JP2005188369A - Air fuel ratio control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems that misfire etc. occurs due to inclination of an air fuel ratio to a lean side when absolute temperature or outdoor air temperature is high and NOx emission amount is increased due to inclination of the air fuel ratio to a rich side when absolute temperature or outdoor air temperature is low, since the air fuel ratio of air fuel mixture supplied to an engine varies with change in oxygen concentration in the atmosphere, and specifically, the air fuel ratio becomes lean (the state where the ratio of fuel in the air fuel mixture is small) when the absolute temperature or the outdoor temperature is high. <P>SOLUTION: An ECU 10 determines whether or not a GHP performs cooling operation (S110). When it is determined that the GHP performs cooling operation, the ECU 10 selects a map of a target PI value for high temperature (high humidity) of an atmospheric condition (S120). Meanwhile, when it is determined that the GHP performs heating operation, the ECU 10 selects a map of a target PI value for low temperature (low humidity) of the atmospheric condition (S125). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a technique of an air-fuel ratio control system that controls an air-fuel ratio of an air-fuel mixture based on a target value map of an air-fuel ratio sensor and a measured value of the air-fuel ratio sensor.

Conventionally, for example, an output (that is, an IP value) of an air-fuel ratio sensor that measures an air-fuel ratio of an air-fuel mixture of an engine, such as GHP (Gas Heat Pump), is stored in advance in an ECU (Electronic Control Unit). There is an air-fuel ratio control system that performs air-fuel ratio control of an air-fuel mixture by operating a fuel control valve so as to achieve a certain target IP value.
Here, the IP value is the output current value (measured value) of the air-fuel ratio sensor. The higher the value, the higher the oxygen concentration (lean state where the fuel component is thin). It shows that the concentration is low (the fuel component is rich and rich).
As an example of a technique related to such an air-fuel ratio control system, there is one as shown in Patent Document 1 below.

JP-A-6-341335

By the way, it is known that conditions such as air temperature and humidity for generating an air-fuel mixture inside the engine (that is, atmospheric conditions) generally change due to the influence of the season, climate, and the like.
Specifically, in general, in summer, the temperature (hereinafter referred to as outside temperature) and humidity (hereinafter referred to as absolute humidity) are high in the atmospheric conditions, while in winter, the outside temperature and absolute humidity are Lower.
It is known that the oxygen concentration (oxygen partial pressure) contained in the atmosphere changes due to the influence of such changes in atmospheric conditions.
Furthermore, it is known that the air-fuel ratio of the air-fuel mixture supplied to the engine also changes as shown in FIG. 2 due to the change in the oxygen concentration in the atmosphere.
FIG. 2 specifically shows the relationship between the absolute humidity and the air-fuel ratio of the air-fuel mixture. When the absolute humidity is higher than that in FIG. 2, the air-fuel ratio becomes lean (the ratio of fuel in the air-fuel mixture is small). I understand that.
Similarly, when the outside air temperature is used instead of the absolute humidity, the relationship between the outside temperature and the air-fuel ratio of the air-fuel mixture is known to be lean when the outside air temperature is high.
Therefore, when the absolute humidity and the outside air temperature are high, the air-fuel ratio is biased toward the lean side, and misfires occur. On the other hand, when the absolute humidity and the outside air temperature are low, the air-fuel ratio is biased toward the rich side. In addition, problems such as an increase in NOx emissions occur.
Such a phenomenon occurs because the air-fuel ratio of the air-fuel mixture is set so that the measured value (IP) of the air-fuel ratio sensor becomes a predetermined target IP value in spite of the change in oxygen concentration due to atmospheric conditions. This is to perform control.
In addition, it is desirable that the air-fuel ratio of the air-fuel mixture is basically stable at a constant ratio that provides the best combustion efficiency at any absolute humidity or outside air temperature, as indicated by the dotted line shown in FIG.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an air-fuel ratio control system capable of appropriately controlling the air-fuel ratio of an air-fuel mixture even when atmospheric conditions change.

  The problems to be solved by the present invention are as described above. Next, means for solving the problems will be described.

That is, according to claim 1, in the air-fuel ratio control system for controlling the air-fuel ratio of the air-fuel mixture based on the target value map of the air-fuel ratio sensor and the measured value of the air-fuel ratio sensor,
The operation can be switched according to atmospheric conditions, and a map corresponding to the atmospheric conditions is provided.
The air-fuel ratio control system is configured to select the map according to the atmospheric conditions.

