Abstract:
A modular fuel injector for an internal combustion engine, including a valve group subassembly and a power group subassembly. The valve group subassembly includes a first stator member, a second stator member, a non-magnetic shell disposed between the first and second stator members, a valve body, and an armature member. The armature member defines a first working air gap with the first stator member and a second working air gap with the second stator member. The armature member includes a closure member proximate an outlet end and contiguous to a seat in a first configuration. The power group subassembly includes an electromagnetic coil surrounding the passage, a housing encasing the coil, and an ovemold encapsulating the coil and the housing. The coil is energizable to provide magnetic flux that flows through the first and second working air gaps in the direction of the longitudinal axis.

Description:
CROSS REFERENCE TO CO-PENDING APPLICATIONS 
   This application claims the benefit of the earlier filing date of U.S. Provisional Application No. 60/477,484 filed Jun. 10, 2003, entitled “Modular Injector with Di-Pole Magnetic Circuit” and having inventors Michael P. Dallmeyer and Harry R. Brooks, which Provisional Application is incorporated by reference herein in its entirety. 

   BACKGROUND OF THE INVENTION 
   A known electromagnetic actuator for an electromagnetic fuel injector includes a stator member, an armature member, a valve body formed of magnetic material, and an electromagnetic coil. The electromagnetic coil is energizable to flow magnetic flux through a magnetic circuit. The magnetic circuit includes the stator member, the armature member, and the valve body. The magnetic flux flows through a working air gap defined by the armature member and the stator member, and creates a magnetic force that attracts the armature member to the stator member. The air gap is a working air gap because magnetic flux flowing through the air gap produces useful work. The armature member is disposed in the valve body and is guided by an inner surface of the valve body during reciprocal movement toward and away from the stator member. The armature member and the inner surface of the valve body, by their radially facing orientation, define a non-working air gap (i.e. a parasitic air gap) that adds reluctance to the magnetic circuit. The air gap is a parasitic air gap because the magnetic flux flowing through the air gap does not produce useful work and also incur magnetic losses in the circuit. One example of a modular fuel injector with a parasitic gap is shown and described in U.S. Pat. No. 6,481,646, the entirety of which is incorporated by reference herein. 
   SUMMARY OF THE INVENTION 
   In an embodiment, the invention provides a modular fuel injector for an internal combustion engine. The modular fuel injector includes a power group subassembly secured to a valve group subassembly. The power group subassembly includes a housing, an electromagnetic coil and an overmold. The housing encases an electromagnetic coil. The overmold surrounds the coil and the housing. The valve group subassembly includes first and second stator members, a non-magnetic shell, a valve body, an armature member, and a seat. The first stator member defines a fluid passage extending along a longitudinal axis. The non-magnetic shell is disposed between the first and second stator members. The valve body is coupled to the second stator member and includes a securement that secures the valve body to the coil housing. The armature member is disposed in the valve body and coupled to a closure member for movement with respect to the first and second stator members between a first configuration with a closure member contiguous to a seat in the first configuration and spaced from the seat in the second configuration. The armature member includes an armature surface with at least a portion contiguous to a plane intersecting the longitudinal axis. A first portion of the armature surface confronts the first stator member to define a first working gap from the armature surface to the first stator member along the longitudinal axis. A second portion of the armature surface confronts the second stator member to define a second working gap from the armature surface to the second stator member along the longitudinal axis. 
   In yet another embodiment, the invention provides a method of manufacturing a modular fuel injector. The method can be achieved by providing a valve group subassembly, providing a power group subassembly, inserting the valve group subassembly into the power group subassembly and securing the valve group subassembly to the power group subassembly. The power group subassembly, as provided, includes a housing, an electromagnetic coil and an overmold. The housing encases an electromagnetic coil. The overmold surrounds the coil and the housing. The valve group subassembly, as provided, includes first and second stator members, a non-magnetic shell, a valve body, an armature member, and a seat. The first stator member defines a fluid passage extending along a longitudinal axis. The non-magnetic shell is disposed between the first and second stator members. The armature member is disposed in the valve body and coupled to a closure member for movement with respect to the first and second stator members between a first configuration with a closure member contiguous to a seat in the first configuration and spaced from the seat in the second configuration. The armature member includes an armature surface with at least a portion contiguous to a plane intersecting the longitudinal axis. A first portion of the armature surface confronts the first stator member to define a first working gap from the armature surface to the first stator member along the longitudinal axis. A second portion of the armature surface confronts the second stator member to define a second working gap from the armature surface to the second stator member along the longitudinal axis. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate the presently preferred embodiments 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 preferred embodiment showing a modular electromagnetic fuel injector that are assembled from power group and valve group subassemblies, which provide a magnetic circuit having a first working air gap and a second working air gap. 
