JPS62247141A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the operating property of an engine, by providing an air-fuel ratio correction coefficient fixing means for fixing an air-fuel ratio correction coefficient when an acceleration-time quantity increase correction coefficient or a deceleration- time quantity decrease correction coefficient is not smaller than a prescribed value. CONSTITUTION:In the operation of an internal combustion engine A, the fed quantity of fuel is determined by a determination means B depending on the state of the operation and corrected by a correction means C to serve to control the fuel for the engine. An aimed air-fuel ratio is found out by a determination means E depending on the state of the operation of the engine. A correction coefficient is calculated by a calculation means F depending on the difference between the aimed air-fuel ratio and the actual air-fuel ratio detected by an air-fuel ratio detection means D, to correct the actual air-fuel ratio by the correction means C through the use of the correction coefficient. At the time of acceleration or deceleration of the engine A, the fed quantity of fuel is corrected through the use of an acceleration- time quantity increase correction coefficient or a deceleration-time quantity decrease correction coefficient set by a setting means G. At that time, if the acceleration-time quantity increase correction coefficient or the deceleration-time quantity decrease correction coefficient is not smaller than a prescribed value, the correction coefficient for the actual air-fuel ratio is fixed by a fixing means H.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an air-fuel ratio control device that controls the air-fuel ratio of an air-fuel mixture supplied into a cylinder of an internal combustion engine.

[Conventional technology]

BACKGROUND ART In recent years, in response to demands for measures against exhaust emissions, improvements in drivability, and fuel efficiency, particularly in internal combustion engines for automobiles, air-fuel ratio control is being performed to accurately control the air-fuel ratio of an air-fuel mixture supplied to a cylinder to a target value.

Therefore, for example, in the case of an internal combustion engine using an electronically controlled fuel injection device, the basic injection layer of fuel is determined based on the intake air temperature and engine speed, and various increase corrections are made depending on the engine state at that time. The actual air-fuel ratio is detected by detecting the oxygen concentration in the engine exhaust passage using a 02 sensor, etc., and the fuel injection amount is controlled by correcting the air-fuel ratio feedback correction coefficient according to the detection result. The air-fuel ratio is controlled to a target value (stoichiometric air-fuel ratio).

In addition, in the case of an internal combustion engine using an electronically controlled carburetor, the basic amount of fuel supplied per engine is determined by the carburetor itself, so the mixture ratio control solenoid installed inside the carburetor can be turned on and off. By controlling on/off the 89Ji correction amount, feedback control is performed to bring the air-fuel ratio into agreement with the target value.

However, in such conventional air-fuel ratio control devices, the stoichiometric air-fuel ratio is required when the engine (hereinafter also referred to as the "engine") is sufficiently warm, and because a three-way catalyst is generally used in the exhaust purification system. Highly accurate air-fuel ratio control using feedback control was performed only under limited operating conditions.

Therefore, during warm-up operation after starting from a cold state or during operating conditions in a high load range, feedback control (closed control) of the air-fuel ratio is not performed as described above, and the air-fuel ratio is stored in advance according to the engine temperature and load condition. Only open control was performed using various fuel increase correction coefficients, etc. 6 As a result, control accuracy deteriorated due to the characteristics of the engine itself, variations in the individual parts of the fuel supply system, or changes over time, causing problems during warm-up and In operating conditions in the high load range, ! Jl: There was a risk of deterioration in energy and drivability.

In addition, in order to achieve significant fuel efficiency, the air-fuel ratio (hereinafter also referred to as rA/FJ) must be adjusted to the stoichiometric air-fuel ratio (Δ/F =
14.7) It is effective to perform lean combustion in a larger lean range. It is necessary to accurately feedback control /F.

In order to solve such problems, for example, JP-A-60-1
As described in Publication No. 78942, an air-fuel ratio detection means (hereinafter also referred to as rA/F sensor) using an air-fuel ratio detection circuit using a new type of oxygen sensor detects the actual air-fuel ratio in the rich range (A/F sensor). In addition, it is possible to detect a wide range from the region where F is smaller than the stoichiometric air-fuel ratio to the region where F is smaller than the stoichiometric air-fuel ratio.

A target air-fuel ratio is determined according to the engine operating state, including an operating range in which the engine's required air-fuel ratio is in a rich range and a lean range, and the target air-fuel ratio matches the air-fuel ratio detected by the A/F sensor. Wide range of eyes 4111fA/F
The applicant has already developed an air-fuel ratio control device that performs feedback control on the air-fuel ratio.

[Problem that the invention seeks to solve]

However, during transient operation of an internal combustion engine, that is, during acceleration or deceleration, the proportion of wall flow in the fuel supplied into the cylinder increases. Sometimes the supply A/F and exhaust A/F (detected A/F) are different.
Moreover, since it is an unsteady phenomenon, there is a problem in that performing feedback control may instead cause adverse effects such as hunting of the A/F.

Therefore, in such a transient state, it is conceivable to stop A/F feedback control and switch to open control, but if feedback control is performed even when one engine is cold and the target A/F is rich, The acceleration increase or deceleration decrease in fuel is larger and takes longer than when the engine is hot.

In other words, especially when the engine is cold, the influence of the correction amount due to acceleration or deceleration becomes large, and there is a problem in that it is not possible to accurately obtain the conditions for stopping feedback control just by changing the throttle valve opening or intake air amount. .

This invention aims to solve such problems.

[Means for solving problems]

Therefore, the air-fuel ratio control device according to the present invention.

When the acceleration increase correction coefficient, which is calculated to correct the air-fuel ratio by increasing fuel during acceleration, or the deceleration reduction correction coefficient, which is calculated to correct the air-fuel ratio by reducing fuel during deceleration, is larger than a predetermined value. , a means for fixing the air-fuel ratio correction coefficient is provided, and its basic configuration is shown in a functional block diagram in FIG.

That is, the intake air amount Qa of the internal combustion 11 [WA, the rotation speed N
The fuel supply amount determined by the ffi fuel supply amount determination means B is corrected by the air-fuel ratio correction means C according to the iH transition layer state such as the cooling water temperature TV, etc., and the air-fuel mixture mixed with the intake air is converted into internal combustion. The air-fuel ratio detection means detects the air-fuel ratio of the mixture from the oxygen IJi in the exhaust gas, and the target air-fuel ratio determination means E determines the operating state of the engine (rotational speed N). The air-fuel ratio correction coefficient calculating means F calculates a correction coefficient α according to the difference from the target air-fuel ratio determined according to the load, cooling water temperature TW, etc.), and the air-fuel ratio correction means C
corrects the air-fuel ratio, and when accelerating or decelerating, the acceleration/deceleration correction coefficient setting means G sets the acceleration increase correction coefficient (KAC).
C) Or in an air-fuel ratio control device in which a deceleration reduction correction coefficient (KDEC) is set and the fuel supply amount is corrected accordingly, the acceleration increase correction coefficient or deceleration reduction correction coefficient set by the acceleration/deceleration correction coefficient setting means G. An air-fuel ratio correction coefficient fixing means (2) for fixing the air-fuel ratio correction coefficient α calculated by the air-fuel ratio correction coefficient calculation means F when the coefficient is equal to or greater than a predetermined value is provided.

[For production]

With this configuration, the condition for stopping the A/F feedback control is determined based on the acceleration increase correction coefficient or the deceleration decrease correction coefficient, and the air-fuel ratio correction coefficient is fixed, so that oven control is performed only for a necessary and sufficient period. By switching, it is possible to prevent deterioration of drivability.

〔Example〕

Embodiments of the present invention will be described below with reference to FIG. 2 and subsequent drawings.

FIG. 2 is a system configuration diagram of an internal combustion engine equipped with an air-fuel ratio control device according to the present invention.

In this system, 1 is an engine main body, and intake air is taken from an air cleaner 2 through an intake pipe 3 into a combustion chamber 1a of each cylinder. It mixes with the fuel injected from the air to form an air-fuel mixture.

Then, the ignition signal IA from the control unit 10
As a result, the spark plugs 5 provided for each cylinder operate sequentially at each ignition timing to combust the intake air-fuel mixture and drive the piston 6. Although an ignition circuit including an ignition coil is actually required, illustration thereof is omitted.

The exhaust gas after combustion is introduced into the catalytic converter 8 through the exhaust pipe 7, where the harmful components in the exhaust gas, such as CHC and C○, are removed.
, NOx) are purified by a three-way catalyst and discharged.

The amount of intake air is determined by the throttle valve inside the intake pipe 3.
The intake air flow rate Qa is detected by the air flow meter 11.

Further, the opening degree Cv of the throttle valve 9 is detected by the throttle valve opening degree sensor 12, and the pressure (intake negative pressure) inside the throttle valve S of the intake pipe 3 is detected by the pressure sensor 13.

Further, the engine speed N is detected by a pulse signal from the crank angle sensor 14, and the engine speed N is detected by the pulse signal from the crank angle sensor 14.
The temperature Tw of the cooling water flowing in h is detected by the water temperature sensor 15, and the oxygen concentration in the exhaust gas is detected by the oxygen sensor 16, respectively. In addition.

Specific examples of the oxygen sensor 16 and its A/F detection circuit will be described later.

A swirl valve 17 is provided near the injector 4 in the intake pipe B, and is driven to open and close by a drive valve 18 operated by negative pressure introduced through a solenoid valve controlled by a signal from the control unit 10. Ru.

This swirl valve 17 is, for example, JP-A-58-195
As seen in Publication No. 048, by closing the intake passage, the intake passage is narrowed to allow the helical boat to pass through, creating a swirl within the combustion chamber 1a and speeding up combustion. It is effective in extending the misfire limit in the engine and achieving stable combustion at lean air-fuel ratios.

Note that ■v is an intake valve, and EV is an exhaust valve, which are each provided for the combustion chamber 1a of each cylinder of the engine body 1.

In addition to controlling the air-fuel ratio according to the present invention, the control unit 10 also controls the ignition timing and the swirl valve. , based on their human power information.

It calculates the fuel injection 1 and ignition timing and outputs the injection signal St and ignition signal IA, and also outputs the control signal for the solenoid valve 1 to control the opening and closing of the swirl valve 17, and as a result, according to the operating state of the engine. This allows for optimal combustion.

This control unit 10 includes a CPU, ROJR
AM and input/output interface (A/D conversion circuit, 0/
A microcomputer (including A conversion circuit), etc., and an output driver circuit.

It is constituted by an air-fuel ratio detection port, etc., which will be described later.

Next, a specific example of the oxygen sensor 16 shown in FIG. 2 and the air-fuel ratio detection circuit that detects a wide range of A/F using the oxygen sensor 16 will be described.

First, the configuration of the oxygen sensor 16 used in this embodiment will be explained with reference to FIG. 3. An air introduction plate 22 having a channel-shaped air introduction part 23 formed thereon is laminated on a substrate 20 on which a heater 21 is provided. A plate-shaped solid electrolyte 24 having oxygen ion conductivity is laminated thereon, and this solid electrolyte 24
A reference electrode 25 is provided on the lower surface, and a pump electrode Fi 26 and a sensor W1 pole 27 are provided on the corresponding upper surface by printing.

Furthermore, on top of this solid electrolyte 24, a plate-shaped body 2 is formed in which a gas introduction part 2 for introducing a constant gas (exhaust gas) is formed into a window shape.
8 are laminated, and a plate-like body 30 having small holes 31 for regulating gas diffusion is laminated thereon.

In addition, the substrate 20. Atmospheric introduction plate 22. and plate-like body 28.
30 is formed of a heat-resistant insulating material such as alumina or mullite, or a heat-resistant alloy. solid electrolyte 24
Examples include ZrO2, Hr02, which are oxygen ion conductors.
, Th02, B 1203 and other oxides with Ca20.
A sintered body containing MgO+Y203+VB203 or the like as a solid solution is used.

Each of the electrodes 25 to 27 has platinum or gold as a main component.

And pump electric f! The i26 and the reference W1 electrode 25 constitute an electrode for flowing a current that causes the movement of oxygen ions in the solid electrolyte 24 and keeps the oxygen partial pressure ratio between the upper and lower surfaces constant, and the sensor electrode 27 and the reference electrode 25, solid electrolyte 24
It constitutes an electrode for detecting the voltage generated by the oxygen partial pressure ratio between both sides of the electrode.

As shown in FIG. 4, the air-fuel ratio detection circuit 40 that detects the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber using the oxygen sensor 16 operates at a voltage +1[ which generates the target voltage Va (negative voltage)]. 41, differential amplifier 42. Pump current supply section 43.
It is composed of a resistor 44 and a current detection section 45 that detects the pump current Ip from the voltage across the resistor 44.

Then, the differential amplifier 42 compares the potential Vs (negative voltage) of the sensor electrode 27 with respect to the reference electrode 25 of the oxygen sensor 16 mentioned above with the target voltage Va, and the difference ΔV s =
Calculate V s −V a.

The pump current supply section 43 receives the output Δ of this differential amplifier 42.
The oxygen sensor 16 pump [1
Pump i11 from 126! Pour out (or pour in) the current Ip. That is, when ΔVs is positive, IP is increased, and when ΔVs is negative, rp is decreased.

The pump current detection section 45 converts the pump current 1p into a voltage Vi (Vi-Ip) based on the potential difference between both ends of the resistor 44, and detects the voltage Vi (Vi-Ip). Note that the pump current Ip is positive in the direction shown by the solid arrow in FIG. 4, and the detected voltage Vi also becomes positive at that time.
In the opposite direction indicated by the dashed arrow, it becomes negative.

The target voltage Va is set between the reference electrode 25 and the sensor when the oxygen concentration within the gas introduction part of the oxygen sensor 16 is maintained at a predetermined value within two days, that is, when the oxygen partial pressure ratio between both surfaces of the solid electrolyte 24 is a predetermined value. The voltage V generated between the electrodes 27
When set to a value corresponding to s, the pump current Tp detected by the air-fuel ratio detection circuit 40 uniquely corresponds to the A/F as shown in FIG.

Therefore, with this circuit, it is possible to accurately detect the cursed air-fuel ratio over a wide range from the rich region to the lean region.

FIG. 6 shows the correspondence between KMR and IP, which will be described later, and which has a reciprocal relationship with A/F.

Note that the air-fuel ratio detection means used in the present invention is not limited to this, and any means that can accurately detect A/F over a wide range from rich to lean ranges may be used. Already known.

Most of the functions of the air-fuel ratio control system according to the present invention are performed by the control unit 10 shown in FIG.

In particular, the functions of each means B, C, and E-H in FIG. 1 are performed by a built-in microcomputer.

In general, the optimum air-fuel ratio for operating an engine varies depending on the specifications of the engine itself as well as the operating conditions including the warm-up condition and load condition of the engine.

An example of the required air-fuel ratio of the engine in a steady state is shown in FIGS. 7 and 8.

The area shown in Figure 7 is the area that is frequently used, including general city driving, and when a three-way catalyst is used in the exhaust purification system, the A/F should be around the stoichiometric air-fuel ratio of approximately 14.7. ,
If an oxidation catalyst is used, leaner air/fuel ratios are generally better.

Region @ is a high-speed, high-load region, and may be operated at the same air-fuel ratio as in region O, but from the perspective of improving fuel efficiency, it is desirable to operate at a leaner region (A/F 20 to 23) than the stoichiometric air-fuel ratio.

Region ■ is a high load fully open range, and it is desirable to operate at a rich air-fuel ratio (rich range; Δ/1710 to 13) in order to obtain high output and to obtain a cooling effect that prevents engine damage due to increased exhaust temperature. .

FIG. 8 shows the relationship between the load on the A-n line shown by the one-point ti line in FIG. 7 and the required air-fuel ratio. As can be seen from this figure, the required air-fuel ratio of the engine is not constant even in a steady state.

FIG. 9 is an example of the required air-fuel ratio during steady no-load conditions when the engine is in a warm-up state. In this figure, the engine cooling water temperature is taken as a parameter for the warm-up state of the engine, and the required air-fuel ratio depending on that and the engine rotation speed is shown.

As is clear from this figure, the lower the engine cooling water temperature and the lower the engine speed, the richer the air-fuel ratio is required.

In this way, the required air-fuel ratio of the engine is determined by the engine rotation speed (rotation speed N) and the load condition (which can be detected by the intake air flow ff1Qa or the intake negative pressure Pv).

Since it differs depending on the cooling water temperature Tw indicating the warm-up state, the target air-fuel ratio (hereinafter referred to as TL) is also calculated and determined based on this input information.

Next, the determination of fuel supply amount and the air-fuel ratio correction function will be explained.

The amount of fuel supplied is determined by the pulse width of the injection signal Si that drives the injector 4 shown in FIG.

This pulse width Ti is calculated and determined by the following equation.

T i =QAXKMRXCOFFXα+TsQA is 1
This is the intake air amount per cylinder, which is calculated from the detection signal Qa from the air flow meter 11 in FIG. 2 and the engine rotation speed N in a steady state of operation.

Corrections based on intake temperature, etc. are added. In addition, during a transient period, the output CV of the throttle valve opening sensor 12 and the pressure sensor 1
It is corrected by the output Pv of 0.

KMR is a coefficient corresponding to the reciprocal of the engine's required air-fuel ratio, and like the target air-fuel ratio T L, is calculated based on the engine speed N, the load state, and the cooling water temperature Tw.

C0EF is a fuel correction coefficient during transient times, and is determined by fuel vaporization, wall flow rate, etc., but specifically, it is determined by the magnitude of acceleration/deceleration, warm-up state (cooling water temperature Tw), operating state, and immediately after startup. It is calculated based on whether or not.

Here, if the increase correction coefficient during acceleration is KACC and the reduction correction coefficient during deceleration is KDEC, then the following results are obtained.

C0EF= (1+KAcc-KDEC) this KACC
and KDEC are also described in Japanese Patent Application Laid-Open No. 58-144642, for example, in Fig. 10 (A,),
As shown in (B) and (C), the on/off of the idle switch (the switch that is on when the accelerator is released and turns off when the pedal is depressed), the rate of change of the throttle valve opening Cv, and the intake pipe pressure Pv It is set as shown by the thick line in FIG. 2(D) depending on the rate of change, and is further modified based on the cooling water temperature Tw.

Alternatively, the initial value of KACC is set to a value corresponding to the cooling water temperature Tw at the time of acceleration judgment, and then, for example, every two revolutions, a new KACC is set by multiplying by a predetermined coefficient β according to the cooling water temperature Tw.
There is also a method of using CC. This can be expressed as an equation as follows.

KACCφ=f (Tw) (φ indicates the initial value) KA
CCn=KACCn-1Xβ (calculated every 2 rotations) 1/2; Tw>70" β= 3/4; 20°<Tw<70'7/
8: Tw<20@Kn) Similarly, for EC, an initial value corresponding to the cooling water temperature Tw is set for deceleration judgment, and then calculated using the following formula.

KDECφ=f (Tw) KDECn=KDECn + Xβ (calculated every 2 rotations) β is the same as the coefficient for calculating KACCn above α is the actual A/F detected by the oxygen sensor 16 and A/F detection circuit 40 described above It is a correction coefficient when performing feedback control so that (sensor output ip) becomes the target air-fuel ratio TL, and is calculated by a linear equation.

α;α′±KpXDip α′=α′(Previous@)±KiXDip (+: When there is a lean shift, -: When there is a rich shift) Dip=l Ip-TLI KP: Proportional capture positive constant Ki : Integral correction constant In this embodiment, this constant Kp (p minute).

As shown in Fig. 11, Ki (i minute) is set to a different value depending on whether the target air-fuel ratio TL is lean, switch, or rich, and whether the target air-fuel ratio TL is deviated to the lean side (lean) or rich side with respect to TL. It is also set to a different value depending on whether there is a deviation (rich deviation).

In Fig. 11, the third character L after Kp and Ki is off by one inch, R is the rich deviation, and the fourth character is S.

R indicates lean, stoichiometric, and rich.

Here, the relationship between the magnitudes of these constants is as follows.

KpLR<KpLS<KpLL K i LR<K i LS<K i LLK p R
R< K p RS < K p RLK i RR<
K i R3<, K i R[, KpRL<KpLL
KpR5<KpLSK p RR<K p L
L K i RL<K i L L K i R3<K
i LSK i RR<K i LR That is, when TL is in the rich range, Kp and Ki are smaller than when it is in the lean range, and in the case of rich deviation, they are made smaller than in the case of lean deviation.

Note that Ts in the formula for determining Ti is the invalid pulse width.

Next, in the control unit 10 of FIG.
The F control operation will be explained with reference to the flowcharts shown in FIGS. 12 and 13.

When the A/F feedback control routine shown in Fig. 12 starts, first in step 1 it is determined whether the feedback control system is malfunctioning, that is, whether the A/F feedback control is being performed normally. .

If there is a failure, another routine, for example, a routine that checks if the oxygen sensor heater is disconnected, sets the failure flag FABN (-1'').

Therefore, if FABN=1 in step 1, it is determined that the feedback control system is malfunctioning, and the following processing related to feedback control is not performed and step 18
Step 20, clamp (fix) the air-fuel ratio correction coefficient α for λ control (in this example, also the correction coefficient α′ based on the integral constant described later) to 100%, and turn the close/open flag FCO to O in step 20. " to return to the main routine. In other words, switch to open control.

This flag FC○ is a flag indicating whether feedback control or oven control is being performed, and "summer" indicates the feedback control state, and "0" indicates the oven control state.

If FABN=1 in step 1, it is determined that the feedback control system is normal and the process proceeds to step 2. Here, the target value T L of A/F is calculated. As described above, this is calculated according to the operating state of the engine (rotational speed, load, cooling water temperature).

Next, in step 3, the output rp of the air-fuel ratio detection circuit described above is
Load. Then, in step 4, TL and delay are performed. This is because the air-fuel ratio is detected on the exhaust side, so there is a time delay in detection from the time the fuel is injected until it burns and the exhaust comes out, so the target value TL calculated at that point This is because the control result will appear after the above-mentioned time, so the target value is delayed by that time.

Next, in step 5, it is determined whether Tp is turned off.

This is because, for example, if the heater of the oxygen sensor is not sufficiently warmed up immediately after startup, the Ip from the air-fuel ratio detection circuit will not flow, so the actual air-fuel ratio cannot be detected at that time. Proceed to , and clamp α and α' to 100%.

If IP is flowing, then it is determined in step 6 whether the engine cooling water temperature is 130°C or less. and 2-30℃
In the following case, that is, when it is very cold, the fuel combustion is not very good and the error becomes large, so proceed to step 18 as well.

Clamp α' to 100% and switch to open control.

If it is not below -30°C in step 6, then in step 7.8, the acceleration increase correction coefficient KACC of the fuel injection amount is greater than the predetermined value, or the deceleration decrease correction coefficient KDE
It is determined whether C is thicker than a predetermined value B, and when either is larger than A or B, or A and +3 may be "0", when KACC or KDEC is present, α and α' are clamped (fixed). )do.

This is the function of the air-fuel ratio correction coefficient fixing means according to the present invention.

Furthermore, in step 9, it is determined whether or not the fuel is cut off, and α, α'
to clamp.

However, clamping in these cases does not necessarily mean that α and α' are clamped to 100%, and the manner of clamping differs depending on whether or not the A/F feedback control was in a steady state at that time.

In other words, if YES in any of steps 7, 8, and 9, the process proceeds to step 9, where the count value of the steady state counter C3TD corresponds to the time required to reach a steady state after feedback control is started. It is determined whether or not the value is larger than a set value X. If it is larger, it has converged to a steady state, so the close/open flag FOC is set to 0 in step 2o and the process returns to the main routine to perform open control.

Here, doing nothing means that the previously calculated α,
Since α′ is clamped as is, for example, α
=l] If it has converged at 0%, keep that 110% as it is.

If the count value of counter C3TD has not reached the set value
Open control will be performed by clamping to %.

On the other hand, if NO in any of steps 7, 8, and 9, feedback control will be performed.

First, in step 10, the close/open flag FCO is checked, and if Fco=t, it means that the previous time was also in the feedback control state, so steps 11 and 12 are skipped and the process proceeds to step 13.

If FCO=0, the previous time was in oven control state,
Since feedback control will be newly performed from now on, the counter C3TD mentioned above is cleared to the initial state in step 11, and the flag FCO is set to 1" in step 12.
(indicating the feedback control state), the process proceeds to step 13.

In step 13, it is checked whether the count value of the counter C3TD is larger than the set value X.

If it is larger, skip step 14 and proceed to step 15; if it is not larger, counter C3TD is incremented in step 14.

Then, in step 15, it is determined whether there is an abnormality in ip, that is, the output voltage Vi corresponding to rp of the air-fuel ratio detection circuit
Check whether it is Ov or 5V (power supply voltage).

Next, in step 16, v! Determine whether I is abnormal. This Vs is the output voltage from the sensor electrode of the oxygen sensor 16, and it is determined whether this voltage is constant at a predetermined value, for example, 0.4V.

Then, in step 17, to calculate αTV, α
In the TW, it is necessary to change the integral of the air-fuel ratio correction coefficient α or the constant of the proportional bone depending on the engine cooling water temperature, so this water temperature correction coefficient is calculated.

That is, when the water temperature is low, the change is slow, so if the feedback speed is increased too much, hunting may occur.

After that, the process advances to the flow shown in FIG.

First, in steps 21 and 22, the A/F target value TL calculated in step 2 is compared with two slice levels (reference values) and distributed into three types of constant sets.

TLI- is the reference value of the A/F target value during lean control, and in step 2I, [I target value T L is larger than TLL, it is lean control, so the process goes to step 23; if it is not larger, it is rich control. Since it is stoichiometric (stoichiometric air-fuel ratio) control, the process advances to step 22.

T1. R is the reference value of the A/F target value during rich control, and in step 22, if the target value Tt is smaller than Tr, R, the control is rich, so the process goes to step 24; if it is not, it is the stoichiometric control, so the process goes to step 25. move on.

In steps 23 to 25, different A/F control constants (integral correction constants and proportional compensation constants for rich deviation and lean deviation) are determined according to each of these control states, as shown in FIG. ).

Proceed to the next step 26, n i P= T p−T
Calculate l-. In other words, the actual value (detected value) of A/F
The difference between the target value and the target value is taken as DiP.

Then, in step 27, it is determined whether DiP is greater than 0. If DiP is greater than 0, the actual value is greater than the target value, indicating lean deviation (hereinafter referred to as "lean deviation"), and D
If iP is smaller than O, the actual value is smaller than the target value, so it is determined that there is a rich deviation (hereinafter referred to as "rich deviation"), and in the case of a rich deviation, the process proceeds to steps 28 to 36, and in the case of a linear deviation If Dir=O (actual value and target value match), the process proceeds to steps 32-37.

In step 28, the product obtained by multiplying the absolute value DiP of DiP (DiP in this case is a negative value) by αTW by the water temperature correction coefficient calculated in step 17 is newly registered as DiP.

Next, in step 29, the rich/lean flag FRL is set to 1.
This flag FRL is a flag indicating whether the previous time was a lean deviation or a true deviation. 1" indicates a lean deviation and 0 indicates a rich deviation. Therefore, in step 29, FRL=1. If there is, it was lean last time and has changed to rich this time, so in step 30, turn off the green ■, ED, and step 3
1 sets the flag FRL to 0".

The green LED is provided in the control unit, and blinks during A/F λ control.
This is to display the operating status of the light (lights up when it is out of rich and turns off when it is out of lean).

If FRL= ] in step 29, the process skips steps 30 and 31 and proceeds to step 36 since there was a rich shift last time as well.

On the other hand, in the case of lean deviation, in step 32 DiP (
In this case, DiP is a positive value) multiplied by the water temperature correction coefficient KaTW and registered as a new DiP, and step 3
At step 3, it is determined whether the rich/lean flag FRL is 1''.

If it is not 1", then it was rich last time and has changed to lean this time, so in step 34 the green LED is turned on and in step 35 the flag FRL is set to 1".

If FRr,=1 in step 33, there was a lean shift last time as well, so steps 34 and 35 are skipped and the process proceeds to step 37.

In steps 36 and 37, correction coefficients α' and α are calculated using the constants set in steps 23 to 25. α is the final air-fuel ratio correction coefficient, and α' is the integral calculated. Therefore, in order to eliminate steady-state deviations, integration is performed and α' is updated and held.

In step 36, α' and α in the case of rich deviation are calculated, and this α' is the previous α' and the integral correction constant K for rich deviation set in any of steps 23 to 25.
It is calculated from the iR and the DiP registered in step 28 using the following formula.

α′=α′ (previous time) −KiRXDiP Then, α is the value of α′, the proportional total correction constant KpR for rich deviation set in any of steps 23 to 25, and the above Di
It is calculated by the following formula using P.

α=α'-KpRXDiP In this case, since the deviation is rich, α must be made small, so KiRXDiP is calculated from α'.

KpRXDiP is respectively decreased.

In step 37, α' and α in the case of lean deviation are similarly calculated using the following equations.

α′=α′ (previous time) +K i LXD i Pα=
α' + KpL It is.

Finally, the calculated air-fuel ratio correction coefficient α is limited between 75% and 125%, and the process returns to the main routine, where the fuel injection pulse width Ti is calculated and feedback control is performed.

〔Effect of the invention〕

As explained above, the air-fuel ratio control device for an internal combustion engine according to the present invention has mr! According to the acceleration increase correction coefficient (KACC) that is set to increase the fuel supply amount during acceleration of A and the deceleration reduction correction coefficient that is set to decrease the fuel supply amount during deceleration.

Determine the conditions for stopping A/F feedback control.

By fixing the air-fuel ratio correction coefficient, it is possible to switch to oven control only for a necessary and sufficient period of time, thereby preventing deterioration in drivability.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram showing the basic configuration of an air-fuel ratio control device for an internal combustion engine according to the present invention, and FIG. 2 is a system configuration diagram of an internal combustion engine showing an embodiment of the present invention. 3 and 4 are schematic sectional views and block circuit diagrams showing examples of an oxygen sensor and an air-fuel ratio detection circuit used to carry out the present invention, and FIGS. 5 and 6 show a wide range of A/F detection circuits.
FIG. 2 is a curve diagram showing general characteristics of an A/F sensor that can detect F. 7 and 8 are explanatory diagrams showing an example of the required air-fuel ratio of the engine in a steady state; FIG. 9 is a three-dimensional map diagram showing an example of the required air-fuel ratio in a steady no-load state when the engine is warmed up; Fig. 10 is a signal waveform diagram for explaining how to obtain the acceleration increase correction coefficient and deceleration reduction correction coefficient, and Fig. 11 shows the feedback control constants for lean deviation and rich deviation depending on the target air-fuel ratio region. 12 and 13 are flowcharts showing the air-fuel ratio control operation in the control unit of FIG. 2. 1...Engine body 2...Air cleaner 3
...Intake pipe 4...Injector 5.
... Spark plug 7 ... Exhaust pipe 8 ... Catalytic converter S ... Throttle valve 10 ... Control unit 11 ... Air flow meter 12 ... Throttle valve opening sensor 13 ... Pressure sensor 14 ... Crank angle sensor 15 ... Water temperature sensor 16 ... Oxygen sensor 17 ... Swirl valve 40 ... Air-fuel ratio detection circuit

Claims (1)

[Claims] 1 Calculate an air-fuel ratio correction coefficient according to the difference between the target air-fuel ratio determined according to the operating state of the internal combustion engine and the actual air-fuel ratio detected by the air-fuel ratio detection means, and use the air-fuel ratio correction coefficient to adjust the internal combustion engine. The system corrects the air-fuel ratio of the air-fuel mixture supplied into the cylinders, performs feedback control so that the actual air-fuel ratio matches the target air-fuel ratio, and sets an acceleration increase correction coefficient during acceleration and a deceleration reduction correction coefficient during deceleration. In the air-fuel ratio control device, the air-fuel ratio correction coefficient is fixed by fixing the air-fuel ratio correction coefficient when the acceleration increase correction coefficient or the deceleration reduction correction coefficient is equal to or greater than a predetermined value. An air-fuel ratio control device for an internal combustion engine, characterized in that: