JP2646695B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for an internal combustion engine in which air-fuel ratio feedback control and learning control are executed.

[Prior Art] Conventionally, in order to improve the purification efficiency of exhaust gas by a three-way catalytic converter, a residual concentration in exhaust gas is detected as an air-fuel ratio signal using an air-fuel ratio sensor provided in an exhaust system of an internal combustion engine. There is known an air-fuel ratio control device that performs feedback control based on the air-fuel ratio signal so that the air-fuel ratio of the internal combustion engine becomes a target air-fuel ratio. In such an air-fuel ratio control device, when the air-fuel ratio detected by the air-fuel ratio sensor switches from the rich side to the lean side from the target air-fuel ratio, the direction in which the amount of fuel supplied to the internal combustion engine is increased. The feedback correction coefficient (hereinafter, referred to as the F / B correction coefficient) is switched in a skipping manner, and when the detected air-fuel ratio is switched to the leaner side from the target air-fuel ratio, the fuel supply amount is reduced. The F / B correction coefficient FAF is switched in a skipping manner in the direction of decreasing the amount, and the basic fuel supply amount τp calculated according to the load of the internal combustion engine is corrected by the F / B correction coefficient FAF, and the actual fuel supply to the internal combustion engine is performed. It was configured to determine the fuel supply amount τ.

In addition, as described in Japanese Patent Application Laid-Open No. 61-11433, for example, this type of device includes the above-described device when performing feedback control.
A configuration in which a learning value FG is calculated so that the F / B correction coefficient FAF becomes a reference value, and the basic fuel supply amount τp is corrected based on the learning value FG, that is, a configuration in which so-called learning control is executed. is there. Specifically, when the F / B correction coefficient FAF is switched in a skip manner as described above, the learning value FG is configured to be increased or decreased for each step and updated.

[Problems to be Solved by the Invention] However, the conventional device in which the above-described air-fuel ratio feedback control and learning control are executed has the following problems, and is expected to be further improved. Was rare.

In a multi-cylinder independent injection internal combustion engine, the injector of a specific cylinder injects a large amount of fuel due to a foreign substance being caught or the like, and the air-fuel ratio of the air-fuel mixture becomes excessively rich and the specific cylinder is misfired. However, when such an abnormality occurs, if the air-fuel ratio feedback control is performed, the air-fuel ratio of the air-fuel mixture is determined to be rich as a whole due to the characteristics of the oxygen sensor. The mixture in the normal cylinder is controlled to the lean side. By the way, even in such a case, rich exhaust is discharged from the abnormal cylinder. In such a situation, when the internal combustion engine shifts to the idle state, the flow rate of the exhaust becomes low. The fuel ratio is individually detected, and the detection result repeats rich and lean in a short cycle. For this reason, as shown in FIG. 6, the F / B correction coefficient FAF calculated based on the detection result of the oxygen sensor is set such that the center is a certain value on the lean side and the vicinity thereof is short on the increasing side and decreasing side. It fluctuates in the cycle TX1. Then,
The learning value FG by the learning control is updated by one step for each change as shown by a dashed line in FIG.
As a result, problems such as rough idle and engine stall occurred. (Note that, when there is no normal cylinder abnormality as described above, as shown in FIG. 7, the F / B correction coefficient FAF has a section that gradually increases and decreases with a predetermined integration constant KX. The reversal cycle TK2 toward the decrease side becomes relatively large, and the above-mentioned sudden change of the learning value FG does not occur.) Further, the injector of the specific cylinder becomes unable to inject fuel due to clogging or the like. In such a case, the F / B correction coefficient FAF has a certain value on the rich side at the center, and fluctuates in the vicinity thereof toward the increasing side and the decreasing side in a short cycle. Then, the learning value FG is updated to the increasing side for each change, and as a result, a problem that the exhaust characteristics deteriorate is caused.

