JPH07279716A - Air-fuel ratio control device for internal combustion engine having exhaust reflux device - Google Patents

Abstract

PURPOSE:To accurately control exhaust in the vicinity a target air-fuel ratio and sufficiently purify it at the time of exhaust reflux. CONSTITUTION:When an air-fuel ratio is shifted from a rich condition to a lean condition, an NOx correction rate FPL for correcting difference of a target air-fuel ratio control point is calculated (S20) based on an NOx density FNO obtained in S17. Renewal is conducted by the use of a value obtained by adding a proportional rate PL in an alpha increasing direction to the FPL (S21). When the air-fuel ratio is shifted from the lean condition to the rich condition, the correction rate is calculated (S22) based on the NOx density FNO. Renewal is conducted by the use of a value obtained by subtracting the proportional rate PR in an alpha decreasing direction from the FPR.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an internal combustion engine equipped with an exhaust gas recirculation system.

[0002]

2. Description of the Related Art In an internal combustion engine, as a measure for exhaust gas purification, CO and HC in the exhaust gas are oxidized in the exhaust system and NO
A three-way catalyst that reduces and purifies _X is becoming popular. Here, the three-way catalyst is set so that the conversion efficiency (purification efficiency) effectively functions in the exhaust state at the time of combustion at the stoichiometric air-fuel ratio. Therefore, the oxygen sensor provided in the exhaust system causes the exhaust property to be changed. It is common to have an electronically controlled fuel injection device that detects the air-fuel ratio from the above and feedback-controls the fuel injection amount so that the air-fuel ratio becomes close to the theoretical air-fuel ratio.

Now, in order to reduce NO _X in the exhaust gas, a part of the exhaust gas is returned to the intake system and re-combusted, so-called EG.
When the R system is provided in the internal combustion engine equipped with the electronically controlled fuel injection device, even if the variation in the performance of the fuel injection valve for each cylinder is taken into consideration, the distribution of the exhaust gas recirculation amount to each cylinder is not uniform. If not, the air-fuel ratio becomes richer in the cylinder with the larger exhaust gas recirculation amount.

Therefore, in the technique disclosed in Japanese Patent Laid-Open No. 2-55849, the fuel injection amount is fed back in accordance with the exhaust gas recirculation condition such as the exhaust gas recirculation ratio so that the air fuel ratio is close to the stoichiometric air fuel ratio. Have control.

[0005]

FIG. 5 also shows the case where the fuel injection amount is feedback controlled so that the air-fuel ratio becomes close to the stoichiometric air-fuel ratio in accordance with the state of exhaust gas recirculation such as the exhaust gas recirculation rate. as such, between the air-fuel ratio that is actually controlled with the control point of the air-fuel ratio should aim, so that the deviation occurs in response to the NO _X concentration in the exhaust gas.

[0006] Here, the correction is performed only exhaust gas recirculation rate to correct the deviation, since the concentration of NO _X in the exhaust gas due to a change in ignition timing, etc. are different, it is impossible to make appropriate correction . The present invention has been made in view of such a conventional situation, in an air-fuel ratio control device for an internal combustion engine including an exhaust gas recirculation device, when exhaust gas recirculation is performed, feedback control the air-fuel ratio accurately to the vicinity of the target air-fuel ratio. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine, which is equipped with an exhaust gas recirculation device that enables sufficient purification of exhaust gas.

[0007]

Therefore, as a means according to the invention of claim 1, as shown in FIG. 1, a part of the exhaust gas is recirculated from the exhaust passage of the engine to the intake system according to the operating state of the engine. Air-fuel ratio feedback that sets an air-fuel ratio feedback correction coefficient using a control constant based on the detection value of the air-fuel ratio detection means that detects the air-fuel ratio of the engine intake air-fuel mixture and the air-fuel ratio detection means. An air-fuel ratio of an internal combustion engine comprising a correction coefficient setting means, and an air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio to near the target air-fuel ratio based on the air-fuel ratio feedback correction coefficient set by the air-fuel ratio feedback correction coefficient setting means. in the control device, and the NO _X concentration detecting means for detecting the concentration of NO _X in the exhaust gas, the NO _X concentration detected by the NO _X concentration detecting means And a configuration and an air-fuel ratio feedback correction coefficient correcting means for correcting the control constant in the air-fuel ratio feedback correction coefficient setting means Zui.

Further, as a means according to the invention of claim 2, the engine operating state for detecting the operating state of the engine is provided, and the NO _x concentration detecting means is provided for the engine speed and the engine detected by the engine operating state. and NO _X base concentration estimation means for estimating the basic concentration of the exhaust gas recirculation rate is set based on the load, NO _X base concentration estimated by the estimation means NO
_It may be constituted by NO _X basic concentration correcting means for correcting the _X basic concentration according to the engine operating state.

As the means according to the third aspect of the present invention, the NO _x basic concentration correcting means may correct the NO _x basic concentration according to the ignition timing. Further, as the means according to the invention of claim 4, the NO _x basic concentration correcting means may be configured to correct the NO _x basic concentration according to the engine torque. Further, as a means according to the invention of claim 5, the NO _x basic concentration correcting means is NO _x.
The basic density may be corrected according to the engine speed.

Further, as the means according to the invention of claim 6, the NO _x concentration detecting means may detect the NO _x concentration in the exhaust gas based on the combustion temperature in the engine combustion chamber. Further, as a means according to the invention of claim 7,
NO _X concentration detecting means may be configured to detect the concentration of NO _X in the exhaust gas based on the combustion pressure in the engine combustion chamber.

[0011]

As a function of the invention described in claim 1, the control constant (for example, proportional or integral) in the air-fuel ratio feedback correction coefficient setting means is corrected based on the NO _X concentration, and the corrected control constant is used. Thus, the air-fuel ratio feedback correction coefficient is set, and feedback control is performed so that the air-fuel ratio becomes close to the target air-fuel ratio based on the correction-set air-fuel ratio feedback correction coefficient.

As the function of the invention described in claim 2, NO
_X concentration, the basic concentration set from the exhaust gas recirculation rate becomes to be obtained by correcting in accordance with the engine operating condition, it can be detected more accurately NO _X concentration.
As a function of the third aspect of the present invention, NO _X concentration becomes a can be obtained by correcting depending on the ignition timing of the basic concentration set from the exhaust gas recirculation rate, more precisely NO
_{The X} concentration can be detected.

The operation of the invention of claim 4 is NO _x
Concentration, the basic concentration set from the exhaust gas recirculation rate becomes to be obtained by correcting in accordance with the engine torque, can be detected more accurately NO _X concentration. As a function of the fifth aspect of the present invention, the NO _X concentration becomes a can be obtained by correcting in accordance with the engine rotational speed basic concentration set from the exhaust gas recirculation rate, is detected more accurately NO _X concentration You can

The operation of the invention of claim 6 is NO _x
The concentration is detected on the basis of the combustion temperature in the engine combustion chamber, it is possible to accurately detect the NO _X concentration.
As a function of the invention of claim 7, wherein, since the NO _X concentration is detected based on the combustion pressure in the engine combustion chamber, it is possible to accurately detect the NO _X concentration.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 2 shows the system configuration according to this embodiment. Air is sucked into the engine 1 through an air cleaner 2, an intake duct 3, a throttle chamber 4 and an intake manifold 5.

The throttle chamber 4 is provided with a throttle valve 6 which works in conjunction with an accelerator pedal (not shown) and controls the intake air flow rate Q. The intake manifold 5 or the intake port of the engine 1 is provided with a fuel injection valve 7 as a fuel supply means for each cylinder. The fuel injection valve 7 is an electromagnetic fuel injection valve, and a solenoid is energized by a drive pulse signal from the control unit 8 to open the valve. The adjusted fuel is injected and supplied to the engine 1.

In addition to the multi-point injection system as in this example, a single-point injection system in which a single fuel injection valve is provided in common for all cylinders may be used. Exhaust gas is discharged from the engine 1 through an exhaust manifold 9, but CO, H in the exhaust gas is discharged to the downstream side.
A three-way catalyst 18 is provided as an exhaust gas purification catalyst that purifies exhaust gas by oxidizing C and reducing NO _X.

On the other hand, part of the exhaust gas discharged from the exhaust manifold 9 is recirculated to the intake manifold 5 by the exhaust gas recirculation passage 21 via the exhaust gas recirculation control valve 22 interposed therein. The exhaust gas recirculation control valve 22 is a diaphragm type valve that is opened by applying suction negative pressure to the engine against the biasing force of the coil spring in the valve closing direction, and the EGR whose duty is controlled by the control unit 8 is controlled. The supply of negative suction pressure to the exhaust gas recirculation control valve 22 is controlled by a control solenoid (not shown).

The control unit 8 receives input signals from various sensors, performs arithmetic processing as described later by a built-in microcomputer, determines a fuel injection amount, and outputs a drive pulse signal having a pulse width corresponding to the fuel injection amount. Is output to the fuel injection valve 7 at a predetermined timing in synchronization with the rotation of the fuel injection valve 7. As the various sensors, a hot-wire type air flow meter 10 is provided in the intake duct 3, and the intake air flow rate Q
Output a voltage signal corresponding to.

A crank angle sensor 11 is provided by being built in a distributor (not shown),
Position signal every 1 ° or 2 ° and 4 cylinders 1
Outputs the reference signal every 80 °. Here, the engine speed N can be calculated by measuring the number of generated position signals or the period of the reference signal within a predetermined time.

A water temperature sensor 12 is provided on the water jacket of the engine 1 and outputs a signal corresponding to the cooling water temperature Tw. The exhaust manifold 9 is provided with an oxygen sensor 13 as air-fuel ratio detecting means. This oxygen sensor 13 has a platinum electrode provided inside and outside the zirconia tube, and further has a platinum catalyst as an oxidation catalyst and a protective layer formed on the outer surface. The oxygen concentration in the atmosphere on the inner surface (constant)
It is a known sensor that outputs a voltage according to the ratio of the oxygen concentration in the exhaust gas on the outer surface side and the output voltage changes rapidly when the air-fuel mixture is burned at the stoichiometric air-fuel ratio.

A combustion temperature sensor 25 is provided facing the combustion chamber of the engine 1 and outputs a signal according to the combustion temperature in the engine combustion chamber. Further, a combustion pressure sensor 27 is provided facing the combustion chamber of the engine 1 and outputs a signal corresponding to the combustion pressure in the engine combustion chamber. Further, the control unit 8 uses the engine key switch as the operating power source and the voltage of the battery 14 for detecting the power source voltage.
It is applied through 15.

[0023] The microcomputer in the control unit 8, the arithmetic processing, 3, 4 and the flow chart (fuel injection amount calculation routine, the proportional-integral control routine, NO _X concentration detecting routine) shown in FIG. 6 according to based program Done. Next, with reference to the drawings, the arithmetic processing by the microcomputer in the control unit 8 will be described.

In the fuel injection amount calculation routine of FIG.
In step 1 (denoted as S1 in the drawing; the same applies hereinafter), the basic fuel injection amount Tp is calculated from the intake air flow rate Q obtained from the signal from the air flow meter 10 and the engine speed N obtained from the signal from the crank angle sensor 11. (= K ・ Q /
N; K is a constant). In step 2, various correction coefficients COEF based on the cooling water temperature Tw and the like are set as necessary.

In step 3, the voltage correction amount Ts is set based on the voltage value of the battery 15. In step 4, the current air-fuel ratio feedback correction coefficient α set by the proportional / integral control routine of FIG. 4 described later is read. In the next step 5, the fuel injection amount Ti is calculated according to the following equation. Ti = Tp · COEF · α + Ts The portion corrected by the air-fuel ratio feedback correction coefficient α in this calculation corresponds to the air-fuel ratio feedback control means.

When the fuel injection amount Ti is calculated, the Ti
A drive pulse signal having a pulse width of is output at a predetermined timing synchronized with the engine rotation, is given to the fuel injection valve 7, and fuel injection is performed. Next, the proportional / integral control routine of FIG. 4 will be described. It should be noted that this routine is executed by a timer interrupt every predetermined time τ ₁ .

In step 11, it is determined whether or not the air-fuel ratio feedback control (FB) condition is satisfied. If NO, in step 12 the air-fuel ratio feedback correction coefficient α is clamped to the reference value 1 or the previous value. Then, this routine ends. If YES, the process proceeds to step 13 and thereafter. In step 13, the output voltage OS of the oxygen sensor 13
R1 is A / D converted and fetched.

In step 14, the output voltage OSR1 of the oxygen sensor 13 is compared with the slice level (reference voltage) SL to determine rich / lean of the air-fuel ratio. If the air-fuel ratio is rich (OSR1 ≧ SL), step 15
If the sensor flag F1 is set (F1 = 1) and the air-fuel ratio is lean (OSR1 <SL), step 16
And resets the sensor flag F1 (F1 = 0), and then proceeds to step 17.

In step 17, a NO _x concentration detection routine, which will be described later, is executed and the obtained NO _x concentration is set as FNO. In step 18, it is determined whether or not the sensor flag F1 has been inverted in the current routine execution. Then, the sensor flag F1 changes from F1 = 0 to 1 or F
When it is reversed from 1 = 1 to 0, the process proceeds to step 19, and whether the current sensor flag F1 is F1 = 0 or F1 =
Judge whether it is 1.

If it is determined that F1 = 0, it is determined that the air-fuel ratio has changed from rich to lean, and the routine proceeds to step 20. Although during the inversion it should be corrected among the first air-fuel ratio in the rich direction, between the air-fuel ratio control point and the air-fuel ratio that is actually controlled should aim NO _X concentration F
The higher the NO, the larger the deviation will occur (see FIG. 5). In thus step 20, in order to correct the deviation, NO _X concentration FNO is higher the larger the value NO _X
The corrected FPL is the NO _X concentration FN obtained in step 17 above.
Calculate based on O.

Then, in step 21, assuming that the air-fuel ratio is changed from rich to lean in step 21, the air-fuel ratio feedback correction value α is increased from the present value in the increasing direction proportional to the lean inversion for setting the air-fuel ratio feedback correction value. Minute PL and the NO _X correction amount FPL calculated in step 20
Update with the value obtained by adding and. If it is determined that F1 = 1, it is determined that the air-fuel ratio has changed from lean to rich, and the routine proceeds to step 22.

At the time of the reversal, the air-fuel ratio should be corrected in the lean direction as soon as possible. However, the higher the NO _X concentration FNO, the greater the difference between the air-fuel ratio control point to be aimed at and the actually controlled air-fuel ratio. Will occur (see FIG. 5). Therefore, in step 22, in order to correct the deviation, the NO _X correction amount FPR that becomes larger as the NO _X concentration FNO is higher is calculated based on the NO _X concentration FNO obtained in step 17.

Then, in step 23, assuming that the air-fuel ratio is changed from lean to rich in step 23, the air-fuel ratio feedback correction value α is proportional to the decrease value given from the current value at the time of rich inversion for setting the air-fuel ratio feedback correction value. The amount PR and the NO _X correction amount FPR calculated in step 22 are updated with the subtracted value. That is, step 20 to step
Reference numeral 23 denotes the function of the air-fuel ratio feedback correction coefficient correction means according to the first aspect of the invention.

On the other hand, if it is determined in step 18 that the sensor flag F1 is not inverted, step
In step 24, it is determined whether the current sensor flag F1 is F1 = 0 or F1 = 1. If it is determined that F1 = 0, it is determined that the air-fuel ratio remains lean, and the routine proceeds to step 25, where the air-fuel ratio feedback correction value α is updated with the current value plus the integral IL. And return as is.

If it is determined that F1 = 1, it is determined that the air-fuel ratio remains rich, and the routine proceeds to step 26, where the air-fuel ratio feedback correction value α is a value obtained by subtracting the integral IR from the current value. Update with and return as is. That is, the proportional / integral control routine described above has a function as an air-fuel ratio feedback correction coefficient setting means.

Next, the NO _x concentration detection routine will be described. FIG. 6 shows a NO _X concentration detection routine according to the first embodiment of the present invention. In step 31, the engine speed N is read by the signal from the crank angle sensor 11.

In step 32, the basic fuel injection amount Tp obtained by the fuel injection amount calculation routine is read. In step 33, the current engine speed N and basic fuel injection are referred to with reference to a map (see FIG. 7) in which the EGR rate is stored in advance for each operating region divided by the engine speed N and the basic fuel injection amount Tp. An EGR rate corresponding to the amount Tp is set.

In step 34, the NO _X basic concentration NO _XST corresponding to the current EGR rate is estimated from the NO _X basic concentration map (see FIG. 8). That is, the step has the function of the NO _X basic concentration estimating means. In step 35,
Referring to a map (not shown) in which the ignition timing ADV (advance value) is stored in advance for each operating region divided by the engine speed N and the basic fuel injection amount Tp, the current engine speed N
And the ignition timing ADV corresponding to the basic fuel injection amount Tp are set.

At step 36, the NO _X concentration correction coefficient corresponding to the ignition timing ADV is obtained from the NO _X concentration correction map (see FIG. 9). In step 37, the NO _X basic concentration NO
_XST is corrected by the NO _X concentration correction coefficient obtained in step 36 to calculate the NO _X concentration FNO. That is, the step
36 and 37 perform the function according to claim 3.

As described above, the NO _X concentration detection routine according to the first embodiment has the configuration according to the inventions of claims 2 and 3, and the more the ignition timing ADV is advanced, the more NO is increased. _{Although the X} concentration becomes high, the influence of the ignition timing is reflected in the NO _X basic concentration NO _XST corresponding to the EGR rate by the NO _X concentration correction coefficient, so that the N concentration is more accurate.
It is possible to detect the O _X concentration (see FIG. 10).

That is, the more advanced the ignition timing ADV is, the higher the NO _X concentration is, so that the deviation between the air-fuel ratio control point to be aimed for and the air-fuel ratio actually controlled becomes large. The NO _x concentration FNO is calculated with high accuracy by the NO _x concentration detection routine according to the embodiment, and the higher the NO _x concentration FNO, the larger the value of the NO _x correction amount FPL, and the earlier the deviation can be corrected, the feedback The controllability of control is improved.

FIG. 11 shows a NO _x concentration detecting routine according to the second embodiment of the present invention. The steps having the same functions as those in the first embodiment shown in FIG. 6 are designated by the same step numbers and the description thereof will be omitted. In step 41, N corresponding to the basic fuel injection amount Tp representing the engine torque
NO _X concentration correction map for O _X concentration correction coefficient (see Fig. 12)
Ask from.

In step 42, the basic NO _X concentration NO _XST
Is corrected by the NO _X concentration correction coefficient obtained in step 41 to calculate the NO _X concentration FNO. That is, steps 41 and 42 perform the function of claim 4. As described above, the NO _X concentration detection routine according to the second embodiment has the configuration according to the invention described in claims 2 and 4,
The NO _x concentration increases as the engine torque increases, but the effect of the engine torque is reduced to E by the NO _x concentration correction coefficient.
Since reflect the NO _X base concentration NO _XST corresponding to GR ratio, it can either be detected more accurately NO _X concentration.

That is, as the engine torque becomes larger,
Since the NO _X concentration becomes high, the deviation between the air-fuel ratio control point to be aimed for and the air-fuel ratio actually controlled becomes large,
According to the NO _X concentration detection routine according to the second embodiment,
The NO _X concentration FNO is accurately calculated, and the NO _X concentration FN is calculated.
The higher O is, the larger the NO _X correction amount FPL becomes, so that the deviation can be corrected quickly, and the controllability of the feedback control is improved.

Next, a NO _x concentration detecting routine according to the third embodiment of the present invention will be described. Since the flowchart is similar to that of FIG. 11, its explanation is omitted and only the function different from the second embodiment will be explained. . In the third embodiment, step 41
Then, the NO _X concentration correction coefficient corresponding to the engine speed N is set to N
Obtained from the O _X density correction map (see FIG. 13).

At step 42, the basic NO _X concentration NO _XST
Is corrected by the NO _X concentration correction coefficient obtained in step 41 to calculate the NO _X concentration FNO. That is, steps 41 and 42 perform the function of claim 5. As described above, the NO _X concentration detecting routine according to the third embodiment has a configuration of the invention according to claim 2 and 5,
The NO _x concentration decreases as the engine speed increases, but the effect of the engine torque is reduced to E by the NO _x concentration correction coefficient.
Since reflect the NO _X base concentration NO _XST corresponding to GR ratio, it can either be detected more accurately NO _X concentration.

That is, the lower the engine speed, the more NO _X
Since the concentration becomes high, the deviation between the air-fuel ratio control point to be aimed for and the air-fuel ratio actually controlled becomes large.
The NO _x concentration FNO is calculated with high accuracy by the NO _x concentration detection routine according to the embodiment, and the higher the NO _x concentration FNO, the larger the value of the NO _x correction amount FPL, and the earlier the deviation can be corrected, the feedback The controllability of control is improved.

Next, a fourth embodiment of the present invention will be described. In the fourth embodiment, the microcomputer in the control unit 8 executes the fuel injection amount calculation routine and the proportional / integral control routine, but does not execute the NO _X concentration detection routine. That is, the combustion temperature sensor 25 is provided so as to face the combustion chamber of the engine 1 and outputs a signal T _F according to the combustion temperature in the engine combustion chamber. In the fourth embodiment, the signal T _F is based on the signal T _F. NO _x concentration map (Fig. 14
Detecting the NO _X concentration FNO in the exhaust gas than the reference).

That is, the fourth embodiment has the function of claim 6. Next, a fifth embodiment of the present invention will be described. Also in the fifth embodiment, the microcomputer in the control unit 8 executes the fuel injection amount calculation routine and the proportional / integral control routine, but does not execute the NO _X concentration detection routine.

That is, the combustion pressure sensor faces the combustion chamber of the engine 1.
Is provided to adjust the combustion pressure in the engine combustion chamber.
Signal P_FIs output in the fifth embodiment.
P_FBased on the combustion temperature map (see Fig. 15)
The combustion temperature in the baking chamber is detected. And the fourth implementation
In the same manner as in the example, NO in exhaust gas based on the combustion temperature _X
The concentration FNO is detected.

That is, the fifth embodiment has the function of claim 7. As described above, in the fourth embodiment, N
Although O _X concentration is detected in a more direct detection method close to,
Since the NO _x concentration increases as the combustion temperature in the engine combustion chamber increases, the NO _x concentration can be detected more accurately by measuring the combustion temperature.

Also in the fifth embodiment, the higher the combustion pressure in the engine combustion chamber, the higher the combustion temperature.
As a result, the NO _X concentration becomes high, so that the NO _X concentration can be detected more accurately by measuring the combustion pressure. That is, also in the fourth and fifth embodiments, the NO _X concentration FNO is accurately detected, and the controllability of the feedback control is improved.

[0053]

As described above, according to the first aspect of the present invention, the control constant in the air-fuel ratio feedback correction coefficient setting means is corrected based on the NO _X concentration, and the corrected air-fuel ratio feedback correction coefficient is calculated. By using this, the fuel supply amount to the engine is corrected and controlled, so that the air-fuel ratio is reliably feedback-controlled to near the stoichiometric air-fuel ratio as the target air-fuel ratio, and even if exhaust gas recirculation is performed, exhaust gas is sufficiently It has the effect of being purified by the original catalyst.

Further, in any one of claims 2 to 7,
In the described invention, NO is more accurate. _XTo detect the concentration
The effect is that you can

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration according to a first aspect of the invention.

FIG. 2 is a system schematic diagram showing an embodiment of the present invention.

FIG. 3 is a flowchart showing a fuel injection amount calculation routine in the above embodiment.

FIG. 4 is a flowchart showing a proportional / integral control routine in the above embodiment.

FIG. 5 is a characteristic diagram showing the relationship between the deviation of the air-fuel ratio and the NO _X concentration FNO.

FIG. 6 is a flowchart showing a NO _x concentration detection routine according to the first embodiment of the present invention.

FIG. 7 is a diagram showing a map of an EGR rate.

FIG. 8 is a diagram showing a map of the NO _X basic concentration NO _XST with respect to the EGR rate.

FIG. 9 is a diagram showing a NO _X concentration correction map for ignition timing ADV.

FIG. 10 is a characteristic diagram illustrating the operation of the first embodiment.

FIG. 11 is a flowchart showing a NO _X concentration detection routine according to the second embodiment of the present invention.

FIG. 12 is a diagram showing a NO _X concentration correction map for engine torque.

FIG. 13 is a diagram showing a NO _X concentration correction map with respect to the engine speed.

FIG. 14 is a diagram showing a map of NO _X concentration.

FIG. 15 is a diagram showing a map of combustion temperature.

[Explanation of symbols]

 1 engine 5 intake manifold 7 fuel injection valve 8 control unit 9 exhaust manifold 11 crank angle sensor 13 oxygen sensor 18 three-way catalyst 21 exhaust gas recirculation passage 22 exhaust gas recirculation control valve 25 combustion temperature sensor 27 combustion pressure sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location F02M 25/07 550 R F02P 5/15

Claims (7)

[Claims] 1. An air-fuel ratio detection means for detecting an air-fuel ratio of an engine intake air-fuel mixture, comprising an exhaust gas recirculation device for recirculating a part of exhaust gas from an exhaust passage of the engine to an intake system in accordance with an operating state of the engine. Based on the detection value of the air-fuel ratio detection means, based on the air-fuel ratio feedback correction coefficient setting means for setting the air-fuel ratio feedback correction coefficient using the control constant, and the air-fuel ratio feedback correction coefficient set by the air-fuel ratio feedback correction coefficient setting means and NO _X concentration detecting means in the air-fuel ratio control system for an internal combustion engine having fuel ratio feedback control means for feedback control to the vicinity of the target air-fuel ratio, and for detecting the concentration of NO _X in the exhaust gas air-fuel ratio Te, NO _X concentration detected air-fuel to correct the control constants in the air-fuel ratio feedback correction coefficient setting means based the NO _X concentration detected by means Air-fuel ratio control system for an internal combustion engine having an exhaust gas recirculation device characterized by comprising: a feedback correction coefficient correcting means. With wherein comprises engine operating condition for detecting an operating condition of the engine, NO _X concentration detecting means, exhaust gas recirculation rate is set based on the differentially engine speed and the engine load detected by said engine operating condition estimating a basic concentration of NO _X base and concentration estimation means, N for correcting the NO _X base concentration estimated by NO _X base concentration estimation means on the engine operating condition
O _X basic density correction means and the air-fuel ratio control apparatus for an internal combustion engine having an exhaust gas recirculation system according to claim 1, characterized by comprising. 3. The air-fuel ratio of an internal combustion engine having an exhaust gas recirculation system according to claim 1, wherein the NO _x basic concentration correcting means is configured to correct the NO _x basic concentration according to ignition timing. Control device. 4. The air-fuel ratio of an internal combustion engine having an exhaust gas recirculation system according to claim 1, wherein the NO _X basic concentration correcting means is configured to correct the NO _X basic concentration according to the engine torque. Control device. 5. The empty space of an internal combustion engine having an exhaust gas recirculation system according to claim 1, wherein said NO _X basic concentration correcting means is configured to correct the NO _X basic concentration according to the engine speed. Fuel ratio control device. 6. An internal combustion engine having an exhaust gas recirculation system according to claim 1, wherein the NO _x concentration detecting means is configured to detect the NO _x concentration in the exhaust gas based on the combustion temperature in the engine combustion chamber. Air-fuel ratio control device. 7. An internal combustion engine having an exhaust gas recirculation system according to claim 1, wherein the NO _X concentration detecting means is configured to detect the NO _X concentration in the exhaust gas based on the combustion pressure in the engine combustion chamber. Air-fuel ratio control device.