U.S. patent application number 10/973398 was filed with the patent office on 2005-04-28 for golf club shaft.
This patent application is currently assigned to Sumitomo Rubber Industries, Ltd.. Invention is credited to Hasegawa, Hiroshi.
Application Number | 20050090326 10/973398 |
Document ID | / |
Family ID | 34510331 |
Filed Date | 2005-04-28 |
United States Patent
Application |
20050090326 |
Kind Code |
A1 |
Hasegawa, Hiroshi |
April 28, 2005 |
Golf club shaft
Abstract
A golf club shaft (10) having a plurality of
flexural-rigidity-reduced regions (R1 through R3) each disposed
adjacently to a side rearward from a corresponding local
maximum-value point (P1 through P3) in flexural rigidity in a full
length of the golf club shaft (10) from a tip (11) thereof where a
head is mounted to a butt (12) thereof where a grip is mounted.
Each of the flexural-rigidity-reduced regions (R1 through R3) has a
flexural rigidity value lower than a flexural rigidity value
(maximum value) (Yp1 through Yp3) of the corresponding local
maximum-value point (P1 through P3) in flexural rigidity. Thereby
the golf club shaft (10) is entirely flexible.
Inventors: |
Hasegawa, Hiroshi; (Hyogo,
JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Sumitomo Rubber Industries,
Ltd.
|
Family ID: |
34510331 |
Appl. No.: |
10/973398 |
Filed: |
October 27, 2004 |
Current U.S.
Class: |
473/319 |
Current CPC
Class: |
A63B 60/08 20151001;
A63B 2209/023 20130101; A63B 53/047 20130101; A63B 60/0081
20200801; A63B 53/0408 20200801; A63B 53/10 20130101; A63B 60/10
20151001; A63B 60/00 20151001; A63B 53/0466 20130101; A63B 53/0412
20200801; A63B 60/06 20151001 |
Class at
Publication: |
473/319 |
International
Class: |
A63B 053/10 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 28, 2003 |
JP |
2003-368158 |
Claims
What is claimed is:
1. A golf club shaft having: a plurality of
flexural-rigidity-reduced regions in an axial direction from a tip
side of said golf shaft toward a butt side thereof, a local
maximum-value point of the flexural-rigidity value is formed in
each region interposed between two of said adjacent
flexural-rigidity-reduced regions, so that a plurality of said
local maximum-value points are disposed in the axial direction from
a tip side of said golf shaft toward a butt side thereof.
2. The golf club shaft according to claim 1, wherein said flexural
rigidity values of said local maximum-value points are equal to
each other or increase in a direction from said tip side toward
said butt side; and flexural rigidity values of local
minimum-points of said flexural-rigidity-reduced regions are equal
to each other or increase in said direction from said tip side
toward said butt side.
3. The golf club shaft according to claim 1, wherein a length of
each of said flexural-rigidity-reduced regions in said axial
direction of said golf club shaft is set to a range not less than
50 mm nor more than 400 mm.
4. The golf club shaft according to claim 2, wherein a length of
each of said flexural-rigidity-reduced regions in said axial
direction of said golf club shaft is set to a range not less than
50 mm nor more than 400 mm.
5. The golf club shaft according to claim 1, wherein at least one
of said flexural-rigidity-reduced regions is formed in a region
from said tip to a position spaced by 500 mm from said tip.
6. The golf club shaft according to claim 2, wherein at least one
of said flexural-rigidity-reduced regions is formed in a region
from said tip to a position spaced by 500 mm from said tip.
7. The golf club shaft according to claim 3, wherein at least one
of said flexural-rigidity-reduced regions is formed in a region
from said tip to a position spaced by 500 mm from said tip.
8. The golf club shaft according to claim 1, wherein a flexural
rigidity value of said local maximum-value point at a tip side is
set to a range of not less than 1.2 times nor more than 2 times as
large as a flexural rigidity value of a local minimum-value point
of said flexural-rigidity-reduced region adjacent to said local
maximum-value point.
9. The golf club shaft according to claim 2, wherein a flexural
rigidity value of said local maximum-value point at a tip side is
set to a range of not less than 1.2 times nor more than 2 times as
large as a flexural rigidity value of a local minimum-value point
of said flexural-rigidity-reduced region adjacent to said local
maximum-value point.
10. The golf club shaft according to claim 3, wherein a flexural
rigidity value of said local maximum-value point at a tip side is
set to a range of not less than 1.2 times nor more than 2 times as
large as a flexural rigidity value of a local minimum-value point
of said flexural-rigidity-reduced region adjacent to said local
maximum-value point.
11. The golf club shaft according to claim 5, wherein a flexural
rigidity value of said local maximum-value point at a tip side is
set to a range of not less than 1.2 times nor more than 2 times as
large as a flexural rigidity value of a local minimum-value point
of said flexural-rigidity-reduced region adjacent to said local
maximum-value point.
12. The golf club shaft according to claim 1, comprising a laminate
of a plurality of prepregs each constructing a bias layer and a
plurality of prepregs each constructing a straight layer, wherein
at least one layer of said straight layers serves as a flexural
rigidity-adjusting layer having a plurality of separate prepregs,
having an equal thickness and different elastic moduli, which are
arranged in an axial direction of said golf club shaft to form said
flexural rigidity distribution.
13. The golf club shaft according to claim 2, comprising a laminate
of a plurality of prepregs each constructing a bias layer and a
plurality of prepregs each constructing a straight layer, wherein
at least one layer of said straight layers serves as a flexural
rigidity-adjusting layer having a plurality of separate prepregs,
having an equal thickness and different elastic moduli, which are
arranged in an axial direction of said golf club shaft to form said
flexural rigidity distribution.
14. The golf club shaft according to claim 3, comprising a laminate
of a plurality of prepregs each constructing a bias layer and a
plurality of prepregs each constructing a straight layer, wherein
at least one layer of said straight layers serves as a flexural
rigidity-adjusting layer having a plurality of separate prepregs,
having an equal thickness and different elastic moduli, which are
arranged in an axial direction of said golf club shaft to form said
flexural rigidity distribution.
