JPH02102334A - Air-fuel ratio feedback control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To enhance accuracy in an air-fuel ratio control, when the air-fuel ratio of a mixture to be supplied is feedback-controlled by using the mean value of coefficients which change with the output of an exhaust gas density detector, by stopping the calculation of the mean value in a feedback control region where the load of an engine is within a prescribed range. CONSTITUTION:During the operation of an internal combustion engine 1, an ECU 5 controls a fuel injection valve 6 on the basis of various engine parameter signals. In other words, when the operation of the engine 1 is in an air-fuel ratio feedback control operation region, the mean value of coefficients which change with the output of an O2 sensor 14 is calculated, and the feedback control of air-fuel ratio is carried out by using at least the calculated mean value. When the load of the engine 1 is less than a first prescribed value, the feedback control is stopped, and the control for increasing the air-fuel ration of the mixture is carried out. In this case, it is so contrived that the calculation of the mean value of coefficients is stopped in the air-fuel ratio feedback control operation region where the load of the engine 1 is greater than the first prescribed value and is less than a second prescribed value.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an air-fuel ratio feedback control method for an internal combustion engine. The present invention relates to an air-fuel ratio feedback control method for an internal combustion engine, in which an average value of air-fuel ratio correction coefficients is calculated, and the calculated average value is used in each operating range of the engine.

(Prior art and its problems) Conventionally, the basic fuel injection time of an internal combustion engine is corrected using an air-fuel ratio feedback correction coefficient obtained based on the output of an exhaust gas concentration detector, and the air-fuel mixture supplied to the engine is adjusted. The fuel ratio is controlled to be the target air-fuel ratio, and the arithmetic average value of the maximum and minimum values of the feedback correction coefficient is determined each time the feedback correction coefficient skips due to the inversion of the output signal of the exhaust gas concentration detector. For example, Japanese Patent Application Laid-Open No. 60-60231 discloses an air-fuel ratio learning control method for an internal combustion engine in which learning control is performed so that the average value approaches a predetermined value.

According to this method, a learning value that brings the average value closer to a predetermined value is set, and the feedback correction coefficient is corrected by the learning value, but in order to prevent the learning value from becoming an abnormal value. Furthermore, calculation of the learned value is stopped when the engine coolant is low, when the engine is idling up, when the intake air temperature is high, and when the engine load is outside a specific value range.

However, during low-speed cruise operation or slow deceleration operation of the engine, the absolute pressure inside the intake pipe is, for example, 177 mm1.
The engine may be operated at an extremely low load such that the load is less than 1g. In this type of engine operation region, which is low-load air-fuel ratio feedback control near the air-fuel ratio lean region, the combustion state of the engine becomes unstable, and especially at high altitudes where atmospheric pressure is low, exhaust pressure decreases and A pressure drop occurs, which also reduces the reliability of the exhaust gas concentration detector output. When the learned value is calculated in such an unstable combustion operating region, the calculated learned value is different from a normal value that accurately represents the engine operating condition, and therefore the engine is not operating in the unstable combustion state. Even after exiting the range, the learned value requires a considerable amount of learning time to return to its normal value. Meanwhile, thus
If the air-fuel ratio of the engine is controlled using the obtained abnormal learning value, highly accurate air-fuel ratio control will not be performed.

(Objective of the Invention) The present invention has been made to solve the problem described in 1. The present invention has been made in order to solve the problem described in 1. An object of the present invention is to provide an air-fuel ratio feedback control method for an internal combustion engine that enables highly accurate air-fuel ratio control of the engine by stopping or delaying learning of an air-fuel ratio correction coefficient that changes depending on the air-fuel ratio.

(Means for Solving the Problems) In order to achieve the above object, a first aspect of the present invention provides an exhaust gas concentration detector disposed in the exhaust system of an internal combustion engine when the engine is operating in an air-fuel ratio feedback control operating region. calculates an average value of coefficients that change according to the output of the engine, uses at least the calculated average value to feedback control the air-fuel ratio of the air-fuel mixture supplied to the engine, detects the load of the engine, stopping the feedback control when the engine load is below a first predetermined value;
In the air-fuel ratio feedback control method for an internal combustion engine that increases the air-fuel ratio of the air-fuel mixture, the air-fuel ratio is such that the engine load is equal to or greater than the first predetermined value and equal to or less than a second predetermined value larger than the first predetermined value. The calculation of the average value of the coefficients is stopped in the feedback control operation region.

Furthermore, a second aspect of the present invention calculates the average value of coefficients that vary depending on the output of an exhaust gas concentration detector disposed in the exhaust system of the engine when the internal combustion engine is operating in the air-fuel ratio feedback control operation region, and Feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the engine using at least the calculated average value, detecting the load of the engine, and performing the feedback control when the load of the engine is less than or equal to a first predetermined value. In the air-fuel ratio feedback control method for an internal combustion engine, the air-fuel ratio of the internal combustion engine is stopped and the air-fuel ratio of the air-fuel mixture is increased.
- the speed at which the latest value of the coefficient is learned in the air-fuel ratio feedback control operation region of less than or equal to the second predetermined value that is greater than the first predetermined value;

This is to slow down the process.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall configuration diagram of a fuel supply control system to which the method of the present invention is applied. Reference numeral 1 indicates, for example, a four-cylinder, four-stroke internal combustion engine, and an intake pipe 2 is connected to the engine 1. A throttle body 3 is provided in the middle of the intake pipe 2, and a throttle valve 3' is provided inside. The throttle valve 3' is equipped with a throttle valve opening sensor (hereinafter 1[y
A u sensor J) 4 is connected in series to convert the opening degree of the throttle valve 3' into an electrical signal and send it to an electronic control unit (hereinafter referred to as rEcU) 5.

On the downstream side of the throttle body 3 of the intake pipe 2 and at the intake pipe 2
A fuel injection valve 6 is provided for each cylinder slightly upstream of an intake valve (not shown), and each injection valve is connected to a fuel pump (not shown) and electrically connected to the ECU 3 to receive signals from the ECU 3. The valve opening time of fuel injection is controlled by.

Further, an intake pipe absolute pressure sensor (hereinafter referred to as IP++
^Sensor J) 8 is provided, and this PIIA
The absolute pressure signal converted into an electric signal by the sensor 8 is supplied to the ECU 3. Also, immediately downstream of the throttle body 3 is an intake air temperature sensor (hereinafter referred to as the "T^sensor").
9 is removed (=I), the intake air temperature is detected and a corresponding electrical signal is output and supplied to the ECU 3.

The engine cooling water temperature sensor (rT) is installed on the engine 1 body.
w sensor] 10 is provided. The Tw sensor 10 consists of a thermistor, etc., and is inserted into the circumferential wall of an engine cylinder filled with cooling water, and converts the detected water temperature signal into an EC.
Supply to U3. In addition, the engine rotation speed sensor (r
A sensor (referred to as "Ne sensor") 11 is installed around a camshaft or crankshaft (not shown) of the engine 1.

The Ne sensor 11 detects the crank angle at a predetermined crank angle position every 180° rotation of the crankshaft of the engine, that is, at a crank angle position before the top dead center (TI) at the start of the intake stroke of each cylinder. Angular position signal (r
This TDC signal is sent to the ECU 3.

A three-way catalyst 13 is disposed in the exhaust pipe 12 of the engine 1, and purifies components such as HC, CO, and NOx in the exhaust gas. The 02 sensor 14 as an exhaust gas concentration detector is installed upstream of the three-way catalyst 13 in the exhaust pipe 12, and detects the oxygen concentration in the exhaust gas and outputs a signal according to the detected value. Supply to 5.

Further, upstream of the 02 sensor 14 of the exhaust pipe 12, there is a lf
A secondary air valve 20 is connected via f19.

This secondary air valve 20 is a normally closed solenoid valve and is electrically connected to the ECU 3. When a valve opening drive signal is supplied from the ECU 3, the secondary air valve 20 opens and supplies secondary air to the exhaust pipe 12 to dilute the exhaust gas.

Furthermore, a vehicle speed sensor (hereinafter referred to as V sensor J) 15 is connected to the ECU 3, which detects the traveling speed V of the vehicle.
A signal (2) from the V sensor 15 is supplied to the ECU 3.

The ECU 3 determines various engine operating states such as an air-fuel ratio feedback control operating range and an open loop control operating range based on the various engine parameter signals described above, and also adjusts the TDC according to the determined engine operating state.
The fuel injection time TOUT at which the fuel injection valve 6 should be opened in synchronization with the signal is calculated based on the following equation (1).

Touy=TiXKo2XKrwXKAsrXKLsX
2=(+) for Krl- Here, Ti indicates the basic fuel injection time of the fuel injection valve 6, and this basic injection time is determined depending on, for example, the intake pipe absolute pressure PB^ and the engine rotation speed Ne. be done. KO2 is a 02 feedback correction coefficient calculated from a calculation program flowchart (FIG. 3) according to the present invention, which will be described later. KTW is the engine water temperature correction coefficient determined according to the engine cooling water temperature Tw, KAST is the post-start fuel increase coefficient applied immediately after engine startup for the purpose of preventing engine stall, etc., and Kts is the fuel mixture lean coefficient. It is.

Further, K1 and K2 are a correction coefficient and a correction variable respectively calculated according to various engine parameter signals, and are used to optimize engine characteristics such as fuel consumption characteristics and engine acceleration characteristics according to engine operating conditions. Set to the required value.

ECU3 is the fuel injection time TO obtained in two series.
Based on UT, a drive signal to open the fuel injection valve 6 is sent! 1 injection valve 6.

FIG. 2 is a block diagram showing the circuit configuration inside the ECU 3 shown in FIG. 1. After the output signal from the Ne sensor 11 shown in FIG. It is supplied to an arithmetic processing unit (hereinafter referred to as rCPUJ) 503 and also to a Me counter 502 . The Me counter 502 measures the time interval from the input of the previous TDC signal pulse from the Ne sensor 11 to the input of the current TDC signal pulse, and its N1 value Me is proportional to the reciprocal of the engine rotation speed Ne. do.

Me counter 502 transfers this N1 value Me to data bus 5.
10 to the CPU 503.

In Figure 1, O■11 sensor 4, PB^ sensor 8, T^ sensor 9.7w sensor 10.02 sensor 14, V sensor 15
Each output signal from each sensor is sent to a level correction circuit 5.
After being corrected to a predetermined voltage level in step 04, the voltage is sequentially supplied to an A/D converter 506 by a multiplexer 505.

The A/D converter 506 sequentially converts the analog output voltage from each sensor mentioned above into a digital signal and sends it to the data bus 5.
10 to the CPU 303.

The CPU 303 is further connected to a read-only memory (hereinafter referred to as FROMJ) 507, a random access memory (hereinafter referred to as RAMJ) 508, and a drive circuit 509 via a data bus 510, and the RAM M2O3 is connected to the C
Temporarily stores the calculation results in P U303 and sends them to RO
M2O3 is a control programmer + executed by CPU 303.
1, a basic injection time 11 map of the fuel injection valve 6, a correction coefficient map, etc., which are read out based on the intake pipe absolute pressure PBA and the engine speed Ne, are stored.

The CPU 303 calculates the fuel injection time 1''OUT of the fuel injection valve 6 according to the various engine parameter signals mentioned above according to the control program stored in the ROM2O3, and sends the calculated value to the drive circuit 509 via the data bus 510.
supply to. The drive circuit 509 supplies the fuel injection valve 6 with a control signal to open the fuel injection valve 6 in accordance with the calculated value.

FIG. 3 is a program flowchart showing the procedure for executing the control method of the present invention, and the program includes the above-mentioned 1'D
Executed every time a C signal pulse occurs.

First, it is determined whether the activation of the 02 sensor 14 is completed or not (step 301), and the answer is affirmative (Yes).
If so, it is determined whether a predetermined time Lx seconds (for example, 60 seconds) has elapsed during which the activation of the 02 sensor 14 has been completed (
Step 3o2). Which of the answers to steps 301 and 302 is negative (No), that is, when the activation of the 02 sensor 14 is not yet completed, or when the predetermined time t, x seconds have not elapsed after activation, the 02 Since feedback control cannot be performed, follow step 3 below.
Open loop control is performed from 03 to 307.

First, in step 303, it is determined whether the engine is in the wide-open throttle range (WOT range) (region ■ in Figure 5, which shows each operating range of the engine in relation to engine speed Ne and intake pipe absolute pressure PB^). Discern. If the answer is affirmative (Yes), that is, the engine is in the WOT region, the 02 feedback correction coefficient KO2 is set to a value of 1.0 and open loop control is performed (step 304).

If the answer to step 303 is negative (No), it is determined whether the engine is in the idle region (region I in FIG. 5) of the 02 feedback control operation region (
Step 305). If the answer is affirmative (Yes), that is, the engine is in the idle region, the correction coefficient KO2 is
Open loop control is performed by setting the average value KpEpo of the correction coefficient KO2 to be described later (step 306). On the other hand, when the answer to step 305 is negative (NO), the correction coefficient Ko2 is set to the average value K of the correction coefficient KO2, which will be described later.
REFI is set to perform open loop control (step 3o7).

When the answers to step 301 and step 302 are both affirmative (Yes), that is, when the predetermined time Lx seconds has passed after the activation of the 02 sensor 14, the vehicle running speed V and T^sensor 9 detected by the V sensor 15 A predetermined value TWO2 is read out from the map according to the intake air temperature T^ detected at (step 308). The map has a predetermined value T 1
1+02 is set so that the predetermined value TWO2 becomes smaller as the intake air temperature]゛^ and the traveling speed V become larger. Next, in step 309, the engine cooling water temperature 'V
w is the predetermined value read out in step 308]' 1
It is determined whether or not it is lower than 1+02. This answer is affirmative (Y
es), that is, the engine cooling water temperature Tw is still at the predetermined value TW.
When the temperature is lower than O2, the 02 feedback control is not performed and the fuel increase open loop control for warming up is performed after step 303.

If the answer to step 309 is negative (No), it is determined in steps 310 to 314 which operating range the engine is in. That is, whether or not the engine speed Ne is lower than a predetermined speed NLor (for example, 600 rpm), that is, whether the engine is in the low speed open loop control operation region (region ■ in FIG. 5) (step 310
), as in step 303, whether or not the engine is in the WOT region (region ■ in FIG. 5) (step 311)
, whether the engine speed Ne is larger than a predetermined speed Nll0F (for example, 3500 rpm), that is, whether the engine is in a high-speed open-loop control operating region (region V in FIG. 5).
) (step 312), whether or not LS is smaller than the value 1.0 in the lean coefficient of the air-fuel mixture, that is, whether the engine is running at a predetermined value (first predetermined value) or less. Whether or not the engine is in the lean region (region ■ in Figure 5) (step 313), which is determined by ) (step 314).

Step 3] The answers to 0 and 314 are both negative (N
o), that is, when the engine is not in any of the open loop control operating regions m, ■, ■, and ■ shown in FIG. 5, the engine is in the operating region where 02 feedback control should be performed (region I or Step 315 as in
and proceed to 316. In step 315, the post-start fuel increase coefficient KAST is set to a value of 1.0, and the engine water temperature correction coefficient KTW is calculated according to the following equation (2), and KTW is set to the calculated value.

KTW=CTIL102 (KTWO-1) + 1-
(2) Here, CTl1+02 is a constant determined according to the engine cooling water temperature Tw, and KTWO is a map value of the engine water temperature correction coefficient read from the map according to the engine cooling water temperature Tw.

Next, in step 316, the average values KREFO and KREFI are set for each feedback control operation region I,
As an initial value, a correction coefficient KO2 is calculated by P term and 1 term addition processing according to the output value of the 02 sensor 14. The above formula (1) is calculated based on the calculated correction coefficient KO2.
), the fuel injection time TOUT is calculated, and fuel is injected from the respective fuel injection valves 6, thereby performing 02 feedback control. Furthermore, in step 316, the engine is
When the engine is in the idle region I of the 02 feedback control region, the average value KREFO of the correction coefficient KO2 is calculated, and when the engine is in the region H other than the idle region of the 02 feedback control region, the average value KREFI of the correction coefficient KO2 is calculated. calculate. Details of this calculation will be described later based on FIG. 4.

Any of the answers to steps 310 to 314 is affirmative (
Yes), that is, if the engine is in any of the open loop control regions ■, ■, V, or Vl shown in FIG. It is determined whether the period continues for a predetermined time To seconds (for example, 0.5 seconds). If this answer is affirmative (Yes), that is, if this state continues for a predetermined time To seconds after the engine shifts to the open loop control region, open loop control is performed in step 303 and thereafter. However, if the answer to step 317 is negative (No), that is, after the engine shifts to the open loop control region, step 31
Proceed to steps 8 to 320.

In step 318, it is determined whether or not 02 feedback control was performed when this program was executed when the TDC signal pulse was generated last time. This answer is affirmative (Yes
), that is, when the engine shifts from the feedback control region to the open loop control region for the first time, step 319, which has the same content as step 315, is executed and the process proceeds to the next step 320, and the answer to step 318 is negative (NO). In this case, step 319 of step 011 has been executed, so step 319 is skipped and the process proceeds to step 320. In step 320, the correction coefficient K
Open loop control is performed while O2 is held at the value of the correction coefficient KO2 at the time of the previous execution of this program.

Average value K of the correction coefficient KO2 in step 316
I! EPO and KI! The EFI is calculated according to the flowcharts shown in FIGS. 4(a) and 4(b) which are two embodiments of the invention.

First, in the flowchart of the embodiment of the first invention shown in FIG. 4(a), the engine operating state is determined in step 4.
01 to 405. That is, the engine cooling water temperature Tw is equal to the predetermined value T read out in step 308.
A predetermined value TWREF greater than 11+02 (for example, 60
°C) (step 401), whether secondary air is being introduced into the exhaust pipe 12 by the secondary air valve 20 (step 402), and whether the air conditioner mounted on the vehicle is operating. (Step 403), whether the intake air temperature T8 is greater than a predetermined temperature TA*Er (for example, 70°C) (Step 404), and whether the engine cooling water temperature Tw is greater than a predetermined high temperature TWAICI (for example, 90°C). It is determined whether or not (step 405).

In steps 401 and 405, the average value Kl! E.F.O.
and engine cooling water temperature Tw for calculating Kv and εF1.
This is to achieve more accurate air-fuel ratio control by narrowing the learning range. Step 402 is performed because, when secondary air is introduced by the secondary air valve 20, the detection signal of the 02 sensor 14 disposed downstream thereof does not represent the air-fuel ratio that should originally be controlled.
02 learning (average value KI!EFa and Kl
! Therefore, when introducing secondary air, the average value Kl! This is to prohibit the calculation of EFO and KREFI. The step 403 is for prohibiting the calculation of the average value Kt[:po and KREFI of the correction coefficient KO2 because the engine load fluctuates rapidly when the air conditioner is in operation, making it unsuitable for learning the correction coefficient KO2. In step 404, when the intake air temperature 1゛^ is high, the intake air density decreases and the air-fuel mixture becomes rich, making it unsuitable for learning the correction coefficient KO2. This is to prohibit the calculation of EFI.

Any of the answers in steps 40+ to 405 is affirmative (
If yes), 02 feedback correction coefficient KO
2. Calculate the average IfiKREFo or KREFI (
Since the operating state of the engine is not suitable for learning the correction coefficient KO2, the program is terminated without performing the calculation.

On the other hand, if all of the answers to steps 401 to 405 are negative (NO), the process proceeds to step 406, where the intake pipe absolute pressure PR^ representing the engine load is set to a predetermined absolute pressure (second predetermined value) PBKREF (for example, 177mmt1
g) Determine whether it is less than. This answer is negative (No
), the average values KREFO and KREFl of the correction coefficient KO2 are calculated according to the following equations (3) and (4), respectively (step 407).

When the engine is in idle region I of the 02 feedback control region, Kl! UFO=CR"'KO2P+9536- CRE
FKI! EF01...(3) When the engine is in a region (2) other than the idle region of the 02 feedback control region, Kgtrt-GenK. 2. +μs” on the tongue *tps’-9 (4) 65536 6553 smile, Cl! EF is a variable that is experimentally set for each region (■) and (■), and is set to an appropriate value from 1 to 65536 according to the specifications of the target air-fuel ratio feedback control device, engine, etc. Ko2p is the proportional term (P
Item) Value of correction coefficient KO2 immediately before or after operation, Kl!
EFO' and Kl! [:Pi' is the average value of the correction coefficients KO2 obtained up to the previous time in each corresponding operating region.

As can be seen from (3) and (4) above, the average value Kl!
II: The calculation of FO and KREFI corresponds to learning the correction coefficient KO2P according to the learning degree (learning speed) CREF/65536.

However, when the answer to step 406 is affirmative (Yes), that is, the engine load is smaller than the second predetermined value (Pl)
In ^(PBKppp), the step 407 is skipped and the average value Kl of the correction coefficient KO2 is calculated. EFO and K I
! E F + is not calculated, and learning of the correction coefficient KO2 when engine combustion is unstable is prohibited.

FIG. 4(b) shows an embodiment of the second invention, and the steps in FIG. 4(b) having the same numbers as the steps shown in FIG. 4(a) are the same as those in FIG. 4(a). ). Perform the same process as the corresponding step. Therefore, in flowchart 1 of the embodiment of the second invention shown in FIG. When the load is smaller than the second predetermined value (PB^<P++Kgu), the constant CKgpp, which will be described later, is set to the value 2'' (=+6,777.216) (step 408), and when negative (NO), the constant is set. Cxpp:p is set to the value 2'' (=65,536) (step 409) and the process advances to step 410. Step 4
In step 10, using the constant CIJEF set in step 408 or 409, when the engine is in idle region 1 of the 02 feedback control region, the following formula (
Calculate the average value KREFO of the correction coefficient KO2 according to 5), and when the engine is in the region ■ other than the idle region of the 02 feedback control region, the following formula (
6), the average value Ku:pt of the correction coefficient KO2 is calculated.

Kgp:po =-”-”'-Ko2P 4-Hiho Hidanse K REpo' -(5) CKRεF
GKI! EFKREFI-Dish KO2F+Ridan Ankutan ni Old 1'...(6) CKREF CK
REF Here, C*Ev is a variable that is experimentally set for each region ■ and ■, and is an appropriate value from l -CKaEF according to the specifications of the target air-fuel ratio feedback control device, engine, etc. KO2P
%KREFO', Kl! EFI' is the same as the one with the same symbol in formulas (3) and (4) above.

As can be seen from the above equations (5) and (6), the constant CKI
! When EF is set to the value 2pa, the average values Kl!EFO and KREFI are set to the previous average values Kg[:po' and KREFI, respectively, compared to when it is set to the value 2''.
', and is not affected much by KO2F, which is the value of the correction coefficient KO2 at the time of the latest 02 sensor inversion. That is, when the combustion state of the engine becomes unstable and the engine load is smaller than the second predetermined value (step 406
(if the answer is affirmative), the correction coefficient KO2 is larger than when it is large.
The learning ratio of the latest value of the coefficient to the average values KREFO and KREFI becomes smaller, that is, the speed at which the latest value of the correction coefficient is learned becomes slower, which prevents the engine from remaining in the unstable combustion operating region for a long time. Because there is usually no
It is possible to avoid learning a large amount of the correction coefficient KO2 obtained when engine combustion is unstable.

