U.S. patent application number 12/100028 was filed with the patent office on 2009-01-22 for iron golf club.
This patent application is currently assigned to K. K. ENDO Seisakusho. Invention is credited to Tomoyuki SAKAI, Masaki SHIBATA.
Application Number | 20090023513 12/100028 |
Document ID | / |
Family ID | 40140556 |
Filed Date | 2009-01-22 |
United States Patent
Application |
20090023513 |
Kind Code |
A1 |
SHIBATA; Masaki ; et
al. |
January 22, 2009 |
IRON GOLF CLUB
Abstract
An iron golf club for enhancing the gear effect and accelerating
backspin of a ball. The head, which comprises a face part having a
ball-hitting surface, a sole part having a ground-contact plane in
the bottom portion of the head, a top part, and a hosel part, is
configured such that the rigidity on the ground-contact plane side
of the bottom portion is lowered by either providing the portion
with a cavity or changing its material. Further, the vertical
moment of inertia of the head is reduced by disposing a weight in
the location of the center of gravity of the head. When the length
of the hosel part is 50 mm or longer, the value of the moment of
inertia becomes less than 800 gcm.sup.2, and when the length of the
hosel part is less than 50 mm, the value of the moment of inertia
becomes 750 gcm.sup.2 or less. These configurations realize a golf
club that enhances the gear effect and accelerates spin of a
ball.
Inventors: |
SHIBATA; Masaki; (Niigata,
JP) ; SAKAI; Tomoyuki; (Niigata, 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: |
40140556 |
Appl. No.: |
12/100028 |
Filed: |
April 9, 2008 |
Current U.S.
Class: |
473/305 |
Current CPC
Class: |
A63B 53/047 20130101;
A63B 53/0475 20130101; A63B 2209/00 20130101; A63B 53/0458
20200801; A63B 53/0433 20200801; A63B 53/042 20200801; A63B
2053/0479 20130101; A63B 53/0408 20200801; A63B 53/0416
20200801 |
Class at
Publication: |
473/305 |
International
Class: |
A63B 53/02 20060101
A63B053/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 9, 2007 |
JP |
2007-101836 |
Claims
1. An iron golf club, comprising: a head having, in a lower portion
thereof, a sole part which has a ground-contact plane, and having,
in an upper portion thereof, a top part, and a face part which has
a ball-hitting surface for striking a ball, and, at one end
thereof, a hosel part which is a shaft connector; and a shaft,
which is connected at one end thereof to the hosel part, a
ground-contact plane side of the head being configured to have low
rigidity.
2. The iron golf club according to claim 1, wherein a top part side
of the head is configured to have relatively higher rigidity than
the ground-contact plane side.
3. The iron golf club according to claim 1, wherein the
ground-contact plane side of the head has a relatively higher
coefficient of rebound than the top part side of the head.
4. The iron golf club according to claim 1, wherein the
ground-contact plane side of the head is in an area nearer to the
sole part side than to an approximate horizontal plane which is
parallel to a score line, and which passes through a location of
the center of gravity.
5. An iron golf club, comprising: a head having, in a lower portion
thereof, a sole part which has a ground-contact plane, and having,
in an upper portion thereof, a top part, and a face part which has
a ball-hitting surface for striking a ball, and, at one end
thereof, a hosel part which is a shaft connector; and a shaft,
which is connected at one end thereof to the hosel part, wherein
when a length of the hosel part is 50 mm or longer, a value of a
moment of inertia centering on an axis that passes horizontally in
a toe-heel direction through the center of gravity of the head is
less than 800 gcm.sup.2.
6. An iron golf club, comprising: a head having, in a lower portion
thereof, a sole part which has a ground-contact plane, and having,
in an upper portion thereof, a top part, and a face part which has
a ball-hitting surface for striking a ball, and, at one end
thereof, a hosel part which is a shaft connector; and a shaft,
which is connected at one end thereof to the hosel part, wherein
when a length of the hosel part is less than 50 mm, a value of a
moment of inertia centering on an axis that passes horizontally in
a toe-heel direction through the center of gravity of the head is
less than 750 gcm.sup.2.
7. The iron golf club according to claim 1, wherein a specific
gravity of a material for configuring the main parts of the head is
6.5 gcm.sup.2 or greater.
8. The iron golf club according to claim 1, wherein the head is
either the head of a short iron or the head of a wedge.
9. The iron golf club according to claim 2, wherein the
ground-contact plane side of the head is in an area nearer to the
sole part side than to an approximate horizontal plane which is
parallel to a score line, and which passes through a location of
the center of gravity.
10. The iron golf club according to claim 3, wherein the
ground-contact plane side of the head is in an area nearer to the
sole part side than to an approximate horizontal plane which is
parallel to a score line, and which passes through a location of
the center of gravity.
11. The iron golf club according to claim 6, wherein a specific
gravity of a material for configuring the main parts of the head is
6.5 gcm.sup.2 or greater.
12. The iron golf club according to claim 6, wherein the head is
either the head of a short iron or the head of a wedge.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an iron golf club that
enhances the gear effect, and more particularly to an iron golf
club that lowers the rigidity of the sole portion of the head,
reduces the head moment of inertia, enhances the gear effect, and
accelerates ball spin.
[0003] 2. Description of the Related Art
[0004] Various improvements have been made to the golf club over
time for enabling stable shots to thereby increase carry and hit
the ball to a precise location. In particular, iron-type golf clubs
include, for example, a pitching wedge or sand wedge. These
iron-type golf clubs, as a rule, are constituted such that the
pitch of the face is predetermined, and a sole surface is provided
in the lower portion relative to a face surface, which is the
ball-hitting surface, and are golf clubs used when ball-hitting
accuracy is demanded in particular.
[0005] A variety of iron golf club structures have been proposed,
and a player selectively uses an iron golf club in accordance with
his preferences. Examples include the flat back type, cavity type,
pocket cavity type, and hollow construction type. These types of
iron golf clubs all commonly have score lines formed in the surface
of the face, and feature measures for stabilizing the amount of
backspin imparted to the ball. In a shot to place the ball on the
green, the hitting stroke is carried out so as to impart backspin
(reverse rotation) to the ball and hit the ball high into the air,
making it possible to stop the ball at a predetermined location on
the target green.
