JPS6260942A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To secure the optimum control for catalyst by setting larger the upper limit value of the air-fuel ratio feedback control constant with high load in comparison with the case with light load. CONSTITUTION:A control constant calculating means calculates the rich skip quantity RSR and the lean skip quantity RSL according to the output V2 of the second air-fuel ratio sensor on the downstream of a catalytic converter, and a control-constant upper-limit calculating means calculates the upper limit values LU of the air-fuel ratio feedback control constants RSR and RSL according to one operation state parameter among the car speed SPD, engine revolution speed Ne, load Q/Ne, intake air quantity Q, intake pressure PM, and the throttle opening degree TA, and the upper limit value is set larger as the parameter increases. Therefore, an upper limit value guard means guards the constants RSR and RSL at the LU, and an air-fuel ratio correction quantity calculating means calculates the air-fuel ratio correction quantity fAF according to the guarded RSR and RSL. Thus, the surging of a car with light load is prevented, and the securing of the emission performance with high load can be made compatible.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides an air-fuel ratio sensor (herein, an oxygen concentration sensor (01 sensor)) 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 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 02 sensor system), the 0□ sensor that detects 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 from the catalytic converter. Due to variations in the output characteristics of the 02 sensor, it is difficult to improve the control efficiency of the air-fuel ratio. It takes 0,
In order to compensate for variations in sensor output characteristics, variations in parts such as fuel injection valves, and changes over time or aging, a second 02 sensor is provided downstream of the catalytic converter, and air-fuel ratio feedback control by the upstream 02 sensor is performed. In addition, a double 02 sensor system that performs air-fuel ratio feedback control using a downstream 02 sensor has already been proposed.

In this double 02 sensor system, although the OX sensor installed downstream of the catalytic converter has a lower response speed than the upstream Ot sensor, it has the advantage of less variation in output characteristics for the following reasons. are doing.

(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 0□ sensor system) based on the outputs of the two 0□ sensors, variations in the output characteristics of the upstream 0□ sensor can be absorbed by the downstream 0□ sensor. In fact, as shown in Figure 2, in a single 0□ sensor system, O
When the output characteristics of the t sensor deteriorate, it directly affects the exhaust emission characteristics, whereas in the double 0□ 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.

[Problem that the invention seeks to solve]

In the double 0□ sensor system described above, since the air-fuel ratio change rate is changed according to the output of the downstream 02 sensor, the degree of vehicle surging changes accordingly.

In particular, when the air-fuel ratio correction coefficient FAF is skipped, the degree of vehicle surging increases.

This is caused by torque fluctuations caused by rapid air-fuel ratio changes. For example, the skip amount R of the air-fuel ratio correction coefficient FAF
3 and the vehicle surging degree, as shown in Figure 3, the vehicle surging degree is under light load (intake air amount Q: small).
On the other hand, when the load is high (intake air amount Q: large)
The allowable vehicle surging degree Dma
The upper limit value LU of the skip amount R3 of the air-fuel ratio correction coefficient FAF at x is different. However, in general, regardless of whether the load is light or high, the skip amount R of the air-fuel ratio correction coefficient PAP is
The upper limit value LU of 3 is constant. For this reason, if we place emphasis on reducing vehicle surging and the surging degree is D when the load is low,
If the skip amount R3 upper limit value is uniformly determined so that it is less than or equal to There is a problem in that the range of change becomes relatively small, resulting in an increase in HC, Co, No, and emissions.

Note that if the air-fuel ratio change width is small, optimal control for the catalyst becomes impossible, leading to an increase in HC, Co2, and NOX emissions.

[Means for solving problems]

An object of the present invention is to provide a double air-fuel ratio sensor system that is capable of preventing vehicle surging during light loads and ensuring emission performance during high loads, and its means are shown in FIG.

In FIG. 1, first and second air-fuel ratio sensors that detect the concentration of specific components in exhaust gas are installed on the upstream and downstream sides of a catalytic converter for purifying exhaust gas, which is installed in the exhaust system of an internal combustion engine. Each is provided. The control constant calculation means calculates an air-fuel ratio feedback control constant, for example, a rich skip amount R, according to the output v2 of the downstream (second) air-fuel ratio sensor.
Calculate SR and lean skip 1iRsL. The control constant upper limit value calculation means is an air-fuel ratio feed pack control constant R3.
R, the upper limit value LU of RSL, the speed sPD of the vehicle on which the engine is mounted, the rotational speed Ne of the engine, the load Q/N e
, intake air i1Q, intake air pressure PM, and 0.2 torque valve opening TA.
Set U large. As a result, the upper limit guard means uses the air-fuel ratio feedback control constant R3R.

