Three-Piece Half-Truck Multibody Dynamics Models for Freight Train Suspensions

A three-piece bogie acts as a support for the freight train car bodies so that they can run on straight and curved tracks. It also absorbs the vibrational energy generated by the track. The three main parts of a traditional three-piece bogie are two side frames and a bolster. The side frames run parallel to the rails and are connected to each other by the bolster, which runs perpendicular to the rail. The side frames are connected to the axles, which are directly connected to the wheels that run on the track through the primary suspension. The primary suspension includes the bearing adapter and pedestal roof. The secondary suspension, which includes the friction wedge and load coils, connects and provides damping on each end of the bolster at its intersection with the side frame. Moreover, the friction wedge aids in warp resistance of the bogie. Because of the wedge’s non-linear frictional characteristics and load sensitive behavior, accurately capturing its dynamics in a computational model proves difficult. Previous work at the Railway Technology Laboratory (RTL) at Virginia Tech focused on better capturing the dynamics of the friction wedge modeled as a 3D rigid body. The current study extends that work to a half-truck model treated as an application of multibody dynamics with unilateral contact to model the friction wedge interactions with the bolster and the side frame. The half-truck model created in MATLAB is a 3D, dynamic, stand-alone model comprised of four rigid bodies: a bolster, two friction wedges, and a side frame assembly. The model allows each wedge four degrees of freedom: vertical displacement, longitudinal displacement (between the bolster and side frame), pitch (rotation around the lateral axis), and yaw (rotation around the vertical axis). The bolster and the side frame have only a vertical translation degree of freedom. The geometry of these bodies can be adjusted for various simulation scenarios. The bolster can be initialized with a pre-defined static yaw (rotation around the vertical axis) and the side frame may be initialized with a predefined pitch/toe geometry (rotation around the lateral axis). The model simulation results have been compared with results from NUCARS®, an industrially used train modeling software developed by the Transportation Technology Center, Inc., for similar inputs.