JPH08312422A - Air-fuel ratio control device of engine - Google Patents

Abstract

PURPOSE: To maintain a logical mixing ratio while suppressing the torque variation of an engine in an idling time following an air-fuel ratio feedback control. CONSTITUTION: While an air-fuel ratio feedback correcting coefficiemt in the idling time after a warm-up to specific cylinders is operated by using a feedback constant in a nonidling time, the air-fuel ratio feedback correcting amount in the idling time after a warm-up to the remaining cylinders is clamped to a specific value, in an operation and clamping means 24, and the air-fuel ratio learning value in the idling time after the warm-up is operated by an operation means 25, depending on the air-fuel ratio feedback correcting coefficient as to the specific cylinders. A standard injection amount is corrected by the air-fuel ratio feedback correction coefficennt and the air-fuel ratio learning amount to the specific cylinders so as to correct the fuel injection amount, while the standard injection amount is corrected by the clamped air-fuel ratio feedback correction coefficient and the air-fuel learning value to the remaining cylinders so as to correct the fuel injection amount, by an oepration means 26.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine air-fuel ratio control device, and more particularly to an air-fuel ratio feedback control using an O ₂ sensor.

[0002]

2. Description of the Related Art A three-way catalyst is provided in an exhaust pipe, and air-fuel ratio feedback control is performed based on an output signal from an O ₂ sensor upstream of the three-way catalyst so that the exhaust air-fuel ratio becomes a stoichiometric air-fuel ratio. In the control system, when the air-fuel ratio feedback control is performed even after idling after warming up, the air-fuel ratio fluctuation accompanying the air-fuel ratio feedback control greatly affects the torque fluctuation of the engine, and in the worst case, hunting occurs and the engine is operated. Performance is deteriorated, set a constant (hereinafter referred to as a feedback constant) for calculating the air-fuel ratio feedback correction coefficient α such as proportional or integral during idle after warm-up to a value smaller than that during non-idle It has been proposed to suppress the fluctuation range of the air-fuel ratio at the time (see Japanese Patent Laid-Open No. 61-81544).

[0003]

However, when the engine is idling after warm-up, the rotation is originally low, and the air-fuel ratio feedback control cycle becomes long even if the feedback constant at the time of non-idling is used, and the controllability of the air-fuel ratio deteriorates. However, if the feedback constant is set to a value smaller than that during non-idle as in the conventional example, the control cycle of the air-fuel ratio during idle after warm-up will be prolonged, and the air-fuel ratio will become lean. By spending more time
After warming up, the engine stability at idle becomes even worse.

On the other hand, the air-fuel ratio feedback control is performed only a few times by using the feedback constant when the engine is idling after warming up, and the air-fuel ratio learning value is calculated based on the air-fuel ratio feedback correction coefficient at that time. At the time of idling thereafter, it is considered that the air-fuel ratio feedback control is stopped only by calculating the fuel injection pulse width using this air-fuel ratio learned value.

However, in this engine, the temperature inside the engine room rises due to insufficient scavenging inside the engine room, and the temperature of the cooling water and the fuel temperature rise temporarily, as when the vehicle is in the idle state from the running state. At this time, the required value of the correction coefficient Ktrm for correcting the air amount detection error varies due to the increase of the cooling water temperature, and the phenomenon that the fuel density decreases due to the increase of the fuel temperature and the supplied fuel mass changes, and so on, gradually. The air-fuel ratio may change and deviate from the theoretical mixing ratio.

First, in detail, since the air amount detection error is a phenomenon associated with intake pulsation, the value of the correction coefficient Ktrm is set by using the throttle valve opening that affects the intake pulsation as a parameter, and the intake detected by the air flow meter is set. The air amount is corrected by multiplying the air amount Qa. On the other hand, at the time of idling when the throttle valve is almost in the fully closed position, the opening degree of the auxiliary air valve provided in the air passage that bypasses the throttle valve is adjusted in order to maintain the idling speed. In this case, as described above, the actual air amount decreases due to the decrease in the air density accompanying the increase in the temperature inside the engine room, which appears as a decrease in idle rotation. In order to maintain (mass), the opening degree of the auxiliary air valve is made larger than that when the temperature in the engine room does not rise. However, since the throttle valve opening does not change at the idle position, only the same value of Ktrm is given when the air amount increases as the idle rotation decreases. That is, the required correction value of the air amount detection error changes by the amount of air adjusted by the auxiliary air valve regardless of the throttle valve opening at the idle position, and the air-fuel ratio learning value deviates from the request at this time. It will come.

With respect to the fuel flow rate, since the passage area determined by the orifice of the injection valve and the flow velocity determined by the fuel pressure are controlled, the volume flow rate is controlled, and the flow rate is adjusted by the opening time of the injection valve. Therefore, when the fuel density decreases due to the increase in fuel temperature, the mass flow rate decreases even if the injection valve opening time is the same, and the air-fuel ratio changes.

As described above, when the air-fuel ratio gradually changes and deviates from the theoretical mixing ratio due to the phenomenon of, not only the stability of the engine is impaired, but also the conversion performance of the catalyst is deteriorated, and the engine is started especially after the idling. If there is an increase in the amount of air, the conversion performance of the catalyst will be significantly reduced and exhaust emission will be deteriorated. Excessive O ₂ is adsorbed to the catalyst due to the shift of the air-fuel ratio to the lean side during idling, and excess CO is adsorbed to the catalyst due to the shift to the rich side. In that case, even if the air-fuel ratio at that time is the theoretical value, the air-fuel ratio inside the catalyst will shift due to the excess O ₂ or CO that was adsorbed earlier, and the exhaust emission will deteriorate. To do.

Therefore, the present invention performs air-fuel ratio feedback control and air-fuel ratio learning during non-idle by using the feedback constant during non-idle only in a specific cylinder during warm-up after idling, while warming the remaining cylinders. The air-fuel ratio feedback correction coefficient is clamped to a predetermined value when the engine is idle, and the air-fuel ratio learning control value calculated for the specific cylinder is used to calculate the fuel injection pulse width for the remaining cylinders. The purpose is to keep the theoretical mixture ratio while suppressing engine torque fluctuations.

[0010]

As shown in FIG. 8, a first invention is a means 21 for calculating a basic injection amount Tp according to an operating condition, and a means 22 for determining whether or not the engine is in a post-warm idle state. And means 23 for determining which cylinder it is,
From these judgment results, the air-fuel ratio feedback correction coefficient for the specific cylinder at the time of idling after warm-up is calculated using the feedback constant at the time of non-idling, and the air-fuel ratio feedback correction coefficient for the remaining cylinders at the time of idling after warm-up is calculated. Means 24 for clamping at a predetermined value, means 25 for calculating the air-fuel ratio learning value αm at the time of idling after warm-up based on the air-fuel ratio feedback correction coefficient for the specific cylinder, and for the specific cylinder, it is calculated for the specific cylinder. The basic fuel injection amount Tp is corrected by the air-fuel ratio feedback correction coefficient and the air-fuel ratio learning value αm, and the fuel injection amount is clamped with respect to the remaining cylinders. And the air-fuel ratio learning value αm, the basic injection amount Tp is corrected to determine the fuel injection amount. It is a means 26 for computing, means for supplying a fuel injection amount by these operations on the corresponding cylinder 27
And.

According to a second aspect of the present invention, in the V-type engine according to the first aspect of the invention, in which the three-way catalyst is provided independently for each bank, the specific cylinder is independently selected for each bank.

According to a third aspect of the present invention, in the first or second aspect of the invention, the air-fuel ratio learning value during idle after the warm-up until the predetermined calculation cycle of the air-fuel ratio feedback correction coefficient elapses. Is not calculated.

According to a fourth aspect of the present invention, in any one of the first to third aspects of the present invention, the update coefficient used for calculating the air-fuel ratio learning value during idle after warm-up is used as an air-fuel ratio feedback during idle after warm-up. It is set to a value that decreases as the ratio of the air-fuel ratio of the specific cylinder under control to the average air-fuel ratio for all cylinders increases.

[0014]

When the idling after warm-up is low and the feedback constant during non-idling is used originally, the air-fuel ratio feedback control cycle becomes long and the controllability of the air-fuel ratio may deteriorate. If the feedback constant is set to a value smaller than that during non-idle, the control cycle of the air-fuel ratio during idle after warm-up will be prolonged, and the time during which the air-fuel ratio is lean will increase. After warming up, the engine stability at idle becomes even worse.

On the other hand, in the first aspect of the invention, the air-fuel ratio of the specific cylinder periodically changes according to the air-fuel ratio feedback correction coefficient of the specific cylinder. Since the same feedback constants used for non-idle air-fuel ratio feedback control are used to calculate the correction coefficient, the air-fuel ratio when the control cycle of the air-fuel ratio is non-idle is used for both the air-fuel ratio of a specific cylinder and the average air-fuel ratio of all cylinders. The control cycle is almost the same as that in the feedback control, and the control cycle does not become long as in the conventional example. In other words, since the lean period during idling does not become long, combustion instability does not occur.

Further, the air-fuel ratio learning value αm is calculated based on the post-warm-up idle-time air-fuel ratio feedback correction coefficient α for the specific cylinder, and the air-fuel ratio learning value αm is used for the remaining cylinders after warm-up idle fuel. Since it is used to calculate the injection amount, the average air-fuel ratio of the remaining cylinders becomes constant near the stoichiometric air-fuel ratio, and combustion stability improves.

Further, since the average air-fuel ratio of all the cylinders is almost the theoretical mixture ratio, the conversion performance of the three-way catalyst is not impaired.

On the other hand, the air-fuel ratio feedback control is performed only a few times by using the feedback constant when the engine is idling after warming up, and the air-fuel ratio learning value is calculated based on the air-fuel ratio feedback correction coefficient at that time. At the time of idling thereafter, the air-fuel ratio feedback control is stopped only by calculating the fuel injection pulse width using this air-fuel ratio learning value. As the cooling water temperature and the fuel temperature rise, the correction coefficient required to correct the air amount detection error varies, the supplied fuel mass changes, and other phenomena occur, gradually changing the air-fuel ratio and causing theoretical mixing. However, in the first aspect of the invention, the air-fuel ratio feedback control must be performed for the specific cylinder at idle after warm-up. Et al., The air-fuel ratio during idling after warm-up is kept near the stoichiometric air-fuel ratio. Even if the air-fuel ratio shifts to the lean side due to a temporary increase in the cooling water temperature or the fuel temperature immediately after idling, the fuel increase for the specific cylinder is performed to return the air-fuel ratio to the rich side, and all cylinders are increased. The average air-fuel ratio of is returned to near the stoichiometric air-fuel ratio.

As described above, according to the first aspect of the present invention, the stoichiometric air-fuel ratio can be maintained without causing the torque fluctuation of the engine due to the air-fuel ratio feedback control, and thereby the stability at idle and the exhaust emission can be achieved. The effect of improvement is obtained.

According to the second aspect of the present invention, in the V-type engine in which the three-way catalyst is provided independently for each bank, the specific cylinder is selected independently for each bank. Therefore, the V-type engine also has the air-fuel ratio feedback control. The stoichiometric air-fuel ratio can be maintained without accompanying engine torque fluctuations, which has the effect of improving stability at idle and exhaust emission.

The air-fuel ratio immediately after the idle is established is strongly influenced by the operating state before the idle is established. For example, in idle after deceleration, the adhering fuel in the port is sucked into the cylinder, so that the air-fuel ratio is temporarily set immediately after the idle is established. However, if the air-fuel ratio learning value is calculated after idling after warming up, the learning value is not stable. However, in the third invention, after the idling state, Until the predetermined calculation cycle of the air-fuel ratio feedback correction coefficient elapses, the air-fuel ratio learning value at the time of idling after warm-up is not calculated, so that the learning value becomes stable.

In the fourth aspect of the present invention, the update coefficient used for calculating the air-fuel ratio learning value at the time of idling after warm-up is used for all cylinders of the air-fuel ratio of the specific cylinder for which air-fuel ratio feedback control is being performed at the time of idling after warm-up. The setting is made in consideration of the ratio to the average air-fuel ratio, for example, when the influence of the air-fuel ratio of the specific cylinder is large, the update coefficient may be set to a small value, so that any cylinder can be selected as the specific cylinder.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, an engine body 1 is provided with a fuel injection valve 7 in an intake passage 8 located downstream of an intake throttle valve 5, and a control unit (abbreviated as C / U in the drawing) 2 Fuel is injected and supplied into the intake air at every predetermined timing so that a predetermined air-fuel ratio is obtained according to the operating condition by the injection signal from the. In this case, the flow rate of fuel supplied to the engine is controlled by volume flow rate, and the flow rate is adjusted by the opening time of the injection valve.

In the control unit 2, the Ref signal and the Pos signal from the crank angle sensor 4, the intake air amount signal from the air flow meter 6, the air-fuel ratio (oxygen concentration) signal from the O ₂ sensor 3 installed in the exhaust passage 8, Further, an engine cooling water temperature signal or the like from the water temperature sensor 11 is input, and the control unit 2 controls the air-fuel ratio based on these signals.

In this air-fuel ratio control, the basic injection pulse width Tp is set to Tp = k from the intake air amount Q and the engine speed Ne.
The calculation is performed by the formula × Q / Ne (where k is a constant), and based on this Tp, the air-fuel ratio feedback control is performed when the air-fuel ratio feedback control condition is satisfied during non-idle.

Further, a correction coefficient Ktrm for correcting the air amount detection error is introduced (known), and this Ktrm is set as a parameter of the throttle valve opening which influences the intake pulsation, and this correction coefficient Ktrm is set. The air amount is corrected by multiplying the intake air amount Qa detected by the air flow meter. That is, the air amount Q for calculating Tp is calculated by Q = Qa × Ktrm.

Since the rotation is originally low at the time of idling after warm-up and the feedback constant at the time of non-idling is used, the air-fuel ratio feedback control cycle may become long and the controllability of the air-fuel ratio may deteriorate. If the feedback constant is set to a value smaller than that in the non-idle state as described above, the control cycle of the air-fuel ratio at the time of idling after warming up is further prolonged, and the engine stability at idling after warming up becomes worse.

On the other hand, the air-fuel ratio feedback control is performed only a few times by using the feedback constant when the engine is idle after warming up, and the air-fuel ratio learning value is calculated based on the air-fuel ratio feedback correction coefficient at that time. At the time of idling thereafter, the air-fuel ratio feedback control is stopped only by calculating the fuel injection pulse width using this air-fuel ratio learned value. When the cooling water temperature or the fuel temperature rises temporarily, the required value for the above Ktrm differs due to the rise of the cooling water temperature, or the fuel density decreases due to the rise of the fuel temperature, and the fuel mass supplied from the injection valve changes. May occur, and the air-fuel ratio may gradually change and deviate from the theoretical mixture ratio.In this case, the stability of the engine Not only Nau, conversion performance of the catalyst deteriorates, the exhaust emission is deteriorated particularly decreases its When after idle is air amount increased starting such catalytic conversion performance significantly.

In order to cope with this, the present invention performs air-fuel ratio feedback control and air-fuel ratio learning in the non-idle state using the feedback constant in the non-idle state only in a specific cylinder during warm-up idle, while the remaining cylinders With respect to, the air-fuel ratio feedback correction coefficient is clamped to a predetermined value during idle after warm-up, and the fuel injection pulse width for the remaining cylinders is calculated using the air-fuel ratio learning value calculated for the specific cylinder.

The contents of this control executed by the control unit 2 will be described with reference to the following flow chart.

First, the flow chart of FIG. 2 is for calculating an air-fuel ratio feedback (abbreviated as F / B in the figure) correction coefficient, and a Ref signal (a crank angle sensor when each cylinder reaches a predetermined crank angle). Reference signal output by 4: crank angle 18 in the case of a 4-cylinder engine
It occurs every 0).

In STEP-1, the engine speed Ne, the basic injection pulse width Tp, and the cooling water temperature Tw are checked to see if the air-fuel ratio feedback control condition is satisfied. The flow ends. The case where the air-fuel ratio feedback control condition is not satisfied is when the engine is started, when the water temperature is low, or the like. Therefore, the air-fuel ratio feedback control condition is satisfied during idling after warm-up.

When the air-fuel ratio feedback control condition is satisfied, in STEP-2, it is checked from the signal from the idle switch whether it is in the idle state (abbreviated as Idle in the figure). If it is not idle, STEP-7, -8 Then, the air-fuel ratio feedback correction coefficient α at the time of non-idling and the air-fuel ratio learning value αm at the time of non-idling are calculated in the same manner as in the conventional case, and the flow of FIG. 2 ends. Since the air-fuel ratio feedback control is proportional-integral control, the feedback constant is proportional P and integral I.

In the idle state, the process proceeds to STEP-3, and it is checked whether the calculation of the air-fuel ratio learning value in the X cycle has ended after the idle state. If the X cycle has not elapsed, it is the same as in the non-idle state. 2 to end the flow of FIG. 2.

Here, the reason why the process does not proceed to STEP-4 and thereafter until the X period elapses after the idle state is set is as follows. The air-fuel ratio immediately after the idling is strongly affected by the operating condition before the idling is established.For example, during idling after deceleration, the adhering fuel in the port is sucked into the cylinder, so the air-fuel ratio is temporarily enriched immediately after the idling is established. I have something to do. Therefore, the period until the air-fuel ratio becomes stable after the idling is established is given in the calculation period of the air-fuel ratio feedback correction coefficient (this is the X period), and the normal air-fuel ratio feedback control is performed for a while to stabilize the air-fuel ratio learning value.

The value of X depends on the type of engine,
For example, a large value may be set when the air-fuel ratio is not stable immediately after idling due to a large amount of adhered fuel in the port, and conversely, a small value may be set when the air-fuel ratio is easy to stabilize.

In STEP-4, it is checked whether the cylinder is a specific cylinder. The specific cylinder is one cylinder (for example, the first cylinder) that performs the air-fuel ratio feedback control during idling.

When it is not the specific cylinder but the remaining cylinders, S
Proceeding to TEP-9, the value of the air-fuel ratio feedback correction coefficient α for the remaining cylinders is clamped to 1 (that is, the air-fuel ratio feedback control is not performed), and the flow of FIG. 2 ends.

If it is a specific cylinder, the process proceeds to STEP-5 and -6 to calculate the air-fuel ratio feedback correction coefficient α at the time of idling after warming up for the specific cylinder and to calculate the air-fuel ratio learning value αm at the time of idling after warming up. Perform calculations and.

The air-fuel ratio feedback control and the air-fuel ratio learning at the time of idling after warm-up are basically the same as the air-fuel ratio feedback control and the air-fuel ratio learning at the time of non-idling, and the feedback constant at the time of non-idling is used as it is. The same thing is used for α and αm.

First, the calculation of the air-fuel ratio feedback correction coefficient α at the time of idling after warming up for a specific cylinder will be described with reference to the flowchart of FIG.

In STEP-1 of FIG. 3, the output of the O ₂ sensor (abbreviated as O 2 / S in the figure) is compared with the slice level VSL for determining rich or lean. In addition, in order to detect the exhaust air-fuel ratio when burning in a specific cylinder, the output of the O ₂ sensor used here is read in the exhaust stroke of the specific cylinder.

When the O ₂ sensor output is larger than VSL, the process proceeds to STEP-2, where the previous O ₂ sensor output and VS are compared.
Compare L. If the previous O ₂ sensor output is larger than VSL, go to STEP-3 and -4.
_{2 If the} sensor output is smaller, STEP-5,
Go to -6. That is, what flows to STEP-3 and -4 is when the air-fuel ratio of this time is rich and the air-fuel ratio of the previous time is rich (when the rich state continues), or STEP-
The flow to 5 and -6 is the moment when the air-fuel ratio is reversed from lean to rich. Therefore, in STEP-3 and -4, the integral I, which is the feedback constant, has a predetermined value -I _0.
(I ₀ > 0) is set to 0 in the proportional component P which is another feedback constant, and STEP-5 and -6
Then, the integral component I is set to 0 and the proportional component P is set to a predetermined value −Pr (Pr>
0) respectively.

Similarly, if the output of the O ₂ sensor is smaller than VSL in STEP-1, the process proceeds to STEP-9 and S
Similar to TEP-2, the previous O ₂ sensor output is compared with VSL. If the previous O ₂ sensor output is smaller, go to STEP-13. If the previous O ₂ sensor output is greater, go to STEP-10. move on. That is, STE
P-13 and -14 flow when the lean state continues, and STEP-10 and -11 flow at the moment when the air-fuel ratio changes from rich to lean. Therefore, in STEP-13 and -14, the integrated value I is set to the predetermined value I _0.
, 0 in proportional P, and STEP-1
At 0 and -11, 0 is set for the integral P and a predetermined value Pl is set for the proportional P.
(Pl> 0) respectively.

On the other hand, since the air-fuel ratio feedback correction coefficient α takes a maximum value at the moment when the air-fuel ratio is changed from lean to rich, in STEP-7, α at this time is stored in the memory as a maximum value αmax, and from rich, Since the air-fuel ratio feedback correction coefficient α takes a minimum value at the moment of lean reversal, in STEP-12 α at this time is stored in the memory as a minimum value αmin. At the time of reversal, again in STEP-8, the maximum value αmax and the minimum value αmi
After calculating the mean value αmean with n, this is also stored in memory. , STEP-15, integral I and proportional P
Is added to the previous air-fuel ratio feedback correction coefficient α to update the air-fuel ratio feedback correction coefficient α, and the flow of FIG. 3 ends.

Next, the air-fuel ratio learning value α during idling after warm-up
The calculation of m will be described with reference to the flowchart of FIG.

In STEP-1 of FIG. 4, the learning condition is satisfied based on the engine operating condition. When the learning condition is not satisfied, the flow of FIG. 4 is terminated.

When the learning condition is satisfied, STEP-2
The average value αmean of the air-fuel ratio feedback correction coefficient stored in the memory is read by, the update coefficient K (0 ≦ K ≦ 1) used to update the learning value is calculated in STEP-3, and the warm-up is performed in STEP-4. The air-fuel ratio learning value αm at the time of idling after the aircraft is αm = αm (previous) + K · (αmean-1) (1) where αm (previous): is updated by the equation of previous αm, and the flow of FIG. 4 is changed. finish.

Since the control center value of the air-fuel ratio feedback correction coefficient α is 1.0 even after idling after warming up, 1-α
The value of mean is an error amount of the air-fuel ratio learning value αm after idling after warming up, and according to the equation (1), the previous value is rewritten by a value obtained by multiplying the error amount of αm by the update coefficient K. Needless to say, the learning value αm is backed up even after the engine is stopped.

The value of K is set in consideration of the ratio of the air-fuel ratio of the specific cylinder for which the air-fuel ratio feedback control is performed at the time of idling after warm-up to the average air-fuel ratio for all cylinders. For example, when the influence of the air-fuel ratio of the specific cylinder is large, K may be set to a small value.

When the post-warm-up idle air-fuel ratio learning value αm common to all cylinders is updated in this way, the flow returns to FIG.
The flow chart of is ended.

The flowchart of FIG. 5 is for calculating the fuel injection pulse width Ti, which is also executed in a cycle of 10 ms. In STEP-1, the basic injection pulse width Tp with which a predetermined air-fuel ratio is obtained is obtained by multiplying Q / Ne by a constant k and a correction coefficient Ktrm for correcting the air amount detection error, and in STEP-2, the fuel injection is performed. The ejection pulse width Ti is calculated by the following formula: Ti = Tp × TFBYA × (α + αm−1) × 2 + Ts (2), and the flow of FIG. 5 ends.

In the equation (2), TFBYA is the target fuel-air ratio, which becomes 1 during idling after warm-up. Ts is a correction amount for correcting the valve opening delay of the injection valve due to the voltage drop.

Since Ti in the equation (2) is a general equation, it is as follows when it is written separately for the specific cylinder and the remaining cylinders at the time of idling after warming up. In other words, every time the engine becomes idle after warm-up, the air-fuel ratio feedback control is performed only in the specific cylinder, and the air-fuel ratio learning value calculated from the air-fuel ratio feedback correction coefficient obtained for the specific cylinder is used in common for all cylinders. Be done.

Specific cylinder: Ti = Tp × (α + αm−1) × 2 + Ts (3) Remaining cylinders: Ti = Tp × (1 + αm−1) × 2 + Ts = Tp × αm × 2 + Ts (4) Control unit 2 Internally, the value of Ti obtained in this way is written in the output register, and when the injection timing for the specific cylinder comes, the drive signal corresponding to the Ti of the formula (3) is applied to the injection valve of the specific cylinder and the remaining At the injection timing for the cylinders, a drive signal corresponding to Ti in equation (4) is output to the injection valves of the remaining cylinders, and fuel injection is performed sequentially (STEP- in FIG. 6).
1). The process of FIG. 6 is specifically performed in synchronization with the Ref signal.

Now, the operation of the present invention will be described.

As described above, the correction coefficient of the correction coefficient for correcting the air amount detection error is temporarily increased immediately after the idling, such as when the running state is changed to the idling state. Even when a phenomenon such as a different required value or a change in the supplied fuel mass occurs and the air-fuel ratio gradually changes and deviates from the stoichiometric mixture ratio, the present invention relates to a specific cylinder during idling after warm-up. Since the air-fuel ratio feedback control is always performed, the air-fuel ratio during idling after warm-up is maintained near the stoichiometric air-fuel ratio. Even if the air-fuel ratio deviates to the lean side due to a temporary increase in the cooling water temperature or the fuel temperature immediately after idling, α is 1.0 for the specific cylinder in order to return the air-fuel ratio to the rich side.
Therefore, the fuel amount is increased for a specific cylinder, and the average air-fuel ratios of all the cylinders are returned to near the stoichiometric air-fuel ratio.

Further, although the air-fuel ratio of the specific cylinder changes periodically according to the air-fuel ratio feedback correction coefficient α of the specific cylinder, it is not calculated in the post-warm idle air-fuel ratio feedback correction coefficient α of the specific cylinder. Since the same feedback constants used for air-fuel ratio feedback control during idling are used, control for air-fuel ratio feedback control when the air-fuel ratio control cycle is non-idle for both the air-fuel ratio of a specific cylinder and the average air-fuel ratio of all cylinders It becomes almost the same as the cycle, and the control cycle does not become longer as in the conventional example (see FIG. 7). In other words, since the lean period during idling does not become long, combustion instability does not occur.

On the other hand, the post-warm idle air-fuel ratio learning value αm common to all cylinders is calculated from the post-warm idle air-fuel ratio feedback correction coefficient α for the specific cylinder, and this air-fuel ratio learning value αm is calculated for the remaining cylinders. Since it is used to set the fuel injection pulse width during idle after warm-up, the air-fuel ratio for the remaining cylinders is constant near the theoretical air-fuel ratio,
Combustion stability is improved.

Further, since the average air-fuel ratios of all the cylinders are almost the theoretical mixing ratio, the conversion performance of the three-way catalyst will not be impaired.

It should be noted that which cylinder is selected as the specific cylinder can be dealt with by appropriately setting the above-mentioned update coefficient K. Furthermore, when a three-way catalyst is provided independently for each bank like a V-type engine, it is necessary to select a specific cylinder independently for each bank.

[0062]

According to the first aspect of the present invention, the stoichiometric air-fuel ratio can be maintained without causing the engine torque fluctuations associated with the air-fuel ratio feedback control, which has the effect of improving the stability at idle and exhaust emission. To be

According to the second aspect of the invention, even in the V-type engine, the stoichiometric air-fuel ratio can be maintained without causing engine torque fluctuations associated with the air-fuel ratio feedback control, thereby improving stability at idle and exhaust emission. The effect is obtained.

In the third aspect of the present invention, the adhering fuel in the port is sucked into the cylinder, so that the air-fuel ratio is temporarily enriched immediately after the idling is established. It is possible to avoid instability of the learning value due to the calculation of.

In the fourth invention, any cylinder can be selected as the specific cylinder.

[Brief description of drawings]

FIG. 1 is a control system diagram of an embodiment.

FIG. 2 is a flowchart for explaining calculation of an air-fuel ratio feedback correction coefficient α.

FIG. 3 is a flowchart for explaining calculation of an air-fuel ratio feedback correction coefficient α for a specific cylinder at the time of idling after warm-up.

FIG. 4 is a flowchart for explaining calculation of an air-fuel ratio learning value αm during idle after warm-up, which is common to all cylinders.

FIG. 5 is a flowchart for explaining calculation of a fuel injection pulse width Ti.

FIG. 6 is a flowchart executed in synchronization with injection timing.

FIG. 7 is a waveform diagram for explaining air-fuel ratio feedback control at the time of idling after warm-up.

FIG. 8 is a diagram corresponding to claims of the first invention.

[Explanation of symbols]

1 Engine Main Body 2 Control Unit 3 O ₂ Sensor 4 Crank Angle Sensor 6 Air Flow Meter 7 Fuel Injection Valve (Fuel Supply Means) 11 Water Temperature Sensor 21 Basic Injection Amount Calculation Means 22 Warm Up Idle Judgment Means 23 Cylinder Judgment Means 24 Air-Fuel Ratio Feedback correction coefficient calculation / clamping means 25 Air-fuel ratio learning value calculation means 26 Fuel injection amount calculation means 27 Fuel supply means

Claims (4)

[Claims] 1. A means for calculating a basic injection amount according to an operating condition, a means for determining whether or not the engine is in a post-warm idle state, a means for determining which cylinder it is, and a specific cylinder based on these determination results. Means for calculating the air-fuel ratio feedback correction coefficient during idle after warm-up using the feedback constant during non-idle, and clamping the air-fuel ratio feedback correction coefficient during idle after warm-up for the remaining cylinders to a predetermined value A means for calculating an air-fuel ratio learning value at the time of idling after warm-up based on the air-fuel ratio feedback correction coefficient for the specific cylinder; and for the specific cylinder, the air-fuel ratio feedback correction coefficient and the air-fuel ratio feedback correction coefficient calculated for the specific cylinder. The fuel injection amount is corrected by correcting the basic injection amount with the air-fuel ratio learning value, and the remaining cylinder is set to the remaining cylinder. Means for correcting the basic injection amount by the clamped air-fuel ratio feedback correction coefficient and the air-fuel ratio learning value, and calculating the fuel injection amount, and supplying the calculated fuel injection amount to the corresponding cylinder. And an air-fuel ratio control device for an engine. 2. The air-fuel ratio control device for an engine according to claim 1, wherein the specific cylinder is independently selected for each bank in a V-type engine in which a three-way catalyst is provided independently for each bank. 3. The air-fuel ratio learning value at the time of idling after warm-up is not calculated until a predetermined calculation cycle of the air-fuel ratio feedback correction coefficient elapses after the idling state. Alternatively, the air-fuel ratio control device for the engine according to item 2. 4. The update coefficient used in the calculation of the air-fuel ratio learning value at the time of idling after warming up is compared with the average air-fuel ratio for all cylinders of the air-fuel ratio of the specific cylinder for which air-fuel ratio feedback control is being performed at the time of idling after warming up. The air-fuel ratio control device for an engine according to any one of claims 1 to 3, wherein the larger the ratio is, the smaller the value is set.