Abstract:
A fuel injector for an internal combustion engine including a body, a stator member, an armature, an electromagnetic coil, and a diamagnetic member. The body includes a passage extending along a longitudinal axis between inlet and outlet ends. The armature member is movable with respect to the stator member between a first configuration and a second configuration, and includes a closure member proximate the outlet end and contiguous to a seat in the first configuration, and spaced from the seat in the second configuration. The electromagnetic coil surrounds the passage, is disposed in a housing, and is energizable to provide magnetic flux that moves the armature between the first and second configuration to permit fuel flow through the passage. The diamagnetic member is proximate the electromagnetic coil so that when the electromagnetic coil is energized the magnetic flux flows around the diamagnetic member.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates generally to an electromagnetic actuator that may be used, for example, in an electromagnetic fuel injector for an internal combustion engine, and more particularly to an electromagnetic actuator having reduced magnetic flux leakage.  
       BACKGROUND OF THE INVENTION  
       [0002]     A known electromagnetic actuator for an electromagnetic fuel injector includes a stator member, an armature member and an electromagnetic coil. The electromagnetic coil is energizable to flow magnetic flux through a designed magnetic circuit. The magnetic circuit includes the stator member and the armature member, and creates a magnetic force to move the armature member relative to the stator member. Some magnetic flux may short-circuit off of the designed magnetic circuit, for example through the coil, rather than through the armature member, resulting in magnetic flux leakage. It is believed that known electromagnetic actuators are designed to reduce magnetic flux leakage by using air gaps or non-magnetic materials to direct the magnetic flux through the designed magnetic circuit.  
         [0003]     In the design of known actuators, the air gaps or non-magnetic materials have a minimum magnetic permeability, μ, assumed to be that of free space, μ o , or 4π×10 −7  Webers/amp-meter in SI units, which in Centimeter-Gram-Second units is the unity relative permeability value, μ r =1. The maximum relative permeability in known designs is usually defined by the ferromagnetic components in the magnetic circuit, the value often being in the thousands. However, in known designs, a significant amount of useful magnetic flux is lost as magnetic flux leakage. It is believed that there is a need to reduce or eliminate this magnetic flux leakage.  
       SUMMARY OF THE INVENTION  
       [0004]     In an embodiment, the invention provides a fuel injector for an internal combustion engine, including a body, a stator member, an armature, an electromagnetic coil, and a diamagnetic member. The body includes a passage extending along a longitudinal axis between inlet and outlet ends. The armature member is movable with respect to the stator member between a first configuration and a second configuration, and includes a closure member proximate the outlet end and contiguous to a seat in the first configuration, and spaced from the seat in the second configuration. The electromagnetic coil surrounds the passage, is disposed in a housing, and is energizable to provide magnetic flux that moves the armature between the first and second configuration to permit fuel flow through the passage. The diamagnetic member is proximate the electromagnetic coil so that when the electromagnetic coil is energized, the magnetic flux flows around the diamagnetic member.  
         [0005]     The diamagnetic member may be formed of bismuth, pyrolytic graphites, perovskite copper-oxides, alkali-metal tungstenates, vandanates, molybdates, titanate niobates, NaWO 3 , YBa 2 Cu 3 O 7 , TiBa 2 Ca 2 Cu 3 O 3 , Al x Ga 1−x As, and Cr, Fe selenides. A magnetic susceptibility of the diamagnetic member may be less than or equal to −0.25, less than or equal to −0.5, or less than or equal to −0.75.  
         [0006]     The electromagnetic coil may include a hollow core. The diamagnetic member may include a wall defining a hollow cylinder, the wall having an inner surface and an outer surface, and first and second ends. The diamagnetic member may be disposed at least partially in the hollow core. The coil housing may surround the coil, the inner surface of the wall may confront a portion of the stator, and the outer surface of the wall may be contiguous to a portion of the coil. The diamagnetic member may include a first flange formed at the first end of the wall, and a second flange formed at the second end of the wall. The first and second flanges may extend radially outward from the outer surface of the wall to define a bobbin. The electromagnetic coil may be disposed proximate the outer surface of the cylindrical wall, and the stator may be at least partially disposed proximate the inner surface of the cylindrical wall. The diamagnetic member may include a polymer having a diamagnetic material suspended therein. A lower surface of the stator member and an upper surface of the armature member may define a working gap, and the diamagnetic member may direct the magnetic flux through the working gap.  
