JPH08165945A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To suppress the fluctuation of an air-fuel ratio by a method wherein a guard for a present correction amount is set from the present fluctuation center of a correction amount when, based on an output from an air-fuel sensor arranged upper stream from a catalyst converter, a correction amount is decided and a fundamental fuel injection amount is adjusted for correction. CONSTITUTION: When, based on an output from an air-fuel ration sensor 9 arranged upper stream from a catalyst converter 8, a correction amount is decided and a fundamental fuel injection amount is adjusted for correction, each time a fundamental fuel injection amount and a correction amount are decided, the present fluctuation center of a fluctuating correction amount is calculated. After the present upper and lower guard value of a correction amount are then calculated, a present fluctuation center is stored as a preceding fluctuation center in preparation for subsequent processing. It is then decided whether or not a present correction amount exceeds the upper guard value and when it exceeds the upper guard value, a correction amount is set as the upper guard value and when it is therebelow, a correction amount is set as the lower guard value when a present correction amount is below the lower guard value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for feedback-controlling an air-fuel ratio of an air-fuel mixture by using an air-fuel ratio sensor arranged upstream of a catalytic converter in an exhaust passage.

[0002]

2. Description of the Related Art In order to determine a target fuel amount to be supplied to a cylinder for realizing a stoichiometric air-fuel ratio based on the amount of air actually supplied to the cylinder, and to supply this target fuel amount to the cylinder. In an internal combustion engine that calculates the basic fuel injection amount necessary for fuel injection and estimates the fuel amount actually supplied to the cylinder based on the air-fuel ratio of the exhaust gas detected by the air-fuel ratio sensor, A feedback air-fuel ratio control device that corrects the basic fuel injection amount based on the difference between the fuel injection amount and the target fuel amount has been proposed.

In the exhaust passage of an internal combustion engine, a three-way catalytic converter that reduces nitrogen oxide and simultaneously oxidizes carbon monoxide and hydrocarbons is usually arranged. This catalytic converter exhibits good purification performance when the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio.However, in general, when the exhaust gas is in a lean state with respect to fluctuations in the air-fuel ratio, excess oxygen is removed. stores the, O ₂ storage ability to maintain exhaust gas by releasing oxygen to the stoichiometric air-fuel ratio is provided when the exhaust gas is a rich state.

This O ₂ storage capacity is finite, and in order to make effective use of this capacity, the air-fuel ratio of the exhaust gas may be either rich or lean next. It is necessary to maintain the oxygen stored in the source catalytic converter at a predetermined amount (for example, half of the maximum oxygen storage amount), which is why the air-fuel ratio control device described above is actually supplied to the cylinder. The correction amount is calculated so that the integral value of the difference between the fuel amount and the target fuel amount converges to zero, and the basic fuel injection amount is corrected.

[0005]

In such an air-fuel ratio control device, when the intake air amount suddenly increases and decreases during rapid engine acceleration / deceleration, etc., and the air-fuel mixture becomes inevitably a lean or rich state. , In order to maintain the oxygen storage amount of the three-way catalytic converter at a predetermined amount, then, in order to make the air-fuel ratio of the mixture air rich or lean, reversely increase or decrease the correction amount. Although a three-way catalytic converter having an O ₂ storage capacity that significantly increases or decreases the basic fuel injection amount cannot instantaneously release or absorb a large amount of oxygen, the air-fuel ratio of such a mixture is greatly reduced. There is a problem in that the O ₂ storage capacity does not function as intended with respect to such changes, and exhaust gas in a rich or lean state passes through the catalytic converter as it is, and exhaust emission deteriorates considerably. You.

In order to prevent a large change in the air-fuel ratio of the air-fuel mixture, guard processing is generally performed so that the absolute value of the correction amount does not exceed a predetermined value. Is to be added to or subtracted from the basic fuel injection amount, and when the measurement of the air amount is not very accurate, it may change in the vicinity of a certain value other than zero, and at this time, in one of the increase or decrease of the correction amount, Even if the change in the correction amount becomes very large, it is not guarded and the above-mentioned problem may still occur.

Therefore, the object of the present invention is based on the output of an air-fuel ratio sensor arranged upstream of the catalytic converter so as to maintain a predetermined amount of oxygen stored in the catalytic converter having an O ₂ storage capacity. In the air-fuel ratio control device that determines the correction amount and adjusts the basic fuel injection amount,
An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine capable of suppressing a large change in the air-fuel ratio of the air-fuel mixture and preventing exhaust gas from being exhausted from a catalytic converter without being sufficiently purified.

[0008]

An air-fuel ratio control system for an internal combustion engine according to the present invention has an upstream side of a catalytic converter so as to maintain a predetermined amount of oxygen stored in the catalytic converter having an O ₂ storage capacity. In the air-fuel ratio control device that determines the correction amount based on the output of the arranged air-fuel ratio sensor and corrects the basic fuel injection amount, a fluctuation center calculating means for calculating the current fluctuation center of the correction amount,
Guard setting means for setting a guard for the current correction amount from the fluctuation center calculated by the fluctuation center calculating means.

[0009]

In the above-described air-fuel ratio control apparatus for an internal combustion engine, the fluctuation center calculating means calculates the current fluctuation center of the correction amount for adjusting the basic fuel injection amount, and the guard setting means calculates in this way. Since the guard for the current correction amount is set from the fluctuation center, the correction amount is suppressed so as not to exceed the guard from the fluctuation center, and the air-fuel mixture mixture does not change significantly.

[0010]

1 is a schematic sectional view of an internal combustion engine equipped with an air-fuel ratio control device according to the present invention. In the figure, 1 is an engine body, 2 is an intake passage, and 3 is an exhaust passage. An air cleaner 4 is installed on the most upstream side of the intake passage 2, and an air flow meter 5 for measuring the intake air amount is installed downstream thereof. A throttle valve 6 is arranged on the upstream side of the surge tank 2a in the intake passage 2, and a fuel injection valve 7 is arranged on the downstream side for each cylinder. Exhaust passage 3
Is provided with a three-way catalytic converter 8 for purifying the exhaust gas, and a linear output type air-fuel ratio sensor 9 capable of detecting the air-fuel ratio of the exhaust gas based on the oxygen concentration in the exhaust gas is provided on the upstream side thereof. It is arranged. Further, a crank angle sensor 11 is installed in the distributor 10, which is an ignition timing control device.

The air flow meter 5, the air-fuel ratio sensor 9, and the crank angle sensor 11 described above are connected to a control device 20, and the control device 20 controls the fuel injection amount of the fuel injection valve 7. FIG. 2 is a block diagram showing this air-fuel ratio control.

In the figure, 30 is an internal combustion engine, and 3
1 is an in-cylinder air amount estimation that estimates the air amount mc supplied to the cylinder using a map or the like based on the air amount ma measured by the air flow meter 5 and the rotation speed N measured by the crank angle sensor 11. It is a means. Reference numeral 32 denotes the fuel supplied to the cylinder by dividing the intake air amount mc estimated by the in-cylinder air amount estimation means 31 by the air-fuel mixture air-fuel ratio α at this time calculated based on the output of the air-fuel ratio sensor 9. Quantity f
It is a fuel amount estimating means for estimating c. Reference numeral 33 is a target fuel amount setting means for calculating a target fuel amount fcr to be supplied into the cylinder by dividing the air amount mc estimated by the in-cylinder air amount estimating means 31 by the theoretical air-fuel ratio αr.

The above two fuel amounts fc and fcr are output to the subtractor 34 to calculate the difference fc-fcr, and this difference is output to the first addition means 36 together with the fuel injection amount setting means 35 and the first addition. In the means 36, the time integral value x of this difference
1 is calculated and output to the fuel injection amount setting means 35. In the fuel injection amount setting means 35, the fuel injection amount fi is calculated so that this difference and its time integral value x1 are simultaneously zero.

When the above-mentioned time integrated value x1 becomes 0, the amount of oxygen stored in the three-way catalytic converter 8 becomes equal to the initial amount. This is because when the air-fuel mixture is lean and the difference is a negative value, the value obtained by multiplying this by the minute time Δt equivalently represents the amount of oxygen newly stored in the three-way catalytic converter 8. Further, when the air-fuel ratio is rich and the difference is a positive value, the value obtained by multiplying this by a minute time Δt is output from the three-way catalytic converter 8 in order to purify the exhaust gas at this time. This is because the amount of released oxygen can be expressed equivalently.

Accordingly, if the fuel injection amount fi is calculated in the fuel injection amount setting means 35 so that the difference fc-fcr and the time integral value x1 thereof become zero, the air-fuel ratio is inevitably changed during engine transient operation. Even if it becomes rich or lean, the oxygen stored in the three-way catalytic converter 8 is set to a predetermined amount in a relatively short time, and at the same time, the mixture air-fuel ratio is set to the stoichiometric air-fuel ratio in order to realize good combustion. You can

In order to ensure the setting of the fuel injection amount fi in the fuel injection amount setting means 35, the second addition means 37 calculates a further time integral value x2 of the above-mentioned time integral value x1 to set the fuel injection amount fi. It is output to the means 35.
Further, since the fuel injection valve 7 injects fuel into the intake passage 2, a part of the fuel injected from the fuel injection valve 7 adheres to the intake passage 2, and at the same time, one of the fuel adhered so far is Part is vaporized and supplied into the cylinder, and thus the injected fuel amount and the fuel amount supplied into the cylinder are not always the same amount, and it is necessary to predict the latter based on the former. As a means therefor, a basic fuel estimation means 38 is provided, and the basic fuel injection quantity fi is calculated based on the target fuel quantity fcr.
m is calculated and output to the fuel injection amount setting means 35, and the fuel injection amount fi of the fuel injection valve 7 is the basic fuel injection amount fi.
It is calculated as the sum of m and the correction amount δfi.

The fuel behavior model shown in the following equations (1) and (2) is used to estimate the basic fuel injection amount fim in the current engine operating state. fw (k + 1) = Pfw (k) + Rfi (k) --- (1) fc (k) = (1-P) fw (k) + (1-R) fi (k) --- (2)

Here, fi (k) is the fuel injection amount at this time, R is the ratio of the injected fuel that is not attached to the wall surface of the intake passage and is not supplied into the cylinder, and fw
(K) is the amount of fuel adhering to the wall surface of the intake passage at this time, and P is the ratio of the fuel adhering to the wall surface of the intake passage not being supplied to the cylinder. Therefore, fw (k + 1) represents the amount of fuel adhering to the wall surface of the intake passage and the like next time, and fc (k) represents the amount of fuel supplied to the cylinder this time. P and R are values determined by experiments and the like, and strictly speaking, they are variables that change depending on the engine temperature, fuel properties, etc., but they may be constants in order to simplify control.

In the above equations (1) and (2), the fuel injection amount fi (k), the fuel amount fw attached to the wall surface of the intake passage, etc.
(K) and the fuel amount fc (k) supplied into the cylinder are represented by the following equations (3), (4), and (5), respectively, with nominal values fim (k), fwm (k), and fcm. (K) and the deviations δfi (k), δfw (k) and δfc (k), and the basic fuel injection amount fim (k) (nominal value of the fuel injection amount) is calculated by the following equation (6). With
Applying modern control theory and the like, the correction amount δfi is set so that the difference fc−fcr and its integrated value are simultaneously converged to zero.
(K) (deviation of fuel injection amount) is calculated. fi (k) = fim (k) + δfi (k) −− (3) fw (k) = fwm (k) + δfw (k) −− (4) fc (k) = fcm (k) + δfc (k) − -(5) fim (k) = (fcr- (1-P) fwm) / (1-R) --- (6)

The correction amount δfi calculated in this way
(K) is guarded according to the flowchart shown in FIG. This flowchart shows the basic fuel injection amount fim
And every time the correction amount δfi is determined. First, in step 101, the current variation center δfic (k) of the correction amount δfi that varies each time is calculated by the following equation (7). δfic (k) = δfic (k−1) * α + δfi (k) * (1-α) −− (7) where δfic (k−1) is the variation center calculated last time by this flowchart, α is a positive number less than 1 and is an appropriate set value.

Next, at step 102, the correction amount δ
The current upper guard value A1 of fi is calculated by the following equation (8), and in step 103, the correction amount δfi
The present lower guard value A2 is calculated by the following equation (9). A1 = δfic (k) + fim (k) * β −− (8) A2 = δfic (k) −fim (k) * β −− (9) where β is a positive number less than 1 and is an appropriate setting value. Is.

Next, in step 104, step 1
The current fluctuation center δfic (k) calculated in 01
In preparation for the next processing, the previous fluctuation center δfic (k−
It is stored as 1) and the process proceeds to step 105.

At step 105, the current correction amount δ
It is determined whether or not fi (k) is greater than or equal to the upper guard value A1, and when this determination is negative, the routine proceeds to step 106, and it is determined whether or not the current correction amount δfi (k) is less than or equal to the lower guard value A2. When it is determined whether or not the determination is negative, the calculated correction amount δfi (k) ends without being changed.

On the other hand, when the determination in step 105 is affirmative, the routine proceeds to step 107, where the correction amount δfi
(K) is set to the upper guard value A1, and the process is terminated, and step 10
When the determination in 6 is affirmative, the routine proceeds to step 108, where the correction amount δfi (k) is set to the lower guard value A2, and the processing ends.

FIG. 4 is a time chart when the correction amount δfi fluctuates around Q (a positive value) due to, for example, a measurement error of the intake air amount. When the correction amount δfi fluctuates in this way, according to the above-mentioned flowchart, Q is calculated as the fluctuation center fic, and the upper guard value A1 and the lower guard value A2 are set around this Q.

Since the general guard processing is performed on the absolute value of the correction amount δfi, that is, the guard values A1 'and A2' are set around zero as shown by the chain double-dashed line. When the correction amount δfi fluctuates in this way, unnecessary guard processing is performed on the increasing side of the correction amount δfi as shown by the dotted line until the oxygen storage amount of the three-way catalytic converter 8 converges to a predetermined value. It takes a considerable amount of time to perform, and on the reduction side, sufficient guard processing is not performed as indicated by the dotted line, the fuel injection amount is considerably reduced, and the three-way catalytic converter 8 absorbs a large amount of excess oxygen over time. Without this, exhaust gas whose nitrogen oxides are not sufficiently purified is discharged from the three-way catalytic converter 8 and exhaust emission deteriorates. However, the correction amount δfi
If the guard processing is performed, the correction amount δfi is surely guarded when the correction amount δfi increases / decreases from the fluctuation center Q by more than a predetermined ratio with respect to the basic fuel injection amount fim at this time.
Such a problem can be prevented, and the change in the air-fuel ratio of the air-fuel mixture can be made relatively small in each fuel injection amount, and the torque fluctuation can be suppressed and the drivability can be prevented from being deteriorated.

In the present embodiment, the method of calculating the current fluctuation center δfic (k) of the correction amount δfi is as follows: the previous fluctuation center δfic (k−1) and the current correction amount δfi (k).
However, for example, for each of a plurality of engine operating regions determined by the engine speed and the engine load, the average value of the correction amount in steady operation is calculated, and this is calculated for each engine. It is also possible to map the variation center in the operating region and call the variation center corresponding to the current engine operating region from this map for use.

[0028]

As described above, according to the air-fuel ratio control apparatus for an internal combustion engine of the present invention, the upstream side of the catalytic converter is maintained so that the oxygen stored in the catalytic converter having the O ₂ storage capacity is maintained at a predetermined amount. In the air-fuel ratio control device that determines the correction amount based on the output of the air-fuel ratio sensor disposed on the side to correct the basic fuel injection amount, the fluctuation center calculation means determines the current correction amount that adjusts the basic fuel injection amount. Since the guard setting means sets the guard for the current correction amount from the fluctuation center calculated in this way, a large fluctuation of the correction amount is reliably suppressed, and the air-fuel ratio of the air-fuel mixture is greatly reduced. Changes are prevented. As a result, the air-fuel ratio of the exhaust gas at this time is
_{2 The} storage capacity is fully functioning and the stoichiometric air-fuel ratio is maintained, and deterioration of exhaust emission is prevented.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an internal combustion engine equipped with an air-fuel ratio control device according to the present invention.

FIG. 2 is a block diagram showing air-fuel ratio control performed by a control device.

FIG. 3 is a flowchart for a correction amount guard process in air-fuel ratio control.

FIG. 4 is a time chart of changes in correction amount.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine main body 2 ... Intake passage 3 ... Exhaust passage 5 ... Air flow meter 7 ... Fuel injection valve 8 ... Three-way catalytic converter 9 ... Linear output type air-fuel ratio sensor

Claims (1)

[Claims] 1. A method for maintaining a predetermined amount of oxygen stored in a catalytic converter having an O ₂ storage capacity,
In an air-fuel ratio control device that determines a correction amount based on the output of an air-fuel ratio sensor arranged on the upstream side of the catalytic converter and corrects the basic fuel injection amount, a fluctuation for calculating the current fluctuation center of the correction amount. An air-fuel ratio control apparatus for an internal combustion engine, comprising: a center calculating means; and a guard setting means for setting a guard for the current correction amount from the fluctuation center calculated by the fluctuation center calculating means.