Abstract:
An internal combustion engine fuel supply system includes a fuel discharge apparatus having a vapor removal system. The fuel discharge apparatus includes an apparatus body, a fuel chamber defined in the body, a fuel inlet connected to a fuel tank, a fuel supply path partially defined by the fuel inlet and connecting the fuel chamber to the fuel tank, a fuel discharge outlet, a fuel return outlet for return of excess fuel to the fuel tank, and a reflux path connecting the fuel supply path to the fuel return outlet. A vapor blocking member is provided in the fuel supply path at a bifurcation point at which the reflux path branches from the fuel supply path. The reflux path is arranged such that vapor blocked by the vapor blocking member rises from the bifurcation point and through the reflux path to the fuel return outlet due to self-buoyancy of the vapor.

Description:
[0001]    This is a continuation application of international application PCT/JP02/07469, filed Jul. 24, 2002. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention pertains to a vapor removal apparatus for a fuel supply system used in an internal combustion engine.  
           [0004]    2. Description of the Related Art  
           [0005]    As an internal combustion engine, an engine equipped with a fixed Venturi-type vaporizer  1  such as that shown in FIG. 5, for example, is known in the conventional art.  
           [0006]    A fuel supply system that supplies fuel F held in a fuel tank  2  to the vaporizer  1  is mounted to the vaporizer  1 .  
           [0007]    The fuel supply system is equipped with a fuel supply path  4  that fluidically connects the fuel tank  2  with a float chamber  3  mounted to the vaporizer  1 , and a fuel pump  5  coupled in the fuel supply path  4  to supply the fuel F from the fuel tank  2  to the float chamber  3 .  
           [0008]    In this type of fuel supply system, when the fuel F is sucked into the fuel pump  5 , air bubbles may be generated in the suctioned fuel F due to negative pressure.  
           [0009]    These air bubbles include vapor generated in the fuel F due to the increase in ambient temperature which accompanies the heating up of the engine. The term “vapor” refers generically to non-liquid gaseous material such as air bubbles and fuel vapor.  
           [0010]    When the air bubbles and vapor are generated in this way, it is assumed that they will be supplied to the vaporizer  1  via the float chamber  3  together with the fuel F. When the fuel F in which the air bubbles and vapor are mixed is supplied to the vaporizer  1 , the following problems occur: (1) an unstable air/fuel ratio in the air-fuel mixture generated in the vaporizer  1 , and (2) difficulty in restarting the engine.  
           [0011]    Accordingly, in an internal combustion engine in which a large amount of vapor or air bubbles are generated because the thermal ambient conditions are poor, or because the engine is susceptible to vibration, a vapor separation tank  6  that temporarily holds the fuel F sent from the fuel pump  5  is located downstream of the fuel pump  5  at a point in the fuel supply path  4 , such that in this vapor separation tank  6 , the vapor and air bubbles are separated so as to rise to the top of the vapor separation tank  6  due to their buoyancy, and the vapor and air bubbles are expelled toward the fuel tank  2  via the vapor return path  7  located at the top of the vapor separation tank  6 .  
           [0012]    However, in this conventional type of fuel supply system for an internal combustion engine, the following problem requiring correction remains.  
           [0013]    That is, while the fuel F is being held in the vapor separation tank  6 , the vapor and air bubbles are separated using their own buoyancy, but when the vapor separation tank  6  is shaken by engine vibration or for some other reason, the fuel F being held in the vapor separation tank  6  is churned. As a result, the vapor and air bubbles are not separated, and therefore, the vapor and air bubbles end up being sent into the vaporizer  1  together with the fuel F.  
         SUMMARY OF THE INVENTION  
         [0014]    The present invention was created in view of the problems that arise in the conventional art, and an object of the present invention is to provide a vapor removal apparatus for a fuel supply system in an internal combustion engine that can reliably remove the vapor generated in the fuel system by guiding it to the fuel tank.  
           [0015]    In order to resolve the problems described above in an internal combustion engine fuel supply system according to the present invention a fuel supply passage fluidically connects a fuel supply apparatus to a fuel tank and a vapor return path branches off from the fuel supply passage and is connected to the fuel tank. A surface tension generating member is provided at a bifurcation point where the vapor return path branches off from the fuel supply passage, so as to cover an opening leading to the fuel supply apparatus and thereby serve as a vapor blocking member.  
           [0016]    According to an embodiment of the present invention, a vapor separation tank that temporarily holds fuel supplied from the fuel tank is provided at the bifurcation point, the vapor return path is connected to the top of this vapor separation tank, an opening leading to the fuel supply apparatus is formed at the bottom of the vapor separation tank, and the surface tension generating member is provided so as to cover this opening. The fuel supply apparatus comprises a vaporizer, and the fuel supply path from the bifurcation point is connected to a float chamber in the vaporizer.  
           [0017]    According to another embodiment of the present invention, the fuel supply apparatus is embodied as a fuel discharge apparatus that is operable to discharge (e.g., inject) fuel into an engine cylinder. The fuel discharge apparatus is arranged in a fuel supply system for an internal combustion system that includes a fuel tank, the fuel discharge apparatus, a fuel supply passage connecting the fuel discharge apparatus to the fuel tank to enable supply of fuel from the fuel tank to the fuel discharge apparatus, and a return passage connecting the fuel tank to the fuel discharge apparatus to enable return of excess fuel from the fuel discharge apparatus to the fuel tank.  
           [0018]    The fuel discharge apparatus preferably comprises: a fuel discharge apparatus body; a fuel chamber defined within the fuel discharge apparatus body; a fuel inlet fluidically connected to the fuel tank; a fuel supply path at least partially defined by the fuel inlet and fluidically connected to the fuel chamber to supply fuel from the fuel tank to the fuel chamber; a fuel discharge outlet fluidically connected to the fuel chamber for discharging fuel from the fuel chamber; a fuel return outlet fluidically connected to the fuel tank via the return passage to allow return of excess fuel to the fuel tank; a reflux path defined in the fuel discharge apparatus body and being fluidically connected between the fuel supply path and the fuel return outlet to allow flow of the excess fuel from the fuel supply path to the fuel return outlet, the reflux path being connected to the fuel supply path at a bifurcation point; and a vapor blocking member provided in the fuel supply path at the bifurcation point to block entry of vapor into the fuel chamber; wherein the reflux path is arranged such that the vapor blocked by the vapor blocking member rises from the bifurcation point and through the reflux path to the fuel return outlet due to self-buoyancy of the vapor.  
           [0019]    The fuel return outlet of the fuel discharge apparatus is preferably disposed vertically above the bifurcation point.  
           [0020]    A fuel pump is preferably operably coupled in the fuel supply passage so as to be located downstream of the fuel tank and upstream of the bifurcation point.  
           [0021]    An inlet check valve is preferably disposed in the fuel supply path between the bifurcation point and the fuel chamber.  
           [0022]    A plunger pump is preferably disposed in the fuel discharge apparatus body, the plunger pump comprising a cylinder mounted in the fuel discharge apparatus body, a plunger slidably disposed in the cylinder for reciprocating movement therein, and a solenoid coil disposed around the cylinder for actuating the plunger to slide within the cylinder; and the reflux path preferably extends in an axial direction of the plunger pump between the cylinder and the solenoid coil.  
           [0023]    The reflux path is preferably connected to the fuel supply path at a bifurcation point in such a manner that the reflux path branches off from the fuel supply path at the bifurcation point and originates at the fuel supply path and leads from the fuel supply path to the fuel return outlet.  
           [0024]    A fuel injection nozzle is preferably provided at the fuel discharge outlet, and a plunger pump is preferably disposed in the fuel discharge apparatus body and operably connected with the fuel chamber to pressurize fuel in the fuel chamber to thereby enable discharge of the fuel from the fuel discharge outlet through the fuel injection nozzle.  
           [0025]    The bifurcation point is preferably disposed within the fuel discharge apparatus body.  
           [0026]    The vapor blocking member preferably comprises a surface tension generating member, and the suitable materials from which the tension generating member can be formed include a porous paper sheet, a perforated metal plate, a sintered body having continuous pores, and a non-woven fabric. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    [0027]FIG. 1 is a schematic structural drawing of a fuel supply system according to a first embodiment of the present invention;  
         [0028]    [0028]FIGS. 2A-2C are drawings to explain the operation of a surface tension generating member according to the present invention;  
         [0029]    [0029]FIG. 3 is a vertical cross-sectional view of a fuel supply apparatus according to a second embodiment of the present invention;  
         [0030]    [0030]FIG. 4 is a horizontal cross-sectional view of a fuel supply apparatus according to a variation of the second embodiment of the present invention; and  
         [0031]    [0031]FIG. 5 is a schematic structural drawing showing an example of a conventional fuel supply system. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]    Embodiments of the present invention will be described below with reference to FIGS. 1-4.  
         [0033]    [0033]FIG. 1 shows an internal combustion engine fuel supply system according to a first embodiment of the present invention. A vaporizer  10  serves as a fuel supply apparatus to supply an air-fuel mixture to the internal combustion engine. The vaporizer  10  is equipped with a main body  9  in which is formed an air intake path  11   a.    
         [0034]    A float chamber  11  that holds fuel F is located below the main body  9 , and a fuel tank  13  is connected to the float chamber  11  via a fuel supply path  12 .  
         [0035]    Partway down the fuel supply path  12  is located a fuel pump  14  that sends the fuel F held in the fuel tank  13  to the float chamber  11  of the vaporizer  10 . A vapor separation tank  15  is located between the fuel pump  14  and the float chamber  11  and serves to temporarily hold the fuel F sent to the float chamber.  
         [0036]    The fuel pump  14  is connected to the vapor separation tank  15  at a top part thereof, while the float chamber  11  is connected to the vapor separation tank  15  at a bottom part thereof.  
         [0037]    Furthermore, a vapor return path  16  is connected to a top part of the vapor separation tank  15  so as to fluidically connect the vapor separation tank  15  to an empty space in a top portion of the fuel tank  13 .  
         [0038]    In the vapor return path  16 , the vapor and air bubbles separated from the fuel F in the vapor separation tank  15  are expelled toward the fuel tank  13  due to their own buoyancy, and the residual fuel F passing through a restriction  17  located along the return path  16  is returned to the fuel tank  13 .  
         [0039]    Also, in this embodiment, a surface tension generating member  18  is located at a bifurcation point at which the return path  16  branches off from the fuel supply path  12  so as to cover an opening that is formed in the vapor separation tank  15  and leads to the fuel supply apparatus (i.e., the vaporizer  10 ).  
         [0040]    The surface tension generating member  18  is a sheet comprising, for example, a porous paper sheet, a perforated metal plate, such as a punched plate or a screen, or a porous sintered body or nonwoven fabric.  
         [0041]    The surface tension generating member  18  will be described in detail below with reference to FIGS. 2A-2C.  
         [0042]    The surface tension generating member  18  has numerous pores  18   a  (one of which is shown in FIG. 2A), and the fuel F passes through these pores  18   a.    
         [0043]    As shown in FIG. 2A, where both sides of the surface tension generating member  18  are permeated by the fuel F, the fuel F is caused to pass through the pores  18   a  of the surface tension generating member  18  due to the difference in pressure ΔP between the pressure at the upstream side of the surface tension generating member  18  and the pressure at the downstream side thereof, as shown in FIG. 2A.  
         [0044]    On the other hand, where vapor V has entered a pore  18   a , as shown in FIG. 2B, a liquid surface is formed by the fuel F on the downstream side of the pore  18   a , surface tension is generated on this liquid surface, and this surface tension creates resistance to prevent the vapor V from passing through the pore  18   a.    
         [0045]    For the vapor V to pass through the surface tension generating member  18 , the pressure difference ΔP must equal or exceed the expulsion pressure P 1  that is necessary to overcome the surface tension.  
         [0046]    Accordingly, as shown in FIG. 2C, when the pressure difference ΔP between the two sides of the surface tension generating member  18  is in a smaller range than the expulsion pressure P 1 , the vapor V does not pass through the surface tension generating member  18 , and only the fuel F passes through the surface tension generating member  18 . Thus, the surface tension generating member  18  serves as a vapor blocking member that allows flow of fuel therethrough but inhibits or prevents flow of vapor therethrough at least under prescribed conditions.  
         [0047]    In FIG. 2C, Q is the quantity of vapor (e.g., air) passing through the surface tension generating member  18 .  
         [0048]    Accordingly, in this embodiment, even where air bubbles become mixed into the fuel F due to vibration or the like at the bifurcation point at which the vapor return path  16  branches off from the fuel supply path  12 , i.e., in the vapor separation tank  15 , and the air bubbles reach the opening leading to the vaporizer  10 , the air bubbles are prevented from entering the vaporizer  10  due to the operation of the surface tension generating member  18 .  
         [0049]    [0049]FIG. 3 shows a second embodiment of the present invention, wherein a fuel injection apparatus  30  is used as the fuel supply (discharge) apparatus described above, and wherein a reflux path  39  branches off from the fuel supply path  12  at a bifurcation point and leads to a return passage  16 . The bifurcation point is located within the fuel injection apparatus  30 .  
         [0050]    To describe this arrangement in detail, the fuel injection apparatus  30  includes a body  31 , a plunger pump P that is mounted inside the body  31  and draws the fuel F in by suction created in a suction stroke and conveys the fuel F by pressure created in a return stroke, and an injection nozzle  32  that is mounted inside the body  31  and injects the fuel F. The plunger pump P comprises a cylinder  33 , a plunger  35  that is slidably mounted inside the cylinder  33  to form a pressure chamber (fuel chamber)  34 , and a solenoid coil  36  that magnetizes the plunger  35 . A suction contact pipe (fuel inlet)  37  that forms at least a portion of the fuel supply path  12  is located at the bottom of the body  31 , a return contact pipe (return outlet)  38  that forms at least a portion of the return path  16  is located at the top of the body  31 , and the reflux path  39  that guides a part of the fuel that has branched off from the fuel supply path  12  to the return passage  16  via the return outlet  38  is located between the cylinder  33  and the solenoid coil  36 .  
         [0051]    In addition, a suction path  33   a  that connects the fuel inlet  37  with the pressure chamber  34  and constitutes part of the fuel supply path  12  is formed at the bottom end of the cylinder  33 , at the bifurcation point at which the reflux path  39  branches off from the fuel supply path  12 . An inlet check valve  40  that operates to permit the fuel F to flow into the pressure chamber  34  only when the plunger  35  is performing a suction stroke is formed partway along the suction path  33   a.    
         [0052]    In this embodiment, a surface tension generating member  41  is located so as to span across the suction path  33   a  at its entrance side (i.e., upstream of the inlet check valve  40 ). For example, as shown in FIG. 3, the surface generating member  41  is preferably mounted so as to cover an upstream opening of a valve body  40   a  of the inlet check valve  40  that forms a valve seat for a valve member  40   b  of the inlet check valve  40 .  
         [0053]    In the fuel injection apparatus  30  having the construction described above, the fuel F is sucked into the pressure chamber  34  via the inlet check valve  40  as the plunger  35  moves up and down. The up-and-down (reciprocating) plunger movement also serves to send the fuel F into the injection nozzle  32  and eject the fuel from the injection nozzle  32 .  
         [0054]    When vapor is mixed in the fuel F supplied from the fuel inlet  37 , the vapor flows into the reflux path  39  due to its own buoyancy and is guided to the fuel tank  13  via the return path  16 .  
         [0055]    Here, even if the vapor is made to flow toward the suction path  33   a , it is prevented from entering the suction path  33   a  by the surface tension generating member  41 , and as a result, vapor is prevented from mixing into the fuel that is to be injected via the injection nozzle  32 .  
         [0056]    The various configurations and sizes of the various constituent elements shown in the embodiments described above are examples only, and various modifications may be made in accordance with design requirements.  
         [0057]    For example, in the second embodiment described above, an example was used in which the surface tension generating member  41  covered the opening to the suction path  33   a , but it is also acceptable if a guide path  42  connected to the suction path  33   a  is formed at a tangent to the cylinder  33  and a surface tension generating member  43  is located so as to cover the opening at the end of the guide path  42 , as shown in FIG. 4.  
         [0058]    Using this construction, the mounting location of the surface tension generating member  43  can be set arbitrarily, or the surface tension generating member  43  can be mounted at a wide part of the reflux path  39 , and thus, the arrangement of the surface tension generating member  43  can be easily determined, and it can be easily mounted.  
         [0059]    As described above, in the vapor removal apparatus for a fuel supply system in an internal combustion engine according to the present invention, when vapor (including, for example, fuel vapor or air bubbles) is mixed into the fuel supplied to the fuel supply apparatus, the fuel vapor and air bubbles can be prevented from passing through and entering the fuel supply apparatus by a surface tension generating apparatus, while an adequate amount of fuel supply is maintained.  
         [0060]    Furthermore, even when the fuel sent to the fuel supply apparatus is churned due to vibration or the like such that the fuel vapor and air bubbles cannot be separated from the fuel by means of their buoyancy, the entry of the fuel vapor and air bubbles into the fuel supply apparatus can be prevented.