Polymer Draft Gear Modeling and Simulation for Improved Longitudinal Train Dynamics

 Indian Railway uses the American Association of Railroads (AAR) standard automatic coupler system in mainline passenger trains. This coupler system includes an AAR H-type coupler for interconnection with other vehicles and a polymer draft gear to dissipate the vibrations and impacts. Although the H-type coupler has minimal slack among other AAR standard couplers, longitudinal jerks and other coupling-related issues are observed in these trains. Therefore, an accurate model of the coupling system is crucial for the precise estimation of in-train longitudinal forces using longitudinal train dynamic simulations. In the numerical models of trains, the complete coupler system is modeled by the dynamic characteristics of draft gear with the coupler slack combined in it. However, the present mathematical models describing the dynamic hysteresis of polymer draft gears are not very accurate due to the oversimplified modeling and availability of limited experimental data. Therefore, in this study, the shortcomings of oversimplification in the modeling of draft gears and the issues related to the availability of limited experimental data are addressed.

A new dynamic model for polymer draft gears is proposed, incorporating the mentioned inadequacies in the purpose statement. The proposed model uses a combined function of exponential and polynomial expressions, fitted on experimental characteristics. The relevant parameter has been identified, and a suitable range of its values has been proposed to control the rates of loading and unloading responses independently. The proposed draft gear model is then implemented in a shunting simulation model of rail vehicles to estimate the safe shunting velocity to avoid structural damage to vehicles.

The proposed model requires a smaller number of tuning parameters and gives a consistent trend even with an insufficient amount of measured data points while closely resembling the realistic behavior of polymer draft gears. It delivers lower unloading and higher loading rates, which are the actual characteristics of a polymer draft gear.

 The proposed model offers an accurate representation of a polymer draft gear. It enables precise assessment of the in-train longitudinal forces. Additionally, the model allows for a more accurate estimation of jerks, which are highly sensitive to these forces' magnitude and rate of change.