JP2006097513A - Air-fuel ratio control device of engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To rapidly converge an air-fuel ratio to a stoichiometric point when an engine is operated at a rich air-fuel ratio after starting and then performs an air-fuel ratio feedback control. <P>SOLUTION: After the activity of an air-fuel ratio sensor is detected, a reducing amount correction factor decreasing with the elapse of time is multiplied by a stability increasing value KSTB of a target air-fuel ratio correcting factor TFBYA to correct the stability increasing value KSTB so as to increase the reducing speed of the stability increasing value KSTB more than a case before the activity is detected while maintaining an air-fuel ratio feedback correction factor ALPHA at a reference value 1. Then, when the output of the air-fuel ratio sensor reaches a stoichiometric equivalent value SST#, the air-fuel ratio feedback control is started. At the starting of the air-fuel ratio feedback control, unburned amount correction value KUB is set based on the stability increasing value KSTB at that time and added to the target air-fuel ratio correction factor TFBYA, and the stability increasing value KSTB is reduced to zero. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an air-fuel ratio control device for an engine, and more particularly to an air-fuel ratio that can be quickly converged to a stoichiometric point when operating at a rich air-fuel ratio immediately after startup and thereafter starting air-fuel ratio feedback control. The present invention relates to a fuel ratio control device.

  The engine air-fuel ratio control device includes a stability increase value KSTB that is set to gradually decrease so as to enrich the air-fuel ratio immediately after startup and then gradually converge the air-fuel ratio to stoichiometric and is corrected by the engine speed and load. Using the target air-fuel ratio correction coefficient TFBYA and the air-fuel ratio feedback correction coefficient ALPHA set so as to converge the air-fuel ratio to stoichiometric based on the signal from the air-fuel ratio sensor under the air-fuel ratio feedback control condition, the fuel injection amount Is calculated and controlled (see Patent Documents 1 and 2).

Here, after detecting the activity of the air-fuel ratio sensor, the stability increase value KSTB in the target air-fuel ratio correction coefficient TFBYA is set to 0, and the decrease (KSTB) is added to the air-fuel ratio feedback correction coefficient ALPHA as an increase. From this, air-fuel ratio feedback control is started, and an unburned component correction value (unburned component equilibrium value) KUB is newly added to the target air-fuel ratio correction coefficient TFBYA. The unburned component correction value KUB is for ensuring stability when heavy fuel is used, and is adapted so that λ = 1 for heavy fuel.
JP-A-9-177580 Japanese Patent Laid-Open No. 10-110645

  However, before the air-fuel ratio sensor is activated, it is richly matched with the stability increase value KSTB to guarantee the air-fuel ratio. When the air-fuel ratio feedback control is started, λ = 1 is set in the air-fuel ratio feedback correction coefficient ALPHA. When the stability increase value KSTB is large due to the restriction due to the gain of the air-fuel ratio feedback control, the air-fuel ratio becomes rich from the start of the air-fuel ratio feedback control until it converges.

Further, the unburned component correction value KUB added after the start of the air-fuel ratio feedback control is adapted with heavy fuel from the viewpoint of ensuring stability, so it becomes rich when light fuel is used, and the air-fuel ratio feedback is increased. The exhaust gas deteriorates until λ = 1 with the correction coefficient ALPHA.
The present invention has been made in view of such a situation, and an object of the present invention is to provide an engine air-fuel ratio control apparatus that can quickly converge an air-fuel ratio to a stoichiometric point.

  Therefore, in the present invention, after detecting the activity of the air-fuel ratio sensor, the stability increase value KSTB is multiplied by the decrease correction coefficient DRTKSTB that decreases with time to correct the stability increase value KSTB. The decrease rate of the property increase value KSTB is made larger than before the detection of the activity, and then the air-fuel ratio feedback control is started when the air-fuel ratio reaches stoichiometry. At the start of the air-fuel ratio feedback control, the unburned fuel correction value KUB is set based on the current stability increase value KSTB and added to the target air-fuel ratio correction coefficient TFBYA. At the same time, the stability increase value KSTB is set to 0. To.

According to the present invention, after detecting the air-fuel ratio activation sensor, the rate of decrease of the stability increase value KSTB is made larger than before the activity detection, so that it does not depend on the gain of the air-fuel ratio feedback control in the normal region. Further, λ = 1 can be set at the upper limit of the drivability requirement.
Further, when the decrease rate of the stability increase value KSTB is increased as compared with that before the activity detection, the stability increase value KSTB is multiplied by the decrease correction coefficient DRTKSTB that decreases with the passage of time. By correcting, even when the rotational load fluctuates during the decrease of the stability increase value KSTB, the stability increase value KSTB including the rotation load correction can be decreased, and both the rotation load correction and the decrease can be achieved. .

  Further, the stability increase value KSTB when the air-fuel ratio reaches stoichiometric changes according to the fuel property, but since this is learned and the unburned component correction value KUB is set, the optimum value according to the fuel property is set. The unburned component correction value KUB can be set, and exhaust is not deteriorated even when light fuel is used.

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.
Air is sucked into the combustion chamber of each cylinder of the engine 1 from the air cleaner 2 through the intake duct 3, the throttle valve 4, and the intake manifold 5. 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 is 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. An air-fuel ratio sensor (O2 sensor) 17 that outputs a signal corresponding to the rich / lean of the exhaust air-fuel ratio is provided. As the air-fuel ratio sensor 16, a wide-area A / F sensor capable of outputting a signal proportional to the change in the air-fuel ratio may be used in addition to a normal O2 sensor. The air-fuel ratio sensor 17 has a built-in heater, and can be activated early by energizing the heater from the start and increasing the element temperature. A signal is also input to the ECU 12 from the start switch 18 and the like.

Next, calculation of the fuel injection amount Ti by the ECU 12 will be described.
The intake air amount Qa detected by the air flow meter 14 and the engine rotational speed Ne detected by the crank angle sensor 13 are read. From the intake air amount Qa and the engine rotational speed Ne, a basic fuel equivalent to stoichiometry is obtained by the following equation. An injection amount (basic injection pulse width) Tp is calculated.
Tp = K × Qa / N where K is a constant.

Then, a separately set target air-fuel ratio correction coefficient TFBYA and air-fuel ratio feedback correction coefficient ALPHA are read, and a final fuel injection amount (injection pulse width) Ti is calculated by the following equation.
Ti = Tp × TFBYA × ALPHA
Both the target air-fuel ratio correction coefficient TFBYA and the air-fuel ratio feedback correction coefficient ALPHA have a reference value (a stoichiometric equivalent value) of 1.

In addition, the calculation of the fuel injection amount (injection pulse width) Ti includes a transient correction based on the change in the throttle opening TVO and the addition of the invalid injection pulse width based on the battery voltage. did.
When the fuel injection amount Ti is calculated, 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, and fuel injection is performed. .

Next, setting of the target air-fuel ratio correction coefficient TFBYA will be described.
The target air-fuel ratio correction coefficient TFBYA is calculated by multiplying the basic target air-fuel ratio correction coefficient TFBYA0 by the correction coefficient THOS as shown in the following equation.
TFBYA = TFBYA0 × THOS
The basic target air-fuel ratio correction coefficient TFBYA0 is a stoichiometric operation in which the target air-fuel ratio is determined for each operation region determined from the engine speed and load by a map using the engine speed and load (for example, target torque) as parameters. In the region, TFBYA0 = 1, and in the rich operation region (KMR region), TFBYA0> 1.

The correction coefficient THOS is calculated by adding the stability increase value KSTB, the unburned component correction value KUB, and the like to the reference value 1 as in the following equation.
THOS = 1 + KSTB + KUB + ...
The stability increase value KSTB is set to gradually decrease so that the air-fuel ratio becomes richer as the water temperature becomes lower immediately after starting, and then the air-fuel ratio gradually converges to stoichiometric as time elapses, and the engine speed and load (for example, target torque) ) Is corrected.

The unburned component correction value KUB is set to ensure stability even when heavy fuel is used after the stability increase value KSTB is set to zero.
Next, the setting of the air-fuel ratio feedback correction coefficient ALPHA will be described.
The air-fuel ratio feedback correction coefficient ALPHA is set to increase or decrease as follows. Under the air-fuel ratio feedback control condition (assuming that at least the air-fuel ratio sensor is in the active state), lean / rich is determined based on the air-fuel ratio sensor output, and when the inversion from rich to lean (previous rich and current lean) ), The air-fuel ratio feedback correction coefficient ALPHA is updated by increasing the proportionally proportional gain (proportional gain) P (ALPHA = ALPHA + P). It is updated by increasing a minute integral (integral gain) I (ALPHA = ALPHA + I).

On the contrary, at the time of reversal from lean to rich (when lean last time and this time rich), the air-fuel ratio feedback correction coefficient ALPHA is reduced by a proportionally set amount P and updated (ALPHA = ALPHA-P), rich When the state continues, the air-fuel ratio feedback correction coefficient ALPHA is reduced by a minute integral I and updated (ALPHA = ALPHA-I).
When the air-fuel ratio feedback control condition is not satisfied, the air-fuel ratio feedback correction coefficient ALPHA is maintained at the reference value 1 (or the last value at the end of the air-fuel ratio feedback control).

FIG. 2 is a flowchart showing the flow of air-fuel ratio control after the engine is started (after the start switch is turned ON → OFF) until the air-fuel ratio feedback control is started. FIG. 5 shows a time chart of this control.
In S1, in order to calculate the stability increase value KSTB, its basic value (the air-fuel ratio is made richer as the water temperature becomes lower immediately after start-up, and then the air-fuel ratio is gradually decreased so as to gradually converge to stoichiometry and the engine speed is set. And a value corrected by the load) kstb is calculated by the following equation.

kstb = (KSTBC + KAS) × KNE
KSTBC is set to gradually decrease so that the air-fuel ratio is enriched immediately after start-up, and then the air-fuel ratio is gradually converged to stoichiometry.
KAS is set to be gradually decreased immediately after the start so that the value of KSTB converges from the increased value at the start to KSTBC.

  KNE is a rotational load correction coefficient for correcting according to the engine speed and the load. KNE = 1 is set in the idle state, and KNE> 1 as the engine speed and the load are higher at times other than idling. Set to Actually, the rotational load correction amount (KNE) is calculated as a part of each of KSTBC and KAS, but here, for easy understanding, the rotational load correction coefficient KNE is shown independently of KSTBC and KAS.

In S2, the reduction correction coefficient DRTKSTB is set to 1 (DRTKSTB = 1).
In S3, as shown in the following equation, the basic value of the stability increase value (the air-fuel ratio is gradually enriched as the water temperature decreases immediately after starting, and then the air-fuel ratio is gradually decreased so as to gradually converge to stoichiometry and the engine speed is increased. And the value corrected by the load) kstb is multiplied by a decrease correction coefficient DRTKSTB (here, DRTKSTB = 1) to calculate the stability increase value KSTB.

KSTB = kstb × DRTKSTB
Here, since DRTKSTB = 1, KSTB = kstb.
In S4, the activity of the air-fuel ratio sensor is determined.
The activity determination is performed according to the flowchart of FIG. In S101, it is determined whether or not the output VO2 of the air-fuel ratio sensor is equal to or higher than a predetermined rich side activity determination level SR #. If the determination in S101 is YES, the process proceeds to S102, and it is determined whether or not a predetermined time T1 # has elapsed under the condition of VO2 ≧ SR # in S101. If the determination in S102 is YES, the process proceeds to S103 to determine whether or not a predetermined time T2 # has elapsed after the start switch (ST / SW) is turned off. If the determination in S103 is YES, that is, if all the determinations in S101 to S103 are YES, the process proceeds to S104, and it is considered that the air-fuel ratio sensor is activated, and the activation detection flag F1 is set to 1.

Therefore, in S4, it is determined whether or not the activity detection flag F1 is 1.
If the determination in S4 is NO, that is, if the activity detection flag F1 = 0, the process returns to S1, and the calculation of the stability increase value KSTB in S1 to S3 is repeated.
Therefore, until the activation of the air-fuel ratio sensor is detected after startup, the stability increase value KSTB becomes richer at the low water temperature immediately after startup, and then gradually converges to stoichiometric over time. It is set so as to be gradually reduced and is corrected by the engine speed and load. Since the target air-fuel ratio correction coefficient TFBYA is determined by the stability increase value KSTB (KUB = 0), the target air-fuel ratio correction coefficient TFBYA is set in the same manner. During this time, the air-fuel ratio feedback correction coefficient ALPHA is maintained at the reference value 1.

If the determination in S4 is YES, that is, if the activity detection flag F1 = 1 (when the activity of the air-fuel ratio sensor is detected), the process proceeds to S5.
In S5, as in S1, the basic value kstb is calculated by the following equation in order to calculate the stability increase value KSTB.
kstb = (KSTBC + KAS) × KNE
In S6, by subtracting the predetermined value DKSTB # from the previous value of the decrease correction coefficient DRTKSTB for each unit time and updating the decrease correction coefficient DRTKSTB to the decrease side (see the following equation), the decrease correction coefficient DRTKSTB is increased from 1. Decrease to zero.

DRTKSTB = DRTKSTB-DKSTB #
In S7, as in S3, the basic value kstb of the stability increase value is multiplied by a decrease correction coefficient DRTKSTB (here, a value gradually decreasing from 1 to 0) as in the following equation, and the stability increase value KSTB is calculated. Is calculated.
KSTB = kstb × DRTKSTB
Here, after the activity is detected, since DRTKSTB gradually decreases from 1 to 0 with respect to before the activity is detected (DRTKSTB = 1), the rate of decrease in the stability increase value KSTB becomes larger than that before the activity is detected.

In S8, it is determined whether or not the air-fuel ratio feedback control (λcon) start condition is satisfied.
Whether or not the air-fuel ratio feedback control (λcon) start condition is satisfied is determined according to the flowchart of FIG. In S201, it is determined whether or not the air-fuel ratio sensor activity detection flag F1 = 1. If the determination in S201 is YES, the process proceeds to S202, in which it is determined whether or not the output VO2 of the air-fuel ratio sensor has reached the stoichiometric equivalent value SST # (VO2 ≦ SST #).

If the determination in S202 is YES, it is determined that the start condition of the air-fuel ratio feedback control (λcon) is reached, the process proceeds to S204, and the λcon start flag F2 is set to 1.
On the other hand, if the determination in S202 is NO, the process proceeds to S203, and it is determined whether or not a predetermined time T3 # has elapsed after the activity detection (F1 = 1). Here, also in the case of YES, it is determined that it is the start condition of the air-fuel ratio feedback control (λcon), the process proceeds to S204, and the λcon start flag F2 is set to 1.

Accordingly, in S8, it is determined whether or not the λcon start flag F2 is 1.
If the determination in S8 is NO, that is, if the λcon start flag F2 = 0, the process returns to S5, and the calculation of the stability increase value KSTB in S5 to S7 is repeated.
Therefore, until the start of air-fuel ratio feedback control after the activation detection, the stability increase value KSTB is decreased until it becomes 0 at a large decrease rate compared with the decrease rate before the activation. Since the target air-fuel ratio correction coefficient TFBYA is determined by this stability increase value KSTB (KUB = 0), the target air-fuel ratio correction coefficient TFBYA is also decreased in the same manner. During this time, the air-fuel ratio feedback correction coefficient ALPHA is maintained at the reference value 1.

If the determination in S8 is YES, that is, if the λcon start flag F2 = 1 (when the air-fuel ratio feedback control start condition is met), S9 to S9 to start the air-fuel ratio feedback control. Proceed to S13.
In S9, by dividing the current stability increase value KSTB by the rotational load correction coefficient KNE, a value (KSTB / KNE) obtained by removing the correction amount due to the engine speed and load from the current stability increase value KSTB is learned. This is stored as a learning value KSTBLMD (KSTBLMD = KSTB / KNE). This is for the basic value of the unburned component correction value KUB.

In S10, the current water temperature TW is detected and stored as the water temperature TW0 at the start of λcon (TW0 = TW).
In S11, the unburned component correction value KUB is calculated according to the following equation.
KUB = KSTBLMD × KUBDTW × KUBICN
That is, the unburned fuel correction value KUB is set by correcting the learning value KSTBLMD of the stability increase value using the correction coefficients KUBDTW and KUBICN.

The correction coefficient KUBDTW is calculated by the following equation.
KUBDTW = (KUBZTW # -TW) / (KUBZTW # -TW0)
KUBZTW # is the unburned component corrected water temperature upper limit value.
Therefore, KUBDTW becomes 1 at the start of λcon because TW = TW0, and after starting λcon, it decreases as the water temperature TW rises. When the water temperature TW reaches the upper limit value KUBZTW #, it becomes 0. Become.

The correction coefficient KUBICN is a value obtained by interpolating the map MKUBIN in accordance with the engine speed Ne and the cylinder intake charging efficiency ITAC.
In S12, the stability increase value KSTB is forcibly set to 0 (KSTB = 0).
Therefore, since the target air-fuel ratio correction coefficient TFBYA is TFBYA = TFBYA0 × (1 + KSTB + KUB +...), As long as TFBYA0 = 1, TFBYA≈1 + KUB.

In S13, air-fuel ratio feedback control (λcon) is started. That is, the air-fuel ratio feedback correction coefficient ALPHA is increased or decreased by proportional / integral control in accordance with the air-fuel ratio sensor signal.
Next, this control (FIG. 5) will be described in comparison with the time chart of the conventional air-fuel ratio control after starting shown in FIG.

  In the conventional air-fuel ratio control after starting (FIG. 7), after the activation of the air-fuel ratio sensor is detected, the stability increase value KSTB in the target air-fuel ratio correction coefficient TFBYA is set to 0, and the decrease (KSTB) is set to the air-fuel ratio. After the feedback correction coefficient ALPHA is added as an increase, air-fuel ratio feedback control (λcon) is started, and a new unburned fuel correction value KUB is added to the target air-fuel ratio correction coefficient TFBYA.

In this case, the convergence of the air-fuel ratio to the stoichiometry depends on the movement of the air-fuel ratio feedback correction coefficient ALPHA, and the movement of ALPHA is governed by the integral gain (I). If it cannot be reduced, convergence to stoichiometry will be delayed.
In addition, since the unburned component correction value KUB is adapted with heavy fuel from the viewpoint of drivability, when using light fuel, it becomes rich until the feedback control converges, and the emission reduction margin is sufficient. It may not be.

  On the other hand, in the present control (FIG. 5), after detecting the activity of the air-fuel ratio sensor, the rate of decrease of the stability increase value KSTB is increased compared to before the activity detection, and thereafter until the air-fuel ratio reaches stoichiometry. The air-fuel ratio feedback correction coefficient ALPHA is maintained at the reference value (1), and the air-fuel ratio feedback control (λcon) is started when the air-fuel ratio reaches the stoichiometric. At the start, the stability increase value at that time is started. An unburned component correction value KUB is set based on KSTB and added to the target air-fuel ratio correction coefficient TFBYA, and at the same time, the stability increase value KSTB is set to zero.

  Therefore, after the activation of the air-fuel ratio sensor is detected, the target air-fuel ratio correction coefficient TFBYA (actually, the stability increase value KSTB) is reduced while the air-fuel ratio feedback correction coefficient ALPHA is clamped at 1 until the air-fuel ratio feedback control is started. Since the process is performed until λ = 1, the air-fuel ratio can be stoichiometrically taken at a high speed regardless of the gain of the air-fuel ratio feedback correction coefficient ALPHA.

In addition, the stability increase value KSTB when the air-fuel ratio reaches stoichiometric changes depending on the fuel properties (heavy and light), and this is learned to set the unburned component correction value KUB. The optimum unburned component correction value KUB can be set according to the properties, and the exhaust is not deteriorated even when light fuel is used.
Further, when the decrease rate of the stability increase value KSTB is increased as compared with that before the activity detection, the stability increase value KSTB is multiplied by the decrease correction coefficient DRTKSTB that decreases with the passage of time. By correcting, even when the rotational load fluctuates during the decrease of the stability increase value KSTB, the stability increase value KSTB including the rotation load correction can be decreased, and both the rotation load correction and the decrease can be achieved. .

  In other words, when the stability increase value KSTB is decreased at a larger decrease rate after the activity detection than before the activity detection, in the method of subtracting the stability increase value KSTB at the time of the activity detection as an initial value by a predetermined value, Even if there is a load fluctuation, the rotational load cannot be corrected, but the rotational load can be corrected by calculating the basic value kstb of the stability increase value after the activity detection by the same method as before the activity detection. By multiplying the basic value kstb by the decrease correction coefficient DRTKSTB as the stability increase value KSTB, it is possible to reduce the amount accurately.

FIG. 6 is a time chart in the case where there is a rotational load fluctuation (an increase in the rotational speed Ne) while the stability increase value KSTB is decreasing in this control.
In this case, the rotational load correction is added to the basic value kstb of the stability increase value, but by multiplying this by the decrease correction coefficient DRTKSTB, the stability increase value KSTB is calculated. While applying, it can be surely reduced.

  According to the present embodiment, the stability increase value KSTB is a value that is gradually decreased so as to enrich the air-fuel ratio immediately after startup and then gradually converge the air-fuel ratio to stoichiometric and is corrected by the engine speed and load. kstb is multiplied by a reduction correction coefficient DRTKSTB, and before the activation of the air-fuel ratio sensor, the reduction correction coefficient DRTKSTB = 1, and after the activation of the air-fuel ratio sensor, the reduction correction coefficient DRTKSTB is set from 1 to 0. By decreasing at a constant speed as time elapses, it is possible to deal with only by switching the reduction correction coefficient DRTKSTB before and after detecting activity.

  Further, according to the present embodiment, the unburned component correction value KUB is set to a value (KSTB / KNE) obtained by removing the correction amount due to the engine speed and load from the stability increase value KSTB. Is obtained. If the rotational load correction is performed when setting the stability increase value KSTB, at the start of the air-fuel ratio feedback control, the stability increase value KSTB at that time is learned as it is, and the unburned component correction value KUB is set. If this is the case, the unburned component correction value KUB is set larger than necessary, and it takes time to make the stoichiometric air-fuel ratio feedback control, and the rich state continues for a long time. In this regard, if the unburned component correction value KUB is set based on the value obtained by removing the correction amount due to the engine speed and the load from the stability increase value KSTB (KSTB / KNE), erroneous learning including the rotational load correction amount is performed. This can prevent the unburned component correction value KUB from becoming excessively rich.

Further, according to the present embodiment, the unburned component correction value KUB is set to an initial value (KSTB / KNE) obtained by removing the correction amount due to the engine speed and load from the stability increase value KSTB, and this is set to the cooling water temperature TW. By performing the correction so as to decrease as the temperature increases, the correction value can be appropriately reduced as the water temperature rises.
Further, according to the present embodiment, the activity of the air-fuel ratio sensor can be accurately detected by detecting it based on the output (VO2) of the air-fuel ratio sensor and the elapsed time after starting (T2 #).

  Further, according to the present embodiment, the air-fuel ratio feedback control has passed a predetermined time (T3 #) after detecting the activity of the air-fuel ratio sensor even when the output of the air-fuel ratio sensor does not reach the stoichiometric equivalent value (SST #). By starting sometimes, even if the rich state continues for some reason, it can be equivalent to stoichiometry by feedback control, and feedback control can be started reliably.

The system figure which shows one Embodiment of this invention Flow chart showing the flow of air-fuel ratio control after startup Flow chart of air-fuel ratio sensor activation determination routine λcon start determination routine flowchart Time chart of air-fuel ratio control after startup Time chart with rotational load compensation Conventional air-fuel ratio control time chart after start

Explanation of symbols

1 engine
6 Fuel injection valve
12 ECU
17 Air-fuel ratio sensor

Claims (6)

A target air-fuel ratio correction coefficient including a stability increase value which is set to gradually decrease so that the air-fuel ratio is gradually converged to stoichiometric after the start, and then the air-fuel ratio gradually converges to stoichiometry, and is corrected by the engine speed and load; An air-fuel ratio control device for an engine that calculates and controls the fuel injection amount using an air-fuel ratio feedback correction coefficient that is set so that the air-fuel ratio converges stoichiometrically based on a signal from the air-fuel ratio sensor under feedback control conditions In
After detecting the activity of the air-fuel ratio sensor, the stability increase value is corrected by multiplying the stability increase value by a decrease correction coefficient that decreases over time, thereby correcting the stability increase value. The air-fuel ratio feedback control is started when the air-fuel ratio reaches the stoichiometric condition after that.
At the start of air-fuel ratio feedback control, an unburned component correction value is set based on the current stability increase value and added to the target air-fuel ratio correction coefficient, and at the same time, the stability increase value is set to zero. An air-fuel ratio control device for an engine characterized by the above. The stability increase value is set so as to enrich the air-fuel ratio immediately after start-up, and then gradually converge the air-fuel ratio to stoichiometric, and a reduction correction coefficient for the value corrected by the engine speed and load. To calculate by multiplying,
2. The reduction correction coefficient is set to 1 before the activation of the air-fuel ratio sensor, and after the activation of the air-fuel ratio sensor, the reduction correction coefficient is decreased from 1 to 0 at a constant speed over time. Engine air-fuel ratio control device.   The engine air-fuel ratio control apparatus according to claim 1 or 2, wherein the unburned component correction value is a value obtained by removing a correction due to engine speed and load from the stability increase value.   The unburned component correction value is set by setting a value obtained by removing the correction amount due to the engine speed and load from the stability increase value as an initial value, and performing correction so as to decrease as the cooling water temperature increases. The engine air-fuel ratio control apparatus according to claim 3.   The engine air-fuel ratio control apparatus according to any one of claims 1 to 4, wherein the activity of the air-fuel ratio sensor is detected based on an output of the air-fuel ratio sensor and an elapsed time after starting.   6. The air-fuel ratio feedback control according to claim 1, wherein the air-fuel ratio feedback control is started when a predetermined time elapses after detecting the activity of the air-fuel ratio sensor even when the output of the air-fuel ratio sensor does not reach the stoichiometric value. The air-fuel ratio control apparatus for an engine according to any one of the above.