Patent Publication Number: US-7591248-B2

Title: Fuel injection system

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a fuel injection system wherein the fuel tank is located below the electronically controlled fuel injection apparatus. 
   2. Description of the Related Art 
   Conventionally, an electronically controlled fuel injection apparatus is known to supply fuel to an engine. In general, an electronically controlled fuel injection apparatus is located below a fuel tank, and there is a case that the fuel tank and the electronically controlled fuel injection apparatus are connected by a fuel supply passage, and fuel is supplied to the electronically controlled fuel injection apparatus from the fuel tank by gravity-drop utilizing head difference. 
   When ambient temperature of an engine rises, vapor is generated in the fuel in the fuel tank or the fuel supply passage. Then, fuel which contains vapor is supplied to the electronically controlled fuel injection apparatus. When vapor is contained in the fuel which is injected from the electronically controlled fuel injection apparatus, an appropriate amount of fuel cannot be injected into an intake passage. Then, problems occur, such that specific air fuel ratio cannot be obtained or malfunctions of restarting occur. 
   It is desirable that vapor is not contained in the fuel which is supplied to the electronically controlled fuel injection apparatus. However, practically, it is impossible to completely prevent vapor from being generated in the fuel which is supplied to an electronically controlled fuel injection apparatus. A conventional configuration to obtain an appropriate air fuel ratio even when fuel which contains vapor is supplied to an electronically controlled fuel injection apparatus is disclosed in Japanese Patent laid-open 2003-42032 (page 3, FIG. 1). In this conventional configuration, a fuel return passage is disposed between an electronically controlled fuel injection apparatus and a fuel tank, and more fuel than the amount to be injected is supplied to the electronically controlled fuel injection apparatus from the fuel tank. Vapor is contained in the supplied fuel at high temperature. Vapor is separated from the fuel inside the electronically controlled fuel injection apparatus, namely, fuel for injection goes downwards and vapor goes upwards. The separated vapor and surplus fuel which was not used by the electronically controlled fuel injection apparatus are returned to the fuel tank through the fuel return passage. In this manner, even when vapor is contained in the fuel which is supplied to an electronically controlled fuel injection apparatus, the fuel to be injected to an engine does not contain vapor and a stable air fuel ratio can be obtained by mixing vapor into the surplus fuel which is returned from the electronically controlled fuel injection apparatus. 
   Conventionally, with a motorcycle, the fuel tank is disposed between the knees or below the seat, and an electronically controlled fuel injection apparatus is disposed below the fuel tank. Then, fuel is supplied to the electronically controlled fuel injection apparatus from the fuel tank by gravity-drop utilizing head difference. With this fuel supply method utilizing head difference, there is an advantage of cost reduction by not having a fuel supply means to supply fuel to an electronically controlled fuel injection apparatus. Further, there is an advantage that vapor moves upwards inside the fuel supply passage and returns to the fuel tank automatically. 
   Depending on the purpose or the layout of an engine, there is a case that the fuel tank has to be located below the electronically controlled fuel injection apparatus. In the case that a fuel tank is located below an electronically controlled fuel injection apparatus, fuel has to be transported upwards to the electronically controlled fuel injection apparatus from the fuel tank via a fuel supply passage by utilizing a fuel pump. 
   In the case that fuel is transported to an electronically controlled fuel injection apparatus from a fuel tank utilizing a fuel pump, fuel transported upwards by the fuel pump returns to the fuel tank via the fuel supply passage when the engine stops, due to lack of stability of a check valve of the fuel pump. Therefore, there arises a problem that fuel supply is delayed when the engine is started or restarted, or that the ease of starting the engine is worsened due to vapor remaining within passages. Further, since the electronically controlled fuel injection apparatus is disposed above the fuel tank, when vapor is contained in the fuel in the fuel supply passage which connects the electronically controlled fuel injection apparatus and the fuel tank, vapor may move upwards through the fuel supply passage, and a large amount of vapor may accumulate in the electronically controlled fuel injection apparatus. Therefore, there arises a problem that fuel containing vapor is injected from the electronically controlled fuel injection apparatus, and an appropriate air fuel ratio cannot be obtained. 
   The present invention was devised in view of the abovementioned problems. The object is to provide a fuel injection system which can inject an appropriate amount of fuel from an electronically controlled fuel injection apparatus while returning vapor existing somewhere in the fuel passages, even in the condition that the fuel tank is disposed below an electronically controlled fuel injection apparatus. 
