Turbofan as turbine engine

Abstract

In a turbofan gas turbine engine, a fan shaft is rotatably mounted and radially supported by a bearing in a bearing support structure-supported from a fixed engine structure by radially frangible bolts and radially extending spokes. The radially inner ends of the radially extending spokes are mounted on a common member that engages the bearing support structure. The radially outer ends of the radially extending spokes are mounted on fixed structure of the engine located radially outwardly of the bearing support structure. The radially extending spokes are held in tension and include a super elastic material to exert a radially inward restoring force on the bearing support structure, subsequent to any radial excursion of at least part of the fan shaft relative to an engine rotational axis (X) following any fracture of the frangible bolts.

What is claimed is: 
     
         1 . A turbofan gas turbine engine comprising a fan mounted on a fan shaft, the fan shaft being normally coaxial with an engine rotational axis, the fan shaft being rotatably mounted and radially supported by a bearing in a bearing support structure, the bearing support structure being supported from a fixed structure of the engine by at least one member, a first end of the at least one member engaging the bearing support structure and a second end of the member being mounted on the fixed structure, the at least one member comprising a super elastic material, the at least one member exerting a radially inward restoring force on the bearing support structure, and hence the fan shaft, subsequent to a radial excursion of at least part of the fan shaft relative to the rotational axis of the engine. 
     
     
         2 . A turbofan gas turbine engine as claimed in  claim 1  wherein the at least one member further comprises at least one generally radially extending member, a radially inner end of the at least one radially extending member being mounted on a common member, the common member engaging the bearing support structure, the radially outer end of the at least one radially extending member being mounted on the fixed structure of the engine located radially outwardly of the bearing support structure, the at least one radially extending member being held in tension, the at least one radially extending member exerting a radially inward restoring force on the bearing support structure, and hence the fan shaft, subsequent to any radial excursion of at least part of the fan shaft relative to the rotational axis of the engine. 
     
     
         3 . A turbofan gas turbine engine as claimed in  claim 2  wherein the at least one radially extending member further comprises a plurality of generally radially extending spokes, the radially inner ends of the radially extending spokes being mounted on a common member, the common member engages the bearing support structure, the radially outer ends of the radially extending spokes being mounted on fixed structure of the engine located radially outwardly of the bearing support structure, the radially extending spokes being held in tension. 
     
     
         4 . A turbofan gas turbine engine as claimed in  claim 3  wherein the radially outer ends of the radially extending spokes are spaced circumferentially from the radially inner ends of the radially extending spokes. 
     
     
         5 . A turbofan gas turbine engine as claimed in  claim 3 , wherein radial gaps are formed between the radially outer ends of the radially extending spokes and the radially outer ends of the corresponding slots in the fixed structure. 
     
     
         6 . A turbofan gas turbine engine as claimed in  claim 2  wherein the at least one radially extending member is selected from the group consisting of at least one disc and at least one cone. 
     
     
         7 . A turbofan gas turbine engine as claimed in  claim 1  wherein the at least one member further comprises at least one generally axially extending member, a first axial end of the at least one axially extending member engaging the bearing support structure, a second axial end of the at least one axially extending member being mounted on the fixed structure of the engine, the at least one axially extending member exerting a radially inward restoring force on the bearing support structure, and hence the fan shaft, subsequent to any radial excursion of at least part of the fan shaft relative to the rotational axis of the engine. 
     
     
         8 . A turbofan gas turbine engine as claimed in  claim 7  wherein the at least one axially extending member comprises at least one drum or at least one beam. 
     
     
         9 . A turbofan gas turbine engine as claimed in  claim 1  wherein the super elastic material comprises a super elastic metal. 
     
     
         10 . A turbofan gas turbine engine as claimed in  claim 9  wherein the super elastic metal comprises a shape memory metal. 
     
     
         11 . A turbofan gas turbine engine as claimed in  claim 10  wherein the shape memory metal comprises Ni—Ti alloy. 
     
     
         12 . A turbofan gas turbine engine as claimed in  claim 9  wherein the super elastic metal comprises Ti—Nb alloy. 
     
     
         13 . A turbofan gas turbine engine as claimed in  claim 9  wherein the super elastic metal is selected from the group consisting of Ti—Ni—Cu, Ti—Ni—Nb, Ti—Ni—Hf, Cu—Zn—Al and Cu—Al—Ni.