U.S. patent application number 10/739002 was filed with the patent office on 2004-09-09 for golf club.
This patent application is currently assigned to K. K. ENDO Seisakusho. Invention is credited to Tsurumaki, Masaei.
Application Number | 20040176183 10/739002 |
Document ID | / |
Family ID | 32716286 |
Filed Date | 2004-09-09 |
United States Patent
Application |
20040176183 |
Kind Code |
A1 |
Tsurumaki, Masaei |
September 9, 2004 |
Golf club
Abstract
A golf club enables a golf ball to be hit farther without a
decrease in ball traveling distance even if it is struck at a lower
point on the club head face. A driver club head includes a face
having a hitting surface, a sole forming the bottom of the head,
etc. The sole is modified for improvement by providing an
elastically deformable area having a recessed or projected
configuration at a position of the sole closer to the face. The
deformable area includes a bent portion formed at the lower end of
the face. A bend is formed between the bent portion and the sole at
an obtuse angle. The sole is provided with a recess or a projection
to lower the rigidity of the sole. Thus, repulsion is enhanced to
increase the ball traveling distance even if the ball is struck at
a lower point on the face.
Inventors: |
Tsurumaki, Masaei;
(Tsubame-shi, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW
SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
K. K. ENDO Seisakusho
Tsubame-shi
JP
|
Family ID: |
32716286 |
Appl. No.: |
10/739002 |
Filed: |
December 19, 2003 |
Current U.S.
Class: |
473/345 |
Current CPC
Class: |
A63B 53/0462 20200801;
A63B 53/0416 20200801; A63B 53/0466 20130101; A63B 53/0433
20200801; A63B 60/52 20151001 |
Class at
Publication: |
473/345 |
International
Class: |
A63B 053/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 20, 2002 |
JP |
2002-369637 |
Jul 8, 2003 |
JP |
2003-193956 |
Claims
What is claimed is:
1. A golf club having a metallic hollow golf club head, said golf
club comprising: a face member disposed at a front of said club
head and having a hitting surface for hitting a golf ball; and a
head body member constituting a remaining part of said club head,
said head body member including: a sole forming a bottom of said
club head; a crown forming a top of said club head; a toe forming a
forepart of said club head; a heel forming a rear part of said club
head; a back positioned opposite said face member to form a back
part of said club head; and a hosel to which a club shaft is
connected; wherein a deformable area that is elastically deformable
in response to hitting of the golf ball on said hitting surface is
provided at a joint between a lower end of said face member and
said sole.
2. A golf club according to claim 1, wherein said deformable area
includes a lower end portion of said face member that is bent at an
angle not less than 90 degrees to form a bent portion, said sole
being joined to said bent portion, said sole being convexly
projected toward the top of said club head in a section taken along
a vertical plane containing a line perpendicular to said hitting
surface.
3. A golf club according to claim 1, wherein said deformable area
includes a lower end portion of said face member that is bent at an
angle not less than 90 degrees to form a bent portion, said sole
being jointed to said bent portion, said sole being convexly
projected away from the top of said club head in a section taken
along a vertical plane containing a line perpendicular to said
hitting surface.
4. A golf club according to claim 1, wherein said deformable area
includes a lower end portion of said face member that is bent at an
angle not less than 90 degrees to form a bent portion, said sole
being joined to said bent portion, said sole being provided with at
least one hole.
5. A golf club according to claim 1, wherein said deformable area
includes a lower end portion of said face member that is bent at an
angle not less than 90 degrees to form a bent portion, said sole
being joined to said bent portion, said sole having a part thereof
replaced with a thin plate.
6. A golf club according to claim 1, wherein said deformable area
includes a lower end portion of said face member that is bent at an
angle not less than 90 degrees to form a bent portion, said sole
being joined to said bent portion, said sole being divided into two
portions at a part thereof, said two portions being displaceable
relative to each other.
7. A golf club according to claim 2 or 3, wherein said sole in said
deformable area has a smaller plate thickness than that of said
bent portion.
8. A golf club according to claim 2, wherein a part of said sole in
said deformable area forms an arch-shaped groove.
9. A golf club according to claim 2, wherein a portion of said sole
that is joined to said bent portion in said deformable area forms a
groove having a surface approximately parallel to said hitting
surface.
10. A golf club according to claim 7, wherein said deformable area
has a gentle bend G formed by intersection of a line S.sub.1
tangent to a surface of said face member with a line S.sub.2
tangent to said bent portion, said bend G having an angle .alpha.
not less than 90 degrees, and a gentle bend H formed by
intersection of said tangent line S.sub.2 with a line S.sub.3
tangent to a surface of said sole, said bend H having an angle
.alpha..sub.1 not less than 90 degrees.
11. A golf club according to claim 10, wherein said deformable area
has at least one arch-shaped groove provided in a surface of said
sole near said bend H, and wherein a gentle bend J is formed by
intersection of a line S.sub.4 tangent to said groove with said
tangent line S.sub.2, said bend J having an angle .alpha..sub.2 not
less than 90 degrees, and a gentle bend K is formed by intersection
of a line S.sub.5 tangent to said groove with said tangent line
S.sub.31 said bend K having an angle .alpha..sub.3 not less than 90
degrees, wherein said bend G, said bend J and said bend K form a
continuous gently curved line.
12. A golf club according to claim 10 or 11, wherein the angle
.alpha. of said bend G is not less than 90 degrees and not more
than 135 degrees, preferably not less than 90 degrees and not more
than 120 degrees.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to golf clubs. More
particularly, the present invention relates to an improved golf
club having a club head sole modified to increase the traveling
distance of golf balls.
[0003] 2. Description of the Related Art
[0004] There are various golf clubs prepared for varying conditions
of golf courses. For the first shot, golf clubs called "drivers"
are usually used in order to get maximum ball traveling distance.
The ball traveling distance affects the score directly. Therefore,
the position of the ball impact point on the golf club head is an
important factor. The hitting surface of the club head is called
"face". Under any conditions, the user (player) will strike the
ball on the face of the club head.
[0005] Usually, the center of gravity of a driver club head as
projected on the club face is located above the center of the face
as seen from a direction perpendicular to the face surface. The
reason for this is as follows. The club head has an approximately
inverted trapezoidal or triangular configuration in terms of the
face configuration, in which the upper side is wider than the lower
side. Accordingly, the mass is inevitably deviated toward the upper
side. In addition, because a part known as "hosel", into which a
shaft is to be inserted, is provided on the top of the club head,
an extra mass is added to the upper side of the head.
[0006] Regarding the center of gravity, even a club head in which
the center of gravity is located at a position approximately 60%
from the bottom surface of the head in terms of the face height,
for example, is called "low-center of gravity model". A ball
striking area called "sweet area" is in the vicinity of the center
of gravity, which is an area capable of sending the ball the
farthest distance. Therefore, in order to make use of the maximum
repulsion power of the head to maximize the ball traveling
distance, it is usually necessary to strike the ball on a sweet
area above the center of the face. However, not only amateur
golfers whose ball impact point is likely to vary but also
professional golfers occasionally shift their ball impact point
intentionally according to golf course conditions.
[0007] For example, in a head (against) wind, golfers usually hit
the ball in such a manner as to produce a low ball trajectory
because if it is hit in the usual manner, the ball will have to fly
against the wind, resulting in a failure to get the desired ball
traveling distance. In this case, the ball impact point is in a
lower area of the club face. This, however, results in degradation
of the repulsive force obtained. Consequently, the ball traveling
distance achievable becomes less than that obtained by striking on
the sweet area. This is because the center of gravity is located at
the upper side of the face, as stated above. That is, because the
sweet area, which is a high-repulsion area, is in the vicinity of
the center of gravity, if the impact point is off this area,
repulsive force reduces undesirably.
[0008] Under these circumstances, various methods have been
proposed to enable a repulsive force comparable to that obtained at
the conventional sweet area to be obtained even at a lower point on
the face to thereby solve the problems associated with the
conventional golf clubs. For example, a golf club has been
disclosed in which the area of a region of the club face that has a
specific coefficient of restitution is specified to minimize the
decrease in ball traveling distance when the ball impact point is
offset from the sweet spot, as a method of increasing repulsive
force [for example, see Japanese Patent Application Unexamined
Publication (KOKAI) No. 2002-17912]. As a method of lowering the
center of gravity and consequently increasing repulsive force at a
lower point on the club face, a technique has been disclosed
wherein a weight member that is wider at the lower side than the
upper side thereof is provided in a lower portion of the club head
[for example, see Japanese Patent Application Unexamined
Publication (KOKAI) No. 2002-17908]. Further, there is known a golf
club having a head arranged to allow its face to be deflected with
good balance [for example, see Japanese Patent Application
Unexamined Publication (KOKAI) No. Hei 11-114102].
[0009] As has been stated above, various methods have been devised
to increase the ball traveling distance under various conditions.
However, the proposed methods have not yet satisfactorily solved
the problems. There is still room for further improvement,
particularly in terms of enhancement of repulsion at a lower point
off the sweet area. The above-described method wherein the area of
a region of the club face that has a specific coefficient of
restitution is specified is specifically carried out by reducing
the thickness of a specific region of the face so that the
thickness varies from the center to the peripheral edge of the
face, thereby consequently enhancing the repulsion effect.
[0010] The above-described face structure may be effective for
specific club heads but is not always reliable. The structure in
which the club face, including the crown, is deflectable with good
balance is also incapable of surely enhancing the repulsion effect
at a lower point on the face. The method wherein a weight member is
provided is effective in its own way but limited in its usefulness
under the recent tendency for club heads to increase in size. That
is, when a club head becomes large in size, addition of a weight
member gives rise to a new problem that the mass of the head
becomes heavy. The golf industry is a world where tradition is
valued originally.
[0011] Substantial changes in the configuration, weight, etc. of
the club head from those of the conventional one require users to
change their golf swing and so forth. This may cause the swing
rhythm to be destroyed. Even if an epoch-making golf club is
developed, it will take a long time for the new golf club to become
established in actual practice. Thus, various problems will occur
if large-scale changes are made to the configuration of golf clubs
that have actually been established. Therefore, it is ideal to
develop a golf club improved in function to satisfy golfers without
substantial change in the configuration of the presently
established golf clubs.
[0012] Accordingly, it is desired to develop a golf club capable of
enlarging the repulsion area, particularly, downward on the club
head face, without making a large difference from the conventional
configuration and without requiring a special arrangement that
limits the functions of the golf club, whereby the repulsion
performance is improved even at a lower point on the club head face
as well as in the conventional sweet area, and thus the ball
traveling distance can be increased stably even under headwind
conditions.
SUMMARY OF THE INVENTION
[0013] The present invention was made in view of the
above-described technical background. Accordingly, the present
invention attains the following objects.
[0014] An object of the present invention is to provide a golf club
improved to increase repulsive force at a lower point on the club
head face so that the ball can be hit farther without a decrease in
ball traveling distance even if it is struck at a point below the
conventional sweet area.
[0015] Another object of the present invention is to provide a golf
club improved in ball hitting performance in comparison to the
conventional golf clubs, despite having the same basic
configuration as the conventional one, simply by modifying a part
of the club head sole, without a change from the conventional
structure in terms of the configuration as seen from the player
upon addressing.
[0016] Still another object of the present invention is to provide
a golf club capable of being produced at reduced costs.
[0017] To attain the above-described objects, the present invention
provides the following golf clubs.
[0018] According to a first aspect thereof, the present invention
provides a golf club having a metallic hollow golf club head. The
golf club includes a face member disposed at the front of the club
head and having a hitting surface for hitting a golf ball. The golf
club further includes a head body member constituting the remaining
part of the club head. The head body member has a sole forming the
bottom of the club head, a crown forming the top of the club head,
a toe forming the forepart of the club head, a heel forming the
rear part of the club head, a back positioned opposite the face
member to form the back part of the club head, and a hosel to which
a club shaft is connected. A deformable area that is elastically
deformable in response to hitting of the golf ball on the hitting
surface is provided at the joint between the lower end of the face
member and the sole.
[0019] A golf club according to a second aspect of the present
invention is a golf club of the first aspect, wherein the
deformable area includes a lower end portion of the face member
that is bent at an angle not less than 90 degrees to form a bent
portion, and the sole is joined to the bent portion. The sole is
convexly projected toward the top of the club head in a section
taken along a vertical plane containing a line perpendicular to the
hitting surface.
[0020] A golf club according to a third aspect of the present
invention is a golf club of the first aspect, wherein the
deformable area includes a lower end portion of the face member
that is bent at an angle not less than 90 degrees to form a bent
portion, and the sole is jointed to the bent portion. The sole is
convexly projected away from the top of the club head in a section
taken along a vertical plane containing a line perpendicular to the
hitting surface.
[0021] A golf club according to a fourth aspect of the present
invention is a golf club of the first aspect, wherein the
deformable area includes a lower end portion of the face member
that is bent at an angle not less than 90 degrees to form a bent
portion, and the sole is joined to the bent portion. The sole is
provided with at least one hole.
[0022] A golf club according to a fifth aspect of the present
invention is a golf club of the first aspect, wherein the
deformable area includes a lower end portion of the face member
that is bent at an angle not less than 90 degrees to form a bent
portion, and the sole is joined to the bent portion. The sole has a
part thereof replaced with a thin plate.
[0023] A golf club according to a sixth aspect of the present
invention is a golf club of the first aspect, wherein the
deformable area includes a lower end portion of the face member
that is bent at an angle not less than 90 degrees to form a bent
portion, and the sole is joined to the bent portion. The sole is
divided into two portions at a part thereof. The two portions are
displaceable relative to each other.
[0024] A golf club according to a seventh aspect of the present
invention is a golf club of the second or third aspect, wherein the
sole in the deformable area has a smaller plate thickness than that
of the bent portion.
[0025] A golf club according to an eighth aspect of the present
invention is a golf club of the second aspect, wherein a part of
the sole in the deformable area forms an arch-shaped groove.
[0026] A golf club according to a ninth aspect of the present
invention is a golf club of the second aspect, wherein a portion of
the sole that is joined to the bent portion in the deformable area
forms a groove having a surface approximately parallel to the
hitting surface.
[0027] A golf club according to a tenth aspect of the present
invention is a golf club of the seventh aspect, wherein the
deformable area has a gentle bend G formed by intersection of a
line S.sub.1 tangent to the surface of the face member with a line
S.sub.2 tangent to the bent portion of the face member. The bend G
has an angle .alpha. not less than 90 degrees. The deformable area
further has a gentle bend H formed by intersection of the tangent
line S.sub.2 with a line S.sub.3 tangent to the surface of the
sole. The bend H has an angle .alpha..sub.1 not less than 90
degrees.
[0028] A golf club according to an eleventh aspect of the present
invention is a golf club of the tenth aspect, wherein the
deformable area has at least one arch-shaped groove provided in a
surface of the sole near the bend H. A gentle bend J is formed by
intersection of a line S.sub.4 tangent to the groove with the
tangent line S.sub.2. The bend J has an angle .alpha..sub.2 not
less than 90 degrees. Further, a gentle bend K is formed by
intersection of a line S.sub.5 tangent to the groove with the
tangent line S.sub.3. The bend K has an angle .alpha..sub.3 not
less than 90 degrees. The bends G, J and K form a continuous gently
curved line.
[0029] A golf club according to a twelfth aspect of the present
invention is a golf club of the tenth or eleventh aspect, wherein
the angle .alpha. of the bend G is not less than 90 degrees and not
more than 135 degrees, preferably not less than 90 degrees and not
more than 120 degrees.
[0030] The above and other objects, features and advantages of the
present invention will become more apparent from the following
description of the preferred embodiments thereof, taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is an external view showing the appearance of a golf
club.
[0032] FIG. 2 is a plan view of a driver club head according to the
present invention.
[0033] FIG. 3 is a front view of the driver club head according to
the present invention.
[0034] FIG. 4 is a side view of the driver club head according to
the present invention, which shows a first embodiment of the
present invention.
[0035] FIG. 5 is a side view of a conventional driver club
head.
[0036] FIG. 6 is a sectional view taken along the line X-X in FIG.
3.
[0037] FIG. 7 is a sectional view showing the details of the
structure shown in FIG. 6.
[0038] FIG. 8 is an explanatory view illustrating a state where a
golf ball has been struck on the face of the club head.
[0039] FIG. 9 is a sectional view showing a third embodiment of the
present invention.
[0040] FIG. 10 is a sectional view showing a fourth embodiment of
the present invention.
[0041] FIG. 11 is a sectional view showing a fifth embodiment of
the present invention.
[0042] FIG. 12 is a sectional view showing a sixth embodiment of
the present invention.
[0043] FIG. 13 is a sectional view showing a seventh embodiment of
the present invention.
[0044] FIG. 14 is a sectional view showing an eighth embodiment of
the present invention, in which the club head has a groove with a
rectangular sectional configuration.
[0045] FIG. 15 is a sectional view showing a ninth embodiment, in
which the club head has a groove with a stepped sectional
configuration.
[0046] FIG. 16 is a sectional view showing a modification in which
a part of the sole of the club head is made of a thin plate to
lower the rigidity of the sole.
[0047] FIG. 17 is a sectional view showing a modification in which
the sole of the club head is divided into two portions to lower the
rigidity of the sole.
[0048] FIG. 18 is a sectional view showing a modification in which
the sole of the club head is provided with at least one hole to
lower the rigidity of the sole 3.
[0049] FIG. 19 is a diagram showing the distribution of
coefficients of restitution in the club head according to the first
embodiment.
[0050] FIG. 20 is a diagram showing the distribution of
coefficients of restitution in a conventional club head.
[0051] FIG. 21 is an explanatory view showing a measurement
comparison as to ball traveling distance between the first
embodiment and the conventional golf club.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0052] Embodiments of the present invention will be described below
in detail with reference to the accompanying drawings.
[0053] FIG. 1 is an external view showing the general structure of
a golf club according to the present invention. Although the
present invention is directed to a metallic hollow golf club head,
the following description of embodiments will be made of an example
in which the present invention is applied to a driver club head. A
driver club head (hereinafter referred to simply as "head") 1 is
supported on a shaft A. FIGS. 2 to 4 show an embodiment of the head
1 as used in a metallic golf club. It should be noted that the
drawings other than FIG. 1 show only the head part. That is,
illustration of the shaft A and other members is omitted
therein.
[0054] FIG. 2 is a plan view. FIG. 3 is a front view, and FIG. 4 is
a side view. As shown in the figures, the head 1 comprises a crown
2 corresponding to the top of the head 1, a sole 3 corresponding to
the bottom of the head 1, a face 4 with which a golf ball is
struck, a toe 5 corresponding to the forepart of the head 1, a heel
6 corresponding to the rear part of the head 1, a back 12
positioned opposite the face 4 to form the back part of the head 1,
and a hosel 7, which is a member for supporting the head 1 on the
shaft A.
[0055] In the manufacture of the head 1, each part comprises either
a single unitized member or a plurality of equally divided members
that are joined together to form one component part. Each component
part is subjected to press working before being joined together
into an integrated structure by welding or the like. For example,
the head 1 comprises five component parts, i.e. a face 4, a sole 3,
a crown 2, a hosel 7, and a weight. Each part is produced as
follows. A plate material is blanked into a predetermined shape.
The blank is formed under heating by hot pressing. The heating
process is performed, for example, at 400.degree. C. for the face
4, and at 900.degree. C. for the sole 3, the crown 2 and other
portions of the head body.
[0056] After being pressed, each component part is deburred
(trimmed) and joined together by TIG arc welding to produce a
driver club head 1. In this embodiment, the constituent material of
the head 1 is a titanium alloy. The component parts are joined
together as follows. The constituent members related to the face 4
and those related to the sole 3 are butt-joined to each other.
Thereafter, the hosel-related members are joined thereto, and the
pressed crown-related members are joined by TIG arc welding. In
this way, the component parts are integrated into a driver club
head 1. After the welding process, the driver club head is
subjected to grinding process and age hardening (5 hours at
515.degree. C.), followed by painting process. Thus, the driver
club head is completed.
[0057] The face 4 has a slightly curved surface and is formed from
a plate-shaped material. In the face 4, a sweet area 9 in the
vicinity of the center 8 of gravity has the maximum coefficient of
restitution. Usually, an effective way of sending a golf ball a
long distance is to hit the ball at the sweet area 9. Therefore,
the coefficient of restitution is set high in this portion of the
face 4. It is well known that as the coefficient of restitution is
increased, the ball traveling distance increases. The coefficient
of restitution is an important factor determining the performance
of golf clubs. For the coefficient of restitution, a criterion of
measurement has been defined by the United States Golf Association
(USGA). The coefficient of restitution is obtained from the
following equation:
V.sub.out/V.sub.in=eM-m/M+m
[0058] In the above equation, m represents the average mass of
balls for testing, M represents the mass of the head, V.sub.out
represents the speed of a testing ball after impact, and V.sub.in
represents the speed of the testing ball before impact.
Accordingly, V.sub.out/V.sub.in shows the speed ratio. Further, e
represents the coefficient of restitution. According to the
definition, golf balls for testing should be Pinnacle Gold (trade
name) golf balls, and testing balls that have previously been
numbered and measured for initial velocity should be used. The
average weight should be 45.4 g.
[0059] It is defined that the testing balls should be stored in a
room at 23.+-.1.0.degree. C., and the impact speed should be 48.8
m/s. In addition, a ball launching apparatus, a trajectory screen
and other testing equipment have been specified in detail.
Regarding a testing method also, rules have been made in detail.
For example, mapping should be performed. A reference value of the
coefficient of restitution is e=0.822. Whether each particular head
is conformable or not is judged by comparing the actual impact
speed ratio with the reference speed ratio on the basis of the
measured mass according to the above-described definition.
[0060] Meanwhile, the coefficient of restitution can be calculated
inversely from the above-described equation, provided that the
other conditions are determined. In other words, the coefficient of
restitution is calculated for various values of the mass of the
head that may be changed, for example, by varying the thickness of
the face 4. In this way, it is possible to judge optimal numerical
value setting. As will be clear from the above-described equation,
the fact that the speed of a golf ball after impact is high means
that the coefficient of restitution is high.
[0061] The present inventor conducted exhaustive studies by
performing testing according to the above-described rules and
attained the present invention in which the conventional sweet area
is extended downward and thus widened.
[0062] Embodiments of the present invention will be described below
in detail. FIG. 5 is a side view of a conventional driver club
head, which corresponds to a side view of the first embodiment of
the present invention shown in FIG. 4. As will be understood from
comparison with FIG. 5, the present invention has an improvement
made on the sole 3. As shown in FIG. 4, a portion of the sole 3
closer to the face 4 is provided with a projection 10 and a groove
11 that extend in a direction connecting the toe 5 and the heel 6.
The projection 10 projects away from the crown 2, and the groove 11
is recessed toward the crown 2. The projection 10 comprises a first
projection 10a and a second projection 10b facing each other across
the groove 11. The first projection 10a is located closer to the
face 4. The second projection 10b is formed as a gentle projection
extending toward the heel 6, which is the rear part of the head
1.
[0063] As shown in FIG. 4, the projection 10 and the groove 11 have
a gently curved configuration as a whole. The face-side projection
10a makes the sole 3 form an obtuse angle .alpha. to the face 4
(see FIG. 6) in a section taken along a vertical plane (plane
containing a straight line in a direction shown by a thread
suspending an object) containing a line perpendicular to the
surface of the face 4. The purpose of providing a recessed and
projected area on the sole 3 is to impart an elastic effect to the
sole 3. The recessed and projected area as an elastically
deformable area B is a constituent part featuring this embodiment.
FIG. 6 is a sectional view taken along the line X-X in FIG. 3,
schematically showing the first embodiment.
[0064] The head 1 is a component formed by press working, as has
been stated above. Accordingly, a portion of the head 1
corresponding to the external line of the head structure shown in
FIG. 6 is defined by pressed members formed of a titanium alloy.
The interior C is a hollow space. In FIG. 6, line D shows the
position of the sole of the conventional club head. In contrast
thereto, this embodiment has a structure in which the sole 3 partly
projects and has the deformable area B at a position closer to the
face 4, as shown in FIG. 6. The projecting height E of the
deformable area B is of the order of 6 mm in this embodiment. When
impact force F is applied to the surface of the face 4 in the
direction of the arrow shown in FIG. 6, the head itself is
elastically deformed complicatedly. In this embodiment, the elastic
deformation is made concentrated toward the sole 3 as much as
possible by providing the recessed and projected deformable area B
on the sole 3.
[0065] As a result, the sole 3 has a considerable elastic effect
even if the face 4 is left unchanged from the conventional
configuration and even if compared to a conventional structure in
which the thickness of the lower portion of the face 4 is reduced
to increase repulsive force, for example. Thus, it is possible to
avoid the problem that the rigidity of the head is undesirably
weakened by excessively reducing the thickness of the face 4 with
the intention of increasing repulsive force. The deformable area B
is not necessarily limited to the configuration shown in this
embodiment. The deformable area B may have any configuration that
produces an elastic effect. However, it is preferable for the
deformable area B to have a recessed and/or projected
configuration.
[0066] FIG. 6 is a schematic view of the X-X section of FIG. 3,
whereas FIG. 7 is a detailed view of the X-X section. Next, the
structure of the deformable area B will be described in detail with
reference to FIG. 7. As has been stated above, the face 4 is bent
at a lower portion thereof toward the sole 3 to form a bent portion
4a. The curving part between the face 4 and the bent portion 4a
constitutes a first bend G.
[0067] The first bend G means a part formed by intersection of a
line S.sub.1 tangent to the face 4 approximately at the center
thereof with a line S.sub.2 tangent to the bent portion 4a
approximately at the center thereof. The bend G is defined by a
gently curved surface contiguous to the tangent lines S.sub.1 and
S.sub.2 at the point of intersection thereof. The angle .alpha. of
the bend G is not less than 90 degrees and not more than 135
degrees. Preferably, the angle .alpha. is not less than 90 degrees
and not more than 120 degrees. This has been confirmed on the basis
of measured data. The angle .alpha. is measured by using a
protractor. The surface of the face 4 is rounded approximately
uniformly. Therefore, the measurement is carried out in such a
manner that when the protractor is applied to the surface of the
face 4, that is, when a tangent is drawn to the face surface, the
gap between the straight line and the curved line is approximately
the same at the left and right sides or at the upper and lower
sides. The bent portion 4a as bent constitutes a part of the sole
3.
[0068] An end portion of the sole 3 is joined to the distal end of
the bent portion 4a by welding. The plate thickness t.sub.2 of the
sole 3 is smaller than the plate thickness t.sub.1 of the face 4.
In the embodiment illustrated in the figures, an arch-shaped groove
I (11) is provided in the sole 3. The groove I is defined by a
gently curved line extending immediately from the end of the sole
3. The end of the arch-shaped groove I forms a continuous gently
curved line and constitutes a third bend J in combination with the
bent portion 4a. The third bend J is formed as a gentle bend by
intersection of the tangent line S.sub.2 to the bent portion 4a
approximately at the center-thereof with a line S.sub.4 tangent to
approximately one rising portion of the groove I. The angle
.alpha..sub.2 of the bend J is an obtuse angle not less than 90
degrees.
[0069] Further, the groove I constitutes a gently curved fourth
bend K in combination with a portion of the sole 3 closer to the
back 12. The fourth bend K is formed as a gentle bend by
intersection of a line S.sub.5 tangent to approximately the other
rising portion of the groove I with a line S.sub.3 tangent to the
sole 3. The angle .alpha..sub.3 of the bend K is an obtuse angle
not less than 90 degrees. Although the illustrated example has only
one arch-shaped groove I, a plurality of arch-shaped grooves may be
provided. Each of the bends G, J and K, including the groove I,
constitutes a part of the deformable area B. With the
above-described structure of the deformable area B, the face-side
portion of the head 1 is kept highly rigid as in the conventional
club head, and the rigidity of the sole-side portion of the head 1
is made lower than that of the face-side portion of the head 1.
[0070] It should be noted that the sectional configuration shown in
FIG. 7 is provided with a single recess (as seen from the outside
of the sole 3). In other words, the sectional configuration shown
in FIG. 7 is as follows. Assuming that the angle (.alpha.) of
clockwise rotation from the tangent line S.sub.1 to the tangent
line S.sub.2 is a plus angle and the angle (.alpha.) of
counterclockwise rotation is a minus angle, the rotation angle
(.alpha.) changes between plus and minus sequentially: the angle
(.alpha.) is plus in rotation from the tangent line S.sub.1 to the
tangent line S.sub.2, plus in rotation from the tangent line
S.sub.2 to the tangent line S.sub.4, minus in rotation from the
tangent line S.sub.4 to the tangent line S.sub.5, and plus in
rotation from the tangent line S.sub.5 to the tangent line S.sub.3.
The fact that there are sequential plus rotations and one minus
rotation from the tangent line S.sub.1 to the tangent line S.sub.3,
that is, there is one rotation angle change between plus and minus,
means that the sole 3 is formed with one recess. If there are two
rotation angle changes between plus and minus, it means that the
sole 3 is formed with two recesses. In the example shown in FIG. 7,
the angle change between plus and minus is within 90 degrees. This
means that the recess is a concave groove having a gentle
curvature.
[0071] If there is no angle change from plus to minus, the sole 3
has no recess. In other words, the head structure may have, roughly
speaking, a sectional configuration along a linear contour defined
by the tangent lines S.sub.2 and S.sub.3 intersecting each other,
in which the sole 3 has a second bend H formed from a projection,
as shown in FIG. 7. The second bend H is formed as a gentle bend by
intersection of the line S.sub.2 tangent to the bent portion 4a
with the line S.sub.3 tangent to the surface of the sole 3
approximately at the center thereof. The angle .alpha..sub.1 of the
second bend H is an obtuse angle not less than 90 degrees.
[0072] The crown 2 has the same structure as in the conventional
club head. The face-side portion of the crown 2 looks unchanged
from the conventional structure as seen from the player upon
addressing. Because the sole-side portion of the head 1 is made
lower in rigidity than the face-side portion of the head 1, the
lower portion of the face 4 is easily deflectable upon hitting a
golf ball. With the gently curved structure, the shock is lessened,
and the likelihood of the head 1 being cracked at impact is
eliminated. In addition, the spring effect is enhanced.
Consequently, the conventional sweet area extends toward the sole
3. That is, the sweet area widens downward. Thus, the repulsion
effect is enhanced.
[0073] If a golf ball is struck at a lower point on the face 4 (at
a position below approximately 60% of the height of the face 4 from
the sole 3), the lower portion of the surface of the face 4 is
deflected by a spring effect produced by deflection of the sole 3
through the gently curved portion and the groove I, thereby
enhancing the repulsion effect. As a result, the golf club
according to this embodiment enables the conventional sweet area to
extend downward on the surface of the face 4 and hence allows the
sweet area to be widened. Accordingly, even if the player strikes a
golf ball at a lower point on the face 4, there will be no decrease
in ball traveling distance as occurs with the conventional golf
clubs. Thus, the golf club according to this embodiment enables the
player to stably get better distance. Further, because it has a
widened sweet area, the head 1 of this embodiment is capable of
increasing the maximum coefficient of restitution.
[0074] FIG. 8 is an explanatory view schematically showing a state
where a ball has been struck on the hitting surface of the face 4.
This is the state F shown in FIG. 6. The theoretical contents of
the above-described structure of the embodiment will be explained
below in detail with reference to FIG. 8. When a ball 23 is struck
on the face 4, the face 4 is deformed toward the back 12 as shown
by the chain double-dashed line in the figure. The ball 23 is also
deformed. If the amount of deformation of the ball 23 is reduced,
the hysteresis loss due to deformation of the ball 23 when it
returns to the previous spherical shape by its own elasticity is
reduced, and thus the impact energy loss of the ball 23 is
minimized. If the amount of deformation of the face 4 is increased,
the amount of deformation of the ball 23 can be reduced relatively.
Consequently, it is possible to increase the coefficient of
restitution and to hit the ball 23 a longer distance.
[0075] When the ball 23 is struck on the face 4, the sole 3 is also
deformed downward in association with the deformation of the face
4. In the conventional club head, the angle formed between the face
4 and the sole 3 is an acute angle, as shown in FIG. 5. Therefore,
the face 4 and the sole 3 are not sufficiently deformable. In this
embodiment, however, the angle between the face 4 and the sole 3 is
set not less than 90 degrees, as shown by G in FIG. 7. As a result,
the face 4, particularly a region below the center of the surface
of the face 4, is lower in rigidity than in the conventional club
head and hence easily elastically deformable upon hitting the ball
23. Thus, the lower portion of the face 4 is elastically deformed
to a considerable extent in comparison to the conventional club
head by a synergistic effect of the face 4 and the sole 3. For this
reason, when the ball 23 is struck on a lower portion of the
hitting surface of the face 4, the ball 23 is sent a longer
distance effectively without lowering the coefficient of
restitution in comparison to the conventional club head.
[0076] FIG. 9 shows a second embodiment of the present invention.
In this case, a portion of the sole 3 closer to the face 4 is
formed with only a projection 13 projecting flat in comparison to
the conventional club head on the assumption that the bend between
the face 4 and the sole 3 is formed at an obtuse angle .alpha. in a
section taken along a vertical plane containing a line
perpendicular to the surface of the face 4. In comparison to the
arrangement of the foregoing embodiment, the club head according to
this embodiment has no groove but a flat projection 13 between the
back 12 and the face 4. When an impact is applied to the face 4,
the projection 13 is elastically deformed to increase the
coefficient of restitution of the club head.
[0077] FIG. 10 shows a third embodiment of the present invention,
in which the whole sole 3 is curvedly projected outward as a
projection 14 over from the face 4 to the back 12.
[0078] FIG. 11 shows a fourth embodiment of the present invention,
in which the whole sole 3 is curvedly projected inward as a recess
15 over from the face 4 to the back 12.
[0079] FIG. 12 shows a fifth embodiment of the present invention,
in which a part of the bent portion 4a closer to the joint with the
sole 3 is bent approximately parallel to the face 4 to form a bent
portion 16 having a turn-back surface. The sole 3 extending from
the bent portion 16 to the back 12 is approximately flat and in a
straight-line form in the sectional view of FIG. 12. When an impact
is applied to the face 4, the bent portion 16 is deformed to a
considerable extent.
[0080] FIG. 13 shows a sixth embodiment of the present invention.
In this case, a portion of the sole 3 closer to the face 4 is
formed with a plurality of recesses and projections on the
assumption that the bend between the face 4 and the sole 3 is
formed at an obtuse angle .alpha. in a section taken along a
vertical plane containing a line perpendicular to the surface of
the face 4. As shown in the figure, three projections 17 and two
grooves 18 are provided. The repulsion effect is the same as the
above. However, the recessed and projected configuration is
somewhat smaller in size than in the above-described example owing
to the restriction on the space.
[0081] FIGS. 14 and 15 show seventh and eighth embodiments,
respectively, of the present invention, in which the groove I (11)
is modified. In FIG. 14, the club head has a groove 19 with a
rectangular sectional configuration. In FIG. 15, the club head has
a groove 20 with a stepped sectional configuration. Both the
seventh and eighth embodiments provide the same advantageous
effects as the above.
[0082] FIG. 16 shows a modification in which the club head is
arranged to lower the rigidity of the sole 3. That is, a part of
the sole 3 is made of a thin plate 21 to lower the rigidity of the
sole 3.
[0083] FIG. 17 shows a modification in which the club head is
arranged to lower the rigidity of the sole 3. The sole 3 is divided
into two portions 3a and 3b so that when an impact is applied to
the face 4, the divided portions 3a and 3b are slidable relative to
each other.
[0084] FIG. 18 shows a modification in which the club head is
arranged to lower the rigidity of the sole 3. A part of the sole 3
closer to the face 4 is provided with at least one hole 22 to lower
the rigidity of the sole 3.
[0085] Although various embodiments have been described above, the
present invention is not necessarily limited to the described
embodiments. The deformable area B preferably has the
above-described recessed and/or projected configuration. However,
the deformable area B may have a gentle V-shaped configuration or a
bellows-like configuration. The deformable area B may have any
configuration, provided that it enhances the elastic effect and
lowers the rigidity of the sole 3.
EXAMPLES
[0086] The following is a description of examples carried out to
examine the improvement in performance with regard to the
above-described club head structures. FIG. 19 shows the results of
an experiment carried out on the golf club according to the first
embodiment. FIG. 19 shows a distribution of coefficients of
restitution measured when a golf ball was struck on the face 4.
Based on the experimental results, points of the same coefficient
of restitution were plotted as contour lines. FIG. 20 shows the
results of an experiment carried out on a conventional golf club
under the same conditions as in the case of FIG. 19. The
experiments were performed under the following conditions:
1 Face material: cold rolled material of Ti-15V-3Cr-3Sn-3Al plate
thickness: 2.9 mm Sole material: Ti-15V-3Cr-3Sn-3Al plate
thickness: 1.15 mm Crown material: Ti-15V-3Cr-3Sn-3Al plate
thickness: 1.0 mm Volume: about 300 cc mass: about 196 g.
[0087] It will be clear from comparison of FIG. 19 with FIG. 20
that high values of the coefficient of restitution are distributed
closer to the sole side in FIG. 19. This means that even if a golf
ball is struck at a point on the face surface closer to the sole,
the ball can be hit a farther distance than with the conventional
golf club.
[0088] FIG. 21 shows measurements of ball traveling distance
obtained by a hitting test using a golf ball hitting robot to
compare the embodiment of the present invention with a conventional
golf club. FIG. 21 shows a measurement comparison at a head speed
of 40 m/s. The height H of the point of measurement is the distance
from the leading edge, as shown in FIG. 21. In FIG. 21, Example
represents the first embodiment of the present invention, and
Comparative Example represents a conventional golf club. The test
was performed by using a golf ball hitting robot. Example and
Comparative Example were carried out under the same hitting
conditions. The hitting conditions are as shown in FIG. 21.
[0089] The specifications of the clubs used in the test are as
follows:
2 Club length: 44.5 inches Balance: D2 Loft angle .beta.: 10.5
degrees Lie angle .gamma.: 56.5 degrees Shaft FLEX: R
[0090] In comparison of the measurements of ball travelling
distance, at a point of measurement at a height H of 18 mm, for
example, the ball travelling distance of Example is 204 yards,
whereas that of Comparative Example is 199 yards. It will be clear
from the difference in the ball travelling distance that the
structure of the present invention is advantageously effective.
[0091] As has been detailed above, the golf club according to the
present invention is arranged such that the sole of the club head
has an elastic effect. Accordingly, repulsive force obtained at a
lower point on the face is increased. Therefore, even if a golf
ball is struck at a point below the conventional sweet area, the
ball can be hit a long distance without a decrease in ball
traveling distance.
[0092] Further, the basic configuration of the club head is left
unchanged from that of the conventional golf clubs, but only a part
of the sole of the club head is modified. Therefore, the external
appearance of the club head looks unchanged from the conventional
structure as seen from the player upon addressing. Nevertheless,
the golf club according to the present invention exhibits improved
ball-hitting performance in comparison to the conventional golf
clubs. Further, the procedure for imparting the elastic effect to
the sole of the club head can be carried out by press working in
the same process as that for the conventional golf clubs except
that the press die needs to be changed. Therefore, there is no
increase in production costs, and the golf club according to the
present invention can be produced by the same manufacturing process
as that for the conventional golf clubs despite the improvement in
performance.
[0093] It should be noted that the present invention is not
necessarily limited to the foregoing embodiments but can be
modified in a variety of ways without departing from the gist of
the present invention.
* * * * *