JPS63189636A - Air-fuel ratio feedback control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To compensate a change with aging, by continuously sensing a period of time during which a sensed value of an exhaust gas concentration shifts from a lean side to a rich side and a period of time during which it shifts from the rich side to the lean side and by changing a control constant based on a ratio of the periods of time in air-fuel ratio feedback control. CONSTITUTION:An electronic control unit 5 calculates a basic amount of fuel injection based on values sensed by a suction gas absolute pressure sensor 8 and an r.p.m. sensor 10 and compares a value sensed by an O2 sensor 13 with a reference value for effecting feedback control of an air-fuel ratio by proportional integral control. The electronic control unit 5 continuously measures a time t1 when a value sensed by the O2 sensor 13 changes from a lean side to a rich side with respect to the reference value and a time t2 when it changes from the rich side to the lean side. Thus, it senses a deviation of an air-fuel ratio based on a ratio between a period of time of t1-t2 and a period of time of t2-t1 and changes an integration constant and a proportion constant so that the deviation is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an air-fuel ratio feedback control method for an internal combustion engine, and in particular to an air-fuel ratio feedback control method for an internal combustion engine that compensates for changes over time in the output characteristics of an exhaust gas concentration detector disposed in the engine's exhaust system. The present invention relates to a fuel ratio feedback control method.

(Technical background and problems) Conventionally, the exhaust concentration (oxygen concentration) detected by an exhaust concentration detector (for example, 03 sensor) placed in the exhaust system of an internal combustion engine is compared with a predetermined reference value. Based on the results, the air-fuel ratio of the mixture supplied to the engine is controlled to the stoichiometric mixture ratio at which the three-way catalyst installed in the engine's exhaust system achieves the maximum conversion efficiency, thereby improving the exhaust gas characteristics. An air-fuel ratio feedback control method for an internal combustion engine is generally used (for example, Japanese Patent Application Laid-open No. 137633/1983).

The 02 sensor used for such air-fuel ratio control uses zirconium oxide etc. as a sensor element, and the amount of oxygen ions passing through the inside of the zirconium oxide etc. is determined by the oxygen partial pressure in the atmosphere and the oxygen content in the exhaust gas. The oxygen concentration in the exhaust gas is detected by changing the output voltage of the O2 sensor in response to the change in pressure.

However, the output characteristics of the O2 sensor configured as described above change over time, and especially after a vehicle equipped with the sensor has undergone endurance driving, its output characteristics deteriorate due to durability, and as a result, under the same conditions It is known that even though air-fuel ratio feedback control is performed, the controlled air-fuel ratio shifts to the rich side compared to when shipped from the factory.

If no measures are taken against such changes in the characteristics of the 02 sensor over time, problems will arise in that the engine's driving performance, fuel efficiency, and exhaust gas characteristics will deteriorate.

(Object of the Invention) The present invention has been made to solve the above-mentioned problems, and it corrects the air-fuel ratio of the air-fuel mixture supplied to the engine according to the degree of change over time in the characteristics of the 0□ sensor. It is an object of the present invention to provide an air-fuel ratio feedback control method for an internal combustion engine that allows the fuel ratio to be achieved.

(Structure of the Invention) In order to achieve such an object, according to the present invention, a detected exhaust concentration value detected by an exhaust concentration detector disposed in the exhaust system of an internal combustion engine is compared with a predetermined reference value, When the detected exhaust gas concentration value changes from the rich side to the lean side or from the lean side to the rich side with respect to the predetermined reference value, the air-fuel ratio of the air-fuel mixture supplied to the engine is adjusted by the first correction value. At least one of proportional control that increases or decreases the air-fuel ratio, and integral control that increases or decreases the air-fuel ratio at predetermined time intervals using second correction values when the detected exhaust gas concentration value is on the lean side or rich side with respect to the predetermined reference value. In the air-fuel ratio feedback control method for an internal combustion engine, which performs feedback control to a target air-fuel ratio, the detected exhaust gas concentration value changes from the lean side to the rich side with respect to the predetermined reference value, and the time point when the detected exhaust gas concentration value changes from the rich side to the lean side with respect to the predetermined reference value. and a second time from the time when the detected exhaust gas concentration value changes from the rich side to the lean side to the time when the detected exhaust gas concentration value changes from the lean side to the rich side with respect to the predetermined reference value. There is provided an air-fuel ratio feedback control method for an internal combustion engine, characterized in that at least one of the first correction value and the second correction value is changed in accordance with the thus determined ratio.

(Embodiment) An embodiment of the present invention will be described below in detail based on the accompanying drawings.

FIG. 1 is a block diagram showing the overall configuration of a fuel supply control device for an internal combustion engine to which the method of the present invention is applied. Reference numeral 1 indicates, for example, a four-cylinder internal combustion engine, and the engine 1
An intake pipe 2 communicating with the atmosphere is connected to the intake pipe 2.
A throttle valve 3 is provided in the middle. A throttle valve opening sensor 4 is connected to the throttle valve 3, which detects the valve opening θ〒H and outputs an electrical signal, and the detection signal is used to detect the air-fuel ratio, etc. as explained below. It is sent to an electronic control unit (hereinafter referred to as rEcUJ) 5, which performs arithmetic processing to calculate and controls the engine.

A fuel injection valve 6 is provided between the engine 1 and the throttle valve 3. The fuel injection valve 6 is connected to the engine 1.
The valve opening time for injecting fuel is controlled by a drive signal supplied from the ECU 3, which is connected to a fuel pump (not shown).

On the other hand, a pipe 7 is provided in the intake pipe 2 downstream of the throttle valve 3.
An intake pipe absolute pressure sensor 8 for detecting the absolute pressure Pe^ in the intake pipe 2 is connected through the intake pipe 2.

The detection signal is sent to the ECU 3.

An engine water temperature sensor 9, which is made of, for example, a thermistor, and detects the temperature Tw of the cooling water is provided on the peripheral wall of the cylinder of the engine 1 filled with cooling water, and its detection signal is sent to the ECU 3.

Engine speed sensor (hereinafter referred to as rNe sensor) 1
0 is installed around the camshaft or crank (not shown) of the engine 1, and this N8 sensor 10 outputs a signal of one pulse (TDC signal) every 180° rotation of the crankshaft, and this TDC signal is It is sent to the ECU 3.

A three-way catalyst 12 is connected to the exhaust pipe 11 of the engine 1, and the three-way catalyst 12 converts HClGo and NOx in the exhaust gas.
An O2 sensor 1, which is an exhaust gas concentration sensor, is installed in the exhaust pipe 11 upstream of the three-way catalyst 12, which purifies the components.
3 is installed, and the 08 sensor 13 detects the oxygen gas concentration in the air gas.

The detection signal (VOW) is sent to the ECU 3.

Furthermore, a vehicle speed sensor 14 that detects the speed Sp of the vehicle is connected to the ECU 3, and a detection signal from the vehicle speed sensor 14 is sent to the ECU 3.

The ECU 3 inputs detection signals from the various sensors mentioned above,
The fuel injection time Tou〒 of the fuel injection valve 6 is calculated by the following equation.

Tou〒=TiXK, The data is read out from the memory device in the ECU 5 based on the data. Ko□ is O, a feedback correction coefficient, which is calculated based on the 08 feedback correction coefficient calculation subroutine, which will be described later. 1 and 2 are a correction coefficient and a correction variable respectively calculated according to the various engine parameter signals, and the fuel efficiency characteristics according to the engine operating state based on the detection signals from the various sensors described above.

A predetermined value is determined so as to optimize various characteristics such as engine acceleration characteristics.

ECU3 calculates the fuel injection time Tou as described above.
A drive signal for opening the fuel injection valve 6 is output based on 〒.

FIG. 2 is a diagram showing the circuit configuration inside the ECU 3 of FIG.
After waveform shaping in step 1, the central processing unit (hereinafter referred to as rcPU)
503 (hereinafter referred to as "rMe counter") 502
Also supplied. The Me counter 502 is the Ne sensor 1
It counts the time interval from the input of the previous TDC signal from 0 to the input of the current TDC signal, and its count value M
e is proportional to the reciprocal of the engine speed No.

The Me counter 502 transfers this count value Me to the data bus 5.
10 to the CPU 503.

On the other hand, the throttle valve opening (θ〒H) sensor 4, the absolute pressure (
PB^) Sensor 8, engine water temperature (Tw) sensor 9.0
2 sensors 13. The output signals from the and vehicle speed (Sp) sensors 14 are respectively applied to a level correction circuit 504, and after being corrected to a predetermined voltage level in the circuit 504, the output signals from the CP
Multiplexer 50 operates based on instructions from U503
5 is sequentially supplied to an analog-to-digital converter (A/D converter) 506. The converter 506 converts the output signals of the aforementioned sensors into digital signals, and supplies the digital signals to the CPU 503 via the data bus 510.

The CPU 503 is further connected to a read-only memory (hereinafter referred to as rROMJ) 507 and a random access memory (hereinafter referred to as rROMJ) via a data bus 510.

rRAMJ) 508 and a drive circuit 509. The ROM 507 is connected to the CPU 50, the details of which will be described later.
3, various data such as correction coefficients and correction variables, and the Ne-PR child table are stored. Further, the RAM 508 temporarily stores calculation results etc. obtained by the execution of the various control programs by the CPU 503.

Then, the CPU 503 reads from the ROM 507 coefficient values or variable values corresponding to the output signals of the respective sensors described above according to the control program stored in the ROM 507.
Alternatively, calculate the fuel injection valve 6 based on the above calculation formula (1).
The fuel injection time Tou〒 is calculated, and the value obtained by this calculation is supplied to the drive circuit 509 via the data bus 510.

The drive circuit 509 calculates the calculated fuel injection time Tou〒
The fuel injection valve 6 is opened over the period of time.

Next, a method of calculating the 0□ feedback correction coefficient Ko according to the change over time in the characteristics of the O3 sensor according to the present invention will be explained.

As mentioned above, 0. The output characteristics of the sensor deteriorate due to endurance driving of the vehicle, and as a result, the feedback-controlled air-fuel ratio is biased towards the rich side or the lean side. The degree of deterioration of this O8 sensor is OII under stable engine running conditions.
Sensor output voltage value ■o.

(Fig. 3) is the time T (Fig. 3 t2~
13.1. -1. ) and the time T+,v required from the time when the output voltage value Vo changes from the rich side to the lean side with respect to the reference value v■F to the time when the output voltage value Vo changes from the lean side to the rich side (t3 in Fig. 3). ~ t4)) can be estimated by the value KOX (= TL, V/TRV) (hereinafter Ttribute v will be referred to as "rich side transition time J", and TLV will be referred to as "lean side transition time"). It has been experimentally confirmed that this KOX value decreases depending on the cumulative mileage of the vehicle, that is, the degree of durability deterioration.

Therefore, in the present invention, the air-fuel ratio is adjusted to the target air-fuel ratio by changing the proportional control correction value or the integral control correction value, which is adjusted to the correction coefficient Ko, by an amount corresponding to the KOX value in air-fuel ratio feedback control, which will be described later. It is precisely controlled.

This embodiment is applied to the case where the proportional control correction value P added to the correction coefficient Ko is changed according to the KOX value. Specifically, the value of KOX is changed to a plurality of predetermined values KOX1 to KOX,
(KOX, >KOX, >KOX, >KOX,), the proportional control correction value P trap is set to the correction value ΔP trap 1, ΔP
g, (Fig. 4) is changed as follows.

(1) When xOX>KOX, it is estimated that the air-fuel ratio is largely biased toward the lean side, and a correction value ΔP- is added to the correction value P trap.

(2) When KOXl>KOX>KOX, (7), it is estimated that the air-fuel ratio is slightly biased toward the lean side, and the correction value P11
A correction value ΔPt, (<ΔPg,) is added to.

(3) When KOX,>KOX>KOX, it is estimated that the air-fuel ratio is controlled approximately equal to the target (theoretical) air-fuel ratio,
Holds the correction value PIIF.

(4) Kox3) When xOX>KOX, it is estimated that the air-fuel ratio is slightly biased toward the rich side, and the correction value PII+
P111 is subtracted from the corrected value.

(5) When KOX<KOX, it is estimated that the air-fuel ratio is largely biased toward the rich side, and the correction value ΔP- is subtracted from the correction value P11.

Figures 5 and 6 show the rich side proportional control correction value P
PP for implementing changes in g! 2 is a program flowchart of a value determination subroutine.

First, in steps 30 to 36, the engine.

It is determined whether the output voltage VO of the 02 sensor 13 is in a predetermined operating state in which it should be reversed at a normal cycle.

That is, in step 30, it is determined whether the temperature of the 02 sensor 13 is sufficiently high based on whether the engine water temperature Tw is greater than a predetermined value Tvox, and then in step 31, it is determined whether the engine is actually under feedback control. Discern. Further, in steps 32 to 35, as a condition for the predetermined operating state, the engine rotation speed No. is set to a predetermined value N.
Determining whether the value is between eox* and NeoxH (
Step 32).

