Golf club shaft having wave shaped reinforced part

Abstract

The present invention relates to a golf club shaft having improved torsion characteristics comprising a base shaft having an internal surface and an external surface, and at least one wave shaped reinforced part on at least one of said surfaces, said wave shaped reinforced part comprising a plurality of reinforcement pieces. The wave shaped reinforced part is located on at least one of the upper portion, midpoint or lower portion. The golf club shafts of the present invention can be made by applying a base section of a prepreg sheet or assembly having a plurality of finger like elements to a portion of a base shaft, wrapping the finger like elements around the base shaft to provide a wave shaped reinforced part having a plurality of reinforcement pieces, and curing the shaft having the wave shaped reinforced part thereon to produce a golf club shaft having a wave shaped reinforced part. Golf clubs made with the shafts of the present invention impart greater flying distance and/or directional accuracy to golf balls struck by the golf clubs. The wave shaped reinforced part provides a means of moving the kick point of the shaft to achieve a desired effect on flying distance and/or accuracy. The present invention provides a convenient means of adjusting the characteristics of a golf club shaft according to the skill level of the intended user.

Description

[0001] This application is a continuation of Ser. No. 10 042 541 filed on Oct. 19, 2001 which is a continuation of Ser. No. 09/472,219 filed on Oct. 26, 1999, now abandoned which is a continuation of Ser. No. 08/896,722 filed on Jul. 18, 1997, now abandoned which was a continuation-in-part of Ser. No. 29/061,700 filed on Oct. 29, 1996, now U.S. Pat. No. D 401,981 and Ser. No. 08/760,079 filed on Dec. 4, 1996, now abandoned. This application claims the benefit of U.S. Provisional Application No. 60/047,697 filed on May 23, 1997.

BACKGROUND OF THE INVENTION

[0002] Since a carbon (graphite) shaft is lighter than a conventional steel shaft, the head speed of a golf club while swinging is increased, thus increasing the flying distance of a ball struck by the golf club. However, a graphite shaft has a disadvantage in that its torsion characteristics are poor. If the torsion characteristics of the shaft are poor, the sweet spot of the club head typically does not strike the ball during impact. When the ball is impacted by areas of the club head other than the sweet spot, the direction of the ball in flight is not exact.

[0003] According to conventional methods for improving torsion characteristics of a shaft, first, the fiber orientation (angle formed by the axis of the shaft with the textile tissue of carbon fiber within prepreg sheet) of torsion layer should be ±45° and the prepreg sheets are used for rolling the shaft several times; however, this method has disadvantages in that flex strength is significantly reduced and the weight of the shaft is increased, even though torsion characteristics are improved.

[0004] Second, steel or aluminum alloy is installed internally and on top of it, prepreg sheets are laminated in such a manner that the textile tissue of carbon fiber (mesh) is at the same position as the axial direction of the shaft; however, the use of steel-type internal conduit may be responsible for increasing weight, thus adversely affecting the light weight of a carbon shaft.

[0005] Meantime, for the improvement of flying distance of a golf ball, much research has focused on the enhancement of golf club head shape and material instead of the golf club shaft. However, the shaft is one of the important factors which influences the flying distance of a golf ball. The relevant conventional methods are as follows:

[0006] Korean Patent Open-Laid No. 95-23427 describes a method of providing some reinforced lines within the shaft but this method has some disadvantages in that the weight of shaft increases.

[0007] Korean Patent Open-Laid No. 96-1936 describes a method of forming the hollow part within the shaft with a hexagon or octagon but its manufacturing process is very complicated over the enhanced effects of flying distance.

[0008] Although these methods of the prior art provide shafts which may be used in golf clubs, these shafts suffer from the disadvantages described above. A need therefore exists for golf club shafts and golf clubs which overcome disadvantages such as those described above.

SUMMARY OF THE INVENTION

[0009] The present invention relates to a golf club shaft comprising a base shaft having an internal surface and an external surface, and at least one wave shaped reinforced part on at least one of the surfaces wherein the wave shaped reinforced part has a plurality of reinforcement pieces. The wave shaped reinforced part is located on at least one of the upper portion, midpoint or lower portion.

[0010] The golf club shafts of the present invention can be made by applying a base section of a prepreg sheet or assembly having a plurality of finger like elements to a portion of a base shaft, wrapping the finger like elements around the base shaft to provide a wave shaped reinforced part having a plurality of reinforcement pieces, and curing the shaft having the wave shaped reinforced part thereon to produce a golf club shaft having a wave shaped reinforced part thereon.

[0011] Golf clubs made with the golf club shafts having at least one wave shaped reinforced part impart greater flying distance and/or directional accuracy to golf balls struck with the golf clubs. The wave shaped reinforced part improves the torsion characteristics of the golf club shaft and provides a means of changing the location of the kick point of the shaft to achieve a desired effect on flying distance and/or directional accuracy. The present invention provides a convenient means of adjusting the characteristics of a golf club shaft according to the skill level of the intended user.

[0012] Having summarized the invention, the invention will now be described in detail by reference to the drawings, detailed description and non-limiting examples.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a front view of a golf club shaft in accordance with a first embodiment of the invention in which a wave-shaped reinforced part is provided at the lower part of the shaft.

[0014] FIG. 2 is a front view of a golf club shaft in accordance with a second embodiment of the invention in which a wave-shaped reinforced part is provided at the upper part of the shaft below the grip end.

[0015] FIG. 3 is a front view of a golf club shaft in accordance with a third embodiment of the invention in which wave-shaped reinforced parts are provided at both the lower part and the upper part of the shaft.

[0016] FIG. 4 is a front view of a golf club shaft in accordance with a fourth embodiment of the present invention in which a wave-shaped reinforced part is provided at the middle part of the shaft.

[0017] FIG. 5 is a front view of a golf club shaft in accordance with a fifth embodiment of the present invention in which a wave-shaped reinforced part is provided at a location midway between the grip end of the shaft and the middle point of the shaft.

[0018] FIG. 6 is a partial longitudinal sectional view of a portion of the shaft according to the invention having a wave shaped reinforcement part that has a sinusoidal configuration.

[0019] FIG. 7 shows frontal views of other possible shapes of waves of wave shaped reinforcement parts useful in the invention.

[0020] FIG. 8 shows the preparatory state of forming the wave shaped reinforced part before wrapping finger like elements of the prepreg sheet around the shaft. The base section of the prepreg sheet or assembly is attached to the base shaft and the finger like elements are shown in an extended state.

[0021] FIG. 9 is a perspective view of a section of a reinforced part of a golf club shaft according to the invention prior to curing of a wave shaped reinforced part showing some of the finger like elements of a prepreg sheet wound around the base shaft to form reinforcement pieces. FIG. 9 also shows some of the finger like elements in an extended state prior to winding around the base shaft.

[0022] FIG. 10 shows shaped reinforcement pieces that are formed by wrapping the finger like elements of the prepreg sheet around the shaft. One of the finger like elements is shown in an extended state to illustrate the effect of forming the finger like elements. The figure also shows a view of tape that is wrapped around the reinforcement pieces prior to curing.

[0023] FIG. 11 shows a golf club shaft having a wave shaped reinforcement part that partially encircles a base shaft.

[0024] FIG. 12 shows a golf club shaft that has rib shaped reinforcement pieces.

[0025] FIG. 13 shows a golf club shaft having a wave shaped reinforcement piece on the interior of the shaft.

[0026] FIG. 14 is a frontal view of a golf club made with a first embodiment of a golf club shaft of the invention in which a wave-shaped reinforced part is provided at the lower part of the base shaft above the hosel.

[0027] FIG. 15 is a frontal view of a golf club made with a second embodiment of a golf club shaft of the invention in which a wave-shaped reinforced part is provided at the upper part of the shaft below the grip

[0028] FIG. 16 is a frontal view of a golf club made with a third embodiment of a golf club shaft of the invention in which wave-shaped reinforced parts are provided at both the lower part and the upper part of the shaft.

[0029] FIG. 17 shows a golf club made with a fourth embodiment of a golf club shaft of the invention in which a wave-shaped reinforced part is located at the midpoint of a base shaft.

[0030] FIG. 18 shows a golf club made with a fifth embodiment of a golf club shaft of the invention in which a wave-shaped reinforced part is located between the midpoint and the grip end of the shaft.

DETAILED DESCRIPTION OF THE INVENTION

[0031] FIG. 1 shows a first embodiment of the golf club shaft 25A of the present invention, in which a wave shaped reinforced part 1 is formed in the lower portion of the golf club shaft. The lower portion of the shaft that portion between the midpoint of the entire length of the shaft and the upper edge 12 of the hosel section. FIG. 1 shows the preferred location a of the reinforced part near hosel section 15. The wave shaped part 1, however, may be located at other positions between the upper edge of the hosel section and the midpoint of the lower portion of the shaft. When wave shaped reinforced part 1 is provided at location a of base shaft 5, there is a significant improvement in torsion characteristics of the golf club shaft.

[0032] The wave shaped reinforced parts of the golf club shafts of the present invention are made up of reinforcement pieces. In wave shaped reinforced part 1, the number of reinforcement pieces is 1 to 6 reinforcement pieces, more preferably 1 to 3 reinforcement pieces. Although a larger number of reinforcement pieces may be applied to the shaft, it is preferred to use at most 6 pieces to minimize the possibility that the weight of the golf club shaft may become excessive and thus reduce the flying distance of the ball.

[0033] Typically, when the number of reinforcement pieces in wave shaped reinforced part 1 is 3 pieces, about 10 percent improvement in torsion characteristics may be expected. As a result, even though the ball is not hit by the sweet spot of the golf club head during impact, the ball generally goes in the desired direction and a bad hook or slice is prevented. Also, when wave-shaped reinforced part 1 is provided at the lower part a of base shaft 5, the kick point moves upward.

[0034] The length of wave shaped reinforced part 1 is about 2 cm to about 15 cm, preferably about 3 cm to about 10 cm.

[0035] FIG. 2 shows a second embodiment of the invention in which a wave shaped reinforced part 1′ is provided in the upper portion of the golf club shaft. The upper portion of the golf club shaft is that portion between the midpoint of the entire length of the shaft and the lower edge of the grip section of the shaft. FIG. 2 shows the preferred location b of the wave shaped reinforced part near grip section 22. However, the wave shaped reinforced part 1′ may be located at other positions between the midpoint of the upper portion of shaft and the lower edge of the grip section. When wave-shaped reinforced part 1′ is provided at location b, the kick point of golf club shaft 25B moves down, away from the grip end 20.

[0036] The total length of wave shaped reinforced part 1′ can range from about 2 cm to about 20 cm, preferably about 3 cm to 15 cm. In wave shaped reinforced part 1′, the number of reinforcement pieces is 1 to 7 reinforcement pieces, more preferably 3 to 5 reinforcement pieces. Although a larger number of reinforcement pieces may be applied to the shaft, it is preferred to use no more than 7 pieces to minimize the possibility that the weight of the golf club shaft may become excessive and thus reduce the flying distance of the ball.

[0037] Generally, if the kick point is located closer to the grip end of the shaft, the flying distance of the ball is enhanced but the direction of the ball is less accurate. In addition, it may become very difficult to make a swing that will produce exact impact at the point where the force of shaft is maximized, creating much difficulty for amateur golfers.

[0038] However, since golf club shafts such as the shaft illustrated in FIG. 2, cause the kick point to move down, the golf club shafts of the invention overcome the aforementioned shortcomings so as to make an exact swing and impact much easier even for amateur golfers. In addition, any loss of flying distance produced by the move-down of the kick point can be countered by extending the length of the base shaft 5. The length of base shaft 5 therefore can be increased to cause the kick point of the resulting golf club shaft to have the same height (from tip 10 of the shaft) as the original height of the kick point on base shaft 5 prior to forming the wave shaped reinforced part thereon so that the flying distance of the ball increases.

[0039] Without wishing to be bound by theory, the following Table 1 shows typical percentages of movement of the kick point which may be expected depending on the number of reinforcement pieces in a wave shaped reinforced part when applied to location b of a base shaft. 1 TABLE 1 PERCENTAGE OF MOVEMENT OF THE KICK NUMBER OF POINT (the percent decrease in the height of the REINFORCEMENT kick point measured from the club head tip of the PIECES shaft) 3 3% 5 5% 7 7%

[0040] Thus, if the height of the kick point of a base shaft (measured from the club head tip 10) is 15 cm without a wave shaped reinforced part 1′, then forming a wave shaped reinforced part having 3 reinforcement pieces at the upper part b of the base shaft moves the kick point “down” to a height 14.5 cm (measured from club head tip 10). This is a 3% decrease in height from the original height of the kick point of the base shaft.

[0041] FIG. 3 shows a third embodiment of the invention in which wave shaped reinforced parts 1 and 1′ are located at both the lower and upper portions of the golf club shaft. FIG. 3 shows the wave shaped reinforced part at the preferred location a near hosel section 15 and the preferred location b near grip section 22 respectively of base shaft 5. However, part 1 may be located at other positions between the midpoint of the lower portion of the shaft and the upper edge of the hosel section 15. Likewise, part 1′ may be located at other positions between the midpoint of the upper portion of the shaft and the lower edge of the grip section. When reinforced parts 1 and 1′ are provided at both location a and location b of the base shaft 5, improvement of ball flight direction may be expected together with a more convenient and exact swing.

[0042] In this embodiment, the total number of reinforcement pieces in wave shaped reinforced parts 1 and 1′ is 5 to 7 pieces. The wave shaped reinforced part 1′ located at upper part b preferably has a larger number of reinforcement pieces than wave shaped reinforced part 1 located at lower part a. Reinforced part 1 typically has 2 to 3 pieces and a length of about 2 cm to about 8 cm. Wave shaped reinforced part 1′ typically has 4 to 5 pieces and a length of about 10 cm to about 15 cm.

[0043] When wave shaped reinforced parts 1 and 1′ are provided as described in this embodiment, improvement of ball flight direction also may be expected together with a more convenient and exact swing. Also, the direction of the kick point moves down relative to the kick point of the base shaft.

[0044] FIG. 4 shows a fourth embodiment of the present invention, in which a wave shaped reinforced part 1A is provided at midpoint m of the length of the base shaft 5. If the wave shaped reinforced part 1A is provided at midpoint m, the kick point moves down relative to the location of the kick point of the base shaft 5.

[0045] In this embodiment, reinforced part 1A typically has 5 to 7 pieces and a length of 2 cm to about 20 cm, preferably about 3 cm to about 15 cm. When reinforced part 1A is provided at midpoint m of base shaft 5, improvement of ball flight direction also may be expected together with a more convenient and exact swing.

[0046] The position of wave shaped reinforced part 1A relative to midpoint m may vary. For example, wave shaped reinforcement part 1A may be provided so as to cause wave shaped reinforced part 1A to extend equally on each side of midpoint m. Wave shaped reinforced part 1A also can be positioned to have unequal portions thereof extend on either side of midpoint m.

[0047] FIG. 5 shows a fifth embodiment of the present invention in which a wave shaped reinforced part 1B is provided midway between the lower edge of grip section 22 and midpoint m of the base shaft 5. In the golf club shaft shown in FIG. 5, the kick point moves down relative to the location of the kick point of the original base shaft 5. In this embodiment, reinforced part 1B typically has 5 to 7 pieces and a length of about 10 cm to about 20 cm. When reinforced part 1B is provided at midpoint m of base shaft 5, improvement of ball flight direction also may be expected together with a more convenient and exact swing.

[0048] FIG. 6 is a partial cross sectional view of a portion of the shaft according to the invention having a wave shaped reinforced part that has a sinusoidal configuration, i.e., the surfaces of the waves are curved as opposed to an angular or compressed wave configuration. The reinforcement pieces of the wave-shaped reinforced parts of the golf club shafts of the invention preferably have a sinusoidal configuration as shown, for example, in FIG. 6.

[0049] The shape of the waves formed by reinforcement pieces may have alternative configurations such as, for example, square wave configuration, triangular wave configuration, compressed wave configuration, and trapezoidal configuration. Examples of these alternative configurations are shown in FIG. 7 which shows frontal views of other possible configurations of wave shaped reinforced parts used in the invention.

[0050] Base Shaft

[0051] The base shafts that can be employed to make the golf club shafts of the present invention include, but are not limited to, commercially available graphite shafts, titanium shafts, steel shafts, fiberglass shafts and other shafts that are suitable for use in making golf clubs. Graphite shafts are preferred as the base shaft. The base shaft can be in an unfinished state, i.e., prior to application of finishing materials such as lacquers. Finished shafts that have been treated with finishing materials can also be used as the base shaft.

[0052] Many prior art golf club shafts such those disclosed in Korean Patent Application No. 96-1939 require complicated manufacturing processes. An advantage of the present invention over golf club shafts of the prior art is that commercially available base shafts can be used to produce the golf club shafts according to the invention. The present invention provides a convenient means of moving the kick point of the golf club shafts according to the skill level of the intended user.

[0053] Prepreg Sheet Starting Material

[0054] Prepreg is the composite industry's term for continuous fiber reinforcement material which is pre-impregnated with a partially cured polymer resin. Prepreg sheets are well known in the art Prepreg sheets are produced by known methods such as that disclosed in Callister, William D., Materials Science and Engineering: An Introduction, John Wiley & Sons, Inc, N.Y. (1994) herein incorporated by reference. Commercially available prepreg sheets can be used to form wave shaped reinforced parts of the golf club shaft according to the invention.

[0055] Prepreg sheets useful in the invention include carbon fiber reinforced prepreg sheets wherein the carbon fibers run in a single direction. Glass fiber reinforced prepreg sheets can also be used wherein the glass fibers are woven to intersect each other in a perpendicular orientation forming a criss-cross pattern. In a preferred embodiment of the invention, the prepreg sheet starting material is an assembly of a glass fiber prepreg sheet on top of a carbon prepreg sheet so that the glass prepreg sheet is on the outside surface of the reinforced part. This type of assembly prevents the carbon fibers from leaking or peeling off during the manufacturing process.

[0056] Prepreg sheets useful in the invention include but are not limited to those which are impregnated with a thermoplastic resin, preferably epoxy resin. The thickness of the prepreg sheet is typically between about 0.1 mm to about 0.15 mm. An example of a carbon fiber prepreg sheet useful in the invention is known as T700 and was obtained through Korea Fiber Co. of Korea.

[0057] Total Weight of Golf Club Shaft with Reinforced Part(s)

[0058] The desired total weight of the golf club shaft with wave shaped reinforced part(s) is an important factor in determining the appropriate thickness of the prepreg sheet and the thickness of the reinforcement pieces. Typical total weights of the golf club shaft can range from about 70 g to about 100 g. It is preferred that the total weight of a golf club shaft for a driver in accordance with the invention which has three or more wave shaped reinforced parts is about 70 g to about 75 g. The preferred total weight for a golf club shaft of the invention which has three or more wave shaped reinforced parts, when used in a 5-iron, is about 68 g to about 72 g.

[0059] Prepreg Sheet Base Section and Finger Like Elements

[0060] FIG. 8 shows base section 2B of prepreg sheet 2A attached vertically onto a portion of base shaft 5. As illustrated in FIG. 8, prepreg sheet 2A has finger like elements 2 that are formed by removing sections from a prepreg sheet starting material. The base section 2B of prepreg sheet 2A is attached to base shaft 5, and finger like elements 2 are shown in a position for wrapping around and onto base shaft 5. Generally, the length of base section 2B of a prepreg sheet corresponds to the desired length of the wave shaped reinforced part.

[0061] As discussed in more detail below, prepreg sheet 2A can be made from a single prepreg sheet or an assembly of prepreg sheets such as a glass fiber prepreg sheet on top of a carbon fiber prepreg sheet. The assembly is cut to form a prepreg sheet 2A with finger like elements 2.

[0062] The finger like elements 2 preferably have an elongated, tapered shape as shown in FIG. 8. Although it is preferred to use finger like elements 2 which have a tapered shape, finger like elements 2 may have a variety of shapes depending on the configuration of the waves desired in the wave shaped reinforced part. The shape of the finger like elements 2 may be readily determined by those of ordinary skill in the art depending on the configuration of the waves desired in the wave shaped reinforced part.

[0063] Finger like elements 2 are formed by cutting a prepreg sheet or assembly by known means such as utility knives, carbide disk cutters, and the like. More advanced cutting means includes die cutting and laser cutting. In the example shown in FIG. 8, finger like elements 2 are curved toward the grip end of the base shaft 5. This configuration is useful to form reinforcement pieces which yield a wave shaped reinforced part that has a sinusoidal configuration. The degree of curvature of the finger like elements used to form a wave shaped reinforced part that has a sinusoidal configuration can readily be determined according to the size and shape of a particular base shaft. For example, when the base shaft tapers in the direction of the club head tip of the base shaft, the length of finger like elements 2 can be increased as the radius of the base shaft decreases toward the tip end of the shaft.

[0064] Shape of the Reinforcement Pieces

[0065] The outer shape of the reinforcement pieces which form a wave-shaped reinforced part can be formed according to the type of wave desired in the wave shaped reinforced part. For example, the reinforcement pieces may have a sinusoidal shape to provide a wave shaped reinforced part having a sinusoidal configuration as shown in FIG. 6. Similarly, the reinforcement piece may have other shapes to provide wave shaped reinforced parts which have, for example, compressed wave configurations, triangular wave configurations, square wave configurations and the like as shown in FIG. 7. Other possible configurations include arc, tetragonal or spiral configurations. A particular configuration can be formed by sanding the waves to the desired configuration. A wave shaped reinforced part that has a spiral form can be formed, for example, by forming a “rope” from carbon fibers. The “rope” is wound spirally around a base shaft to form the desired number of reinforcement pieces.

[0066] Thickness of the Reinforcement Pieces

[0067] FIG. 9 shows a section of a golf club shaft having a wave shaped reinforced part prior to curing. FIG. 9 also shows finger like elements 2 extended prior to winding around the shaft. During manufacture, finger like elements 2 are wrapped around base shaft 5 to form reinforcement pieces 30 having thickness T and overall diameter D. The thickness T of reinforcement pieces such as those shown in FIG. 9 is a function of 1) the desired total weight of the golf club shaft with the wave shaped reinforced part and 2) the taper of the shaft. The thickness T of the reinforcement pieces is at least about 0.5 mm. Typically, the maximum thickness of the reinforcement pieces is about 1.5 mm to maintain the total weight of the golf club shaft within current commercially desirable weight limits.

[0068] In one embodiment of the golf club shaft of the invention, the overall diameters D as shown in FIG. 9 of the base shaft and reinforcement pieces in a wave shaped reinforced part are the same. In this embodiment, the thickness T of each reinforcement piece can vary depending on the taper of the shaft. For example, as the diameter of the base shaft decreases, the thickness T of reinforcement pieces can increase so that the overall diameters D of the base shaft and reinforcement pieces is constant. In another embodiment, the thicknesses of the reinforcement pieces is constant and the overall diameters D of the base shaft and the reinforcement pieces can vary.

[0069] Manufacture and Assembly

[0070] A golf club shaft of the invention is formed by bonding a prepreg sheet or, preferably, a prepreg sheet assembly onto a base shaft. The prepreg sheet or assembly includes a base section and finger-like members joined to the base section. The finger-like members are wrapped around the base shaft to provide a wave shaped reinforced part.

[0071] In one embodiment of the manufacture of the golf club shafts of the invention, the base section of a prepreg sheet or assembly having finger like elements 2 as shown, for example, in FIG. 8, is attached vertically along the length of a desired section of a base shaft by an adhesive such as epoxy resin. Finger like elements 2 are wrapped around base shaft 5 to produce reinforcement pieces 30 such as those shown, for example, in FIG. 9.

[0072] FIG. 10 shows a section of a golf club shaft having a wave shaped reinforced part wherein the reinforcement pieces are covered by tape 40 prior to curing. FIG. 10 also shows a finger like element 2 extended prior to winding around the shaft. During manufacture, finger like elements 2 are wrapped around base shaft to form reinforcement pieces 30 having thickness T and overall diameter D. The resulting wave shaped reinforced part can be covered with carbon tape 40 prior to curing as shown in FIG. 10. The wave shaped reinforced part is cured by heat at an appropriate temperature for the particular prepreg sheet. Generally, the curing temperature and time are functions of the particular prepreg sheet starting material. Curing temperatures and times are widely known and published for various prepreg sheets that can be used alone or in an assembly in the present invention. One skilled in the art can readily determine the time and temperature values for the specific prepreg sheet being used, the length of the reinforced part, and the number and thickness of the reinforcement pieces. The time and temperatures can be selected for full or limited cure.

[0073] Although it is preferred to bond a prepreg sheet or assembly around a base shaft as described above, a wave shaped reinforced part having a sinusoidal configuration shown in FIG. 6 or any of the other configurations shown in FIG. 7 may be formed by well known techniques such as compression molding, flame spraying, plasma deposition and the like.

[0074] In a first embodiment of a compression molding method useful in the invention, one or more layers of uncut prepreg sheet material is wrapped onto the surface of the shaft. The wrapped shaft then is compressed under heat and pressure in a mold having the desired configuration of the waves in the wave shaped reinforced part. Preferably, the wave shaped reinforced part such as reinforced part 1, 1′ is formed on the exterior surface of base shaft 5.

[0075] As an alternative to compression molding, techniques such as flame spraying may be employed to deposit material onto the surface of the shaft to yield a wave shaped reinforced part having a desired wave shape on selected portions of the base shaft.

[0076] Although it is preferred that the wave shaped reinforced part completely encircle the base shaft as shown, for example, in FIG. 10, a wave shaped reinforced part 32 may be formed on selected portions of shaft 25I which only partially encircles the shaft as shown in FIG. 11. Wave shaped reinforced parts which only partially encircle the shaft may readily be formed by techniques such as compression molding and flame spraying. Techniques such as compression molding and flame spraying are especially suitable for forming a golf club shaft 25F which has, for example, rib shaped reinforcement pieces 31 as shown in FIG. 12.

[0077] Compression molding also may be used for example, to form a wave shaped reinforcement pieces 30 on the internal surface of a base shaft 25G as shown for example, in FIG. 13. In this aspect, a rod having expandible sections may be inserted into a base shaft. The expandible sections of the rod then are compressed against the interior surface of the base shaft to form reinforcement pieces. Preferably, the reinforcement pieces are wave shaped to produce a wave shaped reinforced part that has a sinusoidal configuration. Other wave shapes, e.g., any of those shown in FIG. 7, may be made by compression molding.

[0078] FIG. 14 shows a golf club made from a first embodiment of golf club shaft 25A of the present invention in which a wave shaped reinforced part 1 is located at the lower part a of a base shaft 5 near hosel section 15. When wave shaped reinforced part 1 is provided at the lower part a of base shaft 5, there is a significant improvement in torsion characteristics of the golf club shaft.

[0079] FIG. 15 shows a golf club made from a golf club shaft 25B in accordance with a second embodiment of the invention in which wave shaped reinforced part 1′ is located at location b of the golf club shaft near the grip 27. When wave-shaped reinforced part 1′ is provided at location b, the kick point of golf club shaft 25B moves down, away from the grip 27.

[0080] FIG. 16 shows a golf club made from a golf club shaft 25C in accordance with a third embodiment of the invention in which wave shaped reinforced parts 1 and 1′ are located at location a and location b respectively of base shaft 5. When reinforced parts 1 and l′ are provided at both location a and location b of the base shaft 5, improvement of ball flight direction may be expected together with a more convenient and exact swing.

[0081] FIG. 17 shows a golf club 29D made from a golf club shaft 25D in accordance with a fourth embodiment of the invention in which a wave shaped reinforced part 1A is located at the midpoint m of base shaft 5. When reinforced part 1A is provided at midpoint m of base shaft 5, improvement of ball flight direction also may be expected together with a more convenient and exact swing.

[0082] FIG. 18 shows a golf club 29E made from a golf club shaft 25E in accordance with a fifth embodiment of the invention in which a wave shaped reinforced part 1B is located between midpoint m and the lower edge of grip 27 of base shaft 5. When reinforced part 1B is provided at midpoint m of base shaft 5, the kick point moves down and improvement of ball flight direction may be expected together with a more convenient and exact swing.

[0083] The golf club shaft of the present invention has various advantages such as: a) improvement of torsion characteristics of the shaft, b) controllable movement of the kick point of the golf club shaft to a desired location to improve the direction of a golf ball with a more convenient and accurate swing, and c) the ability to further extend the length of the reinforced shaft to improve the flying distance of a golf ball without application of added force, i.e., without the need to employ a higher swing speed. Another advantage is the ability to use of commercially available base shafts to produce the golf club shafts of the present invention thus avoiding the complicated manufacturing processes required by golf club shafts of the prior art.

[0084] Golf clubs made with the shafts of the present invention impart greater flying distance and/or directional accuracy to golf balls struck by the golf clubs. The reinforced part provides a means of moving the kick point of the shaft to achieve a desired effect on flying distance and/or accuracy. The present invention also provides a convenient means of adjusting the characteristics of a golf club shaft according to the skill level of the intended user.

[0085] In addition, the wave-shaped reinforced part offsets the impact wave induced when impacting a ball, thus protecting the human body.

EXAMPLES

[0086] In an illustrative but non-limiting example, a commercially available carbon fiber prepreg sheet known as T700 obtained through Korea Fiber Company of Korea and a commercially available glass fiber prepreg sheet are placed together and then the assembly is cut to form a base section with finger-like elements having curved edges as shown in FIG. 8. Base section 2B of the prepreg assembly is attached along the length of the desired section of the base shaft by epoxy resin and the finger-like elements are wrapped tightly around the base shaft to form a wave shaped reinforced part that has a sinusoidal wave configuration. The resulting wave shaped reinforced part is covered with carbon tape. The covered wave shaped reinforced part is then heat cured by placing the shaft having the wave shaped reinforced part into an oven at 80° C. and then raising the temperature to 120° C. over 30 minutes. Thereafter, the temperature is raised to 130° C. over 60 minutes. The shaft having the cured wave shaped reinforced part thereon then is removed from the oven and cooled to room temperature. After curing is completed, the tape is removed by sandpaper, and the shaft is ground to remove any imperfections and to give the resulting wave shaped reinforced part a smooth finish. Grinding may also be employed to alter the shape of a reinforcement piece or pieces in the cured wave shaped reinforced part to achieve a desired wave configuration.

[0087] In another non-limiting example of the invention, a golf club shaft such as that illustrated in FIG. 2 is produced. In this example, the golf club shaft includes a base shaft that has a weight of 62 gram, and total length of 1143 mm. The original kick point is located 46 cm from the club head tip of the shaft. In accordance with the invention, it is found that after adding a wave shaped reinforced part having a length of 20 cm and having 5 reinforcement pieces, the kick point moves down to 44 cm from the club head tip of the shaft. The weight of the shaft having the reinforced part, measured prior to application of finishing materials such as lacquers and the like, is 68 grams. If it is desired to the same height of kick point as the original base shaft prior to forming the reinforced part thereon, the length of the base shaft may be extended by about 70 mm to about 110 mm.

[0088] The following Tables 2-4 show measurements of carry, and of carry and roll distances (in yards) for a golf club made from a commercially available golf club shaft (“CONTROL”) and the same type of golf club made from a golf club shaft according to the invention (“INVENTION”). The specifications of the Test Clubs were comparable. The clubs were tested in a mechanical swinging device wherein the club head speed was 95 mph. 2 CONTROL Test Club Head: Tour Edge Titanium 950-Driver (9.0°) Club Shaft: Aldila - R/S Flex INVENTION Test Club Head: Tour Edge Titanium 950-Driver Club Shaft: Golf club shaft according to the invention with the wave shaped reinforced part having five reinforcement pieces near the grip section. The upper edge of the reinforced part was located around 2.5 inches below a 10⅜ inch grip. The shaft was made from a graphite base shaft that was 45 inches long.

[0089] 3 TABLE 2 Carry Carry and Roll CENTER HITS Distance (yds) Accuracy Distance (yds) Accuracy CONTROL 235.0 −0.8 281.8 −6.0 Std. Dev. 1.4 4.5 7.4 6.4 INVENTION 244.0 2.4 272.8 2.4 Std. Dev. 3.5 4.5 3.6 4.2

[0090] 4 TABLE 3 Carry Carry and Roll ½ TOE HITS Distance (yds) Accuracy Distance (yds) Accuracy CONTROL 221.4 13.4 271.2 12.8 Std. Dev. 4.7 2.1 8.3 1.9 INVENTION 240.0 2.4 268.8 0.3 Std. Dev. 1.9 2.2 4.8 2.9

[0091] 5 TABLE 4 Carry Carry and Roll ½ HEEL HITS Distance Accuracy Distance Accuracy CONTROL 215.4 −18.8 265.0 −20.0 Std. Dev. 4.6 3.7 INVENTION 235.8 −27.6 271.0 −19.0 Std. Dev. 6.6 10.1 5.7 1.4

Claims

1. A golf club shaft comprising a base shaft having an internal surface and an external surface, and at least one wave shaped reinforced part on at least one of said surfaces, said wave shaped reinforced part comprising a plurality of reinforcement pieces.

2. The golf club shaft of claim 1 wherein said golf club shaft includes an upper portion, a midpoint m, and a lower portion, said wave shaped reinforced part located on at least one of said upper portion, said midpoint m, and said lower portion.

3. The golf club shaft of claim 2 wherein said wave shaped reinforced part is located on said upper portion.

4. The golf club shaft of claim 2 wherein said wave shaped reinforced part is located on said lower portion.

5. The golf club shaft claim 2 wherein said wave shaped reinforced part is located on said midpoint m.

6. The golf club shaft of claim 1 wherein said plurality of reinforcement pieces is at least three reinforcement pieces.

7. The golf club shaft of claim 6 wherein said wave shaped reinforced part is on said external surface of said base shaft.

8. The golf club shaft of claim 7 wherein said wave shaped reinforced part has a length of about 2 cm to about 20 cm.

9. The golf club shaft of claim 8 wherein said wave shaped reinforced part has a sinusoidal configuration.

10. The golf club shaft of claim 1 wherein said reinforcement pieces comprise a carbon fiber prepreg sheet and a glass fiber prepreg sheet.

11. A golf club shaft having an external surface, comprising a base shaft having a tip end for receiving a club head and a grip end for receiving a grip, and a wave shaped reinforced part on said external surface of said base shaft, wherein said wave shaped reinforced part has a length of about 20 cm and includes at least 3 reinforcement pieces, said wave shaped reinforced part having a sinusoidal configuration, and wherein said reinforcement pieces comprise carbon fiber prepreg.

12. The golf club shaft of claim 11 wherein said waved shaped reinforced part has at least 5 reinforcement pieces.

13. The golf club shaft of claim 11 wherein said reinforced part is located on said upper portion.

14. The golf club shaft of claim 11 wherein said base shaft has a length of about 1143 mm and a kickpoint located at about 44 cm from said tip end of said base shaft.

15. The golf club shaft of claim 11 wherein said reinforcement pieces further comprise glass fiber prepreg.

16. A method of making a golf club shaft having a base shaft and a wave shaped reinforced part thereon comprising,

applying a base section 2B of a prepreg sheet having a plurality of finger like elements 2A to a portion of a base shaft,

wrapping said finger like elements 2A around said base shaft to provide a wave shaped reinforced part having a plurality of reinforcement pieces on said base shaft, and

curing said shaft having said wave shaped reinforced part thereon to produce a golf club shaft having a wave shaped reinforced part thereon.

17. The method of claim 16 wherein said wave shaped reinforced part comprises at least 3 reinforced pieces.

18. The method of claim 16 wherein said base shaft has an upper portion, a midpoint m, and a lower portion, and wherein said wave shaped reinforced part is located on at least one of said upper portion, said midpoint m, and said lower portion.

19. The method of claim 16 wherein said prepreg sheet comprises a carbon fiber prepreg sheet.

20. The method of claim 16 wherein said prepreg sheet comprises a glass fiber prepreg sheet joined to a carbon fiber prepreg sheet.

21. A golf club comprising a golf club shaft comprising a base shaft having an internal surface and an external surface, and at least one wave shaped reinforced part on at least one of said surfaces, said wave shaped reinforced part comprising a plurality of reinforcement pieces.

22. The golf club of claim 21 wherein said golf club shaft includes an upper portion, a midpoint m, and a lower portion, said wave shaped reinforced part located on at least one of said upper portion, said midpoint m, and said lower portion.

23. The golf club of claim 22 wherein said wave shaped reinforced part is located on said upper portion.

24. The golf club of claim 22 wherein said wave shaped reinforced part is located on said lower portion.

25. The golf club claim 22 wherein said wave shaped reinforced part is located on said midpoint m.

26. The golf club of claim 21 wherein said plurality of reinforcement pieces is at least three reinforcement pieces.

27. The golf club of claim 26 wherein said wave shaped reinforced part is on said external surface of said tubular shaft member.

28. The golf club of claim 22 wherein said wave shaped reinforced part has a length of about 2 cm to about 15 cm.

29. The golf club of claim 28 wherein said wave shaped reinforced part has a sinusoidal configuration.

30. The golf club of claim 21 wherein said reinforcement pieces comprise a carbon fiber prepreg sheet and a glass fiber prepreg sheet.