JPH09317531A - Air fuel ratio feedback controller for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the concentration of an air-fuel ratio by changing a rear feedback correction coefficient in response to the degree of the deviation when a catalyst or an air-fuel ratio sensor is deteriorated and an air-fuel ratio in a downstream side of the catalyst is deviated from a target air-fuel ratio. SOLUTION: The range of an air-fuel ratio detected by an O2 sensor 47 in a downstream side is divided into four variation ranges with the boundaries of an target air-fuel ratio, a rich base air-fuel ratio and a lean base air-fuel ratio. When an air-fuel ratio detected by the O2 sensor 47 in a downstream side is in the range of the target air-fuel ratio and the rich base air-fuel ratio, a rear feedback correction coefficient is increased and, when the air-fuel ratio detected by the O2 sensor 47 in a downstream side is in the range of the target air-fuel ratio and the leans base air-fuel ratio, the rear feedback correction coefficient is increased more. The feedback correction coefficient is corrected by the O2 sensor 46 in an upstream side by using the rear feedback correction coefficient.

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 feedback control system for an engine, and in particular, to an air-fuel ratio sensor for detecting an air-fuel ratio upstream and downstream of a catalyst provided in an exhaust system. The present invention relates to an air-fuel ratio feedback control device that controls the fuel injection amount of an engine based on the detection result of a fuel ratio sensor.

[0002]

2. Description of the Related Art Electronically controlled fuel injection devices that electronically control the amount of fuel injected into a combustion chamber of an engine together with air are well known, and an appropriate amount of fuel and air are mixed for various engine operating conditions. Is possible. Conventionally,
When such an electronically controlled fuel injection device is used, a sensor for detecting the amount of oxygen contained in the exhaust gas in the exhaust system in order to control the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber to near the stoichiometric air-fuel ratio. The fuel supply amount is adjusted based on the output signal from this sensor.

For example, conventionally, an O ₂ sensor has been installed as a sensor for detecting the air-fuel ratio on the upstream side and the downstream side of the catalyst in the exhaust system, and the air-fuel ratio is based on the output signal from the upstream O ₂ sensor. Feedback control is performed so that the air-fuel ratio becomes stoichiometric, and the downstream side O
Always controlled so as to perform the supply of fuel at the stoichiometric air-fuel ratio near by correcting the output signal from the upstream O ₂ sensor based on the _second sensor of the detection result, the control is performed to achieve the purification of exhaust gas There is.

This is so-called double O ₂ sensor control, and feedback control is performed using this control in response to changes in the output characteristics of the O ₂ sensor due to aging deterioration, etc. Is being purified.

Further, in Japanese Patent Laid-Open No. 7-95383, a wide range air-fuel ratio sensor is adopted as an air-fuel ratio sensor upstream of the catalyst, and the output characteristics change due to various factors of the air-fuel ratio sensor upstream of the catalyst. It is described that the accompanying deterioration of feedback control accuracy is prevented and more reliable control is performed.

[0006]

According to the above publication, it is judged whether the air-fuel ratio detected by the downstream O ₂ sensor is on the rich side or the lean side with reference to the target air-fuel ratio. If it is determined that the rear side is on the rich side or the lean side, the rear feedback correction coefficient is calculated by constant proportional integration. And O ₂ on the upstream side
The feedback correction coefficient obtained by proportionally integrating the detection result of the sensor is corrected by this rear feedback correction coefficient, and is shifted to the rich side or the lean side as a whole to converge the air-fuel ratio to the target air-fuel ratio. .

However, since the rear feedback correction coefficient is always obtained by a constant proportional integral, it is insufficient to correct the feedback correction coefficient according to the degree of change in the air-fuel ratio. For example, even when the air-fuel ratio detected by the O ₂ sensor on the downstream side largely shifts to the rich side than the target air-fuel ratio, the rear feedback obtained by the same proportional-plus-integral control as when slightly shifting to the rich side. Correction is performed using the correction coefficient. Therefore,
Since it is not possible to perform feedback correction sufficiently corresponding to the deviation of the air-fuel ratio, it takes time to converge the air-fuel ratio to the target air-fuel ratio, and the convergence is deteriorated.

