Patent Publication Number: US-5292227-A

Title: Turbine frame

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The preset invention is related to concurrently filed patent application entitled &#34;Turbine Frame&#34; by J. Dawson et al, Ser. No. 07/988,663. 
     The present invention relates generally to gas turbine engines, and, more specifically, to frames therein for supporting bearings and shafts. 
     BACKGROUND OF THE INVENTION 
     Gas turbine engines include one or more rotor shafts supported by bearings which, in turn, are supported by annular frames. The frame includes an annular casing spaced radially outwardly from an annular hub, with a plurality of circumferentially spaced apart struts extending therebetween. The struts may be integrally formed with the casing and hub in a common casting, for example, or may be suitable bolted thereto. In either configuration, the overall frame must have suitable structural rigidity for supporting the rotor shaft to minimize deflections thereof during operation. 
     Furthermore, frames disposed downstream of the engine&#39;s combustor, are, therefore, subject to the hot combustion gases which flow downstream from the combustor and through the engine&#39;s turbine which extracts energy therefrom for rotating the shaft. Since the struts extend radially inwardly from the casing, they necessarily pass through the combustion gases and must, therefore, be suitably protected from the heat thereof. Accordingly, conventional fairings typically surround the struts for providing a barrier against the hot combustion gases, and through which fairings cooling air may be channeled for preventing elevated temperatures of the frame. 
     Such a frame including fairings to protect against the combustion gases, typically referred to as a turbine frame, must, of course, be configured to allow the assembly thereof. In one conventional configuration, the casing, struts, and hub are an integral cast member, and, therefore, each of the fairings must be configured for assembly around each strut. For example, the fairing may be a sheet metal structure having a radial splitline which allows the fairing to be elastically opened for assembly around a respective strut, and then the fairing is suitably joined together at its splitline to complete the assembly. 
     In an alternative configuration, the struts may be integrally joined at one end to ether the casing or the hub, and at its other end bolted to the complementary hub or casing. In this way, the fairing may be an integral hollow member which can be positioned over the free end of the strut prior to joining the strut free end to its respective casing or hub. In such an assembly, provisions must be provided to ensure that the joint between the strut end and the casing or hub provides suitable rigidity to ensure an overall rigid frame to suitably support the rotor shaft. In a typical conventional configuration wherein the strut outer end is bolted to the casing, the casing is an annular member having a plurality of radially extending generally inversely U-shaped slots which receive the strut ends. Conventional expansion bolts extend in generally tangential directions through the spaced apart radial legs defining the U-slot for rigidly joining the strut end to the casing. The expansion bolts provide zero clearance between where they pass through the strut end and the casing to ensure effective transmittal of both compression and tension loads between the strut and the casing. This arrangement allows assembly of the expansion bolts from the exterior of the casing. 
     However, the U-slots themselves provide circumferentially spaced apart discontinuities along the circumference of the casing which interrupt the hoop stress carrying capability of the casing and, therefore, decrease the overall rigidity of the frame. This reduction in rigidity may be minimized by making the strut outer end as small as possible in transverse configuration, with a practical limit being the transverse configuration of the central portion of the strut itself. This relatively small size of the strut outer end also ensures that the fairing surrounding the strut may be made as small as possible since it must be typically assembled over the strut outer end to complete the assembly of the turbine frame. Minimizing the strut, and hence, the fairing, reduces both weight and aerodynamic penalties. 
     Accordingly, it is desirable to have a turbine frame having reduced size struts for reducing the size of the fairing surrounding the strut while also rigidly mounting the strut to both the casing and the hub. In a configuration where the strut is bolted to either the casing or the hub, the joint therebetween should provide suitable rigidity to ensure the overall rigidity of the entire turbine frame for carrying both compression and tension loads through the struts without undesirable deflections of the hub which would affect the proper positioning of the rotor shaft supported thereby. Furthermore, it is also preferable to provide hollow struts to form a common channel through the casing and the hub for channeling air therethrough or for carrying service pipes such as lube oil or scavenge oil pipes into the engine sump located below the hub. This must be done without significantly reducing the overall structural rigidity of the turbine frame due to the required apertures, or interruptions, in either the casing or the hub for carrying the airflow or service pipes therethrough. 
     SUMMARY OF THE INVENTION 
     A turbine frame includes first and second coaxially disposed rings having a plurality of circumferentially spaced apart struts extending therebetween. A plurality of clevises join respective first ends of the struts to the first ring for removably joining the struts thereto. Each of the clevises includes a base removably fixed joined to the first ring, and a pair of legs extending away from the base and spaced apart to define a U-shaped clevis slot receiving the strut first end. The strut first end is removably fixed to the clevis legs by a pair of expansion bolts. The clevis base includes a central aperture aligned with a first port in the first ring for providing access therethrough. The strut first end is disposed in the clevis slot in abutting contact with the first ring through the central aperture of the clevis base for carrying compressive loads directly thereto through the strut. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, in accordance with preferred and exemplary embodiments, together with further objects and advantages thereof, is more particularly described in the following detailed description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a an axial, partly sectional view of a portion of a gas turbine engine showing a turbine frame in accordance with an exemplary embodiment of the present invention. 
