JP2916805B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

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, and more specifically, corrects an air-fuel ratio step for each cylinder to bring an actual air-fuel ratio closer to a target air-fuel ratio. Thus, the correction control of the fuel injection amount is performed.

<Conventional technology> As an internal combustion engine equipped with this kind of air-fuel ratio control device,
2. Description of the Related Art Conventionally, there is one disclosed in JP-A-60-240840.

To explain this, the intake air flow rate Q of the engine detected by the air flow meter and the engine speed N detected by the engine speed sensor such as the crank angle sensor are described.
And the basic fuel injection amount Tp (= K × Q / N; K is a constant) is calculated. Further, various correction coefficients COEF according to the engine operating state such as the engine temperature, and the air-fuel ratio feedback correction coefficient LAMBDA,
A correction amount Ts for correcting a change in the effective valve opening time of the electromagnetic fuel injection valve due to the battery voltage is calculated, and the basic fuel injection amount Tp is corrected and calculated based on the correction amount Ts to obtain a final fuel injection amount Ti ( = Tp x COEF x FAMBDA + Ts).

The various correction coefficients COEF are, for example, COEF = 1 + K _MR
+ K _Tw + K _AS + K _AI + ... where K _MR is the air-fuel ratio correction coefficient, K _Tw is the water temperature increase correction coefficient, K _AS is the start and after start increase correction coefficient, K _AI is a post-idle increase correction coefficient.

By outputting a drive pulse signal having a pulse width corresponding to the fuel injection amount Ti set as described above to an electromagnetic fuel injection valve provided for each cylinder at a predetermined timing, a predetermined amount of fuel is supplied to the engine. Was to be supplied.

The air-fuel ratio feedback correction coefficient LAMBDA calculates the air-fuel ratio of the intake air-fuel mixture of the engine to a target air-fuel ratio (for example, a stoichiometric air-fuel ratio).
The value of the air-fuel ratio feedback correction coefficient LAMBDA is changed by proportional / integral control so that stable control is achieved.

That is, as shown in FIG. 9, the electromotive force changes abruptly due to the oxygen concentration ratio in the exhaust gas when the air-fuel mixture is burned at the stoichiometric air-fuel ratio, and the electromotive force is high on the rich air-fuel mixture side and high on the lean air-fuel mixture side. An oxygen sensor 71 (see, for example, Japanese Utility Model Application Laid-Open No. 61-182846) that reduces the electromotive force is provided in a portion where the exhaust passages of the respective cylinders of the engine 72 are gathered (the gathering portion of the exhaust manifold 73). Is compared with a reference voltage (slice level) corresponding to the stoichiometric air-fuel ratio to determine whether the air-fuel ratio of the engine intake air-fuel mixture (air-fuel ratio of all cylinders) is rich or lean with respect to the stoichiometric air-fuel ratio. For example, the air-fuel ratio is lean (rich)
In the case of, the air-fuel ratio feedback correction coefficient LAMBDA is gradually increased (decreased) by a predetermined integral (I),
The air-fuel ratio is controlled to the stoichiometric air-fuel ratio by increasing (decreasing) the fuel injection amount Ti. At the time of rich / lean reversal of the air-fuel ratio, the air-fuel ratio feedback correction coefficient LAMBDA is changed by a proportional component (P component) larger than the integral component (I component) to enhance 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 a muffler.

Further, in order to avoid exhaust pulsation buffering and increase exhaust efficiency, there is a type in which an exhaust manifold is connected to each of a plurality of cylinder groups each including a plurality of cylinders whose exhaust strokes do not overlap with each other. Each of the cylinder sensors is provided with an oxygen sensor, and the air-fuel ratio feedback control is performed for each corresponding cylinder group based on the signal of each oxygen sensor.

That is, for example, in the case of a four-cylinder internal combustion engine, # 1 cylinder and # 4
Exhaust gas is collected for each of the two cylinder groups of the cylinder and the # 2 and # 3 cylinders, and oxygen sensors are respectively provided at the exhaust collecting portions of the two cylinder groups, and the internal combustion engine is controlled via the oxygen concentration in the exhaust gas. In some cases, the air-fuel ratio of the air-fuel mixture is detected.

<Problems to be Solved by the Invention> However, the air-fuel ratio of the air-fuel mixture is detected by 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, uneven distribution of the intake air between the cylinders of the engine, variation in the characteristics of the fuel injection valve, and the like are present. As shown in FIG. 10, the variation is detected as it is, and is output as a variation (rich / lean) in the air-fuel ratio in the sensor output.

In particular, in a type in which an exhaust manifold is connected for each cylinder group, since the exhaust strokes do not overlap, the oxygen sensor can easily detect variations in the air-fuel ratio between the cylinders.

That is, in a four-cylinder internal combustion engine, exhaust gas is collected for each of two cylinder groups of # 1 cylinder and # 4 cylinder, and # 2 cylinder and # 3 cylinder, and oxygen sensors are respectively provided at the exhaust collecting portions of the two cylinder groups. Taking the oxygen sensor provided at the gathering portion of the # 1 cylinder and the # 4 cylinder in the case where the exhaust gas is provided as an example, when the exhaust of the # 1 cylinder is detected as shown in FIGS. 10 (b) and (c), It is determined that the output voltage from the oxygen sensor is higher than the slice level and the air-fuel ratio of the engine intake air-fuel mixture is rich, and the air-fuel ratio feedback correction coefficient LAMBDA is set to a predetermined proportional value (P) as shown in FIG. Minutes) down.
At the next detection timing, the exhaust of the # 4 cylinder is detected because the engine speed is low. However, if the above-described variation in the air-fuel ratio exists, the exhaust of the # 4 cylinder is detected by the oxygen sensor 20. May be lower than the slice level. In this case, it is determined that the air-fuel ratio of the engine intake air-fuel mixture is lean, and the air-fuel ratio feedback correction coefficient
LAMBDA is increased by a predetermined proportional amount (P amount).

Normally, the value of the air-fuel ratio feedback correction coefficient LAMBDA is changed by the proportional / integral control so that stable control is performed. However, as described above, for example, at the time of idling, there is only a vertical change by a predetermined proportional amount.

Therefore, a predetermined period (T period in FIG. 10 (a))
Means that the air-fuel ratio feedback correction coefficient LAMBDA repeats abnormal reversal, the air-fuel ratio of each cylinder cannot be controlled individually to the target air-fuel ratio, and fluctuations in the air-fuel ratio cannot be sufficiently suppressed. However, there is a problem that the exhaust emission characteristics are deteriorated beyond the capacity of a three-way catalyst for purifying exhaust gas.

Of course, if the oxygen sensor is provided for each cylinder and the air-fuel ratio feedback control is performed independently for each cylinder in accordance with the signal from each sensor, the above problem can be solved. There are problems such as too much.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and can correct the air-fuel ratio step for each cylinder so that the fuel injection amount can be feedback-controlled so that the actual air-fuel ratio approaches the target air-fuel ratio. An object is to provide an air-fuel ratio control device for an internal combustion engine.

<Means for Solving the Problems> To achieve the above object, the present invention provides a first method.
As shown in the figure, an air-fuel ratio control device for an internal combustion engine includes the following means A to K.

(A) an engine operating state detecting means for detecting an engine operating state including at least a parameter relating to an amount of air taken into the engine; (C) 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 detecting means; A rewritable learning correction amount storage unit storing a learning correction amount for correcting the basic fuel injection amount for each area of the operating state. (E) The exhaust component detected by the exhaust component detection unit is converted into an exhaust component of a predetermined cylinder. Cylinder specifying means for specifying (F) Cylinder-specific air-fuel ratio detecting means for detecting an air-fuel ratio for each cylinder based on exhaust components by means of exhaust component detection means and cylinder specifying means (G) Cylinder specific Among the air-fuel ratios of the cylinders detected by the fuel-ratio detecting means, at least initially, a feedback correction value for correcting the basic fuel injection amount so that the air-fuel ratio approaches the target air-fuel ratio based on the detected air-fuel ratio of the reference cylinder. Feedback correction value setting means to be set (H) Deviation judgment for judging a deviation of a correction value of the averaged value of the feedback correction value set by the feedback correction value setting means based on the detected air-fuel ratio of the reference cylinder with respect to the reference value. Means (I) When the deviation of the correction value determined by the deviation determining means is larger than a predetermined level, the air-fuel ratio of the reference cylinder set when the feedback correction value is set as the reference value is brought closer to the target air-fuel ratio. First learning correction amount correcting means for correcting and rewriting the learning correction amount for the reference cylinder as described above. When the deviation of the positive value is equal to or less than the predetermined level, another air-fuel ratio of the other cylinder detected by the cylinder-specific air-fuel ratio detecting means based on the air-fuel ratio of the reference cylinder is made closer to the air-fuel ratio of the reference cylinder. Second learning correction amount correcting means for correcting and rewriting the learning correction amount relating to the cylinder. (K) The feedback correction value set by the feedback correction value setting means and the learning for each cylinder retrieved from the learning correction amount storage means. Fuel injection amount setting means for correcting the basic fuel injection amount based on the correction amount and setting the fuel injection amount for each cylinder <Operation> According to the air-fuel ratio control device having such a configuration, the engine operation state detecting means A When an engine operating state including at least a parameter related to the amount of air taken into the engine is detected, the basic fuel injection amount setting means C sets the basic fuel injection amount based on the engine operating state. Set.

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

Then, at least initially, the feedback correction value setting means G sets a feedback correction value for correcting the basic fuel injection amount based on the detected air-fuel ratio of the reference cylinder so that the air-fuel ratio approaches the target air-fuel ratio.

If the deviation of the averaged value of the feedback correction value set based on the detected air-fuel ratio of the reference cylinder from the reference value is larger than a predetermined level, the first learning correction amount correcting means I sets the correction value to the reference cylinder. Such learning is performed.

If the deviation is equal to or less than the predetermined level, the second learning correction amount correcting means J performs learning on other cylinders based on the air-fuel ratio of the reference cylinder.

The fuel injection amount setting means K sets the fuel injection amount for each cylinder based on the feedback correction value and the learning correction amount for each cylinder.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 2, air is drawn into a four-cylinder internal combustion engine 1 from an air cleaner 2 through an intake duct 3, a throttle valve 4, and an intake manifold 5. A fuel injection valve 6 is provided in each branch of the intake manifold 5 for each cylinder. The fuel injection valve 6 is an electromagnetic fuel injection valve that is energized by a solenoid to open, is de-energized, and closes. The fuel injection valve 6 is energized by a drive pulse signal from a control unit 12 described later, and is opened. The fuel which is pressure-fed from the pump and adjusted to a predetermined pressure by the pressure regulator is injected and supplied.

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

Then, exhaust gas is discharged from the engine 1 through the exhaust manifold 8, the exhaust duct 9, the three-way catalyst 10, and the muffler 11. The three-way catalyst 10 is an exhaust purification device that oxidizes CO and HC in exhaust components and also reduces NO _X to convert it to other harmless substances, and burns the air-fuel mixture at a stoichiometric air-fuel ratio. Sometimes both conversion efficiencies are the best.

The control unit 12 includes a microcomputer including a CPU, a ROM, a RAM, an A / D converter, and an input / output interface, receives input signals from various sensors, performs arithmetic processing as described below, The operation of the fuel injection valve 6 is controlled.

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

In the case of a four-cylinder engine provided with a crank angle sensor 14, a reference signal REF (reference signal) for every 180 ° crank angle and a position signal for every 1 ° or 2 ° crank angle.
Outputs POS (unit signal). Here, by measuring the period of the reference signal REF or the number of occurrences of the position signal POS within a predetermined time, the engine speed N can be calculated, and the reference signal RE
One of F is distinguishable from the other by its pulse width, and is a cylinder discrimination signal of the # 1 cylinder. Further, a water temperature sensor for detecting a cooling water temperature Tw of the water jacket of the engine 1.
15 mags are provided.

Here, the air flow meter 13, crank angle sensor 1
4 and the like correspond to engine operating state detecting means.

Further, as shown in FIG. 3, the exhaust manifold 8 includes two cylinders # 1 and # 4, and # 2 and # 3.
Exhaust gas is collected for each of the two cylinder groups (cylinders whose exhaust strokes are not close to each other are grouped), and the exhaust gas is led to the three-way catalyst 10 and the muffler 11 through the exhaust duct 9, respectively. The above 2 in 8
An oxygen sensor 16 as an exhaust component detecting means is provided at each of the exhaust collecting sections of the two cylinder groups, and detects the air-fuel ratio of the air-fuel mixture taken into the engine 1 via the oxygen concentration in the exhaust.

In this case, the CPU of the microcomputer built in the control unit 12 executes a program (a fuel injection amount calculation routine, a LAMBDA setting routine, a learning routine, an oxygen sensor output sensor ring) on a ROM shown as a flowchart in FIGS. A calculation process is performed in accordance with a (routine) to control the fuel injection.

In this embodiment, # 1 and # 1 are used to simplify the description.
The fuel injection control for the four cylinders will be described with reference to FIGS. 4 to 7, and the description of the other cylinders # 2 and # 3 will be omitted since they are performed similarly.

FIG. 4 is a routine for calculating a fuel injection amount, that is, a routine for calculating a fuel injection amount to be injected into each cylinder, which is executed every predetermined time (for example, 10 ms).

In step 1 (denoted as S1 in the figure, the same applies hereinafter), an intake air flow rate Q detected based on a signal from the air flow meter 13, an engine rotation speed calculated based on a signal from the crank angle sensor 14 N, a water temperature Tw detected based on a signal from the water temperature sensor 15, and the like are input.

In step 2, a basic fuel injection amount Tp = K × Q / 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 speed N.

That is, this step has the function of the basic fuel injection amount setting means.

In step 3, various correction coefficients COEF (= 1 + K _MR + K _Tw
+ K _AS + K _AI + ...) is set based on the water temperature Tw or the like.

In the next step 4, the voltage correction Ts is set based on the battery voltage. This is for correcting a change in the injection flow rate of the fuel injection valve 6 due to a change in the battery voltage.

In step 5, the air-fuel ratio feedback correction coefficient LAMBDA set in another routine is read.

In step 6, the cylinder that performs the latest fuel injection is determined by another routine.

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

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

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

Ti = Tp / 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. Thus, at a predetermined fuel injection timing of the engine rotation synchronous (for example, every one rotation), a drive pulse signal having a pulse width corresponding to the latest set fuel injection amount Ti is supplied to the fuel cylinder provided in the calculation cylinder. The fuel is supplied to the injection valve 6 to perform fuel injection.

That is, the fuel injection amount calculation routine corresponds to a fuel injection amount setting unit.

Next, a LAMBDA setting routine for setting the air-fuel ratio feedback correction coefficient LAMBDA read in the fuel injection amount calculation routine will be described with reference to a flowchart shown in FIG.

In step 21, the output voltage V _O2 of the oxygen sensor 16 corresponding to the exhaust of the output voltage V _{O2 # 1} and # 4 cylinders of the oxygen sensor 16 corresponding to the exhaust of the # 1 cylinder is carried out by oxygen sensor output sampling routine will be described later Read _{# 4} .

In step 22, it is determined whether or not a learning end flag FH _{# 4} set in a learning routine to be described later is set (0 or 1).
If FH _{# 4} = 0, it is determined that the air-fuel ratio learning of the # 4 cylinder has not been completed, and the process proceeds to step 23. First, the air-fuel ratio is determined based on the air-fuel ratio of the # 1 cylinder which is the reference cylinder. A feedback correction value LAMBDA for correcting the basic fuel injection amount calculated in the fuel injection amount calculation routine is set so as to approach the target air-fuel ratio.

In step 22, the learning end flag FH _{# 4} = 1
In the case of, it is assumed that the air-fuel ratio learning of the # 4 cylinder has been completed.
Proceeding to step 24, every time the learning is completed, a feedback correction value LAMBDA is set based on the air-fuel ratio of the # 1 cylinder ( _{VO2 # 1} ) or the air-fuel ratio of the # 4 cylinder ( _{VO2 # 4} ).

That is, step 23 in this routine corresponds to the function of the feedback correction value setting means.

That is, the setting of the feedback correction value LAMBDA has been described in the related art while initially performing rich / lean determination based on the air-fuel ratio of the reference cylinder (# 1 cylinder) detected in the routine of FIG. Set by proportional / integral control.

Further, in order to improve the responsiveness, the feedback control based on the detected air-fuel ratio of the learned cylinder is started every time the learning of the air-fuel ratio of the other cylinder is completed, after the learning of the air-fuel ratio of the reference cylinder is completed, as described later. Things.

Next, a learning value stored in a RAM (not shown) which is one component of the microcomputer and used for calculating the fuel injection amount Ti in the fuel injection amount calculation routine.
A learning routine for rewriting the data corresponding to the cylinder with respect to the LRN will be described with reference to a flowchart shown in FIG.

This routine is executed by a _VO2 sampling interrupt.

In step 30, it is determined whether or not the learning end flag FH _{# 4} is set (1 or 0). If FH _{# 4} = 0, learning relating to the air-fuel ratio of the cylinders other than the reference cylinder (# 4 cylinder) is performed. Since it is not completed, and the air-fuel ratio of each cylinder cannot be individually controlled to the target air-fuel ratio, it is determined that learning needs to be performed, and the process proceeds to step 31.

In step 30, if FH _{# 4} = 1,
Since the learning related to the air-fuel ratio of the # 4 cylinder has also been completed, it is not necessary to perform the learning, and thus this routine ends. However,
In the initial setting before the start of learning, FH _{# 4} = 0.

In step 31, it is determined whether or not the learning for the # 1 cylinder, which is the reference cylinder, has been completed.
It is determined whether FH _{# 1} is set (1 or 0), and FH
_{When # 1} = 0, the air-fuel ratio of the reference cylinder cannot be controlled to the target air-fuel ratio, and 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 LAMB set based on the detected air-fuel ratio of the reference cylinder (# 1 cylinder)
Average value of DA (for example, the average value of values at the time of rich / lean inversion) LAMBDA _MEAN and absolute value | L of deviation from reference value 1
It is determined whether or not AMBDA _MEAN -1 | is greater than a predetermined value NGAVE. That is, the step 32 is a deviation determining means for determining a deviation of a correction value of the averaged value LAMBDA _MEAN of the feedback correction value set based on the detected air-fuel ratio of the reference cylinder by the feedback correction value setting means with respect to the reference value. Equivalent to.

When the absolute value is larger than the predetermined value, in order to eliminate the deviation of the air-fuel ratio of the # 1 cylinder, for example, each area of the engine operating state determined by the basic fuel injection amount Tp and the engine speed N, which are loads, is used. In order to rewrite the learning correction amount LRN _{# 1} for correcting the basic fuel injection amount Tp,
Proceed to step 33.

In step 33, it is determined whether or not the averaged value LAMBDA _MEAN of the feedback correction value is greater than 1, that is, in which direction the average value of the air-fuel ratio of the # 1 cylinder deviates in the rich lean direction. If it is determined that the value is greater than 1, that is, if the air-fuel ratio of the reference cylinder is shifted in the lean direction, the process proceeds to step 34.

In step 34, in order to eliminate the deviation of the air-fuel ratio of the # 1 cylinder, for example, the basic fuel injection amount Tp is determined for each area of the engine operating state determined by the basic fuel injection amount Tp as the load and the engine speed N. Learning correction amount LRN for correction
_The learning correction amount LRN is set so that # 1 is increased by a predetermined amount DHR (where DHR> 0), and the air-fuel ratio of the # 1 cylinder is enriched.
Rewrite _{# 1} .

Then, in step 35, since the learning for the # 1 cylinder, which is the reference cylinder, has not been completed, the # 1 cylinder learning end flag FH _{# 1 is set} to FH _{# 1} = 0.

On the other hand, if it is determined in step 33 that the average value LAMBDA _MEAN of the feedback correction value is smaller than 1, that is, if the air-fuel ratio of the reference cylinder is shifted in the rich direction, the process proceeds to step 36.

In step 36, the learning correction amount LRN _{# 1} is set to a predetermined amount DHR (where DHR>
0), and the learning correction amount LRN _{# 1} is rewritten so as to make the air-fuel ratio of the # 1 cylinder lean.

That is, the functions of steps 33, 34 and 36 correspond to the first learning correction amount correcting means.

If the absolute value | LAMBDA _MEAN −1 | is equal to or smaller than the predetermined value NGAVE in step 32, it is determined that the learning for the # 1 cylinder has been completed, and the process proceeds to step 37, where the learning end flag FH _{# 1}
Is set to FH _{# 1} = 1.

On the other hand, if it is determined in step 31 that FH _{# 1} = 1, it is determined that the learning for the # 1 cylinder, which is the reference cylinder, has been completed, and the process proceeds to step 41 and subsequent steps. The learning related to the # 4 cylinder is performed so that the air-fuel ratio of the four cylinders approaches the air-fuel ratio of the # 1 cylinder.

 Hereinafter, learning of the # 4 cylinder will be described.

In step 41, the output voltage V _{O2 # 4 of} the oxygen sensor 16 corresponding to the exhaust of the # 4 cylinder and the output voltage V _{O2 # 1 of} the oxygen sensor 16 corresponding to the exhaust of the reference cylinder (# 1 cylinder) detected immediately before. Compare with Then, V _{O2 # 4} > V _{O2 # 1} +
If ΔV (ΔV is a positive predetermined value), it is determined that the variation in the rich direction of the # 4 cylinder is large, and the routine proceeds to step 42.

In step 42, a learning correction amount LRN _{# 4} for correcting the basic fuel injection amount Tp for each area of the engine operating state similar to the reference cylinder in order to eliminate the deviation of the air-fuel ratio of the # 4 cylinder.
Is reduced by a predetermined amount DHR (where DHR> 0), and the learning correction amount LRN _{# 4} is rewritten so as to make the air-fuel ratio of the # 4 cylinder lean, and then FH _{# 4} = 0 in step 43.

On the other hand, if it is determined in step 41 that V _{O2 # 4} <V _{O2 # 1−} ΔV, it is determined that the variation in the lean direction of the # 4 cylinder is large, and the process proceeds to step.

In step 44, in order to eliminate the deviation of the air-fuel ratio of the # 4 cylinder, the learning correction amount LRN _{# 4} is increased by a predetermined amount DHR (where DHR> 0), and the learning is performed so as to enrich the air-fuel ratio of the # 4 cylinder. After rewriting the correction amount LRN _{# 4} , at step 43 FH
_{# 4} = 0.

In step 41, V _{O2 # 1} -ΔV ≦ V _{O2 # 4} ≦ V
_In the case of _{O2 # 1} + ΔV, it is determined that the variation in the air-fuel ratio of the # 4 cylinder is small, and no further learning is necessary.
After setting the learning end flag FH _{# 4} = 1 at 45, the process returns.

That is, the functions of steps 41, 42 and 44 correspond to the second learning correction amount correcting means.

Here, the result learned by the learning routine is stored in a RAM (not shown), which is one component of the microcomputer, and the RAM constitutes a learning correction amount storage unit.

FIG. 7 shows a routine for detecting the air-fuel ratio by specifying the cylinder from the exhaust gas. The reference signal REF determines the # 1 cylinder (the determination signal of the # 1 cylinder is #, as shown in FIG. 8). Is output during the intake stroke of one cylinder.) Is executed.

First, in step 61, it is determined whether or not the reference signal REF has been input once since the determination signal of the # 1 cylinder has been input. The time when the reference signal REF is input once after the discrimination signal of the # 1 cylinder is input is when the # 4 cylinder is in the exhaust stroke. In the present embodiment, the exhaust stroke of the # 4 cylinder is the oxygen sensor output voltage V _O2 of the predetermined delay time TMDLY after ₄ from the input of the reference signal REF is shown, in which to sample as an indication of the oxygen concentration ratio in exhaust gas of the fourth cylinder.

In step 62, a timer for measuring the time from the reference signal REF indicating the exhaust stroke of the # 4 cylinder to the sampling timing is started.

Then, in step 63, the measurement time TM by the timer
And the predetermined delay time TMDLY ₄ to determine the predetermined delay time TMDL
It is determined whether or not Y _{4 has} elapsed.

The predetermined delay time TMDLY ₄ is set in consideration of a travel time until the exhaust gas discharged via the exhaust gas reaches the oxygen sensor 16 and a response delay time of the oxygen sensor 16. Therefore, when the predetermined delay time TMDLY ₄ has elapsed since the input of the reference signal REF indicating the exhaust stroke of the # 4 cylinder, the oxygen sensor 16 provided in the exhaust collecting section of the # 1 cylinder and the # 4 cylinder detects the reference time. It can be specified that the oxygen concentration ratio in the exhaust of the # 4 cylinder other than the cylinder is detected.

If it is determined in step 63 that the predetermined delay time TMDLY ₄ has elapsed, the process proceeds to step 64, where the current output voltage of the oxygen sensor 16 is
V _O2 is sampled and this value is used as the reference cylinder # 4
It is assumed that the output value is _{VO2 # 4} corresponding to the exhaust of the cylinder.

If it is determined in step 61 that the input number of the reference signal REF after the cylinder discrimination signal is more than one, the process proceeds to step 65.

In step 65, it is determined whether or not the reference signal REF has been input three times since the determination signal of the # 1 cylinder was input. The case where the reference signal REF is inputted three times after the discrimination signal of the # 1 cylinder is inputted is the eighth case.
As shown in the drawing, this is when the # 1 cylinder is in the exhaust stroke, and in this embodiment, the oxygen sensor output voltage after a predetermined delay time TMDLY ₁ after the input of the reference signal REF indicating the exhaust stroke of the # 1 cylinder. V _O2 is sampled as indicating the oxygen concentration ratio in the exhaust of the # 1 cylinder.

In step 66, a timer for measuring the time from the reference signal REF indicating the exhaust stroke of the # 1 cylinder to the sampling timing is started.

Then, in step 67, the measurement time TM by the timer
And the predetermined delay time TMDLY ₁ to determine the predetermined delay time TMDL
It is determined whether or not Y _{1 has} elapsed.

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

That is, the functions of steps 61 to 63 and steps 65 to 67 correspond to the cylinder specifying means.

If it is determined in step 67 that the predetermined delay time TMDLY ₁ has elapsed, the process proceeds to step 68, where the current output voltage of the oxygen sensor 16 is
V _O2 is sampled and this value is used as the reference cylinder # 1
It is assumed that the output value is _{VO2 # 1} corresponding to the exhaust of the cylinder.

That is, steps 64 and 68 correspond to cylinder-by-cylinder air-fuel ratio detection means.

Therefore, according to the present embodiment, there is uneven distribution of intake air between the cylinders of the engine, variations in the characteristics of the fuel injection valves, and the like. When the output is “lean”, the following learning is performed.

For example, the average value LAMBDA _{MEAN of} the air-fuel ratio feedback correction coefficient LAMBDA set based on the detected air-fuel ratio of the reference cylinder
Is greater than a predetermined level compared to 1, which is a reference value, learning learning for correcting the basic fuel injection amount Tp for each area of the engine operating state in order to eliminate the deviation of the air-fuel ratio of the reference cylinder. Is performed.

If the variation of the average value LAMBDA _MEAN is less than a predetermined level as compared with 1, which is a reference value, # 4
Learning for bringing the air-fuel ratio of the cylinder close to the air-fuel ratio of the # 1 cylinder, which is the reference cylinder, is performed.

Therefore, it is possible to control the air-fuel ratio of each cylinder to the target air-fuel ratio, and it is possible to sufficiently suppress the fluctuation of the air-fuel ratio, so that the exhaust characteristics are constant and the exhaust is sufficiently supplied by the three-way catalyst. In addition, the exhaust emission characteristics are improved.

Note that learning is performed in the same manner as described above, with any one of the other cylinders # 2 and # 3 as a reference cylinder.

Further, even in the case where three or more cylinders are provided with only one oxygen sensor, learning is sequentially performed from the reference cylinder, and the cylinders whose variations have been eliminated by learning use the air-fuel ratio of the cylinder. I just need.

<Effects of the Invention> As described above, according to the present invention, first, air-fuel ratio feedback control is performed with the air-fuel ratio of the reference cylinder, and learning is performed so as to approach the target air-fuel ratio when the air-fuel ratio of the reference cylinder varies. Is performed, and then learning related to cylinders other than the reference cylinder is performed. Therefore, the air-fuel ratio of each cylinder can be controlled to the target air-fuel ratio, and the exhaust characteristics are constant, and the exhaust emission characteristics are improved.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing the configuration of the present invention, FIG. 2 is a system diagram showing one embodiment of the present invention, FIG. 3 is a plan view for explaining the mounting position of the oxygen sensor in FIG. 4 to 7 are flow charts for explaining the air-fuel ratio control in the embodiment, FIG. 8 is a time chart for explaining the timing of the oxygen sensor output sampling time in the embodiment, and FIG. FIG. 10 is a plan view for explaining an oxygen sensor mounting position, and FIG. 10 is a time chart for explaining a conventional problem. 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

Continued on the front page (56) References JP-A-3-115575 (JP, A) JP-A-61-101639 (JP, A) JP-A-3-6037 (JP, U) JP-A 1-148047 (JP) , U) Real opening 61-97546 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) F02D 41/14 F02D 45/00

Claims (1)

(57) [Claims] An engine operating state detecting means for detecting an engine operating state including at least a parameter relating to an amount of air taken into the engine; an engine exhaust component interposed in an exhaust passage of the engine for detecting an engine exhaust component; Exhaust gas component detection means having less than the number of cylinders; basic fuel injection quantity setting means for setting a basic fuel injection quantity based on the engine operation state detected by the engine operation state detection means; A rewritable learning correction amount storage unit storing a learning correction amount for correcting the basic fuel injection amount for each state area, and an exhaust component detected by the exhaust component detection unit is specified as an exhaust component of a predetermined cylinder. Cylinder-specific air-fuel ratio detecting means for detecting an air-fuel ratio for each cylinder based on exhaust components from the exhaust-gas component detecting means and the cylinder specifying means; and A feedback correction value for correcting the basic fuel injection amount so as to bring the air-fuel ratio close to the target air-fuel ratio based on the detected air-fuel ratio of the reference cylinder, at least initially, among the air-fuel ratios detected for each cylinder detected by the output means. Feedback correction value setting means, deviation determination means for determining a deviation of the correction value from the reference value of the averaged value of the feedback correction value set based on the detected air-fuel ratio of the reference cylinder in the feedback correction value setting means, If the deviation of the correction value determined by the deviation determination means is larger than a predetermined level, the reference cylinder is set so that the air-fuel ratio of the reference cylinder set when the feedback correction value is set as the reference value is close to the target air-fuel ratio. A first learning correction amount correcting means for correcting and rewriting the learning correction amount according to the above, and a correction value for the correction value determined by the shift determining means. Is less than or equal to a predetermined level, the learning on the other cylinders is performed so that the air-fuel ratio of the other cylinder detected by the cylinder-specific air-fuel ratio detecting means with reference to the air-fuel ratio of the reference cylinder is close to the air-fuel ratio of the reference cylinder. A second learning correction amount correcting unit for correcting and rewriting the correction amount; a feedback correction value set by the feedback correction value setting unit; and a learning correction amount for each cylinder retrieved from the learning correction amount storage unit. An air-fuel ratio control device for an internal combustion engine, comprising: a fuel injection amount setting means for setting the fuel injection amount for each cylinder by correcting the basic fuel injection amount.