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A primary coil of an ignition coil has a socket with a side wall having an opening, a center core having a body portion with a root located in the opening and a collar portion extending perpendicularly from the root, and a winding wound on the body portion while the socket catches start and end port

A primary coil of an ignition coil has a socket with a side wall having an opening, a center core having a body portion with a root located in the opening and a collar portion extending perpendicularly from the root, and a winding wound on the body portion while the socket catches start and end portions of the winding on respective winding start and end sides. The collar portion is held in the socket. The core is formed by compressing magnetic powder in two divided dies divided through dividing lines which extend along a diagonal line of a rectangle formed by projecting the collar portion on a plane perpendicular to a center axis of the core. The root on the diagonal line is exposed to the opening on the winding start side and is covered with the side wall on the winding end side.

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1. 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 diamete

1. 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, anda 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, anda winding end catching portion disposed on the side wall on a winding end side of the smaller diameter portion; anda 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, andwherein 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. 2. The ignition coil according to claim 1, wherein the center core has a first burr on the root located on the diagonal line on the winding start side and has a second burr on the root located on the diagonal line on the winding end side, the first burr is exposed to the opening, and the second burr is not exposed to the opening. 3. The ignition coil according to claim 1, wherein the winding has a plurality of turns wound in a plurality of winding layers such that the first layer of winding is directly in contact with the winding body portion, and the winding start portion of the winding extends from a specific turn of the winding which is located to be nearest to the collar portion of the center core among the turns of winding in the first winding layer and is supported by the side wall of the connector socket. 4. The ignition coil according to claim 1, wherein the root exposed to the opening of the connector socket on the winding start side is located on an opened side of the collar portion, on which the opened end of the side wall and the catching portions are located, and the root covered with the side wall on the winding end side is located on a closed side of the collar portion opposite to the opened side. 5. The ignition coil according to claim 1, wherein the opening is formed substantially in a U shape having a semicircle at an area of the opening nearest to the bottom wall, and a width of the opening in a direction from the winding start side to the winding end side is substantially equal to a diameter of the smaller diameter portion of the center core. 6. An ignition coil having a primary coil, the primary coil comprising: a center core, formed 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, anda 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, anda winding end catching portion disposed on the side wall; anda 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 and while a winding end portion of the winding is caught by the winding end catching portion,wherein the core die is composed of two divided dies divided through a dividing line extending along a center line which partitions the rectangle formed on the collar portion of the center core, located in the divided dies, into two equal parts, and is substantially perpendicular to a direction directed from the opened end to the bottom wall of the connector socket holding the center core. 7. The ignition coil according to claim 6, wherein the center line of the center core divides each of two longer sides of the rectangle formed on the collar portion of the center core. 8. The ignition coil according to claim 6, wherein the center line of the center core divides each of two shorter sides of the rectangle formed on the collar portion of the center core. 9. The ignition coil according to claim 6, wherein each of the divided dies has an inner wall formed in a releasing taper to form the collar portion such that a width between the sides of the collar portion is gradually shortened as a position of the width recedes from the center line. 10. The ignition coil according to claim 6, wherein the center core has a first burr on a first portion of the root located on the center line and has a second burr on a second portion of the root opposite to the first portion with respect to the center axis of the center core, and none of the first burr and the second burr are exposed to the opening. 11. The ignition coil according to claim 6, wherein the opening is formed substantially in a U shape having a semicircle at an area of the opening nearest to the bottom wall, and a diameter of the semicircle is substantially equal to a diameter of the smaller diameter portion of the center core.