JPS63189642A - Feedback control method for air-fuel ratio in internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the displacement of air fuel ratio due to 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 is transferred from its reference value to a rich side maximum value, to the time in which the exhaust concentration detection value is transferred from the reference value to a lean side minimum value, in the case of an air-fuel ratio feedback control. CONSTITUTION:An electronic control unit 5, which calculates a basic fuel injection quantity 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 the reference value to the rich side maximum value, with the transfer mean time in which the detection output of the O2 sensor 13 reaches from the reference value to the lean side minimum value, and the electronic 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, 0□ sensor) placed in the exhaust system of an internal combustion engine is compared with a predetermined reference value. Based on the comparison results, the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to the stoichiometric mixture ratio that achieves the maximum conversion efficiency of the three-way catalyst disposed in the engine's exhaust system, thereby reducing the exhaust gas. An air-fuel ratio feedback control method for internal combustion engines that aims to improve characteristics, etc. is generally used (for example, Japanese Patent Laid-Open No. 137633/1983).

The zero 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 sensor is adjusted to zero according to this change. The oxygen concentration in the exhaust gas is detected by the change in the

However, the output characteristics of the 03 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 O2 sensor over time, a problem will arise in that the operating performance, fuel efficiency, and exhaust gas characteristics of the engine will deteriorate.

(Object of the Invention) The present invention has been made to solve the above-mentioned problems, and aims to correct 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 0.8 sensor. It is an object of the present invention to provide an air-fuel ratio feedback control method for an internal combustion engine that can achieve an air-fuel ratio.

(Structure of the invention) According to the present invention, this object is achieved.

The detected exhaust concentration value detected by the exhaust concentration detector arranged in the exhaust system of the internal combustion engine is compared with a predetermined reference value, and the air-fuel ratio of the mixture supplied to the engine is determined when the detected exhaust concentration value is the predetermined value. Proportional control that increases or decreases the air-fuel ratio by a first correction value when the reference value changes from the rich side to the lean side or from the lean side to the rich side, and the detected exhaust gas concentration value is on the lean side with respect to the predetermined reference value. Or, in the air-fuel ratio feedback control method for an internal combustion engine, in which the air-fuel ratio is feedback-controlled to the 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 by respective second correction values when the air-fuel ratio is on the rich side. a first time period for the detected exhaust gas concentration value to reach a maximum value on the rich side from the predetermined reference value; and a second time period for the detected exhaust gas concentration value to reach the minimum value on the lean side from the predetermined reference value. Provided is 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 in accordance with the ratio thus determined. .

(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 □, and a throttle valve 3 is provided in the middle of the intake pipe 2. 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 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 rNa sensor) 1
0 is attached around the camshaft or crank (not shown) of the engine 1, and this Ne sensor 10 outputs one pulse signal (TDC signal) every 180° rotation of the crankshaft, and this TDC signal is sent to the ECU 3. sent to.

A three-way catalyst 12 is connected to the exhaust pipe 11 of the engine 1, and the three-way catalyst 12 converts HC in the exhaust gas.

This three-way catalyst 1 performs the purifying action of Co and NOx components.
An O2 sensor 13, which is an exhaust gas concentration sensor, is attached to the exhaust pipe 11 on the upstream side of the exhaust gas.The O3 sensor 13 detects the oxygen gas concentration in the exhaust 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 processors mentioned above,
The fuel injection time Tau〒 of the fuel injection valve 6 is calculated by the following equation.

Tou〒=TiXK, XKo, +, m (1) Here, Ti indicates the basic fuel injection time of the fuel injection valve 6,
This basic injection time is read out from a memory device in the ECUS based on, for example, the intake pipe absolute pressure PB^ and the engine speed No. *Ko is 0. This is a feedback correction coefficient, and is calculated based on the 08 feedback correction coefficient calculation subroutine (FIG. 10), which will be described later. □ and □ are correction coefficients and correction variables respectively calculated according to the various engine parameter signals, and are based on detection signals from the various sensors described above to determine fuel efficiency characteristics, engine acceleration characteristics, etc. according to the engine operating state. A predetermined value is determined so as to optimize the various characteristics of.

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)
5o3 (hereinafter referred to as "rMe counter") 502.
The ++Me counter 502, which is supplied to Proportional.

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

On the other hand, throttle valve opening (θ〒H) sensor 4. Absolute pressure (
PB^) sensor 8, engine water temperature (T w) sensor 9.
The output signals from the 02 sensor 13 and the vehicle speed (Sp) sensor 14 are applied to a level correction circuit 504, and after being corrected to a predetermined voltage level in the circuit 504, the output signals are output from the CP sensor 13 and the vehicle speed (Sp) sensor 14.
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 further connects a read-only memory (hereinafter referred to as rROMJ) 507 and a random access memory (hereinafter referred to as rRAMJ) 50 via a data bus 510.
8 and a drive circuit 509. ROM507
, various control programs executed by the CPU 503 and various data such as correction coefficients and correction variables, the details of which will be described later, and N
Stores e-PII tables, etc. Also, RAM508
temporarily stores calculation results obtained by executing the various control programs in 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 0 and the feedback correction coefficient Ko according to the change over time of the characteristics of the 0□ sensor according to the present invention will be explained.

As described above, the output characteristics of the 02 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 the O2 sensor is the output voltage value Vo of the O3 sensor under stable engine running conditions.

(Figure 3) predetermined reference value Vllll! Time required for transition from F to rich side peak value (maximum value) T*v (3rd
t2 to t□, t1 to t1°) and the time TLV (between t4 and t7 in Figure 3) required for transition from the predetermined reference value v■F to the lean side peak value (minimum value). It can be estimated by the value KOX (=Tcv/Ttrapv) representing It has been experimentally confirmed that this KOX value decreases according to the cumulative mileage of the vehicle, that is, the degree of durability deterioration6.
Output voltage value Vo at the time when the output voltage value Vow, which changes in the direction away from p, reverses the direction of change to the reference value vIF side.

It is.

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 when changing the proportional control correction value PIIttKOx value added to the correction coefficient KO□. Specifically, the value of KOX is changed to a plurality of predetermined values
X4 (KOX, >KOX, >KOX, >KOX,
) Compare the proportional control correction value P* with the correction value ΔP.
The change is made as follows using gΔP*2 (Fig. 4).

(1) When KOX>KOX, +7), it is estimated that the air-fuel ratio is largely biased toward the lean side, and a correction value ΔPIIL1 is added to the correction value P rich.

(2) When KOX□>K OX>K Ox, it is estimated that the air-fuel ratio is slightly biased toward the lean side, and the correction value PR is
A correction value ΔPgL (<ΔP1) is added to .

(3) When KOX,>KOX>KOXI (7), it is estimated that the air-fuel ratio is controlled to be approximately equal to the target It (theoretical) air-fuel ratio, and the correction value Pa is held.

(4) KOX, > KOX > KOX, Noto 1! 'Estimating that the air-fuel ratio is slightly biased toward the rich side, the correction value ΔPa is subtracted from the correction value Pa.

(5) When KOX<KOX4(F), it is estimated that the air-fuel ratio is largely biased toward the rich side, and the correction value ΔPII1. Subtract.

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

First, in steps 30 to 36, the engine.

0, it is determined whether the output voltage VO of the 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.
l! It is determined whether the value is between OXL and N150XH (step 32).

The intake pipe absolute pressure Pa^ is a predetermined value P aoxt, and P e
Determine whether the value is between oxo (step 33)
, the vehicle speed Sp indicating the cruising state of the vehicle is a predetermined value Sp.
It is determined whether or not the value is between L and 5poxo (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 a
A determination is made as to whether or not the value is smaller than ox^ (step 35). Further, in step 36, after these operating conditions are satisfied (after all the determination results in steps 32 to 35 are positive), this operating state remains 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.

Note that if the determination result in any one of steps 30 to 36 is negative (NO), the process proceeds to step 37.

The averaging number count value nAV, which will be described later, is set to O, and the output comparison value VMs=, which will be described later, is set to a predetermined reference value v■F, respectively, and the program ends.

In steps 38 to 58, the KOX value (=Tt, v/T position v) representing the degree of deterioration of the 02 sensor 13 described above is
), the average value TLVAV of the TLV time and the average value TNote^V of the T large v time are calculated.

Below, the average value TL from step 38 to step 58
A method of calculating VAV and TIIIVAV will be explained based on a timing chart of the output voltage value Vo of the 0° sensor shown in FIG.

Now, let us consider a case where the determination result in step 36 becomes affirmative (Yes) for the first time at time t□ in FIG.

First, in step 38, it is determined whether the output voltage value Vo,n of the current loop of the 02 sensor 13 is larger than a predetermined reference value v. At time t1 in FIG. 3, the result of this determination is negative (No), and the process proceeds to step 39, where it is determined whether the output voltage value VO@n-1 of the previous loop is greater than a predetermined reference value vF. At time t1, this determination result is also negative (No), and the process proceeds to step 40.

In step 40, the current output voltage value Vo,n is the output comparison value vM! In this loop, since this output comparison value VMI has been set to the predetermined reference value v large needle in step 37 described above, the determination result is affirmative (Y
es) and proceeds to step 41. In step 41, the count memory value tOXMIE is set to the count value tow of the tax timer at this point, and in the first step 42, the output comparison value VMI is set to the output voltage value Vo, n of the current loop. Set to , and exit this program. Incidentally, since the tox timer is started for the first time by executing step 49, which will be described later, its count value is 0 at this point (time t1 in FIG. 3), and therefore the count memory value t OXM! is 0 until the output voltage value Vo exceeds the predetermined reference value v large needle in the loop after the 0th cycle, that is, from t□ to t in FIG.
Between the three time points, the determination result in step 40 is negative (No).
Then, steps 41 and 42 are skipped and the program ends.

When the output voltage value Vo of the o2 sensor 13 exceeds EF to the predetermined reference value V for the first time in this loop (at time t2 in Figure 3),
The determination result in step 38 is affirmative (Yes),
Proceed to the next step 43.

In step 43, the output voltage value V 02n in the previous loop
It is determined whether or not -1 is larger than a predetermined reference value V*tp, and at time t2, this determination result is negative (No), and in the first step 44, the count memory value toxmt stored at this time is transferred. The time is set as Tax, and the process proceeds to the first step 45.

In step 45, the transition time T set in step 44 is
It is determined whether ox is within the allowable range TOXL''TOXH.

As mentioned above, between time points t and t3, the count memory value t
oxpayt is 0, and the determination result in step 45 is negative (No), so steps 46 to 48 described below are performed.
is skipped and proceeds to step 49.

By performing the determination in step 45 in this way, t1
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 above-mentioned step 41 and the count memory value toxxw set in step 41 becomes a large value, or the case shown in FIG. It is also possible to eliminate extremely short transition times due to noise generation, as shown between times t and t9.

Returning to FIG. 5, in the next step 49, the output comparison value VMI
! is set to the predetermined reference value Vtp again, and the count value tox of the tox timer is reset and started,
Averaging count value nA, which will be described later in the next step 5o.
It is determined whether or not V is equal to or greater than a predetermined number of times NAV. If the determination result is affirmative (Yes), the program from step 59 (see FIG. 6) to be described later is executed, and if negative (No), the main program is executed. Exit the program.

Incidentally, since the count value of the tox timer is reset only in step 49, the value tox is always 0 Figure 3 represents the elapsed time from time t2゜14, 1., etc.).

The output voltage value Vo of the 02 sensor 13 is the predetermined reference value VII.
After exceeding IEF (after time ti), step 38
．． 43 are both affirmative (Yes), the process proceeds to the next step 51, and the output voltage values Vo, n in the current loop are determined.
is the output comparison value vM! It is determined whether or not the value is greater than or equal to the value. In this case, since the value of Vat was set to the predetermined reference value VR1F in step 49 of the previous loop (time point ta), the determination result is affirmative (Yas) and step 52
Then, the count value tox of the tox timer at this point is set to the count storage value toxMw, and in the following step 53, the output comparison value vM! The output voltage value Vo, n in this loop is
Set this to end one program and move on to the first loop.

Between time t2 and time t1 in FIG. 3, the output comparison value VMI is always the output voltage value Vo of the o8 sensor in the previous loop.

However, in this case, the determination result in step 51 is always affirmative (Yes), and step 52.
53 is executed repeatedly. As a result.

As long as the output voltage value Vo updates the maximum value (step 5
1 is affirmative) The value of the count memory value toxmt is the timer count value tox at that time (in this case, t
(elapsed time from point 2) each time, and the output comparison value v is set to the output voltage value Vo,n of the current loop which is the maximum value at this point.

When the output voltage value Vo of the o2 sensor 13 reaches the maximum value and then starts to decrease toward the predetermined reference value V*i+p (
At time t3 in FIG. 3), the determination result in step 51 is negative (No), and at this time, assuming that the output voltage value Vo has reached the maximum value between the previous loop and the current loop, step 52.53 Skip this and exit this program.

As a result, in the subsequent execution of step 51, the output voltage value vO□ is the output comparison value VM representing the maximum value at this point.
As long as the count is below t (vo2 value at time ta), the value of the count storage value toxpgtt (corresponding to time 1-t1 in FIG. 3) is held.

The output voltage value Vo, n of the o3 sensor 13 reaches the predetermined reference value vIII again in this loop! When it goes below F (time t4 in FIG. 3), the determination result in step 38 is negative (No).

The determination result in step 39 is affirmative (Yes),
Proceed to the next step 54.

In step 54, the count memory value toxM at this point is
t (ts-t, time) is set as the transition time TQX, and the process proceeds to the next step 55. In step 55, the transition time To set in step 54 is set as in step 45 described above.
Determine whether or not the current value is within the allowable range TOXL~Toxo, and if the determination result is negative (No), proceed to step 5.
Steps 6 to 58 are skipped and the process proceeds to step 49.

When the determination result in step 55 is affirmative (Yes), the process proceeds to step 56, and the transition time To is set in this way is truly the correction coefficient KN! 〒, KpB〒 is multiplied and the new transition time τox
Let it be c. Correction coefficient KN! ? , KpB〒 is KN! shown in FIGS. 8 and 9 depending on the engine speed No. and the intake pipe absolute pressure Pa^, respectively. 〒-No table, Kps〒-
This is the value read from the PB^ table. In this way, the transition time Tox is corrected by the correction coefficients Kwty and KpB in step 56 based on the engine rotation speed No.
This is because the inversion period of the O8 sensor itself changes significantly in accordance with changes in the intake pipe absolute pressure Pa^.

The transition time Toxc corrected in step 56 is substituted into the following equation (2) in the next step 57, and as a result, the voltage value Vo from the predetermined reference value v■F to the rich side maximum value,
An average value T large ν^vn of the transition time to the noisy side is calculated.

COX 256-COX TtributvAvn = iX Toxc + 7 X T*
vAvn-1...(2) Here, T-contribution vhvn-1 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, which will be described later. 67.69.71
The value COX corresponds to the degree of deterioration of the 02 sensor.

~C0X4 (however, O<COX, ~COX, <256)
is set to

Returning to FIG. 5, in the next step 58, 1 is added to the averaging count value nAV representing the number of executions of transition time averaging based on the above-mentioned equation (2), and the process proceeds to step 49 to obtain an output comparison value. Vxg is set again to the predetermined reference value v large needle, and the count value of the tax timer is reset and started.

In the next step 50, the transition time is averaged a predetermined number of times NAV by the step 57 and step 47 described later.
Whether or not the averaging has been performed is determined by the averaging number count value nAV.
The determination is made based on whether or not the number of times NAV is greater than or equal to the predetermined number of times NAV. Note that the predetermined number of times NAv is set to a required value in step 63, 65, 67, 69, and 71, which will be described later, depending on the degree of deterioration of the 03 sensor.

As described above, the transition time T between time points t2 and t3 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.

The output voltage value Vo of the o2 sensor 13 is the predetermined reference value v■F
After passing below (after time t4), step 38.
Both of the determination results of 39 are negative (No), and step 4
0, and it is determined whether the output voltage values Vo, n in the current loop are less than or equal to the output comparison value Vat. In this case as well, in step 49 of the previous loop (at time t4), the VM
Since the value of IE is set to the predetermined reference value v Ohno, the determination result is affirmative (Yes), and in step 41, the count memory value t0XHK is set to the count value tow of the tox timer at this point, and the following step Output comparison value vM at 42! is set to the output voltage value vO□n in the current loop, and this program ends.

Between time t4 and time t1 in FIG. 3, the output comparison value Vmg is always the output voltage value Vo of the 08 sensor in the previous loop.

However, even in this case, the determination result in step 40 is always affirmative (Yes), and steps 41 and 42 are repeatedly executed.

At time t5 in FIG. 3, the 0. Output voltage value V of sensor 13
When o, reaches its minimum value and begins to rise toward the predetermined reference value v, the determination result in step 40 is negative (
No), and assuming that the output voltage value Vo has reached the minimum value between the previous loop and the current loop, steps 41 and 42 are skipped and the program ends. At this time, the count memory value tOXMN is not updated, and the toxmt value (t4-jg
The output comparison value VMi is also held at the minimum value up to this point (Vo, value at time ts in FIG. 3).

0, the output voltage value Vo of the sensor 13 is the predetermined reference value VRI
Before reaching EF, it falls again and the output comparison value at this point V
MI! (at time ts), the determination result in step 40 becomes affirmative (Yes) again, and the count memory value t
The value of OICMi+ is updated again to the count value tox of the tax timer at this point (time elapsed from time t4), and the output comparison value vM! is also updated to the output voltage value Vo at this point (steps 41 and 42).

0□When the output voltage value Vo of the sensor 13 starts to rise again from the minimum value (at time t'r), the determination result in step 40 becomes negative (NO), and steps 41 and 42 are skipped and the count memory value is stored. t The value of 0XHK is t at this point
The count value tox (t, -t7 time) of the ax timer is
Output comparison value vME is Vo at time t7.

held in value.

The output voltage value Vo of the 02 sensor 13 is the predetermined reference value vII.
When it crosses LEF and rises again (at time t1 in Figure 3),
The determination result in step 38 becomes affirmative (Yss), then the determination result in step 43 becomes negative (No), and the process proceeds to step 44, where the count memory value tox at this point is
mt(t4-tt waiting time to transition time Tox'(=TLV
) and proceed to the first step 45.

In step 45, the transition time Tox is within the allowable range Toxt.
, ~TOXH. Step 4
In step 6, similarly to step 56, the transition time Tox is determined by the correction coefficient KN! according to the engine speed No. and the intake pipe absolute pressure Pa^. Corrected with 〒, Kpa〒, new transition time Tox
Let it be a.

Furthermore, in step 47, the corrected transition time Toxc is substituted into the following equation (3), and the output voltage value Vo from the bottom to the lean side minimum value is set to the predetermined reference value V, the lean side transition time average value Tt, vAvn is calculated.

COX 256-COX TLvAvn = -shi9i-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 step 48, 1 is added to the averaging count value nAV as in step 58, and in step 49
．． Go to 50.

In this way, the calculation of the rich side and lean side transition time average values in steps 38 to 58 is repeated until the averaging count value nAV reaches the predetermined number of times NAV. Value K OX representing the degree of sensor deterioration
This is to obtain (= TLVAV/TIIIVAV) more accurately.

If 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 the determination result in step 50 is affirmative (Yes), steps 59 to 7 in FIG.
7, the rich side proportional control correction value PI11 is corrected according to the degree of deterioration of the O2 sensor 13.

In the determination from steps 59 to 62, the value K OX (= TLVAV/T*VAV
) and the predetermined values KOXL, KOX! , KOX3゜K
Compare each with OX4! (KOXl>KOX,>K
OX,>KOX4) @In other words, in step 59, the rich side transition time average value TIIVAV after the completion of averaging a predetermined number of times
In step 60, whether or not the value obtained by multiplying by a predetermined value KOX is greater than the lean side transition time average value T LVAV after the completion of averaging a predetermined number of times is determined by multiplying the average value T large VAV by a predetermined value K.
It is determined whether the value multiplied by OX2 is thicker than the average value TLVAV. On the other hand, in step 61, it is determined in step 62 whether the value obtained by multiplying the average value TIIVAV by a predetermined value KOX4 is smaller than the average value TLVAV.
Then, it is determined whether the value obtained by multiplying the average value TIIVAV by a predetermined value K OX a is smaller than the average value TLVAV.

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 large is added to the previous correction value Pan−, to obtain the current value P large n, and in the next step 65, the averaging constant COx and the predetermined number of times NAV are calculated.
respectively COxyu(>C0Xo), NAV, (<N
AVll).

Further, when the determination result in step 60 is negative (No),
Since the KOX value is between the predetermined value KOX and KOX, (7), it is estimated that the air-fuel ratio is slightly biased toward the lean side, and in step 66, the previous value P of the rich side proportional control correction value is set.
Adding the correction value Δp*1c<ΔPR,
Ox and the predetermined number of times NAv are respectively COXs (COX
o < COXs < COXt), NAva(N
AY@ > N AVfi > N Avt ).

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 ΔP- is subtracted from the previous value PIIIn-□ 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 NA are calculated.
COX each V.

(=COXi), set to NAv4 (=NAvl).

Further, when the determination result in step 62 is negative (No),
Since the KOX value is between the predetermined value KOX and KOX4, it is estimated that the air-fuel ratio is slightly biased toward the rich side.
In step 70, the previous value PII of the rich side proportional control correction value is
The correction value ΔPIL1 is subtracted from n-, and the current value Pan is set. 9 In the next step 71, the averaging constant COx and the predetermined number of times NAv are set as COXa (=COXa), respectively.
Set to NAv3 (= NAVY).

In this way, the averaging constant COx is set to a larger value <co
By setting the predetermined number of averaging times NAv to a smaller value (NAVl, NAv4) in Xi, cOX4), the degree of averaging of the transition time average values TvAvn and TLvAvn can be accelerated, and the air-fuel ratio can be quickly adjusted. can be controlled to the target air-fuel ratio.

In said step 64.66.68.70 the correction value Δ
PII! or ΔPII1. In step 72, it is determined whether the current value P of the rich side proportional control correction value corrected by
! It is determined whether it is smaller than L, and the step 72.7
When both of the determination results in step 3 are negative (NO), the corrected correction value Pg is set to the current value PIIn (step 74);
If either one of the determination results is affirmative (Yes), the corrected correction value PII11 is set to the previous value P*n-1 (step 75).

In step 76, the thus set correction value Pa□ is stored in the RAM 508 in FIG. 2, and in the next step 77, the averaging number count value nAV is set to 0, and this program is ended.

The correction value PII stored in the RAM 508 in this way is used in the 0□ 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 a feedback correction coefficient calculation subroutine using the rich side proportional control correction value P trap corrected by the method described above.

First, it is determined whether or not the activation of the O2 sensor 13 is completed (step 81). That is, the output voltage value of the O2 sensor 13 is set to the activation starting point Vx (for example, 0 .6v) is detected, and when it reaches Vx, it is determined that it is activated. If the result of this determination is negative (No), the correction coefficient Kost-t,o is set (step 82); on the other hand, 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 has high load operating range and low rotation range.

It includes an idle region, a high rotation region, a lean mixture region, etc., and a high load operation region is, for example, a fuel injection time T out.
is a region where T wot is set to a value larger than a predetermined value T wot . Here, T at 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. The low rotation area is the engine rotation speed Na
is less than a predetermined value N LOP (for example, 700 rpm),
Moreover, the intake pipe absolute pressure Pa^ is the predetermined value PB! This is an area of DL (for example, 360+w++Hg) or higher.

In the idle region, the engine rotation speed Ns is a predetermined rotation speed NH.
OP (for example, a region lower than 101,000 rpm and an absolute pressure Pa^ lower than the predetermined pressure PBIDL, and a high rotation region is a region where the engine rotation speed No is lower than the predetermined rotation speed N
This area is larger than Hop (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 PBL8, which is set to a larger value as the engine speed No. 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 the operating range where feedback control is required, and the process moves to closed loop control.
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 result is negative (No), integral control is performed (from step 90).

In step 85, it is determined whether the output level of the O8 sensor 13 is a low level or not, and if the determination result is affirmative (Yes), the proportional control correction value P trap is set to the rich side proportional control corrected by the PII value determination subroutine described above. Control correction value PIII
The engine rotation speed N is determined by □ and the Ne-P table.
A value corresponding to e is determined (step 86).Next, in step 87, this correction value P is added to the previous value of the correction coefficient Ko. The result of step 85 is negative (No
), set the lean side proportional control correction value PL to No-PL.
Read the child table (Step 88), and subtract the correction value PL read out from the previous value of the correction coefficient Ko (step 88).
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 O2 sensor 13 is at a low level. This discrimination result is positive (
If Yes), count number of TDC signal pulses NI
Add 1 to the value of L (step 91) and obtain the count number N
It is determined whether or not the count number NIL has reached a predetermined value N1 (for example, 4) (step 92). As a result of this determination, the count number NIL
If the count number N has not yet reached N+, the correction coefficient Ko is kept at the value at the previous loop (step 93), and if the count number N has reached N+, the correction coefficient Ko is maintained.

A correction value Δk corresponding to the engine speed Ne is added to (step 94), and the number of pulses N counted so far is
Reset IL to 0 (step 95), and set Nl to N+.
The correction value Δk is added to the correction coefficient Ko each time the correction coefficient Ko is reached. On the other hand, the determination result in step 90 is negative (
If the result is NO), add 1 to the count number N+o of the TDC signal pulse (step 96), and determine whether the count number NIH has reached the predetermined value N1.Step 97) 1 The determination result is negative. In the case of (No), the value of the correction coefficient Ko is kept at the value at the previous loop.Step 98
)0 If the determination result is positive (Yes), the correction coefficient Ko
, to subtract the correction value Δk from step 99), and to reset the counted pulse number NIH to O (step 1).
00), the correction value Δk is subtracted from the correction coefficient Ko every time NIH reaches N+, as described above.

In this way, the rich side proportional control correction value Pt is corrected according to the degree of deterioration of the O2 sensor 13, and the correction value P large thus corrected is used as the O2 feedback correction coefficient Ko.

By applying it to the calculation of 0. If the air-fuel ratio is biased toward the rich side due to deterioration of the sensor 13, the correction coefficient Ko
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 02 sensor 13,
Although the rich side proportional control correction value P large 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. can get.

(Effects of the Invention) As described in detail above, according to the present invention, the detected exhaust gas 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.

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 an air-fuel ratio feedback control method for an internal combustion engine that performs feedback control to a target air-fuel ratio by one method, a first time period for the detected exhaust concentration value to reach a maximum value on the rich side from the predetermined reference value; find a ratio of the second time from the predetermined reference value to a lean minimum value, and change at least one of the first correction value and the second correction value according to the ratio thus obtained. As a result, even if the characteristics of the exhaust gas 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 The exhaust gas characteristics are improved.

[BRIEF DESCRIPTION OF THE DRAWINGS] 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. 3 is a timing chart showing the temporal change in the output voltage value vO2 of the O2 sensor 13 shown in FIG. 6 and 6 are program flowcharts of the P tribute value determination subroutine according to the present invention, and FIG.
7 is a graph showing an engine operating range in which the program flowchart shown in FIG. 6 and FIG. 6 is executed. Figure 8 is a graph showing the relationship between correction coefficient KNi〒 and engine speed Ne, Figure 9 is a graph showing the relationship between correction coefficient Kpa〒 and intake pipe absolute pressure PB^, and Figure 10 is the 02 feedback correction coefficient. FIG. 2 is a program flowchart of a calculation subroutine. 1... Internal combustion engine, 5... Electronic control unit (ECU), 8... Absolute pressure in intake pipe (PB^)
Sensor, 10... Engine speed (Na) 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 for the detected exhaust gas concentration value to reach a maximum value on the rich side from the predetermined reference value, and a second time for the detected exhaust gas concentration value to reach the minimum value on the lean side from the predetermined reference value. An air-fuel ratio feedback control method for an internal combustion engine, characterized in that a ratio between the ratio and the time is determined, and at least one of the first correction value and the second correction value is changed in accordance with the ratio thus determined.