Technology: Better brakes for faster trains

 作者:燕秭钇     |      日期:2019-02-28 06:06:02
By VINCENT KIERNAN in WASHINGTON DC To stop a typical American freight train can require a braking distance of thousands of metres, mainly because of the archaic system that controls the brakes. So railway companies are looking at modern electronic alternatives that will stop their trains more quickly, and allow them to travel faster without compromising safety. The brakes on freight trains are controlled by compressed air in a pipe running from the locomotive. To stop the train, the driver allows some of the compressed air in the pipe to bleed off. As the pressure drop moves down the train, it triggers the brakes on each wagon in turn. But because freight trains are often two or three kilometres long, and the pressure drop cannot travel faster than the speed of sound, it can take 10 seconds or more for the signal to reach the back of the train, says Al Reinschmidt, assistant vice-president for research and engineering at the Association of American Railroads. The association is developing an electronic control system to replace the pneumatic one, which is about a century old. Its electrical signal would reach the back of a long train virtually instantaneously, and so apply the brakes on all the wagons at the same time. That would cut the distance required to stop a train by 40 per cent, Reinschmidt says, meaning trains could travel faster without being any less safe. Some trains – especially coal trains – could travel up to 30 kilometres per hour faster, allowing congested sections of track to carry more traffic. The electronic system also would provide more flexible control over the train’s speed. Under the pneumatic system, the brakes must be released all at once, but the electronic control system would allow the driver to release them by degrees. Reinschmidt says the new system would cost $3000 or less per wagon for the 100 000 freight wagons in the US. ‘We’re hoping to get some equipped with the first generation systems next year,’ he says. Further in the future, a more advanced version of the system would provide what would amount to a computer network through which the wagons would pass information such as whether their bearings are getting dangerously hot. American railway tracks are lined with instruments that monitor the temperature of the wheel bearings on trains as they pass, but the new system would provide quicker,