Abstract:
A variable vane mechanism comprises a variable vane, an inner diameter shroud and a synchronizing mechanism. The variable vane comprises a vane body, an inner diameter trunnion extending radially inwardly from the vane body, and a button connected to the inner diameter trunnion and displaced radially inwardly from the inner diameter trunnion. The shroud comprises a shroud body, a socket extending into the shroud body for receiving the inner diameter trunnion, a flange extending into the socket for engaging the button and inhibiting radial movement of the variable vane, and a synchronizing channel extending through the inner diameter shroud aft of the socket so as to be bounded by the shroud body and opening to the socket. The synchronizing mechanism is disposed inside the synchronizing channel and connects to the inner diameter trunnion.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This is a continuation under 35 U.S.C. 120 of U.S. Pat. No. 7,588,415 having application Ser. No. 11/185,623, entitled “SYNCH RING VARIABLE VANE SYNCHRONIZING MECHANISM FOR INNER DIAMETER VANE SHROUD,” filed Jul. 20, 2005 by J. Giaimo and J. Tirone III. 
     The present application is related to the following applications filed on Jul. 20, 2005: “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) now U.S. Pat. No. 7,665,959; “GEAR TRAIN VARIABLE VANE SYNCHRONIZING MECHANISM FOR INNER DIAMETER VANE SHROUD” by inventors J. Giaimo and J. Tirone III (Ser. No. 11/185,624), now U.S. Pat. No. 7,628,579; “INNER DIAMETER VARIABLE VANE ACTUATION MECHANISM” by inventors J. Giaimo and J. Tirone III (Ser. No. 11/185,995), now U.S. Pat. No. 7,690,889; “LIGHTWEIGHT CAST INNER DIAMETER VANE SHROUD FOR VARIABLE STATOR VANES” by inventors J. Giaimo and J. Tirone III (Ser. No. 11/185,956), now U.S. Pat. No. 7,753,647. All of these applications are incorporated herein by this reference. 
    
    
     STATEMENT OF GOVERNMENT INTEREST 
     The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of N00019-02-C-3003 awarded by the United States Navy. 
    
    
     BACKGROUND 
     This invention relates generally to gas turbine engines and more particularly to variable stator vane assemblies 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. 
     SUMMARY 
     The present invention is related to a variable vane mechanism for use with a gas turbine engine. The variable vane mechanism comprises a variable vane, an inner diameter shroud and a synchronizing mechanism. The variable vane comprises a vane body and an inner diameter trunnion extending radially inwardly from the vane body. The shroud comprises a shroud body, a socket extending into the shroud body for receiving the inner diameter trunnion and a synchronizing channel extending through the inner diameter shroud aft of the socket so as to be bounded by the shroud body and opening to the socket. The synchronizing mechanism is disposed inside the synchronizing channel and connects to the inner diameter trunnion. In another embodiment, the variable vane includes a button connected to the inner diameter trunnion and displaced radially inwardly from the inner diameter trunnion, and the shroud includes a flange extending into the socket for engaging the button and inhibiting radial movement of the variable vane. 
    
    
     
       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 close up of a portion of stator vane array positioned between a fan case and the inner diameter vane shroud of the present invention. 
         FIG. 3  shows section  3 - 3  of  FIG. 2  showing a cross section of the inner diameter vane shroud at the vane sockets. 
     
    
    
     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 synch ring 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 degrees) 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 degrees) the circumference of inner diameter vane shroud  14 , in which case each section has twenty six half-sockets  24 . The synch ring variable vane synchronizing mechanism of the present invention is constructed in smaller segments, such as approximately one half (i.e. 180 degrees) segments, for use in split fan case designs. Additionally, in other embodiments, forward vane shroud component  20  and aft vane shroud component  22  can be made as full rings (i.e. 360 degrees), along with synch ring variable vane synchronizing mechanism, for use in full ring 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 synch ring variable vane synchronizing mechanism of the present invention coordinates their rotation. 
       FIG. 2  shows a close up of a portion of stator vane array  16  positioned between fan case  12  and inner diameter vane shroud  14  of the present invention. Drive vanes  26  and follower vanes  28  are rotatable in sockets  24  of inner diameter vane shroud  14  at an inner diameter end. Drive vanes  26  and follower vanes  28  are rotatable in fan case  12  at an outer diameter end. Section  3 - 3  is taken at a position along inner diameter vane shroud  14  where inner diameter end of follower vane  28 A is inserted in socket  24 A. Forward shroud component  20  and aft shroud component  22  come together to form sockets  24  for securing the inner ends of variable vane array  16 . 
       FIG. 3  shows section  3 - 3  of  FIG. 2  showing a cross section of inner diameter vane shroud  14  at vane socket  24 A. Inner diameter vane shroud  14  includes forward shroud component  20 , aft shroud component  22 , socket  24 A, inner channel  30  and clearance hole  32 . Forward shroud component  20  includes first forward wall  20 A, bottom wall  20 B and aft facing surface  20 C. Aft shroud component  22  includes second forward wall  22 A, multi-faceted aft wall  22 B and top wall  22 C. Socket  24 A connects to neck bore  24 B, button cavity  24 C and C-shaped channel  24 D, which is formed by inner channel  30 . Vane arm  34  includes trunnion hoop  36  and pin hole  37 . Synch ring  38  includes lug  40  and bumper  42 . Follower vane  28 A includes locking insert  44 , trunnion  46 , vane arm post  48  and fastener channel  50 . 
     Locking insert  44  is secured inside of fastener channel  50 . Trunnion hoop  36  of vane arm  34  is inserted over vane arm post  48 . Button  52  is secured around the head of fastener  54 . Fastener  54  is then inserted into fastener channel  50  and threaded into locking insert  44 . Button  52  forces trunnion hoop  36  against trunnion  46  and secures it around vane arm post  48 . In one embodiment, vane arm post  48  and trunnion hoop  36  have a square profile such that when trunnion hoop  36  is inserted around vane arm post  48  they cannot rotate relative to one another. Follower vane  28 A, vane arm  34 , fastener  54  and button  52  are installed into fan case  12 . This process is repeated for all follower vanes  28  and drive vanes  26 . Bumper  42  is positioned on a lower surface of synch ring  38  to assist synch ring  38  in maintaining a circular path through inner channel  30 . Synch ring  38  is positioned inside of aft shroud component  22 . Aft shroud component  22 , along with synch ring  38 , is then positioned against trunnions  46 . Pin  56  is positioned through clearance hole  32 , and into pin hole  37 , securely fastening vane arm  34  to lug  40 . Pin  56  is tight fitting in lug  40  and vane arm  34  is allowed to pivot at pin  56 . The plurality of follower vanes  28  and drive vanes  26  of variable vane array  16  are linked to synch ring  38  in similar fashion. 
     Forward shroud component  20  is positioned against aft shroud component  22  such that socket  24 A fits around button  52 . Button  52  is used to pivotably secure follower vane  28 A inside socket  24 A. Forward shroud component  20  is fastened to aft shroud component  22  as is known in the art. 
     During operation of synch ring variable vane synchronizing mechanism, actuator  18  rotates drive vanes  26 . Vane arms  34  of drive vanes  26  are likewise rotated about trunnion  46 . Synch ring  38  is pushed by vane arms  34  of drive vanes  26  and rotates inside inner channel  30 . Synch ring  38  thereby pulls vane arms  34  connected to follower vanes  28 , which in turn rotates follower vanes  28  the same amount that drive vanes  26  are rotated by actuator  18 . 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 synch ring variable vane synchronizing mechanism. 
     The synch ring variable vane synchronizing mechanism of the present invention can be constructed in smaller segments. In one embodiment, synch ring  38  is divided into first and second segments for use in split fan case designs. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.