The intake pipe absolute pressure Pg^ is the predetermined value P BOXL and P BO
Determining whether the value is between XH (step 33),
The vehicle speed Sp indicating the cruising state of the vehicle is set to a predetermined value SP
It is determined whether or not the value is between OXL and 5POXH (step 34), and the absolute value of the degree of change ΔPa^ in the absolute pressure indicating a stable cruising state is determined within a predetermined width ΔP B
A determination as to whether or not the value is smaller than OX^ (step 35) is executed. Furthermore, in step 36, after these operating conditions are satisfied (after all the determination results in steps 32 to 35 are affirmative), this operating state is maintained for a certain period of time T.
It is determined whether the process has been continued for x.

Therefore, when all the determination results in steps 30 to 36 described above are affirmative (Yes) (the operating state shown in FIG. 7)
, it is determined that the engine is in the predetermined operating state, and the program from step 38 onwards is executed for the first time.

Incidentally, if the determination result in any one of steps 30 to 36 is negative (NO), the process proceeds to step 37, sets the averaging number count value nAV, which will be described later, to O, and ends this program.

In steps 38 to 52, the average value TLVAV of the TLV time for determining the KOX value (=TLl//T large v) representing the degree of deterioration of the oxygen sensor 13 described above;
And VAV is calculated as the average value T of T hole v time.

Below, the average value TL from step 38 to step 52
The calculation method for VAV and TIIIVAV is shown in Figure 3.
The explanation will be based on a timing chart of the output voltage values Vo of the eight sensors.

Now, let us consider a case where the determination result in step 36 becomes positive for the first time at time t1 in FIG. 3.

First, in step 38, it is determined whether the current output voltage value vO□n of the O2 sensor 13 is larger than a predetermined reference value v■F. At the time of construction t in Figure 3, this determination result was negative (N
o), the process proceeds to step 39, where it is determined whether the previous output voltage value Vo, n-2 is larger than the predetermined reference value v trap U. At time t1, this determination result is also negative (No).
This ends the program and moves to the next loop.

Even in subsequent loops, the output voltage value Vo remains the predetermined reference value V.
*tp is exceeded (until time t2 in FIG. 3), the determination results in steps 38 and 39 are both negative (No).

When the output voltage value Vo2 of the o2 sensor 13 increases and exceeds the predetermined reference value VItEF for the first time in this loop (the third
t2), the determination result in step 38 is affirmative (Y
es), and the process proceeds to the next step 40.

In step 40, the output voltage values Vo, n- in the previous loop are
, is larger than the predetermined reference value V than IFF, and at time t2, the result of this determination is negative (No), and at the next step 41, the tox timer starts counting at step 43, which will be described later. The count value tox of is set as the transition time Tox, and the process proceeds to the next step 42. In this step 42, the transition time T set in step 41 is set as the transition time Tox.
It is determined whether ox is within the allowable range TOXL to TOXH.

Since the tox timer has not yet started at time t3 in FIG. 3, the result of this determination is negative (NO), and steps 50 to 52, which will be described later, are skipped and the process proceeds to step 43.The determination in step 42 is performed. Accordingly, ti
An extremely long transition time that occurs during a transition period of the engine operating state, such as when the TOX timer has already been activated before this point, or an extremely short transition time that occurs due to noise generation as shown between time t and ~1s in Figure 3. can also be excluded.

In step 43, the count value of the tox timer is reset and started, and in the next step 44, it is determined whether the averaging number count value nAV, which will be described later, is greater than or equal to a predetermined number of times NAV, and if the determination result is affirmative (Yes). If so, the program from step 59 (FIG. 6) to be described later is executed, and if the answer is negative (No), this program is ended.

In the next and subsequent loops, the output voltage value vO□ of the O2 sensor 13
as long as it exceeds the predetermined reference value v F (Fig. 3 t2~
At time t1), the determination results in steps 38 and 40 are both affirmative (Yes), and one program is ended. Therefore, during this period, the count value of the tax timer is not reset to 1. It comes to represent the elapsed time from the point in time.

0. When the output voltage value Vo of the sensor 13 decreases and the output voltage value Vo crosses the predetermined reference value V large tv in this loop (at time t8 in FIG. 3), the determination in step 38 is performed again. The result is negative (No).

Proceed to step 39. In the current loop (at time ta), the output voltage value Vo, n-1 in the previous loop reaches the predetermined reference value V.
Since it is larger than FF, the determination result becomes affirmative (Yes), and in the next step 45, the count value tox (t, -t, time) of the tox timer at this point is set as the transition time Tox, and the process proceeds to the next step 46. move on.

In step 46, similarly to step 42, step 45
The transition time Tox set in is within the allowable range Toxt.

It is determined whether or not it is within ~Toxo, and if the determination result is negative (No), skip steps 47 to 49 and proceed to step 43.・If the determination result of this step 46 is negative (Yes) Then proceed to step 47,
The correction coefficient KNIE〒,
Multiply by KPBT to obtain a new transition time T oxc.

Correction coefficient KN! 〒, KPBT are the engine speed Ne
and KN! shown in FIGS. 8 and 9 according to the intake pipe absolute pressure PB^! This is the value read from the 〒-No table and the Kpm 〒-Pa^ table. Step 46 like this
The transition time tox is determined by the correction coefficients Kwi〒 and Kps〒.
The reason for correcting is that the transition time, that is, the inversion period of the O8 sensor itself changes significantly in accordance with changes in the engine speed No. and the intake pipe absolute pressure Pa^.

The transition time TOXQ corrected in step 47 is substituted into the following equation (2) in the next step 48, and as a result, o
The output voltage value Vo of the second sensor 13 is the predetermined reference value vREF.
The average value T trap VAVn of the rich side transition time Toxc (=V to T) from the time when the lean side changes to the rich side to the time when the rich side changes to the lean side is calculated.

...(2) Here, T large vAvn-□ is the previous value of the rich side transition time average value, and is an averaging constant for calculating CO or the average value, and is a step 63, 65, 67, 69 described later. .71
The value COX corresponds to the degree of deterioration of the 02 sensor.

~C0X4 (however, O<C0X0~COX, <256).

Returning to FIG. 5, in the next step 48, 1 is added to the averaging count value nAV representing the number of executions of transition time averaging based on the above-mentioned formula (2), and as described above, in step 48,
3, the count value of the tax timer is reset and started.In the next step 44, the count value of the tax timer is reset and started.
8 and step 51 described below to determine whether the averaging number count value nAV representing the number of times the transition time is averaged is greater than or equal to a predetermined number of times NAV.
V is set to a required value in steps 63, 65, 67, 69, and 71, which will be described later, depending on the degree of deterioration of the sensor.

As described above, the transition time T between time points t2 and t3 in FIG.
ox (=T*v) is set, and the rich side transition time average value T is calculated based on the corrected value Toxc of the transition time Tax.
Large VAVn is calculated.

The output voltage value Vo of the 02 sensor 13 is the predetermined reference value VRE.
After going below F (after time ta), step 38.3
Both of the determination results in step 9 are negative (No), and this program ends. Therefore, during this time, the count value of the tox timer is not reset and comes to represent the elapsed time from the 1 degree point.

0, the output voltage value Vo of the sensor 13 increases and reaches the predetermined reference value Vl in this loop! When it crosses F and rises (time t4 in Figure 3), the determination result in step 38 is affirmative (Yes).
Next, the determination result in step 40 is negative (NO).
Then, the process proceeds to step 41.

In step 41, the count value tOX (ta-t*waiting time) of the tox timer at this point (to point) is set as the transition time Tox (=TLv), and the process proceeds to the next step 42, where the transition time Tox is within the allowable range. 0 Next, in step 50, similarly to step 47, the transition time Tox is set to the engine rotation speed N.
a, Correction coefficient KN according to the intake pipe absolute pressure Pa^! 〒、
Kps〒 is corrected and the new transition time Toxc is set.

Furthermore, in step 51, the corrected transition time T oxc
Substituting into the following equation (3), the average lean side transition time from the time when the output voltage value vO□ changes from the rich side to the lean side with respect to the predetermined reference value v■F to the time when the output voltage value changes from the lean side to the rich side A value TbvAvn is calculated.

COX 256-COXTcvAvn
= iX Toxc + 256X TtvAvn-
.

(3) Here, TcvAvn- is the previous value of the lean side transition time average value, and COX is the same averaging constant as in equation (2) above.

In step 52, 1 is added to the averaging count value nAV as in step 49, and in step 43
, 44.

In this way, the calculation of the rich side and lean side transition time average values in steps 38 to 52 is repeated until the averaging count value nAV reaches the predetermined number of times NAV, which is a value representing the degree of deterioration of the 02 sensor. KOX
This is to more accurately determine (= T LVAV / T large vAv).

If the calculation of the rich side and lean side transition time average values is performed a predetermined number of times NAV, and the determination result in step 44 is affirmative (Yes), steps 59 to 77 in FIG.
The rich side proportional control correction value P* is corrected according to the degree of deterioration of the 02 sensor 13.

First, in the determination in steps 59 to 62, a value K OX (= TLVAV/TRV
AV) and the aforementioned predetermined values KOXi, xOXz, KOX
, , KOX, respectively (KOX, >KOX,
>KOX, >KOX4) - That is, in step 59, the rich side transition time average value T* after the completion of averaging a predetermined number of times.
In step 60, whether or not the value obtained by multiplying vAv by a predetermined value KOX is larger than the lean side transition time average value TLVAV after the completion of averaging for a predetermined number of times is determined in step 60. It is determined whether or not the average value TLVAV is greater than the average value TLVAV. On the other hand, in step 61, the value obtained by multiplying the average value T*vAv by a predetermined value KOX is determined to be smaller than the average value TLVAV, and in step 62, the predetermined value KOX is multiplied by the average value T*vAv.

It is determined whether the multiplied value is smaller than the average value TLVAV or not.

Therefore, all the determination results in steps 59 to 62 are affirmative (
If the answer is Yes), the value KOX representing the degree of deterioration is between the predetermined values KOX and KOX, and in this case it is estimated that the air-fuel ratio is controlled to be approximately equal to the target air-fuel ratio, and step 63 is performed. Next, the averaging constant CoX used in equations (2) and (3) and the predetermined number of averaging operations NAV are set to standard values COX, NAV, respectively.

On the other hand, when the determination result in step 59 is negative (NO), since the KOX value is larger than the predetermined value KOX, it is estimated that the air-fuel ratio is largely biased toward the lean side, and step 64 performs rich side proportional control. The correction value ΔP- is added to the previous value P of the correction value n-1 to obtain the current value PRn, and in the first step 65, the averaging constant COX and the predetermined number of times NAV are set as C0X1 (>COX, ), NAV, respectively. (<NA
V, ).

Further, when the determination result in step 60 is negative (No),
Since the KOX value is between the predetermined value KOX1 and KOX, it is estimated that the air-fuel ratio is slightly biased towards the lean side,
In step 66, the previous value P large n of the rich side proportional control correction value
−, is added with the correction value ΔP large (<ΔPg,) to set the current value Pan, and in the next step 67 the averaging constant COX
and the predetermined number of times NAV are COX, (COX, <
C0X2<C:OX,), NAV.

(NAv,>NAv,)NAv□).

Moreover, when the determination result in step 61 is negative (NO),
Since the KOX value is smaller than the predetermined value KOX, it is estimated that the air-fuel ratio is largely biased toward the rich side, and step 6
In step 8, the correction value ΔP- is subtracted from the previous value Pan-1 of the rich side proportional control correction value to obtain the current value Pan, and in the next step 69, the averaging constant COX and the predetermined number of times NAV are respectively set as coX4 (=COXi). , N AV4 (= N
Avl).

Moreover, when the determination result in step 62 is negative (NO),
Since the KOX value is between the predetermined value KOX and KOOX4, it is estimated that the air-fuel ratio is slightly biased toward the rich side, and in step 7o, the rich side proportional control correction value is corrected from the previous value Pan-□. The current value Pan is obtained by subtracting the value ΔP*.
In the next step 71, the averaging constant COX and the predetermined number of times NAV are respectively COXs ("COXJ,
Set to NAV3 (= NAvy).

In this way, depending on the degree of deterioration KOX of the 08 sensor 13, that is, when the air-fuel ratio is largely biased toward the rich side or the lean side, the averaging constant cOX is adjusted to a larger value (COX engineering, COX4), and the averaging is performed. By setting the predetermined number of times NAV to a smaller value (NAvy, NAV4), the degree of averaging of the transition time average values TIIIvAvn and TLvAvn can be accelerated, and the air-fuel ratio can be quickly controlled to the target air-fuel ratio.

In said step 64.66.68.70 the correction value Δ
The current value P of the rich side proportional control correction value corrected by P large or ΔP- is set to the upper limit value PIIIH in step 72.
In step 73, it is determined whether or not the lower limit value PIL is smaller than the lower limit value PIL, and when the determination results in steps 72 and 73 are both negative (NO), the corrected correction value P trap,
is set to the same value P (step 74), and if either one of the determination results is affirmative (Yes), the corrected correction value Pa is set.
, is set to the previous value Pkn-2 (step 75).

In step 76, the thus set correction value P is stored in the RAM 508 in FIG. 2, and in the next step 77, the averaging number count value nAV is set to O, and the program ends.

The correction value Pg stored in the RAM 508 in this way is used in the 02 feedback correction coefficient calculation subroutine, which will be described later, and thereby the correction coefficient Ko.

The value of can be biased towards the rich side or the lean side.

FIG. 10 is a program flowchart of the o8 feedback correction coefficient calculation subroutine using the rich side proportional control correction value PII corrected by the method described above.

First, it is determined whether the activation of the 0□ sensor 13 is completed (step 81). That is, the output voltage value of the 03 sensor 13 is determined to be at the activation starting point Vx (for example, by the internal resistance detection method of the 02 sensor 13). 0.6v), and when it reaches Vx, it is determined that it is activated. If the result of this determination is negative (No), the correction coefficient Ko is set to 1.0 (step 82), while if the result of 1 determination is positive (Yes), the engine is in the open control region. It is determined whether or not (step 83).

This open control includes a high load operation region, a low rotation region, an idle region, a high rotation region, a lean mixture region, etc. In a high load operation region, for example, the fuel injection time Tou〒 is greater than a predetermined value T vot. This is the area set to the value. Here, T vot is a constant and is the lower limit value of the amount of fuel supplied necessary to enrich the air-fuel mixture during high-load operation such as when the throttle valve is fully opened. In the low rotation region, the engine rotation speed Ne is below a predetermined value NLOP (for example, 700 rpm), and the intake pipe absolute pressure Pa^ is a predetermined value PBID1. (For example, 36
ha+Hg) or more.

In the idle region, the engine rotation speed No. is a predetermined rotation speed NH.
OP (for example, 1000 rpm) and the absolute pressure Pg^ is lower than the predetermined pressure PRIDL, and the high rotation region is a region where the engine rotation speed No is lower than the predetermined rotation speed N
This is a region larger than sop (for example, 3000 rpm).

The air-fuel mixture lean region is a region in which the intake pipe absolute pressure Pa^ is smaller than the discrimination value P iu,g which is set to a larger value as the engine speed Ne increases.

When the engine is in any of the above ranges, it is determined that the engine is being operated in the open control range, and in this case, the process proceeds to step 82 and the correction coefficient Ko is set to 1.0.

On the other hand, if the determination result in step 83 is negative (NO), it is determined that the engine is in an operating range that requires feedback control, and the process moves to closed loop control. sensor 1
It is determined whether the output level of 3 has been inverted between the previous input of the TDC signal and the current input (Step 84), and if the determination result is affirmative (Yes), proportional (P term) control is performed (Step 84). If the answer is negative (NO), integral control is performed (step 90 or later).

In step 85, it is determined whether the output level of the O2 sensor 13 is a low level or not, and if the determination result is affirmative (Yes), the proportional control correction value P is set to the rich side corrected by the value determination subroutine. A value corresponding to the engine rotation speed Ne is determined based on the proportional control correction value Pg□ and the No-P* child table (step 86) 0, then step 8
Then, this correction value P* is added to the previous value of the correction coefficient Ko. If the determination result in step 85 is negative (No), the lean side proportional control correction value Pt1Na-Pc is read out from the table according to the engine rotation speed Ne (step 88), and the correction value PL thus read is read out as the correction coefficient Ko.
is subtracted from the previous equivalent value (step 89).

If the determination result in step 84 is negative (NO), integral control is performed as follows. First, in step 90, similarly to step 85, it is determined whether or not the output level of the 0□ sensor 13 is at a low level.
If the answer is Yes), 1 is added to the count number N of TDC signal pulses (step 91), and it is determined whether the count number N has reached a predetermined value N+ (for example, 4).
Step 92), as a result of this determination, the count number N++,
If the count number Nl has not yet reached Nl, the correction coefficient KO□ is kept at the value at the previous loop (Step 93), and if the count number Nl has reached Nl, the correction coefficient KO□ is set according to the engine speed Ne. Add the corrected value Δk (step 94
), the number of pulses Nl counted so far is reset to 0 (step 95), and each time Nl reaches Nl, a correction value Δk is added to the correction coefficient Ko. On the other hand, if the determination result in step 90 is negative (NO), 1 is added to the count number NIH of TDC signal pulses.
is added (step 96), and it is determined whether the count number NIB has reached a predetermined value N+ (step 97). If the determination result is negative (NO), the value of the correction coefficient KO□ is the same as that of the previous loop. If the determination result is affirmative (Yes), the correction value Δ is calculated from the correction coefficient Ko.
k is subtracted (step 99), the counted pulse number NIH is reset to O (step 100), and the correction value Δk is subtracted from the correction coefficient Ko every time NIB reaches Nl as described above.

In this way, the rich side proportional control correction value P trap is corrected according to the degree of deterioration of the 03 sensor 13, and the thus corrected correction value Pg
02 feedback correction coefficient Ko.

By applying this to the calculation of
It is possible to make the air-fuel ratio coincide with the target air-fuel ratio by decreasing the value of , and increasing the value of the correction coefficient Ko if it leans toward the lean side.

In this embodiment, 0□Depending on the degree of deterioration of the sensor unit 3,
Although the rich side proportional control correction value Pλ is corrected, the same effect is not limited to this, but the same effect can be obtained by correcting at least one of the lean side proportional control correction value, the rich side, and the lean side integral control correction value. It will be done.

(Effects of the Invention) As detailed above, according to the present invention, the detected exhaust concentration value detected by the exhaust concentration detector disposed in the exhaust system of the internal combustion engine is compared with a predetermined reference value, and the detected value is compared with a predetermined reference value. When the detected exhaust gas concentration value changes from a rich side to a lean side or from a lean side to a rich side with respect to the predetermined reference value, the air-fuel ratio of the air-fuel mixture is increased or decreased by a first correction value. proportional control and when the detected exhaust gas concentration value is on the lean side or rich side with respect to the predetermined reference value,
In the air-fuel ratio feedback control method for an internal combustion engine, the air-fuel ratio is feedback-controlled to a target air-fuel ratio by at least one of integral control in which the air-fuel ratio is increased or decreased at predetermined intervals using second correction values, wherein the detected exhaust concentration value is the predetermined value. a first time period from the time when the exhaust gas concentration changes from the lean side to the rich side with respect to the reference value to the time when the exhaust gas concentration detection value changes from the rich side to the lean side with respect to the predetermined reference value; and a second time from the time when the lean side changes to the rich side, and at least one of the first correction value and the second correction value is changed according to the ratio thus calculated. As a result, even if the characteristics of the exhaust concentration detector change over time, the air-fuel ratio of the air-fuel mixture can be corrected to achieve the target air-fuel ratio, thereby improving engine operating performance, fuel efficiency, and exhaust emissions. Gas properties are improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of an air-fuel ratio control device that implements the method of the present invention, FIG. 2 is a block diagram showing the internal configuration of the electronic control unit shown in FIG. 1, and FIG. 0. A timing chart showing the change over time in the output voltage value Vo of the sensor 13, FIG. 4 is a graph showing the relationship between the value KOX representing the degree of deterioration of the 02 sensor 13 and the correction value ΔPg, and FIGS. A program flowchart of the P value determination subroutine according to the invention, FIG.
Figure 8 is a graph showing the relationship between the correction coefficient KNIE〒 and the engine speed No. Figure 9 is a graph showing the relationship between the correction coefficient Kpa〒 and the intake air A graph showing the relationship with the pipe absolute pressure PB^, FIG. 10 is a program flowchart of the 0□ feedback correction coefficient Ko, calculation subroutine. 1... Internal combustion engine, 5... Electronic control unit (ECU), 8... Absolute pressure in intake pipe (Pa^)
Sensor, 10...Engine speed (Ne) sensor, 1
3...O2 sensor.

Claims (1)

[Claims] 1. Compare the detected exhaust concentration value detected by the exhaust concentration detector placed in the exhaust system of the internal combustion engine with a predetermined reference value, and determine the air-fuel ratio of the air-fuel mixture supplied to the engine when the detected exhaust concentration value is Proportional control that increases or decreases the air-fuel ratio by a first correction value when the air-fuel ratio changes from a rich side to a lean side or from a lean side to a rich side with respect to a predetermined reference value, and the detected exhaust concentration value is changed with respect to the predetermined reference value. In an air-fuel ratio feedback control method for an internal combustion engine, the air-fuel ratio is feedback-controlled to a target air-fuel ratio by at least one of integral control that increases or decreases the air-fuel ratio at predetermined time intervals using second correction values when the air-fuel ratio is on the lean side or the rich side. , a first time period from when the detected exhaust gas concentration value changes from the lean side to the rich side with respect to the predetermined reference value to when the detected exhaust gas concentration value changes from the rich side to the lean side; The ratio between the time when the value changes from the rich side to the lean side and the second time from the time when the value changes from the lean side to the rich side is calculated, and the first correction value and the second correction value are determined according to the ratio thus calculated. An air-fuel ratio feedback control method for an internal combustion engine, characterized in that at least one of the correction values is changed.