Research On Arm Joint With Variable Stiffness Of High-speed Trains Based On Magnetorheological Technology

The development of China’s high-speed railway has attracted worldwide’s attention,which greatly facilitates people’s travel.The continuous improvement of train speed also puts forward higher requirements for the high-speed stability and curve trafficability of bogie system.On the one hand,the train bogie needs a large positioning stiffness to restrain the hunting motion at high speed.On the other hand,a soft positioning stiffness is needed to adapt to the curvature change when passing through the curved track.The traditional bogie system is difficult to meet the contradictory positioning stiffness requirements.The compromise positioning stiffness design is often used to take into account the high-speed stability and curve trafficability,which limits the further improvement of train running speed and dynamic performance to a certain extent.This work is based on the project of magnetorheological arm joint with variable stiffness of CRRC,research on improving the dynamic performance of the train through the controllable stiffness of the arm joint avoiding changing the main structure of the current bogie.It mainly focuses on solving the contradictory stiffness requirements of high-speed stability and curve trafficability,and reducing the impact of wheel-rail excitation on the train body.The research on the arm joints based on magnetorheological elastomer(MRE)and magnetorheological fluid(MRF)was carried out respectively,and the variable stiffness of the joint was realized through the controllable change of the magnetorheological effect of the material,and the dynamic performance of the train was further developed.Evaluations for demonstrating the improvement in train stability,curve trafficability,and wear reduction were conducted.Finally,the feasibility of the MRE arm joint with bandgap characteristics for vibration isolating is explored.The main research issues are as follows:1.Research on of MRE arm joint with fail-safe characteristics.In order to solve the contradictory stiffness requirements of straight and curved tracks,an MRE arm joint with variable stiffness is proposed.Firstly,the design of the MRE arm joint with multilayer structure and hybrid magnetic field is studied,so that it can meet the design requirements of large working stroke and large stiffness without electric input,and the controllable joint stiffness is realized by using the change of material elastic modulus.Then,considering factors such as magnetic field circuit,structural strength,sample preparation,etc.,an MRE formula suitable for the change of elastic modulus of arm joint was selected,and a prototype was fabricated.Finally,the variable stiffness performance test was carried out with a material testing machine.The test showed that the proposed MRE arm joint achieved a stiffness change effect of about 54.9%under different displacements,and the mechanical response model of the joint was built by using the parameter identification method.2.Dynamic evaluation of trains equipped with MRE arm joints.In order to evaluate the improvement of the dynamic performance of the train by changing the stiffness of the MRE arm joint,the evaluation and analysis of the high-speed stability and the curve trafficability of the high-speed train were carried out.Firstly,starting from the mechanism of hunting motion and high-speed stability,the dynamic equation of linear motion of bogie is established,and the calculation method of linear critical speed is analyzed;The steady-state equation of the bogie when passing through the curve is established.Finally,the dynamic evaluation of trains based on the mechanical response model of MRE arm joint is studied.The simulation evaluation shows that when the positioning stiffness is reduced,the wheelset angle of attack is significantly reduced on curves with different radii,and the curve trafficability is improved.The stiffness requirements of the train in different tracks can be meeted.3.Research on the vibration isolation performance of the MRE arm joint with bandgap characteristics.To reduce the high-frequency vibration transmitted from the wheelset to the bogie,the application of the MRE arm joint with bandgap characteristics in suppressing vibration is explored.First,based on the bandgap generation mechanism of mechanical metamaterials,the parameters of the MRE rubber layer and the steel ring layer are matched and designed to make the MRE arm joint have bandgap characteristics.Then,the vibration transfer equation based on the spring-mass model is established.The bandgap frequency is theoretically calculated,and the distribution of the bandgap is simulated by multiphysics software.Then,an MRE arm joint with bandgap characteristics was fabricated.The existence and adjustable characteristics of the bandgap are verified by vibration test.The vibration test shows that the bandgap frequency of MRE arm joint without power supply is 477 Hz～1165 Hz,and the bandgap frequency of the MRE joint is widened by 123 Hz through current regulation;Then,based on swept frequency excitation,simple harmonic excitation and random excitation,the vibration isolation performance of MRE rotating arm joint is verified,and the average vibration reduction effect is about 39.7%,49.5%and 24.2%under three test conditions;Finally,an on-off control algorithm is established.Through experimental verification,the transmissibility of MRE rotating arm node is significantly reduced in a wide frequency range by adjusting the current.4.Research on MRF arm joints with fail-safe characteristics.In order to overcome the problem that MRE is easily affected by temperature and rubber aging,the research based on the MRF arm joint is carried out.Firstly,the design scheme of introducing the MRF damper into the traditional arm joint of is studied,and the working mechanism of the joint stiffness controllable by changing the damping force of the MRF damper is proposed.Then,the structural design of the MRF damper is carried out,and the piston rod,piston,casing and other components of the MRF damper are optimized and selected from the strength theory and the magnetic field theory,and the MRF damper prototype is produced,and the damping force is 398 N～7854 N.The damping force can change for about 19.8 times.Then,the MRF arm joint was fabricated and tested.The test showed that the stiffness change effect of 66%was achieved.The response of different displacements and frequencies of the MRF arm joint was emphatically analyzed.Finally,the influence of the stiffness change of the MRF arm joint on the wheel-rail wear is explored.The wear power simulation shows that the proposed MRF arm joint can reduce the wear power by about 31.4%on average by changing the stiffness under different curve radii.The wheel and rail wear is effectively reduced.