JP3265866B2 - 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 an evaporative fuel processing apparatus for an internal combustion engine, and more particularly to an evaporative fuel processing apparatus for an internal combustion engine which prevents diffusion of evaporative fuel gas generated in a fuel supply system of a vehicle. is there.

[0002]

2. Description of the Related Art Conventionally, as a prior art document relating to an evaporative fuel treatment apparatus for an internal combustion engine, there is Japanese Patent Laid-Open No. 5-187332.
And Japanese Patent Application Laid-Open No. 6-101544 are known.

[0003] In the former, regarding the prevention of fuel evaporation gas diffusion,
The opening position detection means of the purge control valve is shown, and the amount of change in the opening of the idle speed control valve when the opening of the purge control valve is gradually opened from fully closed is determined. Discloses a technique for detecting the opening degree of a purge control valve when the pressure becomes equal to or more than a predetermined value set in advance as a position where the valve actually started to open.

In the latter, a rising duty ratio at which the purge control valve starts to open at a timing when the air-fuel ratio feedback correction coefficient changes when the purge control valve is turned ON / OFF is detected, and this duty ratio is added to a basic duty ratio. A technique for calculating the actual duty ratio of a purge control valve is shown.

[0005]

When the opening position of the purge control valve is to be detected in accordance with the change in the opening of the idle speed control valve as in the former case, the change in the purge flow rate is large. It is necessary. That is, unless the valve opening amount per step when the purge control valve is gradually opened from the fully closed state is large, it is difficult to clearly detect the valve opening position. Here, in order to reduce the disturbance of the air-fuel ratio due to the evaporation gas, it is necessary that the evaporation concentration is low. For this reason, there has been a problem that it is difficult to detect the opening position of the purge control valve at a high concentration of the evaporation where it is necessary to detect the opening position with higher accuracy.

In the latter case, when the accelerator pedal is depressed and the signal from the idle switch is off, the opening position of the purge control valve is detected. The amount of change in the air-fuel ratio feedback correction coefficient due to the evaporative gas becomes small, and it becomes difficult to detect the valve opening position with high accuracy. The detection of the valve opening position of the purge control valve is normally performed at the start of the purge (when the purge control valve is gradually opened from the fully closed state), but if the valve is not opened slowly in a narrow range near the valve opening position, highly accurate detection is performed. There was a problem that detection became difficult.

Accordingly, the present invention has been made to solve such a problem, and the duty ratio at the rising point of the purge flow rate of the purge control valve is determined by changing the duty ratio at the time of idling where the influence of the evaporation gas on the air-fuel ratio feedback correction amount is large.
At the time of high concentration of the evaporation, the purge control valve (center product) which detects the air-fuel ratio feedback correction amount in accordance with the air-fuel ratio feedback correction amount and takes the median of the tolerance of the purge flow rate learns the deviation from the duty ratio of the rising point of the purge flow rate from the duty ratio. A first object of the present invention is to provide an evaporative fuel treatment apparatus for an internal combustion engine which prevents a flow rate variation due to a control valve tolerance.

Further, before the learning of the duty ratio at the rising point of the purge flow rate of the purge control valve is completed, the purge fuel of the internal combustion engine is prohibited during idling when the tolerance in the purge flow rate of the purge control valve greatly affects the air-fuel ratio. A second problem is to provide a processing device.

[0009]

According to a first aspect of the present invention, there is provided an evaporative fuel processing apparatus for an internal combustion engine, which adsorbs fuel evaporative gas generated in a fuel tank containing a liquid fuel, as shown in FIG. A canister G1 having an adsorbent, a supply passage G2 for guiding the fuel evaporative gas adsorbed by the adsorbent of the canister G1 into the intake pipe by a negative pressure generated in the intake pipe of the internal combustion engine; A purge control valve G3 provided with an adjustable opening and a purge flow control means for controlling the purge flow of the supply passage G2 by adjusting the opening of the purge control valve G3 according to the operating state of the internal combustion engine. G4, air-fuel ratio detection means G5 for detecting the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine, and the air-fuel ratio supplied to the internal combustion engine according to the air-fuel ratio detected by the air-fuel ratio detection means G5. Fuel feedback control means G6 for feedback-controlling the air-fuel ratio of the air-fuel mixture, and fuel vaporization based on the amount of change in the air-fuel ratio feedback value by the air-fuel ratio feedback control means G6 before and after the purge flow rate is changed by the purge flow rate control means G4. An evaporative concentration calculating means G7 for calculating an evaporative concentration of gas; and an idling operation, a high evaporative concentration, and a small load fluctuation.
The purge flow control means G4 controls the purge control valve G
3 is gradually increased stepwise from the fully closed state, and the rising point of the purge flow rate of the purge control valve G3 is opened based on the fluctuation amount of the air-fuel ratio feedback value by the air-fuel ratio feedback control means G6 at that time. And a rising point calculating means G8 for calculating the degree.

FIG. 12 shows a concept of a fuel vapor processing apparatus for an internal combustion engine according to a second aspect of the present invention. The canister G1 has an adsorbent for adsorbing fuel vapor generated in a fuel tank containing liquid fuel. And the canister G1
A supply passage G2 for guiding the fuel evaporative gas adsorbed by the adsorbent into the intake pipe by a negative pressure generated in the intake pipe of the internal combustion engine, and a purge control provided in the middle of the supply passage G2 and having an adjustable opening degree. A valve G3, a purge flow rate control means G4 for controlling the purge flow rate of the supply passage G2 by adjusting the opening degree of the purge control valve G3 according to the operation state of the internal combustion engine, and mixing supplied to the internal combustion engine. Air-fuel ratio detecting means G5 for detecting the air-fuel ratio of air;
Air-fuel ratio feedback control means G6 for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine in accordance with the air-fuel ratio detected by the air-fuel ratio, and the air-fuel ratio before and after the purge flow rate is changed by the purge flow rate control means G4 An evaporative concentration calculating means G7 for calculating an evaporative concentration of the fuel evaporative gas based on the amount of change in the air-fuel ratio feedback value by the feedback control means G6; and the purge flow rate control during idle operation, when the evaporative concentration is high, and when the load fluctuation is small. The opening degree of the purge control valve G3 is repeatedly and stepwise controlled to a fully closed state and a gradually increased opening degree by means G4, and the air-fuel ratio feedback control means G6 at that time is controlled.
And a rising point calculating means G8 for calculating the opening of the rising point of the purge flow rate of the purge control valve G3 based on the fluctuation amount of the air-fuel ratio feedback value.

According to a third aspect of the present invention, there is provided the evaporative fuel processing apparatus for an internal combustion engine, wherein the gradual change of the opening degree of the purge control valve according to the first or second aspect is based on the purging flow rate with respect to the opening being within a predetermined tolerance. The control valve starts from the minimum opening of the rising points of the purge flow rate of the control valve.

[0012]

[0013]

According to a fourth aspect of the present invention, there is provided the evaporative fuel processing apparatus for an internal combustion engine, wherein the calculation of the opening degree of the rising point of the purge flow rate of the purge control valve according to any one of the first to third aspects is performed by the air-fuel ratio. This is carried out when the amount of change in the air-fuel ratio feedback value by the feedback control means has exceeded a predetermined value.

[0015]

[0016]

According to a fifth aspect of the present invention, there is provided an evaporative fuel processing apparatus for an internal combustion engine, wherein the purge control valve according to any one of the first to fourth aspects has an opening of a rising point of an actual purge flow rate and the purge control valve. The learning value obtained by learning the difference between the designed purge flow rate and the opening of the rising point is added to the designed flow rate characteristic of the purge control valve.

[0018]

[0019]

According to the first aspect of the present invention, the opening of the purge control valve by the purge flow rate control means is increased step by step from the fully closed state during the idling operation by the rising point calculation means, when the evaporation is high, and when the load fluctuation is small. The opening of the rising point of the purge flow rate of the purge control valve is calculated based on the fluctuation amount of the air-fuel ratio feedback value by the air-fuel ratio feedback control means at this time.

According to a second aspect of the present invention, the opening degree of the purge control valve by the purge flow rate control means gradually increases to a fully closed state during idling operation by the rising point calculation means, when the evaporation is high, and when the load fluctuation is small. The opening degree at which the purge flow rate of the purge control valve rises is calculated based on the amount of change in the air-fuel ratio feedback value by the air-fuel ratio feedback control means at this time.

According to a third aspect of the present invention, the gradual change in the opening of the purge control valve according to the first or second aspect is based on the fact that the purge flow rate with respect to the opening is within a predetermined tolerance. It starts from the smallest opening of the rising points of the purge flow rate.

[0022]

[0023]

According to a fourth aspect of the present invention, the calculation of the opening of the rising point of the purge flow rate of the purge control valve according to any one of the first to third aspects is performed by the air-fuel ratio feedback control means. This is performed when the amount of change in the air-fuel ratio feedback value due to is greater than or equal to a predetermined value.

[0025]

[0026]

According to a fifth aspect of the present invention, there is provided an evaporative fuel treatment apparatus for an internal combustion engine, wherein the purge control valve according to any one of the first to fourth aspects has an actual opening degree of a rising point of a purge flow rate and a design of the purge control valve. The learning value obtained by learning the difference between the purge flow rate and the opening of the rising point is added to the designed flow characteristic of the purge control valve, and the difference is offset by this difference.

[0028]

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to specific embodiments.

FIG. 1 is a block diagram showing a fuel vapor processing apparatus for an internal combustion engine according to one embodiment of the present invention.

In FIG. 1, an intake pipe 2 and an exhaust pipe 3 are connected to an internal combustion engine 1. An air cleaner 4 for filtering air is disposed upstream of the intake pipe 2.
The air is sucked into the intake pipe 2 via. In the intake pipe 2, a throttle valve 6 that opens and closes in conjunction with an accelerator pedal 5 is provided. A bypass passage 7 is provided so as to bypass the throttle valve 6, and an ISC (Idle Speed Control: idle speed control) valve 8 is arranged in the middle of the bypass passage 7. This ISC valve 8
The intake air amount at the time of idling of the internal combustion engine 1 is adjusted by the opening degree adjustment by the duty ratio control to change the engine speed.

The air from the intake pipe 2 is supplied to the combustion chamber 10 via the intake valve 9. Further, the exhaust gas from the combustion chamber 10 is exhausted to the exhaust pipe 3 via the exhaust valve 11. The exhaust pipe 3 is provided with an O ₂ (oxygen) sensor 12.

On the other hand, a fuel tank 13 containing liquid fuel
Is connected to a fuel pump 14, and the fuel in the fuel tank 13 is transported by the fuel pump 14 in a pressurized state. The fuel from the fuel pump 14 is supplied to a fuel injection valve 15 provided in the intake pipe 2, and the fuel is injected by opening and closing the fuel injection valve 15. The fuel tank 13 is connected to the communication pipe 16.
Is connected to the canister 17, and an adsorbent 19 made of activated carbon for adsorbing fuel evaporative gas is accommodated in the canister body 18. Thereby, the fuel tank 1
The fuel evaporative gas generated in 3 is adsorbed by the adsorbent 19 of the canister 17 through the communication pipe 16. The canister body 18 has an air opening hole 20 that is open to the atmosphere, so that air can be sucked into the inside.

Further, a hose connecting portion 21 is formed in the canister body 18, and one end of a supply pipe 22 is inserted into the hose connecting portion 21. The other end of the supply pipe 22 is connected to a purge control valve 23. This purge control valve 23
Is connected to one end of a supply pipe 24, and the other end of the supply pipe 24 is connected to a purge control valve 23. Therefore, the purge control valve 23 is interposed between the two supply pipes 22 and 24, and the intake pipe 2 and the canister 17 are connected to the supply pipe 22 and the purge control valve 2.
3. The communication can be made via the supply pipe 24. In this communication state, the fuel evaporative gas adsorbed by the adsorbent 19 of the canister 17 can be guided into the intake pipe 2 by the negative pressure generated in the intake pipe 2 of the internal combustion engine 1. The opening of the purge control valve 23 is adjusted by duty ratio control, and the purge flow rate passing through the supply pipes 22 and 24 is changed according to the opening. The supply pipes 22 and 24 are generally formed of a flexible material such as a rubber hose or a nylon hose.

An ECU (Electronic Control Unit) 25 mainly includes a CPU 26, a ROM 27, an R
It is composed of an AM 28 and an input / output circuit 29, and is mutually connected via a common bus 30. ROM27 has C
A control program and data for the PU 26 are stored in advance,
The RAM 28 stores readable and writable data.
Various signals are input to the CPU 26 via the input / output circuit 29. That is, the signal from the O ₂ sensor 12 and the internal combustion engine 1
, A signal from an air conditioner switch 32 for detecting an on / off operation of a car air conditioner, a signal from a headlight switch 33 for detecting a lighting operation of a headlight, a heater blower switch 34 , A signal from an idle switch 35 which is turned on when the accelerator pedal 5 is not depressed, a signal from a vehicle speed sensor 36, a signal from a rotation speed sensor 37 for detecting an engine speed, and a signal from an intake air amount sensor 38. And the signal from the throttle opening sensor 39 are input.

