A contribution to the study of heavy haul railway wagon pneumatic braking systems

Abstract

The pneumatic air brake system in railway trains is critical to the safe and reliable operation of heavy-haul railway transportation. Analysis of the braking performance of the railway wagons often focuses on the behavior and response time of the pneumatic system, consisting of the brake pipe, wagon control valves, wagon brake cylinders, and the wagon air reservoirs. However, for a technology that has been used for centuries and researched for decades in academia, very few architecture or design changes have been introduced to improve the pneumatic air brake system. Two significant design drawbacks of the pneumatic air brake system are slow signal propagation and in series signal passing from wagon to wagon. These drawbacks lead to long stopping distances and, because front wagons begin to brake long before rear wagons, damaging longitudinal shocks between the wagons. While electro-pneumatic brake systems in heavy-haul railway trains are emerging as reliable solutions to the problems faced by purely pneumatic air brake systems, the high cost of implementation and other risk factors have delayed their use in the field. Therefore, purely mechanical, low-cost design solutions are studied in this work. A single design solution has been simulated using mathematical models derived from the Navier-Stokes equations and computationally solved in the C++ programming language to verify system performance. This design solution utilizes a venturi effect to create a vacuum near the outlet of the pneumatic control valve, that enables faster signal propagation through the brake pipe. The faster brake pipe signal was then implemented in a Matlab Simulink longitudinal dynamics model to determine its effect on draft gear couplings. The results indicate that introducing a venturi effect can reduce damage accumulation in the draft gears, at the expense of emergency reservoir air. However, the longitudinal dynamics results require additional study before venturi implementation into the field, as the behavior is not fully controlled and still suffers from similar design flaws as the current system.