Plug-hole-installed ignition coil unit for internal combustion engines

An ignition coil unit to be installed in a hole opened through a cylinder head of an engine, comprising:

• a case having an upper section and a cylindrical section extending from the upper section and inserted in the hole;
• an ignition coil installed in the cylindrical section of the case and comprising a primary coil connected to a power source and a secondary coil connected to a spark plug which is installed in a combustion chamber of a cylinder of the engine for producing spark discharge to ignite air-fuel mixture to generate combustion thereof in the combustion chamber;
• and
• a circuit board on which an ionic-current detection circuit, connected to the secondary coil, which detects ionic-current that flows during the combustion of the air-fuel mixture;
• and a processing circuit, connected to the ionic-current detection circuit, which generates an output indicative of the detected ionic-current, being formed,
• the circuit board being installed in the upper section of the case.