JPH10110645A - Air-fuel ratio control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To converge an air-fuel ratio to be a theoretical one before completion of warming-up of an engine and immediately after starting air-fuel ratio feedback controlling even under individual differences or temporal deterioration of engines. SOLUTION: A learned value of a reference air-fuel ratio is stored in a memory 22 at the starting time of air-fuel ratio feedback controlling. A value which is obtained by correcting the reference air-fuel ratio by the use of the learned value is set as a target air-fuel ratio at the starting time of air-fuel ratio feedback controlling by setting means 23. An air-fuel ratio feedback correction rate α is so computed by means of computing means 25 based on an output of air-fuel ratio sensing means that an actual air-fuel ratio is agreed with a theoretical one when the air-fuel ratio feedback controlling condition is effected before completion of warming up of starting-up of the engine. Air-fuel ratio feedback controlling means 26 performs its controlling through correction of the target air-fuel ratio by the use of the correction rate α. The learned value is updated by learned value updating means 27 based on the air-fuel ratio feedback correction rate after starting the feedback controlling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an air-fuel ratio control device for an engine.

[0002]

2. Description of the Related Art In a three-way catalyst provided in an exhaust pipe, when the air-fuel ratio of the exhaust gas is near the stoichiometric air-fuel ratio, CO, HC and NOx, which are harmful three components in the exhaust gas, are reduced to CO ₂ , H ₂ O, N _2. since can be converted into harmless components of equal (i.e. CO, performs the reduction of the oxidized and NOx in HC), O ₂ of the air-fuel ratio is provided in the exhaust pipe as swings narrow range (window) around the stoichiometric air-fuel ratio Feedback control of the air-fuel ratio is performed based on the sensor output (see Japanese Patent Application Laid-Open No. 58-25533).

[0003]

During a cold start in which the engine becomes unstable, the post-start increase correction coefficient KA is used.
The fuel is increased by S and the water temperature increase correction coefficient KTW, and the engine is stabilized by setting the air-fuel ratio to a value richer than the stoichiometric air-fuel ratio. Here, KAS is a value that decreases at a constant rate over time after starting with a value corresponding to the cooling water temperature at the time of starting as an initial value and becomes 0, and KTW is a value that increases as the cooling water temperature decreases. FIG. 21 shows an example of the fuel increase correction at the time of the cold start. The start injection pulse width TIST is set so that the fuel injection amount at the start is slightly larger than the normal injection amount.
Then, the fuel increase by KAS and the fuel increase by KTW are added to the basic injection pulse width Tp. Note that, for simplicity, the figure shows a case where the idle state is maintained after cranking (Tp is constant at this time).

At the time of a cold start in which such fuel increase is performed, the above-described air-fuel ratio feedback control has been conventionally stopped. However, the three-way catalyst is utilized when the air-fuel ratio feedback control is started as soon as possible after the start. Since the area is expanded and the exhaust performance is improved, the KTW is reset to 0 (that is, the fuel increase by the KTW is stopped) when the output of the O ₂ sensor is activated even during the fuel increase by the KTW. It is conceivable to start the air-fuel ratio feedback control.

[0005] However, as shown in FIG.
By stopping the fuel increase by W, the actual air-fuel ratio (see the second-stage solid line) changes from the rich side to the lean side at once. Since the change of the air-fuel ratio to the lean side appears in the output of the O ₂ sensor, the air-fuel ratio feedback correction coefficient α (see the lowermost stage) is integrated by IL to return the air-fuel ratio to the stoichiometric air-fuel ratio together with the start of the air-fuel ratio feedback control. The actual air-fuel ratio remains largely lean until α catches up (that is, until the actual air-fuel ratio returns to near the stoichiometric air-fuel ratio), and engine stability and drivability are improved. Deteriorate.

Referring to FIG. 11, the point that the actual air-fuel ratio becomes lean when the fuel increase by KTW is stopped before the engine warm-up is completed will be described in detail with reference to FIG. Is a characteristic under a constant temperature condition lower than the temperature (for example, 80 ° C. or higher). After completion of the warm-up of the engine, a constant K of the following equation (1) is set so that the base air-fuel ratio (air-fuel ratio determined by Tp) becomes the stoichiometric air-fuel ratio. since during (engine cold) comes to the lean side from the stoichiometric air-fuel ratio not base air-fuel ratio for unburnt increase is the stoichiometric air-fuel ratio than after completion of warming up, sigma _Pi (shown engine cold The average effective pressure Pi fluctuation rate) and Pi surge (3-7 Hz, which is the frequency band in which humans feel most uncomfortable from the indicated average effective pressure)
KTW must be adapted so that the air-fuel ratio satisfies the stability of the engine when viewed from the point of view of the extracted KTW. Therefore, if KTW is reset to 0 before the completion of engine warm-up, the air-fuel ratio is immediately increased to the base air-fuel ratio (at this time, leaner than the stoichiometric air-fuel ratio).

Here, the unburned portion is a portion of the fuel that does not contribute to the combustion. For example, a portion of the fuel that flows into the crankcase from the piston ring and dissolves in the oil, a portion of the fuel that is discharged as HC without burning as it is, and a cylinder. There is fuel etc. attached to the wall. Also, Pi changes (variation) as the air-fuel ratio becomes leaner, and σ _Pi and Pi surge increase.

[0008] In practice, the air-fuel ratio the fuel increase rate due KTW when starting the feedback control at the timing of the O ₂ activation of the sensor in the engine that are currently marketed are only a far, activation of the O ₂ sensor Even if KTW is reset to 0 at the timing of, the deviation from the stoichiometric air-fuel ratio to the lean side is small. However, when there is a request to further accelerate the start of the air-fuel ratio feedback control by, for example, actively heating the O ₂ sensor with a large-capacity electric heater, the air-fuel ratio when the fuel increase by KTW is stopped is reduced. The degree of leaning also increases, and engine stability and drivability deteriorate.

Therefore, at the timing when the air-fuel ratio feedback control condition is satisfied before the warm-up of the engine is completed, the conventional KT
The fuel increase due to W is stopped and the air-fuel ratio feedback control is started, and the fuel increase corresponding to the increase in the unburned portion from the timing to the completion of warm-up of the engine is newly performed. A device has been proposed that prevents the engine stability and drivability from being deteriorated even when the air-fuel ratio feedback control is started earlier than before (see Japanese Patent Application No. 8-173803). This device is hereinafter referred to as a prior application device. Specifically, the target air-fuel ratio at the start of the air-fuel ratio feedback control before the completion of the warm-up of the engine is determined by the newly introduced unburned fuel amount increase correction coefficient KUB (described later). The unburned fuel amount increase correction coefficient KUB is adapted so that the air-fuel ratio at the start of the air-fuel ratio feedback control becomes the stoichiometric air-fuel ratio.

