Evaporated fuel control apparatus

An evaporated fuel control apparatus includes a fuel tank for storing fuel, a first passage for connecting an internal space of the fuel tank to the atmosphere, the first passage having an opening which is open to the atmosphere, and a fuel vapor separating unit provided in the first passage for separating evaporated fuel of the fuel tank from air fed from the fuel tank to the atmosphere via the fuel vapor separating unit, the fuel vapor separating unit permitting passage of molecular components of air and not permitting passage of molecular components of fuel.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention generally relates to an evaporated fuel control 
apparatus, and more particularly to an apparatus for preventing evaporated 
fuel of a fuel tank of an automotive vehicle from escaping to the 
atmosphere even when the vehicle stays at a high temperature for an 
extended period. 
(2) Description of the Related Art 
Japanese Laid-Open Patent Publication No. 60-153463 discloses an evaporated 
fuel control device in which a fuel tank is connected to a canister having 
an opening that is open to the atmosphere, so that the fuel tank 
communicates with the atmosphere via the opening of the canister. When the 
temperature of fuel within the fuel tank becomes higher, a certain amount 
of fuel is evaporated and the internal pressure of the fuel tank is 
increased. As a certain amount of air is fed from the fuel tank into the 
atmosphere via the opening of the canister due to the increased pressure 
of the fuel tank, the internal pressure of the fuel tank can be maintained 
at a constant level. As the canister provided between the fuel tank and an 
intake passage of the engine contains an absorbent for absorbing 
evaporated fuel, the evaporated fuel supplied from the fuel tank is 
absorbed by the canister, thus preventing the evaporated fuel of the fuel 
tank from escaping to the atmosphere. 
However, when the vehicle is exposed to hot weather for a long period, for 
example while parked, the temperature of fuel within the fuel tank becomes 
very high, and an increasing amount of fuel in the fuel tank is actively 
evaporated. In order to capture all the evaporated fuel supplied from the 
fuel tank, it is necessary to utilize a canister capable of storing a very 
large amount of evaporated fuel. However, the mounting space for mounting 
parts on an automotive vehicle is limited, and it is difficult to mount a 
large-capacity canister on the automotive vehicle. 
SUMMARY OF THE INVENTION 
Accordingly, it is a general object of the present invention to provide a 
novel and useful evaporated fuel control apparatus in which the above 
described problems are eliminated. 
Another, more specific object of the present invention is to provide an 
evaporated fuel control apparatus which can safely and stably prevent 
evaporated fuel of a fuel tank of an automotive vehicle from escaping to 
the atmosphere when the vehicle is under high temperature conditions for 
an extended period. 
Still another object of the present invention is to provide an evaporated 
fuel control apparatus which has a smaller size and requires less mounting 
space for mounting the apparatus on the vehicle than a currently used 
evaporated fuel control apparatus. 
The above mentioned objects of the present invention can be achieved by an 
evaporated fuel control apparatus which includes a fuel tank for storing 
fuel, a first passage for connecting an internal space of the fuel tank to 
the atmosphere, the first passage having an opening which is open to the 
atmosphere, and a fuel vapor separating unit provided in the first passage 
for separating evaporated fuel of the fuel tank from air fed from the fuel 
tank to the atmosphere via the fuel vapor separating unit, the fuel vapor 
separating unit permitting passage of molecular components of air and not 
permitting passage of molecular components of fuel. 
The fuel vapor separating unit according to the present invention permits 
the passage of molecular components of air from the fuel tank to the 
atmosphere in order to adjust the internal pressure of the fuel tank. It 
is possible for the evaporated fuel control apparatus of the present 
invention to safely and stably prevent the evaporated fuel of the fuel 
tank from escaping to the atmosphere when the vehicle is under high 
temperature conditions for an extended period. According to the present 
invention, the capacity of the canister is reduced, and the evaporated 
fuel control apparatus has a smaller size and requires less mounting space 
for mounting the apparatus on the vehicle than a currently used evaporated 
fuel control apparatus. In addition, it is possible for the present 
invention to prevent the fuel vapor separating unit from being clogged 
with liquefied fuel or foreign matter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A description will now be given of a first embodiment of the present 
invention with reference to FIGS. 1 and 2. 
FIG. 1 shows an evaporated fuel control apparatus provided by the first 
embodiment of the present invention. In FIG. 1, there are shown a fuel 
tank 10, a fuel filler neck 11, a fuel feeding pump 12, a fuel pipe 13, 
and a fuel return pipe 14. These parts are mounted on an automotive 
vehicle. A roll-over valve 18 is mounted at an upper portion of the fuel 
tank 10. The roll-over valve 18 functions to close an upper space of the 
fuel tank 10 to prevent the leakage of fuel of the fuel tank 10 when the 
vehicle is rolled over. A vapor passage 19 is connected to the fuel tank 
10 through the roll-over valve 18. At an intermediate portion of the vapor 
passage 19, a fuel vapor separator 20 is provided. An end portion of the 
vapor passage 19, opposite to the fuel tank 10, is formed as an opening 21 
which is open to the atmosphere. A vapor cooling unit 22 is mounted on the 
vapor passage 19, and fuel vapor in the vapor passage 19 is cooled with 
external air passing the vapor cooling unit 22. 
The fuel vapor separator 20 is filled with porous material having pores, 
such as zeolite. The diameter of pores of the porous material is 
approximately 3.5 to 4 angstroms. Thus, the fuel vapor separator 20 
permits the passage of molecular components of air such as oxygen 
molecules, nitrogen molecules and vaporized water molecules whose diameter 
is approximately 3 angstroms or less, and it does not permit the passage 
of molecular components of fuel vapor such as gasoline molecules whose 
diameter is greater than 4 angstroms. 
The vapor cooling unit 22 is provided with an air passage having an air 
inlet 22a and an air outlet 22b. External cooled air supplied from an air 
conditioner of the vehicle enters the vapor cooling unit 22 from the air 
inlet 22a, so that fuel vapor in the vapor passage 19 is cooled with the 
supplied air to a lower temperature. The air passing to the outside of the 
vapor cooling unit 22 from the air outlet 22b is exhausted to the inside 
of the vehicle or to the atmosphere. 
As the ambient temperature of the vehicle becomes higher in the day than in 
the night, the temperature of fuel within the fuel tank 10 changes to a 
higher temperature. The fuel within the fuel tank 10 is evaporated at an 
increasing rate and the amount of fuel vapor is increased with the 
increase of the fuel temperature, so that the internal pressure of the 
fuel tank 10 is increased to a higher pressure. As the internal pressure 
of the fuel tank 10 becomes higher, molecules of air in the fuel tank 10 
pass through the pores of the fuel vapor separator 20, and the air passing 
to the outside of the vapor passage 19 from the opening 21 is discharged 
to the atmosphere as shown in FIG. 2. The internal pressure of the fuel 
tank 10 at this time is in equilibrium with the atmospheric pressure. In 
FIG. 2, the molecules of air are indicated by hollow dots and the 
molecules of fuel vapor are indicated by black dots. 
As the ambient temperature becomes lower in the night than in the day, the 
temperature of fuel within the fuel tank 10 changes to a lower 
temperature. The amount of fuel vapor in the fuel tank 10 is decreased, 
and the internal pressure of the fuel tank 10 becomes lower than the 
atmospheric pressure. A certain amount of air enters the fuel tank 10 
through the fuel vapor separator 20 in the vapor passage 19 due to such a 
negative pressure in the fuel tank 10. As a result, the internal pressure 
of the fuel tank 10 is in equilibrium with the atmospheric pressure. The 
fuel vapor separator 20 at this time prevents the fuel tank 10 from being 
subjected to an excessive negative pressure. 
Next, the function of the fuel vapor separator in the evaporated fuel 
control apparatus will be described with reference to FIGS. 3A and 3B. 
When an internal combustion engine of the vehicle is operating, a certain 
amount of fuel, heated in the vicinity of the engine, is returned to the 
fuel tank 10 through the fuel return pipe 14, and the temperature of the 
fuel within the fuel tank 10 changes to a higher temperature. Especially 
when the engine has been operated at a high ambient temperature for a long 
time, it is likely that the fuel temperature is increased to the boiling 
point so that the saturation pressure of fuel vapor at the temperature 
(the boiling point) becomes higher than the atmospheric pressure. 
FIG. 3A shows an internal condition of the fuel tank 10 when the saturation 
pressure of fuel vapor in the fuel tank 10 is higher than the atmospheric 
pressure. The internal pressure of the fuel tank 10 is high, and there are 
almost no molecular components of air in the fuel tank 10. In order to 
decrease the internal pressure of the fuel tank 10, air cannot be 
discharged from the fuel tank 10. 
