JP3997971B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine that controls an air-fuel ratio so as to exhibit a conversion performance of a catalyst.

  The three-way catalyst efficiently purifies NOx, HC, and CO simultaneously when the catalyst atmosphere is near the theoretical air-fuel ratio. However, if the oxygen storage amount of the three-way catalyst reaches the saturation amount or does not hold oxygen at all, the purification efficiency of HC, CO, and NOx decreases, so the oxygen storage amount of the catalyst is made constant. The air-fuel ratio control of the engine is performed.

As such air-fuel ratio control, conventionally, air-fuel ratio feedback control for performing control so that the detected air-fuel ratio detected by the air-fuel ratio sensor provided in the exhaust passage matches the target air-fuel ratio has been widely performed. As the feedback control, for example, there is PID control, and recently, a method using sliding mode control has been proposed in order to improve robustness (see Patent Document 1).
Japanese Patent Laid-Open No. 8-232713

  However, such feedback control has a limit in improving the response to the target air-fuel ratio. That is, when a large disturbance such as a rich / lean spike enters, the deviation from the target value increases. For this reason, the correction amount is increased in order to correct the deviation. However, when the disturbance disappears thereafter, the correction amount is overcorrected by the correction amount. Therefore, in order to establish the driving performance, the response performance has to be lowered, and the exhaust performance cannot fully exhibit the potential of the air-fuel ratio sensor.

  As described above, in principle, it is unavoidable that the robustness with respect to the disturbance is reduced when the responsiveness is improved in a system having a dead time.

  The present invention has been made paying attention to such a conventional problem, and overcorrection occurs even when a large disturbance such as a rich / lean spike enters without reducing the response performance. It is an object to provide an air-fuel ratio control device for an internal combustion engine.

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected, it is not limited to this.

  The present invention includes a target air-fuel ratio calculating means (21) for calculating a target air-fuel ratio of exhaust gas flowing into the catalyst based on the conversion performance of the catalyst (7), and an air-fuel ratio for detecting the air-fuel ratio of exhaust gas flowing into the catalyst. A fuel ratio detection means (16), a feedback correction amount calculation means (22) for calculating a feedback correction amount based on the detected air-fuel ratio so that the air-fuel ratio detected by the air-fuel ratio detection means becomes the target air-fuel ratio. An air-fuel ratio control device for an internal combustion engine having a fuel injection amount control means (31) for controlling a fuel injection amount based on the feedback correction amount, wherein the lean-side or rich-side combustion limit air-fuel ratio and the target air-fuel ratio Response limit setting means (step) for setting a rich side or lean side response limit air-fuel ratio between the rich side or lean side combustion limit air fuel ratio and the target air fuel ratio based on the fuel ratio. S2) and feedback correction amount limiting means (steps S8 to S10) for limiting the feedback correction amount when the air-fuel ratio detected by the air-fuel ratio detection means exceeds the response limit air-fuel ratio. .

  According to the present invention, the response limit air-fuel ratio is set based on the combustion limit air-fuel ratio and the target air-fuel ratio, and the feedback correction amount is limited when the air-fuel ratio detected by the air-fuel ratio detection means exceeds the response limit air-fuel ratio. As a result, when a spike disturbance more than expected is added, a feedback restriction is applied, and overcorrection is not caused. On the other hand, the conventional high responsiveness can be maintained within the normal air-fuel ratio feedback range.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing an air-fuel ratio control apparatus for an internal combustion engine according to the present invention.

  Reference numeral 1 denotes an engine body, 2 an intake passage, 3 an exhaust passage, 4 a throttle valve, 5 a fuel injection valve, and 6 an ignition plug.

  The fuel injection amount and fuel injection timing from the fuel injection valve 5 and the timing of spark ignition by the spark plug 6 are controlled by the engine controller 11 according to operating conditions. That is, the engine controller 11 inputs a signal from a crank angle sensor (consisting of a position sensor 12 and a phase sensor 13) and a signal of an intake air flow rate from an air flow meter 14 together with a signal from a water temperature sensor 15 and the like based on these signals. Thus, the fuel injection amount and injection timing from the fuel injection valve 5 are controlled, and the timing of spark ignition by the spark plug 6 is controlled.

  The engine exhaust passage 3 is provided with a three-way catalyst 7 having an oxygen storage function and simultaneously purifying NOx, HC and CO when the catalyst atmosphere is near the stoichiometric air-fuel ratio. If the oxygen storage amount of the three-way catalyst 7 reaches a saturation amount or does not hold oxygen at all, the purification efficiency of HC, CO, and NOx decreases. The output of the wide-range air-fuel ratio sensor 16 provided upstream of the three-way catalyst 7 so as to keep the oxygen storage amount of the three-way catalyst 7 constant in order to calculate the amount and keep the conversion efficiency of the three-way catalyst 7 at a maximum. The air-fuel ratio control of the engine is performed based on the output of the O2 sensor 17 provided on the downstream side of the original catalyst 7.

  This control is roughly as follows (for details, refer to JP2003-522898). In other words, the engine controller 11 estimates and calculates the oxygen storage amount of the three-way catalyst 7 based on the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 7 and the intake air amount of the engine. This is divided into HO2 and low speed component LO2. Specifically, when oxygen is absorbed, the high speed component HO2 is preferentially absorbed, and when the high speed component HO2 cannot be absorbed, the calculation is performed assuming that the low speed component LO2 starts to be absorbed. When oxygen is released, if the ratio of the low speed component LO2 to the high speed component HO2 (LO2 / HO2) does not reach a certain ratio AR, oxygen is preferentially released from the high speed component HO2, and the ratio LO2 / HO2 is a constant ratio. Then, the oxygen storage amount is calculated on the assumption that oxygen is released from both the low speed component LO2 and the high speed component HO2 so as to maintain the ratio LO2 / HO2.

  When the calculated high-speed component HO2 of the oxygen storage amount is larger than the target value, the engine air-fuel ratio is controlled to the rich side to decrease the high-speed component HO2, and when it is smaller than the target value, the air-fuel ratio is made lean. To increase the high speed component HO2.

  As a result, the high-speed component HO2 of the oxygen storage amount is maintained at the target value, so even if the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 7 deviates from the stoichiometric air-fuel ratio, the high-speed component HO2 with high responsiveness Immediately oxygen is absorbed or released, the catalyst atmosphere is corrected in the theoretical air-fuel ratio direction, and the conversion efficiency of the three-way catalyst 7 is kept at the maximum.

  Further, when the calculation error accumulates, the calculated oxygen storage amount deviates from the actual oxygen storage amount. However, the oxygen storage amount (the high speed component HO2 and the low speed component) at the timing when the downstream of the three-way catalyst 7 becomes rich or lean. The difference between the calculated value and the actual oxygen storage amount is corrected by resetting LO2).

  Thus, the general control content is to change the target air-fuel ratio in accordance with the oxygen storage amount and to perform the air-fuel ratio feedback control so that the target air-fuel ratio thus changing is obtained.

(Basic concept of the present invention)
Now, in order to facilitate understanding, the basic concept of the present invention will be described.

  First, conventional problems will be described. If the responsiveness is improved in the conventional air-fuel ratio control, the robustness against spike noise (disturbance) deteriorates. This will be described with reference to FIG. That is, when a rich spike occurs, the deviation of the detected air-fuel ratio detected by the air-fuel ratio sensor from the target air-fuel ratio increases (FIG. 10A). For this reason, the air-fuel ratio feedback correction value ALPHA also changes greatly in order to correct the deviation (FIG. 10B). And (1) the rich spike disappears. (2) Since the output of the air-fuel ratio sensor has an exhaust system delay, ALPHA remains lean even after the rich spike disappears. (3) In this state, the lean air-fuel ratio also becomes lean due to the leaned ALPHA component. (4) At the point of time when lean is detected with the exhaust air-fuel ratio, the combustion air-fuel ratio exceeds the lean combustion limit air-fuel ratio, which may lead to misfire. (5) If the dead time between the detection of the exhaust air / fuel ratio and the combustion air / fuel ratio is small and the feedback control is also extremely high response, the leaning of the combustion air / fuel ratio can be improved to some extent, but it must be done completely. I can't.

  Therefore, in the present invention, when the air-fuel ratio (detected air-fuel ratio) changes, the limit air-fuel ratio (response limit air-fuel ratio) of the response range in which the conventional feedback control is performed is set, and when the response limit air-fuel ratio is exceeded, feedback is performed. The control gain is switched (decreased). In this way, when an excessive disturbance such as a rich spike does not enter, the responsiveness can be maintained high, and the feedback is limited when the spike disturbance more than expected is added, so the air-fuel ratio feedback correction value ALPHA does not change too much, and after that, even if the disturbance disappears, it is overcorrected and does not exceed the lean combustion limit air-fuel ratio.

  Note that sliding mode control and PID control can be considered as feedback control applicable to this control. In view of this, the following description will be given, including how much the feedback gain should be set when these controls are applied.

(For sliding mode control)
FIG. 2 is a block diagram when the feedback control is performed by the sliding mode control.

  In the sliding mode control, a sliding mode controller (sliding mode control unit) 22 is provided so as to obtain the target air-fuel ratio. The sliding mode controller 22 includes a switching function calculation unit 23, a nonlinear input calculation unit 24, a linear input calculation unit 25, an integrator 26, an adder 27, a conversion unit 28, and a correction limiting unit 29. The outline of the control of the sliding mode controller 22 is as follows (refer to Japanese Patent Laid-Open No. 2003-90252 for details).

Based on the detected air-fuel ratio AFSAF and the target air-fuel ratio TGABF, the switching function calculator 23 calculates the state quantity σ (n) at the current time n. Based on this state quantity σ (n), the nonlinear input calculator 24 calculates a nonlinear input _unl . Similarly, an equivalent control input u _eq that is a linear input is calculated by the linear input calculation unit 25 based on the state quantity σ (n). The calculated equivalent control input u _eq is integrated by the integrator 26, and the air-fuel ratio manipulated variable u _sl obtained by adding the nonlinear input u _nl to the integrated value is converted to the air-fuel ratio feedback correction coefficient ALPHA by the conversion unit 28. Then, the correction limit unit 29 limits the correction amount. The fuel injection amount calculation unit 31 performs this air-fuel ratio feedback correction value ALPHA and various other corrections on the basic injection pulse width TP, and calculates the fuel injection pulse width CTI by the following equation. The fuel injection valve 5 is driven intermittently using the fuel injection pulse width CTI. The fuel injection pulse width CTI is calculated by the following formula.

CTI = (TP * TFBYA + KATHOS) * (ALPHA + KBLRC-1) + TS + CHOS
However, TFBYA: target equivalence ratio, KATHOS: fuel feedforward correction value, ALPHA: air-fuel ratio feedback correction value, KBLRC: air-fuel ratio learning value, TS: invalid injection pulse width, CHOS: fuel feedforward correction value for each cylinder.

  The basic injection pulse width TP is calculated based on the intake air amount measured by the air flow meter 14.

  The fuel feedforward correction value KATHOS and its cylinder-specific correction value CHOS are the basic injection pulse width TP, the water temperature detected by the water temperature sensor 15, and the rotational speed detected by the crank angle sensor (consisting of the position sensor 12 and the phase sensor 13). Calculate from.

  The target equivalent ratio TFBYA is calculated based on the water temperature detected by the water temperature sensor 15.

  The detected air-fuel ratio AFSAF is detected by the wide area air-fuel ratio sensor 16.

  The target air-fuel ratio TGABF is calculated by the target air-fuel ratio calculation unit 21 based on signals from the wide area air-fuel ratio sensor 16 and the O2 sensor 17.

  Based on the above, specific control contents of the present invention will be described.

  FIG. 3 is a flowchart for calculating a feedback gain (air-fuel ratio feedback correction value ALPHA).

  In step S1, the target air-fuel ratio TGABF is obtained from the amount of oxygen stored in the catalyst as described above.

  In step S2, a feedback response range is calculated based on the target air-fuel ratio TGABF. Here, a method of calculating the feedback response range will be described with reference to FIG. FIG. 4 is a diagram for explaining the concept of the rich side response limit air-fuel ratio. (1) First, the difference between the lean side combustion limit air-fuel ratio LEANLMT and the target air-fuel ratio TGABF is obtained. (2) A value having the same width on the rich side with the target air-fuel ratio TGABF as the center is set as a rich-side response limit air-fuel ratio richlmt.

  For the response limit air-fuel ratio on the lean side, (1) the difference between the rich combustion limit air-fuel ratio RICHLMT and the target air-fuel ratio TGABF is obtained. (2) A value having the same width on the lean side with the target air-fuel ratio TGABF as the center is defined as a lean-side response limit air-fuel ratio leanlmt.

  Note that if the air-fuel ratio is too lean, it will misfire, leading to engine stall or knocking, so the lean side combustion limit air-fuel ratio is determined. For example, A / F = 11.0. If the air-fuel ratio is too rich, the generated torque and response will be reduced, so the rich combustion limit air-fuel ratio is determined. As an example, A / F = 16.0.

  From the above, the upper and lower limit values of the feedback response range can be calculated from the following equations.

Lean side response limit ΔA / F: leanlmt =-(RICHLMT # -TGABF)
Rich side response limit ΔA / F: richlmt =-(LEANLMT # -TGABF)
In this way, setting the rich response limit air-fuel ratio from the lean combustion limit air-fuel ratio (setting the lean response limit air-fuel ratio from the rich combustion limit air-fuel ratio), and the response limit air-fuel ratio It has been found by the inventor that the present inventor has conducted sincere research that it can be expressed by such a simple expression and that appropriate control can be performed without overcorrection.

  Returning again to FIG. When the detected air-fuel ratio AFSAF is within the feedback range in step S3, the process proceeds to step S4 and subsequent steps.

  In step S4, the value of the switching function is obtained. Specifically, this switching function is as follows.

次にステップＳ５において非線形入力ｕ_nl(n)を算出する。具体的には以下である。

Next, in step S5, the nonlinear input u _nl (n) is calculated. Specifically:

続いてステップＳ６において等価制御入力を求める。具体的には以下である。

In step S6, an equivalent control input is obtained. Specifically:

そしてステップＳ７において空燃比フィードバック補正値ALPHAを算出する。その概略について説明すると以下である（詳細は特開２００３−９０２５２号参照）。すなわち、等価制御入力ｕ_eqを積分器２６で積分し、その積分値に非線形入力ｕ_nlを加算して空燃比操作量ｕ_slを算出する。そして以下の式により空燃比フィードバック補正係数ALPHAを算出する。

In step S7, an air-fuel ratio feedback correction value ALPHA is calculated. The outline will be described below (for details, refer to Japanese Patent Application Laid-Open No. 2003-90252). That is, the equivalent control input u _eq is integrated by the integrator 26, and the non-linear input u _nl is added to the integrated value to calculate the air-fuel ratio manipulated variable u _sl . Then, the air-fuel ratio feedback correction coefficient ALPHA is calculated by the following formula.

なお、シリンダ吸入空燃比CYLAFは以下の式により導き出される。

The cylinder intake air-fuel ratio CYLAF is derived from the following equation.

一方、ステップＳ３でフィードバック範囲外であると判定した場合は、ステップＳ８以降に進む。

On the other hand, if it is determined in step S3 that it is outside the feedback range, the process proceeds to step S8 and subsequent steps.

  In step S8, the value of the switching function is obtained. This switching function is specifically as follows, and is applied with a slope correction coefficient SLNTGN.

次にステップＳ９において非線形入力ｕ_nl(n)を算出する。具体的には以下である。

Next, in step S9, the nonlinear input u _nl (n) is calculated. Specifically:

続いてステップＳ１０において傾き補正をいれた等価制御入力を算出する。具体的には以下である。

In step S10, an equivalent control input with inclination correction is calculated. Specifically:

このようにすることで、図５に示すように、検出空燃比AFSAFがフィードバック追従領域内にいる場合は、切換関数の傾きを実線のように大きくとり、追従領域を外れた場合は破線のように傾きを小に変更する。

By doing so, as shown in FIG. 5, when the detected air-fuel ratio AFSAF is in the feedback tracking area, the gradient of the switching function is made large as shown by a solid line, and when the detected air-fuel ratio AFSAF is outside the tracking area, Change the tilt to small.

  (1) When the response limit air-fuel ratio is exceeded, a switching function with a small slope is followed. (2) If it is within the response limit air-fuel ratio, it follows a switching function with a large slope. (3) Therefore, if it is within the response range, the performance is equivalent to the conventional one.

  Next, effects will be described with reference to the time chart of FIG.

  In this embodiment, (1) the difference between the target air-fuel ratio TGABF obtained from the amount of oxygen stored in the catalyst and the lean-side combustion limit air-fuel ratio LEANLMT is obtained. (2) Then, a value having the same range on the rich side with the target air-fuel ratio TGABF as the center is set as the rich-side response limit air-fuel ratio richlmt. (3) When the detected air-fuel ratio AFSAF exceeds richlmt, the switching function slope is lowered by the correction coefficient SLNTGN.

  Due to this decrease in gain, (4) the nonlinear gain becomes a solid line and becomes smaller than the broken line. (5) Although the equivalent control input is reduced and the integration amount is also reduced, the integration is not stopped, so that the steady deviation can be absorbed.

  Therefore, with the above configuration, when a spike disturbance more than expected is added, a feedback restriction is applied, so that overcorrection is not caused. Therefore, in the past (broken line), the air-fuel ratio sometimes exceeded the lean limit and there was a possibility of misfire, but in the present application (solid line), the lean limit is no longer exceeded. Further, since the feedback follow-up range is calculated from the actual air-fuel ratio (detected air-fuel ratio), the feedback speed is not reduced more than necessary. Furthermore, the usual high responsiveness can be maintained within the normal air-fuel ratio feedback range. Also, by changing the slope of the switching function, the feedback speed can be reduced even if the original settings of the nonlinear gain and integral gain are diverted, and the integration does not stop. But it can be absorbed.

(In the case of PID control)
Next, a case where feedback control is performed by PID control will be described. FIG. 7 is a block diagram when feedback control is performed by PID control.

  In this case, a PID controller (PID controller) 42 is provided so that the target air-fuel ratio can be obtained during operation at the stoichiometric air-fuel ratio. The PID controller 42 includes a proportional (P) correction amount calculating unit 43, an integral (I) correction amount calculating unit 44, a differential (D) correction amount calculating unit 45, an adder 46, and a correction limiting unit. 47.

  Then, the PID controller 42 calculates the P component correction amount, the I component correction amount, and the D component correction amount based on the detected air-fuel ratio AFSAF and the target air-fuel ratio TGABF. Then, each correction amount is added to calculate an air-fuel ratio feedback correction value ALPHA. After limiting the correction amount by the correction limiting unit 47, the fuel injection amount calculating unit 31 calculates the fuel injection pulse width CTI as in the case of the sliding mode control. The fuel injection valve 5 is driven intermittently using the fuel injection pulse width CTI.

  Based on the above, specific control contents of the present invention will be described.

  FIG. 8 is a flowchart for calculating a feedback gain (air-fuel ratio feedback correction value ALPHA).

  Steps S1 to S3 are the same as those in the sliding mode control, and thus the description thereof is omitted.

  When the detected air-fuel ratio AFSAF is within the feedback range in step S3, the process proceeds to step S14 and subsequent steps. That is, a proportional (P) correction amount is calculated (step S14), an integral (I) correction amount is calculated (step S15), and both are added to calculate an air-fuel ratio feedback correction value ALPHA (step S15). Step S16). The above control is the same as normal PID control.

  On the other hand, if it is determined in step S3 that it is out of the feedback range, the process proceeds to step S17 and subsequent steps. That is, a proportional (P) correction amount is calculated (step S17). This calculation method is the same as that in step S14, and is the same as the conventional PID control. Then, it is determined whether or not the proportional (P) correction amount is within the maximum amount obtained as follows (step S18). The maximum amount is calculated as follows.

Rich side follow-up P additional amount = TALPGAI * (-(LEANLMT # -TGABF))
However, TALPGAI: P component gain table reference value For the lean side, the maximum amount is calculated by the following equation.
Lean side follow-up P component additional maximum amount = TALPGAI * (-(RICHLMT # -TGABF))
If the maximum amount is not exceeded, the process proceeds to step S19, where the integral gain is obtained by the following equation.

Integral gain when response limit is exceeded = TALIGAI * AFIGDWN #
However, TALIGAI: I component gain table reference value AFIGDWN is a gain correction amount and is a constant less than 1 (for example, AFIGDWN # = 0.5). The integral gain is reduced by multiplying the gain correction coefficient AFIGDWN #.

  On the other hand, if the proportional (P minute) correction amount exceeds the limit limiter value in step S18, the process proceeds to step S20, and the proportional (P minute) correction amount is fixed to the limit limiter value, and the process proceeds to step S19. The integral gain is calculated by multiplying the integral (I) correction amount by AFIGDWN #.

  Next, effects will be described with reference to the time chart of FIG.

  In this embodiment, (1) the difference between the target air-fuel ratio TGABF obtained from the amount of oxygen stored in the catalyst and the lean-side combustion limit air-fuel ratio LEANLMT is obtained. (2) Then, a value having the same range on the rich side with the target air-fuel ratio TGABF as the center is set to the rich-side response limit air-fuel ratio richlmt. (3) Then, when the detected air-fuel ratio AFSAF exceeds richlmt, it is made to follow only the integral (I). (4) That is, the proportional (P) gain is limited by the limiter calculated from the lean combustion limit air-fuel ratio LEANLMT and the target air-fuel ratio TGABF. (5) The integral (I) gain is reduced by multiplying the correction coefficient AFIGDWN. However, since the integration is not stopped, the steady deviation can be absorbed.

  By doing as described above, when a spike disturbance more than expected is added, a feedback restriction is applied, so that overcorrection is not caused. Therefore, the conventional (broken line) may exceed the lean limit air-fuel ratio and there is a possibility of misfire, but in the present application (solid line), the lean limit air-fuel ratio is no longer exceeded. Also, the P component gain limit is calculated from the feedback range and only the I component gain correction value is set, so that the feedback speed can be lowered even if the original setting is used, and the integration is not stopped, so it is constantly large. Even when a disturbance is added, it can be absorbed.

  The present invention is not limited to the embodiment described above, and various modifications and changes can be made within the scope of the technical idea, and it is obvious that these are equivalent to the present invention.

1 is a schematic configuration diagram showing an air-fuel ratio control apparatus for an internal combustion engine according to the present invention. It is a block diagram in the case of performing feedback control by sliding mode control. It is a flowchart which calculates a feedback gain. It is a figure explaining the view of the rich side response limit air-fuel ratio. It is a figure which shows how to move on the phase plane of sliding mode control. It is a time chart explaining an effect. It is a block diagram in the case of performing feedback control by PID control. It is a flowchart which calculates a feedback gain. It is a time chart explaining an effect. It is a figure explaining the conventional problem.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine main body 2 Intake passage 3 Exhaust passage 4 Throttle valve 5 Fuel injection valve 6 Spark plug 7 Three way catalyst 16 Wide area air fuel ratio sensor (air fuel ratio detection means)
21 Target air-fuel ratio calculation unit (target air-fuel ratio calculation means)
22 Sliding mode controller (feedback correction amount calculation means)
31 Fuel injection amount calculation unit (fuel injection amount control means)
Step S2 Response limit setting means Steps S8 to S10 Feedback correction amount limiting means

Claims (6)

Target air-fuel ratio calculating means for calculating a target air-fuel ratio of exhaust gas flowing into the catalyst based on the conversion performance of the catalyst;
Air-fuel ratio detecting means for detecting the air-fuel ratio of the exhaust gas flowing into the catalyst;
Feedback correction amount calculating means for calculating a feedback correction amount based on the detected air-fuel ratio so that the air-fuel ratio detected by the air-fuel ratio detecting means becomes the target air-fuel ratio;
Fuel injection amount control means for controlling the fuel injection amount based on the feedback correction amount;
An air-fuel ratio control apparatus for an internal combustion engine having
Based on the lean or rich combustion limit air-fuel ratio and the target air-fuel ratio, the rich or lean response limit air-fuel ratio is set between the rich or lean combustion limit air-fuel ratio and the target air-fuel ratio. Response limit setting means to be set;
Feedback correction amount limiting means for limiting a feedback correction amount when the air-fuel ratio detected by the air-fuel ratio detection means exceeds the response limit air-fuel ratio;
An air-fuel ratio control apparatus for an internal combustion engine, comprising: The response limit setting means is configured so that the difference between the rich response limit air-fuel ratio and the target air-fuel ratio becomes equal to the difference between the lean combustion limit air-fuel ratio and the target air-fuel ratio. Set the fuel ratio,
The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein: The response limit setting means is configured so that the difference between the lean response limit air-fuel ratio and the target air-fuel ratio becomes equal to the difference between the rich combustion limit air-fuel ratio and the target air-fuel ratio. Set the fuel ratio,
The air-fuel ratio control apparatus for an internal combustion engine according to claim 1 or 2, further comprising: Feedback control is performed by sliding mode control,
The feedback correction amount limiting means limits the feedback correction amount by reducing the slope of the switching function.
The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein Perform feedback control with PID control,
The feedback correction amount limiting means limits the feedback correction amount by limiting the proportional amount.
The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein Perform feedback control with PID control,
The feedback correction amount limiting means limits the feedback correction amount by lowering the integral gain.
The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein

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