JPH08135432A - Catalyst deterioration diagnostic device of internal combustion engine - Google Patents

Abstract

PURPOSE: To precisely carry out a deterioration diagnosis of a catalyst even against an internal combustion engine furnished with a plural number of cylinder groups and to prevent a wrong diagnosis. CONSTITUTION: Out of upstream oxygen sensors 8A, 8B positioned in the upstream of a catalyst device 7 and provided in the middle of exhaust pipe parts 6A, 6B, the oxygen sensor 8A or 8B which is quicker in responsiveness is discriminated (selected) in accordance with response time of a detection signal. A deterioration diagnosis of the catalyst device 7 is carried out by judging whether a reversing ratio of the reversing number of the upstream oxygen sensor 8A, for example, which is quicker in responsiveness and the reversing number of the downstream oxygen sensor 9 is lower than a specified standard value or not. Consequently, the deterioration diagnosis of the catalyst is not influenced by the detection signal from the upstream oxygen sensor 8B which is slower in responsiveness, and it is possible to precisely carry out the deterioration diagnosis of the catalyst by selecting the detection signal from the oxygen sensor 8A which, for example, is quicker in responsiveness, and to efficiently prevent occurrence of a wrong diagnosis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst deterioration diagnosing device for an internal combustion engine, which is preferably used for diagnosing deterioration of a three-way catalyst for purifying exhaust gas of automobiles and the like.

[0002]

2. Description of the Related Art Generally, an engine body of an internal combustion engine, an exhaust passage provided on the exhaust side of the engine body, an exhaust purification catalyst provided in the exhaust passage for purifying exhaust gas by a catalytic reaction, and the exhaust gas. An upstream oxygen sensor that is located upstream of the purification catalyst and that is provided in the middle of the exhaust passage and that detects the oxygen concentration of the exhaust gas upstream of the exhaust purification catalyst, and is located downstream of the exhaust purification catalyst. On the basis of the downstream oxygen sensor provided in the middle of the exhaust passage for detecting the oxygen concentration of the exhaust gas on the downstream side of the exhaust purification catalyst, and the detection signal of the downstream oxygen sensor and the detection signal of the upstream oxygen sensor. A catalyst deterioration diagnosing device for an internal combustion engine including a catalyst deterioration diagnosing means for diagnosing deterioration of the exhaust purification catalyst is known, for example, from Japanese Patent Laid-Open No. 61-286550.

In the catalyst deterioration diagnosing device for an internal combustion engine according to this type of prior art, the ratio of the inversion cycle of the detection signal output from the upstream oxygen sensor to the inversion cycle of the detection signal output from the downstream oxygen sensor. Is compared with a reference value to perform a deterioration diagnosis of the exhaust purification catalyst including, for example, a three-way catalyst.

That is, the air-fuel ratio of the internal combustion engine is feedback-controlled based on the detection signal from the oxygen sensor,
The oxygen concentration (air-fuel ratio) in the exhaust gas flowing in the exhaust passage constantly fluctuates. On the other hand, an exhaust gas purification catalyst composed of a three-way catalyst has an oxygen storage effect, and temporarily stores a part of oxygen contained in the exhaust gas, so that an oxygen sensor arranged downstream of the catalyst. Causes a delay in response to fluctuations in oxygen concentration as compared with the oxygen sensor on the upstream side.

Therefore, in the prior art, the ratio of the inversion period of the detection signal by the upstream oxygen sensor to the inversion period of the detection signal by the downstream oxygen sensor is calculated as the response delay, and this response delay is smaller than that in the normal state. When
Deterioration diagnosis is performed on the assumption that the oxygen storage effect is reduced by the deterioration of the catalyst.

[0006]

By the way, in an internal combustion engine used as an automobile engine or the like, an engine body as an engine body is composed of a plurality of cylinder groups, such as a V-type engine or a horizontally opposed engine. In some cases, an exhaust passage is configured by a plurality of independent exhaust pipe parts for each cylinder group and a merging pipe part formed by merging the exhaust pipe parts with each other on the downstream side.

In this case, since it is necessary to independently feedback-control the air-fuel ratio for each cylinder group, each exhaust pipe portion of the exhaust passage is provided with a separate upstream oxygen sensor. The oxygen concentration in the exhaust gas must be detected for each exhaust pipe section by each upstream oxygen sensor.

However, in this case, a phase difference occurs in the air-fuel ratio feedback control between the cylinder groups, and the downstream oxygen sensor provided on the downstream side of the exhaust purification catalyst changes the detection signal inversion cycle or detects it. There is a problem that the deterioration of the catalyst cannot be accurately diagnosed because the signal may not be inverted.

When an upstream oxygen sensor is provided for each exhaust pipe of each cylinder group, the response of any one of the upstream oxygen sensors is poor (slow). At times, there is a problem in that the oxygen sensor having a slow responsiveness easily causes an erroneous diagnosis in the deterioration diagnosis of the catalyst.

The present invention has been made in view of the above-mentioned problems of the prior art, and the present invention can accurately perform catalyst deterioration diagnosis even for an internal combustion engine having a plurality of cylinder groups, resulting in erroneous diagnosis. It is an object of the present invention to provide a catalyst deterioration diagnosing device for an internal combustion engine, which can effectively prevent the occurrence.

[0011]

In order to solve the above-mentioned problems, a catalyst deterioration diagnosing device for an internal combustion engine according to the invention described in claim 1 has a plurality of cylinder groups as shown in a functional block diagram of FIG. A main body of an internal combustion engine, a plurality of exhaust pipe parts independent of each cylinder group of the engine main body, and an exhaust passage formed of a confluent pipe part in which the respective exhaust pipe parts join each other, and a confluent pipe of the exhaust passage. An exhaust gas purification catalyst that is provided in the middle of the exhaust gas and purifies exhaust gas by a catalytic reaction, and a plurality of upstream oxygens that are provided in each exhaust pipe portion of the exhaust passage and that detect the oxygen concentration of the exhaust gas flowing in each exhaust pipe portion A sensor, a downstream oxygen sensor located on the downstream side of the exhaust purification catalyst and provided in the middle of the merging pipe portion of the exhaust passage for detecting the oxygen concentration of the exhaust gas flowing in the merging pipe portion; Sensor The upstream side oxygen sensor selecting means for selecting the oxygen sensor having the faster response, and the exhaust gas purification catalyst based on the detection signals of the upstream side oxygen sensor and the downstream side oxygen sensor selected by the selecting means. And a catalyst deterioration diagnosing means for diagnosing deterioration.

In this case, as in the invention described in claim 2,
A configuration in which the upstream oxygen sensor selection means selects an oxygen sensor having a faster response time among the upstream oxygen sensors based on the rise-fall time of the detection signal output from each upstream oxygen sensor. Is preferred.

According to a third aspect of the present invention, the catalyst deterioration diagnosing means is provided with the number of times of inversion of the detection signal output from the upstream oxygen sensor within a certain time and the downstream oxygen sensor for a certain time. It is preferable to perform a deterioration diagnosis of the exhaust purification catalyst based on the ratio of the number of inversions of the detection signal output therein.

[0014]

With the above structure, in the invention described in claim 1, the upstream oxygen sensor having the faster response is selected by the upstream oxygen sensor selecting means, and the upstream oxygen sensor selected by the selecting means. Since deterioration diagnosis of the exhaust purification catalyst is performed based on the detection signal of the oxygen sensor and the detection signal of the downstream oxygen sensor, the responsiveness of one of the upstream oxygen sensors becomes slow. In this case, the catalyst deterioration diagnosis will not be erroneously diagnosed.

In this case, as in the invention described in claim 2, the response time of each oxygen sensor can be obtained based on the rise-fall time of the detection signal output from each upstream oxygen sensor. This makes it possible to easily select the oxygen sensor with the faster response time.

Further, as in the invention described in claim 3,
The number of times of inversion of the detection signal output from the upstream oxygen sensor having the faster response selected by the selection means within a certain time is obtained, and the inversion of the detection signal output from the downstream oxygen sensor within a certain time is obtained. By obtaining the number of times and performing the deterioration diagnosis of the exhaust gas purification catalyst based on the ratio of the number of times of both inversions, the accurate deterioration diagnosis can be performed.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A catalyst deterioration diagnosing device for an internal combustion engine according to an embodiment of the present invention will be described below with reference to FIGS.

In the drawing, reference numeral 1 denotes an engine body which constitutes an engine body of an internal combustion engine, and the engine body 1 is composed of, for example, a V-type or horizontally opposed type 6-cylinder engine, and includes three cylinders 1A, 1A ,. First cylinder group and 3
A second cylinder group including cylinders 1B, 1B, ...

Reference numeral 2 denotes an intake pipe 2 connected to the intake side of the engine body 1. The intake pipe 2 is composed of an intake manifold or the like, and each cylinder 1A, 1 is provided at the tip end side thereof.
6 branch pipes 2A, 2A, ..., 2B, 2 communicating with the inside of B
B, ... Are provided. Further, an air cleaner 3 is provided on the base end side of the intake pipe 2, and an air flow meter 4 for detecting an intake air amount Q and a throttle valve 5 are provided between the air cleaner 3 and each branch pipe 2A, 2B. Has been.

Reference numeral 6 denotes an exhaust pipe which constitutes an exhaust passage connected to the exhaust side of the engine body 1. The exhaust pipe 6 is composed of an exhaust manifold or the like, and the tip end side thereof communicates with each cylinder 1A, 1B as each cylinder group. First and second exhaust pipe section 6
A and 6B, and a merging pipe portion 6C located downstream of the exhaust pipe portions 6A and 6B and formed by merging the exhaust pipe portions 6A and 6B with each other. Exhaust gas from each of the cylinders 1A and 1B flows in the exhaust pipe portions 6A and 6B in the directions of arrows A and B to merge with each other, and then the merge pipe portion 6
It flows in C in the direction of arrow C.

Reference numeral 7 denotes a catalyst device as an exhaust purification catalyst provided in the confluent pipe portion 6C of the exhaust pipe 6, and the catalyst device 7
Is composed of a three-way catalyst or the like disposed at an intermediate position of the merging pipe portion 6C, and purifies the exhaust gas flowing in the merging pipe portion 6C in the arrow C direction by a catalytic reaction. Here, since the catalyst device 7 has an oxygen storage effect and temporarily stores a part of oxygen contained in the exhaust gas in the catalyst device 7, the downstream side oxygen sensor 9 described later has an upstream side. As compared with the oxygen sensors 8A and 8B, a response delay with respect to a change in oxygen concentration occurs.

Reference numerals 8A and 8B denote upstream oxygen sensors provided in the exhaust pipe portions 6A and 6B, respectively.
B individually detects the oxygen concentration of the exhaust gas flowing in the directions of arrows A and B in the exhaust pipe portions 6A and 6B, and outputs respective detection signals to the control unit 15 described later. Here, the upstream detection signals output from the oxygen sensors 8A and 8B are output as signals that repeat inversion according to the feedback control of the air-fuel ratio as shown by the characteristic line in FIG. It rises and falls with a rise time Tux and a fall time Tdx with respect to the high level threshold SH.

Reference numeral 9 denotes a downstream oxygen sensor located downstream of the catalyst device 7 and provided in the middle of the merging pipe 6C. The oxygen sensor 9 flows in the merging pipe 6C in the direction of arrow C. Of the gases, the oxygen concentration in the exhaust gas that has passed through the catalyst device 7 is detected. Here, the downstream detection signal output from the oxygen sensor 9 becomes a signal having the characteristics illustrated in FIG. 4, and the feedback control of the oxygen concentration in the exhaust gas on the upstream side of the catalyst device 7 is the air-fuel ratio. Even when it fluctuates due to, the detection signal of the downstream oxygen sensor 9 is delayed in response to fluctuations in oxygen concentration due to the oxygen storage effect of the catalyst device 7.

Next, reference numerals 10, 10, ... Indicate injection valves for injecting fuel into the respective cylinders 1A, 1B of the engine body 1. The respective injection valves 10 are provided in the control unit 15 as shown in FIG. By connecting an injection pulse from the control unit 15 connected to the output side, fuel from a fuel pump (not shown) is supplied to each cylinder 1A, 1B.
It is designed to be sprayed inward. Although each injection valve 10 is omitted in FIG. 2, each injection valve 10 is provided, for example, on the tip side of each branch pipe 2A, 2B of the intake pipe 2.

Further, the engine body 1 is provided with a crank angle sensor 11, a water temperature sensor 12, etc. shown in FIG. 5, the crank angle sensor 11 detects an engine speed N, and the water temperature sensor 12 is a cooling water temperature of the engine body 1. Tw is detected and the operating state of the engine body 1 is monitored.

Reference numeral 13 denotes a throttle sensor disposed near the throttle valve 5 and outside the intake pipe 2. The throttle sensor 13 detects the throttle opening θ of the throttle valve 5 and the engine body 1 It is designed to monitor whether it is in an idle state or in an acceleration state. Reference numeral 14 denotes a vehicle speed sensor that detects the traveling speed of the vehicle as the vehicle speed Vs.

Further, 15 is a control unit composed of a microcomputer or the like, and the control unit 15 has an upstream side oxygen sensor 8 on the input side.
A, 8B, downstream oxygen sensor 9, crank angle sensor 1
1, an air flow meter 4, a water temperature sensor 12, a throttle sensor 13, a vehicle speed sensor 14 and the like are connected, and each output valve is connected with an injector 16 such as an alarm buzzer (alarm lamp).

Then, the control unit 15 determines the basic injection amount Tp based on the intake air amount Q from the air flow meter 4 and the engine speed N from the crank angle sensor 11.

[0029]

## EQU1 ## Tp = K.times.Q / N where K is a constant.

Further, the control unit 15 sets the fuel injection amount Ti from each injection valve 10 to the basic air-fuel ratio learning correction coefficient α'based on the engine speed N and the basic injection amount Tp.
And the air-fuel ratio feedback correction coefficient α by the oxygen sensors 8A, 8B, 9 and various correction coefficients COEF and voltage correction coefficient Ts,

[0031]

## EQU2 ## It has a function of calculating as Ti = Tp × α × α '× COEF + Ts.

Further, the control unit 15 stores the programs and the like shown in FIGS. 6 and 7 in its memory circuit, and performs deterioration diagnosis processing of the catalyst device 7 and the like. The storage circuit of the control unit 15 has a storage area 15A in which a reference value r of an inversion ratio r, which will be described later, is set.
0 and various judgment values Tw0 and θ0 for judging the catalyst diagnosis condition are stored.

The catalyst deterioration diagnosing device for an internal combustion engine according to this embodiment has the above-mentioned structure. Next, the catalyst deterioration diagnosing process by the control unit 15 will be described with reference to FIG.

First, when the engine body 1 is started and the processing operation is started, in step 1, the crank angle sensor 11
From the engine speed N, the intake air amount Q from the air flow meter 4, the cooling water temperature Tw from the water temperature sensor 12, the throttle opening θ by the throttle sensor 13, the vehicle speed Vs by the vehicle speed sensor 14 and the oxygen sensors 8A, 8B, 9 Read various signals such as the detection signal of.

Then, in step 2, it is judged based on the various signals whether or not the oxygen sensor 8A, 8B, 9 has reached the diagnostic range for diagnosing the deterioration. If "YES" is determined, the process proceeds to step 3. Oxygen sensor 8A, 8B, 9
Determines whether is operating normally. Since the deterioration diagnosis of the oxygen sensors 8A, 8B, 9 is known, the description thereof will be omitted here.

Next, if "YES" is determined in step 3 and the oxygen sensors 8A, 8B, 9 are operating normally, the process proceeds to step 4 and the response time ΔT of the upstream oxygen sensors 8A, 8B is set to

[0037]

## EQU3 ## Calculation is performed as ΔT = Σ (Tux + Tdx) / n, and the addition value of the rise time Tux and the fall time Tdx of the detection signal illustrated in FIG. 3 is n times (for example, 20 times).
The response time ΔT for each of the upstream oxygen sensors 8A and 8B is calculated as the average value of the times). And step 5
Then, based on the response time ΔT for each of the upstream oxygen sensors 8A and 8B, the oxygen sensor with the faster response time ΔT is selected as, for example, the upstream oxygen sensor 8A (or 8B).

Next, in step 6, by performing a catalyst diagnosis condition determination process shown in FIG. 7 which will be described later, it is determined in step 7 whether the deterioration diagnosis condition of the catalyst device 7 is satisfied, and "YES" is determined. When the determination is made, the process proceeds to step 8, and the output of the detection signal by the oxygen sensor 8B (or 8A), which has the later response time ΔT, of the upstream oxygen sensors 8A and 8B is stopped (clamped), and the response time ΔT is reduced. Only the detection signal from the faster upstream oxygen sensor 8A (or 8B) is used for air-fuel ratio feedback control or the like.

Then, in step 9, the detection signal of the upstream oxygen sensor 8A, which has a fast response time ΔT, causes the detection signal to be, for example, the threshold value SL (or threshold value SH) shown in FIG. The number of inversions CF on the upstream side is counted, and the number of inversions CR on the downstream side is similarly counted from the detection signal of the downstream oxygen sensor 9 (see FIG. 4) to determine the inversion ratio r of both.

[0040]

## EQU4 ## Calculation is performed as r = CF / CR.

Next, at step 10, it is judged whether or not the reversal ratio r is below a predetermined reference value r0, and "NO".
When it is determined that the process returns to step 1, the process thereafter is repeated. Then, in step 10, "YE
When it is determined to be “S”, the oxygen storage effect of the catalyst device 7 decreases due to the deterioration of the catalyst device 7, and the downstream oxygen sensor 9 has a reversal cycle of the detection signal compared to when the catalyst device 7 is normal. It can be judged that the inversion ratio r has become equal to or less than the reference value r0 by shortening and increasing the number of inversions CR.

Therefore, in this case, the process goes to step 11 to activate the alarm device 16 to notify that the catalyst device 7 is deteriorated, and the process returns at step 12.

Next, the catalyst diagnosis condition determination processing will be described with reference to FIG.

First, in step 21, it is judged whether or not the cooling water temperature Tw of the engine body 1 is equal to or higher than a predetermined judgment value Tw0, and if "YES" is judged, step 2 is executed.
Moving to 2, it is determined whether the vehicle speed Vs is within a predetermined range. When it is determined to be "YES" in step 22, the routine proceeds to step 23, where it is determined whether or not the basic injection amount Tp is within a predetermined range. When it is determined to be "YES", the routine proceeds to step 24 and engine speed N Is within a predetermined range.

When it is judged "YES" at step 24, the routine proceeds to step 25, where the rate of change Δ of the vehicle speed Vs is Δ.
It is determined whether or not Vs is within a predetermined range, and when "YES" is determined, the routine proceeds to step 26, where the oxygen sensor 8
A so-called DOS that corrects a proportional sentence based on the detection signals of A and 9
It is determined whether control is being executed. Then, when "YES" is determined in step 26, the process proceeds to step 27, and it is determined whether or not the throttle opening θ is a predetermined determination value θ0 or more.

When it is determined to be "YES" in step 27, it is determined whether or not the catalyst deterioration diagnosis has not been performed after starting the engine body 1 in step 28, and it is determined to be "YES". Sometimes step 21
Up to step 28, all the conditions are satisfied, both the operating state of the engine body 1 and the running state of the vehicle are in a steady state, the flow rate and temperature of exhaust gas are sufficiently stable, and high diagnostic accuracy is obtained. Since it can be determined that the deterioration condition is satisfied, the process proceeds to step 29 so as to perform the deterioration diagnosis at the time of the DOS control, and the flag process for "the diagnosis condition is satisfied" is performed.

If it is determined to be "NO" in any of the processes from step 21 to step 28, it is not possible to obtain a high diagnostic accuracy even if the catalyst deterioration diagnosis is performed. Therefore, the process proceeds to step 30. A flag process is performed to determine that "the diagnosis condition is not satisfied". Then, by returning to step S31, for example, the process proceeds to step S7 shown in FIG. 6, and the subsequent process is executed while determining whether or not the diagnostic condition is satisfied based on the flag process.

Thus, according to this embodiment, the catalyst device 7
Of the upstream side oxygen sensors 8A, 8B located on the upstream side of the exhaust pipes 6A, 6B, the oxygen sensor 8A or 8B having the faster response is used to detect the response time of the detection signal according to the equation (3). While determining (selecting) based on ΔT,
The response time ΔT is fast. For example, by determining whether the reversal ratio r between the reversal number CF of the upstream oxygen sensor 8A and the reversal number CR of the downstream oxygen sensor 9 is less than or equal to a predetermined reference value r0, Since the deterioration diagnosis of the catalyst device 7 is performed, the following operational effects can be obtained.

