JPH06346775A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To maintain an air-fuel ratio to a target value so as to improve exhaust gas purifying property by changing air-fuel ratio correction on the basis of an air-fuel ratio detecting means arranged downstream according to complex deterioration of the air-fuel ratio detecting means arranged upstream from an exhaust emission control catalyst in an internal combustion engine. CONSTITUTION:In the intake passage 12 of an internal combustion engine 11, a fuel injection valve 15 is arranged downstream from a throttle valve 14. In an exhaust passage 18, first and second air-fuel ratio sensors 19, 21 are arranged above and below a catalytic converter rhodium 20. The fuel injection valve 15 is controlled by a control unit 16 on the basis of respective detection signals of at least respective air-fuel ratio sensors 19, 21. As the result, the air-fuel ratio of the internal combustion engine 11 is controlled. In this case, in the control unit 16, deterioration of the rich side output and responsiveness of the first air-fuel ratio sensor 19 are diagnosed on the basis of a first air-fuel ratio correction amount. As the result, when the deteriorations is diagnosed the second air-fuel ratio correction amount of the second air-fuel ratio sensor 21 is corrected in the direction to suppress rich control of the air-fuel ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for controlling the air-fuel ratio of an internal combustion engine, and more particularly to a device for feedback-controlling the air-fuel ratio by performing air-fuel ratio detection on the upstream side and the downstream side of an exhaust purification catalyst. The present invention relates to a technique for coping with an abnormality in the air-fuel ratio detecting means on the side of the vehicle.

[0002]

2. Description of the Related Art As a conventional general air-fuel ratio control system for an internal combustion engine, there is one disclosed in Japanese Patent Application Laid-Open No. 60-240840. Explaining the outline of this, the basic fuel supply amount T _P corresponding to the amount of air taken into the cylinder by detecting the intake air flow rate Q and the engine speed N of the engine
(= K · Q / N; K is a constant), and the basic fuel supply amount T _P corrected by the engine temperature or the like is detected to detect the oxygen concentration in the exhaust gas to detect the air-fuel ratio of the air-fuel mixture. Feedback correction is performed by using the air-fuel ratio feedback correction coefficient (air-fuel ratio correction amount) set by the signal from the (oxygen sensor), and the fuel supply amount T _I is finally set by performing correction by the battery voltage. .

A drive pulse signal having a pulse width corresponding to the fuel supply amount T _I set in this way is output to the fuel injection valve at a predetermined timing so that a predetermined amount of fuel is injected and supplied to the engine. I have to. The air-fuel ratio feedback correction based on the signal from the air-fuel ratio sensor is performed so as to control the air-fuel ratio near the target air-fuel ratio (theoretical air-fuel ratio). This is interposed in the exhaust system, and C in the exhaust is
The conversion efficiency (purification efficiency) of an exhaust purification catalyst (three-way catalyst) that oxidizes O, HC (hydrocarbons) and reduces NO _X for purification so that the conversion efficiency (purification efficiency) effectively functions in the exhaust state during stoichiometric combustion This is because it is set.

The electromotive force (output voltage) generated by the air-fuel ratio sensor has a characteristic of abruptly changing in the vicinity of the theoretical air-fuel ratio, and this output voltage V ₀ and a reference voltage (slice level) SL corresponding to the theoretical air-fuel ratio are used. Is compared to determine whether the air-fuel ratio of the air-fuel mixture is rich or lean with respect to the stoichiometric air-fuel ratio. Then, for example, when the air-fuel ratio is lean (rich), after increasing (decreasing) a large proportional constant P at the first time when the feedback correction coefficient α for multiplying the basic fuel supply amount T _P is changed to lean (rich), Gradually increase (decrease) by a predetermined integration constant I
The air-fuel ratio is controlled to be close to the stoichiometric air-fuel ratio by increasing (decreasing) the fuel supply amount T _I.

By the way, in the normal air-fuel ratio feedback control device as described above, one air-fuel ratio sensor is provided in the collection portion of the exhaust manifolds as close to the combustion chamber as possible in order to improve the response, but this portion is exhausted. Since the temperature is high, the characteristics of the air-fuel ratio sensor are likely to change due to thermal influences and deterioration, and it is difficult to detect the average air-fuel ratio of all cylinders due to insufficient mixing of exhaust gas for each cylinder. The accuracy was poor, and the air-fuel ratio control accuracy was poor.

In view of this point, it has been proposed to provide an air-fuel ratio sensor on the downstream side of the exhaust purification catalyst and perform feedback control of the air-fuel ratio using the detection values of the two air-fuel ratio sensors (Japanese Patent Laid-Open No. 58-58). (See −48756 publication). That is, since the downstream air-fuel ratio sensor is far from the combustion chamber, it has a difficulty in response, but since it is downstream of the exhaust purification catalyst, the influence of the exhaust component balance (CO, HC, NOx, CO ₂ etc.) The air-fuel ratio on the upstream side, such as the average air-fuel ratio of all cylinders, can be detected because the exhaust gas is less toxic and the amount of poisonous components in the exhaust is less likely to cause characteristic changes due to poisoning. As compared with the sensor, highly accurate and stable detection performance can be obtained.

Therefore, two air-fuel ratio feedback correction coefficients which are respectively set by the same calculation as described above based on the detection values of the two air-fuel ratio sensors are combined, or the air-fuel ratio feedback set by the upstream air-fuel ratio sensor is combined. The variation in the output characteristics of the upstream air-fuel ratio sensor is corrected by correcting the control constant (proportional or integral) of the correction coefficient, the comparison voltage of the output voltage of the upstream air-fuel ratio sensor, and the delay time. The sensor compensates for high-precision air-fuel ratio feedback control.

[0008]

In the air-fuel ratio control device using such two air-fuel ratio sensors, the change in the output characteristics due to the deterioration of the upstream air-fuel ratio sensor is
The air-fuel ratio is compensated to a certain extent by the correction based on the output of the air-fuel ratio sensor on the downstream side, but as the output value on the rich side decreases, the responsiveness decreases and the inversion cycle increases, leading to a composite deterioration. In that case, the normal correction method cannot deal with it.

That is, as shown in FIGS. 7 and 8, the deterioration of the upstream side air-fuel ratio sensor due to only a decrease in the output voltage on the rich side is caused by the shift of the air-fuel ratio to the rich side. By prolonging the rich detection time of the air-fuel ratio sensor, it can be dealt with by correcting the air-fuel ratio to the lean side.On the other hand, for deterioration that only deteriorates the responsiveness, the time shifted to the rich side and the lean side The increase in the time of deviation from the NOx ratio increases simultaneously with the decrease in the NOx conversion ratio due to the enrichment and the decrease in the HC conversion ratio due to the lean conversion. Therefore, the rich side is determined based on the output of the air-fuel ratio sensor on the downstream side. This can be dealt with by performing even correction on the lean side and correction on the lean side.

However, when the rich electromotive force of the upstream side air-fuel ratio sensor is reduced and the responsiveness is also reduced at the same time, the normal method causes excessive correction of the air-fuel ratio in the rich direction. Further, the correction in the lean direction becomes insufficient due to the setting of the upper limit value, and the rich state of the air-fuel ratio is prolonged, so that the exhaust purification performance cannot be sufficiently and effectively exhibited.

The present invention has been made in view of the above conventional problems, and responds to the above-described composite deterioration of the upstream side air-fuel ratio detecting means by the downstream side air-fuel ratio detecting means. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that can maintain the air-fuel ratio near a target value and improve exhaust gas purification performance by changing the correction.

[0012]

Therefore, an air-fuel ratio control system for an internal combustion engine according to the present invention is provided with each means shown in FIG. The first and second air-fuel ratio detecting means are respectively provided on the upstream side and the downstream side of the exhaust purification catalyst provided in the exhaust passage of the engine, and are sensitive to the concentration ratio of the specific gas component in the exhaust gas that changes depending on the air-fuel ratio. Change the output value.

The first air-fuel ratio correction amount calculation means calculates the first air-fuel ratio correction amount by ratio 0 / integral control or integration control according to the output value of the first air-fuel ratio detection means. The second air-fuel ratio detection unit calculates a second air-fuel ratio correction amount for correcting the first air-fuel ratio correction amount, for example, the proportional component or the integral component, according to the output value of the second air-fuel ratio detection unit. To do.

The air-fuel ratio correction amount calculation means calculates a final air-fuel ratio correction amount based on the first air-fuel ratio correction amount and the second air-fuel ratio correction amount. The air-fuel ratio control amount setting means is
A basic air-fuel ratio control amount set based on the engine speed, load, etc. is corrected and set based on the air-fuel ratio correction amount calculated by the air-fuel ratio correction amount calculation means.

An air-fuel ratio control device having such a basic structure is provided with the following respective means characteristic to the present invention. The deterioration diagnosis means diagnoses the rich side output value and the responsiveness deterioration of the first air-fuel ratio detection means based on the value of the first air-fuel ratio correction amount. The second air-fuel ratio correction amount correcting means controls the second air-fuel ratio correction amount to enrich the air-fuel ratio when the abnormality diagnosing means diagnoses that the first air-fuel ratio detecting means is deteriorated. Modify to suppress.

[0016]

If the output value of the first air-fuel ratio detecting means on the rich side decreases and the response deteriorates, a composite deterioration occurs. The fuel ratio correction amount correction means is, for example, normally when the second air-fuel ratio detection means detects a lean state of the air-fuel ratio, and makes correction in the enrichment direction of the air-fuel ratio based on the output value of the first air-fuel ratio detection means. Where the second correction in the direction of further enriching the amount is performed, correction such as stopping or suppressing the second enrichment correction is performed. Further, when the second air-fuel ratio detecting means detects the rich state of the air-fuel ratio, when the second air-fuel ratio detecting means detects the rich state of the air-fuel ratio, the output value of the first air-fuel ratio detecting means In the configuration in which the upper limit of the second correction in the leaning direction of the air-fuel ratio based on the above is set and the upper limit is set, the restriction is released to suppress the enrichment of the air-fuel ratio. .

As a result, the tendency of enrichment of the air-fuel ratio is suppressed even with the combined deterioration of the first air-fuel ratio detecting means,
Exhaust purification performance is improved.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 2 showing the configuration of one embodiment, an air flow meter for detecting an intake air flow rate Q is provided in an intake passage 12 of an engine 11.
A throttle valve 14 for controlling the intake air flow rate Q in cooperation with the accelerator pedal 13 and the accelerator pedal is provided, and an electromagnetic fuel injection valve 15 is provided for each cylinder in the downstream manifold portion.

The fuel injection valve 15 is opened and driven by an injection pulse signal from a control unit 16 having a built-in microcomputer, and is fuel-fed by a fuel pump (not shown) to be injected and supplied with pressure controlled by a pressure regulator. . Further, a water temperature sensor 17 for detecting the cooling water temperature Tw in the cooling jacket of the engine 11 is provided. On the other hand, the exhaust passage 18 is provided with a first air-fuel ratio sensor (first air-fuel ratio detecting means) 19 for detecting the air-fuel ratio of the air-fuel mixture supplied to the engine by detecting the oxygen concentration in the exhaust gas at the manifold collecting portion. A three-way catalyst 20 as an exhaust purification catalyst that purifies the exhaust pipe by oxidizing CO and HC and reducing NO _X in the exhaust is provided in the exhaust pipe on the downstream side, and further on the downstream side of the three-way catalyst 20. Further, a second air-fuel ratio sensor (second air-fuel ratio detecting means) 21 having the same function as the first air-fuel ratio sensor 19 is provided.

Further, a crank angle sensor 22 is built in a distributor (not shown), and the crank unit angle signal output from the crank angle sensor 22 in synchronization with the engine rotation is counted for a predetermined time, or The engine speed N is detected by measuring the cycle of the reference angle signal.
Next, the air-fuel ratio control routine by the control unit 16 will be described with reference to the flowcharts of FIGS.
FIG. 3 shows a fuel injection amount setting routine, and this routine is performed every predetermined period (for example, 10 ms).

In step (denoted by S in the drawing) 1, the unit of rotation per unit rotation is based on the intake air flow rate Q detected by the air flow meter 13 and the engine speed N calculated based on the signal from the crank angle sensor 22. The basic fuel injection amount T _P corresponding to the intake air amount is calculated by the following equation. The function of step 1 corresponds to the basic fuel supply amount setting means.

T _P = K × Q / N (K is a constant) In step 2, various correction coefficients COEF are set based on the cooling water temperature Tw detected by the water temperature sensor 17. In step 3, the feedback correction coefficient α set by the feedback correction coefficient setting routine described later is read.

In step 4, the voltage correction component T _S is set based on the battery voltage value. This is for correcting the change in the injection flow rate of the fuel injection valve 15 due to the battery voltage change. In step 5, the final fuel injection amount T _I
Is calculated according to the following equation. T _I = T _P × COEF × α + T _{S Since} the fuel injection amount T _I corresponds to the air-fuel ratio control amount, the functions from step 1 to step 5 correspond to the air-fuel ratio control amount setting means.

In step 6, the calculated fuel injection valve T
Set _I to output register. As a result, when the predetermined fuel injection timing of engine rotation synchronization is reached,
A drive pulse signal having a pulse width of the calculated fuel injection amount T _I is given to the fuel injection valve 15 to perform fuel injection. Next, the air-fuel ratio feedback correction coefficient setting routine is shown in FIG.
Follow the instructions below. This routine is executed in synchronization with the engine rotation.

In step 11, it is determined whether or not the operating conditions are such that feedback control of the air-fuel ratio is performed. When the operating conditions are not satisfied, this routine is ended.
In this case, the feedback correction coefficient α is clamped to the value at the end of the previous feedback control or a constant reference value, and the feedback control is stopped. In step 12, the signal voltage V _O2 from the first air-fuel ratio sensor 19 is input.

In step 13, the reference value S corresponding to the signal voltage V _O2 input in step 11 and the target air-fuel ratio (theoretical air-fuel ratio)
It is compared with L to determine rich / lean air-fuel ratio. When it is determined that the air-fuel ratio is rich, the step
Proceed to step 14 and determine whether or not it has just changed from lean to rich. If it is determined that the image has just been inverted, proceed to step 15,
The second air-fuel ratio correction amount PHOS set by another routine is input.

Next, the routine proceeds to step 16, where the proportional amount P _R in the decreasing direction given at the time of rich inversion for setting the air-fuel ratio feedback correction coefficient α is updated with a value obtained by subtracting the second air-fuel ratio correction amount PHOS from the reference value P _RO. After that, in step 17, the air-fuel ratio feedback correction coefficient α is set to the proportional value P from the current value.
Update with the value obtained by subtracting _R. Further, when it is determined in step 14 that the output of the first air-fuel ratio sensor 19 is not immediately after reversing from lean to rich, the routine proceeds to step 18, where the air-fuel ratio feedback correction coefficient α is set to the integral value I _R from the current value. Update with the reduced value.

On the other hand, when it is determined in step 13 that the air-fuel ratio is lean, it is similarly determined in step 19 whether or not it is immediately after reversal from rich to lean. If it is immediately after reversal, the second air-fuel ratio is determined in step 20. Enter the fuel ratio correction amount PHOS, and proceed to Step 21.
After updating with the value obtained by adding the second air-fuel ratio correction amount PHOS to the reference value P _L0 of the proportional portion P _{L in} the increasing direction given at the lean reversal of the air-fuel ratio feedback correction coefficient α,
At 22, the air-fuel ratio feedback correction coefficient α is updated with a value obtained by adding the proportional amount P _L to the current value. Further, when it is determined in step 19 that it is not immediately after reversal, the air-fuel ratio feedback correction coefficient α is updated in step 23 with a value obtained by adding the integral I _L to the current value.

In this routine, the air-fuel ratio feedback correction coefficient α is set based on the signal of the first air-fuel ratio sensor 19 using the proportional reference values P _RO, P _LO and the integral parts I _R, I _L. It is considered that the routine is set by correcting the first air-fuel ratio correction amount that is performed by the second air-fuel ratio correction amount PHOS, so this routine is performed by the first air-fuel ratio correction amount calculation means and the air-fuel ratio correction amount calculation. It also has a structure of means.

Next, a routine for setting the second air-fuel ratio correction amount PHOS based on the signal of the second air-fuel ratio sensor will be described with reference to FIG. This routine is executed every predetermined period. In step 31, the output voltage V _O2 'of the second air-fuel ratio sensor is input. In step 32, the reference value SL corresponding to the signal voltage V _O2 'and the target air-fuel ratio (theoretical air-fuel ratio).
To compare rich and lean of the air-fuel ratio.

When the air-fuel ratio is judged to be rich, the routine proceeds to step 33, where it is judged if it is just after reversal from lean to rich. Then, when it is determined to be immediately after reversal, the second air-fuel ratio correction amount PHOS is updated with a value obtained by subtracting a predetermined proportional amount P _HR from the previous value in step 34, and when it is determined not to be immediately after reversal in step 35. predetermined integral amount I _HR from the value
Update with the value obtained by subtracting.

Next, the routine proceeds to step 36, where the value of the diagnosis flag F indicating the diagnosis result of the first air-fuel ratio sensor 19 which is diagnosed in the routine described later is determined. Then, when the diagnosis flag F is 1 and it is diagnosed that the rich electromotive force and the responsiveness of the first air-fuel ratio sensor 19 are both decreased to a predetermined level or less, it is judged that the composite deterioration has occurred, the routine proceeds to step 37. Two
The lower limit value P _{HL L} of the air-fuel ratio correction amount P _HOS is corrected and set from the normal value P _{HLL0 in the} expanding direction. When the value of the diagnosis flag F is 0 and it is determined that the first air-fuel ratio sensor 19 is not _subject to composite deterioration, the routine proceeds to step 38, where the lower limit value is set to the normal value _PHLL0 .

Thereafter, the process proceeds to step 39 and the above step 34
Alternatively, the second air-fuel ratio correction amount P updated and set in step 35
HOS is compared with the limit value P _HLL, and P HOS ≤P _HLL
When it is determined that the following is true, the process proceeds to step 40, where P HOS = P _HLL
Set to. On the other hand, when it is determined in step 32 that the air-fuel ratio is lean, the routine proceeds to step 41, where the value of the diagnosis flag F is discriminated. When F = 1, the routine proceeds to step 42 where the second air-fuel ratio correction amount PHOS The value of 0 as the second
The acceleration control of the enrichment of the air-fuel ratio by the air-fuel ratio correction amount PHOS is stopped.

Further, when the diagnosis flag F is 0 and it is diagnosed that the first air-fuel ratio sensor 19 does not cause the composite deterioration, the routine proceeds to step 43, where it is judged whether or not it is just after reversing from lean to rich. However, if it is determined immediately after the reversal, the second air-fuel ratio correction amount PHOS is updated with a value obtained by adding a predetermined proportional amount P _HL to the previous value in step 44, and if it is determined that it is not immediately after the reversal, the last time in step 45. Predetermined integral I for the value
Update with the added value of _HR .

Then, the process proceeds to step 46 and the step 44
Alternatively, the second air-fuel ratio correction amount P updated and set in step 45
HOS is compared with the upper limit value P _HLU, and P HOS ≧ P
When it is judged as _HLL , the routine proceeds to step 47, where PHOS = P
Set to _HLU . In such a routine, step 37
The function of step 42 constitutes second air-fuel ratio correction amount correction means.

Next, a routine for diagnosing the composite deterioration of the first air-fuel ratio sensor 19 will be described with reference to FIG. still,
This routine constitutes deterioration diagnosis means. Step 51 ~
In step 53, it is determined whether the vehicle speed VSP _{, the} engine speed N _{, and the} basic fuel injection amount T _P are within their respective set ranges, and when it is determined that they are all within the set ranges, that is, a predetermined steady operation is performed. If it is determined to be in the area, step 54
Then, it is determined whether the air-fuel ratio feedback control is being performed.

Then, it is determined that the air-fuel ratio feedback control is in progress.
Is determined, the deterioration diagnosis condition of the first air-fuel ratio sensor 19 is determined.
When it is determined that the condition has been set, the process proceeds to step 55 and thereafter. Step 55
Then, the rich electromotive force of the first air-fuel ratio sensor 19, that is, the maximum
Output voltage V _O2MAXAsk for. In step 56, the maximum
Output voltage V_O2MAXSet value V_M0Compared to V_O2MAX<V
_M0If it is determined that the rich electromotive force has decreased
, And then the next step to make a diagnosis of decreased responsiveness.
Go to page 57 or later.

Next, at step 57, the first air-fuel ratio sensor
Calculate the response time of 19. Specifically, the response time T is calculated by adding the time TLR from the lean air-fuel ratio reversal to the rich air-fuel ratio reversal and the time TRL from the air-fuel ratio reversal rich to the lean air-fuel ratio reversal. . here,
The addition of the two times TLR _and TRL is for excluding the transient state.

At step 58, the added response time T is compared with the set value T _0, and when it is judged that T ≧ T ₀ , the routine proceeds to step 59, where the responsiveness of the first air-fuel ratio sensor 19 decreases. Therefore, it is diagnosed that the composite deterioration is occurring together with the decrease in the rich electromotive force, and the diagnosis flag F is set to 1. With this configuration, the first air-fuel ratio sensor 19
When the rich electromotive force is low and the composite response is low when the responsiveness is low, the second air-fuel ratio sensor 21 detects the lean state of the air-fuel ratio, and normally the second air-fuel ratio is detected.
The acceleration of the enrichment of the air-fuel ratio by the air-fuel ratio adjustment amount PHOS is suppressed by setting the value of the second air-fuel ratio adjustment amount PHOS to 0, and the second air-fuel ratio adjustment amount POS is reduced.
The lean limit of the air-fuel ratio by HOS is promoted as much as possible by increasing the lower limit value P _HLL, and as a result, the control amplitude of the air-fuel ratio is reduced and shifted to the lean side, which results from compound deterioration. The enrichment of the air-fuel ratio is suppressed, and the exhaust purification performance can be improved.

[0040]

As described above, according to the present invention, in the case of a composite deterioration in which the rich-side output value of the air-fuel ratio sensor upstream of the exhaust purification catalyst decreases and the responsiveness also decreases. Is capable of suppressing the enrichment of the air-fuel ratio and improving the exhaust purification performance by changing the value of the second air-fuel ratio correction amount set based on the air-fuel ratio sensor on the downstream side of the exhaust purification catalyst.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration and functions of the present invention.

FIG. 2 is a diagram showing a system configuration of an embodiment of the present invention.

FIG. 3 is a flowchart showing a fuel injection amount setting routine of the above embodiment.

FIG. 4 is a flowchart showing an air-fuel ratio feedback correction coefficient setting routine.

FIG. 5 is a flowchart showing a second air-fuel ratio correction amount setting routine.

FIG. 6 is a flow chart showing a deterioration diagnosis routine of the second air-fuel ratio sensor.

FIG. 7 is a diagram showing a relationship between purification efficiency of an exhaust purification catalyst and deterioration of an upstream air-fuel ratio sensor.

FIG. 8 is a diagram showing a relationship between the purification efficiency and the air-fuel ratio of the exhaust purification catalyst and the deterioration of the upstream side air-fuel ratio sensor.

[Explanation of symbols]

 11 engine 16 control unit 18 exhaust passage 19 first air-fuel ratio sensor 20 three-way catalyst 21 second air-fuel ratio sensor

Claims (1)

[Claims] 1. An output value changing in response to a concentration ratio of a specific gas component in exhaust gas, which is provided upstream and downstream of an exhaust purification catalyst provided in an exhaust passage of an engine, and which changes in response to a concentration ratio of a specific gas component in exhaust gas that changes according to an air-fuel ratio. First and second air-fuel ratio detection means, first air-fuel ratio correction amount calculation means for calculating a first air-fuel ratio correction amount according to an output value of the first air-fuel ratio detection means, and the second Second air-fuel ratio correction amount calculation means for calculating a second air-fuel ratio correction amount for correcting the first air-fuel ratio correction amount according to the output value of the air-fuel ratio detection device; and the first air-fuel ratio correction amount. And an air-fuel ratio correction amount calculating means for calculating a final air-fuel ratio correction amount based on the second air-fuel ratio correction amount, and an air-fuel ratio correction amount calculated by the air-fuel ratio correction amount calculating means. And an air-fuel ratio control amount setting means for correcting and setting the air-fuel ratio control amount. In an air-fuel ratio control device for an engine, deterioration diagnosis means for diagnosing the rich side output value and responsiveness deterioration of the first air-fuel ratio detection means based on the value of the first air-fuel ratio correction amount, and the abnormality diagnosis means. As a result, when it is diagnosed that the first air-fuel ratio detecting means is deteriorated, the second air-fuel ratio correction amount is corrected to correct the second air-fuel ratio correction amount in a direction of suppressing the enrichment control of the air-fuel ratio. An air-fuel ratio control device for an internal combustion engine, comprising: