Draft System for Enhanced Impact Protection and Train Action Control: Validation by Testing and Computer Modeling

Abstract

Abstract Certain types of freight cars that are normally equipped with conventional draft gears to protect car structure from coupling impact forces can benefit from additional buff travel. This reduces the coupler force experienced by the car structure; limiting the potential for structural and fatigue damage and improving wear characteristics. This can be accomplished within the standard draft pocket dimensions, allowing for improvements in both retrofit and new applications. Impact test data will show reductions in coupler force as compared to conventional draft gear systems under identical impact conditions. With additional buff travel available, greater protection is afforded against encounters with higher speed impacts. Train action control can be enhanced through the application of an elastomeric spring with a stiffer non-linear spring rate. Conventional draft systems use a yoke around the draft gear, permitting the full travel of the device in both the draft and buff modes. The free slack transversed in reversal from buff to draft mode, followed by the relatively soft spring rate of a conventional draft gear, especially at low velocity, can result in over-solid conditions and high force peaks. Car separation and car closure velocities are typically low, such as two miles per hour, so the effect of softer spring rate can be detrimental. The stiffer non-linear spring rate offers improved force transfer through each car as the force wave propagates through the train; the gradual and simultaneous buildup of force at each end of the car reduces relative car velocities and thus the severity of force transfer through each coupled connection. The elimination of a mechanical oversolid stop, replaced by the elastomeric spring, as it becomes stiffer with travel, also limits the end force experienced by the freight car structure. Computer modeling will show the advantages of this system during severe transient events, such as train startups and dynamic braking.