U.S. patent application number 13/075786 was filed with the patent office on 2011-10-27 for golf club head.
This patent application is currently assigned to O-TA Precision Industry Co., Ltd.. Invention is credited to Lin Chon Chen, Tsutomu Ibuki, Hitoshi KODAMA, Lee Kung Wen.
Application Number | 20110263349 13/075786 |
Document ID | / |
Family ID | 44816253 |
Filed Date | 2011-10-27 |
United States Patent
Application |
20110263349 |
Kind Code |
A1 |
KODAMA; Hitoshi ; et
al. |
October 27, 2011 |
GOLF CLUB HEAD
Abstract
Disclosed is a golf club head which enables to improve a
direction of a hit ball while assuring a carry and run of the ball
corresponding to a head speed and a position at which the ball is
hit on a face part, and enables to assure a stable direction of a
hit ball while realizing a stable carry and run of the ball even if
the ball is hit at a position other than the sweet spot. More
specifically, in the golf club head, center of figure Cf of the
face part roughly coincides with sweet spot Ss which is a point of
intersection of the face part and a perpendicular line dropped from
the center of gravity of the head toward the face part, and roll
radius R2 of the face part at a position distance Z apart from
center of figure Cf of the face part along vertical axis Lz fulfils
a predetermined conditional equation, provided that a moment of
inertia around an axis orthogonal to a vertical plane containing
sweet spot Ss and a center of gravity of the head is Ix, a distance
from the sweet spot to the center of gravity of the head is Yg, and
a loft angle is .theta..sub.0.
Inventors: |
KODAMA; Hitoshi;
(Toyohashi-shi, JP) ; Ibuki; Tsutomu;
(Toyohashi-shi, JP) ; Wen; Lee Kung; (Ping-Tung
Hsien, TW) ; Chen; Lin Chon; (Pingtung Hsien,
TW) |
Assignee: |
O-TA Precision Industry Co.,
Ltd.
Ping-Tung Hsien
CN
MRC COMPOSITE PRODUCTS CO., LTD.
Toyohashi-shi
JP
|
Family ID: |
44816253 |
Appl. No.: |
13/075786 |
Filed: |
March 30, 2011 |
Current U.S.
Class: |
473/330 |
Current CPC
Class: |
A63B 53/0466 20130101;
A63B 53/0408 20200801 |
Class at
Publication: |
473/330 |
International
Class: |
A63B 53/04 20060101
A63B053/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2010 |
JP |
2010-081166 |
Mar 31, 2010 |
JP |
2010-081167 |
Claims
1. A golf club head comprising: a face part having a curved surface
and being a ball-hitting surface; a crown part connecting to an
upper edge of said face part and composing an upper part; and a
sole part connecting to a lower edge of said face part and
composing a lower part, and satisfying a requirement that a center
of figure of said face part roughly coincide with a sweet spot
which is a point of intersection of said face part and a
perpendicular line dropped from a center of gravity of the head
toward said face part.
2. The golf club head according to claim 1, wherein bulge radius R1
of said face part fulfils the following conditional Equation 1,
provided that a moment of inertia around a vertical axis is Iz and
a distance from the sweet spot to the center of gravity of the head
is Yg. ( Sp + 16 ) Iz 1930 Yg Rb - 30.4 < R 1 < ( Sp + 32 )
Iz 1930 Yg Rb - 60.8 [ Equation 1 ] ##EQU00020##
3. The golf club head according to claim 2, wherein bulge radius R1
of said face part is constant throughout said face part.
4. A golf club head comprising: a face part having a curved surface
and being a ball-hitting surface; a crown part connecting to an
upper edge of said face part and composing an upper part; and a
sole part connecting to a lower edge of said face part and
composing a lower part, and satisfying requirements that a center
of figure of said face part roughly coincide with a sweet spot
which is a point of intersection of said face part and a
perpendicular line dropped from a center of gravity of the head
toward said face part and roll radius R2 of said face part at a
position distance Z apart from a center of figure of said face part
along a vertical axis fulfill the following conditional Equation 2,
provided that a moment of inertia around an axis orthogonal to a
vertical plane containing a sweet spot and a center of gravity of
the head is Ix, a distance from the sweet spot to the center of
gravity of the head is Yg, and a loft angle is .theta..sub.0. 170 z
( 106 Yg - 224 ) z Ix - 2.97 .theta. 0 + 68.1 < R 2 < 170 z (
106 Yg - 224 ) z Ix - 2.97 .theta. 0 + 64.6 [ Equation 2 ]
##EQU00021##
5. The golf club head according to claim 4, wherein roll radius R2
of said face part is constant throughout said face part.
