Rail vehicles have a great advantage over vehicles with rubber tyres: Rolling resistance is low, you hardly lose any energy through friction, which is what makes rail transport so efficient and environmentally friendly. But if you want to brake quickly, then precisely this advantage becomes a disadvantage, because then the highest possible friction is required.
At TU Wien, the braking technology of rail vehicles is now to be studied in more detail and improved - in a new Christian Doppler Laboratory, which was opened on 5th June 2023. This was made possible by the Federal Ministry of Labour and Economic Affairs and the industrial partner Knorr-Bremse.
Minister of Labour and Economic Affairs Martin Kocher emphasises the relevance of the research area: "Shorter braking distances with less material wear increase punctuality and safety of all rail-bound vehicles, i.e. of railways, trams or underground. At the same time, this reduces maintenance costs as well as resource and energy consumption. Excellent basic research, as in this CD laboratory, is the foundation for future innovations in rail transport. This benefits not only passengers and commuters, but also Austria as a business location and the environment."
Sand and Magnets
"The braking distance of rail vehicles is usually much longer than that of cars," says Prof. Johannes Edelmann, who heads the new laboratory. "Particularly in wet conditions or due to contamination such as wet leaves in autumn, problems can often occur." There are different techniques to increase the braking effect on trams or mainline trains. One possibility is sand systems: Sand is transported in the train, which can then be scattered on the rails directly in front of the wheels during braking. This creates more friction.
In addition, magnetic rail brakes are often installed in rail vehicles. "These are a metal frame with electromagnets mounted in the chassis of the rail vehicle," explains Johannes Edelmann. "When braking, the electromagnets are drawn to the rail and drag on the rail."
The contact between the rail and the wheels does not matter at all in this case - even if the wheels slip due to bad conditions, you can still stop with magnetic rail brakes.
Better Braking Performance, less Wear, less Energy Expenditure
Even though the basic principle is quite simple - figuring out exactly how to optimise such braking systems is a highly complicated scientific matter. "For example, you have to understand the dynamic behaviour during the braking process in detail," says Johannes Edelmann. "The individual components can vibrate, which can affect the braking effect." Especially when driving over rail crossings and switches or over dirty rails, the interaction between the braking system and the rail is very complex.
Several research disciplines intertwine here: mechanics, which can be used to describe the movement and calculate friction forces, electrodynamics, which is used to analyse the electromagnetic behaviour of the magnetic rail brake, and tribology, which deals with the wear and tear of materials that rub against each other. Within the framework of the Christian Doppler Laboratory, mathematical models and complex computer simulations will be developed. In addition, measurements will be carried out and a new test stand will be built for this purpose at the TU Wien.
"It's about achieving several goals at once," says Johannes Edelmann. "We want good braking performance, especially in difficult conditions. In addition, better braking systems should minimise wear and protect the infrastructure. And in addition, we also want to minimise the weight of the braking systems to save energy."
About Christian Doppler Laboratories
In Christian Doppler Laboratories, application-oriented basic research is carried out at a high level, with outstanding scientists cooperating with innovative companies. The Christian Doppler Research Association is internationally regarded as a best-practice example for the promotion of this cooperation.
Christian Doppler Laboratories are jointly financed by the public sector and the participating companies. The most important public funding body is the Federal Ministry of Labour and Economic Affairs (BMAW).
Prof. Johannes Edelmann
Institute ofr Mechanics and Mechatronics
Dr. Florian Aigner
PR and Marketing
Resselgasse 3, 1040 Wien
+43 1 58801 41027