On the dynamics of the three-piece-freight truck

Although the three-piece-freight truck is a simple design its mathematical model is very complicated. The model is definitely a nonlinear dynamical system, where the nonlinearities arise from the nonlinear kinematic and dynamical contact relations between wheels and rails, the suspensions and the nonlinear dry friction damping with hysteresis and stick-slip action. The bolster moves both vertically and laterally relative to the truck frames, so the friction forces on the contact surfaces of the wedges must be treated as two-dimensional vectors, and the same holds for the dry friction on the surfaces of the adapters. Due to the clearances between the car body and the side supports on the bolster, the side supports must be modelled as nonlinear dead-band springs. The stick-slip action and the play between elements of the truck makes the dynamical model a structure varying system. We present the dynamical system that models the dynamics of the moving wagon and show the result of numerical dynamical investigations such as the calculation of the critical speed, and the dynamics of the wagon on an irregular track and compare them with test results and simulation results using NUCARS.