 |
Development of the Stick Coil with an integrated Igniter -
Cylindrical Ignition Coil installed into Engine Plug Hole -
Kazutoyo Osuka(DENSO CORPORATION), Masahiro
Sato(DENSO CORPORATION), Masahiro Yamamoto(DENSO CORPORATION), Keisuke
Kawano(DENSO CORPORATION), Takashi Tabata(DENSO CORPORATION)
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. |
