JPH08177652A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To increase a lean operation opportunity so as to improve fuel consumption by calculating an accumulated value of introducing vaporized fuel to an intake system of a mixture, and inhibiting lean air/fuel ratio control when this accumulated value is less than a threshold value based on an engine operating condition and an air/fuel ratio feedback correction value. CONSTITUTION: In a vaporized fuel evapotranspiration preventing device, vaporized fuel generated in a fuel tank, after temporarily adsorbed, is separated, drawn out to an intake system of an internal combustion engine and processed. On the other hand, in an air/fuel ratio feedback control means, based on each detecting result from an operating condition detecting means and an air/fuel ratio detecting means, a basic control value of air/fuel ratio is adjusted to be corrected by an air/fuel ratio feedback correction value. A lean air/fuel ratio control means controls actual air/fuel ratio so as to obtain target lean air/fuel ratio. Here, an accumulated value of introducing vaporized fuel to an intake system of a mixture is calculated by this calculating means. As a result, when the accumulated value is less than a threshold value based on the engine operating condition and the air/fuel ratio feedback correction value, lean air/fuel ratio control is inhibited by this inhibiting means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly to an improvement of a device for controlling the air-fuel ratio by switching it between a stoichiometric air-fuel ratio and a lean air-fuel ratio.

[0002]

2. Description of the Related Art As a conventional air-fuel ratio control system for an internal combustion engine, for example, there is a technique disclosed in Japanese Patent Application Laid-Open No. 2-67441. This is a vaporized fuel evaporation that prevents vaporized fuel from evaporating to the outside air by temporarily adsorbing the vaporized fuel generated in the fuel tank etc. to the canister and sucking the adsorbed vaporized fuel to the engine during engine operation. Avoiding the influence of air fuel ratio learning due to vaporized fuel desorption (purging) in the air conditioner learning control device that is equipped with a preventive device and corrects air-fuel ratio control errors due to product-to-product variations and changes over time. In order to do so, updating of the learning value is prohibited during purging.

On the other hand, when a high-concentration purge gas is introduced during lean operation (diluted air-fuel ratio control), the air-fuel ratio becomes much richer (≦ 18) than the target air-fuel ratio (≈22), There is a problem that the NOx emission amount increases. Since the fuel injection amount is originally small during lean operation, if the purge gas concentration is high, the air-fuel ratio becomes richer than the target air-fuel ratio even if the fuel injection amount is 0. Therefore, in the above conventional example, it is conceivable to prevent the rich operation during the lean operation by prohibiting the lean operation when prohibiting the update of the learning value.

[0004]

However, in such a conventional air-fuel ratio control apparatus for an internal combustion engine, the lean operation is always prohibited during the purging, and the opportunity to perform the lean operation is significantly impaired. However, there is a problem in that the fuel efficiency improvement effect that should be obtained by performing lean operation is significantly reduced.

On the other hand, conventionally, in order to increase the air-fuel ratio control accuracy from the requirement of exhaust reduction, the cumulative purge amount is obtained, the purge gas concentration is estimated based on the cumulative purge amount, and the purge gas flow rate and the purge gas flow rate are determined based on the purge gas concentration. A method of controlling the fuel injection amount is adopted. By applying the purge gas concentration estimation method in this method to the above conventional example, by prohibiting the lean operation only when the air-fuel ratio during lean operation is greatly enriched and the NOx emission amount increases beyond the allowable level, It is possible to secure more lean driving opportunities than the above example.

However, in the conventional air-fuel ratio control device, the lean operation is prohibited until the cumulative purge amount reaches a predetermined threshold value. Therefore, if the threshold value is not appropriate, for example, the state of the canister at the time of starting is substantially reduced. If the threshold value is too close to the sky and the threshold value is larger than the original requirement, the lean operation opportunity is unnecessarily impaired. On the contrary, if the threshold value is too small, the rich purge gas causes a large enrichment during lean operation. Therefore, there is a problem that the amount of NOx emission increases.

The present invention has been made in view of the above conventional problems, and by appropriately setting the condition of the purge gas cumulative value for prohibiting the lean operation, the lean operation is suppressed while suppressing the increase of the NOx emission amount. It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine, which can improve fuel efficiency and the like by giving a sufficient opportunity.

[0008]

Therefore, as shown in FIG. 1, the invention according to claim 1 temporarily adsorbs the evaporated fuel generated in the fuel tank by the adsorbing means, and the adsorbing means adsorbs the engine intake air. And an operating state detecting means for detecting the operating state of the engine, and an evaporative fuel evaporation preventing device for communicating with the system to separate the evaporated fuel adsorbed by the adsorbing means and guide it to the engine intake system for treatment. The air-fuel ratio detecting means for detecting the air-fuel ratio of the intake air-fuel mixture, and the stoichiometric air-fuel ratio for the actual air-fuel ratio of the engine intake air-fuel mixture detected by the air-fuel ratio detecting means in the predetermined operating condition detected by the operating condition detecting means. So that the basic control value of the air-fuel ratio is increased or decreased by the air-fuel ratio feedback correction value to perform feedback control of the air-fuel ratio, and a predetermined value detected by the operating state detection means. A lean air-fuel ratio control means for controlling the actual air-fuel ratio of the engine intake air-fuel mixture to a target lean air-fuel ratio in a rotating state, and mixing the separated evaporated fuel with the lean air-fuel ratio control device. A separated vaporized fuel cumulative value calculating means for calculating a cumulative value of the amount of air introduced into the intake system;
The accumulated value of the separated fuel calculated by the separated fuel accumulated value calculating means is determined based on the operating state of the engine detected by the operating state detecting means and the air-fuel ratio feedback correction value in the air-fuel ratio feedback control means. And a lean air-fuel ratio control inhibiting means that inhibits the lean air-fuel ratio control when it is less than the threshold value.

According to the second aspect of the present invention, the vaporized fuel evaporation prevention apparatus includes a control valve that is opened / closed in a passage for guiding the gas containing the vaporized fuel separated from the adsorbing means to the intake system. The lean air-fuel ratio control prohibiting means is provided,
The threshold value is determined based on the air-fuel ratio feedback correction value and the ratio of the flow rate of the gas containing evaporated fuel to the intake air flow rate.

Further, in the invention according to claim 3, the flow rate of the gas containing the evaporated fuel is set to the intake negative pressure of the engine, the intake air flow rate, the combination of the engine load and the engine rotation speed, the engine rotation speed and the engine intake system. It is characterized in that it is obtained based on any one of the combination with the throttle valve opening degree interposed in the. Further, in the invention according to claim 4, the vaporized fuel evaporation prevention device comprises a control valve whose opening degree is controlled to be variable in a passage for guiding the gas containing the vaporized fuel separated from the adsorbing means to the intake system. Is controlled so that the ratio of the gas containing evaporative fuel to the intake air flow rate is constant.

[0011]

According to the first aspect of the invention, when desorption of the evaporated fuel from the adsorbing means and introduction into the intake system are started, the gas containing the desorbed fuel (hereinafter referred to as purge gas) enriches the air-fuel ratio. As a result, the air-fuel ratio feedback correction value in the air-fuel ratio feedback control greatly changes compared to when the purge gas is not released. Therefore, if the amount of change in the air-fuel ratio feedback correction value is taken as the concentration of the purge gas (concentration of evaporated fuel in the purge gas), for example, when the maximum purge gas concentration after the start of purge is high,
By continuing the purge thereafter, the cumulative value of the purge gas until the concentration of the purge gas at which the lean operation (lean air-fuel ratio control) can be permitted decreases, is increased. Prolong the lean operation prohibition period to the extent that the effect on the fuel ratio can be minimized. Conversely, when the purge gas concentration is low, the cumulative value of the small purge gas decreases to a purge gas concentration at which lean operation with a small effect on the air-fuel ratio can be started.Therefore, by setting the threshold value accordingly, the lean operation can be promptly performed. Let it start.

In this way, the chances of lean operation can be increased as much as possible within a range that does not affect the air-fuel ratio, so fuel consumption can be improved. According to the invention of claim 2, in addition to the purge gas concentration, the ratio of the flow rate of the purge gas to the intake air flow rate actually affects the air-fuel ratio. Therefore, the ratio is considered together with the air-fuel ratio feedback correction value. By determining the threshold value by using the threshold value, more accurate lean operation prohibition control can be performed.

