JP3487163B2 - Evaporative fuel treatment system for internal combustion engine - Google Patents

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 canister for temporarily storing evaporated fuel generated in a fuel tank and a purge control valve provided in a purge passage communicating with an intake passage of an internal combustion engine, and a purge control valve depending on an operating state of the internal combustion engine The purge control means for controlling the opening amount of the purge control valve, the O ₂ sensor for detecting the air-fuel ratio, and the air-fuel ratio which changes when the evaporated fuel is introduced into the intake passage are adjusted to the target air-fuel ratio. There is known an evaporated fuel processing device for an internal combustion engine, which includes an air-fuel ratio adjusting means. This evaporated fuel processing apparatus for an internal combustion engine further includes a vapor concentration calculation means for calculating the concentration of evaporated fuel (hereinafter referred to as "vapor concentration"). The vapor concentration calculating means first sets an initial value of the vapor concentration at the time of starting the internal combustion engine, etc., and then, based on the value of the air-fuel ratio detected by the O ₂ sensor, a coefficient serving as a reference for adjusting the air-fuel ratio. Calculate the value of a certain feedback correction coefficient, then calculate the average value of the feed correction coefficient based on the value of a certain number or more of the feedback correction coefficients, and then update the vapor concentration based on the average value of the feed correction coefficient The vapor concentration update value for calculating the vapor concentration is calculated, the vapor concentration is updated based on the initial value of the vapor concentration and the vapor concentration update value, and the vapor concentration is calculated by repeating this update. An example of this type of evaporated fuel processing apparatus for an internal combustion engine is disclosed in Japanese Patent Application Laid-Open No. 7-305662.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
As described above, the evaporated fuel processing apparatus for an internal combustion engine disclosed in Japanese Patent No. 305662 detects the air-fuel ratio by the O ₂ sensor, then calculates the feedback correction coefficient, and then calculates the average value of the feedback correction coefficient. Then, through the step of calculating the vapor concentration update value, the vapor concentration is updated based on the vapor concentration update value (hereinafter referred to as "vapor concentration learning"). In other words, it takes a considerable time from the necessity of updating the vapor concentration until the vapor concentration is actually updated, that is, during the vapor concentration learning. Therefore, when the amount of intake air taken into the internal combustion engine changes suddenly, such as during transient operation of the internal combustion engine, that is, when the amount of intake air changes, it is adsorbed by the vapor and the canister in the fuel tank. Vapor is purged into the intake passage When the purge flow rate changes suddenly,
The calculated vapor concentration (hereinafter referred to as “calculated vapor concentration”) has a time delay with respect to the actual vapor concentration (hereinafter referred to as “actual vapor concentration”).

Further, the vapor evaporated from the fuel tank becomes more influential than the vapor desorbed from the canister, for example, after a lapse of a predetermined time from the start of the internal combustion engine, and the amount of change in vapor concentration per hour is increased. Becomes larger,
Due to the above-mentioned time delay, the actual vapor concentration and the calculated vapor concentration differ greatly.

If the actual vapor concentration and the calculated vapor concentration differ greatly, the value of the feedback correction coefficient becomes rough. That is, when the calculated vapor concentration becomes larger than the actual vapor concentration, the value of the feedback correction coefficient becomes unnecessarily large. On the other hand, when the calculated vapor concentration becomes smaller than the actual vapor concentration, the value of the feedback correction coefficient becomes unnecessary. It becomes small. As described above, the feedback correction coefficient is a reference coefficient for adjusting the air-fuel ratio, so if the value of the feedback correction coefficient is not maintained at an appropriate value, the air-fuel ratio will not be adjusted properly, and as a result, Therefore, good air-fuel ratio control will not be performed.

In view of the above-mentioned problems, the present invention is for a case where the purge flow rate changes abruptly with a sudden change in the intake air amount, and when the vapor evaporated from the fuel tank is more affected than the vapor desorbed from the canister. Even if the calculated vapor concentration is close to the actual vapor concentration, the feedback correction coefficient is prevented from being set to an inappropriate value, and therefore, a good air-fuel ratio control of the internal combustion engine can be performed. An object is to provide an evaporated fuel processing device.

[0007]

According to the first aspect of the present invention, a canister for temporarily storing evaporated fuel generated in the fuel tank, and the canister and the fuel tank are purged into the intake passage. A purge control valve for controlling the purge flow rate of the fuel vapor, an air-fuel ratio detecting means for detecting an air-fuel ratio, a purge flow rate calculating means for calculating the purge flow rate based on the opening amount of the purge control valve, and an internal combustion engine. In an evaporative fuel treatment system for an internal combustion engine, comprising: an intake air amount detecting means for detecting an intake air amount sucked into a fuel vapor in the fuel vapor purged from the canister and the fuel tank into the intake passage. When the ratio of the fuel vapor from the tank is large and the rate of change of the purge flow rate due to the change of the intake air amount is large, Then, the vapor concentration is calculated based on the air-fuel ratio in the second state where the ratio of the fuel vapor from the fuel tank is small or the change rate of the purge flow rate due to the change of the intake air amount is small. An evaporated fuel processing apparatus for an internal combustion engine is provided, which comprises: a vapor concentration calculating unit that performs the above; and an air-fuel ratio adjusting unit that adjusts the air-fuel ratio to a target air-fuel ratio based on the vapor concentration.

According to a second aspect of the present invention, there is provided the evaporated fuel processing apparatus for an internal combustion engine according to the first aspect, wherein the purge flow rate is calculated based on the duty ratio of the purge control valve. It

In the evaporated fuel processing apparatus for the internal combustion engine according to the first and second aspects, the ratio of the fuel vapor from the fuel tank in the fuel vapor purged from the canister and the fuel tank into the intake passage is large, and In the first state where the change rate of the purge flow rate due to the change of the intake air amount is large, the vapor concentration is calculated based on the air-fuel ratio, that is, the vapor concentration learning is not performed but the change rate of the purge flow rate is directly calculated. Calculate the vapor concentration. Therefore, when the change rate of the purge flow rate due to the change of the intake air amount is large, and the ratio of the fuel vapor from the fuel tank in the fuel vapor purged from the canister and the fuel tank into the intake passage is large, that is, Even when the vapor concentration changes greatly with the change of the purge flow rate, the actual vapor concentration can be accurately calculated. Therefore, the feedback correction coefficient can be prevented from being set to an inappropriate value, and good air-fuel ratio control can be performed.

According to a third aspect of the present invention, there is provided the evaporated fuel processing apparatus for an internal combustion engine according to the first aspect, wherein the rate of change of the purge flow rate is a value that has been smoothed. To be done.

The vaporized fuel processing apparatus for an internal combustion engine according to claim 3 smoothes the rate of change of the purge flow rate. Therefore, when the purge flow rate suddenly changes, the vapor concentration calculated based on the rate of change of the purge flow rate is changed. It is possible to prevent overshoot.

According to the invention described in claim 4, in the first state, the vapor concentration calculating means is based on the rate of change of the purge flow rate, and the fuel vapor purged from the canister into the intake passage is performed. The evaporated fuel processing device for an internal combustion engine according to claim 1, wherein the concentration of the entire fuel vapor purged from the canister and the fuel tank into the intake passage is calculated based on the concentration. It

According to a fourth aspect of the present invention, there is provided a vaporized fuel processing apparatus for an internal combustion engine, wherein when the rate of change of the purge flow rate with the change of the intake air amount is large, the vapor concentration of the fuel vapor from the fuel tank is large. Since the concentration of the entire fuel vapor is calculated in consideration of the property of the fuel vapor from the canister whose concentration does not change so much, the vapor concentration can be accurately calculated.

According to the fifth aspect of the present invention, in the first state, when the purge action is restarted after the purge action is stopped, the vapor concentration calculating means determines the change rate of the purge flow rate. An evaporated fuel processing apparatus for an internal combustion engine according to claim 1, wherein the vapor concentration is calculated based on the vapor concentration and the vapor concentration is corrected to a rich side.

The vaporized fuel processing apparatus for an internal combustion engine according to claim 5 corrects the vapor concentration in consideration of the fact that the fuel vapor adsorbed in the canister is desorbed when the purging is restarted while the purging operation is stopped. It is possible to obtain various vapor concentrations.

According to a sixth aspect of the present invention, the vapor concentration calculation means corrects the vapor concentration based on the purge action stop time, and the vaporized fuel processing of the internal combustion engine according to the fifth aspect is performed. A device is provided.

In the fuel vapor processing apparatus for an internal combustion engine according to a sixth aspect of the present invention, the amount of fuel vapor adsorbed by the canister during the purging operation stop and desorbed when the purging operation is restarted differs depending on the purging operation stop time. Since the vapor concentration is corrected in consideration, an accurate vapor concentration can be obtained.

According to the invention described in claim 7, in the first state, the vapor concentration calculating means is based on the time required for the fuel vapor to flow from the purge control valve to the combustion chamber of the internal combustion engine. An evaporative fuel treatment system for an internal combustion engine according to claim 1, wherein the vapor concentration is calculated.

According to another aspect of the fuel vapor processing apparatus for an internal combustion engine of the present invention, the flow time of the fuel vapor is taken into consideration.
It is possible to prevent a difference between the actual vapor concentration and the calculated vapor concentration in the combustion chamber of the internal combustion engine.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION 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 of an evaporated fuel processing apparatus for an internal combustion engine of the present invention. In FIG. 1, 1 is an engine body, 2 is an intake branch pipe, 3 is an exhaust manifold, and 4 is a fuel injection valve attached to each intake branch pipe 2. 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. In addition, as shown in FIG.
It has a canister 11 with a built-in. This canister 11 has a fuel vapor chamber 12 and an atmosphere chamber 13 on both sides of the activated carbon 10, respectively. The fuel vapor chamber 12 is connected on the one hand to the head space of the fuel tank 15 via a conduit 14 and on the other hand to the surge tank 5 via a conduit 16. A purge control valve 17 controlled by the output signal of the electronic control unit 20 is arranged in the conduit 16. The fuel vapor generated in the fuel tank 15 is sent into the canister 11 via the conduit 14 and adsorbed on the activated carbon 10. When the purge control valve 17 is opened, air is sent from the atmospheric chamber 13 into the conduit 16 through the activated carbon 10. When the air passes through the activated carbon 10, the fuel vapor adsorbed on the activated carbon 10 is desorbed from the activated carbon 10, and thus the air containing the fuel vapor, that is, the fuel vapor, is passed through the conduit 16 to the surge tank 5
Is purged inside.

The electronic control unit 20 is composed of a digital computer, and has a ROM (read only memory) 22, a RAM (random access memory) 23, a CPU (microprocessor) 24, and an input port 25 which are mutually connected by a bidirectional bus 21. And an output port 26. The air flow meter 7 generates an output voltage proportional to the intake air amount, and the output voltage corresponds to the AD converter 2
It is input to the input port 25 via 7. 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 the input port 25. A water temperature sensor 29 that generates 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 “O ₂ sensor”) 30 is attached to the exhaust manifold 3, and the output signal of this O ₂ sensor 30 is input to the input port 25 via the corresponding AD converter 27.

Further, 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 inside the fuel vapor chamber 12, that is, the fuel tank 15.
An output voltage proportional to the pressure of the conduit 16 from the upper space of the fuel tank 15 or 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 each time the crankshaft rotates, for example, 30 degrees. CP
At U24, the engine speed is calculated based on this output pulse. On the other hand, the output port 26 is connected to the fuel injection valve 4 and the purge control valve 17 via the corresponding drive circuits 34, respectively.

FIG. 2 is a flow chart showing a main routine of an air-fuel ratio control method for an internal combustion engine by the fuel vapor treatment system shown in FIG. The evaporated fuel processing device executes a main routine every predetermined cycle. When the execution of the main routine is started, first, at step 201, a feedback correction coefficient FAF which is a correction coefficient which is the basis of the air-fuel ratio control is calculated.

FIG. 3 shows the feedback correction coefficient FA of FIG.
6 is a flowchart showing an F calculation routine. As shown in FIG. 3, first, at step 300, it is judged if the feedback control condition of the air-fuel ratio is satisfied. When the feedback control condition is not satisfied, the routine proceeds to step 313, where the feedback correction coefficient F
AF is fixed to 1.0, and then, in step 314, the average value FAFAV of the feedback correction coefficient is 1.0.
Fixed to. Then, it proceeds to step 312. On the other hand, if the feedback control condition is satisfied, the process proceeds to step 301.

At step 301, it is judged if the output voltage V of the O ₂ sensor 31 is higher than 0.45 (V), that is, if it is rich. When V ≧ 0.45 (V), that is, when rich, the routine proceeds to step 302, where it is judged if it was lean in the previous processing cycle. If it is lean in the previous processing cycle, that is, if it changes from lean to rich, the routine proceeds to step 303, where the feedback correction coefficient FAF is set to FAFL, and the routine proceeds to step 304. In step 304, the skip value S is subtracted from the feedback correction coefficient FAF, so that
The feedback correction coefficient FAF is sharply reduced by the skip value S. Next, in step 305, FAF
The average value FAFAV of L and FAFR is calculated. That is, the average value FAFAV is the feedback correction coefficient F
It is the average value of the fluctuation of AF and is the average value of FAFL and FAFR. Next, at step 306, the skip flag is set. Then, it proceeds to step 312. On the other hand, if it is determined in step 302 that it was rich in the previous processing cycle, the routine proceeds to step 307, where the integral value K (K << S) is subtracted from the feedback correction coefficient FAF, and then the routine proceeds to 312. Therefore, the feedback correction coefficient FAF is gradually reduced.

On the other hand, in step 301, V <0.4
When it is judged to be 5 (V), that is, when it is lean, the routine proceeds to step 308, where it is judged if it was rich in the previous processing cycle. If it is rich in the previous processing cycle, that is, if it changes from rich to lean, the routine proceeds to step 309, where the feedback correction coefficient F
AF is set to FAFR, and the routine proceeds to step 310. In step 310, the skip value S is added to the feedback correction coefficient FAF, so that the feedback correction coefficient FAF
F is rapidly increased by the skip value S. Next, at step 305, the average value FAF of FAFL and FAFR.
AV is calculated. On the other hand, if it is determined in step 308 that the engine was lean in the previous processing cycle, the process proceeds to step 311 and the feedback correction coefficient FA
The integral value K is added to F. Therefore, the feedback correction coefficient FAF is gradually increased.

At step 312, 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 FAF is guarded so that 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, and when the air-fuel ratio becomes lean and the FAF becomes large, the fuel injection time TAU becomes long, so the air-fuel ratio becomes the theoretical air-fuel ratio. Will be maintained. When step 312 ends, the feedback correction coefficient FAF calculation routine ends.

FIG. 4 is a graph showing the relationship between the output voltage V of the O ₂ sensor 30 and the feedback correction coefficient FAF when the air-fuel ratio is maintained at the target air-fuel ratio. As shown in FIG. 4, when the output voltage V of the O ₂ sensor 30 becomes higher than the reference voltage, for example, 0.45 (V), that is, when the air-fuel ratio becomes rich, the feedback correction coefficient FAF sharply decreases by the skip amount S. Then, it is gradually decreased with an integration constant K. On the other hand, O
_{2 When} the output voltage V of the sensor 30 becomes lower than the reference voltage, that is, when the air-fuel ratio becomes lean, the feedback correction coefficient FAF is rapidly increased by the skip amount S, and then gradually increased by the integration constant K.

That is, when the air-fuel ratio becomes rich, the feedback correction coefficient FAF is decreased, so the fuel injection amount is decreased, and when the air-fuel ratio becomes lean, the feedback correction coefficient FAF is increased, and therefore the fuel injection amount is increased. Thus, the air-fuel ratio is controlled to the stoichiometric air-fuel ratio. As shown in FIG. 4, at this time, the feedback correction coefficient FAF moves up and down around the reference value, that is, 1.0.

Further, in FIG. 4, FAFL indicates the value of the feedback correction coefficient FAF when the air-fuel ratio changes from lean to rich, and FAFR indicates the feedback correction coefficient FAF when the air-fuel ratio changes from rich to lean.
Indicates the value of.

Returning to FIG. 2, the evaporative fuel treatment system subsequently executes learning of the air-fuel ratio in step 202. FIG. 5 is a flowchart showing the air-fuel ratio learning routine of FIG. As shown in FIG. 5, first, at step 520, it is judged if the learning condition of the air-fuel ratio is satisfied. When the air-fuel ratio learning condition is not satisfied, the routine jumps to step 528, and when the air-fuel ratio learning condition is satisfied, the routine proceeds to step 521. In step 521, it is determined whether or not the skip flag is set,
If the skip flag is not set, the routine jumps to step 528. On the other hand, when the skip flag is set, the routine proceeds to step 522, where the skip flag is reset, and then the routine proceeds to step 523. That is, each time the feedback correction coefficient FAF is skipped, the process proceeds to step 523.

At step 523, it is judged if the purge rate PGR is zero, that is, if the purge action is being performed. When the purge rate PGR is not zero, that is, when the purge action is being performed, the routine proceeds to the vapor concentration learning routine shown in FIG. On the other hand, the purge rate PGR
Is zero, that is, when the purging action is not performed, the routine proceeds to step 524, where the learning of the air-fuel ratio is performed.

That is, first, at step 524, the average value FAFAV of the feedback correction coefficient is 1.02.
Is determined to be greater than or equal to. FAFAV ≧ 1.0
When it is 2, the routine proceeds to step 527, where the constant value X is added to the learning value KGj of the air-fuel ratio for the learning region j. That is, in this embodiment, a plurality of learning regions j are predetermined according to the engine load, and the learning value KGj of the air-fuel ratio is provided for each learning region j. Therefore, in step 527, the learning value KGj of the air-fuel ratio in the learning region j corresponding to the engine load is updated. Then, it proceeds to step 528.

On the other hand, in step 524, FAFAV
When it is determined that <1.02, step 525
Then, it is determined whether the average value FAFAV of the feedback correction coefficient is smaller than 0.98. FAFAV
When ≦ 0.98, the routine proceeds to step 526, where the constant value X is subtracted from the learning value KGj of the air-fuel ratio of the learning region j according to the engine load. On the other hand, in step 525, FAF
When it is determined that AV> 0.98, that is, FAFA
When V is between 0.98 and 1.02, the routine jumps to step 528 without updating the learning value KGj of the air-fuel ratio.

At steps 528 and 529, initialization processing for learning the vapor concentration is performed. That is, at step 528, it is judged if the engine is being started. If the engine is being started, the routine proceeds to step 529, where the vapor concentration FGPG per unit purge rate is made zero, and the purge execution time count value CPGR is cleared. . Next, the routine proceeds to the fuel injection time calculation routine shown in FIG. On the other hand, when the engine is not started, the routine directly proceeds to the fuel injection time calculation routine shown in FIG.

Returning to FIG. 2, subsequently, the air-fuel ratio control device learns the vapor concentration and / or calculates the fuel injection time.
FIG. 7 is a flow chart showing the vapor concentration learning routine of FIGS. 2 and 5, and FIG. 8 is a flow chart showing the fuel injection time calculation routine of FIGS. 2, 5 and 7.

Before explaining the vapor concentration learning routine of FIG. 7, the concept of the fuel vapor concentration learning will be described with reference to FIG. FIG. 6 is a graph for explaining the concept of vapor concentration learning. The learning of the fuel vapor concentration starts by accurately obtaining the vapor concentration per unit purge rate. The vapor concentration per unit purge rate is FGPG in FIG.
Indicated by. The purge A / F correction coefficient (purge air-fuel ratio correction coefficient) FPG is obtained by multiplying FGPG by the purge rate PGR. The vapor concentration FGPG per unit purge rate is calculated based on the following equation every time the feedback correction coefficient FAF is skipped (S in FIG. 4).

TFG ← (1-FAFAV) / (PGR · a) FGPG ← FGPG + tFG Here, tFG is an FGPG performed at each FAF skip.
FAFAV represents the average value of the feedback correction coefficient (= (FAFL + FAFR) / 2), and a is set to 2 in the present embodiment.

That is, since the air-fuel ratio becomes rich when the purge is started, the feedback correction coefficient FAF becomes small so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. Next, at time t ₁ , when the O ₂ sensor 30 determines that the air-fuel ratio has switched from rich to lean, the feedback correction coefficient FAF
Is increased. In this case, the feedback correction coefficient FAF from the start of purging to the time t ₁
Change amount ΔFAF (ΔFAF = (1.0−FAF)) represents the change amount of the air-fuel ratio due to the purge action, and this change amount ΔFAF represents the fuel vapor concentration at time t ₁ .

When the time t ₁ is reached, the air-fuel ratio is maintained at the stoichiometric air-fuel ratio, and thereafter the average value FAFAV of the feedback correction coefficient is set to 1.0 so that the air-fuel ratio does not deviate from the stoichiometric air-fuel ratio.
Vapor concentration per unit purge rate FGPG
Is gradually updated every time the feedback correction coefficient FAF is skipped. Update amount t per time of FGPG at this time
FG is set to a half of the deviation amount of the average value FAFAV of the feedback correction coefficient with respect to 1.0.
As described above, FG is tFG = (1-FAFAV) / (P
GR ・ 2).

As shown in FIG. 6, when the updating operation of the FGPG is repeated several times, the average value F of the feedback correction coefficient is
AFAV returns to 1.0, after which the vapor concentration FGPG per unit purge rate becomes constant. Thus FGPG
Is constant means that the FGPG at this time accurately represents the vapor concentration per unit purge rate, and therefore the learning of the vapor concentration is completed. On the other hand, the actual fuel vapor concentration is a value obtained by multiplying the vapor concentration FGPG per unit purge rate by the purge rate PGR. Therefore, the purge A / F correction coefficient FPG (= FGPG · PGR) representing the actual fuel vapor concentration is updated every time FGPG is updated as shown in FIG. 6, and increases as the purge rate PGR increases.

If the vapor concentration changes even after the learning of the vapor concentration after the start of the purge is once completed, the feedback correction coefficient FAF deviates from 1.0, and at this time, tFG (= (1-FAFAV) / (PGR
The update amount of FGPG is calculated using a)).

Next, the vapor concentration learning routine of FIG. 7 will be described. The vapor concentration learning routine of FIG. 7 is started when it is determined in step 523 of FIG. 5 described above that the purge action is being performed. As shown in FIG. 7, first, at step 730, it is judged if the average value FAFAV of the feedback correction coefficient is within a certain range, that is, if 1.02>FAFAV> 0.98. . Average value of feedback correction factor FA
When FAV is within the setting range, namely 1.02> FAF
When AV> 0.98, the routine proceeds to step 732, where the update amount tFG of the purge concentration FGPG per unit purge rate.
Is set to zero, and then the process proceeds to step 733. Therefore, at this time, the vapor concentration FGPG is not updated.

On the other hand, when it is determined in step 730 that the average value FAFAV of the feedback correction coefficient exceeds the certain range, that is, FAFAV ≧ 1.02 or FAFAV ≦ 0.98, step 7
In step 31, 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 2. That is, when the average value FAFAV of the feedback correction coefficient exceeds the set range (between 0.98 and 1.02), half the deviation amount of FAFAV with respect to 1.0 is set as the update amount tFG. Then, it proceeds to step 733. In step 733, the vapor concentration FGPG is updated to t
FG is added. Next, at step 734, an update number counter C indicating the update number of the vapor concentration FGPG.
FGPG is incremented by 1. Next, the routine proceeds to the fuel injection time calculation routine shown in FIG.

The fuel injection time calculation routine of FIG. 8 is started when step 528 and / or step 529 of FIG. 5 described above is completed, or when step 734 of FIG. 7 is completed. As shown in FIG. 8, first, at step 840, the basic fuel injection time TP is calculated based on the engine load Q / N and the engine speed N. Next, at step 841, a correction coefficient FW for increasing the warm-up amount, etc.
Is calculated. Next, at step 842, the vapor concentration FGPG per unit purge rate is multiplied by the purge rate PGR to obtain the purge air-fuel ratio correction coefficient FGR (← FGPG
-PGR) is calculated. Next, at step 843, the fuel injection time TAU is calculated based on the following equation, the fuel injection time calculation routine is ended, and the main routine of FIG. 2 is ended.

[0047] TAU ← TP ・ FW ・ (FAF + KGj-FPG) Here, each coefficient represents the following. TP: Basic fuel injection time FW: correction factor FAF: Feedback correction coefficient KGj: Air-fuel ratio learning coefficient FPG: Purge A / F correction coefficient

The basic fuel injection time TP is an injection time obtained by an experiment necessary to make the air-fuel ratio the target air-fuel ratio, and the basic fuel injection time TP is the engine load Q / N.
It is stored in advance in the ROM 22 as a function of (intake air amount Q / engine speed N) and engine speed N. The correction coefficient FW is a collective expression of the warm-up increase coefficient and the acceleration increase coefficient. When it is not necessary to correct the increase, FW =
It becomes 1.0.

The feedback correction coefficient FAF is provided to control the air-fuel ratio to the target air-fuel ratio based on the output signal of the O ₂ sensor 30. Purge A / F correction factor FP
From the start of engine operation to the start of purge, G is set to FPG = 0, and becomes larger as the fuel vapor concentration increases when the purge action starts. When the purge action is temporarily stopped during engine operation, FPG = 0 is set during the purge action stop period.

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 the target air-fuel ratio is the stoichiometric air-fuel ratio in the embodiment shown in FIG. Will be described. 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. This O ₂ sensor 30 generates an output voltage of about 0.9 (V) when the air-fuel ratio is on the rich side, that is, when it is rich, and 0.1 (V when the air-fuel ratio is on the lean side, that is, when it is lean. ) Generate an output voltage of the order of.

Next, referring to FIGS. 9 to 13, the internal routine of the present embodiment is executed by interrupting the main routine of FIG. 2 every 100 msec corresponding to a duty ratio calculation cycle described later. The interrupt routine of the evaporated fuel processing device will be described. FIG. 9 is a flowchart showing an interrupt routine of the evaporated fuel processing apparatus for an internal combustion engine of this embodiment. As shown in FIG. 9, when the evaporated fuel processing device starts the interrupt routine, first, at step 90
The purge rate is calculated at 1.

10 and 11 are flowcharts showing the purge rate calculation routine of FIG. 10 and 1
As shown in FIG. 1, first, at step 1050, it is judged if it is time to calculate the duty ratio of the drive pulse of the purge control valve 17. In the present embodiment, the duty ratio is calculated every 100 msec. When it is not the time to calculate the duty ratio, the purge rate calculation routine is ended as it is. On the other hand, when it is the time to calculate the duty ratio, the routine proceeds to step 1051, where it is judged if the purge condition 1 is satisfied, for example, if the warm-up is completed. If the purge condition 1 is not satisfied, step 1
In 064, initialization processing is performed, and then step 1
At 065, the duty ratio DPG and the purge rate PGR are made zero, and the purge rate calculation routine ends. On the other hand, when the purge condition 1 is satisfied, step 10
The routine proceeds to 52, where it is determined whether or not the purge condition 2 is satisfied, for example, whether or not the air-fuel ratio feedback control is being performed, and whether or not the fuel supply is stopped. If purge condition 2 is not satisfied, step 1
The process proceeds to 065, and when the purge condition 2 is satisfied, the process proceeds to step 1053.

At step 1053, the full-open purge flow rate KP
Full open purge rate PG10, which is the ratio of Q to the intake air amount Ga
0 (← (KPQ / Ga) · 100) is calculated. Here, the fully open purge flow rate KPQ represents the purge flow rate when the purge control valve 17 is fully opened, and the intake air amount Ga is detected by the air flow meter 7 (FIG. 1). The full open purge rate PG100 is a function of, for example, the engine load Q / N (intake air amount Ga / engine speed N) and the engine speed N, and is obtained in advance by an experiment, and is in the form of a map as shown in the table below. It is stored in the ROM 22 in advance.

[0054]

[Table 1]

As the engine load Q / N becomes lower, the full open purge flow rate KPQ with respect to the intake air amount Ga becomes larger. The lower the number N is, the fully open purge flow rate K with respect to the intake air amount Ga
Since PQ increases, as shown in Table 1, the full open purge rate PG100 increases as the engine speed N decreases.

Next, at step 1054, the feedback correction coefficient FAF is set to the upper limit value KFAF15 (= 1.15).
And the lower limit value KFAF85 (= 0.85). KFAF15>FAF> KFAF85
When, that is, when the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio, the routine proceeds to step 1057. At step 1057, the target purge rate tPGR (← PGR is added by adding a constant value KPGRu to the purge rate PGR.
+ KPGRu) is calculated. That is, KFAF15> F
It can be seen that when AF> KFAF85, the target purge rate tPGR is gradually increased every 100 msec.
It should be noted that the target purge rate tPGR has an upper limit P.
Since (P is, for example, 6%) is set, the target purge rate tPGR can only increase to the upper limit value P. Then, the process proceeds to step 1059.

On the other hand, in step 1054, FAF ≧
When it is determined that KFAF15 or FAF ≦ KFAF85, the routine proceeds to step 1058, where the target purge rate tPGR (← PGR-KPGRd) is calculated by subtracting the constant value KPGRd from the purge rate PGR. That is, when the air-fuel ratio cannot be maintained at the stoichiometric air-fuel ratio due to the purge action of the fuel vapor, the target purge rate tPG
R is reduced. A lower limit value S (S = 0%) is set for the target purge rate tPGR. Then, the process proceeds to step 1059.

At step 1059, the target purge rate tPG
By dividing R by the full open purge rate PG100, the duty ratio DPG of the drive pulse of the purge control valve 17 can be obtained.
(← (tPGR / PG100) · 100) is calculated. Therefore, the duty ratio DPG of the drive pulse of the purge control valve 17, that is, the valve opening amount of the purge control valve 17 is controlled according to the ratio of the target purge rate tPGR to the full open purge rate PG100. In this way, the purge control valve 1
7 is controlled according to the ratio of the target purge rate tPGR to the full open purge rate PG100, the target purge rate t
Regardless of the purge rate of PGR, the actual purge rate is maintained at the target purge rate regardless of the operating condition of the engine.

For example, now, the target purge rate tPGR is 2%, and the full open purge rate PG100 in the current operating state.
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 operating state changes and the full-open purge rate PG100 in the changed operating 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.
If changes to 4%, the actual purge rate is maintained at 4% regardless of the engine operating condition.

Next, at step 1060, the full open purge rate PG100 is multiplied by the duty ratio DPG to obtain the actual purge rate PGR (← PG100 (DPG / 1
00)) is calculated. That is, as described above, the duty ratio DPG is represented by (tPGR / PG100) · 100, and in this case, the target purge rate tPGR is the full open purge rate P.
When it becomes larger than G100, the duty ratio DPG becomes 10
It becomes 0% or more. However, the duty ratio DPG is 1
The duty ratio DPG cannot exceed 100% at this time.
Is 100%, the actual purge rate PGR becomes smaller than the target purge rate tPGR. Therefore, the actual purge rate PGR is PG100. (DPG / 10
0).

Next, at step 1061, the duty ratio DPG is made DGO and the purge rate PGR is made PGR0. Next, at step 1062, the purge execution time counter CP representing the time from the start of purging.
GR is incremented by 1, and the purge rate calculation routine ends.

Returning to FIG. 9, next, at step 902, the drive processing of the purge control valve 17 is performed. FIG. 12 is a flowchart showing the purge control valve drive processing routine of FIG. As shown in FIG. 12, in the purge control valve drive processing routine, first, at step 1266, it is determined whether the duty cycle is the output cycle of the duty ratio, that is, the purge control valve 17
It is determined whether or not it is the rising cycle of the driving pulse.
The output cycle of this duty ratio is 100 msec. When it is the output cycle of the duty ratio, the routine proceeds to step 1267, where it is judged if the duty ratio DPG is zero. When DPG = 0, the routine proceeds to step 1271, where the drive pulse YEVP of the purge control valve 17 is turned off.
On the other hand, when DPG = 0 is not satisfied, step 126
8, the drive pulse YEVP for the purge control valve 17 is turned on. Next, at step 1269, the current time T
By adding the duty ratio DPG to IMER, the drive pulse OFF time TDPG (← DPG + TIME
R) is calculated, and the purge control valve drive processing routine ends.

On the other hand, when it is determined in step 1266 that the duty cycle is not the output cycle, the routine proceeds to step 1270, where it is determined whether or not the current time TIMER is the drive pulse off time TDPG. TDPG
= TIMER, the routine proceeds to step 71, where the drive pulse YEVP is turned off and the purge control valve drive processing routine is ended. On the other hand, when TDPG = TIMER is not satisfied,
Then, the purge control valve drive processing routine ends.

Returning to FIG. 9, the evaporated fuel processing apparatus subsequently performs vapor concentration correction control in step 903. FIG. 13 is a flowchart showing a vapor concentration correction control routine. As shown in FIG. 13, in the evaporated fuel processing apparatus, first in step 1301, the full open purge flow rate KPQ is calculated from the intake branch pipe negative pressure detected by the intake branch pipe negative pressure detection means (not shown) and the map shown in FIG. calculate. FIG. 14 is a graph showing the relationship between the negative pressure in the intake branch pipe and the fully open purge flow rate KPQ.
It is stored in M22. As shown in FIG. 14, the full-open purge flow rate KPQ increases as the negative pressure in the intake branch pipe increases.

Returning to FIG. 13, subsequently, at step 1302, the full open purge flow rate KPQ and the current duty ratio DPG.
From the above, the actual purge flow rate PQ is calculated. Subsequently, in step 1303, it is determined whether or not the ratio of the fuel vapor from the fuel tank 15 to the fuel vapor purged from the canister 11 and the fuel tank 15 into the intake branch pipe 2 is large. At 1304, the current purge flow rate PQ is set as the vapor concentration correction purge flow rate PQSM. On the other hand, if YES, the process proceeds to step 1305. still,
For details of the determination method in step 1303,
This will be described later with reference to FIG.

Returning to FIG. 13, in step 1305, it is determined whether the purge rate PGR is zero, and YES
If NO, the vapor concentration correction control routine is ended, and if NO, the routine proceeds to step 1306. Step 1
At 306, the current purge flow rate PQ calculated at step 1302 is regarded as the purge flow rate tPQSM actually sucked into the combustion chamber of the internal combustion engine. Then Step 130
7, the purge flow rate PQS calculated in the previous routine
M and the current purge flow rate t calculated in step 1306
PQSM and purge flow rate of change KPQSM (← PQS
M / tPQSM) is calculated. Then, Step 1308
Then, in step 1309, it is determined whether or not the change in the purge flow rate is large. Specifically, the purge flow rate change rate KPQ
When SM is 1.1 or more or 0.9 or less,
When it is determined that the change in the purge flow rate is large, step 1310 is performed.
Then, the vapor concentration FGPG is corrected based on the purge flow rate change rate KPQSM (FGPG ← FGPG × KPQ).
SM). That is, in the present embodiment, when the ratio of the fuel vapor from the fuel tank 15 in the fuel vapor purged from the canister 11 and the fuel tank 15 into the intake branch pipe 2 is large, the intake air amount changes. When the accompanying change in the purge flow rate is large, the vapor concentration FGPG can be promptly corrected without going through the vapor concentration learning routine shown in FIG. Therefore, the actual vapor concentration FGP
Even when G changes greatly, the actual vapor concentration F
The GPG can be calculated accurately. Returning to FIG.
Then, it proceeds to step 1311.

On the other hand, step 1308 and step 13
If it is determined in 09 that the change in the purge flow rate is small, the process directly proceeds to step 1311. In step 1311, the vapor concentration correction purge flow rate PQSM is updated with the current purge flow rate tPQSM calculated in step 1306, the vapor concentration correction control routine is ended, and the interrupt routine of FIG. 9 is ended.

FIG. 15 is a graph showing the vapor concentration and the purge flow rate during the idle operation and the acceleration operation of the internal combustion engine regarding the fuel vapor passing through the positions A to C in FIG. 1 in the arrow direction. As shown in FIG. 15, the purge flow rate B of the fuel vapor flowing out of the fuel tank 15 does not change during the idle operation and the acceleration operation, or does not change much, but the purge flow rate C of the fuel vapor flowing out of the canister 11 does not change. Becomes larger during acceleration operation than during idle operation (FIG. 15 (b)). Further, the vapor concentration B of the fuel vapor flowing out from the fuel tank 15 and the vapor concentration C of the fuel vapor flowing out via the canister 11 do not change between the idle operation and the acceleration operation (FIG. 15 (c)). Therefore, the vapor concentration A of the fuel vapor that flows out from the fuel tank 15 and the canister 11 and merges is inversely proportional to the purge flow rate and becomes lower during the acceleration operation than during the idle operation.

FIG. 16 is a graph showing the effect of the vapor concentration correction control of this embodiment. In FIG.
FIG. 16A shows the state of the vapor concentration correction control based only on the vapor concentration learning routine of the conventional vaporized fuel processing apparatus, and FIG. The state of the vapor concentration correction control based on the concentration correction control routine is shown. Figure 1
As shown in 6 (a), in the conventional fuel vapor treatment device,
At the start of acceleration at time t _1, the vapor concentration is not immediately reduced even if the purge flow rate PQ increases as the intake air amount increases. Therefore, the feedback correction coefficient FAF increases as the air-fuel ratio (A / F) becomes leaner. For the first time, the vapor concentration FGPG begins to decrease (a '
→ b '). Similarly, at the end of acceleration at time t ₂ , even if the purge flow rate PQ decreases as the intake air amount decreases, the vapor concentration does not immediately increase. Therefore, the feedback correction coefficient FAF decreases as the air-fuel ratio becomes rich. For the first time, the vapor concentration FGPG starts to increase (c ′ → d ′).

On the other hand, as shown in FIG. 16 (b), in the fuel vapor processing apparatus of this embodiment, when the purge flow rate PQ increases with the increase of the intake air amount at the start of acceleration at time t ₁ , the vapor flow rate is immediately increased. The concentration is reduced (a → b). Therefore, the air-fuel ratio does not become so lean, and the feedback correction coefficient FAF does not become too rough. Similarly, the acceleration at the end of time t _2, the purge flow rate PQ with a decrease in the intake air amount
The vapor concentration is immediately increased when is decreased (c →
d). Therefore, the air-fuel ratio does not become so rich, and the feedback correction coefficient FAF does not become too rough.

FIG. 17 is a flowchart showing a part of a vapor concentration correction control routine of the second embodiment of the evaporated fuel processing apparatus for an internal combustion engine of the present invention. In FIG. 17, only the parts different from the first embodiment are shown. As shown in FIG. 17, in the present embodiment, in order to avoid excessive correction of the vapor concentration FGPG, the average value of the current purge flow rate PQ calculated in step 1302 based on the previous purge flow rate PQSM is actually set. Is regarded as the purge flow rate tPQSM drawn into the combustion chamber of the internal combustion engine (tPQSM ← (PQ
+ PQSM) / KSM2, where KSM2 is the smoothing coefficient).

FIG. 18 is a graph showing the purge flow rate tPQSM calculated according to the first embodiment and the purge flow rate tPQSM calculated according to the second embodiment. Figure 1
As shown in FIG. 8, at time t, the purge flow rate tPQSM changes drastically in the first embodiment (broken line in the figure), but in the second embodiment, the purge flow rate tPQSM.
Does not change so much as in the first embodiment because it is annealed in step 1706 (solid line in the figure). According to this smoothing process, the vapor concentration FGPG calculated based on the change rate of the purge flow rate when the purge flow rate PQ suddenly changes.
Can be prevented from overshooting.

FIG. 19 is a flowchart showing a part of a vapor concentration correction control routine of a modified example of the second embodiment of the evaporated fuel processing apparatus for an internal combustion engine of the present invention. In FIG. 19, only the parts different from the first embodiment are shown. FIG. 19
As shown in, in this modification, the purge flow rate tPQSM actually sucked into the combustion chamber of the internal combustion engine is calculated based on the following equation in order to avoid excessive correction of the vapor concentration FGPG. tPQSM ← PQSM + (PQ-PQSM) / KSM where KSM is the smoothing coefficient

FIG. 20 is a graph showing the purge flow rate tPQSM calculated according to the first embodiment and the purge flow rate tPQSM calculated according to the modification of the second embodiment. As shown in FIG. 20, at time t, in the first embodiment, the purge flow rate tPQSM changes drastically (dashed line in the figure), but in the modification of the second embodiment, the purge flow rate tPQSM is changed to step 1906. Since it is annealed, it does not change so much as in the first embodiment (solid line in the figure). This smoothing process can also prevent the vapor concentration FGPG calculated based on the change rate of the purge flow rate from overshooting when the purge flow rate PQ suddenly changes.

FIG. 21 is a flowchart showing a part of the vapor concentration correction control routine of the third embodiment of the evaporated fuel processing apparatus for the internal combustion engine of the present invention. In FIG. 21, only parts different from the first embodiment are shown. As shown in FIG. 21, in the present embodiment, in step 2101, the current duty ratio D is set regardless of the value of the full open purge flow rate KPQ.
The actual purge flow rate PQ (← DPG) is calculated only from PG. According to the present embodiment, in the operating region of the internal combustion engine in which the value of the full-open purge flow rate KPQ does not change so much, it is possible to achieve the same effect as the first embodiment while simplifying the calculation as compared with the first embodiment. You can

22 and 23 are flowcharts showing a part of the vapor concentration correction control routine of the fourth embodiment of the evaporated fuel processing apparatus for the internal combustion engine of the present invention. FIG. 22
Before explaining FIG. 23 and FIG. 23, the reason for applying this embodiment will be described. As described above, in the first embodiment, the vapor concentration FGPG is corrected and controlled based on the purge flow rate change rate KPQSM, and the desorption amount of the fuel vapor desorbed from the canister 11 is not considered. However,
The vapor concentration FGPG differs depending on whether the desorption amount of the fuel vapor desorbed from the canister 11 is large or small. Therefore, in the present embodiment, the purge flow rate change rate KPQ
The vapor concentration FGPG is corrected and controlled based on not only the SM but also the desorption amount of the fuel vapor desorbed from the canister 11.

Further, the basic idea of this embodiment will be described. In the present embodiment, the vapor concentration is corrected and controlled by converting the increase amount of the vapor concentration accompanying the desorption of the fuel vapor from the canister into the increase amount of the vapor concentration accompanying the decrease of the purge flow rate including the fuel vapor. That is, when the vapor concentration increases or decreases as the desorption amount of the fuel vapor from the canister increases or decreases, it is considered that the vapor concentration increases or decreases as the purge flow rate including the fuel vapor decreases or increases. In the present embodiment, the amount of decrease in the purge flow rate corresponding to the amount of desorption of fuel vapor from the canister is defined as the predicted decrease air amount KPQOF.

Returning to FIG. 22 and FIG. 23, only the part of the present embodiment different from the first embodiment will be described below. As shown in FIG. 22 and FIG. 23, in the evaporated fuel processing apparatus, in step 1303, the fuel vapor from the fuel tank 15 occupies in the fuel vapor purged from the canister 11 and the fuel tank 15 into the intake branch pipe 2. It is determined whether or not the ratio is large, and if NO, in step 2300, the basic air amount PQmax and the predicted drop air amount calculation coefficient K are set in order to set the initial value of the predicted drop air amount KPQOF.
Predicted air amount decrease from QR and KPQOF (← PQmax ×
KQR) is calculated. Here, the basic air amount PQmax is a purge flow rate corresponding to when the purge control valve 17 is fully opened. The predicted decrease air amount calculation coefficient KQR is 0.5 in the present embodiment, but can be set to another value as necessary in other embodiments. Subsequent to step 2300 or when it is determined in step 1305 that the purge rate PGR is zero, in step 2301, the purge flow rate calculated in step 1302 is set in order to set the initial value of the smoothed purge flow rate PQSM32. PQ is regarded as the smoothed purge flow rate PQSM32, and the routine proceeds to step 1304.

If it is determined in step 1305 that the purge rate PGR is not zero, in step 2302 the vapor concentration correction direction is detected. FIG. 24 is a flowchart showing the vapor concentration correction direction detection routine of FIG.
As shown in FIG. 24, the evaporative fuel treatment apparatus first, in step 2401, uses the following equation to calculate the current smoothed purge flow rate P.
Calculate QSM32. The degree of annealing in this step is adapted to the extent that the effect of the vapor concentration change remains on the change of the purge flow rate. PQSM32
← PQSM32 + (PQ-PQSM) / KSM32 where KSM32 is the smoothing coefficient

Subsequently, step 2402 and step 240
In step 3, it is determined whether or not the smoothed purge flow rate PQSM32 has increased. If the smoothed purge flow rate PQSM32 has decreased, the process proceeds to steps 2404 and 2405, and if it has not changed much, the process proceeds to steps 2406 and 2407. If it increases, step 24
08 and to step 2409. In step 2404 and step 2405, a vapor concentration + correction flag indicating that the vapor concentration should be corrected to be increased is set (XFPGGU ← 1), and in step 2406 and step 2407, the vapor concentration should be increased or decreased. Set a flag indicating that it is not (XFGPGD ←
0, XFGPGU ← 0), and in Steps 2408 and 2409, a vapor concentration-correction flag indicating that the vapor concentration should be corrected to be reduced is set (XFGPGD ← 1), and the vapor concentration correction direction detection routine is executed. finish.

Returning to FIG. 22 and FIG. 23, subsequently, in steps 2303 and 2304, it is determined whether or not the feedback correction coefficient FAF is within a predetermined range (0.92 to 1.08), and the feedback correction coefficient FAF is determined. Is 0.92 or less, the routine proceeds to step 2305, when the feedback correction coefficient FAF is larger than 0.92 and smaller than 1.08, the routine proceeds to step 2315, and when the feedback correction coefficient FAF is 1.08 or more, the routine proceeds to step 2310. move on. O _{2 in} step 2305
It is determined whether or not the output value of the sensor 30 is 0.45 V or more. If YES, the process proceeds to step 2306, and if NO, the process proceeds to step 2315. In step 2306, it is determined whether or not XFGPGU = 1. If YES, in step 2308 the predicted decrease air amount KPQOF is decreased by a predetermined amount KQ (KPQOF ← KPQOF-K
In the case of Q) and NO, the process proceeds to step 2307. In step 2307, it is determined whether or not XFGPGD = 1,
If YES, in step 2309 the predicted decrease air amount K
Increase PQOF by a predetermined amount KQ (KPQOF ← KP
(QOF + KQ), if NO, the process proceeds to step 2315. On the other hand, in step 2310, it is determined whether or not the output value of the O ₂ sensor 30 is smaller than 0.45 V, the process proceeds to step 2311 if YES, and step 2 if NO.
Proceed to 315. In step 2311, XFGPGU = 1
If YES, step 231
In step 4, the predicted decrease air amount KPQOF is increased by a predetermined amount KQ (KPQOF ← KPQOF + KQ), and if NO, the process proceeds to step 2312. In step 2312, XFG
It is determined whether or not PGD = 1, and if YES, the predicted decrease air amount KPQOF is set to the predetermined amount K in step 2313.
Decrease by Q (KPQOF ← KPQOF-KQ), N
When it is O, the process proceeds to step 2315. That is, when the air-fuel ratio is rich and XFGPGU = 1, the predicted decrease air amount KPQOF is decreased by a predetermined amount KQ in step 2308, and the air-fuel ratio is rich and XFGPGD = 1.
If it is, the predicted decrease air amount KP is determined in step 2309.
When QOF is increased by a predetermined amount KQ and the air-fuel ratio is lean and XFGPGU = 1, in step 2314 the predicted decrease air amount KPQOF is increased by a predetermined amount KQ, and when the air-fuel ratio is lean and XFGPGD = 1. At some time, in step 2313, the predicted decrease air amount KPQOF is decreased by the predetermined amount KQ.

Subsequently, step 2315 to step 231
8, the predicted decrease air amount KPQOF is set to the minimum value KPQMI.
Set within the range of N to the maximum value KPQMAX. Then, in step 1906, tPQSM is calculated, and in step 2
In 319, the purge flow rate change rate KPQSM (← (PQSM-KPQOF) / (tPQ) is calculated from the previous purge flow rate (PQSM-KPQOF) and the current purge flow rate (tPQSM-KPQOF) in consideration of the predicted decrease air amount KPQOF.
SM-KPQOF)) is calculated. According to the present embodiment, the purge flow rate change rate KPQSM can be calculated more accurately than when the desorption amount of the fuel vapor from the canister 11 is not considered.

FIG. 25 is a graph similar to FIG. 15 when the fuel vapor is detached from the canister. As shown in FIG. 25, the vapor concentration at the position A in FIG. 1 is higher than that in the case of FIG. 15 by the amount of desorption of fuel vapor from the canister C. FIG. 26 is a graph showing the purge flow rate of this time or the previous time comparing the case where the desorption of the vapor fuel from the canister is considered and the case where it is not considered. As shown in FIG. 26, when the desorption of vapor fuel from the canister is taken into consideration, the previous purge flow rate (PQSM-KPQOF) or the current purge flow rate (tPQSM-KPQOF) increases as the predicted decrease air amount KPQOF increases. Decrease. on the other hand,
Without considering the desorption of vapor fuel from the canister,
Previous purge flow PQSM or current purge flow tPQ
SM is independent of the predicted drop air amount KPQOF.

FIG. 27 is a graph showing the operational effects of the vapor concentration correction control of this embodiment. As shown in FIG. 27, while the desorption amount of the fuel vapor desorbing from the canister is large (before time t), the predicted decrease air amount KPQOF is set to a large value, but the desorption of the fuel vapor desorbing from the canister is released. When the separation amount decreases (time t), the predicted decrease air amount K
The value of PQOF is reduced in step 2308 of FIG.

FIG. 28 is a flow chart showing a part of the vapor concentration correction control routine of the fifth embodiment of the evaporated fuel processing apparatus for the internal combustion engine of the present invention. In FIG. 28, only parts different from those of the fourth embodiment are shown. As shown in FIG. 28, the evaporative fuel processing apparatus operates as shown in FIG.
Predicted decrease air amount KPQ based on the map shown in FIG.
Calculate OF. FIG. 28B is a map showing the relationship between the vapor concentration FGPG and the predicted decrease air amount KPQOF, and this numerical value is stored in the ROM 22 in advance. As shown in FIG. 28B, when the vapor concentration FGPG is low, the amount of air in the purge flow rate is large, so the predicted decrease air amount KPQOF is set to a smaller value as the vapor concentration FGPG is lighter. .

FIG. 29 is a graph showing the present purge flow rate tPQSM calculated by the delay process in the vapor concentration correction control routine (not shown) of the sixth embodiment of the evaporated fuel treatment apparatus for the internal combustion engine of the present invention. Is. In the present embodiment, a delay process is added when the purge flow rate tPQSM is calculated this time in consideration of the delay until the fuel vapor passing through the conduit (purge passage) 16 actually flows into the combustion chamber of the internal combustion engine. As shown in FIG. 29, the current purge flow rate tPQSM (solid line in the figure) calculated by the delay process in the present embodiment is the delay amount compared to the purge flow rate PQ (broken line in the figure) calculated in step 1302. Change only with a delay.

FIG. 30 is a flowchart showing a part of the vapor concentration correction control routine of the seventh embodiment of the evaporated fuel processing apparatus for the internal combustion engine of the present invention. In FIG. 30, only parts different from those of the first embodiment are shown. As shown in FIG. 30, when it is determined in step 1305 that the purge rate PGR is not zero, the evaporated fuel processing apparatus determines in step 3001 whether XFGPG = 1, that is,
It is determined whether or not the vapor concentration learning is completed. YE
When it is S, it progresses to step 1306, and when it is NO, it progresses to step 3002. In step 3002, it is determined whether or not the feedback correction coefficient skip counter CSKIP is, for example, 3 or more. If YES, the process proceeds to step 3003, and if NO, step 1
Proceed to 304. In step 3003, it is determined whether or not the average value FAFAV of the feedback correction coefficient is within a range of, for example, ± 2%. If YES, step 300
4 and set a vapor concentration learning completion flag (XFGP
When G ← 1), NO, that is, when the relationship between the vapor concentration and the purge flow rate is unstable, the process proceeds to step 1304. According to the present embodiment, for example, when the operating state of the internal combustion engine is unstable and the vapor concentration correction control is performed before the vapor concentration learning is completed, the vapor concentration FGPG overshoots. It is possible to prevent the correction control from being executed.

FIG. 31 is a graph showing the action and effect of the vapor concentration correction control of this embodiment. As shown in FIG. 31, in this embodiment, in step 1303, the ratio of the fuel vapor from the fuel tank 15 in the fuel vapor purged from the canister 11 and the fuel tank 15 into the intake branch pipe 2 increases. The vapor concentration learning is completed (XFGPG = 1) instead of starting the vapor concentration correction control immediately (time t ₁ ) after it is determined that (XTNK = 1).
After that, the vapor concentration correction control is started (after time t ₂ ).

FIG. 32 is a flow chart showing a routine for raising the XTNK = 1 flag necessary for the judgment in step 1303. Step 32 shown in FIG.
01 to step 3205 may be inserted anywhere in the main routine of FIG. 2, but in the above-described first to seventh embodiments, they are inserted before step 733 of FIG. 7. The evaporated fuel processing apparatus first determines in step 3201 whether or not the purge execution counter CPGR is greater than or equal to a predetermined value KCPGR, the process proceeds to step 3202 if YES, and this routine is executed without setting the XTNK = 1 flag if NO. To finish. In step 3202, it is determined whether or not the purge rate PGR is greater than or equal to the predetermined value KPGR, the process proceeds to step 3203 if YES, and the routine ends if NO. In step 3203, it is determined whether the duty ratio DPG is greater than or equal to a predetermined value KDPG20, and if YES, the process proceeds to step 3204.
If NO, this routine ends. In addition, step 3
Instead of 203, whether or not the purge flow rate PQ is equal to or greater than a predetermined value KPQ, or during idle (XIDL = 1)
May be determined. Then, Step 320.
In 4, the feedback correction coefficient FAF is a predetermined value KFAF.
It is determined whether it is equal to or less than 09, that is, whether the air-fuel ratio is richer than a predetermined air-fuel ratio, and when YES, XT
The NK = 1 flag is set, and when NO, this routine is ended. Although not shown, the XTNK = 1 flag is cleared in the initial routine when the internal combustion engine is started.

FIG. 33 is a flow chart showing a routine inserted between step 3203 and step 3204 of FIG. 32 as a modification of the routine of FIG. This routine is for the vapor concentration change flag XT even during continuous running.
It is an example of controlling the purge flow rate so that the NK can be operated. That is, when the vehicle travels over a certain level, the desorption of the fuel vapor from the canister progresses, while the fuel vapor flowing out from the fuel tank increases, so that the conventional purge control is interrupted and the duty ratio (purge flow rate) is determined in step 3306. )
Is to reduce.

FIG. 34 is a vapor concentration correction control routine of the eighth embodiment of the evaporated fuel processing apparatus for an internal combustion engine of the present invention, considering that the fuel vapor generated from the fuel tank is adsorbed to the canister during the purge cut. It is a flowchart showing. As shown in FIG. 34, in the evaporated fuel processing apparatus, first, in step 3401, the ratio of the fuel vapor from the fuel tank 15 in the fuel vapor purged from the canister 11 and the fuel tank 15 into the intake branch pipe 2 is determined. It is determined whether or not it is large (XTNK = 1). If NO, the duty ratio DPG1 is set to the vapor concentration correction duty ratio DPGSM in step 3411 (DPGSM ←
DPG1), and proceeds to step 3412. On the other hand, if YES, the process proceeds to step 3402.

At step 3402, it is judged if the purge rate PGR is zero, and if YES, step 34
If NO, proceed to step 3403. In step 3403, it is determined whether or not the previous duty ratio DPG1 is zero, that is, whether or not the execution of this routine is the first one after the restart of the purge action. If NO, the process proceeds to step 3405 and YES. Then step 3
Proceed to 404. In step 3404, considering that the fuel vapor generated from the fuel tank is adsorbed to the canister during the purge cut, the duty ratio DPG1 regarded as the previous duty ratio is set to the duty ratio DPG of this time.
Smaller than (DPG1 ← DPG × KDPGD
(Here, KDPGD is a coefficient smaller than 1)), and DPG1 is guarded by the minimum value KDPGmin.
That is, in step 3404, the duty ratio DPG1 is reduced, that is, the purge flow rate PQ is considered to be small, so that the vapor concentration FGPG after the restart of purge is increased. Then, the process proceeds to step 3405.

In step 3405, step 3411
Alternatively, based on the previous duty ratio DPGSM obtained in step 3410 of the previous routine, and the current duty ratio tDPGS from the DPG1 and the smoothing coefficient KSM obtained in step 3401 or step 3412 of the previous routine.
M (← DPGSM + (DPG1-DPGSM) / KS
Calculate M). Then, in step 3406, the duty ratio change rate KDPGSM (← DPGSM / tDPGSM) is calculated from the previous duty ratio DPGSM and the current duty ratio tDPGSM calculated in step 3405. Then, Step 3407 and Step 340
At 8, it is determined whether the change in duty ratio is large. Specifically, the duty ratio change rate KDPGSM is 1.
When it is 1 or more or 0.9 or less, it is determined that the change in the duty ratio is large, and the process proceeds to step 3409.
Based on the duty ratio change rate KPQSM, the vapor concentration F
Modify GPG (FGPG ← FGPG × KDPGS
M). That is, in the present embodiment, since the vapor concentration is corrected to the higher side in consideration of the fact that the fuel vapor adsorbed in the canister is desorbed after the purging action is restarted while the purging action is stopped, an accurate vapor concentration is obtained. You can Then, in step 3410, DPGSM is updated by tDPGSM, and in step 3412, DPG1 is updated by DPG, and this routine ends. As a modified example of this embodiment, DPG1 may be obtained by subtracting the predetermined value tKD from DPG, instead of step 3404 (D).
PG1 ← DPG-tKD).

FIG. 35 is a graph showing the effect of the vapor concentration correction control of this embodiment. In FIG.
(A) shows the relationship between time and vapor concentration FGPG, and FIG. 35 (b) shows the relationship between DPGSM and DPG1 and time. As shown in FIG. 35B, the value of DPG1 immediately after the restart of the purge action is D just before the purge cut.
It is smaller than the value of PG1. Because of that,
The value of DPGSM is reduced after resuming the purging action. Therefore, as shown in FIG. 35 (a), the vapor concentration FGP
The value of G is increased after resuming the purging action.

FIG. 36 is a graph showing the vapor concentration and the purge flow rate before the purge cut and after the restart of the purge action regarding the fuel vapor passing through the positions A to C in FIG. 1 in the arrow direction. As shown in FIG. 36, neither the purge flow rate B of the fuel vapor flowing out from the fuel tank 15 nor the purge flow rate C of the fuel vapor flowing out of the canister 11 before or after the purge cut is restarted, or much. It does not change (FIG. 36 (b)). On the other hand, the vapor concentration B of the fuel vapor flowing out from the fuel tank 15 does not change between before the purge cut and after the restart of the purge action.
The vapor concentration C of the fuel vapor flowing out through 1 is higher after the restart of the purge action than before before the purge cut due to the effect that the fuel vapor adsorbed to the canister during the purge cut is desorbed from the canister after the restart of the purge action. (FIG. 36 (c)). Therefore, the vapor concentration A of the fuel vapor that has flowed out of the fuel tank 15 and the canister 11 and merged.
Also, after the purging action is restarted, the density becomes darker than that before the purge cut (FIG. 36 (a)).

FIG. 37 is a flowchart showing a part of the vapor concentration correction control routine of the ninth embodiment of the evaporated fuel processing apparatus for an internal combustion engine of the present invention. In FIG. 37, only the parts different from the seventh embodiment are shown. As shown in FIG. 37, in the present embodiment, when YES is determined in step 3402, the coefficient KDPGD is decreased by a predetermined value KD and guarded by the minimum value KDmin in step 3501. According to this embodiment, the coefficient K is calculated every time this routine is executed (for example, every 10 msec) during the purge cut.
The value of the coefficient KDPGD becomes smaller as the DPGD is reduced and the purge cut time becomes longer. Therefore, when the purge cut time is long, the vapor concentration after the restart of the purge action can be corrected to be richer in consideration of the fact that the amount of the fuel vapor adsorbed in the canister desorbs from the canister increases.

FIG. 38 is a graph showing the effect of the vapor concentration correction control of this embodiment. In FIG.
FIG. 38A shows the relationship between time and vapor concentration FGPG, and FIG. 38B shows the relationship between DPGSM and DPG1 and time. As shown in FIGS. 38 (a) and 38 (b), the vapor concentration FGPG after the restart of the purge action is
Darkens as the purge cut time increases.

FIG. 39 shows an evaporated fuel processing apparatus for an internal combustion engine according to a ninth embodiment of the present invention as a modified example of the ninth embodiment in consideration of the fact that the vapor concentration after restarting the purging action increases as the purge cut time increases. It is the flowchart which showed the vapor density correction control routine of 10th Embodiment. As shown in FIG. 39, in the evaporated fuel processing apparatus, first, in step 3401, the ratio of the fuel vapor from the fuel tank 15 in the fuel vapor purged from the canister 11 and the fuel tank 15 into the intake branch pipe 2 is determined. Large (XTNK
= 1), and if NO, step 3411.
Then, the duty ratio DPG1 is set to the vapor concentration correction duty ratio DPGSM (DPGSM ← DPG1), and the routine proceeds to step 3412. On the other hand, if YES, step 34
Go to 02.

In step 3402, it is judged whether or not the purge rate PGR is zero, and if YES, step 3
At 902, DPGSM is increased by a predetermined value KU and guarded at maximum value KUMAX, and if NO, the process proceeds to step 3601. In step 3601, it is determined whether or not the previous duty ratio DPG1 is zero, that is, whether or not the execution of this routine is the first one after the restart of the purge action. If NO, the process proceeds to step 3405 and YES.
In case of, the process proceeds to step 3406.

In step 3405, step 390
2, step 3411, or the previous duty ratio DPGSM obtained in step 3410 of the previous routine,
DPG1 obtained in step 3412 of the previous routine
This duty ratio tDPG from the smoothing coefficient KSM
SM (← DPGSM + (DPG1-DPGSM) / KS
Calculate M). Then, in step 3406, the duty ratio change rate KDPGSM (← DPGSM / tDPGSM) is calculated from the previous duty ratio DPGSM and the current duty ratio tDPGSM calculated in step 3405. That is, step 3602 is performed during the purge cut.
When the value of DPGSM is increased in, the duty ratio change rate KDPGSM increases.

Subsequently, step 3407 and step 34
At 08, it is determined whether the change in the duty ratio is large. Specifically, the duty ratio change rate KDPGSM is 1.
When it is 1 or more or 0.9 or less, it is determined that the change in the duty ratio is large, and the process proceeds to step 3409.
Based on the duty ratio change rate KPQSM, the vapor concentration F
Modify GPG (FGPG ← FGPG × KDPGS
M). That is, when the purge cut time is long, step 3
At 602, the value of DPGSM is increased and step 34
At 06, the value of the duty ratio change rate KDPGSM is increased, and therefore, the value of the vapor concentration FGPG is increased in this step. Then, in step 3410, the DPG
SM is updated with tDPGSM and D is returned in step 3412.
PG1 is updated with DPG, and this routine ends.

FIG. 40 is a graph showing the effect of the vapor concentration correction control of this embodiment. In FIG.
40A shows the relationship between time and vapor concentration FGPG, and FIG. 40B shows the relationship between DPGSM and DPG1 and time. As shown in FIG. 40 (b), the DPG
The value of SM is increased during the purge cut. Therefore, as shown in FIG. 40 (a), the vapor concentration FGPG after the purge action is restarted becomes darker as the purge cut time becomes longer.

FIG. 41 is a flowchart showing a part of the vapor concentration correction control routine of the eleventh embodiment of the evaporated fuel processing apparatus for an internal combustion engine of the present invention. This embodiment uses the concept of the fourth embodiment and the concept of the tenth embodiment described above. Therefore, only the part of the present embodiment different from the fourth embodiment will be described below. As shown in FIG. 41, if the evaporative fuel processing apparatus determines NO in step 1303, step 13
In 04, the purge flow rate PQ calculated in step 1302 is set to PQSM (PQSM ← PQ). On the other hand, if YES in step 1303, it is determined in step 1305 whether or not the purge rate PGR is zero. If NO, the process proceeds to step 4101, and if YES, the process proceeds to step 4106.

In step 4101, the current purge flow rate tPQSM is calculated by the following equation, and tPQSM ← PQSM +
(PQ-PQSM) / KSM Subsequently, in step 4102, the purge flow rate change rate KPQSM is calculated by the following equation. KPQSM ← (PQSM-KPQOF) / (tPQSM
−KPQOF) × RKPQOF where RKPQOF is the predicted change ratio of the purge air amount decrease.

Subsequently, step 1308 and step 13
At 09, it is determined whether or not the change in the purge flow rate is large. Specifically, when the purge flow rate change rate KPQSM is 1.1 or more, or 0.9 or less, it is determined that the change in the purge flow rate is large, the process proceeds to step 1310, and the vapor flow rate change rate KPQSM is used for the vapor flow rate change. Correct the concentration FGPG (FGPG ← FGPG × KPQSM). on the other hand,
If it is determined in step 1308 and step 1309 that the change in the purge flow rate is small, step 13 is performed as it is.
Proceed to 11. In step 1311, the purge flow rate PQSM for vapor concentration correction is updated with the current purge flow rate tPQSM calculated in step 4101.

Subsequently, at step 4103, the predicted decrease air amount KPQOF is calculated from the map shown in FIG.
FIG. 42 shows the vapor concentration FGPG and the predicted decrease air amount KPQO.
It is a map showing the relationship with F, and this map value is stored in the ROM 22 in advance. As shown in FIG. 42,
The predicted decrease air amount KPQOF is made smaller as the vapor concentration FGPG is smaller, and is made larger when the purge flow rate PQ is larger than when it is small. Returning to FIG. 41, subsequently, in step 4104, the value of KPQOF is set to K.
PQOF1 (KPQOF1 ← KPQOF), and in step 4105, a value of 1.0 is set as RKPQOF (RKPOF
QOF ← 1.0), and this routine ends.

On the other hand, in step 4106, the value of the predicted decrease air amount KPQOF is increased by the predetermined value KPQa based on the same concept as in step 3902 of FIG.
Subsequently, at step 4107, the purge air amount decrease predicted change ratio RK is calculated from the KPQOF updated at step 4106 and the KPQOF1 updated at step 4104.
PQOF (← KPQOF / KPQOF1) is calculated, and this routine ends.

According to the present embodiment, step 4102 is taken into consideration that the vapor concentration is increased when the fuel vapor is desorbed from the canister, and the vapor concentration after the restart of the purge action is increased when the purge cut time is lengthened. By the steps 4106 and 4107 described above, the vapor concentration can be accurately calculated even when the fuel vapor is desorbed from the canister or is purge cut.

FIG. 43 is a graph showing the effect of the vapor concentration correction control of this embodiment. In FIG.
FIG. 43 (a) shows a state of the vapor concentration correction control before and after the purge cut by the conventional evaporated fuel processing apparatus.
(B) shows a state of vapor concentration correction control before and after the purge cut by the evaporated fuel processing apparatus of the present embodiment. As shown in FIG. 43 (a), the conventional evaporated fuel processing device
Even if the purge cut (time t ₁ to time t ₂ ) is executed,
Since it is not considered that the fuel vapor adsorbed to the canister during the purge cut is desorbed from the canister after the purging action is restarted, the vapor concentration FGPG is not so large when the purging action is restarted (time t ₂ ). The correction coefficient FAF changes greatly. on the other hand,
As shown in FIG. 43 (b), the fuel vapor processing apparatus of the present embodiment, when the purge cut (time t ₁ ~ time t ₂₎ is executed, the fuel vapor adsorbed in the canister during the purge cut Purge In consideration of desorption from the canister after resuming the action, it is possible to increase the vapor concentration FGPG at the time of resuming the purging action (time t ₂ ), and thus to prevent the feedback correction coefficient FAF from largely changing. it can.

[0110]

According to the invention described in claims 1 and 2,
The change rate of the purge flow rate due to the change of the intake air amount is large,
Moreover, when the ratio of the fuel vapor from the fuel tank to the fuel vapor purged from the canister and the fuel tank into the intake passage is large, that is, when the vapor concentration changes greatly with the change of the purge flow rate. Even so,
The actual vapor concentration can be calculated accurately. Therefore, the feedback correction coefficient can be prevented from being set to an inappropriate value, and good air-fuel ratio control can be performed.

According to the third aspect of the invention, it is possible to prevent the vapor concentration calculated based on the change rate of the purge flow rate from overshooting when the purge flow rate changes suddenly.

According to the fourth aspect of the present invention, the characteristics of the fuel vapor from the fuel tank in which the vapor concentration changes greatly when the change rate of the purge flow rate with the change in the intake air amount is large, and the vapor concentration changes so much. Since the concentration of the entire fuel vapor is calculated in consideration of the property of the fuel vapor from the canister, the vapor concentration can be accurately calculated.

According to the fifth aspect of the present invention, since the vapor concentration is corrected in consideration of the fact that the fuel vapor adsorbed in the canister is desorbed when the purge is restarted while the purging action is stopped, the accurate vapor concentration is corrected. Obtainable.

According to the sixth aspect of the present invention, it is considered that the amount of fuel vapor adsorbed by the canister when the purge action is stopped and desorbed when the purge is restarted varies depending on the purge action stop time. Since the concentration is corrected, an accurate vapor concentration can be obtained.

According to the seventh aspect of the present invention, it is possible to prevent the actual vapor concentration and the calculated vapor concentration in the combustion chamber of the internal combustion engine from being different by considering the flow time of the fuel vapor.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of an evaporated fuel processing apparatus for an internal combustion engine of the present invention.

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 apparatus shown in FIG.

FIG. 3 is a flowchart showing a feedback correction coefficient FAF calculation routine of FIG.

[Fig. 4] O when the air-fuel ratio is maintained at the target air-fuel ratio
₂ Sensor output voltage V and feedback correction coefficient FAF
It is a graph showing the relationship with.

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

FIG. 6 is a graph illustrating the concept of vapor concentration learning.

FIG. 7 is a flowchart showing a vapor concentration learning routine of FIG.

FIG. 8 is a flowchart showing a fuel injection time calculation routine of FIG.

FIG. 9 is a flowchart showing an interrupt routine of the evaporated fuel processing apparatus for the internal combustion engine of the first embodiment.

FIG. 10 is a flowchart showing a purge rate calculation routine of FIG.

FIG. 11 is a flowchart showing a purge rate calculation routine of FIG.

FIG. 12 is a flowchart showing a purge control valve drive processing routine of FIG.

FIG. 13 is a flowchart showing a vapor concentration correction control routine of FIG.

FIG. 14 is a graph showing the relationship between the negative pressure in the intake branch pipe and the fully open purge flow rate KPQ.

15 is a graph showing vapor concentration and purge flow rate during idle operation and acceleration operation of an internal combustion engine regarding a fuel vapor passing through positions A to C in FIG. 1 in an arrow direction.

FIG. 16 is a graph showing the effect of the vapor concentration correction control of the first embodiment.

FIG. 17 is a flowchart showing a part of a vapor concentration correction control routine of the second embodiment of the evaporated fuel processing apparatus for the internal combustion engine of the present invention.

FIG. 18 is a graph showing a purge flow rate tPQSM calculated according to the first embodiment and a purge flow rate tPQSM calculated according to the second embodiment.

FIG. 19 is a flowchart showing a part of a vapor concentration correction control routine of a modified example of the second embodiment of the evaporated fuel processing apparatus for the internal combustion engine of the present invention.

FIG. 20 is a graph showing a purge flow rate tPQSM calculated according to the first embodiment and a purge flow rate tPQSM calculated according to a modification of the second embodiment.

FIG. 21 is a flowchart showing a part of a vapor concentration correction control routine of the third embodiment of the evaporated fuel processing apparatus for the internal combustion engine of the present invention.

FIG. 22 is a flowchart showing a part of a vapor concentration correction control routine of the fourth embodiment of the evaporated fuel processing apparatus for the internal combustion engine of the present invention.

FIG. 23 is a flowchart showing a part of a vapor concentration correction control routine of the fourth embodiment of the evaporated fuel processing apparatus for the internal combustion engine of the present invention.

FIG. 24 is a flowchart showing a routine for detecting a vapor concentration correction direction in FIG. 22.

FIG. 25 is a graph similar to FIG. 15 when there is desorption of fuel vapor from the canister.

FIG. 26 is a graph showing the present or previous purge flow rate comparing the case where desorption of vapor fuel from the canister is taken into consideration and the case where it is not taken into consideration.

FIG. 27 is a graph showing the function and effect of vapor concentration correction control according to the fourth embodiment.

FIG. 28 is a flowchart showing a part of a vapor concentration correction control routine of the fifth embodiment of the evaporated fuel processing apparatus for the internal combustion engine of the present invention.

FIG. 29 is a graph showing a current purge flow rate tPQSM calculated by delay processing in the vapor concentration correction control routine of the sixth embodiment of the evaporated fuel treatment apparatus for the internal combustion engine of the present invention.

FIG. 30 is a flowchart showing a part of a vapor concentration correction control routine of the seventh embodiment of the evaporated fuel processing apparatus for the internal combustion engine of the present invention.

FIG. 31 is a graph showing the action and effect of vapor concentration correction control of the seventh embodiment.

FIG. 32: XT required for judgment in step 1303
7 is a flowchart showing a routine for setting an NK = 1 flag.

FIG. 33 is a flowchart showing a routine inserted between step 3203 and step 3204 of FIG. 32 as a modification of the routine of FIG. 32.

FIG. 34 is a flow chart showing a vapor concentration correction control routine of an eighth embodiment of the evaporated fuel processing apparatus for the internal combustion engine of the present invention.

FIG. 35 is a graph showing the effect of the vapor concentration correction control of the eighth embodiment.

36 is a graph showing the vapor concentration and the purge flow rate before the purge cut and after the restart of the purge action regarding the fuel vapor passing through the positions A to C in FIG. 1 in the arrow direction.

FIG. 37 is a flowchart showing a part of a vapor concentration correction control routine of a ninth embodiment of the evaporated fuel processing apparatus for an internal combustion engine of the present invention.

FIG. 38 is a graph showing the effect of vapor concentration correction control of the ninth embodiment.

FIG. 39 is a flow chart showing a vapor concentration correction control routine of a tenth embodiment of the evaporated fuel processing apparatus for an internal combustion engine of the present invention.

FIG. 40 is a graph showing the effect of the vapor concentration correction control of the tenth embodiment.

FIG. 41 is a flowchart showing a part of a vapor concentration correction control routine of the eleventh embodiment of the evaporated fuel processing apparatus for an internal combustion engine of the present invention.

FIG. 42: Vapor concentration FGPG and predicted decrease air amount KPQ
It is a map showing the relationship with OF.

FIG. 43 is a graph showing the effect of vapor concentration correction control of the eleventh embodiment.

[Explanation of symbols]

2 ... intake manifold 4 ... fuel injection valves 7 ... air flow meter 11 ... canister 15 ... Fuel tank 17 ... purge control valve 20 ... electronic control unit 30 ... O ₂ sensor

Claims (7)

(57) [Claims] 1. A canister for temporarily storing evaporated fuel generated in a fuel tank, a purge control valve for controlling a purge flow rate of fuel vapor purged from the canister and the fuel tank into an intake passage, and an air-fuel ratio. For detecting the air-fuel ratio, a purge flow rate calculating means for calculating the purge flow rate based on the opening amount of the purge control valve, and an intake air amount detecting means for detecting the intake air amount taken into the internal combustion engine. In the evaporated fuel processing apparatus for an internal combustion engine, the ratio of the fuel vapor from the fuel tank in the fuel vapor purged from the canister and the fuel tank into the intake passage is large, and the intake air amount is In the first state in which the change rate of the purge flow rate due to the change of is large, the vapor concentration is calculated based on the change rate of the purge flow rate, and the vapor concentration is calculated from the fuel tank. Of fuel vapor is small,
Alternatively, in the second state in which the rate of change in the purge flow rate due to the change in the intake air amount is small, a vapor concentration calculating means for calculating the vapor concentration based on the air-fuel ratio and the air-fuel ratio is adjusted to the target air-fuel ratio based on the vapor concentration. And an air-fuel ratio adjusting means for controlling the evaporated fuel. 2. The evaporated fuel processing apparatus for an internal combustion engine according to claim 1, wherein the purge flow rate is calculated based on the duty ratio of the purge control valve. 3. The evaporated fuel processing apparatus for an internal combustion engine according to claim 1, wherein the rate of change of the purge flow rate is a value that has been subjected to a smoothing process. 4. The canister and the vapor concentration calculating means in the first state are based on the rate of change of the purge flow rate and the concentration of fuel vapor purged from the canister into the intake passage. The evaporated fuel processing apparatus for an internal combustion engine according to claim 1, wherein the concentration of the entire fuel vapor purged from the fuel tank into the intake passage is calculated. 5. The vapor concentration calculating means calculates the vapor concentration based on the change rate of the purge flow rate when the purge action is restarted after the purge action is stopped and the purge action is restarted in the first state. The evaporated fuel processing apparatus for an internal combustion engine according to claim 1, wherein the vapor concentration is corrected to a rich side. 6. The evaporated fuel processing apparatus for an internal combustion engine according to claim 5, wherein the vapor concentration calculating means corrects the vapor concentration based on the purge action stop time. 7. The vapor concentration calculating means calculates the vapor concentration based on the time required for the fuel vapor to flow from the purge control valve to the combustion chamber of the internal combustion engine in the first state. The evaporated fuel processing device for an internal combustion engine according to claim 1.