JP3089969B2 - Degradation diagnosis device for exhaust purification catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for diagnosing deterioration of an exhaust purification catalyst, and more particularly to an apparatus having an air-fuel ratio sensor on each of an upstream side and a downstream side of an exhaust purification catalyst.

[0002]

2. Description of the Related Art In recent years, an exhaust system of an automobile gasoline engine is provided with an oxidation-reduction type exhaust purification catalyst (hereinafter, three-way catalyst) in order to reduce harmful exhaust gas components. The three-way catalyst is a device that purifies exhaust gas by oxidizing hydrocarbons (HC) and carbon monoxide (CO) while reducing nitrogen oxides (NO _x ). Since the redox reaction of the three-way catalyst is performed only in a narrow area (window) near the stoichiometric air-fuel ratio, an air-fuel ratio sensor (O ₂ sensor) is installed in the exhaust manifold or the like, and the air-fuel ratio is fed back based on the output signal. Controlling.
On the other hand, the three-way catalyst deteriorates and its purification efficiency decreases as the service period becomes longer.However, since this deterioration can be confirmed only by a method using an exhaust gas tester at the time of periodic inspection or the like, the purification efficiency is reduced. Nevertheless, there was a risk that the device would continue to be used.

[0003] Therefore, in JP-A-61-286550, etc., on the upstream side and the downstream side of the three-way catalyst provided an O ₂ sensor, respectively, the degradation of the three-way catalyst based on the output signal of the O ₂ sensor Is disclosed. In this deterioration diagnosis apparatus, attention is paid to the fact that the air-fuel ratio fluctuates in a short cycle from a target air-fuel ratio (for example, a stoichiometric air-fuel ratio) by feedback control, and the output of the upstream O ₂ sensor that changes in response thereto is focused. By comparing the frequency with that on the downstream side, deterioration of the three-way catalyst is determined.

[0004] That is, since the three-way catalyst has the ability to store the residual oxygen in the exhaust gas, the exhaust gas that has passed through the three-way catalyst contains only a small amount of oxygen. Therefore, when the three-way catalyst maintains the normal purification efficiency, as shown in FIG. 10, the output signal of the downstream O ₂ sensor is less likely to fluctuate, the amplitude becomes smaller, and the inversion frequency becomes smaller. Very low. Thus, the downstream O ₂ sensor and inversion frequency ratio of the upstream O ₂ sensor output signal with the air-fuel ratio fluctuates (downstream O ₂ sensor inversion frequency /
When the inversion frequency of the upstream O ₂ sensor is calculated, the value becomes a very small value.

However, when the three-way catalyst is deteriorated and the purification efficiency is reduced, the purification of harmful exhaust gas components is not carried out, and the capacity for storing oxygen is also reduced. Start passing. As a result, the output signal of the downstream O ₂ sensor also changes in the same manner as the output signal of the upstream O ₂ sensor, and the above-mentioned inversion frequency ratio gradually approaches 1. Therefore, in the above-described deterioration diagnosis device, the deterioration of the three-way catalyst is determined from the relationship between the purification efficiency of the three-way catalyst and the reversal frequency ratio.

[0006]

By the way, the above-mentioned countermeasure is taken.
The conversion frequency ratio not only deteriorates the three-way catalyst, but also
It is known that the value fluctuates depending on the operating conditions.
You. That is, the upstream O _TwoThe inversion frequency of the sensor is
In high-speed, high-load operation areas where the air volume increases,
Conversely, in the low-speed, low-load operation region where the intake air amount is small.
Will be lower. In contrast, the downstream O_TwoInversion frequency of sensor
The number is also related to the maximum purification capacity of the three-way catalyst,
Is upstream O_TwoSmaller than the sensor. Because of this,
If the operating state of the
May not correctly reflect the purification efficiency of the three-way catalyst.
Was.

[0007] That is, in a vehicle mainly driven by traffic congestion in an urban area and a vehicle mainly driven by continuous high-speed driving on an expressway or the like, even if the three-way catalyst is degraded equally, the reversal frequency ratio is low. A large difference occurs, and the timing of determining deterioration is different. Therefore, conventionally, it is impossible to set the reversal frequency ratio, which is the reference for the deterioration determination, to a very high value, and even if the purification efficiency is within the allowable limit, the three-way catalyst may be determined to be deteriorated and replaced. was there. As we all know,
The three-way catalyst is a very expensive part using precious metals such as platinum, and early replacement not only increases maintenance man-hours,
This has also been a problem in terms of resource saving and running costs.

