JPH0763045A - Exhaust emission controlling catalytic degradation diagnoser of internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent any wrong diagnosis from occurring with certainty by installing a catalytic deterioration diagnosis prohibiting means prohibiting any diagnosis by means of a catalytic deterioration diagnostic means at a time when each of plural air-fuel ratio detecting signals is deviated as far as more than the specified value to the target air-fuel ratio in the rich-lean opposite direction. CONSTITUTION:Three oxygen sensors 14a, 14b and 14c as an air-fuel ratio detection means each are installed in an exhaust passage 11 in the downstream of exhaust passages 8a, 8b and a three-way catalyst 10. These oxygen sensors 14a to 14c are those having an output characteristic to be turned over to both rich and lean sides according to the extent of oxygen content in car exhaust gases. A control unit 20 controls an air-fuel ratio of combustion mixture for feedback at each bank on the basis of each output value of the oxygen sensors 14a and 14b. In addition, this control unit 20 prohibits any diagnosis by means of a catalytic deterioration diagnostic means at a time when an air-fuel ratio detecting signal is deviated as far as more than the specified value in the rich-lean opposite direction to the target air-fuel ratio. Thus a wrong diagnosis is preventable with certainty.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification catalyst deterioration diagnosing device for an internal combustion engine, and more particularly to a harmful component (NOx, CO) in exhaust gas discharged from the internal combustion engine which is interposed in an exhaust passage of the internal combustion engine. , HC, etc.) to improve the exhaust gas purification catalyst deterioration diagnosis device for diagnosing deterioration of the catalyst in the exhaust gas purification device that purifies the exhaust gas.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of environmental protection, harmful components (NOx, C) contained in exhaust gas discharged from an internal combustion engine.
There is a strong demand for reduction of O, HC, etc.). for that reason,
An exhaust gas purification device is provided in the middle of the exhaust passage, and the harmful components are oxidized and reduced (purified) by a catalytic reaction of a catalytic converter (three-way catalyst) installed in the exhaust gas purification device, and the harmful components are released into the atmosphere. It is generally practiced to suppress the exhaustion of the. In such a three-way catalyst, when the mixture ratio of the fuel supply amount supplied to the engine and the engine intake air flow rate is close to the stoichiometric air-fuel ratio (1: 14.4), the purification performance is significantly reduced, and thus the exhaust gas is exhausted. An oxygen sensor having an output characteristic that reverses between the rich side and the lean side according to the oxygen concentration of the fuel (theoretical air-fuel ratio as a boundary) is provided in the catalyst upstream side exhaust passage, and the output characteristic of the oxygen sensor is used to By increasing / decreasing the supply amount and the like, the mixture ratio is subjected to rich / lean inversion with the stoichiometric air-fuel ratio as a boundary, and feedback control is performed in the vicinity of the stoichiometric air-fuel ratio with good responsiveness.

By the way, since the reaction heat of the catalyst becomes high due to the catalytic reaction, the catalyst components are sintered, the catalyst carrier is overheated and melted, or the fuel is burned.
Since the catalyst components may be poisoned by impurities in the oil, the initial purification rate may not be maintained (deteriorated) in some cases. In such a deteriorated state, the exhaust harmful component is not purified but is directly discharged into the atmosphere. Therefore, it is diagnosed whether or not the catalyst is deteriorated and the exhaust harmful component is discharged into the atmosphere. It needs to be prevented.

Therefore, as a method of diagnosing the deterioration of the catalyst, for example, in the North American self-diagnosis regulation, etc., the oxygen sensors are arranged on the upstream side and the downstream side of the catalyst, respectively, and the oxygen sensor is arranged on the upstream side of the catalyst during air-fuel ratio control. Catalyst deterioration that detects the difference between the rich / lean inversion frequency of the oxygen sensor provided and the rich / lean inversion frequency of the oxygen sensor provided downstream of the catalyst, and diagnoses the catalyst deterioration based on the detection result. Diagnostic devices have been proposed.

That is, when the reversal frequency of the downstream oxygen sensor is substantially the same as the reversal frequency of the upstream oxygen sensor, the exhaust gas having a predetermined rich / lean reversal frequency on the upstream side of the catalyst is It is assumed that the catalyst is deteriorated and oxygen in the exhaust gas cannot react with the harmful component and flows out to the downstream side of the catalyst while maintaining the inversion frequency, and it is diagnosed that the catalyst is deteriorated. On the other hand, when the catalyst is normal, even if the exhaust gas has a predetermined rich / lean inversion frequency on the upstream side of the catalyst, the catalyst normally reacts with the harmful components contained in the exhaust gas, Due to the oxygen storage effect, the exhaust gas on the downstream side of the catalyst becomes an exhaust gas having a substantially constant theoretical air-fuel ratio with no tendency to rich / lean inversion and flows out from the catalyst. Therefore, when the downstream oxygen sensor inversion frequency is smaller than a predetermined value as compared with the upstream oxygen sensor inversion frequency, the catalyst is diagnosed to be normal (see FIG. 5).

[0006]

However, in a V-type engine, for example, an oxygen sensor is provided in each of the exhaust passages provided in communication with the cylinder groups of the left and right banks, and air-fuel ratio control is performed for each of the left and right banks. In this case, rich / lean inversion is repeated when the output characteristic of one oxygen sensor deviates from the stoichiometric air-fuel ratio to the rich side by a predetermined value or more, and the output characteristic of the other oxygen sensor changes from the stoichiometric air-fuel ratio to the lean side by the predetermined value. If there is a change such that the rich / lean inversion is repeated at the above deviation, the exhaust gas with a rich tendency above a predetermined value and the exhaust gas with a lean tendency above a predetermined value merge at the collecting portion of the exhaust passage. The fuel ratio may become a constant value near the stoichiometric air-fuel ratio.

As described above, when the exhaust gas having a constant value near the stoichiometric air-fuel ratio flows into the catalyst, regardless of whether the catalyst is deteriorated, that is, in the reaction between oxygen in the exhaust gas and the harmful components, Irrespective of the above, a certain amount of exhaust gas always flows out near the stoichiometric air-fuel ratio where there is no tendency to rich / lean inversion even on the downstream side of the catalyst. Therefore, even if the catalyst is deteriorated, the rich / lean inversion frequency of the oxygen sensor on the upstream side of the catalyst is high, and the rich / lean inversion tendency of the oxygen sensor on the downstream side of the catalyst disappears.

Therefore, in the catalyst deterioration diagnosis method for diagnosing catalyst deterioration by comparing the rich / lean inversion frequency of the catalyst upstream side oxygen sensor and the rich / lean inversion frequency of the catalyst downstream side oxygen sensor as described above, Even if it had deteriorated, there was a high possibility that the catalyst would be erroneously diagnosed as not deteriorated. The present invention has been made in view of such conventional problems, and has two exhaust passages communicating with the respective cylinder groups of the right bank and the left bank, such as a V-type engine, and the two exhaust passages. An oxygen sensor is provided for each of the cylinders, and air-fuel ratio control is performed for each of the cylinder groups of the right bank and the left bank according to the output signals of the respective oxygen sensors. When deviation from the stoichiometric air-fuel ratio exceeds the specified value in the rich / lean opposite direction, by prohibiting the catalyst deterioration diagnosis,
An object of the present invention is to provide an exhaust gas catalyst deterioration diagnosing device for an internal combustion engine, which prevents erroneous diagnosis.

[0009]

Therefore, according to the present invention, as shown in FIG. 1, a cylinder of a multi-cylinder internal combustion engine is divided into two groups, a first group and a second group, and the first group communicates with each group. , The second 2
And an exhaust device A, which is connected to an exhaust gas purification catalyst after merging the exhaust passages of the first exhaust passage with each other, and exhausts the exhaust gases while purifying the exhaust gas. The exhaust device A is disposed on the upstream side of the merging portion of the first exhaust passage. First upstream side air-fuel ratio detecting means B for detecting the air-fuel ratio of the intake air-fuel mixture to the first group, and intake air-fuel mixture to the second group arranged downstream of the confluence part of the second exhaust passage. Second upstream side air-fuel ratio detecting means C for detecting the air-fuel ratio of the exhaust gas, downstream side air-fuel ratio detecting means D for detecting the air-fuel ratio of the intake air-fuel mixture of the entire engine disposed downstream of the exhaust purification catalyst, While making the air-fuel ratio of the intake air-fuel mixture of the first group close to the target air-fuel ratio based on the detection signal of the first upstream side air-fuel ratio detecting means B,
Based on the detection signal of the second upstream side air-fuel ratio detecting means C, the fuel supply amount to each group is increased / decreased and fed back so that the air-fuel ratio of the intake mixture to the second group approaches the target air-fuel ratio. Air-fuel ratio feedback control means E for controlling,
During the air-fuel ratio control by the air-fuel ratio feedback control means E, the detection signal of the first upstream side air-fuel ratio detection means B or the detection signal of the second upstream side air-fuel ratio detection means C and the downstream side air-fuel ratio detection means D Catalyst deterioration diagnosis means F for performing deterioration diagnosis of the exhaust gas purification catalyst based on the detection signal
And an air-fuel ratio detection signal of the second upstream air-fuel ratio detection means C, And are rich against the target air-fuel ratio.
A catalyst deterioration diagnosis prohibiting means G is provided for prohibiting the diagnosis by the catalyst deterioration diagnosing means F when the deviation from the lean opposite direction exceeds a predetermined amount.

[0010]

According to this structure, the catalyst deterioration diagnosis inhibiting means causes the air-fuel ratio detection signal of the first upstream side air-fuel ratio detecting means and the air-fuel ratio detecting signal of the second upstream side air-fuel ratio detecting means to When the deviation from the target air-fuel ratio in the opposite direction to the rich / lean is larger than a predetermined amount, the diagnosis by the catalyst deterioration diagnosis means is prohibited. That is, in the merging portion, when the exhaust gas having a rich tendency above a predetermined value and the exhaust gas having a lean tendency above a predetermined value join together, and as a result, the air-fuel ratio becomes a constant value near the theoretical air-fuel ratio, A deterioration diagnosis of the exhaust gas purification catalyst based on the detection signal of the first upstream side air-fuel ratio detection means or the detection signal of the second upstream side air-fuel ratio detection means and the detection signal of the downstream side air-fuel ratio detection means. Since the catalyst deterioration diagnosis by the catalyst deterioration diagnosis means for performing the above is prohibited, erroneous diagnosis can be prevented.

[0011]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, air is drawn into a V-type engine 1 from an air cleaner 2 through an intake duct 3, a throttle valve 4, and intake manifolds 5a and 5b. A fuel injection valve 6 is provided for each cylinder in each branch portion of the intake manifolds 5a, 5b. The fuel injection valve 6 is an electromagnetic fuel injection valve that is opened by energizing a solenoid, is closed by deenergizing, and is opened by being energized by a drive pulse signal from the control unit 20 to open the fuel pump. Fuel, which is pressure-fed from (not shown) and is controlled to a predetermined pressure by a pressure regulator (not shown), is injected and supplied to the engine 1.

A spark plug 7 is provided in each combustion chamber of the engine 1 to spark-ignite and ignite and burn the air-fuel mixture. Then, from the engine 1, exhaust passages 8a, 8b, a collecting pipe 9 thereof, a three-way catalyst 10 as an exhaust purification catalyst, an exhaust pipe 1
Exhaust gas is discharged into the atmosphere through the muffler (not shown). Here, the three-way catalyst 10 is for purifying CO in only satisfactorily exhausted in near stoichiometric air-fuel ratio as described above, the exhaust by performing the reduction of oxidation and NO _X of HC.

The control unit 20 includes a CPU, RO
A microcomputer including an M, a RAM, an A / D converter, an input / output interface, and the like is provided, and the input signals from various sensors are received and the arithmetic processing is performed as described below to operate the fuel injection valve 6. Control. As the various sensors, an air flow meter 12 is provided in the intake duct 3 and outputs a signal according to the intake air flow rate Q of the engine 1.

A crank angle sensor 14 is built in a distributor (not shown in FIG. 2), and a crank unit angle signal output from the crank angle sensor 13 in synchronization with engine rotation is counted for a certain period of time. Alternatively, the engine rotation speed N is detected by measuring the cycle of the crank reference angle signal. Oxygen sensors 14a, 14b, 14c as air-fuel ratio detecting means are provided in the exhaust passages 8a, 8b and the exhaust passage 11 on the downstream side of the three-way catalyst 10, respectively. These oxygen sensors 14a to 14c are sensors having an output characteristic that they are inverted to the rich side and the lean side (at the stoichiometric air-fuel ratio) according to the oxygen concentration in the exhaust gas.

In the control unit 20, based on the output values of the oxygen sensors 14a and 14b, the air-fuel ratio of the air-fuel mixture for combustion in each bank is fed back by proportional integral control centering on the target air-fuel ratio (theoretical air-fuel ratio). It is designed to be controlled. Here, the CPU of the microcomputer built in the control unit 20
Will perform arithmetic processing in the following manner.
Control the fuel injection to the.

That is, the control unit 20 is
From the intake air flow rate Q obtained from the voltage signal from the air flow meter 13 and the engine rotation speed N obtained from the signal from the crank angle sensor 14, the basic fuel injection amount Tp = c × Q / N (c is (Constant) and the final effective fuel injection for each bank by the water temperature correction coefficient Kw, etc. for forcibly correcting to the rich side at low water temperature, the air-fuel ratio feedback correction coefficient α _R (or α _L ), etc. Quantity Te _R (Te _L ) = Tp × (1 + Kw + ...) × α
Calculate _R (or α _L ).

Here, the basic fuel injection amount Tp is set by calculation so that the air-fuel ratio of the air-fuel mixture becomes the stoichiometric air-fuel ratio. However, the actual air-fuel ratio is different in the fuel pressure and the fuel injection valve. Since the deviation from the stoichiometric air-fuel ratio is caused by the individual variations of 6 and the like, feedback control is performed by proportional-plus-integral control based on the outputs of the oxygen sensors 14a and 14b so that the actual air-fuel ratio becomes the stoichiometric air-fuel ratio. In addition, the basic fuel injection amount Tp is corrected as the effective fuel injection amount Te _R (Te _L ).

Therefore, the magnitude of the air-fuel ratio feedback correction coefficient α _R (or α _L ) corresponds to the magnitude of the deviation amount between the actual air-fuel ratio and the theoretical air-fuel ratio. Further, the magnitude of the air-fuel ratio feedback correction coefficient α _R (or α _L ) is also determined when the output characteristics of the oxygen sensors 14a and 14b change and the boundary between rich and lean inversions deviates from the theoretical air-fuel ratio.
The value depends on the amount of deviation.

By the way, the ignition plug 20 provided in each cylinder of the engine 1 has an ignition timing control signal previously set and stored in a map in the control unit 50 based on the basic fuel injection amount Tp and the engine rotation speed N. It is sent to the power transistor and ignited at a predetermined ignition timing.
In this way, the control unit 20 controls the actual air-fuel ratio to be near the stoichiometric air-fuel ratio (oxygen sensor 14
When the output characteristics of a and 14b are also normal), the three-way catalyst 10
Exhaust gas can be satisfactorily purified without lowering the purification efficiency.

However, since the reaction heat of the three-way catalyst 10 becomes high due to the catalytic reaction, the catalyst components are sintered, the catalyst carrier is overheated and melted, or impurities such as fuel and oil are generated. Since the catalyst component may be poisoned, the initial purification performance may not be maintained, and in this case, the exhaust harmful component is not purified but is directly discharged to the atmosphere.

Therefore, in the control unit 20,
As described above, the difference between the rich / lean inversion frequency of the upstream oxygen sensors 14a and 14b of the three-way catalyst 10 and the rich / lean inversion frequency of the downstream oxygen sensor 14c during the air-fuel ratio control is detected. The deterioration of the catalyst is diagnosed by various methods. By the way, for example, when the output characteristic of the oxygen sensor 14a deviates from the stoichiometric air-fuel ratio to the rich side by a predetermined value or more, rich / lean inversion is repeated, and the output characteristic of the oxygen sensor 14b changes from the stoichiometric air-fuel ratio to the lean side by a predetermined value. When the change occurs such that the rich / lean inversion is repeated after the deviation, the exhaust gas having a rich tendency above a predetermined value and the exhaust gas having a lean tendency above a predetermined value are collected.
In some cases, the air-fuel ratio becomes a constant value in the vicinity of the theoretical air-fuel ratio without the tendency of rich / lean reversal because of the merge.

In this case, as described above, the three-way catalyst is used.
Even if 10 is deteriorated, the rich / lean inversion frequency of the oxygen sensors 14a and 14b on the upstream side of the three-way catalyst 10 is high,
Since the rich / lean inversion tendency of the oxygen sensor 14c on the downstream side of the three-way catalyst 10 disappears, the rich / lean inversion frequency of the catalyst upstream side oxygen sensor and the richness of the catalyst downstream side oxygen sensor as described above are eliminated.・ In the catalyst deterioration diagnosis that compares the lean inversion frequency and diagnoses the catalyst deterioration,
There is a high possibility that the catalyst will be erroneously diagnosed as not deteriorated.

