JPH0828317A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To improve fuel consumption performance and suppress deterioration of heater performance and engine performance due to lowering of cooling water temperature. CONSTITUTION:Fuel injected from an injector 4 is taken into an engine 1 in the vicinity of an intake port 1a. A cooling water temperature is detected by a water temperature sensor 25, while an intake temperature is detected by means of an intake temperature sensor 21. An electronic control unit (ECU) 30 executes control in the case that the cooling water temperature is not higher than a reference value, and allows execution of lean control in the case that the temperature is higher than the reference value. The reference water temperature is determined based on the intake temperature at the respective times. When the intake temperature is low, the reference water temperature is high, and when the intake temperature is high, the reference water temperature is low. When the intake temperature is low such as starting time of the engine 1, control for substantially obtaining a theoretical air-fuel ratio is executed in a comparatively long time, and lowering of the cooling water temperature is prevented.

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 system for an internal combustion engine, and more particularly to an air-fuel ratio control system for an internal combustion engine for controlling the switching of the air-fuel ratio according to the cooling water temperature of the internal combustion engine. .

[0002]

2. Description of the Related Art Conventionally, as this type of technique, for example, one disclosed in Japanese Patent Laid-Open No. 62-17340 is known. In such a technique, the residual oxygen concentration in the exhaust gas is basically detected by an air-fuel ratio sensor as an air-fuel ratio signal. Then, based on the air-fuel ratio signal, feedback control is performed so that the air-fuel ratio of the internal combustion engine becomes the target air-fuel ratio. That is, the fuel injection valve is drive-controlled and the fuel injection amount is feedback-controlled so that the actual air-fuel ratio matches the target air-fuel ratio.

In the above technique, the cooling water temperature is detected by the water temperature sensor. Then, when the detected water temperature is lower than a predetermined reference water temperature, control is performed so that the air-fuel ratio becomes the stoichiometric air-fuel ratio (stoichiometric control). Further, when the cooling water temperature becomes higher than the reference water temperature, control (lean control) is performed so that the air-fuel ratio is on the lean side. That is, at the time of starting the internal combustion engine, since the cooling water temperature is low and it is necessary to warm up quickly, stoichiometric control is performed. Also, when the warm-up is completed,
Lean control is performed to improve fuel efficiency.

[0004]

However, in the above prior art, the reference water temperature is always constant regardless of the operating state of the internal combustion engine. Generally, when lean control is executed, the amount of heat generated during combustion tends to be small, and cooling loss tends to decrease. If the lean control is performed when the intake air temperature is still low, the cooling water temperature may decrease due to the small cooling loss, especially during light load traveling. As a result, the performance of the heater using the cooling water as a heat source may be deteriorated.

Further, by excessively using the heater whose performance has deteriorated, the heat of the cooling water is further removed, and the temperature of the cooling water is further lowered.
As a result, the internal combustion engine body becomes overcooled,
There has been a possibility that the performance of the internal combustion engine may be adversely affected because the amount of fuel adhering to the engine wall surface increases or the atomization performance of fuel deteriorates.

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to improve fuel efficiency in an air-fuel ratio control device for an internal combustion engine in which the air-fuel ratio is switched and controlled according to the cooling water temperature. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine, which can be achieved and can suppress deterioration of heater performance and engine performance due to a decrease in cooling water temperature.

[0007]

In order to achieve the above object, in the present invention, as shown in FIG.
And a fuel injection means M2 for injecting fuel into the internal combustion engine M
No. 1 water temperature detecting means M3 for detecting the cooling water temperature, water temperature judging means M4 for judging whether the cooling water temperature is lower or higher than a predetermined reference water temperature, and the cooling water temperature is judged by the water temperature judging means M4 as the reference. When it is determined that the temperature is lower than the water temperature, the fuel injection means is set so that the air-fuel ratio of the air-fuel mixture of the air introduced into the internal combustion engine M1 and the fuel injected from the fuel injection means M2 becomes substantially the stoichiometric air-fuel ratio. M
2 is controlled, and when it is determined that the cooling water temperature is higher than the reference water temperature, an internal combustion engine including an injection amount control means M5 that controls the fuel injection means M2 so that the air-fuel ratio becomes leaner. In the air-fuel ratio control device, an intake air temperature detecting means M6 for detecting the intake air temperature of the internal combustion engine M1 and the reference water temperature is high when the intake air temperature detected by the intake air temperature detecting means M6 is low, and when the intake air temperature is high. Reference water temperature adjusting means M for adjusting the reference water temperature to be low
The point is that 7 and 7 are provided.

[0008]

According to the above construction, as shown in FIG. 1, the fuel is injected into the internal combustion engine M1 by the fuel injection means M2.
Further, the cooling water temperature of the internal combustion engine M1 is detected by the cooling water temperature detecting means M3. Further, the water temperature determination means M4 determines whether the detected cooling water temperature is lower or higher than a predetermined reference water temperature. Then, when it is determined that the cooling water temperature is lower than the reference water temperature, the air-fuel ratio of the air-fuel mixture including the air introduced into the internal combustion engine M1 and the fuel injected from the fuel injection means M2 becomes substantially the stoichiometric air-fuel ratio. The fuel injection means M2 is controlled by the injection amount control means M5.
On the other hand, when it is determined that the cooling water temperature is higher than the reference water temperature, the injection amount control means M5 controls the fuel injection means M2 so that the air-fuel ratio is on the lean side.

Further, in the present invention, the intake air temperature of the internal combustion engine M1 is detected by the intake air temperature detecting means M6. The reference water temperature adjusting means M7 adjusts the reference water temperature to be high when the intake air temperature detected by the intake air temperature detecting means M6 is low and to be low when the intake air temperature is high.

For this reason, when the intake air temperature is low, such as when the internal combustion engine M1 is started, control for making the air-fuel ratio substantially equal to the stoichiometric air-fuel ratio is executed for a relatively long period of time, which prevents the cooling water temperature from decreasing. It On the other hand, when the intake air temperature is high,
It becomes easy to execute the control such that the air-fuel ratio is on the lean side. In such a case, the amount of heat taken by the outside air of the cooling water is small, the temperature of the cooling water is unlikely to drop, and fuel efficiency can be improved.

[0011]

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

FIG. 2 is a schematic configuration diagram showing an air-fuel ratio control device for an engine mounted on a vehicle in this embodiment.
Outside air is taken into an engine 1 as an internal combustion engine having a plurality of cylinders (six cylinders in this embodiment) from an air cleaner 3 through an intake passage 2. Simultaneously with the intake of the outside air, the fuel injected from the injector 4 as the fuel injection means provided for each cylinder in the vicinity of the intake port 1a is taken into the engine 1. Then, the mixture of the taken-in fuel and the external air is introduced into the combustion chamber 1b through the intake valve 5a provided for each cylinder. The air-fuel mixture is exploded / combusted in the combustion chamber 1b, a crankshaft (not shown) is rotated, and a driving force is obtained for the vehicle. After that, the exhaust gas after the explosion / combustion is led out to the exhaust passage 6 where the exhaust manifold for each cylinder gathers through the exhaust valve 5b, and is exhausted to the outside.

A throttle valve 8 which is opened and closed in conjunction with an accelerator pedal (not shown) is provided in the intake passage 2. And this throttle valve 8
The amount of intake air to the intake passage 2 is adjusted by opening and closing. A surge tank 9 for smoothing the pulsation of intake air is provided downstream of the throttle valve 8.

In the intake passage 2, an intake air temperature sensor 21 as an intake air temperature detecting means for detecting the intake air temperature THA is provided near the air cleaner 3. A throttle sensor 22 for detecting the opening of the throttle valve 8, that is, the throttle opening TA is provided near the throttle valve 8. Furthermore, the surge tank 9 has the same tank 9
An intake pressure sensor 23 that communicates with the intake air pressure sensor 32 and detects the intake pressure (intake pressure) PiM is provided.

On the other hand, in the middle of the exhaust passage 6, there are mainly three harmful components in the exhaust gas, namely, hydrocarbons (H
A three-way catalyst 13 is provided as a catalyst device for simultaneously purifying C), carbon monoxide (CO), and nitrogen oxides (NOx). An oxygen sensor 24 for detecting the oxygen concentration OX in the exhaust gas is provided upstream of the three-way catalyst 13 in the exhaust passage 6. The oxygen sensor 24 has a characteristic that the output voltage changes rapidly near the stoichiometric air-fuel ratio.

Further, the engine 1 is provided with a water temperature sensor 25 as a water temperature detecting means for detecting the temperature (cooling water temperature) THW of the cooling water. The ignition signal distributed by the distributor 11 is applied to the ignition plug 10 provided for each cylinder of the engine 1. The distributor 11 is for distributing the high voltage output from the igniter 12 to each spark plug 10 in synchronization with the crank angle of the engine 1. The ignition timing of each spark plug 10 is the high voltage output timing from the igniter 12. Determined by

The distributor 11 is provided with a rotation speed sensor 26 for detecting the rotation speed (engine speed) NE of the engine 1 from the rotation of a rotor (not shown) of the distributor 11. Similarly, the distributor 11 is provided with a crank angle sensor 27 that detects a change in the crank angle of the engine 1 at a predetermined rate according to the rotation of the rotor. In this embodiment,
Assuming that the engine 1 rotates twice for one stroke, the crank angle sensor 27 detects the crank angle at a rate of "30 ° CA". Further, the transmission (not shown) is provided with a vehicle speed sensor 28 that detects a vehicle speed (vehicle speed) SPD and outputs a signal according to the magnitude of the detected value.

Further, in this embodiment, an electronic control unit (hereinafter simply referred to as "ECU") 30 is used to determine the water temperature determination means,
An injection amount control means and a reference water temperature adjusting means are configured. The ECU 30 includes the intake air temperature sensor 21,
A throttle sensor 22, an intake pressure sensor 23, an oxygen sensor 24, a water temperature sensor 25, a rotation speed sensor 26, a crank angle sensor 27 and a vehicle speed sensor 28 are connected to each other. Further, the injector 4 and the igniter 12 are connected to the ECU 30, respectively. And ECU3
0 drives and controls the injector 4 and the igniter 12 based on the detection signals from these sensors 21 to 28.

Next, the structure of the ECU 30 will be described with reference to the block diagram of FIG. The ECU 30 includes a central processing unit (CPU) 31, a read-only memory (ROM) 32 that stores a predetermined control program and the like in advance, and a random access memory (RA) that temporarily stores calculation results of the CPU 31 and the like.
M) 33, a backup RAM 34 for storing previously stored data, and the like. Then, the ECU 30
These units are connected to an external input circuit 35, an external output circuit 36, etc. by a bus 37 to constitute a logical operation circuit.

The external input circuit 35 includes an intake air temperature sensor 21, a throttle sensor 22, an intake air pressure sensor 23,
Oxygen sensor 24, water temperature sensor 25, rotation speed sensor 26,
A crank angle sensor 27, a vehicle speed sensor 28, etc. are connected to each other. The injector 4 and the igniter 12 described above are connected to the external output circuit 36, respectively.

Then, the CPU 31 reads the detection signals from the sensors 21 to 28 as input values via the external input circuit 35. In addition, the CPU 31 is based on these input values,
The injector 4, the igniter 12, and the like are preferably controlled via the external output circuit 36.

In this embodiment, a heater is provided to introduce warm air into the passenger compartment by passing the air sent by the blower through the heat exchanger in the passenger compartment.
The warmed cooling water of the engine 1 is used for heating by the heater.

Next, of the various processing operations executed by the ECU 30 described above, the processing operations for controlling the fuel injection amount to control the air-fuel ratio will be described with reference to FIGS.

The flowchart shown in FIG. 4 shows a "control switching routine" for switching control executed by the ECU 30, which is started at the same time as the cranking of the engine 1 is completed, and thereafter at predetermined time intervals. It is executed by a scheduled interrupt.

When the processing of this routine is started, the EC
First, in step 101, the U30 detects the water temperature sensor 2
5 and the intake air temperature THA, the cooling water temperature THW and the intake air temperature THA are read.

Next, at step 102, it is judged if the cooling water temperature THW read this time is higher than the reference water temperature α. Here, the reference water temperature α is a value determined according to the map shown in FIG. 5 based on the intake air temperature THA at that time. Here, for the heater, the intake air temperature THA
A lower cooling water temperature THW is required, and a higher intake air temperature THA does not require a higher cooling water temperature THW. Therefore, the value required from the heater (minimum required temperature as a reference for switching) has an inverse proportional relationship, as indicated by the broken line in the figure. Therefore, in the present embodiment, the reference water temperature α is set to be higher than the minimum required temperature as shown by the solid line in the figure.
Further, in the figure, when the intake air temperature THA is high, the reference water temperature α does not follow the minimum required temperature.
This is for avoiding that the performance of the engine 1 is affected (such as an increase in the amount of fuel adhering to the wall surface and deterioration of the fuel atomization performance) when the reference water temperature α is too low.

If the cooling water temperature THW is equal to or lower than the reference water temperature α set as described above, sufficient warm-up has not been completed, and if the lean control is switched at this time, the heater If the performance and engine performance may be adversely affected, the process proceeds to step 103. In step 103, the ECU 30 performs stoichiometric control so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. With this stoichiometric control, a sufficient amount of heat generation is obtained, and warm-up is promoted.
Then, the subsequent processing is temporarily terminated.

On the other hand, when the cooling water temperature THW is higher than the reference water temperature α, even if the warm-up is completed and the lean control is switched to the lean control at this moment, there is a possibility that the heater performance and the engine performance are adversely affected. If it is low, the process proceeds to step 104. In step 104, EC
U30 permits the lean control so that the air-fuel ratio is on the lean side in order to improve fuel efficiency. Then, the subsequent processing is temporarily terminated.

As described above, in the "control switching routine", the reference water temperature α is determined based on the intake air temperature THA at that time. And the cooling water temperature TH at that time
If W is equal to or lower than the reference water temperature α, stoichiometric control is executed, and if the cooling water temperature THW is higher than the reference water temperature α, execution of lean control is permitted on the assumption.

Next, control when the execution of lean control is permitted will be described. The flowchart shown in FIG. 6 shows a "lean control routine" for performing lean control executed by the ECU 30, and is executed by a regular interrupt every predetermined time.

When the processing of this routine is started, the EC
First, in step 201, the U30, based on the detection signals from the water temperature sensor 25, the rotation speed sensor 26, and the intake pressure sensor 23, the cooling water temperature THW and the engine rotation speed NE.
And the intake pressure PiM.

Next, at step 202, the water temperature correction coefficient KTHW is calculated based on the cooling water temperature THW read this time.
To calculate. The map shown in FIG. 7 is referred to when calculating the water temperature correction coefficient KTHW. That is, the map shown in FIG. 7 defines the water temperature correction coefficient KTHW for the cooling water temperature THW at that time, and the water temperature correction coefficient KTHW becomes smaller as the cooling water temperature THW becomes higher. Further, when the cooling water temperature THW is equal to or higher than the predetermined temperature, the water temperature correction coefficient KTHW is set to "0".

Next, at step 203, the post-start integrated intake air amount QTOTAL is calculated. Here, the post-start cumulative intake air amount QTOTAL is the total intake air amount from when the engine 1 is started to the present. For example, when the engine 1 is not running at all from the start to the present (however, dead soak, hot soak, etc.), the engine 1 is warmed up, that is, the cooling water rises. It does not contribute much to the temperature, and the integrated intake air amount QTOTAL after starting does not become a very large value.
On the other hand, the post-start-up cumulative intake air amount QTOTAL corresponds to the time period from the start of the engine 1 to the actual warm-up. In this embodiment, the fuel injection amount is calculated based on the engine speed NE and the intake pressure PiM, and the post-start integrated intake air is calculated based on the injection amount, the time from the start of the engine 1 to the present time, and the air-fuel ratio. The quantity QTOTAL is calculated.

Further, in step 204, the post-starting time correction coefficient KTIME is calculated based on the post-starting integrated intake air amount QTOTAL calculated this time. That is, the post-startup time correction coefficient KTIME corresponds to the reciprocal of the time that contributes to the actual warming up from the start of the engine 1, and is calculated by referring to the map shown in FIG. That is, the map shown in FIG. 8 defines the post-starting time correction coefficient KTIME with respect to the cumulative post-starting intake air amount QTOTAL at any given time, and the post-starting time correction coefficient KTI increases as the post-starting cumulative intake air amount QTOTAL increases.
The ME is set to be small. Further, the post-start time correction coefficient KTIME is set to "0" when the post-start cumulative intake air amount QTOTAL is equal to or greater than a predetermined amount.

