Abstract:
A spoked wheel is described that uses flexible spokes having a termination on each end that couple with a rim using nipples. The flexible spokes are supported mid-span by a hub flange cradle that transfers torque from the hub to the rim via two sub-spokes. The hub flange cradle determines whether a sub-spoke is tangential or radial. A plurality of spokes may be used on each side of the wheel.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of co-pending U.S. patent application Ser. No. 12/284,905, entitled “BICYCLE WHEEL HAVING FLEXIBLE SPOKES,” filed on Sep. 26, 2008, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates generally to a spoked wheel that includes a hub, a wheel rim, and a plurality of spokes that transfer torque from the hub to the rim. More specifically, the invention relates to a spoked wheel that uses flexible spokes. 
         [0003]    Performance bicycle wheels are a compromise between weight, and static and dynamic stability. While reducing weight, structural strength must be maintained. 
         [0004]    The spokes of a bicycle wheel and their lacing pattern determine the static and dynamic stability of the wheel. This is most important in rear wheels, because the spokes couple the driving torque from the hub to the wheel rim. Torque transfer must occur with maximum efficiency to maximize the energy exerted by a cyclist. 
         [0005]    A typical spoked wheel has a first set of spokes under tension on one side of the wheel, coupling the rim to a corresponding hub flange and a second set of spokes under tension on the opposite side of the wheel, coupling the rim with a corresponding hub flange. The two hub flanges are set at an axial distance from each other. When the wheel is viewed in section, the hub, spokes, and rim approximate a triangle. 
         [0006]    The spokes on the two sides of the wheel have a camber angle with respect to the median plane of the wheel. The camber angles relate to a wheel&#39;s dish. The angles cause the spoke tensioning to give rise to force components in a direction parallel to the axis of the wheel. Balancing the force components keeps the rim centered in the median plane. 
         [0007]    A rear wheel hub carries at one end a sprocket cassette which is part of the bicycle transmission (drive train) and requires axial space. The spokes set on the drive train side have camber angles that are smaller than the camber angles of the spokes on the opposite side. This requires the smaller camber angle spokes be tensioned more than the opposite side spokes that have greater camber angles in order to maintain the rim position in the median plane of the wheel. Different spoke camber angles may also appear in front wheels, where the hub may be occupied by a brake disk. However, most symmetrically dished front wheels carry less weight and do not have to deal with large torsional loads. 
         [0008]      FIG. 1  shows a partial section view of a prior art rear bicycle wheel  101 . The wheel  101  comprises a hub  103 , a sprocket cassette  105  coupled to the hub  103 , a rim  107  and tire  109 . The hub  103  is coupled to the rim  107  via A (drive train) spokes and B (non-drive side) spokes. The wheel&#39;s median plane M is orthogonal to the hub axis X midpoint. The A spokes located at the drive train hub flange  111  have a camber angle α with respect to the wheel&#39;s median plane M. The B spokes located at the non-drive side hub flange  113  have a camber angle β with respect to the wheel&#39;s median plane M. α is less than β. Each spoke is tensioned with a given tensile force. Corresponding tensile component vectors T A  and T B  are applied to opposite sides of the wheel  101 . The horizontal vector components T AO  and T BO  of T A  and T B  are in a direction parallel to the axis X. 
         [0009]    For wheels having an equal number of spokes on each side of the wheel, the horizontal vector components T AO  and T BO  must be balanced with one another. These forces maintain the rim  107  in the median plane M. However, the tensile force T A  must be greater than the tensile force T B  due to its smaller camber angle. The ratio between the tensile force T A  and T B  must be approximately equal to and opposite to the ratio of the sines of the camber angles α and β. This template applies to each pair of opposing spokes and as a sum with reference to the total tensile forces of the spokes on one side and the opposite side. 
         [0010]    Conventional spokes have at one end threads for engaging a nipple to couple the spoke to a rim, and at the other end an elbow and a head for coupling with a bore of a hub flange. Spokes are made of different types of materials and may be butted, with reduced thickness of the spokes at the center section. The nipple is used to adjust spoke tension. The nipple is usually located at the rim end of the spoke, but may be located at a hub flange. Spokes are usually circular in cross section, but may be flat or oval cross-sectioned to improve rotation aerodynamics. 
         [0011]    Most bicycle wheels on single rider bicycles have 28, 32 or 36 spokes, while wheels on tandem bicycles have 40 or 48 spokes. Wheels with fewer spokes have an aerodynamic advantage as the aerodynamic drag from the spokes is reduced. However, fewer spokes results in a larger section of the rim being unsupported, thereby requiring stronger rims. 
         [0012]    Conventional spoke lacing patterns that transfer torque from the hub to the rim for driven wheels, or wheels with drum or disc brakes, typically require a tangential lacing pattern. The spokes leave the hub at an angle close to 90° (tangential) or at various angles, and usually cross other spokes to the rim. 
         [0013]    Tangentially laced wheels transfer torque because one half of the spokes, called leading spokes, point in the direction of rotation, while the other half, called trailing spokes, point in the opposite direction. The leading and trailing spokes counteract each other when no torque is applied. When forward torque is applied during acceleration, the trailing spokes experience a higher tension while the leading spokes relax. The opposite occurs when braking, with leading spokes experiencing greater tension and trailing spokes relaxing. Leading and trailing spokes allow for the transfer of force in either direction, minimizing tension changes, and due to symmetry, allows the wheel to stay true regardless of the torque applied. 
         [0014]    Wheels which are not required to transfer significant amounts of torque from the hub to the rim may use radial lacing. In radial lacing, the spokes leave a hub flange at zero degrees without crossing another spoke. Radial lacing cannot adequately transfer torque because torque on the hub would induce a stress in the hub flange bore, spoke elbows and nipples, and rim, increasing the likelihood of failure in any one of them. Radial lacing increases the stress on the hub flange since spoke tension pulls straight at localized points. While radial lacing uses shorter spokes which minimize weight, it is offset by the need to use a stronger hub. However, radially-laced wheels are stiffer and more precise than other lacing patterns. 
         [0015]    A mix of radial and tangential lacing may be used on rear wheels with tangential lacing on the drive train side and radial lacing on the opposite side. Most of the torque is transferred by the drive train side of the hub while the opposite side stabilizes the wheel. A wrong-way, half-radial lacing may be used, with radial lacing on the drive train side and tangential lacing on the opposite side. This accounts for wheel dish, the drive train side spokes have greater tension and should not be burdened with transmitting drive torque. This design requires the hub to transmit torque from the drive train side to the opposite side. Many other lacing patterns exist. However, most are for aesthetic reasons. 
         [0016]    What is desired is a bicycle wheel that offers reduced weight while allowing for increased performance. 
       SUMMARY OF THE INVENTION 
       [0017]    The inventor has discovered that it would be desirable to have a light-weight high-performance bicycle wheel without the limitations imposed by conventional spoke designs. Embodiments teach a wheel using flexible spokes having a termination on each end that couple with a rim using nipples. The flexible spokes are supported mid-span by a hub flange cradle that transfers torque from the hub to the rim via two defined sub-spokes. The hub flange cradle determines whether a sub-spoke is tangential or radial. A plurality of spokes may be used on each side of the wheel. 
         [0018]    One aspect of the invention provides a bicycle wheel having flexible spokes. Bicycle wheels according to this aspect of the invention include a wheel rim having a predefined even number of spoke couplings along an inner circumference, the wheel rim further having a surface for attachment of a bicycle tire, flexible spokes having a length defined by two end terminations, wherein a termination couples with a spoke coupling, and a rotatable wheel hub comprising a hub body positioned approximately at a rotational center of the wheel rim, a left flange separated by a predefined axial distance along the hub body from a right flange, the left and right flanges extend radially outward toward the wheel rim from the hub body and have a radial edge, a left flange outer surface that converges towards the wheel rim spoke couplings and a right flange outer surface that converges towards the wheel rim spoke couplings, and means for securing a flexible spoke onto the left and right flange outer surfaces. 
         [0019]    Another aspect of the invention provides means for securing a flexible spoke. Securing means according to this aspect of the invention include a first cradle located on the outer surface of the left flange, and a second cradle located on the outer surface of the right flange, each cradle comprising a groove having two ends that open at a flange radial edge, a groove cross section configured to receive a flexible spoke, and a curve defined between the groove ends. 
         [0020]    Another aspect of the invention provides a wheel hub for a spoked wheel. Wheel hubs according to this aspect of the invention include a hub body, a left flange separated by a predefined axial distance along the hub body from a right flange, the left and right flanges extend radially from the hub body and have a radial edge, and a left flange outer surface that converges towards a wheel median plane which is orthogonal to a hub axis midpoint and a right flange outer surface that converges towards the wheel median plane, and means for securing a flexible spoke onto the left and right flange outer surfaces. 
         [0021]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a partial section view of a prior art rear bicycle wheel. 
           [0023]      FIG. 2  is an exemplary flexible spoke. 
           [0024]      FIG. 3  is a section view of the termination and nipple in  FIG. 2 . 
           [0025]      FIG. 4  is an exemplary axial view of a drive train side hub flange cradle and sub-spoke geometry. 
           [0026]      FIG. 5  is an exemplary hub. 
           [0027]      FIG. 6  is an exemplary cradle section view. 
           [0028]      FIG. 7  is an exemplary wheel embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    Embodiments of the invention will be described with reference to the accompanying drawing figures wherein like numbers represent like elements throughout. Before embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of the examples set forth in the following description or illustrated in the figures. The invention is capable of other embodiments and of being practiced or carried out in a variety of applications and in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
         [0030]    The terms “connected” and “coupled” are used broadly and encompass both direct and indirect connecting, and coupling. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
         [0031]    Embodiments of the invention teach a spoked wheel having a rim and a hub, and a plurality of flexible spokes that couple the hub to the rim based on tensegrity. Tensegrity refers to the integrity of structures as a synergy between balanced tension and compression components. Tension is continuous and compression is discontinuous such that continuous pull is balanced by equivalently discontinuous pushing forces. Embodiments use a plurality of flexible spokes on each side of a wheel and a hub having a corresponding number of cradles that may be located on the inner and/or outer surfaces of each hub flange. 
         [0032]      FIG. 2  shows an exemplary flexible spoke  201 . Each spoke  201  comprises a cable  203 , which may be of a synthetic material, and two end terminations  205 . An end termination  205  includes a region with surface flats  207  configured to receive a tool to prevent the cable  203  from twisting during wheel assembly and a threaded region  209  in matching correspondence with threads of a nipple  211  for coupling with a rim and for tension adjustment. The spoke  201  cable  203  may include an external jacket with modifications, such as a helical spiral  213 , tailored to eliminate Aeolian induced resonance modes and to enhance aerodynamic properties. Aeolian resonance, or vibration, is the result of vortex shedding that creates an alternating pressure imbalance. If an external jacket modification is employed, a predefined region C where the spoke  201  is supported by a hub flange cradle remains unmodified. 
         [0033]      FIG. 3  shows a section view of the termination  205  and nipple  211 . Each termination  205  has a terminal  301  having a hollow, expanding interior cavity  303 . The terminal  301  may be made from hard-coated aluminum, titanium, stainless steel, or other material compatible with the cable  203 . The terminal  301  may be treated to avoid galvanic corrosion, or corrosion, for example, between metal and carbon. 
         [0034]    For composite cables  203 , the individual cable fibers pass into the terminal  301  through an aperture  304  and a high-performance resin  305  is infused into the terminal interior cavity  303 . The resin encapsulates and bonds each individual fiber strand to each other, to the inside surface of the cavity  303 , and to a cone-shaped plug  307  made from compatible materials with its wider end at the terminal  301  end. The result after curing is a spoke  201  cable  203  end entrapped within the terminal  301 . The plug  307 , which may be a cone or truncated cone, uses wedge mechanics to increase holding power. The terminal  301  interior  303  geometry conforms to the cone-shaped plug  307  outside geometry, and as tension on the cable  203  increases, the compression load of the plug increases, gripping the individual fibers and distributing the compressive force evenly over the full length of the fiber bundle. 
         [0035]    Cables  203  made from high modulus fibers are typically stronger than equivalent size wire cable and have a higher fatigue resistance over steel cable. Depending on the fiber and construction, the core strength member may be designed to be 4 to 7 times lighter than the size and strength equivalent wire cable. Each fiber type has unique characteristics and may be selected depending upon the application. Fiber types include Ultra High Molecular Weight Polyethylene (UHMWPE), also known as High-Modulus Polyethylene (HMPE) or High-Performance Polyethylene (HPPE), Liquid Crystal Polymer (LCP) fiber, Aramid, Polybenzobisoxazole (PBO), Polyester, Polyamide, and others. Synthetic cables offer greater strength-to-weight ratios, lower coefficients of thermal expansion, and higher moduli of elasticity than conventional steel components. 
         [0036]    The cable  203  fibers may be formed as parallel fiber cables, twisted strand fiber cables, single braid fiber cables, double braid fiber cables, and other configurations, depending on the strength, allowable elongation, and bending radius. The cable  203  may be coated or jacketed  309  for protection. The jacket  309  may include external modifications to obviate Aeolian induced resonance and improve wheel aerodynamics. 
         [0037]      FIG. 4  shows a hub  401  flange  403 α spoke  201  cradle geometry.  FIG. 5  shows a hub  401  side view (without cassette) showing left and right hub flanges  403 α,  403 β and inner  501 α,  501 β, outer  503 α,  503 β and radial edge  505 α,  505 β surfaces. The complete hub  401 , or various hub components (body, flanges, bearing races, bearing seats, and others) may be made from hard-coated aluminum, titanium, stainless steel, or other material compatible with the cable  203 . The spoke  201  terminals  205  couple with nipples  211 , which couple the spoke  201  to a rim at two different rim locations. Each spoke  201  is supported by a hub flange  403 α,  403 β cradle c  405 ,  407  at a predetermined region C. The C region effectively separates each spoke  201  into two sub-spokes  409   1 ,  409   2 ,  409   3 . Each sub-spoke has a predetermined geometry with respect to the hub axis X, defined by a cradle c  405 ,  407 . As in conventional wheels, the sub-spokes  409   1 ,  409   2 ,  409   3  may be oriented radially, tangentially, or as a combination. 
         [0038]      FIG. 4  shows two sub-spoke orientations. Radial lacing is defined by a sub-spoke  409   1 ,  409   2  that enters the hub flange  403 α perpendicular  411  to a hub tangent. A cradle  405  may be machined, molded or forged in the hub flange  403 α inner  501 α or outer  503 α surface.  FIG. 6  shows a section view of a cradle. A cradle is a groove having a predefined curve, and length with a load bearing curved surface  603  profile  601  sized in matching correspondence with a spoke  201  cable  203 ,  409   1  diameter. The cradle curve for two radial sub-spokes  409   1 ,  409   2  may be a radius. The cradle groove  601  allows for the spoke  201  to fall into the hub flange  403 α during assembly, but is captured after all wheel spokes  201  are tensioned. 
         [0039]    Each hub flange  403 α,  403 β has a predetermined camber angle α and β as defined by the hub  401  width, hub flange  403 α,  403 β effective diameter, sub-spoke length and rim height  107  geometry. The camber angles α and β are approximately parallel with the sub-spokes and result in a hub flange  403 α,  403 β having a hollow cone shape and having inner  501 α,  501 β and outer  503 α,  503 β surfaces at the camber angles α and β. 
         [0040]    For sub-spokes entering a hub flange at an angle that is not perpendicular  413  to a hub tangent, a cradle  407  may have a curve and length defined by, for example, a Bézier curve. A Bézier curve is a parametric curve used to model smooth curves. Quadratic and cubic Bézier curves may be used and are suited for Computer Numerical Control (CNC) machining. A non-radial cradle  407  may be configured to support two non-radial sub-spokes, or a combination of a radial sub-spoke  409   1  and a non-radial sub-spoke  409   3 , or two non-radial sub-spokes. The non-radial sub-spokes function as leading and trailing spokes. The non-radial sub-spoke  409   3  in  FIG. 4  functions as a trailing spoke. 
         [0041]      FIG. 7  shows an exemplary rear wheel  701  comprising a hub  401 , four spokes  201  per wheel side and a rim  107 . One skilled in the art recognizes that a number of different spoke arrangements with corresponding cradle curves and lengths may be practiced. For example, a wheel may employ more spokes on the drive train side than the opposite side and have different radial and non-radial sub-spoke arrangements. The complete wheel  701  may be laterally trued (eliminating local deviations of the rim  107  to the left or right of center M), vertically trued (eliminating local deviations of the wheel radius (the distance from the rim to the center of the hub)), and dish centered (centering the rim plane M between the outside ends of the hub  401 ). The dish may be symmetrical on a front wheel. On a rear wheel, dish will be asymmetrical to accommodate the drive train cassette. 
         [0042]    Two A side spokes use non-radial/radial cradle curves  407  on the external surface of the A side hub flange  403 α (shown solid). The other two A side spokes use non-radial/radial cradle curves  407  on the internal surface of the A side hub flange  403 α (shown broken). Similarly, two B side spokes use non-radial/radial cradle curves  407  on the external surface of the B side hub  401  flange  403 β (shown broken) and the other two B side spokes use non-radial/radial cradle curves  407  on the internal surface of the B side hub  401  flange  403 β (shown broken). Unlike conventional hub-spoke attachments which are typically apertures through a flange perpendicular with the hub body, and localize spoke head-elbow load at one point, the cradles c distribute spoke  201  load C over the entire cradle curve length. 
         [0043]    The exemplary wheel  701  pairs an A side sub-spoke with a B side sub-spoke. Each pair comprises a radial and non-radial sub-spoke meeting at the rim  107  at approximately the same location. If a rim has sufficient width, or by use of a connection element (not shown), the A side sub-spoke and B side sub-spoke may be connected to the rim substantially at the same point effecting a triangle vertice. The connection element may be configured to simultaneously tension the A side sub-spoke/B side sub-spoke pair. 
         [0044]    In a variant of the wheel  701 , the A side hub flange  403 α may be indexed clockwise or anti-clockwise with respect to the B side hub  401  flange  403 β, further separating the A sub-spokes from the B side sub-spokes at the rim  107 . 
         [0045]    One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.