Application of Hydraulic Arm Bushings with Frequency-Dependent Stiffness to Compromise Hunting Stability and Curve Negotiation Performance for a Passenger Coach

The inherent conflict between hunting stability and curve negotiation performance is a well-known challenge in railway vehicle dynamics. Stiff axle guidance of bogies can achieve high stability while good curving performance requires longitudinally soft guidance. To overcome the conflict, the application of hydraulic arm bushings with frequency-dependent stiffness to a passenger coach with small-radius wheels is discussed as a case study in this work.

This type of bushing could provide low longitudinal stiffness when the wheelset yaw frequency is below 1 Hz, and the bushing stiffness becomes much larger when the wheelset yaw frequency exceeds 2 Hz. This frequency-dependent stiffness characteristic enables to achieve high stability on straight tracks and good curving performance in curves, and it can be represented by the Zener model. Four schemes including the nominal guiding design and three hydraulic arm-bushing designs are introduced, and the corresponding performances in various simulation scenarios, such as hunting stability, curving negotiation and long-term wheel wear behaviours, are compared by using the multibody simulations.

The critical hunting speeds for the four schemes SX31, SX3.9, SX1.6 and SX2.0 are 211, 209, 198 and 207 km/h respectively, and they are affected by the largest stiffness in the Zener model. Since the scheme SX1.6 has the smallest static stiffness in the Zener model, it generally has the best curve negotiation performance such as the lowest wheel-rail lateral force and the minimum wear number, and its long-term wheel wear volume is also the lowest among all schemes.

Applying hydraulic arm bushings could significantly reduce the wheelset attack angle and the wear number in curves, especially in tight curves, which can be one of the countermeasures to reduce wear for small-radius wheels. Besides, low static stiffness and high dynamic stiffness are necessary for the arm bushing design to balance stability and curving performance.