   SUMMARY OF THE INVENTION 
   To achieve the abovementioned object, the fuel injection system of the present invention comprises a fuel tank, an electronically controlled fuel injection apparatus which is located above the fuel tank, a fuel reservoir chamber which is located above the electronically controlled fuel injection apparatus, a fuel introduction passage which connects the fuel tank and the fuel reservoir chamber, a fuel pump which introduces fuel from the fuel tank to the fuel reservoir chamber via the fuel introduction passage, a first fuel return passage which connects the fuel reservoir chamber and the fuel tank and returns fuel overflowing from the fuel reservoir chamber and vapor to the fuel tank, a fuel supply passage which connects the fuel reservoir chamber and the electronically controlled fuel injection apparatus, a filter which is disposed at some midpoint of the fuel supply passage or in the fuel reservoir chamber for eliminating vapor from fuel passing through the fuel supply passage, and a second fuel return passage which returns surplus fuel from the electronically controlled fuel injection apparatus and connects the electronically controlled fuel injection apparatus with one of the fuel reservoir chamber and the first fuel return passage at a position above the connecting position at which the fuel reservoir chamber connects with the first fuel return passage. 
   The fuel injection system of the present invention comprises an inner space which is formed in the filter, and a branch passage which branches from some midpoint of the second fuel return passage at a position below the connecting position of the first fuel return passage and the fuel reservoir chamber, and the branch passage and the fuel supply passage are connected with the inner space of the filter, and the branch passage is horizontal or declined from the branching position from the second fuel return passage towards the connecting position with the inner space. In the present invention, the connecting position at which the branch passage connects with the second fuel return passage is the highest position, and the connecting position at which the fuel supply passage on the downstream side of the inner space connects with the electronically controlled fuel injection apparatus is the lowest position in the route from the branch passage through the inner space of the filter to the fuel supply passage on the downstream side of the inner space, and the route from the highest position to the lowest position does not have a portion where the height is reversed (i.e. does not have a portion that rises in the direction from the highest position to the lowest position). In the present invention, the inner diameter of the second fuel return passage above the branching position from the branch passage is equal to or larger than 12 millimeters. In the present invention, the inner diameter of the second fuel return passage below the branching position at which the branch passage branches from the second fuel return passage is smaller than that of the second fuel return passage above the branching position. In the present invention, a filter which does not allow foreign particles to pass through but allows vapor to pass through is disposed at the second fuel return passage above the connecting position at which the fuel reservoir chamber connects with the first fuel return passage. In the present invention, the fuel supply passage projects and opens above the fuel level in the fuel reservoir chamber, and a fuel inlet opening which is formed at the fuel supply passage below the fuel level in the fuel reservoir chamber is covered by a filter. In the present invention, a filter which does not allow foreign particles to pass through but allows vapor to pass through is attached to the projected opening portion on the upstream side of the fuel supply passage. 
   With the present invention, fuel in the fuel tank is stored in the fuel reservoir chamber which is disposed above the electronically controlled fuel injection apparatus by a fuel pump. Then, fuel is supplied to the electronically controlled fuel injection apparatus from the fuel reservoir chamber utilizing head difference. Further, the upper portion of the fuel reservoir chamber and the upper portion of the fuel tank is connected by the first fuel return passage. With this structure, vapor can be ejected from the fuel reservoir chamber to the fuel tank via the first fuel return passage, even when vapor is contained in the fuel in the fuel introduction passage from the fuel tank to the fuel reservoir chamber or the fuel stored in the fuel reservoir chamber. Therefore, vapor contained in the fuel supplied from the fuel reservoir chamber to the electronically controlled fuel injection apparatus can be reduced. In this manner, an appropriate air fuel ratio can be obtained by greatly eliminating vapor from the fuel supplied to the electronically controlled fuel injection apparatus, even when the fuel tank is disposed below the electronically controlled fuel injection apparatus. 
   Further, with the present invention, the electronically controlled fuel injection apparatus and some midpoint of the first fuel return passage are connected by the second fuel return passage, and some midpoint of the second fuel return passage is arranged to be above the connecting position at which the fuel reservoir chamber connects with the first fuel return passage. Further, the branch passage which branches from some midpoint of the second fuel return passage at a position below the connecting position at which the fuel reservoir chamber connects with the first fuel return passage is disposed, and the branch passage is connected with some midpoint of the fuel supply passage. The branch passage is arranged to be horizontal or declining at the connecting position at which the branch passage connects with the second fuel return passage. With this structure, vapor contained in the surplus fuel ejected from the electronically controlled fuel injection apparatus to the second fuel return passage can be returned to the fuel tank after moving upwards in the second fuel return passage, without entering into the branch passage. On the other hand, a part of the surplus fuel ejected from the electronically controlled fuel injection apparatus to the second fuel return passage is introduced to the branch passage after eliminating vapor at the branching position at which the branch passage branches from the second fuel return passage. The vapor-eliminated surplus fuel flows into the fuel supply passage from the branch passage. Then, the surplus fuel can be re-supplied in a circulatory manner as the supply fuel to the electronically controlled fuel injection apparatus. As mentioned above, the surplus fuel ejected from the electronically controlled fuel injection apparatus does not return to the fuel tank. Therefore, compared with a system which returns the surplus fuel ejected from the electronically controlled fuel injection apparatus to the fuel tank, fuel can be efficiently re-supplied. 
