U.S. patent application number 09/396447 was filed with the patent office on 2002-01-31 for wood club head.
This patent application is currently assigned to BRIDGESTONE SPORTS CO., LTD.. Invention is credited to KAJITA, RYOTA.
Application Number | 20020013180 09/396447 |
Document ID | / |
Family ID | 17369514 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020013180 |
Kind Code |
A1 |
KAJITA, RYOTA |
January 31, 2002 |
WOOD CLUB HEAD
Abstract
In a wood club head having a face 2 constituted by convex
surfaces curved vertically and horizontally, a bulge radius forming
the substantially horizontally-curved surface is set to be not
smaller than 15 inches.
Inventors: |
KAJITA, RYOTA; (SAITAMA,
JP) |
Correspondence
Address: |
SUGHRUE MION ZINN
MACPEAK & SEAS PLLC
2100 PENNSYLVANIA AVENUE NW
WASHINGTON
DC
20037
|
Assignee: |
BRIDGESTONE SPORTS CO.,
LTD.
|
Family ID: |
17369514 |
Appl. No.: |
09/396447 |
Filed: |
September 15, 1999 |
Current U.S.
Class: |
473/330 ;
473/324; 473/345; 473/349 |
Current CPC
Class: |
A63B 53/04 20130101;
A63B 53/0408 20200801; A63B 53/0466 20130101; A63B 60/00
20151001 |
Class at
Publication: |
473/330 ;
473/324; 473/345; 473/349 |
International
Class: |
A63B 053/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 16, 1998 |
JP |
HEI 10-261992 |
Claims
What is claimed is:
1. A wood club head comprising a face constituted by convex
surfaces curved vertically and horizontally, wherein a bulge radius
forming the substantially horizontally-curved surface is set to be
not smaller than 15 inches.
2. A wood club head according to claim 1, wherein inertial moment
(IY) around a vertical axis (Y) passing through a center of gravity
of said wood club head is set to be not smaller than 20
g.multidot.mm.multidot.se- c.sup.2 and a distance (ZG) of a
perpendicular drawn from said center of gravity to said face is set
to be not larger than 30 mm, and wherein said bulge radius is set
to be not smaller than 15 inches.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a wood club head having a
face constituted by convex surfaces curved vertically and
horizontally, and particularly to a wood club head having a devised
face.
[0003] 2. Description of the Related Art
[0004] In the background art, the face of a wood club head acting
as a hitting surface is constituted by vertically and horizontally
curved surfaces each having a radius of about 10 inches. The
vertically and horizontally curved surfaces are called a roll and a
bulge respectively. Assume that hitting is performed in the state
where a face 2 of a head 1 is put so as to be perpendicular to a
target. In this case, if that the face 2 is formed to be a flat
surface as shown in FIG. 6, and if a ball B is hit at a sweet spot
S of the face 2 which is an intersecting point between the face 2
and a perpendicular drawn from the center of gravity to the face 2,
the ball B will be hit substantially straight toward the target. If
the ball B is hit at a portion a little to a heel 3 side of the
face 2 off the sweet spot S, however, the head 1 swings
counterclockwise around the center of gravity in FIG. 7 to thereby
make the ball B.sub.1 rotate clockwise (slice spin) as shown by the
ball B.sub.1 in FIG. 7. If the ball B is hit at a portion a little
to a toe 4 side of the face 2, on the contrary, the head 1 swings
clockwise around the center of gravity in FIG. 7 to thereby make
the ball B rotate counterclockwise (hook spin) as shown by the ball
B.sub.2 in FIG. 7. Generally, such a spin generation effect is
called a gear effect. That is, when a ball is hit at a portion a
little to the right or to the left off the sweet spot S of the face
2 in the state where the face 2 is front-viewed, the ball is
subjected to a slice or hook spin so that the ball is made to fly
missing the target direction largely to the right or left and the
directivity of the hit ball is remarkably reduced. In order to
eliminate such a disadvantage, therefore, the face 2 is formed into
a curved surface. Since the ball B.sub.1 and B.sub.2 fly out in the
direction of the normal of the curved surface when a
horizontally-curved surface is formed as the face 2 as shown in
FIG. 8 even when the ball is hit at a portion a little off the
sweet spot S, the foregoing gear effect is canceled so that the
directivity of the ball is improved. Further, such a phenomenon is
generated also in the case where the ball is hit at a portion a
little to the up or down side off the sweet spot S. In this case,
the direction of hitting the ball is corrected by a so-called roll
radius forming a vertically-curved surface and the distance of
flying of the hit ball is increased in place of the foregoing
directivity of the ball. The horizontal bulge radius has been
empirically selected to be about 10 inches for these ten years or
more since a persimmon tree was selected to be used as a material
of a head.
[0005] Recently, as the material of a wood club, however, titanium
or an alloy thereof, which is a metal material having low specific
gravity, high hardness, and high strength, has been frequently
utilized, and the size of a head and the length of a club shaft
have been increased. As a result, the inertial moment of the head
is increased (for example, the value is increased from 10-20
g.multidot.mm.multidot.sec.sup.2 in the case of a persimmon head to
20 g.multidot.mm.multidot.sec.sup.2 or more in the case of a
so-called metal head) so that, even in the case where a ball is hit
at a portion a little off the center, that is, at a portion off the
sweet spot S, a head is suppressed from swinging around the center
of gravity and generation of the foregoing gear effect is reduced.
As a result, there arises a problem that the value of the bulge
radius which has been empirically taken into confidence is made
unsuitable.
SUMMARY OF THE INVENTION
[0006] In order to eliminate the foregoing disadvantage, an object
of the present invention is to provide a wood club head having a
bulge radius which is suitable for a large and hollow head.
[0007] In order to achieve the above object, according to the
present invention, there is provided a wood club head having a face
constituted by convex surfaces curved vertically and horizontally,
wherein a bulge radius forming the substantially
horizontally-curved surface is set to be not smaller than 15
inches.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a perspective view of a head;
[0009] FIG. 2 is a side view of the head;
[0010] FIG. 3 is a graph showing variations in ballistic course due
to bulge radii;
[0011] FIG. 4 is a graph showing a correlation between the bulge
radius and IY and ZG;
[0012] FIG. 5 is a view for explaining a substantially
horizontally-curved surface of a face;
[0013] FIG. 6 is a view showing the state where a ball is hit at a
sweet spot when a face is constituted by a flat surface;
[0014] FIG. 7 is a view showing the state where a ball is hit at
the portions on the heel and toe sides of the face shown in FIG. 6;
and
[0015] FIG. 8 is a view showing a state of off-center hitting in
the case where a bulge and a roll radius are given to the face.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] A preferred embodiment of the present invention will be
described below with reference to the accompanied drawings.
[0017] When the structures of golf club heads are compared with
each other from the point of view of the gear effect with respect
to the inertial moment (IY) around a vertical axis Y passing
through the center of gravity of a head 1 and gravity depth (ZG) of
the head 1 shown in FIGS. 1 and 2, it is found that IY >20
g.multidot.mm.multidot.sec.sup.2 and ZG=20-35 mm in most of
recently-used metal heads while IY =10-20
g.multidot.mm.multidot.sec.sup.2 and ZG=20-30 mm in a
conventionally used persimmon head (wood of No.1-No.5). Generally,
in an iron club head, IY=20-35 g.multidot.mm.multidot.sec.sup.2 and
ZG=0-5 mm. In order to set the bulge radius in accordance with the
difference in structure of a head, that is, in accordance which a
change in degree of the gear effect due to the difference in
inertial moment (IY) and gravity depth (ZG) in the present
invention, the directivity of a hit ball in the case where the
bulge radius of each of club heads different in IY and ZG was
changed in the range of from 5 to 40 inches was evaluated on the
basis of simulation by a computer by using the program of "impact
and ballistic course calculation" developed by the present
Applicant. FIG. 3 shows, as an embodiment, a part of the results.
FIG. 3 shows ballistic courses in the case of using heads having
IY=20 g.multidot.mm.multidot.sec.sup.2 and ZG=30 mm and having the
bulge radii of the face 2 of 5, 8, 10, and 16 inches which were
made on the basis of the head specifications of the large and
hollow driver of Tourstage Z-100produced by our company and having
a titanium alloy head of a volume of 255 cc. In this case, a ball
was hit (by a right-handed person) at a head speed of 45 m/s and at
a position apart by 10 mm from the sweet spot to the heel side.
[0018] In FIG. 3, since hitting is performed in the condition of
off-center to the heel side by 10 mm, the ballistic course is
corrected so as to be curved up in the drawing by application of
the bulge radius forming the horizontally-curved surface of the
face 2; otherwise the ballistic course becomes a slice-type
ballistic course which will be curved down in the drawing because
of the gear effect. Next, a displacement (m) from a ballistic
course (a line A-A in FIG. 3) directed straight toward a target to
the falling point of a ball is measured to thereby obtain the bulge
radius where the displacement of the falling point is zero is
calculated. Then, the bulge radius is substantially 15 inches as
shown in Table 1. That is, in the large and hollow metal head
(IY=20, ZG=30) in this embodiment, it is found that the bulge
radius for making a ball fly straight while the gear effect
generated at the time of off-center hitting is canceled is 15
inches.
1 TABLE 1 Displacement of falling point (m) Bulge radius (inch)
-26.6 5 -11.4 8 -6.3 10 0.6 16
[0019] Further, in this embodiment, in order to examine the
influence of the head speed, the displacement of the falling point
was measured under the condition that the bulge radius was fixed
into 15 inches and the head speed was changed in the range of from
30 to 50 m/s. It is assumed that there is no significant difference
among the displacements so that the setting of the bulge radius
does not depend on the head speed.
[0020] Next, when the bulge radius corresponding to the gear effect
of the head in the case where the inertial moment (IY) and the
gravity depth (ZG) are changed within the ranges of from 10 to 35
g.multidot.mm.multidot.sec.sup.2 and from 15 to 40 mm respectively
which are considered to be the limit value for production of a
large and hollow metal head are obtained in the same manner as in
the simulation evaluation of FIG. 3, a correlation between the
bulge radius and IY and ZG as shown in FIG. 4 is obtained.
[0021] It is found from the correlation that the inertial moment
(IY) and the gravity depth (ZG) of a large and hollow metal head
are empirically within a range of IY.gtoreq.20 and ZG.ltoreq.30 in
practical use (a slanted portion in FIG. 4) so that the bulge
radius of the face 2 is required to be set to be not smaller than
about 15 inches in order to cancel the gear effect caused by
off-center hitting by the head 1 having IY and ZG within the
foregoing ranges substantially perfectly. Therefore, the bulge
radius of the wood club head according to the present invention is
set to be not smaller than 15 inches.
[0022] Further, when a horizontal portion of the face 2 is
constituted not by a single curved surface but by a plurality of
curved surfaces different in radius, or partially including flat
surfaces, the substantially horizontally-curved surface of the face
2 according to the present invention means a single surface (FIG.
5) which represents on average such a plurality of curved surfaces
having different radii and such flat surfaces. Moreover, the bulge
radius at a position a little above/below the center of the face 2
(the point of 1/2 height of the face) is formed from an arc taking
the roll radius into consideration on the basis of the bulge radius
passing through the center, by an ordinary construction method.
Moreover, the substantially hollow structure of a head includes a
structure in which a light filler such as sponge or the like is
filled in the inside of a hollow and shell-like head.
[0023] As described above, according to the present invention, in a
wood club head having a face constituted by convex surfaces curved
vertically and horizontally, a bulge radius forming the
substantially horizontally-curved surface is set to be not smaller
than 15 inches. Accordingly, it is possible to improve the
directivity of a ball even when the ball is hit at a position a
little off the center of the face. Particularly, with respect to a
club head in which the inertial moment (IY) around the vertical
axis (Y) passing through the center of gravity of the club head is
set to be large (not smaller than 20
g.multidot.mm.multidot.sec.sup.2) and the distance of the
perpendicular drawn from the center of gravity of the head to a
face (that is, the gravity depth) is set to be short (not larger
than 30 mm), in the case where a horizontally-curved surface of the
face is formed with the most suitable bulge radius corresponding to
the degree of the gear effect which will be generated when a ball
is hit at a position a little off the center, for example, with
respect to a large and hollow head using light and high-strength
material, the inertial moment (IY) around the vertical axis (Y)
passing through the center of gravity of the head becomes large and
the gravity depth of the head becomes short. When a ball is hit at
a position a little off the center by using such a head, therefore,
the degree of the gear effect is considerably reduced. Accordingly,
the horizontally-curved surface for canceling this gear effect may
be a gentle one. Therefore, the bulge radius is selected to be a
relatively large value. According to the present invention,
therefore, it is possible to set the bulge radius corresponding to
the degree of the gear effect based on the change of the head
structure, and particularly, in a large and substantially hollow
head, the directivity of a hit ball is extremely improved.
* * * * *