Ignition coil unit and ignition system, capable of suppressing deformation of the seal section, used in internal combustion engine

An ignition coil unit used in an internal combustion engine as an attachment to an engine body that includes a cylinder head having a plug hole and a head cover that covers the cylinder head by including an opening hole facing the plug hole, the ignition coil unit comprising:

• a coil unit to generate a high voltage, the coil unit including;
• a main housing to accommodate components used in the coil unit, and
• an auxiliary housing to accommodate a cylindrical high tension tower protruding from the main housing to a tip side in an axial direction;
• and
• a cylindrical coupling unit to couple the coil unit to a spark plug,
• the cylindrical coupling unit including;
• a flexible sealing section extending in an axial direction of the cylindrical coupling unit while fitting to an outer peripheral surface of the high tension tower,
• the flexible sealing section including:
• a first fitting section at a tip of the flexible sealing section, and
• an adhesion portion to tightly contact the head cover, and
• a joint aligning with the flexible sealing section in the axial direction,
• the joint having a second fitting section fitting to the first fitting section of the flexible sealing section, the joint being harder than the sealing section,
• wherein the flexible sealing section further includes a neck portion at least in a region between the adhesion portion and the joint in the axial direction,
• wherein the neck portion is formed by partially narrowing the sealing section radially inwardly.