JP3050030B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for an internal combustion engine provided with a device for treating fuel vapor generated from a fuel tank or the like, and more particularly to a fuel vapor purge state from a purge state or a purge state to a purge state. The present invention relates to a technique for mitigating air-fuel ratio fluctuations at the time of switching to the mode.

[0002]

2. Description of the Related Art Conventionally, fuel vapor generated from a fuel tank or the like of an internal combustion engine is temporarily adsorbed by an adsorbing means (such as a canister filled with an adsorbent), and the adsorbed fuel vapor is absorbed under predetermined engine operating conditions. Some include a fuel vapor processing device that mixes with purge air and purges it into an intake system of an engine for processing.

On the other hand, in an internal combustion engine equipped with an electronically controlled fuel injection device, an air-fuel ratio is detected and a target air-fuel ratio (the stoichiometric air-fuel ratio) is detected.
In order to suppress the air-fuel ratio fluctuation during the transition, the feedback correction amount during the feedback control is averaged to obtain a learning value, and the learning value is used to calculate the base air-fuel ratio to the target air-fuel ratio. It is common practice to set it near.

In the internal combustion engine equipped with the fuel vapor processing device, when the feedback control and learning of the air-fuel ratio are performed, the learning value differs between when the fuel vapor is purged and when the fuel vapor is not purged. When the learning value is used, the air-fuel ratio changes stepwise by switching the presence or absence of the purge. Therefore, there is a configuration in which learning is performed independently in accordance with the presence or absence of a purge, learning values are stored in separate maps, and a map for searching for a learning value is switched in accordance with switching of the purge (Japanese Patent Application Laid-Open No. 62-1987). No. 41960).

[0005]

However, in the system in which the learning value is switched in synchronization with the purge switching, immediately after switching from the purge state of the fuel vapor to the stoppage of the purge, the purge gas (fuel vapor and purge gas) is supplied to the intake system. Since the learning value increases stepwise to a value commensurate with the stoppage of the purge, the residual purge gas is continuously sucked in for a while, and as shown in FIG. However, enrichment of the air-fuel ratio during this period is not avoided, and this may affect drivability and exhaust gas purification performance.

Immediately after switching from the purging of the fuel vapor to the purge state, even if the purge gas richer than the canister is supplied into the intake pipe at the initial stage of the purge, the purge gas is diluted by the air in the intake pipe as shown in FIG. There was a delay in enrichment of the intake air-fuel ratio, and the use of a learning value corresponding to the purge state resulted in a lean state for a while, which again affected the drivability and the exhaust purification performance.

The present invention has been made in view of such a conventional problem, and suppresses a change in the air-fuel ratio at the time of switching from a purge state of fuel vapor to a purge stop state, or at the time of switching from a purge stop state to a purge state. Accordingly, it is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine in which a decrease in drivability and exhaust purification performance is suppressed.

[0008]

Accordingly, as shown in FIG. 1, in the present invention, fuel vapor is temporarily adsorbed by an adsorbing means, and the adsorbed fuel vapor is supplied to the intake system of the engine under predetermined engine operating conditions. and air-fuel ratio basic control amount setting means for setting a basic control amount of the air-fuel ratio and the fuel vapor processing apparatus for purging, based on the operating state detected by the engine operating condition detecting means, air-fuel ratio detected by the air-fuel ratio feedback control conditions Feedback correction amount setting means for setting a feedback correction amount for bringing the air-fuel ratio closer to the target value based on the air-fuel ratio detection signal from the means, and when the fuel vapor is being purged.
Bring the center value of the feedback correction amount closer to the reference value
Learning value for the purge state for purging the fuel vapor
The center of the feedback correction amount when stopped
Learning value for the purge stop state to bring the value closer to the reference value
And a air-fuel ratio control quantity setting means for setting an air-fuel ratio control amount based on the learned value setting means for setting each independently, the basic control amount and the feedback correction amount and said learned value,
The air-fuel ratio control apparatus for an internal combustion engine wherein the fuel
The steam processing unit switches from the purge state to the purge stop state
The purge state learning value and the purge
The learning for the purge state is performed based on the learning value for the stop state.
From the value to the learning value for the purge stop state.
The learning at the time of switching the storage state is calculated, or
The gas processing unit switches from the purge stopped state to the purge state.
The learning value for the purge state and the purge stop
The purge stop state learning value based on the stop state learning value.
From the learned value to the purge state learning value.
And a learning value switching unit configured to calculate learning at the time of the state switching .

For example, the learning value switching means switches a difference between a learning value according to the purge state and a learning value according to the purge stop, and switching of an amount which affects the air-fuel ratio by switching to the purge stop or the purge state. The learning value may be determined based on the later accumulated value. In this case, the amount that affects the air-fuel ratio by switching between the presence and absence of the purge can be an integrated value of a value corresponding to the cylinder intake air amount after the switch, the elapsed time, or the cumulative number of rotations of the engine.

[0010]

When the purge by the fuel vapor processing device is performed, the air-fuel ratio of the purge gas is generally rich with respect to the target air-fuel ratio set by the air-fuel ratio feedback control system. The feedback correction amount is reduced so that the enrichment due to the suction is offset by the decrease in the fuel supply amount, and the learning value is set to be reduced to return it to the reference value. The set learning value is smaller than the learning value at the time of stopping the purge.

Therefore, if the intake of the rich purge gas is stopped simultaneously with the switching from the purge state to the purge stop, the learned value is simultaneously switched to the value learned at the time of the purge stop and increased stepwise. Fluctuations in the air-fuel ratio are suppressed. However, immediately after switching from the purge state to the stoppage of the purge, a considerable amount of purge gas remains in the intake system, and while the purge gas continues to be sucked, the gas is enriched by an amount corresponding to the amount of suction. After the purge is stopped, the concentration of the residual purge gas gradually decreases as the residual purge gas is sucked into the cylinder.

Therefore, the learning value is gradually changed from the learning value in the purge state to the learning value according to the purge stop (the learning value set at the time of the previous purge stop) until the residual purge gas is completely sucked. By switching, it is possible to suppress a change in the air-fuel ratio due to the suction of the residual purge gas. After the learning value is switched in this way, setting of a new learning value at the time of stopping the purge is started by the learning value setting means.

Similarly, immediately after the switching from the stoppage of the purge to the purge state, the purge gas is diluted by the air-fuel mixture in the intake system immediately after the switching, and the air-fuel ratio of the air-fuel mixture sucked into the cylinder is determined by the purge gas flow rate and the intake air flow rate. Is gradually enriched until the air-fuel ratio corresponding to the ratio becomes equilibrium. Therefore, in this case, similarly, the learning value is gradually changed and switched from the learning value at the time of the purge stop to the learning value according to the purge state (the learning value set at the previous purge state) until the equilibrium state is reached. Thus, the fluctuation of the air-fuel ratio can be suppressed, and after the learning value is switched, the setting of the learning value in the new purge state is started by the learning value setting means.

The degree of richness of the residual purge gas concentration in the intake system with respect to the target air-fuel ratio immediately after the switching, or the leanness of the air-fuel ratio of the intake air-fuel mixture immediately after the purge is started, that is, when the purge is stopped, with respect to the air-fuel ratio when the purge state is balanced. The degree is proportional to the difference between the learning value before switching and the learning value after switching, and the rate of change in the degree of richness or leanness thereafter is:
Since the air-fuel ratio is determined by the cumulative value of the amount that affects the air-fuel ratio when the purge is stopped or the purge is started, the learning value is switched based on these factors in response to the change in the air-fuel ratio in the intake system after the switching to change the air-fuel ratio. Can be accurately suppressed.

The amount of residual purge gas is determined by the amount obtained by subtracting the amount sucked into the cylinder after switching from the amount immediately after switching. Here, the amount of residual purge gas taken into the cylinder each time is inversely proportional to the cumulative value of the amount of air taken into the cylinder, and therefore, after switching of the value of the cylinder intake air amount or the equivalent value of the basic fuel injection amount, etc. , The change in the residual purge gas concentration can be predicted with high accuracy. That is, by predicting the residual purge gas amount after switching together with the residual purge gas concentration immediately after switching obtained by the difference between before and after the switching of the learning value, and gradually changing the learning value accordingly, as much as possible. A highly accurate air-fuel ratio fluctuation suppression function can be obtained.

On the other hand, regarding the amount that affects the air-fuel ratio by the start of the purge, the amount of the purge gas drawn into the cylinder is considered to be proportional to the cumulative value of the amount of air drawn into the cylinder after the start of the purge. Similarly, the air-fuel ratio of the cylinder intake air-fuel mixture after the start of the purge can be predicted with high accuracy by using the accumulated value after the switching of the cylinder intake air amount equivalent value.

Although the accuracy is not as high as the value corresponding to the cylinder intake air amount, the elapsed time after switching and the cumulative number of revolutions of the engine are also parameters that can predict the change in the air-fuel ratio of the cylinder intake air-fuel mixture. By changing the learning value based on this, it is possible to suppress the air-fuel ratio fluctuation at the time of switching with high accuracy.

[0018]

Embodiments of the present invention will be described below. In FIG. 2 showing an embodiment, an air cleaner 3, an air flow meter 4 for detecting an intake air flow rate Q, a throttle for controlling an intake air flow rate Q in conjunction with an accelerator pedal (not shown) are provided in an intake passage 2 of an engine 1 from an upstream side. A valve 5 is provided with an electromagnetic fuel injection valve 6 which injects fuel controlled by a pressure regulator from a fuel pump (not shown) into a predetermined pressure by a pressure regulator for each cylinder. Further, an air-fuel ratio sensor 7 that detects an air-fuel ratio of a mixture of fuel and air supplied to the engine through detection of an oxygen concentration in exhaust gas is mounted in an exhaust passage 7 of the engine 1. In addition, a rotation speed sensor 8 for detecting an engine rotation speed N and a water temperature sensor 9 for detecting a cooling water temperature of the engine are provided as sensors for detecting an operation state of the engine 1.

The control of the fuel injection amount by the fuel injection valve 6 is performed by a control unit built in a microcomputer.
10 is to be done. On the other hand, there is provided a processing device for fuel vapor generated from a fuel tank 20 for storing fuel supplied to the engine 1. The fuel vapor processing apparatus causes an adsorbent such as activated carbon filled in the canister 21 to adsorb and collect fuel vapor of the fuel generated in the fuel tank 20,
The fuel adsorbed by the adsorbent is supplied to the intake passage 2 downstream of the throttle valve 5 via the purge control valve 22.

The fuel in the fuel tank 20 is supplied to the canister 21 through a fuel vapor passage 23 provided with a check valve (not shown) which opens when the positive pressure in the fuel tank 20 becomes higher than a predetermined pressure. Steam is introduced, and the control unit is provided in the purge passage 22.
An electromagnetically driven purge control valve 24, which is controlled to be open based on a control signal from 10, is interposed.

Hereinafter, the control by the control unit 10 will be described with reference to various means showing various functions. First, the outline of the fuel injection control will be described.The control unit 10 determines whether or not it is in an air-fuel ratio feedback control area based on signals from the sensors, and when it is determined that this is the control area. The fuel supply from the fuel injection valve 6 is controlled so that the actual air-fuel ratio matches the target air-fuel ratio. Here, the fuel injection pulse width T _i of the injection pulse output to the fuel injection valve 6 is:
It is calculated as follows. The basic injection pulse width calculation means calculates the basic injection pulse width T _P (= K · Q / N) according to the intake air flow rate Q detected by the air flow meter 3 and the engine rotation speed N detected by the rotation speed sensor 8. Is calculated. The air-fuel ratio feedback correction coefficient calculating means includes:
From the deviation between the actual air-fuel ratio detected by the air-fuel ratio sensor 9 and the target air-fuel ratio, a feedback correction coefficient (feedback correction amount) α is calculated by integral control, proportional integral control, or the like.
Learned value calculating means sets the learning value alpha _m to correct so as to approach central value of the feedback correction coefficient alpha (average value) to the reference value (e.g. 1). Specifically, for example, a value obtained by averaging the maximum value and the minimum value of the feedback correction coefficient α when the rich / lean determination result is inverted by the air-fuel ratio sensor 9 is set as the learning value. Here, the setting of the learning value is performed independently when the fuel vapor is purged and when the fuel vapor is not purged, and the obtained learning value _αmp during the purge and the learning value _αmn during the non-purge are separately stored. . The injection pulse width T _i calculating means, purging, a steady state non-purge correction amount COEF of the basic injection pulse width T _P is set based on the detected cooling water temperature and the like in the water temperature sensor 9
Is corrected by the feedback correction coefficient α and the learning value α _mp or α _mn, and further adds the invalid injection pulse width T _S to obtain the final injection pulse width T _i by the following equation. Ask.

T _i = T _P · COEF · (α + α _m ) + T _S Next, purge control in the fuel vapor processing apparatus will be described. The purge ON-OFF determination means determines whether to execute the purge based on operating conditions including the intake air flow rate Q and the engine speed N. When it is determined that the purge is to be performed, the purge control valve DUTY calculating means obtains the target purge rate (the ratio of the purge flow rate to the intake air flow rate Q) according to the engine operating state by changing the valve opening duty of the purge control valve 27. To purge the fuel vapor into the intake system.

Further, as a configuration according to the present invention, the
From the purge state by the
The final air-fuel ratio control when switched to stop
The injection pulse width T which is the quantity_iThe learning value used to set
It is calculated by the purge cut learning value calculation means. Specifically
Is the learning value α in the purge state before switching._mpFrom, after switching
According to the operating state, the setting set at the last
Learning value α remembered _mnTo change gradually
The learning value is calculated as follows.

The learning value switching operation will be described in detail with reference to the flowcharts of FIGS. Step (in the figure, described as S, the same applies hereinafter) In step 1, it is determined whether or not the engine is at the start. If it is determined that the engine has started, the learning value α _mp in the purge state, which will be described later, is replaced with a value equal to the learning value α _mn when the purge is stopped in step 2. This is when the canister starts
This is because the learning value α _mp in the previous purge state cannot be used because the amount of fuel vapor collected in 21 is unknown. The learning value α _mp in the purge state is updated with _mn as an initial value. Even when the amount of fuel vapor in the canister 21 is large, immediately after the start, the air is diluted by the air in the intake system as in the case of the start of the purge during the operation, which will be described later, and the influence of the purge gas suction to the cylinder suction air-fuel mixture occurs. Therefore, fluctuations in the air-fuel ratio can be suppressed by updating the learning value α _mn at the time of stopping the purge as an initial value. On the other hand, the learning value α _mn at the time when the purge is stopped is a learning corresponding to a variation in intake system components and a change with time irrelevant to the purge, and thus is continuously stored in the backup memory.

In step 3, it is determined whether the air-fuel ratio feedback control condition is satisfied.
Then, it is determined whether the purge is currently stopped (OFF). If it is determined that the purging is stopped, the process proceeds to step 5 and the purging is stopped (OF) from the purge state (ON).
It is determined whether or not it has just been switched to F).

If after [0026] the switching straight to reset the accumulated value T _P sum of the basic injection pulse width T _P after switching to zero in step 6, while the subsequent purge stop is determined in step 4 is continued, step advances to 7, wherein comparing the cumulative value T _P sum the set maximum value SUMMAX1, after continuing the accumulation of basic pulse width T _P proceeds to step 8 if smaller than the maximum value SUMMAX1, to step 9 Then, the learning value α _m used for setting the fuel injection amount at the time of switching the purge stop is calculated according to the following equation.

[0027] _{(α mn -α mp) · T} P sum / SUMMAX1 + α mp Namely, the learning value alpha _m is the cumulative value T _P after purge stop switching straight
from an initial value alpha _mp when the sum = 0, is switched gradually increased with increase of the cumulative value T _P sum until alpha _mn becomes accumulated value T _P sum = SUMMAX1. Here, as described above, the amount of the residual purge gas drawn into the cylinder is inversely proportional to the cumulative value of the amount of air drawn into the cylinder, and therefore, the basic injection pulse width set in proportion to the amount of air drawn into the cylinder. T accumulated value T _P sum after switching of _P represents a decrease by inhalation to the residual purge gas cylinder, T _P sum / SUMMAX1 becomes represent a decrease of the residual purge gas concentration. That is,
By increasing the learning value in accordance with the amount of decrease in the residual purge gas concentration after switching the purge stop, the learning value can be set so as to maintain the base air-fuel ratio at the target air-fuel ratio. Of the air-fuel ratio can be suppressed.
FIG. 5 shows this state.

In step 10, the air-fuel ratio feedback correction coefficient α is calculated by integral control or proportional integral control in accordance with the rich / lean detection result of the air-fuel ratio sensor 9. Thus the learned value is changed gradually, the cumulative value T _P sum is determined in step 7 reaches SUMMAX1 proceeds to step 11, after calculating the feedback correction coefficient α as well, the feedback correction coefficient in Step 12 The calculation of a new learning value α _mn is started by performing the averaging process described above for α, and the learning value of the corresponding operating region of the learning value map for non-purge is updated with the calculated learning value and stored. I do.

