JPH0573906B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a fuel supply control device for an internal combustion engine, and more specifically, the present invention relates to a fuel supply control device for an internal combustion engine. The present invention relates to a fuel supply control device for an internal combustion engine.

<Prior Art> This type of fuel supply control device for an internal combustion engine is disclosed, for example, in Japanese Patent Laid-Open No. 56-98540.

This device is designed to allow gasoline and alcohol to be used by switching or mixing them, and is equipped with an alcohol sensor that detects the standard fuel alcohol concentration in the fuel. Based on the detected value of the alcohol sensor, the fuel In addition to correcting and controlling the supply amount, an oxygen sensor is provided to detect the oxygen concentration in the exhaust gas, and the rich lean of the actual air-fuel ratio relative to the target air-fuel ratio is determined through the oxygen concentration in the exhaust gas detected by the oxygen sensor. Based on this detection result, feedback correction control of the fuel supply amount is performed in order to bring the actual air-fuel ratio closer to the target air-fuel ratio in a predetermined operating state.

<Issues to be solved by the invention> By the way, in the conventional engine supply control device for an engine that supports the use of different types of fuels as described above, if the alcohol sensor becomes abnormal and outputs an erroneous detection value, Since the incorrect fuel supply amount correction control is performed based on this incorrect alcohol concentration detection value, the air-fuel ratio deviates greatly from the target air-fuel ratio when air-fuel ratio feedback control is not performed, and the air-fuel ratio feedback control Even if this is done, the feedback correction will not be able to fully correct it, resulting in a large air-fuel ratio deviation.

As a result, when the alcohol sensor is abnormal,
There is a problem that engine operating performance and exhaust properties deteriorate, and in order to solve this problem, the applicant has proposed that when the alcohol sensor is abnormal, the concentration detected by the alcohol sensor is changed at a fixed rate, and the exhaust passage Concentration detection occurs when the air-fuel ratio detected through the exhaust oxygen concentration detected by _{the O 2 sensor} installed in A control device configured to fix the value to a certain value was previously proposed (Japanese Patent Application No. 63-242273 (Japanese Patent Application Laid-Open No. 2-91435)).

However, when changing the detection value of the alcohol sensor as described above, if the rate of change is constant regardless of the engine operating state, it actually changes depending on the engine operating state such as engine speed and engine load. Since the optimum values of the rate of change are different, there is a problem that good air-fuel ratio controllability during fail-safe cannot be maintained.

In other words, if the constant rate of change is larger than the optimum value, there is a response delay time in air-fuel ratio detection by the O ₂ sensor, so as shown in Figure 7, the detected value of the alcohol sensor may not be changed too much. (by overshooting), in reality, the detected value is fixed at a value that deviates from the target air-fuel ratio (true alcohol concentration).Also, by greatly changing the detected value of the alcohol sensor, This results in significant air-fuel ratio fluctuations. On the other hand, if the rate of change of the detected concentration value is smaller than the optimum value, as shown in Figure 8, the air-fuel ratio will not be easily reversed, and during this time the deviation in the air-fuel ratio due to the false detection value of the alcohol sensor cannot be resolved. First, it was becoming impossible to make the fail-safe control function effectively.

The present invention has been made in view of the above-mentioned problems, and when changing the detected value of the alcohol sensor when the alcohol sensor is abnormal, the present invention quickly adjusts the air-fuel ratio to near the target air-fuel ratio while avoiding overshoot of the detected value. It is an object of the present invention to provide a control device that can control the density (correct the detected concentration value to near the true value).

<Means for Solving the Problems> Therefore, in the present invention, as shown in FIG. a basic fuel supply amount setting means for setting a basic fuel supply amount; a reference fuel concentration detection means for detecting a reference fuel concentration in the fuel supplied to the engine; and a reference fuel detected by the reference fuel concentration detection means. concentration correction value setting means for setting a concentration correction value for correcting the basic fuel supply amount based on the concentration of the basic fuel supply amount; a fuel supply amount setting means for correcting and setting the fuel supply amount based on the set concentration correction value; and a fuel supply for driving and controlling the fuel supply means based on the fuel supply amount set by the fuel supply amount setting means. a control means; an air-fuel ratio detection means for detecting a rich/lean air-fuel ratio of an engine intake air-fuel mixture with respect to a target air-fuel ratio via engine exhaust components; an abnormality detection means for detecting an abnormality in the reference fuel concentration detection means; In order to detect the abnormality by the abnormality detection means, the concentration detected by the pre-filled reference fuel concentration detection means is forcibly increased or decreased by integral control according to a predetermined control constant in the direction of reversing the air-fuel ratio detected by the air-fuel ratio detection means; an abnormality fuel concentration changing means that fixes the concentration detected when the air-fuel ratio is reversed; and an integral control constant variable variable that variably sets a predetermined control constant for integral control by the abnormality fuel concentration changing means. A fuel supply control device for an internal combustion engine that can be used by switching or mixing different types of fuel is configured, including a setting means and the following.