RSL is guarded by upper limit value LU. The air-fuel ratio correction amount calculation means uses the output of the upstream (first) air-fuel ratio sensor and the guarded air-fuel ratio feed pack control constant R3R.
, R5L, an air-fuel ratio correction amount FAF is calculated. 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]

According to the above-mentioned means, the upper limit value LU of the air-fuel ratio feedback control constants R3R and RSL is set larger during high loads than during light loads, so that the range of change in the air-fuel ratio can be increased.

〔Example〕

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

FIG. 4 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. 4, an air flow make 3 is provided in the intake passage 2 of the engine body 1. As shown in FIG. The air flow meter 3 directly measures the intake air amount, has a built-in potentiometer, and generates an analog voltage output signal proportional to the intake air amount. This output signal is supplied to an A/D converter 101 with a built-in multiplexer of the control circuit 10. The distributor 4 has a crank angle sensor 5 whose shaft generates a reference position detection pulse signal every 720 degrees in terms of crank angle, and a crank angle sensor 5 which generates a reference position detection pulse signal every 30 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 4 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 boat for each cylinder.

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

The exhaust system downstream of the exhaust manifold 11 is provided with a catalytic converter 12 that accommodates a three-way catalyst that simultaneously purifies three harmful components HC, Co, and 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 02 sensors 13 and 15 generate electrical signals corresponding to the concentration of oxygen components in the exhaust gas. That is, 02 sensor 13
, 15, the control circuit 10 outputs different output voltages depending on whether the air-fuel ratio is lean or lean 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 10 in addition to an A/D converter 101, an input/output interface 102, and a CP port 103.
4, RAM 105, bank up RAM 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 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
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 carryout terminal reaches the "1" level, the flip-flop 109 is set and the drive circuit 110 controls the fuel injection valve 7. stop the movement. In other words, the above fuel injection ITA
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.
At the end of A/D conversion of 01, input/output interface 1
When 02 receives the pulse signal of the crank angle sensor 6,
When receiving an interrupt signal from the clock generation circuit 107,
etc.

The intake air amount data Q and the cooling water temperature data TOW 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 T)lW is updated at predetermined time intervals. Also,
The rotational speed data Ne is 30° CA of the crank angle sensor 6.
It is calculated by each interrupt and stored in a predetermined area of the RAM 105.

FIG. 5 shows a first air-fuel ratio feedback control routine that calculates an air-fuel ratio correction coefficient FAF based on the output of the upstream 02 sensor 13, and is executed every predetermined time, for example, 4 ms.

In step 501, 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 521 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 502.

In step 502, the output vI of the upstream 0□ sensor 13
is A/D converted and taken in, and in step 503, it is determined whether ■1 is the comparison voltage VRI'', for example, 0.45 V or less, that is, it is determined whether the air-fuel ratio is rich or lean. Lean (V+ ≦■ 8.), the first delay counter CDLY 1 is subtracted by 1 in step 504, and the first delay counter CDL is decreased in steps 505 and 506.
Guard Y1 with the minimum value TDR1. Note that the minimum value T
DR1 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 0□ sensor 13, and is defined as a negative value. On the other hand, if rich (V r > V RI ), the first delay counter C
Add 1 to DLY 1 and set the first delay counter CDLY 1 to the maximum value TDL in steps 508 and 509.
Guard with 1. Note that the maximum value TDL 1 is 0 on the upstream side.
□ Lean delay time for maintaining the determination that the state is rich even if the output of the sensor 13 changes from rich to lean, and is defined as a positive value.

Here, the reference for the first delay counter CDLY 1 is set to O, and when CDLYI>0, the air-fuel ratio after delay processing is considered rich, and when CDLY 1≦0, the air-fuel ratio after delay processing is considered lean. shall be taken as a thing.

In the stem 510, the first delay counter CDLY
It is determined whether the sign of 1 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, it is determined in step 511 whether the reversal is from rich to lean or from lean to rich. If it is a reversal from rich to lean, step 512
In step 513, FAF is increased in a skip manner as FAF -FAF +R5R, and conversely, in case of a reversal from lean to rich, in step 513, it is decreased in a skip manner as FAF←FAF-RSL. In other words, skip processing is performed.

If the sign of the first delay counter CDLY is not inverted in step 510, steps 514 and 515
．． Integration processing is performed at 516. That is, step 514
1: Determine whether CDLY 1 < 0, CDL
If Y 1≦0 (lean), F in step 515
AF-FAF+KI, and on the other hand, CDLY 1 > O
(') っ f> T near.

If so, in step 516 FAF-FAF +KI is set. Here, the integral constant Kl is the skip constant RSR, RSL
is set sufficiently small compared to Kl <
I? 5R (RSL). Therefore, step 515 gradually increases the fuel injection amount in the lean state (CDLY 1≦0), and step 516 gradually increases the fuel injection amount in the rich state (CDLY 1≦0).
l > 0), the fuel injection amount is gradually decreased.

The air-fuel ratio correction coefficient FAF calculated in steps 512, 513, 515, and 516 is calculated in steps 517 and '51.
8 is guarded at a minimum value, for example 0.8, and is also guarded at step 519 . At 520, it is guarded at a maximum value of 1.2, for example. 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 in step 522.

Note that step 521 in FIG. 5 can be omitted, and in this case, the value immediately before the air-fuel ratio feedback control jBH is used as the FAF.

FIG. 6 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. Upstream side 0. When the air-fuel ratio signal A/Fl for sochi/lean determination is obtained from the output of the sensor 13 as shown in FIG. 6(A), the first delay counter CDLY 1 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, a delayed air-fuel ratio signal A/Fl' is formed as shown in FIG. 6(C). For example, time t
, even if the air-fuel ratio signal A/F1 changes from lean to rich at time t2, the delayed air-fuel ratio signal A/Fl' remains lean for the rich delay time (-1TDRI) and then changes from lean to rich at time t2. Changes to rich. Even if the air-fuel ratio signal A/Fl changes from rich to lean at time t3, the delayed air-fuel ratio signal A/F 1' remains within the lean delay time TD.
After being held rich by Ll, it changes to lean at time t4. However, is the air-fuel ratio signal A/F 1 at time t5+t6+j? Rich delay time (-TDPI
), it takes time for the first delay counter CDLY 1 to cross the reference value 0, and as a result, the air-fuel ratio signal A/F after the delay processing at time tlI.
l' is inverted. In other words, the air-fuel ratio signal A after the delay processing
/Fl' is more stable than the air-fuel ratio signal A/Fl before the delay process. In this way, the air-fuel ratio correction coefficient FAF 1 shown in FIG. 6(D) is obtained based on the stable air-fuel ratio signal A/Fl' 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 R5R, R3L and delay time T as first air-fuel ratio feedback control constants.
DR1, TDL 1, integral constant! , (in this case, the rich integral constant KIIR and the lean integral constant ILL are set separately), or the output V of the upstream Oz sensor 13.
There is a system that introduces a ρ air-fuel ratio correction coefficient FAF2.

For example, if the rich skip amount RSR 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 RSL 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 R5R is reduced, the controlled air-fuel ratio can be shifted to the lean side. Therefore, the rich skip amount [? SR and Lean Skip (JR
The air-fuel ratio can be controlled by correcting 5L. Also,
Rich delay time (-TDRI) > Lean delay time (T
DLI), the controlled air-fuel ratio can be shifted to the rich side, and conversely, if the lean delay time (TDLI) > rich delay time (-TDPI) is set, 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 TDR1 and TDL1 according to the output of the downstream 0□ sensor 15. Furthermore, by increasing the rich integral constant KIIR, the control air-fuel ratio can be shifted to the rich side, and even by decreasing the lean integral constant KILL, the control air-fuel ratio can be shifted to the rich side. (Then, the controlled air-fuel ratio can be shifted to the lean side, and even if the rich integral constant KIIR is made smaller, the controlled air-fuel ratio can be shifted to the lean side. Therefore, the rich The air-fuel ratio can be controlled by correcting the integral constant KIIR and the lean integral constant KIIL.Furthermore, the comparison voltage ■
By increasing □, the controlled air-fuel ratio can be shifted to the rich side, and by decreasing the comparison voltages v and Il, the controlled air-fuel ratio can be shifted to the lean side. Therefore, by correcting the comparison voltage Vll+ according to the output of the downstream O2 sensor 15, the air-fuel ratio can be controlled.

A double 02 sensor system in which the skip amount as an air-fuel ratio feedback control constant is made variable will be described with reference to FIGS. 7 and 8.

FIG. 7 shows a second air-fuel ratio feedback control routine that calculates the skip amounts RSR and RSL based on the output of the downstream 0□ sensor 15, and is executed every predetermined period of time, for example, every 1 second. In step 701, it is determined whether the downstream side 02 sensor 15 has a closed loop condition. for example,
The closed loop condition is not satisfied when the cooling water temperature is below a predetermined value, when the output signal of the downstream 02 sensor 15 never inverts, when the downstream 0□ sensor 15 is malfunctioning, or during transient operation. , the closed loop condition is satisfied in other cases. If it is not a closed loop condition, proceed to steps 728 and 729 and skip @RSR, RSL to a constant value RSR,.

Let it be R5LO. For example, RS Ro = 5% R3Lo = 5%. Note that steps 728 and 729 can also be deleted. In this case, the value immediately before the end of the air-fuel ratio feedback control is used.

If the loop is closed, the process advances to step 702 and the downstream Ot
The output ■2 of the sensor 15 is A/D converted and taken in, and in step 703 v2 is the comparison voltage V, l□For example, 0.55
It is determined whether the air-fuel ratio is below V, that is, it is determined whether the air-fuel ratio is rich or lean. Note that the comparison voltage VB is set higher than the comparison voltage V□ 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 the upstream and downstream of the catalytic converter 14. be done.

If lean (VZ≦vo), the second delay counter CDLY 2 is subtracted by 1 in step 704, and the second delay counter CDLY 2 is decreased by 1 in steps 705 and 706.
Guard LY 2 with minimum value TDR2. Note that the minimum value TDR2 is a rich delay time for maintaining the lean state even if there is a change from lean to rich≠, and is defined as a negative value. On the other hand, if it is rich (VZ>vR□), the second delay counter CDL is set in step 707.
Y 2 is added by 1, and the second
The delay counter CDLY2 of is guarded at the maximum value TDL2. Note that the maximum value TDL 2 is the lubricant for maintaining the rich state even if there is a change from rich to lean.
delay time, defined as a positive value.

Here again, the reference for the second delay counter CDLY 2 is O, and when CDLY 2 > O, the air-fuel ratio after the delay process is considered rich, and when CDLY 2 ≦ 0, the air-fuel ratio after the delay process is considered lean. shall be deemed.

In step 710, the intake air amount data Q is read from the RAM 105, and it is determined whether Q>Q.
1, it is determined whether Q>Q2. In addition, Ql > Q
, for example, Ql = 20 m'/h.

Qz = 80 m'/h. As a result, Q≦
Q.

If so, skip -11RsR in step 712.

The upper limit value LU of RSL is set to 4%, and if Q<Q≦Q2, LU is set to 6% in step 713, and if Q≧02, LU is set to 8% in step 714. In this way, the larger the parameter Q, the more skip 1R5R,
Set the upper limit value LU of RSL to be large. In addition, the upper limit L
U may be obtained as a value that changes continuously by interpolation calculation, or it may be calculated according to vehicle speed SPD, rotational speed Ne, load Q/Ne, and throttle valve opening TA instead of intake air i1Q. Alternatively, interpolation calculation may be performed using a map based on two or more of these operating state parameters.

In step 715, the second delay counter CDLY2
It is determined whether or not CDLY 2≦0, and as a result, CDLY
If LY2≦0, the air-fuel ratio is determined to be lean and the process proceeds to steps 716 to 721; on the other hand, if CDLY2>0
If so, the air-fuel ratio is determined to be rich and steps 722~
Proceed to 727.

In step 716, i? 5R-RSR+ΔR5 (constant value, for example, 0.08%), that is, rich skip fiRSR is increased to shift the air-fuel ratio to the rich side. In steps 717 and 718, the RSR is guarded at the upper limit value LU. Further, in step 719, RSL-
RSL - ΔRS, that is, rich skip IRSL
to shift the air-fuel ratio to the rich side. For chips 720 and 721, set the RSL to the lower limit, for example 2.5.
Guard with %.

On the other hand, when it is rich (V2 > VRZ), the air-fuel ratio is set to RSR-RSR-ΔRS in step 722, that is, the rich skip 1RsR is decreased to shift the air-fuel ratio to the lean side. In steps 723 and 724, the RSR is guarded at a lower limit of 2.5%. Further, in step 725, RSL-RSL+ΔR5 (constant value) is set, that is, the lean skip IR5L is increased to shift the air-fuel ratio to the lean side. In steps 726 and 727, the RSL is guarded at the upper limit value LU.

RSR and RSL calculated as described above are stored in RAM 10.
5, the routine ends at step 730.

Note that FAF calculated during air-fuel ratio feedback,
I? SR, RSL are temporarily changed to other values FAF', RSR
', RSR' and backup RAM 106
This also helps improve drivability during restarts, etc. The lower limit value of 2.5% in FIG. 7 is a level at which the transient followability is not impaired.

As described above, according to the routine shown in FIG. 7, if the output of the downstream side 02 sensor 15 is lean, the rich skip II
RsR is gradually increased - and lean skip 1lR
5L is gradually decreased, thereby shifting the air-fuel ratio to the rich side. Further, if the output of the downstream 0□ sensor 15 is rich, the rich skip amount R5R is gradually decreased, and the lean skip 11RsL is gradually increased,
As a result, the air-fuel ratio is shifted to the lean side.

FIG. 8 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360° CA. step 80
1, the intake air amount data Q and rotational speed data Ne are read out from the RAM 105 to calculate the basic injection amount TAUP. For example, TAUP-K Q/ Ne (K is a constant)
shall be. At step 802, 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 803, the final injection amount TAU is determined as TAU −TAUP −FAF ・(FWL+α)+
Calculate by β. Note that α and β are correction amounts determined by other operating state parameters. Then step 8
At step 04, the injection NTAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. The routine then ends at step 805.

As described above, when the time corresponding to the injection 1TAll has elapsed, the flip-flop 109 is reset by the carrier signal of the down counter 108, and the fuel injection ends.

Note that the first air-fuel ratio feedback control is performed every 4 ms.
In addition, the second air-fuel ratio feedback control is performed every 1 second, because the air-fuel ratio feedback control is mainly performed by the upstream 02 sensor, which has good responsiveness, and controls by the downstream 02 sensor, which has poor responsiveness. This is for the purpose of doing so.

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 0□ sensor system that introduces a second air-fuel ratio correction factor. 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 R5R and R5L and make only the other variable, which is the delay time TDRI.

It is also possible to fix one of TDL 1 and make only the other variable, or to use the Ricci integral constant KII? It is also possible to fix one of the lean integral constants KIL and make 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 capretor 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 carburetor itself, that is, it is determined according to the intake pipe negative pressure according to the intake air amount and the engine rotation speed. Then, in step 803, the amount of supplied air corresponding to 1 TAU of final fuel injection 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, the upper limit value LU of the air-fuel ratio feedback control constants, for example, R3R and RSL, is set larger at high loads than at light loads, so that the range of change in the air-fuel ratio is relatively controlled. Therefore, optimal control of the catalyst is possible, and HC, C○, NOx
Emissions can be reduced.

[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 double 0□
Fig. 3 is a graph showing the relationship between the air-fuel ratio feedback control constant and the vehicle surging degree; Fig. 4 shows an embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention. 5, 7, and 8 are flowcharts for explaining the operation of the control circuit in FIG. 3, and FIG. 6 is a flowchart for explaining the operation of the control circuit in FIG.
FIG. 4 is a timing chart for supplementary explanation of the chart. 1... Engine body, 3... Air flow meter,
4...Distributor, 5.6...Crank angle sensor, 10...Control circuit, 12...Catalytic converter,
13... Upstream side (first) 0□ sensor, 15... Downstream side (second) O2 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; control constant calculation means for calculating an air-fuel ratio feedback control constant according to an output of the second air-fuel ratio sensor; the speed of the vehicle, the rotational speed of the engine, the load,
control constant upper limit value calculation means that calculates according to any one of operating state parameters such as intake air amount, intake air pressure, and throttle valve opening, and sets the upper limit value to be larger as the operating state parameter becomes larger; and the air-fuel ratio. upper limit value guarding means for guarding a feedback control constant by the upper limit value; and air-fuel ratio correction amount calculation for calculating an air-fuel ratio correction amount according to the output of the first air-fuel ratio sensor and the guarded air-fuel ratio feedback control constant. and an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the air-fuel ratio correction amount.