JP2817106B2 - Air-fuel ratio control method for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control method for an internal combustion engine, and more particularly to a method of feeding back an air-fuel mixture supplied to an engine to a target air-fuel ratio using an exhaust concentration sensor having an output characteristic substantially proportional to the exhaust gas concentration. The present invention relates to an air-fuel ratio control method for controlling.

[0002]

2. Description of the Related Art A detected value of an exhaust gas concentration detected by an exhaust gas concentration detector disposed in an exhaust system of an internal combustion engine is compared with a predetermined reference value to determine an air-fuel ratio of an air-fuel mixture supplied to the engine.
When the exhaust gas concentration detection value changes from the rich side to the lean side or from the lean side to the rich side with respect to the predetermined reference value, proportional control for increasing or decreasing the air-fuel ratio by the first correction value, and the exhaust gas concentration detection value An air-fuel ratio feedback control method of performing feedback control to a target air-fuel ratio by integral control in which the air-fuel ratio is increased / decreased at predetermined intervals by a second correction value when the predetermined reference value is on the lean side or the rich side is conventionally known. More known.

When such a control method is applied to an actual engine, differences in engine specifications (for example, differences in valve timing between an engine for a vehicle having an automatic transmission and an engine for a vehicle having a manual transmission, etc.). However, in order to share the electronic control unit (especially the ROM in the unit), the first and / or the correction value corresponding to the set voltage supplied from the artificially adjustable voltage forming means can be used. Alternatively, it has been proposed to correct the second correction value (JP-A-61-272431).

[0004]

The object of the invention is to be Solved However, the above-mentioned Hisage
In the proposed method, the feedback control
The corresponding correction value for proportional control or integral control is artificially set.
Differences in engine specifications
Target air-fuel ratio setting
It was not possible to deal with the case where the value deviated from the appropriate value. Ma
When an exhaust gas concentration sensor having an output characteristic substantially proportional to the exhaust gas concentration is used, the target air-fuel ratio is changed in accordance with the operating state of the engine. The correction value for control is adjusted according to the voltage that is artificially adjusted regardless of the operating state of the engine.
It is difficult to properly cope with all of the various engine operating states if the correction is made uniformly . That is,
Correct differences in engine specifications and variations in characteristics during mass production
Corrections are made uniformly regardless of the engine operating conditions.
This causes the following problem.

[0005] For example, when the engine is idle, since the amount of intake air is less than the other operating conditions, idle
If corrections are made that are suitable for operating conditions other than the idle state, the problem that idle stability cannot be ensured may occur.
You . Further, when the target air-fuel ratio is set leaner than the stoichiometric air-fuel ratio, if the actual air-fuel ratio further deviates toward the leaner side from the target air-fuel ratio, a problem such as misfire easily occurs. It is not preferable to make the same correction as in the case where the fuel ratio is set to the fuel ratio or the rich side.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and when the feedback control is performed by changing the target air-fuel ratio in accordance with the engine operating state, differences in engine specifications, variations in characteristics during mass production, etc. With appropriate modifications
And to provide an air-fuel ratio control method capable and Turkey to ensure excellent reduction of exhaust emissions and drivability.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention supplies an exhaust gas to an engine using an exhaust gas concentration sensor provided in an exhaust system of an internal combustion engine and having an output characteristic substantially proportional to the exhaust gas concentration. In an air-fuel ratio control method for an internal combustion engine, the air-fuel ratio of an air-fuel mixture is feedback-controlled to a target air-fuel ratio according to an operating state of the engine.
Artificially adjustable multiples corresponding to multiple operating conditions
A variable voltage forming means comprising a variable voltage circuit is provided, in accordance with a plurality of setting voltage supplied from the friendly <br/> varying voltage forming means
A plurality of correction values are set, and the target air-fuel ratio is corrected by the set plurality of correction values.

[0008] Further, the plurality of operating states include an idle operation.
The target air-fuel ratio is set leaner than the stoichiometric air-fuel ratio.
It is desirable to set the operating state to be determined and other operating states .

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is an overall configuration diagram of a control device to which the control method of the present invention is applied. In FIG. 1, reference numeral 1 denotes an intake valve and an exhaust valve (not shown) provided in each cylinder in a pair. DOHC
It is an in-line four-cylinder engine. In the engine 1, the operating characteristics of the intake valve and the exhaust valve (specifically, the valve opening timing and the lift amount, hereinafter referred to as "valve timing") are changed to a high-speed valve timing suitable for a high-speed rotation region of the engine.
It is configured to be switchable to a low-speed valve timing suitable for a low-speed rotation region.

A throttle body 3 is provided in the middle of an intake pipe 2 of the engine 1, and a throttle valve 3 'is provided therein.
Is arranged. A throttle valve opening (θTH) sensor 4 is connected to the throttle valve 3 ′, and outputs an electric signal corresponding to the opening of the throttle valve 3 and supplies it to an electronic control unit (hereinafter referred to as “ECU”) 5. I do. The fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of the intake valve (not shown) of the intake pipe 2, and each injection valve is connected to a fuel pump (not shown). Is electrically connected to the ECU 5 together with the E
The valve opening time of fuel injection is controlled by a signal from the CU 5.

An electromagnetic valve 21 for controlling the switching of the valve timing is connected to the output side of the ECU 5, and the opening and closing operation of the electromagnetic valve 21 is controlled by the ECU 5. The solenoid valve 21 switches the hydraulic pressure of a switching mechanism (not shown) for switching the valve timing between high and low. The valve timing corresponds to the high / low hydraulic pressure. Is switched to The hydraulic pressure of the switching mechanism is detected by a hydraulic pressure (POIL) sensor 20, and a detection signal is supplied to the ECU 5.

On the other hand, immediately downstream of the throttle valve 3, a pipe 7
An absolute pressure signal (PBA) sensor 8 is provided through the intake pipe, and an absolute pressure signal converted into an electric signal by the absolute pressure sensor 8 is supplied to the ECU 5. Further, an intake air temperature (TA) sensor 9 is attached downstream thereof.
Detects intake air temperature TA and outputs the corresponding electrical signal for EC
Supply to U5.

An engine water temperature (TW) sensor 10 mounted on the main body of the engine 1 is composed of a thermistor or the like, detects an engine water temperature (cooling water temperature) TW, outputs a corresponding temperature signal, and supplies it to the ECU 5. Engine speed (NE)
The sensor 11 and the cylinder identification (CYL) sensor 12 are mounted around a camshaft (not shown) of the engine 1 or around a crankshaft. The engine speed sensor 11 is the engine 1
A pulse (hereinafter, referred to as a "TDC signal pulse") at a predetermined crank angle position every time the crankshaft rotates by 180 degrees, and the cylinder discriminating sensor 12 outputs a signal pulse at a predetermined crank angle position of a specific cylinder. These signal pulses are supplied to the ECU 5.

The three-way catalyst 14 is disposed in the exhaust pipe 13 of the engine 1 and purifies components such as HC, CO and NOx in the exhaust gas. An oxygen concentration sensor (hereinafter, referred to as an “LAF sensor”) 15 as an exhaust concentration sensor is an exhaust pipe 13.
Is mounted on the upstream side of the three-way catalyst 14, and outputs an electric signal having a level substantially proportional to the oxygen concentration in the exhaust gas.
Supply to U5.

The ECU 5 further includes an atmospheric pressure (PA) sensor 1.
6. A vehicle speed (VSP) sensor 17, a clutch sensor 18 for detecting engagement / disengagement of a clutch, and a gear position sensor 19 for detecting a shift position of a transmission are connected, and detection signals of these sensors are supplied to the ECU 5.

The ECU 5 shapes input signal waveforms from various sensors, corrects a voltage level to a predetermined level, and converts an analog signal value into a digital signal value. 5b, a storage means 5c for storing various calculation programs executed by the CPU 5b, calculation results, and the like, an output circuit 5d for supplying a drive signal to the fuel injection valve 6, the solenoid valve 21, and the like.

The ECU 5 is provided with a voltage regulator (variable voltage forming means) 51, the output voltage of which is A / A.
It is D-converted and input to the CPU 5b. The voltage regulator 51 is composed of three variable voltage circuits composed of a voltage dividing resistor or the like connected to a constant voltage circuit (not shown) in the present embodiment, and the three variable voltage circuits are individually and individually adjusted. It is possible. The values of first to third mass-production correction variables KCMPRO1 to 3 used in the program of FIG. 2 described later are determined in accordance with the output voltages of these variable voltage circuits.

The voltage regulator 51 is adjusted so as to compensate for variations in the characteristics of the engine and changes over time at the time of assembling the control device shown in FIG. 1 into the engine or at the time of periodic maintenance.

The CPU 5b determines various engine operation states such as a feedback control operation area and an open loop control operation area corresponding to the oxygen concentration in the exhaust gas based on the various engine parameter signals described above, and sets the engine operation state. Accordingly, based on the following equation (1), the TDC
Fuel injection time To of the fuel injection valve 6 synchronized with the signal pulse
ut is calculated.

Tout = Ti × KCMDM × KLAF ×
K ₁ + K ₂ (1) where Ti is a basic fuel amount, specifically, a basic fuel injection time determined according to the engine speed NE and the intake pipe absolute pressure PBA, and this Ti value is determined. Is stored in the storage means 5c.

KCMDM is a corrected target air-fuel ratio coefficient set by a program shown in FIG. 2, which will be described later. The KCMDM is set in accordance with the engine operating state, and the fuel cooling correction coefficient KETV is added to the target air-fuel ratio coefficient KCMD representing the target air-fuel ratio. It is calculated by multiplying. The correction coefficient KETV is a coefficient for correcting the fuel injection amount in advance in consideration of a change in the supplied air-fuel ratio due to a cooling effect caused by actually injecting the fuel, and according to the value of the target air-fuel ratio coefficient KCMD. Is set. As is apparent from the above equation (1), if the target air-fuel ratio coefficient KCMD increases, the fuel injection time Tout increases. Therefore, the KCMD value and the KCMDM value are values proportional to the reciprocal of the so-called air-fuel ratio A / F. Become.

KLAF is an air-fuel ratio correction coefficient. The air-fuel ratio is set so that the air-fuel ratio detected by the LAF sensor 15 matches the target air-fuel ratio during the air-fuel ratio feedback control. Is set to a predetermined value.

K ₁ and K ₂ are other correction coefficients and correction variables calculated in accordance with various engine parameter signals, respectively, for optimizing various characteristics such as a fuel consumption characteristic and an engine acceleration characteristic according to the engine operating state. It is set to the value as intended.

The CPU 5b further outputs a valve timing switching instruction signal in accordance with the operating state of the engine to output the electromagnetic valve 2
1 is performed.

The CPU 5b outputs a signal for driving the fuel injection valve 6 and the solenoid valve 21 via the output circuit 5d based on the result calculated and determined as described above.

FIG. 2 is a flowchart of a program for calculating the target air-fuel ratio coefficient KCMD and the corrected target air-fuel ratio coefficient KCMDM. This program is executed in synchronism with the generation of each TDC signal.

In step S12, it is determined whether or not a shift change is being performed. This determination is made by detecting whether or not the clutch is connected by the clutch sensor 18. If the answer in step S12 is affirmative (YE
S), that is, when a shift change is being performed, a predetermined shift change delay time (for example, 500 milliseconds) tmDLYBS is set in a shift change delay timer tmKBS that measures the elapsed time after the end of the shift change, and this is started (step S13). , F / C delay timer tmA for measuring fuel cut duration
A predetermined F / C delay time tmAFCDLY for FC
(300 milliseconds) is set and started (step S17), and the current value KCMD (n) of KCMD is set to the same value as the previous value KCMD (n- ₁ ) (step S2).
2), proceed to step S39.

If the answer to step S12 is negative (NO),
That is, when the shift change is not being performed, it is determined whether or not the count value of the shift change delay timer tmKBS is 0 (step S14). If this answer is affirmative (YES),
That is, when the predetermined time tmDLYBS has elapsed after the end of the shift change, the process immediately proceeds to step S18, and the answer is negative (NO).
If the mDLYBS has not elapsed, it is determined whether the valve timing has been changed (step S15).
If the answer to step S15 is negative (NO), the process proceeds to step S17, and if affirmative (YES), the shift change delay timer tmKBS is reset to a value of 0 and the process proceeds to step S18.

As described above, the target air-fuel ratio coefficient KCMD is maintained at the previous value during the shift change and before the lapse of the predetermined time tmDLYBS after the end of the shift change. However, when the valve timing is changed, the process immediately proceeds to step S18. Thus, it is possible to prevent the target air-fuel ratio from greatly changing due to a change in the engine operating state during and immediately after the shift change, and to prevent the supplied air-fuel ratio from deviating from a desired value. In this embodiment, when the high-speed valve timing is selected, the KCMD value is not set to a value leaner than the stoichiometric air-fuel ratio (A / F = 14.7) (so-called lean burn control is prohibited). Is changed when the valve timing is changed.
If the previous value of the MD value is maintained, lean burn control may be executed when the high-speed valve timing is selected. To avoid such a situation, immediately stop the previous value of the KCMD value when changing the valve timing. ing.

In step S18, it is determined whether or not fuel cut is being performed. If the answer is affirmative (YES), T
A predetermined value NTDCX (for example, 6) is set in the DC counter NFB (step S19), and the F / C delay timer t
It is determined whether the mAFC count value is 0 (step S20). The TDC counter NFB is provided for changing the control gain of the air-fuel ratio feedback control according to the number of TDC signal pulses after the fuel cut. When the answer to step S20 is negative (NO), that is, when the fuel cut duration is shorter than the predetermined time tmAFCDLY, the process proceeds to step S22, and the KCMD value is held at the previous value. If the answer in step S20 is affirmative (YE
S), that is, fuel cut is performed for a predetermined time tmAFCDLY
When the above is continued, the KCMD value is reduced to substantially the stoichiometric air-fuel ratio (A
/F=14.7) is set to a predetermined value KCMDFC, and the flow advances to step S33.

As described above, when the fuel cut duration is short (less than tmAFCDLY), KCMD
The value is kept at the previous value and the fuel cut duration is tm
When it is equal to or higher than AFCDLY, the predetermined value KCMDFC, which is substantially equivalent to the stoichiometric air-fuel ratio, is set, so that the supply air-fuel ratio immediately after the end of the fuel cut can be appropriately controlled. That is, when the fuel cut duration is short, the engine operation state hardly changes. Therefore, by starting the feedback control from the value immediately before the fuel cut, a desired supply air-fuel ratio can be quickly obtained. If the fuel cut duration is long, KC
Since the MD value is set to substantially the center value, even if the KCMD value set according to the engine operating state after the fuel cut ends is a value on either the lean side or the rich side,
Can follow quickly.

If the answer to step S18 is negative (NO),
That is, when the fuel cut is not being performed, the previous value of the equivalent ratio (hereinafter, referred to as “detected air-fuel ratio”) calculated based on the previous value KCMD (n− ₁ ) of KCMD and the output of the LAF sensor 15 and representing the detected air-fuel ratio is referred to. It is determined whether or not the absolute value of the deviation from the calculated value KACT (n- ₁ ) is equal to or smaller than a predetermined value DKAFC (for example, a value corresponding to 0.8 in A / F conversion) (step S23). When the answer is affirmative (YES), that is, when the deviation is equal to or less than the predetermined value DKAFC, the count value of the TDC counter NFB is reset to a value 0 (step S25), and when the answer is negative (NO), the count value of the NFB is reset to a value 1
Is decremented only (step S24), and step S2
Proceed to 6.

In steps S23 to S25, immediately after the end of the fuel cut, the deviation between the target air-fuel ratio coefficient KCMD and the detected air-fuel ratio KACT is large (DKAFC or more).
At this time, the count value of the TDC counter NFB becomes equal to or more than 1 and the control gain of the air-fuel ratio feedback control becomes N
It is set to a larger value when FB = 0.

In step S26, a predetermined time tmAFCDLY is set in the F / C delay timer and started, and then the reference value KBSM of the target air-fuel ratio coefficient is set.
(Step S27) and the high load target value KWO applied when the engine is in a predetermined high load operation state
T is calculated (step S28), and step S2 is performed.
Go to 9.

In step S27, the reference value KBSM
Is usually the engine speed NE and the absolute pressure PB in the intake pipe.
A is read from the KBSM map set according to A, but when the engine coolant temperature TW is low, it is set to a value read from the KTWLAF map set according to the engine coolant temperature TW and the absolute pressure PBA in the intake pipe. You.
The KBSM map includes a map for high-speed valve timing used when selecting high-speed valve timing and a map for low-speed valve timing used when selecting low-speed valve timing.

In step S28, the high load target value KW
OT is the engine speed NE and the intake pipe absolute pressure PBA
Is read from the KWOT map set in accordance with.
The KWOT map is also provided for high-speed valve timing and for low-speed valve timing. In step S29, it is determined whether or not a flag FWOT set to a value of 1 when the engine is in a predetermined high load operation state is a value of 1, and the answer is negative (NO), that is, the engine is in a predetermined high load operation state. If it is not in the state, the reference value KBSM calculated in step S27 is replaced with the current value KCMD of the target air-fuel ratio coefficient.
The process proceeds to step S33 as (n). When the answer to step S29 is affirmative (YES), that is, when the engine is in the predetermined high load operation state, the high load target value KWOT is set to the reference value K.
It is determined whether or not it is BSM or more (step S30). When the answer is negative (NO), that is, when KWOT <KBSM, the process proceeds to step S32, and the answer is affirmative (YES);
That is, when KWOT ≧ KBSM, KCMD (n) = K
The process proceeds to step S33 as WOT.

Thus, the target air-fuel ratio coefficient KCMD (n)
Is set to the reference value KBSM when the engine is in a state other than the predetermined high load operation state, and when the engine is in the predetermined high load operation state, the larger of the reference value KBSM or the high load target value KWOT, whichever is larger. Is set to

In a step S33, it is determined whether or not the engine is in an idle state. If the answer is affirmative (YES), a first mass production correction variable KCMPRO1 set according to the output voltage of the voltage regulator 51 is set. It is added to the KCMD value (step S35), and the process proceeds to step S38. When the answer to step S33 is negative (NO), that is, when the engine is not in the idle state, it is determined whether the KCMD value is smaller than a predetermined value KCMDZL leaner than the stoichiometric air-fuel ratio (for example, a value corresponding to A / F = 18) (step S33). S34). Step S
34 is negative (NO), that is, KCMD (n) ≧ KCMD
In the case of ZL, the second mass production correction variable KCMPRO2 set according to the output voltage of the voltage
It is added to the MD value (step S36), and the process proceeds to step S38. The answer to step S34 is affirmative (YES), that is, KC
When MD (n) <KCMDZL and the so-called lean burn control is being performed, the third mass-production correction variable KCMPRO3 set according to the output voltage of the voltage regulator 51 is set to K
It is added to the CMD value (step S37), and step S38
Proceed to.

According to steps S33 to S37, the first mass production correction variable K
When CMPRO1 is applied and the engine is in a state other than idle, the value of the target air-fuel ratio coefficient KCMD and a predetermined value KCMDZL
The second or third mass production correction variable KC according to the magnitude relation
Since MPRO2 or KCMPRO3 is applied, 3
The variable voltage circuit provided corresponding to the operating state of
The target air-fuel ratio can be adjusted to
Can be corrected to a value suitable for
Control due to differences, characteristic variations during mass production or aging
Correct the deviation of the air-fuel ratio appropriately to obtain good exhaust gas characteristics and
Drivability can be ensured. In particular, it is advantageous in ensuring the stability of the exhaust gas characteristics in the idle state of the engine and avoiding misfires and fluctuations in engine speed during lean burn control. In other words, variations in mass production and aging
Control air-fuel ratio deviates and exhaust gas characteristics and drivability deteriorate
In such a case, by adjusting the variable voltage circuit
The target air-fuel ratio has been changed to improve the deteriorated exhaust gas characteristics, etc.
Can be For example, factory inspections and vehicle inspections
If it finds any deterioration in exhaust gas characteristics, etc.
The target air-fuel ratio is optimized by adjusting the pressure circuit
To improve exhaust gas characteristics, etc.
it can. In addition, supplements corresponding to each of a plurality of operating conditions are provided.
Correction can be performed, so the exhaust gas
Correction of the corresponding target air-fuel ratio becomes possible. Conventional as described above
In the technology, feedback control is performed by a variable voltage circuit.
The control constant can be adjusted, but the target air-fuel ratio cannot be adjusted.
Therefore, even when the control is stable, the
Deterioration of exhaust gas characteristics etc.
Absent. Adjustments for each of multiple operating conditions
Not suitable for all operating conditions
It is difficult to set a proper setting.

In step S38, a KCMD value limit process is performed. This limit processing is performed so that the difference between the previous value and the current value of KCMD does not exceed an upper limit value set according to the engine operating state, so that the KCMD value is not suddenly changed. However, when the KCMD value is leaner than the stoichiometric air-fuel ratio and the accelerator pedal is suddenly depressed, the KCMD value is immediately increased to a value corresponding to the stoichiometric air-fuel ratio.

After the KCMD limit processing, step S3
In step 9, the corrected target air-fuel ratio coefficient KCMDM is calculated by reading the fuel cooling correction coefficient KETV from the table set according to the KCMD value and multiplying the KCMD value by the KCMD value (step S40). Next, a limit check of the KCMDM value is performed (step S41), and this program ends. In this limit check, it is determined whether or not the KCMDM value is within a range of predetermined upper and lower limit values KCMDMH (for example, a value corresponding to A / F = 8) and KCMDML (for example, A / F = 23). If the value is outside the range, the KCMDM value is set to the upper limit value KCMDMH or the lower limit value KCMDML.

After the execution of this program, in the engine operating state where the air-fuel ratio feedback control is possible, the calculated target air-fuel ratio coefficient KCMD and the detected air-fuel ratio KACT
The air-fuel ratio correction coefficient KLAF is calculated so that

[0044]

According to the present invention, as described above in detail, according to the present invention, d
Variable voltage generating means comprising a plurality of artificially adjustable variable voltage circuits corresponding to a plurality of operating states of the engine.
Then, a plurality of correction values are set according to a plurality of set voltages supplied from the variable voltage forming means , and the target air-fuel ratio of the air-fuel ratio feedback control is corrected by the set plurality of correction values . Therefore, during assembly and maintenance
In each case, the setting voltage of multiple variable voltage circuits
To artificially set a value suitable for the corresponding driving condition
As a result, a correction value suitable for each operating condition can be obtained, so that differences in engine specifications or variations in characteristics during mass production are appropriately corrected to ensure good exhaust gas characteristics and operability. it is as possible out to be. In other words, mass production
The control air-fuel ratio shifts due to yearly changes, etc.
Adjust the variable voltage circuit when the driving characteristics deteriorate
As a result, the target air-fuel ratio has changed,
Properties and the like can be improved. For example, the factory default
When a deterioration in exhaust gas characteristics, etc. is discovered by inspection or vehicle inspection
The target air-fuel ratio by adjusting the variable voltage circuit.
Corrected to an appropriate air-fuel ratio to improve exhaust gas characteristics, etc.
can do. In addition, each of multiple operating conditions
Exhaust gas characteristics etc. deteriorated because corresponding corrections can be made
It is possible to correct the target air-fuel ratio corresponding to the operation state.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a fuel supply control device to which a control method of the present invention is applied.

FIG. 2 is a flowchart of a program for calculating a target air-fuel ratio coefficient (KCMD) and a corrected target air-fuel ratio coefficient (KCMDM).

FIG. 3 is a flowchart of a program for calculating a target air-fuel ratio coefficient (KCMD) and a corrected target air-fuel ratio coefficient (KCMDM).

[Explanation of symbols]

 Reference Signs List 1 internal combustion engine 5 electronic control unit (ECU) 6 fuel injection valve 15 exhaust concentration sensor (oxygen concentration sensor)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-272431 (JP, A) JP-A-63-154832 (JP, A) JP-A-62-247142 (JP, A) 202653 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) F02D 41/14 310 F02D 45/00 312

Claims (2)

(57) [Claims] An air-fuel ratio of an air-fuel mixture supplied to an engine using an exhaust concentration sensor provided in an exhaust system of an internal combustion engine and having an output characteristic substantially proportional to an exhaust gas concentration is set according to an operating state of the engine. in air-fuel ratio control method for an internal combustion engine is feedback-controlled to the air-fuel ratio, the engine
Artificially adjustable for multiple operating conditions
Providing variable voltage forming means comprising a plurality of variable voltage circuits,
Response to a plurality of setting voltage supplied from said variable voltage forming means
A plurality of correction values, and correcting the target air-fuel ratio with the set plurality of correction values. 2. The method according to claim 1, wherein the plurality of operating states include an idle operating state.
The target air-fuel ratio is set leaner than the stoichiometric air-fuel ratio.
2. An air-fuel ratio control method for an internal combustion engine according to claim 1 , wherein the operating state is an operating state other than these .