That is, when the air-fuel ratio feedback control of the engine body 1 is performed using the detection signals from the oxygen sensors 8A, 8B and 9, each cylinder 1A of the engine body 1 is controlled.
A phase difference occurs in the air-fuel ratio feedback control between the (first cylinder group) and each cylinder 1B (second cylinder group), and this phase difference may make it difficult to perform catalyst deterioration diagnosis. Also,
One of the upstream side oxygen sensors 8A and 8B deteriorates or tends to deteriorate, resulting in poor response (slow).
In the case of the deterioration, the responsiveness may affect the catalyst deterioration diagnosis, resulting in an erroneous diagnosis.

Therefore, in the present embodiment, the response times ΔT of the detection signals output from the upstream oxygen sensors 8A and 8B are calculated, and the oxygen sensor with the faster response is selected as the oxygen sensor based on the calculated result. The sensor 8A is discriminated (selected), and for example, the oxygen sensor 8B having the slower response is clamped in the output stopped state. As a result, the deterioration diagnosis of the catalyst is not affected by the detection signal from the upstream oxygen sensor 8B having a slow response,
By selecting, for example, a detection signal from the oxygen sensor 8A having a high responsiveness, the catalyst deterioration diagnosis can be accurately performed, and the occurrence of erroneous diagnosis can be effectively prevented.

Further, the responsiveness of the upstream oxygen sensors 8A and 8B is determined by the addition value of the rising time Tux and the falling time Tdx of the detection signal illustrated in FIG. ), The oxygen sensors 8A, 8
Since the response time ΔT of B is determined, it is possible to easily and accurately select the upstream oxygen sensor 8A (or 8B), which has the faster response, from the upstream oxygen sensors 8A and 8B. it can.

Further, the inversion number CF of the detection signal output from the upstream oxygen sensor 8A (or 8B), which has a faster response, within a certain period of time is obtained, and the downstream oxygen sensor 9 outputs within a certain period of time. Number of detection signal inversions CR
Then, the deterioration diagnosis of the catalyst device 7 is carried out based on the reversal ratio r (r = CF / CR) of both, so that the accurate deterioration diagnosis can be carried out. When the catalyst device 7 is deteriorated, the alarm 16 is activated to promptly notify the driver of the vehicle of the deterioration of the catalyst device 7.

Furthermore, for example, since the oxygen sensor 8B, which has a slower response, is clamped in the output stopped state, each cylinder 1A (first cylinder group) and each cylinder 1B (second cylinder) of the engine body 1 are clamped. The air-fuel ratio feedback control with the group) can be executed based on the detection signals from the oxygen sensors 8A and 9 having a high responsiveness, and the output rotation of the engine body 1 can be further stabilized, and various effects can be obtained. Play.

In the above embodiment, steps 4 and 5 of the program shown in FIG. 6 are specific examples of the upstream oxygen sensor selecting means which is a constituent feature of the present invention, and steps 9 and 10 are catalysts. The specific example of the deterioration diagnosis means is shown.

In the above embodiment, the engine body 1 is composed of a V-type or horizontally opposed 6-cylinder engine, a first cylinder group consisting of three cylinders 1A, 1A, ...
The case where the second cylinder group including the cylinders 1B, 1B, ... Of the cylinders is provided has been described as an example, but the present invention is not limited to this, and for example, the first cylinder group, the second cylinder group, and the third cylinder group. It may be applied to an internal combustion engine including a plurality of cylinder groups including the above.

[0056]

As described in detail above, according to the invention described in claim 1, the oxygen sensor having the faster response is selected by the upstream oxygen sensor selecting means among the upstream oxygen sensors.
Since the catalyst deterioration diagnosis means performs the deterioration diagnosis of the exhaust gas purification catalyst based on the detection signal of the upstream oxygen sensor and the detection signal of the downstream oxygen sensor selected by the selection means, Even if the responsiveness of one of the oxygen sensors becomes slow, this will not cause an erroneous diagnosis in the catalyst deterioration diagnosis, and the catalyst deterioration diagnosis can be accurately performed even in the internal combustion engine having a plurality of cylinder groups. This can be performed, and the occurrence of misdiagnosis can be effectively prevented.

According to the invention described in claim 2,
Rise of detection signal output from each upstream oxygen sensor −
The response of each oxygen sensor can be stably obtained as the response time based on the fall time, and thus the oxygen sensor with the faster response time can be easily and accurately selected.

Further, as in the invention described in claim 3, the number of times of inversion of the detection signal output from the upstream oxygen sensor of the faster response selected by the selecting means within a fixed time is obtained, and Accurate deterioration diagnosis can be carried out by obtaining the number of times of inversion of the detection signal output from the downstream oxygen sensor within a certain period of time and performing deterioration diagnosis of the exhaust purification catalyst based on the ratio of both times of inversion. When the exhaust purification catalyst is deteriorated, by operating a notification means such as an alarm device, it is possible to promptly notify the driver of the vehicle of the deterioration of the exhaust purification catalyst, and so on.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing a catalyst deterioration diagnosis device for an internal combustion engine according to the present invention.

FIG. 2 is an overall configuration diagram showing a catalyst deterioration diagnosing device according to an embodiment of the present invention.

FIG. 3 is a characteristic diagram showing a detection signal of the upstream oxygen sensor shown in FIG.

FIG. 4 is a characteristic diagram showing a detection signal of the downstream oxygen sensor shown in FIG.

FIG. 5 is a control block diagram showing a catalyst deterioration diagnosis device.

FIG. 6 is a flowchart showing a catalyst deterioration diagnosis process.

FIG. 7 is a flowchart showing a catalyst diagnosis condition determination process.

[Explanation of symbols]

 1 Engine Main Body (Engine Main Body) 1A, 1B Cylinder (Cylinder Group) 2 Intake Pipe 6 Exhaust Pipe (Exhaust Passage) 6A, 6B Exhaust Pipe Section 6C Confluent Pipe Section 7 Catalyst Device (Exhaust Purification Catalyst) 8A, 8B Upstream Oxygen Sensor 9 Downstream oxygen sensor 15 Control unit CF, CR Inversion count Tdx Fall time Tux Rise time ΔT Response time

Claims (3)

[Claims] 1. An exhaust gas comprising an engine body of an internal combustion engine having a plurality of cylinder groups, a plurality of exhaust pipe parts independent for each cylinder group of the engine body, and a confluent pipe part in which the exhaust pipe parts join each other. A passage, an exhaust purification catalyst that is provided in the middle of the merging pipe portion of the exhaust passage and purifies the exhaust gas by a catalytic reaction, and oxygen of the exhaust gas that is provided in each exhaust pipe portion of the exhaust passage and flows in each exhaust pipe portion. A plurality of upstream oxygen sensors that detect the concentration, and a downstream side that is located on the downstream side of the exhaust purification catalyst and that is provided midway in the merging pipe portion of the exhaust passage and that detects the oxygen concentration of the exhaust gas flowing in the merging pipe portion. Oxygen sensor, upstream oxygen sensor selecting means for selecting one of the upstream oxygen sensors which has a faster response, detection signal of the upstream oxygen sensor selected by the selecting means, and the downstream oxygen sensor Inspection A catalyst deterioration diagnosing device for an internal combustion engine, comprising a catalyst deterioration diagnosing means for diagnosing deterioration of the exhaust purification catalyst based on an output signal. 2. The upstream side oxygen sensor selecting means has a rising edge of a detection signal output from each of the upstream side oxygen sensors.
The catalyst deterioration diagnosing device for an internal combustion engine according to claim 1, wherein an oxygen sensor having a faster response time is selected from the upstream oxygen sensors based on the fall time. 3. The catalyst deterioration diagnosing means detects the number of reversals of the detection signal output from the upstream oxygen sensor within a fixed time and the number of reversals of the detection signal output from the downstream oxygen sensor within a predetermined time. The catalyst deterioration diagnosing device for an internal combustion engine according to claim 1 or 2, wherein deterioration diagnosis of the exhaust purification catalyst is performed based on the ratio.