JP2000257488A - Air/fuel ratio control unit for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control an air/fuel ratio with high accuracy according to changes of a throttle opening within a low opening region, without especially increasing the number of learning regions. SOLUTION: An electronic control unit(ECU) 30 of an air/fuel ratio control unit for an engine 1 determines the basic fuel injection quantity, based on a throttle opening and an engine speed. Through compensating the basic fuel injection quantity based on a learned value computed for each of a plurality of learning regions to be determined by the throttle opening and the engine speed, the ECU 30 performs feedback control, so that an air/fuel ratio of a combustible mixture supplied to the engine 1 becomes equal to a predetermined stoichiometric air/fuel ratio. When the throttle opening is changed within a low opening region of a throttle valve 5, the ECU 5, the ECU 30 computes a learned theoretical value, in such a manner it predicts the value in the low opening region based on an hourly change of the throttle opening, the throttle opening, and the engine rotational speed. Furthermore, the ECU 30 compensates the basic fuel injection quantity based on the learned theoretical 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 feedback-controlling the air-fuel ratio of a combustible mixture supplied to an engine. More specifically, the present invention relates to an air-fuel ratio control device for an engine in which a basic fuel injection amount determined based on a throttle valve opening and an engine speed is learned and corrected based on an air-fuel ratio.

[0002]

2. Description of the Related Art Conventionally, there is a fuel injection control device which controls a fuel injection amount supplied to an engine according to an operation state of the engine. As one type of this type of control device, a fuel injection amount is controlled based on a basic fuel injection amount determined from an opening degree of a throttle valve (a throttle opening degree) provided in an intake passage of an engine and an engine rotation speed. There are things that I try to do. This kind of type,
This is called a so-called "throttle speed type".
In this type of control device, the fuel injection amount directly changes depending on the throttle opening that is operated, so that the acceleration response of the engine can be improved. On the other hand,
Due to individual variations or dimensional variations of engine components including the throttle body, aging of those components, errors may occur in the basic fuel injection amount supplied to the engine, and the air-fuel ratio of the combustible mixture may deviate. For,
This gap had to be corrected.

Japanese Unexamined Patent Publication No. Sho 59-120732 discloses a "throttle / speed type" fuel injection amount control device capable of correcting deviations in the air-fuel ratio due to individual variations of engine components and aging. Has been disclosed. That is, in this device, a basic pulse width (basic fuel injection amount) for driving an injector that injects fuel into the engine is calculated based on the throttle opening signal and the engine speed signal. Separately, a second basic pulse width (a second basic fuel injection amount) is calculated based on a differential pressure signal before and after the throttle valve and an engine speed signal. Further, a deviation value between the basic pulse width and the second basic pulse width is calculated during steady operation of the engine. By shifting the throttle opening data on the basis of the calculated deviation value, a learning function for always maintaining the optimum mixture ratio is provided.

However, in the apparatus disclosed in the above publication, a differential pressure sensor for detecting a differential pressure across the throttle valve must be specially provided in order to have a learning function for maintaining the optimum mixture ratio, and the configuration is complicated. There was a problem of becoming. In addition, in recent fuel injection control, air-fuel ratio control, in which the air-fuel ratio is feedback-controlled in order to improve the control accuracy, is the mainstream, and learning correction is performed during the control to ensure a learning function. ing. That is, this type of air-fuel ratio control device performs feedback control of the air-fuel ratio of the combustible air-fuel mixture to a target air-fuel ratio set according to the operating state of the engine using an oxygen concentration sensor provided in an exhaust passage of the engine. Like that. For this purpose, the basic fuel injection amount is corrected using an air-fuel ratio correction coefficient calculated based on the actual air-fuel ratio obtained from the output of the oxygen concentration sensor and a predetermined target air-fuel ratio. Further, a difference between the air-fuel ratio correction coefficient and a predetermined stoichiometric air-fuel ratio during engine operation is calculated as a learning value, and the basic fuel injection amount is corrected using the learning value. For example, Japanese Patent Application Laid-Open Nos. 62-203951, 4-203237 and 4-20
No. 3237 discloses an example of such control including air-fuel ratio control.

In general, in the above-described air-fuel ratio control, the operating state of the engine is divided into a plurality of learning areas according to predetermined operating parameters, learning values are calculated in accordance with each of the learning areas, and each of the learning values is non-volatile. It is stored in a memory.

[0006]

By the way, it is conceivable that the above-mentioned air-fuel ratio control is applied to the aforementioned "throttle speed type" fuel injection amount control device.
In this case, the operating state of the engine is divided into a plurality of learning regions according to the throttle opening and the engine rotation speed, and a learning value is calculated for each of the learning regions and stored in the memory.

However, in this case, the influence of individual variations of engine components and aging tends to be greater in the low opening region of the throttle valve than in the high opening region, and learning of air-fuel ratio control is difficult. The value may deviate from the appropriate value. This is because one learning region is relatively large and the number of learning regions set is small. In this case, for example, one learning region is set for the low opening region, and even if the throttle opening changes in that region, the change is used for correcting the basic fuel injection amount based on the learning value. It will be difficult to be reflected. This makes the deviation of the air-fuel ratio relatively large.

In order to cope with the above problem, it is conceivable to increase the set number of learning areas by relatively narrowing the range of each learning area. But in this case,
The learning value is less likely to be updated in the less frequently used learning area, and the accuracy of the learning value is reduced. For this reason, when the learning value for the less frequently used learning region is used for correcting the basic fuel injection amount, the accuracy of the learning value is low,
The air-fuel ratio may be shifted.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to increase the number of learning regions in a so-called throttle-speed type fuel injection amount control for performing air-fuel ratio learning correction. It is an object of the present invention to provide an air-fuel ratio control device for an engine that can control the air-fuel ratio with high accuracy in accordance with a change in the throttle opening in a low opening range without causing any problem.

[0010]

In order to achieve the above object, according to the first aspect of the present invention, a basic fuel injection amount determined based on a throttle valve opening and an engine speed is controlled by opening a throttle valve. The air-fuel ratio of the combustible air-fuel mixture supplied to the engine is corrected based on a learning value calculated for each of a plurality of learning regions set from the degree and the engine rotation speed so that the air-fuel ratio becomes a predetermined stoichiometric air-fuel ratio. In the air-fuel ratio control device for an engine that is controlled, when the throttle valve opening changes in a low opening region of the throttle valve, a change amount of the throttle valve opening per unit time, a throttle valve opening, Prediction calculation means for predictively calculating a theoretical value of the learning value in the low opening region based on the engine rotation speed; And purpose that a basic fuel injection quantity correcting means for correcting the basic fuel injection quantity based on the value.

According to the configuration of the present invention, when the throttle valve opening changes in the low opening region of the throttle valve, the prediction learning calculation means calculates the change amount of the throttle valve opening per unit time and the throttle valve opening. The theoretical value of the learning value in the low opening region is calculated predictively based on the engine speed and the engine speed. Then, the basic fuel injection amount is corrected by the basic fuel injection amount correction means based on the calculated theoretical value of the learned value so that the combustible mixture supplied to the engine has a predetermined stoichiometric air-fuel ratio. Feedback control will be performed. Therefore, in the low opening region, even if the throttle valve opening slightly changes, instead of the normal learning value, based on the theoretical value of the learning value that is predictively calculated according to the change in the throttle valve opening, The basic fuel injection amount is corrected with good compatibility.

According to a second aspect of the present invention, in accordance with the first aspect of the present invention, the learning value already calculated in the low opening region is already calculated in the high opening region. A calculation permitting means for permitting the calculation of the theoretical value of the learning value in the low opening degree region only when the calculated learning value deviates by a predetermined value or more is provided.

According to the configuration of the present invention, the calculation of the theoretical value of the learning value in the low opening region is performed only when the difference between the learning value of the low opening region and the learning value of the high opening region is larger than a predetermined value. When the deviation of the learning value is smaller than a predetermined value, the calculation of the theoretical value of the learning value in the low opening region is not permitted. Therefore, if the learned value already calculated in the low opening region can be used for correcting the basic fuel injection amount, the learned value is effectively used.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment embodying an air-fuel ratio control apparatus for an engine according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a schematic configuration of an engine system mounted on an automobile. The engine 1 is of a multi-cylinder type having a known structure, and in this embodiment,
The engine 1 having four cylinders # 1 to # 4 is employed. The engine 1 explodes and burns fuel and air supplied through the intake passage 2, that is, a combustible air-fuel mixture in the combustion chambers of the cylinders # 1 to # 4, and discharges the exhaust gas after the combustion through the exhaust passage 3. Thereby, a piston (not shown) is driven to rotate the crankshaft 4 to obtain power.

