JP2853554B2 - Catalyst deterioration diagnosis device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an apparatus for diagnosing a deterioration state of a catalyst for purifying exhaust gas of an internal combustion engine.

[0002]

2. Description of the Related Art As a device for purifying exhaust gas of an internal combustion engine, an air-fuel ratio is feedback-controlled to a stoichiometric air-fuel ratio based on an output of an oxygen sensor, and HC and C are supplied to an exhaust passage.
Those having a three-way catalyst for simultaneously oxidizing O and reducing NO have been widely put into practical use.

[0003] When the performance of the three-way catalyst deteriorates due to aging or the like, the conversion efficiency gradually decreases, which hinders exhaust gas purification. It is desirable to take measures such as replacing the catalyst whose performance has deteriorated. Therefore, in order to determine such a state of deterioration of the catalyst, an apparatus disclosed in JP-A-63-205441 has conventionally been used. Proposed.

[0004] This is achieved by disposing oxygen sensors upstream and downstream of a catalyst interposed in an exhaust passage of an internal combustion engine, respectively.
The air-fuel ratio feedback control is executed mainly based on the output signal of the upstream oxygen sensor, and the deterioration of the catalyst is diagnosed based on a comparison between the output signals of the two sensors.

[0005] That is, during the execution of the air-fuel ratio feedback control, the fuel supply amount is controlled by, for example, pseudo proportional integral control based mainly on the output signal of the upstream oxygen sensor, and the actual air-fuel ratio is determined by the stoichiometric air-fuel ratio. And the output signal of the upstream oxygen sensor is slightly rich and lean.
As shown in (a), rich and lean are periodically repeated, and the oxidation and reduction functions of the three-way catalyst are maintained to the maximum.

On the other hand, the air-fuel ratio of the exhaust gas that has passed through the catalyst is such that the oxygen is stored by the action of the catalyst, and the fluctuation of the residual oxygen concentration in the exhaust gas becomes very gentle.
As shown in FIG. 6B, the output signal of the downstream oxygen sensor hardly fluctuates richly and leanly, and has a smaller fluctuation width and a longer cycle than the output signal of the upstream oxygen sensor.

When the oxygen storage capacity decreases due to deterioration of the catalyst, the oxygen concentration in the exhaust gas on the upstream and downstream sides of the catalyst does not change much, and the output signal of the downstream oxygen sensor is shown in FIG. As described above, the reversal is repeated at a cycle approximating the output signal of the upstream oxygen sensor, and the fluctuation width increases.

Therefore, the richness of the upstream oxygen sensor
The inversion period T ₁ of the lean, the downstream oxygen sensor rich,
The ratio T ₁ / T ₂ to the lean reversal period T ₂ is obtained, and when this ratio becomes equal to or more than a predetermined value, it is determined that the catalyst has deteriorated.

As a catalyst deterioration diagnosis apparatus of this type, as proposed in Japanese Patent Application Laid-Open No. 4-1449, the frequency ratio of the output signals of the upstream and downstream oxygen sensors is equal to or higher than a predetermined value (period ratio). In some cases, catalyst deterioration is determined when the number of times determined to be equal to or less than a predetermined value continues for a predetermined number of times or more.

[0010]

However, when the deterioration of the catalyst is diagnosed by comparing the output of the upstream oxygen sensor and the output of the downstream oxygen sensor as described above, it is necessary to accurately measure the output ratio. For example, it is necessary to make a diagnosis based on the output ratio when the output of the upstream oxygen sensor is inverted a predetermined number of times or more.
In order for the output ratio to continuously exceed a predetermined value, it is necessary to set a large measurement time.

However, in such a conventional catalyst deterioration diagnostic apparatus for an internal combustion engine, the operating range based on the air-fuel ratio feedback control is performed under a predetermined condition among all operating conditions of the internal combustion engine. Since the area for diagnosing the deterioration of the engine is set as a predetermined area within the air-fuel ratio feedback area, under the actual operating conditions of an internal combustion engine such as an automobile, if the number of reversals of the output ratio to be measured is set to be large, the measurement time In some cases, the deterioration of the catalyst is determined when the number of times that the frequency ratio of the upstream and downstream oxygen sensors is determined to be equal to or more than a predetermined value continues for a predetermined number of times or more. Is affected by the operating conditions immediately before entering the catalyst deterioration diagnosis area. For example, when idling is performed for a long time, the exhaust When the temperature is low and the catalyst warm-up is insufficient, the characteristics of the catalyst are generally different. In the catalyst deterioration diagnosis area immediately after idling, even if the catalyst is normal, the number of reversals of the upstream and downstream oxygen sensors is approximate. Therefore, it may be erroneously diagnosed as deterioration. On the other hand, in the case where the immediately preceding driving condition is high-load driving such as long climbing,
Since the temperature of the catalyst is high, there is a problem that even a deteriorated catalyst is erroneously diagnosed as normal.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a catalyst deterioration diagnosis apparatus for an internal combustion engine capable of accurately diagnosing catalyst deterioration by suppressing the influence of immediately preceding operating conditions. With the goal.

[0013]

[0014]

[0015]

[0016]

According to a first aspect of the present invention, as shown in FIG. 1, a catalyst provided in an exhaust passage, an upstream air-fuel ratio sensor 50 provided upstream of the catalyst, and a catalyst for the catalyst are provided. A downstream air-fuel ratio sensor 51 disposed downstream, means 52 for determining operating conditions of the engine, and basic fuel injection amount setting means 53 for setting a basic fuel injection amount according to the determination result of the operating conditions.
A correction coefficient calculating means 54 for calculating a feedback correction coefficient α based on the output of the upstream air-fuel ratio sensor, and a fuel injection amount correcting means 55 for correcting the basic fuel injection amount according to the feedback correction coefficient α. In the internal combustion engine provided, the operating condition is a predetermined catalyst deterioration diagnosis area.
The diagnosis during operation located within, an output comparison means 56 for comparing the output of the downstream air-fuel ratio sensor and the output of said upstream air-fuel ratio sensor each time a predetermined period has elapsed, touch the operating conditions of a given
Every time it moves out of the medium deterioration diagnosis area,
The last comparison result obtained from the comparison results
To perform a weighted average with the weighted average calculated after the diagnostic operation
After the stage 59 and the calculation of the weighted average are performed a predetermined number of times,
Determine the deterioration of the catalyst based on the latest weighted average value
A deterioration determination unit 61 ;

Further, the second invention relates to the first invention.
As shown in FIG. 2, there are provided means 62 for calculating the number of reversals by comparing the output of the upstream air-fuel ratio sensor with a threshold value, respectively, and means 63 for calculating the ratio of the number of reversals.

[0018]

[0019]

[0020]

[0021]

According to the first invention , when the operating condition enters a predetermined catalyst deterioration diagnosis area, the comparison between the output of the upstream air-fuel ratio sensor and the output of the downstream air-fuel ratio sensor is shifted to outside the catalyst deterioration diagnosis area.
Until a certain period of time elapses,
Every time it moves out of the deterioration diagnosis area, it goes out of the catalyst deterioration diagnosis area.
The comparison result obtained just before the migration and the diagnosis area up to the previous time
Degradation of catalyst based on average with final comparison results in
Final comparison of multiple catalyst degradation diagnostic areas to determine
By using the results, the effect of operating conditions immediately before the diagnostic area
Erroneous diagnosis of the catalyst
I can.

According to the second invention , the oxygen storage capacity of the catalyst affects the response delay of the downstream air-fuel ratio sensor based on the ratio of the number of inversions of the upstream and downstream air-fuel ratio sensors that reverses between lean and rich. This makes it possible to diagnose the deterioration state of the catalyst with high accuracy.

[0023]

An embodiment of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 3, a catalytic converter 13 composed of a three-way catalyst is interposed in the exhaust passage 2 of the engine 1. An upstream oxygen sensor as an air-fuel ratio sensor is provided upstream of the catalytic converter 13. 14 and a downstream oxygen sensor 15 is also provided downstream.

Both the upstream oxygen sensor 14 and the downstream oxygen sensor 15 generate an electromotive force corresponding to the residual oxygen concentration in the exhaust gas. The air-fuel ratio has a high level (about 1 V) on the rich side (hereinafter, rich) and a low level (about 100 mmV) on the lean side.

On the other hand, in the intake passage 3 of the engine 1, a fuel injection valve 17 for supplying fuel to each intake port is provided for each cylinder, and air passing through an air flow meter 18 for detecting an intake air amount is After being throttled by the throttle valve 5 , it flows into each intake port.

Reference numeral 4 denotes a control unit, which is constituted by, for example, a microprocessor or the like, so that the amount of fuel supplied to the intake passage 3 of the engine 1 via the fuel injection valve 17 basically becomes the stoichiometric air-fuel ratio. Perform feedback control.

For this reason, the control unit 4 includes:
Crank angle sensor 19 for detecting the engine speed, water temperature sensor 16 for detecting the temperature of the cooling water, air flow meter 18
And the signals from the upstream oxygen sensor 14 and the downstream oxygen sensor 15 are input, and the fuel supply amount set to a predetermined ratio with respect to the intake air amount is adjusted by the upstream oxygen sensor. Feedback control is performed based on the output of the sensor 14, and correction is further performed based on the output of the downstream oxygen sensor 15, so that the fuel injection amount is corrected so that the stoichiometric air-fuel ratio is correctly obtained.

The outline of the air-fuel ratio feedback control will be described. First, the basic injection from the fuel injection valve 17 is performed based on the intake air amount Q detected by the air flow meter 18 and the engine speed Ne detected by the crank angle sensor 19. The basic pulse width Tp for determining the amount is calculated by Tp = Q / Ne. The basic pulse width Tp controls the opening time of the fuel injection valve 17, and the basic pulse width Tp is hereinafter referred to as a basic fuel injection amount Tp.

The drive pulse width Ti of the fuel injection valve 17 is determined by adding corrections such as increase correction and feedback correction to the basic injection amount Tp. The drive pulse width Ti is obtained by the following equation.

Ti = Tp × COEF × α + Ts
(1) Here, COEF indicates various increase correction coefficients, and includes, for example, water temperature increase correction according to the cooling water temperature, air-fuel ratio correction at high speed and high load, and the like. Ts is a voltage correction coefficient added according to the battery voltage to correct the invalid time of the fuel injection valve 17.

Here, α is a feedback correction coefficient mainly calculated based on the detection signal of the upstream oxygen sensor 14, and the output signal of the upstream oxygen sensor 14 is set to a predetermined slice level corresponding to the stoichiometric air-fuel ratio. This output signal is a value obtained by pseudo-proportional integration based on the inversion to the rich side or the lean side. If α is 1 or more, the output signal becomes empty on the rich side and if it is less than 1, it becomes empty on the lean side. The fuel ratio is corrected.

For example, from the upstream oxygen sensor 14 in FIG.
When an output signal as shown in FIG. 7A is detected, the corresponding feedback correction coefficient α changes as shown in FIG. 7B. As described above, the feedback correction coefficient α is obtained by pseudo proportional integration. When the feedback is inverted from the rich side to the lean side across a predetermined slice level (S / L) of the upstream oxygen sensor 14, the feedback correction coefficient α is calculated. the coefficient α is subject to a predetermined proportional portion P _L, the integral component is added gradually further a slope of a predetermined integration constant I _L. This feedback correction coefficient α is multiplied by the basic injection amount Tp as described above, and the actual air-fuel ratio gradually increases in concentration.

[0034] When the output signal of the upstream oxygen sensor 14 is inverted from the lean side to the rich side, with the feedback correction coefficient α predetermined proportional portion P _R is subtracted, integral with a slope of a predetermined integration constant I _R Minutes are gradually subtracted. By repeating such control, the actual air-fuel ratio is maintained near the stoichiometric air-fuel ratio while changing at a frequency of about 1 to 2 Hz.

When the fuel is increased or decreased during the air-fuel ratio control by the feedback, for example, at low water temperature, high speed and high load, or during fuel cut during deceleration, the feedback correction coefficient α is fixed at 1. At the same time, open loop control is essentially achieved.

During such air-fuel ratio feedback control, the control unit 4 controls the upstream oxygen sensor 1
4 and a catalyst deterioration diagnosis for determining whether or not the catalytic converter 13 is functioning normally based on the number of inversions of the output of the downstream oxygen sensor 15. That is, the deterioration of the catalyst is determined based on the ratio between the output of the upstream oxygen sensor 14 and the output of the downstream oxygen sensor 15 during a period in which the number of inversions of the output of the upstream oxygen sensor 14 per unit time is equal to or more than a predetermined number. Then, the warning lamp 30 connected to the control unit 4 is turned on according to the determination result.

The catalyst deterioration diagnosis control operation based on the reversal frequency ratio will be described with reference to the flowchart of FIG. This measurement control operation is performed, for example, every predetermined time, and is specifically executed by a timer interrupt process of a microprocessor.

First, at step S1, it is determined whether or not a permission condition for diagnosing catalyst deterioration has been established. The water temperature when the engine starts is higher than a predetermined value.

2. After a lapse of a predetermined time after the engine warm-up.

3. The downstream oxygen sensor 15 is active.

The process proceeds to step S2 only when all of the predetermined conditions 1 to 3 are satisfied. Note that the warm-up state of the engine 1 can be determined from the detection signal of the water temperature sensor 16, and the activated state of the oxygen sensor indicates a state in which the output signal of the downstream oxygen sensor 15 has reached a preset level.

In step S2, it is determined whether or not the operating state of the engine 1 is in a catalyst deterioration diagnosis region where the air-fuel ratio feedback control is performed.

This determination is made based on the following conditions.

4. The vehicle speed VSP is within a predetermined range.

5. The engine speed Ne is within a predetermined range.

6. The engine load, that is, the basic injection amount Tp is within a predetermined range.

When all of the conditions 4 to 6 are satisfied, it is determined that the region is the catalyst deterioration diagnosis region, and the process proceeds to step S3. Note that the vehicle speed VSP is controlled by the control unit 4.
3 shows a signal from a vehicle speed sensor (not shown) connected to the control unit.

In step S3, it is determined whether the number of rich / lean inversions FO2CT of the upstream oxygen sensor 14 for performing the air-fuel ratio feedback control has reached a predetermined value CMSW, and if the number of inversions FO2CT has not reached the CMSW, In step S4, the upstream and downstream oxygen sensors 1
The number of inversions FO2CT and RO2CT of 4 and 15 are each incremented to continue counting the number of inversions, while if the number of inversions FO2CT has reached the predetermined value CMSW, the inversion number ratio HZR is calculated in step S5.

This predetermined value CMSW is determined by the upstream oxygen sensor 1
This is for sampling the reversal frequency ratio HZR at predetermined intervals after entering the diagnostic region with reference to the reversal frequency FO2CT of No. 4 and is preset in accordance with the characteristics of the catalytic converter 13 and the like.

The reversal number ratio HZR is calculated from the reversal number FO2CT of the upstream oxygen sensor 14 and the reversal number RO2CT of the downstream oxygen sensor 15 by the following equation.

HZR = RO2CT / FO2CT
(2) The calculated inversion frequency ratio HZR is the control unit 4
(Not shown) (step S5).

When the catalytic converter 13 is deteriorated, the oxygen storage capacity is reduced, and the reversal number ratio HZR is increased with the reversal number RO2CT of the downstream oxygen sensor 15. At times, the number of inversions RO2CT approaches zero, and the inversion number ratio HZR approaches zero.

After the calculation of the inversion number ratio HZR, the inversion numbers FO2CT and RO2CT are cleared to prepare for the next count (step S6).

As shown in FIG. 4, while the operating conditions of the engine 1 are in the diagnostic region satisfying the conditions of steps S1 and S2, the processing of steps S3 to S6 is repeated, so that the upstream oxygen sensor 14, the downstream oxygen sensor The number of inversions FO2CT and RO2CT of the sensor 15 are counted, and when the number of inversions FO2CT of the upstream oxygen sensor 14 reaches a predetermined value CMSW, the inversion number ratio HZR is updated,
As the inversion frequency ratio HZR, the latest one is always stored.

Here, if the operating conditions are changed and deviate from the diagnostic region shown in FIG. 4, the permission conditions of steps S1 and S2 and the diagnostic region are no longer satisfied, and the diagnostic processing from step S7 is performed.

In step S7, it is determined whether or not the reversal frequency ratio HZR of the memory (not shown) has been cleared. The reversal frequency ratio HZR is cleared after the calculation of the weighted average value HZRATE of the reversal frequency ratio described later is completed. In this step S7, the overlap calculation of the weighted average value HZRATE is prevented. If the weighted average value HZRATE has not been cleared, the process proceeds to step S8-1, and it is determined whether the process has started for the first time in the weighted average process. If this weighted averaging process is the first time, the process proceeds to step S8-2 to set HZRATE = HZR. If not, the process proceeds to step S8-3 to calculate the inversion number ratio average value HZRATE while clearing. If so, the process proceeds to step S11.

Immediately after deviating from the diagnosis area, the inversion frequency ratio H
Since the ZR holds the latest one, step S8-
In step 3, the weighted average value HZRATE is calculated from the following equation based on the latest inversion frequency ratio HZR updated in the immediately preceding diagnostic area.

HZRATE = (HZR + 7 × HZRATE) / 8 (3) Here, HZRATE on the right side is a value calculated in the previous diagnostic area, that is, a value calculated in the diagnostic area before the diagnostic area shown in FIG. HZRATE on the left side is the weighted average value of the inversion number ratio obtained in step S8-3, and the weighted average value HZRATE of the previous diagnosis area
, The influence of the latest reversal frequency ratio HZR is reduced, and the immediately preceding diagnostic region is operable under the condition that the deterioration of the catalytic converter 13 is easily erroneously diagnosed, for example, a long-time high-load operation or a long-time idling. The effect of is reduced.

This weighting is performed by, for example, the inversion frequency ratio HZR.
To the weighted average HZRATE of the previous diagnostic area
The weight is doubled, and this ratio is set in advance in accordance with the characteristics and capacity of the catalytic converter 13 or the characteristics of the engine 1.

When the calculation of the weighted average value HZRATE is completed, the latest inversion number ratio HZR is cleared in step S9, and in step S10, a counter NUMHZ for counting the number of calculation times of the weighted average value HZRATE is incremented.

Then, in step S11, the weighted average value H
It is determined whether the calculation of ZRATE has been performed a predetermined number of times NUMJDG or more. If the calculation of the predetermined number NUMJDG more weighted average HZRATE is made in this determination, the process proceeds to the diagnostic process in step S12 and subsequent termination operation number without a diagnosis process is less than the predetermined number of times NUMJDG I do. The predetermined number NUMHZ is cleared, for example, every time the engine 1 is started, and the predetermined number NUMJZ is cleared.
By appropriately setting the DG, a plurality of diagnostic regions are allowed to elapse immediately after the start of the engine 1 or the like, and the catalytic converter 13
By starting the catalyst deterioration diagnosis after stabilization, the erroneous diagnosis can be suppressed.

In step S12, the above step S8-3 is performed.
Weighted average value HZRATE obtained by the above and a predetermined determination reference value C
A comparison with NGHZ is performed to determine whether the catalytic converter 13 is in a deteriorated state.

In this determination, the weighted average value HZRAT
If E is greater than or equal to the determination reference value CNGHZ, it is determined that the catalytic converter 13 is in a deteriorated state, and
Proceeding to 14, the warning light 30 is turned on to call the driver's attention. On the other hand, if the weighted average value HZRATE is less than the determination reference value CNGHZ, it is determined that the catalytic converter 13 is normal, and the process proceeds to step S13 to turn off the warning lamp 30.

The operation of the control unit 4 will now be described. When the operation state of the engine 1 enters the diagnosis range in the determination of step S2, the control unit 4 performs the number of reversals FO2CT and RO2CT based on the threshold value. Are detected, and the number of reversals FO2C of the upstream oxygen sensor 14 is detected.
Each time T reaches the predetermined number of times CMSW, the inversion number ratio HZR is sequentially updated, and the inversion number ratio HZR is sampled at intervals corresponding to the predetermined number of times CMSW.

If the deviation from the diagnosis area is caused by a change in the operating condition, the final inversion number ratio HZR in this diagnosis area is held as the latest data. And the weighted average value HZRATE calculated in the previous diagnosis area,
Weighted average value H of past diagnostic areas in addition to the latest diagnostic area
The weighting of ZRATE not only makes it possible to average the reversal frequency ratio HZR, but also reduces the influence of the operating conditions immediately before entering the diagnostic region. It is possible to suppress erroneous diagnosis of the catalytic converter 13 due to overheating of the catalyst or overcooling of the catalyst due to idling.

Further, since the diagnostic processing is performed after the calculation of the weighted average value HZRATE is performed a predetermined number of times NUMJDG or more, the deterioration diagnosis in the diagnostic region where the catalytic converter 13 is not sufficiently heated, such as immediately after the start of the engine 1, is performed. At the same time, the deterioration of the catalyst is diagnosed with the weighted average value HZRATE calculated in at least a plurality of diagnosis areas, so that the diagnosis accuracy can be improved.

