JP2000257487A - Evaporative fuel treatment system for internal combustion engine - Google Patents

Abstract

(57) [Problem] To accurately perform air-fuel ratio learning even during execution of fuel vapor purging. SOLUTION: A purge pipe 16 for connecting a fuel tank 15 and an intake branch pipe 2 and a pipe 16 for controlling a purge flow rate which is a flow rate of fuel vapor purged from the fuel tank 15 into the pipe 16 are provided. Purge control valve 17 arranged
An engine operating state detecting means for detecting an operating state of the engine, a fuel injection time calculating means for calculating a fuel injection time TP based on the engine operating state, and a fuel calculated based on the engine operating state. Air-fuel ratio learning execution means for calculating an air-fuel ratio learning coefficient KGj for correcting the injection time TP, and a fuel injection time T calculated based on the engine operating state
A fuel injection time correction means for correcting P with the air-fuel ratio learning coefficient KGj is provided, and the air-fuel ratio learning can be executed by fixing the purge flow rate during the execution of the fuel vapor purge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel vapor treatment system for an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, a purge passage connecting a fuel tank and an intake passage and a purge passage for controlling a purge flow rate of a fuel vapor purged from the fuel tank into the intake passage are arranged in the purge passage. A purge control valve; an engine operating state detecting means for detecting an operating state of the engine; a fuel injection amount calculating means for calculating a fuel injection amount TP based on the engine operating state; and a calculation based on the engine operating state. Air-fuel ratio learning coefficient KG for correcting the calculated fuel injection amount TP
j for calculating an air-fuel ratio learning coefficient, and an air-fuel ratio learning coefficient KG for calculating the fuel injection amount TP calculated based on the engine operating state.
an internal combustion engine that includes a fuel injection amount correction means for correcting the air fuel ratio during the fuel vapor purge cut (PGR = 0), that is, executes the air fuel ratio learning. Is known. An example of this type of evaporative fuel processing apparatus for an internal combustion engine is disclosed in, for example, Japanese Patent Application Laid-Open No. 7-305662.

[0003]

However, Japanese Patent Application Laid-Open No.
In the evaporative fuel processing apparatus for an internal combustion engine described in Japanese Patent Publication No. 305662, in order to execute the air-fuel ratio learning, it is necessary to perform a purge cut of the fuel vapor (a purge rate PGR ← 0, a duty ratio DPG ← 0 of a purge control valve). Because
The amount of purge of the fuel vapor cannot be increased, and the fuel vapor in the fuel tank and the canister (vapor adsorbent) cannot be purged early.

On the other hand, in the evaporative fuel processing apparatus for an internal combustion engine described in Japanese Patent Application Laid-Open No. 7-305662, the purge flow rate is controlled so that the proportion of fuel vapor in the intake air supplied to the combustion chamber becomes constant. It is changed according to a change in the engine operation state. Therefore, even if an attempt is made to execute the air-fuel ratio learning while the fuel vapor is being purged, accurate air-fuel ratio learning cannot be performed because the fuel vapor is changed.

[0005] In view of the above problems, an object of the present invention is to provide an evaporative fuel processing apparatus for an internal combustion engine that can execute air-fuel ratio learning even during execution of fuel vapor purging.

[0006]

According to the first aspect of the present invention, the purge passage connecting the fuel tank and the intake passage and the flow rate of the fuel vapor purged from the fuel tank into the intake passage are determined. A purge control valve disposed in the purge passage for controlling a certain purge flow rate, an engine operating state detecting means for detecting an operating state of the engine, and calculating a fuel injection amount based on the engine operating state. Fuel injection amount calculation means, air-fuel ratio learning execution means for calculating an air-fuel ratio learning coefficient for correcting the fuel injection amount calculated based on the engine operation state, and fuel injection calculated based on the engine operation state A fuel injection amount correcting means for correcting the amount by an air-fuel ratio learning coefficient, wherein the purge flow rate is fixed during purging of the fuel vapor. Becomes constant vapor amount control by controlling the specific purge flow rate value, a fuel vapor treatment system for an internal combustion engine, characterized in that the can execute the air-fuel ratio learning is provided.

In the evaporative fuel processing apparatus for an internal combustion engine according to the first aspect, the purge flow rate is fixed during the execution of the fuel vapor purge, that is, the air-fuel ratio learning is executed by controlling the purge flow rate to a specific purge flow rate value. Even while the fuel vapor is being purged, the fuel correction of the vapor becomes more correct than in the case where the vapor amount is changed proportionally because the fuel vapor amount is kept constant, and the fuel vapor amount is maintained as accurate as during the purge cut of the fuel vapor. Air-fuel ratio learning can be performed. Further, since the execution of the air-fuel ratio learning can be performed even during the execution of the fuel vapor purge, the necessity of performing the fuel vapor purge cut in order to execute the air-fuel ratio learning is eliminated. The vapor purge amount can be increased.

According to the second aspect of the present invention, there is provided fuel vapor generation stability determining means for determining whether the generation of fuel vapor from the fuel tank is stable, and the fuel vapor is being purged. Before the generation of fuel vapor from the fuel tank is stabilized, the air-fuel ratio learning is not performed,
2. The internal combustion engine according to claim 1, wherein the purge flow rate is fixed and the air-fuel ratio learning can be executed during the execution of the fuel vapor purge and after the generation of the fuel vapor from the fuel tank is stabilized. Is provided.

According to the third aspect of the present invention, there is provided a total purge flow rate calculating means for calculating a total purge flow rate after the engine is started, and when the total purge flow rate is small, the fuel vapor from the fuel tank is discharged. 3. The process according to claim 2, wherein the generation of fuel vapor from the fuel tank is determined to be stable when it is determined that the generation is not yet stable and the total purge flow rate is large. An apparatus is provided.

In the fuel vapor processing apparatus for an internal combustion engine according to the second and third aspects, before the generation of fuel vapor from the fuel tank is stabilized, that is, when the total purge flow rate is small,
The air-fuel ratio learning is not executed in view of the fact that the purge flow rate is not actually fixed even if the purge flow rate is fixed. Therefore, it is possible to prevent the air-fuel ratio from being erroneously learned before the generation of the fuel vapor from the fuel tank is stabilized, that is, when the total purge flow rate is small.

According to the fourth aspect of the invention, after the generation of fuel vapor from the fuel tank is stabilized and the purge execution time is short, the purge flow rate is changed according to the engine operating state, 3. The evaporative fuel treatment of an internal combustion engine according to claim 2, wherein after the generation of fuel vapor from the tank is stabilized and the purge execution time is long, the purge flow rate can be fixed regardless of the engine operating state. An apparatus is provided.

According to the fourth aspect of the present invention, even if the purge execution time is short even after the generation of the fuel vapor from the fuel tank is stable, even if the purge flow rate is fixed, it is actually possible to fix the purge flow rate. The air-fuel ratio learning is not executed in view of the fact that the purge flow rate is difficult to fix. Therefore, it is possible to avoid erroneous learning of the air-fuel ratio after the generation of fuel vapor from the fuel tank is stabilized and the purge execution time is short.

According to the fifth aspect of the present invention, when the purge execution time is long and the vapor concentration in the purge passage is high, the purge flow rate is changed according to the engine operating state, and the purge execution time is long. The fuel vapor treatment apparatus for an internal combustion engine according to claim 4, wherein when the vapor concentration in the purge passage is low, the purge flow rate can be fixed regardless of the engine operating state.

According to the fifth aspect of the present invention, even when the generation of fuel vapor from the fuel tank is stabilized and the purge execution time is long, the vapor concentration in the purge passage is reduced. When the temperature is high, the amount of fuel vapor generated in the fuel tank is high due to the high temperature in the fuel tank, and the air-fuel ratio learning is not executed in view of the fact that the purge flow rate is hardly fixed even if the purge flow rate is fixed. Therefore, after the generation of fuel vapor from the fuel tank is stabilized and the purge execution time is long and the vapor concentration in the purge passage is high, the air-fuel ratio is erroneously learned. Can be avoided.

According to the invention described in claim 6, within a predetermined period after the purge is restarted, even if the generation of the fuel vapor from the fuel tank is stabilized, the fuel vapor from the fuel tank can be removed. The fuel vapor treatment device for an internal combustion engine according to claim 2, wherein the generation is regarded as being before the generation becomes stable.

In the evaporative fuel treatment system for an internal combustion engine according to the present invention, even if the purge flow rate is fixed due to the influence of the fuel vapor purged from other than the fuel tank within a predetermined period after the purge is restarted, In view of the fact that the purge flow rate is difficult to be fixed, even after the generation of fuel vapor from the fuel tank is stabilized, it is considered that the generation of fuel vapor from the fuel tank has not yet been stabilized, and the air-fuel ratio learning is performed. Not executed. Therefore, it is possible to prevent the air-fuel ratio from being erroneously learned within a predetermined period after the purge is restarted after the generation of the fuel vapor from the fuel tank is stabilized.

According to the seventh aspect of the present invention, within a predetermined period after the restart of the purge, even if the purge execution time is long, it is considered that the purge execution time is short. According to a fourth aspect of the present invention, there is provided an evaporative fuel processing apparatus for an internal combustion engine.

In the evaporative fuel processing apparatus for an internal combustion engine according to the present invention, even if the purge flow rate is fixed due to the effect of the fuel vapor purged from a portion other than the fuel tank within a predetermined period after the purge is restarted. In view of the fact that the purge flow rate is hard to be fixed, even when the purge execution time is long, it is considered that the purge execution time is short, and the air-fuel ratio learning is not executed. Therefore, it is possible to prevent the air-fuel ratio from being erroneously learned when the purge execution time is long and within a predetermined period after the restart of the purge.

According to an eighth aspect of the present invention, there is provided the evaporative fuel processing apparatus for an internal combustion engine according to the sixth or seventh aspect, wherein the predetermined period is determined according to a purge cut time. You.

In the fuel vapor treatment apparatus for an internal combustion engine according to the present invention, in consideration of the fact that the amount of fuel vapor purged from other than the fuel tank is affected by the purge cut time, the predetermined period is determined by the purge cut time. Is determined. Therefore, it is possible to accurately determine the predetermined period in which the execution of the air-fuel ratio learning should be avoided.

According to the ninth aspect of the present invention, there is provided air-fuel ratio learning execution completion determining means for determining whether or not air-fuel ratio learning has been performed for all regions, and air-fuel ratio learning for all regions has been performed. 2. The evaporative fuel processing of an internal combustion engine according to claim 1, wherein the purge flow rate is not fixed when is executed, and the purge flow rate can be fixed when the air-fuel ratio learning of all the regions has not been executed yet. An apparatus is provided.

In the evaporative fuel processor for an internal combustion engine according to the ninth aspect, the purge flow rate is not fixed when the air-fuel ratio learning for all the regions is performed. Therefore, it is possible to prevent the purge flow rate from being fixed even when it is not necessary to execute the air-fuel ratio learning.

According to the tenth aspect of the present invention, the vapor concentration learning means for calculating the fuel vapor concentration in the purge passage, and the vapor concentration learning for determining whether or not the vapor concentration learning accuracy is good. Accuracy determination means, and when it is determined that the accuracy of the vapor concentration learning is not good after the generation of the fuel vapor from the fuel tank is stabilized, the vapor concentration learning is executed, and the fuel vapor from the fuel tank is determined. The vapor fuel processing apparatus for an internal combustion engine according to claim 1, wherein the vapor concentration learning is not performed when it is determined that the accuracy of the vapor concentration learning is good after the occurrence of is stabilized.

In the evaporative fuel processing apparatus for an internal combustion engine according to the tenth aspect, the vapor concentration learning is not performed when it is determined that the accuracy of the vapor concentration learning is good after the generation of the fuel vapor from the fuel tank is stabilized. . Therefore, it is possible to prevent the vapor concentration learning from being executed more than necessary.

According to the eleventh aspect of the present invention, when the negative pressure in the intake passage is small, it is considered that the vapor concentration learning accuracy is not good. A processing device is provided.

In the fuel vapor treatment apparatus for an internal combustion engine according to the present invention, when the negative pressure in the intake passage is small, the actual purge flow rate cannot be increased to a set value at which the purge flow rate should be fixed, and the fuel vapor concentration changes. In view of this, the purge flow rate is not fixed, and the air-fuel ratio learning is not executed. Therefore, it is possible to prevent the air-fuel ratio from being erroneously learned based on the erroneous purge flow rate.

According to the twelfth aspect of the present invention, the vapor concentration learning means for calculating the fuel vapor concentration in the purge passage, and the vapor concentration learning for determining whether or not the vapor concentration learning accuracy is good. Accuracy purge means, wherein the purge flow rate is fixed to the actual purge flow rate at the time of engine idle operation during which fuel vapor purge is being performed and vapor concentration learning precision is determined to be good. An evaporative fuel treatment device for an internal combustion engine according to claim 1 is provided.

In the evaporative fuel processing apparatus for an internal combustion engine according to the present invention, in consideration of the fact that the influence of the fuel vapor becomes strong due to the small intake air amount during the idle operation of the engine, the fuel vapor is being purged during the execution of the fuel vapor purge. At the time of the engine idling operation in which it is determined that the concentration learning accuracy is good, the purge flow rate is fixed to the actual purge flow rate at that time. Therefore, the reliability of determining whether or not the vapor concentration learning accuracy is good can be improved. Further, since the purge flow rate is fixed to the actual purge flow rate at that time, control of the purge flow rate can be simplified.

According to the thirteenth aspect of the present invention, the vapor concentration learning means for learning the fuel vapor concentration and the elapsed time after the execution of the vapor concentration learning for calculating the elapsed time after the execution of the vapor concentration learning. Calculating means for calculating a purge cut time, a purge cut time calculating means for calculating a purge cut time, and performing vapor concentration learning when the elapsed time after performing the vapor concentration learning is long or when the purge cut time is long. An evaporative fuel treatment device for an internal combustion engine according to claim 1 is provided.

In the fuel vapor treatment apparatus for an internal combustion engine according to the present invention, when the elapsed time after the execution of the vapor concentration learning is long, the vapor concentration learning is forcibly performed in consideration of the fact that the accuracy of the previously learned vapor concentration is reduced. Is executed. Further, when the purge cut time is long, the vapor concentration learning is forcibly executed in view of the great influence of the fuel vapor purged from the parts other than the fuel tank. for that reason,
The vapor concentration learning accuracy can always be maintained at a high level of reliability.

[0031]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram of a first embodiment in which an evaporative fuel treatment apparatus for an internal combustion engine according to the present invention is applied to a multi-cylinder internal combustion engine. In FIG. 1, reference numeral 1 denotes an engine main body, 2 denotes an intake branch, 3 denotes an exhaust manifold, and 4 denotes a fuel injection valve attached to each intake branch 2 respectively. Each intake branch pipe 2 is connected to a common surge tank 5, and this surge tank 5 is connected to an air cleaner 8 via an intake duct 6 and an air flow meter 7. A throttle valve 9 is arranged in the intake duct 6. Further, as shown in FIG. 1, the internal combustion engine includes a canister 11 in which activated carbon 10 is built. The canister 11 has a fuel vapor chamber 12 on each side of the activated carbon 10.
And an atmosphere chamber 13. The fuel vapor chamber 12 is connected on the one hand to the headspace of the fuel tank 15 via a conduit 14,
On the other hand, it is connected to the surge tank 5 via a conduit 16. A purge control valve 17 controlled by an output signal of the electronic control unit 20 is disposed in the conduit 16. The fuel vapor generated in the fuel tank 15 is sent into the canister 11 via the conduit 14 and is adsorbed on the activated carbon 10.
When the purge control valve 17 is opened, air is sent from the atmosphere chamber 13 through the activated carbon 10 and into the conduit 16. When air passes through the activated carbon 10, the fuel vapor adsorbed on the activated carbon 10 is desorbed from the activated carbon 10, so that the air containing the fuel vapor, that is, the fuel vapor is supplied to the surge tank 5 through the conduit 16 in the surge tank 5. Purged.

The electronic control unit 20 is composed of a digital computer, and a ROM (read only memory) 22, a RAM (random access memory) 23, a CPU (microprocessor) 24, and an input port 25 interconnected by a bidirectional bus 21. And an output port 26. The air flow meter 7 generates an output voltage proportional to the amount of intake air, and the output voltage corresponds to the corresponding A / D converter 2.
7 to the input port 25. A throttle switch 28 that is turned on when the throttle valve 9 is at the idling opening is attached to the throttle valve 9, and an output signal of the throttle switch 28 is input to an input port 25. A water temperature sensor 29 for generating an output voltage proportional to the engine cooling water temperature is attached to the engine body 1, and the output voltage of the water temperature sensor 29 is input to the input port 25 via the corresponding AD converter 27. An air-fuel ratio sensor (hereinafter referred to as an “O ₂ sensor”) 30 is attached to the exhaust manifold 3, and an output signal of the O ₂ sensor 30 is input to an input port 25 via a corresponding AD converter 27.

The fuel vapor chamber 12 is connected to a pressure sensor 32 via a conduit 31, and the pressure sensor 32 detects the pressure in the fuel vapor chamber 12. The pressure sensor 32 detects the pressure in the fuel vapor chamber 12, that is, the fuel tank 15
Generates an output voltage proportional to the pressure of the conduit 16 from the upper space of the fuel tank 15 to the purge control valve 17, and this output voltage is input to the input port 25 via the corresponding AD converter 27. . Further, the input port 25 is connected to a crank angle sensor 33 that generates an output pulse every time the crankshaft rotates, for example, 30 degrees. CP
In U24, the engine speed is calculated based on the output pulse. On the other hand, the output ports 26 are connected to the fuel injection valve 4 and the purge control valve 17 via the corresponding drive circuits 34, respectively.

FIGS. 2 and 3 are flowcharts showing the main routine of the method for controlling the air-fuel ratio of the internal combustion engine by the evaporative fuel processing apparatus shown in FIG. The evaporative fuel processing apparatus executes a main routine at predetermined intervals such as 16 msec. When the execution of the main routine is started, first, in step 201, a feedback correction coefficient FAF, which is a correction coefficient serving as a basis for air-fuel ratio control, is calculated.

FIG. 4 is a flowchart showing the feedback correction coefficient FAF calculation routine 201 shown in FIGS. As shown in FIG. 4, the feedback correction coefficient F
In the AF calculation routine, first, in step 400, it is determined whether or not the feedback control condition of the air-fuel ratio is satisfied, such as the cooling water temperature has become equal to or higher than a predetermined temperature, the fuel is not being cut, and the air-fuel ratio sensor has been activated. Is determined.
When the feedback control condition is not satisfied, the routine proceeds to step 413, where the feedback correction coefficient FAF is fixed at 1.0, and then, at step 414, the average value FAFAV of the feedback correction coefficient is fixed at 1.0. Next, the routine proceeds to step 412. On the other hand, when the feedback control condition is satisfied, the routine proceeds to step 401.

In step 401, it is determined whether or not the output voltage V of the O ₂ sensor 30 is higher than 0.45 (V), that is, whether or not the output voltage is rich. When V ≧ 0.45 (V), that is, when rich, the routine proceeds to step 402, where it is determined whether or not the engine was lean during the previous processing cycle. When the process is lean in the previous processing cycle, that is, when the state has changed from lean to rich, the routine proceeds to step 403, where the feedback correction coefficient FAF is set to FAFL, and the routine proceeds to step 404. In step 1304, the skip component S is subtracted from the feedback correction coefficient FAF. Therefore, the feedback correction coefficient FAF is rapidly reduced by the skip component S. Next, the routine proceeds to step 405. On the other hand, if it is determined in step 402 that the air conditioner was rich in the previous processing cycle, the process proceeds to step 40.
Then, the process proceeds to step S7, where the integral component K (K） S) is subtracted from the feedback correction coefficient FAF. Therefore, the feedback correction coefficient FAF is gradually reduced.

On the other hand, in step 401, V <0.4
When it is determined that the value is 5 (V), that is, when the engine is lean, the process proceeds to step 408, and it is determined whether or not the fuel cell was rich in the previous processing cycle. When rich in the previous processing cycle, that is, when the state changes from rich to lean, the routine proceeds to step 409, where the feedback correction coefficient F
AF is set to FAFR, and the routine proceeds to step 410. In step 410, the skip component S is added to the feedback correction coefficient FAF.
AF is rapidly increased by the skip component S. Next, the routine proceeds to step 405. On the other hand, when it is determined in step 408 that the current processing cycle is lean, the process proceeds to step 411, where the integral component K is added to the feedback correction coefficient FAF. Therefore, the feedback correction coefficient FAF is gradually increased.

In step 405, an average value FAFAV of FAFL and FAFR is calculated. That is, the average value FAF
AV is a variation average value of the feedback correction coefficient FAF, and is an average value of FAFL and FAFR. Next, at step 406, a skip flag is set.

In step 412, the feedback correction coefficient FAF is guarded by the upper limit 1.2 and the lower limit 0.8 of the allowable fluctuation range. That is, the value of the FAF is guarded so that the FAF does not become larger than 1.2 and does not become smaller than 0.8. As will be described later, when the air-fuel ratio becomes rich and the FAF becomes small, the fuel injection time TAU becomes short. When the air-fuel ratio becomes lean and the FAF becomes large, the fuel injection time TAU becomes long, so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. Will be maintained. When step 412 ends, the feedback correction coefficient FAF calculation routine ends.

Returning to the description of FIGS. 2 and 3, subsequently, at step 202, the manufacturing errors of the fuel injection valve, the air-fuel ratio sensor, etc.,
An air-fuel ratio learning region is calculated for calculating an air-fuel ratio learning region in which air-fuel ratio learning that suppresses a deviation of the air-fuel ratio due to aging degradation or the like is performed. FIG. 5 is a flowchart showing an air-fuel ratio learning area calculation routine of FIGS. 2 and 3. As shown in FIG. 5, in the air-fuel ratio learning area calculation routine, first, in step 501, an area j in which air-fuel ratio learning is to be performed based on, for example, an intake air amount is calculated. That is, in the present embodiment, the air-fuel ratio learning region is divided into a total of five regions including one region for the idle operation of the engine and four regions for the non-idle operation of the engine. , One area in which the air-fuel ratio learning is to be executed is selected from the five areas. Then step 50
In step 2, it is determined whether or not the area j-1 is the same as the area j. If YES, this routine is terminated.
If NO, skip counter CS in step 503
KIP is set to zero, and this routine ends.

Returning to the description of FIGS. 2 and 3, subsequently, at step 203, it is determined whether the air-fuel ratio learning condition is satisfied. If NO, purge cut is performed in step 211 (the duty ratio DPG ← 0 of the purge control valve 17 and the purge rate PGR ← 0). On the other hand, if YES, the process proceeds to step 204. In step 204, it is determined whether or not the purge condition is satisfied, specifically, for example, whether or not warm-up has been completed, whether or not fuel supply has not been stopped, and the like. If NO, step 209 is executed in step 2
Purge cutting is performed in the same manner as in step 11, and then step 210
The air-fuel ratio learning is performed at.

FIG. 6 is a flowchart showing the air-fuel ratio learning routine of FIGS. 2 and 3. As shown in FIG. 6, in the air-fuel ratio learning routine, first, at step 601, it is determined whether or not the skip counter CSKIP is 3 or more. In the case of NO, the average value FAFAV of the feedback correction coefficient in both the current area j and the previous area has to be calculated although the average value FAFAV of the feedback correction coefficient in the current area j has to be calculated.
In order to prevent V from being calculated, the routine ends without calculating the average value FAFAV of the feedback correction coefficient and performing the air-fuel ratio learning. On the other hand, Y
In the case of ES, the process proceeds to step 602.

In step 602, it is determined whether or not the calculated average value FAFAV of the feedback correction coefficient is 0.98 or less. If YES, step 605
At which the air-fuel ratio learning coefficient KGj is decreased (KG
j ← KGj−x), the process proceeds to step 603 if NO. In step 603, it is determined whether the calculated average value FAFAV of the feedback correction coefficient is equal to or greater than 1.02. If YES, the air-fuel ratio learning coefficient KGj is increased in step 606 (KGj ← KG
j + x), if NO, proceed to step 604. In step 604, the air-fuel ratio learning completion flag XKGj = 1 indicating that the air-fuel ratio learning in the current region j has been completed is set, and this routine ends.

Returning to FIGS. 2 and 3, when YES is determined in step 204, the process proceeds to step 205.
In steps 205 to 207, it is determined whether or not a condition for fixing the purge flow rate, which is a necessary condition for executing the air-fuel ratio learning, is satisfied even when the purge cut is not performed. More specifically, first, at step 205, the total purge flow rate QPGTOT after the engine is started
It is determined whether or not AL is equal to or greater than a predetermined set value KQPG. When the determination is NO, it is determined that the generation of the fuel vapor from the fuel tank 15 has not yet been stabilized, and it is determined that accurate air-fuel ratio learning cannot be performed. That is, the air-fuel ratio learning in step 219 is not performed. On the other hand, if YES, the process proceeds to step 206.

In step 206, it is determined whether or not the purge execution time CPGR after starting the engine is equal to or longer than a predetermined set value KCPGR. In the case of NO, even if the purge flow rate is to be fixed, it is actually difficult to fix the purge flow rate, that is, it is determined that a large amount of purge is required, and the routine proceeds to step 220. That is, the air-fuel ratio learning in step 219 is not performed. On the other hand, if YES, the process proceeds to step 207. In step 207, it is determined whether the fuel vapor concentration FGPG in the conduit 16 as the purge passage is equal to or higher than a predetermined set value KFGPG. Y
At the time of ES, since the temperature in the fuel tank 15 is high, the amount of fuel vapor generated in the fuel tank 15 is large, and it is determined that the purge flow rate is not actually fixed even if the purge flow rate is fixed. . That is, the air-fuel ratio learning in step 219 is not performed. on the other hand,
If NO, the process proceeds to step 208. In step 208, it is determined whether the air-fuel ratio learning has been completed for all the regions. If YES, the process proceeds to step 220, that is, the air-fuel ratio learning in step 219 is not executed. On the other hand, if NO, the process proceeds to step 212,
A fixed purge flow rate control is executed to fix the purge flow rate.

FIG. 7 is a flowchart showing the fixed purge flow rate control routine of FIGS. 2 and 3. As shown in FIG. 7, in the fixed purge flow rate control routine, first in step 701, the duty ratio DP of the purge control valve 17 is set.
G is a predetermined fixed purge flow rate KQPGR and FIG.
Full-open purge flow rate QP10 calculated from the map shown in FIG.
0 (DPG ← KQPGR / QP100
× 100 ≦ 100). FIG. 14 is a map for calculating the fully open purge flow rate QP from the intake branch pipe negative pressure Pm, that is, the purge flow rate when the purge control valve 17 is fully opened.
As shown in FIG. 14, the full-open purge flow rate QP100 increases as the intake branch pipe negative pressure Pm increases, that is, as the intake air amount Ga decreases. Further, the fixed purge flow rate KQPGR is set to a value smaller than the maximum value of the full-open purge flow rate QP100.

Returning to the description of FIG.
Then, the purge rate PGR is calculated from the full open purge rate PG100 and the duty ratio DPG (PGR ← PG100 ×
DPG / 100). Here, the full open purge rate PG100 is a ratio between the full open purge flow rate QP100 and the intake air amount Ga (PG100 = QP100 / Ga × 100), and the intake air amount Ga is detected by the air flow meter 7. still,
In another embodiment, the full-open purge rate PG100 is obtained by an experiment in advance as a function of, for example, the engine load Q / N (intake air amount Ga / engine speed N) and the engine speed N. It is also possible to store the information in advance in the ROM 22.

[0049]

[Table 1]

As the engine load Q / N decreases, the full-open purge flow rate QP100 with respect to the intake air amount Ga increases. Therefore, as shown in Table 1, the full-open purge rate PG100 increases as the engine load Q / N decreases, and the engine speed increases. As the number N decreases, the full-open purge flow rate QP100 with respect to the intake air amount Ga increases. Therefore, as shown in Table 1, the full-open purge rate PG100 increases as the engine speed N decreases.

Returning to the description of FIG.
In step 704, the coefficient DPG0 relating to the duty ratio is updated by the current duty ratio DPG (DPG0 ← DPG), and in step 704, the coefficient PGR0 relating to the purge rate is updated by the current purge rate PGR (PGR0 ← PG).
R). Next, at step 705, the purge counter CPG
R is incremented (CPGR ← CPGR + 1),
In step 706, the total purge flow rate is integrated (QPGT
OTAL ← QPGTOTAL + QP100 × DPG / 1
00), this routine ends.

Returning to the description of FIG. 2 and FIG.
At 0, the calculation of the purge rate is executed. Specifically, the purge flow rate is not fixed to the fixed purge flow rate KQPGR, but the target purge rate is changed according to the value of the feedback correction coefficient FAF. FIGS. 8 and 9 are flowcharts showing the purge rate calculation routine 220 shown in FIGS. As shown in FIGS. 8 and 9, in the purge rate calculation routine, first, in step 801, it is determined whether it is time to calculate the duty ratio of the drive pulse of the purge control valve 17. In the present embodiment, the calculation of the duty ratio is 100
Performed every msec. If it is not time to calculate the duty ratio, the purge rate calculation routine ends as it is. On the other hand, when it is time to calculate the duty ratio, the process proceeds to step 801 to determine whether the purge condition 1 is satisfied.
For example, it is determined whether the warm-up is completed. When the purge condition 1 is not satisfied, the routine proceeds to step 808, where an initialization process is performed. Next, in step 809, the duty ratio DPG and the purge rate PGR are set to zero, and the purge rate calculation routine ends. On the other hand, when the purge condition 1 is satisfied, the process proceeds to step 803 to determine whether the purge condition 2 is satisfied, for example, whether the air-fuel ratio feedback control is being performed, and whether the fuel supply is stopped. It is determined whether or not there is. When the purge condition 2 is not satisfied, the process proceeds to step 809. When the purge condition 2 is satisfied, the process proceeds to step 804.

At step 804, the fully open purge flow rate QP1
Full purge ratio PG1 which is the ratio of the air amount 00 to the intake air amount Ga.
00 (← (QP100 / Ga) · 100) is calculated. Here, the full-open purge flow rate QP100 is the purge control valve 1
7 indicates the purge flow rate when fully opened, and the intake air amount Ga is detected by the air flow meter 7. The full open purge rate PG100 is obtained in the same manner as in the case described in step 702. Next, step 805
Then, the feedback correction coefficient FAF becomes the upper limit value KFAF1.
5 (= 1.15) and lower limit value KFAF85 (= 0.85)
Is determined. KFAF15> FA
If F> KFAF85, that is, if the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio, step 80
Proceed to 6. In step 806, the target purge rate tPG is calculated by adding a constant value KPGRu to the purge rate PGR.
R is calculated (tPGR ← PGR + KPGRu). That is, it is understood that when KFAF15>FAF> KFAF85, the target purge rate tPGR is gradually increased every 100 msec. Note that this target purge rate tPGR
Is set to an upper limit value P (P is, for example, 6%), so that the target purge rate tPGR can only increase to the upper limit value P. Next, the routine proceeds to step 810.

On the other hand, at step 805, FAF ≧ K
If it is determined that FAF15 or FAF ≦ KFAF85, the routine proceeds to step 807, where the purge rate P
The target purge rate tPGR is calculated by subtracting a constant value KPGRd from GR (tPGR ← PGR-K).
PGRd). That is, if the air-fuel ratio cannot be maintained at the stoichiometric air-fuel ratio due to the fuel vapor purge action, the target purge rate t
PGR is reduced. Note that the target purge rate tPG
A lower limit value S (S = 0%) is set for R.
Next, the routine proceeds to step 810.

At step 810, the target purge rate tPGR
Is divided by the full-open purge rate PG100 to calculate the duty ratio DPG of the drive pulse of the purge control valve 17 (DPG ← (tPGR / PG100) · 10
0 ≦ 100%). Therefore, the duty ratio DPG of the drive pulse of the purge control valve 17, that is, the opening amount of the purge control valve 17 is the target purge rate tPG with respect to the full open purge rate PG100.
It will be controlled according to the ratio of R. As described above, when the opening amount of the purge control valve 17 is controlled in accordance with the ratio of the target purge rate tPGR to the fully open purge rate PG100, regardless of the purge rate of the target purge rate tPGR, regardless of the operating state of the engine. The actual purge rate is maintained at the target purge rate.

For example, now, the target purge rate tPGR is 2%, and the fully open purge rate PG100 in the current operating state is set.
Is 10%, the drive pulse duty ratio D
PG is 20%, and the actual purge rate at this time is 2%
Becomes Next, if the operation state changes, and if the fully open purge rate PG100 in the changed operation state becomes 5%, the duty ratio DPG of the drive pulse becomes 40%, and the actual purge rate at this time becomes 2%. That is, if the target purge rate tPGR is 2%, the actual purge rate becomes 2% regardless of the operating state of the engine, and the target purge rate tPGR
Is changed to 4%, the actual purge rate is maintained at 4% regardless of the operating state of the engine.

Next, at step 811, the fully open purge rate P
The actual purge rate PGR is calculated by multiplying G100 by the duty ratio DPG (PGR ← PG10
0 · (DPG / 100)). That is, as described above, the duty ratio DPG is represented by (tPGR / PG100) · 100. In this case, when the target purge rate tPGR becomes larger than the full-open purge rate PG100, the duty ratio DPG becomes 100% or more. However, the duty ratio DPG
Cannot be more than 100%, and the duty ratio D
Since PG is set to 100%, the actual purge rate PGR becomes smaller than the target purge rate tPGR. Therefore, the actual purge rate PGR is PG100 · (DPG /
100).

Next, at step 812, the coefficient DPG0 relating to the duty ratio is updated by the current duty ratio DPG (DPG0 ← DPG), and the coefficient PGR0 relating to the purge rate is updated by the current purge rate PGR (P
GR0 ← PGR Next, at step 813, a purge execution time counter CPGR representing the time since the start of the purge is incremented by 1 (CPGR ← C).
PGR + 1), and terminates the purge rate calculation routine.

Returning to the description of FIG. 2 and FIG.
From 3 to step 218, it is determined whether or not the learning accuracy of the fuel vapor concentration is good. In detail, step 213
It is determined whether the flag XFGPG = 1 indicating that the learning accuracy of the fuel vapor concentration is good is set. In the case of YES, it is determined that it is not necessary to perform the vapor concentration learning in step 221, and it is determined that it is suitable for performing the air-fuel ratio learning under the fixed purge flow rate, and the process proceeds to step 219 to execute the air-fuel ratio learning. On the other hand, if NO, the process proceeds to step 214. In step 214, it is determined whether or not the air-fuel ratio learning completion flag XKGj = 1 indicating that the air-fuel ratio learning in the region j has been completed is set. If NO, proceed to step 221 and YES
In step 215, the process proceeds to step 215.

At step 215, the skip counter C
It is determined whether SKIP is 3 or more. When the determination is NO, it is determined that the learning accuracy of the fuel vapor concentration is not good, and the process proceeds to step 221. When the determination is YES, the process proceeds to step 216. In step 216, it is determined whether the average value FAFAV of the feedback correction coefficient is 0.98 or less. If YES, it is determined that the learning accuracy of the fuel vapor concentration is not good, and the process proceeds to step 221. If NO, the process proceeds to step 217. Step 21
At 7, it is determined whether or not the average value FAFAV of the feedback correction coefficient is 1.02 or more. If YES, it is determined that the learning accuracy of the fuel vapor concentration is not good, and the process proceeds to step 221. If NO, the process proceeds to step 21.
Proceed to 8. When the process proceeds to step 218, it is determined that the learning accuracy of the fuel vapor concentration is good, and in step 218, a flag XFGPG = 1 indicating that the learning accuracy of the fuel vapor concentration is good is set (XFGPG ← 1). Next, at step 219, the air-fuel ratio learning shown in FIG.

That is, in the present embodiment, step 212
, The purge flow rate is fixed during the execution of the fuel vapor purge, and in step 219, the air-fuel ratio learning is executed. Therefore, even while purging fuel vapor,
Air-fuel ratio learning during purge cut of fuel vapor (step 2
As in the case of 10), accurate air-fuel ratio learning can be executed in step 219. Further, since the execution of the air-fuel ratio learning can be performed even during the execution of the fuel vapor purge, the necessity of performing the fuel vapor purge cut in order to execute the air-fuel ratio learning is eliminated. The vapor purge amount can be increased.

Returning to the description of FIG. 2 and FIG.
In step 1, vapor concentration learning is performed. FIG. 10 is a flowchart showing the vapor concentration learning routine 221 of FIGS. As shown in FIG. 10, in the vapor concentration learning routine, first, in step 1001, whether the average value FAFAV of the feedback correction coefficient is within a certain range, that is, whether 1.02>FAFAV> 0.98 is satisfied. It is determined whether or not it is. When the average value FAFAV of the feedback correction coefficient is within the set range, that is, 1.02
If>FAFAV> 0.98, step 100
The routine proceeds to step 3, where the update amount tFG of the vapor concentration FGPG per unit purge rate is set to zero, and then the routine proceeds to step 1004. Therefore, at this time, the vapor concentration FGPG is not updated.

On the other hand, if it is determined in step 1001 that the average value FAFAV of the feedback correction coefficient exceeds a certain range, that is, if FAFAV ≧ 1.02 or FAFAV ≦ 0.98, the routine proceeds to step 1002. The update amount tFG of the vapor concentration FGPG is calculated based on the following equation.

TFG ← (1.0−FAFAV) / (PGR · a) where a is a constant (for example, 2). That is, if the average value FAFAV of the feedback correction coefficient exceeds the set range (between 0.98 and 1.02), the FAFAV for 1.0
Is set as the update amount tFG. Next, the routine proceeds to step 1004. In step 1004, the vapor concentration F
The update amount tFG is added to the GPG (FGPG ← FGP
G + tFG). Next, at step 1005, an update number counter CF indicating the number of updates of the vapor concentration FGPG.
GPG is incremented by 1 (CFGPG ← CF
GPG + 1), and ends this routine.

Returning to the description of FIG. 2 and FIG.
In step 2, the fuel injection time TAU is calculated. FIG. 11 shows FIG.
4 is a flowchart illustrating a fuel injection time calculation routine 222 of FIG. 3. As shown in FIG. 11, in the fuel injection time calculation routine, first, in step 1101, the basic fuel injection time TP is calculated based on the engine load Q / N and the engine speed N. Then step 1102
In, the correction coefficient FW for increasing the warm-up is calculated. Next, at step 1103, the purge air-fuel ratio correction coefficient FPG is calculated by multiplying the vapor concentration FGPG per unit purge rate by the purge rate PGR (FPG ← FG).
PG / PGR). Next, at step 1104, the fuel injection time TAU is calculated based on the following equation, and the fuel injection time calculation routine ends, and the main routine of FIGS. 2 and 3 ends.

TAU ← TP · FW · (FAF + KGj−FPG) Here, each coefficient represents the following. TP: Basic fuel injection time FW: Correction coefficient FAF: Feedback correction coefficient KGj: Air-fuel ratio learning coefficient FPG: Purge air-fuel ratio correction coefficient

The basic fuel injection time TP is an injection time determined by an experiment necessary for setting the air-fuel ratio to the target air-fuel ratio, and the basic fuel injection time TP is the engine load Q / N
(Intake air amount Ga / engine speed N) and engine speed N
Is stored in the ROM 22 in advance as a function of The correction coefficient FW collectively represents the warm-up increase coefficient and the acceleration increase coefficient.
= 1.0.

The feedback correction coefficient FAF is provided for controlling the air-fuel ratio to the target air-fuel ratio based on the output signal of the O ₂ sensor 30. Purge air-fuel ratio correction coefficient FP
G is set to FPG = 0 from the start of the operation of the engine to the start of the purge, and becomes larger as the fuel vapor concentration FGPG becomes higher when the purge action is started. When the purge operation is temporarily stopped during the operation of the engine, FPG is set to 0 during the stop period of the purge operation.

As described above, the feedback correction coefficient FAF is for controlling the air-fuel ratio to the target air-fuel ratio based on the output signal of the O ₂ sensor 30. In this case, any air-fuel ratio may be used as the target air-fuel ratio, but in the present embodiment, the target air-fuel ratio is set to the stoichiometric air-fuel ratio. When the target air-fuel ratio is the stoichiometric air-fuel ratio, an O ₂ sensor whose output voltage changes according to the oxygen concentration in the exhaust gas is used as the air-fuel ratio sensor 30. When the air-fuel ratio is on the rich side, that is, when the air-fuel ratio is rich, the O ₂ sensor 30 is set to 0.
An output voltage of about 9 (V) is generated, and when the air-fuel ratio is lean, that is, lean, an output voltage of about 0.1 (V) is generated.

Next, referring to FIG. 12, the evaporative fuel of the internal combustion engine of this embodiment is interrupted with respect to the main routine of FIGS. 2 and 3 every 100 msec, for example, corresponding to a duty ratio calculation cycle described later. The interrupt routine of the processing device will be described. FIG. 12 is a flowchart showing a purge control valve driving processing routine of the fuel vapor processing apparatus for an internal combustion engine according to the present embodiment. As shown in FIG. 12, in the purge control valve drive processing routine, first, in step 1
At 201, it is determined whether or not it is the output cycle of the duty ratio, that is, whether or not it is the rising cycle of the drive pulse of the purge control valve 17. If it is the output cycle of the duty ratio, the routine proceeds to step 1202, where it is determined whether or not the duty ratio DPG = 0. When DPG = 0, the routine proceeds to step 1206, where the drive pulse YEV for the purge control valve 17 is set.
P is turned off. On the other hand, when DPG is not 0, the routine proceeds to step 1203, where the drive pulse YEVP of the purge control valve 17 is turned on. Then step 120
At 4, the off-time TDPG of the drive pulse is calculated by adding the duty ratio DPG to the current time TIMER (TDPG ← DPG + TIMER), and the purge control valve drive processing routine ends.

On the other hand, if it is determined in step 1201 that it is not the output cycle of the duty ratio, the flow advances to step 1205 to determine whether or not the current time TIMER is the drive pulse off time TDPG. TDPG
When = TIMER, the routine proceeds to step 1206, where the drive pulse YEVP is turned off, and the purge control valve drive processing routine is terminated. On the other hand, when TDPG is not TIMER, the purge control valve drive processing routine is directly terminated.

Hereinafter, the effect of the control according to the present embodiment will be described with reference to FIG. 13 and FIG. FIG. 13 shows a purge rate PGR, a duty ratio DPG, and a purge flow rate QPG.
R, intake branch pipe negative pressure Pm, intake air amount Ga, and vehicle speed SP
FIG. 6 is a diagram showing a relationship between D and time in a case where a purge flow rate is fixed at the time of learning of an air-fuel ratio according to the present embodiment and a case where a purge rate is fixed at the time of learning of an air-fuel ratio. See Figure 1 for details
FIG. 3A is a diagram showing the embodiment in which the purge flow rate is fixed at the time of learning the air-fuel ratio, and FIG. 13B is a diagram showing that the purge rate is fixed at the time of learning the air-fuel ratio. FIG.
As shown in (a), in the present embodiment in which the purge flow rate is fixed during the air-fuel ratio learning, the purge flow rate QPGR is fixed to a predetermined set value, and the purge rate PGR is set to the purge flow rate QPGR fixed to the set value. And the intake air amount Ga. On the other hand, as shown in FIG. 13B, when the purge rate is fixed during the air-fuel ratio learning, the purge rate PGR is maintained at a predetermined upper limit (set purge rate), and the purge flow rate QPGR is maintained at the upper limit. The obtained purge rate PGR and the intake air amount Ga are obtained.

FIG. 15 is a graph showing the relationship between the purge flow rate QPGR, the purge air-fuel ratio correction coefficient FPG, the fuel vapor concentration FGPG, the purge rate PGR, and the intake air amount Ga in comparison with the present embodiment and the conventional one. It is. See Figure 1 for details
FIG. 5 (a) is a diagram showing the embodiment in which the purge flow rate is fixed at the time of learning of the air-fuel ratio, and FIG. 15 (b) is a diagram showing that the purge rate is fixed at the time of learning of the air-fuel ratio. FIG.
As shown in (a), the purge flow rate QPGR does not change even when the intake air amount Ga changes. Therefore, the purge rate PG
R changes in inverse proportion to the intake air amount Ga. Further, under the condition that the purge flow rate QPGR is fixed, the generation of fuel vapor from the fuel tank is stable, and the purge flow rate QPGR is fixed, so that the fuel vapor concentration FGPG in the purge passage becomes constant. As a result, the purge air-fuel ratio correction coefficient FPG (= FGPG × PGR) changes in inverse proportion to the intake air amount Ga. That is, the purge flow rate QP
Since GR is fixed, the amount of fuel vapor supplied into the cylinder becomes constant regardless of the intake air amount Ga. Therefore, the feedback correction coefficient FAF is not affected by the influence of the fuel vapor. Therefore, it is possible to learn other deviations from the air-fuel ratio.

On the other hand, as shown in FIG. 15B, when the purge rate PGR is maintained at the upper limit regardless of the intake air amount Ga, the purge flow rate QPGR is increased with the increase of the intake air amount Ga.
Increase. When the purge flow rate QPGR increases, the fuel vapor in the purge passage moves below the canister 11 (FIG. 1).
Fuel gas concentration FG
PG decreases. As a result, the purge air-fuel ratio correction coefficient FP
G (= FGPG × PGR) indicates that when the intake air amount Ga changes, the change in the purge flow rate QPGR and the fuel vapor concentration F
It changes under the influence of the change in GPG. That is,
Since the purge flow rate QPGR is not fixed, the amount of fuel vapor supplied into the cylinder changes, and the feedback correction coefficient FAF becomes rough under the influence of the fuel vapor. Therefore, the air-fuel ratio learning for other deviations cannot be performed accurately, and the erroneous air-fuel ratio learning is performed.

As described above, in the evaporative fuel processing system for an internal combustion engine according to the present embodiment, during the execution of the purge of the fuel vapor,
That is, when the purge cut is not performed, the purge flow rate is fixed in step 212, and the air-fuel ratio learning is executed in step 219. Since the air-fuel ratio learning is performed with the purge flow rate being fixed, accurate air-fuel ratio learning can be performed even while the fuel vapor is being purged in the same manner as during the fuel vapor purge cut. Further, since the execution of the air-fuel ratio learning can be performed even during the execution of the fuel vapor purge, the necessity of performing the fuel vapor purge cut in order to execute the air-fuel ratio learning is eliminated. The vapor purge amount can be increased.

Further, in the evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment, when the generation of fuel vapor from the fuel tank is not stabilized in step 205, that is, when it is determined that the total purge flow rate is small, the purge flow rate In consideration of the fact that it is difficult to fix the purge flow rate in practice, the process proceeds to step 220, and the air-fuel ratio learning in step 219 is not executed. Therefore, it is possible to prevent the air-fuel ratio from being erroneously learned before the generation of the fuel vapor from the fuel tank is stabilized, that is, when the total purge flow rate is small.

Further, in the evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment, even if it is determined in step 205 that the generation of fuel vapor from the fuel tank has been stabilized, the purge execution time is determined in step 206. When it is determined that the purge flow rate is short, in consideration of the fact that the purge flow rate is actually hard to be fixed even when the purge flow rate is fixed,
Proceeding to step 220, the air-fuel ratio learning in step 219 is not performed. Therefore, it is possible to avoid erroneous learning of the air-fuel ratio after the generation of fuel vapor from the fuel tank is stabilized and the purge execution time is short.

Further, in the evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment, it is determined in step 205 that the generation of fuel vapor from the fuel tank has been stabilized, and it is determined in step 206 that the purge execution time is long. In any case, if it is determined in step 207 that the vapor concentration in the purge passage is high, the fuel tank 15
In view of the fact that a large amount of fuel vapor is generated in the fuel tank 15 due to the high temperature inside the fuel tank 15 and it is actually difficult to fix the purge flow rate even if the purge flow rate is fixed, step 2
Proceeding to 20, the air-fuel ratio learning in step 219 is not executed. Therefore, after the generation of fuel vapor from the fuel tank is stabilized and the purge execution time is long and the vapor concentration in the purge passage is high, the air-fuel ratio is erroneously learned. Can be avoided.

Further, in the evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment, when it is determined in step 208 that the air-fuel ratio learning for all the regions has been performed, step 2 is executed.
Proceeding to 20, the fixed purge flow rate control in step 212 is not executed. Therefore, it is possible to prevent the purge flow rate from being fixed even when it is not necessary to execute the air-fuel ratio learning.

Further, in the evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment, when it is determined that the vapor concentration learning accuracy is good in steps 213 to 218, the process proceeds to step 219, and the vapor concentration learning in step 221 is not executed. Therefore, it is possible to prevent the vapor concentration learning from being executed more than necessary.

FIG. 16 is a flow chart showing a part of a main routine of an internal combustion engine air-fuel ratio control method according to a second embodiment of the internal combustion engine evaporation fuel processing apparatus of the present invention. The evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment has the same configuration as the above-described evaporative fuel processing apparatus for an internal combustion engine according to the first embodiment, unless otherwise specified. As shown in FIG. 16, when NO is determined in step 208 of FIG. 2, it is determined in step 1601 whether or not a flag XFGPG0 = 1 indicating that the learning accuracy of the fuel vapor concentration is good is set. . If YES, the process proceeds to step 212, and if NO, the process proceeds to step 1602. In step 1602, it is determined whether a flag XKGj = 1 indicating that the air-fuel ratio learning has been completed is set. If NO, the process proceeds to step 221 and Y
In the case of ES, the process proceeds to step 1603.

At step 1603, it is determined whether or not the step counter CSKIP is 3 or more. When the determination is NO, it is determined that the learning accuracy of the fuel vapor concentration is not good, and the process proceeds to step 221. When the determination is YES, the process proceeds to step 1604. In step 1604, it is determined whether the average value FAFAV of the feedback correction coefficient is 0.98 or less. If YES, it is determined that the learning accuracy of the fuel vapor concentration is not good, and step 221 is performed.
The process proceeds to step 1605 if NO. In step 1605, the average value FA of the feedback correction coefficient
It is determined whether the FAV is equal to or greater than 1.02. YE
In the case of S, it is determined that the learning accuracy of the fuel vapor concentration is not good, and the process proceeds to step 221, and in the case of NO, the process proceeds to step 1606. In step 1606, it is determined whether the engine is idling. In the case of NO,
Step 221 determines that the engine operating conditions are not appropriate for determining whether the learning accuracy of the fuel vapor concentration is good.
Proceed to. On the other hand, when YES, it is determined that the engine operating conditions are appropriate to determine whether the learning accuracy of the fuel vapor concentration is good, and it is determined that the learning accuracy of the fuel vapor concentration under that condition is good. A flag XFGPG0 = 1 indicating that the learning accuracy of the fuel vapor concentration is good is set (XFGPG0 ← 0).

Next, at step 1608, the current purge flow rate QPGR (= QP100 × DPG / 100) is set to the fixed purge flow rate set value KQPGR to be fixed (KQPGR ← QP100 × DPG / 100). That is, in the above-described first embodiment, the set value KQPGR of the fixed purge flow rate is a predetermined value. However, in the present embodiment, the engine when the learning accuracy of the fuel vapor concentration is determined to be good is determined. The purge flow rate during the idling operation is set to a fixed purge flow rate set value KQPGR to be fixed. Next, at step 212, the fixed purge flow rate control is executed as in the case of the first embodiment.

In the evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment, in consideration of the fact that the influence of the fuel vapor is increased due to the small intake air amount during the engine idling operation, the fuel vapor is being purged, and From 1602 to 1605, when it is determined that the vapor concentration learning accuracy is good, and when it is determined in step 1606 that the engine is idling, the purge flow rate is fixed to the actual purge flow rate at that time in steps 1608 and 212. You. Therefore, the reliability of determining whether or not the vapor concentration learning accuracy is good can be improved.
Further, since the purge flow rate is fixed to the actual purge flow rate at that time, control of the purge flow rate can be simplified.

Hereinafter, a third embodiment of the fuel vapor treatment system for an internal combustion engine according to the present invention will be described. The evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment has the same configuration as the above-described evaporative fuel processing apparatus for an internal combustion engine according to the first embodiment, unless otherwise specified. FIG. 17 shows the total purge flow rate QPGTOT used in step 205 of FIGS.
10 is a flowchart illustrating a purge counter control routine that is executed every 100 msec to change the purge execution time CPGR used in AL and step 206. As shown in FIG. 17, in the purge counter control routine of the present embodiment, first, in step 1701, it is determined whether or not purging is currently being performed. Y
In the case of ES, the process proceeds to step 1704, and in the case of NO, the process proceeds to step 1702. In step 1702, the counter CPGR indicating the purge execution time is decremented by a predetermined value KC (CPGR ← CPGR-KC), and then step 17
In 03, the total purge flow rate QPGTOTAL is subtracted by a predetermined value KQ (QPGTOTAL ← QPGTOTAL-K
Q), this routine ends.

In step 1704, the purge execution time C
It is determined whether or not the PGR is equal to or greater than the predetermined set value KCPGR used in step 206 of FIGS. If YES, the upper limit of the purge execution time CPGR is guarded by the set value KCPGR in step 1705 (CPGR ← KCPGR), and if NO, the process directly proceeds to step 1706. In step 1706, the total purge flow rate QPGTOTAL is set to the predetermined set value KQ used in step 205 of FIGS.
It is determined whether it is equal to or greater than PG. If yes,
In step 1707, the total purge flow rate QPGTOTA
The upper limit of L is guarded by the set value KQPG (QPGT
If OTAL ← KQPG), NO, this routine is terminated.

In the evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment, even if an attempt is made to fix the purge flow rate due to the influence of the fuel vapor purged from other than the fuel tank within a predetermined period after the purge is restarted, In view of the difficulty in fixing the flow rate, the total purge flow rate QPGTOTAL is subtracted in step 1703 during the purge cut. Therefore, even if the total purge flow rate QPGTOTAL should be equal to or greater than the set value KQPG, step 20
5, the total purge flow rate QPGTOTAL is set to the set value KQ.
It is determined that it is smaller than PG. In other words, even after the generation of fuel vapor from the fuel tank is stabilized, it is regarded as before the generation of fuel vapor from the fuel tank is stabilized. As a result, the process proceeds to Step 220, and Step 2
The air-fuel ratio learning at 19 is not executed. Therefore, it is possible to prevent the air-fuel ratio from being erroneously learned within a predetermined period after the purge is restarted after the generation of the fuel vapor from the fuel tank is stabilized.

Furthermore, in the evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment, even if an attempt is made to fix the purge flow rate due to the effect of fuel vapor purged from other than the fuel tank within a predetermined period after the purge is restarted, In consideration of the difficulty in fixing the purge flow rate, step 170 is performed during purge cut.
In 2, the purge execution time CPGR is subtracted. Therefore, the purge execution time CPGR should normally be equal to the set value KC.
Even if it becomes equal to or greater than PGR, it is determined in step 206 that the purge execution time CPGR is smaller than the set value KCPGR. That is, even when the purge execution time is long, it is considered that the purge execution time is short. As a result, the process proceeds to Step 220, and Step 2
The air-fuel ratio learning at 19 is not executed. Therefore, it is possible to prevent the air-fuel ratio from being erroneously learned when the purge execution time is long and within a predetermined period after the restart of the purge.

Further, in the evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment, in consideration of the effect of the purge cut time on the amount of fuel vapor purged from other than the fuel tank, the predetermined period depends on the purge cut time. It is determined. In other words, the larger the number of times that step 1703 is executed during the purge cut, the easier it is to determine NO in step 205. Also, the larger the number of times Step 1702 is executed during the purge cut, the more NO in Step 206
It becomes easy to be judged. Therefore, it is possible to accurately determine the predetermined period in which the execution of the air-fuel ratio learning should be avoided.

Hereinafter, a fourth embodiment of the fuel vapor treatment system for an internal combustion engine according to the present invention will be described. The evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment has the same configuration as the above-described evaporative fuel processing apparatus for an internal combustion engine according to the first embodiment, unless otherwise specified. FIG. 18 shows a purge counter control routine which is executed every 100 msec to reset the flag XFGPG = 1 indicating that the learning accuracy of the fuel vapor concentration used in the determination in step 213 of FIGS. 2 and 3 is good. It is a flowchart shown. As shown in FIG. 18, in the purge counter control routine of the present embodiment, first, in step 1801, a flag XFGPG =
It is determined whether 1 has been set. If YES, proceed to step 1802; if NO, proceed to step 18
Go to 10.

In step 1802, it is determined whether the purging is being performed or not. Step 18 if YES
03, and if NO, the process proceeds to step 1807. In step 1803, a counter CPGO indicating the elapsed time after the execution of the vapor concentration learning in step 221
It is determined whether or not N is equal to or greater than a predetermined set value KCPGON. Step 18 if YES
05, if NO, the counter CPGON is incremented by a predetermined value Kc in step 1804 (CPGON ← CPGON + Kc), and step 180
Go to 5. At step 1805, the counter CPGON
Is greater than or equal to the set value KCPGON.
When YES, that is, when the elapsed time after the execution of the vapor concentration learning is long, it is determined that the reliability of the flag XFGPG = 1 indicating that the learning accuracy of the fuel vapor concentration is good has decreased, and in step 1806, the flag XFGPG is determined. =
1 is cleared (XFGPG ← 0). On the other hand, if NO is determined in the step 1805, this routine is terminated.

When NO is determined in step 1802, that is, when the purge cut is being performed, a counter CP indicating the purge cut time is set in step 1807.
It is determined whether or not GOF is equal to or greater than a predetermined set value KCPGOF. If YES, the process directly proceeds to step 1809; if NO, the counter CPGOF is incremented by a predetermined value Kc in step 1808 (CPGOF ← CPGOF + Kc), and step 1 is executed.
Proceed to 809. In step 1809, the counter CPG
It is determined whether or not OF is equal to or greater than the set value KCPGOF. When YES, that is, when the purge cut time is long, it is determined that the reliability of the flag XFGPG = 1 indicating that the learning accuracy of the fuel vapor concentration is good has decreased, and the flag XFGPG = 1 is cleared in Step 1806 ( XFGPG ← 0). On the other hand, if NO is determined in the step 1809, this routine is ended as it is.

If it is determined in step 1801 that the flag XFGPG = 1 indicating that the learning accuracy of the fuel vapor concentration is good is not set, step 1810
In CPGON, the counter CPGON is initialized (CPGON
← 0), then, in step 1811, the counter CP
GOF is initialized (CPGOF ← 0), and this routine ends.

In the evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment, when it is determined in step 1805 that the elapsed time after the execution of the vapor concentration learning is long, the accuracy of the previously learned vapor concentration is reduced. Step 1
At 806, a flag XFGPG = 1 indicating that the learning accuracy of the fuel vapor concentration is good is cleared. for that reason,
The process does not proceed from step 213 to step 219, but proceeds to step 221. In step 221, vapor concentration learning is executed. Therefore, the vapor concentration learning accuracy can always be maintained at a high level of reliability.

In the evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment, when it is determined in step 1809 that the purge cut time is long, the fuel vapor to be purged from other than the fuel tank has a large effect in consideration of the step. In 1806, the flag XFGPG = 1 indicating that the learning accuracy of the fuel vapor concentration is good is cleared. Therefore, the process does not proceed from step 213 to step 219,
Proceeding to step 221, vapor concentration learning is executed in step 221. Therefore, the vapor concentration learning accuracy can always be maintained at a high level of reliability.

In this embodiment, the elapsed time after the execution of the vapor concentration learning and the purge cut time are used to determine whether or not the flag XFGPG = 1 indicating that the learning accuracy of the fuel vapor concentration is good is cleared. However, in the modified example of this embodiment, instead of the elapsed time after the execution of the vapor concentration learning and the purge cut time, the purge flow rate, the temperature (combustion temperature, intake air temperature, water temperature, oil temperature), the constant purge flow rate duty ratio, and the like are used. It is also possible to use

Hereinafter, a fifth embodiment of the fuel vapor treatment system for an internal combustion engine according to the present invention will be described. The evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment has the same configuration as the above-described evaporative fuel processing apparatus for an internal combustion engine according to the second embodiment, unless otherwise specified. FIG. 19 shows a flag XFGPG = 1 indicating that the learning accuracy of the fuel vapor concentration used in the determination in step 213 of FIGS. 2 and 3 is good, and a flag indicating the completion of the air-fuel ratio learning used in the determination in step 214. 100ms to reset XKG = 1
9 is a flowchart illustrating a purge counter control routine that is executed by interruption every ec. As shown in FIG. 19, in the purge counter control routine of the present embodiment, first, in step 1901, it is determined whether or not the purge is currently being executed. When the result is NO, this routine ends, and
At the time of ES, the process proceeds to step 1902. Step 190
In 2, the total purge flow rate QPGTOTAL is updated (Q
PGTOTAL ← QPGTOTAL + QP100 × DP
G / 100). Next, at step 1903, the total purge flow rate QPGTOTAL is set to a predetermined set value KQPGR.
It is determined whether or not it is equal to or greater than SET. If the determination is NO, this routine ends. If the determination is YES, step 1904 is executed.
Proceed to.

In step 1904, it is determined whether or not the engine is currently idling. If the determination is NO, this routine ends. If the determination is YES, the process proceeds to step 1905. In step 1905, it is determined whether the vehicle speed is 3 km / h or less. If YES, this routine ends. If NO, the reliability of the flag XFGPG = 1 indicating that the learning accuracy of the fuel vapor concentration is good and the reliability of the flag XKG = 1 indicating that the air-fuel ratio learning has been completed are satisfied. It is determined that it has decreased, and in step 1906, the flag X
FGPG = 1 is cleared (XFGPG ← 0), and in step 1907, the flag XKG = 1 is cleared (XKG ← 0).

In this embodiment, the air-fuel ratio learning is executed again at every predetermined purge flow rate (time, etc.), and the accuracy of the air-fuel ratio learning is improved. As described above, while it is determined in step 1904 that the engine is idling,
When it is determined in step 1905 that the vehicle is almost stopped, steps 1906 and 1907 are executed.
In, the learning completion flag is cleared. According to the present embodiment, in addition to the effects of the second embodiment, re-learning is performed after the learning completion flag is cleared, so that learning accuracy is improved.

Hereinafter, a sixth embodiment of the fuel vapor treatment system for an internal combustion engine according to the present invention will be described. The evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment has the same configuration as the above-described evaporative fuel processing apparatus for an internal combustion engine according to the first embodiment, unless otherwise specified. FIG. 20 shows a purge counter control routine that is executed every 100 msec to reset the flag XFGPG = 1 indicating that the learning accuracy of the fuel vapor concentration used in the determination in step 213 of FIGS. 2 and 3 is good. It is a flowchart shown. As shown in FIG. 20, in the purge counter control routine of this embodiment, first, in step 2001, a flag XFGPG =
It is determined whether 1 has been set. If NO, proceed to step 2008; if YES, proceed to step 20
Go to 02. In step 2002, it is determined whether or not purging is currently being performed. If the determination is NO, this routine ends. If the determination is YES, the process proceeds to step 2003.

In step 2003, it is determined whether or not the current full-open purge flow rate QP100 is equal to or less than a predetermined fixed purge flow rate set value KQPGR. When the determination is YES, that is, when the negative pressure Pm in the intake branch pipe is small, for example, during continuous uphill running, a counter CQMA indicating that the full-open purge flow rate has become equal to or less than the fixed purge flow rate set value.
X is increased by a predetermined value Kq (CQMAX ← CQMA
X + Kq). On the other hand, when the determination is NO, that is, when the negative pressure Pm in the intake branch pipe is large, the counter CQMAX has a predetermined value Kq.
q (CQMAX ← CQMAX−Kqq ≧
0). Next, at step 2006, the counter CQMA
It is determined whether X is equal to or greater than a predetermined set value KCQMAX. When the result is NO, this routine ends.
When YES, it is determined that the reliability of the flag XFGPG = 1 indicating that the learning accuracy of the fuel vapor concentration is good is low, and the flag XFGPG = 1 is cleared in step 2007 (XFGPG ← 0). Next, at step 2008, the counter CQMAX is reset, and this routine ends.

In the evaporative fuel processing system for an internal combustion engine according to the present embodiment, in step 2003, the current full-open purge flow rate QP100 is set to a predetermined fixed purge flow rate set value K.
When it is determined that the purge flow rate is equal to or less than QPGR, that is, when it is determined that the negative pressure Pm in the intake branch pipe is small, the actual purge flow rate
In view of the fact that the fuel vapor concentration changes due to the fact that GR (≦ full-open purge flow rate QP100) cannot be increased, it is again determined whether the learning accuracy of the fuel vapor concentration is good. In some cases, the purge flow rate is not fixed. The air-fuel ratio learning is not executed. Therefore, it is possible to prevent the air-fuel ratio from being erroneously learned based on the erroneous purge flow rate.

In the above embodiment, the set value KCQM
AX, the set value KCPGON, the set value KCPGOF, and the like are set to predetermined values. However, the amount of fuel vapor generated from the fuel tank 15 depends on the ambient temperature, the intake air temperature, the fuel temperature in the fuel tank, and the fuel tank pressure. , In accordance with the atmospheric pressure or the like, in another embodiment, the set value KCQMAX,
The values such as the set value KCPGON and the set value KCPGOF are optimized by changing according to the atmospheric temperature, the intake air temperature, the fuel temperature in the fuel tank, the pressure in the fuel tank, the atmospheric pressure, and the like. As an example, FIG. 21 shows a case where the value of the set value KCPMAX is optimized according to the atmospheric temperature. FIG. 21 is a graph showing the relationship between the atmospheric temperature and the set value KCQMAX. As shown in FIG. 21, as the atmospheric temperature increases, the fuel tank 1
In view of the fact that the amount of fuel vapor generated from 5 increases, the set value KCQMAX decreases as the atmospheric temperature increases. As described above, the set value KCQMAX serving as the determination value
And the like are changed in accordance with changes in the ambient temperature or the like, so that the air-fuel ratio learning can be prevented from being erroneously performed while updating the air-fuel ratio learning.

[0104]

According to the first aspect of the present invention, accurate air-fuel ratio learning can be performed even during the purge of the fuel vapor, as during the purge cut of the fuel vapor. Further, the necessity of performing the purge cut of the fuel vapor to execute the air-fuel ratio learning is eliminated, and therefore, the purge amount of the fuel vapor can be increased.

According to the second and third aspects of the invention, it is possible to prevent the air-fuel ratio from being erroneously learned before the generation of fuel vapor from the fuel tank is stabilized, that is, when the total purge flow rate is small. can do.

According to the fourth aspect of the invention, it is possible to prevent the air-fuel ratio from being erroneously learned after the generation of the fuel vapor from the fuel tank is stabilized and the purge execution time is short. Can be.

According to the fifth aspect of the present invention, when the generation of fuel vapor from the fuel tank is stabilized, the purge execution time is long, and the vapor concentration in the purge passage is high. Thus, it is possible to prevent the air-fuel ratio from being learned by mistake.

According to the present invention, it is possible to prevent the air-fuel ratio from being erroneously learned after the generation of the fuel vapor from the fuel tank is stabilized and within a predetermined period after the restart of the purge. be able to.

According to the seventh aspect of the invention, it is possible to prevent the air-fuel ratio from being erroneously learned during a long purge execution time and within a predetermined period after the restart of the purge.

According to the eighth aspect of the present invention, it is possible to accurately determine the predetermined period in which the execution of the air-fuel ratio learning is to be avoided.

According to the ninth aspect, it is possible to prevent the purge flow rate from being fixed even when it is not necessary to execute the air-fuel ratio learning.

According to the tenth aspect, it is possible to prevent the vapor concentration learning from being executed more than necessary.

According to the eleventh aspect of the present invention, it is possible to prevent the air-fuel ratio from being erroneously learned based on the erroneous purge flow rate.

According to the twelfth aspect, it is possible to improve the reliability of determining whether or not the vapor concentration learning accuracy is good. Further, control of the purge flow rate can be simplified.

According to the thirteenth aspect, the vapor concentration learning accuracy can always be maintained at a high level of reliability.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment in which a fuel vapor treatment device for an internal combustion engine of the present invention is applied to a multi-cylinder internal combustion engine.

FIG. 2 is a flowchart showing a main routine of an air-fuel ratio control method for an internal combustion engine by the evaporated fuel processing device shown in FIG.

FIG. 3 is a flowchart showing a main routine of an air-fuel ratio control method for an internal combustion engine by the evaporative fuel processing apparatus shown in FIG. 1;

FIG. 4 is a flowchart showing a feedback correction coefficient FAF calculation routine.

FIG. 5 is a flowchart showing an air-fuel ratio learning area calculation routine.

FIG. 6 is a flowchart showing an air-fuel ratio learning routine.

FIG. 7 is a flowchart showing a fixed purge flow rate control routine.

FIG. 8 is a flowchart illustrating a purge rate calculation routine.

FIG. 9 is a flowchart illustrating a purge rate calculation routine.

FIG. 10 is a flowchart showing a vapor concentration learning routine.

FIG. 11 is a flowchart showing a fuel injection time calculation routine.

FIG. 12 is a flowchart showing a purge control valve driving process routine.

FIG. 13 shows a purge rate PGR, a duty ratio DPG, a purge flow rate QPGR, an intake branch pipe negative pressure Pm, and an intake air amount Ga.
FIG. 7 is a diagram showing a relationship between the vehicle speed SPD and time in the present embodiment in which the purge flow rate is fixed at the time of learning the air-fuel ratio, and in a case in which the purge rate is fixed at the time of learning the air-fuel ratio.

FIG. 14 is a graph showing a relationship between a negative pressure in an intake branch pipe and a full-open purge flow rate.

FIG. 15 is a diagram showing the relationship between a purge flow rate QPGR, a purge air-fuel ratio correction coefficient FPG, a fuel vapor concentration FGPG, a purge rate PGR, and an intake air amount Ga in comparison with the present embodiment and a conventional one. .

FIG. 16 is a flowchart showing a part of a main routine of an internal combustion engine air-fuel ratio control method according to a second embodiment of the internal combustion engine evaporated fuel processing apparatus of the present invention.

FIG. 17 is a flowchart showing a purge counter control routine according to a third embodiment of the fuel vapor processing system for an internal combustion engine of the present invention.

FIG. 18 is a flowchart illustrating a purge counter control routine according to a fourth embodiment of the evaporated fuel processing apparatus for an internal combustion engine of the present invention.

FIG. 19 is a flowchart illustrating a purge counter control routine according to a fifth embodiment of the evaporated fuel processing apparatus for an internal combustion engine of the present invention.

FIG. 20 is a flowchart illustrating a purge counter control routine according to a sixth embodiment of the evaporated fuel processing apparatus for an internal combustion engine of the present invention.

FIG. 21 is a graph showing a relationship between an atmospheric temperature and a set value KCQMAX.

[Explanation of symbols]

 2 ... intake branch 7 ... air flow meter 15 ... fuel tank 16 ... conduit 17 ... purge control valve 20 ... electronic control unit KGj ... air-fuel ratio learning coefficient

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02M 25/08 301 F02M 25/08 301J 301M 301U

Claims (13)

[Claims] 1. A purge passage connecting a fuel tank and an intake passage, and a purge passage for controlling a purge flow rate of a fuel vapor purged from the fuel tank into the intake passage. A purge control valve, an engine operating state detecting means for detecting an operating state of the engine, a fuel injection amount calculating means for calculating a fuel injection amount based on the engine operating state, and a calculation based on the engine operating state. Air-fuel ratio learning execution means for calculating an air-fuel ratio learning coefficient for correcting the obtained fuel injection amount, and fuel injection amount correction for correcting the fuel injection amount calculated based on the engine operating state by the air-fuel ratio learning coefficient Fuel vapor processing apparatus for an internal combustion engine, wherein the air-fuel ratio learning can be executed by fixing the purge flow rate during the execution of the fuel vapor purge. An evaporative fuel processor for an internal combustion engine. 2. A fuel vapor generation stability determining means for determining whether the generation of fuel vapor from the fuel tank is stable, wherein the fuel vapor is being purged while the fuel vapor is being purged. The air-fuel ratio learning is not executed before the generation of the vapor is stabilized.After the fuel vapor is being purged and the generation of the fuel vapor from the fuel tank is stabilized, the purge flow rate is fixed and the air-fuel ratio learning is performed. The fuel vapor processing apparatus for an internal combustion engine according to claim 1, wherein the fuel vapor processing apparatus is executable. 3. A total purge flow rate calculating means for calculating a total purge flow rate after the engine is started, and when the total purge flow rate is small, it is determined that the generation of fuel vapor from the fuel tank is not yet stable. 3. The evaporative fuel processing apparatus for an internal combustion engine according to claim 2, wherein it is determined that the generation of fuel vapor from the fuel tank is stable when the total purge flow rate is large. 4. After the generation of fuel vapor from the fuel tank is stabilized and the purge execution time is short, the purge flow rate is changed according to the engine operating state, and the generation of fuel vapor from the fuel tank is stable. 3. The apparatus according to claim 2, wherein the purge flow rate can be fixed regardless of the operating state of the engine after the purge execution time is long. 5. When the purge execution time is long and the vapor concentration in the purge passage is high, the purge flow rate is changed in accordance with the engine operating state. 5. The apparatus according to claim 4, wherein the purge flow rate can be fixed when the vapor concentration is low irrespective of the operating state of the engine. 6. Within a predetermined period after resumption of purging, it is considered that the generation of fuel vapor from the fuel tank is before the generation of fuel vapor is stabilized even after the generation of fuel vapor from the fuel tank is stabilized. 3. The fuel vapor treatment device for an internal combustion engine according to claim 2, wherein: 7. The internal combustion engine according to claim 4, wherein the purge execution time is regarded as short when the purge execution time is long within a predetermined period after the purge is restarted. Evaporative fuel processing device. 8. An evaporative fuel processing apparatus for an internal combustion engine according to claim 6, wherein said predetermined period is determined according to a purge cut time. 9. An air-fuel ratio learning execution completion judging means for judging whether or not air-fuel ratio learning has been executed for all regions, and a purge flow rate is fixed when air-fuel ratio learning has been executed for all regions. 2. The evaporative fuel processing apparatus for an internal combustion engine according to claim 1, wherein the purge flow rate can be fixed when the air-fuel ratio learning for all the regions has not been performed yet. 10. A fuel cell system comprising: a vapor concentration learning unit for calculating a fuel vapor concentration in the purge passage; and a vapor concentration learning accuracy determining unit for determining whether the vapor concentration learning accuracy is good. When it is determined that the vapor concentration learning accuracy is not good after the generation of fuel vapor from the fuel tank is stabilized, the vapor concentration learning is executed, and after the generation of fuel vapor from the fuel tank is stabilized. 2. The evaporative fuel processing apparatus for an internal combustion engine according to claim 1, wherein the vapor concentration learning is not performed when it is determined that the vapor concentration learning accuracy is good. 11. The evaporative fuel treatment system for an internal combustion engine according to claim 10, wherein when the negative pressure in the intake passage is small, the vapor concentration learning accuracy is considered to be poor. 12. A fuel cell system comprising: a vapor concentration learning unit for calculating a fuel vapor concentration in the purge passage; and a vapor concentration learning accuracy determining unit for determining whether the vapor concentration learning accuracy is good. 2. The internal combustion engine according to claim 1, wherein the purge flow rate is fixed to the actual purge flow rate at the time of engine idle operation during which vapor purge is being performed and the vapor concentration learning accuracy is determined to be good. Evaporative fuel processing device. 13. A vapor concentration learning unit for learning fuel vapor concentration, an elapsed time after vapor concentration learning execution for calculating an elapsed time after execution of the vapor concentration learning, and a purge cut time. The internal combustion engine according to claim 1, further comprising a purge cut time calculating means for performing the vapor concentration learning when the elapsed time after performing the vapor concentration learning is long or when the purge cut time is long. Evaporative fuel treatment equipment.