JPH0660591B2 - Air-fuel ratio controller for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio control device for controlling an air-fuel ratio of a mixture of intake air and fuel supplied into a cylinder of an internal combustion engine.

2. Description of the Related Art Recently, in particular, due to demands for exhaust gas measures, improvement of drivability and fuel efficiency in internal combustion engines for automobiles, air-fuel ratio control for accurately controlling the air-fuel ratio of the air-fuel mixture supplied to the cylinders has been performed. As a conventional air-fuel ratio control device therefor, there is, for example, the one described in the technical manual “ECCS L system engine” issued by Nissan Motor Co., Ltd. in 1979.

In such a conventional air-fuel ratio control device, for example, in the case of an internal combustion engine using an electronically controlled fuel injection device (EGI), the basic injection amount of fuel is determined by the intake air amount and the engine speed, and the Various increase corrections are made according to the engine condition, and the actual air-fuel ratio is detected by detecting the oxygen concentration in the engine exhaust passage using an oxygen sensor, etc., and the air-fuel ratio feedback check corresponding to the detection result is detected. The air-fuel ratio is controlled to the target value by controlling the fuel injection amount by performing the correction using the correction coefficient.

By the way, as an oxygen sensor which is generally used in such an air-fuel ratio control device, there is an on / off type which conventionally detects a logical air-fuel ratio (λ = 1). As described in Japanese Patent Laid-Open No. 58-153155, a lean sensor capable of continuously detecting the air-fuel ratio in the lean range from the theoretical air-fuel ratio (λ = 1) has been developed.

Therefore, the air-fuel ratio is detected using such an oxygen sensor, and the deviation between the detected value and a predetermined target value is calculated,
This deviation is a predetermined constant control coefficient (control time constant),
For example, it is conceivable that the air-fuel ratio correction coefficient is determined based on a value obtained by performing integration processing with the integration coefficient, and the air-fuel ratio correction control is performed based on this air-fuel ratio correction coefficient.

However, regardless of the responsiveness of the oxygen sensor, if the control coefficient is fixed to a fixed value and the air-fuel ratio closed control (feedback control) is performed, the responsiveness of the oxygen sensor and the control coefficient of the feedback control system are controlled. There is a possibility that good feedback control cannot be performed when the matching of the above is not taken.

That is, for example, when the control coefficient is fast for the oxygen sensor having a slow response, the control air-fuel ratio is overshot, and when the control coefficient is slow for the oxygen sensor having a fast response, the controllability of the air-fuel ratio control becomes poor. Occurs.

Therefore, in order to eliminate such inconvenience and perform good feedback control, the response of the oxygen sensor and the control of the control system should be controlled for each individual air-fuel ratio controller during assembly or replacement due to defective oxygen sensor. It suffices to make a matching with the coefficient, but this requires too many man-hours and cannot deal with the change in responsiveness due to deterioration of the oxygen sensor with time.

Aim This invention was made in view of the above points, and it is possible to automatically determine an appropriate control coefficient during closed control according to the responsiveness of an oxygen sensor so that a feedback control with a good air-fuel ratio can be performed. The purpose is to

Therefore, the air-fuel ratio control apparatus for an internal combustion engine according to the present invention, as shown in FIG. 1, is an air-fuel ratio detecting means A for continuously detecting an air-fuel ratio within a predetermined range based on the oxygen concentration in the exhaust passage of the engine. The control coefficient determination means B performs closed control based on the response time of the detected value of the air-fuel ratio to the predetermined change of the air-fuel ratio in the operating state, that is, the response of the oxygen sensor. While determining a control coefficient such as an integration coefficient for determining the air-fuel ratio correction coefficient at the time, the deviation detecting means C detects the deviation between the detection value of the air-fuel ratio detecting means A and a predetermined target value, The air-fuel ratio correction coefficient determination means D processes the deviation detected by the deviation detection means C by the control coefficient determined by the control coefficient determination means B to determine the air-fuel ratio correction coefficient, and the air-fuel ratio correction coefficient is determined based on the air-fuel ratio correction coefficient. The fuel ratio correction means E Ratio is obtained so as to correct control.

Embodiments Embodiments of the present invention will be described below with reference to the accompanying drawings.

