Abstract:
An inner diameter vane shroud accommodates a mechanism for synchronously rotating an away of variable vanes. Particularly, the inner diameter vane shroud has a gear channel that runs circumferentially through the vane shroud. An array of variable vanes is rotatably mounted in the vane shroud at an inner end. The variable vanes comprise vane gears at their inner end, which are rotatable in the gear channel. Disposed between the vane gears of the variable vanes are idler gears. As one of the individual variable vanes is rotated by an actuation source, the other variable vanes of the variable vane away are rotated a like amount by the vane gears and idler gears.

Description:
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) 
   The present application is related to the following copending applications filed on the same day as this application: “RACK AND PINION VARIABLE VANE SYNCHRONIZING MECHANISM FOR INNER DIAMETER VANE SHROUD” by inventors J. Giaimo and J. Tirone III (Ser. No. 11/185,622); “SYNCH RING VARIABLE VANE SYNCHRONIZING MECHANISM FOR INNER DIAMETER VANE SHROUD” by inventors J. Giaimo and J. Tirone III (Ser. No. 11/185,623); “INNER DIAMETER VARIABLE VANE ACTUATION MECHANISM” by inventors J. Giaimo and J. Tirone III (Ser. No. 11/185,995); and “LIGHTWEIGHT CAST INNER DIAMETER VANE SHROUD FOR VARIABLE STATOR VANES” by inventors J. Giaimo and J. Tirone III (Ser. No. 11/185,995). All of these applications are incorporated herein by this reference. 
   BACKGROUND OF THE INVENTION 
   This invention relates generally to gas turbine engines and more particularly to vane shrouds for use in such engines. 
   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. 
   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. 
   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 on the 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 
   The present invention comprises an inner diameter vane shroud that accommodates a mechanism for synchronously rotating an array of variable vanes. Particularly, the invention comprises an inner diameter vane shroud that has a gear channel that runs circumferential through the vane shroud. An array of variable vanes is rotatably mounted in the vane shroud at an inner end. The variable vanes comprise gears at their inner end, which are rotatable in the gear channel. Disposed between the gears of the variable vanes are idler gears. 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 gears and idler gears. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       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. 
       FIG. 2  shows a perspective view of the front of a segment of an array of variable vanes showing the gear train synchronizing mechanism of the present invention. 
       FIG. 3  shows a bottom view of the gear train variable vane synchronizing mechanism of  FIG. 2 , as seen from the center of the stator vane section looking out. 
       FIG. 4  shows a perspective view of the front of a portion of an aft vane shroud component of an inner diameter vane shroud of the present invention. 
       FIG. 5  shows a perspective view of the back of a portion of a forward vane shroud component of an inner diameter vane shroud of the present invention. 
   

   DETAILED DESCRIPTION 
     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 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. 
   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 gear train variable vane synchronizing mechanism of the present invention. Thus, when actuator  18  rotates drive vanes  26 , follower vanes  28  rotate a like amount. 
   Typically, follower vanes  28  encircle the entirety of vane shroud  14 . 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 . In one embodiment, drive vanes  26  are of heavy duty construction to withstand forces applied by actuator  18 . 
   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 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 . Additionally, in other embodiments, the gear train variable vane synchronizing mechanism of the present invention can be constructed in smaller segments, such as approximately one half (i.e. 180°) segments, for use in split fan case designs. 
   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 gear train variable vane synchronizing mechanism of the present invention coordinates their rotation. 
     FIG. 2  shows a perspective view of the front of a segment of variable vane away  16  showing the gear train variable vane synchronizing mechanism of the present invention. Fan case  12 , forward vane shroud component  20  and aft vane shroud component  22  are not shown in order to show the interrelation of the gear train synchronizing mechanism. Follower vanes  28  include inner diameter trunnions  30  for rotating in sockets  24  of inner diameter vane shroud  14 . Follower vanes  28  include outer diameter trunnions  32  for rotating in bosses of fan case  12  (shown in  FIG. 1 ). Inner diameter trunnions include buttons  33 , vane gears  34  and gear posts  35 . Typically, at least one outer trunnion  32  is connected to an actuation source outside of fan case  12 . Inner trunnions  30  are configured for rotating in sockets  24  of vane shroud  14 . 
