Deterministic and stochastic braking distance prediction of disc-braked rail vehicles

A rapid modal shift to rail is inevitable to reduce transportation-related greenhouse gas emissions while meeting the ever-increasing demand for mobility. Due to the nature of rail-bound traffic, the prediction of the braking performance plays a key role in improving the infrastructure capacity without compromising safety. Against this background, this works addresses the complexity of frictional brake forces and contributes to an improved brake performance prediction of disc-braked rail vehicles. By analyzing almost 2000 experimental brake applications conducted on a test rig, this work provides fundamental insights into the deterministic and stochastic behavior of a typical brake pad material applied in rail vehicles. Based on the available data and a thorough literature review, a new friction model is developed and identified for the investigated material. The model is capable of predicting the time-variant and non-linear behavior of the friction forces prevailing during the braking process and outperforms state-of-the-art friction models. In combination with a temperature model, additionally developed and identified in this work, the braking distance resulting from a single brake unit is predicted with an accuracy of 2%. The models are validated using data from more than 80 vehicle brake applications conducted with a multiple unit. Moreover, this work presents a novel probabilistic approach that allows to consider the stochastic nature of frictional brake forces when predicting the brake performance. Based on this approach, it is found that the friction-related scatter prevailing in the brake units of rail vehicles depends on the initial velocity and is a superposition of global and individual phenomena. An exemplary probabilistic analysis conducted in this work reveals that this improved consideration of the friction characteristics offers the potential to reduce the safety margins for ETCS braking curves by up to 14% without compromising safety.