Description
TECHNICAL FIELD
[0001] The present invention relates to a golf club head having a
curvature on a face.
[0002] The present application claims the priority of Japanese
Patent Application No. 2010-081,166 filed on Mar. 31, 2010 and
Japanese Patent Application No. 2010-081,167 filed on Mar. 31,
2010, the contents of which are incorporated herein by
reference.
BACKGROUND ART
[0003] In general, a wood-type golf club head is equipped with a
face part which is a ball-hitting surface, a crown part which
connects to an upper edge of the face part and composes an upper
part, and a sole part which connects to a lower edge of the face
part and composes a lower part, and the face part has a curved
surface. The wood-type golf club head has an entire shape such that
the height and the size become smaller in the direction from the
face part to the rear part.
[0004] In recent years, various shapes have been proposed for such
a wood-type golf club head for improvement of a direction of a hit
golf ball or a distance to the position where a hit golf ball
finally stopped, which is hereinafter referred to as a carry and
run of the ball.
[0005] For example, it is proposed that bulge radius (a radius of
curvature of the curve that is obtained when the face part is cut
by a horizontal plane) of a curved surface which composes a face
part is set in different values at the center and at right and left
sides of the face part (for example, Patent Documents 1 and 2), or
roll radius (a radius of curvature of the curve that is obtained
when the face part is cut by a vertical plane) of a curved surface
which composes a face part is set in different values at the center
and at upper and lower sides of the face part (for example, Patent
Document 5).
[0006] In addition, it is proposed that bulge radius is set at 400
mm or more (for example, Patent Document 3). In addition, it is
proposed that bulge radius is determined in such a way that it
fulfils a predetermined conditional equation concerning a moment of
inertia (for example, Patent Document 4). Further, it is described,
in each document, that the golf club head can improve the direction
of a hit ball.
PRIOR ART REFERENCES
Patent Documents
[0007] Patent Document 1: Japanese Patent Application Laid-Open No.
2005-111,281 [0008] Patent Document 2: Japanese Patent Application
Laid-Open No. 2005-34,540 [0009] Patent Document 3: Japanese Patent
Application Laid-Open No. Hei 11-89,976 [0010] Patent Document 4:
Japanese Patent Application Laid-Open No. 2004-216,173 [0011]
Patent Document 5: Japanese Patent Application Laid-Open No.
2004-501,688
DISCLOSURE OF INVENTION
Problem to be Solved by the Invention
[0012] However, by those golf club heads as mentioned above, it was
not always possible to hit a ball correctly to the aimed direction
and thus it was not possible to assure a stable direction of a hit
ball even if the ball was hit at a sweet spot which enables a large
carry and run of the ball.
[0013] In addition, there was a problem such that a carry and run
of the ball was remarkably lowered when the ball was hit at a
position other than the sweet spot.
[0014] The present invention has been made in view of the
above-mentioned circumstances and an object of the present
invention is to provide a golf club head which enables to improve a
direction of a hit ball while assuring a carry and run of the ball
corresponding to a head speed and a position at which the ball is
hit on a face part, and enables to assure a stable direction of a
hit ball while realizing a stable carry and run of the ball even if
the ball is hit at a position other than the sweet spot.
Means for Solving the Problem
[0015] In order to solve the above-mentioned problems, the present
invention proposes the following measures.
[0016] (1) The present invention is a golf club head having: a face
part having a curved surface and being a ball-hitting surface; a
crown part connecting to an upper edge of said face part and
composing an upper part; and a sole part connecting to a lower edge
of said face part and composing a lower part, and satisfying a
requirement that a center of figure of said face part roughly
coincide with a sweet spot which is a point of intersection of said
face part and a perpendicular line dropped from a center of gravity
of the head toward said face part.
[0017] (2) The golf club head according to (1), wherein bulge
radius R1 of said face part fulfils the following conditional
Equation 1, provided that a moment of inertia around a vertical
axis is Iz and a distance from the sweet spot to the center of
gravity of the head is Yg.
( Sp + 16 ) Iz 1930 Yg Rb - 30.4 < R 1 < ( Sp + 32 ) Iz 1930
Yg Rb - 60.8 [ Equation 1 ] ##EQU00001##
[0018] (3) The golf club head according to (2), wherein bulge
radius R1 of said face part is constant throughout said face
part.
[0019] (4) A golf club head having: a face part having a curved
surface and being a ball-hitting surface; a crown part connecting
to an upper edge of said face part and composing an upper part; and
a sole part connecting to a lower edge of said face part and
composing a lower part, and satisfying requirements that a center
of figure of said face part roughly coincide with a sweet spot
which is a point of intersection of said face part and a
perpendicular line dropped from a center of gravity of the head
toward said face part and roll radius R2 of said face part at a
position distance Z apart from a center of figure of said face part
along a vertical axis fulfill the following conditional Equation 2,
provided that a moment of inertia around an axis orthogonal to a
vertical plane containing a sweet spot and a center of gravity of
the head is Ix, a distance from the sweet spot to the center of
gravity of the head is Yg, and a loft angle is .theta..sub.0.
170 z ( 106 Yg - 224 ) z Ix - 2.97 .theta. 0 + 68.1 < R 2 <
170 z ( 106 Yg - 224 ) z Ix - 2.97 .theta. 0 + 64.6 [ Equation 2 ]
##EQU00002##
[0020] (5) The golf club head according to (4), wherein roll radius
R2 of said face part is constant throughout said face part.
[0021] According to the present invention, it is possible to hit a
ball correctly to the aimed direction as well as to realize a carry
and run of the ball corresponding to a head speed when the ball is
hit at the sweet spot because the center of figure of the face part
roughly coincides with the sweet spot.
[0022] Even if the ball is hit at a position off the sweet spot, it
is possible to realize a carry and run of the ball corresponding to
the position and the head speed and at the same time it is possible
to assure a stable direction of the hit ball corresponding to bulge
radius of the curved surface of the face part.
[0023] In addition, when bulge radius R1 of the face part fulfils
the above conditional Equation 1 depending on a moment of inertia
to be determined by the entire shape of the head and a distance
from the sweet spot to the center of gravity of the head, it is
possible to allow a hit ball to reach in the vicinity of an aimed
position even if the ball is hit at a position other than the sweet
spot because the balance between the direction of the hit ball and
a number of revolutions around the vertical axis to be given to the
ball can be made suitable.
[0024] Further, when roll radius R2 of the curved surface of the
face part at a position, which is distance Z apart from the center
of figure of the face part along the vertical axis, fulfils the
above conditional Equation 2 depending on a moment of inertia to be
determined by the entire shape of the head, a distance from the
sweet spot to the center of gravity of the head, and a loft angle,
it is possible to realize a stable carry and run of the ball even
if the ball is hit at a position other than the sweet spot because
the balance between the direction of the hit ball and a number of
revolutions around the horizontal axis to be given to the ball can
be made suitable.
[0025] Further, as for the above-mentioned golf club head, it is
preferable that bulge radius R1 of the face part be constant
throughout the face part.
[0026] Further, as for the above-mentioned golf club head, it is
preferable that roll radius R2 of the face part be constant
throughout the face part.
[0027] According to this constitution, the curved surface of the
face part can be formed easily and precisely, and at the same time
the balance between the direction of the hit ball and a number of
revolutions around the vertical axis to be given to the ball can be
made suitable as mentioned above and thus it is possible to allow
the hit ball to reach in the vicinity of an aimed position, because
bulge radius R1 of the face part is constant throughout the face
part.
[0028] According to this constitution, the curved surface of the
face part can be formed easily and precisely, and at the same time
the balance between the direction of the hit ball and a number of
revolutions around the horizontal axis to be given to the ball can
be made suitable as mentioned above and thus it is possible to
realize a stable carry and run of the ball, because roll radius R2
of the face part is constant throughout the face part.
Effect of the Invention
[0029] According to the golf club head of the present invention, it
is possible to improve a direction of a hit ball while assuring a
carry and run of the ball corresponding to a head speed and a
position at which the ball is hit on the face part because the
center of figure of the face part roughly coincides with the sweet
spot.
[0030] In addition, it is possible to assure a stable direction of
a hit ball while realizing a stable carry and run of the ball even
if the ball is hit at a position other than the sweet spot because
the roll radius is set to fulfill the above-mentioned conditional
equation depending on the moment of inertia, the position of the
center of gravity of the head, and the loft angle.
BRIEF DESCRIPTION OF DRAWINGS
[0031] FIG. 1: A schematic front view of the golf club head in the
embodiments of the present invention
[0032] FIG. 2: A schematic side sectional view of the golf club
head in the embodiments of the present invention
[0033] FIG. 3: A schematic top view explaining a state when a ball
is hit by the golf club head in the embodiments of the present
invention
[0034] FIG. 4: A schematic side view explaining a state when a ball
is hit by the golf club head in the embodiments of the present
invention
[0035] FIG. 5: A graph representing the relation between the
elevation angle and the number of revolutions around the horizontal
axis of the golf club head in the embodiments of the present
invention
BEST MODE FOR CARRYING OUT THE INVENTION
[0036] FIGS. 1 to 5 show the embodiments of the present
invention.
[0037] As shown in FIGS. 1 to 2, a golf club head 1 of the present
embodiments is equipped with a face part 2 composing a front part,
a crown part 3 composing an upper part, a sole part 4 composing a
lower part, a heel part 5 composing a side part to which a shaft 10
is attached, and a toe part 6 composing a side part opposite to the
heel part 5, and has an entire shape such that the height and the
size become smaller in the direction from the face part 2 to the
rear part.
[0038] The face part 2 composes a ball-hitting surface having a
predetermined bulge radius R1 in the horizontal direction and a
curved surface formed with a predetermined roll radius R2 in the
vertical direction, as described below in detail. In addition, the
crown part 3 connects to an upper edge of the face part 2 and has a
curved surface which goes downward in the direction toward the rear
part. In addition, the sole part 4 connects to a lower edge of the
face part 2 and has a curved surface which goes upward in the
direction toward the rear part.
[0039] In the figures, the mark G represents the center of gravity
of the golf club head 1 of the present embodiments and the position
thereof is unequivocally determined from the shapes, the materials,
and the like of the face part 2, crown part 3, sole part 4, heel
part 5, and toe part 6. In addition, the mark Ss is a point of
intersection of the face part 2 and a perpendicular line dropped
from the center of gravity G of the head toward the face part 2 and
represents a sweet spot. The mark Cf represents the center of
figure of the face part 2. In the present embodiments, the sweet
spot Ss and the center of figure Cf of the face part 2 are allowed
to roughly coincide. Note that, in the present embodiments, the
perpendicular line dropped from the center of gravity G of the head
toward the sole part 4 is referred to as a vertical axis Lz.
[0040] In addition, an axis orthogonal to a vertical plane
containing the center of gravity G of the head and the sweet spot
Ss and extending to the right and left direction is referred to as
a first horizontal axis Lx, and an axis orthogonal to the first
horizontal axis Lx and the vertical axis Lz and extending to the
front-back direction is referred to as a second horizontal axis
Ly.
[0041] As for the golf club head 1 of the present embodiments, it
is possible to hit a ball correctly to the aimed direction as well
as to realize a carry and run of the ball corresponding to a head
speed when the ball is hit at the sweet spot Ss because the center
of figure Cf of the face part 2 roughly coincides with the sweet
spot Ss.
[0042] In addition, as for the golf club head 1 of the present
embodiments, it is possible to realize a stable direction and carry
and run of a hit ball because the face part 2 is formed in such a
way that the bulge radius R1 and the roll radius R2 fulfill the
conditions shown by Equation 3 and Equation 4, respectively.
( Sp + 16 ) Iz 1930 Yg Rb - 30.4 < R 1 < ( Sp + 32 ) Iz 1930
Yg Rb - 60.8 [ Equation 3 ] 170 z ( 106 Yg - 224 ) z Ix - 2.97
.theta. 0 + 68.1 < R 2 < 170 z ( 106 Yg - 224 ) z Ix - 2.97
.theta. 0 + 64.6 [ Equation 4 ] ##EQU00003##
[0043] The mark Yg represents a depth of the center of gravity,
which is a distance from the center of gravity G of the head to the
sweet spot Ss. In addition, the mark .theta..sub.0 represents a
loft angle (degree), which is an inclination angle of the face part
2 against the vertical axis Lz at the center of figure Cf. In
addition, the marks Iz and Ix represent moments of inertia of the
golf club head 1 of the present embodiments around the vertical
axis Lz and the first horizontal axis Lx, respectively. In
addition, Z represents a position on the face part 2 in the
direction of the vertical axis Lz, taking the origin at the center
of figure Cf.
