JP2001050082A - Air-fuel ratio control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extend an operating range where air-fuel ratio control is implemented and reduce emissions immediately after startup of an engine or in a cold state of the engine by setting different air-fuel ratios for respective cylinder or a plurality of cylinders through detecting an air-fuel ratio of each cylinder and correcting a fuel injection amount based on the detection results. SOLUTION: While an engine 100 is operated, a load factor is calculated based on an intake air amount 311 and an engine speed 312 by load factor calculation means 301, and an engine operation range as well as a target air-fuel ratio are calculated by calculation means 301 based on the load factor and engine speed. An actual air-fuel ratio is calculated by actual air-fuel ratio measurement means 314 in which an output signal from an air-fuel ratio sensor 116 is input, and then a deviation from the target air-fuel ratio is calculated. In accordance with the deviation, a correction coefficient is calculated by fuel injection amount correction means 302. The input of the output signal from the air-fuel ratio sensor 116 is implemented after a delay time to be set based on the engine speed, load factor and the like. Therefore a delay of travel time of exhaust gas is compensated.

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 air-fuel ratio control device for controlling an air-fuel ratio for each cylinder according to an operation state.

[0002]

2. Description of the Related Art In engine control, control of the air-fuel ratio has been performed only after the operating state is within a predetermined range and after warming up. This is because an increase in fuel is added immediately after the start or when the cooling water temperature is low, the air-fuel ratio becomes rich, and the air-fuel ratio control cannot be performed. Particularly, since the conventional O ₂ sensor can detect only the stoichiometric region, it is impossible to control the air-fuel ratio in the rich region.

Conventionally, the ratio of the rich state is determined in advance, and the ratio is reduced according to the time or the sum of the injection amounts.
When it became zero, the control was shifted to the control by the O ₂ sensor. An example of such air-fuel ratio control is an air-fuel ratio control method disclosed in Japanese Patent Application Laid-Open No. 60-36748. However, there is a problem that emission cannot be effectively reduced.

[0004]

Although the exhaust gas is purified through the catalyst, the catalytic effect is reduced if the air-fuel ratio is kept constant, so that it is necessary to increase the air-fuel ratio to some extent. For this reason, the engine control device also needs control to increase the deviation of the air-fuel ratio.

[0005] In addition, although the engine is operated in a lean state to improve fuel efficiency, NOx is generated in this case. This NOx
There is known a catalyst which accumulates in the catalyst, but the amount of accumulation is limited. Therefore, by temporarily flowing a rich gas through the catalyst, unburned hydrocarbons are reacted with NOx in the catalyst to reduce NOx in the catalyst.

Conventionally, such air-fuel ratio control involves setting the same air-fuel ratio over all the cylinders of the engine and repeatedly performing lean and rich operations. Therefore, there has been a problem that fluctuations in rotation between rich and lean conditions are large.

Further, in the control using the conventional O ₂ sensor, only the switching of the air-fuel ratio in the vicinity of the stoichiometric condition is known.
When the air-fuel ratio is changed to a lean region or a rich region, there is a problem that the deviation amount is not known.

SUMMARY OF THE INVENTION An object of the present invention is to increase the operating range in which the air-fuel ratio control is performed and to quickly activate the catalyst in order to reduce the emission immediately after the start of the engine or in a cold state.

[0009]

First, an air-fuel ratio sensor capable of measuring the air-fuel ratio of exhaust gas from a rich region to a lean region is used in order to expand an operation region in which air-fuel ratio control is performed.

In order to activate the catalyst early, the problem can be solved by combining means for enriching or leaning the air-fuel ratio of the gas flowing through the catalyst.

[0011]

FIG. 1 shows one configuration of an internal combustion engine according to the present invention.

The internal combustion engine 100 includes an injector 10
1, ignition plug 102, ignition coil 103, throttle 104, idle speed control (ISC) valve 105, water temperature sensor 110, crank angle sensor 11
1, a cam angle sensor 112, a throttle position sensor 113, an intake pipe pressure sensor 114, or an intake air flow meter 115, an air-fuel ratio sensor 116, and a catalyst 118 are attached and connected to an engine control device 120, respectively.

