JP2010255490A - Catalyst abnormality diagnostic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase diagnosis accuracy near criteria and prevent wrong diagnosis. <P>SOLUTION: This catalyst abnormality diagnostic device measures oxygen occlusion capacity of a catalyst with correlated with catalyst temperature. It is determined based on difference between present measurement value and a past measurement value of different catalyst temperature whether the catalyst is normal or not. The present measurement value is corrected based on a parameter indicating response of a catalyst rear sensor for discriminating between an intermediate catalyst near the criteria and an abnormal catalyst if it is not determined as normal. It is determined based on the value after correction whether the catalyst is normal or abnormal. Whether the catalyst is normal or abnormal is determined after eliminating influence of sensor response. Correction is performed if it is not determined as clear intermediate catalyst based on the difference. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an abnormality diagnosis of a catalyst, and more particularly to an apparatus for diagnosing an abnormality of a catalyst disposed in an exhaust passage of an internal combustion engine.

For example, in an internal combustion engine for automobiles, a catalyst for purifying exhaust gas is installed in the exhaust system. Some of these catalysts have an oxygen storage capacity (O ₂ storage capacity). When the air-fuel ratio of the exhaust gas flowing into the catalyst becomes larger than the stoichiometric air-fuel ratio (stoichiometric), that is, when the engine becomes lean, the catalyst having oxygen storage capacity occludes excess oxygen present in the exhaust gas. When the fuel ratio becomes smaller than stoichiometric, that is, when it becomes rich, the stored oxygen is released. For example, in a gasoline engine, air-fuel ratio control is performed so that the exhaust gas flowing into the catalyst is in the vicinity of the stoichiometric. However, if a three-way catalyst having an oxygen storage capacity is used, the actual air-fuel ratio slightly deviates from the stoichiometric depending on the operating conditions. However, such an air-fuel ratio shift can be absorbed by the oxygen storage / release action of the three-way catalyst.

  By the way, when the catalyst deteriorates, the purification rate of the catalyst decreases, but there is a correlation between the degree of deterioration of the catalyst and the degree of decrease of the oxygen storage capacity. Therefore, it is possible to detect deterioration or abnormality of the catalyst by detecting a decrease in oxygen storage capacity. Generally, a method (so-called Cmax method) that performs active air-fuel ratio control that switches the air-fuel ratio alternately and actively between rich and lean, measures the oxygen storage capacity of the catalyst, and diagnoses the deterioration of the catalyst is adopted. .

Japanese Patent Laid-Open No. 10-18886

  By the way, in the active air-fuel ratio control, the air-fuel ratio of the exhaust gas supplied to the catalyst becomes rich or lean in response to the output of the air-fuel ratio sensor installed downstream of the catalyst reversing to lean or rich. Can be switched. Therefore, if the responsiveness of the air-fuel ratio sensor deteriorates due to deterioration or failure, this will have a considerable impact on the measured value of the oxygen storage capacity, leading to deterioration of diagnostic accuracy or causing misdiagnosis. .

  In the technique described in Patent Document 1, in order to detect deterioration in which the responsiveness of the O2 sensor deteriorates, during the air-fuel ratio feedback control, the sensor output inversion period, the first change time from rich to lean, and the lean Each second change time to rich is measured, and when at least one of them is larger than a predetermined value, the sensor is determined to be deteriorated.

  As described above, there already exists a technique for independently detecting deterioration or abnormality of the air-fuel ratio sensor. However, in the catalyst abnormality diagnosis, the responsiveness of the air-fuel ratio sensor slightly affects the measured value of oxygen storage capacity, so let's accurately identify the normality and abnormality of the catalyst near the boundary between the normality and abnormality. In this case, the actual situation is that even if the conventional technology for the air-fuel ratio sensor alone is applied, the requirements cannot be sufficiently satisfied.

  Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a catalyst abnormality diagnosis device that can improve diagnosis accuracy particularly near the criteria and prevent erroneous diagnosis.

According to one aspect of the invention,
An apparatus for diagnosing abnormality of a catalyst disposed in an exhaust passage of an internal combustion engine,
A post-catalyst sensor for detecting an exhaust air-fuel ratio downstream of the catalyst;
Catalyst temperature detection means for detecting or estimating the temperature of the catalyst;
In response to the output of the post-catalyst sensor being reversed to lean or rich, active air-fuel ratio control is executed to switch the air-fuel ratio of the exhaust gas supplied to the catalyst to rich or lean alternately and actively. Fuel ratio control means;
With the execution of the active air-fuel ratio control, measuring means for measuring the oxygen storage capacity of the catalyst in association with the detected or estimated catalyst temperature,
First determination means for determining whether or not the catalyst is normal based on the difference between the value of the oxygen storage capacity measured this time by the measurement means and the value of the oxygen storage capacity measured in the past for different catalyst temperatures. When,
Correction means for correcting the value of the oxygen storage capacity measured this time based on a parameter representing the responsiveness of the post-catalyst sensor when the first determination means does not determine normality;
A second determination means for comparing the corrected oxygen storage capacity value with a predetermined abnormality determination value to determine whether the catalyst is normal or abnormal;
There is provided a catalyst abnormality diagnosis device characterized by comprising:

  According to this, since the oxygen storage capacity measurement value is corrected based on the parameter representing the response of the post-catalyst sensor, it is possible to determine whether the catalyst is normal or abnormal after eliminating the influence of the response of the post-catalyst sensor.

  In addition, before the correction, whether or not the catalyst is normal is determined based on the difference between the current oxygen storage capacity measurement value and the past oxygen storage capacity measurement value for different catalyst temperatures, and is not determined to be normal. Sometimes correct. That is, based on the difference, it can be determined whether or not the catalyst is an obvious intermediate catalyst (a catalyst that is obviously not normal but is not normal but should be determined to be normal). If not, a correction is made to distinguish between the intermediate catalyst near the criteria and the abnormal catalyst. Thereby, the diagnostic accuracy near the criteria can be improved and misdiagnosis can be prevented.

  Preferably, the catalyst abnormality diagnosis device further includes third determination means for comparing the value of the oxygen storage capacity measured by the measurement means with a predetermined normal determination value to determine whether or not the catalyst is normal. The first determination unit executes the determination based on the difference when the third determination unit does not determine normal.

  Thereby, when a catalyst is an obvious normal catalyst, this can be identified first and diagnostic processing can be simplified.

  Preferably, the measurement unit measures the oxygen storage capacity in association with one of the plurality of preset catalyst temperature ranges to which the detected catalyst temperature belongs, and the first determination unit is configured to determine the different catalyst temperature range. As the value of the oxygen storage capacity measured in the past with respect to the temperature, the value of the oxygen storage capacity measured most recently for different catalyst temperature ranges is used.

According to another aspect of the invention,
An apparatus for diagnosing abnormality of a catalyst disposed in an exhaust passage of an internal combustion engine,
A post-catalyst sensor for detecting an exhaust air-fuel ratio downstream of the catalyst;
In response to the output of the post-catalyst sensor being reversed to lean or rich, active air-fuel ratio control is executed to switch the air-fuel ratio of the exhaust gas supplied to the catalyst to rich or lean alternately and actively. Fuel ratio control means;
In accordance with the execution of the active air-fuel ratio control, measuring means for measuring the oxygen storage capacity of the catalyst,
An inversion time measuring means for measuring a lean inversion time and a rich inversion time when the post-catalyst sensor output is inverted to lean and rich respectively;
First determination means for determining whether or not the catalyst is normal based on a lean inversion time and a rich inversion time measured by the inversion time measuring means;
A correction means for correcting the value of the oxygen storage capacity measured this time based on a parameter representing the response of the post-catalyst sensor when the first determination means does not determine normality;
Second determination means for comparing the corrected oxygen storage capacity value with a predetermined abnormality determination value to determine whether the catalyst is normal or abnormal;
There is provided a catalyst abnormality diagnosis device characterized by comprising:

  This also corrects the oxygen storage capacity measurement value based on the parameter representing the response of the post-catalyst sensor, so that it is possible to determine whether the catalyst is normal or abnormal after removing the influence of the response of the post-catalyst sensor.

  Further, before the correction, whether or not the catalyst is normal is determined in advance based on the lean inversion time and the rich inversion time, and correction is performed when it is not determined to be normal. That is, it is determined whether the catalyst is an obvious intermediate catalyst based on the lean inversion time and the rich inversion time, and when the catalyst cannot be determined as an obvious intermediate catalyst, the intermediate catalyst in the vicinity of the criteria and the abnormal catalyst are identified. Make corrections. Thereby, the diagnostic accuracy near the criteria can be improved and misdiagnosis can be prevented.

  Preferably, the catalyst abnormality diagnosis device further includes third determination means for comparing the value of the oxygen storage capacity measured by the measurement means with a predetermined normal determination value to determine whether or not the catalyst is normal. The first determination unit executes a determination based on the lean inversion time and the rich inversion time when the third determination unit does not determine that the normal state is normal.

  Preferably, the first determination unit determines whether the catalyst is normal by comparing a ratio of the lean inversion time and the rich inversion time with a predetermined value.

  Preferably, the catalyst abnormality diagnosis device further includes detection means for detecting a flow rate of exhaust gas supplied to the catalyst or a correlation value thereof, and the first determination means is the exhaust gas detected by the detection means. The predetermined value is set based on the flow rate or its correlation value.

  Preferably, the first determination unit performs the determination when the exhaust gas flow rate detected by the detection unit or a correlation value thereof is within a predetermined range.

  Preferably, the parameter representing the response of the post-catalyst sensor is an inversion time of the post-catalyst sensor output.

  Preferably, the parameter representing the response of the post-catalyst sensor is a time constant of the post-catalyst sensor.

  According to the present invention, it is possible to improve the diagnostic accuracy particularly in the vicinity of the criteria and to achieve an excellent effect of preventing misdiagnosis.

It is the schematic which shows the structure of embodiment of this invention. It is a schematic sectional drawing which shows the structure of a catalyst. It is a time chart of active air fuel ratio control. FIG. 4 is a time chart similar to FIG. 3 for illustrating a method for measuring the oxygen storage capacity. It is a graph which shows the output characteristic of a pre-catalyst sensor and a post-catalyst sensor. It is a graph which shows the relationship between the catalyst temperature and the oxygen storage capacity measured value in the some catalyst from which a deterioration degree differs. It is a graph for demonstrating the influence which the responsiveness of the post-catalyst sensor has on the oxygen storage capacity measurement value. It is a flowchart which shows the procedure of the abnormality diagnosis process according to 1st Example. It is a graph for demonstrating how to obtain | require the latest data. It is a graph for demonstrating how to obtain | require the latest data. It is a graph which shows the relationship between the time constant of a post-catalyst sensor, and rich inversion time. It is a graph which shows the relationship between the time constant of a post-catalyst sensor and a correction coefficient. It is a graph which shows the relationship between intake air amount and inversion time ratio. It is a flowchart which shows the procedure of the abnormality diagnosis process according to 2nd Example.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing the configuration of the present embodiment. As shown in the figure, an engine 1 that is an internal combustion engine burns a mixture of fuel and air in a combustion chamber 3 formed in a cylinder block 2 and reciprocates a piston 4 in the combustion chamber 3 to drive power. Is generated. The engine 1 of the present embodiment is a multi-cylinder engine for automobiles (only one cylinder is shown), and is a spark ignition type internal combustion engine, more specifically, a gasoline engine.

  The cylinder head of the engine 1 is provided with an intake valve Vi that opens and closes an intake port and an exhaust valve Ve that opens and closes an exhaust port for each cylinder. Each intake valve Vi and each exhaust valve Ve are opened and closed by a camshaft (not shown). A spark plug 7 for igniting the air-fuel mixture in the combustion chamber 3 is attached to the top of the cylinder head for each cylinder.

  The intake port of each cylinder is connected to a surge tank 8 serving as an intake manifold through an intake manifold. An intake pipe 13 that forms an intake manifold passage is connected to the upstream side of the surge tank 8, and an air cleaner 9 is provided at the upstream end of the intake pipe 13. The intake pipe 13 is provided with an air flow meter 5 for detecting the amount of air flowing into the engine, that is, the amount of intake air, and an electronically controlled throttle valve 10 in order from the upstream side. An intake passage is formed by the intake port, the intake manifold, the surge tank 8 and the intake pipe 13.

  An injector for injecting fuel into an intake passage, particularly an intake port, that is, a fuel injection valve 12 is provided for each cylinder. The fuel injected from the injector 12 is mixed with intake air to form an air-fuel mixture. The air-fuel mixture is sucked into the combustion chamber 3 when the intake valve Vi is opened, compressed by the piston 4, and ignited and burned by the spark plug 7. It is done.

