage, when the control of increment of fuel is continued for a predetermined time, it is interrupted for a predetermined time while the feed-back control of air-fuel ratio is carried out. Further, the deviation between an actual air-fuel ratio during control of fuel increment and a stoichiometric air-fuel ratio is leanred, and is used for compensating the actual air-fuel ratio during control of fuel increment which is carried out thereafter.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an air-fuel ratio control method for an internal combustion engine, and in particular to a method for controlling the air-fuel ratio of an air-fuel mixture to a value smaller than the stoichiometric air-fuel ratio in accordance with operational requirements. The present invention relates to an air-fuel ratio control method for an internal combustion engine.

[Prior art] Conventionally, when controlling the amount of fuel supplied according to the amount of intake air to an internal combustion engine, the exhaust purification efficiency of a catalytic converter using a three-way catalyst provided in a part of the exhaust pipe has been made sufficient. Therefore, feedback control of the air-fuel ratio is used to estimate the air-fuel ratio of the intake air-fuel mixture based on the exhaust composition, for example, the oxygen concentration in the exhaust gas, correct the fuel supply amount, and adjust the air-fuel ratio of the internal combustion engine to the stoichiometric air-fuel ratio. It has been known. Also, such fee
Based on feedback control, this feedback control is stopped when it is necessary to increase the output of the internal combustion engine due to driving demands such as climbing or acceleration, and the air-fuel ratio is theoretically adjusted based on the intake air amount of the internal combustion engine. A method for controlling the air-fuel ratio of an internal combustion engine is also known, in which the air-fuel ratio is controlled to be smaller than the air-fuel ratio, that is, to be in a rich state (hereinafter referred to as fuel increase control).

[Problems to be Solved by the Invention] Against the background of the prior art, the problem to be solved by the present invention is to stop feedback control of the air-fuel ratio due to operational demands and continue to perform fuel increase control. If the atmospheric temperature or atmospheric pressure changes significantly, or if the altitude of the vehicle changes during fuel increase control due to continuous climbing, etc.
Since the density of intake air changes, when using an intake air amount sensor such as a vane-type intake air amount sensor such as an air flow meter or a Karman vortex type intake air amount sensor that uses Karman vortices, the intake air weight As a result of inaccurate measurement, the actual air-fuel ratio deviates from the target air-fuel ratio during fuel increase control, and accurate air-fuel ratio control may not be possible.

Figure 7 shows the excessive fuel supply rate that occurs when a vehicle climbs from sea level to 4,000 meters while continuing fuel increase control, that is, with the power switch, which indicates a large throttle opening, left on. This shows that. In the figure, the broken line ■ indicates the fuel excess rate ( In other words, the required correction amount for the amount of fuel to be reduced), but these deviations are due to the decrease in atmospheric pressure that accompanies the increase in altitude, that is, the decrease in air density. This is caused by a detection deviation occurring in the detection means.

Therefore, due to operational requirements, feedback control of the air-fuel ratio is stopped and fuel increase control is performed.During this operation, the atmospheric temperature increases, atmospheric pressure decreases, or the air density decreases due to raindrops, etc. If a Karman vortex type intake air amount detection means is used, the air-fuel ratio of the mixture becomes rich due to a deviation in the intake air amount detection. Since this is directly reflected, the air-fuel ratio of the air-fuel mixture may become excessively rich, such as being around 7 to 9, which may lead to smoldering at the spark plug, or misfire and engine stall. There were some possible problems.

[Object of the Invention] The present invention has been made in view of the above points, and its purpose is to control the air-fuel ratio to be smaller than the stoichiometric air-fuel ratio due to operational requirements, instead of feedback control of the air-fuel ratio. An object of the present invention is to provide an air-fuel ratio control method for an internal combustion engine that solves the problem that the actual air-fuel ratio deviates from the target air-fuel ratio due to changes in air density when fuel increase control is continuously performed to increase the amount of fuel.

[Structure of the Invention] The gist of the present invention, which has been made to achieve the above object, is to: adjust the amount of fuel supplied so that the air-fuel ratio of the mixture of fuel and intake air supplied to the internal combustion engine becomes the stoichiometric air-fuel ratio; is feedback-controlled based on the exhaust composition of the internal combustion engine, and when there is an operational requirement, the feedback control is stopped and fuel is increased in order to set the air-fuel ratio of the air-fuel mixture to a target air-fuel ratio smaller than the stoichiometric air-fuel ratio. In an air-fuel ratio control method for an internal combustion engine that performs fuel increase control, when the fuel increase control continues for a predetermined time, the fuel increase control is stopped for a predetermined time and the feedback control is performed, and the fuel increase control is performed while the fuel increase control is being performed. An air-fuel ratio for an internal combustion engine, characterized in that the actual air-fuel ratio during subsequent fuel increase control is corrected toward the target air-fuel ratio by learning the deviation of the actual air-fuel ratio from the stoichiometric air-fuel ratio. It is in the fuel ratio control method.

Next, the basic configuration of the present invention will be explained using the flowchart shown in FIG. As shown in the figure, the method for controlling the air-fuel ratio of an internal combustion engine according to the present invention is repeatedly executed during operation of the internal combustion engine, and includes the following steps: P1: determining whether or not there is an operational demand for increasing fuel amount; P2: Predetermined time T1 after fuel increase control is implemented
P3: After the elapse of time T1, determining whether a predetermined time T2 has elapsed; P4: Performing air-fuel ratio feedback control and correcting the air-fuel ratio. The step of executing value learning, P5: step of canceling the feedback control and implementing fuel increase control, is executed in the following procedure.

That is, during operation of the internal combustion engine, it is determined whether or not there is a request to increase the amount of fuel in order to increase the output.
1) If there is no request, feedback control of the air-fuel ratio is performed to learn the deviation of the actual air-fuel ratio from the stoichiometric air-fuel ratio (Step P4); if the above request is made, control is performed for a predetermined time T1 after the fuel increase control starts. Step P2) to determine whether or not time has elapsed; if not, continue fuel increase control instead of air-fuel ratio feedback control to step P5); if time T1 has elapsed, time T1 has elapsed. After that, it is determined whether the predetermined time T2 has elapsed (step P3), and if the time T2 has not elapsed, even if there is a request for fuel increase control, feedback control of the air-fuel ratio is performed instead to maintain the stoichiometric air. The deviation of the actual air-fuel ratio from the fuel ratio is learned (step P4), and if time T2 has elapsed, the fuel increase control is performed again (step P5). Note that the predetermined time T1 here means the time elapsed from the time when the air-fuel ratio feedback control was switched to the fuel increase control, and even though there is an operational request to increase the fuel amount, First, after feedback control of the air-fuel ratio is performed according to the air-fuel ratio control method of the present invention, the elapse of the time T1 is determined again, with the time point at which the control is switched to fuel increase control again as zero.

In addition, the time T2 for performing the air-fuel ratio feedback control after the predetermined time T1 has elapsed is set as the time until learning of the air-fuel ratio deviation in the feedback control by the air-fuel ratio control is completed, instead of being set as a predetermined time. , it is also possible to configure the air-fuel ratio control method for an internal combustion engine according to the present invention.

[Example J Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 2 is a schematic configuration diagram showing an example of an air-fuel ratio control device including an internal combustion engine and its peripheral devices to which the air-fuel ratio control method of the present invention is applied, in which 1 is the internal combustion engine main body, 2 is an electromagnetic fuel injection A valve 4 represents an oxygen concentration sensor that generates an electric signal in response to 8 degrees of residual oxygen in the exhaust gas from the internal combustion engine 1, and 6 represents an electronic control circuit that controls the air-fuel ratio of the internal combustion engine.

Further, in order to detect various operating conditions of the internal combustion engine 1, an intake air temperature sensor 8. Throttle sensor 12 which detects whether the opening of the throttle valve 10 and the throttle opening is a predetermined value or more using a power switch. A Karman vortex type intake air amount sensor 18 is installed between the air cleaner 15 of the internal combustion engine main body 1 and the surge tank 16, and detects the intake air amount using Karman vortices. internal combustion engine 1
A water temperature sensor 20 for detecting the temperature of the cooling water. A rotation speed sensor 24 is installed facing the rotor 22a inside the distributor 22 and detects the rotation speed of the internal combustion engine 1 by generating 24 pulses per revolution of a crank (not shown). Similarly, a group of sensors such as a cylinder discrimination sensor 25 which generates one pulse per revolution of the crank are provided.

The high voltage pulse generated by the igniter 26 is supplied to the distributor 22.
2 applies this high voltage to a spark plug 30 screwed into the upper part of the cylinder 28 of the internal combustion engine 1 in synchronization with the combustion cycle of each cylinder to ignite the air-fuel mixture. Also, 3
2 is a catalytic converter provided in the exhaust pipe 34 of the internal combustion engine 1.

Next, the internal configuration of the electronic control circuit 6 and the electrical signal system will be explained. The electronic control circuit 6 includes a central processing unit (CPLI) 6o that inputs data, performs calculations, and performs control according to a predetermined program, and a read-only memory <ROM> 62 that stores control programs, etc. in advance.
, a temporary storage memory (RAM 64) in which data, etc. can be freely written and read;
, an output port lower that outputs control signals to the igniter 26, the fuel injection valve 2, etc., and the CPU 60. A data bus 68 and a key switch 71 that interconnect the above-mentioned elements such as R○M62.
The power supply circuit 75 is connected to a battery 73 via a power supply circuit 75 and supplies a stabilized voltage to the entire electronic control circuit 6.

The input port 5 is a Karman vortex type intake air amount sensor 1
8, a pulse input section 65a that inputs pulse signals from the rotation speed sensor 24 and the cylinder discrimination sensor 25, and an intake temperature sensor 8. Throttle sensor 12° II? Elementary concentration sensor 4. It has an analog input section 65b into which an analog signal corresponding to each detection value from the water temperature sensor 20 is input. On the other hand, the crank angle (not shown) of the internal combustion engine 1 is detected by the rotation speed sensor 24.
A signal for driving the igniter 26 and a control signal for opening the fuel injection valve 2 for a fuel injection time determined according to the fuel injection amount are outputted via the output port lower. ing.

The fuel injection valve 2 is controlled and opened by the control signal, and fuel is injected into the intake pipe 14 by receiving fuel from a fuel pump (not shown).

Next, a control routine as an example of the air-fuel ratio control method for an internal combustion engine according to the present invention, which is carried out in the electronic control circuit 6, will be explained with reference to the flowchart shown in FIG. The flowchart in Figure 3 is for instructing whether to perform air-fuel ratio feedback control or alternatively, fuel increase control, according to various conditions. Control is executed by another control routine (not shown) that is repeatedly executed together with this control routine. Since these controls are well known, they will not be specifically explained, but the learned value control executed in the feedback control of the air-fuel ratio will be explained based on the flowchart of FIG.

In FIG. 3, this control routine is started at predetermined time intervals (for example, 4 m5 ec) during operation of a predetermined internal combustion engine, and includes the following steps: 100: determining whether the power switch is on (ON>); 110: A step of incrementing the counter C by 1; 120: A step of determining whether the value of the counter C is greater than or equal to the value CT1 corresponding to a predetermined time T1; 130: The value of the counter C is incremented by 1 after that. A step of determining whether the value is greater than or equal to another value CT2 corresponding to a predetermined time T2, 140: A step of performing a process of returning the value of the counter C to zero, 150: Setting the value of the counter C to zero. 160: Performing a process of canceling the air-fuel ratio feedback control and instructing the implementation of fuel increase control instead; 170: Performing a process of canceling the fuel increase control and instructing the implementation of feedback control. Execute step as follows.

First, in step 100, it is determined whether a power switch (not shown) in the throttle sensor 12 is turned on (rONJ), that is, whether or not the throttle 10 is opened to a predetermined opening degree or more (almost fully open). If the power switch is not turned on, it is assumed that there is no operational requirement for fuel increase control, and the process proceeds to step 15o, where the counter value C on the program is set to zero, and step 170.
Then, a process is performed to output a command to cancel fuel increase control and implement air-fuel ratio feedback control, for example by setting a flag value. On the other hand, in the judgment at step 100, if the accelerator (not shown) is depressed due to driving demands such as acceleration or attack, and the power switch is set to rONJ, the air-fuel ratio of the mixture is normally always lower than the stoichiometric air-fuel ratio. In order to achieve a so-called rich state, fuel increase control is performed instead of air-fuel ratio feedback control, but this control routine also performs air-fuel ratio feedback control under predetermined conditions. The process proceeds to step 110 in order to determine this, and the determinations and processes from step 110 onwards are performed. If the determination in step 100 is rYEsJ (the power switch is on), the process proceeds to step 110, where the counter value C on the program, which is initialized and set to zero when the internal combustion engine 1 is started, is incremented by 1. In the following step 120, it is determined whether the value C of this counter is greater than or equal to a predetermined value CT1.

Here, suppose CTI is 50000. CT2, which will be described later, is 6
If it is 0000, C≧5 after starting fuel increase control.
Until 0oOO, that is, after 50000 X and 4m5ec, the determination at step 120 is rNOJ, and the process moves to step 160. On the other hand, when the determination at step 120 is rYEsJ (when C≧CT1 holds)
If so, the process proceeds to step 130, where it is determined whether the counter value C is 012 or more. Step 13
When the judgment at 0 is rNOJ, time T1 (50000x4n+5ec) after fuel increase control is started.
After the elapse of time T2 (60000x4msec
) has not yet passed, and the process is the same as step 1 described above.
Move to 70. The determination at step 130 is "YES"
, that is, time T2 (60000X
4 m5ec) (7) After the tear lever has elapsed, the process proceeds to step 140, returns the counter value C to zero, and then
Processing moves to step 160.

In step 160, the air-fuel ratio feedback control is stopped and the fuel increase control is performed because the fuel increase control is necessary due to operational demands and the time is within which the fuel increase control can be performed based on the value C of the counter. It performs processing to output commands such as, for example, resetting flag values. Step 160 or Step 1 above
After the completion of step 70, this control routine ends.

Next, learned value control when air-fuel ratio feedback control is performed in an air-fuel ratio control routine (not shown) will be described. FIG. 4 is a flowchart showing a learning value control routine performed in the air-fuel ratio feedback control routine, which is activated as an interrupt routine every time the output voltage of the oxygen Si sensor 4 is reversed between high level and low level. be done.

First, in step 200, the air-fuel ratio feedback correction coefficient FAF is obtained by proportionally integrating the output of the oxygen concentration sensor 4.
A process is performed to obtain the arithmetic average value FAFAV of the peak values. That is, since this routine is started every time the output of the oxygen S degree sensor 4 is reversed, the value of the air-fuel ratio feedback correction coefficient cost FAF immediately after that and the previous peak value F
Arithmetic average value FAFAV= (FAF+F
Processing to obtain AFo1d)/2 is performed. In the following step 210, in preparation for the next process, the feedback correction coefficient FAF of the current air-fuel ratio is set to the previous peak value FAFo.
Processing is performed to store the data in a predetermined area of the RAM 64 as ld. In the next step 220, the counter value Cr on the program is incremented by 11, and in the following step 230, it is determined whether Or≧5. Unless Or≧5, the following processing is not performed and the present control routine ends. Therefore, every time the output of the oxygen concentration sensor 4 is reversed five times, the determination at step 230 is rYEsJ, and the learned value KG is updated or maintained. That is, in step 240 following step 230, the air-fuel ratio feedback correction coefficient FA
A determination is made as to what magnitude relationship the average value FAFA■ of F has with respect to the range of 0.98 to 1.02, which is the value when the air-fuel ratio control has reached equilibrium. This average value F
When AF△■ is less than 0.98, the process goes to step 250.
Proceed to , and change the learning value KG of air-fuel ratio control by β (for example, 3%).
If the average value FAFAV>1.02, the process proceeds to step 260, and the process of adding β to the learned value KG is executed. After the process of step 250 or step 260 described above is completed, or if the determination in step 240 is rYESJ, that is, the average value FAFAV described above is 0.98 or more and 1.02 or less and the learning value is not updated. Then, the process proceeds to step 270, where the counter value Cr incremented in step 220 is returned to zero, and this control routine ends.

As a result of the above-described learned value control routine being repeatedly executed, the deviation of the actual air-fuel ratio from the stoichiometric air-fuel ratio is first reflected in the air-fuel ratio feedback correction coefficient FAF, and is gradually transferred to the learned value KG. In the fuel injection amount control routine (not shown), the fuel injection amount (actually fuel injection time) τ is determined by correcting the basic fuel injection 1itTp, which is determined by the intake air amount and rotational speed of the internal combustion engine 1, using the following equation (1). It has been calculated.

T-KI XTI)XFAFXKG xf (tl, t2.-tm) 10Tv -----
--(1) Here, 1 is a constant, f (mouth, t2
...tm) means other correction coefficients related to warm-up correction etc. performed based on the cooling water temperature of the internal combustion engine 1, etc., and TV means the invalid injection time corresponding to the response time of the fuel injection valve. . Therefore, as shown in FIG. 5, when fuel increase control is continuously performed due to, for example, climbing into the sky, the air-fuel ratio of the internal combustion engine 1 is controlled as follows.

First, when the power switch in the throttle sensor 12 is turned on due to a driving request (in this case, a request for increased output due to climbing), as is clear from the flowchart in FIG. 3, the air-fuel ratio feedback control is first performed. Therefore, in the air-fuel ratio control routine (not shown), the fuel injection amount is controlled based on the output voltage of the oxygen concentration sensor 4 (high level when the air-fuel ratio is rich, low level when the air-fuel ratio is lean). Feedback control that controlled the air-fuel ratio to be the stoichiometric air-fuel ratio by increasing or decreasing the amount is discontinued, and instead, the basic fuel injection determined from the intake air amount and rotational speed of the internal combustion engine is corrected using various correction terms. Fuel increase control is performed to further increase the fuel injection amount, for example, by 20%. However, if the power switch remains on and the fuel increase control continues for more than time T1, it is assumed that there is a possibility that there is a discrepancy in the measurement of the intake air amount by the intake air amount sensor 18, and the fuel increase control is temporarily stopped. is stopped, and feedback control of the air-fuel ratio is performed until a predetermined time T2. In this embodiment, during the execution of the air-fuel ratio feedback control, the air-fuel ratio deviation is learned in the learning routine described using the flowchart of FIG. 4. Therefore, during fuel increase control,
Even if a deviation in the air-fuel ratio occurs due to a change in the density of intake air, in the air-fuel ratio feedback control that is executed after a predetermined gap, this deviation is calculated from the air-fuel ratio feedback correction coefficient FAF to the learned value KG. Since this is learned and canceled, the deviation in air-fuel ratio during fuel increase control is suppressed. As a result, the density of the intake air amount changes due to a sudden drop in atmospheric pressure, a rise in the intake air temperature, or a continuous increase in air temperature, and the amount of intake air involved in combustion is lower than the measured value, causing the air-fuel ratio of the mixture to change. The problem of the engine becoming excessively rich, which could cause the spark plug to swell or misfire, leading to an engine stall, has been satisfactorily solved.

In addition, in this embodiment, deviations in the actual air-fuel ratio due to changes in air density that occur during fuel increase control are learned using air-fuel ratio feedback control, which is basically performed as one of the air-fuel ratio controls for internal combustion engines. Corrected by value control. Therefore, instead of correcting the air-fuel ratio by measuring the altitude of the vehicle, atmospheric pressure, etc., the air-fuel ratio control method does not become complicated.

Next, a second embodiment of the present invention will be described. The air-fuel ratio control method for an internal combustion engine according to the second embodiment is mainly configured with control performed according to the flowchart shown in FIG. In this embodiment as well, calculation of the actual fuel injection amount and control of the fuel injection valve 2, etc. are performed by a well-known control routine (not shown), and the learned value control of the air-fuel ratio in the fuel injection amount control routine is performed by the first control routine. The process is executed according to the flowchart in FIG. 4 described in the embodiment. Steps 300 to 370 shown in the flowchart of FIG. 6 in the second embodiment correspond to steps 100 to 170 in the flowchart shown in FIG. 3 of the first embodiment, respectively, except for step 325. Therefore, the explanation will be omitted.

In the second embodiment, a new step 325 is inserted between steps 320 and 330, and in this step, the average value FAFA of the air-fuel and ratio feedback correction coefficients is
V is near the value 1 during air-fuel ratio feedback control (
(within ±α). The above average value FAFAV is ±α (for example ±0.02
), the judgment in step 235 is rYE.
The process becomes SJ and the process proceeds to step 340. In this case, the control is exactly the same as in the first embodiment. However, if the final judgment in step 235 is that rNOJ, that is, the average value FAFAV of the air-fuel ratio feedback correction coefficient FAF is within ±α with respect to the value 1, the process proceeds to step 33.
0 is skipped and the process moves to step 340. In this case, when performing air-fuel ratio feedback control that is performed at predetermined intervals to correct deviations in the actual air-fuel ratio while there is a request to implement fuel increase control, the actual air-fuel ratio from the stoichiometric air-fuel ratio Once the deviation has been learned, the air-fuel ratio feedback control is canceled and the fuel increase control is resumed even before the preset time T2 has elapsed. Therefore, in addition to the effects of the first embodiment, there is the effect that the request for increased output and appropriate control of the air-fuel ratio can be efficiently balanced.

In these embodiments, a Karman vortex type intake air amount sensor is used to detect the amount of intake air, but the present invention can be similarly applied to a vane type intake air amount sensor such as an air flow meter. Further, in the above-described embodiment, the driving request is determined by the state of the power switch of the throttle sensor 12, but it may be configured to be detected using an accelerator sensor or the like.

Although some embodiments of the present invention have been described above, the present invention is not limited to these embodiments in any way, and can be implemented in various forms without departing from the gist of the present invention. Of course.

[Effects of the Invention] As detailed above, the air-fuel ratio control method for an internal combustion engine of the present invention changes the air-fuel ratio to a target air-fuel ratio smaller than the stoichiometric air-fuel ratio instead of feedback control of the air-fuel ratio in response to operational requirements. When fuel increase control is performed and this fuel increase control continues for a predetermined time, the fuel increase control is stopped for a predetermined time and air-fuel ratio feedback control is performed to adjust the air-fuel ratio that occurred during the fuel increase control. The system is configured to learn the deviation and correct the actual air-fuel ratio during execution of the fuel increase control toward the target air-fuel ratio.

Therefore, even if fuel increase control is continuously performed due to operational demands, feedback control of the air-fuel ratio is performed at predetermined intervals to learn air-fuel ratio deviations caused by changes in intake air density. This provides an excellent effect in that the air-fuel ratio can be maintained at an appropriate level even during continuous execution of fuel increase control without performing detailed altitude measurements.

As a result, the problem of deviation in the air-fuel ratio due to the deviation in the measurement of the amount of intake air that occurs when the density of the intake air decreases while the fuel increase control is continued like a continuous zero, that is, The problem of an excessively rich air-fuel ratio that could cause spark plug smoldering or engine stalling has been fully resolved. This effect is particularly noticeable when using a Karman vortex type intake air amount sensor in which changes in air density are directly reflected in the accuracy of the measurement of the intake air amount.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the basic configuration of the present invention, FIG. 2 is a schematic configuration diagram showing an example of an internal combustion engine and its peripheral devices to which the air-fuel ratio control method for an internal combustion engine of the present invention is applied, and FIG.
Figure 4 is a flowchart showing the first embodiment of the present invention, Figure 4 is a flowchart showing an example of learned value control executed as part of the air-fuel ratio control routine, and Figure 5 is an explanatory diagram showing an example of air-fuel ratio control. , FIG. 6 is a flowchart showing a second embodiment of the present invention, and FIG. 7 is a graph showing a state of excess fuel caused by a deviation in intake air amount measurement. 1... Internal combustion engine 2... Fuel injection valve 4... Oxygen concentration sensor 6... Electronic control circuit 10... Throttle valve 18... Intake air amount sensor 60... CPU

Claims (1)

[Claims] 1. The fuel supply amount is feedback-controlled based on the exhaust composition of the internal combustion engine so that the air-fuel ratio of the mixture of fuel and intake air supplied to the internal combustion engine becomes the stoichiometric air-fuel ratio. , an air-fuel ratio control method for an internal combustion engine, which performs fuel increase control in which the feedback control is stopped and fuel is increased when there is an operational requirement, in order to set the air-fuel ratio of the air-fuel mixture to a target air-fuel ratio that is smaller than the stoichiometric air-fuel ratio. When the fuel increase control continues for a predetermined time, the fuel increase control is stopped for a predetermined time and the feedback control is performed to learn the deviation of the actual air-fuel ratio from the stoichiometric air-fuel ratio that occurred during the execution of the fuel increase control. An air-fuel ratio control method for an internal combustion engine, comprising: correcting the actual air-fuel ratio during fuel increase control to be performed thereafter toward the target air-fuel ratio. 2. The air-fuel ratio control of an internal combustion engine according to claim 1, wherein the feedback control performed after stopping the fuel increase control is performed for a period of time until the feedback control finishes learning the air-fuel ratio deviation that occurred during the execution of the fuel increase control. Method.