The present invention has been made in view of these problems, and in a state where an abnormality of the fuel injection system has occurred in a specific cylinder of a multi-cylinder internal combustion engine, when the internal combustion engine transitions to an idle state,
It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that suppresses a sudden increase or decrease in a learning value FG and prevents a decrease in idle stability.

Configuration of the Invention [Means for Solving the Problems] In order to achieve the object, the present invention has the following structures as means for solving the problems. That is, as shown in FIG. 1, the air-fuel ratio control device for an internal combustion engine according to the present invention includes an air-fuel ratio sensor M2 that detects an air-fuel ratio from an exhaust component of the internal combustion engine M1, and a feedback control condition for the air-fuel ratio that is satisfied. When the air-fuel ratio detected by the air-fuel ratio sensor M2 is switched from the rich side to the lean side from the target air-fuel ratio, the feedback correction coefficient is skipped in a direction to increase the fuel supply amount to the internal combustion engine M1. While switching, when the detected air-fuel ratio is switched from the lean side to the rich side from the target air-fuel ratio,
Feedback correction coefficient setting means M3 for skip-switching the feedback correction coefficient in a direction to decrease the fuel supply amount; learning a value corresponding to a deviation between the air-fuel ratio detected by the air-fuel ratio sensor M2 and the target air-fuel ratio. Learning value setting means M4 for sequentially updating and storing the value as a value, and correcting the basic fuel supply amount calculated according to the load of the internal combustion engine M1 on the basis of the feedback correction coefficient and the learning value, to the internal combustion engine M1. An air-fuel ratio control device for an internal combustion engine, comprising: a fuel supply amount determination unit M5 for determining a fuel supply amount; an idle state detection unit M6 for detecting an idle state of the internal combustion engine M1; and A reversal cycle calculating means M7 for calculating a reversal cycle for reversing from the increasing side to the decreasing side or from the decreasing side to the increasing side; A determination unit M8 for determining whether or not is, when the idle state detection unit M6 detects an idle state, and when the determination unit M8 determines that the inversion cycle is less than a predetermined cycle, The learning value setting means M4
And a prohibition means M9 for prohibiting the update of the learning value by.

[Operation] The air-fuel ratio control device for an internal combustion engine of the present invention configured as described above, when the feedback control condition of the air-fuel ratio is satisfied,
When the air-fuel ratio detected by the air-fuel ratio sensor M2 switches from the rich side (or lean side) to the lean side (or rich side) from the target air-fuel ratio, the feedback correction coefficient is set by the feedback correction coefficient setting means M3. While switching the coefficient in a skipping manner, a value corresponding to a deviation between the air-fuel ratio detected by the air-fuel ratio sensor M2 and the target air-fuel ratio is set as a learning value.
The learning value setting means M4 sequentially updates and stores the basic fuel supply amount calculated according to the load of the internal combustion engine M1,
Based on the feedback correction coefficient and the learning value, correction is made by the fuel supply amount determining means M5 to determine the fuel supply amount to the internal combustion engine M1. Further, the idling state of the internal combustion engine M1 is detected by the idling state detecting means M6, and the inversion cycle in which the feedback correction coefficient is inverted from the increasing side of the fuel supply amount to the decreasing side or from the decreasing side to the increasing side is determined by the inverting cycle calculating means M7. Prohibiting the updating of the learning value by the learning value setting means M4 when the calculating means detects that the internal combustion engine is in an idle state and the determined inversion cycle is shorter than the predetermined cycle by the determining means M8. Prohibited by M9.

Therefore, when the internal combustion engine shifts to the idle state in a state where the abnormality of the fuel injection system occurs in the specific cylinder of the multi-cylinder internal combustion engine, conventionally, the place where the learning value is rapidly updated as described above is conventionally performed. According to the present invention, the learning value FG is not updated, and the learning value FG does not suddenly increase or decrease.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. Second
FIG. 1 is a schematic configuration diagram showing a four-cylinder internal combustion engine 2 to which the present invention is applied and its periphery.

As shown in the figure, an air flow meter 8 for detecting the amount of air (intake air amount) flowing into the intake pipe 4 of the internal combustion engine 2 through a throttle valve 6 and the temperature thereof (intake air temperature) are detected. An intake air temperature sensor 10 or a slot position sensor 12 having a built-in idle switch for detecting an opening degree of the throttle valve 6 and detecting a fully closed state of the throttle valve 6 is provided. The intake pipe 4 is provided with an injector 14 for injecting fuel pressure-fed from a fuel pump (not shown) for each cylinder of the internal combustion engine 2, and flows into the fuel injected from the injector 14 via the throttle valve 6. The air and the air can be mixed and supplied to the internal combustion engine 2.

Further, the internal combustion engine 2 includes an air-fuel ratio sensor 18 for detecting an air-fuel ratio of a fuel-air mixture supplied to the internal combustion engine 2 from an oxygen concentration in exhaust gas flowing through the exhaust pipe 16, a water temperature sensor 20 for detecting a cooling water temperature, and a distributor 22. A predetermined rotation angle (for example,
At every 30 ° C.), once every rotation of the rotation speed sensor 24 and the distributor 22 that generates a pulse signal for detecting the rotation speed of the internal combustion engine 2 (that is, once every two rotations of the internal combustion engine 2).
A cylinder discriminating sensor 26 for outputting a pulse signal for determining a fuel injection timing and an ignition timing is provided, and the operating state thereof can be detected together with the air flow meter 8, the intake air temperature sensor 10, and the throttle position sensor 12. ing.

The detection signal from each of the sensors is transmitted to the electronic control circuit 30.
Is taken in. The electronic control circuit 30 drives the injector 14 and the igniter 32 based on a detection signal from each sensor to execute fuel injection control and ignition timing control. It is configured as an arithmetic circuit.

That is, in the electronic control circuit 30, a CPU 30a that executes fuel injection control and ignition timing control of the internal combustion engine 2 in accordance with a preset control program, and a control program and various data necessary to execute arithmetic processing in the CPU 30a are stored in advance. Recorded RO
M30b, RAM 30c from which various data necessary for executing the arithmetic processing by the CPU 30a are temporarily read, and a battery so that the learning value FG updated at the time of executing the fuel injection control described later is held even when the ignition switch 33 is turned off. Backup as nonvolatile memory backed up by 34
A RAM 30d, an input port 30e for inputting a detection signal from each of the sensors, an injector 14 and an igniter 32
An output port 30f for outputting a drive signal is provided. The electronic control circuit 30 includes a timer circuit (not shown), and the current time and the like can be known from the timer circuit.

Next, the fuel injection control executed by the electronic control circuit 30 will be described with reference to the flowcharts shown in FIGS.

First, FIG. 3 shows that after the ignition switch 34 is turned on, the electronic control circuit 30 repeatedly executes the routine at predetermined time intervals.
9 is a flowchart illustrating a fuel injection amount calculation process for calculating a fuel injection amount from the fuel injection valve (specifically, a valve opening time of the injector 14).

As shown in the figure, when the processing is started, first, step 110 is executed, and based on the detection signals from the throttle position sensor 12 and the rotation speed sensor 24, for example, the rotation speed N of the internal combustion engine 2 is equal to or more than a predetermined rotation speed. Then, it is determined whether a fuel cut control condition that the throttle valve 6 is fully closed is satisfied. If the fuel cut control condition is satisfied, the routine proceeds to step 120, where the fuel injection amount τ is set to 0 so as to prohibit the fuel injection by the injector 14, and the routine process is temporarily terminated.

On the other hand, if it is determined in step 110 that the fuel cut condition is not satisfied, the process proceeds to step 130, where the internal combustion engine 2 detected by the rotation speed sensor 24 and the air flow meter 8
The basic fuel injection amount τp is calculated on the basis of the rotational speed N and the intake air amount Q based on a preset map or an arithmetic expression.

