Arnoux system
The Arnoux system is a train articulation system, for turning on railroad tracks, invented by Jean-Claude-Républicain Arnoux and patented in France in 1838. Arnoux was the chief engineer of the Ligne de Sceaux which was originally built with very tight radii in the area around Sceaux, Hauts-de-Seine.
With the support of the French Academy of Sciences, Arnoux devised a new articulation system that allowed train wheels to turn, the système ferroviaire dit Arnoux ("Arnoux rail system"), and the Ligne de Sceaux was built to test his prototypes. The line started commercial use in 1846. But the operating cost and the use of a broad gauge of 1,750 mm (5 ft 8 7⁄8 in) meant it was not taken up more widely. Invention of the bogie made it redundant. It was abandoned entirely by 1893.
When steam railways were in their infancy, trains comprised a steam locomotive and one or more railway carriages with two fixed axles. As speeds increased, this design caused significant wear to the track and instability in the track ballast.
To ameliorate these faults, Arnoux proposed a system of essieux articulés ("Articulated axles") whereby the yaw angle of the wheels was reduced essentially to zero. Arnoux adapted the system used on horse-carts, which pivoted each axle at its centre, to be applied equally over the two axles together.
Arnoux devised a system of chains and pulleys so that eah the wheels' correctly adjusted in yaw through the curve: as soon as the leading axle started to turn, all other axles would also turn by the same amount. Actually this was a fatal design flaw since in a long train not all carriages are on the same part of the curve. A compromise was to use pulleys of different diameters, with guide wheels on the locomotive to control their motion. Also, using a broad gauge of 1,750 mm (5 ft 8 7⁄8 in) was expected to give greater stability.
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