JP4254520B2 - Engine air-fuel ratio control device - Google Patents

Description

  The present invention relates to an air-fuel ratio control apparatus for an engine that operates at a rich air-fuel ratio immediately after startup and thereafter performs air-fuel ratio feedback control.

Patent Document 1 discloses that an air-fuel ratio sensor is set with a target air-fuel ratio correction coefficient TFBYA that is set so as to enrich the air-fuel ratio immediately after startup and gradually converge the air-fuel ratio to stoichiometric with time, and an air-fuel ratio feedback control condition. In the engine air-fuel ratio control apparatus for calculating and controlling the fuel injection amount using the air-fuel ratio feedback correction coefficient ALPHA set so as to converge the air-fuel ratio to stoichiometric based on the signal from After the detection, it is disclosed that the increment of the fuel injection amount by the target air-fuel ratio correction coefficient TFBYA is set to 0, and the increase is added to the air-fuel ratio feedback correction coefficient ALPHA, and then the control proceeds to the air-fuel ratio feedback control. ing.
JP 2001-23479A

  When the fuel is cold, the vaporization of the fuel is poor, the wall flow increases, and the fuel sucked into the cylinder is insufficient. Therefore, the air-fuel ratio immediately after the start is enriched by the target air-fuel ratio correction coefficient TFBYA to stabilize the combustion, It gradually converges to stoichiometric with the passage of time thereafter. Then, if the amount of increase by the target air-fuel ratio correction coefficient TFBYA remains at the start of the air-fuel ratio feedback control, the amount of increase will be cut, but then the air-fuel ratio will suddenly change to the lean side. Since a torque step is generated and the drivability is deteriorated, the cut amount is added to the air-fuel ratio feedback correction coefficient ALPHA.

  However, since the target air-fuel ratio correction coefficient TFBYA is usually adapted to heavy fuel with poor volatility, the air-fuel ratio immediately after starting is richer in the case of fuel with relatively good volatility such as light fuel. Therefore, if the increased amount is added to the air-fuel ratio feedback correction coefficient ALPHA, convergence to the stoichiometry is delayed, resulting in a problem of emission and fuel consumption deterioration.

In addition, depending on the temperature conditions at start-up and the effects of component variations, the actual air-fuel ratio may be close to the stoichiometry even if the target air-fuel ratio correction coefficient TFBYA is to be enriched. If the operation is started, the air-fuel ratio may be oscillated, and the drivability may be deteriorated.
The present invention has been made paying attention to such a problem, and an object of the present invention is to quickly converge the air-fuel ratio immediately after starting to stoichiometric while suppressing deterioration in drivability.

  For this reason, the air-fuel ratio control apparatus for an engine according to the present invention detects the activity of the air-fuel ratio sensor and the first control for cutting off the amount of increase by the target air-fuel ratio correction coefficient when the activity of the air-fuel ratio sensor is detected. After that, when the second control for decreasing the target air-fuel ratio correction coefficient with the passage of time is selectable, and the output of the air-fuel ratio sensor at the time when the activity is detected is in the rich region, In the first control, the second control is selected when the output of the air-fuel ratio sensor is in the stoichiometric range.

  According to the air-fuel ratio control apparatus for an engine according to the present invention, the air-fuel ratio control method immediately after start-up is switched according to the air-fuel ratio at the time when the activation of the air-fuel ratio sensor is detected, so that the deterioration in drivability is minimized. While suppressing to the limit, the convergence to stoichiometry can be improved, and the emission and fuel consumption can be improved.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system diagram of an engine (internal combustion engine) showing an embodiment of the present invention.
A combustion chamber of each cylinder of the engine 1 includes an air cleaner 2, an intake duct 3, a throttle valve 4.
And air is sucked through the intake manifold 5. The intake air amount Qa is controlled according to the opening degree of the throttle valve 4. Each branch portion of the intake manifold 5 is provided with a fuel injection valve 6 for each cylinder. However, the fuel injection valve 6 may be disposed directly in the combustion chamber.

