JP3988073B2 - Abnormality diagnosis device for exhaust gas sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an abnormality diagnosis device for an exhaust gas sensor for diagnosing the presence or absence of abnormality of the exhaust gas sensor based on the output of an exhaust gas sensor installed on the downstream side of a catalyst for exhaust gas purification.
[0002]
[Prior art]
In recent vehicle exhaust gas purification systems, exhaust gas sensors (air-fuel ratio sensors or oxygen sensors) that detect the air-fuel ratio or rich / lean of exhaust gas are installed upstream and downstream of the exhaust gas purification catalyst, There are some which improve the exhaust gas purification efficiency of the catalyst by feedback control of the air-fuel ratio based on the output of these exhaust gas sensors. In such an exhaust gas purification system, 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 rate is lowered), the deterioration diagnosis of the exhaust gas sensor is performed. There is something to do. In this exhaust gas sensor deterioration diagnosis method, generally, whether the behavior of the exhaust gas sensor output when the air-fuel ratio (target air-fuel ratio) on the upstream side of the catalyst is changed follows the change in the air-fuel ratio on the upstream side of the catalyst with good response. The presence or absence of deterioration of the exhaust gas sensor is determined based on the result.
[0003]
However, the output behavior of the exhaust gas sensor installed on the downstream side of the catalyst is affected by the purification capacity (storage effect) of the catalyst, so the change in the air-fuel ratio on the upstream side of the catalyst is the air-fuel ratio on the downstream side of the catalyst (the output of the exhaust gas sensor). ), A delay time occurs before the change appears, and the delay time changes depending on the purification capacity of the catalyst at that time and the degree of deterioration. Therefore, when the deterioration diagnosis of the exhaust gas sensor is performed based on the output behavior of the exhaust gas sensor on the downstream side of the catalyst, the behavior of the output of the exhaust gas sensor on the downstream side of the catalyst is influenced by the purification capacity (storage effect) of the catalyst at that time. Therefore, it is impossible to accurately determine whether the exhaust gas sensor on the downstream side of the catalyst has deteriorated.
[0004]
Therefore, as shown in JP-A-9-170966, the time until the output of the oxygen sensor on the downstream side of the catalyst changes from the rich side set value to the lean side set value is measured as a response time for each fuel cut. Whether or not the oxygen sensor on the downstream side of the catalyst has deteriorated is determined based on whether the response time is equal to or greater than the deterioration determination value (primary diagnosis). If the result indicates that there is deterioration, the fuel cut continues for a predetermined time or longer. When the elapsed time after returning from the fuel cut reaches the set time, the minimum response time measured so far is read from the memory, compared with the deterioration judgment value, and the response is again In some cases, when the time is determined to be equal to or greater than the deterioration determination value, a definite diagnosis is made that the oxygen sensor on the downstream side of the catalyst is deteriorated.
[0005]
This publication states that the influence of the storage effect of the catalyst can be ignored by the fuel cut when diagnosing the deterioration of the oxygen sensor on the downstream side of the catalyst. In other words, a large amount of lean component (O₂Etc.) and the lean component adsorption amount of the catalyst quickly becomes saturated, so the response time from the start of fuel cut until the air-fuel ratio downstream of the catalyst changes to lean becomes shorter than usual. Utilizing this, the response time of the oxygen sensor on the downstream side of the catalyst is measured at the time of fuel cut, and the deterioration of the oxygen sensor is diagnosed.
[0006]
[Problems to be solved by the invention]
In the above publication, there is a description that the influence of the storage effect of the catalyst can be ignored by the fuel cut when diagnosing the deterioration of the oxygen sensor on the downstream side of the catalyst. Will change the response time. That is, as shown in FIG. 12, when the air-fuel ratio on the upstream side of the catalyst is switched from rich to lean due to fuel cut, the air-fuel ratio (output of the oxygen sensor) on the downstream side of the catalyst is changing from rich to lean. The air-fuel ratio on the downstream side of the catalyst temporarily changes little due to the storage effect of the catalyst, but as the degree of deterioration of the catalyst progresses, the duration of the storage effect becomes shorter and the response time of the oxygen sensor on the downstream side of the catalyst Has a characteristic of shortening. Therefore, even with the diagnosis method of the above publication, the influence of the storage effect of the catalyst cannot be ignored at the time of the deterioration diagnosis of the oxygen sensor on the downstream side of the catalyst, and the presence or absence of deterioration of the oxygen sensor on the downstream side of the catalyst cannot be accurately determined.
[0007]
The present invention has been made in view of such circumstances, and therefore the object of the present invention is to perform an abnormality diagnosis of the exhaust gas sensor on the downstream side of the catalyst under the condition that the influence of the storage effect of the catalyst is less than the conventional one. An object of the present invention is to provide an abnormality diagnosis device for an exhaust gas sensor that can improve the accuracy of abnormality diagnosis of an exhaust gas sensor on the downstream side of the catalyst.
[0008]
[Means for Solving the Problems]
  In order to achieve the above object, an abnormality diagnosis device for an exhaust gas sensor according to claim 1 of the present invention is an exhaust gas sensor (hereinafter referred to as a “downstream exhaust gas sensor”) installed downstream of a catalyst for exhaust gas purification of an internal combustion engine. In the system for diagnosing the presence or absence of abnormality of the downstream exhaust gas sensor based on the output of the sensor abnormality diagnostic means,The amount of intake air isOperating range exceeding the purification capacity of the catalystWhen the air-fuel ratio upstream of the catalyst is changedAn abnormality diagnosis of the downstream side exhaust gas sensor is executed based on the output of the downstream side exhaust gas sensor.
[0009]
In the operating range that exceeds the purification capacity of the catalyst, the storage amount (adsorption amount) of the lean component or rich component of the catalyst becomes saturated and the exhaust gas that passes through the catalyst without being purified increases. The air-fuel ratio change appears with good response as the air-fuel ratio change on the downstream side of the catalyst. This makes it possible to perform abnormality diagnosis of the downstream exhaust gas sensor based on the output of the downstream exhaust gas sensor under the condition that the influence of the storage effect of the catalyst is less than before, and to check whether there is an abnormality in the downstream exhaust gas sensor. It can be determined with high accuracy.
[0010]
Here, the operation region exceeding the purification capacity of the catalyst is an operation region where the flow rate of the rich / lean component in the exhaust gas flowing into the catalyst exceeds the capacity of the catalyst purification reaction (oxidation / reduction / adsorption). . The flow rate of the rich / lean component in the exhaust gas flowing into the catalyst increases as the exhaust gas flow rate increases. Further, the flow rate of exhaust gas flowing into the catalyst can be indirectly detected from the intake air amount detected as the engine control parameter without directly detecting it.
[0011]
  Taking these relationships into account, the claimsIn the invention according to 1,When the intake air amount, which is substitute information for the exhaust gas flow rate, has increased to a region exceeding the purification capacity of the catalyst, the abnormality of the downstream exhaust gas sensor is executed by changing the air-fuel ratio on the upstream side of the catalyst. TheHave. In other words, when the exhaust gas flow rate exceeds the purification capacity of the catalyst, the storage amount (adsorption amount) of the lean component or rich component of the catalyst becomes saturated, and more exhaust gas passes through without being purified by the catalyst. Therefore, if the air-fuel ratio on the upstream side of the catalyst is changed, the change in the air-fuel ratio on the upstream side of the catalyst will appear very well as the change in the air-fuel ratio on the downstream side of the catalyst, without being substantially affected by the storage effect of the catalyst. Thus, abnormality diagnosis of the downstream exhaust gas sensor can be performed with high accuracy.
[0012]
  In this case, the range of the intake air amount for executing the abnormality diagnosis of the downstream side exhaust gas sensor may be a fixed value set in advance.2As described above, the range of the intake air amount for executing the abnormality diagnosis of the downstream side exhaust gas sensor may be set according to the degree of deterioration of the catalyst. In this way, as the degree of deterioration of the catalyst progresses (as the purification capacity of the catalyst decreases), the exhaust gas flow rate (intake air amount) that can be purified by the catalyst decreases. The range of intake air volume for performing the abnormality diagnosis can be expanded to a range of smaller intake air volume, the operating range in which the abnormality diagnosis of the downstream exhaust gas sensor can be performed, and the frequency of abnormality diagnosis can be increased. Can do a lot.
[0013]
  Further, the purification rate characteristic of the catalyst has a characteristic that the purification rate becomes high in a predetermined air-fuel ratio range called a purification window, and the purification rate extremely decreases at other air-fuel ratios. Therefore, as in claim 3, when the air-fuel ratio on the upstream side of the catalyst is in a region exceeding the purification capacity of the catalyst (outer region of the purification window),Switching the richness and leanness of the air / fuel ratio upstream of the catalyst beyond the purification capacity of the catalyst,An abnormality diagnosis of the downstream side exhaust gas sensor may be executed. When the air-fuel ratio exceeds the purification capacity of the catalyst (the air-fuel ratio outside the purification window), the exhaust gas component that passes through without being purified by the catalyst increases. In this state, the air-fuel ratio upstream of the catalystSwitching between rich and lean beyond the purification capacity of the catalystTherefore, the air-fuel ratio change on the upstream side of the catalyst will appear very responsively as the change in the air-fuel ratio on the downstream side of the catalyst without being affected by the storage effect of the catalyst. Can.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
<< Embodiment (1) >>
Hereinafter, an embodiment (1) 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 the engine 11 that is an internal combustion engine, and an air flow meter 14 that detects the intake air amount is provided downstream of the air cleaner 13. A throttle valve 15 and a throttle opening sensor 16 for detecting the throttle opening are provided on the downstream side of the air flow meter 14.
[0015]
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. A spark plug 21 is attached to each cylinder of the engine 11 for each cylinder, and the air-fuel mixture in the cylinder is ignited by spark discharge of each spark plug 21.
[0016]
On the other hand, the exhaust pipe 22 of the engine 11 is provided with a catalyst 23 such as a three-way catalyst for purifying CO, HC, NOx and the like in the exhaust gas, and the exhaust gas on the upstream side and the downstream side of the catalyst 23 respectively. Exhaust gas sensors 24 and 25 (air-fuel ratio sensor, oxygen sensor, etc.) for detecting the air-fuel ratio or lean / rich are provided.
[0017]
A cooling water temperature sensor 26 that detects the cooling water temperature and a crank angle sensor 27 that detects the engine rotation speed are attached to the cylinder block of the engine 11.
[0018]
Outputs of these various sensors are input to an engine control circuit (hereinafter referred to as “ECU”) 28. The ECU 28 is mainly composed of a microcomputer, and executes various control programs stored in a built-in ROM (storage medium), so that the fuel injection amount and ignition of the fuel injection valve 20 are determined according to the engine operating state. The ignition timing of the plug 21 is controlled.
[0019]
Further, the ECU 28 executes the exhaust gas sensor abnormality diagnosis main routine shown in FIG. 2 and the abnormality diagnosis execution subroutine shown in FIG. 3 so that the intake air amount becomes a predetermined abnormality diagnosis execution intake air amount KQ (the purification capacity of the catalyst 23). When the amount of intake air corresponding to the lower limit of the exhaust gas flow rate exceeds the upper limit), the air / fuel ratio is switched between rich / lean and downstream based on the output of the exhaust gas sensor 25 on the downstream side of the catalyst (hereinafter referred to as the “downstream exhaust gas sensor”). An abnormality diagnosis of the side exhaust gas sensor 25 is executed.
[0020]
The exhaust gas sensor abnormality diagnosis main routine shown in FIG. 2 is executed at a predetermined cycle after the ignition switch (not shown) is turned on, and serves as sensor abnormality diagnosis means in the claims. When this routine is started, first, at step 101, it is determined whether or not the intake air amount detected by the air flow meter 14 is equal to or greater than the abnormality diagnosis execution intake air amount KQ. Here, the abnormality diagnosis execution intake air amount KQ is set to an intake air amount that exceeds the purification capability of a catalyst without deterioration (a catalyst equivalent to a new product) in consideration of variations in the purification capability of the catalyst 23.
[0021]
If the intake air amount is less than the abnormality diagnosis execution intake air amount KQ, the program is terminated as it is.
[0022]
On the other hand, if it is determined that the intake air amount is equal to or greater than the abnormality diagnosis execution intake air amount KQ, the process proceeds to step 102 to determine whether an abnormality diagnosis execution condition for the downstream side exhaust gas sensor 25 is satisfied. Here, the abnormality diagnosis execution condition of the downstream side exhaust gas sensor 25 is to satisfy all of the following conditions (1) to (4), for example.
[0023]
(1) The downstream side exhaust gas sensor 25 is in an active state.
(2) The engine is warming up
(3) Engine rotation fluctuation is within the specified range
(4) Engine load fluctuation is within the specified range
The above conditions (3) and (4) are conditions for the engine operating state to become a substantially steady state.
[0024]
If any one of the conditions (1) to (4) is not satisfied, the abnormality diagnosis execution condition for the downstream exhaust gas sensor 25 is not satisfied, and this program is executed without executing the abnormality diagnosis for the downstream exhaust gas sensor 25. Exit.
[0025]
On the other hand, if all of the above conditions (1) to (4) are satisfied, the abnormality diagnosis execution condition for the downstream side exhaust gas sensor 25 is established, and the routine proceeds to step 103 where the abnormality diagnosis execution subroutine shown in FIG. 3 is executed. Then, the abnormality diagnosis of the downstream side exhaust gas sensor 25 is executed as follows.
[0026]
When the abnormality diagnosis execution subroutine of FIG. 3 is started, first, at step 201, rich control for controlling the air-fuel ratio (target air-fuel ratio) upstream of the catalyst to be richer than the stoichiometric air-fuel ratio (for example, target air-fuel ratio = 14). After the rich control is started and after a sufficient time has passed for the output of the downstream side exhaust gas sensor 25 to stabilize, the air-fuel ratio (target air-fuel ratio) on the upstream side of the catalyst is made leaner than the stoichiometric air-fuel ratio. The control is switched to lean control for controlling to (for example, target air-fuel ratio = 16).
[0027]
Thereafter, the routine proceeds to step 202, where the time required from the time t1 when the rich control is switched to the lean control to the time t2 when the output of the downstream exhaust gas sensor 25 changes below the predetermined value V1 is the lean response time TL (see FIG. 4). ), The process proceeds to step 203 where it is determined whether or not the lean response time TL is equal to or less than a predetermined lean response determination value.
[0028]
If the lean response time TL is less than or equal to the lean response determination value, the routine proceeds to step 204 where it is determined that the lean response of the downstream side exhaust gas sensor 25 is normal (no deterioration). On the other hand, if the lean response time TL is longer than the lean response determination value, the routine proceeds to step 205, where it is determined that the lean response of the downstream side exhaust gas sensor 25 is abnormal (with deterioration).
[0029]
Thereafter, the process proceeds to step 206, and after a sufficient time has passed for the output of the downstream side exhaust gas sensor 25 to stabilize after the lean control is started, the lean control is switched to the rich control.
[0030]
Thereafter, the routine proceeds to step 207, where the time required from the time t3 when the lean control is switched to the rich control to the time t4 when the output of the downstream exhaust gas sensor 25 changes to the predetermined value V1 or more is set as the rich response time TR (see FIG. 4). ), The process proceeds to step 208, where it is determined whether or not the rich response time TR is equal to or less than a predetermined rich response determination value.
[0031]
If the rich response time TR is less than or equal to the rich response determination value, the process proceeds to step 209, where it is determined that the rich responsiveness of the downstream side exhaust gas sensor 25 is normal (no deterioration). On the other hand, if the rich response time TR is longer than the rich response determination value, the process proceeds to step 210, and it is determined that the rich response of the downstream side exhaust gas sensor 25 is abnormal (with deterioration).
[0032]
Thereafter, the process proceeds to step 211, where it is determined whether both the lean responsiveness and the rich responsiveness of the downstream side exhaust gas sensor 25 are normal. If both are normal, the process proceeds to step 212, and finally the downstream side exhaust is finally performed. It is determined that the gas sensor 25 is normal (no deterioration). On the other hand, if it is determined that either the lean responsiveness or the rich responsiveness of the downstream side exhaust gas sensor 25 is abnormal (deteriorated), the process proceeds to step 213 and finally the downstream side exhaust gas sensor 25 is abnormal (deteriorated). Yes). At this time, the downstream exhaust gas sensor 25 may be finally determined to be abnormal only when both the lean responsiveness and the rich responsiveness are determined to be abnormal.
[0033]
In this embodiment (1), as shown in FIG. 4, the time required from the time t1 when the rich control is switched to the lean control to the time t2 when the output of the downstream side exhaust gas sensor 25 changes below the predetermined value V1. Is measured as the lean response time TL, and the time required from the time t3 when the lean control is switched to the rich control to the time t4 when the output of the downstream side exhaust gas sensor 25 changes to the predetermined value V1 or more is measured as the rich response time TR. However, as shown in FIG. 5, when the rich control is switched to the lean control, the output of the downstream side exhaust gas sensor 25 is a predetermined interval Va to Vb (when the downstream side exhaust gas sensor 25 is an oxygen sensor). For example, the time required to pass through 0.7 V to 0.2 V) is measured as the lean response time TL, and then the lean control is switched to the rich control. When switched, it is necessary for the output of the downstream exhaust gas sensor 25 to pass through a predetermined section Vb to Va (for example, a section of 0.2 V to 0.7 V when the downstream exhaust gas sensor 25 is an oxygen sensor). The measured time may be measured as the rich response time TR. Further, the determination voltage V1 (Va to Vb) for measuring the lean response time TL and the determination voltage V1 (Vb to Va) for measuring the rich response time TR may be set to different voltages.
[0034]
  As shown in FIG. 6 (a), the intake air amount isSmallWhen there is no air flow (when the intake air amount KQ is smaller than the abnormality diagnosis execution amount), the air-fuel ratio on the downstream side of the catalyst hardly changes due to the storage effect of the catalyst 23 even if the air-fuel ratio on the upstream side (target air-fuel ratio) is switched. Since there is a delay time and the delay time (the duration of the storage effect) changes depending on the deterioration degree of the catalyst 23 (see FIG. 12), the response time of the downstream side exhaust gas sensor 25 is affected by the storage effect of the catalyst 23. Changes, and the presence or absence of abnormality of the downstream side exhaust gas sensor 25 cannot be accurately determined.
[0035]
In contrast, in the present embodiment (1), as shown in FIG. 6B, when the intake air amount is large, specifically, when the abnormality diagnosis execution intake air amount KQ or more, the upstream side of the catalyst. The response time of the downstream exhaust gas sensor 25 is measured by switching the air-fuel ratio (target air-fuel ratio), and abnormality diagnosis of the downstream exhaust gas sensor 25 is performed. When the intake air amount is equal to or greater than the abnormality diagnosis execution intake air amount KQ, the storage amount (adsorption amount) of the lean component or rich component of the catalyst 23 becomes saturated, and the exhaust gas that passes through without being purified by the catalyst 23 increases. Therefore, if the air-fuel ratio (target air-fuel ratio) on the upstream side of the catalyst is switched in such a state, the change in the air-fuel ratio on the upstream side of the catalyst is hardly affected by the storage effect of the catalyst 23 and the downstream side of the catalyst with good response. It appears as a change in the air-fuel ratio. As a result, the abnormality of the downstream side exhaust gas sensor 25 can be diagnosed based on the output of the downstream side exhaust gas sensor 25 under the condition in which the influence of the storage effect of the catalyst 23 is substantially eliminated, and the abnormality of the downstream side exhaust gas sensor 25 is detected. The presence or absence of can be accurately determined.
[0036]
<< Embodiment (2) >>
In the above embodiment (1), the abnormality diagnosis execution intake air amount KQ is set to an intake air amount that exceeds the purification capability of a catalyst without deterioration (a new equivalent catalyst) in consideration of the variation in the purification capability of the catalyst 23. Although it is set, depending on the driving method of the vehicle, road conditions, etc., the frequency of operation where the intake air amount becomes equal to or greater than the abnormality diagnosis execution intake air amount KQ decreases, and the abnormality diagnosis execution frequency of the downstream exhaust gas sensor 25 is reduced. May be reduced.
[0037]
Therefore, in the embodiment (2) of the present invention shown in FIG. 7 and FIG. 8, the purification ability (storage effect) of the catalyst 23 decreases as the deterioration degree ηcat of the catalyst 23 progresses, and purification that can be purified by the catalyst 23. Considering that the possible exhaust gas flow rate (intake air amount) decreases, the deterioration degree ηcat of the catalyst 23 is detected, and the abnormality diagnosis execution intake air amount KQ is set according to the deterioration degree ηcat of the catalyst 23. ing.
[0038]
Hereinafter, the processing content of the exhaust gas sensor abnormality diagnosis main routine of FIG. 7 executed in the present embodiment (2) will be described. When this routine is started, first, in step 301, the deterioration degree ηcat of the catalyst 23 is read. As the deterioration degree ηcat of the catalyst 23, the deterioration degree of the catalyst 23 calculated for determining the presence or absence of deterioration of the catalyst 23 by a catalyst deterioration diagnosis program (not shown) is used.
[0039]
Thereafter, the routine proceeds to step 302, where a map of the abnormality diagnosis execution intake air amount KQ using the deterioration degree ηcat of the catalyst 23 shown in FIG. 8 as a parameter is searched, and the abnormality diagnosis execution corresponding to the current deterioration degree ηcat of the catalyst 23 is performed. An intake air amount KQ is calculated.
[0040]
The map of the abnormality diagnosis execution intake air amount KQ is set so that the abnormality diagnosis execution intake air amount KQ decreases as the deterioration degree ηcat of the catalyst 23 increases. Thus, the abnormality diagnosis execution intake air amount KQ is set to a smaller value as the deterioration degree ηcat of the catalyst 23 progresses (the exhaust gas flow rate that can be purified by the catalyst 23 decreases), and the abnormality diagnosis of the downstream exhaust gas sensor 25 is performed. The range of the intake air amount for executing is expanded to a range of a smaller intake air amount.
[0041]
After calculating the abnormality diagnosis execution intake air amount KQ, the routine proceeds to step 303, where it is determined whether or not the intake air amount detected by the air flow meter 14 is equal to or greater than the abnormality diagnosis execution intake air amount KQ. It is determined whether an abnormality diagnosis execution condition for the side exhaust gas sensor 25 is satisfied.
[0042]
If it is determined that the intake air amount is equal to or greater than the abnormality diagnosis execution intake air amount KQ and the abnormality diagnosis execution condition for the downstream exhaust gas sensor 25 is satisfied, the process proceeds to step 305 and the abnormality diagnosis execution subroutine of FIG. Then, the abnormality diagnosis of the downstream side exhaust gas sensor 25 is executed by the same method as in the embodiment (1).
[0043]
In the present embodiment (2) described above, as the deterioration degree ηcat of the catalyst 23 progresses, the purification ability (storage effect) of the catalyst 23 decreases, and the exhaust gas flow rate (intake air amount) that can be purified by the catalyst 23 increases. In consideration of the fact that the amount of deterioration is reduced, the abnormality diagnosis execution intake air amount KQ is set to a smaller value as the deterioration degree ηcat of the catalyst 23 progresses. Therefore, the intake air amount becomes abnormal in accordance with the deterioration degree ηcat of the catalyst 23. The frequency of operation that becomes the diagnosis execution intake air amount KQ or more increases, and the execution frequency of the abnormality diagnosis of the downstream exhaust gas sensor 25 can be increased.
[0044]
<< Embodiment (3) >>
In each of the above embodiments (1) and (2), when the intake air amount is equal to or greater than the abnormality diagnosis execution intake air amount KQ exceeding the purification ability of the catalyst 23, the air-fuel ratio rich / lean is switched and the downstream side exhaust gas sensor 25 Although the abnormality diagnosis is executed, in the embodiment (3) of the present invention shown in FIGS. 9 to 11, the purification rate characteristic of the catalyst 23 (the purification rate becomes high in a predetermined air-fuel ratio range called a purification window, In consideration of the characteristic that the purification rate is extremely lowered at other air-fuel ratios), the air-fuel ratio (target air-fuel ratio) on the upstream side of the catalyst exceeds the purification ability of the catalyst 23 (air-fuel ratio outside the purification window). In this case, the rich / lean of the air / fuel ratio (target air / fuel ratio) on the upstream side of the catalyst is switched beyond the purification ability of the catalyst 23 to execute the abnormality diagnosis of the downstream side exhaust gas sensor 25.
[0045]
The processing contents of the exhaust gas sensor abnormality diagnosis main routine of FIG. 9 executed in the present embodiment (3) will be described below. When this routine is started, first, in step 401, it is determined whether or not the abnormality diagnosis execution condition for the downstream side exhaust gas sensor 25 is satisfied. If this abnormality diagnosis execution condition is satisfied, the process proceeds to step 402. Then, the abnormality diagnosis execution subroutine of FIG. 3 is executed, and abnormality diagnosis of the downstream side exhaust gas sensor 25 is executed.
[0046]
At this time, in the present embodiment (3), as shown in FIG. 10, when the air-fuel ratio on the upstream side of the catalyst is an air-fuel ratio exceeding the purification ability of the catalyst 23 (air-fuel ratio outside the purification window), In order to switch the rich / lean of the air / fuel ratio on the upstream side, the air / fuel ratio (target air / fuel ratio) on the upstream side of the catalyst is controlled to be richer than the purification window of the catalyst 23 (for example, target air / fuel ratio = 12) during rich control. During lean control, the air-fuel ratio upstream of the catalyst (target air-fuel ratio) is controlled to be leaner than the purification window of the catalyst 23 (for example, target air-fuel ratio = 17).
[0047]
The time required from the time t1 when the rich control is switched to the lean control to the time t2 when the output of the downstream side exhaust gas sensor 25 changes below the predetermined value V1 is measured as the lean response time TL. Compared with the lean response determination value, it is determined whether there is an abnormality in the lean response of the downstream side exhaust gas sensor 25.
[0048]
Thereafter, the rich response time TR is measured from the time t3 when the lean control is switched to the rich control to the time t4 when the output of the downstream side exhaust gas sensor 25 changes to a predetermined value V1 or more, and the rich response time TR is calculated. Compared with the rich response determination value, it is determined whether there is an abnormality in the rich response of the downstream side exhaust gas sensor 25.
[0049]
As shown in FIG. 11, when the rich control is switched to the lean control, the output of the downstream side exhaust gas sensor 25 becomes a predetermined interval Va to Vb (for example, 0. 0 when the downstream side exhaust gas sensor 25 is an oxygen sensor). 7 V to 0.2 V) is measured as a lean response time TL, and then when the lean control is switched to the rich control, the output of the downstream side exhaust gas sensor 25 is set to the predetermined interval Vb to The time required to pass Va (when the downstream exhaust gas sensor 25 is an oxygen sensor, for example, a section of 0.2 V to 0.7 V) may be measured as the rich response time TR. Further, the determination voltage V1 (Va to Vb) for measuring the lean response time TL and the determination voltage V1 (Vb to Va) for measuring the rich response time TR may be set to different voltages.
[0050]
In the embodiment (3) described above, when the air-fuel ratio (target air-fuel ratio) on the upstream side of the catalyst is an air-fuel ratio (air-fuel ratio outside the purification window) exceeding the purification capability of the catalyst 23, the upstream side of the catalyst An abnormality diagnosis of the downstream side exhaust gas sensor 25 is executed by switching the rich / lean of the air / fuel ratio (target air / fuel ratio) beyond the purification ability of the catalyst 23. When the air-fuel ratio exceeds the purification capacity of the catalyst 23 (the air-fuel ratio outside the purification window of the catalyst 23), the exhaust gas component that passes through without being purified by the catalyst 23 increases. Therefore, in this state, the air-fuel ratio on the upstream side of the catalyst By switching between rich and lean, the air-fuel ratio change on the upstream side of the catalyst appears with good response as the air-fuel ratio change on the downstream side of the catalyst with almost no influence of the storage effect of the catalyst 23, and the downstream side exhaust gas sensor 25. The abnormality diagnosis can be performed with high accuracy.
[0051]
The present invention is not limited to the embodiments (1) to (3), and the intake air amount is equal to or greater than the abnormality diagnosis execution intake air amount KQ, and the air-fuel ratio (target air-fuel ratio) on the upstream side of the catalyst is the catalyst. When the air-fuel ratio exceeds the purification capacity of 23 (the air-fuel ratio outside the purification window), the rich / lean state of the air-fuel ratio (target air-fuel ratio) on the upstream side of the catalyst is switched beyond the purification capacity of the catalyst 23 and downstream An abnormality diagnosis of the side exhaust gas sensor 25 may be executed.
[0052]
In the above embodiments (1) to (3), the lean response time TL and the rich response time TR of the downstream exhaust gas sensor 25 when the rich / lean of the air / fuel ratio (target air / fuel ratio) on the upstream side of the catalyst is switched. However, the deterioration of the responsiveness of the downstream exhaust gas sensor 25 is diagnosed by comparing with each of the determination values. However, the abnormality diagnosis method for the downstream exhaust gas sensor 25 may be changed as appropriate.
[0053]
For example, the average lean response time and the average rich response time of the downstream side exhaust gas sensor 25 when the air-fuel ratio rich / lean are alternately switched at a constant cycle are calculated, and the average lean response time and the average rich response time are respectively determined. You may make it diagnose the deterioration of the responsiveness of the downstream side exhaust gas sensor 25 compared with a value.
[0054]
Further, the responsiveness of the downstream exhaust gas sensor 25 based on the frequency ratio or amplitude ratio of the output of the upstream exhaust gas sensor 24 and the output of the downstream exhaust gas sensor 25 when the air-fuel ratio rich / lean is alternately switched at a constant cycle. You may make it diagnose degradation of.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an entire engine control system according to an embodiment (1) of the present invention.
FIG. 2 is a flowchart showing a flow of processing of an exhaust gas sensor abnormality diagnosis main routine of the embodiment (1).
FIG. 3 is a flowchart showing a flow of processing of an abnormality diagnosis execution subroutine.
FIG. 4 is a time chart for explaining the exhaust gas sensor abnormality diagnosis method of the embodiment (1).
FIG. 5 is a time chart for explaining another abnormality diagnosis method for the exhaust gas sensor according to the embodiment (1).
FIG. 6A is a time chart showing the behavior of the air-fuel ratio on the upstream side of the catalyst, the air-fuel ratio on the downstream side of the catalyst, and the output of the downstream exhaust gas sensor when the intake air amount is smaller than the abnormality diagnosis execution intake air amount KQ. (B) is a time chart showing the behavior of the air-fuel ratio upstream of the catalyst, the air-fuel ratio downstream of the catalyst, and the output of the downstream exhaust gas sensor when the intake air amount is larger than the abnormality diagnosis execution intake air amount KQ.
FIG. 7 is a flowchart showing a flow of processing of an exhaust gas sensor abnormality diagnosis main routine of the embodiment (2).
FIG. 8 is a diagram conceptually showing a map that defines the relationship between the degree of catalyst deterioration and the amount of intake air for performing abnormality diagnosis.
FIG. 9 is a flowchart showing a flow of processing of an exhaust gas sensor abnormality diagnosis main routine of the embodiment (3).
FIG. 10 is a time chart for explaining the exhaust gas sensor abnormality diagnosis method of the embodiment (3).
FIG. 11 is a time chart for explaining another abnormality diagnosis method for the exhaust gas sensor according to the embodiment (3).
FIG. 12 is a time chart for explaining the effect of the storage effect of the catalyst and the presence or absence of catalyst deterioration on the change of the air-fuel ratio on the downstream side of the catalyst.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Internal combustion engine (engine), 12 ... Intake pipe, 15 ... Throttle valve, 20 ... Fuel injection valve, 21 ... Spark plug, 22 ... Exhaust pipe, 23 ... Catalyst, 24, 25 ... Exhaust gas sensor, 28 ... ECU (sensor) Abnormal diagnosis means).

Claims (3)

Sensor abnormality diagnosing means for diagnosing the presence or absence of abnormality of the downstream exhaust gas sensor based on the output of an exhaust gas sensor (hereinafter referred to as "downstream exhaust gas sensor") installed downstream of the catalyst for purifying exhaust gas of the internal combustion engine In the exhaust gas sensor abnormality diagnosis device provided,
The sensor abnormality diagnosing means changes the air-fuel ratio on the upstream side of the catalyst when the intake air amount increases to an operation region exceeding the purification capacity of the catalyst, and determines the downstream side based on the output of the downstream side exhaust gas sensor. An exhaust gas sensor abnormality diagnosis device that performs abnormality diagnosis of a side exhaust gas sensor.   2. The exhaust gas sensor abnormality according to claim 1, wherein the sensor abnormality diagnosis unit sets a range of the intake air amount for executing abnormality diagnosis of the downstream exhaust gas sensor in accordance with a degree of deterioration of the catalyst. Diagnostic device. Sensor abnormality diagnosing means for diagnosing the presence or absence of abnormality of the downstream exhaust gas sensor based on the output of an exhaust gas sensor (hereinafter referred to as "downstream exhaust gas sensor") installed downstream of the catalyst for purifying exhaust gas of the internal combustion engine In the exhaust gas sensor abnormality diagnosis device provided,
When the air-fuel ratio on the upstream side of the catalyst is in a region exceeding the purification capacity of the catalyst, the sensor abnormality diagnosis means exceeds the richness and leanness of the air-fuel ratio on the upstream side of the catalyst and exceeds the purification capacity of the catalyst. switching Te, the abnormality diagnosis apparatus for emissions gas sensor you and executes an abnormality diagnosis of the downstream side exhaust gas sensor based on the output of the downstream exhaust gas sensor.

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