Fuel flow limiting device for overspeed and overtemperature control

Claim 1

In a fuel control for a gas turbine engine of the type having: a housing with a main fuel supply conduit; a metering valve for controlling fuel flow in the conduit; a valve driving mechanism operatively connected to the metering valve for positioning the metering valve in accordance with a control signal applied thereto; an electronic computer, responsive to a plurality of engine parameters, operatively connected to the valve driving mechanism for applying the control signal thereto; a lever member for setting a requested speed; a transducer operatively connected to the lever member for directing a requested speed signal to the computer; a drive shaft operatively connected to the lever member for rotation in response to lever member displacements; engagement means to drivingly interconnect the metering valve and the drive shaft such that rotation of the drive shaft positions the metering valve; the improvement comprising: a flow limiting valve mounted in the main fuel supply conduit downstream of the main fuel metering valve; an actuation cylinder disposed in the housing and connected to the flow limiting valve for the positioning thereof; a solenoid operated valve fluidly connected to the actuation cylinder to alternately communicate high and low fuel pressure in the housing for modulating the pressure therein; and a solenoid control circuit adapted to sense engine overspeed and overtemperature error signals for applying pulses having a duty cycle commensurate with the magnitude of the error signals to the solenoid operated valve such that the actuation cylinder positions the flow limiting valve to restrict fuel flow.