Abstract:
A shaft structure with adjustable and self-regulating stiffness is provided for golf clubs, fishing rods, and the like. The shaft structure employs in a presently preferred form a hollow tube in which a piston and a longitudinally spaced platen, each longitudinally slidable, are incorporated. The piston and platen are separated from one another by a spring biasing member. The platen is position controlled longitudinally by a longitudinally extending jackscrew that is rotatable and threadably associated with that platen, but that is longitudinally fixed relative to the tube. The chamber defined on one side of the piston contains a fluid which can be a gas or a liquid, and the platen assumes a position along the shaft which to corresponds to a location where forces on each side of the piston are equalized. Rotating the jack screw causes the platen to move longitudinally, the direction depending upon the direction of jackscrew rotation. This movement causes the piston to relocate to a position where the respective pressures on each side thereof remain equalized.

Description:
FIELD OF THE INVENTION 
   This invention relates to shafts for golf clubs, fishing rods and the like wherein shaft stiffness is adjustable and automatically regulated by controlling internal fluid pressures within hollow portions of the shaft. 
   BACKGROUND OF THE INVENTION 
   Golf shafts are typically manufactured with a predetermined stiffness or flex. The term “stiffness” refers to a shaft&#39;s flex characteristics. A golfer can choose among golf shafts of different stiffnesses produced by various manufacturers. However, one manufacturer&#39;s “regular” flex could be another manufacturer&#39;s “stiff” flex, and vice versa. 
   It is well known that the stiffness or flex of a golf shaft plays a fundamental role in the behavioral characteristics of a golf club. The stiffness of a golf club shaft and the so-called kick point affect, for example, the launch angle or trajectory of the ball and the distance of ball travel. A shaft can have a high kick point (maximum bend closer to the grip), or a low kick point (maximum bend closer to the club head) or a kick point at a location there between Prevailing weather conditions can also affect the optimum stiffness for a club shaft. For example, on a windy day, a golfer might choose to use a club head associated with a shaft that has a low or a high stiffness in order to better control the trajectory of the ball. Or an older golfer may desire to use a golf club with a more flexible shaft than a stiff shaft with the goal of having the ball travel farther. 
   Various proposals to provide a variable stiffness for a golf club shaft (or even a fishing pole) have previously been made that involve using a hollow shaft charged with a gas or liquid fluid that can be pressurized. Increasing the fluid pressure in the shaft increases the shaft stiffness. Such pressurizable shafts are illustrated, for example, by Menzies U.S. Pat. No. 1,831,255, Sears U.S. Pat. No. 2,432,450, Busch U.S. Pat. No. 3,037,775, Burrough U.S. Pat. No. 4,800,668 (a fishing rod), Simmons U.S. Pat. No. 5,316,300, Koch et al. U.S. Pat. No. 5,540,625, and Painter U.S. Pat. No. 5,632,693. 
   So far as is known, these fluid charged, variable stiffness, hollow shaft structures of the prior art suffer from the problem that a change in the external environmental temperature inherently causes a significant change in the internal shaft pressure and thus in the shaft stiffness. The change in shaft thickness occurs because temperature changes cause pressure changes in the shaft fluid. Changes in shaft stiffness can dramatically affect the performance characteristics of a golf club. In view of a shaft stiffness change caused by an external temperature change, the performance characteristics of the shaft will change. Outside environmental temperature changes can occur relatively rapidly not only from day to day, but even during a single round of golf. A golfer&#39;s expectation that the fluid charged shaft of one of his golf clubs maintains a constant flex characteristic is no longer true after a change in the temperature. 
   In order for a golf club whose stiffness is regulated by a fluid in its hollow shaft to be practical, the shaft needs to have a stiffness that not only is adjustable but also is able to maintain a chosen stiffness automatically in response to changes in exterior environmental temperature. The present invention overcomes the inability of prior art fluid-filled shafts to maintain a chosen stiffness environmental temperature changes. A shaft is provided which is stiffness adjustable and automatically maintains a selected stiffness regardless of exterior temperature changes. 
   SUMMARY OF THE INVENTION 
   More particularly, this invention relates to a shaft structure for golf clubs, fishing poles and like apparatus incorporating an inventive flexible shaft structure. The shaft structure is hollow, has an adjustable and selectable stiffness, and automatically regulates the club stiffness when the exterior environmental temperature changes. 
   The hollow shaft has proximal and distal opposite end regions and contains a longitudinally slidable piston and a movable platen that are in longitudinally spaced relationship relative to each other. A chamber is defined in the shaft between the piston and the distal end. The movable platen includes guidance means for preventing rotational movement thereof relative to the shaft. Spring biasing means extends in the shaft between the piston and movable platen. 
   A jackscrew extends longitudinally and preferably axially in the shaft between the proximal end region and the movable platen. The jackscrew has a forward portion that threadably extends through the movable platen and has a rearward portion that extends through the proximal end region so that the jackscrew is rotatable relative thereto, but is not longitudinally translatable relative thereto. In the shaft, a first chamber is defined between the piston and the distal end region and another chamber is defined between the piston and the movable platen. When rotational force is applied to the jackscrew rearward portion, the jackscrew remains longitudinally stationary but rotates and causes the movable platen to move longitudinally and slidably in the shaft, the direction of longitudinal movement of the movable platen being dependent upon the direction of rotation imparted by the applied rotational force. 
   In the assembled shaft structure, the interrelationship between the hollow shaft, the spring biasing means, the movable platen, and the piston is such that two results are achieved:
         The piston assumes a longitudinal location in the shaft where the pressure of fluid (preferably a gas, though a liquid may be employed, if desired) in the first chamber and hence the force imposed upon the piston is approximately equal to force imposed upon the piston by the spring. When external environmental temperature changes cause fluid pressure in the first chamber to change, the piston slidably moves in the shaft until the respective force in the first chamber are equalized by the force created by the spring biasing means, thereby to maintain a selected shaft stiffness.   The force exerted upon the piston by the spring biasing force is changed when the jackscrew is rotated and the movable platen is moved longitudinally in the shaft. This change causes the piston to move longitudinally to a location in the shaft where the force in the first chamber is again approximately equal to the force created by the spring biasing means. Thus, the stiffness of the shaft is selectable.       

   The piston characteristically is preferably in a gas-tight relationship with the respective adjacent portions of the shaft interior walls. 
   The invention is adapted for use in a variety of different embodiments using a number of various components, as those skilled in the art will readily appreciate. 
   In one presently preferred type of embodiment, the shaft proximal end region is provided with modifications that enable better control of the jackscrew or that enable convenient regulation of fluid content and pressures in the shaft chambers using exterior fluid sources. For example, the proximal end region may include an inwardly spaced stationary bulkhead member, and may be provided with means for controllably introducing a fluid into, or withdrawing a fluid from, a predetermined portion of the shaft structure. 
   One object of the present invention is to provide a shaft structure which both has a selectable or adjustable stiffness and also has a shaft stiffness that is automatically self-adjusted to maintain the selected stiffness even though the environmental exterior temperature changes. Such an environmental temperature change inherently causes the shaft internal pressure to change which in turn causes a change in shaft stiffness. With the present invention, a selected shaft stiffness is maintained regardless of external environmental temperature. Thus, the present invention overcomes the above-noted disadvantage of the prior art fluid-filled shaft structures which have no means for maintaining selected shaft stiffness when the exterior environmental temperature changes. 
   Another object of the present invention is to provide a shaft structure which has an adjustable and selectable shaft stiffness. 
   Another object of the present invention is to provide a shaft structure which has both a selectable or adjustable shaft stiffness and also a shaft stiffness that is automatically self-adjusted. Thus, after adjustment to a desired stiffness, the shaft structure automatically self-adjusts so that the desired stiffness is maintained regardless of environmental temperature changes. Hence, single such shaft structure can replace many different combinations and permutations of golf shafts, golf clubs, and manufacturing procedures, and can avoid the need for large inventories of golf clubs with golf club shafts pre-set to different stiffness values, thereby effecting a saving of what would otherwise be an expenditure of substantial amounts of money. 
   Another object of the present invention is to provide a shaft structure that, after adjustment to a desired thickness, automatically self adjusts so that a desired stiffness is maintained regardless of environmental temperature changes. Thus, for example, a golfer can control the shaft stiffness characteristics of a golf club subset, or even all the golf clubs of his entire club set, so that all selected clubs have the same stiffness. 
   Another object of the present invention is to provide a golf club shaft structure which allows a golfer to customize the stiffness of each member of a set of clubs, or of a fishing pole, according to his ability or wishes without being dependent upon the shaft stiffness that happens to result from shaft manufacturing procedures as in the prior art. 
   Another object of the present invention is to provide a fishing rod structure which allows a fisherman to select the stiffness desired for his fishing rod and where once selected the rod will self-maintain the selected thickness regardless of environmental temperature changes. 
   Other and further objects, aims, features, advantages, applications, embodiments and the like regarding the present invention will be apparent to those skilled in the art from the present specification, attached drawings, and appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
       FIG. 1  is an environmental, perspective view of one embodiment of a golf club which incorporates a shaft structure of the present invention; 
       FIGS. 2A and 2B  provide an enlarged, detailed view in vertical axial section of the shaft structure of  FIG. 1  with the club head removed; 
       FIG. 3  is a detailed view of the subassembly employed in the upper end portion of the shaft structure shown in  FIG. 2A ; 
       FIG. 4  is a view similar to  FIG. 2A , but showing fragmentarily an alternative embodiment of the inventive shaft structure; 
       FIG. 5  is a fragmentary vertical axial sectional view similar to  FIG. 2A  but showing another alternative embodiment of a shaft structure of the present invention, the lower portion of the shaft structure being broken away; 
       FIG. 6  is a view similar to  FIG. 5  but showing a further alternative embodiment of a shaft structure of the invention; 
       FIG. 7  is a fragmentary vertical axial sectional view similar to  FIG. 6  but showing a further alternative embodiment of the present invention wherein a handle structure incorporates components of the invention, the handle structure being illustratively disassociatably associated with the upper end region of the shaft portion of a golf club, the head of the club being removed for simplicity, some parts of the golf club being broken away, the handle structure incorporating with a visual indication means that shows the stiffness of the associated shaft portion; 
       FIG. 8  is a transverse sectional view taken along the line VIII—VIII of  FIG. 7 ; 
       FIG. 9  is a side elevational view of the handle structure of  FIG. 7 , the handle structure being axially rotated about 90° relative to its orientation in  FIG. 7 ; 
       FIG. 10  is a fragmentary view of a handle structure similar to that shown in  FIG. 7  but wherein the handle structure incorporates an alternative embodiment of shaft stiffness visual indication means; 
       FIG. 11  is a diagrammatic side elevational view of an embodiment of an illustrative inventive golf club wherein shaft stiffness is controlled by manually regulating the fluid pressure therein; 
       FIG. 12  is a diagrammatic side elevational view of another embodiment of an illustrative inventive golf club where shaft stiffness is controlled by automatically regulating the fluid pressure therein; 
       FIG. 13  is a diagrammatic side elevational view of another embodiment of an illustrative inventive golf club wherein shaft stiffness is controlled by a combination of manual pressure charging with automatic regulation of shaft internal fluid pressure; 
       FIG. 14  is a fragmentary, diagrammatic, exploded view in side elevation of a golf club structure with a shaft having an upper end portion associatable with the lower end portion of a detachable handle, such a structure being further illustrative of that utilizable with the illustrative golf shaft structures shown in  FIGS. 7–9 ,  10 ,  11 ,  12 , and  13 ; and 
       FIG. 15  is a fragmentary view in side elevation illustrating the combination of club structure and actuating separate and remotely situatable control device for valve actuation, such a combination being utilizable in, for example, the golf clubs shown in  FIGS. 12 and 13 . 
   

   DETAILED DESCRIPTION 
     FIGS. 1 ,  2 A,  2 B and  3  show an illustrative golf club  20  that incorporates an embodiment  21  of a shaft structure of the present invention. Shaft structure  21  is associated at its lower or distal end region  22  with a conventional club head  23  (not detailed structurally) and at its upper or proximal end region  24  with an illustrative, circumferentially extending, conventional handle  25  (not detailed structurally). Various club heads and golf club handles can be associated with the shaft structure  21 . As shown, for example, in  FIGS. 2A and 2B , the shaft structure  21  utilizes an elongated, fluid impermeable, hollow, cross-sectionally circular, fluid-holding, elongated tubular shaft  27 . 
   In embodiment  20 , the upper portion of the shaft  27  preferably is provided with a tubular sleeve  38  comprised of metal or the like that is telescopically received therein and that has outside side wall portions that are preferably bonded by a conventional adhesive (not detailed) to adjacent inside wall portions of the shaft  21 . The sleeve  38  acts as a reinforcement for the shaft  27  and may be considered to be part of the shaft  27 . 
   In embodiment  20 , a spacing and positioning sleeve  46  is provided that is slidably and nestably engageable within the upper end portions  42  of sleeve  38 . The upper outer edge adjacent region of sleeve  46  is threaded internally and externally. The external threads are adapted for engagement with adjacent interior threads defined upon the upper end portion  42  of sleeve  38 . The longitudinally lower interior edge adjacent region of sleeve  38  is threaded and adapted for threaded engagement with the peripheral outer cylindrical edge of a bulkhead  47 . When the sleeve  46  is telescopically engaged within the sleeve  38 , sleeve  46  is threadably engaged with the sleeve  38 , and the bulkhead  47  as threadably engaged with the lower end of the sleeve  46  is so is in a longitudinally fixed location that extends transversely across the sleeve  46 , the sleeve  38  and the shaft  27 , as desired. 
   A piston  28  and a movable platen  29  are located in the sleeve  38  and thus in the shaft  27 . The piston  28  and movable platen  29  are normally in longitudinally spaced relationship relative to each other. Piston  28  and movable platen  29  are each independently longitudinally slidable within the sleeve  38 . Piston  28  is in gas tight relationship relative to adjacent interior wall portions of the sleeve  38 . To assure such a gas tight relationship, piston  28  is preferably provided with a small, circumferentially extending groove  31  that is defined medially in its outer cylindrical peripheral surface, and a preferably sealing ring gasket, not shown, is located in groove  31 . If desired, optimally, platen  29  can be correspondingly provided with a groove  32  and provided with a sealing ring gasket (not shown). 
   A first chamber  36  is defined between the bulkhead  47  and the movable platen  29 . A second chamber  37  is defined between piston  28  and movable platen  29 . A third chamber  39  is defined between the piston  28  and the normally closed lower end region  22  of shaft  27  which end region  22  is illustratively provided with a generally transversely extending terminal closing sealing plate  39  that is provided with peripheral edge portions that are adjacent to the shaft  27  and that are conveniently bonded thereto by a conventional adhesive (not detailed) in the assembled golf club  20 . 
   Lower edge portions  41  of the sleeve  38  are preferably in-turned and the upper end portions  42  of the sleeve  38  are longitudinally inset from the upper end of the shaft  27 . The lower edge portions  41  act as a stop that limits downward longitudinal travel of the piston  28 . Between the piston  28  and movable platen  29  a coiled compression spring  43  of steel or the like is preferably located. The spring  43  normally and preferably exerts a force that tends to move piston  28  and movable platen  29  apart. 
   As those skilled in the art will readily appreciate, various alternative arrangements involving the hollow shaft  27 , piston  28  and movable platen  29  and the spring  43  can be employed, if desired. For example, for reasons of shaft structure  21  strength, the lower end region  22  of shaft  27  may be solid. The shaft  27 , the sleeves  38  and  46  and piston  28  and movable platen  29  can each be fabricated of various conventional materials including steel and steel alloys, aluminum and aluminum alloys, titanium and titanium alloys, plastics, fiberglass filled resins including polyesters, fibrous carbon and graphite filled resins including epoxy matrices, polyacrylonitrile and pitch, carbon fiber and other composites, and the like, as those skilled in the art will readily appreciate. For example, if desired, the shaft  27  may be exteriorly tapered and progressively narrowed in cross-sectional diameter proceeding from the upper end region  24  to the lower end region  22  (an illustrative exteriorly tapered embodiment of shaft  27  is not being shown for reasons of simplicity), but it is preferred that the internal diameter of the shaft  27  be uniform and constant over the longitudinal distance of the shaft  27  within which the piston  28  and movable platen  29  are to be slidably movable longitudinally within the shaft  27 . 
   A cap  48  is provided having an in-turned, externally threaded, peripheral lip portion that is adapted to threadably engage interior threads defined at the upper end of the sleeve  46 . A center bore is defined through each of the cap  48  and the bulkhead  47 . A jackscrew  49  is slidably extended through the center bore in the cap  48  until the head  51  of the jackscrew  49  is adjacent the cap  48 . The jackscrew  49  has a threaded forward end region  52  that is threadably engaged with, and extends through, a center bore defined in the movable platen  29 . The body of the jackscrew  49  is here configured so that the threaded forward region  52  has a smaller diameter than the unthreaded rearward region  53  thereof. A shoulder  54  that is defined in the jackscrew  49  between the rearward region  53  and the forward region  52  is adapted to be positioned against the upper side of the bulkhead  47  when the head  51  is adjacent the cap  48 . In the region  52 , a longitudinally short region  57  is provided that is located along and around the jackscrew  49 , that extends above the upper end of the threaded rearward region  53 , and that extends below the bulkhead  47  in the assembled shaft assembly  21 . To retain the jackscrew  49  in association with the cap  48  and with the bulkhead  47 , and with the jackscrew  49  being rotatable relative thereto, a conventional clamp ring  56  is provided. The clamp ring  56  is mounted around and over the region  57  of the jackscrew  49  adjacent to the bulkhead  47 , but permits the jackscrew  49  to be rotated by turning its head  51 . 
   To prevent rotational movement of the movable platen  29 , and to guide longitudinal movement of the movable platen  29  relative to the interior of the sleeve  38  and the shaft  27 , the movable platen  29  is associated with at least one longitudinally extending keyway means. In embodiment  20 , the keyway means is provided by a plurality of circumferentially spaced guide pins  44 . Preferably, two guide pins  44  are utilized that are diametrically opposed to each other relative to the shaft  27  and the movable platen  29 . The pins  44  extend longitudinally from terminal embedment in the movable platen  29  towards the proximal end region  24  and pass slidably through aligned holes in the bulkhead  47 . Preferably, the individual pins  44  have similar lengths, and the length of the pins  44  is such that, in the assembled golf club  20 , when the movable platen  29  has been longitudinally moved along the threads in the threaded forward region  52  of the (revolvably moved) jackscrew  49 , and the movable platen  29  is locatable at a desired position in sleeve  38 , and the pins  44  are still slidably engaged with the bulkhead  47 . Yet, when the movable platen  29  has been longitudinally moved along these threads in region  52  in the opposite direction, the movable platen  29  is locatable adjacent to the region  57 . The pins  44  are fully accommodated in the head chamber  58  that is defined in the sleeve  46  between the cap  48  and the bulkhead  47 . During initial assembly of the club  20 , it is convenient and preferred for piston  28  to be positioned in a forward end region of the sleeve  38  and for the movable platen  29  to be located in sleeve  38  so as to be approximately in a medial position along the threads in region  52  of jackscrew  49 . Various alternative keyway means, component assemblies and assembly techniques can be employed, as those skilled in the art will readily appreciate. 