<Operation> In this configuration, the engine operating state detection means detects the engine operating state, and the basic fuel supply amount setting means sets the basic fuel supply amount based on this engine operating state.

The reference fuel concentration detection means detects the reference fuel concentration in the fuel supplied to the engine, and the concentration correction value setting means performs concentration correction for correcting the basic fuel supply amount based on this reference fuel concentration. Set the value.

The fuel supply amount setting means sets the fuel supply amount by correcting the basic fuel supply amount based on the concentration correction value, and the fuel supply control means drives and controls the fuel supply means based on this fuel supply amount. do.

The above is the function of fuel control when the reference fuel concentration detection means is normal.In order to perform fail-safe control when the reference fuel concentration detection means is abnormal, the abnormality detection means detects an abnormality in the reference fuel concentration detection means, and The rich/lean air-fuel ratio of the engine intake air-fuel mixture with respect to the target air-fuel ratio is detected by the fuel ratio detection means via the engine exhaust component, so that the direction of error in the detected value of the reference fuel concentration detection means can be specified.

When an abnormality in the reference fuel concentration detection means is detected by the abnormality detection means, the abnormality fuel concentration changing means converts the concentration detected value by the reference fuel concentration detection means into the air-fuel ratio detected by the air-fuel ratio detection means. is forcibly increased or decreased in the direction of reversing from rich to lean or from lean to rich by integral control according to a predetermined control constant, and is fixed at the concentration detected value when the air-fuel ratio is reversed.

That is, when an abnormality in the reference fuel concentration detection means is detected, the detected value is forcibly changed in the direction of inverting the air-fuel ratio from the rich/lean state at that time (in the direction of approaching the true concentration detection value), and the air-fuel ratio is When the fuel ratio reverses, it is assumed that the true concentration detection value has been crossed, and the detected value at that time is fixed, and concentration correction control of the basic fuel supply amount is performed based on the detected value immediately after the air-fuel ratio reverses. This is what I did.

Here, when the reference fuel concentration detection means is abnormal, the predetermined control constant used to increase or decrease the detected value by integral control is set by the integral control constant variable setting means to adjust the engine speed, engine load, etc. Prices are set depending on the condition.

That is, when the detection value of the reference fuel concentration detection means is forcibly increased or decreased by the abnormal fuel concentration change means, the concentration correction result is quickly detected by the air-fuel ratio detection means, for example, instead of being changed at a constant rate. Faster when the engine speed is high,
On the other hand, when the engine rotation speed is low, the control constant of the integral control is changed according to the engine operating condition so that the detected concentration value changes slowly, and the detected concentration value is changed at the optimal rate of change under all operating conditions. I tried to get it.

<Example> Examples of the present invention will be described below.

In FIG. 2 showing one embodiment, an engine 1 is configured to be able to use alcohol mixed fuel by switching between gasoline and alcohol as fuel, or by mixing these. Air is admitted via the duct 3, the throttle valve 4 and the intake manifold 5. The planch portion of the intake manifold 5 includes:
A fuel injection valve 6 as a fuel supply means is provided for each cylinder. The fuel injection valve 6 is an electromagnetic fuel injection valve that opens when the solenoid is energized and closes when the energization is stopped, and opens when the solenoid is energized by a drive pulse signal from a control unit 12, which will be described later. Fuel is injected and supplied under pressure from a fuel pump (not shown) and adjusted to a predetermined pressure by a pressure regulator. Although this example is a Maruna point injection system, it may also be a single point injection system in which a single fuel injection valve is provided in common to all cylinders, such as upstream of the throttle valve 4.

An ignition plug 7 is provided in the fuel chamber of the engine 1, which ignites a spark to ignite and burn the air-fuel mixture.

Then, exhaust gas is discharged from the engine 1 via an exhaust manifold 8, an exhaust duct 9, a three-way catalyst 10, and a muffler 11. The three-way catalyst 10 is an exhaust purification device that oxidizes CO and HC in the exhaust components, and also reduces NO _x to convert it into other harmless substances. The best conversion efficiency is obtained when combustion is performed at a fuel ratio of

The control unit 12 includes a CPU, ROM,
Equipped with a microcomputer that includes RAM, an A/D converter, an input/output interface, etc., receives input signals from various sensors, performs arithmetic processing as described below, and controls the operation of the fuel injection valve 6. do.

The various sensors include an air flow meter 1 such as a hot wire type or a flap type in the intake duct 3.
3 is provided, and outputs a voltage signal according to the intake air flow rate Q.

Further, a crank angle sensor 14 is provided, and in the case of a four-cylinder engine, outputs a reference signal for every 180 degrees of crank angle and a unit signal for every 1 degree or 2 degrees of crank angle. Here, the engine rotational speed N can be calculated by measuring the cycle of the reference signal or the number of unit signals generated within a predetermined time.

Further, a water temperature sensor 15 for detecting the cooling water temperature Tw of the water jacket of the engine 1 is provided.

Further, an O ₂ sensor 16 as an air-fuel ratio detecting means is provided at the gathering part of the exhaust manifold 8, and detects the air-fuel ratio of the air-fuel mixture taken into the engine 1 via the oxygen O ₂ concentration in the exhaust gas. The O ₂ sensor 16 is
This is a known method in which the output suddenly changes around the stoichiometric air-fuel ratio, and based on that output, the rich/lean ratio of the actual air-fuel ratio relative to the stoichiometric air-fuel ratio is detected.

Additionally, an alcohol sensor 1 serves as a reference fuel concentration detection means for detecting the concentration ALC of alcohol, which is a reference fuel, in the fuel supplied to the fuel injection valve 6.
7 is provided in a fuel supply pipe or a fuel tank upstream of the fuel injection valve 6.

Here, the CPU of the microcomputer built in the control unit 12 is
Arithmetic processing is performed in accordance with the program on the ROM shown in flowcharts in FIGS. 6 to 6 to control fuel injection and perform fail-safe control in the event of an abnormality in the alcohol sensor 17.

In this embodiment, basic fuel supply amount setting means, fuel supply amount setting means, fuel supply control means,
The functions of concentration correction value setting means, abnormality detection means, abnormality fuel concentration changing means, and integral control constant variable setting means are provided in terms of software as shown in the flowcharts of FIGS. 3 to 6. Ori,
Further, the engine operating state detection means, the air flow meter 13, the crank angle sensor 14, etc. correspond.

The routine shown in the flowchart of FIG. 3 is executed at predetermined minute intervals (for example, 10 ms). First, in step 1 (indicated as S1 in the figure, the same applies hereinafter), the intake air detected by the air flow meter 13 is Air flow rate Q and crank angle sensor 14
The basic fuel injection amount (supply amount) Tp (←K
×Q/N; K is a constant) is calculated.

In step 2, various correction coefficients COEF are set, mainly based on the cooling water temperature Tw detected by the water temperature sensor 15, including an amount increase at startup, an amount increase when the engine is cold, and the like.

In step 3, an air-fuel ratio feedback correction coefficient LAMBDA is set by proportional-integral control to bring the actual air-fuel ratio closer to the target air-fuel ratio (theoretical air-fuel ratio) when in a predetermined feedback control operating region. Specifically, when the actual air-fuel ratio detected by the O ₂ sensor 16 is rich or lean with respect to the target air-fuel ratio, the air-fuel ratio feedback correction coefficient LAMBDA is decreased (increased) by a predetermined integral; When rich/lean is reversed, it is increased or decreased by a predetermined proportional amount P. Here, each of the control constants of the integral part and the proportional part P used in the proportional-integral control of the air-fuel ratio feedback correction coefficient LAMBDA is divided into a plurality of control constants depending on the engine rotational speed N and the basic fuel injection amount Tp representing the engine load. ROM that stores optimal values in advance for each operating condition
This can be found by searching from the map above.

In the next step 4, the alcohol concentration in the supplied fuel detected by the alcohol sensor 17 is
Alcohol concentration correction factor KMET based on ALC
Set.

