Patent Publication Number: US-11655786-B2

Title: Fuel injector

Description:
BACKGROUND 
     The present disclosure concerns a fuel injector. More specifically, a fuel injector for injecting fuel in an internal combustion engine in a motor vehicle. 
     A fuel injector for injecting fuel into a combustion engine comprises a valve driven by means of an electrically driven actuator against the force of a closure spring. The disclosed fuel injector includes improvements that promote fast opening and closure of the valve in an electromagnetically actuated valve, while avoiding instability in the valve components that may cause unintended fuel delivery. 
     SUMMARY OF THE DISCLOSURE 
     A disclosed fuel injector uses an electromagnetic fuel injection valve to control injection of fuel into a combustion engine. The body of the fuel injector is a metal fuel tube that contains the fuel handling components of the valve and defines a fuel flow path from an inlet to a tip of the fuel injector that may project into an engine cylinder. A valve member is coupled to an axially extending needle and armature of a solenoid that opens the valve under control of an engine control system. The solenoid includes a pole fixed to the injector body, a solenoid coupled to the valve needle and a coil surrounding the injector body where the coil generates magnetic flux through the pole and armature to attract the armature to the pole and open the valve. 
     In one embodiment of the disclosed fuel injector the valve needle extends axially through the armature and the armature is coupled to the valve needle between first and second armature stops fixed to the valve needle. The stops are spaced apart from each other along the valve needle an axial distance that is greater than an axial length of the actuator where the actuator contacts the stops, allowing limited relative movement between the armature and the valve needle. An embodiment of the armature defines an axial recess surrounding the valve needle and an armature spring biased between a bottom of the axial recess and a first (upper) armature stop biases the armature toward the second (lower) armature stop to define a gap between the armature and the first (upper) armature stop. A valve closing (return spring) bears on an upper surface of the first (upper) armature stop to bias the valve needle toward the closed position of the valve with the valve member in contact with a valve seal to close the fuel injection valve. The valve needle is held in the closed position by the valve closing (return) spring while the armature is biased toward the second (lower) armature stop and spaced apart from the first (upper) armature stop. The first (upper) armature stop is situated between the armature and the pole, while the second (lower) armature stop is arranged between the armature and the valve member. 
     The armature has a first position axially spaced from the pole to define a first axial gap between the armature and the pole when the valve needle is in the closed position and a second position in contact with the pole when the valve needle is in the open position. The first (upper) and second (lower) armature stops are secured in fixed positions to the valve needle, with the armature axially moveable relative to the valve needle between the first and second armature stops and biased toward the second (lower) armature stop by an armature spring between the armature and the first (upper) armature stop to define a second axial gap between the armature and the first (upper) armature stop when the valve is in the closed position. A return spring is in contact with an upper surface of the first (upper) armature stop for biasing the valve needle away from the pole and toward the closed position. The disclosed coupling between the armature and valve needle separates the momentum changes and impacts of the armature and valve needle in both the opening and closing directions of the fuel injection valve. The disclosed configuration of a valve needle, armature, armature stops and armature spring de-couples the mass of the armature from the valve needle to reduce transmission of impact and changes of momentum from the armature to the valve needle, reducing unintended movement (bouncing) of the valve member and reducing the associated unintended fueling. The disclosed coupling between the armature and valve needle has inventive significance apart from other aspects of the disclosed fuel injector and can be used in conjunction with some, all or none of the other aspects of the disclosed fuel injector. 
     The disclosed coupling between the armature and valve needle may be further specialized where the armature defines an axial recess, and the armature spring is positioned in the axial recess and biased between a bottom of the axial recess and a lower surface of the second armature stop. An embodiment of the armature may define at least one fuel flow passage communicating between the axial recess and an area between the armature and the valve member. An embodiment of the first (upper) armature stop may radially span the axial recess and includes at least one notch on the flange allowing fluid communication from an area between the first (upper) armature stop and the pole and the axial recess. The at least one notch, axial recess, and at least one fuel flow passage permitting fluid communication from the area between the first (upper) armature stop and the pole to the area between the armature and the valve member, e.g., in the direction of fuel flow toward the injector nozzle tip. An embodiment of the armature may define the first and second armature stops both include a periphery defining at least one notch. An embodiment of the first (upper) armature stop may include a radially projecting flange captured axially between the pole and the armature where the distance between the armature and the pole is greater than an axial thickness of the flange, allowing limited axial movement of the valve needle in the opening direction after the armature contacts the pole, though such axial movement of the valve needle is resisted by the valve closure (return) spring and may not actually occur. The disclosed arrangement separates the impact of the armature with the pole from the valve needle, so energy from the impact and change of momentum of the armature is not directly transferred to the valve needle. The refinements of the disclosed coupling between the armature and valve needle may be selected for inclusion in a fuel injector as needed. 
     Another aspect of the disclosure relates to improvements in a magnetic circuit that applies magnetic force to the armature to move the armature toward the pole and open the fuel injection valve against the bias of a valve closure (return) spring. The valve body includes a magnetic upper portion, a non-magnetic intermediate portion, and a magnetic lower portion. The upper portion, intermediate portion, and lower portion are integrally connected to define an uninterrupted cylindrical side wall of the valve body. The armature and pole are arranged in the valve body with an axial gap between the armature and coil surrounded by the non-magnetic intermediate portion of the valve body. A coil surrounds the non-magnetic intermediate portion of the valve body and when energized generates magnetic flux through the pole and armature to attract the armature to the pole. The armature is coupled to the valve needle to move the valve needle toward the open position when the armature is magnetically attracted toward the pole. Since magnetic flux will follow the path of least resistance, the non-magnetic portion of the valve body forces flux to flow through the pole and armature, rather than through the valve body, which improves the force on the armature when the coil is energized. The disclosed magnetic circuit of an embodiment of a fuel injector make the fuel injector more energy efficient and improve the opening speed of the fuel injector. The disclosed magnetic circuit can be employed independent of the disclosed coupling between the armature and valve needle and other aspects of the disclosed fuel injector. The disclosed improvements to the magnetic circuit in an electromagnetic fuel injection valve have inventive significance apart from the other disclosed improvements and can be incorporated into a fuel injector apart from other aspects of the disclosed fuel injector. 
     According to a further aspect of the disclosed fuel injector, a modular power group secures the coil to the valve body and completes a magnetic circuit directing magnetic flux through the pole and armature of an electromagnetic fuel injection valve. An embodiment of a modular power group includes a coil assembly, including an annular coil with conductors extending from the annular coil to an electrical connector, the annular coil embedded in plastic that surrounds the conductors and at least partially forms the electrical connector. A first flux washer surrounds the valve body at one axial end of the coil, a cylindrical housing in contact with the first flux washer and outwardly surrounding the coil, and a second flux washer in contact with the cylindrical housing and extending around a majority of a circumference of the valve body at a second axial end of the coil form a radially outer part of the magnetic circuit for flux generated when the coil is energized. The first flux washer, cylindrical housing and second flux washer form part of a magnetic circuit extending through the armature and pole. The coil generates a magnetic field in the magnetic circuit when energized, and the magnetic field attracts the armature to the pole to move the valve needle toward the open position. The modular power group is of inventive significance apart from the other disclosed aspects of a fuel injector and can be incorporated into a fuel injector separately from the other disclosed improvements. 
     An embodiment of the modular power group of the fuel injector can be further specialized wherein the valve body is connected to an inlet to form a sealed fuel tube and the inlet includes features mating with the coil assembly to retain the coil assembly to the fuel injector. An embodiment of the armature may include the first flux washer, cylindrical housing and second flux washer are welded to each other after assembly to the valve body. In one embodiment the second flux washer is interrupted by a slot and the conductors extend axially through the slot to the electrical connector. This allows the second flux washer to be installed after the coil assembly is inserted into an annular space defined between the valve body and the cylindrical housing. 
     Another aspect of the disclosure relates to an improved valve seat configuration. A fuel injection includes a valve needle is connected to a spherical valve member and moveable along a longitudinal axis between a closed position and an open position. The valve seat defines a valve seal is in contact with an outside surface of the spherical valve member when the valve needle is in the closed position. The valve seal comprises an annular conical surface surrounding a fuel sac. The outside surface of the spherical valve member contacts the valve seal along a line where the valve seal is tangent to the outside surface. The conical surface extends radially inward a first distance to the fuel sac and radially outwardly a second distance approximately equal to the first distance. The conical valve seal surface may include a back cut defining an outer boundary of the valve seal. The position of an annular line of contact between the spherical valve member and the conical valve seal can be adjusted by altering the angle and radial position of the inner and outer boundaries of the valve seal. Embodiments of the valve seat may include guide surfaces arranged to guide axial movement of the spherical valve member between the open and closed positions to maintain alignment between the valve member and the valve seal. The guide surfaces may be portions of a cylinder concentric with a longitudinal axis of the fuel injector. The improved seat configuration is of inventive significance by itself and can be employed independent of the other aspects of the disclosed fuel injector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a longitudinal sectional view through an embodiment of a fuel injector according to aspects of the disclosure; 
         FIG.  2    is an enlarged portion of the sectional view of  FIG.  1   ; 
         FIG.  3    is a partially exploded perspective view of the fuel injector of  FIGS.  1  and  2   ; 
         FIG.  4    is an exterior perspective view of the fuel injector of  FIG.  3    in an assembled state; 
         FIG.  5    is an enlarged partial sectional view of the fuel injector of  FIG.  4    showing a connection between a coil assembly and the inlet end of the fuel module; 
         FIG.  6    is a longitudinal sectional view through a fuel injector valve body according to aspects of the disclosure; 
         FIG.  7    is a longitudinal sectional view through a fuel module incorporating the valve body of  FIG.  6    in an assembled state showing internal components; 
         FIG.  8    is an enlarged perspective sectional view of a valve seat and spherical valve member compatible with the disclosed embodiment of a fuel injector illustrated in  FIGS.  1 - 8   ; 
         FIG.  9    is a bottom perspective view of the valve seat of  FIG.  8   ; 
         FIG.  10    is an enlarged, partial sectional view of the valve seat and spherical valve member of  FIG.  8   ; 
         FIG.  11    is a perspective sectional view of the valve seat and spherical valve member of  FIG.  8   ; 
         FIG.  12    is a longitudinal sectional view through an armature assembled to a valve needle according to aspects of the disclosure; 
         FIG.  13    is a top perspective view of the armature/needle assembly of  FIG.  12   ; 
         FIG.  14    is a partial bottom perspective view of the armature/needle assembly of  FIG.  12   ; 
         FIG.  15    is a longitudinal sectional view through a valve body in functional conjunction with components that generate magnetic force to open the valve; 
         FIG.  16    is an enlarged longitudinal sectional view through a portion of an embodiment of the disclosed fuel injector, showing the position of the armature and valve needle relative to the pole during an initial stage of valve opening; and 
         FIG.  17    is an enlarged longitudinal sectional view through a portion of an embodiments of the disclosed fuel injector, showing the position of the armature, valve needle, and valve member relative to the pole and valve seat when the valve is fully open. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS.  1 - 7   , a solenoid actuated fuel injector  10  dispenses a quantity of fuel that is to be combusted in an internal combustion engine (not shown). The fuel injector  10  extends along a longitudinal axis A-A between an inlet end  12  and an injection end  14  and includes a fuel tube assembly  16  and a power group assembly  18 . The fuel tube assembly  16  contains the “wet” part of the fuel injector  10  that performs fluid handling functions, e.g., defining a fuel flow path from the inlet end  12  to the injection end  14  and allowing or prohibiting flow of fuel from the injection end  14  of the fuel injector  10 . The power group assembly  18  converts electrical signals to a driving force used to open a valve contained in the fuel tube assembly  16  to permit fuel flow from the injection end  14  of the fuel injector  10 . 
       FIGS.  1  and  2    are cross sectional views through an embodiment of a disclosed fuel injector  10  according to aspects of the disclosure. The fuel tube assembly  16  includes an inlet  20  with a sealed connection to a fuel distributor line (not shown). The sealed connection includes an O-ring  22  and back up washer  24  that cooperate with a coupling on the fuel distributor line to compress the O-ring  22 , resulting in a sealed connection that is capable of withstanding fuel pressures from 350 bar up to 1000 bar. From the sealed connection, the inlet  20  extends to an annular, open second end  26  that is received within an open upper end  28  of a valve body  30 . The valve body  30  extends from its connection with the inlet  20  to an opposite end that includes a tip  32  connected to a valve seat  34 . The valve seat  34  includes an inward facing valve seal  36  that cooperates with a valve member  38  connected at one end of a valve needle  40 . The valve seat  34  defines a plurality of fuel injection orifices  42  communicating with a fuel sac  44  bounded by the valve seal  36 . When the valve member  38  is biased into contact with the valve seal  36 , pressurized fuel in the fuel tube assembly  16  above the valve member  38  is prevented from passing into the fuel sac  44  and out of the fuel injection orifices  42 , and when the valve member  38  is moved away from the valve seal  36  as shown in  FIGS.  10  and  17   , fuel passes between the valve member  38  and valve seal  36 , through the fuel sac  44  and out fuel injection orifices  42 . In use, the tip  32  of the fuel injector  10  extends through the cylinder head of an internal combustion engine (not shown) to position the valve seat  34  and its fuel injection orifices  42  in a cylinder of an internal combustion engine as is known in the art. A groove  46  on the tip  32  above the valve seat  34  supports a compression seal  48  which cooperates with a bore in the cylinder head (not shown) to contain pressurized gasses in the engine cylinder. 
     As shown in  FIG.  7   , the fuel tube assembly  16  includes the inlet  20 , the valve body  30  and the valve seat  34 , which form a sealed enclosure surrounding fuel handling components of the fuel injector  10 . The lower end  26  of the inlet  20  is received within the upper end  28  of the valve body  30  and connected by a weld  50 . The valve seat  34  surrounds a lower end of the tip  32  of the valve body  30  and is connected by a weld  52 . The welds  50 ,  52  may be laser welds extending around the respective joints to produce a hermetically sealed fuel tube assembly  16 . The fuel tube assembly  16  defines a fuel flow path extending from the inlet  20  to the fuel injection orifices  42 . A magnetic pole  54  and armature  56  are arranged within the fuel tube assembly  16  so that magnetic force from the power group assembly  18  attracts the armature  56  toward the pole  54 . The armature  56  is coupled to the valve needle  40  and moves the valve member  38  away from the valve seal  36  when the armature  56  is attracted to the pole  54 . According to aspects of the disclosure, the valve needle  40  with attached armature  56  and pole  54  are assembled into the valve body  30  before the inlet  20  is inserted and welded to the valve body  30 . 
     The upper valve body  58  where the valve body  30  connects to the inlet  20  is constructed of magnetic steel and the lower valve body  60  that includes the tip  32  is also constructed of magnetic steel. As best seen in  FIG.  6   , an intermediate portion  62  of the valve body  30  is constructed of non-magnetic metal and is integrally connected to the upper valve body  58  and lower valve body  60 . According to aspects of the disclosure, the integral connection between the upper valve body  58 , non-magnetic intermediate portion  62 , and lower valve body  60  is formed before the valve body  30  is machined into its final shape, resulting in a seamless, leak free tubular valve body  30  surrounding the pole  54  and armature  56  where the magnetic and non-magnetic portions of the valve body  30  are precisely aligned. The non-magnetic intermediate portion  62  of the valve body  30  is positioned at a location that surrounds and axially overlaps with the gap  64  present between the lower end face  66  of the pole  54  and the upper end face  68  of the armature  56  when the valve is in the closed position. As shown in  FIG.  2   , the non-magnetic material of the intermediate portion  62  valve body  30  at this location forces magnetic flux from the solenoid coil  70  to pass entirely through the armature  56  and pole  54  maximizing the force applied to the armature  56  when the coil  70  is energized. Focusing magnetic flux through the pole  54  and armature  56  allows for excellent magnetic feedback for ballistic control of the valve needle  40  and valve member  38 . 
       FIG.  2    illustrates the magnetic circuit  72  in an embodiment of the disclosed fuel injector  10 . The power group assembly  18  includes an annular coil  70  that includes conductors  74  extending to a connector  76 . The connector  76  electrically connects the coil  70  to a control system (not shown) that applies power to the coil  70  to generate magnetic force applied to the armature  56  to move the armature  56 , valve needle  40  and valve member  38  to permit fuel flow through the injector  10 . The control system may be an engine control unit (ECU) that coordinates fuel flow through the fuel injectors of an internal combustion engine with other components of the engine. The configuration and operation of such control systems is well-understood by those skilled in the art and will not be further described. 
     The coil  70  is positioned radially surrounding the non-magnetic intermediate portion  62  of the valve body  30  and the gap  64  between the lower end face  66  of the pole  54  and upper end face  68  of the armature  56 . As best seen in  FIGS.  3  and  4   , the power group assembly  18  is modular, comprising a small number of inexpensive components that are assembled to the outside of the fuel tube assembly  16 . The coil  70  is wound on a bobbin  71  and surrounded by injection molded plastic to form a coil assembly  78  shown in  FIG.  3   . The coil assembly  78  includes conductors  74  that connect the coil  70  to a plug connector  76 . The form of plug connector  76  can be changed to be compatible with different electrical connection systems as needed. The power group assembly  18  also includes a lower flux washer  80  a cylindrical housing  82  and a slotted upper flux washer  84  which, together with the magnetic portions  58 ,  60  of the valve body  30 , pole  54  and armature  56  complete the magnetic circuit  72  shown in  FIG.  2   . The flux washers  80 ,  84  and cylindrical housing  82  are basic shapes of magnetic material that can be inexpensively produced in large quantities. According to aspects of the disclosure, the coil assembly  78  does not incorporate any of the magnetic components that complete the magnetic circuit shown in  FIG.  2   , which allows coil assemblies with different plug connectors  76  to be easily incorporated into a fuel injector at low cost for compatibility with different connection systems. 
     With reference to  FIGS.  3  and  5   , an embodiment of the modular power group assembly  18  is assembled to the fuel tube assembly  18  as follows: The lower flux washer  80  and cylindrical housing  82  are placed over the valve body  30  with the lower flux washer  80  in contact with an annular shoulder  86  on the valve body  30  and welded in place. The coil  70  of the coil assembly  78  is inserted between the housing  82  and the valve body  30  and axially moved toward the lower flux washer  80  to engage a barb  88  on the inlet  20  with a complementary snap  90  on the inside of the injection molded plastic coil assembly  78  as shown in  FIG.  5   . This snapped together connection retains the coil assembly  78  to the fuel tube assembly  16  while the upper flux washer  84  is inserted laterally into a complementary slot defined by the coil assembly  78  at the upper end of the housing  82  and welded in place. The upper flux washer  84  holds the coil  70  in place beneath it, while holding the upper part of the coil assembly  78  upward to axially load the barb  88  and snap  90 . This configuration securely retains the coil assembly  78  to the fuel tube assembly  16  and allows the inlet  20  to support the upper end of the coil assembly  78  and plug connector  76 . After these assembly steps are completed, the power group assembly is retained in an assembled position on the fuel tube assembly  16  as shown in  FIG.  4   . The lower flux washer  80  is welded to the lower valve body  60  at the shoulder  86 , the housing  82  is welded to the lower flux washer  80  and the upper flux washer  84  is welded to the upper end of the housing  82  to ensure that no air gaps interrupt the magnetic circuit  72 . According to aspects of the disclosure, the power group assembly  18  is mounted to the fuel injector  10  as a last step in assembling the fuel injector  10 . 
       FIGS.  12 - 14    illustrate an embodiment of the valve needle  40  and valve member  38  coupled to the armature  56  according to aspects of the disclosure. The armature  56  defines an axial recess  92  and at least one fuel flow passage  94  from the recess  92  to a region below the armature  56 . The fuel flow passage  94  allows fuel to flow through the armature  56  during use of the fuel injector  10 . Two substantially identical armature stops  96   a ,  96   b  limit movement of the armature  56  along the valve needle  40  between the stops  96   a ,  96   b , but the mass of the armature  56  is not directly connected to the valve needle  40  as will be described below. The armature stops  96   a ,  96   b  include notches  98  at their peripheries so that the upper armature stop  96   a  allows fuel to flow into the recess  92  and through the fuel flow passage  94 . The notches  98  do not interfere with the function of the lower armature stop  96   b , so the same component can be used both above and below the armature  56  to reduce cost. The armature stops  96   a ,  96   b  are welded to the valve needle  40  at positions allowing a small amount of relative axial movement between the armature  56  and the valve needle  40 . A coil spring  100  is captured in the axial recess  92  of the armature  56  and biased between the upper armature stop  96   a  and the bottom of the recess  92  to bias the armature  56  away from the upper armature stop  96   a  and against the lower armature stop  96   b . In this arrangement, an axial gap  102  is maintained between the armature  56  and the upper armature stop  96   a  when the valve is closed as shown in  FIGS.  1  and  12   . The relative positions of the upper armature stop  96   a  and armature shown  56  in  FIG.  12    correspond to a state where the coil  70  is not energized and the spring  100  biases the armature  56  away from the upper armature stop  96   b  to open gap  102 . When the coil  70  is energized, the axial gap  102  allows the armature  56  to accelerate rapidly toward the pole  54  for a predetermined distance defined by gap  102  before the shoulder  57  of the armature contacts the flange  95  of the upper armature stop  96   a , causing the valve needle  40  and valve member  38  to move away from the valve seal  36 . During this initial stage of opening the fuel injector valve, the magnetic force applied to the armature  56  compresses the armature spring  100  to close gap  102 . The kinetic energy of the accelerated armature  56  and the narrowing of the gap  64  between the armature  56  and the pole  54  rapidly moves the valve needle  40  and valve member  38  away from the valve seal  36  to begin injection of fuel. 
     The lift or stroke of the valve needle  40  and valve member  38  are defined by the axial gap  64  between the upper end face  68  of the armature  56  and the lower end face  66  of the pole  54  minus the gap  102  between the armature and the upper armature stop. In one embodiment of the disclosed fuel injector, gap  64  is at least twice as large as gap  102 . In other embodiments of a fuel injector according to aspects of the disclosure, the ratio of gap  64  to gap  102  can be between 2:1 and 4:1. Keeping gap  102  small relative to gap  64  permits acceleration of the armature  56  against only the bias of armature spring  100  without significantly delaying opening of the injector valve. During a valve opening event, the armature  56  begins moving toward the pole  54 , closes the gap  102  and contacts the upper armature stop  96   a  as shown in  FIG.  16   . In  FIG.  16   , armature spring  100  is compressed, gap  102  between the shoulder  57  of the armature and flange  95  of upper armature stop  96   a  is closed, gap  103  is opened between the lower end of the armature  56  the lower armature stop  96   b , gap  64  between the upper end face  68  of the armature  56  and the lower end face  66  of the pole  54  has narrowed, but the valve needle  40  has not yet begun to move in the opening direction. When gap  102  has closed, the armature  56  is in contact with upper armature stop  96   a  and begins moving the valve needle  40  against the bias of the valve closing spring  104  until the upper end face  68  of the armature  56  contacts the lower end face  66  of the pole  54  as shown in  FIG.  17   . When the upper end face  68  of the armature  56  contacts the lower end face  66  of the pole  54 , the coil spring  100  inside the armature  56  is compressed, gap  102  between the armature  56  and the upper armature stop  96   a  is closed, gap  103  is present between the armature  56  and the lower armature stop  96   b  as shown in  FIG.  17   . It will be apparent that gaps  102 ,  103  are approximately equal and when gap  102  is opening, gap  103  is closing and vice versa. 
     As shown in  FIG.  2   , upper armature stop  96   a  includes a radially projecting flange  95  that is captured between the lower end face  66  of the pole and an annular shoulder  57  of the armature  56 . As shown in  FIG.  12   , the axial thickness  55  of the flange  95  on the upper armature stop  96   a  may be less than the axial distance  53  between the shoulder  57  and upper end face  68  of the armature  56 , allowing the valve needle  40  (with upper armature stop  96   a , lower armature stop  96   b  and valve member  38 ) to keep moving in the opening direction until gap  103  between the armature  56  and the lower armature stop  96   b  has closed. In one embodiment, the difference between axial thickness  55  and axial distance  53  is greater than gap  103 , so the upper face of flange  95  never impacts the lower end face  66  of the pole  54 . The armature  56  is stopped suddenly by contact with the lower end face  66  of the pole  54 , but this sudden change is not reflected directly to the valve needle  40  due to the relative movement allowed between the valve needle  40  and the armature  56  between stops  96   a  and  96   b . Decoupling the mass of the armature  56  from the valve needle  40  limits transmission of energy from sudden changes in direction/momentum of the armature  56  to the valve needle  40  and valve member  38 , which minimizes unintended fueling at the beginning and end of injection. Stated alternatively, the disclosed connection between the armature  56  and the valve needle  40  promotes settling of the valve needle and valve member after opening or closing to increase linear portion of an injection event by allowing each of the armature  56  and valve needle  40  limited movement relative to each other. In the disclosed fuel injector  10 , the impact of the armature  56  and valve needle  40  are separated from each other in both the opening and closing directions of the valve. 
     The valve member  38  may be a spherical ball welded to the end of the valve needle  40  opposite the armature  56 . When the coil  70  is not energized, a valve closing spring  104  bears on the upper armature stop  96   a  to bias the valve needle  40  and valve member  38  toward the valve seat  34  and a closed position. In the closed position, the outside surface of the valve member  38  is in contact with the valve seal  36 , preventing fuel flow through the fuel injector  10 . The gap  102  between the armature shoulder  57  and the flange  95  of the upper armature stop  96   a  shown in  FIG.  12    is present when the valve needle  40  and valve member  38  are in the closed position because the distance between the facing surfaces of the armature stops  96   a ,  96   b  is slightly greater than the axial length of the armature  56  between its lower surface and the shoulder  57 . The difference between the armature stops  96   a ,  96   b  and the axial length of the armature  56  is the axial dimension of gaps  102 ,  103 . Force from the valve closing spring  104  is applied to the top of the flange  95  of the upper armature stop  96   a  and holds the valve member  38  against the valve seal  36 , but the armature  56  is biased away from the flange  95  of the upper armature stop  96   a  by armature spring  100  to open gap  102 . When not attracted to the pole  54 , the armature  56  can return to a position biased toward the lower armature stop  96   b  and spaced apart from the upper armature stop  96   a . According to aspects of the disclosure the spring rate and force of return spring  104  are greater than the spring rate and force of the armature spring  100 . 
       FIGS.  8 - 11    illustrate a valve seat  34  according to aspects of the disclosure. The valve seat  34  includes a plurality of guide surfaces  106  arranged around the valve member  38  to guide axial movement of the valve member  38 . Beneath the valve member  38 , the valve seat  34  includes a valve seal  36  surrounding a fuel sac  44 . The fuel sac  44  communicates with a plurality of fuel injection orifices  42 , the number and configuration of which can be altered to provide desired fuel flow characteristics during an injection event. The disclosed valve seat  34  defines five fuel injection orifices  42  arranged about the longitudinal axis A-A of the injector  10 , but this is only one example of a possible arrangement of injection orifices. The valve seal  36  is an annular conical surface that is contacted by the valve member  38  when the fuel injector  10  is closed. The spherical outside surface of the valve member  38  will contact the conical valve seal  36  along an annular line of contact where the conical valve seal  36  is tangent to the outside surface of the valve member  38 . As shown in  FIG.  10   , the annular valve seal  36  has a limited radial extent defined by a back cut  108 . The back cut  108  allows fuel flow between the valve member  38  and the valve seal  36  to reach peak flow more quickly than if the surface of the valve seal  36  extended radially outward a large distance beyond the annular contact between the outside surface of the valve member  38  and the valve seal  36 . The back cut  108  also minimizes pressure drop to the seal  36 .  FIG.  10    illustrates the valve member in the open position, separated from the valve seal  36 . 
     With reference to  FIGS.  1  and  2   , the pole  54  is press fit into the upper valve body  58  after the armature/needle assembly is inserted into the lower valve body  60 . The position of the lower end face  66  pole  54  relative to the upper end face  68  of the armature  56  in the closed position defines the lift or stroke of the valve needle  40  and valve member  38  by setting the axial dimension of gap  64  between the upper end face  68  of the armature and the lower end face  66  of the pole  66 . The pole  54  is pressed into the upper valve body  58  until the gap  64  reaches a pre-determined axial distance. The stroke of the valve needle is equal to the axial gap  64  between the pole  54  and the armature  56  minus the axial gap  102  between the armature  56  and the upper armature stop  96   a . When the valve stroke has been calibrated by pressing the pole  54  into position, the valve closing spring  104  is inserted into the center of the pole  54  to rest on top of the upper armature stop  96   a . A metal filter tube  110  is then inserted into the central opening of the pole  54  and press fit to load the valve closing spring  104  to a desired closing force. The force required to move the pole  54  relative to the upper valve body  58  is very high, so that when the valve stroke has been set, the pole  54  remains in the calibrated position. The force required to move the filter tube  110  relative to the pole  54  is relatively low, so that adjustment of the preload on the valve closing spring  104  cannot disturb the position of the pole  54 . The upper end of the filter tube  110  is crimped over a filter  112  and a noise orifice plate  114 . The filter  112  prevents particulates from passing into the injector  10  and possibly clogging the fuel injection orifices  42  or lodging between the valve member  38  and the valve seal  36 . The orifice plate  114  defines a central orifice  116  that allows fuel flow toward the valve seat  34  but reduces reflection of hydraulic pressure waves caused by opening and closing of the valve member  38  upstream into the fuel system. The filter  112  and orifice plate  114  may be inexpensively manufactured from plastic such as nylon and are surrounded and protected by the metal filter tube  110  during assembly. According to aspects of the disclosure, the inlet  20  is inserted and welded to the valve body  30  after the valve stroke and closing force have been calibrated as described above.