   In assembly of club  20 , the piston  28  and the movable platen  29  can be preliminarily positioned in the sleeve  38  that has been telescopically associated with the shaft  27 . Conveniently, the sleeve  46  is preliminarily assembled with the bulkhead  47 , the cap  48 , the jackscrew  49 , the movable platen  29  and the pins  44 . Then the resulting subassembly of these components is then associated with the sleeve  38  through its upper end portion  42 . In this manner of assembly, piston  28  is preliminarily positioned in the sleeve  38 , and the movable platen  29  is preliminarily threadably associated with the jackscrew  49  and associated with the sleeve  38 . The resulting assembly has the component interrelationship shown, for example, in  FIG. 2A . The handle  25  can then be mounted over and about the proximal end region  24  of the shaft  21 . Preferably an access hole  60  is provided in the upper end  59  of the handle  25 . On the assembled club  20 , through hole  60  the polygonally (preferably hexagonally)-sided projecting head of a conventional wrench (not shown) can be extended and matingly received and engaged with a mating polygonally (preferably hexagonally)-sided pocket recess  61  defined in the upper central end of the head  51 . Thereby, the jackscrew  49  can be turned (rotated) to adjust the longitudinal position of the movable platen  29  in the assembled golf club  20 . 
   As the golf club  20  is assembled in an atmospheric environment, inherently, contain a gaseous fluid (i.e., air). Examples of suitable inert, colorless gases include helium, argon, carbon dioxide, nitrogen, air or the like. 
   Instead of a gas, the fluid in chamber  36  can be a selected liquid, such as an inert liquid that has a boiling point which is above ambient temperatures and pressures, for example, a boiling point preferably above about 150 degrees C. Although higher and lower boiling point fluids can be used if desired. A selected liquid can be easily introduced into chamber  36  during assembly of a golf club  20 , as those skilled in the art will readily appreciate. Illustrative suitable inert, stable, non-aqueous liquids include glycols, petroleum hydrocarbon liquids such as oils, synthetic silicone liquids, and the like. 
   If desired, a fluid in a golf club  20  can comprise a mixture of gas and liquid, such as, for example, a stabilized emulsion where, for example, nitrogen or other inert gas comprises the discontinuous phase and a silicone oil or other inert liquid comprises the continuous phase. Such a mixed fluid can be chosen, if desired, so as to have a pressure-responsive compressibility characteristic that is intermediate between the corresponding compressibility characteristics for a gas and for a liquid, as those skilled in the art will appreciate. 
   For reasons of providing the relatively largest practical capacity for incremental or infinitely variable adjustment capacity for shaft stiffness in a shaft structure of the invention, it is presently preferred to employ a fluid in a shaft assembly  27  which is a gas. However, the weight of a golf club can be adjusted by regulating the density of the particular fluid employed in charging chambers defined in golf shafts. For example, to increase golf shaft weight, instead of a gas such as nitrogen or air that is charged to a shaft chamber, one can employ, for instance, an organic liquid, or a synthetic silicone oil, such as one that has a heavy metal chemically incorporated thereinto. 
   Adjustment of pressure in chamber  37  is carried out by adjusting the longitudinal position of the movable platen  29  in the sleeve  38 . A change in then longitudinal position of the movable platen  29  is produced by turning the jackscrew  49 , as above described. Changing the longitudinal position of the movable platen  29  changes the force upon movable platen  29  by virtue of spring  43 . Initially, before a pressure change in chamber  37  is initiated, the pressure in each of second chamber  37  and third chamber  39  is approximately equal since the piston  28  slidably moves in sleeve  38  to a position where the pressures upon opposing faces of the piston  28  are approximately equal. Changing that pressure changes the pressure applied against one face of piston  28 . When the pressure in the third chamber  39  is approximately constant during changes in the pressure of the second chamber  37 , and the pressure in the second chamber  37  is changed (by turning the jackscrew  49 ), the piston  28  is caused to move to a new position where the pressure on each opposed face of the piston  28  is again equalized. The fluid pressure in the chamber  37  is adjusted by means of the position of the movable platen  29  and hence the position of the piston  28  is adjusted. It is preferred for the volume or longitudinal length of the chamber  37 , which is in effect defined by the pressure produced by the spring pressure therein, to be smaller, preferably much smaller, than the volume or longitudinal length of the chamber  39 , which is in effect defined by the pressure of fluid in chamber  39 . Adjusting the position of the piston  28  in the sleeve  38  thus regulates the pressure in third chamber  39  and consequently the stiffness of the shaft  27 . 
   The longitudinal force of the pressure exerted by the spring  43  can be considered to be proportional to the pressure associated with the fluid in chamber  37 . The spring  43  force exerted on piston  28  can be selected so as to be equal to or substantially greater than that exerted by the fluid in chamber  36  on piston  28 . 
   The amount of spring force utilized in chamber  37  can be variously selected. For example, the spring force can be selected so as to determine a desired longitudinal length for the chamber  37  relative to the longitudinal length of the chamber  36 . In the shaft structure  21 , piston  28  assumes a longitudinal position in the shaft  27  where the pressure of the fluid in the first chamber  39  is approximately equal to the pressure of the spring force in the second chamber  37 . Pressure changes in shaft structure  21  are produced by changes in environmental temperature. With the movable platen  29  at a selected location, when, for example, the external environmental temperature changes in the vicinity of a golf club  20 , the temperature of the shaft structure  21  changes, and the pressure of the fluid in the third chamber  39  inherently changes. Responsive to such a pressure change in the chamber  39 , piston  28  moves longitudinally in the shaft  27  until the force provided by the pressure in chamber  39  is equal to the force supplied by the spring  43 . Under the changed conditions, one may desire to move the movable platen  29  longitudinally from one position to another in the sleeve  38  by means of rotation of the jackscrew  49 , thereby to achieve a different stiffness for the shaft structure  21 . Such a movement of movable platen  29  causes the pressure exerted on the piston  28  to change. The result is that the piston  28  moves slidably to a position where the force on each side of the piston  28  is again effectively equalized. 
   Embodiments where external pressure sources are employed to regulate pressure in the chambers of a shaft structure of the invention are illustrated below. 