   The branch passage and the inner space of the filter which is a part of the fuel supply passage are connected, and the surplus fuel from the branch passage flows towards the fuel supply passage at the downstream side. Therefore, even when vapor is accumulated at the filter and generates resistance against the fuel flow for passing through the filter, the flow of the supply fuel to pass through the filter can be smoothed by the flow of the surplus fuel through the inner space. Further, throughout the route from the branch passage through the inner space of the filter to the fuel supply passage at the downstream side of the inner space, there is no portion where the height is reversed from the upper position to the lower position (i.e., there is no rising portion in the direction from the upper position to the lower position). Therefore, the vapor moves upwards and can return from the branch passage to the fuel tank via the second fuel return passage and the first fuel return passage, even when vapor is generated anywhere in the branch passage, the inner space or the fuel supply passage at the downstream side. 
   In either case with a branch passage or without a branch passage, the top portion of the fuel supply passage has an opening portion above the fuel level while passing through the fuel reservoir chamber. With this structure, the vapor generated in the fuel supply passage in a non-operational state can be ejected above the fuel level in the fuel reservoir chamber via the fuel supply passage, and accumulation of vapor to the fuel supply passage can be prevented. Therefore, ease of restarting can be improved. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic drawing showing a first embodiment of a fuel injection system of the present invention. 
       FIG. 2  is an enlarged sectional view of a main part of  FIG. 1 . 
       FIG. 3  is a sectional view of a modified embodiment of  FIG. 2 . 
       FIG. 4  is a sectional view of a modified embodiment of a filter body and a filter shown in  FIG. 2 . 
       FIG. 5  is a sectional view of another modified embodiment of  FIG. 2 . 
       FIG. 6  is a schematic drawing showing a second embodiment of a fuel injection system of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A fuel tank is located below an electronically controlled fuel injection apparatus, and a fuel reservoir chamber is disposed above the electronically controlled fuel injection apparatus. Then, fuel is transported upwards to the fuel reservoir chamber from the fuel tank by a fuel pump, and fuel is supplied to the electronically controlled fuel injection apparatus from the fuel reservoir chamber by head difference. 
   The First Embodiment 
   Next, the present invention is explained with reference to the drawings. 
     FIG. 1  is a schematic drawing of a fuel injection system of the present invention.  FIG. 2  is an enlarged sectional view of a main part of  FIG. 1 . The present invention is devised on the precondition that a fuel tank  10  is located below an electronically controlled fuel injection apparatus  12 . The electronically controlled fuel injection apparatus  12  injects fuel into an intake passage  14  which is connected to an engine (not shown in drawings). The electronically controlled fuel injection apparatus  12  has an injection pump (not shown in drawings), and a vapor separation chamber (not shown in drawings). With the electronically controlled fuel injection apparatus  12 , vapor contained in the fuel introduced inside is collected upwards, and fuel from which vapor is eliminated is injected from a fuel injection nozzle  16 . Then, surplus fuel and vapor are returned outside by a pumping effect of air bubbles (i.e. vapor). The electronically controlled fuel injection apparatus  12  is not limited to the abovementioned structure as long as a large amount of fuel is introduced and a part of the fuel is injected while surplus fuel is returned. 
   In the present invention, a fuel reservoir chamber  18  is disposed above the electronically controlled fuel injection apparatus  12 . The middle height position of the fuel reservoir chamber  18  and the lower position of the fuel tank  10  are connected by a fuel introduction passage  20 . A fuel pump  22  is disposed at some midpoint of the fuel introduction passage  20 . Fuel in the fuel tank  10  is introduced to the fuel reservoir chamber  18  via the fuel introduction passage  20  by the fuel pump  22 . Here, it is also possible to dispose the fuel pump  22  in the fuel tank  10 . 
   The lower position (for example, the bottom portion) of the fuel reservoir chamber  18  and the electronically controlled fuel injection apparatus  12  are connected by a fuel supply passage  24 . The fuel supply passage  24  is basically arranged to decline from the fuel reservoir chamber  18  towards the electronically controlled fuel injection apparatus  12 , although it is possible to partially include a horizontal portion. With the present invention, since the fuel reservoir chamber  18  is located above the electronically controlled fuel injection apparatus  12 , fuel is supplied to the electronically controlled fuel injection apparatus  12  from the fuel reservoir chamber  18  by gravity-drop utilizing head difference. 
   A filter body  28 , in which a filter  26  for eliminating vapor is disposed, is disposed at some midpoint of the fuel supply passage  24 . Here, the fuel supply passage  24  consists of an upper fuel supply passage  24 A which is on the upstream side of the filter body  28 , and a lower fuel supply passage  24 B which is on the downstream side of the filter body  28 . The filter  26  is provided for preventing vapor from passing through. The filter  26  shown in  FIG. 2  is shaped as a hollow cylinder with an inner space  32 . Fuel flows into the inner space  32  from the outer surface of the filter  26  through the thickness of the cylindrical shape. The inner space  32  of the filter  26  is connected to the lower fuel supply passage  24 B. Fuel passing through the filter  26  moves towards the electronically controlled fuel injection apparatus  12  via the lower fuel supply passage  24 B. In  FIG. 1 , the lower fuel supply passage  24 B, connects with the filter  26  at the highest position of the lower fuel supply passage  24 B, and the lower fuel supply passage  24 B connects with the electronically controlled fuel injection apparatus  12  at the lowest position of the lower fuel supply passage  24 B. The lower fuel supply passage  24 B is arranged to not have a portion that rises so that the range from the highest position to the lowest position does not have a portion where the height is reversed (i.e., does not have a rising portion in the direction from the highest to lowest positions). 
   The side wall of the upper position of the fuel reservoir chamber  18  and the upper portion of the fuel tank  10  are connected by a first fuel return passage  30 . The first fuel return passage  30  is basically arranged to decline from the fuel reservoir chamber  18  towards the fuel tank  10 , although it is possible to partially include a horizontal portion. The first fuel return passage  30  is provided for returning surplus fuel in the fuel reservoir chamber  18  to the fuel tank  10  by overflowing, when the height of the fuel level  34  becomes higher than the connecting position at which the first fuel return passage  30  connects with the fuel reservoir chamber. It is also provides for returning vapor in the fuel reservoir chamber  18  to the fuel tank  10 . The inner diameter of the first fuel return passage  30  is preferably large enough so that the overflowing fuel does not clog the cross-section. When ambient temperature of an engine is high, vapor is generated in the fuel flowing in the fuel introduction passage  20  or the fuel stored in the fuel reservoir chamber  18 . However, vapor is ejected above the fuel level  34  in the fuel reservoir chamber  18 . Then, vapor returns to the fuel tank  10  through the first fuel return passage  30 . 
   In the present invention, the upper position of the electronically controlled fuel injection apparatus  12  and the upper position of the fuel reservoir chamber  18 , which is above the connecting position at which the fuel reservoir chamber  18  connects with the first fuel return passage  30 , are connected by a second fuel return passage  36 . Namely, the second fuel return passage  36  includes a high portion which is higher than the connecting position of the fuel reservoir chamber  18  with the first fuel return passage  30 . A filter  37  is disposed at some midpoint of the high portion of the second fuel return passage  36 . The filter  37  captures foreign particles, but allows vapor to pass through. The filter  37  is provided for preventing fuel which includes foreign particles in the fuel reservoir chamber  18  from flowing into the electronically controlled fuel injection apparatus  12  from the second fuel return passage  36  via the later-mentioned branch passage and the fuel supply passage  24 , when a roll-over of a vehicle occurs. 
   Here, as shown in  FIG. 3 , the second fuel return passage  36  is connected with the first fuel return passage  30  instead of with the upper portion of the fuel reservoir chamber  18 . In this case, the connecting position at which the first fuel return passage  30  connects with the second fuel return passage  36  is higher than the connecting position at which the fuel reservoir chamber  18  connects with the first fuel return passage  30 . In  FIG. 3 , as in  FIG. 2 , the filter  37 , which captures foreign particles but allows vapor to pass through, is disposed at some midpoint of the high portion of the second fuel return passage  36 . In addition, the second fuel return passage  36  can be connected with both the upper portion of the fuel reservoir chamber  18  and the upper portion of the first fuel return passage  30 . 
   A branch passage  38  is disposed at some midpoint of the second fuel return passage  36 . The end portion of the branch passage  38  which is at the opposite side of the second fuel return passage  36  is inserted and fitted into a cylindrical filter  26  in the filter body  28 . By connecting the end portion of the branch passage  38  with the inner space  32  of the filter  26 , the branch passage  38  is connected with the lower fuel supply passage  24 B via the inner space  32 . The position where the branch passage  38  branches from the second fuel return passage  36  is lower than the fuel level  34  in the fuel reservoir chamber  18 , that is, the fuel level  34  within a normal up-and-down range. The branch passage  38  is basically arranged to decline from the connecting position with the second fuel return passage  36  towards the inner space  32  of the filter  26 , although it is possible to partially include a horizontal portion. Namely, the branch passage  38  is arranged so that the highest position is the connecting position at which the branch passage  38  connects with the second fuel return passage  36 , and the lowest position is the fitting position at which the branch passage  38  fits into the filter  26 . The branch passage  38  is arranged to not have a portion that rises so that the range from the highest position to the lowest position does not have a portion where the height is reversed (i.e., does not have an inclining portion in the direction from the highest position to the lowest position). Further, it is preferred that the highest position of the inner space  32  of the filter  26  is at the connecting position side at which the inner space  32  connects with the branch passage  38 , and the lowest position is at the connecting side at which the inner space  32  connects with the lower fuel supply passage  24 B. In some cases, being horizontal is acceptable. The inner space  32  is arranged to not have a portion that rises so that the range from the highest position to the lowest position does not have a portion where the height is reversed (i.e., does not have a rising portion in the direction from the highest position to the lowest position). 
   Here, in the second fuel return passage  36 , the portion from the electronically controlled fuel injection apparatus  12  to the branch position from the branch passage  38  is formed as a fuel vapor return passage  40 , and the portion from the branch position from the branch passage  38  to the connecting position with the fuel reservoir chamber  18  is formed as a vapor return passage  42 . Namely, at the top end, the fuel vapor return passage  40  is divided into the vapor return passage  42  and the branch passage  38 . Here, it is preferred that the vapor return passage  42  is arranged to be straight and vertical above the fuel vapor return passage  40 . 
   The inner diameter of the vapor return passage  42  is preferably equal to or larger than 12 mm. When the inner diameter of the vapor return passage  42  is small, vapor sandwiches the fuel. Then, a large amount of the fuel is returned to the fuel reservoir chamber  18  along with vapor through the vapor return passage  42 . When the inner diameter of the vapor return passage  42  is equal to or larger than 12 mm, vapor does not sandwich the fuel and substantially only vapor can pass through the vapor return passage  42 . Further, the inner diameter of the fuel vapor return passage  40  is preferably smaller than the inner diameter of the vapor return passage  42 . With this structure, at the branch position of the vapor return passage  42  and the branch passage  38  at the top end of the fuel vapor return passage  40 , vapor in the fuel vapor return passage  40  is introduced smoothly to the vapor return passage  42 , and fuel which does not include vapor is introduced smoothly to the branch passage  38 . Namely, a vapor separating function can be further performed. 
   Next, the function of the fuel injection system of the present invention is explained. Firstly, in the condition that the fuel reservoir chamber  18  is sufficiently filled with fuel, when fuel is injected from the injection nozzle  16  of the electronically controlled fuel injection apparatus  12  into the intake passage  14 , fuel is supplied from the fuel reservoir chamber  18  to the electronically controlled fuel injection apparatus  12  via the fuel supply passage  24 . Here, the fuel amount supplied from the fuel reservoir chamber  18  to the electronically controlled fuel injection apparatus  12  is determined by the head difference between the height of the fuel level  34  in the fuel reservoir chamber  18  and the injection nozzle  16  of the electronically controlled fuel injection apparatus  12 . The fuel amount which is supplied from the fuel reservoir chamber  18  to the electronically controlled fuel injection apparatus  12  is set to be larger than the fuel amount which is injected from the injection nozzle  16  of the electronically controlled fuel injection apparatus  12  into the intake passage  14 . 
   When the height of the fuel level  34  in the fuel reservoir chamber  18  drops in accordance with the fuel supply to the electronically controlled fuel injection apparatus  12 , fuel is supplied by the fuel pump  22  from the fuel tank  10  to the fuel reservoir chamber  18  via the fuel introduction passage  20 . When the height of the fuel level  34  in the fuel reservoir chamber  18  exceeds the height of the connecting position at which the fuel reservoir chamber  18  connects with the first fuel return passage  30 , fuel overflows from the fuel reservoir chamber  18  via the first fuel return passage  30 . Then, the overflowing fuel returns to the fuel tank  10 . 
   When ambient temperature of an engine is high, vapor is generated in the fuel which is introduced into the fuel reservoir chamber  18  through the fuel introduction passage  20  or the fuel which is already stored in the fuel reservoir chamber  18 . However, vapor is ejected above the fuel level  34  in the fuel reservoir chamber  18 . Vapor ejected above the fuel level  34  returns from the fuel reservoir chamber  18  to the fuel tank  10  via the first fuel return passage  30 . 
   When ambient temperature of an engine is high, vapor is also generated not only in the fuel which is stored in the fuel reservoir chamber  18  but also in the fuel which is flowing through the fuel supply passage  24 . Most vapor which is contained in the fuel stored in the fuel reservoir chamber  18  is ejected above the fuel level  34 . However, there is some vapor in the fuel flowing towards the upper fuel supply passage  24 A (fuel supply passage  24 ) from the fuel reservoir chamber  18 . Vapor which is contained in the fuel flowing from the fuel reservoir chamber  18  towards the electronically controlled fuel injection apparatus  12  via the fuel supply passage  24  is eliminated by the filter  26  in the filter body  28  which is disposed at the downstream side of the upper fuel supply passage  24 A. Therefore, in principle, vapor is not contained in the fuel flowing from the filter  26  towards the lower fuel supply passage  24 B. However, when ambient temperature of an engine is high, a slight amount of vapor is generated in the fuel flowing through the lower fuel supply passage  24 B. Then, fuel which contains vapor is supplied to the electronically controlled fuel injection apparatus  12 . Vapor contained in the fuel which is supplied to the electronically controlled fuel injection apparatus  12  is separated from fuel in the vapor separation chamber (not shown in drawings). Then, fuel from which vapor is eliminated is injected from the injection nozzle  16  of the electronically controlled fuel injection apparatus  12  into the intake passage  14 . 
   Of the fuel which is supplied to the electronically controlled fuel injection apparatus  12 , the fuel which was not injected from the injection nozzle  16  moves upwards in the second fuel return passage  36  (the fuel vapor return passage  40 ) as surplus fuel. Vapor which is contained in the fuel supplied to the electronically controlled fuel injection apparatus  12  also moves upwards in the second fuel return passage  36  (the fuel vapor return passage  40 ) being mixed with the surplus fuel. 
   A portion of the vapor return passage  42  is arranged to be higher than the fuel level  34  in the fuel reservoir chamber  18  before connecting to the fuel reservoir chamber  18 . Therefore, in a non-operating state, fuel level  44  is formed in the vapor return passage  42  to be at the same height as the fuel level  34  in the fuel reservoir chamber  18 . Although vapor is contained in the surplus fuel which is returned from the electronically controlled fuel injection apparatus  12  to the second fuel return passage  36 , in a non-operating state, vapor is ejected above the fuel level  44  in the vapor return passage  42  and introduced above the fuel level  34  in the fuel reservoir chamber  18 . Then, vapor which is introduced into the fuel reservoir chamber  18  returns to the fuel tank  10  via the first fuel return passage  30 . Here, in an operating state, a part of the surplus fuel from the electronically controlled fuel injection apparatus  12  towards the second fuel return passage  36  returns to the fuel reservoir chamber  18  through the vapor return passage  42 . 
   At some midpoint of the second fuel return passage  36 , a portion is arranged to be higher than the connecting position of the fuel reservoir chamber  18  with the first fuel return passage  30 . In the case that the second fuel return passage  36  connects with the fuel reservoir chamber  18 , this structure prevents the fuel in the fuel reservoir chamber  18  from flowing into the second fuel return passage  36  so as not to disturb the returning of the surplus fuel which flows through the second fuel return passage  36  from the electronically controlled fuel injection apparatus  12 . Further, in the case that the second fuel return passage  36  connects with the first fuel return passage  30 , as shown in  FIG. 3 , the structure is so that the fuel which is returned to the fuel tank  10  via the first fuel return passage  30  after overflowing from the fuel reservoir chamber  18  does not disturb the returning of the surplus fuel which flows into and through the second fuel return passage  36  from the first fuel return passage  30 . 
   The branch passage  38  branches from the second fuel return passage  36  which consists of the fuel vapor return passage  40  and the vapor return passage  42  located thereabove. The branch passage  38  extends downwards or horizontally towards the filter  26  from the position where it branches. Therefore, vapor which is contained in the surplus fuel moves upwards though the vapor return passage  42 . Since the branch passage  38  is arranged to extend from the connecting position at which the branch passage  38  connects with the vapor return passage  42  downwards or horizontally towards the fitting position with the filter  26 , in an operating state, fuel which does not contain vapor is introduced to the branch passage  38 . The surplus fuel which flows into the branch passage  38  and does not contain vapor reaches the inner space  32 , and then, is introduced to the lower fuel supply passage  24 B. In this manner, in an operating state, a part of the surplus fuel which had vapor eliminated is returned from the electronically controlled fuel injection apparatus  12  flows into the branch passage  38 , and then, is introduced to the lower fuel supply passage  24 B via the inner space  32  of the filter  26 . In this manner, a part of the surplus fuel which is returned from the electronically controlled fuel injection apparatus  12  is introduced to the fuel supply passage  24  from the branch passage  38 , and can be re-supplied in a circulatory manner for a short distance. Since the re-supplied fuel in a circulatory manner flows from the branch passage  38  to the inner space  32  of the filter  26 , vapor is not mixed into the re-supplied fuel in a circulatory manner. By re-supplying a part of the surplus fuel in a circulatory manner for a short distance, the amount of fuel which is returned to the fuel tank  10  can be reduced. Therefore, compared with the system which returns all the surplus fuel ejected from the electronically controlled fuel injection apparatus  12  to the fuel tank  10 , power consumption of the fuel pump  22  can be decreased. 
   The surplus fuel which does not contain vapor flowing through the branch passage  38  flows from the inner space  28  of the filter  26  towards the lower fuel supply passage  24 B. The flow of the surplus fuel through the inner space  28  induces flow of the supply fuel from the outside of the filter  26  towards the inner space  28 . Namely, even when vapor is accumulated at the filter  26  and generates resistance against the fuel flow for passing through the filter  26  in the thickness direction, the flow of the supply fuel to pass through the filter  26  in the thickness direction can be smoothed by the flow of the surplus fuel through the inner space  28 . 
   In the branch passage  38 , the connecting position at which the branch passage  38  connects with the second fuel return passage  36  is the highest position, and the fitting position at which the branch passage  38  fits with the inner space  32  of the filter  26  is the lowest position. Further, in the inner space  32  of the filter  26 , in principle, the side of the connecting position at which the inner space  32  connects with the branch passage  38  is the highest position, and the connecting side at which the space  32  connects with the lower fuel supply passage  24 B is the lowest position. Furthermore, in the lower fuel supply passage  24 B, the connecting position with the filter  26  is the highest position, and the connecting position at which the lower fuel supply passage  24 B connects with the electronically controlled fuel injection apparatus  12  is the lowest position. For each of the branch passage  38 , the inner space  32  of the filter  26  and the lower fuel supply passage  24 B, the range from the respective highest position to the respective lowest position does not have a portion that rises. As a result, in a non-operating state at high temperature, even when vapor is generated in the fuel anywhere in the branch passage  38 , the inner space  32  of the filter  26  or the lower fuel supply passage  24 B, vapor moves upwards from the lower position to the higher position. Then, vapor can be ejected from the branch passage  38  to the vapor return passage  42 . Then, vapor is ejected from the vapor return passage  42  above the fuel level  34  in the fuel reservoir chamber  18 , and can be returned to the fuel tank  10  via the first fuel return passage  30 . Namely, in the condition that a part of the surplus fuel is re-supplied in a circulatory manner via the branch passage  38 , even when vapor is generated anywhere in the circulation route in a non-operating state, vapor can be returned to the fuel tank  10  from the vapor return passage  42  via the fuel reservoir chamber  18  and the first fuel return passage  30 . 
   Here, in  FIG. 2 , the top end of the branch passage  38  is shaped to be fitted into the cylindrical filter  26 . However, as shown in  FIG. 4 , it is also possible to adopt a structure that the end surface of the cylindrical filter  46  abuts the end surface of the branch passage  38  so as to connect the branch passage  38  and the inner space  48  of the filter  46 . Further, the branch passage  38  is not limited to be merged at the position of the filter  46 . The circulation route can also be formed by merging the branch passage  38  with the fuel supply passage  24 . In the case that the branch passage  38  is merged with the filter  26 ,  46 , the sealing at the connecting position can be improved, and the manufacturing cost thereof can be reduced. 