The present invention has been made in view of the above problems, and an object thereof is to perform feedback control corresponding to a change in the output characteristic of an air-fuel ratio sensor and to converge the air-fuel ratio quickly near the target air-fuel ratio. An object of the present invention is to provide an air-fuel ratio feedback control device for an engine, which has excellent properties.

[0009]

To achieve the above object, an air-fuel ratio feedback control system for an engine according to the present invention sets a target air-fuel ratio and a target air-fuel ratio within a region of an air-fuel ratio detected by an air-fuel ratio sensor on a downstream side. The rich reference air-fuel ratio provided on the rich side of the fuel ratio and the lean reference air-fuel ratio provided on the lean side of the target air-fuel ratio are divided into four deviation regions. Then, the rear feedback correction coefficient is set in the rich side region that exceeds the rich reference air-fuel ratio as compared with the case where the air-fuel ratio detected by the downstream air-fuel ratio sensor is in the region between the target air-fuel ratio and the rich reference air-fuel ratio. In some cases, it is set to a large value, and when the air-fuel ratio detected by the downstream air-fuel ratio sensor is in the region between the target air-fuel ratio and the lean reference air-fuel ratio Set it to be larger when it is in the area. Then, the feedback correction coefficient by the upstream air-fuel ratio sensor is corrected using the rear feedback correction coefficient set according to this deviation region.

Therefore, when a deviation of the air-fuel ratio on the downstream side of the catalyst occurs due to deterioration of the upstream-side air-fuel ratio sensor or the catalyst, etc., the rear-feedback correction coefficient corresponding to the deviation causes the upstream-side air-fuel ratio sensor to detect the deviation. By correcting the feedback correction coefficient, the air-fuel ratio can be converged to near the target air-fuel ratio in a short time.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic overall configuration diagram of an automobile engine in which an engine air-fuel ratio feedback control device according to the present invention is used.

An intake passage 12 and an exhaust passage 14 communicate with the body of the horizontally opposed engine 10. Intake passage 12
An intake chamber 16 is opened in the engine room (not shown) on the upstream side. The downstream side of the intake passage 12 branches from the surge tank 18 and communicates with each cylinder 20, and the downstream end of the intake passage 12 is connected to the intake port 2
2 to communicate with each combustion chamber 24.

In the intake passage 12, from the upstream side thereof,
An air cleaner 30 for removing dust in the air, an air flow meter 32 for detecting the intake air amount Q, and a throttle valve 34 for controlling the intake air amount Q according to the depression amount of an accelerator pedal (not shown) are provided. An injector 36 is provided on the downstream side of the intake passage 12 toward the intake port 22.
Reference numeral 6 is for atomizing and injecting the fuel pressure-fed and supplied from the fuel tank 37.

On the other hand, an exhaust pipe 42 is provided on the upstream side of the exhaust passage 14 so as to communicate with each cylinder of the engine body 10, and the upstream end of the exhaust pipe 42 is connected to each combustion chamber 24 via each exhaust port 28. Is in communication with. The exhaust passage 14 is provided with a catalyst 44 such as a three-way catalyst for purifying the exhaust gas on the upstream side thereof, and its downstream end communicates with a muffler 40 attached to a rear portion (not shown) of the vehicle body. An upstream O ₂ sensor 46 that detects the air-fuel ratio by detecting the oxygen concentration in the exhaust gas is provided on the upstream side of the catalyst 44. The catalyst 44 is provided downstream of the catalyst 44.
A downstream O ₂ sensor 47 is provided to detect the air-fuel ratio by detecting the oxygen concentration in the exhaust gas purified by.

Further, each cylinder head 54 of the engine body 10 is provided with an ignition plug 56 facing the inside of the combustion chamber 24. The ignition plug 56 is supplied with high power via an igniter 55 and an ignition coil 57. Depending on the voltage
The mixture in the combustion chamber 24 is forcibly ignited at a predetermined ignition timing.

The engine body 10 is provided with a crank angle sensor 58 for detecting the crank angle of the engine and the engine speed Ne, and a water temperature sensor 59 for detecting the warm-up state (water temperature Tw) of the engine. Further, the throttle valve 34 is provided with a throttle opening sensor 60 for detecting the throttle opening θ. Then, an electronic control unit (hereinafter, simply referred to as "ECU") 6 which receives the detection signals from these sensors and outputs the control signals to the respective control means of the engine to control the engine operation 6
2 are provided.

FIG. 2 is a structural explanatory view showing the internal structure of the ECU 62 shown in FIG.

As shown in the figure, the ECU 62 has an input interface 62a for inputting a detection signal from each sensor and an output interface 6 for outputting a drive control signal to each member.
2b, a CPU 62c as a main arithmetic unit, a ROM storing a control program and preset fixed data
62d, a RAM for storing data after processing signals from each sensor and data processed by the CPU 62c
62e, a backup RAM 62f for storing learning data and the like, a timer 62g, etc. are connected to each other by a bus line 62h to constitute a microcomputer system.

Next, the first embodiment of the present invention will be described in more detail with reference to the drawings. FIG. 3 is a block diagram showing the main constituent parts of the air-fuel ratio feedback control apparatus according to the present embodiment and the context of the operation of each constituent part.

As shown, the engine operating condition detector 7
Reference numeral 0 denotes a crank angle sensor 58, an air flow meter 32, a throttle opening sensor 60, a water temperature sensor 59, and a vehicle speed sensor (not shown). Based on a detection signal from each sensor, a map or the like stored in the ROM 62d indicates an engine. Detect the current operating state of the.

The reference air-fuel ratio setting unit 72 is a reference air-fuel ratio which is a target of the air-fuel ratio feedback control and a reference air-fuel ratio which is a different reference from the target air-fuel ratio according to the engine operating condition detected by the engine operating condition detecting unit 70. Set the fuel ratio. In the present embodiment, the target air-fuel ratio is set to the stoichiometric air-fuel ratio, and the reference air-fuel ratio is set to the rich reference air-fuel ratio on the rich side and the lean reference air-fuel ratio on the lean side with reference to the theoretical air-fuel ratio.

The feedback correction coefficient calculation unit 74 calculates the feedback correction coefficient α by inputting the detection signal of the upstream O ₂ sensor 46 and performing proportional-plus-integral control (hereinafter simply referred to as "PI control"). The rear feedback correction coefficient calculation unit 76 calculates a rear feedback correction coefficient that corrects the feedback correction coefficient α by PI controlling the detection signal of the downstream O ₂ sensor 47.

The air-fuel ratio feedback control means 76 includes a feedback correction coefficient α calculated by the feedback correction coefficient calculation section 74 and an engine operating state detection section 70.
Feedback control of the air-fuel ratio is performed based on the engine operating state detected by. Then, the fuel injection amount calculation unit 8
0 calculates the fuel injection amount injected from the injector 36.

A method of calculating the fuel injection amount will be described below with reference to FIG.

FIG. 4 is a flow chart for calculating the fuel injection pulse width Ti per unit time, which is performed by the fuel injection amount calculation unit 80 and finally represents the amount of fuel to be injected from the injector 36.

Step (hereinafter simply referred to as "S") S1
In 01, the air flow meter 32 and the crank angle sensor 58
By detecting the intake air amount Q and the engine speed Ne, the current engine operating state is detected. Then, in S102, the basic injection pulse width Tp is calculated from the engine operating state detected in S101.

Here, the basic injection pulse width Tp is calculated by T
p = K × Q / Ne, where K is the injector 36
Is a characteristic correction coefficient possessed by. This basic injection pulse width T
p represents the intake air weight per one engine revolution obtained by dividing the intake air amount Q measured by the air flow meter 32 by the engine speed Ne, and is represented by the injection pulse width like the fuel injection pulse width Ti. be able to.

Next, in S103, the feedback correction coefficient calculation unit 74 calculates the feedback correction coefficient α. Then, in S104, the fuel injection pulse width Ti per unit time, which finally represents the amount of fuel to be injected from the injector 36, is calculated. This fuel injection pulse width Ti
Is calculated by the following equation (1).

Ti = Tp × α × COEF × (1 + KL) + Ts (1) Here, COEF is various correction factors, for example, when the cooling water temperature of the engine is low or when the engine is accelerated, the amount of fuel is increased. Is added for. Further, KL is a learning correction coefficient obtained by referring to the air-fuel ratio learning value table with interpolation calculation. Then, Ts is a voltage correction coefficient for correcting the invalid time varying with the battery voltage, and means the invalid pulse width for ensuring the injection delay of the injector 36. Then, after setting the fuel injection pulse width Ti in S105, the routine exits (RST).

Therefore, in the fuel injection amount calculation section 80, fuel is injected from the injector 36 based on the fuel injection pulse width Ti obtained by the above equation (1).

FIG. 5 is an explanatory view showing the detection result of the upstream O ₂ sensor 46 and the change of the feedback correction coefficient α obtained by the PI control based on this detection result with time. As shown, PI control is performed based on the detection result of the upstream O ₂ sensor 46.

By this PI control, the feedback correction coefficient α is judged to be rich / lean for the current air-fuel ratio by comparing the detection result of the upstream O ₂ sensor 46 with the theoretical air-fuel ratio, and the air-fuel ratio is rich. If it is determined, it decreases at a constant rate (between ab in the figure), and if it is determined to be lean, it increases at a constant rate (between bc), and the air-fuel ratio changes from lean to rich or from rich to lean. When switching, it changes in a staircase. The rate of increase / decrease is determined by the integral amount of PI control (hereinafter, simply referred to as “I minute”), and the skip amount is proportional to PI control (hereinafter, simply “P min”).
Minutes)).

[0033] Then, in order to control the air-fuel ratio to the stoichiometric air-fuel ratio near according to the detection result of the upstream O ₂ sensor 46, the upstream O ₂ feedback correction when the output value of the sensor 46 is switched from lean to rich When the coefficient α is shifted to the lean side (−PL) and conversely the output value of the upstream O ₂ sensor 46 is switched from rich to lean, control is performed to shift the feedback correction coefficient α to the rich side (+ PR). . The amount of this shift varies depending on the output characteristics of the O ₂ sensor, and the P component in consideration of this shift amount can be calculated by the following formula. here,
The P side on the rich side is set as PR and the P side on the lean side is set as PL.

PR = P0 + PSFT + PHOS (2) PL = P0-PSFT-PHOS (3) Here, P0 is a fixed value set in advance in the ROM 62d and indicates a basic skip amount. PSFT is a feedforward value set in advance for each engine operating region according to the self-characteristics of the upstream O ₂ sensor 46. PHOS is a rear feedback correction coefficient that corrects the feedback correction coefficient α based on the detection result of the downstream O ₂ sensor 47. FIG. 5 (A) and FIG. 5 (B)
Shows a PR component and a PL component calculated by equations (2) and (3) using these values.

This rear feedback correction coefficient PHOS
Is controlled so that the air-fuel ratio on the downstream side of the catalyst 44 can also be maintained near the stoichiometric air-fuel ratio, the feedback correction coefficient α is shifted to the rich side or the lean side by the rear feedback correction coefficient PHOS, and the upstream O ₂ sensor 4
The feedback control of the air-fuel ratio can be performed according to the change of the output characteristic of No. 6 or the deterioration of the catalyst 44.

The method of calculating the rear feedback correction coefficient PHOS, which is a feature of the present invention, will be described below with reference to FIGS. 6 and 7. FIG. 6 is an explanatory diagram showing the relationship between the air-fuel ratio on the downstream side of the catalyst 44 and the output value of the downstream O ₂ sensor 47. As shown, the downstream O ₂ sensor 4
The output value of 7 has a substantially crank shape whose output greatly differs from the stoichiometric air-fuel ratio.

The range of the output value is the main slice level Msl which is the target air-fuel ratio (theoretical air-fuel ratio in the present embodiment), and the main slice level Msl is used as a reference for further determination of the air-fuel ratio on the rich side. Rich slice level Rs provided as the rich reference air-fuel ratio
1 and a lean slice level Lsl, which is also provided as a lean reference air-fuel ratio on the lean side, are divided into four regions.

Here, an output region between the main slice level Msl and the rich slice level Rsl is referred to as a deviation b region, and an output region on the rich side of the rich slice level Rsl is referred to as a deviation a region. Further, an output region between the main slice level Msl and the lean slice level Lsl is defined as a deviation c region, and an output region on the lean side of the lean slice level Lsl is defined as a deviation d region.

The rear feedback correction coefficient PHOS is
Different PI control depending on in which of the above deviation regions the output value of the downstream O ₂ sensor 47 exists (hereinafter, simply referred to as PH
It is calculated by the OS calculation PI control). This P
The HOS calculation PI control will be described below with reference to FIG. 7.

FIG. 7 shows the relationship between the change in the rear feedback correction coefficient PHOS calculated by the PHOS calculation PI control and the output value of the downstream O ₂ sensor 47. FIG. A change in the output value of the downstream O ₂ sensor 47 is shown, and FIG. 6B shows a rear feedback correction coefficient PHO obtained by PI controlling the output value.
S is shown.

First, in FIG. 7 (A), the output value of the downstream O ₂ sensor 47 exceeds the main slice level Msl from the lean side (point 1), shifts to the rich side, and the main slice level Msl and rich. Slice level Rsl
And (between lm), the rear feedback correction coefficient PHOS is skipped to the lean side by P minutes set in advance in the deviation b region by the PHOS calculation PI control and gradually reduced to the lean side at I minutes. .

Next, when the output value of the downstream O ₂ sensor 47 exceeds the rich slice level Rsl (point m) and is on the rich side (between mn) of the rich slice level Rsl, the rear feedback correction is performed. The coefficient PHOS is PH
By the PI control for OS calculation, it skips to the lean side by a preset P amount in the deviation a region and gradually decreases to the lean side with an I component larger than the I component in the deviation b region.
Then, when the output value of the downstream O ₂ sensor 47 exceeds the rich slice level Rsl from the rich side (n point) and shifts again to between the main slice level Msl (no), in the deviation b region. It skips to the lean side in P minutes and gradually decreases to the lean side in I minutes.

Then, the output value of the downstream O ₂ sensor 47 exceeds the main slice level Msl from the rich side (o
Point), shift to lean side, and main slice level M
When it is between sl and the lean slice level Lsl (between ops), the rear feedback correction coefficient PHOS is P.
The PI control for HOS calculation skips to the rich side in P minutes set in advance in the deviation c region and gradually increases to the rich side in I minutes. Next, the output value of the downstream O ₂ sensor 47 exceeds the lean slice level Lsl (p
Point), and further to the lean side and on the lean side (between pq) of the lean slice level Lsl, skip to the rich side by a preset P amount in the deviation d area and shift to the deviation c area. I gradually increases to the rich side with I larger than I.

Then, the output value of the downstream O ₂ sensor 47 exceeds the lean slice level Lsl from the lean side and exceeds the lean slice level Lsl (q point), and shifts again to the main slice level Msl (between qr). In this case, the rear feedback correction coefficient PHOS is skipped to the lean side by P minutes in the deviation c region and gradually increased to rich side by I minutes by the PHOS calculation PI control. And
The output value of the downstream O ₂ sensor 47 exceeds the main slice level Msl from the lean side (point r), shifts to the rich side, and is between the main slice level Msl and the rich slice level Rsl (between rs). Deviation b
Skip to the lean side at P minutes in the region and gradually decrease to the lean side at I minutes.

Then, when the output value of the downstream O ₂ sensor 47 exceeds the main slice level from the rich side (point s),
When shifting to the lean side, the rear feedback correction coefficient PHOS is skipped to the rich side by P in the deviation c region and gradually increased to I by the minute by the PI control for PHOS calculation.

As described above, the rich slice level Rsl and the lean slice level Lsl are provided in the air-fuel ratio region,
When the air-fuel ratio exceeds the rich slice level Rsl or the lean slice level Lsl, by performing PI control in the deviation a region and the deviation d region, respectively, the output value of the downstream O ₂ sensor 47, that is, the downstream of the catalyst 44. It is possible to obtain the rear feedback correction coefficient PHOS that is more suitable for the changing state of the air-fuel ratio on the side.

Since the P component added when the rich slice level Rsl and the lean slice level Lsl are exceeded is a minute value, the P component is added beyond the main slice level Msl from the rich side and the lean side. When the rich slice level Rsl and the lean slice level Lsl are exceeded, the control may be performed by changing only the I component without adding the P component.

Further, a plurality of rich slice levels Rsl and a plurality of lean slice levels Lsl are provided on the rich side and the lean side, respectively, to form a plurality of deviation regions, which are different for each deviation region formed and are different from the main slice level Msl.
The PI feedback control is performed more finely by using the deviation area set so that the rear feedback correction coefficient increases as the distance increases, and the rear feedback correction coefficient PHOS
May be asked.

The main slice level Ms1, the rich slice level Rs1, and the lean slice level Ls1.
It is also possible to omit any one of the above and simplify the deviation region into three regions to obtain the rear feedback correction coefficient PHOS.

Further, the rich slice level Rsl and the lean slice level Lsl can be variably set by referring to a one-dimensional map corresponding to the engine operating state by interpolation calculation, and PI control considering the engine operating state can be performed. Perform rear feedback correction coefficient PHOS
May be asked.

As described above, the rear feedback correction coefficient PHO calculated by the PHOS calculation PI control.
By correcting the feedback correction coefficient α using S, the air-fuel ratio on the downstream side of the catalyst 44 deviates to the rich side or the lean side from the theoretical air-fuel ratio due to deterioration of the upstream O ₂ sensor 47 or the catalyst 44 or the like. In this case, the rear feedback correction coefficient PHOS is adjusted according to the degree of deviation.
Can be changed, and the convergence of the air-fuel ratio to the theoretical air-fuel ratio can be improved.

Next, the second embodiment will be described in detail with reference to FIG. FIG. 8 shows the downstream O ₂ sensor 47.
FIG. 6 is an explanatory diagram showing the relationship between the output value and the setting deviation. As shown, the horizontal axis represents the output value of the downstream O ₂ sensor 47,
A large number of deviation areas are provided on the vertical axis. And the downstream side O
The target air-fuel ratio of the air-fuel ratio detected by the ₂ sensor 47 is set as the main slice level Msl value. still,
In this embodiment also, the main slice level Msl is set to the stoichiometric air-fuel ratio.

Further, FIG. 10A shows a one-dimensional map in which a deviation area is set according to the difference between the main slice level Msl and the actual output value of the downstream O ₂ sensor 47. The actual downstream O ₂ sensor 4 is included in this one-dimensional map.
The deviation area is set such that the larger the absolute value of the difference between the output value of 7 and the main slice level Ms1, the larger the value.
Here, the main slice level Msl value is subtracted from the actual output value of the downstream O ₂ sensor 47, and the absolute value can be referred to the deviation area with interpolation calculation using a one-dimensional map. Therefore, by performing the PI control according to the set deviation region, the rear feedback correction coefficient PHOS according to the change in the output value of the downstream O ₂ sensor 47.
Can be calculated.

In the above embodiment, the O on the upstream side is
_{The 2} sensor 46 may be changed to a wide range air-fuel ratio sensor. By this change, the control in which the target air-fuel ratio is set to the stoichiometric air-fuel ratio has been described in the first and second embodiments, but the target air-fuel ratio can be set to the lean side or the rich side.

[0055]

As described above, according to the air-fuel ratio feedback system for an engine of the present invention, the catalyst or the air-fuel ratio sensor upstream of the catalyst is deteriorated, and the air-fuel ratio downstream of the catalyst is reduced. When the fuel ratio deviates from the target air-fuel ratio, the rear feedback correction coefficient can be changed according to the degree of deviation so that the output of the sensor downstream of the catalyst can be maintained near the slice level. Then, by performing the air-fuel ratio feedback control using the feedback correction coefficient corrected by the rear feedback correction coefficient, it becomes possible to improve the convergence of the air-fuel ratio for controlling the air-fuel ratio near the stoichiometric air-fuel ratio.

[Brief description of drawings]

FIG. 1 is a schematic overall configuration diagram of an automobile engine in which an engine air-fuel ratio feedback control device according to the present invention is used.

2 is a configuration explanatory view showing an internal configuration of an ECU 62 shown in FIG.

FIG. 3 is a block diagram showing a main constituent part of the air-fuel ratio feedback control device according to the present embodiment and a front-back relation of operation of each constituent part.

FIG. 4 is a flow chart diagram for calculating a fuel injection pulse width Ti per unit time representing the amount of fuel to be injected from the injector 36.

FIG. 5 is an explanatory diagram showing a detection result of an upstream O ₂ sensor 46 and a change of a feedback correction coefficient α obtained by PI control based on the detection result according to time.

FIG. 6 is an explanatory diagram showing a relationship between an output value of a downstream O ₂ sensor 47 and an air-fuel ratio.

FIG. 7 is an explanatory diagram showing a relationship between a change in a rear feedback correction coefficient PHOS and an output value of a downstream O ₂ sensor 47.

FIG. 8 is an explanatory diagram showing the relationship between the output value of the downstream O ₂ sensor 47 and the setting deviation.

[Explanation of symbols]

10 Engine Body 12 Intake Passage 14 Exhaust Passage 22 Intake Port 24 Combustion Chamber 28 Exhaust Port 30 Air Cleaner 32 Air Flow Meter 34 Throttle Valve 36 Injector 42 Exhaust Pipe 44 Catalyst 46 Upstream O ₂ Sensor 47 Downstream O ₂ Sensor 58 Crank Angle Sensor 59 Water temperature sensor 60 Throttle opening sensor Msl Main slice level Lsl Lean slice level Rsl Rich slice level

Claims (4)

[Claims] 1. An air-fuel ratio sensor for detecting an air-fuel ratio of an engine is provided on each of an upstream side and a downstream side of a catalyst, and an air-fuel ratio obtained by proportional integration based on a detection result of the upstream side air-fuel ratio sensor. In the air-fuel ratio feedback control apparatus for an engine, the feedback correction coefficient is corrected by a rear feedback correction coefficient obtained by proportionally integrating the feedback correction coefficient based on the detection result of the downstream air-fuel ratio sensor. The region of the air-fuel ratio detected by the air-fuel ratio sensor is the boundary between the target air-fuel ratio and the rich reference air-fuel ratio provided on the rich side of the target air-fuel ratio and the lean reference air-fuel ratio provided on the lean side of the target air-fuel ratio. And is divided into four deviation regions, and the air-fuel ratio detected by the downstream air-fuel ratio sensor exists in any of the four deviation regions. The air-fuel ratio determination means for determining whether or not, and the air-fuel ratio detected by the air-fuel ratio sensor on the downstream side by the air-fuel ratio determination means is set in the region between the target air-fuel ratio and the rich reference air-fuel ratio The rear feedback correction coefficient that is set in the rich side region that exceeds the rich reference air-fuel ratio than the rear feedback correction coefficient is set to be large, and the air-fuel ratio detected by the downstream air-fuel ratio sensor is Increase the rear feedback correction coefficient that is set when the engine is in the lean side area that exceeds the lean reference air-fuel ratio than the rear feedback correction coefficient that is set when it is in the area between the target air-fuel ratio and the lean reference air-fuel ratio. An air-fuel ratio feedback control device for an engine, which is set as follows. 2. The air-fuel ratio determining means is provided with a plurality of rich-reference air-fuel ratio regions and lean air-fuel ratio regions that are provided on the rich side and the lean side of the target air-fuel ratio, respectively. It is divided into a plurality of deviation regions with the reference air-fuel ratio as a boundary, and it is determined in which of the plurality of deviation regions the deviation is present, and the rear feedback correction coefficient changing means is detected by the downstream air-fuel ratio sensor. The air-fuel ratio feedback control device for an engine according to claim 1, wherein the rear feedback correction coefficient is set to be larger as the air-fuel ratio is in a richer side or a leaner side of the target air-fuel ratio side. . 3. The rich reference air-fuel ratio and the lean reference air-fuel ratio are variably set by referring to a one-dimensional map corresponding to an engine operating state by interpolation calculation. An air-fuel ratio feedback control device for an engine according to any one of claims. 4. An air-fuel ratio sensor for detecting an air-fuel ratio of an engine is provided on each of an upstream side and a downstream side of a catalyst, and is proportionally integrated based on a detection result of the upstream side air-fuel ratio sensor. An engine air-fuel ratio feedback control device comprising a rear feed correction means for correcting a feedback correction coefficient by a rear feedback correction coefficient calculated based on a detection result of a downstream air-fuel ratio sensor, wherein the downstream air-fuel ratio sensor is used. An output difference calculating means for calculating an output difference between an actually detected output value and a reference target air-fuel ratio, and an output difference calculating means based on the output difference calculated by the output difference calculating means according to an absolute value of the output difference in advance. The deviation of the proportional integral for obtaining the rear feedback correction coefficient is determined by referring to the set one-dimensional deviation grid table. Air-fuel ratio feedback control apparatus for an engine and having Ya and feedback deviation determining means.