JPS6069241A - Air-fuel ratio controlling method for internal-combustion engine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control method for an internal combustion engine, and in particular, to control the air-fuel ratio to a target air-fuel ratio using an air-fuel ratio feedback correction coefficient and a learned value, and to control the air-fuel ratio under predetermined conditions. The present invention relates to an air-fuel ratio control method for an internal combustion engine that controls the fuel ratio to be leaner than a target air-fuel ratio.

[Prior art]

Conventionally, a three-way catalyst has been used to simultaneously purify carbon monoxide, hydrocarbons, and nitrogen oxides in exhaust gas.9 In order to improve the purification rate of this three-way catalyst, the 02 sensor Feedback control is performed to detect the residual oxygen concentration, estimate the air-fuel ratio, and control the air-fuel ratio to near the stoichiometric full fuel ratio. In performing this feedback control, the signal is output from the 02 sensor and processed during the basic fuel injection time TP determined by the engine load (intake pipe pressure PM or intake air it Q/NE per engine revolution) and the engine speed. Multiply the air-fuel ratio feedback correction coefficient (9) FAF'i shown in FIG. 1 to calculate the fuel injection time T AU based on the calculated air-fuel ratio signal,
By opening the fuel injection valve for a time corresponding to this fuel injection time TAU, the air-fuel ratio is controlled to be close to the stoichiometric air-fuel ratio. However, due to environmental changes and changes over time, changes in valve timing due to changes in tabet compliance, changes in characteristics of pressure sensors and air flow meters, and changes in characteristics of fuel injection valves occur, resulting in changes in the required fuel injection amount of fuel injection FFK engines. It may become impossible to control the air-fuel ratio to near the stoichiometric air-fuel ratio. For this reason, air-fuel ratio learning control is performed to control the air-fuel ratio so that it is always near the stoichiometric air-fuel ratio.

In addition, from the perspective of improving fuel efficiency, under certain conditions during feedback control, that is, at light loads after complete warm-up,
It has been proposed to perform feedforward control or one-in control of the air-fuel ratio to leaner than the stoichiometric air-fuel ratio.

The above air-fuel ratio learning side l and lean control are as follows (
1) The fuel injection time TAUi is calculated based on the formula and a predetermined amount of fuel is injected.

TAU=(TP+TAUG)(1+KG)・FAF −
FLEAN-F(t)...(1) However, TA
UG is the learned value when the intake throttle valve is in the idle position, KG is the learned value when the intake throttle valve is not in the idle position, F (
t) is a correction coefficient such as a warm-up phase increase coefficient and a starting phase increase coefficient, F
(2) EAN is a scale correction coefficient of 1 or less. Also, the learning value KG is determined by the engine load, for example,
KGs, 3 when the intake pipe pressure is 200-30011Hy
00~400 Tsubasa HP KG2.400~500
1111Hp uses KGB.

These learning values TAUG, KG (KGI, KG2, K
G 3 ) is learned during air-fuel ratio feedback control and when the engine cooling water temperature exceeds a predetermined value (for example, 80° C.). Os, every time the air-fuel ratio feedback correction coefficient PAP skips, the arithmetic average value FAFAV of the maximum and minimum values of the correction coefficient FAF, that is, the value of the total calculated average value FAFAV is outside the predetermined range (for example, ±2 coefficient). When the learning values TAUG and KGi reach the specified value, the learning values TAUG and KGi are increased or decreased by a predetermined value. That is, when the average value FAFAV exceeds 1.02, the learned values TAUG and KG are increased by a predetermined value, and the average value FAF'
When AV becomes less than 0.98, learning value TAUG,K
A predetermined value is subtracted from G.

Then, the learned values TAUG, KG learned as above
is determined by the above (1
) formula and determines the fuel injection time TAU - As a result, when the average value FAFAV exceeds 1.02, the learned value is increased and the air-fuel ratio is controlled to the rich side, and when the average value FAFAV is less than 0.98. Sometimes the learned value is made smaller and the air-fuel ratio is controlled to the lean side, reducing the average value FAFAV.
Learning control is performed so that the ratio approaches 1, that is, the stoichiometric air-fuel ratio.

-i In addition, the lean correction coefficient FLEAN is set to a value one lower than the intake pipe pressure (or intake air amount per engine revolution) or the intake pipe pressure and engine speed (5). By determining the IJ-ton correction coefficient FLFANk according to the engine operating state under predetermined conditions and applying it to the above equation (1), the fuel injection amount is reduced and lean control is performed. It should be noted that when the execution power of the lean control is not established, the lean control is stopped by setting the value of the lean correction coefficient FLFAN to 1.

