Optimal control for a gas turbine engine

In a gas turbine engine of the turbofan type which includes a variable pitch fan, a variable area fan exhaust nozzle, and a fuel flow valve, an improved control system including a core engine speed sensor, a fan speed sensor, means for providing an indication of actual engine thrust and means for providing an indication of actual turbine inlet temperature, the improvement comprising:

• means for generating control signals representative of nominal values of the fuel flow, fan pitch and fan exhaust nozzle area for providing a desired level of engine performance;
• means for receiving said control signals and for varying the fuel flow, fan pitch and fan exhaust nozzle area in response thereto;
• means for generating signals representative of rated values of core engine speed, fan speed, engine thrust and turbine inlet temperature corresponding to the desired level of engine performance;
• comparison means for comparing the rated core engine speed, fan speed, engine thrust and turbine inlet temperature signals respectively with signals representative of the actual core engine speed, fan speed, engine thrust and turbine inlet temperature and for generating difference signals;
• feedback generator means for receiving said difference signals and for generating fuel flow, fan pitch and fan exhaust nozzle area feedback signals, each of said feedback signals being a function of all of said difference signals;
• and
• means for receiving said feedback signals and for modifying said control signals in response thereto.

A method of controlling a gas turbine engine comprising the steps of:

• (a) generating engine control signals for providing a desired level of engine performance;
• (b) transmitting said control signals to means for varying engine control variables;
• (c) generating signals representative of rated values of engine output variables for the desired level of engine performance;
• (d) generating signals representative of the actual values of engine output variables;
• (e) comparing said rated engine output variable signals with said actual engine output variable signals to produce difference signals;
• (f) weighing said difference signals relative to each other in response to ambient engine operating conditions;
• (g) generating feedback signals for each of said control variable as a function of a plurality of said difference signals;
• and
• (h) modifying said engine control signals in accordance with said feedback signals.

An improved gas turbine engine control system including:

• means for generating engine control signals for maintaining a desired level of engine performance;
• means for receiving said engine control signals and for varying engine control variables in response thereto;
• means for generating signals representative of the actual values of engine output variables;
• means for generating signals representative of rated values of engine output variables for the desired level of engine performance;
• and
• comparison means for comparing the rated engine output variable signals with the corresponding actual engine output variable signals and for generating difference signals
• wherein the improvement comprises:
• feedback generator means for receiving said difference signals and for generating a feedback signal for each of said control variables, each feedback signal being a function of a plurality of said difference signals;
• means responsive to a selected mode of engine operation for tailoring said feedback signals to maintain control of the engine about a particular operating point with said tailoring being accomplished by weighing said difference signals relative to each other;
• and
• means for receiving said feedback signals and for modifying said engine control signals in response thereto.

A method of controlling a gas turbine engine comprising the steps of:

• (a) generating engine control signals for providing a desired level of engine performance;
• (b) transmitting said control signals to means for varying engine control variables;
• (c) generating signals representative of rated values of engine output variables for the desired level of engine performance;
• (d) generating signals representative of the actual values of engine output variables;
• (e) comparing said rated engine output variable signals with said actual engine output variable signals to produce difference signals;
• (f) weighing said difference signals relative to each other in response to the selected mode of engine operation;
• (g) generating feedback signals for each of said control variables as a function of a plurality of said difference signals;
• and
• (h) modifying said engine control signals in accordance with said feedback signals.