Effect of superposed horizontal and vertical curves on curve performance of single-axle forced-steering bogies

Trains running on sections with overlapped vertical and horizontal curves are affected by both vertical and horizontal centrifugal forces, resulting in more complicated wheel-rail interactions compared to operation on horizontal curves alone. This complication undermines the effectiveness of single-axle forced-steering bogies in enhancing the curve passing performance of service trains. To solve this issue, dynamic models were established for service trains respectively with traditional bogies and single-axle forced-steering bogies to facilitate a detailed study. A comparison was conducted to examine the effects of convex and concave vertical curves superimposed with horizontal small-radius curves on curve passing performance and carbody vibration acceleration. Subsequent analysis investigated the influence of track parameters associated with different cross and vertical section on these two aspects for service trains equipped with single-axle forced-steering bogies. Additionally, these indexes were analyzed under different conditions for these trains. The results show that the overlap of convex vertical curves and horizontal small-radius curves further increase the angle of attack on wheelsets, whereas the angle of attack decreases on concave vertical curves. Among various cross and vertical section parameters, the horizontal curve radius has the greatest influence on the performance of service trains, followed by the effect of superelevation. In contrast the influences from both vertical curve radii and gradient differences are limited. Furthermore, both tractive efforts and braking forces contribute to increased lateral forces on wheelsets and lateral vibration accelerations of carbodies. To summarize, service trains with single-axle forced-steering bogies adapt well to track sections with overlapped horizontal and vertical curves, and braking forces significantly influence the curve passing performance of service trains on these sections.