       FIG. 2  is an enlarged view of various components of the modular fuel injector including a first working air gap and the second working air gap of  FIG. 1 . 
       FIG. 3  is a cross-sectional view of a valve group subassembly of  FIG. 1  prior to being inserted into a power group subassembly shown in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Fuel injectors are used to provide a metered amount of fuel to an internal combustion engine. Details of the operation of the modular fuel injector  10  in relation to the operation of the internal combustion engine (not shown) are well known and will not be described in detail herein, except as the operation relates to the preferred embodiments. 
   Referring now to  FIG. 1 , there is shown the modular fuel injector  10 , according to a preferred embodiment. As used herein, like numerals indicate like elements throughout. The modular fuel injector  10  includes a valve group subassembly  21 , also illustrated in  FIG. 2 , having a valve body  12  with an upstream end  11 , a downstream end  13 , and a longitudinal axis A—A extending therethrough. The words “upstream” and “downstream” designate flow directions in the drawing to which reference is made. The upstream end is defined to mean in a direction toward the top of the figure referred, and the downstream end is defined to mean in a direction toward the bottom of the figure. 
   The valve group  21  includes an armature assembly  20  that is reciprocally disposed within the valve body  12  along the longitudinal axis A—A. The valve group  21  further includes an inlet tube  38 , having an upstream end  37 , a downstream end  39 , and an inlet tube channel  41 . The upstream end  37  can be provided with an O-ring retainer to retain an O-ring. The downstream end  39  of the inlet tube  38  is connected to the upstream end  11  of the valve body  12  via a non-magnetic shell  80  and a magnetic stop member  82 . A suitable technique can be used to secure the components, such as hermetic laser welds  50 . 
   The downstream end  39  of the inlet tube  38  is spaced a predetermined distance from upstream end  19  of the armature assembly  20 . This predetermined distance, as measured from the downstream end  39  to the upstream end  19  along the longitudinal axis A—A, represents a first working air gap  15 . The downstream end  84  of the magnetic stop member  82  is spaced a predetermined distance from the upstream end  19  of the armature assembly  20  along the longitudinal axis A—A. This predetermined distance represents a second working air gap  86 . A spring  28 , is disposed at the downstream end  39  of the inlet tube  38 , upstream of the armature assembly. An adjusting tube  36  is disposed a predetermined distance into the channel  41  of the inlet tube  38 . The adjusting tube  36  compresses the spring  28 . The compression of the spring  28  biases the armature assembly  20  to a closed position to preclude fuel flow. 
   A seat  22  and a lower guide  24  are provided within the valve body  12 . The lower guide  24  is located upstream from the seat  22 . Both the lower guide  24  and seat  22  are located downstream of the armature assembly  20  along the longitudinal axis A—A. The lower guide  24  has a plurality of apertures  14  that extend therethrough. The plurality of apertures  14  in the lower guide  24  are disposed circumferentially about the longitudinal axis A—A. The seat  22  has a generally recessed area  72  extending down from the upper surface  23  of the seat  22 , and a generally circular opening  74  extending along the longitudinal axis A—A. A seating surface  73  extends between the recessed area  72  and the opening  74 , and is in the form of a conic frustum. A hermetic weld  48 , located at the downstream end  13  of the valve body  12 , seals the seat  22  at the valve body  12 . 
   The lower guide  24  guides a downstream end  62  of the armature assembly  20 , in the valve body  12 , along the longitudinal axis A—A. An orifice disk  18  is disposed downstream of the seat  22 . An orifice  64  is provided within the orifice disk  18 . The orifice  64  preferably extends through the geometric center of the orifice disk  18  along the longitudinal axis A—A. Alternatively, the orifice  64  can be offset from the axis A—A. A retainer proximate the orifice disk  18  can be used to retain an O-ring. 
   A fuel filter  34  is disposed in the inlet tube channel  41 . The fuel filter  34  removes particulate (not shown) in the fuel that passes through the modular fuel injector  10 . 
   The armature assembly  20  includes a ball  16  welded to the downstream end  62  of an armature tube  56 . An armature surface can be coupled to the armature tube  56 . Preferably, the armature surface is a generally planar, generally circular magnetic disk  52  that extends radially from an upstream end of the armature tube  56 . An interior surface  78  of the valve body  12  acts as a guide  76  for side surface  94  of the disk  52 . The interior surface  78  and the lower guide  24  orients the reciprocal operation of the armature assembly  20  within the valve body  12  along the longitudinal axis A—A. 
   The modular fuel injector  10  further includes a power group subassembly  40 . The power group subassembly  40  includes a coil assembly  43  that cinctures the inlet tube  38 . The coil assembly  43  includes a plastic bobbin  42  and terminals  46 . Coil wire  44  is wound around the plastic bobbin  42 . The terminals  46  are bent to a desired position as shown in  FIG. 1 . A coil housing  60  encases the coil assembly  43 . The coil assembly  43  and housing  60  are then overmolded with a plastic overmold  45  or any other equivalent formable material thereof. The power group subassembly can be assembled as a separate subassembly from the valve group subassembly and tested before being assembled with the valve group subassembly. 
   The valve group subassembly  21  may be assembled and tested as a separate part, and then assembled to the power group subassembly  40 . The valve group subassembly  21 , including the valve body  12 , the armature assembly  20 , the inlet tube  38 , the non-magnetic shell  80  and the magnetic stop member  82 , may be inserted into the downstream end of the power group subassembly  40  such that the non-magnetic shell contacts the downstream end of the plastic bobbin  42 . A first securement  30  can secure an upstream end of the inlet tube  38  to the overmold  45 , and a second securement  95  can secure the valve body  12  to the coil housing by a suitable retention technique such as, for example, welding, bonding or fusing the members together. 
     FIG. 2  is an enlarged view of the first working air gap  15  and the second working air gap  86 . The inlet tube  38  includes a lower surface  90  that is spaced apart a predetermined distance d 1  from the lower surface  90  to an upper surface  92  of the magnetic armature disk  52  along the longitudinal axis. Preferably, the upper surface  92  intersects the longitudinal axis A—A. This predetermined distance represents the first working air gap  15 . A lower surface  84  of the magnetic stop member  82  is spaced a predetermined distance d 2  from the upper surface  92  of the magnetic armature disk  52 . This predetermined distance represents the second working air gap  86  from the upper surface  92  to the lower surface  84  along the longitudinal axis. In a preferred embodiment, the distance d 1  is longer than the distance d 2 . 
   In this preferred configuration, the coil  44  can be energized with a voltage potential (not shown) to generate an electromagnetic flux  88  that flows from the inlet tube  38 , to the coil housing  60 , through magnetic stop member  82 , across the second working gap  86  to the armature disk  52 , from the armature disk  52  across the first working gap  15 , and back to the inlet tube  38 . The flow of flux  88  through the first and second working air gaps generates an electromagnetic force in the first and second working air gaps in the direction of the longitudinal axis A—A that draws the armature assembly  20  against the force of the spring  28 . The armature assembly  20  is displaced across the distance of the second working air gap  86  such that the upper surface  92  of the armature disk  52  contacts and is stopped by the lower surface  84  of the stop member  82 . Because the stop member  82  directs the magnetic flux  88  through the second air gap  86  in the direction of the longitudinal axis A—A, the second air gap  86  constitutes a working air gap. Hence, the magnetic flux  88  flowing through the second working air gap  86  produces useful work in the form an electromagnetic force that attracts the armature disk  52 . 
   Consequently, the stop member  82  can be considered to be a second stator member in addition to the first stator member  38  such that a second magnetic pole is formed at the second working air gap  86 , in addition to the first magnetic pole, which is formed at the first working air gap  15 . Because both air gaps  15  and  86  produce useful work, the efficiency of the magnetic circuit is believed to be increased as compared to known actuators that have one working air gap and one parasitic air gap. 
   Several features of the preferred embodiments facilitate an evenly distributed and miminal wear of the armature disk upper surface  92 . The upper surface  92  of the armature contacting the lower surface  84  of the stop member  82 , rather than contacting the lower surface  90  of the inlet tube  38 , provides a contact area that is more distributed. The armature disk  52  includes a curved side surface  94  that is guided by the interior surface  78  of the valve body  12  as the armature assembly  20  is displaced along the longitudinal axis A—A. Because the side surface  94  is curved, the side surface  94  contacts the interior surface  78  along a line that extends 360° around the perimeter of the side surface  94 . Due to limitations of manufacturing tolerances, the lower surface  84  of the stop member  82  and the upper surface  92  of the armature disk may not be exactly parallel to each other. The line contact between curved side surface  94  and interior surface  78  facilitates a slight tilting (e.g., a ball-in-ring geometry) for a three-degrees-of-freedom of the armature with respect to the longitudinal axis. This feature is believed to allow the lower surface  84  of the stop member  82  and the upper surface  92  of the armature disk, in a preferred embodiment, to contact each other in a plane, thereby for slight misalignment due to tolerances between the armature assembly  20  and the valve body  12 . Preferably, the lower surface  84  of the stop member  82  and the upper surface  92  of the armature disk in the area of contact between theses two surfaces are coated with a layer of chrome to reduce wear of the respective surfaces. U.S. Pat. No. 6,499,668 discloses chroming techniques, and is incorporated by reference in its entirety. The combination of these features produces a consistent flow over the life of the injector. 
   Because the flux  88  flows through the stop member  82 , rather than the valve body  12 , the valve body  12  may be formed of a non-magnetic material such as a 300-Series stainless steel. Thus, the valve body may be formed by cost effective processes such as metal injection molding, stamping operations, or deep drawn operations. 
   In operation, fuel under pressure is provided to the upstream end  37  of the inlet tube  38  of the modular fuel injector assembly  10 . The fuel flows through channel  41  and the fuel filter  34 . From the fuel filter  34 , the fuel flows through the adjusting tube  36  and past the spring  28 . Once past the spring  28 , the fuel passes through a hole  54  in the disk  52  through the armature tube  56  and through an aperture  56 a of the tube  56  into the valve body  12 . The fuel then flows through the plurality of apertures  14  in the lower guide  24  and is contained in the generally recessed area  72  of the seat  22  until the injector assembly  10  is energized. To discharge the fuel from the injector  10 , the coil  44  is energized to create the electromagnetic flux  88  that flows from the inlet tube  38 , to the coil housing  60 , through magnetic stop member  82 , across the second working gap  86  to the armature disk  52 , from the armature disk  52  across the first working gap  15 , back to the inlet tube  38 . The flow of flux  88  through the first and second working air gaps  15  and  86  generates an electromagnetic force in the first and second working air gaps in the direction of the longitudinal axis A—A that draws the armature assembly  20  against the force of the spring  28 . The armature/ball  20  assembly is displaced over the distance of the second working air gap  86  and guided by the interior surface  78  of the valve body  12  and lower guide  24  along the longitudinal axis A—A. The fuel that was contained in the recess  72  of the seat  22  is now free to flow through the circular hole  74  in the seat  22 , through the orifice  64  and into the engine. When the voltage potential is removed from the coil  44 , the electromagnetic flux  88  breaks down. The downward compressive force provided by the spring  28  forces the armature assembly  20  to drop back into the seat  22 , thus preventing the flow of the fuel being metered. 
   As described, the preferred embodiments, including the method of manufacturing the modular injector are not limited to the preferred modular fuel injector described herein but can be utilized for other modular fuel injectors such as, for example, the modular fuel injector shown and described in U.S. Pat. No. 6,676,044 issued to Dallmeyer et al, on 13 Jan. 2004, the entirety of which is incorporated by reference into this application. 
   While the invention has been disclosed with reference to certain preferred embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the invention, as defined in the appended claims and their equivalents thereof. Accordingly, it is intended that the invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims.