JPS63189644A - Feedback control method for air-fuel ratio of internal combustion engine - Google Patents

Abstract

PURPOSE:To compensate aged deterioration of an exhaust sensor, by changing a control constant in accordance with the ratio of time, in which an exhaust concentration detection value reaches from a rich side maximum value to a lean side minimum value, to the time in which the exhaust concentration detection value reaches from the lean side minimum value to the rich side maximum value, in the case of an air-fuel ratio feedback control. CONSTITUTION:An electronic control unit 5, which calculates the basic fuel injection on the basis of detection values from an intake absolute pressure sensor 8 and an engine speed sensor 10, compares a detection value of an O2 sensor 13 with the reference value performing a feedback control of air-fuel ratio by a proportional plus integral control. The electronic control unit 5 compares transfer mean time, in which the detection output of the O2 sensor 13 reaches from a rich side maximum value to a lean side minimum value, with the transfer mean time in which the detection output of the O2 sensor 13 reaches from the lean side minimum value to the rich side maximum value, and the control unit 5, detecting the displacement of the air-fuel ratio, changes a proportional constant and an integration constant in a direction of small decreasing this displacement.

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, 02 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 O2 sensor used for such air-fuel ratio control uses zirconium oxide or the like as a sensor element.

By utilizing the fact that the amount of oxygen ions passing through the inside of zirconium oxide changes depending on the difference between the oxygen partial pressure in the atmosphere and the oxygen partial pressure in the exhaust gas, the output voltage of the 0□ sensor is adjusted according to this change. The oxygen concentration in the exhaust gas is detected by the change in the

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 0□ sensor over time, a problem will arise in that the operating performance, fuel efficiency, and exhaust gas characteristics of the engine will deteriorate.

(Objective of the Invention) The present invention has been made to solve the above-mentioned problems, and the present invention 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 O2 sensor to achieve a target air-fuel ratio. An object of the present invention is to provide an air-fuel ratio feedback control method for an internal combustion engine that can achieve the following.

(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, The air-fuel ratio of the mixture supplied to the engine is set to 1. 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, proportional control is performed to increase or decrease the air-fuel ratio by a first correction value, and the detected exhaust concentration value is changed from a rich side to a lean side or from a lean side to a rich side. When the air-fuel ratio is on the lean side or rich side with respect to the predetermined reference value, 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. In the air-fuel ratio feedback control method, a first time until the detected exhaust gas concentration value changes from a rich side maximum value to a lean side minimum value, and a time until the exhaust gas concentration detection value changes from a lean side minimum value to a rich side maximum value. and a second time period, and at least one of the first correction value and the second correction value is changed according to the ratio thus obtained. A control method is provided.

(Example) Hereinafter, an example of the present invention will be described 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.
One is provided for each cylinder, and is connected to a fuel pump (not shown), and the valve opening time for injecting fuel is controlled by a drive signal supplied from the ECU 3.

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 that detects the absolute pressure Pa^ in the intake pipe 2 is connected via E.
Sent to CU3.

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 attached around the camshaft or crank (not shown) of the engine 1, and this Ne sensor 10 outputs a 1 pulse signal (TDC signal) every 1800 rotations of the crankshaft, and this TDC signal is Sent to ECU3.

A three-way catalyst 12 is connected to the exhaust pipe 11 of the engine 1, and the three-way catalyst 12 converts HC1C○ and NOx in the exhaust gas.
Performs purifying action of ingredients. The exhaust pipe 11 on the upstream side of the three-way catalyst 12 has an O2 sensor 1 which is an exhaust gas concentration sensor.
3 is installed, the 02 sensor 13 detects the oxygen gas concentration in the exhaust gas, and the detection signal (VOZ) is sent to the ECU.
Sent to 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 Touτ of the fuel injection valve 6 is calculated by the following equation.

Tout = Ti read from a memory device within the KO2 is a 0□ feedback correction coefficient, which will be described later. 2 is calculated based on the feedback correction coefficient calculation subroutine. 1 and 2 are a correction coefficient and a correction variable respectively calculated according to the various engine parameter signals, and are used to calculate fuel efficiency characteristics, engine acceleration characteristics, etc. according to the engine operating state based on detection signals from the various sensors described above. A predetermined value is determined so as to optimize the various characteristics of.

