JPS63189635A - Air-fuel ratio feedback control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent an air-fuel ratio from getting out of position due to a change in an exhaust gas sensor with aging, by changing a reference value in accordance with a ratio between periods of time until the exhaust gas sensor reaches a maximum value on a rich side from a reference value and it reaches a minimum value on a lean side from the reference value 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 compares an average shift time during which an output sensed by the O2 sensor 13 shifts from the reference value to a maximum value on a rich side with an average shift time during which it shifts from the reference value to a minimum value on a lean side for sensing a deviation of the air-fuel ratio and corrects the reference value 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, 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 02 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 that permeate 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 02 sensor is adjusted according to this change. This detects the oxygen concentration in exhaust gas based on changes.

However, the output characteristics of the 0□ sensor configured as described above change over time, and especially after a vehicle equipped with the sensor has been running for a long time, its output characteristics deteriorate due to durability, and as a result, when the same condition Even though air-fuel ratio feedback control was performed at the factory.

It is known that the controlled air-fuel ratio shifts to the richer side compared to the time of shipment.

0 like this. If no measures are taken against changes in the characteristics of the sensor over time, there will be problems such as deterioration in engine operating performance, fuel efficiency, and exhaust gas characteristics.

(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 02 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 the above object, according to the present invention, an exhaust concentration detection value detected by an exhaust concentration detector disposed in the exhaust system of an internal combustion engine is compared with a reference value, and a The air-fuel ratio of the supplied air-fuel mixture is proportionally corrected by increasing or decreasing the air-fuel ratio by a first correction 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 reference value. control, and when the detected exhaust gas concentration value is on the lean side or rich side with respect to the reference value, the target air-fuel ratio is achieved by at least one of integral control, which increases or decreases the air-fuel ratio at predetermined time intervals using second correction values. In the air-fuel ratio feedback control method for an internal combustion engine that performs feedback control, a first time period for the detected exhaust concentration value to reach a maximum value on the rich side from the reference value, and a time period for the detected exhaust gas concentration value to change from the reference value to the minimum value on the lean side. There is provided an air-fuel ratio feedback control method for an internal combustion engine, characterized in that the ratio of the reference value to a second time until the reference value is reached is determined, and the reference value is changed in accordance with the ratio thus determined.

(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 that detects the valve opening θTH and outputs an electrical signal is connected to the throttle valve 3, and the detection signal is used to calculate the air-fuel ratio, etc., as described below. The information is sent to an electronic control unit (hereinafter referred to as rEcUJ) 5 which executes arithmetic processing to control 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 rNe sensor) 1
The Ne sensor 10 outputs a 1 pulse signal (TDC signal) every 1000 revolutions of the crankshaft, and this TDC signal is sent to the ECU 3. Sent.

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 02 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 (Vo□) 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 Tau〒 of the fuel injection valve 6 is calculated by the following equation.

Tou = Ti is read from the memory device. Ko is the 02 feedback correction coefficient, which is calculated based on the 02 feedback correction coefficient subroutine (FIG. 10), which will be described later. K and 2 are correction coefficients and correction variables that are calculated according to the various engine parameter signals, respectively, and are used to adjust fuel consumption 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.

ECU3 calculates the fuel injection time Tou as described above.
Based on ↑, a drive signal to open the fuel injection valve 6 is output.

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) 50
2 is also supplied. The Me counter 502 counts the time interval from when the previous TDC signal was input from the Ne sensor 10 to when the current TDC signal was input, and the counted value Me is proportional to the reciprocal of the engine rotation 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 (
PBA) sensor 8, engine water temperature (Tw) sensor 9. o
The output signals from the Sp.
Multiplexer 505 operates based on instructions from 503
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 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
stores various control programs executed by the CPU 503, the details of which will be described later, and various data such as correction coefficients and correction variables. 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 Tout
The fuel injection valve 6 is opened over the period of time.

Next, a method of calculating the 02 feedback correction coefficient Ko according to the change over time in the characteristics of the 02 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 this 02 sensor is determined by a predetermined reference value V large i of the output voltage value Vo2 (Fig. 3) of the 02 sensor under stable engine running conditions.
Time required for transition from p to rich side peak value (maximum value) T*v (between t8 and t3 in Figure 3, between t and t1°)
and the predetermined reference value VR1! Time required for transition from F to lean side peak value (minimum value) TLV (Figure 3 t,
to t7)) can be estimated using the value KOX (=TLv/T large v). 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. The maximum value referred to in the present invention,
The minimum value is the output voltage value Vo at the time when the output voltage value vO□, which changes in the direction away from the reference value v■F, reverses the direction of change toward the reference value vnF.

It is.

Therefore, in the present invention, the air-fuel ratio is adjusted to the target air-fuel ratio by changing the reference value vF in accordance with the KOX value to correct the deviation of the air-fuel ratio toward the rich side or lean side due to the deterioration of the O2 sensor. control accurately.

More specifically, in this embodiment, the value of KOX is set to a plurality of predetermined values KOX, ~KOX4(KOX, >KOX, >K
OX,>KOX4), and according to this result, the reference value V*ip is changed as follows using correction values Δvki, Δv- (FIG. 4).

(1) When KOX>KOXl (7), it is estimated that the air-fuel ratio is largely biased toward the lean side, and a correction value ΔvR2 is added to the reference value VIIEF.

(2) When KOXl>KOX>KOX, (7), it is estimated that the air-fuel ratio is slightly biased toward the lean side, and the reference value v■F
Add the correction value ΔV large (<ΔV large 2) to.

(3) When KOXl>KOX>KOXa (7), it is estimated that the air-fuel ratio is controlled to be approximately equal to the target (theoretical) air-fuel ratio, and the reference value v■F is held.

(4) When KOXa>KOX>KOx4, it is estimated that the air-fuel ratio is slightly biased toward the rich side, and the reference value V trap is set! Subtract the correction value Δvk1 from F.

(5) When KOX<KOX, it is estimated that the air-fuel ratio is largely biased toward the rich side, and the correction value ΔvII11 is subtracted from the reference value v■F.

5 and 6 are program flowcharts of a reference value V+up setting subroutine for executing the above-mentioned method of changing the reference value v*F.

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 0□ sensor 13 should be reversed at a normal cycle.

That is, in step 30, it is determined whether the temperature of the 0□ sensor 13 is sufficiently high based on whether the engine water temperature Tw is greater than a predetermined value TVO'X, and then in step 31, it is determined whether the engine is actually under feedback control. Determine whether or not. 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 Neoxt, Naox.

(step 32), determine whether the intake pipe absolute pressure Pa^ is between the predetermined values PBOXL and PBOXH.
(step 33), the vehicle speed Sp indicating the cruising state of the vehicle is set to a predetermined value SPOX.
It is determined whether or not the value is between L and 5POXH (step 34), and the absolute value of the degree of change ΔPa^ of the absolute pressure indicating a stable cruising state is determined within a predetermined width ΔP aox
A determination as to whether or not the value is smaller than ^ (step 35) is executed. Further, in step 36, after these operating conditions are satisfied (all the determination results in steps 32 to 35 are affirmative)
(Yes), it is determined whether this operating state has been 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, and the output comparison value vMI!, which will be described later, is added to the averaging frequency count value nAvtto, which will be described later. are respectively set to the reference value V(i+p) stored in the RAM 508 in step 76, which will be described later, and the program ends.

In steps 38 to 58, the KOX value (=TLV/T hole v) representing the degree of deterioration of the 02 sensor 13 described above is
The average value TLVAV of the TLV time for determining.

And the average value T large vAv of the TRv time is calculated.

Below, the average value TL from step 38 to step 58
The method of calculating VAV and TλVAV will be explained based on the timing chart of the output voltage value vO□ 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, it is determined whether the output voltage value vO□n of the current loop of the 0□ sensor 13 is larger than the set reference value v large needle. 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 larger than the set reference value V large itp. At time t1, this determination result is also negative (No), and the process proceeds to step 40.

In step 40, it is determined whether the current output voltage value Vo, n is smaller than the output comparison value vME, and in the current loop, this output comparison value vME has been set to the reference value V trap rtv in step 37 described above. The determination result is positive (Y
es), and the process proceeds to step 41.

In step 41, the count memory value toxMtt is set to the count value tax of the tox timer at this point, and in the next step 42, the output comparison value VMi+ is set to the output voltage value Vo2n of the current loop, and this program ends. . Incidentally, since the tox timer is only started by executing step 49, which will be described later, at this point (t1 in Fig. 3)
At the time point ), the count value is O, and therefore the count storage value tox is also O.

In the next and subsequent loops, the output voltage value Vo is the set reference value V+
Until u:p is exceeded, that is, between time t1 and t2 in FIG. 3, the determination result in step 40 becomes negative (NO), and steps 41 and 42 are skipped to end the program.

The output voltage value Vow of 02 sensor 13 is set reference value V trap for the first time in this loop! When F is exceeded (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 Vo2n- in the previous loop is
1 is larger than the set reference value VλtF,
At time t2, this determination result becomes negative (NO), and in the next step 44, the count memory value tOx stored at this time is set as the transition time Tox, and then in the next step 4.
Proceed to step 5.

In step 45, the transition time T set in step 44 is
It is determined whether ox is within the allowable range TOXL to TOXH.

As mentioned above, between time t and time t2, the count memory value t
OXMi: is O, and the determination result of this step 45 is negative (NO), and the process skips steps 46 to 48, which will be described later, and proceeds to step 49.

By performing the determination in step 45 in this way, t1
If the to timer is already activated before the point in time, the count memory value t OXMI set in step 41 is
The extremely long transition time that occurs during the transition period of the engine operating state, such as when the value of t, ~1. Significantly short transition times due to noise generation, such as those shown between the time points, can also be eliminated.

Returning to FIG. 5, in the next step 49, the output comparison value VME
Set it again to the setting reference value Q + egp, reset the count value tox of the tax timer and start it.
Averaging count value nA, which will be described later in the next step 50.
It is determined whether or not V is equal to or greater than a predetermined number of times NAV, and if the determination result is affirmative (Yes), step 5 described later is performed.
The program from 9 onwards (Figure 6) is executed and negative (No.
), this program ends.

Note that the count value of the tox timer is reset only in step 49, so the value tox is always at the point when the output voltage value Vo of the 0° sensor begins to rise or fall across the set reference value v (the feces liver). 3, the elapsed time from time points t2, t4, t9, etc. in Figure 3 is shown.

The output voltage value Vo of the 02 sensor 13 is the set reference value VRE.
After exceeding F (after time t2), step 38.4
If both of the determination results in step 3 are affirmative (Yes), the process proceeds to the next step 51, where it is determined whether the output voltage values Vo, n in the current loop are greater than or equal to the output comparison value VMi. In this case, since the value of VME was set to the setting reference value V*ip in step 49 of the previous loop (time point ti), the determination result becomes affirmative (Yes), and the value of the tox timer at this point is set in step 52. The count value tox is set to the count memory value tOXMIE, and in the subsequent step 53, the output comparison value vM! is set to the output voltage value Vosn in the current loop, one program is ended, and the next loop is started.

Between time t2 and time t1 in FIG. 3, the output comparison value VMI is always the output voltage value Vo of the 03 sensor in the previous loop.

However, in this case, the determination result in step 51 is always affirmative (Yas), 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 count memory value tOXMIE is set each time to the count value tox of the timer at that time (in this case, the elapsed time from time t2), and the output comparison value vMI! is set to the output voltage value vO□n of the current loop, which is the maximum value at this point.

0□When the output voltage value Vo of the sensor 13 reaches the maximum value and then starts to decrease toward the set reference value v■F (the third
t1 in the figure), the determination result in step 51 is negative (N
O), and at this time, assuming that the output voltage value vO□ has reached the maximum value between the previous loop and the current loop, steps 52 and 53 are skipped and the program is ended.

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.
The value of the count memory value tOXME (corresponding to time 1-t1 in FIG. 3) is held as long as it is below i (t, Vo, value at time point).

When the output voltage value vO□n of the 02 sensor 13 falls below the set reference value V*tp again in this loop (at time t4 in Figure 3),
The determination result in the step 38 is negative (No), the determination result in the step 39 is positive (Yes), and the process proceeds to the next step 54.

In step 54, the count memory value toxM at this point is
t (ts-ta) The waiting time is set as the transition time Tox, 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 x is within the tolerance range Toxt, ``Toxo.'' If the determination result is negative (NO), proceed to step 5.
Steps 6 to 58 are skipped and the process proceeds to step 49.

skips the following steps 56 to 58 and proceeds to step 49.

If the determination result in step 55 is affirmative (Yes), the process proceeds to step 56, where the thus set transition time Tox is multiplied by the correction coefficients KNIE〒, KpB〒, and a new transition time T is determined.
Let it be oxc. The correction coefficients KNi〒 and Kpa〒 are adjusted according to the engine speed Ne and the intake pipe absolute pressure Pg^, respectively.
The KNE〒-Na table shown in Fig. and Fig. 9, Kpa
This is the value read from the 〒-PB^ table. In this way, in step 56, the transition time TOX is corrected by the correction coefficients KNt〒 and Kpet, depending on the engine rotation speed N.
This is because the inversion period of the o2 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 set reference value Vbuy! Voltage value vO from F to rich side maximum value
The rich side transition time average value T*vAvn of □ is calculated.

COX 256-COX T large vAvn = i X Toxc +
256 XT large vAvn-1...(
2) Here, T-trap vAvn-1 is the previous value of the rich side transition time average value, and COX is an averaging constant for calculating the average value, and step 63.65.67.69.71 described later
Value COX according to the degree of deterioration of the 02 sensor.

~COX, (where O<COX, -COX4<256).

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. vst is set again to the set reference value v■F, 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°65.67.69.71, which will be described later, depending on the degree of deterioration of the 0□ sensor.

As described above, the transition time T between time points t2 and t□ in FIG.
ox (=T*ν) is set, and the rich side transition time average value T correction^vn is calculated based on the corrected value TOχC of the transition time Tax.

02 After the output voltage value Vo of the sensor 13 falls below the set reference value V scale tp (after time t4), step 3 is performed again.
8. The determination results of 39 are both negative (No).

Proceed to step 40 and output voltage value in this loop ■0□
It is determined whether n is less than or equal to the output comparison value VME.

In this case as well, since the value of vME was set to the set reference value v■F in step 49 of the previous loop (time point 14), the 1 determination result is affirmative (Yes), and step 41
The count memory value tOXMIE is set to tox at this point.
Set the timer count value tox, followed by step 42
The output comparison value Vmg is the output voltage value Vo in this loop,
Set to n and exit this program.

Between time points t and t2 in FIG. 3, the output comparison value VME is always 0□ sensor output voltage value Vo 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 t3 in FIG. 3, the output voltage value v of the 02 sensor 13 is
02 becomes a local minimum value and begins to rise toward the set reference value V large ty, the determination result in step 40 becomes negative (No), and at this time, the output voltage value between the previous loop and the current loop is Assuming that Vo has reached the minimum value, steps 41 and 42 are skipped and the program ends. At this time, the count memory value tOXME is not updated and the tOXME value (j4
ts waiting time) is held, and the output comparison value vME
is also held at the minimum value up to this point (Vo, value at time t5 in FIG. 3).

02 The output voltage value VO of the sensor 13 is equal to the set reference value V.
Before reaching F, it falls again and the output comparison value Vq at this point
When the value falls below g (at time ts), the determination result in step 40 becomes affirmative (Yes) again, and the count memory value to
The value of xpsw is updated again to the count value tQX of the tox timer at this time (time elapsed from time t4), and the output comparison value VME is also updated to the output voltage value Vo,
(steps 41 and 42).

When the output voltage value vO□ of the 02 sensor 13 starts to rise again from the minimum value (time point 11), the determination result in step 4° becomes negative (NO), and steps 41 and 42 are skipped, and the count memory value tOXME is The value of to at this point is
The count value tox (time t4-t7) of the x timer and the output comparison value vME are Vo at time t7.

held in value.

The output voltage value Vo of the 02 sensor 13 is the set reference value VRE.
When it crosses F and rises again (time t8 in Figure 3).

The determination result in step 38 becomes affirmative (Yes), then the determination result in step 430 becomes negative (No), and the process proceeds to step 44, where the count memory value tox at this point is
Mt (t4-t, time) is the transition time Tax (-Tt, v
) and proceed to the next step 45.

In step 45, the transition time Tox is within the allowable range TOXL~
It is determined whether or not it is within ToxH. In step 46, similarly to step 56, the transition time Tox is adjusted by a correction coefficient K according to the engine rotational speed Ne and the intake pipe absolute pressure Pa^.
Correct it with NE〒 and KPB〒 and set it as a new transition time Toxc.

Furthermore, in step 47, the corrected transition time T ax
is substituted into the following equation (3) to calculate the output voltage value Vo from the set reference value Vt1p to the lean side minimum value and the lean side transition time average value TLvAvn.

COX 256-COX Tt, vAvn = -X Toxc + 7 X T
LvAvn-.

(3) Here, TLvAvn-x is the previous value of the lean side transition time average value, and is Co or the same averaging constant as in the above-mentioned equation (2).

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 shift time average values in steps 38 to 58 is repeated until the averaging count value nAV reaches the predetermined number of times NAV, which indicates the degree of deterioration of the 0□ sensor. Value KOX
This is to more accurately determine (= TLVAV/T Note^v).

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 50 is affirmative (Yes), steps 59 to 7 in FIG.
7, the reference value Vl according to the degree of deterioration of the sensor 13
! IEF changes are made.

In the determination from steps 59 to 62, the value K OX (= TLVAV/T*vAv) representing the degree of deterioration of the 02 sensor is determined.
) and the aforementioned predetermined values KOX, , KOX, , KOX3, K
OX, and (KOX, >KOX, >K
OX, >KOx,). That is, in step 59, the rich side transition time average value TIIIVA after the completion of averaging a predetermined number of times is calculated.
In step 60, whether or not the value obtained by multiplying V by a predetermined value KOX is greater than the lean side transition time average value TLVAV after the completion of averaging for a predetermined number of times is determined by multiplying the average value TkvAv by a predetermined value KOX. It is determined whether each value is larger than the average value T_LVAV. On the other hand, in step 61, it is determined in step 62 whether the value obtained by multiplying the average value T large vAv by a predetermined value KOX is smaller than the average value Tt, vAv.
Then, the average value T, VAV, and a predetermined value KOX.

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 (
Yes, ), the value KOX representing the degree of deterioration is between the predetermined value KOX and KOX3. In this case, it is estimated that the air-fuel ratio is controlled to be approximately equal to the target air-fuel ratio, Proceeding to step 63, the averaging constant COx used in the above-mentioned equations (2) and (3) and the above-mentioned predetermined number of averaging times NAV are set to standard values COX(1, NAVll), 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 KOX1, it is estimated that the air-fuel ratio is largely biased toward the lean side, and in step 64, the reference value VFI! :The value of F in the previous loop is large! :
The correction value ΔV- is added to pn-z to obtain the current value vgpn, and in the next step 65, the averaging constant COX and the predetermined number of times NAV are set as C0X1 (>COX, ) and N, respectively.
Set to AV, (<NAVO).

Moreover, when the determination result in step 60 is negative (NO),
The KOX value is a predetermined value KOX.

Since it is between ,)
are added to set the reference value V*1rpn for the current loop, and in the next step 67, the averaging constant COX and the predetermined number of times NAV are calculated as COXs (COXs <COX, <C
OX, ), N AVg (N Av, > N AVI
> N AWL ).

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
8, the value V trap tpn-1 in the previous loop of the reference value V*tp
Subtract the correction value Δv6 from the reference value V for this loop,
*ttyn, and in the first step 69, the averaging constant C
Ox and the predetermined number of times NAV are each COX, (=CO
X, ), N AV4 (= N AVl).

Moreover, when the determination result in step 62 is negative (NO),
The KOX value is a predetermined value KOX3 and KOX.

Since it is between The standard value V*5=pn is set at step 71, and the averaging constant COx and the predetermined number of times NAV are set as COXa (=COXz) and NAV3(=
Set to NAV, ).

In this way, 0. Depending on the degree of deterioration KOX of the sensor 13, that is, when the air-fuel ratio is largely biased towards the rich side or the lean side, the averaging constant CoX is set to a larger value (COXz
, COX4), by setting the averaging predetermined number of times NAv to a smaller value (NAvyu, NAV4), it is possible to accelerate the averaging degree of vAvn and TtvAvn to the transition time average value T, and therefore, the air-fuel ratio can be quickly adjusted. It is possible to control the air-fuel ratio to the target air-fuel ratio.

In said step 64.66.68.70 the correction value Δ
Reference value VIIIEF changed by VR□ or Δv1
In step 72, it is determined whether the value Vgpn in this loop is larger than the predetermined upper limit value V than EFH or not.
It is determined whether or not the value is smaller than a predetermined lower limit value Vxtp+-, and the determination results at steps 72 and 73 are both negative (NO).
), the reference value V■pn obtained in the current loop is set as the reference value v■F (Step 74), and when either one of the determination results is affirmative (Yes), the reference value V■pn obtained in the current loop is set as the reference value v■F. The reference value V*gpn-2 is set to the reference value V trap 1:F (step 75).

In step 76, the reference value v total that has been changed in this way is stored in the RAM 508 in FIG. 2, and in the next step 77, the averaging count value nAV is set to 0, and this program is ended.

The reference value v■F stored in RAM 508 in this way
is stored in steps 37, 38, 39, 43 and 49, and is further used in the 0□ feedback correction coefficient calculation subroutine described later, whereby the correction coefficient K
The value of o can be biased toward the rich side or the lean side.

FIG. 10 is a program flowchart of the o2 feedback correction coefficient calculation subroutine using the reference value VREF that has been changed according to the change in the 0□ sensor over time using the method described above.

First, it is determined whether activation of the 02 sensor 13 has been completed (step 81). That is, the internal resistance detection method of the 02 sensor 13 detects whether the output voltage value of the 02 sensor 13 has reached the activation starting point Vx (for example, 0.6v), and when it reaches Vx, it is determined that the output voltage value of the 02 sensor 13 has been activated. judge. If the determination result is negative (No), the correction coefficient Kos is set to 1.0 (step 82); on the other hand, if the determination result is positive (Yes), the engine is in the open control region. Determine whether or not (step 83)
This open control includes high load operation 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 Tvot is set to a value larger than the predetermined value Tvot. 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 below a predetermined value NLOP (for example, 700 rpm+), and the intake pipe absolute pressure Pa^ is a predetermined value PBIDL (for example, 3
60 city Hg) or more.

In the idle region, the engine rotation speed Ne 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 Ne is lower than the predetermined rotation speed No.
The area is larger than the OP (for example, 3000 rp+m).

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

When it 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 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.
The output voltage value vo2, which is the output level of No. 3, is the reference value v■ determined by the reference value V large EFff constant subroutine (Figures 5 and 6) at the previous input of the TDC signal and at the current input.
Step 84) to determine whether or not the data has been reversed.
If the determination result is positive (Yes), proportional (P-term) control is performed (step 85 onwards), and if negative (NO), integral control is performed (step 90 onwards).

In step 85, 0. It is determined whether the output voltage value vO□ of the sensor 13 is at a low level with respect to the reference value v■F, and if the determination result is affirmative (Yes), the rich side proportional control correction value P trap is set to Ne-Pyt. Engine speed N from the table
e (step 86). Next, in step 87, this correction value P large 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 P is read out from the No-PL child table according to the engine rotation speed Ne (step 88), and the thus read correction value PL is corrected. Coefficient Kot
is subtracted from the previous 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 the output voltage value Vo of the 0□ sensor 13 is at a low level with respect to the reference value Vtv. If this determination result is positive (Yes),
1 is added to the value of 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), and the result of this determination is , if the count number N has not yet reached Nt, the correction coefficient Ko is kept at the value from the previous loop (step 93), and if the count number N has reached N1, the correction coefficient Ko2 is set to the engine rotation. A correction value Δk corresponding to the number Ne is added (step 94), and the number N of pulses counted so far is reset to 0 (step 9
5) A correction value Δk is added to the correction coefficient 93 every time Nt reaches Nt. 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 (step 96).
, it is determined whether the count number NIH has reached a predetermined value Nt (Step 97), and if the determination result is negative (NO), the value of the correction coefficient Ko2 is maintained at the value at the previous loop (Step 98). 1 If the determination result is positive (Yes), subtract the correction value Δk from 02 as the correction coefficient.
9), reset the counted pulse number NIH to 0 (Step 100), same as above, when NIH is N! The correction value Δk is subtracted from the correction coefficient Ko every time the correction coefficient Ko is reached.

In this way, the reference value to be compared with the output voltage value vO□ of the 0□ sensor is changed according to the degree of deterioration of the 0□ sensor 13, and the reference value V t+e after being changed is specifically set as the 0□ 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 time required for determining the rich side of the air-fuel ratio by the 02 sensor can be made longer to reduce the value of the correction coefficient Koz. In this case, on the other hand, the lean side determination time can be made longer to increase the value of the correction coefficient KO2. As a result, the air-fuel ratio is corrected to the lean side or rich side depending on the degree of deterioration of the 02 sensor, and the target air-fuel ratio is achieved.

(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 reference value, and the exhaust gas concentration detected by the exhaust gas concentration detector arranged in the exhaust system of the internal combustion engine is compared with the reference value. proportional control that increases or decreases the air-fuel ratio of the air-fuel mixture by a first correction 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 reference value; , and when the detected exhaust gas concentration value is on the lean side or rich side with respect to the reference value, feedback to the target air-fuel ratio is performed 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 for an internal combustion engine to be controlled, a first time period for the detected exhaust concentration value to reach a maximum value on the rich side from the reference value, and a first time for the detected exhaust gas concentration value to change from the reference value to the minimum value on the lean side. The ratio of the reference value to the second time until It is possible to achieve a target air-fuel ratio by modifying the air-fuel ratio of the air-fuel mixture, 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 Vo of the O2 sensor 13. FIG. 4 is a graph showing the relationship between the value KOX representing the degree of deterioration of the O2 sensor 13 and the correction value Δv trap. FIGS. 5 and 6 are is the reference value V large E according to the present invention
Program flowchart of F setting subroutine, 7th
The figure is a graph showing the engine operating range in which the program flowcharts shown in Figures 5 and 6 are executed, and Figure 8 is a graph showing the correction coefficient KN! A graph showing the relationship between 〒 and engine speed Ne, Figure 9 shows the correction coefficient Kpm 〒 and intake pipe absolute pressure P
A graph showing the relationship with a^, FIG. 10 is a program flowchart of the 02 feedback correction coefficient KO□ calculation subroutine. DESCRIPTION OF SYMBOLS 1... Internal combustion engine, 5... Electronic control unit (ECU), 8... Intake pipe absolute pressure (Pa^) sensor, 10... Engine speed (Ns) sensor, 13
...02 sensor.

Claims (1)

[Claims] 1. Compare the detected exhaust concentration value detected by the exhaust concentration detector arranged in the exhaust system of the internal combustion engine with a reference value, and determine the air-fuel ratio of the air-fuel mixture supplied to the engine when the detected exhaust concentration value is the reference value. Proportional control that increases or decreases the air-fuel ratio by a first correction value when the ratio changes from a rich side to a lean side or from a lean side to a rich side, and the detected exhaust gas concentration value changes from a lean side to a rich side with respect to the reference value. At some point, in an air-fuel ratio feedback control method for an internal combustion engine, in which 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 by respective second correction values, the detected exhaust concentration value is The ratio of the first time for the detected exhaust gas concentration value to reach the rich side maximum value from the reference value and the second time for the detected exhaust gas concentration value to go from the reference value to the lean side minimum value was determined. An air-fuel ratio feedback control method for an internal combustion engine, characterized in that the reference value is changed in accordance with the air-fuel ratio.