Patent Publication Number: US-2005133089-A1

Title: Evaporative gas control valve structure

Description:
BACKGROUND OF THE INVENTION  
      The disclosure of Japanese Patent Application No. 2003-420462 filed on Dec. 18, 2003 including the specification, drawings and abstract, is incorporated herein by reference in its entirety.  
      1. Field of Invention  
      The invention relates to an evaporative gas control valve structure which is provided in a ventilation passage which allows communication between a fuel tank and a canister.  
      2. Description of Related Art  
      A fuel tank for storing fuel to be supplied to a combustion chamber of an engine is provided in an automobile, for example. A ventilation system is provided in the fuel tank such that an amount of air which corresponds to an increase/decrease in an amount of the fuel in the tank can flow in/out through the ventilation system. The ventilation system allows communication between the inside of the fuel tank and a canister. When the fuel tank is supplied with an excessive amount of fuel, part of the fuel is spilled, and the spilled fuel flows toward the canister. As a result, the canister becomes wet and unusable. Accordingly, a fill-up control valve is provided in an upper portion of the fuel tank, and when the fuel tank is filled up, the fill-up control valve blocks the ventilation system such that the air and the fuel do not flow toward the canister.  
      Also, two or more fuel leak prevention valves may be attached to the fuel tank. The fuel leak prevention valves are provided in addition to the aforementioned fill-up control valve, and are usually opened to the atmosphere so as to adjust a change in the pressure in the fuel tank. For example, when a vehicle is tilted, when the vehicle is suddenly stopped, when the vehicle suddenly takes off, or when the vehicle is overturned, the fuel leak prevention valves are closed. Further, an in-tank type fuel pump unit is attached to the fuel tank through a flange.  
       FIG. 8  shows a fuel tank provided with a fill-up control valve and the like. The fuel to be supplied to the engine is stored in the fuel tank  1 . A fill-up control valve A is provided in an upper portion of the fuel tank  1 . The fill-up control valve A is connected to a canister  4  through a ventilation passage  5 . A fuel supply pipe  3  which is closed by a filler cap  2  is attached to the fuel tank  1 . Fuel is supplied to the fuel tank  1  through the fuel supply pipe  3  when necessary.  
      A fuel pump unit  6  and the fill-up control valve A are provided at a center portion of the fuel tank  1 . Further, fuel leak prevention valves B and C having the same function are provided at right and left portions.  
       FIG. 9  shows an example of the aforementioned fill-up control valve A. The fill-up control valve A includes a casing  10  which is inserted in the fuel tank  1 ; a float  11  which is provided in the casing  10 ; a spring  12  which applies an upward force to the float  11 ; a valve element  13  provided in an upper portion of the float  11 ; a ventilation passage  5  having one end connected to a portion on a downstream side of the valve element  13 , and having another end connected to the aforementioned canister  4 , and the like.  
      The casing  10  is a hollow cylindrical container having an upper opening at an upper end thereof and a lower opening at a lower end thereof. A float chamber  17  is formed inside the casing  10 . Plural ventilation holes  18   a  are formed in a side wall of the casing  10 . A valve seat  15  is formed in an upper portion thereof. Further, plural perpendicular ribs  16  are radially formed on an inner surface of the casing at equal intervals. The float  11  is guided by the ribs  16  to move upward and downward. A bottom portion plate  19  having ventilation holes  18  is attached to a bottom portion of the casing  10 . A flange  14  is formed in an outer periphery in a side portion of the casing  10 . The casing  10  is attached to the fuel tank  1  through the flange  14 .  
      The fill-up control valve A has the structure described above. When fuel is supplied to the fuel tank  1  through the fuel supply pipe  3 , the liquid surface of the fuel in the fuel tank  1  rises. When the liquid surface reaches the bottom portion plate  19 , the fuel enters the casing  10  through the ventilation holes  18  in the bottom portion plate  19  and the ventilation holes  18   a  of the side wall of the casing  10 , and pushes the float  11  upward. Then, when the liquid surface of the fuel in the float chamber  17  reaches a predetermined position, the valve element  13  provided in the upper surface of the float  11  contacts the valve seat  15 . When the valve element  13  contacts the valve seat  15 , the ventilation passage  5  is closed. Therefore, when fuel is supplied thereafter, the pressure in the fuel tank  1  is increased, and then the fuel supply is stopped. The liquid surface of the fuel at this time is regarded as a fill-up liquid surface position H.  
       FIG. 10  shows an example of the aforementioned fuel leak prevention valves B and C. Each of the fuel leak prevention valves B and C has the following characteristics. Each of the fuel leak prevention valves B and C is provided at a position higher than the position of the fill-up control valve A. A passage  20  connects a portion on a downstream side of the valve element  13  with the ventilation passage  5  as shown in  FIG. 10 . Also, the valve element  13  of each of the fuel leak prevention valves B and C has the shape as shown in  FIG. 10 . Other portions of the structure thereof are substantially the same as those of the fill-up control valve A in  FIG. 9 . Therefore, the portions which are the same as those in  FIG. 9  are denoted by the same reference numerals, and description thereof will be omitted.  
      Since the fuel leak prevention valves B and C are provided at the position higher than the position of the fill-up control valve A, the fuel leak prevention valves B and C are not closed when fuel is supplied. That is, the fuel leak prevention valves B and C are usually opened. Each of the fuel leak prevention valves B and C is provided through the flange  14  on an upper surface at a portion where an enclosed space is formed when the fuel tank  1  is tilted. The passage  20  allows communication between the portion and the canister  4 , and thus a change in the pressure is reduced. With this arrangement, the fuel leak prevention valve B or C may sink in the fuel depending on the direction in which the fuel tank  1  is tilted. In this case, in the fuel leak prevention valve B or C, the float  11  is moved upward, and the valve element  13  contacts the valve seat  15  so as to close the passage  20 . Therefore, the fuel does not flow out of the fuel tank  1  and to the canister  4 .  
      As described above, each of the fill-up control valve A, and the fuel leak prevention valves B and C has the ventilation holes  18   a  in the side wall of the casing  10  and the ventilation holes  18  in the bottom portion plate  19 . When the liquid surface of the fuel rises, for example, when fuel is supplied, the fuel is introduced to the float chamber  17  in the casing  10  through the ventilation holes  18   a  and the ventilation holes  18 . Thus, the float  11  is moved upward, and the valve element  13  contacts the valve seat  15  so as to close the valve, whereby the outflow of the fuel to the ventilation passage  5  is suppressed.  
      However, when the fuel in the fuel tank is oscillated, for example, when fuel is supplied, or the vehicle is turned, the liquid surface of the fuel is rapidly oscillated. Therefore, the moving fuel at this time rapidly flows into the float chamber  17  through the ventilation holes  18   a  and the ventilation holes  18 . As a result, the fuel may flow to the ventilation passage  5  (or  20 ) before the float  11  is moved upward and the valve is closed, and the fuel may directly flow out to the canister.  
     SUMMARY OF THE INVENTION  
      It is a first object of the invention to provide an evaporative gas control valve structure which suppresses the direct outflow of fuel to a canister even when a liquid surface of fuel is rapidly oscillated.  
      In order to achieve the first object, according to a first aspect of the invention, an evaporative gas control valve structure includes a casing which is attached to a fuel tank; a float which is provided in a space formed in the casing; a ventilation hole which is formed below the casing, and which allows communication between the space and an inside of the fuel tank, and introduces fuel in the fuel tank to the space; and a member which suppresses a flow of the fuel, and which is provided between the float and the ventilation hole.  
      With this configuration, when the fuel in the fuel tank is oscillated, for example, when fuel is supplied, or a vehicle is turned, even if the liquid surface of the fuel is rapidly oscillated and the moving fuel tries to rapidly enter the float chamber through the ventilation hole formed below the casing, the member provided between the float and the ventilation hole suppresses the rapid flow of the fuel before the fuel enters the float chamber. Accordingly, the valve is efficiently closed by the float. Thus, it is possible to reduce the outflow of the fuel to the canister.  
      In the first aspect of the invention, a member that contacts a lower end of the float may be provided in the casing, and plural ventilation holes may be formed in the member at a portion thereof that contacts the lower end of the float. With this configuration, even if the fuel enters the float chamber at normal times or when the liquid surface of the fuel is rapidly oscillated, since part of the fuel enters the plural ventilation holes and thus pushes the float upward, the valve is closed by the float earlier, and the outflow of the fuel to the canister is further reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:  
       FIG. 1  is a cross sectional view showing an evaporative gas control valve structure according to a first embodiment of the invention;  
       FIG. 2  is a cross sectional view showing an evaporative gas control valve structure according to a second embodiment of the invention;  
       FIG. 3  is a cross sectional view showing an evaporative gas control valve structure according to a third embodiment of the invention;  
       FIG. 4  is a cross sectional view showing an evaporative gas control valve structure according to a fourth embodiment of the invention;  
       FIG. 5  is a cross sectional view of  FIG. 4  taken along line V-V;  
       FIG. 6  is a cross sectional view showing an evaporative gas control valve structure according to a fifth embodiment of the invention;  
       FIG. 7  is a cross sectional view showing an evaporative gas control valve structure and a fuel pump unit that are integrated with each other;  
       FIG. 8  is a schematic diagram showing a fill-up control valve, fuel leak prevention valves, and a fuel pump unit that are attached to a fuel tank;  
       FIG. 9  is a cross sectional view showing a conventional fill-up control valve; and  
       FIG. 10  is a cross sectional view showing a conventional fuel leak prevention valve. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       FIG. 1  is a cross sectional view showing an evaporative gas control valve structure. The evaporative gas control valve can be a fill-up control valve or a fuel leak prevention valve. Hereinafter, embodiments in which a fill-up control valve is used will be described.  
      A fill-up control valve structure  30  according to a first embodiment includes a casing  31 , a float  37 , a spring  42 , and the like. The casing  31  is made of resin. The casing  31  has a hollow cylindrical shape having an upper opening  32  at an upper end thereof and a lower opening  33  at a lower end thereof. The upper opening  32  has a small diameter, and the lower opening  33  has a large diameter. A valve seat  34  is formed on an inner surface of the upper opening  32 . A flange  35  used for attaching the fill-up control valve structure  30  to a fuel tank  1  is formed on an outer peripheral surface of the upper opening  32  above the valve seat  34 . A ventilation passage  5  is formed integrally with the upper opening  32 . Plural perpendicular ribs  36  are provided on an inner surface of the casing  31  at equal intervals in a circumferential direction. Thus, the float  37  is guided by the ribs  36  to move upward and downward.  
      The float  37  is made of resin. The float  37  has a generally hollow cylindrical shape having a lower opening. A small-diameter protrusion  39  having a columnar shape is formed on an upper surface of the float  37 . An annular groove portion  38  is formed on an outer periphery of the small-diameter protrusion  39 . An inner peripheral edge of a valve element  40  is fitted into the annular groove portion  38 . The valve element  40  is made of rubber and has a ring shape. When the float  37  is moved upward to the uppermost position, an upper surface of the valve element  40  having the ring shape contacts the valve seat  34 . As a result, communication between a float chamber  41  formed in the casing  31  and the ventilation passage  5  is interrupted. The valve element  40  having the ring shape is fitted into the annular groove portion  38  such that the valve element  40  is slightly movable in the groove portion  38 . Therefore, even if the float  37  is slightly tilted, the communication between the float chamber  41  and the ventilation passage  5  is reliably interrupted.  
      A spring  42  is provided inside the float  37 . The spring  42  is provided between an upper surface of an inner wall of the float  37  and a labyrinth structural body  45  that will be described later. The spring  42  supports upward movement of the float  37 . That is, a spring force of the spring  42  does not move the float  37  upward at normal times. However, when fuel enters the float chamber  41 , the spring force is added to a buoyant force applied to the float  37  by the fuel so that the float  37  can be moved upward quickly.  
      The labyrinth structural body  45  is integrally fitted to the lower opening  33  of the casing  31  by welding or other means. The labyrinth structural body  45  includes three members, which are a bottom member  46 , an intermediate cylinder member  47 , and an upper member  48 , which are made of resin. These three members are integrally formed using resin.  
      The bottom member  46 , which is one of the three members, constitutes a bottom plate of the casing  31 . The bottom member  46  is a hollow cylindrical member including a hollow cylindrical portion  46   a  having a small height, and a flange  46   b  at a lower end thereof. When the labyrinth structural body  45  is inserted from the lower opening  33  of the casing  31 , an inner surface of the casing  31  at a lower end contacts an outer periphery of the cylindrical portion  46   a . A lowermost end of the casing  31  contacts an upper surface of the flange  46   b . Both of the casing  31  and the labyrinth structural body  45  are integrally fixed to each other by welding or other means.  
      The intermediate cylinder member  47  is provided in a hollow portion of the bottom member  46  so as to be concentric with the bottom member  46 . The intermediate cylinder member  47  includes a hollow cylindrical portion  47   a  having a large height and a horizontally extending portion  47   b  at an upper portion thereof. A lower end of the hollow cylindrical portion  47   a  and a lower end of the bottom member  46  are positioned at the same level. An inner surface of the cylindrical portion  46   a  of the bottom member  46  and an outer surface of the hollow cylindrical portion  47   a  of the intermediate cylinder member  47  are connected to each other by plural ribs  50  that are provided at equal intervals in a circumferential direction. Plural ventilation holes  46   c  are formed between the inner surface of the cylindrical portion  46   a  and the outer surface of the hollow cylindrical portion  47   a.    
      At normal times, the plural ventilation holes  46   c  allow evaporative fuel gas to be discharged therethrough. For example, when fuel is supplied or a vehicle is tilted, the plural ventilation holes  46   c  allow the fuel to enter the float chamber  41 . For example, when fuel is supplied or the vehicle is tilted, the float  37  is moved upward due to the fuel entering the float chamber  41 , and accordingly the valve element  40  provided in the upper portion of the float  37  contacts the valve seat  34 , whereby the outflow of the fuel to a canister  4  side is suppressed.  
      When the hollow cylindrical portion  47   a  of the intermediate cylinder member  47  is provided inside the cylindrical portion  46   a  of the bottom member  46 , the position of the horizontally extending portion  47   b  of the intermediate cylinder member  47  is higher than that of the cylindrical portion  46   a  of the bottom member  46 . Thus, a lower chamber  51  is formed between the horizontally extending portion  47   b  and the cylindrical portion  46   a . The ventilation holes  46   c  are formed on an inner side of the horizontally extending portion  47   b  in a plan view. The evaporative gas and the fuel entering the lower chamber  51  through the ventilation holes  46   c  hit a lower surface of the horizontally extending portion  47   b . Thus, the evaporative gas and the fuel flow radially outward, and then flow upward.  
      The upper member  48  is a disk-shaped member which is horizontally provided above the intermediate cylinder member  47 . The upper member  48  constitutes a seat member which the float  37  contacts. The upper member  48  includes a thick member  48   a  at a center thereof, and a thin member  48   b  at an outer portion thereof. The spring  42  is positioned (i.e., centered) by the thick member  48   a  at the center, and the spring  42  is provided between an upper surface of the thin member  48   b  and the upper surface of the inner wall of the float  37 .  
      Plural ventilation holes  49   c  are formed in the thin member  48   b  at the outer portion at equal intervals. The lower end of the float  37  contacts the upper surface of the thin member  48   b . When the lower end of the float  37  contacts the upper surface of the thin member  48 , the plural ventilation holes  49   c  are closed by the lower end of the float  37 . When the fuel flows into an upper chamber  52  that will be described later, the fuel acts on the float  37  through the ventilation holes  49   c  such that the float  37  is moved upward. Thus, upward movement of the float  37  is supported by the fuel.  
      The upper member  48  and the horizontally extending portion  47   b  of the intermediate cylinder member  47  are integrally connected to each other by a bar-shaped support pillar  49  that extends perpendicularly from the center portion of the upper member  48  to the center portion of the horizontally extending portion  47   b  of the intermediate cylinder member  47 . The upper chamber  52  is formed between the upper member  48  and the horizontally extending portion  47   b . In this manner, in the labyrinth structural body  45 , the lower chamber  51  and the upper chamber  52  are constituted by the three members, which are the bottom member  46 , the intermediate cylinder member  47 , and the upper member  48 . Thus, a tortuous passage (a zigzag passage, or roundabout passage) is formed in the labyrinth structural body  45 , as shown by the black arrows. An outlined arrow indicates the flow of the evaporative gas at normal times. The length of the tortuous passage may be set to an appropriate value, by providing an appropriate number of the horizontally extending portions  47   b  at intervals in a vertical direction between the upper member  48  and a first horizontally extending portion  47   b.    
      The action of the fill-up control valve structure  30  is as follows. That is, when fuel is supplied through a fuel supply pipe  3  shown in  FIG. 8  to the fuel tank  1  to which the fill-up control valve structure  30  is attached, the liquid surface of the fuel in the fuel tank  1  may rapidly oscillate. Also, when the vehicle is suddenly turned, when the vehicle is suddenly stopped, or when the vehicle suddenly takes off, the liquid surface of the fuel in the fuel tank  1  may rapidly oscillate. When the liquid surface of the fuel in the fuel tank  1  is rapidly oscillated, the fuel tries to rapidly enter the float chamber  41  through the ventilation holes  46   c  of the labyrinth structural body  45  of the fill-up control valve structure  30 .  
      However, since the tortuous passage is formed between the float  37  in the casing  31  and the ventilation holes  46   c  due to the labyrinth structural body  45  including the three members, which are the bottom member  46 , the intermediate cylinder member  47 , and the upper member  48 , the flow speed of the fuel that enters through the ventilation holes  46   c  at a high speed is reduced as the fuel passes through the tortuous passage constituted by the lower chamber  51  and the upper chamber  52 , as shown by the black arrows. Therefore, the fuel can be prevented from flowing out to the ventilation passage  5  before the ventilation passage  5  is closed by the valve element  40 , which is moved by the float  37 .  
      Also, at normal times, at the time of fuel supply, or the like, the evaporative gas containing fuel may enter the float chamber  41  through the ventilation holes  46   c , and may try to flow out to the ventilation passage  5 . However, since the fuel contained in the evaporative gas is separated from the gas as the evaporative gas passes through the tortuous passage, and the separated fuel flows back through the tortuous passage to the fuel tank  1 , it is possible to reduce an adverse effect of the fuel on the canister  4 .  
       FIG. 2  is a cross sectional view showing an evaporative gas control valve structure according to a second embodiment of the invention. The evaporative gas control valve structure includes a tortuous passage that is different from the tortuous passage according to the first embodiment of the invention. Since the structure according to the second embodiment is the same as the structure according to the first embodiment except for the labyrinth structural body, description of the similar structure will be omitted.  
      A labyrinth structural body  60  is integrally attached to the lower opening  33  of the casing  31 . The labyrinth structural body  60  includes two members, which are a bottom member  61  and an upper member  62 , which are made of resin.  
      The bottom member  61 , which is one of the two members, is a hollow member including an upper wall  61   a , a side wall  61   b , and a bottom wall  61   c . In the bottom member  61 , there is a space  67  which serves as a passage. A first support pillar  61   e  for reinforcement extends perpendicularly at the center thereof. A flange  61   d  is formed in the bottom wall  61   c . When the labyrinth structural body  60  is inserted from the lower opening  33  of the casing  31 , an inner surface of the casing  31  at a lower end contacts an outer periphery of the side wall  61   b , and a lowermost end of the casing  31  contacts an upper surface of the flange  61   d . The labyrinth structural body  60  and the casing  31  are integrally fixed to each other.  
      Further, plural first ventilation holes  63  are formed in the bottom wall  61   c  at a portion near a radially outer end of the bottom wall  61   c . Plural second ventilation holes  64  are formed in the upper wall  61   a  at a portion near a radially inner end of the upper wall  61   a . The tortuous passage is constituted by the first ventilation holes  63 , the space  67 , and the second ventilation holes  64 .  
      At normal times, the plural first ventilation holes  63  and the plural second ventilation holes  64  allow the evaporative fuel gas to be discharged. At the time of fuel supply or the like, the plural first ventilation holes  63  and the plural second ventilation holes  64  allow the fuel to enter the float chamber  41 . At the time of fuel supply or the like, the float  37  is moved upward due to the fuel entering the float chamber  41 , and the valve element  40  provided in the upper portion of the float  37  contacts the valve seat  34 , whereby the outflow of the fuel to the canister  4  side is suppressed.  
      The upper member  62  is a disk-shaped member which is horizontally provided above the bottom member  61 . The upper member  62  constitutes a seat member which the float  37  contacts when it moves downward. The upper member  62  includes a thick member  62   a  at a center thereof, and a thin member  62   b  at an outer portion thereof. The spring  42  is positioned (centered) by the thick member  62   a  at the center, and the spring  42  is provided between an upper surface of the thin member  62   b  and the upper surface of the inner wall of the float  37 .  
      Plural ventilation holes  62   c  are formed at equal intervals in the thin member  62   b  at a radially outer portion. The lower end of the float  37  contacts the upper surface of the thin member  62   b . When the lower end of the float  37  contacts the thin member  62   b , the ventilation holes  62   c  are closed by the lower end of the float  37 . When the fuel flows into an upper chamber  66  that will be described later, the fuel acts on the float  37  through the ventilation holes  62   c  such that the float  37  is moved upward. Thus, upward movement of the float  37  is supported by the fuel.  
      Further, the upper member  62  and the bottom member  61  are integrally connected to each other by a bar-shaped second support pillar  65  that extends perpendicularly from the center portion of the upper member  62  to the center portion of the bottom member  61 . The upper chamber  66  is formed between the upper member  62  and the bottom member  61 . In this manner, in the labyrinth structural body  60  including the bottom member  61  and the upper member  62 , the tortuous passage is constituted by the first ventilation holes  63 , the space  67 , the second ventilation holes  64 , and the upper chamber  66 , as shown by black arrows. An outlined arrow indicates the flow of the evaporative gas at normal times.  
      That is, when the liquid surface of the fuel in the fuel tank  1  is rapidly oscillated, the fuel tries to rapidly enter the float chamber  41  through the first ventilation holes  63  of the labyrinth structural body  60 . However, since the tortuous passage is constituted by the space  67 , the second ventilation holes  64 , and the upper chamber  66  between the float  37  in the casing  31  and the first ventilation holes  63 , the flow speed of the fuel that enters through the first ventilation holes  63  at a high speed is reduced while the fuel passes through the tortuous passage, as shown by the black arrows. Therefore, the fuel can be prevented from flowing out to the ventilation passage  5  before the ventilation passage  5  is closed by the valve element  40  moved by the float  37 , and at least the possibility of the outflow of the fuel to the ventilation passage  5  can be reduced. The length of the tortuous passage may be set to an appropriate value, by providing the appropriate number of bottom members  61  including the space  67  at intervals in the vertical direction. Therefore, the flow speed of the fuel can be effectively reduced, and the effect of separating the fuel from the evaporative gas, that is, the gas-liquid separation effect can be enhanced.  
       FIG. 3  is a cross sectional view showing an evaporative gas control valve structure according to a third embodiment of the invention. In the evaporative gas control valve according to the third embodiment, the shape of a tortuous passage (zigzag passage) constituted by a bottom member is different from the shape of the tortuous passage according to the first and second embodiments. Therefore, the third embodiment will be described focusing on the portions different from those in the previous embodiments.  
      The labyrinth structural body  60  is integrally attached to the lower opening  33  of the casing  31  by welding or other means. The labyrinth structural body  60  includes two members, which are the bottom member  61  and the upper member  62 , which are made of resin.  
      The bottom member  61 , which is one of the two members, is the hollow member. The bottom member  61  includes the upper wall  61   a , the side wall  61   b , and the bottom wall  61   c . In the bottom member  61 , there is the space  67  which serves as the passage. At least one ventilation hole  63  is formed on one side in the bottom wall  61   c , and at least one second ventilation hole  64  is formed on the other side (i.e., the side opposite to the first ventilation hole  63 ) in the upper wall  61   a . Further, two horizontal plates  61   f , which are an upper horizontal plate  61   f  and a lower horizontal plate  61   f  are provided at an upper position and a lower position, respectively inside the bottom member  61 . The lower horizontal plate  61   f  is fixed to an inner surface of the side wall  61   b  on a left side in  FIG. 3 . A gap  61   g  is formed between an end of the lower horizontal plate  61   f  and the inner surface of the side wall  61   b  on a right side in  FIG. 3 . The upper horizontal plate  61   f  is fixed to the inner surface of the side wall  61   b  on the right side in  FIG. 3 . The gap  61   g  is formed between an end of the upper horizontal plate  61   f  and the inner surface of the side wall  61   b  on the left side in  FIG. 3 . Thus, the tortuous passage is formed in the space  67 , as shown by black arrows.  
      The bottom member  61  of the labyrinth structural body  60  is configured to have the shape described above. Also, the length of the tortuous passage whose direction reverses may be set to an appropriate value by increasing or decreasing the number of the horizontal plates  61   f . Therefore, the flow speed of the fuel can be effectively reduced, and the gas-liquid separation effect can be enhanced.  
      Each of  FIG. 4  and  FIG. 5  is a cross sectional view showing an evaporative gas control valve structure according to a fourth embodiment of the invention. The evaporative gas control valve structure includes a spiral passage. According to the fourth embodiment, the shape of a bottom member of a labyrinth structural body is different, as compared to the structures according to the first to the third embodiments. Since the structure according to the fourth embodiment is the same as the structure according to the first embodiment in other respects, description of those other respects will be omitted.  
      A labyrinth structural body  70  is integrally attached to the lower opening  33  of the casing  31  by welding or other means. The labyrinth structural body  70  includes two members, which are a bottom member  71  and an upper member  72 , which are made of resin.  
      The bottom member  71 , which is one of the two members, includes an upper wall  71   a , a side wall  71   b , and a spiral wall  71   d . The spiral wall  71   d  is formed to have a spiral shape in the bottom member  71 . A spiral passage  73  is constituted by the spiral wall  71   d  in the bottom member  71 , as shown in  FIG. 5 . A flange  71   c  is formed in an outer periphery of the side wall  71   b  at a lower end. When the labyrinth structural body  70  is inserted from the lower opening  33  of the casing  31 , the inner surface of the casing  31  contacts the outer periphery of the side wall  71   b , and the lowermost end of the casing  31  contacts an upper surface of the flange  71   c . The labyrinth structural body  70  and the casing  31  are integrally fixed to each other by welding or other means.  
      Further, a first ventilation hole  75  is formed in a bottom portion of the spiral wall  71   d . The spiral passage  73  starts at the first ventilation hole  75 . Communication is provided between the spiral passage  73  and an upper chamber  74  that will be described later. At normal times, the first ventilation hole  75  allows the evaporative fuel gas to be discharged. At the time of fuel supply or the like, the first ventilation hole  75  allows the fuel to enter the float chamber  41 . At the time of fuel supply or the like, the float  37  is moved upward due to the fuel entering the float chamber  41 , and the valve element  40  provided in the upper portion of the float  37  contacts the valve seat  34 , whereby the outflow of the fuel to the canister  4  side is suppressed.  
      The upper member  72  is a disk-shaped member which is horizontally provided above the bottom member  71 . The upper member  72  constitutes a seat member which the float  37  contacts when it moves downward. The upper member  72  includes a thick member  72   a  at a center thereof, and a thin member  72   b  at an outer portion thereof. The spring  42  is positioned (centered) by the thick member  72   a  at the center, and the spring  42  is provided between an upper surface of the thin member  72   b  and the upper surface of the inner wall of the float  37 .  
      Plural ventilation holes  72   c  are formed at equal intervals in the thin member  72   b  at the outer portion. The lower end of the float  37  contacts the upper surface of the thin member  72   b . When the lower end of the float  37  contacts the thin member  72   b , the ventilation holes  72   c  are closed by the lower end of the float  37 . When the fuel flows into the upper chamber  74 , the fuel acts on the float  37  through the ventilation holes  72   c  such that the float  37  is moved upward. Thus, upward movement of the float  37  is supported by the fuel.  
      Further, the upper member  72  and the bottom member  71  are integrally connected to each other by a hollow support pillar  77  that extends perpendicularly from the center portion of the upper member  72  to the center portion of the bottom member  71 . A second ventilation hole  76  is provided in the support pillar  77 . Communication is provided between the second ventilation hole  76  and the upper chamber  74 . Thus, communication is provided between an inside of the fuel tank  1  and the upper chamber  74  through the first ventilation hole  75 , the spiral passage  73 , and the second ventilation hole  76 . In this manner, the labyrinth structural body  70  includes the spiral passage  73 , and allows the fuel to enter the upper chamber  74  according to the route shown by black arrows. An outlined arrow indicates the flow of the evaporative gas.  
      When the liquid surface of the fuel in the fuel tank  1  is rapidly oscillated, the fuel tries to rapidly enter the float chamber  41  through the first ventilation hole  75  of the labyrinth structural body  70 . However, since the spiral passage composed of the spiral passage  73  is formed between the float  37  and the first ventilation hole  75 , the flow speed of the fuel that enters through the first ventilation hole  75  at a high speed is reduced while the fuel passes through the spiral passage  73  as shown by the black arrows. Therefore, the fuel can be prevented from flowing out to the ventilation passage  5  before the ventilation passage is closed by the valve element  40  moved by the float  37 , or at least the possibility of the outflow of the fuel to the ventilation passage  5  can be reduced.  
      Since the labyrinth structural body  70  is configured to have the shape described above, the spiral passage  73  can be configured to have an appropriate length. Therefore, the flow speed of the fuel can be reduced more effectively, and the gas-liquid separation effect can be further enhanced.  
       FIG. 6  is a cross sectional view showing an evaporative gas control valve structure according to a fifth embodiment of the invention. A labyrinth structural body of the evaporative gas control valve structure according to the fifth embodiment is basically the same as the labyrinth structural body according to the first embodiment. However, according to the fifth embodiment, the bottom member  46  and the intermediate cylinder member  47  are formed separately from the upper member  48 . In the following description of the fifth embodiment, the labyrinth structural body according to the first embodiment is employed. However, the labyrinth structural body according to one of the second to fourth embodiments alternatively may be employed in the fifth embodiment. Components that are the same as those in the first embodiment are denoted by the same reference numerals.  
      The labyrinth structural body  45  is integrally attached to the lower opening  33  of the casing  31  by welding or other means. The labyrinth structural body  45  includes the three members, which are the bottom member  46 , the intermediate cylinder member  47 , and the upper member  48  which are made of resin. The bottom member  46  and the intermediate cylinder member  47  are formed separately from the upper member  48 .  
      The bottom member  46 , which is one of the three members, is the cylindrical member having an upper opening at an upper end thereof and a lower opening at a lower end thereof. The bottom member  46  includes a hollow cylindrical portion  53  and a bottom plate portion  54  at a lower end thereof. The lower end portion of the casing  31  is inserted into a cylindrical upper end portion  53   a  of the cylindrical portion  53 . Then, the casing  31  and the cylindrical upper end portion  53   a  of the cylindrical portion  53  are integrally fixed to each other by welding a contact portion therebetween, or by other means.  
      The intermediate cylinder member  47  is provided in a hollow portion of the bottom member  46  so as to be concentric with the bottom member  46 . The intermediate cylinder member  47  includes the hollow cylindrical portion  47   a  whose height is larger than that of the bottom plate portion  54 , and the horizontally extending portion  47   b  at the upper portion thereof. The lower end of the hollow cylindrical portion  47   a  and the lower end of the bottom plate portion  54  are positioned at the same level. The inner surface of the bottom plate portion  54  and the outer surface of the hollow cylindrical portion  47   a  of the intermediate cylinder member  47  are connected to each other by plural ribs  50  that are provided at equal intervals in a circumferential direction. The plural ventilation holes  46   c  are formed between the inner surface of the bottom plate portion  54  and the outer surface of the hollow cylindrical portion  47   a .  
      When the hollow cylindrical portion  47   a  of the intermediate cylinder member  47  is provided inside the bottom plate portion  54 , the horizontally extending portion  47   b  occupies a substantially intermediate position in the cylindrical portion  53 . Thus, the lower chamber  51  is formed between the horizontally extending portion  47   b  and the bottom plate portion  54 . The ventilation holes  46   c  are formed on the inner side of the horizontally extending portion  47   b  in a plan view. The evaporative gas and the fuel entering the lower chamber  51  through the ventilation holes  46   c  hit the lower surface of the horizontally extending portion  47   b . Thus, the evaporative gas and the fuel flow outward, and then flow upward.  
      The upper member  48  is a disk-shaped member which is horizontally provided in the lower opening  33  of the casing  31 , above the intermediate cylinder member  47 . The upper member  48  constitutes the seat member which the float  37  contacts when it moves downward. The upper member  48  includes the thick member  48   a  at the center thereof, and the thin member  48   b  at the outer portion thereof. The spring  42  is positioned (centered) by the thick member  48   a , and the spring  42  is provided between the upper surface of the thin member  48   b  and the upper surface of the inner wall of the float  37 .  
      The upper member  48  is pressed in the lower opening  33  of the casing  31 , as shown in  FIG. 6 . Then, the upper member  48  is fixed to the lower opening  33  by welding or other means. Plural concave grooves  55  are provided at an outer peripheral end of the thin member  48   b . Thus, even when the upper member  48  is attached to the lower end portion of the casing  31 , the fuel and the like can flow from a lower side to an upper side.  
      Further, the plural ventilation holes  49   c  are formed in the thin member  48   b  at equal intervals at a position which the float  37  contacts when it moves downward. When the lower end of the float  37  contacts the upper surface of the thin member  48   b , the plural ventilation holes  49   c  are closed by the lower end of the float  37 . When the fuel flows into the upper chamber  52  that is formed between the upper member  48  and the horizontally extending portion  47   b  of the intermediate cylinder member  47 , the fuel acts on the float  37  through the ventilation holes  49   c  such that the float  37  is moved upward. Thus, upward movement of the float  37  is supported by the fuel.  
      Thus, in the labyrinth structural body  45 , the tortuous passage is constituted by the bottom plate portion  54 , the intermediate cylinder member  47 , and the upper member  48 , as shown by black arrows. The labyrinth structural body  45  has the same effect as that of the labyrinth structural body  45  in the first embodiment. An outlined arrow indicates the flow of the evaporative gas. In the fifth embodiment as well, the length of the tortuous passage may be set to an appropriate value by providing the appropriate number of additional horizontally extending portions  47   b  at intervals in the vertical direction between the upper member  48  and a first horizontally extending portion  47   b , through a support pillar (not shown).  
       FIG. 7  is a cross sectional view showing an evaporative gas control valve structure according to a sixth embodiment of the invention. In the sixth embodiment, the evaporative gas control valve structure is integrated with a fuel pump unit  6 . In the following description of the sixth embodiment, the evaporative gas control valve structure according to the first embodiment is employed. However, the evaporative gas control valve structure according to one of the second to fifth embodiments alternatively may be employed in the sixth embodiment. Components that are the same as those in the first embodiment are denoted by the same reference numerals.  
       FIG. 7  is a schematic view showing the fill-up control valve structure  30  and the fuel pump unit  6  that are integrated with each other. The fuel pump unit  6  is a known pump which includes a pump main body  6   a  and a filter and the like (not shown) that are attached to a bottom portion of the pump main body  6   a . The fuel pump unit  6  is attached to an upper portion of the fuel tank  1  through a flange  56 . The fuel pump unit  6  supplies the fuel in the fuel tank  1  to an engine as shown by an outlined arrow. In  FIG. 7 , the flange  56  for attaching the fuel pump unit  6  to the upper portion of the fuel tank  1  also is used as a flange for attaching the fill-up control valve structure  30  to the upper portion of the fuel tank  1 . Since the fill-up control valve structure  30  is attached to the fuel tank  1  in this manner, it is possible to reduce an area required for attaching the fill-up control valve structure  30  and the fuel pump unit  6  to the fuel tank  1 , and to reduce the number of flange components and man hours required for attaching the flange components. Further, since an area through which the fuel (HC) permeates can be reduced accordingly, a fuel permeation amount can be reduced, which contributes to solving an environmental problem.  
      The invention is not limited to the aforementioned embodiments. Modifications can be appropriately made to the design without departing from the spirit of the invention. For example, in the aforementioned embodiments, the ventilation hole is provided below the casing. However, a second ventilation hole having a small diameter can be provided in a side wall of the casing at an upper side position which moving fuel is unlikely to reach. When the second ventilation hole having the small diameter is provided, the pressure in the fuel tank and the pressure in the float chamber can be made equal quickly. Therefore, the valve element can be moved upward earlier when the fuel tank is filled up.  
      In the aforementioned embodiments, the passage for suppressing the flow of the fuel is provided between the float and the ventilation hole formed below the casing. Therefore, even if the fuel tries to rapidly enter the float chamber through the ventilation hole, the flow speed of the fuel can be reduced by the tortuous passage, and thus, the valve is reliably closed by the float before the fuel flows out to the ventilation passage. Therefore, thus the adverse effect of the fuel on the canister can be prevented, or at least the possibility of the adverse effect of the fuel on the canister can be reduced. Also, the fuel contained in the evaporative gas can be separated from the gas more reliably while the evaporative gas flows in the tortuous passage. Accordingly, the amount of the fuel flowing out to the canister can be reduced by an amount corresponding to the amount of the fuel separated from the gas, and thus the adverse effect of the fuel on the canister can be prevented, or at least the possibility of the adverse effect of the fuel on the canister can be reduced.  
      The embodiments of the invention described above include various types of tortuous passages. The invention, however, is not limited to the illustrated embodiments, which are exemplary.  
      While the invention has been described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the exemplary embodiments and constructions. The invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the exemplary embodiments are shown in various combinations and configurations, which are exemplary, other combinations and configuration, including more, less or only a single element, are also within the spirit and scope of the invention.