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

Abstract

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 typically occur for more than 95 per cent of the service time. A research activity was performed to define a variable pressure system which adapts 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 enables the tilting actuation system to save from 25 per cent to 50 per cent power for its operation depending on the severity of the track and on the operating conditions. This power saving is a small fraction (0.3–0.5 per cent) of the maximum traction power, but it is a large saving (10–20 per cent) of theelectrical power required by the train auxiliary systems. The electrical accumulators and the 400 V/50 Hz generators can thus be made smaller reducing the weight and facilitating the components installation. Moreover, lower average heat dissipation and lower average system pressure lead to a reduction of size and weight of the heat exchanger and to lower stresses in the system components. The overall weight reduction on its turn leads to an indirect power saving. This article presents a description of the system and of the control strategy providing the adaptivity of the pump discharge pressure and 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.