JPH08105342A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

PURPOSE: To accurately control an air-fuel ratio to be lean by restraining the air-fuel ratio dispersion between cylinders with a simple constitution. CONSTITUTION: Air-fuel ratio feedback control is performed by oxygen sensors 9 and 10 for a first cylinder and second to forth cylinders respectively, and the deviation A (=α2-α1) between their respective air-fuel ratio feedback correction coefficient α1 and α2 is stored for each running condition. At the next control of air-fuel ratio to be lean, based on the value B, the sum of this deviation A and the air-fuel ratio feedback correction coefficient of the first cylinder, the width of pulses for fuel injection during the control of air-fuel ratio to be lean for the second to forth cylinders is rectified. With this constitution, the air-fuel ratio dispersion between cylinders is restrained with simple constitution, making accurate air-fuel ratio control to be lean possible.

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 device for an internal combustion engine, and more particularly to an improvement of a device for controlling the air-fuel ratio of an engine intake air-fuel mixture to a lean air-fuel ratio (lean air-fuel ratio).

[0002]

2. Description of the Related Art Conventionally, an intake air-fuel mixture of a multi-cylinder internal combustion engine can be provided with a cheap and simple structure without using an expensive wide-range air-fuel ratio sensor capable of linearly detecting the air-fuel ratio of the engine intake air-fuel mixture. As an air-fuel ratio control device for leaning (raising lean air-fuel ratio, for example, setting intake air weight / fuel weight [A / F] = about 18), a predetermined one upstream from where the exhaust gas from each cylinder joins An oxygen sensor (a sensor that detects whether the air-fuel ratio is rich or lean) is provided only in the exhaust passage of one cylinder, and a rich / lean determination signal from this oxygen sensor is provided before performing lean control. Feedback control to correct the air-fuel ratio control amount (for example, fuel supply amount, intake air flow rate) so that the target air-fuel ratio (theoretical air-fuel ratio) can be obtained based on While modifying the deviation of the air-fuel ratio control value according to the engine or every time degradation such as by using a kick correction amount,
It is known to control the air-fuel ratio so as to obtain a target lean air-fuel ratio in other cylinders by feedforward control.

[0003]

However, in the air-fuel ratio control apparatus as described above, in order to simplify the configuration and reduce the product cost, the air-fuel ratio control value is determined based on only the detection result of one cylinder. Because of the configuration for correcting the deviation, it is not possible to deal with variations in parts accuracy between cylinders, deterioration with time, etc., and it is not possible to perform lean control with high accuracy. For this reason, for example, in the lean control immediately after the start, the early activation of the catalyst and the emission of the unburned fuel (HC) cannot be sufficiently reduced (when there is a deviation from the target lean air-fuel ratio to the rich side), There was a problem that drivability deteriorates (when there is a deviation from the target lean air-fuel ratio to the lean side). If oxygen sensors are provided in all cylinders so that the air-fuel ratio of each cylinder can be detected, variations in air-fuel ratio among the cylinders can be corrected, but in this case, the configuration becomes complicated and the product cost is reduced. There is a drawback such as an increase in

On the other hand, during lean control by the feedforward control, the operating state (for example, water temperature) gradually changes, so-called wall flow fuel amount gradually changes, and the exhaust air-fuel ratio changes. In this case, the exhaust air-fuel ratio deviates from the target lean air-fuel ratio, which causes changes in catalyst activation characteristics and exhaust conversion efficiency, and there is also a problem that catalyst activation or exhaust characteristics cannot be sufficiently improved.

The present invention has been made in view of the above conventional problems, and suppresses the air-fuel ratio variation among the cylinders while suppressing the complication of the configuration and the increase of the product cost, and performs the lean control with high accuracy. It is a first object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that can be used. Further, it is an object of the present invention to further improve the control accuracy in the device.

Further, according to the present invention, even during the lean control by the feedforward control, it is possible to follow the change of the operating state, and the variation in the air-fuel ratio between the cylinders can be suppressed with a simple structure to achieve a highly accurate lean. It is a second object of the present invention to provide an air-fuel ratio control device for an internal combustion engine, which is capable of performing a charge control.

[0007]

Therefore, in the air-fuel ratio control apparatus for an internal combustion engine according to the invention as defined in claim 1,
As shown in FIG. 2, a predetermined oxygen sensor A that detects the oxygen concentration in the exhaust gas of a specific cylinder to detect the air-fuel ratio of the engine intake air-fuel mixture, and a predetermined oxygen sensor A based on the detection result of the first oxygen sensor A A first air-fuel ratio feedback control means C for increasing / decreasing the air-fuel ratio control amount of the specific one cylinder via the first air-fuel ratio feedback correction value B so that the target air-fuel ratio of
And a second oxygen sensor D that detects the oxygen concentration in the exhaust gas after the merging of all cylinders to detect the air-fuel ratio of the engine intake air-fuel mixture, and based on the detection result of the second oxygen sensor D Second air-fuel ratio feedback control means F for increasing / decreasing the air-fuel ratio control amount of the cylinders other than the specific one cylinder via the second air-fuel ratio feedback correction value E so that the fuel ratio can be obtained.
Based on the first air-fuel ratio feedback correction value B, the air-fuel ratio control amount of the specific cylinder is controlled so that a target lean air-fuel ratio leaner than the predetermined target air-fuel ratio is obtained during lean control. First lean control means G for correction,
A second lean control that corrects the air-fuel ratio control amount of cylinders other than the specific one cylinder during lean control based on the second air-fuel ratio feedback correction value E so that the target lean air-fuel ratio is obtained. And means H.

According to the second aspect of the present invention, as shown in FIG. 2, a first oxygen sensor A for detecting the oxygen concentration in the exhaust gas of one specific cylinder to detect the air-fuel ratio of the engine intake air-fuel mixture, Based on the detection result of the first oxygen sensor A, the air-fuel ratio control amount of the specific one cylinder is increased / decreased via a first air-fuel ratio feedback correction value B so as to obtain a predetermined target air-fuel ratio. Based on the air-fuel ratio feedback control means C, the second oxygen sensor D that detects the oxygen concentration in the exhaust gas after all the cylinders have merged to detect the air-fuel ratio of the engine intake air-fuel mixture, and the detection result of the second oxygen sensor. A second air-fuel ratio feedback control means F for increasing / decreasing the air-fuel ratio control amount of cylinders other than the specific one cylinder via a second air-fuel ratio feedback correction value E so as to obtain a predetermined target air-fuel ratio, First air-fuel ratio feedback Correction value B and the second air-fuel ratio feedback correction value E and, in a deviation I deviation calculating means J
And a deviation storage means K for storing the deviation I for each operating state.
And before performing the lean control of the air-fuel ratio of the specific one cylinder after the engine is restarted, based on the detection result of the first oxygen sensor A, the specific target air-fuel ratio is obtained so as to obtain the predetermined target air-fuel ratio. Pre-lean control air-fuel ratio feedback control means M for increasing / decreasing the air-fuel ratio control amount of one cylinder via the third air-fuel ratio feedback correction value L and leaner than the predetermined target air-fuel ratio during lean control. Third lean control means N for correcting the air-fuel ratio control amount of the specific one cylinder based on the third air-fuel ratio feedback correction value L so as to obtain a target lean air-fuel ratio, and during lean control, The deviation I stored in the deviation storage means K and the third air-fuel ratio feedback correction value L for the air-fuel ratio control amounts of the cylinders other than the specific one cylinder so as to obtain the target lean air-fuel ratio.
And a fourth leaning control unit P that corrects based on the sum O of the above.

