Mechanism and suppression of friction-induced vibration in catenary-pantograph system

An unexplained instability phenomenon in railways is known to be caused by sliding friction in a catenary-pantograph system at low speeds. This is an important engineering problem because this instability phenomenon contributes to increased wear of contact wires and requires a train driver to confirm safety, which leads to train delays. Tribological analyses have found an increase in the friction coefficient at low speeds. Pantograph models based on the finite element method, multibody dynamics, and pin-disk model have been proposed for kinematic analyses. However, the mechanism is still uncertain, and no experimental investigations have been conducted. In this study, experimental and numerical investigations are conducted on the instability phenomenon caused by sliding friction. A method for estimating the friction coefficient for an actual pantograph is proposed and applied to experimentally investigate the instability phenomenon. A dynamic model is constructed based on various experiments. The frequency and the stable-unstable boundary of the instability phenomenon obtained in the simulations agree with those obtained in the experiment. From the dynamic model, it is found that the instability is a flutter-type instability caused by the asymmetry of the stiffness matrix due to Coulomb friction. Countermeasures for preventing the instability phenomenon based on the determined mechanism are proposed, and their effectiveness is verified by simulations and experiments. The results could contribute to the design of new pantographs to improve stability and the development of countermeasures for existing pantographs that experience instability.