Abstract:
An inner diameter vane shroud of a variable vane assembly accommodates a synchronization mechanism for coordinating rotation of an array of variable vanes. The inner diameter vane shroud has a gear track that runs circumferentially through the vane shroud. An array of variable vanes is rotatably mounted in the vane shroud at an inner end. Each vane has a gear pinion at its inner end, which interfaces with the gear track. As one of the individual variable vanes is rotated by an actuation source, the other variable vanes of the variable vane array are rotated a like amount by the rack and pinion gear interface.

Description:
[0001]     This invention was made with U.S. Government support under contract number N00019-02-C-3003 awarded by the United States Navy, and the U.S. Government. may have certain rights in the invention. 
     
    
     CROSS-REFERENCE TO RELATED APPLICATION(S)  
       [0002]     The present application is related to the following copending applications filed on the same day as this application: “SYNCH RING VARIABLE VANE SYNCHRONIZING MECHANISM FOR INNER DIAMETER VANE SHROUD” by inventors J. Giaimo and J. Tirone III (attorney docket number U73.12-003); “GEAR TRAIN VARIABLE VANE SYNCHRONIZING MECHANISM FOR INNER DIAMETER VANE SHROUD” by inventors J. Giaimo and J. Tirone III (attorney docket number U73.12-004); “INNER DIAMETER VARIABLE VANE ACTUATION MECHANISM” by inventors J. Giaimo and J. Tirone III (attorney docket number U73.12-005); and “LIGHTWEIGHT CAST INNER DIAMETER VANE SHROUD FOR VARIABLE STATOR VANES” by inventors J. Giaimo and J. Tirone III (attorney docket number U73.12-006). All of these applications are incorporated herein by this reference.  
       BACKGROUND OF THE INVENTION  
       [0003]     This invention relates generally to gas turbine engines and more particularly to variable stator vane assemblies for use in such engines.  
         [0004]     Gas turbine engines operate by combusting a fuel source in compressed air to create heated gases with increased pressure and density. The heated gases are ultimately forced through an exhaust nozzle, which is used to step up the velocity of the exiting gases and in-turn produce thrust for driving an aircraft. The heated gases are also used to drive a turbine for rotating a fan to provide air to a compressor section of the gas turbine engine. Additionally, the heated gases are used to drive a turbine for driving rotor blades inside the compressor section, which provides the compressed air used during combustion. The compressor section of a gas turbine engine typically comprises a series of rotor blade and stator vane stages. At each stage, rotating blades push air past the stationary vanes. Each rotor/stator stage increases the pressure and density of the air. Stators serve two purposes: they convert the kinetic energy of the air into pressure, and they redirect the trajectory of the air coming off the rotors for flow into the next compressor stage.  
         [0005]     The speed range of an aircraft powered by a gas turbine engine is directly related to the level of air pressure generated in the compressor section. For different aircraft speeds, the velocity of the airflow through the gas turbine engine varies. Thus, the incidence of the air onto rotor blades of subsequent compressor stages differs at different aircraft speeds. One way of achieving more efficient performance of the gas turbine engine over the entire speed range, especially at high speed/high pressure ranges, is to use variable stator vanes which can optimize the incidence of the airflow onto subsequent compressor stage rotors.  
         [0006]     Variable stator vanes are typically circumferentially arranged between an outer diameter fan case and an inner diameter vane shroud. Traditionally, mechanisms coordinating the synchronized movement of the variable stator vanes have been located on the outside of the fan case. These systems increase the overall diameter of the compressor section, which is not always desirable or permissible. Also, retrofitting gas turbine engines that use stationary stator vanes for use with variable stator vanes is not always possible. Retrofit variable vane mechanisms positioned outside of the fan case interfere with other external components of the gas turbine engine located on the outside of the fan case. Relocating these other external components is often impossible or too costly. Synchronizing mechanisms also add considerable weight to the gas turbine engine. Thus, there is a need for a lightweight variable vane synchronizing mechanism that does not increase the diameter of the compressor section and does not interfere with other external components of the gas turbine engine.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     In the present invention, an inner diameter vane shroud accommodates a synchronizing mechanism for coordinating rotation of an array of variable vanes. The inner diameter vane shroud has a gear track that runs circumferentially through the vane shroud. An array of variable vanes is rotatably mounted in the vane shroud at an inner end. Each variable vane includes a gear pinion at its inner end, which interfaces with the gear track. As one of the individual variable vanes is rotated by an actuation source, the other variable vanes of the variable vane array are rotated a like amount by the rack and pinion gear interface. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  shows a partially cut away front view of a stator vane section of a gas turbine engine in which the present invention is used.  
         [0009]      FIG. 2A  shows a front view of a segment of the stator vane section of  FIG. 1  between arrows A and C, with the inner diameter vane shroud removed between arrows B and C and the fan case removed.  
         [0010]      FIG. 2B  shows a partially cut away front view of a segment of the inner diameter vane shroud between arrows A and B of  FIG. 1 .  
         [0011]      FIG. 3A  shows a close-up of the rack and pinion mechanism of the present invention shown from the vantage of line D-D in  FIG. 2A .  
         [0012]      FIG. 3B  shows approximately a bottom view of the rack and pinion mechanism of  FIG. 2A  shown from the vantage of the center of the stator vane section looking out.  
     
    
     DETAILED DESCRIPTION  
       [0013]      FIG. 1  shows a partially cut away front view of stator vane section  10  of a gas turbine engine in which the present invention is used. Stator vane section  10  comprises fan case  12 , vane shroud  14 , variable vane array  16  and actuator  18 . Vane shroud  14  is comprised of forward vane shroud component  20  and aft vane shroud component  22 , which form inner diameter vane sockets  24 . A half-socket, or a recess, is located on each of forward vane shroud component  20  and aft vane shroud component  22  to form socket  24 . In  FIG. 1 , only a portion of forward vane shroud component  20  is shown so that the interior of sockets  24  can be seen.  
         [0014]     Variable vane array  16  is comprised of drive vanes  26  and a plurality of follower vanes  28 . Drive vanes  26  and follower vanes  28  are connected inside inner diameter vane shroud  14  by the rack and pinnion variable vane synchronizing mechanism of the present invention. Thus, when actuator  18  rotates drive vanes  26 , follower vanes  28  rotate a like amount.  
         [0015]     Typically, follower vanes  28  encircle the entirety of vane shroud  14 . For clarity, only a portion of variable vane array  16  is shown so that sockets  24  can be seen. Drive vanes  26  and follower vanes  28  are rotatably mounted at the outer diameter of stator vane section  10  in fan case  12 , and at the inner diameter of stator vane section  10  in vane shroud  14 . The number of drive vanes  26  varies in other embodiments and can be as few as one. In one embodiment, variable vane array  16  includes fifty-two follower vanes  28  and two drive vanes  26 . Drive vanes  26  are similar in construction to follower vanes  28  comprising variable vane array  16 . In one embodiment, drive vanes  26  are of heavy duty construction to withstand forces applied by actuator  18 .  
         [0016]     Inner diameter vane shroud  14  can be constructed in component sizes less than the entire circumference of inner diameter vane shroud. In one embodiment, as shown in  FIG. 1 , forward vane shroud component  20  is made of sections approximately one sixth (i.e. 60°) of the circumference of inner diameter vane shroud  14 . In such a case, two sections have nine half-sockets  24  and one section has eight half-sockets  24 . Smaller forward vane shroud components  20  assist in positioning forward vane shroud component  20  under the inner diameter ends of drive vanes  26  and follower vanes  28  when they are inserted in sockets  24 . In one embodiment for use in split fan case designs, aft vane shroud component  22  is made of sections approximately one half (i.e. 180°) the circumference of inner diameter vane shroud  14 , in which case each section has twenty six half-sockets  24 . The rack and pinion variable vane synchronizing mechanism of the present invention is constructed in smaller segments, such as approximately one half (i.e. 180°) segments, for use in split fan case designs. Additionally, in other embodiments, the forward vane shroud component  20  and aft vane shroud component  22  can be made as full rings (i.e. 360°), along with the rack and pinion variable vane synchronizing mechanism, for use in full ring fan case designs.  
         [0017]     Stator vane section  10  is typically located in a compressor section of a gas turbine engine downstream of, or behind, a rotor blade section. Air is forced into stator vane section  10  by a preceding rotor blade section or by a fan. The air that passes through stator vane section  10  typically passes on to an additional rotor blade section. Drive vanes  26  and follower vanes  28  rotate along their respective radial positions in order to control the flow of air through the compressor section of the gas turbine engine. The rack and pinion variable vane synchronizing mechanism of the present invention coordinates their rotation.  
         [0018]      FIG. 2A  shows a front view of a segment of stator vane section  10  of  FIG. 1  between arrows A and C, with the inner diameter vane shroud removed between arrows B and C and the fan case removed. Inner diameter vane shroud  14  is comprised of forward vane shroud component  20  and aft vane shroud component  22 . Forward vane shroud component  20  and aft vane shroud component  22  together form sockets  24  for receiving inner diameter trunnions  30  of follower vanes  28 . Follower vanes  28  include outer diameter trunnions  32  for rotating in bosses of fan case  12  (shown in  FIG. 1 ). The rack and pinion synchronizing mechanism of the present invention is located on the inside of inner diameter vane shroud  14 . Rack and pinion synchronizing mechanism includes gear rack  34 , which can be seen in sockets  24 . Gear rack  34  is slidably positioned in aft vane shroud component  22  at a level at which it can interface with inner diameter trunnions  30 .  
         [0019]      FIG. 2B  shows a partially cut away front view of a segment of inner diameter vane shroud  14  between arrows A and B of  FIG. 1 . The rack and pinion synchronizing mechanism is comprised of gear rack  34  and gear track  36 . Gear track  36  is located on a forward facing surface of aft vane shroud component  22 . Inner diameter trunnion  30  of follower vane  28  is inserted into socket  24  of inner diameter vane shroud  14 . The cut away portion of forward vane shroud component  20  reveals the inside of socket  24 . Socket  24  has a profile that matches that of inner diameter trunnion  30  so that inner diameter trunnion  30  locks into assembled inner diameter vane shroud  14 , yet remains able to rotate in socket  24 . Gear track  36  cuts through aft vane shroud component  22  at a level running through socket  24  so gear rack  34  interfaces with inner diameter trunnion  30 . Gear rack  34  is slidably located in gear track  36  with its gear teeth facing in the forward direction so they can interface with pinion gears of inner diameter trunnions  30 . In one embodiment, gear rack  34  and gear track  36  extend the entire circumference of inner diameter vane shroud  14  to form a single continuous rack and track segment (i.e. 360°). In other embodiments, gear rack  34  and gear track  36  can be constructed in. smaller segments, such as approximately one half (i.e. 180°) segments, for use in split fan case designs.  
         [0020]      FIG. 3A  shows a close-up of the rack and pinion mechanism of the present invention shown from the vantage of line D-D in  FIG. 2A . Forward vane shroud component  20  and aft vane shroud component  22  comprise inner diameter vane shroud  14 . Gear rack  34  includes rack gear teeth  42 . Inner diameter trunnions  30  include pinion gears  38  that include arcuate gear teeth segments  40 . Inner diameter trunnions  30  also include buttons  44 , which are used to pivotably secure follower vanes  28  inside sockets  24 .  
         [0021]     Pinion gears  38  are located on an aft facing portion of inner diameter trunnions  30 . Pinion gears  38  are positioned along inner diameter trunnions  30  such that pinion gears  38  are insertable in gear track  36 . Pinion gears  38  include arcuate gear teeth segments  40  that interface with rack gear teeth  42 . Gear rack  34  is free to slide in gear track  36 , which extends into the circumference of vane shroud  14 . Gear rack  34  is able to continuously rotate the entire circumference of vane shroud  14  within gear track  36 . Rack gear teeth  42  run the entire forward facing circumference of gear rack  34 .  
         [0022]      FIG. 3B  shows approximately a bottom view of the rack and pinion mechanism of  FIG. 2A  shown from the vantage of the center of the stator vane section  10  looking out. Inner diameter vane shroud  14  comprises forward vane shroud component  20  and aft vane shroud component  22 , which clamp around inner diameter trunnions  30  and gear rack  34 . Rack gear teeth  42  and arcuate. gear teeth segments  40  mesh together when forward vane shroud component  20  and aft vane shroud component  22  are coupled together with rack and pinion synchronizing mechanism. Only a portion of the teeth of arcuate gear teeth segments  40  mesh with rack gear teeth  42  at any time. This allows follower stator vanes  28  to rotate and to maintain a gear tooth interface at all times. In the embodiment shown in  FIG. 3B , the teeth located toward the center of arcuate gear tooth segment  40  mesh with rack gear teeth  42  when follower stator vanes  28  are in their centered or zeroed position. The center position can vary, depending on design requirements, depending on their orientation when linked to actuator  18 .  
         [0023]     Gear rack  34  is slidably contained in inner diameter vane shroud  14 . Gear rack  34  synchronizes the rotation of follower stator vanes  28  when drive vanes  26  are rotated by actuator  18 . For example, if drive vanes  28  are rotated clockwise (as shown in  FIG. 3B ), gear rack  34  will be pushed to the left. Gear rack  34  will in-turn push pinion gears  38  to the left through rack gear teeth  42  and arcuate gear tooth segments  40 . This causes follower stator vanes  28  of stator vane array  16  to likewise rotate in a clockwise direction. Thus, the direction of the flow of air exiting stator vane section  10  can be controlled for entry into the next section of the gas turbine engine utilizing the rack and pinion variable vane synchronizing mechanism.  
         [0024]     Gear rack  34  and pinion gears  38  connect all follower stator vanes  28  similarly, such that the selection of drive vanes  26  can be made from any of the array of follower vanes  28 . In one embodiment, follower vanes  28  selected to be the drive vane can be of a heavy duty construction to withstand forces applied by actuator  18 .  
         [0025]     The amount of rotation of drive vanes  26  and follower vanes  28  depends on the length of the actuation stroke, the number of teeth used, the amount of curvature of arcuate gear tooth segments  40 , and other factors that are known in the art. The invention can be tailored to specific design requirements by varying these factors.  
         [0026]     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.