Closed fuel tank system

A fuel tank system includes a tank that stores fuel, a leveling valve that decides a limit liquid surface, a filler pipe that is provided with a fuel filler opening to which a blocking cover is attached at an end portion of the filler pipe, a recirculation pipe that communicates with the filler pipe, a discharge passage that is connected to the leveling valve and branches to a first passage and a second passage, a seal valve, and a release valve that is connected to the tank at a position higher than the limit liquid surface and one of the recirculation pipe and the filer pipe, and is released by a pressure lower than a pressure caused by a head difference between the limit liquid surface and a liquid surface of the fuel at the fuel filler opening.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2012-279287 filed on Dec. 21, 2012, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates, in general, to a closed fuel tank system that tightly closes a fuel tank while an engine is being stopped and prevents vaporized fuel from being discharged into the atmosphere.

2. Background Art

Fuel vapor into which automotive fuel is vaporized contains a large quantity of hydrocarbon (HC). Since such hydrocarbon becomes a substance responsible for air pollution, the discharge of the hydrocarbon into the atmosphere has been regulated in recent years. When the fuel is injected into a fuel tank, the fuel vapor corresponding to a volume of the supplied fuel is discharged from the fuel tank. Further, when the fuel is injected through a fuel filler opening by a fuel filler nozzle, air is drawn into the fuel tank by a force with which the fuel enters, and then the fuel vapor of a volume corresponding to the air is further discharged.

An evaporated fuel discharge restraining device disclosed in Japanese Patent No. 4638319 is equipped with a first evaporated fuel passage connecting a fuel tank to a canister and a second evaporated fuel passage (recirculation pipe) connecting the fuel tank to a filler tube located adjacent to a fuel filler opening. The evaporated fuel discharge restraining device adsorbs evaporated fuel (fuel vapor) corresponding to a volume of supplied fuel to the canister. Further, since the evaporated fuel equal to or more than the volume of the supplied fuel is not generated, the evaporated fuel discharge restraining device disclosed in Japanese Patent No. 4638319 discharges the evaporated fuel to the filler tube adjacent to the fuel filler opening via the second evaporated fuel passage, and suctions the evaporated fuel into the fuel tank, and thereby restraining air from going from the fuel filler opening into the fuel tank.

Incidentally, the fuel vapor is generated in the fuel tank even when no fuel is supplied. When an engine is in operation, the fuel vapor is injected into an intake passage, and is burnt and consumed in the engine. Further, when the engine is not operated, the fuel vapor is adsorbed by the canister. The engine is operated, and thereby the fuel vapor adsorbed to the canister is extracted to the intake passage, and is burnt and consumed.

Accordingly, when the engine is operated for traveling, the fuel vapor is consumed at each time. In other words, when the engine is not in operation, the fuel vapor is not consumed. Especially, in the case of a plug-in hybrid electric vehicle (PHEV), an operating rate of the engine is extremely low. For this reason, simply adsorbing the fuel vapor to the canister cannot sufficiently process the fuel vapor. Further, in countries that severely control emission of harmful substances, a mechanism that does not discharge the fuel vapor is required. Taking these into consideration, in the case of the PHEV, it is considered to employ a closed fuel tank system in which a seal valve is installed on a path leading to the canister and the intake passage so as to prevent the fuel vapor from being discharged from the fuel tank.

When the fuel is supplied for the closed fuel tank system, the seal valve is opened, and the fuel vapor pushed out of the fuel tank is adsorbed by the canister. Further, in the closed fuel tank system, when the fuel tank is filled with the fuel to the maximum volume or is so-called “filled up,” the fuel vapor should be prevented from being discharged from a filler pipe and a recirculation pipe. For this reason, when the fuel tank is filled up, ends of these pipes are provided to be kept immersed below a liquid surface of the fuel, i.e. to be submerged.

The seal valve employed in the closed fuel tank system is in a normally closed state, and is opened when the fuel is supplied. To determine that the fuel supply is performed, a lid covering a portion on which a fuel filler opening is installed is provided with a sensor cooperating with the lid. When an electronic control unit (ECU) detects that the lid is opened on the basis of a signal of the sensor, the ECU determines that the fuel supply is performed and opens the seal valve. When it is determined that the lid is closed, the ECU determines that the fuel supply is terminated and closes the seal valve.

