Abstract:
A stator assembly for an electronically controlled unit-type fuel injector comprising a stack of electrical steel laminations, an electrical coil assembled around the laminations, a pair of terminals terminating the ends of the coil, and an insulating housing body, the laminations having spaced pole faces, the housing body being a settable resin injection molded around the coil, portions of the terminals, and substantially all of the lamination stack but for the lamination stack pole faces at a plane at a side of the housing, the laminations being stamped using a punch and die, the punch sides of the laminations all being oriented in the same direction, determined by registering a minor, deliberate asymmetry in the lamination profile, whereby each lamination is nested in the edge burrs and/or concavity of an adjacent lamination.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to improvements in electronic fuel injector assemblies and, in particular, to an improved electrical stator for solenoid control of the fuel injection timing.  
       PRIOR ART  
       [0002]     It is known to control the timing of injection of fuel into the combustion chamber of a diesel engine by regularly “spilling” fuel being mechanically displaced by a pump plunger until injection is to be initiated. When injection is to occur, the fuel spillage path is blocked by operating a solenoid. The solenoid exists in a relatively hostile environment where it is subjected to extremes of temperature, vibration, and circulating fuel pump pressure. These conditions produce stresses on the solenoid stator that can promote cracks in the stator insulation housing. Such cracks can permit fuel leakage outside of the fuel injector and to the environment.  
       SUMMARY OF THE INVENTION  
       [0003]     The invention provides an improved stator assembly in an electronic fuel injector. The stator assembly comprises a stack of electrical steel laminations, a wire coil surrounding the laminations, and a molded insulating housing encasing the lamination stack. The lamination stack of the invention has a unique arrangement that enables it to be built up with a uniform, essentially void-free construction. This uniform, void-free lamination stack prevents the housing material, when it is being injected, from being forced between laminations. By avoiding even small spaces or gaps between adjacent laminations, the stack excludes insulating material from finding its way into the interior of the stack. A condition in which harmful cracks might occur in the housing body could otherwise exist where insulating material is forced by injection pressures into any voids or crevices in the lamination stack. The existence of flash-like formations of insulating material between laminations can give rise to local stress riser conditions from which cracks may originate. Minute cracks occurring in the interior of the insulating body can propagate to the exterior of the body. An external crack creates a. path for leakage of fuel out of the fuel injector. External fuel leakage requires the removal and replacement of the solenoid stator assembly.  
         [0004]     The invention, in addition to reducing the risk for cracks to develop in the body of the insulation, can offer potential improvements in the performance of the solenoid. The avoidance of air gaps in the lamination stack can produce a stronger magnetic attraction force and greater uniformity or consistency in the performance among solenoids of the same design. Improved performance and consistency of the solenoid assembly can permit greater accuracy in fuel injection timing and, consequently, engine power and/or efficiency.  
         [0005]     An essentially void-free stack of laminations is produced, according to the invention, by orienting the punch side (and therefore the die side) of all of the laminations in the same direction. This can be accomplished by making the main area of the lamination profile, for the most part, symmetrical about a center line, while creating a local and relatively small area non-symmetrical with the corresponding area on the opposite side of the center line. The non-symmetrical area enables the profile to be readily oriented so that punch sides of the laminations can be consistently aligned to the same direction. The proper orientation of the laminations can be readily accomplished manually or by a suitable automated process. By aligning the laminations, any burrs or cupping of the laminations are oriented in the same direction so that the laminations can nest in one another. This nesting avoids air pockets that could otherwise occur where burrs, concave faces, or convex faces of abutting laminations are in contact. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a side view, primarily in section, of an electronically controlled fuel injector;  
         [0007]      FIG. 2  is an enlarged view of a portion of the fuel injector in cross-section and a solenoid stator assembly thereof in elevation;  
         [0008]      FIG. 3  is a cross-sectional view of the stator assembly on still a larger scale; and  
         [0009]      FIG. 4  is a cross-sectional view of the stator assembly in plane perpendicular to the plane of  FIG. 3 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0010]     A unit type fuel injector  10  for operating a diesel engine has a generally known construction disclosed, for example, in U.S. Pat. No. 4,568,021. The injector  10  includes a body  11  in which a pump plunger  12  is disposed. The pump plunger  12  is reciprocated in the body  11  by a follower  13 . The follower  13  and pump plunger  12  connected to it are reciprocated by a cam (not shown) of the engine and a return spring  14 . The plunger  12  displaces fuel from a chamber  16  through a passage  17  and a spill chamber  18  forming a pilot circuit. When the plunger  12  is descending and flow to the spill chamber  18  is blocked, a high injection pressure is developed in the pump chamber  16 . The injection pressure overcomes the spring force closing a needle valve (not shown) and fuel is injected into the associated engine cylinder through the injector tip  19 .  
         [0011]     Fuel is blocked from exhausting to the spill chamber  18  by axial displacement of a valve member  21  against a seat  20 . The valve member  21  is selectively operated to precisely control the timing and duration of fuel injection. A ferromagnetic armature plate  22  is fastened to the valve member  21 . The plate  22  and valve member  21  form an armature that is magnetically drawn towards poles  27 ,  28  of a solenoid stator assembly  23  against the bias of a return spring  24  when a coil  26  of the assembly is electrically energized to close the valve against the seat  20 . When the coil  26  is de-energized, the valve  21  is opened by the spring  24 .  
         [0012]     The stator assembly  23  principally comprises a stack  31  of identical laminations  36 , the coil  26  of wire disposed around the laminations, and an electrically insulating housing  33  molded around the laminations and coil. The laminations  36  of the stack  31  are preferably manufactured by stamping with a punch and die set as is conventional. The illustrated laminations  36  are preferably formed of electrical steel lightly coated with electrical insulating material and have an E-shaped profile. With reference to  FIG. 3 , the profile of each lamination  36  on a large or macroscopic scale is symmetrical about an imaginary line  37  in the middle of a central leg  38 . Distal portions of the central leg  38  and two outward legs  39  and a center of a bridge  41  between the legs each have a circular hole  42  for receiving a steel rivet  43 . In assembly, the rivets  43  hold the laminations  36  together in tight abutting engagement. The central leg  38  is somewhat larger in width than the outward legs  39  to compensate for the presence of its rivet  43  and maintain adequate magnetic flux path characteristics.  
         [0013]     Inspection of the profile of a lamination  36 , shown in  FIG. 3 , reveals that a deliberate minor difference between the right and left side of the profile exists. This difference takes the form of a large radius on a left-outside corner  44  between the bridge  41  and left leg  39  as compared to a relatively smaller outside radius on a corresponding right-hand corner  46 . The small but discernable difference between the left and right corner portions  44 ,  46  is insignificant in effect on the magnetic circuit and function developed by the stator assembly  23 . The difference between the left and right corners  44 ,  46  of the lamination profile is, however, sufficient to enable a human observer by sight or feel and/or an inanimate discriminating device using mechanical, electrical, or optical sensing to differentiate the left side of the lamination  36  from the right side.  
         [0014]     Typically, the laminations  36  are stamped at high speed from sheet stock fed into a punch and die set operating in a punch press. The blanked out laminations  36  are collected in a hopper without regard to maintaining their orientation on any axis. Ordinarily, a stamping will exhibit burrs at its sheared edges, albeit nearly microscopic when the tooling is properly made and well maintained. The burrs will extend at the punch side away from the die side of the lamination  36 . Additionally, a stamped lamination may exhibit slight cupping so that it is also concave on the punch side.  
         [0015]     A person or machine can assemble a stack  31  of laminations  36  so that owing to the minor and magnetically insignificant asymmetry afforded by the difference in radius at the corners  44 ,  46 , their profiles are in registration. This assures that the punch sides of the laminations or blanks  36  are all facing in the same direction. The tendency for burrs or cupping of these laminations to produce gaps or air spaces is effectively eliminated by nesting that results from being aligned in the same direction.  
         [0016]     The coil  26  of electrical wire is wound on a spool  48  and the spool with the coil is assembled around the middle lamination leg  38 . The leads or ends (not shown) of the coil  26  are soldered or otherwise electrically connected to electrical terminals  49 . Before molding of the housing  33 , the terminals  49  are provisionally held in place on the lamination stack  31  by an electrically insulating holder  51 .  
         [0017]     The lamination stack or assembly  31 , coil  26  on the spool  48 , and terminals  49  on the holder  51  are disposed in a mold cavity (not shown) and a settable insulating resin material is injected into the mold to form the housing  33 . The insulating material preferably comprises a thermoset resin such as a commercially available phenolic with a suitable commercially available filler. The phenolic or other resin filler ideally is of the type that is chemically unaffected by diesel fuel.  
         [0018]     As shown in  FIGS. 3 and 4 , the insulating housing  33  completely envelopes the lamination stack  31 , spool  48 , and coil  26 , terminal holder  51 , and terminals  49 , except for portions of the lamination stack at a lower face  52  of the stator assembly  23  and upper projecting portions  53  of the terminals  49 . The lower face  52  of the stator assembly  23  formed by the legs  38 ,  39  and surrounding material of the insulating housing body  33  can be machined or ground to ensure that it is relatively flat. The common flat or planar surface  52  of the lamination legs  38 ,  39  and housing body  33  enables the stator assembly  23  to be reliably sealed with an O-ring  56 . Faces  57 ,  58  of the legs  38 ,  39  at the face  52  constitute the pole faces of the stator assembly  23 . The O-ring  56  has a circular cross-section shown in  FIG. 2  and a rectangular shape when viewed in a plane parallel to the stator assembly face  52 . The O-ring  56  is received in a groove formed in a seat surface  55  of an adapter plate  54 , carried on the main body  11 , that surrounds the armature plate  22 .  
         [0019]     During operation of the engine, fuel is constantly circulated through the injector body at a low pressure of, for example, about 40 psi. Cyclic operation of the pump plunger  12  and closing of the valve  21  develops a high injection pressure at the nozzle. The stator assembly  23  is subjected to fuel circulating or supply pressure, engine vibration, ambient temperature, engine temperature and cyclic electromagnetic pulses during its service. A crack in the housing body  33  can allow fuel driven by the supply pressure to leak from the fuel injector through the housing body. The risk of a crack developing can be dependent on the extent that stress risers and irregularities are molded into the body  33 . The uniform alignment of the laminations  36 , as provided by the invention, allows unintended but difficult to avoid non-planar characteristics existing in the separate laminations  36  to be nested. Consequently, there are essentially no narrow spaces existing between separate laminations  36  where insulation material of the body  33  can be injected even under normally high conventional injection molding pressures. Therefore, settable insulation material has no intra-lamination space to migrate into when injected into the mold that forms the housing  33  and thereby create flash-like formations in such spaces. A flash-like thin formation of insulating material can represent an irregularity and, therefore, a stress riser in the body  33  and a source of a crack. Depending on the size and number of gaps or spaces that might otherwise occur between the laminations  36 , without benefit of the invention, the performance of the solenoid assembly can be adversely affected.  
         [0020]     It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. For instance, the laminations  36  can be arranged with a C-shaped profile and/or the laminations can be welded together rather than being riveted. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.