Abstract:
An example section of a gas turbine engine includes a plurality of variable vanes circumferentially disposed about an engine axis, a first moveable annular ring disposed on an upstream side of the variable vanes, a second movable annular ring disposed on a downstream side of the variable vanes, and a plurality of vane arms, each including a first end secured to the first annular ring and a second end secured to the second annular ring. Movement of the first and second annular rings moves the vane arms, thereby actuating the plurality of variable vanes. An example variable vane assembly includes a vane arm including a portion that engages a variable vane, a first end configured to be secured to a first movable annular ring, and a second end configured to be secured to a second movable annular ring. 
     Movement of the first and second annular rings moves the vane arms, thereby actuating the plurality of variable vanes. An example method of actuating a variable vane assembly includes the steps of securing a variable vane to a vane arm, the vane arm secured to a first movable annular ring at a so first end and a second movable annular ring at a second end, and moving at least one of the first and second rings to move the vane arm.

Description:
BACKGROUND 
       [0001]    This disclosure relates to a variable vane drive system for a gas turbine engine. 
         [0002]    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. The compressor section typically includes low and high pressure compressors, and the turbine section includes low and high pressure turbines. 
         [0003]    A speed reduction device such as an epicyclical gear assembly may be utilized to drive the fan section such that the fan section may rotate at a speed different and typically slower than the turbine section so as to provide a reduced part count approach for increasing the overall propulsive efficiency of the engine. In such engine architectures, a shaft driven by one of the turbine sections provides an input to the epicyclical gear assembly that drives the fan section at a reduced speed such that both the turbine section and the fan section can rotate at closer to optimal speeds. 
         [0004]    Although geared architectures utilized to drive the fan have improved propulsive efficiency, turbine engine manufacturers continue to seek further improvements to engine performance including improvements to thermal, transfer, and propulsive efficiencies. 
         [0005]    Some areas of the engine may include variable vanes. The compressor, for example, may include multiple stages of variable vanes. In some compressor designs, the variable vanes are connected to a synchronizing ring (sync-ring) by vane arms and form a sub-kinematic system for a particular stage. The vanes are driven by the sync-rings, which rotate clockwise and counterclockwise around the compressor case to pivot the vane arms and set the vane angle that optimizes engine operability. During operation, an actuation system drives the sync-ring. The sync-ring can be elastically deflected by reaction forces generated during vane movement. Some variable vane actuation systems may also have “assembly slop” such as gaps or deflections between the sync-ring and vane arm. 
       SUMMARY 
       [0006]    A section of a gas turbine engine according to an exemplary aspect of the present disclosure includes, among other things, a plurality of variable vanes circumferentially disposed about an engine axis, a first moveable annular ring disposed on an upstream side of the variable vanes, a second movable annular ring disposed on a downstream side of the variable vanes, and a plurality of vane arms, each including a first end secured to the first annular ring and a second end secured to the second annular ring, wherein movement of the first and second annular rings moves the vane arms, thereby actuating the plurality of variable vanes. 
         [0007]    In a further non-limiting embodiment of the foregoing engine section, movement of the first and second rings causes the vane arm to pivot about a radially extending axis. 
         [0008]    In a further non-limiting embodiment of either of the foregoing engine sections, the engine section further comprises a bell crank configured to move at least one of the first and second rings. 
         [0009]    In a further non-limiting embodiment of any of the foregoing engine sections, the bell crank is configured to move the first and second rings in opposite circumferential directions. 
         [0010]    In a further non-limiting embodiment of any of the foregoing engine sections, the engine section further comprises an actuator configured to actuate the first bell crank. 
         [0011]    In a further non-limiting embodiment of any of the foregoing engine sections, the engine section further comprises a second engine section including a second plurality of variable vanes circumferentially disposed about the engine axis, a third moveable annular ring disposed on an upstream side of the second plurality of variable vanes, a fourth movable annular ring disposed on a downstream side of the second plurality of vane arms, and a second plurality of vane arms, each including a first end secured to the first annular ring and a second end secured to the second annular ring, wherein movement of the first and second annular rings moves the second plurality of vane arms, thereby actuating the second plurality of variable vanes. 
         [0012]    In a further non-limiting embodiment of any of the foregoing engine sections, the engine section further comprises a second bell crank configured to move at least one of the third and fourth rings. 
         [0013]    In a further non-limiting embodiment of any of the foregoing engine sections, the engine section further comprises a second actuator configured to actuate the second bell crank. 
         [0014]    In a further non-limiting embodiment of any of the foregoing engine sections, the first and second actuators are configured to operate independently of one another. 
         [0015]    In a further non-limiting embodiment of any of the foregoing engine sections, the engine section further comprises a link configured to transfer forces between the first and second bell cranks. 
         [0016]    In a further non-limiting embodiment of any of the foregoing engine sections, the actuator is configured to actuate both the first and second bell cranks. 
         [0017]    In a further non-limiting embodiment of any of the foregoing engine sections, at least one of the first and second rings include at least one load relief slot. 
         [0018]    In a further non-limiting embodiment of any of the foregoing engine sections, the at least one load relief slot is formed around a portion of one of the first and second rings configured to receive the vane arms. 
         [0019]    In a further non-limiting embodiment of any of the foregoing engine sections, the engine section is a compressor section. 
         [0020]    A variable vane assembly according to an exemplary aspect of the present disclosure includes, among other things, a vane arm including a portion that engages a variable vane, a first end configured to be secured to a first movable annular ring, and a second end configured to be secured to a second movable annular ring, wherein movement of the first and second annular rings moves the vane arms, thereby actuating the plurality of variable vanes. 
         [0021]    In a further non-limiting embodiment of the foregoing variable vane assembly, the first end is upstream from the second end, relative to a direction of flow through the variable vane assembly. 
         [0022]    In a further non-limiting embodiment of either of the foregoing variable vane assemblies, the portion that engages the variable vane is between the first and second ends. 
         [0023]    A method of actuating a variable vane assembly according to an exemplary aspect of the present disclosure includes, among other things, securing a variable vane to a vane arm, the vane arm secured to a first movable annular ring at a first end and a second movable annular ring at a second end, and moving at least one of the first and second rings to move the vane arm. 
         [0024]    In a further non-limiting embodiment of the foregoing method of actuating a variable vane assembly, the moving step is provided by a bell crank. 
         [0025]    In a further non-limiting embodiment of either of the foregoing methods of actuating a variable vane assembly, the bell crank is actuated by an actuator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  schematically illustrates an example gas turbine engine. 
           [0027]      FIG. 2  illustrates an example high pressure compressor of the gas turbine engine of  FIG. 1  that includes variable vanes and an independent variable vane drive system. 
           [0028]      FIG. 3   a  illustrates a close-up view of some of the variable vanes of  FIG. 2 . 
           [0029]      FIG. 3   b  illustrates a close-up view of a sync-ring for the variable vanes of  FIG. 3   a  including a load relief slot. 
           [0030]      FIG. 4   a  illustrates a cutaway view of the variable vanes of  FIG. 3   a.    
           [0031]      FIG. 4   b  illustrates a close-up cutaway view of a portion of a fastener for the variable vanes of  FIG. 4   a.    
           [0032]      FIG. 5   a  illustrates a vane arm of the variable vanes of  FIG. 2 . 
           [0033]      FIG. 5   b  illustrates a close-up view of a portion of the vane arm of  FIG. 5   a.    
           [0034]      FIG. 6  illustrates a close-up view of a portion of an actuation system of the variable vanes of  FIG. 2 . 
           [0035]      FIG. 7   a  illustrates an alternate high pressure compressor including variable vanes and a dependent variable vane drive system 
           [0036]      FIG. 7   b  illustrates a close-up view of a portion of the dependent variable vane drive system of  FIG. 7   a.    
       
    
    
     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 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. 
         [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 A. 
         [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 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  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  as well as setting airflow entering the low pressure turbine  46 . 
         [0044]    The core airflow flowpath 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  58  includes vanes  60 , which are in the core airflow path and function as an inlet guide vane for the low pressure turbine  46 . Utilizing the vane  60  of the mid-turbine frame  58  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  58 . 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 (6:1), with an example embodiment being greater than about ten (10:1). 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 air in the bypass flowpath 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]    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 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 in the fan section  22  disclose an example gas turbine engine  20  with increased power transfer efficiency. 
         [0051]    Referring to  FIGS. 2-3   a  with continuing reference to  FIG. 1 , the high pressure compressor  52  may include one or more stages. In the example shown in  FIG. 2 , the high pressure compressor  52  includes first, second, and third stages  62 ,  64 ,  66 , but in another example the high pressure compressor  52  may include a different number of stages. A compressor case  68  may surround portions of the high pressure compressor  52 . 
         [0052]    The high pressure compressor  52  includes a plurality of variable vanes  70  extending radially relative to the engine axis A. The variable vanes  70  include a vane arm  72  including a first end secured to a first annular sync-ring  74   a  and an opposing second end secured to a second annular sync-ring  74   b . The first and second sync-rings  74   a ,  74   b  are movable. In the example shown in  FIG. 2 , the first sync-ring  74   a  is arranged downstream from the second sync-ring  74   b  with respect to the direction of flow through the high pressure compressor  52 . A vane stem  75  is secured to the vane arm  72  by a fastener  77 . The vane stem  75  is connected to a vane trunnion  76 , which is in turn connected to a vane airfoil (not shown). In one example, the vane arm  72  may be secured to the sync-rings  74   a ,  74   b  by bolts  78 , such as eddie bolts. 
