JPH0467574B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an air-fuel ratio control method, and particularly to an air-fuel ratio control method suitable for use in a vehicle internal combustion engine having an electronically controlled fuel injection device. .

[Conventional technology]

The electronically controlled fuel injection system calculates the basic fuel injection time TP based on the engine rotation speed NE detected by the rotation speed sensor and the intake air amount Q detected by the intake air amount sensor, and The final fuel injection time τ is calculated by applying various corrections to the basic fuel injection time TP, and the injection valve is opened for the final fuel injection time τ to inject fuel.

On the other hand, in this type of fuel injection control device that uses a three-way catalytic converter to simultaneously remove CO, HC, and _NO It is desired to control the air-fuel ratio to near the stoichiometric air-fuel ratio. Therefore, an oxygen sensor is installed in the exhaust passage, and under certain conditions, the feedback correction coefficient FAF is adjusted so that the air-fuel ratio becomes close to the stoichiometric air-fuel ratio based on the air-fuel ratio signal from the oxygen sensor.
is calculated to perform air-fuel ratio feedback control.

In an electronically controlled fuel injection system that performs air-fuel ratio feedback control, it compensates for differences in air-fuel ratio due to variations between parts, compensates for air-fuel ratio due to high-altitude driving, and compensates for air-fuel ratio differences due to changes in the intake air amount sensor over time. In order to compensate for changes in the fuel ratio, the air-fuel ratio is learned under predetermined conditions during the feedback control, and a learning correction coefficient FG is calculated.

Then, the final fuel injection time τ is, for example, τ=
It is determined by the formula TP x FAF x FG x K. Here, K is a correction coefficient based on water temperature, intake air temperature, etc.

[Problem to be solved by the invention]

When learning the air-fuel ratio, the fuel evaporated in the fuel tank and stored in the canister (hereinafter referred to as evaporated fuel) enters the combustion chamber under predetermined conditions, including at least that the throttle valve is not fully closed. It must be taken into account that the air-fuel ratio is temporarily enriched. The influence of such evaporated fuel on the air-fuel ratio is shown in Figure 1, and in extreme cases, the intake air amount Q is 100
Even in the area of high air flow rate of about m ³ /h, it may become about 10% rich.

Therefore, if you stop driving the vehicle immediately after learning such changes in the air-fuel ratio due to evaporated fuel, the next time you start the vehicle, the air-fuel ratio will be too lean, causing problems such as poor starting performance. .
Therefore, it is necessary not to learn about air-fuel ratios that are rich due to evaporated fuel.

The above-mentioned compensation for the air-fuel ratio at high altitudes means that the air density becomes smaller at higher altitudes, so the air-fuel ratio is prevented from becoming richer at higher altitudes, but the effect of high altitudes on the air-fuel ratio is As shown in Figure 2, it is almost constant regardless of the amount of intake air.
Therefore, in areas other than the region where the throttle valve is fully closed, it is difficult to determine whether the reason why the air-fuel ratio becomes rich is due to evaporated fuel or high-altitude driving.

On the other hand, if the intake air amount sensor becomes clogged due to changes over time, as shown in FIG. 3, the region where the intake air amount is smaller has an effect on the air-fuel ratio. Therefore, if the air-fuel ratio differs by, for example, 1.5% or more between the throttle valve fully closed region and other regions,
It is determined that the intake air amount sensor is clogged and the air-fuel ratio is λ.
In conventional control that subtracts the learning correction coefficient so that (excess air ratio) = 1, the same learning is performed even when the air-fuel ratio is affected by evaporated fuel as shown in Figure 1, and changes over time are Compensation for the air-fuel ratio due to fuel vapor and compensation for the air-fuel ratio due to evaporated fuel are superimposed, making it difficult to properly compensate for the air-fuel ratio. Furthermore, when descending from a high altitude with the throttle valve fully closed, there is a risk that compensation will not be performed accurately due to the effects of the high altitude.

