Abstract:
The present invention relates to a support structure and a method for assembling a support structure in a turbine or compressor engine for rotatably supporting a rotor member in a stator member. The support structure includes an inner ring, an outer ring and a plurality of struts which extend radially between the inner ring and the outer ring. The inner ring has integrated portions projecting in the direction of the struts and forming end connections for the struts. The integrated end connecting portions of the inner ring are together with the ring made by a metal alloy having initially oversized cross sectional dimensions relative to the cross sectional dimensions of corresponding strut, followed by working at least one lateral surface for removing material. The purpose is to achieve final dimensions and position to conform to the cross sectional dimensions and correct position of each corresponding strut.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present application is a continuation of International Application No. PCT/SE2004/000824, filed May 27, 2004, which is incorporated by reference. 
     
    
       [0002]     The present invention relates to a support structure in a turbine or compressor device. The invention further relates to a method for assembling such a support structure.  
         [0003]     The term turbine device is intended to mean a machine in which the energy present in a flowing fluid (gas, vapor or liquid) is converted into rotational energy by means of blades or vanes. The term compressor device is intended to mean a machine having an inverse function, that is to say rotational energy is converted by means of blades or vanes into kinetic energy in a fluid. The device comprises a rotor and a stator interacting therewith.  
         [0004]     In the following, the device comprises a turbine device, which in turn forms part of a gas turbine. This is a preferred but in no way restrictive application of the invention. The term gas turbine is intended to mean a unit which at least comprises a turbine wheel and a compressor wheel driven by the former, together with a combustion chamber. Gas turbines are used, for example, as engines for vehicles and aircraft, as prime movers for vessels and in power stations for generating electricity.  
         [0005]     The rotor may take the form both of a radial rotor and an axial rotor.  
         [0006]     The term elongate rotor member is here intended to mean the rotor shaft and any further components intended to rotate on the rotor shaft, such as bearings and spacers between the bearings and gears.  
         [0007]     For the support of the rotor member in the stator member of a turbine or compressor and for allowing the high speed flow of gas through the engine the support structure includes a number of radially inner and outer support rings, the inner and outer rings being interconnected by means of radially extending struts. Down stream relative to at least some of the struts flap airfoils are positioned, see for example U.S. Pat. No. 6,619,916, and the interrelationship between the struts and corresponding flaps necessiates a thorough positioning of the struts. For different reasons the inner and outer support rings are preferably manufactured as separate components by casting metal alloy. The struts can be made by metal alloy extrusion or by forming a sheet metal as separate components which are assembled by welding or soldering at each ends with the inner ring and the outer ring. However casting involves normally high tolerances and problems with the accurate positioning of the struts relative to the flap airfoils.  
         [0008]     It is desirable to provide a support structure which provides an accurate positioning of the struts between the inner and outer ring.  
         [0009]     According to an aspect of the present invention, a support structure in a turbine or compressor engine for rotatably supporting a rotor member in a stator member includes an inner ring, an outer ring, and a plurality of struts which extend radially between the inner ring and the outer ring, at least one of the rings having integrated portions projecting in a direction of the struts and forming end connections for the struts, wherein the end connecting portions of the at least one of the rings are together with the ring made by casting a metal alloy having initially oversized cross sectional dimensions relative to the cross sectional dimensions of a corresponding strut and having at least one lateral surface worked for removing material so as to achieve final dimensions and positioning to conform to the cross sectional dimensions and positioning of each corresponding strut.  
         [0010]     According to another aspect of the present invention, a method for assembling a support structure in a turbine or compressor engine for rotatably supporting a rotor member in a stator member is provided, the support structure including an inner ring, an outer ring and a plurality of struts which extend radially between the inner ring and the outer ring, at least one of the rings having integrated portions projecting in a direction of the struts and forming end connecting portions for the struts. According to the method, the end connecting portions of the at least one of the rings are cast together with the ring using a metal alloy having initially oversized cross sectional dimensions relative to the cross sectional dimensions of corresponding strut. At least one lateral surface is worked for removing material, so as to achieve final dimensions and positioning to conform to the cross sectional dimensions and positioning of each corresponding strut.  
         [0011]     By forming an integrated over-sized projecting portion of the inner and/or outer ring and determining the accurate position of each strut where-after the projecting portion can be finally determined as to its position and dimensions by material working off part of each projection. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The invention will be described in more detail below with reference to the embodiment as shown in the drawings attached.  
         [0013]      FIG. 1  is a schematic broken view of a gas turbine engine which can be provided with a support structure according to the present invention,  
         [0014]      FIG. 2  is a perspective view of the support structure,  
         [0015]      FIG. 3  is an end view of the support structure,  
         [0016]      FIG. 4  and  5  are enlarged broken cross sectional views of portions of the support structure,  
         [0017]      FIG. 6  is a schematic view of an arrangement for accomplishment of the method according to the present invention,  
         [0018]      FIG. 7  is a perspective view of a stub end portion forming part of an inner ring of the support structure of the present invention and  
         [0019]      FIG. 8  is a cross sectional view of a strut and a flap airfoil arranged downstream of the strut. 
     
    
     DETAILED DESCRIPTION  
       [0020]      FIG. 1  shows a gas turbine having a stator  1  and a rotor  2  rotatably joumalled in the stator. The stator consists of and encloses different units know per se such as a fan unit  3  consisting of a number of fans, a compressor unit  4  consisting of a number of compressor stages, a combustion unit  5  and a turbine unit  6  consisting of a number of turbines. The stator comprises a tubular housing  7  having an inlet end  8  and an outlet end  9 . The stator further includes support structures  10 ,  11  for supporting the rotor  2 . For example the support structure at the inlet end can form an inlet portion  10  and an outlet portion  11  at the outlet end  9 . The two support structures  10 ,  11  are combined with further support structures, all support structures supporting bearings for the rotational shaft  12  of the rotor.  
         [0021]     Further with reference to  FIG. 2  and  3  the support structure according to the present invention will be described forming an inlet portion  10  in the shown embodiment and consists mainly of a radially inner support ring  13  and a radially outer support ring  14  interconnected by means of a plurality of radially extending struts  15 . The inner ring  13 , the outer ring  14  and each strut  15  are separately manufactured as single units.  FIG. 3  shows the separate inner ring  13  having an inner circumferential surface  16  enclosing a through hole  17  and forming a support for a bearing, not shown, for the rotational shaft  12  of the rotor. The inner ring  13  further has an outer circumferential surface  18  having preferably shape of a conical mantle surface, from which a plurality of stub ends  19  project radially outwards, one stub end for each strut  15 . The stub ends form integral projecting portions of the inner ring  13  and also the outer ring  14 .  
         [0022]     It is apparent from the drawings that the inlet portion  10  has a hollow design forming internal ducts or channels,  20 ,  21  ,  22 ,  23 . In the outer ring a duct  20  is formed as an annular duct being closed in the mounted state against a tubular portion  23  of the stator  1  , see  FIG. 1 . Correspondingly the inner ring  13  forms a duct  23  against a circumferential portion of the bearing. The struts  15  and the stub ends  19  projecting from the inner ring  13  and the outer ring  14  form closed ducts  21 ,  22 . The purpose of the duct is to allow heated air to flow through the struts and the inner ring in order to prevent ice to build up on the nose cone  24 , the struts  15  and the hub formed by the inner ring  13 . Also a risk of building up ice on the movable flap air foils  25 , see  FIG. 8 , will be prevented. As a consequence of the differences of heat energy the outer ring  14  will have a higher temperature than the rest of the inlet portion and will expand, contrary to the other parts of the inlet portion, such as the struts and the inner ring, resulting in stresses which all parts of the structure must withstand. By creating the stub ends  19  forming an integral part of the inner and outer rings  13 ,  14 , weld joints will be achieved having sufficiently high tensile strength.  
         [0023]     The inner ring  13  is preferably made as a casting of metal alloys which normally involve tolerances which do not fulfill the high demands of prerequisites for the positioning the struts  15  of the inlet portion  10 . Further a continuous step-less transition between stub ends  19  and the struts is of great importance for the maintaining high demands on aero dynamics. Also low weight is of great importance.  
         [0024]     To meet the above demands the stub ends are according to the present invention manufactured by casting initially to have oversized dimensions as to the transverse dimensions of the stub ends  19 , i.e. transversally to the longitudinal direction of the struts  15 , see dashed lines in  FIG. 4  and  FIG. 5 . By means of the hollow design of the stub ends and struts said parts consist of wall portions  26 ,  27 ,  28 ,  29 , name enclosing wall portions and also, in the example as shown, a transverse partition wall portion  30 , separating the ducts  21  ,  22 . The partition wall portion is shown in the stub ends, but corresponding partition wall portion is present in each strut  15 . The meaning of the expression over-sized dimensions is that said initial transverse dimension a or c, see  FIG. 4  and  5 , exceeds clearly the transverse dimension b of the corresponding strut  15  as seen in a radial plane of the stator relative to the longitudinal axis of the shaft  12  of the rotor  2 .  
         [0025]     After finalizing the casting operation the cast part of the inlet portion, i.e. the inner ring  FIG. 13  and possibly also the outer ring  14  will be subject to one or two further dimensioning operation by means of working material in order to adapt the shape and dimensions of the stub ends  19  to the shape and dimensions of each separate strut  15  in such way so that there will be a continuous and step-less transition between the end edges  31  of the stub ends and the corresponding end edges  33 ,  34  of the struts  15  and further with a highly accurate positioning of the struts  15  in the inlet portion  10  and relative to the corresponding flap  25 . It is most important that relative positioning of the struts will be arranged with small tolerances to avoid steps between the struts and the flaps which can create exitations propagating to the fan behind the flaps causing a vane crash.  
         [0026]      FIG. 4  shows a reduction of the transverse dimension and adaption to correct position of the strut by removing material from the opposite surfaces  35 ,  36  of a stub end  19  and also from opposite inner surfaces  37 ,  38  of a stub end. Possibly, the material from the inner surfaces can be omitted.  
         [0027]      FIG. 5  shows an extreme situation having a worst possible tolerance result with respect to especially the positioning of the strut. A relatively large amount of material will be removed on one of the outer sides  36  of the wall  27  of the stub end and the inner side  37  of the opposite wall  26  of the stub end. The removal of the material will preferably be made by for example Electro Discharge Machining (EDM) or Electrochemical Machining (ECM) or milling. EDM uses a pulsed direct current in a non-conductive liquid for spark formation, machining the walls of the struts. ECM utilizes electrical energy for creating a chemical reaction dissolving metal from the strut into an electrolytical solution.  
         [0028]      FIG. 6  shows schematically an arrangement in which the inner ring  13  is mounted in a fixture  39  for removing of material from the wall surfaces of the stub ends  19  by means of a computer controlled working machine  40 , such as a milling machine or an EDM apparatus. The machine operates on the basis of input data, including coordinates for each final surface positioning until the final result is achieved for all wall surfaces which avoid from the input data, on a stub end, proceeding with next stub end etc. until all stub ends have been operated on. The struts  15  are correctly positioned and provisionally attached to the stub ends  19  before the removal of material, alternatively the struts are positioned after the material removing operation and a continuous weld are arranged along the whole joint between the end edges  31 - 34  of each stub end  19  and corresponding strut  15 . In the outer ends of the struts corresponding joints are welded between the stub ends  41  projecting inwards from the outer ring  14 . This ring  14  can normally be manufactured with low tolerances for example by ECM, involving that no over-sizing followed by material working is necessary. However, principally the same method according to present invention can also be applied to the stub ends of the outer ring  14 .  
         [0029]      FIG. 8  illustrates the relative positioning of a flap  25  behind one of the struts  15 . The flaps  25  are attached to the structure of the stator  1  separately from the struts and are in the example as shown pivotally journalled relative to an axis  42  which extends radially. It is further apparent that the struts and the flap are not symmetrically shaped or positioned, however their positional inter relationship must be arranged with very low tolerances.  
         [0030]     In the present application, the use of terms such as “including” is open-ended and is intended to have the same meaning as terms such as “comprising” and not preclude the presence of other structure, material, or acts. Similarly, though the use of terms such as “can” or “may” is intended to be open-ended and to reflect that structure, material, or acts are not necessary, the failure to use such terms is not intended to reflect that structure, material, or acts are essential. To the extent that structure, material, or acts are presently considered to be essential, they are identified as such.  
         [0031]     Although the invention has been shown and described with respect to a preferred embodiment thereof it should be understood by those skilled in the art that other various changes and omissions in the form and detail of the invention may be made without departing from the scope thereof.