Patent Publication Number: US-6698664-B2

Title: Modular fuel injector having an integral or interchangeable inlet tube and having an integral filter and dynamic adjustment assembly

Description:
BACKGROUND OF THE INVENTION 
     It is believed that examples of known fuel injection systems use an injector to dispense a quantity of fuel that is to be combusted in an internal combustion engine. It is also believed that the quantity of fuel that is dispensed is varied in accordance with a number of engine parameters such as engine speed, engine load, engine emissions, etc. 
     It is believed that examples of known electronic fuel injection systems monitor at least one of the engine parameters and electrically operate the injector to dispense the fuel. It is believed that examples of known injectors use electro-magnetic coils, piezoelectric elements, or magnetostrictive materials to actuate a valve. 
     It is believed that examples of known valves for injectors include a closure member that is movable with respect to a seat. Fuel flow through the injector is believed to be prohibited when the closure member sealingly contacts the seat, and fuel flow through the injector is believed to be permitted when the closure member is separated from the seat. 
     It is believed that examples of known injectors include a spring providing a force biasing the closure member toward the seat. It is also believed that this biasing force is adjustable in order to set the dynamic properties of the closure member movement with respect to the seat. 
     It is further believed that examples of known injectors include a filter for separating particles from the fuel flow, and include a seal at a connection of the injector to a fuel source. 
     It is believed that such examples of the known injectors have a number of disadvantages. It is believed that examples of known injectors must be assembled entirely in an environment that is substantially free of contaminants. It is also believed that examples of known injectors can only be tested after final assembly has been completed. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a fuel injector can comprise a plurality of modules, each of which can be independently assembled and tested. According to one embodiment of the present invention, the modules can comprise a fluid handling subassembly and an electrical subassembly. These subassemblies can be subsequently assembled to provide a fuel injector according to the present invention. 
     The present invention provides a fuel injector for use with an internal combustion engine. The fuel injector comprises a valve group subassembly and a coil group subassembly. The valve group subassembly includes a tube assembly having a longitudinal axis extending between a first end and a second end. The inlet tube assembly includes an inlet tube, a non-magnetic shell, and a valve body. The inlet tube having a first inlet tube end and a second inlet tube end. The non-magnetic shell having a first shell end connected to the second inlet end at a first connection and further having a second shell end. The valve body having a first valve body end connected to the second end at a second connection and further having a second valve body end. A seat secured at the second end of the tube assembly, the seat defining an opening. An armature assembly disposed within the tube assembly; a member biasing the armature assembly toward the seat. A filter assembly located in the tube assembly, the filter assembly engaging the member and adjusting a biasing force of the member. The coil group subassembly includes a solenoid coil operable to displace the armature assembly with respect to the seat. 
     The present invention further provides a fuel injector for use with an internal combustion engine. The fuel injector comprises a valve group subassembly and a coil group subassembly. The valve group subassembly includes a tube assembly having a longitudinal axis extending between a first end and a second end. The tube assembly includes an inlet tube, a non-magnetic shell, and a valve body. The inlet tube has a first inlet tube end and a second inlet tube end. The non-magnetic shell has a first shell end connected to the second inlet tube end at a first connection and further has a second shell end. The valve body has a first valve body end connected to the second shell end at a second connection and further has a second valve body end. A seat, defining an opening, is secured at the second end of the tube assembly. An armature assembly and an adjusting tube are disposed within the tube assembly. The armature assembly has a first armature assembly. A member biases the armature assembly toward the seat. A filter assembly located in the tube assembly, the filter assembly engaging the member and adjusting a biasing force of the member. The coil group subassembly includes a solenoid coil operable to displace the armature assembly with respect to the seat; and a second attaching portion fixedly connected to the first attaching portion. 
     The present invention also provides for a method of assembling a fuel injector. The method comprises providing a valve group subassembly, providing a coil group subassembly, inserting the valve group subassembly into the coil group subassembly, and connecting first and second attaching portions. The valve group subassembly includes a tube assembly having a longitudinal axis extending between a first end and a second end. The tube assembly includes an inlet tube having a first inlet tube end and a second inlet tube end; a non-magnetic shell having a first shell end connected to the second inlet tube end at a first connection and further having a second shell end; and a valve body having a first valve body end connected to the second shell end at a second connection and further having a second valve body end. A seat secured at the second end of the tube assembly, the seat defining an opening; an armature assembly disposed within the tube assembly; a member biasing the armature assembly toward the seat. A filter assembly located in the tube assembly, the filter assembly engaging the member and adjusting a biasing force of the member; and a first attaching portion. The coil group subassembly includes a solenoid coil operable to displace the armature assembly with respect to the seat; and a second attaching portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate an embodiment of the invention, and, together with the general description given above and the detailed description given below, serve to explain features of the invention. 
     FIG. 1 is a cross-sectional view of a fuel injector according to the present invention. 
     FIG. 2 is a cross-sectional view of a fluid handling subassembly of the fuel injector shown in FIG.  1 . 
     FIG. 2A is a cross-sectional view of an alternative fuel filter assembly for the fluid handling subassembly of the fuel injector of FIG.  1 . 
     FIGS. 2C-2D illustrate alternative combinations of inlet tubes and pole pieces for the fuel injector of FIG.  1 . 
     FIG. 3 is a cross-sectional view of an electrical subassembly of the fuel injector shown in FIG.  1 . 
     FIG. 3A illustrates the coil group subassembly using two overmolds in the present invention. 
     FIG. 4 is an isometric view that illustrates assembling the fluid handling and electrical subassemblies that are shown in FIGS. 2 and 3, respectively. 
     FIG. 5 is a flow chart of the method of assembling the modular fuel injector of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1-4, a solenoid actuated fuel injector  100  dispenses a quantity of fuel that is to be combusted in an internal combustion engine (not shown). The fuel injector  100  extends along a longitudinal axis between a first injector end  238  and a second injector end  239 , and includes a valve group subassembly  200  and a power group subassembly  300 . The valve group subassembly  200  performs fluid handling functions, e.g., defining a fuel flow path and prohibiting fuel flow through the injector  100 . The power group subassembly  300  performs electrical functions, e.g., converting electrical signals to a driving force for permitting fuel flow through the injector  100 . 
     Referring to FIGS. 1 and 2, the valve group subassembly  200  comprises a tube assembly extending along the longitudinal axis A—A between a first tube assembly end  200 A and a second tube assembly end  200 B. The tube assembly includes at least an inlet tube, a non-magnetic shell  230 , and a valve body  240 . The inlet tube has a first inlet tube end proximate to the first tube assembly end  200 A. A second inlet tube end of the inlet tube is connected to a first shell end of the non-magnetic shell  230 . A second shell end of the non-magnetic shell  230  is connected to a first valve body end of the valve body  240 . And a second valve body end of the valve body  240  is proximate to the second tube assembly end  200 B. The inlet tube can be formed by a deep drawing process or by a rolling operation. A pole piece can be integrally formed at the second inlet tube end of the inlet tube or, as shown, a separate pole piece  220  can be connected to a partial inlet tube and connected to the first shell end of the non-magnetic shell  230 . The non-magnetic shell  230  can comprise non-magnetic stainless steel, e.g.,  300  series stainless steels, or other materials that have similar structural and magnetic properties. 
     As shown in FIG. 2, inlet tube  210  is attached to pole piece  220  by means of welds. Formed into the outer surface of pole piece  220  are shoulders  222 A, which, in conjunction with shoulders  222 B of the coil subassembly, act as positive mounting stops when the injector is assembled. As shown in FIGS. 2C and 2D, the length of pole piece is fixed whereas the length of inlet tube can vary according to operating requirements. By forming inlet tube  210  separately from pole piece  220 , different length injectors can be manufactured by using different inlet tube lengths during the assembly process. Inlet tube  220  can be flared at the inlet end to retain the O-ring  290 . 
