JPH0571398A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

PURPOSE:To improve the cleaning efficiency of a catalyst by effecting feedback control of an air-fuel ratio to a value approximately equal to a theoretical air-fuel ratio according to oxygen concentration in exhaust gas without fluctuating the number of revolutions of an engine during idling. CONSTITUTION:An air amount regulating means which regulates an intake air flow rate regardless of operation of an accelerator by a driver is provided. When an internal combustion engine is in its idle running state, an amount of fuel fed to an engine is kept at a substantially constant value. Meanwhile, a flow rate of intake air is regulated through operation of the air amount regulating means according to oxygen concentration in exhaust gas. In this way, feedback control of an air-fuel ratio of fuel-air mixture fed to an internal combustion engine is performed to a value approximately equal to a target air-fuel ratio. Since an amount of energy fed to an engine is held at a constant value in this way, this constitution keeps engine generation torque at a constant value and also prevents the fluctuation of the number of revolutions of an engine even when an air-fuel ratio is changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for feedback-controlling the air-fuel ratio when an internal combustion engine is in a specific operating state such as idling, according to the oxygen concentration in exhaust gas.

[0002]

2. Description of the Related Art Conventionally, an exhaust gas purifying device (three-way catalyst) is arranged in the middle of an exhaust passage of an internal combustion engine, and an O2 sensor for detecting the oxygen concentration in the exhaust gas is arranged to detect oxygen detected by the O2 sensor. By adjusting the amount of fuel supplied to the engine according to the concentration and performing feedback control of the air-fuel ratio near a predetermined air-fuel ratio (for example, stoichiometric air-fuel ratio), nitrogen oxides, carbon monoxide, and unburned gases in the exhaust gas can be obtained. Air-fuel ratio control devices that purify harmful substances such as hydrocarbons are known. More specifically, when the fuel is supplied to the internal combustion engine, the fuel injection amount Qf depends on the intake air amount in the so-called L-Getronics system engine and in accordance with the intake pipe negative pressure in the D-Getronics system engine. The basic amount is determined, and this basic amount is feedback-corrected by the rich / lean signal of the O2 sensor provided in the exhaust system.

In this feedback correction of the fuel amount, even if the fuel injection amount changes, there is a response delay before this change is detected as a change in the oxygen concentration in the exhaust gas.
The output of the O2 sensor changes on and off in accordance with the residual oxygen concentration in the exhaust gas, so that the air-fuel ratio repeats a rich region and a lean region in a predetermined cycle (limit cycle), The air-fuel ratio of the air-fuel mixture supplied to the fuel cell fluctuates across the stoichiometric air-fuel ratio.

[0004]

There is no problem when the above limit cycle is short, but there is a limit to setting this limit cycle short, and as a result, when the limit cycle is operated, the limit cycle is not satisfied. As a result, the engine speed fluctuates and idle performance such as driving feeling deteriorates. The change in the engine speed is caused by the change in the amount of fuel supplied to the engine, in other words, the change in the amount of energy given to the engine. To do.

The present invention has been made in order to solve such a problem, and changes the air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio in accordance with the oxygen concentration in the exhaust gas to improve the purification efficiency of the catalyst. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine, which avoids fluctuations in the engine speed as much as possible and improves the driving feeling during idling.

[0006]

In order to achieve the above-mentioned object, according to the present invention, a fuel injection device for injecting and supplying a required amount of fuel to an internal combustion engine, and oxygen for detecting the oxygen concentration in exhaust gas. In the air-fuel ratio control device comprising a concentration detection means and an air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine, feedback control is performed in the vicinity of the target air-fuel ratio in accordance with the oxygen concentration in the exhaust gas, Providing an air amount increase / decrease means that increases / decreases the intake flow rate regardless of accelerator operation,
When the internal combustion engine is in a specific operating state, the control means maintains the amount of fuel injected and supplied to the fuel injection device substantially constant, while the air amount increasing / decreasing means depends on the oxygen concentration in the exhaust gas. There is provided an air-fuel ratio control device for an internal combustion engine, wherein the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is feedback-controlled to near the target air-fuel ratio.

Further, the air-fuel ratio control system for an internal combustion engine of the present invention further comprises a rotation speed detection means for detecting the engine rotation speed, if necessary, and the specific operation state is an idle operation state, The control means obtains a fuel increase value corresponding to the deviation between the engine speed detected by the speed detecting means and the target idle speed, and injects the fuel amount corrected by the calculated fuel increase value into the fuel injection device. To supply.

[0008]

FIG. 1 shows the conventional air-fuel ratio feedback control. By increasing or decreasing the fuel injection amount Qfl, the air-fuel ratio supplied to the engine fluctuates around the theoretical air-fuel ratio. At this time, considering the generated torque at the stoichiometric air-fuel ratio as a reference, the generated torque also increases / decreases corresponding to the increase / decrease in the fuel injection amount Qfl. On the other hand, as shown in FIG. 2, when the fuel injection amount Qfl is kept constant and the air amount Qa supplied to the engine is increased or decreased, the amount of energy given to the engine is constant, so the generated torque is equal to the theoretical air-fuel ratio. It does not change in the vicinity and can be kept substantially constant.

An air-fuel ratio control system for an internal combustion engine according to the present invention is made based on the above-mentioned findings, and the control means controls the fuel injection system to operate when the internal combustion engine is in a specific operating state such as idle. Keep the supply constant,
The air flow rate is increased / decreased by the air amount increasing / decreasing means to perform feedback control of the air-fuel ratio near the target air-fuel ratio. Further, during idle operation, the fuel supply amount is increased / decreased according to the deviation between the engine speed and the target idle speed, and the engine speed is feedback-controlled near the target idle speed.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 3 shows a schematic configuration of an air-fuel ratio control device for an internal combustion engine according to the present invention. This control device is, for example, a 4-cylinder gasoline engine (hereinafter simply referred to as “engine”) 1
It is applied to 2. An electromagnetic fuel injection valve 16 is arranged adjacent to each intake port in each intake manifold 14 connected to each cylinder of the engine 12.
One end of an intake pipe 20 is connected to the intake manifold 14 via a surge tank 18, and an air cleaner 22 is attached to the other end (atmosphere opening end) of the intake pipe 20. A throttle valve 24 is arranged in the middle of the intake pipe 20. Each fuel injection valve 16 is supplied with fuel from a fuel pump (not shown) through a fuel passage 25, and a fuel whose fuel pressure is adjusted to a constant value by a fuel pressure regulator 26.

The intake pipe 20 is provided with a bypass passage 21 that bypasses the throttle valve 24, and a bypass valve 28 is arranged in the bypass passage 21. This bypass valve 28 is, for example, the pulse motor 2
Is driven by 8a to change the valve opening,
It is connected to an electronic control unit (ECU) 40 described later, the valve opening degree is controlled by a drive signal from the electronic control unit 40, and the amount of auxiliary air supplied to the engine 12 via the bypass passage 21 is adjusted. The bypass passage 21 and the bypass valve 28 constitute an air amount increasing / decreasing means for increasing / decreasing the intake air flow rate regardless of the accelerator operation by the driver.

On the other hand, an exhaust manifold 30 is connected to the exhaust side of each cylinder of the engine 12, and the atmospheric side end of the exhaust manifold 30 is connected to an exhaust pipe 34. A three-way catalyst type catalytic converter (catalytic exhaust gas post-treatment device) 36 is disposed in the middle of the exhaust pipe 34.
An O2 sensor 44 for detecting the amount of oxygen in the exhaust gas is attached to the exhaust manifold 30. The O2 sensor 44 is electrically connected to the input side of the electronic control unit 40 and supplies an oxygen concentration detection signal to the electronic control unit 40.

An ignition plug 13 is provided in each cylinder, and each ignition plug 13 is connected to an electronic control unit 40 via a distributor 38 and an ignition coil (not shown). When the current supplied from the drive circuit (not shown) of the electronic control unit 40 to the primary coil of the ignition coil is cut off, a high voltage is generated in the secondary coil, and this high voltage causes the spark plug 13 to spark. Flies and ignites the air-fuel mixture supplied to the combustion chamber of each cylinder. The timing of igniting the air-fuel mixture (ignition timing) is controlled according to the operating state.