         [0053]    In operation, the sync-rings  74   a ,  74   b  rotate circumferentially about the engine axis A ( FIG. 2 ) in opposite directions to provide circumferential forces to the first and second ends of the vane arm  72 , respectively. Applying these forces causes the vane arm  72  to pivot about a radially extending axis D. 
         [0054]    The vane arm  72  may pivot about the location in which it receives the vane stem  75 . In the example shown, the circumferential forces applied to the vane arm  72  by the sync-rings  74   a ,  74   b  are equal and opposite, but in another example, the circumferential forces applied by the sync-rings  74   a ,  74   b  may be unequal. Movement of the first and second sync-rings  74   a ,  74   b  moves the vane arms  72 , thereby actuating the variable vanes  70 . The forces applied to the vane arm  72  by the sync-rings  74   a ,  74   b  cause the vane stem  75 , the vane trunnion  76  and the vane airfoil (not shown) to rotate about a radially extending axis D. 
         [0055]    The load necessary to rotate the vane arm  72  is split between the two sync-rings  74   a ,  74   b , which provides for relatively even loading on the vane arm  72 . This may reduce component wear to the vane arm  72 , improve concentricity of the sync-rings  74   a ,  74   b  with respect to the high pressure compressor  52  and engine  20 , and generally reduce the likelihood of the variable vanes  70  becoming out of sync with one another. 
         [0056]    The sync-rings  74   a ,  74   b  may include load relief slots  80  which serve to relieve any resistive forces, such as axial forces, that are generated when the vane arms  72  are forced to pivot.  FIG. 3   b  shows a detail view of the load relief slot  80  in the sync-ring  74   a . In another example, the sync-ring  74   b  may also include a load relief slot. The load relief slot  80  may be formed around a hole  84  which receives the bolt  78  for securing the vane arm  72  to the sync-rings  74   a ,  74   b . The load relief slot  80  relieves the resistive forces by permitting some axial movement of bolt  78  when the sync-rings  74   a ,  74   b  rotate. Relief of these resistive forces prevents the sync-rings  74   a ,  74   b  from coming out of alignment with one another and with the high pressure compressor  52 , and prevents elastic deflection of the sync-rings  74   a ,  74   b.    
         [0057]    Referring now to  FIGS. 4   a - 5   b , the vane arm  72  includes a bushing  88  which receives the bolt  78 . A controlled clearance gap  86  is maintained between the bushing  88  and the sync-rings  74   a ,  74   b .The clearance gap  86  provides further axial load relief during variable vane  70  actuation and prevents component wear by allowing for deflection of the vane arm  72  with respect to the sync-rings  74   a ,  74   b . In one example, a channel  87  in the sync-rings  74   a ,  74   b  is U-shaped. 
         [0058]    Referring again to  FIG. 2 , the high pressure compressor  52  is shown with an independent drive system. That is, variable vanes  70  in each stage  62 ,  64 ,  66  may be actuated independently from one another. In this example, actuators  90  apply a load to bell cranks  92 . The bell cranks  92  span both sync rings  74   a ,  74   b  in each stage  62 ,  64 ,  66 . Referring to  FIG. 6 , the actuator  90  may apply a circumferential load to the bell crank  92  such that the bell crank  92  pivots about a central point  94 . The pivoting of the bell crank  92  causes arms  96   a ,  96   b  to rotate one of the sync-rings  74   a ,  74   b  in a clockwise direction and the other of the sync-rings  74   a ,  74   b  in the counterclockwise direction. The sync-rings  74   a ,  74   b  thus apply forces to the vane arms  72  to cause the vane arms  72  to pivot about the radially extending axis D ( FIGS. 3   a  and  4   a ). 
         [0059]      FIGS. 7   a - 7   b  show another example of the high pressure compressor  52  with a dependent drive system. In the dependent drive system, the variable vanes  70  in each stage  62 ,  64 ,  66  may be actuated in unison. An actuator  90 ′ applies an axial load to the bell cranks  92 ′. Links  93  interconnect bell cranks  92 ′. Axial loads applied by the actuator  90 ′ are transferred to each bell crank  92 ′ by a link  93 , actuating the variable vanes  70  as was described above. It should be understood that the high pressure compressor  52  may include an independent drive system, a dependent drive system or, a combination of the two. 
         [0060]    While the variable vane actuation system is described herein in the context of the high pressure compressor  52 , it should be understood that the variable vane actuation system may be used in other parts of the engine which include variable vanes, for example, the high or low pressure turbines  46 ,  54 . 
         [0061]    Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.