Abstract:
A fuel vapor venting system for fuel tanks having a saddle-shaped upper wall. A vapor vent valve is disposed entirely within the tank in each vapor dome compartment formed by the upper tank wall. The vent valves are interconnected by a conduit passing under the lowest portion of the upper tank wall and a drain valve installed in the lowest point of the conduit. The drain valve may be pressure operated or float operated.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to systems for controlling the venting of fuel vapor from a fuel tank and particularly from an on-board motor vehicle fuel tank. Currently, fuel vapor emission control systems are required on light truck passenger motor vehicles. Fuel tanks for such vehicles are often molded of plastic material and configured to conform around structural members of the vehicle such as stiffener members for the vehicle undercarriage or body floor. This often results in the upper or top wall of the tank having a valley formed therein often running longitudinally with respect to the vehicle chassis and which effectively divides the vapor dome within the tank into two or more compartments when the fuel level is not less than that of the lowest level of the valley.  
           [0002]    This compartmentalized vapor dome within the tank has caused problems in providing venting of the fuel vapor from the tank and has resulted in the need for a plurality of vapor vent valves with one valve provided in each separate compartment of the vapor dome.  
           [0003]    Where the fuel vapor vent valves are float operated and are installed in the tank externally through access openings in the upper wall of the tank, it has proven costly and cumbersome to provide the interconnection of the plurality of vent valves to the remote vapor storage device such as a charcoal filled canister. Furthermore, where the tank has a trough or valley formed in the upper surface thereof, it has been required to provide draining of the liquid fuel from the vent valves and lines when the fuel level falls below the lowest level of the valley upon withdrawal of fuel from the tank.  
           [0004]    Thus, it has been desired to provide a way or means of eliminating the need for access openings in the tank wall to install vent valves and to minimize the number of conduit and interconnections thereof required to provide venting of the compartmentalized vapor domes in the fuel tank and to insure drainage of the liquid fuel from the vent system in order to prevent blocking of vapor flow to the storage canister.  
           [0005]    Referring to FIG. 2, a known system has the fuel tank indicated generally at  1  which has an upper wall having an upper level  2  and a lower level  3  such that a separate vapor dome  4  is formed within the tank when the fuel rises above the undersurface of the level  3 .  
           [0006]    A first vapor vent valve  5  is disposed within the vapor dome  4  adjacent the undersurface of the upper level  2 ; and, a second vapor vent valve  6  is disposed adjacent the undersurface of the tank top level  3  and the outlets of the respective valves  5 ,  6  are interconnected by a conduit  7  which passes beneath the undersurface of the lower level  3 . A second conduit  12  is connected to conduit  7  through an access opening  8  in the lower level  3  of the upper wall; and, conduit  12  is connected to a vapor storage canister  9  which has an outlet  10  adapted for connection to the air inlet of an engine. The canister  9  typically has a purge air inlet  11  for admitting atmospheric air to purge the canister upon engine startup.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    The present invention relates to vapor venting of fuel tanks such as for motor vehicles and particularly relates to fuel tanks having a multilevel upper wall and more particularly to tanks having a valley formed in the upper wall for conforming to structural members of the vehicle and thus having a compartmentalized vapor dome. The present invention provides for vapor vent valving in each compartment of the vapor dome interiorly of the tank to eliminate external hose connections along the outer surface of the tank top. The system of the present invention employs a vapor vent valve in each vapor dome compartment and the vent valves are disposed completely interiorly of the tank with the outlets interconnected; and, a single vapor vent line exits through the upper wall of the tank for connection to a storage canister. The interconnecting lines within the tank include a drain valve disposed at the lowest level of the lines passing under valley formed in the upper tank wall. In one embodiment of the invention the drain valve is a one-way pressure operated valve and in an alternate form the drain valve is float operated. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a pictorial schematic of a system with a fuel tank having a multilevel upper wall configuration as connected to a vapor storage canister;  
         [0009]    [0009]FIG. 2 is a cross-section of a fuel tank with interior vent valves of the prior art;  
         [0010]    [0010]FIG. 3 is a cross-section of a float operated drain valve employed in the present invention; and,  
         [0011]    [0011]FIG. 4 is a cross-section of a one-way drain valve employed in an alternate arrangement of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    Referring to FIG. 1, the system of the present invention is indicated generally at  20  and includes a fuel tank indicated generally at  22  having the upper wall thereof formed in a first or highest level  24 , a second lower level  26  spaced therefrom and interconnected by a third or lowest level  28  forming a valley between levels  24  and  26  such as for conforming to the undercarriage or under floor structure of a vehicle. It will be understood however, that the first and second levels  24 ,  26  may alternatively be at the same level as shown in dashed outline in FIG. 1.  
         [0013]    An access opening  30  is formed in the second level  26  of the upper wall of the tank and has received therein a module  32  and which is secured about the opening  30  by an annular flange  34  which is sealed about the opening by any suitable expedient, as for example, weldment. The module  32  may include a fuel pump  36  and a vapor vent valve  38  which is preferably of the float operated type, and which has an inlet  40  for receiving fuel vapor therein and at least one outlet  42  which is connected to an externally extending conduit  44  which is also connected to the inlet of storage canister  46 . Storage canister  46  has an outlet conduit  48  adapted for connection to the air inlet of an engine and has an atmospheric air inlet  50  for providing atmospheric purge air flow through the canister during engine operation.  
         [0014]    A second vapor vent valve, which in the presently preferred practice of the invention is float operated, but may also be pressure operated is disposed in the vapor dome under tank wall portion  24  as denoted by reference numeral  52 . The vent valve  52  has an outlet which is connected through conduit or hose  54  to the outlet  42  of vent valve  38 . The conduit  54  passes under the lowest level section  28  of the tank upper wall; and, conduit  54  has a drain valve indicated generally at  56  disposed therein and located under the lowest section  28  of the upper tank wall as shown in FIG. 1.  
         [0015]    Referring to FIG. 3, the drain valve  56  is shown in one embodiment having a body  58  with an annular outwardly extending flange  60  formed adjacent the upper end thereof which flange is secured to the conduit  54  by snap-locking within an annular receptacle  62  preferably formed internally with a portion of conduit  54  and sealed by labyrinth seal  64 . The body has a valve seat  66  disposed therein which communicates with the interior of the conduit  54  via flow passage  67 .  
         [0016]    A float  68  is slidably disposed within the body and has a flexible membrane valve member  70  provided on the upper end thereof for contacting and closing against valve seat  66  upon the fuel level in the tank rising to the level of the lower surface of the lowest portion  28  of the tank upper wall. Membrane valve number  70  is partially attached to the float  68  about support  69  on the float; and, a centrally located curved surface  71  makes contact with the undersurface of valve member  70  to urge the central region thereof into contact with the valve seat  66 .  
         [0017]    Referring to FIG. 4, an alternate embodiment of the drain valve is illustrated generally at  156  and has a resilient membrane valve member attached to the conduit  154  which has a plurality of drain holes  158  formed therein with the membrane valve member  160  attached thereover on the lower surface of the conduit  154 . The membrane  160  is shown in solid outline and FIG. 4 has closed over the drain holes  158  formed in the lower surface of the conduit and is moved to the open position shown in dashed outline in FIG. 4 under the gravitational force or pressure resulting from the weight of liquid fuel accumulating in the conduit  154 , thus permitting drainage.  
         [0018]    The present invention thus provides a system for venting fuel vapor in a fuel tank having a multilevel upper wall with vapor vent valves disposed completely within the tank and positioned to vent vapor from the various compartments of the vapor dome formed by the contours of the upper wall of the tank and has the outlets of the vent valves interconnected. A drain valve is provided in the upper conduit interconnecting the vent valve outlets at the lowest level of the upper wall of the tank to drain liquid fuel accumulating in the conduit as the tank is refilled and the liquid level rises above the level of the lowest region of the upper wall of the tank. The drain valve comprises a float operated valve in one embodiment and a fluid pressure operated one-way valve in another embodiment.  
         [0019]    Although the invention has hereinabove been described with respect to the illustrated embodiments, it will be understood that the invention is capable of modification and variation and is limited only by the following claims.