Patent Document

BACKGROUND 
       [0001]    Gas turbine engines include one or more compressors for pressurizing a working medium fluid, typically ambient air, which flows through a longitudinally extending compressor flow path. Under some operating conditions, it is desirable to temporarily moderate the pressure at the discharge end of the compressor to prevent or recover from compressor stall or other aerodynamic instabilities. Pressure moderation is usually effected by opening a compressor bleed valve that diverts a portion of the pressurized fluid from the discharge end of the compressor flow path into a lower pressure region. 
         [0002]    An exemplary compressor bleed valve system includes a moveable full hoop valve ring with a pair of ring seal members radially aligned with the bleed duct case seal seats. The compressor bleed duct includes a stationary ring having a pair of resilient seal members adhesively bonded or clamped into respective channels on longitudinally facing surfaces of the ring. A series of circumferentially distributed passages extend through the bleed duct case to join the compressor flow path to a surrounding annular chamber. The compressor bleed duct also includes a moveable valve ring with a cylindrical sleeve and a pair of seal seats radially aligned with the orifice ring seal members. A set of pins extends radially from the valve ring, and each pin includes a roller that engages a carved slot on the orifice ring. A bell crank for operating the valve ring is mounted on a bell crank support bracket by a bell crank pivot. Input and output arrays of the bell crank are connected respectively to an actuator and to the valve ring. 
         [0003]    In operation, the actuator rotates the bell crank about the bell crank pivot so that the bell crank, in turn, drives the valve ring in a spiral motion, positioning the sleeve to cover or uncover the passages. The rollers help guide the valve ring in its spiral path. As the valve ring approaches its fully closed position, the seal members contact the seal seats, compressing them in the longitudinal direction to affect a fluid tight seal. 
       SUMMARY 
       [0004]    According to an exemplary embodiment disclosed herein, a duct assembly for venting flow from an internal portion of a gas turbine engine, has a first piece having a first duct portion extending therethrough, the first piece configured to withstanding backbone loads of the engine, the first piece having a first portion of a duct passing therethrough, and a second piece, the second piece having a second portion of the duct passing therethrough, the second portion and the first portion aligning, the second piece constructed of a lighter material than the first piece. 
         [0005]    In any of the previous embodiments, the first piece is constructed of titanium. 
         [0006]    In any of the previous embodiments, the second piece is constructed of aluminum. 
         [0007]    In any of the previous embodiments, the aluminum is cast aluminum. 
         [0008]    In any of the previous embodiments, the first piece has a plurality of first portions and the second piece has a plurality of second portions. 
         [0009]    In any of the previous embodiments, the second portions are separated by ligaments that minimize losses flowing through the first portions and aligned second portions. 
         [0010]    In any of the previous embodiments, the ligaments are have an airfoil shape. 
         [0011]    In any of the previous embodiments, a seal is disposed between the first piece and the second piece. 
         [0012]    In any of the previous embodiments, the seal is disposed in a groove in one of the first piece and the second piece. 
         [0013]    In any of the previous embodiments, a flange extends axially from one of the first piece and the second piece and a bracket extends radially from the flange to engage an other of the first piece and the second piece. 
         [0014]    In any of the previous embodiments, the bracket engages a side of the other of the first piece and the second piece. 
         [0015]    In any of the previous embodiments, the first piece forms a radially outer wall of a compressor section of the engine. 
         [0016]    In any of the previous embodiments, the first piece attaches to another portion of a radially outer wall of the compressor section, 
         [0017]    In any of the previous embodiments, a radially extending flange extends from the second portion of the duct for engaging a seal. 
         [0018]    In any of the previous embodiments, a platform is disposed on said first portion of said duct, said platform configured to support a ring assembly thereupon. 
         [0019]    In any of the previous embodiments, a mount is disposed on a radially outer surface of said first piece for mounting a bell crank thereupon. 
         [0020]    According to an exemplary embodiment disclosed herein, a method for minimizing weight of a duct assembly includes the steps of selecting a first material to withstand engine backbone loads, selecting a second material that is lighter than the first material, forming aligning ducts in the first material and in the second material, and mating the first material and the second material to form duct assembly. 
