Integral spark plug coil for aircraft-type plug

Claim 1

In an ignition device comprising a step-up coil unit to be associated with an aircraft-type spark plug having a barrel extending up from the shell of the spark plug with threads on the portion of the barrel away from the shell, the improvement comprising said step-up coil unit comprising a tubular metal sleeve having threads for engaging the threads on the barrel of the spark plug, said sleeve defining a radial flange, an insulating bushing having a hub-like configuration arranged substantially coaxial with the sleeve such that a face of the bushing is adjacent the radial flange of the sleeve, and a coil canister sealed to said sleeve having said bushing and a step-up coil contained therein and there being at least one port in the side of the canister adjacent the bushing, a rigid lead journaled in the bushing for completing the electrical circuit between the coil secondary and the spark plug, the space between the radial flange and the bushing defining a narrow annular gap sized to quench a flame attempting to propagate therethrough, whereby upon leakage of the seals in the spark plug pressure does not build up in the spark plug barrel and coil canister but is released through the gap between the radial flange and the bushing and through the ports in the canister and whereby the condition of the spark plug can be checked by inserting a firing probe in the said at least one port.