JPH0472438A - Air-fuel ratio sensor deterioration diagnosis device in air-fuel ratio controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent operation under deteriorated exhaust gas properly with a deteriorated air fuel sensor being used continuously as it is by providing a deterioration diagnosis means operation on the basis of correction level so as to diagnose the deterioration of a first air-fuel ratio sensor based on an increase/decrease compensation level of a control operation quantity by a control operational quantity compensation means. CONSTITUTION:An air-fuel ratio of an engine intake air-mixture is feedback-controlled to a target air-fuel ratio based on output of an upstream side first air-fuel ratio sensor, but deviation of control point caused by deterioration of the upstream side sensor is compensated through such a process as applying increase/decrease compensation to a control operational quantity in such an air-fuel ratio feedback control by means of the second air-fuel ratio sensor on the downstream side. However, when deterioration of the first air-fuel ratio is advanced so as to deviate the control point largely, since a compensation value of the control operational quantity is also largely changed to compensate the deviation, the deterioration of the first air-fuel ratio sensor is diagnosed by a deterioration diagnosis means operating on the basis of correction level based on decrease/increase correction level by means of the compensation value.

Description

Detailed Description of the Invention <Field of Industrial Application> The present invention relates to an air-fuel ratio sensor deterioration diagnosis device in an air-fuel ratio control device for an internal combustion engine. The present invention relates to a device for diagnosing deterioration of a sensor that detects an air-fuel ratio in an air-fuel ratio control device configured to detect a fuel ratio and perform feedback control on the air-fuel ratio of an engine intake air-fuel mixture.

<Prior art> Conventionally, in order to maintain good conversion efficiency in a three-way catalyst installed in the exhaust system for exhaust purification, feedback control of the air-fuel ratio of the engine intake air-fuel mixture to the stoichiometric air-fuel ratio has been carried out. In order to ensure responsiveness, an oxygen sensor that detects the air-fuel ratio via the oxygen concentration in the exhaust gas is installed at a gathering part of the exhaust manifold relatively close to the combustion chamber. Based on the intermediate oxygen concentration, the actual air-fuel ratio (rich/lean) relative to the stoichiometric air-fuel ratio is detected, and the amount of fuel supplied to the engine is feedback-controlled.

However, as mentioned above, the oxygen sensor installed in the exhaust system relatively close to the combustion chamber is exposed to high-temperature exhaust gas, so its characteristics (internal resistance, electromotive force,
(response time) is easy to change, and because the exhaust gas from each cylinder is not sufficiently mixed, it is difficult to detect the average air-fuel ratio of all cylinders, so there is variation in the detection accuracy of the air-fuel ratio.
This was deteriorating the accuracy of air-fuel ratio control.

In view of this, an oxygen sensor is also installed downstream of the catalyst, and two
Various methods have been proposed that feedback control the air-fuel ratio using the detected values of two oxygen sensors (Japanese Patent Laid-Open No. 58-4
(See Publication No. 8756, etc.).

In other words, the downstream oxygen sensor is responsive due to the 02 storage effect of the three-way catalyst (a state in which the amount of oxygen is large when leaner than the stoichiometric air-fuel ratio, and is minimal when richer than the stoichiometric air-fuel ratio, which continues for a certain period of time and output is delayed). However, since it is possible to detect the air-fuel ratio with the best conversion efficiency of Co, HC, and NOx for the three-way catalyst, it is possible to obtain highly accurate and stable detection characteristics that compensate for the deterioration state of the upstream oxygen sensor. .

Therefore, we decided to perform independent feedback control of the air-fuel ratio based on the detected values of the two oxygen sensors.
・Compensate the characteristics of air-fuel ratio feedback control by the upstream oxygen sensor with the downstream oxygen sensor, ensure responsiveness with the upstream sensor, and compensate for the accuracy of the control point on the downstream side. It performs highly accurate air-fuel ratio feedback control.

As a device for compensating the characteristics of air-fuel ratio feedback control by an upstream oxygen sensor with a downstream oxygen sensor, for example, while performing air-fuel ratio feedback control based on the detection of a highly responsive upstream sensor, Detects a shift in the control point, and when the downstream sensor detects whether it is rich or lean relative to the target, the control constant (control manipulated variable) for air-fuel ratio feedback control based on the upstream sensor output is resolved to determine whether it is rich or lean relative to the target. By gradually changing the air-fuel ratio in the direction of
As a result, control is performed in which the average of the control points of the feedback control based on the upstream sensor is set close to the target air-fuel ratio.

<Problems to be Solved by the Invention> As described above, in an air-fuel ratio control device that provides feedback control of the air-fuel ratio by providing air-fuel ratio sensors on the upstream and downstream sides of the catalytic exhaust purification device, the upstream air-fuel ratio sensor Even if the air-fuel ratio deteriorates, it is possible to compensate for this and control the target air-fuel ratio, but if the upstream air-fuel ratio sensor deteriorates or the correction limit is exceeded, feedback control to the target air-fuel ratio becomes impossible, and the exhaust gas This will worsen the condition.

Here, if the upstream air-fuel ratio sensor exceeds the correction limit by the downstream sensor due to an on/off failure such as a wire breakage or short circuit, the wire breakage or short circuit can be detected using conventional methods. Because it can be easily detected by a circuit,
Is it possible to encourage measures such as replacing the upstream sensor?
If the static characteristics of air-fuel ratio detection by the upstream air-fuel ratio sensor deviates significantly or the detection response speed changes significantly, and the correction limit by the downstream sensor is exceeded, this cannot be detected. However, there was a risk that the system would be operated with deteriorated exhaust properties.

The present invention has been made in view of the above-mentioned problems, and is an air-fuel ratio control device that provides feedback control of the air-fuel ratio by providing air-fuel ratio sensors on the upstream and downstream sides of a catalytic exhaust purification device. It is an object of the present invention to provide a diagnostic device capable of diagnosing characteristic deterioration of a side air-fuel ratio sensor, thereby making it possible to avoid operation in a state in which the correction limit is exceeded.

<Means for Solving the Problems> Therefore, in the present invention, an air-fuel ratio sensor deterioration diagnosing device in an air-fuel ratio control device for an internal combustion engine is configured as shown in FIGS. 1 and 2.

In FIG. 1, the first and second air-fuel ratio sensors are installed on the upstream and downstream sides of a catalytic exhaust purification device installed in the exhaust system of an internal combustion engine, respectively, and are used to measure the engine intake air-fuel mixture. It is a sensor whose output value changes in response to the concentration of a specific component in the exhaust gas, which changes depending on the air-fuel ratio.

Further, the air-fuel ratio feedback control means feedback-controls the air-fuel ratio of the engine intake air-fuel mixture to a target air-fuel ratio based on the output value of the first air-fuel ratio sensor on the upstream side.

On the other hand, the control operation amount correction means increases or decreases the control operation amount in the air-fuel ratio feedback control based on rich/lean detection with respect to the target air-fuel ratio based on the output value of the downstream second air-fuel ratio sensor.

The air-fuel ratio control device to which the present invention is applied is configured as described above, and the deterioration diagnosis means based on the correction level constituting the air-fuel ratio sensor deterioration diagnosis device according to the present invention corrects the increase or decrease of the control operation amount by the control operation amount correction means. Deterioration of the first air-fuel ratio sensor is diagnosed based on the level.

Here, as shown in the dotted dose in FIG. Instead of the deterioration diagnosis means based on the level, a deterioration diagnosis means based on the period and the correction level is provided, and the first It is also possible to diagnose deterioration of the air-fuel ratio sensor.

In addition, in FIG. 2, the control operation correction value setting means increases or decreases the control operation amount in the air-fuel ratio feedback control means based on rich/lean detection with respect to the target air-fuel ratio based on the output value of the second air-fuel ratio sensor on the downstream side. The area-specific correction value learning and storage means learns and stores the increase/decrease correction value of the control operation amount set by the control operation correction value setting means for each engine operation area.

Then, the region-specific correction value search means searches the region-specific correction amount storage means for the increase/decrease correction amount of the corresponding driving region, and the control operation amount correction means searches the searched increase/decrease correction value and the control operation correction value. The control operation amount in the air-fuel ratio feedback control means is corrected based on the increase/decrease correction value set by the setting means.

Furthermore, in FIG. 2, the increase/decrease correction average value calculating means calculates the average level of the increase/decrease correction values for each driving region learned by the region-specific correction value learning storage means, and the deterioration diagnosis means based on the average correction value Based on this average level, the deterioration of the first air-fuel ratio sensor on the upstream side is diagnosed.

In the configuration of FIG. 2, as shown by the dotted line, a feedback period detection means is added to the above configuration, and the feedback period detection means detects the air-fuel ratio increase/decrease correction period by the air-fuel ratio feedback control means, while the average correction In place of the deterioration diagnosis means based on the value, a deterioration diagnosis means based on the average correction value and period is provided, and the average level of the region-based correction value calculated by the increase/decrease correction average value calculation means and the period detected by the feedback period detection means are provided. It is also possible to diagnose deterioration of the first air-fuel ratio sensor based on the above.

Further, the uniform correction value storage means shown by the dotted line in FIG. 2 is for uniformly correcting the control operation amount in the entire operating range by using the average level of the increase/decrease correction value calculated by the increase/decrease correction average value calculation means. It is updated and stored as a uniform correction value. In such a configuration, the control operation amount correction means adds to the correction value for each driving region searched by the region correction value search means and the increase/decrease correction value set by the control operation correction value setting means. The control operation amount in the air-fuel ratio feedback control means is corrected based on the uniform correction value stored in the uniform correction value storage means.

<Operation> According to this configuration, the air-fuel ratio of the engine intake air-fuel mixture is feedback-controlled to the target air-fuel ratio based on the output of the first air-fuel ratio sensor on the upstream side, but the control operation amount in the air-fuel ratio feedback control is By performing an increase/decrease correction using the second air-fuel ratio sensor on the downstream side, any shift in the control point due to deterioration of the upstream sensor is compensated for. However, if the deterioration of the first air-fuel ratio sensor progresses and the control point shifts significantly, the correction value of the control operation amount will also change greatly to compensate for this, so the increase/decrease correction level based on the correction value The deterioration of the first air-fuel ratio sensor is diagnosed based on this.

Further, when the correction value of the control operation amount is learned and stored for each driving region, the accuracy of the deterioration diagnosis can be further improved by calculating the average value of the correction values learned for each region and performing the deterioration diagnosis.

Furthermore, if either the rich-lean response time or the lean-rich response time of the air-fuel ratio sensor increases, this will appear as a shift in the control point (air-fuel ratio shift),
Either this appears as an increase in the correction rate of the control manipulated variable and the deterioration can be diagnosed as described above, or even if the response time becomes longer in the rain detection direction and the control center is almost at the target, the air-fuel ratio The amplitude of the fluctuation may become large and the catalyst may be out of the window in which it maintains high conversion efficiency.
Diagnosis accuracy is further improved by using the air-fuel ratio control cycle together with the increase/decrease correction level of the control operation amount as a criterion for deterioration diagnosis.

Further, the average value of the correction values learned for each driving region may be stored as a uniform correction value for uniformly correcting the control operation amount in all driving regions.

<Example> The present invention will be explained in detail below.

In FIG. 3 showing one embodiment, an engine l has an air cleaner 2 to an intake duct 3. Air is sucked in through the throttle valve 4 and the intake manifold 5. A fuel injection valve 6 is provided in a branch portion of the intake manifold 5 for each cylinder. The fuel injection valve 6 is an electromagnetic fuel injection valve that opens when the solenoid is energized and closes when the energization is stopped, and opens when the solenoid is energized by a drive pulse signal from the control unit 12, which will be described later. Fuel is supplied under pressure from a fuel pump (not shown) and adjusted to a predetermined pressure by a pressure regulator, and is injected into the intake manifold 5.

In this embodiment, a multi-point injection system (MP1 system) was used as described above, but a single-point injection system (SP1 system) in which a single fuel injection valve is installed in common for all cylinders, such as upstream of the throttle valve 4, is used.
method).

Each combustion chamber of the engine 1 is provided with a spark plug 7, which ignites a spark to ignite and burn the air-fuel mixture.

From engine 1, exhaust manifold 8° exhaust duct 9. Exhaust gas is discharged via a three-way catalyst (catalytic exhaust purification device) 10 and a muffler 11. The three-way catalyst IO is a catalytic exhaust purification device that oxidizes Co and HC in the exhaust components, and also reduces NOx and converts it into other harmless substances. The reconversion efficiency is the best when the fuel is burned at

The control unit 12 includes a CPU and a ROM.

Equipped with a microcomputer that includes a RAM, an A/D converter, and an input/output interface, it inputs detection signals from various sensors, processes them as described later, and controls the operation of the fuel injection valve 6. Control.

As the various sensors, an air flow meter 13 of a hot wire type or a flap type is provided in the intake duct 3, and outputs a voltage signal according to the intake air flow rate Q of the engine l.

Further, a crank angle sensor 14 is provided, and in the case of a four-cylinder engine, outputs a reference signal for every 180 degrees of crank angle and a unit signal for every 1 degree or 2 degrees of crank angle. Here, the engine rotational speed N can be calculated by measuring the cycle of the reference signal or the number of occurrences of the unit signal within a predetermined time.

Also provided is a water temperature sensor 15 for detecting the cooling water temperature Tw of the water jacket of the engine l.

Furthermore, an exhaust manifold 8 is provided on the upstream side of the three-way catalyst lO.
A first oxygen sensor 16 as a first air-fuel ratio sensor is provided at the gathering part of An oxygen sensor 17 is also provided.

The first oxygen sensor 16 and the second oxygen sensor 17 are known sensors whose output values change in response to the concentration of oxygen as a specific component in the exhaust gas, and the oxygen concentration in the exhaust gas changes at the stoichiometric air-fuel ratio. When the air-fuel ratio is richer than the stoichiometric air-fuel ratio, the voltage is set to around IV, and when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, the voltage is set to around IV, depending on the difference in oxygen concentration between the atmosphere as a reference gas and the exhaust gas. Outputs a voltage near 0 (see Figure 9).

Here, the CPU of the microcomputer built in the control unit 12 performs arithmetic processing according to the programs stored in the ROM shown in the flowcharts of FIGS. 4 to 8, and feedback controls the air-fuel ratio of the engine 1 intake mixture. At the same time, a deterioration diagnosis of the first oxygen sensor 16 provided on the upstream side of the three-way catalyst 10 is performed.

In addition, an air-fuel ratio feedback control means, a control operation amount correction means, a feedback cycle detection means, a deterioration diagnosis means based on a correction level for two cycles, a deterioration diagnosis means based on a correction level,
Control operation correction value setting means.

Functions as a region-specific correction value learning storage means, a region-specific correction value search means, an increase/decrease correction average value calculation means, a deterioration diagnosis means using the average correction value, a deterioration diagnosis means using the average correction value and period, and a uniform correction value storage means. As shown in the flowcharts of FIGS. 4 to 8, a control unit 12 is provided in terms of software.

The program shown in the flowchart of FIG. 4 is an air-fuel ratio feedback for bringing the air-fuel ratio of the engine 1 intake air-fuel mixture closer to the target air-fuel ratio (stoichiometric air-fuel ratio) by increasing/decreasing the fuel injection amount Ti by the fuel injection valve 6. This is for setting the correction coefficient LMD by proportional-integral control.
It is executed every rotation of .

In the flowchart shown in FIG. 4, first, in step 1 (indicated as Sl in the figure, the same applies hereinafter), each region is divided into a plurality of operating regions depending on the engine rotational speed N and the basic fuel injection amount Tp. Data corresponding to the current driving condition is searched and obtained from the map storing the learning correction value PH03S.

In this embodiment, as will be described later, the proportional operation amount (P portion) of the control operation amount when performing proportional integral control of the air-fuel ratio feedback correction coefficient LMD based on the output of the first oxygen sensor 16 is The increase/decrease correction is made based on rich/lean detection with respect to the target air-fuel ratio by the oxygen sensor 17, and the area-specific learned correction value PH03S is the increase/decrease correction value of the proportional operation amount P learned and stored for each operating area. .

In the next step 2, the region-specific learning correction value PH08S obtained by searching from the map in step 1 is stored as the average level of the region-specific learning correction value PH03S in order to uniformly correct the proportional operation amount in all operating regions. The value obtained by adding the fixed uniform correction value PH03M is the final proportional increase/decrease correction value r.
Set as ate.

In step 3, the output voltage of the first oxygen sensor 16 is changed to A/
D convert, read, and set the data to FVo2.

Then, in the next step 4, the voltage Fvo2 read in step 3 is compared with a slice level (500 mV in this example) corresponding to the stoichiometric air-fuel ratio which is the target air-fuel ratio, and the voltage is detected by the yt oxygen sensor 16. It is determined whether the air-fuel ratio of the engine intake air-fuel mixture is rich or lean with respect to the stoichiometric air-fuel ratio.

Here, if it is determined that the voltage Fvo2 is greater than the slice level and the air-fuel ratio is rich, the process proceeds to step 5. In this step 5, a flag FR is determined to determine whether the rich/lean detection is the first time, and if the flag FR is zero, which is the first rich determination, the process proceeds to step 6, where the flag FR is set to 1.

In the next step 7, the output voltage of the second oxygen sensor 17 is A/D converted and read, and the data is set in RVQ2.

Then, in step 8, the voltage RVo2 read in step 7 is compared with a slice level corresponding to the stoichiometric air-fuel ratio (500 mV in this embodiment), which is the target air-fuel ratio, and the voltage RVo2 is detected by the second oxygen sensor 17. It is determined whether the air-fuel ratio of the intake air-fuel mixture is rich or lean with respect to the stoichiometric air-fuel ratio.

Here, if the voltage RV02 exceeds the slice level and is determined to be rich, the process proceeds to step 9, where a predetermined small value (for example, 0.0001) is subtracted from the proportional increase/decrease correction value rate set in step 2. The result is set as a new correction value rate, and in the next step 10, frr, which is a flag for determining rich/lean reversal of the air-fuel ratio detected by the second oxygen sensor 17, is set to 1.

On the other hand, in step 8, if the voltage RVo2 is below the slice level and lean is determined, the process proceeds to step 11, where the proportional increase/decrease correction value rate set in step 2 is determined.
A predetermined small value (for example, 0.0001) is added to
Then, the flag frr is set to φ.

As will be described later, the proportional increase/decrease correction value rate is multiplied by (1-rate) with respect to the proportional operation amount P for decreasing the air-fuel ratio feedback correction coefficient LMD at the first time of rich detection by the first oxygen sensor 16. (1+rat
e), therefore, when the rate is increased when the second oxygen sensor 17 detects lean, the rate is corrected to the side that increases the level of the air-fuel ratio feedback correction coefficient LMD (air-fuel ratio rich direction). Conversely, if the rate is corrected to decrease when the second oxygen sensor 17 detects a rich condition, the level of the air-fuel ratio feedback correction coefficient LMD will be corrected to the side of decreasing (air-fuel ratio lean direction).

Therefore, the feedback correction of the air-fuel ratio based on the detection result of the first oxygen sensor 16 is corrected so that the air-fuel ratio detected by the second oxygen sensor 17 approaches the target air-fuel ratio. Even if the feedback control point deviates from the stoichiometric air-fuel ratio due to deterioration of the air-fuel ratio, this can be compensated for and feedback controllability to the stoichiometric air-fuel ratio can be maintained.

After setting the proportional increase/decrease correction value rate as described above, in the next step 13, the counter Tmont that counts the lean detection time by the first oxygen sensor 16 is set to Tmont.
Set to MONTL. Furthermore, this lean detection time TM
ONTL is data used for diagnosing deterioration of the first oxygen sensor 16, together with the rich detection time TMONTR described later.

In step 14, proportional control of the air-fuel ratio feedback correction coefficient LMD is performed according to the following formula using the proportional increase/decrease correction value rate corrected in step 9 or step 11 and the preset proportional operation amount P. let

LMD + - LMD-P (1-rate) That is, this is the first time of rich detection, and the air-fuel ratio feedback correction coefficient LMD is set to decrease by the above proportional control, and the rich detection state is resolved. Fuel injection amount Ti
will be corrected to decrease.

The air-fuel ratio feedback correction coefficient LMD is a correction term that is multiplied by the basic fuel injection amount Tp (←KXQ/N, is a constant) calculated from the engine rotational speed N and the intake air flow rate Q, and In addition, the injection amount Tp is corrected by a battery voltage correction numerator s, a water temperature correction coefficient, a starting correction coefficient, etc., and the final fuel injection amount Ti is set.

On the other hand, when it is determined in step 5 that the flag FR is 1, the rich detection continues, and in this case, the process proceeds to step 15 to integrally control the air-fuel ratio feedback correction coefficient LMD.

In step 15, the air-fuel ratio feedback correction coefficient LMD is integrally controlled according to the following equation.

LMD-LMD-1-Ti Here, I is a preset integral manipulated variable, and the value obtained by multiplying this integral manipulated variable ■ by the fuel injection amount Ti is subtracted from the previous air-fuel ratio feedback correction coefficient LMD. Then, the air-fuel ratio feedback correction coefficient LMD is corrected to decrease.

Further, in step 4, when a lean air-fuel ratio is detected based on the first oxygen sensor 16, the process proceeds to step 16, and a proportional increase/decrease correction value rate is set in substantially the same manner as in steps 5 to 15 when rich is detected. At the same time, proportional-integral control of the air-fuel ratio feedback correction coefficient LMD is performed (steps 16 to 26). However, when a lean air-fuel ratio is detected based on the first oxygen sensor 16, it is necessary to increase the air-fuel ratio feedback correction coefficient LMD to correct the air-fuel ratio in the rich direction. Control is performed according to the following formula.

LMD+LMD+P (1+rate)LMD=
LMD+I -Ti Furthermore, in the first lean air-fuel ratio based on the first oxygen sensor 16, the rich detection time by the first oxygen sensor 16 is set to TMONTR.

The lean detection time TMONTL and the rich detection time T
The counter Tmont for measuring MONTR is reset to zero in step 27, which proceeds to the first rich or lean detection by the first oxygen sensor 16.
The program shown in the flowchart shown in the figure is configured to update one value every 10 ms, thereby making it possible to alternately measure the lean detection time and the rich detection time.

In addition, at the first time of rich or high detection by the first oxygen sensor 16, the area-specific learning correction value P
Update control of H03S and positive arrest value PH03M is performed.

First, in step 28, the previous value M of the flag frr is
By comparing frr with the current value frr, it is determined whether the air-fuel ratio detected by the second oxygen sensor 17 has reversed.

Here, when it is determined that Mfrr=frr, the air-fuel ratio detected by the second oxygen sensor 17 continues to be in a lean or rich state, and in this case, the area-based learning correction value PH03S is updated. only, or Mfrr=f
At the time of rich/lean reversal where it is determined that it is not rr, the area-based learning correction value PH03S is updated and the uniform correction value PH03M is updated.

When it is determined that Mfrr=frr is not satisfied, first,
In step 29, the flag frr updated this time is set to Mfrr for the next determination in step 28, and in the next step 30, the uniform correction value PH03M is updated.

The update control of the uniform correction value PH03M in step 30 is shown in the flowchart of FIG.

First, in step 51, the area-specific learning correction value PH08S
Counters i and j for counting the addresses in the map that are stored for each of a plurality of operating ranges divided by engine rotational speed N and basic fuel injection amount Tp are reset to zero, respectively.

Then, in the next step 52, the maximum speed N (i) in the i-th region of the plurality of regions of the engine rotation speed N is compared with the current rotation speed N. here,
When N>N (i), it means that the vehicle is being operated at a higher speed range, so the process proceeds to step 53, increments the counter i by 1, and then proceeds to the next step 5.
It is determined whether i, which is counted up in step 4, exceeds the maximum value of i, 7, and if it does not exceed the maximum value, the process returns to step 52 and the speed is set to be lower than the maximum speed within the counted up area. Let them determine whether it is small or not.

In this way, it is possible to determine where the current rotational speed N corresponds to in the grid of engine rotational speeds N on the map by sequentially referring to the area starting from the lowest speed.
When the grid is determined to be ≦N (i), step 5
Proceed to step 6 and set the value of i at that time to I as the final value. However, even if the counter i reaches its maximum value, N≦N (
If the determination of i) is not made, the maximum value is set to I in step 55, and it is assumed that it corresponds to the maximum area of the grid of rotation speed N.

