JPS59136536A - Method of controlling air-fuel ratio of internal-combustion engine - Google Patents

Abstract

PURPOSE:To ensure stability of operation at the time of executing open-loop control, by using a value stored and learnt as the center value of a correction value for the air fuel ratio in feedback control region as an initial value of the correction value for the air-fuel ratio in open-loop control region. CONSTITUTION:In operation of an engine, a control unit 44 controls the air-fuel ratio according to the operational conditions of the engine by way of open-loop control or fedback control based on the output of an O2-sensor 30. When the operational conditions of the engine are changed from feedback control region to open-loop control region, a value stored and learnt as the center value of a correction value for the air-fuel ratio in the feedback control region is used as an initial value of the correction value for the air-fuel ratio in the open-loop control region. In case that these two correction values are different to each other, the initial correction value is brought gradually closer to a reference correction value by a time constant greater than that used when the above learnt value is stored and learnt, and the air-fuel ratio in the open-loop control region is controlled on the basis of the correction value brought closer to the reference correction value.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an air-fuel ratio control method for an internal combustion engine. The present invention relates to an air-fuel ratio control method for an internal combustion engine suitable for controlling the air-fuel ratio of an air-fuel mixture.

[Prior art]

In automobiles and other vehicles equipped with electronic fuel injection devices, the oxygen concentration sensor detects the oxygen concentration in the exhaust gas by determining the engine load range, which indicates the engine load condition, determined from the engine rotation speed and intake air amount. Feedback the air-fuel ratio of the mixture to near the stoichiometric air-fuel ratio based on the detection output 6
1 (Separated into a feedback area for control and an open-loop area for controlling the air-fuel mixture to a rich air-fuel ratio by increasing fuel regardless of the detection output of the oxygen concentration sensor, based on the engine speed and intake air amount. Conventionally, the air-fuel ratio of the air-fuel mixture has been controlled depending on which region the engine load belongs to.

Feedback the air-fuel ratio of the air-fuel mixture to near the stoichiometric air-fuel ratio fi
By controlling the exhaust gas, harmful gases such as carbon monoxide, hydrocarbons, and nitrogen oxides contained in the exhaust gas can be purified into harmless carbon dioxide, water vapor, and nitrogen. Furthermore, if the air-fuel mixture is controlled to be open-loose to a rich air-fuel ratio by increasing the amount of fuel, it is possible to prevent the exhaust temperature from exceeding the permissible limit during high loads, and it is also possible to increase the engine output.

In addition, in a system to which the conventional air-fuel ratio control method is applied, when the engine operating state shifts from the feedback region to the open loop region, a learned value that is memorized and learned with the feedback correction value for the air-fuel ratio in the feedback region as the central value is It has also been conventionally possible to control the air-fuel ratio in the open-loose region based on . That is, after operation in the feedback region,
If we simply control the air-fuel ratio in the open-loose region when we shift to high-load open-loop operation, such as during uphill driving, the base air-fuel ratio in the open-loop region will become too rich (too rich, due to misfires) as we go uphill. Therefore, conventionally, the air-fuel ratio in the open loop region is adjusted based on the learned value that is memorized and learned as the center value of the feedback correction value for the air-fuel ratio in the feedback region, and the air-fuel ratio in the open loop region is adjusted. In order to ensure smooth operation under high loads such as If the air-fuel ratio is controlled in the open-loop region based on the above, it is possible to smoothly perform uphill driving.

However, in systems where conventional methods cannot be applied,
The learned value in the feedback region was applied to air-fuel ratio control in the open loop region, so
When the detection output of the oxygen concentration sensor (hereinafter referred to as the 02 sensor) becomes abnormal during operation in the fuel drop region, air-fuel ratio control in the open loop region is performed based on the learned value r. If this was done, there would be a problem if the exhaust temperature exceeded the allowable limit or the air-fuel ratio became over-rich, resulting in combustion misfire and torque reduction.

For example, as shown in FIG. 1(a), when the 02 Senya element temperature exceeds an unstable temperature (for example, 700°C) due to operation in the map-n-loop region, the operation shifts to the feedback region ( 7. Furthermore, if operation is shifted to the open loop region before the element temperature of the 02 sensor is stabilized, the detection output of the 02 sensor will be in a state of O75 rich and clustered as shown in figure (b). , (C) As shown in the figure, the correction value f(A/F) shifts toward the lean side, and the learned value G(A/'
F) will also memorize and learn the value that deviates to the lean side. At this time, the air-fuel ratio A/F in the foot drop region is (
d) As shown in the figure, the value shifts to the lean side. If we shift from this state to operation in the open loop region ((), change learning ([EG (A/F) to M in the open loop region VC, and perform Okel air-fuel ratio control), as shown by the solid line in the diagram (C), In this case, the correction value for the air-fuel ratio in the open-loop region becomes lower than the standard correction value for the air-fuel ratio during normal operation, and (d) the air-fuel ratio in the open-loop region becomes lower than the standard correction value for the air-fuel ratio during normal operation. A/F
The standard air-fuel ratio during normal operation is also controlled to be low. This results in oats.

Even if the operation shifts to the low-loop region, the amount of fuel is not sufficiently increased, so that the exhaust temperature sometimes exceeds the allowable limit, as shown by the solid line in Figure (e).

Further, as shown in FIG. 2(a), operation is continued in the idle state of 1 and 0? If the temperature of the sensor element remains below 360°C, for example, and the sensor moves to high-load open-loop operation, such as driving uphill,
(b) As shown in the figure, the detection output of the 02 sensor shifts to the lean side and then suddenly shifts to the rich side. Therefore,
(C) Feedback correction value f(A
/'F) suddenly deviates from the standard value to the rich side, and the learned value G(A/F) shown by the broken line also deviates to the rich side together with the vine correction value f(A/F).At this time, The air-fuel ratio A/F is as shown in figure (d),
The air-fuel ratio deviates to the rich side from the value near the stoichiometric air-fuel ratio. As a result,
(e) When air-fuel ratio control is performed in the open loop region based on the learned value G (A/F) as shown in the figure,
(C) As the learned value G(A/F) changes as shown by the solid line in the figure, the air-fuel ratio A/F in the open loop region
(d) changes as shown by the solid line in the figure. If such air-fuel ratio control is continued, the air-fuel ratio A/F will exceed the limit value for fuel misfire and torque reduction.

In this way, in the conventional control method, when air-fuel ratio control is performed in the open loop region based on the learned value in the feed-no-kunk region, if operation is performed in the feedback region, the detection output of the sensor will be abnormal. When this happens, there is a problem that the exhaust temperature exceeds the permissible limit or the torque decreases during operation in the open loop region.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned conventional problems.The purpose of the present invention is to: In a system that performs fuel ratio control, even if the detection output of the 02 sensor becomes abnormal during operation in the feedback region, the air-fuel ratio control for an internal combustion engine can be performed without degrading engine performance during operation in the open loop region. The purpose is to provide a method.

[Summary of the invention]

In order to achieve the above object, the present invention uses a memorized and learned learning value as the central value of the feedback correction value for the air-fuel ratio in the feed pack region when the operating state of the engine shifts from the feed bank region to the open loop region. Based on this, in a system that controls the air-fuel ratio in the open-loop region, when the engine operating state shifts from the feedback region to the open-loop region,
The learning value memorized and learned during operation in the feedback region is used as the initial value of the correction value for the air-fuel ratio in the open loop region, and when this correction value differs from the standard correction value of the feedback correction value, the correction value is set as the initial value. gradually approaches the standard correction value with a time constant that is larger than the time constant when the learning value is stored and learned, and approximates the standard correction value (based on the correction value, the air-fuel ratio in the open loose region is It is characterized by being controlled.

[Example of invention ability]

Hereinafter, the present invention will be described in detail based on the drawing (C).

FIG. 3 shows the configuration of a system to which the present invention is applied.

In FIG. 3, the intake system of an engine 10 is provided with an air flow meter 12, a throttle valve 14, etc., and the suction sucked in via the air flow meter 12 is supplied to an intake manifold 16 via the throttle valve 14. and mixes with the fuel injected from the fuel injection valve 18. The air-fuel mixture is supplied to a combustion chamber 22 via an intake valve 20, is combusted by a spark plug 26 provided in a cylinder head 24, and is discharged to an exhaust system via an exhaust valve 28.

The exhaust system is provided with an 02 sensor 30 that detects the oxygen concentration in the exhaust gas. Based on the detection output of this 02 sensor, a control device (to be described later) adjusts the air-fuel ratio of the air-fuel mixture to near the stoichiometric air-fuel ratio. When the exhaust gas is feedback-controlled, harmful gases contained in the exhaust gas are purified by a three-way catalyst (not shown) provided in the exhaust system and then exhausted.

The cylinder block 32 is provided with a water temperature sensor 34 that detects engine water temperature.

The IJ computer 38 also includes a cylinder discrimination sensor 40, which distributes the ignition signal from the igniter 36 to each cylinder.
A rotation angle sensor 42 is built-in.

Detection outputs from various sensors such as the 01 sensor 30 that detect various operating states of the engine are supplied to the control device 44 .

FIG. 4 shows a configuration in which a microcomputer is used as the control device 44.

The control device 44 includes a CPU 50, as shown in FIG.
It is composed of a RAM 52, a ROM 54, an input/output port 56.58, an output port 0.62, an A/D converter 64, a multiplexer 66, a drive circuit 68.70, a waveform vertical circuit 72, an input circuit 74, and a CPU 50. , RAM52
, a ROM 54, an input/output port 56.58, and an output port 0.62 are connected by a path line 76, respectively.

The detection outputs of the air flow meter 12 and water temperature sensor 34 are supplied to the input/output boat 56 via a multiplexer 66 and an A/D converter 64. The detection outputs of the cylinder discrimination sensor 40 and the rotation angle sensor 42 are supplied to the input/output boat 58 via the waveform shaping circuit 72. Further, the detection output of the Ot sensor 30 is supplied to the input/output board 58 via the input circuit 74.

The igniter 36 has an output capo/)'60 and a drive circuit 68.
An ignition signal can be provided to the side distributor 38 by a control signal provided via the control signal. fuel injection valve 1
8 can control the fuel injection time by a control signal supplied through the output port 2 and the drive circuit 70.

In addition, ROIVI54 contains numerical data of setting values for correcting the air-fuel ratio in the feedback region and open loop region, and the engine load region indicating the immediate engine load condition from the engine rotation speed and intake air amount. Map data divided into regions and feedback regions, and numerical data of fuel injection times associated with air-fuel ratios according to various operating conditions in the feedback region and open loop region are stored.

Here, in the present invention, when the operating state of the engine shifts from the feedback reserve region to the open loop region, the learning value memorized and learned during operation in the feedback region is used as the initial value of the correction value for the air-fuel ratio in the open loop region. ,
When this initial value is different from the standard correction value for the air-fuel ratio during normal operation in the open-loose region, the correction value as the initial value is larger than the time constant when the learning value is memorized and learned. The standard correction value is gradually approached with a time constant, and the fuel ratio in the open loose region is controlled based on the correction value. R in the example
The OM 54 stores numerical data of the standard correction value, numerical data for bringing the correction value closer to the standard correction value, and the like.

Further, the RAM 52 stores the learning value, feedback correction value, and the like.

Furthermore, in this embodiment, since the engine load range is set based on the engine speed and intake air amount, the control device 4
4 determines whether the engine load belongs to the feedback region or the open loop region based on the detection outputs of the air flow meter 12 that detects the intake air amount and the rotation angle sensor 42 that detects the engine rotation speed. It is said that Then, when the control device 44 determines that the engine load belongs to the feedback region based on the detection outputs of the air flow meter 12 and the rotation angle sensor 42, the control device 44 outputs 0. Based on the detection output of the sensor 30, it is possible to control the air-fuel ratio of the air-fuel mixture to near the stoichiometric air-fuel ratio, thereby purifying harmful gases contained in the exhaust gas.
When it is determined that the engine load belongs to the open-loop region, the air-fuel mixture is controlled in an open-loop manner to achieve a rich air-fuel ratio by increasing the amount of fuel, and by increasing the amount of fuel, it is possible to prevent the exhaust temperature from exceeding the permissible limit at high loads. ,
Engine output can be increased.

The present embodiment has the above configuration, and its operation will be explained next.

The flowchart in FIG. 5 shows a time-side injection routine when the present invention is applied to the system shown in FIG.

In FIG. 5, first, in step 100, the detection outputs of the air flow meter 12 and the rotation angle sensor 42 are taken in, and based on the map data indicating the engine load region, it is determined whether the engine load belongs to the feedback region. Do the following. If the determination in this step is YES and the engine load belongs to the feedback area, the process moves to step 102.In step 102, the flag f indicating that the engine load belongs to the feedback area for the first time is set to 1.
, and the process moves to step 104.

In step 104, in order to feedback control the air-fuel ratio of the air-fuel mixture to near the stoichiometric air-fuel ratio,
It is determined whether the detection output of 0 is lean.

If the answer is YES in this step, step 1
06, the feedback correction value f(A
A new feedback correction value f(A/F)i is calculated by adding the set value 0.001 to /F)if.

On the other hand, if the determination in step 104 is NO, the process moves to step 108, where the set value 0.001 is subtracted from the previously obtained feedback correction value f(A/F)*-1, and a new feedback correction value is obtained. Calculate f(A/F)%.

When the engine load is in the feedback region, the processing of step 100, 102, 104, step 106, or step 108 is continued, and the numerical data of the new feedback correction value f(A/F)1 is stored in the RAM 52.

After the processing in step 106 or step 108, the process moves to step 110. In step 110, the feedback correction value f(A/F)i calculated in step 106 or 108 is added to the previously obtained learning value G(A/F)s−1 multiplied by 15, and these values are The value obtained by dividing the value by 16 is calculated as the learned value G(A/F)i, which is memorized and learned as the center value of the feedback correction value for the air-fuel ratio in the feedback region. This learning value G
(A/F)1 is stored in the RAM 52.

Next, the process moves to step 112, where the basic fuel injection time τ is calculated based on the detection outputs of the air flow meter 12 and the rotation angle sensor 42, and the feedback correction value f(A/F)1 calculated in step 106 or 108. A new fuel injection time τ is calculated by multiplying by . After this, the process moves to the main routine, and the fuel injection time calculated in step 112? The viscous injection valve 18 is controlled based on. As a result, the air-fuel ratio of the air-fuel mixture is controlled to be close to the stoichiometric air-fuel ratio.

On the other hand, if the determination in step 100 is NO and the engine load is in the open-loose region, step 11
Move on to 4. In step 114, the above-mentioned flag f
It is determined whether or not is 1.

In this step, since the flag f has already been set to 1 in step 102, the determination is YES and the process moves to step 116. In step 116, the flag f is set to 0.
, and the process moves to step 118. In step 118, the learning value G(A/
F) is set to the initial value f(A/F)l of the correction value for the air-fuel ratio in the open loop region. After this step 1
Proceed to step 12. In this case, the process in step 112 is to calculate the initial value f(A/F)i calculated in the basic fuel injection time t female dip 118, calculate a new fuel injection time τ, and then proceed to the main routine. In the main routine in this case, the fuel injection valve 18 is controlled based on the fuel injection time calculated in step 112. That is, when the operating state of the engine shifts from the feedback region to the open loop region, air-fuel ratio control starts using the learning value memorized and learned in the feedback region as the initial value of the correction value for the air-fuel ratio in the open loop region. be done.

After the processing of steps 118 and 112, step 1 is performed again.
The process moves on to steps 10 and 114. At this time, in step 114, since the 7 lag f has already been set to 0 in step 116, the determination is NO and the process moves to step 120.

In step 120, it is determined whether the initial value f(A/F)1 calculated in step 118 is larger than the standard correction value 1.0. If the determination in this step is YES, the process moves to step 122. Step 12
2, the initial value f(A/F)i-1 obtained last time
Subtract the set value 0.00001 from the new initial value f(
A/F) Calculate I.

On the other hand, if the determination in step 120 is NO, the process moves to step 124, where the previously obtained initial value f(A/F)l
-1 and set value 0.00001 to create new initial value f
Calculate (A/F)i. The initial value f(A/F)i calculated in step 122 or step 124 is stored in the RAM 52.
Then, the process moves to step 112. In step 112, is the basic fuel injection time? 'X step 1
12, or the initial value f(A/
F) Calculate l, calculate a new fuel injection time τ, and proceed to the main routine. In the main routine, the fuel injection valve 18 is controlled based on the fuel injection time τ calculated in step 112, as described above. After this step 1
14. By continuing the processing in step 120, step 122 or step 124, step 112, the initial value f(A/F)i calculated in step 118 becomes the learned value G.
The air-fuel ratio in the open loop region is based on the correction value that approaches the standard correction value 1.0 and approaches the standard correction value 10 with a time constant that is larger than the time constant when (A/F) is memorized and learned. Control takes place.

That is, if it is determined No in step 100 and the operation state shifts from the feedback region to the open loop region, and the initial value f(A/F)i calculated in step 118 is larger than the standard correction value 1.0. Step 100.114
．． The ring formation of 120.122.112 continues, and the initial value f
(A/F)i approaches the standard correction value 1.0 (the air-fuel mixture is controlled by the air-fuel ratio). Even if the detection output of the sensor 30 becomes abnormal and the learned value due to this abnormality is transferred to the operation in the base layer open loop region, the initial value f will be changed based on the learned value as shown by the broken line in the diagram (C).
(A/F) is gradually approximated to the standard correction value. As a result,
(d) As shown by the broken line in the figure, after the detection output of the 02 sensor 30 becomes abnormal, the Z
Even if operation in the open loop region continues, the air-fuel ratio A/F will not exceed the air-fuel ratio limit value that indicates combustion misfire and torque reduction.

Also, the initial value (t?f(A/F
)1 is smaller than the standard correction value 1.0, the processing of steps 110-1114.120 and 124.112 is continued, and the air-fuel ratio gradually approaches the initial value f(A/F)l to 1.0. The mixture is controlled by

Therefore, as shown in FIG. 1, the operation goes from the open loop region where the element temperature of the 02 sensor 30 exceeds the unstable temperature to the feedback region operation, and further when the humidity of the 02 sensor 30 is unstable. Even when the operation shifts to the IT open loop region, the initial value f(, A/F) gradually approaches the standard correction value, as shown by the broken line in FIG. 1(c).

Therefore, as shown by the broken line in Figure (d), the air-fuel ratio A'/F in the open loop region also gradually approaches the standard air-fuel ratio (therefore, the detection output of the 02 sensor becomes abnormal during operation in the feedback region, causing 1. Even if air-fuel ratio control is performed in the open loop region based on the learned value that has been memorized and learned the feedback correction value due to this abnormality, (
e) The exhaust temperature does not exceed the permissible limit, as shown by the dashed line in the figure.

In this way, in this embodiment, when the operating state of the engine shifts from the feedback region to the open loop region, the learning value memorized and learned in the feedback region is
This initial value is set as the initial value of the correction value for the air-fuel ratio in the open-loop region, and this initial value is gradually brought closer to the standard correction value, and air-fuel ratio control in the open-loop region is performed based on the correction value that approximates this standard correction value. Since the operation in the feedback region is being performed, O.