     Referring again to FIG. 2, the inlet tube  210  can be attached to the pole piece  220  at an inner circumferential surface of the pole piece  220 . Alternatively, as shown in FIGS. 2B, an integral inlet tube and pole piece assembly  211  can be attached to the inner circumferential surface of the non-magnetic shell  230 . A seat  250  is secured at the second end of the tube assembly. The seat  250  defines an opening centered on the axis A—A and through which fuel can flow into the internal combustion engine (not shown). The seat  250  includes a sealing surface  252  surrounding the opening. The sealing surface, which faces the interior of the valve body  240 , can be frustoconical or concave in shape, and can have a finished surface. An orifice disk  254  can be used in connection with the seat  250  to provide at least one precisely sized and oriented orifice in order to obtain a particular fuel spray pattern. 
     An armature assembly  260  is disposed in the tube assembly. The armature assembly  260  includes a first armature assembly end having a ferro-magnetic or armature portion  262  and a second armature assembly end having a sealing portion. The armature assembly  260  is disposed in the tube assembly such that the magnetic portion, or “armature,”  262  confronts the pole piece  220 . The sealing portion can include a closure member  264 , e.g., a spherical valve element, that is moveable with respect to the seat  250  and its sealing surface  252 . The closure member  264  is movable between a closed configuration, as shown in FIGS. 1 and 2, and an open configuration (not shown). In the closed configuration, the closure member  264  contiguously engages the sealing surface  252  to prevent fluid flow through the opening. In the open configuration, the closure member  264  is spaced from the seat  250  to permit fluid flow through the opening. The armature assembly  260  may also include a separate intermediate portion  266  connecting the ferro-magnetic or armature portion  262  to the closure member  264 . The intermediate portion or armature tube  266  can be fabricated by various techniques, for example, a plate can be rolled and its seams welded or a blank can be deep-drawn to form a seamless tube. The intermediate portion  266  is preferable due to its ability to reduce magnetic flux leakage from the magnetic circuit of the fuel injector  100 . This ability arises from the fact that the intermediate portion or armature tube  266  can be non-magnetic, thereby magnetically decoupling the magnetic portion or armature  262  from the ferro-magnetic closure member  264 . Because the ferro-magnetic closure member is decoupled from the ferro-magnetic or armature  262 , flux leakage is reduced, thereby improving the efficiency of the magnetic circuit. 
     Fuel flow through the armature assembly  260  can be provided by at least one axially extending through-bore  267  and at least one apertures  268  through a wall of the armature assembly  260 . The apertures  268 , which can be of any shape, are preferably non-circular, e.g., axially elongated, to facilitate the passage of gas bubbles. For example, in the case of a separate intermediate portion  266  that is formed by rolling a sheet substantially into a tube, the apertures  268  can be an axially extending slit defined between non-abutting edges of the rolled sheet. However, the apertures  268 , in addition to the slit, would preferably include openings extending through the sheet. The apertures  268  provide fluid communication between the at least one through-bore  267  and the interior of the valve body  240 . Thus, in the open configuration, fuel can be communicated from the through-bore  267 , through the apertures  268  and the interior of the valve body  240 , around the closure member, and through the opening into the engine. 
     In the case of a spherical valve element providing the closure member  264 , the spherical valve element can be connected to the armature assembly  260  at a diameter that is less than the diameter of the spherical valve element. Such a connection would be on side of the spherical valve element that is opposite contiguous contact with the seat  250 . A lower armature guide can be disposed in the tube assembly, proximate the seat  250 , and would slidingly engage the diameter of the spherical valve element. The lower armature guide can facilitate alignment of the armature assembly  260  along the axis A—A, and can magnetically decouple the closure member  264  from the ferro-magnetic or armature portion  262  of the armature assembly  260 . 
     A resilient member  270  is disposed in the tube assembly and biases the armature assembly  260  toward the seat  250 . A filter assembly  282  comprising a filter  284 A and an integral retaining portion  283  is also disposed in the tube assembly. The filter assembly  282  includes a first end and a second end. The filter  284 A is disposed at one end of the filter assembly  282  and also located proximate to the first end of the tube assembly and apart from the resilient member  270  while the adjusting tube  281  is disposed generally proximate to the second end of the tube assembly. The adjusting tube  281  engages the resilient member  270  and adjusts the biasing force of the member with respect to the tube assembly. In particular, the adjusting tube  281  provides a reaction member against which the resilient member  270  reacts in order to close the injector valve  100  when the power group subassembly  300  is de-energized. The position of the adjusting tube  281  can be retained with respect to the inlet tube  210  by an interference fit between an outer surface of the adjusting tube  281  and an inner surface of the tube assembly. Thus, the position of the adjusting tube  281  with respect to the inlet tube  210  can be used to set a predetermined dynamic characteristic of the armature assembly  260 . 
