Abstract:
A fuel delivery pipe for delivering fuel to a plurality of fuel injection valves corresponding to cylinders of an internal -combustion engine. The fuel delivery pipe includes a pipe body made of carbon steel for machine structural use and a plating film disposed on an inner surface of the pipe body. Preferably the fuel delivery pipe includes a plating film disposed on an outer surface of the pipe body.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from Japanese Patent Application No. 2009-202683 filed on Sep. 2, 2009. The entire content of this priority application is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a fuel delivery pipe and a method of manufacturing the same. 
       BACKGROUND 
       [0003]    A vehicle internal-combustion engine has fuel injection valves and a delivery pipe. The fuel injection valves are provided for respective cylinders. The fuel delivery pipe delivers fuel to each of the fuel injection valves. The fuel delivery pipe is made by aluminium die-casting. 
         [0004]    However, because the fuel delivery pipe has a lower mechanical strength, a fuel delivery pipe having a higher mechanical strength has been required. Besides, it has been reported that high level of alcohol containing fuel reacts directly with (or causes dry corrosion on) aluminium. Furthermore, it has been shown that gasohol also can cause dry corrosion. Because of this, the inner surface of the fuel delivery pipe needs to be plated with alcohol-corrosion resistant material. However, plating aluminium needs zinc immersion as the pretreatment. 
         [0005]    Thus, there is a need for a fuel delivery pipe that has a higher mechanical strength and needs no pretreatment for plating. 
       SUMMARY 
       [0006]    An aspect of the present invention is a fuel delivery pipe for delivering fuel to a plurality of fuel injection valves corresponding to cylinders of an internal-combustion engine. The fuel delivery pipe includes: a pipe body made of carbon steel for machine structural use; and a plating film disposed on an inner surface of the pipe body. 
         [0007]    Another aspect of the present invention is a method of manufacturing a fuel delivery pipe for delivering fuel to a plurality of fuel injection valves corresponding to cylinders of an internal-combustion engine. The method includes the successive steps of: a) manufacturing a pipe body, the manufacturing step including forging carbon steel for machine structural use and successively quenching and tempering the carbon steel; and b) plating the inner and outer surfaces of the pipe body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view illustrating a fuel delivery system of an embodiment; 
           [0009]      FIG. 2  is a sectional view illustrating a configuration of a fuel delivery pipe; and 
           [0010]      FIG. 3  is a sectional view of a pipe body and connecting parts in their assembled condition. 
       
    
    
     DETAILED DESCRIPTION 
     Embodiment  
     (Configuration of Vehicle Fuel Delivery System) 
       [0011]    An embodiment in accordance with the present invention will be described. As illustrated in  FIG. 1 , a vehicle fuel delivery system of this embodiment is installed in a vehicle body  20  of a vehicle  10  to deliver fuel from a tank  40  to an engine  300 . The system includes a pump  230 , a filter  210 , a pressure regulator  220 , a transfer pipe P 1 , an inlet pipe P 2 , a return pipe P 3 , and a fuel delivery pipe  100 . 
         [0012]    The pump  230  pumps up fuel from the tank  40  and transfers the fuel through the transfer pipe P 1  toward the engine  300 . The filter  210  filters the fuel. The fuel is then supplied through the inlet pipe P 2  and through the pressure regulator  220  to the fuel delivery pipe  100 . Specifically, the pressure regulator  220  supplies the fuel to the fuel delivery pipe  100  while regulating the pressure of the fuel at a constant pressure. The fuel which is supplied to the fuel delivery pipe  100  is then delivered to the engine  300 . The fuel which is not supplied to the fuel delivery pipe  100  returns through the return pipe P 3  to the tank  40 . 
         [0013]    The fuel is high alcohol fuel or gasohol. The alcohol may be, for example, methanol, ethanol, butanol, or propanol. 
       (Configuration of Fuel Delivery Pipe) 
       [0014]    As illustrated in  FIG. 2 , the fuel delivery pipe  100  includes a housing  102  (a pipe body) and first and second connecting parts  103 ,  123  to be connected with the housing  102 . 
         [0015]    The housing  102  has an elongated shape as a whole. A cylindrical fuel delivery path  121  runs in the housing  102 . An end (a left end in  FIG. 2 ) of the fuel delivery path  121  is blind, while the other end (a right end in  FIG. 2 ) is open. A first fitting portion  125  (a connecting portion) is formed at the right end of the fuel delivery path  121 . The first fitting portion  125  allows the first connecting part  103  to be fitted therein. 
         [0016]    An inlet path  124  runs in an end side (a right side in  FIG. 2 ) of the fuel delivery pipe  100 , obliquely from the fuel delivery path  121  to the right end of the fuel delivery pipe  100 . One end of the inlet path  124  is in communication with the fuel delivery path  121 . The A second fitting portion  126  (the connecting portion) is formed at the other end of the inlet path  124 . The second fitting portion  126  allows the second connecting part  123  to be fitted therein. 
         [0017]    A plurality of (four in this embodiment) fuel injection valve mounting holes  122  run through a thickness of an outer peripheral surface of the housing  102 . Each fuel injection valve mounting hole  122  allows a fuel injection valve (not illustrated in the drawings) of the engine  300  to be mounted thereto. 
         [0018]    The first connecting part  103  includes a pressure sensor (not illustrated in the drawings). The first connecting part  103  is disposed in the first fitting portion  125  in a manner closing the right end of the fuel delivery path  121 . The second connecting part  123  connects the housing  102  with the inlet pipe P 2  (see  FIG. 1 ). The second connecting part  123  is disposed in the second fitting portion  126 . Thus, the fuel introduced from the inlet path  124  flows into the fuel delivery path  121  and then is injected from the fuel injection valves. 
         [0019]    Each of the housing  102  and the first and second connecting parts  103 ,  123  is a forging of carbon steel for machine structural use (e. g. JIS S45C). The carbon steel for machine structural use will hereinafter be referred to simply as “the carbon steel”. 
         [0020]    A nickel-phosphorus alloy plating film  127  is formed on inner and outer surfaces of the housing  102  and on exposed portions of the first and second connecting parts  103 ,  123 . 
         [0021]    In a condition where the first and second connecting parts  103 ,  123  are assembled as illustrated in  FIG. 3 , the plating film  127  seals both of: a fitting surface of the first connecting part  103  and the pipe body  102 ; and a fitting surface of the second connecting part  123  and the pipe body  102 . Therefore, sealing parts such as O-rings are unnecessary for these surfaces. 
         [0022]    Next, a method of manufacturing the fuel delivery pipe  100  of this embodiment will illustratively be described. The method includes a pipe-body manufacturing step and a plating step. 
       (Pipe-Body Manufacturing Step) 
       [0023]    In the pipe-body manufacturing step, the housing  102  is manufactured by forging and, succeedingly, quenching and tempering a round bar of the carbon steel. 
         [0024]    Specifically, a process of forging the carbon steel is succeeded by the quenching and tempering process. This improves the toughness of the housing  102 . In particular, the carbon steel should contain 0.3 wt % or more carbon to ensure the effect of the quenching and tempering process. The Vickers hardness of the housing  102  after the quenching and tempering process ranges from 230 to 290 HV. 
       (Plating Step) 
       [0025]    Next, nickel-phosphorus plating process is performed on the housing  102  and the first and second connecting parts  103 ,  123  in their assembled condition. 
         [0026]    Specifically, the first and second connecting parts  103 ,  123  are fitted into the first and second connecting portions  125 ,  126 , respectively, so that the housing  102  and the first and second connecting parts are assembled together. Thereafter, the housing  102  with the first and second connecting parts  103 ,  123  is immersed in a plating bath, and, then, electroless nickel-phosphorus plating is performed. 
         [0027]    More specifically, junctions between each parts (a junction between the housing  102  and the first connecting part  103  and a junction between the housing  102  and the second connecting part  123 ) are also plated. Thus, a gap formed in each junction is filled and sealed with the plating film  127 . 
         [0028]    As described above, with the present embodiment, the process of forging the carbon steel is succeeded by the quenching and tempering process. This improves the hardness and toughness of the carbon steel. This makes it possible to manufacture the fuel delivery pipe  100  having a higher mechanical strength. 
         [0029]    An comparative example will now be described. Fuel delivery pipes compared in this example are: a pipe made with an aluminium alloy (JIS ADC10) die casting 2 mm or more in thickness; and a carbon steel (S45C) delivery pipe made by the method of this embodiment into a same shape with the die casting. 
         [0030]    As a result of a loading and unloading test, a crack appeared in the ADC10 fuel delivery pipe after repeating 8,800,000 cycles of applying a load of 2 MPa and then a load of 22 MPa. On the other hand, it was proved that no crack appeared in the S45C fuel delivery pipe even after repeating 10,000,000 cycles of applying a load of 0 MPa and then a load of 50 MPa. 
         [0031]    Furthermore, because the plating process is performed on the housing  102  and the first and second connecting parts in their assembled condition, the plating film fills and seals the gaps formed at a contact portion of the housing  102  and the first connecting part  103  and at a contact portion of the housing  102  and the second connecting part  123 . Therefore, the sealing performance can be ensured without incorporating the sealing parts (such as O-rings) for sealing the gaps at the contact portions. Furthermore, because the housing  102  is made of the carbon steel, the housing  102  can be manufactured without undergoing such pretreatment as would be required in manufacturing an aluminium one. 
         [0032]    Furthermore, because the plating film  127  covers the inner and outer surfaces of the housing  102 , the inner surface can be protected from alcohol corrosion, while the outer surface can be protected from salt corrosion. 
         [0033]    In particular, the inventor has found that the plating film  127  that is 10 μm or more in thickness can surely protect the outer surface from salt corrosion. 
       Other Embodiments  
       [0034]    The present invention is not limited to the embodiment described above with the drawings. For example, following embodiments are also included within the scope of the present invention. 
         [0035]    (1) In the above-described embodiment, electroless nickel-phosphorous plating is adopted as the plating process. The plating method is not limited to this. For example, electroplating can be adopted as the plating process. Furthermore, the plating material has to only be alcohol corrosion resistant. 
         [0036]    (2) In the above-described embodiment, the plating process is performed on the housings  102  and the first and second connecting parts  103 ,  123  in their assembled condition. The present invention is not limited to this. For example, a process of plating each of the parts may be succeeded by the process of assembling these parts. Note only that, in a case of the above-described embodiment, such an effect that no sealing parts are needed for sealing the junctions.