U.S. patent application number 11/151283 was filed with the patent office on 2006-01-12 for golf club.
This patent application is currently assigned to SRI Sports Ltd.. Invention is credited to Hitoshi Oyama.
Application Number | 20060009302 11/151283 |
Document ID | / |
Family ID | 35542086 |
Filed Date | 2006-01-12 |
United States Patent
Application |
20060009302 |
Kind Code |
A1 |
Oyama; Hitoshi |
January 12, 2006 |
Golf club
Abstract
A golf club comprises a shaft and a head, wherein a moment Ix of
inertia of the golf club head around a vertical axis passing
through the center of gravity of the club head is not less than
3800 (gsq.cm), and a shaft-torque T (degrees) of the golf club
shaft and the moment Ix of inertia satisfy the following condition
(1): T=<0.0025.times.Ix-6.0.
Inventors: |
Oyama; Hitoshi; (Kobe-shi,
JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
SRI Sports Ltd.
|
Family ID: |
35542086 |
Appl. No.: |
11/151283 |
Filed: |
June 14, 2005 |
Current U.S.
Class: |
473/282 |
Current CPC
Class: |
A63B 60/14 20151001;
A63B 53/10 20130101; A63B 53/0408 20200801; A63B 53/0412 20200801;
A63B 60/00 20151001; A63B 53/0466 20130101 |
Class at
Publication: |
473/282 |
International
Class: |
A63B 53/00 20060101
A63B053/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 6, 2004 |
JP |
2004-199635 |
Claims
1. A golf club comprising a golf club shaft and a golf club head
attached to a tip end of the golf club shaft, wherein a moment Ix
of inertia of the golf club head around a vertical axis passing
through the center of gravity of the club head is not less than
3800 gsq.cm, and a shaft-torque T degrees of the golf club shaft
and the moment Ix of inertia satisfy the following condition (1):
T=<0.0025.times.Ix-6.0.
2. The golf club according to claim 1, wherein the shaft-torque T
is in a range of from 1.5 to 6.0 degrees.
3. The golf club according to claim 1 or 2, wherein the
shaft-torque and the moment Ix of inertia satisfy the following
condition (2): T=<0.0025.times.Ix-6.3.
4. The golf club according to claim 1 or 2, wherein the
shaft-torque and the moment Ix of inertia satisfy the following
condition (3): T=>0.0025.times.Ix-8.5.
5. The golf club according to claim 1 or 2, wherein the moment Ix
of inertia is in a range of from 4100 to 5500 gsq.cm.
6. A method of designing a golf club composed of a club shaft and a
club head, comprising providing a moment Ix of inertia of not less
than 3800 gsq.cm for the club head, and determining a shaft-torque
T degrees of the club shaft so as to satisfy the following
condition (1): T=<0.0025.times.Ix-6.0.
7. The method according to claim 6, which further comprises
determining the shaft-torque T degrees so as to satisfy the
following condition (3): T>=0.0025.times.Ix-8.5 in addition to
said condition (1): T=<0.0025.times.Ix-6.0.
8. The method according to claim 6 or 7, which further comprises
providing a head volume of not less than 300 cc for the club
head.
9. The method according to claim 6 or 7, which further comprises
providing a weight of not less than 170 g for the club head.
10. The method according to claim 6 or 7, which further comprises
providing an overall length L of not less than 43 inches for the
club.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a golf club and more
particularly to a combination of a club head having a specific
moment of inertia and a club shaft having a specific
shaft-torque.
[0002] Heretofore, in improving the directional stability of the
struck balls, it has been considered to be effective to increase
the moment of inertia of the club head or to change the bending
rigidity and twist rigidity of the club shaft as shown in Japanese
patent application publication NOS. 7-112041, 8-187308, 9-38254 and
11-76479. These prior arts, however, failed to provide discussion
about the relationship between such parameters of the club head and
shaft.
[0003] In general, in the case of golf clubs targeted at
professionals and advanced golfers, the moment Ix of inertia of the
head is relatively small, and also the shaft-torque is relatively
small. Contrary, in the case of golf clubs targeted at
high-handicapped golfers, the moment Ix of inertia and shaft-torque
T are relatively large.
