Golf club shaft

Info

Publication number: 20060128494
Type: Application
Filed: Nov 7, 2005
Publication Date: Jun 15, 2006
Applicant:
Inventor: Tomio Kumamoto (Hyogo)
Application Number: 11/267,161

Abstract

A golf club shaft (10) composed of a metal tube and having a weight not less than 50 g and less than 85 g. A rib (21) is formed on an inner peripheral surface of the golf club shaft (10) and/or a peripheral surface thereof. A rigidity value (EI value) of the golf club shaft (10) at a position spaced at 90 mm from a head-side front end (12) thereof is set to not less than 1.0 kg·mm2 nor more than 2.5 kg·mm2. An outer diameter (D1) of the golf club shaft (10) at a position spaced at 30 mm from the head-side front end (12) thereof is set to not less than 9.5 mm nor more than 15.0 mm.

Description

Description

This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 2004-357416 filed in Japan on Dec. 9, 2004, the entire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a golf club shaft and particularly a golf club shaft, composed of a metal tube, which is lightweight and has a high strength.

DESCRIPTION OF THE RELATED ART

In recent years, to increase the speed of a hit golf ball and hit the golf ball stably, there is a tendency for golf club shaft manufacturers to manufacture a lightweight golf club shaft by making the head heavy concentratedly. Therefore a carbon shaft composed of fiber reinforced resin such as carbon prepreg which is lightweight and has a high specific strength and specific rigidity is most widely used.

The carbon shaft has a low torsional rigidity and is unstable in the direction of a hit ball. Thus in recent years, high-class players take a new look at the directionality and the feeling they have when they hit a ball with a shaft made of metal. Recently it is possible to manufacture a shaft composed of metal tube having a weight of 85 g to 90 g.

Regarding the problem of making a lightweight golf club shaft made of metal and improving the strength thereof, in Japanese Patent Application Laid-Open No. 2002-58764 (patent document 1), there is disclosed the golf club shaft composed of the cold-rolled plate made of maraging steel having a higher strength and toughness than ordinary steel as a material for the golf club shaft made of metal. According to the disclosure, the golf club shaft composed of the above-described material has a high strength and a high torsional rigidity and is lightweight.

In Japanese Patent Application Laid-Open No. 7-51416 (patent document 2), there is disclosed the material made of stainless steel whose surface is coated with the hard ceramic layer such as titanium carbide or titanium nitride formed by sputtering. According to the disclosure, the golf club shaft composed of this material is firm, flexible, and capable of hitting a ball a long distance.

However, to manufacture a shaft that allows female and senior players to swing easily, these conventional arts are required to reduce the weight of the shaft by thinning the material. When the material is thinned, it has a low strength. Considering the balance between the strength of the material and the thickness thereof, there is a limitation in further thinning the material.

In the conventional art, the degree of flexibility of the shaft is adjusted and designed by reducing (stepped portion is formed) the diameter of the metal shaft. In the vicinity of the stepped portion, there is a point at which the thickness of the shaft changes. Thus a bending stress is applied concentratedly to the change point. Consequently the shaft has a low strength.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-described problems. Therefore it is an object of the present invention to provide a metal golf club shaft which has a high strength, is lightweight, and has a proper degree of flexibility.

To solve the above-described problems, the present invention provides a golf club shaft composed of a metal tube and having a weight not less than 50 g and less than 85 g. A rib is formed on an inner peripheral surface of the golf club shaft and/or a peripheral surface thereof. A rigidity value (EI value) of the golf club shaft at a position spaced at 90 mm from a head-side front end thereof is set to not less than 1.0 kg·mm²nor more than 2.5 kg·mm². An outer diameter of the golf club shaft at a position spaced at 30 mm from the head-side front end thereof is set to not less than 9.5 mm nor more than 15.0 mm.

As described above, by forming the rib on the inner peripheral surface of the golf club shaft (hereinafter often referred to as merely shaft) and/or the peripheral surface thereof, the shaft is capable of securing a proper degree of strength and flexibility. Thereby the shaft can be thinned entirely and made as light as 50 g. Further it is possible to design the shaft having a low rigidity by thinning the shaft at its head-side front end which affects the flight distance of a hit ball. Thus the shaft of the present invention is more flexible than the conventional shaft. Thereby female and senior players can swing it easily and increase the head speed, thus hitting a ball a longer distance. Further in addition to the formation of the rib, the outer diameter of the shaft at the position spaced at 30 mm from the head-side front end is set to not less than 9.5 mm nor more than 15.0 mm. That is, the outer diameter of the head side of shaft of the present invention is set larger than that of the head side of the conventional shaft. Thereby it is possible to enhance the strength of the head-side front end which is subjected to a high shock when the ball is hit. Therefore the shaft of the present invention balances favorably among its flexibility, strength, and weight.

The flexibility of the shaft can be varied by adjusting the interval between adjacent ribs or the angle of the rib with respect to the axis of the shaft. Therefore it is unnecessary to reduce the diameter of the shaft unlike the conventional shaft. Thus it is possible to prevent a stress from concentrating on a stepped point at which the thickness of the base is changed. Thereby it is possible to prevent the shaft from being damaged.

The reason the weight of the shaft is set to not less than 50 g and less than 85 g is as described below: When the weight of the shaft is less than 50 g, it is impossible to manufacture a long shaft and make the shaft strong enough to withstand a stress for flexing of the shaft. When the weight of the shaft is more than 85 g, the player has difficulty in swinging the shaft and is incapable of increasing a head speed. Thus the player cannot hit a ball a longer distance. The weight of the shaft is favorably not less than 52 g nor more than 80 g, more favorably not less than 54 g nor more than 70 g, and most favorably not less than 55 g nor more than 65 g.

The reason for specifying the rigidity value of the position spaced at 90 mm from the head-side front end is because a stress is liable to be applied to the position when the player swings.

