JPS63189645A - Feedback control method for air-fuel ratio of internal combustion engine - Google Patents

Abstract

PURPOSE:To compensate aged deterioration of an exhaust sensor, by changing a reference value in accordance with the ratio of time, in which an exhaust concentration detection value reaches from a rich side maximum value to a lean side minimum value, to the time in which the exhaust concentration detection value reaches from the lean side minimum value to the rich side maximum value, in the case of an air-fuel ratio feedback control. CONSTITUTION:An electronic control unit 5, which calculates the basic fuel injection quantity on the basis of detection values from an intake absolute pressure sensor 8 and on engine speed sensor 10, compares a detection value of an O2 sensor 13 with the reference value performing a feedback control of air-fuel ratio by a proportional plus integral control. The electronic control unit 5 compares transfer mean time, in which the detection output of the O2 sensor 13 reaches from a rich side maximum value to a lean side minimum value, with the transfer mean time in which the detection output of the O2 sensor 13 reaches from the lean side minimum value to the rich side maximum value, and the control unit, detecting the displacement of the air-fuel ratio, corrects the reference value 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 a method for compensating for changes over time in the output characteristics of an exhaust gas concentration detector disposed in the exhaust system of the engine. The present invention relates to an air-fuel ratio feedback control method.

(Technical background and problems) Conventionally, the exhaust concentration (oxygen concentration) detected by an exhaust concentration detector (e.g. O2 sensor) placed in the exhaust system of an internal combustion engine is compared with a predetermined reference value. Based on the results, the air-fuel ratio of the mixture supplied to the engine is controlled to the stoichiometric mixture ratio at which the three-way catalyst installed in the engine's exhaust system achieves the maximum conversion efficiency, thereby improving the exhaust gas characteristics. An air-fuel ratio feedback control method for an internal combustion engine is generally used (for example, Japanese Patent Application Laid-open No. 137633/1983).

The O2 sensor used for such air-fuel ratio control uses zirconium oxide, etc. as a sensor element, and the amount of oxygen ions that permeate through the inside of the zirconium oxide, etc. is determined by the oxygen partial pressure in the atmosphere and the oxygen content in the exhaust gas. The oxygen concentration in the exhaust gas is detected by changing the output voltage of the 0□ sensor in response to the change in pressure.

However, the output characteristics of the 02 sensor configured as described above change over time, and especially after a vehicle equipped with the sensor has undergone endurance driving, its output characteristics deteriorate due to durability, and as a result, under the same conditions It is known that even though air-fuel ratio feedback control is performed, the controlled air-fuel ratio shifts to the rich side compared to when shipped from the factory.

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

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

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

The detected exhaust concentration value detected by the exhaust concentration detector placed in the exhaust system of the internal combustion engine is compared with a reference value, and the air-fuel ratio of the air-fuel mixture supplied to the engine is determined when the detected exhaust concentration value is rich with respect to the reference value. Proportional control that increases or decreases the air-fuel ratio by a first correction value when the air-fuel ratio changes from the side to the lean side or from the lean side to the rich side, and when the detected exhaust concentration value is on the lean side or rich side with respect to the reference value. In the air-fuel ratio feedback control method for an internal combustion engine, the exhaust gas concentration detection value is rich. The ratio of the first time from the maximum value on the lean side to the minimum value on the lean side and the second time until the detected exhaust gas concentration value changes from the minimum value on the lean side to the maximum value on the rich side was determined. There is provided an air-fuel ratio feedback control method for an internal combustion engine, characterized in that the reference value is changed according to the air-fuel ratio.

(Example) Hereinafter, an example of the present invention will be described in detail based on the accompanying drawings.

FIG. 1 is a block diagram showing the overall configuration of a fuel supply control device for an internal combustion engine to which the method of the present invention is applied. Reference numeral 1 indicates, for example, a four-cylinder internal combustion engine, and the engine 1
An intake pipe 2 communicating with the atmosphere is connected to the intake pipe 2.
A throttle valve 3 is provided in the middle. A throttle valve opening sensor 4 is connected to the throttle valve 3, which detects the valve opening θ〒H and outputs an electrical signal, and the detection signal is used to detect the air-fuel ratio, etc. as explained below. The information is sent to an electronic control unit (hereinafter referred to as "ECU") 5 that executes 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 rNe sensor) 1
0 is attached around the camshaft or crank (not shown) of the engine 1, and this Ne sensor 1o outputs a signal (TDC signal) of the rotation type Lus every 1800 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 HC in the exhaust gas.

Purifies Go and NOx components. This three-way catalyst 1
The 02 sensor 13, which is an exhaust gas concentration sensor, is attached to the exhaust pipe 11 on the upstream side of the 02 sensor 13, which detects the oxygen gas concentration in the exhaust gas and outputs a detection signal (Vow).
is sent to the ECU 3.

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

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

Tou〒=TiXK, The data is read out from the memory device in the ECU 5 based on the data. Ko is a 0□ feedback correction coefficient, which is calculated based on the 03 feedback correction coefficient calculation subroutine described later. 1 and 2 are correction coefficients and correction variables that are calculated according to the various engine parameter signals, and are based on the detection signals from the various sensors described above to determine the fuel efficiency characteristics according to the engine operating state.
A predetermined value is determined so as to optimize various characteristics such as engine acceleration characteristics.

The ECU 3 uses the fuel injection time Tau obtained as described above.
A drive signal for opening the fuel injection valve 6 is output based on 〒.

FIG. 2 is a diagram showing the circuit configuration inside the ECU 3 shown in FIG.
After waveform shaping in step 1, the central processing unit (hereinafter referred to as rcPU)
503 (hereinafter referred to as "rMa counter") 502
The 0Me counter 502 also supplied to the Ne sensor 1
It counts the time interval from the input of the previous TDC signal from 0 to the input of the current TDC signal, and its count value M
e is proportional to the reciprocal of the engine speed Ng.

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

- direction, throttle valve opening (θ〒H) sensor 4, absolute pressure (Pa^) sensor 8, engine water temperature (Tw) sensor 9,
The output signals from the 02 sensor 13 and the vehicle speed l5p) 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 from the CP
Multiplexer 50 operates based on instructions from U503
5 is sequentially supplied to an analog-to-digital converter (A/D converter) 506. The converter 506 converts the output signals of the aforementioned sensors into digital signals, and supplies the digital signals to the CPU 503 via the data bus 510.

The CPU 503 further includes a read-only memory (hereinafter referred to as rROMJ) 507 via a data server 2510;
Random access memory (hereinafter referred to as "RAM") 5
08 and drive circuit 5094: connected. ROM5
07 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.

The CPU 503 reads coefficient values or variable values corresponding to the output signals of each of the aforementioned sensors from the ROM 507 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 Tau〒 is calculated, and the value obtained by this calculation is supplied to the drive circuit 509 via the data bus 510.

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

Next, a method of calculating the 0 and 02 feedback correction coefficients Ko according to the present invention in response to changes over time in the characteristics of the sensor will be explained.

As described above, the output characteristics of the 0□ sensor deteriorate due to endurance driving of the vehicle, and as a result, the feedback-controlled air-fuel ratio is biased towards the rich side or the lean side. The degree of deterioration of this 02 sensor is determined by the time T*v required for the output voltage value (Fig. 3) to shift from the peak value on the rich side (maximum value) to the peak value on the lean side (minimum value) under stable engine running conditions.
(between t2 and t5 in Figure 3) and the time TLV (between t3 and t4 in Figure 3) required for transition from the lean peak value (minimum value) to the rich peak value (maximum value). It can be estimated by KOX (=TLv/T*v). This KOX value is the cumulative mileage of the vehicle.

In other words, the maximum value and minimum value as used in the present invention, which have been experimentally confirmed to decrease depending on the degree of durability deterioration, are the output voltage value vot that changes in the direction away from the standard value v This is the output voltage value vo2 at the time when the direction of change is reversed to the value vuF side.

Therefore, in the present invention, the air-fuel ratio is adjusted to the target air-fuel ratio by changing the reference value v large needle according to 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 02 sensor. control accurately.

More specifically, in this embodiment, the value of KOX is set to a plurality of predetermined values KOX1 to KOX4 (KOXl>KOX,>KO
X,>KOX4), and according to this result, the reference value V large EF is changed as follows by the correction values ΔV 8, ΔV* (FIG. 4).

(1) When KOX>KOX, it is estimated that the air-fuel ratio is largely biased toward the lean side, and a correction value Δv*2 is added to the reference value v■F.

(2) When KOX,>KOX>KOX2, it is estimated that the air-fuel ratio is slightly biased toward the lean side, and a correction value AV*1 (<ΔV*,) is added to the reference value v*tp.

(3) When KOX2>KOX>KOX (1), it is estimated that the air-fuel ratio is controlled to be approximately equal to the target (theoretical) air-fuel ratio, and the value of the reference value V hole EF is held.

(4) When KOX3>KOX>KOX, (7), it is estimated that the air-fuel ratio is slightly biased toward the rich side, and the reference value V is large i.
Subtract the correction value Δ■trap from p.

(5) When KOX<KOX, it is estimated that the air-fuel ratio is largely biased toward the rich side, and the correction value Δ■llI2 is subtracted from the reference value v■F.

FIGS. 5 and 6 are program flowcharts of a reference value v■F setting subroutine for carrying out the above-described method of changing the reference value vIF.

First, in steps 3o to 36, it is determined whether the engine is in a predetermined operating state in which the output voltage Vo of the 02 sensor 13 should be reversed at a normal cycle.

That is, in step 30, 0. It is determined whether the temperature of the sensor 13 is sufficiently high based on whether the engine water temperature Tw is greater than a predetermined value Twax, and then in step 31 it is determined whether the engine is actually under feedback control. Further, in steps 32 to 35, as conditions for the predetermined operating state, it is determined whether the engine rotation speed Ng is a value between the predetermined values NeoxL and Neoxu (step 32), and the intake pipe absolute pressure Pa^ is determined. is the predetermined value P
It is determined whether the value is between the predetermined value SPOXL and PBOXH (step 33), and whether the vehicle speed SP, which indicates the cruising state of the vehicle, is a value between the predetermined value SPOXL and 5POXH (step 33). 34), and determining whether the absolute value of the degree of change in absolute pressure ΔPa^ indicating a stable cruising state is smaller than a predetermined width ΔPBO)FA (
Step 35) is executed respectively. Furthermore, in step 36, after these operating conditions are satisfied (steps 32 to 3)
After all the determination results in step 5 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, sets the averaging number count value nAV, which will be described later, to 0, and ends this program.

In steps 38 to 52, the KOX value (=TLV/T large v
) to determine the average value of TLV times T LVAV,
and the average value TIIIVAV of T large v time is calculated.

Below, the average value TL from step 38 to step 52
Figure 3 shows how to calculate VAV and TFLV^V02
The explanation will be based on a timing chart of the output voltage value Vo of the sensor.

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. 3.

First, in step 38, the output voltage value vo2n of the current loop of the 02 sensor 13 is equal to the output voltage value V02 of the previous loop.
It is determined whether or not it is greater than n-1. At time t□ in Figure 3, this determination result is affirmative (Yes), and step 3
Proceeding to step 9, the output voltage value Vo, n-, of the previous loop is the output voltage value Vo2n- of the loop before the previous one.

It is determined whether or not the value is larger than that. At time point ti, this determination result also becomes affirmative (Yes), and the program is ended without executing steps after step 48, which will be described later.

When the output voltage value Vo of the o2 sensor 13 reaches the maximum value and starts to fall (time t2 in FIG. 3), the determination result in step 38 becomes negative (No), and the next step 4 is started.
0, the output voltage value Vo,n-1 in the previous loop is the output voltage value Vo,n in the loop before the previous loop, as in step 39.
−, it is determined whether or not it is larger than. Output voltage value Vo,
In the loop immediately after t reaches the maximum value (at time tz), this determination result becomes affirmative (Yes), and in the next step 41, t
The count value tax of the ox timer is set as the transition time Tox, and in the next step 42, the transition time T thus set is set.
Determine whether ox is within the allowable range Toxo.++ The tox timer is used in a loop immediately after the output voltage value vO
Since it is reset and started at , this time the loop (
(time tz), the count value tax becomes O. Therefore, the determination result in step 42 is negative (NO), and the process skips steps 43 to 45, which will be described later, and proceeds to step 46.

By performing the determination in step 42 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 time, or from t4 to t in FIG. 3, which will be described later.

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

In step 46, the count value of the tox timer is reset and started, and in the next step 47, it is determined whether the averaging number count value nAV, which will be described later, is greater than or equal to a predetermined number of times NAV, and if the determination result is affirmative (Yes). If so, the program from step 59 (FIG. 6) to be described later is executed, and if the answer is negative (NO), this program is ended.

In the next and subsequent loops, the output voltage value vo2 of the O2 sensor 13
As long as it falls (between time t2 and time t3 in Figure 3).

The determination results in steps 38 and 40 are both negative (No).
This will end this program. Therefore, during this time ta
The count value of the x timer is 1. without being reset. It represents the elapsed time from the point in time.

When the output voltage value Vo of the 02 sensor 13 reaches the minimum value and starts to rise again (time t1 in FIG. 3), the determination result in step 38 is affirmative (Ygs), and the determination result in the subsequent step 39 is negative ( No), and at this time, assuming that the output voltage value Vo has become the minimum value between the previous loop and the current loop, the process proceeds to step 48. In step 48, as in step 41, the tax timer at this point is The count value tox (t, -t, time) is the transition time Tax
In step 49, similarly to step 42, it is determined whether the transition time Tox set in step 48 is within the allowable range TOXL-TOXI4, and the determination result is negative (NO). ), steps 50 to 52 are skipped and the process proceeds to step 46 described above.

If the determination result in step 49 is affirmative (Yes), the process proceeds to step 50, where the thus set transition time Tax is multiplied by the correction coefficients KNIET, Kpe〒, and is set as a new transition time Toxc. The correction coefficients KNi〒 and KPBT are calculated according to the KNE〒-Ne table and Kp shown in Figs. 8 and 9 according to the engine speed Ne and intake pipe absolute pressure Pa^, respectively.
This is the value read from the a〒-Pa^ table. In this way, the transition time Tax is corrected by the correction coefficients KNI〒, Kps〒 in step 50 because the engine rotational speed N
e. This is because the inversion period of the O2 sensor itself changes significantly in accordance with changes in the absolute pressure PH^ in the intake pipe.

The transition time Toxe corrected in step 5o is substituted into the following equation (2) in the next step 51, and as a result, the voltage value Vo from the rich side maximum value to the lean side minimum value, the rich side transition time An average value T feces VAVn is calculated.

Cox 256-cOXT*vAvn
= 11X Toxe + 256X T*vxvn
−.

...(2) Here, T large VAVn-t is the previous value of the rich side transition time average value, and COX is an averaging constant for calculating the average value, and steps 63, 65, 67, and 69, which will be described later. .71
The value COX corresponds to the degree of deterioration of the 02 sensor.

~COx4 (However, LO<COX, ~C0X4<256)
is set to

Returning to FIG. 5, in the next step 52, 1 is added to the averaging count value nAV representing the number of executions of transition time averaging based on the above-mentioned equation (2), and as described above, in step 46, the tox timer is At step 47, the count value of step 51 is reset and started.
Then, it is determined whether the averaging count value nAV representing the number of times the transition time is averaged in step 44, which will be described later, is greater than or equal to the predetermined number of times NAV. In addition, the predetermined number of times N
AV is set to a required value in steps 63.65 and 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 t1 in FIG.
ax (=T*v) is set, and the rich side transition time average value T large vAvn is calculated based on the corrected value T oxc of the transition time Tax.

In the next transition loop, the output voltage value Vo of the 02 sensor 13,
As long as the value increases (times t and t4 in FIG. 3), the results of the determinations in steps 38 and 39 are both affirmative (Yes), and the program ends. Therefore, during this period, the count value of the tox timer is not reset and represents the elapsed time from time t3.

○When the output voltage value Vo2 of the second sensor 13 starts to fall again after reaching the maximum value (at time t4 in FIG. 3), the determination result in step 38 is negative (No), and the determination result in step 40 is positive ( Yes), and assuming that the output voltage value Vo has reached the maximum value between the previous loop and the current loop, the count value tox of the tax timer at this point is
(t, -t4 hours) is set as the transition time Tox (step 41), and in step 42 it is determined whether or not this transition time Tox is within the allowable range TOXL~Toxo.
Next, the process proceeds to step 43. In this step 43, similarly to step 50, the transition time Tax is adjusted by a correction coefficient KNt according to the engine rotational speed Ne and the intake pipe absolute pressure Pa^.
〒, corrected with KPIIT and set as new transition time Toxc.

Furthermore, in step 44, the corrected transition time Toxc is substituted into the following equation (3) to obtain the average value T t of the transition time on the one side from the output voltage value v02 to the minimum value on the rich side to the maximum value on the rich side. , vAvn are calculated.

COX 256-COX TLvAvn = -X Toxc + 256X
T+-vAvn-.

...(3) T LvAvn-1 is the previous value of the average value of the transition time on the green side, and is Co or the same averaging constant as in the above-mentioned equation (2).

In the next step 45, 1 is added to the averaging count value nAV as in step 52, and the process proceeds to steps 46 and 47 described above.

Furthermore, 0. When the output voltage value Vo of the sensor 13 is decreasing or increasing, if noise as shown in FIG. The determination result of the snap 42 or 49 is negative (No), and the influence on the calculation of the rich side and lean side transition time average values executed in step 44.51 can be eliminated.

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

The calculation of the average value of each transition time to the rich side and the lean side is performed a predetermined number of times NAV, and if the determination result in step 47 is affirmative (Yes), steps 59 to 7 in FIG.
7, the reference value V hole iy is changed according to the degree of deterioration of the O2 sensor 13.

In the determinations in steps 59 to 62, the value K Q X (= TLVAV/TIVA
V) and the aforementioned predetermined values KOX1, KOX, , KOX, .
Compare each with KOX4 (KOXl>KOX, >K
OX, >KOX4). That is, in step 59, it is determined whether the value obtained by multiplying the rich side transition time average value T*vhv after the completion of averaging a predetermined number of times by the predetermined value K OX 1 is greater than the lean side transition time average value T LVAV after the completion of averaging a predetermined number of times. In step 60, it is determined whether the value obtained by multiplying the average value T*vAv by a predetermined value KOX2 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 TvAv by a predetermined value KOX is smaller than the average value TLVAV.
Then, a predetermined value KOX is added to the average value TIIVAV.

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

Therefore, all of the determination results from steps 59 to 62 are positive (
If the answer is Yes), the value KOX representing the degree of deterioration is between the predetermined value KOX and KOX3, 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 the process proceeds to step 63. Next, the averaging constant COX used in equations (2) and (3) described above and the predetermined number of averaging operations NAV described above are set to standard values C0X0 and NAVO, respectively.

On the other hand, if the determination result in step 59 is negative (NO), the KOX value is larger than the predetermined value KOX The value of tp in the previous loop V*1pn-
Add the correction value Δ■1 to x to get the reference value V* for this loop
tpn, and in the next step 65 the averaging constant COX
and the predetermined number of times NAV, respectively COX, (>COX,)
, N Avl (< N AV, ).

Moreover, for the ibis whose determination result in step 60 is negative (No),
The KOX value is a predetermined value KOX.

Therefore, it is estimated that the air-fuel ratio is slightly biased toward the lean side, and in step 66, the reference value V is set to the value v*tpn-t of the previous IP loop, and the correction value AV (<Δv- )
is added to set the reference value V trap 5rpn for this loop, and in the next step 67, the averaging constant COX and the predetermined number of times NAV are calculated as COX, (COX, <COX, <COx
l), set NAV2 (NAv,>NAv2>NAvt).

Further, when the determination result in step 61 is negative (No), the KOX value is smaller than the predetermined value Kox4, so it is estimated that the air-fuel ratio is largely biased toward the rich side, and the reference value V is increased in step 68. ! : Value of v in the previous loop v*tp
The correction value Δv trap 2 is subtracted from n−, to obtain the reference value V*tpn for this loop, and in the next step 69, the averaging constant COX and the predetermined number of times NAv are respectively COX, (=C
OX, ), N AV4 (= N Avl ).

Further, when the determination result in step 62 is negative (No),
Since the KOX value is between the predetermined values KOX and KOX4, it is estimated that the air-fuel ratio is slightly biased toward the rich side, and in step 70, the value V*ip in the previous loop is set to the value V*ip of the previous loop. -1 minus the correction value Δv to set the reference value V*yn in this loop, and in the next step 71, the averaging constant COx and the predetermined number of times NAv are respectively COX
3 (=COXl), set to NAV3 (=NAv,).

In this way, depending on the degree of deterioration KOX of the 0□ sensor 13, that is, when the air-fuel ratio is largely biased toward the rich side or the lean side, the averaging constant COx is adjusted to a larger value (COX-COx4), and the averaging is performed. Set the predetermined number of times NAV to a smaller value (
By setting NAvy, NAv4), the degree of averaging of the transition time average values Ttrap vAvn and TLvAvn can be accelerated, and the air-fuel ratio can be quickly controlled to the target air-fuel ratio.

In said step 64.66.68.70 the correction value Δ
In step 72, it is determined whether or not the reference value Vtributipn, which has been changed by vtribute or Δvfeed2, in this loop is greater than the predetermined upper limit value V*i+eo, and in step 73, it is determined whether the value Vtributeipn in the current loop is greater than the predetermined lower limit value. It is determined whether it is smaller than V*ipt, and the determination results of steps 72 and 73 are both negative (NO).
In this case, the reference value V ultimate obtained in this loop is set as the reference value VR1! : Set to F (step 74), and when either one of the determination results is positive (Yes), the reference value Vtpn- obtained up to the previous loop is set.

is set to the reference value V*tv (step 75).

In step 76, the reference value V ip thus changed is changed to the second
It is stored in the RAM 508 in the figure, and in the first step 77, the averaging count value nAV is set to 0, and the program ends.

The reference value V*y stored in the RAM 508 in this way is used in the zero feedback correction coefficient calculation subroutine described later, thereby making it possible to bias the value of the correction coefficient KO2 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 'V*ip which is changed according to the change in the o2 sensor over time using the method described above.

First, it is determined whether the activation of the O2 sensor 13 is completed (step 81). That is, the output voltage value of the O2 sensor 13 is determined to be at the activation starting point Vx (for example, by the internal resistance detection method of the O2 sensor 13). 0.6v), and when it reaches Vx, it is determined that it is activated. If the result of this determination is negative (NO), the correction coefficient Ko is set to 1.0 (step 82), while if the result of 1 determination is positive (Yes), the engine is in the open control region. It is determined whether or not (step 83).

This open control includes a high-load operating region, a low-speed region, an idle region, a high-speed region, a lean mixture region, etc. In the high-load operating region, for example, the fuel injection time Tau is greater than a predetermined value T wot. This is the area set to the value. Here, T wot is a constant and is the lower limit value of the fuel supply amount 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 mmHg) or higher.

In the idle region, the engine rotation speed Ne is a predetermined rotation speed NH.
OP (for example, lower than 101000 rpm, and the absolute pressure Pa is lower than the predetermined pressure Patot).

In the high rotation region, the engine rotation speed Ne is a predetermined rotation speed No
p (for example, 3000 rpm).

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

When the engine is in any of the above ranges, it is determined that the engine is being operated in the open control range, and in this case, the process proceeds to step 82 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.
The output voltage value vO□, which is the output level of No. 3, is equal to the reference value Vll! between the previous input of the TDC signal and the current input of the TDC signal. The reference value Vl obtained in the F setting subroutine (Figs. 5 and 6)
ll! Step 8: Determine whether F has been reversed or not.
4) If the determination result is affirmative (Yes), proportional (P term) control is performed (from step 85). Denial (No)
In this case, integral control is performed (from step 90).

In 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 v■F, and if the determination result is affirmative (Yes), the rich side proportional control correction value P is read out from the Ne-P large table in accordance with the engine speed Na (step 86), and then in step 87 this correction value P trap is added to the previous value of the correction coefficient Ko2. The determination result in step 85 is negative (NO)
If so, the lean side proportional control correction value P+-1isNe-
Read out the PL child table according to the engine speed Na (step 88), and use the correction value PL thus read as the correction coefficient Ko.

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 O2 sensor 13 is at a lower level than the reference value VIIEF. If this determination result is positive (Yes),
Add 1 to the value of TDC signal pulse count number NIL (
Step 91), and it is determined whether the count number N has reached a predetermined value N+ (for example, 4) (Step 92).

As a result of this determination, if the count number N has not reached N+, the correction coefficient Ko2 is held at the value from the previous loop (step 93), and the count number N is N! If it reaches 02, a correction value Δk corresponding to the engine speed Ne is added to the correction coefficient (step 94), and the number of pulses counted up to that point is reset to O (step 95). A correction value Δk is added to the correction coefficient KO□ every time the value reaches N+. On the other hand, if the determination result in step 9o is negative (No), 1 is added to the count number NIH of TDC signal pulses (step 96
), it is determined whether the count number Ntu has reached a predetermined value N+ (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). ), If the determination result is affirmative (Yes), subtract the correction value Δk from the correction coefficient Ko (step 99), reset the counted pulse number NIH to 0 (step 100), and as above, N+o becomes 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 large EF after the change is specifically changed to 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 time required for determining the rich side of the air-fuel ratio by the O2 sensor can be lengthened to reduce the value of the correction coefficient Ko. If it is biased, 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, 0. The air-fuel ratio is corrected to the lean side or rich side depending on the degree of deterioration of the sensor, and the target air-fuel ratio is achieved.

(Effects of the Invention) As detailed above, according to the present invention, the exhaust gas concentration detection 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 Proportional control for increasing or decreasing the air-fuel ratio of the air-fuel mixture using 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. , 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 during which the detected exhaust concentration value changes from a maximum value on the rich side to a minimum value on the lean side; The ratio of the reference value to the second time until the maximum value is obtained is determined, and the reference value is changed according to the ratio thus obtained, so that even if the characteristics of the exhaust gas concentration detector change over time, The target air-fuel ratio can be achieved 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 a change over time in the output voltage value Vo of the o2 sensor 13, and FIGS. The figure shows the reference value V*t according to the present invention.
Program flowchart of p setting subroutine, seventh
The figure is a graph showing the engine operating range in which the program flowchart shown in Figs. 5 and 6 is executed, Fig. 8 is a graph showing the relationship between the correction coefficient Kwt〒 and the engine speed Ne, and Fig. 9 is the correction coefficient Kpa〒 and intake pipe absolute pressure P
FIG. 10 is a graph showing the relationship between a^ and the 02 feedback correction coefficient Ko. It is a program flowchart of a calculation subroutine. DESCRIPTION OF SYMBOLS 1... Internal combustion engine, 5... Electronic control unit (ECU), 8... Intake pipe absolute pressure (PB^) sensor, 10... Engine speed (Ne) sensor, 13
...02 sensor.

Claims (1)

[Claims] 1. Compare the detected exhaust concentration value detected by the exhaust concentration detector 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 Find the ratio of the first time for the detected exhaust gas concentration value to go from the rich side maximum value to the lean side minimum value and the second time for the detected exhaust gas concentration value to go from the lean side minimum value to the rich side maximum value, and calculate the ratio. An air-fuel ratio feedback control method for an internal combustion engine, characterized in that the reference value is changed in accordance with the determined ratio.