Adaptive control for improved efficiency of hydraulic systems for high-speed tilting trains

Tilting trains are a mature technology using either hydraulic or electrical actuation to perform carbody tilting to reduce centrifugal force in curves at passengers level, thereby maintaining a good passenger comfort at enhanced service speed. The hydraulic actuation systems used in tilting trains operate at constant pressure, which is established to allow operation against the maximum loads at minimum ambient temperatures. However, these conditions occur seldom and unnecessary power is dissipated as heat under normal operating conditions that normally occur for more than 95% of the service time. A research activity was performed to define a variable pressure system adapting the discharge pressure as a function of the outside temperature and of the force to be developed by the actuators. In this system, the variable pressure is established as a function of an appropriate control strategy in order to minimize the power losses while keeping the required dynamic performance. This system architecture provides a large power saving; a reduction between 25 and 50% power is obtained depending on the severity of the track and on the operating conditions. Moreover, lower average heat dissipation and lower average system pressure lead to a reduction of the size of the heat exchanger and to lower stresses in the system components. The paper presents a description of the system and of the control strategy providing the adaptivity of the pump discharge pressure, the thermal and performance analyses, the simulations of the system behaviour at different environmental conditions. This is done for a train in service along tracks for which the time histories of train speed, acceleration and tilt angles were known.