Abstract:
A fuel rail formed by hydroforming. The hydroforming process includes applying a seal onto a fuel tube, and installing fuel injector blocks, including fuel injector ports, onto the tube in desired positions. The fuel tube assembly is placed in a die assembly, and pressurized fluid is supplied to the interior of the tube. The pressurized fluid causes the tube to expand outwardly into engagement with the blocks, and to pierce holes through the tube within each of the blocks to provide fluid communication with the associated fuel injector and other ports.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the forming of fuel rails, and more particularly to forming fuel rails employing a hydroforming process. 
     Vehicles today typically employ fuel injectors to feed fuel to an engine. In particular, there are some engines that operate with direct fuel injection. In a fuel system for a direct injection engine, the fuel is transferred to the combustion chambers (cylinders) under high pressure in order to overcome the pressure within the combustion chambers. A typical high pressure fuel rail includes a hollow conduit having a plurality of U-shaped blocks provided thereon. Each of the blocks has a recessed fuel injector port formed therein to receive a portion of a fuel injector, and also typically includes a mounting member so that the block functions as a mounting bracket as well. These fuel rail assemblies have commonly been manufactured by forming a plurality of fuel holes in the conduit, then brazing or otherwise securing each of the blocks about a respective one of the holes. Although effective, this process is somewhat time consuming and inefficient. Further, it is desirable to avoid the concerns of fuel rails warping during the brazing process in order to avoid the requirement of machining after brazing. Additionally, it is desirable to reduce the chance of creating a leak path for the fuel at the brazing locations. 
     Thus, it is advantageous to have a fuel rail assembly and a method for manufacturing the fuel rail assembly that overcomes the drawbacks of the prior art. 
     SUMMARY OF INVENTION 
     This invention relates to an improved method for manufacturing a fuel rail assembly for use with internal combustion engines employing fuel injectors. In particular, the invention relates to an improved high pressure fuel rail assembly for use with direct injection engines. 
     In its embodiments, the present invention contemplates a method of manufacturing a fuel rail assembly comprising the steps of: providing a hollow tube and a plurality of blocks, wherein each of the blocks has a passage formed therethrough and a recessed fuel injector port, inserting the tube into the passages in the blocks; mounting the tube and blocks in a hydroforming die, and positioning the blocks in desired positions relative to the tube; supplying pressurized fluid to the interior of the tube, causing the tube to expand outwardly into engagement with the blocks; and piercing holes through the tube within each of the blocks to provide fluid communication with the associated recessed fuel injector ports. 
     The present invention further contemplates a method of manufacturing a fuel rail assembly comprising the steps of: providing a hollow tube and a plurality of blocks, wherein each of the blocks has a passage formed therethrough and a recessed fuel injector port; providing at least one seal; inserting the tube into the passages in the blocks; locating the seal between the tube and at least one of the passages; mounting the tube and blocks in a hydroforming die, and positioning the blocks in desired positions relative to the tube; and supplying pressurized fluid to the interior of the tube, causing the tube to expand outwardly into engagement with the seal and the blocks. 
     The present invention also contemplates a fuel injector assembly formed by one of the above noted methods. 
     Accordingly, an object of the present invention is to form an improved fuel rail assembly employing a hydroforming process. 
     An advantage of the present invention is that the fuel rail assembly can be formed more efficiently. 
     Another advantage of the present invention is that the fuel rail assembly formed is less likely to be warped or have potential fuel leak paths. 
    
    
     BRIEF DESCRIPTION DRAWINGS 
     FIG. 1 is a schematic, perspective view of a portion of a fuel rail assembly formed in accordance with the present invention; 
     FIG. 2 is a sectional view taken along line  2 — 2  in FIG. 1, and also shows a schematic of the dies employed in accordance with the methods of the present invention; and 
     FIG. 3 is a partial, cross sectional view taken along line  3 — 3  in FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1-3 illustrate a fuel rail assembly  20  for a typical high pressure fuel, direct injected engine (not shown). The fuel rail assembly  20  includes a main fuel tube  22 , with three spaced fuel injector/mounting blocks  24  and one end feed block  26  mounted thereon. Each block  24 ,  26  includes a fuel tube passage  36  for receiving the outer surface  38  of the fuel tube  22  therethrough. The injector/mounting blocks  24  also include cavities that form fuel injector ports  28 , which are shaped to receive high pressure fuel injectors (not shown). The three fuel injector/mounting blocks  24  each include a mounting bore  30  extending through the blocks  24  for receiving mounting bolts  32 , that mount to the engine. Thus, these blocks  24  act as both supports for the fuel injectors themselves, and also the mechanism for mounting the fuel rail assembly  20  to the engine. The feed block  26  includes a cavity  29  that forms a cross feed port for a cross feed tube (not shown). 
     The finished tube  20  includes four hydropierced holes  34 , one at each of the three blocks  24  aligning with its respective injector port  28 , and one at the block  26  to communicate with the cross feed port. Since these holes  34  are formed during the hydroforming process itself (as discussed below), they needn&#39;t be in the fuel tube  22  prior to the hydroforming process. The blocks  24 ,  26  are fabricated so that each of the passages  36  has a diameter approximately 0.01 to 0.02 inches (0.25 to 0.5 mm) larger than the initial diameter of the outside surface  38  of the fuel tube  22 . This initial difference in diameters may vary depending upon the size and thickness of the components, and what type of seal is used, if any, as is desired for the particular fuel rail assembly being formed. 
     It is preferred, as is shown in this embodiment, to have seals  40  between the fuel tube outer surface  38  and the fuel tube passages  36 . These seals  40  are desired because the fuel rail assembly  20  must retain, without leakage, high pressure fuel as it flows to the engine, under various environmental conditions. The advantage of having these seals  40 , then, is to improve the sealing properties by reducing the chances for a leak path between the tube outside surface  38  and the passage  36 . 
     The relative thickness of the seals  40  are shown exaggerated for clarity in describing the invention. The actual thickness of the seals depends upon the particular type of seal used, among other factors, as is discussed below, but is generally on the order of 0.2 mm or less. 
     The seals  40  can be an adhesive, a sealant, and/or metal, rubber or plastic. If the seal  40  is made of a sealant, then the preferred method is to pre-coat the fuel tube outer surface  38  at least at the locations where the tube holes  34  will be formed prior to installing the blocks  24 ,  26 . The preferred sealant is a pre-applied sealant, which is an application where a liquid medium suspends tiny capsules of sealant. This pre-applied sealant is applied to the fuel tube surface  38  at the appropriate locations and allowed to dry. Then, during the hydroforming process, the high pressure will cause the capsules to rupture, and the sealant will flow and bond to the surfaces. 
     If the seal  40  is made of an adhesive, then it is preferred to pre-coat the tube outer surface  38  at the hole  34  locations with a pre-applied adhesive. These adhesives contain tiny capsules of resin and capsules of hardener that are suspended in a liquid medium. The liquid medium is applied to the tube surface  38 , where a hole  38  will be formed, and is allowed to dry. During the hydroforming process, the high pressure between the tube outer surface  38  and the fuel tube passages  36  will cause the capsules containing the resin and the capsules containing the hardener to rupture, allowing the hardener &amp; resin to mix, thus forming a tight adhesive seal. 
     Instead of, or in addition to, the sealant or adhesive, each seal  40  can include a small strip or coating of material sandwiched between each fuel tube passage  36  and the corresponding portion of the tube outer surface  38 . The sealant or adhesive may be placed on either or both sides of the material, as is desired for the particular application. 
     This material can be a flexible rubber or plastic. It can also be a ductile metal, such as copper. This ductile metal can be coated on the surface of the fuel tube using conventional processes for coating of metals on objects, such as plating or flashing, and can be applied locally, or along the whole tube. In the alternative, the soft metal can take the form of very thin, for example 0.005 inches (0.13 mm) thick, tubular sleeves, each slid between the fuel tube outer surface  38  and a corresponding fuel tube passage  36 . The ductile metal can also be a very thin strip of shim stock, that is wrapped around the fuel tube  22 , with a slight overlapping of the ends of the shim to assure a complete seal. 
     FIG. 2 schematically illustrates the fuel rail assembly  20  after forming, but while still mounted in a hydroforming die assembly  44 . This assembly  44  can include a first end die  46  for sealing one end of the tube  22 , and a second end die  48  for sealing the other end of the tube  22  and providing a conduit for feeding the high pressure fluid into the tube  22  during the hydroforming process. This assembly  44  can also include two side dies  50  for surrounding and controlling the expansion of the tube  22 . The two side dies  50  each include piercing pins  52 , which translate radially inward on hydraulic pistons (not shown), for creating the hydropierced holes in the fuel tube  22  during the hydroforming process. The particular number and configuration of hydroforming dies can vary as is desired, and so the die assembly  44  shown is for illustrative purposes only. 
     The hydroforming process for the fuel rail assembly  20  will now be described. The seals  40  are mounted or formed on the tube outer surface  38 . Each of the blocks  24 ,  26  is then loaded on the fuel tube  22 . The assembly  20  is placed in the hydroforming die assembly  44 , with each of the parts at the desired location and orientation, and the die assembly is closed. 
     The hydroforming now takes place. Pressurized fluid (such as water) is supplied through the second end die  48  to the interior of the fuel tube  22 . To accomplish this, a conventional end feed cylinder (not shown) sealingly engages the second end die  48  in a well known manner. The pressure of the fluid within the tube  22  is increased in a well known manner to such a magnitude that the fuel tube  22  is expanded outwardly into conformance with the die cavity defined by the die assembly  44  and against the fuel tube passages  36 , swaging the blocks  24 ,  26  in place. As a result, the fuel tube  22  is deformed into the desired final shape. One will note that the amount of tube expansion illustrated in FIG. 2 is shown exaggerated for visualization purposes. 
     If a sealant or adhesive is used for the seal  40 , the pressure will rupture the capsules. If a ductile metal is used for the seal  40 , then the pressure will deform the metal, forming a tight seal. At the same time, the holes  34  are pierced through the seals  40  and tube  22 , within each of the blocks  24 ,  26 , to provide fluid with the associated recessed fuel injector ports  28 . The fuel rail assembly may then be removed from the hydroforming dies, and the part is essentially complete, except for some conventional post processing, such as plugging an open end of the fuel rail with an end cap (not shown) in a conventional manner. 
     Although this embodiment shows three fuel injector blocks  24 , which can be used, for example, as one side of a fuel rail assembly in a V-6 engine, fuel rails with other numbers of fuel injectors are also within the scope of the present invention. The fuel rail assembly of the particular embodiment includes three main blocks and one end block, although various numbers of blocks may be employed depending upon the engine and fuel injector configuration. Also, while the blocks  24  include both a fuel injector port and a mounting bore, one can employ two sets of separate blocks, with one set having fuel injector ports and the other including the mounting bores, if so desired. Moreover, while the preferred embodiment describes a high pressure fuel rail for a direct injection engine, the present invention is also applicable to fuel rails for conventional fuel injected engines. 
     While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.