Abstract:
A variable vane assembly includes a variable vane, a trunnion arranged on one end of the variable vane, an inner bushing configured to receive the trunnion in a press fit relationship, and an outer bushing configured to rotatably receive the inner bushing. A retention feature is configured to retain the trunnion axially with respect to the outer bushing. A gas turbine engine and a method of assembling a variable vane assembly are also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/870,923, which was filed on Aug. 28, 2013. 
     
    
     GOVERNMENT CONTRACT 
       [0002]    This invention was made with government support under Contract No. N00019-02-C-3003 awarded by the United States Navy. The government has certain rights in this invention. 
     
    
     BACKGROUND 
       [0003]    This disclosure relates to a bushing for a variable vane assembly. More particularly, the disclosure relates to a bushing for an inner diameter of a variable vane that retains the vane and minimizes wear. 
         [0004]    A gas turbine engine typically includes 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 a ground-based generator for industrial gas turbine engine applications. The compressor and turbine sections include a plurality of rotating blades and vanes spaced between the rows of blades. The vanes serve to direct and control the flow of air through the rows of blades. 
         [0005]    One type of vane is a variable vane. In a variable vane, a vane pivots relative to a radial axis taken from a central axis of the engine. An actuator rotates a first side of the vane to pivot and a second opposed side of the vane is supported for rotation in a shroud. Typically, the actuator is at a radially outer location. In the event of a variable inlet vane failure, the rotated and supported sides of the vane may become disconnected from one another. The supported side of the vane may become liberated from the shroud and may be ingested by the rotating fan or other downstream rotating engine components. The supported side of the vane may include a retention feature to allow it to be retained in the shroud. 
         [0006]    The supported side of the vane generally includes a bushing to facilitate rotation in the shroud. In some current designs, the bushing may be split to allow for the incorporation of a retention feature, reducing the contact area between the bushing and the supported side of the vane and the shroud. Additionally, material selection for bushings is typically limited due to the high-wear conditions in which they operate and the necessity for material matching with the supported side of the vane. 
       SUMMARY 
       [0007]    In one exemplary embodiment, a variable vane assembly includes a variable vane, a trunnion arranged on one end of the variable vane, an inner bushing mated to the trunnion, an outer bushing configured to rotatably receive the inner bushing and a retention feature configured to retain the trunnion with respect to the outer bushing. 
         [0008]    In a further embodiment of the foregoing embodiments, the retention feature is a flange formed on the inner bushing. 
         [0009]    In a further embodiment of any of the foregoing embodiments, the flange is configured to abut an end of the outer bushing and prevent axial movement of the inner flange and the trunnion with respect to the outer bushing. 
         [0010]    In a further embodiment of any of the foregoing embodiments, the outer bushing includes an anti-rotation feature. 
         [0011]    In a further embodiment of any of the foregoing embodiments, the anti-rotation feature is at least one protrusion extending radially from an outer surface of the outer bushing. 
         [0012]    In a further embodiment of any of the foregoing embodiments, the outer bushing includes at least one outer bushing flange. 
         [0013]    In a further embodiment of any of the foregoing embodiments, the anti-rotation feature is at least one flat edge formed in the at least one outer bushing flange. 
         [0014]    In a further embodiment of any of the foregoing embodiments, at least one of the inner and outer bushings are metallic. 
         [0015]    In a further embodiment of any of the foregoing embodiments, the inner and outer bushings are made from the same material. 
         [0016]    In a further embodiment of any of the foregoing embodiments, the inner bushing is mated to the trunnion in a press fit relationship. 
         [0017]    In another exemplary embodiment, a gas turbine engine includes a shroud having a recesses, a variable vane including first and second trunnions at first and second ends of the variable vane, respectively, an inner bushing configured to receive the first trunnion in a press fit relationship, an outer bushing configured to rotatably receive the inner bushing, the outer bushing arranged in the recess, a retention feature configured to retain the first trunnion axially with respect to the outer bushing, and an actuator configured to rotate the variable vane via the second trunnion. 
         [0018]    In a further embodiment of any of the foregoing embodiments, the retention feature is a flange formed on the inner bushing. 
         [0019]    In a further embodiment of any of the foregoing embodiments, the outer bushing includes an anti-rotation feature. 
         [0020]    In a further embodiment of any of the foregoing embodiments, the shroud is configured to mate with the anti-rotation feature. 
         [0021]    In a further embodiment of any of the foregoing embodiments, the first trunnion is radially inwards from the second trunnion with respect to a central axis of the gas turbine engine. 
         [0022]    In another exemplary embodiment, a method of assembling a variable vane assembly includes installing a trunnion of a variable vane into an inner bushing in a press fit relationship, installing the inner bushing into an outer bushing to create a bushing assembly, and retaining the trunnion in the bushing assembly via a retention feature on the inner bushing. 
         [0023]    In a further embodiment of any of the foregoing embodiments, the method further includes the step of installing the bushing assembly into a shroud. 
         [0024]    In another embodiment of any of the forgoing embodiments, the method further includes the step of rotating the variable vane with respect to the shroud. 
