JPS60198346A - Air/fuel ratio control method for internal-combustion engine - Google Patents

Abstract

PURPOSE:To prevent shifting of the air/fuel ratio from the target level under lean control by increasing/decreasing the lean learning level such that the average level of the feedback correction factor will be within predetermined range during feedback control of air/fuel ratio while turning off EGR. CONSTITUTION:In such air/fuel ratio control method where a fuel injection valve 8 is controlled through a control circuit 54 such that the air/fuel ratio is maintained at the target level while employing the air/fuel ratio feedback correction factor to be determined on the basis of the output signal from O2 sensor 44, EGR controller 76 is functioned under specific operational conditions during feedback control thus to recirculate a portion of exhaust gas. If EGR is not performed under feedback control, the lean learning level is increased/decreased such that the average level of said correction factor will be within predetermined range. Under normal operation, said feedback control is stopped and it is controlled such that the air/fuel ratio will be leaner than the target level on the basis of said lean learning level.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an air-fuel ratio control method for an internal combustion engine, and in particular to EGR control for recirculating exhaust gas to the intake system and controlling the air-fuel ratio to be leaner than the stoichiometric air-fuel ratio. The present invention relates to an air-fuel ratio control method for an internal combustion engine that performs control.

(Background of the Invention) Conventionally, a three-way catalyst has been used to simultaneously purify carbon monoxide, hydrocarbons, and nitrogen oxides in exhaust gas, and it is necessary to improve the purification rate of this three-way melting medium. Feedback control is performed to estimate the air-fuel ratio by detecting the residual oxygen concentration in the exhaust gas using a sensor, and to control the air-fuel ratio to near the stoichiometric nitrogen-fuel ratio.In performing this feedback control, engine load (intake pipe pressure The fuel injection time is proportionally integrated based on the air-fuel ratio signal output from the 02 sensor and signal-processed at the basic fuel injection time TP determined by PM or intake air amount per engine rotation (Q/NE) and engine speed. The fuel injection time TAL+ is determined by multiplying the air-fuel ratio feedback correction coefficient FAF shown in FIG. The air-fuel ratio is controlled to be near the same level.However, due to environmental changes and changes over time, changes in pulp timing due to changes in the tappet flance, changes in the characteristics of the pressure sensor and air meter, etc.
Changes in the characteristics of the fuel injection valve may occur, making it impossible to control the fuel injection amount to the engine's required fuel injection amount, and making it impossible to control the air-fuel ratio to near the stoichiometric air-fuel ratio. For this reason, air-fuel ratio learning control is performed to control the air-fuel ratio so that it is always near the stoichiometric air-fuel ratio.

Additionally, from the perspective of lowering the fuel ratio, feedback control is stopped during steady operation at low to medium loads and feedforward control is performed to make the air-fuel ratio leaner than the stoichiometric air-fuel ratio. .

The above air-fuel ratio learning control and lean control are as follows (1
) The fuel injection time TAU is calculated based on the formula and a predetermined amount of fuel is injected.

TAU= (TP+'l'AUG) (1+KG),
FAF, FLEAN.

F(t)-1-τ1...(1) However, TAUG is the learned value when the intake throttle valve is in the idle position, KG is the learned value when the intake throttle valve is not in the idle position, and F(t) ) is a correction coefficient such as a warm-up increase coefficient and a start-up increase coefficient, FLEAN is a slope correction coefficient of 1 or less, τ11
is the invalid injection time of the voltage compensated reservoir. In addition, the learning value KG is determined by the engine load. For example, when the intake pipe pressure is 200 to 300 mmHt, KGI, 3
00~400mn1H5'K G2.400~5
0-mmI (KG3 is adopted when t.

These learning values TAUG, KG (KG, , KG2, K
G3) is learned by the following method according to the state of the intake throttle valve and engine load every time the correction coefficient FAF skips when the engine cooling water temperature exceeds a predetermined value (e.g. 80°C) during air-fuel ratio feedback control. be done. First, every time the air-fuel ratio feedback correction coefficient FAF skips, the arithmetic average value F A F of the maximum and minimum values of the correction coefficient FAF is calculated.
When the average value FAFAVO value falls outside a predetermined range (for example, ±2%), the learned values TAUG and KG are increased or decreased by a predetermined value by learning. That is,
When the average value FAFAV exceeds 1.02, the learned value TA
UG and KG are increased by a predetermined value, and the average values F and AFAV are 0.
．． When the value becomes less than 98, the learned value T AUG.