Under the condition shown in FIG. 3A, the fuel vapor in the vapor passage 
19 is cooled with external cooled air passing the vapor cooling unit 22. A 
certain amount of fuel vapor in the vapor passage 19 is liquefied due to 
the cooling function of the vapor cooling unit 20, and it is returned to 
the fuel tank 10 as shown in FIG. 3B. The fuel temperature at this time is 
no longer increased, and it is possible to prevent the saturation pressure 
of fuel vapor from being higher than the atmospheric pressure. Thus, it is 
possible to prevent the fuel tank 10 from being subjected to an 
excessively high pressure. 
In the first embodiment described above, the fuel vapor separator 20 
permits the passage of molecular components of air from the fuel tank to 
the atmosphere, thereby preventing evaporated fuel of the fuel tank from 
escaping to the atmosphere. The vapor cooling unit 22 is mounted on the 
vapor passage 19 between the fuel tank 10 and the fuel vapor separator 20, 
thereby preventing the fuel tank from being subjected to an excessively 
high pressure when the fuel temperature is high. The evaporated fuel 
control apparatus shown in FIG. 1 is comprised of the fuel vapor separator 
20 and the vapor cooling unit 22, and it thus is possible to provide an 
evaporated fuel control apparatus which has a smaller size and requires a 
less mounting space on the vehicle than a currently used evaporated fuel 
control apparatus. 
FIG. 4 shows a modification of the evaporated fuel control apparatus shown 
in FIG. 1. In FIG. 4, the parts which are the same as corresponding parts 
in FIG. 1 are designated by the same reference numerals, and a description 
thereof will be omitted. In the apparatus shown in FIG. 4, the vapor 
cooling unit 22 is mounted on the fuel return pipe 14. The fuel, heated in 
the vicinity of the engine, is returned to the fuel tank 10 through the 
fuel return pipe 14, and the fuel in the fuel return pipe 14 is cooled 
with external cooled air passing through the vapor cooling unit 22, 
thereby preventing the temperature of fuel within the fuel tank 10 from 
being higher than the boiling point thereof when the engine is operating. 
FIG. 5 shows a different modification of the evaporated fuel control 
apparatus shown in FIG. 1. In the apparatus in FIG. 5, a two-way check 
valve 30 is provided in the vapor passage 19 at an intermediate portion 
between the fuel vapor separator 20 and the vapor cooling unit 22. The 
two-way check valve 30 has a first valve 30a and a second valve 30b. The 
first valve 30a normally functions to close the vapor passage 19 so as to 
prevent the flow of fuel vapor in the direction from the fuel tank 10 to 
the atmosphere. The second valve 30b normally functions to close the vapor 
passage 19 so as to prevent the flow of fuel vapor in the direction from 
the atmosphere to the fuel tank 10. When the fuel tank pressure is higher 
than the atmospheric pressure and a difference between the fuel tank 
pressure and the atmospheric pressure is greater than a prescribed value, 
the first valve 30a is opened so that the fuel vapor is fed from the fuel 
tank 10 to the fuel vapor separator 20 via the two-way check valve 30. 
When the fuel tank pressure is lower than the atmospheric pressure and a 
difference between the atmospheric pressure and the fuel tank pressure is 
greater than a prescribed value, the second valve 30b is opened so that 
the fuel vapor is fed from the fuel vapor separator 20 to the fuel tank 10 
via the two-way check valve 30. 
In the apparatus shown in FIG. 5, the boiling point of fuel within the fuel 
tank 10 becomes higher due to the increased fuel tank pressure, which 
allows the cooling capability needed for the vapor cooling unit 22 to be 
lower than that needed for the vapor cooling unit shown in FIG. 1. The 
amount of air passing through the fuel vapor separator 20 is increased due 
to the two-way check valve 30, and the size of the fuel vapor separator is 
thus reduced. 
FIG. 6 shows a different modification of the evaporated fuel control 
apparatus shown in FIG. 1. In the apparatus shown in FIG. 6, a first 
filter 31 is provided in the vapor passage 19 between the opening 21 and 
the fuel vapor separator 20, and a second filter 32 is provided in the 
vapor passage 19 between the fuel vapor separator 20 and the vapor cooling 
unit 22. These filters serve to protect the pores of the fuel vapor 
separator 20 from being clogged with foreign matter contained in air fuel 
mixture passing through the vapor passage 19. 
FIG. 7 shows a further modification of the evaporated fuel control 
apparatus shown in FIG. 1. In FIG. 7, the parts which are the same as 
corresponding parts in FIG. 6 are designated by the same reference 
numerals, and a description thereof will be omitted. In the apparatus 
shown in FIG. 7, instead of the second filter 32 in FIG. 6, a polymer 
absorbent 35 is attached to the inside peripheral wall of the vapor 
passage 19 where the vapor cooling unit 22 is mounted, and the polymer 
absorbent 35 extends from the fuel vapor separator 20 to the roll-over 
valve 18. The polymer absorbent 35 is made of a high polymer material 
cross-linked with solvent molecules such as gasoline, and is capable of 
absorbing liquefied fuel or the like. As the polymer absorbent 35 absorbs 
liquefied fuel on the inside peripheral wall of the vapor passage 19 due 
to the cooling of the vapor cooling unit 22, it is possible to prevent the 
liquefied fuel from being attached to the surface of the fuel vapor 
separator 20. The polymer absorbent 35 also serves to prevent the pores of 
the fuel vapor separator 20 from being clogged with foreign matter 
contained in the fuel. The liquefied fuel absorbed by the polymer 
absorbent 35 will drop to the fuel tank 10 due to gravity. 
Next, a description will be given of a second embodiment of the present 
invention with reference to FIG. 8. FIG. 8 shows an evaporated fuel 
control apparatus provided by the second embodiment of the present 
invention. In FIG. 8, the parts which are the same as the corresponding 
parts shown in FIG. 1 are designated by the same reference numerals, and a 
description thereof will be omitted. 
In the apparatus shown in FIG. 8, the roll-over valve 18, the vapor passage 
19, the fuel vapor separator 20 and the vapor cooling unit 22 which are 
the same as those shown in FIG. 1 are mounted on the fuel tank 10. In 
addition, a second roll-over valve 38 having a structure and function 
similar to the structure and function of the roll-over valve 18 is mounted 
at an upper portion of the fuel tank 10. A second vapor passage 39 is 
connected at one end to the fuel tank 10 through the second roll-over 
valve 38, and the second vapor passage 39 is connected at the other end to 
an upper portion of a canister 41 through a check valve 40. The canister 
41 contains an absorbent such as active carbon for absorbing fuel vapor, 
and the canister 41 temporarily stores fuel vapor supplied from the fuel 
tank 10 via the second vapor passage 39. The check valve 40 functions to 
open the second vapor passage 39 when the internal pressure of the fuel 
tank 10 is higher than the internal pressure of the canister 41 and the 
difference between these pressures is greater than a prescribed value, so 
that the fuel vapor from the fuel tank 10 is supplied to the canister 41. 
A lower portion of the canister 41 is formed with an air inlet opening 42 
which is open to the atmosphere. A purge passage 43 is connected at one 
end to the upper portion of the canister 41, and this purge passage 43 is 
connected at the other end to an intake passage 44 of the internal 
combustion engine at a portion immediately downstream of a throttle valve 
45 in the intake passage 44. When the engine is operating under a 
prescribed operating condition, the intake passage 44 is subjected to a 
negative pressure, and external air enters the canister 41 from the air 
inlet opening 42. The fuel vapor, temporarily stored in the canister 41, 
is desorbed from the absorbent of the canister 41 due to the flow of air 
from the canister 41 to the intake passage 44, and the fuel vapor is fed 
from the canister 41 into the intake passage 44 via the purge passage 43. 
In the apparatus shown in FIG. 8, when the internal pressure of the fuel 
tank 10 is increased to an excessively high pressure due to the increase 
in the fuel temperature caused by any malfunction or due to the clogging 
of the fuel vapor separator 20, the check valve 40 is opened so that a 
certain amount of fuel vapor is fed from the fuel tank 10 into the 
canister 41 to reduce the internal pressure of the fuel tank 10. The 
canister 41 temporarily stores the fuel vapor supplied from the fuel tank 
10 at this time, and the fuel vapor is fed from the canister 41 into the 
intake passage 44. 
Next, a description will be given of a third embodiment of the present 
invention with reference to FIG. 9. FIG. 9 shows an evaporated fuel 
control apparatus provided by the third embodiment of the present 
invention. In FIG. 9, the parts which are the same as corresponding parts 
shown in FIG. 1 are designated by the same reference numerals, and a 
description thereof will be omitted. 
In the apparatus shown in FIG. 9, an extended vapor passage 49 is connected 
at one end to the fuel tank 10 through the roll-over valve 18, and the 
other end of the extended vapor passage 49 is formed with a first branch 
portion 49a and a second branch portion 49b. The fuel vapor separator 20 
is provided in the middle of the first branch portion 49a, and an edge of 
the first branch portion 49a is formed as the opening 21 which is open to 
the atmosphere. The check valve 40 is provided in the middle of the second 
branch portion 49b, and an edge of the second branch portion 49b is 
connected to a canister 51. 
In FIG. 9, the canister 51 contains an absorbent for absorbing fuel vapor, 
and the canister 51 is provided with an upper chamber 51a above the 
absorbent and a lower chamber 51b below the absorbent. The upper chamber 
51a of the canister 51 communicates with the intake passage 44 via the 
purge passage 43. The lower chamber 51b of the canister 51 is formed with 
the air inlet opening 42 which is open to the atmosphere. 
When the temperature of fuel within the fuel tank 10 is increased to the 
boiling point during the operation of the engine, the check valve 40 is 
opened so that an increasing amount of fuel vapor is fed from the fuel 
tank 10 into the canister 51. As the engine is operating, most of the fuel 
vapor supplied from the fuel tank 10 is fed into the intake passage 44 
through the purge passage 43, and a smaller amount of the fuel vapor 
mentioned above is captured or absorbed by the canister 51. 
Immediately after the engine stops operating, the temperature of fuel 
within the fuel tank 10 changes to a somewhat higher temperature. Thus, 
the internal pressure of the fuel tank 10 changes to a higher pressure due 
to the increased fuel temperature. As only the molecular components of air 
within the fuel tank 10 are exhausted to the atmosphere from the opening 
21 by the fuel vapor separator 20, fuel vapor with nearly 100% 
concentration remains in the fuel tank 10. The check valve 40 is opened so 
that a somewhat greater amount of fuel vapor is absorbed or captured by 
the canister 51. In order to safely store all the fuel vapor supplied from 
the fuel tank 10, it is necessary to make the capacity of the canister 51 
greater than the capacity of the canister 41 shown in FIG. 8. In the 
apparatus shown in FIG. 9, as the saturation pressure of fuel vapor is 
unlikely to be higher than the atmospheric pressure, it is unnecessary to 
mount the vapor cooling unit 22. Also, it is possible to safely prevent 
evaporated fuel of the fuel tank from escaping to the atmosphere when the 
fuel vapor separator 20 is clogged. 
In the apparatus shown in FIG. 9, if the opening 21 is arranged within an 
air cleaner (not shown) in the intake passage 44 of the engine, a filter 
of the air cleaner can be used for protecting the pores of the fuel vapor 
separator 20 from being clogged with foreign matter contained in air fuel 
mixture passing through the vapor passage 49. 
FIG. 10 shows a modification of the evaporated fuel control apparatus shown 
in FIG. 9. In FIG. 10, a two-way check valve 52 is provided in the middle 
of the second branch portion 49b, instead of the check valve 40 shown in 
FIG. 9, and a check valve 53 is provided in the first branch portion 49a 
at a portion between the fuel vapor separator 20 and the opening 21. The 
two-way check valve 52 is provided with a first valve 52a and a second 
valve 52b. 
When the temperature of fuel within the fuel tank 10 gradually changes to a 
lower temperature after the running of the vehicle at a high temperature, 
the internal pressure of the fuel tank 10 will be a pressure lower than 
the atmospheric pressure. In the apparatus shown in FIG. 10, when the 
internal pressure of the fuel tank 10 is lower than the atmospheric 
pressure, the second valve 52b of the two-way check valve 52 is opened due 
to the negative pressure of the fuel tank 10, so that external air enters 
the canister 51 from the air inlet opening 42 and is fed from the canister 
to the fuel tank through the valve 52b. Thus, the fuel vapor temporarily 
stored in the canister 51 can be returned back to the fuel tank 10 through 
the two-way check valve 52. In the apparatus shown in FIG. 10, it is 
possible to safely prevent the evaporated fuel of the fuel tank 10 from 
escaping to the atmosphere through the opening 42 of the canister 51. 
Further, the present invention is not limited to the above described 
embodiments, and variations and modifications may be made without 
departing from the scope of the present invention.