  According to a second aspect of the present invention, the map is selected as an air-fuel ratio control system that performs the selection of the map according to the outside air temperature.

  According to a third aspect of the present invention, the map is selected as an air-fuel ratio control system that selects the map in accordance with humidity.

In the air-fuel ratio control system for controlling the air-fuel ratio of the air-fuel mixture based on the target value of the air-fuel ratio sensor and the measured value of the air-fuel ratio sensor,
An air-fuel ratio control system configured to control the air-fuel ratio of the air-fuel mixture based on a map of correction coefficients for correcting the target value according to atmospheric conditions and the measured value of the air-fuel ratio sensor Has been.

  The present invention is configured as an air-fuel ratio control system comprising the correction coefficient as a map corresponding to the outside air temperature.

  According to a sixth aspect of the present invention, the air-fuel ratio control system is configured such that the higher the outside air temperature is, the smaller the correction coefficient is.

  As effects of the present invention, the following effects can be obtained.

  With the configuration of claim 1, for example, the atmospheric condition is simply recognized from the operating state of the GHP that is the engine power supply destination, and the target IP value map of the air-fuel ratio sensor corresponding to the recognized atmospheric condition is selected. It becomes possible to do. Since the target IP value map can be automatically selected, the measured value (IP value) of the air-fuel ratio sensor is controlled so as to become the target IP value of the selected map. Therefore, it is possible to achieve an effective NOx emission amount, and to improve fuel consumption.

  According to the configuration of the second aspect, it is possible to easily recognize the atmospheric condition using an inexpensive sensor. Similarly to the above, the measured value (IP value) of the air-fuel ratio sensor is set to the target IP value of the selected map. By controlling so that it becomes possible, it becomes possible to realize an ideal NOx emission amount, and to improve the fuel consumption.

  According to the configuration of the third aspect, although it is more expensive than the temperature sensor, it becomes possible to recognize atmospheric conditions in more detail, and to select a target IP value map accurately. By controlling the measured value (IP value) of the sensor so as to be the target IP value of the selected map, it is possible to realize an ideal NOx emission amount, and to improve fuel consumption and the like. It becomes possible.

With the configuration of the fourth aspect, for example, the atmospheric condition is simply recognized from the operating state of the GHP to which the engine power is supplied, and a target IP value map of the air-fuel ratio sensor corresponding to the recognized atmospheric condition is selected. It becomes possible to do. Since the target IP value map can be automatically selected, the measured value (IP value) of the air-fuel ratio sensor is controlled so as to become the target IP value of the selected map. Therefore, it is possible to achieve an effective NOx emission amount, and to improve fuel consumption.
Furthermore, since at least one target IP value is sufficient, it is possible to suppress consumption of the storage area of the ECU and storage means (storage element) as compared with a case where a map of at least two or more target IP values is required. It becomes.

  According to the configuration of the fifth aspect, the correction coefficient can be read at high speed according to the outside air temperature.

  According to the configuration of the sixth aspect of the invention, in order to reduce the target IP value of the air-fuel ratio sensor as the outside air temperature becomes higher, the target IP value becomes smaller. The air-fuel ratio of the air-fuel mixture can be kept at an appropriate value.

Hereinafter, the best mode for carrying out the present invention will be described with reference to the accompanying drawings for understanding of the present invention. The following best mode for carrying out the present invention is an example embodying the present invention, and is not intended to limit the technical scope of the present invention.
FIG. 1 is a schematic configuration diagram of an air-fuel ratio control system according to the best mode for carrying out the present invention, FIG. 2 is a map showing general characteristics regarding absolute humidity and air-fuel ratio of a mixture, and FIG. FIG. 4 is a map showing general characteristics relating to outside air temperature, FIG. 4 is a map showing ideal characteristics relating to NOx and outside air temperature, FIG. 5 is a flowchart showing an example of a series of processes performed by the air-fuel ratio control system, and FIG. Is a map relating to the correction coefficient of the target IP value and the outside air temperature, FIG. 7 is a map showing ideal characteristics relating to NOx and the outside air temperature, and FIG. 8 is a flowchart showing an example of a series of processes performed by the air-fuel ratio control system. .