[0004] AS to golf swing, the professionals and advanced golfers can
make a body-led swing, and the swing path or swing circle and ball
hitting position are stable. And as the head speed is high, the
backspin tends to become excessively increased. Therefore, in the
club heads targeted at professionals and advanced golfers, it is
desirable that the center of gravity of the club head is relatively
low in order to avoid an excessive backspin rather than that the
moment Ix of inertia is increased on the assumption of miss shots.
Further, it is also desirable that the club is sensitive about the
golfer's swing motion, therefore, the moment Ix of inertia and
shaft-torque are limited to small values. In the case of the golf
clubs targeted at professionals and advanced golfers, the
traditional design concepts would appear like that.
[0005] On the contrary, high-handicapped golfers tend to make a
hand swing as the body-led swing is difficult. Especially, the
wrist is much more likely to move largely near the impact position.
As a result, the swing path and ball hitting position become
unstable. Thus, in the case of golf clubs targeted at
high-handicapped golfers, on the assumption of miss shots, it is
desirable that the club head is increased in the moment Ix of
inertia as large as possible. As to the club shaft, on the other
hand, it is considered as ideal that the torque is increased so as
to cancel the variation of the golf club swing motions and also in
order to increase the ball launch angle. In the case of a club
shaft having a large torque, its twist can absorb unfavorable wrist
motion, and thus the directional stability is not so decreased by
the unfavorable wrist motion. During downswing from the top
position, the club head is rotated around the shaft center line due
to the twist of the club shaft, because the center of gravity of
the club head is positioned at a certain distance from the shaft
center line. Accordingly, the amount of the rotation becomes larger
as the shaft-torque becomes larger. If this rotational motion is
large, the ball launch angle becomes increased owing to the loft
angle.
[0006] In general, it is ideal that, during downswing from the top
position, the club face is once largely opened, and the opened club
face is gradually corrected so as to return the club face to square
at impact. However, if the moment Ix of inertia is large, as the
club head is hard to rotate, it is difficult to return the club
face to square at impact, and the club face is liable to open at
impact as shown in FIG. 6. Thus, there is a tendency for the
high-handicapped golfers to further twist the wrist to make the
club face at square, and as a result, the swing is further
disturbed and the ball direction becomes unstable.
SUMMARY OF THE INVENTION
[0007] It is therefore, an object of the present invention to
provide a golf club easy to use for high-handicapped golfers, in
which the returning of the club face at impact and the head
movement when missed a shot are improved and the directional
stability is improved.
[0008] According to the present invention a golf club comprises a
golf club shaft and a golf club head attached to a tip end of the
golf club shaft, wherein a moment Ix of inertia of the golf club
head around a vertical axis passing through the center of gravity
of the club head is not less than 3800 (gsq.cm), and a shaft-torque
T (degrees) of the golf club shaft and the moment Ix of inertia
satisfy the following condition (1): T=<0.0025.times.Ix-6.0.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a front view of a golf club according to the
present invention showing a club head and a club shaft.
[0010] FIG. 2 is a front view of the club head.
[0011] FIG. 3 is a top view of the club head.
[0012] FIG. 4 is a diagram for explaining a method of measuring a
shaft-torque.
[0013] FIG. 5 shows prepreg pieces used to make the club shaft.
[0014] FIG. 6 is a diagram for explaining an inadequate returning
of the club face at impact.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0015] Embodiment of the present invention will now be described in
detail in conjunction with the accompanying drawings.
[0016] According to the present invention, golf club 1 comprises a
club head 2 and a shaft 3 having an end attached to the head and a
butt end provided with a grip 4. The golf club 1 is a wood type
club inclusive of number one to five wood. The golf club 1 in this
embodiment is a number one wood.