An object of the present invention is to propose an air-fuel ratio control method that prevents the effects of high altitude and evaporated fuel when compensating the air-fuel ratio due to a blockage of an intake air amount sensor.

[Means to solve the problem]

The present invention provides a judgment value that is set as an initial value when starting the engine when the throttle valve is not fully closed.
Compare FAFAV2 with the average value FAFAV1 and determine the judgment value.
If FAFAV2 is larger than the average value FAFAV1, a predetermined number is subtracted from the judgment value FAFAV2, and if it is smaller, a predetermined number is added to the judgment value FAFAV2, and the judgment value
When FAFAV2 is within a specified range close to the stoichiometric air-fuel ratio and the throttle valve is fully closed, the arithmetic average value
When FAFAV1 is greater than or equal to a predetermined value, a predetermined number is added to the learning correction coefficient DFC for blockage compensation, and the arithmetic average value is calculated.
When FAFAV1 is less than a predetermined value, a predetermined number is subtracted from the compensation learning correction coefficient DFC and stored;
In other words, after adding or subtracting a predetermined number from the compensation learning correction coefficient DFC, the predetermined value is added to the determination value FAFAV2.

[Effect]

Therefore, only when the throttle valve is fully closed and the judgment value FAFAV2 is within the predetermined range,
In other words, a predetermined number is added to or subtracted from the compensation learning correction coefficient DFC, and the judgment value FAFAV2 is incremented by a predetermined number after such calculation, thereby compensating for the air-fuel ratio due to a blockage in the intake air amount sensor. In addition, when the throttle valve remains fully closed for a long time, for example when descending from a high altitude, the compensation learning correction coefficient DFC is continuously calculated. The risk of being affected is prevented.

〔Example〕

Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 4 shows an example of an electronically controlled fuel injection type internal combustion engine to which the present invention is applied.
Reference numeral 2 indicates an intake passage, 14 a combustion chamber, and 16 an exhaust passage. An intake air amount sensor (air flow meter) 20 provided in the intake passage 12 upstream of the throttle valve 18 is connected to a control circuit 22 via a signal line l1, and generates a voltage according to the amount of intake air. The intake temperature sensor 21 is provided in the intake passage 12 upstream of the throttle valve 18, and is connected to the signal line l.
2 to the control circuit 22, and generates a voltage according to the intake air temperature. Intake air is taken in through an air cleaner and an intake air amount sensor 20 (not shown), and whose flow rate is controlled by a throttle valve 18 that is linked to an accelerator pedal (not shown).
The air is guided to the combustion chamber 14 of each cylinder via the surge tank 24 and intake valve 25.

A fuel injection valve 26 is provided for each cylinder,
The opening/closing is controlled in response to electrical drive pulses supplied from the control circuit 22 via the signal line l3, and pressurized fuel sent from a fuel supply system (not shown) is fed into the intake passage 12 near the intake valve 25, that is, the intake port. Inject intermittently into the area. The exhaust gas after being combusted in the combustion chamber 14 is discharged into the atmosphere via the exhaust valve 28, the exhaust passage 16, and the three-way catalytic converter 30.

Crank angle sensors 34 and 36 are attached to the distributor 32 of the engine, and these sensors 34 and 36 are connected to the control circuit 22 via signal lines 14 and 15. These sensors 34 and 36 output pulse signals each time the crankshaft rotates 30 degrees and 360 degrees, respectively, and these pulse signals are supplied to the control circuit 22 via signal lines l4 and l5, respectively.

The distributor 32 is connected to an igniter 38, and the igniter 38 is connected to the control circuit 22 via a signal line l6.

Reference numeral 40 indicates an idle switch (LL switch) which is linked to the throttle valve 18 and is closed when the throttle valve 18 is fully closed.
It is connected to the control circuit 22 via.

