Hunting Characteristics of a Freight Car in Presence of Secondary Suspension Non-Smooth Contact Dynamics

In this study, the nonlinear damping characteristics of friction wedges in the secondary suspension of a freight truck are investigated considering non-smooth contact, geometry, loss of contact and multi-axis motions. The friction wedge model is integrated to a nonlinear multi-body dynamic model of a three-piece truck to study its hunting characteristics. The 114-degrees-of-freedom model also integrates constraints due to side bearings, axle boxes and center plates, while the wheel/rail contact forces are obtained using FASTSIM algorithm considering non-elliptical contact. The parameters of contact pairs within the suspension are identified to achieve smooth and efficient numerical solutions, while ensuring adequate accuracy. The simulation results are presented to illustrate the hunting properties of the truck in terms of critical speed and oscillation frequency. The results showed subcritical Hopf-bifurcation in the lateral dynamic responses.