Advanced Diagnostics for a Position Control System of the Pantographs of Tilting Trains

High speed tilting trains are a smart solution to guarantee shorter travelling time with respect to conventional trains without the need of major investments to renew the railway network. A design issue associated to the train carbody tilting is the need to keep the pantograph centred with respect to the catenary that runs aligned to the rails. The solution used in most tilting trains is to mechanically link the pantograph to the bogie: it is a simple design concept, but the mechanical structure connecting the pantograph to the bogie takes away useful space from the carbody interior. For this reason, a solution used in recent tilting trains is to connect the pantograph to the carbody roof and implement a position control system in order to keep the pantograph centred with the catenary. This paper specifically addresses the case of a pantograph position control performed by two servovalve controlled, spring centred hydraulic actuators mounted in opposite pair, each equipped with a position transducer for position control and system monitoring. The monitoring system presently implemented in this servocontrol detects the servocontrol failures, but in case the two position transducers provide a conflicting information, it is not always able to sort out which of the two transducers is failed. As a result, a position transducer failure always leads to disabling the tilting function and reducing the train speed, and then to remove and replace the entire pantograph, because the functionality of each individual transducer can only be checked at shop level. An advanced diagnostic system was hence developed 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 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 merits of the presented health management system were assessed running several simulations of a model representing the dynamic response of a train pantograph. These simulations were performed, both in normal and in failed conditions, in order to assess the ability of the implemented advanced diagnostic system to properly identify a failure of one or both position transducers and to avoid false alarms. The transducers health management process described in this paper was first tested simulating different tracks over the whole range of normal operating and environmental conditions, and appropriate limits for the failure detection were established to prevent false alarms. Then, all types of transducers failures and malfunctionings were injected and the ability of the health management system to recognize them was positively assessed. The results of the entire simulation campaign proved the robustness of the proposed transducers health management system and a confidence was hence gained in its ability to detect a transducer failure or malfunctioning with minimum risk of false alarms or missed failures. The implementation of such health management system on a tilting train will thus enable the tilting operation to continue after a failure of a pantograph lateral position sensor, hence allowing the train to maintain its high speed travel for the remainder of the ride. Furthermore, the positive recognition of a transducer failure would greatly ease the maintenance operation, since the failed transducer can be replaced without the need of removing the entire pantograph assembly from the train roof