JP5212826B2 - Catalyst abnormality diagnosis device - Google Patents

Description

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

For example, in an internal combustion engine for a vehicle, 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). This is because 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 it becomes lean, the exhaust gas is exhausted. Excess oxygen present in the gas is adsorbed and held, and when the air-fuel ratio of the catalyst inflow exhaust gas becomes smaller than the stoichiometric, that is, becomes rich, the adsorbed and held 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 stoichiometry. However, the air-fuel ratio shift can be absorbed by the oxygen storage / release action of the three-way catalyst.

  On the other hand, when the catalyst deteriorates, the purification efficiency of the catalyst decreases. There is a correlation between the degree of deterioration of the catalyst and the degree of reduction of the oxygen storage capacity because they are reactions through noble metals. Therefore, it is possible to detect that the catalyst has deteriorated by detecting that the oxygen storage capacity has decreased. In general, active air-fuel ratio control that switches the air-fuel ratio upstream of the catalyst alternately between rich and lean is performed, and the oxygen storage capacity of the catalyst is measured along with the execution of this active air-fuel ratio control to diagnose catalyst deterioration. The so-called method (so-called Cmax method) is employed.

  Incidentally, the air-fuel ratio switching of the active air-fuel ratio control is performed at the timing when the output of the post-catalyst sensor, which is the air-fuel ratio sensor on the downstream side of the catalyst, reaches a predetermined judgment value. Decreases, and the value of the oxygen storage capacity larger than the true value tends to be measured. In this case, there is a problem that a deteriorated catalyst is erroneously diagnosed as normal, and it is necessary to take measures against this problem.

  As one of the countermeasures, Patent Document 1 discloses that the determination value of the post-catalyst sensor output is corrected according to the parameter value correlated with the deterioration degree of the post-catalyst sensor to eliminate the influence of the deterioration of the post-catalyst sensor. Technology is disclosed.

JP 2008-31901 A

  The technique described in Patent Document 1 is also effective in preventing the above-described misdiagnosis, but the following problems still remain.

  That is, in the technique described in Patent Document 1, the degree of deterioration of the post-catalyst sensor is estimated based on the travel distance of the vehicle on which the internal combustion engine is mounted, but there is a possibility that a misdiagnosis cannot be avoided depending on the estimation accuracy. . Further, if the post-catalyst sensor has an abnormality such as poor responsiveness from the beginning due to manufacturing variations or the like, correction based on the degree of deterioration of the post-catalyst sensor cannot be performed, and it is difficult to avoid misdiagnosis.

  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 capable of preventing erroneous diagnosis due to deterioration or abnormality of the post-catalyst sensor.

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 air-fuel ratio of exhaust gas downstream of the catalyst;
Active air-fuel ratio control means for executing active air-fuel ratio control for alternately switching the air-fuel ratio upstream of the catalyst between rich and lean in response to the output of the post-catalyst sensor being inverted;
Measuring means for measuring the oxygen storage capacity of the catalyst in accordance with execution of the active air-fuel ratio control;
Based on a plurality of measurement values measured by the measurement means, a calculation means for calculating an average value of these measurement values and a parameter indicating the degree of variation of the measurement values;
A determination unit that determines abnormality of the catalyst based on the average value and the parameter calculated by the calculation unit;
There is provided a catalyst abnormality diagnosis device characterized by comprising:

  As a result of diligent research, the present inventors have found that the degree of variation in the measured value of oxygen storage capacity is closely related to the deterioration or abnormality of the post-catalyst sensor, and to create the present invention using this fact. It came. When the oxygen storage capacity is measured a plurality of times, the operating state of the engine is usually different for each measurement time, so the degree of activity of the catalyst is different and the oxygen storage capacity measurement value varies. At this time, the smaller the deterioration (the larger the oxygen storage capacity) of the catalyst, the larger the variation, and the larger the parameter indicating the degree of variation in the oxygen storage capacity measurement value. On the other hand, when the post-catalyst sensor is deteriorated, the measured value of the oxygen storage capacity becomes larger than when there is no deterioration. However, since the true oxygen storage capacity of the catalyst does not change, the variation of the oxygen storage capacity measurement value is small, and the parameter indicating the degree of variation is small.

  Therefore, if this characteristic is used, the catalyst is considered while taking into account the presence or absence of deterioration of the post-catalyst sensor based on the average value of a plurality of measured values when the oxygen storage capacity is measured a plurality of times and the parameter indicating the degree of variation. Can be diagnosed with high accuracy. This makes it possible to prevent the aforementioned erroneous diagnosis.

  Preferably, the determination unit also determines abnormality of the post-catalyst sensor based on the average value calculated by the calculation unit and the parameter. Thereby, the abnormality diagnosis of the post-catalyst sensor can be simultaneously performed using the above characteristics.

  Preferably, the catalyst abnormality diagnosis device further includes index value calculation means for calculating an index value of the degree of variation of the measured value based on an operating state of the internal combustion engine, and the determination means is calculated by the index value calculation means. The determination is performed when the calculated index value is greater than a predetermined value, and the determination is not performed when the index value calculated by the index value calculation means is less than or equal to the predetermined value.

  When a plurality of oxygen storage capacities are measured under substantially the same engine operating condition, the variation in the measured values becomes small, and there is a possibility that the same result as when the post-catalyst sensor is deteriorated may be obtained. However, according to this preferred embodiment, the index value indicating the degree of variation of the oxygen storage capacity measurement value from another viewpoint is calculated based on the engine operating state. When the calculated index value is larger than the predetermined value, that is, when the degree of variation is large, abnormality determination is performed, and when the calculated index value is equal to or smaller than the predetermined value, that is, the variation When the condition is such that the degree becomes small, the abnormality determination is not executed. Thereby, diagnostic accuracy can be raised.

  Preferably, the catalyst abnormality diagnosis device further includes a delay unit that delays a measurement end timing for each inversion of the post-catalyst sensor output at the time of measurement by the measurement unit, and the measurement unit includes the time when the delay is executed and The oxygen storage capacity when not executed is measured, and the calculation means calculates the average value and the parameter based on these measurement values.

  As will be understood from the foregoing, it is desirable that the plurality of oxygen storage capacities be measured under conditions where these measured values vary to some extent. Therefore, this preferred embodiment delays the measurement end timing for each inversion of the post-catalyst sensor output, and forcibly creates such a variation condition. Thereby, the dispersion | variation in oxygen storage capacity measurement value is ensured and a diagnostic precision can be improved.

  In this case, preferably, the catalyst abnormality diagnosis device further includes index value calculation means for calculating an index value of the degree of variation of the measurement value based on an operating state of the internal combustion engine, and the delay means calculates the index value. The delay is executed when the index value calculated by the means is equal to or less than a predetermined value. As a result, even when the engine operating conditions are such that the degree of variation becomes small, the variation state can be secured by the delay.

  Preferably, the determination unit determines that the catalyst is normal when the average value is greater than a first predetermined value and the parameter is greater than a second predetermined value, and the average value is the first predetermined value. The catalyst is determined to be abnormal when: The catalyst and the post-catalyst sensor are determined to be abnormal when the average value is greater than the first predetermined value and the parameter is equal to or less than the second predetermined value. .

  Preferably, the parameter includes a variance value of the plurality of measurement values.

  Preferably, the index value calculation means calculates the index value based on a dispersion value of the intake air amount of the internal combustion engine and a dispersion value of the temperature of the catalyst.

  According to the present invention, it is possible to prevent an erroneous diagnosis due to deterioration or abnormality of the post-catalyst sensor.

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 for demonstrating the content of the active air fuel ratio control at the time of abnormality diagnosis. 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 figure which shows the delay pattern of the after-catalyst sensor. It is a figure which shows a diagnostic map. It is a flowchart which shows the procedure of the abnormality diagnosis process of this embodiment. It is a figure which shows another diagnostic map. It is a flowchart of the abnormality diagnosis process of a 1st modification. It is a flowchart of the abnormality diagnosis process of a 2nd modification. It is a flowchart of the abnormality diagnosis process of a 3rd modification.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing the configuration of the present embodiment. As shown in the figure, the internal combustion engine 1 generates power by burning a mixture of fuel and air inside a combustion chamber 3 formed in a cylinder block 2 and reciprocating a piston 4 in the combustion chamber 3. To do. The internal combustion engine 1 is a vehicular multi-cylinder engine (only one cylinder is shown), and is a spark ignition type internal combustion engine, more specifically, a gasoline engine.

  In the cylinder head of the internal combustion engine 1, an intake valve Vi for opening and closing the intake port and an exhaust valve Ve for opening and closing the exhaust port are provided 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 air collecting chamber via a branch pipe for each cylinder. 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. In the intake pipe 13, an air flow meter 5 for detecting the intake air amount (the amount of air flowing into the internal combustion engine) and an electronically controlled throttle valve 10 are incorporated in order from the upstream side. An intake passage is formed by the intake port, the surge tank 8 and the intake pipe 13.

  An injector (fuel injection valve) 12 that injects fuel into the intake passage, particularly into the intake port, 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 a branch pipe for each cylinder. These exhaust ports, branch pipes and exhaust pipe 6 form an exhaust passage. 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. On the upstream side and downstream side of the upstream catalyst 11 or immediately before and immediately after, an air-fuel ratio sensor for detecting the air-fuel ratio of exhaust gas, that is, a pre-catalyst sensor 17 and a post-catalyst sensor 18 are provided. The pre-catalyst sensor 17 is a so-called wide-range air-fuel ratio sensor, can continuously detect an 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 suddenly changes with the theoretical air-fuel ratio as a boundary. The output characteristics of the pre-catalyst sensor 17 and the post-catalyst sensor 18 are shown in FIG.

  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 internal combustion engine 1 and an accelerator that detects the accelerator opening, as shown in the figure. The opening 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 throttle valve 10, the injector 12, 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 ECU 20 feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 3 so that the air-fuel ratio detected by the pre-catalyst sensor 17, that is, the pre-catalyst air-fuel ratio A / Ff matches the target air-fuel ratio A / Ft. . On the other hand, the catalysts 11 and 19 simultaneously purify NOx, HC and CO simultaneously with high efficiency when the air-fuel ratio of the exhaust gas flowing into the catalyst 11 and 19 is the stoichiometric air-fuel ratio (stoichiometric, for example, A / Fs = 14.6). Therefore, the ECU 20 sets the target air-fuel ratio A / Ft equal to the stoichiometric air-fuel ratio during normal operation of the internal combustion engine so that the pre-catalyst air-fuel ratio A / Ff detected by the pre-catalyst sensor 17 matches the stoichiometric air-fuel ratio. Feedback control is performed on the amount of fuel injected from the injector 12. As a result, the air-fuel ratio of the exhaust gas flowing into the catalyst 11 is kept in the vicinity of the theoretical air-fuel ratio, and the maximum purification performance is exhibited in the catalyst 11.

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 material (not shown), and the coating material 31 is held in a state in which a large number of particulate catalyst components 32 are dispersedly arranged. The catalyst 11 is exposed inside. 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 capable of absorbing and releasing oxygen according to the air-fuel ratio of the atmospheric gas. The oxygen storage component is made of, for example, cerium dioxide CeO ₂ or zirconia. For example, if the atmosphere gas of the catalyst component 32 and the coating material 31 is richer than the stoichiometric air-fuel ratio, the oxygen stored in the oxygen storage component present around the catalyst component 32 is released, and as a result, the released oxygen As a result, unburned components such as HC and CO are oxidized and purified. On the contrary, when the atmosphere gas of the catalyst component 32 and the coating material 31 is leaner than the stoichiometric air-fuel ratio, the oxygen storage component present around the catalyst component 32 absorbs oxygen from the atmosphere gas, and as a result, NOx is reduced and purified. The

  By such an oxygen absorption / release action, three exhaust gas components such as NOx, HC and CO are simultaneously purified even if the pre-catalyst air-fuel ratio A / Ff slightly varies from the theoretical air-fuel ratio during normal air-fuel ratio control. can do. Therefore, in normal air-fuel ratio control, it is also possible to purify exhaust gas by causing the pre-catalyst air-fuel ratio A / Ff to oscillate minutely around the theoretical air-fuel ratio and repeat the oxygen absorption and release.

  By the way, in the catalyst 11 in the new state, as described above, a large number of fine particulate catalyst components 32 are uniformly distributed, and the contact probability between the exhaust gas and the catalyst component 32 is kept 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). In this case, the contact probability between the exhaust gas and the catalyst component 32 is lowered, and the purification rate is lowered. 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, the degree of deterioration of the catalyst 11 and the degree of decrease in the oxygen storage capacity of the catalyst 11 are in a correlation. 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. 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. When the abnormality of the catalyst 11 is diagnosed, active air-fuel ratio control is executed by the ECU 20. In the active air-fuel ratio control, the air-fuel ratio upstream of the catalyst 11, that is, the air-fuel ratio of the air-fuel mixture in the combustion chamber 3 and thus the air-fuel ratio of the exhaust gas supplied to the catalyst 11 borders a predetermined center air-fuel ratio A / Fc. Active (forced) and alternating between rich and lean. The air-fuel ratio when switched to the rich side is referred to as rich air-fuel ratio A / Fr, and the air-fuel ratio when switched to the lean side is referred to as lean air-fuel ratio A / Fl.

  The abnormality diagnosis of the catalyst 11 is executed during steady operation of the internal combustion engine 1 and when the catalyst 11 is in the active temperature range. Measurement of the temperature of the catalyst 11 (catalyst bed temperature) may be detected directly using a temperature sensor, but in the present embodiment, it is estimated from the operating state of the internal combustion engine. For example, the ECU 20 estimates the temperature Tc of the catalyst 11 using a preset map based on the intake air amount Ga detected by the air flow meter 5. It should be noted that parameters other than the intake air amount Ga, for example, the engine rotational speed Ne (rpm) may be included in the parameters used for the 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 FIGS. 3A and 3B, the output behavior of the pre-catalyst sensor 17 and the post-catalyst sensor 18 when the active air-fuel ratio control is executed is indicated by a solid line. In FIG. 3A, the target air-fuel ratio A / Ft generated inside the ECU 20 is indicated by a broken line. The output value of the pre-catalyst sensor 17 shown in FIG. 3A is a value converted to the pre-catalyst air-fuel ratio A / Ff. The output value of the post-catalyst sensor 18 shown in FIG. 3B is the output value itself, that is, the value of the output voltage Vr.

  As shown in FIG. 3A, the target air-fuel ratio A / Ft is centered on the theoretical air-fuel ratio A / Fs as the center air-fuel ratio, and then has a predetermined amplitude (rich amplitude Ar, Ar> 0) on the rich side. ) Separated by an air-fuel ratio (rich air-fuel ratio A / Fr) and an air-fuel ratio (lean air-fuel ratio A / Fl) separated from the air-fuel ratio by a predetermined amplitude (lean amplitude Al, Al> 0) on the lean side. And alternately. Following the switching of the target air-fuel ratio A / Ft, the pre-catalyst air-fuel ratio A / Ff as an actual value is also switched with a slight time delay with respect to the target air-fuel ratio A / Ft. From this, it will be understood that the target air-fuel ratio A / Ft and the pre-catalyst air-fuel ratio A / Ff are equivalent except that there is a time delay.

  In the illustrated example, the rich amplitude Ar and the lean amplitude Al are equal. For example, rich air-fuel ratio A / Fr = 14.1, lean air-fuel ratio A / Fl = 15.1, rich amplitude Ar = lean amplitude Al = 0.5. Compared with the normal air-fuel ratio control, the active air-fuel ratio control has a larger amplitude of the air-fuel ratio, that is, the values of the rich amplitude Ar and the lean amplitude Al are larger.

  The target air-fuel ratio A / Ft is switched in response to the output of the post-catalyst sensor 18 being inverted. Basically, the timing or timing at which the target air-fuel ratio A / Ft is switched is the same as the timing at which the output of the post-catalyst sensor 18 reverses from rich to lean, or from lean to rich. As shown in the figure, the output voltage Vr of the post-catalyst sensor 18 changes suddenly at the theoretical air-fuel ratio A / Fs. In order to determine the inversion timing of the output voltage Vr, that is, the timing at which the output voltage Vr is inverted to the rich side and the timing at which the output voltage Vr is inverted to the lean side, two inversion threshold values VR and VL relating to the output voltage Vr are determined in advance. ing. Here, VR is referred to as a rich determination value, and VL is referred to as a lean determination value. VR> VL, for example, VR = 0.59 (V) and VL = 0.21 (V). When the output voltage Vr changes to the lean side, that is, decreases and reaches the lean determination value VL, the output voltage Vr is considered to have been reversed to the lean side, and the post-catalyst air-fuel ratio A / Fr detected by the post-catalyst sensor 18 Is at least leaner than the stoichiometric air-fuel ratio. On the other hand, when the output voltage Vr changes to the rich side, that is, increases and reaches the rich determination value VR, it is considered that the output voltage Vr is reversed to the rich side, and the post-catalyst air-fuel ratio A / Fr is at least greater than the stoichiometric air-fuel ratio. Judged to be rich. As shown in FIG. 5, the rich determination value VR is a value that is larger (rich side) than the stoichiometric equivalent value Vst, and the lean determination value VL is a value that is smaller (lean side) than the stoichiometric equivalent value Vst. The stoichiometric air-fuel ratio is included in a narrow region Y between the air-fuel ratios corresponding to the rich determination value VR and the lean determination value VL (this is referred to as a transition region). The output voltage Vr can only detect whether the post-catalyst air-fuel ratio A / Fr is richer or leaner than the stoichiometric air-fuel ratio, and it is difficult to detect the absolute value of the post-catalyst air-fuel ratio A / Fr.

  As shown in FIGS. 3A and 3B, when the output voltage Vr of the post-catalyst sensor 18 changes from the rich side value to the lean side and becomes equal to the lean determination value VL (time t1), the target The air-fuel ratio A / Ft is switched from the lean air-fuel ratio A / Fl to the rich air-fuel ratio A / Fr. Thereafter, when the output voltage Vr of the post-catalyst sensor 18 changes from the lean side value to the rich side and becomes equal to the rich determination value VR (time t2), the target air-fuel ratio A / Ft is changed from the rich air-fuel ratio A / Fr. The lean air-fuel ratio A / Fl is switched. In this way, every time the output of the post-catalyst sensor 18 is inverted to lean or rich, the air-fuel ratio is actively switched to rich or lean.

  While executing this active air-fuel ratio control, the oxygen storage capacity OSC of the catalyst 11 is measured as follows, and abnormality of the catalyst 11 is determined.

  Referring to FIG. 3, the target air-fuel ratio A / Ft is set to the lean air-fuel ratio A / Fl before time t1, and the lean gas flows into the catalyst 11. At this time, the catalyst 11 continues to absorb oxygen, but when it fully absorbs oxygen, it can no longer absorb oxygen, and the lean gas flows through the catalyst 11 and flows downstream of the catalyst 11. When this happens, the post-catalyst air-fuel ratio A / Fr changes to the lean side, and when the output voltage of the post-catalyst sensor 18 reaches the lean determination value VL (t1), the target air-fuel ratio A / Ft becomes the rich air-fuel ratio A / Fr. Can be switched to.

  This time, rich gas flows into the catalyst 11. At this time, the oxygen stored in the catalyst 11 continues to be released from the catalyst 11. Therefore, the exhaust gas of the theoretical air-fuel ratio A / Fs flows out to the downstream side of the catalyst 11 and the post-catalyst air-fuel ratio A / Fr does not become rich, so the output of the post-catalyst sensor 18 is not reversed. When oxygen is continuously released from the catalyst 11, all of the stored oxygen is eventually released from the catalyst 11, and at that time, no more oxygen can be released, and the rich gas flows through the catalyst 11 and flows downstream of the catalyst 11. When this happens, the post-catalyst air-fuel ratio A / Fr changes to the rich side, and when the output voltage of the post-catalyst sensor 18 reaches the rich determination value VR (t2), the target air-fuel ratio A / Ft becomes the lean air-fuel ratio A / Fl. Can be switched to.

  As described above, the air-fuel ratio on the upstream side of the catalyst 11 is switched to a rich state in response to the post-catalyst sensor output Vr being reversed lean, and in response to the post-catalyst sensor output Vr being richly reversed. The air-fuel ratio on the upstream side of the catalyst 11 is switched to lean.

  The larger the oxygen storage capacity of the catalyst 11, the longer the time during which oxygen can be absorbed 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 air-fuel ratio A / Fs to the time t2 when the post-catalyst sensor output Vr next reverses, the oxygen at every predetermined minute time is obtained by the following equation (1). The storage capacity dOSC is calculated, and the oxygen storage capacity dOSC for each minute time is integrated from time t11 to time t2. Thus, in the reversal period during the rich control, the oxygen storage capacity OSC (in this case, the amount of released oxygen indicated by OSC1 in FIG. 4) is measured as the final integrated value.

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

  Similarly, the oxygen storage capacity (in this case, the stored oxygen amount indicated by OSC2 in FIG. 4) is measured even during the lean control in which the target air-fuel ratio A / Ft is lean. The target air-fuel ratio A / Ft is alternately switched between rich and lean, and the oxygen storage capacity is measured every time rich control and lean control are alternately performed. If a plurality of oxygen storage capacity values are obtained in this way, the average value OSCav is calculated.

  As shown in FIG. 4, the measurement of the oxygen storage capacity during lean control is performed after the target air-fuel ratio A / Ft is switched to the lean air-fuel ratio A / Fl at time t2, and then the pre-catalyst air-fuel ratio A / Ff. From time t21 when the air / fuel ratio reaches the stoichiometric air / fuel ratio A / Fs to time t3 when the target air / fuel ratio A / Ft reverses to the rich side next time, the oxygen storage capacity dOSC for each minute time is calculated by the previous equation (1), The oxygen storage capacity dOSC for each minute time is integrated. The final integrated value is the value of the oxygen storage capacity measured in the inversion period during the lean control. Ideally, the measured value of the oxygen storage capacity is approximately the same when releasing oxygen and storing oxygen.

  Next, a catalyst abnormality determination is made based on the average value OSCav of the oxygen storage capacity measurement values. The method will be described later. When it is determined that the catalyst is abnormal, it is preferable to activate a warning device such as a check lamp in order to notify the user of the fact.

  By the way, as described above, if the post-catalyst sensor 18 is deteriorated or abnormal, the responsiveness is lowered, and a value of the oxygen storage capacity larger than the true value is measured. There is a problem that diagnoses.

  That is, as shown in FIG. 6, when the post-catalyst sensor 18 is deteriorated or abnormal, the change or inversion of the post-catalyst sensor output Vr is delayed from the normal time. As the delay pattern, there are mainly a delay time delay pattern in which the change start timing is delayed and a time constant delay pattern in which the change speed is slow (gradient in the figure becomes gentle).

  As a result of the decrease in responsiveness as described above, the post-catalyst sensor output Vr is delayed in reversing to rich or lean, the accumulated time of the oxygen storage capacity dOSC for every minute time is increased, and the oxygen storage capacity larger than the true value is increased. The value is measured. The abnormality determination basically determines that the catalyst is normal when the oxygen storage capacity measurement value is larger than the predetermined abnormality determination value, so if a larger oxygen storage capacity value is measured, May erroneously determine that an abnormal catalyst having an oxygen storage capacity smaller than the abnormality determination value is normal.

  Therefore, it is necessary to prevent erroneous diagnosis in consideration of deterioration of the post-catalyst sensor 18 and the like.

  As a result of earnest research, the present inventors have found that the degree of variation in the measured value of the oxygen storage capacity is closely related to the deterioration or abnormality of the post-catalyst sensor 18, and this is used to prevent misdiagnosis. A method was developed. This will be described below.

  When the oxygen storage capacity is measured a plurality of times, the operating conditions of the vehicle and the engine are usually different for each measurement time, so the degree of catalyst activity is different and the oxygen storage capacity measurement value varies. At this time, the smaller the deterioration (the larger the oxygen storage capacity) of the catalyst, the larger the variation, and the larger the parameter indicating the degree of variation in the oxygen storage capacity measurement value. On the other hand, when the post-catalyst sensor 18 is deteriorated, the measured value of the oxygen storage capacity becomes larger than when there is no deterioration. However, since the true oxygen storage capacity of the catalyst does not change, the variation of the oxygen storage capacity measurement value is small, and the parameter indicating the degree of variation is small.

  Therefore, if this characteristic is used, the deterioration of the catalyst 11 is considered while considering the presence or absence of deterioration of the post-catalyst sensor 18 based on the average value and the degree of variation of the plurality of measured values when the oxygen storage capacity is measured a plurality of times. Diagnosis can be performed with high accuracy. This makes it possible to prevent the above-described erroneous diagnosis.

  Here, a plurality of measured values of the oxygen storage capacity will be described. When the above-described active air-fuel ratio control is performed once, a plurality of oxygen storage capacities OSC are measured on the rich side and the lean side, and the average value OSCav is obtained. This average value OSCav is treated as one measured value here and is represented by Cmax. That is, Cmax = OSCav. Then, if the active air-fuel ratio control and measurement are executed N times (N is an integer of 2 or more), N average values OSCav are obtained, and N measurement values Cmax are obtained. The average value of the N measurement values Cmax is represented by CmaxAve.

  On the other hand, regarding the degree of variation, in the present embodiment, a dispersion value is used as a parameter indicating the degree of variation and is represented by CmaxV. The variance value CmaxV is calculated by the following equation (2), and the variance value CmaxV increases as the degree of variation increases.

  Next, a catalyst abnormality determination is performed based on the average value CmaxAve and the dispersion value CmaxV. This abnormality determination is performed as shown in the diagnostic map in FIG.

  First, when the average value CmaxAve is greater than a predetermined abnormality determination value X and the variance value CmaxV is greater than a predetermined variance threshold Y, that is, when the average value CmaxAve and the variance value CmaxV are values belonging to the region A, the catalyst 11 is determined to be normal. At this time, a large oxygen storage capacity is measured, and since the measured value of the oxygen storage capacity varies greatly and it can be considered that there is no deterioration of the post-catalyst sensor 18, it is assumed that the measurement has been performed normally. Is determined.

  Further, when the average value CmaxAve is equal to or less than the abnormality determination value X, that is, when the average value CmaxAve is a value belonging to the region B, the catalyst 11 is determined to be deteriorated or abnormal regardless of the magnitude of the dispersion value CmaxV. At this time, even if the post-catalyst sensor 18 is deteriorated and the oxygen storage capacity is measured to be large, only a small value of the oxygen storage capacity is measured, so the catalyst 11 is determined to be deteriorated or abnormal.

  Further, when the average value CmaxAve is larger than the abnormality determination value X and the variance value CmaxV is equal to or less than the variance threshold value Y, that is, when the average value CmaxAve and the variance value CmaxV are values belonging to the region C, the catalyst 11 and the post-catalyst It is determined that both sensors 18 are deteriorated or abnormal. At this time, a large oxygen storage capacity is measured, but there is a possibility that deterioration in the post-catalyst sensor 18 or the like may occur due to a small variation in the measured value of the oxygen storage capacity. There is a possibility that a large oxygen storage capacity is measured due to the deterioration of the post-catalyst sensor 18 or the like. Therefore, since there is a possibility that the measurement has not been performed normally, it is determined that both the catalyst 11 and the post-catalyst sensor 18 are deteriorated or abnormal for completeness.

  In this way, the deterioration or abnormality of the post-catalyst sensor 18 can also be diagnosed. Further, since the diagnosis or abnormality of the catalyst 11 and the deterioration or abnormality of the post-catalyst sensor 18 can be distinguished to some extent, diagnosis accuracy can be improved.

  By the way, as shown in FIG. 6, there are two patterns of response delay of the post-catalyst sensor 18: dead time delay and time constant delay. According to the method of the present embodiment, the change in the output waveform is not evaluated, but the degree of variation in the measured value of the oxygen storage capacity is evaluated to detect deterioration of the post-catalyst sensor 18. It is possible to reliably detect deterioration or the like of the sensor 18.

  Even if the post-catalyst sensor is abnormal from the beginning, it is immediately reflected in the degree of variation in the measured value of the oxygen storage capacity, and the degree of variation becomes small. Therefore, it is possible to reliably detect such abnormality.

  Next, the procedure of abnormality diagnosis processing executed by the ECU 20 will be described with reference to FIG.

  First, in step S101, it is determined whether or not the number of measurements N of the oxygen storage capacity measurement value Cmax is greater than a predetermined value M. The predetermined value M is an arbitrary integer of 1 or more. When N ≦ M, the process enters a standby state. When N> M, the process proceeds to step S102. For example, if M = 4, the process proceeds to step S102 when the oxygen storage capacity is measured five times or more.

  In step S102, an average value CmaxAve of the N oxygen storage capacity measurement values Cmax is calculated.

  Next, the process proceeds to step S103, where the average value CmaxAve is compared with the abnormality determination value X. When CmaxAve ≦ X, the routine proceeds to step S109, where the catalyst 11 is determined to be deteriorated or abnormal (corresponding to the region B in FIG. 7).

  On the other hand, when CmaxAve> X, the routine proceeds to step S104, where the dispersion value CmaxV is calculated from the N oxygen storage capacity measurement values Cmax.

  Next, the process proceeds to step S105, where the variance value CmaxV is compared with the variance threshold value Y. When CmaxV> Y, the routine proceeds to step S106, where it is determined that the catalyst 11 is normal (corresponding to region A in FIG. 7).

  On the other hand, when CmaxV ≦ Y, the routine proceeds to step S107, where the catalyst 11 is determined to be deteriorated or abnormal, and the post-catalyst sensor 18 is determined to be deteriorated or abnormal in step S108 (corresponding to the region C in FIG. 7).

  Next, a modified example will be described.

  First, the first modification will be described. In the basic embodiment described above, when the average value CmaxAve is greater than the abnormality determination value X and the dispersion value CmaxV is equal to or less than the dispersion threshold value Y, the catalyst 11 and the post-catalyst sensor 18 are uniformly diagnosed as being deteriorated or abnormal. However, it is considered that there is a certain limit in the error of the oxygen storage capacity measurement value due to deterioration of the post-catalyst sensor 18 and the like, and when the average value CmaxAve is significantly larger than the abnormality determination value X, the deterioration of the post-catalyst sensor 18 A sufficiently large oxygen storage capacity exceeding the influence of the above is measured, and there may be no problem even if the catalyst 11 is diagnosed as normal.

  Therefore, in the first modification, in addition to the above-described abnormality determination value X, another abnormality determination value larger than this is set. Specifically, as shown in FIG. 9, the abnormality determination value X described above is replaced with a first abnormality determination value X1, and a second abnormality determination value X2 larger than this is set. The difference between the abnormality determination values X1 and X2 is a value corresponding to the upper limit of the error in the oxygen storage capacity measurement value due to deterioration of the post-catalyst sensor 18 or the like.

  Then, as shown in the drawing, the region C of the basic embodiment (FIG. 7) is divided into two, and the region below the second abnormality determination value X2 is the region C where the catalyst 11 and the post-catalyst sensor 18 are determined to be deteriorated or abnormal. A region larger than the second abnormality determination value X2 is defined as a region D where the catalyst 11 is determined to be normal. As a result, there is a possibility that the diagnosis accuracy can be further improved by taking into account the influence of deterioration of the post-catalyst sensor 18 in more detail.

  FIG. 10 shows a procedure of abnormality diagnosis processing according to the first modification. Note that the same steps as in the basic embodiment (FIG. 8) are simply replaced with reference numerals in the 200s, and description thereof is omitted.

  The difference from the basic embodiment is that the abnormality determination value X is replaced with the first abnormality determination value X1 in step S203 'corresponding to step S103, and step S210 is added.

  When CmaxV ≦ Y in step S205, the process proceeds to step S210, and the average value CmaxAve is compared with the second abnormality determination value X2. When CmaxAve> X2, the process proceeds to step S206, where it is determined that the catalyst 11 is normal (corresponding to region D in FIG. 9).

  On the other hand, when CmaxAve ≦ X2, the routine proceeds to step S207, where it is determined that the catalyst 11 is deteriorated or abnormal, and at step S208, the post-catalyst sensor 18 is determined to be deteriorated or abnormal (corresponding to region C in FIG. 9).

  Next, a second modification will be described. In the actual market, it is assumed that a plurality of oxygen storage capacities are measured under different operating conditions of the engine and the vehicle. However, a plurality of oxygen storage capacities may be measured under almost the same engine operating state if the engine operating state does not change, for example, when driving at a constant speed on a highway continues for a long time. If this happens, the variation in the measured value becomes small, and the same result as when the post-catalyst sensor 18 deteriorates may be caused, and the catalyst 11 and the post-catalyst sensor 18 may be erroneously diagnosed as abnormal.

  Therefore, in order to prevent such a misdiagnosis, it is determined whether or not a plurality of oxygen storage capacities have been measured under an engine operating state in which the oxygen storage capacity measurement values vary. Specifically, an index value indicating the degree of variation in the measured value of the oxygen storage capacity from another viewpoint is calculated or estimated based on the engine operating state. Then, when the calculated index value is larger than the predetermined value, abnormality determination is executed, and when the calculated index value is less than the predetermined value, abnormality determination is not executed.

  This will be described specifically. The magnitude of the oxygen storage capacity of the catalyst changes in accordance with the degree of deterioration thereof, the exhaust gas flow rate passing through the catalyst, that is, the intake air amount Ga as a substitute value thereof, and the catalyst temperature Tc. Therefore, the index value CmaxErr is defined as a function of the intake air amount Ga and the catalyst temperature Tc. In the case of the present embodiment, the index value CmaxErr is calculated by the following equation (3), where the dispersion value of the intake air amount Ga is Vga and the dispersion value of the catalyst temperature Tc is Vtc.

However, F and G are predetermined coefficients. The dispersion value Vga of the intake air amount and the dispersion value Vtc of the catalyst temperature are based on the intake air amount Ga and the catalyst temperature Tc detected or estimated for each measurement time, and are obtained from the same equation as shown in the previous equation (2). Calculated.

  If the engine operating state varies for each measurement time, the values of the intake air amount Ga and the catalyst temperature Tc for each measurement time vary, and thus the dispersion values Vga and Vtc increase, and the index value CmaxErr increases. On the contrary, if the engine operating state at each measurement time is substantially constant, the values of the intake air amount Ga and the catalyst temperature Tc at each measurement time do not vary, and the dispersion values Vga and Vtc become small, and the index value CmaxErr also decreases.

  As the engine operating state varies, the measured value of the oxygen storage capacity varies from measurement to measurement. Therefore, the index value CmaxErr is a value correlated with the degree of variation in the measured value of the oxygen storage capacity. Therefore, the index value CmaxErr is compared with the threshold value Z, and if CmaxErr> Z, it can be considered that the engine operating state is such that the measured oxygen storage capacity varies, and if CmaxErr ≦ Z, It can be considered that the engine operating state is not such that the measured storage capacity varies.

  If CmaxErr> Z, the oxygen storage capacity measurement value will vary, and at this time, the abnormality may be determined as usual. However, when CmaxErr ≦ Z, the oxygen storage capacity measurement value should not vary even if the combination of the normal catalyst and the normal sensor is used. Therefore, if the abnormality is determined as usual at this time, the oxygen storage capacity measurement value does not vary because there is no change in the engine operating state. Therefore, it may be judged that there is no variation and misdiagnosis may occur.

  Therefore, by not performing abnormality determination when CmaxErr ≦ Z, it is possible to improve diagnosis accuracy and prevent such erroneous diagnosis.

  FIG. 11 shows a procedure of abnormality diagnosis processing according to the second modification. Note that the same steps as in the basic embodiment (FIG. 8) are simply replaced with reference numerals in the 300s, and the description thereof is omitted.

  The difference from the basic embodiment is that step S310 and step S311 are added between step S301 corresponding to step S101 and step S302 corresponding to step S102.

  When N> M is reached in step S301, the process proceeds to step S310, and the index value CmaxErr is calculated. That is, the respective dispersion values Vga and Vtc are calculated from the data of the intake air amount Ga and the catalyst temperature Tc for N times, and the index value CmaxErr is calculated from the previous equation (3) based on these dispersion values Vga and Vtc.

  Next, in step S311, the calculated index value CmaxErr is compared with a threshold value Z. When CmaxErr> Z, it can be considered that the engine operating state is such that the measured value of the oxygen storage capacity varies, so that the routine proceeds to step S302 and thereafter, and abnormality determination is performed as usual.

  On the other hand, when CmaxErr ≦ Z, since it can be considered that the engine operation state is such that there is no variation in the oxygen storage capacity measurement value at each measurement time, the routine is immediately terminated to prevent erroneous determination.

  Next, a third modification will be described. As will be understood from the foregoing, it is desirable for the abnormality diagnosis of the present embodiment to measure a plurality of oxygen storage capacities under conditions where the oxygen storage capacity measurement values vary to some extent. In the second modified example, it is determined whether or not such a condition is satisfied. If not, the determination is not executed or is canceled.

  On the other hand, in the third modification, the measurement end timing for each inversion of the post-catalyst sensor output Vr is delayed or delayed to forcibly create such a variation condition. As a result, variation in the measured value of the oxygen storage capacity can be ensured, diagnostic accuracy can be improved, and erroneous diagnosis can be prevented.

  This delay or delay is preferably set to a rich determination value VR and a lean determination value VL that define the inversion timing of the post-catalyst sensor output Vr, as shown by a virtual line in FIG. This is done by changing to a leaner value VL ′. By doing so, the inversion timing of the post-catalyst sensor output Vr is delayed by D, and the accumulation or measurement end timing of the oxygen storage capacity is delayed by D. As compared with the case where no delay is performed, a larger oxygen storage capacity is measured, and the oxygen storage capacity measurement value varies.

  While changing the delay amount (preferably increasing), the delay may be executed a plurality of times, and the oxygen storage capacity may be measured each time. Only one of the rich side and the lean side may be delayed. It should be noted that even if the inversion timing is advanced, there is a possibility that the measured value may vary, so that the inversion timing may be advanced. In this case, it is preferable to change the rich determination value VR and the lean determination value VL to a lean value and a rich value, respectively.

  FIG. 12 shows a procedure of abnormality diagnosis processing according to the third modification. Note that the same steps as those in the basic embodiment (FIG. 8) are simply replaced with the 400s, and the description thereof is omitted.

  The difference from the basic embodiment is that step S410 and step S411 ′ are added between step S401 corresponding to step S101 and step S402 corresponding to step S102. S413 is added. Step S410 is the same as step S310 of the second modification (FIG. 11), and step S411 'is a modification of step S311 of the second modification. Thus, the example combined with the 2nd modification is shown here.

When N> M is reached in step S401, the process proceeds to step S410, and the index value CmaxErr is calculated. Next, in step S411 ′, it is determined whether the delay has been performed or whether CmaxErr> Z.
In step S411 ′, when CmaxErr> Z is satisfied, the process proceeds to step S402 and the abnormality determination is performed as usual. That is, in this case, since the variation is secured by the engine operating state, there is no problem even if the abnormality is determined as usual, and the process proceeds to step S402 and subsequent steps.

  On the other hand, when CmaxErr> Z is not satisfied in step S411 ′, that is, when CmaxErr ≦ Z, the process proceeds to step S412 to ensure variation, and the oxygen at the time when this delay is executed in step S413. The storage capacity Cmax is measured. As a result, the oxygen storage capacity measurement value Cmax that is forcibly dispersed is obtained. Here, only one oxygen storage capacity measurement value with delay added is obtained, but as described above, a plurality of oxygen storage capacity measurement values with different delays may be obtained.

  When the measurement is thus completed, the process returns to step S401 again.

  In actual operation, when N> M is first reached in step S401 (ie, N = M + 1), if step S411 ′ becomes no and the process proceeds to steps S412, S413, and S401, the Cmax measurement count N adds a delay. M + 2 including the measurement times at the time. Thereafter, in step S410, the index value CmaxErr is calculated from the data of the intake air amount Ga for M + 2 times and the catalyst temperature Tc.

  Next, when proceeding to step S411 ′, since this time is after the execution of delay, regardless of whether CmaxErr> Z is established or not, the process proceeds to step S402 and subsequent steps and abnormality determination is performed based on the measured oxygen storage capacity value Cmax for M + 2 times. Is done. In particular, in steps S402 and S404, the average value CmaxAve and the variance value CmaxV are calculated based on the measured value for one time when the delay is executed and the measured value for M + 1 times when the delay is not executed.

  In addition, although the example which combined the 2nd modification with the 3rd modification was shown here, the example of a 3rd modification independent is also possible. In this case, the “or CmaxErr> Z” portion of step S410 and step S411 ′ may be omitted.

  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 use and form of the internal combustion engine are arbitrary, and may be other than for vehicles, for example, a direct injection type or the like.

  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 Internal combustion engine 5 Air flow meter 6 Exhaust pipe 11 Upstream catalyst 12 Injector 17 Pre-catalyst sensor 18 Post-catalyst sensor 19 Downstream catalyst 20 Electronic control unit (ECU)
Vr After-catalyst sensor output Cmax Oxygen storage capacity measurement value CmaxAve Average value CmaxV Dispersion value CmaxErr Index value Ga Intake air amount Tc Catalyst temperature

Claims (9)

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 air-fuel ratio of exhaust gas downstream of the catalyst;
Active air-fuel ratio control means for executing active air-fuel ratio control for alternately switching the air-fuel ratio upstream of the catalyst between rich and lean in response to the output of the post-catalyst sensor being inverted;
Measuring means for measuring the oxygen storage capacity of the catalyst in accordance with execution of the active air-fuel ratio control;
Based on a plurality of measurement values measured by the measurement means, a calculation means for calculating an average value of these measurement values and a parameter indicating the degree of variation of these measurement values;
Determination means for determining whether the catalyst is normal or abnormal based on the average value and the parameter calculated by the calculation means;
Equipped with a,
The determination means determines that the catalyst is normal when the average value is greater than a first predetermined value and the parameter is greater than a second predetermined value, and when the average value is equal to or less than the first predetermined value. A catalyst abnormality diagnosis device characterized by determining that the catalyst is abnormal. The catalyst abnormality diagnosis apparatus according to claim 1, wherein the determination unit also determines abnormality of the post-catalyst sensor based on the average value calculated by the calculation unit and the parameter.   The determination means determines that the catalyst and the post-catalyst sensor are abnormal when the average value is greater than the first predetermined value and the parameter is equal to or less than the second predetermined value.
  The catalyst abnormality diagnosis device according to claim 2, wherein   The determination means has the average value larger than the first predetermined value and not larger than a third predetermined value larger than the first predetermined value and the parameter is not larger than the second predetermined value. The catalyst and the post-catalyst sensor are determined to be abnormal, and the catalyst is determined to be normal when the average value is greater than the third predetermined value and the parameter is equal to or less than the second predetermined value.
  The catalyst abnormality diagnosis device according to claim 2, wherein   Index value calculation means for calculating an index value of the degree of variation of the measured value based on the operating state of the internal combustion engine;
  The determination unit performs the determination when the index value calculated by the index value calculation unit is greater than a predetermined value, and when the index value calculated by the index value calculation unit is equal to or less than the predetermined value Do not perform the determination
  The catalyst abnormality diagnosis device according to any one of claims 1 to 4, wherein   A delay means for delaying a measurement end timing for each inversion of the post-catalyst sensor output during measurement by the measurement means;
  The measuring means measures the oxygen storage capacity when the delay is executed and when it is not executed,
  The calculation means calculates the average value and the parameter based on these measurement values.
  The catalyst abnormality diagnosis device according to any one of claims 1 to 4, wherein   Index value calculation means for calculating an index value of the degree of variation of the measured value based on the operating state of the internal combustion engine;
  The delay unit executes the delay when the index value calculated by the index value calculation unit is a predetermined value or less.
  The catalyst abnormality diagnosis device according to claim 6.   The parameter includes a variance value of the plurality of measurement values.
  The catalyst abnormality diagnosis device according to any one of claims 1 to 7, wherein   The index value calculation means calculates the index value based on a dispersion value of the intake air amount of the internal combustion engine and a dispersion value of the temperature of the catalyst.
  The catalyst abnormality diagnosis device according to claim 5 or 7, characterized in that

Images