   A different golf club embodiment  70  that employs a shaft structure  71  of the present invention is seen fragmentarily in  FIG. 4 . Components of club  70  and shaft structure  71  that are similar to corresponding components in club  20  and shaft structure  21  are similarly numbered but with the addition of prime marks thereto for convenient identification purposes. As in club  20 , in club  70 , the shaft  27 ′ is associated with a sleeve  38 ′. The jackscrew  49 ′ is rotatable and is longitudinally and axially extended through a bulkhead  47 ′ that is here located adjacent to the proximal end of shaft  27 ′. The forward end region  52 ′ of the jackscrew  49 ′ is threadably and axially (relative to shaft  27 ′) extended through the center region of movable platen  29 ′. The jackscrew  49 ′ head  51  is adjacent one face of the bulkhead  47 ′ and a clamp ring  56 ′ is positioned adjacent the opposing face of the bulkhead  47 ′, thereby to retain the jackscrew  49 ′ in a longitudinally fixed but rotatable position. The bulkhead  47 ′ is circumferentially threaded and is threadably engaged with mating threads defined on the inner upper edge region of the sleeve  38 ′ while the outer upper edge of the sleeve  38 ′ is threadably engaged with adjacent portions of the shaft  27 ′ so the position of the bulkhead  47 ′ is fixed in the shaft structure  21 ′. 
   In embodiment  70 , the keyway means is provided by a longitudinally extending key ridge  72  that is mounted to and extends longitudinally along an inside surface of the sleeve  38 ′. The movable platen  29 ′ is provided with a longitudinally extending, circumferentially edge located groove  73  which is adapted to engage matingly and slidably move over the ridge  72 , thereby guiding the movable platen  29 ′ longitudinally and preventing rotation thereof. A spring  43  is positioned between the movable platen  29 ′ and the piston  28 ′ in the sleeve  38 ′. 
   Referring to  FIG. 5 , another golf club embodiment  80  is fragmentarily shown which incorporates a shaft structure  79  of the invention. Components of club  80  which are similar to those of club  20  and of club  70  are similarly numbered but with the addition of prime marks thereto for convenient identification purposes. The club  80  incorporates the key ridge  72 ′ as in the club  70  and the movable platen  29 ′ has a groove  73 ′ that engages and slidably moves over the ridge  72 , thereby guiding the movable platen  29 ′ and preventing rotation thereof. The operations of the piston  28 ′ and movable platen  29 ′ are similar to their operations in clubs  20  and  70 . 
   The club  80  is provided with means for separately introducing, if desired, a fluid into chamber  39 ′. Thus, in the club  80 , a chamber  81  is provided between the upper end  59 ′ of the handle  25 ′ and the cap  48 ′. The upper end  59 ′ is provided with a cover  62  for handle  25 . In addition to accommodating the head  51 ′ of the jackscrew  49 ′, the chamber  81  accommodates a conventional valve  82  (valve  82  is preferably being provided with a friction-fitting cap, not detailed for simplicity). A present preference is for the valve  82  to be similar in construction to the needle-type valve used with conventional footballs and the like where a needle-like member associated with a pressurized conduit is inserted into the valve thereby permitting fluid under pressure to pass through the needle like member and through valve  82  and into the interior of the shaft structure  79 . Valve  82  is associated with a conduit  85  that extends generally longitudinally through and downwardly within and radially beneath the handle  25 ′ from the proximal end  24 ′ of the shaft  27 ′ towards the distal end region (not shown) of the shaft  27 ′ along the outside of the shaft  27 ′ to a terminal location that is radially opposite a lower end portion  41 ′ of the sleeve  38 ′. Here, the conduit  85  extends through the respective walls of the shaft  27 ′ and the sleeve  38 ′ and opens into the chamber  39 ′ that is located forwardly of the piston  28 ′. In the embodiment  80 , the conduit  85  is located on the outside surface portions of the shaft  27  preferably, but alternative arrangements can be used, if desired. 
   To charge the chamber  39 ′ with a fluid, the cap on the valve  82  is removed and the valve  82  is associated with a conventional needle type valve connector (not shown) that is itself associated with a delivery hose (not detailed) and a desired fluid is input into the chamber  39 ′ through the valve  82 . Pressure measuring gauge means (conventional) associated with each such delivery hose can indicate accurately the pressure of the fluid so charged into chamber  39 ′, as those skilled in the art will appreciate. 
   Referring to  FIG. 6 , a further golf club embodiment  90  is fragmentarily shown which incorporates a shaft structure  89  of the invention. Components of club  90  which are similar to those of clubs  20 ,  70  and  80  are similarly numbered but with the addition of prime marks thereto for identification purposes. The club  90  incorporates the key ridge  72 ′ and the bulkhead  47 ′ as in the club  70  and the movable platen  29 ′ has a groove  73 ′ that engages and slidably moves over the ridge  72 ′; thereby guiding the movable platen  29 ′ and preventing rotation thereof. The operations of piston  28 ′ and movable platen  29 ′ in embodiment  90  are similar to their operations in clubs  20  and  70 . 
   Similarly to the club  80 , the club  90  is provided with means for separately introducing a fluid into chamber  39 ′. The periphery of bulkhead  47 ′ threadably engages the upper end portion of the sleeve  38 ′ and the sleeve  38 ′ upper end portion threadably engages the proximal end portion  24 ′ of the shaft  27 ′. As in the club  80 , a chamber  81 ′ is provided between the upper face of the bulkhead  47 ′ and the cap  62 ′. In addition to accommodating the head  51 ′ of the jackscrew  49 ′, the chamber  81  accommodates conventional valves  82 ′ that is preferably capped (not detailed). Valve  82 ′ is associated with a conduit  85 ′ that extends from the proximal end  24 ′ of the shaft  27 ′ towards the distal end region (not shown) of the shaft  27 ′ along the outside of the shaft  27 ′ and beneath the handle  25 ′ to a location radially opposite a lower end portion  41  of the sleeve  38 ′ where the conduit  85 ′ extends through the respective walls of the shaft  27 ′ and the sleeve  38 ′ and opens into the chamber  39 ′. In the embodiment  90 , the conduit  85 ′ is located on the outside surface portions of the shaft  27  preferably, but alternative arrangements can be used, if desired. 
   To charge the chamber  39 ′ with a fluid, the cap on the valve  82 ′ is removed and the valve  82 ′ is associated with a conventional valve connector associated with a hose (not detailed but conventional) and a desired fluid is input into the chamber  39 ′. Pressure measuring gauge means (conventional) associated with each such delivery hose can indicate accurately the pressure of the fluid so charged into chamber  39 ′, as those skilled in the art will appreciate. 
   A further embodiment of the invention is illustrated by the golf club structure  92  shown in  FIGS. 7–9 . Certain components of club structure  92  (see, for example,  FIG. 7 ) are similar to, or correspond with, components of the club structure  90  ( FIG. 6 ) and are similarly numbered for convenience. The handle structure  93  of club structure  92  thus incorporates components which are useful in the practice of the invention and which function as above explained. The handle structure  93  is suitable for manufacture and usage as an independent item of commerce for manufacture and sale with golf shafts, such as a golf club shaft  96 , and the like, thereby to provide golf clubs for use by golfers. When the handle structure  93  is connected to a golf club shaft  27 ′, one is enabled to control and regulate the stiffness of the associated golf club  90  as taught herein by the present invention. 
   In golf club structure  92 , the handle structure  93  comprises an independent and separately fabricated subassembly whose lower end region  94  is connected to the upper end region  95  of a hollow golf shaft  27 ′. While various shaft  27 ′/handle  93  interconnection means can be employed, as will readily be appreciated by those skilled in the art, it is presently preferred to have the handle  93  be reversibly interconnected with a shaft  27 ′, thereby permitting the handle  93  to be successively connectable to various shafts  27 ′, if desired, and also permitting the handle  93  to be separated from a shaft  27 ′ for purposes of maintenance, replacement, or the like, as might be desired. 
   A handle structure  93  conveniently and preferably incorporates a tubular shaft  96  which can be similar to shaft  27 ′ in diameter and thickness. In the handle structure  93 , the shaft  96  can be considered to replace the shaft  27 ′. As illustrated in  FIGS. 7 and 14 , for example, one presently preferred interconnection means is illustratively achieved by a nipple  97  with exterior threads extending inwards from each opposite end thereof and which threads are adapted to threadably engage adjacent respective threaded interior regions of the lower end region  94  of shaft  96  and of the upper end region  95  of shaft  27 ′. In handle subassembly  93 , one end of the nipple  97  is adapted to engage threadably and abuttingly the in-turned adjacent end of the sleeve  38 ′ which can aid in centering the nipple  97  between the shaft  96  of the handle  93  and the upper end region of the shaft  27 ′ and in maximizing the strength of the connection between nipple  97 , shaft  96 , and shaft  27 ′, as those skilled in the art will appreciate. As the handle  93  is connected to the shaft  27 ′, the chamber  39 ′ is connected to the chamber  109  in the handle  93  that is located forwardly of the piston  28 ′. 
   The handle  93  incorporates a visual readable stiffness indicating system  100  that shows in real time the stiffness of the associated shaft  27 ′ and shaft  96  based on fluid pressure in chambers  109  and  39 ′. Thus, the telescopically received sleeve  38 ′ in shaft  96  has a longitudinally extending slot  101  defined therein commencing in spaced adjacent relationship to the lower edge portion  41 ′ thereof and extending upwards to a location approximately opposite the lower end portion  87 ′ of jackscrew  49 ′. A peripheral side edge portion of the piston  28 ′ is provided with a projection  102 . The projection  102  is adapted to slidably extend in and along the slot  101  as the piston  28 ′ is slidably moved responsive to slidable movements of the movable platen  29 ′ achieved as above explained. Thus, the position of the projection  102  at any given time is an accurate indication of the pressure or stiffness of the shaft  96  and shaft  27 ′ (analogously to shaft  27  or  27 ′ as above described). 
   The shaft  96  is provided with a slot  103  that is located in radially adjacent relationship to the slot  101 . The slot  103  is provided with a sealingly engaged transparent window  104 , preferably defined by a shock resistant acrylic plastic or the like, through which the position of the projection  102  is visible yet which permits a fluidic pressure provided in the adjacent chamber  109  to be maintained, as desired. The perimeter of the slot  103  and the window  104  can be provided with a mating, longitudinally extending combination of grooves and ridges (not detailed) to provide, preferably with a sealing or adhexive agent, a seating and sealed engagement between slot  103  and window  104 , or the like, as may be desired. 
   The handle  93  exterior surface portions are preferably provided by a readily gripable molded plastic cover  106  which may have an exterior design (not illustrated) suggesting a wrap of strip material or the like, if desired (to resemble the exterior of a conventional golf club handle) and which can be premolded and then slidably extended over the handle shaft  96  beginning at the upper end region  98  thereof. As formed, the cover  106  includes a transparent window  107  that extends longitudinally in and therealong. Conveniently and preferably, the window  107  is molded with the cover  106  and is sized and positioned so as to overlie the window  104  in the assembled handle  93 . 
   Indicia  108  are preferably provided that are located preferably along edge portions of the window  107 . As illustrated in  FIG. 9 , one set of the indicia can include, for example, a well-known stiffness designation that is often referred to as Regular (R), Stiff (S) and Extra Stiff (X), and another set of the indicia can be calibrated in numbers such as are used by those skilled in the art to indicate shaft flexural cycles expressed in cycles per minute. Flexural cycles of a golf shaft or the like can be preliminarily determined at a golf club manufacturing facility or the like. The indicia  108  are preferably oriented in a club  92  so that a golfer can read same while the club is generally in an upright or use orientation, such as illustrated in  FIG. 9 . Other indicia of course can be used as desired without departing from the spirit and scope of the invention. 
   An alternative shaft stiffness indicating system  110  is illustrated in  FIG. 10 . Here the stiffness indicating system  100  is replaced by a combination of pressure sensing transducer  111  and metering device  112  which are both commercially available components. The pressure transducer  111 , as positioned in, for example, chamber  109 , senses pressure in chambers  109  and  39 ′ (and hence measures, with calibration, shaft stiffness). The signal output from transducer  111  is fed through the sidewalls of shaft  96  and sleeve  38 ′ via an interconnecting small cable  113  to the metering device  112 . The device  112  can either use an analog output to cause a needle to rotates responsively to input signals over a calibrated background face dial of a display surface, or use a digital output to cause a calibrated numerical readout to appear on a display device using a liquid crystal or the like. Thus a golfer, for example, views with system  110  a visually readable signal output showing estimated stiffness of the shaft  27 ′ of his selected golf club. Remaining components of handle structure  93  used with system  110  can be as indicated for the club structure  92 , or otherwise as desired. 
     FIGS. 11–13  illustrate golf shaft embodiments of the invention wherein shaft stiffness is determined and regulated without the use of pistons. In the embodiment of  FIG. 11 , shaft stiffness is regulated by shaft internal fluid pressure that is manually adjusted by a golfer or the like. In the embodiment of  FIG. 12 , shaft stiffness is regulated by shaft internal fluid pressure that is automatically adjusted. In the embodiment of  FIG. 13 , shaft stiffness is regulated by shaft internal fluid pressure that is adjusted both manually by a golfer and automatically. 
   Thus, in the embodiment of  FIG. 11 , a conventional canister  112  is employed which is preferably small and that is charged with a compressed gas which is preferably inert. The compression pressure of the gas in the canister  112  is above atmospheric pressure and preferably is initially significantly above atmospheric pressure. The canister  112  is connected to a conduit  113  leading to a manually operated (opened and closed) valve  114 . The valve  114  is further connected via a conduit  115  to a so-called conventional needle (not detailed) and the needle is connected (inserted) into a conventional type needle-fill valve  116  (not detailed). The needle and the valve  116  are each of the conventional type employed with inflatable athletic equipment, such as footballs and the like. Valve  116  is conveniently and preferably joined to and functionally connected with the upper end of a handle-equipped, generally hollow, sealed, internally pressurizable shaft of a golf club  118 A. Connected also into the conduit  115  is a conventional gas pressure gauge  117  which is conveniently of the analog, visually readable type. The gauge  117  can be calibrated to read either in pounds per square inch (gauge) or in shaft stiffness (if the latter, then a preliminary calibration is carried out to correlate pounds per square inch with desired shaft stiffness units). Thus, when the needle valve  116  is functionally associated with the conduit  115 , and the canister  112  is functionally associated with the valve  114 , and the valve  114  is opened, gas passes from the canister  112  into the shaft of the handle-equipped golf club  118 A. The pressure in the club  118 A shaft is allowed to rise to a desired value as shown by gauge  117  corresponding to a desired shaft stiffness whereupon the valve  114  is closed by the user (typically, a golfer). After shaft pressurization, the canister  112  and the conduit  113  can be disconnected from the club  118 A. 
   When the environmental temperature declines to a lower value relative to its initial level, and after the club  118 A becomes equilibrated relative to that lower environmental temperature, then the internal pressure in the shaft decreases. To return the internal shaft pressure to its initial set value, the user increases the internal pressure in the shaft. This can be variously accomplished manually, but in the apparatus of  FIG. 11 , is readily accomplished by reconnecting the canister  112  and the conduit  113  with the valve  114  and allowing gas to pass from the canister  112  through the valve  114  and into the shaft of the club  118 A until the pressure in the shaft, as shown by the gauge  117 , is returned to its initial set value whereupon the user closes the valve  114  and separates the canister  112  and the conduit from the valve  114 . 
   When the environmental temperature rises to a higher value relative to its initial level, and after the club  118 A becomes equilibrated relative to that higher environmental temperature, then the internal pressure in the shaft increases. To return the internal shaft pressure to its initial set value, the user reduces the internal pressure in the shaft. This can be variously accomplished manually, but in the apparatus of  FIG. 11 , is readily accomplished by the user opening the valve  114  to the atmosphere and allowing gas from the shaft of the club  118 A to escape until the gauge  117  shows that the pressure in the shaft of the club  118 A has been reduced to its initial set value whereupon the valve  114  is closed. 
   In the embodiment of  FIG. 12 , the handle  123  of the golf club  118 B is modified. The upper end portion or mouth of the handle  123  is provided with a cap  121 , preferably one that has a down-turned lip peripherally that is provided with internal screw threads that threadably engage outside screw threads located about the mouth of the handle  123 . A cavity  122  is defined internally in the handle  123  adjacent to the handle  123  mouth, the cavity  122  being adapted to receive therein head first a small canister of pressurized gas, such as, illustratively, the canister  112 . The neck region of canister  112  that is adjacent the valved port thereof (not detailed) is adapted to seat against the input orfice of a conventional valve  120  (not detailed) that is mounted in the handle interior. Conventional O-ring members (not detailed) achieve a sealed engagement between the canister  112  neck region and the valve  120  when the cap  121  is abutted against the bottom portion of the canister  112  and the cap  121  closed and screwed down over the mouth of the handle  123  whereby the canister  112  is compressed axially (relative to the handle  123 ) against the valve  120  input orfice. The valve of the canister  112  is thereby opened, but the valve  120  remains initially in a valve closed configuration. 
   The valve  120  is provided with conventional electromechanical arrangement  119  that is adapted to open and close the valve  120  in response to radio pulse signals generated exteriorly and nearby (but relatively remotely) by a small button-equipped actuator box  124  equipped with a conventional radio pulse generating arrangement, such as diagrammatically shown in  FIG. 15 , for example. Preferably, the box  124  contains solid state microcircuitry of the conventional type used in contemporary automobile keys, garage door openers, and the like, for example. When a button on the box  124  is finger actuated by a user, a low strength radio pulse is generated and transmitted to a receptor associated with microcircuitry functionally connected to the valve  120  associated electromechanical means. The pulse actuates and opens the valve  120  causing gas to be discharged from the canister into the shaft of the club  118 B. 
   The valve  120  electromechanical arrangement  119  is further provided with a conventional pressure-sensing transducer and associated microcircuitry which is preliminarily adjusted to shut automatically the valve  120  when a predetermined pressure is achieved in the shaft, the pressure chosen being sufficient to achieve a desired stiffness for the shaft, and the valve  120  once actuated by the box  124  switch button being automatically opened whenever the shaft internal pressure drops below the predetermined pressure. If desired, the valve  120  can be shut off by the same switch button arrangement on box  124 . 
   When the environmental temperature declines to a lower value relative to its initial level, and after the club  118 B becomes equilibrated relative to that lower environmental temperature, then the internal pressure in the shaft decreases. However, when the shaft internal pressure decreases, the valve  120  opens and returns the internal shaft pressure to its initial set value in club  118 B before the switched on valve  120  again shuts off automatically responsive to pressure. 
   When the environmental temperature rises to a higher value relative to its initial level, and after the club  118 B becomes equilibrated relative to that higher environmental temperature, then the internal pressure in the shaft increases. To return the internal shaft pressure to its initial set value, the internal pressure in the shaft is automatically reduced by a valve  124  mounted through the shaft at a location therealong in the club  118 B. Valve  124  like valve  120  is associated with a conventional combination of pressure sensing transducer and microcircuitry (not detailed) that is adapted to open the valve  124  to the atmosphere when the pressure in the shaft of the club  118 B exceeds the initial set value and to close the valve  124  when the pressure in the shaft is at or below the initial set value. Thus, once the initial pressure for the shaft interior is set relative to valves  120  and  124 , the pressure in the shaft of the club  118 B (and thus the stiffness of that shaft) is automatically maintained. 
   In the embodiment of  FIG. 13 , a canister  112  illustratively again employed which is conveniently connected with the upper end of the golf club  118 C in a manner similar to that utilized with the golf club  118 A of  FIG. 11  and the shaft of the golf club  118 C is similarly pressurized to a desired level. 
   When the environmental temperature declines to a lower value relative to its initial set level, and after the club  118 C becomes equilibrated relative to that lower environmental temperature, then the internal pressure in the shaft decreases. To return the internal shaft pressure to its initial set value, the user increases the internal pressure in the shaft. This can be variously accomplished manually, but, in the apparatus of  FIG. 13 , is readily accomplished by reconnecting the canister  112  and the conduit  113  with the valve  114 , as in the apparatus of  FIG. 11 , and the pressure in the shaft of the club  118 C is allowed to rise until the pressure in the shaft, as shown by the gauge  117 , is returned to its initial set value. 
   When the environmental temperature rises to a higher value relative to its initial level, and after the club  118 C becomes equilibrated relative to that higher environmental temperature, then the internal pressure in the shaft increases. To return the internal shaft pressure to its initial set value, the internal pressure in the shaft is automatically reduced in the manner practiced with club  118 B by a valve  124  mounted along the shaft of the club  118 C. Valve  124  opens to the atmosphere when the pressure in the shaft of the club  118 C exceeds the initial set value and closes when the pressure in the shaft is at or below the initial set value. 
   EXAMPLE 
   In golf club  20 , as the environmental temperature T increases, the shaft  21  internal pressure P increases in accordance with the so called ideal gas equation (1):
 
PV=nRT  (1)
 
where: P=gas pressure
         V=volume of gas   n=number of moles of gas   R=a constant   T=temperature       

   In the prior art, the volume of the shaft interior is constant so that pressure must necessarily increase giving rise to an increase in shaft stiffness. In club  20 , as T increases, the pressure P increases proportionately according to equation (1). In order for the pressure P in chamber  36  to remain constant, the volume V must necessarily decrease a proportionate amount when in a static mode (that is, a use situation where the golfer is not adjusting the stiffness of the shaft  71  by changing the position of the movable platen  29 ). As the environmental temperature increases, the pressure in chamber  36  increases and produces a force F upon the piston  28  as summarized by equation (2):
 
F=PA  (2)
 
where: F=force exerted against piston  28 
         P=gas pressure   A=area of piston  28         

   The force exerted tends to move the piston  28  upwards (referring to  FIGS. 2A and 2B ) thereby compressing the spring  43 . The compressing of the spring  43  continues until the point where the force of the spring  43  balances the force of the fluid (illustratively, air) in chamber  36 . 
   The force exerted by the spring  43  is a function of how much the spring  43  is compressed according to equation (3):
 
F=kx  (3)
 
where: F=force exerted by spring  43 
         x=distance spring is compressed   k=spring constant       

   Substituting the force of the gas in chamber  36  from equation (2) and solving for x yields equation (friction of a seal may be ignored) (4):
 
x=(P*A)/k  (4)
 
Therefore, the piston  28  will move x amount of measured units (meters) up (as temperature increases) or down (as temperature decreases) until an equilibrium is reached.
 
   When a golfer chooses to stiffen the shaft  21 , he/she simply turns the jackscrew  49  causing the movable platen  29  to move by a proportionate amount downwards. Moving the movable platen  29  downwards effectively causes spring  43  to compress. Spring  43  compressing introduces a change in force as predicted by equation 3 upon piston  28  causing piston  28  to move downwards. The downward movement of piston  28  reduces the volume and increases pressure in chamber  36 . The resulting pressure can be approximated by the above equations. 
   When a golfer chooses to make shaft  21  less stiff, he/she simply turns the jackscrew  49  causing the movable platen  29  to move by a proportionate amount upwards. Moving the movable platen  29  upwards effectively causes spring  43  to uncompress. Spring  43  uncompressing reduces the force imposed upon piston  28  causing piston  28  to move upwards. The upward movement of piston  28  increases the volume and decreases pressure in chamber  36 . The resulting pressure can be approximated by the above equations. 
   Various modifications, changes and variations in the invention may be apparent to those skilled in the art. Such alterations can be carried out without departing from the spirit and scope of the present invention which is intended only to be limited by the scope and content of the appended claims.