JPH03182659A - Air-fuel ratio feedback control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To improve the conversion efficiency of a three-dimensional catalyst by delaying a timing, at which proportional control is made on an air-fuel ratio feedback correction value, based on a ratio or a difference between a total sum of an increase operation amount of an air-fuel ratio feedback correction value and a total sum of a reduction operation amount. CONSTITUTION:A correction value set means B sets the increase and decrease of an air-fuel ratio feedback correction value based on proportional operation at least during rich/lean inversion so that an air-fuel ratio detected by an air-fuel ratio detecting means A is adjusted to a value approximately equal to a target air-fuel ratio, and a fuel feed control means C corrects and controls a fuel feed amount. In which case, based on a ratio or a difference between a total sum of an increase operation amount of an air-fuel ratio feedback correction value determined by an operation amount total sum detecting means D and a total sum of a reduction operation amount, a proportional control delay means E varies and sets a lag time, by which a timing at which proportional control is made on an air-fuel ratio feedback correction value is delayed, on the increase operation side and on the reduction operation side by a lag time set means F. This constitution maintains the conversion efficiency of a three-dimensional catalyst through production of a storage effect.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an air-fuel ratio feedback control device for an internal combustion engine, and more specifically, it detects the air-fuel ratio of an engine intake air-fuel mixture and adjusts this air-fuel ratio to a target air-fuel ratio. The present invention relates to a device for feedback correcting the amount of fuel supplied to an engine so that the amount of fuel supplied to an engine is approximated.

<Prior Art> The following is known as a fuel supply control device for an internal combustion engine having an air-fuel ratio feedback control function.

The intake air flow rate Q is a state quantity related to the intake air of the engine.
and intake pressure PB, and calculates the basic fuel supply amount TP based on these and the detected value of the engine rotation speed N. In addition, various correction coefficients C0EF including starting increase correction etc. set based on the engine temperature represented by the cooling water temperature Tw,
An air-fuel ratio feedback correction coefficient α that is set based on the air-fuel ratio of the intake air-fuel mixture obtained through detection of the oxygen concentration in the exhaust gas, and a correction numerator that corrects changes in the effective injection time of the fuel injection valve due to battery voltage. Calculate s etc. Then, the basic fuel supply ITp is corrected using the calculated various correction values to obtain the final fuel supply amount Ti (''
TpXCOEFXα+Ts) is set, and the fuel injection valve is opened at a predetermined timing for a time commensurate with the fuel supply amount T1 to control the fuel supply to the engine. See Publication No. 240840, etc.>

The air-fuel ratio feedback correction coefficient α is set, for example, by proportional-integral control. In other words, by taking advantage of the fact that the oxygen concentration in the exhaust gas changes suddenly after reaching the stoichiometric air-fuel ratio, an oxygen sensor installed in the exhaust system adjusts the air-fuel ratio of the engine intake mixture to be richer than the stoichiometric air-fuel ratio (target air-fuel ratio). For example, when the actual air-fuel ratio is richer (leaner) than the stoichiometric air-fuel ratio, the air-fuel ratio feedback correction coefficient α is first decreased by a predetermined proportionality constant P (
Then, it is gradually decreased (increased) in a time-synchronized manner according to the integral operation amount obtained by multiplying the predetermined integral constant I by the fuel supply NTi at that time, until the actual air-fuel ratio is near the stoichiometric air-fuel ratio. It is controlled to repeat the reversal.

(Problems to be Solved by the Invention) By the way, especially in internal combustion engines for automobiles, the exhaust gas is purified by a three-way catalyst device installed in the exhaust system and then discharged into the atmosphere to remove Co and HC.

This three-way catalytic converter for exhaust purification is designed to prevent the air from being polluted by the emission of harmful gases such as NOx, but this three-way catalyst device controls the air-fuel ratio of the engine intake air-fuel mixture to around the stoichiometric air-fuel ratio. Sometimes, the conversion efficiency to CO, HC, and No is the best, and as shown in Figure 9, the larger the swing of the air-fuel ratio, the better the conversion efficiency is known as the storage effect. .

Therefore, when the IIJtlI characteristic to the stoichiometric air-fuel ratio deteriorates due to deterioration of the oxygen sensor, etc., and the conversion efficiency of harmful gas in the three-way catalyst device decreases, the proportional operation amount of the air-fuel ratio feedback correction coefficient α is By increasing the swing range of the air-fuel ratio, the conversion efficiency can be maintained due to the storage effect, but if the fuel supply amount is controlled to increase or decrease with a large proportional operation amount, the air-fuel ratio will increase or decrease as shown in Figure 13. There is a problem in that a large surge torque is generated due to the instantaneous difference in fuel ratio.

Therefore, when increasing the air-fuel ratio deviation to maintain conversion efficiency, it is not practical to increase the proportional operation amount of the air-fuel ratio feedback correction coefficient α, and when the controllability to the stoichiometric air-fuel ratio deteriorates, It has been desired to provide a device that can maintain conversion efficiency by increasing the air-fuel ratio swing while suppressing the generation of surge torque.

