JP2008232022A - Air/fuel ratio control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance learning accuracy of a learning value while controlling an air/fuel ratio by combining main feedback control and subfeedback control in an air/fuel ratio control device. <P>SOLUTION: A main air/fuel ratio sensor 16 and a suboxygen sensor 18 are provided in front of and behind a catalyst 14, respectively. The main feedback control is performed based on the output of the main air/fuel ratio sensor 16. The subfeedback control is performed based on the output of the suboxygen sensor. The amount of correction by the main feedback control is learnt as a main learning value. The main learning value is reflected on the volume of fuel injection. Until the learning of the main learning value is completed, the influence of the subfeedback control to the volume of fuel injection is suppressed. <P>COPYRIGHT: (C)2009,JPO&INPIT

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 performs highly accurate air-fuel ratio control based on outputs of exhaust gas sensors arranged before and after a catalyst in an exhaust passage.

  Conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2005-61356, a system for controlling an air-fuel ratio of an internal combustion engine to a target air-fuel ratio is known. The conventional system includes a main air-fuel ratio sensor upstream of the catalyst disposed in the exhaust passage, and a sub-oxygen sensor downstream of the catalyst.

  The output of the main air-fuel ratio sensor is used for main feedback control for making the air-fuel ratio upstream of the catalyst coincide with the target air-fuel ratio. The sub oxygen sensor is used for sub feedback control for maintaining the air fuel ratio downstream of the catalyst at the target air fuel ratio. By executing these controls in combination, it is possible to control the exhaust air-fuel ratio to the target air-fuel ratio with extremely high accuracy regardless of fluctuations in the operating state of the internal combustion engine, individual differences of the internal combustion engine, or changes over time. It is.

  The conventional system also has a function of learning a correction amount caused by main feedback control and a correction amount caused by sub feedback control. The learned correction amount (hereinafter referred to as “main learning value” and “sub-learning value”) is reflected in the fuel injection amount in the same manner as the correction amount associated with feedback control. If the main learning value and the sub learning value are reflected in the fuel injection amount, the difference between the output of the main air-fuel ratio sensor and the target value, and the difference between the output of the sub oxygen sensor and the target value are inevitably reduced. Therefore, as the learning of the main learning value and the sub learning value progresses, the correction amount that the feedback control should bear becomes a sufficiently small value.

  The correction amount associated with the execution of the main feedback control and the sub feedback control is a parameter calculated every moment during the operation of the internal combustion engine, and is not stored after the internal combustion engine is stopped. On the other hand, the main learning value and the sub-learning value are stored even after the internal combustion engine is stopped, and can be used as correction values immediately after the next start. Therefore, if the main learning value and the sub learning value are learned and stored as executed by the conventional system, it is possible to obtain good air-fuel ratio control accuracy immediately after the start of the internal combustion engine. is there.

JP 2005-61356 A JP-A-6-229291

  In the conventional system, after the internal combustion engine is started, the learning of the main learning value and the learning of the sub learning value proceed simultaneously. In other words, this system advances the learning of the main learning value and the learning of the sub learning value at the same time while simultaneously executing the main feedback control and the sub feedback control.

  If the main feedback control and the sub feedback control are executed at the same time, the fuel injection amount is naturally influenced by the feedback control of both. More specifically, the output of the main air-fuel ratio sensor is a value that is affected by both the main feedback control and the sub feedback control. Similarly, the output of the sub oxygen sensor is a value affected by both the main feedback control and the sub feedback control.

  In an internal combustion engine, in order to obtain good air-fuel ratio control accuracy, the correction amount that the main feedback control should bear on the main learning value and the correction amount that the sub feedback control should bear on the sub learning value are accurate. It is desirable to have been transferred to. However, in the conventional learning method described above, both the main learning value and the sub learning value have a part of the correction amount that the main feedback control should bear and a part of the correction amount that the sub feedback control should bear. It will be transferred in a superimposed state. In this regard, the above-described conventional system still leaves room for improvement in the accuracy of the learning value.

  The present invention has been made to solve the above-described problems, and is an internal combustion engine capable of improving the learning accuracy of a learned value in a system that controls an air-fuel ratio by combining main feedback control and sub-feedback control. An object is to provide an air-fuel ratio control device for an engine.

In order to achieve the above object, a first invention is an air-fuel ratio control apparatus for an internal combustion engine,
A catalyst disposed in an exhaust passage of the internal combustion engine;
A main exhaust gas sensor disposed upstream of the catalyst;
A sub exhaust gas sensor disposed downstream of the catalyst;
Main feedback means for performing main feedback correction on the fuel injection amount so that the difference between the output of the main exhaust gas sensor and its target value becomes small;
Sub-feedback means for performing sub-feedback correction on the fuel injection amount so that the difference between the output of the sub-exhaust gas sensor and its target value is small;
Main learning means for learning a correction amount by the main feedback correction as a main learning value;
Main learning value reflecting means for reflecting the main learning value in the fuel injection amount;
Main learning completion determination means for determining completion of learning of the main learning value;
During the learning of the main learning value, sub-influence suppression means for suppressing the influence of the sub-feedback correction on the fuel injection amount as compared with normal time;
It is characterized by providing.

In a second aspect based on the first aspect, the sub-influence suppression means is
Sub feedback stop means for stopping sub feedback correction of the fuel injection amount during learning of the main learning value;
Sub feedback starting means for starting sub feedback correction of the fuel injection amount after completion of learning of the main learning value;
It is characterized by including.

The third invention is the first invention, wherein
The sub influence suppression means includes sub small gain setting means for setting a feedback gain for sub feedback correction to a small gain smaller than a normal value during learning of the main learning value.

Moreover, 4th invention is set in 3rd invention,
Sub learning means for learning a correction amount by the sub feedback correction as a sub learning value;
Sub learning value reflecting means for reflecting the sub learning value in the fuel injection amount;
During learning of the main learning value, sub learning prohibiting means for prohibiting learning of the sub learning value;
It is characterized by providing.

  According to a fifth invention, in any one of the first to fourth inventions, the main feedback correction feedback gain is set to a large gain larger than the normal value during the learning of the main learning value. Large gain setting means is provided.

The sixth invention is an air-fuel ratio control apparatus for an internal combustion engine,
A catalyst disposed in an exhaust passage of the internal combustion engine;
A main exhaust gas sensor disposed upstream of the catalyst;
A sub exhaust gas sensor disposed downstream of the catalyst;
Main feedback means for performing main feedback correction on the fuel injection amount so that the difference between the output of the main exhaust gas sensor and its target value becomes small;
Sub-feedback means for performing sub-feedback correction on the fuel injection amount so that the difference between the output of the sub-exhaust gas sensor and its target value is small;
Sub learning means for learning a correction amount by the sub feedback correction as a sub learning value;
Sub learning value reflecting means for reflecting the sub learning value in the fuel injection amount;
Sub-learning completion determining means for determining completion of learning of the sub-learning value;
During the learning of the sub-learning value, the main influence suppression means for suppressing the influence of the main feedback correction on the fuel injection amount as compared with the normal time;
It is characterized by providing.

The seventh invention is the sixth invention, wherein
The main influence suppression means is
Main feedback stop means for stopping main feedback correction of the fuel injection amount during learning of the sub-learning value;
Main feedback starting means for starting main feedback correction of the fuel injection amount after completion of learning of the sub learning value;
It is characterized by including.

  According to an eighth aspect based on the sixth aspect, the main influence suppression means sets the feedback gain of the main feedback correction to a small gain smaller than the normal value during learning of the sub-learning value. Main small gain setting means is included.

The ninth invention is the eighth invention, wherein
Main learning means for learning a correction amount by the main feedback correction as a main learning value;
Main learning value reflecting means for reflecting the main learning value in the fuel injection amount;
During learning of the sub learning value, main learning prohibiting means for prohibiting learning of the main learning value;
It is characterized by providing.

  In a tenth aspect according to any one of the sixth to ninth aspects, the sub-feedback correction feedback gain is set to a large gain larger than the normal value during learning of the sub-learning value. Large gain setting means is provided.

  According to the first aspect, during the learning of the main learning value, the influence of the sub feedback correction on the fuel injection amount can be suppressed as compared with the normal time. That is, according to the present invention, the learning of the main learning value can be advanced in a situation where the fuel injection amount is controlled mainly by the main feedback correction. In this case, the influence of the sub feedback correction is less likely to be reflected in the main learning value, and the correction amount that the main feedback control should bear can be accurately transferred to the main learning value.

  According to the second aspect of the invention, the sub feedback correction can be stopped during the learning of the main learning value. In this case, only the correction amount that the main feedback control should bear can be accurately transferred to the main learning value.

  According to the third aspect, by setting the feedback gain of the sub feedback correction to a small gain, it is possible to suppress the influence of the sub feedback correction on the fuel injection amount. According to this method, it is possible to effectively prevent the unpurified gas from being blown downstream of the catalyst during learning of the main learning value while mainly reflecting the influence of the main feedback correction on the main learning value.

  According to the fourth aspect of the present invention, the learning of the sub learning value can be prohibited during the learning of the main learning value. Since the influence of the sub feedback correction is suppressed during the learning of the main learning value, the correction amount that the sub feedback correction should bear is not correctly reflected in the value of the sub feedback correction. According to the present invention, it is possible to avoid the sub-learning value from being learned as an incorrect value under such circumstances.

  According to the fifth aspect, the feedback gain of the main feedback correction can be increased until the learning of the main learning value is completed. When the feedback gain of the main feedback correction increases, the responsiveness of the fuel injection amount to the main feedback correction increases, and as a result, the learning speed of the main learning value increases. For this reason, according to the present invention, it is possible to shorten the time until the completion of learning of the main learning value.

  According to the sixth aspect, during the learning of the sub-learning value, the influence of the main feedback correction on the fuel injection amount can be suppressed as compared with the normal time. That is, according to the present invention, learning of the sub-learning value can be advanced under a situation where the fuel injection amount is controlled mainly by the sub-feedback correction. In this case, the influence of the main feedback correction is less likely to be reflected in the sub-learning value, and the correction amount to be performed by the sub-feedback control is accurately transferred to the sub-learning value.

  According to the seventh aspect, the main feedback correction can be stopped while the sub-learning value is being learned. In this case, only the correction amount that the sub feedback control should bear can be accurately transferred to the sub learning value.

  According to the eighth aspect, the influence of the main feedback correction on the fuel injection amount can be suppressed by setting the feedback gain of the main feedback correction to a small gain. According to this method, during the learning of the sub-learning value, the influence of the sub-feedback correction can be mainly reflected on the sub-learning value while preventing the air-fuel ratio of the exhaust gas flowing into the catalyst from greatly deviating from the target value. .

  According to the ninth aspect, the learning of the main learning value can be prohibited during the learning of the sub learning value. Since the influence of the main feedback correction is suppressed during learning of the sub-learning value, the correction amount that the main feedback correction should bear is not correctly reflected in the main feedback correction value. According to the present invention, it is possible to avoid the main learning value from being learned to an incorrect value under such a situation.

  According to the tenth aspect, the feedback gain of the sub feedback correction can be increased until the learning of the sub learning value is completed. When the feedback gain of the sub feedback correction increases, the responsiveness of the fuel injection amount to the sub feedback correction increases, and as a result, the learning speed of the sub learning value increases. For this reason, according to the present invention, it is possible to shorten the time until the learning of the sub-learning value is completed.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
FIG. 1 is a block diagram for explaining a system configuration according to the first embodiment of the present invention. The system shown in FIG. 1 includes an internal combustion engine 10. A catalyst 14 for purifying exhaust gas is disposed in the exhaust passage 12 of the internal combustion engine 10. A main air-fuel ratio sensor 16 is disposed upstream of the catalyst 14. A sub oxygen sensor 18 is disposed downstream of the catalyst 14.

  The main air-fuel ratio sensor 16 is a sensor that emits an output corresponding to the air-fuel ratio of exhaust gas discharged from the internal combustion engine 10. The sub oxygen sensor 18 is a sensor that changes the output depending on whether the exhaust gas flowing out downstream of the catalyst 14 is rich or lean.

  In FIG. 1, blocks surrounded by a broken line are blocks realized by an ECU (Electronic Control Unit) 20. The ECU 20 includes computer elements such as a CPU, a ROM, and a RAM, and various hardware circuits.

Inside the ECU 20, a main F / B block 22 and a target A / F flock 24 are formed. The target A / F block 24 is a block that generates a signal corresponding to the target air-fuel ratio of the exhaust gas discharged from the internal combustion engine 10. The main F / B block 22 is supplied with a signal generated by the target A / F block 24 together with the output of the main air-fuel ratio sensor 16 described above. The main F / B block 22 calculates a main feedback basic correction value K _MB = f (ΔA / F) based on the difference ΔA / F between them. Furthermore, the main F / B block 22, the correction value K _MB, by multiplying the main feedback gain G _M, and generates a main feedback correction value K _M.

A sub F / B block 26 and a target voltage flock 28 are also formed inside the ECU 20. The target voltage block 28 is a block that generates a voltage corresponding to the target output of the sub oxygen sensor 18. The sub F / B block 26 is supplied with a signal generated by the target voltage block 28 together with the output of the sub oxygen sensor 18 described above. The sub F / B block 26 calculates a sub feedback basic correction value K _SB = g (ΔO ₂ ) based on the difference ΔO ₂ between them. Further, the sub F / B block 26 generates the sub feedback correction value K _S by multiplying the correction value K _SB by the sub feedback gain G _S.

The main feedback correction value K _M and the sub feedback correction value K _S are combined in the combiner 30 and then supplied to the corrector 32. The main feedback correction value K _M, the output of the main air-fuel ratio sensor 16 is reflected. Further, the output of the sub oxygen sensor 18 is reflected in the sub feedback correction value K _S. Therefore, the signal supplied to the corrector 32 is a value reflecting the air-fuel ratio upstream of the catalyst 14 and the air-fuel ratio downstream of the catalyst 14.

