U.S. patent application number 14/694998 was filed with the patent office on 2015-08-13 for golf club head.
This patent application is currently assigned to Taylor Made Golf Company, Inc.. The applicant listed for this patent is Taylor Made Golf Company, Inc.. Invention is credited to Todd P. Beach, Mark Vincent Greaney, Brandon Woolley, Ian Wright.
Application Number | 20150224374 14/694998 |
Document ID | / |
Family ID | 40899812 |
Filed Date | 2015-08-13 |
United States Patent
Application |
20150224374 |
Kind Code |
A1 |
Greaney; Mark Vincent ; et
al. |
August 13, 2015 |
GOLF CLUB HEAD
Abstract
A golf club head comprises a club head body having an external
surface with a heel portion, a toe portion, a crown, a sole, and a
face. The golf club head has a moment of inertia about a CG Z axis,
I.sub.ZZ. In some implementations, I.sub.ZZ is greater than 4150
gcm.sup.2 or greater than 4400 gcm.sup.2. The face comprises a
bulge curvature that satisfies a predetermined mathematical
relationship. In some implementations, a moment of inertia about
the CG X axis, I.sub.xx, exceeds a predetermined value, and
I.sub.zz is greater than I.sub.xx. The face can comprise a roll
curvature, and a ratio of the bulge curvature divided by the roll
curvature, R.sub.C, can be greater than 0.28 and less than
0.75.
Inventors: |
Greaney; Mark Vincent;
(Vista, CA) ; Woolley; Brandon; (Vista, CA)
; Wright; Ian; (Portland, OR) ; Beach; Todd
P.; (Encinitas, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Taylor Made Golf Company, Inc. |
Carlsbad |
CA |
US |
|
|
Assignee: |
Taylor Made Golf Company,
Inc.
|
Family ID: |
40899812 |
Appl. No.: |
14/694998 |
Filed: |
April 23, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14133907 |
Dec 19, 2013 |
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14694998 |
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13657065 |
Oct 22, 2012 |
8616999 |
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14133907 |
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13447609 |
Apr 16, 2012 |
8292756 |
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13657065 |
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13204487 |
Aug 5, 2011 |
8157672 |
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13447609 |
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12316921 |
Dec 16, 2008 |
8012039 |
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13204487 |
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61080203 |
Jul 11, 2008 |
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61008690 |
Dec 21, 2007 |
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Current U.S.
Class: |
473/330 |
Current CPC
Class: |
A63B 53/0466 20130101;
A63B 53/0416 20200801; A63B 53/0408 20200801; A63B 60/00 20151001;
A63B 53/0458 20200801 |
International
Class: |
A63B 53/04 20060101
A63B053/04 |
Claims
1. A golf club head comprising: a club head body having an external
surface with a heel portion, a toe portion, a crown, a sole, and a
face; and a moment of inertia about a CG Z axis, I.sub.ZZ, wherein
I.sub.ZZ is greater than 4400 gcm.sup.2; wherein the face
comprises: a bulge curvature; and wherein the bulge curvature
satisfies the following relationship 1 0.00466 .times. I zz + 23.54
.ltoreq. bu 1 g ecurvature .ltoreq. 1 0.00459 .times. I zz + 14.39
. ##EQU00010##
2. The golf club head of claim 1, wherein the golf club head has a
moment of inertia about a CG X axis, I.sub.XX, and wherein I.sub.XX
is at least 2500 gcm.sup.2 and I.sub.ZZ is greater than
I.sub.xx.
3. The golf club head of claim 1, wherein the bulge curvature is
between 0.016 cm.sup.-1 and 0.027 cm.sup.-1.
4. The golf club head of claim 1, wherein the face comprises a roll
curvature, and wherein the roll curvature is between 0.033
cm.sup.-1 and 0.066 cm.sup.-1.
5. The golf club head of claim 4, wherein a ratio of the bulge
curvature divided by the roll curvature is between 0.28 and 0.75 at
a roll curvature between 0.033 cm.sup.-1 and 0.066 cm.sup.-1.
6. The golf club head of claim 4, wherein a ratio of the bulge
curvature divided by the roll curvature is between about 0.33 and
about 0.75 when the I.sub.zz is between 4400 gcm.sup.2 and 5000
gcm.sup.2.
7. The golf club head of claim 1, wherein a ratio of the bulge
curvature divided by the roll curvature is less than 0.84 at a roll
curvature of 0.049 cm.sup.-1.
8. The golf club head of claim 1, wherein the bulge curvature and
the roll curvature are constant over the face of the golf club
head.
9. A golf club head comprising: a club head body having an external
surface with a heel portion, a toe portion, a crown, a sole, and a
face; a moment of inertia about the CG Z axis, I.sub.zz, wherein
I.sub.zz is greater than 4150 gcm.sup.2; and a moment of inertia
about the CG X axis, I.sub.xx, wherein I.sub.zz is greater than
I.sub.xx; wherein the face comprises a bulge curvature and a roll
curvature; and wherein a ratio of the bulge curvature divided by
the roll curvature, R.sub.C, is greater than 0.28 and less than
0.75.
10. The golf club head of claim 9, wherein the bulge curvature is
between 0.016 cm.sup.-1 and 0.027 cm.sup.-1.
11. The golf club head of claim 9, wherein the bulge curvature is
between 0.023 cm.sup.-1 and 0.027 cm.sup.-1.
12. The golf club head of claim 9, wherein the roll curvature is
between 0.033 cm.sup.-1 and 0.066 cm.sup.-1.
13. The golf club head of claim 9, wherein the ratio of the bulge
curvature divided by the roll curvature, R.sub.C, satisfies the
following: 1 ( 5.6 .times. 10 - 4 * I ZZ ) + 0.222 .ltoreq. R C
.ltoreq. 1 ( 2.8 .times. 10 - 4 * I ZZ ) + 0.111 . ##EQU00011##
14. The golf club head of claim 9, wherein the bulge curvature is
determined by with multiple measurements of the golf club head
taken on an optical comparator.
15. The golf club head of claim 14, wherein measurements for a
given axis are taken at the center of the face, at a first distance
in both directions of the axis and at a second distance in both
directions of the axis, wherein the second distance is longer than
the first distance, thereby yielding five measurement points, and
wherein an arc is fit through the five measurement points to
determine the bulge curvature.
16. The golf club head of claim 9, wherein the face comprises a
front side and a back side that define a variable face
thickness
17. The golf club head of claim 9 wherein the golf club head has a
mass between 170 grams and 220 grams.
18. A golf club head comprising: a club head body having an
external surface with a heel portion, a toe portion, a crown, a
sole, and a face; and a moment of inertia about the CG Z axis,
I.sub.zz, wherein I.sub.zz is greater than 4150 gcm.sup.2; and a
moment of inertia about the CG X axis, I.sub.xx, wherein I.sub.zz
is greater than I.sub.xx; wherein the face comprises: a bulge
curvature; and wherein the bulge curvature satisfies the following
relationship 1 0.00466 * I zz + 23.54 .ltoreq. bu 1 g ecurvature
.ltoreq. 1 0.00459 * I zz + 14.39 . ##EQU00012##
Description
CROSS-REFERENCE TO OTHER APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/133,907, filed Dec. 19, 2013, which is a
continuation of U.S. patent application Ser. No. 13/657,065, filed
Oct. 22, 2012, now U.S. Pat. No. 8,616,999, which is a continuation
of U.S. patent application Ser. No. 13/447,609, filed Apr. 16,
2012, now U.S. Pat. No. 8,292,756, which is a continuation of U.S.
patent application Ser. No. 13/204,487, filed Aug. 5, 2011, now
U.S. Pat. No. 8,157,672, which is a continuation of U.S. patent
application Ser. No. 12/316,921, filed Dec. 16, 2008, now U.S. Pat.
No. 8,012,039, which claims the benefit of U.S. Provisional
Application Nos. 61/080,203, filed Jul. 11, 2008, and 61/008,690,
filed Dec. 21, 2007, all of which applications are incorporated
herein by reference.
FIELD
[0002] The present disclosure relates to a golf club head. More
specifically, the present disclosure relates to a face plate of a
wood-type golf club head, such as a driver or fairway wood, that is
designed to hit a ball farther and more accurately when the face
plate hits the ball outside of the "sweet spot."
BACKGROUND
[0003] When a golf club head strikes a golf ball, a force is seen
on the club head at the point of impact. If the point of impact is
aligned with the center of gravity (CG) of the golf club head in an
area of the club face typically called the sweet spot, then the
force has minimal twisting or tumbling effect on the golf club.
However, if the point of impact is not aligned with the CG, outside
the sweet spot for example, then the force can cause the golf club
head to twist around the CG. This twisting of the golf club head
causes the golf ball to acquire spin. For example, if a typical
right handed golfer hits the ball near the toe of the club this can
cause the club to rotate clockwise when viewed from the top down.
This in turn causes the golf ball to rotate counter-clockwise which
can result in the golf ball curving to the left. This phenomenon is
what is commonly referred to as "gear effect." Recent manufacturing
techniques that allow for a higher coefficient of restitution (COR)
or the use of inverted cone technology (ICT) increase this gear
effect.
[0004] Bulge and roll are golf club face properties that are
generally used to compensate for this gear effect. The term "bulge"
on a golf club typically refers to the rounded properties of the
golf club face from the heel to the toe of the club face. If a club
face is rounded, then the angle that the golf ball leaves the club
face relative to the intended target line will be increased for
off-center shots. For example, if a golf ball is hit near the heel
of the club face, then the ball will leave in an initial direction
to the left of the target line. As suggested above, with an
off-center heel shot the ball can curve to the right so ideally the
two effects will neutralize one another and produce a flight path
that lands the ball close to the intended target line.
[0005] The term "roll" on a golf club typically refers to the
rounded properties of the golf club face from the crown to the sole
of the club face. When the club face hits the ball, the ball
acquires some degree of backspin. Typically this spin is greater
for shots hit below the center line of the club face than for shots
hit above the center line of the club face.
[0006] Recent advances in manufacturing techniques and materials
properties have enabled golf club manufacturers to increasingly
vary the weight, shape and center of gravity of golf club heads.
These advances allow the moment of inertia ("MOI") of the golf club
heads to be increased, as disclosed for example in U.S. Pat. No.
6,648,773 B1 to Evans. Thus, the club head twists less when it
strikes the ball off-center, as described above. This decreased
twisting can lead to decreased ball spin, depending on the location
of ball contact. Recent developments in high MOI clubs having
conventional face configurations can lead to greater deviation for
shots away from center face.
SUMMARY
[0007] In one embodiment, the present disclosure describes a golf
club head comprising a club head body having an external surface
with a heel portion, a toe portion, a crown, a sole, and a face.
The club head further includes a moment of inertia about the CG Z
axis, I.sub.zz, which is at least about 4400 gcm.sup.2. The face
further includes a bulge curvature and a roll curvature, and the
bulge curvature is between about 0 cm.sup.-1 and about 0.027
cm.sup.-1 and the inverse of the bulge curvature is greater than
the inverse of the roll curvature by at least 7.62 cm. In one
embodiment, the moment of inertia about the CG x-axis, I.sub.xx, is
at least about 2500 gcm.sup.2, and in another embodiment I.sub.xx
is at least about 3000 gcm.sup.2. In certain embodiments, I.sub.zz
is greater than I.sub.xx. In another embodiment, the face includes
a front side and a back side that define a variable face
thickness.
[0008] In certain embodiments, the ratio of the bulge curvature
divided by the roll curvature is between about 0.28 and about 0.75
at a roll curvature between about 0.033 cm.sup.-1 and about 0.066
cm.sup.-1. In one embodiment, the ratio of the bulge curvature
divided by the roll curvature is between about 0.33 and about 0.75
when I.sub.zz is between about 4400 gcm.sup.2 and about 5000
gcm.sup.2. In another embodiment, the ratio of the bulge curvature
divided by the roll curvature is between about 0.31 and about 0.67
when the I.sub.zz is between about 5000 gcm.sup.2 and about 5500
gcm.sup.2. In a one embodiment, the ratio of the bulge curvature
dived by the roll curvature is between about 0.28 and about 0.61
when the I.sub.zz is between about 5500 gcm.sup.2 and about 6000
gcm.sup.2. In yet another embodiment, the ratio of the bulge
curvature divided by the roll curvature is between about 0.28 and
about 0.56 when the I.sub.zz is about 6000 gcm.sup.2.
[0009] In certain described embodiments, the bulge curvature is
between about 0.016 cm.sup.-1 and about 0.027 cm.sup.-1. In other
embodiments, the roll curvature is between about 0.033 cm.sup.-1
and about 0.066 cm.sup.-1. In one embodiment, the ratio of the
bulge curvature divided by the roll curvature is less than about
0.84 at a roll curvature of about 0.049 cm.sup.-1. In some
embodiments, the bulge curvature and the roll curvature are
constant over the face of the golf club head.
[0010] In another embodiment, the present disclosure describes a
golf club head comprising a club head body wherein the moment of
inertia abut the CG Z axis, I.sub.zz, is at least about 4400
gcm.sup.2, and the moment of inertia about the CG X axis, I.sub.xx,
is at least about 2500 gcm.sup.2 and I.sub.zz is greater than
I.sub.xx. Further, the ratio of the bulge curvature divided by the
roll curvature, R.sub.C, satisfies the following equation:
1 3.3 .times. 10 - 4 .times. I zz + 0.9154 .ltoreq. R c .ltoreq. 1
1.7 .times. 10 - 4 .times. I zz + 0.4574 . ##EQU00001##
[0011] In some embodiments, the golf club head has a volume greater
than about 300 cubic centimeters, and the golf club head has a mass
between about 170 grams and about 220 grams. In one embodiment, the
golf club head has a volume between about 400 cubic centimeters and
about 470 cubic centimeters.
[0012] In yet another embodiment, the present disclosure describes
a golf club having a grip, a shaft and a golf club head, wherein
the golf club head comprises a club head body wherein the moment of
inertia abut the CG Z axis, I.sub.zz, is at least about 4400
gcm.sup.2, and the moment of inertia about the CG X axis, I.sub.xx,
is at least about 2500 gcm.sup.2 and I.sub.zz is greater than
I.sub.xx. The ratio of the bulge curvature divided by the roll
curvature, R.sub.C, satisfies the following equation:
1 ( 5.6 .times. 10 - 4 * I ZZ ) + 0.222 .ltoreq. R C .ltoreq. 1 (
2.8 .times. 10 - 4 * I ZZ ) + 0.111 . ##EQU00002##
[0013] The foregoing and other objects, features, and advantages of
the invention will become more apparent from the following detailed
description, which proceeds with reference to the accompanying
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is an illustration of an embodiment of a golf club
according to the present disclosure.
[0015] FIG. 2 is an illustration of an embodiment of a golf club
including the club head of FIG. 1.
[0016] FIG. 3 is an illustration of the golf club head striking a
golf ball on the heel of the golf club head.
[0017] FIG. 4 is an exaggerated top-down illustration of an
exemplary flight path of a golf ball hit by a club head with a
first bulge radius.
[0018] FIG. 4A is an exaggerated top-down illustration of an
exemplary flight path of a golf ball hit by a club head with a
second bulge radius.
[0019] FIG. 4B is an exaggerated top-down illustration of different
flight paths of a golf ball according to varying moments of inertia
along the Z axis, I.sub.zz.
[0020] FIG. 5 is a side-view illustration of different flight paths
of a golf ball with varying amounts of backspin according to the
present disclosure.
[0021] FIG. 6A is a cross-sectional illustration along the Z-axis
of the golf club face according to the present disclosure.
[0022] FIG. 6B is a cross-sectional illustration along the X-axis
of the golf club face according to the present disclosure.
[0023] FIG. 7 is a graph of computer simulated experimental results
indicating a preferred roll radius at different club
headspeeds.
[0024] FIG. 8 is a graph illustrating the relationship between
distance and moment of inertia along the X axis, I.sub.xx, using
different roll radii according to the present disclosure.
[0025] FIG. 9 is a graph illustrating the relationship between the
ideal bulge radius and I.sub.zz.
DETAILED DESCRIPTION
General Configuration of the Golf Club Head
[0026] FIGS. 1 and 2 show a golf club 1 comprising a grip 2, a
shaft 3, and a club head 4. The club head 4 includes a center face
5a, a heel 5b, a toe 5c, a crown 5d, and a sole 5e. The club head 4
further comprises a club face 6 including a curvature from the heel
5b to the toe 5c commonly called a bulge 8. The club face 6 also
includes a curvature from the crown 5d to the sole 5e commonly
called a roll 9. In at least one embodiment, the combination of
curvatures may provide a club face 6 with a substantially toroidal
shape, or a shape similar to a section of a toroid. The club face 6
further includes an X-axis X which extends horizontally through the
center face 5a from the heel 5b to the toe 5c, a Z-axis Z which
extends vertically through the center face 5a from the crown 5d to
the sole 5e, and a Y-axis Y which extends horizontally through the
center face and into the page in FIG. 2. The X-axis X, Y-axis Y,
and Z-axis Z are mutually orthogonal to one another.
[0027] As shown in FIG. 3, the club head 4 additionally has a
center of gravity (CG) 5f which is internal to the club head. The
club head 4 has a CG X-axis, a CG Y-axis, and a CG Z-axis which are
mutually orthogonal to one another and pass through the CG 5f to
define a CG coordinate system. The CG X-axis and CG Y-axis lie in a
horizontal plane parallel to a flat ground surface. The CG Z-axis
lies in a vertical plane orthogonal to a flat ground surface. In
one embodiment the CG Y-axis may coincide with the Y-axis Y, but in
most embodiments the axes do not coincide.
[0028] Embodiments of the presently disclosed club head 4 have a
volume between about 300 cubic centimeters (cc) to about 500 cc, as
measured by the currently standard USGA water displacement test.
Preferred embodiments have a volume between about 400 cc to about
470 cc. Other embodiments may have a volume even greater than 500
cc. Additionally, embodiments of the presently disclosed club head
4 have a mass between about 170 grams and about 220 grams, though
higher or lower mass may be used and still stay within the spirit
and scope of the disclosure.
[0029] FIG. 3 is an exaggerated depiction of the club head 4
striking a golf ball 10 on the heel 5b of the club head. As shown,
and as will be further described in FIG. 4B, this imparts a
clockwise spin to the golf ball 10 which causes the golf ball 10 to
curve to the right during flight. As discussed above, striking the
golf ball 10 on the heel 5b of the club head 4 will cause the golf
ball 10 to leave the club head 4 at an angle .THETA. relative to
the CG Y-axis of the club head 4. It will be understood that the
angle .THETA. merely depicts a general angle at which the ball will
leave the club head and is not intended to depict or imply the
actual angle relative to the centerline, or the point from which
that angle would be measured. Angle .THETA. further illustrates
that a ball struck on the heel of the club will initially travel on
a flight path to the left of the centerline.
Bulge and Roll--Terminology
[0030] The method used to obtain the values in the present
disclosure is the optical comparator method. Referring back to FIG.
1, the club face 6 includes a series of score lines 11 which
traverse the width of the club face generally along the X-axis X of
the club head 4. In the optical comparator method, the club head 4
is mounted face down and generally horizontal on a V-block mounted
on an optical comparator. The club head 4 is oriented such that the
score lines 11 are generally parallel with the X-axis of the
optical comparator. More precise orientation steps may also be
used. Measurements are then taken at the geometric center point 5a
on the club face. Further measurements are then taken 20
millimeters away from the geometric center point 5a of the club
face 6 on either side of the geometric center point 5a and along
the X-axis X of the club head, and 30 millimeters away from the
geometric center point of the club face on either side of the
center point and along the X-axis X of the club head. An arc is fit
through these five measure points, for example by using the radius
function on the machine. This arc corresponds to the circumference
of a circle with a given radius. This measurement of radius is what
is meant by the bulge radius.
[0031] To measure the roll, the club head 4 is rotated by 90
degrees such that the Z-axis Z of the club head is generally
parallel to the X-axis of the machine. Measurements are taken at
the geometric center point 5a of the club face. Further
measurements are then taken 15 millimeters away from the geometric
center point 5a and along the Z-axis Z of the club face 6 on either
side of the center point 5a, and 20 millimeters away from the
geometric center point and along the Z-axis of the club face on
either side of the center point. An arc is fit through these five
measurement points. This arc corresponds to the circumference of a
circle with a given radius. This measurement of radius is what is
meant by the roll radius.
[0032] Curvature is defined as 1/R wherein R is the radius of the
circle which corresponds to the measurement arc of the bulge or the
roll. As an example, a bulge with a curvature of 0.020 cm.sup.-1
corresponds to a bulge measured by a bulge measurement arc which is
part of a circle with a radius of 50 cm. A roll with a curvature of
0.050 cm-1 corresponds to a roll measured by a roll measurement arc
which is part of a circle with a radius of 20 cm.
Moments of Inertia (MOI)
[0033] Golf club head moments of inertia are typically defined
about axes extending through the golf club head center of gravity.
In general, and as shown in FIGS. 2 and 3, the club head 4 center
of gravity 5f is positioned within the club head. FIG. 3 further
illustrates the CG X-axis CGX and the CG Y-axis CGY which pass
through the center of gravity 5f. The CG Z-axis (not shown) passes
through the center of gravity 5f and out of the page. The center of
gravity 5f is located approximately midway between the heel 5b and
the toe 5c along the CG X-axis, and approximately midway between
the crown 5d and the sole 5e along the CG Z-axis of the club head
4. Additionally, as shown by FIG. 3, the center of gravity 5f is
located approximately midway between the club face 6 and the rear
of the club 12 along the CG Y-axis of the club head 4. It is
understood that the center of gravity 5f position will vary based
on a variety of club head features.
[0034] A moment of inertia about a golf club head CG X-axis such as
that shown in FIG. 2, is calculated by the following equation:
I.sub.XX=.intg.(y.sup.2+z.sup.2)dm
where y is the distance from a golf club head CG XZ-plane to an
infinitesimal mass dm and z is the distance from a golf club head
CG XY-plane to the infinitesimal mass dm. The golf club head CG
XZ-plane is a plane defined by the golf club head CG X-axis and the
golf club head CG Z-axis, as shown in FIGS. 2 and 3.
[0035] Similarly, a moment of inertia about the golf club head CG
Z-axis is calculated by the following equation:
I.sub.ZZ=.intg.(x.sup.2+y.sup.2)dm
where x is the distance from the golf club head CG YZ-plane to an
infinitesimal mass dm and y is the distance from the golf club head
CG XZ-plane to the infinitesimal mass dm.
[0036] According to the present disclosure, the MOI about the CG X
axis I.sub.xx is at least about 2500 gcm.sup.2 and can be as high
as about 5000 gcm.sup.2. The MOI about the CG Z axis I.sub.zz is
greater than I.sub.xx and is at least about 4400 gcm.sup.2 and can
be as high as about 6000 gcm.sup.2. It is understood that the MOI
about the CG Z axis can be higher than 6000 gcm.sup.2.
[0037] Conventional club face geometry is not necessarily
compatible with high MOI clubs. Thus, a change in bulge and roll
geometry is described in view of these increased MOIs about the CG
X-axis I.sub.xx and the CG Z-axis I.sub.zz.
Increased I.sub.zz and Increased Bulge Radius
[0038] If the MOI around the CG Z axis I.sub.zz is increased, then
the gear effect for off-center hits will be reduced as explained
above. This will result in the golf ball 10 acquiring less spin and
thus curving less in flight. With conventional bulge geometry, the
reduced spin of a heel shot makes it less likely that the ball's
flight path initially to the left of the target line will return to
the target line upon landing. Similarly, with conventional bulge
geometry the reduced spin of a toe shot makes it less likely that
the ball's initial flight path to the right of the intended target
line will return to the target line upon landing. However, if the
radius of the bulge 8 is increased to flatten the club face 6, then
a golf ball 10 struck on the heel 5b of the club head 4 will leave
at a smaller angle .THETA. relative to the centerline of the swing
20, compensating for the reduced gear effect associated with a club
having a relatively high MOI.
[0039] FIG. 4 illustrates a hypothetical club head face 6 that has
an exaggerated bulge but no gear effect striking a golf ball with
the heel 5b of the club head. Flight path 41 shows the flight path
of a golf ball leaving a club head face 6 with a first bulge and
with no gear effect at some angle .THETA..sub.1 relative to the
Y-axis of the golf club 20. By contrast, FIG. 4A illustrates the
flight path 42 of a golf ball leaving a club head face 6' (again
with no gear effect) having a second bulge with a radius greater
than the first bulge shown in FIG. 4. Flight path 42 leaves the
golf club at some angle .THETA..sub.2 relative to Y-axis of the
golf club 20. It can be seen that .THETA..sub.2 is less than
.THETA..sub.1 due to the flatter surface of club head face 6'.
[0040] FIG. 4B illustrates two hypothetical club heads that have no
bulge but do have differing moments of inertia I.sub.zz which
produce differing gear effects as discussed above. Flight path 43
shows the flight path of a golf ball leaving a club head face of a
club having a lower I.sub.zz, and thus a higher gear effect. It can
be seen that the flight path 43 curves more to the right due to
greater ball spin. By contrast, flight path 44 shows the flight
path of a golf ball leaving a club head face having an increased
I.sub.zz, and thus a reduced gear effect. It can be seen that
flight path 44 curves less than flight path 43. As described above,
the flight paths 43, 44 curve because the club head rotates when
the club head strikes a ball at a point not aligned with the center
face of the club head. This twisting causes the ball to acquire a
spin which results in a curved flight path. If the club head has a
higher I.sub.zz then it will twist less than a club head with a
lower I.sub.zz and impart less spin (and thus a straighter flight
path) to the golf ball.
Increased I.sub.xx and Decreased Roll Radius
[0041] Making reference to elements described in FIGS. 1 and 2, the
roll 9 of the club head 4 can contribute to the amount of backspin
that the golf ball 10 acquires when it's struck by the club head 4
at a point on the club face 6 either above or below the center face
5a of the club head 4. Shots struck at a point on the club face 6
below the center face 5a of the club head 4 have a greater amount
of backspin than shots struck above the center face 5a, as
described above. FIG. 5 shows the flight path 51 of a golf ball 10
with a high amount of backspin. It can be seen that the flight path
"balloons" upward and then drops precipitously. By contrast a
flight path 52 is shown of a golf ball 10 with a lower amount of
backspin. It can be seen that the flight path "balloons" much less
and thus the ball travels farther.
[0042] If the roll 9 of the club head is decreased, there will be a
decreased variance between backspin for shots struck above the
center of face 5a of the club head 4 and shots struck below the
center face 5a. A similar effect is observed when the MOI about the
X axis, I.sub.xx, is increased; namely less twisting of the golf
club head 4. When the golf ball 10 is struck at a point below the
center face 5a of the club head 4, this reduction in twisting of
the golf club head 4 ultimately results in less variance in
backspin between shots struck above the center face 5a of the club
head 4 and shots struck below the center face. By combining the
effects of the increased MOI, I.sub.xx, and the decreased roll 9,
the variance of backspin between a shot struck above the center
face 5a of the club head 4 and a shot struck below the center face
5a of the club head 4 will be decreased, thus decreasing the
variance in the landing position of a golf ball 10. Furthermore,
altering the roll of a club head may affect launch angle. Because
the launch angle will also affect the landing position of the ball,
a roll for a golf club head may be selected that balances a desired
launch angle with a desired spin to provide desired performance of
the golf club.
Effects of Variable Face Thickness
[0043] Additional factors may likewise contribute to gear effect.
One such factor is variable face thickness, wherein the club face 6
has a variable thickness at different areas of the club face.
Generally this thickness is measured as defining a front side and a
back side of the club face 6, and then measuring the distance
between the front side and the back side and a plurality of points,
although different measurement techniques are also permissible and
fall within the spirit and scope of this disclosure. Examples of
variable face thickness can be found in U.S. Pat. Nos. 6,800,038,
6,824,475, 6,997,820, and 7,066,832, which are owned by the
assignee of the present disclosure and the contents of which are
herein incorporated by reference. FIGS. 6A and 6B show
cross-sectional views of one possible example of a club face 6
having a variable face thickness which is thinner at a center
portion 7 of the club face than at other areas of the club
face.
[0044] The variable face thickness can create a higher ball speed
for shots struck off center, for example near the heel 5b or the
toe 5c of the club face 6. This effect increases the overall
effective area of the COR on the club face 6. The variable face
thickness can also limit the COR at the center face of the club
face 5a to be below the legal limit. As described above, a higher
COR generally leads to an increased gear effect. It will be
understood, then, that the combination of the COR and the variable
face thickness increases the gear effect for shots struck off
center, thus reinforcing the need for a club face 6 with a higher
bulge 8 and a lower roll 9 to compensate for the increase in gear
effect.
Trends in Simulated Results--Roll
[0045] The preferred embodiment of the present disclosure has a
roll radius that is less than the bulge radius. In certain
embodiments the bulge radius is 7.62 cm greater than the roll
radius. The bulge curvature is between about 0 cm.sup.-1 and about
0.027 cm.sup.-1 and the inverse of the bulge curvature is greater
than the inverse of the roll curvature by at least 7.62 cm,
although other embodiments may have more or less of a difference.
In other words, the bulge curvature, K.sub.b (cm), and roll
curvature, K.sub.r (cm) satisfy the equation:
1 K b .gtoreq. 1 K r + 7.62 ( cm ) ##EQU00003##
[0046] Computer simulations were performed with a variety of
different testing parameters. FIG. 7 shows the average carry
distance, in yards, for a plurality of headspeeds and MOIs about
the X axis I.sub.xx. Graphs are depicted for headspeeds of 70 mph
(72), 90 mph (74), and 103 mph (76). In each of these graphs, the
X-axis depicts roll radii in centimeters, and the Y-axis depicts
the average carry distance in yards. Each line depicts simulated
results for a different MOI about the X axis I.sub.xx as indicated
by the legends 72(a), 74(a), and 76(a), respectively. These graphs
were produced by a computer simulation where the club face impacted
a ball at a point on the club face corresponding to the center
face, 1.27 cm above the point on the club face corresponding to the
center face, and 1.27 cm below the point on the club face
corresponding to the center face. The results of these impacts were
then averaged together. In general, the graphs depict a relatively
constant carry distance from a roll radius of about 20 cm to about
30 cm, corresponding to roll curvatures of about 0.033 cm.sup.-1 to
about 0.050 cm.sup.-1. This constancy can be particularly seen for
higher I.sub.xx values such as the lines corresponding to I.sub.xx
values of 4500 gcm.sup.2 and 5000 gcm.sup.2 shown in graph 76. This
constancy in the computer simulation indicates that, for the
majority of head speeds and I.sub.xx values, the roll radius should
be between about 15.2 cm and about 30.5 cm, corresponding to roll
curvatures of between about 0.033 cm.sup.-1 and about 0.066
cm.sup.-1. As indicated by these computer simulations, an ideal
range of roll radii is between about 20.3 cm and about 25.4 cm,
corresponding to a preferred roll curvature range between about
0.039 cm.sup.-1 and about 0.049 cm.sup.-1.
[0047] FIG. 8 depicts a graph 80 showing roll for a plurality of
different MOI around the CG X axis, I.sub.xx, according to computer
simulations using one exemplary embodiment. For these simulations,
the bulge radius was set at 35.56 cm, corresponding to a bulge
curvature of about 0.028 cm.sup.-1, and the I.sub.zz value was set
at 5160 gcm.sup.2. Impact locations were simulated for impacts at
the point on the club face corresponding to the center face, on the
Z-axis Z 1.27 cm above the center face of the club, and on the
Z-axis Z 1.27 cm below the point on the club face corresponding to
the center face. The average distance (in yards) of ball travel is
depicted along the Y axis of graph 80, and MOI about the CG X axis
I.sub.xx is depicted along the X axis of the graph. Each of the
different lines corresponds to a different roll radius as indicated
by key 82. As can be seen by graph 80, the roll radius for MOI
about the CG X axis I.sub.xx, below about 4150 gcm.sup.2, is 20.3
cm, corresponding to a roll curvature of about 0.049 cm.sup.-1. The
roll radius for MOI about the CG X axis I.sub.xx, above about 4150
gcm.sup.2, is 25.4 cm, corresponding to a roll curvature of about
0.039 cm.sup.-1. In other examples, the relationships may be
different based upon factors such as club size or configuration,
wind, or club headspeed, These factors may combine to alter the
ideal roll radius for different MOI about the CG X axis I.sub.xx,
and may additionally result in different average distance
measurements dependant upon environmental and user-related
factors.
Trends in Simulated Results--Bulge
[0048] Computer simulations were performed to determine bulge radii
for a variety of MOIs about the CG Z axis, I.sub.zz. The data used
to calculate these simulated results is based on a series of
simulated impacts using a variable inertia club model. Impacts were
modeled on the center face X-axis X 1.905 cm away from the point on
the club face corresponding to the center face of the golf club
towards the heel and the toe of the golf club, and on the X-axis X
3.175 cm away from the point on the club face corresponding to the
center face of the golf club towards the heel and the toe. Impact
speeds used were 70 mph, 90 mph, 103 mph, and 130 mph. For this
test, I.sub.zz values ranged from 4000 gcm.sup.2 to 6000 gcm.sup.2.
Results for the tests were then averaged and are shown in Tables 1
and 2, below. Table 1 represents averaged results for hits 1.905 cm
away from the center face of the golf club, and table 2 represents
averaged results for hits 3.175 cm away from the center face of the
golf club. R.sub.Bulge is the bulge radius, in centimeters.
TABLE-US-00001 TABLE 1 Headspeed (MPH) Bulge Radius Equation (cm.)
70 R.sub.Bulge = 0.00466 * I.sub.zz + 23.54 90 R.sub.Bulge =
0.00556 * I.sub.zz + 12.56 103 R.sub.Bulge = 0.00525 * I.sub.zz +
12.15 130 R.sub.Bulge = 0.00459 * I.sub.zz + 14.39
TABLE-US-00002 TABLE 2 Headspeed (MPH) Bulge Radius Equation (cm.)
70 R.sub.Bulge = 0.00592 * I.sub.zz + 16.6 90 R.sub.Bulge = 0.00458
* I.sub.zz + 12.95 103 R.sub.Bulge = 0.00394 * I.sub.zz + 13.5 130
R.sub.Bulge = 0.00306 * I.sub.zz + 14.4
[0049] The results of tables 1 and 2 were then averaged together
according to a statistical model which takes into account impact
location standard deviation versus headspeed at impact. It is
expected that there would be larger deviations for shots which are
further off-center towards the heel or the toe of the club than for
shots closer to the center face of the club. A weighted slope and
intercept for the bulge radius equation shown in Table 1 and 2 were
then found, as shown in Table 3:
TABLE-US-00003 TABLE 3 Headspeed (MPH) Slope Intercept 70 0.00517
20.77 90 0.00522 12.69 103 0.00486 12.56 130 0.00421 14.39
[0050] As can be seen from Table 3, the bulge radius, R.sub.Bulge,
(in centimeters) for a golf club swung with a headspeed of 70 mph,
according to the computer simulation, is
R.sub.Bulge=0.00517*I.sub.zz+20.8. Similarly, the bulge radius,
R.sub.Bulge, (in centimeters) for a golf club swung with a
headspeed of 90 mph is 0.00522*I.sub.zz+12.7. Similar results are
obtained for the other headspeeds by referring to Table 3.
[0051] The slopes and intercepts for each headspeed from Table 3
were then averaged together according to a weighted model dependant
on the likelihood of a golfer swinging a club at that headspeed.
For example, very few players actually swing a golf club with a 130
mph headspeed, however a 90 mph headspeed is more common. This
weighted averaging produced a slope of 0.00505 and an intercept of
13.95. Thus, in one preferred embodiment, the ideal bulge (in
centimeters) for a given MOI about the CG Z axis, I.sub.zz, can be
determined by the equation R.sub.Bulge=0.00505*I.sub.zz+13.95.
[0052] As described above, the preferred MOI about the CG Z axis
I.sub.zz is between about 4400 gcm.sup.2 and about 6000 gcm.sup.2.
Thus the preferred R.sub.Bulge is between about 36.17 cm and about
44.25 cm, respectively corresponding to a preferred bulge curvature
range between about 0.023 cm.sup.-1 and about 0.028 cm.sup.-1. In
other embodiments, the bulge curvature may be even lower, such as
0.016 cm.sup.-1, which corresponds to a bulge radius of about 60.96
cm. In certain extreme embodiments the bulge curvature may be as
low a 0 cm.sup.-1. Different results within a reasonable margin of
error may be obtained using different statistical models, therefore
slight variations of these values are also envisioned.
[0053] FIG. 9 depicts a graph 90 showing a computer simulated bulge
as a function of MOI around the CG Z axis I.sub.zz for one
exemplary embodiment of the present disclosure. Bulge, in
centimeters, is depicted along the Y axis of graph 90, and MOI
about the CG Z axis I.sub.zz is depicted along the X axis of the
graph. As shown by graph 90, bulge is generally related to MOI
around the Z axis I.sub.zz such that the bulge is increased by
roughly five centimeters per 1000 gcm2 increase of MOI around the
CG Z axis I.sub.zz. In other examples, the relationship may be
slightly different based on factors such as the specific club size
or configuration, wind, or club head speed.
Trends in Simulated Results--Bulge/Roll
[0054] As described above, it is envisioned that, in the preferred
embodiment, the radius of the roll is between 20.3 centimeters and
25.4 centimeters. For a roll radius R.sub.Roll of 20.3 centimeters,
this produces the following bulge radius to roll radius
equations:
70 mph : R Bu 1 ge R Roll = 0.00517 * I ZZ + 20.8 20.3 = 2.55
.times. 10 - 4 * I ZZ + 1.02 90 mph : R Bu 1 ge R Roll = 0.00522 *
I ZZ + 12.7 20.3 = 2.57 .times. 10 - 4 * I ZZ + 0.625 103 mph : R
Bu 1 ge R Roll = 0.00486 * I ZZ + 12.6 20.3 = 2.39 .times. 10 - 4 *
I ZZ + 0.613 ##EQU00004##
[0055] For a range of MOI about the CG Z axis I.sub.ZZ between
about 3500 gcm.sup.2 and about 6000 gcm.sup.2, these equations give
the following range of bulge radius to roll radius ratios for each
head speed: [0056] 70 mph: 1.90:1-2.55:1 [0057] 90 mph:
1.53:1-2.17:1 [0058] 103 mph: 1.45:1-2.05:1
[0059] In the preferred embodiment, using the ideal R.sub.Bulge
equation R.sub.Bulge=0.00505*I.sub.zz+13.95, the ratio of the bulge
radius to the roll radius becomes:
R Bu 1 ge R Roll = 0.00505 * I ZZ + 13.95 20.3 = 2.488 .times. 10 -
4 * I ZZ + 0.6875 ##EQU00005##
Using a range of MOIs about the CG Z axis, I.sub.zz, between about
4400 gcm.sup.2 and about 6000 gcm.sup.2, this equation produces a
range for the ratio of the bulge radius to the roll radius between
1.78:1-2.13:1.
[0060] A similar range of ratios can be obtained by using the upper
limit of the preferred roll radius, 25.4 centimeters. The preferred
ratio of the bulge radius to the roll radius becomes:
R Bu 1 ge R Roll = 0.00505 * I ZZ + 13.95 25.4 = 1.988 .times. 10 -
4 * I ZZ + 0.5492 ##EQU00006##
Using a range of MOIs about the CG Z axis, I.sub.zz, between about
4400 gcm.sup.2 and about 6000 gcm.sup.2, this equation produces a
range for the ratio of the bulge radius to the roll radius between
1.42:1-1.74:1
[0061] Because the curvature is defined as 1/R.sub.Bulge or
1/R.sub.Roll, the ratio of the bulge curvature to the roll
curvature can be defined as 1/(R.sub.Bulge/R.sub.Roll). Useful
bounding equations can then be defined according to the computer
simulation for the ratio of the bulge curvature to the roll
curvature, R.sub.C, in the preferred embodiment as:
1 ( 2.488 .times. 10 - 4 * I ZZ ) + 0.6875 .ltoreq. R C .ltoreq. 1
( 1.988 .times. 10 - 4 * I ZZ ) + 0.5492 ##EQU00007##
A broader ratio of curvatures R.sub.C can also be defined using the
broader range of roll radii between 15.24 centimeters and 30.48
centimeters as follows:
1 ( 3.3 .times. 10 - 4 * I ZZ ) + 0.9154 .ltoreq. R C .ltoreq. 1 (
1.7 .times. 10 - 4 * I ZZ ) + 0.4574 ##EQU00008##
Trends in Experimental Results--Bulge
[0062] Experimental testing of varying bulge radii and MOI about
the CG Z axis I.sub.zz was conducted, and the bulge for each
I.sub.zz was found for a plurality of I.sub.zz. The results are
summarized as follows:
TABLE-US-00004 TABLE 4 Curvature Curvature I.sub.zz Bulge
Bulge/Roll Bulge/Roll ratio ratio (g radius (Roll radius: (Roll
radius: (Roll radius: (Roll radius: cm.sup.2) (cm.) 15.24 cm.)
30.48 cm.) 15.24 cm) 30.48 cm.) 4400 40.6 2.67 1.33 0.38 0.75 5000
45.7 3.00 1.50 0.33 0.67 5500 50.0 3.28 1.64 0.31 0.61 6000 54.2
3.56 1.78 0.28 0.56
[0063] The data in Table 4 was then linearly fit to determine a
linear slope and intercept for the bulge radius for differing MOIs
about the CG Z axis, I.sub.zz. In general, experimental testing
results as shown in Table 4 indicate that the ideal bulge radius
for a given MOI about the CG Z axis, I.sub.zz can be found using
the equation R.sub.Bulge=0.0085*I.sub.zz+3.387 where R is the bulge
radius, in centimeters.
[0064] These experimental results further indicate a range for the
ratio of the bulge curvature divided by roll curvature, indicated
by the variable R.sub.C. This range can be expressed by the
equation:
1 ( 5.6 .times. 10 - 4 * I ZZ ) + 0.222 .ltoreq. R C .ltoreq. 1 (
2.8 .times. 10 - 4 * I ZZ ) + 0.111 ##EQU00009##
[0065] Again, the roll radii in the above equation is between 15.24
cm and 30.48 cm. This ratio and these experimental results are
useful in that they indicate a range of preferred bulge curvature
to roll curvature ratios (R.sub.C) for a range of MOIs about the CG
Z axis, I.sub.zz. For example, the overall range for R.sub.C for
I.sub.zz between about 4400 gcm.sup.2 and about 6000 gcm.sup.2 is
between 0.28 and 0.75. The range for R.sub.C for I.sub.zz between
about 4400 gcm.sup.2 and about 5000 gcm.sup.2 is between about 0.33
and 0.75. The other ranges for R.sub.C for this embodiment of the
golf club can be found by reference to Table 1, above.
[0066] At least one advantage of the present invention is that the
bulge and roll ranges described herein more adequately compensate
for gear effect, thus improving accuracy while improving the
distance traveled by a golf ball for large I.sub.zz golf club
heads.
[0067] In addition, at least one advantage of the present invention
is that the bulge and roll curvature ratio described herein
accommodates for variations in swing speed. The bulge and roll
curvature ratio discovered in the experimental test data described
above, achieves maximum performance in large MOI golf club heads
through a variety of swing speeds.
[0068] Furthermore, the bulge to roll ratio range described above
was an unexpected outcome due to the incorrect initial assumption
that bulge to roll ratio would be simply 1:1. In the process of
discovering the present invention, a flatter face unexpectedly
provided a shorter distance golf shot. However, increasing roll
curvature to achieve more distance would sacrifice accuracy under a
1:1 ratio of bulge to roll curvature.
[0069] Thus, the present invention discloses the most preferred and
effective bulge to roll curvature ratio. Therefore, straighter and
longer golf shots are possible.
[0070] In view of the many possible embodiments to which the
principles of the disclosed invention may be applied, it should be
recognized that the illustrated embodiments are only preferred
examples of the invention and should not be taken as limiting the
scope of the invention.
* * * * *