JPS6143236A - Control method of air-fuel ratio - Google Patents

Abstract

PURPOSE:To reduce an influence by aged deterioration and evaporated fuel and accurately compensate air-fuel ratio, by controlling a decision value so as to approach a mean value and to be in out of the update range of a correction coefficient under a condition that the evaporated fuel in a canister is sucked into an intake pipe. CONSTITUTION:If an altitude compensation study correction coefficient FHCAC is not within a range -0.2-0.1, the method, carding a correction coefficient FHAC by -0.2 or 0.1, finishes without studying a compensation study correction coefficient DFC. While if a correction coefficient FHC is within the range, the method, deciding whether or not a throttle valve is fully closed, adds, if it is fully closed, a study quantity GKD to the compensation correction coefficient DFC when a decision value FAFV2 is within a range of 0.98-1.02. And the method finishes by adding 0.002 to the decision value FAFAV2. Accordingly, an influency by the highland and evaporated fuel can be prevented when the correction coefficient DFC is studied because it is arranged so as to decrease smaller than 1.0 even under a condition of the evaporation generated or climbing the highlands that evaporated fuel is sucked into an intake pipe.

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 NB detected by the rotation speed sensor and the intake air amount Q detected by the intake air amount sensor, and determines the engine operation time. Depending on the condition, the basic fuel injection time T
The final fuel injection time τ is calculated by making various corrections to PK, and the injection valve is opened for the final fuel injection time r to fully inject the 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 Nox from exhaust gas as a measure against exhaust emissions, from the viewpoint of efficiently removing the three components mentioned above, , 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 predetermined conditions, a feedback correction coefficient FAFy is calculated 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. Executing control.

In an electronically controlled fuel injection system that performs such 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 due to changes in the intake air amount sensor over time. In order to compensate for changes in the air-fuel ratio, the air-fuel ratio is learned under predetermined conditions during the feedback control, and the learning correction coefficient FG is calculated.

Then, the final fuel injection time τ is 1, for example, τ=TPXF
9 is determined by the formula AFXFGXK.

Here, K is a correction coefficient based on water temperature, intake temperature, etc. [Problem to be solved by the invention] When learning such an air-fuel ratio, #! ! ! Fuel evaporated in the fuel tank and stored in the canister (hereinafter referred to as evaporated fuel) is supplied to 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 fuel ratio will temporarily latch onto the VCIJ. The effect of such evaporated fuel on the air-fuel ratio is
As shown in Figure 2, in extreme cases, the amount of intake air Q
Even in the area of high air flow rate of 100rrl/h 8 degrees, it is about 10
% richer.

Therefore, if you stop driving the vehicle immediately after learning due to changes in the air-fuel ratio due to evaporated fuel, the next time you start the vehicle, the air-fuel ratio will not be too lean, causing problems such as poor starting performance. arise.

For this reason, it is necessary not to learn about the air-fuel ratio that is dependent on evaporated fuel.

The above-mentioned compensation for the air-fuel ratio at high altitudes means that the air density is lower at high altitudes, so the air-fuel ratio at high altitudes is prevented from becoming rich. As shown in FIG. 3, the influence on the intake air is almost constant regardless of the amount of intake air.

For this reason, outside the range where the throttle valve is fully closed,
It is difficult to determine whether the five causes of the rich air-fuel ratio are 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, the area where the intake air amount is small will affect the air-fuel ratio as shown in FIG. Therefore, the air-fuel ratio is, for example, 1.5% between the region where the throttle valve is fully closed and the region other than that.
In the case of the above difference, conventional control determines that the intake air amount sensor is clogged and subtracts a learning correction coefficient so that the air-fuel ratio becomes λ (excess air ratio) = 1.
In the case of the influence of the air-fuel ratio as shown in the figure, learning is similarly performed, and the compensation of the air-fuel ratio due to changes over time and the compensation of the air-fuel ratio due to evaporated fuel are superimposed, making it difficult to properly compensate for the air-fuel ratio. Furthermore, if the vehicle descends from a high altitude with the throttle valve fully closed, there is a risk that compensation for clogging may not be performed accurately due to the effects of the high altitude.

[Means for solving all problems]

From now on, the average value FA of the feedback correction coefficient FAF
The judgment value FAFAV2 related to the average value FAFAvl is predetermined as a learning condition for the air 70-meter blockage compensation learning correction coefficient DFC, which is learned to be large when FAVI is large and small when FAVI is small. In addition to determining that the fuel vapor in the canister is in the intake pipe, the judgment value FA
The FkV2 is made to approach the average value FAFAVI.

[First Embodiment] FIG. 5 shows an example of an electronically controlled fuel injection type internal combustion engine to which the present invention is applied, where 10 is the engine body, 12 is an intake passage,
Reference numeral 14 indicates a combustion chamber, and reference numeral 16 indicates an exhaust passage.

An intake air amount sensor (air 70 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 Jlk, and generates a voltage according to the amount of intake air. The intake air temperature sensor 21 is provided in the intake passage 12 upstream of the throttle valve 18, is connected to the control circuit 22 via the signal 1s72, 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). I am guided by

The fuel injection valve 26 is provided for each cylinder and is controlled to open and close in response to electrical drive pulses supplied from the control circuit 22 via the signal line 3, and is controlled to open and close in response to electrical drive pulses supplied from the fuel supply system (not shown). Pressurized fuel is introduced into the intake passage 12 near the intake valve 25,
That is, it is intermittently injected into the intake boat section. The exhaust gas after being burned in the combustion chamber 14 is passed through the exhaust valve 28 and the exhaust passage 16.
and is discharged into the atmosphere via the three-way catalytic converter 30.

Crank angle sensors 34 and 36 are attached to the distributor 32 of the engine, and these sensors 3
4.36 is connected to the control circuit 22 via a signal line 14.15"k. These sensors 34.36 output pulse signals t each time the crankshaft rotates 30 degrees and 360 degrees. The pulse signals are supplied to the control circuit 22 via signal lines /4.75, respectively.

Distributor 32 is connected to igniter 38,
The igniter 38 is connected to the control circuit 22 via a signal line 76.

Reference numeral 40 indicates an idle switch (L) that is linked to the throttle valve 18 and is closed when the throttle valve 18 is fully closed.
L switch) is connected to the control circuit 22 via the signal line 17.
The exhaust passage 16 connected to the 02 outputs a signal responsive to the oxygen concentration in the exhaust gas, that is, generates an output voltage in steps when the air-fuel ratio is at the stoichiometric air-fuel ratio.
A processor 42 is provided and connected to the control circuit 22 via its output signal amplification line 18. A three-way catalytic converter 30 is provided downstream of this 02 sensor 42 and converts three harmful components in the exhaust gas: IC, Co, and NO.
Purify x components at the same time.

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

As shown in FIG. 6, the control circuit 22 includes a central processing unit (CPU) 22a that controls various devices, and an IJ-only memory (IJ-only memory) in which various numerical values and programs are written in advance.
ROM) 22b, random access memory (RAM) 22 in which numerical values and flags of calculation processes are written in predetermined areas.
c. A/D converter (ADC) 22d that has an analog multiplexer function and converts analog input signals into digital signals; input/output interface <110)zze to which various digital signals are input; input interface to which various digital signals are output; Output interface (Ilo)
22f, backup memory (BU-RAM) 22g that receives power from the auxiliary power source and retains memory when the engine is stopped
, and path line 2 to which each of these devices is connected.
It is composed of 2h-6- et al.

The ROM 22b contains a main processing routine program,
Programs for calculating fuel injection time (pulse width), programs for calculating air-fuel ratio feedback correction coefficients and learning correction coefficients (described later), various other programs, and various data necessary for these calculation processes are stored in advance. There is.

And air flow meter 20, intake temperature sensor 21.02
The sensor 42 and the water temperature sensor 44 are connected to the A/D converter 22
d, and the voltage signals S1, S2, S from each sensor
3. S4 is sequentially converted into a binary signal according to instructions from the CPU 22a.

Pulse signal S5 every 30 degrees of crank angle from crank angle sensor 34, crank angle 3 from crank angle sensor 36
The pulse signal S6 every 60 degrees and the idle signal S7 from the idle switch 40 are respectively I/022 e
The signal is taken into the control circuit 22 via k. Pulse signal S5
A binary signal representing the engine rotational speed is formed based on A signal, etc. is formed. Further, it is determined whether the system throttle valve 18 is substantially fully closed or not based on the idle signal S7.

