JPS63205442A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent degradation of emission by stopping operation of air-fuel ratio correction quantity based on an output from one air-fuel ratio sensor arranged in the downstream of a catalyst converter when the air-fuel ratio correction quantity reaches to predetermined allowable width. CONSTITUTION:First and second air-fuel ratio sensors A1, A2 for detecting concentration of specific component in exhaust gas are arranged at the opposite sides of a catalyst converter. Means B for operating air-fuel ratio correction quantity corresponding to outputs from respective air-fuel ratio sensors A1, A2 is provided. Furthermore, means C for guarding an operated air-fuel ratio correction quantity with a predetermined allowable width and means D for regulating air-fuel ratio of engine corresponding to the air-fuel ratio correction quantity are provided. Means E for judging whether the air-fuel ratio correction quantity has reached to the predetermined allowable width and means F for stopping operation of air-fuel ratio correction quantity based on an output from the second air-fuel ratio sensor A2 according to the result of the judging means E are provided.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides air-fuel ratio sensors (herein, oxygen concentration sensors (02 sensors)) on the upstream and downstream sides of a catalytic converter.
), and relates to an air-fuel ratio control device for an internal combustion engine that performs air-fuel ratio feedback control using a downstream 02 sensor in addition to air-fuel ratio feedback control using an upstream 02 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 0□ sensor, it is difficult to improve the control accuracy of the air-fuel ratio. It takes 02
In order to compensate for variations in sensor output characteristics, variations in parts such as fuel injection valves, and changes over time or aging, a second 0□ sensor is installed downstream of the catalytic converter, and a second 0□ sensor is installed downstream of the catalytic converter. A double O2 sensor system has already been proposed that performs air-fuel ratio feedback control using a downstream O2 sensor in addition to air-fuel ratio feedback control using a downstream O2 sensor.
. In this double O2 sensor system, although the O2 sensor installed downstream of the catalytic converter has a lower response speed than the upstream 0□ sensor, it has the advantage of having smaller variations 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 O2 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, the air-fuel ratio feedback control (double 02 sensor system) based on the outputs of the two 0□ sensors allows the downstream 02 sensor to absorb variations in the output characteristics of the upstream 0□ sensor. In fact, as shown in Figure 2, in the single 02 sensor system, 0□
When the sensor output characteristics deteriorate, it directly affects the exhaust emission characteristics, whereas in the double 0□ sensor system, even if the output characteristics of the upstream 0□ sensor deteriorate, the exhaust emission characteristics do not deteriorate. In other words, double 0□
In the sensor system, good exhaust emissions are guaranteed as long as the downstream 0□ sensor maintains stable output characteristics.

In the double 0□ sensor system described above, the downstream 0
□While the air-fuel ratio feedback control is being executed by the sensor, based on the output of the upstream 0□ sensor (control constants for the air-fuel ratio correction amount FAF, for example, rich skip amount R3R, lean skip amount R3L), the downstream 0□ sensor There is a system that performs variable control based on the output of the downstream 0□ sensor, but when the variable control of the control constant by the output of the downstream 0□ sensor is stopped due to inactivity of the downstream 0□ sensor, etc. Air-fuel ratio feedback control was performed using only the output of the upstream 0□ sensor using the values stored in the bank-up RAM (see Japanese Patent Application Laid-Open No. 1983-1999).
-192828 a). In a system that variably controls control constants, upper and lower limits are set to ensure that transient followability is not impaired and that drivability is not deteriorated due to air-fuel ratio fluctuations. Control constants are subjected to guard processing (see Japanese Patent Laid-Open No. 61-234241).

[Problem that the invention seeks to solve]

However, for example, in an internal combustion engine equipped with a fuel vapor exhaust prevention device, if the temperature in the fuel tank is high and a large amount of vapor is generated from the fuel in the fuel tank, the vapor in the tank will be removed by the purge system. It passes through the canister and is drawn into the combustion chamber, resulting in a very rich air-fuel ratio. If this state continues, the air-fuel ratio correction amount FAF based on the output of the upstream 0□ sensor will be corrected to the lean side, and will stick to the lower limit value provided to prevent overleaning. Moreover, in this case, the air-fuel ratio cannot be completely corrected by the air-fuel ratio correction amount FAF alone, and
Control constant R5R based on sensor.

