Patent Publication Number: US-2022220901-A1

Title: Rotating sleeve controlling clearance of seal assembly of gas turbine engine

Description:
BACKGROUND 
     A gas turbine engine typically includes a fan section, a compressor section, a combustor section, and a turbine section. Air entering the compressor section is compressed and delivered into the combustor section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section. The compressor section typically includes low and high pressure compressors, and the turbine section includes low and high pressure turbines. 
     A gas turbine engine also includes bearings that support rotatable shafts. The bearings require lubricant. Various seals near the rotating shafts contain oil within bearing compartments. During operation of the engine, the seals maintain compartment pressures and keep lubricating oil inside the various compartments. 
     SUMMARY 
     A gas turbine engine according to an exemplary aspect of the present disclosure includes, among other things, a bearing compartment, a shaft configured to rotate during operation of the gas turbine engine, and a sleeve configured to rotate with the shaft during operation of the gas turbine engine. The sleeve includes a variable radial dimension about a circumference of the sleeve. The engine further includes a seal statically mounted relative to the sleeve and configured to cooperate with the sleeve to seal the bearing compartment. 
     In a further non-limiting embodiment of the foregoing gas turbine engine, the sleeve includes a radially outer surface concentric with a center of the shaft. 
     In a further non-limiting embodiment of any of the foregoing gas turbine engines, the sleeve includes a radially inner surface having a center spaced-apart from the center of the radially outer surface of the sleeve. 
     In a further non-limiting embodiment of any of the foregoing gas turbine engines, the center of the shaft is spaced-apart from the center of the radially inner surface of the sleeve. 
     In a further non-limiting embodiment of any of the foregoing gas turbine engines, the gas turbine engine includes a bearing nut mounted directly to the shaft and configured to rotate with the shaft during operation of the gas turbine engine. Further, the sleeve is mounted to the bearing nut, and a minimum radial dimension of the sleeve is circumferentially aligned with a location of the bearing nut corresponding to a maximum deviation between the bearing nut and a reference axis. 
     In a further non-limiting embodiment of any of the foregoing gas turbine engines, the sleeve is arranged such that the center of the radially outer surface of the sleeve is concentric with a center of a radially inner surface of the seal. 
     In a further non-limiting embodiment of any of the foregoing gas turbine engines, the radially inner surface of the sleeve directly contacts a radially outer surface of the bearing nut. 
     In a further non-limiting embodiment of any of the foregoing gas turbine engines, the bearing nut includes a notch adjacent an aft surface thereof, and the sleeve is arranged in the notch such that the radially inner surface of the sleeve directly contacts a radially outer surface of the bearing nut. 
     In a further non-limiting embodiment of any of the foregoing gas turbine engines, the sleeve includes a plurality of projections projecting radially inwardly from the radially inner surface, the bearing nut includes a plurality of axially-extending projections defining slots therebetween, and the projections of the sleeve are received in a respective one of the slots of the bearing nut. 
     In a further non-limiting embodiment of any of the foregoing gas turbine engines, a retaining ring is mounted to the projections of the bearing nut to hold the projections of the sleeve within the slots. 
     In a further non-limiting embodiment of any of the foregoing gas turbine engines, the seal is a brush seal. 
     In a further non-limiting embodiment of any of the foregoing gas turbine engines, the sleeve includes a tab projecting radially outward of a radially outer surface of the sleeve, and the seal is aft of the tab. 
     In a further non-limiting embodiment of any of the foregoing gas turbine engines, the shaft is one of an inner shaft and an outer shaft of the gas turbine engine, and the shaft is rotatably supported by a bearing contained within the bearing compartment. 
     A method according to an exemplary aspect of the present disclosure includes, among other things, mounting a sleeve having a variable radial dimension relative to a shaft of a gas turbine engine such that the sleeve is configured to rotate with rotation of the shaft and such that a seal cooperates with the sleeve to establish a fluid boundary of a bearing compartment of the gas turbine engine. 
     In a further non-limiting embodiment of the foregoing method, the mounting step includes mounting the sleeve to the shaft via a bearing nut. 
     In a further non-limiting embodiment of any of the foregoing methods, the method includes determining a first circumferential location of the bearing nut corresponding to a maximum deviation between the bearing nut and a reference axis, and the mounting step includes aligning the sleeve relative to the bearing nut such that a second circumferential location corresponding to minimum radial dimension of the sleeve is circumferentially aligned with the first circumferential location. 
     In a further non-limiting embodiment of any of the foregoing methods, the mounting step is only performed if it is first determined that a center of the bearing nut is spaced-apart from a center of a radially inner surface of the seal. 
     In a further non-limiting embodiment of any of the foregoing methods, the mounting step includes arranging the sleeve such that a center of a radially outer surface of the sleeve is concentric with a center of a radially inner surface of the seal. 
     In a further non-limiting embodiment of any of the foregoing methods, the seal is a brush seal, the shaft is one of an inner shaft and an outer shaft of the gas turbine engine, and the shaft is rotatably supported by a bearing contained within the bearing compartment. 
     The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates a gas turbine engine. 
         FIG. 2  illustrates a portion of the engine, and in particular illustrates a bearing compartment including a seal assembly. 
         FIG. 3  is a perspective view of an example sleeve mounted relative to an example bearing nut. 
         FIG. 4  is a somewhat schematic, end view of the example bearing nut. 
         FIG. 5  is a somewhat schematic, end view of the example sleeve. 
         FIG. 6  is a somewhat schematic, end view of an example seal, the example sleeve, and the example bearing nut. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a gas turbine engine  20  (“engine  20 ”). The engine  20  is disclosed herein as a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . The fan section  22  drives air along a bypass flow path B in a bypass duct defined within a nacelle  15 , and also drives air along a core flow path C for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures. 
     The exemplary engine  20  generally includes a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36  via several bearing systems  38 . It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided, and the location of bearing systems  38  may be varied as appropriate to the application. 
     The low speed spool  30  generally includes an inner shaft  40  that interconnects, a first (or low) pressure compressor  44  and a first (or low) pressure turbine  46 . The inner shaft  40  is connected to the fan  42  through a speed change mechanism, which in the exemplary engine  20  is illustrated as a geared architecture  48  to drive a fan  42  at a lower speed than the low speed spool  30 . The high speed spool  32  includes an outer shaft  50  that interconnects a second (or high) pressure compressor  52  and a second (or high) pressure turbine  54 . A combustor  56  is arranged in exemplary gas turbine  20  between the high pressure compressor  52  and the high pressure turbine  54 . A mid-turbine frame  57  of the engine static structure  36  may be arranged generally between the high pressure turbine  54  and the low pressure turbine  46 . The mid-turbine frame  57  further supports bearing systems  38  in the turbine section  28 . The inner shaft  40  and the outer shaft  50  are concentric and rotate via bearing systems  38  about the engine central longitudinal axis A which is collinear with their longitudinal axes. 
     The core airflow is compressed by the low pressure compressor  44  then the high pressure compressor  52 , mixed and burned with fuel in the combustor  56 , then expanded over the high pressure turbine  54  and low pressure turbine  46 . The mid-turbine frame  57  includes airfoils  59  which are in the core airflow path C. The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. It will be appreciated that each of the positions of the fan section  22 , compressor section  24 , combustor section  26 , turbine section  28 , and fan drive gear system  48  may be varied. For example, gear system  48  may be located aft of the low pressure compressor, or aft of the combustor section  26  or even aft of turbine section  28 , and fan  42  may be positioned forward or aft of the location of gear system  48 . 
     The engine  20  in one example is a high-bypass geared aircraft engine. In a further example, the engine  20  bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), the geared architecture  48  is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine  46  has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine  20  bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor  44 , and the low pressure turbine  46  has a pressure ratio that is greater than about five 5:1. Low pressure turbine  46  pressure ratio is pressure measured prior to inlet of low pressure turbine  46  as related to the pressure at the outlet of the low pressure turbine  46  prior to an exhaust nozzle. The geared architecture  48  may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3:1 and less than about 5:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans, low bypass engines, and multi-stage fan engines. 
     A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section  22  of the engine  20  is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet (10,668 meters). The flight condition of 0.8 Mach and 35,000 ft (10,668 meters), with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (“TSFC”)”—is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram ° R)/(518.7° R)] 0.5 . The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second (350.5 meters/second). 
       FIG. 2  is a partial cross-sectional view of a bearing compartment  60  of the engine  20 . The bearing compartment  60  includes a bearing assembly  62  and a seal assembly  64  configured to seal the bearing compartment  60  and maintain fluid pressure, particularly oil pressure, in the bearing compartment  60  during operation of the engine  20 . As is known in the art, the bearing assembly  62  may include an inner race, an outer race, and rolling elements, such as balls, configured to roll therebetween. The bearing assembly  62  is mounted relative to a shaft  66  of the engine  20 . The shaft  66  may be rotatably mounted such that the shaft  66  is configured to rotate generally about the engine central longitudinal axis A by one or more bearing assemblies, including additional bearing assemblies within the bearing compartment  60  or in other bearing compartments in the engine  20 . 
     To this end, the bearing compartment  60  is representative of any bearing compartment within the engine  20 . This disclosure is not limited to any specific bearing compartment, and in particular is not limited to a forward or an aft bearing compartment. The “fore” and “aft” directions are labeled for reference in  FIG. 2 . Further, the shaft  66  represents either the inner shaft  40  or the outer shaft  50 . This disclosure is not limited to bearing compartments at any particular engine location, and this disclosure applies to compartments, other than bearing compartments, that are sealed. 
     The seal assembly  64  includes a seal  68  and a sleeve  70  configured to cooperate with one another to establish a seal for the bearing compartment  60 , and in particular to keep oil in the bearing compartment  60 , which, in turn, maintains oil pressure in the bearing compartment  60 . In this example, the seal  68  is a brush seal. The seal  68  could be another type of seal such as a knife edge seal. The seal  68  is fixedly mounted to a static structure of the engine  20 , and therefore does not rotate during operation of the engine  20 . The seal  68  may be circumferentially segmented and may be made of a carbon (C) material, however other arrangements and materials come within the scope of this disclosure. For instance, the seal  68  could be provided by a single, continuous hoop extending, uninterrupted and without segmentation, about the engine central longitudinal axis A. 
     In this disclosure, the seal  68  can either directly contact the sleeve  70  or be arranged such that there is a radial gap G ( FIG. 6 ) between the seal  68  and sleeve  70  during operation of the engine  20 . In the latter example, the seal assembly  64  is known in the art as a non-contacting seal. In either case, the seal  68  and sleeve  70  are in a close relationship, and the relative spacing between the seal  68  and the sleeve  70  is important for maintaining pressure in the bearing compartment  60 . The relative spacing between the seal  68  and the sleeve  70  may be referred to as the clearance of the seal assembly  64 . The present disclosure seeks to control the clearance of the seal assembly  64  so as to provide a substantially uniform clearance about the entire circumference of the seal assembly  64 , whether the seal assembly  64  is a contacting or non-contacting seal. As such, the present disclosure increases the performance of the seal assembly  64  and prolongs the useful life of the same. 
     In this disclosure, the sleeve  70  is mounted to the shaft  66  such that the sleeve  70  rotates during operation of the engine  20  relative to the seal  68  and other static components of the engine  20 . In this regard, the sleeve  70  may be referred to as a rotating sleeve. The sleeve  70  is mounted to the shaft  66  via a bearing nut  72 , in this example. The bearing nut  72  is engaged with the shaft  66  via a threaded connection and is configured to rotate with the shaft  66 . This disclosure is not limited to threaded connections between the bearing nut  72  and the shaft  66 . This disclosure also extends to sleeves directly mounted to the shaft  66  without an intermediate structure, such as the bearing nut  72 . 
     The sleeve  70  is mounted such that the sleeve  70  is axially aligned (i.e., arranged at the same axial location, relative to the engine central longitudinal axis A) with the seal  68 . The sleeve  70  is mounted adjacent an aft end  74  of the bearing nut  72 , in this example. The sleeve  70  includes a main body portion  78  providing a radially outer surface  80 , a radially inner surface  82 , and a radial dimension  84  between the radially outer and inner surfaces  80 ,  82 . The radial dimension  84  is the thickness of the main body portion  78  of the sleeve  70  in the radial direction R. In this disclosure, the radial dimension  84  is variable about a circumference of the sleeve  70  (i.e., in the circumferential direction X). In this disclosure, “axially” refers to a direction substantially parallel to the engine central longitudinal axis A, and “radially” refers to a direction substantially normal to the engine central longitudinal axis A (i.e., in the radial direction R). The term “circumferentially” is used herein to refer to angular positions and/or locations about a reference axis, such as the engine central longitudinal axis A (i.e., in the circumferential direction X). 
     As shown in  FIGS. 2 and 3 , the sleeve  70  may include a tab  86  projecting radially outward from the radially outer surface  80 . The tab  86  is forward of the seal  68 , in this example. Further, as shown in  FIG. 3 , the sleeve  70  is connected to the bearing nut  72  via a plurality of projections  88  which project radially inward of the radially inner surface  82 . The projections  88  are circumferentially spaced-apart from one another such that each projection  88  fits in a slot  90  formed between adjacent axially-extending projections  92  of the bearing nut  72 . A radially inner surface of the projections  92  may include a slot or groove  94  for receiving a retaining ring  96 . The retaining ring  96  is radially aligned with the projections  88  and restricts axially aft movement of the sleeve  70  by holding the projections  88  in place within the slots  90 . 
     In this example, the bearing nut  72  includes a notch  98  adjacent the aft end  74 . In particular, the notch  98  is substantially L-shaped and is open facing an aft location and a radially outer location. The sleeve  70  is arranged in the notch  98  such the radially inner surface  82  of the sleeve  70  directly contacts a radially outer surface  100  of the bearing nut  72 . Further, the notch  98  is sized such that the radially outer surface  80  of the sleeve  70  is radially aligned with an outermost radial surface  102  of the bearing nut  72 . While a particular arrangement in which the sleeve  70  is mounted relative to the bearing nut  72  has been described, this disclosure extends to other arrangements. 
     During operation of the engine  20 , the bearing nut  72  may rotate such that a center  104  of the bearing nut  72  is spaced-apart from a reference axis, namely the engine central longitudinal axis A, as schematically shown in  FIG. 4 . The reference axis may also correspond to center of the seal  68  in some examples. In certain situations, such as situations resulting from manufacturing tolerances or the effects of assembly, the center  104  of the bearing nut  72  is spaced-apart from engine central longitudinal axis A, about which the shaft  66  rotates, such that the bearing nut  72  follows a path  106  as the shaft  66  and bearing nut  72  rotate during operation of the engine  20 . The path  106  is circular and exhibits a constant radius about the engine central longitudinal axis A, and may be referred to as a path of orbit. 
     In such situations in which the center  104  of the bearing nut  72  follows the path  106 , during operation of the engine  20  there is an inconsistent radial distance between a radially inner surface  108  of the seal  68  and the radially outer surface  80  of the sleeve  70  about the circumference of the engine central longitudinal axis A. In this disclosure, the sleeve  70  is configured to provide consistent relative spacing between the radially inner surface  108  of the seal  68  and the radially outer surface  80  of the sleeve  70  such that the seal assembly  64  exhibits a consistent clearance despite the radial offset, and resulting orbit, of the bearing nut  72 . 
       FIG. 5  is an end view of an example sleeve  70 . As shown, the sleeve  70  includes a variable radial dimension  84  between the radially outer and inner surfaces  80 ,  82  about the circumference of the sleeve  70 . The radially outer and inner surfaces  80 ,  82  are circular. Further, the center  110  of the radially outer surface  80  is spaced-apart from, and non-concentric with, the center  112  of the radially inner surface  82 . The sleeve  70  thus includes a circular axial through-hole, defined within the radially inner surface  82 , which is off-center, relative to the center  110  of the radially outer surface  80  of the sleeve  70 . 
     The variable radial dimension  84  exhibits a maximum radial dimension  114  at a circumferential location  116  and exhibits a minimum radial dimension  118  at circumferential location  120 , which is about  180 ° spaced-apart from the circumferential location  116 . The variable radial dimension  84  gradually increases moving circumferentially from the circumferential location  120  to the circumferential location  116 . 
     While a particular shape of the sleeve  70  has been described, other shapes come within the scope of this disclosure. Further, the sleeve  70  may come in a plurality of sizes and shapes. A worker, for example, may have access to a plurality of sleeves of varying sizes and shapes, and may be able to select an appropriate sleeve depending on the magnitude of orbit displayed by the bearing nut  72 . 
     In an example, when mounting the sleeve  70  relative to the shaft  66  and bearing nut  72 , a worker or machine first monitors the behavior of the bearing nut  72  to determine whether the bearing nut  72  is rotating off-center relative to the reference axis. In other words, a worker or machine determines whether the center  104  is spaced-apart from the engine central longitudinal axis A such that the center  104  follows a path  106  of orbit offset from the engine central longitudinal axis A. If the bearing nut  72  is not rotating off-center, the worker or machine may conclude that it is not appropriate to use a variable radial dimension sleeve relative to the rotating or static components of the seal assembly  64 . 
     If, however, the center  104  is spaced-apart from the engine central longitudinal axis A such that the bearing nut  72  does orbit, the worker or machine may then determine a circumferential location on the bearing nut  72  corresponding to a maximum deviation of the bearing nut  72  from the reference axis. In  FIG. 4 , the circumferential location of the bearing nut  72  corresponding to that maximum deviation is labeled at  122  and follows a straight radially-extending line passing through the center  104  and the engine central longitudinal axis A. In other words, locations on the bearing nut  72  circumferentially spaced from location  122  are closer, following straight lines, to the engine central longitudinal axis A than the location  122 . 
     In order to provide a substantially constant gap G between the radially inner surface  108  of the seal  68  and the radially outer surface  80  of the sleeve  70  about the entire circumference of the seal assembly  64 , the sleeve  70  is mounted relative to the bearing nut  72  such that location  120  is circumferentially aligned with location  122 , as shown in  FIG. 6 . When mounted in this manner, the center  110  of the radially outer surface  80  is concentric with the center of the radially inner surface  108  of the seal  68 . Further, in an example, the center  110  lies on the engine central longitudinal axis A. During operation of the engine  20 , the center  104  follows the path  106 , but the center  110  remains in a fixed, or substantially fixed, location, such as on the engine central longitudinal axis A. Thus, the variable radial dimension of the sleeve  70  compensates for the orbit of the bearing nut  72  to provide a substantially constant gap G about the entire circumference of the seal assembly  64 . 
     The sleeve  70  could be mounted to the bearing nut  72  using additional and/or alternative other techniques. As one example, a worker or machine could monitor for a minimum deviation of the bearing nut  72  from the reference axis, and, in that case, the worker/machine would seek to circumferentially align location  126 , corresponding to the circumferential location of the bearing nut  72  having the minimum deviation from the reference axis, with location  116  of the sleeve  70 . The worker/machine could monitor for both the minimum and maximum bearing nut  72  deviations, and compare the locations of the center  110  and the center of the radially inner surface  108  of the seal  68  as checks to ensure proper mounting the sleeve  70  relative to the reference axis A. Regardless, once the relative orientations of the sleeve  70  and the bearing nut  72  are determined, the sleeve  70  is fixedly mounted relative to the bearing nut  72  so as to hold the relative positions of the components, such as by using the projections  88 , slots  90 , and the retaining ring  96  discussed above or using other techniques. 
     It should be understood that terms such as “axial,” “radial,” and “circumferential” are used above with reference to the normal operational attitude of the engine  20 . Further, these terms have been used herein for purposes of explanation, and should not be considered otherwise limiting. Terms such as “generally,” “substantially,” and “about” are not intended to be boundaryless terms, and should be interpreted consistent with the way one skilled in the art would interpret those terms. 
     Although the different examples have the specific components shown in the illustrations, embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. In addition, the various figures accompanying this disclosure are not necessarily to scale, and some features may be exaggerated or minimized to show certain details of a particular component or arrangement. 
     One of ordinary skill in this art would understand that the above-described embodiments are exemplary and non-limiting. That is, modifications of this disclosure would come within the scope of the claims. Accordingly, the following claims should be studied to determine their true scope and content.