Abstract:
A distributorless ignition coil has two high voltage secondary windings wound around a primary winding, with each secondary winding being electrically connected to a respective spark plug. A shield surrounds the secondary windings. The secondary windings share a common center tap between them, and the center tap is electrically connected to the shield, which thus acts as a conductor to convey current back to an end of the shield that conveniently may be connected to ignition components to complete the electrical path, thus obviating the need for an interior wire extending from the center tap inside the coil to the end of the coil case.

Description:
I. FIELD OF THE INVENTION  
       [0001]     The present invention relates to vehicle ignition coils.  
       II. 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, the ends of the secondary windings that are opposite the ends which are connected to the spark plugs must be connected to ground (in a three conductor system) or to the positive pole of the battery in a two conductor system to complete the electrical path. The present invention also understands that if these ends are located axially between oppositely-wound secondary windings, somehow electrical connection must be made from the middle of the ignition coil to the end, for connection to ground or battery positive. As critically recognized by the present invention, owing the relatively small size of modern ignition coils, the space available to run a lead from between the secondary windings and past one of the high voltage secondary windings to an end connector is limited, making electrical connection using a lead internal to the ignition coil difficult and problematic. Having made these critical observations, the invention below is provided.  
       SUMMARY OF THE INVENTION  
       [0006]     A distributorless ignition coil includes a primary winding that can be connected to a source of voltage such as a vehicle battery. First and second secondary windings are in axial sequence to each other and surround the primary winding. Each secondary winding can be electrically connected to a respective spark plug. Also, each secondary winding is inductively coupled to the primary winding when the primary winding is energized, and the secondary windings are configured to transform relatively lower voltage from the primary winding to relatively higher voltage for supply to the spark plugs. A shield surrounds the secondary windings. In accordance with the present invention, the shield is electrically connected to a center tap terminal between the secondary windings, with the center tap terminal being electrically connected to each secondary winding. With this structure, the shield can electrically connect the center tap terminal to ground or to battery voltage as desired.  
         [0007]     In non-limiting implementations the shield defines an end, and the shield is connectable to ground or battery voltage at or substantially near the end. A case can hold the shield and windings and can define a closable open end, and the end of the shield can be juxtaposed with the closable open end of the case.  
         [0008]     In illustrative embodiments the shield may be formed with two tabs defining a space between them for receiving the center tap terminal. The tabs can be crimped to hold the center tap terminal therebetween. Or, the shield may be formed with one and only one tab, with the center tap terminal being welded to the tab. In either case, the secondary windings may be wound oppositely to each other relative to an axial dimension of the coil.  
         [0009]     In another aspect, an ignition coil includes a primary winding receiving voltage from a source of voltage in a vehicle, and first and secondary windings inductively coupled to the primary winding. A shield surrounds the secondary windings and is radially spaced therefrom. The shield defines a substantial portion of a cylinder and establishes a portion of an electrical circuit including the first secondary winding and a first spark plug. The shield also establishes a portion of an electrical circuit including the second secondary winding and a second spark plug.  
         [0010]     In still another aspect, a distributorless ignition system for a vehicle engine includes plural ignition coils. Each ignition coil has first and second secondary windings electrically connected to respective spark plugs. Also, each ignition coil includes a shield surrounding the secondary windings and completing an electrical circuit for each secondary winding.  
         [0011]     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  
       [0012]      FIG. 1  is a an exploded perspective view of the present ignition coil;  
         [0013]      FIG. 2  is a cut-away side elevational view of the present ignition coil;  
         [0014]      FIG. 3  is a perspective view of the ignition coil with the case removed to show the center tap connection to the shield;  
         [0015]      FIG. 4  is a schematic view showing one way for establishing the center tap connection to the shield; and  
         [0016]      FIG. 5  is a schematic view showing another way for establishing the center tap connection to the shield. 
     
    
     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 accordance with principles known in the art. The ignition coil  10  is 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]     Cross-referencing  FIGS. 1 and 2 , 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  FIGS. 1 and 2 , 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. 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 . 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  39  ( FIG. 2 ) such as epoxy may be disposed between the secondary winding spool  28  and the case  16 .  
         [0020]     In accordance with ignition coil principles known in the art, a primary wire winding  42  is wound around a soft iron core  44  that is coaxially disposed within the secondary winding spool  28 . The core  44 , which may be made of silicon steel laminations or compression molded iron particles or other appropriate material, is bounded at its ends by a silicon or rubber buffer cup  46  and a primary cap  48 . The open end of the case  16  is closed by a cover  50 .  
         [0021]     It is to be understood that the primary winding  42  is electrically connected, via a connector member  52  with two or more terminals  54 , to an ignition system that selectively energizes the primary winding  42  from a source of voltage such as a vehicle battery in accordance with ignition coil principles known in the art. As shown best in  FIG. 2 , the connector member  52  is disposed in the case  16  adjacent the open end  18  of the case  16  and, hence, adjacent the end  22  of the shield  20 .  
         [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]     Thus, the terminals  36 ,  38  of the secondary windings  32 ,  34  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  56  with associated terminal cup  58 . A so-called tower  60  may be formed as part of the case  16 , and a mount support bushing  62  ( FIG. 1 ) may be provided to mount the case  16  onto a vehicle.  
         [0024]     In accordance with the present invention and now referring to  FIG. 3 , the shield  20  that surrounds the secondary windings  32 ,  34  is electrically connected to the center tap terminal  40  between the secondary windings  32 ,  34 . In one illustrative embodiment, the shield  20  may be integrally formed with first and second tabs  64 ,  66  that extend into the axial slit  24  and that form a space between them for receiving the center tap terminal  40 . As shown in cross-reference to  FIGS. 3 and 4 , a crimp force, represented by arrows  68 , can be applied to the tabs  64 ,  66  to crimp the terminal  40  between the tabs. Or, only a single tab  66  need be provided, in which case weld electrodes represented by arrows  70  in  FIG. 5  can be used to pinch weld the terminal  40  to the tab  66 . It is to be understood that the structure shown in  FIGS. 3-5  for connecting the center tap of the secondary windings  32 ,  34  to the shield  20  are exemplary and non-limiting.  
         [0025]     Recall that the center tap terminal  40  is electrically connected to each secondary winding  32 ,  34 . Thus, the secondary windings  32 ,  34  are electrically connected to the shield  20 . Further, as best shown in  FIG. 3 , the end  22  of the shield  20  that is juxtaposed with connector member  52  can be electrically coupled to the connector member  52 . For example, a slot  72  may be formed in the end  22  of the shield  20 , and a connector element  74  of the connector member  52  engaged with the slot. With this structure, the shield  20  (and, hence, secondary windings  32 ,  34 ) may be connected, via the connector member  52 , to ground (for three-conductor systems) or to battery positive (for two-conductor systems) at or substantially near the end  22  of the shield  20 , thereby simplifying wiring within the ignition coil  10 .  
         [0026]     It may now be appreciated that the shield  20  establishes a portion of an electrical circuit including the first secondary winding  32  and a first spark plug, and that the shield  20  further establishes a portion of an electrical circuit including the second secondary winding  34  and a second spark plug. That is, the shield  20  completes the electrical circuit for each secondary winding  32 ,  34 .  
         [0027]     While the particular IGNITION COIL WITH SECONDARY WINDING CENTER TAP CONNECTED TO SHIELD as herein shown and described in detail is fully capable of attaining the above-described objects of the invention, it is to be understood that it is the presently preferred embodiment of the present invention and thus, is representative of the subject matter which is broadly contemplated by the present invention, that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural and functional equivalents to the elements of the above-described preferred embodiment that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it is to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. section 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.”