JP2006183591A - Catalyst degradation diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst degradation diagnostic apparatus capable of accurately diagnosing a catalyst for degradation. <P>SOLUTION: This catalyst degradation diagnostic apparatus comprises an air-fuel ratio detection means on the upstream side of the catalyst, an oxygen concentration detection means on the downstream side of the catalyst, an oxygen amount calculation means calculating an oxygen amount released from the catalyst into an exhaust passage and an oxygen amount stored in the catalyst based on the detected air-fuel ratio and an oxygen concentration, a frequency defect determination means determining that the output frequency of the oxygen concentration detection means is abnormal when a difference between the calculated oxygen amount and the maximum oxygen amount calculated to date is equal to or higher than a first prescribed value and continuously setting on a frequency defect flag, and a catalyst degradation diagnostic means calculating the oxygen storage capacity of the catalyst by using the oxygen amount and, based on whether the frequency defect flag is on or not and the oxygen storage capacity, diagnosing the catalyst for degradation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a catalyst deterioration diagnosis apparatus.

Conventionally, by performing air-fuel ratio control that changes the A / F (air-fuel ratio) of air and fuel supplied to the internal combustion engine between rich (rich air-fuel ratio combustion state) and lean (lean combustion state), Deterioration diagnosis of the catalyst (exhaust purification catalyst) provided on the exhaust passage and evaluation of oxygen storage capacity (maximum oxygen storage amount) are performed. For example, an A / F sensor (air-fuel ratio sensor) is provided on the exhaust passage on the upstream side of the catalyst, and an oxygen sensor (O ₂ sensor) is provided on the exhaust passage on the downstream side. A deterioration diagnosis of the catalyst is performed based on the output of the sensor obtained by the execution.

  By the way, an oxygen sensor may generate an abnormal output during execution of air-fuel ratio control for diagnosing catalyst deterioration. For example, the oxygen sensor does not periodically invert the output, but at a timing deviating from the periodic timing, the oxygen sensor outputs a shorter time width than the normal state, and the output inversion of the oxygen sensor occurs abnormally ( Hereinafter, such an output state of the oxygen sensor is referred to as “periodic abnormality”). Such a periodic abnormality generated by the oxygen sensor is not caused by the oxygen storage and release of oxygen by the catalyst, but is caused by poor gas contact with the oxygen sensor or the output characteristics of the oxygen sensor. it is conceivable that.

  Normally, the deterioration diagnosis of the catalyst is performed in a situation where the above-described oxygen sensor cycle abnormality does not occur, or whether or not the oxygen sensor cycle abnormality has occurred is determined, and this determination is made. Deterioration diagnosis is performed. For example, Patent Document 1 discloses an apparatus that obtains oxygen storage capacity by executing air-fuel ratio control to switch the air-fuel ratio to rich or lean, and performs a catalyst deterioration diagnosis based on the obtained oxygen storage capacity. When the difference between the oxygen storage amount (corresponding to the oxygen release amount) obtained by setting the rich value and the oxygen storage amount obtained by setting the lean value is equal to or greater than a predetermined value, the deterioration diagnosis of the catalyst is performed. The technology to be discontinued is described. Further, Patent Document 2 describes a time until the output of the oxygen sensor is inverted from rich to lean (hereinafter, this time is also referred to as “inversion time”) and an inversion time until the output from lean to rich is inverted. A technique for performing a deterioration diagnosis of a catalyst when an average value becomes shorter than a predetermined time is described.

JP 2003-148136 A JP-A-5-106493

  However, the technique described in Patent Document 1 does not consider the oxygen storage amount obtained in the past, and compares only the oxygen storage amount obtained at present and the oxygen storage amount obtained immediately before. Since the deterioration diagnosis has been stopped, accurate deterioration diagnosis may not be performed. For example, even if the difference between the oxygen storage amount obtained this time and the oxygen storage amount obtained immediately before is small, both of these oxygen storage amounts may be abnormally small. In such a case, although the deterioration diagnosis is executed by the method of Patent Document 1, it is not preferable to execute the deterioration diagnosis because the actually obtained oxygen storage amount is abnormally small. Conversely, even if the difference between the oxygen storage amount obtained this time and the oxygen storage amount obtained immediately before is large, the oxygen storage amount obtained immediately before is abnormally small, and the oxygen storage amount obtained this time is normal. There can be. In such a case, the deterioration diagnosis is stopped by the method of Patent Document 1, but it is not preferable to stop the deterioration diagnosis because the oxygen storage amount obtained this time is actually normal.

  Furthermore, even in the technique described in Patent Document 2, the deterioration diagnosis of the catalyst is performed based only on the currently obtained inversion time, and the examination considering the inversion time obtained in the past has not been made. In some cases, an accurate deterioration diagnosis is not performed.

  The present invention has been made to solve such problems, and the object of the present invention is to determine abnormalities in the output of the oxygen sensor taking into account past results, and based on the determination results. An object of the present invention is to provide a catalyst deterioration diagnosis apparatus capable of accurately performing catalyst deterioration diagnosis.

  In one aspect of the present invention, the deterioration of the catalyst provided in the exhaust passage is performed by executing air-fuel ratio control that changes the air-fuel ratio of fuel and air supplied to the internal combustion engine between a rich state and a lean state. A catalyst deterioration diagnosis device that performs diagnosis detects and detects an air-fuel ratio detection means for detecting an air-fuel ratio in the exhaust passage on the upstream side of the catalyst, and an oxygen concentration in the exhaust passage on the downstream side of the catalyst. An oxygen concentration detecting means for outputting a value corresponding to the oxygen concentration; and based on the detected air-fuel ratio and oxygen concentration, the amount of oxygen released from the catalyst into the exhaust passage, and the catalyst occluded When the difference between the oxygen amount calculating means for calculating the oxygen amount and the calculated oxygen amount and the maximum oxygen amount calculated so far is equal to or greater than a first predetermined value, the oxygen concentration detecting means The output cycle is abnormal A periodic abnormality determining means that continues to set the periodic abnormality flag to ON, calculates the oxygen storage capacity of the catalyst using the oxygen amount, whether or not the periodic abnormality flag is on, and the oxygen storage capacity And a catalyst deterioration diagnosis means for performing a deterioration diagnosis of the catalyst based on the above.

  The catalyst deterioration diagnosis device is a device that performs deterioration diagnosis of the catalyst provided in the exhaust passage by changing the air-fuel ratio of the fuel and air supplied to the internal combustion engine between a rich state and a lean state. The air-fuel ratio detecting means (for example, A / F sensor) detects the air-fuel ratio in the exhaust passage upstream of the catalyst, and the oxygen concentration detecting means (for example, oxygen sensor) is in the exhaust passage downstream of the catalyst. Detect oxygen concentration. The oxygen amount calculation means calculates the amount of oxygen released from the catalyst into the exhaust passage and the amount of oxygen stored in the catalyst. The cycle abnormality determination means determines that the output of the oxygen concentration detection means is abnormal when the difference between the calculated oxygen amount and the maximum oxygen amount calculated so far is equal to or greater than a first predetermined value. , Set the cycle abnormality flag to ON. In other words, the cycle abnormality determination unit determines whether or not the output cycle of the oxygen concentration detection unit is abnormal in consideration of the oxygen amount calculated in the past. In addition, when the cycle abnormality flag is turned on, the cycle abnormality determination unit continuously turns on the cycle abnormality flag. This is because once a periodic abnormality occurs in the oxygen concentration detection means, there is a high possibility that a periodic abnormality will continue in the future.

