Development of the Stick Coil with an integrated Igniter - Cylindrical Ignition Coil installed into Engine Plug Hole -


   1.  Abstract
 On the recent ignition system for the petroleum(Gasoline) engines, the traditional distributors and high tension cables are being replaced with an S-DLI system where an ignition coil is configured for each cylinder.  On the other hand, for the engine itself, reducing the space allocated to the ignition coils on the engine head is required due to a tend toward using a DOHC mechanism, a multivalve unit, and a direct injection system.  Concentrating on making effective use of the plug hole where the traditional high tension cable has been fitted, this technology is intended for achieving this assignment by developing a coil, that is, a stick coil seated in the plug hole.

   2.  Description of the technology
 Figure 1 shows a sample set-up with a stick coil incorporating the igniter, which is the drive circuit, on the head.  To develop this stick coil, the primary new technical points in development for breaking through the assignments, such as miniaturization, high voltage resistance, and thermal stress resistance, refer to the following six items: (1)  Miniaturization of the igniter through plastic packaging. The optimum packaging material and igniter construction have been determined by means of three-dimensional flow analysis. (2)  Secondary winding reduced with a high voltage power transistor. The power transistor in the igniter has been improved in breakdown  voltage. (3)  Spool flange eliminated by means of diagonally overlapped winding. (4)  Electric field strength reduced by means of dummy winding. The optimum construction has been determined through analysis on the electric field strength. (5)  Magnetic circuit optimized by means of a cylindrically laminated core. (6)  Thermal stress reduced between different materials (plastics and metals). The optimum construction has been determined through analysis on the thermal stress.
From among these items, the diagonally overlapped winding in (3) and the cylindrically laminated core in (5) have been achieved through co-engineering developments in both product design and manufacturing technique.
As described in Figure 2, while the traditional winding have been wound in the slots partitioned off by "flanges" in order to control the inter-wires voltage below the allowable voltage level of the winding wire insulation, the developed winding, which are referred to as the diagonally overlapped winding, are capable of limiting the inter-wires voltage by diagonally stacking the winding lines, resulting in eliminated "flanges."  As a result, the diameter of the ignition coil was successfully reduced by 10 percent.
As shown in Figure 3, while the traditional laminated core with a stamping process has an occupying area rate between approximate 50 and 70 percent, which refers to the ratio of the core dominating in the circle, the cylindrically laminated core, which has been developed this time, has achieved an occupying area rate of at least 95 percent by combining sheet steel strips of different widths in a "playing card bundle" manner.  As a result, the diameter of the ignition coil was successfully reduced by 10 percent.

     3.  Conclusion
 Successfully put on the mass production market in 1997 for the first time in the world, our products incorporating this technology have been adopted by a lot of engines.
The stick coil concept is accepted and followed not only by the automobile manufactures, but also by the other ignition coil manufactures. This product is referred to as a de facto standard product in the ignition coil market.


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