JP2002030964A - Air-fuel ratio feedback control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure convergence of an air-fuel ratio during input and release of disturbance as a steady deviation is dissolved, in feedback control of an air-fuel ratio using a sliding mode. SOLUTION: A proportional item is calculated from a deviation between a real air-fuel ratio and a target air-fuel ratio and a proportional gain, an integrating item is calculated from the deviation and an integrating gain, and a total sum of them forms a linear item U1. Meanwhile, a switching function σis set such that an air-fuel ratio deviation, a differential value of a deviation, and an integrating value of a deviation form a variable and a non-linear item U2 is calculated. In this case, in a way that the more an absolute value of the air-fuel ratio deviation is increased, the more the integrating gain is corrected to a higher value, a speed of accumulation of the integrating item when shearing of an air-fuel ratio due to input of disturbance occurs is increased and a speed of discharge of the integrating item when the disturbance is released is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio feedback control device for an internal combustion engine, and more particularly to a technique for performing feedback control of an air-fuel ratio of a combustion mixture to a target air-fuel ratio using sliding mode control.

[0002]

2. Description of the Related Art Conventionally, sliding mode control has been known as a highly robust control that suppresses the influence of disturbance, and is often used in robot control and the like. It has been proposed to perform feedback control (JP-A-8-23)
2713).

[0003]

However, in the conventional air-fuel ratio feedback control in the sliding mode,
Since the linear term is calculated in accordance with the deviation from the target air-fuel ratio, there is a problem that when there is a steady deviation of the air-fuel ratio, it is not possible to add a correction for eliminating the steady-state deviation.

[0004] In the normal feedback control based on proportional, integral, and differential operations, if feedback control is performed by the integral operation, the integral term accumulated due to air-fuel ratio fluctuation due to the introduction of disturbance is difficult even if the disturbance is canceled. Unnecessary corrections are made after the disturbance is canceled, which causes a problem that a large air-fuel ratio deviation occurs.

The present invention has been made in view of the above problems, and has as its object to eliminate the steady-state deviation of the air-fuel ratio in the air-fuel ratio feedback control in the sliding mode. It is still another object of the present invention to eliminate the steady-state deviation of the air-fuel ratio and to suppress the fluctuation of the air-fuel ratio when the disturbance is canceled.

[0006]

Therefore, according to the present invention, an air-fuel ratio feedback control amount including a linear term and a non-linear term is obtained by a sliding mode control based on a detected value of an air-fuel ratio and a target air-fuel ratio. In the air-fuel ratio feedback control device for an internal combustion engine having a configuration to calculate, the linear term is calculated including an integral value of a deviation between a detected value of the air-fuel ratio and a target air-fuel ratio, and an integral term calculated from an integral gain. It was configured as follows.

According to this configuration, the linear term includes the integral term calculated from the integral value of the air-fuel ratio deviation and the integral gain, and this integral term holds a correction request for eliminating the steady-state deviation. In the invention according to claim 2, the linear term is:
The calculation is made to include the integral term and a proportional term obtained by multiplying the deviation by a proportional gain.

According to this configuration, the linear term includes the integral term and the proportional term obtained by multiplying the air-fuel ratio deviation by the proportional gain, and the sum of the integral term and the proportional term is regarded as the linear term. According to a third aspect of the present invention, the non-linear term is calculated based on a switching surface using the deviation, an integral value of the deviation, and a differential value of the deviation as variables.

According to this configuration, control is performed so as to be restricted toward the target air-fuel ratio by being restricted on the switching surface using the deviation, the integral value of the deviation and the differential value of the deviation as variables. According to the fourth aspect of the invention, the integral gain is corrected based on the air-fuel ratio deviation. According to this configuration, the integral gain multiplied by the integral value of the air-fuel ratio deviation is not constant, but is corrected in accordance with the air-fuel ratio deviation, and the integral gain is determined based on information on the deviation of the actual air-fuel ratio from the target air-fuel ratio and the direction of change. Be changed.

According to the fifth aspect of the present invention, the integral gain is
The correction is made according to the absolute value of the air-fuel ratio deviation. According to this configuration, the integral gain is corrected depending on how far the actual air-fuel ratio is rich or lean from the target air-fuel ratio. According to the sixth aspect of the invention, the integral gain is corrected to a larger value as the absolute value of the air-fuel ratio deviation increases.

With this configuration, as the actual air-fuel ratio is farther away from the target air-fuel ratio in the rich or lean direction, the integral gain is more corrected, and the integral term obtained with respect to the integral value of the air-fuel ratio deviation is obtained. Becomes larger.
According to the seventh aspect of the invention, the integral gain is corrected according to the rate of change of the air-fuel ratio deviation.

With this configuration, the integral gain is corrected according to the direction of change of the actual air-fuel ratio with respect to the target air-fuel ratio and the rate of change of the air-fuel ratio deviation indicating the change speed. The rate of change is the amount of change in air-fuel ratio deviation per unit time.
According to an eighth aspect of the invention, when the sign of the change rate of the air-fuel ratio deviation and the sign of the air-fuel ratio deviation are the same, the integral gain is increased and corrected.

According to this configuration, when the sign of the air-fuel ratio deviation and the sign of the change rate are the same, for example, although the actual air-fuel ratio is leaner than the target air-fuel ratio, the actual air-fuel ratio further changes lean. This is a state in which the air-fuel ratio deviation tends to increase. In such a state, the integral gain is corrected to increase. According to the ninth aspect of the invention, the integral gain is increased and corrected to be larger as the absolute value of the change rate of the air-fuel ratio deviation is larger.

With this configuration, when the air-fuel ratio deviation tends to increase, the integral gain is corrected to increase as the speed away from the target air-fuel ratio increases. According to a tenth aspect of the present invention, the integral gain is corrected in accordance with the rate of change of the absolute value of the air-fuel ratio deviation. According to such a configuration,
By calculating the absolute value of the air-fuel ratio deviation, the air-fuel ratio deviation with respect to the target air-fuel ratio is obtained regardless of whether the actual air-fuel ratio is rich or lean with respect to the target air-fuel ratio. If the rate is positive, the air-fuel ratio deviation is increasing, and if it is negative, the air-fuel ratio deviation is decreasing and changing toward the target air-fuel ratio. The integration gain is changed.

[0015]

According to the first aspect of the present invention, by including the integral term in the linear term in the sliding mode control, it is possible to reduce the steady-state deviation of the air-fuel ratio while performing highly robust control in which the influence of disturbance is suppressed. There is an effect that it can be eliminated. According to the second aspect of the present invention, by calculating the linear term from the proportional term and the integral term, it is possible to eliminate the steady-state deviation and to secure the stability in the air-fuel ratio feedback control with a long dead time.

According to the third aspect of the invention, the air-fuel ratio deviation, the integral value of the air-fuel ratio deviation, and the differential value of the air-fuel ratio deviation can be brought close to the target air-fuel ratio while maintaining a predetermined equilibrium state. According to the invention described in claim 4, by correcting the integral gain used for calculating the integral term according to the air-fuel ratio deviation, it is possible to set a proper integral gain according to the fluctuation of the actual air-fuel ratio. There is an effect that the convergence to the target air-fuel ratio can be improved by optimizing the accumulation / discharge speed of the fuel.

According to the fifth and sixth aspects of the invention, by increasing the integral gain as the actual air-fuel ratio departs from the target air-fuel ratio, the accumulation / discharge speed of the integral term is increased.
There is an effect that the actual air-fuel ratio can be returned to the target air-fuel ratio with good response. According to the seventh aspect of the present invention, the integral gain can be appropriately corrected based on the information on the change direction and the change speed of the air-fuel ratio deviation, so that the accumulation / discharge speed of the integral term can be optimized to achieve the target air-fuel ratio. There is an effect that convergence can be improved.

According to the eighth, ninth and tenth aspects of the present invention,
When the air-fuel ratio deviation is increasing, the integration gain is greatly corrected to increase the accumulation / discharge speed of the integral term,
There is an effect that the actual air-fuel ratio can be quickly converged to the target air-fuel ratio.

[0019]

Embodiments of the present invention will be described below. FIG. 1 is a system configuration diagram of an internal combustion engine according to the embodiment. In FIG. 1, air is drawn into a combustion chamber of each cylinder of an internal combustion engine 1 mounted on a vehicle via an air cleaner 2, an intake passage 3, and an electronically controlled throttle valve 4 driven to open and close by a motor.

An electromagnetic fuel injection valve 5 for directly injecting fuel (gasoline) into the combustion chamber of each cylinder is provided, and the fuel injected from the fuel injection valve 5 and the intake air serve as a fuel chamber. A mixture is formed. The fuel injection valve 5 is energized by a solenoid in response to an injection pulse signal output from the control unit 20, opens the valve, and injects fuel adjusted to a predetermined pressure. The injected fuel diffuses into the combustion chamber in the case of the intake stroke injection to form a homogeneous mixture, and in the case of the compression stroke injection, forms a stratified mixture around the ignition plug 6. . The mixture formed in the combustion chamber is ignited and burned by the ignition plug 6.

However, the internal combustion engine 1 is not limited to the direct injection gasoline engine described above, but may be an engine configured to inject fuel into an intake port. Exhaust gas from the engine 1 is exhausted from an exhaust passage 7, and an exhaust purification catalyst 8 is interposed in the exhaust passage 7. Further, an evaporative fuel processing device for performing a combustion process on the evaporative fuel generated in the fuel tank 9 is provided.

The canister 10 is a sealed container filled with an adsorbent 11 such as activated carbon. An evaporative fuel introduction pipe 12 extending from the fuel tank 9 is connected to the canister 10. Therefore, the evaporated fuel generated in the fuel tank 9 passes through the evaporated fuel introduction pipe 12 and is guided to the canister 10 to be adsorbed and collected. The canister 10 has a fresh air inlet 13.
Is formed, and a purge pipe 14 is led out. A purge control valve 15 whose opening and closing are controlled by a control signal from a control unit 20 is interposed in the purge pipe 14.

In the above configuration, when the purge control valve 15 is controlled to open, the suction negative pressure of the engine 1 acts on the canister 10, so that air introduced from the fresh air inlet 13 causes the adsorbent 11 of the canister 10. The adsorbed fuel vapor is purged, and purge air is sucked into the intake passage 3 downstream of the throttle valve 4 through the purge pipe 14, and thereafter,
The combustion is performed in the combustion chamber of the engine 1.

The control unit 20 includes a CPU, R
A microcomputer including an OM, a RAM, an A / D converter, an input / output interface, and the like is provided. The microcomputer receives input signals from various sensors and performs arithmetic processing based on the signals.
The operation of the fuel injection valve 5, ignition plug 6, and purge control valve 15 is controlled. As the various sensors, a crank angle sensor 21 for detecting a crank angle of the engine 1 and a cam sensor 22 for extracting a cylinder discrimination signal from a cam shaft are provided.
The rotation speed Ne of the engine is calculated based on the signal from the crank angle sensor 21.

In addition, an air flow meter 23 for detecting an intake air flow rate Q (mass flow rate) upstream of the throttle valve 4 in the intake passage 3, an accelerator sensor 24 for detecting an accelerator pedal depression amount (accelerator opening) APS, a throttle A throttle sensor 25 for detecting the opening TVO of the valve 4, a water temperature sensor 26 for detecting the cooling water temperature Tw of the engine 1, and a wide-range air-fuel ratio for linearly detecting the air-fuel ratio of the combustion mixture in accordance with the oxygen concentration in the exhaust gas. A sensor 27, a vehicle speed sensor 28 for detecting a vehicle speed VSP, and the like are provided.

Here, the structure of the wide-range air-fuel ratio sensor 27 will be described with reference to FIG. Zirconia (ZrO
A positive electrode 32 for measuring oxygen concentration is provided on a substrate 31 made of a solid electrolyte member such as 2). Further, a hollow portion 33 into which air is introduced is opened in the substrate 31, and a negative electrode 34 is provided on the ceiling of the hollow portion 33.
The substrate 31, the + electrode 32, and the −electrode 34 form an oxygen concentration detection unit 35, with the substrate 1, the electrode 1, and the electrode 1 interposed therebetween.

A pair of pump electrodes 37, 3 made of platinum are provided on both surfaces of a solid electrolyte member 36 made of zirconia or the like.
8 is provided.
Then, the oxygen pump section 39 is stacked above the oxygen concentration detection section 35 via a spacer 40 formed in a frame shape of, for example, alumina, and the oxygen concentration detection section 35 and the oxygen pump section 3 are stacked.
9, a hollow chamber 41 is provided.
An introduction hole 42 for introducing exhaust gas from the engine is formed in the solid electrolyte member 36 of the oxygen pump section 39.

The outer periphery of the spacer 40 is filled with an adhesive 43 made of glass so as to secure the hermeticity of the hollow chamber 41 and to provide the solid electrolyte 36 with the substrate 31 and the spacer 40.
Is fixed by bonding. Here, the spacer 4
Since the substrate 0 and the substrate 31 are simultaneously fired and bonded, the hermeticity of the hollow chamber 41 is ensured by bonding the spacer 40 and the solid electrolyte member 36. Further, the oxygen concentration detecting section 39 has a built-in heater 44 for heating.

Then, the oxygen concentration of the exhaust gas introduced into the hollow chamber 41 through the introduction hole 42 is detected from the voltage of the positive electrode 32. Specifically, according to the difference in concentration between the oxygen in the atmosphere in the hollow portion 33 and the oxygen in the exhaust gas in the hollow chamber 41, the substrate 3
Oxygen ions flow through the inside 1, and accordingly, an electromotive force corresponding to the oxygen concentration in the exhaust is generated at the + electrode 32. In accordance with the detection result, the current value flowing to the oxygen pump section 39 is controlled so that the atmosphere in the hollow chamber 41 is kept constant (for example, the stoichiometric air-fuel ratio), and the oxygen concentration in the exhaust gas (exhaust gas) is determined based on the current value. Air-fuel ratio).

Specifically, after the voltage of the positive electrode 32 is amplified by the control circuit 45, the voltage detection resistor 46
Is applied between the electrodes 37 and 38 to keep the oxygen concentration in the hollow chamber 41 constant. For example, when detecting the air-fuel ratio in a lean region where the oxygen concentration in the exhaust gas is high,
A voltage is applied using the outer pump electrode 37 as an anode and the pump electrode 38 on the hollow chamber 41 side as a cathode. Then, oxygen (oxygen ion O ²⁻ ) proportional to the current is pumped out of the hollow chamber 41 to the outside. When the applied voltage is equal to or higher than a predetermined value, the flowing current reaches a limit value, and the limit current value is measured by the control circuit 45 to determine the oxygen concentration in the exhaust gas,
In other words, the exhaust air-fuel ratio can be detected.

Conversely, if the pump electrode 37 is used as a cathode and the pump electrode 38 is used as an anode to pump oxygen into the hollow chamber 41, the air-fuel ratio can be detected in the air-fuel ratio rich region where the oxygen concentration in the exhaust gas is low. I can do it. The limit current is detected from an output voltage of a differential amplifier 47 for detecting a voltage between terminals of the voltage detection resistor 46.

When the predetermined air-fuel ratio feedback control condition is satisfied, the control unit 20 controls the air-fuel ratio in a sliding mode so that the exhaust air-fuel ratio detected by the air-fuel ratio sensor 27 matches the target air-fuel ratio. Perform The control block diagram of FIG. 3 shows the configuration of the sliding mode control unit that calculates the air-fuel ratio feedback correction coefficient ALPHA in the sliding mode.

The air-fuel ratio feedback correction coefficient A
LPHA is a correction term that is multiplied by the fuel injection amount. The fuel injected from the fuel injection valve 5 and the air sucked into the cylinder are corrected by increasing or decreasing the fuel injection amount by the air-fuel ratio feedback correction coefficient ALPHA. The air-fuel ratio of the air-fuel mixture formed by the above is feedback-controlled to the target air-fuel ratio.

The sliding mode control unit shown in FIG. 3 calculates the linear term U1 based on the difference between the air-fuel ratio detected by the air-fuel ratio sensor 27 and the target air-fuel ratio (air-fuel ratio deviation = actual air-fuel ratio-target air-fuel ratio). A linear term calculation unit 511 for calculating the nonlinear term U2 based on the air-fuel ratio deviation, and a nonlinear term calculation unit 512 for calculating the nonlinear term U2 based on the air-fuel ratio deviation. Outputs ALPHA.

The linear term operation unit 511 calculates the air-fuel ratio deviation ×
The proportional gain (= proportional term), ∫ (air-fuel ratio deviation) × integral gain (= integral term), target air-fuel ratio × target gain are calculated, and the calculated results are summed to calculate a linear term U1. In detail, the air-fuel ratio deviation is x1, the coefficient is αi,
If ai, b (i: 1,2,3), U1 = 1 / b ((a0−α3−α1 (a1−α1)) x1−α3 (a1−α1)
The linear term U1 is calculated as ∫ (x1) + a0r).

On the other hand, when the switching function is σ, the chattering prevention coefficient is δ, and the coefficient is K, the nonlinear term operation unit 512 calculates σ = α1 · x1 + d (x1) / dt + α3∫ (x1) U2 = K · σ / (| Σ | + δ) to calculate the nonlinear term U2.

According to the above configuration, the air-fuel ratio detected by the air-fuel ratio sensor 27 approaches the target air-fuel ratio while being constrained on the switching plane where the switching function σ = 0. Here, since the linear term U1 is constituted by a combination of the integral term and the proportional term, the steady-state deviation of the air-fuel ratio can be eliminated, and the dead time until the correction result is detected by the air-fuel ratio sensor 27 is reduced. Control stability can be prevented from deteriorating.

In the above description, the actual air-fuel ratio is the exhaust air-fuel ratio detected by the air-fuel ratio sensor 27. However, the air-fuel ratio in the cylinder is determined by the injection amount, operating conditions, and the air-fuel ratio detected by the air-fuel ratio sensor 27. Estimation may be performed based on the result, and feedback control may be performed using the estimated air-fuel ratio as the actual air-fuel ratio. Alternatively, instead of the air-fuel ratio sensor 27 that detects the exhaust air-fuel ratio from the oxygen concentration in the exhaust, A configuration using an air-fuel ratio sensor that detects the air-fuel ratio in the cylinder from combustion light or the like may be used.

The sliding mode control unit shown in FIG. 3 includes the linear term operation unit 511 and the nonlinear term operation unit 512.
In addition, an integral gain calculator 513 is provided. The integral gain computing section 513 computes the integral gain used for computing the integral term in the linear term computing section 511, and computes the integral gain as shown in the flowchart of FIG.

In the flowchart of FIG. 4, in step S11, the target air-fuel ratio is read, in step S12, the actual air-fuel ratio detected by the air-fuel ratio sensor 27 is read, and in step S13, the air-fuel ratio is calculated as actual air-fuel ratio-target air-fuel ratio. Calculate the fuel ratio deviation. Then, in step S14,
The integral gain is calculated according to the following equation. Integral gain = | air-fuel ratio deviation | × constant Ki If the configuration is such that the integral gain is calculated as described above,
The larger the actual air-fuel ratio deviates from the target air-fuel ratio, the greater the integral gain is set. Can be approached,
When the correction overshoots due to the cancellation of the disturbance, the overshoot can be suppressed by expediting the discharge of the integral term.

The calculation of the integral gain in the integral gain calculator 513 can be performed as shown in the flowchart of FIG. In the flowchart of FIG. 5, the target air-fuel ratio is read in step S21, the actual air-fuel ratio detected by the air-fuel ratio sensor 27 is read in step S22, and the air-fuel ratio deviation is calculated as actual air-fuel ratio-target air-fuel ratio in step S23. Calculate.

In step S24, the rate of change of the air-fuel ratio deviation is calculated. The change rate is calculated as a change amount of the deviation in a predetermined time obtained by subtracting the air-fuel ratio deviation calculated a predetermined time ago from the air-fuel ratio deviation calculated most recently. In step S25, the sign of the air-fuel ratio deviation (plus or minus) and the sign of the change rate (plus or minus)
Is determined to be equal to or not.

For example, if the actual air-fuel ratio is leaner than the target air-fuel ratio, the air-fuel ratio deviation is calculated as a positive value,
When the actual air-fuel ratio tends to lean further, the deviation becomes larger and the rate of change becomes positive. Therefore,
When the sign of the air-fuel ratio deviation and the sign of the change rate are equal,
This indicates a state in which the actual air-fuel ratio is moving away from the target air-fuel ratio, and conversely, if the sign of the air-fuel ratio deviation is different from the sign of the change rate, this indicates a state in which the actual air-fuel ratio is approaching the target air-fuel ratio.

If the sign of the air-fuel ratio deviation is different from the sign of the rate of change, the flow advances to step S26 to set the reference gain to the integral gain. If the sign of the air-fuel ratio deviation is different from the sign of the change rate, as described above, the actual air-fuel ratio is approaching the target air-fuel ratio. Suppress. On the other hand, if the sign of the air-fuel ratio deviation is equal to the sign of the change rate, the process proceeds to step S27, and a value obtained by multiplying the reference gain by x is set as the integral gain at that time.

Here, the x times may be a fixed value, but it is preferable to change the x times according to the absolute value of the rate of change. Specifically, the larger the absolute value of the rate of change, the more the multiple x is increased. Good to be big. When the sign of the air-fuel ratio deviation is equal to the sign of the change rate, in a state where the air-fuel ratio deviation is expanding, if the integral gain is corrected to a larger value at this time, the accumulation of the integral term can be accelerated when a disturbance is introduced. As a result, fluctuations in the air-fuel ratio due to the disturbance can be quickly converged, and when the disturbance is released, the discharge of the integral term can be expedited to suppress the occurrence of overshoot.

The absolute value of the air-fuel ratio deviation is obtained, and when the change rate of the absolute value of the air-fuel ratio deviation is positive, the larger the fixed multiple x or the change rate of the absolute value of the air-fuel ratio deviation, the larger the value. 5 is substantially the same as the processing in the flowchart of FIG.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of an internal combustion engine according to an embodiment.

FIG. 2 is a diagram illustrating an air-fuel ratio sensor and peripheral circuits according to the embodiment.

FIG. 3 is a block diagram showing a configuration of air-fuel ratio feedback control in the embodiment.

FIG. 4 is a flowchart illustrating a first embodiment of an integral gain calculation process according to the embodiment;

FIG. 5 is a flowchart showing a second embodiment of the integral gain calculation process according to the embodiment;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 3 ... Intake path 4 ... Throttle valve 5 ... Fuel injection valve 20 ... Control unit 27 ... Air-fuel ratio sensor 511 ... Linear term calculation part 512 ... Nonlinear term calculation part 513 ... Integral gain calculation part

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G301 HA01 HA04 HA14 HA16 JA03 JA06 JA11 JA18 LB04 LC01 MA01 MA11 NA07 NA09 NB05 ND03 ND45 NE14 PA01Z PA11A PA11Z PB03A PD04Z PE01Z PE03Z PE08Z PE09A PF01Z PF03Z

Claims (10)

[Claims] An air-fuel ratio feedback control device for an internal combustion engine configured to calculate an air-fuel ratio feedback control amount including a linear term and a non-linear term by sliding mode control based on a detected value of an air-fuel ratio and a target air-fuel ratio, The air-fuel ratio of the internal combustion engine, wherein the linear term is calculated to include an integral value of a deviation between a detected value of an air-fuel ratio and a target air-fuel ratio, and an integral term calculated from an integral gain. Feedback control device. 2. The air-fuel ratio of an internal combustion engine according to claim 1, wherein said linear term is calculated including said integral term and a proportional term obtained by multiplying said deviation by a proportional gain. Feedback control device. 3. The internal combustion engine according to claim 1, wherein the non-linear term is calculated based on a switching surface using the deviation, an integral value of the deviation, and a differential value of the deviation as variables. Air-fuel ratio feedback control device. 4. The air-fuel ratio feedback control device for an internal combustion engine according to claim 1, wherein the integral gain is corrected based on the deviation. 5. An air-fuel ratio feedback control system for an internal combustion engine according to claim 4, wherein said integral gain is corrected according to an absolute value of said deviation. 6. The air-fuel ratio feedback control device for an internal combustion engine according to claim 5, wherein the integral gain is corrected to a larger value as the absolute value of the deviation is larger. 7. The air-fuel ratio feedback control device for an internal combustion engine according to claim 4, wherein said integral gain is corrected according to a rate of change of said deviation. 8. The air-fuel ratio feedback control of an internal combustion engine according to claim 7, wherein the integral gain is increased and corrected when the sign of the rate of change of the deviation is the same as the sign of the deviation. apparatus. 9. The air-fuel ratio feedback control device for an internal combustion engine according to claim 8, wherein the integral gain is corrected to increase as the absolute value of the rate of change of the deviation increases. 10. An air-fuel ratio feedback control device for an internal combustion engine according to claim 4, wherein said integral gain is corrected in accordance with a rate of change of said absolute value of said deviation.