JPS6357843A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To get rid of any mislearning as well as to make accurate learning control attainable, by making a controller so as to perform the learning control at a time when the variation of an air-fuel ratio feedback control constant is less than the specified quantity, in the case of a device installing each air-fuel ratio sensor at both upper and lower streams of a catalytic converter. CONSTITUTION:An air-fuel ratio compensation value is operated according to output of an upstream side sensor A, in respective air-fuel ratio sensors A and B installed each at both upper and lower streams of the catalytic converter installed in an exhaust system, and an air-fuel ratio feedback control constant by an operational device C. And, a variation in the said control constant is operated is smaller than the specified quantity or not is discriminated by a discriminating device F. When the variation is smaller than the specified quantity, the control constant is set down to the constant value so as to have both rich side and lean side variations of the air-fuel ratio compensation value symmetrized, while the learning compensation value is operated so as to make the mean value of the air-fuel ratio compensation value to converge on the specified value at a learning device G. And, an air-fuel ratio is adjusted by an air-fuel ratio adjusting device H according to the air-fuel ratio compensation value and the learning compensation value.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides air-fuel ratio sensors (herein, oxygen concentration sensors (OX sensors)) on the upstream and downstream sides of a catalytic converter.
), and relates to an air-fuel ratio control device for an internal combustion engine that performs air-fuel ratio feedback control using a downstream Ot sensor in addition to air-fuel ratio feedback control using an upstream Ot sensor.

[Prior art] In simple air-fuel ratio feedback control (single Oz sensor system), the 03 sensor that detects the oxygen concentration is installed at a location 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. However, due to variations in the output characteristics of the 0□ sensor, it is difficult to improve the control accuracy of the air-fuel ratio. It takes 02
In order to compensate for variations in sensor output characteristics, variations in components such as fuel injection valves, and changes over time or aging, a second 0□ sensor is provided downstream of the catalytic converter, and the air-fuel ratio feedback is provided by the upstream 0□ sensor. A double 02 sensor system that performs air-fuel ratio feedback control using a downstream Ot sensor in addition to control has already been proposed (
Reference: Japanese Patent Application Laid-Open No. 58-48756). This double 0
In a two-sensor system, the at sensor located downstream of the catalytic converter is connected to the upstream 0. Although it has a lower response speed than a sensor, it has the advantage of less variation in output characteristics for the following reason.

(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 performing air-fuel ratio feedback control (double 02 sensor system) based on the outputs of the two 02 sensors, variations in the output characteristics of the upstream 02 sensor can be absorbed by the downstream 02 sensor. In fact, as shown in Figure 2, in the single 02 sensor system, Ot
If the output characteristics of the sensor deteriorate, it will directly affect the exhaust emission characteristics, whereas double 0. In the sensor system, even if the output characteristics of the upstream 01 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 O sensor maintains stable output characteristics.

Even in the double 0□ sensor system mentioned above, air-fuel ratio correction is necessary due to manufacturing variations in parts such as the air flow meter (or pressure sensor) and fuel injection valve, changes over time or aging, changes in air density (changes in atmospheric pressure), etc. Coefficient FAF
may deviate significantly, and therefore may be close to its upper or lower limit. Note that the upper limit value and lower limit value are provided to prevent the air-fuel ratio correction coefficient FAF from being excessively corrected and becoming too large or too small due to some reason, for example, a failure of the upstream O2 sensor. . For example, during air-fuel ratio feedback control, if a transient state with large air-fuel ratio fluctuations occurs, such as sudden acceleration or deceleration, the air-fuel ratio correction coefficient FAF will stick to its upper or lower limit, and the air-fuel ratio The fluctuation margin of the correction coefficient FAF becomes smaller, and further correction becomes impossible. Therefore, it may become impossible to compensate for transient air-fuel ratio changes. In addition, the air-fuel ratio correction coefficient during air-fuel ratio feedback control and the non-air-fuel ratio feedback control (
When the difference between the air-fuel ratio correction coefficient (constant value) and the air-fuel ratio correction coefficient (constant value) increases, the air-fuel ratio deviation during open-loop becomes large, and moreover, the control air-fuel ratio reaches the required level when switching to air-fuel ratio feedback control from open-loop. It takes time to do this, resulting in insufficient correction. As a result, over-richness causes deterioration in fuel efficiency, HC and Co emissions, etc., as well as over-lean deterioration in drivability, deterioration in NOx emissions, etc.

For this reason, learning control is introduced into the double 0□ sensor system, and thereby the average value of the air-fuel ratio correction coefficient FAF, that is, the average of the air-fuel ratio correction coefficient FAF immediately before skipping (aFA
The applicant of the present application has already proposed that pxv be varied around a predetermined value, for example 1.0 (see Japanese Patent Application No. 16742/1983). Therefore, the air-fuel ratio correction coefficient FA
Since F is always close to the predetermined value (1, 0), there is a large fluctuation margin. Therefore, it is possible to compensate for transient air-fuel ratio changes during air-fuel ratio feedback control, and it is possible to compensate for transient air-fuel ratio changes during air-fuel ratio feedback control and during open loop control. The difference in the air-fuel ratio correction coefficient becomes smaller, and therefore, the air-fuel ratio deviation during open loop becomes smaller, and the controlled air-fuel ratio immediately approaches the required level when switching from open loop to air-fuel ratio feedback control.

