JP2007247486A - Failure diagnostic system of exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely diagnose leakage, when closing a flow passage switching valve for switching a main passage and a bypass passage. <P>SOLUTION: As an exhaust emission control device, a small bypass catalytic converter is arranged in a bypass passage parallel to a part of the main passage having a main catalytic converter on the downstream side, and the flow passage switching valve opens and closes the main passage. Air-fuel ratio sensors are respectively provided on the upstream side and the downstream side of the main catalytic converter and the upstream side and the downstream side of the bypass catalytic converter. A leakage diagnosis of the flow passage switching valve is performed by using a periodic change in the engine air-fuel ratio by air-fuel ratio feedback control in a closing position. The exhaust air-fuel ratio AFB on the upstream side of the bypass catalytic converter, changes as it is in the engine air-fuel ratio, and the exhaust air-fuel ratio AFM on the upstream side of the main catalytic converter, changes by delaying like (a), and changes without delaying like (b) in leakage, and becomes like (c) when a catalyst is deteriorated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device in which exhaust gas is guided by a flow path switching valve to a bypass passage side provided with a catalytic converter relatively upstream of an exhaust system immediately after a cold start, and in particular, the flow path switching valve. The present invention relates to a failure diagnosis device for diagnosing leakage of a liquid.

  As conventionally known, in a configuration in which the main catalytic converter is disposed relatively downstream of the exhaust system such as under the floor of a vehicle, the temperature of the catalytic converter rises and is activated after a cold start of the internal combustion engine. In the meantime, a sufficient exhaust purification action cannot be expected. On the other hand, the closer the catalytic converter is to the upstream side of the exhaust system, that is, the internal combustion engine side, the lower the durability due to thermal degradation of the catalyst.

Therefore, as disclosed in Patent Document 1 and Patent Document 2, a bypass channel is provided in parallel with the upstream portion of the main channel including the main catalytic converter, and another bypass catalyst is provided in the bypass channel. 2. Description of the Related Art Conventionally, there has been proposed an exhaust device that guides exhaust gas to the bypass flow path side immediately after a cold start by a switching valve that interposes a converter and switches both of them. In this configuration, the bypass catalytic converter is positioned relatively upstream of the main catalytic converter in the exhaust system and is activated relatively early, so that exhaust purification can be started from an earlier stage. it can.
JP-A-5-321644 JP 2005-188374 A

  In the above configuration, when the flow path switching by the flow path switching valve is insufficient, for example, when the exhaust gas leaks even though the flow path switching valve that opens and closes the main passage is in the closed position. When the main catalytic converter is inactive, unpurified exhaust gas flows out to the outside as it is, which is not preferable. Accordingly, there is a need for a diagnostic device that diagnoses leakage of the flow path switching valve.

  In addition, although the said patent document 2 has proposed the method of detecting the flow volume fall by the adhesion of the deposit of a flow-path switching valve, etc., the leakage of unpurified exhaust gas cannot be diagnosed.

  According to the present invention, a bypass passage is provided in parallel with the upstream portion of the main passage provided with the main catalytic converter on the downstream side, the bypass passage is provided with the bypass catalytic converter, and the upstream portion of the main passage is provided with the bypass passage. In an exhaust gas purification apparatus for an internal combustion engine comprising a flow path switching valve that closes a main passage, a first air-fuel ratio sensor that detects an exhaust air-fuel ratio upstream of the bypass catalytic converter of the bypass passage, and a main passage of the main passage A second air-fuel ratio sensor for detecting an exhaust air-fuel ratio upstream of the catalytic converter, and diagnosing leakage of the flow path switching valve from both detection signals when the flow path switching valve is in the closed position It is characterized by.

  In one aspect of the present invention, while the engine air-fuel ratio is controlled to periodically change between rich and lean, the second air-fuel ratio sensor with respect to the rich and lean change in the first air-fuel ratio sensor. The delay of the change between rich and lean is obtained, and leakage of the flow path switching valve is diagnosed based on this.

  In another aspect of the present invention, while the engine air-fuel ratio is controlled so as to periodically change between rich and lean, the length of the rich and lean period in the first air-fuel ratio sensor and the second The leakage of the flow path switching valve is diagnosed by comparing the lengths of the rich and lean periods in the air-fuel ratio sensor.

  In order to periodically change the engine air-fuel ratio to rich and lean as described above, for example, the periodic change of the engine air-fuel ratio by the air-fuel ratio feedback control using the first air-fuel ratio sensor may be used. it can.

  Alternatively, the engine air-fuel ratio may be forcibly changed periodically at a predetermined cycle at the time of diagnosis. Even when the cycle is forcibly changed in this way, the average air-fuel ratio is maintained at the stoichiometric air-fuel ratio, so there is no deterioration in exhaust emission during diagnosis.

  That is, in the exhaust emission control device having the above configuration, when the flow path switching valve that opens and closes the main passage is in the closed position, the entire amount of exhaust discharged from the internal combustion engine flows to the bypass passage side and passes through the bypass catalytic converter. On the other hand, when the flow path switching valve is in the open position, most of the exhaust discharged from the internal combustion engine flows through the main passage due to the difference in ventilation resistance.

  Diagnosis of leakage of the flow path switching valve is performed, for example, using a periodic change in the engine air-fuel ratio by air-fuel ratio feedback control when the flow path switching valve is in the closed position. Since the first air-fuel ratio sensor is on the upstream side of the bypass catalytic converter, when the engine air-fuel ratio changes periodically, the detection signal changes periodically with the engine air-fuel ratio. On the other hand, on the downstream side of the bypass catalytic converter, the change in the exhaust air-fuel ratio becomes relatively small due to the oxygen storage capability of the catalyst, and changes with a delay from the change in the engine air-fuel ratio.

  If there is no leakage of exhaust gas through the flow path switching valve, the second air-fuel ratio sensor upstream of the main catalytic converter receives only the exhaust gas that has passed through the bypass catalytic converter, so the air-fuel ratio detected by the second air-fuel ratio sensor As described above, changes with a delay with respect to the periodic change of the exhaust air-fuel ratio, and the change becomes small. On the other hand, if the exhaust gas leaks through the flow path switching valve, the exhaust gas discharged from the engine acts on the second air-fuel ratio sensor without passing through the bypass catalytic converter. The detected air-fuel ratio changes at the same cycle and timing as the exhaust air-fuel ratio and thus the detected air-fuel ratio of the first air-fuel ratio sensor. If the difference in passage length from the exhaust port of the engine to the first air-fuel ratio sensor and the second air-fuel ratio sensor is negligible, when there is a leak, both are reversed to rich and lean at exactly the same timing. Will change.

  Therefore, it is possible to diagnose the presence or absence of leakage or the degree of leakage based on the delay in rich / lean changes or the length of the rich / lean period.

  Note that the oxygen storage capacity described above is affected by catalyst deterioration, but in the case of catalyst deterioration, the rich / lean change timing of the first air-fuel ratio sensor and the rich / lean change of the second air-fuel ratio sensor. The timing does not completely match, and the delay is reduced according to the degree of deterioration. Therefore, the presence or absence of leakage and catalyst deterioration can be easily distinguished.

  According to the failure diagnosis apparatus for an exhaust gas purification apparatus for an internal combustion engine according to the present invention, it is possible to reliably diagnose exhaust gas leakage through the flow path switching valve, and to prevent outflow of unpurified exhaust gas to the outside. can do.

  In particular, even during the execution of the diagnosis, the air-fuel ratio periodically changes from rich to lean around the stoichiometric air-fuel ratio, so that the average air-fuel ratio is maintained at or near the stoichiometric air-fuel ratio, and exhaust emissions do not deteriorate.

  Hereinafter, an embodiment in which the present invention is applied to an exhaust purification apparatus for an in-line four-cylinder internal combustion engine will be described in detail with reference to the drawings.

  FIG. 1 is an explanatory view schematically showing the piping layout and control system of the exhaust device of the internal combustion engine. First, the configuration of the exhaust device will be described based on FIG.

  In the cylinder head 1a of the internal combustion engine 1, exhaust ports 2 of cylinders # 1 to # 4 arranged in series are formed so as to open toward the side surfaces, respectively. In addition, the main passage 3 is connected. The four main passages 3 of the # 1 cylinder to the # 4 cylinder merge into one flow path, and the main catalytic converter 4 is disposed on the downstream side thereof. The main catalytic converter 4 has a large capacity arranged under the floor of the vehicle, and includes, for example, a three-way catalyst and an HC trap catalyst as the catalyst. The main passage 3 and the main catalytic converter 4 constitute a main passage through which exhaust flows during normal operation. In addition, a flow path switching valve 5 that opens and closes the main passages 3 at the same time is provided as a flow path switching means at the junction of the four main paths 3 from each cylinder. The flow path switching valve 5 is driven to open and close by an appropriate actuator 5a.

  On the other hand, bypass passages 7 each having a smaller passage sectional area than the main passage 3 are branched from the main passages 3 of the respective cylinders as bypass passages. The branch point 6 that is the upstream end of each bypass passage 7 is set to a position on the upstream side of the main passage 3 as much as possible. The four bypass passages 7 merge into one flow path on the downstream side, and a bypass catalytic converter 8 using a three-way catalyst is interposed immediately after the junction. The bypass catalytic converter 8 has a small capacity as compared with the main catalytic converter 4, and preferably uses a catalyst excellent in low-temperature activity. The downstream end of the bypass passage 7 extending from the outlet side of the bypass catalytic converter 8 is connected to the main passage 3 at a junction 9 upstream of the main catalytic converter 4 in the main passage 3 and downstream of the flow path switching valve 5. ing.

  Here, a main upstream air-fuel ratio sensor 10 and a main downstream air-fuel ratio sensor 11 are arranged at the inlet and outlet of the main catalytic converter 4, respectively, and at the inlet and outlet of the bypass catalytic converter 8. A bypass upstream air-fuel ratio sensor 12 and a bypass downstream air-fuel ratio sensor 13 are disposed, respectively. The main upstream air-fuel ratio sensor 10 and the main downstream air-fuel ratio sensor 11 are for performing known air-fuel ratio feedback control after the activation of the main catalytic converter 4. The fuel ratio (fuel injection amount) is controlled, and the output signal of the downstream air-fuel ratio sensor 11 is used for correcting variations in the control characteristics. Similarly, the bypass upstream air-fuel ratio sensor 12 and bypass downstream air-fuel ratio sensor 13 are for performing known air-fuel ratio feedback control when the bypass catalytic converter 8 is used. 12, the engine air-fuel ratio (fuel injection amount) is controlled, and the output signal of the downstream-side air-fuel ratio sensor 13 is used for correcting variations in the control characteristics. As these air-fuel ratio sensors 10 to 13, either a so-called wide-area type air-fuel ratio sensor having a substantially linear output characteristic corresponding to the exhaust air-fuel ratio or an oxygen sensor having a binary output characteristic of rich or lean is used. However, the upstream air-fuel ratio sensors 10 and 12 are desirably wide-area air-fuel ratio sensors, and the downstream air-fuel ratio sensors 11 and 13 are preferable in terms of controllability in the air-fuel ratio control described above. It is possible to use an oxygen sensor in terms of component costs. The bypass upstream air-fuel ratio sensor 12 corresponds to a “first air-fuel ratio sensor”, and the main upstream air-fuel ratio sensor 10 corresponds to a “second air-fuel ratio sensor”. Note that, when the correction control of the air-fuel ratio feedback control using the downstream air-fuel ratio sensors 11 and 13 is not performed, the downstream air-fuel ratio sensors 11 and 13 can be omitted.

  The internal combustion engine 1 includes a spark plug 21, and a fuel injection valve 23 is disposed in the intake passage 22. Furthermore, a so-called electronically controlled throttle valve 24 that is opened and closed by an actuator such as a motor is disposed upstream of the intake passage 22, and an air flow meter 25 that detects the intake air amount is provided downstream of the air cleaner 26. Yes.

  Various control parameters of the internal combustion engine 1, for example, the fuel injection amount by the fuel injection valve 23, the ignition timing by the spark plug 21, the opening degree of the throttle valve 24, the open / close state of the flow path switching valve 5, etc. 27. In addition to the sensors described above, the engine control unit 27 includes various sensors such as a coolant temperature sensor 28 and an accelerator opening sensor 29 that detects the opening (depression amount) of an accelerator pedal operated by a driver. Detection signal is input. Then, the engine control unit 27 appropriately executes a diagnosis of leakage of the flow path switching valve 5.

  In such a configuration, when the engine temperature or the exhaust temperature after the cold start is low, the flow path switching valve 5 is closed via the actuator 5a, and the main passage 3 is blocked. Therefore, the entire amount of exhaust discharged from each cylinder flows from the branch point 6 to the bypass catalytic converter 8 through the bypass passage 7. The bypass catalytic converter 8 is located upstream of the exhaust system, that is, at a position close to the exhaust port 2 and is small in size, so that it is activated quickly and exhaust purification is started at an early stage.

  On the other hand, when the engine warm-up proceeds and the engine temperature or the exhaust temperature becomes sufficiently high, it is considered that the catalyst of the main catalytic converter 4 has been activated, and the flow path switching valve 5 is opened. Thus, the exhaust discharged from each cylinder mainly passes through the main catalytic converter 4 from the main passage 3. At this time, the bypass passage 7 side is not particularly cut off, but the bypass passage 7 side has a smaller passage cross-sectional area than the main passage 3 side and the bypass catalytic converter 8 is interposed. Due to the difference, most of the exhaust flow passes through the main passage 3 side and hardly flows into the bypass passage 7 side. Therefore, the thermal deterioration of the bypass catalytic converter 8 is sufficiently suppressed.

  Next, the diagnosis of leakage of the flow path switching valve 5 will be described. In the following example, the two upstream air-fuel ratio sensors 10 and 12 are wide-area air-fuel ratio sensors, the two downstream air-fuel ratio sensors 11 and 13 are oxygen sensors, Only the upstream air-fuel ratio sensors 10, 12 are used.

  FIG. 2 is a time chart showing an embodiment of the leakage diagnosis. This leakage diagnosis is based on the air-fuel ratio in which the flow path switching valve 5 is closed after the cold start and the bypass upstream air-fuel ratio sensor 12 is used. It is executed after the feedback control is started (after the activation of the bypass catalytic converter 8). Since the bypass catalytic converter 8 is activated quickly as described above, the air-fuel ratio feedback control is started in a short time after starting. It is also possible to make a diagnosis by temporarily closing the flow path switching valve 5 after completion of warm-up (after activation of the main catalytic converter 4).

  FIG. 2A shows the detected air-fuel ratio AFB detected by the bypass upstream air-fuel ratio sensor 12 and the detected air-fuel ratio detected by the main upstream air-fuel ratio sensor 10 in a normal state, that is, without leakage and without catalyst deterioration of the bypass catalytic converter 8. It is shown in contrast with the fuel ratio AFM. By the known air-fuel ratio feedback control, the fuel injection amount periodically increases and decreases so that the exhaust air-fuel ratio converges to the stoichiometric air-fuel ratio, and the engine air-fuel ratio periodically changes rich and lean. Since the fuel ratio sensor 12 is directly affected by the exhaust gas discharged from the engine, an output signal that directly reflects the change in the engine air-fuel ratio can be obtained. That is, the detected air-fuel ratio AFB of the bypass upstream air-fuel ratio sensor 12 shown corresponds to the engine air-fuel ratio, and can be regarded as the engine air-fuel ratio itself. In response to such a periodic change of the detected air-fuel ratio AFB of the bypass upstream air-fuel ratio sensor 12, the detected air-fuel ratio AFM of the main upstream air-fuel ratio sensor 10 is rich and lean beyond the theoretical air-fuel ratio as shown in the figure. And the timing of the change is later than the detected air-fuel ratio AFB of the bypass upstream air-fuel ratio sensor 12. This is due to the oxygen storage capacity of the catalyst of the bypass catalytic converter 8, and oxygen is absorbed when the exhaust air-fuel ratio becomes lean, and oxygen is released when the exhaust air-fuel ratio becomes rich. Even if the exhaust air-fuel ratio changes periodically between rich and lean, the change does not appear downstream of the bypass catalytic converter 8 until the oxygen storage capacity is saturated.

