Rail Vehicle Dynamics for the 21st Century

Abstract

Although railway vehicles were first used in the 18th century, it was only in the 20th century that engineers began to understand their dynamics and were able to write down, and solve, their equations of motion. The single most fundamental property of a railway vehicle is the use of a steel wheel running on a steel rail with all the traction, braking and guidance forces being transmitted through a small contact area between the wheel and the rail. While the inherent guidance provided by a conical wheelset running on rails was known even to George Stephenson in 1821, who described its kinematic oscillation, it is only in the last 40 years that an adequate theory has been available for vehicle suspension designers to use. It is well known that a mechanical system that is subject to non-conservative forces may become dynamically unstable under certain conditions. In a railway vehicle the non-conservative forces arise at the contact point between the wheel and rail due to creepage, and the sustained lateral and yawing oscillation that results in some vehicles is known as hunting. This paper traces the developments in railway dynamics up to the end of the 20th century and discusses the latest developments, with predictions as to what the future might hold.