JP3323577B2 - Evaporative fuel processor for 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 processing apparatus for an engine, and more particularly to a fuel vapor processing apparatus for an engine in which fuel vapor adsorbed by a canister is supplied to an intake system of the engine.

[0002]

2. Description of the Related Art In an engine of an automobile or the like, for example, in order to prevent air pollution caused by emission of fuel vapor generated in a fuel supply system to the atmosphere, the fuel vapor evaporated in a fuel tank is referred to as purge. In this case, the evaporated fuel is generally once adsorbed in a canister and then supplied into an intake passage during operation of the engine.

In recent years, in order to reduce the size of the canister, for example, Japanese Patent Application Laid-Open No.
As disclosed in Japanese Patent Laid-Open Publication No. 1-107, there is an engine in which the fuel vapor is purged even when the engine is idling.

On the other hand, in this type of engine, in order to improve the exhaust performance while securing a required output, for example, the amount of fuel injected from a fuel injection valve installed facing the intake passage of the engine is reduced. By controlling
In some cases, the air-fuel ratio of an air-fuel mixture supplied to a combustion chamber is controlled. This air-fuel ratio control basically determines a fuel injection amount at which an optimum air-fuel ratio is realized based on an operating state of an engine, and outputs a drive signal having a pulse width set according to the fuel injection amount to the fuel injection amount. It is performed by outputting to the injection valve, but in order to further improve the control accuracy of the air-fuel ratio,
There is a case where the fuel injection amount is feedback-controlled so that the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber converges to a predetermined target air-fuel ratio (for example, stoichiometric air-fuel ratio; air / fuel = 14.7). In this feedback control, for example, the output state changes on the upstream side of a three-way catalytic converter installed in the exhaust system of the engine when the excess air ratio λ (air-fuel ratio / stoichiometric air-fuel ratio) is 1 and the output state changes. _Two sensors are arranged, and when the signal from the sensor indicates a rich state of the air-fuel ratio of the air-fuel mixture in the combustion chamber (fuel rich state; λ <1), the amount of fuel injected from the fuel injection valve is reduced. In addition, when the signal from the sensor indicates a lean state of the air-fuel ratio (fuel is lean; λ> 1), the fuel injection amount is increased so that the air-fuel ratio converges and is maintained at the stoichiometric air-fuel ratio. Done in

[0005]

In the above-described fuel injection type engine, if the fuel vapor is purged during the feedback control of the air-fuel ratio, the following problem may occur. .

That is, during the purge of the fuel vapor,
In addition to the fuel injected from the fuel injection valve, the purge fuel flowing into the intake passage is also sucked into the combustion chamber. In this case, the fuel injected from the fuel injection valve is adjusted so that the air-fuel ratio of the air-fuel mixture in the combustion chamber achieves the stoichiometric air-fuel ratio. The state becomes richer than the air-fuel ratio. In that case, the composition of the exhaust gas after combustion from reflect the air-fuel ratio of the mixture in the combustion chamber, O ₂ atmosphere around the sensor also reflect the air-fuel ratio becomes oxygen-deficient state, of the O ₂ sensor The output indicates a rich state of the air-fuel ratio. In this case, the fuel injection amount from the fuel injection valve is reduced in order to maintain the mixture in the combustion chamber at the stoichiometric air-fuel ratio, but until the output of the O ₂ sensor is inverted from the rich state to the lean state. A response delay occurs during this period, and during that time, the air-fuel ratio is maintained in a rich state, and the exhaust performance deteriorates.

[0007] In particular, during idling operation with a small engine load and a small amount of intake air, the above-mentioned problem occurs remarkably.

According to the present invention, there is provided an engine in which vaporized fuel in a fuel tank is introduced into an intake system under predetermined conditions, when the introduction of the vaporized fuel into the intake system is started during feedback control of the air-fuel ratio. An object of the present invention is to solve the above problem and to efficiently purge evaporated fuel without deteriorating control accuracy of an air-fuel ratio.

[0009]

That is, an evaporative fuel processing apparatus according to the invention of claim 1 of the present application (hereinafter referred to as a first invention) detects an air-fuel ratio of an air-fuel mixture supplied to a combustion chamber of an engine. Air-fuel ratio detecting means, and a fuel supply amount to an intake system such that an air-fuel ratio of an air-fuel mixture in a combustion chamber converges to a predetermined target air-fuel ratio in a predetermined operating region based on an air-fuel ratio signal from the air-fuel ratio detecting means. And a control unit provided in an evaporative fuel supply passage leading to the intake system in an engine in which the evaporative fuel in the fuel tank is introduced into the intake system under predetermined conditions. evaporative fuel supply control means for introducing periodically the evaporative fuel into the intake system is provided by, the evaporated Hatsu燃
Charge supply control means, when introducing the vaporized fuel into the intake system during the air-fuel ratio feedback control by the feedback means, after a predetermined time period immediately after the beginning of the introduction until
Guiding the evaporated fuel introduction period of the evaporative fuel into the intake system between at
An introduction cycle changing means for making the introduction cycle longer than the predetermined time after the start of the introduction , and an air-fuel ratio being changed from a rich state to a lean state after the introduction of the evaporated fuel into the intake system is started.
Supply of evaporated fuel to the intake system until the pressure changes to
The amount is fixed to a relatively small predetermined value and the air-fuel ratio is reset.
After changing to the open state, the supply amount is
Yes and evaporative fuel supply amount controller also increased gradually to a value
Characterized in that it.

[0010]

[0011]

The invention of claim 2 of the present application (hereinafter referred to as “ second
In the fuel vapor processing apparatus for an engine according to the present invention , the introduction cycle changing means in the configuration of the first invention starts introduction of the fuel vapor into the intake system during the feedback control of the air-fuel ratio during the idle operation of the engine. When activated.

[0013]

According to the above arrangement, the following operation can be obtained.

[0014] That is, first, in either of the second invention, when the fuel vapor to the intake system during the feedback control of the air-fuel ratio is introduced, from immediately after the beginning of the introduction until a predetermined time elapses in the evaporative fuel Introduction cycle starts introduction of evaporative fuel
Is set longer than the introduction cycle after the predetermined time has elapsed, so that the amount of evaporative fuel flowing into the intake system is limited, whereby the air-fuel ratio transiently changes from the target air-fuel ratio. A large deviation is prevented, and the convergence to the target air-fuel ratio is also improved.

After the elapse of the predetermined time, the introduction cycle of the evaporated fuel is returned to the normal state, so that the evaporated fuel is also effectively purged.

Further, after the introduction of the fuel vapor into the intake system is started.
Until the air-fuel ratio changes from rich to lean
During the period, the supply amount of evaporated fuel introduced into the intake system is relatively small.
After the air-fuel ratio is changed to the lean state, the supply amount of the evaporated fuel to the intake system is gradually increased, so that the control accuracy of the air-fuel ratio is deteriorated. And the fuel vapor is more effectively purged.

In this case, the supply amount of the evaporated fuel to the intake system is gradually increased because the air-fuel ratio changes from a rich state to a lean state.
Since it is from the time of the change, it becomes possible to effectively purge the evaporated fuel while maintaining good control accuracy of the air-fuel ratio.

According to the second aspect of the present invention , when the introduction of the evaporated fuel into the intake system is started during the feedback control of the air-fuel ratio during the idle operation of the engine, the introduced cycle of the evaporated fuel is shorter than the normal period. Since the length is made longer, the control accuracy of the air-fuel ratio during idling operation with a small engine load and a small intake air amount is prevented from being extremely deteriorated.

[0019]

Embodiments of the present invention will be described below.

As shown in FIG. 1, an engine 1 has an intake passage 5 communicating with a combustion chamber 4 via intake and exhaust valves 2 and 3, respectively.
And an exhaust passage 6. The intake passage 5 is provided with an air cleaner 7 from the upstream side, an air flow sensor 8 for detecting the amount of intake air to the combustion chamber 4, and a throttle valve 9 for adjusting the amount of intake air or the engine output. 4, a fuel injection valve 10 for injecting fuel into
It is installed downstream of a surge tank 11 provided downstream of the throttle valve 9. On the other hand, a three-way catalytic catalytic converter 12 is provided in the exhaust passage 6, and a residual oxygen concentration in the exhaust gas is detected on the upstream side of the catalytic converter 12 so that the inside of the combustion chamber 4 is detected. An O ₂ sensor 13 for detecting the air-fuel ratio of the air-fuel mixture is provided.

The engine 1 is provided with a fuel supply system for supplying fuel to the fuel injection valve 10. The fuel supply system includes a fuel tank 14 for storing fuel, a fuel pump 15 installed in the tank 14, a fuel supply passage 16 for guiding fuel discharged from the pump 15 to a fuel injection valve 10, a fuel supply passage 16, A fuel recovery passage for recovering excess fuel not injected by the injection valve; The fuel recovery passage 17 is provided with a pressure regulator 18 for adjusting the fuel injection pressure.
In other words, when the negative pressure of the intake air is introduced into the pressure regulator 18 from the surge tank 11 in the intake passage 5 through the negative pressure passage 19, the fuel injection from the fuel injection valve 10 is performed in accordance with the negative pressure. The pressure is adjusted.

An upper portion of the fuel tank 14 is connected to an evaporative fuel collecting passage 21 that collects the evaporative fuel evaporated in the tank 14 and guides the fuel to a canister 20. The connected purge passage 22 is connected to the surge tank 11 in the intake passage 5 through a purge control valve 23 that opens when the power is supplied.
It is connected to the. The atmosphere opening passage 24 connected to the lower portion of the canister 20 is guided to the surge tank 11 via a check valve 25. The check valve 25 is configured to shut off the atmosphere opening passage 24 when the surge tank 11 is in a negative pressure state. Therefore, the evaporated fuel guided to the canister 20 through the evaporated fuel collecting passage 21 is supplied to the canister 2.
After the gas is once adsorbed by the activated carbon contained in the purge gas, it is supplied to the intake passage 5 through the purge passage 22 when the purge control valve 23 is opened.

Further, the engine 1 is provided with an electronically controlled control unit (hereinafter referred to as ECU) 30. The ECU 30 includes an intake air amount signal from the air flow sensor 8, an engine speed signal from a rotation sensor 31 for detecting the engine speed, and an idle switch 3 for detecting a fully closed state of the throttle valve 9.
2, a water temperature signal from a water temperature sensor 33 for detecting the engine water temperature, an air-fuel ratio signal from the O ₂ sensor 13, and the engine 1 together with the automatic transmission 26 constituting a power plant of the vehicle. A shift position signal from the shift position sensor 34 and a vehicle speed signal from a vehicle speed sensor 35 for detecting the vehicle speed of the vehicle are input, and based on these signals, fuel injection control from the fuel injection valve 10 and purge The purge control of the evaporated fuel using the control valve 23 is performed.

Here, the fuel injection control performed by the ECU 30 will be described. This fuel injection control is generally performed as follows.

That is, the ECU 30 determines the amount of intake air drawn into the combustion chamber 4 per cycle based on the intake air amount Q indicated by the signal from the air flow sensor 8 and the engine speed Ne indicated by the signal from the rotation sensor 31. Is calculated, the basic injection pulse width Tp corresponding to the value is set, and when a predetermined feedback condition is satisfied, O
_A feedback correction coefficient Cfb is calculated based on the air-fuel ratio signal from the _two sensors 13. That is, the ECU 30
For example, the engine water temperature T indicated by a signal from the water temperature sensor 33
When w is higher than a predetermined value and the engine speed Ne indicated by the signal from the rotation sensor 31 and the basic injection pulse width Tp as a representative characteristic of the engine load, as shown in FIG. When it is determined that the injection pulse width and the injection pulse width belong to the feedback zone Zfb set as a parameter, it is determined that the feedback condition is satisfied, and the feedback is performed when the air-fuel ratio signal from the O ₂ sensor 13 indicates the rich state of the air-fuel ratio. The correction coefficient Cfb is subtracted, and the feedback correction coefficient Cfb is added when the air-fuel ratio signal indicates a lean state of the air-fuel ratio.

The ECU 30 calculates another correction coefficient Co based on a water temperature signal from the water temperature sensor 33 and the like, and calculates the basic injection pulse width Tp, the feedback correction coefficient Cfb, the other correction coefficient Co, and a predetermined value. The final injection pulse width Ti is obtained by substituting the learning correction coefficient Clrn obtained under the condition (1) into the following relational expression.

Ti = Tp (1 + Cfb + Co + Clrn) + Tv Here, Tv represents an invalid injection time in consideration of an operation delay of the fuel injector 10.

Then, the ECU 30 outputs a drive signal corresponding to the final injection pulse width Ti to the fuel injection valve 10.

The purge control, which is a feature of the present invention, is specifically performed as follows in accordance with the flowchart shown in FIG.

That is, after reading various signals, the ECU 30 determines whether or not the above-described air-fuel ratio feedback condition is satisfied (steps S1 and S2). When it is determined that the air-fuel ratio feedback condition is satisfied, the process proceeds to step S3, where it is determined whether the operating state of the engine 1 is an idle operating state based on an idle signal from the idle switch 32 or the like. If not, step S4 is executed, and the standard frequency fo is set as the drive frequency f of the purge control valve 23.
(For example, 10 Hz). And engine 1
After the purge rate Rp is set in accordance with the operation state of the above, a duty drive signal according to the drive frequency f is output to the purge control valve 23 so that the fuel vapor is purged at the purge rate Rp ( Step S5, S
6). Here, in the ECU 30, for example, as shown in FIG. 4, a map of the duty ratio D linearly corresponding to the purge ratio Rp is set.
If N is turned off, the fuel vapor adsorbed by the canister 20 is purged at the purge rate Rp corresponding to the duty rate D.

Returning to the flowchart of FIG.
When it is determined in step S2 that the air-fuel ratio feedback condition is not satisfied, the flow branches to step S7 to set 0 as the purge rate Rp. Therefore, the purge control valve 23 is completely closed, and the purge of the fuel vapor is stopped.

When the ECU 30 determines in step S3 that the operation state of the engine 1 is the idling operation state, the process proceeds to step S8, where the range of the automatic transmission 26 indicated by the signal from the shift position sensor 34 is the D range. If it is determined that the vehicle is in the D range, the process proceeds to step S9, and the vehicle speed Vs of the vehicle indicated by the signal from the vehicle speed sensor 35 is set to the set vehicle speed Vo (for example, 3
km / h). And EC
If U30 determines that the vehicle speed Vs is lower than the set vehicle speed Vo, it checks in step S10 the value of the learning flag Flrn to determine whether the learning processing of the learning correction coefficient Clrn used for fuel injection control has been completed. Then Y
If it is determined to be ES, it is determined in step S11 whether or not the learning process has been completed last time. That is, the learning correction coefficient Cl
It is determined whether or not the learning process of rn has just been completed.

The ECU 30 sets a predetermined value To as a timer value Ts of a purge start timer in step S12 when it determines NO in step S11, that is, when it determines that the learning process has just been completed. In step S13, the air-fuel ratio determination flag Fo
Is set to 1. Then, in step S14, it is determined whether the value of the timer value Ts of the purge start timer is 0 or not.
In the case of O, after decrementing the timer value Ts in step S15, the standard frequency fo is set as the drive frequency f of the purge control valve 23 in step S16.
An initial frequency fs (for example, 5 Hz) lower than (10 Hz) is set, and a predetermined initial value α is set as the purge rate Rp in step S17. Therefore,
Until the process of decrementing the timer value Ts of the purge start timer ends, the purge control valve 23 is opened and closed at a longer cycle than usual.

When the ECU 30 determines in step S14 that the timer value Ts of the purge start timer is 0, the ECU 30 proceeds to step S18 and sets the drive frequency f of the purge control valve 23 to the standard frequency fo. in, it is determined whether the air-fuel ratio determination flag Fo is set to 1 by executing the step S19, the lean state output from the rich state of the O ₂ sensor 13 proceeds to step S20 when it is determined that YES It is determined whether or not it has been inverted. That is, it is determined whether the air-fuel ratio of the air-fuel mixture in the combustion chamber 4 has converged to the stoichiometric air-fuel ratio from the rich state immediately after the start of the purge. And
The ECU 30 determines in step S20 that the O ₂ sensor 1
When it is determined that the output of No. 3 has reversed from the rich state to the lean state, the value of the air-fuel ratio determination flag Fo is cleared to 0 in step S21, and then step S22 is executed to set the feedback correction coefficient Cfb to the negative range. The predetermined feedback lower limit value Fmn (for example, -0.
It is determined whether or not the value is greater than 5). If the determination is YES, the process proceeds to step S23, where the value of the purge increase flag Fz is 1
It is determined whether or not. Here, the purge increase flag Fz is
A flag which is normally set to 1 and which is set to 1 again when the increase timer which starts operation when the value of the flag Fz is cleared to 0 counts a preset operation time. It is.

When the ECU 30 determines in step S23 that the value of the purge increasing flag Fz is 1, the ECU 30 proceeds to step S24 and proceeds to step S24.
A value obtained by adding a predetermined incremental value β to p and a predetermined upper limit value Rmx
Are compared with each other, and the smaller one of the two is replaced with the new purge rate Rp, and the value of the purge increase flag Fz is cleared to 0 in step S25.

On the other hand, when the ECU 30 determines in step S22 that the feedback correction coefficient Cfb is not larger than the feedback lower limit Fmn, the ECU 30 proceeds to step S26 to determine whether the value of the purge reduction flag Fg is 1 or not. . Here, the purge reduction flag Fg
Is set to 1 in normal times, and is set to 1 again when the weight loss timer that starts operating when the value of the flag Fg is cleared to 0 counts a preset operation time. Flag.

When the ECU 30 determines in step S26 that the value of the purge reduction flag Fg is 1, the ECU 30 proceeds to step S27 and executes the current purge rate R
The value obtained by subtracting the predetermined gradual decrease value γ from p is compared with 0, the larger value of the two is replaced with a new purge rate Rp, and the routine proceeds to step S28, where the value of the purge decrease flag Fg is set. Is cleared to 0.

If the ECU 30 determines in step S9 that the vehicle speed Vs of the vehicle is not lower than the set vehicle speed Vo, that is, determines that the vehicle is in a creep running state, the ECU 30 executes step S7 to perform a purge. Set 0 as the rate Rp.

Next, the operation of the embodiment will be described with reference to the time chart shown in FIG.

At the end of deceleration of the vehicle, the throttle valve 9
Are fully closed, and when the idle switch 32 switches from OFF to ON, the learning flag Flrn is set to 1 and the learning process of the learning correction coefficient Clrn is started. Then, the learning process is completed and the learning flag Fl
When rn is cleared to 0, the drive frequency of the purge control valve 23 is set to an initial frequency fs lower than the standard frequency fo, and a predetermined initial value α is set as the purge rate Rp. Therefore, the purge control valve 23 is opened / closed at a longer opening / closing cycle than usual, whereby the introduction amount of the evaporated fuel is suppressed, and the canister 2 is opened at the beginning of the purge.
A large amount of evaporated fuel adsorbed to zero is prevented from flowing into the intake passage 5 rapidly. At this time, the fuel that is not metered is introduced into the intake passage 5, so that the air-fuel ratio of the air-fuel mixture in the combustion chamber 4 becomes richer than the stoichiometric air-fuel ratio. ₂ The vicinity of the sensor 13 also becomes rich reflecting the air-fuel ratio,
In order to make the air-fuel ratio in the combustion chamber 4 converge to the stoichiometric air-fuel ratio, the feedback correction coefficient Cfb decreases linearly as shown by the symbol (A) in the figure.

At the start of the purge, the predetermined value T
The timer value Ts of the purge start timer in which o is set is 0
After a lapse of a predetermined time ts until the driving frequency f of the purge control valve 23 becomes equal to the initial frequency fs.
The standard frequency fo is switched to a higher standard frequency fo.
As a result, the purge control valve 23 opens and closes in a short cycle, and the purge amount per unit time increases. When the air-fuel ratio of the air-fuel mixture in the combustion chamber 4 converges from the rich state after the start of the purge to the stoichiometric air-fuel ratio, the output of the O2 sensor 13 reverses from the rich state to the lean state and decreases immediately after the start of the purge. The purge rate Rp is increased by a predetermined gradually increasing value β when the continuous feedback correction coefficient Cfb changes from decreasing to increasing as shown by the symbol (a) in the figure. On the condition that the feedback correction coefficient Cfb is larger than the feedback lower limit value Fmn, the purge rate R
Until the upper limit value Rmx is reached, p increases stepwise in accordance with the gradually increasing value β as shown by the symbol (c). As a result, the evaporated fuel adsorbed in the canister 20 is effectively purged in a relatively short time while the air-fuel ratio is accurately maintained at the stoichiometric air-fuel ratio.
In this case, as the purge rate Rp increases, the feedback correction coefficient Cfb tends to decrease. However, as shown by the symbol (D), when the feedback correction coefficient Cfb reaches the feedback lower limit value Fmn, The purge rate Rp is reduced by a predetermined gradually decreasing value γ. When the feedback correction coefficient Cfb is regulated by the feedback lower limit Fmn, the purge rate R
p decreases stepwise according to the above-mentioned gradual decrease value γ as shown by the sign (e). The gradual decrease value γ is set to a relatively large value so that the feedback correction coefficient Cfb increases quickly.

In this embodiment, a vehicle equipped with an automatic transmission has been described. However, the present invention can be generally applied to an engine in which air-fuel ratio feedback control is performed.

[0043]

According to the present invention as described above, according to the present invention, when the fuel vapor to the intake system during the feedback control of the air-fuel ratio is introduced, from immediately after the beginning of the introduction until a predetermined time elapses introduction of evaporated fuel The period is the above specified time from the start of introduction of evaporative fuel
Since the time period is longer than the introduction cycle after the lapse of time, the amount of evaporative fuel flowing into the intake system is limited, whereby the air-fuel ratio transiently greatly deviates from the target air-fuel ratio. Is prevented, and the convergence to the target air-fuel ratio is also improved.

After the elapse of the predetermined time, the introduction cycle of the fuel vapor is returned to the normal state, so that the fuel vapor is also effectively purged.

After the introduction of the fuel vapor into the intake system is started.
Until the air-fuel ratio changes from rich to lean
During the period, the supply amount of evaporated fuel introduced into the intake system is relatively small.
After the air-fuel ratio is changed to the lean state, the supply amount of the evaporated fuel to the intake system is gradually increased, so that the control accuracy of the air-fuel ratio is deteriorated. And the fuel vapor is more effectively purged.

In this case, the supply amount of the evaporated fuel to the intake system is gradually increased because the air-fuel ratio changes from a rich state to a lean state.
Since it is from the time of the change, it becomes possible to effectively purge the evaporated fuel while maintaining good control accuracy of the air-fuel ratio.

According to the second aspect of the present invention , when the introduction of the fuel vapor into the intake system is started during the feedback control of the air-fuel ratio during the idle operation of the engine, the cycle of introducing the fuel vapor is shorter than the normal cycle. Since the length is made longer, the control accuracy of the air-fuel ratio during idling operation with a small engine load and a small intake air amount is prevented from being extremely deteriorated.

[Brief description of the drawings]

FIG. 1 is a control system diagram of an engine according to an embodiment.

FIG. 2 is an engine operating region diagram showing an air-fuel ratio feedback control region.

FIG. 3 is a flowchart illustrating purge control according to the embodiment.

FIG. 4 is a characteristic diagram showing a relationship between a purge rate and a duty rate used for controlling a purge control valve.

FIG. 5 is a time chart illustrating the operation of the embodiment.

[Explanation of symbols]

1 engine 5 an intake passage 9 a throttle valve 10 fuel injection valve 13 O ₂ sensor 14 fuel tank 20 canister 21 fuel vapor collection passage 22 purge passage 23 purge control valve 30 ECU 31 rotation sensor 32 idle switch

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F02M 25/08 301 F02D 41/02 301 F02D 41/14 310

Claims (2)

(57) [Claims] An air-fuel ratio detecting means for detecting an air-fuel ratio of an air-fuel mixture supplied to a combustion chamber of an engine, and an air-fuel ratio in the combustion chamber based on an air-fuel ratio signal from the air-fuel ratio detecting means in a predetermined operating region. Feedback means for feedback-controlling the amount of fuel supplied to the intake system so that the air-fuel ratio converges to a predetermined target air-fuel ratio, and introduces fuel vapor in the fuel tank into the intake system under predetermined conditions. as in the a fuel vapor treatment system for an engine, the evaporated fuel supply control means for introducing periodically the evaporative fuel into the intake system by opening and closing the control valve provided in the fuel vapor supply passage leading to the intake system provided is, the evaporation fuel supply control means, when introducing the vaporized fuel into the intake system during the air-fuel ratio feedback control by the feedback means, the predetermined immediately after the beginning of the introduction The predetermined Until between elapses the introduction period of the evaporative fuel into the intake system from the beginning of the introduction of the vaporized fuel
Means for changing the introduction cycle longer than the introduction cycle after the elapse of time , and the air-fuel ratio becomes rich after the introduction of evaporative fuel into the intake system.
Until it changes from the lean state to the lean state.
If the supply of evaporated fuel is fixed at a relatively small predetermined value
In both cases, after the air-fuel ratio changes to lean,
The evaporative fuel processing system for an engine, characterized in that it comprises a vaporized fuel supply amount control means for increasing to a value greater than the predetermined value. 2. The method according to claim 1, wherein the introduction cycle changing means is operated when introduction of the evaporated fuel into the intake system is started during feedback control of the air-fuel ratio during idle operation of the engine. An evaporative fuel processing device for an engine according to claim 1 .