JPH02283834A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the increase of emission and worsening of drivability by a method wherein an airfuel ratio correcting amount is asymmetrically updated, and an asymmetrical update speed is varied according to the degree of deterioration of a ternary catalyst. CONSTITUTION:A ternary catalyst and an air-fuel ratio sensor are disposed in a vertically separated state in the exhaust passage of an internal combustion engine. Based on an output from the airfuel ratio sensor, an air-fuel ratio correction amount is computed by an air-fuel ratio correction amount computing means M1. In this case, the first update speed of an air-fuel ration correction amount when an output from the air-fuel ratio sensor is lean is set to a value higher than a second update speed of that when the output is rich. The degree of deterioration of a three-dimensional catalyst is discriminated by a degree of deterioration discriminating means M2. Variation is effected by an update speed varying means M3 such that, with the increase in the degree of deterioration of the ternary catalyst, the first and second update speeds are decreased, and the degree of the decrease of the first update speed is increased to a value higher than that of the second update speed. According to an air-fuel ratio correction amount, an air-fuel ratio is regulated by an air-fuel ratio regulating means M4.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides an air-fuel ratio sensor (herein, an oxygen concentration sensor (02 sensor)) at least on the downstream side 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.

[Conventional technology]

In simple air-fuel ratio feedback control (single 02 sensor system), the 0□ 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 02 sensor, it is difficult to improve the control accuracy of the air-fuel ratio. It takes 0□
In order to compensate for variations in sensor output characteristics, variations in eight components such as fuel injection valves, and changes over time, a second 02 sensor is installed downstream of the catalytic converter, and air-fuel ratio feedback control is performed by the upstream 02 sensor. In addition, a double 02 sensor system has already been proposed in which air-fuel ratio feedback control is performed using a downstream 02 sensor (see Japanese Patent Application Laid-open No. 147941 (1983)). In this double 02 sensor system, the 02 sensor provided downstream of the catalytic converter has a
Although it has a low response speed, it has the advantage of small variations 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 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,
When the 0□ sensor output characteristics deteriorate, it directly affects the exhaust emission characteristics, whereas in the double 02 sensor system, even if the output characteristics of the upstream 02 sensor deteriorate, the exhaust emission characteristics do not deteriorate. In other words, in the double 0□ sensor system, good exhaust emissions are guaranteed as long as the downstream 02 sensor maintains stable output characteristics.

In the double 02 sensor system described above, as mentioned above, the response speed of the downstream 02 sensor is low, so when its output changes from lean to rich, the average air-fuel ratio upstream of the catalytic converter is already lower than the stoichiometric air-fuel ratio. It has a rich atmosphere that is far off, and as a result, HC, C
o Emissions increase and, on the other hand, when the output of the downstream 02 sensor is reversed from rich to lean, the average air-fuel ratio upstream of the catalytic converter has already become a lean atmosphere that deviates significantly from the stoichiometric air-fuel ratio, and as a result, NOx emissions increase. Furthermore, in a normal double 02 sensor system, when the air-fuel ratio feedback control constant, such as the skip amount, is corrected according to the output of the downstream 02 sensor, the update rate is always constant, and as shown in FIG. The purification characteristic of the three-way catalyst, in which NOx emissions rapidly increase when the purification window W of the three-way catalyst deviates to the lean side, is not taken into account, and as a result, there is a problem in that the purification performance of the three-way catalyst deteriorates.

That is, when the 02 storage effect, which is the purification performance of the three-way catalyst, is large, if the control air-fuel ratio is not shifted to the rich side, NOx emissions will increase. For this reason, the applicant has already proposed that the update speeds of the rich side and lean side of the air-fuel ratio feedback control constant be asymmetrical to make the controlled air-fuel ratio rich (see: JP-A-63-9
Publication No. 7846).

[Problem to be solved by the invention]

However, the deterioration of the three-way catalyst progressed, and the
When the storage effect becomes smaller, the 0□ storage amount becomes smaller, and conversely, unless the control air-fuel ratio is shifted to the lean side, there is a problem that overcorrection will occur on the rich side, leading to deterioration of HC and Co emissions. Since the response delay associated with the reduction in the 02 storage effect of the three-way catalyst is also reduced, over-correction of the control air-fuel ratio also occurs, leading to increased emissions and deterioration of drivability.

The above-mentioned problem also applies to a single air-fuel ratio sensor system in which an air-fuel ratio sensor is provided only downstream of the catalyst.

Therefore, an object of the present invention is to provide an air-fuel ratio sensor system that does not increase emissions or deteriorate drivability even if the 02 storage effect of the three-way catalyst changes.

[Means to solve the problem]

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

That is, a three-way catalyst C installed in the exhaust passage of an internal combustion engine
A downstream air-fuel ratio sensor that detects the air-fuel ratio of the engine is provided at least in the exhaust passage downstream of Cl1o.

The air-fuel ratio correction amount calculation means uses the output v2 of the downstream air-fuel ratio sensor.
The air-fuel ratio correction amount is calculated according to, and at that time, the output V2 of the downstream air-fuel ratio sensor is set to the first update speed of the air-fuel ratio correction amount when the output V2 of the downstream air-fuel ratio sensor is lean. The second update speed k of the air-fuel ratio correction amount when is rich.

Make it bigger. Deterioration degree determination means is CCa of three-way catalyst
The update speed changing means changes the first and second update speeds (km,
kt), and at that time, the degree of decrease in the first update rate kR is set to the second update rate k.

be greater than the rate of decrease. The air-fuel ratio adjustment means adjusts the air-fuel ratio of the engine according to the air-fuel ratio correction amount FAF.

[For production]

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

In other words, in the case of a new catalyst (0□ large storage effect),
ΔR3 is added to the rich side update speed of R2H, which is the air-fuel ratio correction amount (in this case, the skip amount of the double air-fuel ratio sensor system).
is made larger than the update rate kLΔR3 on the lean side, that is, the update rate is made asymmetric with ΔR3°kLΔR3, and the control air-fuel ratio is shifted to the rich side to reduce NOx emissions. Furthermore, both the update speeds kmΔR3 and kLΔR3 are increased to improve the responsiveness of the control air-fuel ratio. However, in the case of a degraded catalyst (02 storage effect small), 0
2 Due to the small storage effect, the update rate kIl Δ
R3,kL If ΔR3 remains large, over-correction of the control air-fuel ratio will occur, and the update speed k.

If ΔR3 and kLΔR3 remain asymmetrical, overcorrection of the control air-fuel ratio toward the rich side will occur. Therefore, in this case, by reducing both the update speeds km ΔR3 and kL ΔR3 and making the degree of decrease in the update speed km ΔR3 on the rich side larger than the degree of decrease in the update speed kLΔR3 on the lean side, the update speeds are increased by 8ΔR3 and kLΔR3. is brought closer to symmetry to prevent the above-mentioned overcorrection.

〔Example〕

FIG. 5 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. In FIG. 5, an air flow meter 3 is provided in an intake passage 2 of an engine main body l. The air flow meter 3 directly measures the amount of intake air, and includes a built-in potentiometer, for example, to generate an analog voltage output signal proportional to the amount of intake air. This output signal is the control circuit IO's built-in multiplexer A.
/D converter 101. The distributor 4 has a shaft that is, for example, 7 in terms of crank angle.
A crank angle sensor 5 that generates a pulse signal for detecting a reference position every 20 degrees, and a crank angle sensor 6 that generates a pulse signal for detecting a reference position every 30 degrees in terms of crank angle.
is provided.

The pulse signals of these crank angle sensors 5 and 6 are supplied to the human output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is supplied to the interrupt terminal of the CPU 103.

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. Cooling water temperature TH of water temperature sensor 9
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.

02 sensor 13.15 generates an electrical signal according to the concentration of oxygen components in the exhaust gas. That is, 02 sensor 13.
15 generates different output voltages in the A/D converter 101 of the control circuit 10 depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio. The control circuit 10 is configured as a micro combinator, for example, and includes an A/D converter 101.
, input/output interface 102 , RAM 104 , R[]M 105 , backup RA in addition to the CPU 103
MIQ5, clock generation circuit 107, etc. are provided.

Further, the throttle valve 16 of the intake passage 2 is provided with an idle switch 17 that generates a signal LL indicating whether the throttle valve 16 is fully closed.

This idle state output signal LL is supplied to the input/output interface 102 of the control circuit 10.

In addition to 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, when the fuel injection amount TAU is calculated, the fuel injection amount TAU is preset in the down counter 108 and the 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 the borrow out terminal reaches the "1" level, the flip-flop 10
9 is set, and the drive circuit 110 stops energizing the fuel injection valve 7. That is, the fuel injection valve 7 is energized by the above-mentioned fuel injection amount TAU, so that an amount of fuel corresponding to the fuel injection amount TAU is sent into the combustion chamber of the engine body 1.

Note that the interrupt generation of the CPU 103 is caused by the A/D converter 10.
After the A/D conversion of step 1 is completed, the input/output interface 102
When the controller receives a pulse signal from the crank angle sensor 6, when it receives an interrupt signal from the clock generation circuit 107, etc.

The intake air amount data Q and the cooling water temperature data THW of the air flow sensor 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, the data Q$ and THW in the 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. 6 shows a first air-fuel ratio feedback control routine for calculating an air-fuel ratio correction coefficient FAF based on the output of the upstream 0□ sensor 13, and is executed every predetermined period of time, for example, every 4 ms.

In step 601, 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, the output signal of the upstream 02 sensor 13 is The closed-loop condition is not satisfied in all cases such as fuel cut, etc., and the closed-loop condition is satisfied in all other cases. If the closed loop condition is not met, the process proceeds directly to step 624. Note that the air-fuel ratio correction coefficient FΔF may be set to 1 or 0.

On the other hand, if the closed loop condition is satisfied, the process proceeds to step 602.

In step 602, the output V+ of the upstream 02 sensor 13 is
is A/D converted and taken in, and in step 603 it is determined whether or not V is less than the comparison voltage Vml, for example 0.45V, that is, it is determined whether the air-fuel ratio is rich or lean, that is, lean (v1≦ V81), step 604
Determine whether the delay counter CDLY is positive or not at C.
If DLY>Q, CDLY is set to 0 in step 605 and the process proceeds to step 606. In step 606,
Decrease the delay counter CDLY by 1, and step 607
．． At 608, the delay counter CDLY is set to the minimum value TDL.
Guard with. In this case, when the delay counter CDLY reaches the minimum value TDL, the first air-fuel ratio flag F1 is set to "0" (lean) in step 609. Note that the minimum value TDL is a lean delay time for maintaining the determination that the fuel is in a rich state even if there is a change from rich to lean in the output of the upstream side 02 sensor 13, and is defined as a negative value. . On the other hand, rich (V + > V *
r), it is determined in step 610 whether the delay counter CDLY is negative or not, and if CDLY<0, CDLY is set to 0 in step 611, and step 612
Proceed to. In Stepro 12, the delay counter CDLY
is incremented by 1, and in steps 613 and 614, the delay counter CDLY is guarded with the 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).The maximum value TDR 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 second sensor 13 changes from lean to rich, and is defined as a positive value.

In step 616, 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 inverted, in step 617, 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, step 618: Trowel FAF -FAF+
I'lSR is increased by 1 in a skip manner, and conversely, if it is a reversal from lean to rich, PAF is increased in step 619.
-FAF-R3L and decrease in a skip manner. In other words, skip processing is performed.

If the sign of the first air-fuel ratio flag F1 is not inverted in step 612, integration processing is performed in steps 620, 621, and 622. That is, in step 620, F1
= “0” or not, and if F1 = “0” (lean), at step 621 PAP -FAF+KIR
On the other hand, if F1="1" (rich), FAF -FAF-KIL is set in step 622. Here, the integral constants KIR, KIL are the skip amounts R3R, R
It is set sufficiently small compared to 3L, that is, KIR
(KIL) <RSR(R3L). Therefore, step 621 gradually increases the fuel injection amount in a lean state (F1="0"), and step 622 gradually increases the fuel injection amount in a rich state! '! (
F1="1") to gradually reduce the fuel injection amount.

The air-fuel ratio correction coefficient FAF calculated in steps 618, 619, 621, and 622 is guarded at a minimum value, for example, 0.8, and at a maximum value, for example, 1.2, at step 623. 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 over-rich or over-lean conditions.

The FAF calculated as described above is stored in the RAM 105, and the routine ends at step 624.

FIG. 7 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. 6. When the air-fuel ratio signal A/F for rich/lean discrimination is obtained from the output of the upstream 02 sensor 13 as shown in FIG. 7(A), the delay counter CD
As shown in FIG. 7(B), LY is counted up in a rich state and counted down in a lean state.

As a result, as shown in FIG. 7(C), a delayed air-fuel ratio signal A/F' (corresponding to flag F1) is formed. For example, 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 maintained lean for the rich delay time TDR, and then at time t2. Changes to rich. Time 1. Even if the air-fuel ratio signal A/F changes from rich to lean at
DL) After being held rich by a considerable amount, it changes to lean at time t4. However, the air-fuel ratio signal A/F is at time js+
When the rich delay time TDR is reversed in a short period like t6+t7, the delay counter CDLY reaches the maximum value TDR.
It takes time to reach t, and as a result, time t.

At , the air-fuel ratio signal A/F' after the delay processing is inverted. .

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

Next, the second air-fuel ratio feedback control by the downstream 02 sensor 15 will be explained. The second air-fuel ratio feedback control includes step amounts RSR and R3L as first air-fuel ratio feedback control constants, and an integral constant KI.
R, IL, delay time TDR, TDL.

Or the comparison voltage V of the output ■ of the upstream O2 sensor 13
There are systems that make l11 variable and systems that introduce a second air-fuel ratio correction coefficient FAF2.

For example, if the rich skip amount R3R is increased, the controlled air-fuel ratio can be shifted to the rich side, and even if the lean skip amount R3L is decreased, the controlled 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 rich side. , 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. Furthermore, by increasing the rich integral constant KIR, the control air-fuel ratio can be shifted to the rich side, and even by decreasing the lean integral constant KIL, the control air-fuel ratio can be shifted to the rich side.On the other hand, by increasing the lean integral constant KIL, the control air-fuel ratio can be shifted to the rich side , the controlled air-fuel ratio can be shifted to the lean side, and even if the rich integral constant KIR 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 integral constant KIR and the lean integral constant KIL according to the output of the downstream 0□ sensor 15. By setting the rich delay time TDR large or the lean delay time (-TDL) small, the control air-fuel ratio can shift to the rich side; conversely, the lean delay time (-T[
By setting lL) large or setting the rich delay time (TDR) small, the controlled air-fuel ratio can be shifted to the lean side.

That is, the air-fuel ratio can be controlled by correcting the delay times TDR and TDL according to the output of the downstream 02 sensor 15. Furthermore, if the comparison voltage VRI is increased, the control air-fuel ratio can be shifted to the rich side, and the comparison voltage V It
By reducing l, the controlled air-fuel ratio can be shifted to the lean side.

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

Making these skip amount, integral constant, delay time, and comparison voltage variable by the downstream 02 sensor has its own advantages. For example, the delay time allows for very delicate air-fuel ratio adjustment, and the skip amount can be controlled with good response without lengthening the air-fuel ratio feedback period unlike the delay time. Therefore, naturally, two or more of these variable amounts can be used in combination.

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

FIG. 8 shows a second air-fuel ratio feedback control routine based on the output of the downstream 02 sensor 15, which is executed every predetermined period of time, for example, every 512fflS.

In steps 801 to 805, it is determined whether the downstream 0□ sensor 15 is in a closed loop condition. For example, in addition to the failure of the closed loop condition determined by the upstream 02 sensor 13 (step 801), when the cooling water temperature THW is below a predetermined value (for example, 70°C) (step 802), the throttle valve 16 is fully opened (LL = “1”). ) (step 803)
, the closed loop condition is not satisfied when the load is light (Q / N e < It is. If it is not a closed-loop condition, the process proceeds to step 821, and if it is a closed-loop condition, the process proceeds to step 806, where the rich skip amount R is
Of the update speed of 3R, the skip amount coefficient is ++, k
L (> 1) is calculated, which will be described later.

In step 807, the output V2 of the downstream side 02 sensor 15 is
In step 808, it is determined whether V2 is equal to or less than the comparison voltage VR, for example, 0.55V, that is, it is determined whether the air-fuel ratio is rich or lean. Note that the comparison voltage VR□ is set higher than the comparison voltage VRI of the output of the upstream side 02 sensor 13, taking into consideration 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 12. However, this setting may be optional. As a result, if V2≦V12 (lean), the process proceeds to step 809, where the second air-fuel ratio flag F2 is set to “0”, and V2 > V112 (lean).
f) If yes, proceed to step 810 and set the second air-fuel ratio flag F2 to "1".

In step 811, it is determined whether the sign of the second air-fuel ratio flag F2 has been inverted, that is, it is determined whether the air-fuel ratio downstream of the catalyst has been inverted. If the air-fuel ratio is inverted, the inversion number counter CREV is incremented by 1 in step 812. Note that this reversal number counter CREV is the ninth
It is used in the update speed calculation routine shown in the figure. next,
In step 813, it is determined based on the value of the second air-fuel ratio flag F2 whether the reversal is from rich to lean or from lean to rich. If it is a reversal from rich to lean, in step 814 RSR = RSR + k tr
・Increase ΔR3 in a skip manner, and conversely, if it is a reversal from lean to rich, RSR-R3 is increased in step 815.
It is decreased in a skip manner to R+kL・ΔR5. In other words, skip processing is performed.

If the sign of the second air-fuel ratio flag F2 is not inverted in step 811, integration processing is performed in steps 816, 817, and 818. That is, in step 816, F2
If F2="0" (lean), RSR-R3R+ΔR5 is set in step 817, and on the other hand, if F2="1" (rich), RSR-R3R+ΔR5 is set in step 818. Let RSR-ΔR5. Note that, as described above, k++ (kL)>1. Therefore,
Step 816 gradually increases the rich skip amount R3R in the lean state (F2="0"), and step 81
7 is rich state (F2="1") and rich skip amount R
Gradually reduce 8R.

In step 819, the rich skip amount R5R is guarded at a maximum value, for example, 7.5%, and a minimum value, for example, 2.5%.
Guard at 5%. Note that the minimum value of 2.5% is a value at a level where transient followability is not impaired, and the maximum value M
AX is a value at a level at which drivability does not deteriorate due to air-fuel ratio fluctuations.

In step 820, the lean skip 1iR3L is
AM105-RSR.

The routine then ends at step 821.

FIG. 9 is a detailed flowchart of the update rate calculation step 806 of FIG. That is, in step 901, a counter CNT for counting a predetermined time is incremented by 1, and in step 902, it is determined that the predetermined time has elapsed (CNT >
CNTO). If the predetermined period has not yet elapsed, the process advances to step 906 and this routine ends. As a result, steps 903 to 905 are executed every predetermined time (CNT=CNTO).

In step 903, the output reversal number CREV of the downstream side 02 sensor 15 is read from the RAM 105, and the one-dimensional map stored in the ROM 104 is used to interpolate and calculate the rich side skip amount coefficient.
A lean side skip amount coefficient kL is calculated by interpolation using the one-dimensional map stored in M104. And step 9
At 05, both counters CNT and CREV are cleared.

In this way, at a predetermined time (CNT = CNTO), the smaller the output reversal number CREV of the downstream side 02 sensor 15, the more
The three-way catalyst has a great effect on new or 02 storage,
On the other hand, the larger the output reversal number CRεV of the downstream 0□ sensor 15, the worse the three-way catalyst is (see FIG. 4). Therefore, the output reversal number CRεV of the downstream 02 sensor 15 indicates the degree of deterioration of the three-way catalyst. Step 903.9 of FIG.
According to 04, the rich side skip coefficient k11 is made larger than the lean side skip amount coefficient, and furthermore, the greater the degree of deterioration of the three-way catalyst (that is, the greater the CREV),
Both coefficients and kL are made symmetrical by making kL smaller and making the degree of decrease in coefficient kL larger than the degree of decrease in coefficient kL.

In addition, in FIG. 8, the skip amount coefficient kl.

kL is variable depending on the degree of deterioration of the three-way catalyst, but k,,k
It is also possible to keep L constant and to vary the integral amount ΔR3 depending on the degree of deterioration of the three-way catalyst.

FIG. 10 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, at 360@CA. Step 10
In the old version, the basic injection amount TAtiP was calculated by reading the intake air amount data Q and rotational speed data Ne from RAJQ5. For example, assume that TAUP←α・Q/N e (α is a constant). In step 1002, the final injection amount TAU is calculated by TAU - TAUP - FAF·β+T.

Note that β and T are correction amounts determined by other operating state parameters. Next, in step 1003, 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 1004.

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

FIG. 11 shows a modification example of FIG. 6, in which the skip amount coefficient km
, kL.

In this case, step 806 in FIG. 8 and the routine in FIG. 9 are omitted.

In FIG. 11, step 1 is added to the routine of FIG.
101 to 1109 are added. In other words, upstream side 0
2 sensor 13 close routine condition is satisfied (step 601), upstream side 0□ sensor 13 output V, 1
The flow of steps 1101 to 1105 is executed every cycle, and the flow of steps 1106 to 1109 is executed at other times.

For example, when the output V of the upstream O2 sensor 13 is not reversed from rich to lean, steps 1106 to 110
9, the maximum value Vm of the output V2 of the downstream O2 sensor 15
ax and the minimum value Vmin are calculated. As a result, when the output v1 of the upstream 02 sensor 13 is reversed from rich to lean, the flow advances to step 1101.

In step 1101, the output v of the downstream sensor 15
The swing width ΔV of 2 is calculated by ΔV4−Vmax −Vrn+n, and in step 1102, ΔV is set to a predetermined value x
It is determined whether the value is 2 or less. If ΔV>Xt, the process directly proceeds to step 1105. In other words, the arrows y, ,Y in Fig. 12
As shown in FIG. 2, the output v2 of the downstream 0□ sensor 15 has a very large swing when changing from lean to rich or from rich to lean, so step 1102 is provided to exclude this.

In step 1102, only when ΔX≦X2, the process proceeds to step 1103, and the rich side skip amount coefficient k is calculated using the one-dimensional map stored in the ROM 104 based on the value ΔV.
g is calculated by interpolation, and in step 1104, the ROM
Using the one-dimensional map stored in 104, the lean side skip amount coefficient kL is calculated by interpolation. And step 11
At step 05, the maximum value xmax and the minimum value Vmin are initialized to the latest value v2.

Note that instead of the amplitude of fluctuation ΔV in steps 1103 and 1104, its average value (or smoothed value) may be used.

As shown in FIG. 12, the output v of the upstream 02 sensor 13
In one period T of 1, the smaller the amplitude ΔV of the output of the downstream 02 sensor 15, the greater the three-way catalyst is new or the 0□ storage effect; The larger the value, the worse the three-way catalyst is. Therefore, the amplitude Δ of the output v2 of the downstream side 02 sensor 15
V indicates the degree of deterioration of the three-way catalyst. Step 11 in Figure 11
According to 03°1104, the rich side skip amount coefficient is
is larger than the lean side skip amount coefficient kL, and further,
The greater the degree of deterioration of the three-way catalyst (that is, the greater ΔV), the smaller both coefficients km and kL are, and the degree of decrease in coefficient kR is made larger than the degree of decrease in coefficient kL, thereby making both coefficients kR1kL symmetrical. It's getting closer.

Note that when the degree of deterioration of the three-way catalyst described above has progressed to a certain degree, an alarm can be activated to notify the driver.

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 every 512 m5, which is because the air-fuel ratio feedback control mainly controls the upstream 02 sensor, which has good responsiveness, and subtly controls the downstream 02 sensor, which has poor responsiveness. This is for the purpose of doing so.

In addition, other control constants in the air-fuel ratio feedback control by the upstream 02 sensor, such as delay time, integral constant, etc., are corrected by the output of the downstream 02 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 amounts R3R, RSL and make only the other variable.
It is also possible to fix one of them and make only the other variable, or to change the Ricci integral constant KIR, IJ-
It is also possible to have one of them fixed and the other variable.

Furthermore, the present invention can also be applied to a single air-fuel ratio sensor system in which an air-fuel ratio sensor is provided only downstream of the catalyst. In this case, the air-fuel ratio correction amount FAF may be directly calculated according to the output of the catalyst downstream air-fuel ratio sensor, and the calculation speed (update speed) may be made variable according to the degree of deterioration of the three-way catalyst. of course,
In this case, the catalyst deterioration degree determination shown in FIGS. 11 and 12 is not applied.

Furthermore, instead of the air flow meter, a Nirman 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.
The electric bleed air control valve controls the air-fuel ratio by adjusting the amount of air bleed from the carburetor and introducing atmospheric air into the main system passage and slow system passage, and controls the amount of secondary air sent to the engine exhaust system. The present invention can be applied to things that need to be adjusted. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 1001 is determined by the carburetor itself,
That is, it is determined according to the intake air amount, the intake pipe negative pressure, and the rotational speed of the engine, and in step 1002, 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. In particular, when a TlO□ sensor is used as the upstream air-fuel ratio sensor, control responsiveness improves,
Overcorrection due to the output of the downstream air-fuel ratio sensor can be prevented.

Further, although the above-described embodiment is constructed using a microcombicoater, that is, a digital circuit, it may also be constructed using an analog circuit.

〔Effect of the invention〕

As explained above, according to the present invention, by asymmetrically updating the air-fuel ratio correction amount (air-fuel ratio feedback control constant in the double air-fuel ratio sensor system),
It is possible to prevent deterioration of emissions and drivability, and since the above-mentioned asymmetrical update speed is variable according to the degree of deterioration of the three-way catalyst, it is possible to reduce the center deviation of the control air-fuel ratio from the stoichiometric air-fuel ratio, thereby reducing emissions. Deterioration can be prevented.

[Brief explanation of drawings]

Figure 1 is an overall block diagram for explaining the present invention in detail, Figure 2 is a single 02 sensor system and a double 02 sensor system.
Figure 3 is a graph showing the purification characteristics of the three-way catalyst; Figure 4 is a diagram explaining the present invention in detail; Figure 5 is the air-fuel ratio of the internal combustion engine according to the present invention. FIG. 6, FIG. 8, FIG. 9, FIG. 10, and FIG. 11 are flowcharts for explaining the operation of the control circuit shown in FIG. 5; FIG. is a timing diagram for supplementary explanation of the flowchart of FIG. 6, and FIG. 12 is a timing diagram for supplementary explanation of the flowchart of FIG. 11. DESCRIPTION OF SYMBOLS 1... Engine body, 2... Air flow meter, 4... Distributor, 5, 6... Crank angle sensor, 10... Control circuit, 12... Catalytic converter, 13... Upstream side 02 sensor, 15... Downstream side 02 sensor, 7... Idle switch.

Claims (1)

[Claims] 1. Three-way catalyst (12) provided in the exhaust passage of an internal combustion engine
and provided in an exhaust passage at least downstream of the three-way catalyst,
a downstream air-fuel ratio sensor (15) that detects the air-fuel ratio of the engine;
), and calculates an air-fuel ratio correction amount according to the output of the downstream air-fuel ratio sensor, and at that time, calculates a first update rate of the air-fuel ratio correction amount when the output of the downstream air-fuel ratio sensor is lean. an air-fuel ratio correction amount calculation means that makes the output of the downstream side air-fuel ratio sensor larger than a second update rate of the air-fuel ratio correction amount when the output of the downstream air-fuel ratio sensor is rich; and a deterioration degree determination means that determines the degree of deterioration of the three-way catalyst. and, as the degree of deterioration of the three-way catalyst increases, the first and second update speeds are made smaller, and at this time, the degree of decrease in the first update rate is set as the degree of decrease in the second update rate. An air-fuel ratio control device for an internal combustion engine, comprising: a larger update speed changing means; and an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the air-fuel ratio correction amount.