In this paper, we analysed theoretically the hunting stability of a high speed vehicle having a small clearance in the connecting position between the truck frame and the bolster anchor when the spring and friction are connected in series against truck turning. According to the theoretical analysis, it was found that the stability of hunting depends on the angular amplitude of the truck. And the limit cycle corresponding with the hunting velocity is a stable limit cycle when the amplitude is small, while the limit cycle is an unstable one when the amplitude is large. Then, the fact that the body hunting ceases to exist in the range between both amplitudes is made clear. Further, the analysis revealed that the stability of hunting is affected by various factors : the stiffness of the bolster anchor, the friction force acting on the side bearer, the clearance in the connecting position between the truck frame and bolster anchor, the damping coefficient of truck turning and the damping coefficient of body suspension and so on.

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For the purpose of increasing the running speed and ensuring the running performance and safety of a high-speed vehicle, it is necessary to improve the prevention of hunting, improve the running performance in passage of curves and suppress erratic vibration due to track irregularities. In the present paper, the steering, Z-link suspension device mechanism, truck on the new conception for the high running stability on both straight and curved sections of the track is presented, and the hunting characteristic is examined in comparison with that of the SHINKANSEN vehicle. From the theoretical calculation, it becomes clear that the new truck has a slight toward expansion of the unstable region of body hunting in comparison with the SHINKANSEN truck. However, supplementing/both the adequate supporting stiffness of the axle and the elastic moment against the truck turning is an effective method of preventing body hunting. Furthermore, increasing the angular displacement of the rear axle to more than that of the front axle has the remarkable effect of raising the critical velocity of the truck hunting.

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It is empirically known that a railway vehicle is by nature, characterized by contra-dictory behaviors on a tangent track and on curves. Hence, it becomes clear that the Z-link-equipped vehicle, which is intended to improve the passing performance on curves, has a slight forward expansion of the unstable region of body hunting in comparison with traditional vehicles. In order to improve this hunting unstability, the steering truck with a unique mechanism, Z-N-link suspension device mechanism, has been developed, which contributes to enhancement of good running performance both on the tangent track and on curves. On the basis of the theoretical analysis, it is recognized that adequate supporting stiffness at the point of connection between N-links is an effective means of increasing the hunting velocity, and that there exist two limit cycles, that is, one is an unstable limit cycle and the other is a stable one. In this paper, a new concept of the steering truck is given, which provides guidelines of future design of high-speed trucks.

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Instead of good effects on the ride comfort, the active suspension may have unfavorable effects on the wheel/rail interaction such as the increase of lateral force on the wheel. This paper deals with an analytical study about the lateral dynamics of two types of railway vehicles, in which an active suspension mechanism controls the running vibration. One vehicle type has the trucks with a bolster and side bearers, and the other type the bolsterless trucks with yaw dampers. The analytical models for the vehicles consider non-linear characteristics such as creep forces and wheel flange/rail side collision. In this study the active suspension has a controller based on the optimal control theory and assumes ideal actuators to be available. Their operations on the track with alignment irregularities are simulated up to the speed of 350km/h. The results show that the active suspension can improve the ride quality without any increase of the wheel lateral force and that the bolsterless truck has better ride quality and occurs smaller wheel lateral force than the other type truck in the higher running speed range.

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