Rail braking systems - Effort and energy dissipation

Ever since the prehistory of railroads, the problem of slowing down and then stopping vehicles, whatever their mode of propulsion, has existed. Friction brakes, which use the friction of one material against another to produce force and dissipate kinetic energy in the form of heat, soon became the preferred method, thanks to their ease of use.

A historian who visited the Leberthal mines in Alsace (France) around 1550 tells us that "a piece of wood, placed horizontally above a wheel, was hinged to the side of the wagon. The driver, who was a child, could thus press his hand or foot against the periphery of the wheel and moderate the speed of these mining carts launched in slight declinations". This is the ancestor of the shoe brake.

During the railway boom of the early 19th century, braking was still based on the friction brake, again in the form of a "shoe brake" that rubbed against the vehicle wheels, inspired directly by the braking system used on stagecoaches of the time.

Such was the case with the railroad between Saint-Étienne and Andrézieux, commissioned in 1827. In the downhill direction, convoys of up to 14 vehicles, each weighing 5 tons, moved forward simply under the influence of gravity. They were therefore equipped with a braking system in the form of two shoes on each wagon, mounted head-to-tail on a lever pivoting around an axis linked to the chassis.

The arrival of the first steam locomotives also saw the introduction of the first dynamic brakes: the distribution of steam to the cylinders was designed in such a way that it was possible to operate in reverse (known as "beating against steam") to slow down the train in the event of an unexpected obstacle on the track.

From then on, and for almost 150 years, braking technology remained virtually unchanged. In the 19th century, however, the first material used to make brake blocks - wood - was replaced by cast iron, due to its greater efficiency (particularly with regard to the risk of fire caused by overheating during braking) and the lower cost made possible by the development of the iron and steel industry at the time.

So it was not until the 1960s, when rail operators in Japan and Europe raced for speed to counter the rise of the automobile and air transport, that new types of brakes were developed. The advent of high-speed trains (200 to 210 km/h) soon revealed the inadequacy and unsuitability of soleplate braking for these applications, firstly because of its low braking capacity (due to the very low friction coefficient of cast iron), and secondly because of the unacceptable thermal stress it generates on the wheel treads. Increased speed led to the introduction of disc brakes and electromagnetic...