Influence of brake force distribution on rack vehicle dynamic behavior during emergency braking

Rack vehicles employ gear-belt braking devices (GBBD) on large slopes to compensate for insufficient adhesive braking force. This design generates complex dynamic interactions between the gear-rack and wheel-rail systems. An improper brake force distribution may trigger wheel slippage and gear-rack impacts, potentially causing brake failure, derailment risk, or rack damage. To elucidate how braking force distribution governs vehicle dynamics and defines its safety boundaries, a novel rack vehicle-track coupled dynamic model integrating multiple braking systems was developed. The model incorporates the Polach creep model to characterise large creepage during the emergency braking process and features a comprehensive GBBD model that accurately captures nonlinear gear-rack engagement. Subsequently, the model's reliability is validated through field tests. Simulation results demonstrate that braking force distribution directly correlates with the longitudinal impact of the wheelsets and induces significant axle load transfer, hereby altering wheel-rail creep characteristics and degrading braking performance. By establishing critical boundaries for braking force distribution, these findings provide a foundation for developing robust braking strategies for complex operational conditions.