Abstract:
A golf club having a hollow shaft whose flexibility is altered by rotating the club handle. Change in flexibility results from change in tension on a wire coinciding with the shaft longitudinal axis. The wire is attached between a longitudinally movable assembly in the handle and a fixed assembly at the shaft lower end. The movable assembly includes outer and inner tension tuner members, a collar, a clamp and bifurcated collet, and outer and inner twist-prevention housings.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims benefit of priority of U.S. Provisional Patent Application Ser. No. 60/170,772, entitled “Adjustable Flexibility Golf Club Shaft,” filed on Dec. 15, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to golf clubs, and more particularly to a wood or iron having a shaft whose flexibility can be incrementally increased or decreased while playing or practicing. 
     2. Description of the Related Art 
     A golf swing is a set of highly complex body movements requiring precise coordination of the hands, arms, shoulders, torso, hips, legs and knees, occurring in proper sequence. As the body coils and then uncoils, power is transferred from the body through the arms and wrists to the club grip, along the shaft, into the clubhead, and into the ball. 
     In a full range of motion swing, the position of the leading arm (i.e., the left arm of a right-handed golfer, or the right arm of a left-handed golfer) is critically important. The backswing is performed as a unitary motion, the entire front side of the body moving together as the knees, hips, trunk and shoulders are rotated, with the leading arm pushing the trailing arm back, and the leading elbow and arm remaining straight. To achieve the broadest possible swing arc, the club is swung straight back from the ball, without breaking the wrists, for as long as the turning of the shoulders and hips will allow. The golfer tries to keep the clubface square to the target line for as long as possible without turning the hands and wrists under, and also tries to keep the leading arm and club in a straight line until the momentum of the swinging clubhead causes the wrists to begin cocking naturally as they reach about hip height. The angle between the hands and shaft is maintained, with the trailing arm bending at the elbow and the leading arm remaining straight. The one-piece motion forces the shoulders to turn from the very beginning of the backswing and ensures they will go on turning until the top of the swing is reached. As the arms stretch and turn, the hips are also forced to turn. At the top of the backswing, the shoulders have turned about twice as far as the hips, the leading arm is straight, and the forearms have rotated. The leading forearm is pronated, i.e., rotated clockwise for a right-handed golfer or rotated counterclockwise for a left-handed golfer, and the trailing forearm is supinated, i.e., rotated counterclockwise for a right-handed golfer or rotated clockwise for a left-handed golfer, causing cocking of the wrists with the shaft generally perpendicular to the leading forearm. Ideally, the back of the leading hand, the wrist and the forearm are in a straight line, with the shaft parallel to the ground and to the target line, and the clubhead pointing toward the target. 
     As the arms reach their fullest extension and the weight of the clubhead causes the wrists to attain their maximum cocking but before the hands reach their highest level or the shoulders finish turning, the lower torso, hips, legs and feet already have initiated the downswing. The golfer pushes hard off the inside of the back foot, throwing weight to the inside of the front foot. The front knee is pulled laterally toward the target and is well forward of the ball before the hands have descended even a few inches. The wrists are kept cocked and the head is kept back behind the ball. The club is pulled into action by the uncoiling of the body and leading arm. Because of the movement of the lower body toward the target and the delay in uncocking the wrists, the arc traversed by the clubhead on the downswing is steeper than the arc on which the clubhead was taken back. 
     In the hitting zone the hips, which were moving laterally in the same forward direction as the knees, begin to turn with respect to the target line. By turning, the hips “clear” a path for the arms to swing past the body. The thrusting legs and hips, by forcing the shoulders to turn, accelerate the arms and club. Just before impact, a point is reached where no further acceleration is possible and, because of centrifugal force, the club must be released into the ball. At that point, the wrists are forced to uncock spontaneously. 
     As the wrists uncock and the back arm starts to straighten, the fully released clubhead whips toward the ball. At impact, the back of the leading hand faces the target, and the leading arm and shaft form a straight line so that the leading hand and arm are slightly ahead of the ball. As the clubhead swings through the ball toward the target, the leading arm is kept straight and moves directly toward the target. The golfer must avoid any independent turning or twisting of the club with the hands and wrists. 
     The release phase is entered just after impact. The trailing arm straightens, but there is no breaking down of the leading arm at the wrist or elbow. Nor is there independent rolling, turning or twisting of the hands, wrists or forearms, until the momentum of the club, combined with the turning body, forces the body to turn and swing to the opposite side of the target line. The leading arm is supinated and the trailing arm is pronated, the forearms being opposite to their rotational position at the top of the backswing. 
     As millions of golfers can attest, it is difficult to meld the separate motions comprising a full range of motion swing so as to achieve impact with the clubface generally square to the ball while the clubhead is moving at a high rate of speed. The present invention entails increasing clubhead speed by flexing the shaft to impart to potential energy additional to that accumulated during the backswing, which is converted into extra clubhead kinetic energy in the hitting zone and at impact. 
     Golf clubs having shafts with modifiable flexure are disclosed in the related art. U.S. Pat. No. 2,992,828 to W. A. Stewart discloses a club having a hollow shaft which is prestressed so as to remain relatively straight during the backswing and downswing, compared to a conventional shaft. In one embodiment a wire inside the shaft and adjacent to the leading edge is maintained under tension between plugs at the top and bottom ends of the shaft. The upper plug receives a bolt which when rotated causes the plug to act as a nut and travel upwardly on the bolt, increasing tension in the wire and thereby compressing the shaft leading edge. Tightening the wire tends to bow the shalt in a direction opposite to the direction the shaft would normally bend on the downswing. The wire is not tensioned sufficiently to bow the shaft but just enough to prestress the shaft or apply a bending stress in a direction opposite to the bending stress applied to the shaft during the downswing. In another embodiment an elongated column member extending the length of the shaft between upper and lower plugs has its trailing edge compressed by screwing a bolt down through the upper plug. This puts tension on the trailing side of the shaft, inducing a bending stress in the shaft opposite to the downswing bending stress. 
     U.S. Pat No. 4,685,682 to J. T. Isabell discloses a golf club connected to a mechanism which increases or decreases shaft flexibility by varying the tension in a wire extending between the handle and clubhead. The wire is offset from the shaft by a bridge which maximizes the effect of small changes in wire tension provided by movement of a threaded connection between the wire and clubhead. Increasing the tension in the mechanism decreases shaft flexibility; decreasing the tension increases flexibility. The device is used to determine the degree of shaft flexibility which maximizes an individual golfer&#39;s clubhead speed at impact, so that a set of clubs can be made that have the same flex characteristics. 
     U.S. Pat. No. 5,865,688 to S. W. Bae discloses a golf club having three flex points along its shaft. At each point, the shaft diameter expands to permit the shaft to flex at that point. When the club is swung, the shaft flexes from a high flex point (i.e., a location proximate to the handle) to a mid flex point to a low flex point (i.e., a location proximate to the clubhead). 
     U.S. Pat. No. 5,931,744 to L. E. Hackman discloses a method for reducing the stiffness of a hollow golf club shaft divided into three segments with each pair of segments connected by cone-shaped bands. The stiffness is changed by slicing or abrading the inner surface of the sidewall which typically is made from a flexible matrix material such as an epoxy, in which elongated, high strength graphite fibers are embedded. Most of the fibers are arranged longitudinally to provide strength and stiffness to resist bending of the shaft. Severing or removing selected fibers reduces the longitudinal stiffness. 
     None of these references address the problem of providing a golf club whose shaft easily can be made more or less flexible so that a golfer can determine through experimental trial which degree of flexibility best suits his particular full range of motion swing. 
     OBJECTS OF THE INVENTION 
     In view of the limitations of the related art, it is an object of the present invention to provide a golf club incorporating a device which allows a player to easily increase or decrease shaft flexibility when playing or practicing. 
     Another object of the invention is to provide a golf club whose shaft flexibility is adjustable with the adjustment calibrated so that any particular state within a range of flexibility can be accurately reproduced. 
     A further object of the invention is to provide a golf club whose shaft imparts kinetic energy to the clubhead in the hitting zone and at impact, additional to that generated in the downswing of a conventional club. 
     Yet another object of the invention is to provide a device altering shaft flexibility which is reliable to operate, inexpensive to manufacture, and readily adaptable to any club having a hollow shaft and clubhead. 
     Other objects of the invention will become evident when the following description is considered with the accompanying drawing figures. In the figures and description, numerals indicate the various features of the invention, like numerals referring to like features throughout both the drawings and description. 
     SUMMARY OF THE INVENTION 
     These and other objects are achieved by the present invention which in one aspect provides a golf club including a handle with a cavity rotatably connected to a hollow shaft upper portion symmetric about a longitudinal axis. The club further includes a hollow flexible shaft central portion attached to the shaft upper portion and a hollow shaft lower portion both symmetric about the axis. The club further includes means for altering the tension on a metallic wire disposed along the axis whose upper end is longitudinally adjustable within the handle cavity, and whose lower end is attached to the shaft lower portion at its lower end. 
     In another aspect the invention provides a golf club including a handle having a cap portion and a rotatable grip upper portion with a cylindrical interior surface determining a cavity. The club further includes: an upper wire-end retainer assembly including a cap-shaped outer tension tuner member having a cylindrical outer surface attached to the grip upper portion and an internal thread; a cylindrical collar having an outer surface and an internal thread which extends upwardly in a cylindrical inner tension tuner member having an external thread in threaded combination with the internal thread of the outer tension tuner member, and an internal thread; a cylindrical outer twist-prevention housing having an upper portion with a polygonal bore and an external thread in threaded combination with the collar internal thread; an inner twist-prevention housing having a central portion with a polygonal cross-section disposed between a cylindrical upper portion having a bore and an external thread smoothly slidable within the bore of the inner tension tuner member and a cylindrical lower portion with an external thread, with the central portion of the inner twist-prevention housing closely received within the polygonal bore; a cap-shaped clamp having an internal thread in threaded combination with the external thread of the inner twist-prevention housing, with the clamp tightening a bifurcated collet having opposed jaws received within the bore of the inner twist-prevention housing upper portion. The outer tension tuner member, cap-shaped clamp, collet, collar, inner tension tuner member, outer twist-prevention housing upper portion, and inner twist-prevention upper portion are received within the cavity, and the retainer assembly moves longitudinally within the cavity when the handle is rotated. 
     The club further includes: a hollow inflexible shaft upper portion, symmetric about a longitudinal axis and covered by a grip lower portion, into which the outer and inner twist-prevention housings extend; a hollow flexible shaft central portion, symmetric about the axis and attached to the shaft upper portion; and a hollow inflexible shaft lower portion attached to the shaft central portion and symmetric about the axis. 
     The club further includes a lower wire-end retainer assembly including a cylindrical sleeve extending in a cylindrical flange, and a ring received within the flange. The flange is rigidly attached to the shaft lower portion at its lower end. 
     The club further includes a metallic wire having opposed upper and lower ends disposed along the axis. The upper end is clamped between the collet jaws, and the lower end is attached to the ring. Moving the upper wire-end longitudinally alters the tension on the wire. 
     A more complete understanding of the present invention and other objects, aspects and advantages thereof will be gained from a consideration of the following description of the preferred embodiment read in conjunction with the accompanying drawings provided herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a golf club with a hollow shaft and clubhead according to the invention. 
     FIG. 2 is a longitudinal sectional view of the FIG. 1 club showing a longitudinally adjustable upper wire-end retainer assembly, a fixed lower wire-end retainer assembly, and a tension wire along the shaft longitudinal axis passing through and centered by six wire support members and clamped between the two assemblies. 
     FIG. 3 is a greatly enlarged sectional view taken along line  3 — 3  in FIG. 1 showing the FIG. 2 lower wire-end retainer assembly including a flanged sleeve and a ring, and the wire lower portion and two lowermost support members. 
     FIG. 4 is an exploded perspective view of the FIGS. 2,  3  lower wire-end retainer assembly, and a partial sectional view of the shaft lower portion. 
     FIG. 5 is an exploded perspective and partial sectional view of the FIG. 1 club handle and upper wire-end retainer assembly, the assembly including a cap-shaped outer tension tuner member, a cap-shaped collet clamp, a bifurcated collet, an inner twist-prevention housing, a collar extending upwardly in an inner tension tuner member, an outer twist-prevention housing, and a stop nut. 
     FIG. 6 is a greatly enlarged sectional view taken along line  6 — 6  in FIG. 1 showing the upper wire-end retainer assembly in its lowermost position resulting in minimum wire tension. 
     FIG. 7 shows the same view as FIG. 6 when the upper wire-end retainer is in its uppermost position resulting in maximum wire tension. 
     FIG. 8 shows one of a plurality of wire support members which is generally spherical and has therethrough a diametral bore. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While the present invention is open to various modifications and alternative constructions, the preferred embodiment shown in the drawings will be described herein in detail. It is to be understood, however, there is no intention to limit the invention to the particular form disclosed. On the contrary, it is intended that the invention cover all modifications, equivalences and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims. 
     Where used herein, the word “connected” means that the two parts referred to (e.g., an external thread and a nut, or the mating of external and internal threads) can be readily separated after being joined together in an interlocking combination. Where used herein, the words “attached” and “attachment” mean that the two parts referred to are either fabricated in a single piece, or glued, clamped or crimped together. However, other forms of attachment may be suitable, consistent with simplicity of manufacture and reliability of operation. 
     Referring to FIGS. 1 and 2, a golf club  10  includes a rotatable handle  12  including a cap portion  13  and a grip upper portion  14  having a generally cylindrical interior surface  14 A and a textured symmetrically tapering exterior surface  14 B, the interior surface and cap portion determining a generally cylindrical cavity  16 . Club  10  further includes a hollow inflexible, downwardly tapering shaft upper portion  18  covered by a grip lower portion  20  having a textured symmetrically tapering exterior surface  20 B, a hollow flexible, downwardly tapering shaft central portion  22 , a hollow clubhead  24  (not part of the invention), and a hollow inflexible shaft lower portion  26  extending into and rigidly attached at an end  26 E to the clubhead. The handle and shaft upper, central and lower portions are symmetric about a common longitudinal axis. Cap portion  13  and grip portions  14  and  20  are conventionally made of a vulcanized rubber. Disposed along and within the shaft upper, central and lower portions is a plurality of wire support members  28 A,  28 B,  28 C,  28 D,  28 E,  28 F, progressively downwardly smaller in size, each of which is generally spherical and has therethrough a diametral bore  30  (see FIG.  8 ). Preferably, the number of support members is six; alternatively, five or seven members can be used. Alternatively, the members can be conical frustums sized to match the shaft&#39;s internal taper. The support members are fabricated from a low friction coefficient material such as a synthetic resinous fluorine-containing polymer or a polyvinyl chloride (PVC) and are rigidly attached to the shaft upper, central and lower portions, preferably adhesively, so that each bore is aligned with the longitudinal axis. 
     Referring to FIG. 2, a tension wire  32  is clamped at opposed upper and lower ends  32 U,  32 L to, respectively, an upper wire-end retainer assembly  34  closely received within the cavity  16 , and a lower wire-end retainer assembly  36  closely received within and rigidly attached to the shaft lower portion end  26 E. As best shown in FIGS. 3 and 6, the wire  32  is threaded through each bore  30  so that the wire is constrained to be disposed along the longitudinal axis. The bores are sized to closely receive but not frictionally interfere with the wire. Preferably, the wire is made from a stainless steel having a Rockwell hardness in the range 40-70, and has a constant diameter in a range from 0.060- to 0.090-inch. Alternatively, the wire is made from a carbon steel having a Rockwell hardness in the range 40-75 with a constant diameter in a range from 0.031- to 0.064-inch, or from tungsten having a Rockwell hardness in the range 75-80 with a constant diameter in a range from 0.031- to 0.055-inch. 
     Referring to FIGS. 3 and 4, lower wire-end retainer assembly  36  includes a generally cylindrical sleeve  40  extending in a generally cylindrical flange  42 , the sleeve and flange having therethrough a common bore  44 . A generally circular ring  46  is closely received within the flange. After inserting wire-end  32 L through the sleeve and into the ring and flange, the wire-end is rigidly attached to the retainer assembly by crimping the ring which, with the wire under tension, is disposed within the flange and constrained upwardly by the relatively narrow diameter sleeve. Flange  42  is rigidly attached to inner wall  26 W of lower shaft portion  26  at end  26 E, thereby providing additional structural integrity to the shaft-clubhead juncture. 
     Referring to FIGS. 5 and 6, the upper wire-end retainer assembly  34  includes a cap-shaped outer tension tuner member  50  having an internal thread  52  and an outer surface  50 S, a cap-shaped collet clamp  54  having an internal thread  56 , a bifuracted collet  58  having jaws  60 A,  60 B with generally planar inner faces  62 A,  62 B, respectively, and an inner twist-prevention housing  64  having a central portion  66  with a polygonal cross-section disposed between a generally cylindrical upper portion  70  with a bore  70 B and an external thread  72 , and a generally cylindrical lower portion  74  with an external thread  76 . Wire  32  is rigidly attached to the assembly  34  when wire-end  32 U is gripped between faces  62 A,  62 B with the collet  58  received within the bore  70 B and the clamp screwed onto member  62  by engaging threads  56  and  72 . As shown in FIG.  5 , handle  12  has a circumferential lower edge  12 E proximate to which are ten embossed numerical indicia “0, 1, 2, 3, 4, 5, 6, 7, 8, 9” evenly spaced around the circumference. Handle  12  is adhesively attached to surface  50 S so that when the handle is rotated through a preselected angle the tuner member  50  also rotates through that angle. As shown in FIGS. 5,  6  and  7 , cap portion  13  has therethrough an air release hole  13 H to allow air to escape from the hollow club  10  when the club is assembled. 
     Referring again to FIGS. 5 and 6, assembly  34  further includes a generally cylindrical collar  80  having an outer surface  80 S adhesively attached to grip upper portion  14  and an internal thread  82 . Collar  80  extends upwardly in a generally cylindrical inner tension tuner member  84  having an external thread  86  and a smooth bore  88 . Assembly  34  further includes a generally cylindrical outer twist-prevention housing  90  having an upper portion  92  with a polygonal bore  94  therethrough and an external thread  96 . Bore  94  closely receives central portion  66  of housing  64 ; member  50  is screwed onto member  84  by engaging threads  52  and  86 ; the lower portion of thread  72  is smoothly slidable within bore  88 ; and member upper portion  92  cooperates with collar  80  through engagement of threads  82  and  96 . A stop-nut  100  is screwed onto thread  76 . 
     Referring to FIGS. 6 and 7, when handle  12  is rotated, outer tension tuner member  50  moves through the same angle as does inner tension tuner member  84 . Thread pairs ( 52 ,  86 ) and ( 56 ,  72 ) are right-handed while thread pair ( 82 ,  96 ) is left-handed, so rotating the handle clockwise causes the entire upper wire-end retainer assembly  34  to translate upwards, thereby increasing the tension on wire  32 , while the wire is protected from being twisted by the interaction of housings  64  and  90 . Conversely, rotating the handle counterclockwise causes assembly  34  to translate downwards, decreasing the wire tension. Preferably, the pitch of the thread pairs is such that assembly  34  moves about  1 . 75  mm for one complete rotation of handle  12 . 
     Referring to FIG. 5, grip lower portion  20  terminates upwardly in a shoulder  102  on which is embossed a vertical index  102 V and upper, middle and lower horizontal indices  102 A,  102 B,  102 C, respectively. Index  102 V allows precise alignment with one of the numerical indicia proximate to edge  12 E so a desired shaft flexibility can be reproduced. As shown in FIGS. 6 and 7, shoulder  102  mates with a shoulder  104  in grip upper portion  14  proximate to edge  12 E. FIG. 6 shows assembly  34  when the handle is rotated fully counterclockwise so the assembly is at its extreme downward position where the shoulders mate. In this position, edge  12 E touches lower index  102 C. FIG. 7 shows the assembly when the handle is rotated fully clockwise so the assembly is at its extreme upward position where the shoulders  102 ,  104  are at maximum separation. In this position, edge  12 E touches upper index  102 A. Stop nut  100  prevents the handle from being rotated too far. 
     Increasing the tension of wire  32  causes the shaft central portion  22  to flex more on the backswing than it otherwise would, storing additional potential energy as the top of the swing is reached. During the downswing this energy is converted into kinetic energy, a process analogous to releasing a bow-string to propel an arrow. This kinetic energy is imparted to the clubhead, resulting in a more powerful impact, compared to using a conventional club, as the clubhead contacts the ball.