   Here, in  FIG. 1  and  FIG. 2 , the filter body  28  is disposed at some midpoint of the fuel supply passage  24  which is located below the fuel reservoir chamber  18 , and the cylindrical filter  26  is disposed in the filter body  28 , and the top end of the branch passage  38  is shaped to be fitted into the cylindrical filter  26 . A modified embodiment as shown in  FIG. 5  can also be possible. With this embodiment, the filter body  28  as shown in  FIG. 1  and  FIG. 2  is eliminated. The upper portion of the fuel supply passage  24  projects and opens above the fuel level  34  in the fuel reservoir chamber  18 . A fuel inlet opening  50  is formed at some midpoint of the fuel supply passage  24  which is located below the fuel level  34  in the fuel reservoir chamber  18 . The cylindrical filter  26  is attached to the fuel supply passage  24  so as to cover the fuel inlet opening  50 . A filter  52  which captures foreign particles while allowing vapor to pass through is disposed at the opening of the fuel supply passage  24  which projects above the fuel level  34 . The filter  52  is provided for preventing fuel which contains foreign particles in the fuel reservoir chamber  18  from flowing into the electronically controlled fuel injection apparatus  12  through the fuel supply passage  24 , when a roll-over of a vehicle occurs. 
   With the fuel injection system shown in  FIG. 5 , fuel in the fuel reservoir chamber  18  reaches inside the fuel supply passage  24  from the fuel inlet opening  50  after passing through the filter  26 . Foreign particles are eliminated from the fuel flowing into the fuel supply passage  24  by the filter  26 . In this fuel injection system, the upper opening of the fuel supply passage  24  is formed above the fuel level  34  in the fuel reservoir chamber  18 . With this structure, even when vapor is generated in the fuel supply passage  24  in a non-operating state, vapor can be ejected above the fuel level  34  in the fuel reservoir chamber  18  through the fuel supply passage  24 . Therefore, ease of restarting can be improved by preventing vapor from accumulating at the fuel supply passage  24 . 
   The Second Embodiment 
   Next, another embodiment of the present invention is explained with reference to the drawings. 
     FIG. 6  is a schematic drawing of the second embodiment of a fuel injection system of the present invention. In  FIG. 6 , the same reference numbers as in  FIG. 1 ,  FIG. 2  and  FIG. 5  represent the same members. In the second embodiment, the fuel tank (shown in  FIG. 1 ) is located below the electronically controlled fuel injection apparatus  12 , and the fuel reservoir chamber  18  is disposed above the electronically controlled fuel injection apparatus  12 , as in the first embodiment. The fuel introduction passage  20  which is connected to the fuel tank  10  is connected at a mid-height of the fuel reservoir chamber  18 . The fuel reservoir chamber  18  and the electronically controlled fuel injection apparatus  12  are connected by the fuel supply passage  24 . The upper portion of the fuel supply passage  24  projects and opens above the fuel level  34  in the fuel reservoir chamber  18 . The fuel inlet opening  50  is formed at some midpoint of the fuel supply passage  24  which is located below the fuel level  34  in the fuel reservoir chamber  18 . The cylindrical filter  26  is attached to the fuel supply passage  24  so as to cover the fuel inlet opening  50 . The filter  52  which captures foreign particles while allowing vapor to pass through is disposed at the top end of the fuel supply passage  24  which projects above the fuel level  34  in the fuel reservoir chamber  18 . The upper position of the fuel reservoir chamber  18  and the fuel tank (shown in  FIG. 1 ) are connected by the first fuel return passage  30 . Further, the electronically controlled fuel injection apparatus  12  and the upper position of the fuel reservoir chamber  18  (the position higher than the connecting position at which the reservoir chamber  18  connects with the first fuel return passage  30 ) are connected by the second fuel return passage  36 . 
   The second embodiment is different from the first embodiment in that the branch passage  38  of the first embodiment is eliminated. As a result, the second fuel return passage  36  connects only with the upper position of the fuel reservoir chamber  18 . Therefore, in an operating state, the surplus fuel which contains vapor from the electronically controlled fuel injection apparatus  12  always returns to the fuel reservoir chamber  18  through the second fuel return passage  36 . In a non-operating state, the fuel level  44  is formed in the second fuel return passage  36 . 
   With the second embodiment, as with the first embodiment, fuel is supplied to the electronically controlled injection apparatus  12  from the fuel reservoir chamber  18  via the fuel supply passage  24  by head difference. The surplus fuel which contains vapor from the electronically controlled fuel injection apparatus  12  returns to the fuel reservoir chamber  18  via the second fuel return passage  36 , and returns to the fuel tank  10  from the fuel reservoir chamber  18  via the first fuel return passage  30 . Further, even when vapor is generated in the second fuel return passage  36  in a non-operating state, vapor returns from the second fuel return passage  36  to the fuel tank  10  via the fuel reservoir chamber  18  and the first fuel return passage  30 . On the other hand, when vapor is generated in the fuel supply passage  24  in a non-operating state, vapor moves upwards in the fuel supply passage  24 , and reaches above the fuel level  34  in the fuel reservoir chamber  18  via the filter  52  through which vapor passes. Then, vapor returns to the fuel tank  10  via the first fuel return passage  30 .