From Ilo 22 f, a fuel injection signal S8 and an ignition signal S9 formed by the percentage type calculation are output to the fuel injection valves 26a to 26d and the igniter 38, respectively.

The fuel injection time (
Injection t) is determined, for example, as follows.

f='rPXFAFXFGXK ・=・・−・−(
1) Here, τ = Final fuel injection time TP = Basic fuel injection time FAF = Feedback correction coefficient FG = Learning correction coefficient = Correction coefficient due to water temperature, intake temperature, etc. The basic fuel injection time TP is determined by the intake air amount Q and the engine. Rotation speed N
Read from a predetermined table based on E,
or determined by calculation.

The feedback correction coefficient FAF is the air-fuel ratio signal S3 from the 02 sensor 42 under feedback control conditions.
If the air-fuel ratio is determined to be lean based on the air-fuel ratio signal S3, the injection amount will be increased to a value such as 1.05, and if the air-fuel ratio is determined to be rich based on the air-fuel ratio signal S3, the injection amount will be increased. If the value is reduced, for example 0.95, the correction coefficient FAF is set to 1 unless the feedback control condition is set.
．． It becomes 0.

An example of the calculation procedure of the feedback correction coefficient FAF is shown in the seventh section.
As shown in the figure.

In step S1, the meeting determines whether a feedback condition is satisfied. For example, the engine water temperature THW is not less than 50°C, not in the starting state or during the post-starting period,
The conditions for feedback control are met when power is not being increased. ft.

If the conditions for pack control are not satisfied, the feedback correction coefficient FAF'k is set to 1.0 in step S2. b1] control is executed and the procedure 1c is completed. It's a happy occasion! "L kf Proceeds to step S3. In step S3, the air-fuel ratio signal S3' is read. In step S4-1, the voltage value e represented by the air-fuel ratio signal S3 is set to "l" when rich, IJ In step 84-2, if the flag is 1, it is determined that the air-fuel ratio is too rich, and Perform the procedure to reduce the fuel ratio to the lean side.

That is, in step S5, the flag CAFL is set to zero and +1l is set.
Proceed to ils6, flag CAFR is 0-11>-No 1-
to judge. When moving to the over-concentrated side for the first time, flag CA
Since FR is zero, the process proceeds to step S8, where a predetermined value αl' is subtracted from the correction coefficient FAF stored in the RAM 22b, and the result is set as a new correction coefficient FAF. Step S9
In this case, the flag CAFR is set to l. Therefore, if excessive concentration is determined twice or more in succession in step 54-2, a negative determination will always be made in step S6 that passes from the second time onwards, and in step S7, a predetermined value βi is determined from the correction coefficient FiF.
t, and use the result as a new correction coefficient FAF.
Finish the calculation.

On the other hand, if the lean richness lag based on the voltage value represented by the signal S3 at =f-1 54-2 is 70'', it is determined that the air-fuel ratio is lean and the air-fuel ratio is set to the rich side. Pe〈hand J
[Execute '. That is, to the procedure SlO? Then, the process proceeds to step S11 as the Nozug CA P'R meeting is zero, and it is determined whether or not the flag CAFL is zero. The first time you move to the ``4 side'', the flag CA FL will be zero, so it is 81
2, a predetermined value α2 is added to the correction coefficient FAF, and the result is set as a new correction coefficient FAy. In step 813, 1 is set to the 7th lag CA k'L. Therefore, if it is determined to be dilute twice or more in succession in step 84-2, a negative determination will always be made in the second and subsequent passes 711811, and in step 814, a predetermined value β2 is added to the correction coefficient F' A F. As a result, a new correction coefficient P”
AI? ', the FAF operation 'tR is completed.

In addition, α work in steps S7, S8.512, and S14,
α2, βl and β2 are predetermined values.

Feedback correction coefficient FAF?9 determined by this calculation means? ]1-The voltage value represented by the air-fuel ratio signal S8 is shown in FIG. 8 together with the lean-rich flag of the air-fuel ratio A/F, which is applied with a VC filter and expressed in °C. To refer to this busy schedule,
When the air-fuel ratio switches from lean 7Jh to rich i or from rich to lean, the correction coefficient F A l'' is skipped by αl or α2, and if it remains lean, a predetermined number β2 is added sequentially, and if it is rich, then the correction coefficient F A l is skipped by αl or α2. Sequential predetermined number β1
is calculated by 1kjc.

The learning correction coefficient FG determined by the control method of the present invention is
It can be expressed by the following formula Vζ.

Here, FHAC=Learning correction coefficient for altitude compensation DFC=Learning correction coefficient Q for altitude compensation of 70 meters of air and intake air amount learning correction coefficient FG are calculated according to the routines shown in FIGS. 1 and 9.

The learning control routine l shown in FIG.
This is activated every time AF is skipped, and step S
21, the latest correction coefficient FAF and the previous correction coefficient FA
FO, that is, the arithmetic average value of the two old and new values FAFAV1?
+- Calculate. Proceeding to step S22, the average value FAFAV
Fully determine whether I is 1 or more, and if it is 1 or less, step 82
3, the amount of advanced compensation learning GKF is “-0,002”.
The meeting, that is, the compensation learning amount GKD is set to "-0,001".

If the average value FAFAVI is 1 or more, the hand JI824
K Oite, advanced compensation learning amount GKFK “0.002” meeting,
In other words, "0.001" is set for compensation learning 1GKD.

In step 825, a complete determination is made as to whether the conditions are such that evaporation occurs (conditions where evaporated fuel can be inhaled). For example, this can be determined based on whether the intake air amount Q is 30 m'/h or more, or whether the throttle valve is opened 2 to 5 degrees or more from fully closed. That is, if the throttle valve is completely removed from the evaporative port (not shown) provided in the intake pipe, the evaporated fuel accumulated in the canister will be sucked in, so the determination is made based on such a state. If the judgment is positive, proceed to step 8.
Proceeding to step 26, it is fully determined whether or not the above-mentioned average value F'AFAV1 is equal to or greater than the compensation learning judgment value FAFAV2, which is increased or decreased under predetermined conditions with "l" set at the time of the lateral start movement, When the average value FAFAVI is greater than or equal to the judgment value FAFAV2, the judgment value FAFAv2K" is determined in step 827.
0.002", the average value FAFAVI is the judgment value F
If it is smaller than AFAv2, 0.002 is subtracted from the determination value FAFAV2 in step 828.

When a negative determination is made in step S25, or in step 827
When the process ends in step 828', the process proceeds to step 829. In step 829, it is determined whether the learning conditions are satisfied. In addition to the essential condition that the air-fuel ratio is under feedback control, the learning condition is also satisfied, for example, when the engine cooling water temperature is 80° C. or higher. If step 829 is affirmatively determined, the process proceeds to step S30, and it is determined whether the count value of counter C8K, which counts the number of skips of correction coefficient FAF, is 5 or more. If step 830 is affirmatively determined, learning control routine 2 shown in FIG. 9 is executed at step 71i831. Then, in step 832, the counter C3Ki is reset to "0".

When a negative determination is made in step 330 or when step S32 is completed, the process proceeds to step 111833, and the counter CS is
The process is incremented by K1-1-1, and in step 834, the latest correction coefficient FAF is set as the previous correction coefficient FAFO, and this series of routines ends.

Next, the learning control routine in the hand J@831K will be explained with reference to FIG.

When this routine is started, it is determined in step 841 whether or not the throttle valve 18 is fully closed based on the idle signal S7, and if an affirmative determination is made, the process proceeds to step S42. If the determination is negative, the process advances to step 847.

In step 842, it is determined whether or not the vehicle speed SPD is zero.
Proceed to step 7. In step S43, the average value FAFAVI is 1.
Fully determine whether the value is 0 or more. This determination is based on the correction coefficient FHA
The purpose is to determine whether the air-fuel ratio C has been learned to be on the rich side, but has been learned to be on the lean side.
If an affirmative determination is made, it is learned to set the air twist ratio to the lean side, and if a negative determination is made, it is learned to set the air-fuel ratio to 'k IJ latch. Step 8
If a positive determination is made in step S43, the process proceeds to step S44, and if a negative determination is made, the process proceeds to step S845. In hand @ S44, the correction coefficient F
l(Determine AC≧guard reference value FHACIt. Step 8
If an affirmative determination is made in step 44 and if an affirmative determination is made in step 845, the process proceeds to step 846.