The throttle valve 5 provided in the intake passage 2 is opened and closed to adjust the amount of air (intake amount) Qa flowing through the passage 2 and taken into each of the cylinders # 1 to # 4. . The valve 5 operates in conjunction with the operation of an accelerator pedal 6 provided in the driver's seat. Throttle sensor 21 provided for throttle valve 5
Is for detecting the opening degree (throttle opening degree) TA of the valve 5 and outputting an electric signal corresponding to the detected value.

A plurality of injectors 7 provided at the intake ports corresponding to each of the cylinders # 1 to # 4 are connected to each of the cylinders # 1 to # 4.
For injecting and supplying fuel. These injectors 7 are provided on a common delivery pipe 8. The delivery pipe 8 is for distributing the fuel pumped from the fuel tank 9 to each of the injectors 7.

A plurality of spark plugs 10 provided in the engine 1 corresponding to each of the cylinders # 1 to # 4 operate upon receiving an ignition signal distributed from a distributor 11. The distributor 11 distributes the high voltage output from the igniter 12 to each spark plug 10 in accordance with the change in the rotation angle of the crankshaft 4, that is, the "crank angle (° CA)". The operation timing of each spark plug 10, that is, the ignition timing is determined by the output timing of the high voltage output from the igniter 12. Therefore, igniter 1
2, the ignition timing of each of the cylinders # 1 to # 4 by each of the ignition plugs 13 is controlled.

The oxygen sensor 23 provided in the exhaust passage 3
Detects the oxygen concentration Ox in the exhaust gas discharged from each of the cylinders # 1 to # 4 to the passage 3, and outputs an electric signal corresponding to the detected value.

The rotational speed sensor 24 provided in the distributor 11 detects the angular speed of the crankshaft 4, that is, the engine rotational speed NE, and outputs an electric signal corresponding to the detected value. The distributor 11 has a rotor (not shown) that rotates in conjunction with the rotation of the crankshaft 4 and has a plurality of teeth on the outer periphery.
Is built-in. The rotation speed sensor 24 includes the rotor
An electromagnetic pickup (not shown) disposed on the outer periphery of the rotor. Each time the electromagnetic pickup detects the passage of each tooth with the rotation of the rotor, the rotation speed sensor 24 outputs one pulse signal. In this embodiment, each time the crank angle advances by 30 ° CA, one pulse signal is output from the rotation speed sensor 24. Similarly, the distributor 11 is provided with a cylinder discrimination sensor 25 for detecting a change in the crank angle at a predetermined rate according to the rotation of the rotor. In this embodiment, assuming that the crankshaft 4 makes two rotations before all of the first cylinder # 1 to the fourth cylinder # 4 sequentially end the combustion stroke, the cylinder discrimination sensor is set at a rate of 720 ° CA. From 25, one pulse signal as the reference position signal GS is output.

The water temperature sensor 26 provided in the engine 1 is
Temperature (cooling water temperature) T of cooling water flowing inside the engine 1
It detects the HW and outputs an electric signal corresponding to the detected value.

In this embodiment, the throttle sensor 21, oxygen sensor 23, rotation speed sensor 24,
The cylinder discrimination sensor 25, the water temperature sensor 26, and the like constitute an operating state detecting means for detecting the operating state of the engine 1.

The above-described injectors 7, delivery pipes 8, fuel tanks 9 and the like constitute a fuel supply device. The electric fuel pump 13 built in the fuel tank 9 pumps up and discharges the fuel stored in the tank 9. The fuel pipe 14 connected to the discharge port side of the fuel pump 13 is connected to the delivery pipe 8 via the fuel filter 15. Here, when the fuel pump 13 operates, the fuel in the fuel tank 9 is discharged from the pump 13 to the fuel pipe 14, and after the foreign matter is removed by the fuel filter 15, the fuel is pumped to the delivery pipe 8. Is distributed to each injector 7. The fuel pumped to each of the injectors 7 is injected into an intake port as the injectors 7 operate, and is supplied to each of the cylinders # 1 to # 4.

In this embodiment, an electronic control unit (EC
U) 30 inputs various signals output from the above-described throttle sensor 21, oxygen sensor 23, rotation speed sensor 24, cylinder discrimination sensor 25, water temperature sensor 26, and the like.
The ECU 30 controls each of the injectors 7 and the igniter 12 based on these input signals to execute fuel injection control including air-fuel ratio control, ignition timing control, and the like. In this embodiment, the ECU 30 corresponds to the prediction learning means, the basic fuel injection amount correcting means, and the calculation permitting means of the first and second aspects of the present invention.

As is well known, the ECU 30 includes a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), a backup RAM, an external input circuit, an external output circuit, and the like. The ECU 30
A logical operation circuit is configured by connecting a CPU, a ROM, a RAM, a backup RAM, an external input circuit, an external output circuit, and the like by a bus. The ROM stores in advance a predetermined control program related to the air-fuel ratio control of the engine and the like. The RAM temporarily stores the calculation results of the CPU. The backup RAM stores data stored in advance. The CPU executes the above-described various controls and the like according to a predetermined control program, based on detection signals of the various sensors 21 and 23 to 26 input through the input circuit.

Here, the ignition timing control is to control the ignition timing of each ignition plug 10 by controlling the igniter 12 according to the operating state of the engine 1. The fuel injection control is to control the amount of fuel injected from each injector 7 (fuel injection amount) and the timing of the injection in accordance with the operating state of the engine 1. In this embodiment, the ECU 30 calculates a basic fuel injection amount TAUBSE based on the throttle opening TA and the engine speed NE, and calculates the basic fuel injection amount TAUB.
The final fuel injection amount TAU is determined by correcting the SE according to various conditions. The air-fuel ratio control is to perform feedback control of an air-fuel ratio of a combustible mixture of fuel and air supplied to the engine 1 based on at least a value detected by the oxygen sensor 23. Hereinafter, the air-fuel ratio control will be briefly described. FIG. 2 shows the oxygen concentration Ox detected by the oxygen sensor 23 in the air-fuel ratio control, the determination of the air-fuel ratio by the ECU 30, and the behavior of the air-fuel ratio correction coefficient FAF.

The ECU 30 corrects the air-fuel ratio based on the value of the oxygen concentration (output voltage) Ox detected by the oxygen sensor 23 so that the air-fuel ratio of the combustible mixture supplied to the engine 1 becomes a predetermined target air-fuel ratio. Calculate the coefficient FAF. Further, E
The CU 30 controls the amount of fuel supplied from each injector 7 to the engine 1 based on the calculated value of the air-fuel ratio correction coefficient FAF. Here, when the air-fuel ratio is rich, the ECU 30 calculates the air-fuel ratio correction coefficient FAF as a subtraction value (shown by a downward-sloping straight line in FIG. 2) for decreasing the amount of fuel supplied from each injector 7. ECU 30
Is the air-fuel ratio correction coefficient FAF when the air-fuel ratio is lean.
Is calculated as an added value for increasing the amount of fuel supplied from each injector 7 (shown by a straight line rising to the right in FIG. 2). That is, the ECU 30 determines whether the air-fuel ratio is rich or lean by comparing the output voltage related to the oxygen concentration Ox detected by the oxygen sensor 23 with a predetermined reference voltage. Then, the ECU 30 reduces the air-fuel ratio correction coefficient FAF at a fixed rate when it is determined that the air-fuel ratio is rich, and increases the air-fuel ratio correction coefficient FAF at a fixed rate when it is determined that the air-fuel ratio is lean. .
When the determination of the air-fuel ratio changes from lean to rich or from rich to lean, the ECU 30 skips the air-fuel ratio correction coefficient FAF stepwise. This skip is
This is a calculation method for increasing the responsiveness of the air-fuel ratio feedback control and bringing the air-fuel ratio closer to the stoichiometric air-fuel ratio.