First, prior to the description of the overall configuration of the embodiment of the present invention, an oxygen sensor and an air-fuel ratio detection circuit that constitute the air-fuel ratio detection means A of FIG. 1 will be described.

2 and 3 are a longitudinal sectional view and an exploded perspective view showing an example of the oxygen sensor.

In this oxygen sensor 1, an atmosphere introduction plate 3 having a groove 3a is laminated on a substrate 2 made of alumina, and a flat plate-shaped oxygen ion conductive first fixed electrolyte 4 is formed on the atmosphere introduction plate 3.
Are stacked, and the air is introduced by the grooves 3a of the air introducing plate 3 and the first solid electrolyte 4 into the air introducing portion 5
Is formed.

Then, on the first solid electrolyte 4, a thickness L (L = 0.
Spacer plate 6 of about 1 mm) is laminated, and this spacer plate 6
A flat plate-shaped second solid electrolyte 7 is laminated on top of the first solid electrolyte 4, the spacer plate 6 and the second solid electrolyte 7 to diffuse the gas into which exhaust gas is introduced. The gas introduction portion 8 is formed as a gap that also serves as a limiting means.

Further, a sensor anode 10 exposed to the atmosphere in the atmosphere introducing section 5 and a sensor cathode 11 exposed to the exhaust gas in the gas introducing section 8 are provided to face each other on both sides of the first solid electrolyte 4,
An oxygen partial pressure ratio detection unit (hereinafter, referred to as “sensor cell”) that outputs a voltage according to the oxygen partial pressure ratio between the sensor anode 10 and the sensor cathode 11, that is, the oxygen partial pressure ratio between the air introduction unit 5 and the gas introduction unit 8. "SC").

Further, a pump cathode 12 exposed to the exhaust gas of the gas introduction part 8 and a pump anode 13 exposed to the exhaust gas as it is are provided on both sides of the second solid electrolyte 7 so as to face each other. An oxygen partial pressure control unit (hereinafter referred to as “pump cell PC”) that controls the oxygen partial pressure of the gas introduction unit 8 according to the amount of current supplied to the anode 13 is configured.

A heater 14 (see FIG. 3) for heating the first solid electrolyte 4 and the second solid electrolyte 7 is printed and formed on the surface of the substrate 2 on the side of the atmosphere introducing plate 3 in order to maintain the activity of the first solid electrolyte 4 and the second solid electrolyte 7. There is.

Further, the sensor cathode 10 and the sensor anode 11 have lead wires 15 and 16, respectively, and the pump cathode 12 and the pump anode 13 have lead wires 17 and 18, respectively, and the heater 1
Lead wires 19 and 20 are connected to 4.

Furthermore, examples of the first and second solid electrolytes 4 and 7 include oxides such as ZrO ₂ , HrO ₂ , ThO ₂ , and Bi ₂ O ₃ and C ₂ O, MgO, Y ₂ O ₂ , and YB ₂ O _3. Each of the electrodes 10 to 13 has platinum or gold as a main component, using a sintered body in which the above components are dissolved.

FIG. 4 is a block diagram showing an example of an air-fuel ratio detection circuit using this oxygen sensor.

In this air-fuel ratio detection circuit 21, the differential amplifier 22
The potential Vs of the sensor anode 10 with respect to the sensor cathode 11 of the sensor cell SC of the oxygen sensor 1, that is, the potential Vs corresponding to the oxygen partial pressure ratio between the gas introduction unit 8 and the atmosphere introduction unit 5, and the target voltage Va from the positive power supply 23. Difference with (Va-
Vs) is detected and the difference voltage ΔV is output.

The pump current supply circuit 24 inputs the differential voltage ΔV from the differential amplifier 22, supplies the pump current Ip to the pump cell PC of the oxygen sensor 1, and supplies the differential voltage ΔV from the differential amplifier 22.
Is controlled so that ΔV = 0 (Vs = Va).

Then, the pump current Ip supplied between the pump anode 13 and the pump cathode 12 from the pump current supply circuit 24 is exchanged for a voltage by the resistor 25, and the voltage across the resistor 25 is detected by the differential amplifier 26. Output as the air-fuel ratio detection output Vi.

Next, the operation of the air-fuel ratio detection means A including the oxygen sensor 1 and the air-fuel ratio detection circuit 21 having the above-described configuration will be described.

First, the pump current supply circuit 24 of the air-fuel ratio detection circuit 21
Is the sensor cathode 1 of the sensor cell SC as described above.
1 and the potential Vs between the sensor anode 10 is the target voltage V
the pump anode 13 of the pump cell PC so as to be a.
Is supplied with a pump current Ip.

Here, the oxygen partial pressure of the atmosphere introducing unit 5 is Pc, and the gas introducing unit 8 is
Assuming that the oxygen partial pressure of Py is Py, the potential Vs between the sensor anode 10 and the sensor cathode 11 of the sensor cell SC is
According to the Nernst equation, Vs = (RT / 4F) · ln (Pc / Py). However, R is a gas constant, T is an absolute temperature, and F is a Faraday constant.

Here, for example, if the target voltage Va is set to 500 mV, the oxygen partial pressure of the gas introduction part 8 is controlled so that the potential Vs = 500 mV. Therefore, if the absolute temperature is 1000 K, the oxygen partial pressure ratio Py / Pc is set. Becomes Py / Pc = 10 ⁻¹⁰ from the above equation and Pc = 0.206 atm, so Py = 0.
It will be 206 x 10 ^-10 atm.

At this time, when the oxygen partial pressure in the exhaust gas is Px, the gas introduction portion 8 which is a gap also serving as a means for limiting the diffusion of the gas.
Assuming that the diffusion coefficient is D, the amount Q of O ₂ that enters into is Q = D (Px−Py) and Py≈0, so that Q≈D · Px.

The O ₂ in an amount equivalent to the amount of the O _2, by the pump current Ip connexion by moving the second solid electrolyte 7, so to maintain the oxygen concentration of the gas inlet portion 8 constant, IparufaQ Ip = It becomes K ₁ · Px. However, K ₁ is a constant.

Therefore, the pump current Ip is as shown in FIG.
The oxygen concentration in the exhaust gas, and consequently the stoichiometric air-fuel ratio, changes continuously with respect to the lean-range air-fuel ratio.

FIG. 6 shows an electronically controlled fuel injection device (EGI) according to the present invention.
FIG. 3 is a block diagram showing the overall configuration of an embodiment applied to a fuel engine that supplies fuel according to FIG.

First, the EGI fuel supply system includes a basic injection amount calculation unit 4
1, an increase correction unit 42, a fuel cut correction unit 43, an air-fuel ratio feedback correction unit 44, which is the air-fuel ratio correction means E in FIG. 1, a battery voltage correction unit 45, a putter transistor 46, and an engine mounting unit. It consists of an Injector 47.

The basic injection amount calculation unit 41 calculates the basic injection amount Tp of fuel for each rotation based on the intake air flow rate Q and the engine speed N.

The various increase correction units 42 use the engine cooling water temperature Tw, the on / off signal of the throttle switch, and the like to determine the basic injection amount T.
Various increase corrections (water temperature increase correction, start and post-start increase increase correction, idle increase increase correction, mixture ratio increase correction, etc.) are performed on p to obtain the corrected injection amount T ₁ .

The fuel cut correction unit 43 receives the fuel cut signal FC from the fuel cut determination unit 60, which will be described later, when the fuel cut signal FC is input.
₁ is multiplied by the fuel cut coefficient to set the corrected injection amount T ₂ to zero.

The air-fuel ratio correction unit 44 includes an air-fuel ratio correction coefficient determination unit 5 which will be described later.
The corrected injection amount T ₂ is multiplied by the air-fuel ratio correction coefficient α from ₃ and output as the corrected injection amount T ₃ .

The battery voltage correction unit 45 corrects the corrected injection amount T ₃ according to the battery voltage VB and outputs a pulse signal Ti having a pulse width corresponding to the fuel injection amount.

As a result, the power transistor 46 drives the injector 47 to inject fuel for a time period corresponding to the pulse width of the pulse signal Ti.

Fuel (for example, gasoline) injected by the injector 47 is mixed with intake air, and the mixture is supplied into the cylinder of the engine and burned.

Next, the portion related to the fuel ratio feedback control system will be described.

First, as described above, the range from the theoretical air-fuel ratio to the lean range is determined by the oxygen sensor (air-fuel ratio sensor) 1 and the air-fuel ratio detection circuit 21 installed in the engine exhaust pipe constituting the air-fuel ratio detecting means A of FIG. Continuously detected air-fuel ratio over,
The air-fuel ratio detection circuit 21 outputs a voltage signal Vi indicating the air-fuel ratio (A / F) at each time point.

The target value determination unit 51 sets the control target air-fuel ratio to the target value TL as a value corresponding to the voltage signal Vi from the air-fuel ratio detection circuit 21.
To decide.

The differential amplifier 52 has a deviation ΔVi (ΔVi = V) between the target value TL from the target value determination unit 51 and the voltage signal Vi which is the actual detected value of the air-fuel ratio input from the air-fuel ratio detection circuit 21.
i-TL) is detected and output.

The target value determining section 51 and the differential amplifier 52 constitute the deviation detecting means C in FIG.

The air-fuel ratio correction coefficient determination unit 53 constitutes the air-fuel ratio correction coefficient determination means D of FIG. 1 together with the fuel cut determination unit 60 described later, and the deviation ΔVi detected by the differential amplifier 52 is integrated coefficient described later. The determining unit 63 performs integration processing with the determined integration coefficient C to determine the air-fuel ratio correction coefficient α, and outputs this air-fuel ratio correction coefficient α to the air-fuel ratio feedback back correcting unit 44.

Accordingly, the air-fuel ratio feedback correction unit 44 corrects the fuel supply amount by multiplying the air-fuel ratio correction coefficient α by the correction injection amount T ₂ corresponding to the predetermined fuel supply amount as described above.

On the other hand, the voltage signal Vi from the air-fuel ratio detection circuit 21 is also input to the first and second comparators 55 and 56.

The first comparator 55 outputs the voltage signal Vi from the air-fuel ratio detection circuit 21 to the first reference value V from the positive power source 57.
Compared _1, and outputs a first comparison signals _{S 1} becomes high level "H" when the Vi ≦ _{V 1.}

In addition, the second comparator 56 includes the air-fuel ratio detection circuit 21.
From the positive power supply 58 and the second reference value V from the positive power supply 58
₂ (V ₂ <V ₁ ) is compared, and a second comparison signal S ₂ that becomes a high level “H” is output when Vi ≧ V ₂ .

The first and second reference values V ₁ and V ₂ of the first and second comparators 55 and 56 are not fixed values,
It can also be set based on the value of the voltage signal Vi from the air-fuel ratio detection circuit 21 immediately before the fuel cut.

The fuel cut determination unit 60 determines whether or not the fuel cut is based on the on / off state of the throttle switch, the engine speed N, the vehicle speed υ, etc., and when the fuel cut condition is satisfied, the fuel cut is set to the high level "H". The command signal FC is output.

The AND circuit 61 includes the first comparator 55 from the first comparator 55.
Comparative Formula No. S _{1 of,} type Fuyuerukatsuto command signal FC from the second comparison signal S ₂ and the Fuyuerukatsuto determination unit 60 from the second comparator 56, the signal S _1,
The determination signal S ₃ that becomes “H” is output only when both S ₂ and FC are “H”.

The response time measuring unit 62 inputs the determination signal S ₃ from the AND circuit 61, measures the time when the determination signal S ₃ is “H”, and outputs the measurement result as the response time measurement signal T ₀ . .

The response time measuring unit 62 may output the measurement result of one time, or may output the average value of the measurement results of several times.

The integration coefficient determination unit 63 inputs the response time measurement signal T ₀ from the response time measurement unit 62, determines an integration coefficient C that is a control coefficient (control time constant) corresponding to this response time T ₀ , It outputs to the air-fuel ratio correction coefficient determination unit 53.

Further, the third comparator 64 includes a response time measuring unit 62.
The response time measurement signal T ₀ from the positive power supply 65 is compared with the _third reference value V ₃ from the positive power source 65, and the clamp command signal S ₄ that becomes “H” when T ₀ ≧ V ₃ is determined as the air-fuel ratio correction coefficient. It is output to the unit 53.

The air-fuel ratio correction coefficient determination unit 53 receives the fuel cut command signal FC from the fuel cut determination unit 60 (FC = “H”) and the clamp signal S ₄ from the third comparator 64. (S ₄ =
At the time of "H", the air-fuel ratio correction coefficient determination α is fixed to a predetermined value.

Further, in this embodiment, the first and second comparators 55 and 56, the positive power supplies 57 and 58, the fuel cut determination unit 60, the AND circuit 61, the response time measurement unit 62 and the integration coefficient determination unit 63 are used as the first. It constitutes the control coefficient determination means B shown in the figure.

Further, the basic injection amount calculation amount 41, various increase correction units 42,
The fuel cut correction unit 43, the air-fuel ratio feedback back correction unit 44, the battery voltage correction unit 45, the air-fuel ratio correction coefficient determination unit 53, the fuel cut determination unit 60, the response time measurement unit 62, and the integration coefficient determination unit 63 are the CPU (central processing unit). , ROM, RAM, I / O (input / output device) and the like.

In this case, the integration coefficient determination unit 63 has a table of each response time T ₀ measured by the response time measurement unit 62 and the integration coefficient C, and the integration is performed by a table backup according to the response time T ₀ . Determine the coefficient C.

Next, the operation of this embodiment thus configured will be described with reference to FIGS. 7 and 8.

First, in the closed control before time t _{0 in} FIG. 7, the deviation between the actual air-fuel ratio and the control target air-fuel ratio corresponds to the actual air-fuel ratio detected by the oxygen sensor 1 and the air-fuel ratio detection circuit 21. The differential amplifier 52 detects the difference ΔVi between the voltage signal Vi and the target value TL from the target value determination unit 51 corresponding to the control target air-fuel ratio, and the air-fuel ratio correction coefficient determination unit 53 determines this deviation ΔVi. The integration coefficient C determined by the unit 63 is integrated to determine the air-fuel ratio correction coefficient determination α, and the air-fuel ratio feedback correction unit 44 corrects the fuel supply amount according to the air-fuel ratio correction coefficient determination α. Therefore, the air-fuel ratio is feedback-controlled to the control target air-fuel ratio.

Therefore, during this closed control, the oxygen sensor 1
Pump current Ip supplied to the air-fuel ratio detection circuit 2
The voltage signal Vi detected from 1 is substantially constant near the target value TL, as shown in FIG.

At this time, the fuel cut command signal FC is not output from the fuel cut determination unit 60 (FC =
"L"), the determination signal S output from the add circuit 61
₃ is the first from the first and second comparators 55 and 56.
Regardless of the second comparison signals S ₁ and S ₂ , it is “L” as shown in FIG. 7B.

Therefore, the integration coefficient determination unit 63 does not change the integration coefficient C output to the air-fuel ratio correction coefficient determination unit 53.

When the fuel cut condition is reached at time t ₀ in FIG. 7 from this state, the fuel cut determination unit 60 outputs the fuel cut command signal FC (FC = “H”), so that the fuel cut correction unit 43 sets T ₂ = 0. It is controlled and the fuel supply is stopped.

Therefore, since the air-fuel mixture drawn into the engine and hence the exhaust gas are in the atmospheric state, the value of the pump current Ip supplied to the oxygen sensor 1, that is, the value of the voltage signal Vi output from the air-fuel ratio detection circuit 21 is As shown in FIG. 7 (a), the fuel cut suddenly changes from the time point t ₀ , that is, increases sharply and saturates at a value corresponding to the atmosphere.

At this time, the voltage signal Vi from the air-fuel ratio detection circuit 21 is also input to the first and second comparators 55 and 56.

Therefore, the second comparison signal S ₂ output from the second comparator 56 is such that the voltage signal Vi from the air-fuel ratio detection circuit 21 is in the range of Vi <V _{2 with} respect to the second reference value V ₂ . ,
That is, before the time point t _{1 in} FIG. 7, it becomes “L”, and when Vi ≧ V ₂ , that is, at the time point t ₁ in FIG. 7, it changes from “L” to “H”.

On the other hand, the first comparison signal S ₁ output from the first comparator 55 is the voltage signal Vi from the air-fuel ratio detection circuit 21.
Is "H" with respect to the first reference value V ₁ during Vi <V ₁ , that is, before time t _{2 in} FIG.
When> V ₁ is reached, that is, at time t ₂ in FIG.

That is, these first and second comparators 55, 5
6, the timing for measuring the rate of change when the voltage signal Vi (detection value) of the air-fuel ratio detection circuit 21 suddenly changes is determined.

At this time, the fuel cut command signal FC output from the fuel cut judgment unit 60 is "H", and therefore the judgment signal S output from the AND circuit 61.
_As shown in FIG. 7 (B), ₃ is a time point t when the second comparison signal S ₂ from the second comparator 56 becomes “H”.
₁ to the first comparison signal S from the first comparator 55
Only until the time t ₂ when ₁ becomes “L”, that is, V
_The high level becomes “H” only during ₂ ≦ Vi ≦ V ₁ .

The time T ₀ during which the determination signal S ₃ from the AND circuit 61 is “H” corresponds to the responsiveness of the oxygen sensor 1.

Therefore, the response time measurement unit 62 measures the time T ₀ during which the determination signal S ₃ of the AND circuit 62 is “H” and outputs it as the response time measurement signal T ₀ .

That is, the rate of change when the voltage signal Vi of the air-fuel ratio detection circuit 21 suddenly changes is the time from when the voltage signal Vi exceeds the second reference value V ₂ to when it exceeds the first reference value V _1. Is measured as.

Accordingly, the integration coefficient determination unit 63 uses the response time T measured by the response time measurement unit 63 from the table showing the relationship between the response time T ₀ and the integration coefficient C as shown in FIG. 8, for example.
_The integration coefficient C corresponding to ₀ is looked up and the integration coefficient C is output to the air-fuel ratio correction coefficient determination unit 53.

Therefore, the air-fuel ratio correction coefficient determination unit 53 subsequently integrates the deviation ΔVi from the differential amplifier 52 with the integration coefficient C to determine the air-fuel ratio correction coefficient α.

The relationship between the response time T ₀ and the integration coefficient C is as shown in FIG. 8 as the response time T ₀ becomes longer.
To reduce.

Accordingly, when the response of the oxygen sensor 1 is fast, the integration coefficient C is increased to improve control followability, and when the response is slow, the integration coefficient C is reduced to prevent occurrence of overshoot, undershoot, hunting, and the like. it can.

That is, the integration coefficient determination unit 63 always determines the most appropriate integration coefficient C corresponding to the responsiveness of the oxygen sensor 1.

Then, in this device, when the response time measurement signal T ₀ reaches the third reference value V ₃ or more (T ₀ ≧ V ₃ ), the clamp signal S ₄ is output from the third comparator 64, Accordingly, the air-fuel ratio correction coefficient determination unit 53 sets the air-fuel ratio correction coefficient α to a predetermined fixed value.

As a result, when the response time T ₀ becomes particularly long, it can be judged that the accuracy of air-fuel ratio detection by the oxygen sensor 1 is deteriorated and good feedback control cannot be performed. Therefore, the feedback control is stopped and the open control is performed. Move to.

As described above, in this air-fuel ratio control device, the response of the oxygen sensor is measured, and the control coefficient at the time of closed control is determined based on the measurement result.

Therefore, even if the response of the oxygen sensor and the control coefficient of the control system are not matched at the time of assembly or replacement of the oxygen sensor, or if the response changes due to deterioration of the oxygen sensor over time. However, since an appropriate control coefficient is automatically determined according to the response of the oxygen sensor, it is possible to always perform feedback control with a good air-fuel ratio, and there is no need to incorporate an oxygen sensor and control system by matching. Production man-hours etc. will decrease.

By the way, it is possible to judge the response based on the output of the oxygen sensor during feedback control to some extent, but in that case, the response of the control system itself changes due to fuel properties and environmental conditions. In particular, it is difficult to accurately determine the change in responsiveness of only the oxygen sensor under operating conditions where the change in the air-fuel ratio is small. On the other hand, as described above, the air-fuel ratio changes sharply in steps during fuel cut, and the responsiveness of the control system itself does not affect the rate of change, so at this point the response peculiar to the oxygen sensor The sex can be accurately determined.

Further, when the responsiveness of the oxygen sensor is extremely poor as in the above-described embodiment, the feedback control is stopped and the open control is performed, whereby the drivability is not adversely affected.

In the above embodiment, the rate of change of the detected value of the air-fuel ratio at the fuel cut, that is, the response time of the oxygen sensor is measured, but the present invention is not limited to this, and the response time when returning from the fuel cut to normal operation May be measured, or the response times of both may be measured.

That is, when the detected value of the air-fuel ratio changes abruptly, there is a transition from the normal closed control to the open control and a transition from the open control to the closed control.

Further, in the above embodiment, the example of the integral coefficient is described as the control coefficient, but generally in the feedback control, the proportional component (P minute), the integral component (I minute), the differential component (D minute).
The control coefficient used in the air-fuel ratio feedback control is not limited to the integral coefficient, and the proportional coefficient and the differential coefficient can be similarly determined.

Furthermore, the oxygen sensor and the air-fuel ratio detection circuit are not limited to those in the above-mentioned embodiment, and any device capable of detecting the air-fuel ratio in the lean range from the theoretical air-fuel ratio may be used, and a wide range from the rich range to the lean range. It may be one that can detect the air-fuel ratio.

As a device capable of detecting from the rich region to the lean region, for example, a device in which the pump current supplied to the sensor of FIG. 2 can be supplied in both directions is considered. Of course, it is not limited to this.

Effect As described above, according to the present invention, the response time to a predetermined change when the detected value of the air-fuel ratio suddenly changes, that is, the responsiveness of the oxygen sensor is measured, and the closed control is performed based on this result. Since the control coefficient of the oxygen sensor is determined, the change in the response of the control system itself, which is affected by the fuel properties and environmental conditions, is eliminated, and the control coefficient during closed control appropriate for the response of the oxygen sensor itself is eliminated. Can be automatically determined, and the feedback control can always be performed with a good air-fuel ratio.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing a basic configuration of an air-fuel ratio control device according to the present invention, FIGS. 2 and 3 are a longitudinal sectional view and an exploded perspective view showing an example of an oxygen sensor used in the present invention, FIG. 4 is a circuit diagram showing an example of an air-fuel ratio detection circuit using this oxygen sensor, FIG. 5 is a diagram showing the relationship between the detection output from the air-fuel ratio detection circuit and the air-fuel ratio, and FIG. 6 is FIG. 8 is a block diagram showing an embodiment in which the present invention is applied to an EGI specification internal combustion engine, and FIG. 7 is a diagram showing changes in the air-fuel ratio detection output at the time of fuel cutting, which is used to explain the operation of FIG. FIG. 5 is a diagram showing a relationship between the response time of the oxygen sensor and the integration coefficient. 1 ... Oxygen sensor, 21 ... Air-fuel ratio detection circuit 44 ... Air-fuel ratio feedback back correction unit 51 ... Target value determination unit, 52 ... Differential amplifier 53 ... Air-fuel ratio correction coefficient determination unit 55 ... First Comparator 56 ... Second comparator 60 ... Fuel cut judgment unit 62 ... Response time measurement unit 63 ... Integration coefficient determination unit

Claims (1)

[Claims] 1. An air-fuel ratio control device for controlling an air-fuel ratio of an air-fuel mixture supplied to a cylinder of an internal combustion engine, wherein air-fuel ratio detecting means for continuously detecting an air-fuel ratio within a predetermined range by an oxygen concentration in an engine exhaust passage. And an operating state in which the detected value of the air-fuel ratio should suddenly change, and the air-fuel ratio correction coefficient during closed control is determined based on the response time of the detected value of the air-fuel ratio to a predetermined change in the air-fuel ratio during the operating state. Control coefficient determining means for determining a control coefficient for controlling the deviation, deviation detecting means for detecting a deviation between a value detected by the air-fuel ratio detecting means and a predetermined target value, and the deviation detected by the deviation detecting means Air-fuel ratio correction coefficient determination means for processing the control coefficient determined by the coefficient determination means to determine the air-fuel ratio correction coefficient, and air for correcting the air-fuel ratio based on the air-fuel ratio correction coefficient determined by the air-fuel ratio correction coefficient determination means Burn Air-fuel ratio control system for an internal combustion engine, characterized in that a correcting means.