[0017] The club head 2 comprises a face portion 2a whose front face
defines a club face F for striking a ball, a crown portion 2b
intersecting the club face F at the upper edge thereof, a sole
portion 2c intersecting the club face F at the lower edge thereof,
a side portion 2d between the crown portion and sole portion which
extends from a toe-side edge to a heel-side edge of the club face
through the back face of the club head, and a hosel portion 2e to
be attached to an end of a club shaft 3.
[0018] Here, the definitions of the undermentioned terms are
provided:
[0019] "Standard state" of the club head is that the club head is
set on a horizontal plane HP so that the shaft center line CL is,
within a vertical plane VP, inclined at its lie angle alpha with
respect to the horizontal plane HP, and the club face F is inclined
at its face angle beta with respect to the vertical plane VP,
wherein the face angle beta is, as shown in FIG. 3, an angle
between a horizontal tangential line N to the sweet spot SS on the
club face F the vertical plane VP.
[0020] "Sweet spot SS" is a point on the club face F which is the
intersecting point of a straight line, which is drawn perpendicular
to the club face F from the center G of gravity of the club head,
with the club face F.
[0021] "Moment Ix of inertia" is a moment of inertia of a club head
alone around the vertical axis VL passing through the center G of
gravity of the club head in the standard state. The club head
includes a coating painting but excludes a socket for the shaft
disposed at the hosel. In this specification, the values measured
with a device manufactured by INERTIA DYNAMICS Inc. are shown.
[0022] "overall length L" of the club is, as shown in FIG. 1,
defined as a length measured in the standard state from the end 4e
of the grip 4 to the intersecting point P of the shaft center line
CL with the horizontal plane HP.
[0023] "Shaft-torque" is a twist angle (degrees) of the shaft 3
when, as shown in FIG. 4, holders M1 and M2 are attached to the
shaft 3 at 40 mm and 865 mm, respectively, from the one end 3a and
a torque of 136.3 Ncm is applied to the holder M2 on the butt end
side while fixing the holder M1 on the tip end side.
[0024] In this embodiment, the club head 2 is hollow and made of at
least one kind of metal material, e.g. aluminum alloy, titanium,
titanium alloy, magnesium alloy, stainless and the like. Aside from
such all-metal head, the head may be a hybrid head including a part
made of a nonmetallic material such as fiber reinforced resinous
material. Further, it may be possible to make the entirety of the
head from one or more kinds of nonmetallic materials.
[0025] The head 2 can be manufactured by assembling a plurality of
parts (for example 2 to 4 parts) which are made through appropriate
methods. For example, a metal part may be manufactured by casting,
forging, press forming or the like. In order to fix one part to
another, various methods, e.g. welding, bonding, soldering
diffusion bonding, caulking and the like can be used in accordance
with the materials of the parts.
[0026] For example by changing the material thickness in the sole
portion 2c and/or side portion 2d, the head 2 is formed to have a
moment Ix of inertia in a range of not less than 3800 gsq.cm,
preferably not less than 3850 gsq.cm, more preferably not less than
4050 gsq.cm. If the moment Ix is less than 3800 gsq.cm, the effect
to control a movement of the club head, which is caused by a
reaction force when missed a shot, becomes insufficient, but rather
the problem in the insufficient return motion of the club head
during downswing becomes not remarkable.
[0027] Although it is preferable that the head has a larger moment
Ix, if in compliance with a golf club rule the upper limit of the
head volume is 470 cc, it will be preferable that the moment Ix is
at most 5500 gsq.cm, more preferably not more than 5000 gsq.cm,
still more preferably not more than 4400 gsq.cm from realistic
views such as production efficiency.
[0028] If the volume of the club head 2 is too small, it is
difficult to increase the moment Ix of inertia. If the volume of
the club head 2 is too large, it is difficult to restrain the club
head weight from increasing and the club has a tendency to become
hard to swing. Thus, the head volume is preferably not less than
300 cc, more preferably not less than 320 cc, still more preferably
not less than 350 cc. when compliance with the R&A golf rule,
the upper limit is 470 cc as noted above.
[0029] If the club head is too light, it becomes impossible to
obtain the above-mentioned large moment Ix of inertia. If the club
head is too heavy, the club has a tendency to become hard to swing.