  On the other hand, the exhaust port of each cylinder is connected to an exhaust pipe 6 forming an exhaust collecting passage through an exhaust manifold. An exhaust passage is formed by the exhaust port, the exhaust manifold, and the exhaust pipe 6. The exhaust pipe 6 is provided with a catalyst composed of a three-way catalyst having oxygen storage capacity, that is, an upstream catalyst 11 and a downstream catalyst 19 in series on the upstream side and the downstream side. For example, the upstream catalyst 11 is disposed immediately after the exhaust manifold, and the downstream catalyst 19 is disposed under the floor of the vehicle.

On the upstream side and downstream side of the upstream catalyst 11, air-fuel ratio sensors that detect the air-fuel ratio of the exhaust gas based on the oxygen concentration, that is, the pre-catalyst sensor 17 and the post-catalyst sensor 18, are provided. As shown in FIG. 5, the pre-catalyst sensor 17 is a so-called wide-range air-fuel ratio sensor, can continuously detect the air-fuel ratio over a relatively wide range, and outputs a signal having a value proportional to the air-fuel ratio. On the other hand, the post-catalyst sensor 18 is a so-called O ₂ sensor, and has a characteristic (Z characteristic) in which the output value changes suddenly at the theoretical air-fuel ratio.

  The spark plug 7, the throttle valve 10, the injector 12, and the like described above are electrically connected to an electronic control unit (hereinafter referred to as ECU) 20 as control means. The ECU 20 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like, all not shown. In addition to the air flow meter 5, the pre-catalyst sensor 17, and the post-catalyst sensor 18, the ECU 20 includes a crank angle sensor 14 that detects the crank angle of the engine 1, and an accelerator opening that detects the accelerator opening, as shown in the figure. The degree sensor 15 and other various sensors are electrically connected via an A / D converter or the like (not shown). The ECU 20 controls the ignition plug 7, the injector 12, the throttle valve 10, etc. so as to obtain a desired output based on the detection values of various sensors, etc., and the ignition timing, fuel injection amount, fuel injection timing, throttle opening. Control the degree etc.

  The catalysts 11 and 19 simultaneously purify NOx, HC and CO with high efficiency when the air-fuel ratio A / F of the exhaust gas flowing into the catalysts 11 and 19 is the stoichiometric air-fuel ratio (stoichiometric, for example, A / Fs = 14.6). Accordingly, in accordance with this characteristic, the ECU 20 adjusts the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 3 (specifically, so that the air-fuel ratio of the exhaust gas flowing into the catalysts 11 and 19 matches the stoichiometry during normal operation of the engine. The amount of fuel injected from the injector 12 is feedback-controlled based on the output of the pre-catalyst sensor 17.

Here, the upstream catalyst 11 to be subjected to abnormality diagnosis will be described in more detail. The downstream catalyst 19 is configured in the same manner as the upstream catalyst 11. As shown in FIG. 2, in the catalyst 11, a coating material 31 is coated on the surface of a carrier base (not shown), and a large number of particulate catalyst components 32 are dispersed and supported on the coating material 31. It is exposed inside the catalyst 11. The catalyst component 32 is mainly composed of a noble metal such as Pt or Pd, and serves as an active point for reacting exhaust gas components such as NOx, HC and CO. On the other hand, the coating material 31 plays the role of a promoter that promotes the reaction at the interface between the exhaust gas and the catalyst component 32 and includes an oxygen storage component that can absorb and release oxygen in accordance with the air-fuel ratio of the atmospheric gas. The oxygen storage component is made of, for example, cerium dioxide CeO ₂ or zirconia. Note that “absorption” or “adsorption” may be used in the same meaning as “occlusion”.

  For example, if the atmospheric gas in the catalyst is leaner than the stoichiometric air-fuel ratio, the oxygen storage component present around the catalyst component 32 absorbs oxygen from the atmospheric gas, and as a result, NOx is reduced and purified. On the other hand, when the atmospheric gas in the catalyst is richer than the stoichiometric air-fuel ratio, oxygen stored in the oxygen storage component is released, and the released oxygen oxidizes and purifies HC and CO.

  Due to this oxygen absorption / release action, even if the air-fuel ratio varies somewhat with respect to stoichiometry during normal stoichiometric air-fuel ratio control, this variation can be absorbed.

  Incidentally, in the new catalyst 11, as described above, a large number of catalyst components 32 are evenly distributed, and the contact probability between the exhaust gas and the catalyst component 32 is maintained high. However, when the catalyst 11 deteriorates, some of the catalyst components 32 are lost, and some of the catalyst components 32 are baked and solidified by exhaust heat (see broken lines in the figure). If it becomes like this, the contact probability of exhaust gas and the catalyst component 32 will fall, and it will become the cause of reducing a purification rate. In addition to this, the amount of the coating material 31 existing around the catalyst component 32, that is, the amount of the oxygen storage component decreases, and the oxygen storage capacity itself decreases.

Thus, there is a correlation between the degree of deterioration of the catalyst 11 and the degree of decrease in the oxygen storage capacity of the catalyst 11. Therefore, in the present embodiment, the deterioration degree of the upstream catalyst 11 is detected by detecting the oxygen storage capacity of the upstream catalyst 11 that has a particularly large influence on the emission, and the abnormality of the upstream catalyst 11 is diagnosed. Here, the oxygen storage capacity of the catalyst 11 is represented by the size of the oxygen storage capacity (OSC; O ₂ Storage Capacity, the unit is g), which is the maximum amount of oxygen that the current catalyst 11 can store.

  The catalyst abnormality diagnosis of the present embodiment is basically based on the Cmax method described above. In the abnormality diagnosis, the active air-fuel ratio control is executed by the ECU 20. That is, the ECU 20 changes the air-fuel ratio of the exhaust gas supplied to the catalyst 11, specifically, the air-fuel ratio of the air-fuel mixture in the combustion chamber 3 alternately and richly and leaning centered on the stoichiometric A / Fs and actively. Switch minutes.

  The abnormality diagnosis is executed when the engine 1 is in a steady operation and when the catalyst 11 is in the activation temperature range. The temperature of the catalyst 11 (catalyst bed temperature) may be detected directly using a temperature sensor, but in the case of the present embodiment, it is estimated from the operating state of the engine.

  For example, the ECU 20 estimates the temperature Tc of the catalyst 11 according to a predetermined map or function (hereinafter referred to as a map or the like) based on the intake air amount Ga detected by the air flow meter 5. Note that parameters other than the intake air amount Ga, such as the engine speed Ne, may be included in the parameters used for catalyst temperature estimation.

  Hereinafter, a method for measuring the oxygen storage capacity of the upstream catalyst 11 will be described with reference to FIGS. 3 and 4.

  In FIG. 3A, the broken line indicates the target air-fuel ratio A / Ft, and the solid line indicates the output of the pre-catalyst sensor 17 (however, the converted value to the pre-catalyst air-fuel ratio A / Ffr). In FIG. 3B, the solid line indicates the output of the post-catalyst sensor 18 (however, the output voltage Vr).

  As shown in the figure, before the time t1, the lean control is executed, the target air-fuel ratio A / Ft is set to the lean air-fuel ratio A / F1 (for example, 15.1), and the catalyst 11 includes the target air-fuel ratio A / Ft and the target air-fuel ratio A / Ft. An equal air-fuel ratio lean gas is supplied. At this time, the catalyst 11 continues to occlude oxygen. However, when the oxygen is occluded until it is saturated, that is, full, oxygen cannot be occluded. As a result, the lean gas passes through the catalyst 11 and flows out downstream of the catalyst 11. When this happens, the output of the post-catalyst sensor 18 changes to the lean side, and at the time t1 when the output voltage Vr reaches a predetermined lean determination value VL (for example, 0.21 V), the target air-fuel ratio A / Ft becomes the rich air-fuel ratio A / F. It is switched to Fr (eg, 14.1). Thus, rich control is started, and rich gas having an air-fuel ratio equal to the target air-fuel ratio A / Ft is supplied.

  When the rich gas is supplied, the catalyst 11 continues to release the stored oxygen. When the stored oxygen is eventually released from the catalyst 11, the catalyst 11 cannot release oxygen at that time, and the rich gas passes through the catalyst 11 and flows out downstream of the catalyst 11. When this happens, the output of the post-catalyst sensor 18 changes to the rich side, and at the time t2 when the output voltage Vr reaches a predetermined rich determination value VR (for example, 0.59 V), the target air-fuel ratio A / Ft becomes the lean air-fuel ratio A / It is switched to Fl. As a result, the lean control is started again, and a lean gas having an air-fuel ratio equal to the target air-fuel ratio A / Ft is supplied.

  When the catalyst 11 again stores oxygen until it is full and the output voltage Vr of the post-catalyst sensor 18 reaches the lean determination value VL, the target air-fuel ratio A / Ft is switched to the rich air-fuel ratio A / Fr at time t3. Rich control is started.

  In this way, every time the catalyst absorbs and releases oxygen or every time the output of the post-catalyst sensor 18 is reversed, the lean control and the rich control are alternately and repeatedly executed.

  While executing this active air-fuel ratio control, the oxygen storage capacity OSC of the catalyst 11 is measured by the following method.

  The larger the oxygen storage capacity of the catalyst 11, the longer the time during which oxygen can be stored or released. That is, when the catalyst has not deteriorated, the inversion period of the post-catalyst sensor output Vr (for example, the time from t1 to t2) becomes longer, and the inversion period becomes shorter as the deterioration of the catalyst proceeds.

  Therefore, using this fact, the oxygen storage capacity OSC is measured as follows. As shown in FIG. 4, immediately after the target air-fuel ratio A / Ft is switched to the rich air-fuel ratio A / Fr at time t1, the pre-catalyst air-fuel ratio A / Ff as an actual value is slightly delayed with the rich air-fuel ratio A / Ff. Switch to Fr. From the time t11 when the pre-catalyst air-fuel ratio A / Ff reaches the stoichiometric A / Fs to the time t2 when the post-catalyst sensor output Vr is next reversed, the oxygen storage capacity for each predetermined calculation cycle is obtained by the following equation (1). dOSC is sequentially calculated, and the oxygen storage capacity dOSC is sequentially accumulated from time t11 to time t2. Thus, the oxygen storage capacity OSC as the final integrated value during the rich control, that is, the amount of released oxygen indicated by OSCb in FIG. 4 is measured.

  Q is the fuel injection amount. When the air-fuel ratio difference ΔA / F is multiplied by the fuel injection amount Q, the air amount that is insufficient or excessive with respect to the stoichiometry can be calculated. σ is a constant representing the proportion of oxygen contained in air (about 0.23).

  Similarly, during lean control, the oxygen storage capacity, that is, the amount of stored oxygen indicated by OSCa in FIG. 4 is measured. Each time the rich control and the lean control are alternately performed, the released oxygen amount and the stored oxygen amount are alternately measured.

  If a plurality of measured values of released oxygen amount and occluded oxygen amount are obtained in this way, it is possible to determine whether the catalyst is normal or abnormal by the following method. However, the determination method described here is slightly different from the determination method of the present embodiment described later. For ease of understanding, here is a simpler example.

  First, the ECU 20 calculates an average value OSCav of the measured values of the released oxygen amount and the stored oxygen amount. The average value OSCav is compared with a predetermined determination value. In this embodiment, there are two types of determination values, a normal determination value α for determining normality and an abnormality determination value β for determining abnormality as shown in FIG. The normality determination value α is larger than the abnormality determination value β. The ECU 20 determines that the catalyst 11 is normal when the average value OSCav is equal to or greater than the normal determination value α, and determines that the catalyst 11 is abnormal when the average value OSCav is equal to or less than the abnormality determination value β. The ECU 20 also determines that the catalyst 11 is normal when the average value OSCav is less than the normal determination value α and greater than the abnormality determination value β. When it is determined that the catalyst is abnormal, it is preferable to activate a warning device (not shown) such as a check lamp in order to notify the user of the fact.

  In the above-described active air-fuel ratio control, the air-fuel ratio of the exhaust gas supplied to the catalyst is changed from lean to rich in response to the output of the post-catalyst sensor 18 being reversed from rich to lean or from lean to rich. Or switch from rich to lean. Therefore, if the responsiveness of the post-catalyst sensor 18 is deteriorated due to deterioration or failure, this has a considerable influence on the measured value of the oxygen storage capacity, which may cause a deterioration in diagnostic accuracy or cause a misdiagnosis. Become.

  That is, referring to FIG. 3, when the responsiveness of the post-catalyst sensor 18 deteriorates, the rich inversion time TR when the output Vr of the post-catalyst sensor 18 reverses from lean to rich and the output of the post-catalyst sensor 18 are rich. The lean reversal time TL when reversing from lean to lean becomes longer. As a result, the integrated time of the oxygen storage capacity dOSC for each calculation cycle becomes longer, and the oxygen storage capacity shifted to the normal side, which is larger than when the response is good, is measured. As a result, the diagnostic accuracy is deteriorated, and there is a possibility that an erroneous diagnosis in which an originally abnormal catalyst is erroneously determined to be normal may occur.

  Note that the rich inversion time TR and the lean inversion time TL are collectively referred to as the inversion time TRL. In the present embodiment, the rich reversal time TR is the time until the post-catalyst sensor output Vr changes from the lean determination value VL to the rich determination value VR, and the lean reversal time TL is the rich post-catalyst sensor output Vr. It means the time until the judgment value VR changes to the lean judgment value VL. However, other definitions are possible.

FIG. 7 is a graph for explaining the influence of whether the response of the post-catalyst sensor 18 is good or bad on the oxygen storage capacity measurement value OSC. Points P _{1 to} P ₅ and line L in the figure show the transition of the measured oxygen storage capacity OSC when the responsiveness of the post-catalyst sensor 18 gradually deteriorates for the catalyst at the same abnormal level.

First, when to have no good response of the post-catalyst sensor 18 normally, as shown at point P _1, the oxygen storage capacity measured value OSC is smaller than the abnormality determination value beta. Therefore, the catalyst is accurately determined to be abnormal.

However, as the post-catalyst sensor 18 deteriorates, the oxygen storage capacity measurement value OSC becomes larger than the abnormality determination value β as indicated by points P ₂ , P ₃ , P ₄ , and P ₅ , and the catalyst is erroneously normal. It is determined.

In this case, as in the point P _5, when the response of the post-catalyst sensor 18, such as too deteriorated, the post-catalyst sensor 18 by the abnormality diagnosis of the air-fuel ratio sensor alone as described in the prior art Can be regarded as abnormal, and the measured value of the oxygen storage capacity itself can be regarded as abnormal. However, when the response deterioration is relatively mild such that the sensor abnormality cannot be diagnosed even by the abnormality diagnosis of the air-fuel ratio sensor alone as in points P _{2 to} P ₄ , the measured value of the oxygen storage capacity itself As a result, an erroneous determination that the catalyst is normal occurs.

Accordingly, the present embodiments also aim to accurately identify normal or abnormal catalysts even for relatively mild sensor response deterioration such as the point P ₂ to P _4.

  On the other hand, FIG. 6 is a graph showing the relationship between the catalyst temperature Tc and the measured oxygen storage capacity OSC for a plurality of catalysts having different degrees of deterioration. Here, it is assumed that the responsiveness of the post-catalyst sensor 18 is normal.

  As shown in the figure, a catalyst that shows a large measured value OSC that is greater than or equal to the normal determination value α, such as a new catalyst, is accurately determined to be normal. A catalyst that shows only a small measured value OSC that is equal to or less than the abnormality determination value β is also accurately determined as abnormal.

  On the other hand, a catalyst that shows a measured value OSC that is less than the normal determination value α and greater than the abnormality determination value β, that is, an intermediate catalyst, is not inherently abnormal and should be determined to be normal. However, some of the intermediate catalysts exhibit a measured value OSC that is slightly larger than the abnormality determination value β. Therefore, it is necessary to accurately distinguish between such a normal intermediate catalyst and an abnormal catalyst that merely shows a measured value OSC that is slightly larger than the abnormality determination value β due to a deterioration in the response of the post-catalyst sensor 18. is there. That is, it is necessary to accurately distinguish the catalyst in the vicinity of the boundary between normal and abnormal (criteria = abnormal determination value β).

  Therefore, in this embodiment, it is first determined (identified) whether the catalyst is clearly normal. If it cannot be determined as normal, it is determined whether or not the catalyst is an obvious intermediate catalyst. In order to discriminate between the intermediate catalyst near the criteria and the abnormal catalyst when it cannot be determined as an obvious intermediate catalyst, the influence of the response of the post-catalyst sensor 18 on the oxygen storage capacity measurement value OSC is removed or eliminated. Make corrections. Then, the corrected oxygen storage capacity measurement value OSC ′ is compared with the abnormality determination value β to determine whether the catalyst is normal or abnormal.

  By performing the correction for removing the influence of the responsiveness of the post-catalyst sensor 18, an accurate oxygen storage capacity measurement value OSC can be obtained even when the post-catalyst sensor 18 is relatively mildly deteriorated in responsiveness as described above. Therefore, the normality / abnormality of the catalyst can be accurately diagnosed. Further, before the correction, it is determined in advance whether or not the catalyst is an obvious intermediate catalyst. If it cannot be determined that the catalyst is an obvious intermediate catalyst, correction is performed to identify the intermediate catalyst near the criteria and the abnormal catalyst. Thereby, the diagnostic accuracy near the criteria can be improved and misdiagnosis can be prevented.

  It should be noted that the step of determining whether the catalyst is clearly normal can be omitted.

  Hereinafter, a first embodiment of the abnormality diagnosis will be described. In the first embodiment, as shown in FIG. 6, in the intermediate catalyst, the ratio of the change amount of the oxygen storage capacity measurement value OSC to the change amount of the catalyst temperature Tc, that is, the change rate (line slope) is large. Thus, one of the features is to identify an obvious intermediate catalyst. This rate of change is greater for the intermediate catalyst than for the abnormal catalyst.

  FIG. 8 shows an abnormality diagnosis procedure executed by the ECU 20 according to the first embodiment.

  First, in step S101, it is determined whether a condition suitable for executing diagnosis, that is, an execution condition is satisfied. For example, the engine is in a steady operation state such that the fluctuation range between the intake air amount Ga detected by the air flow meter 5 and the engine rotational speed Ne calculated based on the output of the crank angle sensor 14 is within a predetermined range. If the upstream catalyst 11 and the catalyst front-rear sensors 17 and 18 are in the active state, the execution condition is satisfied. The execution condition is not limited to the example described here. If the execution condition is not satisfied, the process enters a standby state. If the execution condition is satisfied, the process proceeds to step S102.

  In step S102, the active air-fuel ratio control as described above is executed, and along with this execution, the oxygen storage capacity OSC of the upstream catalyst 11 is measured, and the inversion time TRL is further measured. Further, the catalyst temperature Tc at the time of the measurement is acquired.

  That is, with respect to the oxygen storage capacity OSC, the amount of released oxygen and the average value OSCav of the stored oxygen amount are calculated, and the average value OSCav is used as the current measured value. Hereinafter, the description will proceed by replacing “average value OSCav” with “measured value OSC”. The reversal time TRL is a plurality of rich reversal times TR measured each time the post-catalyst sensor output Vr is reversed to rich, and a plurality of reversal times TRL measured every time the post-catalyst sensor output Vr is reversed to lean. An average value with the lean inversion time TL is calculated, and the average value is set as the current inversion time TRL. Note that the oxygen storage capacity OSC and the inversion time TRL are not necessarily the average value of a plurality of values. For example, only one value may be representatively extracted from a plurality of values, and this value may be used as the current value.

  As for the catalyst temperature Tc, an estimated catalyst temperature at a predetermined time point during execution of the active air-fuel ratio control is acquired. The predetermined time point can be a start time, an intermediate time or an end time of the active air-fuel ratio control. Alternatively, it may be an average value of the estimated catalyst temperature within a predetermined period during execution of active air-fuel ratio control. Thus, the oxygen storage capacity OSC is measured in association with the estimated catalyst temperature Tc, and these data form a pair.

  Next, in step S103, the oxygen storage capacity measurement value OSC is compared with the normality determination value α. When OSC ≧ α, the catalyst 11 can be clearly regarded as normal, so the routine proceeds to step S109, where it is determined that the catalyst 11 is normal. Thus, when the catalyst 11 is an obvious normal catalyst, this is identified first, and the subsequent steps are omitted, so that the diagnostic process can be simplified.

On the other hand, if OSC <α, it is determined in steps S104 and S105 whether the catalyst 11 is an obvious intermediate catalyst.
First, in step S104, it is determined whether there is a value of the oxygen storage capacity OSC measured in the past for different catalyst temperatures. Specifically, it is determined whether or not there is a value of the oxygen storage capacity OSC that is measured most recently in time for a catalyst temperature region different from the current time.
This will be described. As shown in FIG. 9, the catalyst temperature Tc is divided into a plurality of regions in advance as indicated by I, II, and III in the figure. Further, the data A, B, C, and D form a pair of the oxygen storage capacity measurement value OSC and the catalyst temperature region to which the estimated catalyst temperature Tc belongs. When the current data is A in the area III, the data B acquired at the time of the previous diagnosis belongs to the same area III, and thus is not the latest data in step S104. Since the data C acquired at the time of the previous diagnosis belongs to a different region II and is closest in time, it is regarded as the latest data. Although the data D acquired at the time of the diagnosis three times before belongs to a different region I, it is not the latest data because it is not the latest in time.

  In another example shown in FIG. 10, the current data is A in the area III. Since the previous data B belongs to the same region III, it is not the latest data. The data C two times before belongs to a different area I and is the latest in time, and is therefore the latest data. The data D three times before belongs to a different area II and is closer to the current area III than the data C two times before, but is not the latest data because it is not closest in time.

  In step S104, it is determined whether there is such latest data. Since the purpose is to determine the rate of change of the catalyst in the current deteriorated state, it is preferable to set a predetermined time limit in the immediate vicinity of time. For example, the latest data may be extracted only in data before a predetermined trip (for example, 20 trips) or a predetermined number of times (for example, 20 times).

  The catalyst temperature does not necessarily have to be divided into a plurality of regions. If it is past data, it is not always necessary to make it the latest data in time. For example, the data may be one to several times older than the latest data.

  When it is determined in step S104 that there is no latest data, the process returns to step S101, and steps S101 to S104 are repeatedly executed until the latest data is generated.

  On the other hand, if it is determined in step S104 that there is the latest data, the process proceeds to step S105, and the difference ΔOSC between the current oxygen storage capacity measurement value OSC and the oxygen storage capacity measurement value OSCp related to the latest data is | OSC−OSCp. | Is calculated, and this difference ΔOSC is compared with a predetermined intermediate determination value γ.

  That is, when the catalyst is an obvious intermediate catalyst, as shown in FIG. 6, the difference ΔOSC between measured values in different catalyst temperature regions becomes large. On the other hand, when the catalyst is not an obvious intermediate catalyst, the difference ΔOSC becomes small. Therefore, by comparing this difference ΔOSC with the intermediate determination value γ, it is possible to identify whether or not the catalyst is an obvious intermediate catalyst.

  Here, the difference ΔOSC is simply compared with a certain intermediate determination value γ. However, the difference ΔOSC changes depending on the difference in catalyst temperature between the current data and the latest data, specifically, the temperature difference between the catalyst temperature regions. For this reason, the intermediate determination value γ may be variably set based on the temperature difference. Furthermore, a ratio obtained by dividing the difference ΔOSC by the catalyst temperature difference may be compared with a certain intermediate determination value γ. Thus, it becomes possible to improve the identification accuracy of the clear intermediate catalyst.

  In step S105, when ΔOSC ≧ γ, the catalyst can be regarded as an obvious intermediate catalyst. Therefore, the process proceeds to step S109, and the catalyst 11 is determined to be normal.

  On the other hand, when ΔOSC <γ in step S105, the catalyst cannot be regarded as an obvious intermediate catalyst and may show normality due to the influence of the sensor response, so the process proceeds to step S106 and the oxygen storage capacity measurement value The OSC is corrected to remove the influence of the responsiveness of the post-catalyst sensor 18.

  FIG. 11 shows the result of examining the relationship between the time constant T (ms) of the post-catalyst sensor 18 and the rich inversion time TR (s). The time constant T is a parameter that represents the responsiveness of the post-catalyst sensor 18 and is a value unique to the post-catalyst sensor 18. The time constant T of the post-catalyst sensor 18 increases as the post-catalyst sensor 18 deteriorates and its responsiveness deteriorates. The illustrated example shows the results of examining a plurality of conditions in which the intake air amount Ga (g / s), which is a correlation value of the exhaust gas flow rate, and the time constant T, that is, the degree of sensor deterioration, are different.

  As understood, the rich inversion time TR tends to become longer as the time constant T of the post-catalyst sensor 18, that is, the degree of deterioration increases. Further, with respect to the value of the rich inversion time TR with respect to the same time constant T, there is a variation width corresponding to a range between two solid lines depending on the intake air amount Ga, that is, the exhaust gas flow rate. A similar trend is assumed to exist for the lean inversion time TL.

  Therefore, in view of this result, in the present embodiment, the correlation between the time constant T and the rich inversion time TR as shown by the broken line in FIG. 11, particularly the correlation at the center of the variation width, is a map or function (hereinafter referred to as a map or the like). Is stored in the ECU 20 in advance. Then, the ECU 20 calculates a time constant T corresponding to the inversion time TRL measured in step S102 from a map or the like.

  Next, a correction coefficient K corresponding to the time constant T is calculated from a map as shown in FIG. The correction coefficient K is corrected by multiplying the current oxygen storage capacity measurement value OSC. The corrected oxygen storage capacity measurement value is represented by OSC ′.

In the results of FIG. 11, the time constant is inverted time TRL is substantially constant in the range of 0 to T _1. This range is obtained when the post-catalyst sensor 18 has a very good response (for example, a new one). Correspondingly, in the map or the like in FIG. 12, the time constant correction coefficient K when the 0 to T ₁ is a 1, no correction is substantially performed. This is because there is no influence of sensor response delay on the oxygen storage capacity measurement value OSC.

On the other hand, the results of FIG. 11, time constant when the above T _1, also increases reversal time TRL As increase in the time constant T. Correspondingly, the map or the like in FIG. 12, time constant when the T ₁ or more, the correction coefficient K as the increase of the time constant T is reduced from 1. As a result, the oxygen storage capacity measurement value OSC can be corrected to the decreasing side as the response delay of the sensor increases, and the influence of the sensor response can be eliminated.

  As can be seen from the results of FIG. 11, since all of the rich inversion time TR, the lean inversion time TL, and the inversion time TRL are values correlated with the time constant T, the response of the post-catalyst sensor 18 is similar to the time constant T. It can be said that this is a parameter representing Therefore, in this embodiment, the inversion time TRL is used as a parameter, the time constant T is indirectly obtained based on the inversion time TRL, and the correction coefficient K is finally obtained as a correction value. However, it is also possible to obtain the correction coefficient K directly from the inversion time TRL. It is also possible to detect the time constant T itself by other methods and obtain the correction value based on the time constant T.

  If the correction of the oxygen storage capacity measurement value OSC is executed in this way, the corrected oxygen storage capacity measurement value OSC ′ is then compared with the abnormality determination value β in step S107.

  When OSC '> β, the routine proceeds to step S109 where it is determined that the catalyst 11 is normal. On the other hand, when OSC ′ ≦ β, the routine proceeds to step S108, where it is determined that the catalyst 11 is abnormal. Since the influence of the responsiveness of the post-catalyst sensor 18 has already been removed, OSC ′ is the net oxygen storage capacity of the catalyst, and the normality / abnormality of the catalyst 11 can be accurately determined only by comparing OSC ′ with β. Can be determined.

  Next, a second embodiment of the abnormality diagnosis will be described. This second embodiment is characterized in that an obvious intermediate catalyst is identified based on the lean inversion time TL and the rich inversion time TR. More specifically, as shown in FIG. 13, an apparent intermediate catalyst is obtained by utilizing the relationship between the intake air amount Ga and the ratio of the lean inversion time TL and the rich inversion time TR, that is, the inversion time ratio H = TL / TR. Is one of the features.

  FIG. 14 shows an abnormality diagnosis procedure executed by the ECU 20 according to the second embodiment.

  First, in step S201, as in step S101, it is determined whether a diagnosis execution condition is satisfied. When the execution condition is not satisfied, the process enters a standby state. When the execution condition is satisfied, the process proceeds to step S202.

  In step S202, active air-fuel ratio control is executed as in step S102, and the oxygen storage capacity OSC of the upstream catalyst 11 is measured. Further, the lean inversion time TL and the rich inversion time TR are individually measured. Further, the intake air amount Ga at the time of the measurement is acquired.

  For the lean inversion time TL and the rich inversion time TR, the average value of the plurality of lean inversion times measured is the lean inversion time TL, and the average value of the plurality of rich inversion times measured is the rich inversion time TR. Note that it is not always necessary to use an average value of a plurality of values, and only a representative value may be used.

  As for the intake air amount Ga, the intake air amount detected by the air flow meter 5 at a predetermined time point during execution of the active air-fuel ratio control is acquired. The predetermined time point can be a start time, an intermediate time or an end time of the active air-fuel ratio control. Alternatively, it may be an average value of the intake air amount within a predetermined period during execution of active air-fuel ratio control.

  Next, in step S203, the oxygen storage capacity measurement value OSC is compared with the normality determination value α as in step S103. When OSC ≧ α, the routine proceeds to step S210, where it is determined that the catalyst 11 is normal.

On the other hand, if OSC <α, it is determined in steps S204 to S206 whether the catalyst 11 is an obvious intermediate catalyst.
As shown in FIG. 13, regarding the relationship between the intake air amount Ga and the reversal time ratio H = TL / TR, there is a difference as shown between the case of a normal catalyst and the case of an abnormal catalyst. Here, for both the normal catalyst and the abnormal catalyst, the reversal time ratio H tends to increase once and then decrease as the intake air amount Ga increases, that is, the exhaust gas flow rate increases. At this time, in the intake air amount range Ga1 to Ga2 corresponding to the high load operation, the reversal time ratio H of the normal catalyst is smaller than the reversal time ratio H of the abnormal catalyst, and the difference tends to gradually increase. It can be seen.

  The reason for this is that during high-load operation, the oxygen release reaction activity of the catalyst during rich control is improved compared to during low-load operation, the oxygen release amount increases, and the post-catalyst sensor output begins to reverse. This is considered to be because the time until the rich determination value VR is reached becomes longer, that is, the rich inversion time TR becomes longer. Further, it is considered that it takes time until the oxygen releasing ability of the catalyst is improved, the rich gas that has passed through the catalyst in an unreacted state is reduced, and the oxygen concentration of the gas discharged from the catalyst is lowered to the rich determination value VR.

  Therefore, as shown in FIG. 13, in the intake air amount range Ga1 to Ga2, a line S that defines an intermediate determination value δ located between the normal catalyst line and the abnormal catalyst line is determined in advance. S is used to identify obvious intermediate catalysts. That is, when the reversal time ratio H below the line S is obtained, the catalyst is determined as an obvious intermediate catalyst, and when the reversal time ratio H above the line S is obtained, the catalyst is not judged as an obvious intermediate catalyst. The correction as described above is executed.

Returning to FIG. 14, in step S204, it is determined whether or not the intake air amount Ga acquired in step S202 is in the range Ga1 ≦ Ga ≦ Ga2 corresponding to the high load operation.
If it is determined that it is not within this range, the process returns to step S201, the current diagnosis is stopped, and a standby state is reached.

  On the other hand, if it is determined that the value is within this range, the process proceeds to step S205, and an intermediate determination value δ corresponding to the intake air amount Ga acquired in step S202 is calculated. That is, as shown in FIG. 13, the line S changes in the decreasing direction as the intake air amount Ga increases. Therefore, an intermediate determination value δ corresponding to the intake air amount Ga is calculated from a map or the like that prescribes such a relationship.

  Next, in step S206, an inversion time ratio H = TL / TR is calculated from the lean inversion time TL and rich inversion time TR measured in step S202, and the inversion time ratio H is compared with the intermediate determination value δ. Is done.

  When TL / TR ≧ δ, since the catalyst can be regarded as an obvious intermediate catalyst, the routine proceeds to step S210, where it is determined that the catalyst 11 is normal.

  On the other hand, when TL / TR <δ, the catalyst cannot be regarded as an obvious intermediate catalyst and may show normality due to the influence of sensor response, so the process proceeds to step S207, and the same as step S106. Correction is performed.

  In step S208, the corrected oxygen storage capacity measurement value OSC ′ is compared with the abnormality determination value β. When OSC ′> β, the catalyst 11 is normal in step S210, and when OSC ′ ≦ β, the catalyst is determined in step S209. 11 is determined to be abnormal.

  Although the embodiment of the present invention has been described in detail above, various other embodiments of the present invention are conceivable. For example, the engine may be other than for automobiles, and may be a direct injection type or the like. In the above embodiment, the intake air amount is detected and used as the correlation value of the exhaust gas flow rate, but the exhaust gas flow rate may be directly detected and used.

  The present invention includes all modifications, applications, and equivalents included in the spirit of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

1 Engine 5 Air Flow Meter 6 Exhaust Pipe 7 Injector 11 Upstream Catalyst 17 Pre-Catalyst Sensor 18 Post-Catalyst Sensor 19 Downstream Catalyst 20 Electronic Control Unit (ECU)
OSC Oxygen storage capacity ΔOSC Difference K Correction coefficient α Normal determination value β Abnormal determination value γ Intermediate determination value δ Intermediate determination value Tc Catalyst temperature TL Lean inversion time TR Rich inversion time TRL Inversion time H Inversion time ratio Ga Intake air amount T Time constant

Claims (10)

An apparatus for diagnosing abnormality of a catalyst disposed in an exhaust passage of an internal combustion engine,
A post-catalyst sensor for detecting an exhaust air-fuel ratio downstream of the catalyst;
Catalyst temperature detection means for detecting or estimating the temperature of the catalyst;
In response to the output of the post-catalyst sensor being reversed to lean or rich, active air-fuel ratio control is executed to switch the air-fuel ratio of the exhaust gas supplied to the catalyst to rich or lean alternately and actively. Fuel ratio control means;
With the execution of the active air-fuel ratio control, measuring means for measuring the oxygen storage capacity of the catalyst in association with the detected or estimated catalyst temperature,
First determination means for determining whether or not the catalyst is normal based on the difference between the value of the oxygen storage capacity measured this time by the measurement means and the value of the oxygen storage capacity measured in the past for different catalyst temperatures. When,
A correction means for correcting the value of the oxygen storage capacity measured this time based on a parameter representing the response of the post-catalyst sensor when the first determination means does not determine normality;
Second determination means for comparing the corrected oxygen storage capacity value with a predetermined abnormality determination value to determine whether the catalyst is normal or abnormal;
A catalyst abnormality diagnosis device comprising: A third determination means for determining whether or not the catalyst is normal by comparing the value of the oxygen storage capacity measured by the measurement means with a predetermined normal determination value;
2. The catalyst abnormality diagnosis device according to claim 1, wherein the first determination unit performs a determination based on the difference when the third determination unit does not determine that the first determination unit is normal. 3. The measuring means measures the oxygen storage capacity in association with one of the plurality of preset catalyst temperature regions to which the detected or estimated catalyst temperature belongs,
The first determination means uses the value of the oxygen storage capacity measured most recently for different catalyst temperature ranges as the value of the oxygen storage capacity measured in the past for the different catalyst temperatures. Or the catalyst abnormality diagnosis device according to 2; An apparatus for diagnosing abnormality of a catalyst disposed in an exhaust passage of an internal combustion engine,
A post-catalyst sensor for detecting an exhaust air-fuel ratio downstream of the catalyst;
In response to the output of the post-catalyst sensor being reversed to lean or rich, active air-fuel ratio control is executed to switch the air-fuel ratio of the exhaust gas supplied to the catalyst to rich or lean alternately and actively. Fuel ratio control means;
In accordance with the execution of the active air-fuel ratio control, measuring means for measuring the oxygen storage capacity of the catalyst,
An inversion time measuring means for measuring a lean inversion time and a rich inversion time when the post-catalyst sensor output is inverted to lean and rich respectively;
First determination means for determining whether or not the catalyst is normal based on a lean inversion time and a rich inversion time measured by the inversion time measuring means;
A correction means for correcting the value of the oxygen storage capacity measured this time based on a parameter representing the response of the post-catalyst sensor when the first determination means does not determine normality;
Second determination means for comparing the corrected oxygen storage capacity value with a predetermined abnormality determination value to determine whether the catalyst is normal or abnormal;
A catalyst abnormality diagnosis device comprising: A third determination means for determining whether or not the catalyst is normal by comparing the value of the oxygen storage capacity measured by the measurement means with a predetermined normal determination value;
5. The catalyst abnormality according to claim 4, wherein the first determination unit executes a determination based on the lean inversion time and the rich inversion time when the third determination unit does not determine that the normal determination is normal. Diagnostic device. 6. The catalyst according to claim 4, wherein the first determination unit determines whether or not the catalyst is normal by comparing a ratio of the lean inversion time and the rich inversion time with a predetermined value. Abnormality diagnosis device. A detection means for detecting a flow rate of the exhaust gas supplied to the catalyst or a correlation value thereof;
The catalyst abnormality diagnosis apparatus according to claim 6, wherein the first determination unit sets the predetermined value based on an exhaust gas flow rate detected by the detection unit or a correlation value thereof. The catalyst abnormality diagnosis device according to claim 7, wherein the first determination unit performs the determination when the exhaust gas flow rate detected by the detection unit or a correlation value thereof is within a predetermined range. 9. The catalyst abnormality diagnosis device according to claim 1, wherein the parameter representing the response of the post-catalyst sensor is an inversion time of the post-catalyst sensor output. The catalyst abnormality diagnosis device according to any one of claims 1 to 8, wherein the parameter indicating the responsiveness of the post-catalyst sensor is a time constant of the post-catalyst sensor.

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