In the invention described in claim 3 (second invention),
As shown in FIG. 3, based on the first oxygen sensor A that detects the oxygen concentration in the exhaust gas of a specific cylinder to detect the air-fuel ratio of the engine intake air-fuel mixture, and the detection result of the first oxygen sensor A. , A first air-fuel ratio feedback correction value B for the air-fuel ratio control amount of the specific one cylinder so that a predetermined target air-fuel ratio is obtained.
A first air-fuel ratio feedback control means C for increasing / decreasing correction via the second oxygen sensor D for detecting the air-fuel ratio of the engine intake air-fuel mixture by detecting the oxygen concentration in the exhaust gas after all the cylinders merge.
Based on the detection result of the second oxygen sensor D, the air-fuel ratio control amount of the cylinders other than the specific one cylinder is increased / decreased via the second air-fuel ratio feedback correction value E so that a predetermined target air-fuel ratio is obtained. Deviation calculating means J for obtaining a deviation between the second air-fuel ratio feedback control means F, the first air-fuel ratio feedback correction value B, and the second air-fuel ratio feedback correction value E, and the deviation for each operating state. The deviation storage means K to be stored and the air-fuel ratio control amount of the specific one cylinder so as to obtain the predetermined target air-fuel ratio based on the detection result of the first oxygen sensor A during lean control, Fourth
Leaning control hollow fuel ratio feedback control means R for increasing / decreasing correction via an air-fuel ratio feedback correction value Q, and the specific lean air-fuel ratio which is leaner than the predetermined target air-fuel ratio during leaning control. Fifth lean control means S for correcting the air-fuel ratio control amount of cylinders other than one cylinder based on the sum of the deviation stored in the deviation storage means K and the fourth air-fuel ratio feedback correction value Q.
And, and configured.

[0010]

The invention according to claim 1 having the above-mentioned structure,
For example, during stoichiometric operation (near the stoichiometric air-fuel ratio), the first air-fuel ratio feedback correction value corresponding to a specific one cylinder and the average second air-fuel ratio feedback correction value for all cylinders are obtained. And during lean control,
One specific cylinder is made lean through the first air-fuel ratio feedback correction value, while the remaining cylinders are made lean through the second air-fuel ratio feedback correction value. That is, for a specific one cylinder, lean control is performed based on the first air-fuel ratio feedback correction value that is independent of deterioration with time of other cylinders, variation of parts, and the like, whereby deterioration with time and variation of parts of the specific one cylinder are performed. Etc. can be controlled with high accuracy while performing lean control for the remaining cylinders based on the second air-fuel ratio feedback correction value (a value that greatly correlates with the deterioration of the remaining cylinder over time and component variations). Specific control by controlling
Minimize the effects of cylinder deterioration over time and component variations,
The lean control can be performed with high accuracy while correcting the deterioration of the remaining cylinders with time and the variation of parts. That is, with a relatively simple configuration including two oxygen sensors, lean control can be performed with high accuracy while correcting deterioration over time, component variations, etc., without significantly increasing product cost. .

According to the second aspect of the present invention, for example, during stoichiometric operation, a first air-fuel ratio feedback correction value for a specific one cylinder and an average second air-fuel ratio feedback correction value for all cylinders are obtained, Further, the deviation between the second air-fuel ratio feedback correction value and the first air-fuel ratio feedback correction value is obtained, and the deviation is stored according to the operating state. Then, before performing lean control after engine restart, performing air-fuel ratio feedback control based on the detection result of the first oxygen sensor to set a third air-fuel ratio feedback correction value, and then performing lean control,
Based on the third air-fuel ratio feedback correction value, high-precision lean control that is independent of the deterioration of other cylinders over time, component variation, etc. is performed for a specific one cylinder, while the storage is performed for the remaining cylinders. And the third air-fuel ratio feedback correction value (a value that greatly correlates with the deterioration of the remaining cylinders over time, component variations, etc.),
By performing lean control based on the total value, the influence of deterioration over time of the first cylinder and variations in parts, etc. is reduced, and the deterioration over time and variations in parts of the remaining cylinders are corrected with high accuracy while leaning. Control. In addition, specific 1
While the cylinders are performing the air-fuel ratio feedback control by the third air-fuel ratio feedback control means in order to grasp the current air-fuel ratio state, the lean control is started at an early stage for the remaining cylinders (for example, , Based on the second air-fuel ratio feedback correction value), and thereafter, it is possible to switch to highly accurate lean control based on the total value. Therefore, it is possible to promote the early activation of the catalyst at the time of restart and the reduction of the emission of unburned fuel.

