The preliminary analysis suggested that changing the sand output from a time-dependent 400g/30s to a distance-dependent 2g/m, 4g/m or 7.5g/m increased the wheel/rail adhesion available for braking by 150%, 210% and 310% respectively compared to time-dependent sand output.
However, due to the different numbers of tests from the different initial speeds, the statistical robustness of the results is variable. These preliminary estimates are now being refined, and the effect of different sand pipe positions and changes to other parameters is still being analyzed.
The adhesion-related data sets from the measurements (reference conditions and values after sanding) provide a body of data that can now be used in various ways by the participants in the test program.
At Knorr-Bremse, the test data are being used to inform the development of adhesion management concepts as part of the Reproducible Braking Distance (RBD) project. The data sets also provide information that can be used in the design of the sanding systems themselves, for instance with regard to the optimal sand output or different ways of installing the sanding units. The data can also be used to carry out a cost-benefit analysis with a view to optimizing the overall system in terms of operation (adhesion), infrastructure (wheel/rail wear, track superstructure contamination) and maintenance (sand consumption).
The measurement data also complete the picture for tests that have already been carried out on Knorr-Bremse’s ATLAS (Advanced Test Laboratory for Adhesion Based Systems) dynamometer. The values recorded during the in-vehicle testing can be used to validate previous test rig measurements (deceleration, braking distances, etc.). At the same time, the adhesion data from the in-vehicle tests can also be used to define the reference conditions when setting wheel/rail adhesion conditions on the test rig.
DB Systemtechnik is using the results of the data analysis to simulate extremely low wheel/rail adhesion conditions on its wheel slide protection test rig. They hope that by combining test rig and in-vehicle testing they will be able to test the control behavior of wheel slide protection systems over a wider adhesion range without the need for additional in-vehicle testing. It may even be possible to replace some operationally challenging wheel slide protection tests entirely with tests carried out on the test rig.
A knowledge of vehicle braking distance safety under low and extremely low wheel/rail adhesion conditions is particularly important in the context of ATO. It may be necessary to supplement the established UIC 541-05 and EN 15595 standards with additional criteria. To this end, the measurements recorded during the test program provide valuable input data for the wheel slide protection test rig.
The wheel slide protection test rig uses distance- and slippage-dependent adhesion windows as a data base for simulating the wheel/rail contact. These must first be generated from the recorded measurement data. Since wheel/rail adhesion was not measured directly, it is calculated on the basis of the recorded values, taking into account the vehicle parameters as a function of slip speed and the distance covered. Thanks to the high number of individual measurements carried out during the test runs, it is possible to generate a wide range of adhesion profiles for the wheel slide protection test rig (Figure 6).
By modeling variations in the natural conditions that occur during the fall, these profiles provide the basis for test rig testing with extremely low wheel/rail adhesion values.
The reference braking maneuvers when the sanding unit is not activated are of particular interest for this use case. The fact that all the wheelsets in these braking maneuvers were directly affected by the adhesion conditions generated by the track preparation makes it possible to quantify the conditioning effect (i.e. how wheel/rail adhesion is affected when several wheelsets cross the same section).