Note that both the prior application and the present invention cover only the start of the air-fuel ratio feedback control before the completion of the warm-up of the engine (therefore, the present invention does not cover the start of the air-fuel ratio feedback control after the completion of the warm-up of the engine). )
Therefore, hereinafter, when the air-fuel ratio feedback control is started, it is always the time when the air-fuel ratio feedback control is started before the warm-up of the engine is completed.

However, the unburned fuel increase correction coefficient KUB
Required for the same model of engine will vary due to individual differences between the engines, and initially the unburned fuel increase coefficient KUB
However, since the required value for the unburned fuel amount increase correction coefficient KUB deviates from the compatible value due to the deterioration of the engine with time, even if the required value for If the required value of the unburned fuel increase coefficient becomes less than the required value due to the deviation from the required value due to the deterioration of the engine over time, the air-fuel ratio temporarily leans again immediately after the start of the air-fuel ratio feedback control. Conversely, when the value of the unburned fuel increase coefficient exceeds the required value, a temporary enrichment of the air-fuel ratio occurs immediately after the start of the air-fuel ratio feedback control.

Therefore, the present invention introduces a learning value for the basic air-fuel ratio at the start of the air-fuel ratio feedback control, and sets a value obtained by correcting the basic air-fuel ratio with the learning value as a target air-fuel ratio at the start of the air-fuel ratio feedback control. At the same time, the learning value is updated based on the air-fuel ratio feedback correction coefficient α after the start of the air-fuel ratio feedback control, and the learned value is held, so that the required value for the basic air-fuel ratio at the start of the air-fuel ratio feedback control is set to the engine value. The purpose is to converge the air-fuel ratio to the stoichiometric air-fuel ratio immediately after the start of the air-fuel ratio feedback control even if there is variation due to individual differences of the engine or deviation from the required value due to the aging of the engine. .

[0013]

In the first invention, FIG.
As shown in FIG. 5, means 21 for setting a basic air-fuel ratio at the start of the air-fuel ratio feedback control, a memory 22 for storing a learning value for the basic air-fuel ratio, and a value obtained by correcting the basic air-fuel ratio with the learning value Means 23 for setting as a target air-fuel ratio at the start of fuel ratio feedback control, Means 24 for determining whether an air-fuel ratio feedback control condition is satisfied before completion of engine warm-up, and Means 25 for calculating the air-fuel ratio feedback correction amount α based on the output of the air-fuel ratio detection means so that the actual air-fuel ratio becomes the stoichiometric air-fuel ratio when the air-fuel ratio feedback control condition is satisfied. Means 26 for performing feedback control of the air-fuel ratio by correcting the target air-fuel ratio; Means 27 for updating the learning value based on the air-fuel ratio feedback correction amount α after the start.

According to a second aspect, in the first aspect, means 21 for setting the basic air-fuel ratio as shown in FIG.
Means 31 for calculating a basic injection amount Tp for obtaining a stoichiometric air-fuel ratio after completion of warming-up of the engine in accordance with operating conditions; and increasing correction so that the actual air-fuel ratio becomes the stoichiometric air-fuel ratio before completion of warming-up of the engine. It comprises means 32 for calculating the amount KUB, and means 33 for correcting the basic injection amount Tp with the increase correction amount KUB.

In the third invention, as shown in FIG. 25, means 31 for calculating a basic injection amount Tp at which a stoichiometric air-fuel ratio can be obtained according to operating conditions after completion of engine warm-up, Means 32 for calculating the increase correction amount KUB so that the actual air-fuel ratio becomes the stoichiometric air-fuel ratio, a memory 41 for storing a learning value for the increase correction amount, and means for correcting the increase correction amount KUB with the learning value. 42, means 24 for determining whether or not the air-fuel ratio feedback control condition is satisfied before the completion of engine warm-up. Based on the determination result, the actual air-fuel ratio is determined when the air-fuel ratio feedback control condition is satisfied before the completion of engine warm-up. Means 25 for calculating the air-fuel ratio feedback correction amount α based on the output of the air-fuel ratio detection means so as to obtain the stoichiometric air-fuel ratio; Means 43 for calculating the fuel injection amount by correcting the basic injection amount Tp with the increasing correction amount corrected by the learning value, means 44 for supplying the fuel of this injection amount to the engine, and the air-fuel ratio feedback control Means 37 for updating the learning value based on the air-fuel ratio feedback correction amount α after the start.

In a fourth aspect, in the first aspect, the learning value is a value obtained by dividing an engine temperature (for example, water temperature) region into a plurality of regions.

According to a fifth aspect of the present invention, in the second or third aspect, the learning value is a value obtained by dividing an engine temperature (for example, water temperature) region into a plurality of regions.

According to a sixth aspect, in the fourth aspect, the learning value updating means 27, 37 determines whether the engine temperature belongs to the same area or the area has been switched,
Means for sampling the maximum value and the minimum value of the air-fuel ratio feedback correction amount α in the same region when the engine temperature belongs to the same region based on the determination result; and switching when the region is switched based on the determination result. Means for updating the learning value of the area before switching based on the sum of the maximum value and the minimum value of the air-fuel ratio feedback correction amount α for the previous area.

According to a seventh aspect, in the fifth aspect, the learning value updating means 27, 37 determines whether the engine temperature belongs to the same area or the area has been switched,
Means for sampling the maximum value and the minimum value of the air-fuel ratio feedback correction amount α in the same region when the engine temperature belongs to the same region based on the determination result; and switching when the region is switched based on the determination result. Means for updating the learning value of the area before switching based on the sum of the maximum value and the minimum value of the air-fuel ratio feedback correction amount α for the previous area.

According to an eighth aspect of the present invention, in any one of the second, third, fifth and seventh aspects of the invention, the basic value K of the increase correction amount is set.
UB0 is a value that increases as the cooling water temperature TW decreases.

According to a ninth aspect, in the eighth aspect, the basic value KUB0 of the increase correction amount is corrected according to the engine load.

According to a tenth aspect, in the eighth aspect, the basic value KUB0 of the increase correction amount is corrected according to the load and the number of revolutions of the engine.

According to an eleventh aspect, in any one of the first to tenth aspects, the air-fuel ratio detecting means is O _2.
It is determined that the air-fuel ratio feedback condition is satisfied at the timing when the activation of the O ₂ sensor is completed.

In a twelfth aspect, in any one of the first to eleventh aspects, the air-fuel ratio feedback correction amount α is a sum of an integral and a proportional.

[0025]

According to the present invention, when the air-fuel ratio feedback control is started, the required value for the basic air-fuel ratio at the start of the air-fuel ratio feedback control varies due to the individual difference of the engine and the deviation from the required value due to the aging deterioration of the engine. If the appropriate value of the basic air-fuel ratio becomes less than the required value, the air-fuel ratio temporarily becomes lean immediately after the start of the air-fuel ratio feedback control. To return the lean air-fuel ratio to the stoichiometric air-fuel ratio, the air-fuel ratio feedback correction amount changes in a direction to make the air-fuel ratio rich, but until the air-fuel ratio feedback correction amount catches up (that is, the actual air-fuel ratio The actual air-fuel ratio remains large and lean until the air-fuel ratio is settled to near the stoichiometric air-fuel ratio again.

In this case, in the first aspect of the invention, the learning value is updated and held in a direction to make the air-fuel ratio rich after the start of the air-fuel ratio feedback control. The air-fuel ratio at the start of the air-fuel ratio feedback control after the current start moves toward the rich side by the amount of the update,
As a result, the air-fuel ratio at the start of the air-fuel ratio feedback control after the current start is richer than in the previous operation (that is, before learning). With this, if the air-fuel ratio becomes lean immediately after the start of the current air-fuel ratio feedback control, the learning value is updated and held in a direction for further increasing the air-fuel ratio to the rich side.

In this manner, the updating of the learning value in the direction for setting the air-fuel ratio to the rich side continues until the air-fuel ratio does not become lean immediately after the start of the air-fuel ratio feedback control, and the learning value eventually converges. After the convergence of the learning value, each time the engine is started, the stoichiometric air-fuel ratio is controlled immediately after the start of the air-fuel ratio feedback control. Adaptation of the basic air-fuel ratio at the start of the air-fuel ratio feedback control due to variations in the required value for the basic air-fuel ratio at the start of the air-fuel ratio feedback control due to individual differences of the engine and deviations from the required value due to the aging of the engine. Even if the value becomes less than the required value, the learning value compensates for the lack, and as a result, variations in the required value with respect to the basic air-fuel ratio at the start of the air-fuel ratio feedback control due to individual differences of the engine and the engine. Even if there is a deviation from the required value of the required value due to deterioration with time, the air-fuel ratio does not become lean immediately after the start of the air-fuel ratio feedback control.

Similarly, the air-fuel ratio feedback control is started due to the variation in the required value for the basic air-fuel ratio at the start of the air-fuel ratio feedback control due to the individual difference of the engine and the deviation from the required value due to the aging deterioration of the engine. When the adaptation value of the basic air-fuel ratio at the time exceeds the required value, the learning value is updated in a direction to make the air-fuel ratio lean after starting the air-fuel ratio feedback control. The air-fuel ratio does not become rich immediately after the start of the air-fuel ratio feedback control even if the required value for the air-fuel ratio varies due to individual differences between the engines and deviates from the required value due to aging of the engine. .

The required value for the basic air-fuel ratio at the start of the air-fuel ratio feedback control and the required value for the increase correction amount at the start of the air-fuel ratio feedback control differ depending on the engine temperature (for example, the required value for the increase correction amount decreases as the engine temperature decreases. Corresponding to the fourth and fifth
In each of the inventions described above, the learning value is a value for each of the engine temperature regions divided into a plurality of regions. Therefore, even if the engine temperature at the start of the air-fuel ratio feedback control is different, immediately after the start of the air-fuel ratio feedback control, The air-fuel ratio can be controlled to the stoichiometric air-fuel ratio.

In the tenth aspect, the basic value KU of the increase correction amount is set.
Since B0 is corrected according to the engine load and rotation speed,
Not only in the idling state but also in the high rotation and high load state such as when the accelerator pedal is greatly depressed, there is no excess or deficiency in the increase correction amount KUB.

According to the eleventh aspect, it is determined that the air-fuel ratio feedback condition is satisfied at the timing when the activation of the O ₂ sensor is completed.
_The exhaust performance can be further improved as the activation completion timing of the O ₂ sensor is advanced by, for example, actively heating the _two sensors.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 1 denotes an engine body, and a fuel injection valve 7 is provided in an intake passage 8 at a position downstream of a throttle valve 5, and operating conditions are controlled by an injection signal from a control unit 2. The fuel is injected and supplied into the intake air so as to attain a predetermined air-fuel ratio in accordance with the following.

A three-way catalyst 10 is provided in the exhaust passage 9. When the air-fuel ratio of the exhaust gas is near the stoichiometric air-fuel ratio, the three-way catalyst 10 converts CO, HC and NOx into CO ₂ , H
_Since it can be converted into harmless components such as ₂ O and N ₂ , the control unit 2 feeds back the air-fuel ratio based on the output of an O ₂ sensor provided in the exhaust pipe so that the air-fuel ratio swings in a narrow range around the stoichiometric air-fuel ratio. Perform control.

In the control unit 2, during a cold start in which the engine becomes unstable, the post-start increase correction coefficient K
The fuel is increased by AS and the water temperature increase correction coefficient KTW,
The engine is stabilized by setting the air-fuel ratio to a value richer than the stoichiometric air-fuel ratio. After the engine warm-up is completed (for example, when the cooling water temperature is 80 ° C. or higher), the base air-fuel ratio (Tp
The constant K in equation (1) described below is set so that the air-fuel ratio determined by the following equation (1) becomes the stoichiometric air-fuel ratio. because min is increased than after completion of engine warm-up, since the base air-fuel ratio as shown in FIG. 11 comes to the lean side from the stoichiometric air-fuel ratio does not become the stoichiometric air-fuel ratio, it has been viewed sigma _Pi and pi surge engine cold The KTW is adapted according to the cooling water temperature TW so that the air-fuel ratio satisfies the engine stability.

In order to perform such control of the fuel increase and the air-fuel ratio feedback control, the control unit 2 generates a Ref signal from the crank angle sensor 4 (every 180 ° for four cylinders, and every 120 ° for six cylinders). ) And 1 ° signal, intake air amount signal from air flow meter 6,
An air-fuel ratio (oxygen concentration) signal from the O ₂ sensor 3 installed on the upstream side of the three-way catalyst 10 in the exhaust passage 9, an engine cooling water temperature signal from the water temperature sensor 11, and the like are input.

At the time of the cold start in which the fuel increase by the KTW is performed, the air-fuel ratio feedback control has been conventionally stopped. However, it is better to enter the air-fuel ratio feedback control as soon as possible after the start to use the three-way catalyst. Since the exhausted area is expanded and the exhaust performance is improved, the O ₂ sensor is activated early by actively heating the O ₂ sensor with a large capacity electric heater, etc., and the fuel increase by KTW is performed. It is conceivable that the fuel increase by KTW is stopped and the air-fuel ratio feedback control is started at the stage when the output of the O ₂ sensor is activated even during the operation.

However, the actual air-fuel ratio is changed from the rich side to the lean side at once by stopping the fuel increase by KTW. On the other hand, when the air-fuel ratio feedback control is started, the air-fuel ratio feedback correction coefficient α is increased by the integral IL to return the lean air-fuel ratio to the stoichiometric air-fuel ratio. Until the air-fuel ratio is settled near the air-fuel ratio, the actual air-fuel ratio remains large and lean, and the engine stability and drivability deteriorate.

To cope with this, in the prior application, the fuel increase by the conventional KTW is stopped at the timing when the activation of the O ₂ sensor 3 is completed, the air-fuel ratio feedback control is started, and the O ₂ sensor 3 is activated. From the timing of completion of the shift to the completion of warm-up of the engine, a new fuel increase corresponding to the increase in unburned fuel is being performed.

The contents of the control of the prior application executed by the control unit 2 will be described with reference to the following flowchart.

FIG. 2 is a flowchart for calculating the fuel injection pulse width Ti given to the fuel injection valve.
This is executed as a 0 ms job (or a background job).

In step 1, Tp = (Qa / Ne) × K (1) where K is a constant from the intake air amount Qa from the air flow meter 6 and the engine speed Ne detected by the crank angle sensor 4. The basic injection pulse width Tp [ms] is calculated by the equation.
Here, the value of K in equation (1) is Tp after the completion of engine warm-up.
Is set so that the air-fuel ratio (base air-fuel ratio) determined by the above becomes the stoichiometric air-fuel ratio.

In step 2, the target fuel-air ratio equivalent amount TFBY
A [%] is calculated. This TFBYA calculation will be described with reference to the flowchart of FIG.

The flowchart of FIG. 3 is executed by a 10 ms job. In step 11, the post-start increase correction coefficient KA
Calculate S [%]. For example, a table having the contents shown in FIG. 4 is searched from the cooling water temperature TW to obtain an initial value KAS0.
The initial value KAS0 [%] is reduced at a fixed rate with time after starting until it becomes 0.

In step 12, the water temperature increase correction coefficient KTW
[%] And an unburned amount increase correction coefficient KUB [%] are calculated.
The calculation of KTW and KUB will be described with reference to the flowchart of FIG.

The flowchart of FIG. 5 is executed by a 10 ms job. In step 21, the air-fuel ratio feedback control condition (abbreviated as F / B condition in the figure) is determined, and specific contents for this are shown in FIG. The determination of the air-fuel ratio feedback control condition is performed by checking the contents of steps 31 to 35 in FIG. 6 one by one. When all of the items are satisfied, the air-fuel ratio feedback control is permitted. Prohibits air-fuel ratio feedback control. That is, Step 31: At the time of starting Step 32: At the time of high load Step 33: At the time of deceleration (at the time of fuel cut) Step 34: When there is an abnormality in the O ₂ sensor output Step 35: When the O ₂ sensor is in an inactive state In step 37, the air-fuel ratio feedback control is prohibited. Otherwise, the process proceeds to step 36, in which the air-fuel ratio feedback control is permitted.

Here, at the time of starting, the O ₂ sensor 3 is in a state before activation, the air-fuel ratio feedback control cannot be performed, and the engine is operated at an output air-fuel ratio (air-fuel ratio richer than the stoichiometric air-fuel ratio). that than was the air-fuel ratio feedback control at the time of a high load can not be the output air-fuel ratio, it becomes just wasted controlled even if the air-fuel ratio feedback control during deceleration performed with fuel cut, O ₂ sensor 3 If the air-fuel ratio feedback control is performed in an inactive state, an error occurs in the air-fuel ratio feedback correction coefficient α. Therefore, under these conditions, the air-fuel ratio feedback control is prohibited.

Whether or not the O ₂ sensor 3 has been activated is determined by whether or not the output of the O ₂ sensor is within a predetermined range. For example, when the air-fuel ratio feedback control is performed immediately after the cold start, the output of the O ₂ sensor is almost 2
Swinging gradually from around 50 mV, the maximum value is approximately 900 mV and the minimum value is approximately 50 mV when activation is completed.
If the upper limit RH is set slightly higher than 250 mV and the lower limit RL is set slightly lower than 250 mV, the O ₂ sensor output <RL or O ₂
When sensor output ≧ RH, it can be determined that the activation is completed.

After the air-fuel ratio feedback control condition is determined in this manner, the flow returns to FIG. 5. If the air-fuel ratio feedback control condition is not satisfied, a table having the contents shown in FIG. A map containing the contents shown in FIG. 8 is retrieved from the basic value KTW0 [%] of the water temperature increase correction coefficient and the suction negative pressure and the rotation speed Ne to obtain a load rotation correction rate R _KTW [anonymous number] of the water temperature increase correction coefficient. ,
In step 24, the water temperature increase correction coefficient KTW is calculated by the following equation: KTW = KTW0 × R _KTW (2), and in step 25, 0 is set to the unburned fuel increase correction coefficient KUB. At this time, it is the same as without KUB,
The fuel is increased by KTW in the same manner as in the prior art.

On the other hand, when the air-fuel ratio feedback control condition is satisfied, KTW is set to 0 in step 26, and in steps 27 and 28, a table containing the contents of FIG. A map containing the contents shown in FIG. 10 is retrieved from the basic value KUB0 [%] of the fuel increase correction coefficient and the suction negative pressure and the rotation speed Ne, and the load rotation correction rate _{RKUB of the} unburned fuel increase correction coefficient is calculated. ,
In step 29, the unburned fuel amount increase correction coefficient KUB is calculated according to the following equation: KUB = KUB0 × R _KUB (3)

Here, the base air-fuel ratio does not become the stoichiometric air-fuel ratio as shown in FIG. 11 when the engine is cold because the unburned portion increases after the completion of the warm-up of the engine (becomes leaner than the stoichiometric air-fuel ratio). As described above, the unburned fuel increase coefficient KUB is adapted so that the air-fuel ratio becomes the stoichiometric air-fuel ratio even when the unburned fuel increases when the engine is cold.

Specifically, first, a water temperature increase correction coefficient KTW is calculated using the load and the rotation speed as parameters. Unlike the conventional example in which the KTW is calculated using only the cooling water temperature TW as a parameter, the KTW is calculated using the load and the rotation speed as parameters also for the following reasons. The conventional KTW mainly considers the stability of the engine under idle conditions,
On the high load side, the stability was considered to be no problem in the first place, and it was suitable only for the cooling water temperature.
As shown in FIG. 1, if the suction negative pressure (that is, the engine load) is different even at the same cooling water temperature and the same rotation speed, the required value for the KTW will be different. Therefore, if the KTW is adapted so that the suction-negative pressure when the throttle valve 5 is in the fully closed position (for example, the suction-negative pressure at the point A) has an air-fuel ratio that satisfies engine stability, the same cooling water temperature and rotation Even if the throttle valve 5 is opened to a predetermined opening degree by depressing the accelerator pedal, the suction negative pressure (for example, B
KTW will be insufficient when the suction pressure at the point is reached).

Similarly, if the rotational speed is different even at the same cooling water temperature and the same suction negative pressure as shown in FIG. 12, the required value for KTW will be different. K is set so that the air-fuel ratio satisfies the engine stability at the rotation speed (for example, the rotation speed at point C).
If the TW is adapted, the accuracy of the KTW decreases at high rotation speed (for example, the rotation speed at point D) even at the same cooling water temperature and suction negative pressure. Note that the characteristics of the air-fuel ratio with respect to the rotation speed are not uniform, and there are both cases where the air-fuel ratio rises to the right (see the solid line in FIG. 12) and when the air-fuel ratio rises to the left (see the broken line in FIG. 12).

FIG. 11 shows the base air-fuel ratio and the air-fuel ratio satisfying the engine stability when the suction negative pressure is changed while the cooling water temperature and the rotation speed are kept constant when the engine is cold.
FIG. 12 shows the characteristics of the base air-fuel ratio and the air-fuel ratio satisfying the engine stability when the engine speed is changed while the cooling water temperature and the suction negative pressure are kept constant during the cold period of the engine.

Therefore, in the prior application, for example, the basic value KTW0 is adjusted after adjusting the basic value KTW0 of the water temperature increase correction coefficient by making the cooling water temperature different under the conditions of the suction negative pressure and the rotation speed at the time of idling. Even when the rotation speed deviates from the negative suction pressure at the time, the suction negative pressure and the rotation speed are changed so that the air-fuel ratio satisfies the engine stability, and the load rotation correction rate R _KTW of the water temperature increase correction coefficient is adapted. You do it.

Next, in response to the calculation of the water temperature increase correction coefficient KTW using the load and the rotation speed as parameters, the unburned fuel increase correction coefficient KU also uses the load and the rotation speed as parameters.
The reason for calculating B is as follows. As shown in FIG. 11, even if the cooling water temperature is the same and the rotation speed is the same, if the suction negative pressure is different, the required value for the KUB is different.
If the KUB is adapted so that the stoichiometric air-fuel ratio is obtained at the suction negative pressure at the point, if the suction negative pressure at the point B is obtained even at the same cooling water temperature and rotation speed, the KUB becomes insufficient, and FIG. As described above, even if the cooling water temperature is the same and the suction negative pressure is the same, the required value for the KUB is different if the rotation speed is different. Therefore, if the KUB is adapted so that the stoichiometric air-fuel ratio is obtained at the rotation speed at the point C, Even when the cooling water temperature and the suction negative pressure are the same, the accuracy of the KUB decreases at the rotation speed at the point D. Therefore, in the prior application, for example, the cooling water temperature is made different under the condition of the suction negative pressure and the rotation speed during idling. Basic value KU of fuel increase correction coefficient
Even when the basic value KUB0 is conformed and the intake negative pressure and the rotational speed deviate from each other, the intake negative pressure and the rotational speed are made different so that the stoichiometric air-fuel ratio is obtained. The load rotation correction rate R _{KUB of the above} is adapted.

[0056] Figure 8, Figure 10 R _KTW, but shows an example of R _KUB, R _KTW, since the characteristics of the R _KUB is different for each type of engine, adapted for each type of engine eventually. In FIGS. 11 and 12, point A is shown for easy viewing.
KTW and KUB are shown slightly away from points B, C and D. Therefore, it goes without saying that KUB <KTW under the same conditions of the cooling water temperature, the suction negative pressure, and the rotation speed.

The above-mentioned suction negative pressure can be obtained by searching a predetermined map from the intake air amount Qa from the air flow meter and the rotation speed Ne. The suction negative pressure can also be detected by a pressure sensor provided at the collector of the intake manifold. Also, instead of the suction negative pressure,
The basic injection pulse width Tp (or Qa) can also be used.

When the calculation of KTW and KUB is completed in this manner, the flow returns to FIG. 3, and in steps 13 and 14, the increase correction coefficient KHOT [%] and the mixture ratio allocation correction coefficient KMR [%] at the time of high water temperature are the same as in the conventional case. In step 15, the target fuel / air ratio equivalent amount TFBYA [%] is calculated by the following equation using the calculation results of the various correction coefficients: TFBYA = KAS + KTW + KUB + KHOT + KMR (4).

TFBYA in the expression (4) is a value centered on 100%. For example, when the air-fuel ratio feedback control is not established after the cold start of the engine and after the operation of the KAS is completed, the expression TFBYA = 100 + KTW is obtained by the following expression. When the air-fuel ratio feedback control is established, TFBYA = 1
TFBYA is calculated by the equation of 00 + KUB. At this time, from FIGS. 7, 8, 9 and 10, KTW,
KUB takes a certain value and TFBYA becomes a value exceeding 100%, and fuel is increased by increasing Tp.

Returning to FIG. 2 upon completion of the calculation of TFBYA, in step 3, the air-fuel ratio feedback correction coefficient α
Calculate [%]. The calculation of α will be described with reference to the flowchart of FIG. Since the fuel injection is synchronous with the Ref signal and α changes as a result of the fuel injection, FIG.
Is executed in synchronization with the Ref signal.

In step 41, it is determined whether the air-fuel ratio feedback control condition is satisfied. If the condition is not satisfied, the air-fuel ratio feedback correction coefficient α is set to 100 in step 42.
Fix (clamp) to%. As described above, the result obtained by the flow of FIG. 6 is used to determine whether the air-fuel ratio feedback control condition is satisfied.

[0062] air-fuel ratio at the time of establishment of the feedback control condition read the O ₂ sensor output OSR1 [mV] in step 43, the slice this in step 44 the level S
Compare with L [mV]. When OSR1> SL, it is determined that the air conditioner is rich, and the process proceeds to step 45, where it is determined whether the air conditioner was lean last time. As a result, if it is the last lean and this time rich, the routine proceeds to steps 46 and 47, where the air-fuel ratio feedback correction coefficient α is reduced by a proportional amount PR [%].
Steps 48 and 4 when the previous and present times are rich
The program proceeds to 9, and the amount is reduced from α by the integral IR [%]. OS
When R1 ≦ SL, the process proceeds from step 44 to step 50, and it is determined whether or not the previous time was rich. If the previous time was rich and the current time is lean, α is increased by a proportional amount PL [%] in steps 51 and 52. If the current time is lean, α is integrated IL [%] in steps 53 and 54.
Increase only. The above proportional components PR and PL and integral components IR and IL are obtained by searching a predetermined map using Ne and Tp.

When the calculation of α is completed as described above, FIG.
Returning to Step 4 of the above, Ti = (Tp + KATHOS) × (TFBYA / 100) × (α / 100) × 2 + Ts (5) where KATHOS: transient correction amount [ms] Ts: invalid injection pulse width [ms] To calculate the fuel injection pulse width Ti [ms].

Here, in the KATHOS of the formula (5), not all of the injected fuel is sucked into the cylinder, but a part of the injected fuel adheres to, for example, the intake port or the intake valve, and the response is delayed in a liquid state. The correction amount Ts taking into account the so-called fuel wall flow flowing into the cylinder, Ts is an invalid injection pulse width for taking into account the operation delay from the reception of the injection signal to the opening of the fuel injection valve 7, both of which are known. It is.

The Ti in equation (5) is transferred to the output register for driving the fuel injection valve every time the Ref signal is input by another routine (not shown) synchronized with the Ref signal. Once every two revolutions of the engine, fuel injection (ie, sequential injection) is performed for each cylinder with the exhaust stroke as the injection timing.

Here, the operation of the prior application device will be described.

FIG. 14 shows changes in the actual air-fuel ratio, the air-fuel ratio feedback correction coefficient α, and the like when the cold start is performed in the prior application under the same conditions as in the conventional example shown in FIG. In addition,
KTW and KUB are values that decrease as the cooling water temperature TW increases from the start, and that also change as the load and the rotation speed change, as shown in FIG. 14 (see FIGS. 15 and 20 described later). ) Are shown as constant values for simplicity.

In the prior application, KTW is reset to 0 at the completion timing of activation of the O ₂ sensor to start the air-fuel ratio feedback control, and the fuel increase by KUB is newly performed from the timing when KTW is reset to 0. Immediately after the start of the air-fuel ratio feedback control, the actual air-fuel ratio (see the solid line at the second stage) quickly converges to near the stoichiometric air-fuel ratio. As a result, even when the air-fuel ratio feedback control is started when the engine is cold, it is possible to avoid leaning of the air-fuel ratio immediately after the start, so that the start timing of the air-fuel ratio feedback control can be advanced, Exhaust performance can be further improved.

In the prior application, the basic value KTW0 of the water temperature increase correction coefficient is determined by the correction rate R _KTW according to the load and the number of rotations.
In addition, the basic value KUB0 of the unburned fuel amount increase correction coefficient is corrected by the correction rate R _KUB according to the load and the number of rotations, so that not only the idling state but also a high rotation and a high load such as when the accelerator pedal is depressed greatly. KTW, K
There is no excess or shortage in the UB.

This concludes the description of the prior application apparatus.

The required value of the unburned fuel increase coefficient is required due to the variation of the required value for the unburned fuel increase correction coefficient KUB due to the individual difference of the engine and the deviation from the required value of the engine over time. If the air-fuel ratio becomes lean immediately after the start of the air-fuel ratio feedback control, the air-fuel ratio temporarily becomes lean. Immediately after the start, the air-fuel ratio temporarily becomes rich. As shown in FIG. 15, even if the cooling water temperature is the same, if there is an individual difference of the engine or deterioration over time, it may not always be possible to control the stoichiometric air-fuel ratio immediately after the start of the air-fuel ratio feedback control. (The case where the air-fuel ratio leans to the lean side is shown by a solid line, and the case where the air-fuel ratio leans to the rich side is shown by a broken line).

To cope with this, the present invention introduces a learning value for the unburned fuel increase correction coefficient KUB which determines the air-fuel ratio at the start of the air-fuel ratio feedback control, and corrects the learning value with the unburned fuel increase correction coefficient. The target air-fuel ratio at the start of the air-fuel ratio feedback control is determined based on the obtained value, and the learning value is updated based on the air-fuel ratio feedback correction coefficient α after the start of the air-fuel ratio feedback control, and the learned value is held.

Specifically, of the flowcharts of FIGS. 2, 3, 5, 6, and 13 for the prior application device, only the flowchart of FIG. 5 is changed to the flowchart of FIG. 16, and the flowchart of FIG. It is newly provided. In FIG. 16, the same steps as those in FIG. 5 are denoted by the same step numbers.

First, referring to FIG. 16, only steps 61 and 62 are different from FIG. In step 61, a predetermined table is searched from the cooling water temperature TW, and a learning value LR for the basic value KUB0 [%] of the unburned fuel amount increase correction coefficient is retrieved.
Determine NTW [%]. FIG. 17 shows a table of the learning values LRNTW, and the lowest temperature TW1 (for example, −40 ° C.)
To the maximum temperature TWn (for example, 80 ° C.) are divided into a total of n−1 areas every 10 ° C., and independent values are stored for each temperature area. Therefore, in step 61,
The learning value of the area to which the cooling water temperature TW belongs at that time is read. The learning value is stored in the backup RAM. In FIG. 17, numbers from 1 to n-1 are assigned to each area to distinguish each area.

Here, the temperature region is divided into a plurality of regions, and the learning value LRNTW for each region is used as the basic value KUB0 of the unburned fuel amount increase correction coefficient is a value corresponding to the cooling water temperature. It is a combination.

In step 62, the unburned portion correction coefficient KUB [%] is calculated using the learned value LRNTW by the following equation: KUB = (KUB0 + LRNTW-100) × R _KUB (6) That is, in the prior application, the air-fuel ratio at the start of the air-fuel ratio feedback control is determined only by the unburned portion correction coefficient, but in the present invention, the air-fuel ratio feedback control is started by the unburned portion correction coefficient corrected by the learning value. The air-fuel ratio at the time is determined.

FIG. 18 is a flowchart showing the learning value LRNT.
This is for updating W, and is executed by a 10 ms job independently of FIGS.

In step 71, it is determined whether the air-fuel ratio feedback control is being performed. If the air-fuel ratio feedback control is being performed, the cooling water temperature TW is read in steps 72 and 73, and the area in the learning value table where the cooling water temperature TW is located is searched. , The number of the area is stored in the memory k. That is,
The number of the area to which the cooling water temperature at the start of the air-fuel ratio feedback control is stored in the memory k.

In step 74, the initial flag (initial setting to "0" at startup) is checked. Step 74 for the first time after starting
Proceeds to step 75 from the initial flag = 0, sets "1" in the initial flag, and proceeds to step 76 and thereafter.

Steps 76 to 80 sample the maximum value and the minimum value of the air-fuel ratio feedback correction coefficient α while the cooling water temperature TW is in the same region. In step 76, α (obtained by the flow of FIG. 13) is read, and the value of α and the value of the memory AMAX (the initial value is 100
%) In step 77, and when α> AMAX, the flow advances to step 78 to move the value of α to the memory AMAX. Similarly, in step 79, the value of α and the memory AMI
The value of N (initial value is 100%) is compared, and when α <AMIN, the routine proceeds to step 80, where the value of α is transferred to the memory AMIN.

In step 81, the value of the memory k is transferred to the memory kOLD for the next control, and the current control is terminated.

From the next control, since the initial flag is 1 in step 74, the flow advances to step 82 to compare the values stored in the memory k and the memory kOLD. Here, since the memory kOLD contains the number of the area to which the cooling water temperature TW belonged one control cycle before (10 ms before), when the values of the memory k and the memory kOLD match, the cooling water temperature TW is increased. Since it can be determined that it is in the same area as the previous time, the operations of steps 76 to 81 are executed.

While repeating the comparison of the values of memory k and memory kOLD, memory AMAX and memory AMIN
Stores the maximum value and the minimum value of α while the cooling water temperature TW is in the same area.

When the values of the memory k and the memory kOLD no longer match due to the rise of the cooling water temperature, the cooling water temperature T
Since it can be determined that W has moved to an area different from the previous time, the process proceeds from step 82 to step 83 at that timing, and the values of the memory AMAX and the memory AMIN (steps 77 and 7)
DALP = (AMAX + AMIN) / 2-100 (7) Using the equation of (7), the shift amount DA of α from the control center (100%)
LP [%] is obtained, and the learning value of the area to which the cooling water temperature TW last belonged in step 84 from this DALP is LRNTW (new) = LRNTW (old) + KLRN × DALP (8) where LRNTW (new): updated Later learning value LRNTW (old): Learning value before updating KLRN: Update rate (constant) The updated learning value is stored in the area to which the cooling water temperature TW last belonged. Note that the initial value of the learning value is 100%.

In step 85, in order to sample the maximum and minimum values of the air-fuel ratio feedback correction coefficient α again in the shifted area, the memories AMAX and AMIN are reset to 100% of the initial values, and the operations in steps 76 to 81 are performed. Run.

Here, the operation of the present invention will be described with reference to FIGS.

Before learning, since the learning value LRNTW is 100% of the initial value, the above equation (6) is given by KUB = (KUB0 + 100−100) × R _KUB = KUB0 × R _KUB , and Same as case. Here, for the sake of simplicity, it is assumed that R _KUB (correction rate according to load and rotation speed) is a constant value.

Now, the basic value KUB of the unburned fuel amount increase correction coefficient will be described.
When the conforming value of KUB0 is less than the required value due to the variation of the required value with respect to 0 due to the individual difference of the engine or the deviation from the required value due to the aging of the engine, the air-fuel ratio feedback control as shown in FIG. Immediately after the start of the operation, the air-fuel ratio temporarily becomes lean. KUB0 is a value that determines the target air-fuel ratio at the start of the air-fuel ratio feedback control (accurately, the target air-fuel ratio is determined by Tp × (100 + KUB0)). Due to this shortage of KUB0, the air-fuel ratio becomes lean immediately after the start of the air-fuel ratio feedback control. In order to return the air-fuel ratio to the stoichiometric air-fuel ratio, the air-fuel ratio feedback correction coefficient α changes to a side that becomes larger by the integral IL, but until α catches up (that is, the actual air-fuel ratio returns to near the stoichiometric air-fuel ratio again). Until it calms down), the actual air-fuel ratio remains large and lean.

In this case, the cooling water temperature TW was in the region 4 at the timing t1 at the start of the air-fuel ratio feedback control as shown in the figure. Considering the case where the area 5 is shifted from the area 5 to the area 6 at t3, at the timing t3 when the area 5 is shifted to the area 6, the value of α immediately after the time t2 is stored in the memory AMIN and the time t2 is stored in the memory AMAX.
Α at the timing immediately before the time t3 (t2 in the figure).
And the timing immediately after t2, and the timing of t3 and the timing immediately before t3 are substantially the same.) At this time, since the values of the memory AMAX and the memory AMIN both exceed 100%, the deviation DALP from 100%, which is the control center of α, becomes a positive value, and the learning value LRNTW in the area 5 becomes 100%. % Is updated to a value that exceeds the backup R value until the next start.
It is held in AM. Similarly, the learning value of the area 4 and the area 6 is also the deviation amount DAL from the control center of α in each area.
If P is a positive value, it is updated to a value exceeding 100%.

At the next start, if the condition of the cooling water temperature is the same as that at the previous start, the learning value LRNTW is updated by the update of the learning value LRNTW during the previous operation by an amount equal to or greater than 100% (that is, the learning value update amount). Only), the unburned portion correction coefficient KU at the start of the air-fuel ratio feedback control after the current start
B becomes larger and the air-fuel ratio at the start of the air-fuel ratio feedback control after the current start becomes richer than that at the time of the previous operation (that is, before learning), so that the air-fuel ratio becomes lean immediately after the start of the current air-fuel ratio feedback control. The time period for conversion becomes shorter. At this time, if leaning still occurs, the learning value of the region (for example, regions 4 and 5) to which the cooling water temperature belongs during the leaning period is further updated and held.

As described above, if the cooling water temperature conditions before and after the start of the air-fuel ratio feedback control are the same each time the engine is started, the learning value is updated to the increasing side immediately after the start of the air-fuel ratio feedback control. The learning value continues until there is no longer a period in which the fuel ratio becomes lean, and the learning value converges at the timing when the period in which the lean ratio has disappeared. After the convergence of the learning value, as shown in FIG. 20, as long as the condition of the cooling water temperature at the start is the same, the control is performed to the stoichiometric air-fuel ratio immediately after the start of the air-fuel ratio feedback control. Basic value KUB0 of unburned fuel increase correction coefficient
Of the required value for KUB0 is less than the required value due to the variation of the required value due to the individual difference of the engine and the deviation from the required value due to the aging of the engine, the learning value LRNTW is not sufficient. Make up for the minute,
As a result, the air-fuel ratio can be made lean immediately after the start of the air-fuel ratio feedback control even if there is a variation in the required value for KUB0 due to the individual difference of the engine or a deviation from the required value due to the aging of the engine. Absent.

Similarly, when the required value of KUB0 becomes larger than the required value due to the variation of the required value for KUB0 due to the individual difference of the engine and the deviation from the required value due to the deterioration over time of the engine. Since the learning value is updated in the direction of setting the air-fuel ratio to the lean side, even if there is a variation in the required value for KUB0 due to the individual difference of the engine or a deviation from the adapted value of the required value due to the aging of the engine, The air-fuel ratio does not become rich immediately after the start of the air-fuel ratio feedback control.

Although the embodiment has been described with reference to the cooling water temperature as a representative value of the engine temperature, another temperature corresponding to the engine temperature may be used.

[Brief description of the drawings]

FIG. 1 is a control system diagram of one embodiment.

FIG. 2 is a flowchart for explaining a calculation of a fuel injection pulse width Ti.

FIG. 3 is a flowchart illustrating a calculation of a target fuel-air ratio equivalent amount TFBYA.

FIG. 4 is a characteristic diagram of an initial value KAS0 of a post-start increase correction coefficient KAS.

FIG. 5 is a flowchart for explaining the calculation of a water temperature increase correction coefficient KTW and an unburned portion increase correction coefficient KUB of the prior application.

FIG. 6 is a flowchart for explaining determination of an air-fuel ratio feedback control condition.

FIG. 7 is a characteristic diagram of a basic value KTW0 of a water temperature increase correction coefficient.

FIG. 8 is a characteristic diagram of a load rotation correction rate R _KTW of a water temperature increase correction coefficient.

FIG. 9 is a characteristic diagram of a basic value KUB0 of an unburned fuel amount increase correction coefficient.

FIG. 10 shows a load rotation correction ratio R _{KUB of} an unburned fuel amount increase correction coefficient.
FIG.

FIG. 11 is an air-fuel ratio characteristic diagram for explaining the adaptation of the water temperature increase correction coefficient KTW and the unburned portion increase correction coefficient KUB to the suction negative pressure.

FIG. 12 is an air-fuel ratio characteristic diagram for explaining the adaptation of a water temperature increase correction coefficient KTW and an unburned portion increase correction coefficient KUB with respect to the rotation speed.

FIG. 13 is a flowchart illustrating the calculation of an air-fuel ratio feedback correction coefficient α.

FIG. 14 is a waveform diagram for explaining the operation of the prior application device.

FIG. 15 is a waveform diagram for explaining the operation of the prior application device when there is variation due to individual differences of the engine or when the engine has deteriorated with time.

FIG. 16 is a flowchart illustrating a calculation of a water temperature increase correction coefficient KTW and an unburned portion increase correction coefficient KUB according to the embodiment.

FIG. 17 is a diagram showing a table of learning values.

FIG. 18 is a flowchart illustrating updating of a learning value.

FIG. 19 is a waveform chart for explaining the operation of the embodiment.

FIG. 20 is a waveform chart for explaining the operation of the embodiment.

FIG. 21 is a characteristic diagram showing an example of a fuel increase correction at the time of a cold start in a conventional example.

FIG. 22 is a waveform chart for explaining the operation of the conventional example.

FIG. 23 is a diagram corresponding to the claims of the first invention.

FIG. 24 is a diagram corresponding to claims of the second invention.

FIG. 25 is a diagram corresponding to a claim of the third invention.

[Explanation of symbols]

1 engine body 2 control unit 3 O ₂ sensor 4 crank angle sensor 6 the air flow meter 7 the fuel injection valve 10 a three-way catalyst

Claims (12)

[Claims] A means for setting a basic air-fuel ratio at the start of the air-fuel ratio feedback control; a memory for storing a learning value for the basic air-fuel ratio; and a value obtained by correcting the basic air-fuel ratio with the learning value. Means for setting as a target air-fuel ratio at the start of control; means for determining whether an air-fuel ratio feedback control condition before engine warm-up is satisfied; and air-fuel ratio feedback before engine warm-up based on the determination result. Means for calculating the air-fuel ratio feedback correction amount based on the output of the air-fuel ratio detection means so that the actual air-fuel ratio becomes the stoichiometric air-fuel ratio when the control condition is satisfied; and correcting the target air-fuel ratio with the air-fuel ratio feedback correction amount Means for performing feedback control of the air-fuel ratio, and Air-fuel ratio control apparatus for an engine, characterized in that a means for updating the learning value based on the correction amount. 2. The method according to claim 1, wherein the means for setting the basic air-fuel ratio comprises: means for calculating a basic injection amount at which a stoichiometric air-fuel ratio is obtained after the engine has been warmed up, in accordance with operating conditions; 2. The air-fuel ratio control of an engine according to claim 1, comprising: means for calculating an increase correction amount so that the fuel ratio becomes a stoichiometric air-fuel ratio; and means for correcting the basic injection amount with the increase correction amount. apparatus. 3. A means for calculating a basic injection amount for obtaining a stoichiometric air-fuel ratio after completion of warming-up of an engine in accordance with operating conditions, and increasing the actual air-fuel ratio to a stoichiometric air-fuel ratio before completion of warming-up of the engine. Means for calculating a correction amount, a memory for storing a learning value for the increase correction amount, means for correcting the increase correction amount based on the learning value, and when an air-fuel ratio feedback control condition is satisfied before the completion of engine warm-up. Means for determining whether or not the air-fuel ratio feedback correction amount is output from the air-fuel ratio detecting means such that the actual air-fuel ratio becomes the stoichiometric air-fuel ratio when the air-fuel ratio feedback control condition is satisfied before the warm-up of the engine is completed. Means for calculating the fuel injection amount by correcting the basic injection amount with the air-fuel ratio feedback correction amount and the increasing correction amount corrected by the learning value. Means for supplying the injection amount of fuel to the engine; and means for updating the learning value based on the air-fuel ratio feedback correction amount after the start of the air-fuel ratio feedback control. Engine air-fuel ratio control device. 4. The engine air-fuel ratio control device according to claim 1, wherein the learning value is a value for each of a plurality of engine temperature ranges. 5. The air-fuel ratio control device for an engine according to claim 2, wherein the learning value is a value for each of a plurality of divided engine temperature regions. 6. The learning value updating means determines whether the engine temperature belongs to the same area or the area has been switched, and based on the determination result, determines whether the engine temperature belongs to the same area. Means for sampling the maximum value and the minimum value of the air-fuel ratio feedback correction amount at
And means for updating a learning value of the area before switching based on the sum of the maximum value and the minimum value of the air-fuel ratio feedback correction amount for the area before switching when the area is switched from the determination result. The air-fuel ratio control device for an engine according to claim 4, characterized in that: 7. The learning value updating means determines whether the engine temperature belongs to the same area or the area has been switched, and based on the determination result, determines whether the engine temperature belongs to the same area. Means for sampling the maximum value and the minimum value of the air-fuel ratio feedback correction amount at
And means for updating a learning value of the area before switching based on the sum of the maximum value and the minimum value of the air-fuel ratio feedback correction amount for the area before switching when the area is switched from the determination result. The air-fuel ratio control device for an engine according to claim 5, wherein 8. The air-fuel ratio of an engine according to claim 2, wherein the basic value of the increase correction amount is a value that increases as the cooling water temperature decreases. Control device. 9. The air-fuel ratio control device for an engine according to claim 8, wherein a basic value of the increase correction amount is corrected according to an engine load. 10. The system according to claim 8, wherein a basic value of the increase correction amount is corrected according to an engine load and an engine speed.
3. The air-fuel ratio control device for an engine according to claim 1. 11. The air-fuel ratio detecting means is an O ₂ sensor, and it is determined that the air-fuel ratio feedback condition is satisfied when the O ₂ sensor has been activated. An air-fuel ratio control device for an engine according to any one of the above. 12. The method according to claim 1, wherein the air-fuel ratio feedback correction amount is a sum of an integral component and a proportional component.
2. The air-fuel ratio control device for an engine according to any one of 1 to 1.