In this embodiment, the ECU 30 performs the learning correction of the air-fuel ratio. That is, the ECU 30 corrects the basic fuel injection amount TAUBSE based on a learning value calculated for each of a plurality of learning regions defined and partitioned by the throttle opening TA and the engine rotation speed NE, thereby obtaining the air-fuel ratio. Is feedback-controlled so that a predetermined stoichiometric air-fuel ratio is obtained.

Next, among the various controls executed by the ECU 30, the contents of processing for air-fuel ratio control including learning control will be described. FIG. 3 shows a flowchart relating to the air-fuel ratio control. FIG. 4 shows a flowchart relating to the calculation of the learning value KG and its theoretical value (learning theoretical value) KGTA.

The ECU 30 periodically executes the routine shown in FIG. 3 every predetermined period. First, in step 100, E
The CU 30 reads the values of the throttle opening TA, the oxygen concentration Ox, the engine speed NE, and the coolant temperature THW based on the detection signals of the various sensors 21, 23, 24, and 26, respectively.

Next, at step 110, the ECU 30
The basic fuel injection amount TAUBSE is calculated and determined based on the read values of the throttle opening TA and the engine speed NE. The ECU 30 calculates the basic fuel injection amount TA
The calculation of UBSE is performed by referring to predetermined function data.

Next, in step 120, the ECU 30
As described above, the value of the air-fuel ratio correction coefficient FAF is calculated based on the read value of the oxygen concentration Ox.

Next, at step 130, the ECU 30
Based on the read values of the throttle opening TA and the engine speed NE, a learning value KG or a theoretical learning value KGTA, which will be described in detail later, is calculated. Learning value KG and learning theoretical value K
The GTA causes an error in the basic fuel injection amount TAUBSE to be supplied to the engine due to individual variation or dimensional variation of engine components including the throttle body, aging of the components, and the like, resulting in an air-fuel ratio of a combustible mixture. This is for correcting the displacement.

Next, at step 140, the ECU 30
Based on the read value of the cooling water temperature THW, the engine 1
The warm-up correction coefficient KTHW for correcting the basic fuel injection amount TAUBSE is calculated in accordance with the warm-up state.

Next, in step 150, the ECU 30
The basic fuel injection amount TAUBSE calculated as described above,
Air-fuel ratio correction coefficient FAF, learning value KG or learning theoretical value KG
Based on TA and the warm-up correction coefficient KTHW, the value of the final fuel injection amount TAU is calculated according to the following equation (1). TAU = TAUBSE * FAF * (KG or KGTA) * KTHW (1) Here, the learning value KG and the learning theoretical value KGTA are selectively adopted, and in particular, the learning theoretical value KGTA satisfies a predetermined condition. Sometimes, the throttle valve 5 is selectively adopted in a low opening region, that is, a region where the value of the throttle opening TA is relatively small.

Thereafter, at step 160, the ECU 30
Controls the amount of fuel supplied to each of the cylinders # 1 to # 4 of the engine 1 by controlling each of the injectors 7 based on the calculated value of the final fuel injection amount TAU. That is,
The air-fuel ratio of a combustible mixture of fuel and air supplied to each of the cylinders # 1 to # 4 is controlled.

Here, the calculation of the learning value KG or the theoretical learning value KGTA in step 130 will be described in detail with reference to FIG.

When the process proceeds to this routine, in step 200, the ECU 30 determines whether the learning control condition has been satisfied. Here, the learning control condition is the cooling water temperature T
This includes that the HW is equal to or more than a predetermined value (for example, “80 ° C.”) and the engine 1 is in a completely warmed-up state, that the air-fuel ratio feedback control is being performed, and the like. If these learning control conditions are not satisfied, the ECU 30 once terminates the subsequent processing. If the learning control condition is satisfied, the ECU 30 shifts the processing to step 210.

In step 210, the ECU 30 determines that the value of the currently read throttle opening TA is the throttle opening T
A is equal to or more than the lower limit KTAL and the upper limit K in the low opening region of A.
It is determined whether or not it is in the range of TAH or less. Here, if the value of the throttle opening TA is not in the range of the low opening region, the ECU 30 shifts the processing to step 290 to execute normal learning control. What is normal learning control?
That is, a learning value KG is calculated for each of a plurality of learning regions set from the slot opening degree TA and the engine rotation speed NE. In this embodiment, an average value of a plurality of air-fuel ratio correction coefficients FAF calculated in the past corresponding to a corresponding learning region is calculated as a learning value KG in the learning region.
On the other hand, if the value of the throttle opening TA is in the range of the low opening region, the ECU 30 proceeds to step 220.

In step 220, the ECU 30 determines that the absolute value of the difference between the learning value KG1 already calculated in the low opening region and the learning value KG4 already calculated in the high opening region is a predetermined value, that is, the learning value KG. It is determined whether or not it is equal to or more than the lower limit value KKGL. That is, it is determined whether or not the learning value KG1 in the low opening region deviates from the learning value KG4 in the high opening region by the lower limit value KKGL or more. Here, for example, “0.08 to 0.1” can be applied as the lower limit value KKGL. If the learning value KG1 in the low opening region does not deviate from the learning value KG4 in the high opening region by the lower limit value KKGL or more, the ECU 30 shifts the processing to step 290 to execute normal learning control. When the learning value KG1 in the low opening region is deviated from the learning value KG4 in the high opening region by the lower limit value KKGL or more, E
The CU 30 shifts the processing to step 230 described above.

In step 230, the ECU 30 determines whether or not the variation ΔTA of the throttle opening TA per unit time is equal to or greater than a predetermined transient determination reference value KTAFT. That is, it is determined whether or not the engine 1 is in a transient operation state (acceleration operation or deceleration operation state), that is, whether or not the value of the throttle opening TA has changed. When the ECU 30 is not in the transient operation state, the ECU 30 shifts the processing to step 290 to execute the normal learning control. If the vehicle is in the transient operation state, the ECU 30 proceeds to step 24 described above.
Move to 0.

In step 240, the ECU 30 determines whether or not the value of the engine speed NE is equal to or less than the upper limit value KNE. That is, in this embodiment, when the engine rotation speed NE reaches the upper limit KNE, the fuel supply to the engine 1 is cut off (the fuel is cut off).
Therefore, here, it is determined whether the fuel cut is not performed. EC when fuel cut is performed
U30 shifts the processing to step 290 to execute normal learning control. If no fuel cut is performed, E
The CU 30 shifts the processing to step 250.

In step 250, the ECU 30 determines a change amount correction coefficient F for the change amount ΔTA of the throttle opening TA.
Calculate the value of KG. The ECU 30 performs this calculation by referring to, for example, function data (two-dimensional map) as shown in Table 1.

[0044]

[Table 1]

Next, at step 251, the ECU 30
The opening correction coefficient F corresponding to the magnitude of the throttle opening TA
Calculate the value of KGTA. Here, as shown in FIG.
When the throttle valve 5 is opened from a certain throttle opening TA, the change amount of the learning theoretical value KGTA with respect to the change amount ΔTA gradually decreases at each calculation timing of the learning theoretical value KGTA, and the throttle valve 5 is closed from a certain throttle opening TA. In this case, the change amount of the learning theoretical value KGTA with respect to the change amount ΔTA gradually increases at each calculation timing of the learning theoretical value KGTA. Therefore, in this step 251, the opening correction coefficient FKGTA is calculated in order to correct the difference in the change amount of the learning theoretical value KGTA.
The ECU 30 performs this calculation by referring to function data (one-dimensional map) predetermined according to the throttle opening TA.

Next, at step 252, the ECU 30
A value of a rotation speed correction coefficient FKGNE corresponding to the magnitude of the engine rotation speed NE is calculated. Here, as shown in FIG. 6, even at a certain throttle opening TA, the learning value KG and the required learning value KGTA increase as the engine speed NE increases.
And the difference becomes large. Therefore, in step 252, a rotation speed correction coefficient FKGNE is calculated in order to correct the difference in the engine rotation speed NE. ECU3
0 is calculated by referring to function data (one-dimensional map) predetermined according to the engine speed NE.

Thereafter, at step 260, the ECU 30
Means that the learning value KG4 in the high opening region is the learning value K in the low opening region.
It is determined whether it is larger than G1. If the determination is affirmative, the ECU 30 shifts the processing to step 270.
Then, in step 270, the ECU 30 determines the current learning theoretical value KGT based on the previously calculated learning theoretical value KGTAO, the currently calculated change amount correction coefficient FKG, the opening degree correction coefficient FKGTA, and the rotation speed correction coefficient FKGNE.
A is calculated according to the following equation (2), and the subsequent processing is temporarily terminated. KGTA = KGTAO * (1 + FKG) * FKGTA * FKGNE (2) Here, when the learning control condition is first satisfied in step 200 after the operation of the engine 1, the conventional learning value K
G (learning value KG1 in the low opening degree region) is changed to the previous learning theoretical value K
Used as GTAO, and then the learning theoretical value K one time before
GTA is used as the previous learning theoretical value KGTAO.

On the other hand, if the determination in step 260 is negative, the ECU 30 shifts the processing to step 280. Then, in step 280, the ECU 30 determines the current learning theoretical value KGTA based on the previously calculated learning theoretical value KGTAO, the currently calculated change amount correction coefficient FKG, the opening degree correction coefficient FKGTA, and the rotation speed correction coefficient FKGNE.
Is calculated according to the following equation (3), and the subsequent processing is temporarily terminated. KGTA = KGTAO * (1-FKG) * FKGTA * FKGNE (3) The learning value KG and the theoretical learning value KGTA are calculated as described above.

As described above, according to the engine air-fuel ratio control apparatus of this embodiment, the throttle valve 5
In the low opening region, for example, when the slot opening TA slightly changes during the transient operation of the engine 1, the ECU 30 uses the ECU 30 to change the throttle opening TA per unit time Δ
Based on TA, throttle opening TA and engine speed NE, a theoretical learning value KGTA in the low opening range is calculated predictively. Then, the ECU 30 corrects the basic fuel injection amount TAUBSE based on the learned theoretical value KGTA, and performs feedback control so that the combustible air-fuel mixture supplied to the engine 1 has a predetermined stoichiometric air-fuel ratio. Therefore, in the low opening region, even if the throttle opening TA slightly changes, the throttle opening T is replaced with the normal learning value KG.
Learning theoretical value KGT calculated predictively according to the change of A
Based on A, the basic fuel injection amount TAUBSE is corrected with good compatibility. Therefore, in an air-fuel ratio control device that performs learning correction of the air-fuel ratio by a so-called throttle-speed type fuel injection amount control, the air-fuel ratio is controlled with high accuracy in accordance with a change in the throttle opening TA in a low opening region. Will be able to

That is, in the conventional learning control, one learning region in the low opening region is relatively wide, and the influence of individual variation of engine components and aging is greater than in the high opening region. May be deviated from the appropriate value. For this reason, even if the throttle opening TA slightly changes in the low opening range, the change is determined by the learning value KG.
1, the correction of the basic fuel injection amount TAUBSE becomes difficult to be reflected, and the deviation of the air-fuel ratio tends to be relatively large. However, according to the air-fuel ratio control device of this embodiment, the theoretical learning theoretical value KGTA is sequentially and predictively calculated in the low opening region regardless of the magnitude of the change in the throttle opening TA. This will be applied to the correction of the injection amount TAUBSE. Therefore, the throttle opening TA
Is slightly changed, the air-fuel ratio can be appropriately corrected by reflecting the change. In addition, it is not necessary to make the range of each learning region relatively narrow and increase the set number of learning regions. Therefore, there is no possibility that the learning value is not updated in the learning region that is used less frequently and the learning accuracy is not reduced.

FIG. 7 shows the learning theoretical value KGTA of the present embodiment and the conventional learning value K with respect to the change of the throttle opening TA.
An example of the behavior of G is shown. As is clear from FIG. 7, the difference between the conventional learning value KG and the required value is relatively large because it changes for each learning region. On the other hand, the learning theoretical value KGTA of the present embodiment changes at each calculation timing (for example, 13.3 ms), that is, at every unit time with respect to the change amount ΔTA of the throttle opening TA, so It can be seen that the difference is relatively small.

According to the air-fuel ratio control device of this embodiment, the learning value K1 of the learning value KG1 of the high opening region of the learning value KG1 of the low opening region is obtained.
Only when the deviation from G4 is greater than or equal to the predetermined lower limit value KKGL, the ECU 30 allows the calculation of the learning theoretical value KGTA in the low opening degree region. On the other hand, both learning values K
When the deviation between G1 and KG4 is smaller than the predetermined lower limit KKGL, calculation of the learning theoretical value KGTA in the low opening region is not allowed. Therefore, the conventional learning value KG1 already calculated in the low opening region is used as the basic fuel injection amount TAUBSE.
If it can be used for the correction, the learning value KG1 is effectively used. Therefore, even in the low opening range, the air-fuel ratio control using the conventional learning value KG can be appropriately executed according to the learning state of the learning value KG.

It should be noted that the present invention is not limited to the above-described embodiment, and a part of the configuration may be appropriately changed without departing from the spirit of the invention.

[0054]

According to the first aspect of the present invention,
In an air-fuel ratio control device that performs learning correction of the air-fuel ratio by a so-called throttle-speed type fuel injection amount control, the air-fuel ratio is adjusted according to the change in the throttle opening in the low opening region without increasing the number of learning regions. This has the effect that the fuel ratio can be controlled with high precision.

According to the configuration of the invention described in claim 2, in addition to the effect of the invention described in claim 1, in addition to the effect of the air-fuel ratio control using the conventional learning value even in the low opening range, the learning value learning state Can be appropriately executed according to the above.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an engine system according to an embodiment.

FIG. 2 is a time chart showing the determination of the oxygen concentration and the air-fuel ratio and the behavior of the air-fuel ratio correction coefficient.

FIG. 3 is a flowchart related to air-fuel ratio control.

FIG. 4 is a flowchart related to calculation of a learning value and a learning theoretical value.

FIG. 5 is a graph showing a relationship between a change amount of a learning theoretical value and a change amount of a throttle opening degree.

FIG. 6 is a graph showing the relationship between the amount of change in the theoretical learning value and the throttle opening according to the difference in engine speed.

FIG. 7 is a time chart showing an example of behaviors of a learning theoretical value and a conventional learning value with respect to a change in throttle opening.

[Explanation of symbols]

Reference Signs List 1 engine 5 throttle valve 30 ECU (prediction calculation means, basic fuel injection amount correction means, calculation allowance means) TA throttle opening ΔTA change in throttle opening NE engine rotation speed KG learning value KGTA learning theoretical value TAUBSE basic fuel injection amount TAU Final fuel injection amount

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshio Nishio 1-1, Kyowa-cho, Obu-shi, Aichi 1 Ai San Industry Co., Ltd. (72) Inventor Sadao Takagi 2-1-1 Taoyuan, Ikeda-shi, Osaka Daihatsu Industry Co., Ltd. (72) Inventor Yasuhide Inoue 2-1-1 Taoyuan, Ikeda-shi, Osaka F-term (reference) in Daihatsu Industry Co., Ltd. 3G084 AA03 BA09 BA13 CA03 DA12 EB18 EB20 FA10 FA29 FA33 3G301 HA01 HA06 JA18 KA08 LB02 MA01 MA14 ND28 PA11Z PD02A PE01Z

Claims (2)

[Claims] 1. A basic fuel injection amount determined based on a throttle valve opening and an engine rotation speed is calculated for each of a plurality of learning regions set from the throttle valve opening and the engine rotation speed. An air-fuel ratio control device for an engine in which the air-fuel ratio of a combustible mixture supplied to the engine is feedback-controlled so as to be a predetermined stoichiometric air-fuel ratio by making a correction based on a learning value. When the throttle valve opening changes in a region, a learning value in the low opening region is determined based on a change amount per unit time of the throttle valve opening, the throttle valve opening, and the engine rotation speed. Prediction calculation means for predictively calculating the theoretical value of: the basic fuel injection amount based on the calculated theoretical value of the learning value Air-fuel ratio control apparatus for an engine is characterized in that a basic fuel injection quantity correcting means for correcting. 2. The air-fuel ratio control device for an engine according to claim 1, wherein a learning value already calculated in the low opening region deviates from a learning value already calculated in the high opening region by a predetermined value or more. An air-fuel ratio control device for an engine, further comprising: calculation permitting means for permitting calculation of a theoretical value of a learning value in the low opening range only when the calculation is performed.