A MATHEMATICAL SIMULATION OF THE CURVE ENTRY AND CURVE NEGOTIATION DYNAMICS OF FLEXIBLE TWO AXLE RAILWAY TRUCKS

A 43-degree-of-freedom mathematical model of freight car and two trucks has been established, to simulate the dynamic response of the vehicle as it enters and negotiates a curve. The rigid car body is modeled with three degrees of freedom, and each truck is modeled as a five mass system. Each mass in the truck model has four degrees of freedom, (lateral, yaw, vertical, and roll). Clearances at the interfaces of the respective components are accounted for, and non-linear damping (coulomb) is included at all interfaces except the axle journal/side frame interface. Other non-linearities included in this model include spring bottoming effects, friction creep forces and centerplate breakaway friction forces. The equations of motion for this system are solved, and integrated numerically using an iterative method. A parametric study, using this mathematical model, investigated the effects of track curvature, length of spiral, vehicle velocity, center plate friction forces, wheel conicity and initial configuration prior to curve entry on the lateral flange forces during curve entry and negotiation. It is shown that wheel taper greater than 1 in 20, coupled with a decreased center plate friction level and a reduced stiffness in the longitudinal suspension would minimize flange forces during curving, but is a combination which is undesirable for tangent track yawing stability. This mathematical model predicts the curve negotiation response for the flexible freightcar truck commonly used. Recommendations are made for future design work based on this model, which can help resolve the incompatibility between design requirements for curved and tangent track.