The reason the rigidity value of the shaft at the position spaced at 90 mm from the head-side front end 12 is set to not less than 1.0 kg·mm²nor more than 2.5 kg·mm²is as described below. If the rigidity value at the position is less than 1.0 kg·mm², the shaft is so soft and flexible that the shaft is liable to be broken owing to metal fatigue. On the other hand, if the rigidity value at the position is more than 2.5 kg·mm², the shaft is so hard at its head side that the degree of flexibility of the shaft is low when the ball is hit and thus the flight distance of the ball decreases. The lower limit of the rigidity value is favorably not less than 1.2 kg·mm²and more favorably not less than 1.3 kg·mm². The upper limit of the rigidity value is favorably not more than 2.4 kg·mm²and more favorably not more than 2.3 kg·mm².

The reason for specifying the outer diameter of the position spaced at 30 mm from the head-side front end is because the position spaced at 30 mm from the head-side front end is inserted into the neck hole of the head and corresponds to the end surface of the neck hole of the head. The outer diameter of the shaft at the position spaced at 30 mm from the head-side front end is set to not less than 9.5 mm nor more than 15.0 mm is as follows: If the outer diameter of the shaft at the above-described position is set to less than 9.5 mm, the shaft is flexible but has a low strength. On the other hand, if the outer diameter of the shaft at the position thereof is set to more than 9.5 mm, the shaft is so thin that it has a low strength. The lower limit of the outer diameter of the shaft thereof at the position thereof is more favorably not less than 9.3 mm and most favorably not less than 9.4 mm. On the other hand, the upper limit of the outer diameter of the shaft at the position thereof is more favorably not more than 14.0 mm and most favorably not more than 13.5 mm.

The rib may be formed on the inner peripheral surface of the shaft and/or the peripheral surface thereof. But it is preferable to form the rib on the inner peripheral surface thereof, because the peripheral surface thereof can be formed as a smooth surface.

It is preferable to continuously form the rib on the entire circumference of the shaft and in the longitudinal direction thereof to provide the shaft with a strength uniformly for a torsion and bending applied to the shaft in right and left directions.

The rib can be formed in the following configurations described in (1) to (5):

(1): A meshed rib by intersecting with each other a spiral rib inclined in a plus direction with respect to the axis of the shaft and a spiral rib inclined in a minus direction with respect to that of the shaft.

The angle of the rib with respect to the axis of the shaft is favorably not less than ±20° nor more than ±60° and more favorably not less than ±30° nor more than ±45°.

(2): A honeycomb rib formed by continuously arranging polygonally framed ribs.

(3): A latticed rib formed by intersecting ribs extended in parallel with the axial direction of the shaft with ribs extended orthogonally to the axial direction thereof.

(4): A rib formed by continuously arranging triangularly framed ribs, one side of each of which is composed of a rib orthogonal to the axial direction of the shaft.

(5): A rib formed by continuously arranging rhombically framed ribs each having a diagonal rib extended in the axial direction of the shaft and another diagonal rib extended orthogonally to the axial direction thereof. Apexes are connected with each other.

The configuration of (1) allows the shaft to be strong mainly for a stress in a torsional direction. Further it is possible to change the torque of the shaft by varying the interval between adjacent spirals and the angle therebetween.

The configuration of (2) allows the shaft to be strong for a torsion, a stress acting in a bending direction with respect to the axial direction of the shaft, and a stress acting in a crushing direction, namely, a direction orthogonal to the axial direction of the shaft.

The configuration of (3) allows the shaft to be strong mainly for the stress acting in the bending direction with respect to the axial direction (0 degree) of the shaft and the stress acting in the crushing direction, namely, the direction vertical to the axial direction of the shaft.

The configuration of (4) allows the shaft to be strong mainly for stresses acting in the torsional direction and the crushing direction.

The configuration of (5) allows the shaft to be strong mainly for stresses acting in the torsional direction, the crushing direction, and the bending direction.

It is preferable that at least one portion of the rib is formed in a region ranging from a head-side front end of the shaft to a position spaced at 200 mm from the head-side front end or the rib is formed in at least one portion of the region.

The region is subjected to a highest shock when the player hits the ball and deforms in a largest amount. Therefore it is possible to effectively enhance the strength of the shaft by forming the rib on the region (hereinafter referred to as head-side reinforcing region), particularly on the inner peripheral surface thereof.

The rib may be formed entirely over the full length of the shaft or in a part of the head-side reinforcing region.

The projected height of the rib is set to 0.1 mm to 11.0 mm, favorably not less than 0.2 mm, and most favorably not less than 0.3 mm. The upper limit of the projected height of the rib is set to favorably not more than 0.9 mm, and most favorably not more than 0.8 mm. The width of the rib is set to 0.1 mm to 11.0 mm, favorably not less than 0.2 mm, and most favorably not less than 0.3 mm. The upper limit of the width of the rib is set to favorably not more than 0.9 mm, and most favorably not more than 0.8 mm.

The rib may be projected integrally with the inner peripheral surface and/or the peripheral surface of the shaft made of a metal tube by forging or press molding. Alternative the rib may be formed by welding metal wires to each other.

More specifically, preferably, a metal belt-like member having the rib formed by press molding on an inner peripheral surface thereof and/or a peripheral surface thereof is wound tubularly, and mating portions of the belt-like member are welded to each other to form the metal tube.

The present invention provides a golf club shaft composed of a metal tube and having a weight of not less than 50 g and less than 85 g. A rib is formed on an inner peripheral surface of the golf club shaft and/or a peripheral surface thereof. At least one portion of the rib is formed in a region ranging from a grip-side rear end of the shaft to a position spaced at an interval corresponding to not less than 30% nor more than 40% of a full length of the shaft or in a portion of the region including a position spaced at an interval corresponding to 35% of the full length of the shaft from the grip-side rear end. The rigidity value of the region is set to not less than 3.5 kg·mm²nor more than 8.0 kg·mm².

That is, the region ranging from the grip-side rear end of the shaft to the position spaced at the interval corresponding to not less than 30% nor more than 40% of the full length of the shaft affects the player's feeling when the player hits the ball. Therefore the rib is formed in this region (hereinafter referred to as grip-side reinforcing region) to enhance the rigidity at the grip side of the shaft. Thereby the player can obtain a preferable feeling when the player hits the ball.

The grip-side rear end has the largest diameter, but is thin. Thus the grip-side rear end is liable to have a low rigidity and strength. This tendency is particularly so in a lightweight shaft having a weight not less than 50 g nor more than 85 g. To overcome this problem, the rib is formed in the grip-side reinforcing region. Thereby it is possible to securely provide the grip-side reinforcing region with a necessary strength, although a thickening-caused increase of the weight of the shaft is restrained.

Although the rib may be formed in a portion forward from the grip-side reinforcing region, it is preferable to form it in only the grip-side reinforcing region. This is because the portion forward from the grip-side reinforcing region demands a low degree of necessity for reinforcement. In addition, if the rib is formed in a wide range, the weight of the shaft increases. Thereby the shaft is difficult to swing.

The reason the rigidity value of the grip-side reinforcing region is set to not less than 3.5 kg·mm²nor more than 8.0 kg·mm²is as follows: If the rigidity value of the grip-side reinforcing region is less than 3.5 kg·mm², the shaft is flexible and is liable to be broken by fatigue. On the other hand, if the rigidity value of the grip-side reinforcing region is more than 8.0 kg·mm², a thick rib or a high rib is formed and thus the shaft has a large weight. The lower limit of the rigidity value of the grip-side reinforcing region is more favorably not less than 3.7 kg·mm², and most favorably not less than 3.9 kg·mm². The upper limit of the rigidity value of the grip-side reinforcing region is more favorably not more than 7.8 kg·mm², and most favorably not more than 7.6 kg·mm².

The configuration of the rib to be formed in the grip-side reinforcing region is as described in the above-described (1) through (5). The height and width of the rib to be formed in the grip-side reinforcing region may be equal to those described above.

Although it is preferable to form the rib on the inner peripheral surface of the shaft, the rib may be formed on the peripheral surface thereof.

It is favorable that the full length of the shaft is not less than 850 mm nor more than 1194 mm. If the full length of the shaft is less than 850 mm, the shaft is so short that a centrifugal force does not work when the player swings, and the shaft is incapable of hitting the ball a long distance. If the shaft is more than 1194 mm, the shaft is so long that the meeting rate decreases, the direction of the hit ball is inconstant, and the ball is frequently hit at off-center positions. That is, the shaft is incapable of hitting the ball a long distance. The full length of the shaft is more favorably not less than 855 mm nor more than 1181 mm and most favorably not less than 860 mm nor more than 1168 mm.

The thickness (thickness of base excluding rib) of the shaft is favorably not less than 0.15 mm nor more than 0.70 mm. If the thickness of the shaft is less than 0.15 mm, it is difficult to securely provide the shaft with a necessary degree of strength, even though the rib is formed on the shaft. If the thickness of the shaft is more than 0.70 mm, the weight of the shaft is large and hence it is difficult to swing it. The lower limit of the thickness of the shaft is more favorably not less than 0.20 mm and most favorably not less than 0.25 mm. The upper limit of the thickness of the shaft is more favorably not more than 0.65 mm and most favorably not more than 0.60 mm.

Effect of the Invention

As apparent from the foregoing description, according to the present invention, the formation of the rib allows the shaft composed of the metal tube to have a necessary rigidity and strength. Thereby it is possible to thin the base of the shaft. Therefore the metal shaft of the present invention is more lightweight than the conventional metal shaft, has a proper degree of flexibility, and has a necessary degree of strength. The formation of the rib at the grip-side rear end allows the rigidity at the grip side of the shaft to be high and the player to have a good feeling when the player swings. Thus the player can swing the shaft easily and hit the ball a long distance therewith.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a golf club according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing the shaft of the golf club shown in FIG. 1.

FIG. 3A is an enlarged schematic plan view showing the configuration of a rib before a tube for the shaft shown in FIG. 2 is formed.

FIG. 3B is an enlarged sectional view showing the configuration of the rib before the tube for the shaft shown in FIG. 2 is formed.

FIG. 4 is a sectional view showing a golf club shaft according to a second embodiment of the present invention.

FIG. 5A is an enlarged schematic plan view showing the configuration of a rib before a tube for the shaft shown in FIG. 4 is formed.

FIG. 5B is an enlarged sectional view showing the configuration of the rib before the tube for the shaft shown in FIG. 4 is formed.

FIG. 6 is a sectional view showing a golf club shaft according to a third embodiment of the present invention.

FIG. 7 is an enlarged sectional view showing the configuration of a rib before a tube for the shaft shown in FIG. 6 is formed.

FIG. 8 is a sectional view showing a golf club shaft according to a fourth embodiment of the present invention.

FIG. 9 is an enlarged sectional view showing the configuration of a rib before a tube for the shaft shown in FIG. 8 is formed.

FIGS. 10A, 10B, and 10C are a plan view respectively showing the configuration of other internal ribs.

FIG. 11 shows a method of measuring a rigidity value.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be described below with reference to drawings.

FIGS. 1 through 3 show a golf club shaft (hereinafter often referred to as merely shaft) 10 according to a first embodiment of the present invention.

In the shaft 10, a rib 21 is formed on the inner side of a tapered tube body 11 made of steal. A head 14 is mounted on the tube body 11 at its head-side front end 12 having a smaller diameter. A grip 15 is mounted on the tube body 11 at its grip-side rear end 13 having a larger diameter. The full length L of the shaft 10 is set to 955 mm. The weight of the shaft 10 is set to 65 g.

As shown in FIG. 3A, a belt-like steel (belt-like member) 11′ having a thickness of 0.2 mm is press molded to form a rib 20 entirely on one surface 11a′ of the belt-like steel 11′. The belt-like steel 11′ is shaped cylindrically, with the surface 11a′ of the belt-like steel 11′ disposed at the inner side of the belt-like steel 11′. Mating portions of the belt-like steel are welded to each other to form a tube. As shown in FIG. 2, an outer diameter D1 of the shaft 10 at a position spaced at 30 mm from the head-side front end 12 is set to 9.5 mm.

More specifically, spiral ribs 20a inclined at +45° to an X-direction axis of the shaft 10 are press molded in parallel at intervals of 15 mm. Spiral ribs 20b inclined at −45° to the X-direction axis of the shaft 10 are also press molded in parallel at intervals of 15 mm. Meshed ribs 21 are formed continuously and entirely on the one surface of the belt-like steel 11′, with the spiral ribs 20a and 20b intersecting with each other. As shown in FIG. 3B, the ribs 21 are projected at a height H1 of 0.3 mm from the one surface (inner peripheral surface) of the belt-like steel 11′.

Because the rib 21 is formed entirely on the inner peripheral surface of the shaft 10, in a head-side reinforcing region 16 ranging from the head-side front end 12 which deforms in a largest amount when a golf ball is hit to a position spaced at 200 mm from the head-side front end 12, the rigidity value of the shaft 10 at a position spaced at 90 mm from the head-side front end 12 is set to 1.4 kg·mm²falling in the range not less than 1.0 kg·mm²nor more than 2.5 kg·mm².

The rigidity value of a grip-side reinforcing region 17 is set to 4.2 kg·mm²falling in a range not less than 3.5 kg·mm nor more than 8.0 kg·mm². The grip-side reinforcing region 17 ranges from a position 17a spaced at an interval corresponding to 30% of the full length L of the shaft 10 from the grip-side rear end 13 to a position 17b spaced at an interval corresponding to 40% of the full length L thereof from the grip-side rear end 13.

The rib 21 is formed on the entire inner peripheral surface of the shaft 10 having the above-described construction. Thus it is possible to thin the tube body 11 and allow it to have a high strength. In particular, the spiral ribs 21 inclining with respect to the axial direction of the shaft 10 are continuously formed on the entire circumference thereof and in the full length thereof by intersecting the spiral ribs 21 with each other. Therefore it is possible to provide the shaft 10 with a high strength for a stress in a torsional direction.

The shaft 10 is lightweight and can be swung easily. Further a golfer has a feeling of a proper degree of flexibility when the golfer hits the ball.

That is, in the head-side reinforcing region 16 ranging from the head-side front end 12 which deforms in a largest amount when a golf ball is hit to the position spaced at 200 mm from the head-side front end 12, the rigidity value of the shaft 10 is set to not less than 1.0 kg·mm²nor more than 2.5 kg·mm²so that the shaft 10 is softer and more flexible than ordinary shafts. Thus the shaft allows the golfer to hit a ball a longer distance than the ordinary shafts.

An outer diameter D1 of the shaft 10 at the position spaced at 30 mm from the head-side front end 12 is set to 9.5 mm which is longer than that of the ordinary shaft to enhance the strength of the head-side reinforcing region 16 which is subjected to a high shock.

Because the rigidity value of the grip-side reinforcing region 17 is set to the range not less than 3.5 kg·mm²nor more than 8.0 kg·mm², the shaft 10 has a high rigidity at its grip side. Thereby the golfer has a preferable feeling when the golfer hits the ball.

FIGS. 4, 5A, and 5B show a shaft 10 according to a second embodiment of the present invention. Except that a honeycomb rib 22 is formed on the inner peripheral surface of the shaft 10, the shaft 10 of the second embodiment has the same construction as that of the first embodiment. Thus the same parts of the second embodiment as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and description thereof is omitted herein.

More specifically, after the belt-like steel 11′ is press molded by a honeycomb die to form the honeycomb rib 22 on a surface 11a′ thereof, the belt-like steel 11′ is shaped tubularly with the surface 11a′ disposed at the inner side of the belt-like steel 11′ to form the shaft 10. The rib 22 is projected at a height H2 of 0.3 mm from the inner peripheral surface of the belt-like steel 11′. An outer diameter D2 of the shaft 10 at a position spaced at 30 mm from the head-side front end 12 is set to 10.1 mm. The weight of the shaft 10 is set to 55 g.

In the second embodiment, the rib 22 is formed on the inner peripheral surface of the shaft 10. Thus it is possible to thin the tube body 11 to make it lightweight and provide it with a high strength. In particular, as shown in FIG. 5A, because the honeycomb rib 22 is formed, the shaft 10 can be provided with a high strength for a stress in not only a torsional direction, but also in a bending direction and a crushing direction.

Like the shaft of the first embodiment, by forming the rib 22 on the inner peripheral surface of the shaft 10, the rigidity value of the golf club shaft at the position thereof spaced at 90 mm from the head-side front end 12 thereof is set to not less than 1.5 kg·mm². Thereby the shaft 10 is softer and more flexible than ordinary shafts. An outer diameter D2 of the shaft 10 at the position spaced at 30 mm from the head-side front end 12 is set larger than that of the ordinary shaft. The rigidity value of the grip-side reinforcing region 17 is set to 4.5 kg·mm²to allow the shaft 10 to have a high rigidity at the grip side of the shaft 10.

FIGS. 6 and 7 show a shaft 10 according to a third embodiment of the present invention. A spiral rib 23 is formed on the inner peripheral surface of the shaft 10 not entirely over the full length thereof, but a rib 23A is formed at the head side of the shaft 10 and a rib 23B is formed at the grip side thereof.