In step 140, the internal combustion engine 2 is currently in steady operation based on the detection signals from the intake air temperature sensor 10, the throttle position sensor 12, the water temperature sensor 20, etc., and the air-fuel ratio is determined based on the detection signal from the air-fuel ratio sensor 18. It is determined whether an air-fuel ratio feedback control condition for controlling to a target air-fuel ratio (stoichiometric air-fuel ratio) is satisfied.

That is, when the intake air temperature detected by the intake air temperature sensor 10 is low, the throttle opening detected by the throttle position sensor 12 is large, and when the internal combustion engine 2 is accelerating or operating under a high load, or when the water temperature sensor 20 is used. When the detected coolant temperature is low, it is necessary to increase the basic fuel injection amount τp by well-known intake air temperature correction, output increase correction, or warm air increase correction to improve the operability of the internal combustion engine. This step 140 is executed by determining whether or not the operating state of the internal combustion engine 2 satisfies these fuel increase correction execution conditions.

Next, when it is determined in step 140 that the feedback control condition of the air-fuel ratio is satisfied, the process proceeds to step 150, in which a correction coefficient K for increasing the basic fuel injection amount τp is set to 1. Then, the process proceeds to step 160. In step 160, by executing the F / B correction coefficient calculation processing shown in FIG. 4, the feedback control for the air-fuel ratio is performed.
Calculate the F / B correction coefficient FAF.

Here, the F / B correction coefficient calculation processing shown in FIG. 4 will be described first. When the process is started as shown in the figure, first, step 210 is executed to determine whether the air-fuel ratio of the fuel mixture currently supplied to the internal combustion engine 2 is rich based on the detection signal from the air-fuel ratio sensor 18. to decide. And this step 210
If it is determined that the air-fuel ratio is rich in
After resetting the flag FL with 0, the process shifts to step 230 to determine whether or not the flag FR is in a reset state.

This flag FR is reset when the air-fuel ratio is in the lean region in the processing described later.If the flag FR is in the reset state, it is immediately after the current air-fuel ratio is switched from lean to rich in step 230. Judge and step
Move to 240. Then, in step 240, the value of the F / B correction coefficient FAF of the RAM 30c is updated by reducing the preset skip constant RS from the current F / B correction coefficient FAF, and the flag FR is set in the next step 250. The processing of this routine is once ended.

As is well known, when the air-fuel ratio is switched from lean to rich or from rich to lean, the skip constant RS is changed by changing the F / B correction coefficient FAF in a skipping manner so that the air-fuel ratio becomes lean or rich. It is intended to make a quick transition to the side.

Next, if it is determined in step 230 that the flag FR is not in the reset state, that is, if it is not immediately after the air-fuel ratio is switched from lean to rich, the process proceeds to step 260. Then, in step 260, a preset integration constant KI is subtracted from the current F / B correction coefficient FAF, and the F / B in the RAM 30c is subtracted.
The value of the correction coefficient FAF is updated, and the process of this routine is once ended.

As is well known, the integral constant KI is the skip constant RS
After changing the F / B correction coefficient FAF in a skipping manner,
This is for gradually changing the F / B correction coefficient FAF so that the air-fuel ratio is not excessively controlled to the lean side or the rich side.
A small value is set for the skip constant RS.

Next, when it is determined in step 210 that the air-fuel ratio is not in the rich region, that is, when the air-fuel ratio is in the lean region,
Step 270 is executed, and the flag FR is reset.
In the following step 280, it is determined whether or not the current air-fuel ratio has just been switched from rich to lean, based on whether or not the flag FL is in a reset state. When the flag FL is reset and it is determined in step 280 that the air-fuel ratio has just been switched from rich to lean, the next step 290 is executed, and the skip constant RS is added to the current F / B correction coefficient FAF. The addition is performed to update the F / B correction coefficient FAF in the RAM 30c. After that, the flag FL is set in step 292, and the process is temporarily terminated.

Also, if the flag FL is not in the reset state, step 280
If it is determined that the current air-fuel ratio is not immediately after switching from rich to lean, the process proceeds to step 294, where the current F / B
After adding the integration constant KI to the correction coefficient FAF to update the F / B correction coefficient FAF in the RAM 30c, the processing of the present routine is temporarily terminated.

Such F / B correction coefficient calculation processing is performed in step 160 in FIG.
In step 300, it is determined whether the F / B correction coefficient FAF has been updated with a predetermined skip constant RS in the F / B correction coefficient calculation process. If the F / B correction coefficient FAF has been updated with the skip constant RS, the process proceeds to the next step 310 to determine whether or not the internal combustion engine 2 is in an idle state from an idle switch built in the slot position sensor 12. I do. Here, if it is determined that the vehicle is in the idle state, in the following step 320, the F / B correction coefficient FAF
A process of calculating a skip interval CTSKIP for inverting from the increasing side to the decreasing side or from the decreasing side to the increasing side is executed. In detail, the time told updated by the previous skip constant RS stored in the next step 330 described later is subtracted from the current time t at which the F / B correction coefficient FAF is updated by the skip constant RS, and the skip interval CTSKIP Is calculated. Step 33
In the case of 0, the current time t at which the F / B correction coefficient FAF is updated by the skip constant RS is stored in the RAM 30c as the time told updated by the previous skip constant RS, and the process proceeds to step 340.

In step 340, the skip interval CTSKIP is set to the predetermined cycle T
It is determined whether or not this is the case. This predetermined cycle T is determined by the internal combustion engine 2
Is a size corresponding to the shortest skip interval that can be normally taken when all the cylinders normally operate, and is obtained and set in advance through experiments or the like. In step 340, the skip interval CTSKIP
Is determined to be equal to or longer than the predetermined period T, the process proceeds to step 350, a process of calculating a learning value FG is performed, and the process proceeds to step 360. The process of calculating the learning value FG will be described later in detail.

On the other hand, if it is determined in step 340 that the skip interval CTSKIP is smaller than the predetermined period T, the process skips the learning value calculation process in step 350 and proceeds to step 360. If it is determined in step 310 that the vehicle is not in the idle state, the process proceeds to step 350, where a process of calculating a learning value FG is executed.

Then, in step 360, the learning value FG calculated so far is set in the range from the upper limit FGMAX to the lower limit FGMIN.
Execute upper / lower limit guard processing. After that, the process
Migrate to 390.

On the other hand, if it is determined in step 140 that the feedback condition of the air-fuel ratio is not satisfied, the routine proceeds to step 370, where the F / B correction coefficient FAF is set to 1, and the routine proceeds to step 380. Then, at step 380, the intake air temperature sensor 10,
Based on the detection signals from the throttle position sensor 12, the water temperature sensor 20, and the like, an increase correction coefficient K for the basic fuel injection amount τp is calculated, and the routine proceeds to step 390. Step 3
If it is determined that the F / B correction coefficient FAF is not updated by the skip constant RS in step 00, the process also proceeds to step
Migrate to 390.

In step 390, the basic fuel injection amount τp calculated in step 130 is compared with the F / B correction coefficient FAF and the learning value.
The fuel injection amount τ is calculated by performing correction using the following equation τ = τp · FAF · (1 + FG) · K using the FG and the correction coefficient K as parameters, and the processing of this routine is temporarily terminated.

Next, the learning value FG calculation processing executed in step 350 will be described with reference to FIG. In this process, a learning value FG is determined so that the F / B correction coefficient FAF calculated in the F / B correction coefficient calculation process shown in FIG. 4 always becomes a value near the reference value (that is, 1). Processing.

As shown in the figure, when the process is started, first, step 410 is executed, for example, the feedback control of the current air-fuel ratio is being executed, and the cooling water temperature is equal to or higher than a predetermined value and the intake air temperature falls within a predetermined temperature range. It is determined whether or not a learning condition such as being satisfied is satisfied. If it is determined in step 410 that the learning condition is not satisfied, the processing of this routine is terminated.

On the other hand, when it is determined in step 410 that the learning condition is satisfied, the process proceeds to step 420, and the F / B correction coefficient FAF is updated by the predetermined skip constant RS in the F / B correction coefficient calculation process. Is determined. And the F / B correction factor F
If the AF has been updated by the skip constant RS, the process proceeds to the next step 430, where the F / B correction coefficient FAF before the update by the skip constant RS is read from the RAM 30c, and the process proceeds to step 440, where the F / B correction is performed. If the coefficient FAF has not been updated by the skip constant RS, the processing of this routine ends as it is.

Next, at step 440, the average value of the F / B correction coefficient FAF based on the F / B correction coefficient FAF (n) currently read at step 430 and the previously read F / B correction coefficient FAF (n-1). F
Calculate AFAV. In the subsequent step 450, the calculated average value FAFAV is set to a predetermined upper limit value (for example, 1.0
It is determined whether or not 2) has been exceeded, and if it has exceeded the upper limit, the process proceeds to step 460.

In step 460, the learning value FG stored in the backup RAM 30d is set so that the F / B correction coefficient FAF is equal to or less than the upper limit.
The learning value FG is updated by adding a predetermined value α set in advance to the value of, and the processing of this routine is once ended.

On the other hand, if it is determined in step 450 that the average value FAFAV is equal to or less than the upper limit, then step 470 is executed, and the average value FAF
It is determined whether AV has fallen below a preset lower limit (for example, 0.98).

If it is determined in step 470 that the average value FAFAV has fallen below the lower limit value, the process proceeds to step 480. In step 480, the learning value FG is updated by subtracting a preset value β from the value of the learning value FG stored in the backup RAM 30d so that the F / B correction coefficient FAF is equal to or greater than the lower limit. ,
The processing of this routine is once ended.

On the other hand, if it is determined in step 450 that the average value FAFAV is equal to or lower than the upper limit, and if it is determined in step 470 that the average value FAFAV is equal to or higher than the lower limit value, the process of the present routine is temporarily terminated.

As described above, in the present embodiment, it is determined whether or not the internal combustion engine 2 is in the idle state from the idle switch built in the throttle position sensor 12 (step 31).
0) Also, the skip interval CTSKIP in which the F / B correction coefficient FAF is inverted from the increasing side to the decreasing side or from the decreasing side to the increasing side.
Is calculated from the difference between the current time t at which the F / B correction coefficient FAF is updated by the skip constant RS and the time told updated by the previous skip constant RS (step 320), and the skip interval CTSKIP is set to a predetermined period T. It is determined whether or not this is the case (step 340). When the idle state is determined and the skip interval CTSKIP is shorter than the predetermined cycle T, the learning value FG is calculated, that is, the learning value FG is not updated (step 350: FIG. 5). .

For this reason, when the internal combustion engine 2 shifts to the idle state in a state where the fuel injection system abnormality occurs in the specific cylinder of the multi-cylinder internal combustion engine 2, as shown in FIG. However, as shown in the figure, the learning value FG becomes a constant value without being updated to the increasing side or the decreasing side (one-point line of sight). Therefore, the air-fuel ratio of the internal combustion engine becomes over lean, leading to rough idling and engine stall, and the air-fuel ratio becomes over lean, causing no deterioration in exhaust characteristics, etc., and is excellent in idle stability. .

In the above-described embodiment, as the inversion cycle calculation means M7,
The reversal cycle of the F / B correction coefficient FAF was configured to be measured directly from the skip time of the FAF, but instead of this, it is indirectly measured from the detection signal of the air-fuel ratio sensor 18 that determines the value of the FAF. May be configured. That is, when the detection signal of the air-fuel ratio sensor 18 switches from on to off or from off to on, the switching cycle is set to F /
The inversion cycle of the B correction coefficient may be used.

Further, in the above embodiment, when it is determined that the learning value FG is updated in the idle state and the skip interval CTSKIP is shorter than the predetermined cycle T, the learning value FG is replaced. In addition to prohibiting FG updates,
The display lamp may be turned on or an alarm may be output to a diagnosis computer or the like to warn that an abnormality has occurred in the fuel injection system of the specific cylinder of the internal combustion engine 2.

Although one embodiment of the present invention has been described above, the present invention is not limited to such an embodiment, and it goes without saying that the present invention can be implemented in various modes without departing from the gist of the present invention.

Effects of the Invention As described in detail above, according to the air-fuel ratio control apparatus for an internal combustion engine of the present invention, the internal combustion engine shifts to the idle state in a state where an abnormality of the fuel injection system occurs in a specific cylinder of the multi-cylinder internal combustion engine. Also in this case, the learning value FG does not suddenly increase or decrease. Therefore, the air-fuel ratio of the internal combustion engine becomes over lean, leading to rough idle and engine stall, and the air-fuel ratio does not become over-rich, causing deterioration of exhaust characteristics and the like, and excellent idle stability. I have.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of the present invention, FIG. 2 is a schematic configuration diagram showing an internal combustion engine and peripheral devices of the embodiment, FIG.
FIG. 4 is a flowchart showing a fuel injection amount calculation process executed by the electronic control circuit, FIG. 4 is a flowchart showing an F / B correction coefficient calculation process, FIG. 5 is a flowchart showing a learning value calculation process, and FIG. A timing chart showing the effect of the present embodiment together with the change of the feedback correction coefficient and the learning value at the time of abnormality when the cylinder has excessive injection,
FIG. 7 is a timing chart showing changes in the feedback correction coefficient and the learning value in a normal state. M1 internal combustion engine, M2 air-fuel ratio sensor M3 feedback correction coefficient setting means M4 learning value setting means M5 fuel supply amount determining means M6 idle state detecting means M7 reversal cycle calculating means M8 ………………………………………………………………………………………………………………………………………………………………………………………… r haven't read anymore.

Claims (1)

(57) [Claims] An air-fuel ratio sensor for detecting an air-fuel ratio from an exhaust component of an internal combustion engine; and an air-fuel ratio detected by the air-fuel ratio sensor when the air-fuel ratio feedback control condition is satisfied. When switching to the lean side, the feedback correction coefficient is skipped in the direction to increase the fuel supply amount to the internal combustion engine, and the detected air-fuel ratio is shifted from the lean side to the rich side from the target air-fuel ratio. A feedback correction coefficient setting means for skip-switching a feedback correction coefficient in a direction to decrease the fuel supply amount when the fuel supply amount is reduced; and a deviation between an air-fuel ratio detected by the air-fuel ratio sensor and a target air-fuel ratio. Learning value setting means for sequentially updating and storing a value to be performed as a learning value; and a basic fuel supply amount calculated according to the load of the internal combustion engine.
A fuel supply amount determining unit that corrects based on the feedback correction coefficient and the learning value to determine a fuel supply amount to the internal combustion engine. An idle state detecting means for detecting; a reversal cycle calculating means for calculating a reversal cycle in which the feedback correction coefficient reverses from the increasing side of the fuel supply amount to the decreasing side or from the decreasing side to the increasing side of the fuel supply amount; Determining means for determining whether or not the period is less than a predetermined period; and when the idle state is detected by the idle state detecting unit, and when the inverting period is determined to be shorter than the predetermined period by the determining unit, Prohibiting means for prohibiting updating of the learning value by the learning value setting means.