Keywords: hunting motion, nonlinear elasticity, nonlinear dissipation, elasticity, critical speed.

The hunting motion occurring in case of the railway vehicles is a consequence of the reversed conic shape of the wheel rolling surfaces. Below a certain vehicle riding speed, called the critical speed, the hunting motion appears as a damped sinusoidal oscillation along the track centreline. As the speed increases, the wheel-track contact force becomes large enough to cause rail damage, discomfort and eventually can lead to derailment.

Axle hunting is a coupled lateral and yaw self-oscillatory motion which is largely determined by wheel-rail contact geometry. The stability of this motion is an important dynamic problem that determines the maximum operating speed of a railway vehicle. To improve the stability performance, without increasing the rail-wheel interaction forces above safety limits, elastic joints and dissipative devices are used to connect the wheelset to the bogy frame. The influence of passive linear and non-linear dissipative and elasticity forces on the hunting motion stability of a wheelset with elastic joints is studied in this paper.

The effects of linear and nonlinear elastic and damping characteristics of the suspension in horizontal plane are analysed. The nonlinear elastic and damping characteristics used were as given by the new nonlinear devices called SERB and VZN. This type of nonlinear damping is shown to be very useful to completely eliminate the transversal movement instability.

The results of the numerical simulations show that use of linear elasticity and damping in the system, can lead to a certain increase of critical speed, still limited by safety, wear and damage requirements. By using a nonlinear special type of elasticity and damping characteristics, depending on both relative velocity and displacement between the wheelset and the bogy frame, it is shown that the hunting motion cannot become unstable, even for very large values of vehicle speed.

The general conclusions of the paper are:

• By using the nonlinear elastic devices in the both principal directions in the horizontal plane, the hunting motion critical speed can be significantly increased by over 70%.
• By using nonlinear special dissipative devices type VZN, the instability of the hunting motion can be completely eliminated.

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