Modeling of a Roller Rig for Evaluation of Wheel/Rail Contact Mechanics

This paper provides a detailed dynamic model of the electromechanical system for a scaled roller rig that is under construction at the Railway Technology Laboratory of Virginia Tech (RTL) for accurate study of the mechanics and dynamics at wheel-rail interface in railway vehicles. Roller rigs are critical laboratory test equipment for studying rail vehicle dynamics, either as a full railcar or single component. The controlled laboratory environment will provide a successful path for obtaining data on the mechanics and dynamics of the system, including creepage and creep forces at the wheel-rail interface under various conditions. The single-wheel scaled rig under development at RTL includes a wheel that is placed on a roller with similar profile as a U.S. 136 weight rail. The test setup allows for adjusting the wheel load, the wheel angle of attack, the rail cant, and the lateral position of the wheel with respect to the rail (including flanging). The roller and the wheel are each powered independently by two AC motors that enable controlling their relative speed to a high degree of precision, i.e., 0.1 RPM, in order for precisely controlling and simulating various creep conditions that occur in practice. An essential step for the successful design and development of the test rig is modeling the motors and the roller/wheel drivelines. The model includes the electromagnetic dynamics of the AC motors, the compliances and damping of the drivelines, the inertial properties of the motors, shafts, couplers, and the rotating wheels, in a multi-domain (electrical, magnetic, and mechanical) lumped-parameter model. The model is used to determine the damped natural frequencies of the coupled system. The results of the study indicate that the compliances of the driveline mechanics is the most critical element in maintaining a prescribed speed at the driven wheel, and also controlling the relative creep between the wheel and the simulated (round) rail.