Golf club shaft

Abstract

The a golf club shaft includes a sheet member made of fiber reinforced plastic material, preferably in the form of a mesh member having a reticular or net-like structure, secured circumferentially around a cylindrical outer surface of the grip end of the shaft body. Preferably, this sheet member includes an extension that is visible from outside by extending from the club head end of the grip to achieve a distinct appearance and/or to enhance the mechanical strength of the related part which is known to be subjected to a substantial stress in use. The presence of the sheet member not only improves various mechanical characteristics, such as the bending strength and flattening strength and the vibration damping capabilities of the grip portion but also provides a distinct and attractive appearance to the golf club.

Description

TECHNICAL FIELD

The present invention relates to a golf club shaft, and more particularly to a golf club shaft that is light in weight and strong. The golf club shaft of the present invention may also have a distinct appearance and allows the firm and reliable attachment of the grip to the shaft body to be ensured.

BACKGROUND OF THE INVENTION

A conventional golf club shaft is typically constructed such that, when attaching a grip to the grip end of the shaft body, an adhesive or the like is applied to firmly secure the grip to the shaft body. It is desirable that the bending strength, flattening strength and vibration damping capabilities of the part of the shaft body to which this grip is affixed be improved while the golf club shaft needs to be as light in weight as possible. Furthermore, at the end of the follow through movement in a golfer's golf swing, the grip portion of the shaft body tends to hit the golfer's shoulder, and this causes a significant bending stress in the grip portion of the shaft body. It is therefore desirable to reinforce the grip portion of the shaft body.

Further, the outer cylindrical surface of the shaft body is generally smooth, giving rise to various problems. For instance, as some effort and skill are required to ensure that the grip be adequately securely attached to the shaft body, the quality of the attachment may differ from one worker to another. Therefore, a production management measure is required so that a uniform quality may be achieved. This adds to the number of manufacturing steps and adversely affects the production efficiency.

In addition, there are a variety of types of golf clubs, such as woods, irons and putters, and there is a need to easily identify these different types of golf clubs from the outer appearance of the golf club shafts, it is also desirable to give a distinctive, preferably aesthetically attractive appearance to each gold club or shaft to make it more attractive to the potential buyers of the golf clubs. A distinct appearance prevents one's golf clubs from being confused with somebody else's. It is practiced to put colored tape around a suitable part of the club shaft for this purpose, but it is not so agreeable in appearance, and may peel off in time.

BRIEF SUMMARY OF THE INVENTION

With the above-mentioned problems in view, it is an object of the present invention to provide a golf club shaft that makes it possible to enhance various mechanical characteristics, such as the bending strength and flattening strength, and the vibration damping capabilities of the grip portion.

A second object of the present invention is to provide a golf club shaft that can be made lighter weight and can enhance the strength of the grip portion.

A third object of the present invention is to provide a golf club shaft which is constructed such that a grip can be reliably secured to the shaft body.

A fourth object of the present invention is to provide a golf club shaft capable of being differentiated from the standpoint of appearance.

To achieve at least some of such objects, the present invention provides a golf club shaft that includes a sheet member made of fiber reinforced plastic material, preferably in the form of a mesh member having a reticular or net-like structure, secured circumferentially around a cylindrical outer surface of the grip end of the shaft body. Preferably, this sheet member includes an extension that is visible from outside by extending from the club head end of the grip to achieve a distinct appearance and/or to enhance the mechanical strength of the related part which is known to be subjected to a substantial stress in use.

The above-mentioned mesh member can be made into a mesh sheet by weaving a fibrous material into a sheet shape.

The above-mentioned mesh member may comprise a mesh-shaped carbon fiber-reinforced plastic, which is constructed by directly winding a carbon fiber-reinforced plastic-based fibrous material onto the shaft body using a filament winding process.

The above-mentioned mesh member may comprise a mesh-shaped carbon fiber-reinforced plastic, which is constructed by directly winding a carbon fiber-reinforced plastic-based fibrous material onto the shaft body using a braiding process.

The above-mentioned mesh member can be constructed by weaving a fibrous material while orienting linearly extending strands or yarns of the above-mentioned fibrous material in the circumferential direction of the shaft body.

The above-mentioned mesh member can be constructed by weaving a fibrous material while orienting linearly extending strands or yarns of the above-mentioned fibrous material in the axial direction of the shaft body.

The above-mentioned mesh member can be constructed by weaving a fibrous material while orienting linearly extending strands or yarns of the above-mentioned fibrous material at a selected angle relative to the axial direction of the shaft body.

The above-mentioned mesh member can be constructed by weaving a fibrous material while orienting linearly extending strands or yarns of the above-mentioned fibrous material in three mutually different directions in the mesh member.

The above-mentioned mesh member can be constructed by weaving a fibrous material while orienting linearly extending strands or yarns of the above-mentioned fibrous material in four mutually different directions in the mesh member.

The above-mentioned mesh member can be constructed by weaving a fibrous material while having a first strand of the above-mentioned fibrous material oriented in the axial direction of the shaft body, a second strand of the above-mentioned fibrous material oriented in the circumferential direction of the shaft body, and a third and fourth strands of the above-mentioned fibrous material oriented at a 45 degree inclined angle to the axial direction and the circumferential direction of the shaft body in a mutually orthogonal manner.

