Abstract:
An anti-rotation lock for preventing circumferential movement of a stator segment in relation to a split case to which it is mounted is disclosed. A racetrack shaped pocket, disposed within the case and proximate the stator segment, is suitably sized to receive a lug and a spring pin. The lug is received in the pocket and protrudes radially inward from the case and is engagable by the stator segment, thus preventing circumferential movement with respect to the case. The spring pin is received adjacent to the lug and compressively retains the lug in the pocket.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0001]     This invention was made with Government support under N00019-02-C-3003 awarded by the United States Navy. The Government has certain rights in this invention. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     (1) Field of the Invention  
         [0003]     The invention relates to gas turbine engine components, and more particularly to an anti-rotation lock for preventing relative movement between two such components.  
         [0004]     (2) Description of the Related Art  
         [0005]     A gas turbine engine includes one or more forward compressor sections for increasing the pressure of an incoming air stream. Each compressor section includes alternating axial stages of rotating, rotor blades and stationary, stator vanes disposed within a casing structure. The stator vanes are supported by outer shrouds or by inner and outer shrouds. The outer shrouds include a pair of circumferentially extending rails for use in assembly with the casing structure. Multiple stator vanes may be manufactured as a single module, referred to as a stator segment. Stator segments are less expensive to manufacture and allow less air leakage than individual stator vanes.  
         [0006]     To simplify assembly with the rotor blades, the casing structure is typically split axially into two or more arcuate sectors, referred to as a split case. Circumferential grooves, within the internal periphery of the split case, accept the circumferential rails of the stator segment. A thickened flange is located radially outward from the split case for joining the split case with fasteners during assembly. The thickened flanges are referred to as split flanges.  
         [0007]     During assembly, each stator segment is inserted into the split case by engaging the stator segment rails with the corresponding circumferential grooves in the case. Each stator segment is guided into the grooves in turn, until all of the stator segments are loaded. The split case is next fit around a pre-assembled rotor and joined by fasteners at the split flanges.  
         [0008]     During normal operation of the gas turbine engine, temperature variations between the split case and the stator segments necessitate a suitable cold-clearance gap between adjacent stator segments. Also, aerodynamic loading of each stator segment generates a tangential force approaching five hundred pounds. In order to uniformly distribute the cold-clearance gaps and prevent circumferential sliding of the stator segments in the split case grooves, anti-rotation locks must be utilized for each stator segment.  
         [0009]     The requirement for an anti-rotation lock is particularly important at the locations adjacent to the split flanges. If the stator segments rotate circumferentially in the split case grooves and bridge the split flange after assembly, disassembly of the compressor may be difficult or even impossible. Because the split flanges are thicker than the remainder of the split case, contain a plurality of fasteners and are a source of air leakage, an unconventional anti-rotation lock is required at this location.  
         [0010]     Anti-rotation locks of the type described in U.S. Pat. No. 6,537,022 to Housley, et al., are effective in areas of a split case where the locks do not interfere with any external casing features, such as fasteners. In the area of the split flange; however, the fasteners attaching the case sectors preclude their use. Anti-rotation locks as described in U.S. Pat. App. 2003/0082051 to Bertrand, et al., although effective, require precise machining of the split case grooves and stator segments and are susceptible to vibratory wear. Each of the above locks may contribute to increased engine weight and air leakage, which are important considerations as well.  
         [0011]     What is needed is an anti-rotation lock for use at a split flange that does not interfere with external casing features, does not require extensive machining, is not susceptible to vibration and has minimal impact on engine weight and air leakage.  
       BRIEF SUMMARY OF THE INVENTION  
       [0012]     Provided is an anti-rotation lock for preventing relative movement between a stator segment and a split case of a gas turbine engine to which it is mounted.  
         [0013]     An anti-rotation lock contains a pocket in a split case for receiving a lug and a spring pin. The lug protrudes radially inward from the case for engaging a stator segment. The spring pin received in the pocket and adjacent to the lug provides compressive loading of the lug in the pocket.  
         [0014]     Other features and advantages will be apparent from the following more detailed descriptions, taken in conjunction with the accompanying drawings, which illustrate, by way of example, an exemplary embodiment anti-rotation lock.  
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0015]      FIG. 1  is a simplified schematic sectional view of a gas turbine engine along a central, longitudinal axis.  
         [0016]      FIG. 2  is a partial sectional side view of a stator segment assembled in a split case.  
         [0017]      FIG. 3  is a partial perspective view of a split case and an anti-rotation lock installed adjacent to a split flange.  
         [0018]      FIG. 4  is a partial perspective view of a split case with an anti-rotation lock of  FIG. 3  in exploded view.  
         [0019]      FIG. 5A  is a perspective view of an alternate example of a spring pin.  
         [0020]      FIG. 5B  is a perspective view of yet another alternate example of a spring pin. 
     
    
       [0021]     When referring to the drawings, it is understood that like reference numerals designate identical or corresponding parts throughout the several views.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     Referring to  FIG. 1 , a gas turbine engine  10  with a central, longitudinal axis  12  contains one or more compressors  14 , a combustor  16  and one or more turbines  18 . Compressed air is directed axially rearward from the compressors  14 , is mixed with fuel and ignited in the combustor  16  and is directed into the turbines  18  and is eventually discharged from the gas turbine engine  10  as a high velocity gas jet. The turbines  18  drive the compressors  14  through common shafts  20  supported by bearings  22 . The gas turbine engine in this example contains two compressors, a low-pressure compressor  24  and a high-pressure compressor  26 .  
