Wheel slide protection
The non-skid is a means to rail-bound vehicles. He was originally intended to prevent flat spots on wheels, now but also in general the (selective ) controlling the brake slip an axis, in order to reach an optimal utilization of the PSA value between wheel and rail. The railwaymen speaks from slipping when an axis is blocked, but the vehicle continues to move along the rail, the locked wheel at the contact point so slides on her; hence the name. The system works in a similar way as the ABS in a car, but which also serves the preservation of controllability during hard braking above all.
Operation
The braking force exceeds the friction between wheel and rail, the respective axis rotates at a reduced speed (slip) or blocked completely. The antiskid recognizes this and intervenes by braking pressure is reduced in the brake cylinder by venting pulses or limited by blocking the air intake. For dynamic braking is engaged in accordance with the regulation of the brake or the brake may shut down completely.
To detect slippage or sliding of an axis, it is necessary to speed detection of the wheelset. In mechanical antiskid located on each axle in Gleitschutzgehäuse a flywheel mass, the mass forces in the event of sudden decrease in the Radsatzdrehzahl on a vent valve, the brake pressure is reduced either directly or indirectly. The recorded electronic antiskid and compares the speeds via electronic timer of all axles of a vehicle. On the basis of predetermined characteristics of sudden speed reductions are identified, as is the electronic antiskid reacts depending on the technical level on speed differences. Some systems use external sources, such as radar for detecting the actual speed. Depending on how big the slippage is how long it lasts and how suddenly it occurs, is kept constant via solenoid valves, the pressure in the brake cylinder, lowered or increased again.
The probability of experiencing a slip condition on the axles of a vehicle depends largely on the currently prevailing coefficients of friction between wheel and rail. Depending on whether the track is dry, wet or even dirty (ex. foliage ), occur on different coefficients of friction. Tests for Gleitschutzgeräte be performed, inter alia, with soap, in order to test the response of the device in the worst case. However, such trials may not adequately simulate the real situation, especially since there is no universal Reibwertkennlinie, rather the characteristic curve varies depending on many influencing factors. The maximum adhesion, depending on the situation and rail condition at very different (relative) values are slip, so that must be an optimal acting anti-skid device capable of automatically identify the individual characteristic curve and by which to control the brake.
By applying braking sand by the leading vehicle of the coefficient of friction in case of need can be selectively enhanced.
In Germany, the UIC leaflet 541-05 is adopted as the requirement for the function and safety for Gleitschutzgeräte in general.