Patent Publication Number: US-9410428-B2

Title: Turbomachine with clamp coupling shaft and rotor hub together

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with government support under contract number DAAH10-02-2-0005 awarded by the United States Army. The government has certain rights in the invention. 
    
    
     BACKGROUND 
     This disclosure relates to turbomachinery and, more particularly, to the coupling between a rotor hub and a shaft for co-rotation and transfer of energy. 
     Turbomachines are known and used for transferring energy between a rotor and a working fluid. For example, a turbomachine includes a compressor, a turbine, or both. The rotor can be mounted for co-rotation with a shaft. There are various mechanisms for coupling the rotor and the shaft together, such as splined connections and tie-rod mechanisms. Where the rotor and the shaft are made of similar materials, thermally-induced stresses through the coupling mechanism may be nominal or can be relatively easily managed. However, if the rotor and the shaft are made of dissimilar materials, thermally-induced stresses can exceed the strength limits of the materials. 
     SUMMARY 
     A turbomachine according to an exemplary aspect of the present disclosure includes a rotor hub including a central opening there through, a shaft extending through the central opening, and a clamp coupled with the shaft and the rotor hub such that the rotor hub is rotatable with the shaft. 
     In a further non-limiting embodiment of any of the foregoing examples, the clamp is frictionally coupled with the rotor hub. 
     In a further non-limiting embodiment of any of the foregoing examples, the rotor hub is non-metallic and the shaft is metallic. 
     In a further non-limiting embodiment of any of the foregoing examples, the rotor hub is a ceramic material and the shaft is a superalloy material. 
     A further non-limiting embodiment of any of the foregoing example includes a compliant layer between the rotor hub and the clamp, and the compliant layer is selected from the group consisting of platinum metal, gold metal and combinations thereof. 
     In a further non-limiting embodiment of any of the foregoing examples, the clamp includes an engagement surface bearing against the rotor hub, and the engagement surface is sloped at an oblique angle with respect to an axis of rotation of the rotor hub. 
     In a further non-limiting embodiment of any of the foregoing examples, the engagement surface is frusto-conical. 
     In a further non-limiting embodiment of any of the foregoing examples, the rotor hub includes an axially-flared lip around the central opening onto which the clamp is coupled. 
     A further non-limiting embodiment of any of the foregoing examples includes an axially-extending passage between the rotor hub and the shaft. 
     In a further non-limiting embodiment of any of the foregoing examples, the clamp includes cooling passages in fluid communication with the axially-extending passage. 
     In a further non-limiting embodiment of any of the foregoing examples, the rotor hub includes a plurality of blades on an outer periphery thereof. 
     An integrally bladed rotor hub and attachment for a turbomachine according to an exemplary aspect of the present disclosure includes a non-metallic rotor hub extending between a first and second axial side, the non-metallic rotor hub includes a lip extending around central opening, a metallic shaft extending through the central opening, and a clamp is coupled with the shaft. The clamp includes a first clamp member arranged on the first axial side of the non-metallic rotor hub and a second clamp member arranged on the second axial side of the non-metallic rotor hub. The first clamp member and the second clamp member engage the lip such that the non-metallic rotor hub is rotatable with the metallic shaft. 
     In a further non-limiting embodiment of any of the foregoing examples, the non-metallic rotor hub is a ceramic material and the metallic shaft is a superalloy material. 
     In a further non-limiting embodiment of any of the foregoing examples, the first clamp member has a first engagement surface and the second clamp member has a second engagement surface, and the first engagement surface slopes at a first oblique angle with respect to an axis of rotation of the non-metallic rotor hub and the second engagement surface slopes at a second oblique angle with respect to the axis of rotation of the rotor hub. 
     In a further non-limiting embodiment of any of the foregoing examples, the first oblique angle is unequal to the second oblique angle. 
     In a further non-limiting embodiment of any of the foregoing examples, the first oblique angle and the second oblique angle are, independently of each other, less than 50°. 
     In a further non-limiting embodiment of any of the foregoing examples, the lip is axially-flared. 
     A method of operating a turbomachine according to an exemplary aspect of the present disclosure includes providing a rotor hub which includes a central opening there through, a shaft extending through the central opening, and a clamp coupled with the shaft and the rotor hub, rotating one of the shaft or the rotor hub to produce a rotational force, and transferring the rotational force through the clamp to the other of the rotor hub or the shaft to co-rotate the rotor hub and the shaft. 
     In a further non-limiting embodiment of any of the foregoing examples, the transferring of the rotational force includes frictionally transferring the rotational force. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features and advantages of the present disclosure 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. 
         FIG. 1  illustrates an example turbomachine having a clamp coupled with a shaft and a rotor hub such that the rotor hub is rotatable with the shaft. 
         FIG. 2  illustrates another example turbomachine having a clamp that provides for internal cooling passages. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a sectioned view of an example turbomachine  20  taken along a central, rotational axis A.  FIG. 2  illustrates a half section-view of the turbomachine  20 . As can be appreciated, the example turbomachine machine  20  can be a gas turbine engine, such as a ground-based engine, propulsion engine or auxiliary power engine, a pump, an air cycle machine or other type of turbomachine. Turbomachines are configured to transfer energy between a rotor and a working fluid. 
     In this example, the turbomachine  20  includes a rotor hub  22  that is generally rotatable about the central axis A. The rotor hub  22  can be an integrally bladed rotor hub that has a plurality of blades B or, alternatively, can include mounting features for separately mounting the blades B. The rotor hub  22  includes a central opening  24  through which a shaft  26  extends. A clamp  28  is coupled with the shaft  26  and the rotor hub  22  such that the rotor hub  22  is rotatable with the shaft  26 . 
     In this example, the clamp  28  includes a first clamp member  28   a  and a second clamp member  28   b . With respect to the central axis A, the rotor hub  22  includes a first axial side  22   a  and a second axial side  22   b . The first clamp member  28   a  is arranged on the first axial side  22   a  of the rotor hub  22 , and the second clamp member  28   b  is arranged on the second axial side  22   b  of the rotor hub  22 . The rotor hub  22  includes a lip  30  that is axially-flared. The first clamp member  28   a  and the second clamp member  28   b  engage the lip  30 . 
     The first clamp member  28   a  and the second clamp member  28   b  include, respectively, engagement surfaces  32   a / 32   b  that bear against the lip  30  of the rotor hub  22 . The engagement surfaces  32   a / 32   b  are sloped at respective oblique angles, α a /α b , with respect to the central axis A of rotation of the rotor hub  22  such that each of the engagement surfaces  32   a / 32   b  is frusto-conical. In the illustrated example, the oblique angles α a /α b  are unequal. The use of unequal oblique angles α a /α b  permit the steeper one of the engagement surfaces  32   a / 32   b , which here is the engagement surface  32   a , to be axially shorter to provide a more compact arrangement, for example. In a further example, the oblique angles α a /α b  are, independently of each other, less than 50°. In one further example, the oblique angle α a  is or is about 45° and the oblique angle α b  is about 10°. 
     The first clamp member  28   a  and the second clamp member  28   b  are mounted on the shaft  26  at splined interconnections  34 . In this example, a nut  36  and washers  38 , such as Belleville washers, are secured on the shaft  26  to tighten the first clamp member  28   a  and the second clamp member  28   b  around the lip  30  of the rotor hub  22 . Upon tightening, the engagement surfaces  32   a / 32   b  frictionally engage the lip  30 . Upon rotation of the shaft  26  or the rotor hub  22 , the rotational force provided is transferred through the clamp  28  to the other of rotor hub  22  or the shaft  26  to co-rotate the rotor hub  22  and the shaft  26 . For example, the frictional engagement provided by the clamp  28  is the exclusive coupling and transfer mechanism between the rotor hub  22  and the shaft  26 . In a turbine, the rotor hub  22  (e.g., a turbine rotor hub) would drive rotation of the shaft  26 , such as to drive a compressor C. Alternatively, in a compressor, the shaft  26  would drive rotation of the rotor hub  22   22  (e.g., a compressor rotor hub). 
     Due to a difference in the coefficients of thermal expansion between non-metallic and metallic materials, couplings between dissimilar materials in a turbomachine can generate high thermal stresses on the materials. For example, although ceramic material is relatively strong in compression, it can be brittle in tension. Thus, couplings that thermally-induce tensile loads on ceramic components can debit the lifetime of the component and can preclude the use of ceramic materials for rotor hubs. However, the clamp  28  fastens the rotor hub  22  in compression and thus permits the rotor hub  22  to be made of a ceramic material, while the shaft  26  and the clamp  28  can be made of a metallic material, such as superalloy materials. As can be appreciated however, the clamp  28  is not limited to use where the rotor hub  22  is ceramic material and can also be used where the rotor hub  22  and the shaft  26  are similar or identical materials or with other dissimilar metallic or non-metallic materials. 
       FIG. 2  illustrates a modified example with a clamp  128  that includes cooling passages  140 . In this disclosure, like reference numerals designate like elements where appropriate and reference numerals with the addition of one-hundred or multiples thereof designate modified elements that are understood to incorporate the same features and benefits of the corresponding elements. An axial passage  142  is provided between the rotor hub  22  and the shaft  26 . The cooling passages  140  of the clamp  128  are in a fluid communication with the axial passage  142 . A cooling flow F can be provided through the cooling passages  140  into the axial passage  142 . In this example, the cooling flow F exits through the second clamp member  128   b . The cooling flow F can then be purged upwardly and adjacent the blade B to limit or prevent relatively hot gas flow from bypassing the blade B and flowing toward the clamp  128 . 
     Additionally, a compliant layer  144  is arranged between the lip  30  of the rotor hub  22  and the clamp  128 . For example, the compliant layer  144  is a metallic material, such as platinum metal, gold metal or a combination thereof. The compliant layer  144  is soft relative to the materials of the rotor hub  22  and the clamp  128 . Thus, the compliant layer  144  can deform to accommodate thermal growth between the rotor hub  22  and the clamp  128 . Additionally, the compliant layer  144  can serve to distribute stress over the area of the lip  30  such that if there is an imperfection in the rotor hub  22 , such as a void or micro-crack, the stress will not be concentrated at the imperfection. 
     Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments. 
     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.