Then, various signals are stored in the ROM 26 by the CPU 26.
7, the fuel injection valve 15 and the purge control valve 2 via the input / output circuit 29 based on programs and data in the RAM 28, etc.
3. The drive of the ISC valve 8 is controlled. That is, the CPU 26
The purge control valve 23 according to the operating state of the internal combustion engine 1
Is adjusted, and the purge flow rate passing through the supply pipes 22 and 24 is controlled. That is, the opening degree of the purge control valve 23 is calculated and controlled by the CPU 26 so that the purge flow rate becomes a predetermined ratio with respect to the intake air amount detected by the intake air amount sensor 38.
Further, the opening degree is adjusted the intake air amount of the ISC valve 8 so that the target speed during the idle operation of the internal combustion engine 1 is controlled by the CPU 26, further, to the internal combustion engine 1 detected by the O ₂ sensor 12 The air-fuel ratio of the air-fuel mixture is controlled to be constant. That is, the basic injection time is calculated by the CPU 26 from the engine speed by the rotation speed sensor 37 and the intake air amount by the intake air amount sensor 38, and the basic injection time is corrected by the air-fuel ratio feedback correction coefficient cfb and the like, and the final injection time is calculated. Is calculated, and fuel injection at a predetermined injection timing by the fuel injection valve 15 is executed.

<Air-fuel ratio feedback control routine: see FIGS. 2 and 3> Next, the processing procedure of the air-fuel ratio feedback control of the CPU 26 used in the evaporative fuel processing apparatus for an internal combustion engine according to one embodiment of the present invention will be described. This will be described with reference to the timing chart of FIG. 3 based on the flowchart of FIG. This routine is executed every predetermined time. As shown in FIG. 3, the output voltage corresponding to the O ₂ sensor signal from the O ₂ sensor 12 is compared with the comparison voltage Vref, and the rich / lean mixture is determined.

First, in step S101, it is determined whether a condition for air-fuel ratio feedback (F / B) control is satisfied. This condition is, for example, when the cooling water temperature detected by the water temperature sensor 31 is 40 ° C. or higher and the throttle opening detected by the throttle opening sensor 39 is 70 ° or lower. If the determination condition in step S101 is not satisfied, the process proceeds to step S102, the air-fuel ratio feedback correction coefficient cfb is set to 0.0, and the routine ends.

[0039] On the other hand, if the condition of step S101 is satisfied, the process proceeds to step S103, whether the air-fuel ratio is rich is determined by the O ₂ sensor signal from the O ₂ sensor 12. When the determination condition of step S103 is satisfied, the process proceeds to step S104, and it is determined whether the state has been changed from lean to rich by comparing with the previous detection result. When the determination condition of step S104 is satisfied,
In step S105, the air-fuel ratio feedback correction coefficient cfb-α (α: skip amount) is set as a new air-fuel ratio feedback correction coefficient, and the routine ends. On the other hand, if there is no lean-to-rich reversal in step S104, the process proceeds to step S106, where the air-fuel ratio feedback correction coefficient cfb-β (β: integral amount, α> β) is set as a new air-fuel ratio feedback correction coefficient cfb. End the routine.

On the other hand, if the determination condition in step S103 is not satisfied, the flow shifts to step S107, where it is compared with the previous detection result to determine whether the state has been changed from rich to lean. When the determination condition of step S107 is satisfied, the process proceeds to step S108, the air-fuel ratio feedback correction coefficient cfb + α is set as a new air-fuel ratio feedback correction coefficient, and the routine ends. On the other hand, step S
If there is no reversal from rich to lean at 107, the process proceeds to step S109, and the air-fuel ratio feedback correction coefficient c
fb + β is a new air-fuel ratio feedback correction coefficient cfb
Is completed, and this routine ends.

Therefore, if there is a reversal between rich and lean due to the processing of steps S103 to S109, the air-fuel ratio feedback correction coefficient cfb is changed (skipped) in a stepwise manner to increase or decrease the fuel injection amount, and is rich or lean. When it remains, the air-fuel ratio feedback correction coefficient cfb is gradually increased or decreased.

By the way, the purge control valve 23 has a Dut as shown in FIG.
Purging flow rate qprg with respect to y (duty ratio) [%]
[1 / min] There is variation in characteristics. That is, the purge control valve 23 supplies the purge flow rate qpr to the duty signal.
There is a variation between the upper limit product and the lower limit product with respect to the center product in which g takes the median of the tolerance. In FIG. 4, Duty2 is used.
Purge flow rate qprg at 0, 50, 100 [%]
The tolerance of [l / min] is indicated by oblique lines.

The effect of the variation in the purge flow rate characteristic of the purge control valve 23 on the air-fuel ratio control during the execution of the purge control will be described with reference to FIG.

As shown in FIG. 5A, in the purge control valve 23 which is in the mode, in the idling state (low purge flow rate region), the actual purge is performed based on the purge flow rate (map value of the center product) calculated by the CPU 26. The flow rate becomes large, and the evaporation concentration learning value flprg (the deviation of the air-fuel ratio feedback correction coefficient cfb per 1% of the purge rate) becomes large. Conversely, during traveling (high purge flow rate region), the actual purge flow rate becomes smaller than the purge flow rate (map value of the center product) calculated by the CPU 26, and the concentration learning value becomes smaller. With this one,
When the idling time and the traveling time are alternately repeated, the concentration learning value hunts, and the air-fuel ratio feedback value is disturbed until the concentration learning value is stabilized. Similarly, in the purge control valve 23 in the mode, the concentration learning value becomes small during idling (low purge flow rate region), and conversely, the concentration learning value becomes large during running (high purge flow rate region). If the idling and the running are alternately repeated, the concentration learning value hunts, and the air-fuel ratio feedback value is disturbed until the concentration learning value is stabilized (see FIG. 5B).

In order to solve such a problem due to the tolerance of the purge control valve 23, in the present embodiment, the purge control valve 23 is gradually opened from the fully closed state (the duty is gradually increased from 0%. The rising point (defined as the ZERO point) of the purge flow rate at which the purge control valve 23 rises is learned, and the ZERO points of all the purge control valves 23 are made the same.
The ratio of the flow characteristic in the tolerance of the purge control valve 23 with respect to the center product is the same in the entire operation range.

<ZERO Point Learning Control Routine: See FIGS. 6, 7, and 8> Next, the ZERO point learning control of the CPU 26 used in the evaporative fuel processing apparatus for the internal combustion engine according to one embodiment of the present invention. The processing procedure will be described based on the flowchart in FIG. 6 and the timing chart in FIG. 7 and the characteristic diagram in FIG.

First, in step S201, it is determined whether ZERO point learning has not been performed from IG (ignition switch) ON. This is because the ZERO point learning is performed once in one run. When the determination condition of step S201 is satisfied, the process proceeds to step S202,
It is determined whether the accelerator pedal 5 is not depressed, the idle signal from the idle switch 35 is ON, and the vehicle is idling. When the determination condition of step S202 is satisfied, the process proceeds to step S203, and it is determined whether the later-described evaporation concentration learning value flprg exceeds a predetermined value of 6% and the evaporation concentration is high. This is performed when the evaporative gas has a large influence on the air-fuel ratio feedback correction coefficient cfb. When the determination condition of step S203 is satisfied, the process proceeds to step S204,
It is determined whether the load fluctuation is small. This is to prevent erroneous learning due to a change in the air-fuel ratio feedback correction coefficient cfb when the load changes. When the determination condition of step S204 is satisfied, the process proceeds to step S205, and ZERO
Assuming that the point learning execution provisional condition is satisfied, the ZERO point learning execution provisional condition flag xlzeexe0 is set to 1 (time t2 in FIG. 7). Steps S201, S202, S2
When each of the determination conditions in steps 03 and S204 is not satisfied, the present routine is terminated without any operation.

Next, the flow shifts to step S206, where ZER
It is determined whether six skips have elapsed since the provisional condition of the O-point learning execution was satisfied. Here, after the provisional condition for executing the ZERO point learning is satisfied, the air-fuel ratio feedback correction coefficient cfb is waited until the air-fuel ratio feedback correction coefficient cfb is stabilized.
Is determined to have stabilized, the flow shifts to step S207, and ZER
The average value cfb0 of the air-fuel ratio feedback correction coefficient immediately before the O-point learning execution condition is satisfied is detected, and the flow shifts to step S208. In step S208, it is determined that the ZERO point learning execution condition is satisfied, and the ZERO point learning execution condition flag xl
zexe = 1 is set (time t3 in FIG. 7).

Then, the flow shifts to step S209, where it is determined whether or not it is the first ZERO point learning during traveling.
When the determination condition of step S209 is satisfied, the process proceeds to step S210, and the duty is gradually changed from the fully closed state of the purge control valve 23. The duty change range is as follows:
Since it is known in advance from the purge flow rate characteristic of the purge control valve 23 that the duty at the rising point of the purge flow rate is from 4.5% at the minimum to 7.5% at the maximum (considering the durability of the purge control valve 23), 4 0.5% to 7.5%. That is, since all the purge control valves 23 are in the fully closed state when the duty is less than 4.5%, in order to shorten the time until the completion of the ZERO point learning, the gradual change of the duty is offset after the ZERO point learning execution condition is satisfied, The value KPTPZE1 (4.5
%). Since the duty at the completion of the ZERO point learning does not exceed 7.5%, a maximum value guard for preventing erroneous learning is provided, and the gradual change of the duty is finished at 7.5%.

Here, when the judgment condition of step S209 is not satisfied, the flow shifts to step S211 and the ZER
In order to shorten the time until the completion of the O-point learning, if the execution condition of the ZERO point learning is not satisfied before the completion of the ZERO point learning after the start of the duty gradual change, the gradual change of the duty at the next execution of the ZERO point learning is performed by the offset value KPTPZE1 (4.5
%), The gradual change is started from the last duty when the previous ZERO point learning is executed. However, due to a change in the purge flow rate characteristic, the purge control valve 23 is opened at the time of the current gradual change at the duty when the purge control valve 23 was closed at the time of the previous gradual change, the purge gas flows in, and the air-fuel ratio feedback correction coefficient at the time of starting the ZERO point learning. In order to prevent the cfb from being displaced by the influence of the purge gas, Duty is set to 0 when the ZERO point learning execution provisional condition is satisfied, and when the ZERO point learning execution condition is satisfied, the last Duty when the previous ZERO point learning execution was performed.
The gradual change is started from.

Next, the flow shifts to step S212, where the duty at the time of the previous execution of the ZERO point learning is set to the gradually changing amount KPTPZE.
2 is added to make Duty. At this time, if the amount of the gradual change of the duty is too large, a high-concentration evaporative gas flows in abruptly, and the controllability of the air-fuel ratio deteriorates.
In order to prevent this problem, the gradual change amount of the duty is determined when the duty ratio is gradually changed by using the purge control valve 23 (durable product) which is the upper purge flow rate product when the evaporative gas is at a high concentration.
The variation of the air-fuel ratio feedback correction coefficient cfb is set to be equal to or less than a predetermined value (3%). In this embodiment,
KPTPZE2 is set to 0.
5% is set.

Next, the flow shifts to step S213, where Dut
It is determined whether the time from the increase of y is less than 3 seconds. In other words, the detection of the ZERO point is performed by the amount of change from the average value of the air-fuel ratio feedback correction coefficient cfb.
It is necessary to set the air-fuel ratio feedback correction coefficient cfb to be stable, and the gradual change period is set to 3 seconds. When the determination condition of step S213 is satisfied, the process proceeds to step S214, and it is determined whether the value of | cfbm-cfb0 | exceeds 2% of the predetermined value KPZEFB1. Until the determination condition of step S214 is satisfied,
The process of step S212 is executed every 3 seconds, and Du is executed.
The ty is gradually changed by 0.5%. That is, if the duty is gradually changed from the fully closed state of the purge control valve 23 during the idling operation with a small amount of intake air and the high concentration of the evaporation, the Z
When the purge control valve 23 starts to open beyond the ERO point and the evaporative gas starts to flow, the air-fuel ratio feedback correction coefficient cf
b fluctuates to the rich side. For this reason, when the average value of the air-fuel ratio feedback correction coefficient cfb fluctuates by more than 2% of the predetermined value KPZEFB1 as compared with before the start of the ZERO point learning, the D of the purge flow rate rising point of the purge control valve 23 is changed.
and the learning is completed (time t4 in FIG. 7).

Further details will be described below.

If cfb1 is the air-fuel ratio feedback value immediately before skipping and cfb2 is the average value of cfb1, the following equation (1) is established.

[0055]

Cfb2 [i] = (cfb1 [i] + cfb1 [i-1]) / 2 (1) Further, if cfbm is a smoothed value of cfb2, the following equation (2) is established. Here, KPCFBN1 is a smoothing coefficient (0.75).

[0056]

Cfbm [i] = KPCFBN1 * cfbm [i−1] + (1 + KPCFBN1) * cfb2 [i] (2) Then, cfb0 is set immediately before the ZERO point learning execution condition is satisfied (the purge control valve 23 Cfbm when closed), ZE
The average value cfbm of the air-fuel ratio feedback correction coefficient when the duty is gradually changed during the execution of the RO point learning has changed by a predetermined value (2%) from the average value cfb0 of the air-fuel ratio feedback correction coefficient immediately before the ZERO point learning execution condition is satisfied. When, that is,
When | cfbm-cfb0 |> 2%, the duty of the purge flow rate rising point of the purge control valve 23 is recognized, and the learning is completed.

When the condition of step S214 is satisfied, the flow shifts to step S215, where TPR, which is the actual duty of the purge flow rate rising point of the purge control valve 23, is used.
GOFF1 is calculated. Duty (TPRGOFF1) of actual rising point of purge flow rate of purge control valve 23
Means that the subtraction correction of Duty and the detection while the average value cfbm of the air-fuel ratio feedback correction coefficient fluctuates by a predetermined value (2%) after the purge flow rate actually rises are gradually changed by 0.5.
It is necessary to correct for the detection error caused by the gradual change of the duty of%. First, since the former subtraction correction value differs depending on the concentration of the evaporative gas, the subtraction correction value is detected by a table corresponding to the evaporative concentration learning value flprg (the deviation of the air-fuel ratio feedback correction coefficient cfb per 1% of the purge rate). That is, when the evaporative concentration is high, the duty value is small during the period when the average value cfbm of the air-fuel ratio feedback correction coefficient fluctuates by a predetermined value (2%) after the purge flow rate actually rises. When the evaporative concentration is low, the duty value is large during the period when the average value cfbm of the air-fuel ratio feedback correction coefficient fluctuates by a predetermined value (2%) after the purge flow rate actually rises, so that the subtraction value is large. .

Next, the correction of the detection error by the duty gradually changing amount of 0.5% is １ ／ of the gradually changing amount of 0.5%, that is, 0.2%.
5% shall be subtracted. For example, the gradual change of the duty is 0.5% from the offset value KPTPZE1 (4.5%).
4.5%, 5.0%, 5.5%, respectively,
Is 5.5%, the duty of the actual rising point of the purge flow rate is between 5.0% and 5.5%, and thus the central value of the detected value is 5.25%. As described above, 1/2 (= 0.25%) of the gradually changing amount of 0.5% is subtracted.

Next, the flow shifts to step S216, where ZE
TPR which is the duty of the rising point of the purge flow rate in the center product flow rate characteristic calculated by the CPU before the RO point learning.
GOFF2 is calculated. Before ZERO point learning, CPU
The calculation of the duty of the purge control valve 23 is performed by a (purge flow)-(differential pressure across the purge control valve) map corresponding to the flow characteristic (Duty-purge flow characteristic) of the center product of the purge control valve 23. The duty (TPRGOFF2) of the rising point of the purge flow rate before learning the ZERO point is ZE
Since it is the duty of the rising point of the purge flow rate calculated by the CPU immediately before the completion of the RO point learning, the differential pressure at that time and (purge flow rate) = 0 and (purge flow rate)-(purge control valve front-back differential pressure) map It is calculated by

Next, the flow shifts to step S217, where ZE
Tprgoff which is an RO point learning correction value is calculated.
At the time of the first learning after connecting the battery, the rising point Duty (TPRGOFF1) of the actual purge control valve flow rate and ZERO
Rise point Duty (T
PRGOFF2) TPR for the second and subsequent learning
A ZERO point learning correction value tprgoff is calculated as an average value of the difference between GOFF1 and TPRGOFF2. That is, at the time of the first learning after the connection of the battery, the ZERO point learning correction value tprgoff is calculated by the following equation (3).

[0061]

## EQU00003 ## tprgoff = TPRGOFF1-TPRGOFF2 (3) In the second and subsequent learnings, a ZERO point learning correction value tprgoff is calculated by the following equation (4). Here, KPZEN
This is the annealing coefficient (0.75).

[0062]

Tprgoff = KPZEN * tprgoff [i-1] + (1-KPZEN) * (TPRGOFF1-TPRGOFF2) (4) Next, the process proceeds to step S218, where the purge control valve 23 is operated.
Of the rising point of the purge flow rate is corrected, and this routine ends. That is, the purge control valve 23 is added by adding the ZERO point learning correction value tprgoff calculated in step S217 to the Duty calculated from the (purge flow rate)-(purge control valve differential pressure) map.
(The shift from the center product flow characteristic shown in FIG. 8 to the flow characteristic after the ZERO point learning), and the actual duty ratio of the rising point of the purge flow rate of the purge control valve 23 (Duty-purge flow characteristic). TPRGOFF1) and C
The duty (TPRGOFF2) of the rising point of the purge flow rate of the purge control valve 23 calculated by the PU is matched.

Further, before the ZERO point learning is completed, there is a possibility that the air-fuel ratio controllability of the purge during idling operation in the low purge flow rate region may be deteriorated due to a shift in the duty of the rising point of the purge flow rate of the purge control valve 23. Therefore, before the ZERO point learning is completed, the purge during idling operation is prohibited.

<Evaporation Concentration Learning Routine: See FIG. 9> The evaporation concentration learning routine for calculating the evaporation concentration learning value (flprg) in step S203 in FIG. 6 will be described with reference to FIG.

In step S301, it is determined whether purging is being performed. When the purging is not being performed, this routine ends without performing any operation. Step S30
If the purge is being performed in step S1, the process proceeds to step S302, and the average value cf of the air-fuel ratio feedback correction coefficient cfb is obtained.
bm is read. Next, the process proceeds to step S303.
The deviation of the cfbm value from the reference value cfb0 (cfbm−
It is determined whether or not (cfb0) exceeds 2%. When the inequality expression in step S303 is satisfied, that is, when the deviation (cfbm-cfb0) exceeds 2% and the engine is lean, it is possible to determine that the evaporation concentration learning value flprg is thin. The learning value flprg is subtracted by 0.2%.

On the other hand, if the inequality in step S303 does not hold, the flow shifts to step S305, where the deviation (cf
bm-cfb0) is less than -2%.
When the inequality in step S305 is satisfied,
When the deviation (cfbm-cfb0) is less than -2% and the state is close to rich, it can be determined that the evaporation concentration learning value flprg is high. Therefore, the process proceeds to step S306, where the evaporation concentration learning value flprg is added by 0.2%. . Also,
When the inequality in step S305 is not satisfied, that is, when the deviation (cfbm-cfb0) is stable within ± 2%, the flow shifts to step S307, and the evaporative concentration learning value flprg at that time is held. After the processing of step S304, step S306, and step S307, the process proceeds to step S308, and as the upper and lower limit check of the evaporative concentration learning value flprg, the evaporative concentration learning value f
It is checked whether lprg is within 0% to 25%,
This routine ends.

As described above, the evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment includes the canister 17 having the adsorbent 19 for adsorbing the fuel evaporative gas generated in the fuel tank 13 containing the liquid fuel, and the canister 17. A supply passage including supply pipes 22 and 24 for guiding the fuel evaporative gas adsorbed by the adsorbent 19 into the intake pipe 2 by a negative pressure generated in the intake pipe 2 of the internal combustion engine 1, and is provided in the middle of the supply path. A purge control valve 23 having an adjustable opening degree, and a purge flow rate achieved by a CPU 26 controlling the purge flow rate of the supply passage by adjusting the opening degree of the purge control valve 23 in accordance with the operation state of the internal combustion engine 1. and control means, the air-fuel ratio detecting means consisting of O ₂ sensor 12 for detecting an air-fuel ratio of the mixture supplied to the internal combustion engine 1, the internal combustion engine 1 in accordance with the air-fuel ratio detected by the air-fuel ratio detecting means Air-fuel ratio feedback control means achieved by the CPU 26 for feedback-controlling the air-fuel ratio of the supplied air-fuel mixture, and air-fuel ratio feedback correction coefficient by the air-fuel ratio feedback control means before and after changing the purge flow rate by the purge flow rate control means CPU 2 that calculates the evaporation concentration of fuel evaporative gas based on the amount of fluctuation
6, during the idling operation in which the idle switch 35 is ON, when the evaporative concentration is high by the evaporative concentration calculating means, and when the air conditioner switch 32, the headlight switch 33, and the heater blower switch 34 are operated. When the load variation is small, which is both OFF, the opening of the purge control valve 23 is gradually increased stepwise from the fully closed state by the purge flow rate control means, and the air-fuel ratio feedback correction by the air-fuel ratio feedback control means at that time is performed. A rising point calculating means, which is achieved by the CPU 26 and calculates the opening of the rising point of the purge flow rate of the purge control valve 23 based on the fluctuation amount of the coefficient, is provided as an embodiment of the present invention. be able to.

Therefore, in the rising point calculating means by the CPU 26, the opening degree of the purge control valve 23 by the purge flow rate control means by the CPU 26 is changed from the fully closed state to the stepped state during the idling operation, when the evaporation is at a high concentration, and when the load fluctuation is small. The opening of the rising point of the purge flow rate of the purge control valve 23 is calculated based on the amount of change of the air-fuel ratio feedback correction coefficient by the air-fuel ratio feedback control means of the CPU 26 at this time. The correction based on the opening degree of the rising point of the purge flow rate prevents the flow rate variation of the purge control valve 23 caused by the tolerance of the purge flow rate with respect to the opening degree.

In the evaporative fuel treatment system for an internal combustion engine according to the present embodiment, the gradual change of the opening of the purge control valve 23 is based on the rise of the purge flow of the purge control valve 23 when the purge flow with respect to the opening is within a predetermined tolerance. Starting from the smallest opening of the points, this can be the embodiment of claim 3.

Therefore, the gradual change of the opening of the purge control valve 23 is started from the smallest opening of the rising points of the purge flow of the purge control valve whose purge flow relative to the opening is within a predetermined tolerance. There is no wasted time in gradually changing the opening of the valve 23.

In the evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment, the one-step gradual change in the opening degree of the purge control valve 23 is determined by the air-fuel ratio feedback correction coefficient by the air-fuel ratio feedback control means during the gradual change. The variation amount is set so as to be equal to or less than a predetermined value, and this can be regarded as the embodiment of claim 4.

Therefore, the gradual change amount of the opening degree of the purge control valve in one step is set so that the amount of change of the air-fuel ratio feedback correction coefficient by the air-fuel ratio feedback control means at the time of the gradual change becomes equal to or less than a predetermined value. The gradually changing amount of the opening of the valve 23 is appropriately set.

Further, in the evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment, the air-fuel ratio feedback correction coefficient by the air-fuel ratio feedback control means after the gradual change becomes stable during the gradual change period of the opening of the purge control valve 23. Such a value is set, and this can be regarded as the embodiment of claim 5.

Accordingly, the gradual change cycle of the opening of the purge control valve is set to a value that stabilizes the air-fuel ratio feedback correction coefficient by the air-fuel ratio feedback control means after the gradual change. The gradual change period is set appropriately.

In the evaporative fuel treatment system for an internal combustion engine according to the present embodiment, the opening of the rising point of the purge flow rate of the purge control valve 23 is calculated by the variation amount of the air-fuel ratio feedback correction coefficient by the air-fuel ratio feedback control means. Is carried out when the value is equal to or more than a predetermined value.
Of the present invention.

Accordingly, the calculation of the opening of the rising point of the purge flow rate of the purge control valve is performed when the amount of change of the air-fuel ratio feedback correction coefficient by the air-fuel ratio feedback control means exceeds a predetermined value. The opening degree of the rising point of the purge flow rate of 23 is accurately calculated.

Further, in the evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment, the calculation of the opening of the rising point of the purge flow rate of the purge control valve may be performed by the variation amount of the air-fuel ratio feedback correction coefficient by the air-fuel ratio feedback control means. Is subtracted and corrected from the opening estimated to be required for the predetermined value to change, and further,
This is performed by correcting the detection error by performing the gradual change of the opening degree of the purge control valve in a stepwise manner, and this can be an embodiment of claim 7.

Accordingly, the calculation of the opening of the rising point of the purge flow rate of the purge control valve is performed based on the opening which is estimated to be required for the variation of the air-fuel ratio feedback correction coefficient by the air-fuel ratio feedback control means to change by a predetermined value. The subtraction correction is performed, and the gradual change of the opening of the purge control valve is performed in a stepwise manner to correct the detection error, so that the opening of the rising point of the purge flow rate of the purge control valve 23 is accurately calculated. You.

Furthermore, in the fuel vapor treatment apparatus for an internal combustion engine according to the present embodiment, the opening to be subtracted and corrected is a value corresponding to a previously detected evaporative concentration value. Of the present invention.

Therefore, the opening to be subtracted is set to a value corresponding to the evaporative concentration value detected in advance, and the reliability of the opening at that time is improved.

The evaporative fuel treatment apparatus for an internal combustion engine according to the present embodiment has an opening of the rising point of the actual purge flow rate of the purge control valve 23 and an opening degree of the rising point of the designed purge flow rate of the purge control valve 23. Is added to the designed flow rate characteristic of the purge control valve 23. This can be regarded as the embodiment of claim 9.

Therefore, the learning value obtained by learning the difference between the opening degree of the rising point of the actual purge flow rate of the purge control valve and the opening degree of the rising point of the purge flow rate in the design of the purge control valve is determined in the design of the purge control valve. , And is offset by the difference, thereby preventing the purge control valve 23 from varying based on the tolerance of the purge flow rate.

The evaporative fuel treatment apparatus for an internal combustion engine according to the present embodiment has the opening degree of the rising point of the actual purge flow rate of the purge control valve 23 and the opening degree of the rising point of the designed purge flow rate of the purge control valve 23. Before the learning of the difference from the above is completed, the purge by the purge control valve 23 during the idling operation is prohibited, and this can be the embodiment of claim 10.

Therefore, before the learning of the difference between the actual opening of the rising point of the purge flow rate of the purge control valve and the designed opening of the rising point of the purge flow rate of the purge control valve is completed, the purge during idle operation is completed. Purging by the control valve is prohibited, and the effect of the purge flow rate tolerance of the purge control valve 23 on the air-fuel ratio is eliminated.

In the above embodiment, the opening of the purge control valve 23 is gradually increased stepwise from the fully closed state. However, the opening of the purge control valve 23 is gradually increased to the fully closed state. The control may be repeated stepwise with the opening degree.
An example of such a control will be described with reference to FIGS.

FIG. 10 shows ZE of FIG. 6 in the above embodiment.
FIG. 11 shows another processing procedure of the RO point learning control.
4 shows a timing chart in the ZERO point learning control of FIG.

Steps S401 to S411 and S415 to S421 in the flowchart of FIG. 10 correspond to steps S201 to S211 and S212 in the flowchart of FIG.
Steps S218 will not be described in detail.

That is, before the processing of step S212 in the flowchart of FIG.
FIG. 10 is a flowchart to which 414 is added. In FIG. 6, in order to detect the duty at the rising point of the purge flow rate of the purge control valve 23, the duty is gradually increased in a stepwise manner. On the other hand, in FIG. 10, the time from the time when the duty is increased in step S412 is 3 seconds.
After that, the purge control valve 23 is fully closed (Duty ← 0) in step S413, and step S414 is performed.
Then, it waits until the time of Duty = 0 becomes 3 sec. In this manner, the duty of the purge control valve 23 is alternately repeated every 3 seconds between the fully closed state (Duty ← 0) and the duty to gradually increase.

As described above, the evaporative fuel processing apparatus for an internal combustion engine according to the present embodiment includes the canister 17 having the adsorbent 19 for adsorbing the fuel evaporative gas generated in the fuel tank 13 containing the liquid fuel, and the canister 17. A supply passage including supply pipes 22 and 24 for guiding the fuel evaporative gas adsorbed by the adsorbent 19 into the intake pipe 2 by a negative pressure generated in the intake pipe 2 of the internal combustion engine 1, and is provided in the middle of the supply path. A purge control valve 23 having an adjustable opening degree, and a purge flow rate achieved by a CPU 26 controlling the purge flow rate of the supply passage by adjusting the opening degree of the purge control valve 23 in accordance with the operation state of the internal combustion engine 1. and control means, the air-fuel ratio detecting means consisting of O ₂ sensor 12 for detecting an air-fuel ratio of the mixture supplied to the internal combustion engine 1, the internal combustion engine 1 in accordance with the air-fuel ratio detected by the air-fuel ratio detecting means Air-fuel ratio feedback control means achieved by the CPU 26 for feedback-controlling the air-fuel ratio of the supplied air-fuel mixture, and air-fuel ratio feedback correction coefficient by the air-fuel ratio feedback control means before and after changing the purge flow rate by the purge flow rate control means CPU 2 that calculates the evaporation concentration of fuel evaporative gas based on the amount of fluctuation
6, during the idling operation in which the idle switch 35 is ON, when the evaporative concentration is high by the evaporative concentration calculating means, and when the air conditioner switch 32, the headlight switch 33, and the heater blower switch 34 are operated. When the load variation is small, both of which are OFF, the opening of the purge control valve 23 is repeatedly and stepwise controlled by the purge flow control means to the fully closed state and the gradually increased opening, and the air-fuel ratio at that time is controlled. A rising point calculating means which is achieved by the CPU 26 which calculates the opening of the rising point of the purge flow rate of the purge control valve 23 based on the variation amount of the air-fuel ratio feedback correction coefficient by the feedback control means. An embodiment according to claim 2 can be provided.

Therefore, in the rising point calculating means by the CPU 26, the opening degree of the purge control valve 23 by the purge flow rate control means by the CPU 26 gradually changes to the fully closed state during idling operation, when the evaporation is high, and when the load fluctuation is small. The opening degree of the rising point of the purge flow rate of the purge control valve 23 is controlled based on the amount of change of the air-fuel ratio feedback correction coefficient by the air-fuel ratio feedback control means by the CPU 26 at this time. The calculated and corrected correction based on the opening of the rising point of the purge flow rate of the purge control valve 23 prevents the flow rate variation of the purge control valve 23 caused by the tolerance of the purge flow rate with respect to the opening degree.

[0091]

As described above, according to the evaporative fuel treatment system for an internal combustion engine of claim 1, when the internal combustion engine is idling, when the evaporation is at a high concentration, and when the load fluctuation is small, the purge flow control means is provided. The opening degree of the purge control valve is gradually increased stepwise from the fully-closed state by using the air-fuel ratio feedback control means at that time. The opening of the rising point of the purge flow rate can be accurately calculated.

According to the second aspect of the present invention, during the idling operation of the internal combustion engine, when the evaporative concentration is high,
In addition, when the load fluctuation is small, the opening degree of the purge control valve is repeatedly and stepwise controlled to the fully closed state and the gradually increased opening degree using the purge flow rate control means, and the air-fuel ratio feedback at that time is performed. The opening of the rising point of the purge flow rate of the purge control valve can be accurately calculated by the rising point calculation means based on the amount of change in the air-fuel ratio feedback value by the control means.

According to the third aspect of the present invention, in addition to the effects of the first and second aspects, the gradual change in the opening degree of the purge control valve is such that the purge flow rate with respect to the opening degree has a predetermined tolerance. By starting from the minimum opening of the rising points of the purge flow rates of the purge control valves in the inside, wasteful time in gradually changing the opening of the purge control valve can be eliminated.

[0094]

[0095]

According to the fourth aspect of the present invention, in addition to the effect of any one of the first to third aspects, the opening degree of the rising point of the purge flow rate of the purge control valve is calculated. This is performed when the amount of change in the air-fuel ratio feedback value by the air-fuel ratio feedback control means is equal to or greater than a predetermined value, so that the opening of the purge flow rate of the purge control valve at the rising point can be accurately calculated.

[0097]

[0098]

According to the fifth aspect of the present invention, in addition to the effect of any one of the first to fourth aspects, in addition to the effect of the first aspect, the opening degree of the rising point of the actual purge flow rate of the purge control valve is increased. The learning value obtained by learning the difference between the designed purge control valve purge flow rate and the opening of the rising point is added to the designed purge control valve flow characteristic, and the difference is offset by this difference. Variations due to the tolerance of the purge flow rate can be prevented.

[0100]

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an evaporative fuel processing apparatus for an internal combustion engine according to one embodiment of the present invention.

FIG. 2 is a flowchart showing a processing procedure of air-fuel ratio feedback control of a CPU used in an evaporative fuel processing apparatus for an internal combustion engine according to one embodiment of the present invention.

FIG. 3 is a timing chart in the air-fuel ratio feedback control of the evaporative fuel treatment apparatus for the internal combustion engine according to one embodiment of the present invention.

FIG. 4 is a characteristic diagram showing a tolerance range of a purge flow rate with respect to a duty of a purge control valve in an evaporative fuel processing apparatus for an internal combustion engine according to one embodiment of the present invention.

FIG. 5 is an explanatory diagram showing the influence of the variation in the purge flow rate characteristic of the purge control valve on the air-fuel ratio control during the execution of the purge control in the evaporative fuel processing apparatus for an internal combustion engine according to one embodiment of the present invention. .

FIG. 6 is a flowchart showing a processing procedure of ZERO point learning control of a CPU used in an evaporative fuel processing apparatus for an internal combustion engine according to one embodiment of the present invention.

FIG. 7 is a timing chart in the ZERO point learning control of the evaporative fuel processing apparatus for the internal combustion engine according to one embodiment of the present invention.

FIG. 8 is a diagram illustrating ZER in the ZERO point learning control of the evaporative fuel treatment apparatus for the internal combustion engine according to one embodiment of the present invention.
FIG. 9 is an explanatory diagram illustrating an O-point learning correction amount.

FIG. 9 is a flowchart showing a processing procedure for evaporative concentration learning of a CPU used in an evaporative fuel processing apparatus for an internal combustion engine according to one embodiment of the present invention.

FIG. 10 is a flowchart illustrating another processing procedure of the ZERO point learning control of FIG. 6;

FIG. 11 is a timing chart in the ZERO point learning control of FIG.

FIG. 12 is a block diagram showing a concept corresponding to claims 1 and 2.

[Explanation of symbols]

 Reference Signs List 1 internal combustion engine 6 throttle valve 8 ISC valve 15 fuel injection valve 17 canister 23 purge control valve 25 ECU (electronic control device)

Claims (5)

(57) [Claims] 1. A canister having an adsorbent for adsorbing fuel evaporative gas generated in a fuel tank containing liquid fuel, and the fuel evaporative gas adsorbed by the adsorbent of the canister is generated in an intake pipe of an internal combustion engine. A supply passage that is guided into the intake pipe by a negative pressure, a purge control valve that is provided in the middle of the supply passage, and has an adjustable opening, and an opening of the purge control valve that is adjusted according to an operation state of the internal combustion engine. A purge flow rate control means for controlling a purge flow rate of the supply passage, an air-fuel ratio detection means for detecting an air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine, and an air-fuel ratio detected by the air-fuel ratio detection means. Air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine accordingly, and before and after changing the purge flow rate by the purge flow rate control means. Evaporative concentration calculating means for calculating the evaporative concentration of the fuel evaporative gas based on the amount of change in the air-fuel ratio feedback value by the air-fuel ratio feedback control means during the idle operation, when the evaporative concentration is high, and when the load fluctuation is small, The opening degree of the purge control valve is gradually increased stepwise from the fully closed state by the flow rate control means, and the purge flow rate of the purge control valve is determined based on the amount of change of the air-fuel ratio feedback value by the air-fuel ratio feedback control means at that time. A rising point calculating means for calculating an opening degree of a rising point of the engine. 2. A canister having an adsorbent for adsorbing fuel evaporative gas generated in a fuel tank containing liquid fuel, and the fuel evaporative gas adsorbed on the adsorbent of the canister is generated in an intake pipe of an internal combustion engine. A supply passage that is guided into the intake pipe by a negative pressure, a purge control valve that is provided in the middle of the supply passage, and has an adjustable opening, and an opening of the purge control valve that is adjusted according to an operation state of the internal combustion engine. A purge flow rate control means for controlling a purge flow rate of the supply passage, an air-fuel ratio detection means for detecting an air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine, and an air-fuel ratio detected by the air-fuel ratio detection means. Air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine accordingly, and before and after changing the purge flow rate by the purge flow rate control means. Evaporative concentration calculating means for calculating the evaporative concentration of the fuel evaporative gas based on the amount of change in the air-fuel ratio feedback value by the air-fuel ratio feedback control means during the idle operation, when the evaporative concentration is high, and when the load fluctuation is small, The flow control means repeatedly controls the opening degree of the purge control valve in a fully closed state and a gradually increased opening degree in a stepwise manner, and the variation amount of the air-fuel ratio feedback value by the air-fuel ratio feedback control means at that time is controlled. A rising point calculating means for calculating an opening of a rising point of a purge flow rate of the purge control valve based on the purge control valve. 3. The gradual change in the opening degree of the purge control valve is started from a minimum opening degree of a rising point of the purge flow rate of the purge control valve in which a purge flow rate with respect to the opening degree is within a predetermined tolerance. The fuel vapor treatment device for an internal combustion engine according to claim 1 or 2, wherein 4. The method according to claim 1, wherein the calculation of the opening of the rising point of the purge flow rate of the purge control valve is performed when the amount of change in the air-fuel ratio feedback value by the air-fuel ratio feedback control means becomes equal to or greater than a predetermined value. An evaporative fuel processing apparatus for an internal combustion engine according to any one of claims 1 to 3 , wherein: 5. A learning value obtained by learning a difference between an opening degree of a rising point of an actual purge flow rate of the purge control valve and an opening degree of a rising point of a designed purge flow rate of the purge control valve. The fuel vapor processing apparatus for an internal combustion engine according to any one of claims 1 to 4 , wherein the fuel flow rate is added to a design flow rate characteristic of (1).