According to the third aspect of the invention, since the opening of the control valve is constant, the purge gas flow rate is determined by the differential pressure before and after the control, that is, the intake negative pressure. Therefore, in the case where the intake negative pressure can be directly detected, based on the detected value, other intake air flow rate, a combination of the engine load and the engine rotation speed, the engine rotation speed and the throttle valve opening degree interposed in the engine intake system, Since the intake negative pressure can be estimated by the combination of the above, the purge gas flow rate can be obtained based on any of them.

According to the fourth aspect of the present invention, since the control valve having the variable opening degree is provided, the ratio of the purge gas flow rate to the intake air flow rate can be controlled to be constant by controlling the opening degree. The inside air-fuel ratio can be satisfactorily controlled, and since the ratio of the purge gas flow rate to the intake air flow rate is constant when setting the threshold value, the threshold value can be variably set only by the air-fuel ratio feedback correction value.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, an intake passage 2 of an engine 1 is provided with an air flow meter 5 for detecting an intake air flow rate Q sucked through an air cleaner 4 and a throttle valve 6 for controlling the intake air flow rate Q in conjunction with an accelerator pedal. ing. An electromagnetic fuel injection valve 7 for injecting and supplying fuel for each cylinder is provided in a manifold portion downstream of the throttle valve 6.

Further, in the exhaust passage 3 of the engine 1, an oxygen sensor 8 is provided as an air-fuel ratio detecting means for detecting the air-fuel ratio of the intake air-fuel mixture by detecting the oxygen concentration in the exhaust gas at the manifold collecting portion, and the downstream thereof. On the side, a three-way catalyst 9 is provided as an exhaust gas purification catalyst that purifies the exhaust gas by maximizing the oxidation of CO and HC and the reduction of NO _x in the exhaust gas near the stoichiometric air-fuel ratio.

Further, the distributor 10 has a built-in crank angle sensor 11, and the control unit 50 counts a crank unit angle signal output from the crank angle sensor 11 in synchronization with engine rotation for a certain period of time. Alternatively, the cycle of the crank reference angle signal is measured to detect the engine rotation speed Ne. The control unit 50 calculates a fuel amount corresponding to the target air-fuel ratio from the fuel injection valve 7 based on the values detected by the various sensors by a method described later, and has a pulse width corresponding to the fuel amount. The injection pulse signal is output to the fuel injection valve 7. Fuel injection valve 7
The valve is driven by the injection pulse signal to inject and supply the fuel, which is pressure-fed from a fuel pump (not shown) and is controlled to a predetermined pressure by the pressure regulator. The air-fuel ratio is controlled by controlling the injection amount.

By the way, a purge passage 13 which connects the space above the liquid surface of the fuel tank 12 and the downstream portion of the throttle valve 6 of the intake passage 2 of the engine 1 is provided. A canister 14 as an adsorbing means capable of temporarily adsorbing the evaporated fuel generated in 12 or the like is interposed. A purge control valve 15 is provided downstream of the canister 14 in the purge passage 13, and the purge control valve 15 is opened based on a signal from the control unit 50 when the engine 1 is in a predetermined operating state. As a result, the canister 14 is connected to the engine 1
Intake negative pressure is introduced, the adsorbed fuel vapor is released from the canister 14, and the fuel vapor (hereinafter,
It is called purge gas. ) Is sucked.
This structure is the evaporated fuel evaporation prevention device. In the first embodiment, the purge control valve 15 is composed of a diaphragm type actuator driven by an intake negative pressure, and opens when intake negative pressure is applied to the pressure working chamber and when it is opened to atmospheric pressure. A switch that only switches between open and close is used so that the switch is closed (corresponding to claims 2 and 3). In this case, since the opening degree of the purge control valve 15 is constant, the purge gas flow rate is determined by the differential pressure across the air, that is, the intake negative pressure.

The throttle valve 6 is provided with a throttle sensor 60 for detecting the opening of the throttle valve 6 and an idle switch 61 which is turned on when the throttle valve 6 is fully closed, and the engine 1 detects the cooling water temperature. A water temperature sensor 62 is provided, and a vehicle speed sensor 63 that detects the vehicle speed is provided. The control unit 50 having the functions of air-fuel ratio feedback control means, lean air-fuel ratio control means, leaving evaporated fuel cumulative value calculation means, lean air-fuel ratio control prohibiting means includes a CPU, a ROM,
It is equipped with a microcomputer including a RAM, an A / D converter, an input / output interface, etc., receives input signals from various sensors, and RO shown in each flowchart.
Arithmetic processing is performed according to the program on M.

