Golf club shaft with superelastic tensioning device

Abstract

A shaft for a golf club or other sporting equipment is disclosed, wherein the shaft is hollow and contains a wire or cable placed under tension therein, the wire being made of a superelastic material. The wire is connected at one end to a variation device such as a cam which varies the tension on the wire and thus the bending stiffness of the golf club. Because the wire is made of a superelastic material, for example Nitinol, it can reversibly elongate in response to pre-tensioning and dynamic stresses encountered during swinging the golf club, in order to counterbalance and accommodate, the stress encountered during normal use of the golf club, thus ensuring a long life and preventing damage to the golf club shaft.

What is claimed is:  
     
         1 . A sporting device having a variable stiffness shaft, comprising: 
 a hollow shaft;    a length of a superelastic alloy placed under tension within the hollow shaft and affixed thereto at two points on the shaft, the alloy capable of reversibly elongating to accommodate an applied stress; and    variation means for adjusting the tension of the tensioning device, whereby increasing the tension reduces the bending stiffness of the shaft.    
     
     
         2 . The sporting device of  claim 1 , wherein the superelastic alloy is Nitinol.  
     
     
         3 . The sporting device of  claim 1 , wherein the superelastic alloy can reversibly elongate by up to approximately 8% to accommodate the applied stress.  
     
     
         4 . The sporting device of  claim 1 , wherein the applied stress includes a pre-stress applied to the length of superelastic alloy by the variation means.  
     
     
         5 . The sporting device of  claim 1 , wherein the applied stress includes a dynamic stress produced during a swing.  
     
     
         6 . The sporting device of  claim 1 , wherein the length of superelastic alloy comprises a wire affixed at one end to the shaft, and affixed at the opposing end to the variation means, the variation means transmitting the tension of the wire to the shaft.  
     
     
         7 . The sporting device of  claim 1 , wherein the length of superelastic alloy comprises a plurality of wires affixed at one end to the shaft, and affixed at the opposing end to the variation means, the variation means transmitting the tension of the wires to the shaft.  
     
     
         8 . The sporting device of  claim 1 , wherein the variation means is a cam.  
     
     
         9 . The sporting device of  claim 1 , wherein the variation means is a pinned retractable piece.  
     
     
         10 . The sporting device of  claim 1 , wherein the variation means is a lockable lead screw.  
     
     
         11 . The sporting device of  claim 9 , wherein the lead screw is varied by an external actuator.  
     
     
         12 . The sporting device of  claim 1 , wherein the variation means is a pump.  
     
     
         13 . The sporting device of  claim 1 , wherein the variation means is a sleeve screw.  
     
     
         14 . The sporting device of  claim 1 , wherein the variation means is a displacement actuator powered by an external source.  
     
     
         15 . The sporting device of  claim 1 , and further comprising a constraint insert for preventing dynamic vibration of the length of superelastic alloy.  
     
     
         16 . The sporting device of  claim 15 , wherein the constraint insert comprises a material selected from the group consisting of low density foam, plastic, and elastomers.  
     
     
         17 . The sporting device of  claim 15 , and further comprising a plurality of discrete inserts.  
     
     
         18 . The sporting device of  claim 15 , wherein the constraint insert is a single constraint insert extending substantially along the length of the shaft.  
     
     
         19 . The sporting device of  claim 15 , wherein the constraint insert is held in the shaft by compression.  
     
     
         20 . The sporting device of  claim 15 , wherein the constraint insert is held in the shaft by adhesive.  
     
     
         21 . The sporting device of  claim 1 , wherein the sporting device is selected from the group consisting of a golf club, a tennis racket, a ski pole, a hockey stick, a baseball bat, a fishing pole, a hurling stick, a lacrosse stick, and a vaulting pole.  
     
     
         22 . A golf club having a variable stiffness shaft, comprising: 
 a hollow shaft;    a wire disposed within the hollow shaft and affixed thereto at two points on the shaft, wherein the wire is made of a superelastic alloy which reversibly elongates to accommodate an applied stress; and    variation means for varying the tension of the wire, whereby increasing the tension of the wire reduces the bending stiffness of the shaft.    
     
     
         23 . The golf club of  claim 22 , wherein the superelastic alloy is Nitinol which can reversibly elongate by up to approximately 8%.  
     
     
         24 . The sporting device of  claim 22 , wherein the applied stress includes a pre-stress applied to the length of superelastic alloy by the variation means.  
     
     
         25 . The sporting device of  claim 22 , wherein the applied stress includes a dynamic stress produced during a swing.  
     
     
         24 . The golf club of  claim 21 , wherein the superelastic alloy is selected from the group consisting of nickel and aluminum (Ni—Al); copper and zinc and another element Cu—Zn—X (where the other element X is silicon (Si), tin (Sn), or aluminum (Al)); copper and zinc (Cu—Zn); copper and tin (Cu—Sn); copper and aluminum and nickel (Cu—Al—Ni); iron and platinum (Fe—Pt); iron and manganese and silicon (Fe—Mn—Si); and manganese and copper (Mn—Cu).  
     
     
         25 . The golf club of  claim 21 , wherein the wire is affixed at one end to the shaft, and affixed at the opposing end to the variation means, the variation means transmitting the tension of the wire to the shaft.  
     
     
         26 . The golf club of  claim 25 , wherein the tensioning device comprises a plurality of wires affixed at one end to the shaft, and affixed at the opposing end to the variation means, the variation means transmitting the tension of the wires to the shaft.  
     
     
         27 . The golf club of  claim 21 , wherein the variation means is a cam.