Patent Publication Number: US-2020284166-A1

Title: Cover secured by captive fastener

Description:
FIELD 
     The present disclosure relates generally to gas turbine engines and, more particularly, to cover plates secured by captive fasteners, allowing for inspection, repair or replacement of components within the gas turbine engines with reduced risk of foreign object damage. 
     BACKGROUND 
     Gas turbine engines typically include a fan section, a compressor section, a combustor section and a turbine section. During operation, air is pressurized in the compressor section and mixed with fuel and burned in the combustor section to generate hot combustion gases. The hot combustion gases are then communicated through the turbine section, where energy is extracted from the hot combustion gases to power the compressor section, the fan section and various other loads occurring within or proximate a gas turbine engine. 
     A core engine of a gas turbine engine typically includes the compressor, the combustor and the turbine, each of which is surrounded by a core engine casing. During the life cycles of such components, inspection, repair or replacement is often required. Various techniques for accomplishing such inspection, repair or replacement require removal or disassembly of the core engine casing, sections thereof or cover plates configured to enclose critical components of the engine. Such disassembly, even when limited to removal of cover plates, may result in inadvertent foreign object debris being introduced into the engine prior to reassembly. The foreign object debris may result in damage to the engine upon being placed back in operation. 
     SUMMARY 
     A cover assembly is disclosed. In various embodiments, the cover assembly includes a cover configured to close a passageway through a casing, the cover having a first keyhole slot; and a first captive fastener configured to extend through the first keyhole slot and into the casing. 
     In various embodiments, the casing defines a casing contour and the cover defines a cover contour having the same shape as the casing contour. In various embodiments, the cover is configured to slide along the casing in a longitudinal direction. In various embodiments, the first keyhole slot is disposed on a first lateral side of the cover. In various embodiments, a second keyhole slot is disposed on a second lateral side of the cover. In various embodiments, the first keyhole slot and the second keyhole slot are aligned in the longitudinal direction. 
     In various embodiments, the first captive fastener includes a threaded body configured to extend through the casing. In various embodiments, the first captive fastener includes a first blocking member disposed on a first distal end of the first captive fastener. In various embodiments, a second captive fastener is configured to extend through the second keyhole slot and into the casing. 
     In various embodiments, the first captive fastener includes a first blocking member configured to prevent the first captive fastener from being removed from the casing. In various embodiments, a second captive fastener is configured to extend through a second keyhole slot and into the casing, the second captive fastener including a second blocking member configured to prevent the second captive fastener from being removed from the casing. 
     In various embodiments, the first keyhole slot and the second keyhole slot are aligned in a longitudinal direction and disposed, respectively, on a first lateral side and a second lateral side of the cover with respect to the longitudinal direction. In various embodiments, the first blocking member comprises at least one of a deformed portion, a weld and a pin member disposed on a first distal end of the first captive fastener. 
     A gas turbine engine is disclosed. In various embodiments, the gas turbine engine includes a casing; a cover configured to close a passageway through the casing, the cover having a first keyhole slot and a second keyhole slot, both the first keyhole slot and the second keyhole slot aligned along a longitudinal direction; a first captive fastener configured to extend through the first keyhole slot and into the casing; and a second captive fastener configured to extend through the second keyhole slot and into the casing. 
     In various embodiments, the first keyhole slot is disposed on a first lateral side of the cover and the second keyhole slot is disposed on a second lateral side of the cover. In various embodiments, the first captive fastener includes a first blocking member configured to prevent the first captive fastener from being removed from the casing and the second captive fastener includes a second blocking member configured to prevent the second captive fastener from being removed from the casing. In various embodiments, the first blocking member comprises at least one of a first deformed portion, a first weld and a first pin member disposed on a first distal end of the first captive fastener and the second blocking member comprises at least one of a second deformed portion, a second weld and a second pin member disposed on a second distal end of the second captive fastener. 
     A method for accessing a component housed within a casing is disclosed. In various embodiments, the method includes the steps of releasing a first captive fastener extending through a first keyhole slot of a cover and into the casing; releasing a second captive fastener extending through a second keyhole slot of the cover and into the casing; sliding the cover in a longitudinal direction with respect to the first keyhole slot and the second keyhole slot; and removing the cover from the casing to expose the component. 