15. The golf club shaft according to claim 5, comprising a laminate
of a plurality of prepregs each constructing a bias layer and a
plurality of prepregs each constructing a straight layer, wherein
at least one layer of said straight layers serves as a flexural
rigidity-adjusting layer having a plurality of separate prepregs,
having an equal thickness and different elastic moduli, which are
arranged in an axial direction of said golf club shaft to form said
flexural rigidity distribution.
Description
[0001] This nonprovisional application claims priority under 35
U.S.C. .sctn. 119(a) on Patent Application No(s) . 2003-368158
filed in Japan on Oct. 28, 2003, the entire contents of which are
hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a golf club shaft and more
particularly to a golf club shaft flexible to increase the head
speed thereof.
[0004] 2. Description of the Related Art
[0005] In recent years, with the increase of powerless elderly and
female golfers, there is a demand for development of a golf club
shaft capable of hitting a ball a long distance even with a small
power. To comply with this demand, it is important to make the golf
club shaft lightweight, provide the golf club head with a high
restitution performance, and make the head speed high when a player
swings.
[0006] The head speed of the golf club shaft can be increased by
making it flexible. Thus the conventional golf club shaft is so
constructed that the increase amount of the flexural rigidity value
thereof increases from its tip at which the head is mounted toward
its butt at which the grip is mounted. Although the golf club shaft
having such a rigidity distribution is apt to flex at its tip, the
entire golf club shaft does not flex favorably. Thus there is room
for improvement of the head speed of the golf club shaft. Therefore
proposals of increasing the head speed by improving the rigidity
distribution of the golf club shaft have been hitherto made.
[0007] In the golf club shaft disclosed in Japanese Patent
Application Laid-Open No. 2002-35184 (patent document 1), as shown
in FIG. 9, the flexural rigidity distribution curve C3 has the
maximum value in the central part Y of the golf club shaft and the
maximum value, at the butt (rear end of golf club shaft) B, larger
than the maximum value in the central part Y.
[0008] The golf club shaft disclosed in Japanese Patent Application
Laid-Open No. 2003-24490 (patent document 2) has the following
rigidity distribution: the central reinforcing layer in which the
fiber of the reinforced fiber has an orientation angle of 0.degree.
to 5.degree. is formed at the central part of the golf club shaft.
As shown in FIG. 10, at the central part of the golf club shaft,
the value (EI value) of the flexural rigidity thereof increases
from its tip toward its butt. At the parts of the golf club shaft
other than the central part thereof, the increase rate of the
flexural rigidity becomes higher from its tip toward its butt,
whereas at the central part of the golf club shaft, the increase
rate of the flexural rigidity becomes lower from its tip toward its
butt. Thereby the rigidity of the central part of the golf club
shaft is higher than that of the central part of the conventional
golf club shaft. Thus a player can utilize the flexing of the
entire golf club shaft when the player swings, thus increasing the
head speed.
[0009] However, the golf club shaft disclosed in the patent
document 1 has only one portion having the maximum rigidity value
other than the maximum rigidity value disposed at the butt side.
Thus the golf club shaft flexes locally at the rigidity
value-reduced portion disposed forward and rearward from the
position having the maximum rigidity value. Therefore the player is
liable to have a feeling of physical disorder. In addition a stress
concentrates on the rigidity value-reduced portion disposed forward
and rearward from the position having the local maximum rigidity
value. Consequently the golf club shaft a low strength.
[0010] In the golf club shaft disclosed in the patent document 2,
only the central part of the golf club shaft where the central
reinforcing layer is provided is heavy and thick. Therefore the
player has a feeling of physical disorder when the player swings.
In addition difference in level is formed at the boundary between
the central reinforcing layer and other parts. Thus the golf club
shaft has an unfavorable accomplishment.
SUMMARY OF THE INVENTION
[0011] 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 golf club shaft which can be swung
preferably without a feeling of physical disorder, flexes well
entirely, and is high in its head speed.
[0012] To achieve the object, the golf club shaft of the present
invention has a plurality of flexural-rigidity-reduced regions in
an axial direction from a tip side of said golf shaft toward a butt
side thereof, a local maximum-value point of the flexural-rigidity
value is formed in each region interposed between two of said
adjacent flexural-rigidity-reduced regions, so that a plurality of
said local maximum-value points are disposed in the axial direction
from a tip side of said golf shaft toward a butt side thereof.
[0013] The flexural rigidity value of the flexural-rigidity-reduced
region interposed between the adjacent local maximum-value points
is set to not more than that of the tip-side local maximum-value
point in flexural rigidity adjacent to the
flexural-rigidity-reduced region. When a local maximum-value point
having a small flexural rigidity is present in one
flexural-rigidity-reduced region, the local maximum-value point is
included in the one flexural-rigidity-reduced region.
[0014] As described above, the flexural-rigidity-reduced regions
each having a low flexural rigidity and making the shaft to flex
easily are formed at a plurality of portions in the full length of
the shaft. Therefore the shaft flexes entirely like a whip. Unlike
the conventional shaft which flexes locally, namely, in only the
vicinity of its tip or only at its central portion, the shaft of
the present invention flexes entirely and greatly. Thus it is easy
to increase the head speed and hence possible to hit a ball a long
distance with a small power. Since the shaft flexes entirely, a
player can swing smoothly without a feeling of physical disorder.
Accordingly there is a small variation in the distance between a
hitting point and the sweet spot. Thus it is possible to improve
the directional property of a ball.
[0015] It is possible to realize a natural flexing of the shaft by
providing the shaft with a large number of
flexural-rigidity-reduced regions. It is preferable to form the
flexural-rigidity-reduced region at least three portions for a
wood. It is preferable to form the flexural-rigidity-reduced region
at four portions for a long wood. It is preferable to form the
flexural-rigidity-reduced region at least two portions for an iron.