The fuel is transported from a fuel tank 1014 by a fuel pump 1011, and is kept at a constant fuel pressure by a fuel pressure control valve 1012.

A knock sensor 1013 for detecting the occurrence of knocking is attached near the combustion chamber, and can detect the occurrence of knocking by capturing a signal specific to the occurrence of knocking.

The engine control unit 120 takes in the output of the intake pipe pressure sensor 114 or the intake air flow meter 115,
The actual intake air amount Qa per unit time is calculated by converting the sensor voltage into a predetermined table. At the same time, the pulse signal of the crank angle sensor 111 is measured, and the engine speed NDATA is calculated according to the number of pulses within a predetermined time or the time interval of the pulses. Intake air amount Q per unit time
a is divided by NDATA and further divided by the number of cylinders to calculate the intake air amount Qacy1 for each cylinder once.
By multiplying Qacy1 by a predetermined count KTI, Qacy1
The amount of fuel TI that can be burned is calculated, and the injector 101 is opened for a predetermined period by adding a correction described later, thereby injecting the required amount of fuel to generate an air-fuel mixture for each combustion.

The following correction coefficient CO is used for calculating the fuel amount TI.
EFn is multiplied. KTW, KWO in COEFn
T, KAS, and APLHAn.

First, the fuel amount is corrected according to the values of the water temperature sensor 110 and the throttle position sensor 113.
The correction terms are KTW and KWOT.

The oxygen concentration of the exhaust gas is measured by an air-fuel ratio sensor 116, and a voltage signal corresponding to the air-fuel ratio is input to the engine control device 120. Then, a deviation from the air-fuel ratio is determined for each cylinder, and if there is a deviation, the correction coefficient ALPH
Correct An.

Furthermore, since the fuel is poorly vaporized immediately after the start of the engine, the concentration of the air-fuel mixture in the suction pipe becomes lower than in a normal operation state. Therefore, it is necessary to inject a large amount of fuel to make up the concentration. This coefficient is defined as KAS.

FIG. 2A shows the characteristics of the air-fuel ratio sensor used in the embodiment of the present invention.

The characteristics are such that the voltage is low when the air-fuel ratio is rich, and increases as the air-fuel ratio becomes lean. When the air-fuel ratio control is performed using this sensor, the engine control can be performed at a constant air-fuel ratio by performing the feedback control on the target air-fuel ratio.

However, if a rich gas always flows through the catalyst for purifying the exhaust gas, there is no supply of oxygen, so that the purification rate decreases. Therefore, perturbation of the air-fuel ratio (perturbation) equivalent to the air-fuel ratio control near the stoichiometric state by the conventional O ₂ sensor is required. As shown in FIG. 2B, it is necessary to change the air-fuel ratio to a rich or lean region, supply oxygen to the catalyst in a lean state, and consume the oxygen in a rich state.

FIG. 3 is a block diagram showing an example of the program of the present invention.

In this embodiment, the target air-fuel ratio calculating means 30
1, fuel injection amount correction means 302, rotation fluctuation rate calculation means 3
04, fuel injection amount calculation means 305, fuel injection means 306
The internal combustion engine (engine) 100 is controlled by this.

The target air-fuel ratio calculation means 301 receives an intake air amount (or intake pipe pressure) 311 and a rotation speed 312. Further, the load ratio 313 is determined by the rotation speed and the intake air amount.
Is calculated. The target air-fuel ratio calculating means detects the operating range of the engine from the rotation speed and the load factor, and determines the air-fuel ratio TSTIK to be operated.

Next, the output signal of the air-fuel ratio sensor 116 is fetched, the actual air-fuel ratio according to FIG. 2 is measured, and the actual air-fuel ratio is obtained by the actual air-fuel ratio measuring means 314.

The operation in the engine control device will be described with reference to FIG.

