Low-cost frangible cable for gas turbine engine

#The present invention relates generally to an automatic safety system for avoidance of an over-speed condition in the event of a rotor shaft failure of a gas turbine engine, and more particularly, to an improved emergency fuel shut-off system for a gas turbine engine.

#An aircraft gas turbine engine requires an automatic mechanism to shut it down should any of the rotor shafts break, which can result in a turbine over-speed condition and possible disc burst. In an aircraft engine, failure of the low-pressure turbine shaft (which is relatively less stiff and strong than the high-speed rotor shaft) for example, and the resultant uncontrolled speed increase of the driving side (the low pressure turbine) of the low-pressure turbine shaft, can lead to destruction of the engine and damage to the aircraft, thereby resulting a considerable danger to persons and property. Emergency engine shutdown is required and is typically accomplished by shutting down the fuel supply to the fuel nozzles of the engine. In gas turbine engines various devices for the mechanical or electronic detection of shaft failure and for the subsequent interruption of the fuel supply to avoid or control a dangerous over-speed condition, are well known. Generally, the known electronic safety systems of gas turbine engines are disadvantageous in that the time delay until shut off of the fuel supply is relatively long. High costs are also incurred by the required cooling or heat shielding of the sensors and electrical connections situated in the hot zone of the rotor shafts. The known mechanical shut-off systems conventionally employ, for example, a reference shaft co-axially associated with a turbine shaft, and connected to the driven end thereof. In the event of shaft failure the resultant rotation of the turbine shaft relative to the reference shaft, is used to mechanically actuate the fuel valve. This type of mechanical system also requires a relatively long corresponding time delay and results in more difficulties in the design and assembly of the engine.

#Accordingly, there is a need to provide an improved emergency fuel shut-off system for gas turbine engines in the event of a shaft failure.

#Reference is now made to the accompanying drawings depicting aspects of the present invention, in which:

#FIG. 1 is a schematic cross-sectional view of a turbofan gas turbine engine as an example illustrating an application of the present invention;

#FIG. 2 is a schematic illustration showing an emergency fuel shut-off system for a gas turbine engine, incorporating one embodiment of the present invention illustrated in the engine of FIG. 1;

#Referring to FIG. 1, a gas turbine engine incorporating an embodiment of the present invention is presented as an example of the application of the present invention and includes a housing 10, a core casing 13, a low pressure rotor assembly seen generally at 12 which includes a rotor shaft (referred to as N1 shaft 15 hereinafter) interconnecting a fan assembly 14, a low pressure compressor assembly 16 and a low pressure turbine assembly 18, and a high pressure rotor assembly seen generally at 20 which includes a rotor shaft (referred to as N2 shaft 25 hereinafter) interconnecting a high pressure compressor assembly 22 and a high pressure turbine assembly 24. The core casing 13 surrounds the low and high pressure rotor assemblies 12 and 20 in order to define a main fluid path (not indicated) therethrough, including a chamber 26 containing and surrounding a combustor 28. An auxiliary gear box (referred to as an AGB 30 hereinafter) is attached to the housing 10 and is drivingly connected to the N2 shaft 25 through a tower shaft 32. A fuel control unit (referred to as an FCU 34 hereinafter), for example, is connected to and driven by the AGB 30 to provide a fuel supply through a fuel passage (not shown) and a plurality of fuel nozzles 36, into the combustor 28 for combustion during engine operation.

#Each of the N1 and N2 shafts 15, 25 has a driving side which is the rear end thereof including the respective low and high turbine assemblies 18, 24, and a driven side which is the front end thereof including the respective fan assemblies 14 with low pressure compressor assembly 16 and high pressure compressor assembly 22. If one of the N1 and N2 shafts 15, 25 fails between the driving and driven sides thereof, the rotational speed of the corresponding one of the turbine assemblies 18, 24 will rapidly increase beyond control because of the sudden loss of torque load. In order to prevent the over-speed of the turbine assemblies in the event of a rotor shaft failure, an emergency fuel shut-off system of the present invention is provided.

#As an embodiment of the present invention the emergency fuel shut-off system in FIG. 1 is only related to the N1 shaft 15 because the N2 shaft 25 is relatively stiffer and stronger than the N1 shaft 15 and is less likely to break. Nevertherless, it should be understood that the emergency fuel shut-off of the present invention is equally applicable to the N2 shaft 25.