JPS63295831A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent drivability and emission from deteriorating, by providing a downstream side air-fuel ratio sensor, which detects air-fuel ratio of an internal combustion engine, and a correcting means which stops correction of an air-fuel ratio feedback control constant in the specific time. CONSTITUTION:An internal combustion engine provides in its exhaust passage a ternary catalyst CCRO, and a downstream side air-fuel ratio sensor, which detects air-fuel ratio of the engine, is provided in the exhaust passage in the downstream side of the ternary catalyst CCRO. A discriminating means discriminates the duration time CNT for whether or not it exceeds the predetermined time (n). In the point of the duration time exceeding the predetermined time, an air-fuel ratio control amount FAF is increased or decreased by the predetermined amount in a reverse direction to the direction the control amount is increased or decreased during the duration time. In this way, emission can be prevented from deteriorating by preventing an air-fuel ratio overcorrected condition before its occurrence.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides air-fuel ratio sensors (herein, oxygen concentration sensors (Oz sensors)) on the upstream and downstream sides of a catalytic converter.
The present invention relates to an air-fuel ratio control device for an internal combustion engine that performs air-fuel ratio feedback control using a downstream 02 sensor in addition to air-fuel ratio feedback control using an upstream 0□ sensor.

[Conventional technology]

In simple air-fuel ratio feedback control (single 0□ sensor system), the 02 sensor that detects oxygen concentration is installed in the exhaust system as close to the combustion chamber as possible, that is, in the gathering part of the exhaust manifold upstream of the catalytic converter. Due to variations in the output characteristics of the 0□ sensor, it is difficult to improve the accuracy of controlling the air-fuel ratio. It takes Ot
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 O2 sensor is provided downstream of the catalytic converter, and air-fuel ratio feedback control by the upstream Ot sensor is performed. In addition, a double 02 sensor system that performs air-fuel ratio feedback control using a downstream O2 sensor has already been proposed (
Reference: JP-A-58-48756, JP-A-61-2
34241, etc.), to be more specific, it is proportional to the output of the upstream air-fuel ratio sensor.

Calculate the air-fuel ratio feedback amount using integral control etc.
In addition, the average air-fuel ratio is corrected by changing the air-fuel ratio feedback control constants used when calculating this air-fuel ratio feedback amount, such as the skip amount, integral constant, delay time, comparison voltage, etc., by the output of the downstream air-fuel ratio sensor. There is. In this double 02 sensor system, although 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, it has the advantage of less variation in output characteristics for the following reasons. have.

(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 0□ 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 0□ sensor system) based on the outputs of the two 0□ sensors, variations in the output characteristics of the upstream 02 sensor can be absorbed by the downstream 0□ sensor. In fact, as shown in Figure 2, in a single 0□ sensor system, 0□
If the output characteristics of the sensor deteriorate, it will directly affect the exhaust emission/notion characteristics, whereas in the double 0□ sensor system, even if the output characteristics of the upstream 0□ sensor deteriorate, the exhaust emission characteristics will deteriorate. do not. In other words, in the double 02 sensor system, as long as the downstream 0□ sensor maintains stable output characteristics, good exhaust emissions are guaranteed.

Also, in the single 02 sensor system mentioned above,
By providing the 02 sensor downstream of the catalyst, the above (
A system that takes advantage of the advantages of 1), (2), and (3) has also been proposed (Japanese Unexamined Patent Publication No. 135243/1983).

[Problem that the invention seeks to solve]

However, the above-mentioned 20□ sensor system or the single 0□ sensor system in which the Ot sensor is arranged downstream of the catalyst has the following problems. In other words, in general, a three-way catalyst takes in 0□ when the air-fuel ratio is lean, and when the air-fuel ratio becomes rich, it takes in Co and HC and causes them to react with the 0□ taken in when the air-fuel ratio is lean. 02 storage effect, even if the gas flowing into the three-way catalyst changes from a lean air-fuel ratio to a rich air-fuel ratio, the gas flowing out from the three-way catalyst does not immediately change to a rich air-fuel ratio. At the time when the downstream air-fuel ratio sensor detects a rich air-fuel ratio, the air-fuel ratio adjustment amount (for example, the amount of fuel amount correction) is largely shifted toward the rich side due to the control up to that point.