In the above embodiment, the number of reversals FO of the outputs of the upstream oxygen sensor 14 and the downstream oxygen sensor 15 is referred to as FO.
The deterioration was determined based on 2CT and RO2CT,
As shown in FIG. 9, it is also possible to determine the deterioration by the period ratio based on the inversion periods T ₁ and T ₂ . When the determination of the catalytic converter 13 is performed based on this cycle ratio, it can be determined that the catalytic converter 13 has deteriorated when the weighted average value HZRATE is smaller than the predetermined value in the determination of step S12.

[0068]

[0069]

[0070]

[0071]

As described above, the first invention is the latest one.
In addition to the diagnostic area of
The catalyst degradation diagnosis is performed based on the average
Suppress erroneous diagnosis based on the effect of operating conditions immediately before the disconnection area
In addition to performing average calculations a predetermined number of times,
Efficient averaging of results to improve catalyst degradation diagnostic accuracy
Can be raised.

In a second aspect of the present invention, the output comparing means compares the output of the upstream air-fuel ratio sensor and the output of the downstream air-fuel ratio sensor with a threshold value to calculate the number of inversions. Means for calculating the ratio of the number of reversals, so that the deterioration state of the catalyst can be diagnosed with high accuracy from the response delay of the downstream air-fuel ratio sensor based on the oxygen storage capacity of the catalyst.

[Brief description of the drawings]

FIG. 1 is a claim correspondence diagram showing a configuration of a first invention.

FIG. 2 is a claim correspondence diagram showing a configuration of a second invention.

FIG. 3 is a block diagram showing one embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a relationship between an operation region and a reversal frequency ratio HZR.

FIG. 5 is a flowchart illustrating an example of control of catalyst deterioration diagnosis.

FIG. 6 is a graph showing output waveforms of an upstream oxygen sensor and a downstream oxygen sensor.

FIG. 7 is a graph showing an output signal of an upstream oxygen sensor and a feedback correction coefficient.

[Explanation of symbols]

 Reference Signs List 4 Control unit 13 Three-way catalyst 14 Upstream oxygen sensor 15 Downstream oxygen sensor 50 Upstream air-fuel ratio sensor 51 Downstream air-fuel ratio sensor 52 Operating condition determination means 53 Basic injection amount setting means 54 Correction coefficient calculation means 55 Fuel correction amount calculation Means 56 Output comparing means 57 Comparison number judging means 58 Updating means 59 Weighted averaging means 60 Calculation count judging means 61 Deterioration judging means

Claims (2)

(57) [Claims] 1. A catalyst disposed in an exhaust passage, an upstream air-fuel ratio sensor disposed upstream of the catalyst, a downstream air-fuel ratio sensor disposed downstream of the catalyst, and operating conditions of the engine. Determining means, basic fuel injection quantity setting means for setting a basic fuel injection quantity according to the result of the determination of the operating condition, and correction coefficient calculating means for calculating a feedback correction coefficient based on an output of the upstream air-fuel ratio sensor. A fuel injection amount correcting means for correcting the basic fuel injection amount according to the feedback correction coefficient, wherein the operating condition is within a predetermined catalyst deterioration diagnosis region.
An output comparing means for comparing the output of the upstream air-fuel ratio sensor with the output of the downstream air-fuel ratio sensor every time a predetermined period elapses, and each time the operating condition shifts to outside a predetermined catalyst deterioration diagnosis area.
Finally, of the comparison results obtained during this diagnostic operation,
The calculated comparison result and the weighted flat calculated after the previous diagnostic operation
Means for calculating the weighted average of the average value and the latest weighted value after the calculation of the weighted average is performed a predetermined number of times.
Deterioration determining means for determining the deterioration of the catalyst based on the average value
A catalyst deterioration diagnosis device for an internal combustion engine , comprising: a stage ; 2. The air-fuel ratio detector according to claim 2 , wherein
Sensor output and the downstream air-fuel ratio sensor output, respectively.
Means for calculating the number of inversions by comparing with a threshold value,
Means for calculating the ratio of the number of turns is provided.
The catalyst degradation diagnosis device for an internal combustion engine according to claim 1.