Next, at step 205, the basic lean correction coefficient KLEANB is calculated based on the engine speed NE and the intake pressure PiM read this time. This basic lean correction coefficient KLEANB is a basic correction coefficient when performing lean control, and is calculated by referring to the map shown in FIG. That is, FIG.
The map shown in is the basic lean correction coefficient KLEAN for the engine speed NE and the intake pressure PiM at that time.
In the three-dimensional map in which B is defined, the basic lean correction coefficient KLEANB is obtained by interpolation calculation.

Then, in step 206, the water temperature correction coefficient KTHW calculated this time and the post-starting time correction coefficient K are calculated.
The lean correction coefficient KLEAN is calculated based on TIME and the basic lean correction coefficient KLEANB. That is,
For the value obtained by adding the water temperature correction coefficient KTHW and the after-start time correction coefficient KTIME to “1”, the basic lean correction coefficient K
The value obtained by multiplying LEANB is set as the lean correction coefficient KLEAN [(1 + KTHW + KTIME) * KLE
ANB = KLEAN]. Therefore, the water temperature correction coefficient KTH
W, if the post-startup time correction coefficient KTIME is small,
The lean correction coefficient KLEAN is the basic lean correction coefficient KLE.
The value is close to ANB.

In step 207, the final injection amount TA is calculated based on the basic injection amount TAUB calculated by a separate routine and the lean correction coefficient KLEAN calculated this time.
Calculate U. That is, a value obtained by multiplying the basic injection amount TAUB by the lean correction coefficient KLEAN is set as the final injection amount TAU. Then, the subsequent processing is temporarily terminated.

As described above, in the "lean control routine", the water temperature correction coefficient KTHW based on the apparent cooling water temperature THW is calculated from time to time, and based on the time period from the start of the engine 1 to the actual warm-up. A post-startup time correction coefficient KTIME is calculated. Then, the lean correction coefficient KLEAN is calculated based on these values and is reflected in the fuel injection amount (final injection amount TAU).

As described above in detail, according to the air-fuel ratio control apparatus of the present embodiment, the stoichiometric control is executed in the "control switching routine" when the cooling water temperature THW at that time is equal to or lower than the reference water temperature α. The cooling water temperature THW is the reference water temperature α
If it is higher than this, it is allowed on the assumption that lean control is executed. Here, the reference water temperature α is the intake air temperature T at that time.
It is determined based on HA, and the reference water temperature α is adjusted to be high when the intake air temperature THA is low, and adjusted to be low when the intake air temperature THA is high. Therefore, the engine 1
When the intake air temperature THA is low, such as when the engine is started, control is performed such that the air-fuel ratio becomes substantially the stoichiometric air-fuel ratio for a relatively long period of time, which prevents the cooling water temperature THW from decreasing.
Therefore, it is possible to prevent the performance of the heater using the cooling water as a heat source from being deteriorated due to the decrease in the cooling water temperature THW.

Further, by excessively using the heater having deteriorated performance, it is possible to prevent the engine 1 from being overcooled due to the heat of the cooling water being further removed. As a result, it is possible to prevent the engine performance from being adversely affected by increasing the amount of fuel adhering to the wall surface or deteriorating the fuel atomization performance.

On the other hand, when the intake air temperature THA is high, it is easy to execute control so that the air-fuel ratio becomes lean. In such a case, the warming-up is sufficiently performed, the amount of heat taken by the outside air of the cooling water is small, and the cooling water temperature T
HW is less likely to decrease. Therefore, it is possible to sufficiently improve fuel efficiency.

Further, when executing the lean control in the "lean control routine", not only the water temperature correction coefficient KTHW based on the apparent cooling water temperature THW but also the time contributed to the actual warm-up from the start of the engine 1 is used. The post-startup time correction coefficient KTIME is also calculated.
Then, based on those values, the lean correction coefficient KLEA
N was calculated and reflected in the final injection amount TAU.
Therefore, even if the apparent cooling water temperature THW is high due to dead soak, hot soak, etc., and in fact, sufficient warm-up is not performed, according to the present embodiment, this is taken into consideration. , It's not always lean. As a result, it is possible to further prevent the deterioration of the performance of the engine 1.

The present invention is not limited to the above embodiment, but may be configured as follows, for example. (1) In the above embodiment, the cumulative intake air amount QTOTAL after starting
Is configured such that the fuel injection amount is calculated based on the engine speed NE and the intake pressure PiM, and is calculated based on the injection amount, the time from the start of the engine 1 to the present time, and the air-fuel ratio. . However, in the vicinity of the air cleaner 3,
When an air flow meter for detecting the amount of air taken into the engine 1 through the intake passage 2 (intake air amount) is provided, it is based on the detected value and the time from the start of the engine 1 to the present time. QTO
You may make it calculate TAL.

(2) The gradients of various maps in the above embodiment are not limited to those shown in the drawings. (3) In the above embodiment, when performing lean control,
Water temperature correction coefficient KTHW, time after start correction coefficient KTIME
Etc., and the final injection amount TAU is calculated based on them, but if the cooling water temperature THW becomes higher than the reference water temperature α, the fuel injection amount is uniformly reduced to make the air-fuel ratio lean. You may make it perform simple control.

The technical idea which is not described in the claims of the present invention and which can be grasped from the above-mentioned embodiment will be described below together with its effect. (A) In the air-fuel ratio control device for an internal combustion engine according to claim 1, when it is determined that the cooling water temperature is higher than the reference water temperature, the air-fuel ratio becomes a lean side according to an actual warm-up degree. A second injection amount control means for controlling the fuel injection means is provided. With such a configuration, it is possible to further prevent deterioration of the performance of the internal combustion engine.

[0046]

As described in detail above, according to the present invention,
In an air-fuel ratio control device for an internal combustion engine that controls switching of the air-fuel ratio according to the cooling water temperature, it is possible to improve fuel efficiency and suppress deterioration of heater performance and engine performance due to lowering of cooling water temperature. It has an excellent effect that it can.

[Brief description of drawings]

FIG. 1 is a conceptual configuration diagram illustrating a basic conceptual configuration of the present invention.

FIG. 2 is a schematic configuration diagram showing an air-fuel ratio control device for an engine in one embodiment embodying the present invention.

FIG. 3 is a block diagram showing an electrical configuration of an ECU in one embodiment.

FIG. 4 is a flowchart showing a “control switching routine” executed by the ECU in one embodiment.

FIG. 5 is a map defining a relationship between a reference water temperature and an intake air temperature in one embodiment.

FIG. 6 is a flowchart showing a “lean control routine” executed by the ECU in one embodiment.

FIG. 7 is a map defining a relationship between a cooling water temperature and a water temperature correction coefficient in one embodiment.

FIG. 8 is a map that defines a relationship between a post-start time correction coefficient and a post-start integrated intake air amount in one embodiment.

FIG. 9 is a map that defines the relationship between the basic lean correction coefficient and the engine speed and intake pressure in one embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine as an internal combustion engine, 4 ... Injector as fuel injection means, 21 ... Intake temperature sensor as intake temperature detection means, 25 ... Water temperature sensor as water temperature detection means, 3
0 ... ECU constituting water temperature determination means, injection amount control means, and reference water temperature adjustment means.

Claims (1)

[Claims] 1. A fuel injection means for injecting fuel into an internal combustion engine, a water temperature detection means for detecting a cooling water temperature of the internal combustion engine, and a judgment as to whether the cooling water temperature is lower or higher than a predetermined reference water temperature. When the cooling water temperature is judged to be lower than the reference water temperature by the water temperature judging means and the water temperature judging means, the mixture of air introduced into the internal combustion engine and fuel injected from the fuel injection means The fuel injection means is controlled so that the air-fuel ratio becomes substantially the stoichiometric air-fuel ratio, and when it is determined that the cooling water temperature is higher than the reference water temperature, the fuel injection means is controlled so that the air-fuel ratio becomes lean. In an air-fuel ratio control device for an internal combustion engine, which comprises an injection amount control means, an intake air temperature detection means for detecting an intake air temperature of the internal combustion engine, and an intake air temperature detected by the intake air temperature detection means are low. Sometimes the reference water temperature is high, the air-fuel ratio control apparatus for an internal combustion engine wherein when the intake air temperature is high is characterized by providing a reference water temperature adjusting means for adjusting to the reference water temperature is low.