It is preferable to form the flexural-rigidity-reduced region at
three portions for a long iron.
[0016] The flexural rigidity values of the local maximum-value
points in flexural rigidity are equal to each other or increase in
a direction from the tip side toward the butt side; and flexural
rigidity values of local minimum-points of the
flexural-rigidity-reduced regions are equal to each other or
increase in the direction from the tip side toward the butt
side.
[0017] If the flexural rigidity values of the local maximum-value
points in flexural rigidity are equal to each other and if the
flexural rigidity values of the local minimum-points of the
flexural-rigidity-reduced regions are equal to each other, the
shaft is capable of flexing entirely favorably without giving a
feeling of physical disorder to the player.
[0018] If the flexural rigidity values of the local maximum-value
points in flexural rigidity and if the flexural rigidity values of
the local minimum-points of the flexural-rigidity-reduced regions
increase in the direction from the tip side toward the butt side,
the shaft gives player's hands a proper degree of firmness without
having a feeling of physical disorder, when the player swings.
[0019] It is favorable that the length of each of the
flexural-rigidity-reduced regions in the axial direction of the
shaft is set to a range not less than 50 mm nor more than 400 mm.
If the length of the flexural-rigidity-reduced region is larger
than 400 mm, the number of the flexural-rigidity-reduced regions
decreases. Consequently the degree of smooth flexing of the shaft
becomes low and hence the player has a feeling of physical disorder
when the player swings. If the length of the
flexural-rigidity-reduced region is smaller than 50 mm, it is
difficult to form the flexural-rigidity-reduced region. The length
of the flexural-rigidity-reduced region in the axial direction of
the shaft is more favorably not less than 50 mm nor more than 300
mm and most favorably not less than 50 mm nor more than 200 mm.
[0020] At least one of the flexural-rigidity-reduced regions is
formed in a region from the tip to a position spaced by 500 mm from
the tip. Thereby it is possible to reliably flex the shaft at its
head-mounting side. Thus it is possible to increase the head speed
to a higher extent.
[0021] It is preferable to form the local maximum-value point in
flexural rigidity at both the tip and the butt. It is preferable
that the flexural rigidity value is large to fix the head to the
tip of the shaft. Thereby the butt side of the shaft is capable of
giving the player a feeling that the shaft flexes smoothly.
[0022] It is preferable that a flexural rigidity value of the local
maximum-value point in flexural rigidity at a tip side is set to a
range of not less than 1.2 times nor more than two times as large
as a flexural rigidity value of a local minimum-value point of the
flexural-rigidity-reduced region adjacent to the local
maximum-value point in flexural rigidity.
[0023] If the flexural rigidity value of the local maximum-value
point in flexural rigidity at the tip side is set to less than 1.2
times as large as the flexural rigidity value of the local
minimum-value point of the flexural-rigidity-reduced region, the
shaft cannot be flexed sufficiently, and a low head
speed-increasing effect is obtained. If the flexural rigidity value
of the local maximum-value point in flexural rigidity at the tip
side is set to more than 2.0 times as large as the flexural
rigidity value of the local minimum-value point of the
flexural-rigidity-reduced region, there is a big difference between
the flexural rigidity value of the local maximum-value point in
flexural rigidity at the tip side and the flexural rigidity value
of the local minimum-value point of the flexural-rigidity-reduced
region. Consequently the flexing degree of the shaft
deteriorates.
[0024] The shaft is composed of a laminate of a plurality of
prepregs each constructing a bias layer and a plurality of prepregs
each constructing a straight layer. At least one layer of the
straight layers serves as a flexural rigidity-adjusting layer
having a plurality of separate prepregs, having an equal thickness
and different elastic moduli, which are arranged in an axial
direction of the shaft to form the flexural rigidity distribution.
When the prepregs have different elastic moduli and an equal number
of turns of the prepregs and an equal thickness to vary the
flexural rigidity value of the shaft, the outer diameter of the
shaft does not become locally large or small. Thus the shaft does
not give the player a feeling of physical disorder in its external
form, and further the weight of the shaft does not increase.
[0025] The above-described method is not limited to the formation
of the shaft by layering prepregs one upon another. In addition,
the above-described method can be used when filament winding is
used to form the shaft. In this case, a reinforcing fiber whose
elastic modulus is partly different can be used.
[0026] As apparent from the foregoing description, in the present
invention, a plurality of flexural-rigidity-reduced regions whose
values become lower from the tip side of the shaft toward the butt
side thereof is formed over the full length of the shaft. Therefore
the shaft is capable of flexing not locally but entirely smoothly
like a whip and allows the player to make a natural swing without
giving the player a feeling of physical disorder. Thereby the
player can increase the head speed and hit a ball a long distance.
Further it is possible to improve the directional property of a
ball. At least one flexural-rigidity-reduce- d region is formed in
the region from the tip to the position spaced by 500 mm from the
tip. Thus it is easy to travel the golf club head easily and
increase the head speed efficiently.
[0027] The flexural rigidity values of the local maximum and
minimum points in flexural rigidity become increasingly large in
the direction from the tip side of the shaft toward the butt side
thereof. Consequently the shaft is capable of flexing naturally and
smoothly, thus giving player's hands a proper degree of firmness.
The flexural rigidity value of the tip-side local maximum-value
point in flexural rigidity is set to the range of not less than 1.2
times nor more than two times as large as the flexural rigidity
value of the local minimum-value point of the
flexural-rigidity-reduced region adjacent to the tip-side local
maximum-value point in flexural rigidity. Thereby the player
obtains the effect of increasing the head speed and a feeling that
the shaft flexes preferably.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a schematic view showing a golf club shaft
according to a first embodiment of the present invention.
[0029] FIG. 2 shows a layering construction of fiber reinforced
prepregs, mounted on a mandrel, used for the golf club shaft
according to the first embodiment of the present invention.
[0030] FIG. 3 is a graph showing a flexural rigidity distribution
of the golf club shaft according to the first embodiment of the
present invention.
[0031] FIG. 4 shows a layering construction of fiber reinforced
prepregs, mounted on a mandrel, used for a golf club shaft
according to a second embodiment of the present invention.
[0032] FIG. 5 is a graph showing a flexural rigidity distribution
of the golf club. shaft according to the second embodiment of the
present invention.
[0033] FIG. 6 shows a layering construction of fiber reinforced
prepregs, mounted on a mandrel, used for a golf club shaft
according to a third embodiment of the present invention.
[0034] FIG. 7 is a graph showing a flexural rigidity distribution
of the golf club shaft according to the third embodiment of the
present invention.
[0035] FIG. 8 is a graph showing flexural rigidity distribution
curves A through F of examples 1 through 3 and comparison examples
1 through 3.
[0036] FIG. 9 is a graph showing a flexural rigidity distribution
of a conventional art.
[0037] FIG. 10 is a graph showing a flexural rigidity distribution
of another conventional art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] The embodiments of the present invention will be described
below with reference to drawings.
[0039] FIGS. 1 through 3 show a golf club shaft (hereinafter
referred to as merely shaft) 10 according to a first embodiment of
the present invention. The shaft 10 is tapered, long, and
cylindrical. The shaft 10 is composed of a laminate of prepregs 21
through 24 layered one upon another. A head 13 is attached to the
shaft 10 at one end (tip) 11 thereof having the smallest diameter.
A grip 14 is attached to the shaft 10 at the other end (butt) 12
having the largest diameter. The entire length of the shaft 1 is
set to 0.8 to 1.2 mm. In this embodiment, the entire length of the
shaft 10 is set to 1050 mm. The outer diameter of the shaft 10 at
its tip is set to 8.0 to 12.0 mm. In this embodiment, the outer
diameter of the shaft 10 at its tip 11 is set to 9.0 mm. The outer
diameter of the shaft 10 at its butt 12 is set to 13.0 to 20.0 mm.
In this embodiment, the outer diameter of the shaft 10 at its butt
is set to 15.0 mm.
[0040] The shaft 10 is formed as follows: After prepregs composed
of resin and reinforcing fibers impregnated with the resin are
wound around a mandrel 20 by a sheet winding method to layer them
one upon another, a tape (not shown) made of polypropylene is
lapped on the laminate of the prepregs. Thereafter the tape-lapped
laminate is heated in an oven under pressure to harden the resin so
that the resin and the reinforcing fibers are integrally molded.
Thereafter the mandrel 20 is drawn out of the laminate. After the
surface of the shaft 10 is polished, it is painted.
[0041] The prepreg constructing the shaft 10 consists of prepregs
21, 22 each forming a bias layer and prepregs 23, 24 each forming a
straight layer.
[0042] In the prepregs 21 through 24, reinforcing fibers F21, F22,
F24, F23a and F23b, and F24 consisting of carbon fiber are
impregnated with epoxy resin.
[0043] The weight percentage of the resin of each of the prepregs
21 through 24 is set to not less than 20 nor more than 45. The
thickness of each of the prepregs is set to not less than 0.01 mm
nor more than 0.3 mm and preferably not less than 0.05 mm nor more
than 0.15 mm. The elastic modulus of each of the prepregs is set to
not less than 5 t/mm.sup.2 nor more than 100 t/mm.sup.2. The
flexural strength of each of the prepregs in a direction 0.degree.
with respect to the reinforcing fiber is set to 100 kgf/mm.sup.2
nor more than 200 kgf/mm.sup.2. The number of grams of each of the
prepregs per 1 m.sup.2 is set to not less than 5 g nor more than
500 g. The number of grams of the carbon fiber per 1 m.sup.2 is set
to not less than 5 g nor more than 300 g.
[0044] Glass fiber or boron fiber may be used as the reinforcing
fiber. Thermosetting resin other than epoxy resin may be used as
the resin.
[0045] More specifically, the thickness of each of the prepregs 21,
22 is set to 0.1 mm. Each of the prepregs 21, 22 is wound over the
full length of the shaft. The mandrel 20 is wound with three turns
of each of the prepregs 21, 22 to obtain the winding width thereof.
The reinforcing fibers F21 and F22 form angles of +45.degree. and
-45.degree. respectively with respect to the axis of the shaft. The
elastic modulus of each of the reinforcing fibers F21 and F22 is
set to 30 t/mm.sup.2. The prepregs 21 and 22 are wound around the
mandrel 20 with the prepregs 21 and 22 layered one upon
another.
[0046] The prepreg 23 is composed of four prepregs 23a having a
high elastic modulus (hereinafter referred to as
high-elastic-modulus prepreg 23a) and three prepregs 23b having a
low elastic modulus (hereinafter referred to as low-elastic-modulus
prepreg 23b), constructing a straight layer for adjusting the
flexural rigidity of the shaft 10, which have an equal thickness of
0.1 mm. The mandrel 20 is wound with two turns of the
high-elastic-modulus prepregs 23a and the low-elastic-modulus
prepregs 23b to obtain the winding width of the prepreg 23. The
high-elastic-modulus prepregs 23a and-the low-elastic-modulus
prepregs 23b are alternately wound in a length of 150 mm around the
mandrel 20 with the high-elastic-modulus prepregs 23a and the
low-elastic-modulus prepregs 23b arranged in the axial direction of
the shaft 10.
[0047] More specifically, the high-elastic-modulus prepregs 23a and
the low-elastic-modulus prepregs 23b each having a length of 150 mm
are alternately arranged from the tip 11 of the shaft 10 toward the
butt in the order of the high-elastic-modulus prepreg 23a, the
low-elastic-modulus prepreg 23b, the high-elastic-modulus prepreg
23a, the low-elastic-modulus prepreg 23b, the high-elastic-modulus
prepreg 23a, the low-elastic-modulus prepreg 23b, and the
high-elastic-modulus prepreg 23a.
[0048] The elastic modulus of the high-elastic-modulus prepreg 23a
is set to 30 t/mm.sup.2. The elastic modulus of the
low-elastic-modulus prepreg 23b is set to 5 t/mm.sup.2. The
reinforcing fiber F23a of the prepreg 23a and the reinforcing fiber
F23b of the prepreg 23b have an orientation angle not less than
0.degree. nor more than 10.degree. with respect to the axis of the
shaft 10. In the first embodiment, each of the reinforcing fiber
F23a and the reinforcing fiber F23a has an orientation angle of
0.degree. with respect to the axis of the shaft to form the prepreg
23 as a straight layer.
[0049] The prepreg 24 has a thickness of 0.1 mm. The mandrel 20 was
wound with two turns of the high-elastic-modulus prepregs 23a and
the low-elastic-modulus prepregs 23b to obtain the winding width of
the prepreg 24. The reinforcing fiber F24 has an orientation angle
not less than 0.degree. nor more than 10.degree. with respect to
the axis of the shaft. In the first embodiment, the reinforcing
fiber F24 has an orientation angle of 0.degree. with respect to the
axis of the shaft to form the prepreg 24 as a straight layer. The
prepreg 24 has an elastic modulus of 25 t/mm.sup.2.
[0050] As described above, the high-elastic-modulus prepreg 23a and
the low-elastic-modulus prepreg 23b of the prepreg 23 constructing
the flexural rigidity-adjusting straight layer are alternately
arranged along the axis of the shaft 10 to construct a flexural
rigidity distribution in which a first local maximum-value point P1
(hereinafter referred to as merely local maximum-value point)
through a fourth local maximum-value point P4 are formed along the
axis of the shaft 10 at a given interval provided between the first
local maximum-value point P1 and the second local maximum-value
point P2, between the second local maximum-value point P2 and the
third local maximum-value point P3, and between the third local
maximum-value point P3 and the fourth local maximum-value point P4,
as shown in FIG. 3.
[0051] More specifically, the first local maximum-value point P1 is
axially formed at a position proximate to the tip 11 of the shaft
10. The second local maximum-value point P2 is axially formed at a
position spaced at an interval of 225 mm from the first local
maximum-value point P1. The third local maximum-value point P3 is
axially formed at a position spaced at the interval of 225 mm from
the second local maximum-value point P2. The fourth local
maximum-value point P4 is axially formed at the butt spaced at the
interval of 225 mm from the third local maximum-value point P3.
[0052] The flexural rigidity values (local maximum value) Yp1
through Yp4 of the first local maximum-value point through the
fourth local maximum-value point are set to 2 kgm.sup.2, 4
kgm.sup.2, 6 kgm.sup.2, and 8 kgm.sup.2 respectively. Thus the
following relationship establishes among the flexural rigidity
values (local maximum values) Yp1 through Yp4:
Yp1<Yp2<Yp3<Yp4. Thus the local maximum value Yp2 is twice
as large as the local maximum value Yp1. The local maximum value
Yp3 is 1.5 times as large as the local maximum value Yp2. The local
maximum value Yp4 is 1.3 times as large as the local maximum value
Yp3.
[0053] A first flexural-rigidity-reduced region R1 is formed at the
butt side with respect to the first local maximum-value point P1,
namely, between the first local maximum-value point P1 and the
second local maximum-value point P2. The flexural rigidity value of
the first flexural-rigidity-reduced region R1 is set to not more
than the flexural rigidity value Yp1 of the first local
maximum-value point P1. That is, in the first
flexural-rigidity-reduced region R1, the rigidity value thereof is
not more than that of the adjacent tip-side first local
maximum-value point P1.
[0054] Similarly a second flexural-rigidity-reduced region R2 is
formed at the butt side with respect to the second local
maximum-value point P2, namely, between the second local
maximum-value point P2 and the third local maximum-value point P3.
The flexural rigidity value of the second flexural-rigidity-reduced
region R2 is set lower than the flexural rigidity value Yp2 of the
second local maximum-value point P2. Similarly a third
flexural-rigidity-reduced region R3 is formed at the butt side with
respect to the third local maximum-value point P3, namely, between
the third local maximum-value point P3 and the fourth local
maximum-value point P4. The flexural rigidity value of the third
flexural-rigidity-reduced region R3 is set lower than the flexural
rigidity value Yp3 of the third local maximum-value point P3.
[0055] In local minimum-value points Q1 through Q3 in flexural
rigidity of the flexural-rigidity-reduced regions R1 through R3,
the flexural rigidity values (local minimum values) Yq1, Yq2, and
Yq3 of the local minimum-value points Q1, Q2, and Q3 in flexural
rigidity are set to 1 kgm.sup.2, 3 kgm.sup.2, 5 kgm.sup.2
respectively. Thus the following relationship establishes among the
flexural rigidity values (local minimum values) Yq1 through Yq3:
Yq1<Yq2<Yq3. Therefore the local maximum value Yp1 is twice
as large as the local minimum value Yq1. The local maximum value
Yp2 is 1.3 times as large as the local minimum value Yq2. The local
maximum value Yp3 is 1.2 times as large as the local minimum value
Yq3.
[0056] In the above-described construction of the shaft 10, the
three flexural-rigidity-reduced regions R1 through R3 are formed
each in the length of 250 mm in the axial direction of the shaft
10. Thus it is possible to flex the shaft 10 entirely like a whip,
because the shaft 10 flexes greatly in the three
flexural-rigidity-reduced regions R1 through R3. Therefore unlike
the conventional shaft which flexes locally greatly, a player can
swing preferably without a feeling of physical disorder, increase
the head speed, and hit a ball a long distance.
[0057] The entire flexural-rigidity-reduced region R1 is disposed
from the tip 11 of the shaft 10 to a position within 400 mm of the
tip 11. Therefore it is easy to travel the golf club head easily
and increase the head speed efficiently.
[0058] The local maximum values and the local minimum values are so
set that the flexural rigidity value of the local maximum-value
point at a tip side is set to a range of not less than 1.2 times
nor more than two times as large as the flexural rigidity value of
the local minimum-value point of the flexural-rigidity-reduced
region adjacent to the local maximum-value point. Therefore the
shaft 10 is capable of flexing entirely sufficiently and smoothly
and increasing the head speed without giving a player a feeling of
physical disorder.
[0059] The high-elastic-modulus prepregs 23a and the
low-elastic-modulus prepregs 23b having an equal thickness and
composing the prepreg 23 constructing the flexural
rigidity-adjusting straight layer are wound over the full length of
the shaft 10. Thus no difference in level is generated on the
surface of the shaft. Hence the shaft 10 does not give a feeling of
physical disorder to the player.
[0060] FIGS. 4 and 5 show the second embodiment of the present
invention. The construction of the shaft 10 of the second
embodiment is similar to that of the shaft of the first embodiment
except that of the prepregs 21 through 24 constructing the shaft
10, the construction of the prepreg 23 constructing the
rigidity-adjusting straight layer are different from that of the
first embodiment. Therefore the same parts of the shaft of the
second embodiment as those of the first embodiment are denoted by
the reference numerals of the first embodiment, and description of
the same parts of the shaft of the second embodiment as those of
the first embodiment is omitted herein.
[0061] As shown in FIG. 4, in the prepreg 23 constructing the
rigidity-adjusting straight layer, the high-elastic-modulus
prepregs 23a having a length of 150 mm and the low-elastic-modulus
prepregs 23b having a length of 300 mm are arranged alternately
from the tip 11 of the shaft 10 toward the butt thereof in the
order of the high-elastic-modulus prepreg 23a, the
low-elastic-modulus prepreg 23b, the high-elastic-modulus prepreg
23a, and the low-elastic-modulus prepreg 23b. In addition, the
high-elastic-modulus prepreg 23a is disposed in a remaining portion
of the shaft 10 at its butt side. The elastic modulus of the
high-elastic-modulus prepreg 23a is set to 30 t/mm.sup.2. The
elastic modulus of the low-elastic-modulus prepreg 23b is set to 5
t/mm.sup.2.
[0062] As shown in FIG. 5, local maximum-value points P1 through P3
are formed on the shaft 10 having the above-described construction.
The following relationship establishes among the flexural rigidity
values (local maximum values) Yp1 through Yp3 of the local
maximum-value points P1 through P3: Yp1<Yp2<Yp3.
[0063] The flexural-rigidity-reduced region R1 is formed at the
butt side with respect to the local maximum-value point P1, namely,
between the local maximum-value point P1 and the local
maximum-value point P2. The flexural rigidity value of the
flexural-rigidity-reduced region R1 is set lower than the flexural
rigidity value Yp1 of the local maximum-value point P1. The
flexural-rigidity-reduced region R2 is formed at the butt side with
respect to the local maximum-value point P2, namely, between the
local maximum-value point P2 and the local maximum-value point P3.
The flexural rigidity value of the flexural-rigidity-reduced region
R2 is set lower than the flexural rigidity value Yp2 of the local
maximum-value point P2. In the flexural-rigidity-reduced regions R1
and R2, the following relationship establishes among the flexural
rigidity values (local minimum values) Yq1 and Yq2 of the local
minimum-value points Q1 and Q2 in flexural rigidity:
Yq1<Yq2.
[0064] The shaft 10 having the above-described construction has the
three local maximum-value points P1 through P3 and the two
flexural-rigidity-reduced regions R1 and R2. However, the
difference between the local maximum flexural rigidity value and
the local minimum flexural rigidity value in the second embodiment
is larger than the difference between the local maximum flexural
rigidity value and the local minimum flexural rigidity value in the
first embodiment. Thus the shaft 10 of the second embodiment can be
flexed as smoothly and greatly as the shaft of the first
embodiment.
[0065] FIGS. 6 and 7 show the third embodiment of the present
invention. The construction of the shaft of the third embodiment is
similar to that of the shaft of the second embodiment except that
the construction of the prepreg 23 constructing the
rigidity-adjusting straight layer is different from that of the
second embodiment in that the prepreg 23a disposed at the butt side
of the shaft 10 of the second embodiment is replaced with a prepreg
23d having an elastic modulus different from that of the prepreg
23a. Therefore the same parts of the shaft of the third embodiment
as those of the first embodiment are denoted by the reference
numerals of the second embodiment, and description of the same
parts of the shaft of the third embodiment as those of the second
embodiment is omitted herein.
[0066] As shown in FIGS. 5 and 6, in the fiber reinforced prepreg
23, the following high-elastic-modulus prepregs and
low-elastic-modulus prepregs are arranged from the tip 11 of the
shaft 10 toward the butt thereof in the order of the
high-elastic-modulus prepreg 23a having a length of 150 mm, the
low-elastic-modulus prepreg 23b having a length of 300 mm, a
high-elastic-modulus prepreg 23c having a length of 150 mm, and the
low-elastic-modulus prepreg 23b. In addition a high-elastic-modulus
prepreg 23d is disposed in a remaining portion of the shaft 10 at
its butt side. The elastic modulus of the high-elastic-modulus
prepreg 23c is set to 20 t/mm.sup.2. The elastic modulus of the
high-elastic-modulus prepreg 23d is set to 80 t/mm.sup.2. The
elastic modulus of the low-elastic-modulus prepreg 23b is set to 5
t/mm.sup.2.
[0067] As shown in FIG. 7, three local maximum-value points P1
through P3 are formed on the shaft 10 having the above-described
construction. The flexural-rigidity-reduced region R1 is formed at
the butt side with respect to the local maximum-value point P1,
namely, between the local maximum-value points P1 and P2. The
flexural rigidity value of the flexural-rigidity-reduced region R1
is set lower than the flexural rigidity value Yp1 of the local
maximum-value point P1. The flexural-rigidity-reduced region R2 is
formed at the butt side with respect to the local maximum-value
point P2, namely, between the local maximum-value point P2 and the
local maximum-value point P3. The flexural rigidity value of the
flexural-rigidity-reduced region R2 is set lower than the flexural
rigidity value Yp2 of the local maximum-value point P2. In the
flexural-rigidity-reduced regions R1 and R2, the following
relationship establishes among the flexural rigidity values (local
minimum values) Yq1 and Yq2 of the local minimum-value points Q1
and Q2 in flexural rigidity: Yq1<Yq2.
[0068] In the shaft 10 having the above-described construction, the
difference between the local minimum flexural rigidity value Yq1
and the local maximum flexural rigidity value Yp1 in the third
embodiment is set larger than the difference between the local
minimum flexural rigidity value Yq1 and the local maximum flexural
rigidity value Yp1 in the second embodiment. Further the difference
between the local minimum flexural rigidity value Yq2 and the local
maximum flexural rigidity value Yp2 in the third embodiment is set
larger than the difference between the local minimum flexural
rigidity value Yq2 and the local maximum flexural rigidity value
Yp2 in the second embodiment. However, both the ratio of the local
maximum flexural rigidity value Yp2 to the local minimum flexural
rigidity value Yq1 and the ratio of the local maximum flexural
rigidity value Yp3 to the local minimum flexural rigidity value Yq2
are set to not more than two. Therefore it is possible to increase
the head speed and flex the shaft 10 preferably. Further because
the prepreg 23d having a very high elastic modulus is disposed at
the butt side, the rigidity in the vicinity of the grip 14 is high.
Thus the shaft 10 gives player's hands a proper degree of firmness
when the player swings.
EXAMPLES
[0069] The shaft of each of the examples 1 through 3 and the
comparison examples 1 through 3 was prepared by differentiating the
elastic moduli of prepregs constructing the rigidity-adjusting
straight layer from each other and differentiating the dispositions
and constructions of prepregs from each other. The same head was
mounted on each of the shafts to conduct a comparison test for
comparing head speeds, the distance between a hitting point and the
sweet spot, and a feeling testers had at a ball-hitting time. Table
3 shows evaluations of the test results.
[0070] A head mounted on the shaft was made of titanium. The head
had a volume of 380 cc and a weight of 200 g. A rubber grip
specially made was mounted on the shaft. The number of the golf
club was W#1.
1TABLE 1 Distance from tip 0.about.150 mm 150.about.300 mm
300.about.450 mm 450.about.600 mm 600.about.750 mm 750.about.900 mm
900.about.butt side Example 1 Mandrel 5 6.5 8 9.5 11 12.5 14
diameter Prepreg a c a c a c a Example 2 Mandrel 5 6.5 8 9.5 11
12.5 14 diameter Prepreg a c c a c c a Example 3 Mandrel 5 6.5 8
9.5 11 12.5 14 diameter Prepreg d c c d c c e Comparison Mandrel 5
6.5 8 9.5 11 12.5 14 example 1 diameter Prepreg a a d d d a a
Comparison Mandrel 5 6.5 8 9.5 11 12.5 14 example 2 diameter
Prepreg a a a e a a a Comparison Mandrel 5 6.5 8 9.5 11 12.5 14
example 3 diameter Prepreg a a a a a a a
[0071]
2 TABLE 2 Elastic modulus Thickness Number of grams of PP/mm.sup.2
[t/mm.sup.2] [mm] [g/m.sup.2] a 30 0.1 125 b 25 0.1 125 c 5 0.1 125
d 40 0.1 125 e 80 0.1 125
[0072]
3 TABLE 3 Distance of hitting Feeling Head speed point from SS (SD)
(maximum number [m/s] [mm] of marks is 10) Example 1 40.3 1.5 8.6
Example 2 40.5 1.7 9.1 Example 3 39.9 1.7 8.8 Comparison 37.8 3.7
6.8 example 1 Comparison 38.9 2.8 4.3 example 2 Comparison 38.5 3.0
7.0 example 3
[0073] The shaft of each of the examples 1 through 3 and the
comparison examples 1 through 3 was formed by a sheet winding
method. In each shaft, two prepregs (a) forming the bias layer were
wound three times at the inner-layer side of the prepreg
constructing the rigidity-adjusting straight layer in such a way
that reinforcing fibers of the prepregs (a) intersected with each
other. A prepreg (b) (8255S-12 produced by Toray Industries Inc.)
constructing the straight layer was wound twice at the outer-layer
side to integrate the prepregs (a) and (b) with each other. Table 2
shows the elastic modulus of each of the prepregs (a) and (b), the
thickness of prepregs, and the g/m.sup.2 of prepregs (PP). The
length of each shaft was set to 1050 mm. The mandrels had the same
configuration. Each mandrel was tapered from the butt toward the
tip. Table 1 shows the outer diameter of the mandrel.
Example 1
[0074] The construction of the shaft of the example 1 was the same
as that of the first embodiment shown in FIG. 2. More specifically,
the shaft had prepregs constructing the rigidity-adjusting straight
layer. High-elastic-modulus prepregs (a) (MR35DC-125S produced by
Mitsubishi Rayon Inc.) having a length of 150 mm and
low-elastic-modulus prepregs (c) (E1026D-12N produced by Nippon
Graphite Fiber Inc.) having a length of 150 mm were arranged
alternately from the tip of the shaft toward the butt thereof. The
high-elastic-modulus prepreg (a) was disposed in a remaining
portion of the shaft 10 at its butt side. The total number of the
high-elastic-modulus prepregs (a) and the low-elastic-modulus
prepregs (c) was seven. The elastic modulus of the
high-elastic-modulus prepreg (a) was set to 30 t/mm.sup.2. The
elastic modulus of the low-elastic-modulus prepreg (c) was set to
5t/mm.sup.2. As a result, the distribution of the flexural rigidity
was the same as that of FIG. 3 (curve A of FIG. 8).
Example 2
[0075] The construction of the shaft of the example 2 was the same
as that of the second embodiment shown in FIG. 4. As prepregs
constructing the rigidity-adjusting straight layer, the
high-elastic-modulus prepregs (a) having a length of 150 mm and the
low-elastic-modulus prepregs (c) having a length of 30 mm were
arranged alternately from the tip of the shaft toward the butt
thereof in the order of the high-elastic-modulus prepreg (a) having
a length of 150 mm, the low-elastic-modulus prepreg (c) having a
length of 300 mm. In addition, the high-elastic-modulus prepreg (a)
was disposed in a remaining portion of the shaft 10 at its butt
side. The elastic modulus of the high-elastic-modulus prepreg (a)
was set to 30 t/mm.sup.2. The elastic modulus of the
low-elastic-modulus prepreg (c) was set to 5 t/mm.sup.2. As a
result, the distribution of the flexural rigidity was the same as
that of FIG. 5 (curve B of FIG. 8).
Example 3
[0076] The construction of the shaft of the example 3 was the same
as that of the third embodiment. As prepregs constructing the
rigidity-adjusting straight layer, the following prepregs were
disposed from the tip of the shaft toward the butt thereof in the
order of a high-elastic-modulus prepreg (d) (HRX350C-130C produced
by Mitsubishi Rayon Inc.) having a length of 150 mm, a
low-elastic-modulus prepreg (c) having a length of 300 mm, the
high-elastic-modulus prepreg (d) having a length of 150 mm, and the
low-elastic-modulus prepreg (c) having a length of 300 mm. In
addition a super-high-elastic-modulus prepreg (e) (E8026C-12S
produced by Nippon Graphite Fiber Inc.) was disposed in a remaining
portion of the shaft 10 at its butt side. The elastic modulus of
the high-elastic-modulus prepreg (d) is set to 40 t/mm.sup.2. The
elastic modulus of the high-elastic-modulus prepreg (d) was set to
40 t/mm.sup.2. The elastic modulus of the low-elastic-modulus
prepreg (c) was set to 5 t/mm.sup.2. As a result, the distribution
of the flexural rigidity was the same as that of FIG. 7 (curve C of
FIG. 8).
Comparison Example 1
[0077] As prepregs constructing the rigidity-adjusting straight
layer, the following high-elastic-modulus prepregs were arranged
from the tip of the shaft toward the butt thereof in the order of
the high-elastic-modulus prepreg (a) having a length of 300 mm and
the high-elastic-modulus prepreg (d) having a length of 450 mm. In
addition, the high-elastic-modulus prepreg (a) was disposed in a
remaining portion of the shaft 10 at its butt side. The elastic
modulus of the high-elastic-modulus prepreg (a) was set to 30
t/mm.sup.2. The elastic modulus of the high-elastic-modulus prepreg
(d) was set to 40 t/mm.sup.2.
Comparison Example 2
[0078] As the prepreg constructing the rigidity-adjusting straight
layer, the following prepregs were disposed from the tip of the
shaft toward the butt thereof in the order of the
high-elastic-modulus prepreg (a) having a length of 450 mm and the
super-high-elastic-modulus prepreg e having a length of 150 mm. In
addition, the high-elastic-modulus prepreg (a) was disposed in a
remaining portion of the shaft 10 at its butt side. The elastic
modulus of the high-elastic-modulus prepreg (a) was set to 30
t/mm.sup.2. The elastic modulus of the super-high-elastic-modulus
prepreg e was set to 80 t/mm.sup.2.
Comparison Example 3
[0079] The entire rigidity-adjusting straight layer consisted of
one high-elastic-modulus prepreg (a) having an elastic modulus of
30 t/mm.sup.2.
[0080] Method of Measuring Head Speed
[0081] H/S was computed by measuring the position of the head at
1000 .mu.s and 3000 .mu.s immediately before an impact time.
[0082] Method of Measuring Distance Between Hitting Point and Sweet
Spot
[0083] The distance between a hitting point of and the sweet spot
was measured to measure variations of the distance.
[0084] Method of Evaluating Feeling at Ball-Hitting Time
[0085] Ten testers were requested to hit 10 balls with each shaft
to make evaluations on a maximum of 10 points. The testers gave
higher marks for shafts which gave the testers a better feeling.
Table 3 shows the average of marks given by the testers. The
testers had a handicap of nine in average. The 10 testers was 48 in
average.
[0086] As shown with the curves A through C of FIG. 8, in the
shafts of the examples 1 through 3 each having a plurality of the
flexural-rigidity-reduced regions, the flexural rigidity value
thereof increased from the tip thereof toward the butt thereof. As
shown in FIG. 3, the head speed of each of the shafts of the
examples 1 through 3 was high and there was a small variation in
the distance between the hitting point and the sweet spot. This
indicates that the shafts flexed favorably and thus the testers
could swing without a feeling of physical disorder. This was proved
by the fact that high marks were given in the evaluation of
feeling.
[0087] The shaft of the comparison example 1 did not have the
flexural-rigidity-reduced region whose flexural rigidity value
decreases from the tip thereof toward its butt. The shaft had a
flexural rigidity value which was comparatively high at the central
portion thereof. The shaft of the comparison example 2 , the
flexural rigidity value increased locally greatly at a position of
the central portion thereof, and the flexural-rigidity-reduced
region was present at only one portion on the side rearward from
the local maximum-value point. The shaft of the comparison example
3 , the flexural rigidity value increased with the increase of the
diameter thereof from its tip toward its butt, and the flexural
rigidity distribution curve was almost linear with inclining gently
upward toward the right.
[0088] The shafts of the comparison examples 1 through 3 had only
one flexural-rigidity-reduced region or no
flexural-rigidity-reduced region. Table 3 indicates that the head
speed of these shafts was low and that there was a large variation
in the distance between the hitting point and the sweet spot.
Therefore the shafts did not flex smoothly and the testers had a
feeling of physical disorder in their swings. This was proved by
the fact that low marks were given in the evaluation of
feeling.
* * * * *