Keywords: high speed vehicle, hunting stability, suspension parameter, equivalent conicity.

In the present work, a conventional four-axle high speed passenger car is considered to investigate the influence of critical parameters on running stability. It originates from a high speed passenger car in China operating with the maximum speed of 350km/h. In order to ensure safe operation of high speed vehicles without hunting instability, the influence of the primary suspension stiffness, equivalent conicity, yaw damper, suspension parameter of traction motor and emergency spring parameter have been analysed. At last, it comes to the conclusion of the design principles of vehicle suspensions.

The hunting stability is the most important problem which limits the maximum safe operating speed of high speed passenger cars. Such performance is primarily affected by the suspension parameters of the bogie and the wheel-rail contact. Many works have already been published in the area of vehicle stability but most simulation work is done using simplified models. The main purpose of this paper is to build a detailed high speed vehicle model to study the influence of suspension parameters on the hunting stability and to try to obtain general results.

The numerical simulation results show that suspension parameters should be designed using the following principles: For an adequate hunting stability the optimal match between the primary longitudinal stiffness and the primary lateral stiffness exists in a narrow L-shaped band. With an increase in the values of equivalent conicity, an L-shaped band moves in the direction of the high primary suspension stiffness. In order to assure a high stability both in new and worn wheel-rail conditions, an appropriate stiff primary longitudinal suspension should be adopted.

There is an optimum series stiffness for the yaw damper which can assure that the vehicle achieves maximum stability. The yaw damper series stiffness in the rigid bogie vehicle should be less than that in the flexible bogie vehicle to achieve a maximum critical speed.

It is the lateral motion of the traction motor that has a large influence on the hunting stability, while the yaw motion of the traction motor has little influence on it. The highest critical speed is obtained with a traction motor flexible suspension. To achieve a high critical speed for the bogie with flexible motor suspension, the stiffer the primary longitudinal suspension is, the lower the motor lateral frequency should be assured. Careful selection of the motor lateral frequency and damping ratio should be ensured, otherwise the critical speed in the traction motor flexible suspension may be lower than that in the motor rigid suspension.

The highest critical speed is obtained with the horizontal stiffness of an emergency spring of the order of magnitude of 0.1MN/m, and an optimal horizontal stiffness of the emergency spring can ensure a stable operation at 350km/h. In this condition, the friction coefficient has a great effect on the critical speed, the larger the friction coefficient the larger the critical speed. When the horizontal stiffness of the emergency spring approaches an order of magnitude of 10MN/m, the critical speed of vehicle can achieve 250km/h, and in this condition the friction coefficient has a little effect on the critical speed.

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