JP2004060613A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air-fuel ratio control device for an internal combustion engine for suitably controlling an air-fuel ratio even during an decrease in the amount of intake air. <P>SOLUTION: A feedback fuel correction amount etdfi (=fuel deviation edfckm×proportional gain GnFBP+fuel deviation integration value esdfc×integral gain GnFBI) is calculated by proportional and integral operation (PI operation), in accordance with the result of the air-fuel ratio detected by an air-fuel ratio sensor for linearly detecting the air-fuel ratio of the engine. When a vehicle is in the process of deceleration, the fuel deviation integration value esdfc is set to be zero. When the vehicle is not in the process of deceleration, a guard with a feedback correction guard rate egddfi is set in the fuel deviation integration value esdfc. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an air-fuel ratio control device for an internal combustion engine that performs feedback control to optimize the air-fuel ratio of a combustible air-fuel mixture supplied to the internal combustion engine.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a three-way catalyst that simultaneously promotes oxidation of unburned components (HC, CO) and reduction of nitrogen oxides (NOx) in exhaust gas has been used as an exhaust gas purification measure in an automobile engine. I have. In order to increase the oxidation / reduction ability by such a three-way catalyst, it is necessary to control the air-fuel ratio (A / F) indicating the combustion state of the engine to be close to the stoichiometric air-fuel ratio (window). Therefore, in the fuel injection control in the engine, an oxygen sensor is provided in the exhaust passage to detect whether the air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio based on the oxygen concentration remaining in the exhaust gas, and the fuel is detected based on the sensor output. The air-fuel ratio feedback control for correcting the amount is performed.
[0003]
In recent years, an internal combustion engine that controls the air-fuel ratio so that the three-way catalyst can always exhibit a constant and stable purification performance has been developed. That is, the three-way catalyst has an oxygen storage capacity, which adsorbs excess oxygen when the exhaust gas is lean and releases insufficient oxygen when the exhaust gas is rich. This purifies the exhaust gas. Such capabilities are finite. Therefore, in order to make effective use of the oxygen storage capacity, the amount of oxygen stored in the three-way catalyst must be determined so that the air-fuel ratio of the exhaust gas may be next rich or lean. It is necessary to maintain a fixed amount (eg half the maximum oxygen storage). If the amount of oxygen stored in the three-way catalyst is maintained in such a manner, a constant oxygen adsorption / desorption action can be always achieved, and as a result, a constant oxidation / reduction ability by the three-way catalyst can always be obtained. .
[0004]
As described above, in the internal combustion engine which controls the oxygen storage amount to maintain the purification performance of the three-way catalyst, an air-fuel ratio sensor capable of linearly detecting the air-fuel ratio is used, and the detection result of the air-fuel ratio is used. , The air-fuel ratio feedback control by the proportional and integral operation (PI operation) is performed. That is, the next fuel correction amount = fuel deviation × GnFBP + Σ (fuel deviation) × GnFBI
However, the fuel deviation = (the amount of fuel actually burned in the cylinder) − (the target amount of fuel with the intake air amount as the stoichiometric air-fuel ratio)
The amount of actually burned fuel = the amount of intake air / the detected air-fuel ratio GnFBP = proportional gain GnFBI = integral gain, the feedback fuel correction amount is calculated.
[0005]
As can be seen from the above equation for calculating the fuel correction amount, the proportional term is a component that acts to maintain the air-fuel ratio at the stoichiometric air-fuel ratio, and the integral term is a component that acts to eliminate the steady-state deviation (offset). is there. That is, by the action of the integral term, the oxygen storage amount in the three-way catalyst is kept constant.
[0006]
[Problems to be solved by the invention]
In the above-described constant oxygen storage amount control system, the absolute value of the feedback fuel correction amount is guarded within a range of a predetermined ratio with respect to the target fuel amount in order to suppress the air-fuel ratio from becoming rough due to the influence of disturbance. Has become. FIG. 7 is a time chart showing an example of the air-fuel ratio control in such an oxygen storage amount constant control system.
