A magnetorheological damper developed by Strojírna Oslavany with the researchers from the Faculty of Mechanical Engineering, the Brno University of Technology, is ten times faster than other dampers. In cooperation with Škoda Transportation from the PPF Group, they have also been tested. The damper makes it possible to increase the maximum permitted speed of trains and is also more gentle on tracks and switches. Thanks to the rapid onset of the damping force, scientists are thinking that the so-called semi-active damper could react immediately to changes on the track or on the road based on signals from various sensors.
The principle of a magnetorheological damper has been known for a long time: it uses a special liquid in which small iron particles about the size of a few micrometres are dispersed. When a magnetic field is created in the damper by an electric current, the iron particles are chained in such a way that they put up more resistance when the liquid flows through the piston, thus increasing the damping force. The result is a damper whose force can be easily regulated.
The researchers from the Brno Faculty of Mechanical Engineering have figured out how to significantly speed up these dampers. "When we apply an electric current to an electromagnetic coil, it takes a while for the required magnitude of the magnetic field to form and the iron particles to condense in the liquid. This time response is usually from 20 to 300 milliseconds, depending on the size of the damper. If we want the damper to react immediately to, for example, uneven road surfaces, such a response is relatively slow. We managed to reduce the time response of the damper to 1.2 to 1.5 milliseconds, so we are more than ten times faster," the researcher Michal Kubík from the Institute of Machine and Industrial Design, FME BUT, explains. Just for comparison: one blink of the human eye takes about 100 to 150 milliseconds, a hundred times longer than the new damper can respond.
Thanks to the rapid response, scientists are thinking about so-called semi-active regulation. The damper would be connected to sensors and a control unit that would regulate the damping force in real time. The researchers from Strojírna Oslavany and BUT see great potential in the application of a fast damper on the rail vehicle chassis. "Specifically, we are working on a vibration damper that dampens unwanted chassis vibrations when a certain speed is exceeded. Under certain conditions, this unwanted movement can cause the train to derail, and in order not to do so, the locomotives have a given maximum permitted speed. Our goal is to increase the speed of the locomotive with the help of new dampers. In addition, these dampers are more gentle on the rails. When passing through switches or curves at low speed, the dampers will not exert an unnecessarily large force, which will reduce the wear on the vehicle and infrastructure and thus the subsequent maintenance costs,” Kubík explains.
The researchers have developed two dampers: slower, called adaptive, and the mentioned above fast, or semi-active. At first glance, the difference between them is one: semi-active has grooves in the piston, which eliminate the formation of electric eddy currents and thus reduce the time response. "It looks simple, but it took us several years of development. The width, depth, number and location of the grooves have a great influence on the function, it was not easy to develop an ideal variant," Kubík says. While the semi-active damper has so far only been tested in the laboratory, its "generation older" version, the so-called adaptive damper, has already been tested on the rails. "We tested the dampers on a test rail in Minden, Germany, on our products. I have to praise the cooperation with experts from BUT and I firmly believe that their innovations will prevail on the market," Petr Špalek, the chief engineer from Škoda Transportation added.
BUT even has a patented technical solution. The development took place within the title of grants of the Ministry of Industry and Trade of the Czech Republic.