Abstract:
A seal assembly for sealing a rotatable shaft in a gas turbine engine, wherein the shaft includes sections of greater shaft diameter located both forward and aft of the seal shaft coupling point is provided. The seal assembly includes a first semi-annular segment with a first end, a second end, and a plurality of seal teeth, where the first and second ends each include an overlap joint. The seal assembly also includes a second semi-annular segment with a first end, a second end, and a plurality of seal teeth, where the first and second ends each include an overlap joint. The first end of the second segment is coupled to the first end of the first segment, and the second end of the second segment is coupled to the second end of the first segment.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/639403, filed Apr. 27, 2012, which is incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The field of the invention relates generally to gas turbines, and more particularly to methods and a system for a seal assembly for an inter-shaft seal in a gas turbine engine. 
         [0003]    Labyrinth seals are widely used on rotatable shafts to regulate secondary air flows and provide a radial clearance between low speed shafts and high speed shafts in gas turbine engines. Generally, in more detail, the seals include a series of parallel teeth that facilitate regulating a flow past the teeth and capturing any excess oil. The tips of the teeth provide the clearance between the two shafts. Newer generation engines include shafts made of strong, but brittle materials that may not be as tolerant of the rubbing that typical seal teeth endure during engine operation. The rubbing can cause localized micro-cracking in the shaft. Seals made of a single unit that are integral to the shaft may not be allowable in some situations due to material or stress concerns. Additionally, sections of greater shaft diameter located both forward and aft of the seal can prevent implementation of the seal on an unbroken ring of material. Accordingly, a seal that is separable and not subject to the torque load of the shaft, which results in greater flexibility in design at a lower cost for repair and maintenance is desirable. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    In one aspect, a seal assembly for sealing a rotatable shaft in a gas turbine engine, wherein the shaft includes sections of greater shaft diameter located both forward and aft of the seal shaft coupling point is provided. The seal assembly includes a first semi-annular segment with a first end, a second end, and a plurality of seal teeth, where the first and second ends each include an overlap joint. The seal assembly also includes a second semi-annular segment with a first end, a second end, and a plurality of seal teeth, where the first and second ends each include an overlap joint. The first end of the second segment is coupled to the first end of the first segment, and the second end of the second segment is coupled to the second end of the first segment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a cross-sectional view of an exemplary gas turbine engine assembly for use in propelling an aircraft. 
           [0006]      FIG. 2  is an enlarged cross-sectional view of the exemplary seal shown in  FIG. 1  in relation to the first and second shafts. 
           [0007]      FIG. 3  is a perspective view of an exemplary seal in accordance with the present invention. 
           [0008]      FIG. 4  is a cross-sectional view of the seal on the first shaft taken at line  4 - 4  in  FIG. 3 . 
           [0009]      FIG. 5  is a perspective view of an alignment pin connecting the two segments of the seal shown in  FIGS. 3 and 4 . 
           [0010]      FIG. 6  is a perspective view of an alternate embodiment of the seal in accordance with the present invention. 
           [0011]      FIG. 7  is a cross-sectional view of the seal on the first shaft taken at line  7 - 7  in  FIG. 6 . 
           [0012]      FIG. 8  is a perspective view of an alternate embodiment of the seal in accordance with the present invention. 
           [0013]      FIG. 9  is a cross-sectional view of the seal on the first shaft taken at line  9 - 9  in  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    The following detailed description illustrates an inter-shaft seal and a method of assembling the same by way of example and not by way of limitation. The description enables one of ordinary skill in the art to make and use the disclosure, and the description describes several embodiments of the disclosure, including what is presently believed to be the best mode of carrying out the disclosure. The disclosure is described herein as being applied to a preferred embodiment, namely, an inter-shaft seal and a method of assembling the same. However, it is contemplated that this disclosure has general application to shaft seals in a broad range of systems and in a variety of industrial and/or consumer applications. 
         [0015]      FIG. 1  is a cross-sectional view of an exemplary gas turbine engine (GTE)  10 . GTE  10  includes a fan assembly  12 , a core gas turbine engine section  14  coupled downstream from fan assembly  12 , and a low-pressure turbine  16  coupled downstream from the core gas turbine engine section  14 . In the exemplary embodiment, core gas turbine engine section  14  includes a multi-stage booster compressor  18 , a high-pressure compressor  20 , a combustor  22 , and a high-pressure turbine  24 . GTE  10  also includes an inlet  26  and an exhaust  28 . In the exemplary embodiment, low-pressure turbine  16  and booster compressor  20  are coupled together via a first drive shaft  30 , and compressor  18  and high-pressure turbine  24  are coupled together via a second drive shaft  32 . 
         [0016]    In operation, air is drawn into engine inlet  26 , and compressed through booster compressor  18  and high pressure compressor  20 . The compressed air is channeled to combustor  22  where it is mixed with fuel and ignited to produce air flow through high pressure turbine  24  and low pressure turbine  16 , and exits through exhaust  28 . 
         [0017]      FIG. 2  is an enlarged cross-sectional view of the gas turbine engine shown in  FIG. 1 . GTE  10  includes a seal  34  coupled to first shaft  30 . Seal  34  is separable from shaft  30  and includes at least two segments such that it may be installed or removed on a complete shaft without needing clearance on either end of the shaft. Moreover, being made of at least two segments facilitates installation of seal  34  on a shaft even when the shaft has a greater diameter on both sides of seal  34  installation point, which provides much greater flexibility in where seal  34  is located on a shaft. Seal  34  may include, as desired, labyrinth tooth material of the same material, or different material, as/than the shaft  30 , respectively. Seal  34  may be coupled to shaft  30  in multiple ways, which are described below. 
         [0018]      FIG. 3  is a perspective view of an exemplary seal  34  in accordance with the present invention. Seal  34  includes a first half circle-shaped segment  300  and a second half circle-shaped segment  302 . First segment  300  includes a first end having a connector  304  and a second end having a connector  306 . Second segment  302  includes a first end having a connector  308  and a second end having a connector  310 . First segment  300  and second segment  302  assemble by an overlap joint, by joining connectors  304  and  308 , and connectors  306  and  310 . The overlap joint allows seal  34  to carry a hoop load. Segments  300  and  302  each include a plurality of seal teeth  312 . 
         [0019]      FIG. 4  is a cross-sectional view of seal  34  (shown in  FIG. 3 ) coupled to a shaft taken at line  4 - 4  in  FIG. 3 . In the exemplary embodiment, the shaft is shaft  30  (shown in  FIG. 1 ). The primary retention for seal  34  is an interference fit between seal  34  and a shoulder  400  of shaft  30 . First segment  300  includes a shoulder  402  (shown in  FIG. 3 ) that enables secondary axial and tangential retention on shaft  30 . 
         [0020]    Assembly of first and second segments  300  and  302  about shaft  30  is accomplished by heating both first and second segments  300  and  302  to a predetermined temperature, sliding first segment  300  in from a side of shaft  30 , and sliding second segment  302  axially such that connectors  308  and  310  engage the mating halves of connectors  304  and  306 , respectively. When allowed to equalize in temperature with shaft  30 , an interference fit is generated between first and second segments  300  and  302  and shaft  30 . First and second segments  300  and  302  enable the ring formed by their coupling to carry hoop stress. To hold first and second segments  300  and  302  together, a retaining ring  404  is expanded into a slot  406 . Moreover, with reference to  FIG. 5 , an alignment pin  500  is placed in an alignment orifice  502  formed between first and second segments  300  and  302  (shown in  FIGS. 3 and 4 ). Alignment pin  500  is then trapped by the retaining ring, which is installed last. 
         [0021]      FIG. 6  is a perspective view of an alternative embodiment of seal  34  in accordance with the present invention. Seal  34  includes first inner ring segment  600 , second inner ring segment  602 , first outer ring segment  604 , and second outer ring segment  606 . First and second inner ring segments  600  and  602  are similar to first and second segments  300  and  302 , as described in  FIGS. 3-5 , less the retaining ring, and are coupled to a shaft in the same manner. Seal  34  also includes first outer ring segment  604  and second outer ring segment  606  coupled together about first and second inner ring segments  600  and  602 . Outer ring segments  604  and  606  each include a plurality of seal teeth  608 . 
         [0022]      FIG. 7  is a cross-sectional view of seal  34  on shaft  30  (shown in  FIG. 1 ) taken at line  7 - 7  in  FIG. 6 . The primary retention of seal  34  is accomplished by an interference fit to shaft  30 , and secondary axial retention is accomplished by protrusions  701  on the inner diameter of seal  34  on either side of a shoulder  700  of shaft  30 . Secondary tangential retention is provided by a tab  702  which engages with a keyway  704  on shaft  30 . The four ring segments  600 ,  602 ,  604 , and  606  are coupled along two 360 degree seams  708  between the segments. Segments  600 ,  602 ,  604 , and  606  may be coupled by welding and brazing. 
         [0023]    Assembly of first and second segments  600  and  602  about shaft  30  is accomplished by heating both first and second inner ring segments  600  and  602 , sliding first inner ring segment  600  in from the side, and sliding second inner ring segment  602  axially such that connector  610  engages the mating half of connector  612 , and another set of connectors (not shown) engage on the other side of seal  34 . When allowed to equalize in temperature with shaft  30 , an interference fit is generated between first and second inner ring segments  600  and  602  and shaft  30 , enabling segments  600  and  602  to carry hoop stress. Following this initial assembly step, two 180 degree segments, first outer ring segment  604  and second outer ring segment  606 , are coupled to the ring created by first and second inner ring segments  600  and  602 , and welded in place. The weld joint is formed along the two 360 degree seams between outer ring segments  604  and  606 , and inner ring segments  600  and  602 . Seal teeth  608  are finish machined following assembly and welding of segments  600 ,  602 ,  604 , and  606  to ensure tooth alignment and tip runout requirements are met. 
         [0024]      FIG. 8  is a perspective view of an alternate embodiment of seal  34  in accordance with the present invention.  FIG. 9  is a cross-sectional view of separable seal  34  on a shaft taken at line  9 - 9  in  FIG. 8 . Seal  34  is comprised of a plurality of identical segments  800 . In the exemplary embodiment, seal  34  includes four identical segments  800 . Segments  800  are connected to shaft  30  (shown in  FIG. 1 ) by a dovetail joint. Segments  800  each include a plurality of seal teeth  802 . 
         [0025]    Segments  800  are assembled about shaft  30  (shown in  FIG. 1 ) by inserting them through a load slot  804  in shaft  30 . Segments  800  are then rotated around load slot  804  until all segments  800  are in place. For each segment  800 , a set screw (not shown) is installed through a tapped hole  806  located in each segment  800 . The screw engages with a dimple  900  in shaft  30  to provide secondary retention. Each segment  800  has only a dovetail pressure face over the central 50% of its arc length, allowing load slot  804  to be smaller in size. 
         [0026]    The seal assembly described herein enables installation of a separable seal on a shaft where integral teeth and/or a one piece ring are not usable. The seal assembly provides a 360 degree ring that can be installed on a completed shaft without needing clearance on either end for installation. The assembly provides different connection options depending on the specifications required. 
         [0027]    While multiple inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the invent of embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure. 
         [0028]    Examples are used to disclose the embodiments, including the best mode, and also to enable any person skilled in the art to practice the apparatus and/or method, including making and using any devices or systems and performing any incorporated methods. These examples are not intended to be exhaustive or to limit the disclosure to the precise steps and/or forms disclosed, and many modifications and variations are possible in light of the above teaching. Features described herein may be combined in any combination. Steps of a method described herein may be performed in any sequence that is physically possible. 
         [0029]    All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms. The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. 
         [0030]    It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited. 
         [0031]    In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.