First, the schematic configuration of the air-fuel ratio control system according to the best mode for carrying out the present invention will be described with reference to FIG.
Further, the engine of the air-fuel ratio control system described below may be a gas engine such as GHP (Gas Heat Pump) or a gasoline engine.
First, the mixer 20 that generates air-fuel mixture by mixing air (outside air) taken from the air cleaner 30 and fuel such as gas will be described.
The mixer 20 is mainly configured to mainly include a venturi 23, a fuel control valve 22, a fixed valve 21, a fuel increase valve 27, and a throttle valve 25.
The piston 45 of the engine 60 is lowered and the pressure in the cylinder (combustion chamber) 40 becomes negative. Air is taken in from the air cleaner 30 through the venturi 23.
The venturi 23 has a narrow air passage, a fuel supply passage is communicated with the narrow portion, and a portion of the air flow where the flow of air is fast sucks fuel from the fuel supply passage using negative pressure. To produce a mixture.
The amount of fuel supplied to the venturi 23 is adjusted by the fuel control valve 22.
Specifically, the amount of the fuel is adjusted by controlling a solenoid as an actuator for driving the valve body of the fuel control valve 22 by an ECU 10 (electronic control unit) which is an example of a control unit. The fuel control valve 22 may be abbreviated as “GVM”.
As shown in FIG. 1, as a system for supplying fuel to the venturi 23, there is a system that passes through the fixed valve 21 in addition to the system that passes through the fuel control valve 22.
This fixed valve 21 is for supplying only a predetermined amount of fuel to the venturi 23.
Therefore, the valve of the fixed valve 21 is not controlled by the ECU 10 or the like, but is only adjusted in advance during maintenance such as when the mixer 20 is manufactured or installed, and is fixed at a constant opening during operation. .
That is, the ECU 10 controls the fuel control valve 22 so that the air-fuel ratio in the air-fuel mixture generated by the venturi 23 can be changed.
The air-fuel mixture generated in this way reaches the throttle valve 25, and the flow rate of the air-fuel mixture passing through the throttle valve 25 varies depending on the opening degree of the throttle valve 25.
Specifically, the opening degree of the valve body of the throttle valve 25 is changed by driving a stepping motor as an actuator, and the stepping motor is controlled by the ECU 10.
Therefore, the flow rate of the air-fuel mixture passing through increases by opening the throttle valve 25, while the flow rate of the air-fuel mixture passing through decreases by closing the opening.

Further, the fuel increase valve 27 may be provided downstream of the throttle valve 25 (engine 60 side).
The function of the fuel increase valve 27 is opened when only the fuel supplied from the fuel control valve 22 is insufficient for the fuel contained in the air-fuel mixture.
Specifically, when the opening degree of the throttle valve 25 (throttle opening degree) is close to full open, etc., it operates particularly when it is desired to make the air-fuel ratio of the air-fuel mixture rich. In a control state that cannot be compensated for by the control valve, it operates complementarily.
That is, the fuel increase valve 27 shown in FIG. 1 is not necessarily a necessary component for the air-fuel ratio control system of the present invention, but FIG. 1 shows an example in which the fuel increase valve 27 is provided. Therefore, in the following description, it is assumed that the fuel increase valve 27 is not provided.

Further, the air-fuel mixture that has passed through the throttle valve 25 is sucked into the cylinder 40 of the engine 60 through the suction valve 41, compressed by the piston 45 with the suction valve 41 and the exhaust valve 42 closed, and then by the spark plug 43. Explodes on ignition.
The crankshaft is rotated by the raising and lowering of the piston 45, and the rotation angle and the rotation speed are detected by the rotation speed sensor 44 and input to the ECU 10.
The exhaust gas after the explosion is discharged through the exhaust valve 42.
At this time, the air-fuel ratio sensor 50 measures the air-fuel ratio (generally oxygen) in the exhaust gas, and is provided in an exhaust passage such as an exhaust manifold. The ECU 10 is based on the detection result of the air-fuel ratio sensor 50. The air / fuel ratio of the air-fuel mixture sucked into the cylinder 40 can be calculated.
Specifically, a measured value (output) that is a result of measurement by the air-fuel ratio sensor 50 is output as a current magnitude (hereinafter simply referred to as “IP value”), and this IP value is the ECU 10. Will be entered.
Further, the air-fuel ratio sensor 50 described here outputs the IP value as a larger value as the amount of oxygen contained in the exhaust gas is larger, while the IP value is smaller as the amount of oxygen contained in the exhaust gas is smaller. As the output characteristic. That is, the IP value is proportional to the actual air-fuel ratio of the air-fuel mixture.
Therefore, the ECU 10 performs fuel control so that the IP value measured by the air-fuel ratio sensor 50 becomes the target IP value stored in advance in the ECU 10 so that the actual air-fuel ratio of the air-fuel mixture approaches the target air-fuel ratio. The valve 22 and the throttle valve 25 are controlled.
Further, this target IP value may be stored in advance as a map in the storage means (for example, ROM) of the ECU 10 in association with the engine speed and load detected by the engine speed sensor 44.
The air-fuel ratio sensor 50 is warmed by a heater or the like since it is necessary to activate the element itself at a certain temperature when starting measurement.
The temperature in this case is also controlled by the ECU 10 or the like.

By the way, in the conventional air-fuel ratio control system, since the characteristics as shown in FIGS. 2 and 3 are exhibited, as described above, the air-fuel ratio becomes rich when the absolute humidity or the outside air temperature is low, and the NOx emission amount On the other hand, if the absolute humidity or the outside air temperature is high, the air-fuel ratio becomes lean and the amount of NOx emission decreases, but a problem such as misfire occurs.
Therefore, ideally, as shown in FIG. 4, when the outside air temperature is low, the air-fuel ratio is controlled so as to suppress the NOx emission amount. On the other hand, when the outside air temperature is high, misfire or the like does not occur. In addition, it is desirable to perform control so that the air-fuel ratio is close to a rich level and the amount of NOx emission is the same as when the outside air temperature is low.
Specifically, such control is performed so that the air-fuel ratio approaches lean (IP value large) when the outside air temperature is low, and the air-fuel ratio approaches rich (IP value small) when the outside air temperature is high. It becomes possible by controlling to.
That is, when the outside air temperature is low, the target IP value is increased so that the IP value of the air-fuel ratio sensor 50 becomes large, and when the outside air temperature is high, the target IP value so that the IP value of the air-fuel ratio sensor 50 becomes small. Make it smaller.
Specifically, a plurality of target IP value maps (graphs, numerical data, etc.), which are target values of the air-fuel ratio sensor 50, are stored in advance in the ECU 10, and appropriate according to atmospheric conditions such as outside air temperature and absolute humidity. A target IP value map is selected and switched.
Of course, the plurality of maps stored in advance in the ECU 10 correspond to various atmospheric conditions.
As described above, the ECU 10 measures the atmospheric conditions using a temperature sensor, a humidity sensor, etc. separately provided, and selects a target IP value map according to the result, thereby determining an appropriate target IP value and performing air-fuel ratio control. It is possible to do it.
However, if the atmospheric conditions are measured using a temperature sensor, a humidity sensor, or the like as described above, the number of monitoring points of the ECU 10 increases, so that the burden on the ECU 10 itself increases, and the cost for separately providing the above two sensors. There is a problem such as an increase.
Therefore, as a method for easily recognizing atmospheric conditions by another method, there is the following method.
As a method for simply recognizing atmospheric conditions, the ECU 10 recognizes the outline of atmospheric conditions by determining whether the GHP, which is an example of the power supply destination of the engine 60, is in cooling operation or heating operation. May be.
That is, the ECU 10 recognizes that the atmospheric condition is high (high humidity) when the GHP is in cooling operation, and recognizes that the atmospheric condition is low (humidity) when the GHP is in heating operation. .
A specific example of processing for simply recognizing atmospheric conditions in this way will be described with reference to the flowchart of FIG.
Since the temperature sensor is generally inexpensive, it has been conventionally provided in the air-fuel ratio control system. Accordingly, in the following description, the temperature sensor is not shown, but the air-fuel ratio control system of the present invention is also provided with a temperature sensor, and the outside air temperature is sensed by the ECU 10 via the temperature sensor. And

First, the ECU 10 determines whether or not the GHP is in a cooling operation (S110).
When it is determined that the cooling operation is performed according to the determination in step S110, the ECU 10 recognizes that the atmospheric condition is high temperature (high humidity), and on the other hand, when it is determined that the cooling operation is not performed (heating operation). The ECU 10 recognizes that the atmospheric condition is low temperature (low humidity).
That is, the outline of the atmospheric condition is recognized based on the determination in step S110.
Then, when it is determined that the GHP is in the cooling operation, the ECU 10 selects map data in which the target IP value for the high atmospheric temperature (high humidity) is described from the storage area of the ECU 10 (S120). .
On the other hand, when it is determined that the GHP is in the heating operation, the ECU 10 selects, from the storage area of the ECU 10 or the like, the map data in which the target IP value for the atmospheric condition is low (low humidity) is described (S125). .
That is, the ECU 10 determines whether or not the GHP is in the cooling operation by performing the processing of the above steps S110, S120, and S125, simply recognizes the atmospheric condition, and determines the air condition according to the recognized atmospheric condition. It becomes possible to select a map of the target IP value of the fuel ratio sensor 50.
That is, since it is possible to automatically select the target IP value map, the ECU 10 controls the measured value (IP value) of the air-fuel ratio sensor 50 to be the target IP value of the selected map. By doing so, it is possible to realize an ideal NOx emission amount as shown in FIG. 4 and to improve fuel consumption. A specific processing example will be described in step S130 and step S140 below.
After the processes of step S120 and step S125, the process proceeds to step S130.

Subsequently, the ECU 10 acquires a measurement value of the air-fuel ratio sensor 50, that is, an IP value (S130).
The ECU 10 then controls the fuel control valve 22 (GVM) and the like so that the IP value measured in step S130 (measured value of the air-fuel ratio sensor 50) follows the map of the target IP value selected in step S120 or step S125. Is operated (S140).
When the fuel control valve 22 is activated by the processing of step S140, the air-fuel ratio of the air-fuel mixture takes a value that approximates the dotted line shown in FIG. 2, and is stable at a constant ratio that improves the combustion efficiency of the air-fuel mixture. It becomes possible to make it.

In the determination of step S110, the case has been described in which the atmospheric condition is simply recognized by determining the operating state of the GHP (cooling operation / heating operation) and the target IP value map is selected. If the cost and the capability of the ECU 10 are within an acceptable range, a humidity sensor may be provided in the air-fuel ratio control system, and the atmospheric conditions may be determined based on the measured values of the sensors.
For example, instead of the determination in S110, a threshold humidity that is a reference for selecting a target IP value map is stored in advance in the ECU 10, so that the ECU 10 compares the humidity acquired from the humidity sensor with the threshold humidity. By doing so, a map of target IP values may be selected.
Similarly, a target IP value map may be selected by recognizing atmospheric conditions by a temperature sensor provided and making a determination based on a threshold temperature.

The air-fuel ratio control system described above selects a target IP value map that is a target value of the measured value (IP value) of the air-fuel ratio sensor 50 in accordance with atmospheric conditions such as the outside air temperature and absolute humidity, and the air-fuel ratio sensor 50 The air-fuel ratio control of the air-fuel mixture is performed so that the measured value becomes the selected target IP value.
However, since the air-fuel ratio control system needs to store a plurality of types of maps corresponding to atmospheric conditions in the storage unit connected to the ECU 10 or the ECU 10, a large storage capacity is required.
Therefore, in the following, an air-fuel ratio control system that has the effect of improving the combustion efficiency of the air-fuel ratio of the air-fuel mixture as described above while suppressing the necessary storage capacity as described above will be described.

In the following, it is assumed that at least one target IP value is stored in advance in the ECU 10 and the like, and a correction coefficient map (hereinafter referred to as “correction map”) for multiplying the target IP value is also stored in advance. To do.
Here, the correction map will be described with reference to FIG.
As shown in FIG. 6, the correction map is such that the correction coefficient becomes smaller as the outside air temperature, which is an example of the atmospheric condition, increases.
Therefore, at least one target IP value is stored in the ECU 10 or the like, a correction coefficient is acquired from the correction map that is also stored in the ECU 10 or the like according to atmospheric conditions such as the outside air temperature, and the target IP value is multiplied. Thus, it becomes possible to perform correction to decrease the target IP value as the outside air temperature increases.
That is, it is possible to determine an appropriate target IP value according to the outside air temperature.
By such a process, the air-fuel ratio of the air-fuel mixture is made leaner (IP value is large) when the outside air temperature is low, and the air-fuel ratio is made rich (IP value) when the outside air temperature is high, as described above. Therefore, it is possible to take a value approximate to the dotted line shown in FIG. 2 and stabilize it at a constant ratio that improves the combustion efficiency.
As a result, as shown in FIG. 7, it is possible to make the NOx emission amount uniform within a certain range of the shaded portion in the entire outside air temperature. Note that the dotted line in FIG. 7 indicates a case where the target IP value is not corrected.
A specific example of such processing will be described with reference to the flowchart of FIG.

First, the ECU 10 acquires a predetermined target IP value and a correction map (S210).
In step S210, a target IP value and a correction map stored in advance in storage means connected to the ECU 10, ECU 10, etc. are acquired.
Then, the ECU 10 acquires the temperature of the atmosphere (that is, the outside air temperature) sucked from the air cleaner 30 of the engine 60 from a temperature sensor or the like (S220).
Further, the ECU 10 calculates a correction coefficient corresponding to the outside air temperature acquired in step S220 from the correction map (S225).
Then, the ECU 10 multiplies the target IP value acquired in step S210 by the correction coefficient calculated in step S225 to calculate a value (correction value) obtained by correcting the target IP value according to the outside temperature ( S230).
Subsequently, an IP value that is a measurement value of the air-fuel ratio sensor 50 is acquired (S240).
Control is performed by operating the fuel control valve 22 (GVM) so that the IP value, which is the measurement value of the air-fuel ratio sensor 50 acquired in step S240, becomes the correction value of the target IP value calculated in step S230 (step S230). S250).
By performing such processing, the air-fuel ratio of the air-fuel mixture takes a value that approximates the dotted line shown in FIG. 2 and can be stabilized at a constant ratio that improves the combustion efficiency of the air-fuel mixture. It becomes.
Further, when performing the processes of steps S210 to S250, at least one target IP value may be used. Therefore, a map of at least two or more target IP values is required when performing the process already described with reference to FIG. Compared with the case where it does, it becomes possible to suppress consumption of the storage area of the storage means connected to ECU10 or ECU10.
That is, even if the storage capacity of the storage unit connected to the ECU 10 or the ECU 10 is small, it is possible to correct the target IP value according to the outside air temperature and control the air-fuel ratio of the air-fuel mixture.

1 is a schematic configuration diagram of an air-fuel ratio control system according to the best mode for carrying out the present invention. A map showing the general characteristics of the absolute humidity and air / fuel ratio of the mixture. A map showing the general characteristics of NOx and ambient temperature. A map showing ideal characteristics for NOx and ambient temperature. The flowchart which showed an example of the series of processes which an air fuel ratio control system performs. The map regarding the correction coefficient of target IP value, and outside temperature. A map showing ideal characteristics for NOx and ambient temperature. The flowchart which showed an example of the series of processes which an air fuel ratio control system performs.

Explanation of symbols

10 ECU
DESCRIPTION OF SYMBOLS 20 Mixer 21 Fixed valve 22 Fuel control valve 23 Venturi 25 Throttle valve 27 Fuel increase valve 30 Air cleaner 50 Air fuel ratio sensor 60 Engine

Claims (6)

In the air-fuel ratio control system for controlling the air-fuel ratio of the air-fuel mixture based on the target value map of the air-fuel ratio sensor and the measured value of the air-fuel ratio sensor,
The operation can be switched according to atmospheric conditions, and a map corresponding to the atmospheric conditions is provided.
An air-fuel ratio control system, wherein the map is selected according to the atmospheric conditions.   The air-fuel ratio control system according to claim 1, wherein the map is selected according to an outside air temperature.   The air-fuel ratio control system according to claim 1, wherein the map is selected according to humidity. In the air-fuel ratio control system for controlling the air-fuel ratio of the air-fuel mixture based on the target value of the air-fuel ratio sensor and the measured value of the air-fuel ratio sensor,
An air-fuel ratio control system for controlling an air-fuel ratio of an air-fuel mixture based on a map of a correction coefficient for correcting the target value according to atmospheric conditions and a measured value of the air-fuel ratio sensor.   The air-fuel ratio control system according to claim 4, wherein the correction coefficient is provided as a map corresponding to the outside air temperature. The air-fuel ratio control system according to claim 4 or 5, wherein the correction coefficient is set to be smaller as the outside air temperature is higher.

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