The above-mentioned mesh member can be constructed by weaving a fibrous material using a hexagon mesh weaving process. The above-mentioned mesh member can be constructed so as to form a hexagonal pattern by weaving a fibrous material. The above-mentioned mesh member can be constructed so as to form a pentagonal pattern by weaving a fibrous material. The above-mentioned mesh member can be constructed by weaving a fibrous material using a prepreg.

The above-mentioned mesh member can be constituted by a member having reticular belt-like fiber portions and voids defined between these belt-like fiber portions, and can be exposed from the grip toward the club head, and the color of the underlying surface of the shaft body can be visible through these voids which may consist of pure voids or have a layer of at least semi-transparent plastic material.

The above-mentioned mesh member can be constituted by a member having reticular belt-like fiber portions and voids defined between these belt-like fiber portions, and can be exposed from the above-mentioned grip toward the club head, and the outer surface of the shaft body may have a color that shows through the voids of the mesh member.

The above-mentioned mesh member can have one to 30 of these void(s) or crossover portion(s) per square centimeter. The above-mentioned mesh member can be constructed such that the circumscribed circle diameter of each void is 0.5 mm to 10 mm. The above-mentioned mesh member can be constructed by weaving a fibrous material, and the width of this fibrous material can be 0.2 mm to 5 mm. The above-mentioned mesh member can be constructed by weaving a fibrous material, and the thickness of this fibrous material can be 0.05 mm to 0.50 mm. The above-mentioned mesh member can be constructed such that it weighs 80 g/m² to 240 g/m².

In this application, the terms such as “reticular” and “net-like” should be understood in their broad senses, and accordingly should include any planar structure of fibrous reinforcing members that include belt-like or thread-like fiber portions where the fibrous material exists and voids that are defined between such fiber portions that are formed by weaving, braiding, winding, perforating and molding among other possibilities. In such cases, voids may define recessed portions. When the fiber portions are formed by weaving, braiding or winding, there are cross over portions where at least two runs of the fibrous material cross each other, and these portions give rise to raised portions while the voids give rise to recessed portions. Depending on how the sheet member is formed, the voids may consist of pure voids or may include at least a layer of plastic material which preferably is at least partly transparent although it is not absolutely necessary for implementing the present invention.

In a golf club shaft according to the present invention, because the structure is such that a grip can be secured to the outer surface of the sheet member typically consisting of a carbon fiber-reinforced plastic material (for example, reinforced by a mesh member consisting of a tri-axial woven fabric, a tetra-axial woven fabric, or a mesh-shaped carbon fiber-reinforced plastic constructed by directly winding a carbon fiber-reinforced plastic-based fibrous material onto the above-mentioned shaft body using a filament winding process or a braiding process, or a mesh-shaped carbon fiber-reinforced plastic constructed by directly weaving or braiding a carbon fiber-reinforced plastic-based fibrous material onto the shaft body using a weaving or braiding process), which is affixed circumferentially to the grip end of a steel shaft body, the mesh member-based grip part can achieve, in particular, the effect of enhanced strength, such as bending strength and flattening strength, and the effect of being made lighter weight in line with the enhanced strength, and, in addition, improve vibration damping characteristics. Needless to say, by constituting the mesh member by weaving a fibrous material in a variety of modes, such as a hexagon mesh weaving process, it also becomes possible to realize the above-mentioned differentiation in terms of appearance, and more particularly, it becomes possible to further enhance the strength of the golf club shaft, and to make it lighter weight. In other words, it becomes possible to achieve a super lightweight golf club shaft, something that has been impossible to achieve with the conventional plain metal shaft body. More specifically, by reinforcing a golf club shaft using a mesh member that weighs around 2 grams to 10 grams, it is possible to manufacture an ultra-lightweight shaft of less than 80 grams while having the strength required of a golf club shaft.

In addition, the friction action or resistance action resulting from the irregular surface texture of the mesh member or sheet member (voids, crossover portions and belt-like fiber portions) makes it possible to securely fasten a grip to the shaft body. Therefore, in the process of bonding or otherwise securing a grip to the shaft body, the quality of the attachment between the grip and shaft body can be made highly uniform without regards to the difference in skill among the workers.

Further, since exposing a portion of the mesh member from the grip toward the club head can make the color of the underlying surface of the shaft body visible through the voids, the golf club shaft can be differentiated from the standpoint of appearance. Plating may be used to applying different colors to the shaft body.

Furthermore, steel is superior as a material for a golf club shaft, and has various advantages over carbon reinforced plastic material, such as a higher toughness, an ability to undergo a large deflection without losing the resiliency, a high resistance to twisting, a high resistance to scratching, etc. Although steel is preferred as the material for the shaft body to which the present invention is applied, aluminum, titanium and various alloys may also be used as the material for the shaft body when implementing the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a golf club 1, which uses a golf club shaft 2 in accordance with a first embodiment of the present invention;

FIG. 2 is a plan view showing one example of a sheet member 6 having reticular shapes of a regular hexagon and a triangle in accordance with the first embodiment of the present invention;

FIG. 3 is a plan view showing another example of a sheet member 6 having a reticular shape of a regular hexagon in accordance with the first embodiment of the present invention;

FIG. 4 is a plan view showing another example of a sheet member 6 having a reticular shape of a regular square in accordance with the first embodiment of the present invention;