Decrease KG by a predetermined value.

And the learning value TAUG learned as described above.

KG is applied to the above equation (1) depending on the opening/closing state of the intake throttle valve and the magnitude of the intake pipe pressure (or the amount of intake air per engine revolution), and the fuel injection time TAU is determined.

As a result, when the average value FAFAV exceeds 1.02, the learned value is increased and the air-fuel ratio is controlled to the rich side.
When the average value FAFAV is less than 0.98, the learned value is reduced and the air-fuel ratio is controlled to the lean side, and the average value FAF
Learning control is performed so that AV approaches 1, that is, the stoichiometric air-fuel ratio.

In addition, the lean correction coefficient FLEAN is set to a value of 1 or less based on the intake pipe pressure (or the amount of intake air per engine revolution) or the intake pipe pressure and the engine speed, and it depends on the engine operating state under specified conditions. By applying the lean correction coefficient FLEAN to the equation (1) above, the fuel injection amount is reduced and lean control is performed. Incidentally, when the lean control execution conditions are not satisfied, the lean control is stopped by setting the value of the lean correction coefficient FLEAN to 1.

In order to further improve fuel efficiency in the air-fuel ratio control method described above, it is possible to introduce EGR, but if EGR is introduced even during air-fuel ratio lean control, misfires are likely to occur, combustion deteriorates, and torque decreases. As the torque decreases, the throttle valve is opened and the fuel injection amount is increased to compensate for the low torque, which actually worsens fuel efficiency. Therefore, it is necessary to introduce EGR only during air-fuel ratio feedback control, but since the fuel injection amount during lean control is calculated based on the learned value that is corrected during feedback control, this learned value is If the value is corrected when an error occurs, a problem arises in that the air-fuel ratio during lean control in which EGR is not introduced cannot be controlled to the target air-fuel ratio. In other words, due to changes over time, carbon, etc. in the exhaust gas may adhere to the valve seat of the EGR valve, making the EGR passage narrower and reducing EGR3l. When the amount of EGR decreases, the learned value is corrected to become smaller. . Since lean control is performed using the learning value corrected in this way, the air-fuel ratio during lean control deviates from the target.

OBJECT OF THE INVENTION The present invention has been made to solve the above problems, and is
An object of the present invention is to provide an air-fuel ratio control method for an internal combustion engine that further improves fuel efficiency by introducing EGR and prevents the air-fuel ratio during lean control from deviating from the target by introducing EGR.

[Summary of the invention]

In order to achieve the above object, the present invention provides an internal combustion engine that performs feedback control so that the air-fuel ratio becomes a target air-fuel ratio using an air-fuel ratio feedback correction coefficient determined based on the output of an 02 sensor that detects the residual oxygen concentration in exhaust gas. In an engine air-fuel ratio control method, exhaust gas is recirculated to the intake system under specific operating conditions during feedback control, and when feedback control is in progress and exhaust gas is not recirculated, the air-fuel ratio feedback correction coefficient is The lean learning value is increased or decreased so that the average value of It is characterized by being controlled so that

〔Effect of the invention〕

According to the present invention, the air-fuel ratio during lean control is prevented from deviating from the target based on the lean learning value that is corrected when EGi is not introduced, and fuel efficiency is further improved. is obtained.

[Embodiments of the invention]

Figure 2 shows an internal combustion engine to which the present invention is applied.
Give an example. This engine is a so-called single-point injector type engine that determines the basic fuel injection time based on intake pipe pressure and engine speed, and is equipped with one fuel injection valve that supplies fuel to each cylinder.

