JPH1150919A - Evaporative fuel emission preventing device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make any evaporative fuel, to be taken into an internal combustion engine in course of driving, so as to keep it in an optimal quantity at all times as preventing this evaporative fuel from being emitted to the atmosphere. SOLUTION: This evaporative fuel emission preventer calculates an on-off duty ratio DRV of a purge control valve calculating a maximum possible evaporative fuel processing quantity Qcap (S6) being fed to an intake pipe according to engine speed NE and intake pipe inner absolute pressure PBA (S7). Likewise, a purge flow rate Qprg to be purged to an intake system from a canister is calculated according to the on-off duty ratio DRV (S8), and concentration NV(%) of evaporative fuel to be purged from the canister according to an integrating purge quantity timely integrated with this purge flow rate Qprg from the purge starting is calculated (S9). Next, an evaporative fuel purge quantity Qvp is calculated (S10) from the product between the purge flow rate Qprg and the concentration NV. In addition, tank pressure and an on-off duty ratio (DRO) are controlled (S11 to S16) so as to make an evaporative fuel processing quantity QV to be taken into the intake pipe via the tank pressure and the control value not to exceed the value made up of deducting the evaporative fuel purge quantity Qvp from the maximum possible evaporative fuel processing quantity Qcap in the intake pipe.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for preventing evaporative fuel from being released from an internal combustion engine, which always keeps the inside of a fuel tank at a negative pressure to prevent the release of evaporative fuel.

[0002]

2. Description of the Related Art When an internal combustion engine is operated, the pressure in the fuel tank is reduced to a negative pressure, and the internal pressure of the fuel tank is maintained at a negative pressure even after the internal combustion engine is stopped as well as during the operation of the internal combustion engine. The present applicant has already proposed an evaporative fuel release prevention device for an internal combustion engine which prevents the evaporative fuel in the fuel tank from being released to the outside air even when the cap is opened (see, for example, Japanese Patent Application No. Hei 9 (1994) No. 9-131). -116257
issue).

In this device, a tank pressure control valve for opening and closing a fuel tank that connects a fuel tank and an intake pipe of an internal combustion engine is provided by using a negative pressure in the intake pipe during operation of the internal combustion engine. The opening of the tank pressure control valve is feedback-controlled according to the internal pressure of the fuel tank so that the internal pressure of the fuel tank becomes the target pressure value. In such a device, a canister (ORVR (on-board fuel vapor recirculation) canister) dedicated to refueling is provided, and a fuel tank and an ORV are usually provided.
The R canister is connected via an ORVR solenoid valve which opens only when refueling, and the intake pipe and the ORVR canister are connected via a purge control valve.

[0004] With this arrangement, most fuel vapor generated during fueling is adsorbed by the ORVR canister, and the adsorbed fuel vapor is ad- justed in accordance with the load of the internal combustion engine during operation of the internal combustion engine and during purging. The opening of the purge control valve is controlled to purge the fuel vapor into the intake pipe.

[0005]

However, in the above prior art, during the operation of the internal combustion engine and during the execution of the purge, the evaporated fuel for depressurizing the fuel tank through the tank pressure control valve and the fuel for the ORVR are used. Since it is necessary to simultaneously supply both the fuel vapor for purging through the canister to the intake pipe, there is a problem that the fuel mixture in the intake pipe becomes excessively rich and adversely affects exhaust gas emission and operability. is there.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to prevent a fuel vapor from being released into the atmosphere and supply the fuel vapor to an intake system during operation of an internal combustion engine. It is an object of the present invention to provide an evaporative fuel emission prevention device for an internal combustion engine, which can maintain an optimal amount of evaporative fuel.

[0007]

According to a first aspect of the present invention, there is provided an evaporative fuel release prevention apparatus for an internal combustion engine, comprising: a canister connected to a fuel tank; and an intake system of the canister and the internal combustion engine. A purge passage connecting the
A first control valve provided in the purge passage for opening and closing the purge passage; an evaporative fuel passage connecting the fuel tank to an intake system of the internal combustion engine; and an opening and closing the evaporative fuel passage provided in the evaporative fuel passage. An operating state detecting means for detecting an operating state of the internal combustion engine, and calculating a maximum possible evaporative fuel processing amount based on the operating state of the internal combustion engine. First calculating means for calculating the amount of fuel vapor purged from the canister based on the opening degree of the first control valve, and suctioned into the intake system via the second control valve. Control means for controlling the opening of the second control valve so that the amount of evaporated fuel does not exceed the amount obtained by subtracting the amount of evaporated fuel purge from the maximum possible amount of evaporated fuel processed.

[0008] With this configuration, the opening degree of the second control valve provided in the evaporative fuel passage connecting the fuel tank and the intake system of the internal combustion engine is increased by the evaporative fuel sucked into the intake system via the second control valve. Since the amount is controlled so as not to exceed the maximum possible evaporative fuel processing amount based on the operating state of the internal combustion engine minus the amount of evaporative fuel purge from the canister via the first control valve, the intake air via the second control valve is controlled. The sum of the amount of evaporative fuel sucked into the system and the amount of evaporative fuel purge from the canister via the first control valve is prevented from exceeding the maximum possible amount of evaporative fuel that can be supplied to the intake system. While maintaining the optimum amount of fuel vapor to be supplied to the intake pipe during operation of the internal combustion engine, exhaust gas emission and operation due to excessive enrichment of the fuel mixture in the intake system Prevent deterioration of properties Rukoto can.

According to a second aspect of the present invention, there is provided the evaporative fuel release prevention apparatus for an internal combustion engine according to the first aspect, wherein the second calculating means is based on an opening degree of the first control valve. Calculating the vaporized fuel purge flow rate and the vaporized fuel cumulative purge amount, calculating the vaporized fuel concentration during the purge based on the cumulative purge amount, and multiplying the vaporized fuel purge flow rate by the vaporized fuel concentration. The fuel purge amount is calculated.

With this configuration, the amount of fuel vapor purge from the canister to the intake system can be accurately calculated with a simple configuration.

According to a third aspect of the present invention, there is provided the evaporative fuel release prevention apparatus for an internal combustion engine according to the first or second aspect, wherein the control means further comprises: when the internal combustion engine is operating and when it is stopped. The opening degree of the second control valve is controlled so that the internal pressure of the fuel tank becomes negative at times.

With this configuration, the inside of the fuel tank is maintained at a negative pressure during the operation of the internal combustion engine as well as after the engine is stopped, and the fuel vapor in the fuel tank is prevented from being released to the outside air even when the filler cap is opened for refueling. can do.

[0013]

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

FIG. 1 is an overall configuration diagram showing a configuration of an apparatus for preventing fuel vapor emission from an internal combustion engine according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an internal combustion engine having, for example, four cylinders (hereinafter simply referred to as "engine"), and a throttle valve 3 is disposed in the intake pipe 2 of the engine 1. A throttle valve opening (θTH) sensor 4 is connected to the throttle valve 3, and outputs an electric signal according to the opening of the throttle valve 3 to an electronic control unit (hereinafter referred to as (ECU)) 5. Supply.

The fuel injection valve 6 is provided for each cylinder in the middle of the intake pipe 2 and slightly upstream of an intake valve (not shown) between the engine 1 and the throttle valve 3. Each fuel injection valve 6 is connected to a sealed fuel tank 9 via a fuel supply pipe 7, and a fuel pump 8 is provided in the fuel supply pipe 7. The fuel tank 9 has a filler port 10 for refueling, and a filler cap 11 is attached to the filler port 10.

The fuel injection valve 6 is electrically connected to the ECU 5, and a signal from the ECU 5 controls a valve opening time of fuel injection.

An intake pipe absolute pressure (P) for detecting an intake pipe absolute pressure PBA is provided downstream of the throttle valve 3 of the intake pipe 2.
A BA) sensor 13 and an intake air temperature (TA) sensor 14 for detecting an intake air temperature TA as an outside air temperature are mounted. The fuel tank 9 has a tank internal pressure Pt of the fuel tank 9.
And a fuel temperature (Tg) sensor 16 for detecting the temperature Tg of the fuel in the fuel tank 9.

The engine speed (N) is detected around the camshaft or crankshaft (not shown) of the engine 1.
E) The sensor 17 is attached. The NE sensor 17 outputs a pulse (TDC signal pulse) at a predetermined crank angle position every time the crankshaft of the engine 1 rotates 180 degrees. The detection signals of these sensors 13 to 17 are provided by ECU
5 is supplied.

Next, a configuration for controlling the internal pressure of the fuel tank 9 to a negative pressure will be described.

The fuel tank 9 is connected to the intake pipe 2 downstream of the throttle valve 3 via an evaporative fuel passage 20.
A tank pressure control valve 30 as a second control valve for opening and closing the evaporative fuel passage 20 to control the internal pressure of the fuel tank 9 is provided in the middle of the evaporative fuel passage 20. The tank pressure control valve 30 controls the supply flow rate of the evaporated fuel generated in the fuel tank 9 to the intake pipe 2 by changing the on-off duty ratio of the control signal (the opening degree of the second control valve). The operation of the control valve 30 is controlled by the ECU 5. The control valve 30 may be a linear control type solenoid valve whose opening can be changed linearly.

A cut-off valve 21 is provided at the connection between the fuel vapor passage 20 and the fuel tank 9. The cutoff valve 21 is a float valve that closes when the fuel tank 9 is full or when the inclination of the fuel tank 9 increases.

Next, a configuration for preventing the fuel vapor in the fuel tank 9 from being released to the atmosphere at the time of refueling will be described.

A canister 33 is connected to the fuel tank 9 via a charge passage 31. The canister 33 is connected to a downstream side of the throttle valve 3 of the intake pipe 2 via a purge passage 32.

In the middle of the charge passage 31, a tank relief valve 35 is provided. The tank relief valve 35 is
The internal pressure of a portion of the charge passage 31 closer to the fuel tank 9 than the tank relief valve 35 (hereinafter referred to as a “fuel tank system”) is increased to a first predetermined range (for example, −32 with respect to the atmospheric pressure).
0 to +100 mmHg), the valve opens and the first
The valve is configured to close within a predetermined range. Specifically, the tank relief valve 35 is a positive pressure valve that opens when the internal pressure of the fuel tank system is equal to or more than “+100 mmHg” and a negative pressure valve that opens when the internal pressure is equal to or less than “−320 mmHg” (both are not shown). ) Is a mechanical two-way valve composed of: Each of the positive pressure valve and the negative pressure valve includes a valve body, a spring that presses the valve body in a valve closing direction, and a seat that can close the flow path by contacting the valve body pressed by the spring. This is a so-called check valve. In addition, other types of directional control valves may be used for the tank relief valve 35, and when an electromagnetic valve is used,
The operation may be controlled by the ECU 5 according to the tank internal pressure Pt.

The first predetermined range is set so as to include a value that can be taken by a target pressure value Po of the negative pressure control of the fuel tank 9 described later, and the fuel tank 9 and the charge passage 31 are set.
Is set within the range of withstand pressure. This makes it possible to control the fuel tank 9 to a negative pressure while avoiding the fuel tank system from being in an over-negative pressure state or an over-positive pressure state exceeding its withstand pressure.

A solenoid valve 36 (ORVR solenoid valve) is provided in the bypass passage 31a bypassing the tank relief valve 35.
Is provided. The operation of the electromagnetic valve 36 is controlled by the ECU 5, and is opened when refueling, and is closed otherwise, and guides the fuel vapor in the fuel tank 9 to the canister 33 when refueling.

The canister 33 has a built-in activated carbon for adsorbing fuel vapor from the fuel tank 9 and can communicate with the atmosphere through an atmosphere opening passage 37. The canister 33 is an ORVR canister normally provided exclusively for preventing the evaporative fuel from being released into the atmosphere at the time of refueling. In this embodiment, the fuel tank 9 is used when the overpressure of the fuel tank 9 described later is relieved. It also functions to prevent the evaporative fuel inside from being released to the atmosphere.

A vent shut valve (open / close valve) 38 is provided in the middle of the atmosphere opening passage 37. The vent shut valve 38 is a so-called normally-closed valve whose operation is controlled by the ECU 5 and is opened at the time of refueling or during execution of a purge, and closed at other times.

A canister relief valve 39 is provided in a bypass passage 37a that bypasses the vent shut valve 38. The canister relief valve 39 is connected from the canister 33 in the bypass passage 37a to the canister relief valve 39.
(Hereinafter referred to as “canister system”) to a second predetermined range (for example, −10 with respect to the atmospheric pressure).
0 to +90 mmHg), and the valve is closed within the second predetermined range. Specifically, the canister relief valve 39 is connected to the bypass passage 37.
The positive pressure valve that opens when the internal pressure of the canister system with respect to the pressure (that is, the atmospheric pressure) of the portion on the atmosphere side from the canister relief valve 39 a is equal to or more than “+90 mmHg” and opens when the internal pressure is equal to or less than “−100 mmHg” This is a mechanical two-way valve including a negative pressure valve (both not shown), and is configured similarly to the tank relief valve 35. Note that a directional control valve of another type may be used for the canister relief valve 39. If an electromagnetic valve is used, a sensor for detecting the internal pressure of the canister 33 is separately provided, and the ECU 5 is operated in accordance with the detected value. May control the operation of the solenoid valve.

The second predetermined range is set within the first predetermined range, and smoothes overpressure and overpressure of the fuel tank 9 described later. Further, the second predetermined range is set within the range of the withstand pressure of the canister system, and prevents the canister system from being in an over-negative pressure state or an over-positive pressure state exceeding the withstand pressure.

A purge control valve 34 as a first control valve is provided between the canister 33 and the intake pipe 2 in the purge passage 32. The purge control valve 34 is an electromagnetic valve configured so that the flow rate can be continuously controlled by changing the on-off duty ratio of the control signal (the opening degree of the first control valve). Operation is ECU5
Is controlled by

The ECU 5 shapes input signal waveforms from various sensors and the like, corrects a voltage level to a predetermined level, and converts an analog signal value into a digital signal value. In addition to a storage means for storing a calculation program executed by the CPU, a calculation result, and the like, the fuel injection valve 6, the tank pressure control valve 30, the purge control valve 34, the solenoid valve 36, and the vent shut valve 38 It comprises an output circuit for supplying a drive signal and the like.

The CPU of the ECU 5 has a NE sensor 17, θ
The control of the amount of fuel supplied to the engine 1 is performed in accordance with the output signals of various sensors such as the TH sensor 3 and the PBA sensor 13. Since the fuel amount control is not the subject of the present invention, the description is omitted.

In such a configuration, each of the above-described valves operates as follows depending on the situation, such as when refueling or purging.

First, at the time of refueling, as described above, the solenoid valve 3
6 and the vent shut valve 38 are opened. As a result, the evaporated fuel generated in the fuel tank 9 upon refueling is adsorbed to the canister 33 via the electromagnetic valve 36, and the air from which the fuel has been removed is discharged to the atmosphere via the vent shut valve 38. Therefore, it is possible to prevent the evaporative fuel from being released into the atmosphere during refueling.

Next, at the time of purging, the solenoid valve 36 is closed.
The vent shut valve 38 is opened, the purge control valve 34 is controlled to open, and the negative pressure of the intake pipe 2 is reduced by the canister 3.
Acts on 3. Then, the atmosphere is supplied to the canister 33 via the vent shut valve 38, and the fuel adsorbed by the canister 33 is supplied to the intake pipe 2 via the purge control valve 34.
Purged. Therefore, the evaporated fuel generated in the fuel tank 9 is burned in the combustion chamber without being released to the atmosphere.
During the purge, the tank pressure control valve 30 changes the internal pressure of the fuel tank 9 due to the negative pressure of the intake pipe 2 to a target pressure value Po described later.
The opening is controlled so that

Next, when the internal pressures of the fuel tank 9 and the canister 33 fluctuate excessively, the tank relief valve 35 and the canister relief valve 39 are opened to eliminate them. Both relief valves 35 and 39 operate regardless of the open / closed state of the solenoid valve 36 and the vent shut valve 38, and can operate even when the vehicle is stopped.

The evaporative emission control process for calculating the opening of the tank pressure control valve 30 will now be described with reference to FIG. FIG. 2 is a flowchart showing a program for performing a fuel vapor emission prevention control process in the fuel vapor emission prevention device for an internal combustion engine according to the embodiment of the present invention. This process is executed every predetermined time (for example, every 10 mmsec).

First, at step S1, it is determined whether or not the engine 1 is operating, for example, by detecting cranking of the engine 1, and at step S2, it is determined whether or not the engine 1 is operating.
It is determined whether or not is during fuel cut. As a result of the determinations in steps S1 and S2, when the engine 1 is stopped or the fuel is being cut, the CPU of the ECU 5 determines the negative pressure in the fuel tank 9 controlled to a target pressure value Po described later. In order to hold the pressure, the tank pressure control valve 30 is closed (step S3), and the process ends.

As a result of the determinations in steps S1 and S2, if the engine 1 is operating and the fuel is not being cut, the absolute pressure PBA in the intake pipe detected by the PBA sensor 13 is taken in (step S4). The engine speed NE detected by the NE sensor 17 is fetched (step S5). In the present embodiment, PBA
The sensor 13 and the NE sensor 17 correspond to “operating state detecting means” in the claims.

Next, at step S6, the engine speed N
Q and Qca shown in FIG. 4 according to E and the intake pipe absolute pressure PBA.
The p table is searched to calculate the maximum possible evaporated fuel processing amount Qcap (l / min) that can be supplied to the intake pipe 2. The maximum possible evaporated fuel processing amount Qcap is the engine speed NE.
And the operating state of the engine 1 based on the intake pipe absolute pressure PBA. In the present embodiment, step S6 corresponds to "first calculating means" in the claims.

Next, in step S7, DR shown in FIG. 5 is set according to the engine speed NE and the intake pipe absolute pressure PBA.
The V table is searched to calculate the on-off duty ratio DRV of the purge control valve 34. Evaporated fuel at a flow rate corresponding to the on-off duty ratio DRV is purged from the canister 33 into the intake pipe 2 via the purge control valve 34.

Next, at step S8, the purge control valve 3
The Qprg table shown in FIG. 6 is searched according to the on / off duty ratio DRV of No. 4 to determine the purge flow rate Qprg (l /
min). The purge flow rate Qprg is a fuel vapor purge flow rate that is purged from the canister 33 to the intake pipe 2.

After calculating the purge flow rate Qprg, step S
In step 9, the integrated purge amount Qpin (l) is calculated by integrating the purge flow rate Qprg with time from the start of the purge, and the NV table shown in FIG. 7 is searched according to the integrated purge amount Qpin to be purged from the canister 33. The concentration NV (%) of the fuel vapor is calculated.

Next, in step S10, the evaporated fuel purge amount Qvp to be sucked into the intake pipe 2 is calculated by the following equation (1). In the present embodiment, this step S1
0 corresponds to the "second calculating means" in the claims.

Qvp = Qprg × NV (1) In step S11, the fuel tank 9 is calculated by the following equation (2).
The amount of vaporized fuel QV that can be supplied to the intake pipe 2 for the negative pressure reduction process is determined.

QV = Qcap−Qvp (2) That is, the above-mentioned evaporated fuel amount QV is calculated from the maximum possible evaporated fuel processing amount Qcap that can be supplied to the intake pipe 2 by the purge control valve 3.
4 is a value obtained by subtracting the evaporated fuel purge amount Qvp via the control valve 4, and this QV value is the maximum value assigned to the negative pressure processing of the tank pressure fuel tank 9 via the control valve 30.

Further, in step S12, the above-mentioned step S
The DRN shown in FIG.
The table is searched to calculate the on-off duty ratio DRN of the tank pressure control valve 30 according to the evaporated fuel amount QV.
The retrieved on-off duty ratio DRN of the tank pressure control valve 30 is used as a target duty ratio D of the tank pressure control valve 30 to be described later, which is applied at the time of negative pressure processing of the fuel tank 9.
This is the upper limit of RO.

Next, in step S13, a target duty ratio DRO of the tank pressure control valve 30 is calculated by a process of calculating a target duty ratio DRO of the tank control valve 30 described later.

Next, in step S14, FIG.
The negative pressure execution flag FNC, which indicates that the negative pressure of the fuel tank 9 should be executed, is set to "1".
If the flag FNC is "0" and the fuel tank 9 is not to be depressurized, the routine proceeds to step S3.
On the other hand, when the flag FNC is "1" and the negative pressure of the fuel tank 9 can be executed, the process proceeds to step S15, and the process proceeds to step S13. It is determined whether or not the target duty ratio DRO of the tank pressure control valve 30 calculated in step S12 is larger than the duty ratio DRN calculated in step S12.
If O ≦ DRN, the process proceeds to step S16 to control the opening of the control valve 30 based on the target duty ratio DRO.

On the other hand, if DRO> DRN in step S15, DRO is set to DRN (step S1).
7) The process proceeds to step S16 to set the target duty ratio DRO
The opening of the control valve 30 is controlled based on In the present embodiment, steps S15 to S17 correspond to “control means” in the claims.

According to the processing of FIG. 2 described above, the amount of evaporated fuel QV that can be supplied to the intake pipe 2 for the negative pressure processing of the fuel tank 9 is changed to the maximum possible evaporated fuel processing quantity that can be supplied to the intake pipe 2. The on-off duty ratio of the tank pressure control valve 30 provided in the evaporative fuel passage 20 connecting the fuel tank 9 and the intake pipe 2 is obtained by subtracting the evaporative fuel purge amount Qvp via the purge control valve 34 from Qcap. DRO)
Is controlled so as not to exceed the duty ratio DRN of the control valve 30 corresponding to the evaporated fuel amount QV that can be supplied to the intake pipe 2 via the control valve 30 (steps S15 to S1).
6) The maximum possible evaporated fuel processing amount Qc that can be supplied to the intake pipe 2 by adding the evaporated fuel amount QV and the evaporated fuel purge amount Qvp.
Ap can be prevented from deteriorating exhaust gas emission and operability due to excessive concentration of the air-fuel mixture in the intake pipe 2.

Hereinafter, the process of calculating the target duty ratio DRO of the tank pressure control valve 30 in step S13 of FIG. 2 will be described with reference to FIG. FIG. 3 is a flowchart of a program for calculating the target duty ratio DRO of the tank pressure control valve 30 in step S13 in FIG. This program is executed in synchronization with the processing of FIG.

First, in step S31, it is determined whether or not the engine 1 is operating by detecting cranking of the engine 1, and the like, and in step S32, it is determined whether or not the engine 1 is in fuel cut. . Step S
As a result of the determinations in steps S31 and S32, if the engine 1 is stopped or the fuel is being cut, the present process is immediately terminated.

As a result of the determinations in steps S31 and S32, if the engine 1 is operating and the fuel is not being cut, the fuel temperature Tg in the fuel tank 9 detected by the Tg sensor 16 is taken (step S33). Then, the internal pressure Pt of the fuel tank 9 detected by the Pt sensor 15 is taken (step S34). further,
Intake pipe absolute pressure PB detected by PBA sensor 13
A (step S35) and the NE sensor 1
The engine speed NE detected at step 7 is taken (step S36).

Next, the target pressure value Po in the fuel tank 9 is set.
(Absolute pressure, mmHg) is calculated by a predetermined setting method (for example, a setting method described in Japanese Patent Application No. Hei 9-116257) (step S37). The target pressure value Po is an excessively negative pressure value that allows for a predicted tank pressure increase in the fuel tank 9 so that the negative pressure in the fuel tank 9 can be maintained even after the engine 1 is stopped. is there. As a factor of the predictable increase in the tank internal pressure in the fuel tank 9, the component contained in the fuel that evaporates at a temperature lower than the fuel temperature evaporates due to the retained heat amount of the fuel in the fuel tank 9 at that temperature. In addition, a part of the fuel evaporates in the same manner as described above due to a rise in the temperature of the fuel in the fuel tank 9 due to a rise in the outside air temperature.

Next, it is determined whether or not the tank internal pressure Pt of the fuel tank 9 is larger than the target pressure value Po (step S3).
8) When Pt ≦ Po, it is not necessary to further reduce the tank internal pressure Pt of the fuel tank 9 to a negative pressure.
In step 9, the flag FNC is set to "0" and the process ends.

If Pt> Po in the step S38, the process proceeds to a step S40, where it is determined whether or not the intake pipe absolute pressure PBA is smaller than the tank internal pressure Pt.
If so, it is determined that the tank internal pressure Pt cannot be further reduced to a negative pressure by the intake pipe absolute pressure PBA, and step S
At step 39, the flag FNC is set to "0", and the process is terminated.

When PBA <Pt in the step S40, the target duty ratio DRO of the control valve 30 shown in FIG. 9 according to the engine speed NE and the intake pipe absolute pressure PBA.
(%) Is retrieved (step S41). In FIG. 9, the target duty ratio DRO (%) of the control valve 30 is set to increase as at least one of the engine speed NE and the intake pipe absolute pressure PBA increases. The target duty ratio DRO is such that the tank internal pressure Pt in the fuel tank 9 is equal to the target pressure value Po (absolute pressure, mmHg).
Take a value such that The flag FNC is set to “1”, and the process ends.

According to the processing of FIG.
The target duty ratio DRO of the control valve 30 corresponding to the target pressure value Po in the fuel tank 9 can be set such that the negative pressure in the fuel tank 9 can be maintained even after the stop.

[0061]

As described in detail above, claim 1 is as follows.
According to the evaporative fuel release prevention device for an internal combustion engine, the opening degree of the second control valve provided in the evaporative fuel passage connecting the fuel tank and the intake system of the internal combustion engine is controlled by the intake system via the second control valve. The control is performed so that the amount of evaporated fuel sucked into the engine does not exceed the amount obtained by subtracting the amount of evaporated fuel purge from the canister via the first control valve from the maximum possible evaporated fuel processing amount based on the operating state of the internal combustion engine. The sum of the amount of evaporated fuel sucked into the intake system via the control valve and the amount of fuel vapor purged from the canister via the first control valve is prevented from exceeding the maximum possible evaporated fuel processing amount that can be supplied to the intake system. As a result, the amount of fuel vapor supplied to the intake pipe during operation of the internal combustion engine can be maintained at an optimum amount while preventing the fuel vapor from being released into the atmosphere, and the fuel mixture in the intake system is over-concentrated. Exhaust emissions and drivability It is possible to prevent the deterioration.

According to the second aspect of the present invention, the amount of evaporative fuel purge from the canister to the intake system can be accurately calculated with a simple configuration.

According to the third aspect of the present invention, the internal pressure of the fuel tank is maintained at a negative pressure during the operation of the internal combustion engine as well as after the internal combustion engine is stopped, and the filler cap is opened for refueling. It is possible to prevent the fuel vapor in the fuel tank from being released to the outside air.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing a configuration of an evaporative fuel emission prevention device for an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a flowchart of a program of an evaporative fuel emission prevention control process by the evaporative fuel emission prevention device according to the embodiment.

FIG. 3 is a flowchart of a program for calculating a target duty ratio DRO of a control valve 30 in step S13 of FIG. 2;

FIG. 4 is a diagram showing a Qcap table used in the processing of FIG. 2;

FIG. 5 is a diagram showing a DRV table used in the processing of FIG. 2;

FIG. 6 is a diagram showing a Qprg table used in the processing of FIG. 2;

FIG. 7 is a diagram showing an NV table used in the processing of FIG. 2;

FIG. 8 is a diagram showing a DRN table used in the processing of FIG. 2;

FIG. 9 is a graph showing the relationship between the engine speed and the intake pipe absolute pressure for explaining a method of setting the target duty ratio DRO of the control valve 30.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Intake pipe 3 Throttle 5 ECU (Control means, 1st calculation means, 2nd calculation means) 9 Fuel tank 10 Filler port 11 Filler cap 13 Absolute pressure sensor in intake pipe (Operation state detecting means) 15 Tank pressure sensor 16 Fuel temperature sensor 17 Rotation speed sensor (operating state detecting means) 20 Evaporated fuel passage 30 Tank pressure control valve (second control valve) 31 Evaporated fuel release suppression system 34 Purge control valve (first control valve)

Claims (3)

[Claims] 1. A canister connected to a fuel tank,
A purge passage connecting the canister to an intake system of the internal combustion engine; a first control valve provided in the purge passage to open and close the purge passage; and an evaporative fuel connecting the fuel tank to the intake system of the internal combustion engine. An operating state detecting means for detecting an operating state of the internal combustion engine, wherein the operating state detecting means includes: a passage; and a second control valve provided in the evaporative fuel passage to open and close the evaporative fuel passage. First calculating means for calculating a maximum possible evaporative fuel processing amount based on an operation state of the internal combustion engine, and second calculating means for calculating an evaporative fuel purge amount from the canister based on an opening degree of the first control valve. Opening of the second control valve so that the amount of evaporated fuel sucked into the intake system via the second control valve does not exceed an amount obtained by subtracting the evaporated fuel purge amount from the maximum possible evaporated fuel processing amount. To Vapor fuel discharge preventing apparatus for an internal combustion engine, characterized in that it comprises a Gosuru control means. 2. The evaporative fuel purge flow rate and the evaporative fuel integrated purge amount are calculated based on the opening of the first control valve, and the evaporative fuel concentration during the purge is calculated based on the integrated purge amount. 2. The apparatus according to claim 1, wherein the evaporative fuel purge amount is calculated by multiplying the evaporative fuel purge flow rate by the evaporative fuel concentration. 3. The control means further controls the opening of the second control valve so that the internal pressure of the fuel tank becomes negative when the internal combustion engine is operating and when it is stopped. An apparatus for preventing fuel vapor from being released from an internal combustion engine according to claim 1 or 2.