JPH04116237A - Air-fuel ratio controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To correct difference in air-fuel ratios at every cylinder and make a real air-fuel ratio close to a target air-fuel ratio by determining a cylinder to be learned by means of the difference in feedback compensated values and the air-fuel ratio detected at each cylinder. CONSTITUTION:Oxygen sensors 16 are provided at the exhaust collection part of two cylinder groups of which exhaust strokes are not close to each other in an exhaust manihold 8, and an air-fuel ratio of air-mixture sucked into an engine 1 via oxygen concentration in the exhaust air is detected. In the case deviation in the air-fuel ratios of a specified cylinder is at a specified level or more, a feedback compensated value is set by a control unit 12 based on an average level of the detected air-fuel ratios at every cylinder. A learning compensation quantity of the cylinder of which air-fuel ratio is deviated in the same direction as the deviated direction of equalized value of the feedback compensation value is corrected and rewritten. Consequently, since the difference in the air-fuel ratio at every cylinder is corrected, a fuel injection quantity is feedback-controlled so that the real air-fuel ratio comes close to the target air-fuel ratio.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an air-fuel ratio control device for an internal combustion engine.
The present invention relates to correction control of the fuel injection amount by correcting the air-fuel ratio difference between cylinders so that the actual air-fuel ratio approaches the target air-fuel ratio.

<Prior Art> Conventionally, an internal combustion engine equipped with this type of air-fuel ratio control device is disclosed in Japanese Patent Application Laid-Open No. 60-240840.

To explain this, the basic fuel injection amount Tp (=KXQ/N; is a constant), and further calculates various correction coefficients C0EF according to engine operating conditions such as engine temperature, and air-fuel ratio feedback correction coefficient L.
AMBDA and a correction numerator s for correcting the change in the effective valve opening time of the electromagnetic fuel injection valve due to battery voltage are respectively calculated, and the basic fuel injection amount Tp is corrected and calculated using these to perform the final fuel injection. Quantity Ti (=TpXCO
EFXLMBDA+Ts).

Note that the various correction coefficients C0EF are, for example, COE F
” 1 +KMR+ Kt=+KAS+KAI+...
It is calculated by the formula, where K~ is the air-fuel ratio correction coefficient, K? w is a water temperature increase correction coefficient, KAs is a starting and post-starting increase correction coefficient, and KAI is a post-idling increase correction coefficient.

Then, by outputting a drive pulse signal with a pulse width corresponding to the fuel injection amount Ti thus set to the electromagnetic fuel injection valve provided for each cylinder at a predetermined timing, a predetermined amount of fuel is supplied to the engine. It was intended to be supplied by injection.

The air-fuel ratio feedback correction coefficient LAMBDA is for controlling the air-fuel ratio of the intake air-fuel mixture of the engine to a target air-fuel ratio (for example, the stoichiometric air-fuel ratio), and the value of the air-fuel ratio feedback correction coefficient LAMBDA is proportional to integral. It is changed by control to ensure stable control.

That is, as shown in Fig. 9, when the mixture is combusted at the stoichiometric air-fuel ratio, the electromotive force changes suddenly depending on the oxygen concentration ratio in the exhaust gas, and the electromotive force is high on the rich mixture side and low on the lean mixture side. Oxygen sensor with low electromotive force (Utility Model No. 61-18284)
6, etc.) is provided at the part where the exhaust passages of each cylinder of the engine 72 are collected (the collection part of the exhaust manifold 73), and the output voltage from the oxygen sensor 71 and the reference voltage (corresponding to the stoichiometric air-fuel ratio) are provided. slice level) to determine whether the air-fuel ratio of the engine intake mixture (the air-fuel ratio of the golden cylinder) is rich or lean with respect to the stoichiometric air-fuel ratio. For example, if the air-fuel ratio is lean (rich), The air-fuel ratio is controlled to the stoichiometric air-fuel ratio by gradually increasing (decreasing) the air-fuel ratio feedback correction coefficient LAMBDA by a predetermined integral (1 minute) and increasing (decreasing) the fuel injection amount Ti. Note that when the air-fuel ratio is reversed from rich to lean, the air-fuel ratio feedback correction coefficient LAMBDA is changed by a proportional amount (P) larger than the integral (1 minute) to improve control responsiveness.

