Simulation of a freight train brake system with 120 valves

A freight car air brake system simulation model that is based on air flow dynamics and function principle of the '120' control valve is established. Functions of unsteady air flows in the air brake pipes, the boundary conditions used in the air brake system, and the calculation method for pressures in the brake pipe, brake cylinder, and auxiliary air reservoir are discussed. A comparison of the simulation results with the experiment test results is made to verify the validity of the simulation. The results of the simulations, including long and short train with large and small pressure reduction service brake application, release, and emergency brake application, show good consistence with the experiment results on pressure change and its timing in the brake pipe, brake cylinder, and auxiliary reservoir, with the exception of long train at small pressure reduction application. This indicates that the simulation model can correctly predict the pressure behaviour of the unsteady air flows in the air brake system and component movements in the '120' control valve. The model can simulate braking characteristics of a freight train consisting of Lip to four locomotives. The simulation results can be used to successfully predict the braking distances and to assist longitudinal, dynamic, and impact force analyses of a train. The simulation is useful in the design, research, and development of brake systems and can provide insight into how components of the '120' air brake control valve work.