Further, the fuel filler opening is mounted with a cap. When the cap is separated to supply the fuel, the lid is opened before that. That is, the seal valve is opened before the cap is separated. Even when a pressure in the fuel tank is higher than an atmospheric pressure by the fuel vapor, the seal valve is opened, and the fuel vapor is discharged to the canister. Thus, since the pressure in the fuel tank becomes the atmospheric pressure before the cap is separated, the fuel vapor is not discharged from the fuel filler opening. When the fuel supply is completed, the cap is attached to the fuel filler opening, and then the lid is closed. That is, the seal valve is closed after the cap is attached. Accordingly, the fuel vapor vaporized in the fuel tank is discharged to the canister through the seal valve until the cap is attached to the fuel filler opening.

However, due to a cause such as a failure, when the seal valve is closed before the cap is attached to the fuel filler opening, the fuel vapor is discharged from the fuel filler opening through the filler pipe and the recirculation pipe. Especially, in the fuel tank that has been filled up, since the filler pipe and the recirculation pipe are submerged in the fuel tank, when the seal valve is closed, the fuel vapor is kept sealed in the fuel tank.

Therefore, when the pressure in the fuel tank is raised due to the vaporization of the fuel, the fuel is pushed up to the fuel filler opening. The fuel has a smaller specific gravity than water, a head from the fuel tank to the fuel filler opening accounts for less than 1 meter. Hence, when the seal valve is left closed without the cap being mounted in the state in which the fuel tank is filled up, the fuel overflows from the fuel filler opening.

Accordingly, the present invention is intended to provide a closed fuel tank system in which, when the seal valve is left closed without the cap being mounted in the state in which the fuel tank is filled up, the fuel does not overflow from the fuel filler opening.

SUMMARY OF THE INVENTION

(1) According to an aspect of the invention, a fuel tank system includes a tank that stores fuel, a leveling valve that decides a limit liquid surface which corresponds to a volume limit of the fuel stored in the tank, a filler pipe that extends from the tank at a position lower than the limit liquid surface and is provided with a fuel filler opening to which a blocking cover is attached at an end portion of the filler pipe, a recirculation pipe that extends from the tank at a position lower than the limit liquid surface and communicates with the filler pipe, a discharge passage that is connected to the leveling valve and branches to a first passage leading to a canister adsorbing fuel vapor and a second passage leading to an intake passage of an engine at a branch portion, a seal valve that is installed on the discharge passage between the leveling valve and the branch portion and seals up the tank, and a release valve one end of which is connected to the tank at a position higher than the limit liquid surface, the other end of which is connected to one of the recirculation pipe and the filer pipe, and is released by a pressure lower than a pressure caused by a head difference between the limit liquid surface and a liquid surface of the fuel at the fuel filler opening when the fuel up to the fuel filler opening to discharge the fuel vapor in the tank to at least one of the filler pipe and the recirculation pipe.

(2) In the configuration (1), the release valve is disposed inside the tank.

(3) In the configurations of (1) or (2), the release valve discharges the fuel vapor to the recirculation pipe.

(4) In the configuration of (1) or (2), the release valve discharges the fuel vapor in the tank to at least one of the filler pipe and the recirculation pipe at a position higher than a position which the fuel reaches by a release pressure of the release valve.

The fuel tank system according to the present invention is equipped with the release valve communicating with a portion above the limit liquid surface of the tank. The release valve is opened by a pressure lower than a pressure caused by a head difference between the limit liquid surface of the fuel FL in the tank and a liquid surface of the fuel FL at the fuel filler opening when the fuel is pushed up to the fuel filler opening, and discharges the fuel vapor in the tank to at least one of the filler pipe and the recirculation pipe. Accordingly, in a full state in which the tank is filled with the fuel to the limit liquid surface, and when the blocking cover is being detached, even when the seal valve is left closed, the fuel in the tank does not overflow from the fuel filler opening.

Further, according to the inventive fuel tank system in which the release valve is disposed inside the tank, in comparison with when the release valve is disposed outside the tank, a layout such as piping is simplified. As such, manufacturing cost of the fuel tank system is reduced, and workability when the fuel tank system is mounted on a vehicle is improved.

According to the inventive fuel tank system equipped with the release valve discharging the fuel vapor to the recirculation pipe, since the recirculation pipe is connected to the filler pipe located adjacent to the fuel filler opening, even when the fuel that has already entered the recirculation pipe is ejected when the fuel vapor is discharged, the fuel does not overflow from the fuel filler opening. Further, since the recirculation pipe has a smaller inner diameter than the filler pipe, a quantity of the ejected fuel is small.

Furthermore, according to the inventive fuel tank system in which the fuel vapor is discharged to at least one of the filler pipe and the recirculation pipe, which are higher than a position which the fuel reaches, by a pressure set to be opened, when the fuel vapor is discharged, the fuel does not spout out.

DESCRIPTION OF PREFERRED EMBODIMENT

A closed fuel tank system10of a first embodiment according to the present invention will be described with reference toFIGS. 1 to 4. The fuel tank system10shown inFIG. 1is a so-called closed fuel tank system10in which, when an engine1is being stopped, fuel vapor FV generated in a tank11is sealed in the tank11. Such a fuel tank system10is equipped with the tank11, a leveling valve112, a filler pipe12, a recirculation pipe13, discharge passage14, a seal valve15, and a release valve16.

The tank11stores fuel FL and is equipped therein with a leveling valve112and a rollover valve113in addition to a pressure sensor111for measuring a pressure. The leveling valve112decides a limit liquid surface Lmax indicating a volume limit of the fuel FL stored in the tank11. The filler pipe12extends from the interior of the tank11which is lower than the limit liquid surface Lmax of the tank11, and has a fuel filler opening121in an end thereof outside the tank11. A cap122serving as a blocking cover is attached to the fuel filler opening121, and the fuel filler opening121is tightly closed. A lid123is attached to cover the fuel filler opening121. The lid123is provided with a lid sensor124for detecting opening. Further, the fuel filler opening121is equipped with a guide125for guiding a fuel filler nozzle N shown inFIG. 3. Alternatively, instead of providing the lid sensor124, output of a switch provided for a driver's seat in order to open the lid123may be used.

Further, as shown inFIG. 1, the recirculation pipe13extends from the from the interior of the tank11which is lower than the limit liquid surface Lmax of the tank11so as to be almost parallel with the filler pipe12, and communicates with the filler pipe12adjacent to the fuel filler opening121. As shown inFIG. 3, the recirculation pipe13returns the fuel vapor FV in the tank11to the vicinity of the fuel filler opening121so as to prevent external air from being suctioned from the fuel filler opening121when the fuel FL is being supplied through the filler pipe12.

As shown inFIG. 1, the discharge passage14is connected to the leveling valve112inside the tank11. The discharge passage14is divided into a first passage141and a second passage142by a branch143. A tip of the first passage141is connected to a canister17, which has an adsorbent capturing the fuel vapor FV, via a bypass solenoid valve171. A tip of the second passage142is connected to an intake passage18of the engine1via a purge solenoid valve181. The bypass solenoid valve171is opened when the fuel vapor FV discharged during fuel supply is being forcibly adsorbed and when the fuel vapor FV adsorbed to the canister17is being purged. The purge solenoid valve181is opened when the fuel vapor FV can be burnt and consumed on the basis of an air-fuel ratio when the engine1is in operation.

The seal valve15is installed on the discharge passage14from the tank11to the branch143. The seal valve15is a solenoid valve opened when power is supplied. When the fuel FL is supplied to the tank11, and when the fuel vapor FV collected in the tank11is burnt and consumed in the engine1, the seal valve15is opened. In the other cases, the seal valve15is closed. A pressure sensor144is further installed on the discharge passage14between the seal valve15and the tank11.

The release valve16is connected to a gaseous phase of the tank11in which the fuel FL is filled up to the volume limit, and is opened by a pressure lower than a head of the fuel FL up to the fuel filler opening121. When the release valve16is opened, the fuel vapor FV in the tank11is discharged to at least one of the filler pipe12and the recirculation pipe13.

In the present embodiment, as shown inFIG. 2, the release valve16is disposed in the interior of the tank11which is higher than the limit liquid surface Lmax in the event of a so-called “full” state in which the tank11is filled with the fuel FL up to the volume limit, and is attached to the recirculation pipe13extending to the interior of the tank11. As shown inFIG. 4, when the release valve16is opened, the fuel vapor FV in the tank11is sent to the side of the fuel filler opening121through the recirculation pipe13.

Further, the pressure sensor111, the lid sensor124, the seal valve15, the bypass solenoid valve171, and the purge solenoid valve181are connected to an electronic control unit (ECU)20of a vehicle. The ECU20is also connected to the engine1and a vehicle speed sensor.

In the fuel tank system10configured as described above, flows of the fuel FL and the fuel vapor FV in the filler pipe12and the recirculation pipe13when the fuel FL is supplied are shown inFIG. 3.

First, a condition of each part when the fuel supply is performed will be described. When the lid123is opened to perform the fuel supply, the ECU20detects this by means of the lid sensor124. When it is determined that the lid123is opened, the ECU20opens the seal valve15and the bypass solenoid valve171. The fuel supply is initiated, after the cap122is detached and the fuel filler nozzle N is inserted into the fuel filler opening121.

When the liquid surface of the fuel FL is being located below the filler pipe12and the recirculation pipe13, as shown inFIG. 3, the fuel FL is supplied from the filler pipe12, and the fuel vapor FV pushed out of the tank11is sent up to the vicinity of the fuel filler opening121through the recirculation pipe13. The fuel vapor FV is sent to the tank11again along with the fuel FL supplied from the fuel filler nozzle N. Thereby, the external air is inhibited from entering the tank. The fuel vapor FV discharged by a rise in the liquid surface of the fuel FL in the tank11is sent and adsorbed to the canister17via the discharge passage14on which the seal valve15is opened.

When the fuel FL becomes the so-called “full” state in which the fuel is filled up to the limit liquid surface Lmax that corresponds to the volume limit of the tank11, as shown in

FIG. 2, ends of the filler pipe12and the recirculation pipe13inside the tank11becomes a so-called “submerged” state in which they are immersed to a position lower than the limit liquid surface Lmax of the fuel FL. As the filler pipe12and the recirculation pipe13are submerged, flow resistance is sharply changed. As such, the supplied fuel FL fills the filler pipe12. The fuel filler nozzle N detects that the tank11is filled up by means of a sensor of a tip thereof, and the supply of the fuel FL is stopped.

The filler pipe12and the recirculation pipe13are submerged, and the seal valve15is opened. As such, the fuel vapor FV generated in the tank11does not rise to the fuel filler opening121during separating the fuel filler nozzle N from the fuel filler opening121and attaching the cap122. After the cap122is attached, the lid123is closed. When it is detected by the lid sensor124that the lid123is closed, the ECU20determines that the fuel supply is completed, and closes the seal valve15and the bypass solenoid valve171. Further, the ECU20detects a liquid pressure of the fuel FL by means of the pressure sensor111, and determines that the tank is filled up.

The fuel FL is always evaporated to become the fuel vapor FV and increases an internal pressure of the tank11. When the internal pressure of the tank11rises above a prescribed value, this is detected by the pressure sensor144. When the engine1is operated, the ECU20is operated to cause the fuel vapor FV to be burnt and consumed in the engine1to lower the internal pressure of the tank11. The ECU opens the seal valve15with the bypass solenoid valve171closed, and checks a timing on the basis of the air-fuel ration of the engine1to open the purge solenoid valve181. The fuel vapor FV is introduced from the intake passage18of the engine1, and is burnt and consumed in the engine1.

When the engine1is not operated, and when it is detected that a detected value of the pressure sensor144exceeds the prescribed value, the ECU20may open the seal valve15and the bypass solenoid valve171, and cause the fuel vapor FV to be adsorbed to the canister17. Further, the ECU20performs control to force the fuel vapor FV to be purged from the canister17while the engine1is in operation on the basis of an accumulated time for which the fuel vapor FV is forcibly adsorbed to the canister17. When the fuel vapor FV is forcibly purged from the canister17, the ECU20closes the seal valve15and opens the bypass solenoid valve171. The ECU20checks the timing on the basis of the air-fuel ratio of the operated engine1to open the purge solenoid valve181. The fuel vapor FV captured to the canister17is expelled from the canister17by the external air introduced from the opposite side of the canister with respect to the bypass solenoid valve171to the canister via a filter172, and is sent from the first passage141to the intake passage18of the engine1via the second passage142as indicated inFIG. 3with an arrow of a broken line.

This closed fuel tank system10includes the release valve16. The release valve16is released by a pressure lower than a pressure caused by a head difference between the limit liquid surface Lmax of the FL in the tank11and a liquid surface of the fuel FL at the fuel filler opening121when the fuel FL is pushed up to the fuel filler opening121. The release valve16produces an effect during the fuel supply during which the cap122is detached, and when there occurs a situation in which the seal valve15is closed after the tank11is filled up. What is assumed as the situation in which the seal valve15is closed when the cap122is detached, and when the tank11is filled up includes (1) when the vehicle is left in a complete state of an automatic supply of the fuel FL, and a continuous open time set for the seal valve15is exceeded, (2) when the lid123is closed without mounting the cap122, and (3) when the supply of power to the seal valve15is interrupted.

In any case, when the seal valve15is closed, the fuel vapor FV is generated, and the internal pressure of the tank11rises to push up the fuel FL in the submerged filler pipe12and the recirculation pipe13. In this case, since the release valve16is released by a pressure lower than a pressure caused by a head difference between the limit liquid surface Lmax of the fuel FL in the tank11and a liquid surface of the fuel FL at the fuel filler opening121when the fuel FL is pushed up to the fuel filler opening121, the fuel vapor FV in the tank11is discharged to the recirculation pipe13before the fuel FL reaches the fuel filler opening121. The discharged fuel vapor FV flows to the side of the fuel filler opening121. Thereby, the pressure in the tank11is lowered, and the pushed fuel FL is also returned back to the tank11. Accordingly, the fuel FL does not leak from the fuel filler opening.

Meanwhile, in any one of a situation in which the lid sensor124detects that the lid123is in an opened state, a situation in which the pressure sensor111detects that the fuel FL is filled up, and a situation in which it is detected that a given time has lapsed after it is detected that the fuel FL is filled up, when it is detected that the seal valve15is closed, or that the supply of power is interrupted, the ECU20may notify a warning.

A fuel tank system10of a second embodiment according to the present invention will be described with reference toFIG. 5. Components having the same function as the fuel tank system10of the first embodiment are given the same numerals in the figure, and detailed description thereof is explained by the description in the first embodiment.

In the fuel tank system10of the second embodiment, a release valve16is different from the release valve16of the fuel tank system10of the first embodiment. The release valve16is connected to at least one of a filler pipe12and a recirculation pipe13at a height higher than a position which fuel FL reaches by a release pressure of the release valve16, and discharges fuel vapor FV in a tank11. In detail, as shown inFIG. 5, the release valve16is disposed in a gaseous phase in the tank11which is located above the limit liquid surface Lmax, and a high-pressure side thereof is exposed to the gaseous phase. A low-pressure side of the release valve16is connected to the recirculation pipe13at the height higher than the position which fuel FL reaches by the release pressure of the release valve16, via a discharge pipe161. As shown inFIG. 5, the connected position is located outside the tank11.

According to the fuel tank system10configured as described above, in the state in which the cap122is detached from the fuel filler opening121, and when the tank11is filled up, even when the seal valve15is closed, the fuel vapor FV is discharged to the recirculation pipe13at the height higher than a position at which the fuel FL is pushed up by a pressure at which the release valve16is set to be released. In other words, the liquid surface of the fuel FL in the recirculation pipe13communicates with the fuel filler opening121opened to the air and does not also arrive to the position at which the fuel FL is pushed up by the pressure at which the release valve16is set to be released. As such, the fuel vapor FV is discharged to the recirculation pipe13with low resistance. Since the pressure in the tank11is lowered, the fuel FL pushed up in the recirculation pipe13returns to the tank11. Further, since the recirculation pipe13communicates with the filler pipe12in the vicinity of the fuel filler opening121, the fuel FL pushed up in the filler pipe12returns to the tank11. A direction in which the discharged fuel vapor FV flows is turned to the filler pipe12by the guide125installed in the fuel filler opening121, the liquid surface in the filler pipe12is lowered, and the fuel vapor FV is drawn into the filler pipe12. Accordingly, a quantity of the fuel vapor FV discharged from the fuel filler opening121can be suppressed.