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May 27, 2008
- Testing on hill climbs and in freight transport
- Bosch magneto ignition replaces Daimler’s hot tube ignition
- New ignition technology proves itself in racing
This trial run marked the beginning of a new era in engine technology at Daimler-Motoren-Gesellschaft (DMG): up until then, all automobiles of the Stuttgart brand had been equipped with the hot tube ignition which Gottlieb Daimler had invented for the high-speed gasoline engine in 1883. But the brilliantly simple system soon would be unable to cope with the increasingly higher speeds of the new engines.
And so the new generation of electric ignition developed by Robert Bosch, the electrical engineering pioneer from Stuttgart, came at exactly the right time in 1898. Daimler had one of his belt-driven cars equipped with Bosch’s low-voltage magneto ignition and tested the vehicle for five long days in the Austrian Alps in July 1898.
DMG also installed electric ignition in a few trucks for testing purposes. The results of the journey through the Alps and the truck tests were convincing: the Phoenix cars introduced in 1897, with outputs of four hp (2.9 kW) and six hp (4.4 kW), were being sold by DMG with the low-voltage magneto ignition as early as fall 1898.
From experiment to large-scale production
Electric ignition of mixtures of gas and air had been discovered over a hundred years before Bosch’s low-voltage magneto ignition: in 1777 Alessandro Volta ignited marsh gas with an electric spark. However, the method was not really ready for practical, large-scale use in the automobile until almost the turn of the twentieth century.
Several inventions paved the way for the modern magneto ignition: in 1801 the French road construction engineer Philippe Lebon d’Humberain took out a patent on a gas engine with electric ignition, but did not build this machine. In 1807 the Swiss politician and inventor Isaac de Rivaz considered firing an internal combustion engine by a method similar to Volta’s pistol. Etienne Lenoir developed his gas engine in 1859 and was issued a patent for it in 1860. Ignition was already effected by a sparkplug consisting of two platinum wires insulated with porcelain: this was the archetype of the buzzer ignition based on the Ruhmkorff coil. Later, Carl Benz would rely on a variant of the buzzer ignition.
In 1876 Nikolaus August Otto developed his four-stroke engine which had a flame ignition with slide valve. Siemens was working on an electric ignition for the Otto engine in 1877, but only the magneto-electric ignition with impulse coupling, developed by Otto himself in 1884, attained maturity.
The Viennese machinist Siegfried Marcus already came very close to the future magneto ignition with his electric low-voltage contact-breaker ignition. Patented in 1883, the ignition worked with a movable center electrode in the cylinder; the ignition current was produced by a floating armature.
Daimler banks on the hot tube
Gottlieb Daimler and Wilhelm Maybach elected to take a very different route when they built the first high-speed engine in 1883. The hot tube ignition was regarded as the most important innovation of their engine. It ensured reliable ignition and made the desired increase in engine speed possible versus the Deutz gas engines. The first experimental engine managed as much as 600 rpm, appreciably more than the maximum 120 rpm for gas engines until then.
A key advantage compared to Otto’s flame ignition was the elimination of controlling parts: the hot tube, open towards the engine, was connected with the combustion chamber of the cylinder by a duct. A burner kept the tube, whose outer end was sealed gas-tight, red-hot. On each compression stroke a part of the mixture was forced into the tube by compression and ignited by the heat. Daimler’s first motorized carriage of 1886 also had an engine with hot tube ignition.
Bosch and the ignition
In his “Workshop for Precision Mechanics and Electrical Engineering” opened in 1886, Robert Bosch constructed a magneto ignition for use with stationary engines in 1887. This magneto-electric impulse coupling ignition enabled engine speeds of as much as 300 rpm. A wound armature oscillated between magnets and induced a current in the armature winding. At the moment ignition took place in the combustion chamber of the cylinder, this current was transformed by a mechanical impulse coupling control into a spark that ignited the mixture.
Bosch improved Otto’s solution in several steps. Among other things he adopted powerful U-shaped magnets such as employed by millers. In 1897 – Bosch produced the 1000th magneto ignition with oscillating armature in that year – the first successful tests were conducted to install the magneto ignition in a motor vehicle.
But the key to the future of the magneto as standard ignition device in the automobile was the introduction of an oscillating sleeve which permitted the armature between the magnets to remain at rest. The idea for this modification came from mechanic Arnold Zähringer, who worked for Bosch since 1890 and later became plant manager in Stuttgart.
With this new sleeve design, Bosch was able to make the magneto impulse coupling ignition ready for use in motor vehicles. Further steps in the development of the low-voltage magneto ignition were the revolving armature (1900) and finally the revolving sleeve (1901). The Bosch high-voltage magneto ignition of 1902 built upon this last evolutionary stage.
Demonstrations for Daimler and Benz
In 1898 Robert Bosch presented the new ignition to potential customers including the automotive pioneers Gottlieb Daimler and Carl Benz. Daimler recognized the innovative achievement embodied by this solution and decided to subject it to a lengthy test under the less favorable conditions of an Alpine tour. The test in Tyrol in July 1898 lasted five days. Afterwards, and following further testing in DMG trucks, the decision was taken to replace the hot tube in Daimler automotive engines as soon as possible with the Bosch low-voltage magneto ignition with oscillating sleeve.
The Phoenix car series (models with four-hp two-cylinder engine and six-hp four-cylinder engine) already featured the new ignition as of fall 1898. The first Mercedes model series of 1900/1901 then used the low-voltage magneto impulse coupling ignition in all units. The same goes for the Mercedes Simplex models of 1902 and 1903 as well as the Mercedes Simplex and the four-cylinder DMG models from 1904 to 1910.
The only exception was the 55 hp Mercedes built from 1907 (from 1909 this model was called 31/55 hp Mercedes), which had a dual magneto and battery ignition. This dual ignition was also used in the DMG six-cylinder models in the years 1907 to 1911.
Racing successes and the road to high-voltage ignition
The Bosch low-voltage magneto ignition proved its worth in the automobiles of Daimler-Motoren-Gesellschaft in everyday operation, jut as it did in competition driving. The first Mercedes which took the winner’s laurels in three French races in 1901 and scored further victories in that same year attained legendary status.
At Bosch, work on the next generation of ignition technology meanwhile was in progress: the high-voltage magneto ignition with sparkplug introduced in 1902 reduced the number of mechanical parts especially in the combustion chamber and made even higher engine speeds possible. Bosch delivered the first high-voltage magneto ignition to a reliable partner on September 24, 1902: to Daimler-Motoren-Gesellschaft. The magneto ignition remained the most frequently used system in automobiles well into the 1930s. It was finally superseded by the battery ignition which emerged in the 1920s.