The ECU 3 uses the fuel injection time Tau obtained 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 (rCPU
503 (hereinafter referred to as "rMe counter") 502
The sMs counter 502 also supplied to 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 Ne.

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 (
Pa^) sensor 8, engine water temperature (Tw) sensor 9.
The output signals from the 0□ sensor 13 and the vehicle speed (Sp) sensor 14 are respectively applied to a level correction circuit 504,
After being corrected to a predetermined voltage level in the circuit 504, C
Multiplexer 5 that operates based on commands from PU503
05, the signals are 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 further includes a read-only memory (hereinafter referred to as “ROM”) 507 via a data bus 510;
Random access memory (hereinafter referred to as rRAMJ) 5
08 and a drive circuit 509. ROM50
7 stores various control programs executed by the CPU 503, the details of which will be described later, various data such as correction coefficients and correction variables, and tables and the like in N e -P. Also, RAM5
08 temporarily stores calculation results obtained by executing the various control programs in the CPU 503.

CPU 503i*, ROM 5074: Read out or calculate the coefficient value or variable value corresponding to the output signal of each sensor described above from the ROM 507 according to the stored control program, and adjust the fuel injection valve based on the above calculation formula (1). 6 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 T.
The fuel injection valve 6 is opened across au〒.

Next, a method of calculating the 02 feedback correction coefficient Ko according to the change in characteristics of the 0□ sensor according to the present invention over time will be explained.

As described above, the output characteristics of the O2 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 02 sensor is determined by the rich side peak value (maximum value) of the output voltage value (Figure 3) under stable engine running conditions.
Time required for transition to peak value (minimum value) on side TII
v (between t2 and t1 in Figure 3) and the time TLV (between t3 and t4 in Figure 3) required for transition from the lean peak value (minimum value) to the rich peak value (maximum value). It can be estimated by the value KOX (=TLv/Tv). This KOX value is the cumulative mileage of the vehicle.

In other words, the maximum value and minimum value as used in the present invention, which have been experimentally confirmed to decrease depending on the degree of durability deterioration, are the output voltage value Vo that changes in the direction away from the reference value v Ohno. This is the output voltage value Vo at the time when the direction of change is reversed to the value Vwtp side.

Therefore, in the present invention, the air-fuel ratio can be accurately adjusted to the target air-fuel ratio by changing the proportional control correction value or the integral control correction value, which is added or subtracted to the correction coefficient Ko2, by an amount corresponding to the KOX value in air-fuel ratio feedback control, which will be described later. It is intended to be controlled.

This embodiment is applied to the case where the proportional control correction value P added to the correction coefficient KO
4 (KOX, >KOX, >KOX, >KOX,), the proportional control correction value P large is set to the correction value ΔP trap 8, ΔP
- (Figure 4), change as follows.

(1) When KOX>KOXl, it is estimated that the air-fuel ratio is largely biased toward the lean side, and a correction value ΔP*2 is added to the correction value PII.

(2) When KOX,>KOX>KOX, it is estimated that the air-fuel ratio is slightly biased toward the lean side, and a correction value ΔPII11 (2 for <ΔP) is added to the correction value P large.

(3) Estimating that the air-fuel ratio is controlled approximately equal to the target (theoretical) air-fuel ratio when KOX,>KOX>KOX3,
The correction value P* is held.

(4) When KOXI>KOX>KOX4, it is estimated that the air-fuel ratio is slightly biased toward the rich side, and the correction value ΔPIII□ is subtracted from the correction value PII.

(5) When KOX<KOX4 (7), it is estimated that the air-fuel ratio is largely biased toward the rich side, and the correction value ΔP*2 is subtracted from the correction value P.

Figures 5 and 6 show the rich side proportional control correction value P
It is a program flowchart of the P purchase price determination subroutine for implementing the change of a.

