JPH1054276A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate change with the lapse of time an air/fuel ratio sensor and correct its output. SOLUTION: When fuel is cut off and oxygen concentration in the exhaust gas is not lower than a prescribed value (S1-4), the output voltage Vr of an element part in an air/fuel ratio sensor is sampled for a prescribed time (S5-7). At the time of the initial use of the air/fuel ratio sensor, the peak value of the sampled output voltage is stored in the ring buffer of the first storage area, and an average value or a standard deviation of (n) numbers of peak values is calculated and stored (S10, 18, 19). At the time of estimating change with the lapse of time of the air/fuel ratio sensor, the peak value of the sampled output voltage is stored in the ring buffer of the second storage area and the average value or the standard deviation of (n) numbers of peak values is calculated and stored (S10-12). An air/fuel ratio λ is corrected with a set correction factor Ks based on the deviation Dsigm of the average value or the standard deviation which are stored in the first storage area or the second storage area, and air/fuel ratio feedback control is conducted based on the corrected air/fuel ratio λ (S14-17) at the time of estimating the change with the lapse of time.

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 control device for an internal combustion engine, and more particularly to a technique for correcting a change over time of a wide-range air-fuel ratio sensor.

[0002]

2. Description of the Related Art In recent years, in order to prevent deterioration of exhaust characteristics due to failure of an engine control system or deterioration with the passage of time, a self-diagnosis of whether or not the control system has a failure or has not deteriorated with time has been performed. There is an increasing need for a system for notifying drivers and maintenance personnel of this information. For this reason, it is necessary to enhance the diagnostic function of the sensors and actuators and to reliably perform the correction function and the deterioration determination for compensating for the deterioration with time, and are disclosed in, for example, JP-A-4-112939 and JP-A-4-112941. As described above, in a gasoline engine using a three-way catalyst, a technology has been devised in which oxygen sensors (air-fuel ratio sensors) are arranged before and after the catalyst, and the accuracy of air-fuel ratio control is improved based on each sensing result. I have.

[0003]

However, in a system such as a lean-burn engine in which the air-fuel ratio is reduced without using a three-way catalyst to improve the exhaust characteristics, a wide range of air-fuel ratios can be detected. Since the wide-range air-fuel ratio sensor is used to control the air-fuel ratio to match the operating state of the engine, it is not possible to perform a determination process as in the prior art for controlling the air-fuel ratio to the stoichiometric air-fuel ratio (14.7).

It is also conceivable to arrange a plurality of wide-range air-fuel ratio sensors in the exhaust passage and to perform processing by majority decision or the like with redundancy, but since the wide-range air-fuel ratio sensor is expensive, it is not a practical method. is not. In view of the above problems, the present invention provides an air-fuel ratio control device for an internal combustion engine that estimates a change with time from a change in output characteristics of a wide-range air-fuel ratio sensor and corrects the change with time. With the goal.

[0005]

For this reason, as shown in FIG. 1, the invention according to claim 1 is provided in an exhaust passage of an engine for detecting a wide range of air-fuel ratios based on oxygen concentration in exhaust gas. A fuel ratio sensor A, a combustion state determining means B for determining the presence or absence of combustion in the engine, and a resistance value of the element portion of the air-fuel ratio sensor A when the combustion state determining means B determines that the fuel is not in a combustion state. Resistance value detection means C for detecting, first storage means D for storing an initial resistance value of the sensor element portion,
A second storage unit for storing a resistance value of the sensor element unit during use of the air-fuel ratio sensor; and a second storage unit based on a deviation of resistance values of element units stored in the first storage unit and the second storage unit. Correction coefficient setting means F for setting a correction coefficient for correcting the output value of the air-fuel ratio sensor A, and output value correction means G for correcting the output value of the air-fuel ratio sensor A using the correction coefficient
And air-fuel ratio feedback control means H for performing feedback control of the air-fuel ratio based on the corrected output value of the air-fuel ratio sensor A.

With this configuration, the output value of the air-fuel ratio sensor is corrected by the correction coefficient set based on the deviation between the initial resistance value of the sensor element and the resistance during use of the sensor element. Done. That is, the output value of the air-fuel ratio sensor is corrected based on the change in the resistance value of the sensor element. According to a second aspect of the present invention, the combustion state determining means includes an opening degree detecting means for detecting an opening degree of a throttle valve interposed in an intake passage of the engine, and an engine rotational speed detecting means for detecting a rotational speed of the engine. And the oxygen concentration based on the air-fuel ratio signal from the air-fuel ratio sensor is a predetermined value or more,
When the detected throttle opening is less than a predetermined value and the engine speed is equal to or more than a predetermined value, or when the engine speed is equal to or more than a predetermined value, the engine is determined to be in a non-combustion state.

With this configuration, the fuel cut state in which the fuel supply to the engine is stopped, that is, the non-combustion state of the engine is determined with high accuracy. According to a third aspect of the present invention, the resistance value detecting means detects a resistance value via an output voltage of an element of the air-fuel ratio sensor. If you do this,
Even without directly detecting the resistance value of the element part of the air-fuel ratio sensor,
The resistance value is indirectly detected via the output voltage of the sensor element.

The invention according to claim 4 includes detection number counting means for counting the number of times of detection of the resistance value of the sensor element portion from the start of use of the air-fuel ratio sensor, and the first storage means comprises:
The resistance value when the counted number of times of resistance value detection is less than a predetermined value is stored, and the second storage unit stores the resistance value when the counted number of times of resistance value detection is equal to or more than a predetermined value.

With this configuration, the resistance value of the sensor element portion when the number of times of resistance value detection is less than the predetermined value becomes the initial resistance value, and the resistance value of the sensor element portion when the number of times of resistance value detection is equal to or more than the predetermined value. Is the resistance value in use. The invention according to claim 5, wherein the first storage means and the second storage means store the maximum value of the resistance value of the element portion of the air-fuel ratio sensor detected by the resistance value detection means within a predetermined time. I made it.

[0010] In this way, characteristic data is extracted from the fluctuating detection values (resistance values of the sensor element portion). The invention according to claim 6 is configured to include reset means for resetting the number of times of resistance value detection by the detection number counting means when the air-fuel ratio sensor is replaced. With this configuration, when the air-fuel ratio sensor is replaced, the resistance value of the sensor element at the time of initial use of the air-fuel ratio sensor is newly stored.

According to a seventh aspect of the present invention, the resistance value of the element portion of the air-fuel ratio sensor is determined by changing the resistance value of the electrodes provided on opposite end faces of the solid electrolyte of the oxygen ion conductor constituting the element portion of the air-fuel ratio sensor. Between the resistance values. In this way, a change in the output characteristic due to a change over time of the air-fuel ratio sensor can be accurately estimated.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the attached drawings. FIG. 2 shows an embodiment of a compressed natural gas (hereinafter referred to as “CNG”) engine provided with an air-fuel ratio control device according to the present invention. Air flows into a CNG engine (hereinafter referred to as “engine”) 1 through an intake passage 4 in which an air cleaner, a mixer 2 and a throttle valve 3 (not shown) are interposed. The mixer 2 includes a venturi 2a that generates a negative pressure by reducing an intake passage area.
And a fuel injection solenoid valve 2b driven and controlled by a duty-controlled feedback solenoid. Then, CNG stored in gas in the cylinder 5 is pushed out of the cylinder 5 and supplied to the regulator 8 through the fuel pipe 6a and the fuel cutoff valve 7. The CNG supplied to the regulator 8 is heated by the engine cooling water to become a gas of approximately atmospheric pressure, and is sucked by the Venturi negative pressure according to the flow rate of the intake air passing through the mixer 2 via the fuel pipe 6 b and the fuel cutoff valve 9. , Mixed with the intake air and supplied to the engine 1.

A bypass passage 10 that bypasses the throttle valve 3 is formed in the intake passage 4, and an idle control valve 11 interposed therein regulates the intake air flow during idling. Reference numeral 12 not described above is a spark plug for performing spark ignition on a mixture of air and CNG, reference numeral 13 is a diaphragm valve driven by a negative pressure for opening and closing the throttle valve 3, and reference numeral 14 is Reference numeral 15 denotes a negative pressure introduction passage for supplying suction negative pressure downstream of the throttle valve 3 as a drive source to the diaphragm valve 13, and a reference numeral 15 is a solenoid interposed in the negative pressure introduction passage 14 for adjusting the supply negative pressure to the diaphragm valve 13. It is a valve.

