Heavy Haul Train Simulation of Air Brake System and Longitudinal Dynamics

Abstract

The primary purpose of this study is to provide a unified simulation analysis of the in-train longitudinal dynamics that occur during braking as a result of the coupler force delays caused by the inherent delays in pneumatic airbrakes, commonly used in freight trains. The airbrake force delays and the resulting in-train longitudinal dynamics are directly proportional to the number and position of locomotives and railcars in a train consist. A comprehensive model of pneumatic brakes is presented, including the effect of the pressure drop due to various components and pipe length in a train brake system. The temporal profile of the airbrake cylinder pressure closely matches the brake force and the resulting coupler force, which is then used in a multibody dynamic model of the train that represents the railcars as lumped masses connected together with springs and dampers, representing coupler longitudinal dynamics. The unified airbrake and train dynamic model is arranged such that the user can simulate various train configurations and routes through a convenient, graphical, user interface. A simulation study is presented for a train with one lead locomotive and 106 railcars. The results of the study show that the brake cylinder pressure and the resulting braking and coupler forces are vastly different from the front to the rear of the train. Both the cylinder pressure and coupler forces are delayed in direct proportion to the position of the railcar from the front to the rear. Additionally, the simulation results clearly show the in-train longitudinal dynamic variations that occur during braking, in the form of an oscillatory force at the coupler.