Let's go back to Nicolaus Otto. He is considered to be the inventor of the low-voltage ignition. This was the first electric ignition which had a fairly determinable ignition point (1884). In principle, we are dealing here with a coil, which however, is stored in a permanent magnetic field. In addition, a shaft driven by the engine, at half the crankshaft RPM which operates a, not very elegant lever (snapper) (see picture) once per rotation, which is shortly afterwards returned to it's original position by a spring, this is also called 'snap-off-ignition'.
This lever causes the opening of a contact in the combustion chamber and at the same time, through the fitting movement of the coil in the magnetic field, a spark is given off. Although the spark is created by induction, no special tension conversion takes place, as is the case with the ignition coil. By the way, Otto never took out a patent on this ignition, which gave Bosch the opportunity to further the development in his company. As compensation, Otto's engines supposedly, profited from Bosch's inventions, without Otto having to make any special payments.
The original development was used by Otto in stationary engines with a low maximum RPM, because only with this ignition, could the interference-free operation with petrol be guaranteed. This ignition seemed to be too heavy and too sluggish for higher RPM and for use in a motor vehicle. This is where Bosch's further development helped, instead of a heavy armature, a light sleeve swung around this and thus, directed the magnetic effect to the coil. Through a special gearbox in the mechanical connection to the engine, the ignition point could even be adjusted for higher RPM.
What did this ignition look like in the combustion chamber? Apart from the piston-movement there was also a movable ignition-lever, an ignition flange and an ignition pin. Quite a lot for the available area, which should be as spherical as possible to accomodate the mixture to be burned. Bosch recognised the dilemma and gave his master-electrician the task of making sure that only one sparking took place in the combustion chamber, without there being any moving parts of the ignition coming into play.
He developed the armature below the movable sleeve further, gave it two windings, similar to the ignition coils of today, he installed an interrupter in the primary winding, thus providing for a high-voltage arc. At this point, the first cams, contacts and also condensers appeared, which would also play an important role in the battery-ignition. However, this ignition system still generated ist own power, thus, it did not have to rely on a battery.
The high-voltage ignition was a great success. At the same time, the spark plug was now also necessary, to ensure that, through suitable insulation, the ignition spark only took place where is was to be used. It's production turned the Bosch company into a big enterprise. Nonetheless, they could not claim to have invented the spark plug. This honour must probably go to Carl Benz, who used them in his first vehicles after 1885. 05/12