The present invention was made in view of the above problems, and when the controllability to the stoichiometric air-fuel ratio deteriorates and the conversion efficiency deteriorates,
It is an object of the present invention to provide an air-fuel ratio feedback control device that can maintain the conversion efficiency of a three-way catalyst by utilizing the storage effect while avoiding an increase in surge torque.

<Means for Solving the Problems> Therefore, in the present invention, as shown in FIG. An air-fuel ratio feedback correction value for feedback correcting the fuel supply amount so that the actual air-fuel ratio approaches the target air-fuel ratio based on the rich lean of the air-fuel ratio detected by the means, at least at the time of rich/lean reversal. a correction value setting means for increasing or decreasing the amount of fuel supplied to the engine based on the air-fuel ratio feedback correction value set thereby; In the air-fuel ratio feedback control device for an internal combustion engine, the operation amount sum detection means calculates the sum of the increase operation amount and the sum of the decrease operation amount of the air-fuel ratio feedback correction value by the correction value setting means, respectively; A delay time for delaying the timing of proportional control of the air-fuel ratio feedback correction value by the correction value setting means based on the ratio or difference between the sum of the increase operation amount and the sum of the decrease operation amount determined by the summation detection means. a delay time setting means that is variably set on the decreasing operation side, and a proportional control that forcibly delays the timing of the proportional control by the correction value setting means in accordance with the delay time of the proportional control set by the delay time setting means. A delay means is provided.

Here, as shown by the dotted line in Figure 1, the total delay time is set based on the engine operating conditions, the total time of the increase operation side and the decrease operation side of the proportional control delay time variably set by the delay time setting means. The delay time setting means may be configured to variably set a ratio at which the total time set by the total delay time setting means is divided into an increasing operation side and a decreasing operation side.

In addition, as shown in the dot green stone in Figure 1, the transient operation detection means detects the transient operation state of the engine, and the proportional control delay means detects the transient operation state of the engine by means of the transient operation detection means. It is preferable to provide a transient operation detecting means for prohibiting transient operation when the detection is detected.

Furthermore, as shown in FIG. 2, the air-fuel ratio detecting means detects whether the air-fuel ratio of the engine intake air-fuel mixture is rich or lean with respect to the target air-fuel ratio, and the air-fuel ratio detecting means detects whether the air-fuel ratio is rich or lean with respect to the target air-fuel ratio. correction value proportional-integral control means for increasing or decreasing an air-fuel ratio feedback correction value by proportional-integral control for feedback-correcting the fuel supply amount so that the actual air-fuel ratio approaches the target air-fuel ratio; An air-fuel ratio feedback control device for an internal combustion engine, comprising: fuel supply control means for correcting and controlling the amount of fuel supplied to the engine based on an air-fuel ratio feedback correction value; A total operation amount detection means for calculating the sum of the increase operation amount and the total sum of the decrease operation amount of the correction value, and a difference between the sum of the increase operation amount and the sum of the decrease operation amount obtained by this operation amount sum detection means. A delay in which the delay time for delaying the timing of proportional control of the air-fuel ratio feedback correction value by the correction value proportional integral control means is variably set for the increase operation side and the decrease operation side so that the target value corresponds to the integral operation amount. A time setting means and a proportional control delay means for forcibly delaying the timing of the proportional control by the correction value proportional integral control means according to the proportional control delay time set by the delay time setting means are provided.

Here, it is preferable that the delay time setting means is configured to variably set the delay time using an average value obtained when the sum of the manipulated variables is calculated as the integral manipulated variable.

Further, the delay time setting means weighted averages the difference between the sum of the increased manipulated variables and the sum of the decreased manipulated variables by the integral manipulated variable, and sets the proportional control delay time so that this weighted average result becomes the target value. It is better to configure it so that it can be set variably.

<Operation> In the invention having the configuration shown in FIG.
The air-fuel ratio feedback correction value is used to correct the fuel supply amount so that the detected air-fuel ratio approaches the target air-fuel ratio.
The fuel supply control means corrects and controls the fuel supply amount based on the air-fuel ratio feedback correction value to perform feedback control of the air-fuel ratio. be exposed.

Here, the manipulated variable sum detection means calculates the sum of the increasing manipulated variable and the decreasing manipulated variable of the air-fuel ratio feedback correction value, respectively. Then, the delay time setting means decreases the delay time for delaying the timing for proportionally controlling the air-fuel ratio feedback correction value based on the ratio or difference between the sum of the increase operation amount and the sum of the decrease operation amount. Variable settings are made for each side. The proportional control delay means forcibly delays the timing of proportional control of the air-fuel ratio feedback correction value in accordance with the delay time for each increase/decrease operation by proportional control set as described above.

That is, based on the balance change between the increase operation amount and the decrease operation amount of the air-fuel ratio feedback correction value, the timing of the increase operation or decrease operation in the proportional control is delayed,
The purpose is to maintain a balance between increases and decreases in the manipulated variable while increasing the air-fuel ratio swing range.

