In this paper, a model of the electropneumatic brake used on subway trains is developed; it facilitates brake system analysis, fault diagnosis and controller design. This objective is met by decomposing an electropneumatic brake into smaller modules and developing detailed models at three levels. The basic subcomponent models of the electropneumatic brake are built using a lumped parameter method. Then individual models are developed based on the subcomponent models. Finally, a complete model of the electropneumatic brake is developed by assembling all the valve models. Simulation models of these three levels are built using Matlab-Simulink. Important subcomponent models are verified by comparison with experimental results. Furthermore, a test rig is set-up to validate the complete brake model. Experimental and simulated results suggest that the model is able to closely predict the behaviour of the electropneumatic brake: brake filling and releasing time differences between experimental and simulated results are less than 10%; the cause of steady state pressure error of a real electropneumatic brake can be explained using the model; other behaviour of a real electropneumatic brake (sharp pressure jump and drop, pressure oscillation, thermal exchange) can be predicted and better understood using the proposed model.
This paper proposes the design of an aerodynamic braking device for a high-speed train. The design is based on the parameters of the high-speed train and the working principles of airplane wings. The proposed device is a unidirectional opening model driven by hydraulics. The prototype uses hard-wired signals to transmit braking commands on eight levels. The important characteristics of the device include a synchronous action and a fault-oriented security design. Its functions include service braking, gradual braking, emergency braking and self-checking. Simulation results show that deceleration in the high-speed zone between 250 and 500 km/h can be improved by between 8 and 60%. When the train runs at 500 km/h, the braking deceleration rate can be improved by 0.12 m/s 2 . The simulation results are found to agree with wind tunnel test results. The braking characteristics are also investigated using a test bed, which mimics the aerodynamic load exerted on the prototype when the train is running between 0 and 550 km/h. It is clearly demonstrated that the proposed principle of the aerodynamic braking system is feasible and its design scheme is reasonable. The aerodynamic braking device can survive a 50,000 N aerodynamic load, and the time taken to achieve the maximum braking capacity, which is the time taken to take the brake panel from its closed position of À5 to the maximum angle of 75 , is less than 3 s. The proposed prototype therefore offers an important step in the design of practical systems.
The current thermal model of railway disc braking is rather coarse as the heat source is treated to be uniformly distributed. By using a Gaussian mixture function, the thermal behavior of railway disc braking was modeled. Simulations and full-scale rig tests of emergency braking about metro train at 40-100km/h were conducted. The differences between the maximum temperatures calculated by the Gaussian mixture heat source method (GMHS Method) and measurements are 2.56-4.71°C. The relative errors between the maximum temperatures calculated by the GMHS Method and thermal mechanical coupling method (TMC Method) are no more than 2.53%. The temperature curves obtained by the GMHS Method oscillate about their centerline with the same oscillating period to the TMC Method. The time cost by the GMHS Method is only 0.91%-3.05% of the TMC Method at the same conditions. The results indicate that the proposed GMHS Method is accurate and efficient, which is more suitable for engineering application.
Friction is the bond linking the tangential and normal forces at the wheel-rail interface. Modeling friction is the precondition for the wheel-rail adhesion calculation. In this work, the critical role of friction in the calculation of wheel-rail adhesion is discussed. Four types of friction models (Coulomb model, linear model + Coulomb model, rational model and exponential model) which are commonly used for the calculation of wheel-rail adhesion are reviewed, in particular with regard to their structural characteristics and application state. The adhesion coefficients calculated from these four friction models using the Polach model are analyzed by comparison with the measured values. The rational model and the exponential model are more flexible for defining the falling friction, and the adhesion coefficient calculated by these two models is highly consistent with the measured one. Though the rational model and exponential model describe the falling friction well, the existing friction models are not applicable for calculating adhesion after considering more realistic factors, such as thermal effect, contaminants and so on. Developing a novel and practical friction model to accurately describe the wheel-rail friction behavior is still an essential but challenging and significant task. This review provides a reference for the selection of existing friction models and generates fresh insights into developing novel and practical friction models.
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