The electromechanical braking is a novel braking mode, which is the development direction of the electrification and intelligent train braking system. In this paper, a coupled-rigid-flexible model of the EMB unit is developed, and dynamic characteristics of the EMB unit are analysed based on the model. Firstly, assumed mode method is used to describe the axial and torsional vibration of the screw in nut-screw assembly, and lumped mass method is used to describe motions of other components in the EMB unit. Secondly, the EMB unit model is established and simulated in Matlab/Simulink software based on electro-mechanical and rigid-flexible coupling characteristics. Then the model parameters are calibrated by experiment. Finally, the simulated model is studied to analyse the influence of various factors on the dynamic characteristics of the EMB unit. The results indicate that an increment in viscous damping flats the fluctuation of the pushout force. The maximal pushout force decreases and the changing trend of force is different along with the rotational structure damping increases. The flexible vibration of the screw results in higher pushout force, meanwhile the fluctuation of the force is greater with higher braking instruction current value. When the ratio of the screw length to the screw cross-sectional diameter is 30, the pushout force varies along with the friction pairs wear under vibration. The study can provide references for structure design, control design and fault diagnosis of EMB units.

Electromechanical brake (EMB) is a novel braking mode for railway trains. The reliability of the braking system is important for railway system safety. According to the RAMS (Reliability, Availability, Maintainability and Safety) requirements for railway applications, the key issues of prognostics and health management (PHM) for EMB systems are discussed at first. Consequently, the dominant tasks of the PHM system are confirmed, containing the battery State-of-Charge (SOC) and State-of-Health (SOH) estimation, electric components condition monitor, and mechanical crack prediction. Then the critical failure modes of the EMB system and their failure mechanisms are analyzed. Based on the above analysis, a PHM system developed for EMB systems and its working flow are introduced. The vehicle operation parameters, the brake control commands, and the sensor signals are inputs of the PHM system. These inputs are processed and gathered as health indicators. Then the PHM system adopts the physical model or the hybrid algorithms to track the failure mode and components. Finally, the PHM system locates the health stage of the EMB system. The primary health indicators for EMB systems are the braking distance and emergency battery capacity. And the health indicators for components are mapped with the corresponding failure modes. The estimation for the battery SOC and SOH is established based on the test results of battery properties. The model-based and data-driven hybrid method is utilized to detect the crack growth of mechanical components and the degradation in electric properties. The PHM system is useful for condition-based maintenance. And it is meaningful for the reliability and safety improvement of the EMB systems.

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Aerodynamic brake is a clean and environmentally friendly braking mode, which does not use mechanical friction as a braking force. This paper describes the development of a small-distributed aerodynamic brake prototype, including its structure, working principle, ground test, and test results. A computational fluid dynamics (CFD) method is developed to obtain the aerodynamic forces of the prototype, and the simulation results are validated by performing a wind tunnel test. On the basis of the CFD simulation, the panel opening process and braking process are modelled to analyse the vertical dynamic characteristics of a high-speed electromagnetic suspension maglev with aerodynamic brakes. In addition, a vehicle, guideway, and levitation controller are modelled. Finally, a three-car system dynamic model is solved to obtain the influences of the opening time, initial braking position, and feedback gains. The aerodynamic forces of the first car show the most significant changes when the braking panels are opened. The increase in the longitudinal force is 15461.16N, and the vertical force varies from a lift force of 35342.98N to a downforce of 40721.35N. The maximum guideway deflection decreases as the opening time increases. The difference between the deflections obtained at opening times of 0.064 s and 0.6 s is 1.2 mm. Furthermore, vertical accelerations decrease as the opening time increases. The condition in which the vehicle brakes when the first car enters the object guideway has the largest influence on the deflection of the guideway. To ensure levitation stability influenced by the vertical change of the first car, a high feedback gain for the levitation clearance change is required. However, the levitation stability with aerodynamic brakes is weakly affected by the feedback gains for the observed velocity and acceleration of the system.