As a sensor for controlling the air-fuel ratio,
A wide-range air-fuel ratio sensor 17 (hereinafter referred to as an “air-fuel ratio sensor”, which will be described later in detail) interposed in an exhaust passage 16 of the engine 1, is attached to a crankshaft (not shown) of the engine 1, and synchronizes with a rotation of the engine to a crank unit angle. A crank angle sensor 18 for outputting a signal (engine speed detecting means),
A cooling water temperature sensor 20 provided on the water jacket portion 19a of the cylinder block 19 and detecting a cooling water temperature;
An opening sensor 21 (opening detecting means) which is attached to the throttle valve 3 and detects the opening of the throttle valve 3 is provided. These outputs are output from the CPU 22a, ROM 22b, R
The signal is input to the control unit 22 including the AM 22c, the input interface 22d, the output interface 22e, and the internal bus 22f. The control unit 22 counts a crank unit angle signal output from the crank angle sensor 18 to calculate an engine rotation speed, and also determines a combustion state determination unit, a resistance value detection unit, a detection number counting unit, a reset unit, It has functions as a first storage unit, a second storage unit, a correction coefficient setting unit, an output value correction unit, and an air-fuel ratio feedback control unit.

Furthermore, the control unit 22 includes:
An ON / OFF signal of the ignition switch 23 is input, and a power supply voltage is applied from the battery 24. Next, details of the air-fuel ratio sensor 17 used in the present embodiment will be described with reference to FIGS. In FIG. 3 showing the details of the sensor element portion of the air-fuel ratio sensor 17, the air-fuel ratio sensor 17 has a porous electrode 17b made of platinum on opposite end surfaces of zirconia 17a as a solid electrolyte of an oxygen ion conductor. 17c are provided respectively. If there is a difference in oxygen concentration between the front and back of the zirconia 17a, the oxygen diffuses in the zirconia 17a, and has a property of shifting from a higher oxygen concentration to a lower oxygen concentration to be in an equilibrium state. Therefore, utilizing this property, the electromotive force (output voltage) Vr generated between the two electrodes in accordance with the oxygen partial pressure difference between the reference gas and the non-detection gas (engine exhaust) is fixed to the fixed resistor 17.
It is detected as a voltage Vs between both ends of d.

The output characteristic of the air-fuel ratio sensor 17 is, as shown in FIG. 4, the output voltage Vs with increasing oxygen concentration.
Increases substantially in proportion to each other, and as shown in FIG. 5, the output current Ip corresponds to the one-to-one depending on the air-fuel ratio. That is,
Since the air-fuel ratio and the output current Ip correspond one-to-one, air-fuel ratio control for controlling the air-fuel mixture to a desired air-fuel ratio can be performed.

Here, the principle of estimating the change over time of the air-fuel ratio sensor 17 will be described. Since the resistance value between the electrodes of the element portion of the air-fuel ratio sensor 17 has a characteristic that changes with time and gradually increases, the resistance value between the electrodes is changed to the output voltage V between the electrodes.
It is detected as r (the resistance value and the output voltage are closely related), and a change with time is estimated from the change in the output voltage Vr. Specifically, the air-fuel ratio sensor 1 under substantially the same conditions
7, the difference Vr ₁ -Vr ₀ between the output voltage Vr ₀ at the time of initial use and the output voltage Vr ₁ at the time of estimating the change with time is calculated, and the difference Vr ₁
Based on −Vr ₀ , a correction coefficient Ks is set with reference to a correction coefficient map, and the air-fuel ratio is corrected using the correction coefficient Ks. In the actual control, in order to improve the accuracy of estimating the change with time, the same condition is applied to a state in which the fuel supply to which the air-fuel ratio feedback control is not performed is stopped (in this case, the combustion is not performed). (The engine exhaust is in the same state as the atmosphere because it is not described), and the output voltage Vr uses the average value or the standard deviation of a plurality of data.

The air-fuel ratio control described above is executed in software by a program stored in a ROM 22b constituting the control unit 22. FIG.
Indicates the contents of control by this program, and is in the form of a subrun executed every predetermined time. Step 1
In the figure, the throttle opening θ is read from the opening sensor 21 and the engine rotation speed Ne is calculated based on the crank unit angle signal from the crank angle sensor 18.

In step 2, it is determined whether or not a condition for stopping fuel supply to the engine 1 (hereinafter referred to as "fuel cut condition") is satisfied based on the throttle opening θ and the engine speed Ne. Condition satisfied (Yes)
If so, the process proceeds to step 3, and if the fuel cut condition is not satisfied (No), the process proceeds to step 14. Here, the case where the fuel cut condition is satisfied is, for example, the following case.

