10450: As an alternative to the braking percentage, a mean brake deceleration can also be provided. Where is the difference and what is better?

When the braking percentage is set, the effective braking deceleration depends on the initial speed before braking and the gradient of the line. If, on the other hand, the mean braking deceleration is specified concretely, there is no dependence on speed and gradient. Hence it is important to consider what this means in practice and whether it is realistic.

Due to the dependency of the friction values on speed of the wheels and driving speed, unregulated friction brakes (that means classic rail brakes) are always speed-dependent. A non-speed-dependent brake would have to be regulated (and / or essentially not use friction to work). This may well be the case for modern engines and multiple units. Specifically, it would mean that a control circuit (e.g. on-board computer) permanently controls the intensity and ratio of the different brakes so as to give an approximately constant braking acceleration.

The operational brake deceleration is not dependent on the gradient of the line, assuming that the vehicle applies the given brake deceleration even in the strongest slope, and uses a correspondingly lower brake force for less inclined slopes or gradients, in order to provide the given brake deceleration. This would mean that the vehicle will only use its full braking capacity at the strongest slope.

It would also be conceivable that a mixture of both is present: the vehicle always tries to set the same brake deceleration regardless of the inclination; however, the vehicle will not be able to do so in steeper slopes, resulting in a lower brake deceleration. Such a brake would only be independent of inclination to a certain extent.

Finally, it must also be noted that the braking deceleration is also dictated by the driver at the braking pitch or the driving- and brake-lever. Strictly speaking, the control circuit could also close via the driver, if he varies the braking effect sufficiently quickly and sensitively so that an approximately constant deceleration of the braking deceleration occurs. However, this is unrealistic, at least for long trains, solely because of the inertia of the pneumatic brake.

Conclusion: The specification of the mean braking deceleration is realistic for modern, controlled multiple units and multiple unit train-sets, especially if they only use friction brakes to a small extend. It is not realistic for classic trains and also not for modern locomotives when they pull long and / or heavy trains with friction brakes.

Note: Further information on brake settings in FBS can be found under FBS documentation / brakes as well as here (German PDF, 181kB).

Last update on 19.03.2020 by iRFP Support.

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