         [0025]    In another embodiment of any of the forgoing embodiments, the method includes the step of preventing rotation of the outer bushing relative to the shroud via an anti-rotation feature. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
           [0027]      FIG. 1  schematically illustrates an example industrial gas turbine engine. 
           [0028]      FIG. 2  illustrates a variable vane assembly. 
           [0029]      FIG. 3  illustrates a cross-sectional view of a portion of the variable vane assembly on  FIG. 2 . 
           [0030]      FIG. 4  illustrates a bushing assembly. 
           [0031]      FIG. 5 a    illustrates a cress sectional view of the bushing assembly of  FIG. 4 . 
           [0032]      FIG. 5 b    illustrates the bushing assembly of  FIG. 4  installed in a shroud. 
           [0033]      FIG. 6  illustrates a portion of the variable vane assembly of  FIG. 2  installed in the shroud. 
           [0034]      FIG. 7 a    illustrates a cross-sectional view of an alternate variable vane assembly. 
           [0035]      FIG. 7 b    illustrates an alternate outer bushing. 
           [0036]      FIG. 7 c    illustrates the alternate outer bushing of  FIG. 7 b    installed in an alternate shroud. 
       
    
    
     DETAILED DESCRIPTION 
       [0037]      FIG. 1  schematically illustrates an example gas turbine engine  20  that includes a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . Alternative engines might include an augmenter section (not shown) among other systems or features. The fan section  22  drives air along a bypass flow path B while the compressor section  24  draws air in along a core flow path C where air is compressed and communicated to a combustor section  26 . In the combustor section  26 , air is mixed with fuel and ignited to generate a high pressure exhaust gas stream that expands through the turbine section  28  where energy is extracted and utilized to drive the fan section  22  and the compressor section  24 . 
         [0038]    Although the disclosed non-limiting embodiment depicts a turbofan gas turbine engine, 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; for example a turbine engine including a three-spool architecture in which three spools concentrically rotate about a common axis and where a low spool enables a low pressure turbine to drive a fan via a gearbox, an intermediate spool that enables an intermediate pressure turbine to drive a first compressor of the compressor section, and a high spool that enables a high pressure turbine to drive a high pressure compressor of the compressor section. 
         [0039]    The example engine  20  generally includes a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis X 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. 
         [0040]    The low speed spool  30  generally includes an inner shaft  40  that connects a fan  42  and a low pressure (or first) compressor section  44  to a low pressure (or first) turbine section  46 . The inner shaft  40  drives the fan  42  through a speed change device, such 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 high pressure (or second) compressor section  52  and a high pressure (or second) turbine section  54 . The inner shaft  40  and the outer shaft  50  are concentric and rotate via the bearing systems  38  about the engine central longitudinal axis X. 
         [0041]    A combustor  56  is arranged between the high pressure compressor  52  and the high pressure turbine  54 . In one example, the high pressure turbine  54  includes at least two stages to provide a double stage high pressure turbine  54 . In another example, the high pressure turbine  54  includes only a single stage. As used herein, a “high pressure” compressor or turbine experiences a higher pressure than a corresponding “low pressure” compressor or turbine. 
         [0042]    The example low pressure turbine  46  has a pressure ratio that is greater than about five (5). The pressure ratio of the example low pressure turbine  46  is measured prior to an inlet of the low pressure turbine  46  as related to the pressure measured at the outlet of the low pressure turbine  46  prior to an exhaust nozzle. 
         [0043]    A mid-turbine frame  57  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  57  further supports bearing systems  38  in the turbine section  28  as well as setting airflow entering the low pressure turbine  46 . 
         [0044]    The core airflow C is compressed by the low pressure compressor  44  then by the high pressure compressor  52  mixed with fuel and ignited in the combustor  56  to produce high speed exhaust gases that are then expanded through the high pressure turbine  54  and low pressure turbine  46 . The mid-turbine frame  57  includes vanes  59 , which are in the core airflow path and function as an inlet guide vane for the low pressure turbine  46 . Utilizing the vane  59  of the mid-turbine frame  57  as the inlet guide vane for low pressure turbine  46  decreases the length of the low pressure turbine  46  without increasing the axial length of the mid-turbine frame  57 . Reducing or eliminating the number of vanes in the low pressure turbine  46  shortens the axial length of the turbine section  28 . Thus, the compactness of the gas turbine engine  20  is increased and a higher power density may be achieved. 
         [0045]    The disclosed gas turbine engine  20  in one example is a high-bypass geared aircraft engine. In a further example, the gas turbine engine  20  includes a bypass ratio greater than about six (6), with an example embodiment being greater than about ten (10). The example geared architecture  48  is an epicyclical gear train, such as a planetary gear system, star gear system or other known gear system, with a gear reduction ratio of greater than about 2.3. 
         [0046]    In one disclosed embodiment, the gas turbine engine  20  includes a bypass ratio greater than about ten (10:1) and the fan diameter is significantly larger than an outer diameter of the low pressure compressor  44 . It should be understood, however, that the above parameters are only exemplary of one embodiment of a gas turbine engine including a geared architecture and that the present disclosure is applicable to other gas turbine engines. 
         [0047]    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. The flight condition of 0.8 Mach and 35,000 ft., with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of pound-mass (lbm) of fuel per hour being burned divided by pound-force (lbf) of thrust the engine produces at that minimum point. 
         [0048]    “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 1.50. In another non-limiting embodiment the low fan pressure ratio is less than about 1.45. 
         [0049]    “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. 
         [0050]    Referring to  FIGS. 2-3 , an example variable vane assembly  100  is shown. A variable vane  102  includes first and second trunnions  104 ,  105  and an airfoil  106 . The first trunnion  104  is arranged in a recess  107  in a shroud  108 . The shroud  108  may be circumferentially split into first and second halves  110 ,  112 . In one example, the first trunnion  104  is located on a radially inner side of the variable vane  102  with respect to the engine axis X, and the second trunnion  105  is located on a radially outer side of the variable vane  102 . The second trunnion  105  may be actuated by an actuator  109 . The actuator  109  causes the vane to pivot about an axis T of the trunnion  104 . In another example, the first trunnion  104  may be connected to the actuator  109  and the second trunnion  105  may be supported in the shroud. 
         [0051]    The trunnion  104  is arranged in an inner bushing  114 . The inner bushing  114  includes a retention feature. The retention feature may be a flange  116 . In this example, the trunnion  104  and the inner bushing  114  are mated in a press fit relationship. However, in another example, the trunnion  104  may be mated to the inner bushing  114  in another fashion. The inner bushing  114  is arranged in an outer bushing  118 . The outer bushing is received in the recess  107 . 
         [0052]      FIG. 4  shows the inner and outer bushings  114 ,  118  which together form a bushing assembly  120 . The flange  116  mates the inner bushing  114  to the outer bushing  118  by preventing axial movement of the inner bushing  114  away from the engine axis X. In one example, the vane  102  may be installed in the bushing assembly  120 . Then, the bushing assembly  120  may be installed into the shroud  108 . The inner bushing  114  is retained in the outer bushing  118  by the flange  116 . The press fit relationship between the trunnion  104  and the inner bushing  114  ( FIG. 3 ) retains the vane  102  in the inner bushing  114 . This arrangement serves to retain the vane  102  in the bushing assembly  120  and the shroud  108  via the inner and outer bushings  114 ,  118 . 
         [0053]    The outer bushing  118  includes one or more anti-rotation features. The anti-rotation features may be protrusions  122  which extend radially outward from an outer surface of the outer bushing  118 . Referring to  FIGS. 5 a - b    and  FIG. 6 , the protrusions  122  are received in a slot  124  in the first half  110  of the shroud  108 , preventing the outer bushing  118  from rotating about the trunnion axis T ( FIGS. 2-3 ). 
         [0054]    Because the primary wear takes place between the inner and outer bushings  114 ,  118 , a variety of materials can be matched to provide the desired wear characteristics. In one example, both the inner and outer bushings  114 ,  118  may be metallic. For example, the metal may be a steel or steel alloy, a nickel-chromium alloy such as Inconel 625 or Inconel 718, or a cobalt-chromium alloy such as Haynes 25. The inner and outer bushings  114 ,  118  may be made of the same or different materials, and may have coatings or surface treatments. 
         [0055]      FIGS. 7 a   -b show an alternate bushing  218  and shroud  208 . In this example, the outer bushing  218  includes first and second outer bushing flanges  219   a,    219   b . The first and second outer bushing flanges are on the radially inner and outer ends of the outer bushing  118  with respect to the engine axis X, respectively. The outer flange  219   b  is retained in the shroud  208  by shoulders  230 , preventing radial movement of the outer bushing  218  towards the engine axis X. Similarly, the inner flange  219   a  is retained by shoulders  232 , preventing radial movement of the outer flange away from the engine axis X. The inner bushing  114  is received inside the outer bushing  218 . The flange  116  on the inner bushing  114  is also retained by the shoulders  232 , and is disposed radially inward from the inner outer bushing flange  219   a  with respect to the engine axis X. 
         [0056]    The flanges  219   a,    219   b  may include at least one flat edge  221  which serves as an anti-rotation feature. In the example shown, the outer bushing flanges  219   a,    219   b  each include two flat edges  221  spaced circumferentially opposite from one another. Referring to  FIG. 7 c   , the flat edges  221  of the inner flanges  219   a  abut first and second axial lips  234   a,    234   b  formed in the shroud  208 , preventing the outer bushing  218  from rotating along the trunnion axis T. 
         [0057]    Similar to the previous example, the trunnion  104  and the inner bushing  114  are mated in a press fit relationship, retaining the trunnion  104  in the inner bushing  114 . The inner bushing  114  is retained in the outer bushing  218  by the inner bushing flange  116 . The outer bushing  218  is retained in the shroud  208  by the inner and outer flanges  219   a ,  219   b.    
         [0058]    Although example embodiments have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.