JPH0734937A - Air-fuel ratio feedback controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To suppress the deterioration of controllability and exhaust property of an air-fuel ratio by continuing control by either one of air-fuel ratio sensors where no abnormality is generated at a heater, when the air-fuel ratio sensor with a heater is arranged per cylinder group, and the air-fuel ratio is feedback- controlled. CONSTITUTION:Respective exhaust manifolds 8, 9 are arranged on both V type banks in an internal combustion engine 1, and these downstream parts are mode confuence by an exhaust passage 10. Precatalysts 11, 12 are arranged on the respective exhaust passages 8, 9, and a main catalyst 13 is arranged on the exhaust passage 10, respectively. In this case, respective oxygen sensors 14, 15 provided with respective heaters 14a, 15a for heating sensor elements are arranged respectively, upstream from the respective pre-catalysts 11, 12. A fuel injection valve 5 is controlled per cylinder group by detection output of the respective oxygen sensors 14, 15, in a control unit 6. In the case, one of abnormality of the heaters 14a, 15a is diagnosed, the control is continued by the detection output at the side where a normal condition is diagnosed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio feedback control system for an internal combustion engine, and more specifically, to an air-fuel ratio feedback control using an air-fuel ratio sensor equipped with a heater for activating elements in a low exhaust temperature environment. The present invention relates to a countermeasure technique when an abnormality occurs in the heater in a device to be performed.

[0002]

2. Description of the Related Art Conventionally, an oxygen sensor (air-fuel ratio sensor) whose output value changes in response to the oxygen concentration in exhaust gas is provided in an engine exhaust passage, and an engine intake air-fuel mixture is controlled based on the output value of the oxygen sensor. There is known an air-fuel ratio feedback control device that detects an air-fuel ratio and feedback-controls a fuel injection amount in a direction to bring the detected air-fuel ratio closer to a target air-fuel ratio (see Japanese Patent Laid-Open No. 60-240840).

In general, the oxygen sensor cannot exhibit desired output characteristics unless the temperature reaches a predetermined activation temperature. Therefore, the desired air-fuel ratio control is performed even immediately after starting or under other operating conditions where the exhaust temperature is low. In order to obtain the desired characteristics, some oxygen sensors are provided with a heater so that desired output characteristics can be maintained without being affected by the exhaust gas temperature.

[0004]

By the way, at the time of starting, it is required to start the air-fuel ratio feedback control at an early stage in order to suppress the emission amount of HC at the time of starting. In this respect, if the oxygen sensor is provided with a heater as described above, it is possible to activate the sensor immediately after starting by heating the heater and start the air-fuel ratio feedback control early, and also after the start. The feedback control can be performed with good response without being greatly affected by the exhaust gas temperature.

However, heater disconnection, heater deterioration,
If the heater does not generate heat normally due to a decrease in battery voltage, the oxygen sensor is delayed in activation, so in a system that determines activation of the oxygen sensor based on its output and then starts feedback control, Sufficient control under conditions where the start of the air-fuel ratio feedback control is delayed, and even after the air-fuel ratio feedback control is started, the exhaust temperature is low and the sensor element cannot be sufficiently activated without heating the heater. There is a problem that a response cannot be obtained and convergence to the target air-fuel ratio is poor.

Here, in a V-type engine or the like, an oxygen sensor with a heater may be provided for each bank so that the air-fuel ratio feedback control is performed for each bank. When an abnormality occurs in the heater of the oxygen sensor, the air-fuel ratio feedback control has already started in the normal bank, but the other bank in which the heater abnormality has occurred waits for the exhaust temperature to rise and is delayed. An imbalance occurs in that control is started.

Further, in the bank where the heater abnormality occurs, the desired control response cannot be obtained in the low exhaust temperature state where the element activity cannot be secured even after the air-fuel ratio feedback control is started. When the increase in the amount during operation is added, the emission of HC is increased due to the deterioration of the control response. In the worst case, if both the heaters of both banks become abnormal, a large amount of them will be generated at the time of starting compared to normal. HC
There is a fear that will be discharged.

The present invention has been made in view of the above problems, and is an engine that can be divided into a plurality of cylinder groups, such as a V-type engine, and of course, an air-fuel ratio sensor with a heater is provided for each cylinder group. In addition, in an air-fuel ratio feedback control device that performs air-fuel ratio feedback control for each cylinder group, it is an object of the present invention to avoid a significant deterioration in air-fuel ratio controllability even if a heater abnormality occurs.