[0006] With regard to prior art for increasing the gear effect in
order to impart greater backspin to the ball, this applicant has
also proposed a golf club of a construction that forms the
height-distance, from the horizontal plane on which the surface of
the sole of the head makes contact with the ground to the center of
gravity of the head, larger than the radius of the ball, making it
easier to impart spin to the ball (Refer to Japanese Patent
Laid-open Number 2006-149478). Further, this applicant has proposed
a golf club of a construction that either increases the flexibility
of the face or the relative displacement of the face relative to
the head at impact, thereby making it easier to impart spin to the
ball (Refer to Japanese Patent Laid-open Number 2007-44445).
Furthermore, as an example of improvement technology related to
score lines, an iron golf club that forms sharp edges on the score
lines to impart backspin to the ball is known (for example,
Japanese Patent Laid-open Number 2004-141277).
[0007] Generally speaking, a golf club that imparts spin to the
ball has score lines formed in the surface of the face as described
above. Upon impact, the ball moves relatively along the surface of
this face as it spins, and the ball is gripped by the edges of the
score lines at this time, imparting stable spin to the ball. To put
more spin on the ball, various improvements have been proposed for
the surface of the face on which effective score lines are
formed.
[0008] However, groove profile (marking) rules designed to
establish certain restrictions on the formation of this score line
groove have been studied internationally, and regulations were
recently proposed. That is, as a new regulatory proposal for club
face marking and spin generation, first, the value obtained by
dividing the gross cross-sectional area of the score line groove by
the pitch of the groove (groove width+spacing) will be restricted
to 0.0025 square inches per inch (0.0635 mm.sup.2/mm). Second, the
sharpness of the edge (angle) of a groove will be restricted to a
lowest effective radius of 0.010 inches (0.254 mm).
[0009] A certain degree of regulation has been applied to score
lines for some time, but now stricter regulations are going to be
put into place. Therefore, changing the score line groove, for
example, carrying out an improvement that makes the angle of the
edge of the groove sharper so as to heighten the spin effect will
be restricted in the future.
[0010] As mentioned above, improvements applied to the score lines
of the surface of the face of a golf club will be restricted in the
future, and an improvement designed to make the groove edges
sharper will be substantially impossible. Therefore, other methods
will have to be considered. Enhancing the gear effect to impart
more backspin to the ball improves the performance of the golf
club, and is not limited to the surface of the face alone. However,
even though there are score line regulations that restrict
improvements thereto, there is still room for improvement to
aspects other than the score line, and this is what is
required.
SUMMARY OF THE INVENTION
[0011] The present invention has been developed to solve for the
problems inherent in the prior art as described hereinabove, and
achieves the following object. An object of the present invention
is to provide a golf club, which is an iron golf club designed to
enhance the gear effect to make it easier to impart spin to a golf
ball.
[0012] The present invention employs the following means for
achieving the above-mentioned object.
[0013] An iron golf club of a first invention comprises: a head
having, in a lower portion thereof, a sole part which has a
ground-contact plane, and having, in an upper portion thereof, a
top part, and a face part which has a ball-hitting surface for
striking a ball, and, at one end thereof, a hosel part which is a
shaft connector; and a shaft, which is connected at one end thereof
to the hosel part, a ground-contact plane side of the head being
configured to have low rigidity.
[0014] An iron golf club of a second invention according to the
first invention, the top part side of the head being configured to
have relatively higher rigidity than the ground-contact plane
side.
[0015] An iron golf club of a third invention according to the
first invention, the ground-contact plane side of the head having a
relatively higher coefficient of rebound than the top part side of
the head.
[0016] An iron golf club of a fourth invention according to the
first through the third inventions, the ground-contact plane side
of the head being in an area nearer to the sole part side than to
an approximate horizontal plane which is parallel to the score
lines, and which passes through the center of gravity.
[0017] An iron golf club of a fifth invention comprises: a head
having, in a lower portion thereof, a sole part which has a
ground-contact plane, and having, in an upper portion thereof, a
top part, and a face part which has a ball-hitting surface for
striking a ball, and, at one end thereof, a hosel part which is a
shaft connector; and a shaft which is connected at one end thereof
to the hosel part, and when the length of the above-mentioned hosel
part is 50 mm or longer, the value of a moment of inertia centering
on the axis that passes horizontally through center of gravity of
the above-mentioned head in the toe-heel direction is less than 800
gcm.sup.2. Preferably, this moment of inertia can be 770 gcm.sup.2
or less.
[0018] An iron golf club of a sixth invention comprises: a head
having, in a lower portion thereof, a sole part which has a
ground-contact plane, and having, in an upper portion thereof, a
top part, and a face part which has a ball-hitting surface for
striking a ball, and, at one end thereof, a hosel part which is a
shaft connector; and a shaft which is connected at one end thereof
to the hosel part, and when the length of the above-mentioned hosel
part is less than 50 mm, the value of a moment of inertia centering
on the axis that passes horizontally through the center of gravity
of the above-mentioned head in the toe-heel direction is less than
750 gcm.sup.2.
[0019] An iron golf club of a seventh invention according to the
first through the sixth inventions, the specific gravity of the
material that constitutes the main part of the above-mentioned head
being 6.5 gcm.sup.2 or greater.
[0020] An iron golf club of an eighth invention according to the
first through the seventh inventions, the above-mentioned head
being either the head of a short iron or the head of a wedge.
[0021] All of these inventions lower the rigidity of the lower
portion of the head and reduce the moment of inertia of the head,
thereby increasing the gear effect and making it easier to impart
spin. Means such as those described below are effective for
achieving this.
[0022] Firstly, the head has means for configuring a hollow body
having a cavity on the inside of the ground-contact plane side
only.
[0023] Secondly, the head has means for configuring a hollow body
having a cavity on the inside, and for the sole part only to be
comprised of a material with a lower Young's modulus than the other
parts.
[0024] Thirdly, the head has means for configuring a hollow body
having a cavity on the inside of the ground-contact plane side
only, and for laminating a material with a high mechanical strength
composition between the face part and the other parts above this
cavity.
[0025] Fourthly, the head has means for configuring a hollow body
having a cavity on the inside, and for a groove, the wall thickness
of which is partially thinner than the other parts, to be formed in
the sole part only.
[0026] Fifthly, the head has means for configuring a hollow body
having a cavity on the inside, and for forming the wall thickness
portion of the upper portion of the face part thicker than the wall
thickness portion of the lower portion.
[0027] Sixthly, the head has means for configuring a hollow body
having a cavity on the inside, and for a partially thinner groove
to be formed in the lower portion of the face part.
[0028] Seventhly, the head has means for configuring a hollow body
having a cavity on the inside, and for forming the material
composition of the lower portion of the face part at a relatively
lower hardness than the material composition of the upper portion
in a face part of the same material composition.
[0029] Eighthly, the head has means for configuring a hollow body
having a cavity on the inside, and for the upper portion and lower
portion of the face part to be materials of different composition,
and for forming the material of the lower portion into a lower
hardness material that is relatively softer than the material of
the upper portion.
[0030] Ninthly, the head has means for configuring a hollow body
having a cavity on the inside, and for the parts other than the
face part to be the same material, and for forming the material
composition of the lower portion of the head at a relatively lower
hardness than the material composition of the upper portion.
[0031] Tenthly, the head has means for configuring a hollow body
having a cavity on the inside, and for the upper portion and lower
portion of the parts other than the face part to be materials of
different composition, and for forming the material of the lower
portion into a material having a hardness that is relatively softer
than the material of the upper portion.
[0032] Eleventhly, the head has means for configuring a hollow body
having a cavity on the inside, and for the material of the lower
portion of the face part to be formed at a relatively lower Young's
modulus than the material of the upper portion.
[0033] Twelfthly, the head has means for configuring a hollow body
having a cavity on the inside, and for the material of the lower
portion of the parts other than the face part to be formed at a
relatively lower Young's modulus than the material of the upper
portion.
[0034] Thirteenthly, the head has means for a through-groove, which
parallels a score line formed in the ball-hitting surface of the
face part, to be formed in the middle portion of the head on the
back side of the face part.
[0035] Fourteenthly, the head has means for a pocket-shaped groove,
which parallels a score line formed in the ball-hitting surface of
the face part, and which is open at the tip of the toe side, to be
formed in the middle portion of the head on the back side of the
face part.
[0036] Fifteenthly, the head has means for a groove to be formed
perpendicularly to the ground-contact plane in the lower portion of
the head up to an intermediate location.
[0037] Sixteenthly, the head has means for an elastic member to be
disposed in the groove formed perpendicularly to the ground-contact
plane in the lower portion of the head up to an intermediate
location.
[0038] Seventeenthly, the head has means for disposing in the
vicinity of the center of gravity of the head a weight for reducing
the vertical moment of inertia.
[0039] Eighteenthly, the head has means by which the vicinity of
the center of gravity of the head, where a weight is disposed to
reduce the vertical moment of inertia, is formed in a groove.
[0040] Nineteenthly, the head has means for configuring a hollow
body having a cavity on the inside, and for a weight for reducing
the vertical moment of inertia to be disposed in the vicinity of
the center of gravity of the head, and for the above-mentioned
cavity to be formed in a vertically intermediate portion of a part
other than the face part.
[0041] Twentiethly, the head has means for configuring a hollow
body having a cavity on the inside, and for a weight for reducing
the vertical moment of inertia to be disposed in the vicinity of
the center of gravity of the head, and for the above-mentioned
cavity to be formed in a vertically intermediate portion of the
face part.
[0042] Twenty-firstly, the head has means for a weight for reducing
the vertical moment of inertia to be disposed in the vicinity of
the center of gravity of the head, and for forming a groove in a
vertically intermediate portion, and furthermore, for forming a
hollow body, which is a cavity, on the inside of the sole part side
of the lower portion of this groove.
[0043] Twenty-secondly, the head has means for a weight for
reducing the vertical moment of inertia to be disposed in the
vicinity of the center of gravity of the head, and, in addition,
for this weight to be disposed in the upper end of the lower
portion of a part of the head other than the face part.
[0044] As described in detail hereinabove, the iron golf club of
the present invention is such that configuring the head to increase
the flexibility of the lower portion of the face, or configuring
the head to reduce the moment of inertia, that is, deforming the
lower portion of the head to achieve a structure, by which the club
readily rotate, makes it possible for the surface of the face to
bend backward and rotate in the downward direction, and to lengthen
the ball holding (contact) period, thereby enhancing the gear
effect more than that of the prior art. Therefore, rotation in the
reverse direction is effectively imparted to the ball. Thus, the
iron golf club of the present invention is able to impart a greater
amount of backspin to the ball.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] FIG. 1 is a general view of an iron golf club;
[0046] FIG. 2 is a schematic diagram showing the state immediately
prior to a ball being impacted by the head;
[0047] FIG. 3 is a schematic diagram showing the state immediately
after a ball has been impacted by the head;
[0048] FIG. 4 is a schematic diagram of an embodiment for reducing
rigidity by forming the lower portion of the head as a hollow
body;
[0049] FIG. 5 is a schematic diagram of an embodiment for reducing
the rigidity of the lower portion of the head by forming the head
as a hollow body, and giving the material composition of the sole
part a lower Young's modulus;
[0050] FIG. 6 is a schematic diagram of an embodiment for reducing
the rigidity of the lower portion of the head by forming the lower
portion of the head as a hollow body, and disposing a high strength
material in the upper portion;
[0051] FIG. 7 is a schematic diagram of an embodiment for reducing
rigidity by forming the head as a hollow body, and forming one part
of the lower portion of a part other than the face into a
groove;
[0052] FIG. 8 is a schematic diagram of an embodiment for reducing
the rigidity of the lower portion of the head by forming the head
as a hollow body, and making the wall thickness of the lower
portion of the face thinner than the wall thickness of the upper
portion;
[0053] FIG. 9 is a schematic diagram of an embodiment for reducing
rigidity by forming the head as a hollow body, and forming one part
of the lower portion of the face into a groove;
[0054] FIG. 10 is a schematic diagram of an embodiment for reducing
the rigidity of the lower portion of the head by forming the head
as a hollow body, making the face the same material, making the
material composition of the upper portion a higher hardness, and
making the material composition of the lower portion a lower
hardness;
[0055] FIG. 11 is a schematic diagram of an embodiment for reducing
the rigidity of the lower portion of the head by forming the head
as a hollow body, using a high hardness material in the upper
portion of the face, and using a low hardness material in the lower
portion of the face;
[0056] FIG. 12 is a schematic diagram of an embodiment for reducing
the rigidity of the lower portion of the head by forming the head
as a hollow body, making the parts other than the face the same
material, using a high hardness material composition in the upper
portion, and using a low hardness material composition in the lower
portion;
[0057] FIG. 13 is a schematic diagram of an embodiment for reducing
the rigidity of the lower portion of the head by forming the head
as a hollow body, making the upper portion of a part other than the
face a high hardness material, and making the power portion a low
hardness material;
[0058] FIG. 14 is a schematic diagram of an embodiment for reducing
the rigidity of the lower portion of the head by forming the head
as a hollow body, making the upper portion of the face a material
with a high Young's modulus, and making the lower portion of the
face a low Young's modulus material;
[0059] FIG. 15 is a schematic diagram of an embodiment for reducing
the rigidity of the lower portion of the head by forming the head
as a hollow body, making the upper portion of a part other than the
face a material with a high Young's modulus, and making the lower
portion a low Young's modulus material;
[0060] FIG. 16 is a schematic diagram of an embodiment for reducing
the rigidity of the lower portion of the head by providing an
approximately horizontal through-groove in the location of the
center of gravity on the back surface of the head;
[0061] FIG. 17 is a side view of FIG. 16;
[0062] FIG. 18 is a schematic diagram of an embodiment for reducing
the rigidity of the lower portion of the head by providing a pocket
groove open on the toe side at the location of the center of
gravity on the back surface of the head;
[0063] FIG. 19 is a side view of FIG. 18;
[0064] FIG. 20 is a schematic diagram of an embodiment for reducing
the rigidity of the lower portion of the head by providing a
slit-shaped groove perpendicularly to the ground-contact plane in
the lower portion of the head;
[0065] FIG. 21 is a schematic diagram of an embodiment for reducing
the rigidity of the lower portion of the head by disposing an
elastic body in a slit-shaped groove of the same shape of FIG.