FIG. 3 shows a flowchart of a routine for calculating the lean operation permission cumulative purge amount (threshold value for determining the lean operation prohibition time) in the first embodiment. This flow is executed at predetermined time intervals ΔT. Step
At 201, it is judged whether the purge is being executed (the purge control valve 15 is open). If not, the routine proceeds to step 203, where the value of the purge time measuring counter TPRG is reset to 0 and the flow is ended. .

When purging is executed, the routine proceeds to step 202, where the counter TPRG is incremented, and then step
The routine proceeds to 204, where it is determined whether the count value TPRG has reached the predetermined value TALCHK, and before reaching the count value, the flow is terminated without calculating the threshold value. In the present invention, the threshold value is calculated based on the air-fuel ratio feedback correction coefficient α, but due to the delay of the feedback control system, it cannot be distinguished from the case where the purge gas concentration is high even though the purge gas concentration is high immediately after the start of the purge. Since the feedback correction coefficient α remains near the reference value (the reference value of the value that increases / decreases during non-purging, 1.0), this flow is not performed for a predetermined time until the feedback correction coefficient α largely deviates from the reference value. Processing. When the above process is not performed, the value of the lean operation permission cumulative purge amount also becomes a small value because the deviation of the air-fuel ratio feedback correction coefficient α from the reference value is small, and soon after the start of the purge, the purge gas concentration is still lower than the allowable value. Although there is a possibility that the lean operation permission condition will be satisfied even though it is high, such a situation can be avoided by performing the processing.

Next, at step 205, the difference between the reference value (1.0) of the air-fuel ratio feedback correction coefficient α and the current α is obtained, this value is compared with the value DALP, and the difference is larger than the current value of DALP. If so, this value is updated as a new DALP in step 206. The initial value of this DALP is set to 0. As a result, the air-fuel ratio feedback correction coefficient α is set to the reference value due to the enrichment of the air-fuel ratio by the purge gas by the processing of steps 205 and 206.
When it becomes smaller than 1.0, updating of the DALP value is started, and α
DALP increases with the decrease of. DALP always holds the maximum value up to that point.

Here, the higher the purge gas concentration, the greater the degree of enrichment, so the DALP becomes greater. If the shortest lean operation inhibition time determined by the preset minimum value of the lean operation permission cumulative purge amount is longer than the execution time interval ΔT of this flow, the DALP is large due to the above processing while the lean inhibition is performed. Since the value is updated, the lean prohibition time will not be shorter than the request. In this case, TALCHK
Can be zero.

Subsequently, at step 207, the purge amount ΔPRGQ per unit time is obtained. This calculation method will be described later. In the first embodiment, the flow rate of the purge gas is determined by the purge orifice diameter and the suction negative pressure, and the flow rate is not controlled in detail. The degree to which the air-fuel ratio is enriched by the purge gas is influenced not only by the purge gas concentration but also by the ratio of the purge gas flow rate to the intake air flow rate (hereinafter referred to as the purge rate). Therefore, in step 208, the intake air flow rate QA is calculated. .

Then, in step 209, the purge rate PRGRAT is calculated from the intake air flow rate and the ΔPRGQ (PRGAT).
RAT = ΔPRGQ / QA), the routine proceeds to step 210, and the lean operation permission cumulative purge amount PGQLEN is obtained based on the purge rate PRGRAT and the DALP. Here, the higher the purge gas concentration, the more time it takes to make it to an acceptable level, so PGQL
Since it is necessary to set EN to a large value and DALP increases as the purge gas concentration increases, PGQLEN also increases as DALP increases. Also, as a matter of course, if the purge rate is small, the influence of the purge gas on the air-fuel ratio is small, so DALP
PGQLEN is set to be smaller as PRGRAT is larger, even if the same.

Next, FIG. 4 shows the flow of a subroutine for calculating the purge amount ΔPRGQ per unit time in the step 207. First, in step 301, the throttle valve opening T
VO and engine speed NE are input, and in step 302, throttle opening area ATVO is set to ATVO = ATH {1-c
os (TVO)}.

Next, in step 303, the intake negative pressure (boost pressure) is retrieved from the map based on the calculated throttle opening area ATVO and the engine speed NE, and further step
In 304, the purge amount ΔPRGQ per unit time is retrieved from the map for the retrieved intake negative pressure (mmHg). Figure 5
[Fig. 3] is a flow chart of a lean operation permission determination routine in the first embodiment.