[0008] The present invention has been made in view of the above situation,
It is an object of the present invention to provide an exhaust gas purifying catalyst deterioration diagnosis device capable of judging deterioration of a three-way catalyst with high accuracy even when a specific operating state is prominent.

[0009]

Therefore, according to the present invention, an upstream air-fuel ratio sensor provided upstream of an exhaust purification catalyst in an exhaust passage of an internal combustion engine, and an exhaust purification catalyst in the exhaust passage are provided. The output signal of the downstream air-fuel ratio sensor provided on the downstream side and the output signal of the upstream air-fuel ratio sensor are predetermined.
Reversal at the threshold value corresponding to the target air-fuel ratio
The air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is
Air-fuel ratio control means for performing the feedback control; operating state detecting means for detecting the operating state of the internal combustion engine; and an operating state detected by the operating state detecting means, wherein the operating state is detected in any of a plurality of preset operating regions. An operating region determining unit that determines whether the output signal is included, and an inversion frequency of an output signal of the upstream air-fuel ratio sensor and an output signal of the downstream air-fuel ratio sensor according to a determination result of the operating region determining unit . Inversion frequency
Calculate the inversion frequency ratio from this, based on this inversion frequency ratio ,
A deterioration information amount calculating means for repeatedly calculating the catalyst deterioration information amount for each of the operation regions; and a deterioration information amount calculating means.
The average of the amount of catalyst deterioration information for each operation
A degradation diagnosis device for an exhaust gas purification catalyst, comprising: a degradation determination unit that determines the degradation of the exhaust gas purification catalyst based on the integrated value of the average value .

[0010]

[0011] In a preferred embodiment of the addition, the present invention, the deterioration diagnostic apparatus according to claim 1, wherein the degradation information amount calculating means, the integrated an integrated value of the average value of the inversion frequency ratio of the catalyst deterioration amount of information It is better to calculate as a value divided by the number of times.

Further, in this case , the deterioration information amount calculating means calculates the catalyst deterioration information amount for each of the operating regions .
Is preferred . Further, at this time , the deterioration determination means is configured to determine that the average number of times of integration for each of the operation regions by the deterioration information amount calculation means exceeds a predetermined number of times set in advance for each of the operation regions. It is preferable that the deterioration determination is performed based on the integrated value of the values.

At this time, the deterioration judging means sets an average value of values obtained by dividing the integrated value of the average value for each of the operating regions by the deterioration information amount calculating means by the respective number of times of integration as a predetermined judgment value. It is preferable to make the above-mentioned deterioration judgment by comparing. Further, in claim 2, in degradation diagnostic apparatus according to claim 1 Symbol <br/> placing, before Symbol deterioration determination means, the accumulated number of times the catalyst deterioration information of the operation for each area by the degradation information amount calculation means It is proposed that the deterioration determination is performed when the number of times exceeds a predetermined number of times set in advance for each operation region.

Further, in the apparatus for diagnosing deterioration of 請 Motomeko 1, wherein the plurality of operating areas is preferably to be set based on the load information of at least the internal combustion engine.
Further, in the apparatus for diagnosing deterioration of 請 Motomeko 1, wherein the plurality of operating regions comprise at least high-speed, high-load operation region and a low-speed, low-load operation region is preferred.

Further, the deterioration diagnostic apparatus according to claim 1, wherein the degradation information amount calculation unit, when the operating state is shifted among the plurality of operating areas within the predetermined time, the catalyst deterioration amount of information Preferably, the operation is aborted.

