Patent Publication Number: US-2023139607-A1

Title: Locking tab-washer

Description:
TECHNICAL FIELD 
     The disclosure relates generally to aircraft engines and, more particularly, to fasteners in aircraft engines. 
     BACKGROUND 
     Locking tab washer as used in aircraft engines to rotatably lock a fastener such as a bolt in place once torqued. Typical locking tab washers require a bolt head to be oriented at specific angles to provide satisfactory alignment of the locking tabs with the bolt head flats for locking. As such, the bolt may often require being over or under-torqued from its predetermined torque degree for satisfactory locking alignment. Improvements are thus desirable. 
     SUMMARY 
     In one aspect, there is provided a locking tab washer for rotatably locking a bolt fastened to a component in an aircraft engine, the bolt having a bolt head with repeated flat surfaces, the locking tab washer comprising: an opening extending from a front surface of the locking tab washer to a rear surface of the locking tab washer, with an axis defined through a center of the opening; at least four locking tabs positioned about the opening and circumferentially spaced apart from one another at integer multiples of a common angle relative to the center of the opening, the at least four locking tabs bendable towards the opening in a first direction relative to the axis to rotatably lock the bolt; and a retaining feature positioned about the opening and operable to rotatably retain the locking tab washer to the component. 
     In another aspect, there is provided a locking assembly for joining two components in an aircraft engine, comprising: a locking tab washer having an opening extending from a front surface of the locking tab washer to a rear surface of the locking tab washer with an axis defined through a center of the opening, the rear surface disposed against a first of the two components with the opening aligned with apertures in the first of the two components and a second of the two components, at least four locking tabs positioned about the opening and bendable towards the opening in a first direction relative to the axis, and a retaining feature positioned about the opening and engaging an anti-rotation surface of one of the two components; and a bolt having a bolt head with a plurality of flat surfaces, and a shank rotatably received through the opening and through the apertures in the two components, the bolt torqued to a predetermined degree, each of the plurality of flat surfaces of the bolt having a loaded half surface and an unloaded half surface when the bolt is torqued, at least one of the at least four locking tabs bendable towards the bolt head with at least half of its width aligned with a loaded half surface of a corresponding flat surface to prevent untorqueing of the bolt when the bolt is torqued. 
     In a further aspect, there is provided a method for joining two components in an aircraft engine, comprising: positioning a locking tab washer against a first of the two components with an opening in the locking tab washer aligned with apertures in the first of the two components and in a second of the two components; inserting a bolt through the opening and through the apertures in the two components; torqueing the bolt to a predetermined degree; and bending at least four locking tabs positioned about the opening in the locking tab washer towards a head of the bolt to rotatably lock the bolt, the at least four locking tabs having a predetermined angular distribution about the opening, the predetermined angular distribution selected so that at least one of the at least four locking tabs has at least half of its width aligned with a loaded half surface of a corresponding flat surface of the bolt regardless of a relative angular position between the head of the bolt and the locking tab washer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference is now made to the accompanying figures in which: 
         FIG.  1    is a schematic cross sectional view of a gas turbine engine; 
         FIG.  2    is a perspective view of a locking assembly in accordance with an embodiment of the present disclosure; 
         FIG.  3    is a perspective view of a locking tab washer for the locking assembly of  FIG.  2   ; 
         FIGS.  4 A- 4 D  are front views of the locking assembly of  FIG.  2    with the locking tab washer in various rotational positions; 
         FIG.  5    is a front view of a locking assembly in accordance with an embodiment of the present disclosure; 
         FIG.  6    is a front view of a locking tab washer in accordance with an embodiment of the present disclosure; 
         FIG.  7    is a front view of a locking tab washer in accordance with an embodiment of the present disclosure; 
         FIG.  8    is a front view of a locking tab washer in accordance with an embodiment of the present disclosure; and 
         FIGS.  9 A- 9 B  are front and perspective views, respectively, of a locking tab washer in accordance with an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    illustrates an aircraft engine, for instance, a gas turbine engine  10  of a type preferably provided for use in subsonic flight. The exemplified engine  10  is depicted in  FIG.  1    is a turboprop having a propeller  12 . The engine  10  has, in serial flow communication, a compressor section  14  for pressurizing the air, a combustor  16  in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section  18  for extracting energy from the combustion gases. The engine  10  has a shaft  20  drivingly engaged to the propeller  12  via a reduction gear box  22 . Although  FIG.  1    depicts engine  10  as a reverse-flow turboprop-type engine, the present disclosure is applicable to other engine types as well, for instance turboshaft and turbofan type engines. 
     Referring to  FIG.  2   , an exemplary locking assembly  30  within engine  10  according to the present disclosure is shown. In the depicted case, although not necessarily the case in all embodiments, a bolt  40  is operable to retain a first component  50  to an adjacent second component  60 . In the depicted case, the first component  50  is a flange of an exhaust duct, and the second component  60  is a flange of a power turbine stator housing, although other components of the engine  10  may be contemplated as well. As will be discussed in further detail below, a locking tab washer  70  is operable to rotatably lock the bolt  40  in place once the bolt  40  is torqued to a predetermined degree, regardless of the rotational orientation of the bolt  40 . 
     The depicted bolt  40  is a single hex bolt having a bolt head  41  with six flat surfaces  42  about its outer circumference. A partially or fully threaded shank (not shown) extends from the shank and is receivable through corresponding apertures (not shown) in the first and second components  50 ,  60 . The bolt  40  is fastenable, for instance via a nut (not shown) rotatably engageable with a threaded end of the shank on an opposite side of the second component  60 , illustratively on the hidden opposite side of the flange of the second component  60 . Other means for fastening the bolt, for instance threading in one or both of the apertures in the first and second components  50 ,  60 , may be contemplated as well. As will be discussed in further detail below, each flat surface  42  of the bolt head  41  is divided into two portions or half surfaces relative to a direction of rotation of the bolt: an unloaded half surface  42   a  and a loaded half surface  42   b . After the bolt  40  is installed and torqued to a predetermined degree, for instance in a clockwise direction when looking at the page, pressure applied to one or more of the loaded half surfaces  42   b  by a corresponding portion of the locking tab washer  70  may prevent the bolt  40  from untorqueing, thereby preventing the assembly  30  from coming apart. 
     Referring additionally to  FIG.  3   , the depicted locking tab washer  70  includes a front surface  71 , a rear surface  72 , and a central opening  73  extending from the front surface  71  to the rear surface  72 . An axis A is defined through a center C 1  of the opening  73 . Upon assembly of the locking assembly  30 , the bolt  40  is alignable with the opening  73  and apertures (not shown) in the first component  50  and second component  60  along the axis A. According to various embodiments of the present disclosure, the locking tab washer  70  may include at least four locking tabs  74  circumferentially oriented about the opening  73  with reference to the center C 1  so that, when the locking assembly  30  is assembled and the bolt torqued, the locking tabs  74  are indexed at unique locations or positions along the flat surfaces  42  of the bolt  40  so that the bolt may be rotatably locked by at least one locking tab  74 , regardless of its rotational orientation. Various numbers of locking tabs  74  and relative circumferential spacing between tabs may be contemplated. To ensure unique positions or locations along the flat surfaces  42 , the circularly repeating pattern of the bolt&#39;s flat surfaces  42  (i.e. three hundred degrees divided by six sides of a single hex bolt, giving sixty degrees) may be divided by the number of locking tabs  74  on the locking tab washer  70 , and multiple integers of that result may be used as the circumferential spacing between circumferentially adjacent locking tabs  74 . 
     The depicted locking tab washer  70  in  FIG.  3    includes four locking tabs  74  positioned about the opening  73 . Based on the above, the locking tabs  74  may be circumferentially spaced apart from each other at integer multiples of fifteen degrees. Illustratively, a first angle θ 1  between circumferentially adjacent locking tabs  74   1  and  74   2  measures ninety degrees, a second angle θ 2  between circumferentially adjacent locking tabs  74   2  and  74   3  measures forty five degrees, and a third angle θ 3  between circumferentially adjacent locking tabs  74   2  and  74   3  measures ninety degrees. Other angles between adjacent locking tabs  74  may be contemplated as well. 
     In other cases, locking tab washers  70  may include more than four locking tabs  74 . For instance, a locking tab washer  70  may include five locking tabs  74  that are circumferentially spaced apart from each other at integer multiples of twelve degrees. In various cases, variations of plus-or-minus one degree may apply with respect to the selected degree (or multiple thereof) of spacing. 
     As will be discussed in further detail below, the circumferential spacing between adjacent locking tabs  74  may allow the locking tab washer  70  to rotatably lock the bolt  40  once the bolt  40  is torqued to a predetermined degree regardless of the relative angle between the bolt head  41  and the locking tab washer  70  and without requiring the bolt  40  to be additionally over or under-torqued. 
     In the depicted case, the locking tabs  74  are bendable at a crease  74   a  at an intersection between the locking tab  74  and the front surface  71  of the locking tab washer  70 . The locking tabs  74  are thus bendable towards the opening  73  in a first direction D 1  relative to the axis A to rotatably retain or lock the bolt  40  in place once the bolt  40  is torqued, as will be discussed in further detail below. In the depicted embodiment, although not necessarily the case in all embodiments, the locking tabs  74  are pre-bent along respective creases  74   a , thereby rendering the locking tab washer  70  mistake proof and only installable in its correct orientation. In other embodiments, one or more of the locking tabs  74  may be pre-bent along respective crease(s)  74   a , for instance to indicate the correct orientation for installation. In the shown case, each locking tab  74  has a narrowing width as it extends from the crease  74   a  towards a radially distal end  74   b  thereof, forming a triangular-like cross-sectional shape. Other shapes for the locking tabs  74  may be contemplated as well. 
     The locking tab washer  70  further includes a retaining feature to rotatably retain the locking tab washer  74  to the first component  50  and/or the second component  60  by engaging a respective surface on the first component  50  and/or the second component  60  as the bolt  40  is torqued. In the embodiment shown in  FIGS.  2 - 3   , the retaining feature includes a pair of anti-rotation tabs  75  positioned about the circumference of the locking tab washer  70 . Each anti-rotation tab  75  includes a first portion  75   a  extending radially outwardly relative to the opening  73  and a second portion extending in a second direction D 2  relative to the axis A and opposite the first direction D 1 . In an assembled configuration, the anti-rotation tabs  75  are operable to engage radially outer surfaces of the first component  50  and the second component  60 . 
     As depicted in  FIG.  2   , the first component  50  is an exhaust duct having a radially inner surface  51 , a flange  52  with an aperture (not shown) for the bolt&#39;s shank (not shown) to pass therethrough and a radially outer surface  53  with scalloped edges  54 . The depicted second component  60 , the turbine rotor stator housing, similarly has a flange with an aperture (not shown) for the bolt&#39;s shank to pass therethrough and a radially outer surface  61  with scalloped edges  62 . Other engine components may be contemplated as well. In the depicted case, the anti-rotation tabs  75  are operable to abut against the scalloped edges  54 ,  62  of the first component  50  and the second component  60 , respectively, when the locking tab washer  70  is installed. The first portions  75   a  may be dimensioned, i.e. its radial length, so that only one of the anti-rotation tabs  75  may abut a respective scalloped edge  54  of the first component  50  and a respective scalloped edge  62  of the second component  60  at a time. The abutting anti-rotation tab  75  may be alternated, for instance, by rotating the locking tab washer  70  relative to the center C 1 . 
     An exemplary method for joining the two components  50 ,  60  will now be described. The locking tab washer  70  is positioned against the first component  50  the opening  73  aligned with apertures (not shown) in the components  50 ,  60 . The bolt  40  is inserted through the opening  73  and through the apertures in the components  50 ,  60 . The bolt  40  is tightened to a predetermined degree. The at four locking tabs  74  positioned about the opening  73  in the locking tab washer  70  are bent towards the head  41  of the bolt  40  to rotatably lock the bolt  40 , with at least one of the at least four locking tabs  74  having a major portion of its width, for instance at least half of its width, aligned with a loaded half surface  42   b  of a corresponding flat surface  42  of the bolt  40  to prevent untorqueing of the bolt  40 . Variations and additional steps may be contemplated as well. 
     In the embodiment depicted in  FIG.  2   , the above-described method may further include abutting one of the anti-rotation tabs  75  against the scalloped edges  54  as the bolt  40  is being torqued. The selected anti-rotation tab  75  is that which requires the applied pressure, for instance against the other anti-rotation tab  75  via a drift or other like tool, to be in a rotational direction opposite the torqueing of the bolt  40 . Thus, once the bolt is torqued, any untorqueing motion will be interrupted by the anti-rotation tab  75  abutting the scalloped edges  54  and/or  62  (or other radially-outward surface of the first  50  or second  60  component). 
     Referring additionally to  FIGS.  4 A- 4 D , regardless of the orientation of the torqued bolt  40 , at least one of the illustratively four locking tabs  74  will be in a position to lock the bolt  40  in place once bent towards the bolt head  41  due to its alignment with respective loaded half surface  42   b .  FIGS.  4 A- 4 D  illustrate four rotational orientations of the bolt  40  with reference to a rotational center C 2  of the bolt  40  aligned with axis A. Illustratively, the bolt  40  is rotated by fifteen degrees in a clockwise direction from  FIG.  4 A  to  FIG.  4 B , from  FIG.  4 B , to  FIG.  4 C , and from  FIG.  4 C , to  FIG.  4 D  to depict the operability of the four locking tabs  74 , denoted in  FIGS.  4 A- 4 D  as  74   1 ,  74   2 ,  74   3  and  74   4 . In the bolt&#39;s position as depicted in  FIG.  4 A , locking tabs  74   2  and  74   4  are operable to rotatably lock the bolt  40  once bent by having at least half of their widths aligned with respective loaded half surfaces  42   b . In the bolt&#39;s position as depicted in  FIG.  4 B , locking tabs  74   1  and  74   4  are operable to rotatably lock the bolt  40  once bent by having at least half of their widths aligned with respective loaded half surfaces  42   b . In the bolt&#39;s position as depicted in  FIG.  4 C , locking tabs  74   1  and  74   3  are operable to rotatably lock the bolt  40  once bent by having at least half of their widths aligned with respective loaded half surfaces  42   b . In the bolt&#39;s position as depicted in  FIG.  4 D , locking tabs  74   2  and  74   3  are operable to rotatably lock the bolt  40  once bent by having at least half of their widths aligned with respective loaded half surfaces  42   b . Other combinations of bolt orientations and locking tabs  74  may be contemplated as well. Regardless of the orientation of the bolt  40 , the arrangement of the locking tabs  74  about the opening  73  may ensure that at least one of the locking tabs  74  may prevent untorqueing of the bolt  40 . 
     In other embodiments, other retaining features for the locking tab washer  70  may be contemplated. Referring to  FIG.  5   , in the depicted embodiment, the locking tab washer  70  includes a pair of feet  76  extending radially outwardly from the opening  73  and operable to retain the locking tab washer  70  in place. Once the locking tab washer  70  is installed on the first component  50 , illustratively the exhaust duct flange  52 , the feet  76  are operable to abut against a radially inner surface  51  of the first component  50 , illustratively an outer diameter of the exhaust duct. As was the case in the previous embodiment, one of the two feet  76  may be operable to abut the radially inner surface  51  at a time, for instance based on the direction of rotation of the torqued bolt  40 . In the embodiment shown in  FIG.  5   , the two feet are shown to be symmetric about a center line L normal to the center C 2  and axis A. In other cases, for instances as depicted by the locking tab washer shown in  FIG.  6   , the two feet  76  may be asymmetric about the center line L, i.e. having different dimensions and shapes. In other cases, for instance as depicted by the locking tab washer  70  in  FIG.  7   , the locking tab washer  70  may include a single foot  76  operable to abut the radially inner surface  51  of the first component  50  upon torqueing of the bolt  40 . Various sizes and shapes of the foot/feet  76  may be contemplated, for instance on the type and dimensions of the first component  50 . In each of the shown locking tabs washers  70  of  FIGS.  5 - 7   , the locking tabs  74  are shown to be circumferentially spaced apart, i.e. having first angle θ 1 , second angle θ 2 , and third angle θ 3  of forty five degrees from one another for optimized bolt locking. Other relative angles second angle θ 1 , θ 2 , θ 3  may be contemplated as well. Other relative angles may be contemplated as well. 
     Referring to  FIG.  8   , in some embodiments, the locking tab washer  70  may include two openings  73  and be operable to rotatably lock two adjacent bolts  40 . Each opening  73  has a center C 1  with an axis A protruding therethrough. This locking tab washer  70  may be referred to as a gang tab washer, as the retaining feature includes a linking member  77  joining a first opening  73  to a second opening  73 . Each opening  73  is surrounded by locking tabs  74 , illustratively four locking tabs  74 . In the depicted case, the locking tabs  74  are shown to be circumferentially spaced apart, i.e. having first angle θ 1 , second angle θ 2 , and third angle θ 3  of forty five degrees from one another for optimized bolt locking. Other relative angles θ 1 , θ 2 , θ 3  may be contemplated as well. In the depicted case, each opening  73  is surrounded by locking tabs  74  circumferentially spaced apart in a same arrangement, i.e. with forty five degree spacing between circumferentially-adjacent locking tabs  74 . In other cases, the circumferential arrangement may differ around one opening  73  and around the other. In the depicted case, the retaining feature, i.e. the linking member  77 , may not require engagement with the other components of the locking assembly  30 , for instance the first component  50  or the second component  60 , as the presence of the two torqued bolts  40  provide retention to each other via the linking member  77 . 
     Referring to  FIG.  9   , in some embodiments, the locking tab washer  70  may include as a retaining feature a key  78  protruding in the second direction D 2  opposite the first direction D 1 . The key  78  has a first portion  78   a  protruding radially outwardly relative the opening  73  and a second portion  78   b  protruding in the second direction D 2  and operable to engage with a slot in the first component  50  to prevent rotation of the locking tab washer  70  with respect to the first component  50  once installed, thus retaining the bolt  40  to the first component  50  once the bolt  40  is torqued and the locking tabs  74  bent. In the depicted locking tabs washer  70  of  FIGS.  9 A- 9 B , the locking tabs  74  are shown to be circumferentially spaced apart, i.e. having first angle θ 1 , second angle θ 2 , and third angle θ 3  of forty five degrees from one another for optimized bolt locking. Other relative angles second angle θ 1 , θ 2 , θ 3  may be contemplated as well. 
     It can be appreciated from the foregoing that at least some embodiments have a locking tab washer  70  with locking tabs  74  providing bolt-locking functionality independently of the orientation of the bolt head  41 , thereby allowing the bolt  40  to be torqued to its predetermined degree rather than under or over-torqued to ensure proper rotational locking, which may improve the bolt&#39;s sturdiness and reliability in the locking assembly  30 . 
     The embodiments described in this document provide non-limiting examples of possible implementations of the present technology. Upon review of the present disclosure, a person of ordinary skill in the art will recognize that changes may be made to the embodiments described herein without departing from the scope of the present technology. Yet further modifications could be implemented by a person of ordinary skill in the art in view of the present disclosure, which modifications would be within the scope of the present technology.