22nd Congress of International Council of the Aeronautical Sciences, Harrogate, UK, 28 August - 1st September, 2000
Paper ICAS 2000-6.3.3

FLOW CONTROL ELECTRO-HYDRAULIC SERVO VALVE ASSEMBLY WITH IN-BUILT AUTOMATIC FAILURE DETECTION AND COMPENSATION

J. J. Álvarez García
Industria de Turbopropulsores, S.A.

Keywords: control, electro-hydraulic servo valve, automatic failure detection

The main contribution to the overall critical failure rate of an engine control system based on a dual lane digital electronic controller may be attributed to the actuation system. It is usual practice to design the control system such that reversionary or alternative control actions may be introduced in the event of actuator failure. These actions protect the engine from major damage but usually impose a severe restriction in engine modulation and may also involve a quite complex logic and therefore be inherently untrustworthy. An accepted approach to mitigate these limitations consists in providing redundancy of the weakest point in the actuation system (normally the electro-hydraulic servo valve driving the actuation piston) such that control may be transferred from the failed to the operative component and a similar engine response may be attained by the alternative control. This paper describes an actuation system, following this approach, which does not require failure detection by the digital electronic controller and minimises undesirable transients by reducing failure detection and reaction times as well as preventing excessively large actuator excursions during the transfer process.

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