Abstract:
Disengagement of C-clips in turbine shroud assemblies is prevented by providing each C-clip with at least one anti-rocking pad. The anti-rocking pad is disposed on a radially inner surface of the C-clip so as to make snug contact with a portion of the shroud adjacent to the C-clip. The snug contact limits rocking motion of the C-clip, thereby preventing C-clip disengagernent.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH &amp; 
     DEVELOPMENT 
     The U.S. Government may have certain rights in this invention pursuant to contract number F33657-95-C-0055 awarded by the Department of the Air Force. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to gas turbine engines and more particularly to shroud assemblies utilized in the high pressure turbine section of such engines. 
     A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and ignited for generating hot combustion gases. These gases flow downstream to one or more turbines that extact energy therefrom to power the compressor and provide useful work such as powering an aircraft in flight A turbine section commonly includes a stationary turbine nozzle disposed at the outlet of the combustor for channeling combustion gases into a turbine rotor disposed downstream thereof. The turbine rotor indudes a plurality of circumferentially spaced apart fan blades extending radially outwardly from a rotor disk that rotates about the centerline axis of the engine. 
     The turbine section further includes a shroud assembly located immediately downstream of the turbine nozzle. The shroud assembly closely surrounds the turbine rotor and thus defines the outer boundary for the hot combustion gases flowing through the turbine. A typical shroud assembly comprises a shroud support which is fastened to the engine outer case and which in turn supports a plurality of shrouds. The shrouds are held in place, in part, by arcuate retaining members commonly referred to as C-clips. Specifically, the C-clips hold the aft end of the shrouds in place against the shroud hangers via an interference fit. 
     The interference fit normally provides excellent retention of the shrouds. However, there can be a tendency for the C-clips to back off in some instances because of a thermal ratcheting phenomenon. That is, although the shrouds and C-clips are segmented to accommodate for thermal expansion, there is a possibility that the thenmal loads within the shroud assembly can cause the C-clip to rock and thereby overcome the interference fit clamp loads. In some cases, there may be enough of a gap between the C-clip aft face and the adjacent nozzle outer band to allow for C-clip disengagement Such disengagement could result in severe hardware damage. 
     Accordingly, there is a need for a C-clip design that eliminates C-clip back-off. 
     SUMMARY OF THE INVENTION 
     The above-mentioned needs are met by the present invention which provides a C-clip having at least one anti-rocking pad disposed thereon. The anti-rocking pad makes snug contact with the portion of the shroud adjacent to the C-clip so as to limit arny rocking motion of the C-clip, thereby preventing C-clip disengagement. 
     Other objects and advantages of the present invention will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding part of the specification. The invention, however, may be best understood by reference to the following description taken in conjunction with the accompanying drawing FIGS. in which: 
     FIG. 1 is an axial sectional view of a shroud assembly including the C-clip of the present invention. 
     FIG. 2 is an enlarged sectional view of the shroud assembly of FIG. 1 showing the C-clip in mote detail. 
     FIG. 3 is a perspective view of the C-clip of FIG.  2 . 
     FIG. 4 is an aft-looking-forward end view showing a first embodiment of the C-clip of the present invention. 
     FIG. 5 is an aft-looking-forward end view showing a second embodiment of the C-clip of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views, FIG. 1 shows a shroud assembly  10  in closely surrounding relation with turbine blades  12  carried by a rotor disk (not shown) in the high pressure turbine section of a gas turbine engine. The shroud assembly  10  includes a plurality of arcuate shrouds  14  (only one shown in FIG. 1) arranged in an annular array so as to encircle the turbine blades  12 . The shrouds  14  are held in position by a shroud support  16  which, in turn, is supported by the engine outer case (not shown) in a conventional manner. 
     The shroud support  16  includes an axially extending forward hook  18  and an axially extending aft hook  20 . The shroud support  16  also has an aft lip wear surface  22  formed on its aft face. The aft lip wear surface  22  provides a contact surface for a leaf seal  24  which is disposed between the shroud assembly  10  and the nozzle outer band  26  of the adjacent stator assembly. A conventional flow divider  28  is attached to the shroud support  16  via bolts  30 . 
     Each shroud  14  includes a base  32  having radially outwardly extending forward and aft rails  34  and  36 , respectively. A forward mounting flange  38  extends forwardly from the forward rail  34  of each shroud  14 , and an aft mounting flange  40  extends rearwardly from the aft rail  36  of each shroud  14 . The aft mounting flanges  40  of each shroud  14  are juxtaposed with the aft hook  20  of the shroud support  16  and are held in Icace by a plurality of retaining members  42  commonly referred to as C-clips. 
     The C-clips  42  comprise arcuate body members that are C-shaped in cross section and snugly overlap the aft mounting flanges  40  and the aft hook  20  so as to clamp the aft ends of the shrouds  14  in place against the shroud support  16 . Although they could be formed as a single continuous ring, the C-clips  42  are preferably segmented to accommodate thermal expansion. Typically, one C-clip  42  clamps an entire shroud plus one-half of each adjacent shroud. In which case, there are twice as many shrouds  14  as there are Iclips  42 . 
     As mentioned above, repetitive thermal expansion and contraction can sometimes cause conventional C-clips to rock with respect to their associated mounting flanges and hooks. If unchecked, such rocking could cause C-clip disengagement. To counter the rocking effect, at least one anti-rocking pad  46  is disposed on the radially inner surface (with respect to the centerline axis of the engine) of the C-clip  42 . As described in more detail below, the antirocking pad  46  contacts the shroud  14  so as to limit the C-clip&#39;s capacity to rock. 
     The forward end of each shroud  14  is supported from the shroud support  16  via conventional shroud hangers  48 . Each shroud hanger  48  includes a first hook  50  that engages the forward hook  18  of the shroud support  16  and a second hook  52  that engages the forward mounting flange  38  of each shroud  14 . The shroud hangers  48  are also secured to the shroud support  16  by fasteners  54 . A conventional cooling air distributor  56  is disposed between the shroud  14  and the shroud support  16  for distributing cooling air to the shrouds  14  and adjacent structure. It should be noted that the present invention is not limited to the shroud assembly shown in FIG.  1 . In other shroud assemblies, the aft end of the shroud is clamped to a shroud hanger, instead of directly to a shroud support, via a C-clip. The C-clip of the present invention is equally applicable to this type of configuration or any other type of shroud supporting structure that uses a C-clip. 
     Referring to FIGS. 2 and 3, a C-clip  42  is shown in greater detail. As mentioned above, each C-clip  42  comprises an arcuate body member that is C-shaped in cross section. Specifically, the C-clip  42  includes a connector portion  58  having first and second tines  60 ,  62  extending therefrom, with the first tine  60  being located radially inside of the second tine  62 . The second tine  62  engages the aft hook  20 , and the first tine  60  engages the aft mounting flange  40 . To engage the aft mounting flange  40 , the first tine  60  is located in a gap  64  formed between the aft nmounting flange  40  and the rearmost portion of the shroud base  32 . 
     The anti-rocking pad  46  is disposed on the radially inner surface of the first fine  60  so as to be located between the C-clip  42  and the shroud base  32 . The thickness of the anti-rocking pad  46  is such that it will contact the shroud base  32 . That is, the combined thickness of the first tine  60  and the anti-rocking pad  46  is substantially equal to the width of the gap  64 . Typically, the thickness of the antirocking pad  46  will be in the range of about 0.01-0.02 inches. 
     The firm contact between the anti-rocking pad  46  and the base  32  of the shroud  14  limits the capacity the C-clip  42  to rock with respect to the aft hook  20  and the aft mounting flange  40 . Accordingly, the anti-rocking pad  46  reduces the possibility of C-clip disengagement. To best eliminate C-clip rocking action, the anti-rocking pad  46  is preferably located near the aft end of the C-clip  42 . The anti-rocking pad  46  can be made of any suitable material and is preferably made of the same material as the C-clip  42 . The anti-rocking pad  46  can be a separate element attached to the C-clip  42  by conventional means such as welding or bonding, or it can be integrally formed with the C-clip  42 . 
     Turning to FIG. 4, it can be seen, in one preferred ernbodiment, that the anti-rocking pad  46  is drcumferentially centered on the radially inner surface of the first Une  60 . That is, the anti-rocking pad  46  is located about midway between the opposing ends of the C-clip  42 . FIG. 5 shows anothe- preferred embodiment in which three anti-rocking pads  46  are disposed on the radially inner surface of the first tine  60 . One anti-rocking pad  46  is located midway between the opposing ends of the C-clip  42 , a second anti-rocking pad  46  is located near a first end of the C-clip  42  and a third anti-rocking pad  46  is located near the other end of the C-clip  42 . The multiple anti-rocking pads of FIG. 5 are generally not as wide as the single anti-rocking pad of FIG.  4 . 
     The foregoing has described a C-clip having an anti-rocking pad that eliminates C-clip back-off. In addition to eliminating the potential of C-clip disengagement, the C-clip of the present invention provides further advantages in that it requires only limited modification to existing C-clip configurations and requires essentially no modification to other shroud assembly structure. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention as defined in the appended claims.