JPH074322A - Supply device for evaporated fuel of engine - Google Patents

Abstract

PURPOSE:To restrain deviation of air-fuel ratio due to supply of evaporated fuel so as to prevent deterioration of emission by accurately correcting purge regardless of dispersion of the flow characteristic of a purge flow control valve. CONSTITUTION:On the upper stream of a purge valve 29 interposed on the purge passage 28 of a canister 20, a three-way solenoid valve 30 by which the purge passage 28 can be selectively changed to the canister 26 side or the atmosphere side is provided. A purge correction quantity for correcting deviation of air-fuel ratio due to purge of evaporated fuel is set on a map based on the air-fuel ratio feedback correction quantity when the three-way solenoid valve 30 is released to the atmosphere. Further, the purge correction quantity reflects an idling learning value at non-idling, and hence the purge flow as the parameter can be obtained from the lowered quantity of the detected value of an intake air quantity when the three-way solenoid valve 30 is released to the atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an evaporated fuel supply device for an engine which adsorbs and stores evaporated fuel generated in a fuel tank or the like and supplies it to an intake system during engine operation.

[0002]

2. Description of the Related Art Generally, in an engine of an automobile or the like, an evaporated fuel generated in a fuel tank is adsorbed and stored in a canister,
An evaporated fuel supply device is provided so as to supply it to the intake system during engine operation. In order to prevent the air-fuel ratio from shifting due to the supply of the evaporated fuel, it is possible to release the evaporated fuel from the canister (called purging) only in the region where the air-fuel ratio feedback control is performed. It has been conventionally proposed as described in JP-A No. 60-33316.

By the way, in recent automobiles, the engine output has been increased and the engine room has become smaller due to the expansion of living space and the like, so that the temperature in the engine room easily rises and the amount of fuel vapor generated increases. Tend. And this tendency is remarkable especially in an engine using highly volatile gasoline. Therefore, in order to prevent the canister from being saturated, the purge zone has a small intake air amount like idle and the supply of evaporative fuel adversely affects combustion stability, so it is expanded to the area that was previously excluded and purging per cycle is performed. It is required to increase the quantity.

Therefore, in order to expand the purge zone to the idle region and correct the deviation of the air-fuel ratio due to a large amount of purge, not only the purge flow rate is controlled according to the operating state of the engine as in the conventional case, but also the purge is performed. Attempts have been made to set a correction amount for air-fuel ratio control (referred to as a purge correction amount) according to the flow rate and to correct the control amount for air-fuel ratio control by this purge correction amount.

The purge correction amount is based on the flow rate characteristic of the purge flow rate control valve (purge valve) for controlling the purge flow rate, and the learning value (idle learning value) of the purge correction amount during idling is corrected during non-idling (partial region). It has been proposed that this is reflected in the amount, and that the basic idle learning value at that time is calculated based on the air-fuel ratio feedback correction amount set based on the output of the exhaust sensor during idling. In this case, the purge correction amount (CLR
N) is calculated and set by the following equation.

CLRN = (PGTTL / PGIDL) ×
(N ₀ / N _e ) × (C _e0 / C _e ) × CLRNIDP where PGTTL is the purge flow rate (when not idle), PG
IDL is the purge flow rate during idling, N _e is the engine speed (when not idling), N ₀ is the engine speed when idling (idling speed), C _e is the intake charge amount (when not idling), and C _e0 is This is the intake charge amount when idling. Also, C
LRNIDP is an idle learning value of the purge correction amount.

[0007]

In response to the demand for increasing the purge amount of the evaporated fuel, the purge zone is expanded to a region where the intake air amount is small at the time of idling and the purge amount of the evaporated fuel is increased, and In order to prevent the deviation of the air-fuel ratio due to the increased purged flow rate of evaporated fuel, the correction amount of the air-fuel ratio control (purge correction amount) according to the purge flow rate is reflected in a manner that reflects the learning value at idle as described above. Is preferable to control the air-fuel ratio control amount by the purge correction amount, but it is difficult to suppress the variation of the purge flow amount within the allowable range because of the fact that the flow valve has a too large flow rate tolerance under the present circumstances. Therefore, the logic of the above-mentioned calculation formula is not practically established, the accuracy of the purge correction amount is deteriorated, and the air-fuel ratio is deviated to deteriorate the emission. There is.

The present invention has been made in view of the above problems, and sets an accurate purge correction amount regardless of variations in the flow rate characteristics of the purge flow rate control valve for controlling the purge flow rate of the evaporated fuel, and the evaporated fuel is set. It is an object of the present invention to provide an evaporated fuel supply device for an engine, which can suppress the shift of the air-fuel ratio due to the purging of the engine and prevent the deterioration of the emission.

[0009]

SUMMARY OF THE INVENTION The present invention is to realize a highly accurate purge correction that is not affected by variations in flow rate characteristics by actually measuring the purge flow rate by a purge flow rate control valve. Is as follows.

That is, in the configuration of the first aspect of the invention, the air-fuel ratio control amount according to the operating state of the engine is corrected by the air-fuel ratio feedback correction amount based on the output of the exhaust sensor that detects the exhaust gas component, and the engine air An evaporative fuel supply apparatus for an engine, comprising an air-fuel ratio control means for converging a fuel ratio to a target air-fuel ratio, wherein the first invention is evaporative fuel adsorbing means for accumulating evaporated fuel generated in a fuel tank or the like by adsorption, A purge passage for connecting the purge outlet of the evaporated fuel adsorbing means to the intake system, and a purge flow rate control for controlling the purge flow rate of the evaporated fuel from the evaporated fuel adsorbing means, which is interposed in the purge passage, according to the operating state of the engine. A valve, switching means for switching the communication of the purge passage to the evaporative fuel adsorbing means side to the atmosphere side, and a flow rate characteristic of the purge flow rate control valve. The purge correction means for correcting the control amount of the air-fuel ratio control by the air-fuel ratio control means is provided, and the air-fuel ratio feedback correction is performed in the state where the purge passage is communicated to the atmosphere side by the switching means. And a purge correction amount setting means for setting the purge correction amount based on the amount.

Further, according to the second aspect of the invention, the air-fuel ratio control amount according to the operating state of the engine is corrected by the air-fuel ratio feedback correction amount based on the output of the exhaust sensor which detects the exhaust gas component, and the engine air An output of a rotation sensor that detects the engine speed by providing an air-fuel ratio control unit that converges the fuel ratio to a target air-fuel ratio and controlling the bypass control valve provided in a bypass passage that bypasses the throttle valve and supplies bypass air to the engine An evaporative fuel supply system for an engine, comprising an idle speed feedback control means for controlling the amount of bypass air so as to converge the idle speed of the engine to a target idle speed based on The evaporated fuel adsorbing means for storing fuel by adsorption and the purge outlet of the evaporated fuel adsorbing means are connected to the intake air And a purge passage control valve for controlling the purge flow rate of the evaporated fuel from the evaporated fuel adsorbing means according to the operating state of the engine, the purge passage being connected to the To the atmosphere side, and a purge correction for correcting the control amount of the air-fuel ratio control by the air-fuel ratio control means by the purge correction amount based on the flow rate characteristic of the purge flow rate control valve. Means and a purge correction amount setting means for setting the purge correction amount based on the amount of decrease in the air flow rate upstream of the purge passage connection position when the purge passage is communicated to the atmosphere side by the switching means. It is characterized by

Further, according to the third aspect of the invention, the air-fuel ratio control amount according to the operating state of the engine is corrected by the air-fuel ratio feedback correction amount based on the output of the exhaust sensor detecting the exhaust gas component, and the engine air An output of a rotation sensor that detects the engine speed by providing an air-fuel ratio control unit that converges the fuel ratio to a target air-fuel ratio and controlling the bypass control valve provided in a bypass passage that bypasses the throttle valve and supplies bypass air to the engine An evaporative fuel supply system for an engine, comprising an idle speed feedback control means for controlling the amount of bypass air so as to converge the idle speed of the engine to a target idle speed based on The evaporated fuel adsorbing means for storing fuel by adsorption and the purge outlet of the evaporated fuel adsorbing means are connected to the intake air And a purge passage control valve for controlling the purge flow rate of the evaporated fuel from the evaporated fuel adsorbing means according to the operating state of the engine, the purge passage being connected to the To the atmosphere side, and a purge correction for correcting the control amount of the air-fuel ratio control by the air-fuel ratio control means by the purge correction amount based on the flow rate characteristic of the purge flow rate control valve. Means, an idle learning value calculating means for calculating an idle learning value of the purge correction amount based on the air-fuel ratio feedback correction amount at the time of idling, and the idle learning value is calculated by a predetermined calculation formula using a purge flow rate as a parameter. Reflection means for reflecting the purge correction amount during idling, and the purge when the purge passage is communicated to the atmosphere side by the switching means Characterized in that a purge flow rate learning value computing means for computing a learning value of the purge flow for the arithmetic expression based on the decrease amount of the air flow at the road-connection position upstream.

[0013]

The evaporated fuel generated in the engine fuel tank or the like is adsorbed and stored in the evaporated fuel adsorbing means, and the purge flow rate of the adsorbed and stored evaporated fuel from the evaporated fuel adsorbing means is changed to the operating state of the engine by the purge flow control valve. The purge amount of the evaporated fuel is supplied to the intake system of the engine through the purge passage.

According to the configuration of the first invention,
In order to set the purge correction amount, the purge passage is switched from communicating with the evaporative fuel adsorption means side to communicating with the atmosphere side, and thus the air-fuel ratio feedback correction amount based on the output of the exhaust sensor when switched to the atmosphere side is set. The purge correction amount is set based on this, and the control amount of the air-fuel ratio control is corrected by this purge correction amount in the direction of suppressing the deviation of the air-fuel ratio. In this manner, when the purge passage is switched to the atmosphere side, the amount of air corresponding to the purge flow rate is increased and supplied to the intake system instead of the evaporated fuel, and this is reflected in the air-fuel ratio feedback correction amount. Therefore, by setting the purge correction amount based on the air-fuel ratio feedback correction amount in this state, it is possible to set the purge correction amount based on the actual measured value of the purge flow rate.

According to the structure of the second aspect of the invention, the purge passage is switched from the communication with the evaporative fuel adsorbing means to the communication with the atmosphere, so that the purge correction amount is set. At this time, the purge correction amount is set based on the amount of decrease in the air flow rate upstream of the purge passage connection position, and the control amount of the air-fuel ratio control is corrected by this purge correction amount in the direction of suppressing the deviation of the air-fuel ratio. In this way, when the purge passage is switched to the atmosphere side, the amount of air corresponding to the purge flow rate is increased and supplied to the intake system instead of the evaporated fuel, so that the upstream side air in the state where the idle speed feedback means operates. The flow rate decreases by the amount corresponding to the purge flow rate. Therefore, by setting the purge correction amount based on the amount of decrease in the upstream air amount at this time, the purge correction amount can also be set based on the actual measurement value of the purge flow rate.

According to the third aspect of the invention, the idle learning value of the purge correction amount for the air-fuel ratio control is calculated based on the air-fuel ratio feedback correction amount during idling. Then, the learning value of the purge flow rate is calculated based on the amount of decrease in the air flow rate upstream of the purge passage connection position when the purge passage is switched from the communication to the evaporative fuel adsorption means side to the communication to the atmosphere side, and the purge flow rate is calculated. The purge correction amount during non-idle is set by reflecting the idle learning value to the purge correction amount during non-idle by a predetermined arithmetic expression as a parameter, and the control amount of the air-fuel ratio control is set by this purge correction amount. Is corrected in a direction to suppress the deviation of. In this case, when the purge passage is switched to the atmosphere side, the amount of air corresponding to the purge flow rate is increased and supplied to the intake system instead of the evaporated fuel, so that the upstream air flow rate when the idle speed feedback means is activated. Is reduced by the amount corresponding to the purge flow rate. Therefore, the purge correction amount at the time of non-idling can be accurately set by establishing an arithmetic expression by considering the amount of decrease in the upstream air flow rate at this time as the purge flow rate.

[0017]

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

Example 1. 1 is a system diagram of Embodiment 1 of the present invention. In the figure, 1 is an engine body.
The engine body 1 includes a cylinder block 2 forming a plurality of cylinders arranged in a row and a piston 3 arranged in each cylinder.
And a cylinder head 4 fixed to the upper part of the cylinder block 2.

The intake system of the engine includes an intake manifold 5 connected to the cylinder head 4 and an intake manifold 5.
The throttle body 6 is connected to the inlet of the throttle body 6, the intake pipe 7 is arranged upstream of the throttle body 6, and the air cleaner 9 is connected to the tip of the intake pipe 7 via an air flow meter 8. And the throttle body 6
A butterfly-type throttle valve 10 is disposed in the intake manifold 5, and a fuel injection valve 11 is attached to each independent intake passage portion 5a of the intake manifold 5 in the vicinity of the connecting position on the cylinder head 4 side. A bypass passage 11 that bypasses the throttle valve 10 is formed in the intake system of the engine, and a duty control type ISC (idle speed control) valve 1 that controls the bypass flow rate is provided in the bypass passage 11.
2 are arranged.

The exhaust system of the engine includes an exhaust manifold 13 connected to the cylinder head 4 at a position facing the intake manifold 5, a catalytic converter 14 connected to a tip end collecting portion of the exhaust manifold 13, and the catalytic converter 14. The exhaust pipe 15 is connected to the downstream side. The exhaust system is provided with O ₂ sensors 16 and 17 upstream and downstream of the catalytic converter 14, respectively.

Fuel (gasoline) in a fuel tank 18 is supplied to each fuel injection valve 11 arranged in an independent intake passage portion for each cylinder through a fuel supply passage 19. Excess fuel from each fuel injection valve 11 is returned to the fuel tank 18 via the fuel return passage 20.

The fuel supply passage 19 is connected to a discharge port of a fuel pump 21 built in the fuel tank 18.
A low-pressure side fuel filter 22 is arranged on the suction side of the fuel pump 21, and a high-pressure side fuel filter 23 is arranged on the fuel supply passage 19. A pressure regulator 24 for adjusting the fuel pressure is arranged in the fuel return passage 20.

The upper space of the fuel tank 18 is connected to the canister 26 by a communication passage 25, and the communication passage 25 is provided with a two-way valve 27. The purge passage 28 extending from the purge outlet of the canister 26 is a surge tank 5b that constitutes the collecting portion of the intake manifold 5.
And a purge valve 29, which is a duty control type flow rate control valve, is provided in the middle of the purge passage 28. Further, in the purge passage 28, a three-way solenoid valve 30 is provided upstream of the purge valve 29 so as to selectively switch the passage 28 between the canister 26 side and the atmosphere side. An air introduction passage 31 is connected to the canister 26, and an air filter 32 is provided in the atmosphere introduction passage 31. An air control valve 33 is provided on the canister 26 side of the air introduction passage 31 with the air filter 31 interposed therebetween, and a check valve 34 is provided on the atmosphere opening side. The pressure regulator 24 is connected to a boost pressure passage 35 that guides a boost pressure serving as a reference pressure, and the solenoid valve 3 is provided in the middle of the boost pressure passage 35.
6 is provided.

The engine body 1 is provided with a rotation sensor 37 for detecting the rotation angle of the engine output shaft (crankshaft), and a water temperature sensor 38 for detecting the cooling water temperature of the engine. The detection signals of the rotation sensor 37 and the water temperature sensor 38 are input to a control unit 39 composed of a microcomputer. Further, the control unit 39 receives a detection signal of the air flow meter 8, a detection signal of each of the O ₂ sensors 16 and 17 on the upstream and downstream sides of the catalyst, and a throttle sensor 40 for detecting the opening of the throttle valve 10. Detection signal is input. Then, based on these various signals, the control unit 39 calculates the fuel injection amount, the bypass air amount, the purge flow rate, and the fuel injection valve 11, the ISC valve 12, and the purge valve 29, respectively. It

The air-fuel ratio of the engine is controlled by the fuel injection amount from the fuel injection valve 11. Therefore, the basic injection amount is calculated based on the engine speed calculated from the output of the rotation sensor 37 and the intake air amount detected by the air flow meter 8, and various corrections based on the output of the water temperature sensor 38 are added to the basic injection amount. When the air-fuel ratio feedback control execution condition that the water temperature is a predetermined value (for example, 40 ° C.) or more is satisfied in the predetermined feedback region on the low / medium load side, the air-fuel ratio is set to the target air-fuel ratio based on the output of the upstream O ₂ sensor 16. An air-fuel ratio feedback correction amount for converging to the fuel ratio is calculated, and the downstream O ₂ sensor 17
Is added to the fuel injection valve 11, and a correction based on a purge correction amount described later is added to determine a final fuel injection amount, and an injection pulse corresponding to the fuel injection amount is supplied to the fuel injection valve 11. It is output and fuel injection is executed.

The engine speed during idling is controlled to a predetermined target idle speed by feedback control of the bypass air amount. Therefore, the drive duty of the ISC valve 12 is calculated based on the deviation between the actual engine speed and the target idle speed, and the ISC valve 12 is controlled.

The supply of the evaporated fuel to the intake system is controlled by the purge valve 29. Therefore, it is determined whether or not the predetermined purge execution condition is satisfied in the air-fuel ratio feedback region, and when the purge execution condition is satisfied, the control duty of the barge valve 29 is set by the map so that the purge flow rate is in accordance with the operating state of the engine. Is set.

The evaporative fuel generated in the fuel tank 18 is adsorbed and stored by the canister 26, and the purge flow rate is controlled and supplied to the intake system when the purge execution condition is satisfied as described above. The amount of purge correction is set based on the flow rate characteristic of the purge valve 29 to correct the deviation of the fuel injection amount. The amount of purge correction corrects the fuel injection amount.

The purge correction amount is set as follows and is updated, for example, every time the engine is started. That is, in the air-fuel ratio feedback region, the purge passage 28
The three-way solenoid valve 30 is opened to the atmosphere side. Then, in this way, the purge passage 28 becomes the canister 26.
The purge correction amount according to the purge duty is set by the map based on the air-fuel ratio feedback correction amount when the side is switched to the atmosphere side.

FIG. 2 is a flow chart for learning the purge correction amount in the first embodiment. This flow of purge correction amount learning is to set the purge correction amount in five stages, and comprises steps S101 to S110. When started, first, in S101, various signals such as engine speed, load, and water temperature are read. Then, in S102, it is determined whether it is in the air-fuel ratio feedback region.

If it is determined in S102 that it is not in the feedback region, the flow is ended as it is. If it is in the feedback region, the process proceeds to S103, the purge valve 29 is turned off (fully closed), and then S104.
Then, the three-way solenoid valve 30 is opened to the atmosphere side. Then, the process proceeds to S105, the purge valve 29 is turned on,
First, set the first-stage purge duty (V ₁ ),
In S106, the air-fuel ratio feedback correction amount (C _FB ) at that time is read. Then, read the purge correction amount corresponding to V ₁ by map as parameters C _FB in S107 (CLRN), corresponding to the V ₁ CLRN
Is stored in S108.

Then, the process proceeds to S109, and it is determined whether the current purge duty (V _n ) is the fifth stage purge duty (V ₅ ). If it is not V _{5, the} process proceeds to S110 and V _n is advanced by one stage. Then, S106 to S108
Storing CLRN for each V _n repeat, V _n in S109
The flow ends when is in the fifth stage.

Example 2. FIG. 3 is a flowchart for executing the purge correction amount learning according to the second embodiment of the present invention. In the case of this embodiment, the basic control of the entire system and the air-fuel ratio, idle speed, purge flow rate, etc. is the same as in the first embodiment.

In the case of this embodiment, the purge correction amount of the air-fuel ratio control is set in such a manner that the idle learning value is reflected in the non-idle state. That is, the basic idle learning value is calculated based on the air-fuel ratio feedback correction amount based on the output of the exhaust sensor during idling, and the purge correction amount during non-idling is set by the following equation.

CLRN = (PGTTL / PGIDL) ×
(N ₀ / N _e ) × (C _e0 / C _e ) × CLRNIDP where CLRN is the purge correction amount (non-idle), PGTTL is the purge flow rate (non-idle), PGI
DL is the purge flow rate during idling, N _e is the engine speed (when not idling), N ₀ is the engine speed when idling (idling speed), C _e is the intake charge amount (when not idling), and C _e0 is This is the intake charge amount when idling. Also, C
LRNIDP is an idle learning value of the purge correction amount.

Here, the purge flow rate (PGIDL) at the time of idling in the above equation is three-way solenoid valve 3
The purge passage 28 is switched from the canister 26 side to the atmosphere side by 0, and at that time, the amount of decrease in the intake air amount detected by the air flow meter 8 is observed while the engine speed is converged to the target idle speed by the control of bypass air. Required by

The purge correction amount learning of this embodiment is S201.
When the engine is started, it is first determined in S201 based on the throttle valve opening and the engine speed. Then, when it is not idle, it returns as it is, and when it is idle, S2
Go to 02.

In S202, it is checked whether the purge condition is satisfied. Then, if the purge condition is not satisfied, the process directly returns, and if the purge condition is satisfied, the process proceeds to S203.

In S203, it is checked whether the purge flow rate has been learned. If learning has been completed, the measured value (Q _a1 ) of the intake air amount (idle air amount) is read in S204, and then the purge valve 29 is turned ON (purge duty = 10%) in S205 and the three-way solenoid valve is set. Open 30 to the atmosphere side. Then, in S206, it is checked whether or not the engine speed converges to the target idle speed by the idle speed control (ISC), wait until it converges, and if so, in S207, the measured value (Q _a2 ) is read.

Next, in step S208, the flow rate (PGQ _a ) of the purge valve 29 is obtained in the form of the difference between Q _a1 and Q _a2 . Then, in S209, the three-way solenoid valve 30 is closed to the atmosphere (communicating with the canister side), and in S210, the PGQ _a is regarded as the idle purge flow rate, and is reflected in the above arithmetic expression for air-fuel ratio correction, and in S211 the purge correction amount learning To execute.

If the purge flow rate has been learned in S203, the program proceeds to S211 and the purge correction amount learning is executed.

In the above embodiment, one purge valve is provided in the purge passage, and a three-way solenoid valve is provided upstream of the purge valve in the passage so that communication with the canister can be switched to communication with the atmosphere. As described above, the configuration of this part is such that two purge valves are provided in parallel and one of them has a large flow rate (for example, 40 liters / mi).
The partial purge valve of n) and the other one may be a small flow rate (for example, 5 liters / min) idle dedicated purge valve, and a three-way solenoid valve may be arranged upstream of the branch passage of the idle dedicated purge valve.

[0043]

Since the present invention is constituted as described above, a highly accurate purge correction amount for air-fuel ratio control is set regardless of variations in the flow rate characteristics of the purge flow rate control valve, and when evaporative fuel is supplied. It is possible to suppress the deviation of the air-fuel ratio of the engine and prevent the deterioration of emission.

[Brief description of drawings]

FIG. 1 is a system diagram of a first embodiment of the present invention.

FIG. 2 is a flowchart for executing purge correction amount learning according to the first embodiment of the present invention.

FIG. 3 is a flowchart for executing purge correction amount learning according to the second embodiment of the present invention.

[Explanation of symbols]

1 Engine Body 8 Air Flow Meter 11 Bypass Passage 12 ISC Valve 16, 17 O ₂ Sensor 18 Fuel Tank 26 Canister (Evaporated Fuel Adsorbing Means) 28 Purge Passage 29 Purge Valve 30 Three-way Solenoid Valve 37 Rotation Sensor 38 Water Temperature Sensor 39 Control Unit

Claims (3)

[Claims] 1. An air-fuel ratio control amount according to an operating state of an engine is corrected by an air-fuel ratio feedback correction amount based on an output of an exhaust sensor that detects an exhaust gas component, and the engine air-fuel ratio is converged to a target air-fuel ratio. An evaporative fuel supply device for an engine, comprising an air-fuel ratio control means, wherein evaporative fuel adsorbing means for accumulating evaporated fuel generated in a fuel tank or the like, and a purge outlet of the evaporative fuel adsorbing means are connected to the intake system. A purge passage, and a purge flow control valve that is provided in the purge passage and controls the purge flow rate of the evaporated fuel from the evaporated fuel adsorbing means according to the operating state of the engine.
An air-fuel ratio controlled by the air-fuel ratio control means by a switching means for switching the communication of the purge passage to the evaporative fuel adsorption means side to the atmosphere side and a purge correction amount based on the flow rate characteristic of the purge flow rate control valve. Purge correction means for correcting the control amount of control, and purge correction amount setting means for setting the purge correction amount based on the feedback correction amount when the purge passage is in communication with the atmosphere by the switching means. An evaporative fuel supply device for an engine, characterized by being provided. 2. The air-fuel ratio control amount according to the operating state of the engine is corrected by an air-fuel ratio feedback correction amount based on the output of an exhaust sensor that detects an exhaust gas component, and the air-fuel ratio of the engine is converged to a target air-fuel ratio. The engine is equipped with an air-fuel ratio control means, and idle rotation of the engine is performed based on the output of a rotation sensor that detects the engine speed by controlling a bypass control valve provided in a bypass passage that bypasses the throttle valve and supplies bypass air to the engine. An evaporative fuel supply apparatus for an engine, comprising an idle speed feedback control means for controlling a bypass air amount so as to converge the number to a target idle speed, the evaporative fuel storing adsorbed fuel vapor generated in a fuel tank or the like by adsorption. Adsorption means, and a purge passage connecting the purge outlet of the evaporated fuel adsorption means to the intake system, A purge flow rate control valve that is interposed in the purge passage and controls the purge flow rate of the evaporated fuel from the evaporated fuel adsorbing means according to the operating state of the engine and the communication of the purge passage to the evaporated fuel adsorbing means side to the atmosphere side Switching means for switching to the communication, purge purge means for correcting the control amount of the air-fuel ratio control by the air-fuel ratio control means by the purge correction amount based on the flow rate characteristic of the purge flow rate control valve, and the switching means. An engine comprising: a purge correction amount setting means for setting the purge correction amount based on a reduction amount of an air flow rate upstream of the purge passage connection position when the purge passage is connected to the atmosphere side. Evaporative fuel supply device. 3. An air-fuel ratio control amount according to an operating state of the engine is corrected by an air-fuel ratio feedback correction amount based on an output of an exhaust sensor that detects an exhaust gas component, and the air-fuel ratio of the engine is converged to a target air-fuel ratio. The engine is equipped with an air-fuel ratio control means, and idle rotation of the engine is performed based on the output of a rotation sensor that detects the engine speed by controlling a bypass control valve provided in a bypass passage that bypasses the throttle valve and supplies bypass air to the engine. An evaporative fuel supply apparatus for an engine, comprising an idle speed feedback control means for controlling a bypass air amount so as to converge the number to a target idle speed, the evaporative fuel storing adsorbed fuel vapor generated in a fuel tank or the like by adsorption. Adsorption means, and a purge passage connecting the purge outlet of the evaporated fuel adsorption means to the intake system, A purge flow rate control valve that is interposed in the purge passage and controls the purge flow rate of the evaporated fuel from the evaporated fuel adsorbing means according to the operating state of the engine and the communication of the purge passage to the evaporated fuel adsorbing means side to the atmosphere side Switching means for switching to the communication of the purge flow control valve, purge correction means for correcting the control amount of the air-fuel ratio control by the air-fuel ratio control means by the purge correction amount based on the flow rate characteristic of the purge flow rate control valve, Idle learning value calculation means for calculating an idle learning value of the purge correction amount based on the air-fuel ratio feedback correction amount, and the idle correction value as a purge correction amount at the time of non-idle by a predetermined calculation formula having a purge flow rate as a parameter. The reflecting means for reflecting and the empty space upstream of the purge passage connecting position when the purge passage is connected to the atmosphere side by the switching means. Evaporative fuel supply system for an engine, characterized in that a purge flow rate learning value computing means for computing a learning value of the purge flow for the arithmetic expression based on the decrease of the flow rate.