Keywords: equivalent conicity, vehicle dynamics, stability, hunting, track forces, radial steering index.

The stability of a railway vehicle is influenced by the vehicle suspension characteristics but is also greatly dependant on the geometry of the wheel and rail profiles. It is common practice for railway engineers to design a train considering a wide range of operating conicity between the wheel and the rails. The European standard EN15302 [1] specifies how the equivalent conicity should be calculated and EN14363 [2] shows how it should be considered when testing a new or modified vehicle for homologation. It is stated that the equivalent conicity should be calculated assuming the tangent track condition, i.e. no curve radius. The authors have investigated the limit of application of this assumption by modelling the behaviour of a single axle to work out an equivalent conicity, comparing the results obtained with and without considering the radius term on the kinematic equation of motion of the axle. The results showed that greater than 2500m, the conicity function was mostly unchanged for the reference profiles S1002 and EPS for the wheel on 60E1 (1:40) and 60E2 (1:40) for the rails, while below such a radius the conicity function could be highly affected.

The study then focused on the investigation of the behaviour of full vehicles, i.e. high speed passenger as well as lower running speed freight wagons, using vehicle dynamics simulation software. The trade-off between running instability and associated dynamic lateral track forces; and the quasi-static lateral forces associated with curves and high cant deficiencies was investigated using colour coded maps of speed against curve radius.

Based on the passenger vehicle simulation, the main finding of this work tends to support the current industry practice that considers equivalent conicity only for curves with a radius higher than 2500m. For the simulated cases the instabilities observed tend to disappear as the radius tightens and are replaced by high quasi-static lateral forces at high cant deficiency. On the other hand the results obtained from the freight vehicles showed that there is a certain range of conditions where both dynamics and quasi-static forces are coexistent. Depending on the profiles considered, unstable motion can even sustain itself at lower than critical speed for a specific curve radius below 2500m.

1

EN 15302:2008+A1:2010 E, "Railway applications - method for determining the equivalent conicity", European Committee of Standardization, 2010.

2

EN 14363:2005 E, "Railway applications - testing for the acceptance of running characteristics of railway vehicles - testing of running behaviour and stationary tests", European Committee of Standardization, 2005.

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