  The fuel injection valve 6 is an electromagnetic fuel injection valve (injector) that opens when the solenoid is energized and closes when the energization is stopped, and a drive pulse signal from an engine control unit (hereinafter referred to as ECU) 12 described later. The fuel is energized to open the valve, and the fuel is pumped from a fuel pump (not shown) and adjusted to a predetermined pressure by a pressure regulator. Therefore, the fuel injection amount is controlled by the pulse width of the drive pulse signal.

Each combustion chamber of the engine 1 is provided with a spark plug 7, which sparks and ignites and burns the air-fuel mixture.
Exhaust gas from each combustion chamber of the engine 1 is discharged through an exhaust manifold 8. Further, an EGR passage 9 is led out from the exhaust manifold 8, whereby a part of the exhaust is recirculated to the intake manifold 5 via the EGR valve 10.

On the other hand, an exhaust purification catalyst 11 is provided in the exhaust passage so as to be positioned immediately below the exhaust manifold 8.
The ECU 12 includes a microcomputer that includes a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like, receives input signals from various sensors, performs arithmetic processing as described later, and performs fuel injection. 6 and the operation of the spark plug 7 and the like are controlled.

The various sensors include a crank angle sensor 13 that can detect the engine speed Ne together with the crank angle based on the crankshaft or camshaft rotation of the engine 1, an air flow meter 14 that detects the intake air amount Qa in the intake duct 3, and a throttle valve. 4 includes a throttle sensor 15 (including an idle switch that is turned on when the throttle valve 4 is fully closed), a water temperature sensor 16 that detects the cooling water temperature Tw of the engine 1, and an exhaust manifold 8. O ₂ sensor 17 as an air-fuel ratio sensor for outputting a signal corresponding to a rich-lean exhaust air-fuel ratio, the O ₂ sensor near the exhaust temperature (or the temperature of the O ₂ sensor) such as a temperature sensor 18 for detecting the tO ₂ Is provided. The O ₂ sensor 17 has a built-in heater, and early activation can be achieved by energizing the heater from the start and increasing the element temperature. In place of the O ₂ sensor, an A / F sensor whose output changes linearly with respect to the air-fuel ratio may be used. An operation signal from the start switch 19 and the like is further input to the ECU 12.

Next, the process performed by ECU12 is demonstrated using a flowchart.
FIG. 2 is a flowchart of the fuel injection amount calculation routine, which is executed in time synchronization or rotation synchronization after the engine is started (after the start switch is turned ON → OFF). Note that the fuel injection amount at the start is calculated by another method.
In S1, the intake air amount Qa detected by the air flow meter and the engine speed Ne detected by the crank angle sensor are read. The intake air amount Qa is smoothed based on the detection signal, but is omitted in the flow.

In S2, a basic fuel injection amount (basic injection pulse width) Tp is calculated from the read intake air amount Qa and the engine speed Ne by the following equation.
Tp = K × Qa / Ne However, K is a constant. In S3, a target air-fuel ratio correction coefficient (post-startup air-fuel ratio enrichment correction coefficient) TFBYA and an air-fuel ratio feedback correction coefficient ALPHA set as described later are read and The final fuel injection amount (injection pulse width) Ti is calculated.

Ti = Tp × TFBYA × ALPHA
Note that the reference value of the target air-fuel ratio correction coefficient TFBYA and the air-fuel ratio feedback correction coefficient ALPHA is 1. In addition, the calculation of the fuel injection amount (injection pulse width) Ti includes transient correction based on the change in the throttle opening TVO, addition of the invalid injection pulse width based on the battery voltage, etc., but is omitted here. To do.

When the fuel injection amount Ti is calculated in this way, a drive pulse signal having a pulse width corresponding to Ti is output to the fuel injection valve 6 at a predetermined timing for each cylinder in synchronism with engine rotation. Is done.
FIG. 3 is a flowchart showing air-fuel ratio control after startup. Here, the target air-fuel ratio correction coefficient (post-startup air-fuel ratio enrichment correction coefficient) TFBYA and the air-fuel ratio feedback correction coefficient ALPHA are set.

In S11, the water temperature Tw at the time of start is detected, and the initial value KAS of the fuel increase rate after the start (hereinafter referred to as the increase rate after start) and the subsequent unit decrease rate ΔK are set accordingly (next) See formula).
KAS = f1 (Tw)
ΔK = f2 (Tw)
Specifically, the initial value KAS of the post-starting increase rate is set to be larger as the starting water temperature Tw is lower, and the unit decreasing rate ΔK is set to be smaller so that the amount of water decreases over time as the starting water temperature Tw is lower. .

In S12, the target air-fuel ratio correction coefficient TFBYA is set based on the post-startup increase rate KAS, and the air-fuel ratio feedback correction coefficient ALPHA is fixed to 1 (see the following equation).
TFBYA = 1 + KAS
ALPHA = 1
The set value here is used to calculate the first fuel injection amount Ti after start-up, and the air-fuel ratio is enriched by the target air-fuel ratio correction coefficient TFBYA.

  Thereafter, in S13, the post-start increase rate KAS is decreased by the unit decrease rate ΔK by time synchronization (KAS = KAS−ΔK), and the target air-fuel ratio correction coefficient TFBYA is set based on the decreased post-start increase rate KAS. By calculating (TFBYA = 1 + KAS), the target air-fuel ratio correction coefficient TFBYA is decreased. By setting the target air-fuel ratio correction coefficient TFBYA as described above, it is possible to enrich the air-fuel ratio immediately after start-up and gradually converge the air-fuel ratio to stoichiometric with the passage of time thereafter.

In S14, it is determined whether or not the exhaust gas temperature (O ₂ sensor temperature) TO ₂ exceeds a predetermined activation determination level SL. TO ₂ returns to S13 if less activity determination level SL, to reduce the target air-fuel ratio correction coefficient TFBYA. On the other hand, if TO ₂ exceeds the activity determination level SL, it is determined that the activity of the O ₂ sensor has been detected, and the process proceeds from S 14 to S 15. Here, the activity determination is performed based on the exhaust temperature (the temperature of the O ₂ sensor), but other methods (for example, activity determination based on the element resistance value of the O ₂ sensor) may be used. Good.

In S15, it is determined whether or not the output voltage VO ₂ of the O ₂ sensor is in a predetermined stoichiometric region (VO _SL1 ≧ VO ₂ ≧ VO _SL2 ). If the output voltage VO ₂ is in the stoichiometric region, the air-fuel ratio is in the vicinity of the stoichiometric when the O ₂ sensor is active, and the process proceeds to S16. If not, the process proceeds to S17. Note that VO _SL1 used here is a value determined in advance as a rich slice level, and VO _SL2 (<VO _SL1 ) is a value determined in advance as a lean slice level.

  In S16, it is determined whether or not the post-startup increase rate KAS has become 0 (whether or not the target air-fuel ratio correction coefficient TFBYA has become 1). If the increased amount after starting KAS = 0 (TFBYA = 1), the routine proceeds to normal air-fuel ratio feedback control (λ control) (see FIG. 4). At this time, the target air-fuel ratio correction coefficient TFBYA = 1 and the air-fuel ratio feedback correction coefficient ALPHA (initial value) = 1. On the other hand, if KAS> 0 (TFBYA> 1), the process returns to S13, and subsequently TFBYA is decreased.

As a result, even if the activity of the O ₂ sensor is detected (even if the start of the air-fuel ratio feedback control is permitted), if the air-fuel ratio at that time is near the stoichiometry, the air-fuel ratio feedback control is immediately started. The air-fuel ratio feedback control is started after waiting for the increase rate KAS after starting to become zero. However, even if the air-fuel ratio at the time of activation of the O ₂ sensor is near the stoichiometry, when the output voltage of the O ₂ sensor deviates from the stoichiometric region until the correction factor KAS after the start becomes zero after that, The process proceeds from S15 to S17, and the process described later is performed.

In S17, the output voltage VO ₂ of the O ₂ sensor (it is in the rich region) exceeding the rich side slice level VO _SL1 determines whether. Air-fuel ratio at the time of activity of the O ₂ sensor in the case of YES advances to S18 as being rich, and if NO, it proceeds to S19 as the air-fuel ratio at the time of activity of the O ₂ sensor is lean.
In S18, the amount of increase (KAS) by the target air-fuel ratio correction coefficient TFBYA is cut (set to 0 here), and then the routine proceeds to normal air-fuel ratio feedback control (λ control). Therefore, at this time, the target air-fuel ratio correction coefficient TFBYA = 1 and the air-fuel ratio feedback correction coefficient ALPHA (initial value) = 1.

  In S19, the amount of increase (KAS) by the target air-fuel ratio correction coefficient TFBYA is cut (set to 0 here), and the amount of increase (KAS) is added to the air-fuel ratio feedback correction coefficient ALPHA, and then the normal air-fuel ratio Transition to feedback control (λ control). Accordingly, at this time, the target air-fuel ratio correction coefficient TFBYA = 1 and the air-fuel ratio feedback correction coefficient ALPHA (initial value) = 1 + KAS.

Thus, in the case when O ₂ sensor activation air-fuel ratio is rich, and cut increment by the target air-fuel ratio correction coefficient TFBYA the (KAS), immediately the air-fuel ratio feedback control is started, the air-fuel ratio at the time of the O ₂ sensor activity Is lean, the amount of increase (KAS) by the target air-fuel ratio correction coefficient TFBYA is cut and the amount of increase (KAS) is added to the air-fuel ratio feedback correction coefficient ALPHA, and the air-fuel ratio feedback control is immediately started. Will be.

FIG. 4 is a flowchart of normal air-fuel ratio feedback control (normal λ control).
In S21, lean / rich is determined based on the output voltage of the O ₂ sensor. If lean, the process proceeds to S22, and if rich, the process proceeds to S25.
In S22, it is determined whether or not the inversion from rich to lean (previous rich). If the inversion from rich to lean is performed, the process proceeds to S23, and if the lean state is continuing, the process proceeds to S24.

In S23, the air-fuel ratio feedback correction coefficient ALPHA is increased by a relatively large proportional proportion (proportional constant) P and updated (ALPHA = ALPHA + P).
In S24, the air-fuel ratio feedback correction coefficient ALPHA is increased by a minute integral (integral constant) I and updated (ALPHA = ALPHA + I).
In S25, it is determined whether or not the reversal from lean to rich (previous lean). If the inversion from lean to rich is performed, the process proceeds to S26, and if the rich state is continued, the process proceeds to S27.

In S26, the air-fuel ratio feedback correction coefficient ALPHA is decreased and updated by a proportionally set proportional amount P (ALPHA = ALPHA-P).
In S27, the air-fuel ratio feedback correction coefficient ALPHA is reduced by a minute integral I and updated (ALPHA = ALPHA-I).
FIG. 5 is a time chart in the present embodiment. 5, the case where the air-fuel ratio at the time of the O ₂ sensor activation is rich solid, the air-fuel ratio at the time of the O ₂ sensor activity shows the case of near stoichiometric in broken lines.

By setting the target air-fuel ratio correction coefficient TFBYA, control is performed so that the air-fuel ratio is enriched immediately after start-up and the air-fuel ratio is gradually converged to stoichiometric with the passage of time thereafter.
Here, when the activity of the O ₂ sensor is detected (time t1), as indicated by the solid line, if the output voltage VO ₂ of the O ₂ sensor exceeds the rich side slice level VO _SL1 (that is, the air-fuel ratio becomes smaller). When rich, the amount of increase (KAS) by the target air-fuel ratio correction coefficient TFBYA is set to 0, the air-fuel ratio feedback correction coefficient ALPHA is set to 1, and air-fuel ratio feedback control is immediately started.

As described above, when the air-fuel ratio is rich at the time when the activity of the O ₂ sensor is detected, the air-fuel ratio feedback control is immediately started, so that the convergence to the stoichiometry can be accelerated and the emission and fuel consumption can be improved.
On the other hand, when the activity of the O ₂ sensor is detected (time t1), as shown by the broken line, if the output voltage VO ₂ of the O ₂ sensor is between the rich side slice level VO _SL1 and the lean side slice level VOSL2 ( That is, when the air-fuel ratio is in the vicinity of stoichiometry, the target air-fuel ratio correction coefficient TFBYA is continuously decreased, and the air-fuel ratio feedback control is started when the increase (KAS) becomes 0 (time tb).

When the air-fuel ratio when the O ₂ sensor is active is close to the stoichiometry, there is no adverse effect on the emission and drivability even if it is left as it is. However, when the air-fuel ratio feedback control is started, the air-fuel ratio is converged to stoichiometric. However, since the actual air-fuel ratio is vibrated by the feedback control, the drivability may be deteriorated. Therefore, when the air-fuel ratio is already in the vicinity of the stoichiometry, the start of the air-fuel ratio feedback control is intentionally delayed, that is, waiting for the amount of increase (KAS) by the target air-fuel ratio correction coefficient TFBYA to become zero. Thus, the air-fuel ratio feedback control is started to prevent the deterioration of drivability due to the vibration of the air-fuel ratio.

According to this embodiment, when the air-fuel ratio is rich when the activity of the O ₂ sensor is detected, the increase (KAS) by the target air-fuel ratio correction coefficient TFBYA is cut and the air-fuel ratio feedback control is started. _2. When the air-fuel ratio at the time of sensor activation is near the stoichiometric range, the increase amount (KAS) by the target air-fuel ratio correction coefficient TFBYA is decreased with time, and this increase amount (KAS) is close to 0 (0 or almost 0). Since the air-fuel ratio feedback control is started after that, the convergence to the stoichiometry can be accelerated and the emission and fuel consumption can be improved while suppressing deterioration in drivability.

In the above description, when the air-fuel ratio when the O ₂ sensor is active is in the vicinity of stoichiometry, the air-fuel ratio feedback control is started after waiting for the increase (KAS) by the target air-fuel ratio correction coefficient TFBYA to become zero. However, even if KAS is not completely zero, substantially the same effect can be obtained even if the air-fuel ratio feedback control is started when it becomes close to zero.

Further, even when the air-fuel ratio when the O ₂ sensor is active is near the stoichiometry and the increase (KAS) by the target air-fuel ratio correction coefficient TFBYA is decreased with time, the output voltage of the O ₂ sensor is in the middle When (air-fuel ratio) deviates from the stoichiometric range, the amount of increase (KAS) is set to 0, and the air-fuel ratio feedback control is started, so that the air-fuel ratio suddenly changes due to changes in operating conditions and the like. However, the convergence to stoichiometry can be maintained well.

FIG. 6 is a flowchart showing a second embodiment of air-fuel ratio control after startup, and is used instead of FIG.
In FIG. 6, S31 to S38 and S40 are the same as S11 to S18 and S20 in FIG.
In S38, the increase (KAS) by the target air-fuel ratio correction coefficient TFBYA is cut (set to 0 in this case), and then the process proceeds to S39.

In S39, it is determined whether or not the output voltage VO ₂ of the O ₂ sensor has reached the feedback control start determination slice level VO _SL3 (<VO _SL1 ). When the output voltage of the O ₂ sensor reaches VO _SL3 , the routine _proceeds to normal air-fuel ratio feedback control (λ control) (see FIG. 4). At this time, the target air-fuel ratio correction coefficient TFBYA = 1 and the air-fuel ratio feedback correction coefficient ALPHA (initial value) = 1.

FIG. 7 is a time chart when the second embodiment is used as the air-fuel ratio control after starting. Similar to FIG. 5, the case where the air-fuel ratio at the time of the O ₂ sensor activation is rich solid, the air-fuel ratio at the time of the O ₂ sensor activity shows the case of near stoichiometric in broken lines.
By setting the target air-fuel ratio correction coefficient TFBYA, control is performed so that the air-fuel ratio is enriched immediately after start-up and the air-fuel ratio is gradually converged to stoichiometric with the passage of time thereafter.

Here, when the activity of the O ₂ sensor is detected (time t1), as indicated by the solid line, if the output voltage VO ₂ of the O ₂ sensor exceeds the rich side slice level VO _SL1 (that is, the air-fuel ratio becomes smaller). When rich, the amount of increase (KAS) by the target air-fuel ratio correction coefficient TFBYA is set to 0, but unlike the first embodiment (see FIG. 5), at this time (time t1), air-fuel ratio feedback control (λ control) ), The air-fuel ratio feedback control is started after the output voltage VO ₂ of the O ₂ sensor reaches the feedback control start determination slice level VO _SL3 (time ta).

As a result, after the effect of setting the amount of increase (KAS) by the target air-fuel ratio correction coefficient TFBYA to 0 is reflected (waiting for the detection delay), the air-fuel ratio feedback control based on the detected air-fuel ratio (signal from the O ₂ sensor) Therefore, the overcorrection (overcontrol) as shown by the one-dot chain line in the figure can be suppressed to prevent the drivability from deteriorating, and the convergence to the stoichiometry can be accelerated.
On the other hand, when the activity of the O ₂ sensor is detected (time t1), if the output voltage VO ₂ of the O ₂ sensor is between the rich side slice level VO _SL1 and the lean side slice level VO _SL2 (that is, the air-fuel ratio is Subsequently, the target air-fuel ratio correction coefficient TFBYA is decreased, and the air-fuel ratio feedback control is started when the increase (KAS) becomes 0 (time tb).

In this embodiment, the air-fuel ratio feedback control is started when the output voltage of the O ₂ sensor reaches the feedback control start determination slice level VO _SL3 . For example, the increase amount (KAS) is set to 0. After that, the air-fuel ratio feedback control may be started after waiting for the output voltage of the O ₂ sensor to change (decrease) by a predetermined amount or more.
According to this embodiment, compared with the first embodiment (FIG. 3), the air-fuel ratio feedback control is started from the time when the output voltage of the air-fuel ratio sensor reaches the feedback control start determination slice level when the air-fuel ratio is rich. As a result, overshoot due to overcorrection can be suppressed to prevent deterioration in drivability, and convergence to stoichiometry can be accelerated.

FIG. 8 is a flowchart showing a third embodiment of air-fuel ratio control after startup, and is used instead of FIG.
In FIG. 8, S41 to S47 and S51 are the same as S11 to S17 and S20 in FIG.
In S48, the ignition timing advance correction amount ΔIT (= f3 (VO ₂ )) is set according to the output voltage (air-fuel ratio) of the O ₂ sensor. Specifically, the advance correction amount ΔIT is set to be larger as the output voltage of the O ₂ sensor is higher (as the air-fuel ratio is richer).

In S49, the corrected ignition timing is calculated from the basic ignition timing ITbase and the advance angle correction amount ΔIT by the following equation and output to the spark plug 7 (ignition timing retardation correction is performed).
IT = ITbase-ΔIT
The basic ignition timing ITbase is calculated by referring to the basic ignition timing map assigned according to the engine speed Ne and the basic fuel injection amount Tp. In addition, the basic ignition timing ITbase is calculated based on the coolant temperature Tw and the throttle opening TVO, but is omitted here.

In S50, the increase (KAS) by the target air-fuel ratio correction coefficient TFBYA is cut (set to 0 here), and the routine proceeds to normal air-fuel ratio feedback control (λ control). At this time, the target air-fuel ratio correction coefficient TFBYA = 1 and the air-fuel ratio feedback correction coefficient ALPHA (initial value) = 1.
When the air-fuel ratio is rich when the O ₂ sensor is active, air-fuel ratio feedback control is performed. At the start of this air-fuel ratio feedback control, the amount of increase (KAS) by the target air-fuel ratio correction coefficient TFBYA is set to zero. There is a risk that the fuel ratio suddenly changes to the lean side and a torque step occurs. And this torque level | step difference is so large that an air fuel ratio is rich at the time of feedback control start. Therefore, when starting the air-fuel ratio feedback control, the richer the air-fuel ratio, the more the amount of torque step immediately after the start of the air-fuel ratio feedback control is compensated by advancing the ignition timing (correcting the advance angle). Minimize occurrence.

Thereby, immediately after the start, the convergence to the stoichiometric can be accelerated to improve the emission and the fuel consumption, and the occurrence of the torque step immediately after the start of the air-fuel ratio feedback control can be suppressed to the minimum.
In this embodiment, the ignition timing is corrected to advance to suppress the torque step immediately after the start of air-fuel ratio feedback control. However, the start of air-fuel ratio feedback control (switching from open control to feedback control) is performed. ) Other control may be used as long as it compensates the torque decrease at the time. For example, instead of or in addition to the advance correction of the ignition timing, the intake air amount Qa may be corrected to increase. . In this case, the intake air amount is increased as the output voltage of the O ₂ sensor is higher (as the air-fuel ratio is richer).

FIG. 9 is a time chart when the third embodiment is used as the air-fuel ratio control after starting. 5, similarly to FIG. 7, a case where the air-fuel ratio at the time of the O ₂ sensor activation is rich solid, the air-fuel ratio at the time of the O ₂ sensor activity shows the case of near stoichiometric in broken lines.
By setting the target air-fuel ratio correction coefficient TFBYA, control is performed so that the air-fuel ratio is enriched immediately after start-up and the air-fuel ratio is gradually converged to stoichiometric with the passage of time thereafter.

Here, when the activity of the O ₂ sensor is detected (time t1), as indicated by the solid line, if the output voltage VO ₂ of the O ₂ sensor exceeds the rich side slice level VO _SL1 (that is, the air-fuel ratio becomes smaller). When rich, the amount of increase (KAS) by the target air-fuel ratio correction coefficient TFBYA is set to 0, the air-fuel ratio feedback correction coefficient ALPHA is set to 1, and air-fuel ratio feedback control is immediately started. At this time, torque correction control (ignition timing advance correction or / and intake air amount Qa increase correction) that compensates for the torque decrease associated with the start of air-fuel ratio feedback control is also started.

As described above, when the air-fuel ratio is rich at the time when the activity of the O ₂ sensor is detected, the air-fuel ratio feedback control is started immediately and the torque correction control is executed to accelerate the convergence to the stoichiometric emission. In addition, while improving fuel efficiency, it is possible to prevent the deterioration of drivability by suppressing the occurrence of a torque step (torque reduction caused by setting the increase KAS to 0) accompanying the start of air-fuel ratio feedback control.

On the other hand, when the activity of the O ₂ sensor is detected (time t1), as shown by the broken line, if the output voltage VO ₂ of the O ₂ sensor is between the rich side slice level VO _SL1 and the lean side slice level VOSL2 ( That is, when the air-fuel ratio is in the vicinity of stoichiometry, the target air-fuel ratio correction coefficient TFBYA is continuously decreased, and the air-fuel ratio feedback control is started when the increase (KAS) becomes 0 (time tb).

According to this embodiment, torque correction control (ignition timing advance correction, intake air amount increase correction, etc.) is executed at the start of air-fuel ratio feedback control, so that convergence to stoichiometry is accelerated and emissions and fuel consumption are improved. However, it is possible to prevent the deterioration of drivability by suppressing the generation of torque steps accompanying the start of air-fuel ratio feedback control.
In the third embodiment, as in the second embodiment (FIG. 5), when the air-fuel ratio is rich, the output voltage VO ₂ of the O ₂ sensor reaches the feedback control start determination slice level VO _SL3. Air-fuel ratio feedback control may be started. In this way, the amount of torque increase by torque correction control can be made smaller.

1 is a system diagram of an engine showing an embodiment of the present invention. It is a flowchart of a fuel injection amount calculation routine. It is a flowchart which shows 1st Embodiment of the air fuel ratio control after a start. It is a flowchart of an air-fuel ratio feedback control routine. It is a time chart of a 1st embodiment. It is a flowchart which shows 2nd Embodiment of the air fuel ratio control after a start. It is a time chart of a 2nd embodiment. It is a flowchart which shows 3rd Embodiment of the air fuel ratio control after a start. It is a time chart of a 3rd embodiment.

Explanation of symbols

1 ... engine, the throttle valve ... 4,6 ... fuel injection valve, 7 ... spark plug, 12 ... ECU, 17 ... O ₂ sensor

Claims (8)

Immediately after start-up, the air-fuel ratio is enriched, and over time, the air-fuel ratio is gradually converged to the stoichiometric value. In an air-fuel ratio control device for an engine that calculates and controls a fuel injection amount using an air-fuel ratio feedback correction coefficient that is set so as to converge the fuel ratio to stoichiometry,
A first control that cuts off the amount of increase by the target air-fuel ratio correction coefficient when detecting the activity of the air-fuel ratio sensor;
After the activity of the air-fuel ratio sensor is detected, the second control for reducing the target air-fuel ratio correction coefficient over time can be selected.
When the air-fuel ratio sensor activity is detected, the first control is performed when the output of the air-fuel ratio sensor is in a rich region, and the second control is performed when the output of the air-fuel ratio sensor is in a predetermined stoichiometric region. An air-fuel ratio control apparatus for an engine characterized by selecting the control.   When the output of the air-fuel ratio sensor is in a rich region at the time when the activity of the air-fuel ratio sensor is detected, the amount of increase by the target air-fuel ratio correction coefficient is cut and air-fuel ratio feedback control is started. The engine air-fuel ratio control apparatus according to claim 1.   If the output of the air-fuel ratio sensor is in a rich region at the time when the activity of the air-fuel ratio sensor is detected, the amount of increase by the target air-fuel ratio correction coefficient is cut, and then the output of the air-fuel ratio sensor is fed back to a predetermined feedback 2. The air-fuel ratio control apparatus for an engine according to claim 1, wherein the air-fuel ratio feedback control is started after reaching the control start determination slice level.   When the output of the air-fuel ratio sensor is detected and the output of the air-fuel ratio sensor is in a predetermined stoichiometric region, the target air-fuel ratio correction coefficient is decreased with time, and the amount of increase by the target air-fuel ratio correction coefficient is increased. The air-fuel ratio control apparatus for an engine according to any one of claims 1 to 3, wherein the air-fuel ratio feedback control is started after the value becomes close to zero.   While the target air-fuel ratio correction coefficient is being decreased, when the output of the air-fuel ratio sensor deviates from a predetermined stoichiometric range, the increase by the target air-fuel ratio correction coefficient is cut and air-fuel ratio feedback control is started. The engine air-fuel ratio control apparatus according to claim 4, wherein   6. The torque correction control according to claim 2, wherein the air-fuel ratio feedback control is started and torque correction control is performed so as to compensate for a decrease caused by cutting off the increase due to the target air-fuel ratio correction coefficient. An air-fuel ratio control device for an engine according to one of the above.   7. The engine air-fuel ratio control apparatus according to claim 6, wherein the torque correction control sets a correction amount based on an output of the air-fuel ratio sensor at the time when activity is detected. The engine air-fuel ratio control apparatus according to claim 6 or 7, wherein the torque correction control performs at least one of ignition timing advance correction and intake air amount increase correction.

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