Abstract:
An ignition coil intended for application in automotive internal combustion engines includes a generally cylindrically magnetic core defining opposed first and second ends and a primary coil concentrically wound externally about the core axially between the opposed ends. A secondary coil assembly including an insulating spool and a secondary coil wound thereon is concentrically disposed externally of the primary coil and magnetic core. One terminal of the primary coil is connected to a controlled voltage source and the other terminal to an electrical ground. One terminal of the secondary coil is connected to the high voltage terminal of at least one spark plug and the other terminal is connected to an electrical ground. The magnetic core is constructed from low carbon steel rope, preferably in a 1x37 format.

Description:
RELATED PATENT APPLICATION 
       [0001]    This application is related to U.S. application Ser. No. 763,574 filed 10 Dec. 1996, entitled “Integrated Ignition Coil and Spark Plug”, now U.S. Pat. No. 5,706,792 issued 13 Jan. 1998, the specification of which is expressly incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention is related to internal combustion engine ignition apparatus and, more particularly, to high voltage ignition source hardware. 
       BACKGROUND OF THE INVENTION 
       [0003]    Ignition apparatus for providing a spark to the combustion chamber of an internal combustion engine characterized by a combined spark plug and ignition coil have been proposed in the prior art. For example, U.S. Pat. No. 1,164,113 to Orswell entitled “Sparking Plug”, U.S. Pat. No. 1,302,308 to Cavanagh entitled “Spark Coil for Ignition”, U.S. Pat. No. 2,441,047 to Wall entitled “Transformer Spark Plug”, U.S. Pat. No. 2,459,856 to Wall entitled “Transformer Spark Plug”, U.S. Pat. No. 2,467,531 to Lamphere entitled “Ignition System and Spark Plug”, and U.S. Pat. No. 2,467,534 to Osterman entitled “Ignition Unit” all disclose combined ignition coils and spark plugs. 
         [0004]    More recently, improved internal combustion engine ignition apparatus has been described in the patent literature. For example, U.S. Pat. No. 5,015,982 to Skinner et al. entitled “Ignition Coil”, U.S. Pat. No. 6,522,232 B2 to Paul et al. entitled “Ignition Apparatus Having Reduced Electric Field HV Terminal Arrangement”, U.S. Pat. No. 6,556,118 B1 to Skinner entitled “Separate Mount Ignition Coil Utilizing a Progressive Wound Secondary Winding”, and U.S. Pat. No. 6,679,236 B2 to Skinner et al. entitled Ignition System Having High Resistivity Core” all disclose commercially viable ignition coil designs. 
         [0005]    Modern internal combustion engines, particularly those characterized by plural intake and exhaust valve arrangements and overhead cam valve actuation configurations, have very limited space available for providing structurally adequate spark plug wells. Unfortunately for single coil per cylinder spark sources, including combined spark plug and ignition coil apparatus, decreasing spark plug well diameter makes single coil per cylinder ignition systems difficult to successfully implement for a variety of reasons. Among the problems which must be overcome include limited diametrical clearance between the spark plug well and the ignition apparatus, high temperatures especially given the minimal clearances in the limited spark plug wells, and access for installation and removal of the spark plug and ignition coil. 
         [0006]    Radio frequency interference (RFI) continues to be a challenge for ignition system designers. Unfortunately for single coil per cylinder spark sources, including combined spark plug and ignition coil apparatus, the nature of such installations do not afford much opportunity for shielding against such RFI. Additionally, each individual ignition source in such distributed single coil per cylinder systems has associated therewith a system voltage line to increasing the ease with which RFI generated by one ignition source may couple in cross talk to the other ignition sources respective system voltage supply lines. Additionally, each supply line may experience substantial direct capacitive coupling of RFI generated by the associated ignition source. 
         [0007]    Ignition coils have been previously proposed which employ one of several known magnetic core configurations and materials. Cylindrical cores have been manufactured out of bundles formed of individual parallel strands of wire, steel laminations of varying widths and out of “solid” materials such as composite iron (plastic coated powdered iron) and soft ferrites. Although suitable for their intended application, such prior approaches could be difficult and relatively expensive to produce, particularly in large-scale production, such as in the automotive industry. Furthermore, certain prior approaches had inherent inefficiencies such as high eddy current losses, inefficient packing of conductors within an allocated volume and air pockets entrained within the composite materials forming the magnetic core. 