That is, with a relatively simple structure including two oxygen sensors, it is possible to correct deterioration over time and variations in parts, etc., without increasing the product cost significantly, and it is highly accurate and lean after restarting the engine from an early stage. It is possible to control the conversion. The invention according to claim 3 (second aspect)
Inventive), for example, at the time of stoichiometric operation,
A first air-fuel ratio feedback correction value for a cylinder and an average second air-fuel ratio feedback correction value for all cylinders are obtained, and the second air-fuel ratio feedback correction value and the first air-fuel ratio feedback correction value are obtained. And the deviation is obtained, and the deviation is stored according to the operating state. And
During lean control, for one specific cylinder, air-fuel ratio feedback control based on the detection result of the first oxygen sensor is performed to set a fourth air-fuel ratio feedback correction value, while for the remaining cylinders. The sum of the stored deviation and the fourth air-fuel ratio feedback correction value (a value that greatly correlates with the deterioration of the remaining cylinders over time, component variations, etc.), and leans based on the sum. Get control.

As a result, during lean control, for example, even when the operating state (for example, the water temperature) gradually changes, the so-called wall flow fuel amount gradually changes, and the exhaust air-fuel ratio also changes. Since the change characteristic can be grasped by the fourth air-fuel ratio feedback correction value obtained from the air-fuel ratio feedback control in the specific one cylinder, the change characteristic can be grasped and the leaning control of the remaining cylinders can be performed. Since it is possible to correct the control target value, it is possible to correct the deterioration over time and the variation of parts while suppressing the deviation of the exhaust air-fuel ratio from the target lean air-fuel ratio, thereby sufficiently activating the catalyst or exhaust characteristics. Will also be able to improve. In other words, with a relatively simple configuration including two oxygen sensors, deterioration over time, component variations, etc. can be corrected without significantly increasing the product cost, and the air-fuel ratio can be adjusted by following changes in operating conditions. It can be corrected, and thus more accurate lean control can be achieved.

[0014]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 4, an intake passage 2 of an engine 1 is provided with an air flow meter 3 for detecting an intake air flow rate Q of intake air sucked through an air cleaner and a throttle valve 4 for controlling the intake air flow rate Q in conjunction with an accelerator pedal. Has been. An electromagnetic fuel injection valve 6 for injecting and supplying fuel to each cylinder is provided in a branch portion 5 of the manifold downstream of the throttle valve 4.

The fuel injection valve 6 is opened and driven by an injection pulse signal from a control unit 50, which will be described later. The fuel injection valve 6 is pressure-fed from a fuel pump (not shown) and a predetermined amount of fuel controlled by a pressure regulator is injected and supplied. . In addition, a first oxygen sensor 9 that detects the air-fuel ratio by detecting the concentration of oxygen (other components may be included) in the exhaust gas from a specific cylinder is provided in the branch portion 7 of the exhaust manifold of the engine 1 (main In the embodiment, the oxygen concentration in the exhaust gas of the first cylinder is detected), and a second oxygen sensor 10 is provided in the exhaust passage 8 on the downstream side thereof. Incidentally, further downstream, CO in the exhaust gas up to near the stoichiometric air-fuel ratio, oxidation of HC, and exhibit the reducing action of NO _X,
A three-way catalyst 11 is provided as an exhaust purification catalyst that purifies exhaust gas.

The first and second oxygen sensors 9 and 10 output a voltage according to the oxygen concentration in the exhaust gas and compare this voltage with a predetermined slice level SL (for example, equivalent to the theoretical air-fuel ratio). Therefore, rich / lean determination of the air-fuel ratio can be performed. The control unit 50
A microcomputer including a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like is provided, receives input signals from various sensors, and injects the injection amount of the fuel injection valve 6 as follows. (That is, the air-fuel ratio control amount)
Control.

As the various sensors, there are the above-mentioned first and first sensors.
The second oxygen sensors 9 and 10 and the air flow meter 3 are provided. In addition, a crank angle sensor 12 is provided on the crankshaft or camshaft of the engine 1, and the crank angle sensor 12 synchronizes with the engine rotation. The engine rotation speed Ne is detected by counting the output crank unit angle signal for a certain period of time or measuring the cycle of the crank reference angle signal. A water temperature sensor 13 as an engine temperature detecting means is provided facing the cooling jacket of the engine 1, and the engine water temperature T
It is designed to detect w.

In the control unit 50, the intake air flow rate Q obtained from the voltage signal from the air flow meter 3
And the engine rotation speed Ne obtained from the signal from the crank angle sensor 12, a basic fuel injection pulse width (corresponding to the fuel injection amount) Tp = c × Q / Ne (c is a constant) is calculated, and at the time of low water temperature. The final effective fuel injection pulse width Te = Tp × (1 + Kw + Kas + ...) By the water temperature correction coefficient Kw forcibly correcting to the rich side, the start and post-start increase amount correction coefficient Kas, the air-fuel ratio feedback correction coefficient α, etc.
・) × α + Ts is calculated. Ts is a voltage correction amount.

Then, this effective fuel injection pulse width Te is sent to the fuel injection valve 6 as a drive pulse signal, and the fuel adjusted to a predetermined amount is injected and supplied. The air-fuel ratio feedback correction coefficient α is increased / decreased by proportional-plus-integral (PI) control based on the rich / lean inversion output of the oxygen sensor. Based on this, the control unit 50 corrects the basic fuel pulse width Tp to perform combustion. The air-fuel ratio of the air-fuel mixture is feedback-controlled near the target air-fuel ratio (theoretical air-fuel ratio). In this example, two oxygen sensors are used, and as described below, the first oxygen sensor is used.
The air-fuel ratio feedback correction coefficient can be set separately for each of the cylinders and the second to nth cylinders (the fourth cylinder in this embodiment).

Here, the air-fuel ratio control of the engine 1 performed by the control unit 50 having the functions of the respective means of the present invention as software will be described with reference to the flowchart of FIG. In step (indicated as S in the figure. The same applies hereinafter) 1, the current target air-fuel ratio is set to stoichiometric (theoretical air-fuel ratio, near A / F = 14.7) or lean (for example, It is determined whether A / F = 18) is set. If it is set to stoichiki, proceed to step 2, and if it is set to lean, proceed to step 8.

In step 2, feedback control is performed for the first cylinder based on the rich / lean determination output result of the first oxygen sensor 9 (corresponding to the first air-fuel ratio feedback control means of the present invention). That is, the fuel injection pulse width Te of the first cylinder is set as follows. Te = Tp × (1 + Kw + Kas + ...) × α1 + Ts In step 3, the second cylinder to the n-th cylinder (in the present embodiment,
For n = 4), feedback control is performed based on the rich / lean inversion output result of the second oxygen sensor 10 (corresponding to the second air-fuel ratio feedback control means of the present invention). That is, the fuel injection pulse width T of the second cylinder to the nth cylinder
e is set as follows.

Te = Tp × (1 + Kw + Kas + ...) × α2 + Ts In step 4, the average value Aα1 of the air-fuel ratio feedback correction coefficient α1 in the feedback control of the first cylinder.
(Corresponding to the first air-fuel ratio feedback correction value of the present invention) is determined. In step 5, the average value Aα2 (corresponding to the second air-fuel ratio feedback correction value of the present invention) of the air-fuel ratio feedback correction coefficient α2 in the feedback control of the second cylinder to the n-th cylinder is obtained.

In step 6, the difference A = (Aα2-A) between the average values α1 and α2 of the two air-fuel ratio feedback correction coefficients.
Find α1). The step 6 corresponds to the deviation calculating means of the present invention. In step 7, the operating state (Ne, T
The value of A is stored (backed up) corresponding to (p, Tw, etc.), and the process returns to step 1.

The step 7 corresponds to the deviation storage means of the present invention. On the other hand, if it is determined in step 1 that lean is set, the process proceeds to step 8. In step 8, the first cylinder is emptied based on the rich / lean determination output result of the first oxygen sensor 9. Performs feedback control of the fuel ratio. Immediately leaning the remaining cylinders to some extent is advantageous in that the air-fuel ratio of the engine as a whole can be made lean early and catalyst activation, exhaust performance improvement, fuel efficiency improvement, etc. can be achieved.

The step 8 corresponds to the air-fuel ratio feedback control means before lean control of the present invention. In step 9, the average value AαL1 (corresponding to the third air-fuel ratio feedback correction value of the present invention) of the air-fuel ratio feedback correction coefficient αL1 in the feedback control of the first cylinder is obtained, and lean control is performed using this AαL1 ( This corresponds to the third lean control of the present invention).

That is, Te = [Tp × (1 + Kw + Kas + ...) × AαL1
+ Ts] × Z Z is a lean target value (= 14.7 / target lean air-fuel ratio). In step 10, based on the current driving condition, A
Search for the value of. In step 11, the total value B =
(AαL1 + A) is calculated, and the second cylinder to the nth cylinder are
Is used for lean control (corresponding to the fourth lean control of the present invention).

That is, Te = [Tp × (1 + Kw + Kas + ...) × B + T
s] × Z After that, this flow is ended. In addition, steps 6, 7,
Reference numeral 8 denotes a post-start lean control (that is, a post-start lean control for the purpose of early activation of the catalyst after start and reduction of emission of unburned fuel (HC)).
This is a particularly effective step when performing air-fuel ratio feedback control once after startup, and using the air-fuel ratio feedback correction coefficient at this time to correct deterioration over time and correcting differences in operating conditions). It may be omitted during lean control for NOx / fuel efficiency improvement after the completion of the engine (that is, after the air-fuel ratio feedback control has already been performed after the start and the air-fuel ratio feedback correction coefficients Aα1 and Aα2 have been obtained. If you want to lean control. In such a case, A obtained in step 4 instead of using AαL1 in step 9
using α1 (corresponding to the first lean control of the present invention),
In step 10, instead of B, Aα2 obtained in step 5
Should be used (corresponding to the second lean control of the present invention) (corresponding to the invention according to claim 1).

By the way, even during the lean control, the air-fuel ratio feedback control is continued as it is without leaning the first cylinder (corresponding to the lean control hollow fuel ratio feedback control means of the second invention. ), Only the second cylinder to the n-th cylinder may be made lean (corresponding to the fifth lean control means of the second invention) (that is, the lean control of the first cylinder in step 9 is omitted. May be).

As a result, even when the water temperature or the like changes and the wall-flow fuel amount changes, the air-fuel ratio feedback correction coefficient AαL1 corresponding thereto can be successively obtained. Therefore, this AαL1 and the deviation A can be obtained. As a result, it becomes possible to correct the air-fuel ratios of the second cylinder to the n-th cylinder in response to changes in operating conditions such as changes in water temperature while correcting deterioration over time and variations in parts, etc. It can be highly accurate. In this case, it is preferable to slightly increase the lean tendency of the second cylinder to the n-th cylinder so that the target lean air-fuel ratio can be obtained for the entire engine.

