A dynamic model for a four-axle power car was established and analyzed by using software
SIMPACK and the nonlinear response analysis in time domain with random track irregularity to improve its
dynamic performances. The numerical results show that the optimum damping coefficients of the secondary
lateral damper, the primary and secondaryvertical dampers are often certain forthis kind of power cars, but
the effect of the change in unloading force on the riding quality can be reduced by increasing unloading
velocity to ensure its riding quality. For a four-axle power carwith secondary big deflection helical springs,
it is important that the secondary lateral stop clearance matches well with the secondary lateral damping
characteristic to obtain a good dynamic curve negotiating performance.