In step 5, a voltage correction amount Ts is set to correct changes in the effective opening time of the electromagnetic fuel injection valve 6 due to battery voltage.

Then, in the next step 6, the basic fuel injection amount Tp is corrected according to the following formula to set the final fuel injection amount (supply amount) Ti.

Ti←Tp×COEF×LAMBDA×KMET+Ts In the next step 7, the fuel injection amount Ti is set in the output register. As a result, at the predetermined fuel injection timing, the latest fuel injection amount Ti set in this output register is read out, and
Fuel is injected and supplied to the engine 1 by applying a drive pulse signal with a pulse width corresponding to this fuel injection amount Ti to the fuel injection valve 6.

By the way, the alcohol concentration correction coefficient KMET used for calculating the fuel injection amount Ti is set based on the detected value of the alcohol sensor 17 as described above.
7 becomes abnormal and outputs a detected value different from the actual concentration, the air-fuel ratio controllability deteriorates and drivability becomes impaired. For this reason, a fail-safe control function in the event of an abnormality in the alcohol sensor 17 is provided as shown in FIGS. 4 to 6.

The routine shown in the flowchart of FIG. 4 is an abnormality determination routine for the alcohol sensor 17 that is executed at predetermined intervals. First, in step 11, the detected value ALC from the alcohol sensor 17 is read.

Then, in the next step 12, the detected value ALC read in step 11 during the previous execution,
The deviation ΔALC from the detected value ALC read this time is determined, and it is determined whether this deviation ΔALC is within the set value. Here, if the deviation ΔALC is within the set value, there is a possibility that the detected value ALC is an abnormal value, but since it is in a stable state, it is not immediately recognized that the alcohol sensor 17 is abnormal. , the deviation ΔALC is greater than the set value and the detected value
When the ALC is changing at a large rate, this is a phenomenon that is not recognized when the alcohol sensor 17 is normal, so the process jumps to step 18 and a determination is made as to whether the alcohol sensor 17 is abnormal.

If it is determined in step 12 that the deviation ΔALC is within the set value, the process proceeds to step 13, where air-fuel ratio feedback control is performed to bring the actual air-fuel ratio closer to the stoichiometric air-fuel ratio, which is the target air-fuel ratio. In other words, it is determined whether the operating range is in which air-fuel ratio feedback control is to be performed.

If the air-fuel ratio feedback control is in progress, the process advances to step 14 to check whether the feedback control is in a normal state repeating rich-lean correction, and conversely to check whether the air-fuel ratio feedback correction coefficient
Determine whether LAMBDA is stuck at its upper or lower limit values for a long time, making control virtually impossible.

Here, the air-fuel ratio feedback correction coefficient
If it is determined that the LAMBDA is stuck and good feedback correction control is not being performed, the process proceeds to step 15 and the idle speed feedback control (ISC control) is not being performed (clamping). Determine whether or not.

Although not shown in FIG. 2, the feedback control of the idle rotation speed is a method of controlling the idle speed by controlling the amount of air supplied through an auxiliary air passage that bypasses the throttle valve 4. When such idle rotation feedback control is performed, the air-fuel ratio may also vary as the engine rotation speed N fluctuates around the target idle rotation speed. .

Therefore, when idle rotation feedback control is performed, there is a possibility that the variation in the air-fuel ratio feedback correction coefficient LAMBDA is due to idle rotation control, so step 1
The routine is ended without performing the abnormality determination in step 6. On the other hand, when in a clamped state where idle rotation feedback control is not performed,
It is estimated that the deviation of the air-fuel ratio feedback correction coefficient LAMBDA toward the upper and lower limits is due to incorrect concentration correction based on the abnormality detection value of the alcohol sensor 17, and the process proceeds to step 16 to determine whether the alcohol sensor 17 is abnormal.

In this way, the detection value of the alcohol sensor 17
When the ALC is changing at a rate higher than a predetermined rate,
When the air-fuel ratio feedback correction coefficient LAMBDA approaches the upper and lower limits during idle rotation control clamping, the alcohol sensor
is determined to be abnormal.

Based on this abnormality determination, a fail-safe control routine shown in the flowchart of FIG. 5 is executed.

This routine is executed in synchronization with the engine rotation, and first, in step 21, the fourth
It is determined whether or not there is an abnormality determination of the alcohol sensor 17 made according to the routine shown in the flowchart in the figure, and if an abnormality determination is not made, this routine is ended as is, but if an abnormality determination is made. If so, the process advances to step 22 and subsequent steps to execute predetermined fail-safe control.

In step 22, it is determined whether this is the first execution of this routine since the alcohol sensor 17 was determined to be abnormal.

Then, if it is determined that it is the first time, step 2
The process proceeds to step 3, and the direction in which the air-fuel ratio deviates between rich and lean when the alcohol sensor 17 is abnormal is stored based on the detection by the O ₂ sensor 16.

In the next step 26, the current O ₂ sensor 16
The richness of the target air-fuel ratio is based on the detected value.
Determine whether the alcohol is lean, and if it is rich, proceed to step 27 and check the detected value of the alcohol sensor 17.
The detected concentration is forcibly corrected to increase by adding a predetermined integral _C1 to ALC (previous value), and the alcohol concentration correction coefficient KMET is set based on this upwardly corrected alcohol concentration ALC. That is, as the alcohol concentration increases, the amount of fuel to be supplied for the same amount of air decreases, so when the air-fuel ratio is rich, the alcohol sensor 1
Since the detected value ALC of No. 7 is a lower concentration than the actual concentration, it is estimated that the amount of fuel is excessive. Therefore, the concentration is corrected to increase in order to decrease the fuel injection amount Ti. On the other hand, step 2
If it is determined in step 6 that the air-fuel ratio is lean, the process proceeds to step 28 where the alcohol sensor 17
A predetermined integral _C2 is subtracted from the detected value ALC (previous value) to forcibly correct the detected concentration. This reduction correction control is performed for the opposite reason to the rich determination.

If it is determined in step 22 that it is not the first time, the process advances to step 24. In step 24,
Alcohol concentration according to step 27 or 28
It is determined whether or not the air-fuel ratio has been reversed from the initial air-fuel ratio state stored in step 23 due to the forced increase/decrease correction of the ALC. Then, if the air-fuel ratio has not reversed from the state at the time when the abnormality of the alcohol sensor 17 was detected, step 2 is performed.
Proceed to step 6 to determine the alcohol concentration according to the current air-fuel ratio.
Perform ALC increase/decrease correction again. If it is determined that the air-fuel ratio has reversed, the process proceeds to step 25, where the alcohol concentration ALC resulting from the previous increase/decrease correction is clamped, and the subsequent alcohol concentration correction coefficient is calculated based on the alcohol concentration ALC immediately after the air-fuel ratio is reversed. Enable KMET settings to be performed.

For example, if an abnormality in the alcohol sensor 17 causes it to output a value lower than the actual alcohol concentration and the air-fuel ratio becomes rich, the alcohol concentration ALC is gradually increased and the air-fuel ratio is reversed from rich to lean. By estimating that the alcohol concentration has crossed the true alcohol concentration and clamping the alcohol concentration ALC at that time, fuel correction is performed based on the alcohol concentration ALC that is close to the true value even when the alcohol sensor 17 is abnormal. It is designed to be controlled.

By the way, step 27 and step 28
The predetermined integrals (control constants) C ₁ and C ₂ used to correct the increase/decrease in the alcohol concentration ALC are variably set according to the engine operating state according to the routine shown in the flowchart of FIG.

The routine shown in the flowchart of FIG. 6 is executed at the same timing as the routine shown in the flowchart of FIG. 5 in synchronization with engine rotation.

First, in step 31, values corresponding to the current engine rotational speed N and basic fuel injection amount Tp are retrieved and read from the map of the integral I used for integral control of the air-fuel ratio feedback correction coefficient LAMBDA. Therefore, the integral read in step 31 is a control constant that increases or decreases the air-fuel ratio feedback correction coefficient LAMBDA in the air-fuel ratio feedback control operation region.

In the next step 32, the integral read in step 31 is multiplied by a constant _K1 for correcting the value optimal for increasing integral control of alcohol concentration.
The calculation result is set as the integral _C1 used when increasing the alcohol concentration ALC in step 27 when the alcohol sensor 17 is abnormal.

In addition, in step 33, the integral read in step 31 is multiplied by a constant _K2 for correcting the value optimal for the integral control to decrease the alcohol concentration.
The calculation result is set as the integral _C2 used when controlling the alcohol concentration ALC to decrease in step 28 when the alcohol sensor 17 is abnormal.

As described above, in this embodiment, when the alcohol concentration detection value ALC is increased or decreased by integral control in the direction in which the air-fuel ratio is reversed when the alcohol sensor 17 is abnormal, the basic fuel injection that represents the engine rotational speed N and the engine load is used. Integral control is performed in synchronization with engine rotation using integrals C ₁ and C ₂ that are variably set according to the amount Tp. Therefore, even if the optimum rate of change in the alcohol concentration ALC varies depending on the engine operating state, the alcohol concentration detection value ALC can be quickly adjusted to the true value when the alcohol sensor 17 is abnormal, while avoiding overshoot. This value can be approximated. here,
The engine rotation speed N is high and the concentration correction result is quickly obtained.
It is fast when detected by the O ₂ sensor 16, and
The alcohol concentration is adjusted so that the change in the concentration correction coefficient KMET (alcohol concentration ALC) becomes smaller at low engine load when the fuel injection amount Ti changes greatly.
It is preferable to change the ALC.

In particular, if the alcohol concentration ALC is changed by a value based on the integral constant of the air-fuel ratio feedback correction coefficient LAMBDA, as in the case of this embodiment, the integral constant in the air-fuel ratio feedback control will not overshoot the air-fuel ratio. Since the settings are variably set taking into consideration the control response and control response, it is possible to easily set the alcohol concentration ALC to the optimum value according to the operating conditions without having to perform detailed matching of the integral constant for integral control of the alcohol concentration ALC. It is something that can be changed.

<Effects of the Invention> As explained above, according to the present invention, when the means for detecting the reference fuel concentration is abnormal, the detected concentration value is forcibly increased or decreased in the direction of reversing the air-fuel ratio by integral control according to a predetermined control constant. The control constant is configured to be fixed at the concentration detected when the air-fuel ratio is reversed, while the predetermined control constant is variably set according to the engine operating state, so that the means for detecting the reference fuel concentration does not detect abnormalities. When this occurs, the detected concentration value can be quickly corrected to near the true value without overshooting, and the engine operability can be quickly and favorably restored in the event of an abnormality in concentration detection. There is an effect.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the configuration of the present invention, Figure 2 is a block diagram showing the configuration of the present invention.
The figure is a system schematic diagram showing an embodiment of the present invention, Figures 3 to 6 are flowcharts showing control details in the above embodiment, and Figures 7 and 8 respectively explain problems with conventional control. This is a time chart for DESCRIPTION OF SYMBOLS 1... Engine, 6... Fuel injection valve, 12... Control unit, 13... Air flow meter, 14... Crank angle sensor, 16... O ₂ sensor, 17... Alcohol sensor.

Claims (1)

[Scope of Claims] 1. A fuel supply control device for an internal combustion engine that can be used by switching or mixing different types of fuel, comprising: an engine operating state detection means for detecting an engine operating state; and an engine operating state detection means. basic fuel supply amount setting means for setting a basic fuel supply amount based on the engine operating state detected by the means; reference fuel concentration detection means for detecting a reference fuel concentration in the fuel supplied to the engine; concentration correction value setting means for setting a concentration correction value for correcting the basic fuel supply amount based on the concentration of the reference fuel detected by the reference fuel concentration detection means; a fuel supply amount setting means for correcting and setting the fuel supply amount based on the concentration correction value; and a fuel supply control means for driving and controlling the fuel supply means based on the fuel supply amount set by the fuel supply amount setting means. and an air-fuel ratio detection means for detecting a rich/lean air-fuel ratio of an engine intake air-fuel mixture with respect to a target air-fuel ratio via engine exhaust components; an abnormality detection means for detecting an abnormality in the reference fuel concentration detection means; When an abnormality is detected by the detection means, the concentration detected by the reference fuel concentration detection means is forcibly increased or decreased by integral control according to a predetermined control constant in a direction that reverses the air-fuel ratio detected by the air-fuel ratio detection means, and the air-fuel ratio is increased or decreased. an abnormality fuel concentration changing means that fixes the concentration detected at the time of inversion; and an integral control constant variable setting means that variably sets a predetermined control constant for integral control by the abnormality fuel concentration changing means depending on the engine operating state. 1. A fuel supply control device for an internal combustion engine, comprising: