JPH07247888A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To perform constantly proper correction of an injection amount by using a learning value without executing and stopping recirculation of exhaust gas and to prevent a specified component in exhaust gas from exceeding an allowable value especially when exhaust gas is not recirculated and correction of an injection amount by using an air-fuel ratio correction amount is not effected. CONSTITUTION:An electronic control device (ECU) 41 releases an EGR passage 28 by an EGR valve 29 when the running state of an engine 1 is within an exhaust gas recirculation (RGR) execution region. The ECU 41 calculates an injection amount from a fuel injection valve 19 based on detecting values from various sensors. The ECU 41 corrects an injection amount by means of an air-fuel ratio feedback correction factor and a learning value stored and updated classified by the running region of the engine 1. When the running region of the engine 1 is outside the EGR execution region and correction of an injection amount using a correction factor is stopped, a learning value is limited by a learning upper limit corresponding to an allowable value so that a specified component in exhaust gas is prevented from exceeding an allowable value through reflection of a learning value to an injection amount.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine in which a part of exhaust gas discharged from a combustion chamber is returned to an intake passage and a fuel injection valve is controlled to supply a desired amount of fuel to the combustion chamber. The present invention relates to a fuel injection control device adapted to supply the fuel.

[0002]

2. Description of the Related Art Conventionally, in a general internal combustion engine, fuel is injected from a fuel injection valve into air flowing in an intake passage to generate a mixture. This air-fuel mixture is ignited by the spark plug and burned in the combustion chamber. Gas generated by combustion (exhaust gas) is purified by the catalyst in the exhaust passage and then discharged to the outside of the engine.

In the above internal combustion engine, the fuel injection by the fuel injection valve is controlled by the electronic control unit. In this fuel injection control, the injection amount is calculated based on the operating state of the engine, and the injection amount is corrected by the air-fuel ratio correction amount and the learning value. Then, the fuel injection valve is drive-controlled so as to obtain the corrected injection amount.

The air-fuel ratio correction amount is for converging the air-fuel ratio of the air-fuel mixture to a predetermined value such as the theoretical air-fuel ratio, and is determined based on the detection value of the oxygen sensor in the exhaust passage. The air-fuel ratio is the weight ratio of air to fuel in the air-fuel mixture, and the theoretical air-fuel ratio is the air-fuel ratio of the air-fuel mixture containing just enough oxygen to completely oxidize the fuel.

Further, the learned value is for coping with variations in the internal combustion engine, variations with time, variations in the air-fuel ratio due to operating environment conditions, and the like. The learned values are set for each operating region of the internal combustion engine, and these learned values are stored in the memory of the electronic control unit. Then, when the air-fuel ratio measured by the oxygen sensor deviates from the predetermined range, the learned value in the operating region corresponding to the operating state at that time is rewritten. The learning value is rewritten even when the predetermined learning condition is satisfied. Then, a learning value corresponding to the operating state of the internal combustion engine at that time is selected and used for correcting the injection amount. The correction of the injection amount using the air-fuel ratio correction amount and the learning value is performed when the cooling water temperature of the internal combustion engine is equal to or higher than a predetermined value.

On the other hand, in an internal combustion engine that uses gasoline as a fuel, for example, the nitrogen oxides (NO
An exhaust gas recirculation device may be installed to reduce x). This device includes an exhaust gas recirculation passage that connects the exhaust passage and the intake passage, and a flow control valve provided in the passage. In the exhaust gas recirculation device, if the operating state of the internal combustion engine at that time is within the recirculation execution region, the flow control valve opens the exhaust gas recirculation passage. When a part of the exhaust gas is returned to the intake passage by this opening, the combustion temperature of the air-fuel mixture is lowered and the generation of NOx is suppressed.

As shown in FIG. 10, the recirculation execution region is a region in which the cooling water temperature of the internal combustion engine is a predetermined value (for example, 50 ° C.) or more and is defined by the engine rotation speed and the engine load of the internal combustion engine. Is part of. In FIG. 10, a portion excluding the recirculation execution region (a portion of high load and high rotation, etc.) or the entire region where the cooling water temperature is lower than a predetermined value is the recirculation stop region as shown in FIG. There is.

In an internal combustion engine equipped with the above exhaust gas recirculation device and in which the injection amount is corrected by the air-fuel ratio correction amount and the learning value, the learning value is rewritten when the exhaust gas recirculation is executed. Therefore, if the operating state of the internal combustion engine at that time is within the recirculation execution region, the injection amount is appropriately corrected by the learning value. Therefore, when the fuel injection valve is controlled based on the injection amount obtained by the correction, the air-fuel ratio of the air-fuel mixture converges to the stoichiometric air-fuel ratio.

However, even if the cooling water temperature is lower than a predetermined value and the exhaust gas recirculation is stopped, if the learned value is used for correcting the injection amount in the same manner as described above, in some cases,
The injection amount may be excessively increased or decreased. At this time, since the injection amount correction using the air-fuel ratio correction amount is not performed, a specific component (hydrocarbon H) in the exhaust gas is corrected especially when an excessive increase correction is performed.
C, carbon monoxide CO, etc.) will increase.

As a related technique for dealing with the above problem, there is an "air-fuel ratio control device for an internal combustion engine" disclosed in Japanese Patent Laid-Open No. 4-1439, for example. In this technique, the learning value is rewritten independently by using different control maps when the exhaust gas recirculation is executed and when it is stopped. Then, the injection amount is corrected by using a different learning value depending on the presence or absence of exhaust gas recirculation.

[0011]

However, in the technique disclosed in the above publication, the operation region in which the learning value is rewritten includes the recirculation execution region. Therefore, although the learning value for recirculation stop can be rewritten in the recirculation stop area of FIG. 10, the learning value for recirculation stop cannot be rewritten in the recirculation execution area. As a result, when the cooling water temperature becomes lower than the predetermined value and the exhaust gas recirculation is stopped, it is difficult to correct the injection amount using the learning value in the region surrounded by the two-dot chain line in FIG. 11.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to always appropriately correct an injection amount using a learned value regardless of whether exhaust gas recirculation is executed or stopped. A fuel injection control device for an internal combustion engine is provided.

[0013]

In order to achieve the above object, the first invention according to claim 1 is, as shown by a solid line in FIG. 1, an intake passage M communicating with a combustion chamber M2 of an internal combustion engine M1.
3, a fuel injection valve M4 provided in the engine 3, an operating state detecting means M5 for detecting an operating state of the internal combustion engine M1, and a fuel injection valve M according to a detection value of the operating state detecting means M5.
Fuel injection valve M4 for driving and controlling the fuel injection valve M4 so that the injection amount is calculated by the injection amount calculation unit M6, and the fuel is discharged from the combustion chamber M2. Based on the detection value of the flow rate control valve M9 provided in the exhaust gas recirculation passage M8 for guiding a part of the exhaust gas to the intake passage M3 and the operating state detection means M5, the internal combustion engine M1 at that time is detected. If the operating state is within the recirculation execution region, the flow rate control valve M9 is controlled to open the exhaust gas recirculation passage M8. When the operating state deviates from the recirculation execution region, the flow rate control valve M9 is controlled. Exhaust gas recirculation control means M for closing the exhaust gas recirculation passage M8
10, an air-fuel ratio detecting means M11 for detecting the air-fuel ratio of the internal combustion engine, and an air-fuel ratio for converging the air-fuel ratio of the air-fuel mixture to a predetermined value according to the detection value of the air-fuel ratio detecting means M11. Air-fuel ratio correction amount calculation means M1 for calculating the correction amount
2, a first injection amount correction unit M13 that corrects the injection amount by the injection amount calculation unit M6 based on the air-fuel ratio correction amount by the air-fuel ratio correction amount calculation unit M12, and a learning value for each operating region of the internal combustion engine M1. Learning value storage means M1 in which
4 and the learned value rewriting means M15 for rewriting the learned value in the operating region of the learned value storage means M14 corresponding to the operating state at that time when the air-fuel ratio by the air-fuel ratio detecting means M11 is out of a predetermined range. When the operating state of the internal combustion engine M1 is out of the recirculation execution region and the correction of the injection amount using the air-fuel ratio correction amount by the first injection amount correction means M13 is stopped, the learning value is injected. In order to prevent the specific component in the exhaust gas from exceeding the allowable value by being reflected in the amount, the learning upper limit value corresponding to the allowable value is compared with the learning value of the learning value storage means M14, and the learning value is When the learning value is larger than the learning upper limit value, the learning value changing means M16 for forcibly changing the learning value to the learning upper limit value, and the operating state detecting means M5 corresponding to the operating state of the internal combustion engine M1 at that time And a second injection quantity correction means M17 for correcting the injection amount of the injection amount calculating means M6 by using the learning value of 習値 storage means M14.

In addition to the structure of the first invention, a second invention according to claim 2 is, as shown by a chain double-dashed line in FIG.
Atmospheric pressure detecting means M18 for detecting a change in atmospheric pressure, and with the decrease in atmospheric pressure by the atmospheric pressure detecting means M18,
A learning upper limit value changing means M19 for reducing the learning upper limit value of the learning value changing means M16 is provided.

[0015]

In the first aspect of the invention, the injection amount calculation means M6
Calculates the injection amount according to the operating state of the internal combustion engine M1 detected by the operating state detecting means M5. The injection control means M7 drives and controls the fuel injection valve M4 so that the calculated injection amount is obtained. Then, fuel is injected from the fuel injection valve M4, and the fuel mixes with the air flowing through the intake passage M3 to form a mixture. After the air-fuel mixture is taken into the combustion chamber M2, it is burned and discharged from the combustion chamber M2.

Further, the exhaust gas recirculation control means M10 controls the flow rate control valve M9 to control the exhaust gas recirculation passage M8 if the operating state of the internal combustion engine M1 at that time is within the recirculation execution region.
To release. Then, a part of the exhaust gas discharged from the combustion chamber M2 is guided to the intake passage M3. Since most of this exhaust gas is an inert gas, the combustion temperature of the air-fuel mixture is lowered, and the generation of specific components in the exhaust gas is suppressed. The exhaust gas recirculation control means M10 controls the flow rate control valve M9 to close the exhaust gas recirculation passage M8 when the operating state deviates from the recirculation execution region.

Further, the air-fuel ratio correction amount calculation means M12 is
An air-fuel ratio correction amount for converging the air-fuel ratio to a predetermined value is calculated according to the air-fuel ratio detected by the air-fuel ratio detecting means M11. As this predetermined value, for example, an air-fuel ratio (stoichiometric air-fuel ratio) of the air-fuel mixture containing just enough oxygen to completely oxidize the fuel is adopted. The first injection amount correction means M13 corrects the injection amount of the injection amount calculation means M6 based on the calculated air-fuel ratio correction amount. When the fuel injection valve M4 is drive-controlled by the injection control unit M7 so that the corrected injection amount is obtained, the air-fuel ratio converges to a predetermined value such as the theoretical air-fuel ratio.

When the air-fuel ratio deviates from the predetermined range, the learning value rewriting means M15 rewrites the learning value in the operating region of the learning value storage means M14 corresponding to the operating state at that time. Further, the learning value changing means M16, when the operating state of the internal combustion engine M1 is out of the recirculation execution region, and when the correction of the injection amount using the air-fuel ratio correction amount by the first injection amount correction means M13 is stopped. , Learning value storage means M14 as follows
Limit the learning value of. That is, the learning value changing means M
Reference numeral 16 denotes a learning upper limit value and learning value storage means M14 corresponding to the allowable value in order to prevent the specific component in the exhaust gas from exceeding the allowable value due to the learning value being reflected in the injection amount.
Compare with the learning value of. The learning value changing means M16 uses the learning value as it is when the learning value is equal to or less than the learning upper limit value, and forcibly changes the learning value to the learning upper limit value when the learning value is larger than the learning upper limit value.

The second injection amount correction means M17 is
The injection amount of the injection amount calculation means M6 is corrected using the learning value of the learning value storage means M14 corresponding to the operation state of the internal combustion engine M1 at that time by the operation state detection means M5. The injection control means M7 drives and controls the fuel injection valve M4 so as to obtain the corrected injection amount.

Therefore, when the operating state of the internal combustion engine M1 belongs to the recirculation execution region, or when the first injection amount correction means M is used.
When the injection amount is corrected by using the air-fuel ratio correction amount by 13, the learning value rewritten by the learning value rewriting means M15 is used as it is for the correction of the injection amount. Then, since the learned value is a value rewritten when the exhaust gas recirculation is executed, the injection amount is appropriately corrected by the learned value. Therefore, when the fuel injection valve M4 is controlled based on the corrected injection amount, the air-fuel ratio of the air-fuel mixture converges to a predetermined value such as the theoretical air-fuel ratio.

