JP2518252B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention provides an air-fuel ratio sensor (in this specification, an oxygen concentration sensor (O ₂ sensor)) on the upstream and downstream sides of a catalytic converter. O ₂ relates to an air-fuel ratio control apparatus for an internal combustion engine which performs air-fuel ratio feedback control by the O ₂ sensor downstream in addition to the air-fuel ratio feedback control by the sensor.

[Conventional technology]

In simple air-fuel ratio feedback control (single O ₂ sensor system), an O ₂ sensor that detects oxygen concentration is provided in the exhaust system as close as possible to the combustion chamber, that is, at the exhaust manifold upstream of the catalytic converter. In addition, the variation in the output characteristics of the O ₂ sensor hinders the improvement of the air-fuel ratio control accuracy. Such O ₂ component variation variation and the fuel injection valve and the output characteristics of the sensor, to compensate for time or secular change, a second O ₂ sensor disposed downstream of the catalytic converter, by the upstream O ₂ sensor Downstream O ₂ in addition to air-fuel ratio feedback control
Double O ₂ with air-fuel ratio feedback control by sensor
Sensor systems have already been proposed (see:
-48756 publication). In this double O ₂ sensor system,
O ₂ sensor provided downstream of the catalytic converter, compared with the upstream O ₂ sensor, but has a low response speed,
There is an advantage that the variation in output characteristics is small for the following reasons.

(1) Since the exhaust gas temperature is low downstream of the catalytic converter, there is little thermal effect.

(2) Downstream of the catalytic converter, various poisons are trapped in the catalyst, so that the amount of poisoning of the downstream O ₂ 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 the equilibrium state.

Therefore, as described above, the air-fuel ratio feedback control based on the outputs of the two O ₂ sensors (double O ₂ sensor system), the variations in the output characteristic of the upstream O ₂ sensor can be absorbed by the downstream O ₂ sensor. In fact, as shown in FIG. 2, when the output characteristics of the O ₂ sensor deteriorate in the single O ₂ sensor system, the exhaust emission characteristics are directly affected, whereas in the double O ₂ sensor system, the upstream side Even if the output characteristics of the O ₂ sensor deteriorate, the exhaust emission characteristics do not deteriorate. That is, in the double O ₂ sensor system, good exhaust emissions are guaranteed as long as the downstream O ₂ sensor maintains stable output characteristics.

In the double O ₂ sensor system described above, the downstream O ₂
In the air-fuel ratio feedback control execution by the sensor, the air-fuel ratio correction amount FAF based on the output of the upstream O ₂ sensor
Control constants for example the rich skip amount RSR, there is a system for variably controlled based lean skip amount RSL in the output of the downstream O ₂ sensor, by the output of the downstream O ₂ sensor by inactivation or the like of the downstream O ₂ sensor When stopping the variable control of the control constant, the upstream O is used by using the value stored in the backup RAM when the control constant is variably controlled.
_The air-fuel ratio feedback control was performed only by the outputs of the _two sensors (see JP-A-61-192828). Further, in a system in which the control constant is variably controlled, an upper limit value and a lower limit value are set so that transient followability is not impaired and drivability is not deteriorated due to air-fuel ratio fluctuations. The constant is guarded (see Japanese Patent Laid-Open No. 61-234241).

[Problems to be solved by the invention]

However, for example, in an internal combustion engine equipped with a fuel vapor emission prevention device, when 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 is purged by the purge system. It is drawn into the combustion chamber through the canister, and thus the air-fuel ratio becomes very rich. If the condition persists, the air-fuel ratio correction amount FAF based on the output of the upstream O ₂ sensor is corrected to the lean side,
It will stick to the lower limit provided for the prevention of Ovaleen. Moreover, in this case, the air-fuel ratio cannot be corrected only by the air-fuel ratio correction amount FAF, and the control constants RSR and RSL based on the downstream O ₂ sensor are also overcorrected to the lean side. After the engine was stopped in this state,
When the vehicle is brought into a nearly steady running state again, the backup RAM
Over-corrected control constant RSR on the lean side stored in
Since the air-fuel ratio adjustment amount FAF is calculated using RSL, the rate of increase of the air-fuel ratio adjustment amount FAF is small, and moreover, the fuel temperature in the tank drops due to engine stoppage and the amount of steam is small, so the downstream side O _{The 2} sensor has a problem that it keeps the lean output for a while and causes increase of NO _X emission and deterioration of drivability.

In this way, if the air-fuel ratio correction amount FAF based on the upstream O ₂ sensor output is tolerated and the lower limit value is recorded for some reason, the double O ₂ sensor system's original upstream O ₂ sensor output There is a problem that the function of controlling the desired air-fuel ratio by detecting the deviation of the average air-fuel ratio due to the air-fuel ratio feedback result cannot be exhibited, and as described above, if the air-fuel ratio is leaner or richer, it is further downstream. Side O ₂ sensor output is judged to have been activated by lean-to-rich or rich-to-lean output reversal, and downstream O ₂
In the case of starting the air-fuel ratio feedback based on the output of the sensor, there is a problem that the start of the feedback is delayed.

[Means for solving problems]

The means for solving the above problem is shown in FIG. In FIG. 1, first and second air-fuel ratio sensors for detecting a specific component concentration in exhaust gas are provided on the upstream side and the downstream side of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine. Each is provided. Air-fuel ratio correction amount calculating means for calculating an air-fuel ratio correction amount FAF according to the output V ₂ of the upstream (first) air-fuel ratio output V ₁ and downstream of the sensor (second) air-fuel ratio sensor. The guard means guards the calculated air-fuel ratio correction amount FAF within a predetermined allowable range, for example, 1.2 to 0.8, and the air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine according to the air-fuel ratio correction amount FAF. On the other hand, the allowable width reaching determination means determines whether or not the air-fuel ratio correction amount FAF reaches the predetermined allowable width, and as a result, when the air-fuel ratio correction amount FAF reaches the predetermined allowable width, the stop means Output of the downstream air-fuel ratio sensor
The calculation of the air-fuel ratio correction amount by V ₂ is stopped.

[Work]

According to the above-mentioned means, when the air-fuel ratio correction amount FAF reaches its allowable range, the air-fuel ratio feedback control by the downstream side 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 an intake passage 2 of an engine body 1. The air flow meter 3 directly measures the amount of intake air, and has a built-in potentiometer to generate an analog voltage output signal proportional to the amount of intake air. This output signal is output from the A / D converter 1 with built-in multiplexer in the control circuit 10.
Supplied to 01. The distributor 4 has a crank angle sensor 5 whose axis generates, for example, a reference position detection pulse signal every 720 ° in terms of crank angle, and a reference position detection pulse signal in every 30 degrees which is converted into crank angle. A generated crank angle sensor 6 is provided. The pulse signals of the crank angle sensors 5 and 6 are supplied to an input / output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is supplied to an interrupt terminal of the CPU 103.

Further, the intake passage 2 is provided with a fuel injection valve 7 for supplying pressurized fuel from the fuel supply system to the intake port for each cylinder.

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

The exhaust system downstream of the exhaust manifold 11, a catalytic converter 12 is provided to accommodate the three harmful components HC in the exhaust gas, CO, a three-way catalyst that simultaneously purifies NO _X.

The exhaust manifold 11 has a catalytic converter 12
A first O ₂ sensor 13 is provided on the upstream side, and a second O ₂ sensor 15 is provided on the exhaust pipe 14 downstream of the catalytic converter 12. The O ₂ sensors 13 and 15 generate an electric signal corresponding to the concentration of the oxygen component in the exhaust gas. That is, the O ₂ sensor 1
3,15 are different output voltages depending on whether the air-fuel ratio is leaner or richer than the theoretical air-fuel ratio.
Occurs at 01.

The control circuit 10 is configured as a microcomputer, for example, and includes an A / D converter 101, an input / output interface 10
2.In addition to CPU103, ROM104, RAM105, backup RAM10
6. A clock generation circuit 107 and the like are provided.

Further, in the control circuit 10, the down counter 108, the flip-flop 109, and the drive circuit 110 include the fuel injection valve 7
Is for controlling. That is, when the fuel injection amount TAU is calculated in a routine described later, 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 a clock signal (not shown) and the carry-out terminal finally becomes "1" level, the flip-flop 109 is set and the drive circuit 110 sets the fuel injection valve 7 Stop energizing. That is, the fuel injection valve 7 is energized by the above-described fuel injection amount TAU, so that an amount of fuel corresponding to the fuel injection amount TAU is sent to the combustion chamber of the engine body 1.

Note that the CPU 103 generates an interrupt when the A / D conversion of the A / D converter 101 ends, when the input / output interface 102 receives the pulse signal of the crank angle sensor 6,
When an interrupt signal from 7 is received, and so on.

The intake air amount data Q of the air flow meter 3 and the cooling water temperature data THW are fetched by an A / D conversion routine executed every predetermined time and stored in a predetermined area of the RAM 105.
That is, the data Q and THW in the RAM 105 are updated every predetermined time. Further, the rotation speed data Ne is calculated by the interruption of the crank angle sensor 6 every 30 ° CA and RA
It is stored in a predetermined area of M105.

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

FIG. 4 is a first air-fuel ratio feedback control routine for calculating the air-fuel ratio correction coefficient FAF based on the output of the upstream O ₂ sensor 13, which is executed every predetermined time, for example, 4 ms.

In step 401, it is determined whether or not the closed loop (feedback) condition of the air-fuel ratio by the upstream O ₂ sensor 13 is satisfied. For example, when the cooling water temperature is less than or equal to a predetermined value of 60 ° C., during engine start, during starting increase, during warm-up increase, during power increase, when the output V _{1 of} the upstream O ₂ sensor 13 has never been reversed, The closed loop condition is not satisfied during the fuel cut, and the closed loop condition is satisfied in other cases. When the closed loop condition is not satisfied, the process directly proceeds to step 429. That is, in this case, FAF is the value immediately before the end of closed loop control. On the other hand, if the closed loop condition is satisfied, step 402
Proceed to.

In step 402, the output V ₁ of the upstream O ₂ sensor 13 is A / D converted and taken in, and in step 403 it is determined whether or not V ₁ is a comparison voltage V _R1 such as 0.45 V or less, that is, the air-fuel ratio is It is determined whether rich or lean, that is, if the air-fuel ratio is rich or lean (V ₁ ≤V _R1 ), it is determined in step 404 whether the delay counter CDLY is positive, and if CDLY> 0, the step is determined. CDLY is set to 0 at 405, and the routine proceeds to step 406. In step 406, 1 is subtracted from the delay count CDLY, and in steps 407 and 408, the delay counter CDLY is guarded by the minimum value TDL. In this case, the delay counter CDLY is the minimum value TDL
When it reaches, the first air-fuel ratio flag F1 is set to "0" (lean) at step 409. The minimum value TDL is a lean delay time for holding the determination that the output is rich, even if there is a change from rich to lean in the output of the upstream O ₂ sensor 13, and is defined as a negative value. It On the other hand,
If rich (V ₁ > V _R1 ), it is determined in step 410 whether the delay counter CDLY is negative. If CDLY <0, CDLY is set to 0 in step 411, and the process proceeds to step 412. In step 412, 1 is added to the delay counter CDLY, and in steps 413 and 414, the delay counter CDLY is guarded by the maximum value TDR. In this case, the delay counter CDLY is the maximum value TDR
When it reaches, the first air-fuel ratio flag F1 is set to "1" (rich) in step 415. It should be noted that the maximum value TDR is a rich delay time for holding a judgment that the output is a lean state even if there is a change from lean to rich in the output of the upstream O ₂ sensor 13, and is defined as a positive value. It

In step 416, it is determined whether or not the sign of the first air-fuel ratio flag F1 has been inverted, that is, whether or not the air-fuel ratio after the delay processing has been inverted. If the air-fuel ratio is reversed, it is determined in step 417 whether the reversal is from rich to lean or from lean to rich according to the value of the first air-fuel ratio flag F1. If it is inversion from rich to lean, in step 418, the rich skip amount RSR is read from the backup RAM 106 and skipped to increase from FAF to FAF + RSR. Conversely, if it is inversion from lean to rich, the process proceeds to step 419. The lean skip amount RSL is read from the backup RAM 106 and FAF ← FAF−RSL is reduced in a skip manner. That is, skip processing is performed.

If the sign of the first air-fuel ratio flag F1 has not been inverted at step 416, the integration processing is performed at steps 420, 421 and 422. That is, in step 420, it is determined whether or not F1 = "0". If F1 = "0" (lean), the FAF is determined in step 421.
← FAF + KIR, while if F1 = "1" (rich), FAF ← FAF-KIL is set in step 622. Where the integration constant KI
R and KIL are set sufficiently smaller than the skip constants RSR and RSL, that is, KIR (KIL) <RSR (RSL). Therefore, step 421 gradually increases the fuel injection amount in the lean state (F1 = “0”), and step 422 increases the fuel injection amount (F1 = “0”).
The fuel injection amount is gradually reduced by "1").

The air-fuel ratio correction coefficient FAF calculated in steps 418, 419, 421 and 422 is guarded to the minimum value, for example 0.8, in steps 423 and 424. In this case, when FAF reaches the minimum value of 0.8, the air-fuel ratio feedback execution flag FB by the downstream O ₂ sensor 15 is set to “0” in step 425, and FB is set to “1” in other cases. Also, in steps 427 and 428, the maximum value, for example 1.2, is guarded. Thus, 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 with that value to prevent over-rich or over-lean.

The FAF calculated as described above is stored in the RAM 105, and this routine ends at step 429.

FIG. 5 is a timing chart for supplementarily explaining the operation according to the flowchart of FIG. When the rich / lean air-fuel ratio signal A / F is obtained from the output of the upstream O ₂ sensor 13 as shown in FIG.
As shown in FIG. 5 (B), the count is performed in the rich state and the count is reduced in the lean state. As a result, a delayed air-fuel ratio signal A / F '(corresponding to the flag F1) is formed as shown in FIG. 5 (C). For example, the air-fuel ratio signal A / F is changed from lean to rich at time t _1, the air-fuel ratio signal A / F which is delayed processed 'at time t ₂ after being held lean only the rich delay time TDR Change richly. Also the air-fuel ratio signal A / F from the rich at time t ₃ is changed to the lean air-fuel ratio signal A / F which is delayed processed '
Changes to lean at time t ₄ after being held rich only equivalent lean delay time (-TDL). However, if the air-fuel ratio signal A / F is inverted in a period shorter than the rich delay time TDR or the lean delay time (-TDL) as at times t ₅ , t ₆ , and t ₇ , the delay counter CDLY reaches the maximum value TDR. Time is required, and as a result, the delayed air-fuel ratio signal A / F ′ is inverted at time t ₈ . That is, 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, the stable air-fuel ratio signal A /
Based on F ', the air-fuel ratio correction coefficient FAF shown in Fig. 5 (D)
Is obtained.

Next, the second air-fuel ratio feedback control by the downstream O ₂ sensor 15 will be described. As the second air-fuel ratio feedback control, the skip amounts RSR, RSL, the integration constants KIR, KIL, the delay times TDR, TDL, or the output V ₁ of the upstream O ₂ sensor 13 as the first air-fuel ratio feedback control constant are determined. There are a system that makes the comparison voltage V _R1 variable, and a system that introduces the second air-fuel ratio correction coefficient FAF2.

For example, if the rich skip amount RSR is increased, the control air-fuel ratio can be shifted to the rich side, and even if the lean skip amount RSL is decreased, the control air-fuel ratio can be shifted to the rich side, while the lean skip amount RSL is increased. , The control air-fuel ratio can be shifted to the lean side, and the rich skip amount
Even if the RSR is reduced, the control air-fuel ratio can be shifted to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the rich skip amount RSR and the lean skip amount RSL according to the output of the downstream O ₂ sensor 15. Further, if the rich integration constant KIR is increased, the control air-fuel ratio can be shifted to the rich side, and even if the lean integration constant KIL is decreased, the control air-fuel ratio can be shifted to the rich side, while the lean integration constant KIL is increased. Then, the control air-fuel ratio can be shifted to the lean side, and the control air-fuel ratio can be shifted to the lean side even if the rich integration constant KIR is reduced. Accordingly, the air-fuel ratio can be controlled by correcting the rich integration constant KIR and the lean integration constant KIL in accordance with the output of the downstream O ₂ sensor 15. Rich delay time TDR>
If the lean delay time (-TDL) is set, the control air-fuel ratio can shift to the rich side, and conversely, the lean delay time (-TDL)
By setting> rich delay time (TDR), the control air-fuel ratio can shift to the lean side. That is, the air-fuel ratio can be controlled by correcting the delay times TDR, (-TDL) according to the output of the downstream O ₂ sensor 15. Furthermore, it shifts the control air-fuel ratio by increasing the comparison voltage V _R1 to the rich side, also, possible shifts the control air-fuel ratio by decreasing the reference voltage V _R1 to the lean side. Accordingly, the air-fuel ratio can be controlled by correcting the reference voltage V _R1 in accordance with the output of the downstream O ₂ sensor 15.

A double O ₂ sensor system having a variable skip amount as an air-fuel ratio feedback control constant will be described with reference to FIG.

FIG. 6 is a second air-fuel ratio feedback control routine for calculating the skip amounts RSR, RSL based on the output of the downstream O ₂ sensor 15, and is executed every predetermined time, for example, every 1 s. In step 601, it is determined whether or not the closed loop condition by the downstream O ₂ sensor 15 is satisfied. For example, when the cooling water temperature is below a predetermined value, for example 70 ° C, when the output signal of the downstream O ₂ sensor 15 never reverses, when the downstream O ₂ sensor 15 has a failure, during transient operation, on-idle (LL = “1”) etc., the closed loop condition is not satisfied, and in other cases, the closed loop condition is satisfied. If it is not a closed loop condition, the process directly proceeds to step 617. In this case, RSR and RSL are set to values immediately before the end of closed loop control (values in backup RAM).

If it is a closed loop, the routine proceeds to step 602, where it is judged if the air-fuel ratio feedback control execution flag FB is "1".
That is, it is determined whether the FAF has reached the minimum value of 0.8.
If FAF has reached the minimum value of 0.8 (FB = “0”), the process also proceeds to step 617 and the skip amounts RSR and RSL are not updated. On the other hand, if FAF has not reached the minimum value of 0.8, the process proceeds to step 603. In step 603, the output V ₂ of the downstream O ₂ sensor 15 is A / D converted and taken in, and it is determined whether or not V ₂ ≦ V _R2 (lean). The comparison voltage V _R2 is, for example, 0.55V.
As a result, if V ₂ ≤V _R2 (lean), steps 605 to 61
Go to 0, while if V ₂ > V _R2 (rich), go to step 61.
Go to 1-616.

In step 605, the rich skip amount RSR is read from the backup RAM 106 and RSR ← RSR + ΔRS, that is,
The rich skip amount RSR is increased to shift the air-fuel ratio to the rich side. In steps 606 and 607, the RSR is guarded with the maximum value MAX, for example 7.5%. Further, in step 608, the lean skip amount RSL is read from the backup RAM 106 to make RSL ← RSL−ΔRS, that is, the lean skip amount RSL.
Is reduced to shift the air-fuel ratio to the rich side. Step
In 609 and 610, RSL is guarded with the minimum value MIN, for example, 2.5%.

On the other hand, when V ₁ > V _R2 (rich) in step 604, the rich skip amount RSR is read from the backup RAM 106 in step 611 to set RSR ← RSR−ΔRS, that is,
The rich skip amount RSR is reduced to shift the air-fuel ratio to the lean side. In steps 612 and 613, RSR is guarded with the minimum value MIN. Furthermore, backup R in step 614
Read lean skip amount RSL from AM106 and RSL ← RSL + Δ
RS, that is, the lean skip amount RSL is increased to shift the air-fuel ratio to the lean side. In steps 615 and 616, R
Guard SL at maximum value MAX.

RSR and RSL calculated as above are backup RAM10
After being stored in 6, the routine ends in step 617.

It should be noted that the minimum value MIN in FIG. 6 is a level value at which transient followability is not impaired, and the maximum value MIN is a level value at which drivability deterioration due to air-fuel ratio fluctuations does not occur.

In this way, when the air-fuel ratio correction coefficient FAF reaches the minimum value 0.8 of the allowable width, the air-fuel ratio feedback control by the downstream O ₂ 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. In step 701
Intake air amount data Q and rotation speed data Ne from RAM 105
To calculate the basic injection amount TAUP. For example TAUP ←
Let α · Q / Ne (α is a constant). RAM105 at step 702
Further, the cooling water temperature data THW is read out, and the warm-up increase value FWL is interpolated and calculated based on the one-dimensional map stored in the ROM 104. In step 703, the final injection amount TAU is calculated by TAU ← TAUP · FAF · (FWL + β + 1) + γ. Here, β and γ are correction amounts determined by other operation state parameters. Then step 704
Then, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start the fuel injection. Then, in step 705, this routine ends. As described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the carry-out signal of the down counter 108, and the fuel injection ends.

Also, 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 s because the air-fuel ratio feedback control is mainly performed by the upstream O ₂ sensor with good response and the downstream O ₂ sensor with poor response is used for control. This is because they are obeyed.

Further, a double O ₂ sensor that corrects other control constants in the air-fuel ratio feedback control by the upstream O ₂ sensor, such as delay time and integration constant, by the output of the downstream O ₂ sensor.
The present invention can be applied to a sensor system and also to a double O ₂ sensor system that introduces a second air-fuel ratio correction coefficient. In addition, 2 of the skip amount, delay time, and integration constant
The controllability can be improved by controlling the two at the same time. Further, either one of the skip amounts RSR and RSL can be fixed and only the other can be made variable, or one of the delay times TDR and TDL can be fixed and only the other can be made variable, or the rich integration constant KIR , It is also possible to fix one of the lean integration constants KIL and make the other variable.

Further, as the intake air amount sensor, a Karman vortex sensor, a heat wire sensor, or the like can be used instead of the air flow meter.

Further, in the above-described embodiment, the fuel injection amount is calculated according to the intake air amount and the engine speed, but the fuel injection amount is calculated according to the intake air pressure and the engine speed, or the throttle valve opening and the engine speed. The fuel injection amount may be calculated.

Further, in the above-described embodiment, the internal combustion engine in which the fuel injection amount to the intake system is controlled by the fuel injection valve has been shown, but the present invention can also be applied to a chabletter internal combustion engine. For example, the air-fuel ratio is controlled by adjusting the intake air amount of the engine using an electric air control valve (EACV).
Electric bleed air control valve adjusts the air bleed amount of the carburetor to control the air-fuel ratio by introducing air into the main passage and the slow passage, and controls the amount of secondary air sent to the exhaust system of the engine. The present invention can be applied to a device to be adjusted. 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, the intake pipe negative pressure according to the intake air amount and the engine speed, and the step 703 At, the supply air amount corresponding to the final fuel injection amount TAU is calculated.

Furthermore, in the above-described embodiment, the O ₂ sensor is used as the air-fuel ratio sensor, but a CO sensor, a lean mixture sensor, or the like may be used.

Further, although the above-mentioned embodiment is constituted by a microcomputer, that is, a digital circuit, it may be constituted by an analog circuit.

〔The invention's effect〕

As described above, according to the present invention, the air-fuel ratio correction amount by the output of the upstream side air-fuel ratio sensor is guarded within an allowable width, and the emission and drivability deteriorate when the double air-fuel ratio sensor system cannot perform its original function. Can be prevented.

[Brief description of drawings]

FIG. 1 is an overall block diagram for explaining the configuration of the present invention, FIG. 2 is an exhaust emission characteristic diagram for explaining a single O ₂ sensor system and a double O ₂ sensor system, and FIG. 3 is an internal combustion engine according to the present invention. FIG. 4, FIG. 6, FIG. 7 are flowcharts for explaining the operation of the control circuit of FIG. 3, and FIG. 5 is a flowchart of FIG. FIG. 9 is a timing chart for supplementary explanation of the flowchart. 1 ... Engine main body, 3 ... Air flow meter, 4 ... Distributor, 5,6 ... Crank angle sensor, 10 ... Control circuit, 12 ... Catalytic converter, 13 ... Upstream side (first) O ₁ Sensor, 15 ... Downstream (second) O ₂ sensor.

Claims (1)

(57) [Claims] 1. A first and a second detector, which are respectively provided on the upstream side and the downstream side of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine, for detecting a concentration of a specific component in the exhaust gas. An 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, and a guard of the calculated air-fuel ratio correction amount within a predetermined allowable width. Guard means, an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the air-fuel ratio correction amount, and an allowable width reaching for determining whether the air-fuel ratio correction amount has reached the predetermined allowable width. An air conditioner for an internal combustion engine, comprising: a determining unit; and a stopping unit that stops 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. Fuel ratio control device.