Air cleaner 2 is connected to throttle body 6 via inlet pipe 4. One fuel injection valve 8 is installed on the upstream side of the throttle body 6, and on the downstream side of the fuel injection valve 8, there is an intake valve that adjusts the amount of air-fuel mixture sucked into the combustion chamber of the engine in conjunction with the accelerator pedal. A throttle valve 10 is arranged. The intake throttle valve 10 includes an idle switch 12 that is turned on when the intake throttle valve is in the idle position (fully closed), a throttle sensor 15 that detects the opening of the intake throttle valve, and a power switch 17 that is turned on when the intake throttle valve is opened. is installed. Further, on the downstream side of the intake throttle valve 10, there is a pressure sensor 14 for detecting the absolute pressure of the intake pipe.
is installed.

The throttle body 6 is connected to an intake manifold 16 having branch pipes connected to each cylinder of the engine, and the intake manifold 16 includes an intake temperature sensor 18 that measures the intake air temperature from the temperature of the air-fuel mixture passing through the intake manifold. is installed. The upstream bottom portion 16a of the intake manifold 16 is provided with a riser portion 20 through which engine cooling water is circulated to heat the air-fuel mixture.

Reference numeral 22 designates a well-known engine body, in which a combustion guide 28 is formed between the bottom surface of the piston 24 and the inner wall of the cylinder 26, and the air-fuel mixture taken in at 7/pL is connected to the intake valve 30 by the spark plug. It is ignited by 32. A water jacket 34 is formed around the cylinder 26, and engine cooling water is circulated through the water jacket 34 to cool the cylinder 26 and the like. And cylinder block 3
6 houses an engine coolant temperature sensor 38 that detects the temperature of the engine coolant in the water jacket 34.

An exhaust manifold 42 is connected to an exhaust boat (not shown) of the cylinder head 40, and an 02 sensor 44 for detecting the residual oxygen concentration in exhaust gas is attached downstream of the exhaust manifold 42. Furthermore, the exhaust manifold 42 is connected to an exhaust pipe 48 via a fusion converter 46 filled with a three-way catalyst.

An EGR pipe 74 is provided to communicate between the intake manifold 16 and the exhaust manifold 42, and this EGR pipe 74 controls the amount of EGR flowing through the EGR pipe, and also controls the amount of EGR flowing through the EGR pipe. An EGR control device 76 consisting of an EGR vacuum modulator is installed. Therefore, when the vacuum switching pulp solenoid of the EGR control device 76 is energized and opened, the EGR is transferred from the exhaust manifold to the intake manifold.
When R is introduced and the solenoid of the EGR control device 76 is de-energized and the valve is closed, the introduction of EGR is stopped.

The spark plug 32 is connected via a distributor 50 and an igniter 52 to a control circuit 54 composed of a microcomputer or the like.

The distributor 50 includes an engine rotation angle sensor 56 and a cylinder discrimination sensor 58, each of which includes a signal rotor fixed to the distributor shaft and a pickup fixed to the distributor housing.
is installed.

In the case of a 6-cylinder engine, this cylinder discrimination sensor 58 detects one nohalus at a reference position (for example, top dead center of a specific cylinder) every time the distributor shaft makes one revolution, that is, every two revolutions of the engine (720° CA). The engine rotation angle sensor 56 outputs one pulse every 30° CA, for example. Note that 77 is a vehicle speed sensor.

The control circuit 54 includes a central processing unit (CPU) 60 including an arithmetic logic unit and registers, a read-only memory (ROM) 62 that stores control programs, etc., a random access memory (RAM) 64, and a backup RAM (Bty).
-RAM) 66, input/output capo 1 (Ilo) 68, analog-digital converter (ADC) 70, timer 80, counter 82, and buses 72 such as data buses and control paths that connect these. .

The l1068 receives a cylinder discrimination signal from the cylinder discrimination sensor 58, an engine rotation speed signal from the engine rotation angle sensor 56, a power signal from the power switch 17, a vehicle speed signal from the vehicle speed sensor 77, and an idle signal from the idle switch 12. At the same time, a fuel injection signal for controlling the fuel injection valve 8 and an ignition signal for controlling the igniter 52 are outputted via a drive circuit (not shown). Further, l1068 is connected via a drive circuit 78 to the base of a transistor Tr whose emitter is grounded. The collector of this transistor Tr is connected to the battery via a resistor R and a solenoid L of the EGR control device. The ADC 70 includes an intake pipe pressure signal from the pressure sensor 14, an intake temperature signal from the intake temperature sensor 18, a water temperature signal from the water temperature sensor 38, and a throttle sensor 1.
The intake soft valve opening signal from 5 and the air-fuel ratio signal from 0□ sensor 44 are input, and these signals are sequentially converted into digital signals according to instructions from CPU 60. R above
The OM62 includes a control program shown in the following processing routine, a program for calculating the fuel injection time TAU,
Correction coefficients such as lean correction coefficient FLEAN and EGR correction coefficient FEGR are stored in advance.

In this embodiment, the fuel injection amount TAU is calculated according to the following equation (3).

TAU-(TP-4-TAUG)-(1+FKG)・F
W.I.

, FAF-FTHA, (1+FTC+F'LEAN+F
EGR-2)+τ1 (3) However, FKG is set to KGn during air-fuel ratio feedback control, and set to KGL during air-fuel ratio lean control.

Here, TP is the basic fuel injection time determined by intake pipe pressure and engine speed, '! "ALIG is the learning value during idling, KGn is the learning value during off-idling, FWL is the warm-up correction coefficient, FAF is the air-fuel ratio feedback correction coefficient, F'l'nA is the intake temperature correction coefficient, and FTC is the transient correction coefficient. coefficient, FLEAN is lean correction coefficient, FEGR is EGR
The correction coefficient, KGL, is the lean learning value, and TV is the invalid injection time for voltage compensation.

The transient correction coefficient FTC is set to a positive predetermined value during acceleration, a negative predetermined value during deceleration, and 0 in steady state.
It is said that The lean correction coefficients FI and EAN are set to 1 during feedback control, and are set to a value of 1 or less according to the intake pipe pressure PM during lean control, as shown in FIG. The EGR correction coefficient FEGR is set to 1 when EGR is not introduced, that is, during air-fuel ratio lean control,
When introducing EGR, that is, during air-fuel ratio feedback control, a predetermined pressure (for example, 500 r
++u+Ht) is set to a value of 1 or less, which is small according to the intake pipe pressure and becomes large according to the intake pipe pressure above a predetermined pressure. Further, the off-idle learning value KGn (n-1, 2, . . . 6) is determined according to the range of the intake pipe pressure PM, as shown in the table below.

Table KGn Intake pipe pressure PM range KG1 180mnlHf≦PM (260nnnHf
KG 2 260nm [r≦PM(340nvrHfK
G 3 340n+mHS'≦PM(420uni
)t VKG4 420+nmElf≦PM(500n
nnHVKG 5 500mmHf≦PM〈580nI
mI(fK G 6 580u++nHf≦PM(66
0m+nHf The above learning values TAUG and KGn are modified by the learning routine shown in FIG. ) is applied to the expression. However, KGI is PM< 18 On+mH
It is also applied to equation (3) in the region e of f (KG6 is P
Equation (3) is also applied in the region where M>660 mmHf.

Furthermore, the lean learning value KGL is modified by the learning routine shown in FIG. 6, and is applied to the above equation (3) during lean control.

A learning routine for correcting the learning values TAUG, KGn and the lean learning value KGL will be explained with reference to FIG. This learning routine lasts for a predetermined period of time (e.g. 48 m5ec
) is executed every time.

First, in step 100, it is determined whether or not the idle switch 12 is on, that is, whether or not the engine idle link is activated. When the idle switch is on, step 1
01, it is determined whether the engine speed Ne is less than 100 Orpm and the intake pipe pressure PM is more than 200 mmHP. If the judgment in step 101 is affirmative, that is, if it is a normal idle link, step 107
In step 101, it is determined whether the learning condition is satisfied or not. On the other hand, if the determination in step 101 is negative, that is, in the case of cranking, idle up, etc., the process returns to the main routine without learning.

On the other hand, if the idle switch is off, step 10
In Step 2, it is determined whether the lean learning count value T (counted in Fig. 7) is 0 or not, and if the count value T is O, the intake pipe pressure PM is set to 180 +run in Step 103.
Is it within the range of 660 m+nHt from H5'?
That is, it is determined whether the learning value KGn is within the learning range. When the intake pipe pressure PM is within the learning range, the current intake pipe pressure PM is determined in step 104.
The learning value KGn corresponding to is set as KG, and in step 107 it is determined whether the learning condition is satisfied. On the other hand, if the lean learning count value T is not 0, the intake pipe pressure PM is changed from 200 mmH9 to 500 mmH9 in step 105.
It is determined whether the range of 1 nnHf is included or not, that is, whether it is in a steady state. If the determination in step 105 is affirmative, the lean learning value KGL is set to KG in step 106, that is, the lean learning value rt A MKGL is set to the work RAM.
KG, and in step 107 it is determined whether the learning conditions are satisfied.

The following conditions can be considered as learning conditions in step 107, and the learning conditions are satisfied when all of these conditions are determined to be affirmative.

(1) Air-fuel ratio feedback control is in progress.

(2) The engine cooling water temperature THW is set to a predetermined temperature (for example, 8
Is it above 0℃?

(3) The acceleration of the vehicle is a predetermined value (for example, 0.7i/h2
) or less?

(4) Is the intake temperature within the specified range (4oC to 90C)?

(5) Atmospheric pressure is a predetermined value (for example, 650 rranHf
) Are you driving at any of the following high altitudes?

When it is determined in step 107 that the learning condition is satisfied, in step 108 the air-fuel ratio feed ratio correction coefficient FA is determined.
It is determined whether or not the air-fuel ratio F has sagged or not, and if it is skipped, the air-fuel ratio feedback correction coefficient FAFO value at the time of skip is read in step 109, and the average value FAF of the air-fuel ratio feedback correction coefficient FAFO at the time of skip is read in step 110.
Calculate AV. This average value F A i+'' A V is the correction coefficient FAFO value at the time of skip (A, B in Fig. 1,
The upper limit value ( For example, 1
．． 1) is exceeded, and in step 112 the average value F
A F' A V is the lower limit of a predetermined range (for example, (1
, 95). Average value F”A
If FAV exceeds the upper limit, step 1
13, it is determined whether the idle switch is on or not;
When the idle switch is on, in step 114, the idle learning value TAUG is set to a predetermined value (for example, 10 μs).
Make it thicker, and increase the step (for example, 0.05) when the idle switch is off. On the other hand, when the average value FAFAV is less than the lower limit value, it is determined in step 116 whether or not the idle switch is on; When the idle switch is off, the learned value KG of the off-idle value is decreased by a predetermined value (eg 'o, os) in step 118.

Since the learned values KGn and KGL are set to KG in step 104 and step 106, the learned value KGn or lean learning value K is set in step 115 and step 118.
GL will be revised.

As a result of the above, when the air-fuel ratio is equal to the target desired fuel-fuel ratio (IJ-), the average value FAFAV exceeds the one-hi limit value, so the learned values KGn and TAUG are increased and the above ( 3) Feedback control is performed so that the fuel injection amount increases. This ensures that the average value FAFAV falls within a predetermined range. On the other hand, when the air-fuel ratio is richer than the target air-fuel ratio, the average value FAFA
Since V becomes less than the lower limit value, the learned values KGn and TAUG are reduced, and feedback control is performed so that the fuel injection amount is reduced according to the above equation (3). Accordingly, the average value FA
The FAV is set to a value within a predetermined range. Note that the lean learning value KGL is applied to the above equation (3) together with the learning value TAUG, and is used for air-fuel ratio lean control to be described later.

Figure 7 shows whether the learning value KGn is corrected or the lean learning value KGL
This routine is executed at predetermined intervals to count the lean learning count value T that determines whether to modify the lean learning count value T. First, in step 120, it is determined whether or not it is time to start the engine. Whether or not it is time to start can be determined by, for example, the engine speed, and when the engine speed is a predetermined value (
For example, when it is below 500 rPm, it is determined that it is time to start. Then, when it is determined that it is time to start, step 121
to set the count value T of the counter 82 to a predetermined value (for example, 300
) and return. When it is determined in step 120 that the starting state has passed, it is determined in step 122 whether or not the engine coolant temperature THW is a predetermined temperature (for example, 80° C.) or higher. During the process, the process directly returns to the main routine, and if the cooling water temperature THW is equal to or higher than the predetermined temperature, it is determined in step 123 whether a predetermined time (for example, 1 second) has elapsed based on the value of the timer 80. Then, only when a predetermined time has elapsed, it is determined in step 124 whether or not the count value "r" is 0. If the count value T is not 0, the count value is incremented by one day in step 125.

1. FIG. 8 shows a routine for calculating the EGR sleeve correction coefficient FEGR. First, in step 129 it is determined whether the count value T is 0 or not. If the count value T is 0, it is determined in step 130 whether the idle switch is on or not. Decide whether or not
If the idle switch is off, it is determined in step 131 whether lean control is being performed. Whether or not lean control is in progress can be determined based on the value of the lean correction coefficient FLEAN. If the lean correction coefficient FLEAN is less than 1, it is determined that lean control is in progress. When lean control is not being performed, that is, when feedback control is being performed, the engine cooling water temperature T is determined in step 132.
Determine whether the HW is below a predetermined temperature (for example, 50°C),
If the temperature exceeds the predetermined temperature, it is determined in step 133 whether the throttle opening THO detected by the throttle sensor 15 is less than or equal to a predetermined opening (for example, 30°). When the throttle opening T)10 is less than the predetermined opening, a correction coefficient FEGR for the current intake pipe pressure PM is calculated by interpolation from the map shown in FIG. 5 in step 134. On the other hand, when the count value T is not 0, when the idle switch is on, when lean control is in progress, when the engine coolant temperature is cold below the predetermined temperature, and when the throttle opening exceeds the predetermined opening (for example) < In step 135, the correction coefficient FEGR is applied to the power increase region where the switch 17 is on.
Let the value of be 1.

FIG. 9 shows a routine for controlling the EGR control device 76. In step 140, the correction coefficient FEGR is set to 1.
If it is FEGR-1, then in step 142, the EGR control device's exhaust switching valve is energized, the EGR loop is closed, and the introduction of EGR is stopped. On the other hand, in the case of FEGRAl, step 14
Step 1: Open the EGR node and introduce EGR.

When EGR is introduced, the correction coefficient FEGR has a value less than 1, and as will be described later, the lean correction coefficient FLEAN is 1 during feedback control, so the 0 in equation (3) above becomes 1. -1-F, LEAN-FEGR-2 (1...(4)
Then, the amount of fuel injection is reduced depending on the intake pipe pressure and therefore the amount of EGR introduced. On the other hand, when the introduction of EGR is stopped, such as during an idle link during feedback control, FEGR becomes -1, so the l-1-
FEGR-2 becomes O, and the fuel injection amount is not reduced by the correction coefficient FEGR.

Next, a calculation processing routine for the lean correction coefficient FLEAN regarding the lean control will be explained with reference to FIG. First, in step 150, mode condition XMOD
Determine whether E holds true. This mode condition is established when the engine is not starting, is not increasing storage after starting, or is not increasing output. Whether or not the engine is starting is determined based on the ignition signal and engine speed signal, and the ignition switch is turned on. In addition, when the engine speed is less than or equal to a predetermined value (for example, 5QQrpm), it is determined that the engine is in the starting state. In addition, whether or not the quantity after starting is within the quantity is determined by whether or not the quantity increasing coefficient after starting, which is attenuated by a predetermined amount at every predetermined number of injections after starting, is 0. It is judged that it is not. Whether or not the output is being increased is determined based on a power increase coefficient that is set to a predetermined value (for example, 0.15) when the power switch 17 is on and the cooling water temperature is above a predetermined value (for example, 20 degrees Celsius). When the power increase coefficient is 0, it is determined that the power is not being increased.

When the mode condition XMODE is not satisfied, feedback control is performed with the lean correction coefficient FLEAN set to 1 in step 158, and when the mode condition XMODE is satisfied, the starting temperature correction coefficient ADD is set in step 151.
Determine whether or not is 0.

This starting temperature correction coefficient ADD is for correcting fluctuations in the air-fuel ratio due to the temperature difference between the engine cooling water temperature and the intake manifold wall surface temperature. In the engine shown in FIG. 2, if the distance from the fuel injection valve to the combustion chamber is long and the intake manifold wall temperature is low, the air-fuel ratio correction based on the engine cooling water temperature alone is not sufficient, so this coefficient ADD is especially necessary. The starting temperature correction coefficient ADD is determined by subtracting a predetermined value from an initial value determined in inverse proportion to the intake air temperature at predetermined intervals to attenuate it to zero.

When it is determined in step 151 that the starting temperature correction coefficient ADD is not 0, that is, when starting temperature correction is being performed, the process proceeds to step 158, and when the starting temperature correction coefficient ADD is O, that is, starting temperature correction has been completed. If so, it is determined in step 152 whether the engine coolant temperature THW is equal to or higher than a predetermined value (for example, 80° C.). When the coolant temperature THW is less than a predetermined value, that is, during warm-up, the process proceeds to step 158, and when the coolant temperature THW is above the predetermined value, that is, after complete warm-up, it is determined in step 153 whether lean control is being performed. Whether lean control is in progress or not, lean correction coefficient FLEAN is 1.
You can judge whether it is or not.

When it is determined in step 153 that lean control is being performed, in step 154, the change rate (hereinafter referred to as second derivative value) of the vehicle speed change rate ΔSPD within a predetermined time (for example, 2 seconds) ΔS P D / 2 See is set to a predetermined value. (for example, 5 bn/h) or less, it is determined whether or not there is sudden acceleration. Second-order differential value ΔS P D / 2
When See exceeds a predetermined value, it is determined that there is a sudden acceleration and the process proceeds to step 158, and when it is less than the predetermined value, the process proceeds to step 155. On the other hand, when lean control is not in progress, that is, when feedback control is in progress, in step 156, the second-order differential value Δ
If it is determined whether SPD/2Bec is less than or equal to a predetermined value smaller than the predetermined value in step 1540 (e.g., 7 kIn/h), it is determined whether the acceleration is gradual or not, and the air-fuel ratio feedback correction coefficient is determined in step 157. The average value FAFAV of is the value corresponding to the stoichiometric air-fuel ratio (i.e. 1)
(for example, 0.99<FAFAV<t,
o Determine whether the value in 1) is met. If the determinations in steps 156 and 157 are negative, it is determined that lean control is not possible and the process proceeds to step 158. If both of these determinations are affirmative, it is determined that lean control is possible and the process proceeds to step 155. .

As a result of the above, even when the amount of variation in the learned value is small, that is, when the average value FAFAV is within a predetermined range that includes the value corresponding to the stoichiometric air-fuel ratio, it is determined that lean control I3f is possible, and conventionally lean control is impossible. Lean control is now possible even in areas that have been previously determined.

In step 155, it is determined whether the load is light by determining whether the opening degree THO of the intake throttle valve is less than or equal to a predetermined value (for example, 30 degrees). The opening degree THO of this intake throttle valve is
This can be determined based on whether or not the power switch 17 is turned on. When the opening degree THA of the intake throttle valve exceeds a predetermined value, that is, when the load is high, step 158
When the opening degree THA of the intake throttle valve is less than a predetermined value, that is, when the load is light, the count value T is set to 0 in step 126.
If the count value T is 0, step 15
At step 9, it is determined whether the idle switch is off or not, and it is determined whether the intake throttle valve is open or not. On the other hand, if the count value T is not 0, the process advances to step 158.

When the idle switch is off in step 159, in step 160, the lean correction coefficients Fl and EAN are calculated according to the current intake pipe pressure PM from the lean correction coefficient FLEAN map shown in FIG. 4 stored in the ROM. Request the interpolation method and load it into register A. Next step 16
In step 1, it is determined whether or not lean control is being performed, and if lean control is being performed, the value of register A is set as the lean correction coefficient FLEAN in step 163, and lean control is subsequently performed. on the other hand,
If lean control is not in progress, the vehicle speed is set to 5P in step 162.
When D7>z exceeds a predetermined value (for example, 10 kR/h), the value in register A is set as the lean correction coefficient FLEAN in step 163 to perform one-step control. On the other hand, when the vehicle speed is below a predetermined value, that is, when the vehicle is started, the lean correction coefficient FLEAN is set to 1 in step 167, and the lean control is stopped.

When the idle switch is on, the average value NAV of the engine speed within a predetermined time is determined in step 164;
In the next step 165, it is determined whether the average value NAV exceeds a predetermined value B (for example, 600 rpm).

When the average value NAV is less than the predetermined value B, the lean control is stopped in step 167, and when the average value NAV exceeds the predetermined value B, the lean correction coefficient FLEAN is adjusted in step 166.
Lean control is performed by setting the value to a predetermined value less than 1 (for example, 0.92). In this way, by performing lean control by setting the lean correction coefficient FLEAN to a predetermined value when the idle switch is turned on, it is possible to prevent idle instability due to hunting caused by intake pipe pressure fluctuations.

The lean correction coefficient FLEAN calculated as above and the lean learning value KGL corrected in FIG.
) is applied to the fuel injection time TALI during lean control.
is used for calculation. During lean control, the correction coefficient FEG
Since R is set to 1, the fuel injection time TAU is shortened according to the lean correction coefficient FLEAN, and the air-fuel ratio is controlled to be leaner than the target air-fuel ratio during feedback control.

In addition, although the engine in which the basic fuel injection time is determined by the intake pipe pressure and engine speed and uses one fuel injection valve has been described above, the engine to which the present invention is applied is not limited to this. It can also be applied to engines in which the basic fuel injection time is determined based on the amount of intake air per revolution and the engine speed, and to engines with fuel injection valves for each cylinder that protrude into the intake manifold. .

[Brief explanation of drawings]

FIG. 1 is a diagram showing an air-fuel ratio signal and a feedback correction coefficient, FIG. 2 is a block diagram showing a configuration example of the present invention including an engine to which the present invention is applied, and FIG. 3 is a diagram of the control circuit of FIG. A block diagram showing an example, FIG. 4 is a diagram showing a map of lean correction coefficients, FIG. 5 is a diagram showing a map of correction coefficients FEGH, and FIG. 6 is a flowchart showing a learning routine in an embodiment of the present invention. , FIG. 7 is a flowchart showing the routine for counting the lean learning counter of the above embodiment, FIG. 8 is a flowchart showing the calculation routine of the correction coefficient FEGR, FIG. 9 is a flowchart showing the EGR pulp control routine, and FIG. 10 3 is a flowchart showing a beam correction coefficient calculation routine. 8...Fuel injection valve, 10...Intake throttle valve, 14...
-Pressure sensor, 44...02 sensor, 54...control circuit, 76...EGR control device. Agent Tatsuyuki Unuma (and 1 other person) Figure 1 Figure 1, Figure 2 Figure 4 ＼ Figure 1! 4 → oy tube Hf) PM (mmHg abs) Figure 5 Figure 7 Figure 8 Figure 9

Claims (1)

[Claims] (1) In an air-fuel ratio control method for an internal combustion engine in which feedback control is performed so that the air-fuel ratio reaches a target air-fuel ratio using an air-fuel ratio feedback correction coefficient determined based on the output of an 02 sensor that detects the residual oxygen concentration in exhaust gas. , exhaust gas is recirculated to the intake system under specific operating conditions during feedback control, and the average value of the air-fuel ratio feedback correction coefficient is within the applicable range when feedback control is in progress and exhaust gas is not recirculated to the intake system. The lean learning value is increased or decreased so as to reach the lean learning value, and the feedback control is stopped during normal operation to control the air-fuel ratio to become leaner than the target air-fuel ratio based on the lean learning value. Air-fuel ratio control method for internal combustion engines.