When the idle switch 61 is in the non-idle state by not detecting the state of the idle switch 61 (S401, S402), when the cooling water temperature TW detected by the water temperature sensor 62 is in the range of the lower limit set value TWL to the upper limit set value TWH ( S403, S404), the basic fuel injection amount TP detected as the representative value of the load is the lower limit set value TP
When it is in the range of L to the upper limit set value TPH (S404, S406),
When the engine speed NE detected by the crank angle sensor 11 is in the range of the lower limit set value NEL to the upper limit set value NEH (S
407, S408), when the throttle valve opening TVO detected by the throttle sensor 60 is less than or equal to the set value TVOH (S409, S41).
0), the vehicle speed VSP detected by the vehicle speed sensor 63 is the set value VS.
When PL or more (S411, S412), vehicle speed change amount ΔVS
When P is equal to or lower than the set value DVH (S413, S414), all operating conditions are within the lean operation permission range, and the cumulative purge amount PRGQ is the lean operation permission cumulative purge amount PG.
When QLEN is reached (S415), the lean operation permission flag FLEAN for permitting lean operation is set to 1 (S41).
6), otherwise, lean operation permission flag FLEAN
Is set to 0 (S417).

FIG. 6 shows a flow chart of a routine showing the opening / closing control of the purge control valve. Explaining based on the figure, the idle switch 61 is on (S501, S502),
The cooling water temperature TW is within the range of TWCPL ≤ TW ≤ TWCPH (S503, S504), and the basic fuel injection amount TP which is the engine load is within the range of TPCPL ≤ TP ≤ TPCPH.
When the purge operation condition of (S505, S506) is satisfied, the purge control valve 15 is opened to perform the purge, otherwise the purge control valve 15 is closed to prohibit the purge (S507, S506).
508).

FIG. 7 is a diagram showing the operation and effect of this embodiment. Explaining based on the figure, since the purge is started and the air-fuel ratio becomes rich due to its influence, the air-fuel ratio feedback control tries to correct it and the air-fuel ratio feedback correction coefficient α largely deviates from the vicinity of the reference value and decreases. When it changes to a minimum value, the difference between the reference value 1.0 and the minimum value becomes DALP. The lean permitted cumulative purge amount PGQLEN is obtained from the DALP and the purge rate PRGRAT obtained based on the operating state at this time, and the cumulative purge amount P
When RGQ becomes equal to or higher than PGQLEN, the operation shifts to lean operation (other lean permission conditions are already established). In this embodiment, air-fuel ratio feedback control is not performed during lean operation. Since the lean operation is started after waiting until the purge gas concentration becomes low, the NOx emission amount can be suppressed within the allowable range without significantly enriching the target air-fuel ratio while performing the purge during the lean operation.

FIG. 8 shows the lean operation permission cumulative purge amount PGQ.
The flow of the 2nd example which asks for LEN is shown. In the second embodiment, a duty control valve that can control the purge gas flow rate so that the purge rate is always a constant value is used as the purge control valve (corresponding to claim 4). Compared with the flow of the first embodiment shown in FIG. 3, step 701 to step
Step 706 is the same as step 201 to step 206, but there is no need to calculate the purge rate, so in step 707 only the DALP is used and the lean operation permission cumulative purge amount PGQL is calculated.
EN can be calculated. Moreover, if the purge rate is controlled to be constant by using such a purge control valve with variable opening,
Good control of air-fuel ratio during purging.

[0032]

According to the first aspect of the present invention, since the threshold value of the cumulative value of the purge gas, which is the condition for prohibiting lean operation, is determined under the condition including the air-fuel ratio feedback correction value, the air-fuel ratio is affected. The chances of lean driving can be increased as much as possible within the range where there is no fuel consumption, and fuel efficiency can be significantly improved.

According to the second aspect of the invention, since the threshold value is determined based on the purge gas concentration and the ratio of the flow rate of the purge gas to the intake air flow rate, it is possible to perform lean operation prohibition control with higher accuracy. Claim 3
According to the invention of claim 1, the purge gas flow rate when the control valve with a constant opening is provided can be easily obtained by the intake negative pressure or various operating states for estimating the intake negative pressure, whereby the intake air The threshold value can be determined in consideration of the ratio of the purge gas flow rate to the flow rate.

According to the fourth aspect of the present invention, since the control valve having a variable opening is provided to control the ratio of the flow rate of the purge gas to be constant, the air-fuel ratio control during purging can be favorably performed and the air-fuel ratio feedback correction can be performed. The threshold can be variably set only by the value.

[Brief description of drawings]

FIG. 1 is a block diagram according to the present invention.

FIG. 2 is an overall configuration diagram of an embodiment according to the present invention.

FIG. 3 is a flow chart of a routine for calculating a lean operation permission cumulative purge amount in the above embodiment, a flow chart showing a lean operation permission / prohibition determination routine.

FIG. 4 is a flowchart of a routine for calculating a cumulative purge amount in the above embodiment.

FIG. 5 is a flowchart of a lean operation approval / disapproval determination routine.

FIG. 6 is a flowchart showing a control routine for the purge control valve.

FIG. 7 is a time chart showing the action and effect of the above embodiment.

FIG. 8 is a flowchart of a routine for calculating a cumulative purge amount in the second embodiment.

[Explanation of symbols]

 1 Engine 2 Intake Passage 3 Exhaust Passage 5 Air Flow Meter 7 Fuel Injection Valve 8 Oxygen Sensor 11 Crank Angle Sensor 50 Control Unit 60 Throttle Sensor 61 Idle Switch 62 Water Temperature Sensor 63 Vehicle Speed Sensor

Claims (4)

[Claims] Claim: What is claimed is: 1. Evaporative fuel generated in a fuel tank is temporarily adsorbed by an adsorbing means, the adsorbing means is communicated with an engine intake system, and the evaporated fuel adsorbed by the adsorbing means is separated to remove the engine fuel intake system. In addition to the evaporative fuel transpiration prevention device designed to guide and process, the operating state detecting means for detecting the engine operating state, the air-fuel ratio detecting means for detecting the air-fuel ratio of the engine intake air-fuel mixture, and the operating state detecting means are provided. The basic control value of the air-fuel ratio is increased or decreased by the air-fuel ratio feedback correction value so that the actual air-fuel ratio of the engine intake air-fuel mixture detected by the air-fuel ratio detecting means in the detected predetermined operating state approaches the theoretical air-fuel ratio. The air-fuel ratio feedback control means for feedback controlling the air-fuel ratio and the actual lean air-fuel ratio of the engine intake air-fuel mixture in the predetermined operating condition detected by the operating condition detecting means become the target lean air-fuel ratio. In the air-fuel ratio control apparatus for an internal combustion engine, the lean air-fuel ratio control means for controlling the above is provided, and the accumulated evaporated fuel cumulative value calculation for calculating the cumulative value of the introduction amount of the separated evaporated fuel mixture into the intake system. A lean air-fuel ratio control when the accumulated value of the desorbed fuel calculated by the means for calculating the desorbed fuel cumulative value is less than a threshold value determined based on a condition including an air-fuel ratio feedback correction value in the air-fuel ratio feedback control means. An air-fuel ratio control device for an internal combustion engine, comprising: lean air-fuel ratio control prohibiting means for prohibiting 2. The evaporation fuel evaporation prevention device comprises a control valve which is opened / closed in a passage for introducing a gas containing evaporated fuel separated from the adsorption means to an intake system, and the lean air-fuel ratio control is prohibited. The means determines the threshold value based on the air-fuel ratio feedback correction value and the ratio of the flow rate of the gas containing the evaporated fuel to the intake air flow rate. Air-fuel ratio control device for internal combustion engine. 3. The flow rate of the gas containing the evaporated fuel, the intake negative pressure of the engine, the intake air flow rate, the combination of the engine load and the engine speed, the engine speed and the throttle valve opening in the engine intake system. The air-fuel ratio control device for an internal combustion engine according to claim 2, wherein the air-fuel ratio control device calculates the air-fuel ratio according to any one of a combination with a degree. 4. The evaporation fuel evaporation prevention device comprises a control valve whose opening degree is controlled to be variable in a passage for guiding a gas containing evaporated fuel separated from the adsorption means to an intake system, and the opening degree of the control valve is controlled. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the ratio of the gas containing the evaporated fuel to the intake air flow rate is controlled to be constant.