The Arnoux system is a train articulation system, for turning on railroad tracks, invented by Jean-Claude-Républicain Arnoux and

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A ...

ed in France in 1838. Arnoux was the chief engineer of the

Ligne de Sceaux The Ligne de Sceaux (Sceaux Line) was a railway line in France running from Paris, which initially linked the Place Denfert-Rochereau (then called the ''Place d'Enfer'', in Paris, to the town of Sceaux. The line originally opened in 1846 as a br ...

which was originally built with very tight radii in the area around

Sceaux, Hauts-de-Seine Sceaux () is a commune in the Hauts-de-Seine department in the southern suburbs of Paris, France. It is located from the centre of Paris. In 2019, Sceaux had a population of 20,004. A wealthy city Sceaux is famous for the Château de Sceaux, ...

. With the support of the French Academy of Sciences, Arnoux devised a new articulation system that allowed train wheels to turn, the ("Arnoux rail system"), and the

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 meant it was not taken up more widely. Invention of the bogie made it redundant. It was abandoned entirely by 1893.

System

Problem

When steam railways were in their infancy, trains comprised a steam locomotive and one or more

railway carriage A railroad car, railcar (American and Canadian English), railway wagon, railway carriage, railway truck, railwagon, railcarriage or railtruck (British English and UIC), also called a train car, train wagon, train carriage or train truck, is a ...

s with two fixed axles. As speeds increased, this design caused significant

wear Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology. Wear in ...

to the track and instability in the

track ballast Track ballast forms the trackbed upon which railroad ties (sleepers) are laid. It is packed between, below, and around the ties. It is used to bear the load from the railroad ties, to facilitate drainage of water, and also to keep down veget ...

Proposed solution

To ameliorate these faults, Arnoux proposed a system of ("Articulated axles") whereby the

yaw angle The Euler angles are three angles introduced by Leonhard Euler to describe the orientation of a rigid body with respect to a fixed coordinate system.Novi Commentarii academiae scientiarum Petropolitanae 20, 1776, pp. 189–207 (E478PDF/ref> The ...

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 each of 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 was expected to give greater stability. This system was not suitable for steam locomotives so Arnoux invented a separate system for them. The locomotives had a 2-4-2 wheel arrangement and the driving wheels were

flange A flange is a protruded ridge, lip or rim, either external or internal, that serves to increase strength (as the flange of an iron beam such as an I-beam or a T-beam); for easy attachment/transfer of contact force with another object (as the f ...

less. The carrying wheels were arranged to pivot and were controlled by near-horizontal guide wheels.

Patent application

Arnoux applied for his patent, number 8342, on 28 March 1838.

Practical application

Trials and the Grand Prix de l'Institut

Trials took place at

Saint-Mandé Saint-Mandé () is a high-end commune of the Val-de-Marne department in Île-de-France in the eastern suburbs of Paris, France. It is located from the center of Paris. It is one of the smallest communes of the Île-de-France by land area, but i ...

between 1839 and 1840 in a circuit constructed by Alexis Dulong. These trials successfully demonstrated the stability and safety of the system. Public bodies, the

Duke of Aumale Duke is a male title either of a monarch ruling over a duchy, or of a member of royalty, or nobility. As rulers, dukes are ranked below emperors, kings, grand princes, grand dukes, and sovereign princes. As royalty or nobility, they are ran ...

and numerous members of the French Academy of Sciences,: contains a description of the prize and a long study of the advantages and disadvantages of the Arnoux System including François Arago. All unanimously praised the system. After this experience, Arnoux was awarded the ("Grand Prize for Mechanical Engineering") by the Institute.

Concession & opening of the Ligne de Sceaux

At the suggestion of François Arago, the Arnoux system was implemented on the

from

Paris Paris () is the Capital city, capital and List of communes in France with over 20,000 inhabitants, most populous city of France, with an estimated population of 2,165,423 residents in 2019 in an area of more than 105 km² (41 sq mi), ma ...

. On 5 September 1844, Arnoux and the Minister of Public Works signed a contract to build and operate the line. The line began service in 1846, starting from the ("Hell's Gate") (see Gare de Denfert-Rochereau) with a curved passenger building of radius on a

balloon loop A balloon loop, turning loop, or reversing loop ( North American Terminology) allows a rail vehicle or train to reverse direction without having to shunt or stop. Balloon loops can be useful for passenger trains and unit freight trains. Bal ...

to allow trains to reverse direction. The route then had its first stop at

Arcueil Arcueil () is a commune in the Val-de-Marne department in the southern suburbs of Paris, France. It is located from the center of Paris. Name The name Arcueil was recorded for the first time in 1119 as ''Arcoloï'', and later in the 12th ...

, then Bourg-la-Reine on a radius curve. The incline towards Sceaux was straight until the station at

Fontenay-aux-Roses Fontenay-aux-Roses () is a commune in the southwestern suburbs of Paris, France. It is located from the center of Paris. In 1880 a girls school École Normale Supérieure was opened in the town. It was one of the most prestigious of Paris and ...

, then had a succession of curves at ; the gradient was up to 11 mm/m (1.1%, 1:91), which was significant. All together the line was long.

Alternatives

In fact, the problem was solved by the bogie, which was invented in the USA shortly after opening, but this was unknown in Europe at the time. The Arnoux system bears some similarity to Cleminson's patent system. Both are designed to keep the axles radial to the curvature of the track.

Talgo Talgo (officially Patentes Talgo, SAU) is a Spanish manufacturer of intercity, standard, and high-speed passenger trains. Corporate history TALGO, an abbreviation of Tren Articulado Ligero Goicoechea Oriol (English: ''Lightweight articulated tr ...

utilise independent wheels mounted in a "rodal" between cars. Linkage rods keep the "rodal" aligned tangentially with the track. Like Arnoux, this system originally utilised (Iberian) broad gauge tracks, but recent versions are used on standard gauge or utilise variable gauge. Current research may redeem the Arnoux system by replacing its mechanical steering linkages with modern electronic systems. The most promising approach places independent traction motors in each wheel which not only propel the vehicle but also steer the individual wheelset by means of torque vectoring which promises reduced weight and complexity over current bogies whilst also reducing wear on both train and track.Actiwheel: A revolutionary traction technology
SET Limited
German Aerospace Centre Examples include Actiwheel and their proposed running gear for the Next Generation Train.

Abandonment

Use of the Arnoux System from Paris to Limours was abandoned in 1883 during negotiations with the government and the Compagnie du Chemin de Fer d'Orléans à Rouen for construction of new lines. and the

was the only one built to its design, with its unusual track gauge and specific construction of carriages and locomotives. The track was replaced overnight with standard gauge in May 1891.

Sources

* * * * Revue Générale des Chemins de Fer, 1895

References

{{Locomotive running gear Arnoux History of rail transport in France