Authors: Saeed Mohammadi, Asghar Nasr
Addresses: Mechanical Engineering Department, Iran University of Science and Technology, Narmak, Tehran 16884, Iran. ' School of Railway Engineering, Iran University of Science and Technology, Narmak, Tehran 16884, Iran
Abstract: For heavy haul trains, which must be coupled often, there is no alternative to the air brake system. In these trains, the cars at the end of the train brake a few seconds later than those at the front. The time delay between the braking of the adjacent cars depends very much on the transmission speed of the pressure wave (brake signal) in the main brake pipe, which is about 10-25% less than the speed of sound in free air. The later braking of the cars at the rear of the trains means that the rear cars run into the front cars, producing large compression forces on the buffers and couplings. These compression forces are mainly of longitudinal nature and are considered to be responsible for large amount of expenses regarding rolling stock and track sub- and super-structures repairs, as well as deterioration of safety operation of the trains. The braking time delay of the adjacent cars, and hence the in-train dynamic interaction of the trains, differs very much by changing the location of the power units (locomotives) along the trains. In the present paper, using a simulation technique, an attempt is made to study the effect of power unit location along the train length on in-train longitudinal forces during emergency brake application. The results indicate dramatic changes in the way that cars interact dynamically with each other and in the magnitudes of the in-train longitudinal compression and tension forces along the train. The freight trains considered are those currently used by Iranian railways.
Keywords: train dynamics; in-train longitudinal forces; locomotive brake handling; brake delay time; locomotive dynamics; compression forces; rolling stock; track repair; railways; safety; power units; power unit location; simulation; emergency braking; Iran.
International Journal of Vehicle Systems Modelling and Testing, 2010 Vol.5 No.2/3, pp.176 - 196
Received: 14 Sep 2009
Accepted: 31 Jan 2010
Published online: 25 Nov 2010 *