Abstract:
A split shroud system for a gas turbine engine having a pair of annular-shaped shrouds that each have an inner pocket; to form a pair of inner pockets. Each of the pair of pockets having liner parts that form a circle. Liner parts of one of the pair of pockets facing liner parts of the other of the pair of pockets to form liner part pairs. One of each of said of pair of liner parts has a mutual abutting surface that forms a plurality of slots for accepting a plurality of vane inner trunnions.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0001]     This invention was made with Government support under F33615-99-D-2051-0010 awarded by the United States Air Force. The Government has certain rights in this invention. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a shroud for a gas turbine engine. More particularly, the present invention relates to an inner liner for a shroud for a gas turbine engine. Still more particularly, the present invention relates to an inner graphitic carbon liner that is received in a shroud of a gas turbine engine to reduce the overall engine weight and cost and vane trunnion wear.  
         [0004]     2. Description of Prior Art  
         [0005]     The operating environment for a turbofan engine and its various component is extremely harsh. The vibrations due to normal use at operating speeds are extreme. The operating temperature of some of the components are also extremely high. One of the many components that may experience wear in the engine due to vibrations and high temperature are the variable vanes&#39; inner trunnions.  
         [0006]     Currently, the trunnions are encased within a carbon steel split bushing. The split bushing is secured between a carbon steel split inner shroud. During wear, the carbon steel bushing and carbon steel split liner vibrate against one another and cause considerable wear on the vane&#39;s inner diameter trunnion encased in the bushing. The wear on the trunnion reduces the lifecycle of the trunnion and increases maintenance time and expense due to required replacement/refurbishment of the entire vane.  
         [0007]     Therefore there exists a need for a shroud that can receive a sacrificial graphitic carbon liner to hold a vane trunnion, thereby reducing trunnion replacement/refurbishment costs, overall engine weight and cost of ownership and maintenance.  
       SUMMARY OF THE INVENTION  
       [0008]     It is an object of the present invention to provide an engine shroud having a reduced weight.  
         [0009]     It is also an object of the present invention to provide a split engine shroud that is manufactured from titanium.  
         [0010]     It is another object of the present invention to provide an engine shroud that is manufactured to accommodate a graphitic material wear surface.  
         [0011]     It is still another object of the present invention to provide titanium shroud that accommodates an inner graphitic liner.  
         [0012]     It is still yet another object of the present invention to provide a titanium shroud that eliminates the need for a split carbon steel bushing around a vane trunnion.  
         [0013]     It is a further object of the present invention to reduce the maintenance cost associated with vane trunnion repair.  
         [0014]     It is still a further object of the present invention to provide a vane trunnion that does not need a hard coat for its wear surface.  
         [0015]     It is still yet a further object of the present invention to provide an engine shroud that has a wear surface that is operational at elevated temperatures.  
         [0016]     It is yet a still further object of the present invention to provide a graphitic liner that can easily be reused or replaced.  
         [0017]     It is still yet another object of the present invention to provide an engine shroud that increases vane life.  
         [0018]     These and other objects and advantages of the present invention are achieved by the present invention that provides a split engine shroud system having a pair of annular-shaped shrouds that each contain an inner pocket to form a pair of facing pockets. The invention also provides for a pair of liners contained within one of the pair of pockets and the other of the pair of liners contained in the other pocket. Each pair of liners have a mutually contacting surface that forms a plurality of slots.  
         [0019]     A split engine shroud system having a pair of annular-shaped shrouds that each have an inner pocket; to form a pair of inner pockets. Each of the pair of pockets having liner segments that firm a circle. Liner segments of one of the pair of pockets facing liner segments of the other of the pair of pockets to form liner segment pairs. One of each of said of pair of liner segments has a mutual abutting surface that forms a plurality of slots. The liner parts and the plurality of slots accept wear caused by the trunnions during operation flight conditions of the engine.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a partial cut-away cross-sectional view of a turbofan engine of the present invention;  
         [0021]      FIG. 2  is a partial cross-sectional view of the shrouds and vanes of the turbofan engine of  FIG. 1 , specifically showing the 4 th , 5 th  and 6 th  stages of the present invention;  
         [0022]      FIG. 3  is a partial cut-away perspective view of the turbofan engine showing the shrouds and vanes of the engine of  FIG. 1 ;  
         [0023]      FIG. 4  is an exploded perspective view of a shroud, vane and bushing configuration of the prior art;  
         [0024]      FIG. 5  is an exploded perspective view of the shroud, graphitic liner and vane of the present invention;  
         [0025]      FIG. 6  is a cross-sectional view of the shroud with a graphitic liner of the present invention; and  
         [0026]      FIG. 7  is a partial perspective view of the shroud with the graphitic liner of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     Referring to the drawings, and in particular to  FIG. 1 . An axial flow gas turbine engine  10  used for powering an aircraft in flight or powering an electrical generator, is shown. Engine  10  typically includes, in serial flow communication, a fan module  15 , a high pressure compressor  20 , a combustor  25 , a high pressure turbine  30 , and a low pressure turbine  35 . Combustor  25  generates combustion gases that are channeled in succession to high pressure turbine  30  where they are expanded to drive the high pressure turbine  30 , and then to the low pressure turbine  35  where they are further expanded to drive the low pressure turbine  35 . High pressure turbine  30  is drivingly connected to the high pressure compressor  20  via a first rotor shaft  40 , and low pressure turbine  35  is drivingly connected to the fan module  15  via a second rotor shaft  45 .  
         [0028]     Referring to  FIGS. 2 and 3 , high pressure compressor  20  typically includes a series of variable  55 ,  60  and  65  and fixed stator vane stages used to direct the gas flow during compression for engine  10  and aircraft use. The annular dimension of each of stages  55 ,  60  and  65  becomes increasingly smaller to compress the air for use in following engine stages. Compressor stage  55  or the 4 th  stage is formed of a plurality of circumferentially arranged cantilevered inlet guide vanes  70 . Each of the stages of the compressor  20  includes a set of circumferentially arranged vanes  70  captured between a compressor case  75  of the compressor  20  and a vane shroud  80 . The shroud  80  provides an aerodynamic flowpath boundary of the high pressure compressor  20 . Shroud  80  comprises a plurality of shroud segments  85  that extend completely around the inner circumference of compressor  20  to retain all vanes  70  of stages  55 ,  60  and  65 .  
         [0029]     Referring to the prior art of  FIG. 4 , a vane  90  includes an inner trunnion  95  at its end closest to the interior of the engine. Inner trunnion  95  is made from a very hard material such as tempered steel and typically has a hard coating applied. Inner trunnion  95  is used to retain vane  90  in an inner vane shroud  100 , while allowing the vane  90  to rotate about the trunnion  95 . Inner vane shroud  100  has two identical portions that are each made from a material such as carbon steel. A split bushing  105  encases inner trunnion  95  before it is placed in and held by inner vane shroud  100 . Split bushing  105  is made from a material such as a carbon steel. Similarly, an outer bushing (not shown) is used to retain vane in compressor case  75 . A bolt  120  and nut  125  secure the portions of shroud  100  in the axial direction.  
         [0030]     During operation of the engine  10 , constant aerodynamic pressure forces associated with the operation of the high pressure compressor  20  load the inner shroud toward the stator case. Further, the vibrations between the bushing  105  and the inner trunnion  95  generate extreme stresses and friction. High temperatures can be generated between mutual surfaces of contacting components and cause wear and oxidation.  
         [0031]     Referring to  FIGS. 5 through 7 , of the current invention, a vane  130  has an inner trunnion  135  that is enclosed in a split shroud or a liner  140  without any bushing. The trunnion  135  is preferably made from a strong lightweight material such as titanium. Trunnion  135  has an outer bearing surface  145 . Liner  140  is preferably made from a material such as graphitic carbon and has two identical components having a plurality of parts  150   a  and  150   b.  Parts  150   a  have opposing surfaces  155   a  and  155   b  and parts  150   b  have opposing surfaces  160   a  and  160   b.  Surfaces  155   b  and  160   b  form a plurality of slots  158  after parts  150   a  and  150   b  are fully assembled. Shroud  165  has numerous components including two portions  170   a  and  170   b.  Shroud portions  170   a  receive liner parts  150   a  and shroud portions  170   b  receive liner segments  150   b.  Shroud portions  170   a  form a pocket  185   a  and shroud portions  170   b  form a pocket  185   b.  Parts  150   a  and  150   b  of liner  140  are each friction fit into pockets  185   a  and  185   b,  respectively. A series of bolts  175  and nuts  180  secure the shroud portions and liner parts together.  
         [0032]     During use, trunnion surface  145  interacts with liner surfaces  155   b  and  160   b.  The intense pressures generated between these surfaces contributes to wear which will be absorbed by the graphitic carbon liner and not the vane trunnion. The graphitic carbon liner is sacrificial to the vane. The graphitic carbon material of liner  140  can withstand operating temperatures without oxidizing. Additionally, because the graphitic carbon material is self-lubricating, the wear against trunnion surface  145  is reduced or eliminated. Further, the self-lubricating quality of the graphitic carbon material eliminates the need for hard coat agents to be applied to the trunnion surface  145 .  
         [0033]     The graphitic carbon liner  140  can also be repositioned circumferentially or reversed axially and re-used. Liner  140  is a relatively larger component and can be easily machined or milled on appropriate machinery without compromising its function. In contrast, a bushing  105  made from graphitic carbon could not be accurately or economically machined because of its complex shape, small size and need to be split.  
         [0034]     By using the graphitic carbon liner  140 , the vane trunnion will have reduced wear. Additionally, the liner  140  has an extended operational life because each of the two liner components  150   a  and  150   b  can be reversed and re-inserted into opposite shroud portions  170   b  or  170   a,  respectively, so that surfaces  155   b  and  160   b  are facing. Thus, inner liner parts  150   a  and  150   b  can be re-inserted into the opposing shroud portions such that the previously machined surfaces  155   b  and  160   b  are still exposed. With this reversed re-insertion the sides of the facing surfaces that did not wear during the first interval will be exposed to use during the second interval operation, thus further extending the useful life of the liner. Alternatively, the previously unmachined and non-exposed surfaces  155   a  and  160   a  can be exposed and machined for use.  
         [0035]     Liner surfaces  155   b  and  160   b  provide lubrication against trunnion surface  145 , during operation. Graphitic carbon liner  140  will reduce the vane trunnion wear therefore; minimal repair of the trunnion is required after the first interval.  
         [0036]     A shroud  165  is machined to have inner pockets  185   a  and  185   b  that receive liner  140 . While shroud  165  can be made from materials such as carbon steel, a strong lightweight material such as titanium is preferred. By using a material such as titanium, for the shroud, the overall weight of the engine is greatly reduced. Further, the lower weight will reduce the degree of wear on the mutually contacting surfaces.  
         [0037]     While the instant disclosure has been described with reference to one or more exemplary embodiments, 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 thereof. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.