Patent ID: 8319591

Claim:
An ignition coil having a primary coil, the primary coil comprising: a center core, farmed by compressing magnetic powder packed in a core die, having a smaller diameter portion, a larger diameter portion, a winding body portion being composed of the smaller diameter portion and the larger diameter portion and being formed substantially in a columnar shape with a step, and a collar portion extending from a root of the smaller diameter portion in outer directions, perpendicular to a center axis of the center core, so as to form substantially a rectangle on a plane perpendicular to the center axis; a connector socket, formed in a cylindrical shape to fixedly hold the collar portion of the center core, having a bottom wall, a side wall surrounding the bottom wall so as to have an opened end and an opening, the opened end being placed opposite to the bottom wall through the side wall, the opening extending from the opened end toward the bottom wall, the collar portion of the center core being fixedly held in a space surrounded by the bottom wall and the side wall, the root of the smaller diameter portion being located in the opening, a winding start catching portion disposed on the side wall, and a winding end catching portion disposed on the side wall on a winding end side of the smaller diameter portion; and a winding which is wound on the winding body portion while a winding start portion of the winding is caught by the winding start catching portion on a winding start side of the smaller diameter portion and while a winding end portion of the winding is caught by the winding end catching portion on a winding end side of the smaller diameter portion opposite to the winding start side, wherein the core die is composed of two divided dies divided through a dividing line which extends along a diagonal line of the rectangle of the collar portion packed in the dies, and wherein the root of the smaller diameter portion on a segment of the diagonal line positioned on the winding start side is exposed to the opening of the connector socket while the root is substantially covered with the side wall on another segment of the diagonal line positioned on the winding end side.