Abstract:
The invention provides an insert for a golf club shaft that stiffens and strengthens the tip of the shaft and reduces oscillations in the shaft during the swing of the club and dampens vibrations due to impact with the golf ball and/or the ground. In preferred embodiments, the insert comprises a rod portion that increases stiffness and foam and adhesive portions that dampen vibration.

Description:
[0001]     This application claims priority to provisional patent application Nos. 60/762,181 filed Jan. 25, 2006, and 60/703,496 filed Jul. 28, 2005, both titled GOLF CLUB TIP INSERT. 
     
    
     FIELD  
       [0002]     This invention relates to the field of golf equipment. More particularly, this invention relates to a tip insert for a golf club shaft.  
       BACKGROUND  
       [0003]     When a golf club strikes a golf ball, a considerable amount of impact force is transferred from the club head to the tip of the shaft. Immediately prior to ball impact during the downswing, the shaft has a tendency to oscillate up and down. If the stiffness of the tip of the shaft is not sufficient, oscillations of as much as ±1.5 inches at the toe of the club head can occur which will severely impact shot accuracy. Wedges are particularly prone to faulty hits due to toe up/down oscillations.  
         [0004]     The swing of the club and the impact with the ball can also induce high frequency vibration modes in the shaft. When the club face impacts the ball at an off-center position, high frequency vibrations can be induced at the grip of the club. Such vibrations are not only uncomfortable to the golfer, but they can also have a detrimental effect on the desired transfer of force from the club head to the ball.  
         [0005]     What is needed, therefore, is means for stiffening the tip section of the club shaft and dampening shaft vibration, while also providing additional strength to the tip section of the golf club shaft.  
       SUMMARY  
       [0006]     These and other needs are met by a golf club having a substantially cylindrical shaft with a proximal shaft end, a distal shaft end, and a distal hollow region disposed adjacent the distal shaft end. The golf club includes a club head having a hosel for receiving the distal shaft end. The hosel has an exit point and an overlap region wherein the hosel and the distal hollow region of the shaft overlap each other. A shaft insert is disposed within the distal hollow region of the shaft. The shaft insert includes a rod portion and one or more spacers for substantially centering the rod portion within the distal hollow region of the shaft.  
         [0007]     In some preferred embodiments, the rod portion is formed from aluminum, titanium, fiberglass or graphite composite, and the one or more spacers are formed of a resilient polymeric foam material or flowable adhesive surrounding the rod portion. The spacers of the shaft insert may comprise one or more strips of compliant material disposed between an outer surface of the rod portion and an inner surface of the distal hollow region of the shaft. The strips may be spaced apart radially about the outer surface of the rod portion and disposed substantially parallel to an axial centerline of the rod portion and may be continuous or segmented, or the strips may be in the shape of a helix wrapping around the rod portion or continuous around the circumference of the insert tube.  
         [0008]     Preferably, a distal end of the rod portion of the shaft insert is disposed adjacent the distal shaft end or within the overlap region of the hosel. In some preferred embodiments, shaft insert is positioned so that the exit point of the hosel falls between the distal and proximal ends of the rod portion of the shaft insert.  
         [0009]     In one embodiment, the invention provides a golf club having a shaft and a shaft insert. The shaft has proximal and distal ends between which are a plurality of tubular sections each having an inner surface with a diameter that is different from the other tubular sections. The tubular sections of the shaft include a first tubular section having a first inner diameter and a second tubular section having a second inner diameter which is less than the first inner diameter. The second tubular section is disposed closer to distal end of the shaft than is the first tubular section. The shaft insert is disposed at least partially within the first and second tubular sections of the shaft. The shaft insert includes a rod portion, a tubular resilient portion and one or more spacers. The rod portion has an outer rod surface with an outer rod diameter, a distal rod end, a proximal rod end, a distal rod region disposed adjacent the distal rod end and a proximal rod region disposed adjacent the proximal rod end. The tubular resilient portion is disposed between the outer rod surface of the proximal rod region and the inner surface of the first tubular section of the shaft. The one or more spacers of the shaft insert are disposed between the outer surface of the distal rod region and the inner surface of the second tubular section of the shaft.  
         [0010]     In another embodiment, the invention provides a shaft insert for a golf club, wherein the golf club has a substantially cylindrical shaft with a proximal shaft end disposed adjacent a grip of the golf club, a distal shaft end disposed adjacent a club head of the golf club, and a distal hollow section disposed adjacent the distal shaft end. The distal hollow section of the shaft is defined by an inner shaft diameter. The shaft insert includes a rod portion that is configured to be inserted into the distal hollow section of the shaft. The shaft insert also includes means for substantially centering the rod portion within the distal hollow section of the shaft when the rod portion is inserted therein.  
         [0011]     In another aspect, the invention provides a method for installing a shaft insert in a substantially cylindrical hollow shaft of a golf club, where the shaft has a proximal shaft end, a distal shaft end and a distal hollow region disposed adjacent the distal shaft end. The shaft insert has a proximal insert end and a distal insert end. The method includes the steps of: (a) swabbing an adhesive material inside the distal hollow region of the shaft; (b) inserting the distal insert end into the proximal shaft end; (c) pushing the shaft insert toward the distal shaft end until the distal insert end is adjacent the distal shaft end; (d) removing any excess adhesive material that exits the distal shaft end; and (e) curing the adhesive material within the shaft. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Further advantages of the invention are apparent by reference to the detailed description in conjunction with the figures, wherein elements are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein:  
         [0013]      FIG. 1  depicts a shaft insert positioned relative to a hosel of a golf club head according to a preferred embodiment of the invention and  
         [0014]      FIG. 2  depicts a golf club shaft according to a preferred embodiment of the invention;  
         [0015]      FIG. 3  depicts a shaft insert according to a preferred embodiment of the invention;  
         [0016]      FIG. 4  depicts the shaft insert of  FIG. 3  assembled into a golf club shaft according to a preferred embodiment of the invention;  
         [0017]      FIG. 5  depicts a shaft insert according to an alternative embodiment of the invention;  
         [0018]      FIG. 6  depicts the shaft insert of  FIG. 5  assembled into a golf club shaft according to an alternative embodiment of the invention; and  
         [0019]      FIG. 7  depicts a perspective view of an alternative embodiment of a shaft insert. 
     
    
     DETAILED DESCRIPTION  
       [0020]      FIG. 1  depicts a golf club  30  having a shaft  10  comprising shaft sections  12   a ,  12   b  and  12   c  of decreasing size. A club head  32  is attached to the shaft  10  at the end of section  12   c . The club head  32  includes a hosel  34  which receives and is rigidly attached to the end of shaft section  12   c . Although the club  30  depicted in  FIG. 1  has sections with different cross-sectional sizes, it will be appreciated that the invention described herein is also applicable to a golf club having a constant cross-sectional size along the length of the shaft. The invention is also applicable to a club having a tapered cross-sectional size along the length of the shaft. The enlarged section of  FIG. 1  depicts a cross-sectional view of a region of the shaft  10  where the end section  12   c  engages the hosel  34  of the club head  32 . The enlarged section of  FIG. 1  also depicts a shaft insert  14  provided within a hollow portion of the shaft section  12   c . Various aspects of the shaft insert  14  are describe in more detail hereinafter.  
         [0021]      FIG. 2  depicts cross sectional views of the golf club shaft  10  of  FIG. 1 . As shown in  FIG. 2 , the shaft  10  transitions from the large diameter portion  12   a  to the medium diameter portion  12   b  to the small diameter portion  12   c . The small diameter portion  12   c  is also referred to herein as the tip end of the club shaft. In preferred embodiments, the golf club shaft  10  may be steel, graphite composite, or any other sufficiently rigid material.  
         [0022]      FIG. 3  depicts cross sectional views of a preferred embodiment of a shaft insert  14  which comprises a foam portion  16  surrounding a rod portion  18 . In the preferred embodiment, the rod portion  18  is a hollow cylinder formed from a isotropic homogeneous material, such as aluminum or titanium. The rod portion  18  may also be formed from thermoplastic, fiberglass or graphite composite materials. Thus, it should be appreciated that the invention is not limited to any particular material of the rod portion  18 . Although in the preferred embodiment the rod portion  18  is hollow, it could also be solid. Further, the rod portion  18  may take on other shapes besides cylindrical. For example, in alternative embodiments, the cross section of the rod portion  18  is polygonal or star-shaped. It should be further appreciated that the rod portion  18  need not have a consistent diameter throughout its length, as alternative embodiments of the invention implement a tapered rod portion. In preferred embodiments, the length of the rod portion  18  is from about 2 inches to about 15 inches, depending on the configuration of the golf club  30 .  
         [0023]     In the preferred embodiment, the foam portion  16  is cylindrical and has an outside diameter corresponding to the inside diameter of the portion  12   b  of the shaft  10 . The inside diameter of the foam portion  16  preferably corresponds to the outside diameter of the rod portion  18 . In preferred embodiments, the foam portion  16  is a resilient polymeric foam material having high vibration dampening characteristics. It should be appreciated that the invention is not limited to any particular material of the foam portion  16 . Although in the preferred embodiment the foam portion  16  is cylindrical, the cross section of its inner and outer surfaces could take on other shapes, such as polygonal. Most preferably, the shape of the inner surface of the foam portion  16  corresponds to the shape of the outer surface of the rod portion  18 . In the preferred embodiment, the foam portion  16  is about 1 to 4 inches long.  
         [0024]      FIG. 4  depicts a preferred embodiment of the shaft insert  14  assembled into the shaft  10 . As shown in  FIG. 4 , the outer surface of the foam portion  16  preferably fits snuggly against the inner surface of the portion  12   b  of the shaft  10 . In the preferred embodiment, the outer diameter of the rod portion  18  is somewhat less than the inner diameter of the tip  12   c  of the shaft  10 . The space between the outer surface of the rod portion  18  and the inner surface of the tip  12   c  of the shaft is preferably filled with a compliant adhesive  20 , such as rubber cement. While the adhesive  20  secures the insert  14  within the shaft  10 , it also provides for vibration damping. In some preferred embodiments, an adhesive layer may be used to secure the foam portion  16  to the rod portion  18 . Adhesive may also be used to secure the foam portion  16  to the inside surface of the shaft portion  12   b.    
         [0025]     In the embodiment of  FIG. 4 , the distal end  14   a  of the insert  14  substantially coincides with the distal end  12   d  of the shaft  10 . However, it should be appreciated that the lateral position of the shaft insert  14  in the shaft  10  can vary from that shown in  FIG. 4 , such that the distal end  14   a  of the insert  14  does not coincide with the distal end  12   d  of the shaft  10 . As shown in  FIG. 1 , the shaft insert  14  is preferably positioned laterally such that the exit point  34   a  of the hostel  34  is disposed adjacent a central portion of the insert  14 . In this manner, the shaft insert  14  provides increased strength in the club shaft  10  at a critical point on the shaft  10 , which point is prone to high stress and potential breakage during impact of the club head  32  with the ball.  
         [0026]     It has been determined through impact testing that the shaft insert  14  substantially increases the stiffness of the tip  12   c  of the shaft, while the foam portion  16  and the adhesive layer  20  considerably dampen vibrations in the shaft  10 . Depending on the materials selected for the insert  14 , the insert  14  may also be constructed to selectively adjust the weight of the tip  12   c  of the shaft  10 .  
         [0027]     An alternative embodiment of the insert  14  is depicted in  FIGS. 5 and 6 . In this embodiment, spacing between the rod portion  18  and the section  12   c  of the shaft  10  is maintained by compliant stays or spacers  22 . Preferably, the spacers  22  comprise strips of foam or other compliant material that are attached to the outer surface of the rod portion  18  before the rod portion  18  is inserted into the shaft portion  12   c . As shown in view D-D of  FIG. 5  and view F-F of  FIG. 6 , the spacers  22  of one embodiment are radially spaced substantially equally about the circumference of the rod portion  18 . While the spacers  22  keep the rod portion  18  substantially centered in the shaft portion  12   c , the spacers  22  also dampen vibration in the shaft  10  when a golf club head impacts a golf ball.  
         [0028]     Although the embodiment of  FIGS. 5 and 6  includes three spacers  22  separated by about 120 degrees about the rod portion  18 , it will be appreciated that other embodiments may include more spacers  22  radially spaced at smaller angles. In alternative embodiments, a single cylindrical spacer  22  may be used that completely surrounds the circumference of the rod portion  18 . In yet other embodiments, the spacer  22  comprises one or more strips of compliant material wrapped in a helical fashion down the length of the rod portion  18 . In some embodiments, the one or more strips of compliant material are continuous down the full length of the rod portion  18 . In other embodiments, the strips are segmented. Thus, the invention is not limited to any particular number, spacing or shape of the compliant spacers  22 .  
         [0029]     Preferably, the spacers  22  are attached to the outer surface of the rod portion  18 , such as by a thin layer of adhesive disposed between the spacer  22  and rod portion  18 . In a preferred embodiment, the adhesive layer is an integral portion of the spacer  22 , such as the adhesive provided on foam strips used as window and door seals.  
         [0030]     Although foam is a preferred material for the spacers  22 , other compliant materials could be used, such as rubber or other elastomeric materials, or materials such as latex or silicon caulk that are applied as a liquid and cure to form compliant spacers  22 .  
         [0031]     In one alternative embodiment, the compliant spacers  22  are used in combination with the compliant adhesive  20  to keep the rod portion  18  substantially centered in the portion  12   c  of the shaft and to dampen vibration.  
         [0032]     In one embodiment depicted in  FIG. 7 , the spacers  22  are integral to the rod portion  18  of the insert  14 . In the example of  FIG. 7 , the spacers  22  are radial splines formed at the outer surface of the rod portion  18 . Such structure may be formed by extrusion or injection molding of a thermoplastic material. If the outer diameter of the rod portion (D in  FIG. 7 ) is slightly greater than the inner diameter of the shaft  10 , the tips  40  of the splines  22  may collapse or bend to accommodate a press fit into the shaft  10 . This collapsing or bending of the tips  40  make this embodiment of the spacers  22  compliant enough to provide for centering of the insert  14  within the shaft  10  without imparting detrimental stress to the shaft during the press fit installation.  
         [0033]     To assemble a golf club  30  including the preferred embodiment of the shaft insert  14  within the shaft  10 , an optional compliant adhesive may be used to form the adhesive layer  20  within the shaft  10 . The adhesive is preferably swabbed inside the tip of the shaft  10  from the distal end  12   d  up to the length of the insert  14 . The distal end  14   a  of the insert  14  is then inserted into the proximal (butt) end of the shaft  10  and is gently pushed through the hollow shaft  10  using a long ramrod until the distal end  14   a  of the insert  14  is substantially flush with the distal (tip) end  12   d  of the shaft  10 . Any adhesive that extrudes from the shaft tip end  12   d  is cleaned from the exterior surface of the shaft  10  immediately with a rag or other cleaning means. A small implement, such as a pointed rod or skewer, is then used to clean any adhesive that may have migrated inside the hollow portion of the tip insert  14 . In the preferred embodiment, it is important to keep a complete airway passage open from the proximal end to the distal end of the shaft  10  before installing a club head  32  on the tip end of the shaft  10 . The shaft  10  is then placed on a drying rack until the adhesive cures.  
         [0034]     Placing a shaft insert at the tip end of a golf club shaft according to the present invention provides several significant advantages over prior art shaft inserts placed in the grip end or other locations within a shaft. Placement of the shaft insert at the tip end makes the tip stiffer, thereby stabilizing the shaft tip and minimizing oscillations caused by the club head striking a golf ball or shaft responses to downswing load immediately prior to ball impact. In addition to oscillations induced in the shaft by contact of the club head with a golf ball, the resulting impact also causes bending or twisting of the shaft. This bending or twisting causes ovaling of the substantially circular cross section of the tip section of the shaft in conventional golf clubs without tip inserts and in clubs with shaft inserts at the grip end of the shaft. Placement of a shaft insert at the tip end of the shaft minimizes this ovaling by maintaining the substantially circular cross section of the shaft, thereby improving the bending or torsional strength of the shaft. Placement of the shaft insert at the tip end of the shaft also helps attenuate the vibration at its source, the club head, before the vibrations travel up the shaft. This minimizes the occurrence of vibration resonances and standing waves along the length of the shaft. The use of tip inserts also helps to minimize the overall weight of the shaft as compared to inserts placed in the grip end. This is because tip inserts generally have a smaller diameter than inserts placed in the grip section or other portions of the club shaft. A factor important to both golf club manufacturers and golfers is that inserts at the tip end can be used most effectively to shift the center of gravity of the shaft towards the tip. This provides for more effective fine tuning of the club swing weight.  
         [0035]     In addition to the aforementioned performance advantages of placing a shaft insert in the tip end of the shaft as opposed to the grip end or other locations within the shaft, placement of certain preferred embodiments of the shaft insert at the tip end also enhances the safety of the golfer. When the tip section of the shaft of a conventional golf club breaks apart from the upper portion of the shaft, the tip section and club head completely detach from the upper shaft and pose a risk to the golfer and other individuals within close proximity, as a heavy flying club head and broken shaft with a jagged edge pose a serious risk of injury to an individual struck by the projectile. If, however, an insert in the tip section is made of certain materials such as fiber composites, the fibers hold the broken sections of the shaft together, allowing a golfer to stop using the broken golf club and avoid injury before the tip section breaks cleanly away from the upper portion of the shaft.  
         [0036]     The foregoing description of preferred embodiments for this invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated.