Freight wagons are usually equipped with the standard Union Internationale des Chemins de Fer pneumatic brake. On long trains, the propagation of the pneumatic signals along the pipe and different braking/loading conditions may produce delays and/or differences in the application of the braking effort along the train. This phenomenon may cause heavy longitudinal forces exchanged between wagons through buffers and draw gear. In particular, the workgroup n.6 (freight trains composition) of the Italcertifer committee has performed some preliminary studies concerning the application of LL braking operative conditions on freight wagons trains travelling on Italian lines. Partners have cooperated in this workgroup; however, in this paper, the attention is focused on methodologies and results concerning the contribution of University of Florence. The results of this activity, coordinated by RFI-CESIFER have been used to emanate the 20/07 rule of the RFI ('Modifiche alia Prefazione Generale all'Orario di Servizio') which modify the composition criterion rules of freight trains on the Italian Railways in order to introduce and discipline the application of the LL braking operative condition. In order to optimise time issue, resources and accuracy of obtained results, the RFI and the other partners chose a limited number of vehicles and compositions that satisfy the following issues: (1) wide diffused vehicles, whose technical data and behaviour are well known; (2) selected vehicles have to be chosen with features that are quite meaningful considering the statistical composition of trains on the railway line; (3) wagons with a wide variability range of loading and braking percentage conditions in order to exploit with a single vehicle model a wide range of possible service conditions; (4) homogeneous train compositions where the sensitivity to single parameters can be easily analysed. The procedure involves the development of a full model of the pneumatic plant and a mechanical model that, according to specifications of the requested activity, may be mono-dimensional or tri-dimensional. The models have been deliberately developed using commercial software (Amesim, Matlab-Simulink, Adams Rail), in order to make easier data and knowledge sharing. The model of the braking plant was finely calibrated and validated using experimental measurements on the pneumatic plant of a freight train; the model of brake pads friction factor was adjusted on experimental data and technical documentation of the simulated vehicles in order to fit the dependence from speed and clamping force. Results of the model was compared with RFI statistical measurements showing an impressive correlation between simulations and the behaviour recorded on real working conditions, especially if it is considered that RFI statistical measurements were not known when the model was initially developed. The accordance between RFI statistical measurements and simulation results involves that the calculated longitudinal forces are quite realistic, and the model is able to fit the general physical behaviour of the system. The importance of this study has been recognised by C.I.F.I. (Collegio Ingegneri Ferroviari Italiani), which has awarded this study with the Mallegori award. As a short term development, a more sophisticated model of buffers and draw gear may be developed in order to better fit the nonlinear behaviour of damping elements. For a longer term development, numerical efficiency of tri-dimensional model has to be improved in order to make possible a wider application of this kind of more sophisticated analysis for parametric investigations of situations in which the interaction with lateral dynamics cannot be neglected. However, the aim of the paper was to present how a synergic use of mono-dimensional and tridimensional models can be used to study the longitudinal behaviour of a long freight train convoy with particular attention to the use of commercially available tools in order to facilitate knowledge sharing between research teams and the final industrial customer. In this sense, the simulation of the LL braking configuration for the Italian railway may be considered an interesting benchmark, thanks to the availability of data from Italian railway operators concerning derailments due to high compression efforts on buffers and ruptures due to traction forces applied to draw gears.


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    Title :

    Preliminary studies concerning the application of different braking arrangements on Italian freight trains


    Additional title:

    Vorbereitende Studien zur Anwendung verschiedener Bremseinrichtungen bei italienischen Güterzügen



    Published in:

    Vehicle System Dynamics ; 49 , 8-12 ; 1339-1365


    Publication date :

    2011


    Size :

    27 Seiten, 29 Bilder, 7 Tabellen, 21 Quellen




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English





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