In this way, when it is detected whether the current rotational speed N corresponds to the corresponding grid position, next, the current basic fuel injection amount Tp or the corresponding grid position (J) is detected in the same way (steps 57 to 5). 61).

Then, in step 62, the area-specific learning correction value PH03 is
A counter c that adds up the number of rich/lean reversal detections by the second oxygen sensor 17 for each map grid in which S is stored.
nt (1) Upload 1 data of the grid corresponding to the current operating state among (J). The counter cnt
(I) By (J), the area-specific learning correction value PH03
It is possible to determine whether the rich/lean reversal is detected by the second oxygen sensor 17 corresponding to each S, and the area-specific learning correction value PH03S is determined by the number of rich/lean reversals detected by the second oxygen sensor 17. Since the purpose is to control the average air-fuel ratio to the stoichiometric air-fuel ratio, the counter c corresponding to the area-specific learning correction value PH03S
When the value of nt (I) (J) is large, it means that the learning of the area-specific learning correction value PH03S is progressing accordingly. Conversely, when the value of counter Cnt (1) (J) is small, Learning has not progressed sufficiently, and the reliability of the area-specific learning correction value PH03S can be considered to be low.

Utilizing the characteristics of the counter cnt (1) (:J), from step 63 onwards, only the area-specific learning correction values PH03S in which learning has sufficiently progressed are picked up, and the uniform correction value PH03M is set as the average level of these. Configure update settings.

In step 63, counters i and j are reset to zero as in step 51, and the learning correction value P for each area is set.
Zcn for counting the number of samplings of H08S
Reset t to zero.

Then, first, leave the counter j as zero and count up i sequentially from zero, and step 6
4, the counter cnt (I) (J) at that time or the predetermined value (
For example, when it is determined that 5) or more is true, in step 65, the area-specific learning correction value PH03S data (MAP (
I) Add Cl3) to the integrated value SUM - 3UM
10 MAP [I] [J]), when the integrated value SUM is updated, the sampling number Zcnt is set to 1 in step 66.
Make it hot.

Then, until it is determined in step 67 that the counter i has exceeded the maximum value, the counter i is incremented by 1 in step 68 and the determination in step 64 is performed again.

Then, when it is determined that the counter i has exceeded the maximum value and sampling has been completed for all grids when the counter j is fixed and the counter i is changed, the process advances to step 69, where the counter j is incremented by 1 and the next In step 7o, the counter i is reset to zero, and the counter i is sequentially counted up from zero below the air-filled counter j to sample the area-based learning correction value PH03S.

In this way, the determination in step 64 is performed until it is determined in step 71 that the counter j has reached the maximum value, and it is determined that the counter cnt (I) (J) is greater than or equal to the predetermined value, in other words. After calculating the integrated value SUM of the area-based learning correction value PH03S in which learning has sufficiently progressed and the sample number Zcnt of the integrated value, in the next step 71, the uniform correction value PH03M is updated according to the following formula.

Here, the above-mentioned X is a weight constant of the weighted average, and for example, this X is set to a value of about 1/4, and the uniform correction value PH03M from the previous time is used for area-specific learning where learning has progressed sufficiently. Average value of correction value PH03S (S UM/Z c n
t ) and a new uniform correction value PH03.
This is to find M.

The proportional operation amount P is uniformly corrected in all driving ranges by the negative arrest positive value PH03M.

Returning again to the flowchart in FIG. 4, updating the map value of the area-based learning correction value PH03S will be explained in step 3.
1 to step 41 and step 51 to step 6
In the same manner as in 1, find the grid position CI)(J) of the map corresponding to the current operating conditions.

Then, in step 42, the data of the region-based learning correction value PH03S of the corresponding grid is converted into the proportional increase/decrease correction value rat.
Rewrite it to the value obtained by subtracting 03M (one arrest positive value P) from e. The map to be rewritten here is searched in step 1 above, and the area-specific learning correction value PH0SS or the proportional operation amount P according to the driving condition at that time is rewritten. It is intended to be used for correction of

Next, control related to the air-fuel ratio sensor deterioration diagnosis according to the present invention will be explained according to the programs shown in the flowcharts of FIGS. 7 and 8.

The program shown in the flowchart of FIG. 7 is processed in the background, and in step 81, as described above, the absolute value of the uniform correction value PH03M stored as the average level of the area-based learning correction value PHOSS is compared with a predetermined value. If the value has increased to the level of the regulation correction value PH03M or more than a predetermined value, the first oxygen sensor 16 installed on the upstream side of the catalyst has deteriorated, or the compensation control by the second oxygen sensor 17 has occurred. It is determined that the conversion efficiency of the three-way catalyst 10 can no longer be maintained as the conversion efficiency of the three-way catalyst 10 can no longer be maintained. Then, in the next step 82, it is displayed that the progress of deterioration of the first oxygen sensor 16 has been diagnosed.

The display of the deterioration diagnosis is performed by, for example, a display device installed near the driver's seat of the vehicle, and the driver is asked to display the first oxygen sensor 1.
Encourage the exchange of 6.

The shift in the air-fuel ratio control point due to deterioration of the first oxygen sensor 16 on the upstream side is compensated for by correcting the proportional operation amount P of the air-fuel ratio feedback correction coefficient LMD as described above, or the shift in the air-fuel ratio control point due to the deterioration progresses and the control point shifts. As the deviation increases, it becomes necessary to correct the proportional operation amount P to a greater extent. Therefore, when the proportional increase/decrease correction value rate reaches the absolute value level or exceeds a predetermined value, the first oxygen sensor 16 It can be assumed that the deterioration is progressing.

That is, for example, if the rich → lean response time of the first oxygen sensor 16 increases, the air-fuel ratio control point will shift to the lean side, and the non-proportional increase/decrease correction value rate is set to a reference value to compensate for this. If the lean-to-rich response time increases, the air-fuel ratio control point will shift to the rich side, and the non-proportional increase/decrease correction value rate is set to compensate for this. Therefore, in either case, as the response time changes significantly, the absolute value level of the non-proportional increase/decrease correction value rate increases,
It is possible to diagnose deterioration.

However, the area-specific learning correction value P for areas where learning has not progressed
H03S has a habit of showing an abnormal level even when the first oxygen sensor 16 has not deteriorated, so diagnosing deterioration based on the absolute value level of the proportional increase/decrease correction value rate each time reduces the diagnostic accuracy. Therefore, it is desirable to perform deterioration diagnosis based on the uniform correction value PH03M, which is the average level of the area-specific learned correction values PH03S, which have undergone learning as described above.

If either the rich lean response time or lean → rich response time of the first oxygen sensor 16 increases due to deterioration, it will appear as a shift in the control point (air-fuel ratio shift), and the non-proportional increase/decrease correction value will change. This increases the absolute value level of the rate, and whether it is possible to diagnose deterioration as described above, or even if the deviation of the control point is small, the response time increases in the direction of rain detection and the air-fuel ratio changes. Even when the amplitude of fluctuation becomes large, the conversion efficiency in the catalyst cannot be maintained, so the period of the output waveform of the first oxygen sensor 16, in other words, the period of feedback control based on the detection of the first oxygen sensor 16 also changes. It is preferable to detect and diagnose deterioration, and an embodiment thereof is shown in the flowchart of FIG.

The program shown in the flowchart of FIG. 8 is processed in the background. First, in step 91, when diagnosing deterioration based on the air-fuel ratio feedback control period, changes in the air-fuel ratio feedback control period depending on the engine rotational speed N are performed. Correction bone 0F to compensate for
ST is found by searching from a preset map.

Then, in the next step 92, the lean detection time TMONTR determined in the flowchart of FIG.
and a period obtained as an addition value of the rich detection time TMONTL, a period obtained by adding the correction bone 0FST to the period obtained by correction, and an absolute value of the -rhythm correction value PH03M. Based on a preset map, reference is made to the area corresponding to the current period and the correction level of the control operation amount.

Then, in the next step 93, it is determined whether or not the area referenced in step 92 is included in the degraded area (the shaded area in the flowchart), and if it falls within the degraded area, the degradation diagnosis is performed in step 94. Display.

In the deterioration diagnosis based on the period (TMONTRfTMONTL+〇FST) and l PH03M1, as described above, if l PH03M 1 is large, it is diagnosed as deterioration, or even if l PH03M l is small, but the period is long, it is diagnosed as deterioration. It is intended to be done.

This makes it possible to diagnose deterioration of the first oxygen sensor 16 even when the response time increases in the rain detection direction and the deviation of the control point is small but the fluctuation of the air-fuel ratio becomes large. l PH03M When diagnosing deterioration based only on I, the diagnostic range can be expanded to a greater extent.

In this embodiment, the proportional operation amount P is corrected to increase or decrease based on the -arrest positive value PH03M. In this case, it is sufficient to calculate the average level of the region-specific learning correction value PH03S of the region where learning is progressing only for deterioration diagnosis.

<Effects of the Invention> As explained above, according to the present invention, air-fuel ratio sensors are provided on the upstream side and the downstream side of the catalytic exhaust purification device, respectively.
To diagnose deterioration of an upstream air-fuel ratio sensor that exceeds a compensation limit in an air-fuel ratio control device configured to perform air-fuel ratio feedback control while compensating for a shift in a control point due to deterioration of an upstream air-fuel ratio sensor. Therefore, based on this diagnosis result, it is possible to prompt the replacement of the air-fuel ratio sensor, which may have the effect of preventing the air-fuel ratio sensor from continuing to be used even though it has deteriorated, thereby preventing the vehicle from being operated with deteriorated exhaust characteristics. be.

[Brief explanation of drawings]

Figures 1 and 2 are block diagrams showing the configuration of the present invention, Figure 3 is a system schematic diagram showing an embodiment of the present invention, and Figures 4 to 8 are air-fuel ratio feedback in the above embodiment. Flow chart showing the state of control, No. 9
The figure is a diagram showing the relationship between the conversion efficiency of a three-way catalyst and the air-fuel ratio. l... Engine 6... Fuel injection valve 8... Exhaust manifold IO... Three-way catalyst (catalytic exhaust purification device) 12... Control unit 16...
First oxygen sensor (first air-fuel ratio sensor) Su (second air-fuel ratio sensor) 17...Second oxygen sensor Patent applicant Japan Electronics Co., Ltd. Agent Patent attorney Fujio Sasashima 5. Go (De029 蕩6 fig. j 72 箪 8 fig., BGJ 9th Prisoner

Claims (5)

[Claims] (1) Installed on the upstream and downstream sides of a catalytic exhaust purification device installed in the exhaust system of an internal combustion engine, output is generated in response to the concentration of a specific component in the exhaust gas, which changes depending on the air-fuel ratio of the engine intake air-fuel mixture. first and second air-fuel ratio sensors whose values change; air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio of the engine intake air-fuel mixture to a target air-fuel ratio based on the output value of the first air-fuel ratio sensor; a control operation amount correction means for increasing or decreasing the control operation amount in the air-fuel ratio feedback control means based on rich/lean detection with respect to the target air-fuel ratio based on the output value of the second air-fuel ratio sensor; The air-fuel ratio control device for an engine includes a deterioration diagnosis means based on a correction level for diagnosing deterioration of the first air-fuel ratio sensor based on an increase/decrease correction level of the control operation amount by the control operation amount correction means. An air-fuel ratio sensor deterioration diagnostic device in an air-fuel ratio control device for an internal combustion engine. (2) Feedback period detection means for detecting the air-fuel ratio increase/decrease correction period by the air-fuel ratio feedback control means is provided, and instead of the deterioration diagnosis means based on the correction level, the period detected by the feedback period detection means and the 2. The internal combustion engine according to claim 1, further comprising deterioration diagnosing means based on a period and a correction level for diagnosing deterioration of the first air-fuel ratio sensor based on an increase/decrease correction level of the control operation amount by the control operation amount correction means. An air-fuel ratio sensor deterioration diagnostic device for an air-fuel ratio control device. (3) Installed on the upstream and downstream sides of a catalytic exhaust purification device installed in the exhaust system of an internal combustion engine, output is generated in response to the concentration of a specific component in the exhaust gas, which changes depending on the air-fuel ratio of the engine intake air-fuel mixture. first and second air-fuel ratio sensors whose values change; air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio of the engine intake air-fuel mixture to a target air-fuel ratio based on the output value of the first air-fuel ratio sensor; control operation correction value setting means for setting an increase/decrease correction value for the control operation amount in the air-fuel ratio feedback control means based on rich/lean detection with respect to the target air-fuel ratio based on the output value of the second air-fuel ratio sensor; Area-specific correction value learning and storage means for learning and storing the increase/decrease correction value of the control operation amount set by the correction value setting means for each engine operating region; a correction value search means for each region to be searched; and the air-fuel ratio feedback control means based on the correction value for each driving region searched by the correction value search means for each region and the increase/decrease correction value set by the control operation correction value setting means. In an air-fuel ratio control device for an internal combustion engine, the air-fuel ratio control device for an internal combustion engine is configured to include: a control operation amount correction means for correcting a control operation amount in the area; an increase/decrease correction average value calculation means for calculating a level; and deterioration based on the average correction value for diagnosing deterioration of the first air-fuel ratio sensor based on the average level of the region-specific correction values calculated by the increase/decrease correction average value calculation means. What is claimed is: 1. An air-fuel ratio sensor deterioration diagnostic device for an air-fuel ratio control device for an internal combustion engine, comprising: a diagnostic means; (4) Feedback cycle detection means for detecting the air-fuel ratio increase/decrease correction cycle by the air-fuel ratio feedback control means is provided, and instead of the deterioration diagnosis means based on the average correction value, the increase/decrease correction average value calculation means calculates the The present invention is characterized by further comprising a deterioration diagnosis means based on an average correction value and period for diagnosing deterioration of the first air-fuel ratio sensor based on the average level of the region-based correction value and the period detected by the feedback period detection means. An air-fuel ratio sensor deterioration diagnostic device in an air-fuel ratio control device for an internal combustion engine according to claim 2. (5) Uniform correction value storage means for updating and storing the average level of the increase/decrease correction value calculated by the increase/decrease correction average value calculation means as a uniform correction value for uniformly correcting the control operation amount in all operating regions. The control operation amount correction means includes, in addition to the correction value for each driving region searched by the region-specific correction value search means and the increase/decrease correction value set by the control operation correction value setting means, the uniform correction value storage means. The air-fuel ratio control for an internal combustion engine according to claim 4 or 5, wherein the control operation amount in the air-fuel ratio feedback control means is corrected based on the uniform correction value stored in the air-fuel ratio control unit. Air-fuel ratio sensor deterioration diagnostic device for equipment.