First, in steps 30 to 36, it is determined whether the engine is in a predetermined operating state in which the output voltage Vo of the O2 sensor 13 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 Twox, and then in step 31, it is determined whether the engine is actually under feedback control. Determine. Further, in steps 32 to 35, as conditions for the predetermined operating state, it is determined whether the engine rotation speed No is a value between the predetermined values N eoxL and N eoxu (step 32), and the intake pipe absolute pressure Pa is determined. It is determined whether ^ is a value between a predetermined value PaoxL and PBOXH (step 33), and whether the vehicle speed Sp indicating the cruising state of the vehicle is a value between a predetermined value SPOXL and 5poxo. or not (step 34), and the degree of change in the absolute pressure ΔPa^ indicating a stable cruising state.
A determination is made as to whether the absolute value of is smaller than the predetermined width ΔP BOX^ (step 35). Further step 3
In step 6, after these operating conditions are satisfied (after all the determination results in steps 32 to 35 are affirmative (Yes)),
It is determined whether this operating state has continued for a certain period of time Tx.

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 0, and ends this program.

Steps 38 to 52 have been described above. KOX value (=TLV/T *v
) to determine the average value of TLV times T LVAV,
And the average value Ttrap vAv of Tkv time is calculated.

Below, the average value TL from step 38 to step 52
VAV, T The method for calculating VAV will be explained based on the timing chart of the output voltage value vo2 of the 02 sensor shown in FIG.

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

First, in step 38, the output voltage value vO□n of the current loop of the 0□ sensor 13 is changed to the output voltage value VO□n of the previous loop.
It is determined whether the value is greater than n-. At time t1 in FIG. 3, this determination result is affirmative (Yes), and step 3
Proceeding to step 9, the output voltage value Vo2n-1 of the previous loop is the output voltage value Vo,n- of the loop two days before the previous.

It is determined whether or not the value is larger than that. At time t□, the result of this determination is also affirmative (Yes), and the program is ended without executing steps 48 onwards, which will be described later.

When the output voltage value Vo of the Q2 sensor 13 reaches the maximum value and starts to fall (time t2 in FIG. 3), the determination result in step 38 becomes negative (NO), and the next step 4 is started.
At o, as in step 39, the output voltage value Votn-1 in the previous loop is changed to the output voltage value Vo,n in the loop before the previous one.
It is determined whether or not the value is greater than -2. Output voltage value Vo,
In the loop immediately after t reaches the maximum value (at time tz), this determination result becomes affirmative (Yes), and in the next step 41, t
The count value tox of the ax timer is set as the transition time Tox, and in the next step 42, the transition time T thus set is set.
Determine whether ax is within the allowable range TOXL"TOXH.The tax timer is reset and started in step 46, which will be described later, in the loop immediately after the output voltage value Vo2 reaches the maximum value or minimum value, so this time loop (tz
At this point in time), the count value tax becomes O. Therefore,
The determination result in step 42 is negative (NO), and steps 43 to 45, which will be described later, are skipped and step 46 is performed.
Proceed to.

By making the determination in step 42 in this way, the extremely long transition time that occurs during the transition period of the engine operating state, such as when the tox timer has already been activated before the time tU, or the time t4 to t4 in FIG. t.

It is also possible to eliminate significantly short transition times due to noise generation, etc., as shown between time points.

In step 46, the count value of the tox timer is reset and started, and in the next step 47, 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 0□ sensor 13,
As long as the value decreases (between time t2 and time t1 in FIG. 3), the results of the determinations in steps 38 and 40 become negative (NO), and the program ends. Therefore, during this period, the count value of the tox timer is not reset and is 1. It represents the elapsed time from the point in time.

When the output voltage value vO□ of the 0□ sensor 13 reaches the minimum value and starts to rise again (at time t1 in FIG. 3), the determination result in step 38 is positive (Yes), and the determination result in the subsequent step 39 is positive. If the result is negative (NO), it is assumed that the output voltage value vO□ has reached the minimum value between the previous loop and the current loop, and the process proceeds to step 48. In step 48, as in step 41, the current Tox timer count value toxCt2-t3 time) is set as transition time Tox
In step 49, similarly to step 42, it is determined whether the transition time To set in step 48 is within the allowable range TOXL''TOXH.

If the determination result is negative (No), steps 50 to 52 are skipped and the process proceeds to step 46 described above.

If the determination result in step 49 is affirmative (Yes), the process proceeds to step 50, where the thus set transition time Tax is multiplied by the correction coefficients Knit, Kpe〒, and the result is set as a new transition time Toxc. The correction coefficients Kstt and Kpa are determined according to the engine speed Ne and the intake pipe absolute pressure Pa^, respectively, using the KNE〒-Ne table shown in Figs. 8 and 9, K
This is the value read from the pa〒-PB^ table. The reason why the transition time Tox is corrected by the correction coefficients Kst〒 and KPB〒 in step 50 in this way is that the reversal period of the 0□ sensor itself changes significantly depending on changes in the engine speed Ne and the intake pipe absolute pressure Pa^. It is for change.

The transition time T oxc corrected in step 50 is substituted into the following equation (2) in the next step 51.

As a result, the rich side transition time average value TgoodVAVn of the voltage value Vo from the rich side maximum value to the lean side minimum value is calculated.

...(2) Here, T good vAvn-, is the previous value of the rich side transition time average value, COX is the averaging constant for calculating the average value, and steps 63, 65, 67, 69 described later .7
0 in 1. Value COX depending on the degree of sensor deterioration.

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

Returning to FIG. 5, in the next step 52, 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 46, the tax timer is At step 47, the count value of step 51 is reset and started.
Then, it is determined whether the averaging count value nAV representing the number of times the transition time is averaged in step 44, which will be described later, is greater than or equal to the predetermined number of times NAV. In addition, the predetermined number of times N
Av 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 02 sensor.

As described above, the transition time T between time points t2 and t1 in FIG.
ax (=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 Tox.
*vAvn is calculated.

In the next and subsequent loops, the output voltage value Vo of the 02 sensor 13,
As long as the value increases (times t and t4 in FIG. 3), the results of the determinations in steps 38 and 39 are both affirmative (Yes), and the program ends. Therefore, during this period, the count value of the tox timer is not reset and is 1. It represents the elapsed time from the point in time.

When the output voltage value vo2 of the 02 sensor 13 reaches the maximum value, it starts to fall again (at time t9 in FIG. 3).

Assuming that the determination result in step 38 is negative (No), the determination result in step 40 is positive (Yes), and that the output voltage value vO□ has reached the maximum value between the previous loop and the current loop, The count value tox (t, -t, time) of the tox timer at this point is set as the transition time Tox (step 41), and it is determined in step 42 whether or not this transition time Tax is within the allowable range TOXL to Toxo. Then, the process proceeds to step 43, in which the transition time Tax
is the engine speed Na.

Correction coefficient Ksit according to intake pipe absolute pressure Pa^, K
It is corrected by pa〒 and set as a new transition time Toxc.

Furthermore, in step 44, the corrected transition time Toxc is substituted into the following equation (3) to obtain the output voltage value Vo, the average value T of the transition time from the lean side minimum value to the rich side maximum value. bvAvn is calculated.

COX 256-COX TLvAvn = -X Toxc +
256 X TLvAvn-1...(3
) Here, TLvAvn-1 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 the next step 45, 1 is added to the averaging count value nAV as in step 52, and the process proceeds to steps 46 and 47 described above.

In addition, when the output voltage value vo2 of the 0□ sensor 13 is decreasing or increasing, if noise as shown in FIG. 3 occurs between time t4 and time t5, the transition time Tax becomes a significantly short value. If the determination result in step 42 or 49 is negative (No), it is possible to eliminate the influence on the calculation of the rich side and lean side transition time average values executed in step 44.51.

Further, the reason why the calculation of the rich side and lean side transition time average values in steps 38 to 52 is repeated in this way until the averaging count value nAV reaches the predetermined number of times NAV is based on the degree of deterioration of the 0□ sensor. The value KO representing
This is to obtain X (:TLVAV/TIIVAV) more accurately.

The calculation of the average value of each transition time to the rich side and the lean side is performed a predetermined number of times NAV, and if the determination result in step 47 is affirmative (Yes), steps 59 to 7 in FIG.
7, the rich side proportional control correction value P trap is corrected according to the degree of deterioration of the 0□ sensor 13.

In the determinations in steps 59 to 62, the value KOX (=TLvAv/T*vAv) representing the degree of deterioration of the O2 sensor and the aforementioned predetermined value KOX1. KOX2, KOXl, KOX
4 (KOX, >KOX, >KOX, >
KOX4). That is, in step 59, a predetermined value K is set to the rich side transition time average value TltVAV after the completion of averaging a predetermined number of times.
In step 60, a predetermined value KOX2 is added to the average value TIIIVAV to determine whether the value multiplied by OX is greater than the lean side transition time average value TLVAV after the completion of averaging a predetermined number of times.
It is determined whether the multiplied value is larger than the average value TLVAV. On the other hand, in step 61, it is determined whether the value obtained by multiplying the average value TIIIvAv by a predetermined value KOX4 is smaller than the average value TLVAV, and in step 62, the predetermined value KOX is determined to be the average value TIIIvAv.

It is determined whether the multiplied value is smaller than the average value TLVAV.

Therefore, all of the determination results from steps 59 to 62 are positive (
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 COXe and NAVO, 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 n-1 to the previous value P of the correction value to obtain the current value Pan, and in the next step 65, the averaging constant COx and the predetermined number of times NAV are calculated.
are COX(〉COXa) and NAVl(<NA
VO).

Moreover, when the determination result in step 60 is negative (NO),
The KOX values are predetermined values KOX□ and KOX.

Since the air-fuel ratio is between 1 and 2, it is estimated that the air-fuel ratio is slightly biased toward the lean side, and in step 66, a correction value ΔP □ (ku ΔP-) is added to the previous value P*n-1 of the rich side proportional control correction value. The current value is Pan, and in the next step 67, the averaging constant COx and the predetermined number of times NAV are calculated as C0X2(
COX, <COX, <COX□), NAV.

(NAv,>NAv2)NAvx).

Moreover, when the determination result in step 61 is negative (NO),
Since the KOX value is smaller than the predetermined value KOX4, it is estimated that the air-fuel ratio is largely biased toward the rich side, and step 6
In step 8, the correction value ΔP1 is subtracted from the previous value pHn-1 of the rich side proportional control correction value to set n to the current value P, and in the next step 69, the averaging constant COx and the predetermined number of times NAV are calculated as C0X4 (=COX , ), N AVl (= N
AVl).

Further, 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 70, the previous value of the rich-side proportional control correction value is set to Subtract the correction value ΔP* from the current value Pi!
n, and in the next step 71, the averaging constant COX and the predetermined number of times NAV are respectively COX3 (" COXl)
, set to NAv3 (= NAV2).

do.

In this way, the averaging constant COx is set to a larger value (COXl
. The fuel ratio can be controlled to the target air-fuel ratio.

In said step 64.66.68.70 the correction value Δ
The current value Pan of the rich side proportional control correction value corrected by PIIL or ΔP- is set to the upper limit value PII in step 72.
The lower limit value PIIL is determined in step 73 to determine whether the value is greater than N.
It is determined whether the corrected value P is smaller than the corrected value P.
a, is set to the current value Pan (step 74), and when either one of the determination results is affirmative (Yes), the corrected correction value PII+1 is set to the previous value P trap n-1 (step 7
5).

In step 76, the thus set correction value P large is stored in the RAM 508 in FIG. 2, and in the first step 77, the averaging count value nAV is set to 0, and the program is terminated.

The correction value P large thus stored in the RAM 508 is used in the 02 feedback correction coefficient calculation subroutine to be described later, thereby making it possible to bias the value of the correction coefficient KO□ toward the rich side or the lean side.

FIG. 10 is a program flowchart of the 02 feedback correction coefficient calculation subroutine using the rich side proportional control correction value P* corrected by the method described above.

First, it is determined whether activation of the O2 sensor 13 has been completed (step 81). That is, ○.

02 sensor 13 depending on the internal resistance detection method of sensor 13
The output voltage value of is the activation starting point V x (e.g. 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 operating region, a low-speed region, an idle region, a high-speed region, a lean mixture region, etc. The high-load operating region includes, for example, a value in which the fuel injection time Tou〒 is larger than a predetermined value Twot. This is the area set to . Here, Twot is a constant and is the lower limit 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 a predetermined value N LOP (for example, 700 rpm
m) or less, and the intake pipe absolute pressure Pa^ is a predetermined value PBI
This is a region of DL (for example, 360 mmHg) or higher.

