Abstract:
A turbine assembly comprising a first rotatable component having a first lip with a first axial facing surface and a second rotatable component having a second lip with a second axial facing surface. The components are held together by an axial load so that the first and second axial surfaces are in frictional contact across a radial plane whereby torque is transmitted between the components. A pilot ring mounted either above or below the radial contact plane maintains the radial position of the two components.

Description:
REFERENCE TO A RELATED APPLICATION 
     This application is a continuation-in-part of copending U.S. patent application Ser. No. 09/290,593, filed Apr. 13, 1999 and entitled “Integral Ceramic Blisk Assembly”. 
    
    
     TECHNICAL FIELD 
     The present invention relates to gas turbine engines and in particular to an assembly of rotating components that use single piece pilot rings for radial piloting of adjacent components and frictional contact for torque transmission between these components. 
     BACKGROUND OF THE INVENTION 
     Rings have been used in gas turbine engines for many purposes. For example, Meininghaus, U.S. Pat. No. 2,356,605 uses rings 17 between adjacent turbine rims to increase bending stiffness. 
     FIG. 1, in Kington et al., U.S. Pat. No. 5,664,413 shows a single piece pilot ring 54 disposed between a back-to-back centrifugal compressor and radial turbine. The pilot ring 54 serves two functions referred to as a radial function and an axial function. The radial function is maintaining concentricity between the compressor rotor 35 and the turbine rotor 37. This requires the pilot ring 54 to maintain radial contact with both rotors during assembly of the engine and during operation. During operation of the engine, the radial growth due to thermal and/or centrifugal expansion of the turbine rotor is significantly greater than that of the compressor rotor. As a result, the pilot ring 54 must roll to accomplish the radial function. The axial function is transferring the axial load between the two rotors which requires that the axial ends of the ring remain parallel. As a consequence, the ring cannot roll freely as the turbine rotor thermally grows at a faster rate than the compressor rotor, requiring large radial interference fits between the pilot ring and the rotors. Some of the disadvantages associated with large interference fits are that they require a large temperature difference of the components during assembly, the ring can pop off the compressor rotor if assembly is not completed quickly, clocking of the turbine relative to the compressor to achieve balance and “run out” is difficult, and large stresses can be generated in the ring causing it to yield which in turn can result in high vibrations in the engine. 
     To overcome these disadvantages, Kington further discloses a dual pilot ring 80 for use between a back-to-back centrifugal compressor and radial turbine. The dual pilot ring uncouples the axial function from the radial function by providing an inner ring for radial piloting the compressor rotor and turbine rotor, and an outer ring for transmitting axial loads. The two rings are separated by a clearance gap. As a result, the inner ring is no longer constrained by axial loads and is free to roll as the two rotors thermally and/or centrifugally grow at different rates. 
     Referring to FIGS. 1A and 1B, a typical prior art friction drive piloting system includes a first component  1  having a lower lip  2  clamped up to a second component  3  having an upper lip  4 . The components are radially piloted through the lips  2  and  4  and axially piloted through either the upper or lower axial facing surfaces  5 ,  6 ,  7 , and  8 . The torque transfer is primarily carried through these axial facing surfaces when the two components are clamped together represented by the arrows labeled with an “F”. Under operating conditions, the two components may grow radially at different rates due to thermal and centrifugal effects of the rotating components. These friction drive systems typically require large interference fits, represented by arrows  9 , to maintain radial piloting under the varying conditions. These large interference fits make it difficult to assemble and disassemble the components. This piloting scheme has also been known to cause face distortion, see FIG. 1B, which can change the rotor unbalance and increase the engine vibrations. 
     Accordingly, there is a need for a turbine assembly of rotating components in a gas turbine engine that uses a single piece pilot ring for radial piloting and frictional contact for torque transmission. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an assembly of rotating components that uses single piece pilot rings for radial piloting of the components and frictional contact between the faces of the assembled components for torque transmission between the components. 
     The present invention meets this objective by providing an assembly that includes a first rotatable component having a first lip with a first axial facing surface and a second rotatable component having a second lip with a second axial facing surface. The components are held together by an axial load so that the first and second axial surfaces are in frictional contact across a radial plane whereby torque is transmitted between the components. A pilot ring is mounted either above or below the radial contact plane to maintain the radial position of the two components. These and other objects, features and advantages of the present invention, are specifically set forth in, or will become apparent from, the following detailed description of a preferred embodiment of the invention then read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B are illustrations of a prior art friction drive piloting system. 
     FIG. 2 is a cross-section of a gas turbine engine turbine section showing rotating components coupled as contemplated by the present invention. 
     FIG. 3 is an enlarged view of the circled portion  3  of FIG.  2 . 
     FIG. 4 is the same view as FIG. 3 showing the affect of thermal and/or centrifugal mismatch and the ability of the pilot ring to roll. 
     FIG. 5 a perspective view of the pilot ring used in coupling the rotating components as shown in FIG.  2 . 
     FIG. 6 is an illustration of an alternative embodiment of the pilot ring contemplated by the present invention. 
     FIG. 7 is a cross-section of a gas turbine engine section in which the pilot ring contemplated by the present invention is disposed between rotating components that are bolted together. 
     FIG. 8 is a cross-section of a gas turbine engine section in which the pilot ring is extended in length to provide shaft retention during the loss of axial clamp load. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, FIG. 2 shows a portion of a gas turbine engine generally denoted by reference numeral  10  which is symmetric about an axial centerline  12 . Going from right to left in the axial direction, the engine portion is comprised of the following components. A rotating component  16  having an axial facing surface  19  on a lip  18  that frictionally engages an axial facing surface  20  on a first lip  22  of compressor wheel  14 . The compressor wheel  14  has a second lip  26  with an axial facing surface  28  that frictionally engages an axial facing surface  48  on a first lip  46  of a shaft member  24  that positions rotating shaft  13 . A seal  23  is mounted to the shaft member  24  for sealingly engaging a housing portion  30 . A first stage stator  32 , having an array of vanes, is coupled on its inner diameter to the housing portion  30  and on its outer diameter to a turbine shroud, not shown. Moving downstream, (i.e. right to left), the shaft member  24  has a second lip  25 . Adjacent the shaft member  24  is the first rotor stage  40 . The first rotor stage  40  is comprised of a wheel  42  having a plurality of blades  44  extending from the perimeter of the wheel. The wheel  42  has a lip  47  that frictionally engages lip  25  with a prior art interference fit as illustrated in FIG. 1A (facing surfaces  6  and  7  from FIG. 1A are not included in FIG.  2 ). On its opposite axial side, the wheel  42  is coupled to the wheel  62  of the second stage rotor  60  by a conventional curvic coupling  61 . The second stage rotor  60  in turn is coupled to a third stage rotor  80  by another curvic coupling  81 . The second and third stage rotor are each comprised of a wheel,  62 ,  82  and a plurality of blades  64 ,  84 . Disposed between the first stage rotor  40  and the second stage rotor  60  is a second stage stator  50  and between the second stage rotor  60  and the third stage rotor  80  is a third stage stator  70 . Rotating components  14 ,  16 ,  24 ,  40 ,  60 , and  80  are annular and their inner surfaces define a bore  15  that extends axially through the center of the turbine section  10 . Also located between first stage rotor  40  and second stage rotor  60  is a rotating seal  91 . Rotating seal  91  may function to prevent air movement from the outer cavity between first stage rotor  40  and second stage rotor  60  to the inner cavity defined by the bore  15 . A tie shaft  13  is disposed within the bore  15  and applied an axial force that holds these rotating components together resulting in the frictional contact among the various surfaces mentioned above. Torque is transmitted through the frictional contact causing the components  14 ,  16 ,  24 ,  40 ,  60 , and  80  to rotate. This axial force, represented by the letter “F” in FIGS. 3 and 4, is on the order of 30,000 lbf and this method of holding the components together is referred to as a lock-up. The actual axial load applied is dependent upon the torque being carried across the component faces. These rotating components are made from conventional gas turbine engine materials. 
     Still referring to FIG. 2, the lips  18  and  22  are configured to define an inner annular recess  21  extending along the inner diameter of the lips and beneath the radial plane of frictional contact between axial surfaces  19  and  20 . Press fit into the recess  21  is a pilot ring  100 . Similarly, as shown more clearly in FIG. 3, the lips  26  and  46  are configured to define an outer annular recess  27  extending along the outer diameter of the lips and over the radial plane of frictional contact between axial surfaces  28  and  48 . Press fit into the recess  27  is a second pilot ring  100 . With this arrangement the pilot ring  100  is not exposed to the axial load. 
     Referring to FIG. 4, the arrows  90  show the direction that the wheel  14  and shaft member  24  may move during operation of the engine as these components heat up, cool down, or grow radially due to speed at different rates. Because the pilot ring  100  is compliant to such differential growth, it can maintain the relative radial position of these two components to each other within acceptable tolerances. Importantly, because the pilot ring does not have to transmit the axial load it can more easily pivot radially and maintain contact with both components with out a large press fit. That is displacement of one end of the ring, while in the free-state, results in a rolling action and subsequent decrease in diameter at the other end. This rolling effect provides improved means to pilot adjacent components without the large interference fits found in prior art friction drive systems where the radial piloting feature is exposed to the axial clamping load and consequently has a very limited ability to roll. 
     Referring to FIG. 5, the pilot ring  100  may have a plurality of circumferentially spaced slots  102  on both of its axial edges. On the portion of these edges without a slot the edges are rounded. The slots and rounded edges make the pilot ring more compliant and allow for rolling in the radial direction as the various parts around the ring grow at different thermal rates. This helps to reduce the contact stresses. The pilot ring  100  may have a radially outward facing surface  104  or a radially inward facing surface  106  which provide radial positioning or piloting when the rings are mounted in the engine and improve ring rolling. 
     In one alternative embodiment shown in FIG. 6, splines, pins or keys  110  can be incorporated into the ring  100  and adjacent parts of the assembly to prevent slippage in the event that the toque load exceeds the ability of the contacting axial surfaces to transfer the torque. 
     Thus a novel pilot ring is provided that makes the adjacent components easier to manufacture and balance. When the pilot rings are positioned on the outside, no balance tool is required which eliminates tooling errors and lowers the rotating group unbalance. The components can also be machined off of its centers reducing the time and cost to manufacture the component. Pilot rings and the contacting surfaces are easier to manufacture, inspect and repair than curvic couplings and provides better face parallelism. As a result, component tolerances and controls can be relaxed in comparison to components coupled by a curvic coupling. 
     The pilot ring  100  can also be employed in a wide variety of locations in a gas turbine engine. FIG. 7 shows a turbine assembly  110  with first and second turbine wheels  112 ,  114 . Each of the wheels  112 ,  114  has a flange portion  116 ,  118  that are bolted together. In this embodiment, the pilot ring  100  is mounted in a groove  120  that circumscribes the bolted flanges. FIG. 8, shows a compressor assembly  130  in which a compressor wheel  132  is coupled to a shaft portion  134  and the pilot ring  100  is mounted in a groove  138  and lengthened to contribute to the containment of the shaft  140  in the event of a loss of tie shaft load. 
     Various other modifications and alterations to the above-described preferred embodiments will be apparent to those skilled in the art. 
     Accordingly, these descriptions of the invention should be considered exemplary and not as limiting the scope and spirit of the invention as set forth in the following claims.