Fuel control unit

Abstract: Two turbine engines are connected to a common gear box to drive a common load, such as a helicopter rotor, and circuitry is provided for controlling the two mechanically intercoupled engines in order to provide: (1) individual temperature shutoff for the engines, (2) limitation on the maximum total torque supplied by the two engines to avoid exceeding the power handling capability of the gear box for the associated load, (3) speed control for the engines, and (4) substantially equal sharing of the torque load by the two engines. By suitably combining the signals which require analysis, and supplying a single properly conditioned signal to the fuel control unit of each engine, tight control without oscillation or cycling may be achieved. Notch filtering to avoid reinforcement of mechanical resonances, and a variable response characteristic depending on the magnitude of the error signal may be included in the circuitry. Through the use of the circuitry noted above, and the avoidance of duplicate or conflicting feedback loops, a tighter servo control may be achieved without adverse results such as oscillation or overshoot. The pilot input is both a coarse mechanical input applied to set the fuel control units of both turbine engines to a level above the expected final power output level, and a relatively precise electrical signal which is supplied to the electronic control circuitry which cuts back the fuel supplied by one or both of the fuel control units.