Ignition coil for ignition systems of internal combustion engines

The secondary winding (15) and the coil body (14) carrying it are manufactured in a chambered realization, and the radial extension (height) of each chamber winding (29) decreases toward the higher chamber potential in accordance with the law of geometrical progression, so that the insulating distance (30, 31) between the secondary winding (15) and areas of the ignition coil that carry a lower potential increases with an increasingly higher chamber potential. As a result, the volume and the weight of the ignition coil are reduced, while the electrical output remains the same.

BACKGROUND 
The invention relates generally to an ignition coil for ignition systems of 
internal combustion engines and more particularly to a coil with an 
insulating gap between the primary and secondary windings. In ignition 
coils of this kind, the insulating distance between the secondary winding 
carrying the high voltage and areas of the ignition coil having a lower 
potential is proportionate to the highest voltage between two potentials; 
this is known to be in the area of the high voltage output of the 
secondary winding. 
Because the secondary winding is coaxial with the hollow-cylindrical 
primary winding, the insulating distance must necessarily exist over the 
entire length of the secondary winding, and in the vicinity of the first 
chamber of the secondary winding this distance is oversized, so that a 
larger quantity of potting resin is required, and the weight of the 
ignition coil is increased unnecessarily. 
THE INVENTION 
With the ignition coil for ignition systems of internal combustion engines 
according to the invention, the size and weight of the ignition coil are 
reduced, while its output remains the same. Briefly, the invention is to 
provide that the insulating distance of the individual chambers of the 
secondary winding be only so large as to correspond to the existing 
voltage between the chamber potential and the lower potential of the 
adjacent area of the ignition coil. 
Advantageous further features of the invention are provided. With the 
embodiment of the ignition coil including a tapered coil winding form the 
application of the invention to a preferred embodiment of an ignition coil 
is illustrated. The embodiment of the ignition coil with a geometrically 
decreasing winding height provides the stepped change between two adjacent 
chambers that is most favorable in terms of the insulating distance. With 
the embodiment of the ignition coil including struts of trapezoidal 
cross-section, a secure position of the individual windings in the chamber 
and favorable resistance of the struts to bending are attained. 
The area of the insertion or assembly opening, which is formed by the end 
face of the coil body of the primary winding and the bottom of the 
housing, must be absolutely tight while the ignition coil is potted--which 
is done without the iron core. In order to attain this tightness, it is 
already known to mold a sheath onto the end face of the coil body and to 
the housing bottom and to join these parts with an interference fit. 
It is also known to dispose respective integral lids, outwardly 
offstanding, on the end face of the coil body and on the housing bottom, 
next to join both lids with a press fit and then to cut off these lids at 
a distance from the housing bottom. It is further known to have an 
inwardly pointing sheath protrude from the housing bottom, thereby spacing 
the iron core apart from the coil body. All of these previously known 
sealing means are expensive in terms of manufacturing processes. 
With the further development of the ignition coil with removable lid 
segments, the required tightness in the vicinity of the insertion opening 
is attained at low engineering expense. Because the potting of the 
ignition coil is effected before the two lids are removed, both 
predetermined breaking points provide the required sealing, and only after 
the potting compound has cooled are both bottoms cut off and the iron core 
inserted.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT 
In an ignition system for internal combustion engines, FIG. 1 shows shows 
an ignition coil with a laminated iron core 10, which is disposed 
coaxially with the axis 11 of the ignition coil, and a coil body 12 
coaxial with the iron core 10 and having a primary winding 13. Also 
coaxial therewith is a coil body 14 in chambered form and having a 
secondary winding 15. 
A cup-shaped, substantially hollow-cylindrical housing 16 of plastic has an 
insertion opening 17 in its bottom for securing the coil body 12 having 
the primary winding 13 and the iron core 10. At its periphery 18 the coil 
body 12 is enlarged to form a receptacle for a dome 19 having a contact 
bush 20 molded inside it for the secondary connection of the ignition coil 
and receives two primary connection bolts 21 (only one of which is 
visible) for effecting a connection with the battery or ignition 
distributor or switching device. The first end segment 24 of the primary 
winding 13 makes contact with one connection bolt 21. The second end 
segment 24' of the primary winding and the second end segment 23' of the 
secondary winding 15 are fixed on a connection element 22' which makes 
contact with the other connection bolt, the one not shown. The first end 
segment 23 of the secondary winding 15 makes contact via a connection 
element 22 with the contact bush 20. 
The coil body 14 realized in chambered form has a frustoconical inner wall 
segment 25 which becomes wider toward the outside, a virtually cylindrical 
inner wall segment 25', and forms eight annular chambers 26, for example, 
which are defined by seven inner annular struts 27 and two outer annular 
struts 28, 28'. The axial cross section of each annular strut is 
trapezoidal, and the narrow sides of the trapezoid form part of the outer 
boundary of the coil body 14. The radial extension, that is, the height, 
of each chamber winding 29 of the secondary winding 16 decreases in 
geometrical progression toward the higher chamber potential, and the 
individual chamber windings 29 are disposed such that the insulating 
distance between the secondary winding 15 and areas of the ignition coil 
that carry a lower potential increases with an increasingly higher chamber 
potential. Thus the insulating distance 30, 30', of the chamber winding 
having the highest chamber potential, from the primary winding 13 or from 
the outside of the housing 16 is greater than the insulating distance 31, 
31' of the chamber winding having the smallest corresponding chamber 
potential. The elements of the ignition coil are secured in the housing 16 
in an insulating manner by means of a potting compound 32 shown by shading 
in the peripheral area only. 
The graduation of the chamber windings 29 in terms of their height and 
cross-sectional surface area does not have to correspond exclusively to a 
geometrical progression; it can also be accomplished taking manufacturing 
considerations and structural strength into account. 
As shown in FIG. 2, the bottom 36 of the housing 16 of the ignition coil 
has an opening rim 33 curved inward, which is integrally adjoined via a 
predetermined breaking point 35 by a hat-shaped lid 41. A hat-shaped lid 
40 is likewise molded to the end face of the coil body 12 via a 
predetermined breaking point 34; during the axial joining of the coil 12 
and the housing 16, the lid 40 is inserted into the lid 41. 
Subsequently the ignition coil is potted with potting compound 32, and 
after the compound has cooled, both lids 40, 41 are cut off by a tool at 
the predetermined breaking points 34, 35. Then the iron core (FIG. 1) is 
inserted into the insertion opening 17 in such a manner that the end 
segment of the iron core 10 protrudes partway past the bottom 36 of the 
housing 10. 
The housing 16 and the coil body 12 are preferably manufactured from the 
thermoplastic polybutylene, reinforced with glass fibers.