Even if the detection output of the sensor 30 is abnormal or the abnormal value is stored as a learned value, this prevents the exhaust temperature from exceeding the permissible limit during operation in the open loop region, or the torque from decreasing due to fuel misfire. can do.

In addition, in this embodiment, the time constant when the initial value is approximated to the standard correction value in steps 122 and 124 is larger than the predetermined number when the learning value is calculated in steps 106 and 108. Therefore, it approximates the standard correction value (
When air-fuel ratio control is performed in the open loop region based on the correction value, air-fuel ratio control can be performed smoothly.

Furthermore, in this embodiment, as shown in FIG.
．． When the detection output of the sensor 30 is normal, the learned value G (A/
F) is stored in its box, so even if the operation continues in the order of feedback region 1 open loop region → feedback region → organic lube region, the air-fuel ratio in the open loop region will change as shown in figure (b). is corrected using the learned value CIA/F) as the initial value, and the air-fuel ratio A/
F changes as shown in (e).

Therefore, as shown in Figure (d), the exhaust temperature does not exceed the permissible limit.

〔Effect of the invention〕

As explained above, according to the present invention, when the operating state of the engine shifts from the feedback region to the open loop region, the learning value memorized and learned in the feedback region is used as the initial correction value for the air-fuel ratio in the open loop region. value, and if this correction value differs from the standard correction value for the air-fuel ratio when operating normally in the open loop region,
The correction value as the initial value is gradually brought closer to the standard correction value with a time constant that is larger than the time constant when the learning value is memorized and learned to approximate the standard correction value and based on the correction value. Since air-fuel ratio control is performed in the open-loop region, the detection output of the 02 sensor becomes abnormal when operation is performed in the feedback region, and air-fuel ratio control in the open-loop region is performed based on the abnormal learning value. Even if this is done, there is an excellent effect in that it is possible to prevent torque from decreasing due to p5 where the exhaust temperature exceeds the allowable limit value or fuel misfire during operation in the open loop region.

[Brief explanation of the drawing]

(a) to (e) in Fig. 1 are engine characteristic diagrams for explaining air-fuel ratio control when the temperature of the sensor exceeds the temperature range, and (a) to (d) in Fig. 2 are FIG. 3 is a system configuration diagram of an internal combustion engine to which the present invention is applied, and FIG. FIG. 5 is a flow chart for explaining the operation when the present invention is applied to the system shown in FIG. 3, and FIG. 6 is an air-fuel ratio control according to the present invention. FIG. 4 is an engine characteristic diagram illustrating the effect when applied to the system of FIG. 3. FIG. 10... Engine, 12... Air flow meter, 18
...Fuel injection valve, 30...02 sensor, 34...
Water flow sensor, 40...Cylinder discrimination unit, 42...Rotation angle sensor, 44...Control device. Agent Tatsuyuki Unuma (and 2 others)

Claims (1)

[Claims] (1) The engine load range, which indicates the engine load condition, is determined from the engine rotation speed and the intake air flow, and the air-fuel ratio of the air-fuel mixture is determined based on the detection output of the oxygen concentration sensor that detects the oxygen concentration in the exhaust gas. It is divided into a feedback region where feedback control is performed near the stoichiometric air-fuel ratio, and an open-loop region where the air-fuel mixture is controlled in an open-loop manner to maintain a rich air-fuel ratio by increasing fuel regardless of the detection output of the oxygen concentration sensor. In the air-fuel ratio control method for an internal combustion engine, which controls the air-fuel ratio of the air-fuel mixture according to the air amount and to which region the engine load belongs, when the operating state of the engine shifts from the feedback region to the open loop region, the fee, The learned value memorized and learned as the center value of the feedback correction value for the fuel ratio in the dopuck region is used as the initial value of the correction value for the air-fuel ratio in the open loop region, and if this correction value differs from the standard correction value, the standard correction is performed. A method for controlling an air-fuel ratio of an internal combustion engine, characterized in that the air-fuel ratio in an open loop region is controlled based on the correction value so as to gradually approach the standard correction value.