Therefore, in the control unit 20,
The oxygen sensor 14a, 14b changes its output characteristics by a predetermined value or more, that is, the boundary of rich / lean inversion of the oxygen sensor 14a, 14b deviates from the theoretical air-fuel ratio by a predetermined value or more in the opposite direction to rich / lean. When the air-fuel ratio feedback correction coefficient α _R determined based on 14a and the air-fuel ratio feedback correction coefficient α _L determined based on the oxygen sensor 14b respectively deviate in the opposite rich / lean directions by a predetermined value or more, Deterioration diagnosis is prohibited.

The inhibition control of the catalyst deterioration diagnosis performed by the control unit 20 will be described below with reference to the flowchart shown in FIG. In step 1 (denoted as S1 in the figure; the same applies hereinafter), it is determined whether or not air-fuel ratio control is being executed. If yes, go to step 2
In the case of O, this flow ends.

In step 2, the exhaust passage 8 on the right bank side
The average value A of the air-fuel ratio feedback correction coefficient α _R , which is determined based on the detection signal of the oxygen sensor 14a provided in a.
Find α _R. In step 3, the average value Aα _L of the air-fuel ratio feedback correction coefficient α _L determined based on the detection signal of the oxygen sensor 14b arranged in the exhaust passage 8b on the left bank side is obtained.

In step 4, the Aα _R is subtracted from a reference value (100 in this case) to obtain a judgment value RA (= 1).
00-Aα _R ) and proceeds to step 5. Step 5
Then, the absolute value | RA | of the determination value RA is compared with a preset comparison value A. When | RA | <A, the routine proceeds to step 11, where execution of catalyst deterioration diagnosis is permitted.
If | RA | ≧ A, the process proceeds to step 6.

In step 6, the Aα _L is subtracted from a reference value (100 in this case) to obtain a judgment value LA (= 1.
00-Aα _L ), and proceeds to step 7. Step 7
Then, the absolute value | LA | of the judgment value LA is compared with a preset comparison value A. When | LA | <A, the routine proceeds to step 11, where execution of the catalyst deterioration diagnosis is permitted.
If | LA | ≧ A, the process proceeds to step 8.

At step 8, the judgment value RA and the judgment value LA are added to obtain a judgment value TA (= RA + LA). In step 9, the absolute value of the judgment value TA | TA |
Is compared with a preset comparison value B. | TA
If |> A, the process proceeds to step 11 to permit execution of catalyst deterioration diagnosis. If | TA | ≦ A, the routine proceeds to step 10 to prohibit the catalyst deterioration diagnosis (see FIG. 4).

As described above, according to the present embodiment, the change in the output characteristics of the oxygen sensors 14a and 14b beyond a predetermined value, that is, the boundary between the rich and lean inversions of the oxygen sensors 14a and 14b is the rich lean lean from the theoretical air-fuel ratio. The air-fuel ratio feedback correction coefficient α _R determined based on the oxygen sensor 14a due to the deviation in the opposite direction by a predetermined value or more, and the oxygen sensor
When the air-fuel ratio feedback correction coefficient α _L, which is determined based on 14b, deviates from the rich / lean opposite direction by a predetermined value or more, the catalyst deterioration diagnosis is prohibited, so that the output characteristic of the oxygen sensor 14a is changed. When the lean / lean inversion is repeated when the stoichiometric air-fuel ratio deviates to the rich side, and the output characteristic of the oxygen sensor 14b changes such that the rich / lean inversion repeats when the stoichiometric air-fuel ratio deviates to the lean side, a rich tendency occurs. Exhaust gas and lean exhaust gas join together at the collecting portion 9 and the air-fuel ratio becomes a constant value in the vicinity of the theoretical air-fuel ratio with no rich-lean inversion tendency, resulting in erroneous diagnosis of catalyst deterioration diagnosis. Therefore, the catalyst deterioration can be accurately diagnosed.

In the present embodiment, the rich / lean reversal frequency of the oxygen sensors 14a, 14b on the upstream side of the three-way catalyst 10 and the rich / lean reversal frequency of the oxygen sensor 14c on the downstream side of the three-way catalyst 10, Although the catalyst deterioration diagnosis method for diagnosing the catalyst deterioration is explained by comparing the above, of course, based on the rich / lean inversion characteristics of the upstream oxygen sensor and the downstream oxygen sensor (for example, comparing the inversion time etc. Also, it is applicable to other catalyst deterioration diagnosis methods for diagnosing catalyst deterioration. Further, although the V-type engine has been described, the present invention is not limited to this, and the cylinder group is divided into two and the air-fuel ratio control is performed for each cylinder group not only in the horizontally opposed type but also in the series type. It is obvious that the present embodiment can be applied if it is one.

[0031]

As described above, according to the present invention,
By the catalyst deterioration diagnosis prohibiting means, the air-fuel ratio detection signal of the first upstream side air-fuel ratio detecting means and the air-fuel ratio detecting signal of the second upstream side air-fuel ratio detecting means are respectively rich with respect to the target air-fuel ratio. When the deviation from the lean opposite direction exceeds a predetermined amount, the diagnosis by the catalyst deterioration diagnosis means is prohibited. That is, in the merging portion, when the exhaust gas having a rich tendency above a predetermined value and the exhaust gas having a lean tendency above a predetermined value join together, and as a result, the air-fuel ratio becomes a constant value near the theoretical air-fuel ratio, A deterioration diagnosis of the exhaust gas purification catalyst based on the detection signal of the first upstream side air-fuel ratio detection means or the detection signal of the second upstream side air-fuel ratio detection means and the detection signal of the downstream side air-fuel ratio detection means. The catalyst deterioration diagnosis by the catalyst deterioration diagnosis means for performing the above is prohibited, and erroneous diagnosis can be surely prevented.

[Brief description of drawings]

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

FIG. 2 is an overall configuration diagram showing an embodiment according to the present invention.

FIG. 3 is a flowchart illustrating a catalyst deterioration diagnosis prohibition control according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating determination values RA, LA, TA and comparison values A, B according to the present invention.

FIG. 5 is a diagram for explaining the rich / lean inversion characteristics of the two oxygen sensors provided on the catalyst upstream side and the catalyst downstream side when the catalyst is deteriorated.

[Explanation of symbols]

 1 Engine 6 Fuel Injection Valve 8a Exhaust Passage 8b Exhaust Passage 9 Assembly 10 Three Way Catalyst 13 Air Flow Meter 14a Oxygen Sensor 14b Oxygen Sensor 14c Oxygen Sensor 20 Control Unit

Claims (1)

[Claims] 1. A cylinder of a multi-cylinder internal combustion engine is divided into two groups, a first group and a second group, and first and second exhaust passages communicating with the respective groups are joined at a downstream portion, and thereafter, An exhaust device connected to an exhaust gas purification catalyst for exhausting the exhaust gas while purifying the exhaust gas; and an exhaust device arranged upstream of the merging portion of the first exhaust passage.
A first upstream side air-fuel ratio detecting means for detecting an air-fuel ratio of the intake air-fuel mixture into the group; and a second upstream side air-fuel ratio detecting means arranged downstream of the merging portion of the second exhaust passage.
Second upstream air-fuel ratio detection means for detecting the air-fuel ratio of the intake air-fuel mixture to the group, and downstream air-fuel ratio detection for detecting the air-fuel ratio of the intake air-fuel mixture of the entire engine arranged downstream of the exhaust purification catalyst. And a detection signal of the second upstream side air-fuel ratio detection means while making the air-fuel ratio of the intake air-fuel mixture of the first group approach the target air-fuel ratio based on the detection signal of the first upstream side air-fuel ratio detection means. Air-fuel ratio feedback control means for performing feedback control by increasing or decreasing the fuel supply amount to each group so that the air-fuel ratio of the intake air-fuel mixture to the second group approaches the target air-fuel ratio on the basis of the air-fuel ratio feedback control. At the time of air-fuel ratio control by means, based on the detection signal of the first upstream side air-fuel ratio detecting means or the detection signal of the second upstream side air-fuel ratio detecting means, and the detection signal of the downstream side air-fuel ratio detecting means, Exhaust purification touch In the exhaust gas purification catalyst deterioration diagnosing device for an internal combustion engine, which comprises a catalyst deterioration diagnosing means for diagnosing deterioration of the air-fuel ratio, an air-fuel ratio detection signal of the first upstream air-fuel ratio detecting means, and a second upstream air-fuel ratio. And a catalyst deterioration diagnosis prohibiting means for prohibiting the diagnosis by the catalyst deterioration diagnosing means when the air-fuel ratio detection signal of the detecting means deviates from the target air-fuel ratio by a predetermined amount or more in the opposite rich / lean directions. An exhaust gas purification catalyst deterioration diagnosing device for an internal combustion engine.