Patent Page: The Humble Spark Plug

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By Richard Backus | Mar 9, 2020


Gottlob Honold’s 1914 patent for a “sparking device” more closely resembles the spark plug as we know it. First patented in Germany in 1902, it featured an electro-magnetic coil (b) which pulled up the center terminal (c), breaking the ground with the spark plug body (e) to produce a spark.

Given the spark plug’s critical role in the successful development and proliferation of the internal combustion engine, it’s interesting how little we appear to know about the details of precisely who invented the spark plug, and when.

According to several sources, the first spark plug was invented by Edmond Berger in 1839. Little information exists to explain the why and how of Berger’s invention, which he apparently never patented. Further, we have to wonder exactly what his spark plug was designed for, as the internal combustion engine had yet to be invented when Berger is said to have crafted his invention.

The need for a relatively simple, reliable device to ignite the compressed fuel/air charge in an internal combustion manifested itself greatly as the internal combustion engine took hold first in industry, and then as a power source for personal transportation. Etienne Lenoir, the inventor of one of the very first internal combustion engines, in 1858, patented an electric ignition in 1860, and is therefore sometimes credited with inventing the spark plug.

Many early engines used flame ignition to ignite the fuel/air charge. Battery and low-tension magneto ignition systems with make-and-break igniters further improved gas engine tuning and reliability, but there were limits to how it worked, especially as engine speeds increased in automotive applications. Igniter ignitions required constant attention, and the need to create a more reliable method for ignition became increasingly important.

Looking at the historical record, it seems reasonable to assume the basic principle of spark plug ignition was perceived and pursued by multiple people at the same time. In 1898, pioneering electrical engineer Nikola Tesla patented an “electrical igniter for gas engines” that was also likely the first capacitive-discharge system. It laid out the basic elements of spark plug ignition, with a high-tension coil and an insulated electrode. Tesla’s design used the piston as the grounding electrode.

Although the Lodge Plug Co. in England is noted as designing its first plug in 1903, the record suggests that the first commercially successful spark plug was patented by the Robert Bosch company in 1902. Designed by Bosch engineer Gottlob Honold, it contained an electro-magnetic coil that pulled a center electrode from its seat at the base of the spark plug, a spark being generated as it did so. It was in many ways a compact make-and-break, and like the spark plug we’ve come to know it had a threaded base that screwed into the cylinder, greatly improving ease of installation and removal for service. Porcelain was used for insulation.

Nikola Tesla’s 1898 patent for an “electrical igniter for gas engines” used a high-tension coil and a capacitor to feed voltage to an electrode (L) that was insulated from the cylinder (A), with the piston (B) acting as the grounding electrode. 

Despite the Bosch corporation’s strong presence in North America, Honold’s design wasn’t patented in the U.S. until 1914, by which time the number of spark plug manufacturers had literally exploded. According to the Spark Plug Collectors of America, some 6,700 (!) spark plug brands were offered from the early 1900s to the mid-1930s.

One of the earliest and most successful was headed up by Frenchman Albert Champion, who began making spark plugs in Boston around 1905. Interestingly, after parting with his eponymous company about 1908, Albert Champion founded Champion Spark Plug Co. in 1910, which due to litigation with the Albert Champion Co. became AC Spark Plug Co., “AC” being Albert Champion’s initials.

Ford famously began using Champion spark plugs starting in 1911, by which time the spark plug had taken on the basic characteristics we are familiar with today; a porcelain-type insulator with a center electrode, and a side electrode on a metal base. Central to the adoption of spark plug ignition was the successful development of the high-tension magneto and coil. A major development in spark plug reliability came in 1915, when New Jersey-based Frenchtown Porcelain Co. developed its “775” porcelain formula, which had superior heat and vibration qualities than the porcelain or mica formulas previously used. A few years later plug manufacturers began using sillimanite, an aluminosilicate mineral highly resistant to heat, in their porcelain. Albert Champion set up a mining operation in the Sierra Nevada Mountains of California, where the mineral was plentiful, to provide a ready supply of sillimanite for the porcelain used in AC spark plugs. – Richard Backus


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