[0007]
As shown in FIG. 7, for example, the feedback correction rate edfirst which is the ratio of the feedback fuel correction amount to the target fuel amount is guarded within a range of ± 20%. Now, at time t11, when the throttle opening eta decreases and the intake air amount ega sharply decreases, the vehicle is decelerated. Therefore, the air-fuel ratio A / F takes a value on the rich side. At this time, the fuel deviation takes a positive value and the proportional term takes a decreasing value. Further, the fuel deviation integrated value esdfc is added and increased, and the integral term takes a value on the decreasing side. While the intake air amount ega is decreasing, the air-fuel ratio A / F has a large value on the rich side, so the proportional term continues to take a value on the decreasing side, the fuel deviation integrated value esdfc continues to be added and increases, and the integral term Takes a value on the weight loss side.
[0008]
In a period T11 after the time t12 when the decrease in the intake air amount ega has almost stopped, the feedback correction rate edfirst is guarded within a range of ± 2%. When the air-fuel ratio A / F becomes a stable value on the rich side, the fuel deviation gradually decreases, the value on the decreasing side of the proportional term gradually increases, and the air-fuel ratio A / F becomes a value near the stoichiometric air-fuel ratio. It becomes. However, the fuel deviation integrated value esdfc is added and continues to increase, and the integral term takes a large value on the decreasing side.
[0009]
In a period T12 following the period T11, the guard of the feedback correction rate edfirst is gradually changed to a range of ± 20%.
In a period T13 following the period T12, the air-fuel ratio A / F takes a value leaner than the stoichiometric air-fuel ratio, so the fuel deviation takes a negative value and the proportional term takes a value on the increasing side. Although the fuel deviation at this time is a negative value but its magnitude is small, the fuel deviation integrated value esdfc cannot be completely reduced, and the integral term takes the maximum value on the decreasing side. Therefore, the feedback correction rate edfirst is attached to the lower limit guard of -20%, and the weight loss becomes excessive. In this period T13, the air-fuel ratio A / F takes a large value on the lean side.
[0010]
Further, in a period T14 subsequent to the period T13, when the air-fuel ratio A / F becomes a stable value on the lean side, the fuel deviation is maintained at a negative value, and the proportional term takes a value on the increasing side. The fuel deviation integrated value esdfc gradually decreases, and although the integral term is a value on the decreasing side, its magnitude is small. Along with the change in the value of the integral term, the feedback correction rate edfirst also changes. In this period T14, the air-fuel ratio A / F continues to be over-lean.
[0011]
As described above, in the air-fuel ratio control in the constant oxygen storage amount control system, when the vehicle is in a deceleration state and the intake air amount ega decreases, the integral term in the feedback fuel correction amount becomes excessively large, and after the deceleration is over, the integral term becomes excessive. There is a problem that the air-fuel ratio control cannot be performed satisfactorily continuously with the lean operation.
[0012]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that can appropriately perform air-fuel ratio control even when the intake air amount decreases. .
[0013]
[Means for Solving the Problems]
Hereinafter, the means for achieving the above object and the effects thereof will be described.
An invention according to claim 1 includes a three-way catalyst having an oxygen storage capacity provided in an exhaust passage of an internal combustion engine, an air-fuel ratio sensor provided upstream of the three-way catalyst and linearly detecting an air-fuel ratio. Target fuel amount calculating means for calculating a target fuel amount that sets the air-fuel ratio of the air-fuel mixture to a stoichiometric air-fuel ratio in accordance with the intake air amount of the internal combustion engine; and, based on an output of the air-fuel ratio sensor, An air-fuel ratio feedback control means for calculating a feedback correction amount consisting of a proportional term consisting of a fuel deviation for converging to a fuel ratio and an integral term of the fuel deviation. And a limiter for limiting an integral term in the feedback correction amount to a predetermined value.
[0014]
When the vehicle decelerates, the intake air amount sharply decreases and the air-fuel ratio becomes rich, and this rich air-fuel ratio is maintained until the intake air amount is stabilized. Therefore, the fuel deviation is maintained at a positive value, and the integral term in the feedback correction amount increases. Therefore, the air-fuel ratio becomes over lean when the intake air amount is stabilized. In addition, since the intake air amount is small, the fuel deviation for setting the air-fuel ratio to the stoichiometric air-fuel ratio is also a small value, so it takes a long time to reduce the integral term, and the overlean continues after deceleration ends. And the air-fuel ratio becomes rough.
[0015]
In this regard, according to the above configuration, the integral term in the feedback correction amount is limited to a predetermined value when the vehicle is decelerated. Therefore, the fuel deviation for setting the air-fuel ratio to the stoichiometric air-fuel ratio has a small value, but the integral term limited to a predetermined value can be reduced in a short time, and the air-fuel ratio is quickly changed to the stoichiometric air-fuel ratio after the end of the deceleration. And the air-fuel ratio control can be suitably performed.
[0016]
According to a second aspect of the present invention, in the air-fuel ratio control apparatus for an internal combustion engine according to the first aspect, the limiting means sets an integral term in the feedback correction amount to zero when the vehicle is decelerated. .
[0017]
According to the above configuration, the integral term in the feedback correction amount is set to zero during deceleration of the vehicle. Therefore, in order to set the air-fuel ratio to the stoichiometric air-fuel ratio in a state where the intake air amount is stabilized, only the proportional term in the feedback correction amount needs to be set. As a result, the air-fuel ratio control can be suitably performed.
[0018]
According to a third aspect of the present invention, there is provided a three-way catalyst having an oxygen storage capacity provided in an exhaust passage of an internal combustion engine, and an air-fuel ratio sensor provided upstream of the three-way catalyst and linearly detecting an air-fuel ratio. Target fuel amount calculating means for calculating a target fuel amount that sets the air-fuel ratio of the air-fuel mixture to a stoichiometric air-fuel ratio in accordance with the intake air amount of the internal combustion engine; and, based on an output of the air-fuel ratio sensor, An air-fuel ratio feedback control means for calculating a feedback correction amount comprising a proportional term consisting of a fuel deviation and an integral term of the fuel deviation for converging on the fuel ratio. A guard means for guarding the absolute value of the integral term within a range of a predetermined ratio with respect to the target fuel amount is provided.
[0019]
When the intake air amount decreases, the air-fuel ratio becomes rich, and this rich air-fuel ratio is maintained until the intake air amount is stabilized. Therefore, the fuel deviation is maintained at a positive value, and the integral term in the feedback correction amount increases. Therefore, the air-fuel ratio becomes lean when the intake air amount is stabilized. In addition, since the intake air amount is small, the fuel deviation for setting the air-fuel ratio to the stoichiometric air-fuel ratio is also a small value. Therefore, a long time is required to reduce the integral term, and the lean continues after the end of the deceleration. As a result, the air-fuel ratio becomes rough.
[0020]
In this regard, according to the above configuration, the absolute value of the integral term in the feedback correction amount is guarded within a range of a predetermined ratio to the target fuel amount. Therefore, the fuel deviation for making the air-fuel ratio the stoichiometric air-fuel ratio is a small value, but the integral term can be reduced in a short time, and the air-fuel ratio is brought to the stoichiometric air-fuel ratio early after the intake air amount decreases. Thus, the air-fuel ratio control can be suitably performed.
[0021]
According to a fourth aspect of the present invention, in the air-fuel ratio control apparatus for an internal combustion engine according to the third aspect, further, a limiting means for limiting an integral term in the feedback correction amount to a predetermined value when the vehicle is decelerated. It is characterized by having.
[0022]
According to the above configuration, the same operation and effect as those of the third aspect of the invention can be obtained, and the stoichiometric air-fuel ratio can be set to the stoichiometric air-fuel ratio even after the end of the deceleration, so that the air-fuel ratio control can be suitably performed. become able to.
[0023]
According to a fifth aspect of the present invention, in the air-fuel ratio control apparatus for an internal combustion engine according to the fourth aspect, the limiting means sets an integral term in the feedback correction amount to zero when the vehicle is decelerated. .
[0024]
According to the above configuration, the same operation and effect as those of the third aspect of the invention can be obtained, and the stoichiometric air-fuel ratio can be set to the stoichiometric air-fuel ratio even after the end of the deceleration, so that the air-fuel ratio control can be suitably performed. become able to.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an air-fuel ratio control apparatus for an internal combustion engine according to the present invention will be described with reference to FIGS.
[0026]
FIG. 1 is a schematic configuration diagram showing an engine system of an automobile provided with an air-fuel ratio control device according to the present embodiment.
An intake passage 2 of an engine 1 as an internal combustion engine is connected to an air cleaner (not shown), and the intake passage 2 is provided with a throttle valve 5 upstream of a surge tank 6. The intake passage 2 includes an intake air amount sensor 7, a throttle position sensor 8, an intake air temperature sensor 9, and the like.
[0027]
Among these sensors, the intake air amount sensor 7 is arranged on the upstream side of the throttle valve 5, and the intake air amount sensor 7 detects an intake air amount ega taken into the engine 1. The throttle position sensor 8 includes an opening sensor that outputs opening information of the throttle valve 5 that is opened and closed based on a depression operation of an accelerator pedal (not shown), and an idle switch that is turned on when the throttle valve 5 is fully closed. . Further, the intake air temperature sensor 9 detects the temperature (intake air temperature) THA of the air taken into the engine 1.
[0028]
A fuel injection valve 10 is provided in the intake passage 2. Fuel pumped from a fuel tank (not shown) is injected in response to the operation of the fuel injection valve 10, mixed with air sucked through the intake passage 2, and supplied into the combustion chamber 3 of the engine 1.
[0029]
The exhaust passage 4 of the engine 1 includes a three-way catalyst 20, an air-fuel ratio (A / F) sensor 11 provided upstream of the three-way catalyst 20, and an oxygen sensor 12 provided downstream of the three-way catalyst 20. ing. The three-way catalyst 20 has an oxygen storage capacity, adsorbs an excess amount of oxygen when the exhaust gas is lean, and releases an insufficient amount of oxygen when the exhaust gas is rich. It purifies carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) contained in the exhaust gas that is discharged. As shown in FIG. 2, the A / F sensor 11 linearly detects the air-fuel ratio based on the oxygen concentration in the exhaust gas. The oxygen sensor 12 detects whether the air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio based on the oxygen concentration in the exhaust gas after passing through the three-way catalyst 20, as shown in FIG.
[0030]
In addition, the engine 1 is provided with an igniter, an ignition coil, and the like (not shown), and the ignition voltage is applied to an ignition plug 14 provided in the combustion chamber 3 of each cylinder.
[0031]
The engine 1 is cooled by cooling water circulating in the cylinder block 1a, and the temperature of the cooling water is detected by a water temperature sensor 17 provided in the cylinder block 1a.
[0032]
In such an engine system, the output of each sensor described above is input to an electronic control unit (hereinafter, referred to as an ECU) 30 that plays a role of a control system of the engine 1.
[0033]
The ECU 30 is mainly configured by a microcomputer including a CPU, a ROM, a RAM, a backup RAM, and the like. The ECU 30 is connected to sensors such as a throttle position sensor 8, an intake air amount sensor 7, an intake air temperature sensor 9, a water temperature sensor 17, and an A / F sensor 11 and an oxygen sensor 12. The ECU 30 is connected with the fuel injection valve 10, the igniter, and the like.
[0034]
The ECU 30 executes various controls such as fuel injection control of the engine 1 and air-fuel ratio control based on the output of each sensor taken in. In order to effectively utilize the oxygen storage capacity of the three-way catalyst 20, the oxygen stored in the three-way catalyst 20 is controlled so that the air-fuel ratio of the exhaust gas may be either rich or lean next. Is required to be maintained at a predetermined amount (for example, half of the maximum oxygen storage amount). If the amount of oxygen stored in the three-way catalyst 20 is maintained in such a manner, a constant oxygen adsorbing / releasing action is always possible, and as a result, the constant oxidation / reduction ability of the three-way catalyst 20 is always maintained. can get. Therefore, in the present embodiment, the air-fuel ratio control is performed such that the oxygen storage amount is constant in order to maintain the purification performance of the three-way catalyst of the three-way catalyst 20.
[0035]
Next, the air-fuel ratio feedback control executed in the present embodiment will be described with reference to the flowchart of FIG. This routine is executed every predetermined crank angle.
[0036]
Prior to this processing, the amount of intake air taken into the cylinder is calculated based on the output from the intake amount sensor 7, and the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio based on the amount of intake air and the stoichiometric air-fuel ratio. Therefore, the target fuel amount etaubs to be supplied into the cylinder is calculated. In the present embodiment, the air-fuel ratio feedback control based on the proportional and integral operation (PI operation) is performed based on the detection result of the air-fuel ratio by the A / F sensor 11. That is, etdfi = edfckm × GnFBP + esdfc × GnFBI
By the above calculation, the feedback fuel correction amount is calculated.
[0037]
Here, etdfi: fuel correction amount edfckm: fuel deviation = (fuel amount actually burned in the cylinder) − (target fuel amount with the intake air amount as the stoichiometric air-fuel ratio)
esdfc: integrated value of fuel deviation = Σedfckm
GnFBP = proportional gain GnFBI = integral gain As shown in FIG. 4, when this processing is started, first, in step 110, it is determined whether or not the vehicle is decelerating. Here, if it is determined that the vehicle is decelerating (step 110: YES), the fuel deviation integrated value esdfc of the integral term in the feedback fuel correction amount is set to 0, and then the process proceeds to step 150.
[0038]
On the other hand, if it is determined in step 110 that the vehicle is not decelerating (step 110: NO), the process proceeds to step 130. In step 130, an integrated value guard t_sdfcgd for the integrated value esdfc of the integral term in the feedback fuel correction amount is set based on the following equation.
[0039]
t_sdfcgd ← etaubs × egddfi / (− GnFBI)
Here, egddfi is a feedback correction guard ratio (absolute value). The feedback correction guard ratio egddfi guards the feedback fuel correction amount etdfi within a predetermined ratio range with respect to the target fuel amount etaubs in order to suppress the air-fuel ratio from becoming rough due to disturbance in the engine system of the present embodiment. It is for.
[0040]
Next, in step 140, the present fuel deviation edfckm is added to the previous fuel deviation integrated value esdfc to calculate the fuel deviation integrated value esdfc up to this time, and -t_sdfcgd ≦ the fuel deviation integrated value up to this time. esdfc is set to satisfy ≦ t_sdfcgd.
[0041]
Then, in step 150, the feedback fuel correction amount etdfi is calculated as etdfi = edfckm × GnFBP + esdfc × GnFBI. In the feedback fuel correction amount etdfi, guard is set for the fuel deviation integrated value esdfc in the integral term by the feedback correction guard rate egddfi.
[0042]
Next, an example of the air-fuel ratio control in the present embodiment will be described with reference to FIGS. FIG. 5 is a time chart showing an example of the air-fuel ratio control during deceleration of the vehicle, and FIG. 6 is a time chart showing an example of the air-fuel ratio control when the vehicle is not decelerating.
[0043]
First, FIG. 5 will be described. For example, the feedback correction rate edfirst, which is the ratio of the feedback fuel correction amount etdfi to the target fuel amount etaubs, is guarded within a range of ± 20%.
[0044]
Now, at time t1, when the throttle opening eta decreases and the intake air amount ega sharply decreases, the vehicle is decelerated. Therefore, the air-fuel ratio A / F takes a value on the rich side. At this time, the proportional term takes a value on the decreasing side, but since the fuel deviation integrated value esdfc is made zero, the integral term becomes zero. In the period T1 after the time t1 at which the intake air amount ega stabilizes, the air-fuel ratio A / F changes from rich to stoichiometric by the proportional term.
[0045]
Next, FIG. 6 will be described. Also in this example, the feedback correction rate edfirst, which is the ratio of the feedback fuel correction amount etdfi to the target fuel amount etaubs, is guarded within a range of ± 20%.
[0046]
It is now assumed that, at time t3, when the throttle opening eta decreases and the intake air amount ega sharply decreases, the air-fuel ratio A / F is a value on the rich side. Even if the proportional term changes as shown by the broken line based on this air-fuel ratio A / F, the increase and decrease of the fuel deviation integrated value esdfc are guarded by the feedback correction guard rate egddfi (± 20%) as shown by the chain line. Have been. Therefore, in the period T3 after the time t3, when the proportional term takes a value on the increasing side after the decrease of the intake air amount ega, the fuel deviation integrated value esdfc decreases. Therefore, the feedback correction rate edfirst does not stick to the feedback correction guard rate egddfi (± 20%), and the air-fuel ratio A / F changes to the stoichiometric air-fuel ratio early after the intake air amount decreases. .
[0047]
As described above, according to the air-fuel ratio control device of the present embodiment, the following effects can be obtained.
In the present embodiment, the air-fuel ratio feedback control is performed by the feedback correction amount including the proportional term including the fuel deviation and the integral term of the fuel deviation for converging the air-fuel ratio to the stoichiometric air-fuel ratio. When the vehicle decelerates, the fuel deviation integrated value esdfc of the integral term in the feedback correction amount is limited to a predetermined value (zero). Therefore, even if the intake air amount becomes small after the vehicle decelerates and the fuel deviation for bringing the air-fuel ratio to the stoichiometric air-fuel ratio becomes a small value, the integral term can be reduced in a short time, and The fuel ratio can be brought to the stoichiometric air-fuel ratio at an early stage, and the air-fuel ratio control can be suitably performed.
[0048]
In the present embodiment, the air-fuel ratio feedback control is performed by the feedback correction amount including the proportional term including the fuel deviation and the integral term of the fuel deviation for converging the air-fuel ratio to the stoichiometric air-fuel ratio. When the vehicle is not decelerating, the absolute value of the integral term in the feedback correction amount is guarded within a range of a predetermined ratio to the target fuel amount. Therefore, even if the fuel deviation for bringing the air-fuel ratio to the stoichiometric air-fuel ratio becomes small after the intake air amount decreases, the integral term can be reduced in a short time, and the air-fuel ratio becomes low after the intake air amount decreases. The fuel ratio can be brought to the stoichiometric air-fuel ratio at an early stage, and the air-fuel ratio control can be suitably performed.
[0049]
The embodiment is not limited to the above, but may be modified as follows.
In the above-described embodiment, the engine 1 in which fuel is injected by the fuel injection valve 10 in the intake passage 2 is embodied. However, the engine may be embodied as a type in which fuel is directly injected into the combustion chamber 3.
[0050]
In the above-described embodiment, the fuel deviation integrated value esdfc in the feedback fuel correction amount is set to zero when the vehicle decelerates, but may be set to any value near zero.
[0051]
In the above embodiment, the fuel deviation integrated value esdfc in the feedback fuel correction amount is guarded by the feedback correction guard rate egddfi when the vehicle is not decelerating. However, the guard may be performed by other values. .
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment of an air-fuel ratio control device according to the present invention.
FIG. 2 is a characteristic diagram showing a relationship between an air-fuel ratio and an A / F sensor output voltage.
FIG. 3 is a characteristic diagram showing a relationship between an air-fuel ratio and an oxygen sensor output voltage.
FIG. 4 is a flowchart illustrating an air-fuel ratio feedback control procedure according to the embodiment;
FIG. 5 is a time chart showing an air-fuel ratio control mode according to the embodiment.
FIG. 6 is a time chart showing an air-fuel ratio control mode according to the embodiment.
FIG. 7 is a time chart showing an air-fuel ratio control mode of a conventional device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Intake passage, 3 ... Combustion chamber, 4 ... Exhaust passage, 5 ... Throttle valve, 6 ... Surge tank, 7 ... Intake amount sensor, 8 ... Throttle position sensor (opening sensor), 9 ... Intake temperature Sensor: 10: fuel injection valve, 11: air-fuel ratio (A / F) sensor, 12: oxygen sensor, 14: spark plug, 17: water temperature sensor, 20: three-way catalyst, 30: target fuel amount calculation means, air-fuel ratio ECU (electronic control device) as feedback control means, restriction means, and guard means.

Claims (5)

A three-way catalyst having an oxygen storage capacity provided in an exhaust passage of an internal combustion engine,
An air-fuel ratio sensor provided upstream of the three-way catalyst and linearly detecting an air-fuel ratio,
Target fuel amount calculation means for calculating a target fuel amount that sets the air-fuel ratio of the air-fuel mixture to a stoichiometric air-fuel ratio according to the intake air amount of the internal combustion engine,
Air-fuel ratio feedback control means for calculating a feedback correction amount consisting of a proportional term consisting of a fuel deviation and an integral term of the fuel deviation for converging the air-fuel ratio to a stoichiometric air-fuel ratio based on the output of the air-fuel ratio sensor;
In an air-fuel ratio control device for an internal combustion engine having
An air-fuel ratio control device for an internal combustion engine, comprising: limiting means for limiting an integral term in the feedback correction amount to a predetermined value when the vehicle is decelerated. The air-fuel ratio control device for an internal combustion engine according to claim 1,
The air-fuel ratio control device for an internal combustion engine, wherein the limiting unit sets an integral term in the feedback correction amount to zero when the vehicle decelerates. A three-way catalyst having an oxygen storage capacity provided in an exhaust passage of an internal combustion engine,
An air-fuel ratio sensor provided upstream of the three-way catalyst and linearly detecting an air-fuel ratio,
Target fuel amount calculation means for calculating a target fuel amount that sets the air-fuel ratio of the air-fuel mixture to a stoichiometric air-fuel ratio according to the intake air amount of the internal combustion engine,
Air-fuel ratio feedback control means for calculating a feedback correction amount consisting of a proportional term consisting of a fuel deviation and an integral term of the fuel deviation for converging the air-fuel ratio to a stoichiometric air-fuel ratio based on the output of the air-fuel ratio sensor;
In an air-fuel ratio control device for an internal combustion engine having
An air-fuel ratio control device for an internal combustion engine, comprising a guard means for guarding an absolute value of an integral term in the feedback correction amount within a range of a predetermined ratio with respect to the target fuel amount. The air-fuel ratio control device for an internal combustion engine according to claim 3,
An air-fuel ratio control device for an internal combustion engine, further comprising limiting means for limiting an integral term in the feedback correction amount to a predetermined value when the vehicle decelerates. The air-fuel ratio control device for an internal combustion engine according to claim 4,
The air-fuel ratio control device for an internal combustion engine, wherein the limiting unit sets an integral term in the feedback correction amount to zero when the vehicle decelerates.

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