     FIG. 2 is a transverse view of the turbine frame illustrated in FIG. 1 taken along line 2--2. 
     FIG. 3 is an exploded view of a portion of one of the struts and mating clevises of the turbine frame illustrated in FIG. 2. 
     FIG. 4 is a top view of a portion of the turbine frame illustrated in FIG. 1 taken along line 4--4. 
     FIG. 5 is a transverse, partly sectional view of the turbine frame illustrated in FIG. 4 showing a strut outer end joined to the casing by the clevis and taken along line 5--5. 
     FIG. 6 is a bottom, partly section view of the strut and clevis joined to the casing illustrated in FIG. 1 and taken along line 6--6. 
     FIG. 7 is a transverse, partly sectional view of the outer end of the strut joined to the casing by clevis of FIG. 6 taken along line 7--7. 
     FIG. 8 is an axial sectional view of a portion of at turbine frame in accordance with a second embodiment of the present invention illustrating service lines extending through the struts thereof. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Illustrated schematically in FIG. 1 is a portion of an exemplary gas turbine engine 10 having an axial, or longitudinal centerline axis 12. Conventionally disposed about the centerline axis 12 in serial flow communication are a fan, compressor, and combustor (all not shown), high pressure turbine (HPT) 20, and low pressure turbine (LPT, also no shown), all of which are conventional. A first shaft (not shown) joins the compressor to the HPT 20, and a second shaft 26 joins the fan to the LPT. During operation, air enters the fan, a portion of which is compressed in the compressor to flow to the combustor wherein it is mixed with fuel and ignited for generating combustion gases 30 which flow downstream through the HPT 20 and the LPT which extract energy therefrom for rotating the first and second shafts. 
     An annular turbine frame 32 in accordance with one embodiment of the present invention is provided for supporting a conventional bearing 34 which, in turn, supports one end of the second shaft 26 for allowing rotation thereof. Alternatively, the frame 32 may support the aft end of the HPT shaft (not shown). The turbine frame 32 is disposed downstream of the HPT 20 and, therefore, must be protected from the combustion gases 30 which flow therethrough. 
     The turbine frame 32 as illustrated in FIGS. 1 and 2 includes a first structural ring 36, or casing for example, disposed coaxially about the centerline axis 12. The frame 32 also includes a second structural ring 38, or hub for example, disposed coaxially with the first ring 36 about the centerline axis 12 and spaced radially inwardly therefrom. A plurality of circumferentially spaced apart hollow struts 40 extend radially between the first and second rings 36 and 38 and are fixedly joined thereto. 
     The frame 32 also includes a plurality of conventional fairings 42 each of which conventionally surrounds a respective one of the struts 40 for protecting the struts from the combustion gases 30 which flow through the turbine frame 32. Conventionally joined to the hub 38 is a conventional, generally conical sump member 44 which supports the bearing 34 in its central bore. 
     Each of the struts 40 includes a first, or outer, end 40a and a radially opposite second, or inner, end 40b, with an elongate center portion 40c extending therebetween. As shown in FIG. 1 and additionally in FIG. 3, the strut 40 is hollow and includes a through channel 46 extending completely through the strut 40 from the outer end 40a and through the center portion 40c to the inner end 40b. 
     As shown in FIGS. 1, 4, and 5 the casing 36 includes a plurality of circumferentially spaced apart first ports 48 extending radially therethrough, and the hub 38 (see FIG. 1) similarly includes a plurality of circumferentially spaced apart second ports 50 extending radially therethrough. 
     In the exemplary embodiment illustrated in FIG. 1, the inner ends 40b of the struts 40 are integrally formed with the hub 38 in a common casting, for example, and the outer ends 40a of the struts 40 are removably fixedly joined to the casing 36 in accordance with the present invention. In alternate embodiments, the strut outer ends 40a may be integrally joined to the casing 36 in a common casting, for example, with the strut inner ends 40b being removably joined to the hub 38 also in accordance with the present invention. In either configuration, the turbine frame 32 further includes a plurality of clevises 52 which removably join the strut outer ends 40a to the casing 36 in the configuration illustrated in FIGS. 1 and 3, or removably join the inner ends 40b to the hub 38 (not shown). In either configuration, each of the clevises 52 is disposed between a respective one of the strut ends 40a, 40b and the respective ring, i.e. casing 36 or hub 38, in alignment with respective ones of the first or second ports 48, 50 for removably joining the struts 40 to the first or second ring, i.e. casing 36 or hub 38, for both carrying loads and providing access therethrough. 
