Patent Publication Number: US-2021180639-A1

Title: Fasteners for wheel and brake assemblies

Description:
FIELD 
     The present disclosure relates to aircraft wheel and brake assemblies and, more particularly, to tie bolts used with aircraft brake and wheel assemblies. 
     BACKGROUND 
     Conventional aircraft wheel assemblies may be of the split wheel type, in which two wheel sections are secured together to form the wheel. Frequently, the two wheel sections are secured to each other using a number of circumferentially spaced tie bolt assemblies having a bolt head at one end and a nut at the opposing end or base. In similar fashion, aircraft brake assemblies use tie bolts to secure a piston housing to a torque plate. Aircraft wheel and brake assemblies tend to be heavy, and thereby benefit from weight-saving measures. The nuts, bolts, rivets and the like employed for securing the structural elements of an airplane contribute a substantial portion to the total weight of the airplane since a very large number of fasteners are used. Thus, there has been a long effort to reduce the weight of fasteners without substantially decreasing strength or preferably decreasing weight while increasing strength. Even an apparently small decrease in weight on an individual fastener can have a large impact on the total weight of an airplane. 
     SUMMARY 
     A tie bolt is disclosed. In various embodiments, the tie bolt includes a shank having a first end and a second end; and a counterbore disposed at the second end of the shank, opposite the first end, the counterbore having a counterbore depth and a counterbore diameter. 
     In various embodiments, the counterbore includes a counterbore portion that is substantially cylindrical along the counterbore depth. In various embodiments, the counterbore includes a counterbore end portion extending from the counterbore portion toward the first end of the shank. In various embodiments, the counterbore end portion defines a conical shape. In various embodiments, the counterbore end portion defines a hemispherical shape. 
     In various embodiments, the shank defines a shank diameter and the counterbore diameter is equal to between eight-tenths and one-half of the shank diameter. In various embodiments, the shank diameter is between seven-tenths inch and eight tenths inch. In various embodiments, the counterbore depth is between zero inch and one-half inch. In various embodiments, the counterbore includes a counterbore portion that is substantially cylindrical along the counterbore depth. In various embodiments, the counterbore includes a counterbore end portion extending from the counterbore portion toward the first end of the shank. In various embodiments, the counterbore end portion defines at least one of a conical shape and a hemispherical shape. 
     A wheel assembly is disclosed. In various embodiments, the wheel assembly includes an inboard wheel section having a plurality of inboard bolt holes; an outboard wheel section having a plurality of outboard bolt holes and configured to mate with the inboard wheel section; and a tie bolt configured to extend through at least one of the plurality of inboard bolt holes and at least one of the plurality of outboard bolt holes, the tie bolt comprising a shank having a first end and a second end, and a counterbore disposed at the second end of the shank, opposite the first end, the counterbore having a counterbore depth and a counterbore diameter. 
     In various embodiments, the shank defines a shank diameter and the counterbore diameter is equal to between one-half and eight-tenths of the shank diameter. In various embodiments, the counterbore includes a counterbore portion that is substantially cylindrical along the counterbore depth. In various embodiments, the shank diameter is between seven-tenths inch and eight tenths inch. In various embodiments, the counterbore depth is between zero inch and one-half inch. 
     A brake mechanism for use with a wheel assembly is disclosed. In various embodiments, the brake mechanism includes a piston housing having a plurality of piston housing bolt holes; a torque plate barrel having a plurality of torque plate barrel bolt holes and configured to mate with the piston housing; and a tie bolt configured to extend through at least one of the plurality of piston housing bolt holes and at least one of the plurality of torque plate barrel bolt holes, the tie bolt comprising a shank having a first end and a second end, and a counterbore disposed at the second end of the shank, opposite the first end, the counterbore having a counterbore depth and a counterbore diameter. 
     In various embodiments, the shank defines a shank diameter and the counterbore diameter is equal to between one-half and eight-tenths of the shank diameter. In various embodiments, the shank diameter is between seven-tenths inch and eight tenths inch. In various embodiments, the counterbore depth is between zero inch and one-half inch. 
     The forgoing features and elements may be combined in any combination, 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 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. 
         FIGS. 1A and 1B  provide a perspective schematic view and a cross sectional view of a portion of an aircraft wheel assembly, in accordance with various embodiments; 
         FIG. 2  provides a cross sectional schematic view of a portion of an aircraft wheel and brake assembly, in accordance with various embodiments; 
         FIGS. 3A, 3B and 3C  provide cross sectional schematic views of various tie bolts, in accordance with various embodiments; and 
         FIG. 4  provides a graph of root stress as a function of counterbore depth, 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. 
     The present disclosure describes various embodiments of wheel assemblies and brake assemblies including tie bolt systems. Such tie bolt systems may include counterbore portions at the base of the tie bolts. Referring now to  FIGS. 1A and 1B , a wheel assembly  100  is illustrated in accordance with various embodiments. The wheel assembly  100  comprises a split wheel assembly. For example, the wheel assembly  100  may comprise an inboard wheel section  102  (or a first wheel section) coupled to an outboard wheel section  104  (or a second wheel section). As illustrated, the inboard wheel section  102  and the outboard wheel section  104  are generally configured to rotate about a central axis  106 . In various embodiments, the inboard wheel section  102  may comprise a plurality of inboard bolt holes  108  and the outboard wheel section  104  may comprise a plurality of outboard bolt holes  110 . In various embodiments, the inboard wheel section  102  and the outboard wheel section  104  may be oriented such that the plurality of inboard bolt holes  108  and the plurality of outboard bolt holes  110  are radially aligned. In various embodiments, the inboard wheel section  102  and the outboard wheel section  104  are coupled together by a plurality of tie bolts  150 , with each of the plurality of tie bolts  150  being disposed through respective ones of the plurality of inboard bolt holes  108  and the plurality of outboard bolt holes  110 . Each of the plurality of tie bolts  150  is typically secured in position by a nut  152 . A head washer  154  may be positioned between a head portion  156  of each tie bolt and an inboard flange  120  of the inboard wheel section  102 . Similarly, a nut washer  158  may be positioned between the nut  152  and an outboard flange  122  of the outboard wheel section  104 . 
     In various embodiments, the inboard wheel section  102  may comprise an inboard mating face  112  and the outboard wheel section  104  may comprise an outboard mating face  114 . In various embodiments, the plurality of inboard bolt holes  108  is spaced circumferentially about the inboard mating face  112  and the plurality of outboard bolt holes  110  is spaced circumferentially about the outboard mating face  114 . In response to the plurality of tie bolts  150  being properly tightened, the inboard mating face  112  and the outboard mating face  114  may contact each other in substantially parallel planes. In various embodiments, the inboard wheel section  102  may further comprise a tubewell portion  116 , which may comprise a thin web extending at least partially between an inboard end  117  and an outboard end  118 , and is subjected to large forces upon inflation of a tire disposed about the tubewell portion  116 . 
     Referring now to  FIG. 2 , there is schematically depicted a brake mechanism  200  configured for use with a wheel assembly, such as, for example, the wheel assembly  100  described above with reference to  FIGS. 1A and 1B . In various embodiments, the brake mechanism  200  is mounted on an axle  202  for use with a wheel  204  disposed on and configured to rotate about the axle  202  via one or more bearing assemblies  203 . A central axis  206  (colinear with the central axis  106  described above) extends through the axle  202  and defines a center of rotation of the wheel  204 . A torque plate barrel  208  (sometimes referred to as a torque tube or barrel or a torque plate) is aligned concentrically with the central axis  206 , and the wheel  204  is rotatable relative to the torque plate barrel  208 . 
     The brake mechanism  200  includes a piston assembly  210 , a pressure plate  212  disposed adjacent the piston assembly  210 , an end plate  214  positioned a distal location from the piston assembly  210 , and a plurality of rotor disks  216  interleaved with a plurality of stator disks  218  positioned intermediate the pressure plate  212  and the end plate  214 . The pressure plate  212 , the plurality of rotor disks  216 , the plurality of stator disks  218  and the end plate  214  together form a brake heat sink or brake stack  220 . The pressure plate  212 , the end plate  214  and the plurality of stator disks  218  are mounted to the torque plate barrel  208  and remain rotationally stationary relative to the axle  202 . The plurality of rotor disks  216  is mounted to the wheel  204  and rotate with respect to each of the pressure plate  212 , the end plate  214  and the plurality of stator disks  218 . 
     An actuating mechanism for the brake mechanism  200  includes a plurality of piston assemblies, including the piston assembly  210 , circumferentially spaced around a piston housing  222  (only one piston assembly is illustrated in  FIG. 2 ). In various embodiments, the piston housing  222  and the torque plate barrel  208  are coupled together by a plurality of tie bolts  250 , with each of the plurality of tie bolts  250  being disposed through respective ones of a plurality of piston housing bolt holes  224  and a plurality of torque plate barrel bolt holes  226 . Each of the plurality of tie bolts  250  is typically secured in position by a threaded portion  228  within the torque plate barrel  208 . A head washer  254  may be positioned between a head portion  256  of each tie bolt and an inboard flange  230  of the piston housing  222 . 
     Referring now to  FIG. 3A , a tie bolt  350  is illustrated, similar to one of the plurality of tie bolts  150  and the plurality of tie bolts  250  illustrated in  FIGS. 1A and 1B  and  FIG. 2 , respectively. In various embodiments, the tie bolt  350  includes a shank  370  that defines a shank diameter  362  and a shank length  366 . Without loss of generality, the shank diameter  362  may be defined as the pitch diameter of the tie bolt  350 , with the pitch diameter being defined as an average of the root diameter and the crest diameter of a bolt thread  372  that extends along at least a portion of the shank length  366 . In various embodiments, the tie bolt  350  includes a counterbore  351  that extends a counterbore depth  364  into the shank  370  from a base  374  toward a head  376  of the tie bolt  350 . The head  376  of the tie bolt  350  is disposed at a first end of the shank  370  and the counterbore  351  is disposed at a second end of the shank  370 . In various embodiments, the counterbore  351  defines a cylindrical hole having a counterbore diameter  360  that extends from the base  374  and into the shank  370  along the counterbore depth  364 . 
     In similar fashion, a tie bolt  352  is illustrated in  FIG. 3B  as having a counterbore  353  with a counterbore end portion  378  that defines a conical shape extending from a counterbore portion  379  that is generally cylindrical and that otherwise shares similar characteristics as does the counterbore  351  described above—i.e., the counterbore portion  379  shares the counterbore diameter  360  and the counterbore depth  364  as does the counterbore  351  described above with reference to  FIG. 3A . Similarly, a tie bolt  354  is illustrated in  FIG. 3C  as having a counterbore  355  with a counterbore end portion  380  that defines a hemispherical shape extending from a counterbore portion  381  that is generally cylindrical and that otherwise shares similar characteristics as does the counterbore  351  described above—i.e., the counterbore portion  381  shares the counterbore diameter  360  and the counterbore depth  364  as does the counterbore  351  described above with reference to  FIG. 3A . 
     Referring again to  FIG. 3A , the counterbore  351  is sized, in accordance with various embodiments, such that the root stress of the main load bearing threads (e.g., the first three threads in engagement with a nut or some other internally threaded member, such as a torque plate barrel) does not exceed the loads or stresses (e.g., the allowable shear or principal stresses) placed on the threads of the tie bolt  350  during operation. In various embodiments, for example, the counterbore diameter  360  (C DIA ), normalized by the shank diameter  362  (S DIA ), is equal to eight-tenths (0.80) or less; or, in various embodiments, C DIA /S DIA  is equal to two-thirds (0.667) or less; or, in various embodiments, C DIA /S DIA  is equal to one-half (0.50) or less. In various embodiments, the counterbore depth  364  may extend any length along the shank length  366 , but at larger counterbore diameters (e.g., C DIA /S DIA  equal to between one-half (0.50) and eight-tenths (0.80)), the counterbore depth  364  should generally not extend past the first three threads in engagement with a nut or some other internally threaded member; excepting, however, where the counterbore includes a counterbore end portion extending from a cylindrically shaped counterbore portion, such as, for example, the counterbore end portion  378  and the counterbore end portion  380  illustrated in  FIGS. 3B and 3C , respectively. Note that while the tie bolts described in the disclosure generally include a head located at a first end of a shank opposite the base or the second end of the shank, the disclosure contemplates all-thread shanks, where counterbores are disposed at one or both of the first end and the second end and where the head is replaced, for example, with a nut threaded onto the first end of the shank. 
     Referring now to  FIG. 4 , a graph  400  illustrates a simulated effect on maximum root stress that a counterbore produces as a function of counterbore depth. By way of example, the shank diameter of the tie bolt is three-quarter (0.75) inch (≈19.0 mm) and the counterbore diameter is one-half (0.50) inch (≈12.7 mm). These dimensions provide a value of C DIA /S DIA  equal to two-thirds (0.667). Referring to  FIG. 4 , a counterbore depth equal to 0.125 inch (≈3.2 mm) produces a less than one percent (1%) increase in the maximum root stress over a threshold value of maximum root stress with no counterbore. Similarly, a counterbore depth equal to 0.25 inch (≈6.4 mm) produces an approximately two percent (2%) increase in the maximum root stress over the threshold value of maximum root stress with no counterbore. Deeper counterbores produce correspondingly higher percentage increases in maximum root stress, as illustrated. 
     At the lower depths (e.g., at the 0.125 inch (≈3.2 mm) and the 0.25 inch (≈6.4 mm) depths), the weight savings per bolt are, respectively, approximately 0.00729 lbs (≈3.30 grams) and approximately 0.01458 lbs (≈6.60 grams). On a wheel and brake system for a large commercial aircraft having, for example, eight (8) braked positions, each having twenty (20) tie bolts for each wheel assembly (e.g., the wheel assembly  100  described above with reference to  FIGS. 1A and 1B ) and twelve (12) tie bolts for each brake mechanism (e.g., the brake mechanism  200  described above with reference to  FIG. 2 ), with each tie bolt having a shank diameter equal to three-quarter (0.75) inch (≈19.0 mm) and a counterbore diameter equal to one-half (0.50) inch (≈12.7 mm), the total weight savings for the aircraft is, respectively, approximately 1.75 lbs (≈793.7 grams) and approximately 3.5 lbs (≈1587.5 grams). 
     While this example provides analysis of a tie bolt having a shank diameter equal to three-quarter (0.75) inch (≈19.0 mm) and a counterbore diameter equal to one-half (0.50) inch (≈12.7 mm), it is contemplated that similar beneficial effects of weight saving without substantial increase in maximum root stress will be observed in tie bolts having shank diameters in the range of several inches to fractions of an inch. For example, in various embodiments, the shank diameter is between two (2) inches (≈50.8 mm) and one-quarter (0.25) inch (≈6.35 mm); in various embodiments, the shank diameter is between one (1) inch (≈25.4 mm) and one-half (0.50) inch (≈12.7 mm); and in various embodiments, the shank diameter is between eight-tenths (0.80) inch (≈20.32 mm) and seven-tenths (0.70) inch (≈17.78 mm). Corresponding ranges for C DIA /S DIA  is equal to eight-tenths (0.80) or less; or, in various embodiments, C DIA /S DIA  is equal to two-thirds (0.667) or less; or, in various embodiments, C DIA /S DIA  is equal to one-half (0.50) or less. The counterbore depth for all cases ranges from one-tenth (0.10) S DIA  to eight-tenths (0.80) S DIA , though other depths are contemplated depending on the location of the shank of the first engaged thread. The result for all ranges is a significant weight savings with minimal increase in the maximum root stress. 
     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.