         [0023]     A typical gas turbine engine high-pressure compressor  26  includes alternating axial stages of rotating, rotor blades  28  and stationary, stator vanes  30  disposed within a casing structure  32  made of aluminum, titanium, steel or nickel alloy. The casing structure  32  is typically split axially into two or more arcuate segments, joined together by fasteners  34  at one or more split flanges  36 . A casing structure of this type is hereinafter referred to as a split case.  
         [0024]     Stator vanes  30  may be variable or fixed pitch. Variable pitch stator vanes pivot about a series of trunnions in the split case  32 , while fixed pitch stator vanes maintain a constant angle. Fixed pitch stator vanes  30  are supported by an outer shroud  38  (shown in  FIG. 2 ), and in some instances, an inner shroud  40 . Typically, a number of fixed pitch stator vanes  30  may be manufactured together in a single module, called a stator segment. Stator segments are cantilevered radially inward from the split case  32  by the outer shrouds  38 .  
         [0025]     A stator segment  30  is shown in  FIG. 2  installed in a split case  32 . The stator segment  30  includes a pair of ‘L’ section, segment rails  42  extending radially outward from, and circumferentially about, the outer shroud  38 . The areas radially between the segment rails  42  and the outer shroud  38  form a pair of segment grooves  44 . Except for a circumferentially localized stop  46 , the material extending axially between the segment rails  42  is removed to reduce weight. Although the foregoing describes a stator segment, it is to be understood that non-segmented stator vanes comprise similar construction details.  
         [0026]     The split case  32  of  FIG. 2  comprises a radially inner surface  48  a radially outer surface  50  and one or more circumferential ribs  52  for reducing deflection when an internal pressure load is applied by the compressed air. A split flange  36  extends radially outward from the outer surface  50  and axially the length of the split case  32 . A number of holes  54  (shown in  FIGS. 3,4 ) penetrate the split flange  36  for use in joining the split case  32  with fasteners  34  during assembly. Extending radially inward from the inner surface  48  at the axial location of the stator segments  30 , are pairs of ‘L’ section case rails  58 . The areas radially between the case rails  58  and the inner surface  48 , form circumferential case grooves  60 . The case grooves  60  correspond to the segment rails  42 , allowing a stator segment to be introduced into the inner case in a sliding arrangement during assembly.  
         [0027]     Referring now to  FIGS. 3 and 4 , an anti-rotation lock  61  is installed in a split case  32 , between a pair of case rails  58  and adjacent to a split flange  36 . The anti-rotation lock  61  comprises a pocket  62 , a lug  64  and a spring pin  66 . The lug  64  is received in the pocket  62 , and protrudes radially inward from the inner surface  48  for engaging a stator segment  30 . The spring pin  66  is compressed slightly while received in the pocket  62 , adjacent to the lug  64 . The compressive loading of the spring pin  62  prevents movement of the lug  64  within the pocket  62  due to vibration and cyclic loading during normal operation. A more detailed description of the various features of the anti-rotation lock  61  follows.  
         [0028]     The pocket  62  as shown in  FIG. 4  may be racetrack shaped with an axial length  68 , circumferential width  70  and radial depth  72  sized to accept the lug  64  and the spring pin  66 . The radial depth  72  does not intersect the holes  54  and does not contribute to any compressed air leakage. In one example, the pocket is machined using a conventional, 0.250 inch milling cutter; however, forging, electrodischarge machining (EDM) or any other suitable method may be used.  
         [0029]     The lug  64  includes a base  74 , a crown  76  and a recess  78 , conforming to the shape of the engaged spring pin  66 . The base  74  is received in the pocket  62  and the crown  76  protrudes radially inward from the inner surface  48  of the split case  32 . The crown  76  extends beyond the circumferential width  70  of the pocket  62 , forming an overhang  80 . The overhang  80  ensures the stator segment  30  engages only the crown  76  of the lug  64  and not the spring pin  66 . A base chamfer  82  ensures full radial engagement of the base  74  in the pocket  62 , and a crown chamfer  84  prevents interference between the crown  76  and the stator rails  42 . The recess  78  conforms to the curvature of the engaged spring pin  66  to ensure consistent contact and to prevent a loss of compressive loading. In one example, the lug  64  is made of nickel; however, stainless steel or any other suitable material may be used.  
         [0030]     A first example of a spring pin  66  is a hollow cylinder, split lengthwise by a single slot  86 . Alternately, a spring pin  166  (shown in  FIG. 5A ) may include a single helical slot  186  or a spring pin  266  (shown in  FIG. 5B ) may contain a coil  270  instead of a slot. An outer diameter  88  of the spring pin  66  is slightly larger than the pocket width  70  prior to being received in the pocket  62 . When the spring pin  66  is received in the pocket  62 , the outer diameter  88  is compressed slightly to fit inside the pocket width  70 . The received spring pin  66  exerts a compressive load that retains the lug  64  in the pocket  62 , thus preventing excessive wear due to vibration and cyclic loading during operation.  
         [0031]     The foregoing has described an anti-rotation lock for preventing circumferential movement between a stator segment and a split case to which it is mounted. 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 appended claims.