Patent Publication Number: US-2019178381-A1

Title: Face seal arrangement with air load force balance recovery for improved failure mitigation strategies

Description:
FIELD 
     The disclosure relates generally to face seals and face seal arrangements in gas turbine engines. 
     BACKGROUND 
     Face seal failure is typically observed as premature sealing face wear tending to result in a decreased seal closing force. The decrease in seal closing force tends to result in instability of the seal against the face and may tend to increase the wear rate and may result in additional damage to the seal or may tend to result in damage to the gas turbine engine or gas turbine engine hardware surrounding the seal. 
     SUMMARY 
     In various embodiments the present disclosure provides a force balanced face seal comprising a seal housing comprising an annular extrusion, a seal support, wherein the annular extrusion is disposed within the seal support, and a primary seal coupled to the seal housing, wherein the primary seal comprises a sealing face, a base opposite the sealing face and proximate the seal housing. 
     In various embodiments, the primary seal further comprises an inner diameter and an outer diameter, wherein the inner diameter comprises an inner diameter feature geometry over a portion of the inner diameter between the sealing face and the base. In various embodiments, the inner diameter feature geometry comprises one of a ramp or a double step. In various embodiments, the inner diameter feature geometry comprises one of a radial geometry, a multi radial geometry, a convex geometry, or a concave geometry. In various embodiments, the seal housing is driven axially, with respect to an axis of the annular extrusion, away from the seal support in response to a seal closing force. In various embodiments, the seal closing force is a function of a spring force and a pressure force. In various embodiments, the pressure force is a function of the inner diameter feature geometry and a wear condition of the primary seal, and wherein the spring force is a function of the wear condition of the seal, and wherein the wear condition of the seal corresponds to a distance. In various embodiments, the spring force changes at a first rate with respect to the wear condition and the pressure force changes at a second rate with respect to the inner diameter feature geometry and the wear condition, wherein the first rate defines a decrease in the spring force between an initial wear condition and a complete wear condition, wherein the inner diameter feature geometry is such that the second rate defines a decrease in the pressure force between the initial wear condition and the complete wear condition greater than the decrease in the spring force between the initial wear condition and the complete wear condition. In various embodiments, in response to the complete wear condition, the inner diameter feature geometry is worn away. 
     In various embodiments, the present disclosure provides a gas turbine engine comprising a compressor section configured to compress a gas, a combustor section aft of the compressor section and configured to combust the gas, and a force balanced face seal, comprising a seal housing comprising an annular extrusion, a seal support, wherein the annular extrusion is disposed within the seal support, and a primary seal coupled to the seal housing, wherein the primary seal comprises a sealing face and a base opposite the sealing face and proximate the seal housing. 
     In various embodiments, the primary seal further comprises an inner diameter and an outer diameter, wherein the inner diameter comprises an inner diameter feature geometry over a portion of the inner diameter between the sealing face and the base. In various embodiments, the inner diameter feature geometry comprises one of a ramp or a double step. In various embodiments, the inner diameter feature geometry comprises one of a radial geometry, a multi radial geometry, a convex geometry, or a concave geometry. In various embodiments, the seal housing is driven axially, with respect to an axis of the annular extrusion, away from the seal support in response to a seal closing force. In various embodiments, the primary seal divides a high pressure compartment and a low pressure compartment, wherein the seal closing force is a function of a spring force and a pressure force, wherein the pressure force acts against the spring force in response to a pressure difference between the high pressure compartment and the low pressure compartment. In various embodiments, the pressure force is a function of the inner diameter feature geometry and a wear condition of the primary seal, and wherein the spring force is a function of the wear condition of the seal, and wherein the wear condition of the seal corresponds to a distance. In various embodiments, the spring force changes at a first rate with respect to the wear condition and the pressure force changes at a second rate with respect to the inner diameter feature geometry and the wear condition, wherein the first rate defines a decrease in the spring force between an initial wear condition and a complete wear condition, wherein the inner diameter feature geometry is such that the second rate defines a decrease in the pressure force between the initial wear condition and the complete wear condition greater than the decrease in the spring force between the initial wear condition and the complete wear condition. In various embodiments, in response to the complete wear condition, the inner diameter feature geometry is worn away. In various embodiments, the seal housing further comprises an alignment tab having a forward face and the seal support comprises an alignment pin having a flange, wherein the forward face of the alignment tab contacts the flange in response to the compete wear condition 
     In various embodiments, the present disclosure provides method of manufacturing a force balanced face seal, the method comprising determining a spring force component and a pressure force component of a seal closing force of a seal housing having a primary seal comprising an inner diameter, wherein the pressure force component acts against the spring force component, calculating an inner diameter geometry of the inner diameter of the primary seal such that a decrease in the pressure force component between an initial wear condition and a complete wear condition is greater than a decrease in spring force component between the initial wear condition and the complete wear condition, forming the inner diameter geometry over a portion of the inner diameter of the primary seal between a sealing face and a base of the primary seal, coupling the primary seal to the seal housing having the annular extrusion and inserting the annular extrusion into a seal support comprising an alignment pin and a spring and coupling the seal support about a shaft of a gas turbine engine and contacting the sealing face with a seal seat of the shaft. 
     The forgoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated herein otherwise. These features and elements as well as the operation of the disclosed embodiments will become more apparent in light of the following description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present disclosures, however, may best be obtained by referring to the detailed description and claims when considered in connection with the drawing figures, wherein like numerals denote like elements. 
         FIG. 1  illustrates an exemplary gas turbine engine, in accordance with various embodiments; 
         FIG. 2A  illustrates a force balanced face seal, in accordance with various embodiments; 
         FIG. 2B  illustrates a force balanced face seal, in accordance with various embodiments; 
         FIG. 3  illustrates a cross section of a force balanced face seal, in accordance with various embodiments; 
         FIG. 4  illustrates a cross section of a force balanced face seal, in accordance with various embodiments; 
         FIG. 5  illustrates a cross section of a force balanced face seal in various wear conditions, in accordance with various embodiments; 
         FIG. 6  illustrates a graphical representation of a change in seal closing force of a force balanced face seal; and 
         FIG. 7  illustrates a method of manufacturing a force balanced face seal, in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration and their best mode. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosures, it should be understood that other embodiments may be realized and that logical, chemical, and mechanical changes may be made without departing from the spirit and scope of the disclosures. Thus, the detailed description herein is presented for purposes of illustration only and not of limitation. For example, the steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented. Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component or step may include a singular embodiment or step. Also, any reference to attached, fixed, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option. Additionally, any reference to without contact (or similar phrases) may also include reduced contact or minimal contact. 
     In various embodiments and with reference to  FIG. 1 , a gas turbine engine  20  is provided. Gas turbine engine  20  may be a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . Alternative engines may include, for example, an augmenter section among other systems or features. In operation, fan section  22  can drive air along a bypass flow-path B while compressor section  24  can drive air for compression and communication into combustor section  26  then expansion through turbine section  28 . Although depicted as a turbofan gas turbine engine  20  herein, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines including turbojet engines, a low-bypass turbofans, a high bypass turbofans, or any other gas turbine known to those skilled in the art including single spool and three-spool architectures. 
     Gas turbine engine  20  may generally comprise a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A-A′ relative to an engine static structure  36  via one or more bearing systems  38  (shown as bearing system  38 - 1  and bearing system  38 - 2  in  FIG. 2 ). It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided, including for example, bearing system  38 , bearing system  38 - 1 , and bearing system  38 - 2 . 
     Low speed spool  30  may generally comprise an inner shaft  40  that interconnects a fan  42 , a low pressure (or first) compressor section  44  (also referred to a low pressure compressor) and a low pressure (or first) turbine section  46 . Inner shaft  40  may be connected to fan  42  through a geared architecture  48  that can drive fan  42  at a lower speed than low speed spool  30 . Geared architecture  48  may comprise a gear assembly  60  enclosed within a gear housing  62 . Gear assembly  60  couples inner shaft  40  to a rotating fan structure. High speed spool  32  may comprise an outer shaft  50  that interconnects a high pressure compressor (“HPC”)  52  (e.g., a second compressor section) and high pressure (or second) turbine section  54 . A combustor  56  may be located between HPC  52  and high pressure turbine  54 . A mid-turbine frame  57  of engine static structure  36  may be located generally between high pressure turbine  54  and low pressure turbine  46 . Mid-turbine frame  57  may support one or more bearing systems  38  in turbine section  28 . Inner shaft  40  and outer shaft  50  may be concentric and rotate via bearing systems  38  about the engine central longitudinal axis A-A′, which is collinear with their longitudinal axes. As used herein, a “high pressure” compressor or turbine experiences a higher pressure than a corresponding “low pressure” compressor or turbine. 
     The core airflow C may be compressed by low pressure compressor  44  then HPC  52 , mixed and burned with fuel in combustor  56 , then expanded over high pressure turbine  54  and low pressure turbine  46 . Mid-turbine frame  57  includes airfoils  59  which are in the core airflow path. Low pressure turbine  46 , and high pressure turbine  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. 
     In various embodiments, HPC  52  may comprise alternating rows of rotating rotors and stationary stators. Stators may have a cantilevered configuration or a shrouded configuration. More specifically, a stator may comprise a stator vane, a casing support and a hub support. In this regard, a stator vane may be supported along an outer diameter by a casing support and along an inner diameter by a hub support. In contrast, a cantilevered stator may comprise a stator vane that is only retained and/or supported at the casing (e.g., along an outer diameter). 
     In various embodiments, rotors may be configured to compress and spin a fluid flow. Stators may be configured to receive and straighten the fluid flow. In operation, the fluid flow discharged from the trailing edge of stators may be straightened (e.g., the flow may be directed in a substantially parallel path to the centerline of the engine and/or HPC) to increase and/or improve the efficiency of the engine and, more specifically, to achieve maximum and/or near maximum compression and efficiency when the straightened air is compressed and spun by rotor  64 . 
     According to various embodiments and with additional reference to  FIGS. 2A and 2B , a gas turbine engine such as gas turbine engine  20  may comprise a force balanced face seal  200 . Force balanced face seal  200  comprises a primary seal  202  which may be press fit into seal housing  204 . Seal housing  204  has an annular extrusion  206  disposed within seal support  208 . In various embodiments, seal support  208  may comprise alignment pins  210  extending axially outward from forward face  230  of seal support  208  and spring pockets  228  cut axially inward of forward face  230 . In various embodiments, seal housing  204  may comprise spring tabs  224  coupled to coil springs  226  and alignment tabs  212  having alignment channels  214 . In various embodiments, sleeves  216  may be disposed over alignment pins  210  and comprise a flat portion  232  configured to interface with a corresponding flat portion of inner surface  234  of alignment channels  214 . 
     In various embodiments, seal housing  204  is aligned circumferentially with seal support  208  when alignment pins  210  are disposed within alignment channels  241  and flat portion  232  is in contact with inner surface  234 . In response, annular extrusion  206  may be slid axially inward toward forward face  230  and coil springs  226  may be disposed within spring pockets  228  tending thereby to compress coil springs  226 . In various embodiments, flange  218  is fitted against sleeve  216  over a distal end of alignment pin  210 . In various embodiments, flange  218  is coupled to alignment pin  210  by cotter pin  220  and an interference between flange  218  and forward face  222  of alignment tab  212  tends to inhibit seal housing  204  and annular extrusion  206  from backing out seal support  208 . 
     In various embodiments and with additional reference to  FIG. 3 , force balanced face seal  200  is shown in cross section as installed in a gas turbine engine such as gas turbine engine  20 . Force balanced face seal  200  is coupled to case  326  at seal support  208 . A shaft  320  comprising a seal seat  312  is disposed within the annulus of annular extrusion  206  of seal housing  204 . In various embodiments, primary seal  202  comprises a seal material  300  having an inner diameter  304 , an outer diameter  306 , a sealing face  308 , and a base  310 . In various embodiments, a ramp  302  may be cut over a portion of inner diameter  304  inward of inner diameter  304  toward outer diameter  306 . In various embodiments a step  328  may be cut inward from outer diameter  306  toward inner diameter  304  and sealing face  308  may be defined between step  328  and ramp  302 . In various embodiments, seal housing  204  may comprise a secondary seal  316  at a distal end of annular extrusion  206  opposite primary seal  202 . In various embodiments, secondary seal  316  may seal against seal support  208 . 
     In various embodiments, coil springs  226  may impart a spring force F s  upon seal housing  204  driving seal housing axially away from seal support  208  and relatively toward seal seat  312  tending thereby to drive sealing face  308  of primary seal  202  into contact with seating face  314  of seal seat  312 . In various embodiments, primary seal  202  may divide a high pressure compartment  322  and a low pressure compartment  324  and, in response to a difference in pressure between the high pressure compartment  322  and the low pressure compartment  324 , a pressure force F p  may tend to act at ramp  302  and thereby tend to reduce spring force F s . In various embodiments, F p  may be a function of an area of ramp  302 . In various embodiments, a seal closing force F c  may be a function of the spring force F s  and the pressure force F p . In other words, F p  and F s  may be components of the seal closing force F c  upon seal housing  204  tending to drive seal housing axially away from seal support  208  and relatively toward seal seat  312  tending thereby to drive sealing face  308  of primary seal  202  into contact with seating face  314  of seal seat  312 . 
     In various embodiments, when primary seal  202  is initially contacted at sealing face  308  with seal seat  312  at seating face  314  forward face  222  of alignment tab  212  may be separated from flange  218  by a distance D corresponding to a wear condition of primary seal  202 . In various embodiments, in response to a wear condition of primary seal  202 , seal material  300  may be abraded or lost at sealing face  308  tending to allow coil springs  226  to expand and drive seal housing  204  toward seal seat  312 . In various embodiments, and with brief reference to  FIG. 5 , in response to a wear condition of primary seal  202 , distance D may correspond to an initial distance (D i ) and decrease through intermediate distances (D 1 , D 2  . . . D n ) as primary seal progressively wears from an initial wear condition (W i ) through various wear conditions (W 1 , W 2  . . . W n ) toward a complete wear condition (W c ). In various embodiments, in response to a complete wear condition of primary seal  202  alignment tab  212  may contact flange  218  at forward face  222  tending thereby to inhibit contact between sealing face  308  and seating face  314 . In various embodiments, the spring force F s  may decrease linearly with respect to a decrease in D. In various embodiments, the area of ramp  302  may tend to decrease linearly with respect to the decrease in D tending thereby to decrease the pressure force F p  and, in response, an area of sealing face  308  may increase. In this regard, the seal closing force F c  may be balanced with respect to the spring force F s  and the pressure force F p  in response to a configuration of ramp  302 . In various embodiments, F p  may tend to resist F s  and F c  may be balanced such that the decrease in F s  is less than the decrease in F p . Stated another way, the seal closing force F c  may be balanced such that F p  decreases at a greater rate with respect to D than does F s . 
     In various embodiments and with additional reference to  FIG. 4 , force balanced face seal  200  is shown in cross section as installed in a gas turbine engine such as gas turbine engine  20  comprising a primary seal  400 . In various embodiments, primary seal  400  comprises a seal material  402  having an inner diameter  404 , an outer diameter  406 , a sealing face  408 , and a base  410 . In various embodiments, double step  412  may be cut into seal material  402  inward from inner diameter  404  toward outer diameter  406  and a step  414  may be cut into seal material  402  inward from outer diameter  406  toward inner diameter  404 . In various embodiments, sealing face  408  may be defined between step  414  and double step  412 . In various embodiments, F p  may be a function of an area of double step  412 . In various embodiments, the area of double step  412  may tend to decrease as step function with respect to the decrease in D tending thereby to decrease the pressure force F p  and, in response, an area of sealing face  308  may increase. In this regard, the seal closing force F c  may be balanced with respect to the spring force F s  and the pressure force F p  in response to a configuration of double step  412 . In various embodiments, F p  may tend to resist F s  and F c  may be balanced such that the decrease in F s  is less than the decrease in F p . Stated another way, the seal closing force F c  may be balanced such that, on average, F p  decreases at a greater rate with respect to D than does F s . 
     In various embodiments, a primary seal such as, for example, primary seal  202  or primary seal  400 , may comprise inner diameter features (such as, for example, double step  412  or ramp  302 ) at an internal diameter, such as inner diameter  304 , between a sealing face, such as sealing face  308 , and a base, such as base  318 . In various embodiments, inner diameter features may be defined by an inner diameter feature geometry comprising at least one of a radial, or a multi radial, or a concave, or a convex, geometry. In various embodiments, the pressure force F p  may be a function of the inner diameter feature geometry. In various embodiments, the internal diameter feature may change with respect to D and, in this regard, the seal closing force Fc may be balanced with respect to the spring force F s  and the pressure force F p  as the primary seal progressively wears through various wear conditions toward a complete wear condition. In various embodiments, F p  may tend to resist Fs and Fc may be balanced such that the decrease in F s  is less than the decrease in F p . Stated another way, the seal closing force F c  may be balanced such that, on average, F p  decreases at a greater rate with respect to D than does Fs. In various embodiments, a seal material such as, for example, seal material  300  or seal material  402 , may comprise one of a carbon, a ceramic, a composite, a rubber, or a synthetic rubber. 
     In various embodiments and with additional reference to  FIG. 5 , primary seal  202  and primary seal  400  are illustrated in cross section in various wear conditions. In various embodiments, primary seal  202  comprising ramp  302  is illustrated in an initial wear condition Wi and in contact with seal seat  312 . A distance D i , corresponding to the initial wear condition Wi, is defined between flange  215  and forward face  222  of alignment tab  212 . In various embodiments and in response to an operational use of primary seal  202 , primary seal  202  may progress through intermediate wear conditions W 1  and W 2 . In various embodiments, wear condition W 1  corresponds to a decreased distance D 1  between flange  215  and forward face  222  of alignment tab  212  and a reduced ramp area  302 W 1 , where the reduced ramp area  302 W 1  is less than the ramp area  302 W 1  and the distance D 1  is less than D i . In various embodiments, wear condition W 2  corresponds to a decreased distance D 2  between flange  215  and forward face  222  of alignment tab  212  and a reduced ramp area  302 W 2 , where the ramp area  302 W 2  is less than the ramp area  302 W 1  and the distance D 2  is less than the distance D 1 . In various embodiments, primary seal  202  may progress through any number of intermediate wear conditions (W n ) prior to reaching a completed wear condition W c  where ramp  302  of primary seal  202  is, in response, worn away and flange  215  is thereby in contact with forward face  222  of alignment tab  212  generating an interference  500  tending to inhibit contact between primary seal  202  and seal seat  312 . 
     In various embodiments, and in like manner to primary seal  202 , primary seal  400  is illustrated in an initial wear condition Wi and in contact with seal seat  312 . The distance Di, corresponding to the initial wear condition Wi, is defined between flange  215  and forward face  222  of alignment tab  212 . In a like manner to primary seal  202  and, in response to an operation use of primary seal  400 , primary seal  400  may progress through intermediate wear conditions W 1  and W 2 , as described above, corresponding to reduced distances D 1  and D 2  where D i  is greater than D 1  and where D 1  is greater than D 2 , and corresponding to reduced double step areas  412 W 1  and  412 W 2  where  412 W 1  is greater than  412 W 2 . In various embodiments, primary seal  400  may progress through any number of intermediate wear conditions (W n ) prior to reaching the completed wear condition W c  where double step  412  of primary seal  400  is, in response, worn away and flange  215  is thereby in contact with forward face  222  of alignment tab  212  generating interference  500  tending to inhibit contact between primary seal  400  and seal seat  312 . 
     In various embodiments and with additional reference to  FIG. 6 , a graphical representation of a change in seal closing force of a force balanced face seal is shown. Plot  600  of distance D with respect to a change in seal closing force F c  is illustrated for a force balanced face seal  200  having been balanced such that the decrease in Fs is less than the decrease in F p . Point  602  corresponds to the initial wear condition W i  and point  604  corresponds to the completed wear condition and intermediate points correspond to intermediate wear conditions. Line  606  shows the loss in spring force F s  as coil springs  226  expand. Line  608  shows the change seal closing force F c  attributable to the change in F p  for primary seal  202  and line  610  shows the change seal closing force F c  attributable to F p  for primary seal  400 . 
     In various embodiments and with reference now to  FIG. 7 , a method  700  of manufacturing a force balanced face seal may comprise determining a spring force component and a pressure force component ( 702 ) of a seal closing force of a seal housing having a primary seal comprising an inner diameter, wherein the pressure force component acts against the spring force component. In various embodiments, the method may further comprise calculating an inner diameter geometry of the inner diameter of the primary seal ( 704 ) such that a decrease in the pressure force component between an initial wear condition and a complete wear condition is greater than a decrease in spring force component between the initial wear condition and the complete wear condition. In various embodiments, the method may further comprise forming the inner diameter geometry about the inner diameter of the primary seal between a sealing face and a base of the primary seal ( 706 ). In various embodiments, the method may further comprise coupling the primary seal to the seal housing having the annular extrusion and inserting the annular extrusion into a seal support comprising an alignment pin and a spring ( 708 ). In various embodiments, the method may further comprise coupling the seal support about a shaft of a gas turbine engine and contacting the sealing face with a seal seat of the shaft ( 710 ). 
     Benefits, other advantages, and solutions to problems have been described herein with regard to specific embodiments. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical system. However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the disclosures. 
     The scope of the disclosures is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” Moreover, where a phrase similar to “at least one of A, B, or C” is used in the claims, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, B and C may be present in a single embodiment; for example, A and B, A and C, B and C, or A and B and C. Different cross-hatching is used throughout the figures to denote different parts but not necessarily to denote the same or different materials. 
     Systems, methods and apparatus are provided herein. In the detailed description herein, references to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiment 
     Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element is intended to invoke 35 U.S.C. 112(f) unless the element is expressly recited using the phrase “means for.” As used herein, the terms “comprises”, “comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.