However, when learning the learning value, the learning value is
Since AF is executed every time the AF skips, if an abnormality such as a disconnection of the O2 sensor occurs, learning will not be performed, and especially in engines where the required fuel injection amount deviates to the rich side of the air-fuel ratio, the learned value will not reach the correct value. When the lean control conditions are met and lean control is executed without increasing the air-fuel ratio
There was a problem that the stability deteriorated.

[Purpose of the invention]

The present invention has been made to solve the above problems, and
It is an object of the present invention to provide an air-fuel ratio control method that does not cause deterioration of drivability in steering control when a senna abnormality occurs.

(6) [Structure of the Invention] In order to achieve the above object, the present invention provides an air-fuel ratio feedback correction coefficient obtained based on an output signal of an 02 sensor that detects the residual oxygen concentration in exhaust gas and the air-fuel ratio feedback correction coefficient. Using a learning value that is changed by learning so that the average value of is closer to the value corresponding to the target air-fuel ratio,
Feedback control is performed so that the air-fuel ratio of the air-fuel mixture becomes the target air-fuel ratio by correcting the basic fuel injection time determined by the engine load and engine speed. In an air-fuel ratio control method for an internal combustion engine that performs lean control so that the fuel ratio is on the lean side,
The present invention is characterized in that the lean control is stopped when the output signal of the 02 sensor indicates a lean air-fuel ratio under the condition that the amount of fuel injected from the fuel injection lid is increased more than the target air-fuel ratio.

As a result, when the output signal of the 02 sensor indicates a lean air-fuel ratio under the condition that the fuel injection amount is increased by p compared to the amount relative to the target air-fuel ratio, that is, the output signal of the 02 sensor indicates that the air-fuel ratio is lean even though the air-fuel ratio is rich. When the air-fuel ratio indicates a lean air-fuel ratio, it is determined that the 02 sensor is abnormal and the lean control is discontinued.

〔Effect of the invention〕

Therefore, according to the present invention, it is possible to prevent deterioration of drivability due to air-fuel ratio overlean.

[Embodiments of the invention]

Next, hardware of an embodiment including an internal combustion engine to which the present invention is applied will be described in detail with reference to FIG. Air cleaner 1 is connected to throttle body 5 via inlet pipe 3. The throttle body 5 is provided with a fuel injection valve 7 on its upstream side, and an intake throttle valve 9 is provided downstream of the fuel injection valve 7 to adjust the intake air level in conjunction with an accelerator pedal (not shown).
An intake pipe absolute pressure sensor 11 is provided downstream of the intake throttle valve 9 to measure the absolute pressure at that location. Furthermore,
A valve opening position sensor 2 that measures the opening position t'ft of the intake throttle υ valve 9, an idle switch 4 that turns on only when the intake throttle valve 9 is in the idle position (when it is fully closed), and A power switch 6 that is turned on only when the opening degree of the valve 9 is 30 degrees or more is attached in association with the intake throttle valve 9.

The throttle body 5 is connected to an intake manifold 13 having branch pipes connected to each cylinder of the engine,
The intake manifold 13 is provided with an intake temperature sensor 15 that measures the temperature of intake air therein. On the bottom wall 13a before branching of the intake manifold) 13, there is a riser part 1 for circulating engine cooling water and heating the air-fuel mixture.
7 is provided.

19 is a well-known and customary engine body, l), piston 21;
The combustion chamber 2 is formed by the cylinder 23 and cylinder head 25.
7 is defined, through the intake valve 29 and the combustion chamber 27
The air-fuel mixture sucked into the engine is ignited by the spark plug 31. A quarter jacket 33 is formed around the cylinder 23, and engine cooling water is circulated through the water jacket 33 to cool parts including the cylinder 23. An engine coolant temperature sensor 37 is provided on the outer wall of the cylinder block 35 to measure the temperature of the engine coolant in the water bucket (9).

An exhaust manifold 39 is connected to an exhaust boat (not shown) of the cylinder head 25, and an 02 sensor 41 for measuring the residual oxygen concentration in the exhaust gas is provided downstream of the exhaust manifold 39. The exhaust manifold 39 is connected to an exhaust pipe 45 via a three-way catalytic converter 43.

47 is a transmission connected to the engine body 19;
A vehicle speed sensor 49 is attached to measure the speed of the vehicle based on the rotational speed of the final output shaft.

Further, 51 is a key switch, 53 is an igniter, and 55 is a distributor. The distributor 55 is provided with an Ne sensor 57 that outputs an on/off signal at every predetermined crank angle θ1, and the output signal determines the engine rotational speed. It is possible to know the predetermined crank angle position, and also to turn on/off at every angle θ2 larger than the above angle θ1.
A G sensor 59 that outputs an off signal is provided, and the output signal is used to determine the number of cylinders and to detect the top dead center position.

(lO) Also, 60 indicates a battery, 62 indicates an indicator lamp; a control circuit 61 composed of a microcomputer, etc., includes a valve opening position sensor 2, an idle switch switch 4, a power switch 6.4 days 4 sensor 11, intake temperature sensor 5. Engine cooling water temperature sensor 37.09 Sensor 4], Vehicle speed sensor 49, Key switch 51, Ne
The sensor 57, the G sensor 59, the display lamp 62, and the battery 60 are connected to the water temperature signal S6, air-fuel ratio signal S7, vehicle speed signal S8, ignition signal S9, engine speed signal S10, cylinder discrimination signal 811, and battery voltage signal 814. is input from each sensor. Also,
The control circuit 61 is also connected to the fuel injection valve 7 and the igniter 53, and generates a fuel injection signal 8 based on a predetermined calculation.
12 and an ignition signal 813, and also outputs an abnormality signal 815 to the display lamp 62.

As shown in FIG. 3, the control circuit 61 includes a central processing unit (cPU) 61a that controls various devices, a central processing unit (cPU) 61a in which various numerical values and programs are written in advance, and a one-dono memory (RO).
M) 6 l b, Random access memory (RAM) 61 in which numerical values and flags of the calculation process are written in a predetermined area.
c - A converting analog input signal into digital signal
/D converter (ADC) 61d, input/output interface Cl10) 61e to which various digital signals are input and various digital signals are output, backup memory (BU-RAM) 61 which is supplied with power from the auxiliary power source and retains memory when the engine is stopped. f, and path lines 61g to which these devices are respectively connected. The above RAM contains learning values T AUG, KG? A storage area is prepared, and the program of the above formula (1), the map of the lean correction coefficient 1FLEAN shown in FIG. 4, and other constants are stored in advance in the ROM.
A lean control prohibition flag F is prepared in the U-RAM.

In the above engine, fuel is injected from the fuel injection valve according to the following procedure. First, the engine speed Ne calculated based on the engine speed signal S1 is read, and the intake pipe pressure PM is also read based on the intake pipe pressure signal S4. Next, based on the engine speed Ne and the intake pipe pressure PM, the basic fuel injection time TP is determined from a map of the basic fuel injection time by two-dimensional interpolation or calculation.

Next, the fuel injection time TAU is determined based on the above equation (1), and the fuel injection valve is opened for a time corresponding to this fuel injection time TAU to fully inject the fuel. However, in this embodiment, one learned value TAUG and one learned value KG are adopted, and the learned value TAUG is applied to the above equation (1) for all operating ranges regardless of the on/off state of the throttle switch. The learned value KG is applied to the above equation (1) for the entire operating range when the throttle switch is off. Further, when the lean control condition is satisfied, the lean correction coefficient FLEAN is applied to the above equation (1), the fuel injection amount is reduced from the fuel injection amount during feedback control, and lean control is executed.

Next, a processing routine of an embodiment in which the present invention is applied to the above engine will be described in detail.

(13) FIG. 5 shows the learning routine of this embodiment that is executed every predetermined time (for example, 48 m5ec). First, in step 100, it is checked whether the intake throttle valve 9 is in the idle position or not by turning off the idle switch. Judging from the condition. When the idle switch is off, in step 101 it is determined whether the intake pipe pressure PM is within the range of 200 μHjl to 400 uHP, that is, whether the intake pipe pressure PM is within the learning range. This intake pipe pressure range indicates the intake pipe pressure in a constant rate running state. Further, since the percentage deviation of the average value FAFAV is approximately the same in all driving ranges, the learning range is defined only in the constant rate driving state. When the intake pipe pressure PM is within the learning range, the learning conditions in step 103 and subsequent steps are determined and learning is performed, and when the intake pipe pressure PM is not within the learning range, no learning is performed and the learning value is learned. Proceed to next routine. On the other hand, when the idle switch is on, in step 102, the engine speed Ne is set to a predetermined value (for example, 1010
It is determined whether or not the engine speed is less than 00 rpm and the intake pipe pressure PM exceeds a predetermined value C14) (for example, 200 HP'). If the determination in step 102 is affirmative, that is, in the case of a normal idle link, the learning conditions from step 103 onwards are determined and the learning value is learned, and step 102
If the judgment is negative, that is, when cranking or idling up, the process proceeds to the next routine without learning.

In step 103, it is determined whether feedback control is being performed so that the air-fuel ratio becomes the stoichiometric air-fuel ratio, which is the target air-fuel ratio, based on the output signal of the 02 sensor. If feedback control is not in progress, for example if lean control u' is being performed, abnormal learning may be affected, so proceed to the next routine without learning, and if buoy pack control is in progress, the engine is stopped in step 104. Cooling water temperature Tl (
It is determined whether W exceeds a predetermined value (for example, 80° C.). When the coolant temperature THW is below a predetermined value, learning is not performed because the engine is warming up, and when the coolant temperature THW exceeds a predetermined value, it is determined in step 105 whether the atmospheric pressure PMA exceeds a predetermined pressure (for example, 650 tgHjE). Decide whether or not. This atmospheric pressure PMA can be detected by taking in the intake pipe pressure signal S4 under the condition that the intake pipe pressure and the atmospheric pressure are equal. This condition is that the intake throttle valve is fully open and the engine speed Ne is below a predetermined value (for example, 200 rpm). When it is determined in step 105 that the atmospheric pressure PMA is below a predetermined value, that is, forest learning is not performed when driving at a high altitude, and when it is determined that the atmospheric pressure exceeds the predetermined value, the process is performed for a predetermined period of time (for example, 2 sec) in step 106. The change in the rate of change in vehicle speed ΔSPD within the range ΔSPD, that is, the rate of change in the rate of change in vehicle speed within a predetermined value (for example, 0.
7b/h). Learning is not performed when the rate of change of the vehicle speed is greater than a predetermined value, that is, during acceleration, and when it is less than the predetermined value, the intake temperature T is determined in step 107.
HA is within a specified range (for example, 40°C (THA (90°C)
The temperature is determined as follows. When the intake air temperature THA is outside the predetermined range, that is, at extremely low temperatures and high temperatures, abnormal learning occurs and no learning is performed, and when the temperature is within the fixed range, the vertical fuel ratio feedback correction coefficient F'A is set in step 108.
It is determined whether P has skipped or not, and learning of the learning value is performed in step 109 only when it has skipped.

Above step 10<? An example of learning will be explained based on the processing routine of FIG. First, in step 110, it is determined whether the air-fuel ratio feedback correction coefficient FAF has skipped a predetermined number of times, and only when the air-fuel ratio feedback correction coefficient FAF has skipped a predetermined number of times, in step 111, the average value F A is calculated based on the above equation (2).
Calculate F p, Vt. Here, the reason why the average value is calculated after skipping a predetermined number of times is because the change in the air-fuel ratio feedback correction coefficient is unstable immediately after shifting from lean control, which is oven loop control, to feedback control. Therefore, the unstable air-fuel ratio feedback correction coefficient is not used in calculations.

In the next step 112, it is determined whether the average value FAFAV exceeds 1. If it exceeds 1, that is, if the air-fuel ratio is as high as the stoichiometric air-fuel ratio, then in step 113 it is determined whether the idle switch is on or not. is determined, and when the idle switch is on (17), the learned value TAUG is set to a predetermined amount (for example, o
, oozl), and when the idle switch is off, the learned value KG(z is increased by a predetermined amount (e.g., 8
μsec) Increase. On the other hand, when the average value FAFAv is less than 1, that is, when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, it is determined in step 116 whether or not the idle switch is on, and when the idle switch is on, the learned value TAUG is Predetermined! (For example, 0.002
), and when the idle switch is off, the learned value KG is set to a predetermined ft (for example, 8 μsec) in step 118.
) decrease.

The learning value learned as described above is applied to Equation (1) according to the on/off state of the throttle switch, and the air-fuel ratio is learning-controlled.

Next is O! Determine whether the sensor is abnormal or not and set or reset the lean control prohibition flag Ff: 02
The sensor check routine will be explained with reference to FIG. First, in step 70, it is determined whether or not the engine coolant temperature THW is higher than a predetermined temperature (for example, (1B) 50°C), thereby determining whether or not the warm-up amount has been increased and the 02 sensor is activated. to decide. If the cooling water temperature THW is less than the predetermined temperature, it is assumed that the 02 sensor is not activated even though the warm-up amount has been increased, and this is inappropriate for the 02 sensor abnormality check, so the process directly proceeds to the next routine. Cooling water temperature THW
When the temperature is higher than a predetermined temperature, it is determined in step 71 whether or not fuel injection is being cut. This fuel injection cut is executed when the engine speed is 10,000 rpm during deceleration.During the fuel injection cut, there is no exhaust emission, and the routine continues to the next routine. In step 72, the engine speed Ne is set to a predetermined value (for example, 1
500 rpm) or more for a predetermined period of time (for example, 2 m
in) Determine whether or not it has continued. Engine speed N
When e is less than a predetermined value, that is, when the engine speed is low such as when idling, the exhaust emission is low and the reaction speed is slow even if the 02 sensor is activated, which is inappropriate for the 02 sensor abnormality check, so proceed to the next routine. Go on,
When the engine speed Ne is above the predetermined value 1'-1, that is, the exhaust emissions are large. When the reaction speed of the 02 sensor is fast, after a predetermined time elapses, that is, the 02 sensor output is the full output signal corresponding to the residual oxygen concentration in the exhaust gas. After the time has elapsed, it is determined in step 73 whether or not a predetermined time (for example, 1 sec) has elapsed since the power increase was executed. This power increase m is to increase the fuel injection needle by a predetermined amount when the power switch is on, and if the power increase is not performed, proceed directly to the next routine.
If power increase t is being performed, 02 is set in step 74.
Determine whether the sensor output indicates a lean air-fuel ratio.

02 When the sensor output indicates lean, that is, 02
If the 02 sensor output indicates lean even though the air-fuel ratio is controlled to be rich under conditions in which the 02 sensor operates normally, it is determined that the 02 sensor is abnormal and the BU- When the RAMK is prepared, the one-in control prohibition flag F is set, and at step 77, an abnormality signal 8 is output.
15 and lights up the display lamp 62 to indicate the 02 sensor abnormality 2. On the other hand, when the 02 sensor output indicates rich, the lean control prohibition flag Ftl is reset in step 76.

Next, the control switching routine of this embodiment will be explained with reference to FIG. This routine is executed at predetermined intervals, and in step 120 the engine coolant temperature T
Whether the HW exceeds a predetermined value (e.g. 80°C) or for a predetermined time (e.g. 2 sec) in step 121
Change rate of change in vehicle speed ΔSPD within ΔSPD/
2see (hereinafter referred to as second-order differential value) is a predetermined value (for example,
0.7 KrII/h) or not, and step 1
22, the intake throttle valve opening TA reaches a predetermined value (for example, 3
00), it is determined whether the lean control conditions are satisfied. Note that whether or not the intake throttle valve opening degree TA is a predetermined value can be determined by whether or not the power switch is turned on.

When the engine cooling water temperature THW-1) is below a predetermined value, that is, when the vehicle is in a V-engine, the second derivative of the vehicle speed ΔSPD/(21
) When 2@ec is above a predetermined value, that is, when the engine is accelerating, or when the intake throttle valve opening TA is above a predetermined value, that is, when the load is high, lean control is impossible, so step 125 is performed. Lean correction coefficient F T, E A N
? 1, air-fuel ratio feedback control is performed and the process returns. On the other hand, if the determination in step 120% 121 or 122 is affirmative, that is, if the vehicle is in a steady running state under light load after complete warm-up, it is determined in step 123 whether or not the lean control prohibition flag F has been reset. If the flag F is reset, Mai executes lean control in step 126 because the 02 sensor is normal and lean control is possible. 02 when 7 lag F is set
Since the sensor is abnormal, lean control is not performed even if the lean control conditions are met, and fuel is injected at step 124 with the basic fuel injection time TP set as the fuel injection time TAU.

Next, an example of the calculation processing routine for the lean correction coefficient FLFAN in the lean control in step 126 will be described with reference to FIG. 9. Amazzu, C22) When it is determined in step 128 that the lean control conditions of steps 120 to 123 are satisfied, the process proceeds to step 129, and when it is determined that the lean control conditions are not satisfied, step 137 and lean correction coefficient F
Feedback control is performed with LEAN set to 1.

In step 129, it is determined whether the intake throttle valve is open by determining whether the idle switch is off (8 or not), and when the idle switch is off, in step 130, the From the map of the lean correction coefficient FLEAN shown in Figure 4, the lean correction coefficient FLEAN't- is determined according to the current intake pipe pressure PM.
Load it into register A using interpolation. In the next step 131, a full judgment is made as to whether or not lean control is being performed. If lean control is being performed, then in step 133, the values of register A are set as lean correction coefficients PL and EAN, and lean control is subsequently performed.

On the other hand, if lean control is not in progress, step 132 determines whether the vehicle 18PD751 has a predetermined value (for example, 10 Km/h). By determining whether or not the value exceeds the predetermined value, it is determined whether or not the driving is steady. If the value exceeds the predetermined value, that is, during steady driving, the value of the Regis entry is changed to the lean correction coefficient FLEA in step 133.
Perform full lean control as N.

On the other hand, when the vehicle speed is less than a predetermined value, that is, at the time of starting, the lean control is stopped in step 137 by setting the lean correction coefficient FLEANil.

When the idle switch is on, the average value NAVi of the engine speed within a predetermined time is determined in step 134, and it is determined in the next step 135 whether the average value NAV exceeds a predetermined value B (for example, 600 rpm). . When the average value NAV is less than the predetermined value B, the lean control is stopped in step 137, and when the average value NAV exceeds the predetermined value B, the lean correction coefficient FLEAN' is adjusted in step 136.
Lean control is performed with a predetermined value (for example, 0.92) less than e1. In this way, by performing lean control by setting the lean correction coefficient FLEAN'i to the predetermined value when the idle switch is turned on, it is possible to prevent idle instability due to hunting caused by intake pipe pressure fluctuations.

According to the above embodiment, since the learning area is one area and the learning values are two, it is possible to reduce the storage area of the memory and reduce the number of words of the program. In addition, since the indicator lamp lights up when the 02 sensor is abnormal, it is possible to notify the driver of the abnormality, and the lean control prohibition flag 'iBU-RAM
Since the ignition switch is turned on, the O
? This provides the advantage that the sensor abnormality determination result can be retained.

In addition, although the engine in which the basic fuel injection time is determined by the intake pipe pressure and engine speed and uses one fuel injection valve has been described above, the engine to which the present invention is applied is not limited to this. The present invention can also be applied to an engine in which the basic fuel injection time is determined based on the amount of intake air per engine rotation and the engine rotational speed, or to an engine in which each cylinder is provided with a fuel injection valve protruding from the intake manifold.

(25)

[Brief explanation of the drawing]

Figure 1 shows the fuel narrowing ratio signal and feedback correction coefficient.
Figures F1 and 12 are block diagrams showing a configuration example of the present invention including an engine to which the present invention is applied; Figure 3 is a block diagram showing an example of the control circuit of Figure 2; Figures 1 and 15 are flowcharts showing the learning routine in the embodiment of the present invention, and Figure 6 shows the learning values of the embodiment! - Calculate A - A stagnation diagram showing chin, shi, 7 diagram ゛@
Flowchart showing 02 sensor check A, -chin in the example of Takeshi, r; 8 is a flowchart showing the control 1 switching routine of this embodiment, and FIG. It is. 7...Fuel injection valve, 9...Intake ilt, valve, 11
...Pressure sensor, 15...Intake temperature sensor, 41...
-02 sensor, 49...vehicle speed sensor, 61...control circuit. Agent Tatsuyuki Unuma (1 person) (26) Ka4 Haji0 = L Shikiku Iwao 1 Horiichiko)゛Koshi Denyo I 1i 7 Figure 118 Figure

Claims (1)

[Claims] (1) Through learning, the air-fuel ratio feedback correction coefficient obtained based on the output signal of the 02 sensor that detects the residual oxygen concentration in exhaust gas and the average value of the air-fuel ratio feedback correction coefficient approach the value corresponding to the target air-fuel ratio. Using the changed learning value, feedback control is performed so that the air-fuel ratio of the mixture reaches the target air-fuel ratio by correcting the basic fuel injection time determined by the engine load and engine speed, and the mixture is controlled at light load after warm-up. In an air-fuel ratio control method for an internal combustion engine that performs lean control so that the air-fuel ratio of air is leaner than the target air-fuel ratio, the output of the 02 sensor under the condition that the amount of fuel injection is increased relative to the target air-fuel ratio. 1. A method for controlling an air-fuel ratio of an internal combustion engine, characterized in that when a signal indicates a lean air-fuel ratio, the above-mentioned one-on control is stopped. (1)