As described above, according to this embodiment,
During the stoichiometric operation, the air-fuel ratio feedback correction coefficient Aα1 of the first cylinder and the average air-fuel ratio feedback correction coefficient Aα2 of all cylinders are obtained, and the average air-fuel ratio feedback correction coefficient Aα2 of all cylinders is obtained. , First
Difference between the cylinder air-fuel ratio feedback correction coefficient Aα1 and A
By obtaining (= Aα2-Aα1), it is possible to ascertain the deterioration over time of the first cylinder, variations in parts, and the like, as well as the deterioration over time of the cylinders other than the first cylinder, variations in parts, and the like. At this time, for the first cylinder, the air-fuel ratio feedback correction coefficient ALα1 of the first cylinder, which is independent of the deterioration of other cylinders over time, component variations, etc.
By performing lean control based on (or Aα1 may be used as described above), lean control can be performed while highly accurately correcting deterioration of the first cylinder over time, component variations, and the like. For the remaining cylinders, the above difference A and the air-fuel ratio feedback correction coefficient A of the first cylinder are used.
The sum B of Lα1 (or Aα1) and B (= ALα1
[Or A [alpha] 1] + [A [alpha] 2-A [alpha] 1], that is, a value that greatly correlates with time-dependent deterioration of cylinders other than the first cylinder, component variations, etc.)
Minimize the effects of cylinder deterioration over time and component variations,
Leaning control can be performed with high accuracy while correcting the deterioration of the remaining cylinders over time, component variations, and the like. That is, with the relatively simple configuration including the two oxygen sensors 9 and 10, it is possible to perform lean control with high accuracy while correcting deterioration over time, component variation, and the like without significantly increasing the product cost. .

[0031]

As described above, according to the invention described in claim 1, due to the relatively simple structure including the two oxygen sensors, deterioration with time and parts can be achieved without significantly increasing the product cost. It is possible to perform lean control with high accuracy while correcting variations and the like.

According to the second aspect of the present invention, with a relatively simple structure including two oxygen sensors, high accuracy can be achieved while correcting deterioration over time, component variations, etc. without significantly increasing the product cost. It is possible to perform lean control after restarting the engine. According to the third aspect of the present invention, during the lean control, the air-fuel ratio feedback control based on the detection result of the first oxygen sensor is performed for the specific one cylinder to set the fourth air-fuel ratio feedback correction value. On the other hand, for the remaining cylinders, the total value of the stored deviation and the fourth air-fuel ratio feedback correction value (a value that greatly correlates with the deterioration of the remaining cylinders over time, component variations, etc.) Since the lean control is performed based on the total value, it is possible to follow the change in the operating state even during the lean control, and at the same time correct the deterioration with time and the variation of parts. Highly accurate lean control can be performed. That is, 2
With a relatively simple configuration with two oxygen sensors, it is possible to correct deterioration over time and component variations, etc. without significantly increasing product cost, and to correct the air-fuel ratio by following changes in operating conditions. Therefore, more accurate lean control can be achieved.

[Brief description of drawings]

FIG. 1 is a block diagram according to the invention described in claim 1.

FIG. 2 is a block diagram according to the invention described in claim 2.

FIG. 3 is a block diagram according to the invention of claim 3;

FIG. 4 is an overall configuration diagram of an embodiment according to the present invention.

FIG. 5 is a flowchart illustrating air-fuel ratio feedback control according to the embodiment.

[Explanation of symbols]

 1 Engine 3 Air Flow Meter 6 Fuel Injection Valve 7 Branch Portion of Exhaust Manifold of First Cylinder 8 Exhaust Passage 9 First Oxygen Sensor 10 Second Oxygen Sensor 11 Three-way Catalyst 12 Crank Angle Sensor 13 Water Temperature Sensor 50 Control Unit

Claims (3)