  Then, the catalyst deterioration diagnosis means calculates the oxygen storage capacity of the catalyst using the oxygen amount, and performs a deterioration diagnosis of the catalyst based on whether or not the periodic abnormality flag is on and the oxygen storage capacity. That is, the catalyst deterioration diagnosis means divides the catalyst deterioration diagnosis method according to whether or not the periodic abnormality flag is on. As a result, the catalyst deterioration diagnosis means can perform an appropriate catalyst deterioration diagnosis in consideration of the possibility that the value obtained after the periodic abnormality flag is turned on is affected by the periodic abnormality. It becomes. As a result, the catalyst deterioration diagnosis apparatus can accurately perform the deterioration diagnosis of the catalyst even when the oxygen concentration detection means has a periodic abnormality. As a result, it is possible to shorten the time required for the deterioration diagnosis of the catalyst. In addition, according to the above-described catalyst deterioration diagnosis device, it is not necessary to set the internal combustion engine or the like in a situation where the cycle abnormality of the oxygen concentration detection means does not occur (for example, the internal combustion engine is set to a high load range).

  In one aspect of the catalyst deterioration diagnostic apparatus, the first predetermined value is at least a value larger than a value that can be calculated from a deteriorated catalyst.

  In this aspect, the first predetermined value used when evaluating the difference between the calculated oxygen amount and the maximum oxygen amount is at least larger than a value that can be calculated from a deteriorated catalyst. it can. That is, the first predetermined value is set to a value that cannot be obtained in a deteriorated catalyst. As a result, it is possible to prevent a decrease in detection accuracy for a deteriorated catalyst.

  In another aspect of the catalyst deterioration diagnosis device, the catalyst deterioration diagnosis unit is configured such that when the period abnormality flag is on and the oxygen storage capacity is less than a second predetermined value, The storage capacity is not used for deterioration diagnosis of the catalyst.

  In this aspect, the catalyst deterioration diagnosis means can discard the oxygen storage capacity when the periodic abnormality flag is on and the oxygen storage capacity is less than the second predetermined value. That is, the catalyst deterioration diagnosis unit may calculate the oxygen storage capacity that is equal to or greater than the second predetermined value because the calculated oxygen storage capacity may not be accurate when the oxygen concentration detection unit has a periodic abnormality. Discard everything except abilities. In other words, the catalyst deterioration diagnosis unit performs the deterioration diagnosis using the oxygen storage capability if the oxygen storage capability is equal to or greater than the second predetermined value even if the cycle abnormality of the oxygen concentration detection unit occurs. As a result, not the correct oxygen storage capacity but the oxygen storage capacity that has become the same level as the value obtained from the deteriorated catalyst as a result of the reduction due to the cycle abnormality is not adopted. Therefore, the chance of deterioration diagnosis for the catalyst can be increased. Therefore, it is possible to prevent the catalyst from being diagnosed with improper deterioration, and it is possible to appropriately perform the deterioration diagnosis of the catalyst even when a periodic abnormality occurs.

  In another aspect of the catalyst deterioration diagnosis device, the catalyst deterioration diagnosis means may be configured to detect the oxygen even if the periodic abnormality flag is ON and the oxygen storage capacity is less than the second predetermined value. When the storage capacity is equal to or greater than a value that can be calculated from a deteriorated catalyst, the oxygen storage capacity is used for deterioration diagnosis of the catalyst.

  In this aspect, the catalyst deterioration diagnosis means does not discard the oxygen storage capacity when the oxygen storage capacity is less than the second predetermined value but is greater than or equal to a value that can be calculated from the deteriorated catalyst. . That is, when the oxygen storage capacity is the above value, the catalyst is not deteriorated, and therefore it can be determined that the catalyst is normal, so the oxygen storage capacity is not discarded. This makes it possible to shorten the time required for the deterioration diagnosis of the catalyst.

  In another aspect of the catalyst deterioration diagnosis device, the catalyst deterioration diagnosis means, when the oxygen storage capacity calculated before the period abnormality flag is turned on is less than the second predetermined value, After the period abnormality flag is turned on, the oxygen storage capacity is discarded.

  In this aspect, the catalyst deterioration diagnosis means calculates the oxygen storage capacity that should not be used for the deterioration diagnosis of the catalyst (for example, the oxygen storage capacity calculated as a clearly small value) calculated when the periodic abnormality flag is off. Discard when the periodic error flag is turned on. As a result, no error occurs in the deterioration diagnosis of the catalyst, and as a result, the deterioration diagnosis of the catalyst can be accurately executed.

  In another aspect of the catalyst deterioration diagnostic apparatus, the periodic abnormality determination unit may be configured such that when the periodic abnormality flag is on, the accumulated number of times when the oxygen storage capacity is not used reaches a predetermined number. In addition, the cycle abnormality flag is switched from on to off, and the maximum oxygen amount calculated up to now is cleared.

  In this aspect, the cycle abnormality determining means switches the cycle abnormality flag from on to off when the integrated value of the number of times the oxygen storage capacity is discarded reaches a predetermined number of times, and also calculates the maximum oxygen calculated up to now. Clear (reset) the amount. After the last trip (“trip” refers to the period from when the internal combustion engine starts to when it stops) is diagnosed as normal, the current trip when the catalyst deteriorates abnormally, such as melting. However, since the cycle abnormality flag is turned on, it is not possible to determine abnormality in the catalyst during the current trip. Therefore, the cycle abnormality determination means determines that the cycle abnormality determination is not correct when the oxygen storage capacity is continuously discarded in a situation where the cycle abnormality occurs. Specifically, the cycle abnormality flag is switched from on to off, and the maximum oxygen amount calculated up to now is cleared. Note that the cycle abnormality determination means waits for the number of calculations that can obtain a value close to the true value if the catalyst is a normal catalyst. As described above, it is possible to immediately detect abnormality of the catalyst.

  Preferably, in the catalyst deterioration diagnosis device, the periodic abnormality determination unit can use the oxygen amount as the maximum oxygen amount when the currently calculated oxygen amount exceeds the maximum oxygen amount. . As a result, even when the calculated amount of oxygen is increasing, it is possible to always determine abnormality of the cycle using a new amount of oxygen.

  More preferably, the cycle abnormality determination means does not execute the determination until the maximum oxygen amount is determined. For example, after the battery is cleared, the catalyst deterioration diagnosis device does not store the amount of oxygen used for comparison. Therefore, the initially calculated amount of oxygen can be stored as the maximum amount of oxygen.

  More preferably, the period abnormality determining means does not use the oxygen amount obtained immediately after the start of execution of the air-fuel ratio control for the determination. This is because it is unclear how much oxygen remains in the catalyst immediately after the start of air-fuel ratio control, so the amount of oxygen determined in this case is the exact amount of oxygen that the catalyst 2 can store. This is because it may not be shown.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

[Configuration of catalyst deterioration diagnosis device]
First, a catalyst deterioration diagnosis apparatus according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing a schematic configuration of a vehicle 10 equipped with a catalyst deterioration diagnosis device.

  The vehicle 10 includes an internal combustion engine 1, a catalyst 2, an ECU (Engine Control Unit) 3, an intake passage 4, an exhaust passage 5, a fuel injection valve 6, an A / F sensor 7, an oxygen sensor 8, Is provided. Note that the catalyst deterioration diagnosis apparatus according to the present embodiment is mainly composed of the ECU 3, the fuel injection valve 6, the oxygen sensor 8, and the like.

  The internal combustion engine 1 is a device that generates power by exploding an air-fuel mixture in a combustion chamber. The internal combustion engine 1 introduces air 9 a and fuel from the intake passage 4, and discharges the exhaust gas 9 b after burning the fuel to the exhaust passage 5. As the internal combustion engine 1, for example, an engine such as a gasoline engine or a diesel engine can be used.

  The catalyst 2 is provided on the exhaust passage 5 and purifies the exhaust gas 9 b discharged from the internal combustion engine 1. For example, the catalyst 2 may be a three-way catalyst that purifies NOx (nitrogen oxide), HC (hydrocarbon), CO (carbon monoxide), etc. in the exhaust gas.

  The fuel injection valve 6 is a device capable of adjusting the amount of fuel supplied to the internal combustion engine 1 (that is, the fuel injection amount). The fuel injection valve 6 is controlled by a control signal S3 supplied from an ECU 3 described later.

  The A / F sensor 7 is provided on the exhaust passage 5 upstream of the catalyst 2. The A / F sensor 7 detects the air-fuel ratio of the exhaust gas 9b and outputs a signal S1 corresponding to the detected air-fuel ratio to the ECU 3. On the other hand, the oxygen sensor 8 is provided on the exhaust passage 5 on the downstream side of the catalyst 2. The oxygen sensor 8 detects the oxygen concentration in the exhaust gas 9c after passing through the catalyst 2, and outputs a signal S2 corresponding to the detected oxygen concentration to the ECU 3. Thus, the A / F sensor 7 functions as air-fuel ratio detection means, and the oxygen sensor 8 functions as oxygen concentration detection means.

  The ECU 3 includes a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like (not shown). The ECU 3 supplies the control signal S3 to the fuel injection valve 6 on the basis of the signals S1 and S2 output from the A / F sensor 7 and the oxygen sensor 8, thereby performing air-fuel ratio control (ie, air-fuel ratio feedback control). ). Further, the ECU 3 diagnoses the deterioration of the catalyst 2 based on the air-fuel ratio output from the A / F sensor 7 and the oxygen concentration output from the oxygen sensor 8 during the execution of the air-fuel ratio control. Thus, in the present invention, the ECU 3 functions as an oxygen amount calculation means, a period abnormality determination means, and a catalyst deterioration diagnosis means. The specific process performed by the ECU 3 will be described later in detail.

  Next, basic air-fuel ratio control that is performed when the deterioration diagnosis of the catalyst 2 is performed will be described with reference to FIG.

  FIG. 2 is a diagram showing sensor output obtained when the ECU 3 executes air-fuel ratio control in which the air-fuel ratio is changed between rich and lean, and the horizontal axis indicates time. Such air-fuel ratio control is executed when performing deterioration diagnosis of the catalyst 2.

  FIG. 2A shows the air-fuel ratio output from the A / F sensor 7. In this case, the air-fuel ratio output from the A / F sensor 7 indicates the ratio of fuel to air in the exhaust gas 9 b discharged from the internal combustion engine 1. The A / F sensor 7 outputs a predetermined value when the air-fuel ratio is stoichiometric (theoretical air-fuel ratio), and when the air-fuel ratio is rich, the output becomes smaller than the predetermined value, and when the air-fuel ratio is lean The output becomes larger than the predetermined value.

  FIG. 2B shows the oxygen concentration output from the oxygen sensor 8. In this case, the output of the oxygen sensor 8 indicates the oxygen concentration in the exhaust gas 9 c downstream of the catalyst 2. As shown in FIG. 2B, the oxygen sensor 8 has a small output when the oxygen concentration in the exhaust gas 9c is large (that is, the air-fuel ratio is lean), and the oxygen concentration in the exhaust gas 9c is small (that is, When the air-fuel ratio is rich), the output becomes large.

  Next, air-fuel ratio control will be described. As shown in FIGS. 2A and 2B, when the target air-fuel ratio is changed from the stoichiometric state to the rich state because the oxygen sensor 8 has a lean output by the air-fuel ratio control (time t1a), the catalyst 2 releases the oxygen occluded until then, the oxygen concentration in the exhaust gas 9c does not decrease, and the output of the oxygen sensor 8 decreases. However, since the oxygen storage capacity of the catalyst 2 is limited, if all of the oxygen stored by the catalyst 2 is released, the oxygen concentration in the exhaust gas 9c rapidly decreases, and the output of the oxygen sensor 8 increases rapidly. To increase. That is, the output of the oxygen sensor 8 is inverted. When the output value of the oxygen sensor 8 increases to the predetermined determination value 13a due to the decrease in oxygen concentration, the ECU 3 shifts the target air-fuel ratio from the rich state to the lean state (time t1b).

  In the lean state, the exhaust gas 9c is in a state where oxygen is excessive, but since the catalyst 2 stores the oxygen, the oxygen concentration in the exhaust gas 9c does not initially increase. However, when the catalyst 2 stores oxygen to the limit of the storage capacity, the oxygen concentration in the exhaust gas 9c increases rapidly thereafter. That is, the output of the oxygen sensor 8 is inverted. When the output value of the oxygen sensor 8 decreases to the predetermined determination value 13b, the ECU 3 changes the target air-fuel ratio from the lean state to the rich state (time t1c). Thereafter, similar control is repeated.

  Thus, by switching the target air-fuel ratio to lean when the catalyst 2 has completely released oxygen, the catalyst 2 can immediately store oxygen, and when the catalyst 2 has fully stored oxygen, the target air-fuel ratio can be stored. By switching to rich, oxygen can be released from the catalyst 2 immediately. That is, by performing such air-fuel ratio control, oxygen can be effectively released from the catalyst 2 and oxygen can be effectively stored in the catalyst 2.

  FIG. 2C shows the amount of oxygen released from the catalyst 2 (oxygen release amount) and the amount of oxygen stored by the catalyst 2 (oxygen storage amount). The oxygen release amount and the oxygen storage amount are amounts calculated by the ECU 3 based on the output from the A / F sensor 7, the opening amount of the fuel injection valve 6, and the like. That is, the oxygen release amount and the oxygen storage amount are calculated from the air-fuel ratio (A / F) in the exhaust gas 9b and the fuel injection amount.

  As shown in FIG. 2C, when the air-fuel ratio is rich, the catalyst 2 releases oxygen at a constant rate, and when the air-fuel ratio is lean, the catalyst 2 stores oxygen at a constant rate. To do. Further, when the output of the oxygen sensor 8 reaches the determination value 13a, in other words, when the target air-fuel ratio is reversed from rich to lean, the catalyst 2 is switched from the oxygen release state to the oxygen storage state. Normally, when the output of the oxygen sensor 8 reaches the determination value 13a, the catalyst 2 has completely released the stored oxygen. Further, when the output of the oxygen sensor 8 reaches the determination value 13b, in other words, when the target air-fuel ratio is reversed from lean to rich, the catalyst 2 is switched from the oxygen release state to the oxygen storage state. Normally, when the output of the oxygen sensor 8 reaches the determination value 13b, the catalyst 2 stores oxygen to the limit.

  When the output of the oxygen sensor 8 reaches the determination value 13a, that is, when the output of the oxygen sensor 8 is inverted, the calculated oxygen release amount is the amount indicated by reference numeral 11. Further, when the output of the oxygen sensor 8 reaches the determination value 13b, that is, when the output of the oxygen sensor 8 is inverted, the calculated oxygen storage amount is an amount indicated by reference numeral 12. In this case, the oxygen release amount 11 is the amount of oxygen when the oxygen stored in the catalyst 2 is almost completely released, and the oxygen storage amount 12 is the amount of oxygen when the catalyst 2 stores oxygen almost to the limit. It is. In the following, the oxygen release amount 11 is expressed as “OSAR”, the oxygen storage amount 12 is expressed as “OSAL”, and these are collectively expressed simply as “oxygen storage amount OSA” (the oxygen release amount is referred to as the oxygen storage amount). Because it is equivalent). The oxygen release amount OSAR corresponds to the area of the region 14a in the output of the A / F sensor 7, and the oxygen storage amount OSAL corresponds to the area of the region 14b in the output of the A / F sensor 7.

  The ECU 3 calculates the oxygen release amount OSAR when the output of the oxygen sensor 8 reaches the determination value 13a, and calculates the oxygen storage amount OSAL when the output of the oxygen sensor 8 reaches the determination value 13b. Specifically, the ECU 3 obtains the oxygen release amount OSAR and the oxygen storage amount OSAL based on the output of the A / F sensor 7. For example, the ECU 3 calculates the oxygen release amount OSAR based on the area of the region 14a in the output of the A / F sensor 7 at time t1b, and based on the area of the region 14b in the output of the A / F sensor 7 at time t1c. To calculate the oxygen release amount OSAL.

  Then, the ECU 3 calculates the amount of oxygen that can be stored by the catalyst 2 based on the calculated oxygen release amount OSAR and oxygen storage amount OSAL (hereinafter, this amount is referred to as “oxygen storage capacity Cmax”). . Specifically, the ECU 3 sets the average value of the oxygen release amount OSAR and the oxygen storage amount OSAL as the oxygen storage capacity Cmax. For example, the ECU 3 obtains the oxygen storage capacity Cmax from the oxygen release amount OSAR calculated based on the area of the region 14a and the oxygen storage amount OSAL calculated based on the area of the region 14b at time t1c. Further, the ECU 3 obtains the oxygen storage capacity Cmax from the oxygen release amount OSAR calculated based on the area of the region 14b and the oxygen storage amount OSAL calculated based on the area of the region 14c at time t1d. That is, the ECU 3 calculates the oxygen storage amount OSA every time the output of the oxygen sensor 8 is inverted, and calculates the oxygen storage capacity Cmax based on the oxygen storage amount OSA obtained last time and the oxygen storage amount OSA obtained this time. calculate.

  Based on the oxygen storage capacity Cmax thus determined, the ECU 3 performs a deterioration diagnosis of the catalyst 2. For example, the ECU 3 determines that the catalyst 2 is normal when the obtained oxygen storage capacity Cmax is greater than or equal to a predetermined value, and the catalyst 2 deteriorates when the oxygen storage capacity Cmax is less than the predetermined value. It is determined that

  Here, a case where the oxygen sensor 8 generates a cycle abnormality will be described. Usually, the output of the oxygen sensor 8 is periodically reversed (see FIG. 2B). However, the oxygen sensor 8 does not periodically invert the output, and at a timing deviating from the periodic timing, physically before the oxygen release amount OSAR and the oxygen storage amount OSAL reach the original values, An output with a small time width (hereinafter referred to as “short time width output”) may occur. In other words, the output may be inverted at a timing when the oxygen sensor 8 deviates from the periodic timing. Such an abnormal cycle of the oxygen sensor 8 is not caused by the oxygen occlusion and oxygen release action of the catalyst 2 but is caused by a poor gas contact of the oxygen sensor 8 or an output characteristic of the oxygen sensor 8. It is thought that there is. In other words, the cycle abnormality of the oxygen sensor 8 also occurs when the catalyst 2 is normal.

  A specific example of the periodic abnormality of the oxygen sensor 8 is shown in FIG. 3 (a) shows the output of the A / F sensor 7, FIG. 3 (b) shows the output of the oxygen sensor 8, and FIG. 3 (c) shows the calculated oxygen storage capacity Cmax. The axis shows time.

  As shown in FIG. 3B, the oxygen sensor 8 generates a short-time output at a timing deviating from the periodic timing as indicated by reference numeral 15a, and the output is inverted. That is, it can be said that the oxygen sensor 8 has a periodic abnormality. In this case, the output of the A / F sensor 7 changes corresponding to the output of the oxygen sensor 8 as shown in FIG.

  In addition, when a periodic abnormality occurs in the oxygen sensor 8, the calculated oxygen storage capacity Cmax is clearly calculated as a small amount as indicated by reference numeral 15b in FIG. As described above, the oxygen storage capacity Cmax obtained when the periodic abnormality of the oxygen sensor 8 occurs does not accurately indicate the amount that the catalyst 2 can store oxygen. It is not preferable to perform the deterioration diagnosis of 2.

[Circuit abnormality judgment method]
Next, a method for determining the periodic abnormality of the oxygen sensor 8 as described above will be described. The cycle abnormality determination is performed by the ECU 3.

  First, the basic concept of the periodic abnormality determination method will be briefly described. The ECU 3 changes the oxygen storage amount OSA (oxygen release amount) based on the output of the A / F sensor 7 every time the output of the oxygen sensor 8 is inverted, in other words, every time the air-fuel ratio is switched from rich to lean or from lean to rich. OSAR and oxygen storage amount OSAL are included). The ECU 3 stores the maximum value of the oxygen storage amount OSA calculated in the past as the maximum oxygen storage amount OSAmax. Then, the ECU 3 determines whether or not the oxygen sensor 8 has an abnormal cycle by comparing the obtained oxygen storage amount OSA with the maximum oxygen storage amount OSAmax calculated so far.

  Specifically, the ECU 3 obtains a difference between the maximum oxygen storage amount OSAmax calculated up to now and the oxygen storage amount OSA obtained this time, and the obtained difference (assumed to use an absolute value) is a predetermined value ( Hereinafter, this predetermined value is referred to as a “periodic abnormality determination value.”) When it is equal to or greater than this, it is determined that a periodic abnormality has occurred. In this case, the ECU 3 sets the “period abnormality flag” to ON. When the periodic abnormality flag is turned on, the obtained oxygen storage amount OSA is a value that is considerably smaller than the normal value, and therefore there is a high possibility that the oxygen sensor 8 has caused a periodic abnormality. As described above, the ECU 3 functions as a cycle abnormality determination unit of the oxygen sensor 8. The period abnormality determination value corresponds to the first predetermined value.

  Here, a specific method for determining the periodic abnormality of the oxygen sensor 8 will be described with reference to FIG. FIG. 4A shows the output of the A / F sensor 7, FIG. 4B shows ON / OFF of the cycle abnormality flag, and the horizontal axis indicates time. FIG. 4 shows the result after the start of air-fuel ratio control for diagnosing deterioration of the catalyst 2.

  As shown in FIG. 4A, the A / F sensor 7 shows outputs indicated by reference numerals 20a to 20f after the start of the air-fuel ratio control. The ECU 3 performs a cycle abnormality determination on the output of the A / F sensor 7 as described above. Specifically, every time the air-fuel ratio is switched from rich to lean or from lean to rich, the ECU 3 calculates the oxygen storage amount OSA calculated based on the output of the A / F sensor 7 and the stored maximum oxygen storage amount. A difference from OSAmax is calculated, and if the calculated difference is equal to or greater than the period abnormality determination value, the period abnormality flag is turned on. Note that the ECU 3 does not use the oxygen storage amount OSA obtained immediately after the air-fuel ratio control and obtained from the output indicated by the reference numeral 20a of the A / F sensor 7 for the period abnormality determination. This is because it is unclear how much oxygen remains in the catalyst 2 immediately after the start of the air-fuel ratio control. Therefore, the oxygen storage amount OSA obtained in this case is the amount of oxygen that the catalyst 2 can store. This is because it may not be an accurate indication.

  Therefore, the ECU 3 sequentially performs periodic abnormality determination on the outputs indicated by reference numerals 20b to 20f of the A / F sensor 7 without performing periodic abnormality determination on the output indicated by reference numeral 20a of the A / F sensor 7. Specifically, the ECU 3 calculates the oxygen storage amount OSA based on the output indicated by reference numerals 20b to 20f of the A / F sensor 7 and specifically based on the area formed by the outputs indicated by reference numerals 20b to 20f.

  In this case, since the difference between the oxygen storage amount OSA obtained from the outputs indicated by reference numerals 20b to 20e and the maximum oxygen storage amount OSAmax is less than the periodic abnormality determination value, the ECU 3 does not turn on the periodic abnormality flag. However, since the difference between the oxygen storage amount OSA obtained based on the output indicated by reference numeral 20f and the maximum oxygen storage amount OSAmax is equal to or greater than the periodic abnormality determination value, the ECU 3 performs the oxygen storage amount OSA based on the output indicated by reference numeral 20f. After the calculation, the cycle abnormality flag is turned on (time t2). The ECU 3 basically switches the cycle abnormality flag from on to off even if the difference between the oxygen storage amount OSA and the maximum oxygen storage amount OSAmax calculated after time t2 is equal to or less than the cycle abnormality determination value. Absent. This is because once a periodic abnormality occurs, there is a high possibility that a periodic abnormality will continue to occur.

  As described above, the ECU 3 uses the maximum oxygen storage amount OSAmax calculated up to now to determine whether or not the oxygen sensor 8 has a periodic abnormality. As a result, the ECU 3 can appropriately detect the periodic abnormality of the oxygen sensor 8 based on the past results. Further, the ECU 3 continues to set the periodic abnormality flag to ON after switching the periodic abnormality flag to ON, assuming that the periodic abnormality will continue to occur once the periodic abnormality has occurred. Then, the ECU 3 executes a catalyst deterioration diagnosis method, which will be described later, based on whether the periodic abnormality flag is on or off. As a result, the ECU 3 performs an appropriate deterioration diagnosis of the catalyst 2 taking into consideration that the plurality of outputs obtained after the cycle abnormality flag is switched on is affected by the cycle abnormality of the oxygen sensor 8. Can be done. Therefore, the deterioration diagnosis of the catalyst 2 can be accurately performed.

  The above-described maximum oxygen storage amount OSAmax is basically the maximum oxygen storage amount OSA obtained in the previous trip (“trip” means the period from the start to the stop of the internal combustion engine 1). Is used. That is, the ECU 3 stores the maximum oxygen storage amount OSAmax in a memory (not shown).

  The present invention is not limited to setting the maximum oxygen storage amount OSAmax to the maximum oxygen storage amount obtained in the previous trip. Instead, the maximum oxygen storage amount obtained in a plurality of past trips is used. You may set to the average value of quantity.

  Further, in the present invention, the maximum oxygen storage amount OSAmax is continuously used without being changed during the current trip, that is, the maximum oxygen storage amount OSAmax is not limited to being used as a fixed value. If the maximum oxygen storage amount OSAmax is not used as a fixed value and an oxygen storage amount OSA greater than the stored maximum oxygen storage amount OSAmax is obtained, the obtained oxygen storage amount OSA is used as a new maximum oxygen storage amount. It may be stored as OSAmax. That is, the maximum oxygen storage amount OSAmax may be updated with the oxygen storage amount OSA obtained during the current trip. In this case, as the maximum oxygen storage amount OSAmax used at the start of air-fuel ratio control, the maximum oxygen storage amount OSAmax in the previous trip or the average value of the maximum oxygen storage amount OSAmax obtained in a plurality of past trips is used. Specifically, every time the ECU 3 obtains the oxygen storage amount OSA, the ECU 3 compares the value with the already stored maximum oxygen storage amount OSAmax, and the obtained oxygen storage amount OSA is equal to or greater than the maximum oxygen storage amount OSAmax. Then, the maximum oxygen storage amount OSAmax is updated, and the subsequent periodic abnormality determination is performed using the updated maximum oxygen storage amount OSAmax.

  The maximum oxygen storage amount OSAmax is reset when the battery is cleared (for example, when a battery (not shown) in the vehicle 10 is replaced). That is, the maximum oxygen storage amount OSAmax stored in the ECU 3 is deleted when the battery is cleared.

  The period abnormality determination value is set to a value that cannot be taken by the deteriorated catalyst 2, specifically, a value that is at least larger than a value that can be calculated from the deteriorated catalyst 2. As an example, the difference between the oxygen storage amount OSA and the maximum oxygen storage amount OSAmax is calculated from a plurality of experimentally deteriorated catalysts 2, and a range in which these differences can be obtained is obtained. A value larger than this range is set. The reason why the periodic abnormality determination value is set to such a value is to prevent the periodic abnormality flag from being turned on illegally with respect to the output of the A / F sensor 7 in the deteriorated catalyst 2 or the like. is there. Thereby, it becomes possible to prevent the deterioration of the deterioration diagnosis accuracy for the deteriorated catalyst 2.

  Further, the periodic abnormality determination value is not limited to being set to a constant, and may be a variable that is changed according to the state in the internal combustion engine 1. For example, the period abnormality determination value can be set to a variable that changes based on either the temperature of the catalyst 2 or the intake air amount, or both the temperature of the catalyst 2 and the intake air amount.

  In the above, the embodiment in which the periodic abnormality determination of the oxygen sensor 8 is performed based on the oxygen storage amount OSA of the catalyst 2 has been described. However, in other embodiments, the output of the oxygen sensor 8 is inverted instead of the oxygen storage amount OSA. On the basis of the accumulated intake air amount until this time, it is possible to determine the abnormality of the cycle of the oxygen sensor 8. In still another embodiment, it is possible to determine the period abnormality of the oxygen sensor 8 based on the time until the output of the oxygen sensor 8 is reversed (reversal time).

[Catalyst deterioration diagnosis method]
Next, a catalyst deterioration diagnosis method performed based on the periodic abnormality flag of the oxygen sensor 8 will be described.

(First embodiment)
First, a first embodiment of the catalyst deterioration diagnosis method will be described. The catalyst deterioration diagnosis method according to the first embodiment is executed by the ECU 3.

  The ECU 3 basically calculates the oxygen storage capacity Cmax based on the oxygen release amount OSAR and the oxygen storage amount OSAL, and performs the deterioration diagnosis of the catalyst 2 based on the oxygen storage capacity Cmax. Specifically, the ECU 3 calculates an average value of a plurality of oxygen storage capacities Cmax when the oxygen storage capacity Cmax is obtained a predetermined number of times, and the average value is a predetermined value (hereinafter, this predetermined value is referred to as a “deterioration determination value”). The deterioration diagnosis of the catalyst 2 is performed by determining whether or not the above is satisfied. When the periodic abnormality flag is off, basically all the calculated oxygen storage capacities Cmax are used for deterioration diagnosis.

  In the catalyst deterioration diagnosis method according to the first embodiment, the ECU 3 determines that the periodic abnormality flag related to the oxygen sensor 8 is ON, and the obtained oxygen storage capacity Cmax is a predetermined value (hereinafter, this predetermined value is “underestimated”). If it is less than "determination value"), this oxygen storage capacity Cmax is not used for the deterioration diagnosis of the catalyst 2, that is, the oxygen storage capacity Cmax is discarded. In other words, when the periodic abnormality flag related to the oxygen sensor 8 is on, only the oxygen storage capacity Cmax that is equal to or greater than the underdetermination value is employed for the deterioration diagnosis of the catalyst 2. As described above, when the periodic abnormality flag is on, the ECU 3 determines whether to discard or adopt the obtained oxygen storage capacity Cmax, and uses only the oxygen storage capacity Cmax employed by the determination. Diagnose the deterioration of the catalyst 2. The underdetermination value corresponds to the second predetermined value.

  Here, the catalyst deterioration diagnosis method according to the first embodiment will be specifically described with reference to FIG. 5 (a) shows the output of the A / F sensor 7, FIG. 5 (b) shows on / off of the cycle abnormality flag, and FIG. 5 (c) shows an effective Cmax counter (oxygen occlusion used for deterioration diagnosis). The number of capability Cmax), and the horizontal axis represents time.

