Power plant variable geometry control

Claim 1

Means for controlling the variable geometry of gas turbine engine having a mechanism for varying the power turbine stator geometry or the gas generator exhaust nozzle geometry and having a fuel control for regulating the flow of fuel thereto, comprising: actuating means connected to said mechanism for changing the variable geometry; first computing means for selecting the higher of two pressure signals fed thereto; second computing means for selecting the lower of two pressure signals fed thereto, the output of said second computing means being fed to said first computing means as one of said two pressure signals; feedback valve means responsive to the position of said actuating means for metering hydraulic fluid pressure to said second computing means as one of said two pressure signals; a first control valve responsive to the position of a servovalve for metering hydraulic fluid; a second control valve responsive to the speed error between the actual corrected speed and the desired corrected speed of the gas turbine engine for metering hydraulic fluid, said second control valve disposed in series with said first control valve, the fluid pressure between said control valves being fed to said second computing means as the other of said two pressure signals; normally open solenoid valve means for metering hydraulic fluid pressure to said first computing means as the other of said two pressure signals, said solenoid valve closing in response to deceleration of the gas turbine engine; and servovalve means responsive to a function of the acceleration fuel flow to the gas turbine engine and to a signal, which is the higher of the two pressure signals, from said first computing means for controlling the position of said actuating means.