  A basic fuel injection amount block 34 and an engine load block 36 are formed inside the ECU 20. The engine load block 36 supplies a signal corresponding to the load KL and the rotational speed NE of the internal combustion engine 10 to the basic fuel injection amount block 34. The basic fuel injection amount block 34 receives these signals and calculates a basic fuel injection amount TAUB to be commanded to the internal combustion engine 10.

The corrector 32 corrects the basic fuel injection amount TAUB calculated by the basic fuel injection amount block 34 with the correction value supplied from the synthesizer 30. Specifically, when the combined value of the main feedback correction value K _M and the sub feedback correction value K _S requires enrichment of the air-fuel ratio, the corrector 32 performs the basic fuel injection amount TAUB. To correct the increase. On the other hand, when the above composite value requires lean air-fuel ratio, the corrector 32 corrects the basic fuel injection amount TAUB. As a result, the fuel injection amount for the internal combustion engine 10 is adjusted so that the air-fuel ratio above and below the catalyst 14 becomes the target air-fuel ratio.

[Main learning and sub learning]
In the present embodiment, ECU 20 is in executing the main feedback control and the sub feedback control, advances the learning of the main feedback correction value K _M and the sub-feedback correction value K _S. That is, the main feedback correction value K _M and the sub feedback correction value K _S converge to values according to individual differences and changes with time of the internal combustion engine 10 as the operation of the internal combustion engine 10 continues.

Without being the main feedback correction value K _M and the sub-feedback correction value K _S learning, if the reset along with the stop of the internal combustion engine 10, at the time of start of the internal combustion engine 10, a large off-the initial value from the convergence value The main feedback control and the sub-feedback control are executed using this. As a result, the main feedback correction value K _M and the sub-feedback correction value K _S is, until a proper convergence value, a bad situation control accuracy of the air-fuel ratio continues over a relatively long period of time.

Therefore, in this embodiment, during the operation of the internal combustion engine 10, the main feedback correction value K _M and the sub-feedback correction value K _S, is set to be transferring to the main learning value and the sub learning value respectively. The main learning value and the sub learning value are stored without being reset even when the internal combustion engine 10 is stopped. Further, they learned value, during operation of the internal combustion engine 10, similarly to the main feedback correction value K _M and the sub-feedback correction value K _S, it is reflected in the fuel injection amount.

According to such a method, the influence of stationary individual differences and changes with time superimposed on the internal combustion engine 10 is absorbed by the main learning value and the sub-learning value. In this case, the main feedback correction value K _M and the sub-feedback correction value K _S is consequently reaches a convergence value without deviating far from the initial value (reference value). Accordingly, the time until the stable feedback control is realized after the internal combustion engine 10 is started is shortened, and the air-fuel ratio control accuracy in the internal combustion engine 10 is improved. Therefore, according to the system of the present embodiment, excellent emission characteristics can be given to the internal combustion engine 10.

[Interference between main F / B control and sub F / B control, and features of this embodiment]
Meanwhile, the system of the present embodiment, as described above, the synthesis value of the main feedback correction value K _M and the sub feedback correction value K _S, is set to be corrected basic fuel injection quantity TAUB. In this case, the fuel injection amount TAU after correction, the influence of the main feedback correction value K _M, the influence of the sub-feedback correction value K _S, becomes as having been received together.

Originally, it is desirable that the main learning value is learned so that the air-fuel ratio upstream of the catalyst 14 matches the target air-fuel ratio by reflecting the value on the fuel injection amount TAU. However, in a situation where the main feedback control and the sub feedback control is executed simultaneously by the synthesized value of the main feedback correction value K _M and the sub-feedback correction value K _S is reflected in the fuel injection amount TAU, the air-fuel ratio Is controlled to the target air-fuel ratio. In this case, the main feedback correction value K _M is not necessarily become a value that the air-fuel ratio of the catalyst 14 upstream may be matched to the target air-fuel ratio by itself. Thus, by transferring the main feedback correction value K _M in the main learning value, be advanced learning, not necessarily the main learning value that satisfies the above requirements is obtained.

  The same situation applies to sub-learning values. For this reason, in the system of this embodiment, the main learning value and the sub-learning value are simply learned at the same time while executing the combination of the main feedback control and the sub-feedback control, so that they are learned to appropriate values. Is difficult.

  Therefore, in the present embodiment, the learning of the main learning value is advanced after the influence of the sub feedback control on the fuel injection amount is suppressed. Further, the sub-learning value is learned after the influence of the main feedback control on the fuel injection amount is suppressed. According to such a method, the correction amount that the main feedback control should bear can be correctly transferred to the main learning value. Further, the correction amount that the sub main feedback control should bear can be correctly transferred to the sub learning value. For this reason, according to the system of the present embodiment, the main learning value and the sub-learning value can be converged to appropriate values, respectively.

[Specific Processing in Embodiment 1]
FIG. 2 is a flowchart of a routine executed by the ECU 20 to realize the above function. In the routine shown in FIG. 2, it is first determined whether or not the execution condition of the main F / B control is satisfied (step 100). Here, specifically, it is determined whether or not the main air-fuel ratio sensor 16 is active.

  If the determination in step 100 is negative, the current routine is terminated as it is. On the other hand, if this determination is affirmed, then the output of the main air-fuel ratio sensor 16 is detected (step 102).

Next, a difference ΔA / F between the output A / F and the target air-fuel ratio A / Ft is calculated (step 104). Further, based on the difference ΔA / F, a main feedback basic correction value K _MB = f (ΔA / F) is calculated (step 106). The main feedback basic correction value K _MB is a value for eliminating ΔA / F (for example, the sum of a proportional term, an integral term, and a derivative term of ΔA / F). The ECU 20 stores a rule f for calculating K _MB , and here, K _MB is calculated according to the rule f.

  Next, it is determined whether or not the learning completion history of the main learning value is recorded (step 108). Immediately after the internal combustion engine 10 is started, this history is reset by the initialization process. In this case, it is determined that the condition of this step 108 is not satisfied.

If the learning completion of the main learning value is not recognized, the main feedback control gain is then set to the normal gain _GMN (step 110).

Next, main feedback control is executed using the normal gain G _MN (step 112). Specifically, first, the main feedback correction value K _M = K _MB × G _MN is calculated by first multiplying the main feedback basic correction value K _MB by the normal gain G _MN . Then, processing for reflecting the main feedback correction value K _M in the fuel injection amount TAU is performed.

Following the above process, on the basis of the main feedback correction value K _M used in the current processing cycle, the learning of the main learning value is advanced (step 114). Specifically, the main learning value is learned so as to approach the smoothed value of the main feedback correction value K _M. Main learning values, as described above, similarly to the main feedback correction value K _M, is reflected in the fuel injection amount TAU. Therefore, the main learning value approaches the smoothed value of the main feedback correction value K _M, the correction was done by the main feedback correction value K _M becomes a state which is realized by the main learning value. As a result, it decreases the correction amount to bear the main feedback correction value K _M, (strictly, smoothed value of K _M is) that the value K _M converges sufficiently small value.

  In the routine shown in FIG. 2, it is next determined whether or not the main learning value calculated in the current processing cycle has sufficiently converged (step 116). In the present embodiment, it is determined that the learning of the main learning value is completed when this condition is recognized. However, the learning of the main learning value is continuously performed even after completion of learning is determined. In this specification, for the sake of clarity, the update of the learning value until learning completion is determined is referred to as “learning”, and after the learning completion is determined, updating is referred to as “update” as it is to distinguish between the two. It shall be.

  If the main learning value has changed larger than the determination value from the previous cycle to the current cycle in step 116, the convergence determination is denied. In this case, the process of step 120 is jumped, and then it is determined whether or not a learning completion history of the main learning value exists (step 118).

Immediately after the internal combustion engine 10 is started, the learning completion history is reset, so the condition of step 118 is not satisfied. In this case, the process cycle for this time is immediately terminated without performing the process for the sub feedback control. Until the learning of the main learning value is completed, the fuel injection amount TAU is controlled only by the main feedback control by the normal gain _GMN by repeating the above processing.

If the fuel injection amount TAU is controlled only by the main feedback control, the main feedback correction value K _M, there is no room for reaching influence of the sub-feedback. For this reason, according to said process, a main learning value can be converged on the value which is not influenced by subfeedback control. In other words, according to the above processing, the correction value that the main feedback control should bear can be appropriately transferred to the main learning value.

  By repeatedly executing the above processing, learning of the main learning value is advanced. As a result, it is eventually determined in step 116 that the main learning value has sufficiently converged. In this case, after the process of step 116, the completion history of the main learning value is set (step 120).

  When the completion history of the main learning value is set, in the subsequent step 118, the existence of the history is recognized. As a result, it is next determined whether or not the sub F / B control execution condition is satisfied (step 122). Here, when the execution condition of the sub F / B control is not satisfied, the current processing cycle is ended as it is.

  On the other hand, if the sub F / B control execution condition is satisfied, the processing for sub F / B control is subsequently performed. Here, first, the output of the sub oxygen sensor 18 is detected (step 124).

Next, a difference ΔO ₂ between the output O ₂ and the target air-fuel ratio O ₂ t is calculated (step 126). Further, a sub feedback basic correction value K _SB = g (ΔO ₂ ) is calculated based on the difference ΔO ₂ (step 128). The sub feedback basic correction value K _SB is a value for eliminating ΔO ₂ (for example, the sum of a proportional term, an integral term, and a derivative term of ΔO ₂ ). ECU20 stores a rule g for calculating the K _SB, where, K _SB is calculated according to the rule f.

  Next, it is determined whether or not the learning completion history of the sub learning value is recorded (step 130). Immediately after the internal combustion engine 10 is started, this history is reset by the initialization process. In this case, it is determined that the condition of step 130 is not satisfied.

If learning completion sub learned value is not recognized, then the gain of the sub-feedback control is set to a large gain G _SL than the normal gain G _SN (step 132).

Next, sub-feedback control is executed using the large gain G _SN (step 134). Specifically, first, the sub feedback correction value K _S = K _SB × G _SL is calculated by multiplying the above-described sub feedback basic correction value K _SB by the large gain G _SL . Next, a process for reflecting the sub feedback correction value K _S in the fuel injection amount TAU is executed.

Subsequent to the above processing, learning of the sub learning value is advanced based on the sub feedback correction value K _S used in the current processing cycle (step 136). Specifically, the sub learned value is learned so as to approach the smoothed value of the sub-feedback correction value K _M. As described above, the sub-learning value is reflected in the fuel injection amount TAU, similar to the sub-feedback correction value K _S. Therefore, the sub-learning value approaches the smoothed value of the sub-feedback correction value K _S, the correction that had been made by the sub-feedback correction value K _S is a state which is realized by the main learning value. As a result, the correction amount that the sub-feedback correction value K _S should bear becomes small, and the value K _S converges to a sufficiently small value (strictly, the smooth value of K _S ).

  In the routine shown in FIG. 2, it is next determined whether or not the sub-learning value calculated in the current processing cycle has sufficiently converged (step 138). Here, if the sub-learning value has changed larger than the determination value from the previous cycle to the current cycle, the determination of convergence is denied. In this case, the processing of step 144 is jumped, and the current processing cycle is immediately terminated thereafter.

  When the routine shown in FIG. 2 is started again following the above processing, it is determined in step 108 that the learning completion history of the main learning value exists. As a result, following step 108, it is determined whether a learning completion history of sub-learning values exists (step 140).

Immediately after the sub F / B control is started, it is determined that learning of the sub learning value is not completed. In this case, then, the gain of the main feedback control is changed to a smaller small gain G _MS compared to normal gain G _MN (step 142). Thereafter, in step 112, the main feedback control by the small gain G _MS is performed. In step 114, based on the small gain G _MS by the feedback correction value KM, learning of the main learning value is advanced.

Until learning of the sub learning value is completed by the above processes are repeated, and the sub-feedback control in a large gain G _SL, and the main feedback control in the small gain GMS is executed. Sub feedback control, when carried out at atmospheric gain G _SL, since the influence of the delta O.D. ₂ is reflected on the sensitive fuel injection amount TAU, sub learning value changes to rapidly convergent value. Further, when the main feedback control is executed with the small gain _GMS , the influence of the main feedback control is suppressed, and the correction value that the sub feedback control should bear is correctly transferred to the sub learning value. For this reason, according to said process, the learning of a sublearning value can be completed appropriately in a short time.

  When the above process is repeatedly executed, the learning of the sub-learning value proceeds. Eventually, in step 138, it is determined that the sub-learning value has sufficiently converged. In this case, after the process of step 138, the completion history of the sub-learning value is set (step 144).

After the sub-learning value completion history is set, when the routine shown in FIG. 2 is started, it is determined in step 140 that the sub-learning value learning completion history exists. As a result, the gain of the main feedback control is returned to the normal gain _GMN by the processing of step 110. Similarly, in the subsequent processing cycle, the presence of a learning completion history of sub-learning is also recognized in step 130. As a result, the gain of the sub feedback control is also changed to the normal gain _GSN . For this reason, according to said process, after completion of the learning of the main learning value and the sub learning value, the main feedback control and the sub feedback control can coexist by a normal method.

  As described above, according to the routine shown in FIG. 2, the correction value that the main feedback control should bear is transferred to the main learning value, and the correction aichi that the sub feedback control should bear to the sub learning value. Can do. For this reason, according to the system of the present embodiment, the main learning value and the sub learning value can be converged to appropriate values, respectively, using a method in which main feedback control and sub feedback control coexist.

  By the way, in the first embodiment described above, during the learning of the sub-learning value, the execution of the main feedback control is maintained after the gain is lowered. In order to maintain the air-fuel ratio upstream of the catalyst 14 in the vicinity of the target air-fuel ratio, it is desirable to adopt such a method. However, when an environment in which the main feedback control can be stopped is prepared, the main feedback control is performed. The learning of the sub-learning value may be advanced after stopping. This also applies to the second embodiment described below.

In Embodiment 1 described above, when the learning of the sub-learning value is advanced, the gain of the sub-feedback control is set to the large gain G _SL , but the present invention is not limited to this. . That is, the learning of the sub-learning value may be executed using the normal gain _GSN after suppressing the influence of the main feedback. This also applies to the second embodiment described below.

In Embodiment 1 described above, when the learning of the main learning value is advanced, the gain of the main feedback control is set to the normal gain _GMN . However, the present invention is not limited to this. . That is, the learning of the main learning value may be advanced after the gain of the main feedback control is set to a large gain that is larger than the normal gain _GMN . This also applies to the second embodiment described below.

  In Embodiment 1 described above, updating of the main learning value is not prohibited even during learning of the sub-learning value, but the present invention is not limited to this. That is, during the learning of the sub-learning value, the updating of the main learning value may be prohibited in order to prevent the main learning value from being updated to an incorrect value. This also applies to the second embodiment described below.

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 a routine shown in FIG. 3 described later in place of the routine shown in FIG. 2 in the configuration shown in FIG.

  In the first embodiment described above, the sub-feedback control is stopped during the learning of the main learning value. From the viewpoint of preventing the main learning value from being affected by the sub-feedback control, the technique used in the first embodiment is effective. However, according to such a method, the air-fuel ratio downstream of the catalyst 14 tends to deviate from the target air-fuel ratio during learning of the main learning value.

Therefore, in the present embodiment, in the learning value of the main learning value, the sub feedback control is executed after lowering the gain together with the main feedback control. However, in this case, the sub feedback correction value K _S does not exactly match the value for making the air-fuel ratio downstream of the catalyst 14 coincide with the target air-fuel ratio. Accordingly, when learning of the sub-learning value is advanced under such a situation, a situation may occur in which the sub-learning value is learned to an inappropriate value. For this reason, in the present embodiment, during the learning of the main learning value, the learning of the sub learning value is prohibited, and the sub feedback control with a reduced gain is executed.

[Specific Processing in Second Embodiment]
FIG. 3 is a flowchart of a routine executed by the ECU 20 in the present embodiment. In the routine shown in FIG. 3, the step 150 is inserted in parallel with the step 120, the steps 130, 132 and 146 are deleted, and the position of the step 118 is immediately after the step 120 to immediately after the step 134. The routine is the same as that shown in FIG.

  When the ECU 20 executes the routine shown in FIG. 3, the gain of the sub feedback control is reduced until the convergence of the main learning value is determined in step 116 (step 150). Thereafter, as long as the sub F / B control execution condition is satisfied, the sub feedback control is executed with the reduced gain (see steps 122 to 134).

  However, until the learning of the main learning value is completed, the condition of step 118 is not satisfied, and the processing of step 136, that is, the learning processing of the sub learning value is not executed. As described above, according to the routine shown in FIG. 3, the sub feedback control can be executed with the gain reduced while prohibiting the learning of the sub learning value until the learning of the main learning value is completed. For this reason, according to the system of this embodiment, the air-fuel ratio downstream of the catalyst can be accurately maintained in the vicinity of the target air-fuel ratio while preventing the false learning of the sub-learning value during learning of the main learning value. .

  In the system of this embodiment, when the learning of the main learning value is completed, the learning completion history of the main learning value is set by the process of step 120. In this case, since the process of step 150 is jumped, the gain of the sub feedback is set to a normal value. Therefore, after the learning of the main learning value is completed, the sub feedback control is executed with a normal gain.

Further, in this case, it is determined in step 118 that the condition is satisfied. For this reason, the learning of the sub-learning value is advanced by the process of step 136. After learning the main learning value has been completed, until the learning of the sub learning value is completed, as in the case of routines shown in FIG. 2, the process of step 142, the gain of the main feedback control is small the gain G _MS The Therefore, the sub-learning value is a value greatly affected by the sub-feedback control. For this reason, the correction value that the sub feedback control should bear is correctly transferred to the sub learning value.

  As described above, according to the routine shown in FIG. 3, the main learning value and the sub learning value can be converged to appropriate values during each learning period. Further, according to this routine, the air-fuel ratio downstream of the catalyst during the learning of the main learning value can be made to match the target value more accurately than in the case of the first embodiment. For this reason, according to the system of the present embodiment, the learning of the main learning value and the sub-learning value can be advanced with the same accuracy as the system of the first embodiment, and compared with the system of the first embodiment. Further, even better emission characteristics can be given to the internal combustion engine 10.

  In the second embodiment described above, the learning of the sub-learning value is prohibited during the learning of the main learning value, so that the learning of the sub-learning value is prohibited. However, the present invention is not limited to this. Is not to be done. That is, when the learning accuracy of the sub learning value can be ignored, the sub learning value may be learned even during the learning of the main learning value.

  In Embodiment 2 described above, the sub feedback control gain is set to the normal value during the learning of the sub learning value, but the present invention is not limited to this. That is, as in the case of the first embodiment, during learning of a sub-learning value, the gain of sub-feedback control may be increased to increase the learning speed.

It is a block diagram for demonstrating the structure of Embodiment 1 of this invention. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a flowchart of the routine performed in Embodiment 2 of this invention.

Explanation of symbols

10 Internal combustion engine 14 Catalyst 16 Main air-fuel ratio sensor 18 Sub oxygen sensor 20 ECU (Electronic Control Unit)

Claims (10)

A catalyst disposed in an exhaust passage of the internal combustion engine;
A main exhaust gas sensor disposed upstream of the catalyst;
A sub exhaust gas sensor disposed downstream of the catalyst;
Main feedback means for performing main feedback correction on the fuel injection amount so that the difference between the output of the main exhaust gas sensor and its target value becomes small;
Sub-feedback means for performing sub-feedback correction on the fuel injection amount so that the difference between the output of the sub-exhaust gas sensor and its target value is small;
Main learning means for learning a correction amount by the main feedback correction as a main learning value;
Main learning value reflecting means for reflecting the main learning value in the fuel injection amount;
Main learning completion determination means for determining completion of learning of the main learning value;
During the learning of the main learning value, sub-influence suppression means for suppressing the influence of the sub-feedback correction on the fuel injection amount as compared with normal time;
An air-fuel ratio control apparatus for an internal combustion engine, comprising: The sub-effect suppression means is
Sub feedback stop means for stopping sub feedback correction of the fuel injection amount during learning of the main learning value;
Sub feedback starting means for starting sub feedback correction of the fuel injection amount after completion of learning of the main learning value;
The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, comprising:   The sub influence suppression means includes sub small gain setting means for setting a feedback gain of sub feedback correction to a small gain smaller than a normal value during learning of the main learning value. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1. Sub learning means for learning a correction amount by the sub feedback correction as a sub learning value;
Sub learning value reflecting means for reflecting the sub learning value in the fuel injection amount;
During learning of the main learning value, sub learning prohibiting means for prohibiting learning of the sub learning value;
The air-fuel ratio control apparatus for an internal combustion engine according to claim 3, further comprising:   5. The main large gain setting means for setting a feedback gain for main feedback correction to a large gain larger than a normal value during learning of the main learning value. 2. An air-fuel ratio control device for an internal combustion engine according to the item. A catalyst disposed in an exhaust passage of the internal combustion engine;
A main exhaust gas sensor disposed upstream of the catalyst;
A sub exhaust gas sensor disposed downstream of the catalyst;
Main feedback means for performing main feedback correction on the fuel injection amount so that the difference between the output of the main exhaust gas sensor and its target value becomes small;
Sub-feedback means for performing sub-feedback correction on the fuel injection amount so that the difference between the output of the sub-exhaust gas sensor and its target value is small;
Sub learning means for learning a correction amount by the sub feedback correction as a sub learning value;
Sub learning value reflecting means for reflecting the sub learning value in the fuel injection amount;
Sub-learning completion determining means for determining completion of learning of the sub-learning value;
During the learning of the sub-learning value, the main influence suppression means for suppressing the influence of the main feedback correction on the fuel injection amount as compared with the normal time;
An air-fuel ratio control apparatus for an internal combustion engine, comprising: The main influence suppression means is
Main feedback stop means for stopping main feedback correction of the fuel injection amount during learning of the sub-learning value;
Main feedback starting means for starting main feedback correction of the fuel injection amount after completion of learning of the sub learning value;
The air-fuel ratio control apparatus for an internal combustion engine according to claim 6, comprising:   The main influence suppressing means includes main small gain setting means for setting a feedback gain of main feedback correction to a small gain smaller than a normal value during learning of the sub-learning value. The air-fuel ratio control apparatus for an internal combustion engine according to claim 6. Main learning means for learning a correction amount by the main feedback correction as a main learning value;
Main learning value reflecting means for reflecting the main learning value in the fuel injection amount;
During learning of the sub learning value, main learning prohibiting means for prohibiting learning of the main learning value;
The air-fuel ratio control apparatus for an internal combustion engine according to claim 8, further comprising:   The sub-large gain setting means for setting a feedback gain for sub-feedback correction to a large gain larger than a normal value during learning of the sub-learning value is provided. 2. An air-fuel ratio control device for an internal combustion engine according to the item.

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