Self-excited Vibrations of Magnetic Track Brakes (MTB)
Railway mobility is a very energy-efficient way of transport. Above all, this is a matter of the steel-steel contact between the railway wheel and the rail. The rolling resistance is only about a tenth of tyre-road contact. In combination with trends to higher vehicle velocities and travelling mass, demands on the braking systems increases. However, brakes which act on the wheel respectively on the wheelset (e.g. disc brakes, electrodynamic brakes), have limitations due to the small friction coefficient in the wheel-rail contact. To guarantee safe operations in particular in emergency situations or when the rails are contaminated, wet, or covered with leaves or snow, additional braking systems are deployed to develop additional braking forces.
Magnetic track brakes (mtb), depicted in Figure 1, which are independent from the wheel-rail contact, are a common braking system to generate additional braking forces. Electromagnets installed in the bogie are lowered onto the rail and generate a magnetic attraction force between the brake and the rail. This creates a frictional force in the magnet-rail contact, which is transmitted to the bogie by the structure of the brake.
In the past, track brakes in main-line vehicles were deactivated at about 25 km/h, because of occurring deceleration jerks. Due to higher demands on brake performance, operators nowadays choose to use the track brake until (nearly) full stop, to add additional safety margins in stopping distances.
During field tests, severe vibrations of the magnetic track brake were measured at velocities below 25 km/h, causing discomfort, noise and also high loads on mechanical components.
The aim of this project was to analyse the self-excited vibrations at the track brake in detail, to explore the mechanisms causing them, and finding possible remedies for mitigation.
By developing mathematical models of the complex electromagnetic-mechanical coupled problem, and applying analytical and numerical methods of stability theory, two mechanisms that may cause the measured self-excited vibrations were identified. Based on these findings, new designs of the mtb to mitigate self-excited vibrations have been derived.
Figure 2 shows the consequence of self-excited vibrations in the braking force for the original (first picture) and for three new designs developed. It is obvious that the new designs are able to mitigate or even diminish occurring vibrations while the effective brake force was increased.
Figure 2: Longitudinal brake forces in relation to the equivalent brake force, for the original (left plot) and three new designs
Interested in impressions of field tests?
Watch our video on a braking manoeuvre of an mtb!
Tippelt, Daniel, Johannes Edelmann, Manfred Plöchl, and Michael Jirout. "Analysis of self-excited vibrations of an electromagnetic track brake, opens an external URL in a new window." In The IAVSD International Symposium on Dynamics of Vehicles on Roads and Tracks, pp. 442-451. Springer, Cham, 2019.
Tippelt, Daniel, Johannes Edelmann, Manfred Plöchl, and Michael Jirout. "Modelling, analysis and mitigation of self-excited vibrations of a magnetic track brake, opens an external URL in a new window." Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit 236, no. 6 (2022): 684-694.
Tippelt, D. "Self-excited vibrations of a magnetic track brake – modelling, analysis and mitigation". PhD Thesis. TU Wien, 2022
- 2015 - 2022