The exhaust passage 16 outputs a signal responsive to the oxygen concentration in the exhaust gas, that is, a signal with two different values depending on whether the air-fuel ratio is on the lean side or rich side with respect to the stoichiometric air-fuel ratio. _O2 that generates the output voltage
A sensor 42 is provided, the output signal of which is connected to the signal line l.
8 to the control circuit 22. The three-way catalytic converter 30 is provided downstream of this O ₂ sensor 42, and simultaneously purifies the three harmful components HC, CO, and NO _x components in the exhaust gas.

Further, reference numeral 44 detects the engine cooling water temperature,
This is a water temperature sensor that generates a voltage according to the temperature, and is attached to the cylinder block 46 and connected to the control circuit 22 via a signal line 19.

As shown in FIG. 5, the control circuit 22 includes a central processing unit (CPU) 22a that controls various devices;
It has a read-only memory (ROM) 22b in which various numerical values and programs are written in advance, a random access memory (RAM) 22c in which numerical values and flags in the calculation process are written in a predetermined area, and an analog multiplexer function, and can accept analog input signals. A/D converter (ADC) that converts to digital signals
22d, input/output interface (I/O) 22e to which various digital signals are input, input/output interface (I/O) 22f to which various digital signals are output, is supplied with power from the auxiliary power source and retains memory when the engine is stopped. It is composed of a backup memory (BU-RAM) 22g, and a bus line 22h to which each of these devices is connected.

The ROM 22b contains a main processing routine program, a program for calculating fuel injection time (pulse width), a program for calculating an air-fuel ratio feedback correction coefficient, a learning correction coefficient to be described later, and various other programs, as well as programs for calculating these calculations. Various necessary data are stored in advance.

And air flow meter 20, intake temperature sensor 2
1. O ₂ sensor 42 and water temperature sensor 44 are A/D
It is connected to a converter 22d, and voltage signals S1, S2, S3, S4 from each sensor are sequentially converted into binary signals according to instructions from the CPU 22a.

A pulse signal S5 for every 30 degrees of crank angle from the crank angle sensor 34, a pulse signal S6 for every 360 degrees of crank angle from the crank angle sensor 36, and an idle signal S7 from the idle switch 40 are transmitted via the I/O 22e. The signal is taken into the control circuit 22. A binary signal representing the engine speed is formed based on the pulse signal S5, and the pulse signals S5 and S6 work together to generate a request signal for calculating the fuel injection pulse width, an interrupt signal for starting fuel injection, and a cylinder discrimination signal. etc. are formed. Further, it is determined based on the idle signal S7 whether the throttle valve 18 is substantially fully closed.

The I/O 22f outputs a fuel injection signal S8 and an ignition signal S9 formed by various calculations to the fuel injection valves 26a to 26d and the igniter 38, respectively.

The fuel injection time (injection amount) in the internal combustion engine configured as described above is determined, for example, as follows.

τ=TP×FAF×FG×K...(1) Here, τ=Final fuel injection time TP=Basic fuel injection time FAF=Feedback correction coefficient FG=Learning correction coefficient K=Correction coefficient based on water temperature, intake temperature, etc. Basic The fuel injection time TP is determined by reading from a predetermined table or by calculation based on the intake air amount Q and the engine speed NE.

The feedback correction coefficient FAF is a value that increases the injection amount if it is determined that the air-fuel ratio is lean based on the air-fuel ratio signal S3 from the O ₂ sensor 42 under feedback control conditions, for example.
1.05, and if the air-fuel ratio is determined to be rich based on the air-fuel ratio signal S3, it will be a value that reduces the injection amount, for example 0.95, and if it is not under the feedback control condition, the correction coefficient FAF will be 1.0.

An example of the calculation procedure for the feedback correction coefficient FAF is shown in FIG.

In step S1, it is determined whether a feedback condition is satisfied. For example, if the engine water temperature THW is not in the starting state or increasing after starting,
The conditions for feedback control are met when the temperature is 50°C or higher and the power is not being increased. If the conditions for feedback control are not satisfied, step S2
Then, set the feedback correction coefficient FAF to 1.0 so that no feedback control is executed, and end this procedure. If the conditions are met, proceed to step S3
Proceed to. In step S3, the air-fuel ratio signal S3 is read. In step S4', a filter is applied to the voltage value represented by the air-fuel ratio signal S3, and the voltage value is set to "1" when the air-fuel ratio signal is rich;
An air-fuel ratio lean rich flag is formed so that it becomes "0" when the air-fuel ratio is lean, and in step S4, if the flag is "1", it is determined that the air-fuel ratio is too rich and the air-fuel ratio is set to the lean side. Take steps to achieve this.

That is, in step S5, the flag CAFL is set to zero, and the process proceeds to step S6, where it is determined whether the flag CAFR is zero. When it first shifts to the over-concentrated side, a flag is displayed.
Since CAFR is zero, proceed to step S8, and RAM2
A predetermined value α1 is subtracted from the correction coefficient FAF stored in 2b, and the result is set as a new correction coefficient FAF. In step S9, the flag CAFR is set to 1. Therefore, if excessive concentration is determined twice or more in succession in step S4, a negative determination will always be made in step S6 passed from the second time onwards, and in step S7, a predetermined value β1 is subtracted from the correction coefficient FAF, and the result is The FAF calculation is ended using the result as a new correction coefficient FAF.

On the other hand, if the lean rich flag based on the voltage value represented by the signal S3 is "0" in step S4, it is determined that the air-fuel ratio is lean, and the procedure is executed to make the air-fuel ratio rich. That is, in step S10, the flag CAFR is set to zero, and the process proceeds to step S11, where it is determined whether the flag CAFL is zero. When shifting to the lean side for the first time, the flag CAFL is zero, so proceed to step S12, add a predetermined value α2 to the correction coefficient FAF, and use the result as a new correction coefficient FAF.
shall be. In step S13, the flag CAFL is set to 1.
shall be. Therefore, if it is determined that it is diluted twice or more in succession in step S4, a negative determination is always made in step S11 passed from the second time onwards, and in step S14, a predetermined value β2 is added to the correction coefficient FAF, and the result is The FAF calculation is ended with as a new correction coefficient FAF.

Note that α1, α2, β1, and β2 in steps S7, S8, S12, and S14 are predetermined values.

The feedback correction coefficient FAF determined by this calculation means is shown in FIG. 7 together with the lean rich flag of the air-fuel ratio A/F, which is expressed by filtering the voltage value represented by the air-fuel ratio signal S3. Referring to this figure, when the air-fuel ratio switches from lean to rich or from rich to lean, the correction coefficient
FAF is skipped by α1 or α2, and if it remains lean, a predetermined number β1 is successively subtracted, and if it remains rich, a predetermined number β2 is successively added.

Learning correction coefficient determined by the control method of the present invention
FG can be expressed by the following equation.

FG = (1 + FHAC + DFC / Q) ... (2) where, FHAC = learning correction coefficient for altitude compensation DFC = learning correction coefficient for compensating for airflow meter blockage Q = intake air amount The learning correction coefficient FG is shown in Fig. 8, It is calculated according to the routines shown in FIGS. 9 and 10.

The learning control routine 1 shown in FIG. 8 is started every time the above-mentioned correction coefficient FAF is skipped, and in step S21, the latest correction coefficient FAF is
and the previous correction coefficient FAFO, that is, the arithmetic average value FAFAV1 of the two old and new values. Step S22
In step S23, it is determined whether the average value FAFAV1 is greater than or equal to 1, and if it is less than 1, "-0.002" is set to the altitude compensation learning amount GKF, that is, "-0.001" is set to the compensation learning amount GKD. Set. Average value
If FAFAV1 is 1 or more, in step S24, the advanced compensation learning amount GKF is set to "0.002", that is, the compensation learning amount GKD is set to "0.001".

In step S25, it is determined based on the idle signal S7 whether the throttle valve 18 is not fully closed. If an affirmative determination is made, the process proceeds to step S26, in which it is determined whether the above-mentioned average value FAFAV1 is set to "1" at the time of engine startup and is increased or decreased under predetermined conditions, that is, is equal to or greater than the compensation learning determination value FAFAV2,
When the average value FAFAV1 is greater than or equal to the judgment value FAFAV2, "0.002" is added to the judgment value FAFAV2 in step S27, and the average value FAFAV1 becomes the judgment value.
If it is smaller than FAFAV2, "0.002" is subtracted from the determination value FAFAV2 in step S28.

When a negative determination is made in step S25, or when steps S27 and S28 are completed, the process advances to step S29. In step S29, it is determined whether learning conditions are satisfied. It is an essential condition that the air-fuel ratio is under feedback control, and in addition, the learning condition is satisfied, for example, when the engine cooling water temperature is 80° C. or higher. If step S29 is affirmatively determined, the process proceeds to step S30, and the correction coefficient is
It is determined whether the count value of the counter CSK that counts the number of skips in FAF is 5 or more. If an affirmative determination is made in step S30, a learning control routine 2 shown in FIG. 9 is executed in step S31. Then, in step S32, the counter CSK is reset to "0".

When a negative determination is made in step S30 or when step S32 is completed, the process proceeds to step S33, where the counter CSK is incremented by +1, and in step S34, the latest correction coefficient FAF is set as the previous correction coefficient.
This series of routines ends as FAFO.

Next, the learning control routine in step S31 will be explained with reference to FIG.

When this routine is started, it is determined in step S51 whether the throttle valve 18 is fully closed based on the idle signal S7, and if an affirmative determination is made, step S5
Proceed to step 2. If a negative determination is made, the process advances to step S53.
In step S52, using the latest data of the correction coefficient FHAC and the latest data of the guard value FHACI, which is calculated only when the throttle valve 18 is fully closed, the calculation 3×FHAC+FHACI/4 is executed, and the result is latest guard value
FHACI.

In step S53, 0.03 is subtracted from the latest guard value FHACI obtained in step S52, and the result is stored in the A register. In the next step S54, the correction coefficient FHAC is subtracted from step S23 of the routine in FIG. Or learning amount GKF set in S24
is added to obtain the latest correction coefficient FHAC. Next, in step S55, the correction coefficient FHAC is
It is determined whether the value is greater than or equal to the value in the A register, and if a negative determination is made, the process proceeds to step S56, and if an affirmative determination is made, the process proceeds to step S57. That is, if the correction coefficient FHAC is smaller than (guard value FHACI - 0.03), the correction coefficient FHAC is changed to (guard value FHACI - 0.03) in step S56.
FHACI−0.03).

In step S57, it is determined whether the correction coefficient FHAC is greater than or equal to -0.20 and less than or equal to 0.10, and if it is not within that range, in step S58, the correction coefficient is
Guard FHAC at -0.20 or 0.10, that is, end this routine without learning the compensation learning correction coefficient DFC. In step S57, if the correction coefficient FHAC is within the range, step S5
Proceed to step 9. In step S59, it is determined whether the throttle valve 18 is fully closed, and if it is fully closed,
In step S60, the judgment value FAFAV2 is 0.98.
With the above, it is determined whether the value is 1.02 or less. If it is within that range, in step S61, the compensation correction coefficient DFC is set in step S61 of the routine of FIG.
Learning amount set in 23 or S24
Add GKD. Then, in step S62,
Add 0.002 to the judgment value FAFAV2 and end this series of routines.

Next, with reference to FIG. 10, a calculation routine for the learning correction coefficient FG to be reflected in the fuel injection time τ will be described.

When this routine is started, in step S71, the latest correction coefficient DFC obtained in step S61 of the routine of FIG. Divide by the air amount Q and store in the A register. Next, in step S72, it is determined whether the value of the A register is greater than or equal to -0.15 and less than or equal to 0.05, and if the value of the A register is not within that range, the value of the A register is changed in step S73. Guard with -0.15 or 0.05 and proceed to step S74
Proceed to. On the other hand, in step S72, even if the value of the A register is within the range, step S7
Proceed to step 4.

In step S74, the ninth
The latest correction coefficient FHAC obtained in step S56 or S58 of the routine shown in the figure and the value of the A register are added to 1, which is the reference value of the learning correction coefficient FG, to obtain the learning correction coefficient FG. And step S7
5, the learning correction coefficient FG is the standard value 1
Is it greater than or equal to −0.25 and less than or equal to 0.15, i.e.
It is determined whether 0.75≦FG≦1.15, and if the learning correction coefficient FG is within this range, this series of routines is ended. On the other hand, if the learning correction coefficient is not within that range, in step S76, the learning correction coefficient
This series of routines is completed by guarding FG by -0.25 or 0.15 with respect to the reference value 1, that is, by limiting the lower limit to 0.75 and the upper limit to 1.15.

Using the feedback correction coefficient FAF and learning correction coefficient FG obtained in this way, the final fuel injection time τ is obtained by equation (1), and the fuel injection signal S8 has a pulse width corresponding to this final fuel injection time τ. is generated, and the injection valve 26 is driven by the signal S8.

In this example, the learning correction coefficient for altitude compensation is
The learning amount of FHAC is 0.002, that is, the learning amount of compensation learning correction coefficient DFC is 0.001, and the learning correction coefficient FHAC for altitude compensation changes quickly, so the altitude changes relatively quickly, such as when climbing a hill at high altitude. On the other hand, when the altitude changes relatively slowly, such as when the airflow meter is clogged, sufficient compensation can be made using the compensation learning correction coefficient DFC. Become.

In addition, at idle when the air-fuel ratio is not affected by evaporated fuel, in other words, when the throttle valve is fully closed, the guard value FHACI is set to the altitude compensation learning correction coefficient FHAC.
Since the altitude compensation learning correction coefficient FHAC for cases other than fully closed throttle is guarded with the value obtained by subtracting 0.03 from the guard value, it is possible to prevent the influence of evaporated fuel on altitude compensation.

Further, the judgment value FAFAV2, which is set to 1 as an initial value when starting the engine, is the average value of the feedback correction coefficient under the condition that the throttle valve is open in steps S25 to S27 and S28 in FIG.
Changes will be made little by little to follow changes in FAFAV1.
If this change is executed repeatedly, the judgment value
FAFAV2 corresponds to the average value FAFAV1 when the throttle valve is open. Therefore,
As can be understood from FIGS. 1 to 3, this FAFAV2 is a value influenced by the high altitude and evaporated fuel, but is not influenced by the clogging of the intake air amount sensor. On the other hand, as is clear from FIG. 3, it is preferable to perform compensation learning when the throttle valve is fully closed. However, even if the throttle valve is fully closed, if the influence of the high altitude shown in FIG. 2 remains, it is difficult to perform proper blockage compensation learning. Therefore, in this embodiment, step S59 in FIG.
As shown in S60, the throttle valve is fully closed and FAFAV2 is close to the stoichiometric air-fuel ratio (0.98≦
FAFAV2≦1.02), in other words, after sufficient learning has been performed to remove the effects of high altitude and evaporated fuel, the learning of the compensation learning correction coefficient DFC is actually executed in step S61. I made it. This gives the correction factor
When learning DFC, the effects of high altitude and evaporated fuel can be prevented.

In addition, in step S62 of FIG. 9, the determination value
The reason for adding 0.002 to FAFAV2 is for the following reason: When the throttle valve is fully closed for a long time when traveling downhill, the increase in the time required to fully close the throttle valve increases in step S2
Since steps S27 and S28 are not executed,
FAFAV2 is unchanged. Therefore, once the determination in step S60 in FIG. 9 becomes negative, step S61, that is, compensatory learning, will be executed every time the process is executed. Therefore, in step S62
Add a predetermined value (0.002) to FAFAV2 and step S6
By making it outside the range of 0, in other words, the number of times compensation learning is executed is limited. Note that step S62 limits the number of times compensation learning is executed even when driving downhill from a high altitude, but since the change over time in the intake air amount sensor is small, the frequency of learning is limited. Even if it becomes small, there is no practical problem. In addition, when driving downhill from a high altitude, the learning correction coefficient for altitude compensation
FHAC learning is performed.

〔Effect of the invention〕

As described above, according to the present invention, when compensating for the air-fuel ratio due to clogging of the intake air amount sensor, it is possible to prevent the influence of evaporated fuel and the influence of high altitudes.

[Brief explanation of drawings]

Figure 1 is a diagram showing the influence of air-fuel ratio due to evaporated fuel, Figure 2 is a diagram showing the influence of air-fuel ratio due to high altitude,
Fig. 3 is a diagram showing the influence of air-fuel ratio due to blockage of intake air amount, Fig. 4 is a block diagram showing an example of an internal combustion engine to which the method of the present invention is applied, and Fig. 5 is a detailed example of its control circuit. Block diagram, Figure 6 is a flowchart showing an example of the feedback correction coefficient, Figure 7 is a flowchart showing an example of the feedback correction coefficient.
The figure shows the flag and correction coefficient according to the air-fuel ratio signal S3.
A time chart showing FAF, and FIGS. 8, 9, and 10 are flowcharts each showing an example of learning control in the method of the present invention. 10... Engine body, 18... Throttle valve, 20...
Air flow meter, 22...control circuit, 34, 36...
Crank angle sensor, 40...Idle switch, 4
2... _O2 sensor.

Claims (1)

[Scope of Claims] 1. Calculate the basic fuel injection time TP based on the intake air amount Q and the engine speed NE, and adjust the measured air-fuel ratio so that the air-fuel ratio becomes the stoichiometric air-fuel ratio under predetermined feedback conditions. The feedback correction coefficient FAF is calculated and stored according to the fuel ratio, and in response to the measured air-fuel ratio changing from rich to lean or from lean to rich, the feedback correction coefficient FAF is skipped by a predetermined number to perform feedback correction. Two old and new feedback correction coefficients immediately before and after the coefficient FAF skips
Calculates the arithmetic mean value FAFAV1 of the FAF values, and when the arithmetic mean value FAFAV1 is greater than a predetermined value, adds a predetermined number to the altitude compensation learning correction coefficient FHAC,
Learning correction coefficient for altitude compensation when below a predetermined value
Subtract a predetermined number from FHAC and memorize it, and when the throttle valve is not fully closed, compare the judgment value FAFAV2, whose initial value was set at engine startup, with the arithmetic average value FAFAV1, and then calculate the judgment value.
If FAFAV2 is larger than the arithmetic average value FAFAV1, a predetermined number is subtracted from the judgment value FAFAV2, and if it is smaller, a predetermined number is added to the judgment value FAFAV2. When fully closed and the arithmetic average value FAFAV1 is greater than or equal to a predetermined value, a predetermined number is added to the learning correction coefficient DFC for compensation, and when the arithmetic mean value FAFAV1 is less than or equal to the predetermined value, the learning correction coefficient for compensation is added. After subtracting a predetermined number from DFC and storing it, that is, adding or subtracting a predetermined number from DFC, the predetermined value is added to judgment value FAFAV2, and the stored learning correction coefficient for altitude compensation is calculated.
An air-fuel ratio control method characterized by correcting a basic fuel injection time TP using FHAC, that is, a compensation learning correction coefficient DFC and a feedback correction coefficient FAF, to calculate a final fuel injection time τ.