Abstract
Highly detailed computer models are required for design and development of modern flight control systems, capable of emulating with high accuracy the behaviour of on-board equipment. At the same time, different simplified models are needed, specifically intended for operations such as the optimization of preliminary design and the development of diagnostic or prognostic strategies. These simplified models are required to combine sufficient levels of accuracy and reliability with reduced computational costs, to minimize the computational burden associated with prognostic and optimization algorithms. In this work, we focus on electro-hydraulic actuators, since they are critical subsystems in terms of safety and availability of the aircraft. Advanced monitoring and prognostic algorithms require new numerical models, combining an acceptable computational effort with a satisfying ability to simulate their performance and dynamics. To this purpose, this paper proposes a new simplified numerical model of the servovalve fluid-dynamic behaviour. This numerical algorithm, based on a very compact semi-empirical formulation, is intended to take into account in a simplified but sufficiently accurate way several typical effects related to the SV spool geometry and the operating conditions. To evaluate the approximations introduced by this model into a system-level simulation, it has been integrated into a dedicated numerical model simulating a simple electrohydraulic on-board actuator, and compared with a higher fidelity servovalve model.
Highlights
In this work, we consider a typical electrohydraulic servoactuator architecture
It has been shown that strong linearity assumptions on the spool operation may noticeably degrade the accuracy of the whole servoactuator model in some operating conditions [5, 6]
In zero-flow conditions, each control port absolute pressure is close to the supply or return pressure when the corresponding passageway is completely opened
Summary
The valve spool displacement xS rules the opening and closing of the four passageways, each characterized by its overlaps or underlap, to connect each control port either to the supply or return port This allows to provide the desired relationship between flow and absolute pressure for each control port (P1 and P2), for given oil characteristics [5,6,7,8]. Most common simplified servo-valve models available in literature simulate the fluiddynamic behaviour through a linearized approach, based on two coefficients that can be measured experimentally: the pressure gain (GP) and the flow gain (GQ) [7]. The most evident weakness of this approach is the inability to evaluate the pressure saturation due to the limited supply value, and the actual stall conditions of the motor element
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