In addition, a three-way catalyst with sufficient functionality tends to cause a considerable delay in changing the air-fuel ratio in the opposite direction, and therefore, such an overcorrection state may occur after 41! If this continues, emissions will deteriorate.

Therefore, an object of the present invention is to prevent such an air-fuel ratio overcorrection state and perform air-fuel ratio control that does not cause deterioration of emissions.

[Means for solving problems]

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

As shown in FIG. 1B.

FIG. 1A shows a dual air/fuel ratio sensor system.

That is, a three-way catalyst C installed in the exhaust passage of an internal combustion engine
An upstream air-fuel ratio sensor is provided in the exhaust passage upstream of C*o to detect the air-fuel ratio of the engine, and a three-way catalyst CC
A downstream air-fuel ratio sensor that detects the air-fuel ratio of the engine is provided in the exhaust passage downstream of *o. The comparison means compares the output Vt of the downstream air-fuel ratio sensor with a predetermined value v0. Depending on the comparison result of the comparison means, the control constant calculation means calculates an air-fuel ratio feedback control constant such as the skip amount RSR,
Gradually increase or decrease R3L. On the other hand, the duration measuring means measures the duration CNT of the comparison result after the comparison result of the comparison means is reversed, and the determining means determines whether the duration CNT exceeds a predetermined period of time. As a result, when the determining means determines that the duration exceeds a predetermined time (CNT>n), the correction means increases or decreases the air-fuel ratio feedback control constants RSR and R3L during the duration. To greatly increase or decrease in the opposite direction. The feedback amount calculation means calculates the output V of the upstream air-fuel ratio sensor using the air-fuel ratio feedback control constant obtained by the control constant calculation means and the correction means.

The air-fuel ratio adjustment means calculates an air-fuel ratio feedback amount according to the air-fuel ratio feedback amount, and adjusts the air-fuel ratio of the engine based on the air-fuel ratio feedback amount.

FIG. 1B shows a single air/fuel ratio sensor system. That is, three-way catalyst CCI. A downstream air-fuel ratio sensor is provided in the exhaust passage on the downstream side of the engine to detect the air-fuel ratio of the engine. The comparison means compares the output v2 of the downstream air-fuel ratio sensor with a predetermined value vR1. The control amount calculation means increases or decreases the air-fuel ratio control amount FAF in accordance with the comparison result of the comparison means. On the other hand, the duration measuring means measures the duration CNT of the comparison result after the comparison result of the comparison means is reversed, and the determining means determines whether or not the duration CNT exceeds the predetermined time tag. When the determination means determines that the duration exceeds a predetermined time (CNT>n), the air-fuel ratio control amount FAF is changed by a predetermined amount in the opposite direction to the direction in which it was increased or decreased during the duration. increase or decrease.

The air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine based on the air-fuel ratio control amount FAF.

- [Operation] According to the above-described means, when the rich/lean reversal period of the output of the downstream side air-fuel ratio sensor becomes large, the air-fuel ratio feedback control constant or the air-fuel ratio control amount is temporarily reversely corrected.

〔Example〕

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 %ffi, has a built-in potentiometer, and generates an analog voltage output signal proportional to the amount of intake air. This output signal is output from the multiplexer built-in A/D of the control circuit 10.
It is supplied to converter 101. distributor 4
For example, the crank angle sensor 5 generates a reference position detection pulse signal every 720 degrees in terms of crank angle, and the crank angle sensor 5 generates a reference position detection pulse signal every 30 degrees in terms of crank angle. A crank angle sensor 6 is provided. 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 CPI
It is supplied to the interrupt terminal of J103.

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 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 the three toxic components HC, Co, and NOx 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 o2 sensors 13 and 15 generate electrical signals according 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 an A/D converter 1
01, input/output interface 102, CPU 10
In addition to 3, 120M 104, RAM 105, backup RAM 106, 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, when the down counter 108 counts the clock signal (not shown) and finally its carrier terminal becomes "1" level, the flip-flop 109 is turned on 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. That is, data Q and THW in RAM 105 are updated at predetermined intervals. Further, the rotational speed data Ne is calculated by the interruption of the crank angle sensor 6 every 30° CA, 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 0□ sensor 13, and is executed every predetermined period of time, for example, 4 ms.

In step 401, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the upstream 02 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 427 and the air-fuel ratio correction coefficient FAF is set to 1.0. In addition, F.A.
F may be a value immediately before the end of closed loop control.

In this case, proceed directly to step 428. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 402.

In step 402, the output of the upstream 0□ sensor 13 is
In step 403, it is determined whether or not 1 is less than the comparison voltage vR1, for example, 0.45V.In other words, it is determined whether the air-fuel ratio is rich or lean.In other words, if the air-fuel ratio is lean. (V+:5V□), skip 404 to determine whether delay counter CDLY is positive or not, and if CDLY>O, step 405 to determine whether CDLY is positive or not.
Set Y to O and proceed to step 406. In step 406, the delay counter CDLY is decremented by 1, and in step 4
07. At 408, set the delay counter CDLY to the minimum value T.
Guard with DL. In this case, the delay counter CDL
When Y reaches the minimum value TDL, the first air-fuel ratio flag F1 is set to "0" (lean) in step 409. The minimum value TDL is determined by the change from rich to lean in the output of the upstream 02 sensor 13. This is a lean delay time for maintaining the determination that the state is rich even if there is a change, and is defined as a negative value. On the other hand, if it is rich (V,>V□), the delay counter CDLY is set in step 410.
If CDLY<0, skip 411 to set CDLY to O, and proceed to step 412.

In step 712, the delay counter CDLY is incremented by 1, and in steps 413 and 414, the delay counter CDLY is incremented by 1.
Guard LY with maximum value TDR.

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 415. In addition, the maximum value TD
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 416, it is determined whether the sign of the first air-fuel ratio flag F1 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 is reversed, 1. Based on the value of the first air-fuel ratio flag F1, it is determined whether the reversal is from rich to lean or from lean to rich. If it is a reversal from rich to lean, in step 418 FAF 4-FAF+R
5R in a skip manner, and conversely, if it is a reversal from lean to rich, FAF 4-F is increased in step 419.
Decrease in skips as AF+RSL. In other words, skip processing is performed.

If the sign of the first air-fuel ratio flag F1 is not inverted in step 412, integration processing is performed in steps 420, 421 and 422. That is, in step 420, F1
If F1="0" (lean), FAF-FAF+KIR is determined in step 421, and on the other hand, if F1="1" (rich), step 4 is determined.
At step 22, FAF←FAF + KIL.

Here, integral constants KIR, KIL Hasteff constant Rs
R.

It is set sufficiently small compared to RSL, that is, KI
R(KIL)<RSR(RSL). Therefore, step 421 gradually increases the fuel injection amount in the lean state (F1="θ"), and step 422 gradually increases the fuel injection amount in the rich state (F1="θ").
1=“1”), the fuel injection amount is gradually decreased.

The air-fuel ratio correction coefficient FAF calculated in steps 418, 419, 421, and 422 is guarded at a minimum value such as 0.8 in steps 423 and 424, and is guarded at a maximum value such as 1. Guarded by 2. 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 at step 428.

FIG. 5 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 Oz sensor 13 as shown in FIG. 5(A), the delay counter CD
As shown in FIG. 5(B), LY is counted up in a rich state and counted down in a lean state.

As a result, a delayed air-fuel ratio signal A/F' (corresponding to flag Fl) is formed as shown in FIG. 5(C).

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
/F' is held constant for the rich delay time TDR, and then changes to rich at time t2. Even if the air-fuel ratio signal A/F changes from rich to lean at time t, the air-fuel ratio signal A/F' subjected to the delay processing is delayed by the lean delay time (-
TDL) After being held at Sochi for a considerable amount, it changes to Lean at time t4. However, the air-fuel ratio signal A/F' changes at time tS+1, . When the rich delay time TDR is inverted in a short period such as 1W, it takes time for the delay counter CDLY to reach the maximum value TDR, and as a result, the 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. 5(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 R5L as first air-fuel ratio feedback control constants, and an integral constant KI.
R, KIL, delay time TDR.

There is a system in which TDL or the comparison voltage Vll of 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 skip ff1R5R is increased, the control air-fuel ratio can be shifted to the rich side, and even if the lean skip IR3L is decreased, the control air-fuel ratio can be shifted to the rich side.On the other hand, if the lean skip amount R3L is increased ( , the controlled air-fuel ratio can be shifted to the lean side, and even if the rich skip IR3R 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 1R3R and the lean skip amount R3L according to the output of the downstream OT 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. If rich delay time TDR>lean delay time (-TDL) is set, the control air-fuel ratio can be shifted to the rich side, and conversely, lean delay time (-'TDt,
) > rich delay time (TDR), 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 02 sensor 15. Furthermore, by increasing the comparison voltage ■□, the control air-fuel ratio can be shifted to the rich side,
Further, by reducing the comparison voltage Vll, the control air-fuel ratio can be shifted to the lean side. Therefore, by correcting the comparison voltage Vll+ according to the output of the downstream Ot sensor 15, the air-fuel ratio can be controlled.

Set these skip amount, integral constant, delay time, and comparison voltage to 0. Each sensor has its own advantages. For example, the delay time allows very delicate air-fuel ratio adjustment, and the skip amount allows responsive control without requiring a long air-fuel ratio feedback control cycle like the delay time. Therefore, naturally, two or more of these variable amounts can be used in combination.

A double O2 sensor system in which the skip amount as an air-fuel ratio feedhack control constant is made variable will be described with reference to FIG.

FIG. 6 shows a second air-fuel ratio feedback control routine that calculates the skip amounts R3R and R3L based on the output of the downstream 02 sensor 15.
Executed every +ms. In steps 601 to 605,
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 upstream O2 sensor 13 (step 601), the cooling water temperature T
When HW is below a predetermined value (for example, 70°C) (step 602), when the throttle valve 16 is fully closed (LL="1") (step 603'), the downstream side 02 sensor 15
When the output Vt has never crossed the reference voltage (that is, when the downstream 0.0 sensor 15 is not activated) (step 604), when the load is light (Q/N, <
Xi ) (step 605), etc., the closed loop condition is not satisfied, and in other cases, the closed loop condition is not satisfied.

If it is not a closed loop condition, steps 614.630-63
2 to step 633.

That is, when the closed loop condition is not satisfied, step 6
At step 30, the counter CNT is cleared and step 631
Set the rich skip amount R3R to a constant value RS Ro,
In step 632, the lean skip 1iR3L is set to a constant value RS Lo and the process proceeds to step 633. Note that rich skip 1R3R and lean skip IR3L are set to values immediately before the end of closed loop control or learned values (backup RA
M 106 value).

If the closed loop condition is satisfied by the downstream 0□ sensor 15, the process advances to steps 606 to 628, and the downstream 0□ sensor 1
The air-fuel ratio feedback control is substantially performed using the output (2) of No.5.

In step 606, the output v2 of the downstream 0□ sensor 15 is A/D converted and taken in, and in step 607, v2 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 lean. As a result, in step 607, if ■2≦V++z (lean), the process proceeds to steps 608 to 617; on the other hand, if Vz >
If it is Vat (rich), the process advances to steps 618-627.

In step 608, the second air-fuel ratio flag F2 is set to "O".
(lean), and in step 609 it is determined whether or not the second air-fuel ratio flag F2 is inverted, that is, the downstream side is 0. It is determined whether the air-fuel ratio based on the output vt of the sensor 15 has reversed from rich to lean.

As a result, when the second flag F2 is inverted, the counter CNT is cleared in step 610, and the counter CNT is cleared in step 610.
11, rich skip amount R3R from RAM 105
is read out and set to RSR4-RSR+ΔRS (constant value), that is, the rich skip amount R3R is increased to shift the air-fuel ratio to the rich side, and further, in step 612, R
Read the lean skip amount R3L from AM 105 and set R
SL-RSL-ΔR3, that is, the rich skip amount R3L is decreased to shift the air-fuel ratio to the rich side.

On the other hand, if the second air-fuel ratio flag F2 is not inverted in step 614, the counter CNT is counted up in step 613, and in step 614 CNT>n (
a predetermined value). In other words, the duration of the second air-fuel ratio flag F2 after inversion is the predetermined value (n x 512m
5) is exceeded. As a result, C.N.T.
If fa n, the skip amounts R3R and R3L are shifted to the rich side in steps 611 and 612 in the same manner as described above.

On the other hand, when the counter CNT reaches the predetermined value n in step 614, the counter CNT is cleared in step 615, 5R=R3R- is set to -n-ΔR3 in step 616, and 5L=R3L+ is set to -n in step 617. Let n・ΔR3. In this case, if =-, for example, the rich skip ilRS R, lean will change within a predetermined time ('['' = n x 512m5), or the edge skip amount R3R, lean skip 1lR5L will change by n・ΔR3. The skip amount R3L will be reversed.

After that, since the counter CNT is cleared in step 615, the flow returns to step 611.
．． Proceed to 612, and at the same time as above, rich skip amount R3R
, change the lean ski knob 1R3L to the rich side.

Similarly, in step 618, the second air-fuel ratio flag F2
is set to "1" (rich), and in step 619 it is determined whether or not the second air-fuel ratio flag F2 is inverted, that is, the downstream side is 0. It is determined whether the air-fuel ratio based on the output (2) of the sensor 15 has reversed from lean to rich. As a result, when the second flag F2 is inverted, the counter CNT is cleared in step 620, and the RAM
Read the rich skip amount R3R from 105 and set RSR←
RSR-ΔR3, that is, rich skip amount R5R
is decreased to shift the air-fuel ratio to the lean side.Furthermore, in step 622, the lean skip amount R3L is transferred from the RAM 105 to RSL-RSL+ΔR5, that is, the rich skip amount R3L is increased to shift the air-fuel ratio to the lean side. to the lean side.

“On the other hand, if the second air-fuel ratio flag F2 is not inverted in step 624, then in step 623 the counter CNT
is counted up, and it is determined in step 624 whether CNT>n. That is, it is determined whether the duration of the second air-fuel ratio flag F2 after inversion exceeds a predetermined value (n x 512 m5). As a result, if CNT≦n, the skip amounts R8R and R3L are shifted to the lean side in the same manner as described above in steps 621 and 622.

On the other hand, when the counter CNT reaches the predetermined value n in step 624, the counter CNT
is cleared, and in step 626, SR "R4P+ is set to -n-ΔR5, and in step 627, RSL"-RSL, - is set to -n-ΔR3. Therefore, in this case, the predetermined time (T=nx512+
Rich skip IRS R, lean skip amount R3L changed within n・ΔR3 2UC=--)
Only rich skip 1lR3R, lean skip IR3
L will end up going backwards.

After that, since the counter CNT is cleared in step 625, the flow returns to step 62L.
Proceed to 622, rich skip 1R3R as above
, the lean skip amount R3L is changed to the lean side.

In this way, due to the 0□ storage effect, the downstream 02
When the output V2 of sensor 5 becomes difficult to reverse,
At time (T = n x 512 m5), rich skip 1RsR and lean skip fJR3L are reversely corrected in step 616.617 or 626.627, thereby reducing subsequent overcorrection.

Note that n used in steps 614 and 624 may be a different value, and may be determined by taking into consideration the influence of the air-fuel ratio detection delay.

Also, ΔR of step 611.612.621.622
3 may also be different values, and the correction speed can be optimized in accordance with the engine characteristics, in particular, to reduce NO.

Step 628 includes R2H, R calculated as described above.
It performs guard processing of SL, for example, the maximum value M
It is stored in the RAM 105 while being guarded with A X = 7.5% and the minimum value MIN = 2.5%. In addition, the minimum value M
IN is a value at a level where transient followability is not impaired,
Further, the maximum value MAX is a value at a level at which drivability does not deteriorate due to air-fuel ratio fluctuations.

The routine of FIG. 6 then ends at step 632.

According to the routine shown in FIG. 6, if the intake air amount Q is relatively small or the catalyst is new, the catalyst 0. The storage effect is large, and as a result, the downstream side 02 sensor 15
When the inversion period of the output V2 becomes more than nX512m5,
As shown in FIG. 7, the rich skip amount R3R and the lean skip amount R3L are at time 1. The previous correction (to
-t+) and is corrected in the opposite direction. For example, time t, xt
.

If the correction amount in between is R, then the reverse correction is made by R/2. In Fig. 7, n is a value such that the time n x512 ras is about 5 minutes, and ΔRS = 0.00
If it is 5%, R will be about 1 to 2%. Also, the dotted line indicates the conventional case, in which case the downstream 0□ sensor 1
When the reversal period of the output 5 (2) becomes larger, the rich skip amount R3R and the lean skip amount RSL are over-corrected.

Further, according to the routine shown in FIG. 6, if the amount of intake air is relatively large or the catalyst is old, the catalyst is 0! Storage effect is small. Therefore, in this case, as shown in FIG. 8, the reversal period of the output v2 of the downstream 0□ sensor 15 does not exceed nX512+ms, and as a result, the rich skip amount R3R and lean skip amount R3L are not reversely corrected. .

Note that FAF calculated during air-fuel ratio feedback,
Convert RSR and RSL to other values and use backup R.
It can also be stored in the AM 106, which helps improve drivability during restarts, etc. 6th
The minimum value MIN in the figure is a value at a level that does not impair transient followability, and the maximum value MIN is a value at a level at which drivability does not deteriorate due to air-fuel ratio fluctuations.

FIG. 9 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360° CA.

In step 901, the intake air amount data Q and the rotational speed data Ne are read out from the RAM 105, and the basic injection amount R is read out.
Calculate AUP. For example, TAUP-α・Q/Ne(
α is a constant). RAM 105 at step 902
Read the cooling water temperature data T) (W and store it in RAM 104.
The warm-up increase value FWL is calculated by interpolation using the one-dimensional map stored in the . In step 903, the final injection amount TAU is determined as TAU 4-TAUP-FAF ・(FWL+β
)+γ. Note that β·T is a correction amount 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. This routine then ends in step 905. In addition, as mentioned above, the injection amount T
When the time corresponding to AU has passed, the down counter 10
The flip-flop 109 is activated by the carrier signal of 8.
is reset and fuel injection ends.

Further, the predetermined value n in steps 614 and 624 in FIG.
It may be changed depending on. In the case of intake air amount Q,
As shown in FIG. 10, the value n is inversely proportional to the intake air amount Q. Furthermore, when the intake air amount Q varies, it may be changed according to an average value or a smoothed value of the intake air amount Q. Thereby, it is possible to effectively compensate for the fact that the detection delay of the air-fuel ratio by the catalyst varies depending on the load (intake air amount).

In addition, the first air-fuel ratio feedback control is performed every 4tas, and the second air-fuel ratio feedback control is performed every 512m5.
Air-fuel ratio feedback control is performed every time on the upstream side with good responsiveness, 0. Mainly controlled by sensors,
This is because control by the downstream 02 sensor, which has poor responsiveness, is performed in a subordinate manner.

Furthermore, a double 0□ sensor system that corrects other control constants such as delay time, integral constant, etc. in the air-fuel ratio feedback control by the upstream Ot sensor using the output of the downstream Ot sensor also has a second air-fuel ratio control constant. The invention can also be applied to double-0 sensor systems that introduce correction factors. 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 skips IR3R and R3L and make only the other variable.
It is also possible to fix one of L and make only the other variable.
Or Rich integral constant KIR, Lean integral constant KIL
It is also possible to have one of them 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.

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 901 is determined by the carburetor 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 in step 903, the supplied air amount corresponding to the final fuel injection amount 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.

In addition, when an 02 sensor is provided only downstream of the catalyst to perform air-fuel ratio feedback control, R3R and R3L of the second air-fuel ratio feedback routine may be calculated as FAF instead of the first air-fuel ratio feedback routine described above. That is, step 611 in FIG.
−FAF+ΔFAF, and step 616 is FAF←F
Set -n-ΔFAI' to AF-, and set step 621 to FA
F←FAF−ΔFAF, Ste, Pro 26 is FAF'
-FAF+ is set to -n・ΔFAF, and step 630 is set to F
Set AF←1,0, and step 612.617.622.
The air-fuel ratio correction coefficient FAF can be obtained by deleting 627°631.

[Effects of the Invention] As explained above, according to the present invention, when the duration after reversal of the output of the downstream air-fuel ratio sensor becomes greater than a predetermined value, the downstream air-fuel ratio sensor By temporarily stopping the correction of the fuel ratio feedback control constant or the air-fuel pressure control amount in the opposite direction, it is possible to prevent over-correction of the air-fuel ratio feedback control constant, for example, R3R, R5L, thereby improving transient followability. It is possible to prevent deterioration of drivability, deterioration of emissions, etc.

[Brief explanation of drawings]

Figures 1A and 1B are overall block diagrams for explaining the present invention in detail, Figure 2 is a single 02 sensor system and a double 0□
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. 6A, Fig. 6B, Fig. 9; is a flowchart for explaining the operation of the control circuit in FIG. 3, FIG. 5 is a timing diagram for supplementary explanation of the flowchart in FIG. 4, and FIG. 6 is a diagram showing the combination of FIGS. 6A and 6B. , Figure 7,
FIG. 8 is a timing diagram for supplementary explanation of the flowcharts in FIGS. 6A and 6B, and FIG. 10 is a graph showing a modification example of steps 614 and 624 in FIG. 6B. 1... Engine body, 3... Air flow meter,
4...Distributor, 5.6...Crank angle sensor, 10...Control circuit, 12...Catalytic converter,
13...upstream side 0. Sensor, 15...Downstream Ox sensor.

Claims (1)

[Claims] 1. A three-way catalyst provided in an exhaust passage of an internal combustion engine; and an upstream air-fuel ratio sensor provided in the exhaust passage upstream of the three-way catalyst to detect the air-fuel ratio of the engine. , a downstream air-fuel ratio sensor that is provided in the exhaust passage downstream of the three-way catalyst and detects the air-fuel ratio of the engine; and a comparison means that compares the output of the downstream air-fuel ratio sensor with a predetermined value. control constant calculation means for gradually increasing or decreasing the air-fuel ratio feedback control constant according to the comparison result of the comparison means; a duration measuring means for measuring the duration of the comparison result after the comparison result of the comparison means is reversed; a determining means for determining whether or not a time period has exceeded a predetermined time; and when the determining means determines that the duration has exceeded a predetermined time, the air-fuel ratio feedback control constant is set to a constant value for the duration of the predetermined time. a correction means that greatly increases or decreases in the direction opposite to the direction in which the air-fuel ratio is increased or decreased; and the control constant calculation means and the air-fuel ratio feedback control constant obtained by the correction means are used to adjust the output of the upstream air-fuel ratio sensor. an air-fuel ratio control device for an internal combustion engine, comprising: a feedback amount calculation means for calculating an air-fuel ratio feedback amount according to the calculated air-fuel ratio feedback amount; and an air-fuel ratio adjustment means for adjusting the air-fuel ratio of the engine based on the calculated air-fuel ratio feedback amount. . 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the predetermined time is variable according to a load parameter of the engine. 3. a three-way catalyst provided in the exhaust passage of the internal combustion engine; a downstream air-fuel ratio sensor provided in the exhaust passage downstream of the three-way catalyst to detect the air-fuel ratio of the engine; and the downstream air-fuel ratio. a comparison means for comparing the output of the sensor with a predetermined value; a control amount calculation means for increasing or decreasing the air-fuel ratio control amount according to the comparison result of the comparison means; and a time period of the comparison result after the comparison result of the comparison means is reversed. a duration measuring means for measuring the duration; a determining means for determining whether or not the duration exceeds a predetermined time; when the determining means determines that the duration exceeds the predetermined time, the a correction means for increasing or decreasing the air-fuel ratio control amount by a predetermined amount in a direction opposite to the direction in which the air-fuel ratio control amount was increased or decreased during the duration; and adjusting the air-fuel ratio of the engine based on the corrected air-fuel ratio control amount. An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio adjusting means; 4. The air-fuel ratio control device for an internal combustion engine according to claim 3, wherein the predetermined time is variable according to a load parameter of the engine.