Abstract:
An ignition coil has a primary core supporting a primary winding that is connectable to an engine ignition system and a secondary winding inductively couplable to the primary winding and surrounding the primary winding. The secondary winding can be connected to an engine spark plug assembly. A flux director surroundingly engages the core. The flux director is a single, unitary piece of steel that is not made of composite Iron particles.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to vehicle ignition coils. 
       BACKGROUND OF THE INVENTION 
       [0002]    Ignition coils are components that use the coupling between a primary winding and a secondary winding to transform relatively low voltages from the battery into high voltages that are supplied to the spark plugs in vehicle gasoline engines. The spark plugs start the internal combustion process that drives the rods and hence, crankshaft and axles. In older systems, a single ignition coil is provided, and a distributor sends the pulses from the coil through respective high voltage spark plug wires to the spark plugs in the cylinders in accordance with a timing that is established by the distributor. 
         [0003]    In relatively modern engines, an engine can have several ignition coils, one for each cylinder or for each pair of cylinders, thereby advantageously eliminating the need for distributors and high voltage wires and also providing more precise control of the engine timing. One example of such an ignition coil system is set forth in U.S. Pat. No. 6,556,118, owned by the present assignee and incorporated herein by reference. 
         [0004]    When such a coil is used to energize two spark plugs (either for two different cylinders or for a single cylinder in an engine that has two spark plugs per cylinder), two secondary windings surround the low voltage-carrying primary winding that is wound on an interior ferromagnetic core, with the secondary windings being radially spaced from the primary winding. Each secondary winding, owing to the inductive coupling between it and the primary winding and the different numbers of winding turns between the primary and secondary windings, produces a high voltage that is sent to a respective spark plug. 
         [0005]    As understood herein, pole pieces can be coupled to the core for purposes of advantageously directing magnetic flux. As also understood herein, however, existing pole pieces typically are made of coated iron powder and cannot be press fit onto the core, requiring a relatively complex support to hold the pole piece onto the core. The present invention understands that the support reduces the area available for the primary winding, thereby undesirably increasing the length of the core required to support the winding. 
       SUMMARY OF THE INVENTION 
       [0006]    An ignition coil has a core supporting a primary winding that can be connected to an engine ignition system and one or more secondary windings inductively couplable to the primary winding and surrounding the primary winding, with the secondary winding being connectable to an engine spark plug assembly. A flux director surroundingly engages the core. The flux director is a single, unitary piece of steel that is not made of composite Iron particles. 
         [0007]    For example, the flux director may be made by stamping 65A800 steel. If desired, one or more thin laminations configured identically to the flux director in transverse cross-section may be provided. The flux director can be U-shaped in transverse cross-section and can be formed with a round central cavity for receiving the core therein. With the above structure only smooth formed edges of the flux director face toward the primary winding of the core to minimize stress concentration, with sharp edges formed by corners of the flux director facing away from the windings. 
         [0008]    A wire support may also be provided on the core to connect the primary winding to an ignition system. The wire support can be a relatively simple and advantageously thin support having a thickness “t” of no more than about one-half millimeter. 
         [0009]    In some implementations the flux director has an annular inner lip pressed against the core and an outer annular skirt lengthened along an axis of the core in the direction of flux. 
         [0010]    In another aspect, an ignition coil has a core supporting a primary winding that is connected to an engine ignition system and one or more secondary windings inductively couplable to the primary winding and surrounding the primary winding, with the secondary winding being connected to an engine spark plug assembly. A flux director that is not made of composite Iron particles surroundingly engages an end of the core. 
         [0011]    In still another aspect, a method for making an ignition coil for an engine includes providing a core supporting a primary winding and configuring a terminal of the primary winding for connection to an engine ignition system. The method also includes providing a secondary winding configured for being inductively couplable to the primary winding and surrounding the primary winding, and configuring a terminal of the secondary winding for connection to an engine spark plug assembly. The method entails providing flux direction on the core without using composite Iron particles. 
         [0012]    The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is an exploded perspective view of a non-limiting ignition coil in accordance with present principles, schematically showing the ignition system that energizes the primary winding; 
           [0014]      FIG. 2  is a transverse cut-away view of the primary core with flux director and wire support; 
           [0015]      FIG. 3  is a perspective view of the primary core with flux director and wire support; and 
           [0016]      FIG. 4  is a schematic side view of the primary core with a flux director. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0017]    Referring initially to  FIG. 1 , an ignition coil is shown, generally designated  10 , for use in energizing at least one spark plug (only a single spark  12  shown) that is disposed in a high voltage spark plug boot  14  and that extends into an engine cylinder. In non-limiting applications the ignition coil  10  can be but one of plural coils that would be used in an engine having more than two cylinders in a distributorless ignition system, i.e., no distributor exists between the ignition coil  10  and its spark plugs  12 . 
         [0018]    In the non-limiting embodiment shown, the ignition coil  10  includes a case  16  that defines a closable open end  18 . An electrically conductive magnetic shield  20  made of, e.g., silicon steel, is disposed within the case  16  substantially coaxially with the case  16  to magnetically isolate the below-described windings from exterior components. As shown, an end  22  of the shield  20  is juxtaposed with the closable open end  18  of the case  16 . In the embodiment shown the shield  20  defines a substantial portion of a cylinder, i.e., the shield  20  may define, for instance, an axial slit  24  in an otherwise cylindrical surface to limit eddy current losses in the shield. If desired, a rubber-like shield buffer ring  26  may be disposed between the shield  20  and case  16  to accommodate thermal expansion and contraction of the metal parts. 
         [0019]    As shown in  FIG. 1 , the shield  20  closely surrounds a secondary winding spool  28  that is generally cylindrical and that has axially-spaced ribs  30  that together define a segmented winding path. At least one and, in the non-limiting embodiment shown, first and second electrically conductive wire secondary windings  32 ,  34  are disposed in the winding path defined by the spool  28  and are in axial sequence to each other. A spark plug end of the first secondary winding  32  is connected to a first terminal  36 , while a spark plug end of the second secondary winding  34  is connected to a second terminal  38 , it being understood that when the coil  10  is used to energize only a single spark plug, then only one secondary winding and, hence, only one terminal at the spark plug end of the secondary winding need be provided. 
         [0020]    The ends of the secondary windings  32 ,  34  that are opposite to the spark plug ends are each connected to a center tap terminal  40 , which may be established by one or more electrical conductors, e.g., by a wire having a square cross-section. The secondary windings  32 ,  34  may be wound oppositely to each other relative to the axial dimension of the coil  10 . A dielectric material such as epoxy may be disposed between the secondary winding spool  28  and the case  16 . 
         [0021]    A primary wire winding  42  is wound around a soft iron core  44  that is coaxially disposed within the secondary winding spool  28 . It is to be understood that the primary winding  42  is electrically connected, via a wire support  46 , with two “T” posts  48  that allow the wires to be held in place until they are connected to terminals  68  and  69  in a connector housing  67 . In turn, the connector housing  67  is configured to mate with a wiring harness of an ignition system “I” that selectively energizes the primary winding  42  from a source of voltage such as a vehicle battery or other part of an ignition system. 
         [0022]    When the primary winding  42  is energized, the cooperation between the core  44 , primary winding  42 , and secondary windings  32 ,  34  results in inductive coupling between the primary winding  42  and secondary windings  32 ,  34 . Owing to this coupling and to the different number of turns between primary and secondary, the relatively low battery voltage in the primary winding  42  is transformed into relatively higher voltages in the secondary windings  32 ,  34  for provision of the higher voltages to the spark plugs. 
         [0023]    The non-limiting terminals  36 ,  38  of the secondary windings  32 ,  34  (when two secondary windings for energizing two spark plugs are provided) are connected to respective spark plugs using connector structure known in the art, e.g., each terminal  36 ,  38  may be electrically connected to a respective spring  50  with associated terminal cup  52 . A so-called tower  54  may be formed as part of the case  16 . 
         [0024]    In accordance with the present invention and in cross-reference to  FIGS. 1-3 , at one end of the core  44  a flux director  56  is disposed. If required for greater energy levels, additional thin steel laminations  58  that are configured identically to the flux director  56  in transverse cross-section as shown may be pressed flush against the flux director and may be formed with dimples  60  for better securing the laminations  58  onto each other and the flux director  56 . 
         [0025]    In one embodiment the flux director  56  is a single, unitary piece of steel that consequently is not made of composite Iron particles. The flux director  56  may be made by stamping, e.g., 65A800 steel into the configuration shown. 
         [0026]    As best shown in  FIG. 2 , the flux director  56  may be U-shaped in transverse cross-section and is formed with a round central cavity  62  for closely receiving the core  44  therein. The cavity  62  may be open at the top as shown. With this structure, advantageously only smooth formed edges face toward the winding area of the core  44  to minimize stress concentration in epoxy  64  that may be deposited in the annular region between the flux director  56  and core  44  to hold the components together. Sharp edges indicated at  66  that are formed by the corners of the flux director  56  face away from the winding area and are pressed into the plastic case of the coil  10 . Because the flux director  56  is a single unitary piece of steel requiring no complex holder, the wire support  46  may be a simple single piece structure as shown that is very thin, e.g., that may have a thickness “t” ( FIG. 1 ) of one-half millimeter or so, to maximize the area of the core  44  that is available for the primary winding  42 . 
         [0027]      FIG. 4  shows that a primary core  100  may be engaged at one end with a single piece steel flux director  102  in accordance with present principles, with the flux director  102  having an annular inner lip  104  that is pressed against the core  100  and an outer annular skirt  106  that may be lengthened along the axis of the core  100  as shown in phantom as needed in the direction of flux. 
         [0028]    While the particular FLUX DIRECTOR FOR IGNITION COIL ASSEMBLY is herein shown and described in detail, it is to be understood that the subject matter which is encompassed by the present invention is limited only by the claims.