Patent Publication Number: US-2022227170-A1

Title: Hub structure and hub for a bicycle

Description:
TECHNICAL FIELD 
     The disclosure relates to bicycles, and more particularly, to bicycle hubs. 
     BACKGROUND 
     Cycling has always been popular for its various roles, including transportation, travel, leisure, exercise, sports, and competition. Cycling&#39;s popularity spans all demographics of users, and includes recreational riders, amateur riders, avid rides, professional riders, and athletes. In recent years, bike-sharing and related services have increased in popularity, with many cities and regions creating incentives, programs, and services organized to provide sustainable and healthy transportation for their citizens. 
     A conventional bicycle often includes a freewheel mechanism, such as a freehub, to allow a rider to stop pedaling while the bicycle is still in forward motion. However, components used in the freewheel mechanism may increase the weight of the hub. In the pursuit of improving cycling speed and efficiency, it would be desirable to reduce the total weight of the bicycle by developing a simplified, lightweight freewheel mechanism used in the hub. 
     SUMMARY OF THE PRESENT DISCLOSURE 
     Consistent with some embodiments, a hub structure for use in a freewheel mechanism of a bicycle hub is provided. The hub structure includes a tubular body defining a hollow cavity. The tubular body includes a first surface and a second surface. The first surface defines a first groove extending along an axial direction of the tubular body. The first groove is defined by an inner sidewall surrounding the hollow cavity, an outer sidewall spaced from and configured to face the inner sidewall, and a bottom surface coupling the inner sidewall and the outer sidewall. 
     Consistent with some embodiments, a hub for a bicycle is provided. The hub for the bicycle includes a hub structure, a positioning plate mounted on a hub base, and a spring attached between the positioning plate and the hub structure. The hub structure includes a tubular body defining a hollow cavity, the tubular body including a first surface and a second surface, the first surface defining a first groove extending along an axial direction of the tubular body. The first groove is defined by a first inner sidewall surrounding the hollow cavity, a first outer sidewall spaced from and configured to face the first inner sidewall, and a bottom surface coupling the first inner sidewall and the first outer sidewall. 
     Consistent with some embodiments, a hub structure is provided. The hub structure includes a tubular body, an inner ring, and an outer ring. The tubular body includes a first surface and a second surface and defines a hollow cavity. Axial engagement components are arranged on the second surface. The inner ring protrudes from the first surface of the tubular body along an axial direction of the tubular body and substantially surrounds the hollow cavity. The outer ring protrudes from the first surface of the tubular body along the axial direction of the tubular body and substantially surrounds the inner ring. A height of the inner ring may be substantially equal to or greater than a height of the outer ring. 
     It is to be understood that the foregoing general descriptions and the following detailed descriptions are exemplary and explanatory only, and are not restrictive of the disclosure, as claimed. 
    
    
     
       DETAILED DESCRIPTION OF THE DRAWINGS 
       Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several exemplary embodiments and, together with the corresponding descriptions, provide examples for explaining the disclosed embodiment consistent with the present disclosure and related principles. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  is a perspective view illustrating a bicycle, according to an embodiment of the present disclosure. 
         FIG. 2  is a side view of a hub for the bicycle shown in  FIG. 1 , according to an embodiment of the present disclosure. 
         FIG. 3  is a cross-sectional view of the hub of  FIG. 2 , according to an embodiment of the present disclosure. 
         FIG. 4  is a perspective view of the hub of  FIG. 2 , according to an embodiment of the present disclosure. 
         FIG. 5  is a front view of a hub, according to an embodiment of the present disclosure. 
         FIG. 6  is an exploded view of a hub, according to an embodiment of the present disclosure. 
         FIG. 7  illustrates a freewheel mechanism of a hub, according to an embodiment of the present disclosure. 
         FIG. 8  is a perspective view of a rotor-side toothed disc unit, according to an embodiment of the present disclosure. 
         FIG. 9  is a back view of a rotor-side toothed disc unit, according to an embodiment of the present disclosure. 
         FIG. 10  is a cross-sectional view of a rotor-side toothed disc unit, according to an embodiment of the present disclosure. 
         FIG. 11  is a perspective view of a positioning plate, according to an embodiment of the present disclosure. 
         FIG. 12  is a cross-sectional view of the positioning plate shown in  FIG. 11 , according to an embodiment of the present disclosure. 
         FIG. 13  is a cross-sectional view of a positioning plate, according to an embodiment of the present disclosure. 
         FIG. 14  illustrates a rotor-side toothed disc unit, including a spring and a positioning plate, according to an embodiment of the present disclosure. 
         FIG. 15  is a cross-sectional view of the rotor-side toothed disc unit shown in  FIG. 14 , according to an embodiment of the present disclosure. 
         FIG. 16A  illustrates a hub-side toothed disc unit and rotor-side toothed disc unit engaged to each other, according to an embodiment of the present disclosure. 
         FIG. 16B  and  FIG. 16C  are perspective views of the engaged toothed disc units shown in  FIG. 16A , according to embodiments of the present disclosure. 
         FIG. 17A  and  FIG. 17B  illustrate a rotor-side toothed disc unit and the spring, according to embodiments of the present disclosure. 
         FIGS. 18A and 18B  illustrate a rotor-side toothed disc unit and the spring, according to embodiments of the present disclosure. 
         FIGS. 19A and 19B  illustrate a rotor-side toothed disc unit and the spring, according to embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings and disclosed herein. The implementations set forth in the following description of embodiments are examples of systems and methods consistent with the aspects related to the disclosure and do not limit the scope of the present disclosure. 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     The terms used in this specification generally have their ordinary meanings in the art and in the specific context where each term is used. The use of examples in this specification, including examples of any terms discussed herein, is illustrative only, and in no way limits the scope and meaning of the disclosure or of any exemplified term. Likewise, the present disclosure is not limited to various embodiments given in this specification. 
     Although the terms “first,” “second,” etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
       FIG. 1  is a perspective view illustrating a bicycle  10 , according to some embodiments of the present disclosure. As shown in  FIG. 1 , the bicycle  10  includes a frame  20 . In some embodiments, the frame  20  may include a head tube portion  21 , a top tube portion  22 , a down tube portion  23 , a seat tube portion  24 , a pair of seat stays  25 , a pair of chain stays  26 , and a fork  27 , but the present disclosure is not limited thereto. In various embodiments, the frame  20  of the bicycle  10  may have different designs. 
     The bicycle  10  also includes a handlebar  12  with one or more front brakes for stopping the bicycle  10 , a seat  13 , at least one front wheel  14 , at least one rear wheel  15 , a crank unit  16  including crank arm(s)  162  and pedal(s)  164 , and a hub  17 . As shown in  FIG. 1 , the handlebar  12  is coupled to the head tube portion  21  of frame  20 . The seat  13  is coupled to the seat tube portion  24  of the frame  20 . A wheel rim of the rear wheel  15  may define a rotation axis and may be configured to receive a tire. Hub  17  may be arranged to extend along the rotation axis rear wheel  15 . Hub  17  may be radially spaced apart from the wheel rim of the rear wheel  15 . Hub  17  can be, for example, a freehub. When a rider of bicycle  10  stops pedaling, hub  17  may freewheel, or turn freely, in the forward direction independently of the sprockets, so that pedals  164  do not turn with rear wheel  15 . A plurality of spokes  18  may extend radially between hub  17  and the wheel rim of rear wheel  15 . Spokes  18  interconnect hub  17  and a spoke-mounting wall on the wheel rim of rear wheel  15 . In some embodiments, one or more covering units (not shown) can be mounted respectively on left and right sides of rear wheel  15  to confine a receiving space therebetween for receiving spokes  18 . 
     When the user pedals, the pedaling drives crank unit  16  operationally connected to a driving member, such as a chain, via one or more variable diameter chain gears. Accordingly, the rotation of the driving member communicates a driving force to hub  17  associated with rear wheel  15 . The operation of the pedals  164  can thereby drive rear wheel  15  and propel bicycle  10  forward. 
     A pair of seat stays  25  and a pair of chain stays  26  can be constructed to support rear wheel  15  at one end. Similarly, fork  27  may include a pair of fork blades or fork legs extending from generally opposite ends of a fork crown, and maybe constructed to support front wheel  14  at one end. Accordingly, the rider can control handlebar  12  to communicate to fork  27  to facilitate rotation of front wheel  14  relative to frame  20  along a longitudinal axis of bicycle  10 . 
     It is noted that the construction of bicycle  10  depicted in  FIG. 1  is merely an example and is not meant to limit the present disclosure. The present disclosure is applicable to various bicycle configurations, including various street or road bike configurations, or other bicycles with more aggressive suspension systems commonly found in off-road or mountain bike frame configurations, and/or hybrids, cross-over or multi-purpose bicycle frame configurations. 
       FIG. 2  and  FIG. 3  are respective side and cross-sectional views of a hub  100  for the bicycle  10  shown in  FIG. 1 , according to some embodiments of the present disclosure. As previously described above in  FIG. 1 , in some embodiments, hub  100  may be mounted in the center of a bicycle wheel (e.g., rear wheel  15  of  FIG. 1 ) and attached to spokes (e.g., spokes  18  of  FIG. 1 ), which connect to the rim of the bicycle wheel. As shown in  FIG. 2 , hub  100  may include a hub body  110  rotatably mounted on a hub axle (not shown in  FIG. 2 ) and connected to a rotor housing  132 , and a hub-side cover  102  and a rotor-side cover  136  mounted onto the hub axle. Bearings and other components are arranged within the hub body  110  and the rotor housing  132 . As shown in  FIG. 3 , in some embodiments, inside the hub body  110  and the rotor housing  132 , hub  100  may include hub axle  114 , a sealing device (e.g., an oil seal)  104  mounted between the hub-side cover  102  and the hub axle  114  to provide a tight seal, bearing units  106 ,  108 ,  126 , and  128 , a sealing device  112 , a sleeve body  116  disposed between bearing units  108  and  126 , a hub-side toothed disc unit  118 , a rotor-side toothed disc unit  120 , a spring  122 , a positioning plate  124 , a sleeve body  130  disposed between the bearing units  126  and  128 , a sealing device (e.g., an oil seal)  134  mounted between the rotor-side cover  136  and the hub axle  114  to provide a tight seal. Hub axle  114  is configured to attach a wheel to a bicycle and provides support for bearings on which the wheel rotates. 
     As shown in  FIG. 2  and  FIG. 3 , hub-side cover  102  and the rotor-side cover  136  are mounted onto the respective two ends of hub axle  114 . Sealing device  112  is configured to seal between hub body  110  and rotor housing  132 , and other internal components, such as the bearing units and the freewheel system inside the hub  100 . In some embodiments, hub axle  114  may be made of fiber reinforced plastic to reduce the weight of hub  100 . 
       FIG. 4  is a perspective view of hub  100  of  FIG. 2 , according to some embodiments of the present disclosure. Consistent with  FIG. 2  and  FIG. 3 , on the rotor side, the hub body  110  is connected to the rotor housing  132  and the rotor-side cover  136  is mounted onto one end of the hub axle  114 . On the hub side, the hub-side cover  102  is mounted onto the other end of the hub axle  114 . As shown in  FIG. 4 , hub body  110  of hub  100  includes two flanges  410  and  420 , to which spokes (e.g., spokes  18  in  FIG. 1 ) can be attached, on each side. For example, each of hub flanges  410  and  420  may be formed with multiple equiangularly displaced spoke apertures  412 ,  422 .  FIG. 5  is a front view of the hub  100  showing a design of the flanges  410  and  420 , according to some embodiments of the present disclosure. Referring to  FIG. 5 , in some embodiments, there may be eight spoke apertures  412  in one hub flange  410 , and four spoke apertures  422  in another hub flange  420 , but the present disclosure is not limited thereto. 
       FIG. 6  is an exploded view of a hub  100 , according to an embodiment of the present disclosure. Referring to  FIG. 6 , bearing units  106 ,  108 ,  126  and  128 , sleeve bodies  116  and  130 , toothed disc units  118  and  120 , spring  122  and positioning plate  124  forming the freewheel system can be installed and mounted to hub axle  114  through the respective hollow cavities of the components and arranged within hub body  110  or rotor housing  132 . It is noted that in some embodiments, spring  112  and positioning plate  124  can also be arranged between the toothed disc unit  118  and the bearing unit  108  to achieve similar functions. The arrangement illustrated in  FIG. 6  is an example and not meant to limit the present disclosure. 
       FIG. 7  illustrates a freewheel mechanism  700  including hub-side toothed disc unit  118 , rotor-side toothed disc unit  120 , and spring  122 , according to an embodiment of the present disclosure. As shown in  FIG. 7 , when the user pedals in a driving direction (e.g., the pedaling direction that drives the bicycle forward), toothed disc units  118  and  120  may be engaged with each other via axial toothings. Accordingly, the torque applied by the pedaling force is reliably transmitted between rotor-side toothed disc unit  120  and hub-side toothed disc unit  118 . On the other hand, when the user stops pedaling or pedals backward in an opposite direction, toothed disc units  118  and  120  are configured to axially diverge from one another, thus providing the freewheeling function. In other words, hub-side toothed disc unit  118  is rotatable with respect to rotor-side toothed disc unit  120 , which permits the wheel to rotate freely while the pedals are stationary or rotating in the opposite direction. To ensure engagement of toothed disc units  118  and  120  when a user pedals in the driving direction, toothed disc units  118  and  120  are urged toward one another by spring  122 , which functions as a biasing device. In some embodiments, spring  122  may be a coil spring, such as conical coil springs or cylindrical spring, but the present disclosure is not limited thereto. The spring  122  may be a flat wire coil spring, a round wire coil spring, or a wave spring, which will be described in more details below. 
       FIG. 8  is a perspective view of a rotor-side toothed disc unit  120 , according to an embodiment of the present disclosure. As shown in  FIG. 8 , rotor-side toothed disc unit  120  includes a tubular body  810  having a first surface  812  and a second surface  814 . A base  818  of tubular body  810  defines a hollow cavity  816  for mounting to hub axle  114  (not shown in  FIG. 8 ). On first surface  812 , a groove  820  extends along an axial direction of tubular body  810 . As shown in  FIG. 8 , in some embodiments, groove  820  separates an inner ring  830  and an outer ring  840  protruding from a base  818  of tubular body  810  along an axial direction of tubular body  810 . Inner ring  830  substantially surrounds hollow cavity  816  and outer ring  840  substantially surrounds inner ring  830 . 
     In the embodiment depicted in  FIG. 8 , an outer contour of outer ring  840  may form a non-round shape corresponding to an inner contour of the hub component, such as the hub body or a receiving ring fixed or attached to the hub body, so that the rotor-side toothed disc unit  120  can be inserted into the hub, guaranteeing a simple axial displacement while ensuring a non-rotatable arrangement of the rotor-side toothed disc unit  120  with respect to the hub body to provide the freewheel function. 
       FIG. 9  is a back view of a rotor-side toothed disc unit  120 , showing second surface  814  of rotor-side toothed disc unit  120 , according to an embodiment of the present disclosure. As shown in  FIG. 9 , multiple axial engagement components (e.g., toothings)  910  are arranged on base  818 , surrounding hollow cavity  816 , at surface  814 , which is the opposite surface to the surface  812  having groove  820  (not shown in  FIG. 9 ). In various embodiments, the rotor-side toothed disc unit  120  may be a structure with  90  toothings, or a structure with  60  toothings, but the disclosure is not limited thereto. As explained above, axial engagement components  910  of rotor-side toothed disc unit  120  correspond to the axial engagement components of hub-side toothed disc unit  118 , so that the toothed disc units  118  and  120  can be engaged with each other via the axial engagement components, or disengaged with each other based on the rotate direction to achieve the freewheeling function. 
       FIG. 10  is a cross-sectional view of a rotor-side toothed disc unit  120 , according to an embodiment of the present disclosure. As depicted in the figure, axial engagement components  910  are arranged on base  818  on one side, and inner ring  830  and outer ring  840  respectively protrude from base  818  on the other side. Accordingly, groove  820  in rotor-side toothed disc unit  120  may form a u-shaped cross section extending in a direction parallel to the axis directed toward the hub axle. 
     Particularly, groove  820  is defined by an inner sidewall  1020  surrounding hollow cavity  816 , an outer sidewall  1030  in facing relation to and spaced from inner sidewall  1020 , and a bottom surface  1010  that couples inner sidewall  1020  and outer sidewall  1030 . By providing groove  820  on rotor-side toothed disc unit  120 , a total weight of hub  100  can be reduced. In some embodiments, groove  820  can be formed by a mechanical etching process applied to tubular body  810 . For example, during manufacturing, a milling cutter may be used to remove a portion of tubular body  810  to form inner sidewall  1020 , outer sidewall  1030 , and bottom surface  1010  defining groove  820 . In some embodiments, a depth of groove  820  may be greater than or substantially equal to half of a height H 3  of base  818  along the axial direction (e.g., the direction toward hub axle  114 ). By this design, when the rotor-side toothed disc unit  120  is used with a round wire coil spring arranged partially within the groove  820 , the round wire coil spring can be securely located in the groove  820 , which prevents the spring from malfunctioning by, for example, rolling out from the groove  820 . In addition, with the groove  820  being configured to securely receive the round wire coil spring therein, the spring force can be distributed more evenly throughout the rotor-side toothed disc unit  120 , thereby preventing the misalignment of the rotor-side toothed disc unit  120 . 
     In addition, as shown in  FIG. 10 , a height H 1  of inner ring  830  is greater than a height H 2  of outer ring  840 , and is substantially equal to or greater than height H 3  of base  818 , but the present disclosure is not limited thereto. In some other embodiments, height H 1  of inner ring  830  can also be substantially equal to height H 2  of outer ring  840 . Alternatively stated, the height of inner sidewall  1020  may be greater than or substantially equal to the height of outer sidewall  1030 . In the design shown in  FIG. 10 , the greater height H 1  of inner ring  830  is able to provide a contact area between the inner ring  830  and the inner part of the round wire coil spring to support and align the spring properly, avoiding the misalignment of the rotor-side toothed disc unit  120  due to potential uneven spring force distribution. In addition, by reducing the height H 2  of outer ring  840  and removing extra portions of the outer ring  840 , the total weight of the hub structure can be further reduced. Moreover, in some embodiments, a thickness T 1  of outer ring  840  may be greater than a thickness T 2  of inner ring  830 . Alternatively stated, outer sidewall  1030  is thicker than inner sidewall  1020 . Accordingly, when the rotor-side toothed disc unit  120  is used with a flat wire coil spring that contacts the outer ring  840 , a contact area between the flat wire coil spring and the rotor-side toothed disc unit  120  may be greater to provide sufficient and even spring force to the rotor-side toothed disc unit  120 . 
       FIG. 11  is a perspective view of a positioning plate  124 , according to an embodiment of the present disclosure.  FIG. 12  is cross-sectional view of the positioning plate  124  shown in  FIG. 11 , according to an embodiment of the present disclosure. As shown in  FIG. 11  and  FIG. 12 , in some embodiments, positioning plate  124  also defines a groove  1110  extending along the axial direction (e.g., the direction toward hub axle  114 ). Groove  1110  may be defined by a bottom surface  1210 , an inner sidewall  1220  and an outer sidewall  1230  in facing relation to and spaced from inner sidewall  1220  by bottom surface  1210 . As shown in  FIG. 12 , in some embodiments, a height of the inner sidewall  1220  is substantially equal to a height of the outer sidewall  1230 , but the present disclosure is not limited thereto. For example,  FIG. 13  is a cross-sectional view of a positioning plate  124 , according to an embodiment of the present disclosure. For the positioning plate  124  of  FIG. 13 , a height of the outer sidewall  1230  may be greater than a height of the inner sidewall  1220 . In addition, in the embodiments of  FIG. 12  and  FIG. 13 , the inner sidewall  1220  is thicker than the outer sidewall  1230 , but the present disclosure is not limited thereto. In some other embodiments, outer sidewall  1230  may be thicker than inner sidewall  1220  or outer sidewall  1230  and inner sidewall  1220  may have the same thickness. 
       FIG. 14  illustrates a rotor-side toothed disc unit  120 , spring  122  and positioning plate  124 , according to an embodiment of the present disclosure. As shown in  FIG. 14 , spring  122  is attached between positioning plate  124  and rotor-side toothed disc unit  120 . In some embodiments, as shown in  FIG. 14 , spring  122  is attached to the bottom surface of the groove in rotor-side toothed disc unit  120 , is partially arranged within the groove at one end, and is attached to positioning plate  124  at the other end. In other words, at least a portion of spring  122  is arranged within the groove. In some embodiments, positioning plate  124  is mounted on or arranged within bearing unit  126  and is configured to position spring  122  to prevent undesired displacement of spring  122  causing misalignment between spring  122  and bearing unit  126 , which may result in damage to bicycle components or malfunction when a user is cycling. 
       FIG. 15  is a cross-sectional view of the rotor-side toothed disc unit  120  shown in  FIG. 14 , according to an embodiment of the present disclosure. As shown in  FIG. 15 , in some embodiments, a height of inner sidewall  1020  plus a height of inner sidewall  1220  is substantially equal to a height of outer sidewall  1030  plus a height of outer sidewall  1230 . Alternatively stated, when spring  122  is compressed, positioning plate  124  may be configured to abut inner ring  830  and outer ring  840  at the same time and cover spring  122  to avoid undesired shifting or misalignment of spring  122 . In some other embodiments, a height of outer sidewall  1030  plus a height of outer sidewall  1230  is greater than a height of inner sidewall  1020  plus a height of inner sidewall  1220 . Alternatively stated, when spring  122  is compressed, positioning plate  124  may be configured to abut only outer ring  840  while inner ring  830  and positioning plate  124  are spaced apart. 
       FIG. 16A  illustrates a hub-side toothed disc unit  118  and rotor-side toothed disc unit  120  engaged to each other, according to an embodiment of the present disclosure.  FIG. 16B  and  FIG. 16C  are two perspective views of the engaged toothed disc units  118  and  120  shown in  FIG. 16A , according to embodiments of the present disclosure. As shown in  FIGS. 16A-16C , in some embodiments, a height of inner sidewall  1020  of rotor-side toothed disc unit  120  may be substantially equal to a height of outer sidewall  1030  of rotor-side toothed disc unit  120 , forming a u-shaped cross section extending in a first direction parallel to the axial direction. 
     In addition, as depicted in  FIGS. 16A-16C , hub-side toothed disc unit  118  may also include a groove  1610  with groove  1610  forming a u-shaped cross section extending in the opposite direction of the first direction. As shown in  FIG. 16A , in some embodiments, a height of inner sidewall  1620  of hub-side toothed disc unit  118  may be substantially equal to a height of outer sidewall  1630  of hub-side toothed disc unit  118 . In other words, a height of the inner ring of hub-side toothed disc unit  118  may be substantially equal to a height of the outer ring of hub-side toothed disc unit  118 . In some embodiments, the hub-side toothed disc unit  118  and the rotor-side toothed disc unit  120  can be used interchangeably. Accordingly, the design of the rotor-side toothed disc unit  120  mentioned above can also be applied to the hub-side toothed disc unit  118 . 
     In some embodiments, a depth or a width of groove  1610  on hub-side toothed disc unit  118  may be different from a depth or a width of groove  820  on rotor-side toothed disc unit  120 . As shown in  FIG. 16A , for example, groove  1610  may be shallower and wider than groove  820 , but the present disclosure is not limited thereto. By providing groove  1610  on hub-side toothed disc unit  118 , a total weight of hub  100  can be further reduced. Similar to groove  820 , groove  1610  may be formed by a mechanical etching process applied to hub-side toothed disc unit  118 . 
       FIGS. 17A and 17B  illustrate a rotor-side toothed disc unit  120  and spring  122 , according to embodiments of the present disclosure. As shown in the embodiments of  FIG. 17A  and  FIG. 17B , spring  122  may be attached to surface  812  of tubular body  810  and not arranged within groove  820 . For example, in some embodiments, spring  122  may be a flat wire coil spring with a wire diameter d 1  greater than a width W 1  of groove  820 . The flat wire coil spring depicted in  FIG. 17A  and  FIG. 17B , for example, may be attached to an outer ring part or an inner ring part. In some embodiments, the flat wire coil spring is attached to the outer ring part with a greater thickness to increase the contact area between the rotor-side toothed disc unit  120  and spring  122 , to distribute the spring force more evenly throughout the rotor-side toothed disc unit  120  and to prevent the misalignment of the rotor-side toothed disc unit  120 . 
       FIG. 18A  and  FIG. 18B  illustrate a rotor-side toothed disc unit  120  and spring  122 , according to embodiments of the present disclosure. As shown in the embodiments of  FIG. 18A  and  FIG. 18B , in some embodiments, spring  122  is attached to bottom surface  1010  and at least a portion of spring  122  is within groove  820 . For example, in some embodiments, spring  122  may be a round wire coil spring with a wire diameter d 2  smaller than a width W 2  of groove  820 . 
     In some embodiments, the width W 2  of groove  820  is specifically designed to guarantee that the round wire coil spring, having a wire diameter d 2  smaller than the width W 2 , is applicable to provide proper spring force. Alternatively, a flat wire coil spring or a wave spring can be used in place of the round wire coil in some embodiments to provide a more suitable spring force. In some embodiments, the width W 2  of groove  820  is associated with the diameter and/or the thickness of the rotor-side toothed disc unit  120 . For example, the width W 2  may be in a range of ¼ to ⅔ of the thickness of the rotor-side toothed disc unit  120 . 
       FIGS. 19A and 19B  illustrate a rotor-side toothed disc unit  120  and spring  122 , according to embodiments of the present disclosure. Similar to  FIG. 17A  and  FIG. 17B , in the embodiments of  FIG. 19A  and  FIG. 19B , spring  122  may be attached to surface  812  of tubular body  810  and not arranged within groove  820 . For example, in some embodiments, spring  122  may be a wave spring with a wire diameter greater than a width W 3  of groove  820 . The wave spring depicted in  FIG. 19A  and  FIG. 19B , for example, may be attached to an outer ring part or an inner ring part. In some embodiments, the wave spring is attached to the outer ring part with a greater thickness to increase the contact area between the rotor-side toothed disc unit  120  and spring  122 , to distribute the spring force more evenly throughout the rotor-side toothed disc unit  120  and to prevent the misalignment of the rotor-side toothed disc unit  120 . 
     As used herein, the term “or” encompasses all possible combinations, except where infeasible. For example, if it is stated that a device, structure, or module may include A or B, then, unless specifically stated otherwise or infeasible, the device, structure, or module may include A, or B, or A and B. As a second example, if it is stated that a device, structure, or module may include A, B, or C, then, unless specifically stated otherwise or infeasible, it may include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C. 
     In the drawings and specification, there have been disclosed embodiments. It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system and related methods. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed system and related methods.