     In various embodiments, the step of releasing the first captive fastener includes unthreading the first captive fastener a first distance from the casing and releasing the second captive fastener includes unthreading the second captive fastener a second distance from the casing. In various embodiments, the first captive fastener includes a first blocking member configured to prevent the first captive fastener from being removed from the casing and the second captive fastener includes a second blocking member configured to prevent the second captive fastener from being removed from the casing. 
    
    
     
       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 disclosure, however, may best be obtained by referring to the following detailed description and claims in connection with the following drawings. While the drawings illustrate various embodiments employing the principles described herein, the drawings do not limit the scope of the claims. 
         FIG. 1  is a schematic view of a gas turbine engine, in accordance with various embodiments; 
         FIG. 2  is a schematic view of a casing of a gas turbine engine having a cover assembly, including a cover secured to a casing with captive fasteners, in accordance with various embodiments; 
         FIGS. 3A, 3B and 3C  are perspective views of a cover assembly, including a cover secured to a casing with captive fasteners, showing steps of disassembly, in accordance with various embodiments; 
         FIGS. 4A, 4B and 4C  are side views of captive fasteners used with a cover assembly for an engine casing, in accordance with various embodiments; and 
         FIG. 5  illustrates a method for accessing a component housed within a casing, in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description of various embodiments herein makes reference to the accompanying drawings, which show various embodiments by way of illustration. While these various embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, it should be understood that other embodiments may be realized and that changes may be made without departing from the scope of the disclosure. Thus, the detailed description herein is presented for purposes of illustration only and not of limitation. 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 or any other possible attachment option. Additionally, any reference to without contact (or similar phrases) may also include reduced contact or minimal contact. It should also be understood that unless specifically stated otherwise, references to “a,” “an” or “the” may include one or more than one and that reference to an item in the singular may also include the item in the plural. Further, all ranges may include upper and lower values and all ranges and ratio limits disclosed herein may be combined. 
     Referring now to the drawings,  FIG. 1  schematically illustrates a gas turbine engine  20 . The gas turbine 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 , while the compressor section  24  drives air along a core or primary flow path C for compression and communication into the combustor section  26  and 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. 
     The gas turbine 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 . The low speed spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a low pressure compressor  44  and a low pressure turbine  46 . The inner shaft  40  is connected to the fan  42  through a speed change mechanism, which in this gas turbine engine  20  is illustrated as a fan drive gear system  48  configured to drive the 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 high pressure compressor  52  and a high pressure turbine  54 . A combustor  56  is arranged in the gas turbine engine  20  between the high pressure compressor  52  and the high pressure turbine  54 . A mid-turbine frame  57  of the engine static structure  36  is arranged generally between the high pressure turbine  54  and the low pressure turbine  46  and may include airfoils  59  in the core flow path C for guiding the flow into the low pressure turbine  46 . The mid-turbine frame  57  further supports the several bearing systems  38  in the turbine section  28 . The inner shaft  40  and the outer shaft  50  are concentric and rotate via the several bearing systems  38  about the engine central longitudinal axis A, which is collinear with longitudinal axes of the inner shaft  40  and the outer shaft  50 . 
     The air in the core flow path C is compressed by the low pressure compressor  44  and then the high pressure compressor  52 , mixed and burned with fuel in the combustor  56 , and then expanded over the high pressure turbine  54  and low pressure turbine  46 . The low pressure turbine  46  and the high pressure turbine  54  rotationally drive the respective low speed spool  30  and the high speed spool  32  in response to the expansion. It will be appreciated that each of the positions of the fan section  22 , the compressor section  24 , the combustor section  26 , the turbine section  28 , and the fan drive gear system  48  may be varied. For example, the fan drive gear system  48  may be located aft of the combustor section  26  or even aft of the turbine section  28 , and the fan section  22  may be positioned forward or aft of the location of the fan drive gear system  48 . 
     In various embodiments, a cover assembly  100  is removably secured to a casing  102  that surrounds the various components within the core flow path C, including, for example, the low pressure compressor  44 , the high pressure compressor  52 , the combustor  56 , the high pressure turbine  54  and the low pressure turbine  46 . In various embodiments, the cover assembly includes a cover  104  and one or more captive fasteners  106  configured to extend through the cover  104  and into the casing  102 . The cover assembly  100  permits access to various of the components housed within the casing  102 . For example, removal of the cover  104  provides access to a passageway  108  that extends through the casing  102 . Access to the passageway  108  then provides access to at least one of the various components housed within the casing  102 , such as, for example, a turbine rotor or stator blade disposed on one of the high pressure turbine  54  and the low pressure turbine  46  or a compressor rotor or stator blade disposed on one of the low pressure compressor  44  and the high pressure compressor  52 . Access to the various components enables inspection, repair or replacement of the components without disassembly of the casing  102 . 
     Referring now to  FIG. 2 , a cover assembly  200 , removably secured to a casing  202  that encloses a core flow path C, is illustrated. In various embodiments, the cover assembly  200  includes a cover  204  configured to close a passageway  208  and one or more captive fasteners  206 . The cover  204  may define a cover contour (e.g., a curved surface) configured to mate with a casing contour (e.g., a cylindrical surface defined by the casing  202 ). Mating of the cover contour with the casing contour enables the cover  204  to close or to seal the passageway  208 , thus preventing gases flowing within the core flow path C defined by the casing  202 , such as, for example, the core flow path C described above with reference to  FIG. 1 , from leaking or otherwise escaping the core flow path C during operation. 
     In various embodiments, the one or more captive fasteners  206  may include, for example, a first captive fastener  220  configured to extend through a first keyhole slot  222  and into the casing  202  and a second captive fastener  224  configured to extend through a second keyhole slot  226  and into the casing  202 . In various embodiments, the first keyhole slot  222  extends through the cover  204  and includes a first engagement portion  228  and a first release portion  230 . The first engagement portion  228  is configured to engage with a first head portion  232  of the first captive fastener  220  when the first captive fastener  220  is secured against the casing  202  (e.g., by tightly threading the first captive fastener  220  to the casing  202 ). Conversely, the first release portion  230  is configured to disengage with the first head portion  232  of the first captive fastener  220  when the first captive fastener  220  is unsecured against the casing  202  (e.g., by loosely threading the first captive fastener  220  to the casing  202 ). 
     In various embodiments, the first engagement portion  228  defines a characteristic dimension (e.g., a first engagement portion width or diameter  234 ) that is less than a characteristic dimension of the first head portion  232  (e.g., a first head portion diameter  236 ), while the first release portion  230  defines a characteristic dimension (e.g., a first release portion width or diameter  238 ) that is greater than the characteristic dimension of the first head portion  232 . The characteristic dimension of the first engagement portion  228  being less than the characteristic dimension of the first head portion  232  enables the first captive fastener  220  to secure the cover  204  to the casing  202  when the first captive fastener  220  is secured against the casing  202 . Conversely, the characteristic dimension of the first release portion  230  being less than the characteristic dimension of the first head portion  232  enables the cover  204  to be removed from the first captive fastener  220 , as well as from the casing  202 , when the first captive fastener  220  is unsecured against the casing  202 . 
     In various embodiments, the second keyhole slot  226  extends through the cover  204  and includes a second engagement portion  240  and a second release portion  242 . The second engagement portion  240  is configured to engage with a second head portion  244  of the second captive fastener  224  when the second captive fastener  224  is secured against the casing  202  (e.g., by tightly threading the second captive fastener  224  to the casing  202 ). Conversely, the second release portion  242  is configured to disengage with the second head portion  244  of the second captive fastener  224  when the second captive fastener  224  is unsecured against the casing  202  (e.g., by loosely threading the second captive fastener  224  to the casing  202 ). Similar to the description regarding the first keyhole slot  222 , the second engagement portion  240  defines a characteristic dimension (e.g., a second engagement portion width or diameter) that is less than a characteristic dimension of the second head portion  244  (e.g., a second head portion diameter), while the second release portion  242  defines a characteristic dimension (e.g., a second release portion width or diameter) that is greater than the characteristic dimension of the second head portion  244 . The characteristic dimension of the second engagement portion  240  being less than the characteristic dimension of the second head portion  244  enables the second captive fastener  224  to secure the cover  204  to the casing  202  when the second captive fastener  224  is tightly against the casing  202 . Conversely, the characteristic dimension of the second release portion  242  being less than the characteristic dimension of the second head portion  244  enables the cover  204  to be removed from the second captive fastener  224 , as well as being removed from the casing  202 , when the second captive fastener  224  is unsecured against the casing  202 . 
     Referring now to  FIGS. 3A, 3B and 3C , various views of a cover assembly  300 , showing various steps of removing a cover  304  of the cover assembly  300  from a casing  302  to provide access to a passageway  308 , are illustrated. In various embodiments, the cover assembly  300  includes the cover  304  and one or more captive fasteners  306 . Similar to the cover assembly  200  described above with reference to  FIG. 2 , the one or more captive fasteners  306  may include, for example, a first captive fastener  320  configured to extend through a first keyhole slot  322  and into the casing  302  and a second captive fastener  324  configured to extend through a second keyhole slot  326  and into the casing  302 . Various operational and dimensional characteristics of the first keyhole slot  322  and the second keyhole slot  326 , with respect to the first captive fastener  320  and the second captive fastener  324 , respectively, are similar to those described above with reference to  FIG. 2  and, therefore, are not repeated here. 
     Referring now to  FIG. 3A , the cover  304  is shown secured to the casing  302 . More specifically, the first captive fastener  320  is secured against the casing  302  (e.g., by tightly threading the first captive fastener  320  to the casing  302 ) and thereby locks a first engagement portion  328  to the casing  302 . Likewise, the second captive fastener  324  is secured to the casing  302  (e.g., by tightly threading the second captive fastener  324  to the casing  302 ) and thereby locks a second engagement portion  340  to the casing  302 . In various embodiments, the first captive fastener  320  and the first keyhole slot  322  are disposed on a first lateral side  350  of the casing  302  and the cover  304 , respectively, with respect to a longitudinal direction L. Similarly, in various embodiments, the second captive fastener  324  and the second keyhole slot  326  are disposed on a second lateral side  352  of the casing  302  and the cover  304 , respectively, with respect to the longitudinal direction L. In various embodiments, the first keyhole slot  322  defines a first longitudinal orientation L 1  and the second keyhole slot  326  defines a second longitudinal orientation L 2 , one or both of which are aligned with (e.g., parallel to) the longitudinal direction L. 
     Referring now to  FIGS. 3B and 3C , in various embodiments, when the first captive fastener  320  and the second captive fastener  324  are unsecured against the casing  302  (e.g., by loosely threading the first captive fastener  320  and the second captive fastener  324  to the casing  302 ) the cover  304  is configured to slide along the casing in the longitudinal direction L. Referring to  FIG. 3B , for example, when the first captive fastener  320  and the second captive fastener  324  are unsecured against the casing  302 , the cover  304  is enabled to slide in the longitudinal direction L such that a first release portion  330  of the first keyhole slot  322  is positioned proximate the first captive fastener  320  and a second release portion  342  of the second keyhole slot  326  is positioned proximate the second captive fastener  324 . So positioned, as illustrated in  FIG. 3C , the cover  304  is enabled for removal from the casing  302 , thereby exposing the passageway  308  for inspection, repair or replacement of components housed by the casing  302 . In various embodiments, the cover  304  is secured against the casing  302  by reversing the order of the steps described above and illustrated in  FIGS. 3A-3C . 
     Referring now to  FIGS. 4A, 4B and 4C , various captive fasteners, similar to the one or more captive fasteners  206  described above with reference to  FIG. 2  and to the one or more captive fasteners  306  described above with reference to  FIGS. 3A-3C  are illustrated, in accordance with various embodiments. Referring to  FIG. 1A , for example, a captive fastener  460  is illustrated as securing a cover  404  against a casing  402 . In various embodiments, the captive fastener  460  includes a head portion  462  configured for engaging an engagement portion  464  of a keyhole slot  466 . The captive fastener  460  includes a threaded body  468  configured for threadedly engaging a threaded aperture  470  that extends through the casing  402 . In various embodiments, the threaded body  468  and the threaded aperture  470  enable the captive fastener  460  to be secured against the casing  402  (e.g., by tightly threading the captive fastener  460  to the casing  402 ), thereby securing the cover  404  to the casing  402 , similar, for example, to the cover  304  being secured to the casing  302 , as illustrated in  FIG. 3A . The threaded body  468  and the threaded aperture  470  also enable the captive fastener  460  to be unsecured against the casing  402  (e.g., by loosely threading the captive fastener  460  to the casing  402 ), thereby enabling the cover  404  to slide with respect to the casing  402 , similar, for example, to the cover  304  being unsecured and slid with respect to the casing  302 , and then removed from the casing  302 , as illustrated in  FIGS. 3B and 3C . 
     In various embodiments, the captive fastener  460  includes a blocking member  472  disposed at a distal end  474  (e.g., at a first distal end or a second distal end) of the threaded body  468 . The blocking member prevents the captive fastener  460  from being removed from the casing  402  during removal of the cover  404  from the casing  402 . In various embodiments, as illustrated in  FIG. 4A , the blocking member  472  may comprise a deformed portion  476  (e.g., a first deformed portion or a second deformed portion) disposed at the distal end  474  of the captive fastener  460 . The deformed portion  476  may be provided at the distal end  474  of the captive fastener  460  by mechanically deforming the distal end  474  following initial placement of the captive fastener  460  through the casing  402 . The deformation may be regular, leading to a generally axisymmetric deformation about an axis of the captive fastener  460  or may be irregular, such as, for example, deformation of the threaded body  468  on a single side of the captive fastener  460 . In all cases, the deformed portion  476  is configured to prevent the captive fastener  460  from being withdrawn from the casing  402  following its initial placement therein. In various embodiments, as illustrated in  FIGS. 4B and 4C , the blocking member  472  may take any of a variety of other forms, such as, for example, a pin member  475  (e.g., a first pin member or a second pin member) extending through the threaded body  468  (see  FIG. 4B ) or a weld  480  (e.g., a first weld or a second weld) positioned on the threaded body  468  (see  FIG. 4C ). In general, the disclosure contemplates the captive fastener  460  and the blocking member  472  associated with the captive fastener  460  assuming other forms, with or without the threaded body  468 , for example, so long as the captive fastener  460  is rendered incapable of being withdrawn from the casing  402  during the process of removal of the cover  404  from the casing  402 . 
     Referring now to  FIG. 5 , a method  500  for accessing a component housed within a casing is described with reference to the following steps. In various embodiments, a first step  502  includes releasing a first captive fastener extending through a first keyhole slot of a cover and into the casing. Similarly, a second step  504  includes releasing a second captive fastener extending through a second keyhole slot of the cover and into the casing. A third step  506  includes sliding the cover in a longitudinal direction with respect to the first keyhole slot and the second keyhole slot. A fourth step  508  includes removing the cover from the casing to expose the component. 
     In various embodiments, the step of releasing the first captive fastener includes unthreading the first captive fastener a first distance from the casing and releasing the second captive fastener includes unthreading the second captive fastener a second distance from the casing, wherein the first distance and the second distance are any distance sufficient to enable the cover to become unsecured to the casing and to readily slide away from the first captive fastener and the second captive fastener. In various embodiments, the first captive fastener may include a first blocking member configured to prevent the first captive fastener from being removed from the casing and the second captive fastener may include a second blocking member configured to prevent the second captive fastener from being removed from the casing. 
     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 disclosure. The scope of the disclosure 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,” “various embodiments,” 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 embodiments. 
     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 herein is to be construed under the provisions of 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. 
     Finally, it should be understood that any of the above described concepts can be used alone or in combination with any or all of the other above described concepts. Although various embodiments have been disclosed and described, one of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. Accordingly, the description is not intended to be exhaustive or to limit the principles described or illustrated herein to any precise form. Many modifications and variations are possible in light of the above teaching.