Lateral Stability Performance in Uni-Directional Rollingstock

Abstract

The worn wheel profiles generated by uni-directional wagon travel produce different profile shapes on the leading and trailing wheelsets of each bogie. In the case examined both leading and trailing wheels wear to profiles having greater effective wheel conicity. The leading worn wheels exhibit flange and tread wear and the worn profile has highly nonlinear conicity having little vertical displacement over the middle range of lateral displacement. A large vertical displacement is still achieved by the worn leading wheel profile in the last section of the flangeway clearance. The worn trailing wheels have only tread wear with near linear effective conicity across the flangeway. The hunting instability performances of the vehicle with the uni-directional wheel wear profiles is shown to have a higher critical speed than new wheel profiles due to the mismatch of the leading and trailing wheel profiles. The leading wheels of the bogie hunt with a wavelength of 26-30 m whilst the trailing wheels hunt at a wavelength of 12-16 m. Because of the differing frequency responses in the front and rear wheelsets of each bogie, lateral instability is damped for the worn wheel profiles. The worn profiles' curving performance is also improved due to increases in the total profile conicity. Individually the leading wheel worn profile with its nonlinear conicity across the flangeway has lower critical speed than a new wheel profile, the non-linear shape leading to chaotic lateral instability. The trailing wheel profile with its highly linear conicity across the middle of the flangeway has classic sinusoidal hunting at a much reduced critical speed and much reduced wavelength. The worn wheel profiles by themselves for both leading wheel and trailing wheel are found to have critical speeds 80% of the new wheel profile critical speed. In combination as found in a wagon operating in one direction, the leading and trailing wheel profiles produce a critical hunting speed 125% of the new wheel profiles' critical hunting speed.