Abstract:
An evaporative emission control system is provided which includes an upper valve casing defining a vent conduit, a lower valve casing disposed under the upper valve casing, and a float disposed within the lower valve casing. The float is vertically movable depending upon a liquid level of fuel in a fuel tank, and includes a valve portion that faces the upper valve casing. A valve port formed between the upper valve casing and the lower valve casing is opened and closed by the valve portion of the float. The upper valve casing defines a space between the vent conduit and the valve port. A flow restricting device is disposed in the space of the upper valve casing so as to obstruct flow of fuel from the valve port to the vent conduit.

Description:
INCORPORATION BY REFERENCE  
         [0001]    The disclosure of Japanese Patent Application No. HEI 11-369719 filed on Dec. 27, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.  
         BACKGROUND OF THE INVENTION  
       Field of the Invention  
         [0002]    The invention relates to an evaporative emission control system that prevents fuel vapors in a vehicular fuel tank from being discharged into the atmosphere and, more particularly, to an evaporative emission control system that prevents fuel from being transferred to a canister through a vapor vent line when the fuel tank is filled up and prevents fuel from flowing out of the tank when the vehicle inclines or rolls over.  
         Discussion of Related Art  
         [0003]    A vehicular fuel tank is provided with a liquid level sensing valve, a fuel cut valve and the like. The liquid level sensing valve is adapted to close a vapor vent line when the tank is filled up. The fuel cut valve is adapted to close an evaporation line to prevent fuel from flowing out of the line, for example, when the vehicle inclines or rolls over. Each of these valves includes a float that vertically moves in accordance with the liquid level of the fuel.  
           [0004]    Hereinafter, one example of evaporative emission control systems as part of the related art will be described with reference to FIG. 1. A valve casing  4  incorporating a liquid level sensing valve  2  and a fuel cut valve  3  formed as a unit is mounted on the fuel tank  1 . The valve casing  4  is composed of a lower valve casing  4 A and an upper valve casing  4 B disposed above the lower valve casing  4 A. A liquid level sensing float  5  and a fuel cut float  6  are disposed in the lower valve casing  4 A.  
           [0005]    A valve portion  7  is provided on an upper surface of the liquid level sensing float  5 . Also, a valve portion  8  is provided by an upper portion of the fuel cut float  6 . Valve ports  9 ,  10  are formed between the lower valve casing  4 A and the upper valve casing  4 B. The valve port  9  is opened and closed by the valve portion  7 , and the valve port  10  is opened and closed by the valve portion  8 . The upper valve casing  4 B is provided with a vent conduit  11 , which communicates with the valve port  9  through a space  12 . The space  12  also communicates with the valve port  10  through a conduit  13 .  
           [0006]    The operation of the evaporative emission control system of the related art shown in FIG. 1 will be now described.  
           [0007]    If the pressure of fuel vapors in the fuel tank  1  becomes high during refueling, fuel vapors flow through the valve port  9  formed in the valve casing  4 , and are discharged into a canister (not shown), an intake pipe (not shown) and the like through the vent conduit  11 , as indicated by arrow P in FIG. 1.  
           [0008]    If the liquid level of the fuel in the fuel tank  1  is elevated, the liquid level sensing float  5  rises and the valve body  7  closes the valve port  9 . This prevents fuel from being directly fed to the canister.  
           [0009]    If the pressure of fuel vapors in the fuel tank  1  remains high during normal operations, the liquid level sensing float  5  sticks to the valve port  9 . In this case, since the vent conduit  11  remains closed, it is necessary to reduce the pressure in the fuel tank  1 . To this end, the pressure is released through the valve port of the fuel cut valve  23  so that the liquid level sensing float falls because of its own weight.  
           [0010]    If the vehicle inclines by a large degree or rolls over, a large amount of fuel in the fuel tank  1  may flow towards the canister through the valve port  10  and the conduit  13 . However, when the vehicle inclines by a large degree or rolls over, the fuel cut float  6  rises and the valve body  8  closes the valve port  10 , whereby fuel is prevented from flowing out.  
           [0011]    In the aforementioned structure as shown in FIG. 1, the liquid level sensing float  5  and the fuel cut float  6  are disposed in the same valve casing  4 . However, other structures are also known in which the liquid level sensing float and the fuel cut float are individually disposed in separate valve casings.  
           [0012]    Another example of evaporative emission control systems as part of the related art will be described with reference to FIG. 2. A liquid level sensing valve  22  and a fuel cut valve  23  are separately mounted on a fuel tank  21 . A valve casing  24  of the liquid level sensing valve  22  is formed with a vent conduit  25 , and a valve casing  26  of the fuel cut valve  23  is formed with a conduit  27 . A space  28  is formed in the valve casing  24  of the liquid level sensing valve  22 . A connection port  29  that extends from the space  28  is connected to the conduit  27  by means of a hose  30 .  
           [0013]    The example shown in FIG. 2 also performs substantially the same operation as the example shown in FIG. 1. That is, if the liquid level of fuel in the fuel tank  21  becomes high, the liquid level sensing valve  22  closes the vent conduit  25 . This prevents fuel from being directly fed to the canister and the like.  
           [0014]    If the pressure of fuel vapors in the fuel tank  21  remains high during normal operations, the float of the liquid level sensing valve  22  sticks to the valve port, and the vent conduit  25  remains closed. Therefore, it is necessary to reduce the pressure in the fuel tank  21 . To this end, the pressure in the fuel tank  21  is released through the valve port of the fuel cut valve  23 , so that the float of the liquid level sensing valve  22  falls because of its own weight.  
           [0015]    If the vehicle inclines by a large extent or rolls over, a large amount of fuel in the fuel tank  21  may flow towards the canister through the valve port of the fuel cut valve  23  and the conduit  27 . However, when the vehicle inclines by a large degree or rolls over, the float of the fuel cut valve  23  rises and the valve port is closed, whereby fuel is prevented from flowing out.  
           [0016]    However, the aforementioned evaporative emission control systems as part of the related art have the following disadvantages.  
           [0017]    First of all, since the space  12 ,  28  is directly connected to the vent conduit  11 ,  25  with no intervening member therebetween, the fuel that has leaked out from the valve port  9  due to vibration of the vehicle, or the like, may be transferred toward the canister and degrade the canister.  
           [0018]    Furthermore, the valve port  9  may be directly exposed to the fuel in the fuel tank, and therefore the fuel is more likely to leak through the valve port  9 .  
           [0019]    With regard to the structure in which the connection port  29  of the liquid level sensing valve  22  and the conduit  27  of the fuel cut valve  23  are connected with each other by the hose  30 , the connecting operation cannot be accomplished in a simple manner. It thus takes a lot of time and labor to provide the system as shown in FIG. 2, while requiring many types of parts or components.  
         SUMMARY OF THE INVENTION  
         [0020]    It is thus an object of the invention to reduce or eliminate the disadvantages of the evaporative emission control systems as the related art, and to provide an evaporative emission control system that achieves reduction of the amount of leaking fuel, simplified procedure of mounting or connecting pipes, and reduction of the number of types of required parts or components.  
           [0021]    To accomplish the above object, an evaporative emission control system is provided according to the present invention, which includes: an upper valve casing defining a vent conduit; a lower valve casing disposed under the upper valve casing; a float disposed within the lower valve casing, the float being vertically movable depending upon a liquid level of fuel in a fuel tank, the float including a valve portion that faces the upper valve casing; a valve port provided between the upper valve casing and the lower valve casing, the valve port being opened and closed by the valve portion of the float, the upper valve casing defining a space between the vent conduit and the valve port; and a flow restricting device disposed in the space of the upper valve casing so as to obstruct flow of fuel from the valve port to the vent conduit.  
           [0022]    In one preferred form of the invention, the flow restricting device consists of a shield device that reduces a cross-sectional area of the space through which the valve port communicates with the vent conduit.  
           [0023]    In another preferred form of the invention, the flow restricting device defines a helical passage in the space of the upper valve casing.  
           [0024]    In a further preferred form of the invention, the flow restricting device consists of at least one partition wall that divides the space of the upper valve casing into two or more chambers that are arranged in a vertical direction. In this case, each of the partition walls has a through-hole formed therethrough.  
           [0025]    The evaporative emission control system as described above may further include a cut valve having a vent port. In this system, the upper valve casing may be provided with a cut valve connection port that is open to the above-indicated space of the upper valve casing, and is connected to the vent port of the cut valve.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    [0026]FIG. 1 is a cross-sectional view showing one example of evaporative emission control system as part of the related art.  
         [0027]    [0027]FIG. 2 is a cross-sectional view showing another example of evaporative emission control system as part of the related art.  
         [0028]    [0028]FIG. 3 is a cross-sectional view showing an evaporative emission control system according to a first embodiment of the invention.  
         [0029]    [0029]FIG. 4 is a cross-sectional view taken along line A-A of FIG. 3.  
         [0030]    [0030]FIG. 5 is a cross-sectional view of an evaporative emission control system according to a second embodiment of the invention.  
         [0031]    [0031]FIG. 6 is a cross-sectional view taken along line B-B of FIG. 5.  
         [0032]    [0032]FIG. 7 is a cross-sectional view of an evaporative emission control system according to a third embodiment of the invention.  
         [0033]    [0033]FIG. 8 is a cross-sectional view of an evaporative emission control system according to a fourth embodiment of the invention.  
         [0034]    [0034]FIG. 9 is a cross-sectional view of an evaporative emission control system according to a fifth embodiment of the invention, wherein a fuel cut valve is disposed separately from a liquid level sensing valve.  
         [0035]    [0035]FIG. 10 is a cross-sectional view of an evaporative emission control system according to a sixth embodiment of the invention, wherein a fuel cut valve is disposed separately from a liquid level sensing valve.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0036]    Some preferred embodiments of the invention will be described with reference to the drawings.  
         [0037]    The invention mainly has three features. As the first feature, an obstruction wall or walls for preventing flow of fuel between a space and a vent conduit in the liquid level sensing valve is provided for reducing the amount of fuel leaking from the fuel tank.  
         [0038]    As the second feature, in order to prevent a valve port of the liquid level sensing valve from being directly exposed to fuel, the liquid level sensing valve is covered with a cylindrical cover.  
         [0039]    As the third feature, a connection port of the liquid level sensing valve and a conduit of the fuel cut valve are connected to each other by a connector so that the connecting process can be quickly carried out in a simple manner, or may be connected by a hose, using a nipple fitted on the connection port to facilitate the connecting process. This leads to a reduction in the number of types of required parts or components.  
         [0040]    A first embodiment of the invention will be described with reference to FIGS. 3 and 4. This embodiment is characterized in that an obstruction wall or walls for preventing flow of fuel between a space and a vent conduit of a liquid level sensing valve is/are provided for reducing the amount of leaking fuel.  
         [0041]    A valve casing of a liquid level sensing valve  41  is composed of a lower valve casing  42  and an upper valve casing  43  disposed above the lower valve casing  42 .  
         [0042]    Afloat  44  is disposed in the lower valve casing  42 . A valve portion  45  is provided on an upper surface of the float  44 . A valve port  46  is formed between the lower valve casing  42  and the upper valve casing  43 . The valve port  46  is opened and closed by the valve portion  45 . The upper valve casing  43  is formed with a vent conduit  47 , and a space  48  is formed between the vent conduit  47  and the valve port  46 .  
         [0043]    With the above arrangement, the float  44  vertically moves in accordance with the level of the liquid surface in a fuel tank (not shown), and the valve portion  45  of the float  44  opens and closes the valve port  46 , so that the vent conduit  47  communicates with the interior of the fuel tank when the valve port  46  is in the open state.  
         [0044]    In this embodiment of the invention, a shield device  49  is disposed in the space  48  so as to reduce the cross-sectional area of the passage through which fuel vapors flow.  
         [0045]    More specifically, the shield device  49  consists of alternately arranged shield members  49 A,  49 B. The shield members  49 A protrude downwards from the upper wall of the upper casing  43 , and the shield members  49 B protrude upwards from the lower wall of the upper casing  43 . While the shield members  49 A,  49 B are formed as integral parts of the upper casing  42  in this embodiment, the shield members may be provided as separate members formed independently of the upper casing  43 .  
         [0046]    The fuel cut valve is not illustrated in FIGS. 3 and 4. The fuel cut valve may either be assembled as a unit with the liquid level sensing valve as in the related art shown in FIGS. 1 and 2, or may be disposed separately from the liquid level sensing valve.  
         [0047]    In the evaporative emission control system constructed as described above, the shield member  49  prevents fuel from freely flowing through the space in which the member  49  is located, thus making it possible to reduce the amount of fuel leaking out through the valve port  46 .  
         [0048]    The structure and number of the shield members are not specifically limited. However, it is preferable to alternately arrange the shield members  49 A protruding downwards and the shield members  49 B protruding upwards, because the amount of leaking fuel can be reduced more effectively.  
         [0049]    The arrangement for obstructing flow of fuel is not limited to that of the first embodiment, but may be that as provided in a second embodiment of the invention shown in FIGS. 5 and 6.  
         [0050]    In the space between the valve port  46  and the vent conduit  47  in this embodiment, a helical passage  48 A is formed or defined by a helical wall portion that is an integral portion of the upper casing  43 . The helical passage  48 A may also be defined by a separate member (shield member) provided independently of the upper casing  43 . Since other structural components are the same as those of the first embodiment, they are simply denoted by the same reference numerals and will not be described.  
         [0051]    Since the helical passage  48 A prevents fuel from freely flowing through the space in which the passage  48 A is located, it is possible to reduce the amount of fuel leaking out through the valve port  46 .  
         [0052]    The arrangement for obstructing flow of fuel is not limited to those of the illustrated embodiments, but may be that as provided in a third embodiment of the invention shown in FIG. 7.  
         [0053]    In this embodiment, the space between the valve port  46  and the vent conduit  47  is divided into vertically arranged multi-stage chambers  48 B,  48 C and  48 D. Through-holes  50  are formed in partition walls  53 ,  54  for defining these chambers  48 B,  48 C and  48 D.  
         [0054]    Because other structural components are the same as those of the illustrated embodiments, they are simply denoted by the same reference numerals and will not be described.  
         [0055]    With the above arrangement having the multi-stage chambers  48 B,  48 C and  48 D, the partition walls  53 ,  54  serve to obstruct free flow of fuel through the space between the valve port  46  and the vent conduit  47 , and it is therefore possible to reduce the amount of fuel leaking out through the valve port  46 .  
         [0056]    As shown in FIG. 7,.if the through-holes  50  formed in the partition walls  53 ,  54  are not aligned with each other, that is, if the through-holes  50  are located with their centers offset from each other, the resistance to flow of the fuel is further increased, thus making it possible to further reduce the amount of fuel leaking out through the valve port  46 .  
         [0057]    In the aforementioned embodiments, the flow resistance in the space prevents fuel from leaking out through the valve port of the liquid level sensing valve. In a fourth embodiment of the invention as shown in FIG. 8, on the other hand, fuel is prevented from reaching the valve port of the liquid level sensing valve.  
         [0058]    More specifically, an inflow opening  51  that allows passage of fuel or fuel vapors therethrough is formed in the lower valve casing  42 . A cylindrical cover  52  for covering the inflow opening  51  is formed integrally with or separately from the upper casing  43 .  
         [0059]    This embodiment may also employ the arrangements of the first to third embodiments. Namely, the shield members may be disposed in the space, or the helical conduit may be formed, or the space may be formed as multi-stage chambers. Also in this embodiment, since other structural components are the same as those of the aforementioned embodiments, they are simply denoted by the same reference numerals and will not be described.  
         [0060]    Referring next to FIG. 9, an example including a connecting structure between a conduit of a separately provided fuel cut valve and a connection port of a liquid level sensing valve will be described as a fifth embodiment of the invention.  
         [0061]    A cut valve connection port  62  is formed in an upper valve casing  61  of the liquid level sensing valve. A vent port  64  of a fuel cut valve  63  is fitted into the cut valve connection port  62 , so that the fuel cut valve  63  communicates with a space  65  formed in the liquid level sensing valve.  
         [0062]    In this embodiment, the cut valve connection port  62  of the liquid level sensing valve (or the vent port  64  of the fuel cut valve  63 ) is directly fitted into and connected with the vent port  64  of the fuel cut valve  63  (or the cut valve connection port  62  of the liquid level sensing valve).  
         [0063]    In the above embodiment, the cut valve connection port and the vent port of the cut valve are directly connected with each other through a connector structure. However, according to the invention, they may be connected with each other through a hose as shown in FIG. 10.  
         [0064]    Namely, a nipple  73  is fitted into a connection port  71  communicating with the space  48  of the liquid level sensing valve. A hose  74  is fitted at one end onto a vent port  72  of the fuel cut valve, and is fitted at the other end onto the nipple  73 .  
         [0065]    The embodiments of FIG. 9 and FIG. 10 may also employ the arrangements of the first to third embodiments. Namely, the shield members may be disposed in the space, or the helical conduit may be formed, or the space may be formed as multi-stage chambers. Also in these embodiments, since other structural components are the same as those of the aforementioned embodiments, they are simply denoted by the same reference numerals and will not be described.