"Protos of Nonnendamm was a German car manufacturing company founded in 1898 in Berlin by engineers Alfred Sternberg and Oscar Heymann.
Sternberg initially manufactured a series ...
of small motors, 2.5 hp single-cylinder air-cooled, and others water-cooled of 3.5 hp. In 1905 he began producing Protos automobiles, developing the new ´kompensmotor´ or compensated motor, giving a smooth, fast ride. To dampen engine vibrations, Sternberg designed a motor with two cylinders and a third piston set at 180 degrees from the other two and having no other function than to act as a counterbalance to the two working pistons. This revolutionary design worked well and was much quieter than other twin engines in the country, providing up to 14 hp and remaining in production for several years. " - (en.wikipedia.org 30.01.2020)