   The gear train synchronizing mechanism of the present invention is located on the inside of inner diameter vane shroud  14 . The gear train synchronizing mechanism includes vane gears  34  and idler gears  36 . The gear train synchronizing mechanism is a simple gear train consisting of alternating driven gears (vane gears  34 ) and idler gears (idler gears  36 ). The gear train is aligned in a circular fashion so as to form a closed loop of interconnected gears within vane shroud  14 . In other embodiments, the gear train is shaped in arcuate segments, such as approximately half circle (i.e. 180°) segments for use in split fan case designs. Inner trunnions  30  link follower stator vanes  28  with the gear train synchronizing mechanism. Thus, when one of the outer trunnions  32  is rotated by an actuation source, such as the outer trunnions of drive vanes  26 , follower vanes  28  rotate in unison by way of the gear train. 
   Inner trunnions  30  include vane gears  34  at their inner diameter end. Positioned between vane gears  34  are idler gears  36 . Vane gears  34  are positioned in an inner gear channel of vane shroud  14  when assembled with forward shroud component  20  and aft shroud component  22 . Idler gears  36  are rotatably mounted within the inner gear channel of vane shroud  14 . In one embodiment, alternating vane gears  34  and idler gears  36  continue around the entire circumference of vane shroud  14  in conjunction with a full variable vane array  16 . In one embodiment, variable vane array  16  includes fifty-four vane gears  34  and fifty-four idler gears  36 . 
     FIG. 3  shows a bottom view of the gear train variable vane synchronizing mechanism of  FIG. 2 , as seen from the center of the stator vane section looking out. Vane gears  34 A- 34 D are located at the inner diameter end of follower vanes  28 , at the tip of inner trunnions  30 . Vane gears  34 A- 34 D are allowed to rotate in the inner gear channel of vane shroud  14 . Idler gears  36 A- 36 C are rotatably mounted in the inner gear channel between vane gears  34 A- 34 D. 
   When one or more of outer trunnions  32  is rotated by an actuation source, the rotation of individual follower vanes  28 A- 28 D is coordinated with the gear train synchronizing mechanism. For example, if stator vane  28 A is rotated in a clock-wise direction (as shown in  FIG. 3 ) by actuator  18 , idler gear  36 A is rotated counter-clock-wise by stator vane  26 A. Remaining vane gears  34 B- 34 D and idler gears  36 B- 36 C rotate in a like manner. Vane gear  34 B is rotated clock-wise by idler gear  36 A. Idler gear  36 B is rotated counter-clock-wise by vane gear  34 B. Vane gear  34 C is rotated clock-wise by idler gear  36 B. Idler gear  36 C is rotated counter-clock-wise by vane gear  34 C. Vane gear  34 D is rotated clock-wise by idler gear  36 C. This same type of alternating rotation of vane gears and idler gears continues throughout the length of the gear train. Thus, actuation of a single vane rotates the entirety of follower vanes  28  an equal amount. 
     FIG. 4  shows a perspective view of the front of a portion of aft vane shroud component  22  of inner diameter vane shroud  14  of the present invention. Aft vane shroud component  22  includes aft recesses  38 A- 38 H for receiving inner trunnions  30  of drive vanes  26  and follower vanes  28 . Inner trunnions  30  are inserted into aft recesses  38 A- 38 H such that vane gears  34  are located in aft inner gear channel  40 A. Idler gears  36  are rotatably positioned in aft gear channel  40 A at intervals between aft recesses  38 A- 38 H at positions  42 A- 42 G. 
     FIG. 5  shows a perspective view of the back of a portion of forward vane shroud component  20  of inner diameter vane shroud  14  of the present invention. Forward vane shroud component  20  includes forward recesses  44 A- 44 H for receiving inner trunnions  30  of drive vanes  26  and follower vanes  28 . Forward vane shroud component  20  is coupled with aft vane shroud component  22  such that aft recesses  38 A- 38 H and forward recesses  44 A- 44 H match up, respectively. Inner trunnions  30  are positioned inside aft recesses  38 A- 38 H and forward recesses  44 A- 44 H, and vane gears  34  are positioned inside aft gear channel  40 A and forward gear channel  40 B. Idler gears  36  are positioned at intervals between forward recesses  44 A- 44 H at positions  46 A- 46 G, inside aft gear channel  40 A and forward gear channel  40 B. Thus, drive vanes  26  and follower vanes  28  are secured with forward shroud component  20  and aft shroud component  22 . The gear train comprised of vane gears  34  and idler gears  36  is operably located in aft gear channel  40 A and forward gear channel  40 B in order to facilitate synchronized rotation of individual stator vanes  26 . 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 gear train variable vane synchronizing mechanism. 
   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.