[0016]

In the deterioration diagnosis apparatus according to the first aspect, the deterioration information amount calculating means may determine , for example, that the deterioration information amount is lower than the inversion frequency of the upstream air-fuel ratio sensor.
Divide the reversal frequency of the upstream air-fuel ratio sensor to obtain the reversal frequency ratio.
Calculate and touch each operating area based on this inversion frequency ratio.
While repeatedly calculating the medium deterioration information amount , the operating state detecting unit determines which of the plurality of operating regions the current operating state is included in, and the deterioration determining unit further determines the amount of catalyst deterioration determining information for each operating region. The deterioration of the exhaust gas purification catalyst is determined based on the integrated value of the average values of the above .

[0017]

[0018] In a preferred embodiment of the degradation diagnosis device of claim 1, the deterioration information quantity calculation device, for example, by integrating the average value of the inversion frequency ratio more than a predetermined number of times, dividing the integrated value by the accumulated number To calculate the catalyst deterioration information amount. In this case, in a further preferred aspect, the deterioration information amount calculation means individually calculates the catalyst deterioration information amount for, for example, a low speed / low load operation region or a high speed / high load operation region.

At this time, in a further preferred embodiment ,
For example, when an average value equal to or more than a predetermined number is integrated for each operation region, the deterioration determination means calculates the catalyst deterioration information amount by averaging the integrated values, compares the calculated information with the deterioration determination threshold value, and compares the amount with the deterioration determination threshold value. Deterioration is determined. Also, at this time,
In a preferred embodiment , for example, when a predetermined number or more of the average values are integrated for each operation region, the deterioration determination unit divides each integrated value by the number of integration times, and then averages them to obtain a catalyst deterioration information amount. Is calculated, and this is compared with a deterioration determination threshold value to determine the deterioration of the exhaust purification catalyst.

Further, in the deterioration diagnostic apparatus according to claim 2, For example <br/>, the deterioration determining means, each of the accumulated number exceeds the set number for each operating region, by dividing the integrated value by the accumulated number Then, the amount of catalyst deterioration information is calculated by averaging, and this is compared with a deterioration determination threshold value to determine the deterioration of the exhaust purification catalyst.

Further, the deterioration diagnosis apparatus according to claim 1 is preferable.
In the aspect , the operation region is divided into a plurality of regions based on, for example, intake air amount information and intake pipe negative pressure. Further, in another preferred embodiment of deterioration diagnostic apparatus according to claim 1, operating range, for example, high-speed and the inversion frequency of the upstream-side air-fuel ratio sensor is higher
It is divided into a high load operation region and a low speed / low load operation region in which the reversal frequency is low.

Further, in another preferred embodiment of the degradation diagnosis device of claim 1, the deterioration information quantity calculation device, for example, when the operating state changes from the first operating region to the second operating region within the predetermined period of time , The calculation of the catalyst deterioration information amount for the first operation region is stopped, and the calculation of the catalyst deterioration information amount for the second operation region is started.

[0023]

An embodiment of the present invention will be described below with reference to the drawings.
I will tell. FIG. 1 shows an inside view of the apparatus provided with the deterioration diagnosis apparatus according to the present invention.
It is a schematic structure figure showing a fuel engine. In FIG.
The fuel injection valve 3 is installed in the intake port 2 of each cylinder 1 for each cylinder.
Air cleaning via the attached intake manifold 4
Na 5, Karman vortex air flow sensor 6, throttle
Valve 7, ISC (idle speed controller) 8
Are connected. Also, exhaust port
An exhaust pipe 12 is provided at 10 through an exhaust manifold 11.
The exhaust pipe 12 is connected to a three-way catalyst 13 and
A muffler (not shown) is attached. Exhaust pipe 12
In the pipeline, upstream and downstream of the three-way catalyst 13 are provided, respectively.
Upstream O_TwoSensor 14 and downstream O _TwoSensor 15 and
Is being worn. These O_TwoSensors 14 and 15 are three-way
Reacts with the oxygen in the exhaust gas before and after passing through the medium 13,
Generates a voltage corresponding to the concentration of

The engine 1 has a crank angle sensor 20 for detecting an engine rotation speed Ne and the like, and a cooling water temperature TW.
A throttle sensor 22 for detecting the opening θTH of the throttle valve 7 and an atmospheric pressure sensor 2 for detecting the atmospheric pressure Ta are provided in the intake system.
3. Various sensors such as an intake air temperature sensor 24 for detecting the intake air temperature Ta are connected. In the figure, reference numeral 30 denotes a spark plug disposed above a combustion chamber 31;
This is an ignition coil that outputs a high voltage to the ignition coil.

On the other hand, an input / output device (not shown) and a storage device (RO
M, RAM, nonvolatile RAM, etc.), central processing unit (CP
U), an ECU (engine control unit) 40 including a timer counter and the like is provided. ECU40
In addition to the above, various sensors and switches are connected to the input side, and detection information from these is input. The output side is connected to the fuel injection valve 3, the ISC 8, the ignition coil 32, and the like, to which the optimum value calculated based on input information from various sensors is output. Then, ECU 40 includes a fuel injection, ignition timing, in addition to performing the control of ISC, etc., both the O ₂ sensor 14, 1
The catalyst deterioration diagnosis is also executed based on the output signal of No. 5. In the figure, reference numeral 41 denotes a warning light installed in the vehicle compartment, which is turned on when the three-way catalyst 13 is deteriorated, and alerts the driver.

First, the fuel injection control in this embodiment will be briefly described. At the same time as the driver starts the engine 1, the fuel injection control by the ECU 40 is executed. When this control is started, the ECU 40 obtains the intake air amount information A / N per intake stroke based on the output signals of the air flow sensor 6 and the crank angle sensor 20, and determines the value and the target air-fuel ratio (normally, the stoichiometric air-fuel ratio). ) To calculate the basic fuel injection time TBASE. Next, the ECU 40 corrects the basic fuel injection time TBASE based on the output signals of the atmospheric pressure sensor 23 and the intake temperature sensor 24, and further warms up based on the output signals of the water temperature sensor 21, the throttle sensor 22, and the like. The fuel injection time TINJ is calculated by performing a correction for increasing the amount of the engine or a correction for increasing the acceleration. Then, the ECU 40 adds the invalid injection time TD for complementing the valve opening delay of the fuel injection valve 3 to the fuel injection time TINJ obtained in this way, and then adds the fuel injection valve via a fuel injection valve driver (not shown). 3 is driven.

Now, activation of the upstream O ₂ sensor 14 has been completed, the engine 1 is not in a high-load, high-speed operation state, and so on.
When predetermined operating conditions are satisfied, the ECU 40 starts air-fuel ratio feedback control. When this control starts, EC
U40, the output voltage VOF with a predetermined threshold value VTH of the upstream O ₂ sensor 14 (e.g., 0.5V) to compare the magnitude of the performs feedback correction of the air-fuel ratio. That is, the upstream O
_{The two} sensors 14 determine that the air-fuel ratio of the mixture is the stoichiometric air-fuel ratio (14.
7) before and after the output voltage VOF reaches the maximum voltage (for example,
Since the output voltage VOF falls below the threshold value VTH (for example, 0.5 V) since the output voltage VOF falls below the threshold voltage VTH (for example, 0.5 V), the fuel injection time TINJ is gradually increased to shift to the rich side. Conversely, when the output voltage VOF exceeds the threshold value VTH, the fuel injection time TINJ is gradually shortened to shift to the lean side. As a result, the air-fuel ratio of the air-fuel mixture is always maintained near the stoichiometric air-fuel ratio, and the three-way catalyst 13 purifies the exhaust gas with high efficiency.

In the air-fuel ratio feedback control in this embodiment, learning correction is performed so that the central value of the feedback correction coefficient becomes 1.0, and the learning correction amount is stored in the nonvolatile RAM.
To be stored. Then, by using the learning correction amount,
The accuracy of the above-described open loop control is improved, and the amount of deviation at the start of feedback control is reduced.

The procedure for diagnosing catalyst deterioration in this embodiment will be described below with reference to flowcharts shown in FIGS. 2 to 7 and graphs shown in FIGS. When the driver turns on the ignition switch and starts the engine 1, the catalyst deterioration diagnosis subroutine shown in FIGS. 2 and 3 is executed. When this subroutine is started, the ECU 40 first reads input information from each sensor into the RAM in step S2 in FIG. 2, and then determines in step S4 whether a condition (diagnosis condition) for performing catalyst deterioration diagnosis is satisfied. Determine whether or not. Here, that the air-fuel ratio feedback control is implemented,
It is sequentially confirmed that both O ₂ sensors 14 and 15 are operating normally, and when all the conditions are satisfied, the determination result is Y.
The answer is es (affirmative), but in the case of No (negative), the process returns to the start without performing the subsequent processing.

When the diagnosis condition is satisfied and the result of the determination in step S4 is Yes, the ECU 40 next executes a reversal frequency ratio calculation subroutine shown in FIGS. 4 and 5 in step S6. When this subroutine is started, the ECU 40 first reads the input information from each sensor into the RAM again in step S42 of FIG. 4, and then in step S44, based on the intake air amount information A / N, the engine rotation speed Ne, etc. The operating state of the vehicle has not transitioned between the low-speed / low-load operation area (A area) and the high-speed / high-load operation area (B area) on the map of FIG. 8 since the previous processing. Is determined.
And if this determination is Yes, ECU 40 detects the upstream reversal frequency fF, based on an output signal from the upstream O ₂ sensor 14 in step S46. As the detection method, for example, a predetermined time (e.g., 10 seconds) in obtains the number of times the output voltage VOF of the upstream O ₂ sensor 14 has crossed the threshold VTH (e.g., 0.5V), as the number of It is assumed that the upstream inversion frequency is fF. Upstream inversion frequency f
When the detection of F is completed, the ECU 40 proceeds to step S4.
In the same manner as the upstream inversion frequency fF, the downstream O
_The downstream inversion frequency fR is detected based on the output voltage VOR of the _second sensor 15.

Next, the ECU 40 calculates an inversion frequency ratio α (= fR / fF) from the upstream inversion frequency fF and the downstream inversion frequency fR in step S50, and then proceeds to step S5.
2, the sum of the value and the inversion frequency ratio α up to the previous time αto
From tal (n-1), an addition value αtotal (n) up to the current (n-th) time is calculated by the following equation. αtotal (n) = αtotal (n−1) + α Next, in step S54, the ECU 40 determines whether the timer T has started counting up simultaneously with this subroutine.
Is determined to have exceeded a predetermined time TA (10 seconds in this embodiment), and if this determination is No, the process returns to the start and the above-described processing is repeated.

After returning to the start, the ECU 40 continues to add the inversion frequency ratio α as long as the determination in step S54 is No (that is, until the value of the timer T exceeds the predetermined time TA). When the value of the timer T exceeds the predetermined time TA and the determination in step S54 becomes Yes, the ECU 40
Is the addition value αtota at the current time in step S56 of FIG.
From l (n) and the number of additions n, an average value αave of the inversion frequency ratio α is calculated by the following equation.

Αave = αtotal (n) / n Next, in step S58, the ECU 40 determines whether or not the current operation state is in the area A on the map of FIG. 8, and if this determination is Yes, After substituting the average value αave for the A-region inversion frequency ratio αA in step S60, the process proceeds to step S6.
In step 2, the area A flag FA is set to 1 and the subroutine is terminated. If the determination in step S58 is No, the average value αave is substituted for the B region inversion frequency ratio αB in step S64, and the subroutine is terminated with the A region flag FA set to 0 in step S66.

On the other hand, during the execution of the inversion frequency ratio calculation subroutine, if the determination in step S44 is No, the EC
U40 resets the addition value αtotal (n) and the number of additions n to 0 in step S68, resets the value of the timer T to 0 in step S70, and proceeds to step S46. That is, if the operation state shifts between the area A and the area B before the value of the timer T exceeds the predetermined time TA, it is determined that there has been no processing up to that point, and the inversion frequency ratio α in the new area. Is started. This is because, if the average value αave of the inversion frequency ratio α is calculated based on data in a very short time, the influence of erroneous detection due to noise or the like may increase.

After ending the inversion frequency ratio calculation subroutine, the ECU 40 determines whether or not the A region flag FA is 1 in step S8 of the catalyst deterioration diagnosis subroutine. If this determination is Yes, step S10
After calculating the A-region integrated value αAaccu by the following formula, 1 is added to the A-region integrated number NA in step S12. αAaccu = αAaccu + αA If the determination in step S8 is No, step S8
After calculating the B area integrated value αBaccu by the following equation at 14,
In step S12, 1 is added to the B area integration number NB.

ΑBaccu = αBaccu + αB where A region integrated value αAaccu, B region integrated value αBaccu, A
The area integration number NA and the B area integration number NB
The data is stored in the AM, and the initial values for a new vehicle are all set to 0. Except when a multi-use tester is used for maintenance, these data are not externally initialized even when the deterioration diagnosis is performed for a long time.

When the calculation of the A-region integrated value αAaccu or the B-region integrated value αBaccu is completed, the ECU 40 determines in step S18 whether the A-region integrated number NA has exceeded a predetermined value NAX (10 in this embodiment). If the determination is No, the process returns to the start and repeats the above-described processing. If the determination in step S18 is Yes, the ECU 40 determines in step S20 that the B-region integration number NB is equal to the predetermined value NBX.
It is determined whether or not (in this embodiment, 10) has been exceeded, and if this determination is No, the process returns to the start and the above-described processing is repeated.

If the determinations in steps S18 and S20 are both Yes, the ECU 40 next calculates an overall area average value αABave (catalytic deterioration information amount) based on the following equation in step S22. αABave = 0.5 × (αAaccu / NA + αBaccu / NB
Next, the ECU 40 determines in step S24 that the entire area average value αAB
It is determined whether or not the value of ave is greater than a predetermined determination threshold THc (for example, 0.8). If this determination is No, the three-way catalyst 13 has not deteriorated, and the graph of FIG. As shown, the lower limit E1 of the purification efficiency ECAT (for example, about 85%)
With the above, it is diagnosed that it is functioning normally, and step S26 is performed.
Then, the normal processing subroutine of FIG. 6 is executed.

In the normal processing subroutine, first, in step S82, the warning lamp 41 is turned off and the three-way catalyst 1 is turned off.
3 indicates to the driver that it is functioning properly. Next, in step S84, the ECU 40 performs an operation of deleting the failure code so that the failure code corresponding to the deterioration of the three-way catalyst 13 does not remain in the RAM. On the other hand, the global average value αABave exceeds the determination threshold THc, and the determination result of step S24 is Yes.
, The three-way catalyst 13 deteriorates and the purification efficiency E
Diagnose that CAT has fallen below the lower limit E1 (about 85%),
In step S28, the deterioration processing subroutine of FIG. 7 is executed.

In the deterioration processing subroutine, first, in step S92, the warning lamp 41 is turned on to notify the driver of the deterioration of the three-way catalyst 13 and urge repair. Then, in step S94, the ECU 40 stores a failure code corresponding to the deterioration of the three-way catalyst 13 in the RAM. Thus, when performing repair, the details of the failure can be easily known by reading out the failure code, and the response such as replacement of the three-way catalyst 13 can be promptly performed.

When the normal processing subroutine or the deterioration processing subroutine is completed, the ECU 40 proceeds to step S3.
0, the A area integrated value αAaccu, the B area integrated value αBaccu,
After resetting the values of the A-area integrated number NA and the B-area integrated number NB to 0, the process returns to the start and the catalyst deterioration diagnosis subroutine is started again. In the present embodiment, since the deterioration diagnosis of the three-way catalyst is performed in such a procedure, the calculation results in the A region and the B region are reflected in the averaged value in the entire region average value αABave. Therefore, the specific operation state is prominent, and the calculation frequency of the inversion frequency ratio α is A
Even in the case where the three-way catalyst is biased to the area or the area B, the deterioration of the three-way catalyst can be accurately determined, and the early replacement of the three-way catalyst can be prevented.

Although the description of the concrete embodiment has been finished, the embodiments of the present invention are not limited to this embodiment. For example,
In the above-described embodiment, the operation region is divided into two, and the integration of the inversion frequency is performed. However, this may be performed by dividing the operation region into three or more. Or the like may be performed only based on the engine load information. Further, in the above embodiment, the catalyst deterioration information amount (average value over the entire area) is calculated based on the integrated value of the inversion frequency ratio in each operation region until the normality determination or the deterioration determination is performed. The deterioration information amount may be calculated based on the latest integrated value of the predetermined number of times.
Further, the catalyst deterioration determination may be stopped when the upstream O ₂ sensor, which is easily deteriorated by heat, is deteriorated. In the above embodiment, a voltage output type O ₂ sensor is used as the air-fuel ratio sensor. However, a current output type sensor such as a linear air-fuel ratio sensor may be used. Further, starting with the specific procedure of the control, the specific values such as the respective thresholds can be appropriately changed without departing from the gist of the present invention.

[0043]

According to the first aspect of the present invention, there is provided an upstream air-fuel ratio sensor provided upstream of an exhaust purification catalyst in an exhaust passage of an internal combustion engine; The output signal of the downstream air-fuel ratio sensor provided on the downstream side and the output signal of the upstream air-fuel ratio sensor
As inversion is repeated at the threshold corresponding to the target air-fuel ratio,
The air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is
Air-fuel ratio control means for controlling the operating state of the internal combustion engine, operating state detecting means for detecting the operating state of the internal combustion engine, and an operating state detected by the operating state detecting means. or a determined operating region determining means that is included in, the reversal frequency of the determination result according to the output signal of the inverting frequency of the output signal of said upstream air-fuel ratio sensor said downstream air-fuel ratio sensor of this operating region determining means From
Calculates the inversion frequency ratio, based on the inversion frequency ratio, and degradation information amount calculating means for repeatedly calculating a catalyst deterioration information amount the each operating region, Repetitive this degradation information amount calculation means
Average catalyst deterioration information amount for each operation region that returns computed Ri
A deterioration determining means for determining the deterioration of the exhaust gas purification catalyst is provided based on the integrated value of the values , so that even when a specific operating state is prominent, the average of the amount of catalyst deterioration information can be averaged for each operation region. The catalyst degradation information without bias.
Information and erroneous detection due to noise, etc.
Effect can be reduced, and the inversion frequency ratio
It is determined that the exhaust purification catalyst has deteriorated when
By doing so, accurate deterioration determination can be performed.

[0044]

[0045]

[0046] In a preferable embodiment of the deterioration diagnosis apparatus according to claim 1, wherein the degradation information amount calculating means, the value obtained by dividing the integrated value by the integration number of the catalyst deterioration information quantity average value of the inversion frequency ratio The calculation accuracy of the catalyst deterioration information amount is further improved, and accurate deterioration determination can be performed. In this case, as a more preferable aspect, the deterioration information amount calculating means preferably calculates the catalyst deterioration information amount for each of the operation regions, whereby even if a specific operating state is prominent, it is averaged. It is possible to make an accurate deterioration determination.

At this time, a more preferable embodiment is adopted.
The deterioration determination means may be configured to calculate the average value when the number of times of integration of the average value for each of the operation areas by the deterioration information amount calculation means exceeds a predetermined number of times set in advance for each of the operation areas. It is better to make the deterioration judgment based on the value .
In this manner, sufficient data can be obtained for each operation region, and accurate deterioration determination can be performed.

At this time, a more preferable mode is adopted.
The deterioration determining means compares the integrated value of the average value for each of the operating regions by the deterioration information amount calculating means with each of the number of integrations, and compares the average value with a predetermined determination value. It is better to make a judgment,
Ri, even if the specific operating state protrude can be obtained catalyst deterioration information amount unpolarized, it is possible to accurately deterioration determination.

Further, according to the deterioration diagnosis apparatus of the second aspect ,
In the deterioration diagnostic apparatus according to claim 1 Symbol placement, before Symbol deterioration determining means, a predetermined number of times the accumulated number of times the catalyst deterioration information amount is set in advance for each of the operating region of the operating each region by the degradation information amount calculation means Is exceeded, the deterioration determination is performed, so that a sufficient amount of catalyst deterioration information can be obtained for each operation region, and accurate deterioration determination can be performed.

[0050] In addition, preferred the deterioration diagnosis apparatus of 請 Motomeko 1, wherein
As Shii embodiment, the plurality of operating regions being set based on load information of at least the internal combustion engine is good, this
As a result , it is possible to obtain a catalyst deterioration information amount in which an increase or decrease in the amount of intake air that affects the inversion frequency ratio is taken into account, and accurate deterioration determination can be performed. As another preferred embodiment of the apparatus for diagnosing deterioration of 請 Motomeko 1, wherein the plurality of operating regions comprise at least high-speed, high-load operation region and a low-speed, low-load operation zone well, thereby, bias It is possible to obtain the catalyst deterioration information amount based on the inversion frequency ratio without
Accurate deterioration determination can be performed.

[0051] As another preferred embodiment of the deterioration diagnosis apparatus according to claim 1, wherein the degradation information amount calculation unit, when the operating state is shifted among the plurality of operating areas within the predetermined time, the It is preferable to stop the calculation of the amount of catalyst deterioration information, so that the amount of catalyst deterioration information based on too little data can be removed, and accurate deterioration determination can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an internal combustion engine including a deterioration diagnosis device according to the present invention.

FIG. 2 is a flowchart showing a procedure of a catalyst deterioration diagnosis subroutine.

FIG. 3 is a flowchart illustrating a procedure of a catalyst deterioration diagnosis subroutine.

FIG. 4 is a flowchart illustrating a procedure of an inversion frequency ratio calculation subroutine.

FIG. 5 is a flowchart illustrating a procedure of an inversion frequency ratio calculation subroutine.

FIG. 6 is a flowchart illustrating a procedure of a normal processing subroutine.

FIG. 7 is a flowchart illustrating a procedure of a degradation processing subroutine.

FIG. 8 is an area map in which intake air amount information and engine rotation speed are used as parameters.

FIG. 9 is a graph showing a relationship between a catalyst deterioration information amount and a purification efficiency.

FIG. 10 is a graph showing output voltages of an upstream O ₂ sensor and a downstream O ₂ sensor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine 12 Exhaust pipe 13 Three-way catalyst 14 Upstream O ₂ sensor 15 Downstream O ₂ sensor 40 ECU 41 Warning light

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI F02D 45/00 358 F02D 45/00 358Z (72) Inventor Toshiro Nomura 33-3-8 Shiba 5-chome, Minato-ku, Tokyo Mitsubishi Motors Inside (72) Inventor Eiji Kanao 5-33-8 Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Corporation (56) References JP-A-7-247830 (JP, A) JP-A-3-3 253714 (JP, A) JP-A-3-57862 (JP, A) JP-A-61-286550 (JP, A) JP-A-5-98949 (JP, A) JP-A-7-243342 (JP, A) JP-A-7-310536 (JP, A) Japanese Utility Model 63-128221 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 3/20 F01N 9/00 F02D 41/14 F02D 45/00

Claims (2)

(57) [Claims] 1. A upstream air-fuel ratio sensor disposed upstream of the exhaust purification catalyst in an exhaust passage of an internal combustion engine, and a downstream-side air-fuel ratio sensor provided downstream of the exhaust purification catalyst in the exhaust passage, wherein The output signal of the upstream air-fuel ratio sensor is set to a predetermined target air-fuel ratio.
So that the inversion is repeated at a threshold value corresponding to
Feedback control of air-fuel ratio of air-fuel mixture supplied to engine
Air-fuel ratio controlling means, operating state detecting means for detecting an operating state of the internal combustion engine, and an operating state detected by the operating state detecting means is included in any of a plurality of preset operating regions. and operating region determining means for determining, according to the judgment result of the operating range determining means, inversion frequency from the inversion frequency of the output signal of said downstream air-fuel ratio sensor and the inverting frequency of the output signal of said upstream air-fuel ratio sensor Play ratio
Calculated and, based on this inversion frequency ratio, and degradation information amount calculating means for repeatedly calculating a catalyst deterioration information amount the each operating region, the catalyst deterioration information for each operation region that is repeated calculation by the deterioration information amount calculation means Based on the integrated value of the average amount,
A degradation diagnosis device for an exhaust purification catalyst, comprising: a degradation determination unit that determines degradation of the exhaust purification catalyst. 2. A pre-Symbol deterioration determining means, when the accumulated number of times the catalyst deterioration information of the operation for each area by the degradation information amount calculation means exceeds a preset predetermined number of times for each of the operating region, Performing the deterioration determination,
Deterioration diagnosis device for an exhaust gas purifying catalyst of claim 1 Symbol placement.