     The filter assembly  282  includes a cup-shaped filtering element  284 A and an integral-retaining portion  283  for positioning an O-ring  290  proximate the first end of the tube assembly. The O-ring  290  circumscribes the first end of the tube assembly and provides a seal at a connection of the injector  100  to a fuel source (not shown). The retaining portion  283  retains the O-ring  290  and the filter element with respect to the tube assembly. 
     Two variations on the fuel filter of FIG. 1 are shown in FIGS. 1A and 2A. In FIG. 1A, a fuel filter assembly  282 ″ with filter  285  is attached to the adjusting tube  280 ′. Likewise, in FIG. 2A, the filter assembly  282 ″ includes an inverted-cup filtering element  284 B attached to an adjusting tube  280 ″. Similar to adjusting tube  281  described above, the adjusting tube  280 ′ or  280 ″ of the respective fuel filter assembly  282 ′ or  282 ″ engages the resilient member  270  and adjusts the biasing force of the member with respect to the tube assembly. In particular, the adjusting tube  280 ′ or  280 ″ provides a reaction member against which the resilient member  270  reacts in order to close the injector valve  100  when the power group subassembly  300  is de-energized. The position of the adjusting tube  280 ′ or  280 ″ can be retained with respect to the inlet tube  210  by an interference fit between an outer surface of the adjusting tube  280 ′ or  280 ″ and an inner surface of the tube assembly. 
     The valve group subassembly  200  can be assembled as follows. The non-magnetic shell  230  is connected to the inlet tube  210  and to the valve body. The adjusting tube  280 A or the filter assembly  282 ′ or  282 ″ is inserted along the axis A—A from the first end  200 A of the tube assembly. Next, the resilient member  270  and the armature assembly  260  (which was previously assembled) are inserted along the axis A—A from the injector end  239  of the valve body  240 . The adjusting tube  280 A, the filter assembly  282 ′ or  282 ″ can be inserted into the inlet tube  210  to a predetermined distance so as to permit the adjusting tube  280 A,  280 B or  280 C to preload the resilient member  270 . Positioning of the filter assembly  282 , and hence the adjusting tube  280 B or  280 C with respect to the inlet tube  210  can be used to adjust the dynamic properties of the resilient member  270 , e.g., so as to ensure that the armature assembly  260  does not float or bounce during injection pulses. The seat  250  and orifice disk  254  are then inserted along the axis A—A from the second valve body end of the valve body. The seat  250  and orifice disk  254  can be fixedly attached to one another or to the valve body by known attachment techniques such as laser welding, crimping, friction welding, conventional welding, etc. 
     Referring to FIGS. 1 and 3, the power group subassembly  300  comprises an electromagnetic coil  310 , at least one terminal  320 , a housing  330 , and an overmold  340 . The electromagnetic coil  310  comprises a wire  312  that that can be wound on a bobbin  314  and electrically connected to electrical contacts on the bobbin  314 . When energized, the coil generates magnetic flux that moves the armature assembly  260  toward the open configuration, thereby allowing the fuel to flow through the opening. De-energizing the electromagnetic coil  310  allows the resilient member  270  to return the armature assembly  260  to the closed configuration, thereby shutting off the fuel flow. The housing, which provides a return path for the magnetic flux, generally comprises a ferro-magnetic cylinder  332  surrounding the electromagnetic coil  310  and a flux washer  334  extending from the cylinder toward the axis A—A. The washer  334  can be integrally formed with or separately attached to the cylinder. The housing  330  can include holes, slots, or other features to break-up eddy currents that can occur when the coil is de-energized. 
     The overmold  340  maintains the relative orientation and position of the electromagnetic coil  310 , the at least one terminal  320  (two are used in the illustrated example), and the housing  330 . The overmold  340  includes an electrical harness connector  321  portion in which a portion of the terminal  320  is exposed. The terminal  320  and the electrical harness connector  321  portion can engage a mating connector, e.g., part of a vehicle wiring harness (not shown), to facilitate connecting the injector  100  to an electrical power supply (not shown) for energizing the electromagnetic coil  310 . 
     The coil group subassembly  300  can be constructed as follows. A plastic bobbin  314  can be molded with at least one electrical contact portion  322 . The wire  312  for the electromagnetic coil  310  is wound around the plastic bobbin  314  and connected to at least one electrical contact portion  322 . The housing  330  is then placed over the electromagnetic coil  310  and bobbin unit. A terminal  320 , which is pre-bent to a proper shape, is then electrically connected to each electrical contact portion  322 . An overmold  340  is then formed to maintain the relative assembly of the coil/bobbin unit, housing  330 , and terminal  320 . The overmold  340  also provides a structural case for the injector and provides predetermined electrical and thermal insulating properties. A separate collar can be connected, e.g., by bonding, and can provide an application specific characteristic such as an orientation feature or an identification feature for the injector  100 . Thus, the overmold  340  provides a universal arrangement that can be modified with the addition of a suitable collar. To reduce manufacturing and inventory costs, the coil/bobbin unit can be the same for different applications. As such, the terminal  320  and overmold  340  (or collar, if used) can be varied in size and shape to suit particular tube assembly lengths, mounting configurations, electrical connectors, etc. 
     In particular, as shown in FIG. 3A, a two-piece overmold allows for a first overmold  341  that is application specific while the second overmold  342  can be for all applications. The first overmold  341  is bonded to a second overmold  342 , allowing both to act as electrical and thermal insulators for the injector  100 . Additionally, a portion of the housing  330  can extend axially beyond an end of the overmold  340  and can be formed with a flange to retain an O-ring. 
     As is particularly shown in FIGS. 1 and 4, the valve group subassembly  200  can be inserted into the coil group subassembly  300 . Thus, the injector  100  is made of two modular subassemblies that can be assembled and tested separately, and then connected together to form the injector  100 . The valve group subassembly  200  and the coil group subassembly  300  can be fixedly attached by adhesive, welding, or another equivalent attachment process. According to a preferred embodiment, a hole  360  through the overmold  340  exposes the housing  330  and provides access for laser welding the housing  330  to the valve body  240 . The filter and the retainer, which may be an integral unit, can be connected to the first tube assembly end  200 A of the tube unit. The O-rings can be mounted at the respective first and second injector ends. 
     The first injector end  238  can be coupled to the fuel supply of an internal combustion engine (not shown). The O-ring  290  can be used to seal the first injector end  238  to the fuel supply so that fuel from a fuel rail (not shown) is supplied to the tube assembly, with the O-ring  290  making a fluid tight seal, at the connection between the injector  100  and the fuel rail (not shown). 
     In operation, the electromagnetic coil  310  is energized, thereby generating magnetic flux in the magnetic circuit. The magnetic flux moves armature assembly  260  (along the axis A—A, according to a preferred embodiment) towards the pole piece  220 , i.e., closing the working air gap. This movement of the armature assembly  260  separates the closure member  264  from the seat  250  and allows fuel to flow from the fuel rail (not shown), through the inlet tube  210 , the through-bore  267 , the apertures  268  and the valve body  240 , between the seat  250  and the closure member  264 , through the orifice disk  254  into the internal combustion engine (not shown). When the electromagnetic coil  310  is de-energized, the armature assembly  260  is moved by the bias of the resilient member  270  to contiguously engage the closure member  264  with the seat  250 , and thereby prevent fuel flow through the injector  100 . 
     Referring to FIG. 5, a preferred assembly process can be as follows: 
     1. A pre-assembled valve body and non-magnetic sleeve is located with the valve body oriented up. 
     2. A screen retainer, e.g., a lift sleeve, is loaded into the valve body/non-magnetic sleeve assembly. 
     3. A lower screen can be loaded into the valve body/non-magnetic sleeve assembly. 
     4. A pre-assembled seat and guide assembly is loaded into the valve body/non-magnetic sleeve assembly. 
     5. The seat/guide assembly is pressed to a desired position within the valve body/non-magnetic sleeve assembly. 
     6. The valve body is welded, e.g., by a continuous wave laser forming a hermetic lap seal, to the seat. 
     7. A first leak test is performed on the valve body/non-magnetic sleeve assembly. This test can be performed pneumatically. 
     8. The valve body/non-magnetic sleeve assembly is inverted so that the non-magnetic sleeve is oriented up. 
     9. An armature assembly is loaded into the valve body/non-magnetic sleeve assembly. 
     10. A pole piece is loaded into the valve body/non-magnetic sleeve assembly and pressed to a pre-lift position. 
     11. Dynamically, e.g., pneumatically, purge valve body/non-magnetic sleeve assembly. 
     12. Set lift. 
     13. The non-magnetic sleeve is welded, e.g., with a tack weld, to the pole piece. 
     14. The non-magnetic sleeve is welded, e.g., by a continuous wave laser forming a hermetic lap seal, to the pole piece. 
     15. Verify lift 
     16. A spring is loaded into the valve body/non-magnetic sleeve assembly. 
     17. A filter/adjusting tube is loaded into the valve body/non-magnetic sleeve assembly and pressed to a pre-cal position. 
     18. An inlet tube is connected to the valve body/non-magnetic sleeve assembly to generally establish the fuel group subassembly. 
     19. Axially press the fuel group subassembly to the desired over-all length. 
     20. The inlet tube is welded, e.g., by a continuous wave laser forming a hermetic lap seal, to the pole piece. 
     21. A second leak test is performed on the fuel group subassembly. This test can be performed pneumatically. 
     22. The fuel group subassembly is inverted so that the seat is oriented up. 
     23. An orifice is punched and loaded on the seat. 
     24. The orifice is welded, e.g., by a continuous wave laser forming a hermetic lap seal, to the seat. 
     25. The rotational orientation of the fuel group subassembly/orifice can be established with a “look/orient/look” procedure. 
     26. The fuel group subassembly is inserted into the (pre-assembled) power group subassembly. 
     27. The power group subassembly is pressed to a desired axial position with respect to the fuel group subassembly. 
     28. The rotational orientation of the fuel group subassembly/orifice/power group subassembly can be verified. 
     29. The power group subassembly can be laser marked with information such as part number, serial number, performance data, a logo, etc. 
     30. Perform a high-potential electrical test. 
     31. The housing of the power group subassembly is tack welded to the valve body. 
     32. A lower O-ring can be installed. Alternatively, this lower O-ring can be installed as a post test operation. 
     33. An upper O-ring is installed. 
     34. Invert the fully assembled fuel injector. 
     35. Transfer the injector to a test rig. 
     To set the lift, i.e., ensure the proper injector lift distance, there are at least four different techniques that can be utilized. According to a first technique, a crush ring or a washer that is inserted into the valve body  240  between the lower guide  257  and the valve body  240  can be deformed. According to a second technique, the relative axial position of the valve body  240  and the non-magnetic shell  230  can be adjusted before the two parts are affixed together. According to a third technique, the relative axial position of the non-magnetic shell  230  and the pole piece  220  can be adjusted before the two parts are affixed together. And according to a fourth technique, a lift sleeve  255  can be displaced axially within the valve body  240 . If the lift sleeve technique is used, the position of the lift sleeve can be adjusted by moving the lift sleeve axially. The lift distance can be measured with a test probe. Once the lift is correct, the sleeve is welded to the valve body  240 , e.g., by laser welding. Next, the valve body  240  is attached to the inlet tube  210  assembly by a weld, preferably a laser weld. The assembled fuel group subassembly  200  is then tested, e.g., for leakage. 
     As is shown in FIG. 5, the lift set procedure may not be able to progress at the same rate as the other procedures. Thus, a single production line can be split into a plurality (two are shown) of parallel lift setting stations, which can thereafter be recombined back into a single production line. 
     The preparation of the power group sub-assembly, which can include (a) the housing  330 , (b) the bobbin assembly including the terminals  320 , (c) the flux washer  334 , and (d) the overmold  340 , can be performed separately from the fuel group subassembly. 
     According to a preferred embodiment, wire  312  is wound onto a pre-formed bobbin  314  with at least one electrical contact  322  molded thereon. The bobbin assembly is inserted into a pre-formed housing  330 . To provide a return path for the magnetic flux between the pole piece  220  and the housing  330 , flux washer  334  is mounted on the bobbin assembly. A pre-bent terminal  320  having axially extending connector portions  324  are coupled to the electrical contact portions  322  and brazed, soldered welded, or preferably resistance welded. The partially assembled power group assembly is now placed into a mold (not shown). By virtue of its pre-bent shape, the terminals  320  will be positioned in the proper orientation with the harness connector  321  when a polymer is poured or injected into the mold. Alternatively, two separate molds (not shown) can be used to form a two-piece overmold as described with respect to FIG.  3 A. The assembled power group subassembly  300  can be mounted on a test stand to determine the solenoid&#39;s pull force, coil resistance and the drop in voltage as the solenoid is saturated. 
     The inserting of the fuel group subassembly  200  into the power group subassembly  300  operation can involve setting the relative rotational orientation of fuel group subassembly  200  with respect to the power group subassembly  300 . The inserting operation can be accomplished by one of two methods: “top-down” or “bottom-up.” According to the former, the power group subassembly  300  is slid downward from the top of the fuel group subassembly  200 , and according to the latter, the power group subassembly  300  is slid upward from the bottom of the fuel group subassembly  200 . In situations where the inlet tube  210  assembly includes a flared first end, bottom-up method is required. Also in these situations, the O-ring  290  that is retained by the flared first end can be positioned around the power group subassembly  300  prior to sliding the fuel group subassembly  200  into the power group subassembly  300 . After inserting the fuel group subassembly  200  into the power group subassembly  300 , these two subassemblies are affixed together, e.g., by welding, such as laser welding. According to a preferred embodiment, the overmold  340  includes an opening  360  that exposes a portion of the housing  330 . This opening  360  provides access for a welding implement to weld the housing  330  with respect to the valve body  240 . Of course, other methods or affixing the subassemblies with respect to one another can be used. Finally, the O-ring  290  at either end of the fuel injector can be installed. 
     The method of assembling the preferred embodiments, and the preferred embodiments themselves, are believed to provide manufacturing advantages and benefits. For example, because of the modular arrangement only the valve group subassembly is required to be assembled in a “clean” room environment. The power group subassembly  300  can be separately assembled outside such an environment, thereby reducing manufacturing costs. Also, the modularity of the subassemblies permits separate pre-assembly testing of the valve and the coil assemblies. Since only those individual subassemblies that test unacceptable are discarded, as opposed to discarding fully assembled injectors, manufacturing costs are reduced. Further, the use of universal components (e.g., the coil/bobbin unit, non-magnetic shell  230 , seat  250 , closure member  264 , filter/retainer assembly  282 , etc.) enables inventory costs to be reduced and permits a “just-in-time” assembly of application specific injectors. Only those components that need to vary for a particular application, e.g., the terminals  320  and inlet tube  210  need to be separately stocked. Another advantage is that by locating the working air gap, i.e., between the armature assembly  260  and the pole piece  220 , within the electromagnetic coil  310 , the number of windings can be reduced. In addition to cost savings in the amount of wire  312  that is used, less energy is required to produce the required magnetic flux and less heat builds-up in the coil (this heat must be dissipated to ensure consistent operation of the injector). Yet another advantage is that the modular construction enables the orifice disk  254  to be attached at a later stage in the assembly process, even as the final step of the assembly process. This just-in-time assembly of the orifice disk  254  allows the selection of extended valve bodies depending on the operating requirement. Further advantages of the modular assembly include out-sourcing construction of the power group subassembly  300 , which does not need to occur in a clean room environment. And even if the power group subassembly  300  is not out-sourced, the cost of providing additional clean room space is reduced. 
     While the preferred embodiments have been disclosed with reference to certain embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims, and equivalents thereof.