(Effects of the Invention) As detailed above, the first invention provides an internal combustion engine that changes in accordance with the output of an exhaust gas concentration detector disposed in the exhaust system of the engine during operation in the air-fuel ratio feedback control operating region. calculate the average value of the coefficients, use at least the calculated average value to feedback control the air-fuel ratio of the air-fuel mixture supplied to the engine, detect the load of the engine, and detect the load of the engine when the load of the engine is the first. In the air-fuel ratio feedback control method for an internal combustion engine, the feedback control is stopped and the air-fuel ratio of the air-fuel mixture is increased when the air-fuel ratio is equal to or less than the first predetermined value, and when the load of the engine is equal to or greater than the first predetermined value, The second value is greater than the predetermined value.
In the air-fuel ratio feedback control operating region below the predetermined value of
The calculation of the average value of the coefficients is stopped, and the second invention further provides an exhaust gas concentration detector disposed at an angle of 4 degrees in the exhaust system of the internal combustion engine when the internal combustion engine is operating in an air-fuel ratio feedback control operating region. calculates an average value of coefficients that change according to the output of the engine, uses at least the calculated average value to feedback control the air-fuel ratio of the air-fuel mixture supplied to the engine, detects the load of the engine, In the air-fuel ratio feedback control method for an internal combustion engine, the feedback control is stopped and the air-fuel ratio of the air-fuel mixture is increased when the engine load is below the first predetermined value, wherein the engine load is above the first predetermined value. In the air-fuel ratio feedback control operation region where the air-fuel ratio is larger than the first predetermined value and is less than or equal to the second predetermined value, the speed at which the latest value of the coefficient is learned is slowed down. Furthermore, it is possible to improve the responsiveness of engine air-fuel ratio control when the engine load changes from a low load region to a high load region.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a fuel supply control device for carrying out the air-fuel ratio feedback control method for an internal combustion engine according to the present invention, and FIG. 2 shows an example of the internal configuration of the electronic control unit shown in FIG. A block diagram showing an embodiment,
FIG. 3 is a flowchart showing a procedure for carrying out the control method of the present invention, FIG. 4 is a flowchart showing a subroutine for calculating the average value KREF of KO2 in step 316 in FIG. 3, and FIG. FIG. 3 is a diagram showing regions. ■...Internal combustion engine, 5...Electronic control unit (ECU), 6...Fuel injection valve, 8...Intake pipe absolute pressure (PBA) sensor, 11...Engine speed (Ne) sensor , 12...Exhaust pipe, 14...O2 sensor (exhaust gas concentration detector), KO2...02 feedback correction coefficient (coefficient), Kl! EFO and KRE
FI = average value of KO2, P[REF...predetermined absolute pressure (second predetermined value).

Claims (1)

[Scope of Claims] 1. Calculating the average value of coefficients that vary depending on the output of an exhaust gas concentration detector disposed in the exhaust system of the engine when the internal combustion engine is operating in an air-fuel ratio feedback control operating region, Feedback controlling the air-fuel ratio of the air-fuel mixture supplied to the engine using at least the calculated average value, detecting the load of the engine, and controlling the feedback when the load of the engine is equal to or less than a first predetermined value. In the air-fuel ratio feedback control method for an internal combustion engine, in which the engine load is equal to or higher than the first predetermined value and the air-fuel ratio of the air-fuel mixture is increased.
An air-fuel ratio feedback control method for an internal combustion engine, characterized in that calculation of the average value of the coefficients is stopped in an air-fuel ratio feedback control operation region below a second predetermined value that is larger than a predetermined value. 2. Calculate the average value of coefficients that change according to the output of an exhaust gas concentration detector disposed in the exhaust system of the engine when the internal combustion engine is operating in the air-fuel ratio feedback control operation region, and calculate the calculated average value. is used to feedback control the air-fuel ratio of the air-fuel mixture supplied to the engine, detect the load of the engine, and stop the feedback control when the load of the engine is less than or equal to a first predetermined value; In the air-fuel ratio feedback control method for an internal combustion engine that increases the air-fuel ratio of air, the engine load is equal to or higher than the first predetermined value and the first
1. An air-fuel ratio feedback control method for an internal combustion engine, comprising slowing down the speed at which the latest value of the coefficient is learned in an air-fuel ratio feedback control operating region below a second predetermined value that is larger than a predetermined value.