In step 846, using the latest data of the correction coefficient FHAC and the guard reference value F)tic I, 3XFHAC+
Performed on FHACI calculation, resulting in all the latest guard reference values FHA
CI.

In step 847, 0.03' is subtracted from the latest standard value FHACI obtained in step 846 and the result is stored in the iA register.In the next step 848, the correction coefficient FHkC as shown in FIG. Routine hand J@S 23
Alternatively, the learning 1GKF set in step 824 is added to obtain the latest correction coefficient F II A C. Next step S49
, the correction coefficient Fl (AC is equal to or greater than the value in the A register) is fully determined, and if a negative determination is made, step S50
If the determination is affirmative, the process advances to step 851. That is, the correction coefficient FHAC is (guard reference value F HA CI
-0,03), in step 850 the correction coefficient FF1Ac is set to (guard reference value F) (A CI-0
,03).

In step 851, it is determined whether the correction coefficient FHAC is greater than or equal to -0.20 and less than or equal to 0.10. If it is not within that range, in step 852, the correction coefficient F
is guarded with -0, 20 and Fio, io, that is, this routine ends without learning the compensation learning correction coefficient DFC. In step 851, the correction coefficient F)
(If AC is within the range, proceed to step 5.9. In step 853, it is determined whether the value and throttle valve 18 are fully closed. If it is fully closed, in step S5+, It is determined whether the determination value FAFAV2 is greater than or equal to 0.98 and less than or equal to 1602.

If it is within that range, in step S55, the compensation correction coefficient DFC is
Learning titG set in 23 or 824
Add K Dkk. And in hand JIIS56,
Add 0.002 k to the judgment value FAFAV2 and end this series of routines. Based on the FHAC and DFCK learned in this way, the learning correction coefficient FG is determined from the second equation, and the fuel injection time τ is determined. This is reflected in the first equation to be calculated.

In this example, in order to learn the compensation learning correction coefficient DFc'l, the judgment value FA related to the average value FAFAVI
I am using FAV2. This judgment value FAFAV2 is determined by the average value FAFAV2 when the conditions for sucking the evaporated fuel from the canister into the intake pipe (evaporation generation conditions) are satisfied.
The determination value is made to gradually approach AVI, and therefore, under the occurrence of evaporation, the judgment value is made to be smaller than 1.0.

Also, it may be smaller than 1.0 when pitching at high altitudes.

Then, when this judgment value FAFAV2 is within a predetermined range, for example within a range of 0.98 or more and 1.02 or less, under driving conditions that are not affected by the occurrence of evaporation, or when not climbing at high altitudes, that is, for compensation purposes. The learning correction coefficient DFC is now learned. Therefore, when learning the correction coefficient DFC, all influences caused by high altitudes and evaporated fuel can be avoided. In particular, the determination in step S25 in FIG. 1 can be made based on whether the idle signal is off or not, but it is possible to make the determination in step S25 in FIG. The following effects can be obtained.

It is now assumed that the engine is being operated in the state shown in FIG. 1O (A). Here, the condition under which the idle signal is on and no evaporation is generated is when the throttle valve is slightly opened to the extent that it does not overhang the evaporation boat and the load is light. In such a case, if the determination is made based on whether the idle signal is off in step 825 of FIG. 1, the following problem arises. FIG. 10(B)
As F becomes smaller and its average value FAFAVI becomes smaller, the 1 judgment value FAFAV2 also becomes smaller, and the correction coefficient PH increases each time the hand 111848″ft in Fig. 9 is passed.
AC becomes smaller. FM (AC does not become smaller than the lower limit value determined in step 847 in FIG. The distortion correction coefficient FHAC is 0.
Since the feedback correction coefficient FAF is maintained at 97', the feedback correction coefficient FAF becomes even smaller.

As a result, the judgment value FAFAV2 also becomes smaller; on the other hand,
After time t3, vaporized fuel is no longer sucked into the intake pipe.
The air-fuel ratio becomes lean due to the influence of FAF and FHAC, which are already small values, and as a result, the feedback correction coefficient FAF increases, so the determination value FAFAV2 also becomes sharper and the correction coefficient F)iAC increases.

In this way, between time points t3 and t4, FAFA'V2O!
However, since FHAC is updated every five times FAF skips, the determination value FAFAV2 increases quickly.

Now, if the idle signal is turned on (throttle valve is fully closed) at time t4 as shown in Figure 1O CB)K, and the judgment value FAFAv2 is approximately 1.0 at that time, then at time t4 In the end, the correction coefficient FHAC has become a small value due to the influence of the evaporative pump which returns it to 1.0. However, after time t4, steps S51 and S5 in FIG.
3. An affirmative determination is made in S54, and in step S55, the supplementary conventional learning correction coefficient DFC is learned, resulting in a value that is unrelated to the original air flow meter distortion. In addition, due to DFC learning, the learning correction coefficient FHAC value for altitude compensation becomes smaller by the learning amount of DFC, and as a result, the guard reference value FHA, which is the reference for the lower limit of FHkC, becomes smaller.
CI becomes undesirably small.

Therefore, in step 825 of FIG. 1, by determining whether the evaporation occurs or not, steps 826 and S27 and 828 of FIG. 1 are not passed after time t3 of FIG. good. As a result, the determination value FAFA42 is not updated between time points t3 and t5, as shown in FIG.
The determination of 0.98 is denied, and as a result, the correction coefficient DF
Erroneous learning of C is prevented.

In addition, in this embodiment, since the lower limit value of the AC correction coefficient Fl (AC) is determined in steps 841-350 of FIG. 9, the AC correction coefficient FHAC is
is not too small, and the correction coefficient FHAC quickly returns to its normal value due to learning during operation when no evaporation occurs, thus minimizing the influence of evaporated fuel on altitude compensation. be able to. In addition, the guard reference value FHAC
When updating I, it is determined whether the average value FAFAVI indicating the so-called base air-fuel ratio is less than or equal to 1, and according to the result of that determination, that is, when the current base air-fuel ratio is on the lean side, F HA c>1' HA At the time of CI, when the base air ratio is on the rich side, the guard reference value FHACI17 is set only when puAc and paAcx.
) has been updated, so even if the evaporation occurs under certain driving conditions, such as when driving in LA4 mode in the United States, the lower limit of the correction coefficient FHAC will be updated to the correct guard reference value Fl (regulated according to ACI). Therefore, the correction coefficient FHAC is also learned correctly.
This will be described in detail with reference to Figures (N to (E)').

Assume that the engine is now being operated in the state shown in FIG. 11(A). As shown in the guard reference value FI (if the ACIt idle signal is on, the guard reference value FI is always updated as shown in Fig. 11), the guard reference value F f (A CI is At time t1-t2, the idle signal is off, that is, the throttle valve is open, so it is not updated and the initial value 1.Ok is maintained.'On the other hand, as shown in FIG. 11 (Q), the correction coefficient FHAC is It is affected by evaporation from time tl.In other words, due to the occurrence of evaporation, the average value FAFAVl indicating the base air-fuel ratio becomes 1.
Due to being smaller than 0, the correction coefficient FHAC
becomes smaller each time the learning routine is performed, but since the first lower limit value is determined by (guard reference value FHACI-0,03), the lower limit value does not become smaller than 0.97. Further, from time t2 to t3, the idle signal is turned on, that is, the throttle valve is fully closed, and the evaporation generation is stopped. Therefore, under the occurrence of evaporation, the value is small, as shown in Fig. 11 (Q
In this case, the average value FAFAVI is larger than 1.0 due to the correction coefficient FHAC which has been learned up to 0.97. As a result, the correction coefficient becomes larger every time the learning routine is performed.

On the other hand, from time t2 to t3, the guard reference value FHACI can be updated, and gradually decreases according to the value of the correction coefficient FHAC, and the correction coefficient FHAC and the guard reference value FHA
When the CI approaches, the guard reference value FHACI is used after that.
gradually increases, but when the guard reference value FHACI is 1.
When the idle signal turns off at time t3 on the plane returning to 0,
The value 0.99 at time t3 becomes the guard reference value FHACI at time t3 to t4. Therefore, time t3~
At t4, the lower limit value of the correction coefficient FHAC is the second lower limit value 0.
．． It becomes 96. If such operating conditions continue, the lower limit value will become even smaller, and the correction coefficient FHAC will become too small due to the occurrence of evaporation, making it difficult to perform the original altitude compensation.

Even if the throttle valve is fully closed, FHAC (FHACI) is
As long as this is not the case, the update of the SIGARD reference value FHAcr is not executed (see (2) in FIG. 11), and therefore the lower limit value of the correction coefficient FHAC is 0. Therefore, even if such operating conditions continue, the lower limit value will not become extremely smaller than 0.97, and the original altitude compensation will be performed without being affected by the influence of the evaporator. It can definitely be done.

〔Effect of the invention〕

According to the present invention, the correction coefficient DFC for compensating for clogging of the air flow meter due to changes over time is as small as ζ.
It is updated and learned only when the average value FAFAVI of the feedback correction coefficient FAF and the related judgment value FAFAV2 are within a predetermined range. condition), the judgment value FAFAV2 is set to the average value FAFAV
Since the determination value FAFAV2 is set to be close to I, the determination value FAFAV2 becomes a small value outside the above range under the evaporation generation condition, and therefore updating of the correction coefficient DFC is prohibited. Also,
The conditions for evaporation generation are that the XOt y+ valve is opened to the extent that the evaporation boat in the intake pipe (the boat where evaporated fuel from the canister is sucked into the intake pipe) is at least slightly open, but the throttle The judgment value FAFAV also applies when climbing to a high altitude with the valve opened beyond such an opening degree.
2 deviates from the above-mentioned determination value, updating of the correction coefficient DFC for compensating for clogging of the air flow meter is also prohibited in this case. Therefore, the correction coefficient DFC for compensating for the pressure of the air flow meter is
Learning is done in accordance with the original purpose without having to take a class.

[Brief explanation of drawings]

Figure 1 shows -911! of the present invention! A flowchart showing a learning control routine as an example. Figure 2 is a diagram showing the influence of evaporated fuel on the air-fuel ratio. Figure 3 is a diagram showing the influence of the air-fuel ratio due to high altitude.
Figure 4 is a diagram showing the influence of the air-fuel ratio due to the intake air amount reduction, Figure 5 is a diagram showing an example of an internal combustion engine to which the method of the present invention is applied, and Figure 6 is a diagram showing its control. A block diagram showing a detailed example of the circuit, FIG. 7 is a flowchart showing an example of a feedback correction coefficient, and FIG. 8 is a time chart showing a flag and correction coefficient FAF according to the air-fuel ratio signal S3.
9 is a flowchart showing an example of the learning control routine 2 of the routine in FIG. 1, and FIG.
are the idle signal, the judgment value FAFAV2, the correction coefficient pHhc, and the WR positive coefficient DFCf), respectively, and the time chart in FIG. 11(A) to all-) are respectively. Idle signal, card reference value FHACI, correction coefficient FH
It is a time chart of Ac. 10... Engine body, 18... Throttle valve, 20...
...Air flow meter, 22...Control circuit, 34.36
...Crank angle sensor, 40...Idle switch, 42...02 sensor. Agent Tatsu Unuma 2nd figure 3rd figure LL neon figure 4 figure 6 figure 7 rfR figure 8

Claims (1)

[Claims] (1) Calculate the basic fuel injection time TP based on the intake air amount Q and the engine speed NE, and adjust it according to the measured air-fuel ratio so that the air-fuel ratio becomes the stoichiometric air-fuel ratio under predetermined feedback conditions. calculates the feedback correction coefficient FAF, skips the feedback correction coefficient FAF by a predetermined number in response to the measured air-fuel ratio changing from rich to lean or from lean to rich, and skips the feedback correction coefficient FAF by a predetermined number of times immediately before the feedback correction coefficient FAF skips or Calculate the arithmetic average value FAFAV1 of the two immediately following new and old values, determine the conditions under which the evaporated fuel in the canister is not sucked into the intake pipe, and when the above conditions are satisfied, determine the judgment value FAFAV2.
is compared with the average value FAFAV1, and the judgment value FAFAV2 is determined.
is larger than the average value FAFAV1, the judgment value FAFAV
2 is made smaller, and if it is smaller, the judgment value FAFAV2 is increased, and when the judgment value FAFAV2 is idle and within a predetermined range, that is, the compensation learning correction coefficient DFC
, and determines the final fuel injection time τ based on at least the basic fuel injection time TP, the feedback correction coefficient FAF, and the compensation learning correction coefficient DFC. Fuel ratio control method.