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Low-voltage/high-voltage ignition
Regarding Figure 1:
Snapper with pendulum anchor (bottom) and spring in the housing (top), Connecting rod to the engine (bottom right). |
Let’s get back to Otto. He is also regarded as the inventor of low-voltage ignition. That was the first electric ignition system with a reasonably controllable ignition timing (1884). In principle, we are dealing here with just
a single coil, which, however, is mounted so that it oscillates within a permanent magnetic field. In addition, there is a shaft driven by the engine at half the crankshaft speed, which fully actuates a rather bulky
lever (catcher - see image) once per revolution; which shortly thereafter returns to its initial position due to spring force, which is why this design is also called 'snap-action ignition'.
This lever causes a contact to open in the combustion chamber, and the simultaneous movement of the coil within the magnetic field creates a opening spark there. Although the spark is generated by induction, there is no
specific voltage conversion, as occurs, for example, in an ignition coil. Incidentally, Otto had not patented this ignition system, which gave Bosch the opportunity to have it further developed at its facility. In return, Otto
allegedly benefited from Bosch’s inventions in his engines without having to pay extra for them.
The original design was used by Otto in stationary engines with low maximum speeds, because only this type of ignition ensured smooth operation with gasoline. This ignition system seemed too heavy and too sluggish
for higher RPMs and use in a motor vehicle. Bosch's improvement helped by using a lightweight sleeve that swung around the heavy armature, thereby controlling the magnetic effect on the coil. Thanks to a special
transmission in the mechanical connection to the engine, it was now even possible to adjust the ignition timing at higher RPMs.
What did the combustion chamber look like during this ignition? In addition to the piston movement, there was also a movable ignition lever, an ignition flange, and an ignition pin. That's quite a lot for a space that should
ideally be spherical and provided for a burning mixture. Bosch recognized the dilemma and tasked his master, Honold, with ensuring that only a single spark would jump across the combustion chamber, without any
moving parts in the ignition system.
He further developed the anchor resting under the movable sleeve, gave it two windings similar to today's ignition coils, built an interrupter into the primary winding and thus ensured a spark discharge with high voltage.
This is where cams, contacts, and the capacitor first appeared-components that would later play a key role in battery ignition as well. But at that time, the ignition system still generated its own power and was therefore not
dependent on a battery.
High-voltage ignition became a great success. At the same time, spark plugs were needed to ensure that the spark was generated exactly where it was needed, thanks to proper insulation. Their production turned Bosch
into a major corporation. Nevertheless, one cannot claim to be the inventor of the spark plug. That honor probably belongs more to Karl Benz, who used them as early as 1885 in the engines of his first vehicles.
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