JP2008063995A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To early complete sub-feedback learning, even when low load operation continues, in an air-fuel ratio control device of an internal combustion engine. <P>SOLUTION: The suction air volume is increased in the low load operation of the internal combustion engine, up to completing the sub-feedback learning. Efficiency of the internal combustion engine is reduced so as to increase the suction air volume and to restrain an increase in output caused by an increase in the suction air volume. For example, reduction in heat efficiency of the internal combustion engine by an ignition timing delay, is effective as a means for reducing the efficiency in the internal combustion engine. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and in particular, a shift in the control center of feedback control based on a deviation between an output signal of an air-fuel ratio sensor arranged upstream of the catalyst and a theoretical air-fuel ratio is arranged downstream of the catalyst. The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine that learns through feedback control based on a deviation between an output signal of an oxygen sensor and a reference signal.

  Conventionally, as disclosed in Patent Document 1, for example, an air-fuel ratio sensor is disposed upstream of the catalyst, an oxygen sensor is disposed downstream of the catalyst, and the air-fuel ratio is controlled based on signals from these two sensors. An air-fuel ratio control device is known. The air-fuel ratio sensor is a sensor that outputs a signal corresponding to the air-fuel ratio of the exhaust gas. The oxygen sensor is a sensor that outputs a signal corresponding to the oxygen concentration of the exhaust gas, and has a characteristic that the output signal is inverted with respect to the air-fuel ratio with respect to the stoichiometric air-fuel ratio. In the conventional air-fuel ratio control device disclosed in Patent Document 1, feedback control is performed to control the fuel injection amount so that the air-fuel ratio of the exhaust gas flowing into the catalyst becomes the stoichiometric air-fuel ratio based on a signal output from the air-fuel ratio sensor. Has been done.

  In addition, in the conventional air-fuel ratio control device, in addition to the feedback control described above, control that reflects the signal output from the oxygen sensor in the fuel injection amount (this is called sub-feedback control) is also performed. In the sub feedback control, a correction value (sub F / B correction value) is calculated based on the deviation between the output signal of the oxygen sensor and the reference signal, and the sub F / B correction value is reflected in the output signal of the air-fuel ratio sensor. . The sub F / B correction value indicates whether the air-fuel ratio of the exhaust gas flowing into the catalyst is shifted to the lean / rich side with respect to the stoichiometric air-fuel ratio. According to this, even when there is a deviation in the output of the air-fuel ratio sensor, the deviation can be corrected and the fuel injection amount can be controlled so that the actual air-fuel ratio approaches the theoretical air-fuel ratio.

Further, in the conventional air-fuel ratio control device, learning is performed by using a smoothed sub F / B correction value in the time direction as a learning value (sub F / B learning value). This is called sub-feedback learning. Although the sub F / B correction value reflects the vibration of the output signal of the oxygen sensor, the sub F / B correction value can be attenuated by smoothing the sub F / B correction value in the time direction. Only stationary components included in the B correction value can be extracted. The sub F / B learning value corresponds to a steady deviation between the control center of the air-fuel ratio feedback control based on the output signal of the air-fuel ratio sensor and the theoretical air-fuel ratio. By adding the sub F / B learning value to the output signal of the air-fuel ratio sensor, the air-fuel ratio is corrected so as to compensate for the deviation, and the actual air-fuel ratio can be quickly brought close to the stoichiometric air-fuel ratio.
JP 2004-316523 A

  The sub F / B correction value includes a vibration component based on the vibration of the output signal of the oxygen sensor. This vibration component is incorporated into the sub F / B learning value by the smoothing process, so that the sub F / B learning value converges within a certain range. In the conventional air-fuel ratio control apparatus, when the number of inversions of the output signal of the oxygen sensor exceeds a predetermined number, it is determined that the sub F / B learning value is stable.

  The vibration of the output signal of the oxygen sensor is caused by the change of the atmosphere in the catalyst from rich to lean or from lean to rich. If the gas change in the catalyst is fast, the inversion cycle of the output signal of the oxygen sensor is shortened. Conversely, if the gas change in the catalyst is slow, the inversion cycle of the output signal of the oxygen sensor is long.

  The speed at which the gas in the catalyst is replaced is determined by the flow rate of the exhaust gas passing through the catalyst. In a situation where the exhaust gas flow rate is small, such as during low-load operation of an internal combustion engine, the replacement of gas in the catalyst is slow. For this reason, when the low-load operation of the internal combustion engine continues, the inversion cycle of the output signal of the oxygen sensor is prolonged, so that the completion of the sub-feedback learning is delayed. Even if the air-fuel ratio control is performed based on the sub-F / B learning value for which learning has not been completed, the actual air-fuel ratio cannot be brought close to the stoichiometric air-fuel ratio, and good emission characteristics may not be obtained.

  The present invention has been made to solve the above-described problems, and provides an air-fuel ratio control apparatus for an internal combustion engine capable of completing sub-feedback learning at an early stage even when low-load operation continues. The purpose is to do.

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 that outputs a signal corresponding to the air-fuel ratio of the exhaust gas flowing into the catalyst;
An oxygen sensor that outputs a signal corresponding to the oxygen concentration of the exhaust gas that has passed through the catalyst;
Fuel injection amount calculating means for calculating the fuel injection amount from the intake air amount;
Main feedback means for correcting the fuel injection amount by feedback control based on the deviation between the output signal of the air-fuel ratio sensor and the theoretical air-fuel ratio;
Sub-feedback means for correcting a main feedback correction value calculated by the main feedback means by feedback control based on a deviation between an output signal of the oxygen sensor and a reference value corresponding to the theoretical air-fuel ratio;
Learning means for learning a learning value for compensating for a steady deviation between the control center of the feedback control by the main feedback means and the theoretical air-fuel ratio from the sub-feedback correction value calculated by the sub-feedback means;
Learning completion determination means for determining whether learning by the learning means is completed;
Intake air amount adjusting means for increasing the intake air amount during low load operation of the internal combustion engine until it is determined that learning is completed;
Efficiency reducing means for reducing the efficiency of the internal combustion engine so as to suppress an increase in output accompanying an increase in the intake air amount when the intake air amount is increased by the intake air amount adjusting means;
It is characterized by having.

According to a second invention, in the first invention,
The learning completion determining means determines that learning is completed when the number of inversions of the output signal of the oxygen sensor exceeds a predetermined number.

According to a third invention, in the first invention,
The learning completion determining means determines that learning is completed when the learning value continues within a predetermined range for a predetermined time.

A fourth invention is any one of the first to third inventions,
The efficiency reducing means reduces the thermal efficiency of the internal combustion engine by retarding the ignition timing.

According to a fifth invention, in any one of the first to third inventions,
The efficiency reducing means reduces the mechanical efficiency of the internal combustion engine by increasing the load of an auxiliary machine driven by the internal combustion engine.

  According to the first invention, during low-load operation, the exchange of gas in the catalyst can be promoted by increasing the amount of intake air, and consequently the learning speed of sub-feedback learning based on the output signal of the oxygen sensor can be increased. it can. Further, when the intake air amount is increased, the fuel injection amount is also increased. However, since the efficiency of the internal combustion engine is also reduced at the same time as the intake air amount is increased, the output is increased with the increase of the intake air amount. Is suppressed. That is, according to the first invention, the sub-feedback learning can be completed early without affecting the output of the internal combustion engine.

  According to the second invention, by determining the completion of sub feedback learning based on the number of inversions of the output signal of the oxygen sensor related to the intake air amount, the period for increasing the intake air amount is set without excess or deficiency. Can do.

  According to the third aspect, by determining the completion of the sub-feedback learning based on the stable state of the learning value, the period for increasing the intake air amount can be set without excess or deficiency.

  According to the fourth aspect of the invention, the efficiency of the internal combustion engine can be quickly reduced without delaying the increase in the intake air amount due to the retard of the ignition timing.

  According to the fifth aspect of the invention, the efficiency of the internal combustion engine can be quickly reduced without increasing the intake air amount by increasing the load of the auxiliary machine.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram for explaining the overall configuration of an internal combustion engine system in which an air-fuel ratio control apparatus according to an embodiment of the present invention is incorporated. As shown in the figure, an exhaust passage 4 is connected to the internal combustion engine 2. In the exhaust passage 4, catalysts 6 and 8 for purifying harmful components (NOx, CO, HC) in the exhaust gas are arranged in two stages. At least the upstream catalyst 6 is a catalyst having an oxygen storage capacity. The upstream catalyst 6 is disposed close to the exhaust manifold, and the downstream catalyst 8 is disposed under the floor of the vehicle. A whole area air-fuel ratio sensor 12 is attached upstream of the catalyst 6, and an oxygen sensor 14 is attached downstream of the catalyst 6. The global air-fuel ratio sensor 12 is a sensor that exhibits output characteristics linear with respect to the air-fuel ratio. The oxygen sensor 14 is a sensor that outputs a signal corresponding to the oxygen concentration in the gas, and has an output characteristic that the output signal is inverted with respect to the air-fuel ratio with respect to the stoichiometric air-fuel ratio.

