JPH01285635A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent worsening of fuel consumption and drivability by a method wherein in a region in which the frequency of engine running is relatively low in the given running region of an engine, the gain of feedback control of an engine state quantity is increased. CONSTITUTION:When it is discriminated by a feedback control condition discriminating means A that the feedback control condition of an internal combustion engine is satisfied, feedback control is made on an engine state control amount by a feedback control means C so that an engine state detected by a detecting means B is brought into a satisfactory state. In this case, it is discriminated by a learning condition discriminating means D whether the learning condition of an engine is satisfied, and when it is satisfied, a value responding to the control amount is stored in each running region by a learning-classified-by-region means E. Meanwhile, when it is not satisfied, a value responding to a control amount of the region forms an initial value of a control amount each time transition of a given running region is effected. In region in which the frequency of engine running is relatively low, the gain of feedback control of a control amount is increased by a gain regulating means F.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides air-fuel ratio sensors (herein, oxygen concentration sensors (Ot sensors)) on the upstream and downstream sides of a catalytic converter.
) or a pseudo-double air-fuel ratio sensor system that uses the output frequency of an upstream Ot sensor instead of the output of the downstream Oz sensor.

[Conventional technology]

In simple air-fuel ratio feedback control (single O2 sensor system), the 0□ sensor that detects oxygen concentration is installed at a point in the exhaust system as close to the combustion chamber as possible, that is, at the gathering part of the exhaust manifold upstream of the catalytic converter. Due to variations in the output characteristics of the O sensor, it is difficult to improve the control accuracy of the air-fuel ratio. It takes 0□
In order to compensate for variations in sensor output characteristics, variations in parts such as fuel injection valves, and changes over time or aging, a second 02 sensor is provided downstream of the catalytic converter, and air-fuel ratio feedback control by the upstream Ot sensor is performed. In addition, Double 0! performs air-fuel ratio feedback control using the downstream Ot sensor! A sensor system has already been devised (
Reference: Japanese Patent Application Laid-open No. 58-72647), this double 0
In the □ sensor system, the 02 sensor installed on the downstream side of the catalytic converter has a lower response speed than the 0□ sensor on the upstream side, but it has the advantage of less variation in output characteristics for the following reasons. ing.

(1) Downstream of the catalytic converter, the exhaust gas temperature is low, so there is little thermal influence.

(2) Since various poisons are trapped in the catalyst downstream of the catalytic converter, the amount of poisoning of the downstream 02 sensor is small.

(3) The exhaust gas is sufficiently mixed downstream of the catalytic converter, and the oxygen concentration in the exhaust gas is close to an equilibrium state.

Therefore, as described above, by air-fuel ratio feedback control (double Ox sensor system) based on the outputs of the two 0□ sensors, variations in the output characteristics of the upstream Ot sensor can be absorbed by the downstream Ot sensor. In fact, as shown in FIG. In the sensor system, 0□
If the output characteristics of the sensor deteriorate, it will directly affect the exhaust emission characteristics, whereas with the double Ox sensor system, even if the output characteristics of the upstream 0□ sensor deteriorate,
Exhaust emission characteristics are not deteriorated. That is, double 0
! In the sensor system, good exhaust emissions are guaranteed as long as the downstream 08 sensor maintains stable output characteristics.

In the above-mentioned double 0□ sensor system, the required level for air-fuel ratio correction during feedback control (hereinafter referred to as air-fuel ratio required level) may be significantly different from that during non-feedback control. The following problem occurs at the time when feedback control is started using two Of sensors. That is, in this case, the air-fuel ratio feedback control speed by the downstream 02 sensor is normally 0□ on the upstream side.
Since it is set small compared to the air-fuel ratio feedback control speed by the sensor, the air-fuel ratio control amount controlled by the air-fuel ratio feedback control by the downstream sensor 03, for example, skip ii l? sR.

It takes time for the RSL to reach the required skip amount level, and in turn, it takes time for the air-fuel ratio to reach the required control level due to air-fuel ratio feedback control, resulting in insufficient correction, This leads to deterioration of fuel efficiency, deterioration of drivability, deterioration of emissions, etc.

Additionally, even during air-fuel ratio feedback control, when the engine state transitions to a different operating range, the air-fuel ratio control level may still deviate from the air-fuel ratio request level, and in this case as well, insufficient correction may occur. , leading to deterioration of fuel efficiency, deterioration of drivability, deterioration of emissions, etc.

For example, due to the 02 storage effect of the catalyst, the amount of gas is smaller in the low load range than in the high load range, and the amount of 0□ consumption stored in the catalyst is small, so the downstream Ot sensor takes a longer time to indicate lean. , As a result, the air-fuel ratio control amount R5R in the high load range and the low load range.

The RSL value shifts. This is particularly noticeable when a new catalyst with a large Ot storage effect is used.

Therefore, when the load changes from a low load range to a high load range, the air-fuel ratio feedback period of the downstream Ot sensor is relatively long, so the downstream Ot sensor has a relatively long time. A control delay occurs, causing the air-fuel ratio to become over-left, resulting in deterioration of fuel efficiency and emissions.

For this reason, the applicant of the present application has already divided engine load conditions such as intake air amount, intake air pressure, throttle valve opening, rotational speed, vehicle speed, or reversal cycle of the output of the upstream 02 sensor into multiple categories. If the engine load state belongs to the same operating range and the engine satisfies the learning conditions, calculate the center value of the air-fuel ratio control amount, The center value of the control amount is stored for each operating region, and when the engine does not satisfy the air-fuel ratio feedback conditions or when the engine state changes to a different operating region thereafter, the air-fuel ratio control amount is set to the current operating region. We propose block learning control that uses the center value of the air-fuel ratio control amount stored in the area. (Reference: JP-A-62-6
According to Japanese Patent Application No. 0941, Japanese Patent Application No. 61-241484, Japanese Patent Application No. 63-14614), at the start of air-fuel ratio feedback control by the downstream Ox sensor, tα
Starting from the center value of the air-fuel ratio control amount, and even when the engine state changes to a different operating range,
It starts from the center value of the air-fuel ratio control amount stored for each operating region.

[Problem to be solved by the invention]

However, in the area-specific learning control using the driving area described above, depending on the parameters of the driving area division and the method of area division, there may be few learning opportunities (erroneous learning may occur.For example, as shown in FIG. In operating region A, the required level of the air-fuel ratio control amount, for example, rich skip amount R3R, can be learned;
In this case, the required level cannot be learned because the system transitions to operating region A before learning the required level. In other words, when learning, the required level, that is, the center value of the air-fuel ratio indicated by the engine, is detected. Sufficient time is required;
As a result, a state in which learning cannot be performed may occur, and if a learning value is determined in a short period of time, an accurate center value cannot be learned due to the influence of transients.As a result, even after starting feedback control and during feedback control, the engine There is a problem in that when the state of the vehicle changes to a different condition, it causes deterioration in fuel efficiency, deterioration in drivability, deterioration in emissions, etc.

An object of the present invention is to provide a region-specific learning control system that sufficiently prevents deterioration of fuel efficiency, deterioration of drivability, deterioration of emissions, etc.

[Means to solve the problem]

A means for solving the above problem is shown in FIG.

That is, the engine state detection means, such as an Ox sensor, detects a predetermined state of the engine, and the feedback control condition determination means determines whether or not the feedback control conditions of the engine are satisfied. As a result, when the engine feedback control condition is satisfied, the feedback control means changes the engine state manipulated variable, for example, the rich skip amount R3R, to the detection result of the engine state detection means so that the engine is in a predetermined state, for example, the stoichiometric air-fuel ratio state. Feedback control is performed accordingly. Also,
The learning condition determining means determines whether the learning conditions of the institution are satisfied. As a result, when the engine learning condition is satisfied, the region-based learning means stores a value, for example, an average value R3R, corresponding to the engine state manipulated variable R3R for each predetermined movement region of the engine. Further, the region-specific learning means sets the engine state manipulated variable R3R corresponding to R2H as the initial value of the engine state manipulated variable R3R when the feedback control condition is not satisfied and every time the engine changes from one predetermined operating region to another. The feedback gain adjustment means increases the gain of the feedback control H of the engine state manipulated variable R3R in a region where the engine is operated relatively less frequently among the predetermined operating regions of the engine, compared to other regions. It is.

Note that areas with few learning opportunities are, for example, high-speed areas when vehicle speed is selected as a parameter for area classification, and low-load areas when load is selected as a parameter for segmentation. It depends on how the areas are divided.

[For production]

The operation of the above means will be explained with reference to FIG.

In region B where there are few learning opportunities, the gain of feedback control of rich skip R3R as an engine state manipulated variable, that is, the change speed is made larger than in other region A.
In the illustrated example, in region A, there is only integral control (ΔR5), but in region B, skip control (R3S
KP) was further introduced. As a result, even in areas where there are few opportunities for learning, the required level can be learned, and there is less erroneous learning.

〔Example〕

FIG. 5 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. In FIG. 5, an air flow meter 3 is provided in the intake passage 2 of the engine body 1. As shown in FIG. The air flow meter 3 directly measures the intake air amount, has a built-in potentiometer, and generates an analog voltage output signal proportional to the intake air amount. This output signal is supplied to an A/D converter 101 with a built-in multiplexer of the control circuit 10. The distributor 4 has a crank angle sensor 5 whose shaft generates a reference position detection pulse signal every 720 degrees in terms of crank angle, and a crank angle sensor 5 which generates a reference position detection pulse signal every 30'' in terms of crank angle. A crank angle sensor 6 is provided to generate pulse signals.The pulse signals of these crank angle sensors 5 and 6 are supplied to the input/output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is sent to the CPU 10.
3 interrupt terminal.

Further, the intake passage 2 is provided with a fuel injection valve 7 for supplying pressurized fuel from a fuel supply system to the intake boat for each cylinder.

Further, a water temperature sensor 9 for detecting the temperature of cooling water is provided in the water jacket 8 of the cylinder block of the engine body 1. Water temperature sensor 9 indicates cooling water temperature TH
Generates an analog voltage electrical signal according to W. This output is also supplied to the A/D converter 101.

The exhaust system downstream of the exhaust manifold 11 is provided with a catalytic converter 12 that accommodates a three-way catalyst that simultaneously purifies three harmful components HC, CO, and NO in the exhaust gas.

The exhaust manifold 11 includes a catalytic converter 1.
A first Ot sensor 13 is provided on the upstream side of the catalytic converter 12, and a second Ot sensor 15 is provided on the exhaust pipe 14 on the downstream side of the catalytic converter 12.

The 0□ sensors 13 and 15 generate electrical signals corresponding to the concentration of oxygen components in the exhaust gas. That is, 0□ sensor 13
, 15 is an A/D control circuit 10 which outputs different output voltages depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.
occurs in converter 101.

Further, the throttle valve 16 of the intake passage 2 is provided with an idle switch 17 for detecting whether the throttle valve 16 is fully closed, and this output signal is supplied to the input/output interface 102 of the control circuit 10. Ru.

Reference numeral 18 denotes a vehicle speed sensor, which is composed of, for example, a permanent magnet and a reed switch, and its output is sent to the control circuit 10.
It is sent to the vehicle speed formation circuit 111.

The control circuit 10 is configured as a microcomputer, for example, and includes an A/D converter 101, a human output interface 102, a CPU 103, a vehicle speed formation circuit 111, and a ROM 104, a RAM 105, and a backup RO.
M106, a clock generation circuit 107, etc. are provided.

Further, in the control circuit 10, a down counter 108,
Flip-flop 109 and drive circuit 110 are for controlling fuel injection valve 7.

That is, in the routine described later, the fuel injection amount TAU
is calculated, the fuel injection amount TAU is counted down by the down counter 1.
08 and flip-flop 109
Also cents. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, the down counter 108
counts a clock signal (not shown) and finally when its carrier terminal reaches the "1" level, the flip-flop 109 is reset and the drive circuit 110 stops energizing the fuel injection valve 7. . That is, the fuel injection valve 7 is energized by the above-mentioned fuel injection amount TAU, so that an amount of fuel corresponding to the fuel injection amount TAU is sent into the combustion chamber of the engine body 1.

Note that the A/D converter 10 which generates interrupts in the CPU 103
1, the input/output interface 102
When the controller receives a pulse signal from the crank angle sensor 6, when it receives an interrupt signal from the clock generation circuit 107, etc.

The intake air amount data Q and cooling water temperature data THW of the air flow meter 3 are taken in by an A/D conversion routine executed at predetermined time intervals and stored in a predetermined area of the RAM 105. That is, data Q and THW in RAM 105 are updated at predetermined time intervals. Further, the rotational speed data No. is calculated by interruption every 30''CA of the crank angle sensor 6 and is stored in a predetermined area of the RAM 105.

FIG. 6 shows a first air-fuel ratio feedback control routine for calculating an air-fuel ratio correction coefficient FAF based on the output of the upstream 0□ sensor 13, and is executed every predetermined period of time, for example, every 4 hours.

In step 601, the upstream side 0! It is determined whether a closed loop (feedback) condition for the air-fuel ratio by the sensor 13 is satisfied. For example, when the cooling water temperature is below a predetermined value, the output signal of the upstream Ox sensor 13 is never reversed while the engine is starting, increasing the amount after starting, increasing the warm-up amount, increasing the power, or increasing the OTP amount to prevent catalyst overheating. The closed-loop condition does not hold true in all cases such as fuel cut, etc., and the closed-loop condition holds in all other cases. If the closed-loop condition is not satisfied, the process proceeds to step 627 and sets FAF to the value immediately before the end of the closed-loop control. Note that a certain value, for example 1.0
You can also use it as On the other hand, if the closed loop condition is satisfied, the process proceeds to step 602.

In step 602, the upstream side 0. The output V of the sensor 13,
is A/D converted and taken in, and in step 603 it is determined whether V is less than the comparison voltage Vll, for example 0.45V, that is, it is determined whether the air-fuel ratio is rich or lean. If (V+≦V□), it is determined whether the delay counter CDLY is positive or not in step 604, and if CDLY>0, CDL is
Set Y to 0 and proceed to step 606. In step 606, delay counter CDLY is subtracted by 1, and step 6
07, the delay counter CDLY is guarded at the minimum value TDL at 608. In this case, the delay counter CD
When LY reaches the minimum value TDL, step 609
, the first air-fuel ratio flag F1 is set to "O" (lean), and the minimum value TDL is determined to be a rich state even if there is a change from rich to lean in the output of the upstream OR sensor 13. Lean delay state to maintain , defined as a negative value. On the other hand, rich (V + >
V□), it is determined in step 610 whether the delay counter CDLY is negative or not, and if CDLY<Q, CDLY is set to O in step 611.
Proceed to step 2. In step 612, the delay counter CDL
Y is incremented by 1, and the delay counter CDLY is guarded at the maximum value TDR in steps 613 and 614.

In this case, when the delay counter CDLY reaches the maximum value TDR, the first air-fuel ratio flag F1 is set to "1" (rich) in step 615.
R is a rich delay time for maintaining the determination that the engine is in a lean state even if there is a change from lean to rich in the output of the upstream Ox sensor 13, and is defined as a positive value.

In step 616, it is determined whether the sign of the first air-fuel ratio flag Fl has been inverted, that is, it is determined whether the air-fuel ratio after the delay processing has been inverted. If the air-fuel ratio has been reversed, then in step 617, it is determined based on the value of the first air-fuel ratio flag F1 whether the reversal is from rich to lean or from lean to rich. If it is a reversal from rich to lean, in step 618 FAP←FAF + RS
Increase R and skip, and conversely, reverse from lean to rich to lever, step 619 NiteFAP-FA
F-RSL and skipping decrease. In other words, skip processing is performed.

If the sign of the first air-fuel ratio flag F1 is not inverted in step 616, integration processing is performed in steps 620, 621, and 622, that is, in step 620, F1
= “θ” or not, and if Fl = “0” (lean), set FAF←FAF +KIR in step 621, and on the other hand, if Fl = “1” (rich), step 6
In 22, FAF -FAF-) [ru. Here, the integral constants KIR and KIL are set sufficiently small compared to RSR and RSL.
L) < RSR (RSL). Therefore, step 621 gradually increases the fuel injection amount in the lean state Li (Fl-“0”), and step 622 gradually increases the fuel injection amount in the rich state (F1
="1") to gradually reduce the fuel injection amount.

The air-fuel ratio correction coefficient FAF calculated in steps 618, 619, 621, and 622 is guarded at a minimum value of, for example, 0.8 in steps 623 and 624, and is guarded at a maximum value of, for example, 1.2 in steps 625 and 626. is guarded. As a result, for some reason, the air-fuel ratio correction coefficient F
When the AF becomes too large or too small, the air-fuel ratio of the engine is controlled using that value to prevent over-rich or over-lean conditions.

The FAF calculated as described above is stored in the RAM 105, and the routine ends in step 627.

FIG. 7 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. 6. Upstream side 0. When the air-fuel ratio signal A/F for rich/lean discrimination is obtained from the output of the sensor 13 as shown in FIG. 7(A), the delay counter CD
As shown in FIG. 7(B), LY is counted up in a rich state and counted down in a lean state.

As a result, as shown in FIG. 7(C), a delayed air-fuel ratio signal A/F' (corresponding to flag F1) is formed. For example, time 1. Even if the air-fuel ratio signal A/F' changes from lean to rich at time 1t, the delayed air-fuel ratio signal A/F' changes to rich at time 1t after being held lean for the rich delay time TDR. Even if the air-fuel ratio signal A/F changes from rich to lean at time 0 t, the air-fuel ratio signal A/F' subjected to the delay processing is delayed by the lean delay time (-
After being held rich by an amount equivalent to TDL), it changes to lean at time t4. However, when the air-fuel ratio signal A/F' is reversed in a short period of the rich delay time TDR as at time tSrt&+tff, it takes time for the delay counter CDLY to reach the maximum value TDR, and as a result, at time t
, the air-fuel ratio signal A/F' after the delay processing is inverted.

