Conventional railway freight car systems, in general, exhibit hunting phenomenon due to self induced oscillations of the wheelsets. The hunting phenomenon increases component wear, and imposes limitation on the operating speeds. Alternatively, independently rotating wheels (IRW) within an axle eliminate hunting, however, the hunting performance of IRW is improved at the expense of wheelset guiding capabilities. In this study, an elasto-damper coupling is introduced between the IRW, and its potential to improve the critical speed of freight car system are investigated. The concept of Elasto-Damper Coupled Wheelset (EDCW) can offer a compromise between the excellent guiding capability of rigid wheelset and improved hunting performance of IRW.

This dissertation primarily investigates the influence of an elasto-damper coupling on the stability and steady-state curving behaviour of a freight car system. The evaluation of stability and curving performance of EDCW is carried out in three phases. In the initial phase of the investigation, an analytical model of a single EDCW is developed and analysis of its stability behaviour on tangent track is presented. A truck model with pseudo-car body is developed in the second phase, where the initial wheelset model is extended to incorporate truck dynamics. Tangent track stability analysis of the truck model is carried out, and the optimal wheelset coupler parameters to maximize critical speed are established. Finally a steady-state curving model of the truck incorporating EDCW is formulated, and the influence of wheelset coupler on the curving performance is investigated.

In all phases of this study, only linearized models are considered, and the analytical models are validated in their limiting case against simulated and experimental results of conventional system. A comprehensive parametric study is carried out to examine the influence of various parameters on the stability and curving performance of an EDCW and truck incorporating EDCW systems. The results of the investigations show, that a speed dependent optimal coupler damper can provide over 100% improvement of tangent track critical speed in comparison to a conventional system. However, the steady-state curving performance of the truck with an optimal coupler is deteriorated in terms of lateral response to track curvature, when compared to that of conventional system. Since curved track may be negotiated under the guidance of flange, based on the results of this study, the concept of EDCW appears to be a strong candidate for the high speed freight cars of the future.