When setting the delay time of the proportional control for the increase operation side and the decrease operation side, the total delay time for each increase/decrease operation is set by the total delay time setting means based on the engine operating conditions, and this total time is set. The ratio of division between the increase operation side and the decrease operation side can be set variably, so that if you want to increase the delay time of one side based on the ratio or difference of the total amount of operation, you can decrease the delay time of the other side at the same time. do.

Furthermore, when a transient operating state of the engine is detected, the transient delay inhibiting means prohibits a forced delay in the proportional control, thereby preventing the air-fuel ratio controllability during the transient from being deteriorated due to the delay in the proportional control.

Furthermore, in the invention having the configuration shown in FIG. 2, when the air-fuel ratio feedback correction value is increased or decreased by proportional-integral control by the correction value proportional-integral control means, the difference between the sum of increasing manipulated variables and the sum of decreasing manipulated variables The delay time for delaying the timing of proportional control of the air-fuel ratio feedback correction value is variably set for the increase operation side and the decrease operation side so that the value becomes the target value according to the integral operation amount. The delay time is set in response to the change in the manipulated variable balance requirement.

In addition, when setting the delay time so that the difference between the sum of increasing manipulated variables and the sum of decreasing manipulated variables becomes the target value according to the integral manipulated variable as described above, the sum of the manipulated variables is calculated as the integral manipulated variable. By using the average value when

Furthermore, the difference between the sum of the increasing manipulated variables and the total sum of decreasing manipulated variables is divided by the integral manipulated variable, and the values are weighted averaged, and the proportional control delay time is variably set so that this weighted average result becomes the target value.
To prevent variation in operation amount balance from being greatly influenced by delay time setting.

<Example> The present invention will be explained in detail below.

In FIG. 3 showing one embodiment, an internal combustion engine l is connected to an air cleaner 2 through an intake duct 3. Air is taken in via the throttle valve 4 and the intake manifold 5.

A fuel injection valve 6 is provided in a branch portion of the intake manifold 5 for each cylinder. The fuel injection valve 6 opens when the solenoid is energized, and closes when the solenoid is de-energized!
The magnetic fuel injection valve is energized by a drive pulse signal from the control unit 12 to open the valve, and injects and supplies fuel that is pressure-fed from a fuel pump (not shown) and adjusted to a predetermined pressure by a pressure regulator.

The combustion chamber of each cylinder of the engine 1 is provided with a spark plug 7, which ignites a spark to ignite and burn the air-fuel mixture.

From engine 1, exhaust manifold 8° exhaust duct 9. Exhaust gas is discharged via a three-way catalyst 10 and a muffler 11.

The control unit 12 includes a CPU and a ROM.

It is equipped with a microcomputer that includes a RAM, an A/D converter, a human output interface, etc., and receives input signals from various sensors and processes them as described below.
Controls the driving of the fuel injection valve 6.

As the various sensors mentioned above, an air flow meter 13 is provided in the intake duct 3, and the air flow meter 13 is installed in the intake duct 3 to measure the intake air flow I of the engine 1.
Outputs a voltage signal corresponding to Q.

Further, a crank angle sensor 14 is provided, and in the case of a four-cylinder engine, outputs a reference signal REF for each crank angle of 180'' and a unit signal PO3 for each crank angle of 1° or 2″. Here, the engine rotational speed N can be calculated by measuring the period of the reference signal REF or the number of occurrences of the unit signal PO3 within a predetermined time.

The water jacket of the engine 1 is provided with a water temperature sensor 15 that detects the cooling water temperature Tw.

Further, an oxygen 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 concentration in the exhaust gas.

The oxygen sensor 16 is a known sensor that can determine whether the actual air-fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio by utilizing the fact that the oxygen concentration in the exhaust gas changes suddenly with the stoichiometric air-fuel ratio as a boundary.

Further, the throttle valve 4 is provided with a throttle sensor 17 that detects the opening degree TVO of the throttle valve 4 using a potentiometer.

In this configuration, the microcomputer built into the control unit 12 calculates the basic fuel injection amount Tp based on the intake air flow rate Q and the engine rotational speed N, and calculates the actual fuel injection amount based on the detected value of the oxygen sensor 16. An air-fuel ratio feedback correction coefficient α (air-fuel ratio feedback correction 4fL) for correcting the basic fuel injection amount Tp so as to bring the fuel ratio closer to the target air-fuel ratio (theoretical air-fuel ratio) is set by proportional-integral control, and the basic fuel injection amount Tp is The final fuel injection amount Ti is set by correcting the air-fuel ratio feedback correction coefficient α and various correction values set based on other operating conditions. Then, a drive pulse signal having a pulse width corresponding to the fuel injection amount Ti is outputted to the fuel injection valve 6 at a predetermined timing to control fuel supply to the engine 1.

Next, the control unit 12 controls the setting of the air-fuel ratio feedback correction coefficient α and the fuel injection amount Ti.
The explanation will be made according to the programs shown in the flowcharts shown in FIGS.

In this embodiment, the correction value setting means, the fuel supply control means, the operation amount total detection means, the delay time setting means, the proportional control delay means 9 and the total time setting means.

The functions as a transient operation detection means and a transient operation detection means are as follows.
The software is provided as shown in the flowcharts of FIGS. 4 to 6, respectively.

The program shown in the flowchart of FIG. 4 is executed at predetermined minute intervals and is used to feedback correct the actual air-fuel ratio to the stoichiometric air-fuel ratio (target air-fuel ratio). ) is set to increase or decrease by proportional-integral control.

First, step 1 (indicated as Sl in the figure).

The same applies hereafter) to read the output of the oxygen sensor 16, and in the next step 2, the manipulated variable in proportional integral control is based on the basic fuel injection ITp calculated from the intake air flow rate Q and the engine speed N and the engine speed N. A proportional component P and an integral component I are set.

In step 3, the output of the oxygen sensor 16 and the stoichiometric air-fuel ratio (
It is determined whether the air-fuel ratio of the intake air-fuel mixture is rich or lean with respect to the stoichiometric air-fuel ratio by comparing it with the slice level corresponding to the target air-fuel ratio.

Here, if it is determined that the fuel is rich, the process proceeds to step 4, and it is determined whether the flag PL for determining the first rich determination is 1 or not.

When PL is l, in normal control, the correction coefficient α is reduced by the proportional amount P immediately upon reversal from full to rich, but in this embodiment, such proportional control is performed in the next step 5. It is determined whether a timer tmR for delay control is zero.

As will be described later, the timer tmR is set during integral control in a lean air-fuel ratio state, and when the 1-hour timer tmR is not zero, the process proceeds to step 6, where the timer tmR is decreased by 1, and then step 25
Then, the operation to increase the correction coefficient α by integral control in the lean air-fuel ratio state is continued. In other words, even if the air-fuel ratio is reversed from lean to rich, proportional control is not performed immediately, but the lean air-fuel ratio is maintained until the timer tmR, in which a predetermined delay time is set, counts down to zero from the time of the air-fuel ratio reversal. This is to continue the increasing integral control of the correction coefficient α performed in .

After the air-fuel ratio is reversed to rich, the timer tmR measures the delay time and when the timer tmR reaches zero,
Proceeding to step 7, the PL for determining reversal to rich is reset to zero, and the PR for determining reversal to lean is set to 1.

In the next step 8, the proportional amount P is subtracted from the previous correction coefficient α, so that the fuel injection amount Ti is corrected to decrease by such proportional control.

In the next step 9, ΣαL is set to the sum of the manipulated variables (proportional component P and integral component I) when the correction coefficient α is controlled to decrease by proportional integral control, and the total manipulated variable during increasing control is set. difference from ΣαR (←ΣαL−Σα
By calculating R) and comparing this difference with a certain predetermined value (target value), it is possible to determine whether the air-fuel ratio is controlled to the lean side or to the lean side by controlling the increase/decrease of the fuel injection amount Ti using the correction coefficient α. Determine whether the

That is, for example, if ΣαL - ΣαR exceeds a predetermined value and Σα
When L is larger than the target, the decreasing control amount ΣαL of the correction coefficient α is larger than the increasing control amount ΣαR, which indicates that the balance of increase/decrease control is shifted in the decreasing direction, so in this case, the air-fuel ratio is controlled to the lean side.

Therefore, when it is determined in step 9 that ΣαL - ΣαR exceeds the predetermined value, it is necessary to increase the increase control amount of the correction coefficient α to correct it to the rich side. In order to increase the time to delay proportional control when reversing to
Adding a predetermined value to ratio, which is the ratio between mR and tm, L, is the time during which the control to increase the correction coefficient α by integral control is continued even after the delay time tmR is increased and the air-fuel ratio is reversed to rich. In this way, the increase operation amount ΣαR of the correction coefficient α is increased.

On the other hand, when it is determined in step 9 that ΣαL - ΣαR is less than the predetermined value, the increase/decrease operation amount of the correction coefficient α is large and the air-fuel ratio is controlled to the rich side. Since it is necessary to increase the reduction operation amount ΣαL of the correction integer α in order to balance the ratio r
Even after the air-fuel ratio is turned lean by subtracting a predetermined value from the atio, the control for reducing the correction coefficient α is continued for a longer time by integral control, and the operation amount ΣαL for reducing the correction coefficient α is increased. We aim to

In this way, when the delay time of the proportional control is set corresponding to each increase/decrease control so that the balance of the increase/decrease operation amount of the correction coefficient α becomes the target, in the next step 12,
The proportional operation amount P in step 8 this time is set to Σα[7, so that the sum of the reduction operation amounts of the correction coefficient α until the next proportional control is performed is set to ΣαL.

When proportional control is executed after a predetermined delay time tmR after the air-fuel ratio is reversed to the rich air-fuel ratio as described above, the next time it is determined that PL is not 1 in step 4, the process proceeds to step 13-''. The correction coefficient α is set to decrease by integral control, and in the next step 14, the current integral I is added to ΣαL, which sets the sum of the reduction operation amount of the correction coefficient α, and then, in step 12, the proportional The operating amount for decreasing the correction coefficient α until the hand P is set is set to ΣαL.Furthermore, the next step 1
In step 5, a timer tmL is set to a time for delaying proportional control when the current air-fuel ratio rich state is resolved and the air-fuel ratio is reversed to a lean air-fuel ratio.

The timer tmL has a total delay time t m (+
t mR + t mL), 1-rati.

The smaller the ratio, the longer the delay time is set in the timer tmL with respect to the sum Lm of delay times set according to the operating conditions. Furthermore, as will be described later, the timer mR is set to a delay time of t m The sum of the delay time tmL and the delay time tmL becomes the Lm determined based on the operating conditions.

On the other hand, when it is determined in step 3 that the air-fuel ratio is lean, the same control as in the rich determination is performed, and when it is determined that PR is 1 in step 16, the delay time of the proportional control is Until the timer tmL for measurement reaches zero, the timer tmL is decreased by l in step 18, and then the process proceeds to step 13, so that the decreasing integral control at the time of rich detection is continued. and,
When the timer LmL reaches zero, the proportional hand P is added to the correction coefficient α and updated, and then the total delay time tm is calculated based on the difference between the increase operation amount ΣαR and the decrease operation lid ΣαL of the correction coefficient α. Ratio ratio for dividing.

is controlled to increase or decrease so that the target is a balance between the increase operation amount ΣαR and the decrease operation amount ΣαL of the correction coefficient α.

When the neatness coefficient α is increased by proportional control, the proportional needle P is set to ΣαR, and the integral I, which is the manipulated variable of the increasing control by the integral control that follows, is integrated into this ΣαR, and the correction coefficient The sum of the increasing operation amount of α is the above Σ
Set it to αR.

In this way, if the delay time of the proportional control is set for each increase/decrease control based on the balance change between the increase operation amount ΣαR and the decrease control amount ΣαL of the correction coefficient α, as shown in FIG. Increase/decrease operation amount ΣαR and decrease control witΣα
Correction control can be performed so that L and L are in a predetermined balanced state,
Even if this slightly deteriorates the controllability to the stoichiometric air-fuel ratio, as shown in Figure 8, by delaying the proportional control, surge torque can be suppressed and the swing range of the air-fuel ratio around the stoichiometric air-fuel ratio can be increased. Therefore, the conversion efficiency of NOx, Co, and HC in the three-way catalyst 10 can be maintained in a good state due to the storage effect (see FIG. 9) due to the increase in the air-fuel ratio swing range.

In addition, since the total sum of delay control times tm is determined by the operating conditions, it is possible to respond to changes in the required delay time for each operating condition. It is possible to prevent variations in storage effect from occurring.

By the way, if the above-mentioned proportional control is delayed even during transient operation, as shown in Figure 10, the air-fuel ratio will change significantly from the stoichiometric air-fuel ratio even though air-fuel ratio fluctuations are already large during transient operation. Therefore, it is desirable to prohibit a delay in proportional control during a transient period, since this will make it impossible to maintain the conversion efficiency of harmful exhaust gas components in the three-way catalyst 10.

Prohibition of delay in proportional control during such transient operation is performed according to the program shown in the flowchart of FIG.

The program shown in the flowchart of FIG. 5 is executed at predetermined minute intervals. First, in step 31, the opening TVO of the throttle valve 4 is manually set, and in the next step 32, the opening TVO change amount during the program execution cycle is determined. Transient operation is determined based on whether ΔTVO is approximately zero.

Then, during a transient period when the opening degree of the throttle valve 4 is changing, a predetermined value is set in the transient discrimination timer Acc t+w in step 33, and the process proceeds to step 34. When the opening degree TVO of the throttle valve 4 is constant ( ΔTVOξO)
, jump to step 33 and proceed to step 34.

In step 34, it is determined whether or not the transient discrimination timer Acctm is zero, and if it is not zero, the timer Acctm is decreased by 1 in step 35, and then
In step 36, the total delay time tm is set to zero, and the delay times tmR and tmL are both set to zero so that no delay control is performed.

That is, within a predetermined period of time after the opening degree change of the throttle valve 4 has stopped, it is regarded as a transient operating state, and a delay in proportional control in such a transient operating state is prohibited.
In the steady operating state where the timer Acctn+ is zero, in step 37, the tm of the corresponding operating condition is searched and determined from the tm map set in advance using the basic fuel injection ITp and the engine rotational speed N as parameters. The total sum tm of delay times retrieved is divided into a delay time tmL during increasing proportional control of the correction coefficient α and a delay time tmR during decreasing proportional control.

The correction coefficient α, which is increased or decreased by the proportional-integral control as described above, is used for correction control of the basic fuel injection amount Tp in the fuel injection amount setting program shown in the flowchart of FIG.

The program shown in the flowchart of FIG. 6 is also executed at predetermined minute intervals, and first, the steering knob 41 performs basic fuel injection I based on the intake air flow rate Q and the engine rotational speed N.
Tp (-KxQ/NHK is a constant) is calculated.

Then, in the next step 42, the air-fuel ratio feedback correction coefficient α is set by the program shown in the flowchart of FIG. The basic fuel injection amount Tp is corrected by various correction coefficients C0EF, correction numerator s for correcting changes in the effective injection time of the fuel injection valve 6 due to battery voltage, etc., and the final fuel injection amount Ti(← 'rpxαXC0EF+T
Set S).

Here, the fuel injection amount (fuel supply amount) Ti, which is updated and set every predetermined minute time, is read out at a predetermined injection timing, and a drive pulse signal with a pulse width corresponding to the read fuel injection amount Ti is By being sent to the injection valve 6, the fuel injection valve 6 is driven open for a time corresponding to the fuel injection amount Ti, and the amount of fuel supplied to the engine is controlled.

By the way, in the above embodiment, the delay time t for delaying the proportional control is set such that the difference between the increasing manipulated variable ΣαR and the decreasing manipulated variable ΣαL of the air-fuel ratio feedback correction coefficient α becomes the target value.
mL, tmR ratio ratio.

However, if the magnitude of the integral operation M (integral ■) changes, it is necessary to change the target as shown in FIG. 11, and as shown in the program shown in the flowchart of FIG. , the increase operation amount ΣαR of the correction coefficient α
From the viewpoint of improving control accuracy, it is desirable to perform control so that the difference between ΣαL and the reduced manipulated variable becomes a target value corresponding to the integral manipulated variable.

The program shown in the flowchart of FIG. 12 increases or decreases the air-fuel ratio feedback correction coefficient α by proportional-integral control in the same way as the program shown in the flowchart of FIG. The explanation will focus on the different processing contents, and common symbols will be used to omit the explanation of the common processing contents.

The functions of the correction value proportional integral control means, operation amount sum detection means, delay time setting means, and proportional control delay means in the invention configuration shown in FIG. 2 are performed by software as shown in the flowchart of FIG. The fuel supply control means performs the same processing as the program shown in the flowchart of FIG. 6 above.

If the air-fuel ratio is in a rich determination state and PL is determined to be 1 in step 54, and proportional control has not yet been executed after switching to a rich air-fuel ratio, step 5
In step 5, it is determined whether or not the timer tmR for measuring the delay time of the proportional control is zero. If it is not zero, the timer LmR is decreased by 1 in step 56, and then the increasing integral control in the lean state is continued.

When the timer tmR reaches zero and the delay time has elapsed since the rich inversion of the air-fuel ratio, in step 58 the air-fuel ratio feedback correction coefficient α is set to be decreased by the proportional bone P, and in step 59 the correction coefficient α is reduced. The value of ΣαR in which the increased operation amount is integrated is set to mαR.

Then, in the next step 60, the difference between mαR and mα on which the value of the decreasing operation amount ΣαL was similarly set in step 81 is calculated as the average of the integral operation amount ΣI R/r when ΣαR is calculated. and the average ΣI L/l of the integral operation amount when calculating ΣαL, and the calculation result is set in X.

That is, the above-mentioned X is a value obtained by dividing the difference between the increasing operation amount 31mαR of the correction coefficient α and the decreasing operation amount mαL by the average of the integral operation amount, and by controlling the delay time so that such X becomes the target. , increase the manipulated variable Σα to the target according to the integral manipulated variable.
The difference between R and the reduction operation amount ΣαL is controlled.

Note that the reason why the average of the integral manipulated variables is determined as described above is that in integral control, the manipulated variables vary depending on the time.

After calculating X in step 60, in the next step 61, a weighted average value Xav of this X is calculated according to the following formula to suppress variations each time X is calculated.

After calculating the weighted average (1wXav) of the X in step 61, in the next step 62, this weighted average value Determine whether or not the

Here, when the increasing manipulated variable ΣαR in the proportional integral control is larger than the decreasing manipulated variable ΣαL and the air-fuel ratio tends to become lynching, where Xav is larger than the target value, step 6
Proceed to step 3 to determine the time period during which the increase control of the correction coefficient α by integral control is continued even after the rich inversion, that is, step 5.
The TMR for setting the time for delaying the reduction setting of the correction coefficient α by the proportional control in step 8 is decreased by 1, so that the time for delaying the proportional control for inverting to rich and then changing to lean is shortened.

Then, in the next step 64, it is determined whether the TMR as a result of the reduction setting in step 63 has become less than zero. When the TMR is set to decrease to less than zero, the TMR is set to zero in step 65, and
TML, which determines the time to delay the proportional control that enriches the air-fuel ratio when switching to lean, is increased by 1. In this way, when the air-fuel ratio tends to be controlled toward the rich side due to the manipulated variable balance of the correction coefficient On the contrary, by shortening the time during which the enrichment integral control is continued (by shortening the delay time of the lean proportional control), the tendency toward enrichment is suppressed in total.

On the other hand, when it is determined in step 62 that there is a lean trend, the delay time of the proportional control is adjusted in the opposite way to the above case, and the increase operation amount of the correction coefficient α is increased, so that the lean trend is achieved. Allow the trend to resolve (steps 66-68).

In the next step 69, the proportional bone P, which is the manipulated variable of the proportional control performed in step 58 in response to the rich reversal of the air-fuel ratio, is set to ΣαL, which samples the sum of the decreasing manipulated variables of the correction coefficient α, In the next step 70, ΣIR, which is a sample of the sum of the integral operation lids used during the increase control of the correction coefficient α, is reset to zero, and the ΣIR
r, which counted the number of samples of the integral manipulated variable integrated into
Reset to zero.

Then, in step 71, the TML set in steps 62 to 68 is set to a timer tmL that measures the delay time of the increase proportional control.

In this way, when the air-fuel ratio is reversed to a rich air-fuel ratio, the correction coefficient α is set to be decreased by proportional control, and in the subsequent rich air-fuel ratio state, the correction coefficient α is set to be gradually decreased by integral control.

That is, in step 72, the value obtained by multiplying the integral I set based on the operating conditions in step 52 by the latest fuel injection amount Ti is subtracted from the previous correction coefficient α, and in the next step 73, the correction coefficient α is subtracted from the previous correction coefficient α. In order to obtain the sum of the reduced manipulated variables of the coefficient α, lXTi used for the current integral control is added to ΣαL and updated.Furthermore, in the next step 74, only the integral manipulated variables of the decreased manipulated variables are integrated. In order to do this, ΣIL is updated by adding lXTi, which is the manipulated variable used in the current integral control. In addition, in step 75, l for counting the number of integrations of the integral operation amount in step 74 is set to 1.
Similarly, when increasing the correction coefficient α, the sum of the manipulated variables is sampled as ΣαR, and the sum of the integral manipulated variables among these manipulated variables is sampled as ΣIR (sampling number r ), and after a predetermined delay control, the correction coefficient α is increased by proportional control in step 80, and then step 82 is performed in the same manner as in step 60.
The difference between the increasing manipulated variable and the decreasing manipulated variable is divided by the average of the integral manipulated variables (Li!X is calculated, and then the next step 83
Then, the latest X is weighted averaged with the weighted average value Xav up to the previous time, and Xav is updated. Then, this Xav is compared with a constant target value to determine the deviation of the air-fuel ratio control point based on the balance of the increase/decrease operation amount of the correction coefficient α, and the delay time of the proportional control is set in a direction to eliminate this.

In the above embodiment, the air-fuel ratio feedback correction coefficient α
The delay time of the proportional control was determined so that the value X obtained by dividing the difference between the increasing manipulated variable ΣαR and the decreasing manipulated variable ΣαL by the average value of the integral manipulated variable becomes a constant target value. The delay time may be determined so that the difference between the increased manipulated variable ΣαR and the decreased manipulated variable ΣαL becomes a target value corrected by the integral manipulated variable.

In this way, according to this embodiment, the target difference between the increased manipulated variable ΣαR and decreased manipulated variable ΣαL to obtain the desired conversion efficiency changes depending on the difference in the integral manipulated variable, as shown in FIG. Since ΣαR−ΣαL can be adjusted to a target corresponding to a change in the integral operation amount, a delay time that can maintain the conversion efficiency of exhaust harmful components can be set even if the integral operation amount varies greatly depending on the operating conditions.

In this embodiment, the delay time is set so that the difference between the increasing manipulated variable ΣαR and the decreasing manipulated variable ΣαL of the air-fuel ratio feedback correction coefficient α becomes the target, so that the desired conversion efficiency can be maintained. , increasing manipulated variable ΣαR and decreasing manipulated variable Σα
It is clear that similar control can be performed based on the ratio of I.

<Effects of the Invention> As explained above, according to the present invention, even if the controllability to the stoichiometric air-fuel ratio deteriorates somewhat, the swing range of the air-fuel ratio can be increased while suppressing an increase in surge torque. Conversion efficiency in a three-way catalyst that purifies exhaust gas can be maintained by generating a storage effect. In addition, by setting the sum of the delay time of increasing proportional control and the delay time of decreasing proportional control according to operating conditions, surge torque performance and storage effect level can be adjusted according to changes in required delay time depending on operating conditions. can be made uniform. Furthermore, by prohibiting a delay in proportional control during transient operation, it is possible to prevent air-fuel ratio controllability during transient operation from deteriorating.

In addition, when controlling the air-fuel ratio feedback correction value to increase or decrease using proportional-integral control, even if the required balance between the increased and decreased manipulated variables changes due to changes in the integral manipulated variable, the increased and decreased manipulated variables By controlling the difference or ratio between the two to a target according to the integral operation amount, the conversion efficiency can be maintained with high accuracy even if the integral operation amount changes.

[Brief explanation of drawings]

FIGS. 1 and 2 are block diagrams showing the configuration of the present invention, FIG. 3 is a system schematic diagram showing an embodiment of the present invention, and FIGS. 4 to 6 show control details in the above embodiment, respectively. 7 is a diagram showing the control characteristics in the same embodiment as above; FIG. 8 is a diagram showing the relationship between the surge torque level and the air-fuel ratio swing; and FIG. 9 is a diagram showing the relationship between the surge torque level and the air-fuel ratio swing. A line diagram showing the relationship with conversion efficiency, Figure 10 is a time chart showing the effect of delaying proportional control during a transient period, and Figure 11 shows the target change in the balance of increase/decrease operation amount due to changes in the integral operation amount. FIG. 12 is a flowchart showing another embodiment of the air-fuel ratio feedback correction value setting control according to the present invention, and FIG. 13 is a diagram showing the relationship between the proportional operation amount and surge torque. 1... Engine 4... Throttle valve 6... Fuel injection valve 10... Three-way catalyst 12... Control unit 13... Air flow meter 1
4...Crank angle sensor 16...Oxygen sensor
17...Throttle sensor

Claims (6)

[Claims] (1) An air-fuel ratio detection means for detecting whether the air-fuel ratio of the engine intake air-fuel mixture is rich or lean with respect to the target air-fuel ratio, and an actual air-fuel ratio is detected based on the rich or lean air-fuel ratio detected by the air-fuel ratio detection means. a correction value setting means for increasing or decreasing an air-fuel ratio feedback correction value for feedback-correcting a fuel supply amount so as to approach a target air-fuel ratio based on a control operation including at least proportional control during rich/lean reversal; An air-fuel ratio feedback control device for an internal combustion engine, comprising: a fuel supply control means for correcting and controlling the amount of fuel supplied to the engine based on the air-fuel ratio feedback correction value determined by the correction value setting means; A total operation amount detection means for determining the sum of the increase operation amount and the sum of the decrease operation amount of the feedback correction value, and a ratio between the sum of the increase operation amount and the sum of the decrease operation amount determined by the operation amount sum detection means. or delay time setting means for variably setting a delay time for delaying the timing of proportional control of the air-fuel ratio feedback correction value by the correction value setting means on the increase operation side and the decrease operation side, respectively, based on the difference; and the delay time setting means. An air-fuel ratio feedback control device for an internal combustion engine, comprising: proportional control delay means for forcibly delaying the timing of the proportional control by the correction value setting means according to the delay time of the proportional control set by the means. . (2) a total delay time setting means for setting a total time of an increase operation side and a decrease operation side of the proportional control delay time variably set by the delay time setting means based on engine operating conditions; 2. The air-fuel ratio feedback control device for an internal combustion engine according to claim 1, wherein the means is configured to variably set a ratio at which the set total time is divided into an increasing operation side and a decreasing operation side. (3) A transient operation detection means for detecting a transient operation state of the engine, and a forced delay of proportional control by the proportional control delay means is prohibited when a transient operation state of the engine is detected by the transient operation detection means. 3. The air-fuel ratio feedback control device for an internal combustion engine according to claim 1, further comprising: a transient delay prohibition means for inhibiting a transition. (4) air-fuel ratio detection means for detecting the rich/lean air-fuel ratio of the engine intake air-fuel mixture with respect to the target air-fuel ratio; and an air-fuel ratio detection means for detecting the rich/lean air-fuel ratio detected by the air-fuel ratio detection means; correction value proportional-integral control means for increasing or decreasing an air-fuel ratio feedback correction value by proportional-integral control for feedback-correcting the fuel supply amount so as to bring it closer to the target air-fuel ratio; In an air-fuel ratio feedback control device for an internal combustion engine, the air-fuel ratio feedback control device includes: fuel supply control means for correcting and controlling the amount of fuel supplied to the engine; and a total operation amount detection means for calculating the sum of the operation amount and the sum of the decrease operation amount, respectively, and the difference between the sum of the increase operation amount and the sum of the decrease operation amount determined by the operation amount sum detection means is a target value corresponding to the integral operation amount. a delay time setting means for variably setting a delay time for delaying the timing of proportionally controlling the air-fuel ratio feedback correction value by the correction value proportional-integral control means on an increase operation side and a decrease operation side, respectively, so that the delay an air-fuel ratio of an internal combustion engine, comprising: proportional control delay means for forcibly delaying the timing of the proportional control by the correction value proportional integral control means according to the proportional control delay time set by the time setting means; Feedback control device. (5) The internal combustion engine according to claim 4, wherein the delay time setting means is configured to variably set the delay time using an average value obtained when the sum of the manipulated variables is calculated as the integral manipulated variable. Air-fuel ratio feedback control device. (6) The delay time setting means performs a weighted average of the difference between the sum of the increasing manipulated variables and the sum of the decreasing manipulated variables by the integral manipulated variable, and performs proportional control so that the weighted average result becomes the target value. 6. The air-fuel ratio feedback control device for an internal combustion engine according to claim 4, wherein the air-fuel ratio feedback control device for an internal combustion engine is configured to variably set the delay time.