         [0021]    In any of the previous embodiments, the method includes aligning the second material radially outwardly from the first material such that the ducts align. 
         [0022]    In any of the previous embodiments, the method includes creating ligaments that are airfoil shaped between ducts in the first material. 
         [0023]    In any of the previous embodiments, the method includes casting the ligaments of the second material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
           [0025]      FIG. 1  is a cross-section of a portion of a gas turbine engine. 
           [0026]      FIG. 2  is a portion of the gas turbine engine taken along the lines  2 - 2  in  FIG. 1 . 
           [0027]      FIG. 3A  is a perspective view of a bell crank for opening and closing of valves depicted in  FIG. 2 . 
           [0028]      FIG. 3B  is a cross-sectional view of the four bar linkage as shown in  3 A. 
           [0029]      FIG. 3  is a side view cutaway of the bell crank four bar configuration of  FIG. 3A . 
           [0030]      FIG. 4A  is an isolated view of a portion of the four bar configuration of  FIG. 3A . 
           [0031]      FIG. 4B  is a portion of a mounting system for the bell crank of  FIG. 3A . 
           [0032]      FIG. 5  is a side view cutaway of the valve assembly of  FIG. 1 . 
           [0033]      FIG. 5A  is a side view cutaway of a bulb seal of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    Referring now to  FIG. 1 , an engine  10 , such as a gas turbine engine is shown. The engine  10  has a nacelle  15  that extends around blades  20 . The blades  20  are attached to a shaft (not shown) passing through the core  25  of the engine  10 . The core  25  is held in place by struts  30 . The blades  20  provide a first airflow  35  between the core  25  and the nacelle  15 , and a second airflow  40  passing through compressor section  45  in the core  25 . The core is enclosed by a core casing  53 . A bleed assembly  55  is disposed between the core casing  53  and the compressor section  45 . The bleed assembly  55  (shown within lines  2 - 2 ) includes a ring-shaped bleed valve  60 , a ring-shaped bleed duct assembly  65  that acts as a portion of an compressor section outer wall, bleed ducts  70  passing through the bleed duct assembly  65 , a linkage assembly  75 . A firewall  79  is disposed next to the bleed assembly  55 . 
         [0035]    Referring now to  FIG. 2 , the details of the bleed duct assembly  65  are shown. The bleed duct assembly  65  has an inner case  80 , which is either forged or cast, load-bearing, high-temperature resistant material such as titanium or the like (including a ceramic), and an outer case  85 , which bears less load and stress may be made of lower strength, lighter metal such as aluminum. A duct  90 , which has a first portion  95  in the inner case  80 , and a second portion  100  in the outer case  85  is separated circumferentially by ligaments such as airfoils  105  between adjacent circumferential ducts  90 . 
         [0036]    The inner casing  80  has a body  110  having a central area  115  having a first land  120  on a top portion  125  of the body  110 . The top portion  125  has a groove  130  in which an o-ring  135  is disposed to act as a seal to minimize air from escaping between the duct portions  95 ,  100 . Bolt hole  140  is disposed in a side portion  145  of the body  110  for attaching the outer case  85  to the inner case  80  by means of a bolt  150 . The inner casing  80  has an aft extension  155  having an axial attachment hole  160  to attach to an adjacent core segment  165  (see  FIG. 1 ). The body  110  also has a fore extension  170  having a flange  175  extending radially outwardly therefrom. The flange  175  has an opening  180  for attaching to another adjacent core segment  185  (see  FIG. 1 ). 
         [0037]    On a radially outer surface of the body  110 , a platform  190 , which supports the bleed valve  60 , is disposed thereon. There are a plurality of platforms disposed circumferentially about the body  110  to support the valve  60 . The platforms has a cylindrical top  195  that has a flat cross-section and is covered by a low wear material  200  that is somewhat lubricious to allow the bleed valve  60  to slide thereon without snagging. 
         [0038]    The outer case  85  has a body  205  having an aft flange  210  depending radially inwardly from the body  205 . The aft flange  210  has a hole  215  aligning with bolt hole  140  through which bolt  150  extends into the bolt hole  140  to attach the outer case  85  to the inner case  80 . The outer case body  205  has a flange  220  extending radially outward to mate with the bleed valve  60  as will be discussed infra. The body  205  also has a fore side  225  that mates with the bleed valve  60  as will be discussed infra. The body  205  has a second land  230  that mates with the first land  120  when the bolt  150  is inserted into hole  140 . When the bolt  150  is tightened, the first land  120  and the second land  230  secure the O-ring  135  to minimize any air leakage between the bolts. The o-ring  135  gets compressed when the case halves are installed. 
         [0039]    The airfoils  100 , or ligaments disposed between ducts  90  are shaped to direct the flow of air flowing through the duct  90  to enhance flow with minimal losses therethrough so that the air siphoned from the compressor section  45  may be used efficiency downstream of the ducts  90 . The outer case  85  is aluminum to allow more complex flow patterns of the duct second portion  100  to be machined or formed to maximize efficiency of the air flowing therethrough. The first portion  95  in the inner case  80  and the second portion  100  in the outer case  85  are smoothed to minimize losses. Furthermore, the outer case  85  is made of aluminum or the like to save weight and the inner case is made of titanium to improve the capability of the bleed duct assembly  65  to handle engine backbone loads. Because the inner case handles the backbone loads, the outer case  85  may be made of aluminum where weight may be saved. Because the outer case  85  is cast, more shaped airfoils may be used to reduce aerodynamic losses and reduce backflow upon the compressor section  45 . 
         [0040]    A user would choose a first material as an inner case  80  to withstand the backbone loads of the engine  10 , then choose a lighter material as an outer case  85  to form a lighter bleed duct assembly  65 . The user would then form the duct  90  for instance by casting the outer case  85  and forging the inner case  80  and then join the two segments as mentioned hereinabove. 
         [0041]    Referring now to  FIGS. 3A-C  and  4 A-B, the linkage assembly  75  is shown. The linkage assembly  75  has a fore bell crank assembly  235 , an aft bell crank assembly  240 , a fore connecting link  245  and a bridge arm  250 . 
         [0042]    The aft bell crank  240  has a body  255  from which brackets  260  extend circumferentially and radially inwardly therefrom. A rotation pin  265  extends through the body  255  to hold a bell crank  280 . The body  255  has a flange  270  extending radially outwardly therefrom. The upper flange  270  has holes  275  passing axially therethrough for joining with the bridge arm  250 . The bell crank  280  is seated within the body  255  and has an upper arm  285  for attaching to the fore connecting link  245  and a lower arm  290  disposed radially inwardly from the upper arm  285  attaching to an aft connecting link  295 . The aft connecting link  295  attaches to an actuator (not shown). 
         [0043]    The brackets  260  have a base  300  and webs  305  that attach to the aft bell crank body  255 . The brackets  300  sit upon land  310  on the stationary inner case  80 . A pin  315  extends radially outwardly from the land  210  for insertion into the locator hole  320  in the base  300 . Bolt  323  connects the bracket  260  to the inner case  80 . 
         [0044]    The fore bell crank assembly  235  has a body  325 . A pin  330  extends through clevis  335  to anchor crank  337  therein (See  FIG. 3B ). The body has a lower flange  340  that forms a bracket  345  having openings  350 . Pin openings  355  (See  FIG. 3C ) are utilized to locate the bracket  345  in an adjacent core segment  165  (see  FIG. 1 ). The body  325  has an upper surface  360  from which locator pin  365  extends. The upper surface has bolt holes  370  that secure bridge arm  250  thereto as will be discussed herein. The crank  337  has a first arm  375  attaching to the bleed valve  60  and a second arm  380  attaching to the fore connecting link  245 . The second arm  380  is angularly displaced from the first arm  375  so that the bleed valve  60  moves an appropriate amount as desired to meter flow through the bleed duct assembly  65 . 
         [0045]    The bridge arm  250  has a key-like shape having a flat triangular section  390  that has openings  394  for mating with the bolt holes  370  and an aperture  397  for mating with the pin  365  to attach the bridge arm  385  to the fore bell crank assembly. The bridge arm  250  also has a shank  395  which narrows axially and expands radially from the triangular section  390 . A t-shaped assembly  400  is formed by ears  405  that extend circumferentially from an end  407  of the shank  395 . The ears have openings  410  through which fasteners  415  extend to mate with the holes  275  in the upper flange  270  of the aft bell crank  240 . The openings  394  and aperture  397  may be oversized to allow for circumferential misalignment. 