[0009]

Therefore, an air-fuel ratio feedback control system for an internal combustion engine according to the present invention is constructed as shown in FIG. In FIG. 1, the air-fuel ratio sensor is
A sensor whose output value changes in response to the concentration of a specific component in the exhaust gas that changes depending on the air-fuel ratio of the engine intake air-fuel mixture, and is equipped with a heater for heating the sensor element. , An exhaust system independently provided for each of the plurality of cylinder groups.

The cylinder group-specific correction value calculation means calculates an air-fuel ratio feedback correction value for each cylinder group based on the output value of the air-fuel ratio sensor, and the cylinder group-specific air-fuel ratio control means calculates the calculated cylinders. The fuel supply amount is corrected and controlled for each cylinder group based on the air-fuel ratio feedback correction value for each group. On the other hand, the heater abnormality diagnosis means diagnoses whether the heater provided in the air-fuel ratio sensor is normal or abnormal for each air-fuel ratio sensor.

The heater abnormality correction control means, when the heater abnormality diagnosing means diagnoses the heater abnormality by only a part of the air-fuel ratio sensors, the air-fuel ratio sensor based on the output value of the abnormality-diagnosed air-fuel ratio sensor is used. The calculation of the fuel ratio feedback correction value is stopped, and the correction of the fuel supply amount by the cylinder group-by-cylinder group air-fuel ratio control means for the cylinder group to which the air-fuel ratio sensor for which the heater abnormality has been diagnosed is corrected by the air-fuel ratio for which the heater is normally diagnosed. The correction is performed based on the air-fuel ratio feedback correction value calculated by the correction value calculating means for each cylinder group based on the sensor.

Here, in addition to the above-mentioned configuration, a low exhaust temperature state detecting means for detecting a state where the engine exhaust temperature is below a predetermined temperature, and the heater abnormality diagnosing means diagnoses the heater abnormality in all the air-fuel ratio sensors. At this time, the calculation characteristic of the air-fuel ratio feedback correction value by the cylinder group correction value calculation means is corrected only when the low exhaust temperature state detection means detects a state where the exhaust temperature is equal to or lower than a predetermined temperature. It is preferable to provide a calculation characteristic correction means for calculating the air-fuel ratio feedback correction value for each cylinder group based on the output value of each air-fuel ratio sensor.

[0013]

With this configuration, when all the heaters in the heater-equipped air-fuel ratio sensor provided for each cylinder group are normal, air-fuel ratio feedback control is performed for each cylinder group based on the output value of each air-fuel ratio sensor. Is applied. On the other hand, when a heater abnormality occurs in a part of the plurality of air-fuel ratio sensors, that is, when a cylinder group in which the heater is normal and a cylinder group in which the heater is abnormal are separated, it is diagnosed that the heater is abnormal. The calculation of the air-fuel ratio feedback correction value using the above-described air-fuel ratio sensor is stopped. Then, in the cylinder group in which the heater abnormality is diagnosed, the fuel supply amount is corrected based on the air-fuel ratio feedback correction value calculated using the output value of the air-fuel ratio sensor in which the other heaters are diagnosed as normal. .

Further, when the heater abnormality is diagnosed in all the cylinder groups, the correction request in the cylinder group in which the heater is normal as described above is applied to the cylinder group in which the heater is diagnosed as abnormal. Control cannot be performed. However, if air-fuel ratio feedback control is normally performed without heating by the heater, activation of the element due to exhaust temperature cannot be obtained, and controllability is greatly deteriorated in the state where heating by the heater is originally required. Will be done.

Therefore, an abnormality occurs in the heaters of all cylinder groups,
However, when the exhaust temperature is low, the control point is corrected by correcting the calculation characteristic of the air-fuel ratio feedback correction value, which is performed using the output value of the air-fuel ratio sensor with the abnormal heater. It is possible to prevent a large amount of HC from being discharged in the increase correction state by correcting the calculation characteristic on the lean side.