In other words, the air-fuel ratio signal A/F' after the delay process is more stable than the air-fuel ratio signal A/F before the delay process. In this manner, the air-fuel ratio correction coefficient FAF shown in FIG. 7(D) is obtained based on the stable air-fuel ratio signal A/F' after the delay processing.

Next, the second air-fuel ratio feedback control by the downstream 0□ sensor 15 will be explained. The second air-fuel ratio feedback control includes skip amounts RSR and RSL as the first air-fuel ratio feedback control constants, and an integral constant K.
IR, KIL, delay time TDR.

TDL or the output of the upstream Ot sensor 13 ■.

There are two systems: a system that makes the comparison voltage V□ variable, and a system that introduces a second air-fuel ratio correction coefficient FAF2.

For example, if the rich skip amount R3R is increased, the controlled air-fuel ratio can be shifted to the rich side, and even if the lean skip IR3L is decreased, the controlled air-fuel ratio can be shifted to the rich side.On the other hand, if the lean skip 1JR3L is increased,
The controlled air-fuel ratio can be shifted to the lean side, and even if the rich skip amount R3R is made small, the controlled air-fuel ratio can be shifted to the lean side.

Therefore, the air-fuel ratio can be controlled by correcting the rich skip IR3R and the lean skip amount RSL according to the output of the downstream 02 sensor 15.

In addition, by increasing the rich integral constant KIR, the control air-fuel ratio can be shifted to the rich side, and the lean integral constant KIL
The control air-fuel ratio can be shifted to the rich side by making the lean integral constant KIL larger, and the control air-fuel ratio can also be shifted to the lean side by increasing the lean integral constant KIL. The fuel ratio can be shifted to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the rich integral constant KIR and the lean integral constant KIL according to the output of the downstream O sensor 15. Increase the rich delay time TDR or change the lean delay time If the time (-TDL) is set small, the controlled air-fuel ratio can be shifted to the rich side; conversely, if the lean delay time (-TDL) is set large or the rich delay time (
If TDR) is set small, the controlled air-fuel ratio can be shifted to the lean side. That is, the air-fuel ratio can be controlled by correcting the delay times TDR and TDL according to the output of the downstream 0□ sensor 15. Furthermore, by increasing the comparison voltage ■□, the controlled air-fuel ratio can be shifted to the rich side, and by decreasing the comparison voltage V□, the controlled air-fuel ratio can be shifted to the lean side. Therefore, by correcting the comparison voltage v1 according to the output of the downstream zero sensor 15, the air-fuel ratio can be controlled.

Making these skip amount, integral constant, delay time, and comparison voltage variable by the downstream Ot sensor has its own advantages. For example, the delay time allows for very delicate air-fuel ratio adjustments, and the skip amount does not lengthen the air-fuel ratio feedback cycle (which allows for control with good response), unlike the delay time. Of course, two or more of these variable amounts can be used in combination.

Next, a double 0□ sensor system in which the skip amount as an air-fuel ratio feedback control constant is made variable will be described.

FIG. 8 shows a second air-fuel ratio feedback control routine for calculating the skip amounts RSR and RSL based on the output of the downstream 08 sensor 15.
Executed for each fertilizer. In step 801, vehicle speed SPD data SPD is fetched from the vehicle speed forming circuit 111, and n=5PD/ΔSPO, where ΔSPD is calculated as a constant value. Note that n is an integer, and SPD/ΔSPD
The decimal places shall be rounded down. In this way, the vehicle speed SPD is in the region 0≦SPD<ΔSPD $■ region ΔSPD≦SPD<2 ・Δsp.

Area (k-1”) Δ 5PD5 SPD<
It is up to the referee to decide which category it belongs to: k or ΔSPD. Note that the vehicle speed SPD in step 806 may be a rounded value.

In steps 802 to 806, it is determined whether the downstream side 02 sensor 15 is in a closed loop condition. For example, in addition to the failure of the closed loop condition determined by the downstream O2 sensor 13 (step 802), when the cooling water temperature THW is below a predetermined value (for example, 70°C) (step 803), the throttle valve 16 is fully closed (LL = “1 ”) (step 804)
, when the downstream O2 sensor 15 is not activated (step 8o5), when the load is light (Q/Ne≦X,) (step 805), when the downstream Ot sensor 15 is not activated (step 806), etc. The closed-loop condition is not satisfied, and the closed-loop condition is satisfied in other cases. If the condition is not a closed loop condition, the process proceeds to step 824.

If the closed loop condition is satisfied, the process advances to step 807. That is, it is determined whether the current operating range n and the previous operating range no are the same. If they are the same (n=no),
Proceed to step 808.

On the other hand, when the range n of the vehicle speed SPD changes or when the closed loop is not established by the downstream Ot sensor 15,
Proceeding to step 824, the rich skip amount R5R is set to the learning value RSRG of the corresponding area n of the backup RAM 106.
(n).

In step 808, the output V of the downstream 0□ sensor I5!
is A/D converted and taken in, and in step 809, vt is the comparison voltage ■. For example, it is determined whether the voltage is 0.55V or less.

In other words, it is determined whether the air-fuel ratio is rich or on. In addition,
Comparison voltage■. is set higher than the comparison voltage V□ of the output of the upstream Ox sensor 13, taking into consideration that the output characteristics differ due to the influence of raw gas and the deterioration rate differs between the upstream and downstream of the catalytic converter 12. As a result, ■z≦V
If Rt (lean), the second air-fuel ratio flag F2 is set to "0" in step 810, and on the other hand, V, >VR2(
rich), the second air-fuel ratio flag F2 is set to 'l'' in step 811. Next, in step 812, it is determined whether or not the second air-fuel ratio flag F2 has been inverted.As a result, If it is reversed, it is determined in step 813 whether the learning condition is satisfied (learning execution flag F = "1"), and if the learning condition is satisfied, the process is performed in step 814.
The learning execution flag F and the learning step 814 will be described later.

In step 815, it is determined whether the current area n is an area with low learning frequency. For example, here, vehicle speed SPD
It is determined whether or not it is in the area where X, (60 km/h) is traveling. If it is a region with low learning frequency (SP[l>L),
Proceeding to step 816, skip control (step 817
~819) and integral control (steps 820~822)
On the other hand, if the learning frequency is high (SPD≦Xz), the process proceeds to steps 820 to 822 and only integral control is performed.

Skip control of steps 817 to 819 is performed in step 8.
It is executed only when the output V8 of the downstream 0□ sensor 15 is reversed at step 16. That is, in step 817, it is determined whether the output t of the downstream Ot sensor 15 is high or rich. As a result, if it is lean (F2-"0"), the rich skip amount R5R is skipped by a relatively large value R55KP in step 818, and on the other hand, if it is rich (F2-"bi), step 818 skips. At step 8-19, the rich skip amount R3R is decreased by the value R55KP in a skip manner.

Note that the skip amount R55 at steps 818 and 819
KP may be different or variable.

On the other hand, if the learning frequency is high (SPD≦X+), or even if the learning frequency is low but the output V2 of the downstream 0° sensor 15 is not inverted, step 8
Integral control is performed at 20-822. That is, in step 820, it is determined whether the output V2 of the downstream 0□ sensor 15 is lean or rich. As a result, if lean (F2
="0"), rich skip 1iR at step 821
5R is increased by a relatively small value ΔR5, while if rich, P11R5R is decreased by a value ΔR5. Note that the integral amount ΔR3 in steps 821 and 822 may be different or may be variable. Step 823 performs the guard processing of the calculated R2H as described above, for example, the minimum value M I N = 2.5%,
Guard at maximum value M A X -7.5%. In addition,
The minimum value MIN is a level at which transient followability is not impaired, and the maximum value MAX is a level at which drivability does not deteriorate due to air-fuel ratio fluctuations.

In step 825, the lean skip 1lR3L is
Calculate with AM105-R2H. That is, R3R+RSL=10%.

In step 826, area n is set to no in preparation for the next execution.

After R2H calculated as described above is stored in the RAM 105, this routine ends in step 827.

In this way, according to the routine in Figure 8, as shown in Figure 9, areas with many learning opportunities (SPD: 5 x z)
Then, the rich skip amount RSR is integrally controlled by the value ΔR3 according to the output vt of the downstream Ot sensor 15, and on the other hand, in the region with many learning opportunities (SPD > xz), the downstream Ot sensor 15
Ridge skip fiR3 according to the output V2 of the sensor 15
R is integrally controlled with a value ΔR3 and skip-adjusted with a value R55KP. That is, in a region where there are few learning opportunities, the gain of feedback control of the rich skip amount R3R is increased.

Next, the learning execution flag F and the learning control step 814 in FIG. 8 will be explained.

FIG. 10 shows a routine for setting the learning execution flag FG, which is executed every predetermined period of time, for example, every 512 turns or every predetermined crank angle, for example, 180' CA. Steps 1001 to 1005 are step 80 in FIG.
1 to 805 are the same, but differ only in step 1002. That is, in step 1002, the cooling water temperature THW falls within a predetermined range, for example, 70°C<THW<
Determine whether the temperature is 90°C or not. That is, a stable cooling water temperature is determined.

The process proceeds to step 1006 only when all the conditions in steps 1001 to 1005 are satisfied.

In step 1006, it is determined whether the amount of change ΔQ of the intake air amount data Q per time or per crank angle is less than a constant value A, and as a result, if ΔQ≧, step 1006 is performed.
09, the counter C, is cleared, and when ΔQ<A, the counter C, is counted up in step 1007, and C is cleared in step 100B.

>B (constant value), the learning execution flag F is set to "1" in step 101O, and in other cases, the learning execution flag FG is set to "0" in step 1011.
Note that the counter C is guarded at a certain maximum value. The routine then ends at step 1012.

In this way, under the conditions where the air-fuel ratio feedback control by the upstream 0□ sensor 13 and the air-fuel ratio feedback control by the downstream O2 sensor 15 are being performed, the conditions are limited by the cooling water temperature THW, and Only when a stable state in which the amount change ΔQ is smaller than the constant value A continues for a certain period of time, the learning execution flag F is set to "1" and learning control is executed.

FIG. 11 is a detailed flowchart of the learning step 814 of FIG. As mentioned above, this routine is executed when the output signal of the downstream Ot sensor 15 is inverted.
Executed when the learning conditions are met. In addition, in this learning step, as shown in the table below, the learning value is calculated for each region n and the backup l? Store in AMIQ5.

In step 1101, the current rich skip amount R5R
and the previous rich skip IR5RO, that is, R5R←(R2H+RSRO)/2, and in step 1102, the learned value R5RG (n) of the rich skip amount of the current area n is set to the average value m In other words, in step 1103, the learning value R5R is set as
G (n) is stored in the corresponding area of the bank up RAM 106.

In step 1104, R2H is set to RS in preparation for the next execution.
RO, and the routine ends at step 1105.

FIG. 12 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360'cA.

In step 1201, the RAM 105 reads out the intake air amount data Q and rotational speed data Ne, and calculates the basic injection amount TAIIP. For example, TAUP-α・Q/
Ne (α is a constant). RA at step 1202
)1105, read out the cooling water temperature data THW and store it in the ROM.
The warm-up increase value FW is determined by the one-dimensional map stored in 104.
Calculate L by interpolation. As shown in the figure, this warm-up increase value FWL is set to decrease as the current cooling water temperature THW increases. In step 1203, the final injection amount TAU is determined as TAU-TAIIP-FAF ・(FWL+β)+
Calculate by 7. Note that β and γ are correction amounts determined by other operating state parameters, such as a signal from a throttle position sensor (not shown), a signal from an intake air temperature sensor, battery voltage, etc. These are also correction amounts determined by the RAM 105. Next, in step 1204, the injection amount TAU is set in the down counter 108, and the flip-flop 109 is
Set to start fuel injection. This routine then ends in step 1205. As described above, when the time corresponding to 11 TAU of injection has elapsed, the flip-flop 109 is reset by the carrier signal of the down counter 108, and the fuel injection ends.

Note that each vehicle speed region does not need to be divided at equal intervals by a constant value ΔSPD, and may be divided at irregular intervals.

In addition, regions are divided based on other parameters such as intake air amount, intake air pressure, throttle valve opening, rotation speed, intake air amount per rotation (Q/Ne), and amount of reversal period of the output of the upstream 02 sensor. You can.

In addition, areas with low learning frequency may be determined in advance, and
The number of reversals of the output of the downstream Ot sensor in each region may be observed, and a region with a small number of reversals may be set as a region with a low learning frequency.

Furthermore, the first air-fuel ratio feedback control is performed every 4 m.
In addition, the second air-fuel ratio feedback control is performed every 512 m because the air-fuel ratio step feedback control is mainly controlled by the upstream Ot sensor, which has good response, and the control is performed by the downstream Ot sensor, which has poor response. This is to follow.

In addition, other control constants in the air-fuel ratio feedback control by the upstream 0□ sensor, such as delay time, integral constant, and comparison voltage of the upstream Ot sensor (reference: JP-A-55-3
7562) etc. on the downstream side.

The present invention can also be applied to a double 08 sensor system that corrects based on the output of a sensor or a double 08 sensor system that introduces a second air-fuel ratio correction coefficient. Furthermore, the rich deviation and lean deviation of the air-fuel ratio upstream of the catalyst are estimated based on the output frequency of the upstream Ox sensor instead of the downstream Ot sensor, and the air-fuel ratio feedback control constant is made variable in accordance with this deviation amount. The present invention can also be applied to a pseudo double 08 sensor system.

Furthermore, instead of the air flow meter, a Karman vortex sensor, a heat wire sensor, or the like may be used as the intake air amount sensor.

Furthermore, in the above embodiment, the fuel injection amount is calculated according to the intake air amount and the engine rotation speed, but the fuel injection amount is calculated according to the intake air pressure and the engine rotation speed, or the throttle valve opening and the engine rotation speed. The fuel injection amount may also be calculated.

Further, in the above embodiment, an internal combustion engine is shown in which the amount of fuel injected into the intake system is controlled by a fuel injection valve, but the present invention can also be applied to a carburetor type internal combustion engine. For example, an electric air control valve (EACV) is used to control the air-fuel ratio by adjusting the intake air amount of the engine, and an electric bleed air control valve is used to adjust the amount of air bleed from the carburetor to control the main system passage and slow air. The present invention can be applied to devices that control the air-fuel ratio by introducing atmospheric air into system passages, devices that adjust the amount of secondary air sent to the exhaust system of an engine, and the like. In this case, the basic injection ITAIIP in step 1201
A corresponding basic fuel injection amount is determined by the carburetor itself, that is, depending on the intake pipe negative pressure depending on the intake air amount and the rotational speed of the engine, and in step 1203, the supply air corresponding to the final fuel injection amount TAU is determined. The quantity is calculated.

Further, in the above embodiment, an OT sensor is used as the air-fuel ratio sensor, but a CO sensor, a lean mixture sensor, etc. may also be used.

Furthermore, although the embodiments described above are constructed using a microcomputer, that is, a digital circuit, they may also be constructed using an analog circuit.

〔Effect of the invention〕

As explained above, according to the present invention, by adopting learning control that increases the gain of air-fuel ratio feedback control in regions where learning frequency is low, the required level can be learned early, and sufficient learning can be performed in each region. As a result, deterioration in fuel efficiency, drivability, emissions, etc. can be prevented.

[Brief explanation of the drawing]

Figure 1 is an overall block diagram for explaining the present invention in detail, Figure 2 is a single 02 sensor system and a double 08 sensor system.
FIG. 3 is a graph showing the required level of the conventional air-fuel ratio control amount, FIG. 4 is a graph showing the required level of the air-fuel ratio control amount according to the present invention, and FIG. 5 is a graph showing the required level of the air-fuel ratio control amount according to the present invention. Air-fuel ratio of the internal combustion engine according to the present invention! 6, 8, 10, 11, and 12 are flowcharts for explaining the operation of the control circuit in FIG. Figures 7 and 9 are timing diagrams for supplementary explanation of the flowcharts in Figures 6 and 8. 1... Engine body, 3... Air flow meter, 4... Distributor, 5. 6... Crank angle sensor, lO... Control circuit, 12... Catalytic converter, 13... Upstream O2 sensor, 15... Downstream Ot sensor, 17... Idle switch. Ox

Claims (1)

[Scope of Claims] 1. Engine state detection means for detecting a predetermined state of the internal combustion engine; Feedback control condition determining means for determining whether feedback control conditions for the engine are satisfied; Feedback control conditions for the engine feedback control means for feedback controlling an engine state manipulated variable according to a detection result of the engine state detection means so that the engine is in a predetermined state when the above is satisfied; and whether or not a learning condition for the engine is satisfied. a learning condition determination means for determining a learning condition for the engine; and storing a value corresponding to the engine state manipulated variable for each predetermined operating region of the engine when the learning condition for the engine is satisfied; region-specific learning means for setting a value corresponding to the engine state manipulated variable in the region as an initial value of the engine state manipulated variable for each transition in a predetermined operating region of the engine; an air-fuel ratio control device for an internal combustion engine, comprising: feedback gain adjusting means for increasing a feedback control gain of the engine state manipulated variable in a region where the frequency of engine operation is low compared to other regions.