[0044] Hereinafter, Equation 3 which is a conditional equation
concerning the bulge radius R1 and Equation 4 which is a
conditional equation concerning the roll radius R2 will be
explained in detail, in turn.
(Concerning Bulge Radius R1)
[0045] FIG. 3 shows a state in which a ball is hit at a position a
predetermined distance X shifted from the origin along the first
horizontal axis Lx on the face part 2, taking the center of figure
Cf (the sweet spot Ss) as the origin.
[0046] In FIG. 3, a ball radius is referred to as Rb (mm), a
contact time between the ball and the face part 2 when the ball is
hit is referred to as t (s), and a force to be allowed to act on
the face part 2 by the ball is referred to as F (N). Number of
revolutions Ng1 (rpm) of gear revolution (hereinafter, referred to
as number of gear revolutions) which is generated by an action of
the moment caused by hitting the ball at a position shifted from
the center of figure Cf, among the revolutions around the vertical
axis Lz to be generated on the ball, is determined by the following
equation.
Ng 1 = F t 2 6 t Rb Yg Iz 180 .pi. X [ Equation 5 ]
##EQU00004##
[0047] In addition, a spin rate which represents a friction
coefficient between the ball and the face part 2 of the golf club
head 1 of the present embodiments is referred to as Sp. Number of
revolutions Na1 (rpm) of compression revolution (hereinafter,
referred to as number of compression revolutions) which is
generated by an angle change during the contact time t (s) which
starts with the contact between the ball and the face part 2 and
ends with the separation thereof caused by repulsion of the ball,
among the revolutions around the vertical axis Lz to be generated
on the ball, is determined by the following equation.
Na 1 = - Sp 1 R 1 180 .pi. X [ Equation 6 ] ##EQU00005##
[0048] Therefore, in the state shown by FIG. 3, total number of
revolutions Nt1 (rpm) around the vertical axis Lz to be generated
on the ball is a sum of number of gear revolutions Ng1 and number
of compression revolutions Na1, which is shown by the following
equation.
Nt 1 = F t 2 6 t Rb Yg Iz 180 .pi. X - Sp 1 R 1 180 .pi. X [
Equation 7 ] ##EQU00006##
[0049] In addition, in FIG. 3, gear angle Ag1 (degree), which is a
shift of a direction to be generated against the direction along
the second horizontal axis Ly by hitting the ball at a position
shifted from the center of figure Cf, is determined by the
following equation.
Ag 1 = K ( F t 2 ) 1 Iz 180 .pi. X [ Equation 8 ] ##EQU00007##
[0050] In addition, compression angle Aa1 (degree), which is a
shift of a direction to be generated against the direction along
the second horizontal axis Ly by an angle change during the contact
time t (s) which starts with the contact between the ball and the
face part 2 and ends with the separation thereof caused by
repulsion of the ball, is determined by the following equation.
Aa 1 = K 1 R 1 180 .pi. X [ Equation 9 ] ##EQU00008##
[0051] Note that, the mark K in [Equation 8] and [Equation 9]
represents a substantial efficiency.
[0052] Therefore, in the state shown by FIG. 3, shift angle At1
(degree), which causes a shift of a direction in which the ball
substantially flies against the direction along the second
horizontal axis Ly, is a sum of gear angle Ag1 and compression
angle Aa1 as shown by the following equation.
At 1 = { K ( F t 2 ) 1 Iz 180 .pi. X + K 1 R 1 180 .pi. X } [
Equation 10 ] ##EQU00009##
[0053] As described above, when the ball is hit at a predetermined
position of the face part 2, the ball flies depending on shift
angle At1 against the second horizontal axis Ly and depending on
total number of revolutions Nt1 around the vertical axis Lz while
rotating. Provided that the ratio of shift angle At1 to total
number of revolutions Nt1 is P (=Nt1/At1), bulge radius R1 is
expressed by the following equation.
R 1 = ( Sp + P K ) Iz F t 2 ( Yg 6 t Rb - P K ) [ Equation 11 ]
##EQU00010##
[0054] In the case of ordinary balls, a range of radius Rb is
around 13 to 22 mm, and spin rate Sp is around 100 to 200. In
addition, substantial efficiency K is generally around 0.8.
[0055] In addition, contact time t of the ball and the face part 2
at the time of hitting and force F to be allowed to act on the face
part 2 by the ball are around 2/10,000 (s) and 7,000 (N),
respectively, when calculated by use of the head speed (35 m/s) of
ordinary users.
[0056] Therefore, by substituting these values in Equation 11,
bulge radius R1 is expressed by the following equation by use of
ratio P of shift angle At1 to total number of revolutions Nt1,
moment of inertia Iz of the golf club head 1 around the vertical
axis Lz, and depth Yg of the center of gravity.
R 1 = ( Sp + 0.8 P ) Iz 1930 Yg Rb - 1.52 P [ Equation 12 ]
##EQU00011##
[0057] Now, the balls were practically hit while bulge radius R1 of
the face part 2 was varied and the position of the face part 2 at
which the balls were hit was shifted in various ways along the
first horizontal axis Lx, and the direction where the ball finally
dropped was measured.
[0058] Note that, in the present measurement, it is necessary to
hit the ball with a constant head speed and orbit and precisely at
a desired position of the face part 2. Consequently, the
measurement was carried out by use of a golf swing robot, ROBO IV,
manufactured by Miyamae Co., Ltd., while various golf clubs having
various club heads with various bulge radii R1 were independently
attached to this machine.
[0059] Ratio P of shift angle At1 to total number of revolutions
Nt1, when the balls were hit while bulge radius R1 of the face part
2 was varied and the position of the face part 2 at which the balls
were hit was shifted in various ways along the first horizontal
axis Lx, was calculated based on the above-mentioned Equation 5 to
Equation 10.
[0060] As a result, it was found that, when ratio P of shift angle
At1 to total number of revolutions Nt1 fulfils the following
equation, the ball can be dropped at a desired direction because,
even if the ball flies out with shift angle At1, it rotates around
the vertical axis Lz with total number of revolutions Nt1 and
curves adequately.
20.ltoreq.P.ltoreq.40 [Equation 13]
[0061] By substituting Equation 12 into Equation 13, a relational
expression was obtained as shown by Equation 14. Therefore, it is
possible to allow a hit ball to drop at a desired direction by
setting bulge radius R1 in such a way that it can fulfill Equation
14, even if the position of the face part 2 at which the ball is
hit is shifted along the first horizontal axis Lx in any
amount.
[0062] Note that, each numerical value contained in Equation 14
changes depending on a kind of a ball or a head speed, but the
change thereof is small as compared with the change in the value of
P. In the case when an ordinarily ball is used and a head speed is
in the ordinary range of 25 to 55 m/s, the same effect as above can
be obtained by allowing bulge radius R1 to fulfill Equation 14.
[0063] In addition, bulge radius R1 may be changed along the first
horizontal axis Lx as long as it fulfils Equation 14.
[0064] However, it is possible to form a curved surface of the face
part easily and precisely by allowing bulge radius R1 to be
constant throughout the face part 2 while allowing bulge radius R1
to fulfill Equation 14.
( Sp + 16 ) Iz 1930 Yg Rb - 30.4 < R 1 < ( Sp + 32 ) Iz 1930
Yg Rb - 60.8 [ Equation 14 ] ##EQU00012##
(Concerning Roll Radius R2)
[0065] FIG. 4 shows a state in which a ball is hit at a position a
predetermined distance Z shifted from the origin along the vertical
axis Lz on the face part 2, taking the center of figure Cf (the
sweet spot Ss) as the origin.
[0066] In FIG. 4, number of gear revolutions Ng2 (rpm) which is
generated by an action of the moment caused by hitting the ball at
a position shifted from the center of figure Cf, among the
revolutions around the first horizontal axis Lx to be generated on
the ball, is determined by the following equation.
Ng 2 = F t 2 6 t Rb Yg Ix 180 .pi. Z [ Equation 15 ]
##EQU00013##
[0067] In addition, number of compression revolutions Na2 (rpm)
which is generated by an angle change during the contact time t (s)
which starts with the contact between the ball and the face part 2
and ends with the separation thereof caused by repulsion of the
ball, among the revolutions around the first horizontal axis Lx to
be generated on the ball, is determined by the following
equation.
Na 2 = - Sp ( 1 R 2 Z + .theta. 0 ) 180 .pi. [ Equation 16 ]
##EQU00014##
[0068] Therefore, in the state shown by FIG. 4, total number of
revolutions Nt2 (rpm) around the first horizontal axis Lx to be
generated on the ball is a sum of number of gear revolutions Ng2
and number of compression revolutions Na2, which is shown by the
following equation.
Nt 2 = F t 2 6 t Rb Yg Ix 180 .pi. Z - Sp ( 1 R 2 Z + .theta. 0 )
180 .pi. [ Equation 17 ] ##EQU00015##
[0069] In addition, in FIG. 4, gear angle Ag2 (degree), which
causes a changed portion to be generated by hitting the ball at a
position shifted from the center of figure Cf in a hitting angle of
the ball against the second horizontal axis Ly, namely an elevation
angle, is determined by the following equation.
Ag 2 = K F t 2 1 Ix 180 .pi. Z [ Equation 18 ] ##EQU00016##
[0070] In addition, compression angle Aa2 (degree), which causes a
changed portion to be generated by an angle change during the
contact time t (s) which starts with the contact between the ball
and the face part 2 and ends with the separation thereof caused by
repulsion of the ball in the elevation angle, is determined by the
following equation.
Aa 2 = - K ( 1 R 2 Z + .theta. 0 ) 180 .pi. [ Equation 19 ]
##EQU00017##
[0071] Therefore, in the state shown by FIG. 4, elevation angle At2
(degree) of the ball is a sum of gear angle Ag2 and compression
angle Aa2 as shown by the following equation.
At 2 = K ( 1 R 2 + F t 2 1 Ix ) 180 .pi. Z + K .theta. 0 180 .pi. [
Equation 20 ] ##EQU00018##
[0072] Now, the balls were practically hit while roll radius R2 of
the face part 2 was varied and the position of the face part 2 at
which the balls were hit was variously shifted along the vertical
axis Lz, and the distance to the position where the ball finally
stopped, namely, the carry and run of the ball, was measured.
[0073] Note that, in the present measurement, the measurement was
carried out in the same manner as mentioned above by use of a golf
swing robot, ROBO IV, manufactured by Miyamae Co., Ltd., while
various golf clubs having various club heads with various roll
radii R2 were independently attached to this machine.
[0074] Note that, in the present measurement, two conditions of the
head speed, 35 m/s and 40 m/s, were used. In addition, shift angle
At2 and total number of revolutions Nt2, when the ball was hit
while roll radius R2 of the face part 2 was varied and the position
of the face part 2 at which the ball was hit was variously shifted
along the vertical axis Lz, were calculated based on the
above-mentioned Equation 15 to Equation 20.
[0075] Note that, in the same manner as in the calculation of bulge
radius R1, radius Rb of the ball of 22 mm, spin rate Sp of 90,
substantial efficiency K of 0.8, contact time t of 2/10,000 (s),
and force F of 7,000 (N) were used in the above-mentioned Equation
15 to Equation 20.
[0076] Each carry and run of the ball (including runs) in each case
of head speed 35 m/s and 40 m/s, and the corresponding calculated
values of elevation angle At2 and total number of revolutions Nt2
are shown in Table 1. In addition, the relation between elevation
angle At2 and total number of revolutions Nt2 shown in Table 1 is
shown in FIG. 5.
[0077] As shown in Table 1 and FIG. 5, in the case when the
predetermined carry and run of the ball corresponding to the head
speed is assured (specifically, a carry and run of 183 m or more in
the case of the head speed of 35 m/s and a carry and run of 242 m
or more in the case of the head speed of 40 m/s), it is found that
the plots of elevation angle At2 versus total number of revolutions
Nt2 distribute within a linear belt-like range, regardless of the
head speed.
[0078] In other words, in order to assure a carry and run of the
ball not less than a certain distance, it is only necessary to
allow elevation angle At2 of the ball hit out and total number of
revolutions Nt2 around the first horizontal axis Lx given to the
ball to fulfill a predetermined relation, and this relation can be
shown by the following approximation derived from FIG. 5.
TABLE-US-00001 TABLE 1 Head speed Carry Elevation angle Gear angle
Compression angle Total number of Number of gear Number of
compression (m/sec) (m) At2 (degree) Ag2 (degree) Aa2 (degree)
revolutions Nt2 (rpm) revolutions Ng2 (rpm) revolutions Na2 (rpm)
40 237 16.9 0.368 16.6 -2312 528 -2840 40 247 15.9 0.368 15.6 -2142
528 -2670 40 239 15.4 0.368 15.1 -2057 528 -2585 40 239 10.3 -0.368
10.7 -2357 -528 -1829 40 244 11.3 -0.368 11.6 -2524 -528 -1996 40
241 11.8 -0.368 12.1 -2607 -528 -2080 35 175 18.5 0.306 18.2 -2312
417 -2729 35 184 17.5 0.306 17.2 -2162 417 -2578 35 181 17.0 0.306
16.7 -2087 417 -2503 35 180 11.9 -0.306 12.3 -2254 -417 -1838 35
186 12.9 -0.306 13.2 -2401 -417 -1984 35 182 13.4 -0.306 13.7 -2475
-417 -2058
100At2-3900.ltoreq.Nt2.ltoreq.100At2-3700 [Equation 21]
[0079] By substituting Equation 17 and Equation 20 in which radius
Rb, spin rate Sp, substantial efficiency K, contact time t, and
force F having the above-mentioned values are used into Equation
21, a relational expression can be obtained as shown by Equation
22. Therefore, it is possible to allow the ball to realize a carry
and run not less than a certain distance corresponding to the head
speed by setting roll radius R2 in such a way that it can fulfill
Equation 22, even if the position of the face part 2 at which the
ball is hit is shifted along the vertical axis Lz in any
amount.
[0080] Note that, each numerical value contained in Equation 22
changes depending on a kind of ball or a head speed, but, similarly
as in Equation 14, the change thereof is small as compared with the
change in the value of P. In the case when an ordinarily ball is
used and a head speed is in the ordinary range of 25 to 55 m/s, the
same effect as above can be obtained by allowing roll radius R2 to
fulfill Equation 22.
[0081] In addition, in Equation 22, when the position of the face
part 2 at which the ball is hit is shifted along the vertical axis
Lz, the value of Z changes and thereby the conditional equation
differs. However, it is possible to form a curved surface of the
face part easily and precisely by allowing a constant roll radius
R2 to fulfill the condition throughout the face part 2.
170 z ( 106 Yg - 224 ) z Ix - 297 .theta. 0 + 68.1 < R 2 <
170 z ( 106 Yg - 224 ) z Ix - 297 .theta. 0 + 64.6 [ Equation 22 ]
##EQU00019##
[0082] As mentioned above, according to the golf club head 1 of the
present embodiments, it is possible to improve a direction of a hit
ball while assuring a carry and run of the ball corresponding to a
head speed and a position at which the ball is hit on the face part
2 because the center of figure Cf of the face part 2 roughly
coincides with the sweet spot Ss.
[0083] In addition, the balance between the direction of a ball hit
out (directional angle) and the number of revolutions around the
vertical axis Lz to be given to the ball can be made suitable and
thus it is possible to allow the hit ball to reach in the vicinity
of an aimed position even if the ball is hit at a position other
than the sweet spot Ss because bulge radius R1 fulfils Equation
14.
[0084] Further, the balance between the direction of a ball hit out
(elevation angle) and the number of revolutions around the first
horizontal axis Lx to be given to the ball can be made suitable and
thus it is possible to realize a stable carry and run of the ball
even if the ball is hit at a position other than the sweet spot Ss
because roll radius fulfils Equation 22.
[0085] The embodiments of the present invention have been explained
in detail with reference to Figures, but the specific constitution
is not limited to these embodiments and can include variations
without departing from the scope or spirit of the invention.
INDUSTRIAL APPLICABILITY
[0086] The present invention can provide a golf club head which
enables to improve a direction of a hit ball while assuring a carry
and run of the ball corresponding to a head speed and a position at
which the ball is hit on a face part, and enables to assure a
stable direction of a hit ball while realizing a stable carry and
run of the ball even if the ball is hit at a position other than
the sweet spot.
EXPLANATION OF NUMERALS
[0087] 1: golf club head [0088] 2: face part [0089] 3: crown part
[0090] 4: heel part [0091] Cf: center of figure (of the face part)
[0092] G: center of gravity of the head [0093] R1: bulge radius
[0094] R2: roll radius [0095] Ss: sweet spot
* * * * *