United Technologies Corporation

Douglas A Parsons

Mark A Johnston

John E Games

Gerald L DePardo

A engine control system for helicopters and the like in which free turbine speed is isochronously controlled by a more robust control system having increased bandwidth due to loop architecture and filter implementation accomplished via closed loop control. Dual notch (feedback compensation) is used with design forward path compensation, including variable lead/position of the lead, variable gain and implementation of integrator/proportional. Superior transient control is achieved by the use of a multi-loop governing design using different error compensations when on 'NF' loop control and when not on 'NF' loop control, and with 'bumpless' inner loop reference by the combination of compensation switching and re-initialization of a common integrator. Parallel select logic with dynamic compensation is used separating the system control loops and the selection process of the controlling functions, as they pertain to the application of control loops designed form small signal stability to large transients. A torque loop limitation as a direct function of the speed loop gains provides a predetermined limit to the governed speed excursion in the event of an in-range failure of the torque signal, or an unannounced fail fix on one engine or system of the twin engine application.

Control system for gas turbine helicopter engines and the like

Parameters indicative of gas turbine engine operational characteristics are sensed and the signals processed to derive further operational characteristic information therefrom, each information signal being compared in a subroutine to a corresponding threshold signal for exceedence thereof, the magnitude of each threshold signal being indicative of incipiency of compressor stall, a counter being incremented in the subroutine upon any threshold exceedence occurrence, the amount of counter increment depending on the ability of each information signal to predict the incipiency of stall, the higher the counter value the greater the stall incipiency. The counter is decremented during each subroutine execution, the counter value during the current subroutine execution being compared to that of the previous subroutine execution to determine the direction of stall incipiency. The counter is utilized as a bias signal to an engine acceleration schedule to vary the rate of acceleration as the counter is varied.

Gas turbine stall/surge identification and recovery

The existence of autorotation of a load (e.g., a helicopter rotor system) coupled to the free turbine of a gas turbine engine is determined and a signal indicative thereof enables an integrator which, upon autorotation, integrates rate-based recovery anticipation provided thereto, the integrator output providing a time-composite bias signal to the main control portion of the engine fuel control to increase the speed of the gas generator of the engine in anticipation of rotor reengagement with the free turbine. The amount of recovery error is determined from the rotor speed error and is multiplied with the integrator output, the product being fed, upon completion of autorotation recovery, to the integrator input whose output now provides a controlled removal of the bias signal from the main control portion so as to minimize transients induced therein.

Helicopter autorotation detection and recovery

The speed of the gas generator of a gas turbine engine is measured and summed with the rate of change of the gas generator speed and the sum is input to a schedule which outputs desired engine acceleration as a function of gas generator speed, the input thereby providing an anticipation to the schedule output so as to result in a dynamic shift of the schedule. In an exemplary embodiment of the invention in a helicopter fuel control, the amount of anticipation provided by the schedule input allows the fuel control to accurately control the engine to the desired acceleration schedule.

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Enfield, CT, United States of America

Douglas A Parsons