[Claims] 1. A first oxygen sensor for detecting an oxygen concentration in exhaust gas of a specific one cylinder to detect an air-fuel ratio of an engine intake air-fuel mixture, and a predetermined target based on a detection result of the first oxygen sensor. First air-fuel ratio feedback control means for increasing / decreasing the air-fuel ratio control amount of the specific one cylinder so as to obtain an air-fuel ratio through a first air-fuel ratio feedback correction value, and oxygen concentration in exhaust gas after all the cylinders join. And a second oxygen sensor for detecting the air-fuel ratio of the engine intake air-fuel mixture, and a cylinder other than the specific one cylinder so that a predetermined target air-fuel ratio can be obtained based on the detection result of the second oxygen sensor. Second air-fuel ratio feedback control means for increasing / decreasing the air-fuel ratio control amount of the second air-fuel ratio feedback correction value, and a target lean air-fuel ratio leaner than the predetermined target air-fuel ratio is obtained during lean control. like First lean control means for correcting the air-fuel ratio control amount of the specific one cylinder based on the first air-fuel ratio feedback correction value, and the target lean air-fuel ratio so as to obtain the target lean air-fuel ratio during lean control. An air-fuel ratio control device for an internal combustion engine, comprising: a second lean control unit that corrects an air-fuel ratio control amount of a cylinder other than a specific one cylinder based on the second air-fuel ratio feedback correction value. . 2. A first oxygen sensor for detecting an oxygen concentration in exhaust gas of a specific one cylinder to detect an air-fuel ratio of an engine intake air-fuel mixture, and a predetermined target based on a detection result of the first oxygen sensor. First air-fuel ratio feedback control means for increasing / decreasing the air-fuel ratio control amount of the specific one cylinder so as to obtain an air-fuel ratio through a first air-fuel ratio feedback correction value, and oxygen concentration in exhaust gas after all the cylinders join. And a second oxygen sensor for detecting the air-fuel ratio of the engine intake air-fuel mixture, and a cylinder other than the specific one cylinder so that a predetermined target air-fuel ratio can be obtained based on the detection result of the second oxygen sensor. Between the second air-fuel ratio feedback control means for increasing / decreasing the air-fuel ratio control amount of the second air-fuel ratio feedback correction value, the first air-fuel ratio feedback correction value, and the second air-fuel ratio feedback correction value And a deviation storage means for storing the deviation for each operating state, and a detection result of the first oxygen sensor before performing lean control of the air-fuel ratio of the specific one cylinder after the engine is restarted. And a pre-lean control air-fuel ratio feedback control means for increasing / decreasing the air-fuel ratio control amount of the specific one cylinder through a third air-fuel ratio feedback correction value so as to obtain the predetermined target air-fuel ratio. During the lean control, the air-fuel ratio control amount of the specific one cylinder is corrected based on the third air-fuel ratio feedback correction value so that a target lean air-fuel ratio that is leaner than the predetermined target air-fuel ratio is obtained. A third lean control means, a deviation stored in the deviation storage means for an air-fuel ratio control amount of cylinders other than the specific one cylinder so that the target lean air-fuel ratio is obtained during lean control, An air-fuel ratio control device for an internal combustion engine, comprising: a fourth lean control unit that corrects the third air-fuel ratio feedback correction value based on the sum of the values. 3. A first oxygen sensor for detecting an oxygen concentration in exhaust gas of a specific one cylinder to detect an air-fuel ratio of an engine intake air-fuel mixture, and a predetermined target based on a detection result of the first oxygen sensor. First air-fuel ratio feedback control means for increasing / decreasing the air-fuel ratio control amount of the specific one cylinder so as to obtain an air-fuel ratio through a first air-fuel ratio feedback correction value, and oxygen concentration in exhaust gas after all the cylinders join. And a second oxygen sensor for detecting the air-fuel ratio of the engine intake air-fuel mixture, and a cylinder other than the specific one cylinder so that a predetermined target air-fuel ratio can be obtained based on the detection result of the second oxygen sensor. Between the second air-fuel ratio feedback control means for increasing / decreasing the air-fuel ratio control amount of the second air-fuel ratio feedback correction value, the first air-fuel ratio feedback correction value, and the second air-fuel ratio feedback correction value A deviation calculation means for calculating the deviation for each operating state; and a predetermined target air-fuel ratio based on the detection result of the first oxygen sensor during lean control. Leaning control hollow fuel ratio feedback control means for increasing / decreasing the air-fuel ratio control amount of the specific one cylinder through a fourth air-fuel ratio feedback correction value, and leaner than the predetermined target air-fuel ratio during leaning control. Based on the sum of the deviation stored in the deviation storage means and the fourth air-fuel ratio feedback correction value, the air-fuel ratio control amount of the cylinders other than the specific one cylinder so as to obtain the target lean air-fuel ratio. An air-fuel ratio control system for an internal combustion engine, comprising: