Study on engine mounting

Since close to 20 years dedicated to the dynamic calculations and the associated railway structures design, one of the recurrent questions is concerning the link between a dynamic load according to the time and its quasi-static equivalence. On that subject, the main hypothesis applied to the crashworthy devices located at the extremities of the train vehicles is the following: the dynamic resistance of the carbody structure is from 1,5 to 2,33 times the static design load at the corresponding level. With this crushing force level, the available crushing lengths and the energy absorption in the reference collision scenarios, the crashworthy pre-design of the train is achieved.

A recent example of problem linked to the static design of systems functioning under dynamic conditions corresponds to the engine mounts behaviour of the locomotives during a rough shunting. Indeed, the direct use of the formula F = m.g with a dynamic coefficient limited to +20%, considering the engine mass as rigid and the standardized deceleration limit, doesn't permit to obtain the real behaviour of the supports and can lead to the deformation of these elements.

A first study, based on the use of crash simulation tools, contributed to estimate the deceleration level during a rough shunting accident where the engine mounts were distorted. According to the estimated deceleration level lower than the one applied for the engine mounts design, these devices were reinforced by the supplier and were validated with a theoretical extrapolation of static design results. Considering the lack of calibration of the mounts distortions during the collision, we achieved simulations with the RADIOSS software to replicate distortions and to validate the components reinforcement.

Nevertheless, the necessary theoretical load to distort the engine mounts corresponds to an important deceleration level, higher than the one observed during the real accident. The first simulations, dedicated to the understanding of the difference between theoretical and real behaviours, didn't give a meaningful answer. Therefore, it would be necessary to continue the study on this problem in order to understand the behaviour of these devices in case of collision and to avoid the weak design of the future engine mounts.

The Author

Patrick Jumin
SNCF
4 allée des Gémeaux
721000 LE MANS / France

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