         [0046]    The webs  305  of the aft bell crank assembly  240  are designed to flex during thermal loading while providing stiffness for operating loads. The bridge arm  250  limits deflection of the cantilevered fore bell crank assembly  235  and aft bell crank assembly  240  and provides more stiffness to the linkage assembly  75 . Shims  417  are placed between the t-section  400  and the upper flange  270  to eliminate axial tolerance gaps during assembly. 
         [0047]    Because the area to mount the brackets  260  to the inner case  80  is limited, the required stiffness and deflection of the aft bell crank assembly  240  is provided by providing the bridge arm  250  between the aft bell crank  240  and the fore bell crank assembly  235 , which is attached to the flange of the adjacent core segment  165 . The bridge arm  250  is designed not to buckle or deflect during excessively unloading. The aft brackets  260  are more flexible to allow for controlled deflection of the fore bell crank assembly  235  and the aft bell crank assembly  240  caused by thermal growth of the inner case  80 . 
         [0048]    Referring to  FIGS. 4 and 3C , it can be seen that the aft connecting link  295  and the lower arm  290  (See  FIG. 3A ) are lower than the upper arm  285  to allow a motive force of the actuator (now shown) to move up and over the radially extending flange  220 , which is used by the bleed valve  60  as will be discussed herein. The motive force rotates the bell crank  280  about pin  265 , moving the fore connecting link  245  axially and rotationally. The fore connecting link  245  rotates the first arm  375  about the pin  330  thereby causing the rotation of the second arm  380  that moves the bleed valve partially axially and partially in rotation to modulate the degree of air flowing through the bleed duct assembly  65 . 
         [0049]    Referring now to  FIGS. 5 and 5A , the bleed valve  60  is shown. The bleed valve  60  has a body  420  having a clevis section  425 , a midsection  440  a forward section  430  and an aft section  450 . A first seal holder  435  extends radially inward from the midsection  440  of the body  420 . A second seal holder  445  extends from the aft section  450  of the body  420 . 
         [0050]    Referring now to  FIG. 5A , a seal  455  is shown in a seal holder  435  or  445 . Each seal has a cylindrically extending body  460 , a flat cross-section reinforcing strip  465  extending from the extending body  460  and a bulbous section  470  attaching at one end of the body  460 . Each bulbous section has an opening  475 . In the first seal holder  435 , the opening is adjacent and facing the pressure section of the duct  90  so that high pressure air is forced through the opening  495  to allow the bulb to expand. This expansion helps make the seal  455  more effective. Similarly the opening  495  in the second seal holder  445  is also placed so the opening  475  is exposed to the pressure extending through the duct  90  to allow it to be filled with high pressure air as well. The strip  465  extends towards the bulbous section  470 . 
         [0051]    A shaft  485  extends upwardly from the flat portion  480  at periodical positions around the seal  455  to attach the seal to the seal holders  435 ,  445 . A shank  490  of a rivet  497  (or other fastener) extends through a center of the shaft  485 . The rivet  495  has a head  500 , a tail  505 , and a bottom  515 . The bottom  515  fits within a recess  510  in each seal holder  435 ,  445 . As can be seen in  FIG. 5 , because the bottom  515  slides upon the low wear material  200 , the tail  505  must be recessed so as to not damage the low wear material  200 . The cylindrical body  460  fits within a groove  520  placed within each seal holder cylindrical  435 ,  445 . There are no sharp edges within the groove  520  to avoid damaging the seal  455 . The groove  520  is easy to machine relative to the prior art in which a seal is held within a groove with raised ridges extending towards each other between a cylindrical body and a bulbous section of a seal. The groove  520  presented herein is far more easily machined than in the prior art. Furthermore, because the seal  455  is riveted to the seal holders  435 ,  445 , they are not torn out of their channels as with the prior art bonded seals. The seal is also relatively easy to replace by removing the rivets  495 . 
         [0052]    The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.

Technology Category: 2