     More specifically, and referring to FIGS. 3, 5, and 6, each of the clevises 52 includes an arcuate base 54 disposed against the inner circumference of the casing 36, and includes a plurality of mounting holes 56, eight being shown for example, for receiving a respective plurality of mounting bolts 58, with corresponding nuts, therethrough to removably fixedly join the base 54 to the casing 36. The base 54 includes a central aperture 60 aligned with a respective one of the first ports 48. 
     The clevis 52 also includes first and second legs 62, 64 extending radially inwardly away from the base 54 and being preferably integral therewith, which legs 62, 64 are spaced circumferentially apart and joined together at their ends to define a generally axially extending U-shaped clevis slot, or pocket 66 which receives the strut outer end 40a. The first and second legs 62, 64 and the strut outer end 40a have a pair of generally axially spaced apart line-drilled bores 68 extending therethrough as shown in FIGS. 3 and 7 which receive a respective pair of conventional expansion bolts 70 for removably fixedly joining the strut outer end 40a to the first and second legs 62, 64, with the strut through channel 46 being disposed generally axially between the two expansion bolts 70 and aligned with both the base aperture 60 and the first port 48 as shown in more particularity in FIGS. 5 and 6. 
     As shown in FIGS. 1 and 2, for example, the casing 36 includes a pair of axially spaced apart, annular stiffening ribs 72 disposed on opposite, axial sides of the clevises 52 and the first ports 48 for carrying loads between the struts 40 and the casing 36 without interruption by the first ports 48, for example. The respective stiffening ribs 72 are continuous and uninterrupted annular members which carry loads in the hoop-stress direction without interruption by either the ports 48 or the struts 40 joined to the casing 36. In this way, loads may be transmitted from the hub 38 through the struts 40 and through the clevises 52 to the casing 36, with the stiffening ribs 72 ensuring substantially rigid annular members to which the struts 40 are connected. In the exemplary embodiment illustrated in FIGS. 1 and 2, the strut inner end 40b is integrally formed with the hub 38, whereas the strut outer end 40a is joined to the casing 36 using the clevis 52. The clevis base 54 is rigidly mounted to the casing 36 by the eight mounting bolts 58, and the strut outer end 40a is rigidly mounted to the first and second legs 62, 64 by the expansion bolt pair 70. 
     As shown in FIG. 3, the clevis 52 preferably also includes a plurality of gussets 74 integrally joining the clevis first and second legs 62, 64 to the clevis base 54 for carrying bending loads transmitted through the strut 40 and the casing 36. These gussets 74 improve the rigidity of the clevis 52 while minimizing the weight thereof and allow the strut outer end 40a to be made as small as possible for minimizing the size of the fairing 42. 
     More specifically, and referring firstly to FIGS. 2, 3, and 5, the strut outer end 40a is sized substantially equal in transverse section with the strut center portion 40c, although they have generally different configurations, for allowing the strut outer end 40a to fit through a respective one of the fairings 42 during assembly. In this exemplary embodiment, the fairing 42 is a one-piece cast hollow member which may be assembled with the strut 40 solely by being radially positioned downwardly over the strut outer end 40a and into position around the strut center portion 40c. As shown in FIG. 3, the strut outer end 40a is generally rectangular and is about the same size as the strut center portion 40c, which is generally airfoil-shaped, to fit through the fairing 42 with minimum clearance therewith for maintaining a relatively small size of the fairing 42. 
     In view of this relatively small size of the strut outer end 40a, the clevis first and second legs 62, 64 are reinforced with the gussets 74 to increase the rigidity between the strut outer end 40a when it is joined into the clevis 52. As shown in FIGS. 5 and 7, the strut outer end 40a is preferably disposed in the clevis slot 66 in abutting contact with the inner surface 37 of the casing 36 through the clevis base central aperture 60 for carrying compressive loads directly thereto through the strut 40 during operation. The expansion bolts 70 as shown in FIG. 7, for example, carry tension loads through the struts 40 and between the casing 36 and the hub 38, with compressive loads being carried primarily through direct contact between the strut outer end 40a and the casing 36, although compressive loads may also be carried through the expansion bolts 70 as well. In this way, effective load transverse from the hub 38 and through the struts 40 into the casing 36 is effected for improving the overall rigidity of the turbine frame 32. 
     Referring again to FIG. 5, the strut outer end 40a is also disposed in the clevis slot 66 in sealing arrangement with the first port 48 through the central aperture 60 for channeling airflow through the ports 48 and 50 of the casing 36 and hub 38. In the exemplary embodiment illustrated in FIG. 1, for example, cooling air 76 is allowed to flow through the casing first ports 48 and downwardly through the central apertures 60 of the clevises 52 and in turn through the struts 40 and hub second ports 50 for conventional use inside the engine. By configuring the strut outer end 40a to directly contact the inner surface of the casing 36 around the entire perimeter of the channel 46 as shown in FIG. 5, an effective seal is provided between the strut outer end 40a and the casing 36 at the first ports 48 for ensuring flow of the cooling air 76 therethrough, while also allowing compressive loads to be channeled from the hub 38 and through the struts 40 and clevis apertures 60 directly between the strut outer ends 40a and the casing 36. 
     As illustrated in FIGS. 4 and 5, for example, the casing 36 includes a plurality of auxiliary ports 78, each auxiliary port 78 being disposed adjacent to a respective one of the first ports 48 and between the pair of casing stiffening ribs 72. The clevis base 54 also includes a complementary auxiliary aperture 80 spaced from the central aperture 60 on opposite sides of the first leg 62, for example, and aligned in flow communication with the auxiliary port 78. In this way the cooling airflow 76 channeled between the ribs 72 is split between the first and auxiliary ports 48 and 78 to flow separately between the central and auxiliary apertures 60 and 80 through the clevis base 54. The air through the central aperture 60 enters the strut 40 and flows through the channel 46, and the air channeled through the auxiliary aperture 80 may be used for cooling other structures as desired. By abutting the strut outer end 40a directly against the inside surface of the casing 36 around the first port 48, an effective seal is created therewith to ensure the separate flow of the airflow 76 through the ports 48, 78 into the respective apertures 70, 80. And, compressive loads between the strut 40 and thee casing 36 are directly transmitted through this abutting joint and carried by the ribs 72 for maintaining rigidity of the turbine frame 32 without significant affect by the several relatively small ports 48, 78 surrounding the casing 36 between the ribs 72. 
     Since the struts 40 terminate inside the casing 36 and are joined thereto by the clevises 52, they do not penetrate the casing 36 as in conventional designs which decrease the effective rigidity of the frame. The ports 48 and 78 are relatively small as compared to the penetrations of the casing 36 which would otherwise be required for mounting the strut outer ends 40a in a conventional manner and, therefore, do not significantly decrease the rigidity of the assembled frame 32. 
     Although in this exemplary embodiment, the strut channel 46 is provided for directly channeling the cooling air 76 therethrough, in alternate embodiments, conventional service lines or pipes for carrying oil, for example, may be routed through the casing 36, hub 38, and corresponding struts 40 for channeling oil to and from the region of the sump 44. FIG. 8 illustrates an alternate embodiment of the invention wherein the frame 32 is configured for carrying through the casing 36, one of the struts 40, and the hub 38, a pair of conventional service pipes 82 which carry lubrication oil, for example. The clevis 52 joins the strut 40 to the casing 36 as described above for obtaining improved rigidity of the turbine frame 32 while still allowing the service pipes 82 to pass through the casing 36 and through the clevis 52 for routing through the strut 40 without reducing the overall rigidity of the turbine frame 32. 
     Since the several clevises 52 and struts 40 must be assembled accurately with the casing 36, each of the clevises 52 preferably includes an axial stop or tab 84 extending axially forwardly from the base 54 as shown in FIGS. 1 and 3 which is predetermined sized to abut a radially inwardly extending flange 86 of the casing 36 for accurately axially aligning all of the clevises 52, and in turn the struts 40. 
     The resulting turbine frame 32 provides substantial overall rigidity even though the strut outer ends 40a are removably joined to the casing 36 using the respective clevises 52, while also providing access through the individual struts 40 for the cooling air 76 or the conventional service pipes. The turbine frame 32 allows an improved method of manufacture wherein the individual clevises 52 may firstly be temporarily joined to the strut outer ends 40a for allowing the bores 68 to be line-drilled therethrough for providing continuous and pre-aligned bores 68 for receiving the respective expansion bolts 70. The outer surface of the pre-assembled clevises 52 and the strut ends 40a may then be conventionally ground to a suitable arc for mating with the inner diameter of the casing 36. The clevises 52 may then be located in position in the casing 36 so that the mounting holes 56 may be line-drilled to extend also through the casing 36 for providing effective alignment of the clevis 52 therewith for receiving the mounting bolts 58. For increased rigidity of the turbine frame assembly 32, and to ensure repeatability of the reassembly, the clevis 52 and strut end 40a may be ground to establish an interference fit to the casing 36. 
     While there have been described herein that are considered to be preferred and exemplary embodiments of the present invention, other modifications of the invention shall be apparent to those skilled in the art from the teachings herein, and it is, therefore, desired to be secured in the appended claims all such modifications as fall within the true spirit and scope of the invention. 
     Accordingly, what is desired to be secured by Letters Patent of the United States is the invention as defined and differentiated in the following claims: