摘要：Vibration behaviors of bogie hunting motion contain key information that dominates the dynamic performance of rail vehicles,in which the eigenvalue of each mode reflects the damping ratio and the natural *** paper focuses on the root loci curves of bogie hunting motion,starting from a rigid bogie,then to a bogie with flexible primary *** regard to the rigid bogie,analytical formulas for the eigenvalues,the critical speed as well as the corresponding hunting frequency are derived and *** for the flexible bogie,the root loci curves are calculated *** study shows that both free rigid bogie and free wheelset are dynamically unstable at any *** critical speed increases with diminished wheel-rail conicity,track gauge,and wheelset and bogie inertia,and with increased wheelbase and wheel *** dominating factors such as the stiffness of the primary suspension and the wheel-rail conicity should be optimized for a practical *** influences of the damping coefficients and the variations of creep coefficients are *** motor suspension affects the root loci curves and the critical speed *** inappropriate motor suspension design and rigidly suspended motor reduce the critical *** increase of critical speed by a motor suspension can only be achieved when the lower natural frequency of the motor-bogie frame-wheelsets system coincides with or is close to the hunting *** care should be taken for the design of motor suspension,the first is to avoid the decreased damping ratio in a certain speed range below the critical speed and the second is that the variations of parameters should not induce the rapid reduction of the critical *** main feature of the present study is that the root loci curves,which are derived as analytical formulas or calculated numerically,are used to study the vibrational behaviors of bogie hunting *** the influencing laws of the dominating pa