JPH0526935B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention provides a method for controlling the air-fuel ratio of a mixture to be combusted when the operating state of an engine satisfies predetermined conditions.
The present invention relates to an air-fuel ratio control device for an engine that controls the air-fuel ratio to be leaner or richer than near the stoichiometric air-fuel ratio.

(Prior art) Generally, in vehicle engines that use a three-way catalytic converter to purify exhaust gas, it is necessary to maintain the air-fuel ratio of the air-fuel mixture used for combustion near the stoichiometric air-fuel ratio. Therefore, an air-fuel ratio sensor such as an O ₂ sensor is provided in the exhaust passage, and the air-fuel ratio is feedback-controlled based on a signal obtained from the air-fuel ratio sensor.
When the air-fuel ratio is maintained near the stoichiometric air-fuel ratio through such feedback control, the three-way catalytic converter smoothly oxidizes HC and CO and reduces NOx, promoting purification of exhaust gas. .

On the other hand, in order to improve fuel consumption efficiency, it is necessary to control the air-fuel ratio to be higher than the stoichiometric air-fuel ratio and shift it to the lean side, or, for example, when a large engine output is required, such as when accelerating a vehicle. In some cases, it may be desired to control the air-fuel ratio to be lower than the vicinity of the stoichiometric air-fuel ratio and shift it to the rich side.

However, since the output characteristics of the air-fuel ratio sensors that have been used for conventional purposes vary around the stoichiometric air-fuel ratio, feedback control based on the signal obtained from the air-fuel ratio sensor may not change the air-fuel ratio. It is not possible to shift the air-fuel ratio to the lean side or rich side from near the stoichiometric air-fuel ratio and maintain it. For this reason, in conventional engine air-fuel ratio control devices, in order to shift the air-fuel ratio from near the stoichiometric air-fuel ratio to the lean side or rich side and maintain it, the engine load and engine speed expressed by the intake air amount and intake negative pressure are The basic fuel injection amount is calculated based on the number, and the final fuel injection amount obtained by adding correction to the calculated basic fuel injection amount is used.
It is said to perform open-loop control of the air-fuel ratio.

However, with the engine air-fuel ratio control device that calculates the basic fuel injection amount and performs open-loop control of the air-fuel ratio, control is affected by changes in engine characteristics over time, changes in the operating environment, etc. There is a problem that the control becomes unstable or the control accuracy decreases, making it difficult to always obtain a desired air-fuel ratio. For this reason, as disclosed in Japanese Patent Application Laid-Open No. 57-105530, for example, feedback control is performed to bring the air-fuel ratio close to the stoichiometric air-fuel ratio based on the signal obtained from the air-fuel ratio sensor. Learning is performed to determine the feedback correction amount that corrects excess or deficiency in the fuel injection amount during control, and when performing open loop control of the air-fuel ratio, the fuel injection amount is corrected using the learned value obtained through learning. A method has been proposed in which the air-fuel ratio is controlled to maintain the air-fuel ratio at a target air-fuel ratio different from the vicinity of the stoichiometric air-fuel ratio after absorbing changes over time of the engine.

By the way, as mentioned above, an engine air-fuel ratio control device that corrects the fuel injection amount using a learning value obtained by feedback control of the air-fuel ratio when performing open-loop control of the air-fuel ratio is disclosed in the above-mentioned publication. As shown in the figure, only the feedback correction amount when the engine is in one operating state is used as a learning value to correct the fuel injection amount in the previous operating state when performing open loop control. However, since the fuel injection amount varies depending on the engine operating state, during open-loop control, for example, in low-load operating conditions, the learned value is used to correct the fuel injection amount, making it possible to accurately obtain a predetermined target air-fuel ratio. Even if this is done, there is a problem in that under high-load operating conditions, control errors occur due to differences in engine operating conditions, making it impossible to obtain a predetermined target air-fuel ratio. For this reason, feedback control is performed for each operating region obtained by dividing the engine operating state into multiple regions, and learning is performed to calculate the amount of feedback correction for each operating region. The amount is stored as a learned value in each operating region in each storage zone of a storage means having a plurality of partitioned storage zones corresponding to each operating region, and each time the engine is operated, one operation is performed. The learning value stored in the storage zone corresponding to the storage zone of the storage means is updated in the storage area, and when this is completed, the air-fuel ratio is shifted to open-loop control in the operating area, and the control is performed according to the operating state of the engine. It has been considered to correct the fuel injection amount using learned values.

However, as described above, the feedback correction amount is calculated for each operating region and these are stored as learning values in each storage zone of the storage means, and when the updating of the learning value for one storage zone is completed, the feedback correction amount is In an engine air-fuel ratio control device that corrects the fuel injection amount using a learned value stored in a storage zone, during feedback control to obtain the learned value, the air-fuel ratio is close to the stoichiometric air-fuel ratio. On the other hand, during open loop control, the air-fuel ratio is shifted to the lean side or rich side from the vicinity of the stoichiometric air-fuel ratio. For this reason, for example, when performing open-loop control to shift the air-fuel ratio to the lean side, the vertical axis in Figure 5 represents the air-fuel ratio (A/F), and the horizontal axis represents the elapsed time.
As shown by the chain lines in the graph represented by Periods during which operation is performed near the stoichiometric air-fuel ratio H ₁ , H ₂ , H ₃ ...
When the operation region ends, the air-fuel ratio immediately enters open-loop control periods G ₁ , G ₂ , G ₃ , etc. in which the air-fuel ratio is shifted to the lean side, and the air-fuel ratio is shifted from near the stoichiometric air-fuel ratio to the lean side, and When the operating state of the engine shifts to another operating range, the lean air-fuel ratio must be shifted to near the stoichiometric air-fuel ratio. Therefore, when switching from feedback control to open loop control, or from open loop control to feedback control There is a possibility that the air-fuel ratio changes rapidly during the transition to , and this may lead to frequent torque fluctuations.

(Object of the Invention) In view of the above, the present invention aims to adjust the air-fuel ratio of the mixture for combustion to near the stoichiometric air-fuel ratio based on the signal obtained from the air-fuel ratio sensor when the engine is operated under predetermined conditions. The engine operating state is divided into a plurality of regions, and the feedback control is performed for each operating region obtained by dividing the engine operating state into a plurality of regions. The feedback correction amount for each operating region is stored as a learning value in the storage zone of the storage means, and during open loop control to maintain the air-fuel ratio leaner or richer than near the stoichiometric air-fuel ratio, the storage means stores the feedback correction amount for each operating region as a learned value. The fuel injection amount is corrected using the stored learning value, and when updating the learning value stored in the storage means, it is possible to change the amount of fuel injection from feedback control to open loop control or from open loop control to feedback control. It is an object of the present invention to provide an air-fuel ratio control device for an engine that can suggest torque fluctuations that occur when transitioning to control.

(Structure of the Invention) An air-fuel ratio control device for an engine according to the present invention includes an air-fuel ratio sensor whose output characteristics change near the stoichiometric air-fuel ratio, and a signal obtained from the air-fuel ratio sensor to adjust the air-fuel ratio to the stoichiometric air-fuel ratio. Feedback control means performs feedback control to improve the neighborhood, and feedback control means performs feedback control for each of the operating regions obtained by dividing the engine operating state into a plurality of regions when the engine operating state satisfies a predetermined condition. a correction amount calculation means that performs learning to calculate a feedback correction amount to compensate for excess or deficiency in the amount of high-grade fuel by performing feedback control according to the method; storage means for storing the learning value in each of the plurality of storage zones; The memory update completion detection means detects that the update of the memory of the learned values in a plurality of predetermined values has been completed, and the memory update completion detection means detects that the memory update has been completed when the engine operating state satisfies the predetermined control condition. After the end of the update is detected, fuel is supplied with the fuel supply amount calculated using the learning value stored in the storage means, and the air-fuel ratio is adjusted to the lean side or rich side from the vicinity of the stoichiometric air-fuel ratio. and fuel supply control means for open-loop control.

With this configuration, when transitioning from air-fuel ratio feedback control to open-loop control, or from open-loop control to feedback control, the frequency of torque fluctuations caused by sudden changes in the air-fuel ratio can be reduced. The amount of fluctuation can be effectively suggested, and the driving characteristics of the vehicle to which such engine air-fuel ratio control is performed can be made stable.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an example of an engine air-fuel ratio control device according to the present invention together with the main parts of an engine to which the device is applied.

In FIG. 1, the flow rate of intake air introduced into the intake passage 2 via the air cleaner 1 is detected by an air flow sensor 21, and a detection signal ISa corresponding to the intake air flow rate is sent from the air flow sensor 21 to a control unit 30, which will be described later. supplied to
Further, the temperature of the intake air passing through the air flow sensor 21 (intake air temperature) is detected by the intake air temperature sensor 22, and a detection signal ISt corresponding to the intake air temperature is supplied from the intake air temperature sensor 22 to the control unit 30. The intake air flow rate is regulated by a throttle valve 3 provided in the intake passage 2, and the throttle valve 3 changes its opening degree in response to depression of an accelerator pedal (not shown). There is. The opening of the throttle valve 3 is detected by the throttle opening sensor 23, and a detection signal ISh corresponding to the opening of the throttle valve 3 is supplied from the throttle opening sensor 23 to the control unit 30.

The intake air that has passed through the throttle valve 3 is guided to the combustion chamber 15 of the engine body 9 via the surge tank 4 and the intake valve 5. surge tank 4
An intake pressure sensor 24 is disposed at the intake pressure sensor 24, and a detection signal ISb corresponding to the intake negative pressure is supplied from the intake pressure sensor 24 to the control unit 30.

Further, a fuel injection valve 6 is provided at a predetermined position in the intake passage 2. This fuel injection valve 6,
The injection pulse signal OCp supplied from the control unit 30 controls opening and closing at predetermined timing, and the fuel supplied under pressure from a fuel supply system (not shown) is transferred to the downstream part of the intake passage 2 near the combustion chamber 15 ( Inject intermittently towards the intake port. The air-fuel mixture sucked into the combustion chamber 15 is ignited by the spark plug 8 and combusted, thereby operating the engine.

At this time, the signal disk plate 16 provided in connection with the crankshaft of the crank mechanism that converts the return movement of the piston 10 into rotational movement.
The rotation speed (rotation angle) of the signal disk plate 16, that is, the engine rotation speed (rotation speed) is detected by the crank angle sensor 26, and a detection signal ISn corresponding to the engine rotation speed is detected by the crank angle sensor 26. 26 to control unit 30
supplied to Further, a water temperature sensor 25 is attached to the engine body 9, and a detection signal corresponding to the engine cooling water temperature is sent from the water temperature sensor 25.
ISs are supplied to the control unit 30.

The burned mixture (exhaust gas) is transferred to the exhaust valve 7.
The exhaust passage 12 is discharged into the exhaust passage 12 via
An O ₂ sensor 27 as an air-fuel ratio sensor is installed in the engine, and the output characteristics of this O ₂ sensor 27 change near the stoichiometric air-fuel ratio.
That is, the O ₂ sensor 27 detects the oxygen concentration in the exhaust gas, and the air-fuel ratio of the mixture used for combustion is on the lean side and the rich side with respect to the stoichiometric air-fuel ratio. A binary detection new ISo having different voltage levels is generated and supplied to the control unit 30. A three-way catalytic converter 13 is provided downstream of the O ₂ sensor 27 in the exhaust passage 12 to purify HC, CO, and NOx in the exhaust gas.

Detection signals from each of the above-mentioned sensors 21 to 27
The control unit 30 to which ISa, ISt, ISh, ISb, ISs, ISn, and ISo are supplied includes an A/D converter (analog/digital converter) 31 and a ROM (read only memory) as main components.
32, a RAM (Random Access Memory) 33, a CPU (Central Processing Unit) 34, etc., are constructed using a microcomputer. The control unit 30 receives a signal corresponding to the on/off state of the ignition switch 28.
ISi is also supplied and control unit 3
0, the ignition switch 28 is turned on and the engine is started, and furthermore, the ignition switch 28 is in the operating state after that, and the ignition switch 28 is turned on and the engine is started.
8 is turned off so that it can be detected that the engine is in a non-operating state. and,
The CPU 34 performs arithmetic processing based on data obtained from each detection signal described above while exchanging data with the RAM 33 according to instructions from the ROM 32, and determines the fuel injection amount and injection based on the output data. An injection pulse signal OCp that determines the timing is supplied from the control unit 30 to the fuel injection valve 6.

Based on the above-described configuration, when the ignition switch 28 is turned on and the engine is started, the control unit 30 outputs the detection signal ISn.
The basic injection amount Qs is calculated based on the engine speed Ne represented by the engine speed Ne and the intake air flow rate Am represented by the detection signal ISa.
The final injection amount Qe is obtained by correcting it based on the intake air temperature Ta, etc. indicated by Tw and the detection signal ISt, and the injection pulse signal OCp is generated so that the fuel is injected from the fuel injection bar 6 with this final injection amount Qe. Supplied to the injection valve 6.

Then, when the operating state of the engine satisfies the predetermined learning conditions, for example, the cooling water temperature
When Tw reaches the predetermined value T1 or _more , the warm-up operation ends,
The voltage level of the detection signal ISo from the O ₂ sensor 27 is
The level indicating that the O ₂ sensor 27 is in an active state that works normally, for example, 0.6V or higher, and the detection signal is
When the rate of change dθ/dt of the throttle opening θ, which is represented by ISh, falls within a predetermined range (α≦dθ/dt<β), that is, when the vehicle equipped with this engine is not in an acceleration or deceleration state, Based on the detection signal ISo from the O ₂ sensor 27, the control unit 30 brings the air-fuel ratio of the air-fuel mixture provided for combustion close to the stoichiometric air-fuel ratio and starts feedback control. When the feedback control is started, the fuel injection amount is increased or decreased in a zigzag pattern toward the lean side and the rich side after reaching the amount at which the air-fuel ratio of the air-fuel mixture reaches the stoichiometric air-fuel ratio, as shown in FIG. At this time, the control unit 30 controls the peak value of the fuel injection amount.
The average value of Pa and the bottom value Ba is calculated, and this average value is used to perform learning to calculate the feedback correction amount Fb to compensate for the excess or deficiency of the basic injection amount Qs with respect to the final injection amount Qe. The amount Fb is stored in a predetermined area of the RAM 33 as a learned value Gf, and thereafter the fuel injection amount is corrected using this learned value Gf.

When the engine is in one of the operating regions obtained by dividing the operating state into a plurality of regions after the engine has started, the control unit 30 controls:
As mentioned above, the learning value Gf is determined by the total N. For example,
After running 8 times, the learning value from these 8 times of learning
The average value of Gf ₁ to Gf ₈ , that is, the average learned value Gfa is calculated, and this average learned value Gfa is stored in the memory zone corresponding to the relevant operation area of the RAM 33 at the end of the previous operation already stored there. Average learning value
Instead of Gfa, a new value is stored, and the average learning value Gfa is updated.

Here, the RAM 33 has the engine rotation speed Ne on the horizontal axis and the vertical axis as shown in FIG.
For example, intake negative pressure Bp or intake air flow rate Am
It is provided with a storage zone corresponding to the learning value map shown by arranging the engine load Le represented by . On this learning value map, the engine operating state is divided into four operating ranges Z1, Z2, Z3, and Z4, and these operating ranges of RAM33
The four storage zones corresponding to Z1, Z2, Z3 and Z4 contain the average learning values obtained for each driving area.
Gfa is memorized. Therefore, in order to update the average learning value Gfa stored in the four storage zones corresponding to the operating areas Z1, Z2, Z3 and Z4 of the RAM 33,
Feedback control is performed to bring the air-fuel ratio close to the stoichiometric air-fuel ratio for each of the operating regions Z1, Z2, Z3, and Z4. In such a case, if the average learned value Gfa in one operating region, for example Z1, is updated, if the open loop control of the air-fuel ratio is immediately shifted, the air-fuel ratio will suddenly change as described above. Torque fluctuations will occur due to the changes.

Therefore, in the book, the CPU 34 operates in the operating area Z1,
All or any of Z2, Z3 and Z4, here in particular, are in the commonly used range. For example, it functions to prevent transition from air-fuel ratio feedback control to open-loop control until all updates of the average learning value Gfa in the operating regions Z1, Z2, and Z3 are completed.
In this way, multiple predetermined operating areas (Z1, Z2 and
Since the transition from air-fuel ratio feedback control to open-loop control is prevented until the update of the average learning value Gfa in operating regions Z1, Z2, and Z3) is completed,
The air-fuel ratio is maintained near the stoichiometric air-fuel ratio until the update of the average learning value Gfa for all of
Therefore, during this period, the air-fuel ratio does not change suddenly even during the transition between the operating ranges Z1, Z2, and Z3, and as a result, the frequency and degree of torque fluctuations are significantly reduced.

Then, as described above, the operating areas Z1 and Z2 are
After the update of the average learning value Gfa for each of Z3 and Z3 is completed, if the engine operating state satisfies the predetermined control conditions, the air-fuel ratio is shifted to the lean side or rich side from the vicinity of the stoichiometric air-fuel ratio. Shift to open-loop control of the maintained air-fuel ratio.
In this open-loop control of the air-fuel ratio, the updated average learning value Gfa is used to calculate the basic injection amount Qs.
The correction coefficient GK set in order to obtain the final injection amount Re necessary to obtain a target air-fuel ratio that is leaner or richer than near the stoichiometric air-fuel ratio is corrected by the calculation. As a result, the final injection amount Re
In order to reduce or increase the amount by a predetermined amount, and to inject fuel from the fuel injection valve 6 with this corrected final injection amount Re, an injection having a predetermined pulse width according to the corrected final injection amount Re is performed. Forming a pulse signal OCp, the fuel injection valve 6
supply to.

The above-mentioned control is mainly performed by operating the CPU 34 of the control unit 30.
An example of a program executed by the CPU 34 will be explained with reference to the flowchart in FIG. 4.

In order to avoid redundant explanations, this example shows a program that performs open-loop control, that is, lean control, which shifts the air-fuel ratio from near the stoichiometric air-fuel ratio to the lean side and maintains it. Even in the case of rich control in which the fuel ratio is shifted to the rich side from near the fuel ratio and maintained, the basic control operation procedure of the CPU 34 is the same.

In this program, after starting, an initialization is performed in a process 51, and the learning flag _kx is set to 0, and the program proceeds to a decision 52. In addition, the learning flag k _x
are engine operating ranges Z1, Z2, and Z3, which will be described later.
It shows learning flags k ₁ , k ₂ and k ₃ that are set when the average learning value in is updated. At decision 52, it is determined whether the engine has started or not. This determination is made by determining whether or not the ignition switch 28 is turned on based on the signal ISi corresponding to the on/off state of the ignition switch 28. If the engine is not started, this judgment is repeated, and if the engine is not started, the process proceeds to process 53, where various detection signals ISa, ISt,
Input ISh, ISb, ISs, ISn, ISo, etc. In the subsequent process 54, the basic injection amount Qs is calculated based on the engine speed Ne obtained from the detection signal ISn and the intake air flow rate Am or intake negative pressure Bp obtained from the detection signal ISa or ISb. Basic injection amount Qs, detection signal ISs as required
Engine cooling water temperature Tw and detection signal obtained from
Correction is made based on the intake air temperature Ta etc. obtained from ISt.

Next, the process proceeds to decision 55, in which feedback control is performed to control the air-fuel ratio to near the stoichiometric air-fuel ratio for each of the engine operating ranges Z1, Z2, and Z3, and a feedback correction amount that corrects excess or deficiency with respect to the fuel injection amount Qs is determined. Determine whether the learning to be calculated is completed. This judgment is based on the learning plug
This is done by determining whether k ₁ , k ₂ and k ₃ are all 1, and if learning is not completed,
That is, if at least one of the learning flags k ₁ , k ₂ and k ₃ is not 1, the process proceeds to decision 56, and if learning is completed, that is, the learning flag
If k ₁ , k ₂ and k ₃ are all 1, proceed to decision 57. In decision 56, it is determined whether the operating state of the engine satisfies learning conditions. As mentioned above, this judgment is made when, for example, the cooling water temperature Tw is equal to or higher than a predetermined value _T1 , the O2 sensor 27 is in an active state, and the rate of change dθ/dt of the throttle opening θ is within a predetermined range (α≦dθ/dt<β ), and if it is determined that the learning condition is not satisfied, in process 58, the basic injection amount Qs
An increase correction for acceleration or a reduction correction for deceleration is added to the final injection amount Qe, and the process proceeds to process 59. Then, in process 59, an injection pulse signal OCp having a pulse width for injecting fuel from the fuel injection valve 6 with the final injection amount Qe calculated in process 58 is formed, and this is output, and the process returns to decision 52.

On the other hand, if it is determined in decision 56 that the learning conditions are satisfied, process 60
Then, feedback control is performed to bring the air-fuel ratio close to the stoichiometric air-fuel ratio. At this time, the average value of the peak value Pa and bottom value Ba of the fuel injection amount as shown in FIG.
Go to 1. In process 61, the feedback correction amount Fb calculated in process 60 is set as the learning value Gf.
It is stored in a predetermined storage zone of the RAM 33. Next, proceeding to decision 62, it is determined whether zone learning is complete. This judgment is based on zone learning for updating the average learned value Gfa in each of the operating regions Z1, Z2, Z3, and Z4 shown in the learned value map as shown in the third learning value map mentioned above, that is, the feedback correction amount Fb. The calculation is performed by determining whether or not the calculation has been performed N times (for example, 8 times) in each of the driving regions Z1, Z2, Z3, and Z4. This determination is made in the RAM 33 in the process 61.
This is done by counting the number of learning values Gf stored in each storage zone of the operating area Z1,
Each time the zone learning for Z2, Z3 and Z4 is completed, the process proceeds to process 63, and the operation area Z1,
If zone learning for each of Z2, Z3, and z4 is not completed, proceed to process 64.

In process 64, in process 61, RAM 33
Using the learned value Gf stored in , the basic injection amount Qs is corrected so that the air-fuel ratio of the air-fuel mixture becomes close to the stoichiometric air-fuel ratio, and the process proceeds to process 59, where the basic injection amount Qs is adjusted according to the final injection amount Qe corrected in process 59. An injection pulse signal OCp having a pulse width is formed and outputted to the fuel injection valve 6, and the process returns to process 52.

In addition, in the process 63 that proceeds when the zone learning is completed, the average value of the learning values Gf obtained by the N learnings stored for each of the driving regions Z1, Z2, and Z3, that is, the average learning value Gfa is calculated. Operating area Z1, Z2
In place of the average learning value Gfa at the end of the previous engine operation, which is calculated for each of Z3 and Z3 and is already stored in each storage zone of the RAM 33 corresponding to the operating ranges Z1, Z2, and Z3, Newly memorize and update the average learning value Gfa.

In the following process 65, operating regions Z1, Z2, Z3
When the average learned value Gfa in the operating areas Z1, Z2, and Z3 is updated, the operating area
Learning flag k ₁ = 1 for Z1, Z2, and Z3, respectively;
After setting k ₂ = 1 and k ₃ = 1, the process proceeds to process 64, in which the basic injection amount Qs is corrected using the learned value Gf, and the injection pulse signal OCp is output in process 59, as in the case described above. .

On the other hand, in decision 57, which proceeds after it is determined that the learning has been completed in the aforementioned decision 55, it is determined whether the operating state of the engine satisfies the lean control condition. This judgment is made under lean control conditions, for example, engine cooling water temperature Tw is above a predetermined value _T2 , engine load Le expressed by intake negative pressure Bp or intake air flow rate Am is below a predetermined value, and engine speed Ne is below N2. and the rate of change dθ/dt of the throttle opening θ satisfies a predetermined range (α≦dθ/dt<β). When each of the above conditions is met, lean control is performed. Proceed to process 67 to do so. In process 67,
Using the updated average learning value Gfa, for example, correct the correction coefficient Gk, which represents the reduction rate during lean control with respect to the basic injection amount Qs, and adjust the basic injection amount.
Qs and the corrected correction coefficient Gk are calculated to calculate the final injection amount Re during lean control, and the process proceeds to process 59. Then, in process 59, an injection pulse signal OCp having a pulse width corresponding to the final injection amount Re during lean control is formed,
After outputting it to the fuel injection valve 6, the process returns to the decision unit 52.

On the other hand, if it is determined that the decision 57 is not a lean control condition, the process proceeds to process 66, in which an increase correction for acceleration or a reduction correction for deceleration is added to the final injection amount.
Qe is calculated, and then the process proceeds to process 59, in which, as in the case described above, an injection pulse signal OCp having a pulse width corresponding to the final injection amount Qe calculated in process 66 is formed, and it is sent to the fuel injection valve 6. After outputting, the process returns to decision 52.

In the above example, the case where lean control of the air-fuel ratio is performed is explained, but even when performing rich control of the air-fuel ratio, slight changes such as changing lean control conditions to rich control conditions may be made. Just a similar program can be applied.

(Effects of the Invention) As is clear from the above description, according to the engine air-fuel ratio control device according to the present invention, when the engine is operated under predetermined conditions, the engine Feedback control that controls the fuel ratio to near the stoichiometric air-fuel ratio is performed for each operating region obtained by dividing the engine operating state into multiple regions, and a feedback correction amount that corrects excess or deficiency with respect to the fuel supply amount is calculated. The calculated feedback correction amount for each operating region is stored as a learned value in the storage zone of the storage means, and this learning and storage of the learned value is performed, for example, every time the engine is started. During open loop control in which the air-fuel ratio is maintained on the lean side or rich side near the stoichiometric air-fuel ratio, the fuel supply amount is corrected using the learned value updated and stored in the storage means. Moreover, by being configured so that the transition from air-fuel ratio feedback control to open-loop control is not performed until after the learned values have been updated for all of a plurality of predetermined operating regions, the air-fuel ratio Open-loop control that maintains the air-fuel ratio on the lean side or rich side of the vicinity of the stoichiometric air-fuel ratio is performed when updating the learned value stored in the storage means after absorbing changes in the air-fuel ratio control conditions due to aging of the engine, etc. The frequency and amount of sudden changes in the air-fuel ratio are effectively reduced, and therefore torque fluctuations can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an example of an engine air-fuel ratio control device according to the present invention together with the main parts of an engine to which the device is applied, and FIG. 2 is provided to explain the operation of the example shown in FIG. 1. Characteristic diagram, Figure 3 is the first
FIG. 4 is a flowchart showing an example of a program executed by the microcomputer used in the control unit of the example shown in FIG. The figure is a characteristic diagram used to explain the operation of the engine air-fuel ratio control device. In the figure, 21 is an air flow sensor, 22 is an intake temperature sensor, 23 is a throttle opening sensor, 24 is an intake pressure sensor, 25 is a water temperature sensor, 26 is a crank angle sensor, 27 is an O ₂ sensor, and 28 is an ignition switch. , 30 is a control unit.

Claims (1)

[Scope of Claims] 1. An air-fuel ratio sensor whose output characteristics change near the stoichiometric air-fuel ratio; and an air-fuel ratio sensor that adjusts the air-fuel ratio of the air-fuel mixture to be subjected to combustion to near the stoichiometric air-fuel ratio based on a signal obtained from the air-fuel ratio sensor. a feedback control means for performing feedback control to achieve the desired performance; and a feedback control means for performing feedback control for each of the operating regions obtained by dividing the engine operating state into a plurality of regions when the engine operating state satisfies a predetermined condition. a correction amount calculating means that performs learning to calculate a feedback correction amount to compensate for excess or deficiency in the amount of fuel supplied by performing feedback control according to the method; storage means for storing the learned value in a corresponding one of the plurality of storage zones; and memory updating for updating the memory of the learned value in each of the plurality of storage zones by using the correction amount calculation means and the storage means. means, a memory update completion detection means for detecting that the update of the memory of the learned value in a predetermined plurality of the plurality of memory zones has been completed; After the end of the memory update is detected by the memory update end detection means, fuel is supplied at a fuel supply amount calculated using the learning value stored in the memory means, and the fuel is supplied for combustion. An air-fuel ratio control device for an engine, comprising: fuel supply control means for controlling the air-fuel ratio of the air-fuel mixture to be leaner or richer than near the stoichiometric air-fuel ratio.