Abstract: Based on the theory of vehicle-track coupled dynamics, a dynamic model for the three-piece-bogie wagon and track structure system is established. The major nonlinearities containing in the wagon system, such as the wheel/rail contact, the axle-box clearance, the wedge Coulomb friction, and the rhombus distortion of bogie frame, are considered in the model. Taking the Chinese main type wagon with Z8A three-piece-bogie as an example, the nonlinear lateral running stability of the wagon is analyzed theoretically. It is shown that the critical hunting stability speed is only 78 km/h in the case of unloaded wagon. A field running experiment is carried out and the results shows that strong hunting motion occurs when an empty wagon with the Z8A type bogie runs on a straight track with the speed of 75 km/h. The predominant frequency of the hunting motion of the car body is 2.69 Hz, and the wavelength of the hunting motion is 7.745 m.

Key words: Hunting stability, Nonlinear dynamics, Rail vehicle, Wagon