ABSTRACT
The automobile electrical system, from the very first days of propulsion by internal combustion engine technology, was used only for igniting fuel in the engine’s cylinders. In the more than 100 years of the automobile, the electrical system has become a major consideration in the design and performance of the entire vehicle. In the early years leading up to 1912, ignition of the fuel-air mixture in the cylinders was one of the major challenges. There were attempts at ignition using open-flame, hot-wire, and hot-tube igniters, but none were satisfactory due to the fact that the timing of the ignition event was highly variable and critical for proper function of the engine, not to mention the difficulty of implementation of the various alternatives. Creating an electric spark inside the cylinder was the most straightforward approach [1]. The earliest electrical ignition systems were actually low voltage systems in which a cam outside the cylinder drove a mechanical arm in the cylinder that made intermittent contact with a stationary rod that was inserted into the cylinder through an insulating sleeve and connected to a series of dry cells through a small inductor. When the contact in the cylinder closed a current would build up in the inductor, and when the contact opened a spark discharge occurred, igniting the gas mixture. This low voltage ignition system was used on single cylinder and multi-cylinder engines. Because control of spark timing was so difficult, the next step was to place a spark plug in the cylinder and to apply very high voltage to ionize the spark gap under the high chamber pressure existing in the cylinder at the time of ignition. These early systems used a magneto, a type of alternating current generator, that was either low tension or high tension depending on whether or not a high voltage winding was placed on the same core as the 6V primary. Power for the primary was again provided by a series of dry cells to power the system while the engine was hand cranked. Later a system based on a Rumkoff coil located in the engine compartment was used to provide nearly continuous high voltage to the center contact of a distributor. This ignition system relied on a small wooden cased transformer module having a magnetic armature that energized a relay-like switch that would open the primary winding when sufficient magnetic charge was accumulated. Interruption of the primary winding current by opening the contact resulted in high voltage induced across the secondary winding as the stored magnetic field collapsed, sending 20kV or higher to the distributor and on to the appropriate cylinder. This electro-mechanical ignition system was very noisy both audibly and electrically since the spark source was virtually continuous.