[0016]

EXAMPLES Examples of the present invention will be described below. Referring to FIG. 2 showing an embodiment, an air flow meter 3 for detecting an intake air flow rate Q of an engine is provided in an intake passage 2 of a V-type internal combustion engine 1, and an engine 1 is interlocked with an accelerator pedal (not shown).
A throttle valve 4 for controlling the intake air flow rate Q is provided, and an electromagnetic fuel injection valve 5 is provided for each cylinder at a branch portion of a downstream intake manifold.

The fuel injection valve 5 is opened and driven by an injection pulse signal from a control unit 6 having a built-in microcomputer, and is fed with pressure from a fuel pump (not shown) to the engine to be controlled to a predetermined pressure by a pressure regulator. Supply by injection. Further, a water temperature sensor 7 for detecting the cooling water temperature Tw in the cooling jacket of the engine 1.
Is provided.

On the other hand, when one of the V-shaped banks of the engine 1 is the right bank and the other is the left bank, the exhaust manifolds 8, 8 are individually provided for each bank (cylinder group).
9 (exhaust system) is provided, and the exhaust is led out independently for each bank. The exhaust manifolds 8 and 9 are joined together on the downstream side to form one exhaust passage 10, and the exhaust gas discharged by the exhaust manifolds 8 and 9 for each bank is joined and exhausted in the exhaust passage 10. To be done.

Pre-catalysts 11 and 12 for purifying exhaust gas are attached to the confluent portions of the exhaust manifolds 8 and 9, respectively, and a main catalyst 13 is attached to the exhaust passage 10. Further, at the confluence of the exhaust manifolds 8, 9 upstream of the pre-catalysts 11, 12, oxygen as an air-fuel ratio sensor for detecting the air-fuel ratio of the engine intake air-fuel mixture by detecting the oxygen concentration in the exhaust gas. Sensors 14 and 15 are attached to detect the oxygen concentration in the exhaust gas for each bank.

The oxygen sensors 14 and 15 are known sensors whose output value changes in response to the oxygen concentration in the exhaust gas, and the fact that the oxygen concentration in the exhaust gas suddenly changes at the theoretical air-fuel ratio is used. However, it is a rich / lean sensor capable of detecting rich / lean of the exhaust air-fuel ratio with respect to the theoretical air-fuel ratio. Furthermore,
Each oxygen sensor 14, 15 is provided with a heater 14a, 15a for heating the sensor element.

Further, a crank angle sensor 17 for extracting a rotation signal from the cam shaft or the crank shaft is provided, and the unit angle signal output from the crank angle sensor 17 for each unit crank angle is counted for a certain period of time, or The engine rotation speed Ne is detected by measuring the cycle of the reference angle signal output for each predetermined piston position. The control unit 6 calculates the basic fuel injection amount Tp based on the intake air flow rate Q and the engine rotation speed Ne, and also calculates the air-fuel ratio for each bank detected by the oxygen sensors 14 and 15 as the target air-fuel ratio (theoretical). Air-fuel ratio feedback correction coefficients αR, αL (air-fuel ratio feedback correction values)
Is calculated for each cylinder group by proportional-plus-integral control.

Further, a correction request for each operating region is learned for each cylinder group based on the air-fuel ratio feedback correction coefficients αR, αL calculated for each cylinder group, and the basic fuel injection amount Tp is learned.
And air-fuel ratio learning correction values KBLRR, KBLR for each cylinder group stored for each operating region divided by the engine rotation speed Ne
L is rewritten based on the learning result. Then, the basic fuel injection amount Tp is set to the air-fuel ratio feedback correction coefficients αR and αL and the air-fuel ratio learning correction value KBLR.
By correcting with R and KBLRL, the final fuel injection amount TiR for each cylinder group (← Tp × αR × KBLR
R), TiL (← Tp × αL × KBLRL),
An injection pulse signal is sent to the corresponding fuel injection valve 5 according to the fuel injection amount TiR, TiL for each cylinder group to control the fuel injection amount while performing the air-fuel ratio control for each cylinder group.

The air-fuel ratio feedback control when the heaters 14a and 15a are abnormal, which is a feature of this embodiment, will now be described with reference to the flow charts of FIGS. In the present embodiment, the cylinder group-based correction value calculation means,
The functions of the air-fuel ratio control means for each cylinder group, the heater abnormality diagnosis means, the heater abnormality correction control means, the calculation characteristic correction means, and the low exhaust temperature state detection means are described in the description and in FIGS.
The control unit 6 is provided as software as shown in the flowchart of FIG.

In the flow chart of FIG. 3, first, in step 1 (denoted as S1 in the figure.
O of heaters 14a, 15a attached to each oxygen sensor 14, 15
It is determined whether or not the N condition is satisfied. That is, the heaters 14a and 15
In the case of controlling ON / OFF of a according to the conditions, the heater is energized only when the exhaust gas temperature is low and the sensor element cannot be activated without heating by the heaters 14a, 15a. In this embodiment, at least the warm-up time and the low load time are included.

The heaters 14a and 15 are continuously operated during engine operation.
It may be configured to energize a. Heater 14
When controlling the ON / OFF switching of a and 15a and the OFF condition is satisfied, the heater 14a and
This is a condition that the desired output characteristics can be obtained without heating by 15a. In this case, even if the desired amount of heat is not obtained due to deterioration of the heaters 14a, 15a, it is not possible to directly discharge the air. Since it does not affect the fuel ratio feedback control,
Proceed to step 7 and normally use one oxygen sensor for each bank.
Use 4 and 15 to execute air-fuel ratio control.

On the other hand, under the condition that the heaters 14a and 15a are turned on, if the heating by the heaters 14a and 15a is not actually performed normally, the activation of the sensor element cannot be obtained and the normal control is performed as it is. Is executed, the air-fuel ratio controllability will be greatly deteriorated. Therefore, the process proceeds to step 2 and subsequent steps, the heat generation amount (power W) of each heater 14a, 15a is calculated respectively, and it is diagnosed based on the calculation result whether or not each heater 14a, 15a is normally generating heat.

In step 2, the voltage V applied to each heater 14a, 15a is monitored, and in the next step 3,
The current value I in each heater 14a, 15a is monitored. Then, in step 4, the electric power W (capacity) in each of the heaters 14a and 15a is based on the monitoring result of the voltage / current.
Is calculated for each. In addition, in the above description, it is possible to detect the state in which the amount of heat generated is decreased due to the deterioration of the heater by obtaining the electric power. However, for simplicity, the heater 14a,
It may be configured to determine whether or not the energizing circuit for 15a is broken.

When the electric power in each of the heaters 14a and 15a is calculated as described above, in the next step 5, the electric power in the heater 14a of the oxygen sensor 14 provided in the right bank is compared with a predetermined value to obtain the right electric power. The oxygen sensor 14 of the bank determines whether or not the heater 14a normally generates heat. Here, when it is determined that the heat generation amount of the heater 14a does not decrease (including disconnection), subsequently, in step 6, the oxygen sensor 15 of the left bank determines whether or not the heater 15a normally generates heat. .

When it is determined in step 6 that the heater 15a is normal, the heaters 14 are set in both the right bank and the left bank.
It has been confirmed that a and 15a generate heat normally, and in this case, the oxygen sensors 14 and 15 can be heated by the heater to maintain the desired active state. 7, the normal air-fuel ratio control is executed.

On the other hand, when it is determined in step 6 that the heat generation amount of the heater 15a in the left bank has decreased, step 8
Proceeds to step S31 to stop the calculation of the air-fuel ratio feedback correction coefficient αL for the left bank, which is to be calculated using the oxygen sensor 15 in which the heater 15a has been diagnosed abnormal, and instead, the heater is normally diagnosed on the right. The injection amount TiL for the left bank is calculated using the air-fuel ratio feedback correction coefficient αR for the right bank calculated using the oxygen sensor 14 of the bank (TiL ← Tp × αR × KBLRL).

Therefore, at this time, the learning update of the air-fuel ratio learning value KBLRL in the left bank is interrupted. On the other hand, when it is determined in step 5 that the heat generation amount of the heater 14a of the right bank has been reduced, the process proceeds to step 9 and the heat generation amount reduction of the heater 15a of the left bank is diagnosed. When it is determined in step 9 that the heater 15a of the left bank is normally generating heat, the heater 14a of the right bank is
Will only be abnormal, in this case the step
Go to 10.

In step 10, as in the case of step 8, the calculation of the air-fuel ratio feedback correction coefficient αR using the oxygen sensor 14 of the right bank for which the abnormality is diagnosed is stopped,
Instead, a normally diagnosed left bank oxygen sensor 15
The injection amount TiR for the right bank is calculated by using the air-fuel ratio feedback correction coefficient αL for the left bank calculated by using (TiR ← Tp × αL × KBLRR).

For example, when the activation of the oxygen sensors 14 and 15 which are discriminated based on the sensor output is included as a condition for starting the air-fuel ratio feedback control at the time of start-up, the oxygen in which the calorific value of the heater is reduced is generated. The start of the air-fuel ratio feedback control using the sensor will be delayed. Here, in the case of a configuration having an independent air-fuel ratio feedback control system for each bank as in the V-type engine described above, the heater of the oxygen sensor of one bank is normal, and the heater of the oxygen sensor of the other bank is When the amount of heat generated by the heater is reduced, the control of the bank in which the heater is normal is started early, whereas the control in the bank in which the heater is abnormal is started with a large delay. turn into. Then, in the bank in which the heater abnormality occurs, the feedback control is delayed, so that the exhaust property immediately after the start is significantly deteriorated (the amount of HC is increased) as compared with the other bank.

However, the independent air-fuel ratio feedback control for each bank is for precisely controlling a slight difference in correction request between banks, and basically it is estimated that there is no great difference in correction request. It Therefore, the air-fuel ratio feedback correction coefficient α calculated for the other bank is applied to the bank in which the start of the feedback control is delayed due to the abnormality of the heater.
As a result, it is possible to avoid a large delay in the start of the feedback control due to the heater abnormality, and apparently the feedback control is normally started, so that it is possible to avoid an increase in the amount of HC discharged due to the heater abnormality. .

Also, even when the heater is not started, the air-fuel ratio feedback correction coefficient α calculated at the desired response speed due to the normal heat generation of the heater is applied to the other bank in which the response speed deteriorates due to the abnormality of the heater. Thus, the air-fuel ratio can be stabilized at the target air-fuel ratio at an early stage even in the bank where the heater abnormality occurs. On the other hand, if the heater abnormality in the left bank is diagnosed in step 9, it means that the heater abnormality has occurred in both banks, and the heater has an air-fuel ratio feedback correction calculated using a normal oxygen sensor. The above-described control of applying the coefficient α to the bank having the heater abnormality cannot be performed.

Therefore, in the above case, the step
Proceed to 11 to execute the control shown in the flowchart of FIG. In the flowchart of FIG. 4, first, in step 21, it is confirmed that the air-fuel ratio feedback control is being performed in each bank. If feedback control is in progress, it is determined in step 22 whether the engine rotation speed Ne is less than or equal to a predetermined speed. If it is at a predetermined low rotation speed, further in step 23, the basic fuel injection amount Tp is set. It is determined whether (engine load) is less than or equal to a predetermined value.

If it is determined in the steps 22 and 23 that the engine is in the low rotation / low load region, the process proceeds to step 24, and the air-fuel ratio feedback correction coefficient α
In proportional / integral control of R and αL, lean air-fuel ratio →
At the time of rich inversion, the proportional constant P _L for correcting the correction coefficients αR and αL to decrease in a skip manner is increased and corrected. By the increase correction of the proportional constant P _L , the control point of the air-fuel ratio feedback control is corrected to the lean side.

That is, the low rotation / low load region of the engine which is discriminated is an operating region where engine exhaust is low, and since the heater is abnormal, the response speeds of the oxygen sensors 14 and 15 are poor. , When the air-fuel ratio feedback control is started during warm-up immediately after the start, the deterioration of the control response prevents the enrichment of the base air-fuel ratio due to the increase correction from being converged with good response, and the control start due to the heater abnormality. Along with the delay, the HC emission amount at the time of starting will be greatly increased.

Therefore, the increase in the HC emission amount is reduced as much as possible by correcting the control point of the air-fuel ratio feedback control to the lean side by correcting the increase in the proportional constant P _L. Further, in step 25, it prohibits the air-fuel ratio learning in each bank, while performing the increase correction of the proportional constant P _L, to avoid being erroneously learned.

The increase correction of the proportional constant P _L may be limited to the case where the increase correction corresponding to the water temperature is added, but it is controlled to be leaner than the target air-fuel ratio. However, since it is in the low exhaust temperature region, it rarely bounces back to NOx, so the above limitation is not always necessary. Further, the low exhaust temperature state may be determined by the engine temperature and load as described above, or may be directly detected by the exhaust temperature sensor.

By the way, in the above embodiment, when the heaters of both banks are abnormal, the proportional constant P _L is increased and corrected in order to correct the control point of the air-fuel ratio feedback control to the lean side. , Correction of judgment level in rich / lean judgment based on outputs of oxygen sensors 14 and 15,
The delay time from the detection of the rich / lean inversion to the actual execution of the proportional control may be modified.

Further, in the present embodiment, the case where the present invention is applied to the V-type internal combustion engine has been shown. However, in addition to this, the exhaust gas is exhausted for every plural cylinders (6 cylinders, 3 cylinders) in the horizontally opposed engine or the series multi-cylinder engine. The engine may be configured to discharge all at once.
The engine may be divided into three or more cylinder groups.

[0043]

As described above, according to the present invention, in the air-fuel ratio feedback control device for providing the air-fuel ratio sensor with the heater for each cylinder group and performing the air-fuel ratio feedback control for each cylinder group, the heater abnormality is detected. Even if it occurs, there is an effect that it is possible to prevent the air-fuel ratio controllability from being greatly deteriorated, and particularly to improve the exhaust property immediately after starting when an abnormality occurs in the heater.

[Brief description of drawings]

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

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

FIG. 3 is a flowchart showing air-fuel ratio control when the heater is abnormal.

FIG. 4 is a flowchart showing air-fuel ratio control when the heater is abnormal.

[Explanation of symbols]

 1 engine 3 air flow meter 4 throttle valve 5 fuel injection valve 6 control unit 7 water temperature sensor 8, 9 exhaust manifold 10 exhaust passage 11, 12 pre-catalyst 13 main catalyst 14, 15 oxygen sensor (air-fuel ratio sensor) 14a, 15b heater 17 crank Corner sensor

Claims (2)

[Claims] 1. An independent exhaust system is provided for each of a plurality of cylinder groups,
An air-fuel ratio sensor in which an output value changes in response to the concentration of a specific component in exhaust gas that changes according to the air-fuel ratio of an engine intake air-fuel mixture, wherein an air-fuel ratio sensor provided with a heater for heating a sensor element is used. While being provided in each independent exhaust system, a cylinder group-based correction value calculation means for calculating an air-fuel ratio feedback correction value for each cylinder group based on the output values of these air-fuel ratio sensors, and a cylinder group-based correction value calculation means An air-fuel ratio feedback control device for an internal combustion engine, comprising: a cylinder-group-specific air-fuel ratio control means for correcting and controlling the fuel supply amount for each cylinder group based on the air-fuel ratio feedback correction value for each cylinder group, Heater abnormality diagnosing means for diagnosing the normality / abnormality of the heater provided in the fuel ratio sensor for each air-fuel ratio sensor, and only part of the air-fuel ratio sensor by the heater abnormality diagnosing means When a heater abnormality is diagnosed, the calculation of the air-fuel ratio feedback correction value based on the output value of the air-fuel ratio sensor for which the abnormality is diagnosed is stopped, and the air-fuel ratio sensor for which the heater abnormality is diagnosed is used for the corresponding cylinder group. A heater for correcting the fuel supply amount by the cylinder group-specific air-fuel ratio control means based on the air-fuel ratio feedback correction value calculated by the cylinder group-specific correction value calculation means based on the air-fuel ratio sensor whose heater is normally diagnosed. An air-fuel ratio feedback control device for an internal combustion engine, comprising: an abnormal correction control means; 2. A low exhaust temperature state detecting means for detecting a state in which an engine exhaust temperature is lower than a predetermined temperature, and the low exhaust temperature detecting means when the heater abnormality diagnosing means diagnoses a heater abnormality in all the air-fuel ratio sensors. Only when the state in which the exhaust temperature is lower than or equal to the predetermined temperature is detected by the temperature state detection means, the calculation characteristics of the air-fuel ratio feedback correction value by the cylinder group correction value calculation means are corrected to The air-fuel ratio feedback control device for an internal combustion engine according to claim 1, further comprising: arithmetic characteristic correction means for calculating an air-fuel ratio feedback correction value based on an output value of each air-fuel ratio sensor.