The tram wheel roller rig in the Educational and Research Centre in Transport has been very busy recently. During the autumn, researchers made various modifications and improvements of the roller rig design to modify it for wet testing or renewal of the measuring chain, so at the beginning of December they were ready for the planned experiments.
The train approaches a stop signal, the driver applies the brake at danger, and it actually stops, but it is only the wheels that have stopped as the train goes on and the locked wheels slide over a layer of fallen leaves on the rails. Such may be an unfavourable scenario in the rail transport on a track at a beautifully coloured autumn forest. For such a case, every locomotive and railcar has a device to release sand under the wheels. But this method is not free of drawbacks, and modern rail transport of the future considers other options to deal with bad adhesion conditions; some even speak of "optimizing" or "management" of adhesion in the wheel–rail contact.
View of roller rig wheels – that is where experiments are conducted
Pardubice researchers collaborate with experts from Sheffield, England
Experiments aimed at transmission of braking forces between the wheels and the rails in low adhesion conditions took place at Jan Perner Transport Faculty last December. Researchers from Pardubice and from Sheffield, England, cooperated in the tests, which were also attended by doctoral students from Turkey. The University of Sheffield is the principal investigator of relevant research projects, the final part of which, however, requires measurements on a test bench at full scale. In the laboratories of the Educational and Research Centre in Transport, there are now two such devices, one of which has now been used for this research task in international cooperation.
The essence of the function of the tram wheel roller rig, as the device is called, is rolling of the tram wheel against a large roller, called a rotating rail, both of which are placed in a steel frame and equipped with their own engines. This simulates the ride of the vehicle on the track, including the possibility of developing traction or braking force in both directions. This roller rig, located in the basement laboratory for electric drives, underwent minor adjustments last year - most importantly, they were equipped with covers against splash and the measuring chain was improved. In December, colleagues from the UK arrived and brought a device to spray wheels with water, various brackets and tools and a hand blender to manufacture perfectly sliding slurry of dry leaves. The test bench was then used for braking without slip as well as with full slip in order to measure adhesion characteristics for different contaminated conditions - oil, water, slurry of leaves and the like. At the same time, the speed of rotation of the wheels (5 to 50 km / h) and the load of the wheel was altered. As a matter of course, they also tested the effectiveness of different methods for cleansing wheels while moving.
Testing a tram wheel sliding in the laboratory of the Educational and Research Centre in Transport
The tests resulted in amounts of data, which are now in the final stage of evaluation to obtain conclusions of completed research tasks, and experience for more experiments in the same cooperation planned for this year.
Ing. Petr Voltr, PhD.
Educational and Research Centre in Transport, DFJP