Keywords: non-linear stability, railway vehicle lateral stability, stability in curved track, track gauge, railway vehicle dynamical model, computer simulation.

This paper represents new results obtained while looking for information on the influence of the track gauge on railway vehicle stability on a curved track. Such information will be helpful in looking for the solution to prevent hunting motion on a curved track, as the supposition exists that smaller gauges reduce the risk of hunting. It could also influence vehicle approval procedures that refer to stability on a curved track. The authors used their method to study non-linear lateral stability of railway vehicles on circular track curves (CC). The method is based on a bifurcation approach to stability, used for straight track (ST) analysis. In this approach bifurcation plots are drawn first, basing on simulations, and then analysed. New in the method is the use of the stability maps that represent two kinds of the complex bifurcation plots. Here the results for the entire range of curve radii, and a ST, are represented together. The use of this method was focused on studying the influence of different factors on the stability. One of such factors, studied in this paper, is the track gauge.

The object in this study is two-axle freight car. Two pairs of nominal wheel-rail profiles were tested. These are S1002/UIC60 and SZDwheel/R65 pairs. Their choice is not incidental. Their properties for a nominal gauge of 2b=1435mm are different. In the case of the first pair periodic solutions above the critical velocity appear for all curve radii. For the second pair they appear when the radius is greater than 2150m, while for smaller radii just quasi-static behaviour exists. For the needs of this study four additional gauges were adopted for each pair, three smaller and one greater than the nominal one.

In the main, it was shown in the present study that a decrease in the track gauge reduces the appearance of hunting motion in a curved track. On the other hand, the effect is very much limited for the first pair of the profiles and significant for the second one. Moderate decreases in the gauge, in case of the first pair, removed the periodic solutions for a radius of 600m only, completely for 2b=1429mm and partly for 2b=1432mm. In the case of the second pair it moved the boundary value of R, below which no periodic solutions exist, up to radius of 2900m for 2b=1433mm and R less than 4390m for 2b=1431mm. For these gauges periodic solutions were also removed partly when the radius was 3000m and 6000m, respectively. In the case of the smallest gauges considered the periodic motion was completely removed for both pairs of the profiles and all radii, including a straight track. These gauges reduced the wheel-rail clearance almost completely, so the question concerning the safety of the vehicle motion when applying them in a real track.

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