Patent Document

BACKGROUND 
       [0001]    A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section. A speed reduction device such as a gear assembly may be utilized to drive the fan section such that the fan section may rotate at a speed different than the turbine section so as to increase the overall propulsive efficiency of the engine. 
         [0002]    In such engine architectures, a shaft driven by the turbine section provides an input to the gear assembly. The shaft may be constructed from multiple sections assembled together. Assembly of the various shaft sections may be performed utilizing press fits. A press fit assembly may include heating of one part to allow another part to fit therein. Heating to expand one component is complicated if several components are within a heated region. Non-uniform heating of some portions of a shaft interface can induce unwanted stress on parts, such as bearing assemblies. Accordingly, it is desirable to develop an assembly method that enables expansion by the application of heat without damage to surrounding parts. 
       SUMMARY 
       [0003]    In one exemplary embodiment, a method of assembling mating components includes the steps of heating an inner surface of a first cavity of a first part to generate a first expansion, heating an outer surface of a component surrounding an outer periphery of the first part to generate a second expansion of the component that corresponds to the first expansion of the first part, inserting a second part into the first cavity while the first part is in an expanded condition, and cooling the first part to contract around the second part. 
         [0004]    In a further embodiment of the above, includes heating the inner surface with a first inductive coil disposed within the first cavity and heating the outer surface of the component with a second inductive coil disposed about the outer surface. 
         [0005]    In a further embodiment of any of the above, the first part includes a first shaft including a splined interior surface and the second part includes a second shaft including a splined exterior surface receivable within the splined interior surface of the first part. 
         [0006]    In a further embodiment of any of the above, the first shaft includes a coupling shaft for driving a geared architecture and the second shaft includes a shaft driven by a turbine section of a gas turbine engine. 
         [0007]    In a further embodiment of any of the above, the component includes a bearing assembly supporting rotation of the first part. The bearing assembly includes an inner race, an outer race and a bearing disposed there 
         [0008]    between and the method includes heating the bearing assembly to expand the inner race and outer race in proportion to expansion of the first part. 
         [0009]    In a further embodiment of the above, includes a housing supporting the bearing assembly. The method includes application of heat to the housing to generate expansion of the bearing assembly in proportion to expansion of the first part. 
         [0010]    In a further embodiment of any of the above, includes detecting expansion with a sensor to determine if a predetermined amount of expansion between the first part and the component has occurred to enable installation of the second part into the first part. 
         [0011]    In a further embodiment of any of the above, the first part is heated to a first temperature and the component is heated to a second temperature that is different than the first temperature. 
         [0012]    In another exemplary embodiment, a method of mating shaft sections for a gas turbine engine, the method including the steps of assembling a bearing assembly about an outer surface of a first shaft, heating an inner race of the bearing assembly, heating an outer race of the bearing assembly separately from heating of the inner race and at the same time as heating the inner race, inserting a portion of a second shaft into a cavity of the first shaft, and cooling the first shaft, the second shaft, the inner race and the outer race of the bearing assembly such that the first shaft shrinks onto the second shaft. 
         [0013]    In a further embodiment of the above, heating the inner race of the bearing assembly includes inserting a heating device into an inner cavity of the first shaft to an axial location corresponding to a position of the inner race on the outer surface of the first shaft and heating the inner race through the inner cavity of the first shaft. 
         [0014]    In a further embodiment of any of the above, heating the outer race of the bearing assembly includes positioning a heating device about an outer surface of the outer bearing race and heating the outer bearing race to expand the outer bearing race proportionate to expansion of the inner race. 
         [0015]    In a further embodiment of any of the above, including expanding the cavity of the first shaft to provide a fit for a portion of the second shaft. 
         [0016]    In a further embodiment of any of the above, an interface between the cavity of the first shaft and an outer surface of the second shaft includes a splined connection. 
         [0017]    In a further embodiment of any of the above, including a first inductive heating element received within the first cavity for imparting heat to the first shaft and the inner bearing race and a second inductive heating element disposed about the outer housing. 
         [0018]    In a further embodiment of any of the above, including a housing supporting the bearing assembly and heating of the outer bearing race includes heating the housing in an axial location corresponding to an axial position of the outer bearing race. 
         [0019]    Although the different examples have the specific components shown in the illustrations, embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. 
         [0020]    These and other features disclosed herein can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a schematic view of an embodiment of a gas turbine engine. 
           [0022]      FIG. 2  is a schematic representation of an embodiment of a first shaft component assembled to a second shaft 
           [0023]      FIG. 3  is a schematic view of an example method of mating two shaft parts together. 
           [0024]      FIG. 4  is another schematic representation of an embodiment of a heating step for assembly two shaft components. 
           [0025]      FIG. 5  is a schematic representation of the mating step between first and second shaft components. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      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 flow path B in a bypass duct defined within a nacelle, while the compressor section  24  drives air along a core flow path C for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a two-spool 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 two-spool turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures. 
         [0027]    The exemplary 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, and the location of bearing systems  38  may be varied as appropriate to the application. 
         [0028]    The low speed spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a first (or low) pressure compressor  44  and a first (or low) pressure turbine  46 . The inner shaft  40  is connected to the fan  42  through a speed change mechanism, which in exemplary gas turbine engine  20  is illustrated as 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 second (or high) pressure compressor  52  and a second (or high) pressure turbine  54 . A combustor  56  is arranged in exemplary gas turbine  20  between the high pressure compressor  52  and the high pressure turbine  54 . A mid-turbine frame  58  of the engine static structure  36  is arranged generally between the high pressure turbine  54  and the low pressure turbine  46 . The mid-turbine frame  58  further supports bearing systems  38  in the turbine section  28 . The inner shaft  40  and the outer shaft  50  are concentric and rotate via bearing systems  38  about the engine central longitudinal axis A which is collinear with their longitudinal axes. 
         [0029]    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 mid-turbine frame  58  includes airfoils  60  which are in the core airflow path C. The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. It will be appreciated that each of the positions of the fan section  22 , compressor section  24 , combustor section  26 , turbine section  28 , and fan drive gear system  48  may be varied. For example, gear system  48  may be located aft of combustor section  26  or even aft of turbine section  28 , and fan section  22  may be positioned forward or aft of the location of gear system  48 . 
         [0030]    The engine  20  in one example is a high-bypass geared aircraft engine. In a further example, the engine  20  bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), the geared architecture  48  is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine  46  has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine  20  bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor  44 , and the low pressure turbine  46  has a pressure ratio that is greater than about five 5:1. Low pressure turbine  46  pressure ratio is pressure measured prior to inlet of low pressure turbine  46  as related to the pressure at the outlet of the low pressure turbine  46  prior to an exhaust nozzle. The geared architecture  48  may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans. 
         [0031]    A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section  22  of the engine  20  is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet (10.67 km). The flight condition of 0.8 Mach and 35,000 ft (10.67 km), with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram ° R)/(518.7° R)]0.5. The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second (350 m/second). 
         [0032]    The example gas turbine engine includes the fan  42  that comprises in one non-limiting embodiment less than about twenty-six (26) fan blades. In another non-limiting embodiment, the fan section  22  includes less than about twenty (20) fan blades. Moreover, in one disclosed embodiment the low pressure turbine  46  includes no more than about six (6) turbine rotors schematically indicated at  34 . In another non-limiting example embodiment the low pressure turbine  46  includes about three (3) turbine rotors. A ratio between the number of fan blades  42  and the number of low pressure turbine rotors is between about 3.3 and about 8.6. The example low pressure turbine  46  provides the driving power to rotate the fan section  22  and therefore the relationship between the number of turbine rotors  34  in the low pressure turbine  46  and the number of blades  42  in the fan section  22  disclose an example gas turbine engine  20  with increased power transfer efficiency. 
         [0033]    The example gas turbine engine  20  includes the geared architecture  48  that drives the fan section  22 . The geared architecture  48  is driven by the turbine section  28  through a shaft  40 . A coupling shaft  62  is disposed between the shaft  40  and the geared architecture  48 . The coupling shaft  62  includes features that can accommodate movement and misalignment of the shaft  40  relative to the geared architecture  48 . The ability to accommodate this misalignment enables the geared architecture  48  to function and increases the efficiency of the geared architecture by reducing the amount of wear that may occur due to misalignment. 
         [0034]    An interface between the coupling shaft  62  that transfers power into the geared architecture  48  and the turbine shaft  40  is provided after the low pressure compressor  44  and prior to the geared architecture  48 . The coupling shaft  62  is connected to the geared architecture  48 . The coupling shaft  62  is supported by a bearing assembly  64 . The bearing assembly  64  is mounted outboard of the interface of the shaft  62  and the turbine shaft  40 . It should be appreciated that assembly of the coupling shaft  62  to the shaft  40  is provided as a disclosed example, and that the method and structures disclosed are contemplated for use with any interface where two shafts or other structures are assembled together. 
         [0035]    Referring to  FIG. 2  with continued reference to  FIG. 1 , the shaft  40  is coupled to the coupling shaft  62  through a splined interface  88 . In this example, the shaft  40  includes splined portion  86  ( FIG. 5 ) disposed about an outer surface of a portion of the shaft  40 . The coupling shaft  62  includes an inner cavity  68  that includes a plurality of interior splines  70  ( FIGS. 3 and 5 ) that mate with the splined portion  86  on the shaft  40 . Assembly of the shafts is provided as a tight press fit sometimes referred to as a snap fit. The press fit between the shaft  40  and the coupling shaft  62  is accomplished by heating the coupling shaft  62  to expand the cavity  68  that enables insertion of the splined portion  86  of the shaft  40 . 
         [0036]    The assembly sequence for assembling the gas turbine engine requires that a bearing assembly  64  is first assembled to an outer surface of the coupling shaft  62 . In this example, the bearing assembly  64  includes an inner race  72  that is supported on an outer surface of the coupling shaft  62 . The bearing assembly  64  further includes an outer race  74  and a bearing  76  disposed between the inner and outer races  72 ,  74 . The bearing  76  may include bearings disposed within a cage. The outer race  74  is in turn supported by a housing  66 . The housing  66  supports the bearing assembly  64  that in turn supports rotation of the coupling shaft  62 . 
         [0037]    Heating of this complex stack of parts complicates the assembly process. Heating the coupling shaft  62  causes a thermal expansion. Because the inner bearing race  72  and the outer bearing race  74  are not uniformly heated, they do not expand in a uniform manner and can induce stresses on and between the inner race  72  and the outer race  74 . The non-uniform heating can induce undesired stresses on the bearing assembly. 
         [0038]    Accordingly, the example method provides steps for expanding the coupling shaft  62  to receive a portion of the turbine shaft  40  without damaging or otherwise imparting undue stresses and strains on the example bearing assembly  64 . The temperature range is defined to provide a desired temperature differential that is does not damage the bearing assembly  64 . 
         [0039]    Referring to  FIG. 3  with continued reference to  FIG. 1 , the example method begins by inserting inductive coils  78  into the cavity  68  of the coupling shaft  62 . A second set of inductive coils  80  are disposed about an outer surface of the housing  66  at an axial location that corresponds to the position of the bearing assembly  64  on the coupling shaft  62 . A power source  82  powers the inductive coils  78 ,  80 . It should be understood that inductive coils  78 ,  80  are shown by way of example, and other heating devices and structures could be utilized and are within the contemplation of this disclosure. 
         [0040]    The disclosed example assembly method includes the initial step of assembling the bearing assembly  64  to the outer surface of the coupling shafts  62 . The interior inductive coil  78  is then inserted into the cavity  68  of the coupling shaft  62 . In this example, the inner cavity  68  includes the splines  70  that mate with the corresponding splined portion  86  of the shaft  40 . An outer or second inductive coil  80  is placed against the housing  66  at an axial location proximate to the bearing assembly  64 . Application of heat with both the inner and outer inductive coils  78 ,  80  provides a uniform thermal expansion of the coupling shaft  62  and the bearing assembly  64 . 
         [0041]    The second inductive coil  80  heats the housing  66  and also the outer bearing race  74  such that the coupling shaft  62 , the inner bearing race  72  and the outer bearing race  74  are all expanded uniformly. The shaft  62  may be of a different material than the material utilized for the bearing races  72 ,  74  and therefore include different thermal properties. Accordingly, the specific energy and heat induced by the second conductive coil  80  may be different than the heat induced by the first inductive coil  78 . In this example, heat imparted into the coupling shaft  62  and the inner and outer bearing races  72  and  74  is matched to provide a uniform amount of the thermal expansion that does not incur undue stresses on any of the components. The amount of thermal expansion is dependent on the thermal properties of each of the components and therefore the heat induced by the first coil  78  may be different than the heat induced by the second coil  80 . Moreover, the second coil  80  may impart an increased amount of heat to expand the outer race  74  in a manner that will relieve stresses and not impart undue strain on the bearings  76  that is disposed between the inner and outer races  72 ,  74 . 
         [0042]    A sensor  84  is disposed proximate to the coupling shaft  62  and bearing assembly  64 . The sensor  84  can be utilized to detect a range of expansion to determine if the coupling shaft  62  is expanded sufficiently to receive the shaft  40  or the sensor  84  may be utilized to determine when a specific temperature has been obtained by each of the components. As appreciated, a specific temperature can be correlated with a desired expansion rate and thereby determining a temperature of a specific component can provide information indicative of the amount of expansion that has occurred. 
         [0043]    Once the coupling shaft  62  is expanded to a desired diameter determined to provide for acceptance of the splined portion  86 , the inductive coils  78  and  80  are removed and the spline portion  86  of the shaft  40  is inserted into the cavity  68 . It should be understood that although a splined interface is disclosed, other interfaces as are known within the art are within the contemplation of this disclosure. 
         [0044]    Once the shaft  40  is inserted into the coupling shaft  62 , the shafts  40 ,  62  and bearing assembly  64  are cooled such that coupling shaft constricts around the shaft  40  to form a snap or tight press fit. The tight press fit is desirable as it provides for a secure inner connection between the torque transferring shafts. 
         [0045]    Accordingly, the example method of assembling mating shaft components enables assembly of two shaft components in complex tolerance stack up conditions. 
         [0046]    Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the scope and content of this disclosure.

Technology Category: 2