Study On Dynamic Influence Of A Primary Positioning Unit With Alterable Longitudinal Stiffness

As is known to all, the development of high speed rolling stock has become an urge since China determined to build up its own modern transport & logistics. From a dynamic perspective, on one hand, the hunting stability of rolling stock is one of the bottleneck that prevents it from running at a higher speed, which means high speed rolling stock must have better hunting stability. On the other hand, the fact is that curve lines takes up about 1/3 of domestic existing railway lines, many of which have small radii. High speed rolling stock have to be adapted to them, which means they need to have a satisfactory ability of curve negotiating. Research shows that the stiffness of primary longitudinal positioning plays a significant role in rolling stock dynamics, which can enhance the hunting critical velocity by when increased while can improve the curve negotiating ability when decreased. That is to say, the demands for the primary longitudinal positioning stiffness from the two aspects of rolling stock dynamics are irreconcilable.Solutions to this contradiction mainly separate into two:radial bogie technology and suspension control technology. The former solves the problem by changing the traditional bogie structure while the latter does it by introducing a control system. Up to now, these two methods have already been put into practice, and some of them went well, though in general the former is more widely used. Having been fully aware of the former studies, a new scheme is brought up in this thesis, in which the primary longitudinal stiffness is alternative when rolling stock runs along straight lines or curve lines, so as to mitigate the contradiction..First, theoretically, mathematical models of a free wheel set, an elastically positioning wheel set, and a bogie are built, which can represent rolling stock negotiating curve lines as well as straight lines, and by which the influence of primary longitudinal stiffness is indicated. Next, the design of a primary positioning unit with alterable longitudinal stiffness is put forward. Based on the blocking design method, main components such as the detecting block, the control block, and the actuator block are systematically discussed and analyzed, during which the yaw angle of the steering wheel set is decided to be taken as the input variable, the signal processing method is decided, and so is the two-level stiffness-angular displacement characteristics. Finally, a co-simulation model of the experimental locomotive including the control block modeled by SIMULINK and the dynamic block modeled by SIMPACK is built. And the dynamic influence of the positioning unit is evaluated in comparison with the original locomotive model.The results are adequate. (1) The experimental locomotive has a higher hunting critical velocity, and has a higher primary longitudinal positioning stiffness, which means the unit can improve the hunting stability of a locomotive. (2) Both vertical and lateral ride qualities of the experimental and the original locomotives are almost the same, which means the unit can barely be of the benefit to the ride quality. (3) When it comes to curve lines, the experimental locomotive has lower primary longitudinal stiffness and smaller attack angles, wheel sets of which are closer to the ideal radial direction. On curves in different radii, the lateral force on wheel sets, the derailment coefficient, the reduction rate of wheel load, and the wheel-rail wear of the experimental locomotive are all lower than the original one, which means the unit can considerably improve the curve negotiating ability, on condition that the curve radii are within the adjusting range of the unit. In addition, benefits that the unit brings will eventually go down as curve radii become larger.To sum up, by building a co-simulation model of a locomotive with a unit that has alternative primary longitudinal positioning stiffness, it is proved that the unit can ease the contradiction between the hunting stability and the curve negotiating ability, and these improvements take effect in a certain range. The study in this thesis could be of some reference use when relating to a fully improvement of rolling stock dynamics.