Liquid cutoff valve unit

A liquid cutoff valve unit provided for a sealed container in which a liquid fills comprises a discharge passage formed to an upper portion of the sealed container in a used state and adapted to discharge the gas therein, a float valve moving in accordance with a buoyancy so as to open or close the discharge passage, a float chamber in which the float valve is accommodated and having a size enabling the float valve to be moved therein and an urging means such as spring for urging the float valve in a valve closing direction. The float valve is provided with a cylindrical member having an upper end closed and a lower end opened to provide an inner cylindrical space formed as an air reservoir and at least one communication port opened to a side wall section of the cylindrical member and adapted to establish communication between an inside and an outside of the air reservoir. The float chamber is provided with at least one opened window section formed to a side wall section thereof at a position corresponding to the communication port of the float chamber so that a gas in the sealed container finely pass through the opened window section.

BACKGROUND OF THE INVENTION 
The present invention relates to a liquid cutoff valve unit provided for a 
fuel tank of, for example, a vehicle, capable of discharging gas such as 
fuel steam from a discharge passage connected to the cutoff valve unit and 
preventing liquid such as fuel from leaking outside the discharge passage. 
FIG. 7 shows one conventional liquid cutoff valve unit of the kind 
mentioned above, which is provided for a fuel tank of a vehicle. 
Referring to FIG. 7, a liquid cutoff valve unit 102 is mounted to an upper 
portion of a fuel tank 101 and adapted to flow air and fuel steam G101 in 
the fuel tank 101 into a canister 104 through a discharge line 103 to 
thereby liquify the fuel steam G101 and feed it to an intake side of an 
engine, not shown for preventing the generated fuel steam G101 from 
causing a counterflow thereof and discharging through an fuel supply port. 
The liquid cutoff valve unit 102 is also provided with a function for 
preventing a fuel L101 from leaking through the discharge line 103 at a 
time when a liquid level of the fuel L101 in the tank 101 rises when the 
fuel is supplied or a vehicle body is oscillated or when a vehicle is 
tilted or rolled. 
FIGS. 8A and 8B are sectional views of the cutoff valve unit 102 of FIG. 7 
for the explanation of the structure and functions thereof, in which FIG. 
8A shows a normal (used) state that the cutoff valve unit 102 does not 
attain a liquid cutoff function and the fuel steam G101 can be discharged 
and FIG. 8B shows a state that the liquid cutoff valve unit is closed when 
a liquid level of the fuel L101 rises, and attains the liquid cutoff 
function. 
In FIGS. 8A and 8B, a float chamber 110a, in which a float 111 is 
accommodated, is formed in a case member 110. The float 111 floats by a 
buoyancy (floating force) caused by a force of the fuel L101 flowing into 
the inside of the float chamber 110a through a communication port 112a 
formed to a cap 112 mounted to an lower end portion of the case member 110 
and then rises upward in the illustrated state. 
A valve body 111a in form of annular seal performing a sealing function is 
disposed to an upper portion of the float 111 and a valve seat 111b 
corresponding to the valve body 111a is disposed to an upper portion of 
the float chamber 110a. The float 111 has an approximately cylindrical 
structure having an upper sealed end (on the side to which the valve body 
111a is mounted), and the inner cylindrical portion is formed as an air 
reservoir 111b to thereby obtain the buoyancy. The valve body 111a and the 
valve seat 110b constitutes, in combination, a float valve 105. Reference 
numeral 113 denotes a spring as an urging means for adjusting the buoyancy 
of the float 111 and the spring 113 always urges the float 111 with a 
urging force smaller than the self-weight of the float 111 in such a 
manner that the float is not moved upward and the float valve 105 is not 
closed at a normally standing attitude as far as any buoyancy is not 
applied. 
The valve seat 119b is formed as one end portion of a cylindrical vent 
member 110c, which has another one end portion formed as a valve seat 
portion 110d connected to the discharge line 103 through a diaphragm valve 
120 abutting against the valve seat portion 110d. The diaphragm valve 120 
is opened by a pressure difference between the inner pressure of the 
diaphragm valve 120 and the inner pressure of the fuel tank 101, and in 
order to introduce a pressure corresponding to an atmospheric pressure (or 
negative pressure), a filler port 106 is provided for a working chamber 
R101 and the filler port 106 is connected to a filler tube (fuel supply 
portion) 107 through a filler line 108 as shown in FIG. 7. 
In a state that the pressure difference between the inside of the fuel tank 
101 and the working chamber R101 is small, the valve seat portion 101b is 
closed because of the urging force of the spring 121 in the valve closing 
direction and the valve seat portion 101b is opened at a time when a 
pressure more than a predetermined pressure difference, for example, at a 
time of fuel supply, is created, the diaphragm valve 120 is opened to 
thereby flow out the fuel steam G101 into the discharge line 103. 
The diaphragm valve 120 is further provided with an orifice 122 for 
achieving fine (minute) communication between the working chamber R101 and 
the inside of the fuel tank and the working chamber R101 so as to 
discharge the fuel L101, by a little amount, flowing into the working 
chamber R101, into the fuel tank 101. 
In the structure mentioned above, the reason why the working chamber R101 
does not take a position released for introducing the atmosphere and takes 
a position sealed through the connection to the filler tube 107 resides in 
that the fuel steam G101 passing through the orifice 122 and pressure 
films of the diaphragm valve 120 can be prevented from being directly 
discharged into the atmosphere. Such a case as that the fuel steam G101 
passes through the pressure film will occurs in a case where the pressure 
film is formed of a thin film made of a rubber elastic material. Further, 
the fuel supply port formed to the opened end of the filler tube 107 is 
generally closed by a cap and the fuel cannot be discharged outward 
therethrough by the venturi effect of the fuel L101. 
Accordingly, in the state of FIG. 8A, the float 111 is positioned downward 
without receiving any buoyancy of the fuel L101, and when the inner 
pressure of the fuel tank 101 is increased at a time of, for example, fuel 
supply, the fuel steam G101 passes the communication port 110e opened to 
the upper portion of the float chamber 110a and flows into the vent 
portion 110c through the valve body 111a and the valve seat 110b which are 
now opened. The fuel steam G101 is then flowed towards the discharge line 
103 through the diaphragm valve 120 which has been opened by the pressure 
difference caused at this time. 
On the other hand, in the state of FIG. 8B, the liquid, i.e. fuel, level is 
increased upward by, for example, fuel supply and the fuel L101 is then 
flowed into the float chamber 110a. In this instance, the float 111 is 
moved upward and the float valve 105 is closed to thereby cutoff the 
communication with the discharge line 103. 
Under the state mentioned above, the fuel steam G101 in the fuel tank 101 
is also not discharged, and when the fuel is further supplied, the liquid 
level in the filler tube 107 is increased and the operation of, for 
example, an fuel supply gun is automatically stopped, thus stopping the 
fuel supply. When the liquid level L101a in the fuel L101 in the float 
chamber 101 downs, the float 111 is also moved downward to thereby open 
the float valve 105 in the state such as shown in FIG. 8A. 
In the conventional structure of the liquid cutoff valve unit 102 mentioned 
above, the buoyancy of the float 111 largely depends on an air reservoir 
111b formed inside the float 111. Accordingly, in the state of the fuel 
tank 101 which has normal standing attitude, the air and the fuel steam 
G101 are not flowed out from the air reservoir 111b and the buoyancy is 
hence not largely lowered. However, in a case where a vehicle is largely 
tilted or rolled over, the air and fuel steam G101 in the air reservoir 
111b are flowed out and, hence, the buoyancy of the float 111 will be 
changed. 
FIG. 9 includes views for explaining a roll-over test executed for 
confirming and evaluating the fact whether the liquid cutoff valve unit 
102 can maintain its normal functions even if the buoyancy of the float 
111 varies. 
In the roll-over test, it is necessary to confirm and evaluate the 
functions of the liquid cutoff valve unit 102 at the roll-over time of the 
vehicle with respect to the filling condition of the fuel L101 from 
approximately fuel empty state to approximately fuel fill-up state in the 
fuel tank 101. For example, test are performed with respect to the fuel 
amount in the fuel tank 101 by gradually changing the fuel to the amount 
of 1/4 (approximately empty state), 1/2, 3/4 and 4/4 (approximately 
fill-up state), and the respective views of FIG. 9 represent the roll-over 
tests performed at the time of the fuel fill-up state in the tank 101. 
More in detail, FIG. 9A shows a test starting state in which the fuel tank 
101 is in a normal standing attitude and the liquid level L101a gives 
buoyancy to the float 111, which is hence moved upward to thereby close 
the float valve 105. 
FIG. 9B shows a state in which the fuel tank 101 is rotated rightward, as 
viewed, by 90.degree. about the inner central portion of volume C1 thereof 
as the rotational axis. In this step, a change of time from the state of 
FIG. 9A to that of FIG. 9B constitutes one condition for the test, and in 
this example, it is assumed that it takes three minutes. The state of FIG. 
9B is maintained for five minutes. 
In a manner similar to that mentioned above, the fuel tank 101 is rolled 
succeedingly by 90.degree. from the state shown in FIG. 9B to the state 
shown in FIG. 9C, then from the state shown in FIG. 9C to the state shown 
in FIG. 9D, and finally, to the state shown in FIG. 9E, which is the same 
standing state as that shown in FIG. 9A after one rotation of the fuel 
tank 101. This rotation cycle is repeated by several times in the same 
direction or reverse direction, and thereafter, fuel leaking amount during 
such rotation cycles of the fuel tank 101 is measured. According to this 
manner, the function of the liquid cutoff valve unit 102 is examined and 
evaluated. 
However, in the structure of the float 111 in which the air (including the 
fuel steam G101) existing in the air reservoir 111b, there may cause a 
case where the air in the air reservoir 111b is vented (breathed) and, in 
such case, when the fuel tank 101 is turned from the state shown in FIG. 
9A to the states shown in FIGS. 9B and 9C during the first one rotation 
cycle, the air does not substantially exist in the air reservoir 111b in 
the state shown in FIG. 9E. In this state, the buoyancy of the float 111 
is reduced and the float valve 105 easily takes a valve opened state. From 
this state, the fuel tank 101 is further rotated, there may cause a case 
where much fuel leaking through the opened float valve 105 during the 
rotating process from the state shown in FIG. 9A to the state shown in 
FIG. 9B is observed and measured by the roll-over tests. 
In further conventional art, there has been provided, as a countermeasure 
to such problem, a liquid cutoff valve unit 202 shown in FIG. 10 having a 
structure in which the float 111 is formed, at its upper end portion, with 
a predetermined number of fine communication ports 203, each having a 
small diameter, for venting the air from the air reservoir 111b for 
reducing the buoyancy caused by the air in the air reservoir 111b, and the 
reduced buoyancy is adjusted by increasing a spring constant of the spring 
113. The other structural elements of the liquid cutoff valve unit 202 of 
FIG. 10 other than the above structure are substantially the same as those 
of the cutoff valve unit 102, the descriptions thereof are omitted herein 
by adding the same reference numerals in FIG. 10. 
According to this structure, however, the valve opened degree, i.e. 
position, of the float valve 105 is changed in response to the fuel supply 
speed, and much difference will be caused in the fuel fill-up amount at 
the fuel supply time. That is, in a case where the fuel supply is 
performed slowly to gradually increase the liquid level L101a in the fuel 
tank 101, the air in the air reservoir 111b is discharged through the 
communication port 203 in accordance with the increasing, i.e. rising, of 
the liquid level L101a and, hence, when the liquid level reaches a 
relatively high position, the float valve 105 is closed as shown in the 
state of FIG. 11A. On the other hand, in a case where the liquid level 
L101a is rapidly increased, the air in the air reservoir 111b to be 
discharged through the communication port 203 is temporarily stored 
therein because the air discharging does not follow up to the rapid 
increasing of the liquid level L101a, and this stored air acts to the 
float 111 as buoyancy. A large amount of air, including the fuel steam 
G101, is discharged through the valve seat portion 110b, which results in 
the pressure lowering by which a sucking force is applied to the float 111 
to easily open the same. Accordingly, in such case, the float valve 105 
may be closed at the lower liquid level in the fuel tank 101 as shown in 
the state of FIG. 11B. 
Thus, as mentioned above, when the fuel is rapidly supplied, the float 
valve 105 is closed faster in time, corresponding to the difference D1 in 
the liquid surface levels L101a between the states of FIGS. 11a and 11B. 
Therefore, the float valve 105 is closed at different liquid level in the 
fuel tank 101 in response to the difference fuel supply speeds, resulting 
in the difference of the fuel fill-up amount in the tank 101. 
SUMMARY OF THE INVENTION 
An object of the present invention is to substantially eliminate defects or 
drawbacks encountered in the prior art described above and to provide a 
liquid cutoff valve unit capable of maintaining stable valve closing 
characteristics and preventing a fuel from leaking even in a roll-over 
time of a vehicle, for example, and also capable of performing a stable 
operation such as a reducing fuel fill up amount variation even in a time 
of different fuel supply speed and amount being irregularly changed. 
This and other objects can be achieved according to the present invention 
by providing a liquid cutoff valve unit provided for a sealed container in 
which a liquid fills, comprising: 
a discharge passage formed to an upper portion of the sealed container in a 
used state and adapted to discharge the gas therein; 
a float valve moving in accordance with a buoyancy so as to open or close 
the discharge passage; 
a float chamber in which the float valve is accommodated and having a size 
enabling the float valve to be moved therein; and 
a spring member for urging the float valve in a valve closing direction, 
the float valve being provided with a cylindrical member having an upper 
end closed and a lower end opened to provide an inner cylindrical space 
formed as an air reservoir and at least one communication port opened to 
an upper side wall of the cylindrical member and, adapted to establish 
communication between an inside and an outside of the air reservoir, and 
the float chamber being provided with at least one opened window section 
formed to a side wall section thereof at a position corresponding to the 
communication port of the float chamber so that a gas in the sealed 
container finely pass through the opened window section. 
In preferred embodiment in this aspect, the communication port of the float 
valve is located at a position lower than the location of the opened 
window section at a time when the float valve takes a lower position and 
no buoyancy acts thereon and, when the buoyancy acts thereon and the float 
valve is raised, the communication port takes a position corresponding to 
the location of the opened window section. 
The communication port has a width substantially equal to that of the 
opened window section. A plurality of communication ports are formed and a 
plurality of opened window sections are formed so as to correspond to the 
communication ports in numbers and positions. 
According to the structures described above, in a state where the liquid in 
the sealed container has a low liquid level, the float valve is in the 
open-valve state and the gas in the sealed container is enabled to be 
discharged into the discharge passage through the opened window section 
formed to the side wall section of the float chamber. In accordance with 
the increasing of the liquid level of the liquid supplied in the sealed 
container, the buoyancy acts on the cylindrical member of the float valve 
to thereby close the discharge passage. 
In the above operation, in the case of the low liquid supply speed (low 
liquid level rising speed), the gas existing in the air reservoir is 
gradually breathed through the communication port, so that the buoyancy 
due to the gas in the air reservoir does not act on the float valve and, 
hence, the float valve is moved in the valve closing direction by the 
buoyancy of the cylindrical member itself and the urging force of the 
urging member, thus the discharge passage having been closed. 
Further, in the above operation, in the case of the high liquid supply 
speed (high liquid level rising speed), a lot of gas may be generated and 
the liquid surface may be waved, resulting in that the amount of the gas 
existing in or introduced into the air reservoir exceeds the amount of the 
gas vented through the communication port. Accordingly, the buoyancy is 
applied to the float valve and, hence, the float valve is closed at the 
liquid level lower than that for closing the float valve at the low liquid 
supply speed. 
However, in the state where the float valve is opened at the high liquid 
supply speed, the gas in the air reservoir is sucked and discharged, by 
the negative pressure phenomenon, through the communication port by the 
velocity of the gas flowing from the opened window section into the 
discharge passage through the float chamber, so that the buoyancy due to 
the gas in the air reservoir is lowered and the float valve is hard to be 
closed. As a result, the liquid level for closing the float valve rises to 
a liquid level for closing the float valve at the low liquid supply speed. 
The inner spaces of the air reservoir and the sealed container are 
communicated through the opposing communication port and opened window 
section and the gas flows minutely smoothly therebetween, whereby the 
liquid level in the air reservoir properly changes in accordance with the 
waved condition of the liquid level, and the increasing or decreasing of 
the buoyancy due to the air existing in the air reservoir can be 
significantly reduced and the stable operation of the float valve can be 
achieved. 
According to another structure of the present invention mentioned above, in 
the state where the float valve is positioned at a lower level, the air in 
the sealed container does not flow into the communication port through the 
opened window section formed to the float chamber and is introduced to the 
discharge passage, so that the lowering of the discharge amount of the gas 
can be prevented. When the liquid level is increased and the float valve 
is moved upward to a position where the communication port opposes to the 
opened window section, the float valve is closed by the negative pressure 
mentioned above and the stability of the float valve against the waved 
liquid surface can be ensured. 
The nature and further characteristic features of the present invention 
will be made more clear from the following description made with reference 
to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will be described hereunder with reference to the 
accompanying drawings. 
First Embodiment 
FIGS. 1A and 1B show a first embodiment of the liquid cutoff valve unit 1 
according to the present invention, and the liquid cutoff valve unit 1 is 
a valve, as mentioned in the background of the invention herein, to be 
mounted to an upper portion of, for example, a fuel tank 101 of a vehicle, 
as a sealed container. Fuel steam G (air) and the like gas is discharged 
to a discharge line 103 connected to the liquid cutoff valve unit 1 by 
means of a float valve which is usually opened at a normal standing 
attitude, but a liquid such as fuel L is not prevented from leaking into 
the discharge line 103, even at a time when the fuel is supplied or a 
vehicle is tilted or rolled over, by closing the float valve. 
More in detail, with reference to FIG. 1A, the liquid cutoff valve unit 1 
is provided with a housing 2 thereof having an inside float chamber 2a in 
which a float 3 is accommodated. The float 3 is moved upward, as viewed in 
FIG. 1A, by a buoyancy by means of the fuel L flowed into the float 
chamber 2a through a communication port 4a formed to a cap 4 mounted on 
the lower side of the housing 2. 
A valve body 3a is provided for an upper end portion of the float 3 so as 
to project upward and a valve seat 7 constituting one end portion of a 
cylindrical vent portion 6 constituting a portion of a discharge passage 
is disposed at an upper portion, corresponding to the valve body 3a, of 
the float chamber 2a. Thus, a float valve 5 is composed of the float 3, 
the valve body 3a and the valve seat 7. 
The float 3 is composed of a cylindrical member having an upper end portion 
(a side to which the valve body 3a is provided) which is sealed and a 
lower end portion which is opened. An inner cylindrical space of the float 
3 is formed as an air reservoir 3b, and at the central portion thereof, a 
cylindrical spring guide 3c is formed towards the opened lower end side 
thereof. 
The float 3 has an upper side wall portion to which a communication port 3d 
communicating the air reservoir 3b and an outside of the float 3 (float 
chamber 2a) is formed. An opened window section 2b, through which a fuel 
steam G can pass slightly, is formed to a portion of the housing 2 
corresponding to the communication port 3d. 
FIG. 1B is a view showing the float 3 taken out from the float chamber 2a 
with the communication port 3d disposed on the front side. In this 
embodiment, the communication port 3d is formed with its width having a 
length about 1/6 of the circumferential length in the circumferential 
direction thereof and its height having a length about 1/4 of the width. 
The present embodiment may be provided with a plurality of communication 
ports 3d to proper portions in the circumferential direction of the float 
3, and for example, two communication ports 3d may be formed to opposing 
portions in the circumferential direction of the float 3 or three 
communication ports 3d may be formed at portions in the circumferential 
direction thereof with equal interval. 
The opened window section 2b has a bilateral width approximately equal to 
that of the communication port 3d and a height about two times of that 
thereof for ensuring an area to discharge the fuel steam G even if the 
float 3 is moved by the buoyancy. A plurality of opened window sections 2b 
may be provided in correspondence to the plurality of the communication 
ports 3d in numbers or positions, and this is an optional design matter 
made as occasion demands. In this embodiment, the lower edge portion of 
the communication port 3d and that of the opened window section 2b are 
positioned to portions substantially equal to each other in height in a 
location that the float 3 is positioned at its downward position. 
Accordingly, when the liquid level of the fuel L rises, the gas (air and 
fuel steam G, which may be called hereunder simply as air) existing in the 
air reservoir 3b in the inner cylindrical portion is vented, so that any 
buoyancy due to the air is not applied to the float 3, and therefore, the 
float 3 floats by a buoyancy due to the self-weight thereof and the urging 
force of a spring 8 to thereby close the float valve 5. 
As mentioned above, the spring 8 is disposed as urging means for adjusting 
the buoyancy of the float 3, and the spring 8 always urges the float 3 
with a urging force smaller than the self-weight of the float 3. However, 
in the normal (standing) attitude of the float 3, the spring 8 does not 
push up the float 3 and not open the float valve 5 as far as any buoyancy 
is not applied. 
The vent portion 6 has the other end portion formed as a valve seat 9 which 
is operatively connected to the discharge line 103 through a diaphragm 
valve 10, abutting against the valve seat 9, and a discharge port 11. 
The diaphragm valve 10 is opened in response to the pressure difference 
from the inside pressure of the fuel tank 101, so that a pressure 
approximately corresponding to the atmospheric pressure (or negative 
pressure) is introduced into a working chamber R1, and a filler port 106 
is provided for the working chamber R1 so as to communicate the filler 
port 106 with a filler tube 107 (fuel supply portion) through a filler 
line 108 as shown in FIG. 7. 
In an occasion that the pressure difference between the inner pressure of 
the fuel tank 101 and that of the working chamber R1 is small, the 
diaphragm 10a is urged in the valve-closing direction by the spring 13 and 
the valve seat portion 9 is closed, and in a time when the pressure 
difference becomes large more than a predetermined one through, for 
example, fuel supply, it is opened to thereby discharge the fuel steam G 
into the discharge line 103 through the discharge port 11. 
Furthermore, the diaphragm valve 10 is provided with an orifice 12 
performing the fine communication between the inside of the fuel tank 101 
and the inside of the working chamber R1, enabling to finely discharge the 
fuel L flowing into the working chamber side into the fuel tank side. 
The reason why the working chamber does not take a release state at which 
the atmospheric pressure can be introduced resides in that the fuel steam 
G passing through the orifice and a pressure film of the diaphragm valve 
10 is not directly discharged into the atmosphere, because, in a case of 
the pressure film being a thin film formed of a rubber-like elastic 
material, the fuel steam G may pass the pressure film. Further, the fuel 
supply port formed to the opened end of the filler tube 107 is usually 
closed by a cap and the fuel is not discharged, at the supply time, 
because of the venturi effect of the fuel L. 
The liquid cutoff valve unit 1 according to this embodiment will be 
described hereunder. 
In the state of FIG. 1A, in which the float 3 is positioned to a lower 
portion without receiving no buoyancy of the fuel L and the float valve 3 
is hence opened. When the inner pressure of the fuel tank 101 is increased 
at a time of the fuel supply, for example, the fuel steam G passes the 
opened window section 2b opened to the upper portion of the float chamber 
2a and then flows into the vent portion through the valve seat portion 7. 
Thereafter, the fuel steam G passes the diaphragm valve 10, which is now 
opened because of the pressure difference, and is discharged to the 
discharge line 103. 
Further, the float 3 is not designed so as to utilize the air, as buoyancy, 
stored in the air reservoir 3b formed in the inner cylindrical portion of 
the float 3, and accordingly, even if a roll-over test be carried out for 
observing and evaluating whether the function of the liquid cutoff valve 
unit 1 can be maintained at a roll-over time of a vehicle such as shown in 
FIGS. 9A-9E the urging force of the float 3 in the valve opening direction 
is less changed and the valve is not opened, thereby preventing a large 
amount of fuel leaking from causing. Furthermore, in order to suppress the 
change of the buoyancy caused by the air stored inside the cylindrical 
spring guide 3c disposed at the central portion of the air reservoir 3b, 
it may be possible to close or seal the inner cylindrical portion or fill 
up with a floating member. 
Concerning the change of the full filling amount at the fuel supply time 
due to the change of the closed position of the float valve with respect 
to the change of the oil supply speed, which has been provided as one 
problem of the conventional structure, the change of the full filling 
amount can be reduced by operating the liquid cutoff valve unit 1 in the 
following manner. 
Referring to FIGS. 2A and 2B showing the operating state of the liquid 
cutoff valve unit 1 at a time of the low speed oil supply, in which FIG. 
2A shows the state that the liquid level La rises to the 1/3 position in 
the entire length of the float from the lower side thereof and FIG. 2B 
shows the state that the float 3 floats and the float valve 5 is closed. 
At a time of the low fuel supply speed, i.e. low liquid level rising speed, 
since the air stored in the air reservoir 3b is gradually vented through 
the communication port 3d as shown with arrow A1, the buoyancy due to the 
air in the reservoir 3b does not act on the float 3. The air in the fuel 
tank 101 flows, as shown with arrow A2, into the vent portion 6 through 
the float valve 5 now being opened and is then discharged into the 
discharge line 103 through the diaphragm valve 10 now opened by the 
pressure difference. 
When the fuel supply is continued, the liquid level La rises gradually and 
the float valve 5 is moved in the valve closing direction to close the 
same by the buoyancy corresponding to the volume of the float itself and 
the urging force of the spring 8. That is, in the valve closing state of 
FIG. 2B, since the fuel L is flowed in the air reservoir 3b and no air 
hence exists, the buoyancy of the air is not generated. 
On the other hand, in the case of the high fuel supply speed, i.e. high 
liquid level rising speed, a large amounts of the fuel steam G and air are 
generated and the liquid surface is waved, so that the amount of the air 
existing in the air reservoir 3b and the amount of the introduced air 
exceeds the amount of the air breathing through the communication port 3d, 
giving the buoyancy to the float valve, and accordingly, the float valve 5 
may be closed at the liquid level lower than that at the low fuel supply 
speed time. 
In the state shown in FIG. 3A in which the float valve 5 is opened at the 
high oil supply speed, the air flows into the float chamber 2a through the 
opened window section 2b opposing to the communication port 3d, then flows 
from the float valve 5, now opened state, to the diaphragm valve 10, now 
also opened by the pressure difference, through the vent portion 6, and 
finally, flow into the discharge line 103 (in directions A4, A5). 
In this operation, the air in the air reservoir 3b is sucked and discharged 
from the communication port 3d in the direction A6 by the velocity of the 
air flowing into the float chamber 2a from the opened window section 2b 
(due to negative pressure phenomenon caused by the velocity of the air). 
Accordingly, the buoyancy due to the air in the air reservoir 3b is 
lowered and it is hard to open the float valve 5, and as a result, the 
liquid level for closing the float valve 5 at the time of the high fuel 
supply speed is raised so as to be close to the liquid level for closing 
the float valve 5 at the time of the low fuel supply speed. 
That is, as shown in FIG. 3A, the air in the air reservoir 3b is sucked by 
the flow velocity of the air flowing into the float chamber 2a in the 
direction A4 to thereby reduce the inner pressure of the air reservoir 3b. 
According to such phenomenon, the liquid level Lb in the air reservoir 3b 
becomes higher, by an amount of d1, than the liquid level La in the fuel 
tank 101 through the fuel supply, and the weight of the fuel corresponding 
to the height d1 is added to the weight of the float 3, causing a state 
not to easily close the valve. 
FIG. 3B shows the state that the liquid level La rises and the float valve 
5 is hence closed. When the float valve 5 takes a position to be nearly 
closed, the valve opened degree is decreased, and the air flow amount and 
the air velocity, in the direction A4, are also decreased, thus making 
small the negative pressure to be generated. However, after the increasing 
of the liquid level Lb in the air reservoir 3b to the height of the 
communication port 3d, the fuel L will flow through the communication port 
3d even if the negative pressure be maintained, and hence, the float valve 
is closed with the weight reduced condition of the fuel L loaded to the 
float 3, thus realizing the stable valve closing operation. 
The smooth fine (minute) communication between the inner spaces of the air 
reservoir 3b and the fuel tank 101 will be established by the presence of 
the opposing communication port 3d and the opened window section 2b, 
whereby the liquid level Lb inside the air reservoir 3b can properly 
changes in accordance with the waved liquid level caused by the fuel 
supply and the increasing and decreasing of the buoyancy caused by the air 
in the air reservoir 3b can be also reduced, thus stabling the behavior of 
the float 3. 
FIG. 4 includes views showing the liquid levels of the float valve 5 at 
which it is closed at the high and low fuel supply speeds in the 
conventional liquid cutoff valve units 102 and 202 and the liquid cutoff 
valve unit 1 of the first embodiment of the present invention and also 
includes a Table showing the difference (deviation) of the liquid levels 
for closing the float valve due to the valve closing characteristics and 
the fuel supply speeds at the time when the roll-over test was carried 
out. 
With reference to FIG. 4, the letter "H" denotes the liquid level at the 
high fuel supply speed and the term "LOW" denotes the liquid level at the 
low fuel supply speed. With the liquid cutoff valve unit 202, the valve 
closing characteristics could be improved at the roll-over test by 
providing a small-diametered communication port 203, to the upper portion 
of the float 111, for breathing the air, but in such case, the difference 
in the liquid levels (distance D1 in FIG. 4) for closing the float valve 
in accordance with the fuel supply speeds was made large. 
However, with the liquid cutoff valve unit 1 according to the first 
embodiment of the present invention, an improved valve closing 
characteristics at the time of the roll-over test could be realized, and 
moreover, the difference in the liquid levels (distance D2 in FIG. 4) for 
closing the float valve in accordance with the fuel supply speeds could be 
preferably suppressed. 
Second Embodiment 
FIG. 5 shows a sectional view of the liquid cutoff valve unit 21 according 
to the second embodiment of the present invention, which differs from that 
of the first embodiment in that the communication port 3d is positioned 
below the opened window section 22 in the state of no buoyancy to the 
float valve 5. In an actual structure of the liquid cutoff valve unit 21, 
the lower edge portion of the opened window section 22 is designed so as 
to be higher than that of the liquid cutoff valve unit 1. 
According to this structure of the second embodiment, in the state that the 
float valve 5 of the liquid cutoff valve unit 21 is disposed to a lower 
position, almost all the air flowing from the opened window section 22 of 
the float chamber 2a flows from the opened float valve 5 towards the vent 
portion in the direction A7, so that any circulation flow passing through 
the communication port 3d of the float 3 and returning to the fuel tank is 
substantially not caused, thus performing an effective discharging. 
When the float valve 5 floats according to the rising of the liquid level, 
the communication port 3d and the opened window section 22 take opposed 
positional relationship. Accordingly, the air in the air reservoir 3b is 
sucked and discharged, as like as a case of FIG. 3A, and the buoyancy due 
to the air existing in the air reservoir 3b is lowered and the float valve 
5 is hard to be opened. As a result, in this embodiment, the liquid level 
for closing the float valve 5 is raised to be close to a liquid level 
suitable for closing the float valve 5 at the time of the low fuel supply 
speed. 
At the same time, since the fine communication of the air between the inner 
spaces of the air reservoir 3b and the fuel tank 101 can be smoothly 
established, whereby the liquid level Lb inside the air reservoir 3b can 
properly changes in accordance with the waved liquid level caused by the 
fuel supply and the increasing and decreasing of the buoyancy caused by 
the air in the air reservoir 3b can be also reduced, thus stabilizing the 
behavior of the float 3. 
In order to confirm the improved functions and effects of the liquid cutoff 
valve unit according to the second embodiment of the present invention, 
changes in the fuel supply amounts due to the fuel supply speed (liquid 
level height at the time of the float valve being closed) were measured by 
utilizing a testing (test) device T1 shown in FIG. 6. 
There was used the testing device T1 comprising a sealing vessel 31, having 
substantially the same volume as that of the fuel tank to be actually 
used, an fuel supply port 32, an air supply port 33 which are formed to 
the upper portions of the vessel 31, an air supply port 33 and a mounting 
hole 34 to which the liquid cutoff valve unit is detachably mounted. 
The fuel is supplied to the fuel supply port 32 from a fuel pump, not 
shown, and regulated in amount to a predetermined rate by an fuel flow 
rate regulating valve 34, and in the like manner, the air is supplied to 
the air supply port 33 from an air supply source, not shown, and regulated 
in amount to a predetermined rate by an air flow rate regulating valve 35. 
In order to confirm the advantageous effects and functions of the present 
invention, the changes in fuel supply amounts due to the fuel supply 
speeds of the conventional liquid cutoff valve unit 202 and that 1 of the 
present invention were compared. 
That is, by using the testing devices T1 to which the conventional liquid 
cutoff valve unit and that of the present invention were mounted, the 
liquid rising speeds and the air flow rates were set to the same 
predetermined amounts in both the testing devices T1 and the liquid levels 
DT at which the float valves are closed were measured (these liquid levels 
were called lock points). Further, the liquid levels DT were distances 
each between the upper end portion of the valve body of the float valve 
and the liquid surface level, these liquid levels having been compared 
with each other. 
The conditions as to the liquid rising speeds and the air flow rates are 
shown in the following Table 1, in which the liquid rising speeds and the 
air flow rates were set to 4 mm/sec and to 40 l/min at the reference fuel 
speed time, set to 1 mm/sec and to 15 l/min at the low fuel supply speed 
time and set to 5 mm/sec and to 70 l/min at the high fuel supply speed 
time, respectively. 
TABLE 1 
______________________________________ 
Conditions 
Liquid Level Air Flow Rate 
Oil Supply Speed 
Rising Speed (mm/sec) 
(l/min) 
______________________________________ 
Reference Supply 
4 40 
Low Supply Speed 
1 15 
High Supply Speed 
5 70 
______________________________________ 
The measured results are shown in the following Table 2. From the Table 2, 
it will be found that, according to the conventional liquid cutoff valve 
unit 202, the width between the low and high fuel supply speed times was 
6.65 mm in range at the lock points, but according to the liquid cutoff 
valve unit 1 of the present invention, the width therebetween was 5.25 mm, 
thus conforming the width reduction of 1.4 mm. This fact was resulted from 
the reduction by 21% of the range at the lock point of the conventional 
liquid cutoff valve unit 202, thus confirming the advantageous effects of 
the present invention. 
TABLE 2 
______________________________________ 
Lock Point Position (DT) (mm) 
Oil Supply Speed 
U202 *1 U1 *2 Difference 
______________________________________ 
Reference Supply 
20.8 20.5 0.3 
Speed 
Low Supply Speed (A) 
17.85 17.75 0.1 
High Supply Speed (B) 
24.5 23.0 1.5 
Lock Point Range 
6.65 5.25 1.4 
R: .vertline.(A)-(B).vertline. (21% Down) 
______________________________________ 
(U202: conventional liquid cutoff valve unit 202 and U1: liquid cutoff 
valve unit 1 of the present invention) (*1:n=10 *2:n=2, averaging data) 
As mentioned above, according to the liquid cutoff valve units of the 
present invention, the stable valve closing characteristics can be 
maintained even in the roll-over time of a vehicle, for example, and the 
fuel leaking can be effectively prevented. Moreover, the change of the 
liquid level, due to the change of the fuel supply speed, at which the 
float valve is closed, can be preferably reduced and the changes of the 
fuel supply amount (change of the full filling amount due to the automatic 
stop of an fuel gun, for example) can also be reduced. 
Furthermore, since the fine air communication can be established between 
the inner spaces of the air reservoir and the fuel tank, the increasing or 
decreasing the buoyancy due to the air existing in the air reservoir can 
also be reduced, so that smooth valve opening/closing operation can be 
realized. 
Still furthermore, according to the structure in which the communication 
port of the float valve is positioned lower than that of the opened window 
section, the lowering of the air discharge amount from the float valve now 
opened can be effectively prevented. 
It is to be noted that the present invention is not limited to the 
described embodiment and many other changes and modifications may be made 
without departing from the scopes of the appended claims.