More specifically, the head-side rib 23A is formed continuously and circumferentially in a region ranging from the head-side front end 12 to a position spaced at 180 mm from the head-side front end 12. The grip-side rib 23B is formed continuously and circumferentially in a region ranging from the grip-side rear end 13 to a position spaced at 200 mm (about 21% of full length L of shaft) from the grip-side rear end 13.

The inclination of the spiral rib 23 with respect to the X-direction axis of the shaft 10 and the configuration of the spiral rib 23 are the same as those of the rib 21 of the first embodiment. The method of forming the spiral rib 23 is also the same as the method of forming the rib 21 of the first embodiment. As shown in FIG. 7, the rib 23 is projected at a height H3 of 0.5 mm from the inner peripheral surface of the belt-like steel 11′.

An outer diameter D3 of the shaft 10 at a position spaced at 30 mm from the head-side front end 12 is set to 9.5 mm. The weight of the shaft 10 is set to 65 g.

The rigidity value of the shaft 10 at the position spaced at 90 mm from the head-side front end 12 is set to 1.4 kg·mm². The rigidity value of the grip-side reinforcing region of the shaft 10 is set to 6.5 kg·mm².

In the third embodiment, the head-side rib 23A is formed in a great part of the head-side reinforcing region which is subjected to a large shock when the player hits the ball. In addition, the grip-side rib 23B is formed in a region including a part of the grip-side reinforcing region which affects the player's feeling when the player hits the ball. Therefore it is possible to enhance the strength of the shaft effectively, although an increase of its weight is restrained. Because the rib 23 is projected in a large amount H3 from the inner peripheral surface of the belt-like steel 11′, particularly the grip-side reinforcing region 17 in which the grip-side rib 23B is formed has a very high rigidity value. Therefore the shaft 10 gives the player the feeling of firmness at the grip side thereof and allows the player to hit the ball at off-center positions decreasingly. Thereby the player can hit the ball a long distance.

FIGS. 8 and 9 show a shaft 10 according to a fourth embodiment of the present invention. In the fourth embodiment, a honeycomb head-side rib 24A is formed on the inner peripheral surface of the shaft 10 at the head side thereof, and a grip-side honeycomb rib 24B is formed on the inner peripheral surface of the shaft 10 at the grip side thereof. Except the configuration of the rib, the shaft of the fourth embodiment has the same construction as that of the shaft of the third embodiment. Thus the same parts of the fourth embodiment as those of the third embodiment are denoted by the same reference numerals as those of the third embodiment, and description thereof is omitted herein.

The head-side rib 24A is formed continuously and circumferentially in the region ranging from the head-side front end 12 to the position spaced at 180 mm from the head-side front end 12. The grip-side rib 24B is formed continuously and circumferentially in the region ranging from the grip-side rear end 13 to the position spaced at 200 mm (about 21% of full length L of shaft) from the grip-side rear end 13. The method of forming the honeycomb rib 24 is the same as the method of forming the rib 22 of the second embodiment. As shown in FIG. 9, the rib 24 is projected at a height H4 of 0.5 mm from the inner peripheral surface of the belt-like steel 11′.

An outer diameter D4 of the shaft 10 at the position spaced at 30 mm from the head-side front end 12 is set to 10.1 mm. The weight of the shaft 10 is set to 55 g.

The rigidity value of the shaft 10 at the position spaced at 90 mm from the head-side front end 12 is set to 1.5 kg·mm². The rigidity value of the grip-side reinforcing region of the shaft 10 is set to 7.8 kg·mm².

Like the shaft of the third embodiment, the shaft of the fourth embodiment has a very high rigidity at its grip side and gives the player the feeling of firmness at its grip side thereof. Further because the shaft is more lightweight than the shaft of the third embodiment, the player can swing it easily and at a high speed. Thereby the player can hit the ball a long distance.

The present invention is not limited to the above-described embodiment. For example, the rib may be formed on the head-side peripheral surface of the shaft 10 or/and the grip-side peripheral surface thereof in addition to forming the rib on the inner peripheral surface thereof. Further the rib may be formed on both the inner peripheral surface of the shaft 10 and the peripheral surface thereof.

When formation of the rib on the peripheral surface of the shaft allows the shaft to be decorative. When the rib is formed on both the peripheral surface of the shaft 10 and its inner peripheral surface, it is preferable to form the rib on the entire inner peripheral surface thereof and on a part of the head-side reinforcing region on the peripheral surface of the shaft and on a part of the grip-side reinforcing region on the peripheral surface thereof.

As shown in FIG. 10A, the rib may be shaped as described below: For example, it is possible to form a rib by continuously arranging triangularly framed ribs, one side of each of which is composed of a rib orthogonal (circumferential direction) to the axial direction of the shaft.

As shown in FIG. 10B, it is possible to form a quadrilaterally framed rib 26 by intersecting ribs 26a extended in the X-direction axis of the shaft 10 with ribs 26b extended in the circumferential direction thereof to form a lattice as a whole.

As shown in FIG. 10C, it is possible to continuously form a rhombic rib 27 having a diagonal line extended in the axial direction of the shaft 10 and another diagonal line extended orthogonally to the axial direction thereof.

Although the ribs are shown with one solid line in FIGS. 10A through 10C, they have the above-described width respectively.

Instead of forming continuous linear ribs, they may be dotted as projections sectionally triangular or circular.

The rib may be formed in a portion of the head-side reinforcing region 16 or projected therefrom to the grip side of the shaft. Further the rib may be formed in a portion of the grip-side reinforcing region 17 or projected therefrom to the grip side of the shaft and/or to the head side thereof.

Examples 1 through 4 of the golf club shaft of the present invention and golf club shafts of comparison examples 1 through 4 are described in detail below. Although the effect of the present invention is clarified in the examples, the present invention is not limited to the examples.

As shown in table 1, the golf club shafts of the examples 1 through 4 and the comparison examples 1 through 4 were prepared. They had different weights, different outer diameters at the position spaced at 30 mm from the head-side front end 12 thereof, different configurations of the rib formed on the inner peripheral surface thereof (hereinafter referred to as internal rib 21). Internal ribs 21 were formed at different positions thereof. They had different projected heights of the internal rib 21, different rigidity values (EI value) at the position spaced at 90 mm from the head-side front end 12, and different rigidity values (EI value) at the grip-side reinforcing region 17. By using these shafts, the three-point bending strength at the head side and the grip side of each shaft and the flight distance of balls hit with golf clubs composed of the shafts respectively were measured. In addition, a ball-hitting test was conducted to examine the easiness degree of each golf club.

The shafts of the examples 1 through 4 and the comparison examples 1 through 4 were made of steel having a length of 955 mm. The shafts were manufactured by the same method as that used to form the shafts of the above-described embodiments. The internal rib 21 of the shaft 10 of each of the examples 1 through 4 was continuously formed on the entire circumference thereof.

TABLE 1 Comparison Comparison Comparison Comparison Example 1 Example 2 Example 3 Example 4 Weight (g) of shaft 120 90 95 89 EI value (kg · mm²) at position spaced at 90 mm from front 0.9 0.6 0.7 1.2 end Diameter (mm) of front end 9.2 9.2 9.2 10 Configuration of internal rib Not formed Not formed Not formed Not formed Position of internal rib — — — — EI value (kg · mm²) in region ranging from grip-side rear 3.4 2.8 3 2.7 end to position spaced at interval corresponding to 30% to 40% of length of shaft Three-point bending strength (kgf) at position spaced 180 165 175 170 at 90 mm from front end Three-point bending strength (kgf) at position spaced 95 84 88 83 at 175 mm from rear end Ball-hitting test Can you swing easily? x Δ Δ Δ Flight distance of hit ball 161 165 163 164 Example 1 Example 2 Example 3 Example 4 Weight (g) of shaft 65 55 65 55 EI value (kg · mm²) at position spaced 1.4 1.5 1.4 1.5 at 90 mm from front end Diameter (mm) of front end 9.5 10.1 9.5 10.1 Configuration of internal rib Formed Formed Formed (spiral) Formed (honeycomb) (spiral) (honeycomb) Position of internal rib Full length Full length From front end to From front end to position spaced at position spaced at 180 mm therefrom 180 mm therefrom From rear end to From rear end to position spaced at position spaced at 200 mm therefrom 200 mm therefrom EI value (kg · mm²) in region ranging 4.2 4.5 6.5 7.8 from grip-side rear end to position spaced at interval corresponding to 30% to 40% of length of shaft Three-point bending strength (kgf) at 210 225 210 225 position spaced at 90 mm from front end Three-point bending strength (kgf) at 95 92 95 92 position spaced at 175 mm from rear end Ball-hitting test ◯ ◯ ⊚ ⊚ Can you swing easily? Flight distance of hit ball 185 188 190 195

Method of Measuring Rigidity Value

As shown in FIG. 11, using a universal testing machine 50, the rigidity value EI of each shaft 10 was measured by using a three-point bending method which was carried out by flexing the shaft 10. The rigidity value was computed by using the following equation. The shaft 10 was disposed on jigs 52A and 52B in such a way that the measuring points were under an indenter 51 of the universal testing machine 50. The interval between the jigs 52A and 52B was set to 200 mm. The radius of curvature of the indenter 51 at its front end was 75R. The radius of curvature of each of the jigs 52A and 52B at its leading end was 2R. The indenter 51 was moved downward at a speed of 5 mm/minute to flex the shaft 10. When a load of 20 kgf was applied to the shaft 10, the movement of the indenter 51 was finished, and the flexural amount of the shaft 10 at that time was measured.

Computation of Rigidity Value
EI(kg·mm²)=(Maximum load F×(distance between supporting points)²)/(48×flexural amount)

EXAMPLE 1

The shaft of the example 1 had the same construction as that of the shaft of the first embodiment. More specifically, the weight of the shaft was set to 65 g. The outer diameter of the shaft at the position spaced at 30 mm from the head-side front end 12 was set to 9.5 mm. The internal rib 21 was composed of the spiral rib 20a and the spiral rib 20b intersected with the spiral rib 20a. The internal rib 21 was formed over the full length of the shaft 10. The internal rib 21 was projected at a height H1 of 0.3 mm from the inner peripheral surface of the shaft 10. The rigidity value (EI value) of the shaft 10 at the position spaced at 90 mm from the head-side front end 12 was set to 1.4 kg·mm². The rigidity value of the grip-side reinforcing region 17 was set to 4.2 kg·mm².

EXAMPLE 2

The shaft of the example 2 had the same construction as that of the shaft of the second embodiment. More specifically, the weight of the shaft was set to 55 g. The outer diameter of the shaft at the position spaced at 30 mm from the head-side front end 12 was set to 10.1 mm. The internal rib 22 was honeycomb. The internal rib 22 was formed over the full length of the shaft 10. The internal rib 22 was projected at a height H1 of 0.3 mm from the surface of the shaft 10. The rigidity value (EI value) of the shaft 10 at the position spaced at 90 mm from the head-side front end 12 was set to 1.5 kg·mm². The rigidity value of the grip-side reinforcing region 17 was set to 4.5 kg·mm².

EXAMPLE 3

The shaft of the example 3 had the same construction as that of the shaft of the third embodiment. More specifically, the weight of the shaft was set to 65 g. The outer diameter of the shaft at the position spaced at 30 mm from the head-side front end 12 was set to 9.5 mm. The internal rib 23 was composed of the spiral rib 23A which is formed at head side of the shaft 10 and the spiral rib 23B which is formed at grip side thereof. The internal ribs 23 were formed in the region ranging from the head-side front end 12 to the position spaced at 180 mm from the head-side front end 12 and in the region ranging from the grip-side rear end 13 to the position spaced at 200 mm from the grip-side rear end 13. The internal rib 23 was projected at a height H1 of 0.5 mm from the inner peripheral surface of the shaft 10. The rigidity value (EI value) of the shaft 10 at the position spaced at 90 mm from the head-side front end 12 was set to 1.4 kg·mm². The rigidity value of the grip-side reinforcing region 17 was set to 6.5 kg·mm².

EXAMPLE 4

The shaft of the example 4 had the same construction as that of the shaft of the fourth embodiment. More specifically, the weight of the shaft was set to 55 g. The outer diameter of the shaft at the position spaced at 30 mm from the head-side front end 12 was set to 10.1 mm. The internal ribs 24 was composed of the honeycomb head-side rib 24A which is formed at head side of the shaft 10 and the honeycomb grip-side rib 24B which is formed at grip side thereof. The internal rib 24 was formed in the region ranging from the head-side front end 12 to the position spaced at 180 mm from the head-side front end 12 and in the region ranging from the grip-side rear end 13 to the position spaced at 200 mm from the grip-side rear end 13. The internal rib 24 was projected at a height H1 of 0.5 mm from the inner peripheral surface of the shaft 10. The rigidity value (EI value) of the shaft 10 at the position spaced at 90 mm from the head-side front end 12 was set to 1.5 kg·mm². The rigidity value of the grip-side reinforcing region 17 was set to 7.8 kg·mm².

COMPARISON EXAMPLE 1

The internal rib was not formed on the shaft of the comparison example 1. The degree of flexibility of the shaft was adjusted by reducing (stepped portion (portions) was formed) the diameter of a portion (portions) thereof. The rigidity value of the head-side front end and that of the grip-side reinforcing region were set lower than those of the shafts of the examples to make the shaft flexible. More specifically, the weight of the shaft was set to 120 g. The outer diameter of the shaft at the position spaced at 30 mm from the head-side front end 12 was set to 9.2 mm. The rigidity value (EI value) of the shaft 10 at the position spaced at 90 mm from the head-side front end 12 was set to 0.9 kg·mm². The rigidity value (EI value) of the grip-side reinforcing region 17 was set to 3.4 kg·mm².

COMPARISON EXAMPLE 2

The shaft of the comparison example 2 was thinner than the shaft of the comparison example 1 to make the former lightweight. More specifically, the weight of the shaft was set to 90 g. The outer diameter of the shaft at the position spaced at 30 mm from the head-side front end 12 was set to 9.2 mm. The rigidity value (EI value) of the shaft 10 at the position spaced at 90 mm from the head-side front end 12 was set to 0.6 kg·mm². The rigidity value (EI value) of the grip-side reinforcing region 17 was set to 2.8 kg·mm².

COMPARISON EXAMPLE 3

The shaft of the comparison example 3 was a little thinner than the shaft of the comparison example 1 to make the former lightweight. More specifically, the weight of the shaft was set to 95 g. The outer diameter of the shaft at the position spaced at 30 mm from the head-side front end 12 was set to 9.2 mm. The rigidity value (EI value) of the shaft 10 at the position spaced at 90 mm from the head-side front end 12 was set to 0.7 kg·mm². The rigidity value (EI value) of the grip-side reinforcing region 17 was set to 3 kg·mm².

COMPARISON EXAMPLE 4

The shaft of the comparison example 4 was thinner than the shaft of the comparison example 2 to make the former lightweight. But the outer diameter of the shaft of the comparison example 4 at its head-side front end was set larger than that of the comparison example 2. More specifically, the weight of the shaft was set to 89 g. The outer diameter of the shaft at the position spaced at 30 mm from the head-side front end 12 was set to 10 mm. The rigidity value (EI value) of the shaft 10 at the position spaced at 90 mm from the head-side front end 12 was set to 1.2 kg-mm². The rigidity value (EI value) of the grip-side reinforcing region 17 was set to 2.7 kg·mm².

Three-Point Bending Strength Test

The measuring condition was identical to that in the method of measuring the rigidity value. A load was applied until the shaft 10 was broken to measure a load at the time when the shaft 10 was broken. The three-point bending strength was measured at a position spaced at 90 mm from the head-side front end 12 of the shaft 10 and a position spaced at 175 mm from the grip-side rear end 13 thereof.

Ball-Hitting Test

One tester was requested to hit 20 balls with each of iron golf clubs #5 composed of the shafts of the examples and the comparison examples respectively to make a sensory evaluation on the degree of ease (◯, Δ, X) the player felt when the player swung each iron golf club.

Measurement of Flight Distance of Hit Ball

The tester hit 20 balls with each iron golf club #5. Table 1 shows the mean flight distance (yard) of the 20 hit balls.

As indicated in table 1, the shaft of each of the examples 1 through 4 had a high degree of strength at its head side and grip side, could be swung favorably, and allowed balls to be hit a long distance. This is because the shaft of each of the examples 1 through 4 had the rib formed on the inner peripheral surface thereof to secure a necessary strength and in addition, was lightweight. The head-side front end of each of the shafts of the examples 1 through 4 had a strength high enough to withstand a strong shock and a degree of flexibility appropriate enough to hit the ball a long distance. Further because the grip-side rear end of the shaft of each of the examples 1 through 4 had a high rigidity at the grip side thereof, the player had a high degree of firmness when the player swung. Thus in the ball-hitting test, the shaft of each of the examples 1 through 4 had a good evaluation that the shafts were easy to swing.

The shaft of each of the comparison examples 1 through 4 had change points in the thickness thereof because the diameter of a portion (portions) was reduced, were narrow at the head-side front end thereof, and had a very low rigidity value. Thus the shafts had a low degree of strength. Further the shafts had a large weight and were not high in the rigidity at the grip side thereof. Thus in the ball-hitting test, the shafts had an evaluation that they were difficult to swing and were incapable of hitting the ball a long distance.

Comparing the shafts of the examples 1 through 4 with one another, the shafts of the examples 3 and 4 having the internal rib projected in the larger amount from the head-side front end and the grip-side rear end had a higher rigidity at the grip side thereof than the shafts of the examples 1 and 2 having the rib projected in the lower amount from the full length thereof. Therefore in the ball-hitting test, the shafts of the examples 3 and 4 had a good evaluation that they were easy to swing and were capable of hitting the ball a long distance.

Claims

1. A golf club shaft composed of a metal tube and having a weight not less than 50 g and less than 85 g, wherein a rib is formed on an inner peripheral surface of said golf club shaft and/or a peripheral surface thereof;

a rigidity value of said golf club shaft at a position spaced at 90 mm from a head-side front end thereof is set to not less than 1.0 kg·mm2 nor more than 2.5 kg·mm2; and

an outer diameter of said golf club shaft at a position spaced at 30 mm from said head-side front end thereof is set to not less than 9.5 mm nor more than 15.0 mm.

2. The golf club shaft according to claim 1, wherein said rib is projected from an inner peripheral surface of said golf club shaft in such a way that at least one portion of said rib is formed in a region ranging from said head-side front end of said shaft to a position spaced at 200 mm from said head-side front end; or said rib is formed in at least one portion of said region.

3. The golf club shaft according to claim 1, wherein said rib is formed evenly over a full length of a circumference of said golf club shaft; and

said rib is configured as a meshed rib by intersecting with each other a spiral rib inclined in a plus direction with respect to an axis of said shaft and a spiral rib inclined in a minus direction with respect to said axis of said shaft; as a honeycomb rib formed by continuously arranging polygonally framed ribs; as a latticed rib formed by intersecting ribs extended in parallel with said axial direction of said shaft with ribs extended orthogonally to said axial direction thereof; as a rib formed by continuously arranging triangularly framed ribs, one side of each of which is composed of a rib orthogonal to said axial direction of said shaft, and as a rib formed by continuously arranging rhombically framed ribs each having a diagonal rib extended in said axial direction of said shaft and another diagonal rib extended orthogonally to said axial direction thereof.

4. The golf club shaft according to claim 2, wherein said rib is formed evenly over a full length of a circumference of said golf club shaft; and

said rib is configured as a meshed rib by intersecting with each other a spiral rib inclined in a plus direction with respect to an axis of said shaft and a spiral rib inclined in a minus direction with respect to said axis of said shaft; as a honeycomb rib formed by continuously arranging polygonally framed ribs; as a latticed rib formed by intersecting ribs extended in parallel with said axial direction of said shaft with ribs extended orthogonally to said axial direction thereof; as a rib formed by continuously arranging triangularly framed ribs, one side of each of which is composed of a rib orthogonal to said axial direction of said shaft, and as a rib formed by continuously arranging rhombically framed ribs each having a diagonal rib extended in said axial direction of said shaft and another diagonal rib extended orthogonally to said axial direction thereof.

5. A golf club shaft composed of a metal tube and having a weight of not less than 50 g and less than 85 g,

wherein a rib is formed on an inner peripheral surface of said golf club shaft and/or a peripheral surface thereof; and

at least one portion of said rib is formed in a region ranging from a grip-side rear end of said shaft to a position spaced at an interval corresponding to not less than 30% nor more than 40% of a full length of said shaft or in a portion of said region including a position spaced at an interval corresponding to 35% of said full length of said shaft from said grip-side rear end; and

a rigidity value of said region is set to not less than 3.5 kg·mm2 nor more than 8.0 kg·mm2.

6. The golf club shaft according to claim 1, wherein a projected height of said rib is set to 0.1 mm to 11.0 mm; and a width thereof is set to 0.1 mm to 11.0 mm.

7. The golf club shaft according to claim 2, wherein a projected height of said rib is set to 0.1 mm to 11.0 mm; and a width thereof is set to 0.1 mm to 11.0 mm.

8. The golf club shaft according to claim 3, wherein a projected height of said rib is set to 0.1 mm to 11.0 mm; and a width thereof is set to 0.1 mm to 11.0 mm.

9. The golf club shaft according to claim 4, wherein a projected height of said rib is set to 0.1 mm to 11.0 mm; and a width thereof is set to 0.1 mm to 11.0 mm.

10. The golf club shaft according to claim 5, wherein a projected height of said rib is set to 0.1 mm to 11.0 mm; and a width thereof is set to 0.1 mm to 11.0 mm.

11. The golf club shaft according to claim 1, wherein a metal belt-like member having said rib formed by press molding on an inner peripheral surface thereof and/or a peripheral surface thereof is wound tubularly, and mating portions of said belt-like member are welded to each other to form said metal tube.

12. The golf club shaft according to claim 2, wherein a metal belt-like member having said rib formed by press molding on an inner peripheral surface thereof and/or a peripheral surface thereof is wound tubularly, and mating portions of said belt-like member are welded to each other to form said metal tube.

13. The golf club shaft according to claim 3, wherein a metal belt-like member having said rib formed by press molding on an inner peripheral surface thereof and/or a peripheral surface thereof is wound tubularly, and mating portions of said belt-like member are welded to each other to form said metal tube.

14. The golf club shaft according to claim 4, wherein a metal belt-like member having said rib formed by press molding on an inner peripheral surface thereof and/or a peripheral surface thereof is wound tubularly, and mating portions of said belt-like member are welded to each other to form said metal tube.

15. The golf club shaft according to claim 5, wherein a metal belt-like member having said rib formed by press molding on an inner peripheral surface thereof and/or a peripheral surface thereof is wound tubularly, and mating portions of said belt-like member are welded to each other to form said metal tube.

16. The golf club shaft according to claim 6, wherein a metal belt-like member having said rib formed by press molding on an inner peripheral surface thereof and/or a peripheral surface thereof is wound tubularly, and mating portions of said belt-like member are welded to each other to form said metal tube.