(1) When the throttle opening θ is smaller than a predetermined value and the engine speed Ne is higher than a predetermined value. That is, when fuel supply is stopped during deceleration to reduce HC and improve fuel efficiency. (2) The case where the engine speed Ne becomes higher than a predetermined value. That is, when the increase in the engine speed Ne is suppressed to protect the engine.

In step 3, the output voltage Vs (see FIG. 3) from the air-fuel ratio sensor 17 is read. In step 4, it is determined whether or not the output voltage Vs from the air-fuel ratio sensor 17 is equal to or higher than the fuel cut determination level. If the output voltage Vs is equal to or higher than the determination level (Yes), the process proceeds to step 5; If there is, go to step 14. That is, there is a characteristic (see FIG. 4) that the oxygen concentration in the engine exhaust increases as the output voltage Vs of the air-fuel ratio sensor 17 increases (see FIG. 4). Here, in addition to the determination of the fuel cut condition in step 2, it is determined whether or not the output voltage Vs is equal to or higher than the determination level. This is because the temporal change of the air-fuel ratio sensor 17 is estimated with high accuracy. It is necessary to make the estimation conditions at the start of use of the air-fuel ratio sensor 17 and at the time of estimating the change over time the same as much as possible, and to stop the fuel supply to the engine 1 with high accuracy in order to make the estimation conditions more strict. Because. Note that the processing of Steps 1 to 4 corresponds to combustion state determination means.

In step 5, the timer is started, and the measurement of the elapsed time from the start of the fuel cut is started. In step 6, the output voltage Vr (see FIG. 3) is read from the air-fuel ratio sensor 17 as a resistance value between the electrodes, and stored in the RAM 22c constituting the control unit 22.

In step 7, after the fuel cut is started by the timer started in step 5, the TME
It is determined whether or not M (seconds) has elapsed. If not (No), the process returns to step 6, and the reading and storing of the output voltage Vr between the electrodes are repeated. Step 5 to Step 7
By the processing of (1), the sampling of the output voltage Vr during TMEM (second) after the start of the fuel cut is performed, and this processing corresponds to the resistance value detecting means.

In step 8, it is determined whether or not the air-fuel ratio sensor 17 has been newly replaced.
s) The process proceeds to step 9 where a counter k (detection number counting means) described later is reset. This determination may be made based on, for example, a flag backed up in the RAM 22c constituting the control unit 22. Note that the processing in step 9 corresponds to a reset unit.

In step 10, it is determined whether or not the value of the counter k is equal to or greater than a predetermined value MAXk.
s), the process proceeds to step 11, where the value is less than MAXk (N
If it is o), go to step 18. This counter k
Is set to 0 at the time of initial installation and replacement of the air-fuel ratio sensor 17 (see step 9), and holds the number of times of sampling of the output voltage Vr between the electrodes of the air-fuel ratio sensor 17.

In step 11, a peak voltage (maximum voltage) Vrpk is extracted from the output voltage Vr between the electrodes stored in step 6, and this peak voltage Vrpk is changed to n.
The data is stored in the m-th ring buffer (second storage means) in the second storage area for storing the data. This m is, for example, using the remainder obtained by dividing the counter k by n, and using the latest n
The number of peak voltages Vrpk are stored.

In step 12, an average value or a standard deviation is calculated from the n peak voltages Vrpk stored in the ring buffer of the second storage area. In step 13, the counter k is incremented. In step 14, a deviation Dsigm of an average value or a standard deviation of a first storage area and a second storage area described later is calculated. Specifically, as shown in FIG. 8, the average values stored in the first storage area and the second storage area are respectively Xrn0 and Xrn1, and the standard deviation is σ.
Assuming that rn0 and σrn1, Dsigm = Xrn1−Xrn0 or Dsigm = (Xrn1−σrn1) − (Xrn0−σ
rn0).

In step 15, based on the calculated Dsig, a correction coefficient Ks is searched by referring to a correction coefficient map shown in FIG. Steps 14 and 15
Corresponds to the correction coefficient setting means. In step 16, the air-fuel ratio λ detected from the air-fuel ratio sensor 17 is corrected based on the correction coefficient Ks as λ = λ × Ks. In addition,
This processing corresponds to output value correction means.

In step 17, air-fuel ratio feedback control is performed based on the corrected air-fuel ratio λ (air-fuel ratio feedback control means), and the process is terminated. Step 18
Then, the output voltage V between the electrodes stored in step 6
The peak voltage (maximum voltage) Vrpk is extracted from r,
This peak voltage Vrpk is stored in a first memory storing n data.
The data is stored in the m-th ring buffer (first storage means) in the storage area. For m, for example, the remainder obtained by dividing the counter k by n is used so that the latest n peak voltages Vrpk are stored.

In step 19, an average value or a standard deviation is calculated from the n peak voltages Vrpk stored in the ring buffer of the first storage area. In step 20, the counter k is incremented, and the process proceeds to step 17, where the air-fuel ratio feedback control is performed based on the air-fuel ratio λ detected by the air-fuel ratio sensor 17.

In this way, the average value or standard deviation obtained from the variation distribution of the voltage peak value Vrpk during the initial use of the air-fuel ratio sensor 17 and the voltage peak value Vrpk at the time of estimating the temporal change of the air-fuel ratio sensor 17 are obtained. Find the deviation from the average or standard deviation found from the variation distribution,
Based on the deviation, the correction coefficient Ks of the air-fuel ratio sensor 17 can be obtained from a preset correction coefficient map. And, when performing the air-fuel ratio feedback control,
By correcting the output value of the air-fuel ratio sensor 17 with the correction coefficient Ks, for example, the output correction by the change over time of the output of the wide-range air-fuel ratio sensor used for the target air-fuel ratio control that changes depending on the engine operating state in a lean burn engine or the like can be performed. It can be carried out.

The condition for detecting the voltage peak value Vrpk between the electrodes of the air-fuel ratio sensor 17 is the time of fuel cut determined based on the throttle opening θ and the engine speed Ne. Is determined based on the output voltage Vs of the air-fuel ratio sensor 17, the detection states at the time of initial use of the air-fuel ratio sensor 17 and at the time of estimating the change over time can be made the same as much as possible. The estimation accuracy can be improved.

Further, when the air-fuel ratio sensor 17 is replaced halfway, the counter k is reset. In this case, the variation distribution of the voltage peak value Vrpk during the initial use of the air-fuel ratio sensor 17 is obtained. The average value or the standard deviation is calculated again, and it is possible to prevent the estimation accuracy of the change over time due to the individual difference of the air-fuel ratio sensor 17 from decreasing.

In this embodiment, the air-fuel ratio sensor 17
In order to make the conditions for detecting the voltage peak value Vrpk between the electrodes at the time of initial use and at the time of estimating the change over time the same as possible, the fuel supply to the engine was restricted when the fuel cut was stopped. It may be immediately after the start of the engine and when combustion is not being performed.

[0035]

As described above, according to the first aspect of the present invention, the deviation between the initial resistance value of the sensor element portion and the resistance value during use of the sensor element portion, that is, the sensor element due to aging. A correction coefficient for the output value of the air-fuel ratio sensor is set based on the change in the resistance value of the section. When the air-fuel ratio feedback control is performed, the output value of the air-fuel ratio sensor is corrected by the set correction coefficient, so that, for example, a wide area used for target air-fuel ratio control that changes depending on the engine operating state in a lean burn engine or the like. The output can be corrected based on the change over time of the output of the air-fuel ratio sensor, and the accuracy of the air-fuel ratio control can be improved, and the exhaust properties can be improved.

According to the second aspect of the present invention, the fuel cut state in which the fuel supply to the engine is stopped, that is, the non-combustion state of the engine is determined with high accuracy. The determination conditions at the time of estimating the change over time can be made the same as much as possible, and the estimation accuracy of the change over time can be further improved. According to the third aspect of the present invention, the resistance value is indirectly detected via the output voltage of the sensor element portion without directly detecting the resistance value of the element portion of the air-fuel ratio sensor. The voltage can be A / D converted and processed by the control unit, and the mechanism for detecting the resistance value of the sensor element can be simplified.

According to the fourth aspect of the present invention, the resistance value of the sensor element portion when the number of times of resistance value detection is less than the predetermined value becomes the initial resistance value, and the sensor element when the number of times of resistance value detection is more than the predetermined value. Since the resistance value of the part becomes the resistance value in use,
With the simple control of comparing the magnitudes of the resistance value detection times, the initial resistance value and the resistance value in use can be distinguished.

