JP2005315110A - Air fuel ratio control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately correct characteristics of an air fuel ratio sensor based on output of an oxygen sensor, in regard to an air fuel ratio control device for an internal combustion engine equipped with the air fuel ratio sensor in the upstream side of a catalyst and the oxygen sensor in the downstream side. <P>SOLUTION: Lean control of an upstream air fuel ratio is performed such that the catalyst is in a full state (Step 100 to 102). When the full state is formed, the upstream air fuel ratio is controlled such that output of the air fuel ratio sensor corresponds to a theoretical air fuel ratio corresponding value stoich (Step 104 to 106). When output O2 of the oxygen sensor 18 becomes lean output, it is determined that lean deviation occurs in stoich and the value is made richer (Step 112). When the output O2 becomes rich output, it is determined that rich deviation occurs in stoich and the value is made leaner (Step 120). When determination completion time passes while the output O2 remains stoichiometric output, the processing is completed without change (Step 116). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly to an air-fuel ratio control apparatus for an internal combustion engine that includes an air-fuel ratio sensor upstream of a catalyst and an oxygen sensor downstream of the catalyst.

  Conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-138964, there is known an internal combustion engine that includes a catalyst and an air-fuel ratio sensor and an oxygen sensor disposed before and after the catalyst in an exhaust passage. In the conventional internal combustion engine, the output characteristic of the air-fuel ratio sensor upstream of the catalyst can be corrected based on the output of the oxygen sensor downstream of the catalyst. Specifically, here, the oxygen sensor emits a rich output or a lean output in a situation where the air-fuel ratio sensor emits an output corresponding to the stoichiometric air-fuel ratio (hereinafter referred to as “theoretical air-fuel ratio corresponding value”). If it is, it is determined that a rich shift or a lean shift has occurred in the theoretical air-fuel ratio correspondence value. Then, the stoichiometric air-fuel ratio corresponding value is corrected so that these deviations disappear.

  When the output of the air-fuel ratio sensor is controlled to the value in a situation where a rich deviation occurs in the theoretical air-fuel ratio correspondence value, the air-fuel ratio of the exhaust gas actually flowing into the catalyst becomes rich. In this case, eventually, rich exhaust gas blows down downstream of the catalyst, and the output of the oxygen sensor becomes rich output. On the contrary, when the output of the air-fuel ratio sensor is controlled to that value in a situation where a lean deviation occurs in the stoichiometric air-fuel ratio corresponding value, the output of the oxygen sensor eventually becomes a lean output.

  In the above-described conventional internal combustion engine, in these cases, the stoichiometric air-fuel ratio corresponding value can be corrected in such a direction that the deviation of the exhaust air-fuel ratio disappears. For this reason, in the conventional internal combustion engine, highly accurate air-fuel ratio control can be executed, and good emission characteristics can be realized.

JP 2003-138964 A JP 2003-148207 A

  Incidentally, an appropriate oxygen storage capacity is given to the catalyst disposed in the exhaust passage of the internal combustion engine. The catalyst uses its capacity to purify the exhaust gas by storing excess oxygen when lean exhaust gas is circulating. Further, when rich exhaust gas is circulating, the exhaust gas is purified by releasing the oxygen deficiency. For this reason, the relationship between the air-fuel ratio of the exhaust gas flowing into the catalyst and the output of the oxygen sensor disposed downstream of the catalyst varies greatly depending on what oxygen storage state the catalyst is in.

  Specifically, for example, in a state where oxygen is fully stored in the catalyst (hereinafter referred to as a “full state”), the oxygen-fuel ratio of the exhaust gas flowing into the catalyst is only slightly lean and the oxygen The sensor immediately produces a lean output. Further, in a state where oxygen is not occluded in the catalyst (hereinafter referred to as “empty state”), the oxygen sensor immediately produces a rich output only when the air-fuel ratio of the exhaust gas flowing into the catalyst is slightly richly biased. Occur. On the other hand, if the catalyst has adequately occluded oxygen, even if the air-fuel ratio of the exhaust gas flowing into the catalyst is large and deviates from the stoichiometric air-fuel ratio, the output of the oxygen sensor will be stoichiometric for some time. The output is maintained.

  The conventional internal combustion engine described above determines the air-fuel ratio of the exhaust gas flowing into the catalyst based on the output of an oxygen sensor arranged downstream of the catalyst, and corrects the theoretical air-fuel ratio corresponding value based on the determination. I am going to do that. However, the correction is made here without considering what oxygen storage state the catalyst is in. For this reason, in the above-described conventional internal combustion engine, the characteristic relating to the correction of the stoichiometric air-fuel ratio varies depending on the oxygen storage state of the catalyst, and as a result, the stoichiometric air-fuel ratio corresponding value cannot be accurately corrected. Sometimes.

  The present invention has been made to solve the above-described problems. In correcting the characteristics of the air-fuel ratio sensor arranged upstream of the catalyst based on the output of the oxygen sensor arranged downstream of the catalyst, It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that can be corrected accurately by taking into account the oxygen storage state.

In order to achieve the above object, a first invention is an air-fuel ratio control apparatus for an internal combustion engine comprising a catalyst in an exhaust passage,
An air-fuel ratio sensor disposed upstream of the catalyst;
An oxygen sensor disposed downstream of the catalyst;
Preparation state forming means for controlling the exhaust air-fuel ratio upstream of the catalyst so that the catalyst is in a full state in which oxygen is fully occluded or in an empty state in which all the occluded oxygen is released;
A stoichiometric state forming means for controlling the exhaust air / fuel ratio so that the output of the air / fuel ratio sensor becomes a stoichiometric air / fuel ratio corresponding value after the full state or the air state is formed;
A deviation occurrence determination means for determining whether or not a deviation occurs in the theoretical air-fuel ratio corresponding value based on the output of the oxygen sensor after the output of the air-fuel ratio sensor has reached the theoretical air-fuel ratio corresponding value;
It is characterized by providing.

According to a second invention, in the first invention, learning means for calculating a learning value of the theoretical air-fuel ratio corresponding value based on an output of the oxygen sensor;
Sensor abnormality determination means for determining abnormality of the air-fuel ratio sensor when a difference between a learned value of the theoretical air-fuel ratio corresponding value and a reference value of the theoretical air-fuel ratio corresponding value exceeds a determination value;
It is characterized by providing.

Further, in a third invention according to the first or second invention, the deviation occurrence determination means is
An elapsed time counter that counts an elapsed time after the output of the air-fuel ratio sensor becomes a theoretical air-fuel ratio correspondence value;
A deviation occurrence recognition means for judging that a deviation has occurred in the theoretical air-fuel ratio corresponding value when the output of the oxygen sensor becomes a rich output or a lean output before the elapsed time reaches the determination completion time. ,
Cmax detection means for detecting the maximum oxygen storage amount of the catalyst;
Determination completion time setting means for setting the determination completion time based on the maximum oxygen storage amount;
It is characterized by providing.

Further, in a fourth invention according to any one of the first to third inventions, the deviation occurrence determination means is
An elapsed time counter that counts an elapsed time after the output of the air-fuel ratio sensor becomes a theoretical air-fuel ratio correspondence value;
A deviation occurrence recognition means for judging that a deviation has occurred in the theoretical air-fuel ratio corresponding value when the output of the oxygen sensor becomes a rich output or a lean output before the elapsed time reaches the determination completion time. ,
Intake air amount detection means for detecting the intake air amount of the internal combustion engine;
Determination completion time setting means for setting the determination completion time based on the intake air amount;
It is characterized by providing.

Further, a fifth aspect of the present invention provides the air amount detection means for detecting an intake air amount of the internal combustion engine according to any one of the first to fourth aspects,
A determination prohibiting means for prohibiting continuation of processing for determining whether or not a deviation occurs in the theoretical air-fuel ratio corresponding value when the intake air amount exceeds a determination allowable amount;
It is characterized by providing.

According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the exhaust air / fuel ratio is set so that an output of the air / fuel ratio sensor becomes a stoichiometric air / fuel ratio corresponding value after the full state is formed. An inversion time detecting means for detecting a rich inversion time required for the output of the oxygen sensor to invert to a rich output under controlled conditions;
An injection amount detection means for detecting a fuel injection amount per unit time in the rich inversion time process;
Cmax detection means for detecting the maximum oxygen storage amount of the catalyst;
A deviation direction determination means for determining whether the theoretical air-fuel ratio correspondence value is shifted to the rich side or to the lean side;
When it is determined that the theoretical air-fuel ratio correspondence value is shifted to the rich side, based on the rich inversion time, the fuel injection amount per unit time in the process of the rich inversion time, and the maximum oxygen storage amount, Learning means for calculating a learned value of the theoretical air-fuel ratio corresponding value;
It is characterized by providing.

In addition, according to a seventh invention, in any one of the first to sixth inventions, the exhaust air-fuel ratio is set so that an output of the air-fuel ratio sensor becomes a stoichiometric air-fuel ratio corresponding value after the empty state is formed. Under controlled conditions, an inversion time detecting means for detecting a lean inversion time required until the output of the oxygen sensor is inverted to a lean output;
Injection amount detection means for detecting a fuel injection amount per unit time in the course of the lean reversal time;
Cmax detection means for detecting the maximum oxygen storage amount of the catalyst;
A deviation direction determination means for determining whether the theoretical air-fuel ratio correspondence value is shifted to the rich side or to the lean side;
When it is determined that the theoretical air-fuel ratio correspondence value is shifted to the lean side, based on the lean inversion time, the fuel injection amount per unit time in the course of the lean inversion time, and the maximum oxygen storage amount, Learning means for calculating a learned value of the theoretical air-fuel ratio corresponding value;
It is characterized by providing.

The eighth invention is an air-fuel ratio control device for an internal combustion engine comprising a catalyst in an exhaust passage,
An air-fuel ratio sensor disposed upstream of the catalyst;
An oxygen sensor disposed downstream of the catalyst;
Preparation state forming means for controlling the exhaust air-fuel ratio upstream of the catalyst so that the catalyst is in a full state in which oxygen is fully occluded or in an empty state in which all the occluded oxygen is released;
A sweep control means for sweeping the exhaust air-fuel ratio so that the output of the air-fuel ratio sensor intersects the theoretical air-fuel ratio corresponding value after the full state or the empty state is formed;
Output storage means for storing the output of the air-fuel ratio sensor in the process of sweeping the exhaust air-fuel ratio;
The output of the air-fuel ratio sensor at a time point that is back by the response delay time of the oxygen sensor from the time when the output of the oxygen sensor is changed to the stoichiometric output due to the sweep of the exhaust air-fuel ratio is the value corresponding to the theoretical air-fuel ratio. Learning means as learning values;
It is characterized by providing.

  In a ninth aspect based on the eighth aspect, when the difference between the learned value of the theoretical air-fuel ratio corresponding value and the reference value of the theoretical air-fuel ratio corresponding value exceeds a determination value, the air-fuel ratio sensor malfunctions. It is characterized by comprising a sensor abnormality judging means for judging the above.

  According to a tenth aspect of the present invention, in the eighth or ninth aspect of the invention, the sweep control means determines whether the output of the air-fuel ratio sensor and the stoichiometric air-fuel ratio corresponding value after the full state or the empty state is formed Until the difference reaches a predetermined value, the exhaust air-fuel ratio is changed abruptly as compared with the subsequent sweep.

Further, an eleventh aspect of the invention is any one of the eighth to tenth aspects of the invention,
An air amount detecting means for detecting an intake air amount of the internal combustion engine;
Learning prohibiting means for prohibiting continuation of processing for advancing learning of the theoretical air-fuel ratio corresponding value when the intake air amount exceeds a determination allowable amount;
It is characterized by providing.

  According to the first aspect of the present invention, the exhaust air / fuel ratio can be controlled so that the output of the air / fuel ratio sensor becomes the stoichiometric air / fuel ratio corresponding value after the catalyst becomes full or empty. Based on the output of the subsequent oxygen sensor, it can be determined whether or not there is a deviation in the theoretical air-fuel ratio correspondence value. In this case, whether or not there is a deviation in the theoretical air-fuel ratio correspondence value is always determined under a situation where the oxygen storage state of the catalyst is fixed. Therefore, according to the present invention, it is always possible to accurately determine whether or not there is a deviation in the stoichiometric air-fuel ratio value based on the output of the oxygen sensor without being affected by the oxygen storage state of the catalyst. Can do.

  According to the second invention, when the learned value of the theoretical air-fuel ratio corresponding value is calculated based on the output of the oxygen sensor and the learned value is greatly deviated from the reference value, the abnormality of the air-fuel ratio sensor is detected. Can be determined.

  According to the third invention, after the output of the air-fuel ratio sensor becomes the stoichiometric air-fuel ratio corresponding value, depending on whether the output of the oxygen sensor has become a rich output or a lean output before the determination completion time elapses. It is possible to determine whether or not there is a deviation in the theoretical air-fuel ratio correspondence value. The determination completion time can be set based on the maximum oxygen storage amount of the catalyst. The downstream of the catalyst, the richer or leaner gas is harder to blow through as the maximum oxygen storage amount increases. According to the present invention, the influence can be eliminated by appropriately setting the determination completion time, and it is possible to determine with high accuracy whether or not there is a deviation in the theoretical air-fuel ratio correspondence value.

  According to the fourth invention, after the output of the air-fuel ratio sensor reaches the theoretical air-fuel ratio correspondence value, depending on whether the output of the oxygen sensor has become a rich output or a lean output before the determination completion time elapses. It is possible to determine whether or not there is a deviation in the theoretical air-fuel ratio correspondence value. The determination completion time can be set based on the intake air amount of the internal combustion engine. As the intake air amount of the internal combustion engine increases, the richer or leaner gas is easily blown downstream of the catalyst. According to the present invention, the influence can be eliminated by appropriately setting the determination completion time, and it is possible to determine with high accuracy whether or not there is a deviation in the theoretical air-fuel ratio correspondence value.

  According to the fifth aspect, when the intake air amount exceeds the determination allowable amount, it is possible to prohibit the continuation of the process for determining whether or not there is a deviation in the theoretical air-fuel ratio correspondence value. That is, in this case, it is possible to prohibit execution of processing for bringing the catalyst into a full state or an empty state, and further processing for determining whether or not there is a deviation in the theoretical air-fuel ratio correspondence value. In a situation where a large amount of intake air is generated, if an attempt is made to bring the catalyst into a full state or an empty state, a rich or lean gas tends to blow through a large amount downstream of the catalyst. In such a situation, since the output of the oxygen sensor is likely to change, it is difficult to accurately determine whether or not there is a deviation in the theoretical air-fuel ratio correspondence value. According to the present invention, it is possible to effectively prevent deterioration of emissions and erroneous determination under such circumstances.

  According to the sixth aspect of the present invention, when a rich shift occurs in the stoichiometric air-fuel ratio correspondence value, the time until the oxygen sensor emits a rich output (rich inversion time) and the unit time in the process of the rich inversion time Based on the fuel injection amount and the maximum oxygen storage amount of the catalyst, the learned value of the theoretical air-fuel ratio correspondence value can be accurately calculated.

  According to the seventh aspect of the present invention, when a lean deviation occurs in the stoichiometric air-fuel ratio correspondence value, the time until the oxygen sensor issues a lean output (lean reversal time) and the unit time in the process of the lean reversal time. Based on the fuel injection amount and the maximum oxygen storage amount of the catalyst, the learned value of the theoretical air-fuel ratio correspondence value can be accurately calculated.

  According to the eighth aspect of the present invention, the exhaust air-fuel ratio can be swept so that the output of the air-fuel ratio sensor intersects the theoretical air-fuel ratio corresponding value after the catalyst is brought into a full state or an empty state. At this time, the output of the oxygen sensor changes to a stoichiometric output after a response delay time due to an exhaust gas transport delay or the like after the exhaust air / fuel ratio upstream of the catalyst becomes the stoichiometric air / fuel ratio. According to the present invention, the learning value of the stoichiometric air-fuel ratio corresponding value is accurately obtained by reading the output of the air-fuel ratio sensor at the time point that is earlier than the time point when the output of the oxygen sensor changes to the stoichiometric output by the response delay time. Can be set.

  According to the ninth aspect of the present invention, when the learning value of the theoretical air-fuel ratio corresponding value is set by the method of sweeping the exhaust air-fuel ratio and the learning value is greatly deviated from the reference value, the air-fuel ratio sensor Abnormality can be determined.

  According to the tenth aspect of the present invention, the air-fuel ratio can be rapidly changed until the air-fuel ratio of the exhaust gas flowing into the catalyst becomes a value close to the stoichiometric air-fuel ratio after the catalyst is made full or empty. it can. Then, the theoretical air-fuel ratio correspondence value can be learned with high accuracy by gently sweeping the exhaust air-fuel ratio before and after the exhaust air-fuel ratio crosses the theoretical air-fuel ratio.

  According to the eleventh aspect of the invention, processing for learning the stoichiometric air-fuel ratio corresponding value can be prohibited under a situation where the intake air amount exceeds the allowable determination amount. For this reason, according to the present invention, it is possible to effectively prevent the emission from deteriorating under such circumstances and the theoretical air-fuel ratio corresponding value from being set to an inappropriate value.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining the configuration of the first embodiment of the present invention. The system of this embodiment includes an internal combustion engine 10. An exhaust passage 12 communicates with the internal combustion engine 10. The exhaust passage 12 includes a catalyst 14 for purifying exhaust gas flowing through the exhaust passage 12. The catalyst 14 has the ability to store oxygen with the maximum oxygen storage amount Cmax as the upper limit.

  More specifically, the catalyst 14 stores excess oxygen while reducing NOx when the exhaust gas discharged from the internal combustion engine 10 is lean, that is, when the exhaust gas contains NOx. By doing so, exhaust gas is purified. If the exhaust gas discharged from the internal combustion engine 10 is rich and contains unburned components such as HC and CO, the exhaust gas is exhausted by oxidizing the components while releasing the stored oxygen. Purify the gas.

  Therefore, when an appropriate amount of oxygen is stored in the catalyst 14, even if the exhaust gas discharged from the internal combustion engine 10 is rich, the exhaust gas adjusted to the stoichiometric air-fuel ratio is downstream of the catalyst 14. It will be leaked. Further, when an appropriate oxygen storage capacity is left in the catalyst 14, even if the exhaust gas discharged from the internal combustion engine 10 is lean, the exhaust gas adjusted to the stoichiometric air-fuel ratio is downstream of the catalyst 14. Gas will flow out.

  The system of this embodiment includes an air-fuel ratio sensor 16 upstream of the catalyst 14. The air-fuel ratio sensor 16 has a characteristic of changing the output substantially linearly with respect to the air-fuel ratio of the exhaust gas flowing therearound. Therefore, the correspondence between the output of the air-fuel ratio sensor 16 and the air-fuel ratio of the exhaust gas discharged from the internal combustion engine 10, that is, the exhaust air-fuel ratio upstream of the catalyst 14 (hereinafter referred to as “upstream air-fuel ratio”) is known. If so, the upstream air-fuel ratio can be detected based on the output.

  An oxygen sensor 18 is disposed downstream of the catalyst 14. FIG. 2 is a diagram for explaining the output characteristics of the oxygen sensor 18. In FIG. 2, the horizontal axis represents the exhaust air-fuel ratio downstream of the catalyst 14 (hereinafter referred to as “downstream air-fuel ratio”), and the vertical axis represents the output (voltage value) of the oxygen sensor 18. As shown in FIG. 2, the oxygen sensor 18 exhibits a hysteresis characteristic with respect to a change in the downstream air-fuel ratio, and greatly changes its output before and after the downstream air-fuel ratio passes through the stoichiometric air-fuel ratio (stoichiometry).

  More specifically, the output of the oxygen sensor 18 becomes a lean output of about 0.2 [V] when the downstream air-fuel ratio is lean, and is slightly smaller than the lean output when the downstream air-fuel ratio becomes stoichiometric from that state. High lean side stoichiometric output. When the downstream air-fuel ratio further changes and becomes rich, the output of the oxygen sensor 18 becomes a rich output of about 1.0 [V]. The output of the oxygen sensor 18 becomes a rich side stoichiometric output slightly lower than the rich output when the downstream air-fuel ratio changes from rich to stoichiometric. When the downstream air-fuel ratio further changes and becomes lean, the output of the oxygen sensor 18 changes to a lean output of about 0.2 [V].

  The system of the present embodiment includes an ECU (Electronic Control Unit) 20. Both the output of the air-fuel ratio sensor 16 and the output of the oxygen sensor 18 are supplied to the ECU 20. The ECU 20 also includes an air flow meter for measuring the intake air amount Ga, a rotational speed sensor for measuring the engine rotational speed Ne, a throttle sensor (none of which is shown) for detecting the throttle opening degree TA, etc. These various sensors and various actuators such as injectors are connected. The ECU 20 can control the states of various actuators based on the output signals of those sensors.

[Operation of Embodiment 1]
According to the system of this embodiment, as described above, if the correspondence between the output of the air-fuel ratio sensor 16 and the upstream air-fuel ratio is known, the upstream air-fuel ratio can be detected based on the output. However, since the correspondence relationship is affected by variations in the air-fuel ratio sensor 16 and changes over time, it cannot be determined uniformly for all internal combustion engines.

  On the other hand, the proportional relationship established between the upstream air-fuel ratio and the output of the air-fuel ratio sensor 16 does not vary so much. For this reason, if the output value corresponding to a known air-fuel ratio can be detected at at least one point, the relationship between the two can be determined with high accuracy. In view of this, the system according to the present embodiment uses an approach described below to output an output value (hereinafter referred to as “theoretical air / fuel ratio corresponding value stoich”) generated by the air / fuel ratio sensor 16 corresponding to the theoretical air / fuel ratio on the vehicle. Learning is done as appropriate.

  FIG. 3 is a timing chart for explaining the principle of a method in which the system of the present embodiment learns the stoichiometric air-fuel ratio correspondence value stoich. More specifically, FIG. 3A shows an example of a change that occurs in the upstream air-fuel ratio when learning the stoichiometric air-fuel ratio corresponding value stoich. 3 (B) and 3 (C) show the oxygen storage amount OSA of the catalyst 14 and the output of the oxygen sensor 18 when the upstream air-fuel ratio changes as shown in FIG. 3 (A). The change that occurs in O2 is shown.

  When learning the stoichiometric air-fuel ratio corresponding value stoich, the system of the present embodiment first performs processing for bringing the catalyst 14 into a full state or an empty state, that is, the catalyst 14 is filled with oxygen to the maximum oxygen storage amount Cmax. A process for occlusion or a process for releasing all oxygen in the catalyst 14 is executed. In the example shown in FIG. 3, before the time t1, the upstream air-fuel ratio is intentionally maintained lean to bring the catalyst 14 into a full state.

  The oxygen storage amount OSA of the catalyst 14 increases with time, and reaches the maximum oxygen storage amount Cmax at time t1. Until the oxygen storage amount OSA approaches Cmax to some extent, the lean exhaust gas is purified by the catalyst 14, and the exhaust gas adjusted to stoichiometric flows out downstream of the catalyst 14. During this time, the output O2 of the oxygen sensor 18 becomes the rich side stoichiometric output. When the oxygen storage amount OSA reaches a value close to Cmax and lean exhaust gas starts to flow downstream of the catalyst 14, the output O2 of the oxygen sensor 18 is suddenly reversed to the lean output.

  When the output O2 of the oxygen sensor 18 is inverted to a lean output, the ECU 20 determines that the catalyst 14 is full, and then performs control for setting the upstream air-fuel ratio to the stoichiometric air-fuel ratio (hereinafter referred to as “stoichiometric control”). Start). In the stoichiometric control, specifically, the upstream air-fuel ratio is adjusted so that the output of the air-fuel ratio sensor 16 matches the current theoretical air-fuel ratio correspondence value, that is, the fuel supply amount to the internal combustion engine 10 is adjusted. Is executed.

  The waveform shown by the solid line in FIG. 3 is a waveform obtained when the stoichiometric air-fuel ratio corresponding value stoich used here is accurate. That is, in this case, the upstream air-fuel ratio is actually controlled to the stoichiometric air-fuel ratio by performing the stoichiometric control described above. As a result, the oxygen storage amount OSA of the catalyst 14 is maintained at the maximum oxygen storage amount Cmax without increasing or decreasing. The output O2 of the oxygen sensor 18 is maintained at the lean side stoichiometric output after time t2 when the upstream air-fuel ratio becomes stoichiometric.

  The waveform indicated by the alternate long and short dash line in FIG. 3 is obtained when the stoichiometric air-fuel ratio corresponding value stoich is shifted to the lean side (larger side), and as a result, lean deviation occurs in the upstream air-fuel ratio as the stoichiometric control is executed. It is a waveform. If there is a lean shift in the upstream air-fuel ratio after the start of stoichiometric control, naturally lean gas will continue to flow downstream of the catalyst 14. Therefore, in this case, the output O2 of the oxygen sensor 18 is maintained as a lean output even after time t2.

  The waveform indicated by the broken line in FIG. 3 is obtained when the stoichiometric air-fuel ratio corresponding value stoich has shifted to the rich side (smaller side), resulting in a rich shift in the upstream air-fuel ratio during execution of stoichiometric control. It is a waveform to be generated. If there is a rich shift in the upstream air-fuel ratio, the oxygen storage amount OSA of the catalyst 14 gradually decreases after the start of the stoichiometric control, and eventually becomes zero. While oxygen remains in the catalyst 14, the air-fuel ratio downstream of the catalyst 14 is stoichiometric, so the output of the oxygen sensor 18 is maintained at the lean side stoichiometric output. When the oxygen storage amount OSA becomes near zero, rich gas begins to flow downstream of the catalyst 14, and as a result, the output O2 of the oxygen sensor 18 is inverted to the rich output.

  As described above, when the stoichiometric control is started after the catalyst 14 is in the full state, the output O2 of the oxygen sensor 18 is stoichiometric for a long period only when the stoichiometric air-fuel ratio corresponding value stoich is correctly learned. Maintain output. Similarly, also when the stoichiometric control is executed after the catalyst 14 is in an empty state, the output O2 of the oxygen sensor 18 is stoichiometric for a long period only when the stoichiometric air-fuel ratio corresponding value stoich is correctly learned. Maintain output. Therefore, whether or not the stoichiometric air-fuel ratio corresponding value stoich is a correct value is determined by checking whether or not the output O2 of the oxygen sensor 18 is maintained at the stoichiometric output for a sufficiently long time after the start of the stoichiometric control. It is possible to judge by.

  By the way, the output O2 of the oxygen sensor 18 is a rich output or a lean output during the execution of the stoichiometric control if there is a deviation in the stoichiometric air-fuel ratio corresponding value stoich even if the full state or the empty state is not formed in advance. If the deviation does not occur, the stoichiometric output is maintained during the stoichiometric control. Therefore, whether or not there is a deviation in the stoichiometric air-fuel ratio corresponding value stoich can be determined with a certain degree of accuracy without forming a full state or an empty state in advance.

  However, if the oxygen storage state at the start of the stoichiometric control is left to the future, the relationship between the magnitude of the deviation occurring in the stoichiometric air-fuel ratio corresponding value stoich and the time until the output O2 of the oxygen sensor 18 is reversed. A large fluctuation occurs. In this case, by determining whether or not the output O2 of the oxygen sensor 18 is inverted during a certain determination time, it is always determined with high accuracy whether or not a non-negligible deviation occurs in the stoichiometric air-fuel ratio corresponding value stoich. I can't.

  In other words, when the rich deviation occurs in the stoichiometric air-fuel ratio corresponding value stoich, if the full state is formed at the start of the stoichiometric control, the time until the inversion of the output O2 of the oxygen sensor 18 tends to be long. On the other hand, if the oxygen storage amount OSA is small at the start, the time required for reversing the output O2 tends to be short. In other words, the output O2 of the oxygen sensor 18 is reversed to a rich output during the determination time even if a certain amount of rich deviation occurs in the stoichiometric air-fuel ratio corresponding value stoich if a large amount of OSA is secured at the start of stoichiometric control. On the other hand, when the OSA at the start is small, only a slight deviation occurs in the stoichiometric air-fuel ratio corresponding value stoich, and the output is inverted to the rich output during the inversion time. For this reason, if the stoichiometric control is started with the oxygen storage state of the catalyst 14 depending on the situation, there is a strict difference in the criteria regarding the deviation determination according to the amount of the oxygen storage amount OSA at the start. It will be.

  On the other hand, in the system of the present embodiment, the catalyst 18 is always in a full state or an empty state before the start of the stoichiometric control. In this case, the occurrence of the deviation of the stoichiometric air-fuel ratio corresponding value stoich is recognized only when it exceeds a preset allowable limit, and the criterion for determination regarding the occurrence of deviation can be stabilized. For this reason, according to the system of the present embodiment, it is possible to determine with high accuracy whether or not an unreasonable deviation occurs in the stoichiometric air-fuel ratio corresponding value stoich.

[Specific Processing in Embodiment 1]
FIG. 4A and FIG. 4B are flowcharts of routines executed by the ECU 20 in the present embodiment in order to realize the above functions. More specifically, FIG. 4A is a flowchart for determining whether or not there is a deviation in the stoichiometric air-fuel ratio corresponding value stoich by executing stoichiometric control after the catalyst 14 is in a full state. . FIG. 4B is a flowchart for determining whether or not there is a deviation in the stoichiometric air-fuel ratio corresponding value stoich by executing stoichiometric control after the catalyst 14 is in an empty state.

  In the system of this embodiment, every time a predetermined learning execution condition is satisfied, the routine shown in FIG. 4A and the routine shown in FIG. 4B are alternately executed a predetermined number of times (at least once). . The learning execution condition is repeatedly established as appropriate every time the internal combustion engine 10 is started, the vehicle travels a predetermined distance, or a predetermined time elapses.

  In the routine shown in FIG. 4A, first, a process of making the upstream air-fuel ratio lean is executed (step 100). Next, it is determined whether or not the output O2 of the oxygen sensor 18 is inverted to a lean output (step 102). Until the inversion to the lean output is recognized, the processes of steps 100 and 102 are repeatedly executed.

  When it is recognized that the output O2 is inverted to the lean output, the upstream air-fuel ratio target is changed to the stoichiometric air-fuel ratio, and the stoichiometric control is started (step 104). Here, specifically, the output target of the air-fuel ratio sensor 16 is set to the current theoretical air-fuel ratio corresponding value, and the process of feedback-controlling the fuel supply amount to the internal combustion engine 10 is executed so that they match. The

  When the stoichiometric control is started, it is next determined whether or not the output of the air-fuel ratio sensor 16 actually matches the stoichiometric air-fuel ratio corresponding value stoich (step 106). As a result, if it is determined that the two still do not match, the process of step 104 is executed again. On the other hand, if it is determined that the two have already been matched, after resetting the counter counter (step 108), it is determined whether or not the output O2 of the oxygen sensor 18 is a lean output (step 110).

  If the output O2 of the oxygen sensor 18 remains lean even though the output of the air-fuel ratio sensor 16 matches the stoichiometric air-fuel ratio corresponding value stoich, the stoichiometric air-fuel ratio corresponding value stoich shifts to the lean side. As a result, it can be determined that there is a lean shift in the upstream air-fuel ratio. For this reason, when the condition in step 110 is satisfied, a process for enriching the stoichiometric air-fuel ratio corresponding value stoich by a predetermined value is executed (step 112).

  On the other hand, if it is determined in step 110 that the output O2 of the oxygen sensor 18 is not a lean output, it is next determined whether or not the output O2 is a rich output (step 114). When the stoichiometric air-fuel ratio corresponding value stoich appropriately corresponds to the stoichiometric air-fuel ratio, stoichiometric exhaust gas necessarily flows out downstream of the catalyst 14. Further, even when the stoichiometric air-fuel ratio corresponding value stoich has shifted to the rich side, and as a result, the upstream air-fuel ratio has shifted to a rich level, stoichiometric gas remains downstream until the oxygen in the catalyst 14 is consumed. leak. Therefore, in this step 114, it is determined that the output O2 of the oxygen sensor 18 is not a rich output anyway for a while after the stoichiometric control is started.

  In this case, it is next determined whether or not the count value of the counter Counter exceeds the lean side determination completion time L_TIME (step 116). If it is recognized that Counter> L_TIME is established, the current process is terminated. On the other hand, if the condition is not satisfied, the counter is incremented (step 118), and then the process of step 110 is executed again.

  The lean side determination completion time L_TIME is a time during which the output O2 of the oxygen sensor 18 is maintained at the stoichiometric output after the stoichiometric control is started when a rich deviation of the allowable limit occurs in the stoichiometric air-fuel ratio corresponding value stoich. It corresponds. Therefore, if the establishment of Counter> L_TIME is recognized before the output O2 is reversed to the rich output, the theoretical air-fuel ratio corresponding value stoich does not have a rich shift exceeding the allowable limit value, that is, the theoretical air-fuel ratio corresponding value. It can be judged that stoich is properly learned at this stage. According to the processing flow described above, in this case, the stoichiometric air-fuel ratio corresponding value stoich can be maintained at the current value.

  When the rich deviation exceeding the allowable limit occurs in the stoichiometric air-fuel ratio corresponding value stoich, the output O2 of the oxygen sensor 18 is reversed to the rich output before the counter> L_TIME is established. When the output O2 is inverted to a rich output, the condition in step 114 is satisfied, and a process for leaning the stoichiometric air-fuel ratio corresponding value stoich by a predetermined value is executed (step 120). As a result, the shift amount toward the rich side is reduced, and the stoichiometric air-fuel ratio corresponding value stoich is brought close to the appropriate value.

  As described above, according to the routine shown in FIG. 4A, when a lean deviation occurs in the stoichiometric air-fuel ratio corresponding value stoich, the occurrence of the deviation is immediately determined after the start of the stoichiometric control, In addition, the stoichiometric air-fuel ratio corresponding value stoich can be corrected so that the lean deviation is eliminated. In addition, when the rich deviation occurs in the stoichiometric air-fuel ratio corresponding value stoich, the stoichiometric air-fuel ratio corresponding value stoich can be corrected only when the deviation exceeds the allowable limit value. For this reason, according to the system of the present embodiment, the stoichiometric air-fuel ratio corresponding value stoich can be quickly and accurately corrected to an appropriate value by executing the routine shown in FIG.

  The routine shown in FIG. 4B is the same as the routine shown in FIG. 4A except that rich and lean are reversed. Therefore, detailed description thereof is omitted here. According to this routine, when the rich deviation has occurred in the stoichiometric air-fuel ratio corresponding value stoich, it is determined immediately after the start of the stoichiometric control, and the rich deviation is eliminated. The stoichiometric air-fuel ratio corresponding value stoich can be corrected. Further, when a lean deviation occurs in the stoichiometric air-fuel ratio corresponding value stoich, the stoichiometric air-fuel ratio corresponding value stoich can be corrected only when the deviation exceeds the allowable limit value. For this reason, according to the system of the present embodiment, the stoichiometric air-fuel ratio corresponding value stoich can be quickly and accurately corrected to an appropriate value by executing the routine shown in FIG.

  The system of the present embodiment further increases the learning accuracy of the stoichiometric air-fuel ratio corresponding value stoich by alternately executing the routine shown in FIG. 4A and the routine shown in FIG. 4B. . However, these routines are not necessarily executed in combination with each other, and only one of the routines may be executed to advance learning of the stoichiometric air-fuel ratio corresponding value stoich.

  In the first embodiment described above, when the output of the oxygen sensor O2 is recognized as a lean output in step 110 in the routine shown in FIG. 4A, the routine shown in FIG. In step 140, when it is recognized that the output of the oxygen sensor O2 is a rich output, the deviation of the stoichiometric air-fuel ratio corresponding value stoich is immediately recognized and corrected (steps 112 and 142). However, the present invention is not limited to this. That is, when the routine shown in FIG. 4 (A) and the routine shown in FIG. 4 (B) are executed alternately, these corrections are omitted, and in both cases of rich deviation and lean deviation. Only when a deviation exceeding the allowable limit value has occurred, the deviation of the stoichiometric air-fuel ratio corresponding value stoich may be recognized and the value may be corrected.

  In the first embodiment described above, the ECU 20 executes the processing of steps 100 to 102 or the processing of steps 130 to 132, whereby the “preparation state forming means” in the first invention is the step 104 or By executing the process of 134, the “stoichiometric state forming means” in the first aspect of the invention performs the processes of steps 106 to 120 or steps 136 to 150 of “the deviation occurrence determining means in the first aspect of the invention”. "Is realized.

Embodiment 2. FIG.
[Features of Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIG. The system of the present embodiment can be realized by causing the ECU 20 to execute the routine shown in FIG. 5 using the configuration shown in FIG.

  In the system of the present embodiment, the stoichiometric air-fuel ratio corresponding value stoich of the air-fuel ratio sensor 16 is learned by the same method as in the first embodiment. The stoichiometric air-fuel ratio corresponding value stoich includes fluctuations due to changes in the air-fuel ratio sensor 16 over time and individual differences. However, if an unreasonably large fluctuation occurs, it is determined that an abnormality has occurred in the air-fuel ratio sensor 16. Should. Therefore, the system of the present embodiment determines that the air-fuel ratio sensor 16 is abnormal when the learned value of the stoichiometric air-fuel ratio corresponding value stoich deviates unduly from a predetermined reference value.

[Specific Processing in Second Embodiment]
FIG. 5A and FIG. 5B are flowcharts of routines executed by the ECU 20 in the present embodiment in order to realize the above functions. More specifically, the routine shown in FIG. 5A is a flowchart for performing stoichiometric control after the catalyst 14 is in a full state to advance learning of the stoichiometric air-fuel ratio corresponding value stoich. FIG. 5B is a flowchart for performing stoichiometric control after the catalyst 14 is in an empty state to advance learning of the stoichiometric air-fuel ratio corresponding value stoich.

  These routines are the same as those shown in FIG. 4A or FIG. 4 except that steps 160 to 162 are added after step 116 and steps 170 to 172 are added after step 146, respectively. This is the same as the routine shown in (B). Hereinafter, of the steps shown in FIG. 5A and FIG. 5B, the same steps as those shown in FIG. 4A or FIG. Omitted or simplified.

  In the routine shown in FIG. 5A, if it is determined in step 116 that the counter value exceeds the lean side determination completion time L_TIME, that is, it is determined that the current stoichiometric air-fuel ratio corresponding value stoich is appropriate. If the stoichiometric air-fuel ratio corresponding value stoich is corrected by the processing of step 112 or 120, whether or not the latest stoichiometric air-fuel ratio corresponding value stoich is within the normal range following those processing. Is determined (step 160).

  The ECU 20 stores a stoichiometric air-fuel ratio corresponding value stoich generated by the air-fuel ratio sensor 16 showing standard characteristics as a reference value. More specifically, in step 160, it is determined whether or not the amount of deviation between the stoichiometric air-fuel ratio corresponding value stoich obtained by learning and the reference value is within a preset allowable limit. . As a result, when it is determined that the above deviation amount is within the allowable limit, the current routine is terminated. On the other hand, if it is determined that the above deviation amount is outside the allowable limit, it is determined that the air-fuel ratio sensor 16 is abnormal (step 162).

  Also in the routine shown in FIG. 5B, substantially the same processing as the routine shown in FIG. That is, also here, when the stoichiometric air-fuel ratio corresponding value stoich obtained by learning is out of the preset allowable limit, the abnormality of the air-fuel ratio sensor 16 is determined (steps 170 and 172).

  As described above, according to the routine described above, when the stoichiometric air-fuel ratio corresponding value stoich becomes an unreasonable value that cannot normally occur, it is possible to quickly determine the abnormality of the air-fuel ratio sensor 16. For this reason, according to the system of this embodiment, when an abnormality occurs in the air-fuel ratio sensor 16, it is possible to effectively prevent the state from being left for a long time.

  In the second embodiment described above, when the learning value of the stoichiometric air-fuel ratio corresponding value stoich becomes an abnormal value, the abnormality of the air-fuel ratio sensor 16 is immediately determined. It is not limited to. That is, when abnormality of the stoichiometric air-fuel ratio corresponding value stoich is recognized, the abnormality determination process of the air-fuel ratio sensor 16 may be executed again, and the presence or absence of abnormality may be determined based on the result.

  In the second embodiment described above, a preset reference value is used to determine whether or not the learned value of the stoichiometric air-fuel ratio corresponding value stoich is normal. It is not limited. That is, the reference value may be the stoichiometric air-fuel ratio corresponding value stoich learned at an early stage such as the time of vehicle shipment from the factory. According to such a setting, it is possible to accurately detect the occurrence of abnormality due to deterioration over time without being affected by individual differences in the air-fuel ratio sensor 16.

  In the second embodiment described above, the ECU 20 executes the processing of step 112, 120, 142 or 150, so that the “learning means” in the second invention is the steps 160 to 162 or steps 170 to 172. By executing the process, the “sensor abnormality determining means” in the second aspect of the invention is realized.

Embodiment 3 FIG.
[Features of Embodiment 3]
Next, a third embodiment of the present invention will be described with reference to FIG. The system of the present embodiment can be realized by causing the ECU 20 to execute the routine shown in FIG. 6 together with the routine shown in FIG. 4 or 5 using the configuration shown in FIG.

  In the first or second embodiment described above, after the stoichiometric control is started with the catalyst 14 in a full state, the output O2 of the oxygen sensor 18 maintains the stoichiometric output until the count value of the counter Counter reaches the lean side determination completion time L_TIME. In this case, it is determined that the stoichiometric air-fuel ratio corresponding value stoich is an appropriate value (see step 116). Similarly, here, after the stoichiometric control is started with the catalyst 14 being in an empty state, the stoichiometric output is maintained when the output O2 of the oxygen sensor 18 maintains the stoichiometric output until the count value of the counter Counter reaches the rich side determination completion time R_TIME. It is determined that the fuel ratio corresponding value stoich is an appropriate value (see step 146).

  By the way, after the stoichiometric control is started, the time required until the output O2 of the oxygen sensor 18 is reversed expands and contracts according to the maximum oxygen storage amount Cmax of the catalyst 14. Specifically, when the stoichiometric control is started according to the routine shown in FIG. 4 (A) or FIG. 5 (A), until it is determined in step 114 that the output O2 of the oxygen sensor 18 is inverted to the rich output thereafter. The time increases as the maximum oxygen storage amount Cmax of the catalyst 14 increases. Similarly, when the stoichiometric control is started according to the routine shown in FIG. 4B or FIG. 5B, the time until it is determined in step 144 that the output O2 of the oxygen sensor 18 is inverted to the lean output is The longer the maximum oxygen storage amount Cmax of the catalyst 14, the longer the time. The maximum oxygen storage amount Cmax of the catalyst 14 changes (decreases) as the deterioration of the catalyst 14 progresses.

  Therefore, in order to strictly determine whether or not the deviation amount occurring in the stoichiometric air-fuel ratio corresponding value stoich exceeds the allowable limit, a period for monitoring whether or not the output O2 of the oxygen sensor 18 is inverted. That is, it is appropriate to expand and contract the lean side determination completion time L_TIME and the rich side determination completion time R_TIME in accordance with the maximum oxygen storage amount Cmax of the catalyst 14. Therefore, in the system of the present embodiment, after detecting the maximum oxygen storage amount Cmax of the catalyst 14, the lean side determination completion time L_TIME and the rich side determination completion time R_TIME are appropriately set according to the detected value Cmax. It was.

[Specific Processing in Embodiment 3]
FIG. 6 shows a flowchart of a routine executed by the ECU 20 to set the lean side determination completion time L_TIME and the rich side determination completion time R_TIME in the present embodiment. According to the routine shown in FIG. 6, first, the maximum oxygen storage amount Cmax of the catalyst 14 is detected (step 180). The ECU 20 measures the maximum oxygen storage amount Cmax by executing another routine, and here, the measured value is read out. Note that the method for measuring the maximum oxygen storage amount Cmax is the same as the known method disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-19542, and therefore detailed description thereof is omitted.

  Next, the lean side determination completion time L_TIME and the rich side determination completion time R_TIME are set based on the maximum oxygen storage amount Cmax (step 182). The ECU 20 stores a map that defines the lean side determination completion time L_TIME and the rich side determination completion time R_TIME in relation to the maximum oxygen storage amount Cmax. Here, L_TIME and R_TIME are set by referring to the map.

  The map referred to in step 182 is set such that L_TIME and R_TIME become longer as the maximum oxygen storage amount Cmax increases as shown in the frame. Therefore, according to the system of the present embodiment, the period for monitoring whether or not the output O2 of the oxygen sensor 18 is inverted is longer as the Cmax is larger, and shorter as the Cmax is smaller. It can be.

  Assuming that L_TIME and R_TIME are changed according to Cmax as described above, the variation of Cmax is determined while taking the method of judging whether or not there is a deviation by observing whether output O2 is inverted during L_TIME or R_TIME. Therefore, it is possible to prevent the judgment standard from becoming unstable. Therefore, according to the system of the present embodiment, it is possible to determine the occurrence of the deviation only when the deviation exceeding the allowable limit occurs in the stoichiometric air-fuel ratio corresponding value stoich with stable accuracy.

  In the third embodiment described above, the ECU 20 performs the process of step 108 shown in FIG. 4 (A) or FIG. 5 (A) or the process of step 138 shown in FIG. 4 (B) or FIG. 5 (B). By executing the above, the “elapsed time counter” according to the third aspect of the invention is processed in step 110 or 114 shown in FIG. 4A or FIG. 5A, or in FIG. 4B or FIG. By executing the processing of step 140 or 144 shown in (2), the “deviation occurrence recognition means” in the third aspect of the invention is realized. Further, here, the ECU 20 executes the process of Step 180, so that the “Cmax detection means” in the third invention executes the process of Step 182, and the “determination completion time setting” in the third invention is executed. Each means is realized.

Embodiment 4 FIG.
[Features of Embodiment 4]
Next, a fourth embodiment of the present invention will be described with reference to FIG. The system of the present embodiment can be realized by causing the ECU 20 to execute the routine shown in FIG. 7 together with the routine shown in FIG. 4 or 5 using the configuration shown in FIG.

  In the system of the first or second embodiment described above, the time required for the output O2 of the oxygen sensor 18 to reverse after the start of stoichiometric control expands or contracts according to the gas flow rate per unit time flowing into the catalyst 14. To do. Specifically, when the stoichiometric control is started according to the routine shown in FIG. 4 (A) or FIG. 5 (A), until it is determined in step 114 that the output O2 of the oxygen sensor 18 is inverted to the rich output thereafter. The time becomes longer as the exhaust gas flow rate per unit time is smaller. Similarly, when the stoichiometric control is started according to the routine shown in FIG. 4B or FIG. 5B, the time until it is determined in step 144 that the output O2 of the oxygen sensor 18 is inverted to the lean output is The smaller the exhaust gas flow rate per unit time, the longer it takes.

  Therefore, in order to strictly determine whether or not the deviation amount occurring in the stoichiometric air-fuel ratio corresponding value stoich exceeds the allowable limit, a period for monitoring whether or not the output O2 of the oxygen sensor 18 is inverted. That is, it is appropriate to expand and contract the lean side determination completion time L_TIME and the rich side determination completion time R_TIME in accordance with the exhaust gas flow rate per unit time, that is, the intake air amount Ga of the internal combustion engine 10. Therefore, in the system of the present embodiment, the lean side determination completion time L_TIME and the rich side determination completion time R_TIME are appropriately set according to the amount of the intake air amount Ga after the start of the stoichiometric control.

[Specific Processing in Embodiment 4]
FIG. 7 shows a flowchart of a routine executed by the ECU 20 for setting the lean side determination completion time L_TIME and the rich side determination completion time R_TIME in the present embodiment. The routine shown in FIG. 7 is started simultaneously with the start of stoichiometric control according to the routine shown in FIG. 4 (A), FIG. 4 (B), FIG. 5 (A) or FIG. 5 (B).

  According to this routine, first, the intake air amount Ga of the internal combustion engine 10 is detected (step 190). Next, the smoothed value GaSM of the intake air amount Ga after the start of the stoichiometric control is updated based on the latest Ga (step 192).

  Next, a lean side determination completion time L_TIME and a rich side determination completion time R_TIME are set based on the smooth value GaSM (step 194). The ECU 20 stores a map that defines the lean side determination completion time L_TIME and the rich side determination completion time R_TIME in relation to the smoothed value GaSM of the intake air amount Ga. Here, L_TIME and R_TIME are set by referring to the map.

  The map referred to in step 194 is set such that L_TIME and R_TIME become shorter as the smoothing value GaSM increases as shown in the frame. Therefore, according to the system of this embodiment, the period for monitoring whether or not the output O2 of the oxygen sensor 18 is inverted is shorter as the GaSM is larger, and as the GaSM is smaller, the period is longer. It can be.

  Assuming that L_TIME and R_TIME are changed according to the smoothing value GaSM as described above, inhaling while taking the technique of judging whether or not there is a deviation by checking whether the output O2 is inverted during L_TIME or R_TIME It is possible to prevent the judgment standard from becoming unstable due to the influence of the air amount Ga. Therefore, according to the system of the present embodiment, it is possible to determine the occurrence of the deviation only when the deviation exceeding the allowable limit occurs in the stoichiometric air-fuel ratio corresponding value stoich with stable accuracy.

  In the fourth embodiment described above, the ECU 20 performs the process of step 108 shown in FIG. 4A or 5A, or the process of step 138 shown in FIG. 4B or 5B. By executing the above, the “elapsed time counter” according to the fourth aspect of the invention is the process of step 110 or 114 shown in FIG. 4A or 5A, or FIG. 4B or FIG. By executing the processing of step 140 or 144 shown in (4), the “deviation occurrence recognition means” in the fourth aspect of the present invention is realized. Further, here, when the ECU 20 executes the process of step 190, the “intake air amount detecting means” in the fourth invention executes the process of step 194, and the “determination complete” in the fourth invention is executed. Each “time setting means” is realized.

Embodiment 5. FIG.
Next, a fifth embodiment of the present invention will be described with reference to FIG. The system of the present embodiment can be realized by causing the ECU 20 to execute the routine shown in FIG. 8 using the configuration shown in FIG.

  In the system of the present embodiment, the stoichiometric air-fuel ratio corresponding value stoich of the air-fuel ratio sensor 16 is learned by the same method as in the first embodiment. That is, the system of the present embodiment performs the stoichiometric control after the catalyst 14 is in a full state or an empty state, and advances learning of the stoichiometric air-fuel ratio corresponding value stoich based on the subsequent output O2 of the oxygen sensor 18.

  By the way, when the catalyst 14 is in a full state, the upstream air-fuel ratio is intentionally maintained lean. Further, when the catalyst 14 is in an empty state, the upstream air-fuel ratio is intentionally maintained rich. Immediately after the catalyst 14 becomes full or empty, a lean exhaust gas or a rich exhaust gas (hereinafter referred to as “unpurified gas”) flows out downstream of the catalyst 14.

  The flow rate of the unpurified gas flowing out at the above timing increases as the intake air amount Ga at that timing increases. Therefore, if an attempt is made to create a full state or an empty state under a situation where a large amount of intake air Ga is generated, the emission characteristics are likely to deteriorate as these states are formed.

  Further, in the system of the present embodiment, after the stoichiometric control is started, whether or not there is a deviation in the stoichiometric air-fuel ratio corresponding value stoich is determined based on whether or not the output O2 of the oxygen sensor 18 becomes a rich output or a lean output. When a large amount of intake air Ga is generated, unpurified gas may be blown downstream of the catalyst 14 even if oxygen and oxygen storage capacity remain in the catalyst 14. In this case, although the deviation amount of the stoichiometric air-fuel ratio corresponding value stoich is within the allowable limit value, a change in the output of the oxygen sensor 18 is recognized, and the occurrence of deviation may be erroneously determined.

  As described above, in a situation where the intake air amount Ga is generated in a large amount, if the learning process of the stoichiometric air-fuel ratio corresponding value stoich is executed, the emission characteristics deteriorate or the stoichiometric air-fuel ratio corresponding value stoich Inconveniences such as misjudgment are likely to occur. Therefore, in the present embodiment, the execution of the learning process of the stoichiometric air-fuel ratio corresponding value stoich is prohibited under a situation where the intake air amount Ga is large.

[Specific Processing in Embodiment 5]
FIG. 8A and FIG. 8B are flowcharts of routines executed by the ECU 20 in the present embodiment in order to realize the above functions. Here, the routine shown in FIG. 8A shows that the processing of steps 200 to 202 is added before step 100, and the processing of steps 204 to 206 is added before step 110. Except for this, the routine is the same as the routine shown in FIG. Hereinafter, among the steps illustrated in FIG. 8A, the same steps as those illustrated in FIG. 4A are denoted by the same reference numerals, and description thereof is omitted or simplified.

  In the routine shown in FIG. 8A, first, the intake air amount Ga of the internal combustion engine 10 is detected (step 200). Next, it is determined whether the intake air amount Ga is equal to or greater than a predetermined determination value GaTH (step 202). The determination value GaTH is an upper limit value of Ga that allows the learning of the stoichiometric air-fuel ratio corresponding value stoich to proceed without causing deterioration of emissions or the above-described erroneous determination.

  Therefore, when the establishment of Ga ≧ GaTH is recognized, it can be determined that the learning process of the stoichiometric air-fuel ratio corresponding value stoich should not be continued. In the routine shown in FIG. 8A, in this case, the current processing cycle is immediately terminated. On the other hand, if it is determined that the above condition is not satisfied, it can be determined that the current intake air amount Ga is an amount capable of executing an appropriate learning process. In this case, the processing after step 100 is executed in order to advance the learning processing.

  In the routine shown in FIG. 8A, when it is determined in step 102 that the output O2 of the oxygen sensor 10 is not inverted to the lean output, the process of step 200 is executed again. Therefore, according to this routine, when an excessive intake air amount Ga is generated before the catalyst 14 becomes full, the learning process of the stoichiometric air-fuel ratio corresponding value stoich can be immediately terminated at that time.

  Further, according to the routine shown in FIG. 8A, after the stoichiometric control is started, the detection of the intake air amount Ga and the determination of Ga ≧ GaTH are executed again after the process of step 108 (step 204, 206). As a result, when the establishment of Ga ≧ GaTH is recognized, the current processing cycle is immediately terminated. Only when Ga ≧ GaTH is not established, the processing after step 110 is executed.

  If it is determined in the processing after step 110 that the output O2 of the oxygen sensor 18 has not changed to either the lean output or the rich output, in step 116, the count value of the Counter reaches the lean side determination completion time L_TIME. Is determined. If this condition is not satisfied, the process of step 204 is executed again. Therefore, according to the routine shown in FIG. 8A, even when the intake air amount Ga becomes large during the execution of the stoichiometric control, the learning process of the stoichiometric air-fuel ratio corresponding value stoich can be immediately terminated. it can.

  The routine shown in FIG. 8B is the same as the routine shown in FIG. 8A except that rich and lean are reversed. Therefore, detailed description thereof is omitted here. According to the routine shown in FIG. 8B, the stoichiometric control is executed after the catalyst 14 is in an empty state, and the learning of the stoichiometric air-fuel ratio corresponding value stoich is advanced, and the intake air amount Ga is an unduly large value. In this case, it is possible to realize a function of stopping the learning immediately when it becomes.

  As described above, according to the routine shown in FIG. 8A and the routine shown in FIG. 8B, the process for bringing the catalyst 14 into the full state or the empty state, or the output O2 of the oxygen sensor 18. If the intake air amount Ga becomes an unreasonably large value in the process of determining whether or not reversal occurs, learning of the stoichiometric air-fuel ratio corresponding value stoich can be immediately terminated at that time. For this reason, according to the system of this embodiment, even if the intake air amount GA becomes large during the learning process, the emission characteristics deteriorate due to the influence, or the deviation of the stoichiometric air-fuel ratio corresponding value stoich is erroneously determined. It is possible to reliably prevent the occurrence of inconveniences such as

  In the fifth embodiment described above, the ECU 20 executes the processing of step 200, 204, 210 or 214, whereby the “air amount detection means” in the fifth aspect of the invention is changed to steps 202, 206, 212 or By executing the process 216, the “determination prohibiting means” in the fifth aspect of the present invention is realized.

Embodiment 6 FIG.
[Features of Embodiment 6]
Next, a sixth embodiment of the present invention will be described with reference to FIG. The system of the present embodiment can be realized by causing the ECU 20 to execute the routine shown in FIG. 9 using the configuration shown in FIG.

  In the system of the first embodiment described above, when a deviation in the stoichiometric air-fuel ratio corresponding value stoich is recognized, the learning is advanced by enriching or leaning the value by a predetermined value. On the other hand, the system of the present embodiment is characterized in that the learning value of the stoichiometric air-fuel ratio corresponding value stoich is obtained by model calculation. Hereinafter, a method for calculating the learning value by model calculation will be described.

  As in the case of the first embodiment, the system of the present embodiment starts the stoichiometric control with the catalyst 14 in a full state or an empty state, and then determines whether or not the output of the oxygen sensor 18 is reversed. Based on this, it is determined whether or not a deviation occurs in the stoichiometric air-fuel ratio corresponding value stoich. Here, it is assumed that a rich shift occurs in the stoichiometric air-fuel ratio corresponding value stoich. In this case, when the stoichiometric control is started from the full state, the output O2 of the oxygen sensor 18 is inverted to the rich output when all the oxygen in the catalyst 14 is consumed.

The value of fuel injected during the stoichiometric control is mfr, the time required for the output O2 of the oxygen sensor 18 to reverse after the start of the stoichiometric control is t _R , and the true theoretical air-fuel ratio correspondence value When stoich is stoich_A / F, the maximum oxygen storage amount Cmax of the catalyst 14 can be expressed as follows using the current stoichiometric air-fuel ratio corresponding value stoich.
Cmax = 0.23 * (stoich_A / F-stoich) * mfr * t _R (1)
However, “0.23” in the equation (1) is a weight ratio of oxygen in the air.

When the above equation (1) is rewritten, the true theoretical air-fuel ratio corresponding value stoich_A / F can be expressed as follows.
stoich_A / F = stoich + Cmax / (0.23 * mfr * t _R ) (2)

Therefore, the true stoichiometric air fuel ratio corresponding value stoich_A / F is the current stoichiometric air fuel ratio corresponding value stoich, the maximum oxygen storage amount Cmax of the catalyst 14, the fuel injection amount mfr per unit time during the stoichiometric control, and the oxygen sensor. If the time t _R required for the 18 outputs O2 to be inverted to the rich output is known, it can be obtained by calculation by substituting them into the above equation (2).

If a lean deviation occurs in the stoichiometric air-fuel ratio corresponding value stoich, the time until the output O2 of the oxygen sensor 18 is reversed to the lean output after the stoichiometric control is started with the catalyst 14 being in an empty state is assumed to be t _L. The following relationship is established.
Cmax = 0.23 * (stoich−stoich_A / F) * mfr * t _L (3)

Then, by rewriting the above equation (3), the true theoretical air-fuel ratio corresponding value stoich_A / F can be expressed as follows.
stoich_A / F = stoich−Cmax / (0.23 * mfr * t _R ) (4)

Accordingly, in this case, the current stoichiometric air-fuel ratio corresponding value stoich, the maximum oxygen storage amount Cmax of the catalyst 14, the fuel injection amount mfr per unit time during the stoichiometric control, and the output O2 of the oxygen sensor 18 are lean outputs. By substituting the time t _L required for inversion into the above equation (4), the true stoichiometric air-fuel ratio corresponding value stoich_A / F can be obtained by calculation.

[Specific Processing in Embodiment 6]
FIG. 9A and FIG. 9B are flowcharts of routines executed by the ECU 20 in the present embodiment in order to realize the above functions. Here, the routine shown in FIG. 9A is the same as the routine shown in FIG. 9 except that the processing of step 220 is added after step 114 and the processing of step 120 is replaced with the processing of steps 222 to 228. This is the same as the routine shown in FIG. Hereinafter, among the steps illustrated in FIG. 9A, the same steps as those illustrated in FIG. 4A are denoted by the same reference numerals, and description thereof is omitted or simplified.

  In the routine shown in FIG. 9A, after the stoichiometric control is started, during the period in which both of the conditions of steps 110 and 114 are negated, the fuel injection per unit time for the internal combustion engine 10 is performed following these processes. A quantity mfr is detected (step 220). As a premise for driving the injector, the ECU 20 calculates the fuel injection amount (fuel injection time) per cycle by a known method. Here, the fuel injection amount mfr per unit time is calculated based on the fuel injection amount.

  Further, according to the routine shown in FIG. 9A, when it is determined by the process of step 114 that the output O2 of the oxygen sensor 18 is inverted to the rich output, first, the average value of mfr in the process of performing the stoichiometric control is performed. mfrave is calculated (step 222). Next, the maximum oxygen storage amount Cmax of the catalyst 14 is detected (step 224). Note that the maximum oxygen storage amount Cmax is calculated by a known method by another routine.

Next, a time t _R required for the oxygen sensor 18 to reverse to rich output is calculated (step 226). According to the routine shown in FIG. 9A, at the stage where step 226 is executed, the value corresponding to the time t _R is counted by the counter Counter. Here, the time t _R is calculated by converting the count value.

Next, by substituting the stoichiometric air-fuel ratio corresponding value stoich used in the stoichiometric control and mfrave, Cmax, and t _R acquired by the processing of the above steps 222 to 226 into the above equation (2) ( mfrave is substituted as mfr), and the true theoretical air-fuel ratio corresponding value stoich_A / F is calculated. Then, the value obtained as a result is updated as a new stoichiometric air-fuel ratio corresponding value stoich (step 228).

  As described above, according to the routine shown in FIG. 9A, after the stoichiometric control is started in a state where the catalyst 14 is in a full state, the output O2 of the oxygen sensor 18 is inverted to a rich output. Using (2) above, the stoichiometric air-fuel ratio corresponding value stoich can be updated by model calculation. According to such a model calculation, it is possible to advance the learning with high accuracy as compared with the case where the stoichiometric air-fuel ratio corresponding value stoich is made lean by a predetermined value.

  The routine shown in FIG. 9B is the same as the routine shown in FIG. 9A except that rich and lean are reversed. Therefore, detailed description thereof is omitted here. According to the routine shown in FIG. 9B, after the stoichiometric control is started in a state where the catalyst 14 is in an empty state, when the output O2 of the oxygen sensor 18 is reversed to the lean output, the above (4) is performed. The theoretical air-fuel ratio corresponding value stoich can be updated by the model calculation. According to such a model calculation, it is possible to advance the learning with higher accuracy than when the stoichiometric air-fuel ratio corresponding value stoich is enriched by a predetermined value.

  As described above, according to the routine shown in FIG. 9 (A) and the routine shown in FIG. 9 (B), the learning of the stoichiometric air-fuel ratio corresponding value stoich is advanced more accurately than in the case of the first embodiment. It is possible. Therefore, according to the system of the present embodiment, the stoichiometric air-fuel ratio corresponding value stoich can be converged to an appropriate value with high accuracy in a short time compared to the case of the first embodiment.

  In the above-described sixth embodiment, the ECU 20 executes the process of step 226, so that the “reversal time detection means” in the sixth aspect of the invention executes the process of step 222. The “injection amount detection means” in the invention executes the process of step 224, and the “Cmax detection means” in the sixth invention executes the processes of steps 110 and 114 in the sixth invention. The “learning direction determination means” implements the “learning means” according to the sixth aspect of the present invention by executing the processing of step 228.

  In the above-described sixth embodiment, the ECU 20 executes the process of step 236 so that the “reversal time detection means” in the seventh invention executes the process of step 232 so that the seventh The “injection amount detection means” in the invention executes the processing of step 234 above, and the “Cmax detection means” in the seventh invention executes the processing of steps 140 and 144 in the seventh invention. The “learning direction determination means” implements the “learning means” in the seventh aspect of the invention by executing the processing of step 238.

Embodiment 7 FIG.
[Features of Embodiment 7]
Next, a seventh embodiment of the present invention will be described with reference to FIG. 10 and FIG. The system of the present embodiment can be realized by causing the ECU 20 to execute the routine shown in FIG. 11 using the configuration shown in FIG.

  In the system shown in FIG. 1, if the upstream air-fuel ratio is made lean under the condition that the catalyst 14 is full, the downstream air-fuel ratio is also made lean. When the upstream air-fuel ratio is gradually lowered to the stoichiometric air-fuel ratio from this state, the change is reflected in the downstream air-fuel ratio with a delay d corresponding to the exhaust gas transport time. As a result, the output O2 of the oxygen sensor 18 changes from the lean output to the lean side stoichiometric output when the delay d elapses after the upstream air-fuel ratio becomes the stoichiometric air-fuel ratio.

  Similarly, when the upstream air-fuel ratio is increased from rich to the stoichiometric air-fuel ratio in a situation where the catalyst 14 is in an empty state, the output O2 of the oxygen sensor 18 is obtained after the upstream air-fuel ratio becomes the stoichiometric air-fuel ratio. When the delay d elapses, the rich output changes to the rich side stoichiometric output. That is, when the upstream air-fuel ratio is swept as described above, a rule is established that the output O2 of the oxygen sensor 18 is inverted when the delay d elapses after the upstream air-fuel ratio becomes the stoichiometric air-fuel ratio.

  If such a rule is established, the point in time when the upstream air-fuel ratio is the stoichiometric air-fuel ratio can be specified by going back by the delay d from the point in time when the output of the oxygen sensor 18 is reversed. If the output of the air-fuel ratio sensor 16 is recorded in the process of sweeping the upstream air-fuel ratio, the output value generated by the air-fuel ratio sensor 16 when the upstream air-fuel ratio is the stoichiometric air-fuel ratio, that is, the air-fuel ratio. The stoichiometric air-fuel ratio corresponding value stoich of the fuel ratio sensor 16 can be accurately detected. Therefore, the system of the present embodiment learns the theoretical air-fuel ratio corresponding value stoich according to the principle described above.

[Operation of Embodiment 7]
FIG. 10 is a timing chart for explaining the operation when the stoichiometric air-fuel ratio corresponding value stoich is learned by sweeping the upstream air-fuel ratio from lean to the stoichiometric air-fuel ratio after the catalyst 14 is in a full state. . More specifically, FIG. 10A shows the output waveform of the air-fuel ratio sensor 16, FIG. 10B shows the output waveform of the oxygen sensor 18, and FIG. 10C shows the oxygen storage amount of the catalyst 14. Each shows the change in OSA.

  In the example shown in FIG. 10, the oxygen storage amount OSA of the catalyst 14 is set to the maximum oxygen storage amount Cmax at time t0. That is, the catalyst 14 is in a full state at time t0. The ECU 20 in the present embodiment controls the fuel injection amount so that the upstream air-fuel ratio becomes a predetermined lean air-fuel ratio until the catalyst 14 becomes full. Then, when it is recognized that the catalyst 14 is full, the upstream air-fuel ratio is then swept toward the stoichiometric air-fuel ratio.

  In the process of sweeping the upstream air-fuel ratio, as shown in FIG. 10A, the output of the air-fuel ratio sensor 16 gradually changes to a small value. Here, since the oxygen in the catalyst 14 does not decrease while the upstream air-fuel ratio belongs to the lean region, the oxygen storage amount OSA is maintained at the maximum oxygen storage amount Cmax. Further, during this time, since lean gas blows out downstream of the catalyst 14, the output O2 of the oxygen sensor 18 is maintained at the lean output.

  In the example shown in FIG. 10, the upstream air-fuel ratio has reached the stoichiometric air-fuel ratio at time t1-d. That is, at the time t1-d, the output of the air-fuel ratio sensor 16 shows the true stoichiometric air-fuel ratio corresponding value stoich. Then, after the time t1-d, the upstream air-fuel ratio becomes rich, so oxygen in the catalyst 14 begins to be released, and as a result, the oxygen storage amount OSA starts to decrease.

  After time t1-d, during the period in which the catalyst 14 releases the stored oxygen, the rich exhaust gas is purified to stoichiometric gas by the action of the catalyst 14. Therefore, after the time t1 when the gas flowing into the catalyst 14 reaches the periphery of the oxygen sensor 18 at the time t1-d, the output O2 becomes the rich side stoichiometric output.

  The delay d required for the gas flowing into the catalyst 14 to reach the periphery of the oxygen sensor 18 depends on the operating state of the internal combustion engine 10 (particularly, the intake air amount Ga), and further on the deterioration state of the catalyst 14 (that is, Cmax). Value). In the present embodiment, the ECU 20 has a function of estimating the delay d according to a predetermined rule based on the operating state of the internal combustion engine and the maximum oxygen storage amount Cmax of the catalyst 14.

  Further, the ECU 20 has a function of storing the output of the air-fuel ratio sensor 18 in a period from when the upstream air-fuel ratio sweep is started until the output O2 of the oxygen sensor 18 is reversed. For this reason, the ECU 20 reads the output of the air-fuel ratio sensor 16 generated at the time t1−d that is backed by the delay d from the time t1 at the time t1 when the inversion of the output O2 is recognized, and the value is the true theory. It can be learned as the air-fuel ratio corresponding value stoich.

[Specific Processing in Embodiment 7]
FIG. 11A shows a flowchart of a routine executed by the ECU 20 in order to realize the operation shown in FIG. In the routine shown in FIG. 11A, first, the deterioration state (maximum oxygen storage amount Cmax) of the catalyst 14 and the operation state (intake air amount Ga, load L, engine speed Ne, etc.) of the internal combustion engine 10 are detected. The Based on the detection results, a delay d due to the transport of exhaust gas, more specifically, a response delay d interposed between the output of the air-fuel ratio sensor 16 and the output O2 of the oxygen sensor 18 is obtained. Calculated (step 240). The ECU 20 stores a map that defines the delay d in relation to the deterioration state of the internal combustion catalyst 14 and the operation state of the internal combustion engine. Here, the delay d corresponding to the current situation is calculated by referring to the map.

  In the routine shown in FIG. 11A, next, the upstream air-fuel ratio is controlled to be lean so that the catalyst 14 is in a full state (step 240). Next, in order to determine whether or not the catalyst 14 has become full, it is determined whether or not the output O2 of the oxygen sensor 18 has been reversed to a lean output (step 242). When it is recognized that the output O2 of the oxygen sensor 18 is inverted to the lean output, the upstream air-fuel ratio starts to be swept toward the stoichiometric air-fuel ratio (step 246).

  The ECU 20 starts recording the output of the air-fuel ratio sensor 18 (step 248), and determines whether the output O2 of the oxygen sensor 18 has changed to a stoichiometric output while continuing the recording (step 250). When it is determined that the output O2 has changed to the stoichiometric output, the output of the air-fuel ratio sensor 16 at the time point that is backed by the delay d from the present time is read, and the value is made the stoichiometric air-fuel ratio corresponding value stoich ( Step 252). According to the above processing, the operation shown in FIG. 10 can be realized and the true stoichiometric air-fuel ratio corresponding value stoich can be learned with high accuracy.

  The ECU 20 can also learn the true stoichiometric air-fuel ratio corresponding value stoich by maintaining the upstream air-fuel ratio rich so that the catalyst 14 is in an empty state and then sweeping the upstream air-fuel ratio to the lean side. FIG. 11B is a flowchart of a routine executed by the ECU 20 in order to learn the stoichiometric air-fuel ratio corresponding value stoich in such a procedure. Note that this routine is the same as the routine shown in FIG. 11A except that the rich and lean states are reversed, and therefore detailed description thereof is omitted here.

