Ignition coil

An ignition coil comprising:

• a primary coil;
• a secondary coil magnetically coupled to the primary coil, the secondary coil coaxially wound radially outside of the primary coil;
• a central core disposed radially inside of the primary coil with both ends projecting from both of the primary coil and the secondary coil in a coil axial direction,
• the central core having:
• a central core front end face at a front end thereof facing forward in the coil axial direction, and
• a pair of central core rear end oblique surfaces at a rear end thereof, the pair of central core rear end oblique surfaces being symmetrically inclined with a central axis of the central core;
• and
• a pair of split cores surrounding the primary coil and the secondary coil together with the central core,
• the pair of split cores respectively facing outer peripheral portions of the secondary coil in an orthogonal direction orthogonal to the coil axial direction,
• the pair of split cores respectively forming two closed magnetic paths with the central core,
• at least one of the pair of the split cores having a first opposing face to face the central core front end face and partially form the closed magnetic path, the first opposing face orthogonally extended to the coil axial direction,
• the pair of split cores respectively having two second oblique opposing surfaces which are symmetric with the central axis of the central core when attached thereto, the pair of split cores mutually facing each other in the orthogonal direction while contacting the central core rear end oblique surfaces,
• wherein at least one of the second oblique opposing surfaces and the central core rear end oblique surface contacting the at least one of second oblique opposing surfaces are inclined at substantially the same degree of angle from the central axis of the central core and increasingly approach the other one of the central core rear end surfaces in the orthogonal direction in proportion to a distance of a portion of each of the at least one of the second oblique opposing surfaces and the central core rear end oblique surface from the first opposing face of the at least one of the pair of the split cores in the coil axial direction.