Variable Stiffness Damper Used In High Speed Train

The vibration of high speed train would be increased when vehicles operate at high speed due to the track irregularity and other factors. The vibration of train influence stability and security of train and the ride comfort of the passengers. Passive dampers are widely used in the train normally, which relies on the collocation between damper and spring to control vibration, but the control effect is restricted in a certain working conditions. Active vibration control systems have good performance in vibration control, but the control strategy is complicated and requires large amounts of external energy.With the development of the intelligent materials, researchers did a lot of investigations for material applications and obtained good achievements. Magnetorheological (MR) fluid is widely applied in the vibration control, because of the characterization of rheology change ability with the intensity of magnetic field. MR damper normally only be used as a variable damping device. The novelty of this thesis is to design a variable stiffness MR damper, whose damping and stiffness can change with variable control current.This thesis firstly introduces the characteristics of the MR fluid and the types of MR dampers. The hysteretic features of physical model of MR fluid are also introduced. A conventional MR damper is designed and fabricated. The dynamic behavior of the deisgned damper is tested in MTS. Simulation and experiment indicate that the damping of the conventional MR damper changed a lot by the external current while the stiffness nearly remain the same.A model of a semi-active system with variable stiffness and damping is then proposed. The semi-active system is consisted of damping element and stiffness element in series or parallel structure. The system dynamics equation of original model and equivalent model are listed. Then, the transfer function and frequency domain function can be obtained. Comparing the frequency domain function between original model and equivalent model, equivalent damping and stiffness can be achieved. The relationship between the different parameters of system and equivalent damping and stiffness of system can be indicated.Finally, a MR damper with stiffness variable ability is designed and fabricated. The MR device is tested by MTS and the mechanisms of the dynamic behavior is analyzed by physical principles at the basis of MR fluid model.