R5L will also be overcorrected to the lean side. After the engine is stopped in such a state, when the engine is brought back to a near-steady running state, the air-fuel ratio correction amount FAF is adjusted using the control constants R5R and R3L, which are stored in the backup RAM and are overcorrected toward the lean side. is calculated, the air-fuel ratio correction amount F
The rate of increase in AF is small, and since the fuel temperature in the tank decreases due to the engine stop and there is little steam, the downstream 02 sensor maintains a lean output for a while, and the NO
This has caused problems such as an increase in x emissions and deterioration of drivability.

In this way, if the air-fuel ratio correction amount FAF based on the upstream 02 sensor output is guarded to the lower limit value due to some factor, the air-fuel ratio of the upstream 02 sensor output that is original to the double 02 sensor system There is a problem that the function of detecting the deviation in the average air-fuel ratio due to the feedback result and controlling it to the desired air-fuel ratio cannot be achieved, and
As mentioned above, when the air-fuel ratio leans toward the lean or rich side,
Furthermore, if the downstream 0□ sensor output is determined to have been activated upon reversal of the output from lean to rich or rich to lean, and the air-fuel ratio feedback based on the output of the downstream 0□ sensor is started, the feedback is started. There is also the problem of delays.

[Means for solving problems]

A means for solving the above-mentioned problems is shown in FIG. In FIG. 1, first and second air-fuel ratio sensors for detecting the concentration of specific components in exhaust gas are provided on the upstream side of a catalytic converter for exhaust gas purification, which are provided in the exhaust system of an internal combustion engine;
Each is provided on the downstream side. The air-fuel ratio correction amount calculation means calculates the air-fuel ratio correction amount FAF according to the output (1) of the upstream (first) air-fuel ratio sensor and the output (2) of the downstream (second) air-fuel ratio sensor. The guard means adjusts the calculated air-fuel ratio correction amount FAF to a predetermined tolerance range, for example, 1.2.
~0.8, and the air-fuel ratio adjustment means adjusts the air-fuel ratio correction amount F.
Adjust the air-fuel ratio of the engine according to AF. On the other hand, the permissible width reaching determination means determines whether the air-fuel ratio correction amount FAF has reached the predetermined permissible width, and as a result, the air-fuel ratio correction amount FA
When F reaches a predetermined allowable range, the stopping means stops the calculation of the air-fuel ratio correction amount based on the output v2 of the downstream air-fuel ratio sensor.

[For production]

According to the above-mentioned means, when the air-fuel ratio correction amount FAF reaches its permissible range, the air-fuel ratio feedback control by the downstream air-fuel ratio sensor is stopped.

〔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 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 5.6 are supplied to the input/output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is
It is supplied to the interrupt terminal of a.

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.

A catalytic converter 12 that accommodates a three-way catalyst that simultaneously purifies three harmful components HC, GO, and NOx in exhaust gas is provided in the exhaust system downstream of the exhaust manifold 11.

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, 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 wholesale circuit 10 is configured as a microcomputer, for example, and includes an A/D converter 101, a human output interface 102, a CPU 103, and an RO old 04°RA.
l'1105, a backup RAM 106, a clock generation circuit 107, etc. are provided.

In addition, in the control wholesale circuit 10, a down counter 108
, flip-flop 109, and drive circuit 110 are for controlling the 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 carrier terminal becomes "L" level, the flip-flop 109 is set and the drive circuit 110 controls the fuel injection valve 7. Stop biasing. In other words, the above fuel injection amount TA
The fuel injection valve 7 is energized by U, and therefore the fuel injection amount T
An amount of fuel corresponding to the AU is sent to the combustion chamber of the engine body 1.

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

The intake air amount data Q and cooling water temperature data THW of the air flow meter 3 are taken in by an A/D conversion routine executed at predetermined time intervals and stored in a predetermined area of the RAM 105. That is, data Q and THW in RAM 105 are updated at predetermined time intervals. Further, the rotational speed data Ne is calculated by the interruption of the crank angle sensor 6 every 30 degrees, and is stored in a predetermined area of the RAM 105.

The operation of the control circuit shown in FIG. 3 will be explained below.

FIG. 4 shows a first air-fuel ratio feed hack 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 401, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the upstream 0□ sensor 13 is satisfied. For example, if the cooling water temperature is a predetermined value of 60°C
In the following cases, the closed loop condition is not satisfied when the engine is starting, when the engine is running after starting, when the power is increasing during warm-up, when the power is increasing, when the output VI of the upstream 02 sensor 13 has never been reversed, when the fuel is cut, etc. In other cases, the closed loop condition is satisfied.

If the closed loop condition does not hold, directly step 429
Proceed to. That is, in this case, FAF is set to the value immediately before the end of the closed loop control. 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
is A/D converted and fetched, and in step 403, it is determined whether or not the comparison voltage VRI, for example, 0.45V or less, is determined.In other words, it is determined whether the air-fuel ratio is rich or lean.In other words, whether the air-fuel ratio is rich or not. or lean (Vl ≦V RI ), the delay counter CDLY is set in step 404.
Determine if is positive or not, and if CDLY>0, step 4
In step 05, CDLY is set to 0, and the process proceeds to step 406. In step 406, the delay counter CDLY is decremented by 1, and in steps 407 and 408, the delay counter CDLY is
Guard LY with minimum value TDL.

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 409. In addition, the minimum value TD
L is a lean delay time for maintaining the determination that the rich state is present even if the output of the upstream 02 sensor 13 changes from rich to lean, and is defined as a negative value. On the other hand, if it is rich (Vl > VRI), it is determined in step 410 whether the delay counter CDLY is negative or not, and if CDLY <0, it is determined in step 411 that the delay counter CDLY is negative or not.
Set DLY to 0 and proceed to step 412. Step 41
In step 2, the delay counter CDLY is incremented by 1, and in steps 413 and 414, the delay counter CDLY is guarded at 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) 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 the output of the upstream 0□ sensor 13 changes from lean to rich, 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, and it is determined whether the air-fuel ratio after the delay processing has been inverted. If the air-fuel ratio is reversed, in step 417, it is determined whether the reversal is from rich to lean or from lean to rich, based on the value of the first air-fuel ratio flag F1. If it is a reversal from rich to lean, in step 418, pick up RAM10.
Read the rich skip amount R3R from 6 and set it to FAF-FA.
On the contrary, if it is a reversal from lean to rich, the lean skip amount R3L is read from the backup RAM 106 in step 419 and is decreased in a skip manner to FAF 4 - FAF = R5L. In other words, skip processing is performed.

If the sign of the first air-fuel ratio flag F1 is not inverted in step 412, steps 420, 421, 42
Integration processing is performed in step 2. That is, at step 420,
Determine whether Fl-“0” or not, and if Fl-“0” (lean), FAF-FAF +K at step 421
IR, and if F1="1" (rich), FAF-FAF+KIL is set in step 622.

Here, the integral constants KIR and KIL are the skip constants R5R
, R3L, that is, K
IR(KIL)<R3R(R3L). Therefore,
Step 421 gradually increases the fuel injection amount in a lean state (Fl-“0”), and step 422 gradually increases the fuel injection amount in a rich state B (
Fl-“1”) to gradually reduce the fuel injection amount.

The air-fuel ratio correction coefficient FAF calculated in steps 418, 419, 421, and 422 is guarded at a minimum value, for example, 0.8, in steps 423 and 424. In this case, F
When the AF reaches the minimum value of 0.8, step 42
5, the air-fuel ratio feedback execution flag FB by the downstream 0□ sensor 15 is set to "0", and at other times, FB-
Set to “1”. Also, in steps 427 and 428, it is guarded at a maximum value, for example, 1.2. 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 429.

Figure 5 shows the operation according to flowchart 1 in Figure 4.
! It is a timing chart for supplementary explanation. The output of the upstream 0□sensor 3 makes it rich as shown in Fig. 5 (A).
When the air-fuel ratio signal A/F for lean determination is obtained, the delay counter CDLY is counted up in the rich state and counted down in the lean state, as shown in FIG. 5(B). As a result, as shown in FIG. 5(C), the delayed air-fuel ratio signal A/F' (corresponding to flag F1)
is formed. For example, at time t, the air-fuel ratio signal A/
Even if F changes from lean to rich, the delayed air-fuel ratio signal A/F' changes to rich at time t2 after being held lean for the rich delay time TDR. Even if the air-fuel ratio signal A/F changes from rich to lean at time t, the delayed air-fuel ratio signal A/F' is held rich for an amount equivalent to the lean delay time (-TDL), and then returns to time t4. Changes to lean. However, the air-fuel ratio signal A/
F is the rich delay time T as time tS+j+++t7
If it reverses in a period shorter than DR, the delay counter CD
It takes time for LY to reach the maximum value TDR, and as a result, the air-fuel ratio signal A/F' after the delay process is inverted at time t8. In other words, the air-fuel ratio signal A/F after the delay processing
' is more stable than the air-fuel ratio signal A/F before the delay processing. In this way, stable air-fuel ratio signal A/F after delay processing
Based on ', the air-fuel ratio correction coefficient FA shown in Figure 5 (D)
F is obtained.

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 as the first air-fuel ratio feedback control constants, and an integral constant K.
There is a system in which the IR, KIL % delay time TDR, TDL or the comparison voltage VRI 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 amount R3R is increased, the controlled air-fuel ratio can be shifted to the rich side, and even if the lean skip i RS L is decreased, the controlled air-fuel ratio can be shifted to the rich side, and on the other hand, if the lean skip 1R3L is increased, , the controlled air-fuel ratio can be shifted to the lean side, and even if the rich skip amount R3R is made small, the controlled air-fuel ratio can be shifted to the lean side.

Therefore, the air-fuel ratio can be controlled by correcting the rich skip amount R3R and the lean skip amount R3L according to the output of the downstream 02 sensor 15.

In addition, by increasing the rich integral constant KIR, the control air-fuel ratio can be shifted to the rich side, and the lean integral constant KIL
On the other hand, increasing the lean integral constant KIL allows the controlled air-fuel ratio to be shifted to the lean side, and even if the rich integral constant KTR 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 (-TDL)>>
By setting the 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, if the comparison voltage V B 1 is increased, the control air-fuel ratio can be shifted to the rich side, and the comparison voltage VRI
By decreasing , the control air-fuel ratio can be shifted to the lean side. Therefore, depending on the output of the downstream 0□ sensor 15, the comparison voltage V
The air-fuel ratio can be controlled by correcting Rl.

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

FIG. 6 shows a second air-fuel ratio feedback control routine that calculates skip amounts R5R and R3L based on the output of the downstream 0□ sensor 15, and is executed for a predetermined period of time, for example, every IS. In step 601, it is determined whether the downstream 0□ sensor 15 is in a closed loop condition. for example,
When the cooling water temperature is below a predetermined value, for example 70°C, the downstream side is 0.
□When the output signal of the sensor 15 never inverts, when the downstream 0□sensor 15 is out of order, during transient operation, on-idle (LL-“1”), etc., the closed loop condition is not satisfied. , the closed loop condition is satisfied in other cases. If the condition is not a closed loop condition, the process directly advances to step 617.

In this case, R3R and R3 are set as values immediately before the end of closed loop control (values in the backup RAM).

If the loop is closed, the process proceeds to step 602, where it is determined whether the air-fuel ratio feedback control execution flag FB is "1". That is, it is determined whether FAF has reached the minimum value of 0.8. If FAF has reached the minimum value of 0.8 (F
B-“0”), the process also proceeds to step 617, and the skip amounts R3R and R3L are not updated. On the other hand, if FAF has reached the minimum value of 0.8, the process proceeds to step 603. In step 603, the output ■2 of the downstream 0□ sensor 15 is set to A
/D conversion is carried out, and it is determined whether V, ≦VRZ (lean).

Note that the comparison voltage ■3□ is, for example, 0.55V. As a result, if ■2≦■8□ (lean), step 60
Proceed to 5-610, and on the other hand, VZ > VH2 (rich)
If so, proceed to steps 611-616.

In step 605, the rich skip amount R3R is read from the bank up RAM 106 and R3R-R5R+ΔR
3, that is, the rich skip amount R3R is increased to shift the air-fuel ratio to the rich side. Steps 606, 60
7 Te guards R3R at the maximum value MAX, for example 7.5%. Furthermore, in step 608, the lean skip amount R3L is read from the backup RAM 106 and R3L is read out from the backup RAM 106.
5L 4-R5L-ΔR5, that is, the lean skip amount R3L is decreased to shift the air-fuel ratio to the rich side. In steps 609 and 610, R3 is set to the minimum value MIN.
For example, guard at 2.5%.