FIG. 5 is a plan view showing another example of a sheet member 6 having a reticular shape of a regular triangle in accordance with the first embodiment of the present invention;

FIG. 6 is a front view of an essential element showing a process for attaching a sheet member 6 to a shaft body 5 in accordance with the first embodiment of the present invention;

FIG. 7 is a cross-sectional view of an essential element showing a process for attaching a grip 3 to a shaft body 5, which is covered with a sheet member 6 in accordance with the first embodiment of the present invention;

FIG. 8 is a front view showing examples of the structures of golf clubs 1 comprising a set made up of woods, irons and a putter in accordance with the first embodiment of the present invention;

FIG. 9 is an oblique view of a 50 mm long first test piece 20 made from the grip 3 part of the shaft body 5 for carrying out a flattening strength test in accordance with the first embodiment of the present invention;

FIG. 10 is an oblique view of a 50 mm long second test piece 21a made from the grip 3 part of the shaft body 5 for carrying out a flattening strength test in accordance with the first embodiment of the present invention;

FIG. 11 is a simplified side view of a flattening strength testing device 22 for carrying out a flattening strength test in accordance with the first embodiment of the present invention;

FIG. 12 is a graph showing the results of a flattening strength test for carrying out a flattening strength test in accordance with the first embodiment of the present invention;

FIG. 13 is a simplified side view of a three-point bending strength testing device 30;

FIG. 14 is a simplified side view of an Izod impact value testing device 40;

FIG. 15 is a simplified side view of a device 50 for testing vibration-damping capabilities;

FIG. 16 is a graph showing the relationship of a frequency response function relative to a frequency for testing vibration-damping capabilities;

FIG. 17 is a table showing the difference between the value of a frequency response function of a plain shaft body 5, and the value of a frequency response function of a shaft body 5 with a sheet member 6 attached, at specified frequencies;

FIG. 18 is a front view of an essential element of the grip end 7 part of a golf club shaft 60 in accordance with a second embodiment of the present invention;

FIG. 19 is a front view of an essential element of the grip end 7 part of a golf club shaft 70 in accordance with a third embodiment of the present invention;

FIG. 20 is a plan view of another example of a mesh material (a mesh sheet 80 of a tetra-axial woven fabric) of the present invention; and

FIG. 21 is a table of the results of experiments concerning flattening strength, three-point bending strength and Izod impact values, respectively, for a plain shaft and a shaft body 5 wrapped with a mesh sheet 80 in accordance with the present invention (tetra-axial composite)

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Since the structure is such that a grip is attached to a steel shaft body by interposing a fiber-reinforced plastic sheet member, that includes a fibrous reinforcing member typically having a reticular (or net-like) structure, the present invention achieves an ultra-lightweight golf club shaft, which enhances the bending strength, flattening strength and vibration damping capabilities of the grip part, and, in addition, improves grip fixability, and makes possible differentiation from the standpoint of appearance as well.

FIG. 1 is a front view of a golf club 1, and the golf club 1 has a golf club shaft 2, a grip 3 and a club head 4. The golf club shaft 2 has a shaft body 5 and a sheet member 6. The shaft body 5 is formed of steel, and the grip 3 can be mounted to the grip end 7 on one end thereof, and a club head 4 can be mounted to the club head end 8 on the other end thereof.

The sheet member 6 is secured circumferentially in one continuous turn to the grip end 7 of the shaft body 5, and has a longitudinal length that extends from the shaft body end 5A toward the club head 4 until it is exposed from the grip 3, and a grip 3 can be secured to the outer cylindrical surface of this sheet member 6. In this embodiment, the two edges of the sheet member 6 extending in the axial direction of the shaft body 5 substantially abut each other without any overlap although it is all within the spirit of the present invention to wrap it short of the full turn or by more than one turn. The ring-shaped exposed portion 6A of the sheet member 6 presents a distinctive appearance. Typically, the reinforcing fiber shows through the surrounding plastic material, and adds to distinctive appearance owing to its reticular, knit, wound or other structure. The sheet member 6 may extend to the very end of the grip end 5A or may terminate short of the terminal end of the shaft body by a predetermined longitudinal length of, preferably, 60 mm or less.

When the object is to differentiate the golf club shaft 2 itself from the standpoint of appearance in particular, the sheet member 6 fastening or securing mode can, of course, be continuous, discontinuous or intermittent in either the circumferential or axial directions of the shaft body 5. However, when the object is to enhance the bending strength, flattening strength or vibration damping capabilities of the shaft body part, and make it lighter weight, it is desirable that the sheet member 6 be secured by wrapping it circumferentially one full turn around the shaft body 5 although it is well within the spirit of the present invention to wrap it by more than one turn or slightly less than one turn.

The sheet member 6 can employ a carbon fiber-reinforced plastic or a prepreg thereof. Although carbon fiber is preferred as a reinforcing material, it is also possible depending on the case to use other fibrous material such as glass fibers, boron fibers, metallic fibers or other fiber material that is capable to achieving a high mechanical strength particularly when placed in a matrix of epoxy or other resin or plastic material. A prepreg is a material that is formed by impregnating a resin into a carbon fiber or other such fiber material (preferably, an extremely thin yarn called “spread fiber yarn”) in advance, and the resin can be cured so that the prepreg becomes firmly bonded to the shaft body 5 by heating. Each of these spread fiber yarns may consist of a large number of filaments, typically between 1,000 and 3,000 filaments which may be twisted with one another.