Further, when the operating state of the internal combustion engine M1 is out of the recirculation execution region and the correction of the injection amount using the air-fuel ratio correction amount by the first injection amount correction means M13 is stopped, the learning value Is less than or equal to the learning upper limit value, the learning value is used as it is for correction of the injection amount, and if the learning value is larger than the learning upper limit value, the learning upper limit value is used as a learning value for correction of the injection amount. Therefore, although the injection amount is not corrected using the air-fuel ratio correction amount, the injection amount is not excessively increased and corrected by the learning value.

By the way, the atmospheric pressure is lowered at a position above sea level above the level ground, and the amount of exhaust gas recirculation is reduced. For this reason, if the same learning value as that for flat land is used, the injection amount may be excessively increased and corrected. On the other hand, in the second invention, the learning upper limit value changing means M19 is accompanied by a decrease in the atmospheric pressure detected by the atmospheric pressure detecting means M18.
The learning upper limit value in the learning value changing means M16 is changed to a small value. Therefore, the increase of the learning value due to the decrease of the exhaust gas recirculation amount is offset by the change of the learning upper limit value.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment embodying the first and second inventions will be described below with reference to FIGS.

FIG. 2 is a schematic configuration diagram of a gasoline engine (hereinafter, simply referred to as an engine) 1 as an internal combustion engine mounted on a vehicle. Cylinder block 1a of engine 1
, A plurality of cylinders (only one is shown in the figure) 2 are arranged in parallel in the thickness direction of the paper. A piston 3 is housed in each cylinder 2 so as to be vertically reciprocable. The piston 3 is connected to the crankshaft 5 by a connecting rod 4.

A combustion chamber 6 is formed above the piston 3, and an intake passage 7 and an exhaust passage 8 communicate therewith.
The communication portion between the combustion chamber 6 and the intake passage 7 serves as an intake port 9. The intake port 9 is opened and closed by an intake valve 11 attached to the cylinder head 1b. Further, the communication portion between the combustion chamber 6 and the exhaust passage 8 is the exhaust port 1
It is 0. Exhaust port 10 is cylinder head 1
It is opened and closed by the exhaust valve 12 attached to b.

In the intake passage 7, the combustion chamber 6 is arranged from the upstream side.
Toward the air cleaner 13, throttle body 1
4, a surge tank 15, and an intake manifold 16 are provided, and the air outside the engine 1 is taken into the combustion chamber 6 via these. A throttle valve 17 is supported by a shaft 18 in the throttle body 14 so as to be integrally rotatable. The shaft 18 is connected to an accelerator pedal (not shown) by a cable or the like. When the driver depresses the accelerator pedal, the depressing operation is transmitted to the shaft 18 via a cable or the like, and the throttle valve 17 rotates integrally with the shaft 18. The flow passage area of the intake passage 7 changes according to the rotation angle of the throttle valve 17, and the amount of air flowing through the intake passage 7 is adjusted. Surge tank 1
Reference numeral 5 is a tank for smoothing the pulsation of intake air and preventing intake interference of each cylinder.

The intake manifold 16 is provided with an electromagnetic fuel injection valve 19 for supplying fuel to each cylinder. The fuel injection valve 19 includes a needle valve, a solenoid coil, and the like. When the solenoid coil is energized, the needle valve moves and the injection port is opened.
High-pressure fuel is injected with the opening of the injection port. Then, the fuel injected from each fuel injection valve 19 and the intake passage 7
The air-fuel mixture including the air introduced into the combustion chamber 6 is introduced into the combustion chamber 6 through the intake port 9 when the intake valve 11 is opened.

In order to ignite the air-fuel mixture introduced into the combustion chamber 6, a semiconductor ignition type ignition device 20 is provided. The ignition device 20 includes an igniter 21, an ignition coil 22, a distributor 23, and an ignition plug 24 for each cylinder.

The igniter 21 is ignited by an ignition coil 22 based on an ignition signal from the outside (electronic control device described later).
Allows or blocks the energization of the primary coil of. When the power supply to the primary coil is cut off, a high voltage secondary voltage is generated in the secondary coil of the ignition coil 22. This secondary voltage is distributed by the distributor 23 to the ignition plugs 24 for each cylinder. Then, a current flows between the electrodes of the plug 24 (discharge occurs), and a spark is generated.

The air-fuel mixture introduced into the combustion chamber 6 is burned by the ignition of the spark plug 24. Due to this combustion, the piston 3 operates, and its reciprocating motion is converted into rotary motion by the connecting rod 4, and the crankshaft 5
Is driven to rotate. The gas (exhaust gas) generated by the combustion in the combustion chamber 6 is led from the exhaust port 10 to the exhaust passage 8 when the exhaust valve 12 is opened.

In the exhaust passage 8, an exhaust manifold 25 and a catalytic converter 26 are arranged in this order from the combustion chamber 6 toward the downstream side, through which exhaust gas is exhausted to the outside of the engine 1. The catalytic converter 26 is a device that purifies hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) in exhaust gas by the action of a catalyst.

In the engine 1, a part of the exhaust gas in the exhaust passage 8 is returned to the intake passage 7 and the exhaust gas is recirculated.
An exhaust gas recirculation device (EGR device) 27 for performing gas recirculation is provided. EGR device 27
Is an exhaust gas recirculation passage (EGR passage) 2 that connects the exhaust passage 8 and the intake passage 7 while bypassing the combustion chamber 6.
8 and an EGR valve 29 as a flow rate control valve disposed in the passage 28.

The EGR valve 29 includes a step motor 31 and
The rotor 31a has a valve body 31b attached to the tip thereof. In this EGR valve 29, the rotor 31a of the step motor 31 rotates in response to the pulse signal, and the rotation changes the lift amount of the valve body 31b. The flow passage area of the EGR passage 28 changes according to this change, and the intake passage 7
The flow rate of the exhaust gas returned to is adjusted.

The following various sensors are used to detect the operating condition of the engine 1 and the condition around it. In the intake passage 7, near the air cleaner 13,
An intake air temperature sensor 32 for detecting the temperature of the air flowing through the passage 7 (intake air temperature THA) is attached. A throttle sensor 33 is attached to the throttle body 14. The sensor 33 outputs an idle signal when the throttle valve 17 closes the intake passage 7. Further, in the throttle sensor 33, the throttle valve 17 has the intake passage 7
When the valve is opened even slightly, the rotation angle (throttle opening TA) of the throttle valve 17 is detected. The surge tank 15 is provided with a semiconductor type intake pressure sensor 34 for detecting the pressure (intake pressure PM) in the surge tank 15 when the vacuum is used as a reference.

A water temperature sensor 35 for detecting the temperature of the cooling water of the engine 1 (cooling water temperature THW) is attached to the cylinder block 1a. Distributor 2
3, a rotation speed sensor 36 for detecting the rotation speed of the crankshaft 5 (engine rotation speed NE),
A reference position sensor 37 for detecting the reference position of the crank angle is provided. The rotation speed sensor 36 is composed of a timing rotor having a large number of protrusions on its outer circumference, and a pickup coil arranged outside the timing rotor. The sensor 36 outputs a pulsed rotation speed signal each time the protrusion on the timing rotor passes in front of the pickup coil as the crankshaft 5 rotates. The reference position sensor 37 is composed of a timing rotor having one protrusion on its outer circumference and a pickup coil arranged outside the timing rotor. The sensor 37 outputs a pulse-like reference position signal each time one protrusion on the timing rotor passes in front of the pickup coil as the crankshaft 5 rotates.

An oxygen sensor 38 for detecting the oxygen concentration in the exhaust gas is attached to the exhaust manifold 25. The oxygen sensor 38 is formed by coating a zirconia element with platinum and outputs a voltage (output voltage V) according to the concentration of oxygen as shown in FIG. Oxygen sensor 3
No. 8 has a characteristic that the output voltage V suddenly changes near the stoichiometric air-fuel ratio (14.5).

Further, in the passenger compartment, the atmospheric pressure (absolute pressure) P
A semiconductor-type atmospheric pressure sensor 39 for detecting A is provided. Of the various sensors 32 to 39 described above, the intake pressure sensor 34 and the rotation speed sensor 36 constitute an operating state detecting means. Further, the oxygen sensor 38 constitutes a part of the air-fuel ratio detecting means, and the atmospheric pressure sensor 39
The atmospheric pressure detecting means is constituted by.

The vehicle has a fuel injection valve 19, an igniter 21, and an EG based on the detection signals of the sensors 32 to 39.
An electronic control unit (hereinafter referred to as ECU) 41 is provided to control each operation of the R valve 29.

As shown in FIG. 3, the ECU 41 includes a central processing unit (hereinafter referred to as CPU) 42, a read-only memory (hereinafter referred to as ROM) 43, a random access memory (hereinafter referred to as RAM) which constitutes an air-fuel ratio detecting means together with the oxygen sensor 38. 44), backup RAM 45,
An external input circuit 46 and an external output circuit 47 are provided, and these are connected to each other by a bus 48. The ROM 43 stores a predetermined control program and initial data in advance. The CPU 42 executes various arithmetic processes according to the control program and initial data. RAM44 is CPU4
The calculation result by 2 is temporarily stored. Backup R
The AM 45 is backed up by a battery (not shown) to retain various data in the RAM 44 even after the power supply to the ECU 41 is stopped.

An intake temperature signal from the intake temperature sensor 32, a throttle opening signal and an idle signal from the throttle sensor 33, an intake pressure signal from the intake pressure sensor 34,
Cooling water temperature signal from the water temperature sensor 35, rotation speed sensor 3
The rotation speed signal from the control unit 6, the reference position signal from the reference position sensor 37, the oxygen concentration signal from the oxygen sensor 38, and the atmospheric pressure signal from the atmospheric pressure sensor 39 are input to the external input circuit 46. Based on these signals, the CPU 42 determines the intake air temperature T
HA, throttle opening TA, idle signal, intake pressure P
M, cooling water temperature THW, engine speed NE, crank angle reference position, oxygen concentration, atmospheric pressure PA, etc. are detected.

On the other hand, the CPU 42 controls the igniter 21 via the external output circuit 47. That is, engine 1
The optimum ignition timing according to the operating state of is stored in advance in the ROM 43, and the CPU 42 detects the operating state of the engine 1 by the signals from the various sensors and calculates the optimal ignition timing. Then, the CPU 42 uses the external output circuit 47.
An ignition signal is output to the igniter 21 via the to control the ignition timing of the ignition plug 24.

Now, the flow chart of FIG.
The routine for driving and controlling the EGR valve 29 is shown among the respective processes executed by. The flowchart of FIG. 7 shows a routine for calculating the amount of fuel injected from the fuel injection valve 19 (injection amount). Here, the injection amount is determined by the time (injection time) during which the needle valve of the fuel injection valve 19 is open, that is, the energization time to the solenoid coil. Therefore, in the routine of FIG. 7, the injection time TAU is calculated as the injection amount. Further, the flowchart of FIG. 9 is used when calculating the injection time TAU in FIG.
The learning routine for updating and storing the learning values KG0 and KGi is shown. Both routines are repeatedly executed during the period from the start of the engine 1 to the stop thereof.

In the EGR control routine of FIG. 4, first, at step 101, the intake pressure PM and the engine speed N
E and cooling water temperature THW are read. Then, in step 102, the read values PM, NE, TH
Based on W, it is determined whether the operating state of the engine 1 at that time is an operating state for recirculating exhaust gas. Two maps stored in advance in the ROM 43 are used for this determination. In the map of FIG. 5, the cooling water temperature TH
When W is equal to or greater than a predetermined value α (for example, 50 ° C.), the recirculation execution region (EGR execution region) Z1 and the recirculation stop region (E
GR stop area) Z2 is defined. Further, the map of FIG. 6 defines a recirculation stop region (EGR stop region) Z3 when the cooling water temperature THW is lower than the predetermined value α. As is apparent from FIG. 6, when the cooling water temperature THW is lower than the predetermined value α, the EGR is always stopped regardless of the engine speed NE and the intake pressure PM. Then, with reference to these maps, it is determined which of the zones Z1 to Z3 the operating state of the engine 1 at that time belongs to.

When it is determined in step 102 that the EGR execution area Z1 is set, the routine proceeds to step 103, where the EGR valve 2
A target step number of 9 is calculated. ROM for this calculation
A map (not shown) stored in advance in 43 is used. This map defines the target number of steps with the engine speed NE and the intake pressure PM as parameters.

On the other hand, in step 102, the EGR stop region Z
If it is determined to be 2, Z3, the process proceeds to step 104, and the target number of steps is set to "0" to close the EGR passage 28.

When the target step number is determined in step 103 or 104, a pulse signal corresponding to the target step number is output to the step motor 31 of the EGR valve 29 via the external output circuit 47 in step 105. In response to this signal, the rotor 31a of the step motor 31 rotates by a predetermined angle and the lift amount of the valve body 31b changes, and the EGR
The flow passage area of the passage 28 is adjusted. As a result, the flow rate of the exhaust gas returned to the intake passage 7 through the EGR passage 28 is adjusted. When the processing of step 105 is executed, this routine is once terminated.

Here, the processing of steps 101 to 105 of the above-mentioned EGR control routine corresponds to the exhaust gas recirculation control means. Next, the injection time calculation routine of FIG. 7 will be described. First, in step 201, it is determined whether or not it is the timing to calculate the injection time TAU of the fuel injection valve 19 based on the engine rotation speed NE. When it is not this calculation timing, this routine is once ended.

On the other hand, if it is the injection timing TAU calculation timing, the routine proceeds to step 202, where the injection time TAU is calculated according to the following equation (1). TAU = TP × FEGR × f (1) In the above formula (1), TP is a basic injection time for making the air-fuel ratio the stoichiometric air-fuel ratio, and is calculated as follows. The ROM 43 stores in advance a map that defines the basic injection time with the engine speed NE and the intake pressure PM as parameters. With reference to this map, the basic injection time TP corresponding to the engine rotation speed NE and the intake pressure PM at that time is calculated.

FEGR is a correction coefficient for correcting the basic injection time TP when executing EGR. That is, when the EGR is executed, the proportion of air in the air-fuel mixture is smaller than when the EGR is stopped. Therefore, EG
When the same amount of fuel is injected as when R is stopped, the air-fuel ratio becomes excessively smaller than the stoichiometric air-fuel ratio. Therefore, so that the air-fuel ratio becomes the stoichiometric air-fuel ratio even when this EGR is executed,
The correction coefficient FEGR is used to correct the basic injection time TP short. A map stored in advance in the ROM 43 is used when calculating the correction coefficient FEGR. In this map, the correction coefficient FEGR is defined with the engine speed NE and the intake pressure PM as parameters. Then, referring to the map, the engine speed N at that time
A correction coefficient FEGR corresponding to E and intake pressure PM is obtained,
The value is multiplied by the basic injection time TP. Therefore, the injection time TAU obtained by the correction takes into consideration the influence of EGR.

Further, f is a correction coefficient calculated by the sum or product of various coefficients. The various coefficients include, for example, intake air temperature, warm-up increase, post-start increase, output increase, air-fuel ratio feedback control, and the like.

The coefficient relating to the intake air temperature is for correcting the deviation of the air-fuel ratio caused by the difference in the intake air density due to the intake air temperature, and is obtained based on the intake air temperature THA. The coefficient relating to the warm-up increase amount is for increasing the basic injection time TP for the purpose of improving the driving performance during cold, and is obtained based on the intake air temperature THA. The coefficient related to the post-startup amount increase is for stabilizing the engine speed NE immediately after the start of the engine 1, and is obtained based on the cooling water temperature THW.

The coefficient relating to the output increase is for correcting the basic injection time TP longer when the engine 1 or the catalyst in the catalytic converter 26 is easily overheated. The correction using this coefficient improves the operating performance of the engine 1 under high load and suppresses the temperature rise of the catalyst. The coefficient related to the output increase is the intake pressure PM, the engine speed N
E, throttle opening TA, etc.

An air-fuel ratio correction amount (feedback correction coefficient FA
F) is used. The correction coefficient FAF is for correcting the basic injection time TP so that the air-fuel ratio of the air-fuel mixture converges to the stoichiometric air-fuel ratio. This correction coefficient FAF is obtained as follows in a routine different from that of FIG.

As shown in FIG. 8, the output voltage V of the oxygen sensor 38 is compared with the reference value Vr for the stoichiometric air-fuel ratio, and if the output voltage V is higher than the reference value Vr, it is judged to be rich,
If it is lower than the reference value Vr, it is determined to be lean. In the case of rich, it is determined whether or not lean is determined to be rich by comparing with the previous detection result. When lean is reversed to rich, FAF-RS (RS is a skip amount) is set as a new correction coefficient FAF, and when lean is not reversed to rich, FAF-KI (KI is an integral amount, RS ≧ KI) is newly updated. The correction coefficient FAF is used.

Further, when the air-fuel ratio based on the signal from the oxygen sensor 38 is lean, it is compared with the previous detection result and it is judged whether or not the state is changed from rich to lean. When reversing from rich to lean, FAF + RS becomes a new correction factor F
In addition to AF, if there is no inversion from rich to lean, FAF + KI is set as a new correction coefficient FAF. Therefore,
When the air-fuel ratio is reversed between rich and lean, the correction coefficient FAF changes (skips) stepwise, and when the air-fuel ratio is rich or lean, the correction coefficient FAF gradually increases or decreases. In this way, the correction coefficient FAF for converging the air-fuel ratio to the stoichiometric air-fuel ratio according to the detection value of the oxygen sensor 38.
Is required. This correction coefficient FAF is used as the basic injection time TP.
To multiply.

When the air-fuel ratio is controlled to the stoichiometric air-fuel ratio, the correction coefficient FAF fluctuates around "1.0". Moreover, when the temperature is low, the detection accuracy of the oxygen sensor 38 decreases. From this viewpoint, the basic injection time TP using the correction coefficient FAF is used when the engine 1 is started or when the cooling water temperature THW is low since the time has not elapsed sufficiently since the start.
Is not corrected. Further, in order to ensure the traveling performance of the vehicle, even when the air-fuel ratio is set to be richer than the theoretical air-fuel ratio (during high load / high speed running), the basic injection time TP is corrected using the correction coefficient FAF. Is not done.

When the injection time TAU is calculated as described above, in step 203 of FIG. 7, it is determined whether or not the idle signal is output from the throttle sensor 33, that is, whether the throttle valve 17 closes the intake passage 7. Determine whether or not. If the idle signal is output, it is determined that the engine 1 is in the idle state, and step 21
2, the idling learning value KG0 is multiplied by the injection time TAU obtained in step 202. The multiplication result is set as a new injection time TAU, and this routine is once ended.

On the other hand, if the determination condition of step 203 is not satisfied, it is determined that the engine 1 is not in the idle state, and the learning value KGi is determined in step 204.
More specifically, the intake pressure P is stored in the backup RAM 45.
The range that M can take is divided into “i” areas, and the learning value KGi is associated with each area and set. For example, as the learning value KGi, 100 mmHg ≦ PM ≦ 200 mm
KG1 in the region of Hg, KG2 in the region of 200 mmHg ≦ PM ≦ 300 mmHg, KG3 in the region of 300 mmHg ≦ PM ≦ 400 mmHg, KG4 in the region of 400 mmHg ≦ PM ≦ 500 mmHg, KG4 in the region of 500 mmHg ≦ PM ≦ 600 mmHg
5, can be set.

Then, the region to which the intake pressure PM at that time belongs is selected, and the learning value KGi corresponding to that region is determined. Since the obtained learning value KGi is a rough one, the learning value KGi is calculated in the next step 205.
i is interpolated to obtain a learning value KGx corresponding to the intake pressure PM at that time. The learning values KG0 and KGi are calculated by a learning routine described later, and are updated and stored each time the correction coefficient FAF is skipped.

Subsequently, at step 206, it is determined whether the operating state of the engine 1 belongs to the EGR execution region Z1 based on the cooling water temperature THW, the engine speed NE, and the intake pressure PM. If this determination condition is satisfied, the process proceeds to step 211, and if not, the process proceeds to step 207.

In step 207, the correction coefficient FAF
It is determined whether or not a condition for executing the air-fuel ratio feedback control using is satisfied. Instead of this determination, it may be determined whether the cooling water temperature THW is equal to or lower than a predetermined value. If the determination condition of step 207 is satisfied, the process proceeds to step 211, and if not, the process proceeds to step 208.

At step 208, the learning upper limit value KGma
Calculate x. This learning upper limit value KGmax is the learning value KG
This is to prevent the specific components (HC, CO) in the exhaust gas from exceeding the allowable value by reflecting x in the injection time TAU, and a value corresponding to the allowable value is set. More specifically, in the ROM 43, a range (for example, 500 to 760 mmHg) that the atmospheric pressure PA can take is divided into a plurality of areas, and the learning upper limit value KGmax is set in association with each area. The learning upper limit value KGmax is set to a smaller value in a region where the atmospheric pressure PA is lower.

Then, it is determined to which area the actual atmospheric pressure PA detected by the atmospheric pressure sensor 39 belongs, and the learning upper limit value KGmax corresponding to the area is interpolated. By this interpolation calculation, the learning upper limit value KGmax corresponding to the atmospheric pressure PA at that time is determined.

Next, at step 209, the learning value KGx obtained at step 205 is the learning upper limit value KG.
It is determined whether it is less than or equal to max. If this determination condition is satisfied, the routine proceeds to step 211. If not, the learning upper limit value KGmax is set as the learning value KGx at step 210, and the routine proceeds to step 211.

Then, steps 206, 207 and 209
Or in step 211, which is a transition from 210,
The learning value K is added to the injection time TAU obtained in step 202.
Gx is multiplied, and the multiplication result is set as a new injection time TAU. Therefore, in the EGR execution region Z1, when the feedback control of the air-fuel ratio is being performed, and when the learning value KGx is less than or equal to the learning upper limit value KGmax corresponding to the atmospheric pressure PA at that time, the learning in step 205 is performed. The value KGx is reflected as it is in the calculation of the injection time TAU. On the other hand, when the feedback control of the air-fuel ratio is not in the EGR execution region Z1, and the learning value KGx is larger than the learning upper limit value KGmax at that time, the learning value KGx is the learning upper limit value KGmax. It is reflected in the calculation of the injection time TAU in the state of being restricted to.

The learning value KGx is limited as described above for the following reason. Even if the EGR is not performed and the basic injection time TP is not corrected by the correction coefficient FAF, the basic injection time TP is always corrected using the learning value KGx in the same manner as above. Suppose Then, in some cases, the injection time TAU may become excessively long or short. The injection time TAU becomes excessively long because the learning value KGx larger than the appropriate value is used. In such a case, for example, when the EGR amount is reduced by moving from a low altitude (flat land) to a high altitude (high altitude), the EGR
It is possible that a predetermined amount of exhaust gas was not recirculated due to the accumulation of foreign matter in the passage 28. Besides that, EG
Correction coefficient FEGR for reducing the injection amount when executing R
As a result, it is possible that a value larger than the appropriate value is set.

At this time, since the basic injection time TP is not corrected using the correction coefficient FAF, especially when the injection time TAU becomes excessively long (when an excessive increase correction is made). Specific components in exhaust gas may exceed the allowable value. Therefore, in order to prevent such a problem, the learning value KGx is set not to be larger than the learning upper limit value KGmax corresponding to the allowable value.

Step 211 or 21 as described above
When the injection time TAU is calculated in 2, this routine is once ended. Then, in another routine, the injection time T
A drive signal corresponding to AU is output to the fuel injection valve 19 via the external output circuit 47. In response to this signal, the fuel injection valve 1
The energization time to the solenoid coil 9 is controlled, the time the needle valve is open is adjusted, and a predetermined amount of fuel is injected from the injection valve 19. Here, in the injection time calculation routine, the backup RAM 45 storing the learning value KGi for each operating region of the engine 1 corresponds to the learning value storage means. The calculation process of the basic injection time TP corresponds to the injection amount calculation means. The calculation process of the correction coefficient FAF corresponds to the air-fuel ratio correction amount calculation means, and the correction process of the injection time TP using the correction coefficient FAF corresponds to the first injection amount correction means. In addition, steps 206, 207, 209, 2
Each processing of 10 corresponds to the learning value changing means, and the fuel injection valve 1
The output processing of the drive signal to 9 corresponds to the injection control means.
Further, the processing of step 208 corresponds to the learning upper limit value changing means, and the processing of step 211 corresponds to the second injection amount correcting means.

Next, the learning routine of FIG. 9 will be described. First, in step 301, it is determined whether or not the learning condition is satisfied. This learning condition is, for example, during feedback control of the air-fuel ratio and when the cooling water temperature THW is 80 ° C.
The above is mentioned.

If the learning condition is satisfied, step 3
At 02, it is determined whether the air-fuel ratio is reversed between rich and lean and the correction coefficient FAF is skipped.
If skipped, the value of the correction coefficient FAF immediately before the skip is read in the next step 303, and step 304
Then, the arithmetic mean value FAFAV with the correction coefficient FAF immediately before the previous skip is calculated.

Then, in step 305, the arithmetic mean value FA
It is determined whether FAV is larger than “1.01”.
This value "1.01" is an upper limit value of a predetermined range including the value of the correction coefficient FAF corresponding to the target air-fuel ratio during feedback control ("1.0" when the target air-fuel ratio is the stoichiometric air-fuel ratio). .

When the arithmetic mean value FAFAV is larger than "1.01", whether or not the idle signal is output from the throttle sensor 33 in step 306, that is, whether the throttle valve 17 closes the intake passage 7 or not. Determine whether or not.

If the idle signal is output, it is determined that the engine 1 is in the idle state, and step 307
At the previous learning value KG0 at idle, "0.0
05 ”is added. The addition result is used as a new learning value KG0.
Then, it is stored in the backup RAM 45, and this routine is once ended. On the other hand, when the idle signal is not output, it is determined that the engine 1 is not in the idle state, and in step 308, "0.005" is added to the learning value KGi at the time of the previous feedback control. Backup the result of the addition as a new learning value KGi
This is stored in the AM 45, and this routine is once ended.

In step 305, the arithmetic mean value F
If the AFAV is equal to or less than the upper limit value “1.01”, the process proceeds to step 309, and the arithmetic mean value FAFAV is “0.
It is determined whether it is less than "99". This value "0.99" is
The value of the correction coefficient FAF corresponding to the target air-fuel ratio during feedback control (when the target air-fuel ratio is the theoretical air-fuel ratio, "1.
0 ”) is a lower limit value of a predetermined range. Arithmetic mean value FA
If the FAV is less than the lower limit value “0.99”, step 31
At 0, it is determined whether the idle signal is output from the throttle sensor 33, that is, whether the throttle valve 17 closes the intake passage 7.

If the idle signal is output, it is determined that the engine 1 is in the idle state, and step 211
In the previous idling, the learning value KG0 is changed to "0.
"005" is subtracted. The subtraction result is used as a new learning value KG.
0 is stored in the backup RAM 45, and this routine is once ended. On the other hand, when the idle signal is not output, it is determined that the engine 1 is not in the idle state, and in step 312, "0.005" is subtracted from the learning value KGi at the time of the previous feedback control.
The subtraction result is stored in the backup RAM 45 as a new learning value KGi, and this routine is once ended.

On the other hand, the arithmetic mean value FA in step 309
When FAV is “0.99” or more, that is, 0.
When 99 ≦ FAFAV ≦ 1.01, learning values KG0, K
The Gi is not updated, and this routine is temporarily terminated.

Further, when the determination condition of step 301 is not satisfied, or when the determination condition of step 301 is satisfied but the determination condition of step 302 is not satisfied, the learning values KG0 and KGi are not updated. This learning routine is once ended without performing.

In this way, when the air-fuel ratio is leaner than the target air-fuel ratio, the arithmetic mean value FAFAV exceeds the upper limit value ("1.01"), so the learning values KG0, KG.
i is changed to a large value. On the other hand, when the air-fuel ratio is richer than the target air-fuel ratio, the arithmetic mean value FAFA
Since V is less than the lower limit value (“0.99”), the learning value K
G0 and KGi are changed to small values. Then, the learning values KG0 and KGi are reflected in the injection time TAU in steps 211 and 212 of FIG. As a result, the arithmetic mean value F
AFAV falls within the range of "0.99" or more and "1.01" or less.

In the learning routine described above, each processing of steps 305 to 312 corresponds to learning value rewriting means. As described above, in this embodiment, the range in which the intake pressure PM can be taken is divided into a plurality of regions, and the learning value KGi is associated with each region and stored in the backup RAM 45. The basic injection time TP is corrected using the correction coefficient FAF, the cooling water temperature THW is equal to or greater than the predetermined value α, and the arithmetic mean value FAFAV of the correction coefficient FAF is in a predetermined range (0.99 ≦ FAFAV ≦ 1. 01), the learning value KGi of the region to which the intake pressure PM at that time belongs
Is rewritten.

Further, when the operating state of the engine 1 deviates from the EGR execution region Z1 and the correction of the basic injection time TP using the correction coefficient FAF is stopped, the learning value KGx is limited. That is, in order to prevent the specific component (HC, CO, etc.) in the exhaust gas from exceeding the allowable value by reflecting the learned value KGx in the basic injection time TP,
Learning upper limit value KGmax and learning value KG corresponding to the allowable value
x is compared. Learning value KGx is learning upper limit value KGmax
In the following cases, the learning value KGx is used as it is,
When the learning value KGx is larger than the learning upper limit value KGmax, the learning value KGx is forcibly changed to the learning upper limit value KGmax.

Then, the basic injection time TP is corrected by using the learning value KGx corresponding to the intake pressure PM at that time by the intake pressure sensor 34. The fuel injection valve 19 is drive-controlled based on the injection time TAU obtained by the correction.

Therefore, when the operating state of the engine 1 belongs to the EGR execution region Z1 or when the basic injection time TP is corrected using the correction coefficient FAF, the learned value rewritten as described above. KGx is used as it is for the correction of the basic injection time TP. Then, since the learned value KGx is a value rewritten when the EGR is executed, the basic injection time TP is properly corrected by the learned value KGx. Therefore, when the fuel injection valve 19 is controlled based on the corrected injection time TAU, the air-fuel ratio of the air-fuel mixture is converged to the stoichiometric air-fuel ratio.

Further, when the operating state of the engine 1 is out of the EGR execution region Z1 and the correction of the basic injection time TP using the correction coefficient FAF is stopped, the learning value KGx is less than or equal to the learning upper limit value KGmax. For example, the learned value KGx is used as it is for the correction of the basic injection time TP. If the learning value KGx is larger than the learning upper limit value KGmax, the learning upper limit value KGmax is used as the learning value KGx for correcting the basic injection time TP. Therefore, although the basic injection time TP is not corrected using the correction coefficient FAF, the basic injection time T is set by the learned value KGx.
P is not excessively increased and corrected.

Therefore, unlike the prior art in which the injection amount is corrected using the learning value independently learned according to the execution and stop of the EGR, the learning is performed even in the region where the cooling water temperature THW is lower than the predetermined value α. The injection amount can be corrected using the value KGx. Moreover, since the learning value KGx is limited by the learning upper limit value KGmax, it is possible to reliably prevent the specific component in the exhaust gas from exceeding the allowable value.

Further, since the atmospheric pressure PA decreases and the EGR amount decreases at a position higher than the level ground, the injection time TAU becomes excessive by correction if the learning upper limit value KGmax similar to the level ground is used. May be long. On the other hand, in the present embodiment, the learning upper limit value KGmax is changed to a smaller value as the atmospheric pressure PA decreases. Therefore, E
The increase in the learning value due to the decrease in the GR amount is the learning upper limit value K.
It is offset by the change of Gmax. Therefore, the engine 1
Even when the vehicle is driven at a different altitude above sea level, the learning value is always limited by the appropriate learning upper limit value KGmax, and the basic injection time TP can be prevented from becoming excessively long.

The present invention can be embodied in another embodiment as follows. (1) In the above embodiment, the learning upper limit value KGmax is changed according to the atmospheric pressure PA at that time, but this processing (step 208 of the injection time calculation routine of FIG. 7) may be omitted.

(2) The method of calculating the fuel injection amount may be changed to a method other than the above embodiment. For example, the intake air amount per one cycle of the engine may be estimated from the intake pressure PM and the engine rotation speed NE, and the basic injection time may be calculated based on the estimated value (speed density method). Further, the intake air amount per one cycle of the engine may be estimated from the throttle opening TA and the engine speed NE, and the basic injection time may be calculated based on the estimated intake air amount (throttle speed method).

[0088]

As described above in detail, according to the first invention, when the operating state of the internal combustion engine is out of the recirculation execution region and the correction of the injection amount using the air-fuel ratio correction amount is stopped. , The learning upper limit value and the learning value are compared. When the learning value is larger than the learning upper limit value, the learning value is forcibly changed to the learning upper limit value. Then, the injection amount is corrected by using the learning value corresponding to the operating state of the internal combustion engine at that time.

Therefore, regardless of whether the exhaust gas recirculation is executed or stopped, it is possible to always properly correct the injection amount using the learned value. Then, it is possible to prevent the specific component in the exhaust gas from exceeding the allowable value when the exhaust gas recirculation is not performed and the injection amount correction using the air-fuel ratio correction amount is not performed.

Further, in the second aspect of the invention, the learning upper limit value is reduced as the atmospheric pressure decreases. Therefore, in addition to the effect of the first invention, even when the internal combustion engine is operated at a different sea level, the learning value is limited by the appropriate learning upper limit value and the injection amount is excessively increased and corrected. It can be prevented.

[Brief description of drawings]

FIG. 1 is a conceptual configuration diagram of first and second inventions.

FIG. 2 is a schematic configuration diagram showing an engine and its peripheral devices in an embodiment embodying the first and second inventions.

FIG. 3 is a block diagram showing an internal configuration and the like of an electronic control unit (ECU).

FIG. 4 is a flowchart showing an EGR control routine executed by a CPU.

FIG. 5 is a characteristic diagram showing a map used for determination of an EGR execution region when the cooling water temperature is equal to or higher than a predetermined value.

FIG. 6 is a characteristic diagram showing a map used for determination of an EGR execution region when the cooling water temperature is lower than a predetermined value.

FIG. 7 is a flowchart showing an injection time calculation routine executed by a CPU.

FIG. 8 is a characteristic diagram showing a correspondence relationship between an output voltage of an oxygen sensor and a feedback correction coefficient.

FIG. 9 is a flowchart showing a learning routine executed by a CPU.

FIG. 10 is a characteristic diagram showing a recirculation execution region and a recirculation stop region when the cooling water temperature is equal to or higher than a predetermined value in the related art.

FIG. 11 is a characteristic diagram showing a recirculation stop region when the cooling water temperature is lower than a predetermined value in the prior art.

[Explanation of symbols]

1 ... a gasoline engine as an internal combustion engine, 6 ... a combustion chamber,
Reference numeral 7 ... Intake passage, 19 ... Fuel injection valve, 28 ... EGR passage as exhaust gas recirculation passage, 29 ... EGR valve as flow control valve, 34 ... Intake pressure sensor which constitutes a part of operating state detecting means, 36 ... A rotational speed sensor that constitutes a part of the operating state detecting means, 38 ... an oxygen sensor that constitutes a part of the air-fuel ratio detecting means, 39 ... an atmospheric pressure sensor as an atmospheric pressure detecting means, 45 ... a learning value storing means Backup RA
M, PM ... Intake pressure, NE ... Engine speed, TP ... Basic injection time corresponding to injection amount, FAF ... Feedback correction coefficient as air-fuel ratio correction amount, KG0, KGi, KG
x ... learning value, KGmax ... learning upper limit value, Z1 ... EGR execution region.

Claims (2)

[Claims] 1. A fuel injection valve provided in an intake passage communicating with a combustion chamber of an internal combustion engine, an operating state detecting means for detecting an operating state of the internal combustion engine, and a detected value of the operating state detecting means. Injection amount calculation means for calculating the injection amount from the corresponding fuel injection valve, injection control means for drivingly controlling the fuel injection valve so that the injection amount by the injection amount calculation means is achieved, and the discharge amount from the combustion chamber Based on the flow rate control valve provided in the exhaust gas recirculation passage for guiding a part of the exhaust gas to the intake passage and the detection value of the operating state detection means, the operating state of the internal combustion engine at that time is recirculated. Exhaust gas that controls the flow rate control valve to open the exhaust gas recirculation passage if inside the region, and controls the flow rate control valve to close the exhaust gas recirculation passage when the operating state deviates from the recirculation execution region. Recirculation control A stage, an air-fuel ratio detection means for detecting the air-fuel ratio of the internal combustion engine, and an air-fuel ratio correction amount for converging the air-fuel ratio of the air-fuel mixture to a predetermined value according to the detection value of the air-fuel ratio detection means. An air-fuel ratio correction amount calculation means, a first injection amount correction means for correcting the injection amount by the injection amount calculation means based on the air-fuel ratio correction amount by the air-fuel ratio correction amount calculation means, and an operating region of the internal combustion engine Learning value storage means that stores a learning value in advance for each, and when the air-fuel ratio by the air-fuel ratio detection means deviates from a predetermined range, learning of the operating region of the learning value storage means corresponding to the operating state at that time Learning value rewriting means for rewriting the value, the operating state of the internal combustion engine is out of the recirculation execution region, and the correction of the injection amount using the air-fuel ratio correction amount by the first injection amount correction means is stopped. Sometimes the learning value In order to prevent the specific component in the exhaust gas from exceeding the allowable value by being reflected in the injection amount, the learning upper limit value corresponding to the allowable value and the learning value of the learning value storage means are compared, and the learning value is When the learning value is larger than the learning upper limit value, the learning value changing means for forcibly changing the learning value to the learning upper limit value, and the learning value storage means corresponding to the operating state of the internal combustion engine at that time by the operating state detecting means A fuel injection control device for an internal combustion engine, comprising: a second injection amount correction unit that corrects the injection amount of the injection amount calculation unit using a learned value. 2. An atmospheric pressure detecting means for detecting a change in atmospheric pressure, and a learning upper limit value changing means for decreasing a learning upper limit value of the learning value changing means as the atmospheric pressure is lowered by the atmospheric pressure detecting means. The fuel injection control device for an internal combustion engine according to claim 1, which is provided.