JP2002161785A - Air/fuel ratio control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the accuracy in estimation of a stored oxygen amount at exhaust reflux from degrading resulting in lowering the accuracy of air/fuel ratio control in an air/fuel ratio control device for an internal combustion engine for estimating the oxygen amount stored in a catalyst from an intake air amount and air/fuel ratio to control the air/fuel ratio based on the estimation value. SOLUTION: The intake air amount is corrected to the value including a refluxed exhaust fraction by multiplying the intake air amount (a new air intake amount) detected with an air flow meter by a correction coefficient set according to an exhaust reflux rate. The oxygen amount stored in the catalyst is estimated from the corrected intake air amount and and air/fuel ratio deviation Δλ, and then the feedback correction coefficient of air/fuel ratio is set so that the stored oxygen amount becomes a target value.

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 an internal combustion engine, and more particularly to an air-fuel ratio control device configured to control the air-fuel ratio of a combustion mixture based on the stored oxygen amount of a catalyst.

[0002]

2. Description of the Related Art Conventionally, the amount of oxygen stored in a catalyst has been estimated from the air-fuel ratio (oxygen concentration) detected by an oxygen sensor provided upstream of the catalyst and the amount of intake air. There is known an air-fuel ratio control device configured to correct the air-fuel ratio (fuel injection amount) of a combustion air-fuel mixture to a value (Japanese Patent Laid-Open Nos. 6-249028 and 10-1).
No. 84425, etc.).

[0003]

In the above estimation of the stored oxygen amount, instead of directly measuring the exhaust gas amount, a detected value of the intake air amount considered to be substantially equal to the exhaust gas amount is used. . However, in an engine equipped with an exhaust gas recirculation device that recirculates part of exhaust gas to the intake system, when exhaust gas recirculation is performed, recirculated exhaust gas is added to fresh air detected by an air flow meter and flows to the exhaust system. A difference may occur between the intake air amount detected by the air flow meter and the actual exhaust gas amount, causing an estimation error in the stored oxygen amount and deteriorating the air-fuel ratio control accuracy.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and can accurately estimate a stored oxygen amount from an intake air amount even in a state in which exhaust gas recirculation is performed, thereby maintaining air-fuel ratio control accuracy. It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that can be used.

[0005]

According to the present invention, the amount of oxygen stored in a catalyst disposed in an exhaust pipe is estimated based on the amount of intake air of an engine and the concentration of oxygen in exhaust gas.
An air-fuel ratio control device for an internal combustion engine that controls an air-fuel ratio of a combustion air-fuel mixture based on the estimated stored oxygen amount, wherein an intake air amount used for estimating the stored oxygen amount is corrected according to an exhaust gas recirculation rate. did.

According to this configuration, when the exhaust gas recirculation is performed, a difference occurs between the intake air amount and the exhaust gas amount. Therefore, a correction for compensating the difference according to the exhaust gas recirculation rate is made with respect to the intake air amount. And the stored oxygen amount is estimated based on the corrected intake air amount. According to the second aspect of the present invention, the detected value of the fresh air intake amount is corrected to increase more as the exhaust gas recirculation rate increases.

With this configuration, the amount of fresh air intake detected by the air flow meter does not include the amount of recirculated exhaust gas. Therefore, the higher the exhaust gas recirculation rate (the larger the amount of recirculated exhaust gas),
The detected value of the fresh air intake amount is increased and corrected to be larger. According to the third aspect of the invention, the intake air amount is corrected and set by a correction coefficient set according to the exhaust gas recirculation rate.

According to this configuration, the correction coefficient is set by calculation based on the exhaust gas recirculation rate at that time or by searching from a table, and the detected value of the intake air amount is corrected by the correction coefficient. Is used to estimate the amount of stored oxygen. According to a fourth aspect of the present invention, there is provided an air-fuel ratio control device for an internal combustion engine for estimating a stored oxygen amount of a catalyst interposed in an exhaust pipe and controlling an air-fuel ratio of a combustion mixture based on the estimated stored oxygen amount. The exhaust gas amount is estimated from the fresh air intake amount of the engine and the exhaust gas recirculation rate, and the stored oxygen amount is estimated based on the estimated exhaust gas amount and the oxygen concentration in the exhaust gas.

According to this configuration, since the addition result of the fresh air intake amount and the recirculation exhaust gas is the exhaust gas amount, the exhaust gas amount is estimated from the fresh air intake amount and the exhaust gas recirculation rate, and based on the estimated value. Estimate the amount of stored oxygen.

[0010]

According to the first aspect of the present invention, by correcting the intake air amount according to the exhaust gas recirculation rate, the intake air amount is made equivalent to the exhaust gas even during the exhaust gas recirculation, so that the stored oxygen of the catalyst is reduced. The amount can be estimated, and the effect of maintaining the estimation accuracy of the stored oxygen amount can be maintained.

According to the second aspect of the present invention, the amount of recirculated exhaust gas increases in accordance with the increase in the recirculation ratio of exhaust gas, and the amount of recirculated exhaust gas becomes equal to the amount of exhaust gas in addition to the amount of fresh air intake. There is an effect that the intake air amount used for estimating the oxygen amount can be corrected. According to the invention described in claim 3,
There is an effect that the intake air amount can be corrected to a value including the recirculated exhaust gas by a correction coefficient according to the exhaust gas recirculation rate.

According to the fourth aspect of the present invention, in response to the addition of the fresh air intake amount and the exhaust gas returned to the intake system by the exhaust gas recirculation being the exhaust gas amount, the detected value of the fresh air intake amount is determined. There is an effect that the exhaust gas amount can be estimated with high accuracy, and thus the estimation accuracy of the stored oxygen amount can be maintained.

[0013]

Embodiments of the present invention will be described below. FIG. 1 is a system configuration diagram of an internal combustion engine according to the embodiment. In FIG. 1, air is drawn into a combustion chamber of each cylinder of an internal combustion engine 1 mounted on a vehicle via an air cleaner 2, an intake passage 3, and an electronically controlled throttle valve 4 driven to open and close by a motor.

An electromagnetic fuel injection valve 5 for directly injecting fuel (gasoline) into the combustion chamber of each cylinder is provided, and the fuel injected from the fuel injection valve 5 and the sucked air are used in the combustion chamber. A mixture is formed. The fuel injection valve 5 is energized by a solenoid in response to an injection pulse signal output from the control unit 20, opens the valve, and injects fuel adjusted to a predetermined pressure.

The air-fuel mixture formed in the combustion chamber is
Ignition combustion. The internal combustion engine 1 is not limited to the direct in-cylinder gasoline engine described above, but may be an internal combustion engine configured to inject fuel into an intake port. Exhaust gas from the engine 1 is exhausted from an exhaust passage 7, and an exhaust purification catalyst 8 is interposed in the exhaust passage 7.

The catalyst 8 is a three-way catalyst having an oxygen storage capacity, and comprises carbon monoxide C, which is a harmful three component in exhaust gas.
Oxidates O and hydrocarbons HC, and produces NOx
Is converted to harmless carbon dioxide, water vapor and nitrogen. The purification performance of the three-way catalyst 8 is highest when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio,
When the exhaust air-fuel ratio is lean and the amount of oxygen is excessive, the oxidizing action becomes active but the reducing action becomes inactive. Conversely, when the exhaust air-fuel ratio is rich and the amount of oxygen is small, the oxidizing action becomes inactive However, the reduction action becomes active.

However, since the three-way catalyst 8 has the ability to store oxygen (oxygen storage effect), when the exhaust air-fuel ratio becomes temporarily rich, the previously stored oxygen is used. Conversely, when the exhaust air-fuel ratio temporarily becomes lean, excess oxygen is stored to maintain exhaust purification performance. Therefore, when the air-fuel ratio deviates from the stoichiometric air-fuel ratio to the lean side, nitrogen oxide NOx can be reduced, and when the air-fuel ratio deviates from the stoichiometric air-fuel ratio to the rich side, carbon monoxide CO and hydrocarbon HC can be oxidized. In order to achieve this, the amount of oxygen stored in the three-way catalyst 8 (storage oxygen amount) is maintained at about half the maximum amount that can be stored, excess oxygen is stored, and the amount of oxygen required for the oxidation treatment is maintained. It is required that oxygen be desorbed and supplied.

Therefore, the control unit 20
Is in the operating range where the target air-fuel ratio is the stoichiometric air-fuel ratio,
The stored oxygen amount in the three-way catalyst 8 is estimated, and when the estimated stored oxygen amount is smaller than the target amount (about half of the maximum stored oxygen amount), the air-fuel ratio is made lean to increase the stored oxygen amount, Conversely, when the estimated stored oxygen amount is larger than the target amount, the fuel injection amount by the fuel injection valve 5 is increased so that the air-fuel ratio is enriched to remove excess oxygen and reduce the stored oxygen amount. Feedback control is performed.

An exhaust gas recirculation (EGR) device for recirculating a part of the exhaust gas of the engine 1 to the intake side is provided. The exhaust gas recirculation device includes an exhaust gas recirculation passage 18 that connects the exhaust manifold 16 and the intake collector unit 17, and an electronically controlled EGR control valve 19 interposed in the exhaust gas recirculation passage 18. When the EGR control valve 19 is controlled to open, a part of the exhaust gas is recirculated to the intake collector 17 due to the differential pressure across the valve 19.

The control unit 20 includes a CP
A microcomputer including U, ROM, RAM, A / D converter, input / output interface, etc., receives input signals from various sensors, performs arithmetic processing based on these signals, and controls the electronically controlled throttle valve 4. Opening, fuel injection valve 5
And the ignition timing of the ignition plug 6, and the exhaust gas recirculation rate is controlled through the control of the electronically controlled EGR control valve 19.

In the control of the exhaust gas recirculation rate, a target exhaust gas recirculation rate is set based on operating conditions such as an engine load and an engine rotation speed, and the target is controlled by an actuator such as a step motor or an electromagnetic coil for driving the valve 19. An EGR control signal corresponding to the exhaust gas recirculation rate is output. As the various sensors, a crank angle sensor 21 for detecting a crank angle of the engine 1 and a cam sensor 22 for extracting a cylinder discrimination signal from a cam shaft are provided.
The engine speed Ne is calculated based on the signal from the engine.

In addition, an air flow meter 23 for detecting an intake air amount Q upstream of the throttle valve 4 in the intake passage 3, an accelerator sensor 24 for detecting an accelerator pedal depression amount (accelerator opening) APS, and opening of the throttle valve 4 Degree TVO
Sensor 25 for detecting the temperature of the engine, the cooling water temperature T of the engine 1
A water temperature sensor 26 for detecting w, an oxygen sensor 27 for detecting oxygen concentration in exhaust gas over a wide area, a vehicle speed sensor 28 for detecting a vehicle speed VSP, and the like are provided.

Here, how the control unit 20 controls the air-fuel ratio based on the stored oxygen amount will be described with reference to the block diagram of FIG. In the block diagram of FIG. 2, a correction coefficient setting unit 101 sets a correction coefficient for correcting the intake air amount Q detected by the air flow meter 23 based on the exhaust gas recirculation rate (EGR rate) at that time.

The correction coefficient is set to 1.0 when the exhaust gas recirculation rate is 0, that is, when the exhaust gas recirculation is stopped, and is set to a larger value as the exhaust gas recirculation rate increases. still,
The setting of the correction coefficient is performed by searching a correction coefficient corresponding to the exhaust gas recirculation rate from a table stored in advance, or by performing an operation using the exhaust gas recirculation rate as a variable. The air flow meter 23 detects the fresh air intake amount of the engine, but when the exhaust gas recirculation is performed, the exhaust gas recirculated together with the fresh air flows into the engine, and the exhaust gas amount becomes the fresh air amount and the recirculated exhaust amount. Is added.

Therefore, in the state where exhaust gas recirculation is performed, if the amount of stored oxygen is estimated based on the amount of fresh air detected by the air flow meter 23 indicating the amount of exhaust gas, the amount of stored oxygen is estimated based on an amount smaller than the actual amount of exhaust gas. Therefore, the stored oxygen amount is estimated based on the determined oxygen amount, and the estimation accuracy of the stored oxygen amount is reduced. Therefore,
In order to estimate the stored oxygen amount according to the actual exhaust gas amount, the detected value of the intake air amount is increased and corrected by the amount of the recirculated exhaust gas,
After the corrected intake air amount correctly indicates the actual exhaust gas amount, the configuration is used for estimating the stored oxygen amount.

In other words, the value corrected by the correction coefficient corresponds to the amount of exhaust gas including the recirculated exhaust gas. The correction coefficient set by the correction coefficient setting unit 101 is multiplied by the intake air amount Q detected by the air flow meter 23, and the intake air amount Q (exhaust gas amount) after the multiplication correction.
Is multiplied by the deviation Δλ between the stoichiometric air-fuel ratio (excess air ratio λ = 1) and the air-fuel ratio detected by the oxygen sensor 27.

The air-fuel ratio deviation Δλ has a positive value if the air-fuel ratio of the combustion mixture is leaner than the stoichiometric air-fuel ratio, and has a negative value if the air-fuel ratio is rich. If the fuel ratio is leaner, the stored oxygen amount in the catalyst 8 increases and changes. If the air-fuel ratio of the combustion mixture is richer than the stoichiometric air-fuel ratio, the stored oxygen amount in the catalyst 8 decreases and changes. .

The result of multiplication of the intake air amount Q and the air-fuel ratio deviation Δλ is multiplied by a constant K.
2, the stored oxygen amount in the catalyst 8 is obtained. Here, since the intake air amount Q used for estimating the stored oxygen amount is corrected to a value including the recirculated exhaust gas at the time of exhaust gas recirculation, the stored air amount Q is stored in accordance with the actual exhaust gas amount even at the time of exhaust gas recirculation. The amount of oxygen can be determined.

Next, a deviation between the estimated value of the stored oxygen amount output from the integrator 102 and a target value which is about half of the maximum stored oxygen amount is calculated. Then, the feedback correction coefficient setting unit 103 to which the data on the deviation of the stored oxygen amount is input calculates a feedback correction coefficient of the air-fuel ratio so that the estimated value of the stored oxygen amount matches the target value.

That is, when the stored oxygen amount is smaller than the target amount, the air-fuel ratio is made lean to increase the stored oxygen amount. Conversely, when the stored oxygen amount is larger than the target amount, the air-fuel ratio is made rich. The feedback correction coefficient is set so that excess oxygen is desorbed to reduce the amount of stored oxygen. The injection amount calculation unit 104 corrects the basic fuel injection amount using the feedback correction coefficient to calculate a final fuel injection amount, and outputs an injection pulse signal corresponding to the fuel injection amount to the fuel injection valve 5. .

In the above description, the intake air amount Q is detected by the air flow meter 23. However, in the configuration in which the intake air amount is detected based on the intake pressure, there is an error between the intake air amount and the exhaust gas amount during exhaust gas recirculation. If this occurs, or in a configuration in which the intake air amount is estimated from the throttle opening and the engine speed, a correction according to the exhaust gas recirculation rate is made to the intake air amount, so that the stored oxygen amount can be estimated even during exhaust gas recirculation. Accuracy can be maintained.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of an internal combustion engine according to an embodiment.

FIG. 2 is a block diagram showing air-fuel ratio control in the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 4 ... Throttle valve 5 ... Fuel injection valve 6 ... Spark plug 8 ... Catalyst 18 ... Exhaust recirculation passage 19 ... Electric control EGR control valve 20 ... Control unit 21 ... Crank angle sensor 23 ... Air flow meter 27 ... Oxygen sensor 101 ... Correction coefficient setting unit 102 ... Integrator 103 ... Feedback correction coefficient setting unit 104 ... Injection amount calculation unit

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Claims (4)

[Claims] An estimated amount of oxygen stored in a catalyst interposed in an exhaust pipe is estimated based on an intake air amount of an engine and an oxygen concentration in exhaust gas. An air-fuel ratio control device for an internal combustion engine for controlling a fuel ratio, wherein an intake air amount used for estimating the stored oxygen amount is corrected according to an exhaust gas recirculation rate. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the detected value of the fresh air intake amount is corrected to increase more as the exhaust gas recirculation rate is higher. 3. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the intake air amount is corrected and set by a correction coefficient set according to an exhaust gas recirculation rate. 4. An air-fuel ratio control device for an internal combustion engine for estimating a stored oxygen amount of a catalyst disposed in an exhaust pipe and controlling an air-fuel ratio of a combustion air-fuel mixture based on the estimated stored oxygen amount. Estimating an exhaust gas amount from a fresh air intake amount and an exhaust gas recirculation rate, and estimating the stored oxygen amount based on the estimated exhaust gas amount and an oxygen concentration in the exhaust gas. Control device.