         [0007]     In another embodiment, the invention provides an actuator including a stator member, an armature member, an electromagnetic coil, and a diamagnetic member. The diamagnetic member is proximate the coil, and has a magnetic susceptibility of less than −0.15 so that when the electromagnetic coil is energized, the diamagnetic member forms a barrier to magnetic flux.  
         [0008]     The diamagnetic member may include a wall defining a hollow cylinder, the wall having an inner surface and an outer surface, and first and second ends. A thickness of the wall may be approximately 20 microns or greater.  
         [0009]     The diamagnetic member may include a first flange formed at the first end of the wall, and a second flange formed at the second end of the wall. The first and second flanges may extend radially outward from the outer surface of the wall to define a bobbin. The diamagnetic member may include a polymer having a diamagnetic material suspended therein.  
         [0010]     In yet another embodiment, the invention provides a method of actuating an electromagnetic actuator having a stator member, an armature member, and an electromagnetic coil. The method includes forming a barrier to magnetic flux, and directing the magnetic flux between the stator member and the armature member. The forming a barrier to magnetic flux may include providing a diamagnetic member having a magnetic susceptibility of less than or equal to −0.15. The method may include generating an axial magnetic force between the stator member and the armature member; and increasing the axial magnetic force by about 14% with another diamagnetic member having a magnetic susceptibility of less than or equal to −0.98. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     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.  
         [0012]      FIG. 1  is a cross-sectional view of an electromagnetic fuel injector including a magnetic circuit, according to an embodiment of the invention.  
         [0013]      FIG. 2  is an exploded view of components of a magnetic circuit, according to an embodiment of the invention.  
         [0014]      FIG. 3A  is a schematic illustration of a conventional magnetic circuit.  
         [0015]      FIG. 3B  is a schematic illustration of a magnetic circuit, according to an embodiment of the invention.  
         [0016]      FIG. 4A  is another schematic illustration of a conventional magnetic circuit.  
         [0017]      FIG. 4B  is another schematic illustration of a magnetic circuit, according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]      FIGS. 1, 2 ,  3 B and  4 B illustrate preferred embodiments. One preferred embodiment, an electromagnetic fuel injector  100 , is provided. The fuel injector  100  includes an inlet tube  102 , an adjustment tube  104 , a filter assembly  106 , an electromagnetic coil assembly  108 , a biasing spring  110 , an armature assembly  112  including an armature member  112 A and closure member  112 B, a diamagnetic member  114 , an overmold  118 , a first ferromagnetic body  116 , a second body  120 , a ferromagnetic coil assembly housing  124 , a guide member  126 , and a seat  128 .  
         [0019]     Referring to  FIG. 2 , coil assembly  108  may include a plastic bobbin  130  on which an electromagnetic coil  132  is wound. Respective terminations of coil  132  connect to respective terminals  134  that are shaped and, in cooperation with a surround  118 A, formed as an integral part of overmold  118 , to form an electrical connector for connecting the fuel injector  100  to an electronic control circuit (not shown) that operates the fuel injector  100 . The diamagnetic member  114  can be inserted into the coil or formed unitarily as part of the bobbin  130 .  
         [0020]     Inlet tube  102  may be formed of a ferromagnetic material so that a lower end  102 A of the inlet tube is a stator member, as described below. Inlet tube  102  includes a fuel inlet opening  136  at the exposed upper end. Filter assembly  106  can be fitted proximate the open upper end of adjustment tube  104  to filter any particulate material from the fuel entering through inlet opening  136 , before the fuel enters adjustment tube  104 . After passing through a passageway  104 A in adjustment tube  104 , fuel enters a volume  138  that is cooperatively defined by confronting ends of inlet tube  102  and armature assembly  112 , and that contains spring  110 . Armature assembly  112  includes a passageway  112 E that communicates volume  138  with the seat  128 .  
         [0021]     Fuel injector  100  may be calibrated by positioning adjustment tube  104  axially within inlet tube  102  to preload spring  110  to a desired bias force. The bias force urges the closure member  112 B to be seated on seat  128  so as to close the central hole through the seat.  
         [0022]     In operation, the electromagnetic coil  132  is energized, thereby generating magnetic flux in a magnetic circuit that includes ferromagnetic components of the fuel injector  100 . The magnetic circuit includes the stator member  102 A, the coil housing  124 , the body  116 , and the armature member  112 A. The magnetic flux moves from the body  116 , across a side air gap between the armature  112 A and the body  116 , through the armature  112 A, and across a working air gap between end portions  102 B and  112 C, and through the stator member  102 , thereby creating a magnetic force across the working gap to move the armature member  112 A toward the stator member  102 A along the axis A-A, closing the working gap. This movement of the armature assembly  112  separates the closure member  112 B from the seat  128 , and allows fuel to flow from a fuel rail (not shown), through the inlet tube  102 , the passageway  104 A, the aperture  112 E, the body  120 , and through an opening in the seat  128  into the internal combustion engine (not shown). When the electromagnetic coil  132  is de-energized, the armature assembly  112  is moved by the bias of the spring  110  to seal the closure member  112 B on the seat  128 , and thereby prevent fuel flow through the injector  100 .  
         [0023]     As the magnetic flux flows along the magnetic circuit, some magnetic flux may not flow along the desired magnetic flow path, i.e. “short circuiting” the designed magnetic circuit, for example through the electromagnetic coil  132 , rather than through the armature member  112 A, resulting in magnetic flux leakage. As described, a preferred technique to reduce the flux leakage is by focusing the magnetic flux along the magnetic circuit with a diamagnetic member. Magnetic susceptibility is a measure of a material&#39;s acceptance of magnetic flux. If the magnetic susceptibility of a material is positive in value, then the material is paramagnetic, ferrimagnetic or ferromagnetic. If the magnetic susceptibility of a material is negative in value, then the material is diamagnetic. And if the magnetic susceptibility of a material is zero, then the material is anti-ferromagnetic. Magnetic susceptibility, κ, in terms of relative permeability, is: μ−1−κ. Therefore, the magnetic susceptibility of free space is zero, κ o =0. There are, however, materials with negative relative magnetic susceptibilities. These materials may be referred to as diamagnetic if their susceptibilities are slightly negative, giant-diamagnetic if their susceptibilities are strongly negative, or Meissner Effect materials (named for Walter Meissner, 1933) if they exhibit a total exclusion of magnetic fields. Meissner effect materials are at negative unity magnetic susceptibility, which would give them a relative permeability of zero, μ r =0. By using negative magnetic susceptibility materials to focus magnetic flux along a designed magnetic circuit, magnetic flux leakage may be reduced or practically eliminated. Diamagnetic member  114  focuses the magnetic flux through the armature member  112 A, and reduces or practically eliminates magnetic flux leakage.  
         [0024]     Diamagnetic member  114  may be formed of any suitable material having a magnetic susceptibility in a range of −1.0≦κ≦0. For example, diamagnetic member  114  may be formed of bismuth, pyrolytic graphites, perovskite copper-oxides, alkali-metal tungstenates, vandanates, molybdates, and titanate niobates. Examples include NaWO 3 , YBa 2 Cu 3 O 7 , TiBa 2 Ca 2 Cu 3 O 3 , Al x Ga 1−x As, and Cr, Fe selenides. The diamagnetic member  114  may be formed of a polymer having a diamagnetic material suspended in the polymer. For example, the polymer may be olefin, acrylate, urethane or silicone. Preferably, the diamagnetic member  114  is characterized by its diamagnetic property in static magnetic fields, and by a negative magnetic susceptibility, regardless of electrical conductivity. Referring to  FIG. 2 , the diamagnetic member may include a wall  144  defining a hollow cylinder. The wall  144  may have an inner surface  146 , an outer surface  148 , and first and second ends  150 ,  152 . The diamagnetic member may be disposed in a hollow core  142  of the coil assembly  108 .  
         [0025]     For comparative illustrations of advantages of the preferred embodiments,  FIGS. 3A and 3B  show magnetic flux in a magnetic circuit.  FIG. 3A  schematically illustrates magnetic flux in a magnetic circuit that does not include a diamagnetic member  114 . The magnetic circuit includes the stator member  102 A, the coil housing  124 , and the armature member  112 A. The magnetic flux  154  moves from housing  124 , across a parasitic air gap between the housing and the armature, through the armature  112 A, and across a working air gap between end portions  102 B and  112 C, and through the stator member  102 A, thereby creating a magnetic force across the working gap to move the armature member  112 A toward the stator member  102 A and closing the working gap. As the magnetic flux flows along the magnetic circuit, some magnetic flux  156  short circuits off of the designed magnetic circuit, for example through the electromagnetic coil  132 , rather than through the armature member  112 A, resulting in magnetic flux leakage.  
         [0026]      FIG. 3B  schematically illustrates magnetic flux in a magnetic circuit that includes a diamagnetic member  114 . In the embodiment of  FIG. 3B , the diamagnetic member  114  includes a first flange  158  formed at the first end  150  of the wall  144 , and a second flange  160  formed at the second end  152  of the wall  144 . The first and second flanges  158 ,  160  extend radially outward from the outer surface  148  of the wall to define a bobbin. The electromagnetic coil  132  may be disposed proximate the outer surface  148  of the cylindrical wall  144 , and the stator member  112 A may be disposed proximate the inner surface  146  of the cylindrical wall  144 . The magnetic circuit includes the stator member  102 A, the coil housing  124 , and the armature member  112 A. The magnetic flux  154  moves from housing  124 , across a parasitic air gap between the housing and the armature, through the armature  112 A, and across a working air gap between end portions  102 B and  112 C, and through the stator member  102 A, thereby creating a magnetic force across the working gap to move the armature member  112 A toward the stator member  102 A and closing the working gap. As the magnetic flux flows along the magnetic circuit, the magnetic flux flows around the diamagnetic member  114 , rather than through the diamagnetic member, due to its negative magnetic susceptibility, so that magnetic flux leakage, through the coil  132  for example, is reduced or practically eliminated. The diamagnetic member  114  forms a barrier to the magnetic flux so that substantially no magnetic flux flows across the the diamagnetic member. Because magnetic flux leakage is reduced or eliminated, the magnetic flux is focused through the stator member  112 A and the working gap, thus increasing flux density to provide a larger magnetic force to move the armature member  112 A toward the stator member  102 A.  
         [0027]      FIGS. 4A and 4B  illustrate the results of static magnetic modeling of the electromagnetic fuel injector  100  shown in  FIG. 1 . The working gap was set at 255 microns. Magnetomotive force was selected at 1000 Ampere-turns, close to the operating level of the injector  100  in normal use.  FIG. 4A  is a plot of magnetic flux in a fuel injector including cross-sectional area  113  having a permeability μ r =1, or κ=0, as with air, nylon, or non-magnetic stainless steel. Essentially, area  113  is non-diamagnetic. Magnetic flux leakage  156  flows through the coil  132 . A static force of 18.26 N is generated in the working gap when the essentially non-diamagnetic area  113  is used.  
         [0028]      FIG. 4B  is a plot of magnetic flux in a fuel injector having member  114  formed of a material having a permeability of near-Meissner effect material such as hyperconductive polymer with μ r &lt;0.02, or κ=−0.98. Magnetic flux leakage across the coil  156  is reduced or practically eliminated. A static force of 20.83 N is generated in the working gap when a diamagnetic member  114  is used in place of the area  113 . The static force increased by approximately 14%, which is believed to be a significantly unexpected increase in the magnitude of force generated. As used herein, the term “member” can include a separate member or a unitarily formed portion of another structure.  
         [0029]     While preferred embodiments of the invention are described with reference to the fuel injector assembly  100  illustrated in  FIG. 1 , it is to be understood that preferred embodiments of the invention may be included with other fuel injector assemblies. For example, embodiments of the invention may be included with modular the fuel injector assemblies shown and described in U.S. Pat. No. 6,676,044, the entirety of which is incorporated by reference.  
         [0030]     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.