Abstract:
Method comprising providing a signal tube extending generally from an engine component disposed on a hot side of a firewall in a gas turbine engine to at least one engine control mechanism disposed on a cool side of the firewall. A fuse in the signal tube is operable responsive to a breach in the signal tube to change from a first condition to a second condition to prevent an over-temperature situation on the cool side of the firewall. The engine control mechanism operates the engine according to a first operating logic utilizing a pressure signal related to a static pressure of a fluid in the signal tube. Loss of the pressure signal causes the engine control mechanism to change to a second operating logic which does not utilize the pressure signal.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to systems and apparatuses for preventing over temperature conditions in a non-fire zone of an aircraft engine, and more specifically to an over temperature fuse in a signal tube. 
         [0002]    In the art, the full authority digital electronics control (FADEC) for a gas turbine engine utilizes a pressure signal from the combustor for control of the engine. Because a broken signal tube could allow hot air to enter the fan compartment, a non-fire zone, the FADEC shuts down the engine in a broken signal tube condition. The broken signal tube could be due to, for example, improper maintenance, tube fatigue, or foreign object damage from the aircraft to the engine. 
         [0003]    For weight considerations, the signal tube is usually not insulated in the non-fire zone. Additionally, many engine programs use composites in the fan and nacelle compartments where leaking high temperature air can do damage. Temperature sensors and shut-off valves could be used to minimize the risk of leakage, but reliability, cost, and weight are negative factors. 
         [0004]    Accordingly, it would be desirable to have a low cost, low weight, detection system that seals off flow of high temperature air in the non-fire zone. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    The above-mentioned need or needs may be met by exemplary embodiments that provide an alternative to engine shut down when a failure occurs in the signal tube and also prevents over-temperature conditions in the non-fire zone. 
         [0006]    In an exemplary embodiment, a method includes providing a signal tube extending generally from an engine component disposed on a hot side of a firewall in a gas turbine engine to at least one engine control mechanism disposed on a cool side of the firewall. A first portion of the signal tube is generally disposed on the hot side and a second portion of the signal tube is generally disposed on the cool side. The method includes providing a fuse in the first portion, wherein the signal tube includes a flow path therethrough at least partly defined by a pathway through the fuse. 
         [0007]    In an exemplary embodiment, a method includes providing at least one engine control mechanism disposed on a cool side of a firewall in a gas turbine engine, wherein the engine control mechanism is operative to selectively control the gas turbine engine according to a first operating logic or a second operating logic, wherein the first operating logic utilizes a pressure signal, and wherein the second operating logic does not utilize the pressure signal. The method includes providing a signal tube extending generally from an engine component disposed on a hot side of the firewall in a gas turbine engine to the at least one engine control mechanism, wherein a first portion of the signal tube is generally disposed on the hot side and a second portion of the signal tube is generally disposed on the cool side. The method further includes providing a fuse in a first portion of a signal tube, wherein the signal tube includes a flow path therethrough at least partly defined by a pathway through the fuse. When the fuse is in a first condition, the pathway is substantially unobstructed such that the signal tube is operable to provide the pressure signal related to a static pressure of a fluid in the signal tube to the at least one engine control mechanism, and when the fuse is in a second condition, the pathway is substantially obstructed so that the signal tube does not provide the pressure signal to the at least one engine control mechanism. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding part of the specification. The invention, however, may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
           [0009]      FIG. 1  is a schematic representation of a prior art system for delivering a pressure signal from a combustor to a full authority digital electronic control (FADEC). 
           [0010]      FIG. 2  is a schematic representation of a system including a fuse in the pressure signal tube. 
           [0011]      FIG. 3  is a partial cross-sectional view of a signal tube showing a fuse in a first condition having an unobstructed pathway therethrough. 
           [0012]      FIG. 4  is a partial cross-sectional view of a signal tube showing a fuse in a second condition wherein the pathway is obstructed. 
           [0013]      FIG. 5  illustrates an alternate fitting for a fuse. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Referring to the drawings wherein identical reference numerals denote the same elements,  FIG. 1  illustrates the general current state of the art. In general terms, an apparatus  10 , such as a gas turbine engine for an aircraft, includes an engine component  12 , such as a combustor. An engine control mechanism  14 , such as a full authority digital electronics control (FADEC), receives information from the engine component  12 . A signal tube  20  generally extends from the component  12  to the control mechanism  14 . The signal tube may be operative, for example, to provide information concerning the pressure in the combustor. In an exemplary embodiment, the signal tube contains generally static fluid, i.e., air. The pressure from the signal tube is input to the engine control or FADEC. Under current operating protocol, a loss of pressure signal to the engine control mechanism initiates an engine shutdown operation. 
         [0015]    As is known in the art, an aircraft engine may employ one or more firewalls  22  to separate a fire-zone (“hot side”) from a non-fire zone (“cool side”). Aviation regulations and other requirements mandate that hot air or other gases should not enter the non-fire zone. For example, some components on the cool side are formed of composite materials that are not rated for high temperature exposure. Also, due to weight considerations, some components disposed on the cool side do not have insulation or other fire protection. In some engine designs, the control mechanism or FADEC is disposed in a non-fire zone. In such designs, the signal tube  20  extends from the combustor on the hot side, to the control mechanism on the cool side. 
         [0016]    Under normal operating conditions, the static fluid in the signal tube  20  is generally at ambient temperature. If a break or other breach (improper connections, etc) were to occur in the signal tube  20 , the usually static fluid contained therein would leak to the surroundings and hot fluid (air) from the combustor would begin flowing in the tube and leaking through the breach. If the break or other breach occurs in the non-fire zone, the leaking fluid would exceed allowable temperature requirements. 
         [0017]    In current operating protocols, if the engine control  14  or FADEC does not receive a pressure signal, due to a break or other breach, the engine is ordered to shut down in order to prevent over-temperature conditions on the cool side. If the break or other breach is due to a problem with the second engine, for example foreign object debris, the automatic shutdown of the remaining engine could create a hazardous condition. Although current safeguards use reinforcement in the nacelle to minimize the risk of a two engine aircraft experiencing engine shut down, an alternative solution is disclosed to add robustness and/or reduce nacelle weight. 
         [0018]    With reference to  FIG. 2 , in an exemplary embodiment, engine  30  includes a signal tube  40  that extends between an engine component  42  on a hot side of a firewall  44  and an engine control mechanism  46  on a cool side of firewall  44 . The exemplary signal tube  40  defines a flow path  48  therein. The signal tube  40  includes at least a first portion  50  extending on the hot side and a second portion  52  extending on the cool side. 
         [0019]    With reference to  FIGS. 2 and 3 , in an exemplary embodiment, the signal tube  40  comprises shaped metal tubing  53  in operative connection with a substantially tubular fuse  54 . Fuse  54  defines an inner pathway  56  forming a part of flow path  48 . In an exemplary embodiment, fuse  54  includes fittings  58  at each end which are adapted to engage fuse  54  with the metal tubing  53 . Many options are available for engaging the fuse with the metal tubing and the fittings  58  are merely exemplary. 
         [0020]    An exemplary fuse  54  includes at least one inner member  60  disposed adjacent the flow path  48 . In an exemplary embodiment, the inner member  60  comprises a hose formed of a temperature-sensitive material. In an exemplary embodiment, the temperature-sensitive material is deformable upon exposure to temperatures greater than a predetermined temperature. For example, an exemplary temperature-sensitive material comprises polytetrafloroethylene (PTFE) which melts upon exposures greater than 600° F. (326° C.). In other exemplary embodiments, the inner member  60  may comprise other temperature-sensitive materials such as brazing compounds. In an exemplary embodiment, the inner member  60  is operative to deform or melt at temperatures less than typical temperatures of air in a combustor. For example, the inner member  60  should melt or deform at temperatures less than about 1000° F. (538° C.). The melting or deforming temperature must be high enough that the inner member  60  remains intact during exposure to the ambient temperatures on the hot side. 
         [0021]    In an exemplary embodiment, fuse  54  includes an outer member  64  substantially enclosing inner member  60 . In an exemplary embodiment, the outer member  64  comprises a metal braid so as to provide reinforcement and flexibility for fuse  54 . In an exemplary embodiment, the outer member  64  is operative to provide information about a condition of the fuse  54 . For example, in an exemplary embodiment, an observer is able to perceive a condition of the fuse  54  upon visual perception of the outer member  64 . Visual perception of the outer member  64  as shown in  FIG. 3  shows that the fuse  54  is in a first condition having an operable pathway therethrough. 
         [0022]    As illustrated in  FIG. 2 , when operable, the signal tube  40  provides a pressure signal to at least one engine control mechanism  46  or FADEC. The signal tube  40  essentially contains static fluid (air) at ambient temperature along the length of flow path  48 . Thus, the second portion  52 , which extends on the cool side of the firewall  44 , is able to meet the imposed temperature requirements. If a break or other breach  70 , shown in phantom, occurs in the signal tube  40 , hot fluid (air) at about 1000° F. (or greater) will flow through the signal tube  40  from the engine component  42 , i.e., combustor, toward the breach. As shown in  FIG. 4 , if the breach is downstream of the fuse  54 , eventually the inner member  60  will be exposed to temperatures greater than the predetermined temperature, i.e., about 600° F. (316° C.). Upon exposure to the elevated temperatures, the temperature-sensitive inner member  60  deforms (melts) and blocks fluid flow through flow path  48 . In an exemplary embodiment, the hot fluid flows through the outer member  64  into the surrounding environment on the hot side of the firewall  44 . The outer member  64  exhibits discoloration or scorching  72  due to the passage of the hot fluid therethrough. Thus, visual inspection of the outer member  64  provides information about the condition of the fuse  54 . In a second condition, the pathway  56  is obstructed. Additionally, some melted material  74  may seep through the metal braid to provide visual information about the condition of the fuse  54 . Because the hot fluid cannot flow to the second portion  52  of the signal tube, but is discharged on the hot side of the firewall, the second portion  52  (on the cool side) does not exceed temperature requirements. 
         [0023]    If a breach  70  occurs in the signal tube  40  and the engine control mechanism does not receive the expected pressure signal, the engine control mechanism  46  is operable to use an alternative operating logic. The alternative operating logic allows engine operation without the pressure input from signal tube  40 . 
         [0024]      FIG. 5  illustrates an alternate fitting  80  that may be employed in exemplary embodiments of fuse  54 . Such a fitting  80  is merely exemplary and other alternative fittings may be used as will be appreciated by those with skill in the art. 
         [0025]    Additionally, the alternate logic may be employed in other situations where the pressure signal is not received. For example, frozen moisture in the signal tube may prevent receipt of the pressure signal. Rather than engine shut down, the engine could be operated under the alternate operating logic. Such alternate logics are currently known and may be utilized within the scope of this disclosure. 
         [0026]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.