20;
[0066] FIG. 22 is a schematic diagram showing the lowering of the
vertical moment of inertia of the head;
[0067] FIG. 23 is a schematic diagram showing the state of a
conventional moment of inertia;
[0068] FIG. 24 is a schematic diagram showing the state immediately
prior to a ball being impacted by the head using the same type
diagram as FIG. 22;
[0069] FIG. 25 is a schematic diagram showing the state immediately
after a ball has been impacted by the head using the same type
diagram as FIG. 22;
[0070] FIG. 26 is a schematic diagram of an embodiment for lowering
the moment of inertia by providing a weight in a groove in the face
side in the vicinity of the center of gravity of the head;
[0071] FIG. 27 is a side view of FIG. 26;
[0072] FIG. 28 is a schematic diagram of an embodiment for lowering
the moment of inertia by forming the head as a hollow body, and
disposing a weight in the location of the center of gravity of a
part other than the face;
[0073] FIG. 29 is a side view of FIG. 28;
[0074] FIG. 30 is a schematic diagram of an embodiment for lowering
the moment of inertia by forming the head as a hollow body, and
disposing a weight in a location in the vicinity of the center of
gravity portion of the face;
[0075] FIG. 31 is a side view of FIG. 30;
[0076] FIG. 32 is a schematic diagram of an embodiment for lowering
the moment of inertia by disposing a weight in a location in the
vicinity of the center of gravity portion of the back surface of
the head;
[0077] FIG. 33 is a side view of FIG. 32;
[0078] FIG. 34 is a schematic diagram of an embodiment for lowering
the moment of inertia by disposing a weight in a location in the
vicinity of the center of gravity portion at the end of a part
other than the face that rises up from the lower portion of the
sole;
[0079] FIG. 35 is a side view of FIG. 34;
[0080] FIG. 36 is a side view of the head showing the face part in
which score lines have been provided; and
[0081] FIG. 37 is a schematic diagram of the head showing a
through-axis, which is at an angle to an axis that is parallel to
the ground-contact plane.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0082] The embodiments of the present invention will be explained
below on the basis of the figures. The golf club targeted by the
present invention is an iron golf club. FIG. 1 is a general view
showing the overall appearance of an iron golf club. FIGS. 2 and 3
are schematic diagrams of side views, with FIG. 2 showing the state
immediately prior to a ball being impacted by the head. FIG. 3
shows the state immediately after the ball has been impacted by the
head. The basic structure of the iron golf club is widely known,
and a detailed explanation will be omitted, but to make it easier
to understand the present invention, an outline of the iron golf
club will be explained below.
[0083] In iron golf club related to the present invention, as shown
in FIG. 1, is configured from a head 1, which forms a face part 2
on the front face, a hosel part 3, which is the shaft connector to
the shaft side, a top part 4 in the upper portion, a toe part 5 in
the front portion, and a sole part 6 in the lower portion, which
makes contact with the ground; and a shaft 7, which is connected to
the hosel part 3 of this head 1. Further, the angle of tilt of the
ball-hitting surface relative to a perpendicular line (vertical
line) to the ground-contact horizontal plane 11 of the sole part 6
is the loft angle .delta. (Refer to FIG. 2).
[0084] Score lines 8 are carved into the ball-hitting surface of
the face part 2. The invention of the golf club, in which the
height from the ground-contact horizontal plane 11 of the sole part
6 up to the location of the head's center of gravity 9 is formed to
be larger than the radius of the ball 10, is the proposal of the
same applicants as those of the present invention, but since the
present invention offers an effective structure for the spin
effect, this golf club will be used as an example for explaining
the spin effect. As shown in FIGS. 2 and 3, on the downswing, the
head 1 describes a circular arc relative to the ball 10 so as to
get under the ball 10 at impact.
[0085] At this time, the ball-hitting surface of the face part 2
makes contact and hits the ball 10 by getting under the ball 10.
The result is that the ball 10 indents slightly at impact, catches
on the edges of the score lines 8, rotates in a counterclockwise
direction as indicated by Arrow A of FIG. 3, and backspin is
imparted to the ball 10. In accordance with the swing at impact,
the ball 10 moves upwardly in relation to the ball-hitting surface
in the direction indicated by Arrow B in the figure, and, while
spinning, is hit in the direction indicated by Arrow C.
[0086] When the ball 10 is impacted by the head 1 upon being hit,
since the height D of the center of gravity 9 of the head 1 is
above the center of the ball 10, the sole part 6 side of the
ball-hitting surface is momentarily pulled down, and the
ball-hitting surface moves rotationally in the clockwise direction
as if to rise up. That is, the loft angle .delta. momentarily
becomes smaller (refer to FIG. 3), and as a result, generates a
gear effect which imparts spin to the ball 10 in the opposite
direction of the rotational movement of this ball-hitting surface,
accelerating the backspin. Further, the applicant of the present
invention has also proposed enhancing the spin effect via another
method, but the figures do not show the other invention (Refer to
Japanese Patent Laid-open Number 2007-44445).
[0087] This is the result of providing a displacement part, by
which either the flexibility of the face, or the relative
displacement of the face relative to the head increases at impact.
More specifically, continuous peripheral grooves are provided on
both sides of the face, and displacement grooves are provided on
the front side of the face in only three directions: toward the top
side edge, the toe side edge and the leading edge. Upon impact,
these displacement grooves generate relative displacement, which
has the heel side as the center of rotation and becomes larger at
the toe side, making it easy to hit the ball using the gear
effect.