The engine control unit includes a microcomputer 401 and a ROM 40 storing programs and data.
2, RAM 403 used for temporary storage of data, input circuit 404 for taking in signals from sensors attached to the engine, timer and clock circuit 405 capable of generating an interrupt to the microcomputer for a predetermined time, can be turned on / off by a command from the microcomputer Output circuit 40
6, etc. The input circuit 404 takes in the electric load information 4041 as digital information, and A / D converts a sensor signal voltage of an intake air amount, an air-fuel ratio sensor, or the like into digital data.

An output signal of the crank angle sensor as a reference angle pulse and an output signal of a cam angle sensor as a cylinder discrimination pulse are generated by a microcomputer through a waveform shaping input circuit to generate an interrupt. An interrupt can be used to determine the cylinder of the engine, or the pulse edge time interval TDATA
, The rotation number NDATA is calculated by taking the reciprocal.

Further, the intake air amount Qa is determined according to the sensor voltage.
, And Qa is divided by the number of cylinders and the number of revolutions to obtain a basic intake air amount Qacy1 per operation.

The basic fuel injection amount is obtained by multiplying Qacy1 by a coefficient KTI obtained from the flow characteristics of the injector.

The calculation result is added to the current time by the output compare circuit of the output circuit 406 to cause a compare match to occur, and the injector is opened for a time corresponding to the required fuel amount.

Since Qacy1 is proportional to the output of the engine,
By multiplying Qacy1 by a multiplier, it can be converted into a load factor LDATA with the maximum output time being 100%.

At the same time, the ignition timing set by the rotational speed and the load factor is obtained, an ignition output is issued, and the ignition coil is driven by the pulse output.

Further, control parameters in the microcomputer can be monitored by the communication means 407.

The output of the target air-fuel ratio calculating means 301 and the output of the actual air-fuel ratio calculating means 314 are used as fuel injection amount correcting means 302.
When the actual air-fuel ratio is higher than the target air-fuel ratio (lean state), the correction coefficient ALPHAn is increased. When low (rich), ALPHAn is reduced. Where A
LPHAn is a value set for each cylinder, and n indicates a cylinder number.

The output signal of the air-fuel ratio sensor is taken in at the timing shown in FIG. 5 for each cylinder. In this embodiment, only one air-fuel ratio sensor is shown, but in this case, the exhaust pipe is configured so that the exhaust gas of each cylinder is applied to the air-fuel ratio sensor at different timings. . The number of air-fuel ratio sensors is not limited to one,
It may be configured to be attached to the exhaust pipe of each cylinder. Or
A configuration may be adopted in which one air-fuel ratio sensor is attached to a plurality of cylinders having exhaust pipes arranged so that the flow of exhaust gas does not interfere.

As shown in FIG. 5 (a), the reference angle position signal REF of each cylinder is set as a start timing, a delay time is provided according to the rotation speed, load factor or intake air amount, and the output of the air-fuel ratio sensor is taken in. Compensates for a delay in the movement time of the exhaust gas from the exhaust valve to the air-fuel ratio sensor.

Alternatively, as shown in FIG. 5 (b), the data is taken from the REF at regular intervals, and the data of the timing corresponding to the exhaust gas movement delay time according to the rotation speed, the load factor or the intake air amount is applied to the corresponding cylinder. Is the air-fuel ratio RABFn.

Next, the air-fuel ratio control for each cylinder will be described. The target air-fuel ratio is set, for example, for each cylinder for a predetermined period after the engine is started. The target air-fuel ratio is a common control value KS for obtaining a stoichiometric condition based on the rotational speed and the load factor in accordance with the operating range of the engine.
First seek TIK. At the same time, a KAS for increasing the fuel injection amount in accordance with the time after the start and a KTW for increasing the fuel injection amount in accordance with the water temperature are obtained. As long as KAS and KTW are not zero,
In some cases, the drivability is ensured by setting the air-fuel ratio of each cylinder to a rich state. During this time, the air-fuel ratio control is not performed. KA
After S and KTW become zero, a dither method for selecting a rich state and a lean state is employed. Dither variation is KDI
Z, and KRICH and KLEAN are calculated as follows (KDR is a coefficient that varies to the rich side, and KDL is a coefficient that varies to the lean side).

KRICH = KSTIK−KDIZ * KDR KLEAN = KSTIK + KDIZ * KDL However, it takes time to start control by dither, and the air-fuel ratio up to that time is made rich.
Does not reduce exhaust gas levels.

As an example of introducing the dither method from the start,
Emission can be reduced by using the sum of KAS and KTW instead of KDIZ. That is, for the common target value, a value KAS that increases according to the time after starting and a value KTW that increases according to the water temperature are represented by K
Subtract air-fuel ratio KRICH from STIK
Is determined as follows.

KRICH = KSTIK− (KAS + KTW) * KDR As a result, the air-fuel ratio can be changed to the rich side by an increased amount with respect to KSTIK. On the other hand, a target air-fuel ratio KLEAN that is leaner than KTGT is determined as follows.

KLEAN = KSTIK + (KAS + KTW) * KDL At the same time, while KAS or KTW is not zero, combustion is unstable and the ignition timing is delayed to cope with the situation.

Further, which cylinder is made rich or lean is realized by the pattern KSRL. For example,
Data is selected in accordance with a bit corresponding to a KSRL cylinder for selecting rich and lean for each predetermined time or for each REF signal. In FIG. 6, even-numbered bits and odd-numbered bits are selected for each cylinder. One cylinder has bits 0 and 1, 2
The cylinder is selected as bits 2 and 3, hereinafter bits 4 and 5, stoichiometric if both bits are 0, rich if the even side is 1, and lean data if the odd side is 1. . The KSRL changes according to the operating state. The initial value of KSRL may be a value according to the water temperature or the time after the engine is started.

As shown in FIG. 7, data setting is selected according to KAS or KTW. If it is necessary to make the entire air-fuel ratio rich during the period when the KAS is not zero after the engine is started, data KSRL1 in which only a bit pattern for selecting rich or stoichiometric data may be used. Alternatively, a period in which the KAS is not zero (70
1) may be changed so that KDL = 0 or KDL <KDR (702). Alternatively, the setting may be such that half or more of the number of cylinders is rich and half or less is lean.

In the normal operation state, the set value KDIZ determined by the intake air amount or the rotation speed and the load factor is changed to KAS or KT.
Use instead of W.

After the start, as time elapses and the water temperature rises,
KD when KAS or KTW is smaller than KDIZ
IZ may be selected (703, 704).

The calculation of KAS and KTW may be performed by a method of making the value zero according to the integrated value of the intake air amount.

When the intake air amount is equal to or more than a predetermined value, the amount of exhaust gas passing through the catalyst becomes larger than the amount of processing of the catalyst, and the purification rate decreases. Since the level deteriorates, it is necessary to limit the target air-fuel ratio to stoichiometric.

When the REF signal is interrupted, the R
The combination of AM bits is checked, and if a rich state is selected, KRICH is used as a coefficient. Similarly, when the lean state is selected, KLEAN is used as a coefficient. Therefore,
The target air-fuel ratio TABFn for each cylinder is KSTIK, KRICH,
The value is selected from KLEAN. The air-fuel ratio of the corresponding cylinder is compared with the target air-fuel ratio, and the difference DABFn is obtained.

DABFn = TABFn-RABFn PID control is performed based on the difference DABFn. That is, as shown in FIG. 8, the coefficient KP of the proportional part, the coefficient KI of the integrating part, and the coefficient KD of the differentiating part are respectively obtained, and the following operation is performed on DABFn to obtain ALPHAn.

ALPHAn = KP * DABFn + KI *
IDABBFn + KD * DDAFn Here, IDABFn is an integrated value of DABFn, and IDABFn = DABFn + IDABFn (i-1).

DDABFn is a difference from the previous value of DABFn, and DDABFn = DABFn-DABFn (i-1).

KP, KI, and KD are values obtained by searching a map or a table according to the operating state.

Next, a method of changing the KSRL will be described with reference to FIG. When the number of KSRLs is one, only a specific cylinder continues to be in a rich or lean state, so that there is a possibility that rotation fluctuation occurs in a specific pattern. So, KS
By preparing a plurality of RLs and switching the pattern to be used every time the crankshaft of the engine makes two rotations, rotation fluctuation can be suppressed.

For example, k KSRLs are prepared, and every two rotations of the crankshaft of the engine, the l-th (l ≦ k) of the KSRL
Use the pattern And the pattern to use is k
When it comes to the first, the next is to return to the first (Fig. 9
(a)). Alternatively, there is a method in which the pattern length of the KSRL is made longer than the number of cylinders and the corresponding bit position of the cylinder is shifted every two revolutions of the crankshaft of the engine (FIG. 9).
(b)).

Next, a method for determining the rotation fluctuation will be described with reference to FIG. As shown in FIG. 10- (a), the rotation fluctuation is detected by measuring a time interval TDATA of the reference angular position of each cylinder.

The rotational speed NELE is obtained from TDATA [i] (i = 1 to the number of cylinders) of each cylinder. NELE is a predetermined value K
By dividing DATA by TDATA, NLE = KDATA / TDATA is obtained.

The rotation fluctuation rate dN is obtained as follows.

DN = f (NELE) When the calculation function f () is calculated using, for example, an IIR filter format, a value 801 obtained by multiplying NELE by ki0 is input, and past operation values 802 and 803 are multiplied by coefficients to obtain the function f (). , 8031 to obtain a new calculated value dNtemp 805. These calculated values 802 and 80
3,805 is multiplied by the coefficients 8021, 8022, and 8023 to obtain the sum as the rotational fluctuation rate dN806. The calculation is obtained as follows.

DN = dNtemp + ko1 * dNtemp [i−
1] + ko2 * dNtemp [i-2] dNtemp = ki0 * NELE + ki1 * dNtemp [i-
1] + ki2 * dNtemp [i-2] The calculation method is not limited to IIR, but may be FIR type. Alternatively, it may be calculated directly from TDATA.

As shown in FIG. 10- (b), the difference between KRICH and KLEAN is corrected to be small according to the rotation fluctuation rate dN. That is, KDR and KDL are made to approach 0.

At the same time, the ignition timing is also corrected. When operating in a lean state, it is necessary to set the ignition timing near TDC because of poor ignition performance. Therefore, with respect to the ignition timing for each cylinder, the ignition timing is changed immediately on the retard side in the TDC direction, and dynamic limit is advanced on the advance side by a predetermined change amount. That is, as shown in FIG. 11, the ignition timing of the cylinder on which KLEAN is selected is set to the retarded side ignition timing, and even when KSTIK or KRICH is selected, the ignition timing is not returned to the normal position, but is set to a predetermined rotation speed. , The ignition timing is advanced by ΔDLS. Thus, rotation fluctuation can be suppressed while ensuring ignitability.

Next, the diagnosis of the air-fuel ratio control will be described with reference to FIG. The diagnosis items include abnormality of the air-fuel ratio sensor and abnormality detection of the control value. First, if the signal voltage of the air-fuel ratio sensor is out of the normal range, or if the signal output of the air-fuel ratio sensor does not change while operating while changing the air-fuel ratio for each cylinder, it is determined that the air-fuel ratio sensor is abnormal. . In this case, the control by changing the air-fuel ratio for each cylinder is stopped, and the operation is performed with stoichiometry. That is, it is KSTIKE. However, KTW or KA
If S is not zero, run on KRICH. further,
The time TMDABn until DABFn becomes zero is measured, and if TMDABn is equal to or longer than a predetermined time, it is considered that the air-fuel ratio control is abnormal. If the cylinder number for controlling the air-fuel ratio does not match the air-fuel ratio of the corresponding cylinder based on the output of the air-fuel ratio sensor, or if there is an abnormality in the exhaust system, or the response delay of the air-fuel ratio sensor has become larger than the initial value. In this case, the air-fuel ratio control becomes abnormal. Also in this case, the air-fuel ratio control for each cylinder is stopped, and the operation is performed with stoichiometry. That is, it is KSTIK.
However, if KTW or KAS is not zero, KRI
Drive on CH.

In the embodiment of the present invention, only one cylinder has been described. However, it is also possible to set different target air-fuel ratios for a plurality of cylinders and control them for each cylinder. Alternatively, a plurality of cylinders may be grouped, and a target air-fuel ratio may be set for each group. In particular, by setting the target air-fuel ratio for each cylinder, it is possible to compensate for the difference in air charging efficiency between the cylinders.

[0067]

According to the present invention, since the air-fuel ratio of the exhaust gas to the catalyst can be controlled immediately after the start of the engine, the activation of the catalyst can be accelerated and the emission can be reduced.

Conventionally, knock control is performed by retarding the ignition timing while catching the occurrence of knock. However, the occurrence of knock is avoided by setting the target air-fuel ratio to a rich state for the cylinder in which knock occurs. It is also possible.

[Brief description of the drawings]

FIG. 1 is an engine configuration diagram of an embodiment of the present invention.

FIG. 2 is a characteristic diagram of an air-fuel ratio sensor.

FIG. 3 is a block diagram of a program.

FIG. 4 is an operation diagram in the engine control device.

FIG. 5 is a timing of taking in the output of the air-fuel ratio sensor.

FIG. 6 is an explanatory diagram of a calculation method of a target air-fuel ratio.

FIG. 7 is an explanatory diagram of selection of shift pattern data.

FIG. 8 is an explanatory diagram of PID control.

FIG. 9 is an explanatory diagram of a method of changing a KSRL.

FIG. 10 is an explanatory diagram of calculation of a rotation fluctuation rate.

FIG. 11 is an explanatory diagram of dynamic limitation of ignition timing.

FIG. 12 is a diagnosis diagram of air-fuel ratio control.

[Explanation of symbols]

100: internal combustion engine, 101: injector, 102: spark plug, 103: ignition coil, 104: throttle
105 ... ISC valve, 110 ... water temperature sensor, 111 ...
Crank angle sensor, 112: cam angle sensor, 113: throttle position sensor, 114: intake pipe pressure sensor, 115: intake air flow meter, 116: air-fuel ratio sensor,
118: catalyst, 120: engine control device, 1011 ...
Fuel pump, 1012 ... fuel pressure control valve, 1013 ... knock sensor.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yutaka Takaku 2520 Odaiba, Hitachinaka-shi, Ibaraki F-term in the Automotive Equipment Group of Hitachi, Ltd. (reference) 3G301 HA06 HA18 JA00 JA21 JA22 JB01 JB09 KA01 LA00 LA04 LB02 MA01 MA11 NA03 NA04 NA05 NA08 NB03 NB07 NC02 ND02 NE01 NE13 NE14 NE15 NE22 NE24 PA01Z PA07Z PA11Z PA17Z PC00Z PC08Z PD03A PE01Z PE02Z PE03Z PE05Z PE08Z

Claims (19)

[Claims] An air-fuel ratio control device for controlling an air-fuel ratio in accordance with an operating state of an engine, comprising: a sensor for detecting an air-fuel ratio of exhaust gas; means for detecting an air-fuel ratio substantially for each cylinder; An air-fuel ratio control device comprising: means for correcting a fuel injection amount in accordance with a detection result of a detection means, and giving a different air-fuel ratio to each cylinder or a plurality of cylinders. 2. An air-fuel ratio control device comprising a sensor for detecting an air-fuel ratio of exhaust gas and controlling an air-fuel ratio in accordance with an operation state of an engine, means for detecting an air-fuel ratio substantially for each cylinder, Correction means for correcting the fuel injection amount according to the detection result of the detection means is provided, and a different target air-fuel ratio is set for each cylinder or each of a plurality of cylinders, and for each cylinder or for each of a plurality of cylinders according to the target air-fuel ratio. An air-fuel ratio control device, wherein the fuel injection amount is corrected by the correction means so as to obtain a different air-fuel ratio. 3. The method according to claim 1, wherein the target air-fuel ratio is set to an air-fuel ratio different from the stoichiometric air-fuel ratio for each cylinder or for each of a plurality of cylinders, and is alternately repeated for each cylinder or for each of a plurality of cylinders. An air-fuel ratio control device comprising: 4. An air-fuel ratio control device for controlling an air-fuel ratio according to an operating state of an engine, comprising: a sensor for detecting an air-fuel ratio of exhaust gas; measuring an air-fuel ratio for each cylinder; A means for correcting the injection amount is provided, and a stoichiometric air-fuel ratio or a target air-fuel ratio richer or leaner than the stoichiometric air-fuel ratio is set for each cylinder or for each of a plurality of cylinders, and the stoichiometric air-fuel ratio state, the rich state, and the lean state are set. An air-fuel ratio control apparatus characterized in that the combustion of the air-fuel ratio is repeated alternately for each cylinder or for each of a plurality of cylinders. 5. An air-fuel ratio control device for controlling an air-fuel ratio according to an operating state of an engine, comprising: a sensor for detecting an air-fuel ratio of exhaust gas; measuring an air-fuel ratio for each cylinder; A means for correcting the injection amount is provided, and a stoichiometric air-fuel ratio or a target air-fuel ratio richer or leaner than the stoichiometric air-fuel ratio is set for each cylinder or for each of a plurality of cylinders, and the stoichiometric air-fuel ratio state, the rich state, and the lean state are set. Is alternately repeated for each cylinder or for each of a plurality of cylinders, and the stoichiometric air-fuel ratio state, the rich state, or the lean state is assigned to a different cylinder or a plurality of different cylinders after a predetermined rotation according to the engine speed. Air-fuel ratio control device. 6. An air-fuel ratio control device for detecting an air-fuel ratio of exhaust gas, controlling an air-fuel ratio according to an operating state of an engine, measuring an air-fuel ratio for each cylinder, and detecting a fuel according to an output of the air-fuel ratio sensor. A means for correcting the injection amount is provided, and a stoichiometric air-fuel ratio or a target air-fuel ratio richer or leaner than the stoichiometric air-fuel ratio is set for each cylinder or for each of a plurality of cylinders, and the stoichiometric air-fuel ratio state, the rich state, and the lean state are set. Is alternately repeated for each cylinder or for each of a plurality of cylinders, and the stoichiometric air-fuel ratio state, the rich state, or the lean state is assigned to a different cylinder or a plurality of different cylinders after a predetermined time has elapsed according to the engine speed. Characteristic air-fuel ratio control device. 7. A method according to claim 2, wherein after the engine is started, a period in which a different target air-fuel ratio is set for each cylinder or for each of a plurality of cylinders is changed in accordance with the intake air amount. Air-fuel ratio control device. 8. The air-fuel ratio control device according to claim 2, wherein the stoichiometric air-fuel ratio or the combustion in the rich state or the lean state is maintained for the number of times of combustion corresponding to the rotation speed. 9. The air-fuel ratio control device according to claim 2, wherein the stoichiometric air-fuel ratio or the combustion in the rich state or the lean state is continued for a predetermined number of times of combustion. 10. An air-fuel ratio control device including a sensor for detecting an air-fuel ratio of exhaust gas and controlling an air-fuel ratio in accordance with an operation state of an engine, wherein a target air-fuel ratio is set for each cylinder or for each of a plurality of cylinders. Measure the time to reach the target air-fuel ratio, if the time to reach the target air-fuel ratio is more than a predetermined value,
An air-fuel ratio control device that diagnoses that air-fuel ratio control is abnormal. 11. An air-fuel ratio control device for controlling an air-fuel ratio in accordance with an operating state of an engine, comprising: a sensor for detecting an air-fuel ratio of exhaust gas; A means for correcting the injection amount is provided, a target air-fuel ratio in a rich state or a lean state is set for each cylinder or for each of a plurality of cylinders, which is richer or leaner than the stoichiometric air-fuel ratio, and combustion in the rich state and the lean state is performed for each cylinder or for each of a plurality of cylinders. An air-fuel ratio control device, which alternately repeats the above, performs an air-fuel ratio sensor output measurement at a reference angle position of an engine, and compares the air-fuel ratio for each cylinder with a target air-fuel ratio for each cylinder. . 12. An air-fuel ratio control device for controlling an air-fuel ratio in accordance with an operating state of an engine, comprising: a sensor for detecting an air-fuel ratio of exhaust gas; measuring an air-fuel ratio for each cylinder; A means for correcting the injection amount is provided, a target air-fuel ratio in a rich state or a lean state is set for each cylinder or for each of a plurality of cylinders, which is richer or leaner than the stoichiometric air-fuel ratio, and combustion in the rich state and the lean state is performed for each cylinder or for each of a plurality of cylinders. In the air-fuel ratio control device, the air-fuel ratio sensor output measurement is performed after a predetermined delay time from the reference angle position of the engine, and the air-fuel ratio for each cylinder is compared with the target air-fuel ratio for each cylinder. Air-fuel ratio control device. 13. An air-fuel ratio control device for controlling an air-fuel ratio according to an operating state of an engine, comprising: a sensor for detecting an air-fuel ratio of exhaust gas; measuring an air-fuel ratio for each cylinder; A means for correcting the injection amount is provided, a target air-fuel ratio in a rich state or a lean state is set for each cylinder or for each of a plurality of cylinders, which is richer or leaner than the stoichiometric air-fuel ratio, and combustion in the rich state and the lean state is performed for each cylinder or for each of a plurality of cylinders. In the air-fuel ratio control device which alternately repeats the above, the output measurement of the air-fuel ratio sensor is performed at predetermined time intervals from the reference angle position of the engine.
An air-fuel ratio control apparatus, wherein the air-fuel ratio control is performed for a plurality of cylinders a plurality of times to calculate and calculate an air-fuel ratio for each cylinder from the measurement result of the air-fuel ratio sensor output, and to compare the calculated air-fuel ratio with a target air-fuel ratio for each cylinder. 14. An air-fuel ratio control device for controlling an air-fuel ratio according to an operating state of an engine, comprising: a sensor for detecting an air-fuel ratio of exhaust gas; measuring an air-fuel ratio for each cylinder; A means for correcting the injection amount is provided, a target air-fuel ratio in a rich state or a lean state is set for each cylinder or for each of a plurality of cylinders, which is richer or leaner than the stoichiometric air-fuel ratio, and combustion in the rich state and the lean state is performed for each cylinder or for each of a plurality of cylinders. The air-fuel ratio control device, wherein the air-fuel ratio control device is configured to diagnose that the air-fuel ratio control is abnormal when no air-fuel ratio fluctuation is detected. 15. An air-fuel ratio control device for controlling an air-fuel ratio in accordance with an operating state of an engine, comprising: a sensor for detecting an air-fuel ratio of exhaust gas; measuring an air-fuel ratio for each cylinder; A means for correcting the injection amount is provided, a target air-fuel ratio in a rich state or a lean state is set for each cylinder or for each of a plurality of cylinders, which is richer or leaner than the stoichiometric air-fuel ratio, and combustion in the rich state and the lean state is performed for each cylinder or for each of a plurality of cylinders. An air-fuel ratio control device that alternately repeats the operation of the air-fuel ratio control, characterized in that a means for measuring engine rotation fluctuation is provided, and when the rotation fluctuation is equal to or greater than a predetermined value, lean-state combustion approaches a predetermined amount to the stoichiometric air-fuel ratio. apparatus. 16. The air-fuel ratio control device according to claim 13, wherein when the air-fuel ratio control is abnormal, the same target air-fuel ratio is set for all cylinders to perform the air-fuel ratio control. 17. The air-fuel ratio control device according to claim 15, wherein when the rotation fluctuation is equal to or greater than a predetermined value, the same target air-fuel ratio is set for all cylinders to perform air-fuel ratio control. 18. The air-fuel ratio control according to claim 2, wherein the same target air-fuel ratio is set for all cylinders when the integrated value of the intake air amount after the start is equal to or more than a predetermined value. Air-fuel ratio control device. 19. An air-fuel ratio control apparatus according to claim 2, wherein when the intake air amount is equal to or more than a predetermined value, the same target air-fuel ratio is set for all cylinders to perform air-fuel ratio control.