The electronic control unit 40 includes a central processing unit (not shown), a control program for executing idle speed feedback control, calculating air-fuel ratio feedback control, etc., a storage device for storing various program variables, input / output. It is composed of devices and the like. The storage device includes, in addition to ROM and RAM, a non-volatile battery backup RAM that does not lose its stored contents even after the engine 12 is stopped.

The above-mentioned fuel injection valves 16 are electrically connected to the output side of the electronic control unit 40, and the electronic control unit 4
The valve is opened by a drive signal from 0, and a required amount of fuel is injected and supplied to each cylinder as described later in detail. On the input side of the electronic control unit 40, in addition to various sensors for detecting the operating state of the engine 12, for example, the above-mentioned O2 sensor 44, are attached near the open end of the intake pipe 20 to detect the Karman vortex. An air flow sensor 42 that outputs a pulse proportional to the intake air amount, and an intake air temperature sensor 4 that is provided in the air cleaner 22 and detects the intake air temperature Ta.
6. A throttle opening sensor 48 for detecting the valve opening of the throttle valve 24, and a distributor 38 connected to the camshaft for providing a pulse each time the predetermined crank angle position at or near the top dead center is detected. A crank angle sensor 50 that outputs a signal (TDC signal), which is also provided in the distributor 38, allows a specific cylinder (for example, the first cylinder) to have a predetermined crank angle position (for example, the first cylinder).
A cylinder discrimination sensor 52 for detecting that it is at the compression top dead center or an angular position slightly before that, a water temperature sensor 54 for detecting the cooling water temperature TW of the engine 12, an idle switch 56 for detecting the fully closed position of the throttle valve 24, Atmospheric pressure Pa
Further, an atmospheric pressure sensor 58 for detecting the temperature, an air conditioner switch (not shown) for detecting the operating state of the air conditioner, a battery sensor for detecting the battery voltage, and the like, which are not shown, are connected, and these sensors output a detection signal to the electronic control unit 40. Supply to.

The electronic control unit 40 detects an operating state such as a predetermined idle speed feedback control operating state and an air-fuel ratio feedback control operating state based on the detection signals of the various sensors described above, as will be described later in detail. Calculate the fuel injection amount Qfl according to the detected engine operating state,
A drive signal is supplied to each fuel injection valve 16 for a valve opening time corresponding to the calculated fuel injection amount Qfl to open it.
A required amount of fuel is injected and supplied to each cylinder. Further, when a specific operating state (idle operating state) is detected, the valve opening degree (position value of the pulse motor 28a) Pobj (t) of the bypass valve 28 is calculated, as will be described in detail later, and according to the present invention. The idle air-fuel ratio feedback control is executed and the idle speed feedback control is executed.

Since the crank angle sensor 50 outputs the TDC signal at every 180 ° of the crank angle, the electronic control unit 40 detects the engine speed Ne from the reciprocal of the pulse generation interval (stroke cycle) of the TDC signal. can do. Further, the electronic control unit 40 stores the ignition sequence of the cylinders, that is, the fuel supply sequence to each cylinder, and the cylinder discrimination sensor 52 described above detects the predetermined crank angle position of the specific cylinder, Next, it is possible to determine which cylinder should be injected and supplied with fuel.

4 to 6 show a flowchart of an idle air-fuel ratio control routine executed by the electronic control unit 40. This routine is executed at a predetermined cycle, for example, every time the crank angle sensor 50 outputs the above TDC signal. To be done. The electronic control unit 40 first inputs the operating state of the engine 12 detected by the various sensors described above (step S10). Then, it is determined from the detected operating state whether the engine 12 is in an operating state in which the air-fuel ratio feedback control may be performed (step S1).
2). For this determination, for example, it is determined that a predetermined time has elapsed since the engine 12 was started, that the cooling water temperature TW is equal to or higher than a predetermined value, and if all of these conditions are satisfied. , It is determined that the air-fuel ratio feedback control may be started.

The determination result of step S12 is negative (No).
In the case of, the feedback correction coefficient K _FB used for the calculation of the fuel injection amount Qfl (described later) is set to the value 1 (step S14), and the integral term value K _I of this feedback correction coefficient K _FB is reset to the value 0. (Step S16), the process proceeds to step S30 in FIG. In step S30, it is determined whether or not the engine 12 is in an operating state in which the idle speed feedback control may be executed. To make this determination,
For example, the idle switch 56 is outputting an ON signal, the engine speed Ne is below a predetermined value,
It is determined whether or not conditions such as the cooling water temperature TW being equal to or higher than a predetermined value are satisfied, and when all of these conditions are satisfied, it is determined that the idle speed feedback control may be executed.

If the determination result in step S30 is negative,
That is, when the engine 12 is not in the operating state in which the air-fuel ratio feedback control is possible and is not in the operating state in which the idle speed feedback control is performed, the engine 12 is operated according to the operating state from the map stored in advance in the storage device. Then, the position value Pobj (t) of the bypass valve 28 is read, and the pulse motor 28a is driven to the position corresponding to the read position value Pobj (t) (step S3).
2). The map for obtaining the position value Pobj (t) stores, for example, a value according to the engine speed Ne,
Auxiliary air according to the engine operating state is bypass passage 21
Is supplied to the engine 12 from this, and the supply of this auxiliary air prevents a rapid decrease in the engine speed Ne when the throttle valve 24 is suddenly closed.

Next, in step S44, the fuel injection amount Qfl supplied to the engine 12 is calculated. The electronic control unit 40 calculates this fuel injection amount Qfl by the following equation (A1). Qfl = (A / N) ÷ (A / F) × K × K _FB (A1) where A / N is the amount of intake air taken into the cylinder during one intake stroke, and is calculated from the air flow sensor 42. It is determined according to the output Karman vortex generation cycle and the engine speed Ne. A / F is a target air-fuel ratio, and is set to a constant value 14.7 which is, for example, the theoretical air-fuel ratio. K is various correction coefficients, and these correction coefficients include a water temperature correction coefficient set in accordance with the engine cooling water temperature TW, an intake air temperature Ta, an atmospheric correction coefficient set in accordance with the atmospheric pressure Pa, and the throttle valve 24. The acceleration increase correction coefficient set according to the valve opening speed, the fuel increase correction after the fuel cut, the engine start increase correction, and the like are included.
K _FB is the above-mentioned O ₂ feedback correction coefficient.

Then, the electronic control unit 40 controls the fuel injection valve 1 over the valve opening time corresponding to the calculated fuel injection amount Qfl.
The drive signal for opening the valve 6 is supplied to the injection valve 16, the fuel of the injection amount Qfl is injected, and the routine ends. Next, when the determination result of step S30 is affirmative (Yes), subsequent steps S34 to S42 are executed, and the idle speed feedback control by the conventional method is executed. First, in step S34, it is determined whether the position value Pobj (t) of the bypass valve 28 may be updated, that is, whether the update cycle has elapsed. Large-capacity surge tank 1 for the intake system of the engine 12
8 is arranged, and even if the amount of auxiliary air is changed, there is a time delay before its effect appears. If the next position value Pobj (t) is calculated and executed without recognizing this effect, engine control may become unstable. Therefore, the update cycle is set, and the position value Pobj (t) is set for each update cycle.

If the determination result of step S34 is affirmative, the current engine speed Ne and the target idle speed N
The deviation ΔN from tg is calculated (step S36). ΔN = Ne-Ntg (A2) Then, the correction value ΔP of the position value Pobj (t) is calculated according to the deviation ΔN (step S38). The method of calculating the correction value ΔP is not particularly limited,
Various conventionally known methods such as PID control can be applied. When the calculation of the correction value ΔP is completed, the correction value ΔP is added to the previous position value Pobj (t-1) to obtain the current value Pobj (t), and the position corresponding to the obtained position value Pobj (t) is obtained. The pulse motor 28a is driven (step S40).

Pobj (t) = Pobj (t-1) + ΔP (A3) If it is determined in step S34 that the update cycle has not yet elapsed, the current value Pobj (t) of the position value of the pulse motor 28a is obtained. Is held at the previous value Pobj (t-1) (equation (A
4)), the pulse motor 28a is driven to a position corresponding to the same position value as the previous time (step S42).

Pobj (t) = Pobj (t-1) (A4) In this way, when the current engine speed Ne is lower than the target idle speed Ntg, the correction value ΔP increases the auxiliary air amount. If the value is high, the value is set to be decreased. Then, after performing such feedback control of the auxiliary air amount, the fuel injection amount Qfl is calculated in step S44 described above, and the required amount of fuel is supplied to the engine 1.
The engine speed Ne is feedback-controlled so that the engine speed Ne is stabilized near the target idle speed Ntg.

Returning to FIG. 4, when the engine 12 is in the operating state in which the air-fuel ratio feedback control may be performed and the result of the determination in step S12 is affirmative, step S18
Then, the output value of the O2 sensor 44 is compared with a predetermined value to determine whether the value is on the fuel rich (rich) side, that is, whether the rich signal is output. When the rich signal is output, steps S20 and S22 are executed, and feedback correction coefficient K _FB and integral term value K
_I is calculated by the following equations (A5) and (A6).

K _FB = 1− (K _P / 2) + K _I (A5) K _I = K _I −ΔI (A6) where K _P is a proportional term value and is set to a constant value. There is. ΔI is a predetermined minute value for gradually reducing the integral term value K _I. Therefore, the feedback correction coefficient K _FB is
By the execution of step S20, the value is set to a value smaller than the value 1 by (K _P / 2), and each time this step S20 is executed, the value is set to a smaller value for ΔI.

On the other hand, in step S18, if the determination result is negative, that is, if the air-fuel ratio of the air-fuel mixture supplied to the engine 12 is higher than the stoichiometric air-fuel ratio (fuel lean side value), steps S24 and S26. By executing the feedback correction coefficient K _FB and the integral term value K _I by the following equation (A
Calculate by 7) and (A8). _{K FB = 1 + (K P} / 2) + K I ...... (A7) by executing _{K I = K I + ΔI ......} (A8) a step S24, the feedback correction coefficient K _FB, from the value 1 (K _P / 2) Is set to a large value, and thereafter, each time step S24 is executed, it is set to a large value for ΔI.

When the setting of the feedback correction coefficient K _FB is completed, step S50 of FIG. 6 is executed. In this step, similarly to step S30 described above, it is determined whether or not the engine 12 is in an operating state in which the idle speed feedback control may be executed. When the determination result is negative, that is, when the engine 12 may execute the air-fuel ratio feedback control but is not in the operating state in which the idle speed feedback control should be executed, the above-described step S32 of FIG. Step S44 is executed. In this case, the fuel quantity Q supplied to the engine 12
fl is corrected by the feedback correction coefficient K _FB , and the air-fuel ratio is O2 feedback controlled by increasing or decreasing the amount of fuel supplied to the engine 12.

On the other hand, when the engine 12 is in the operating state in which the idle speed feedback control may be executed and the result of the determination in step S50 is affirmative, the air-fuel ratio feedback control and idle according to the present invention in steps S52 to S60 are performed. The rotation speed feedback control is executed. First, the electronic control unit 40 determines the current engine speed Ne and the target idle speed Ntg based on the above-mentioned formula (A2).
The deviation ΔN between the difference and is calculated (step S52). And
The fuel increase amount Q _Ne is calculated according to the calculated deviation ΔN (step S54). FIG. 7 shows a fuel increase map stored in advance in the storage device described above. If the deviation ΔN is larger than 0, that is, the engine speed Ne is larger than the target idle speed Ntg, the fuel increase Q _Ne is negative. Is set to a positive value if it is small, and this fuel increase amount Q _Ne is added to the fuel injection amount Qfl calculated by the equation (A1). That is, the fuel injection amount Qfl is calculated by the following equation (A9) (step S5).
6).

Qfl = (A / N) ÷ (A / F) × K × K _FB + Q _Ne (A9) Then, the electronic control unit 40 calculates the fuel injection amount Qfl
The drive signal for opening the fuel injection valve 16 is supplied to the injection valve 16 for the valve opening time corresponding to, and the fuel of the injection amount Qfl is injected. Next, in step S58, the correction value ΔP of the position value Pobj (t) is calculated according to the feedback correction coefficient K _FB . The method of calculating the correction value ΔP in this case is not particularly limited, but for example, the correction value ΔP corresponding to the correction coefficient K _FB is read from the map shown in FIG.
When the calculation of the correction value ΔP is completed, the correction value ΔP is added to the previous position value Pobj (t-1) by using the above-mentioned equation (A3) to obtain the current value Pobj (t), and the obtained position value Pobj The pulse motor 28a is driven to the position corresponding to (t) (step S60).

When it is judged from the oxygen concentration in the exhaust gas that the air-fuel ratio supplied to the engine 12 is larger than the stoichiometric air-fuel ratio (fuel lean side value), the feedback correction coefficient K _FB is greater than the value 1. A large value is set, and the correction value ΔP is set to a negative value. Therefore, the amount of auxiliary air supplied to the engine 12 via the bypass passage 21 is reduced, and the intake flow rate of the engine 12 is reduced. On the other hand, if the fluctuation of the engine speed Ne is not taken into consideration, the value of the feedback correction coefficient term K _FB in the equation (A9) is larger than the value 1, so that it contributes to the side that increases the fuel injection amount Qfl. However, since the value of the (A / N) term is reduced by the correction value ΔP, the calculated fuel injection amount Qfl is kept substantially constant. Therefore, in this case, the air-fuel ratio is corrected to a smaller value (to the rich side) as the intake flow rate decreases. On the contrary, when it is determined that the air-fuel ratio supplied to the engine 12 is smaller than the theoretical air-fuel ratio (value on the fuel rich side), the feedback correction coefficient K _FB is set to a threshold value smaller than the value 1, and the correction is performed. The value ΔP is set to a positive value, the auxiliary air supplied to the engine 12 via the bypass passage 21 increases, and the intake air flow rate of the engine 12 increases. On the other hand, since the feedback correction coefficient term K _FB in the equation (A9) is smaller than the value 1, it contributes to the side that reduces the fuel injection amount Qfl, but the value of the (A / N) term increases. Therefore, after all, the calculated fuel injection amount Qfl is kept substantially constant. Therefore, when the rich signal is output from the O2 sensor 44, the air-fuel ratio is corrected to a larger value (to the lean side) as the intake flow rate increases.

As described above, in the air-fuel ratio feedback control of the present invention, the fuel injection amount supplied to the engine 12 is kept substantially constant, and the intake air flow rate is increased or decreased to feed back the air-fuel ratio in the vicinity of the theoretical air-fuel ratio. You will be in control. Since the amount of fuel supplied to the engine 12 is kept substantially constant, the amount of energy given to the engine 12 does not change, therefore the amount of engine torque generated does not change, and the engine speed does not change even if the air-fuel ratio is changed. There is no need to worry about changing Ne. On the other hand, with respect to the fluctuation of the engine speed Ne, the fuel injection amount is increased / decreased (increased / decreased by the fuel increase amount Q _Ne ) according to the deviation ΔN from the target idle speed Ntg, and feedback control is performed. The responsiveness of the number feedback control is also improved.

The fuel injection amount Qfl calculated by the above equation (A9) is held at a constant value by multiplying it by the feedback correction coefficient K _FB. Although it may be considered that the engine speed is not maintained, it is sufficient if the engine speed does not change beyond the allowable range due to a change in the amount of energy applied to the engine 12,
In such a case, it can be considered that the engine speed Ne is kept substantially constant.

The air-fuel ratio control system for an internal combustion engine of the present invention is particularly effective for air-fuel ratio control in an operating state in which the engine speed during idle control is feedback-controlled as in the above embodiment. When only the air-fuel ratio feedback control is performed, the specific operating state of the present invention is not particularly limited to the idle operating state. Furthermore,
It goes without saying that the air amount increasing / decreasing means for increasing / decreasing the intake air flow rate regardless of the driver's accelerator operation is not limited to the one for controlling the opening / closing of the bypass valve 28 to adjust the intake air amount as in the present embodiment. There may be a device or the like that forcibly opens and closes the throttle valve near its fully closed position to adjust the intake air amount, regardless of the accelerator pedal depression amount.

[0036]

As is apparent from the above description, according to the air-fuel ratio control system for an internal combustion engine of the present invention, an air amount increasing / decreasing means for increasing / decreasing the intake air flow rate is provided regardless of the accelerator operation by the driver. When the engine is in a specific operating state such as idle, while maintaining the fuel amount to be injected and supplied to the fuel injection device substantially constant, the air amount increasing / decreasing means is activated according to the oxygen concentration in the exhaust gas. The intake air flow rate is increased / decreased, and thus the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is feedback-controlled to, for example, near the target air-fuel ratio of the theoretical air-fuel ratio. The torque is maintained substantially constant, and therefore the engine generated torque becomes constant. As a result, the purification efficiency of the catalyst can be improved by changing the air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio according to the oxygen concentration in the exhaust gas without changing the engine speed. Further, during the engine speed feedback control during idling, in addition to the air-fuel ratio feedback control described above, by increasing or decreasing the fuel supply amount according to the deviation between the engine speed and the target idle speed, the engine speed feedback control It is possible to improve responsiveness, further suppress fluctuations in engine speed, and improve driving feeling during idling.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between changes in the air-fuel ratio and torque with respect to changes in the amount of fuel supplied to the engine in order to explain a conventional air-fuel ratio control method.

FIG. 2 is a graph showing the relationship between changes in the air-fuel ratio and torque with respect to changes in the amount of air supplied to the engine, in order to explain the air-fuel ratio control method of the present invention.

FIG. 3 is a diagram showing a schematic configuration of an air-fuel ratio control device of the present invention.

FIG. 4 is a flowchart showing a control procedure of air-fuel ratio control executed by the air-fuel ratio control device of the present invention.

5 is a flowchart showing a control procedure of air-fuel ratio control, which is subsequent to the flowchart shown in FIG.

6 is another flowchart showing the control procedure of the air-fuel ratio control, which is subsequent to the flowchart shown in FIG.

FIG. 7 is a graph showing a relationship between an engine speed deviation ΔN and a fuel increase amount Q _Ne .

FIG. 8 is a graph showing a relationship between an O 2 feedback correction coefficient K _FB used for calculating a fuel injection amount Qfl and a bypass valve position correction value ΔP.

[Explanation of symbols]

 12 internal combustion engine 16 fuel injection valve 24 throttle valve 21 bypass passage (air amount adjusting means) 28 bypass valve (air amount adjusting means) 40 electronic control unit (ECU) 44 O2 sensor 50 crank angle sensor

Claims (2)

[Claims] 1. A fuel injection device for injecting a required amount of fuel to an internal combustion engine, an oxygen concentration detecting means for detecting an oxygen concentration in exhaust gas, and an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine In an air-fuel ratio control device having a control means for performing feedback control in the vicinity of a target air-fuel ratio according to the oxygen concentration in gas, an air amount increasing / decreasing means for increasing / decreasing an intake flow rate regardless of an accelerator operation by a driver is provided, and the control is performed. The means keeps the amount of fuel injected and supplied to the fuel injection device substantially constant when the internal combustion engine is in a specific operating state, while operating the air amount increasing / decreasing means according to the oxygen concentration in the exhaust gas. The air-fuel ratio of the internal-combustion engine is controlled by feedback control so that the air-fuel ratio of the air-fuel mixture supplied to the internal-combustion engine is controlled near the target air-fuel ratio. Control device. 2. A rotation speed detecting means for detecting an engine rotation speed is further provided, wherein the specific operation state is an idle operation state, and the control means controls the engine rotation speed detected by the rotation speed detecting means. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein a fuel increase value corresponding to a deviation from a target idle speed is obtained, and the fuel injection device is made to inject and supply the fuel amount corrected by the obtained fuel increase value.