Abstract:
An ignition coil engages an inner surface of a bore of an engine, the providing access to a spark plug. The engagement is a boltless cam-lock engagement. A spring is associated with the engagement to hold the assembly in tension, and the spring also contacts a ground terminal in the ignition coil and the base of the spark plug to provide a short electrical path for radiofrequency interference (RFI) dissipation.

Description:
I. FIELD OF THE INVENTION 
     The present invention relates to vehicle ignition coils. 
     II. BACKGROUND OF THE INVENTION 
     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. 
     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. 
     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. 
     As also understood herein, it would be advantageous to ameliorate stray radiofrequency interference (RFI) transient signals that otherwise can be induced from spark plug operation, because RFI signals can undesirably interfere with other components in the vehicle. 
     SUMMARY OF THE INVENTION 
     An ignition coil has a core supporting a primary winding and one or more secondary windings inductively couplable to the primary winding. The secondary winding is associated with an electrical ground. A plastic case holds the windings and is associated with a generally cylindrical plug engagement fitting defining an axis. An elongated slit is formed through the fitting and has an elongated slit segment that is parallel to the axis, with the slit segment being configured for slidably receiving a protrusion associated with a bore of an engine to facilitate mechanical coupling of the case. Also, a generally ring-shaped electrically conductive terminal is disposed on the fitting and is electrically connected to the electrical ground. A spring is juxtaposed with the fitting and is configured to surround a boot of the spark plug. Per present principles, the terminal is oriented to electrically contact the spring and the spring is configured to electrically contact a base of the spark plug to establish an electrical path between the secondary winding and the base. 
     In another aspect, an ignition coil has a primary winding receiving voltage from a source of voltage in a vehicle and a secondary winding inductively couplable to the primary winding. A case holds the windings and is engageable in a cam lock engagement with a spark plug assembly. Also, a spring is associated with the cam lock engagement and establishes a path for electrical communication between the secondary winding and a spark plug of the spark plug assembly. 
     In still another aspect, an assembly includes a spark plug assembly including a boot and a spark plug, and an ignition coil mechanically coupled to the spark plug assembly using a boltless mounting. A spring that is associated with the boltless mounting electrically connects the base of the spark plug to an electrical ground associated with a secondary winding of the ignition coil. 
     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 
         FIG. 1  is a side cross-sectional view showing the ignition coil, one of the spark plug boots, and the sleeve with grounding spring; and 
         FIG. 2  is a cut-away side elevational view of the sleeve. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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 plug  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  shown and described herein may be but one of plural coils that could be used to energize two spark plugs 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 , although present principles are not limited to the specific coil  10  shown. 
     Accordingly and for purposes of illustrative disclosure, the ignition coil  10  may include various components including a secondary winding spool  28  that can bear first and second electrically conductive wire secondary windings  32 ,  34 . In the non-limiting embodiment shown, the secondary windings  32 ,  34  can be in axial sequence to each other. 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  such as epoxy may be disposed between the secondary winding spool  28  and the case  16 . In any case, in non-limiting embodiments the secondary winding or windings can be connected to a secondary winding ground terminal  40 , which may be established by one or more electrical conductors. 
     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. 
     It is to be understood that the primary winding  42  is electrically connected, via a connector member  52 , 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. 
     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. 
     Thus, a power terminal  54  of, e.g., the secondary windings  32  can be connected to a respective spark plug using connector structure known in the art, e.g., the power terminal  54  may be electrically connected to an internal spring  56  with associated terminal cup  58 . 
     In accordance with present principles and cross-referencing  FIGS. 1 and 2 , the ignition coil  10  may be formed with or attached to a rigid hollow generally cylindrical plug engagement fitting  60  defining an axis  62 . As shown, an elongated L-shaped slit  64  is formed through the wall of the fitting  60  and has an elongated slit segment  66  that is parallel to the axis  62 . The slit segment  66  is configured for slidably receiving a protrusion  68  that on the inner surface of a bore on the engine, with the bore providing access to the spark plug. The bore may be, without limitation, part of a cam cover or spark plug wall, the feature(s) on the engine in the area where the spark plug mounts to the engine. This facilitates mechanically coupling the coil assembly to the engine by a cam lock that is established when the coil assembly is rotated to move the protrusion into the end channel  69  of the slit  64 . 
     As envisioned herein, a generally ring-shaped electrically conductive ground terminal  70  is disposed on the fitting  60  by, e.g., overmolding the fitting  60  on the terminal  70  or pressing the terminal  70  into the open end of the fitting as shown, or around an inside surface of the fitting. It is to be understood that the terminal  70  is electrically connected to the electrical ground terminal  40  of the secondary winding. 
     An external spring  72  is juxtaposed with the fitting  60  and is configured to surround the boot  14  in compression. The ground terminal  70  is oriented to electrically contact the spring  72 . Also, the spring  72  electrically contacts the base  74  of the spark plug  12 , and in this way establishes an electrical path between the secondary winding and the base of the spark plug. It may now be appreciated that the spring  72  both establishes a ground path from the spark plug as well as establishes a counter-force to secure the boltless mechanical coupling between the boot  14  and coil  14  afforded by the cooperation of the slit  64  and protrusion  68 . 
     While the particular IGNITION COIL WITH SPRING-LOADED BOLTLESS MOUNTING TO SPARK PLUG 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.