JP7639619B2 - Abnormality determination device and method, and computer program - Google Patents

Description

The present invention relates to the technical field of an abnormality determination device and method, as well as a computer program, for determining an abnormality in a sensor provided downstream of a catalyst arranged in the exhaust passage of an internal combustion engine.

As an example of this type of device, a device has been proposed that diagnoses the deterioration of an exhaust gas sensor downstream of an exhaust gas purification catalyst in the exhaust passage of an internal combustion engine, and prohibits the determination of the deterioration of the exhaust gas sensor if a parameter value corresponding to the period from the start of fuel cut to the time when the output value of the exhaust gas sensor changes to a predetermined output value is less than a predetermined threshold value (see Patent Document 1).

Patent No. 5287809

In Patent Document 1, in order to prevent erroneous judgments, the deterioration judgment of the sensor is prohibited when the parameter value is less than a predetermined threshold value. However, when the deterioration judgment is prohibited, the opportunities for judging the deterioration of the exhaust gas sensor are reduced. In other words, there is room for improvement in the technology described in Patent Document 1.

The present invention has been made in consideration of the above circumstances, and aims to provide an abnormality determination device, method, and computer program that can reduce the occurrence of erroneous determinations while suppressing the reduction in opportunities for sensor abnormality determinations.

An abnormality determination device according to one embodiment of the present invention comprises a determination means for determining whether or not the sensor is abnormal based on an index relating to an output change of the sensor that detects oxygen in the exhaust gas, and a detection means for detecting an accumulated air amount from the time when the air-fuel ratio of the inlet gas sucked into the catalyst becomes lean until the air-fuel ratio of the outlet gas discharged from the catalyst becomes lean when a fuel cut is performed to stop the supply of fuel to the internal combustion engine, and the determination means corrects the index according to the accumulated air amount , and the index indicates the change in output of the sensor per unit time .

An abnormality determination method according to one embodiment of the present invention includes a determination step of determining whether or not a sensor that detects oxygen in the exhaust gas is abnormal, based on an index related to an output change of the sensor that is disposed downstream of a catalyst arranged in an exhaust passage of an internal combustion engine, and a detection step of detecting an accumulated air amount from when the air-fuel ratio of inlet gases sucked into the catalyst becomes lean until the air-fuel ratio of outlet gases discharged from the catalyst becomes lean when a fuel cut is performed to stop fuel supply to the internal combustion engine, wherein in the determination step, the index is corrected according to the accumulated air amount , and the index indicates a change in output of the sensor per unit time .

A computer program according to one embodiment of the present invention causes a computer of an abnormality determination device, which is provided downstream of a catalyst arranged in an exhaust passage of an internal combustion engine and determines an abnormality in a sensor that detects oxygen in the exhaust, to function as: determination means for determining whether the sensor is abnormal based on an index related to a change in output of the sensor; and detection means for detecting, when a fuel cut is performed to stop fuel supply to the internal combustion engine, an accumulated air amount from the time when the air-fuel ratio of inlet gases sucked into the catalyst becomes lean to the time when the air-fuel ratio of outlet gases discharged from the catalyst becomes lean, and the determination means corrects the index according to the accumulated air amount, and the index indicates a change in output of the sensor per unit time .

1 is a diagram showing a configuration of a vehicle according to a first embodiment. FIG. 4 is a diagram showing an example of a change in output of an A/F sensor over time. 4 is a flowchart showing an operation of an ECU according to the first embodiment. 5 is a flowchart showing an operation of an ECU according to a first modified example of the first embodiment. 10 is a flowchart showing an operation of an ECU according to a second modified example of the first embodiment. FIG. 11 is a diagram showing a configuration of a vehicle according to a second embodiment. 10 is a flowchart showing an operation of an ECU according to a second embodiment. 13 is a flowchart showing an operation of an ECU according to a first modified example of the second embodiment. 10 is a flowchart showing an operation of an ECU according to a second modified example of the second embodiment. FIG. 1 is a block diagram showing a configuration of a computer according to an embodiment.

First Embodiment
A first embodiment of an abnormality determination device will be described with reference to Fig. 1 to Fig. 3. Here, an example of the abnormality determination device is an ECU (Electronic Control Unit) 30 mounted on a vehicle 1. That is, in this embodiment, at least a part of the ECU 30 for controlling the vehicle 1 is used as the abnormality determination device.

In FIG. 1, the vehicle 1 includes an engine 10, an intake passage 11 connected to an intake port of the engine 10, and an exhaust passage 12 connected to an exhaust port of the engine 10. A catalyst 13 and a catalyst 14 are arranged in the exhaust passage 12. For example, a three-way catalyst or an oxidation catalyst can be applied to the catalysts 13 and 14. The type of catalyst 13 and the type of catalyst 14 may be the same or different.

An air flow sensor 21 that detects the amount of air taken into the engine 10 is provided in the intake passage 11. An air-fuel ratio (A/F) sensor 22 that detects oxygen in the exhaust is provided downstream of the catalyst 13 and upstream of the catalyst 14 in the exhaust passage 12. An air-fuel ratio sensor 23 that detects oxygen in the exhaust is provided downstream of the catalyst 14 in the exhaust passage 12. Note that an oxygen ( _O2 ) sensor may be used instead of the air-fuel ratio sensors 22 and 23.

The ECU 30 as an abnormality determination device has a control unit 31, an acquisition unit 32, and a determination unit 33, which are implemented as a logical block logically realized therein or as a processing circuit physically realized. The control unit 31 is configured to be able to perform a fuel cut (F/C) to stop the supply of fuel to the engine 10. The acquisition unit 32 acquires the outputs of the air flow sensor 21 and the air-fuel ratio sensors 22 and 23. The determination unit 33 performs an abnormality determination process to determine whether the air-fuel ratio sensor 23 is abnormal. Note that the determination unit 33 may perform an abnormality determination process on the air-fuel ratio sensor 22, for example, in addition to the air-fuel ratio sensor 23.

The following describes the abnormality determination process performed by the determination unit 33. The determination unit 33 determines whether the air-fuel ratio sensor 23 is normal or deteriorated (i.e., abnormal) based on the output of the air-fuel ratio sensor 23 when fuel cut is being performed by the control unit 31.

When a fuel cut is performed, the amount of oxygen (or oxygen concentration) in the exhaust increases, so the output of the air-fuel ratio sensor 23 changes to the lean side (i.e., the air-fuel ratio value increases). At this time, the responsiveness of the air-fuel ratio sensor 23 (i.e., the change in the output of the air-fuel ratio sensor 23 in response to the change in the amount of oxygen in the exhaust) deteriorates as the deterioration of the air-fuel ratio sensor 23 progresses. The determination unit 33 determines whether the air-fuel ratio sensor 23 is abnormal from the responsiveness of the air-fuel ratio sensor 23 based on the output of the air-fuel ratio sensor 23.

According to the research of the present inventors, it has been found that the responsiveness of the air-fuel ratio sensor 23 varies depending on the degree of deterioration of the air-fuel ratio sensor 23 as well as the oxygen storage state of the catalyst 14.

Specifically, the constituents of catalysts such as catalyst 14 include substances that store oxygen regardless of the oxygen concentration in the exhaust gas, and substances that store oxygen only when the oxygen concentration in the exhaust gas is relatively high. As described above, when fuel cut is performed, the amount of oxygen in the exhaust gas increases. If there is a substance in the catalyst that does not store oxygen, oxygen is stored in this substance after fuel cut is performed. If there is a relatively large amount of substance in the catalyst that does not store oxygen, a relatively large amount of oxygen is stored in the catalyst, so the amount of oxygen in the exhaust gas downstream of the catalyst hardly changes for a while after fuel cut is performed, and after the catalyst has stored a sufficient amount of oxygen, the amount of oxygen in the exhaust gas downstream of the catalyst increases rapidly. On the other hand, if there is a relatively small amount of substance in the catalyst that does not store oxygen, oxygen is stored in the catalyst, but the oxygen that was not stored in the catalyst flows downstream of the catalyst, so the amount of oxygen in the exhaust gas downstream of the catalyst increases relatively slowly after fuel cut is performed.

The effect of this on the responsiveness of the air-fuel ratio sensor 23 will be explained with reference to FIG. 2. In the graph in the middle of FIG. 2 (A/F sensor 23 output (normal)), the solid line (i) is an example of the time change in the output of a normal air-fuel ratio sensor 23 when the amount of substances that do not store oxygen in the catalyst 14 is relatively large, and the dashed line (ii) is an example of the time change in the output of a normal air-fuel ratio sensor 23 when the amount of substances that do not store oxygen in the catalyst 14 is relatively small. When the amount of substances that do not store oxygen in the catalyst 14 is relatively large, the amount of oxygen in the exhaust downstream of the catalyst 14 increases rapidly, so the output of the air-fuel ratio sensor 23 also increases rapidly (see solid line (i)). When the amount of substances that do not store oxygen in the catalyst 14 is relatively small, the amount of oxygen in the exhaust downstream of the catalyst 14 increases relatively slowly, so the output of the air-fuel ratio sensor 23 also increases relatively slowly (see dashed line (ii)).

In the graph at the bottom of Figure 2 (A/F sensor 23 output (abnormal)), the solid line (i) is an example of the change over time in the output of a deteriorated air-fuel ratio sensor 23 when there is a relatively large amount of material that does not store oxygen in the catalyst 14, and the dashed line (ii) is an example of the change over time in the output of a deteriorated air-fuel ratio sensor 23 when there is a relatively small amount of material that does not store oxygen in the catalyst 14.

In FIG. 2, there is a time lag between when the F/C flag is turned ON (i.e., when fuel cut is started) and when a change appears in the output of the air-fuel ratio sensor 23. This is because, for example, oxygen in the exhaust gas is absorbed by the catalysts 13 and 14.

When we look at the degree of increase in the output of the air-fuel ratio sensor 23 (specifically, the slope), the slope of the solid line (i) in the graph in the lower part of Figure 2 is gentler than the slope of the solid line (i) in the graph in the middle part of Figure 2. In other words, this slope is an index that shows the responsiveness of the air-fuel ratio sensor 23. In this way, when the air-fuel ratio sensor 23 deteriorates (i.e., is abnormal), the slope becomes gentler. The same can be said for the dashed line (ii).

On the other hand, when comparing the slope of the dashed line (ii) in the graph in the middle of Figure 2 with the slope of the solid line (i) in the graph in the bottom of Figure 2, no significant difference is found between the two. In other words, even if the responsiveness of the air-fuel ratio sensor 23 is different, depending on the amount of material in the catalyst 14 that does not store oxygen (i.e., the oxygen storage state of the catalyst 14), it may not be possible to correctly determine an abnormality in the air-fuel ratio sensor 23 from the slope based on the output of the air-fuel ratio sensor 23.

The inventors of the present application have discovered that the amount of intake air until the output of the air-fuel ratio sensor 23 starts to change to the lean side (i.e., the value of the output of the air-fuel ratio sensor 23 starts to increase) is affected by the oxygen storage state of the catalyst 14. Therefore, in this embodiment, the abnormality determination process for the air-fuel ratio sensor 23 is performed taking into account the amount of intake air.

Next, the abnormality determination process according to this embodiment will be described with reference to the flowchart in FIG. 3. In the flowchart in FIG. 3, the control unit 31 performs a fuel cut (step S101). Next, the determination unit 33 determines whether the value indicated by the output of the air-fuel ratio sensor 22 acquired by the acquisition unit 32 is greater than a first predetermined value (step S102).

The "first predetermined value" is a value that determines whether or not to start accumulating the intake air amount Ga, and is set in advance as a fixed value or as a variable value according to some physical quantity or parameter. In this embodiment, accumulation of the intake air amount Ga starts at the timing when the amount of oxygen or oxygen concentration in the exhaust upstream of the catalyst 14 starts to increase due to fuel cut. Such a first predetermined value can be set by experimentally, empirically, or by simulation, by determining, for example, the range of possible values of the output of the air-fuel ratio sensor 22 when the air-fuel ratio upstream of the catalyst 14 is lean, and taking into consideration the lower limit of the determined range and the error in the output of the air-fuel ratio sensor 22.

If it is determined in the process of step S102 that the value indicated by the output of the air-fuel ratio sensor 22 is smaller than the first predetermined value (step S102: No), the process of step S102 is performed again. In other words, a standby state is entered until the value indicated by the output of the air-fuel ratio sensor 22 becomes larger than the first predetermined value. Note that if the value indicated by the output of the air-fuel ratio sensor 22 is "equal" to the first predetermined value, it may be treated as being included in either one.

If it is determined in the processing of step S102 that the value indicated by the output of the air-fuel ratio sensor 22 is greater than the first predetermined value (step S102: Yes), the determination unit 33 starts accumulating the intake air volume Ga based on the output of the air flow sensor 21 acquired by the acquisition unit 32 (step S103).

Next, the determination unit 33 determines whether the value indicated by the output of the air-fuel ratio sensor 23 acquired by the acquisition unit 32 is greater than the second predetermined value (step S104). In the process of step S104, if it is determined that the value indicated by the output of the air-fuel ratio sensor 23 is smaller than the second predetermined value (step S104: No), the process of step S104 is performed again. In other words, a standby state is entered until the value indicated by the output of the air-fuel ratio sensor 23 becomes greater than the second predetermined value. Note that if the value indicated by the output of the air-fuel ratio sensor 23 is "equal" to the second predetermined value, it may be treated as being included in either one.

The "second predetermined value" is a value that determines whether or not to end the accumulation of the intake air amount Ga, and is set in advance as a fixed value or as a variable value according to some physical quantity or parameter. In this embodiment, the accumulation of the intake air amount Ga is ended at the timing when the amount of oxygen or oxygen concentration in the exhaust downstream of the catalyst 14 begins to increase due to fuel cut. Such a second predetermined value may be set by experimentally, empirically, or by simulation, determining the range that the output value of the air-fuel ratio sensor 23 can take when the air-fuel ratio downstream of the catalyst 14 is lean, for example, and taking into consideration the lower limit of the determined range and the error in the output of the air-fuel ratio sensor 23. The second predetermined value may be the same as the first predetermined value.

If it is determined in the processing of step S104 that the value indicated by the output of the air-fuel ratio sensor 23 is greater than the second predetermined value (step S104: Yes), the determination unit 33 ends the accumulation of the intake air volume Ga (step S105).

Next, the determination unit 33 calculates a parameter related to the abnormality determination of the air-fuel ratio sensor 23 (here, the "slope", i.e., the change in the output of the air-fuel ratio sensor 23 per unit time) (step S106). In parallel with or before or after the processing of step S106, the determination unit 33 calculates a correction term for the above parameter from the integrated value of the intake air amount Ga (step S107).

A relatively small cumulative value of the intake air amount Ga indicates that the amount of substances not storing oxygen contained in the catalyst 14 was relatively small. In other words, a relatively large cumulative value of the intake air amount Ga indicates that the amount of substances not storing oxygen contained in the catalyst 14 was relatively large.

When the amount of substances that do not store oxygen contained in the catalyst 14 is relatively small, the slope of the output of the air-fuel ratio sensor 23 is smaller than when the amount of substances that do not store oxygen contained in the catalyst 14 is relatively large (see, for example, FIG. 2). Therefore, the determination unit 33 calculates the above correction term from the integrated value of the intake air amount Ga so that when the integrated value of the intake air amount Ga is relatively small, the value of the above correction term is larger than when the integrated value of the intake air amount Ga is relatively large.

Next, the determination unit 33 corrects the parameter calculated in the process of step S106 based on the correction term calculated in the process of step S107 (step S108). The parameter may be corrected, for example, by adding the value of the correction term to the parameter. The parameter correction method is not limited to this, and may be any method that reduces the effect of the oxygen storage state of the catalyst 14 on the parameter.

The determination unit 33 determines whether the corrected parameter is greater than the first threshold value in the process of step S108 (step S109). If the corrected parameter is greater than the first threshold value in the process of step S109 (step S109: Yes), the determination unit 33 determines that the air-fuel ratio sensor 23 is normal (step S110). On the other hand, if the corrected parameter is less than the first threshold value in the process of step S109 (step S109: No), the determination unit 33 determines that the air-fuel ratio sensor 23 is abnormal (or deteriorated) (step S111).

The "first threshold" is a value that determines whether the air-fuel ratio sensor 23 is normal or abnormal, and is set in advance as a fixed value or as a variable value according to some physical quantity or parameter. Such a first threshold can be set by, for example, determining the relationship between the degree of deterioration of the air-fuel ratio sensor 23 and a parameter related to the abnormality determination of the air-fuel ratio sensor 23 experimentally, empirically, or by simulation, and setting the value of the parameter that corresponds to the boundary of the allowable range of deterioration of the air-fuel ratio sensor 23 based on the determined relationship. Note that if the corrected parameter is "equal" to the first threshold, it can be treated as being included in either one.

(Technical effect)
According to the ECU 30 serving as the abnormality determination device, the influence of the oxygen storage state of the catalyst 14 on the abnormality determination process is reduced, and then a determination is made as to whether or not the air-fuel ratio sensor 23 is abnormal. Therefore, according to the present embodiment, it is possible to perform an abnormality determination of the air-fuel ratio sensor 23 regardless of the oxygen storage state of the catalyst 14. In addition, since the influence of the oxygen storage state of the catalyst 14 on the abnormality determination process is reduced, it is possible to suppress the occurrence of erroneous determination in the abnormality determination of the air-fuel ratio sensor 23. Therefore, according to the ECU 30 serving as the abnormality determination device, it is possible to suppress a decrease in the opportunities for determining an abnormality of the air-fuel ratio sensor 23 while suppressing the occurrence of erroneous determination.

(First Modification)
A first modification of the abnormality determination process described above will be described with reference to the flowchart of Fig. 4. In the abnormality determination process described above, the parameters related to abnormality determination of the air-fuel ratio sensor 23 are corrected in accordance with the integrated value of the intake air amount Ga. In contrast, in the first modification, the first threshold value related to abnormality determination (see step S109 described above) is corrected in accordance with the integrated value of the intake air amount Ga.

In other words, in this first modified example, the first threshold value for abnormality determination is corrected according to the integrated value of the intake air amount Ga, which reflects the oxygen storage state of the catalyst 14, thereby reducing the effect of the oxygen storage state of the catalyst 14 on the abnormality determination process.

In FIG. 4, in parallel with or before or after the processing of step S106, the judgment unit 33 of the ECU 30 calculates the correction term for the first threshold value from the integrated value of the intake air amount Ga (step S201). When the amount of substances not storing oxygen contained in the catalyst 14 is relatively small (i.e., when the integrated value of the intake air amount Ga is small), the slope of the output of the air-fuel ratio sensor 23 is smaller than when the amount of substances not storing oxygen contained in the catalyst 14 is relatively large. Therefore, when the integrated value of the intake air amount Ga is relatively small, the judgment unit 33 calculates the correction term from the integrated value of the intake air amount Ga so that the absolute value of the correction term is larger than when the integrated value of the intake air amount Ga is relatively large.

Next, the determination unit 33 corrects the first threshold value based on the correction term calculated in the process of step S201 (step S202). The correction of the first threshold value may be performed, for example, by subtracting the value of the correction term from the first threshold value. The method of correcting the first threshold value is not limited to this, and any method that reduces the effect of the oxygen storage state of the catalyst 14 on the parameter may be used. Then, the process of step S109 is performed.

(Second Modification)
A second modification of the abnormality determination process described above will be described with reference to the flowchart of Fig. 5. In the second modification, the main focus is on suppressing erroneous determination caused by the influence of the oxygen storage state of the catalyst 14 on the abnormality determination process.

In FIG. 5, after the processing of step S105, the judgment unit 33 of the ECU 30 judges whether the accumulated value of the intake air amount Ga is greater than a third predetermined value (step S301). In the processing of step S301, if it is judged that the accumulated value of the intake air amount Ga is greater than the third predetermined value (step S301: Yes), the judgment unit 33 performs an abnormality judgment of the air-fuel ratio sensor 23 (step S302). On the other hand, in the processing of step S301, if it is judged that the accumulated value of the intake air amount Ga is less than the third predetermined value (step S301: No), the judgment unit 33 stops the abnormality judgment of the air-fuel ratio sensor 23 (step S303).

The "third predetermined value" is a value that determines whether or not to perform an abnormality determination of the air-fuel ratio sensor 23, and is set in advance as a fixed value or as a variable value corresponding to some physical quantity or parameter. Such a third predetermined value can be set by, for example, determining the relationship between the integrated value of the intake air amount Ga and the occurrence rate of erroneous determination in the abnormality determination, experimentally, empirically, or by simulation, and setting the integrated value of the intake air amount Ga at which the occurrence rate of erroneous determination is within an acceptable range based on the relationship. Note that if the integrated value of the intake air amount Ga is "equal" to the third predetermined value, it can be treated as including either case.

(others)
(1) The integrated value of the intake air amount Ga may be obtained as follows: (i) from the integrated value of the intake air amount Ga from the start of fuel cut (e.g., from the time when the F/C flag is turned ON) to the time when the value indicated by the output of the air-fuel ratio sensor 23 becomes larger than a second predetermined value (e.g., to the time when the processing in step S104 described above becomes Yes), (ii) from the integrated value of the intake air amount Ga from the start of fuel cut to the time when the value indicated by the output of the air-fuel ratio sensor 22 becomes larger than a first predetermined value (e.g., to the time when the processing in step S102 described above becomes Yes) may be obtained.

(2) In the process of step S107 described above, in addition to the correction term for the parameter, a correction term for the first threshold may be calculated from the integrated value of the intake air amount Ga. Similarly, in the process of step S201 described above, in addition to the correction term for the first threshold, a correction term for the parameter may be calculated from the integrated value of the intake air amount Ga. In other words, both the parameter related to the abnormality determination of the air-fuel ratio sensor 23 and the first threshold related to the abnormality determination may be corrected according to the integrated value of the intake air amount Ga.

Second Embodiment
A second embodiment of the abnormality determination device will be described with reference to Figures 6 and 7. Here, an ECU 30 mounted on a vehicle 2 is taken as an example of an abnormality determination device. The second embodiment is similar to the first embodiment described above, except that the operation of the ECU 30 as an abnormality determination device is partially different. Therefore, the second embodiment will be appropriately omitted from the description of the first embodiment, and the common parts in the drawings will be indicated by the same reference numerals, and the fundamental differences will be described with reference to Figures 6 and 7.

In FIG. 6, the vehicle 2 includes an engine 10, an intake passage 11 connected to an intake port of the engine 10, and an exhaust passage 12 connected to an exhaust port of the engine 10. A catalyst 13 is disposed in the exhaust passage 12.

The intake passage 11 is provided with an airflow sensor 21 that detects the amount of air taken into the engine 10. An air-fuel ratio sensor 22 that detects the oxygen in the exhaust is provided downstream of the catalyst 13 in the exhaust passage 12.

The ECU 30 as an abnormality determination device includes a control unit 31, an acquisition unit 32, and a determination unit 33. The control unit 31 is configured to be able to perform a fuel cut to stop the supply of fuel to the engine 10. The acquisition unit 32 acquires the outputs of the air flow sensor 21 and the air-fuel ratio sensor 22. The determination unit 33 performs an abnormality determination process to determine whether the air-fuel ratio sensor 22 is abnormal or not. Next, the abnormality determination process according to this embodiment will be described with reference to the flowchart of FIG. 7. In the flowchart of FIG. 7, the control unit 31 performs a fuel cut (step S401). At this time, the determination unit 33 starts accumulating the intake air amount Ga based on the output of the air flow sensor 21 acquired by the acquisition unit 32 (step S402).

Next, the determination unit 33 determines whether the value indicated by the output of the air-fuel ratio sensor 22 acquired by the acquisition unit 32 is greater than the fourth predetermined value (step S403). In the process of step S403, if it is determined that the value indicated by the output of the air-fuel ratio sensor 22 is smaller than the fourth predetermined value (step S403: No), the process of step S403 is performed again. In other words, a standby state is entered until the value indicated by the output of the air-fuel ratio sensor 22 becomes greater than the fourth predetermined value. Note that if the value indicated by the output of the air-fuel ratio sensor 22 is "equal" to the fourth predetermined value, it may be treated as being included in either one.

The "fourth predetermined value" is a value that determines whether or not to end the accumulation of the intake air amount Ga, and is set in advance as a fixed value or as a variable value according to some physical quantity or parameter. In this embodiment, the accumulation of the intake air amount Ga is ended at the timing when the amount of oxygen or oxygen concentration in the exhaust downstream of the catalyst 13 begins to increase due to fuel cut. Such a fourth predetermined value can be set by experimentally, empirically, or by simulation to determine the range that the output value of the air-fuel ratio sensor 22 can take when, for example, the air-fuel ratio downstream of the catalyst 13 is lean, and taking into consideration the lower limit of the determined range and the error in the output of the air-fuel ratio sensor 22.

If it is determined in the processing of step S403 that the value indicated by the output of the air-fuel ratio sensor 22 is greater than the fourth predetermined value (step S403: Yes), the determination unit 33 ends the accumulation of the intake air amount Ga (step S404).

Next, the determination unit 33 calculates a parameter related to the abnormality determination of the air-fuel ratio sensor 22 (here, the "slope", i.e., the change in the output of the air-fuel ratio sensor 22 per unit time) (step S405). In parallel with or before or after the processing of step S405, the determination unit 33 calculates a correction term for the above parameter from the integrated value of the intake air amount Ga (step S406).

A relatively small cumulative value of the intake air amount Ga indicates that the amount of substances not storing oxygen contained in the catalyst 13 was relatively small. In other words, a relatively large cumulative value of the intake air amount Ga indicates that the amount of substances not storing oxygen contained in the catalyst 13 was relatively large.

When the amount of substances not storing oxygen contained in the catalyst 13 is relatively small, the slope of the output of the air-fuel ratio sensor 22 is smaller than when the amount of substances not storing oxygen contained in the catalyst 13 is relatively large. Therefore, the determination unit 33 calculates the above correction term from the integrated value of the intake air amount Ga so that when the integrated value of the intake air amount Ga is relatively small, the value of the above correction term is larger than when the integrated value of the intake air amount Ga is relatively large.

Next, the determination unit 33 corrects the parameter calculated in the process of step S405 based on the correction term calculated in the process of step S406 (step S407). The parameter may be corrected, for example, by adding the value of the correction term to the parameter. The parameter correction method is not limited to this, and may be any method that reduces the effect of the oxygen storage state of the catalyst 13 on the parameter.

The determination unit 33 determines whether the corrected parameter is greater than the second threshold value in the process of step S407 (step S408). If the corrected parameter is greater than the second threshold value in the process of step S408 (step S408: Yes), the determination unit 33 determines that the air-fuel ratio sensor 22 is normal (step S409). On the other hand, if the corrected parameter is less than the second threshold value in the process of step S408 (step S408: No), the determination unit 33 determines that the air-fuel ratio sensor 22 is abnormal (or deteriorated) (step S410).

The "second threshold" is a value that determines whether the air-fuel ratio sensor 22 is normal or abnormal, and is set in advance as a fixed value or as a variable value according to some physical quantity or parameter. Such a second threshold can be set by, for example, determining the relationship between the degree of deterioration of the air-fuel ratio sensor 22 and a parameter related to the abnormality determination of the air-fuel ratio sensor 22 experimentally, empirically, or by simulation, and setting the value of the parameter that corresponds to the boundary of the allowable range of deterioration of the air-fuel ratio sensor 22 based on the determined relationship. Note that if the corrected parameter is "equal" to the second threshold, it can be treated as being included in either one.

(Technical effect)
According to the ECU 30 serving as the abnormality determination device, the influence of the oxygen storage state of the catalyst 13 on the abnormality determination process is reduced, and then a determination is made as to whether or not the air-fuel ratio sensor 22 is abnormal. Therefore, according to the present embodiment, it is possible to perform an abnormality determination of the air-fuel ratio sensor 22 regardless of the oxygen storage state of the catalyst 13. In addition, since the influence of the oxygen storage state of the catalyst 13 on the abnormality determination process is reduced, it is possible to suppress the occurrence of erroneous determination in the abnormality determination of the air-fuel ratio sensor 22. Therefore, according to the ECU 30 serving as the abnormality determination device, it is possible to suppress a decrease in the opportunities for determining an abnormality of the air-fuel ratio sensor 22 while suppressing the occurrence of erroneous determination.

(First Modification)
A first modification of the abnormality determination process described above will be described with reference to the flowchart of Fig. 8. In the abnormality determination process described above, the parameters related to abnormality determination of the air-fuel ratio sensor 22 are corrected in accordance with the integrated value of the intake air amount Ga. In contrast, in the first modification, the second threshold value related to abnormality determination (see step S408 described above) is corrected in accordance with the integrated value of the intake air amount Ga.

In other words, in this first modified example, the second threshold value for abnormality determination is corrected according to the integrated value of the intake air amount Ga, which reflects the oxygen storage state of the catalyst 13, thereby reducing the effect of the oxygen storage state of the catalyst 13 on the abnormality determination process.

In FIG. 8, in parallel with or before or after the processing of step S405, the judgment unit 33 of the ECU 30 calculates the correction term for the second threshold value from the integrated value of the intake air amount Ga (step S501). When the amount of substances not storing oxygen contained in the catalyst 13 is relatively small (i.e., when the integrated value of the intake air amount Ga is small), the slope of the output of the air-fuel ratio sensor 22 is smaller than when the amount of substances not storing oxygen contained in the catalyst 13 is relatively large. Therefore, when the integrated value of the intake air amount Ga is relatively small, the judgment unit 33 calculates the above correction term from the integrated value of the intake air amount Ga so that the absolute value of the above correction term is larger than when the integrated value of the intake air amount Ga is relatively large.

Next, the determination unit 33 corrects the second threshold value based on the correction term calculated in the processing of step S501 (step S502). The second threshold value may be corrected, for example, by subtracting the value of the correction term from the second threshold value. The method of correcting the second threshold value is not limited to this, and any method that reduces the effect of the oxygen storage state of the catalyst 13 on the parameter may be used. Then, the processing of step S408 is performed.

(Second Modification)
A second modification of the abnormality determination process described above will be described with reference to the flowchart of Fig. 9. In the second modification, the main focus is on suppressing erroneous determination caused by the influence of the oxygen storage state of the catalyst 13 on the abnormality determination process.

In FIG. 9, after the processing of step S404, the judgment unit 33 of the ECU 30 judges whether the accumulated value of the intake air amount Ga is greater than a fifth predetermined value (step S601). In the processing of step S601, if it is judged that the accumulated value of the intake air amount Ga is greater than the fifth predetermined value (step S601: Yes), the judgment unit 33 performs an abnormality judgment of the air-fuel ratio sensor 22 (step S602). On the other hand, in the processing of step S601, if it is judged that the accumulated value of the intake air amount Ga is less than the fifth predetermined value (step S601: No), the judgment unit 33 stops the abnormality judgment of the air-fuel ratio sensor 22 (step S603).

The "fifth predetermined value" is a value that determines whether or not to perform an abnormality determination of the air-fuel ratio sensor 22, and is set in advance as a fixed value or as a variable value corresponding to some physical quantity or parameter. Such a fifth predetermined value can be set by, for example, determining the relationship between the integrated value of the intake air amount Ga and the occurrence rate of erroneous determination in the abnormality determination, experimentally, empirically, or by simulation, and setting the integrated value of the intake air amount Ga at which the occurrence rate of erroneous determination is within an acceptable range based on the relationship. Note that if the integrated value of the intake air amount Ga is "equal" to the fifth predetermined value, it can be treated as including either case.

(others)
The abnormality determination process according to the second embodiment may be applied to the abnormality determination of the air-fuel ratio sensor 22 in the first embodiment.

<Computer Program>
An embodiment relating to a computer program will be described with reference to Fig. 10. Fig. 10 is a block diagram showing the configuration of a computer according to the embodiment.

In FIG. 10, a computer 50 constitutes an abnormality determination device (for example, the ECU 30 described above). The computer 50 is configured with a CPU (Central Processing Unit) 51, a RAM (Random Access Memory) 52, a HDD (Hard Disk Drive) 53, and an I/O (Input/Output) 54. The CPU 51, RAM 52, HDD 53, and I/O 54 are interconnected by a bus 55. A computer program 531 according to this embodiment is pre-stored in the HDD 53.

(First aspect)
A description will be given of the processing of the CPU 51 in accordance with the computer program 531. Here, a description will be given of the processing of the CPU 51 in the vehicle 1 (see FIG. 1) in accordance with the computer program 531 when determining whether or not the air-fuel ratio sensor 23 is abnormal.

The CPU 51 performs fuel cut of the engine 10. Next, the CPU 51 determines whether the value indicated by the output of the air-fuel ratio sensor 22 obtained via the I/O 54 is greater than a first predetermined value. If the value indicated by the output of the air-fuel ratio sensor 22 is greater than the first predetermined value, the CPU 51 starts integrating the intake air amount Ga based on the output of the air flow sensor 21 obtained via the I/O 54.

Next, the CPU 51 determines whether the value indicated by the output of the air-fuel ratio sensor 23 acquired via the I/O 54 is greater than a second predetermined value. If the value indicated by the output of the air-fuel ratio sensor 23 is greater than the second predetermined value, the CPU 51 ends the accumulation of the intake air amount Ga.

Next, the CPU 51 calculates parameters related to abnormality determination of the air-fuel ratio sensor 23. The CPU 51 calculates at least one of a correction term for the above parameter and a correction term for the first threshold related to abnormality determination from the integrated value of the intake air amount Ga. The CPU 51 corrects the parameter based on the correction term for the parameter and/or corrects the first threshold based on the correction term for the first threshold.

Next, the CPU 51 determines whether a parameter related to the abnormality determination of the air-fuel ratio sensor 23 is greater than a first threshold value. If it is determined that the parameter is greater than the first threshold value, the CPU 51 determines that the air-fuel ratio sensor 23 is normal. On the other hand, if it is determined that the parameter is less than the first threshold value, the CPU 51 determines that the air-fuel ratio sensor 23 is abnormal (or deteriorated).

The CPU 51 may stop determining whether the air-fuel ratio sensor 23 is abnormal if the cumulative value of the intake air volume Ga is smaller than a third predetermined value.

(Second Aspect)
Here, a process of the CPU 51 in the vehicle 2 (see FIG. 6) when the computer program 531 determines whether or not the air-fuel ratio sensor 22 is abnormal will be described.

The CPU 51 performs fuel cut of the engine 10. At this time, the CPU 51 starts integrating the intake air amount Ga based on the output of the air flow sensor 21 acquired via the I/O 54. Next, the CPU 51 determines whether the value indicated by the output of the air-fuel ratio sensor 22 acquired via the I/O 54 is greater than a fourth predetermined value. If the value indicated by the output of the air-fuel ratio sensor 22 is greater than the fourth predetermined value, the CPU 51 ends the integration of the intake air amount Ga.

Next, the CPU 51 calculates a parameter related to the abnormality determination of the air-fuel ratio sensor 22. The CPU 51 calculates at least one of a correction term for the above parameter and a correction term for the second threshold related to the abnormality determination from the integrated value of the intake air amount Ga. The CPU 51 corrects the parameter based on the correction term for the parameter and/or corrects the second threshold based on the correction term for the second threshold.

Next, the CPU 51 determines whether the parameter related to the abnormality determination of the air-fuel ratio sensor 22 is greater than a second threshold value. If it is determined that the parameter is greater than the second threshold value, the CPU 51 determines that the air-fuel ratio sensor 22 is normal. On the other hand, if it is determined that the parameter is less than the second threshold value, the CPU 51 determines that the air-fuel ratio sensor 22 is abnormal (or deteriorated).

The CPU 51 may stop determining whether the air-fuel ratio sensor 22 is abnormal if the integrated value of the intake air amount Ga is smaller than a fifth predetermined value.

The computer program 531 may be stored in the HDD 53 by the computer 50 reading the computer program 531 from a recording medium, such as an optical disk, such as a CD-ROM (Compact Disc Read Only Memory), or a USB (Universal Serial Bus) memory, that stores the computer program 531. Alternatively, the computer 50 may download the computer program 531 via a network, such as the Internet, and thereby the computer program 531 may be stored in the HDD 53.

According to computer program 531, like the abnormality determination device in the first and second embodiments (including various modified examples) described above, it is possible to suppress the occurrence of erroneous determination while suppressing a decrease in the opportunities for determining an abnormality in the air-fuel ratio sensor. According to computer program 531, it is possible to relatively easily realize the abnormality determination device in the first and second embodiments (including various modified examples) described above.

Various aspects of the invention derived from the embodiments and modifications described above are described below.

The abnormality determination device according to one aspect of the invention is provided downstream of a catalyst arranged in an exhaust passage of an internal combustion engine, and includes a determination means for determining whether the sensor is abnormal based on an index related to a change in the output of the sensor that detects oxygen in the exhaust gas, and a detection means for detecting an accumulated amount of air from when the air-fuel ratio of the inlet gas sucked into the catalyst becomes lean to when the air-fuel ratio of the outlet gas discharged from the catalyst becomes lean when a fuel cut is being performed to stop the supply of fuel to the internal combustion engine, and the determination means corrects at least one of the index and a determination value for determining whether the sensor is abnormal according to the accumulated amount of air.

In the above-described embodiment, the "engine 10" corresponds to an example of an "internal combustion engine," the "air-fuel ratio sensors 22 and 23" correspond to an example of a "sensor," the "ECU 30" corresponds to an example of an "abnormality determination device," and the "determination unit 33" corresponds to an example of a "determination means" and a "detection means."

In the abnormality determination device, the determination means may increase the correction amount related to the index when the accumulated air volume is small compared to when the accumulated air volume is large.

In the abnormality determination device, the determination means may set the determination value to be smaller when the accumulated air volume is small than when the accumulated air volume is large.

In the abnormality determination device, a first catalyst and a second catalyst downstream of the first catalyst are disposed in the exhaust passage, a first sensor that detects oxygen in the exhaust is provided downstream of the first catalyst and upstream of the second catalyst in the exhaust passage, and a second sensor that detects oxygen in the exhaust is provided downstream of the second catalyst in the exhaust passage, and the determination means may determine whether the second sensor is abnormal.

In this aspect, the detection means may detect that the air-fuel ratio of the incoming gas has become lean based on the output of the first sensor, and may detect that the air-fuel ratio of the outgoing gas has become lean based on the output of the second sensor.

The abnormality determination method according to one aspect of the invention includes a determination step of determining whether or not the sensor is abnormal based on an index related to an output change of the sensor that is disposed downstream of a catalyst arranged in an exhaust passage of an internal combustion engine and detects oxygen in the exhaust gas, and a detection step of detecting an accumulated air amount from when the air-fuel ratio of the inlet gas sucked into the catalyst becomes lean to when the air-fuel ratio of the outlet gas discharged from the catalyst becomes lean when a fuel cut is performed to stop the fuel supply to the internal combustion engine, and in the determination step, at least one of the index and a determination value for determining whether or not the sensor is abnormal is corrected according to the accumulated air amount.

A computer program according to one aspect of the invention causes a computer of an abnormality determination device that is provided downstream of a catalyst arranged in an exhaust passage of an internal combustion engine and determines an abnormality in a sensor that detects oxygen in the exhaust gas to function as a determination means that determines whether the sensor is abnormal based on an index related to a change in the output of the sensor, and a detection means that detects the accumulated air volume from when the air-fuel ratio of the inlet gas sucked into the catalyst becomes lean to when the air-fuel ratio of the outlet gas discharged from the catalyst becomes lean when a fuel cut is being performed to stop the supply of fuel to the internal combustion engine, and the determination means corrects at least one of the index and a determination value for determining whether the sensor is abnormal depending on the accumulated air volume.

The present invention is not limited to the above-described embodiment, but may be modified as appropriate within the scope of the claims and the entire specification without violating the spirit or concept of the invention, and the abnormality determination device, method, and computer program that involve such modifications are also included in the technical scope of the present invention.

1, 2...vehicle, 10...engine, 11...intake passage, 12...exhaust passage, 13, 14...catalyst, 21...air flow sensor, 22, 23...air-fuel ratio sensor, 30...ECU, 31...control unit, 32...acquisition unit, 33...determination unit

Claims (6)

a determination means for determining whether or not the sensor is abnormal based on an index relating to an output change of the sensor, the determination means being provided downstream of a catalyst disposed in an exhaust passage of the internal combustion engine and detecting oxygen in the exhaust gas;
a detection means for detecting an integrated amount of air from when the air-fuel ratio of inlet gas drawn into the catalyst becomes lean until the air-fuel ratio of outlet gas discharged from the catalyst becomes lean when a fuel cut is being performed to stop the supply of fuel to the internal combustion engine;
Equipped with
The determination means corrects the index in accordance with the cumulative air amount ,
The index indicates the change in the output of the sensor per unit time.
An abnormality determination device comprising: The abnormality determination device according to claim 1, characterized in that the determination means increases the correction amount related to the index when the cumulative air volume is small compared to when the cumulative air volume is large. a first catalyst and a second catalyst downstream of the first catalyst are disposed in the exhaust passage,
a first sensor that detects oxygen in the exhaust gas is provided downstream of the first catalyst and upstream of the second catalyst in the exhaust passage, and a second sensor that detects oxygen in the exhaust gas is provided downstream of the second catalyst in the exhaust passage,
3. The abnormality determination device according to claim 1 , wherein the determination means determines whether or not the second sensor serving as the sensor is abnormal. 4. The abnormality determination device according to claim 3, wherein the detection means detects that the air-fuel ratio of the inlet gas has become lean based on the output of the first sensor, and detects that the air-fuel ratio of the outlet gas has become lean based on the output of the second sensor. a determination step of determining whether or not a sensor that detects oxygen in exhaust gas is abnormal based on an index related to an output change of the sensor, the sensor being provided downstream of a catalyst arranged in an exhaust passage of an internal combustion engine;
a detection step of detecting an integrated air amount from when an air-fuel ratio of inlet gas sucked into the catalyst becomes lean to when an air-fuel ratio of outlet gas discharged from the catalyst becomes lean when a fuel cut is being performed to stop the supply of fuel to the internal combustion engine;
Including,
In the determination step, the index is corrected according to the cumulative air amount ,
The index indicates the change in the output of the sensor per unit time.
The abnormality determination method according to the present invention is characterized in that a computer for an abnormality determination device that is provided downstream of a catalyst disposed in an exhaust passage of an internal combustion engine and determines an abnormality in a sensor that detects oxygen in exhaust gas;
a determination means for determining whether or not the sensor is abnormal based on an index relating to a change in output of the sensor;
a detection means for detecting an integrated amount of air from when the air-fuel ratio of inlet gas drawn into the catalyst becomes lean until the air-fuel ratio of outlet gas discharged from the catalyst becomes lean when a fuel cut is being performed to stop the supply of fuel to the internal combustion engine;
Function as a
The determination means corrects the index in accordance with the cumulative air amount ,
The index indicates the change in the output of the sensor per unit time.
A computer program comprising:

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