Abstract:
Described is an ignition coil for an internal combustion engine having a housing with a plug connector, wherein the plug connector has an elastomeric cap slid onto a tubular housing section that surrounds a terminal contact. This disclosure provides that the terminal contact is surrounded by a circumferential slot, in which an inner edge of the cap sits.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to DE 10 2016 113 451.1, filed Jul. 21, 2016, the entire disclosure of which is hereby incorporated herein by reference in its entirety. 
       BACKGROUND 
       [0002]    The invention relates to an ignition coil generally of the type disclosed in U.S. Pat. No. 6,191,674 B1. 
         [0003]    The electrical connection of an ignition coil to a spark plug is made by a plug connector, into which a sparkplug is inserted. This plug connector can have an elastomeric cap, which is slid onto a tubular housing section. An elastomeric cap can seal the plug connection with the spark plug against moisture, and impede high-voltage discharges. 
       SUMMARY 
       [0004]    This disclosure teaches how the dielectric strength of the plug connector of an ignition coil can be improved. 
         [0005]    In an ignition coil according to this disclosure, the terminal contact of the plug connector that is slid onto a spark plug is surrounded by a circumferential slot, in which an inner edge of a circular elastomeric cap sits, which is slid onto a tubular housing section of the ignition coil. In this way, the creepage distance from the terminal contact to the external side of the cap can be lengthened. This leads to an increased dielectric strength. 
         [0006]    The increased dielectric strength makes it possible to shorten the plug connector as it is no longer necessary to insert the spark plug so deep into the plug connector. The less far the spark plug is inserted into the plug connector, the shorter the creepage distances, and then the lower the dielectric strength. The circumferential slot, which surrounds the terminal contact and in which sits an inner edge of the elastomeric cap, makes it possible to ensure a sufficiently large creepage distance, and hence a sufficient dielectric strength, even given a shortened plug connector. The cap may fill the circumferential slot completely or almost completely, for example it may fill out ⅘ of the circumferential slot volume or more. However, this is not required for achieving a lengthened creepage distance. 
         [0007]    An advantageous refinement of this disclosure provides that the terminal contact be inserted in an electrically insulating sleeve, and that the circumferential slot be formed between the electrically insulating sleeve and an internal surface of the tubular housing section. This facilitates production. 
         [0008]    The sleeve preferably ends flush with the terminal contact, or projects over and beyond it opposite the plugging direction, i.e., toward a spark plug inserted into the plug connector. As a result, the creepage distance can be further lengthened. 
         [0009]    Another advantageous refinement of this disclosure provides that the sleeve has a collar, for example a thickened section that abuts against the interior side of the housing. From a production standpoint, this makes it very easy to form the circumferential slot, e.g., by inserting the sleeve into the housing. For example, the sleeve can be pressed into the housing. 
         [0010]    Another advantageous refinement of this disclosure provides that the elastomeric cap is made out of silicone. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: 
           [0012]      FIG. 1  is a schematic view of an ignition coil without cap; and 
           [0013]      FIG. 2  shows a sectional view of a detail of the ignition coil. 
       
    
    
     DESCRIPTION 
       [0014]    The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of this disclosure. 
         [0015]    The ignition coil shown on  FIG. 1  comprises a housing  1 , in which is arranged a transformer, which provides an output voltage for a spark plug from an input voltage, which may for example be provided by the electrical system of a vehicle. The ignition coil comprises a first plug connector  2  for connection to a power source, for example the electrical system of a vehicle, and a second plug connector  3  for sliding onto a spark plug. The plug connector  3  forms a dome-like high-voltage terminal. The interior side of the high-voltage terminal is sometimes referred to as a dome. 
         [0016]      FIG. 2  shows the plug connector  3  configured for receiving a spark plug in a cut detailed view together with an attached elastomeric cap  4 . The circular elastomeric cap  4  is attached to a tubular housing section  5 , which surrounds a terminal contact  6 . The terminal contact  6  is surrounded in the tubular housing section  5  by a circumferential slot  13 , into which the cap  4  projects. 
         [0017]    As shown on  FIG. 2 , the cap  4  essentially fills out the circumferential slot completely. An inner edge  4 a or rim of the circular cap  4  is thus arranged in the circumferential slot. The cap  4  can touch the floor  14  of the circumferential slot, as depicted on  FIG. 2 , or end a distance away from it, thereby leaving a free space on the floor of the circumferential groove. 
         [0018]    The circumferential groove in combination with the cap  4 , which may consist, e.g., of silicone, causes the creepage distance to lengthen from the terminal contact  6  to the exterior side of the cap  4 . As a result, the tubular housing section  5  or the plug connector  3  can be shortened, without detracting from the dielectric strength in the process. 
         [0019]    The terminal contact  6  sits in an electrically insulating sleeve  7 . The circumferential slot into which the elastomeric cap  4  projects is formed between the electrically insulating sleeve  7  and an inner surface of the tubular housing section  5 . In the embodiment shown, the sleeve  7  ends flush with the terminal contact  6 , but can also project over and beyond it. 
         [0020]    An interference resistor  8  can be arranged in the electrically insulating sleeve  7 . The terminal contact  6  can be designed as a metal cap of the interference resistor  8 . At its opposite end, the interference resistor  8  can carry another metal cap  11 , which secures it to the transformer of the ignition coil. 
         [0021]    The electrically insulating sleeve  7  can be pressed into the tubular housing section  5 . In order to make it easier to secure the sleeve  7  in the tubular housing section  5 , the sleeve  7  can have a thickened section, for example a bead  9 , which abuts against the tubular housing section  5  on the inside. 
         [0022]    The exterior side of the tubular housing section can have a continuous projection  10 , which engages into a circumferential slot or groove of the elastomeric cap  4 . For example, the continuous projection  10  can be a latching hook and improve the hold of the elastomeric cap  4  on the tubular housing section  5 . 
         [0023]    While exemplary embodiments have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of this disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims. 
       REFERENCE LIST 
       [0000]    
       
           1  Housing 
           2  Plug connector 
           3  Plug connector 
           4  Cap 
           5  Housing section 
           6  Terminal contact 
           7  Sleeve 
           8  Interference resistor 
           9  Bead 
           10  Projection 
           11  Metal cap 
           13  Circumferential slot 
           14  Floor 
           15  Groove