JPH05321773A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To perform accurate learning in a specified area while maintaining sufficient purge quantity with respect to the air-fuel ratio control device for an internal combustion engine that possesses learning control function as well as an evapo-purge system. CONSTITUTION:An air-fuel ratio control device for an internal combustion engine possesses a fuel injection quantity setting means A1, an air-fuel ratio feedback control means A2, a learning control means A5 that calculates a learning value based on a vapor/air-fuel ratio correction coefficient, and also reflects this learning value to fuel injection quantity at specified time, and an evapo-purge system A4, and the learning control means A3 is composed of first correction coefficient calculating means A5 that calculates a lone-term average air-fuel ratio correction coefficient, second correction coefficient calculating means A6 that calculates a short-term average air-fuel ratio correction coefficient, and a learning value setting means A7 that calculates the difference between the long-term average air-fuel ratio correction coefficient and the short-term average air-fuel ratio correction coefficient, and also determines the learning value based on the difference determined.

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 system for an internal combustion engine, and more particularly to an air-fuel ratio control system for an internal combustion engine having an evaporative purge system and a learning control function.

[0002]

2. Description of the Related Art A canister for temporarily storing evaporated fuel is provided, an air-fuel ratio sensor is provided in an engine exhaust passage, and a fuel is provided so that the air-fuel ratio becomes a target air-fuel ratio based on an output signal of the air-fuel ratio sensor. Feedback correction coefficient (FA
Conventionally, an internal combustion engine is known which is corrected by F).

Further, for example, in the case of an internal combustion engine which uses the intake pipe pressure to detect the intake air amount, the basic fuel injection amount in one step is calculated by the surge tank internal pressure measured by the intake pipe pressure sensor and the engine speed. However, it is necessary to correct the basic injection amount map due to characteristic shifts of sensors, actuators (for example, injectors), etc. due to deterioration over time. Therefore, there is known a configuration in which the engine state is divided into regions according to the intake pipe pressure, a learning value is provided for each region, and the learning value is increased or decreased according to the deviation from the FAF reference value to absorb deterioration over time.

An example of this type of air-fuel ratio control device is the device disclosed in Japanese Utility Model Laid-Open No. 2-94339. The air-fuel ratio control device disclosed in the publication has a configuration in which a purge region is overlapped with a predetermined learning region and a learning value is calculated for each region.

[0005]

However, since the air-fuel ratio control device disclosed in the above publication is a control that is performed on the assumption that the influence of purge is constant in each region,
There is a problem that accurate learning cannot be performed when a system intentionally changes the influence of purging in a certain region or when the adsorption amount in the canister changes.

As a method of solving this problem, it is conceivable to slow down the learning update speed. In this case, although the purge influence change and the like can be excluded, on the contrary, the purge influence is grasped with good responsiveness. There is a problem that it cannot be done.

The present invention has been made in view of the above points, and compares the average values of two types of air-fuel ratio correction coefficients having different periods obtained from the air-fuel ratio correction coefficient and compares the average values with each other in a predetermined region over time. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine, which can perform accurate learning in the predetermined region while securing a sufficient purge amount by learning the influence amount.

[0008]

FIG. 1 shows the principle of the present invention.

As shown in the figure, in order to solve the above problems, in the present invention, a fuel injection amount setting means (A1) for calculating the fuel injection amount and an empty space provided in the engine exhaust passage (1) are provided. Air-fuel ratio feedback control means that calculates the air-fuel ratio correction coefficient from the detection result of the fuel ratio detection sensor (2) and controls the fuel injection amount setting means (A1) so that the air-fuel ratio becomes the target air-fuel ratio based on this air-fuel ratio correction coefficient. (A2) and a learning value based on the air-fuel ratio correction coefficient calculated by the air-fuel ratio feedback control means (A2), and the learning value is calculated at a predetermined time by the fuel injection amount setting means (A
Learning control means (A3) to reflect the fuel injection amount calculated by 1)
And an evaporative purge system (A4) for purging fuel vapor from the canister (3) that temporarily stores evaporated fuel into the intake passage (5) of the internal combustion engine (4). The learning control means (A3) calculates the long-term average air-fuel ratio correction coefficient by averaging the air-fuel ratio correction coefficient over a relatively large period, and the engine and the engine. Second correction coefficient calculating means (A6) for calculating a short-term average air-fuel ratio correction coefficient by averaging a relatively small period of the air-fuel ratio correction coefficient in each of the predetermined areas determined by the state, and the long-term average Learning value setting means (A7) for calculating the difference between the air-fuel ratio correction coefficient and the short-term average air-fuel ratio correction coefficient and for obtaining a learning value based on the obtained difference
It is characterized by being constituted by

[0010]

FIG. 2 is a diagram for explaining the operation of the present invention. FIG. 1A shows the first correction coefficient calculation means (A) based on the air-fuel ratio correction coefficient (feedback correction coefficient; hereinafter referred to as FAF) calculated by the air-fuel ratio feedback control means.
Long-term average air-fuel ratio correction coefficient (hereinafter F
AFSM) and the short-term average air-fuel ratio correction coefficient (hereinafter FAFA) obtained by the second correction coefficient calculation means (A6).
(Referred to as V). Further, FIG. 3B shows a purged state by the evaporative purge system (A4). The figure shows the case where the purge is started at time t1.

Since the fuel concentration in the air-fuel mixture rises when the purge is started, the FAF becomes small so that the air-fuel ratio becomes the stoichiometric air-fuel ratio, and accordingly FAFSM and FAF.
AV also becomes smaller. Also, evaporative purge system (A4)
Since the amount of purged fuel decreases as the purging by means of is completed, FAFSM and FAFAV behave gradually.

[0012] Here, the influence of the purge has almost no error between the regions and gradually changes over the entire region. Therefore, in order to eliminate the other influences and take the influence of the purge, FAFSM is obtained by multiplying the FAF by a large averaging (average of a relatively large period) in accordance with the change of the influence of the purge. Therefore, even if there is a factor that changes the FAF value due to deterioration over time in the predetermined region (for example, the region defined by the intake pipe pressure), the FAFSM value is greatly affected by this factor. There is no such thing, and a gentle characteristic curve as shown in the figure is drawn. That is, FAFS
M is a value that follows the influence of purging by eliminating the influence of deterioration over time.

On the other hand, FAFAV is a value obtained by averaging FAF in a relatively small period, and therefore is greatly affected by changes in FAF within a predetermined region due to deterioration over time and the like. Thus, a characteristic curve having a drastic change in the range of the above area is drawn. Therefore, F
AFAV is a value that reflects both the effects of deterioration over time and the effects of purging.

On the other hand, the learning value (hereinafter referred to as KGj) desired to be obtained by the feedback learning control is a value which does not reflect the influence of the purge. Therefore, FAFSM and FA
Considering FAV, FAFSM is a value in which the influence of deterioration over time and the like is moderated, and therefore only the influence of purge is reflected. FAFAV also reflects the influence of purging as well as the influence of deterioration over time. Therefore, by obtaining the difference between FAFSM and FAFAV, it is possible to cancel the influence of the purge, and it is possible to obtain the learning value KGj that reflects only the influence of deterioration over time.

A specific example of obtaining KGj based on the above principle will be described with reference to FIG. Now, assume that the predetermined area determined by the engine state is the area between times t2 and t3 in the figure. In this region, FAFSM, which is a value obtained by averaging a relatively large period of FAF, is indicated by arrow A in FIG.
It becomes the value shown in. Further, FAFAV, which is a value obtained by averaging FAF in a relatively small period, has a value indicated by arrow B in the figure. As described above, FAFSM is a value that reflects only the effect of purging that is not affected by deterioration over time, and FAFAV is a value that reflects both the effects of deterioration over time and the effect of purging. , The learning value KGj that reflects only the influence of deterioration over time can be obtained as FAFSM and FAFAV, and the learning value KGj becomes a value indicated by an arrow C in the figure.

The learning value KGj thus obtained
Is reflected in the fuel injection amount calculated by the fuel injection amount setting means (A1) at a predetermined time (when the engine state becomes the same as the engine state in the region) by the learning control means (A3). Since the learning value KGj learned as described above is not affected by the purge, it is possible to perform accurate learning control without erroneous learning.

[0017]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 3 is a schematic configuration diagram of an internal combustion engine (engine) 10 equipped with an air-fuel ratio control device according to an embodiment of the present invention.

In the figure, 11 is an engine body, 12 is an intake branch pipe, 13 is an exhaust manifold, and 14 is each intake branch pipe 12.
The fuel injection valve attached to each of these is shown. Each intake branch pipe 1
2 is connected to a common surge tank 15, and this surge tank 15 is connected to an air cleaner 18 via an intake duct 16. A throttle valve 19 is provided in the intake duct 16, and an intake pressure sensor 17 for measuring the pressure in the intake pipe for estimating the intake air amount is provided in the surge tank 15.
Are arranged.

The engine 10 also has an evaporative purge system 22. In the figure, 21 is a canister that constitutes the evaporation purge system 22, and this canister 2
The activated carbon 20 is built in the unit 1. Canister 21
Has a fuel vapor chamber 23a and an atmosphere chamber 23b on both sides of the activated carbon 20, respectively. The fuel vapor chamber 23 a is connected to the fuel tank 25 via the conduit 24 on the one hand, and is connected to the surge tank 15 via the conduit 26 on the other hand. A purge control valve 27, which is controlled by the output signal of the electronic control unit 30, is provided in the conduit 26.

The fuel vapor generated in the fuel tank 25 is sent into the canister 21 via the conduit 24 and adsorbed on the activated carbon 20. When the purge control valve 27 is opened, air is sent from the atmosphere chamber 23b into the conduit 26 through the activated carbon 20. When the air passes through the activated carbon 20, the fuel vapor adsorbed on the activated carbon 20 is separated from the activated carbon 20, and the air containing the fuel vapor, that is, vapor is purged into the surge tank 15 via the conduit 26.

The electronic control unit 30 is composed of a digital computer, and a ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, an input port 35 which are mutually connected by a bidirectional bus 31. , And an output port 36. The intake pressure sensor 17 provided in the surge tank 15 detects the pressure in the intake pipe, and its output signal is input to the input port 35 via the A / D converter 37.

The throttle valve 19 includes the throttle valve 19
A throttle switch 38 that is turned on when the valve is at the idling opening is attached, and an output signal of the throttle switch 38 is input to the input port 35. Engine body 11
A water temperature sensor 39 that generates an output voltage proportional to the engine cooling water temperature is attached to the engine, and the output voltage of the water temperature sensor 39 is input to the input port 35 via the A / D converter 40. An air-fuel ratio sensor (O ₂ sensor) 41 is attached to the exhaust manifold 13, and an output signal of the air-fuel ratio sensor 41 is input to the input port 35 via the A / D converter 42. Further, the input port 35 is connected to a crank angle sensor 43 that generates an output pulse each time the crankshaft rotates, for example, 30 ° CA. The CPU 34 calculates the engine speed (NE) based on this output pulse. On the other hand, the output port 36 has a corresponding drive circuit 44, 4
It is connected to the fuel injection valve 14 and the purge control valve 27 via 5.

The air-fuel ratio control device according to the present invention comprises a fuel injection amount setting means (A1), an air-fuel ratio feedback control means (A2),
Learning control means (A3), and first correction coefficient calculation means (A5) and second correction coefficient calculation means (A that compose the learning control means (A3).
6) and learning value setting means (A7), each of these constituent means is configured as a software program executed by the electronic control unit 30. Hereinafter, the air-fuel ratio control and the learning control executed by the electronic control unit 30 will be described.

FIG. 4 is a flow chart showing a learning control routine, and FIG. 5 shows FAFSM, FA for obtaining a long-term average air-fuel ratio correction coefficient (hereinafter referred to as FAFSM) and a short-term average air-fuel ratio correction coefficient (hereinafter referred to as FAFAV).
It is a flowchart which shows a FAV calculation routine. First, for convenience of description, FAFSM and FAFA will be described with reference to FIG.
A calculation routine for V will be described.

Step 10 (hereinafter, step is abbreviated as S) is a process for calculating FAFSM.
Is calculated by the following formula.

FAFSM = FAFSM + (FAF−FAFSM) / N
In the equation, FAFSM on the right side is a value calculated in the previous routine process, FAF is a feedback correction coefficient, and N is a smoothing constant. The feedback correction coefficient (hereinafter referred to as FAF) is calculated by a feedback correction coefficient calculation routine (not shown) based on the output signal supplied from the air-fuel ratio sensor 41.
34 is a value to be calculated. The latest FAF value obtained by the feedback correction coefficient calculation routine is inserted into the equation.

Now, the engine state in which FAF is required is the state in which the purge control valve 27 is opened and the vapor is purged from the canister 21 into the surge tank 15 (hereinafter, this state is referred to as the purge state). Then, since the fuel concentration with respect to the intake air amount increases, the FAF decreases the air-fuel ratio to make it the stoichiometric air-fuel ratio. That is, FAF has a value that reflects the effect of purging. Further, as described above, the engine body 11 is set in a region set by the engine state (in this embodiment, the intake pressure PW detected by the intake pressure sensor 17).
The value reflects the influence of the air-fuel ratio deviation caused by the deterioration over time, etc., which is present for each of the above.

However, as is clear from the equation, FA
FSM is the FAFSM calculated last time from this FAF.
Is subtracted and divided by the averaging constant N to obtain a value obtained by adding to the FAFSM calculated last time. That is, FAFSM is a value obtained by averaging a relatively large period of FAF. For this reason, even if there is a factor that changes the value of FAF due to deterioration over time in the above-mentioned predetermined region, the value of FAFSM is hardly affected by this factor. Therefore, as described above with reference to FIG. 2, the change in FAFSM becomes a gentle characteristic curve.

The following S12 is a process for calculating FAFAV. FAFAV is calculated by the following formula.

FAFAV = (FAF ₀ + FAF) / 2 In the above equation, FAF ₀ is the feedback correction coefficient obtained by the calculation processing of the previous feedback correction coefficient calculation routine, and FAF is the feedback correction coefficient calculation routine of this time. It is the latest feedback correction coefficient obtained by the arithmetic processing. That is, in S12, the feedback correction coefficient FA calculated respectively by the feedback correction coefficient calculation routine processing of the previous time and this time is calculated.
The arithmetic mean value of F ₀ and FAF is calculated. Therefore, FAFAV obtained by the formula is the FAF obtained in S10.
It is a value obtained by averaging the FAF in a relatively small period as compared with SM.

Now, as in the case of the FAFSM described above, F
Assuming that the engine state for which AF is required is the purged state, FAF has a value that reflects both the influence of the purge and the influence of the air-fuel ratio deviation due to deterioration over time existing in the region. Also, as is clear from the formula,
FAFAV is the feedback correction coefficient FA of the previous time and this time.
Since it is an arithmetic mean value of F ₀ and FAF, it is a value that is greatly affected by the purge, unlike FAFSM. That is, FA
The FAV is a value that largely reflects both the effect of purging and the effect of deterioration over time.

Therefore, as shown in FIG. 2, FAFAV generally exhibits characteristics corresponding to purging as in the case of FAFSM, but in each area unit, it is affected by deterioration over time, etc. Shows the characteristic of protruding vertically.

Then, the FAFS obtained as described above
A learning control routine executed by the electronic control unit 30 based on the values of M and FAFAV will be described with reference to FIG.

When the processing shown in the figure is started, first, S20
At, it is determined whether the learning execution condition is satisfied. Here, the learning execution condition is, for example, that the air-fuel ratio feedback control is being performed, that the air-fuel ratio sensor 41 is normal, and the like. If this learning execution condition is not satisfied, the learning control process after S22 is not executed and the process ends.

On the other hand, if an affirmative decision is made in S20, the processing advances to S22, in which it is decided whether or not the purge rate is zero. This determination is made based on, for example, whether the purge control valve 27 of the evaporative purge system 22 is open.
When the purge rate is zero, that is, when the purge is not performed and the influence of the barge does not affect the learned value, the learning control process at the time of the purge after S24 is not executed and the process is terminated. Has been done.

If the purge rate is not zero in S22, that is, if the purge is being executed, the process proceeds to S24, where the absolute value of (FAFSM-1.0) is 0.02.
Judge whether the value exceeds. As described in S10 of FIG. 5, since FAFSM is an average value of FAF in a relatively long period, it fluctuates around 1.0 as in FAF. Therefore, in S24, FAFSM is 1.0
The absolute value of the fluctuation value is calculated, and it is determined whether or not the fluctuation value is a predetermined value (0.02 in this embodiment) or more.

If the fluctuation value exceeds the predetermined value, the process proceeds to S26, and the purge fuel concentration coefficient FGPG per unit purge rate is calculated. This purge fuel concentration coefficient (hereinafter referred to as FGPG) is calculated by the following equation.

FGPG = FGPG + (FAFSM-1.0) / (purge rate) ... In the above equation, FGPG on the right side is the purge fuel concentration coefficient per unit purge rate calculated in the previous learning control routine, and FAFSM is the current value. FAFSM, FAF
This is calculated by the AV calculation routine (see FIG. 5). Further, the purge rate in the formula means the purge control valve 27.
Is the ratio of the purge amount determined by the opening of the intake air and the intake air estimated from the output of the intake pressure sensor 17.

This FGPG is F by the processing of S24.
The configuration is updated only when the AFSM exceeds a predetermined value (0.02 in this embodiment). Thus, F
The configuration that is updated only when the AFSM exceeds the predetermined value is that the calculated value of FAFSM may temporarily change due to the influence of disturbance or the like, and the influence of this disturbance is not reflected in FGPG. This is to guard.

As described above, the changes in FAFSM are reflected in the FGPG in a timely manner by the processing in S24 and S26. Therefore, the value of FGPG obtained from the formula based on FAFSM is a value that reflects the purged state of the evaporation purge system 22. This FGPG is a value calculated to obtain the purge correction coefficient FPB as described later, and thus the purge correction coefficient FP obtained from the FGPG.
G also has a value that reflects the purged state of the evaporation purge system 22.

At S28, first (FAFSM-FA
FAV) is calculated. This is calculated in S28 (FA
The meaning of (FSM-FAFAV) will be described using FIG. 2 again. It should be noted that similar to the above description, an explanation will be given by taking the time period between t1 and t3 as an example. FAFSM is the value indicated by arrow A in the figure. FAFAV is the value indicated by arrow B in the figure. As described above, FAFSM is a value that reflects only the effect of purging that is not affected by deterioration over time, and FAFAV is a value that reflects both the effects of deterioration over time and the effect of purging. Therefore, FAFSM and FAF
By determining the difference from AV, the effect of purging can be offset, and a value that reflects only the effect of deterioration over time, which is indicated by arrow C in the figure, can be calculated. in this way,
According to the present invention, the influence of the purge is canceled during the calculation of (FAFSM-FAFAV), so that the learning control can be performed even while the evaporative purge system 22 is performing the purge.

On the other hand, as described above (FAFSM-FAF
Since the value of (AV) reflects only the influence of deterioration over time, it is possible to use this value directly as the learning value of the period area. However, in this embodiment (FAF
The value of (SM-FAFAV) is not directly used as the learning value, but the learning value KG is obtained by the processing shown in S28 to S34.
j is updated. Hereinafter, each processing of S28 to S34 will be described.

In S28, first (FAFSM-FA
When the value of FAV) is calculated, it is subsequently determined whether or not the calculated value exceeds a predetermined value (0.02 in this embodiment). And (FAFSM-FAFAV)
If the value of exceeds the predetermined value, the process proceeds to S30, the learning value KGj is calculated based on the following equation, and the learning value KGj of the region corresponding to the current engine state is updated.

KGj = KGj-0.02 ... On the other hand, if the value of (FAFSM-FAFAV) is less than or equal to the predetermined value, the process proceeds to S32, where (FAFSM-
It is determined whether the value of (FAFAV) is less than -0.02. And the value of (FAFSM-FAFAV) is -0.
If it is less than 02, the process proceeds to S34, where the learning value K
Gj is calculated based on the following formula, and the learning value KGj of the region corresponding to the current engine state is updated.

KGj = KGj + 0.02 The value of (FAFSM-FAFAV) is -0.02 in S32.
If determined to be the above, the learning control routine process ends without updating the learning value KGj.

KG on the right side of the above equations and equations
j is a learning value set at the time of the previous update.
Further, the storage area of the learning value KGj is constituted by a plurality of areas defined by, for example, the intake pipe pressure PW, as shown in FIG. 7. Then, the above-mentioned update processing is executed for each area. For example, if the value of the intake pipe pressure PW during execution of the learning control routine shown in FIG. 4 is within the region PW ₃ , this region P
The learning value KGj ₃ stored in W ₃ is updated.

Returning to FIG. 4 again, description will be made. S28 mentioned above
The process of S34 to S34 is summarized as follows.

(1) When FAFSM-FAFAV> 0.02 → Update learning value KGj to (KGj-0.02) (2) When FAFSM-FAFAV <-0.02 → Learning value KG
j is updated to (KGj + 0.02) (3) When -0.02 ≤ FAFSM-FAFAV ≤ 0.02 → Learning value KGj is not updated, as shown in (3) above, -0.02 ≤ FAFSM-FA.
If FAV ≦ 0.02, the learning value KGj is not updated. In this way, when the value of (FAFSM-FAFAV) is in the above range, the updating process is not performed, because the change of (FAFSM-FAFAV) in the above range is caused by the disturbance included in the value of FAFSM or FAFAV. This is because it is almost always caused. When such an error value due to disturbance is reflected in the learning value KGj, there is a possibility that accurate air-fuel ratio control may not be performed. Therefore, by providing the guard of the above (3), highly accurate learning control that is not affected by disturbance or the like becomes possible.

In this embodiment, (FAFSM-FAF
If the value of (AV) is greater than the error range (that is, in the case of (1) and (2) above), (FAFSM-FAFA
The value itself of (V) is not used as the learning value KGj, but (FA
When the value of (FSM-FAFAV) is equal to or greater than a predetermined value, the learning value KGj stored at the time of the previous update is set to the learning value KGj.
Only 0.02 is subtracted, and when the value of (FAFSM-FAFAV) becomes equal to or less than the predetermined value, the learning value KGj stored at the time of the previous update is added by 0.02.
That is, in the present embodiment, the learning value KGj changes slowly at the time of updating.

As described above, the configuration in which the learning value KGj changes slowly at the time of updating is (FAFSM
This is to prevent the sudden change from affecting the engine state when the value of (FAFAV) suddenly changes and greatly differs from the learning value KGj stored at the time of the previous update. Therefore, the stable engine state can be maintained even during the purging, and the driver's viability can be improved. Further, as described above, the influence of the purge is canceled during the calculation of (FAFSM-FAFAV) performed in S28, so that the learning control can be performed even during the purging, and therefore the learning control is executed. Since it is not necessary to stop the purging, the purging amount can be increased.

FIG. 6 shows the learning value KG obtained as described above.
9 shows a TAU correction routine for correcting the fuel injection amount TAU with j and the purge correction coefficient FPB. In S30 shown in the figure, based on the purge fuel concentration coefficient FGPG per unit purge rate obtained in S26 of FIG.
The purge correction coefficient FPG is calculated by the following equation.

FPG = 1 + (FGPG-1) * (purge rate) ... In S32, the fuel injection amount TAU that has undergone another correction (for example, warm-up increase correction, acceleration increase correction, etc.) is compared with FIG. Is corrected by the learning value KGj obtained by executing the learning control routine shown in (4) and the purge correction coefficient FPG obtained by the above equation, and finally the fuel injection amount for driving the fuel injection valve 14 is performed. TAU 'is calculated. The learning value KGj for correcting the fuel injection amount TAU in S34 is a value that is not affected by the purge, that is, only the effect due to deterioration over time that is desired to be taken in as a learning value is reflected. Therefore, the air-fuel ratio of the engine 10 can always be set to the optimum state even if there is deterioration over time.

In the above-mentioned embodiment, the value shown as the predetermined value (value of 0.02) is just an example, and the present invention is not limited to this.

In this embodiment, the intake pressure sensor is used as a means for calculating the intake air amount, and the intake air amount is estimated from the output of the intake pressure sensor. It goes without saying that the present invention can be applied to an engine configured to measure the quantity value by other means (for example, an air flow meter, a Karman vortex flowmeter, etc.).

[0055]

As described above, according to the present invention, the FAFSM, which is a value that reflects only the effect of purging that has been dampened by the effect of deterioration over time, and the effect of deterioration over time and the effect of purging are both. The effect of the purge can be offset by obtaining the difference from FAFAV, which is the reflected value, so that the subtracted value reflects only the effect of deterioration over time, that is, the value that does not reflect the effect of the purge. Therefore, learning control can be performed even during purging, the purging amount can be increased, and the influence of purging is not reflected.
Since the learning value is obtained from the difference between AFSM and FAFAV, the learning value is an accurate value that reflects only the deterioration over time of the engine, etc., and has the advantage that the accuracy of the air-fuel ratio control that is executed can be improved. ..

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a view for explaining the operation of the present invention.

FIG. 3 is a schematic configuration diagram of an engine equipped with an air-fuel ratio control device according to an embodiment of the present invention.

FIG. 4 is a flowchart showing a learning control routine.

FIG. 5 is a flowchart showing a calculation routine of FAFSM and FAFAV.

FIG. 6 is a flowchart showing a TAU correction routine.

FIG. 7 is a diagram showing a storage area for learning values.

[Explanation of symbols]

10 Engine 11 Engine Main Body 12 Intake Branch Pipe 13 Exhaust Manifold 14 Fuel Injection Valve 17 Intake Pressure Sensor 19 Throttle Valve 20 Activated Carbon 21 Canister 22 Evaporative Purge System 23a Fuel Vapor Chamber 23b Atmosphere Chamber 24, 26 Conduit 25 Fuel Tank 27 Purge Control Valve 30 Electronic control unit 38 Throttle switch 39 Water temperature sensor 41 Air-fuel ratio sensor (O ₂ sensor) 43 Crank angle sensor

Claims (1)

[Claims] 1. A fuel injection amount setting means for calculating a fuel injection amount, and an air-fuel ratio correction coefficient is calculated from a detection result of an air-fuel ratio detection sensor arranged in an engine exhaust passage, and an air-fuel ratio correction coefficient is calculated based on the air-fuel ratio correction coefficient. Air-fuel ratio feedback control means for controlling the fuel injection amount setting means so that the fuel ratio becomes the target air-fuel ratio, and a learning value is calculated based on the air-fuel ratio correction coefficient calculated by the air-fuel ratio feedback control means, and the learning value is calculated. A learning control means for reflecting the fuel injection amount calculated by the fuel injection amount setting means at a predetermined time, and an evaporative purge system for purging the fuel vapor from the canister that temporarily stores the evaporated fuel into the intake passage of the internal combustion engine. An air-fuel ratio control device for an internal combustion engine, comprising: a learning control means for calculating a long-term average air-fuel ratio correction coefficient by averaging a relatively large period of the air-fuel ratio correction coefficient. And a second correction coefficient calculating means for calculating a short-term average air-fuel ratio correction coefficient by averaging a relatively small period of the air-fuel ratio correction coefficient in each of predetermined regions determined by the engine state. And a learning value setting means for calculating a difference between the long-term average air-fuel ratio correction coefficient and the short-term average air-fuel ratio correction coefficient and for obtaining a learning value based on the obtained difference. An air-fuel ratio control device for an internal combustion engine.