  On the other hand, FIG. 2B shows the characteristics when the exhaust gas leaks through the flow path switching valve 5 in the closed position. Since the detected air-fuel ratio AFB of the bypass upstream air-fuel ratio sensor 12 is not affected by the presence or absence of leakage, it is not different from the normal state of (a). On the other hand, since the exhaust gas leaked from the flow path switching valve 5 without passing through the bypass catalytic converter 8 acts on the main upstream air-fuel ratio sensor 10, the detected air-fuel ratio AFM is detected by the bypass upstream air-fuel ratio sensor. Inverted to rich and lean at the same timing as the detected air-fuel ratio AFB of 12. Note that the rich and lean values, that is, the amplitude of the period change, are mixed with the exhaust gas that has passed through the bypass catalytic converter 8 and diluted, and therefore are smaller than the amplitude of the detected air-fuel ratio AFB of the bypass upstream air-fuel ratio sensor 12. It becomes.

  Therefore, for example, the delay Δt of the rich / lean change in the detected air-fuel ratio AFM of the main upstream air-fuel ratio sensor 10 with respect to the change timing of the rich / lean change in the detected air-fuel ratio AFB of the bypass upstream air-fuel ratio sensor 12 is obtained. If it is smaller than the reference value, leakage can be diagnosed.

  Alternatively, the length t1 of the rich / lean period in the detected air-fuel ratio AFB of the bypass upstream air-fuel ratio sensor 12 and the length t2 of the rich / lean period in the detected air-fuel ratio AFM of the main upstream air-fuel ratio sensor 10 are compared. Then, when both are substantially equal, it can be diagnosed as leakage.

  Of course, these diagnoses can be made more reliable by obtaining, for example, an average of a plurality of air-fuel ratio changes. As is apparent from the figure, the delay Δt is substantially equal to the difference between the periods t1 and t2 (t1−t2).

  On the other hand, FIG. 2C shows a change in the detected air-fuel ratio AFM when the catalyst of the bypass catalytic converter 8 has deteriorated to some extent. As shown in the figure, when the oxygen storage capacity decreases due to catalyst deterioration, the basic tendency of the detected air-fuel ratio AFM of the main upstream air-fuel ratio sensor 10 does not change, but changes to rich and lean earlier. . That is, the delay Δt from the change in the detected air-fuel ratio AFB of the bypass upstream air-fuel ratio sensor 12 is reduced, and the rich and lean period t2 is also increased. Here, if the catalyst deterioration is extremely advanced and the oxygen storage capacity becomes 0, the delay Δt and the period t2 cannot be distinguished from the case of FIG. 2 (b). Since it progresses gradually, the delay Δt and the period t2 show intermediate values between the characteristics of FIG. 2A and the characteristics of FIG. Therefore, it is possible to diagnose the catalyst deterioration at this stage, and it can be reliably identified as leakage of the flow path switching valve 5.

  For example, when the delay Δt is shorter than the first reference value, it is diagnosed that there is leakage, and when it is larger than the second reference value, it is diagnosed that there is no leakage, and the first reference value and the second reference value Is in a predetermined range (between the third reference value and the fourth reference value), the catalyst deterioration of the bypass catalytic converter 8 can be diagnosed. Note that the third reference value and the fourth reference value may be set equal to the first reference value and the second reference value, respectively.

  Alternatively, the length t1 of the rich / lean period in the detected air-fuel ratio AFB of the bypass upstream air-fuel ratio sensor 12 and the length t2 of the rich / lean period in the detected air-fuel ratio AFM of the main upstream air-fuel ratio sensor 10 are obtained. When the time t2 is substantially shorter than the time period t1, it is diagnosed that there is no leakage. When the time period t2 is within a certain range compared to the time period t1, the bypass catalyst is diagnosed. It is possible to diagnose the catalyst deterioration of the converter 8.

  As described above, according to the above-described embodiment, the leakage diagnosis of the flow path switching valve 5 can be performed while the normal air-fuel ratio feedback control is continued, and the exhaust emission during the diagnosis is not deteriorated. Further, it is possible to make a leak diagnosis with high accuracy by discriminating from catalyst deterioration.

  Next, FIG. 3 is a time chart showing different embodiments of the leakage diagnosis. This leakage diagnosis is executed after the flow path switching valve 5 is closed after the cold start and the bypass catalytic converter 8 is activated. However, in particular, for diagnosis, the engine air-fuel ratio is forcibly changed to rich and lean with a constant period and constant amplitude.

  Similar to FIG. 2 described above, FIG. 3A shows the characteristics when normal (no leakage, no catalyst deterioration), FIG. 3B shows the characteristics when leakage occurs, and FIG. 3C shows the characteristics when catalyst deterioration occurs. The principle and method of diagnosis are the same as in the above-described embodiment.

  In the above-described embodiment described with reference to FIG. 2, the cycle and amplitude of the engine air-fuel ratio rich and lean changes are not necessarily constant depending on the engine operating conditions, but according to this embodiment, the engine air-fuel ratio changes. Since it becomes a thing of a fixed period and a fixed amplitude, the precision of a leakage diagnosis and a catalyst deterioration diagnosis becomes higher. Even when the engine air-fuel ratio is forcibly changed in this way, the average air-fuel ratio is maintained in the vicinity of the stoichiometric air-fuel ratio because it periodically changes rich and lean across the stoichiometric air-fuel ratio. Exhaust emissions will not deteriorate. As shown in FIG. 3A, it is desirable to set the period of change in the engine air-fuel ratio so that it does not become excessively long in consideration of the oxygen storage capacity of the catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows the structure of the internal combustion engine which concerns on this invention. The time chart which shows one Example of a leakage diagnosis. The time chart which shows the different Example of a leakage diagnosis.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Main passage 4 ... Main catalytic converter 5 ... Flow path switching valve 6 ... Branch point 7 ... Bypass passage 8 ... Bypass catalytic converter 9 ... Junction point 10 ... Main upstream air-fuel ratio sensor 11 ... Main downstream air-fuel ratio sensor 12 ... Bypass upstream air-fuel ratio sensor 13 ... Bypass downstream air-fuel ratio sensor 27 ... Engine control unit

Claims (7)

  A bypass passage is provided in parallel with the upstream portion of the main passage provided with the main catalytic converter on the downstream side, the bypass passage is provided with the bypass passage, and the main passage is blocked at the upstream portion of the main passage. In the exhaust gas purification apparatus for an internal combustion engine, the first air-fuel ratio sensor for detecting the exhaust air-fuel ratio upstream of the bypass catalytic converter in the bypass passage, and the main catalytic converter upstream of the main passage And a second air-fuel ratio sensor for detecting the exhaust air-fuel ratio of the exhaust gas, and diagnosing leakage of the flow path switching valve from both detection signals when the flow path switching valve is in the closed position. Failure diagnosis device for exhaust gas purification device of internal combustion engine.   While controlling the engine air-fuel ratio so as to periodically change between rich and lean, the delay of the rich and lean change in the second air-fuel ratio sensor with respect to the rich and lean change in the first air-fuel ratio sensor is reduced. 2. The failure diagnosis device for an exhaust gas purification device for an internal combustion engine according to claim 1, wherein the leakage of the flow path switching valve is diagnosed based on the obtained value.   While the engine air-fuel ratio is controlled so as to periodically change between rich and lean, the length of the rich and lean period in the first air-fuel ratio sensor and the length of the rich and lean period in the second air-fuel ratio sensor The failure diagnosis device for an exhaust gas purification device for an internal combustion engine according to claim 1, wherein the leakage of the flow path switching valve is diagnosed by comparing with the length.   4. The failure diagnosis device for an exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein a periodic change of the engine air-fuel ratio by air-fuel ratio feedback control using the first air-fuel ratio sensor is utilized.   The failure diagnosis device for an exhaust gas purification device for an internal combustion engine according to claim 2 or 3, wherein the engine air-fuel ratio is forcibly changed periodically at a predetermined cycle during diagnosis.   When the above delay is shorter than the first reference value, it is diagnosed that there is leakage, and when it is larger than the second reference value, it is diagnosed that there is no leakage, and between the first reference value and the second reference value. 3. The failure diagnosis device for an exhaust gas purification device for an internal combustion engine according to claim 2, wherein the failure of the bypass catalytic converter is diagnosed when it is within the predetermined range. When the length of the rich / lean period in the second air-fuel ratio sensor is substantially equal to the length of the rich / lean period in the first air-fuel ratio sensor, it is diagnosed that there is a leak, and the leak occurs when it is relatively short 4. The failure diagnosis device for an exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the failure diagnosis device diagnoses that there is none and diagnoses the catalyst deterioration of the bypass catalytic converter when it is in an intermediate range.

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