Stability and Curving Mechanics of Rail Vehicles

This paper presents a unified treatment of stability and curving mechanics of steel wheel/steel rail vehicles utilizing low order, predominantly linear models. The analysis is applicable to both conventional and self-steering radial passenger trucks. A six degree of freedom truck model is utilized to illustrate the various instability modes that can occur due to the destabilizing influence of a wheelset. It is shown that the individual wheelset mode, the rigid truck mode and the carbody mode are of academic interest only, while the elastically coupled wheelset mode is the one which limits the performance of intercity trucks. Carbody resonance can occur but is controlled by relatively small amounts of damping in the secondary lateral suspension. A four degree of freedom steady-state curving model is used to investigate the influence of shear and bending stiffness on both off and on-flange curving performance. It is shown that a low bending stiffness provides superior on and off-flange curving and that the selection of the shear stiffness depends upon the severity of the curves to be negotiated. A low shear stiffness improves the ability of the truck to stay off the flange while a high shear stiffness results in a “floating” truck which flanges earlier but results in the lowest flange forces and angle of attack once flange contact occurs.