When designing the railway vehicle, the most important thing in dynamics is limit speed or running stability in straight line. In order to maintain the vehicle in stable condition when running straight line, the primary suspension should be hard. But if the primary suspension is hard, then the curving performance is bad. The primary suspension has to be soft for good curving performance. Therefore there must be compromising between running stability in straight line and curving performance. There are many curves in subway line of big city. Because of the curve, some problems are suggested like squeal noise and wear of wheel flange. The best solution for squeal noise and wheel flange wear is vehicle running on curve smoothly. In order to reduce the squeal noise and wear of wheel flange in curves, a possibility of adopting MR(Magnetic-Rheology) damper as a longitudinal damper in primary suspension system was studied. Before studying the semi-active steering bogie by using MR damper, the limit speed of railway vehicle was reviewed according to the variation of primary suspension and wheel tread conicity. When the equivalent conicity has large value(larger than 1/10 in this study), the limit speed is increased according to growing up of longitudinal stiffness of primary suspension. In this study the stiffness of primary suspension was decreased for good curving performance. The MR damper used to increase the running stability in straight line. The simulation program for running and curving performance was made by using MATLAB/Simulink S/W. The running stability and curving performance of the subway vehicle with MR damper was analyzed by using the program.
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