Keywords: high speed railway, high-speed bogie, safety stability margin, anti-hunting absorption-band mode, over-damped anti-hunting mode, lateral track-shift force.

For high-speed railway (HSR) practice, the lateral track-shift force must be under control. Since the lateral track-shift force is very important for high-speed running, i.e. the higher the traction coefficient, the higher possibility that surface damage will occur on wheel-rail contact, the yaw lag must therefore be depressed by the anti-hunting absorption-band mode, instead of an over-damped anti-hunting mode.

This paper shows how to improve the safety stability margin by the novel theory of an anti-hunting absorption-band. Under the small displacement disturbance hypothesis, the anti-hunting dynamical stiffness is shown in the frequecy response of the dashpot and spring in-series unit, which is the first non-linearity of a high-speed bogie. Through the comparative calculation of bogies with traction motors laterally-elastic-suspended on bogie frames, it can be seen that the lateral track-shift force of a rear wheelset is sensitive to the anti-hunting in-series stiffness rather than the anti-hunting damping rate.

With the measuring data of an anti-hunting damper testrig from the German company ZF Sachs AG, the novel theory of an anti-hunting absorption-band is established with the Piao-Liang determining criterion for anti-hunting in-series stiffness. The following HSR experience indicates that the 300km/h HSR practices must be advanced robustly using the above novel theory:

1. The vibration alarm is a special failure trouble in the particular HSR line. By using the above novel theory, the simulation analyses show that there are two reasons that concern the vibration alarm: firstly, the safety stability margin is not sufficient, that is, the commercial velocity is approximately 280-300km/h according to the original design; secondly, if the local conformal contact is formed arising from the uncertainty of the wheel-rail contact, the blowing-off of anti-hunting dampers will take place, for whch lateral flutter of the trailer bogie frame will appear. A small hunting oscillation is therefore not safe for the HSR running because of the pitching lag of the non-linearity of the trailer bogie frame, which is the second non-linearity of the high-speed bogie.
2. The coach shaking phenomenon arises from the stability non-linearity, which is the third non-linearity of the high-speed bogie. Through a comparative study of root-locus diagrams, the rule can be formulated such that the stability margin of the rear bogie is made smaller and smaller with the anti-hunting in-series stiffness increasing, and some coach shaking problems become apparent i.e. the tail coach with the relative larger coefficient of longitudinal eccentric loading.
3. As a result of the above two HSR experiences, it is demonstrated that there is an optimal value of the anti-hunting in-series stiffness, by which the best feature of anti-hunting absorption-band is achieved. The velocity space of commercial HSR practice is therefore broadened by the above novel theory, for example, the best economic velocity can be increased from 300km/h to 350km/h.

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