Multi-Chamber Actuator Using Digital Pump for Position and Velocity Control Applied in Aircraft

This paper presents a multi-chamber hydraulic actuator controlled by digital pumps and on/off valves, in order to improve the efficiency of hydraulic systems applied in aircraft for flight control. Hydraulic positioning systems are used in many different applications, such as mobile machinery, industry and aerospace. In aircraft, the hydraulic actuators are used at flight control surfaces, cargo doors, steering, landing gear and so one. However, the massive use of resistive control techniques, which throttles the passages of the hydraulic fluid, associated with internal leakage of the hydraulic components, make these systems low energy efficient. In order to improve their energy efficiency, digital hydraulics emerges as a promising solution mainly for mobile applications. In this paper a hydraulic positioning system for aircraft control surfaces using a multi-chamber actuator controlled by on/off valves and a digital pump is proposed. The use of a digital pump with three fixed displacement pumps can provide eight different volumetric displacement outputs. The multi-chamber actuator with four areas can operate in two different modes, normal or regenerative, resulting in six different equivalent areas. The regenerative mode allows the actuator to achieve higher actuation velocity values with smaller pumps. These equivalent areas combined with the different supplied flow rates can deliver 43 different discrete output velocity values for the actuator, in steady-state. For the system dynamic analyses, three mathematical simulation models were developed using MATLAB/Simulink and Hopsan, one for the digital system, and two for the conventional solutions applied in aircraft (Servo Hydraulic Actuators (SHA) and Electro Hydrostatic Actuator (EHA)). The simulation results demonstrate that the digital actuator can achieve, for position control, a maximum position error, in a steady-state, of 0.7 mm. From the energy consumption point of view, the digital circuit consumes 31 times less energy when compared with the SHA and 1.7 when compared to the EHA, resulting in an energy efficiency of 54%.