According to the fifth aspect of the present invention, since characteristic data is extracted from the fluctuating detection values, it is possible to improve the estimation accuracy of the change over time of the air-fuel ratio sensor. According to the invention of claim 6, when the air-fuel ratio sensor is replaced, the resistance value of the sensor element portion at the time of initial use of the air-fuel ratio sensor is newly stored, so that the individual difference of the air-fuel ratio sensor accompanying the replacement is stored. , It is possible to prevent the estimation accuracy of the change with time from being lowered.

According to the seventh aspect of the present invention, it is possible to accurately estimate a change in output characteristics of the air-fuel ratio sensor due to a change over time.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to claims of the present invention.

FIG. 2 is a system diagram showing an embodiment of an air-fuel ratio control device according to the present invention.

FIG. 3 is a detailed view of an air-fuel ratio sensor element used in the above system.

FIG. 4 is a diagram showing an oxygen concentration-output voltage characteristic of the air-fuel ratio sensor according to the first embodiment;

FIG. 5 is a diagram showing an air-fuel ratio-output current characteristic of the air-fuel ratio sensor according to the first embodiment;

FIG. 6 is a flowchart showing air-fuel ratio control contents according to the first embodiment;

FIG. 7 is a diagram showing a correction coefficient map according to the first embodiment;

FIG. 8 is a diagram showing a distribution state of a resistance value of the sensor element unit according to the first embodiment;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 3 Throttle valve 4 Intake passage 16 Exhaust passage 17 Air-fuel ratio sensor 18 Crank angle sensor 21 Opening sensor 22 Control unit

Claims (7)

[Claims] 1. An air-fuel ratio sensor interposed in an exhaust passage of an engine for detecting a wide range of air-fuel ratios based on oxygen concentration in exhaust gas, and combustion state determining means for determining whether or not combustion occurs in the engine.
Resistance value detecting means for detecting a resistance value of an element portion of the air-fuel ratio sensor when the combustion state determining means determines that the air-fuel ratio sensor is in a non-combustion state; and first storage for storing an initial resistance value of the sensor element portion. Means, a second storage means for storing a resistance value of the sensor element portion during use of the air-fuel ratio sensor, and a deviation of a resistance value of the element portion stored in the first storage means and the second storage means. Correction coefficient setting means for setting a correction coefficient for correcting the output value of the air-fuel ratio sensor; output value correction means for correcting the output value of the air-fuel ratio sensor by the correction coefficient; and a corrected output value of the air-fuel ratio sensor An air-fuel ratio control device for an internal combustion engine, comprising: air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio based on the air-fuel ratio. 2. The engine according to claim 1, wherein the combustion state determining means includes an opening degree detecting means for detecting an opening degree of a throttle valve interposed in an intake passage of the engine, and an engine rotational speed detecting means for detecting a rotational speed of the engine. Wherein the oxygen concentration based on the air-fuel ratio signal from the air-fuel ratio sensor is equal to or higher than a predetermined value, the detected throttle opening is lower than a predetermined value, and the engine speed is equal to or higher than a predetermined value, or 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the engine is determined to be in a non-combustion state when is equal to or more than a predetermined value. 3. An air-fuel ratio control device for an internal combustion engine according to claim 1, wherein said resistance value detecting means detects a resistance value based on an output voltage of an element portion of said air-fuel ratio sensor. . 4. A detection number counting means for counting the number of times of detection of the resistance value of the sensor element portion from the start of use of the air-fuel ratio sensor, wherein the first storage means stores the counted number of times of resistance value detection at a predetermined value. When the resistance value is less than, the second storage means,
The resistance value when the counted number of times of resistance value detection is equal to or more than a predetermined value is stored.
An air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 3. 5. A storage device according to claim 1, wherein said first storage means and said second storage means store a maximum value of a resistance value of an element of said air-fuel ratio sensor detected within a predetermined time by said resistance value detection means. The air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 4, wherein: 6. The apparatus according to claim 1, further comprising reset means for resetting the number of times of resistance value detection by said detection number counting means when said air-fuel ratio sensor is replaced. An air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 3. 7. The resistance value of the element portion of the air-fuel ratio sensor is the resistance value between electrodes provided on opposite end surfaces of the solid electrolyte of the oxygen ion conductor constituting the element portion of the air-fuel ratio sensor. The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein: