Effects of Braking Characteristics on the Longitudinal Dynamics of Short Passenger Trains

This original study investigates comprehensively the effects on longitudinal dynamics of short trains determined by usual combinations of different brake types that currently equip passenger railcars in operation: disc brake in fast-action and cast iron brake block system in fast high power action mode. The interest on such research is determined by the differences between the braking characteristics determined by two major aspects: the specific dependency of friction coefficient between wheel and cast iron blocks, respectively, brake discs and pads on velocity and normal forces applied on frictional couples, as well as by the brake cylinders air pressure evolution during the process. Preliminary studies and results of numerical simulations performed on single railcars submitted to braking constitute reasonable qualitative argumentation of the present research. Taking into account certain assumptions in order to eliminate, as much as possible, any aspect potentially disturbing the direct influence of braking characteristics, an original longitudinal dynamics simulation program was developed. The filling characteristics of air brake distributors were experimentally determined on static computerized testing system in the Braking Laboratory of the Faculty of Transports in University POLITEHNICA of Bucharest. The data files were adequately implemented into the simulation program. The results of numerical simulations indicate that braking characteristics have major influence on longitudinal dynamics of the train. We identified three patterns of in-train force evolutions, depending on the configuration of the braking systems featuring each vehicle of the train. Regarding operational aspects, the arrangement of railcars with different brake systems in the train composition affects the longitudinal dynamic reactions. We recommend measures to increase traffic safety and passengers comfort.