Abstract:
A fuel tank is provided with: a fuel pump; a main tank section which has the fuel pump arranged therein and stores a fuel; a sub-tank section wherein the fuel is stored; and a siphon tube which is arranged over the main tank section and the sub-tank section, and sucks the fuel by means of the fuel pump. The open end of the siphon tube on the main tank section side is arranged outside a jet pump for suction.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a fuel tank equipped with a fuel pump, a first reservoir portion in which the fuel pump is arranged and in which a fuel is retained, a second reservoir portion in which the fuel is retained, and a siphon tube disposed across the first reservoir portion and the second reservoir portion, suction being carried out in the siphon tube via the fuel pump. 
       BACKGROUND ART 
       [0002]    A fuel tank is used for supplying fuel to an internal combustion engine. For example, in a 4WD (four wheel drive) vehicle or a FR (front engine, rear drive) vehicle, in order to avoid the propeller shaft that passes through the center of the vehicle, a so-called saddle type fuel tank, in which the center of a bottom part of the fuel tank in the widthwise direction of the vehicle is recessed upwardly, has been adopted. 
         [0003]    Generally, a saddle type fuel tank is divided into a first reservoir portion that retains fuel, and a second reservoir portion that also retains fuel therein. In the first reservoir portion and the second reservoir portion, systems are installed respectively for transporting (i.e., pumping) the fuel. For this reason, compared to a 2WD (two wheel drive) vehicle, two respective fuel pumping systems are required, which leads to a rise in cost and increases the scale of the fuel tank. 
         [0004]    Thus, a fuel tank level balancing device is known, as disclosed in Japanese Laid-Open Patent Publication No. 10-061515. This apparatus, as shown in  FIG. 5 , includes a fuel tank  1  having two divided compartments  1   a ,  1   b , and having a structure in which the fuel levels inside the divided compartments  1   a ,  1   b  are maintained in balance via a siphon  2 . 
         [0005]    A fuel pump module  3  is disposed in the divided compartment  1   b , and in an outlet of the fuel pump module  3 , a bypass pressure regulator  4  is disposed. A conduit pipe  5  is connected to an outlet of the regulator  4 , whereby a liquid fuel is supplied through the conduit pipe  5  to a nozzle  6   a  of an injection pump  6 . The injection pump  6  is operated by the liquid fuel, which is supplied to the nozzle  6   a , such that fuel is suctioned through the interior of the siphon  2  from each of two respective fuel pickups  2   a ,  2   b.    
         [0006]    As a result thereof, the fuel levels in the divided compartments  1   a ,  1   b  are maintained in balance via the siphon  2 , and the overall fuel level of the vehicle can be monitored with a single fuel level sensor  7 . 
         [0007]    In the aforementioned Japanese Laid-Open Patent Publication No. 10-061515, the fuel pickups  2   a ,  2   b , which are disposed at respective ends of the siphon  2 , are arranged on the inside interior walls (inner walls that are mutually adjacent to each other) of the divided compartments  1   a ,  1   b . Owing thereto, there is a concern that when the fuel tank  1  is inclined to the left or to the right upon parking of the vehicle, or when the vehicle is being driven around a curve, a greater than necessary amount of fuel will be transferred via the siphon. 
         [0008]    In particular, in the case that the fuel tank  1  is inclined in the direction of the arrow A 1 , the fuel pickup  2   b  is disposed downwardly from (i.e., at a lower position than) a suction inlet  3   a  of the fuel pump module  3 . Accordingly, almost all of the fuel in the divided compartment  1   b  becomes transferred, via the fuel pickup  2   b , to the side of the divided compartment  1   a . As a result, fuel cannot be supplied through the pump module  3 , and the start-up performance of the engine is deteriorated. 
       SUMMARY OF INVENTION 
       [0009]    The present invention is made to resolve this type of problem. An object of the invention is to provide a fuel tank which suppresses excess transfer of fuel in an amount more than needed between a first reservoir portion and a second reservoir portion, at times when the vehicle is being driven around a curve, or when the vehicle is parked on an incline, and which enables the engine to reliably be started by means of a simple structure. 
         [0010]    The present invention concerns a fuel tank comprising a fuel pump, a first reservoir portion in which the fuel pump is arranged and in which a fuel is retained, a second reservoir portion in which the fuel is retained, and a siphon tube disposed across the first reservoir portion and the second reservoir portion, suction being carried out in the siphon tube via the fuel pump. 
         [0011]    In the fuel tank, an open end of the siphon tube, which opens into the first reservoir portion, is disposed more toward an outer side of the fuel tank than the fuel pump. 
         [0012]    With the present invention, the open end of the siphon tube that opens into the first reservoir portion is disposed more outwardly, i.e., closer to the outer side, than the fuel pump. Owing thereto, when the vehicle is driven around a curve or is parked on an incline, excessive transfer of fuel in an amount more than needed, in particular, from the first reservoir portion in which the fuel pump is disposed to the second reservoir portion, can be prevented from occurring. Accordingly, by means of a simple structure, fuel can reliably be supplied to the engine via the fuel pump, and the start-up performance of the engine can suitably be improved. 
         [0013]    The above objects, features and advantages shall be made clearer from the following explanation of a preferred embodiment of the invention, presented in conjunction with the appended drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  is a schematic structural view of a fuel supply system, in which a fuel tank according to an embodiment of the invention is incorporated; 
           [0015]      FIG. 2  is a view describing the fuel tank in a condition when it is shipped from the factory; 
           [0016]      FIG. 3  is a view describing the fuel tank in a condition when the vehicle is parked on an incline, or when the vehicle is being driven around a curve; 
           [0017]      FIG. 4  is a view describing the fuel tank in a condition when the vehicle is being driven in a continuously revolving manner; and 
           [0018]      FIG. 5  is a view describing a fuel tank level balancing device as disclosed in Japanese Laid-Open Patent Publication No. 10-061515. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0019]    As shown in  FIG. 1 , a fuel tank  10  according to an embodiment of the present invention is incorporated into a fuel supply system  12 . The fuel tank  10  is constructed as a saddle-type fuel tank, and is mounted onto a non-illustrated vehicle. An upwardly curved saddle portion  14  is disposed in a substantially central bottom part in the vehicle widthwise direction (the direction of the arrow A) of the fuel tank  10 . A main tank portion (first reservoir portion)  16  and a sub-tank portion (second reservoir portion)  18  are formed by the saddle portion  14 . 
         [0020]    A fuel pump module  20  is disposed in the main tank portion  16 . A fuel pump  22  constituting part of the fuel pump module  20  is equipped with a pumping jet pump  24 , having a fuel suction inlet  24   a  that opens at a bottom part  16   a  of the main tank portion  16 , whereas a pressure regulator  26  is connected on an outlet side of the fuel pump  22 . 
         [0021]    The pressure regulator  26  supplies fuel F to a non-illustrated engine via a fuel pipeline  28  and comprises a suction branching pipe  30 . On one end (lower end) of the suction branching pipe  30 , a suction jet pump  32  is provided. 
         [0022]    Inside the fuel tank  10 , a siphon tube  34  is arranged across each of bottom parts  16   a ,  18   a  of the main tank portion  16  and the sub-tank portion  18 . A three-way joint  36  is disposed at a midway upper side portion of the siphon tube  34 , and in the three-way joint  36 , a suction connector  36   a  is arranged, in which a backflow prevention valve  38  is disposed. One end of a suction tube  40  is connected to the suction connector  36   a , and the other end of the suction tube  40  is connected to a suction side (negative pressure side) of the suction jet pump  32 . 
         [0023]    An open end  34   a  of the siphon tube  34  on the side of the main tank portion  16  is disposed more toward the outer side than the suction jet pump  32 , or more specifically, is disposed on the bottom part  16   a  of the main tank portion  16  adjacent to an outside inner wall  16   b , which is separated from the sub-tank portion  18 . A switching valve  42   a  is installed in the open end  34   a . The switching valve  42   a  closes the open end  34   a  upon detection of air, while on the other hand, causes the open end  34   a  to be opened upon detection of fluid therein. 
         [0024]    An open end  34   b  of the siphon tube  34  on the side of the sub-tank portion  18 , in a similar manner, is disposed on the bottom part  18   a  of the sub-tank portion  18  adjacent to an outside inner wall  18   b , which is separated from the main tank portion  16 . In the open end  34   b , a switching valve  42   b  is installed, which is closed upon detection of air, while on the other hand, is opened upon detection of liquid therein. 
         [0025]    A float  44  for detecting the position of a liquid surface Fs of the fuel F stored in the main tank portion  16  is disposed in the fuel pump module  20 . A fuel gauge  46 , which detects the remaining fuel amount from the liquid surface Fs detected by the float  44 , is connected to an ECU (electronic control unit)  48  that serves as a controller. An inclination angle detecting sensor (fuel imbalance condition detector)  50 , which detects an inclination angle of the fuel tank  10 , and a yaw rate sensor (fuel imbalance condition detector)  52 , which detects a yaw rate of the fuel tank  10 , are connected to the ECU  48 . 
         [0026]    Operations of the fuel tank  10  shall be described below in relation to the fuel supply system  12  in which the fuel tank  10  is incorporated. 
         [0027]    At first, as shown in  FIG. 2 , for example, when shipped from the factory, start-up of the engine is performed in a state where the fuel F is retained only in the main tank portion  16 . Owing thereto, the fuel pump  22  that constitutes the fuel pump module  20  is driven, and the fuel F, which is stored in the main tank portion  16 , is drawn in from the fuel suction inlet  24   a  under an action of the pumping jet pump  24 . 
         [0028]    The fuel F is supplied to the engine from the pressure regulator  26  and via the fuel pipeline  28 . On the other hand, the fuel F is supplied to the suction jet pump  32  via the suction branching pipe  30 , whereby a negative pressure is generated in the suction tube  40 . The suction tube  40  communicates with the siphon tube  34  via the three-way joint  36 , and suction is generated in the interior of the siphon tube  34 . 
         [0029]    Concerning the siphon tube  34 , one open end  34   a  thereof is disposed inside the fuel F which is retained in the main tank portion  16 , whereas the other open end  34   b  thereof is arranged in the sub-tank portion  18 , which contains no fuel F therein, while the switching valve  42   b  thereof is closed. Accordingly, under an action of the suction jet pump  32 , the interior of the siphon tube  34  is subjected to suction, and the fuel F, which is suctioned up from the one open end  34   a  of the siphon tube  34  is transferred over to the other open end  34   b  side of the siphon tube  34 . 
         [0030]    At the open end  34   b , as a result of the fuel F being supplied thereto, the switching valve  42   b  opens and the fuel F from the main tank portion  16  side is delivered to the sub-tank portion  18  side, whereupon a siphoning function is brought about by the siphon tube  34 . Owing thereto, respective liquid surfaces Fs of the fuel F in the main tank portion  16  and the fuel F that is transferred into the sub-tank portion  18  arrive at positions having the same height. 
         [0031]    Further, as shown in  FIG. 3 , when the vehicle is parked on an incline, or when the vehicle is driven around a curve, a condition occurs in which the fuel tank  10  becomes inclined with respect to the vehicle widthwise direction (the direction of arrow A). Accordingly, it is easy for the fuel F retained in the main tank portion  16  and the fuel F maintained in the sub-tank portion  18  to become unbalanced. 
         [0032]    Consequently, in a condition where the vehicle is parked on an incline, the inclination angle detecting sensor  50  detects the inclination angle of the fuel tank  10 , and when it is judged that the detected inclination angle is equal to or greater than a preset angle (for example, 5° to 6°), detection of the remaining fuel amount by the fuel gauge  46  is regulated for a fixed time only by the ECU  48 . 
         [0033]    Further, when the vehicle is being driven around a curve, the yaw rate is detected by the yaw rate sensor  52 , and when it is judged that the detected yaw rate (horizontal G) is equal to or greater than a preset value (e.g., 0.1 G), detection of the remaining fuel amount by the fuel gauge  46  is regulated for a fixed time only. 
         [0034]    Still further, when the inclination angle detected by the inclination angle detecting sensor  50  is equal to or greater than the preset angle, or when the yaw rate detected by the yaw rate sensor  52  is equal to or greater than the preset value, detection of the remaining amount by the fuel gauge  46  is halted for a fixed time only, and when normal conditions are restored and after a predetermined time thereafter (the time required for the fuel in the main tank portion  16  and the sub-tank portion  18  to be placed in balance by the siphon tube  34 ), detection of the remaining amount can be carried out again. 
         [0035]    As a result thereof, by regulating the detection of the remaining fuel amount in cases where a liquid surface difference at or above a prescribed value is generated between the main tank portion  16  and the sub-tank portion  18 , errors in detection of the remaining fuel amount can be prevented. 
         [0036]    At the inclined condition of the fuel tank  10  shown in  FIG. 3 , by means of the siphoning effect of the siphon tube  34 , the fuel F in the main tank portion  16 , which is inclined upwardly, is transferred into the sub-tank portion  18  that is located on the downward side. Owing thereto, the liquid surfaces Fs of the main tank portion  16  and the sub-tank portion  18 , respectively, can be adjusted to attain the same position. 
         [0037]    Further, when the engine is stopped, under operation of the backflow prevention valve  38 , which is arranged in the suction connector  36   a  of the three-way joint  36 , backflow from the suction tube  40  to the side of the siphon tube  34  does not occur. Accordingly, the siphon tube  34  can possess a desired siphoning effect, and the function whereby each of the liquid surfaces Fs of the main tank portion  16  and the sub-tank portion  18  are kept in balance can be continued and maintained. 
         [0038]    In this case, according to the present embodiment, the open end  34   a  of the siphon tube  34  on the side of the main tank portion  16  is arranged more outwardly (more toward the outer side) than the suction jet pump  32 . More specifically, both open ends  34   a ,  34   b  of the siphon tube  34  are disposed on respective bottom parts  16   a ,  18   a  of the main tank portion  16  and the sub-tank portion  18 , and further, are disposed adjacent to the outside inner walls  16   b ,  18   b  that are separated mutually from each other. Owing thereto, when the main tank portion  16  becomes inclined with the sub-tank portion  18  being oriented downwardly therefrom, the fuel suction inlet  24   a  of the fuel pump  22  is positioned lower than the open end  34   a  of the siphon tube  34  (see  FIG. 3 ). 
         [0039]    As a result thereof, when the vehicle is being driven around a curve or is parked on an incline, in particular, excessive transfer of the fuel F from the main tank portion  16  in which the fuel pump  22  is disposed into the sub-tank portion  18  can be prevented from occurring. Accordingly, with a simple structure, the fuel F can reliably be supplied to the engine through the fuel pump  22 , and the start-up performance of the engine can suitably be improved. 
         [0040]    Still further, as shown in  FIG. 4 , by the vehicle being driven in a continuously revolving manner or the like, a case may occur in which the liquid surfaces Fs inside the fuel tank  10  experience vertical variations. At this time, the switching valves  42   a ,  42   b  are installed, respectively, in both open ends  34   a ,  34   b  of the siphon tube  34 , and the open ends  34   a ,  34   b  are opened only at a time when fuel F is present therein. Owing thereto, introduction of air into the interior of the siphon tube  34  is prevented, and a suitable siphoning effect can reliably be maintained. 
         [0041]    In addition, by continuously operating the suction jet pump  32  via the fuel pump  22 , suction is normally created in the siphon tube  34  via the three-way joint  36 . As a result thereof, the siphon tube  34  can reliably and suitably maintain the desired siphoning effect, so that faults in the fuel supply to the engine can be suppressed.