Abstract:
A fuel tank assembly for a motorcycle and a method for assembly thereof, in which a fuel pump can reliably suck in fuel when a fuel level fluctuates in response to acceleration, deceleration or changing posture of the motorcycle, and when there is little fuel in the tank. The invention provides a cup disposed on the bottom of the fuel tank which may house a fuel pump and a fuel suction filter. Because the fuel suction filter is mounted within the cup, it is not necessary to pass the filter through a hole in the bottom of the tank during assembly. This allows the use of a large filter without forming a large hole in the tank, and further increases the fuel capacity of the tank. A peripheral edge of the tank opening hinders the flow of fuel from the cup to the tank during changes in motorcycle posture, which maintains the fuel suction filter&#39;s submergence in fuel.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a fuel tank assembly for a motorcycle, and a method of assembling the fuel tank assembly. More particularly, a fuel tank is described in which the fuel pump can reliably suck in fuel when the fuel level is low and when the fuel level fluctuates extensively. 
     2. Background Art 
     A configuration of a motorcycle fuel tank is known which includes a fuel pump at the bottom of the fuel tank, the pump serving to suck in fuel from the bottom of the tank. This arrangement is disclosed in Japanese Patent Laid-Open No. Hei. 1-257686, entitled “Fuel Tank”. In FIGS. 1 through 3 and 5 of the related art, a pair of right and left main frames 14, 14 extend rearwardly from the rear end of a cylindrical steering shaft 12 of the body frame 10. A fuel tank 50 is placed on the main frames 14, has a protrusion 52 formed at the bottom thereof, and extends downwardly through the main frames 14. The protrusion 52 has an opening 64 on its bottom, through which a fuel pump 62 and a filter 73 are inserted into the fuel tank 50. The opening 64 is closed by a cover plate 66. 
     In the foregoing background art the filter 73 may be exposed to air if the fuel tank 50 houses a small amount of fuel, and if the fuel level fluctuates extensively due to acceleration deceleration or a change in posture of the motorcycle. This result is undesirable because when air is sucked in via the exposed filter 73, the fuel pump 62 rotates idly and cannot reliably suck fuel in. 
     In order to improve the suction performance of the fuel pump, the suction resistance of the filter may be reduced by using a large filter 73. However, the larger the filter 73, the larger the opening 64 must be in order to allow insertion of the filter into the tank. In order to maintain the rigidity of the fuel tank 50 with such a large filter, either a peripheral edge of the large opening 64 must be reinforced, or the fuel tank 50 must be thickened. These modifications are undesirable because they increase the weight and cost of manufacture of the fuel tank. 
     SUMMARY OF THE INVENTION 
     The fuel tank assembly of the present invention overcomes one or more of the disadvantages associated with conventional fuel tank assemblies. 
     The invention provides an apparatus and method of assembly that enable fuel to be reliably sucked in by a fuel pump even when the fuel tank houses a small amount of fuel, and further when the fuel level fluctuates extensively due to acceleration, deceleration or changing posture of a motorcycle. 
     The invention also provides an apparatus and method of assembly allowing the installation of a large fuel suction filter in a fuel tank having a small opening. 
     The invention further provides an apparatus and method of assembly allowing the use of a large fuel suction filter without reinforcement of a peripheral edge of the tank opening. 
     The invention additionally provides a fuel tank assembly of increased capacity. 
     In order to accomplish the foregoing objects, a motorcycle fuel tank assembly is provided having a fuel pump unit which is partially disposed in a cup having an open end, a fuel suction filter of the fuel pump unit is disposed within the cup, an opening having a diameter smaller than an inner diameter of the cup is formed on a bottom surface of the fuel tank, a portion of the fuel pump unit is inserted into the fuel tank via the opening, and the cup is attached to the fuel tank, thus forming a fuel tank assembly. Portions of the fuel pump unit which may be inserted through the opening into the fuel tank include the fuel pump, a flow path filter, connecting hoses, etc. 
     In this configuration, when the fuel level in the tank fluctuates extensively due to acceleration, deceleration or changing attitude of the motorcycle, and while there is a small amount of fuel in the fuel tank, a peripheral edge of the small opening prevents fuel from flowing into the fuel tank from the cup. As a result, the fuel suction filter is not exposed to air and can therefore reliably suck fuel without drawing air. 
     Because the relatively large fuel suction filter is housed within the cup, and need not pass through the opening in the fuel tank during assembly, the opening for inserting the fuel pump into the fuel tank may have a diameter which is smaller than an inner diameter of the cup. Therefore, it is not necessary to reinforce the peripheral edge of the small opening. It is further not necessary to thicken the fuel tank. 
     Further scope and applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, and various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
     FIG. 1 is a perspective view of a motorcycle to which the invention is applicable. 
     FIG. 2 is a side elevation of the fuel tank assembly and the elements of the motorcycle in the vicinity of the fuel tank. 
     FIG. 3 is a sectional view taken along line  3 — 3  in FIG.  2 . 
     FIG. 4 is a sectional view of the fuel pump unit mounting structure of the invention. 
     FIG. 5 is an exploded perspective view of the fuel pump unit mounting structure. 
     FIGS. 6 a  and  6   b  show the operation of the fuel tank assembly. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention will be described with reference to an embodiment shown in the accompanying drawings. “Front, rear, right, left, upper and lower” sides denote directions as viewed by a rider. “Fr” denotes the front side, “Rr” denotes the rear side, “L” denotes the left side, and “R” denotes the right side. 
     FIG. 1 is a perspective view of the motorcycle to which the invention is applicable. The motorcycle  1  is of a fill cowling type, and includes an upper cowl  2  covering the front upper part of a body frame (not shown), a windscreen  3  attached to the upper part of the upper cowl  2 , an inner half cowl  4  covering the front lower part of the body frame, right and left lower cowls  5  covering front lower sides of the body frame (only the left lower cowl  5  is shown in FIG.  1 ), a seat cowl  7  surrounding the lower part of a seat  6  at the rear part of the body frame, a front mudguard  9  covering the upper part of a front wheel  8 , and a rear mudguard  12  covering the upper part of a rear wheel  11 . The motorcycle  1  also includes a fuel tank  41  in front of the seat  6 . Reference numeral  21  represents a steering bar handle,  22  represents a window for a head lamp and indicators,  23  represents mirrors,  24  represents a muffler,  25  represents a rear grab rail,  26  represents tail lamps, and  27  represents a center stand. 
     FIG. 2 is a side sectional view of selected elements of the motorcycle in the vicinity of the fuel tank assembly  40 , specifically showing the relationship between the body frame  31  and the fuel tank  41 . The body frame  31  includes a head pipe  31   a,  and a pair of right and left main frames  31   b  extending obliquely downward from the head pipe  31   a.  An engine  32  is attached to the front lower parts of the main frames  31   b,  and an air cleaner  33  and the fuel tank  41  are disposed at the front upper parts of the main frame  31   b.  An outlet of the air cleaner  33  is connected to an inlet port of the engine  32  via passage  32   a  in throttle body  34 . The fuel tank  41  includes a thin front half  42  covering the upper part of the air cleaner  33  and a thick rear half  43  extending further downward compared with the front half  42 . A fuel pump unit  50  is provided on the bottom surface  44  of the thick rear half  43  of tank  41 . Reference numeral  32   b  represents an exhaust port of the engine,  35  and  36  represent fuel tank supporting stays,  37  represents an oil tank,  45  represents a lid located within recessed portion  46 , and  47  represents a fuel pipe. 
     FIG. 3 is a sectional view taken along line  3 — 3  in FIG. 2, specifically showing that a pair of right and left protrusions  48  extend downwardly from a bottom surface  44  at the rear half  43  of the fuel tank  41 , and that the fuel pump unit  50  is disposed at the center of the bottom surface  44  of the rear half  43 . A fuel pump mounting structure of the invention has a cross-section as shown in FIG. 4, in which the relationship between the fuel tank  41  and the fuel pump unit  50  (refer to FIG. 3) is shown on an enlarged scale. 
     FIG. 4 is a sectional view of the fuel pump unit mounting structure. The fuel pump unit  50  includes: a cup  51  having an open end or top, and a predetermined depth; a fuel suction filter  52  positioned near the bottom  51   a  of the cup  51 ; the fuel pump  53  having a suction port  53   a  connected to the fuel suction filter  52 ; a flow path filter  55  connected to a discharge port  53   b  of the fuel pump  53  using a first hose  54 ; a fuel supply port  57  connected to the flow path filter  55  using a second hose  56 ; a return pipe  58  provided on the bottom  51   a  of the cup  51 ; a stand  59  supporting the fuel pump  53  in the cup  51  and the flow path filter  55 ; and an external connector  63  connected to the fuel pump  53  using two lead wires  61  and  62 . 
     Specifically, in the fuel pump unit  50 , the fuel pump  53  is arranged above the fuel suction filter  52 . A fuel path made of the first curved hose  54  (in the shape of an inverted U) extends downwardly from a fuel discharge port  53   b  at the upper part of the fuel pump  53 . The flow path filter  55 , second hose  56  and fuel supply port  57  are positioned below an outlet of the first hose  54 . The fuel supply port  57  is then connected to the bottom  51   a  of the cup  51 . The fuel flow path of the fuel pump unit  50  is therefore substantially in the shape of an inverted U. In the fuel pump unit  50 , the fuel pump  53 , the first hose  54 , the flow path filter  55  and second hose  56  all project upwardly from the cup  51 . These parts are collectively referred to as the “projecting part  50 A” for convenience. The essential parts of the fuel pump  53  can include the majority of the fuel pump unit elements, except for the suction port  53   a  and discharge port  53   b.    
     In the cup  51 , the fuel supply port  57 , the return pipe  58  and the external connector  63  are arranged on the bottom  51   a  in such a manner so as to not overlap with the fuel suction filter  52 . The cup  51  has a flange  51   b  at its open top end which may be an integral part of the cup. The fuel suction filter  52  has a diameter which is larger than that of the fuel pump  53 , in order to obtain a sufficient filtering area and a reduced suction resistance. However, an inner diameter D 3  of the cup  51  can be easily determined in accordance with the diameter of the fuel suction filter  52 . The reduced suction resistance of the fuel suction filter  52  improves the suction performance of the fuel pump  53 . In this configuration, the fuel suction filter  52  is located between the opening  44   a  in the bottom surface  44  of the tank and the bottom of the cup  51   a,  and is spaced above the bottom of the cup  51   a.    
     An electric motor driven pump or an electromagnetic plunger pump are suitable for use as the fuel pump  53 . The return pipe  58  returns fuel to the cup  51  from a fuel supply system (not shown). 
     The stand  59  is in the shape of a channel and extends upwardly from the bottom  51   a  of the cup  51 . The stand  59  supports, near its center, the underside of the fuel pump  53  via a cushion  64  placed on a lateral stay  59   a  and, at its upper part, supports a top part of the fuel pump  53  using a band  65 . The stand  59  also fixedly supports the flow path filter  55  behind the fuel pump  53 , which is secured by a band  66 . The fuel pump unit  50  is therefore integrally assembled on the bottom  51   a  of the cup  51 . 
     As for the fuel pump unit mounting structure, the cup  51  is attached on the bottom  44  of the fuel tank  41  in the following manner An opening  44   a  is formed on the bottom  44  of the fuel tank  41 , and an edge  44   b  of the opening  44   a  is stepped slightly downward. A fixing ring  71  is fixedly attached around the edge  44   a;  a seal ring  72  is brought into contact with the edge  44   a;  an annular lining  73  is attached under the seal ring  72 ; a flange  51   b  of the cup  51  is attached under the annular lining  73 ; and a flange  51   b  is fastened to the fixing ring  71  using nuts  74  and bolts  75 . The edge  44   b  slightly projects from the bottom  44 , resulting in a very rigid fuel tank  41 . 
     The method of assembling the fuel tank assembly will now be more fully described. The fuel pump unit  50  is attached to the fuel tank  41  by inserting the projecting part  50 A into the fuel tank  41 . Elements of the fuel pump unit such as the fuel pump, the flow path filter and connecting hoses may be inserted so that they extend into the interior of the fuel tank  41 . Thereafter, the cup  51  is attached to the bottom surface  44  of the fuel tank, and forms a seal with the fuel tank  41 . The fuel pump unit is secured within the fuel tank by virtue of its attachment to the cup  51 , and the added free volume of the cup  51  increases the capacity of the fuel tank  41 . 
     The opening  44   a  is a small hole which allows the projecting part  50 A to pass through to reach the interior of the fuel tank  41 . A diameter D 1  of the opening  44   a  is slightly larger than the maximum width D 2  of the projection  50 A. Further, since it is not necessary to insert the fuel suction filter  52  through the opening  44   a,  the diameter D 1  of the opening  44   a  can be made smaller than an inner diameter D 3  of the cup  51 . The small opening  44   a  does not adversely affect the rigidity of the fuel tank  41 . Therefore, it is not necessary to thicken the fuel tank  41  or to attach a reinforcing ring around the opening  44   a  in order to strengthen the fuel tank  41 . This simplifies construction of the fuel tank  41  and reduces its weight. 
     The fuel suction filter  52  of the fuel pump unit  50  is housed within the cup  51 , which is effective in reducing the height of the projecting part  50 A which is inserted into the fuel tank  41 . The top level of the projecting part  50 A is lowered in the fuel tank  41 , so that other components (such as a float type level meter, or pipes) can be easily arranged within the tank. 
     The fuel flow will now be described. The fuel tank  41  and cup  51  communicate each other via the opening  44   a.  When the fuel pump  53  is activated, fuel in the cup  51  flows to a fuel injection system (not shown) via the fuel suction filter  52 , the fuel pump  53 , the first hose  54 , the flow path filter  55 , the second hose  56 , and finally through the fuel supply port  57 . Superfluous fuel in the fuel injection system is returned to the cup  51  via the return pipe  58 . 
     Referring now to FIG. 5, the fixing ring  71  is a substantially corrugated washer having a plurality of downward projections  71   a  on the underside thereof at specified intervals, and is spotwelded, or attached by some similar process, to the bottom  44  of the fuel tank  41 . Each of the downward projections  71   a  is provided with a downward bolt  74 . The seal ring  72  is formed with a plurality of through-holes  72   a  through which the downward projections  71   a  pass. 
     FIGS.  6 ( a ) and  6 ( b ) show the operation of the fuel tank of the invention. Specifically, FIG.  6 ( a ) is a side view of the rear part of the fuel tank  41 . For the sake of illustration, it is assumed here that there is a small amount of fuel in the fuel tank  41 . If the motorcycle  1  is accelerated, a fuel level L 1  of fuel G is inclined rearwardly. In this state, the edge  44   b  of the opening  44   a  reduces the amount of fuel G flowing from the cup  51  to the fuel tank  41 , and helps to maintain the filter  52  submerged in fuel. 
     FIG.  6 ( b ) is a front sectional view of the rear part of the fuel tank  41 . For the sake of illustration, it is assumed that the motorcycle performs cornering while a small amount fuel is left in the fuel tank  41 . The fuel G flows in the direction in which the motorcycle is inclined, and a fuel level L 2  is maintained at horizontal. The edge  44   b  reduces the amount of fuel flowing from the cup  51  into the fuel tank  41 . 
     As can be seen in FIGS.  6 ( a ) and  6 ( b ), the edge  44   b  extends toward the center of the opening  44   b  by an amount corresponding to a difference between the diameter D 1  of the opening  44   a  and the inner diameter D 3  of the cup  51 . Therefore, the edge  44   b  reduces the amount of fuel G flowing into the fuel tank  41  from the cup  51 . This arrangement prevents fuel G from flowing from the cup  51  into the fuel tank even in the case of acceleration, deceleration or cornering of the motorcycle, when the fuel level L 1  or L 2  is expected to fluctuate excessively. This advantageously prevents the fuel suction filter  52  from being exposed to air, and therefore enables the fuel pump  53  to reliably suck fuel without drawing air. 
     In the foregoing embodiment, the cup  51  may be cylindrical, or formed of any shape or configuration suitable for retention of the fuel suction filter and/or related fuel pump unit elements. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.