Abstract:
A method for assembling a gas turbine engine includes coupling a first structure within the gas turbine engine, wherein the first structure includes a plurality of sockets extending from a radially outer surface of the first structure, and coupling a second structure to the first structure by inserting a radial pin through the second structure and into each respective socket such that the first structure is aligned axially, circumferentially, and with respect to an engine centerline axis extending through the gas turbine engine, where the position of the pins relative to the second structure is adjustable.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to gas turbine engines, and more particularly to methods and apparatus for assembling gas turbine engines.  
         [0002]     At least some known gas turbine engines include axisymmetric structures, such as combustors for example. During operation, thermal differentials between the concentric axisymmetric flowpath components may result in thermal stresses being induced. Although providing for relative radial movement between the concentric axisymmetric structures may facilitate reducing such thermal stresses, such arrangements make it more difficult to maintain at least some of the axisymmetric hardware substantially concentric to the engine centerline axis to facilitate proper operation of the gas turbine engine. Moreover, thermal differentials between the axisymmetric structures may result in excessive loads resulting in relatively high cyclic stress and/or fatigue cracks in the axisymmetric structures.  
         [0003]     For example, as shown in  FIG. 1 , at least one known gas turbine engine includes a combustor casing that includes a plurality of radially oriented pins  2  that engage female bushings  3  that are coupled to the combustor  4 . The pins are threaded into the combustor outer casing  5 , which surrounds the combustor. In operation, the combustor, which is considerably hotter than the casing, is free to expand in a radial direction.  
         [0004]     However, as shown in  FIG. 1 , to assemble the combustor within the gas turbine engine, the dimensional tolerances of the components require a radial clearance in the fit of the male pin to the female bushing to permit assembly. As a result, during operation, only a portion of the radial pins support the axial load and react to tangential forces. As such, these radial pins may experience increased wear compared to other radial pins utilized to support the combustor. In addition, slight dimensional misalignment of either the pins, the bushing bores, or both, may cause the load to be concentrated on either the edge of the bushing and/or the end of the pin. This concentrated load on what is initially a point contact on the pin and/or bushing again may result in increased wear of the bushing and/or the pin.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0005]     In one aspect, a method for assembling a gas turbine engine is provided. The method includes coupling a first structure within the gas turbine engine, wherein the first structure includes a plurality of sockets extending from a radially outer surface of the first structure, and coupling a second structure to the first structure by inserting a radial pin through the second structure and into each respective socket such that the first structure is aligned axially, circumferentially, and with respect to an engine centerline axis extending through the gas turbine engine.  
         [0006]     In another aspect, an assembly for coupling an axisymmetric structure within the gas turbine engine is provided. The axisymmetric structure includes at least one mounting bushing extending from a radially outer surface of the axisymmetric structure. The assembly includes a pin having a crowned surface inserted at least partially into the mounting bushing such that the pin provides both axial and tangential support to the axisymmetric structure, and a retaining device to secure the pin to a portion of the gas turbine engine.  
         [0007]     In a further aspect, a gas turbine engine is provided. The gas turbine engine includes an axisymmetric structure within the gas turbine engine, wherein the axisymmetric structure includes at least two mounting bushings extending from a radially outer surface of the axisymmetric structure, and an assembly for coupling the axisymmetric structure within the gas turbine engine. The assembly includes a pin having a crowned surface inserted at least partially into the mounting bushing such that the pin provides both axial and tangential support to the axisymmetric structure, and a retaining device to secure the pin to a portion of the gas turbine engine.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a cross-sectional view of a prior art radial pin;  
         [0009]      FIG. 2  is a schematic view of an exemplary gas turbine engine;  
         [0010]      FIG. 3  is a cross-sectional view of a portion of the gas turbine engine shown in  FIG. 1 ;  
         [0011]      FIG. 4  is a cross-sectional view of an exemplary attachment assembly, during initial assembly, that may be utilized with the gas turbine engine shown in  FIG. 1 ;  
         [0012]      FIG. 5  is a cross-sectional view of the attachment assembly shown in  FIG. 4  during final assembly;  
         [0013]      FIG. 6  is a cross-sectional view of a portion of the attachment assembly shown in  FIGS. 4 and 5 ;  
         [0014]      FIG. 7  is a cross-sectional view of an exemplary attachment assembly that may be utilized with the gas turbine engine shown in  FIG. 1 ;  
         [0015]      FIG. 8  is a cross-sectional view of the an optional attachment assembly shown in  FIG. 7 ;  
         [0016]      FIG. 9  is a cross-sectional view of an exemplary attachment assembly that may be utilized with the gas turbine engine shown in  FIG. 1 ; and  
         [0017]      FIG. 10  is a top view of the attachment assembly shown in  FIG. 9 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]      FIG. 2  is a schematic illustration of a gas turbine engine assembly  10  including a fan assembly  12  and a core engine  13  including a high pressure compressor  14 , a combustor  16 , and a high pressure turbine  18 . In the exemplary embodiment, gas turbine engine assembly  10  also includes a low pressure turbine  20  and a booster  22 . Fan assembly  12  includes an array of fan blades  24  extending radially outward from a rotor disc  26 . Gas turbine engine assembly  10  has an intake side  27  and an exhaust side  29 . In one embodiment, the gas turbine engine is a CF6-50 available from General Electric Company, Cincinnati, Ohio. Fan assembly  12 , turbine  20 , and booster  22  are coupled together by a first rotor shaft  31 , and compressor  14  and turbine  18  are coupled together by a second rotor shaft  33 .  
         [0019]     During operation, air flows axially through fan assembly  12 , in a direction that is substantially parallel to a central axis  34  extending through engine  10 , and compressed air is supplied to high pressure compressor  14 . The highly compressed air is delivered to combustor  16 . Airflow (not shown in  FIG. 2 ) from combustor  16  drives turbines  18  and  20 , and turbine  20  drives fan assembly  12  by way of shaft  31 .  
         [0020]      FIG. 3  is a cross-sectional view of combustor  16  shown in  FIG. 2 . In the exemplary embodiment, combustor  16  includes an annular outer liner  40 , an annular inner liner  42 , and a combustor dome assembly  44  extending between outer and inner liners  40  and  42 , respectively.  
         [0021]     Outer liner  40  and inner liner  42  are spaced radially inward from a combustor casing  46  and define a combustion chamber  48 . Combustor casing  46  is generally annular and extends downstream from an exit  50  of a compressor, such as compressor  14  shown in  FIG. 1 . Outer liner  40  and combustor casing  46  define an outer passageway  52  and inner liner  42  and an inner support structure (not shown) define an inner passageway  54 . Outer and inner liners  40  and  42 , respectively, extend to a turbine inlet nozzle  58  disposed downstream from combustion chamber  48 .  
         [0022]     In the exemplary embodiment, combustor dome assembly  44  is arranged in a single annular configuration. In another embodiment, combustor dome assembly  44  is arranged in a double annular configuration. In a further embodiment, combustor dome assembly  44  is arranged in a triple annular configuration. In the exemplary embodiment, combustor dome assembly  44  provides structural support to an upstream end of combustor  16 . More specifically, gas turbine engine assembly  10  includes an attachment assembly to facilitate securing combustor  16  within core gas turbine engine  13  utilizing combustor dome assembly  44 .  
         [0023]      FIG. 4  is an exemplary attachment assembly  100 , shown during initial assembly, that may be utilized to secure an axisymmetric structure, such as combustor  16  within a gas turbine engine, such as gas turbine engine  10 .  FIG. 5  is a second view of attachment assembly  100  during final assembly.  FIG. 6  is a cross-sectional view of the alignment pin shown in  FIGS. 4 and 5 . Although, the attachment assemblies are described herein with respect to exemplary gas turbine engine  10 , it should be realized that the attachment assemblies may be utilized to install and/or align an axisymmetric structure in a wide variety of gas turbine engines.  
         [0024]     In the exemplary embodiment, attachment assembly  100  includes a plurality of radially oriented alignment pins  110  that each inserted through a respective threaded bushing  112  to engage a respective female bushing  114  that is coupled to combustor  16 . During assembly, the alignment pins  110  are threaded into the combustor outer casing  116 , which surrounds combustor  16 .  
         [0025]     More specifically, each alignment pin  110  includes a first portion  120 , a second portion  122 , and a third portion  124 . In the exemplary embodiment, portions  120 ,  122  and  124  are formed as a unitary alignment pin  110 . First portion  120  has a first end  130  that is utilized by an operator to hold alignment pin  110  during engine assembly and a second end  132  that is coupled to second portion  122 . First end  130  has a shape that is configured to allow an operator to hold the end, for example, first end  130  may have at least two flat surfaces  134  to allow an operator to utilize a wrench to hold alignment pin  110 . First portion  120  also includes a plurality of threads  136  that are sized to receive a retaining apparatus discussed further herein.  
         [0026]     Second portion  122  includes a first end  140  that is coupled to first portion second end  132  and a second end  142  that is coupled to third portion  124 . Second portion  122  has a diameter  144  that is sized such that second portion  122  may be inserted through retaining bushing  112  described further herein. Moreover, second portion  122  has a length  146  that is sized to enable first portion  120  and third portion  124  to extend outwardly from bushing  112  as shown in  FIGS. 4 and 5 .  
         [0027]     Third portion  124  includes a first end  150  that is coupled to second portion second end  142  and a second end  152  that is at least partially inserted into bushing  114 . Third portion  124  includes a crowned portion  154  that is coupled proximate to second end  152 . In the exemplary embodiment, crowned portion  154  is formed unitarily with third portion  124  and thus also formed unitarily with first and second portions  122  and  124 , respectively. Crowned portion  154  extends from third portion second end  152  at least partially toward third portion first end  150 . More specifically, crowned portion  154  has a first diameter  160  at second end  152 . Crowned portion  154  then gradually tapers outwardly in the direction of first end  150  to an apex wherein crowned portion  154  has a second diameter  162  that is greater than the first diameter  160 . Crowned portion  154  then gradually tapers inwardly in the direction of first end  150  until the diameter of the crowned portion is approximately equal to the diameter of second end  152 , i.e. diameter  160 .  
         [0028]     In the exemplary embodiment, crowned portion  154 , i.e. the crowned surface of pin  110  which engages bushing  114  facilitates allowing misalignment of the pin centerline with the axis of the bushing diameter while maintaining a line contact, rather than a point contact as in the prior art, thus provides a superior wear surface. Moreover, the crowned portion  154 , defined by a relatively large, two inches or greater partial radius, is such that, when a very small amount of radial pin wears occurs, the line contact becomes contact over a relatively large area. This large area then serves to reduce the contact stress level resulting from the axial/ tangential combustor loads and therefore serves to further retard wear and improve durability.  
         [0029]     Third portion  124  also includes a platform or shoulder  164  that is coupled proximate to third portion first end  150 . In the exemplary embodiment, the shoulder  164  has a diameter  166  that is greater than an inner diameter  168  of bushing  112 .  
         [0030]     Attachment assembly  100  also includes a washer  170  that is sized to circumscribe at least a portion of alignment pin  110  and a retaining nut  172  that is threadably coupled to first portion to facilitate securing alignment pin  110  to bushing  112 .  
         [0031]     During assembly, alignment pin third portion  124  is inserted through an, opening in combustor outer casing  116  and is at least partially inserted into bushing  114  such that at least a portion of crowned portion  154  is in contact with bushing  114 . More specifically, the crowned portion  154  of alignment pin  110  is now a relatively close diametrical fit to bushing  114 . Accordingly, the combustor bushing  114  positional tolerance is accommodated by the axial and tangential clearance that is provided by a space  180  that is defined between the alignment pin  110  and the bushing  112 , i.e. the alignment pin “floats” within bushing  112 . During assembly, the clearance  180  allows the pin  110  to engage the combustor bushing  114  and thus “finds a home” in the tangential and axial directions relative to the casing. The retaining bushing  112  is then installed which secures the alignment pin in a radial direction with respect to the combustor, The washer  170  and retaining nut  172  are then coupled to the alignment pin  110  to secure the alignment pin  110  in this axial/tangential position.  
         [0032]     As a result, the pin/bushing clearance necessary in the prior art design is eliminated, wear capability and durability are improved for any axisymmetric structure pin-mounted connection because all of the pins will share the applied axial and tangential loads, rather than as few as two or three pins sharing the applied axial and tangential loads as shown in the prior art. Moreover, the crowned pin interface surface represents an additional improvement in wear capability.  
         [0033]      FIG. 7  is an exemplary attachment assembly  200  that may be utilized to secure an axisymmetric structure, such as combustor  16  within a gas turbine engine, such as gas turbine engine  10 . Although, the attachment assembly is described herein with respect to exemplary gas turbine engine  10 , it should be realized that the attachment assembly may be utilized to install and/or align an axisymmetric structure in a wide variety of gas turbine engines.  
         [0034]     In the exemplary embodiment, attachment assembly  200  includes a plurality of radially oriented alignment pins  210  that are each inserted through a respective threaded bushing  212  to engage a respective female bushing  114  that is coupled to combustor  16 . During assembly, the threaded bushings  212  are threaded into the combustor outer casing  116 , which surrounds combustor  16 .  
         [0035]     More specifically, each alignment pin  210  has a substantially T-shaped cross-sectional profile and includes a head portion  220  that is utilized to secure alignment pin  210  within bushing  212 , a shaft portion  222  having a first end  224  that is coupled to head portion  220  and a second end  226  that is coupled to a crowned portion  228 ;  
         [0036]     In the exemplary embodiment, crowned portion  228  is formed unitarily with head portion  220  and shaft portion  222 . Crowned portion  228  extends from an end  230  of alignment pin  210  at least partially toward shaft portion  222 . More specifically, crowned portion  228  has a first diameter  232  at end  230 . Crowned portion  228  then gradually tapers outwardly in the direction of shaft portion  222  to an apex wherein crowned portion  228  has a second diameter  234  that is greater than the first diameter  232 . Crowned portion  228  then gradually tapers inwardly in the direction of shaft portion  222  until the diameter of the crowned portion is approximately equal to the diameter of shaft portion  222 , i.e. diameter  232 .  
         [0037]     In the exemplary embodiment, crowned portion  228 , i.e. the crowned surface of pin  210  which engages bushing  114 , facilitates allowing misalignment of the pin centerline with the axis of the bushing diameter while maintaining a line contact, rather than a point contact as in the prior art, and thus provides a superior wear surface. Moreover, the crowned portion  228 , defined by a relatively large, two inches or greater partial radius, is such that, when a very small amount of radial pin wears occurs, the line contact becomes contact over a relatively large area. This large area then serves to reduce the contact stress level resulting from the axial/tangential combustor loads and therefore serves to further retard wear and improve durability. Attachment assembly  200  also includes a retaining device or plug  240  that is sized to couple the pin  210  to bushing  212 .  
         [0038]     During assembly, bushing  212  is coupled within an opening  211  defined through combustor outer casing  116  using a plurality of threads  213 . Crowned portion  228  is inserted through the bushing  212  and is at least partially inserted into bushing  114  such that at least a portion of crowned portion  228  is in contact with bushing  114 . More specifically, the crowned portion  228  of alignment pin  210  is now a relatively close diametrical fit to bushing  114 . Accordingly, the combustor bushing  114  positional tolerance is accommodated by the axial and tangential clearance that is provided by a space  242  that is defined between the alignment pin head portion  220  and an interior surface of bushing  212 . During assembly, the clearance  242  allows the pin  210  to engage the combustor bushing  114  and thus “finds a home” in the tangential and axial directions relative to the casing. The retaining device  240  is then installed which secures the alignment pin  210  in a radial direction with respect to the combustor. Retaining device  240  includes a plurality of threads  241  that are sized to enable the retaining device  240  to be coupled within bushing  212 . In the exemplary embodiment, retaining device  240  also includes a recess  250  that is sized to receive a tool to facilitate securing retaining device  240  to bushing  212  and thus to facilitate securing alignment pin  210  within bushing  212 . Optionally, retaining device  240  does not include recess  250 , rather retaining device  240  includes a portion (not shown) extending from retaining device  240  that is sized to receive a tool that may be utilized to secure retaining device  240  within bushing  212 .  
         [0039]     In an optional configuration, shown in  FIG. 8 , head portion  220  includes a disassembly aid  260  that may be utilized by an operator to remove pin  210 . More specifically, the disassembly aid  260  includes a threaded extension portion  261  that is formed unitarily with head portion  220  and is configured to allow pin  210  to be removed from bushing  212 . Moreover, retaining device  240  may include at least one recess  262  that is sized to receive a tool that may be utilized to secure retaining device  240  within bushing  212 .  
         [0040]      FIG. 9  is top view of an exemplary attachment assembly  300  that may be utilized to secure an axisymmetric structure, such as combustor  16  within a gas turbine engine, such as gas turbine engine  10 .  FIG. 10  is a cross-sectional view of attachment assembly  300 . Although, the attachment assembly is described herein with respect to exemplary gas turbine engine  10 , it should be realized that the attachment assembly may be utilized to install and/or align an axisymmetric structure in a wide variety of gas turbine engines.  
         [0041]     In the exemplary embodiment, attachment assembly  300  includes a plurality of radially oriented alignment pins  310  that are each inserted through a respective threaded opening  343  to engage a respective female bushing  114  that is coupled to combustor  16  (not shown). During assembly, the alignment pins  310  are threaded into the combustor outer casing  116 , which surrounds combustor  16 .  
         [0042]     More specifically, each alignment pin  310  has a substantially T-shaped cross-sectional profile and includes a head portion  320  that is utilized to secure alignment pin  310  within an opening  321  that is defined in combustor outer casing  116 , a shaft portion  322  having a first end  324  that is coupled to head portion  320  and a second end  326  that is coupled to a crowned portion  328 .  
         [0043]     In the exemplary embodiment, crowned portion  328  is formed unitarily with head portion  320  and shaft portion  322 . Crowned portion  328  extends from an end  330  of alignment pin  310  at least partially toward shaft portion  322 . More specifically, crowned portion  328  has a first diameter  332  at end  330 . Crowned portion  328  then gradually tapers outwardly in the direction of shaft portion  322  to an apex wherein crowned portion  328  has a second diameter  334  that is greater than the first diameter  332 . Crowned portion  328  then gradually tapers inwardly in the direction of shaft portion  322  until the diameter of the crowned portion is approximately equal to the diameter of shaft portion  322 , i.e. diameter  332 .  
         [0044]     In the exemplary embodiment, crowned portion  328 , i.e. the crowned surface of pin  310  which engages bushing  114 , facilitates allowing misalignment of the pin centerline with the axis of the bushing diameter while maintaining a line contact, rather than a point contact as in the prior art, and thus provides a superior wear surface. Moreover, the crowned portion  328 , defined by a relatively large, two inches or greater partial radius, is such that, when a very small amount of radial pin wears occurs, the line contact becomes contact over a relatively large area. This large area then serves to reduce the contact stress level resulting from the axial/tangential combustor loads and therefore serves to further retard wear and improve durability. Attachment assembly  300  also includes a retaining device or plug  340  that is sized to be secured within opening  321  that is defined in combustor outer casing  116 .  
         [0045]     During assembly, crowned portion  328  is inserted through an opening in combustor outer casing  116  and is at least partially inserted into bushing  114  such that at least a portion of crowned portion  328  is in contact with bushing  114 . More specifically, the crowned portion  328  of alignment pin  310  is now a relatively close diametrical fit to bushing  114 . Accordingly, the combustor bushing  114  positional tolerance is accommodated by the axial and tangential clearance that is provided by a space  342  and  321  that is defined between the alignment pin head portion  320  and an interior surface of opening  321 .  
         [0046]     During assembly, the clearance  342  allows the pin  310  to engage the combustor bushing  114  and thus “finds a home” in the tangential and axial directions relative to the casing  116 . The retaining device  340  is then installed which secures the alignment pin  310  in a radial direction with respect to the combustor. Retaining device  340  includes a plurality of threads  341  that are sized to enable the retaining device  340  to be coupled within an opening  343  defined through combustor outer casing  116 .  
         [0047]     In the exemplary embodiment, shown in  FIG. 9 , retaining device  340  also includes a plurality of recesses  350  that are sized to receive a tool to facilitate securing retaining device  340  to combustor outer casing  116 . Optionally, retaining device  340  does not include recesses  350 , rather retaining device  340  includes a portion (not shown) extending from retaining device  340  that is sized to receive a tool that may be utilized to secure retaining device  340  combustor outer casing  116 .  
         [0048]     As a result, the pin/bushing clearance necessary in the prior art design is eliminated, wear capability and durability are improved for any axisymmetric structure pin-mounted connection because all of the pins will share the applied axial and tangential loads, rather than as few as two or three pins sharing the applied axial and tangential loads as shown in the prior art. Moreover, the crowned pin interface surface represents an additional improvement in wear capability.  
         [0049]     Exemplary embodiments of gas turbine engine axisymmetric structure alignment assemblies are described above in detail. The alignment assemblies illustrated are not limited to the specific embodiments described herein, but rather, components of each alignment assembly may be utilized independently and separately from other components described herein. For example, although a combustor is described herein, the alignment assemblies may also be used to align a variety of interior structure hardware to hardware other than a combustor.  
         [0050]     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention may be practiced with modification within the spirit and scope of the claims.