JP2009108681A - Abnormality diagnostic device for exhaust gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve abnormality detection accuracy of an exhaust gas sensor (hereinafter referred to as "catalyst downstream side sensor") installed on the downstream side of a catalyst for exhaust gas purification. <P>SOLUTION: Response time TL required for passage of output of the catalyst downstream side sensor through a predetermined section during fuel cut is measured and average suction air quantity GAav for a predetermined period is determined. When the average suction air quantity GAav exceeds predetermined quantity, it is determined that dispersion of the response time TL is small, and presence/absence of an abnormality (responsiveness deterioration) of the catalyst downstream side sensor is determined by comparing the response time TL with an abnormality determination value. When the average suction air quantity GAav is lower than the predetermined quantity, it is determined that dispersion of the response time TL is large, the abnormality diagnosis of the catalyst downstream side sensor is prohibited. Thus, even when the abnormality determination value is set stricter than that in conventional cases, determination failure caused by the dispersion of the response time TL can be prevented, so as to improve the abnormality detection accuracy of the catalyst downstream side sensor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an abnormality diagnosis device for an exhaust gas sensor that performs an abnormality diagnosis of the exhaust gas sensor based on an output change characteristic of the exhaust gas sensor installed on the downstream side of the exhaust gas purification catalyst during a fuel cut of the internal combustion engine. is there.

  In recent years, in vehicles equipped with an internal combustion engine, an exhaust gas purification catalyst is installed in an exhaust pipe, and an exhaust gas sensor (empty air / fuel ratio) for detecting the air-fuel ratio or rich / lean of the exhaust gas on the upstream side and downstream side of the catalyst, respectively. In some cases, an air-fuel ratio sensor or an oxygen sensor) is installed, and the exhaust gas purification efficiency of the catalyst is improved by feedback control of the air-fuel ratio based on the output of these exhaust gas sensors. In such an exhaust gas purification system, an abnormality diagnosis of the exhaust gas sensor is performed in order to prevent the operation from being continued in a state where the exhaust gas sensor is deteriorated and the air-fuel ratio control accuracy is lowered (a state where the exhaust gas purification efficiency is lowered). There is a need to do.

  In general, the output of an exhaust gas sensor (hereinafter referred to as “catalyst downstream sensor”) installed on the downstream side of the catalyst is affected by the oxygen storage amount (lean component storage amount) of the catalyst. It changes late.

Considering such characteristics, as described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2001-215205), the downstream side of the catalyst during the fuel cut of the internal combustion engine or after the fuel cut ends (after the fuel injection starts). There is a sensor that performs sensor failure determination. This depends on whether the output of the downstream sensor of the catalyst has become leaner than the threshold when a predetermined time has elapsed since the air-fuel ratio upstream of the catalyst changed in the lean direction after the fuel cut was started. It is determined whether the catalyst downstream sensor is normal. If the failure determination is not performed during the fuel cut, the downstream side of the catalyst is between the end of the fuel cut and the predetermined time after the air-fuel ratio on the upstream side of the catalyst changes in the rich direction. It is determined whether or not the catalyst downstream sensor is normal depending on whether or not the sensor output is richer than the threshold value. At that time, if the output of the downstream sensor of the catalyst is leaner than the threshold when a predetermined time has elapsed from the end of the fuel cut, if the integrated amount of exhaust gas from the end of the fuel cut is less than the predetermined value, the catalyst Hold down the failure judgment of the downstream sensor. As a result, the change of the air-fuel ratio downstream of the catalyst in the rich direction is delayed due to the shortage of the integrated amount of exhaust gas (rich component supply amount) after the fuel cut ends, and the output of the catalyst downstream sensor is leaner than the threshold value. Is prevented from being erroneously determined to be a failure of the catalyst downstream sensor.
JP 2001-215205 A

  By the way, the present inventor believes that the output change characteristic of the downstream sensor of the catalyst when the air-fuel ratio on the downstream side of the catalyst changes in the lean direction during the fuel cut of the internal combustion engine (for example, the output of the downstream sensor of the catalyst passes a predetermined section). We are researching a system that determines whether there is an abnormality (responsiveness degradation) in the downstream sensor of the catalyst by comparing the response time required for The problem was revealed.

  In recent years, the abnormality determination value for determining the output change characteristic (for example, response time) of the catalyst downstream sensor can be made stricter than before, and the detection accuracy of the catalyst downstream sensor abnormality (responsiveness degradation) can be improved. It is becoming required. However, according to the experiment result of the present inventor, when the intake air amount (exhaust air amount) during fuel cut is small, the variation range of the output change characteristic (for example, response time) of the downstream sensor of the catalyst tends to increase. It has been found. For this reason, if the abnormality determination value is strict, the output change characteristic of the downstream sensor of the catalyst is within the normal fluctuation range when the amount of intake air during the fuel cut is small and the variation range of the output change characteristic of the catalyst downstream sensor is large. Even if there is, there is a possibility that the abnormality determination value is exceeded and a normal catalyst downstream sensor is erroneously determined to be abnormal. For this reason, there is a problem that the abnormality determination value cannot be made very strict and the requirement for improving the abnormality detection accuracy of the catalyst downstream sensor cannot be satisfied.

  In the conventional technology, the variation in the output change characteristic of the downstream sensor of the catalyst due to the influence of the intake air amount during the fuel cut described above is not taken into consideration. Problems due to variations in sensor output change characteristics cannot be solved.

  The present invention has been made in consideration of such circumstances, and therefore the object of the present invention is to make the abnormality determination value for determining the output change characteristic of the downstream sensor of the catalyst stricter than before, It is possible to prevent misjudgment of abnormality diagnosis due to variations in the output change characteristics of the downstream sensor of the catalyst due to the influence of the intake air amount during fuel cut, and to meet the demand for improving the abnormality detection accuracy of the downstream sensor of the catalyst An object of the present invention is to provide an abnormality diagnosis device for an exhaust gas sensor.

  In order to achieve the above object, the invention according to claim 1 is directed to an output of an exhaust gas sensor (hereinafter referred to as “catalyst downstream sensor”) installed downstream of an exhaust gas purifying catalyst during fuel cut of an internal combustion engine. In an abnormality diagnosis device for an exhaust gas sensor having an abnormality diagnosis means for diagnosing an abnormality of the downstream sensor of the catalyst based on a change characteristic, an intake air amount determination is made as to whether or not the intake air amount during fuel cut is a predetermined amount or more. The abnormality diagnosis of the catalyst downstream side sensor is permitted by the abnormality diagnosis permission means when it is determined by the means and it is determined that the intake air amount during the fuel cut is greater than or equal to a predetermined amount.

  In this configuration, when it is determined that the intake air amount (exhaust air amount) during the fuel cut is greater than or equal to a predetermined amount, it is determined that the variation range of the output change characteristic of the catalyst downstream sensor is small, and the catalyst downstream sensor On the other hand, when it is determined that the intake air amount during fuel cut is smaller than the predetermined amount, it is determined that the variation range of the output change characteristic of the catalyst downstream sensor is large, and the catalyst Abnormal diagnosis of the downstream sensor can be prohibited. As a result, even if the abnormality determination value for determining the output change characteristic of the catalyst downstream sensor is made stricter than before, the amount of intake air during fuel cut is small and the variation range of the output change characteristic of the catalyst downstream sensor is small. If it is larger, it is possible to prevent the normal catalyst downstream sensor from being erroneously determined to be abnormal, and therefore the abnormality determination value can be made stricter than before, and the abnormality detection accuracy of the catalyst downstream sensor can be improved.

  In this case, the intake air amount may be detected by an air flow meter or the like during the fuel cut, and it may be determined whether or not the intake air amount during the fuel cut is a predetermined amount or more. In addition, it may be determined whether or not the intake air amount is greater than or equal to a predetermined amount based on an idle rotation speed control amount of the internal combustion engine during fuel cut. Since the intake air amount changes according to the idle speed control amount during fuel cut (for example, the opening of the idle speed control valve or the opening of the throttle valve), the intake air amount can be reduced by using the idle speed control amount. It can be determined whether or not it is a fixed amount or more.

  Further, as in claim 3, it may be determined whether the intake air amount is a predetermined amount or more based on the rotational speed of the internal combustion engine during fuel cut. Since the intake air amount changes according to the rotational speed of the internal combustion engine during fuel cut, it is possible to determine whether or not the intake air amount is greater than or equal to a predetermined amount by using the rotational speed of the internal combustion engine.

  Further, as in claim 4, it may be determined whether the intake air amount is a predetermined amount or more based on the load of the internal combustion engine during fuel cut. Since the load (for example, intake pressure) of the internal combustion engine changes according to the intake air amount during the fuel cut, it can be determined whether the intake air amount is equal to or greater than a predetermined amount by using the load of the internal combustion engine. .

  Further, as in claim 5, it may be determined whether or not the intake air amount is a predetermined amount or more based on the vehicle speed during fuel cut. Since the rotational speed of the internal combustion engine changes in accordance with the vehicle speed during fuel cut and the intake air amount changes, using the vehicle speed makes it possible to determine whether the intake air amount is greater than or equal to a predetermined amount. Even if the vehicle speed is the same, the rotational speed of the internal combustion engine changes due to the shift speed of the transmission and the intake air amount changes. Therefore, whether or not the intake air amount is greater than or equal to a predetermined amount based on the vehicle speed and the shift speed is determined. It may be determined.

  The present invention always inhales during the entire period of fuel cut (a period from the start of fuel cut to the end of fuel cut) or a predetermined period (for example, a period from the start of fuel cut until the output of the catalyst downstream sensor changes to a predetermined value). The abnormality diagnosis of the downstream sensor of the catalyst may be permitted when it is determined that the air amount is equal to or greater than the predetermined amount. However, as in claim 6, the average intake air amount over the entire period during fuel cut An abnormality diagnosis of the catalyst downstream sensor may be permitted when it is determined that the value or the integrated value is greater than or equal to a predetermined amount.

  If the average value or integrated value of the intake air amount over the entire period during the fuel cut is greater than or equal to the predetermined amount, the intake air amount when the output of the catalyst downstream sensor changes in the lean direction during the fuel cut is greater than or equal to the predetermined amount. Since it can be determined that the variation range of the output change characteristic when the output of the downstream sensor of the catalyst changes in the lean direction is small, the average value or integrated value of the intake air amount over the entire period during the fuel cut is greater than or equal to the predetermined amount If it is determined that the abnormality diagnosis of the catalyst downstream sensor is permitted, the abnormality diagnosis of the catalyst downstream sensor can be permitted when the variation range of the output change characteristic of the catalyst downstream sensor is small. .

  Alternatively, as in claim 7, when it is determined that the average value or integrated value of the intake air amount during the period from the start of fuel cut until the output of the catalyst downstream sensor changes to a predetermined value is greater than or equal to the predetermined amount. In addition, abnormality diagnosis of the catalyst downstream sensor may be permitted.

  If the average or integrated value of the intake air amount during the period from the start of fuel cut until the output of the catalyst downstream sensor changes to a predetermined value, the output of the catalyst downstream sensor during the fuel cut is in the lean direction It can be determined that the amount of intake air at the time of changing to a predetermined amount or more and the variation range of the output change characteristic when the output of the catalyst downstream sensor changes in the lean direction is small. If it is determined that the average value or integrated value of the intake air amount during the period until the output changes to the predetermined value is greater than or equal to the predetermined amount, the abnormality diagnosis of the downstream sensor of the catalyst is permitted. When the variation range of the output change characteristic of the side sensor is small, abnormality diagnosis of the downstream sensor of the catalyst can be permitted.

  Further, the abnormality diagnosis of the catalyst downstream side sensor may be permitted when it is determined that the intake air amount at the start of fuel cut is equal to or greater than a predetermined amount. Alternatively, as described in claim 9, when it is determined that the intake air amount when the output of the catalyst downstream sensor changes to a predetermined value during the fuel cut is greater than or equal to the predetermined value, the abnormality diagnosis of the catalyst downstream sensor is performed. May be allowed. In this way, the process of calculating the average value of the intake air amount or the information for determining it (the average value of the idle rotation speed control amount, etc.) is omitted, and the calculation load of the control circuit is reduced, and the fuel is reduced. It is possible to determine the intake air amount during the cut and permit abnormality diagnosis of the downstream sensor of the catalyst when the variation range of the output change characteristic of the downstream sensor of the catalyst is small.

  Several embodiments embodying the best mode for carrying out the present invention will be described below.

A first embodiment of the present invention will be described with reference to FIGS.
First, a schematic configuration of the entire engine control system will be described with reference to FIG.
An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of an in-line four-cylinder engine 11 which is an internal combustion engine, for example. An intake air temperature sensor 42 for detection is provided. As the intake air temperature sensor 42, a type integrated with the air flow meter 14 may be used, or a type provided separately from the air flow meter 14 may be used. On the downstream side of the air flow meter 14, a throttle valve 15 whose opening is adjusted by a motor or the like, and a throttle opening sensor 16 for detecting the opening (throttle opening) of the throttle valve 15 are provided.

  Further, a surge tank 17 is provided on the downstream side of the throttle valve 15, and an intake pipe pressure sensor 18 for detecting the intake pipe pressure is provided in the surge tank 17. The surge tank 17 is provided with an intake manifold 19 for introducing air into each cylinder of the engine 11, and a fuel injection valve 20 for injecting fuel is attached in the vicinity of the intake port of the intake manifold 19 of each cylinder. Yes. During engine operation, the fuel in the fuel tank 21 is sent to the delivery pipe 23 by the fuel pump 22 and fuel is injected from the fuel injection valve 20 of each cylinder at each injection timing of each cylinder. A fuel temperature sensor 24 for detecting the fuel temperature (fuel temperature) is attached to the delivery pipe 23.

  Further, the engine 11 is provided with variable valve timing mechanisms 27 and 28 for changing the valve timing (opening / closing timing) of the intake valve 25 and the exhaust valve 26, respectively. Further, the engine 11 is provided with an intake cam angle sensor 31 and an exhaust cam angle sensor 32 that output a cam angle signal in synchronization with the rotation of the intake cam shaft 29 and the exhaust cam shaft 30, and the crank of the engine 11. A crank angle sensor 33 that outputs a pulse of a crank angle signal at every predetermined crank angle (for example, every 30 ° C. A) in synchronization with the rotation of the shaft is provided.

  On the other hand, an air-fuel ratio sensor 37 for detecting the air-fuel ratio of the exhaust gas is installed in the exhaust gas confluence section 36 where the exhaust manifolds 35 of the cylinders of the engine 11 merge. A catalyst 38 such as a three-way catalyst for purifying CO, HC, NOx, etc. is provided. Further, an oxygen sensor (hereinafter referred to as “catalyst downstream sensor”) 41 that detects the rich / lean of the exhaust gas that has passed through the catalyst 38 is installed on the downstream side of the catalyst 38. A cooling water temperature sensor 43 for detecting the cooling water temperature is attached to the cylinder block of the engine 11.

  Outputs of the various sensors described above are input to an engine control circuit (hereinafter referred to as “ECU”) 40. The ECU 40 is mainly composed of a microcomputer, and executes various engine control programs stored in a built-in ROM (storage medium), so that the fuel of the fuel injection valve 20 of each cylinder according to the engine operating state. Control injection quantity and ignition timing.

  Further, the ECU 40 performs an abnormality diagnosis of the catalyst downstream side sensor 41 as follows by executing a catalyst downstream side sensor abnormality diagnosis routine of FIG. 2 described later. As shown in the time chart of FIG. 3, when the air-fuel ratio on the downstream side of the catalyst changes in the lean direction and the output of the catalyst downstream side sensor 41 changes in the lean direction during the fuel cut of the engine 11, the catalyst downstream side sensor The time required for 41 outputs to pass through a predetermined section (section from the upper threshold value to the lower threshold value) is measured as a response time TL (output change characteristic).

  Further, an average intake air amount GAav (an average value of the intake air amount detected by the air flow meter 14) in a period from the start of the fuel cut until the output of the catalyst downstream sensor 41 decreases to a predetermined value (for example, a lower threshold value) is obtained. . Note that the average intake air amount GAav in the entire period during the fuel cut (the period from the start of the fuel cut to the end of the fuel cut) may be obtained.

  It is determined whether or not the average intake air amount GAav is greater than or equal to a predetermined amount. If it is determined that the average intake air amount GAav is greater than or equal to the predetermined amount, the output of the catalyst downstream side sensor 41 is output during fuel cut. It is determined that the intake air amount (exhaust air amount) when changing in the lean direction is equal to or greater than a predetermined amount, and the variation range of the response time TL when the output of the catalyst downstream sensor 41 changes in the lean direction is small. Abnormal diagnosis of the downstream sensor 41 is permitted. This function corresponds to abnormality diagnosis permission means in the claims.

  In this case, it is determined whether or not the response time TL of the catalyst downstream side sensor 41 is larger than the abnormality determination value, and when it is determined that the response time TL of the catalyst downstream side sensor 41 is larger than the abnormality determination value, It is determined that there is an abnormality (responsiveness deterioration) in the catalyst downstream side sensor 41. On the other hand, when it is determined that the response time TL of the catalyst downstream sensor 41 is equal to or less than the abnormality determination value, it is determined that the catalyst downstream sensor 41 is not abnormal (normal).

  On the other hand, if it is determined that the average intake air amount GAav is smaller than the predetermined amount, it is determined that the variation range of the response time TL when the output of the catalyst downstream sensor 41 changes in the lean direction is large, and the catalyst Abnormal diagnosis of the downstream sensor 41 is prohibited. Thus, when the amount of intake air during fuel cut is small and the variation range of the response time TL of the catalyst downstream sensor 41 is large, it is possible to prevent the normal catalyst downstream sensor 41 from being erroneously determined to be abnormal.

  The abnormality diagnosis of the catalyst downstream sensor 41 of the first embodiment described above is executed by the ECU 40 according to the catalyst downstream sensor abnormality diagnosis routine of FIG. The processing contents of this routine will be described below.

The catalyst downstream side sensor abnormality diagnosis routine shown in FIG. 2 is executed at a predetermined cycle while the ECU 40 is turned on, and serves as abnormality diagnosis means in the claims. When this routine is started, first, in step 101, it is determined whether or not an abnormality diagnosis execution condition is satisfied based on, for example, the following conditions (1) to (3).
(1) The catalyst downstream sensor 41 is in an active state.
(2) Cooling water temperature is higher than the specified value
(3) No other abnormality has occurred

If all of these conditions (1) to (3) are satisfied, the abnormality diagnosis execution condition is satisfied, but if any one of the above conditions (1) to (3) is not satisfied, The diagnosis execution condition is not satisfied.
If it is determined in step 101 that the abnormality diagnosis execution condition is not satisfied, this routine is terminated without performing the processing from step 102 onward.

  On the other hand, if it is determined in step 101 that the abnormality diagnosis execution condition is satisfied, the processing after step 102 is performed as follows. First, in step 102, it is determined whether or not the fuel cut duration exceeds a predetermined time (for example, 5 seconds). When it is determined that the fuel cut duration exceeds a predetermined time, the flow proceeds to step 103, where It is determined whether the output of the catalyst downstream sensor 41 at the start of cutting is higher than a predetermined voltage. This predetermined voltage is set to a value higher than an upper threshold value (for example, 0.55 V) in a predetermined section in which the response time TL of the catalyst downstream side sensor 41 is measured.

  If it is determined in step 103 that the output of the catalyst downstream sensor 41 at the start of fuel cut is equal to or lower than the predetermined voltage, the output of the catalyst downstream sensor 41 at the start of fuel cut has already been output. Since the response time TL is close to the upper threshold value of the predetermined interval, it is determined that the delay in the output change of the catalyst downstream sensor 41 by the catalyst 38 has a large effect on the response time TL, and the processing from step 104 is performed. This routine is terminated without any processing.

  On the other hand, if it is determined in step 103 that the output of the catalyst downstream side sensor 41 at the start of fuel cut is higher than a predetermined voltage, the routine proceeds to step 104 where the air-fuel ratio on the downstream side of the catalyst is lean during the fuel cut. When the output of the catalyst downstream sensor 41 changes in the direction and changes in the lean direction, the time required for the output of the catalyst downstream sensor 41 to pass through the predetermined section, specifically, the catalyst downstream sensor 41 Is measured as the response time TL for the time required for the output to decrease from the upper threshold (for example, 0.55 V) to the lower threshold (for example, 0.3 V).

  Thereafter, the process proceeds to step 105, where the average intake air amount GAav (intake air amount detected by the air flow meter 14) from the start of fuel cut until the output of the catalyst downstream sensor 41 decreases to a predetermined value (for example, the lower threshold value). Average value). Note that the average intake air amount GAav in the entire period during the fuel cut (the period from the start of the fuel cut to the end of the fuel cut) may be obtained. Further, the integrated value of the intake air amount may be used.

  Thereafter, the routine proceeds to step 106, where it is determined whether or not the average intake air amount GAav is equal to or greater than a predetermined amount. The processing of these steps 105 and 106 serves as intake air amount determination means in the claims.

  If it is determined in step 106 that the average intake air amount GAav is greater than or equal to a predetermined amount, the intake air amount (exhaust air amount) when the output of the catalyst downstream sensor 41 changes in the lean direction during fuel cut. ) Is equal to or greater than a predetermined amount, and the variation range of the response time TL when the output of the catalyst downstream sensor 41 changes in the lean direction is determined to be small, and abnormality diagnosis of the catalyst downstream sensor 41 is permitted. This function corresponds to abnormality diagnosis permission means in the claims.

  Thereafter, the routine proceeds to step 107, where it is determined whether or not the response time TL of the catalyst downstream side sensor 41 is larger than the abnormality determination value. As a result, when it is determined that the response time TL of the catalyst downstream side sensor 41 is larger than the abnormality determination value, the process proceeds to step 108, where it is determined that there is an abnormality (responsiveness deterioration) of the catalyst downstream side sensor 41. Set the flag to ON and turn on the warning lamp (not shown) on the instrument panel of the driver's seat or display the warning on the warning display section (not shown) of the instrument panel of the driver's seat Then, a warning is given to the driver, and the abnormality information (abnormality code or the like) is rewritable nonvolatile memory such as a backup RAM (not shown) of the ECU 40 (a rewritable memory that holds stored data even when the ECU 40 is powered off). ) And finish this routine.

  On the other hand, when it is determined in step 107 that the response time TL of the catalyst downstream sensor 41 is equal to or less than the abnormality determination value, the process proceeds to step 109, and there is no abnormality (normal) in the catalyst downstream sensor 41. Is determined, the abnormality flag is kept OFF, and this routine is terminated.

  On the other hand, if it is determined in step 106 that the average intake air amount GAav is smaller than the predetermined amount, the variation range of the response time TL when the output of the catalyst downstream sensor 41 changes in the lean direction is large. Determination is made, and the abnormality diagnosis of the catalyst downstream sensor 41 is prohibited by ending this routine without performing the processing from step 107 onward.

  An execution example of the abnormality diagnosis of the catalyst downstream sensor 41 of the first embodiment described above will be described with reference to the time chart of FIG. During the fuel cut of the engine 11, at a time t1 when a predetermined time has elapsed from the time t0 when the fuel cut is started, it is determined whether or not the output of the catalyst downstream sensor 41 at the start of the fuel cut is higher than a predetermined voltage. When the output of the catalyst downstream sensor 41 at the start of the fuel cut is higher than a predetermined voltage, the output of the catalyst downstream sensor 41 changes when the output of the catalyst downstream sensor 41 changes in the lean direction during the fuel cut. The time required from the time t2 when the current passes the upper threshold to the time t3 when the lower threshold is passed is measured as the response time TL.

  Further, an average intake air amount GAav in a period from the fuel cut start time t0 to the time t3 when the output of the catalyst downstream sensor 41 decreases to the lower threshold is obtained, and when this average intake air amount GAav is equal to or greater than a predetermined amount. Then, it is determined that the variation range of the response time TL of the catalyst downstream sensor 41 is small, the abnormality diagnosis of the catalyst downstream sensor 41 is permitted, and whether or not the response time TL of the catalyst downstream sensor 41 is larger than the abnormality determination value. Determine whether. As a result, when it is determined that the response time TL of the catalyst downstream sensor 41 is longer than the abnormality determination value, it is determined that the catalyst downstream sensor 41 is abnormal (responsiveness deterioration) and the abnormality flag is set to ON. To do. In contrast, if it is determined that the response time TL of the catalyst downstream sensor 41 is equal to or less than the abnormality determination value, it is determined that the catalyst downstream sensor 41 is not abnormal (normal) and the abnormality flag is kept OFF. To do.

  On the other hand, when it is determined that the average intake air amount GAav is smaller than the predetermined amount, it is determined that the variation range of the response time TL of the catalyst downstream sensor 41 is large, and abnormality diagnosis of the catalyst downstream sensor 41 is prohibited. To do. Thereby, even if the abnormality determination value for determining the response time TL of the catalyst downstream sensor 41 is stricter than before, the intake air amount during fuel cut is small and the response time TL of the catalyst downstream sensor 41 varies. When the range is large, it is possible to prevent the normal catalyst downstream sensor 41 from erroneously determining that there is an abnormality. Therefore, the abnormality determination value is made stricter than before and the abnormality detection accuracy of the catalyst downstream sensor 41 is improved. Can do.

  In the first embodiment, a predetermined period during the fuel cut (a period from the start of the fuel cut until the output of the catalyst downstream sensor 41 decreases to a predetermined value) or an entire period (a period from the start of the fuel cut to the end of the fuel cut). When the average intake air amount is determined to be equal to or greater than the predetermined amount, the abnormality diagnosis of the catalyst downstream sensor 41 is permitted. However, the intake air amount is always constant during the predetermined period or the entire period during the fuel cut. An abnormality diagnosis of the catalyst downstream side sensor 41 may be permitted when it is determined that the amount is equal to or greater than the fixed amount.

  Next, Embodiment 2 of the present invention will be described with reference to FIG. However, the description of the substantially same parts as those of the first embodiment will be simplified, and different parts from the first embodiment will be mainly described.

  In the second embodiment, when the catalyst downstream side sensor abnormality diagnosis routine of FIG. 4 is executed, when it is determined that the intake air amount GA detected by the air flow meter 14 at the start of fuel cut is equal to or greater than a predetermined amount, the catalyst It is determined that the variation range of the response time TL of the downstream side sensor 41 is small, and abnormality diagnosis of the catalyst downstream side sensor 41 is permitted.

  The routine of FIG. 4 is obtained by changing steps 105 and 106 of the routine of FIG. 2 described in the first embodiment to steps 105a and 106a, respectively. The same.

  Hereinafter, the processing content of the catalyst downstream side sensor abnormality diagnosis routine of FIG. 4 will be described. In this routine, if the abnormality diagnosis execution condition is satisfied, whether or not the output of the catalyst downstream side sensor 41 at the start of the fuel cut is higher than a predetermined voltage when the duration of the fuel cut exceeds a predetermined time. Is determined (steps 101 to 103).

  If it is determined that the output of the catalyst downstream sensor 41 at the start of fuel cut is higher than the predetermined voltage, in step 104, the output of the catalyst downstream sensor 41 is a predetermined interval (interval from the upper threshold value to the lower threshold value). ) Is measured as the response time TL, and then the process proceeds to step 105a, where the intake air amount GA detected by the air flow meter 14 at the start of fuel cut is read.

  Thereafter, the process proceeds to step 106a, where it is determined whether or not the intake air amount GA at the start of fuel cut is greater than or equal to a predetermined amount, and it is determined that the intake air amount GA at the start of fuel cut is greater than or equal to a predetermined amount. Therefore, it is determined that the variation range of the response time TL when the output of the catalyst downstream sensor 41 changes in the lean direction is small, and abnormality diagnosis of the catalyst downstream sensor 41 is permitted.

  In this case, it is determined whether or not the response time TL of the catalyst downstream side sensor 41 is larger than the abnormality determination value, and when it is determined that the response time TL of the catalyst downstream side sensor 41 is larger than the abnormality determination value, When it is determined that there is an abnormality (responsiveness degradation) in the catalyst downstream sensor 41 and it is determined that the response time TL of the catalyst downstream sensor 41 is equal to or less than the abnormality determination value, there is no abnormality in the catalyst downstream sensor 41 ( Normal) (steps 107 to 109).

  On the other hand, if it is determined in step 106a that the average intake air amount GAav is smaller than the predetermined amount, the variation range of the response time TL when the output of the catalyst downstream sensor 41 changes in the lean direction is large. Judgment is made and abnormality diagnosis of the catalyst downstream sensor 41 is prohibited.

  Also in the second embodiment described above, when the variation range of the response time TL of the catalyst downstream side sensor 41 is small, abnormality diagnosis of the catalyst downstream side sensor 41 can be permitted, and substantially the same effect as the first embodiment. And the calculation load on the ECU 40 can be reduced by omitting the process of calculating the average value of the intake air amount.

  In the second embodiment, the abnormality diagnosis of the catalyst downstream side sensor 41 is permitted when it is determined that the intake air amount GA at the start of the fuel cut is greater than or equal to the predetermined amount. When it is determined that the intake air amount GA when the output of the catalyst downstream sensor 41 has decreased to a predetermined value (for example, the lower threshold) is greater than or equal to the predetermined amount, abnormality diagnosis of the catalyst downstream sensor 41 is permitted. Anyway.

  In each of the first and second embodiments, the intake air amount is detected by the air flow meter 14 during the fuel cut (a predetermined period or all of the fuel cut, at the start of the fuel cut, or a predetermined time during the fuel cut), Whether or not the intake air amount during fuel cut is greater than or equal to a predetermined amount is determined. For example, whether or not the intake air amount is greater than or equal to a predetermined amount based on the idle rotation speed control amount during fuel cut. May be determined. Here, in the case of a system that controls the idling speed by the idling speed control valve, the idling speed control valve opening corresponds to the idling speed control amount, and the idling speed control amount is controlled by the throttle opening. The throttle opening corresponds to the idle rotation speed control amount. Since the intake air amount changes according to the idle rotation speed control amount (the opening degree of the idle speed control valve and the throttle opening degree) during fuel cut, if the idle rotation speed control amount is used, the intake air amount exceeds a predetermined amount. It can be determined whether or not there is.

  Further, it may be determined whether or not the intake air amount is a predetermined amount or more based on the engine rotation speed value during fuel cut. Since the intake air amount changes according to the engine rotation speed during fuel cut, it is possible to determine whether or not the intake air amount is greater than or equal to a predetermined amount by using the engine rotation speed.

  Further, it may be determined whether the intake air amount is a predetermined amount or more based on the engine load (for example, intake pressure) during the fuel cut. Since the engine load changes according to the intake air amount during fuel cut, it is possible to determine whether the intake air amount is equal to or greater than a predetermined amount by using the engine load.

  Further, it may be determined whether the intake air amount is a predetermined amount or more based on the vehicle speed during the fuel cut. Since the engine rotation speed changes in accordance with the vehicle speed during fuel cut and the intake air amount changes, it can be determined whether the intake air amount is equal to or greater than a predetermined amount by using the vehicle speed. Even if the vehicle speed is the same, the engine speed changes depending on the gear position of the transmission and the intake air amount changes. Therefore, whether or not the intake air amount is greater than or equal to a predetermined amount based on the vehicle speed and the gear position during fuel cut. You may make it determine.

  Further, it is determined whether or not the intake air amount is a predetermined amount or more by using any two or more of the idle rotational speed control amount, the engine rotational speed, the engine load, the vehicle speed, and the gear position during the fuel cut. Anyway.

  In the first and second embodiments, the response time (the time required for the output of the catalyst downstream side sensor 41 to pass through the predetermined section) is used as the output change characteristic of the catalyst downstream side sensor 41. However, the present invention is not limited to this, and the rate of change when the output of the catalyst downstream sensor 41 passes through a predetermined section, the amount of change and the rate of change of the output of the catalyst downstream sensor 41 during the predetermined period, and the like. You may make it use as a change characteristic.

  In the first and second embodiments, the present invention is applied to a system using an oxygen sensor as the catalyst downstream sensor 41. However, the present invention is applied to a system using an air-fuel ratio sensor as the catalyst downstream sensor 41. May be.

It is a schematic block diagram of the whole engine control system in Example 1 of this invention. 6 is a flowchart for explaining a flow of processing of a catalyst downstream side sensor abnormality diagnosis routine of Example 1; 6 is a time chart for explaining an execution example of catalyst downstream side sensor abnormality diagnosis of Example 1. FIG. 6 is a flowchart for explaining a flow of processing of a catalyst downstream side sensor abnormality diagnosis routine of Embodiment 2.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 14 ... Air flow meter, 15 ... Throttle valve, 20 ... Fuel injection valve, 38 ... Catalyst, 40 ... ECU (abnormality diagnosis means, abnormality diagnosis permission means, intake air amount determination) Means), 41 ... Catalyst downstream sensor

Claims (9)

An abnormality that diagnoses abnormality of the downstream sensor of the catalyst based on the output change characteristic of an exhaust gas sensor (hereinafter referred to as “catalyst downstream sensor”) installed downstream of the exhaust gas purifying catalyst during fuel cut of the internal combustion engine In the exhaust gas sensor abnormality diagnosis device provided with a diagnostic means,
Intake air amount determination means for determining whether or not the intake air amount during the fuel cut is a predetermined amount or more;
Abnormality diagnosis permission means for permitting abnormality diagnosis of the catalyst downstream sensor by the abnormality diagnosis means when the intake air amount determination means determines that the amount of intake air during the fuel cut is greater than or equal to a predetermined amount. An exhaust gas sensor abnormality diagnosis device characterized by comprising:   The intake air amount determination means determines whether or not the intake air amount is a predetermined amount or more based on an idle rotation speed control amount of the internal combustion engine during the fuel cut. An abnormality diagnosis device for exhaust gas sensors.   The exhaust according to claim 1 or 2, wherein the intake air amount determination means determines whether or not the intake air amount is a predetermined amount or more based on a rotational speed of the internal combustion engine during the fuel cut. Gas sensor abnormality diagnosis device.   The intake air amount determination means determines whether or not the intake air amount is a predetermined amount or more based on a load of the internal combustion engine during the fuel cut. Abnormality diagnosis device for exhaust gas sensors.   The exhaust gas sensor according to any one of claims 1 to 4, wherein the intake air amount determination means determines whether or not the intake air amount is a predetermined amount or more based on a vehicle speed during the fuel cut. Abnormality diagnosis device. The intake air amount determination means determines whether the average value or integrated value of the intake air amount over the entire period during the fuel cut is a predetermined amount or more,
The abnormality diagnosis permission unit is configured to detect the catalyst by the abnormality diagnosis unit when the intake air amount determination unit determines that the average value or integrated value of the intake air amount over the entire period during the fuel cut is equal to or greater than a predetermined amount. The abnormality diagnosis device for an exhaust gas sensor according to any one of claims 1 to 5, wherein abnormality diagnosis of the downstream sensor is permitted. The intake air amount determination means determines whether the average value or integrated value of the intake air amount in a period from the start of the fuel cut until the output of the catalyst downstream sensor changes to a predetermined value is greater than or equal to a predetermined amount. And
The abnormality diagnosis permission means is configured such that an average value or integrated value of the intake air amount during a period from the start of the fuel cut by the intake air amount determination means until the output of the catalyst downstream sensor changes to a predetermined value is greater than or equal to a predetermined amount. The abnormality diagnosis device for an exhaust gas sensor according to any one of claims 1 to 5, wherein abnormality diagnosis of the downstream sensor of the catalyst by the abnormality diagnosis means is permitted when it is determined that the abnormality exists. The intake air amount determination means determines whether or not the intake air amount at the start of the fuel cut is a predetermined amount or more;
The abnormality diagnosis permission unit permits the abnormality diagnosis of the downstream sensor of the catalyst by the abnormality diagnosis unit when the intake air amount determination unit determines that the intake air amount at the start of the fuel cut is equal to or greater than a predetermined amount. An abnormality diagnosis apparatus for an exhaust gas sensor according to any one of claims 1 to 5. The intake air amount determination means determines whether or not the intake air amount when the output of the catalyst downstream sensor changes to a predetermined value during the fuel cut is greater than or equal to a predetermined amount;
The abnormality diagnosis permission unit is configured to determine when the intake air amount determination unit determines that the intake air amount when the output of the catalyst downstream sensor changes to a predetermined value during the fuel cut is greater than or equal to a predetermined amount. The abnormality diagnosis device for an exhaust gas sensor according to any one of claims 1 to 5, wherein abnormality diagnosis of the downstream sensor of the catalyst is permitted by an abnormality diagnosis means.

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