[0088] These technologies are effective in their own ways, but as
mentioned above, improvements to the ball-hitting surface of the
face part 2, such as changing the performance of the score lines 8
in particular, are restricted by new regulations. Therefore, an
optimum method must be devised by improving a part other than the
surface of the face part 2. With regard to the face part 2, the
ball 10 is normally impacted by the lower portion of the face. As
described hereinabove, the impacted ball 10 moves up the
score-lined ball-hitting surface while relatively making contact
with the score lines 8, and the ball 10 rotates in the
counterclockwise direction, being imparted with backspin.
[0089] In support of this, the present invention has been
configured such that, when the ball 10 is impacted by the lower
portion of the face, the structure of the lower portion of the head
changes so as to make the backward bending of this lower portion
vary relatively easily. That is, as described hereinabove, in this
embodiment for enhancing the gear effect, the ball-hitting region
of the lower portion of the face in particular moves relatively
rotationally toward the rear at impact having the location of the
center of gravity 9 of the head 1 as the fulcrum, that is, the head
1 is structured so as to be able to bend backward.
[0090] By so doing, the ball 10 does not immediately move
subsequent to impact, but rather, the lower portion of the face
moves relatively rotationally backward, that is, the lower portion
of the face readily bends backward, thereby allowing the ball 10 to
held at (be in contact with) the ball-hitting surface longer. As a
result, the movement of the ball 10 up the ball-hitting surface is
lengthened, that is, the contact time increases, thereby promoting
the grip on the ball 10 and increasing the gear effect, resulting
in the ball 10 being hit with a lot of backspin. Thus, the present
invention is constituted to solve for the problems described above,
and to further increase the gear effect and accelerate spin. This
embodiment will be explained more specifically below.
Embodiments for Reducing Rigidity of Lower Portion of Head
[0091] This embodiment is an example of a constitution that reduces
the rigidity of the lower portion of the head, that is, a
constitution that uses a flexible structure or a readily deformable
structure, and imparts a relative rotational movement to the head
at impact, thereby enhancing the gear effect and accelerating the
backspin of the ball.
[0092] The iron head shown in FIG. 4 has a hollow body having a
cavity 20 on the inside only in the lower portion of the head 1,
that is, on the ground-contact plane side of the sole part. This
cavity 20 is a void of the ground-contact plane side surrounded by
the back side of the face part 21 and a part 22 other than the face
part 21. This is an example in which the lower portion is given
lower rigidity and made flexible by making the upper portion solid
and forming a cavity in the lower portion so as to relatively vary
vertical rigidity. Furthermore, the rigidity referred to in the
present invention is defined as follows. When a load P acts on one
part of a solid, and the amount of deformation generated at this
load point is represented as u, the amount of deformation u in an
elastic body is proportional to the load P. That is, the equation
becomes u=.alpha.P. This proportional constant .alpha. is
flexibility, and rigidity is represented by 1/.alpha.=K.
[0093] The iron head shown in FIG. 5 is an example in which the
head 1 is configured as a hollow body having a cavity 23 on the
inside, and the material composition of the lower portion of the
head 1, that is, the material composition of the sole part side of
a part 24 other than the face part 21 of the ground-contact plane,
uses a material with a low Young's modulus 25. This is another
example in which the ground-contact plane side is made flexible by
making the rigidity lower than that of the upper portion.
[0094] The iron head shown in FIG. 6 is an example in which the
lower portion of the head 1, that is, the ground-contact plane side
only is configured into a hollow body having a cavity 20 on the
inside, and a high strength material 27 is disposed so as to be
sandwiched between the face part 21 of the upper portion of the
head 1 and a part 26 other than the face part 21. This is another
example of making the ground-contact plane side flexible by making
the rigidity lower than that of the upper portion so as to
relatively vary the rigidity of the lower portion and upper portion
of the head 1.
[0095] The iron head shown in FIG. 7 is an example in which the
head 1 is configured as a hollow body having a cavity 23 on the
inside, and inside this cavity 23 a groove 29 is provided in the
lower portion of the head in one portion of the ground-contact
plane side of a part 28 other than the face part 21. This example
is one that makes the ground-contact plane side of the head 1
flexible by using a groove 29 to make the rigidity lower than that
of the upper portion.
[0096] The iron head shown in FIG. 8 is an example in which the
head 1 is configured as a hollow body having a cavity 23 on the
inside, and a step is provided in the wall thickness of the face
part 30. That is, the configuration of the face 30 is constituted
such that the ball-hitting surface of the face part 30 is flush,
and a step is provided inside the cavity 23 thereof, thereby making
the upper portion thick-walled 31 and the lower portion thin-walled
32. As a result, the rigidity of the lower portion of the face part
30 is made lower than that of the upper portion, thereby making the
lower portion of the head flexible.
[0097] The iron head shown in FIG. 9 is an example in which the
head 1 is configured as a hollow body having a cavity 23 on the
inside, and a groove 34 is provided in the lower portion of the
face part 33. That is, the face configuration is such that the
ball-hitting surface of the face part 33 is flush, and a groove 34
is provided on the backside of the face part 33 in one portion of
the ground-contact plane side. Consequently, this example is one in
which the lower portion of the head is made flexible by making the
rigidity of the lower portion of the face part 33 lower than that
of the upper portion.
[0098] The iron head shown in FIG. 10 is an example in which the
head 1 is configured as a hollow body having a cavity 23 on the
inside, and the hardness of the upper portion and lower portion of
the face part 35 differs. That is, the face part 35 comprises the
same material, but the upper portion comprises a high hardness
composition 35a, and the lower portion comprises a low hardness
composition 35b. The constitution is such that the rigidity of the
upper portion and lower portion of the face part 35 varies
relatively in accordance with the difference in material hardness
between the high hardness composition 35a and the low hardness
composition 35b. As a result, this is an example in which the lower
portion of the head is made flexible by making the rigidity of the
lower portion of the face part 35 lower than that of the upper
portion.
[0099] The iron head shown in FIG. 11 is an example in which the
head 1 is configured as a hollow body having a cavity 23 on the
inside, and the hardness of the material used in the upper portion
and lower portion of the face part 36 differs. That is, it is a
configuration in which the upper portion of the face part 36
comprises a high hardness material 36a, and the lower portion
comprises a low hardness material 36b, and the different hardness
materials are welded together. The constitution is such that the
rigidity of the upper portion and lower portion of the face part 36
varies relatively in accordance with the difference in hardness
between the high hardness material 36a and the low hardness
material 36b. As a result, this is an example in which the lower
portion of the head is made flexible by making the rigidity of the
lower portion of the face part 36 lower than that of the upper
portion.
[0100] The iron head shown in FIG. 12 is an example in which the
head 1 is configured as a hollow body having a cavity 23 on the
inside, and the hardness of the upper portion and lower portion of
a part 37 other than the face part 21 differs. That is, the part 37
other than the face part 21 comprises the same material, but the
upper portion comprises a high hardness composition 37a, and the
lower portion comprises a low hardness composition 37b. The
constitution is such that the rigidity of the upper portion and
lower portion of the part 37 other than the face part 21 varies
relatively in accordance with the difference in hardness between
the high hardness composition 37a and the low hardness composition
37b. As a result, this is an example in which the lower portion of
the head is made flexible by making the rigidity of the lower
portion of the part 37 other than the face part 21 lower than that
of the upper portion.
[0101] The iron head shown in FIG. 13 is an example in which the
head 1 is configured as a hollow body having a cavity 23 on the
inside, and the hardness of the upper portion and lower portion of
a part 38 other than the face part 21 differs. That is, it is a
configuration in which the upper portion of the part 38 other than
the face part 21 comprises a high hardness material 38a and the
lower portion comprises a low hardness material 38b, and the two
different hardness materials are welded together. The constitution
is such that the rigidity of the upper portion and lower portion of
the part 38 other than the face part 21 varies relatively in
accordance with the difference in hardness between the high
hardness material 38a and the low hardness material 38b. As a
result, this is an example in which the lower portion of the head
is made flexible by making the rigidity of the lower portion of the
part 38 other than the face part 21 lower than that of the upper
portion.
[0102] The iron head shown in FIG. 14 is an example in which the
head 1 is configured as a hollow body having a cavity 23 on the
inside, and the upper portion and lower portion of the face 39
comprise a different Young's modulus. That is, it is a structure in
which the upper portion of the face part 39 comprises a material
with a high Young's modulus 39a, the lower portion comprises a
material with a low Young's modulus 39b, and the two different
Young's modulus materials are welded together. The constitution is
such that the rigidity of the upper portion and lower portion of
the face part 39 varies relatively in accordance with the
difference in the Young's modulus between the high Young's modulus
material 39a and the low Young's modulus material 39b. As a result,
this is an example in which the lower portion of the head is made
flexible by making the rigidity of the lower portion of the face
part 39 lower than that of the upper portion.
[0103] The iron head shown in FIG. 15 is an example in which the
head 1 is configured as a hollow body having a cavity 23 on the
inside, and the Young's modulus of the upper portion and lower
portion of a part 40 other than the face part 21 differs. That is,
it is a configuration in which the upper portion of the part 40
other than the face part 21 comprises a high Young's modulus
material 40a, the lower portion comprises a low Young's modulus
material 40b, and the two different Young's modulus materials are
welded together. The constitution is such that the rigidity of the
upper portion and lower portion of the part 40 other than the face
part 21 varies relatively in accordance with the difference in the
Young's modulus between the high Young's modulus material 40a and
the low Young's modulus material 40b. As a result, this is an
example in which the lower portion of the head is made flexible by
making the rigidity of the lower portion of the part 40 other than
the face part 21 lower than that of the upper portion.
[0104] Furthermore, a method other than those cited above, such as
heat treatment, can be selected as means for varying the hardness
or Young's modulus.
[0105] The iron head shown in FIG. 16 is an example in which a
through-groove 42, which is provided on the back side of the head
41, and which parallels the score lines formed in the ball-hitting
surface of the face part, is formed in the intermediate portion of
the head on the back side of the face part. FIG. 17 is a side view
of FIG. 16. The through-groove 42 is a groove that passes through
(penetrates) the head 41 from the toe part 5 side to the hosel part
3 side. Since the intermediate portion of the head 41, which is
configured by the through-groove 42, constitutes a lower rigidity
than that of the upper portion and lower portion of the head 41,
the configuration is such that the lower portion of the head 41 is
flexible at impact. Consequently, the lower portion of the head 41
has lower rigidity and is flexible.
[0106] The iron head shown in FIG. 18 is an example in which a
pocket-shaped groove 44, which is provided on the back side of the
head 43, parallels the score lines formed in the ball-hitting
surface of the face part, and is open at the tip of the toe side,
is formed in the intermediate portion of the head 43 on the back
side of the face part. FIG. 19 is a side view of FIG. 18. The tip
of the toe part 5 side of the pocket-shaped groove 44 of this iron
head is open, and since this pocket-shaped groove 44 part has low
rigidity, the lower portion of the head 43 is flexible at impact.
Consequently, the lower portion of the head 43 has lower rigidity
and is flexible.
[0107] The iron head shown in FIG. 20 is an example of a
configuration in which a groove 46 is formed in the lower portion
of the head 45 approximately perpendicularly (vertically) from the
ground-contact plane, more accurately, at a sharp angle
(practically the loft angle) from the vertical, up to an
intermediate location. It is an example in which the groove 46 is
provided in a slit shape in a part 47 other than the face part,
which is practically integrated with the back side of the face
part, and the wall thickness of the lower portion of the face part
is relatively thinner than the wall thickness of the upper portion
of the face part. In accordance with this configuration, the lower
portion of the head becomes flexible at impact. Consequently, the
lower portion of the head has lower rigidity and is flexible.
[0108] The iron head shown in FIG. 21, like that of FIG. 20, is an
example in which a groove 46 is formed from the bottom surface of
the sole part up to an intermediate location in the direction of
the ground-contact plane loft angle relative to the lower portion
of the head 45, and an elastic member 48, such as a piece of rubber
or a piece of plastic, is disposed in this groove 46. This is
another example in which the lower portion of the head is
configured to be flexible at impact, and consequently, the lower
portion of the head has lower rigidity and is thereby flexible.
Embodiments for Reducing the Moment of Inertia
[0109] These are examples in which the configurations are designed
to reduce the vertical moment of inertia of the head to facilitate
the bending of the head at impact, thereby imparting relative
rotational movement to the head upon impact, enhancing the gear
effect and accelerating the backspin of the ball.
[0110] The iron head shown in FIG. 22 is a schematic diagram
showing an example of a head that reduces the vertical moment of
inertia. FIG. 23 shows the head of an iron golf club in the
configuration of the prior art as a comparative example. The center
of gravity of the head is in the same location in the examples of
both FIG. 22 and FIG. 23. The differences between these two
examples will be explained. In the case of the prior art iron head
shown in FIG. 23, there is significant resistance to the relative
rotational movement of the head 51. This shows a state in which the
head 51 resists rotation, and the vertical moment of inertia around
the location of the center of gravity of this head 51 exceeds 850
gcm.sup.2.
[0111] By contrast, in the case of the iron head shown in FIG. 22,
the inventor reduced the resistance of the head 50 to relative
rotational movement, and made it easier for the head to rotate by
changing the configuration of the head 50 rather than changing the
surface of the face of the head 50. The difference in the size of
the moment of inertia with the iron head shown in FIG. 23 is
illustrated by the rotating arrows a and b. The iron head shown in
FIG. 24 illustrates the state immediately prior to the ball 53
being impacted by the face part 52 of the head 50, and when the
ball 53 is impacted by the head 50, this state changes as shown in
FIG. 25. Spin is imparted to the ball 53, and the ball 53 rotates
in the counterclockwise direction as illustrated by arrows, moving
relatively along the ball-hitting surface of the face 52.
[0112] Further, the position of the head 50 immediately prior to
impact changes from that illustrated by the dotted lines 50a to the
position illustrated by the solid lines shown in the figure. This
state generates a vertical moment of inertia relative to the head
50, and the head 50 moves relatively rotationally around the
location of the center of gravity 54. The moment of inertia of the
head 50 becomes small, and the rotational deformation becomes
larger than that shown in FIG. 23. As a result, in the case of the
iron head shown in FIG. 22, the vertical moment of inertia is less
than 800 gcm.sup.2 when the hosel part is 50 mm or longer (This
definition will be explained hereinbelow.).
[0113] As described hereinabove, an iron golf club constituting the
present invention is configured from a head 1, comprising: a sole
part 6 having, in the lower portion thereof, a ground-contact
plane, and having, in the upper portion thereof, a top part 4, and
a face part 2 having a ball-hitting surface for striking a ball,
and at one end thereof a hosel part 3 which is a shaft connector;
and a shaft 7, which is connected at one end thereof to the hosel
part 3. When the length of this hosel part 3 is 50 mm or longer,
the value of the moment of inertia around an axis that passes
horizontally in the toe-heel direction through the center of
gravity of the head 50 is less than 800 gcm.sup.2.
[0114] Further, when the length of this hosel part 3 is less than
50 mm, the value of the moment of inertia around an axis that
passes horizontally in the toe-heel direction through the center of
gravity of the head 50 is less than 750 gcm.sup.2. A specific
embodiment of this will be explained next. To reduce the moment of
inertia, a weight will be disposed in the vicinity of the location
of the center of gravity of the head.
[0115] The iron head shown in FIG. 26 is a configuration in which a
weight 55 for reducing the vertical moment of inertia is disposed
in the vicinity of the center of gravity of the head 56, a groove
57 is formed in the face side of the vicinity of the center of
gravity thereof, and the weight 55 is disposed in this groove 57.
FIG. 27 is a side view of FIG. 26. The weight 55 is disposed in a
location that is centered around an axis that passes horizontally
through the location of the center of gravity of the head 56 in the
toe-heel direction approximately parallelly to the ground-contact
plane, that is, from the tip portion of the toe part 58 side to the
hosel part 59 side.
[0116] Further, the sole part side portion 60 of the head 56 is
configured as a hollow body 62 having a cavity 61 on the inside.
Furthermore, although not shown in the figure, the upper portion of
this hollow body 62 can be opened to form an indentation. Using
this configuration decreases the weight of the lower portion of the
head, thereby reducing the moment of inertia and at the same time
lowering the rigidity of the lower portion of the head.
[0117] The iron head shown in FIG. 28 is an example in which the
head 64 is configured as a hollow body having a cavity 65 on the
inside, and a weight 63 for reducing the vertical moment of inertia
is disposed in the vicinity of the center of gravity of the head
64. FIG. 29 is a side view of FIG. 28. The weight 63 is disposed in
a location in the vicinity of the center of gravity of a part 66
other than the face part. The weight 63 is disposed in the
intermediate portion of a location that is centered around an axis
that passes horizontally in the toe-heel direction through a
location in the vicinity of the center of gravity of the head 64,
and approximately parallelly to the ground-contact plane, that is,
from the toe part 58 side to the hosel part 59 side.
[0118] The iron head shown in FIG. 30 is an example in which the
head 68 is configured as a hollow body having a cavity 65 on the
inside, and a weight 67 for reducing the vertical moment of inertia
is disposed in the vicinity of the center of gravity of the head
68. FIG. 31 is a side view of FIG. 30. The weight 67 is disposed in
the intermediate portion of a location that is centered around an
axis that passes horizontally in the toe-heel direction through a
location in the vicinity of the center of gravity of the head 68,
and approximately parallelly to the ground-contact plane, that is,
from the toe part 58 side to the hosel part 59 side.
[0119] The iron head shown in FIG. 32 is an example in which a
weight 70 is disposed in the vicinity of the center of gravity on
the back side of the head 71. FIG. 33 is a side view of FIG. 32.
This example is a configuration, which is similar to opening the
upper portion of the hollow body 62 of the iron head shown in FIG.
26 to form an indentation. The weight 70 is disposed along a
location in the vicinity of the center of gravity of the head 71,
and approximately parallelly to the ground-contact plane the same
as in the iron head shown in FIG. 26. That is, the weight 70 is
disposed in a location centered on an axis that passes horizontally
in the toe-heel direction from the tip of the toe part 58 side to
the hosel part 59 side.
[0120] The iron head shown in FIG. 34 is an example in which a
weight 72 for reducing the vertical moment of inertia is disposed
in a location in the vicinity of the center of gravity of the head
73, near the top of a part 74 other than the face part that rises
upward from the lower portion of the head, that is, near the tip of
the upper portion (apex) 74a, and in a location in the vicinity of
the center of gravity. FIG. 35 is a side view of FIG. 34. The
weight 72 is dispose in the intermediate portion between the top
and the sole, and is centered on an axis passing horizontally in
the toe-heel direction through a location in the vicinity of the
center of gravity of the head 73, and approximately parallelly to
the ground-contact plane, that is, from the toe part 58 side to the
hosel part 59 side.
[0121] The iron head shown in FIG. 36 is a side view showing the
score lines 8 in the face part 2. The score lines 8 of the iron
head 1 shown in FIG. 36 are placed above the ground-contact plane
11 so as to be parallel in relationship to the ground-contact plane
11 of the sole part 6. In this example, location G is a location
approximately 1/2 the height (vertically) from the top part 4 of
the face part 2 plane to the sole part 6. This location G is
accurately projected perpendicularly to the face plane of the face
part 2 from the center of gravity of the head 1.