In the idle region, the engine rotation speed Ne is a predetermined rotation speed No.
op (for example, a region lower than 101,000 rpm, and in which the absolute pressure Pa^ is lower than the predetermined pressure PBIDL).

In the high rotation region, the engine rotation speed Ne is the predetermined rotation speed NHO
This is a region larger than P (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 PBLS, 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, where the correction coefficient Ko2 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 the operating range where feedback control is required, and the process moves to closed loop control.
It is determined whether or not the output level of No. 3 has been inverted between the previous input of the TDC signal and the current input. Step 84) If the determination result of No. 1 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 02 sensor 13 is a low level or not, and if the determination result is positive (Yes), the proportional control correction value P is set to The side proportional control correction value P* is determined to be a value corresponding to the engine speed Ne based on the Ne-P* child table (step 86) 0, then step 8
In step 7, this correction value P trap is added to the previous value of the correction coefficient KO2. If the determination result in step 85 is negative (NO).

Step 88) Read the lean side proportional control correction value PL from the Ne-PL table according to the engine rotation speed Ne.
, the thus read correction value PL is subtracted from the previous equivalent value of the correction coefficient Ko (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 the output level of the 02 sensor 13 is low. This discrimination result is positive (
If yes).

Add 1 to the value of the count number N of TDC signal pulses (step 91), and the count number N+t becomes the predetermined value N+(
For example, it is determined whether or not 4) has been reached (step 92).
As a result of this determination, if the count number NIL has not yet reached N+, the correction coefficient Ko2 is kept at the value from the previous loop (step 93), and if the count number NIL has reached N+, the correction coefficient Ko2 is A correction value Δk corresponding to the engine speed Ne is added to KO□ (step 94), and the number of pulses NIL counted up to that point is reset to O (step 95), so that Nl becomes N! The correction coefficient KO□
A correction value Δk is added to . On the other hand, if the determination result in step 90 is negative (No), T
1 is added to the count number NIH of DC signal pulses (step 96), and it is determined whether the count number NIB has reached a predetermined value N1 (step 97), and the determination result is negative (N
O), the correction coefficient Ko.

The value of is kept at the value at the previous loop (step 98), and if the determination result is affirmative (Yes), the correction coefficient Ko.

Step 99) to subtract the correction value Δk from
0), the correction value Δk is subtracted from the correction coefficient Ko every time the NIH reaches N+, as described above.

In this way, the rich side proportional control correction value Pλ is corrected according to the degree of deterioration of the 02 sensor 13, and the correction value P1 thus corrected is
1 as o2 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, depending on the degree of deterioration of the O2 sensor 13,
Although the rich side proportional control correction value PIII is corrected, 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, in which the detected exhaust concentration value is on the rich side, 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 time intervals using second correction values. The ratio of the first time from the maximum value to the minimum value on the lean side and the second time until the detected exhaust gas concentration value changes from the minimum value on the lean side to the maximum value on the rich side is determined, and the ratio thus determined is calculated. Since at least one of the first correction value and the second correction value is changed according to the The target air-fuel ratio can be achieved through correction, thereby improving engine operating performance, fuel efficiency, and exhaust gas characteristics.

[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. FIG. 4 is a timing chart showing the change over time in the output voltage value Vo2 of the 02 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 ΔP trap. FIGS. A program flowchart of the P value determination subroutine according to the present invention, FIG.
FIG. 8 is a graph showing the relationship between the correction coefficient KNtr and the engine rotation speed Na,
FIG. 9 is a graph showing the relationship between the correction coefficient KPB↑ and the intake pipe absolute pressure PB^, and FIG. 10 is a program flowchart of the 02 feedback correction coefficient Ko and calculation subroutine. DESCRIPTION OF SYMBOLS 1... Internal combustion engine, 5... Electronic control unit (ECU), 8... Intake pipe absolute pressure (Pa^) sensor, 10... Engine speed (Ne) sensor, 13
...02 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 for the detected exhaust gas concentration value to go from a rich side maximum value to a lean side minimum value, and a second time for the exhaust gas concentration detected value to go from a lean side minimum value to a rich side maximum value. 1. An air-fuel ratio feedback control method for an internal combustion engine, characterized in that the ratio is determined, and at least one of the first correction value and the second correction value is changed according to the ratio thus determined.