       SUMMARY OF THE INVENTION 
       [0008]    Therefore, it is an object of the present invention to provide a new, low cost and easily produced integrated spark plug and ignition coil apparatus. 
         [0009]    It is preferred that such an apparatus shall include a magnetic core which is produced to net shape, avoiding blanking, post-forming machining and finishing operations to compactly fit within its assembled package within extremely slender spark plug access wells. 
         [0010]    In the preferred embodiment of the invention, the inventive ignition coil apparatus includes a generally cylindrical magnetic core having opposed first and second ends with a secondary coil concentrically wound about the core between the first and second ends. A secondary coil assembly including an insulating spool and secondary coil wound thereon is concentrically disposed with the primary coil and magnetic core. Means are provided for electrically interconnecting one terminal of the primary coil to a controlled voltage source and another terminal to an electrical ground. Furthermore, means are provided for electrically interconnecting one terminal of the secondary coil to the high voltage terminal of one or more associated spark plugs and another terminal to an electrical ground. Finally, the magnetic core is composed of a wire rope formed of a plurality of helically arranged low carbon steel or iron strands extending between the first and second ends. 
         [0011]    According to another aspect of the invention, a method of forming an ignition coil apparatus comprising a magnetic core, a primary coil and a secondary coil assembly including an insulating spool and secondary coil wound thereon, comprises the steps of drawing a predetermined length of wire rope from a substantially continuous supply, straightening the predetermined length of wire rope, wrapping a conductor about the length of the wire rope to form the primary coil, severing the length of wire rope from the continuous supply to form the magnetic core and concentrically positioning the magnetic core and primary coil within the secondary coil assembly. 
         [0012]    It is further desired that, in one particular embodiment of the invention, an integrated spark plug and ignition apparatus package, including the inventive magnetic core, can physically be fit within extremely slender spark plug access wells and be able to adequately manage the extreme temperature conditions associated with such placement. 
         [0013]    Additionally, it is desirable that an integrated spark plug and ignition coil minimize the radiation of RFI to the surroundings. 
         [0014]    These and other objects of the invention are provided for in an improved integrated spark plug and ignition coil apparatus wherein the inherent capacitive and inductive characteristics are advantageously adapted for attenuation of RFI. In accordance with the present invention, 
         [0015]    These and other features and advantages of this invention will become apparent upon reading the following specification, which, along with the drawings, describes preferred and alternative embodiments of the invention in detail. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0017]      FIG. 1 , is a cross-sectional view of a preferred embodiment of an integrated ignition coil and spark plug in accordance with the present invention; 
           [0018]      FIG. 1A , is a fragmentary, cross-sectional view of a portion of  FIG. 1 , on an enlarged scale, illustrating structural details adjacent one end of the electromagnetic core; 
           [0019]      FIG. 1B , is a fragmentary, cross-sectional view of a portion of  FIG. 1 , on an enlarged scale, illustrating structural details adjacent the other end of the electromagnetic core; 
           [0020]      FIG. 2 , is a simplified mechanical and electrical schematic illustration of the integrated ignition coil and spark plug in accordance with the present invention; 
           [0021]      FIG. 3 , represents an equivalent electrical circuit of an integrated ignition coil and spark plug in accordance with the present invention; 
           [0022]      FIG. 4 , is a cross-sectional view of a preferred wire rope construction employed as the electromagnetic core of the integrated ignition coil and spark plug of  FIG. 1 , on a greatly enlarged scale; 
           [0023]      FIG. 5 , is a cross-sectional view of an alternative wire rope construction employed as the electromagnetic core of the integrated ignition coil and spark plug of  FIG. 1 , on a greatly enlarged scale; and 
           [0024]      FIG. 6 , is schematic diagram of a manufacturing line for processing the electromagnetic core and primary coil assemble of the integrated ignition coil and spark plug of  FIG. 1 . 
       
    
    
       [0025]    Although the drawings represent embodiments of the present invention, the drawings are not necessarily to scale and certain features may be exaggerated in order to illustrate and explain the present invention. The exemplification set forth herein illustrates an embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    Referring to the figures, and particularly to  FIGS. 1 ,  1 A and  1 B, a preferred embodiment of an integrated ignition coil and spark plug assembly in accordance with the present invention is illustrated in partial sectional view and is generally designated by the reference numeral  10 . The integrated ignition coil and spark plug assembly  10  is adapted for installation with a conventional internal combustion engine through a spark plug well and in threaded engagement with a spark plug opening into an engine combustion chamber. The assembly  10  has a substantially rigid outer case  51  at one end of which is a spark plug assembly  59  and at the other end of which is a connector body  11  for establishing an external electrical interface. The assembly  10  further comprises a substantially slender high voltage transformer including substantially coaxially arranged primary and secondary windings and a high permeability magnetic core. All high voltage ignition system components are housed within or are not part of the integrated ignition coil and spark plug assembly  10 . 
         [0027]    Generally, the structure is adapted for drop-in assembly of components and sub-assemblies as later described. 
         [0028]    A secondary spool  21  is formed from an injection molded plastic insulating material having a high temperature tolerance such as a polybutylene terephthalate (PBT) thermoplastic polyester for example sold under the trade name Valox® by General Electric. The spool  21  has a plurality of axially spaced, radially outwardly directed ribs  38 . Adjacent pairs of ribs  38  define channels therebetween. The radial depth of the respective channels decreases from one end of the spool  21  to the other by way of a progressive gradual flare of the spool body  21  away from the primary coil  23  such that the space between the inner diameter of spool  21  and the primary winding  23  progressively increases from the connector body end to the spark plug end of the assembly  10 . The voltage gradient in the axial direction which increases toward the spark plug end of the secondary coil  37  requires increased dielectric insulation between the secondary and primary coils  37  and  23 , respectively, and is provided for by way of the progressively increased separation between the secondary and primary coils  37  and  23 , respectively, and dielectric fluid therebetween as described in a later point. A spacer  29 , also preferably a terephthalate (PBT) thermoplastic such as Valox®, and a spring  27  are fitted to the interior of secondary spool  21  at the end thereof having the shallowest channels between ribs  38 . A secondary grounding terminal  19  and a secondary negative terminal  35  are hot upset to secure the respective secondary terminals  19 ,  35  to the secondary spool  21 . Secondary coil  37  is then wound on the spool  21  between ribs  38  which defines winding slots. Secondary coil  37  has more turns in the deeper channels relative to fewer turns in the progressively shallower channels. In the present embodiment, the secondary spool  21  has 23 channels which are wound to fabricate the secondary coil  37 . For example, in the exemplary embodiment, secondary coil  37  may be comprised of 24,893 total turns of No. 44 AWG wire, the number of turns in each channel being progressively reduced from the previous channel in accordance with the progressive reduction in channel depths. All 23 channel windings are electrically connected in series by cross-over connections that extend through slots in the ribs  38 . Such a coil arrangement is generally referred to in the art as a segment wound coil and is generally preferred over conventional layer wound coils for reasons of manufacturing simplicity and decreased capacitance. 
         [0029]    The low voltage or ground lead of secondary coil  37  is terminated to a tang  19 B of the secondary grounding terminal  19 , and the negative lead of the secondary coil  37  is terminated to a tang  35 A of the secondary negative terminal  35 . Both terminal leads of the secondary coil  37  are wrapped and then soldered such as by hot dip solder operation. Respective tangs  19 B and  35 A are folded toward one another against the secondary spool  21  to lie substantially axially against or in proximity to the secondary spool  21 . 
         [0030]    In previous designs, such as that described in U.S. Pat. No. 5,706,792, the core of an integrated ignition coil and spark plug assembly is manufactured from plastic coated iron particles in a compression molding operation. The iron particles are carried by a binder of electrical insulating material. The iron particles may have a mean particle size of about 0.004 inches. In production of a part, the iron particles are coated with a liquid thermoplastic material which encapsulates the individual particles. The coated iron particles are placed in a heated mold press where the composite material is compressed to the desired shape and density. The final molded part is then comprised of iron particles in a binder of cured thermoplastic material. By way of example, the final molded part may be, by weight, about 99% iron particles and about 1% plastic material. By volume, the part may be about 96% iron particles and about 4% plastic material. Because of the elongated shape of a core produced by this process, the type of compression molding process utilized applies primary compressive forces normal to the major axis of the piece to provide uniform compaction throughout. Such core fabrication was previously preferred since cost effective round cross section cores may be produced thereby. After the core is molded, it is finish machined such as by grinding to provide a smooth surface absent, for example, sharp molding parting lines otherwise detrimental to the intended direct primary coil winding thereon. 
         [0031]    The applicants have determined that the core  25 , when formed of a length of braided, woven or twist-formed material such as low carbon steel strands (also known as iron or steel rope), can provide adequate performance within the integrated ignition coil and spark plug assembly  10  described herein. Furthermore, the use of iron rope substantially reduces the material and manufacturing processing costs of the core  25 . Conceptually, standard bulk iron rope can be purchased in continuous form as a reel or coil. Thereafter, a segment of the rope would be locally straightened, have a coating of heat resistant material (tape, heat shrink tubing, etc.) applied to cover the outer surface thereof and then cut to a required length. The preferred embodiment would employ standard 1x37 type wire rope construction to minimize the diameter of the individual wire strands to minimize eddy current losses. Alternatively, a 1x19 type wire rope construction can also be employed, but would result in increased eddy current losses within the individual strands. The minimal contact between adjacent round wire strands in the wire rope construction limits the eddy current flow between wires to negligible levels, thus allowing standard coatings for corrosion, such as zinc, to be used. The twist in the wire rope, which inherently serves to hold it together, results in no adverse thermal or magnetic properties when used as an ignition core which are detrimental to overall performance of integrated ignition coil and spark plug assembly  10 . The twist does, however, have the distinct advantage of allowing the severed length of wire rope forming the core  25  to maintain its form and eliminates the necessity of expensive production tools and secondary machining operations. Another option for using wire rope as an ignition core is the application of a fly winder to wind the primary winding  23  over the wire rope, prior to cutting it to length. With this approach, the primary winding  23  also serves to mechanically hold the core together. In this case, the above described tape or shrink wrap tube over the core can be optional. Preferably, a protective cap can be employed to hold the wire rope in place as it is fed into the fly winder. After the wire rope is wrapped, the core opposite the cap is cut off and the cap repositioned length of wire rope on the roll. 
         [0032]    Referring to  FIG. 4 , a typical cross-section of the preferred type 1x37 type steel rope  80  is illustrated. An appropriate length of this type of steel rope  80  is cut-off normally to its axis of elongation (A). Steel rope  80  is constructed of  37  individual strands  82 , each of which is ideally coated with a layer  84  of relatively non-conductive material such as naturally occurring oxide. Alternatively, unplated raw steel or various types of anodizing or plating (such as zinc) can be successfully employed. The individual strands  82  are tightly packed with one another to approximate line-to-line contact between adjacent strands  82 , minimizing the amount of air within the volume defined by the steel rope  80  and approximating a cylindrical overall shape. The strands  82  can be formed, by way of example, from ferrite based material such as low carbon steel, iron, 400 series stainless steel, and the like. 
         [0033]    In typical applications within automotive internal combustion engines envisioned by the inventors, each steel rope  80  core should have an axial length within the range of 25.0 mm to 80.0 mm. The individual strands  82  are of the same constant or nominal diameter within the range of 0.5 mm to 2.0 mm. The strands  82  are generally helically arranged (with the possible exception of the center strand) along their entire axial length. The outer strands  82  have a characteristic continuous wrap angle exceeding 180° (½ turn) to collectively self-engage one another and retain the steel rope in its illustrated configuration during the manufacturing/assembly process. 
         [0034]    Referring to  FIG. 5 , a typical cross-section of an alternative type 1x19 type steel rope  86  is illustrated. As in the case of the preferred embodiment described in conjunction with  FIG. 4 , an appropriate length of this type of steel rope  86  is cut-off normally to its axis of elongation (B). Steel rope  86  is constructed of  19  individual strands  88 , each of which is preferably coated with a layer  90  of relatively non-conductive material. 
         [0035]    As in the case of the above described prior art composite core, the primary coil  23  is wound directly on the outer surface of the presently inventive core  25 . The windings are formed from insulated wire, which are wound directly upon the outer cylindrical surface of the core  25 . The primary coil  23  may be comprised of two winding layers each being comprised of  127  turns of No. 23 AWG wire. Adhesive coatings, though not foreseeably required, may be applied to the primary coil  23  such as by conventional felt dispenser during the winding process or by way of a partially cured epoxy coat on the wire which is heat cured after winding. The winding of the primary coil  23  directly upon the core  25  provides for efficient heat transfer of the primary resistive losses and improved magnetic coupling which is known to vary substantially inversely proportionally with the volume between the primary winding  23  and the core  25 . 
         [0036]    The connector body  11  is also preferably molded from Valox®, however, in a conventional insert molding process to capture the core grounding terminal  41  and a pair of primary terminals (not illustrated). The core grounding terminal  41  has a portion thereof exposed at the base of an axial cavity  55  at the interior end portion of connector body  11 . The primary terminals extend into a connector well  53  for coupling to the primary energization circuitry external to the integrated ignition coil and spark plug assembly  10 . A radially yieldable connector  15  is crimped to core grounding terminal  41 , allowing for a terminal tail portion to be extensibly disposed therefrom. A core grounding spring  39  is assembled into the cavity at the interior end portion of the connector body  11 . The core  25  is assembled to the interior end portion of the connector body  11  compressing the core grounding spring  39  to establish positive electrical contact between the core  25  and the core grounding terminal  41 . The terminal leads (not illustrated) of the primary coil  23  are connected to the insert molded primary terminals by soldering. 
         [0037]    The primary sub-assembly is next inserted into the secondary spool  21  with a slight interference fit of the outer surface of the interior end portion of the connector body  11  to the interior surface of the secondary spool  21 . A spring jumper  17  flexibly connects the tang  19 A of the secondary grounding terminal  19  to the terminal tail portion extensibly disposed from the core grounding terminal  41 . 
         [0038]    The outer case  51  is formed from round tube stock preferably comprising nickel plated 1008 steel or other adequate magnetic material. Where higher strength may be required, such as, for example, in unusually long cases  5   1 , a higher carbon steel or a magnetic stainless steel may be substituted. A portion of the case  51  at the end adjacent the connector body  11  is preferably formed by a conventional swage operation to provide a plurality of flat surfaces to provide a fastening head, such as a hexagonal fastening head  56  for engagement with standard drive tools. Additionally, the extreme end is rolled inwardly to provide necessary strength for torques applied to the fastening head  56  and to provide a shelf for trapping a ring clip  43  between the case  51  and the connector body  11 . The previously assembled primary and secondary sub-assemblies are loaded into the case  51  from the spark plug end to a positive stop provided by the swaged end acting on a portion of the connector body  11 . Additionally, a plurality of radially extending spacers  57  provide for substantial centering and limited range of radial motion of the primary and secondary sub-assemblies within the case  51 . 
         [0039]    The entire assembly is then filled with a predetermined volume of fluidic dielectric suitable for the high temperature and high voltage environment of the integrated ignition coil and spark plug assembly  10 . A general category of Polydimethyl siloxane oils have demonstrated dielectric properties, volume resistivity properties and heat dissipation properties considered to be adequate for automotive engine applications. For example, one such commercially available fluid is identified as SF97-50 silicone dielectric fluid available from General Electric Corporation. Another such commercially available fluid includes 561™ fluid marketed by Dow Corning. The volume of fluid fill is sufficient to completely submerge the secondary assembly when the integrated ignition coil and spark plug assembly  10  is in a normally installed position. A volume between the connector body  11  just below the O-ring  13  and the top of the secondary assembly provides an expansion chamber  63  for volumes of fluid displaced during the normal course of thermal expansions of the components and the effective volume changes of the primary and secondary sub-assemblies. After fluid fill, the ring clip  53  is installed to prevent the primary and secondary assemblies from being pulled back through the case opening. 
         [0040]    Next, the spark plug assembly  59  is installed to close the end of the case  51  opposite the connector body  11 . The spark plug assembly  59  includes a conductive outer shell  33  surrounding a ceramic spark plug insulator  31  through which axially passes a high voltage center electrode  47  (hereinafter the negative electrode) including an RFI suppression resistor (not illustrated). The conductive outer shell  33  tapers down to a threaded portion  77  which threadably engages into the combustion cylinder head of the associated internal combustion engine. Extending from the bottom of threaded portion  77  and over center of an exposed portion  71  of negative electrode  47  is a complementary ground electrode  73 . An ionization gap  45  is thereby established between respective negative and positive electrodes  47  and  73 . Surrounding an exposed portion of the negative electrode  47  and in electrical contact therewith is a high voltage contact spring  49 . The distal end of the high voltage contact spring  49  is engaged with a recessed portion of the spacer  29 . An interior tang  35 B integral with the secondary negative terminal  35  is in electrical contact with the contact spring  49  to thereby couple the high voltage output of the secondary coil  37  to the electrode  47 . A weld seam  61  runs about the entire perimeter between the end of the case  51  and the conductive housing  33  of the spark plug assembly  59  such as by a conventional resistance welding process thus completing the assembly steps of the integrated ignition coil and spark plug assembly  10  and providing a structurally robust, electrical and hermetically sealed joint. 
         [0041]    With reference now to  FIGS. 2 and 3 , the embodiment of the invention illustrated with particularity in  FIG. 1  is shown in simplified form wherein certain of the electrical and magnetic circuit elements are labeled with primed designations of corresponding features of  FIG. 1 . The core  25 ′ is shown surrounded in progressive coaxial fashion by primary coil  23 ′, secondary coil  37 ′ and outer case  51 ′. One lead of the primary coil  23 ′ is seen to be coupled to system voltage labeled B+ in the riffle. The B+ coupling would be by way of an external connection provided by the connector body  11  ( FIG. 1 ) at one end of the assembly. The other lead of the primary coil  23 ′ is selectively coupled to vehicle or chassis ground by way of a controllable semi-conductor switch  70 . Semi-conductor switch  70  is controlled in a well known manner in accordance with predetermined ignition timing objectives for each cylinder by a conventional spark timing module in response to sensed angles of engine rotation as is generally well known in the art. The core  25 ′ and the primary coil  23 ′ capacitively couple, one with the other, the equivalent capacitance being labeled C 2  in  FIGS. 2 and 3 . The equivalent capacitance C 2  is relatively large due in great part to the proximity of the core  25 ′ and the primary coil  23 ′. One lead of the secondary coil  37 ′ is directly coupled to the exposed portion  71  ′ of the negative electrode of the spark plug assembly  59 ′. The other (secondary) electrode  73 ′ of the spark plug assembly  59 ′ is direct coupled to vehicle ground. The secondary coil  37 ′ and the primary coil  23 ′ capacitively couple, one with the other, the equivalent capacitance being labeled C 1  in  FIGS. 2 and 3 . The outer case  51 ′ encloses the core  25 ′ as well as the primary and secondary coils  23 ′ and  37 ′, respectively. 
         [0042]    In accordance with the invention, the outer case  51 ′ is directly coupled to the vehicle ground by way of the threaded portion  77  of the spark plug assembly  59  ( FIG. 1 ). The core  25 ′ is also, in accordance with the present invention, directly coupled to vehicle ground through the outer case  51 ′, as described in accordance with the embodiment illustrated in  FIG. 1 . The outer case  51 ′ and the secondary coil  37 ′ capacitively couple, one with the other, the equivalent capacitance being labeled C 3  in  FIGS. 2 and 3 . Attenuation of the RFI generated by the sparking event of the spark plug is advantageously provided by a ladder type RFI filter modeled by a simplified equivalent circuit in  FIG. 3 : As indicated, the proximity of the primary winding  23  afforded by the direct winding thereof on the core  25  ( FIG. 1 ) provides a relatively large equivalent capacitance C 2 . The grounding of the outer case  25  establishes an equivalent capacitance C 3  between the vehicle ground and then secondary winding  37  ( FIG. 1 ) on one side of the equivalent primary inductance Lp. The grounding of the core  25  establishes an equivalent capacitance C 2  between the vehicle ground and the other side of the equivalent primary inductance Lp. RFI otherwise capacitively coupled in parallel across the equivalent primary inductance Lp, especially because of the inherently large capacitive effects of winding the primary coil  23  directly upon the core  25  ( FIG. 1 ), is instead attenuated by the equivalent ladder network, thus greatly reducing the direct coupling to the supply voltage B+. 
         [0043]    Referring to  FIG. 6 , a manufacturing process or line, shown generally at  92 , illustrates a simple, inexpensive method for producing magnetic cores  94  for use in ignition coil apparatus as described herein. A large (substantially continuous) supply roll  96  of wire rope  98  plays off wire rope  98 , as indicated by arrow  99 , which then passes around guide pulleys  100 ,  102 . Guide pulleys  100 ,  102  are controllably displacable, as indicated by arrows  104 ,  106 , to tension the wire rope  98  passing thereover. Thereafter, the wire rope  98  passes over another guide pulley  108  and between three pairs of straightening pulleys  110 ,  112  and  114 . Next, temporary bands  116  are applied to wire rope  98  at spaced points therealong to define the respective predetermined end points with a length of wire rope  98  therebetween. The bands  116  are provided by a feed mechanism (not illustrated) and are applied to the wire rope  98  by a suitable clamping mechanism  118  which reciprocates as indicated by arrows  120 . 
         [0044]    In the next process step, a layer of electrically insulating contact adhesive  122  is applied between adjacent bands  116  on wire rope  98  by a dispenser  124  connected to a reservoir  126 . Thereafter, a fly winder  128  draws a feed of wire  130  off a continuous spool  132  as indicated by arrow  134 . The fly winder  128  serves to axially wrap the wire  130  over the adhesive layer  122  on the adjacent length of wire rope  98 , effecting adhesive bonding thereof. This step effects formation of the primary coil  136 . Wire  130  is severed by a sheer  140 , completing formation of the primary coil  136 . Finally, the length of wire rope  98  between adjacent bands  116  is severed from the remainder of the in-process wire rope  98  by a pair of sheers  140 ,  142 , or other suitable device. The output of process line  92  consists of assemblies  144  of magnetic cores  94  and primary coils  136 , which are accumulated for subsequent final assembly in the ignition coil, and the chaff  146  consisting of stubs of wire rope  98  and bands  98  are discarded or recycled. 
         [0045]    As best viewed in  FIGS. 1A and 1B , almost the entire axial length of the magnetic core  25  is swaddled by the primary coil  23 . This prevents any relative movement or separation of the strands of the woven rope making up the magnetic core. The idealized wire rope cross-sections depicted in  FIGS. 4 and 5  are actually hexagonally-shaped as opposed to truly circular. Wire ropes with differing strand sizes and arrangements can be employed in known wrap configurations to more closely approximate a circular cross-section. 
         [0046]      FIG. 1A  depicts the uppermost end portion  148  of the wire rope core  25  which is not covered by the primary coil  23 . Uppermost portion  148  of the wire rope core  25  is nestingly disposed within a downwardly opening pocket  150  integrally formed within connector body  11  to prevent any unraveling of the strands of the wire rope core  25  in application. The core grounding spring  39  is disposed within the pocket  150  and continuously bears downwardly against the upper end surface  152  of the wire rope core  25  to maintain an electrical interconnection therewith. 
         [0047]      FIG. 1B  depicts the lowermost end portion  154  of the wire rope core  25  which is not covered by the primary coil  23 . Lowermost portion  154  of the wire rope core  25  is nestingly disposed within an upwardly opening pocket  156  integrally formed within the spacer  29  to prevent any unraveling of the strands of the wire rope core  25  in application. The compression spring  27  is disposed within the pocket  156  and continuously bears upwardly against the lower end surface  158  of the wire rope core  25  to maintain the wire rope core  25  in its illustrated position. 
         [0048]    It is to be understood that the invention has been described with reference to specific embodiments and variations to provide the features and advantages previously described and that the embodiments are susceptible of modification as will be apparent to those skilled in the art. 
         [0049]    Furthermore, it is contemplated that many alternative, common inexpensive materials can be employed to construct the basis constituent components. Accordingly, the forgoing is not to be construed in a limiting sense. 
         [0050]    The invention has been described in an illustrative manner, and it is to be understood that the terminology, which has been used is intended to be in the nature of words of description rather than of limitation. 
         [0051]    Obviously, many modifications and variations of the present invention are possible in light of the above teachings. For example, although the present invention is illustrated as embodied in a so called “pencil core structure” wherein the spark plug assembly and the ignition coil are integrated into a single apparatus, it can also be applied with equal success within separate mount ignition coil/spark plug(s) arrangements such as those described in the specifications of the patent references incorporated herein. It can be applied with and without dielectric fluids. It is, therefore, to be understood that within the scope of the appended claims, wherein reference numerals are merely for illustrative purposes and convenience and are not in any way limiting, the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the Doctrine of Equivalents, may be practiced otherwise than is specifically described.