  As shown in FIG. 5A, the A / F sensor 7 generates outputs as indicated by reference numerals 25a to 25h. As described above, the ECU 3 calculates the respective oxygen storage amounts OSA based on the outputs indicated by the reference numerals 25a to 25h of the A / F sensor 7 and specifically based on the areas formed by the outputs indicated by the reference numerals 25a to 25h. To do. In this case, since the difference between the oxygen storage amount OSA obtained based on the output indicated by reference numeral 25a and the maximum oxygen storage amount OSAmax is equal to or greater than the periodic abnormality determination value, the ECU 3 turns on the periodic abnormality flag (time t3a). ).

  Next, at time t3b, the ECU 3 calculates the oxygen storage capacity Cmax based on the oxygen storage amount OSA corresponding to the output indicated by reference numeral 25a and the oxygen storage amount OSA corresponding to the output indicated by reference numeral 25b. In this case, since the calculated oxygen storage capacity Cmax is less than the underdetermination value, the ECU 3 discards the oxygen storage capacity Cmax. Similarly, at time t3c, the ECU 3 calculates the oxygen storage capacity Cmax based on the oxygen storage amount OSA corresponding to the output indicated by reference numeral 25b and the oxygen storage amount OSA corresponding to the output indicated by reference numeral 25c. The ECU 3 discards the oxygen storage capacity Cmax calculated at the time t3c because it is also less than the underdetermination value. On the other hand, at time t3d, the oxygen storage capacity Cmax calculated because the oxygen storage amount OSA corresponding to the output indicated by reference numeral 25d is large, and the oxygen storage capacity Cmax is greater than or equal to the underdetermination value. This oxygen storage capacity Cmax is adopted as being effective. In this case, as shown in FIG. 5C, the valid Cmax counter is counted up.

  The ECU 3 repeatedly determines whether to discard or adopt the oxygen storage capacity Cmax by such a procedure. Thereby, the ECU 3 discards the oxygen storage capacity Cmax calculated at the times t3f and t3g, and adopts the oxygen storage capacity Cmax calculated at the times t3e and t3h.

  The ECU 3 performs the deterioration diagnosis of the catalyst 2 based on the obtained plurality of oxygen storage capacities Cmax when the number of times that the oxygen storage capacity Cmax is adopted reaches a predetermined number of times, and turns on the periodic abnormality flag. Switch off. For example, when the predetermined number of times is set to 3, since the effective Cmax counter becomes “3” at time t3h, the ECU 3 performs deterioration diagnosis of the catalyst 2 and switches the cycle abnormality flag from on to off at time t3h. . Specifically, the ECU 3 performs deterioration diagnosis of the catalyst 2 at time t3h based on the oxygen storage capacity Cmax employed at times t3d, t3e, and t3h.

  As described above, in the catalyst deterioration diagnosis method according to the first embodiment, whether or not the calculated oxygen storage capacity Cmax should be discarded or adopted when the oxygen sensor 8 has an abnormal cycle is determined. Then, the deterioration diagnosis of the catalyst 2 is performed by using the underdetermination value. Thereby, since the deterioration diagnosis is not performed using the oxygen storage capacity Cmax to be discarded, it is possible to prevent the catalyst 2 from being erroneously determined. Furthermore, even if the oxygen sensor 8 has a cycle abnormality, the deterioration diagnosis is performed using the oxygen storage capacity Cmax to be adopted. As a result, the time required for the deterioration diagnosis of the catalyst 2 can be shortened. Become. Thus, according to the catalyst deterioration diagnosis method according to the first embodiment, the deterioration diagnosis of the catalyst 2 can be performed accurately and quickly even if the oxygen sensor 8 has a periodic abnormality. Thereby, in order to diagnose deterioration of the catalyst 2, there is no need to change the state of the oxygen sensor 8 to a state in which no abnormality occurs (for example, the internal combustion engine 1 is set to a high load range). In other words, according to the catalyst deterioration diagnosis method according to the first embodiment, the deterioration diagnosis execution range of the catalyst 2 is not limited to a high load region in which a periodic abnormality is unlikely to occur.

  The underdetermination value used for determining whether to discard / adopt the oxygen storage capacity Cmax is larger than the deterioration determination value used for the deterioration diagnosis of the catalyst 2. In other words, the underdetermination value uses at least a value larger than the oxygen storage capacity Cmax that can be calculated from the deteriorated catalyst 2. Thereby, it is possible to prevent the deterioration diagnosis of the catalyst 2 from being performed using the oxygen storage capacity Cmax reduced to a value less than the same value as that obtained from the catalyst 2 that has deteriorated due to the cycle abnormality.

  If the underdetermination value is set to a value larger than the deterioration determination value as described above, there is a high possibility that the oxygen storage capacity Cmax is discarded. Therefore, the oxygen storage capacity Cmax used for determining the deterioration of the catalyst 2 is adopted a predetermined number of times. It may take time to do. In this case, if the air-fuel ratio control performed for the deterioration diagnosis of the catalyst 2 is executed for a long time, there is a possibility that the emission may be reduced or the drivability may be deteriorated. Therefore, when it is desired to quickly determine the deterioration of the catalyst 2, even if the oxygen storage capacity Cmax is less than the underdetermination value, the oxygen storage capacity Cmax is larger than the deterioration determination value. The oxygen storage capacity Cmax can be used without being discarded. For example, when a periodic abnormality of the oxygen sensor 8 has occurred but the catalyst 2 is normal, the calculated oxygen storage capacity Cmax is always smaller than the amount of oxygen that the catalyst 2 can actually store. It should be calculated, and a value larger than this cannot be calculated. Therefore, even if a periodic abnormality occurs in the oxygen sensor 8, if the oxygen storage capacity Cmax is larger than the deterioration determination value, the catalyst 2 is not deteriorated based on the oxygen storage capacity Cmax (normal) It is also possible to make a determination. As described above, by adopting / discarding the oxygen storage capacity Cmax, the oxygen storage capacity Cmax of the same level as the value obtained from the catalyst 2 that has deteriorated due to the cycle abnormality is not employed, and the catalyst 2 is not used. The chance of deterioration diagnosis can be increased. That is, the time until the number of times the oxygen storage capacity Cmax is adopted reaches a predetermined number can be shortened.

  Further, instead of setting the underdetermination value to a value larger than the deterioration determination value as described above, the underdetermination value may be set to a value substantially the same as the deterioration determination value. This also shortens the time until the number of times of adopting the oxygen storage capacity Cmax reaches the predetermined number without adopting the oxygen storage capacity Cmax calculated from the deteriorated catalyst 2.

(Second embodiment)
Next, a catalyst deterioration diagnosis method according to the second embodiment will be described. The catalyst deterioration diagnosis method according to the second embodiment is executed by the ECU 3. The catalyst deterioration diagnosis method according to the second embodiment is basically executed based on the catalyst deterioration diagnosis method according to the first embodiment described above.

  According to the catalyst deterioration diagnosis method according to the first embodiment described above, basically, the oxygen storage capacity Cmax calculated when the periodic abnormality flag is off is not discarded. However, when the maximum oxygen storage amount OSAmax is set to a relatively small value (for example, when deterioration diagnosis of the catalyst 2 is performed after the battery is cleared), the periodic abnormality flag is set even if the obtained oxygen storage amount OSA is small. Since it is not turned on, the required oxygen storage capacity Cmax is adopted without being discarded. Since the oxygen storage capacity Cmax obtained in such a case may not accurately indicate the capacity of the catalyst 2, it is not preferable to perform the deterioration diagnosis of the catalyst 2 based on this.

  Therefore, in the catalyst deterioration diagnosis method according to the second embodiment, the oxygen storage capacity Cmax that should not be used for the deterioration diagnosis of the catalyst 2 calculated when the cycle abnormality flag is off is switched on. Discard when. Specifically, the ECU 3 discards the oxygen storage capacity Cmax that is less than the above-described underdetermination value calculated when the cycle abnormality flag is off when the cycle abnormality flag is switched from off to on. The reason for discarding the oxygen storage capacity Cmax when the periodic abnormality flag is switched from OFF to ON is that the oxygen storage capacity Cmax that is less than the underdetermination value is calculated when the periodic abnormality flag is OFF. Even if a small oxygen storage amount OSA is obtained, when an accurate oxygen storage amount OSA is subsequently obtained, the difference between the oxygen storage amount OSA and the maximum oxygen storage amount OSAmax is equal to or greater than the periodic abnormality determination value. This is because the cycle abnormality flag is switched from OFF to ON.

  Here, the catalyst deterioration diagnosis method according to the second embodiment will be specifically described with reference to FIG. 6 (a) shows the output of the A / F sensor 7, FIG. 6 (b) shows the on / off of the cycle abnormality flag, FIG. 6 (c) shows the effective Cmax counter, Shows time.

  As shown in FIG. 6A, the A / F sensor 7 generates outputs as indicated by reference numerals 28a to 28h. In this case, since the maximum oxygen storage amount OSAmax is small although the oxygen storage amount OSA obtained from the output of the A / F sensor 7 indicated by reference numerals 28a, 28b, and 28c is a relatively small value, the ECU 3 The cycle abnormality flag is not switched from OFF to ON (time t4a, t4b). Therefore, the ECU 3 employs the oxygen storage capacity Cmax even if the calculated oxygen storage capacity Cmax is less than the underdetermination value.

  However, at time t4c, the oxygen storage amount OSA obtained from the output of the A / F sensor 7 indicated by reference numeral 28d exceeds the maximum oxygen storage amount OSAmax, and the difference between the oxygen storage amount OSA and the maximum oxygen storage amount OSAmax is determined as a periodic abnormality. Since it becomes equal to or greater than the value, the ECU 3 switches the cycle abnormality flag from off to on. At this time, the ECU 3 determines whether or not the oxygen storage capacity Cmax employed before the time t4c (that is, when the periodic abnormality flag is off) can be used for the deterioration diagnosis of the catalyst 2 as it is. In this case, since the oxygen storage capacity Cmax obtained at times t4a and t4b is less than the underdetermination value, the ECU 3 discards these two oxygen storage capacities Cmax and sets the effective Cmax counter to “0”. To do. At the same time, the ECU 3 employs the oxygen storage capacity Cmax because the oxygen storage capacity Cmax calculated at time t4c is equal to or greater than the underdetermination value. Therefore, as shown in FIG. 6C, the effective Cmax counter is counted up from “0” to “1” (time t4c).

  The ECU 3 employs these oxygen storage capacities Cmax because the oxygen storage capacities Cmax calculated at times t4d and t4g are equal to or greater than the underdetermination value. Furthermore, since the effective Cmax counter reaches a predetermined number (three times) at time t4g, the ECU 3 performs a deterioration diagnosis of the catalyst 2. Specifically, the ECU 3 performs the deterioration diagnosis of the catalyst 2 based on the oxygen storage capacity Cmax employed at times t4c, t4e, and t4g.

  As described above, according to the catalyst deterioration diagnosis method according to the second embodiment, the oxygen storage capacity Cmax less than the underdetermination value obtained when the periodic abnormality flag is off is switched on. Since it is sometimes discarded, the deterioration diagnosis of the catalyst 2 can be performed accurately.

(Third embodiment)
Next, a catalyst deterioration diagnosis method according to the third embodiment will be described. The catalyst deterioration diagnosis method according to the third embodiment is executed by the ECU 3. The catalyst deterioration diagnosis method according to the third embodiment is basically performed based on the catalyst deterioration diagnosis method according to the first embodiment and the second embodiment described above.

  According to the catalyst deterioration diagnosis method according to the first embodiment, when the periodic abnormality flag is on, if the obtained oxygen storage capacity Cmax is less than the underdetermination value, the oxygen storage capacity Cmax is discarded. Is done. However, when the obtained oxygen storage capacity Cmax is continuously less than the underdetermination value, the oxygen storage capacity Cmax continues to be discarded, and it takes time to obtain the oxygen storage capacity Cmax for a predetermined number of times. . In particular, for example, when the catalyst 2 is abnormally deteriorated (for example, melted) after being diagnosed as normal in the previous trip, for example, there is a high possibility that the oxygen storage capacity Cmax is continuously discarded. Therefore, if the oxygen storage capacity Cmax is continuously discarded, it may take time to determine that the catalyst 2 that has deteriorated is deteriorated.

  Therefore, in the third embodiment, a catalyst deterioration diagnosis method is performed so that the deterioration diagnosis of the catalyst 2 is promoted when the oxygen storage capacity Cmax continues to be discarded. Specifically, the ECU 3 turns off the cycle abnormality flag and resets (clears) other variables when the number of times the oxygen storage capacity Cmax is continuously discarded reaches a predetermined number. Thereby, since the opportunity to perform a deterioration diagnosis with respect to the catalyst 2 increases, the frequency of detecting the deteriorated catalyst 2 increases.

  Here, the catalyst deterioration diagnosis method according to the third embodiment will be specifically described with reference to FIG. FIG. 7A shows the output of the A / F sensor 7, FIG. 7B shows ON / OFF of the cycle abnormality flag, and FIG. 7C shows the effective Cmax counter. Shows time.

  As shown in FIG. 7A, the A / F sensor 7 generates outputs as indicated by reference numerals 30a to 30g. In this case, since the difference between the oxygen storage amount OSA calculated from the output of the A / F sensor 7 indicated by reference numeral 30a and the maximum oxygen storage amount OSAmax is greater than or equal to the periodic abnormality determination value at the time t5a, the ECU 3 Switch the flag from off to on. Further, the ECU 3 discards the oxygen storage capacity Cmax because the oxygen storage capacity Cmax calculated at time t5a is less than the underdetermination value.

  Then, the ECU 3 similarly discards the calculated oxygen storage capacity Cmax at times t5b to t5g. Thereby, at time t5g, the number of times the oxygen storage capacity Cmax is continuously discarded reaches a predetermined number (in this case, “7 times”), and thus the ECU 3 switches the cycle abnormality flag from on to off. Further, at time t5g, the ECU 3 resets the stored maximum oxygen storage amount OSAmax and updates it with the maximum oxygen storage amount OSA obtained in the current trip. In addition, the ECU 3 also resets the effective Cmax counter and the like (assuming “0 times”).

  Thus, in the catalyst deterioration diagnosis method according to the third example, when the oxygen storage capacity Cmax is continuously discarded, the cycle abnormality flag is switched from on to off. As a result, even if the calculated oxygen storage capacity Cmax is less than the underdetermination value, the oxygen storage capacity Cmax can be employed. As described above, according to the catalyst deterioration diagnosis method according to the third embodiment, it is possible to immediately detect the catalyst 2 rapidly deteriorated as described above.

  In the above description, the method for diagnosing catalyst deterioration based on the number of times the oxygen storage capacity Cmax is continuously discarded has been described. However, instead of the number of times of continuous discard, the oxygen storage capacity is stored when the periodic abnormality flag is on. The catalyst deterioration diagnosis may be performed based on the integrated value of the number of times that the capacity Cmax is discarded. Also in this case, when the integrated value of the number of times the oxygen storage capacity Cmax is discarded reaches a predetermined number, the cycle abnormality flag and the like are reset.

(Fourth embodiment)
Next, a catalyst deterioration diagnosis method according to the fourth embodiment will be described. The catalyst deterioration diagnosis method according to the fourth embodiment is executed by the ECU 3. The catalyst deterioration diagnosis method according to the fourth embodiment is basically performed based on the catalyst deterioration diagnosis method according to the first to third embodiments described above.

  The catalyst deterioration diagnosis method according to the fourth embodiment is mainly performed after the battery is cleared. Immediately after the battery is cleared, since the ECU 3 does not store the maximum oxygen storage amount OSAmax, the ECU 3 performs the following processing.

  The catalyst deterioration diagnosis method according to the fourth embodiment will be specifically described with reference to FIG. FIG. 8A shows the output of the A / F sensor 7, FIG. 8B shows ON / OFF of the cycle abnormality flag, and FIG. 8C shows the effective Cmax counter. Shows time.

  As shown in FIG. 8A, the A / F sensor 7 generates outputs as indicated by reference numerals 32a to 32g. In this case, air-fuel ratio control for diagnosing deterioration of the catalyst 2 is started at time t6a. Therefore, the ECU 3 does not calculate the oxygen storage amount OSA from the output indicated by reference numeral 32a at time t6b. Further, the ECU 3 does not calculate the oxygen storage capacity Cmax at time t6b.

  At time t6c, the ECU 3 calculates the oxygen storage amount OSA from the output indicated by reference numeral 32b. In this example, since the air-fuel ratio control is performed after the battery is cleared, the ECU 3 does not yet store the maximum oxygen storage amount OSAmax, so the oxygen storage amount OSA calculated at time t6c is set as the maximum oxygen storage amount OSAmax. Remember. Therefore, at time t6c, the ECU 3 does not perform processing for comparing the maximum oxygen storage amount OSAmax with the obtained oxygen storage amount OSA, that is, processing for determining the periodic abnormality of the oxygen sensor 8. Further, at time t6c, since the oxygen storage amount OSA is not obtained at time t6b, the ECU 3 does not calculate the oxygen storage capacity Cmax.

  Although the oxygen storage amount OSA calculated at times t6d and t6e is small, the maximum oxygen storage amount OSAmax calculated at time t6c is small, so the ECU 3 does not switch the cycle abnormality flag from off to on. Therefore, the ECU 3 employs the calculated oxygen storage capacity Cmax at times t6d and t6e.

  At time t6f, the oxygen storage amount OSA exceeding the stored maximum oxygen storage amount OSAmax is calculated, and the difference between the oxygen storage amount OSA and the maximum oxygen storage amount OSAmax is equal to or greater than the periodic abnormality determination value. Switches the cycle abnormality flag from off to on. At the same time, since the oxygen storage capacity Cmax obtained at times t6d and t6e is less than the underdetermination value, the ECU 3 discards these two oxygen storage capacities Cmax and sets the effective Cmax counter to “0”. . At the same time, at time t6f, the ECU 3 employs the oxygen storage capacity Cmax because the oxygen storage capacity Cmax calculated at time t6f is equal to or greater than the underdetermination value. Therefore, the valid Cmax counter is counted up from “0” to “1”.

  Since the oxygen storage capacity Cmax calculated at times t6g and t6h is equal to or greater than the underdetermination value, the ECU 3 employs these oxygen storage capacities Cmax. Furthermore, since the effective Cmax counter reaches a predetermined number (three times) at time t6h, the ECU 3 executes a deterioration diagnosis of the catalyst 2.

  As described above, according to the catalyst deterioration diagnosis method according to the fourth embodiment, the deterioration diagnosis of the catalyst 2 can be performed by appropriately adopting the oxygen storage capacity Cmax to be used for the deterioration diagnosis of the catalyst 2 even after the battery is cleared. Can be performed accurately.

It is a block diagram which shows schematic structure of the vehicle by which the catalyst deterioration diagnostic apparatus based on this invention is mounted. It is a figure for demonstrating the air fuel ratio control performed for the deterioration diagnosis of a catalyst. It is a figure for demonstrating the case where an oxygen sensor generate | occur | produces a cycle abnormality. It is a figure for demonstrating the method of determining the period abnormality of an oxygen sensor. It is a figure for demonstrating 1st Example of the catalyst deterioration diagnostic method of this invention. It is a figure for demonstrating 2nd Example of the catalyst deterioration diagnostic method of this invention. It is a figure for demonstrating 3rd Example of the catalyst deterioration diagnostic method of this invention. It is a figure for demonstrating 4th Example of the catalyst deterioration diagnostic method of this invention.

Explanation of symbols

1 Internal combustion engine 2 Catalyst 3 ECU
5 Exhaust passage 6 Fuel injection valve 7 A / F sensor 8 Oxygen sensor 10 Vehicle

Claims (9)

A catalyst deterioration diagnosis device that performs deterioration diagnosis of a catalyst provided in an exhaust passage by executing air-fuel ratio control that changes the air-fuel ratio of fuel and air supplied to an internal combustion engine between a rich state and a lean state. There,
Air-fuel ratio detecting means for detecting an air-fuel ratio in the exhaust passage on the upstream side of the catalyst;
Oxygen concentration detection means for detecting the oxygen concentration in the exhaust passage on the downstream side of the catalyst and outputting a value corresponding to the detected oxygen concentration;
Oxygen amount calculating means for calculating the amount of oxygen released from the catalyst into the exhaust passage and the amount of oxygen stored in the catalyst based on the detected air-fuel ratio and the oxygen concentration;
When the difference between the calculated oxygen amount and the maximum oxygen amount calculated so far is equal to or greater than a first predetermined value, it is determined that the output cycle of the oxygen concentration detection means is abnormal, and the cycle Periodic abnormality determination means for setting the abnormality flag to ON;
A catalyst deterioration diagnosing means for calculating an oxygen storage capacity of the catalyst using the oxygen amount, and performing a deterioration diagnosis of the catalyst based on whether or not the periodic abnormality flag is on and the oxygen storage capacity; A catalyst deterioration diagnosis apparatus comprising:   2. The catalyst deterioration diagnosis apparatus according to claim 1, wherein the first predetermined value is at least a value that can be calculated from a deteriorated catalyst.   The catalyst deterioration diagnosis means does not use the oxygen storage capacity for the deterioration diagnosis of the catalyst when the periodic abnormality flag is ON and the oxygen storage capacity is less than a second predetermined value. The catalyst deterioration diagnosis apparatus according to claim 1, wherein   The catalyst deterioration diagnosing means can calculate the oxygen storage capacity from a deteriorated catalyst even if the periodic abnormality flag is ON and the oxygen storage capacity is less than the second predetermined value. 4. The catalyst deterioration diagnosis device according to claim 3, wherein when the value is equal to or greater than the value, the oxygen storage capacity is used for deterioration diagnosis of the catalyst.   When the oxygen storage capacity calculated before the periodic abnormality flag is turned on is less than the second predetermined value, the catalyst deterioration diagnosis unit performs the oxygen deterioration after the periodic abnormality flag is turned on. The catalyst deterioration diagnosis device according to claim 3 or 4, wherein the storage capacity is discarded.   The periodic abnormality determination means switches the periodic abnormality flag from on to off when the accumulated value of the number of times the oxygen storage capacity is not used reaches a predetermined number when the periodic abnormality flag is on. The catalyst deterioration diagnosis apparatus according to any one of claims 1 to 5, wherein the maximum oxygen amount calculated up to the present time is cleared.   The cycle abnormality determining means uses the oxygen amount as the maximum oxygen amount when the currently calculated oxygen amount exceeds the maximum oxygen amount. The catalyst deterioration diagnosis device according to Item.   The catalyst deterioration diagnosis device according to any one of claims 1 to 7, wherein the cycle abnormality determination unit does not perform the determination until the maximum oxygen amount is determined.   The catalyst deterioration according to any one of claims 1 to 8, wherein the cycle abnormality determination unit does not use the oxygen amount obtained immediately after the start of the execution of the air-fuel ratio control for the determination. Diagnostic device.

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