Thus, the weight of the club head is preferably set in the range of
not less than 170 grams, more preferably not less than 175 grams,
still more preferably not less than 180 grams, but preferably not
more than 230 grams, more preferably not more than 220 grams, still
more preferably not more than 210 grams.
[0030] Therefore, the effective control of the head movement when
missed a shot and the return motion of the club head during
downswing can be achieved
[0031] In this embodiment, in order to make a club which is easy to
swing through, the shaft 3 is made from a fiber reinforced resinous
material to have a tubular structure. Further, in view of
flexibility of designing and controllability of the shaft torque,
the use of a fiber reinforced resinous material is preferable.
[0032] As shown in FIG. 4, the outer diameter of the shaft is
decreased from one end 3b provided with a grip 4 to the other end
3a provided with the head 2.
[0033] According to the present invention, the torque T (degrees)
of the shaft 3 satisfies the following condition (1)
T=<0.0025.times.Ix-6.0 (1) preferably, the following condition
(2) T=<0.0025.times.Ix-6.3 (2) more preferably, the following
condition (3) T>=0.0025.times.Ix-8.5 (3) wherein Ix is the
above-mentioned moment Ix of inertia of the head.
[0034] By satisfying these conditions, the twist of the shaft 3
during downswing can be controlled to decrease the rotational
motion of the club head 2 during downswing. As a result, the club
face F becomes easy to return to its original address position, and
the hitting directions become stable.
[0035] The shaft 3 may be manufactured by various methods, for
example: winding or applying prepreg sheets around a mandrel;
winding reinforcing filaments around a mandrel; molding the fiber
reinforced resinous material by pressurizing the inside and the
like.
[0036] In this embodiment, the winding of prepreg sheets is
employed.
[0037] In the case of the shaft made from prepreg, it is necessary
to increase the number of bias prepreg plies in order to decrease
the torque. This results in a heavy shaft which is relatively hard
to swing. If the torque T is too small, the hit feeling becomes
hard and unfavorable. Further, there is a possibility that the
hitting directions become unstable because an improper wrist motion
during golf swing is sensitively transferred to the club head
2.
[0038] Therefore, it is preferable that the torque T is set to be
not less than 1.5 degrees, more preferably not less than 2.0
degrees, still more preferably not less than 2.5 degrees.
[0039] Although the upper limit of the torque T is determined by
the above-mentioned conditional expressions (1) and (2), it is
absolutely desirable that the upper limit is not more than 7.0
degrees, more preferably not more than 6.5 degrees, still more
preferably not more than 6.0 degrees.
[0040] In the case of a club head having a larger moment Ix of
inertia, if a ball hits off the sweet spot, as the club head is
hard to rotate, the impact force is directly transmitted to the
player's hands and as a result, the hit feeling becomes hard. When
the condition (3) is satisfied, as the lower limit of the shaft
torque is changed according to the moment Ix of inertia, the impact
force is absorbed by the twist of the club shaft and a good hit
feel can be obtained. Thus, both of the directional stability and
hit feeling can be achieved.
[0041] If the overall length L of the club 1 is too short, it is
difficult to obtain a long traveling distance or flying distance as
the head speed becomes relatively slow. If the overall length L is
too long, it becomes difficult that the sweet spot meets the ball
and the club becomes awkward.
[0042] Therefore, the overall length L is preferably set in the
range of not less than 43 inches, more preferably not less than 44
inches, still more preferably not less than 45 inches, but
preferably not more than 48 inches, more preferably not more than
47 inches.
Comparison Tests
[0043] Wood-type golf clubs (driver) having the specifications
shown in Table 1 were made and tested for the stability of hitting
direction and the hit feelings.
[0044] The club heads each have a two-piece structure composed of a
head main body formed by casting a titanium alloy 6-4Ti, and a face
member formed by press-molding and milling a rolled titanium alloy
6-4Ti, and the face member and head main body were united by TIG
welding.
[0045] The club heads had a volume of 420 cc and a weight of 195
grams in common, but the heads had different thickness
distributions as the thickness was changed in the sole portion and
side portion to change the moment Ix of inertia.
[0046] The shafts were each formed by applying prepreg pieces. AS
shown in FIG. 5, to form bias plies and longitudinal plies, two
kinds of prepreg manufactured by Toray Industries, Inc., were
used.
[0047] <Bias Ply> [0048] Reinforcing fiber: M40J (tensile
elastic modulus 377GPa) [0049] Resinous material: Epoxy resin
[0050] Resin content: 25%
[0051] <Longitudinal Plies> [0052] Reinforcing fiber: M30S
(tensile elastic modulus 294 Gpa) [0053] Resinous material: Epoxy
resin [0054] Resin content: 25%
[0055] The shaft-torque can be changed by increasing or decreasing
the tensile elastic modulus of the reinforcing fiber, but if the
modulus exceeds 450 Gpa, then the strength is decreased and the
shaft is liable to be broken. Thus, in order to avoid a drastically
change in modulus, the shaft-torque was adjusted by changing the
number of bias plies or layers.
[0056] In the shaft of Ex. 1, the total number of bias plies was
two on the butt end side and five on the tip end side. In the
others, the torque was changed by decreasing or increasing the
number of plies by the same number on both of the butt end side and
tip end side. In order that all the shafts had the same flex, the
areal weight of the prepreg used as the longitudinal plies was
changed.
[0057] The heads and shafts were assembled, and wood type golf
clubs having an overall length of 45 inches were made.
[0058] Directional Stability Test:
[0059] Each of ten golfers having handicaps ranging from 20 to 35
struck three-piece balls (commercially available as "Hi-BRID
everio" manufactured by SRI Sports, co., Ltd.) ten times with each
of the golf clubs. Then, the shortest distance of the stop position
of the ball from a straight line drawn from the hitting point to
the target point was measured to obtain a hundred measured values
(ten times.times.ten golfers) per a golf club. The results are
indicated in Table 1 as the average of a hundred values. The
smaller the value, the better the directional stability.
[0060] Hit Feeling Test:
[0061] Through the above-mentioned directional stability test, the
golfers evaluated the hit feeling of each club based on the
following criteria. TABLE-US-00001 5: soft and very good 4: fairly
soft and good 3: usual 2: slightly hard and not good 1: hard and
singularly bad
[0062] The average values of the ten golfers' evaluations are
indicated in Table 1.
[0063] Swing Feeing Test:
[0064] Through the above-mentioned directional stability test, the
golfers evaluated the swing feeling of each club based on the
following criteria. TABLE-US-00002 5: very easy 4: easy 3: usual 2:
slightly difficult 1: very difficult
[0065] The average values of the ten golfers' evaluations are
indicated in Table 1. TABLE-US-00003 TABLE 1 Club Ref. 1 Ref. 2 Ex.
1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Moment Ix
of inertia 3850 4400 3850 4100 4400 4100 4100 4100 3960 4300 4250
4350 (g sq. cm) Shaft-torque T (degs.) 4.5 5.7 3.3 4 4.7 2.5 2 1.3
2.8 3.7 2.3 2.8 Shaft weight (g) 50 48 58 53 50 63 67 75 61 55 65
61 Directional stability 56.8 51.2 36.7 33.2 31.6 30.8 29.2 26.3
35.3 31.2 29.6 30.3 (distance in yard) Hit feeling 4.3 4.5 4 4.2
4.4 3.3 2.6 2.1 3.6 3.7 2.5 2.8 Swing feeing 4.3 4.1 3.6 3.9 4.5
3.1 2.7 2.2 3.3 3.8 2.9 3.5
[0066] From the test results, it was confirmed that the directional
stability can be improved.
[0067] As descried above, in the golf club according to the present
invention, as the moment is limited in a specific range,
directional stability can be maintained even when missed a shot.
Further, by providing a lower limit for the shaft-torque, an
incidental unfavorable wrist motion at or near impact becomes hard
to transmit to the club head, and the directional stability can be
improved. Also hit feeling can be improved.
* * * * *