Patent Publication Number: US-9896966-B2

Title: Tie rod for a gas turbine engine

Description:
BACKGROUND 
     The present disclosure relates to a gas turbine engine, and more particularly to a static structure thereof. 
     In a turbine section of a gas turbine engine, tie rods typically extend between an annular outer case structure and an annular inner case structure of a core path through which hot core exhaust gases are communicated. Each tie rod is often shielded by a respective aerodynamically shaped fairing. 
     The tie rods may be relatively thick to withstand engine vibrations and other load-bearing forces. Enlargement of the tie rods require relatively larger fairings which may result in relatively greater resistance to the hot core exhaust gasflow. 
     SUMMARY 
     A tie rod according to an exemplary aspect of the present disclosure includes a gusset which extends between a rod and a base. 
     A static structure of a gas turbine engine according to an exemplary aspect of the present disclosure includes a multiple of tie rods which radially extend between an annular inner turbine exhaust case and an annular outer turbine exhaust case, at least one of the multiple of tie rods include a gusset. 
     A method of assembling a multiple of tie rods into a gas turbine engine according to an exemplary aspect of the present disclosure includes positing a vane structure within an annular outer turbine exhaust case; inserting a tie rod into at least one vane of the vane structure, the tie rod includes a gusset between a base and a rod which extends from the base; securing the tie rod to an annular inner turbine exhaust case; threading a tie rod nut to an end section of the tie rod to a predefined torque; and securing the tie rod nut to the annular inner turbine exhaust case. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
         FIG. 1  is a schematic cross-section of a gas turbine engine; 
         FIG. 2  is an enlarged sectional view of a Turbine section of the gas turbine engine; 
         FIG. 3  is an exploded view a mid-turbine case structure of the turbine section; 
         FIG. 4  is a rear perspective view of a vane structure located within the annular outer turbine exhaust case; 
         FIG. 5  is a rear perspective view of a multiple of tie rods inserted within the vane structure; 
         FIG. 6  is a rear perspective view of an annular inner turbine exhaust case located within the vane structure; 
         FIG. 7  is a rear perspective view of a multiple of tie rod nuts each threaded to an end section of each of the multiple of tie rods; 
         FIG. 8  is a front perspective view of a mid-turbine case structure of the gas turbine engine static structure; 
         FIG. 9  is a side view of a tie rod according to one non-limiting embodiment; 
         FIG. 10  is a front view of the tie rod of  FIG. 9 ; 
         FIG. 11  is a top view of the tie rod of  FIG. 9 ; and 
         FIG. 12  is a perspective view of another tie rod according to another non-limiting embodiment; 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a gas turbine engine  20 . The gas turbine engine  20  is disclosed herein as a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . Alternative engines might include an augmentor section (not shown) among other systems or features. The fan section  22  drives air along a bypass flowpath while the compressor section  24  drives air along a core flowpath for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines. 
     The engine  20  generally includes a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36  via several bearing systems  38 . It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided. 
     The low speed spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a low pressure compressor  44  and a low pressure turbine  46 . The inner shaft  40  is connected to the fan  42  through a geared architecture  48  to drive the fan  42  at a lower speed than the low speed spool  30 . The high speed spool  32  includes an outer shaft  50  that interconnects a high pressure compressor  52  and high pressure turbine  54 . A combustor  56  is arranged between the high pressure compressor  52  and the high pressure turbine  54 . The inner shaft  40  and the outer shaft  50  are concentric and rotate about the engine central longitudinal axis A which is collinear with their longitudinal axes. 
     The core airflow is compressed by the low pressure compressor  44  then the high pressure compressor  52 , mixed and burned with fuel in the combustor  56 , then expanded over the high pressure turbine  54  and low pressure turbine  46 . The turbines  54 ,  46  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. 
     With reference to  FIG. 2 , the turbine section  28  generally includes static structure  36 T which is disclosed herein as a mid-turbine case of the gas turbine engine  20 . The mid-turbine case static structure includes an annular inner turbine exhaust case  60 , an annular outer turbine exhaust case  62 , a vane structure  64 , a multiple of tie rods  66  and a respective multiple of tie rod nuts  68  (also shown in  FIG. 3 ). The annular inner turbine exhaust case  62  typically supports a bearing system  38  as well as other components such as seal cartridge structures within which the inner and outer shafts  40 ,  50  rotate. 
     Each of the tie rods  66  are fastened to the annular inner turbine exhaust case  60  through a multiple of fasteners  70  such that the annular outer turbine exhaust case  62  is spaced relative thereto. Each of the tie rods  66  are fastened to the annular outer turbine exhaust case  62  by the respective tie rod nut  68  which is threaded via an inner diameter thread  72  to an outer diameter thread  74  of an end section  76  of each tie rod  66 . 
     Each tie rod nut  68  is then secured to the annular outer turbine exhaust case  62  with one or more fasteners  78  which extend thru “phone dial” holes  80  in the tie rod nut  68 . That is, the multiple of holes  80  are arrayed in a circle within a flange  81  of each tie rod nut  68 . The tie rod nut  68  is threaded to the end section  76  to a predefined torque, such that at least one of the “phone dial” holes  80  become aligned with respective apertures  82  in the annular outer turbine exhaust case  62  into which fasteners  78  (two shown in  FIG. 2 ) are received to lock the tie rod nut  68  into position. 
     In a method of assembly, the vane structure  64  is located within the annular outer turbine exhaust case  62  ( FIG. 4 ). Each of the multiple of tie rods  66  are then inserted into a multiple of vanes  88  of the vane structure  64  ( FIG. 5 ). It should be appreciated that each vane  88  of the disclosed multiple need not include a tie rod  66 . It should also be appreciated that the vane structure  64  may be manufactured of a multiple of sections or a single integral component which minimizes flow path leakage. 
     The annular inner turbine exhaust case  60  is then inserted into the vane structure  64  and the multiple of tie rods  66  are secured thereto by the fasteners  70  which may be inserted from an inner diameter of the annular inner turbine exhaust case  60 . The tie rod nut  68  is then threaded to the end section  76  of each of the multiple of tie rods  66  to the predefined torque to center the annular inner turbine exhaust case  60  therein along axis A ( FIG. 8 ). The “phone dial” holes  80  are aligned with the respective apertures  82  in the annular outer turbine exhaust case  62  to receive the fasteners  78  and thereby lock the tie rod nut  68  into position. 
     With reference to  FIG. 9 , each tie rod  66  generally includes a base  90 , a hollow rod  92  which extends therefrom to the threaded end section  76  and at least one gusset  94  which extends between the base  90  and the hollow rod  92  ( FIGS. 10 and 11 ). The hollow rod  92  may provide a secondary cooling air flow path therethrough. The tie rod  66  may be manufactured of a high temperature alloy such as Inco 718. 
     In the disclosed non-limiting embodiment, the gusset  94  may be generally triangular in shape to facilitate insertion into a respective vane  88  in the assembly method described above. That is, the gusset  94  is aligned generally fore and aft along the engine axis A with respect to the airfoils shaped vane  88 . The gusset  94  further facilitates relatively smaller fairings to minimize resistance to the flow of the hot core exhaust gases through the turbine section yet minimize bending and dishing of the annular inner turbine exhaust case  60 . 
     With reference to  FIG. 12 , another non-limiting embodiment of a tie rod  66 A is illustrated. The tie rod  66 A includes a gusset  94  with a beam  100  and a web  102 . 
     A large axial pressure load exists across this structure due to higher pressure upstream in the high pressure turbine (HPT) versus the lower pressures downstream in the low pressure turbine (LPT). The rod gussets provide a truss like structure that more effectively resists this load (and reduces axial deflection) than pure radial spoke like rods. Reducing axial deflection of the inner case limits seal excursions and better centers the bearing rolling elements on their races. The fact that the gussetted rods are removable, accommodates one piece flowpath vane assemblies (reduced gaspath leakage for improved efficiency). 
     A large axial pressure load typically exists across the mid-turbine case due to higher pressure upstream in the high pressure turbine  54  (HPT) versus the lower pressures downstream in the low pressure turbine  46  (LPT). The gussets  94  provide a truss like structure that more effectively resists this load (and reduces axial deflection) than conventional radial spoke like rods. Reductions in the axial deflection of the annular inner turbine exhaust case  60  limits seal excursions and better centers bearing rolling elements on their races of the bearing system  38 . The tie rods  66  are removable to also accommodate a one piece flowpath vane structure  64  which provides for a reduced gaspath leakage and improved efficiency. 
     The tie rods  66  also resist out-of-plane bearing loads such as a blade-out unbalance condition, though the other forces may also apply which, for example, may be present if the engine architecture does not allow a bearing to be centered in the plane of the tie rod  66  or if the tie rod  66  straddles a bearing compartment that contains multiple bearing systems  38 . 
     It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting. 
     It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. 
     Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure. 
     The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.