In FIG. 9, 74 is an air cleaner, 75 is a throttle valve, 76 is an intake manifold, 77 is a three-way catalyst, and 78 is an air cleaner.
is a muffler.

In addition, in order to avoid exhaust pulsation buffering and increase exhaust efficiency,
There are cylinder groups that are made up of multiple cylinders whose exhaust strokes do not overlap, and which are divided into cylinder groups and connected to exhaust manifolds.
In this system, an oxygen sensor is installed in each exhaust manifold collecting section, and air-fuel ratio feedback control is performed for each corresponding cylinder group based on the signal from each oxygen sensor.

That is, for example, in the case of a 4-cylinder internal combustion engine, exhaust gas is collected for each of two cylinder groups, cylinder #l and cylinder #4, and cylinder #2 and #3, and is sent to the exhaust collection section of each of the two cylinder groups. Some engines are equipped with an oxygen sensor to detect the air-fuel ratio of the air-fuel mixture taken into the internal combustion engine via the oxygen concentration in the exhaust gas.

<Problem to be solved by the invention> However, in this way, the air-fuel ratio of the air-fuel mixture is detected using a smaller number of oxygen sensors than the number of cylinders, and the value of the air-fuel ratio feedback correction coefficient LAMBDA is determined based on the air-fuel ratio. In the case where the air-fuel ratio is controlled to the stoichiometric air-fuel ratio by changing the air-fuel ratio, if there is unevenness in the intake distribution of engine exhaust components, variations in the characteristics of the fuel injection valve, etc., the air-fuel ratio may become unstable, especially when the engine speed is low, such as when idling. As shown in FIG. 10, the above-mentioned variations are detected as they are, and are outputted as variations (rich/lean) in the air-fuel ratio in the sensor output.

In particular, in the case of a type in which exhaust manifolds are connected to each cylinder group, the exhaust strokes do not overlap, making it easy for the oxygen sensor to accurately detect variations in air-fuel ratio between cylinders.

That is, in a four-cylinder internal combustion engine, exhaust gas is collected in two groups of cylinders, cylinder #l and cylinder #4, and cylinder #2 and #3, and oxygen sensors are installed at the exhaust gas collection portions of the two cylinder groups, respectively. Taking as an example an oxygen sensor installed at the meeting point of cylinder #1 and cylinder #4 in the case where cylinder #1 and cylinder #4 are installed, FIG. 10(b) shows an example.

When the exhaust from #l cylinder is detected as shown in (C), the output voltage from the oxygen sensor is higher than the slice level, and it is determined that the air-fuel ratio of the engine intake mixture is rich.
As shown in figure (a), the air-fuel ratio feedback correction coefficient LAM
Lower BDA by a predetermined proportional amount (P). At the next detection timing, since the engine speed is low, #4
The exhaust from the cylinder is detected, but if there is the above-mentioned air-fuel ratio variation, the output voltage from the oxygen sensor 20 may be lower than the slice level when the exhaust from the #4 cylinder is detected. In this case, it is determined that the air-fuel ratio of the engine intake mixture is lean, and the air-fuel ratio feedback correction coefficient LAMB
DA is increased by a predetermined proportional amount (P).

Normally, the value of the air-fuel ratio feedback correction coefficient LAMBDA is changed by proportional/integral control to ensure stable control, but as mentioned above, for example, when idling,
There is only a vertical change by a predetermined proportional amount.

Therefore, the predetermined period (T period in FIG. 10(a))
The air-fuel ratio feedback correction coefficient LAMBDA repeats abnormal reversals, making it impossible to individually control the air-fuel ratio of each cylinder to the target air-fuel ratio, and unable to sufficiently suppress fluctuations in the air-fuel ratio, resulting in poor exhaust properties. is not constant, and there is a problem that the exhaust emission characteristics deteriorate beyond the ability of the three-way catalyst to purify the exhaust gas.

Of course, the above problems could be solved by providing an oxygen sensor for each cylinder and performing independent air-fuel ratio feedback control for each cylinder according to the signals from each sensor, but this would significantly increase costs and require multi-system control. There are problems such as too much.

The present invention has been made in view of the above problems, and it is possible to perform feedback control of the fuel injection amount so that the actual air-fuel ratio approaches the target air-fuel ratio by correcting the air-fuel ratio difference between cylinders. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine.

<Means for Solving the Problems> Therefore, in order to achieve the above object, the present invention configures an air-fuel ratio control device for an internal combustion engine including the following means A-, as shown in FIG. do.

(A) Engine operating state detection means that detects the engine operating state including at least parameters related to the amount of air taken into the engine. (B) An engine operating state detection means that is installed in the exhaust passage of the engine and detects engine exhaust components and detects the number of engine exhaust components. Exhaust component detection means (C) that is smaller than the number of cylinders; Basic fuel injection amount setting means (D) that sets a basic fuel injection amount based on the engine operating state detected by the engine operating state detection means; A rewritable learning correction amount storage means (E) that stores a learning correction amount for correcting the basic fuel injection amount for each area of the operating state. Cylinder specifying means (F) for specifying; Cylinder-by-cylinder air-fuel ratio detecting means (G) for detecting the air-fuel ratio for each cylinder based on the exhaust components by the exhaust component detecting means and the cylinder specifying means; If the variation in the air-fuel ratio for each cylinder is less than a predetermined level, a feedback first correction value is set for correcting the basic fuel injection amount so that the detected air-fuel ratio for each cylinder approaches the target air-fuel ratio. Correction value setting means (H) When the variation in the air-fuel ratio of each cylinder detected by the cylinder-by-cylinder air-fuel ratio detection means is equal to or higher than a predetermined level, the basic fuel is adjusted based on the average level of the air-fuel ratio detected for each cylinder. Feedback second correction value setting means (I) for setting a feedback second correction value for correcting the injection amount Air-fuel ratio deviation direction for detecting the rich-norm deviation direction of the averaged value of the feedback second correction value with respect to the reference value (J) correcting a learning correction amount of a cylinder whose air-fuel ratio deviates in the same direction as the air-fuel ratio deviation direction detected by the air-fuel ratio deviation direction detection means in a direction that eliminates the air-fuel ratio deviation; Learning correction amount modification means (K) for rewriting the feedback first correction value or feedback second correction value set by the feedback first correction value setting means or feedback second correction value setting means, and the learning correction amount storage means Fuel injection amount setting means for setting the fuel injection amount for each cylinder by correcting the basic fuel injection amount based on the learning correction amount retrieved from the engine operation. When the state detection means A detects the engine operating state including a small number of parameters related to the amount of air taken into the engine,
Basic fuel injection amount setting means C based on this engine operating state
or set the basic fuel injection amount.

The cylinder-by-cylinder air-fuel ratio detecting means F detects the exhaust components of the predetermined cylinder specified by the cylinder specifying means E, using the exhaust component detecting means B.

When the variation in the air-fuel ratio detected by the cylinder-by-cylinder air-fuel ratio detection means F is less than a predetermined level, the feedback first correction value setting means G causes the detected air-fuel ratio for each cylinder to approach the target air-fuel ratio. A feedback first correction value for correcting the basic fuel injection amount is set, and when the variation in the air-fuel ratio is equal to or higher than a predetermined level, the feedback second correction value setting means H adjusts the average of the detected air-fuel ratios for each cylinder. A second feedback correction value is set based on the level.

Then, the learned correction amount correcting means J determines the learning correction amount of the cylinder whose air-fuel ratio deviates in the same direction as the deviation direction of the averaged value of the feedback second correction value detected by the air-fuel ratio deviation direction detecting means. will be corrected and rewritten.

Then, the fuel injection amount setting means K sets the fuel injection amount for each cylinder based on the feedback first or second correction value and the learning correction value.

<Example> An embodiment of the present invention will be described below based on the drawings.

In FIG. 2, a four-cylinder internal combustion engine 1 is connected to an air cleaner 2 through an intake duct 3. Air is sucked in through the throttle valve 4 and the intake manifold 5.

A fuel injection valve 6 is provided in a branch portion of the intake manifold 5 for each cylinder. The fuel injection valve 6 is an electromagnetic fuel injection valve that is energized to open the solenoid and then closed by being de-energized. Fuel is injected and supplied under pressure from the pump and adjusted to a predetermined pressure by a pressure regulator.

An ignition plug 7 is provided in the combustion chamber of the engine 1, which ignites a spark to ignite and burn the air-fuel mixture.

From engine l, exhaust manifold 8° exhaust duct 9. Exhaust gas is discharged via a three-way catalyst 10 and a muffler 11. The three-way catalyst 10 is an exhaust purification device that oxidizes Co and HC in exhaust components, and also reduces NOx and converts it into other harmless substances, and when the mixture is combusted at the stoichiometric air-fuel ratio. The conversion efficiency is the best.

The control unit 12 includes a CPU and a ROM.

It is equipped with a microcomputer including a RAM, an A/D converter, and an input/output interface, and receives input signals from various sensors, performs arithmetic processing as described below, and controls the operation of the fuel injection valve 6. .

As the various sensors described above, a hot wire type or flap type air flow meter 13 is provided in the intake duct 3, and outputs a voltage signal according to the intake air flow rate Q.

In addition, a crank angle sensor 14 is provided, and in the case of a 4-cylinder engine, a reference signal RE is sent every 180 degrees of crank angle.
F (reference signal) and position signal PO3 (unit signal) every 1° or 2° of crank angle are output. Here, by measuring the period of the reference signal REF or the number of occurrences of the position signal PO3 within a predetermined time, it is possible to calculate the engine rotational speed N, and one of the reference signals REF is different from the other. It can be identified by the pulse width and serves as a cylinder discrimination signal for the #1 cylinder. Further, a water temperature sensor 15 for detecting the cooling water temperature Tw of the water jacket of the engine 1 is provided.

Here, the air flow meter 13. The crank angle sensor 14 or the like corresponds to the engine operating state detection means.

Furthermore, the exhaust manifold 8, as shown in FIG.
Exhaust gas is collected into two groups of cylinders: #1 cylinder and #4 cylinder, and #2 cylinder and #3 cylinder (cylinders that are not close to each other in the exhaust stroke are grouped), and are exhausted through the exhaust duct 9. is introduced to the three-way catalyst 10 and the muffler 11, and the two in the exhaust manifold 8
Oxygen sensors 16 as exhaust component detection means are provided at the exhaust gas collecting portions of the two cylinder groups, respectively, and detect the air-fuel ratio of the air-fuel mixture taken into the engine 1 via the oxygen concentration in the exhaust gas.

Here, the CPU of the microcomputer built into the control unit 12 executes programs (fuel injection amount calculation routine, LAMBDA setting routine, learning routine, oxygen sensor output sampling routine, oxygen sensor output sampling routine) on the ROM shown as flowcharts in FIGS. 4 to 7. ) to control fuel injection.

In this example, #l and #4 are used to simplify the explanation.
The fuel injection control for the cylinders will be described based on FIGS. 4 to 7, and the description of the other cylinders #2 and #3 will be omitted as they are performed in the same manner.

FIG. 4 shows a fuel injection amount calculation routine, that is, a routine for calculating the fuel injection amount to be injected to each cylinder, and is executed every predetermined time (for example, 10 m5).

Step 1 (Indicated as Sl in the figure. The same applies below)
Here, the intake air flow rate Q detected based on the signal from the air flow meter 13, the engine rotation speed N calculated based on the signal from the crank angle sensor 14, and the water temperature sensor 1
The water temperature Tw etc. detected based on the signal from 5 is input.

In step 2, a basic fuel injection amount Tp=KxQ/N (K is a constant) corresponding to the intake air flow rate per unit rotation is calculated from the intake air flow rate Q and the engine rotational speed N.

That is, step 2 functions as a basic fuel injection amount setting means.

In step 3, various correction coefficients C0FF (=1+Kxx
To ten? -10RAS+KAI+...) is set based on the water temperature Tw, etc.

In the next step 4, a voltage correction numerator s is set based on the battery voltage. This is to correct changes in the injection flow rate of the fuel injection valve 6 due to changes in battery voltage.

In step 5, the air-fuel ratio feedback correction coefficient LAMBDA is set in the LAMBDA setting routine described later.
Load.

In step 6, the cylinder to which fuel is most recently injected is determined by a separate routine similar to the oxygen sensor output sump and ring routine described later.

In step 7, a learned value LRN of the basic fuel injection amount corresponding to the cylinder in which the fuel injection is performed, which is set in a learning routine to be described later, is read.

In step 8, the value obtained by adding the learned value LRN to the basic fuel injection amount Tp calculated in step 2 is set as the new basic fuel injection amount Tp.

In step 9, the fuel injection amount Ti is calculated according to the following equation.

'r:='rp-COEF-LAMBDA+Ts In step 10, the fuel injection amount Ti set in step 9 is set in the output register for the calculation cylinder. As a result, at a predetermined fuel injection timing synchronized with engine rotation (for example, every rotation), a drive pulse signal with a pulse width corresponding to the latest set fuel injection amount Ti is applied to the fuel provided in the calculation cylinder. The fuel is applied to the injection valve 6 to perform fuel injection.

That is, it corresponds to the fuel injection amount calculation routine or fuel injection amount setting means.

Next, LAM sets the air-fuel ratio feedback correction coefficient LAMBDA read in the fuel injection amount calculation routine.
The BDA setting routine will be explained with reference to the flowchart shown in FIG.

In step 21, the output voltage V004 of the oxygen sensor 16 corresponding to the exhaust gas of the #l cylinder (12□ and the output voltage V004 of the oxygen sensor 16 corresponding to the exhaust gas of the #4 cylinder Load.

In step 22, the deviation (Vo2., -■.6.4) of the output voltage read in step 21 is calculated, and the absolute value of the deviation (l Vo2□I-VO□41) and the predetermined value X are calculated. Compare, l Vo2s+ VO214l <x
If no, proceed to step 23.

In step 23, since the variation in air-fuel ratio between cylinders is small, the output voltage (Vozs
An air-fuel ratio feedback correction coefficient LAMBDA (corresponding to the feedback first correction value) is set corresponding to the output voltage (or V O2# 4 ).

Then, in step 24, the cylinder variation flag FH is set to FH, assuming that the variation in air-fuel ratio between cylinders is small.
=0.

On the other hand, step 22 is Vow-+Vow
-a If I≧X, proceed to step 25.

In step 25, an average value AVeVot of the output voltages V 01 @l and V o 2 m 4 is calculated.

In step 26, an air-fuel ratio feedback correction coefficient LAMBDAAvt (corresponding to the second feedback correction value) corresponding to the average value AveVo* is set.

In step 27, assuming that the air-fuel ratio of each cylinder still varies, the cylinder variation flag FH is set to FH=1.

That is, step 23 functions as a feedback first correction value setting means, and step 26 functions as a feedback second correction value setting means.
It functions as a correction value setting means.

Next, regarding the learning value LRN stored in the RAM (not shown) which is a component of the microcomputer mentioned above and used to calculate the fuel injection amount Ti in the fuel injection amount calculation routine, A learning routine for rewriting the data will be explained with reference to the flowchart shown in FIG.

This routine is executed by Vo, a sampling interrupt.

In step 31, it is determined whether the cylinder variation flag FH set in the LAMBDA setting routine described above is on (1 or O). If FH=1, there is a variation in the air-fuel ratio between the cylinders, and each cylinder Since the air-fuel ratios cannot be individually controlled to the target air-fuel ratios, it is determined that learning needs to be performed, and the process proceeds to step 32.

In step 32, the air-fuel ratio feedback correction coefficient LA
Average value of MBDAA□ (e.g. average value of values during rich/lean inversion) Whether LAMBDA, EAN is greater than the reference value 1, that is, the average value of the air-fuel ratio of #1 cylinder and #4 cylinder It is determined whether the air-fuel ratio has deviated in the rich or lean direction, and if it is determined that the air-fuel ratio is greater than 1, that is, the air-fuel ratio has deviated in the lean direction, the process proceeds to step 33.

That is, step 32 functions as an air-fuel ratio deviation direction detection means.

In step 33, the output voltage V O2$1 of the oxygen sensor 16 corresponding to the exhaust gas of #l cylinder and the average value AveV
. Compare with 2. And Vows'<AVeV. 2
In this case, it is determined that the lean tendency of the #1 cylinder is large, and the process proceeds to step 34.

In step 34, in order to eliminate the deviation in the air-fuel ratio of the #1 cylinder, for each area of the engine operating state determined by the basic fuel injection amount Tp, which is the load, and the engine rotation speed N,
Learning correction amount L for correcting the basic fuel injection amount Tp
RN, , is increased by a predetermined amount DHR (however, DIR>O), and the learning correction amount LRN□ is rewritten so as to enrich the air-fuel ratio of the #1 cylinder.

On the other hand, in step 33, if V O2g +≧AveVo2, the #4 cylinder tends to run rich compared to the rich trend of the #1 cylinder, and the average value of the air-fuel ratios of the #1 cylinder and #4 cylinder increases. is determined to be deviated in the lean direction, and the process proceeds to step 35.

In step 35, in order to eliminate the deviation in the air-fuel ratio of the #4 cylinder, the basic fuel injection is performed for each area of the engine operating state determined by the basic fuel injection amount Tp, which is the load, and the engine rotational speed N, for example. The learning correction amount LRN, , for correcting the amount Tp is increased by a predetermined amount DIR (however, DHR>0), and the learning correction amount LRN, , is rewritten so as to enrich the air-fuel ratio of the #4 cylinder.

Further, in step 32, the average value LAMBDAME of the air-fuel ratio feedback correction coefficients LAMBDAA, .
AN is smaller than the reference value 1, i.e. #l cylinder and #
If it is determined that the average value of the air-fuel ratio with respect to the four cylinders deviates in the rich direction, the process proceeds to step 36.

In step 36, similarly to step 33, the output voltage V O2 of the oxygen sensor 16 corresponding to the exhaust gas of the #l cylinder is determined.
#1 and the average value AveV. , and compare. And Vo2m+>AVeV. In the case of , it is determined that the rich tendency of the #1 cylinder is large, and the process proceeds to step 37.

In step 37, in order to eliminate the deviation in the air-fuel ratio of the #1 cylinder, for each area of the engine operating state determined by the basic fuel injection amount Tp, which is the load, and the engine rotation speed N,
Learning correction amount L for correcting the basic fuel injection amount Tp
RN, , is decreased by a predetermined amount DHR (however, DHR>O), and the learning correction amount LRN, , is rewritten so as to lean the air-fuel ratio of the #1 cylinder.

Meanwhile, in step 36, V O! # I≦AveVo2
In this case, it is determined that the rich tendency of the #4 cylinder is greater than the lean tendency of the #1 cylinder, and therefore the average value of the air-fuel ratio of the #1 cylinder and the #4 cylinder is deviated in the rich direction. Proceed to step 38.

In step 38, in order to eliminate the deviation in the air-fuel ratio of the #4 cylinder, for each area of the engine operating state determined by the basic fuel injection amount Tp, which is the load, and the engine rotation speed N,
Learning correction amount L for correcting the basic fuel injection amount Tp
The learning correction amount LRN, , is rewritten so as to decrease RN, , by a predetermined amount DHR (however, DHR>0) and lean the air-fuel ratio of the #4 cylinder.

Further, in step 31, if FH=O, the air-fuel ratio of each cylinder can be individually controlled to the target air-fuel ratio, so there is no need to perform learning, and this routine is ended.

That is, the functions of steps 34.35 and 37.38 correspond to the learning correction amount modification means.

Here, the results learned by the learning routine are stored in a RAM (not shown), which is a component of the microcomputer, so the RAM constitutes learning correction amount storage means.

Figure 7 shows an oxygen sensor output sampling routine that identifies the cylinder from the exhaust gas and detects the air-fuel ratio, and shows a discrimination signal for the #1 cylinder of the reference signal REF (this discrimination signal for the #1 cylinder is shown in Figure 8). , which is output during the intake stroke of the #1 cylinder.) is executed manually.

First, in step 51, it is determined whether the reference signal REF has been input once after the discrimination signal for cylinder #l has been input. When the reference signal REF is input once after the discrimination signal for the #1 cylinder is input, it is when the #4 cylinder is in the exhaust stroke. In this embodiment, the exhaust stroke of the #4 cylinder is reference signal RE
The oxygen sensor output voltage VO after a predetermined delay time TMDLY after F is input is sampled as indicating the oxygen concentration ratio in the exhaust gas of the #4 cylinder.

In step 52, a timer is started to measure the time from the reference signal REF indicating the exhaust stroke of the #4 cylinder to the sampling timing.

Then, in step 53, the time T measured by the timer
M and a predetermined delay time TMDLY are compared to determine whether the predetermined delay time TMDLY has elapsed.

The predetermined delay time TMDLY4 is set in consideration of the travel time for the exhaust gas exhausted through the exhaust gas to reach the oxygen sensor 16 and the response delay time of the oxygen sensor 16. Therefore, when the predetermined delay time TMDLY has elapsed since the reference signal REF indicating the exhaust stroke of the #4 cylinder was input, the oxygen sensor 16 provided at the exhaust gas collecting section of the #1 cylinder and the #4 cylinder detects the reference signal REF. The oxygen concentration ratio in the exhaust gas of cylinder #4, which is not a cylinder, can be identified as being detected.

When it is determined in step 53 that the predetermined delay time TMDLY4 has elapsed, the process proceeds to step 54, where the current oxygen sensor 16
The output voltage V. 2 is sampled, and this value is used as the output value V corresponding to the exhaust of the #4 cylinder, which is the reference cylinder. Suppose it is 7.4.

Further, if in step 51 the reference signal REF after the cylinder discrimination signal is input more than several months, step 55
Proceed to.

In step 55, it is determined whether the reference signal REF has been input three times since the #1 cylinder discrimination signal was input. When the reference signal REF is input three times after the #1 cylinder discrimination signal is input,
As shown in FIG. 8, the #1 cylinder is in the exhaust stroke, and in this embodiment, the predetermined delay time TMD is set after the reference signal REF indicating the exhaust stroke of the #1 cylinder is input.
Oxygen sensor output voltage after LY1 ■. 2 is sampled as indicating the oxygen concentration ratio in the exhaust gas of the #1 cylinder.

In step 56, a timer is started to measure the time from the reference signal REF indicating the exhaust stroke of the #1 cylinder to the sampling timing.

Then, in step 57, the time measured by the timer T
M and a predetermined delay time TMDLY are compared to determine whether or not the predetermined delay time TMDLY has elapsed.

The predetermined delay time TMDLY is set in consideration of the travel time until the exhaust gas discharged via the exhaust gas reaches the oxygen sensor 16 and the response delay time of the oxygen sensor 16. Therefore, when the predetermined delay time TMDLY has elapsed since the input of the reference signal REF indicating the exhaust stroke of the #1 cylinder, the oxygen sensor 16 provided at the exhaust gas collecting portion of the #1 cylinder and the #4 cylinder detects the reference signal REF. It can be specified that the oxygen concentration ratio in the exhaust gas of cylinder #1 is detected. Therefore, in this way, the oxygen concentration ratio of the reference cylinder can be detected separately in the oxygen sensor 16 exposed to the exhaust gas of the two cylinders.

That is, the functions of steps 51 to 53 and steps 55 to 57 correspond to cylinder specifying means.

When it is determined in step 57 that the predetermined delay time TMDLY has elapsed, the process proceeds to step 58, where the current oxygen sensor 16
The output voltage V. 2 is sampled, and this value is used as an output value V corresponding to the exhaust gas of the #l cylinder, which is the reference cylinder. 2.1.

That is, steps 54 and 58 correspond to cylinder-specific air-fuel ratio detection means.

Therefore, according to this embodiment, there are unevenness in intake air distribution among engine cylinders, variations in fuel injection valve characteristics, etc., and variations in the air-fuel ratio (rich, If the result is output as lean), the following learning will be performed.

For example, the air-fuel ratio feedback correction coefficient LAMBDAA
Average value of YE LAMB [lA, tAN or reference value ■
If it is determined that the lean tendency of #1 cylinder is large (if the air-fuel ratio deviates in the lean direction),
In order to correct the deviation in the air-fuel ratio of the #1 cylinder, the basic fuel injection amount Tp is corrected for each area of the engine operating state determined by, for example, the basic fuel injection amount Tp, which is the load, and the engine rotational speed N. Further, the average value L of the air-fuel ratio feedback correction coefficient LAMBDAA=E is carried out.
If AMBDA, EA, is smaller than the reference value l (
When the air-fuel ratio deviates in the rich direction), if it is determined that the rich tendency of the #1 cylinder is large, learning is performed to eliminate the deviation in the air-fuel ratio of the #1 cylinder.

Further, learning to eliminate the deviation in the air-fuel ratio of the #4 cylinder is performed in the same manner as described above.

As a result, it becomes possible to control the air-fuel ratio of each cylinder to the target air-fuel ratio, and it is possible to sufficiently suppress fluctuations in the air-fuel ratio, so that the exhaust properties are constant and the exhaust gas is sufficiently controlled by the three-way catalyst. , improve exhaust emission characteristics.

Note that learning is performed for the other cylinders #2 and #3 in the same manner as described above.

Furthermore, even in systems with three or more cylinders equipped with only one oxygen sensor, when there are variations, air-fuel ratio feedback control is performed based on the average value of the air-fuel ratios of all cylinders, and the air-fuel ratio of the cylinder with large variations is controlled. The configuration may be such that the learning correction is carried out sequentially, and the air-fuel ratio of that cylinder is used for the cylinders for which variations have been eliminated by the learning.

<Effects of the Invention> As explained above, according to the present invention, the cylinder to be learned is determined based on the magnitude of the feedback correction value and the air-fuel ratio detected for each cylinder, and the air-fuel ratio of the cylinders with large variations is sequentially learned. Since the air-fuel ratio step difference between cylinders is corrected, it is possible to perform feedback control of the fuel injection amount so that the actual air-fuel ratio approaches the target air-fuel ratio, and the exhaust emission characteristics are improved.

[Brief explanation of the drawing]

Fig. 1 is a functional block diagram showing the configuration of the present invention, Fig. 2 is a system diagram showing an embodiment of the invention, and Fig. 3 is a plan view for explaining the mounting position of the oxygen sensor in Fig. 2. , FIGS. 4 to 7 are flowcharts for explaining the air-fuel ratio control in the above embodiment, FIG. 8 is a time chart for explaining the timing of the oxygen sensor output sampling time in the above embodiment, and FIG. 9 is a flowchart for explaining the air-fuel ratio control in the above embodiment. A plan view of the conventional oxygen sensor installation is used to explain the position, and FIG. 10 is a time chart for explaining the problems of the conventional method. 1... Engine 6... Fuel injection valve 8... Exhaust manifold 10... Three-way catalyst 12... Control unit 13... Air flow meter
14...Crank angle sensor 16...Oxygen sensor Patent applicant Japan Electronics Co., Ltd. Agent Patent attorney Fujio Sasashima Figure 4 l0m5 Bu Figure 7

Claims (1)

[Scope of Claims] An engine operating state detection means for detecting an engine operating state including at least parameters related to the amount of air taken into the engine; Exhaust component detection means whose number is smaller than the number of cylinders; Basic fuel injection amount setting means for setting a basic fuel injection amount based on the engine operating state detected by the engine operating state detection means; A rewritable learning correction amount storage means storing a learning correction amount for correcting the basic fuel injection amount for each area of the operating state, and identifying the exhaust component detected by the exhaust component detection means as an exhaust component of a predetermined cylinder. cylinder specific air-fuel ratio detection means for detecting the air-fuel ratio for each cylinder based on the exhaust components from the exhaust component detection means and the cylinder specification means; If the variation in the air-fuel ratio is less than a predetermined level, setting a feedback first correction value that corrects the basic fuel injection amount so that the detected air-fuel ratio for each cylinder approaches the target air-fuel ratio. and correcting the basic fuel injection amount based on the average level of the detected air-fuel ratio for each cylinder, if the variation in the air-fuel ratio for each cylinder detected by the cylinder-by-cylinder air-fuel ratio detection means is equal to or higher than a predetermined level. a feedback second correction value setting means for setting a feedback second correction value to be adjusted; and an air-fuel ratio deviation direction detection means for detecting a rich/lean deviation direction of the averaged value of the feedback second correction value with respect to a reference value; learning correction amount correction means for correcting and rewriting the learning correction amount of a cylinder whose air-fuel ratio deviates in the same direction as the air-fuel ratio deviation direction detected by the air-fuel ratio deviation direction detection means in a direction that eliminates the air-fuel ratio deviation; and the feedback first correction value or feedback second correction value set by the feedback first correction value setting means or feedback second correction value setting means, and the learning correction amount retrieved from the learning correction amount storage means. An air-fuel ratio control device for an internal combustion engine, comprising: fuel injection amount setting means for correcting the basic fuel injection amount based on the basic fuel injection amount and setting the fuel injection amount for each cylinder.