JP2001098980A - Air-fuel ratio learning controller for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct a rich side air-fuel ratio in an enriching area to enhance control precision for a value of an exhaust toxic component. SOLUTION: A control means is provided, wherein plurally divided engine operation areas are provided to be set in a feedback area and the enriching area, and an air-fuel ratio is feedback-controlled in the feedback area to come to a specified air-fuel ratio set as a target air-fuel ratio based on a detected signal output from an exhaust sensor and is learning-controlled to update a correction value for the feedback control, and wherein the air-fuel ratio is controlled in the enriching area to be brought into a rich side air-fuel ratio set in a side richer than the specified air-fuel ratio as the target air-fuel ratio and is learning-controlled to keep the feedback control when the engine operation area is transitted from the feedback area to the enriching area, so as to update the correction value for the feedback control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine air-fuel ratio learning control system, and more particularly to an engine air-fuel ratio control system capable of correcting a rich air-fuel ratio in an enrich operation region and improving the management accuracy of exhaust harmful component values. The present invention relates to a fuel ratio learning control device.

[0002]

2. Description of the Related Art Some engines mounted on vehicles are equipped with an air-fuel ratio learning control device. The air-fuel ratio learning control device of the engine performs feedback control based on a detection signal output from the O2 sensor serving as an exhaust sensor so that the air-fuel ratio becomes a specific air-fuel ratio set as the target air-fuel ratio, for example, stoichiometric. Learning control to update the correction value of. Further, the air-fuel ratio learning control device uses a WOT (WHOLE OPEN THROTT).
In a situation where the amount of intake air is large, such as at the time of LE), the air-fuel ratio is controlled as a target air-fuel ratio to a rich side air-fuel ratio that is set richer than the stoichiometric value. And

[0003] Such an air-fuel ratio learning control device for an engine is disclosed in JP-A-9-195824 and JP-A-11-195824.
Japanese Unexamined Patent Publication Nos. 6453/1994, 5-26083 and 9-329050.

Japanese Unexamined Patent Application Publication No. 9-195824 discloses that when a predetermined lean set operation state is established within an oxygen concentration feedback operation control area under a predetermined condition, the previous lean set operation state is set. A learning control method for an electronic fuel injection control device that performs fuel injection control based on a learning map updated based on data, wherein the control amount is calculated and the learning map is not updated during the lean set operation state. The calculation result is stored in a memory, and the learning map is updated based on the latest data stored in the memory when the vehicle deviates from the lean set operation state.

[0005] Japanese Unexamined Patent Publication No. 11-6453 discloses that an ignition timing and an air-fuel ratio in a lean operation are each initialized so that a margin from an allowable stability limit is equal even if operating conditions are different. Means, means for igniting according to the default ignition timing during lean operation, means for storing an air-fuel ratio learning value, means for correcting the default air-fuel ratio during lean operation with this air-fuel ratio learning value, Means for controlling the amount of fuel supplied to the engine so as to have a corrected air-fuel ratio;
Means for detecting the stability of the engine, means for determining whether a feedback control condition based on the stability during lean operation is satisfied, and a stability detection value that matches the control target value of the stability when the feedback control condition is satisfied. Means for updating the air-fuel ratio learning value so as to perform

Japanese Patent Application Laid-Open No. Hei 5-26083 discloses an air-fuel ratio feedback control based on an output of an air-fuel ratio sensor provided in an exhaust pipe based on an intake air amount measured by an air amount sensor. While storing the air-fuel ratio feedback control coefficient as a learning value in the corresponding operation area of the data storage map with the fuel injection pulse width and the grid axis,
In an internal combustion engine using an electronically controlled fuel injection system that performs subsequent control using the stored learning values, the air-fuel ratio feedback control coefficient at a point of an arbitrary engine speed and fuel injection pulse width is used to determine the corresponding point. A value obtained by multiplying the feedback control coefficient by a certain reduction correction coefficient is accommodated as a learning value in the accommodation section of the map grid point having a specification larger than the air amount of.

Japanese Unexamined Patent Application Publication No. 9-329050 discloses a first air-fuel ratio learning value table corresponding to an engine operation range when it is determined that an engine is in a steady operation state based on a predetermined determination condition. The air-fuel ratio learning value stored in the region is updated according to the air-fuel ratio feedback correction coefficient, and after the air-fuel ratio learning value in the first region is updated,
The learning value of the air-fuel ratio of each of the adjacent regions adjacent to the first region is stored in the first region and the average learning value obtained by averaging the learning values of the air-fuel ratio stored in the three regions outside the vicinity of the adjacent region. It is updated by the average value with the air-fuel ratio learning value.

[0008]

In the conventional air-fuel ratio learning control device for an engine, the air-fuel ratio is feedback-controlled by a detection signal from an O2 sensor as an exhaust sensor, and a correction value of the feedback control is learned and controlled. are doing.

However, in the air-fuel ratio learning control device using the O2 sensor, when the air-fuel ratio is controlled to become the rich air-fuel ratio set as the target air-fuel ratio, the O2 sensor reacts at the rich air-fuel ratio. Therefore, there is a problem that learning control of the air-fuel ratio cannot be performed, and there is a disadvantage that the rich air-fuel ratio cannot be corrected using the learned correction value.

Further, the air-fuel ratio learning control device has a problem that the air-fuel ratio may deviate from the power air-fuel ratio due to variations or the like within the tolerances of parts, and this deviation cannot be corrected.

For this reason, when the air-fuel ratio learning control device controls the air-fuel ratio to become the rich air-fuel ratio set as the target air-fuel ratio, the situation where the air-fuel ratio deviates from the rich air-fuel ratio which is the target air-fuel ratio may occur. Even if it occurs, it cannot be corrected to an appropriate value, and there is a disadvantage that the exhaust harmful component value is deteriorated.

[0012]

Therefore, in order to eliminate the above-mentioned disadvantages, the present invention divides the operating region of the engine into a plurality of regions based on the engine speed and the engine load, and sets the divided regions into a feedback region and an enrich region. In the feedback region, feedback control is performed so that the air-fuel ratio becomes a specific air-fuel ratio set as a target air-fuel ratio based on a detection signal output from an exhaust sensor provided in an exhaust passage of the engine, and a correction value of the feedback control. Learning control to update the air-fuel ratio in the enriched region so that the air-fuel ratio becomes a rich air-fuel ratio that is set to a richer side than the specific air-fuel ratio as the target air-fuel ratio. The feedback control is continued when the transition from the Characterized in that a control means for performing learning control to update the correction value of Dobakku control.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The air-fuel ratio learning control device according to the present invention is characterized in that, when the operating region of the engine shifts from the feedback region to the enrichment region, the feedback control is continued and the correction value of the feedback control is adjusted by the control means. By performing the learning control so as to update, the rich air-fuel ratio in the enrichment region can be corrected using the correction value updated by the learning control.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 6 show a first embodiment of the present invention. In FIG. 4, reference numeral 2 denotes an engine mounted on a vehicle (not shown), 4 denotes a cylinder block, 6 denotes a cylinder head, 8 denotes a piston, and 10 denotes a combustion chamber.

The engine 2 has an air intake passage 22 communicating with the combustion chamber 10 by sequentially connecting an air cleaner 12, an intake pipe 14, a throttle body 16, a surge tank 18, and an intake manifold 20 as an intake system. A throttle valve 24 is provided in the intake passage 22 of the throttle body 16.

The engine 2 has an exhaust passage 32 communicating with the combustion chamber 10 by sequentially connecting an exhaust manifold 26, an exhaust pipe 28, and a catalytic converter 30 as an exhaust system. A catalyst 34 is provided in the catalytic converter 30. Reference numeral 36 denotes a first blow-by gas pipe, 38 denotes a second blow-by gas pipe, and 40 denotes a PCV valve.

The engine 2 is provided with a fuel injection valve 42 in the intake manifold 20 so as to be directed toward the combustion chamber 10.
The fuel injection valve 42 is connected to a fuel tank 46 by a fuel supply passage 44. A fuel pump 48 for supplying fuel to the fuel supply passage 44 is provided in the fuel tank 46. A fuel filter 50 is provided in the fuel supply passage 44.

In the middle of the fuel supply passage 44, a pressure regulator 52 for adjusting the fuel pressure is provided. The pressure regulator 52 is connected to the surge tank 18.
The pressure in the intake passage 22 is introduced as an adjustment pressure through the adjustment pressure passage 54, the fuel pressure is adjusted to a predetermined pressure, and excess fuel is returned to the fuel tank 46 through the fuel return passage 56.

In the fuel tank 46, an evaporation passage 58 is provided.
Communicates with one end of the The other end of the evaporation passage 58
It is communicated with the canister 60. A two-way valve 62 is provided in the middle of the evaporation passage 58. One end of a purge passage 64 communicates with the canister 60. The other end of the purge passage 64 communicates with the intake passage 22 of the surge tank 18. A purge control valve 66 is provided in the middle of the purge passage 64.

The engine 2 bypasses the throttle valve 24 and connects to the intake passage 22 of the intake pipe 14 and the throttle body 1.
6 is provided with a bypass air passage 68 communicating with the intake passage 22. In the middle of the bypass air passage 68, an idle control valve (ISC valve) 70 for adjusting the amount of bypass air and controlling the idle speed is provided.

The engine 2 is provided with an ignition coil / igniter 72 constituting an ignition mechanism, an engine speed sensor (CKP sensor) 74 for detecting the engine speed, and a cylinder discriminating sensor (CM) for discriminating the cylinder.
P sensor) 76, and the intake passage 2 of the surge tank 18
2, an intake pressure sensor 80 for detecting an intake pressure introduced from a detection pressure passage 78, a water temperature sensor 82 for detecting a coolant temperature of the engine 2, and a throttle sensor 84 for detecting a throttle opening of the throttle valve 24. Temperature sensor 8 for detecting the temperature of the intake air in the intake passage 22
6, an O2 sensor 88 for detecting the oxygen concentration in the exhaust gas of the exhaust passage 32 is provided.
Is provided with a catalyst temperature sensor 90 for detecting the temperature of the catalyst.

The fuel injection valve 42, fuel pump 48, purge control valve 66, idle control valve 70, ignition coil / igniter 72, engine speed sensor 74, cylinder discriminating sensor 76, intake pressure sensor 80, and water temperature sensor 82
The throttle sensor 84, the intake air temperature sensor 86, the O2 sensor 88, and the catalyst temperature sensor 90 are connected to control means 94 constituting an air-fuel ratio learning control device 92. Also,
The controller 94 is connected to the catalyst temperature sensor 90 via a warning light 96, and is connected to a battery 98.

As shown in FIG. 5, the control means 94 includes a fuel injection control unit 100, an ignition timing control unit 102, an idle (I
SC) Controller 104, Purge Controller 106, Fuel Pump Relay Controller 108, Radiator Fan Relay Controller 1
10. Air conditioner (A / C) control unit 112, automatic transmission (AT) control signal generation unit 114, automatic transmission (AT)
A control unit 116, a battery reverse connection protection unit 118, a fail-safe function unit 120, and a self-diagnosis unit 122 are provided.

On the input side of the control means 94, an ignition switch 124, a starter 126, the cylinder discrimination sensor 76, the engine speed sensor 74, the throttle sensor 84, the intake pressure sensor 80, and the water temperature sensor 8 are provided.
2. The intake air temperature sensor 86, the O2 sensor 88, the vehicle speed sensor 128, the electric load 130, the air conditioner (A / C) evaporator thermistor 132, the air conditioner (A / C) switch 134, the blower fan 136, the air conditioner (A / C)
Pressure switch 138, test switch 140, automatic transmission (AT) 142, automatic transmission (AT) shift switch 144, D range switch 146, power steering switch 148, diagnosis switch 15
0 is connected.

On the output side of the control means 94, the fuel injection valve 42, the ignition coil / igniter 72, the idle (ISC) control valve 70, the purge control valve 6
6. The fuel pump relay 152 of the fuel pump 48, the radiator fan relay 156 of the radiator cooling fan 154, the tachometer / electric power steering controller 158, the air conditioner (A / C) compressor relay 160, the air conditioner (A / C) condenser fan relay 162 , An automatic transmission (AT) controller 164, a continuously variable transmission (CVT) controller 166, an automatic transmission (A
T) Shift solenoid valve 168, main relay 17
0, the check engine lamp 172 is connected.

As shown in FIG. 6, the control means 94 includes an engine speed sensor 74, a cylinder discriminating sensor 76, an intake pressure sensor 80, a water temperature sensor 82, a throttle sensor 84, an intake temperature sensor 86, an O2 sensor 88, a catalyst temperature sensor. A detection signal is input from an ignition switch 90, an ignition switch 124, a starter 126, a vehicle speed sensor 128, an electric load 130, an air conditioner (A / C) evaporator thermistor 1
32, air conditioner (A / C) switch 134, blower fan 136, air conditioner (A / C) pressure switch 13
8, test switch 140, automatic transmission (AT) 14
2. Automatic transmission (AT) shift switch 144, D range switch 146, power steering switch 14
8. A signal is input from the diagnosis switch 150.

The control means 94 controls the detection signals from the engine speed sensor 74 and the like and the ignition switch 1
The operation of the fuel injection valve 42, the fuel pump 48, the purge control valve 66, the idle control valve 70, and the ignition coil / igniter 72 is controlled by signals from the fuel cell 24, the fuel injection amount (air-fuel ratio), the purge amount, and the idle rotation. Control the number, ignition timing, etc.

As shown in FIG. 2, in the air-fuel ratio learning control device 92, an operating region of the engine 2 is divided into a plurality of regions according to an engine speed and an engine load (for example, intake pressure, etc.). The operating regions divided into a plurality of regions are set and provided as a feedback region j and an enrichment region i, respectively. In this embodiment, a plurality of operating regions are divided into a plurality of feedback regions j1 to j1.
j6 and a plurality of enriched regions i1 to i6.

The control means 94 controls each feedback area j
In 1 to j6, the air-fuel ratio becomes a specific air-fuel ratio (for example, stoichiometric) set as the target air-fuel ratio based on the detection signal output from the O2 sensor 88 which is an exhaust sensor provided in the exhaust passage 32 of the engine 2. Learning control to update the correction value of the feedback control.

The control means 94 controls the enrichment area i
In 1 to i6, control is performed so that the air-fuel ratio becomes a rich air-fuel ratio that is set to be richer than the specific air-fuel ratio as the target air-fuel ratio. The rich air-fuel ratio is set by a rich air-fuel ratio basic map (not shown).

As shown in FIG. 3, when the operating range of the engine 2 shifts from the feedback ranges j1 to j6 to the enriched ranges i1 to i6, the control means 94 continues the feedback control to correct the feedback control value. Learning control is performed so as to update.

At this time, when the operating region of the engine 2 shifts from the feedback regions j1 to j6 to the enrich regions i1 to i6 for the first time, the control means 94 continues the feedback control and updates the correction value of the feedback control. When the operating region of the engine 2 shifts from the feedback regions j1 to j6 to the enrich regions i1 to i6, the feedback control is continued for the set time t to update the correction value of the feedback control. Implement learning control to perform

Next, the air-fuel ratio learning control will be described with reference to a flowchart.

When the control is started (step 200), the air-fuel ratio learning control device 92 determines whether or not the operation region is in the enrichment regions i1 to i6 based on the engine speed and the engine load (step 202).

If this determination (step 202) is NO, the process is repeated until this determination (step 202) becomes YES. At this time, since the operation range of the engine 2 is in one of the feedback ranges j1 to j6, the specific air-fuel ratio (for example, 12.
Feedback control is performed so as to satisfy 5), and learning control is performed to update the correction value of the feedback control.

If the determination (step 202) is YES, it is determined whether or not the transition from the feedback areas j1 to j6 to the enriched areas i1 to i6 has been made for the first time (step 204).

If the determination (step 204) is YES, the timer 174 built in the control means 94 is set (step 206) to start timekeeping, the feedback control is continued, and the correction value of the feedback control is adjusted. Learning control is performed so as to update (step 208), and it is determined whether or not the time Δt measured by the timer 174 has become equal to or longer than the set time t (step 210).

In step 208, since the operating region of the engine 2 is in any one of the enrich regions i1 to i6, the rich air-fuel ratio (for example, 14.7) is read from the rich air-fuel ratio basic map. The learning control is performed such that the correction value at this time is multiplied by a coefficient and updated as a learning value.

If the determination (step 210) is NO, the process returns to step 208 to control the air-fuel ratio to be the rich side air-fuel ratio. Control. If this determination (step 210) is YES, the learning value that is the correction value learned by the learning control is reflected on the rich air-fuel ratio read from the rich air-fuel ratio basic map (step 2).
12) to correct the rich-side air-fuel ratio, and control is performed so that the corrected rich-side air-fuel ratio becomes the end (step 214).

Thus, the air-fuel ratio learning control device 92
The operating state of the engine 2 is in the feedback range j1 to j6.
, The feedback control is continued immediately by the O2 sensor 88 for the set time t, and the learning control is performed, without immediately stopping the feedback control even if the process shifts from one of the enrichment regions i1 to i6.

In the determination (step 204), if the transition from the feedback areas j1 to j6 to the enrichment areas i1 to i6 is not the first time and is NO, the routine jumps to step 212 and is read from the rich side air-fuel ratio basic map. The learned value, which is the correction value previously learned by the learning control, is reflected on the rich air-fuel ratio to be read (step 212).
Then, the rich-side air-fuel ratio is corrected, and control is performed such that the corrected rich-side air-fuel ratio becomes equal to the end (step 21).
4).

Also, the feedback areas j1 to j6
When the learning is completed in the enriched area i, for example, the enriched area i1, which has been transferred to the enriched areas i1 to i6, learning is performed even if the enriched area i1 is shifted to another enriched area i2 to i6. Not performed.

As described above, the air-fuel ratio learning control device 92
As shown in FIG. 3, learning control is performed by the control means 94 so that when the operating region of the engine 2 shifts from the feedback region j to the enrichment region i, the feedback control is continued to update the correction value of the feedback control. By using the correction value updated by the learning control, the rich air-fuel ratio in the enrichment region i can be corrected.

Therefore, the air-fuel ratio learning control device 92
If the air-fuel ratio is controlled to be the rich-side air-fuel ratio set as the target air-fuel ratio, the rich-side air-fuel ratio can be adjusted to an appropriate value even if a situation occurs that deviates from the rich-side air-fuel ratio that is the target air-fuel ratio. Value can be corrected.

Thus, the air-fuel ratio learning control device 92
Can prevent the deterioration of the exhaust harmful component value in the enrichment region i, and can improve the management accuracy of the exhaust harmful component value.

FIG. 7 shows a second embodiment. The air-fuel ratio learning control device 92 of the second embodiment changes and sets the set time t for continuing the feedback control according to the transition speed v when the operation region of the engine 2 transitions from the feedback region j to the enrich region i. It is.

For example, as shown by the solid line in FIG. 7, when the operating region of the engine 2 shifts rapidly from the feedback region j to the enrich region i (sudden acceleration operation state) and the shift speed v is high (v1), The set time t for continuing the feedback control is set short (t1). Thus, in the enrichment region i, it is possible to avoid the inconvenience of performing the feedback control unnecessarily in a state where the O2 sensor 88 does not react due to the rich air-fuel ratio.

As shown by a dashed line in FIG. 7, the operating region of the engine 2 gradually shifts from the feedback region j to the enrich region i (slow acceleration operation state) and the shift speed v
Is longer (v2), the set time t for continuing the feedback control is set longer (t2). Thus, in the enrichment region i, the execution time of the feedback control by the O2 sensor 88 can be lengthened to increase the frequency of updating the correction value.

For this reason, the air-fuel ratio learning control device 92 of the second embodiment changes the set time t for continuing the feedback control in accordance with the transition speed v, thereby eliminating unnecessary feedback control and reducing the control speed. The accuracy of learning can be increased by increasing the frequency of updating the correction value.

FIG. 8 shows a third embodiment. The air-fuel ratio learning control device 92 of the third embodiment sets an intermediate region k between the feedback region j and the enrichment region i, and transitions from the feedback region j to the enrichment region i or from the enrichment region i to the feedback region j.
Prior to the shift to, feedback control is performed in each of the intermediate regions k.

For example, when shifting from the feedback area j to the enrichment area i, feedback control based on the rich air-fuel ratio is performed in the intermediate area k, and learning control is performed so as to update the correction value of the feedback control. The rich-side air-fuel ratio is corrected by the correction value of the learning control, and control is performed so that the corrected rich-side air-fuel ratio is obtained in the enrichment region i. Thus, in the enrich region i, the rich air-fuel ratio can be quickly corrected to an appropriate value.

Further, when shifting from the enrichment region i to the feedback region j, the feedback control based on the specific air-fuel ratio is performed in the intermediate region k, and the learning control is performed so as to update the correction value of the feedback control. The specific air-fuel ratio is corrected by the correction value of the learning control, and the feedback control is performed so that the corrected specific air-fuel ratio is obtained in the feedback region j. Thereby, in the feedback area j, the specific air-fuel ratio can be quickly corrected to an appropriate value.

For this reason, the air-fuel ratio learning control device 92 of the third embodiment changes the enrichment region i from the feedback region j to the enrichment region i.
In the transition to the feedback region j from the enrichment region i or the feedback region j, the control accuracy to the target air-fuel ratio can be improved by quickly correcting the rich side air-fuel ratio or the specific air-fuel ratio to an appropriate value. it can.

FIG. 9 shows a fourth embodiment. The air-fuel ratio learning control device 92 of the fourth embodiment includes an O2 sensor 88.
A fresh air supply means (not shown) for supplying fresh air is provided in the central area m of the enriched area i after the transition from the feedback area j to the enriched area i, as shown in FIG. By blowing fresh air onto the O2 sensor 88, the O2 sensor 88 is made responsive and feedback control is performed.

As described above, the air-fuel ratio learning control device 92 according to the fourth embodiment can perform the feedback control in the central region m after the transition from the feedback region j to the enrichment region i. Can be implemented so that the rich air-fuel ratio in the central region m of the enrich region i can be corrected using the correction value updated by the learning control.

As described above, the air-fuel ratio learning control device 92 according to the fourth embodiment can perform the learning control by the feedback control in the central region m of the enrich region i, thereby setting the rich-side air-fuel ratio to a more appropriate value. The correction can be performed, and the deterioration of the exhaust harmful component value in the enrichment region i can be reliably prevented, so that the management accuracy of the exhaust harmful component value can be further improved.

[0057]

As described above, according to the air-fuel ratio learning control device of the present invention, when the operating range of the engine shifts from the feedback range to the enrichment range, the feedback control is continued by the control means to correct the feedback control. By implementing learning control to update the value,
Using the correction value updated by the learning control, the rich air-fuel ratio in the enrichment region can be corrected.

Therefore, the air-fuel ratio learning control device of the present invention, when controlling the air-fuel ratio to be the rich air-fuel ratio set as the target air-fuel ratio, sets the target air-fuel ratio to the rich air-fuel ratio. Even if a deviation occurs, the rich-side air-fuel ratio can be corrected to an appropriate value, whereby deterioration of the exhaust harmful component value can be prevented, and the management accuracy of the exhaust harmful component value can be improved.

[Brief description of the drawings]

FIG. 1 is a flowchart of air-fuel ratio learning control according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a feedback region and an enrichment region set by an engine speed and an engine load.

FIG. 3 is a diagram illustrating a transition from a feedback area to an enrichment area.

FIG. 4 is a schematic configuration diagram of an air-fuel ratio learning control device.

FIG. 5 is a schematic configuration diagram of a control unit.

FIG. 6 is a flowchart of an air-fuel ratio learning control device.

FIG. 7 is a diagram illustrating a shift from a feedback area to an enrichment area according to the second embodiment.

FIG. 8 is a diagram illustrating a transition between a feedback area and an enrichment area according to a third embodiment.

FIG. 9 is a diagram illustrating a shift from a feedback area to an enrichment area according to the fourth embodiment.

[Description of Signs] 2 Engine 22 Intake passage 32 Exhaust passage 42 Fuel injection valve 74 Engine speed sensor 76 Cylinder discrimination sensor 80 Intake pressure sensor 82 Water temperature sensor 84 Throttle sensor 86 Intake temperature sensor 88 O2 sensor 90 Catalyst temperature sensor 92 Air-fuel ratio Learning control device 94 Control means

Claims (3)

[Claims] An exhaust sensor provided in a feedback region and an enrich region is provided by dividing an operation region of an engine into a plurality of regions according to an engine speed and an engine load, and the feedback region is provided in an exhaust passage of the engine. The feedback control is performed so that the air-fuel ratio becomes the specific air-fuel ratio set as the target air-fuel ratio based on the detection signal output from the control unit, and the learning control is performed so that the correction value of the feedback control is updated. The air-fuel ratio is controlled to be a rich-side air-fuel ratio that is set to a richer side than the specific air-fuel ratio, and the feedback control is continued when the operating region of the engine shifts from the feedback region to the enrichment region. Implement learning control to update the correction value of feedback control An air-fuel ratio learning control device for an engine, comprising: 2. The control means executes learning control so that when the operating region of the engine shifts from the feedback region to the enrichment region for the first time, the feedback control is continued and the correction value of the feedback control is updated. The air-fuel ratio learning control device for an engine according to claim 1, wherein the control device is a control unit. 3. The learning control according to claim 1, wherein the control means continues the feedback control for a set time when the operating range of the engine shifts from the feedback range to the enrichment range and updates the correction value of the feedback control. The engine air-fuel ratio learning control device according to claim 1, wherein the control unit is a control unit that performs the control.