  In the internal combustion engine system, an ECU (Electronic Control Unit) 10 is provided as a control device that comprehensively controls the operation of the entire system. The entire area air-fuel ratio sensor 12 and the oxygen sensor 14 are connected to the ECU 10. The ECU 10 feedback-controls the fuel injection amount so that the air-fuel ratio of the exhaust gas flowing into the catalyst 6 becomes the stoichiometric air-fuel ratio based on the output signals of the entire area air-fuel ratio sensor 12 and the oxygen sensor 14. Hereinafter, this feedback control is referred to as air-fuel ratio feedback control.

  The air-fuel ratio feedback control executed by the ECU 10 includes main feedback control and sub feedback control. In the main feedback control, a correction value (hereinafter referred to as a main F / B correction value) is calculated based on the deviation between the output signal of the global air-fuel ratio sensor 12 and the theoretical air-fuel ratio, and fuel is generated using the main F / B correction value. The injection amount is corrected. The basic value of the fuel injection amount is determined based on the intake air amount measured by an air flow meter (not shown).

  In the sub feedback control, a correction value (hereinafter referred to as a sub F / B correction value) is calculated based on the deviation between the output signal of the oxygen sensor 14 and the reference signal, and the sub F / B correction value is calculated by the global air / fuel ratio sensor 12. The main F / B correction value is corrected by reflecting it in the output signal. In the sub-feedback control, a stationary component included in the sub F / B correction value is learned as a learning value (hereinafter referred to as a sub F / B learning value). Hereinafter, this process is referred to as sub-feedback learning. The sub-F / B learning value is reflected in the output signal of the global air-fuel ratio sensor 12, so that the fuel injection amount is corrected so as to compensate for a steady deviation included in the output signal of the global air-fuel ratio sensor 12, and promptly. It becomes possible to bring the actual air-fuel ratio closer to the stoichiometric air-fuel ratio.

  Below, the method of the sub feedback learning performed in sub feedback control is demonstrated concretely. The learning method described below is an example of a sub-feedback learning method that can be used in the present invention. It is also possible to perform sub-feedback learning by other methods.

In the sub feedback control, based on the deviation between the output signal OXS from the oxygen sensor 14 and the reference signal SFBO, the sub F / B correction value evafsfb is calculated by the following equation (1). In the following equation (1), GainP is the proportional gain of the P term (proportional term), and GainI is the integral gain of the I term (integral term).
evafsfb = (SFBO−OXS) × GainP + Σ (SFBO−OXS) × GainI (1)

The sub F / B learning value is calculated from the sub F / B correction value evafsfb. First, the sub F / B correction value evafsfb is smoothed in the time direction by the following equation (2). In the following equation (2), evafsfbsm is the smooth value of the sub F / B correction value evafsfb, evafsfbsm on the left side is the updated smooth value, and evafsfbsm on the right side is the smoothed value before update. Further, the smoothing coefficient n is a numerical value larger than 1.
evafsfbsm = evafsfbsm + (evafsfb−evafsfbsm) / n (2)

The smooth value evafsfbsm is data for updating the sub F / B learning value, and the learning update amount edvafsfbg is calculated from the learning update data evafsfbsm by the following equation (3). The learning update reflection amount m is a numerical value larger than 1.
edvafsfbg = evafsfbsm / m (3)

The learning update amount edvafsfbg calculated by the above equation (3) is the update amount of the sub F / B learning value. The sub F / B learning value is updated every time fuel injection is performed a predetermined number of times. In the present embodiment, the sub F / B learning value is represented as an integrated value of the learning update amount edvafsfbg. As shown in the following equation (4), the learning update amount edvafsfbg is added to the previous value evafefbg (i-1) of the sub F / B learning value, and the sub F / B learning value evafefbg is updated.
evafsfbg = evafsfbg (i-1) + edvafsfbg (4)

After the sub F / B learning value evafsfbg is updated, the sub F / B correction value evafsfb is corrected by the following equation (5). In the following equation (5), evafsfb on the left side is a corrected sub F / B correction value, and evafsfb on the right side is a sub F / B correction value before correction (sub F / B correction value calculated by equation (1)). ).
evafsfb = evafsfb−edvafsfbg (5)

Further, the deviation integral value esumvo is corrected by the following equation (6). The deviation integral value esumvo is an integral value Σ (SFBO−OXS) of deviation between the output signal OXS from the oxygen sensor 14 and the reference signal SFBO, and is used for the calculation of the above formula (1). In the following equation (6), esumvo (i-1) on the right side indicates the previous value of the deviation integral value esumvo.
esumvo = esumvo (i-1)-(edvafsfbg / GainI) (6)

Further, the learning update data evafsfbsm is corrected by the following equation (7). In the following equation (7), evafsfbsm on the left side is the learning update data after correction, and evafsfbsm on the right side is the learning update data before correction. The corrected learning update data evafsfbsm is used for the next calculation of the learning update data evafsfbsm.
evafsfbsm = evafsfbsm−edvafsfbg (7)

  A correction value for correcting a constant error included in the output signal of the global air-fuel ratio sensor 12 by the series of processing expressed by the equations (5) to (7) is obtained from the sub F / B correction value evafsfb. It is transferred to the sub F / B learning value evafefbg. As a result, the output signal of the global air-fuel ratio sensor 12 is prevented from being double corrected by the sub F / B learning value evafsfbg and the sub F / B correction value evafsfb.

  The sub feedback learning by the above method is performed until the sub F / B learning value converges within a certain range. Meanwhile, fuel cut is prohibited. When the fuel cut is executed, the air-fuel ratio of the gas flowing into the catalyst 6 greatly shifts to the lean side, and the oxygen storage amount of the catalyst 6 temporarily becomes saturated. In such a situation, the output signal of the oxygen sensor 14 is greatly biased to the lean side with respect to the reference signal. However, this deviation is not caused by the deviation of the output signal of the entire area air-fuel ratio sensor 12, and if this deviation is incorporated in the sub F / B learning value, the learning accuracy of the sub F / B learning value is lowered. become. Therefore, the fuel cut is prohibited until the sub feedback learning is completed, and the fuel cut is permitted on the condition that the learning is completed.

  In this embodiment, after the start of learning, when the number of inversions of the output signal of the oxygen sensor 14 exceeds a predetermined number, the sub F / B learning value has converged to a certain range, that is, the sub feedback learning has been completed. It is determined. When the output signal of the oxygen sensor 14 is inverted, the sub F / B correction value calculated from the output signal of the oxygen sensor 14 is vibrated. Since the sub F / B learning value is learned from the sub F / B correction value, the sub F / B learning value also vibrates due to the influence of the vibration component. However, the vibration component is smoothed through the smoothing process according to the above equation (2), and the sub F / B learning value becomes stable as the vibration wave of the sub F / B correction value taken into the smoothing process increases. Go. From this, it is possible to easily and accurately determine the completion of learning by determining the progress of sub-feedback learning based on the number of inversions of the output signal of the oxygen sensor 14.

  After sub feedback learning is completed, highly accurate sub feedback control is possible, and the air-fuel ratio of the exhaust gas flowing into the catalyst 6 can be brought closer to the stoichiometric air-fuel ratio more accurately. Further, since the prohibition of fuel cut is canceled upon completion of learning, fuel efficiency can be improved by executing the fuel cut. For these reasons, it is desirable that the sub-feedback learning be completed early.

  The learning speed of the sub F / B learning value depends on the inversion speed of the output signal of the oxygen sensor 14. The inversion speed of the output signal of the oxygen sensor 14 is determined by the flow rate of the exhaust gas that passes through the catalyst 6. For this reason, in a situation where the flow rate of the exhaust gas is small, such as during low-load operation, the reversal speed of the output signal of the oxygen sensor 14 also decreases because the gas replacement in the catalyst 6 is slow. However, in order to realize early learning completion, it is necessary not to reduce the flow rate of the exhaust gas during the learning period without depending on the operating state of the internal combustion engine 2.

  Therefore, the ECU 10 executes the control described below as a means for realizing early completion of the sub-feedback learning. The flowchart of FIG. 2 shows an engine control routine for realizing early learning completion. Note that the routine shown in FIG. 2 is executed each time sub-feedback learning is performed. The sub-feedback learning is performed not only when the internal combustion engine 2 is first operated, but also when the battery is removed from the ECU 10 and the stored contents of the memory are cleared. Further, the learning is performed again when the fuel property of the fuel to be used is changed or when the type of the fuel to be used is changed (for example, when the fuel is changed from gasoline to alcohol).

  In the first step S2 of the routine shown in FIG. 2, it is determined whether or not the sub feedback control is being executed. If sub feedback control is being executed, the determination in step S4 is further performed. In step S4, it is determined whether or not the sub feedback learning is completed. As described above, when the number of inversions of the output signal of the oxygen sensor 14 exceeds a predetermined number, it is determined that the sub feedback learning has been completed.

  When the sub feedback control is being executed and the sub feedback learning is not completed, the determination in step S6 is further performed. In step S6, it is determined whether or not the internal combustion engine 2 is operating at a low load. Whether the internal combustion engine 2 is operated in a low load range or a medium and high load range is determined from the accelerator opening and the engine speed.

  When the internal combustion engine 2 is operating at a low load, the process of step S8 is executed. In step S8, the throttle is opened larger than the normal throttle opening determined from the accelerator opening. In addition, the ignition timing is retarded together with the expansion of the throttle opening.

  According to normal engine control, the throttle opening during low load operation is small, and the amount of intake air is accordingly reduced. However, according to the processing in step S8, the amount of intake air becomes larger than the amount of intake air realized by normal engine control by increasing the throttle opening. As a result, the replacement of the gas in the catalyst 6 can be accelerated to promote the inversion of the output signal of the oxygen sensor 14 and the learning speed of the sub F / B learning value during the low load operation can be prevented from being lowered.

  Further, when the intake air amount increases, the fuel injection amount also increases. Therefore, according to the normal engine control, the increase in the throttle opening degree increases the output of the internal combustion engine 2. However, according to the process of step S8, the thermal efficiency of the internal combustion engine 2 is lowered due to the retard of the ignition timing, so that an increase in output accompanying an increase in the intake air amount is suppressed. That is, according to the process of step S8, the progress of the sub-feedback learning can be promoted without affecting the output of the internal combustion engine 2.

  If the result of determination in step S6 is not low load operation, that is, if the operating state of the internal combustion engine 2 is medium to high load operation, the process of step S10 is executed. In step S10, normal engine control is selected. That is, the throttle opening is not increased and the ignition timing is not retarded during low-load operation. This is because a sufficient exhaust gas flow rate can be obtained during medium and high load operation, so that sub-feedback learning can be advanced without performing control as in low load operation.

  After the process of step S8 or step S10, the determinations of step S2 and step S4 are performed again. If the result of determination in step S2 is that sub feedback control is not being executed, or if the result of determination in step S4 is that sub feedback learning has been completed, the process proceeds to step S12. In step S12, normal engine control is selected. After the process of step S12, this routine ends.

  In the present embodiment, the “fuel injection amount calculating means” according to the first aspect of the present invention is realized by the ECU 10 calculating the basic value of the fuel injection amount from the intake air amount. Further, the “main feedback unit” according to the first aspect of the present invention is realized by the ECU 10 executing the main feedback control. Further, the “sub feedback unit” according to the first aspect of the present invention is realized by the ECU 10 executing the sub feedback control. Further, the “learning means” according to the first aspect of the present invention is realized by the ECU 10 performing sub-feedback learning.

  Further, in the present embodiment, the “learning completion determination means” according to the first and second inventions is realized by the ECU 10 executing the process of step S4 of the routine shown in FIG. Further, the “intake air amount adjusting means” according to the first aspect of the present invention is realized by the ECU 10 executing the processes of steps S6 and S8. Further, the “efficiency lowering means” according to the first and fourth aspects of the present invention is realized by the ECU 10 executing the processes of step S6 and step S8.

  While the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the following modifications may be made.

  In the above embodiment, the progress of the sub feedback learning is determined by the number of inversions of the output signal of the oxygen sensor 14. However, if the sub F / B learning value is continuously within a predetermined range for a predetermined time, it is possible to determine that the sub feedback learning has been completed. According to this, the “learning completion determination means” according to the first and third inventions is realized.

  It is also effective to lower the compression ratio as a means for suppressing an increase in the output of the internal combustion engine 2 accompanying an increase in the intake air amount. The thermal efficiency of the internal combustion engine 2 can be reduced by reducing the compression ratio. Decreasing the compression ratio can be realized by changing the valve timing of the intake valve. Further, if the internal combustion engine has a variable compression ratio mechanism that changes the combustion chamber volume, the compression ratio may be lowered by the variable compression ratio mechanism. This also implements the “efficiency reduction means” according to the first invention.

  It is also effective to introduce EGR as a means for suppressing an increase in output of the internal combustion engine 2 accompanying an increase in the intake air amount. If EGR has already been introduced, the EGR rate may be increased. By introducing EGR or increasing the EGR rate, the combustion of the air-fuel mixture can be slowed down, and the thermal efficiency of the internal combustion engine 2 can be reduced. This also implements the “efficiency reduction means” according to the first invention.

  It is also effective to reduce the mechanical efficiency of the internal combustion engine 2 as a means for suppressing an increase in the output of the internal combustion engine 2 accompanying an increase in the intake air amount. Specifically, the load on an auxiliary machine driven by the internal combustion engine 2, such as an alternator or an air conditioner compressor, is increased. By making the auxiliary machine consume the output of the internal combustion engine 2, an increase in the output transmitted to the drive system can be suppressed. According to this, the “efficiency lowering means” according to the first and fifth inventions is realized.

  The means for increasing the intake air amount is not limited to the throttle. If the internal combustion engine has a variable lift mechanism that can change the lift amount of the intake valve and controls the intake air amount by the lift amount, the intake air amount can be increased using the variable lift mechanism. In this case, in normal engine control, the lift amount of the intake valve during low-load operation is small, and the intake air amount is accordingly reduced. However, when the sub-feedback learning is not completed, the amount of intake air can be increased more than the amount of intake air realized by normal engine control by increasing the lift amount by the variable lift mechanism.

  The sensor disposed upstream of the catalyst may be any sensor (air-fuel ratio sensor) that outputs a signal corresponding to the air-fuel ratio of the exhaust gas flowing into the catalyst, and is not limited to a global air-fuel ratio sensor. An oxygen sensor arranged downstream of the catalyst in the above embodiment can also be used as the air-fuel ratio sensor.

It is a figure for demonstrating the structure of the internal combustion engine system to which the air fuel ratio control apparatus as embodiment of this invention was applied. It is a flowchart which shows the routine of the engine control performed in embodiment of this invention.

Explanation of symbols

2 Internal combustion engine 4 Exhaust passage 6, 8 Catalyst 10 ECU
12 Global air-fuel ratio sensor 14 Oxygen sensor

Claims (5)

An air-fuel ratio control device for an internal combustion engine including a catalyst in an exhaust passage,
An air-fuel ratio sensor that outputs a signal corresponding to the air-fuel ratio of the exhaust gas flowing into the catalyst;
An oxygen sensor that outputs a signal corresponding to the oxygen concentration of the exhaust gas that has passed through the catalyst;
Fuel injection amount calculating means for calculating the fuel injection amount from the intake air amount;
Main feedback means for correcting the fuel injection amount by feedback control based on the deviation between the output signal of the air-fuel ratio sensor and the theoretical air-fuel ratio;
Sub-feedback means for correcting a main feedback correction value calculated by the main feedback means by feedback control based on a deviation between an output signal of the oxygen sensor and a reference value corresponding to the theoretical air-fuel ratio;
Learning means for learning a learning value for compensating for a steady deviation between the control center of the feedback control by the main feedback means and the theoretical air-fuel ratio from the sub-feedback correction value calculated by the sub-feedback means;
Learning completion determination means for determining whether learning by the learning means is completed;
Intake air amount adjusting means for increasing the intake air amount during low load operation of the internal combustion engine until it is determined that learning is completed;
Efficiency reducing means for reducing the efficiency of the internal combustion engine so as to suppress an increase in output accompanying an increase in the intake air amount when the intake air amount is increased by the intake air amount adjusting means;
An air-fuel ratio control apparatus for an internal combustion engine, comprising:   2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the learning completion determination means determines that learning is completed when the number of inversions of the output signal of the oxygen sensor exceeds a predetermined number.   2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the learning completion determination means determines that learning is completed when the learning value continuously falls within a predetermined range for a predetermined time.   The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the efficiency reduction means reduces the thermal efficiency of the internal combustion engine by retarding the ignition timing.   The internal combustion engine according to any one of claims 1 to 3, wherein the efficiency reduction means reduces the mechanical efficiency of the internal combustion engine by increasing a load of an auxiliary machine driven by the internal combustion engine. Air-fuel ratio control device.

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