[Problem that the invention seeks to solve]

The above learning control is based on the average value FA of the air-fuel ratio correction coefficient FAF.
The learning value F is set so that FAV converges to a predetermined value (1, 0).
G) It calculates IAC, and is originally performed in response to changes in air density (driving at high altitudes). Therefore, in order to prevent the learning control from overcorrecting the learning value FGHAC due to the influence of the evaporator and causing the air-fuel ratio to become overrich or overlean, the learning value FG)IAc also has an upper and lower limit value. It is provided. However, in the double 02 sensor system, the base air-fuel ratio is controlled by varying the amount of deviation of the air-fuel ratio correction coefficient FAF from a predetermined value, for example 1.0, so the average value FAFAV of the air-fuel ratio correction coefficient FAF is , even though there is no change in air density (driving at high altitude), the downstream side is 0. It changes due to air-fuel ratio feedback control by the sensor, and as a result, the learned value FGHAC may be subjected to learning control and become a value close to its upper limit or lower limit.

Therefore, in this case, the fluctuation margin of the learning value FG)IAC becomes small, and further learning control becomes impossible. In other words, in this state, even if there is a change in air density (driving at high altitude), it is impossible to compensate for the change in air density, resulting in problems such as deterioration in fuel efficiency, deterioration in emissions, deterioration in drivability, etc.

Furthermore, in the double 02 sensor system, when air-fuel ratio feedback control 11 is performed by both the upstream and downstream O2 sensors, the air-fuel ratio feedback control constants, such as skip control constants R5R, RSL, are
Due to the air-fuel ratio feedback control by the sensor, it is normally asymmetrical (R5R# R5L).

Therefore, during this period, if the learning correction amount FGHAC is calculated so that the average value FAFAV of the air-fuel ratio correction coefficients FAF immediately before the skip becomes a predetermined value, for example 1.0, the average value FAFAV becomes the air-fuel ratio correction coefficient FAF. There is also the problem that erroneous learning occurs because the average value of , that is, the true air-fuel ratio deviation is not represented.

Therefore, an object of the present invention is to provide a double air-fuel ratio sensor system that is capable of performing sufficient and accurate learning control only when there is a change in air density.

[Means for solving problems]

A means for solving the above problems is shown in FIG. 1A.

As shown in FIG. 1B.

In FIG. 1A, first and second air-fuel ratio sensors for detecting the concentration of specific components in exhaust gas are provided on the upstream side of a catalytic converter for exhaust gas purification, which are provided in the exhaust system of an internal combustion engine;
Each is provided on the downstream side. The air-fuel ratio correction amount calculation means calculates the air-fuel ratio correction amount FAF according to air-fuel ratio feedback control constants such as skip IR5R, R5L and the output V of the upstream (first) air-fuel ratio sensor. The control constant change calculation means calculates the air-fuel ratio feedback control constant R.
The control constant change amount determining means calculates the change amount ΔR5R of the air-fuel ratio feedback control constant R3R.
It is determined whether 3R is smaller than a predetermined amount α. As a result, the amount of change ΔR3 in the air-fuel ratio feedback control constant R3R
When R is smaller than a predetermined amount (ΔR3R<α), the control constant calculation means calculates the air-fuel ratio feedback control constant R3R,
R5L is the rich l of air-fuel ratio correction amount FAF! l! The l change and the lean side change are set to a constant value so that they are symmetrical, and when the change amount ΔR3R of the air-fuel ratio feedback control constant R3R is larger than a predetermined amount, the output v2 of the downstream (second) air-fuel ratio sensor Accordingly, the air-fuel ratio feedback control constant R
Calculate 5R and R5L. Further, only when the change amount ΔR5R of the air-fuel ratio feedback control constant R5R is smaller than the predetermined amount α, the learning means calculates the learning correction amount FGHAC so that the average value FAFAV of the air-fuel ratio correction IFAF converges to the predetermined value 1.0. do. The air-fuel ratio adjustment means adjusts the air-fuel ratio of the engine according to the air-fuel ratio correction amount FAF and the learning correction amount FGHAC.

Further, in FIG. 1B, compared to FIG. 1A, engine load detection means for detecting the engine load, for example, intake air fiQ, and engine load determination means for determining whether the engine load Q is smaller than a predetermined value β. is added. As a result,
Change amount ΔR3R of air-fuel ratio feedback control constant R3R
is smaller than a predetermined amount (ΔR3R<α) and the engine load is smaller than a predetermined value (Q<β), the control constant calculation means sets the air-fuel ratio feedback control constants RSR and RSL to symmetrical constant values, and the other When the amount of change ΔR3R in the fuel ratio feed control constant R3R is larger than a predetermined amount or when the engine load Q is larger than the predetermined value β, the air-fuel ratio is adjusted according to the output v2 of the downstream (second) air-fuel ratio sensor. Calculate feedback control constants R5R and RSL. Furthermore, the amount of change ΔR3 of the air-fuel ratio feedback control constant R3R
Only when R is smaller than the predetermined amount α and the engine load Q is smaller than the predetermined value β, the learning means adjusts the learning correction amount FGIIAC so that the average value FAFAV of the air-fuel ratio correction amount FAF converges to the predetermined value 1.0. calculate.

[For production]

According to the configuration of FIG. 1A described above, only when the amount of change ΔR3R of the air-fuel ratio feedback control constant R3R is smaller than the predetermined amount α, according to the configuration of FIG. 1B, the engine load Q is further reduced.
Learning control is performed only when the downstream air-fuel ratio sensor is smaller than the predetermined value β, that is, only when the air-fuel ratio feedback control by the downstream air-fuel ratio sensor is sufficiently stable.

The air-fuel ratio feedback control by the sensor is stopped, that is, the air-fuel ratio feedback control constants R5R, ll5L
.

is a constant value and symmetrical (for example, RSR=RSL=5~
1%), so there is no false learning.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 3 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. 3, 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 axis generates a reference position detection pulse signal every 720° 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 which generates a signal. The pulse signals of these crank angle sensors 5.6 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 1.
03 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 port 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 corresponding 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, No. 1, in the exhaust gas.

The exhaust manifold 11 includes a catalytic converter 1.
A first 02 sensor 13 is provided on the upstream side of the catalytic converter 12, and a second 02 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, the control circuit 10 outputs different output voltages depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.
This occurs in the D converter 101.

The control circuit 10 is configured as a microcomputer, for example, and includes a ROM 104, an R
AM 105, Backup I? Al'l 106
, 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 rear guard routine, 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
is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts the clock signal (not shown) and finally its carrier terminal becomes "L" level, the flip-flop 109 is set and the drive circuit 110 controls the fuel injection valve 7. Stop biasing. In other words, the above fuel injection amount TA
The fuel injection valve 7 is energized by U, and therefore the fuel injection amount T
An amount of fuel corresponding to the AU is sent to the combustion chamber of the engine body 1.

Note that the interrupt generation of the CPU 103 is caused by the A/D converter 1.
When the A/D conversion of 01 is completed, the input/output interface 10
2 receives a pulse signal from the crank angle sensor 6, 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. In other words, data Q in RAM 105
and THW are updated at predetermined intervals. Further, the rotational speed data Ne is calculated by an interrupt of the crank angle sensor 6 every 30° C.A, and is stored in a predetermined area of the RAM 105.

FIG. 4 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 02 sensor 13, and is executed every predetermined period of time, for example, every 4 m.

In step 401, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the upstream 0□ sensor 13 is satisfied. For example, when the cooling water temperature is below a predetermined value, when the engine is starting, when increasing the amount after starting, during warm-up increasing, when increasing the power, when the output signal of the upstream 0□ sensor 13 has never been reversed, when the fuel is cut, etc. The closed-loop condition is not satisfied in all cases, and the closed-loop condition is satisfied in all other cases.

If the closed loop condition is not satisfied, the process proceeds to step 429 and the air-fuel ratio correction coefficient FAF is set to 1.0. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 402.

In step 402, the upstream side O, the output Vl of the sensor 13
In step 403, it is determined whether ■1 is less than or equal to the comparison voltage V□, for example, 0.45V.
That is, it is determined whether the air-fuel ratio is rich or lean. In other words, if the air-fuel ratio is rich or lean (V + ≦V□), the first delay counter CDLY is determined in step 404.
It is determined whether I is positive or not, and if CDLYI>O, CDLYI is set to 0 in Stellar P405 and the process proceeds to step 406. In steps 407 and 408, the first delay counter CDLYI is guarded at the minimum value TDLI. Similarly, in this case, the first delay counter CDLYI is equal to the minimum value TDL.
When reaching I, the first air-fuel ratio flag F1 is set to "0" (lean) in step 409. Note that the minimum value TDLL is a lean delay time for maintaining the determination that the rich state is present even if the output of the upstream Ot sensor 13 changes from rich to lean, and is defined as a negative value. Ru. On the other hand, if it is rich (V+ > V*+), the first delay counter CDLY is set in step 410.
It is determined whether I is negative or not, and if CDLYI < 0, CDLYI is set to 0 in step 411, and step 412
Proceed to.

In steps 413 and 414, the first delay counter CDLYI is guarded at the maximum value TDRI, and in this case, when the first delay counter CDLYI reaches the maximum value TDPI, the first air-fuel ratio flag F1 is set to " 1” (rich). In addition, the maximum value TDP
I is 0 on the upstream side. This is a rich delay time for maintaining the determination that the lean state is present even if the output of the sensor 13 changes from lean to rich, and is defined as a positive value.

In step 416, the first delay counter CDLY
It is determined whether the sign of I has been reversed, that is, it is determined whether the air-fuel ratio after the delay processing has been reversed. If the air-fuel ratio is reversed, in step 417, it is determined based on the learning control execution flag F whether the learning conditions are satisfied. As a result, when Gaku21 conditions are met (FG
= "1") Proceed to step 418 and perform learning control.

Note that learning conditions and learning control will be described later.

Next, in step 419, the first air-fuel ratio flag F1
The value of determines whether the reversal is from rich to lean or from lean to rich. If it is a reversal from rich to lean, in step 420 FAF 4-FAF+
R3R is increased in a skip manner, and conversely, if it is a reversal from lean to rich, FAF←FA is increased in step 421.
Decrease in skips with F-R3L. In other words, skip processing is performed.

If the sign of the first air-fuel ratio flag Fl is not inverted in step 416, integration processing is performed in steps 422, 423, and 424. That is, in step 422, F1
= “O” or not, and if F1 = “O” (lean), set FAF-FAF+KI in step 423,
On the other hand, if F1="1" (rich), step 42
4 as FAF-FAF-K I. Here, the integral constant Kl is the skip constant R3R.

It is set sufficiently small compared to R3L, that is, KT
<R3R (R3L). Therefore, step 423 is a lean/! 3 (F1="O"), the fuel injection amount is gradually increased, and step 424 is a rich state (F1="1").
) to gradually reduce the fuel injection amount.

The air-fuel ratio correction coefficient FAF calculated in steps 420, 421, 423, and 424 is guarded at a minimum value of, for example, 0.8 in steps 425 and 426, and is guarded at a maximum value of, for example, 1.2 in steps 427 and 428. will be guarded. As a result, if the air-fuel ratio correction coefficient FAF becomes too large or too small for some reason, the air-fuel ratio of the engine is controlled using that value to prevent overrich.
Prevent over lean.

The FAF calculated as described above is stored in the RAM 105, and the routine ends at step 430.

FIG. 5 is a detailed flowchart of the learning control step 418 in FIG. = “1”), and is executed every time the air-fuel ratio correction coefficient FAF is skipped.

That is, in step 501, the air-fuel ratio correction coefficient FAF
(7) Average value FAFAV, FAFAV ← (FAF + FAFO) / However, F
The AFO is calculated based on the FAF value immediately before the previous skip, and in step 502, the FAF is set as FAFO4-FAF in preparation for the next calculation. Next, in step 503, AFAF - FAFAV -1,0 is calculated.

Next, in step 504, it is determined whether AFAF>0 or not. As a result, if AFAF>0, the learning correction amount FGHAC is set as FGHAC←, FGHAC in step 505.
+ΔFGHAC, step 506,5
07, the guard is set to the maximum value, for example, 1.05. On the other hand, if ΔFAF≦0, the learning correction I
FGHAc, FGIIAC←FGHAC−ΔFGHA
C, and in steps 509 and 510, it is guarded at a minimum value, for example, 0.90. In addition, 1ΔFAF
FGHAC may be updated only when 1>K (positive value). In this way, according to the learning control, the learning correction amount F is adjusted such that the air-fuel ratio correction coefficient FAF converges to 1.0.
GHAC is increased or decreased.

As will be described later, when the learning control routine shown in FIG. 5 is executed, the second air-fuel ratio feedback control shown in FIG. 7, which will be described later, is not performed.

FIG. 6 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. 4. When the air-fuel ratio signal A/F for rich/lean discrimination is obtained from the output of the upstream Ot sensor 13 as shown in FIG. 6(A), the first delay counter CDLYI is set as shown in FIG. 6(B). , is counted up in the rich state and counted down in the lean state. As a result, as shown in FIG. 6(C), a delayed air-fuel ratio signal A/F' (corresponding to flag F1) is formed. For example, even if the air-fuel ratio signal A/F changes from lean to rich at time t, the delayed air-fuel ratio signal A/Fl' is maintained lean for the rich delay time TDRI, and then at time t2. Changes to rich. Time t
Even if the air-fuel ratio signal A/F changes from rich to lean at , the delayed air-fuel ratio signal A/F' is held rich for an amount equivalent to the lean delay time (-TDLL), and then at time t4. Change to lean. However, the air-fuel ratio signal A/
F is at time t5, t4. Rich delay time T as shown in t7
If it is inverted in a period shorter than DRI, it takes time for the first delay counter CDLYI to reach the maximum value TDPI, and as a result, the air-fuel ratio signal A/F' after the delay process is inverted at time t. Ru. 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. 6(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 02 sensor 15 will be explained. As the second air-fuel ratio feedback control, the skip amount RSI? as the first air-fuel ratio feedback control constant? , RSL, IR for the integral constant, and KIL delay time TDRI.

There is a system in which the comparison voltage V□ of the TDLI or the output ■1 of the upstream 02 sensor 13 is made variable, and a system in which a second air-fuel ratio correction coefficient FAF2 is introduced.

For example, if the rich step amount R3R is increased, the controlled air-fuel ratio can be shifted to the rich side, and even if the lean skip 1R3L is decreased, the controlled air-fuel ratio can be shifted to the rich side.On the other hand, if the lean skip 11R3L 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 amount R3R and the lean skip amount R3L 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
On the other hand, increasing the lean integral constant KIL allows the controlled air-fuel ratio to be shifted to the lean side, and even if the rich integral constant KIR is decreased, the controlled air-fuel ratio cannot be shifted to the rich side. You can move 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 0□ sensor 15. By setting rich delay time TDRI > lean delay time (-TDLI), the control air-fuel ratio can be shifted to the rich side; conversely, by setting lean delay time (-TDLI)
LI) > rich delay time (TDRI),
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 TDRI and TDLI according to the output of the downstream 0□ sensor 15. Furthermore, if the comparison voltage V□ is increased, the control air-fuel ratio can be shifted to the rich side, and the comparison voltage VR
By reducing I, the control air-fuel ratio can be shifted to the lean side.

Therefore, by correcting the comparison voltage V□ according to the output of the downstream 02 sensor 15, the air-fuel ratio can be controlled.

A double 0□ sensor system in which the skip amount as an air-fuel ratio feedback control constant is made variable will be described with reference to FIG.

FIG. 7 shows a second air-fuel ratio feedback control routine that calculates skip 1lRsR and RSL based on the output of the downstream 0□ sensor 15 for a predetermined period of time, for example, 1.
executed every time. In step 701, it is determined whether the downstream side 02 sensor 15 is in a closed loop condition. For example, when the cooling water temperature is below a predetermined value and the output signal of the downstream Ot sensor 15 never inverts, the downstream Ot sensor 15
is out of order, during transient operation, on-idle (LL
="1"), etc., the closed loop condition is not satisfied.
In other cases, the closed loop condition is met. If it is not a closed loop condition, step 736. The process proceeds to step 737, where the skip amounts RSR and RSL are set to a constant value, for example, 5%. In other words,
Symmetrical skip control is performed. In this case, the other air-fuel ratio feedback control constant KIR.

KIL: If TDR and TDL are also symmetrical, the air-fuel ratio correction coefficient FAF will be symmetrically controlled by the routine shown in FIG.

If it is a closed loop, proceed to step 702, and the downstream side 02
The output V2 of the sensor 15 is A/D converted and taken in, and in step 703 it is determined whether or not v2 is less than the comparison voltage v0, for example, 0.55V, that is, it is determined whether the air-fuel ratio is rich or lean. Note that the comparison voltage Vllll is set higher than the comparison voltage VRI of the output of the upstream 0□ sensor 13, taking into account that the output characteristics differ due to the influence of raw gas and the deterioration rate differs between upstream and downstream of the catalytic converter 14. be done.

Note that steps 703 to 715 are steps 40 in FIG.
Corresponds to 3 to 415. Therefore, the comparison result at step 703 is delayed by the delay times TDR2 and TDL2, and the second air-fuel ratio flag F2 is set.

Step 716~? 20 is a routine for determining learning conditions. That is, in step 716, RA
Read the intake air amount data Q from M105, and calculate Q β(
(constant value). If Q≧β, step 7
Proceed to step 17, set the learning execution love F to 0, and perform step 7.
Proceed to steps 21-732. In other words, no learning control is performed. This is because if learning control is performed when the intake air fiQ is large, there is a possibility that the learning value FC)IAc will be over-corrected due to the influence of the evaporator. On the other hand, if Q is β, the learning condition is determined in steps 718 and 719 according to the change in rich skip ff1 (in this case, RSR).

In other words, it is determined in step 718 whether or not the second air-fuel ratio flag F2 has been inverted, and only when the second air-fuel ratio flag F2 has been inverted, the learning condition is determined in step 719, and if it has not been inverted, learning is executed. Flag F.

is not changed. Note that the learning condition determination in step 719 will be described later. Then, in step 720, it is determined whether the love Fe to be learned is "1" or not; as a result, F6
If = "1", proceed to steps 736-737 and skip fiR3R, set RSL to a constant value of 5%, FG = "0"
If so, proceed to steps 721-736.

In step 721, it is determined whether or not the second air-fuel ratio flag F2 is "0". As a result, if F2 - "0" (lean), the process proceeds to steps 722 to 727;
l'' (rich), the process proceeds to steps 728-732.

In step 722, RSR,4-RSR50ΔRS
(−a constant value, for example, 0.08%), that is, the rich skip 1RSR during air-fuel ratio feedback is increased to shift the air-fuel ratio to the rich side. Step 724°7
In No. 25, RSR is guarded at a maximum value MAX, for example, 6.2%. Furthermore, in step 725, RSL←R
3L - ΔRS, that is, the rich skip amount R3L during air-fuel ratio feedback! to shift the air-fuel ratio to the rich side. In steps 726 and 727, the RS
Guard L at a minimum value MIN, for example 2.5%.

On the other hand, when rich (F2-“1”), step 7
At step 28, RSR,←RSRI-ΔRS is set, that is, the rich skip amount R3Rf during air-fuel ratio feedback is decreased to shift the air-fuel ratio to the lean side. Step 73
0. At 731, RSR is guarded at the minimum value MIN. Furthermore, in step 731, R3L is set to RSL (a constant value), that is, the lean skip amount R3L during air-fuel ratio feedback is increased to shift the air-fuel ratio to the lean side. In steps 732 and 733, RSL is guarded at the maximum value MAX.

Step 734. RSRth-RSR4 at 135,
After setting RSL←R5L and storing RSR and RSL in the RAM 105, this routine ends in step 735.

Note that FAF calculated during air-fuel ratio feedback,
RSR, , RSL, - once other values FAF', R
Convert to SR'R5R' and backup RAM 106
This also helps improve drivability during restarts, etc. The minimum value MIN in FIG. 7 is a value at which transient followability is not impaired, and the maximum value MIN is a value at a level at which drivability does not deteriorate due to air-fuel ratio fluctuations.

In this way, only when the intake air i1Q is small (Q<β) and the change in the air-fuel ratio feedback control constant, for example, RSR, is small, the learning execution flag F6 is set to "1" and the learning control is executed. Step 736.73
Skip fiR5R due to 7.

RSL is set to a constant value, for example, 5% (RSR=RSL), and therefore, in this case, the first air-fuel ratio feedback control by the upstream Ot sensor 13 is based on the air-fuel ratio correction coefficient FAF.
will be symmetrically controlled.

FIG. 8 is a detailed flowchart of the learning condition determination step 719 of FIG. 7, which is executed every time the output signal of the delayed downstream O2 sensor 15 is inverted, as described above.

In step 801, the average value R3RAV of the rich skip amount R3R is calculated as RSRAV ←(RSR+R5RO/
SRO is the value of R8R immediately before the reversal of the delay counter CDIJ2 of the previous cylinder 2.
At 02, the average value RSRAV is rounded directly RSRAVX
Calculate /N by . In step 803, the smoothed value RS
The counter CR3RAV for calculating the amount of change in RAVX is incremented by 1, and in step 804 it is determined whether the counter CR3RAV has reached the predetermined value C0, that is, the downstream side 02 sensor 15
It is determined whether the number of inversions of the output signal becomes 00 or not. If CR3RAV > Co, proceed to step 805; if CRSAFAV ≦co, proceed to step 8
Jump to 12.

In step 805, the amount of change in the smoothed value RSRAVX,
In other words, the air-fuel ratio change amount ΔRSRAVX is
X ←I R5RAVX-R5RAVXO+However, R
5RAVXO is the number of reversals before C0 (7) R3RAVX17
) value, and in step 806, the air-fuel ratio change amount ΔR5
It is determined whether RAVX is larger than a predetermined amount α.

As a result, if ΔR5RAνX>α, step 80
7, the learning control execution flag F6 is set to “0”, and on the other hand, Δ
If RSRAVX≦α, the process advances to step 808, and it is determined whether other learning conditions are satisfied.

Other learning conditions include, for example, that the cooling water temperature THE is 70° C.<THW<90° C. under the air-fuel ratio feedback control (step 401) by the upstream 02 sensor 13. If even one of these other learning conditions is not satisfied, the learning control execution flag F is also set in step 807.
c is set to "0", and the learning control execution flag Fc is set at step 809 only when all learning conditions are satisfied.
”. In step 810, the counter CR5RAV
is cleared, and in step 811 R5RAVX is set to R5R.
As AVXO, in preparation for the next execution, RSR is set to RSRO in step 812, and this routine ends in step 813.

In addition, in the routine of FIG. 8, rich skip IR3R
Instead of the amount of change in lean skip amount RSL, the amount of change in lean skip amount RSL may be used.

In other words, the routine shown in FIG. 8 prohibits the learning control and controls the air-fuel ratio feedback by the downstream 02 sensor 15 when the skip amount change amount is large and the air-fuel ratio feedback control by the downstream 02 sensor 15 is unstable. When the amount of change in the skip amount that is stable is small, learning control is performed together with air-fuel ratio feedback control by the downstream 0□ sensor 15.

FIG. 9 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360°C. Step 901
Then, the intake air amount data Q and the rotational speed data Ne are read out from the RAM 105 to calculate the basic injection amount TALIP. For example, assume that TAUP=K Q/N e (K is a constant). In step 902, the cooling water temperature data THW is read from the RAM 105, and a warm-up increase value FWL is calculated by interpolation using the one-dimensional map stored in the ROM 104. In step 903, the final injection amount TAU is calculated as TAtl-TAUP・(FAF+FGHAC)・(
Calculate by FWL+α)+β. Note that α and β are correction amounts determined by other operating state parameters. Next, in step 904, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. And step 9
This routine ends at 05.

As described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the carrier signal of the down counter 108, and the fuel injection ends.

FIG. 10 is a timing diagram for supplementary explanation of the flowcharts of FIGS. 4, 5, 7, 8, and 9. As shown in Figure 10 (A), intake air -1lQ
changes as shown in FIG. 10 (rich skip amount R3
When R changes, time t, xjz, time t, ~
At t6, as shown in FIG. 10(C), the learning value FGHAC is updated by learning control, but at that time, the downstream O
The air-fuel ratio feedback control by the t sensor 15 is discontinued, and the rich skip 11R3R and lean skip 1
lR3L is set to the same constant value as shown in FIG. 10(B). On the other hand, at times t to t4, the intake air i1Q is small (Q<β), but the change ΔR3 in the skip amount R5R
Since R is large, learning control is prohibited, and air-fuel ratio feedback control by the downstream 02 sensor 15 is performed.

In the learning control shown in Fig. 5, the arithmetic average of the air-fuel ratio correction coefficients FAF immediately before the skip is calculated as the average value FAFAV, but the integral amount of the air-fuel ratio correction coefficients FAF is calculated as the average value (+!!FAFAV). In other words, in this case, as shown in FIG. 11, the positive integral amount SP (or its rounded value) and the negative integral amount S8
(or its rounded value) is updated so that the learned value FGHAC becomes equal to the learned value FGHAC. Thereby, even if the air-fuel ratio correction coefficient FAF changes asymmetrically, an accurate learning correction amount FGIIAc can be obtained.

Further, for the load detection in step 717 in FIG. 7, other operating state parameters such as intake air pressure, throttle valve opening, and engine rotational speed can also be used.

In addition, the first air-fuel ratio feedback control is performed every 4 ms.
In addition, the second air-fuel ratio feedback control is performed for each IS because the air-fuel ratio feedback control is mainly performed by the upstream 0□ sensor, which has good responsiveness, and is controlled by the downstream 0□ sensor, which has poor responsiveness. This is to perform control accordingly.

In addition, the double 0 that corrects other control constants in the air-fuel ratio feedback control by the upstream 0□ sensor, such as delay time, integral constant, etc., by the output of the downstream 0□ sensor
□The present invention can be applied to a sensor system as well as a double 02 sensor system that introduces a second air-fuel ratio correction coefficient. Furthermore, controllability can be improved by simultaneously controlling two of the skip amount, delay time, and integral constant.

Furthermore, it is also possible to fix one of the skip l RSR and RSL and make only the other variable.
, TDLI is often fixed and only the other variable, or one of the rich integral constant KIR and the lean integral constant KIL is fixed and the other variable.

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 by

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) adjusts the intake air amount of the engine to control the air-fuel ratio, and an electric bleed air control valve adjusts the amount of air bleed from the carburetor to control the main system passage and The present invention can be applied to devices that control the air-fuel ratio by introducing atmospheric air into the slow system passage, devices that adjust the amount of secondary air sent to the exhaust system of an engine, and the like. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 801 is determined by the capretor itself,
That is, it is determined according to the intake pipe negative pressure corresponding to the intake air amount and the rotational speed of the engine, and the supplied air amount corresponding to the final fuel injection IITAU is calculated in step 803.

Further, in the above-described embodiment, the 02 sensor was 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.

The present invention can also be applied to systems that control the air-fuel ratio by introducing atmospheric air into the slow system passage, systems that adjust the amount of secondary air sent to the exhaust system of an engine, etc. In this case,
The basic fuel injection amount corresponding to the basic injection 1TAtlo in step 901 is determined by the carburetor itself, that is, it is determined according to the intake pipe negative pressure depending on the intake air amount and the engine rotation speed, and the final fuel injection amount is determined in step 903. A supply air amount corresponding to TAU is calculated.

Furthermore, in the above embodiment, the 02 sensor was used as the air-fuel ratio sensor, but a CO sensor, 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, learning control is prohibited when the load is large or when the air-fuel ratio feedback control by the downstream air-fuel ratio sensor is unstable. Feedback control can be performed preferentially, and since the air-fuel ratio feedback control constant is symmetrically fixed when updating the learning value, it is possible to sufficiently compensate for changes in air density. It is possible to prevent deterioration of fuel efficiency, deterioration of emissions, deterioration of drivability, etc.

Rock diagram, Figure 2 is single 0! sensor system and double O,
Fig. 3 is an overall schematic diagram showing an embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention; Fig. 4, Fig. 5, Fig. 7, Fig. 8; , FIG. 9 is a flow chart for explaining the operation of the control circuit in FIG. 3, FIG. 6 is a timing diagram for supplementary explanation of the flow chart in FIG. 4, FIG. 10 is a flow chart for explaining the operation of the control circuit in FIG. A timing diagram for supplementary explanation of the flowcharts of FIGS. 7, 8, and 9, and FIG. 11 is a timing diagram for explaining a modification of FIG. 5.

1... Engine body, 3... Air flow meter,
4... Distributor, 5.6... Crank angle sensor, 10... Control circuit, 12... Catalytic converter, 13... Upstream side (first) 02 sensor, 15...
Downstream side (second) 0□ sensor.

Claims (1)

[Scope of Claims] 1. A first catalytic converter installed on the upstream side and downstream side of a catalytic converter for purifying exhaust gas provided in the exhaust system of an internal combustion engine, and configured to detect the concentration of a specific component in the exhaust gas. a second air-fuel ratio sensor; an air-fuel ratio correction amount calculating means for calculating an air-fuel ratio correction amount according to the output of the first air-fuel ratio sensor and an air-fuel ratio feedback control constant; and an amount of change in the air-fuel ratio feedback control constant. control constant change amount calculating means for calculating the amount of change in the air-fuel ratio feedback control constant; control constant change amount determining means for determining whether the amount of change in the air-fuel ratio feedback control constant is smaller than a predetermined amount; When the air-fuel ratio feedback control constant is smaller than a predetermined amount, the air-fuel ratio feedback control constant is set to a constant value so that a rich side change and a lean side change of the air-fuel ratio correction amount are symmetrical, and the amount of change in the air-fuel ratio feedback control constant is set to the predetermined value. control constant calculation means for calculating the air-fuel ratio feedback control constant according to the output of the second air-fuel ratio sensor when the output of the second air-fuel ratio sensor is greater than the predetermined amount; learning means for calculating a learning correction amount so that the average value of the air-fuel ratio correction amount converges to the predetermined value; and an air-fuel ratio adjustment for adjusting the air-fuel ratio of the engine according to the air-fuel ratio correction amount and the learning correction amount. An air-fuel ratio control device for an internal combustion engine, comprising: means. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the average value of the air-fuel ratio correction amount is an arithmetic average value immediately before reversal of the air-fuel ratio correction amount. 3. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the average value of the air-fuel ratio correction amount is an integral amount of the air-fuel ratio correction amount. 4. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio feedback control constant is a skip control constant. 5. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio feedback control constant is an integral control constant. 6. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio feedback control constant is a delay time. 7. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio feedback control constant is a comparison voltage of the output of the first air-fuel ratio sensor. 8. First and second air-fuel ratio sensors that are installed on the upstream and downstream sides of a catalytic converter for purifying exhaust gas in the exhaust system of an internal combustion engine, respectively, and detect the concentration of a specific component in the exhaust gas. and an air-fuel ratio correction amount calculation means for calculating an air-fuel ratio correction amount according to the output of the first air-fuel ratio sensor and an air-fuel ratio feedback control constant, and a control constant change for calculating the amount of change in the air-fuel ratio feedback control constant. control constant change amount determining means for determining whether the amount of change in the air-fuel ratio feedback control constant is smaller than a predetermined amount; engine load detecting means for detecting the load on the engine; is smaller than a predetermined value; and when the amount of change in the air-fuel ratio feedback control constant is smaller than the predetermined amount and the load of the engine is smaller than the predetermined value, the air-fuel ratio feedback control is performed. The constant is set to a symmetrical constant value, and when the amount of change in the air-fuel ratio feedback control constant is larger than the predetermined value or when the load of the engine is larger than the predetermined value, the control is performed according to the output of the second air-fuel ratio sensor. control constant calculating means for calculating an air-fuel ratio feedback control constant; and averaging the air-fuel ratio correction amount only when the amount of change in the air-fuel ratio feedback control constant is smaller than the predetermined amount and the load of the engine is smaller than the predetermined value. A learning means for calculating a learning correction amount so that the value converges to the predetermined value; and an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the air-fuel ratio correction amount and the learning correction amount. Air-fuel ratio control device for internal combustion engines. 9. The air-fuel ratio control device for an internal combustion engine according to claim 8, wherein the average value of the air-fuel ratio correction amount is an arithmetic average value immediately before reversal of the air-fuel ratio correction amount. 10. The air-fuel ratio control device for an internal combustion engine according to claim 8, wherein the average value of the air-fuel ratio correction amount is an integral amount of the air-fuel ratio correction amount. 11. The air-fuel ratio control device for an internal combustion engine according to claim 8, wherein the air-fuel ratio feedback control constant is a skip control constant. 12. The air-fuel ratio control device for an internal combustion engine according to claim 8, wherein the air-fuel ratio feedback control constant is an integral control constant. 13. The air-fuel ratio control device for an internal combustion engine according to claim 8, wherein the air-fuel ratio feedback control constant is a delay time. 14. Claim 8, wherein the air-fuel ratio feedback control constant is a comparison voltage of the first air-fuel ratio sensor output.
The air-fuel ratio control device for an internal combustion engine according to item 1.