More specifically, the sheet member 6 may comprise reticular belt-like fiber portions 9 and voids 10 defined between these belt-like fiber portions 9. More preferably, the sheet member 6 is formed of the belt-like fiber portions 9 made from a carbon fiber-reinforced plastic or other such fibrous material by weaving, braiding winding or knitting. For instance, “hexagon mesh weaving process (or what is commonly referred to as “tri-axial circular weaving”) may be used.

In addition, regardless of whether the sheet member 6 is formed from a flat sheet, or formed from a fibrous material such that the crossover portions are formed three-dimensionally, if at least one strand of the fibrous material (belt-like fiber portion 9) extends linearly in the circumferential direction of the shaft body 5 as a part of the forming pattern of the fibrous material, the flattening strength of the shaft body 5 can be improved. If at least one strand of the fibrous material (belt-like fiber portion 9) extends linearly in the axial direction of the shaft body 5 as a part of the forming pattern of the fibrous material, the bending strength of the shaft body 5 can be improved. By suitably combining different orientations of such linear parts of the formation of the fibrous material, it is possible to adjust the mechanical properties and vibration damping properties of the shaft main body 5.

The reticular structure of the sheet member 6 can adopt any desired shape, such as a hexagon, pentagon, quadrate or other such square, rhombus, triangle or circle, and, in addition, a shape that combines these shapes.

For example, FIG. 2 is a plan view showing one example of a sheet member 6 having a reticular structure represented by regular hexagons and triangles, and belt-like fiber portions 9 of a carbon fiber-reinforced plastic are woven into a mesh by a hexagon mesh weaving process using a fibrous material, and voids 10 of relatively large regular hexagons and relatively small regular triangles are formed between the belt-like fiber portions 9. These belt-like fiber portions 9 and the resulting crossover portions 11, each having a predetermined thickness, constitute raised portions, and the voids 10 constitute recessed portions of the final sheet member 6.

The hexagon mesh, as shown in FIG. 2, is constructed by weaving such that fibrous materials (belt-like fiber portions 9), which mutually extend in three directions (tri-axially) at intersecting angles of 120 degrees, are woven or braided into a hexagonal shape. The hexagon mesh thus has what can be called as three-dimensional crossover portions 11 such that each run of the fibrous materials, which intersect at the crossover portions 11, alternates between upper and lower positions from one crossover portion 11 to the next.

The sheet member 6 may have one to 30 recessed portion(s) or raised portion(s) for each square centimeter as a measure of the coarseness of the sheet member 6 in the case of the illustrated embodiment. The sheet member 6 may have such a structure that each void defines a circumscribed circle which is 0.5 mm to 10 mm in diameter.

For example, in the structure shown in FIG. 2, each of the regular hexagonal voids may define a circumscribed circle C1 having a diameter of approximately 2 mm, and each of the regular triangular voids may define a circumscribed circle C2 having a diameter of approximately 1 mm.

FIG. 3 is a plan view showing another example of a sheet member 6 having a reticular shape defining regular hexagonal voids 10, and in this sheet member 6, by making the width of the belt-like fiber portions 9 wider, the area occupied by the belt-like fiber portions 9 and the crossover portions 11 (defining raised portions) is made larger, and the voids 10 having the hexagonal shape (defining recessed portions) is made smaller. Each of the regular hexagonal voids 10 may define a circumscribed circle C3 having a diameter of approximately 1.5 mm while there is essentially no triangular voids or each regular triangular void is reduced to defining a circumscribed circle having an essentially zero diameter.

The width of this belt-like fiber portion 9 may be from 0.2 mm to 5 mm. This width is 1 mm in the embodiment illustrated in FIG. 3. Also, the thickness of this belt-like fiber portion 9 may be from 0.05 to 0.50 mm. The sheet member 6 may weigh from 80 to 240 g/m².

FIG. 4 is a plan view showing yet another example of a sheet member 6 having a reticular structure formed by weaving or braiding the belt-like fiber portions 9 in a rectangular grid-like manner. In this case also, each run of the belt-like fiber portions 9 may alternate between upper and lower positions with respect to the other run of the belt-like fiber portions 9 from one crossover point to the next. The voids 10 defined by the belt-like fiber portions 9 are each provided with a square shape.

FIG. 5 is a plan view showing yet another example of a sheet member 6 having a reticular structure formed by weaving or braiding the belt-like fiber portions 9 of the sheet member 6 that are oriented at different angles that are 60-degree apart. In this case also, each run of the belt-like fiber portions 9 may alternate between upper and lower positions with respect to the other run of the belt-like fiber portions 9 from one crossover point to the next. The voids 10 defined by the belt-like fiber portions 9 are each provided with a regular triangular shape.

FIG. 6 and FIG. 7 illustrate the process of mounting the sheet member 6 and the grip 3 to the shaft body 5. FIG. 6 is a front view of the essential components and shows the sheet member 6 in the form of a prepreg or the like wrapped around the grip end 7 of the shaft body 5 by one full turn. As shown in the enlarged portion of FIG. 6, the sheet member 6 is temporarily secured to the shaft body 5 by wrapping a synthetic resin tape 12 at a prescribed spiral pitch around the outer surface of the sheet member 6. Alternatively, this sheet member 6 may also be temporarily secured to the periphery of the shaft body 5 by applying a suitable adhesive, instead of using a tape.

While the sheet member 6 is temporarily secured to the grip end of the shaft main body 5 in this fashion, the sheet member 6 is heated to a prescribed temperature inside a heating oven 13. After this curing process, the synthetic resin tape 12 is removed, and this reveals the color and texture of the shaft body 5 itself through the voids 10 of the sheet member 6.

FIG. 7 is a cross-sectional view of the essential components and shows the process of mounting the grip 3 the part of the shaft body 5 already covered by the sheet member 6. First of all, an adhesive 14 is applied to the outer surface of the sheet member 6. A rubber grip 3 in an inflated state by virtue of air pressure applied from the inside thereof is fit on the grip end of the shaft body 5. The air pressure is removed, and this causes the grip 3 to return to its original shape and firmly and resiliently adhere to the outer surface of the sheet member 6. With the help of the adhesive 14, the grip 6 is firmly and permanently attached to the grip end 7 of the shaft body 5.

Since the grip 3 is bonded to the grip end 7 of the shaft body 5 via the sheet member 6, the grip can be firmly secured to the shaft body 5 on account of a large friction that exits between the grip 3 and sheet member 6 primarily owing to the irregular surface texture of the sheet member 6.

Furthermore, as shown in FIG. 1 in particular, by having a part of the sheet member 6 (exposed portion 6A) extend beyond the club head end of the grip 3, it is possible to produce a distinctive feature on account of the particular color and texture of the sheet member 6, and this is beneficial in enhancing the appearance of the golf club in addition to increasing the mechanical strength of the affected part.

In other words, by forming the belt-like fiber portions 9 in a specific pattern so as to define voids 10 of different shapes, such as a hexagon, pentagon, square, rhombus, triangle, circle or other such pattern, it is possible, especially when the belt-like fiber portions 9 are formed from carbon fiber-reinforced plastic, to achieve a unique appearance owing to a pronounced contrast between the metallic hue of the shaft body 5 and the pitch black color of the belt-like fiber portions 9. In particular, owing to the fact that the metallic hue of the shaft body 5 shows through the voids of the sheet member 6, the sheet member 6 acquires a unique appearance, and this enhances the aesthetic appearance of the golf club shaft. Furthermore, the shaft body 5 may be given with other colors (such as orange, yellow, green, blue, purple, etc.), for instance by plating, and an additional distinct feature may be accomplished so that the design choices of the golf club may be greatly expanded.

FIG. 8 is a front view showing a set of golf clubs 1 including wood and iron clubs and a putter according to the present invention (although the club heads are omitted from illustration), and each of these respective golf clubs 1 includes a sheet member 6 including an extension 6A exposed from the grip 3 so that the club set may be given with a uniform design. It is also possible to differentiate each club of the set from the others by changing the design of the mesh structure of each shaft and/or changing the color of the underlying surface of the shaft body 5 that shows through the voids 10 of the sheet member extension 6A from one shaft to the other.

Furthermore, the presence of the sheet member 6 in the grip end of the shaft body 5 increases the rigidity, bending and flattening strengths and vibration damping capabilities of this part. It is particularly the case because the sheet member 6 (including the extension 6A thereof) is provided in the part of the shaft body 5 which is adjacent to the club head end of the grip where severe stresses are known to occur. By thus effectively strengthening the essential or strategic part of the club shaft, it becomes possible to minimize the weight of the club shaft without in any way compromising the mechanical strength thereof or to maximize the mechanical strength of the club shaft for a given weight of the club shaft.

In particular, by making the belt-like fiber portions 9 from a carbon fiber-reinforced plastic or other such fibrous material, and weaving or braiding this by using a “hexagon mesh weaving process” or other similar process so as to orient at least one strand of the fibrous material (belt-like fiber portion 9), which extends linearly in the net-like structure of the belt-like fiber portions 9 in the sheet member 6, in the circumferential direction, axial direction or other directions of the shaft body 5, it is possible to improve the bending strength, flattening strength, and vibration damping capabilities of the shaft body 5.

A process of wrapping and securing a sheet member 6 in the form of a prepreg made of a carbon fiber-reinforced plastic (as described in connection with FIG. 3) to a steel shaft body 5 is described in the following with reference to FIGS. 9 to 11.

FIG. 9 is a perspective view of a 50 mm-long first test piece 20 cut from the grip end of the shaft body 5 for flattening strength tests, and FIG. 10 is a perspective view of a similar 50 mm-long second test piece 21a cut from the grip end of the shaft body 5 and wrapped by the sheet member 6 according to the present invention that extends 40 mm from the terminal end 5A of the shaft body 5. The strands of fibrous materials (belt-like fiber portions 9) include those that extend linearly in the circumferential direction of the shaft body 5. A third test piece 21b was also prepared that includes two layers of the sheet member 6 and is otherwise same as the second test piece 21a. In all of these test pieces, the outer diameter was 14.80 mm, and the wall thickness was 0.288 mm. The fibrous material (belt-like fiber portions 9) of the sheet member 6 was 1 mm wide and 0.07 mm thick.

FIG. 11 is a simplified perspective view of a flattening strength testing device 22 for the first test piece 20 and second test pieces 21a and 21b, and the flattening strength testing device 22 has a metallic anvil 23 and a metallic load applicator 24, an actuator 25 and a load sensor 26. A load was continuously applied by the actuator 25 to the first test piece 20 and the second test pieces 21a and 21b placed between the anvil 23 and load applicator 24 by lowering the load applicator 24 at the rate of 5 mm/min until the first test piece 20 and second test pieces 21 fractured, and the load at the time of fracture and displacement of the load applicator 24 were measured in each case by the load sensor 26.

FIG. 12 is a graph showing the results of the flattening strength test, and the first test piece 20, which was not provided with the sheet member 6, fractured at the load of 70 kgf. The second test piece 21a, which was fitted with a layer of the sheet member 6, fractured at the load of 80 kgf. The third test piece 21b, which was covered with two layers of the sheet member 6, fractured at the load of 82 kgf.

The test demonstrated that wrapping a layer of the hexagon-mesh-woven sheet member 6 around the shaft body 5 improved the flattening strength by 14%, and wrapping two layers of the mesh sheets 6 around the shaft body 5 improved the flattening strength by 17%.

FIG. 13 is a simplified side view of a three-point bending strength testing device 30 that comprises a pair of supports 31 that are spaced apart by 300 mm, a load applicator 32 and a load sensor 33 that measures the load and displacement of the load applicator 32. The test pieces similar to those of the flattening test described in connection with FIGS. 9 to 11 were used except that each test piece was approximately 350 mm long, and the sheet member 9 extended by a length of slightly more that 300 mm in an intermediate part of the test piece.

Each test piece was symmetrically placed on the supports 31, and the load applicator 32 was applied to a middle point of the test piece between the two supports continuously at the loading rate of 20 mm/min until the test piece fractured. The displacement of the load applicator 32 and load at the time of the fracture were measured by using the load sensor 33 for each test piece.

The first test piece 20, which was not wrapped by the sheet member 6, fractured at the load of 40.6 kgf. The second test piece 21a, which was wrapped by one layer of the sheet member 6, fractured at the load of 46.2 kgf. In other words, it was demonstrated that wrapping one layer of the hexagon-mesh-woven sheet member 6 around the shaft body 5 increased the bending strength by 13.8%.

FIG. 14 is a simplified side view of an Izod impact value testing device 40, and the Izod impact value testing device 40 has a base portion 41, a test piece mount 42 attached to the center of this base portion 41, a frame 43, a pivot shaft 44 provided in an upper part of the frame 43, a swing arm 45 that freely rotates around the pivot shaft 44, a hammer 46 affixed to the tip of the swing arm 45 and an impact value indicator 47 indicating the angular position of the swing arm 45.

Test pieces similar to the first and second test pieces 20 and 21a similar to those illustrated in FIG. 9 and FIG. 10 were prepared. Each test piece was affixed upright on the test piece mount 42. The hammer 46 was released from a certain angular position, and let freely fall under the gravitational force until it impacts the test piece. The load at the time of the fracture was measured by using the impact value indicator 47.

According to the measurement results, the first test piece 20, which was not wrapped by the sheet member 6, fractured at the impact force of 9.1 ft-lbs (foot-pounds). The second test piece 21a, which was wrapped by one layer of the sheet member 6, fractured at the impact force of 9.9 ft-lbs. In other words, wrapping one layer of the hexagon-mesh-woven sheet member 6 around the shaft body 5 improved the Izod impact value by 8.8%.

Next, vibration damping capabilities were also tested. This test is also called as an impact response test or a transfer function measurement test. FIG. 15 is a simplified side view of a vibration-damping capabilities testing device 50, and shows both a steel shaft body 5 which is not wrapped by the sheet member 6, and a steel shaft body 51 which is wrapped by the sheet member 6. Furthermore, the lengths of the shaft bodies 5, 51 are designated by letter L, and the sheet member 6 is affixed to the shaft body 51 so as to extend the length of 400 mm from the shaft body end 51A.

This vibration-damping capabilities testing device 50 has a pair of supports 52 that are suspended on strings at points that are 0.224L away from the grip end and club head end of each shaft body 5, respectively, an impulse hammer 53 and an accelerometer 54 mounted on the shaft body 5 at a point 150 mm away from the grip end. An impact is applied to one of the support points 52 on the club head end side by using the impulse hammer 53, and the accelerometer 54 measured the resulting acceleration of the corresponding point on the shaft body 5.

The impulse hammer kit was made by PCB Piezotronics, Inc., and an FFT analyzer made by Ono Sokki Co., Ltd. was used to analyze the data obtained from the accelerometer 54. A frequency response function (A/F) was identified by using the impact by the impulse hammer 53 as the input F and the acceleration measured by the accelerometer 54 as the output A. Twenty cycles of test were performed for each set of data. The highest frequency was 2.5 kHz and the resolution power was 4,096 N.

FIG. 16 is a graph showing the relationship between the frequency response function and the frequency, and the dotted line in the graph indicates the shaft body 5 not wrapped by the sheet member 6, and the solid line indicates the shaft body 51 wrapped by the sheet member 6 according to the present invention, respectively.

As demonstrated in the graph, the shaft body 51 wrapped by the sheet member 6 is significantly lower in the frequency response function particularly in the high frequency range as compared with the shaft body 5 without the sheet member. It is known that the vibrations of the higher frequency range strongly affect the behavior of the club shaft at the time of ball impact, and the test result clearly indicates a substantial improvement in vibration damping capabilities in such a high frequency range.

FIG. 17 is a table showing the differences, at specified frequencies, between the value of the frequency response function of the shaft body 5 without the sheet member 6 and the value of the frequency response function of the shaft body 51 with the sheet member 6. As is clear from this table, significant differences were recorded at various frequencies.

The sheet member 6 of the present invention is not limited to those described above, and can also be implemented by directly wrapping a fibrous material around the grip end 7 of a shaft body 5. FIG. 18 is a front view of an essential part of such an embodiment. A carbon fiber-reinforced plastic fibrous material 61 consisting of a single yarn or a plurality of yarns is wrapped around the grip end 7 of a golf club shaft 60 by using a filament winding process. It the illustrated embodiment, a pair of yarns of the carbon fiber-reinforced plastic fibrous material 61 are wrapped around the grip end 7 of a golf club shaft 60 spirally at a prescribed angle relative to each other. Therefore, voids having a rhombus shape are formed between the yarns of the carbon fiber-reinforced plastic fibrous material 61.

The carbon fiber-reinforced plastic fibrous material 61 is formed by impregnating a resin material into strands of carbon fibers or other such fibrous material (that may consist of extremely thin threads called “spread fiber yarns”) in advance. Each spread fiber yarn may consist of 1,000 to 3,000 filaments.

The thickness of the carbon fiber-reinforced plastic fibrous material 61 can be between 0.05 mm and 0.3 nun, and preferably about 0.07 mm, and the width can be between 0.2 mm and 5 mm, and preferably 3 mm. This can be prepared in the same way as the belt-like fiber portions 9 of the sheet member 6 in the previous embodiments. The mesh-shaped carbon fiber-reinforced plastic 62 can also be constructed by winding any number of yarns to achieve a desired mesh-like pattern. Alternatively, the mesh-shaped carbon fiber-reinforced plastic may be formed as a sheet member before it is wrapped around the grip end 7 of the shaft body 5, or the mesh-shaped carbon fiber-reinforced plastic may be directly braided around the grip end 7 of the shaft body 5.

A golf club shaft 60 based on this embodiment can also demonstrate an enhanced bending and flattening strengths and vibration damping capabilities. Also, the irregular surface texture on the surface of the sheet member 6 increases the friction between the grip and shaft main body, and ensures a firm and reliable attachment between the grip and shaft body. This embodiment also provides the distinct appearance owing to the presence of a net-like sheet member extending under the grip and beyond the club head end of the grip by a desired length.

FIG. 19 is a front view of an essential part of the grip end 7 of a golf club shaft 70 given as yet another embodiment of the present invention. A mesh-shaped carbon fiber-reinforced plastic 71, similar to the mesh-shaped carbon fiber-reinforced plastic 62 of the golf club shaft 60 shown in FIG. 18, is affixed as a mesh member by directly braiding a carbon fiber-reinforced plastic fibrous material 61 in a variety of patterns onto a shaft body 5 using a braiding process. This mesh-shaped carbon fiber-reinforced plastic 71 defines rhombus or parallelogram-shaped voids. This embodiment provides similar advantages as those of the previous embodiment.

FIG. 20 is a plan view of a mesh sheet 80 of a tetra-axial braided fabric, and the mesh sheet 80 is constructed by three-dimensionally braiding a fibrous material (belt-like fiber portions 9) just like the tri-axial woven fabric-based sheet member 6 (refer to FIG. 2 and FIG. 3) before it is wrapped around the grip end 7 of the shaft body 5. It is also possible to directly braid the fibrous material (belt-like fiber portions 9) around the grip end 7 of the shaft body 5.

The mesh sheet 80 has strands or yarns of belt-like fiber portions 9, which extend linearly in four mutually different directions. In other words, the mesh sheet 80 has a strand 9A of a belt-like fiber portion 9, which is oriented in the axial direction of a shaft body 5, a strand 9B of a belt-like fiber portion 9, which is oriented in the circumferential direction of the shaft body 5, and two strands 9C and 9D of belt-like fiber portions 9, which are oriented at a 45-degree inclined angle to the axial direction and the circumferential direction of the shaft body 5.

The width and thickness of a belt-like fiber portion 9 can be selected in the same was as those of the sheet member 6 (FIG. 3), and the example shown in the drawing has a width of 1 mm. The pitch between strands 9A and 9B is 3.2 mm, and the pitch between strands 9C and 9D is 4.5 mm, and these strands are three-dimensionally braided into mesh shapes as shown in the FIG. 20. Furthermore, the voids of the mesh sheet 80 define a pentagonal shape, and the diameter of the circumscribed circle C4 thereof is, for example, 2.3 mm.

Various tests were also performed on the thus constructed sheet member 80 in the same was as on the sheet member 6. More specifically, the carbon fiber-reinforced plastic prepreg-based mesh sheet 80 was wrapped around and secured to a steel shaft body 5, and flattening strength testing was carried out in the same manner as was explained in connection with FIG. 9 through FIG. 12, a three-point bending strength testing was carried out in the same manner as was explained in connection with FIG. 13 and an Izod impact value test was carried out in the same manner as was explained in connection with FIG. 14.

FIG. 21 is a table of the results of the tests concerning flattening strength, three-point bending strength and Izod impact values, respectively, for a plain shaft and a shaft body 5 wrapped by a mesh sheet 80 in accordance with the present invention (tetra-axial composite). The letter N in the table indicates the number of specimens, and the respective figures for the flattening strength, three-point bending strength and Izod impact value show the average values of these samples.

As shown in the table, despite a weight difference of only 2.8 grams (increase of 3.7%), the shaft body 5 wrapped by a mesh sheet 80 in accordance with the present invention (tetra-axial composite) was able to achieve increases of approximately 15%, 24%, and 48%, respectively, with regard to the flattening strength, three-point bending strength and Izod impact value.

Further, the results of carrying out vibration damping capabilities testing similar to that described in connection with FIG. 15 through FIG. 17 demonstrated that the shaft body 5 wrapped by a mesh sheet 80 in accordance with the present invention (tetra-axial composite) was able to achieve the same vibration damping capabilities as the tri-axial composite sheet member 6 (FIG. 3).

Thus, reinforcing a golf club shaft using a sheet member 6, 80 that weighs around between two and 10 grams, or a slightly heavier material resulting from a mesh member, such as a mesh-shaped carbon fiber-reinforced plastic 62, 71, makes it possible to manufacture an ultra-lightweight shaft (golf club shafts 1, 60, 70), which, even though it weighs less than 80 grams, still has the flattening strength and bending strength that are no less than those of the conventional shafts.

Although the present invention has been described in terms of preferred embodiments thereof, it is obvious to a person skilled in the art that various alterations and modifications are possible without departing from the scope of the present invention which is set forth in the appended claims.

The contents of the original Japanese patent applications on which the Paris Convention priority claim is made for the present application are incorporated in this application by reference.

Claims

1. A golf club shaft, comprising: a shaft body including a grip end and a club head end; a sheet member made of fiber reinforced plastic material secured circumferentially around a cylindrical outer surface of the grip end of said shaft body; and a grip affixed around an outer surface of said sheet member.

2. The golf club shaft according to claim 1, wherein said sheet member comprises a mesh sheet formed by weaving or knitting fibrous material.

3. The golf club shaft according to claim 1, wherein said sheet member comprises a mesh sheet formed by winding fibrous material around said shaft body by using a filament winding process.

4. The golf club shaft according to claim 1, wherein said sheet member comprises a mesh sheet formed by winding fibrous material around said shaft body by using a braiding process.

5. The golf club shaft according to claim 1, wherein said sheet member comprises a mesh of fibrous material that includes a yarn extending linearly circumferentially around the shaft body.

6. The golf club shaft according to claim 1, wherein said sheet member comprises a mesh of fibrous material that includes a yarn extending linearly axially along a length of the shaft body.

7. The golf club shaft according to claim 1, wherein said sheet member comprises a mesh of fibrous material that includes a yarn extending linearly at an oblique angle with respect to a circumferential line around the shaft body.

8. The golf club shaft according to claim 1, wherein said sheet member comprises a mesh of fibrous material that includes a plurality of yarns extending linearly at different angles.

9. The golf club shaft according to claim 8, wherein the yarns include a first yarn oriented in an axial direction of the shaft body, a second yarn extending circumferentially around the shaft body, a third yarn extending at a 45 degree angle with respect to the second yarn and a fourth yarn extending at a 45 degree angle in an opposite direction with respect to the second yarn.

10. The golf club shaft according to claim 1, wherein said sheet member comprises a mesh of fibrous material which is constructed by weaving a fibrous material using a hexagon mesh weaving process.

11. The golf club shaft according to claim 1, wherein said sheet member comprises a mesh of fibrous material which is constructed so as to form a polygonal pattern by weaving a fibrous material.

12. The golf club shaft according to claim 1, wherein said sheet member comprises a mesh of fibrous material which is constructed by weaving a fibrous material using a prepreg.

13. The golf club shaft according to claim 1, wherein said sheet member includes an extension that extends a prescribed length from a club head end of the grip.

14. The golf club shaft according to claim 13, wherein at least the extension of said sheet member comprises a mesh of fibrous material which defines voids between the fibrous material, the voids being at least semi-transparent by absence of material or by presence of at least semi-transparent plastic material.

15. The golf club shaft according to claim 14, wherein at least the part of the club body underlying the extension of said sheet member is given with a distinct color so as to show through the voids of the sheet material.

16. The golf club shaft according to claim 14, wherein the mesh of fibrous material define one to 30 voids per square centimeter.

17. The golf club shaft according to claim 14, wherein each void defines a circumscribed circle having a diameter of 0.5 mm to 10 mm.

18. The golf club shaft according to claim 1, wherein the sheet member comprises a mesh of fiber material formed by weaving or braiding yarns, and each yarn has a width of 0.2 mm to 5 mm.

19. The golf club shaft according to claim 1, wherein the sheet member comprises a mesh of fiber material formed by weaving or braiding yarns, and each yarn has a thickness of 0.05 mm to 0.5 mm.

20. The golf club shaft according to claim 1, wherein the sheet member comprises a mesh of fiber material formed by weaving or braiding yarns, and weighs 80 g/cm2 to 240 g/cm2.