On the other hand, when VZ>VR□ (rich) in step 604, the backup RAM 106 is
Read the rich skip amount R8R from R3R-R5R.
-ΔR3, that is, the rich skip amount R3R is decreased to shift the air-fuel ratio to the lean side. Step 612
, 613, R3R is guarded at the minimum value MIN.

Furthermore, in step 614, the Pasokua Tsubu RAM 10
Read the lean skip amount R3L from 6 and set R3 upper - R5
L-ΔR3, that is, the lean skip amount R3L is increased to shift the air-fuel ratio to the lean side. Step 61
5,616, guard R3 with the minimum value MAX.

After R3R and R3L calculated as described above are stored in the backup RAM 106, this routine ends in step 617.

Note that the minimum value MIN in FIG. 6 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.

In this way, when the air-fuel ratio correction coefficient FAF reaches its minimum allowable range of 0.8, the air-fuel ratio feedback control by the downstream O2 sensor 15 is stopped.

FIG. 7 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360'' CA.Step 70
1, the basic injection amount TAUP is calculated by reading the intake air amount data Q and the rotational speed data Ne from the RAM 105. For example, assume that TAUP←α·Q/Ne (α is a constant). In step 702, 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 703, the final injection amount TAU is set to TAU 4-TAU
Calculate by P −FAF ・(FWL+β+1)+T. Note that β and T are correction amounts determined by other operating state parameters. Next, in step 704, the injection amount TAU is entered in the down counter 108, and the flip-flop 109 is set to start fuel injection. The routine then ends at step 705. As described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the carrier signal of the down counter 108, and the fuel injection ends.

In addition, the first air-fuel ratio feedback control is performed every 4 hours, and the second air-fuel ratio feedbank control is performed every IS, because the air-fuel ratio feedback control is controlled by the upstream O2 sensor, which has good responsiveness. This is because the control is performed primarily by the downstream O2 sensor, which has poor responsiveness.

Furthermore, a double 0□ sensor system 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 O2 sensor also includes a double 0□ sensor system. The present invention can also be applied to a double 02 sensor system that introduces an air-fuel ratio correction factor of 2. 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 results in a delay time TDR.

It is also possible to fix one of TDL and make only the other variable, or to change the lean integral constant KIR, lean integral constant K
It is also possible to have one of the ILs 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 link bleed air control valve adjusts the amount of air bleed from the carburetor to control the main system passage. The present invention can also be applied to systems that control the air-fuel ratio by introducing atmospheric air into the slow system passage, systems that adjust the amount of secondary air sent to the exhaust system of an engine, and the like. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 701 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 703, the supplied air amount corresponding to the final fuel injection amount TAU is calculated.

Further, in the above embodiment, a 0□ sensor was used as the air-fuel ratio sensor, but a CO sensor, a lean mixture sensor, etc. may also be used.

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

〔Effect of the invention〕

As explained above, according to the present invention, the air-fuel ratio correction amount based on the upstream air-fuel ratio sensor output is guarded within the permissible range, resulting in deterioration of emissions and drivability when the double air-fuel ratio sensor system cannot perform its original function. can be prevented.

[Brief explanation of the drawing]

Figure 1 is an overall block diagram for explaining the present invention in detail, Figure 2 is a single 0□ sensor system and a double 02 sensor system.
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; Figs. 4, 6, and 7 are Fig. 3; FIG. 5 is a timing diagram for supplementary explanation of the flowchart in FIG. 4. DESCRIPTION OF SYMBOLS 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) 0□ sensor.

Claims (1)

[Scope of Claims] 1. A first catalytic converter installed on the upstream side and downstream side of a catalytic converter for purifying exhaust gas provided in the exhaust system of an internal combustion engine, and configured to detect the concentration of a specific component in the exhaust gas. a second air-fuel ratio sensor; an air-fuel ratio correction amount calculation means for calculating an air-fuel ratio correction amount according to the outputs of the first and second air-fuel ratio sensors; a guard means for guarding based on a width; an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the air-fuel ratio correction amount; and determining whether the air-fuel ratio correction amount has reached the predetermined allowable width. an internal combustion engine comprising: a determination means for determining whether the air-fuel ratio correction amount has reached the predetermined allowable width; and a stop means for stopping the calculation of the air-fuel ratio correction amount based on the output of the second air-fuel ratio sensor when the air-fuel ratio correction amount reaches the predetermined allowable width. Engine air-fuel ratio control device.