  The system according to this embodiment further increases the learning accuracy of the stoichiometric air-fuel ratio corresponding value stoich by alternately executing the routine shown in FIG. 11A and the routine shown in FIG. However, these routines are not necessarily executed in combination with each other, and only one of the routines may be executed to advance learning of the stoichiometric air-fuel ratio corresponding value stoich.

  As described above, according to the system of the present embodiment, the output generated when the air-fuel ratio sensor 16 is actually surrounded by the exhaust gas of the stoichiometric air-fuel ratio by going back in time considering the delay d. It can be detected and the output can be made the stoichiometric air-fuel ratio corresponding value stoich. According to such a method, the learning accuracy can be further improved as compared with a case where learning is advanced by simply enriching or leaning the stoichiometric air-fuel ratio corresponding value stoich by a predetermined value. Therefore, according to the system of the present embodiment, it is possible to learn the stoichiometric air-fuel ratio corresponding value stoich with higher accuracy than the systems of the first to sixth embodiments.

  In the seventh embodiment described above, the learned value of the stoichiometric air-fuel ratio corresponding value stoich is not used for the abnormality determination of the air-fuel ratio sensor 16, but the present invention is not limited to this. That is, as in the case of the second embodiment described above, it is determined whether or not the stoich obtained by learning is an abnormal value. If the abnormality is recognized, the air-fuel ratio sensor 16 is detected at that time. The abnormality determination process of the air-fuel ratio sensor 16 may be started again. In this case, whether or not the stoichiometric air-fuel ratio corresponding value stoich is a normal value may be determined based on a deviation from a preset reference value, as in the case of the second embodiment described above. Alternatively, the determination may be made based on the deviation from the stoich learned in the initial stage, such as when the vehicle is shipped.

  In the seventh embodiment described above, the learning of the stoichiometric air-fuel ratio corresponding value stoich is always executed regardless of the amount of intake air Ga, but the present invention is not limited to this. is not. That is, also in the system of the present embodiment, the learning of the stoichiometric air-fuel ratio corresponding value stoich may be stopped under the situation where the intake air amount Ga is large as in the case of the fifth embodiment described above.

  Further, in Embodiment 7 described above, after the catalyst 14 becomes full or empty, the upstream air-fuel ratio is swept at a uniform change rate, but the present invention is not limited to this. Absent. In other words, when learning stoich by the above-described method, the upstream air-fuel ratio only needs to change at a reasonable speed before and after crossing the stoichiometric air-fuel ratio. There is no need. For this reason, the upstream air-fuel ratio may be changed at a rapid sweep speed or stepwise until the catalyst 14 reaches a value close to the theoretical air-fuel ratio after the catalyst 14 is in a full state or an empty state.

It is a figure for demonstrating the structure of Embodiment 1 of this invention. It is a figure for demonstrating the output characteristic of the oxygen sensor shown in FIG. 4 is a timing chart for explaining the principle of a method in which the system of Embodiment 1 of the present invention learns a stoichiometric air-fuel ratio correspondence value stoich. It is a flowchart of the routine performed in Embodiment 1 of this invention. It is a flowchart of the routine performed in Embodiment 2 of this invention. It is a flowchart of the routine performed in Embodiment 3 of the present invention. It is a flowchart of the routine performed in Embodiment 4 of this invention. It is a flowchart of the routine performed in Embodiment 5 of this invention. It is a flowchart of the routine performed in Embodiment 6 of this invention. It is a timing chart for demonstrating the principle of the method in which the system of Embodiment 7 of this invention learns stoichiometric air fuel ratio corresponding value stoich. It is a flowchart of the routine performed in Embodiment 7 of this invention.

Explanation of symbols

10 Internal combustion engine 14 Catalyst 16 Air-fuel ratio sensor 18 Oxygen sensor 20 ECU (Electronic Control Unit)
stoich Theoretical air / fuel ratio

Claims (11)

An air-fuel ratio control device for an internal combustion engine including a catalyst in an exhaust passage,
An air-fuel ratio sensor disposed upstream of the catalyst;
An oxygen sensor disposed downstream of the catalyst;
Preparation state forming means for controlling the exhaust air-fuel ratio upstream of the catalyst so that the catalyst is in a full state in which oxygen is fully occluded or in an empty state in which all the occluded oxygen is released;
A stoichiometric state forming means for controlling the exhaust air / fuel ratio so that the output of the air / fuel ratio sensor becomes a stoichiometric air / fuel ratio corresponding value after the full state or the air state is formed;
A deviation occurrence determination means for determining whether or not a deviation occurs in the theoretical air-fuel ratio corresponding value based on the output of the oxygen sensor after the output of the air-fuel ratio sensor has reached the theoretical air-fuel ratio corresponding value;
An air-fuel ratio control apparatus for an internal combustion engine, comprising: Learning means for calculating a learned value of the theoretical air-fuel ratio corresponding value based on the output of the oxygen sensor;
Sensor abnormality determination means for determining abnormality of the air-fuel ratio sensor when a difference between a learned value of the theoretical air-fuel ratio corresponding value and a reference value of the theoretical air-fuel ratio corresponding value exceeds a determination value;
The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, further comprising: The deviation occurrence determination means is
An elapsed time counter that counts an elapsed time after the output of the air-fuel ratio sensor becomes a theoretical air-fuel ratio correspondence value;
A deviation occurrence recognition means for judging that a deviation has occurred in the theoretical air-fuel ratio corresponding value when the output of the oxygen sensor becomes a rich output or a lean output before the elapsed time reaches the determination completion time. ,
Cmax detection means for detecting the maximum oxygen storage amount of the catalyst;
Determination completion time setting means for setting the determination completion time based on the maximum oxygen storage amount;
The air-fuel ratio control apparatus for an internal combustion engine according to claim 1 or 2, further comprising: The deviation occurrence determination means is
An elapsed time counter that counts an elapsed time after the output of the air-fuel ratio sensor becomes a theoretical air-fuel ratio correspondence value;
A deviation occurrence recognition means for judging that a deviation has occurred in the theoretical air-fuel ratio corresponding value when the output of the oxygen sensor becomes a rich output or a lean output before the elapsed time reaches the determination completion time. ,
Intake air amount detection means for detecting the intake air amount of the internal combustion engine;
Determination completion time setting means for setting the determination completion time based on the intake air amount;
The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 3, further comprising: An air amount detecting means for detecting an intake air amount of the internal combustion engine;
A determination prohibiting means for prohibiting continuation of processing for determining whether or not a deviation occurs in the theoretical air-fuel ratio corresponding value when the intake air amount exceeds a determination allowable amount;
The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 4, further comprising: After the full state is formed, until the exhaust gas air-fuel ratio is controlled so that the output of the air-fuel ratio sensor becomes a stoichiometric air-fuel ratio corresponding value, until the output of the oxygen sensor is reversed to a rich output Inversion time detection means for detecting the rich inversion time required for
An injection amount detection means for detecting a fuel injection amount per unit time in the rich inversion time process;
Cmax detection means for detecting the maximum oxygen storage amount of the catalyst;
A deviation direction determination means for determining whether the theoretical air-fuel ratio correspondence value is shifted to the rich side or to the lean side;
When it is determined that the theoretical air-fuel ratio correspondence value has shifted to the rich side, based on the rich inversion time, the fuel injection amount per unit time in the process of the rich inversion time, and the maximum oxygen storage amount, Learning means for calculating a learned value of the theoretical air-fuel ratio corresponding value;
The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 5, further comprising: After the air condition is formed, until the output of the oxygen sensor is reversed to a lean output under the condition that the exhaust air / fuel ratio is controlled so that the output of the air / fuel ratio sensor becomes a stoichiometric air / fuel ratio corresponding value. An inversion time detecting means for detecting a lean inversion time required for
Injection amount detection means for detecting a fuel injection amount per unit time in the course of the lean reversal time;
Cmax detection means for detecting the maximum oxygen storage amount of the catalyst;
A deviation direction determination means for determining whether the theoretical air-fuel ratio correspondence value is shifted to the rich side or to the lean side;
When it is determined that the theoretical air-fuel ratio correspondence value is shifted to the lean side, based on the lean inversion time, the fuel injection amount per unit time in the course of the lean inversion time, and the maximum oxygen storage amount, Learning means for calculating a learned value of the theoretical air-fuel ratio corresponding value;
The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 6, further comprising: An air-fuel ratio control device for an internal combustion engine including a catalyst in an exhaust passage,
An air-fuel ratio sensor disposed upstream of the catalyst;
An oxygen sensor disposed downstream of the catalyst;
Preparation state forming means for controlling the exhaust air-fuel ratio upstream of the catalyst so that the catalyst is in a full state in which oxygen is fully occluded or in an empty state in which all the occluded oxygen is released;
A sweep control means for sweeping the exhaust air-fuel ratio so that the output of the air-fuel ratio sensor intersects the theoretical air-fuel ratio corresponding value after the full state or the empty state is formed;
Output storage means for storing the output of the air-fuel ratio sensor in the process of sweeping the exhaust air-fuel ratio;
The output of the air-fuel ratio sensor at a time point that is back by the response delay time of the oxygen sensor from the time when the output of the oxygen sensor is changed to the stoichiometric output due to the sweep of the exhaust air-fuel ratio is the value corresponding to the theoretical air-fuel ratio. Learning means as learning values;
An air-fuel ratio control apparatus for an internal combustion engine, comprising:   Sensor abnormality determining means is provided for determining abnormality of the air-fuel ratio sensor when a difference between a learned value of the theoretical air-fuel ratio corresponding value and a reference value of the theoretical air-fuel ratio corresponding value exceeds a determination value. The air-fuel ratio control apparatus for an internal combustion engine according to claim 8.   The sweep control means, after the full state or the empty state is formed, until the difference between the output of the air-fuel ratio sensor and the theoretical air-fuel ratio corresponding value becomes a predetermined value, as compared with the time of the subsequent sweep, The air-fuel ratio control apparatus for an internal combustion engine according to claim 8 or 9, wherein the exhaust air-fuel ratio is rapidly changed. An air amount detecting means for detecting an intake air amount of the internal combustion engine;
Learning prohibiting means for prohibiting continuation of processing for advancing learning of the theoretical air-fuel ratio corresponding value when the intake air amount exceeds a determination allowable amount;
The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 8 to 10, characterized by comprising:

Images