If it is determined in step 4 that the purging is being performed, the process proceeds to step 13 where the purging is stopped (OF).
It is determined whether or not the state has just been switched from F) to the purge state (ON). If after switching straight, the cumulative value T _P sum of the basic injection pulse width T _P after switching in step 14 is reset to zero, while the subsequent purge state is determined in step 4 is continued, the process proceeds to step 15 the comparison with the accumulated value T _P sum the set maximum value SUMMAX2, after continuing the accumulation of basic pulse width T _P proceeds to step 16, if less than the maximum value SUMMAX2, purge the program proceeds to step 17 A learning value α _m used for setting the fuel injection amount at the time of state switching is calculated according to the following equation.

(Α _mp −α _mn ) · T _P sum / SUMMAX2 + α _mn That is, the learning value α _m is the accumulated value T _P immediately after switching the purge state.
From the initial value α _mn when sum = 0, the cumulative value T _P sum = SU
MMAX2 and until alpha _mp is switched gradually decreased according to increase of the cumulative value T _P sum. That is, in this case, the amount of the purge gas sucked into the cylinder after the switching is proportional to the amount of the cylinder intake air after the switching. Therefore, the concentration of the cylinder intake air-fuel mixture gradually increases in accordance with the amount of the cylinder suction purge gas that increases after the switching. Therefore, the learning value can be set so as to maintain the base air-fuel ratio at the target air-fuel ratio by decreasing the learning value in accordance with this. Can be suppressed. FIG. 6 shows this state. In addition, the SUMMAX
The value of 1 and SUMMAX2 may be the same value, but may be set to different values.

In step 18, the air-fuel ratio feedback correction coefficient α is calculated by integral control or proportional integral control according to the result of rich / lean detection of the air-fuel ratio sensor 9. Thus the learned value is changed gradually, the cumulative value T _P sum is determined in step 16 reaches SUMMAX2 proceeds to step 19, after calculating the feedback correction coefficient α as well, the feedback correction coefficient in step 20 The calculation of a new learning value α _mn is started by performing the above-described averaging process on α, and the learning value of the corresponding operating region of the learning value map for purging is updated with the calculated learning value and stored. .

In the second embodiment, learning is performed by using the elapsed time after switching or the cumulative number of revolutions of the engine as an amount that affects the air-fuel ratio after switching from the purge state to the purge stop state or after switching from the purge stop to the purge state. The value is switched. That is, in the routine shown in FIG. 3, the use of the accumulated rotation number Nsum after switching elapsed time Tsum or engine instead of the cumulative value T _P sum of the basic injection pulse width T _P in step 7, the intake system before handover The elapsed time or the cumulative number of rotations SUMMAX, which is estimated to have no purge gas or air-fuel mixture remaining therein, is set and calculated from the same equation.

In this method, depending on the operating conditions, FIG.
As shown in FIG. 8, an opening may occur between the residual purge gas concentration in the intake system and the feedback correction coefficient.
For example, there is a case where the load is smaller than the set load, the cylinder intake air amount is small, and the residual purge gas remains even after the set elapsed time or the set cumulative number of rotations has passed, or the predetermined purge gas concentration is not balanced. . However, the present embodiment is simpler in terms of control, and if the air-fuel ratio turbulence due to the purge stop or the purge start is matched in accordance with the operating conditions that are particularly problematic, the same effect as in the first embodiment can be obtained. Can be expected.

[0034]

As described above, according to the present invention, when the fuel vapor is switched from the purge state to the purge state or from the purge state to the purge state, new learning of the air-fuel ratio according to the state after the switching is performed. Until the start, the learning value is gradually changed from the learning value corresponding to the presence / absence of the purge before switching to the learning value corresponding to the presence / absence of the purge after switching, so that the switching is performed. Fluctuations in the air-fuel ratio due to inhalation of the purge gas or air-fuel mixture remaining before the switching can be suppressed, and deterioration _in drivability at the time of switching and reduction in exhaust purification performance can be prevented.

Further, by setting the learning value at the time of switching based on the difference between the learning values before and after the switching and the cumulative value of the influence amount on the air-fuel ratio by the switching, the residual purge gas and the residual air-fuel mixture can be set. The learning value can be set in accordance with the change in the concentration, and the air-fuel ratio fluctuation suppressing effect can be enhanced. In particular, when the amount of influence of the purge switching on the air-fuel ratio is a value corresponding to the amount of intake air, the learning value can be set by accurately detecting the concentration change of the residual purge gas or the residual air-fuel mixture, and the air-fuel ratio fluctuation suppressing effect. Can be increased as much as possible. Further, when the same amount of influence is the elapsed time after switching or the cumulative number of rotations of the engine, the same effect can be obtained with simple control, although the accuracy is slightly inferior.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration and functions of the present invention.

FIG. 2 is a diagram showing a system configuration according to an embodiment of the present invention.

FIG. 3 is a flowchart showing a first stage of a first embodiment of a learning value switching routine;

FIG. 4 is a flowchart showing a latter part of the first embodiment of the learning value switching routine;

FIG. 5 is a time chart showing changes in various state quantities when switching from a purge state to a purge stop in the first embodiment.

FIG. 6 is a time chart showing changes in various state quantities at the time of switching from a purge stop to a purge state in the first embodiment.

FIG. 7 is a time chart showing changes in various state quantities when switching from a purge state to a purge stop in the second embodiment.

FIG. 8 is a time chart showing changes in various state quantities when switching from a purge stop to a purge state in the second embodiment.

FIG. 9 is a time chart showing changes in various state quantities at the time of switching from a conventional purge state to a purge stop.

FIG. 10 is a time chart showing changes in various state quantities at the time of switching from a conventional purge stop to a purge state.

[Explanation of symbols]

 Reference Signs List 1 engine 2 intake passage 4 air flow meter 6 fuel injection valve 7 air-fuel ratio sensor 8 rotation speed sensor 10 control unit 21 canister 22 purge passage 24 purge control valve

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-131843 (JP, A) JP-A-4-279755 (JP, A) JP-A-2-245458 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) F02M 25/08 301 F02D 41/02 330 F02D 41/14 310

Claims (5)

(57) [Claims] 1. A fuel vapor processing apparatus for temporarily adsorbing fuel vapor to an adsorbing means and purging the adsorbed fuel vapor to an intake system of the engine under predetermined engine operating conditions, and detecting the fuel vapor by an engine operating state detecting means. Air-fuel ratio basic control amount setting means for setting a basic control amount of the air-fuel ratio based on the operated state, and an air-fuel ratio target value based on an air-fuel ratio detection signal from the air-fuel ratio detection means under air-fuel ratio feedback control conditions. Feedback correction amount setting means for setting a feedback correction amount for approaching the fuel vapor, and the feedback correction amount when the fuel vapor is being purged.
To set the center value of the feedback correction amount close to the reference value.
The state learning value and the purge of the fuel vapor are stopped.
The center value of the feedback correction amount
And the learning value for the purge stop state to approach
A learning value setting means for setting the stand, the air-fuel ratio of an internal combustion engine equipped with a fuel ratio control quantity setting means for setting the air-fuel ratio control quantity based on the basic control amount and the feedback correction amount and said learned value In the control device, the fuel vapor processing device is in a purge stopped state from a purge state.
For a predetermined period after switching to the learning value for the purge state,
And the purge stop state learning value.
From the learning value for the purge stop state to the learning value for the purge stop state.
Is calculated when the purge state is changed, or
The fuel vapor processor goes from the purge stopped state to the purge state
For a predetermined period after the switching, the learning value for the purge state is
The purge stop is performed based on the purge stop state learning value.
Gradual change from the learning value for state to the learning value for purge state
An air-fuel ratio control device for an internal combustion engine, characterized by comprising learning value switching means for calculating learning when a purge state is switched. 2. The learning value switching means determines a learning value based on a difference between the learning values before and after the switching and a cumulative value after the switching of an amount that affects the air-fuel ratio by stopping or starting the purge. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein: 3. The method according to claim 2, wherein the amount that affects the air-fuel ratio due to the purge stop or the purge start is an integrated value of a value corresponding to the cylinder intake air amount after the purge stop or the purge start. 3. The air-fuel ratio control device for an internal combustion engine according to claim 1. 4. The air-fuel ratio control for an internal combustion engine according to claim 2, wherein the amount that affects the air-fuel ratio by the purge stop or the purge start is an elapsed time after the purge stop or the purge start. apparatus. 5. The system according to claim 2, wherein the amount of the air-fuel ratio that affects the purge stop or the purge start is the cumulative number of revolutions of the engine after the purge stop or the purge start.
3. The air-fuel ratio control device for an internal combustion engine according to claim 1.