[0122] A horizontal axis P, which passes through this location G,
is parallel to the score lines 8, and, in addition, is
approximately parallel to the ground-contact plane 11. A horizontal
plane comprising this horizontal axis P constitutes the approximate
horizontal axis P for the ball-hitting surface of the face part 2.
The head 1 of this embodiment is constituted so as to lower the
rigidity and enhance the coefficient of rebound of the portion
below the approximate horizontal plane passing through this
location G, that is, the sole part of the ground-contact plane 11
side.
[0123] Further, it is possible to reduce the moment of inertia by
making the region near this location G heavier than the other
member. The hosel part 3 is generally vertically closer to the top
part 4 side than to this location G. Thus, when the length (L) of
the hosel part 3 is long, the center of gravity of the head 1 moves
relatively closer to the top part 4 side. Therefore, when the
length (L) of the hosel part 3 is short, the center of gravity of
the head 1 moves relatively closer to the sole part 6 side, thereby
consequently contributing toward lowering the location of the
center of gravity, and reducing the moment of inertia. Furthermore,
it is supposed that length (L) of the hosel part is the length the
center line of the hosel part from the point where this line
intersects the upper end plane of the hosel part to the point where
it intersects the sole plane (refer to FIG. 37).
[0124] The iron head shown in FIG. 37 shows an example of a shape
in which an axis passing through location G is higher (has greater
taper) at the toe side of the top part 4 than at the heel side, as
shown in FIGS. 27, 29, 31, 33 and 35. That is, as shown in FIG. 36,
the head 1 is positioned so that the score lines become horizontal.
At this time, the angle formed by an axis that runs parallel to the
upper surface of the top part 4 toward the hosel part 3 and the
ground-contact plane 11 is the angle of intersection .alpha.. A
line segment that passes through approximately 1/2 the angle of
this angle of intersection .alpha. is treated as a through-axis S.
The relationship between the axis line S of this through-axis and
the central axis line of the shaft 7 is closer to that of a right
angle than the relationship between the axis line S of the
through-axis and an axis line parallel to the ground-contact plane
11. The examples of the respective heads shown in the
above-mentioned FIGS. 27, 29, 31, 33, and 35 constitute
configurations that dispose weights along an axis close to this
through axis S.
[0125] It is preferable that the specific gravity of the material
for configuring the main parts of the head for reducing the
vertical moment of inertia described hereinabove is 6.5 gcm.sup.3
or greater. Further, it is preferable that the target iron golf
club has a large loft angle, and be used as either a so-called
short iron or a wedge. The embodiments of the present invention are
configured as described hereinabove, but, needless to say, the
present invention is not limited to these embodiments.
Embodiment 1
[0126] Next, tests were carried out to show the effect of an
embodiment of the present invention. The golf club head used in the
tests was related to the iron head shown in FIGS. 32 and 33, and
the results of the test hits using the first through the third
embodiments are shown in Table 1. In this example, the length (L)
of the hosel part was 54 mm, and an iron head, which, with the
exception of the sole part, did not have a built-up thickness on
the back side, that is, had a plate-shaped face, was used. The
configuration was such that the weight 70 of FIG. 32 was affixed as
surplus thickness to this plate-shaped face at the location of the
center of gravity, and this weight weighed 100 g. The first through
the third embodiments changed the moment of inertia by gradually
changing the location of this weight. The respective moments of
inertia ranged from 715 gcm.sup.2 to 770 gcm.sup.2. The score lines
were formed using a press.
[0127] In the comparative example, the moment of inertia using the
same method was 800 gcm.sup.2. Prior art 1 is a normal muscle back
wedge, and the score lines were formed using a press. Prior art 2
forms the score lines using engraving (cutting with a tool).
Engraving produces a sharper score line angle than press forming,
and in the past this method was used to increase the amount of
spin, but this will be regulated in the future as mentioned
hereinabove. The hitting tests were carried out at a head speed of
30 m/s, and used the same conditions for prior art and comparative
examples. The results of these test hits showed the effect of the
example of this proposal shown in FIG. 22 as compared to the prior
art shown in FIG. 23.
TABLE-US-00001 TABLE 1 Measured Values for Moments of Inertia
(Example Using Prior Art of FIG. 32) Compara- Embodi- Embodi-
Embodi- Prior Prior tive ment ment ment Art 1 Art 2 Example 1 2 3
Hosel 73 73 54 54 54 54 Length (mm) Moment 980 980 800 770 740 715
of Inertia (g cm.sup.2) Amount 9045 9430 8965 9185 9200 9358 of
Spin (rpm)
When the moment of inertia was 800 gcm.sup.2, the amount of spin
was almost identical to the amount of spin in Prior Art 1, and when
the value of the moment of inertia became smaller, the amount of
spin increased. From these, it has been proved that when the hosel
length is 50 mm or more, the moment of inertia can be 800 gcm.sup.2
or less. From these results, when the hosel length is 50 mm or
less, the moment of inertia can be less than 750 gcm.sup.2.
Embodiment 2
[0128] This is an embodiment of golf clubs related to the iron
heads shown in FIGS. 20 and 21, and the results of test hits at X
through W of the face part shown in FIG. 36 are shown in Table 2.
In this example, the thickness of the face at the slit part was 2
mm, the slit width was 1.5 mm, and the depth of the slit from the
bottom surface of the sole was 30 mm. The test-hit locations are at
right angles to the score lines as shown in the figure, and
treating the location of the center of gravity G as the boundary,
prescribe the top part side locations as X and Y, and the sole part
side locations as Z and W.
[0129] The respective test-hit locations are at the same locations
in the toe-heel direction, and are positioned 5 mm apart between
the top part and the sole part. As a result, the data in Table 2
below demonstrates that the coefficient of rebound figures at the
location of the center of gravity boundary and on the sole part
side of this boundary were higher than those of the prior art,
which did not have a slit.
TABLE-US-00002 TABLE 2 Measured Coefficient of Rebound Values
Location Prior Art Example of FIG. 20 X 0.670 0.667 Y 0.752 0.750 G
0.769 0.770 Z 0.750 0.757 W 0.670 0.682
[0130] Further, the figures for the amount of spin were larger than
those of the prior art as shown in Table 3. The head speed for
these test hits was 30 m/s.
TABLE-US-00003 TABLE 3 Measured Spin Values Prior Art Example of
FIG. 20 Ball Rotation Speed (rpm) 9045 9528
* * * * *