Health management system for the pantographs of tilting trains

Tilting trains are provided with the ability of rotating their carbodies of several degrees with respect to the bogies about the longitudinal axis of the train. This permits a train to travel at a high speed while maintaining an acceptable passenger ride quality with respect to the lateral acceleration, and the consequent lateral force, received by the passengers when the train travels on a curved track at a speed in excess of the balance speed built into the curve geometry. When the carbody is tilted with respect to the bogie, the train pantograph needs to remain centered with respect to the overhead catenary, which is aligned with the track. The conventional solution is to mechanically link the pantograph to the bogie, but recent tilting trains have the pantograph connected to the carbody roof while a position servoloop continuously control the pantograph position such to keep it centered with the catenary. The merit of this design is to allow a gain of the useful volume inside the carbody. The pantograph position servoloop uses two position sensors providing a redundant position information to close the pantograph feedback loop and perform system monitoring. The monitoring functions presently implemented in pantograph position controls are able to detect the servocontrol failures, but in case of conflicting information from the two position transducers they are not always able to sort out which of the two transducer is failed because some failures of the position transducers cannot be detected by simply looking at the output signals of the transducer. As a result, if a difference between the output signals of the two position transducers is detected, the tilting function is disabled and the train speed is reduced. Also, the entire pantograph is then removed and replaced because the functionality of each individual transducer can only be checked at shop level. Developing better diagnostic techniques for the pantograph position control system have been encouraged by the train companies, but no work on this subject has so far been performed. A research activity was hence conducted by the Authors, that was aimed at developing an advanced diagnostic system that can both identify the presence of a failure and recognize which of the two position transducers is the failed one. In case of a transducer failure it is thus possible to isolate the failed transducer and keep the pantograph position control operational, thereby retaining the train tilting function. A further merit of the advanced diagnostic system is the reduction of maintenance time and costs because the failed transducer can be replaced without removing the entire pantograph from the train. The general architecture of this innovative diagnostic system, the associated algorithms, the mathematical models for the system simulation and validation, the simulation results and the possible future developments of this health management system are presented in the paper.