U.S. patent application number 11/303626 was filed with the patent office on 2006-05-04 for golf club head with variable flexural stiffness for controlled ball flight and trajectory.
Invention is credited to Laurent Bissonnette, Nicholas M. Nardacci.
Application Number | 20060094531 11/303626 |
Document ID | / |
Family ID | 34555466 |
Filed Date | 2006-05-04 |
United States Patent
Application |
20060094531 |
Kind Code |
A1 |
Bissonnette; Laurent ; et
al. |
May 4, 2006 |
Golf club head with variable flexural stiffness for controlled ball
flight and trajectory
Abstract
The present invention relates to a golf club head with a hitting
face. The hitting face comprises a directional control portion,
which has at least two zones with different flexural stiffness,
such that when the hitting face strikes a golf ball the two zones
deform differently to selectively control the direction of the
flight of the golf ball. The directional control portion may
comprise an upper zone and a lower zone, where the upper zone has a
lower flexural stiffness. Alternatively, the lower zone has a lower
flexural stiffness. On the other hand, the directional control
portion may comprise a left zone and a right zone, and either the
left or right zone may have a lower flexural stiffness to
selectively control the lateral launch angle either to the left of
right. The hitting face may further comprise a central zone
disposed within the directional control zone, wherein the central
zone has a flexural stiffness of at least about three times greater
than the flexural stiffness of the directional control zone.
Inventors: |
Bissonnette; Laurent;
(Portsmouth, RI) ; Nardacci; Nicholas M.;
(Bristol, RI) |
Correspondence
Address: |
ACUSHNET COMPANY
333 BRIDGE STREET
P. O. BOX 965
FAIRHAVEN
MA
02719
US
|
Family ID: |
34555466 |
Appl. No.: |
11/303626 |
Filed: |
December 16, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10428051 |
May 1, 2003 |
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11303626 |
Dec 16, 2005 |
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09551771 |
Apr 18, 2000 |
6605007 |
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10428051 |
May 1, 2003 |
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Current U.S.
Class: |
473/329 ;
473/342; 473/345; 473/349 |
Current CPC
Class: |
A63B 60/002 20200801;
G01N 2291/02854 20130101; A63B 53/0408 20200801; A63B 53/0416
20200801; G01N 29/045 20130101; G01N 2291/014 20130101; A63B
53/0458 20200801; A63B 53/045 20200801; A63B 60/00 20151001; A63B
2209/00 20130101; A63B 53/0454 20200801; A63B 53/0466 20130101;
A63B 60/42 20151001 |
Class at
Publication: |
473/329 ;
473/342; 473/345; 473/349 |
International
Class: |
A63B 53/04 20060101
A63B053/04 |
Claims
1. A golf club head adapted for attachment to a shaft and having a
hitting face, wherein the hitting face comprises a central portion
and an intermediate portion surrounding the central portion, said
central portion contains the geometric center of the hitting face,
and wherein the central portion and the intermediate portion have
different flexural stiffness such that after impact with a golf
ball the central portion is substantially un-deformed.
2. The golf club head of claim 1, wherein after impact with the
golf ball, the intermediate portion deforms.
3. The golf club head of claim 1, wherein the flexural stiffness of
the central portion is at least about three times greater than the
flexural stiffness of the intermediate portion.
4. The golf club head of claim 3, wherein the flexural stiffness of
the central portion is at least about six times greater than the
flexural stiffness of the intermediate portion.
5. The golf club head of claim 4, wherein the flexural stiffness of
the central portion is at least about twelve times greater than the
flexural stiffness of the intermediate portion.
6. A golf club head adapted for attachment to a shaft and having a
hitting face, wherein the hitting face comprises a central portion
and an intermediate portion said central portion contains the
geometric center of the hitting face, and wherein the central
portion and the intermediate portion have different flexural
stiffness such that after an impact with a golf ball the central
portion is movable into and out of an outer surface of the hitting
face.
7. The golf club head of claim 6, wherein after impact with the
golf ball, the intermediate portion deforms.
8. The golf club head of claim 6, wherein the flexural stiffness of
the central portion is at least about three times greater than the
flexural stiffness of the intermediate portion.
9. The golf club head of claim 8, wherein the flexural stiffness of
the central portion is at least about six times greater than the
flexural stiffness of the intermediate portion.
10. The golf club head of claim 9, wherein the flexural stiffness
of the central portion is at least about twelve times greater than
the flexural stiffness of the intermediate portion.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a divisional application of
co-pending U.S. patent application No. 10/428,051 filed May 1,
2003, which is a continuation-in-part of co-pending U.S. patent
application No. 09/551,771 filed on Apr. 18, 2000, now U.S. Pat.
No. 6,605,007. The parent patent applications are incorporated
herein in their entirety.
FIELD OF THE INVENTION
[0002] The invention is an improved golf club head. More
particularly, the invention is a golf club head with an improved
striking face having discrete zones with varying flexural
stiffness, improved accuracy, and a high coefficient of
restitution.
BACKGROUND OF THE INVENTION
[0003] The complexities of golf club design are well-known. The
specifications for each component of the club (i.e., the club head,
shaft, hosel, grip, and subcomponents thereof) directly impact the
performance of the club. Thus, by varying the design
specifications, a golf club can be tailored to have specific
performance characteristics.
[0004] The design of club heads has long been studied. Among the
more prominent considerations in club head design are loft, lie,
face angle, horizontal face bulge, vertical face roll, face
progression, face size, sole curvature, center of gravity, material
selection, and overall head weight. While this basic set of
criteria is generally the focus of golf club engineering, several
other design aspects must also be addressed. The interior design of
the club head may be tailored to achieve particular
characteristics, such as the inclusion of hosel or shaft attachment
means, perimeter weights on the face or body of the club head, and
fillers within hollow club heads to improve acoustics.
[0005] Golf club heads must also be strong to withstand the
repeated impacts that occur during collisions between the golf club
and the ball. The loading that occurs during this transient event
can accelerate the golf ball to about four orders of magnitude
greater than gravity. Thus, the club face and body should be
designed to resist permanent deformation or catastrophic failure by
material yield or fracture. Conventional hollow metal wood drivers
made from titanium typically have a uniform face thickness
exceeding 0.010 inch to ensure structural integrity of the club
head.
[0006] Players generally seek a metal wood driver and golf ball
combination that delivers maximum distance and landing accuracy.
The distance a ball travels after impact is dictated by the
magnitude and direction of the ball's translational velocity and
the ball's rotational velocity or spin. Environmental conditions,
including atmospheric pressure, humidity, temperature, and wind
speed further influence the ball's flight. However, these
environmental effects are beyond the control of the golf equipment
manufacturer. Golf ball landing accuracy is driven by a number of
factors as well. Some of these factors are attributed to club head
design, such as center of gravity, face curvature and club face
flexibility.
[0007] The United States Golf Association (USGA), the governing
body for the rules of golf in the United States, has specifications
for the performance of golf balls. These performance specifications
dictate the size and weight of a conforming golf ball. One USGA
rule limits the golf ball's initial velocity after a prescribed
impact to 250 feet per second .+-.2% (or 255 feet per second
maximum initial velocity). To achieve greater golf ball travel
distance, ball velocity after impact must be maximized while
remaining within this rule.
[0008] Generally, golf ball travel distance is a function of the
total kinetic energy imparted to the ball during impact with the
club head, along with associated environmental effects. During
impact, kinetic energy is transferred from the club and stored as
elastic strain energy in the club head and as viscoelastic strain
energy in the ball. After impact, the stored energy in the ball and
in the club is transformed back into kinetic energy in the form of
translational and rotational velocity of the ball as well as the
club. Since the collision is not perfectly elastic, a portion of
energy is dissipated in club head vibration and in viscoelastic
relaxation of the ball. Viscoelastic relaxation is a material
property of the polymeric materials used in all manufactured golf
balls.
[0009] Viscoelastic relaxation of the ball is a parasitic energy
source, which is dependent upon the rate of deformation. To
minimize this effect, the rate of deformation must be reduced. This
may be accomplished by allowing more club face deformation during
impact. Since metallic deformation may be purely elastic, the
strain energy stored in the club face is returned to the ball after
impact thereby increasing the ball's outbound velocity after
impact.
[0010] A variety of techniques may be utilized to vary the
allowable deformation of the club face, including uniform face
thinning, thinned faces with ribbed stiffeners and varying
thickness, among others. These designs should have sufficient
structural integrity to withstand repeated impacts without
permanent deformation of the club face. In general, conventional
club heads also exhibit wide variations in the coefficient of
restitution (COR) depending on the impact location on the face of
the club. Furthermore, the accuracy of conventional clubs is highly
dependent on impact location.
[0011] Thus, there is a need for a golf club head with a hitting
face that maximizes golf ball travel distance while maintaining
golf ball landing accuracy.
SUMMARY OF THE INVENTION
[0012] The present invention relates to a golf club head adapted
for attachment to a shaft. The head includes a face and a body. The
face is configured and dimensioned so that it includes a central
portion and an adjacent surrounding intermediate portion. The
central portion is relatively rigid and the intermediate portion is
relatively flexible so that upon ball impact, the intermediate
portion of the face deforms to provide high ball velocity, while
the central portion is substantially un-deformed so that the ball
flies on-target. Thus, upon ball impact the deformation of the
intermediate portion allows the central region to move into and out
of the club head as a unit. As a result, the head exhibits a
coefficient of restitution greater than 0.81.
[0013] The above is accomplished by providing the central portion
with a first flexural stiffness and the intermediate portion with a
second flexural stiffness. Flexural stiffness is defined as Young's
modulus or elastic modulus (E) times the portion's thickness (t)
cubed or Et.sup.3. The first flexural stiffness is substantially
different from the second flexural stiffness. As a result, upon
ball impact, the intermediate portion exhibits substantial
deformation so that the central portion moves into the club head,
and the central portion exhibits minimal deformation.
[0014] In one embodiment, the first flexural stiffness is at least
three times the second flexural stiffness. In other embodiments,
the first flexural stiffness is six to twelve times the second
flexural stiffness. More preferably, the first flexural stiffness
is greater than 25,000 lb-in. Most preferably, the first flexural
stiffness is greater than 55,000 lb-in. Preferably, the second
flexural stiffness is less than 16,000 lb-in. More preferably, the
second flexural stiffness is less than 10,000 lb-in.
[0015] Since the flexural stiffness is a function of material and
thickness, the following techniques can be used to achieve the
substantial difference between the first and second flexural
stiffness: 1) different materials can be used for each portion, 2)
different thicknesses can be used for each portion, or 3) different
materials and thicknesses can be used for each portion. For
example, in one embodiment, the thickness of the central portion is
greater than the thickness of the intermediate portion and the
material for both portions is the same, e.g., titanium or
steel.
[0016] The golf club head further includes a perimeter portion
disposed between the intermediate portion and the body of the club.
In one embodiment, the perimeter portion has a third flexural
stiffness that is at least two times greater than the second
flexural stiffness. The area of the perimeter portion preferably
comprises less than 30% of the total area of the club head
face.
[0017] In an alternative embodiment, a golf club head includes a
shell that defines an inner cavity and a face. The face defines a
face area and includes a first portion in the center and a second
portion adjacent thereto. The first portion has a first thickness
and defines a first area. The second portion has a second
thickness. The first area is between about 15% and about 60% of the
total face area, and the first thickness is greater than the second
thickness. More preferably, the first area is between about 20% and
50% of the face area. The shell further includes a top crown
portion and a spaced-apart sole plate, a heel portion and a spaced
toe portion, and a rear spaced from the face.
[0018] In the club heads discussed above, the first, second, and
third portions can have various shapes, such as the shape of the
face or an elliptical shape. Furthermore, the club head inner
cavities can have a volume greater than about 250 cubic
centimeters, and more preferably a volume greater than about 275
cubic centimeters. It is preferred that the face of the club head
has a loft of less than about 13.degree..
[0019] In addition, the central, intermediate, and perimeter
portions can each have variable thicknesses.
[0020] Another feature of the present invention is locating the
center of gravity of the club head with respect to a Cartesian
coordinate system. The origin of the Cartesian coordinate system
preferably coincides with the geometric center of the hitting face.
The X-axis is a horizontal axis positioned tangent to the geometric
center of the hitting face with the positive direction toward the
heel of the club. The Y-axis is another horizontal axis orthogonal
to the X-axis with the positive direction toward the rear of the
club. The Z-axis is a vertical axis orthogonal to both the X-axis
and Y-axis with the positive direction toward the crown of the
club. The center of gravity is preferably located behind and lower
than the geometric center of the face.
[0021] In one embodiment, the center of gravity is spaced from the
geometric center along the Z-axis by a first distance of at least
about 0.1''. More preferably, the center of gravity is spaced 30
from the geometric center along the Z-axis toward the sole plate,
wherein the first distance is at least about 0.15''. In another
embodiment, the center of gravity is spaced a second distance from
the geometric center along the X-axis, wherein the second distance
is less than about 0.02''. In addition, the center of gravity is
spaced a third distance from the geometric center along the Y-axis
toward the rear portion, wherein the third distance is less than
about 1.25''.
[0022] The present invention is also directed to a golf club head
having a hitting face and adapted for attachment to a shaft. The
face includes a total face area and first primary resonant
frequency, which is preferably less than about 2900 Hz. The face
further includes a central zone that includes a geometric center of
the face, and an intermediate zone disposed adjacent the central
zone. The central zone has a first flexural stiffness and a central
zone area that is at least 15% of the total face area. The
intermediate zone has a second flexural stiffness. The first
flexural stiffness is at least 25,000 lb-in and greater than the
second flexural stiffness.
[0023] An embodiment of the present invention is directed to a golf
club head adapted for attachment to a shaft and having a hitting
face, wherein the hitting face comprises a directional control
portion, said directional controlled portion comprises two or more
zones having different flexural stiffness, such that when the
hitting face impacts a golf ball the zones exhibit different
degrees of deformation to selectively control the direction of the
flight of the golf ball. The hitting face may further include a
central portion disposed within the directional control portion,
which contains a geometric center of the hitting face, and the
flexural stiffness of the central portion is at least about three
times, preferably at least about six times and more preferably at
least about twelve times, greater than the flexural stiffness of
the directional control portion.
[0024] The golf club head may further have a perimeter portion
disposed around the directional control portion, wherein the
flexural stiffness of the perimeter portion is at least about two
times greater than the flexural stiffness of the directional
control portion. In accordance to one aspect, the flexural
stiffness of a first zone of said two or more directional control
zones is between about 8,500 lbin to about 60,000 lbin. The
flexural stiffness of a second zone of said two or more zones is
about 0.5 time to about two times the flexural stiffness of the
first zone. Furthermore, the flexural stiffness of a third zone of
said two or more zones is about 0.7 times to about 1.3 times the
flexural stiffness of the first zone, and the flexural stiffness of
a fourth zone of said two or more zones is about 0.7 times to about
two times the flexural stiffness of the first zone.
[0025] The directional control portion may comprise an upper crown
zone and a lower heel zone, or may comprise a lateral heel zone and
a lateral toe zone. Alternatively, the directional control portion
may comprise all four of these zones. Preferably, these four zones
are delineated by a vertical center line and a horizontal center
line of the hitting face.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Preferred features of the present invention are disclosed in
the accompanying drawings, wherein similar reference characters
denote similar elements throughout the several views, and
wherein:
[0027] FIG. 1 is a toe side, front, and perspective view of a first
embodiment of a golf club head of the present invention;
[0028] FIG. 2 is a heel side, rear, and perspective view of the
golf club head of FIG. 1;
[0029] FIG. 3 is a front, elevational view of the golf club head of
FIG. 1;
[0030] FIG. 3A is a cross-sectional view of the face of the golf
club head of FIG. 3 along line 3A-3A;
[0031] FIG. 3B shows a cross-sectional view the face of the golf
club head of FIG. 3 along line 3B-3B;
[0032] FIG. 4 is a top view of the golf club head of FIG. 1;
[0033] FIG. 5 is a bottom, perspective view of the golf club head
of FIG. 1;
[0034] FIG. 6 is a toe side, front, and perspective view of a
second embodiment of a golf club head of the present invention;
[0035] FIG. 7 is a front, elevational view of the golf club head of
FIG. 6;
[0036] FIG. 7A is a cross-sectional view of the face of the golf
club head of FIG. 7 along line 7A-7A;
[0037] FIG. 7B shows a cross-sectional view the face of the golf
club head of FIG. 7 along line 7B-7B;
[0038] FIG. 8 is a toe side, front, and perspective view of a third
embodiment of a golf club head of the present invention;
[0039] FIG. 9 is a front, elevational view of the golf club head of
FIG. 8;
[0040] FIG. 9A is a cross-sectional view of the face of the golf
club head of FIG. 9 along line 9A-9A;
[0041] FIG. 10 is a toe side, front, and perspective view of a
fourth embodiment of a golf club head of the present invention;
[0042] FIG. 11 is a front, elevational view of the golf club head
of FIG. 10;
[0043] FIG. 11A is a cross-sectional view of the face of the golf
club head of FIG. 11 along line 11A-11A;
[0044] FIG. 12 is an enlarged, front view of a golf club head with
ultrasonic thickness measurement locations indicated;
[0045] FIG. 13 is a schematic representation of the apparatus for
taking an ultrasonic thickness measurement on the face of a club
head;
[0046] FIG. 14 is an enlarged, elevational view of a portion of the
face of a laminated golf club head of the present invention;
[0047] FIG. 15 is a schematic representation of a testing apparatus
for obtaining frequency response data from a club head;
[0048] FIG. 15A is a perspective view of an attached mass for use
with the testing apparatus of FIG. 15;
[0049] FIG. 16 is a graph of inertance versus frequency for a
conventional club head;
[0050] FIG. 17 is a graph of inertance versus frequency for the
inventive club head;
[0051] FIG. 18 is a graph of COR versus face thickness for two
alternative titanium alloys;
[0052] FIG. 19 is a graph of COR versus first resonant frequency
for two alternative titanium alloys;
[0053] FIGS. 20-23 are front, elevational views of another
embodiment in accordance to the present invention; and
[0054] FIGS. 24-26 are perspective and front, elevational views of
another embodiment in accordance to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0055] Referring to FIGS. 1-5, a first embodiment of a golf club
head 10 of the present invention is shown. Club head 10 includes
shell 12 with body 14, hitting face 16, toe portion 18, heel
portion 20, sole plate 22, hosel 24, bottom portion 26, crown
portion 28, and rear portion 29. The sole plate 22 fits in a recess
30 (as shown in FIG. 5) in the bottom portion 26 of body 14. The
shell 12 and sole plate 22 create an inner cavity 31 (as shown in
FIG. 5). The hitting face 16 has an exterior surface 32 and an
interior surface 34. The exterior surface 32 may optionally have
grooves 35.
[0056] A golf club shaft (not shown) is attached at hosel 24 and is
disposed along a shaft axis SHA. The hosel may extend to the bottom
of the club head, may terminate at a location between the top and
bottom portions of the head, or the hosel can terminate flush with
the top portion and extend into the cavity in the head.
[0057] Inner cavity 31 of club head 10 may be empty, or
alternatively may be filled with foam or other low specific gravity
material. It is preferred that the inner cavity 31 has a volume
greater than 250 cubic centimeters, and more preferably greater
than 275 cubic centimeters. Preferably, the mass of the inventive
club head is greater than 150 grams but less than 220 grams.
[0058] Referring to FIGS. 3-3B, the face 16 includes a central zone
or portion 36, an intermediate zone or surrounding portion 38
adjacent the central zone 36, and an optional perimeter zone or
outer portion 40. The intermediate zone 38 preferably surrounds
central zone 36, and the perimeter zone 40 preferably surrounds the
intermediate zone 38. The perimeter zone 40 is located between the
intermediate zone 38 and crown portion 28. In the following
specification and claims, the central zone 36 is a contiguous zone
centrally located on the hitting face 16 and containing a geometric
center ("GC") of the hitting face.
[0059] Zones 36, 38 and 40 have a shape that is similar to the
shape of hitting face 16 only with a smaller area, as discussed in
detail below. Preferably, zones 36, 38 and 40 are substantially
concentric to each other within hitting face 16. The central zone
36 has a first thickness t.sub.1. The intermediate zone 38 has a
second thickness t.sub.2. The first thickness t.sub.1 is greater
than the second thickness t.sub.2. Typically, when the club head is
cast, the perimeter zone 40 will be thicker than the intermediate
zone 38. However, the present invention is not limited to this
configuration. Preferably, the first thickness t.sub.1 is equal to
about one and a half (1.5) times the thickness t.sub.2 to about
four (4) times the thickness t.sub.2 of the intermediate zone
38.
[0060] The thickness relationships between the zones 36, 38, and 40
are provided so that a predetermined relationship exists between
flexural stiffness exhibited by each of the zones. Flexural
stiffness (FS) of each zone is defined by the following simplified
formula: FS=E.times.t.sup.3 where, [0061] E=the elastic modulus or
Young's modulus of the material of the zone; and [0062] t=the
thickness of the zone.
[0063] The central zone 36 has a first flexural stiffness FS.sub.1.
The intermediate zone 38 has a second flexural stiffness FS.sub.2.
The perimeter zone 40 has a third flexural stiffness FS.sub.3. The
predetermined relationship between the portions is that the first
flexural stiffness FS.sub.1 is substantially greater than the
second flexural stiffness FS.sub.2, and optionally the third
flexural stiffness FS.sub.3 is substantially greater than the
second flexural stiffness FS.sub.2. Preferably, the first flexural
stiffness FS.sub.1 is at least three times greater than the second
flexural stiffness FS.sub.2. As a ratio the following relationship
must be satisfied: (FS.sub.1/FS.sub.2).gtoreq.3. This expression
means that the ratio of the central zone flexural stiffness
FS.sub.1 to the intermediate zone flexural stiffness FS.sub.2 is
equal to or greater than 3.0. When the above ratio of flexural
stiffness is less than three, the central zone sustains excessive
deformation during impact and accuracy of the club is diminished.
More preferably, the first flexural stiffness FS.sub.1 is at least
six to twelve times greater than the second flexural stiffness
FS.sub.2. Most preferably, the first flexural stiffness FS.sub.1 is
about eight times greater than the second flexural stiffness
FS.sub.2.
[0064] Preferably, the third flexural stiffness FS.sub.3 is at
least two times greater than the second flexural stiffness
FS.sub.2. Thus, the following relationship must be satisfied:
(FS.sub.3/FS.sub.2).gtoreq.2. In club head 10 (as shown in FIG. 3),
the above flexural stiffness relationships are achieved by
selecting a certain material with a particular elastic modulus and
varying the thickness of the zones. In another embodiment, the
flexural stiffness relationships can be achieved by varying the
materials of the zones with respect to one another so that the
zones have different elastic moduli and the thickness is changed
accordingly. Thus, the thickness of the portions can be the same or
different depending on the elastic modulus of the material of each
portion. It is also possible to obtain the required flexural
stiffness ratio through the use of structural ribs, reinforcing
plates, and thickness parameters.
[0065] Quantitatively, it is preferred that the first flexural
stiffness FS.sub.1 is greater than 20,000 lb-in. When the first
flexural stiffness is less than 20,000 lb-in excessive deformation
of the central region can occur during impact-and accuracy is
diminished. More preferably, the first flexural stiffness FS.sub.1
is greater than 55,000 lb-in. Preferably, the second flexural
stiffness FS.sub.2 is less than 16,000 lb-in. When the second
flexural stiffness is greater than 16,000 lb-in the COR the
resultant ball velocity is reduced. More preferably, the second
flexural stiffness FS.sub.2 is less than 10,000 lb-in and, most
preferably, less than 7,000 lb-in.
[0066] Referring to FIG. 3, it is preferred that central portion 36
has a first area that is between about 15% and about 60% of the
exterior surface area 32 or face area. The percentage of face area
is computed by dividing the area of each zone 36, 38, or 40 by the
total face area of exterior surface 32. It should be noted that the
total face area of the exterior surface 32 is equivalent to the sum
of areas of the zones 36, 38, and 40. In a preferred embodiment,
the central zone first area is greater than about 15% and less than
about 60% of the total face area. When the central zone 36 is less
than 15% of the total face area, then accuracy can be diminished.
When central portion 36 is greater than 60% of the face area 32,
then COR can be diminished.
[0067] Referring again to FIG. 1, the club head 10 is further
formed so that a center of gravity of the club head has a
predetermined relationship with respect to a Cartesian coordinate
system with a center located on the exterior surface and coincident
with the geometric center GC of the face 16. The face includes a
vertical centerline VCL and a horizontal centerline HCL
perpendicular thereto. The geometric face center GC is at the
intersection of these centerlines VCL and HCL. Preferably, the
geometric center of the central zone 36 is coincident with the club
face geometric center GC.
[0068] The Cartesian coordinate system is defined when the club
head is resting on a flat surface (i.e., at its natural loft) and
includes three axes, as illustrated in FIG. 1. The origin of the
Cartesian coordinate system preferably coincides with the geometric
center of the hitting face. The X-axis is a horizontal axis
positioned tangent to the geometric center of the hitting face with
the positive direction toward the heel of the club. The Y-axis is
another horizontal axis orthogonal to the X-axis with the positive
direction toward the rear of the club. The Z-axis is a vertical
axis orthogonal to both the X-axis and Y-axis with the positive
direction toward the crown of the club. The center of gravity is
preferably located behind and lower than the geometric center of
the face.
[0069] Referring to FIG. 1, the location of the center of gravity
is defined by coordinates for the center of gravity CG.sub.z,
CG.sub.y, and CG.sub.x with respect to the Z, X, and Y axes,
respectively. In the vertical direction along the Z-axis, the
center of gravity coordinate is designated CG.sub.z, and is spaced
a first distance D1 from the geometric face center G along the
Z-axis. The first distance D1 is at least about -0.1 inches, and
more preferably the first distance D1 is at least about -0.15
inches so that the center of gravity in the vertical direction is
below the geometric center GC.
[0070] In the horizontal direction along the X-axis, the center of
gravity coordinate is designated CG.sub.x, and is spaced a second
distance D2 from the geometric face center GC. The second distance
D2 is less than about 0.02 inches and greater than -0.02 inches so
that the center of gravity in the horizontal direction is spaced
from the center GG by no further than the magnitude of distance
D2.
[0071] Referring to FIG. 1, along the Y-axis, the center of gravity
coordinate is designated CG.sub.y, and is spaced a third distance
D3 from the geometric face center GC preferably toward the rear
portion 29. The center of gravity CG.sub.y in the third direction
is spaced from the center GC toward the rear portion 29 by no
further than the magnitude of the third distance D3. The third
distance D3 is preferably equal to or less than about 1.25 inches
and, more preferably, less than about 1 inch.
EXAMPLES
[0072] These and other aspects of the present invention may be more
fully understood with reference to the following non-limiting
examples, which are merely illustrative of embodiments of the
present invention golf club head, and are not to be construed as
limiting the invention, the scope of which is defined by the
appended claims. TABLE-US-00001 TABLE 1 FLEXURAL STIFFNESS
INFORMATION Comparative Comparative Comparative Inventive Parameter
Example 1 Example 2 Example 3 Example Thickness of Center Zone
0.115 0.130 0.095 0.150 (inches) Thickness of First 0.115 0.100
0.098 0.075 Intermediate Zone (inches) Thickness of Second 0.115
0.080 0.100 0.075 Intermediate Zone (inches) Thickness of Perimeter
0.115 0.150 0.120 0.120 Portion (inches) E of All Portions (psi)
1.65E+07 1.65E+07 1.65E+07 1.65E+07 FS of Center Portion 25094
36251 14147 55688 (lb-in) FS of First Intermediate 25094 16500
15530 6961 zone (lb-in) FS of Second Intermediate 25094 8448 16500
6961 Zone (lb-in) FS of Perimeter Zone 25094 55688 28512 28512
(lb-in) FS.sub.1/FS.sub.2 1.0 2.2 0.9 8.0 FS.sub.3/FS.sub.2 1.0 3.4
1.8 4.1
[0073] Comparative Examples 1-3 are club heads configured and
dimensioned as indicated above with materials so that the zones
have certain values. As a result, the ratio of the central zone
flexural stiffness and adjacent intermediate zone flexural
stiffness for the Comparative Examples are 1.0, 2.2, and 0.9. These
ratios are outside of the preferred ratio that
(FS.sub.1/FS.sub.3.gtoreq.3) in accordance to one aspect of the
present invention. On the other hand, the Inventive Example is
configured and dimensioned so that (FS.sub.1/FS.sub.3=about 8). In
the examples above, the intermediate zone is defined by a first
intermediate zone adjacent the central zone and a second
intermediate zone adjacent the first intermediate zone. The
perimeter zone is adjacent the intermediate zone(s).
[0074] Comparative Examples 1 and 3 have a ratio of
FS.sub.3/FS.sub.2 of 1.0 and 1.8, respectively. These ratios are
also outside of the preferred ratio (FS.sub.3/FS.sub.2.gtoreq.2) in
accordance to another aspect of the present invention. Comparative
Example 2 and the Inventive Example satisfy such a ratio with
values of about 3.4 and 4. 1, respectively. TABLE-US-00002 TABLE 2
CENTER OF GRAVITY INFORMATION Comparative Comparative Comparative
Inventive Parameter Example 1 Example 2 Example 3 Example CG.sub.z
Location 0.074 0.074 0.074 -0.120 (inches).sup.1 CG.sub.x Location
0.133 0.137 0.137 -0.001 (inches).sup.2 CG.sub.y Location 1.159
1.159 1.182 0.991 (inches).sup.3 .sup.1Positive z is toward the
crown from GC .sup.2Positive x is toward the toe from GC
.sup.3Positive y is toward the back from the GC
[0075] The center of gravity for the Inventive Example club head
was achieved by the configuration and dimensions of the club head
in additional to adding a weight of 31.5 grams to the sole plate.
Other known methods of weight manipulation can be used to achieve
the inventive center of gravity location as set forth above.
[0076] Thus, referring to FIG. 1, in the club head example of the
present invention the center of gravity is preferably located along
the Z-axis at least 0.10 inches below the geometric face center GC,
along the X-axis within 0.01 inches from the geometric face center
GC, and along the y-axis within 1.25 inches from the geometric face
center GC. The Parameter column of Table 2 describes for each
center of gravity location or coordinate the distance that the
center of gravity is spaced from the face geometric center GC with
respect to a Cartesian coordinate system along particular axes. The
centers of gravity for Comparative Examples 1-3 are not located
properly with respect to the inventive requirements along the Z-
and X-axes. The center of gravity for the Inventive Example is
located properly with respect to the inventive requirements in the
Z, X, and Y axes. TABLE-US-00003 TABLE 3 TEST RESULTS Comparative
Comparative Comparative Inventive Parameter Example 1 Example 2
Example 3 Example Maximum COR 0.807 0.808 0.829 0.830 Average COR
0.765 0.766 0.783 0.789 Maximum Total 290 286 291 298 Distance
(yards) Landing Area 950 255 1000 341 (yards.sup.2)
[0077] The test results enumerated in Table 3 were generated using
computational techniques, which included finite element analysis
models. When computer modeling the exemplary club heads, the
following assumptions were made: club head loft of 8.5.degree.;
club head mass of 201 grams; and club head material is 6AL-4V
titanium alloy. The golf ball used was a two-piece solid ball.
Finite element models were used to predict ball launch conditions
and a trajectory model was used to predict distance and landing
area. The impact condition for the swing used in the total distance
and landing area predictions or tests had a club head velocity of
109.1 mph and an attack angle of .+-.2 degrees, the club was
oriented such that the vertical plane of the face was at an angle
of 8.5 degrees relative to the velocity vector. The impact
condition used for club coefficient of restitution (COR) tests was
consistent with the USGA Rules for Golf, specifically, Rule 4-1e
Appendix II Revision 2 dated Feb. 8, 1999.
[0078] COR or coefficient of restitution is one way of measuring
ball resiliency. The coefficient of restitution (COR) is the ratio
of the velocity of separation to the velocity of approach. In this
model, therefore, COR was determined using the following formula:
(V.sub.club-post-V.sub.ball-post)/(V.sub.ball-pre-V.sub.club-pre)
[0079] V.sub.club-post represents the velocity of the club after
impact; [0080] V.sub.ball-post represents the velocity of the ball
after impact; [0081] V.sub.club-pre represents the velocity of the
club before impact (a value of zero for USGA COR conditions); and
[0082] V.sub.ball-post represents the velocity of the ball before
impact.
[0083] COR, in general, depends on the shape and material
properties of the colliding bodies. A perfectly elastic impact has
a COR of one (1.0), indicating that no energy is lost, while a
perfectly inelastic or perfectly plastic impact has a COR of zero
(0.0), indicating that the colliding bodies did not separate after
impact resulting in a maximum loss of energy. Consequently, high
COR values are indicative of greater ball velocity and travel and
total distance. Club heads with thinner faces also have higher COR
values, as exhibited by Comparative Example 3 as compared to the
Comparative Club 1. However, unexpectedly the Inventive Example has
the highest COR. For the inventive club head, preferably the COR is
greater than about 0.81, and more preferably greater than about
0.83.
[0084] It is expected that as COR increases the ball flight
distance will increase and the maximum total distance will also
increase. The Inventive Example has the highest COR and also the
highest maximum total distance.
[0085] It as also expected that as COR increases the shot accuracy
will decrease. However, the Inventive Example has the highest COR
and the greatest accuracy as illustrated by the data for Landing
Area. The Landing Area is an area encompassing the position of nine
balls, which impact the club face at various locations. The nine
impact locations were equally spaced within a rectangular region 1
inch wide and 0.5 inches high, centered on the geometric center of
the club face. The club head of the Inventive Example has a very
small Landing Area of 341 square yards. The Comparative Example 3,
which is the only Comparative Example with a sufficient COR of at
least 0.81, has a Landing Area of 1000 square yards, which is
significantly greater than the Landing Area for the Inventive Club.
The smaller the landing area, the greater the accuracy of the
club.
[0086] Several alternative embodiments of the invention are
possible. The features of the invention include flexural stiffness
for distinct zones or portions of the club face, as well as the
ratio of flexural stiffness between portions. A wide variety of rib
configurations and material alternatives may be used to attain the
requisite flexural stiffness and flexural stiffness ratio of the
face portions.
[0087] In FIGS. 3-3B, a preferred embodiment of the club 10 is
shown. The club 10 has a face 16 with the following construction.
The central zone 36 has a thickness, t.sub.1, of about 0.150
inches, the intermediate zone 38 has thickness, t.sub.2, of about
0.075 inches, and the perimeter zone 40 has thickness, t.sub.3, of
about 0.120 inches. Furthermore, the central zone 36 comprises
about 20% of the total face surface area and the perimeter zone 40
is less than about 20% of the total face surface area. Each of the
three zones 36, 38, and 40 has uniform thickness within the zone
and are constructed from a single homogeneous material, preferably
a titanium alloy, with a Young's modulus (E) of approximately
16.5.times.10.sup.6 lbs/in.sup.2.
[0088] Referring to FIGS. 3-3B, the flexural stiffness, FS.sub.z,
can also be defined by the following general equation: FS z = i = 1
n .times. A i j = 1 n .times. .times. A j .times. E i .times. t i 3
##EQU1## where; [0089] A.sub.i is defined as the area of a
constituent within a zone, [0090] E.sub.i is the Young's modulus in
pounds per square inch of the constituent within a zone, j = 1 n
.times. A j .times. .times. represents .times. .times. the .times.
.times. total .times. .times. area .times. .times. of .times.
.times. the .times. .times. zone , ##EQU2## [0091] t.sub.i is the
thickness or average thickness in inches of a constituent within a
zone, [0092] n is the number of constituents within a zone. This
general equation reduces to the simplified equation
FS.sub.z=Et.sup.3, stated above when each zone has a uniform
thickness and a constant Young's modulus.
[0093] Using this simplified equation, the flexural stiffness can
be calculated for the central and abutting zones and the flexural
stiffness ratio can be computed. The flexural stiffness ratio for
the preferred embodiment golf club head 10 is calculated as, FS c =
E c .times. t c 3 = ( 16.5 10 6 .times. .times. lb .times. /
.times. in 2 ) .times. ( 0.15 .times. .times. in ) 3 = 55 , 689
.times. .times. .times. lb in , and ##EQU3## FS I = E I .times. t I
3 = ( 16.5 10 6 .times. .times. lb .times. / .times. in 2 ) .times.
( 0.075 .times. .times. in ) 3 = 6 , 961 .times. .times. lb in ,
##EQU3.2## where FS.sub.c is the flexural stiffness of central
region 36 (also denoted FS.sub.1 as herein) and FS.sub.I is the
flexural stiffness of intermediate region 38 (also denoted FS.sub.2
as herein). These values are also reported in Table 1, above.
Hence, the ratio of flexural modulus of golf club head 10 is
(FS.sub.c/FS.sub.I)=8.0.
[0094] In FIG. 6, an alternate embodiment of the club head 110 is
shown to illustrate an alternate construction of hitting face 116
that results in a similar flexural stiffness ratio of the central
portion to the abutting intermediate zone as the embodiment of FIG.
3. In the club head 110, the face 116 has an elliptically shaped
central zone 136 an adjacent intermediate zone 138. The central
zone 136 occupies about 30 percent of the total face surface
area.
[0095] Referring to FIGS. 7-7B, the central zone 136 includes a
ribbed support structure 137a (shown in phantom) that extends from
the interior surface of the face. The asterisk-shaped ribbed
structure, which comprises a plurality of ribs or legs, stiffens
the central zone. The thickness of the ribbed portion 137a of the
central zone t.sub.1A is about 0.225 inches. The width of the rib,
w, is about 0.085 inches. The thickness of the remaining portion
137b between the ribs of the central zone t.sub.1B is about 0.09
inches. The ribbed structure 137a is defined such that it comprises
about 25 percent of the surface area of the central zone. The
intermediate zone 138 has a uniform thickness, t.sub.2, of about
0.075 inches and extends to the boundary of the face 116 with no
defined perimeter zone. The face 116 is preferably made of a
homogeneous titanium alloy with a Young's modulus (E) of
16.5.times.10.sup.6 lbs/in.sup.2.
[0096] Referring to FIGS. 6-7B, the flexural stiffness ratio
between the central region 136 and the abutting intermediate zone
138 is computed, as follows:
[0097] Area of the elliptical central region 136 is
A.sub.C=.pi..times.b.times.a, where "b" is 1/2 of the major axis of
the ellipse and "a" is 1/2 of the minor axis of the ellipse. When
the major axis is 2 inches and the minor axis is 1 inch, the area
of the central region is 1.57 in.sup.2.
[0098] The area of the ribs is simply its width (WI=0.085 inch)
times its length (LI=4.6 inch) or A.sub.r=WI.times.LI=0.39
in.sup.2.
[0099] Hence, the non-rib area
A.sub.NR=A.sub.c-A.sub.r=(1.57-0.39)=1.18 in.sup.2.
[0100] Thus, the general flexural stiffness equation stated above
reduces to FS c = ( A r / A c ) .times. E .function. ( t 1 .times.
.times. A ) 3 + ( A NR / A C ) .times. E .function. ( t 2 .times. B
) 3 , .times. FS c = ( 0.39 / 1.57 ) .times. ( 16.5 10 6 .times.
.times. lb .times. / .times. in 2 ) .times. ( 0.225 .times. .times.
in ) 3 + ( 1.18 / 1.57 ) .times. ( 16.5 10 6 .times. .times. lb
.times. / .times. in 2 ) .times. ( 0.090 .times. .times. in ) 3 ,
.times. FS c = 56 , 008 .times. lb in , and ##EQU4## FS I = E
.function. ( t 2 ) 3 , = ( 16.5 10 6 .times. .times. lb .times. /
.times. in 2 ) .times. ( 0.075 .times. .times. in ) 3 , = 6 , 961
.times. .times. lb in . ##EQU4.2## Hence,
(FS.sub.c/FS.sub.I)=8.05.
[0101] It should be noted that ribs, welts, pimples, or other
discrete thickness variations within a zone are handled as discrete
elements within a particular zone and are computed in accordance
with the governing general equation for flexural stiffness
discussed above.
[0102] In FIG. 8, an alternate embodiment of the club head 210 is
shown to illustrate an alternate construction of face 216 that
results in a similar flexural stiffness ratio of the central zone
to the abutting intermediate zone as the embodiment of FIG. 3. In
the club head 210, the face 216 has a central zone 236 and an
adjacent intermediate zone 238. The central zone 236 is about 30
percent of the total face surface area. The club head 210 does not
have a defined perimeter zone.
[0103] Referring to FIGS. 9-9A, the central zone 236 has a uniform
thickness of t.sub.1 of about 0.140 inches. The intermediate zone
238 has a continuously tapered thickness from the face perimeter
inward to the central zone 236. The thickness of the intermediate
zone 238 is defined to change linearly.
[0104] The intermediate zone 238 has an inner thickness, t.sub.2A,
of about 0.07 inches at the boundary of the central zone 236 and
the intermediate zone 238. The intermediate zone 238 has an outer
thickness, t.sub.2B, of about 0.10 inches. The outer thickness is
at the face perimeter. In instances of non-uniform thickness,
within a zone, and primarily in relation to a continuous tapered
zone, an average thickness may be used to compute the flexural
stiffness for the zone. This approximation simplifies the
calculation and is physically based on elastic shell theory.
[0105] In this embodiment, two different homogenous materials are
used. The central zone 236 is preferably made from a stainless
steel having a Young's modulus of 30.0.times.10.sup.6 lbs/in.sup.2
and the adjacent intermediate zone 238 is made from a titanium
alloy with a Young's modulus of 16.5.times.10.sup.6
lbs/in.sup.2.
[0106] Referring to FIGS. 8-9A, the flexural stiffness ratio
between the central and adjacent zone is computed. FS c = E c
.function. ( t 1 ) 3 , = ( 30 10 6 .times. .times. lb .times. /
.times. in 2 ) .times. ( 0.140 .times. .times. in ) 3 , = 82 , 320
.times. .times. lb in , .times. FS I = E I .function. ( ( t 2
.times. A + t 2 .times. B ) / 2 ) 3 , = ( 16.5 10 6 .times. .times.
lb .times. / .times. in 2 ) .times. ( ( 0.1 + 0.07 ) .times. in
.times. / .times. 2 ) 3 , = 10 , 133 .times. .times. lb in .
##EQU5## Hence, (FS.sub.c/FS.sub.I)=8.12.
[0107] In FIG. 10, an alternate embodiment of the club head 310 is
shown to illustrate an alternate construction of face 316 that
results in a similar flexural stiffness ratio of the central zone
to the abutting intermediate zone as the embodiment of FIG. 3. In
the club head 310, the face 316 has an elliptically shaped central
zone 336 and an adjacent intermediate zone 338. The central zone
336 is formed using two materials 337a (shown in phantom) and 337b
(shown in phantom).
[0108] The central zone 336 has a uniform thickness, t.sub.1, of
about 0.140 inches. The first material 337a is a titanium alloy
with a Young's modulus of 16.5.times.10.sup.6 lbs/in.sup.2. The
second material 337b is stainless steel and has a Young's modulus
of 30.times.10.sup.6 lbs/in.sup.2. The central zone 336 comprises
about 60 percent stainless steel.
[0109] Furthermore, the central zone 336 is elliptically shaped and
comprises about 25 percent of the total face surface area. The
intermediate zone 338 with the perimeter zone 340 comprises of no
more than 20 percent of the total face surface area. The
intermediate zone has a uniform thickness, t.sub.2, of about 0.08
inches and is constructed from the same titanium alloy as the
central zone 336.
[0110] Referring to FIGS. 10-11A, the flexural stiffness ratio
between the central region 336 and intermediate zone 338 can be
computed, as follows.
[0111] Using the equation for determining the area for an ellipse,
stated above, when the major axis is about 1.8 inch and the minor
axis is about 0.9 inch, the area of central region 336 is
A.sub.C=1.272 in.sup.2. As discussed above, the area of stainless
steel (A.sub.S) is 60 percent and the area of titanium or non-steel
(A.sub.NS) is 40 percent. FS c = ( A s / A c ) .times. E s
.function. ( t 1 ) 3 + ( A NS / A C ) .times. E t .function. ( t 1
) 3 , .times. FS c = ( 0.60 ) .times. ( 30 10 6 .times. .times. lb
.times. / .times. in 2 ) .times. ( 0.14 .times. .times. in ) 3 + (
0.40 ) .times. ( 16.5 10 6 .times. .times. lb .times. / .times. in
2 ) .times. ( 0.14 .times. .times. in ) 3 , .times. FS c = 67 , 502
.times. .times. lb in , and ##EQU6## FS I = E t .function. ( t 2 )
3 , = ( 16.5 10 6 .times. .times. lb .times. / .times. in 2 )
.times. ( 0.080 .times. .times. in ) 3 , = 8 , 448 .times. .times.
lb in . ##EQU6.2## Hence, (FS.sub.c/FS.sub.I)=8.0.
[0112] The golf club head embodiments 10, 110, 210, and 310
discussed in FIGS. 1-11A demonstrate four unique face constructions
which result in a similar flexural stiffness ratio, where the
central zone to the adjacent zone ratio is greater than or equal to
three and, more particularly, about eight. In cases where the face
construction is uncertain due to manufacturing tolerances or
methods or for other possible reasons, a nondestructive test method
of determining the flexural stiffness ratio for a given face
construction may be used.
[0113] Referring to FIG. 12, a typical club 410 is shown with an
unknown face thickness profile. Preferably, something is known
regarding the construction materials of the face or has been
determined experimentally through test methods known to those of
ordinary skill in the art. In FIG. 12, a random distribution of
points is shown on face 416. This distribution is referred to
herein as a "point cloud" or predetermined point distribution.
Points labeled C indicate a position in the central zone 436.
Points labeled I indicate a position in the intermediate zone 438.
Points labeled P indicate a position in the perimeter zone 440. The
numbers following the position letters "C", "I" or "P" indicate
relative face position.
[0114] Using the defined point cloud, an ultrasonic measurement
device 450 (as shown in FIG. 13) can be used to map the face 416
thickness profile. The point cloud technique has the advantage of
capturing discrete variations in face thickness such as the
presence of ribs or abrupt thickness changes. One preferred
ultrasonic measurement device includes a Panametrics Model 25DL
ultrasonic thickness device 455 and a Panametrics model M208 probe
460. The sensor or device 455 and the probe or transducer 460 are
commercially available from Panametrics, Inc. of Waltham, Mass.
[0115] Referring to FIG. 12, the face thickness data obtained from
the ultrasonic measurement, along with material modulus
information, is then used to define the central, intermediate and
possibly perimeter zones. The central zone 436 is defined by
constructing an area comprising of a specific percentage of the
total face surface area and including the geometric center GC. The
point cloud thickness data within the defined zone is then averaged
or broken into distinct elements within the zone. If the latter is
required, the area percentages for the elements within the zone are
calculated. The calculation for FSz previously outlined is then
carried out to determine the flexural stiffness ratio between the
central and adjacent zone 436 and 438, respectively.
[0116] The following example illustrates the technique. In Table 4,
random face thickness measurements are shown for titanium alloy
club 410 (as shown in FIG. 12) with an unknown face thickness
profile. The technique described above is used. TABLE-US-00004
TABLE 4 ULTRASONIC FACE THICKNESS DATA Position Thickness C1 0.132
C2 0.127 C3 0.131 C4 0.125 C5 0.136 C6 0.130 C7 0.127 C8 0.129 C9
0.133 C10 0.138 C11 0.134 C12 0.131 I1 0.102 I2 0.103 I3 0.098 I4
0.096 I5 0.088 I6 0.089 I7 0.089 I8 0.094 I9 0.097 I10 0.099 I11
0.100 I12 0.103 I13 0.106 I14 0.102 I15 0.105 I16 0.101 I17 0.100
I18 0.103 I19 0.107 I20 0.106 P1 0.110 P2 0.115 P3 0.117 P4 0.119
P5 0.120 P6 0.114 P7 0.117 P8 0.109 P9 0.108 P10 0.111 P11 0.115
P12 0.118 P13 0.109 P14 0.108 P15 0.112 P16 0.112 P17 0.115 P18
0.109 P19 0.117 P20 0.120
[0117] FIG. 12 shows the measured data points and the projected
central, intermediate and perimeter zones 436, 438 and 440. Based
on these projected areas, the percentage of each zone can be
estimated or computed more accurately by other techniques, such as
face scanning. The data defines three zones, the actual central
zone with an average thickness of 0.131 inches; the actual
intermediate zone with an average thickness of 0.099 inches, and
the perimeter zone with an average thickness of 0.114 inches.
Furthermore, the area of the central zone has been estimated to be
about 23 percent of the total face surface area, and the perimeter
zone is estimated to comprise of about 35 percent of the total face
area. Based on this information a flexural stiffness ratio can be
computed as set forth below.
[0118] With regard to the calculation of face flexural stiffness
and the flexural stiffness ratio, the aforementioned embodiments
and point cloud example all consider hitting faces, which possess
isotropic material property and symmetry with regard to a
mid-surface of the face structure. Material isotropy, however, is
not a necessary condition of the invention. And the invention can
include club heads with anisiotropic materials. The flexural
stiffness or the flexural stiffness ratio can be used with
ansiotropic constructions. These calculations would still be
applicable but of a more general form, as discussed below.
[0119] The notion of symmetry with regard to a mid-surface of the
face simplifies the calculations of flexural stiffness. The
calculation of flexural stiffness for asymmetric shell structures
with respect to the mid-surface is common in composite structures
where laminate shell theory is applicable. Here the Kirkhoff shell
assumptions are applicable. Referring to FIG. 14, an asymmetric
isotropic laminate 500 is shown with N lamina or layers 502.
Furthermore, the laminate is described to be of thickness, t, with
x.sub.i being directed distances or coordinates in accordance with
FIG. 14. The positive direction is defined to be downward and the
laminate points x.sub.i defining the directed distance to the
bottom of the k.sup.th laminate layer. For example, x.sub.0=-t/2
and x.sub.N=+t/2 for a laminate of thickness t made comprised of N
layers.
[0120] Further complexity is added if the lamina can be constructed
of multiple materials, M. In this case, the area percentage, Ai is
included in the flexural stiffness calculation, as before in a
separate summation over the lamina. The most general form of
computing the flexural stiffness in this situation is, as stated
above: FS z = i = 1 n .times. A i j = 1 n .times. A j .times. E i
.times. t i 3 ##EQU7##
[0121] Due to the geometric construction of the lamina about the
mid-surface, asymmetry results, i.e., the laminate lacks material
symmetry about the mid-surface of the laminate. However, this
asymmetry does not change the calculated values for the flexural
stiffness only the resulting forces and moments in the laminate
structure under applied loads. An example of this type of
construction would be a titanium alloy face of uniform thickness
and first modulus E.sub.t, where the central zone is backed by a
steel member of width half the thickness of the titanium portion,
and having second modulus E.sub.s. In this example, the flexural
stiffness can be approximated by the simplified equation, as
follows: FS z = 1 / 3 .times. i = 1 M .times. [ E .function. ( x k
3 - x k - 1 3 ) ] .times. i .times. .times. FS z = 1 / 3 .times. {
[ E s .function. ( x 0 3 - x 1 3 ) ] + E t .function. ( x 1 3 - x 2
3 ) ] } .times. .times. here , x 0 = - t / 2 , x 1 = t / 2 - WI
.times. .times. and .times. .times. x 2 = t / 2 , substitution
.times. .times. .times. yielding .times. .times. FS z = 1 / 3
.times. { [ E s .function. ( ( - t / 2 ) 3 - ( t / 2 - WI ) 3 ) ] +
E t .function. ( ( t / 2 - WI ) 3 - ( t / 2 ) 3 ) ] } ##EQU8## If
t=0.125, then WI=0.083 and FS of this zone is 3,745 lbin, where the
thickness of the steel layer is about one-half of the thickness of
the titanium layer.
[0122] Referring to FIG. 15, a testing apparatus 650 for measuring
inertance is schematically illustrated. Generally, inertance is a
frequency response. More specifically, inertance is a measure of
the stiffness of a structure, in this instance the club face, at
various frequencies of vibration. The units of inertance are
acceleration units over force units. A preferred first resonant
frequency for the inventive face is located where the inertance is
maximized.
[0123] The test apparatus 650 includes club head 652, a rigid mass
654, an accelerometer 656, and an impact hammer 658. The mass 654
is preferably a cylindrical steel rod with a diameter of 1 inch.
Referring to FIGS. 15 and 15A, the mass 654 preferably has a
cylindrical cavity 659 at one end for receiving the accelerometer
656 and a slot 660 to accommodate the cable 662. The accelerometer
656 is connected to the geometric center of the face of the club
head 652 with a high modulus adhesive 657, such as a cyanoacrylate
based adhesive, Loctite 409, available from Loctite Corp.,
Newington, Conn. The mass 654 is then placed over the accelerometer
656 and also secured to the club face with cyanoacrylate adhesive.
The combined mass of the mass 654 and the accelerometer 656 should
equal the mass of a golf ball or 1.62 oz. The impact hammer 658 has
an integral force transducer 658a and is movable toward and away
from the free end 654a of the rigid mass, as indicated by the arrow
I, to impact the mass 654, which is attached to the club head face
at the geometric center. The impact force or excitation force is
normal to the club face, and upon impact is transmitted to the
hitting face through the mass 654.
[0124] The testing apparatus 650 further includes a junction box
and ICP power supply 660 and cables 662 electrically connected to
the accelerometer 656 and the impact hammer transducer 658a. The
junction box and ICP power supply 660 is in turn connected to a
digital signal processing board 664, located within a computer 665
with signal processing software 667. The digital signal processing
board 664, computer 665 and software 667 are used to condition
frequency signals and calculate the frequency response functions.
The accelerometer 656, transducer 658a, junction box and ICP power
supply 660, cables 662, digital signal processing board 664,
computer 665, and software 667 are commercially available and one
of ordinary skill in the art can readily identify and obtain
inertance values for golf clubs using these components. Typically,
the data from 20 impacts are averaged to reduce noise and improve
measurement accuracy. The following TABLE 5 lists specific model
numbers for the vibration equipment shown in FIG. 13.
TABLE-US-00005 TABLE 5 VIBRATION EQUIPMENT Reference Number Part
Model # Supplier 656 Accelerometer 352A10 Modal Shop of Cincinnati,
OH 658 Impact Hammer 086C01 Modal Shop 662 Cables 002T01 Modal Shop
660 Junction Box & ICP BNC 2140 National Instruments power of
Dallas, TX 664 DSP Board NI 4551 National Instruments 665 Computer
Dell Dell Computers of Optiplex Round Rock, TX Gxi 667 Software
Virtual National Bench Instruments DSA 2.5.1
[0125] Referring to FIG. 16, a graph of inertance versus frequency
for a conventional club head is shown. The conventional club head
is a Callaway Great Big Bertha War Bird with an eight degree loft.
The inertance I shown is the result of testing using apparatus 650
of FIG. 15. The point II at a frequency of 3330 Hertz represents
the first primary resonant frequency, which occurs at the first
primary maxima inertance for the inertance function I. A maxima,
which does not represent a primary resonant natural frequency of
the face, is also present in FIG. 16 at a frequency of 2572 Hertz,
which is the point 12. These secondary maxima I.sub.2 are
characterized by inertance transitions of a magnitude of less than
10 decibels. These secondary maxima may be due to crown, sole or
skirt vibrations that are not acting perpendicular to the plane of
the club face. Secondary maxima do not correlate with COR and ball
velocity, since the vibration response is either small in magnitude
or alternately not coincident with ball response. The COR for the
conventional club head tested was measured in accordance with USGA,
Rule 4-1e Appendix II Revision 2 dated Feb. 8, 1999 and was found
to be 0.785. The preferred first primary resonant frequency of
vibration is defined by the following relationship:
1/(2.times.contact duration)<I.sub.1<3/(2.times.contact
duration)
[0126] The contact duration is the time interval during which the
ball is in contact with the club face. The contact duration for a
typical driver impact is about 500 microseconds
(500.times.10.sup.-6 second). Thus, the preferred primary resonant
frequency of vibration for the club head is between about 1000 and
3000 Hz. The closer the contact time is to the lower limit, the
higher the COR and thus the higher the rebound ball velocity. More
preferably, the first primary resonant frequency is less than 2900
Hz.
[0127] FIG. 17 illustrates the inertance function of the inventive
club head. The first primary resonant frequency is at 2632 Hz, and
the COR of this inventive club was measured to be 0.824. The COR of
the invention club is greater than the conventional club of FIG.
16, and therefore will provide greater ball rebound velocity.
[0128] Several example club heads were produced with two
commercially available titanium alloys 6AL-4V and SP700. The clubs
were produced with a variety of uniform face thickness. FIG. 18
illustrates that as face thickness is reduced for a given titanium
alloy the COR increases in a linear fashion. However, different
titanium alloys with slightly different moduli have distinct trend
lines and thickness alone is insufficient to predict COR. FIG. 19
illustrates a plot of COR versus first primary resonant frequency
for the same set of club heads as those of FIG. 18. FIG. 18
illustrates that first primary resonant frequency is predictive of
COR regardless of titanium alloy. The first primary resonant
frequency of a club head may be used as a quality control factor to
ensure compliance with USGA COR rules.
[0129] In accordance to another embodiment of the present
invention, hitting face 16 is divided into two or more
non-concentric regions having distinct flexural stiffness as
illustrated in FIGS. 20-23. Club head 510 comprises toe 18, heel
20, sole plate 22, hosel 24, crown 28, and back portions similar to
the other inventive clubs described above. Club head 510 further
has a hitting face 516 that comprises an upper or crown face
portion 520 and a lower or sole face portion 522. Club head 510 may
also have an optional perimeter portion 540. Preferably, the
flexural stiffness of the crown face portion 520 is different than
the flexural stiffness of the sole face portion 522.
[0130] In accordance to one aspect, the flexural stiffness of crown
face portion 520 is preferably about one half of the flexural
stiffness of the sole face portion 522. In other words, the
flexural stiffness of hitting face 516 varies and more specifically
increases in the direction from crown 28 to sole 22. During an
on-center or near center impact with a golf ball, as the hitting
face deforms, crown face portion 520 deforms more than sole face
portion 522 due to its lower flexural stiffness. This shift in the
deformation causes a corresponding increase in launch angle of the
golf ball, when compared to a similar golf club with a similar club
loft angle but without the varying crown-to-sole flexural
stiffness.
[0131] The increase in the launch angle of the golf ball achieved
by the crown-to-sole flexural stiffness variation depends on a
number of factors, including the location of the impacts on the
hitting face and the flexural stiffness at the location of the
impacts. Conversely, the launch angle of the golf ball can be
reduced by reversing the crown-to-sole flexural stiffness
variation, i.e., the flexural stiffness of the crown face portion
520 is higher than the flexural stiffness of the sole face portion
522. In this embodiment, the launch angle decreases because the
sole face portion deforms more than the crown face portion.
[0132] Preferably, the flexural stiffness (Et.sup.3) for the crown
face portion 520 of hitting face 516 is between about 8,500 lbin
and about 60,000 lbin, and the flexural stiffness of the sole face
portion 522 is about twice (200%) of the flexural stiffness of the
crown face portion 520 or less, such that the launch angle of the
golf ball increases. On the other hand, the flexural stiffness of
the sole face portion is about one-half (50%) of the flexural
stiffness of the crown face portion or more such that the launch
angle of the golf ball decreases. Suitable ratios of flexural
stiffness between these portions include 4::1, 1::4, 2::3 or
3::2.
[0133] In accordance to another aspect of the present invention, as
illustrated in FIG. 21 hitting face 516 of club head 510 comprises
heel face portion 524 and toe face portion 526, such that the
flexural stiffness of hitting face 516 varies in the heel-to-toe
direction. Similar to the embodiment shown in FIG. 20, this hitting
face also selectively and locally deforms to direct the angle of
the golf ball in a desirable lateral direction. More specifically,
for on-center or near-center impacts when the flexural stiffness of
heel face portion 524 is lower than the flexural stiffness of toe
face portion 526, the heel face portion deforms more to direct the
angle of the ball more to the left of a right-handed golfer's body
to compensate a tendency to slice or hook the ball to the right. On
the other hand, when the flexural stiffness of the toe face portion
526 is lower than the flexural stiffness of the heel face portion
524, the toe face portion deforms more to direct the golf ball to
the right of a right-handed golfer's body to compensate for a
tendency to slice or hook the ball to the left.
[0134] Preferably, the flexural stiffness (Et.sup.3) for the heel
face portion 524 of hitting face 516 is between about 8,500 lbin
and about 60,000 lbin, and the flexural stiffness of the toe face
portion 526 is about twice (200%) of the flexural stiffness of the
heel face portion 524 or less, such that the flight of the golf
ball is directed to the left. On the other hand, the flexural
stiffness of the toe face portion is about one-half (50%) of the
flexural stiffness of the heel face portion or more such that the
flight of the golf ball is directed to the right. Suitable ratios
of flexural stiffness between these portions include 4::1, 1::4,
2::3 or 3::2.
[0135] In accordance to another aspect of the present invention,
the advantages of the hitting face shown in FIG. 20 and in FIG. 21
can be realized in a single hitting face, as illustrated in FIG.
22. Here, hitting face 516 comprises four portions: crown-heel
portion 528, crown-toe portion 530, sole-toe portion 532 and
sole-heel portion 534. The flexural stiffness of hitting face 516
can vary in both the crown-to-sole and heel-to-toe directions. The
flexural stiffness can either increase or decrease in either
direction. Hence, the advantages of altering the vertical launch
angle and the lateral direction of the flight of a golf ball can be
realized on a single golf club head.
[0136] Preferably, the flexural stiffness of the crown-heel portion
528 is between about 8,500 lbin and about 60,000 lbin. The flexural
stiffness of the crown-toe portion 530 is preferably about 70% to
about 130% of the flexural stifffiess of crown-heel portion 528.
The flexural stiffness of the sole-toe portion 532 is preferably
about 50% to about 130% of the flexural stiffness of crown-heel
portion 528. The flexural stiffness of the sole-heel portion 534 is
preferably about 70% to about 200% of the flexural stiffness of
crown-heel portion 528.
[0137] Alternatively, the hitting face 516 may comprise two or more
non-concentric portions that make up any regular or irregular
shape, such as the embodiment illustrated in FIG. 23. Furthermore,
the boundaries between the non-concentric regions do not have to be
substantially horizontal or substantially vertical.
[0138] Another readily apparent advantage of this embodiment is
that it can reduce the manufacturing costs for golf clubs. The
flexural stiffness of the hitting face can be altered in accordance
to the present invention to achieve the effect of multiple lofts
for a given head club design having a fixed loft angle. Tooling for
a single mold with various face cavity inserts can produce a family
of club heads having varying effective loft angles, albeit with a
same exterior loft angle.
[0139] In accordance to another embodiment of the present
invention, the advantages of the embodiments shown in FIGS. 1-19,
i.e., having a rigid central portion 36, 136, 236, 336 or 446 and
relatively flexible intermediate portion 38, 138, 238, 338 or 448,
so that upon impact the intermediate portion deforms to provide
high initial velocity while the central portion is substantially
un-deformed so that the ball flies on-target
(FS.sub.c/FS.sub.I.gtoreq.3), among others, can be combined with
the advantages of the embodiments shown in FIGS. 20-23, i.e.,
vertical and lateral control of the ball's flight. As illustrated
in FIGS. 24-25, golf club head 610 comprises hitting face 616,
which has a central portion 36, 136, 236, 336 or 436 surrounded by
an intermediate portion comprising crown intermediate portion 620
and sole intermediate portion 622. Face 616 may also comprise an
optional perimeter region (not shown). Preferably, the ratio of
flexural stiffness between the central region and any portion of
the intermediate region is greater than or equal to about 3.0, and
more preferably between about 6.0 and about 12.0. In other words,
this ratio between the central region and the crown intermediate
portion 620 and between the central region and the sole
intermediate portion 622 is greater than or equal to about 3.0, and
more preferably between about 6.0 and about 12.0.
[0140] In this embodiment, preferably the flexural stiffness of the
two intermediate portions 620 and 622 are different. Crown
intermediate portion 620 may have a lower flexural stiffness than
sole intermediate portion 622, or vice versa, depending on the
desired launch angle of the ball. In one non-limiting example, the
ratio of flexural stiffness between the central region and the
crown intermediate portion 620 is about 9.0, while the same ratio
between the central region and the sole intermediate portion is
about 6.0 to control the launch angle of the golf ball.
[0141] On the other hand, to control the lateral launch angle of
the golf ball while maintaining the high initial velocity produced
by the (FS.sub.c/FS.sub.I.gtoreq.3) flexural stiffness ratio,
hitting face 616 may comprise central region 36, 136, 236, 336 or
436 and an intermediate region comprising heel intermediate portion
624 and toe intermediate portion 626, as shown in FIG. 26.
Preferably, the ratio of flexural stiffness between the central
region and any portion of the intermediate region is greater than
or equal to about 3.0, and more preferably between about 6.0 and
about 12.0. In other words, this ratio between the central region
and the heel intermediate portion 620 and between the central
region and the toe intermediate portion 622 is greater than or
equal to about 3.0, and more preferably between about 6.0 and about
12.0, or greater than 12.0.
[0142] In this embodiment, preferably the flexural stiffness of the
two intermediate portions 624 and 626 are different. Heel
intermediate portion 620 may have a lower flexural stiffness than
toe intermediate portion 622, or vice versa, depending on the
desired lateral angle of the ball. In one non-limiting example, the
ratio of flexural stiffness between the central region and the heel
intermediate portion 620 is about 9.0, while the same ratio between
the central region and the toe intermediate portion is about 6.0 to
control the lateral angle of the golf ball.
[0143] In accordance to another aspect of the invention, hitting
face 616 may comprise a central region, as discussed above, and an
intermediate region comprising four portions: crown-heel
intermediate portion, crown-toe intermediate portion, sole-toe
intermediate portion and sole-heel intermediate portion, similar to
the embodiment shown in FIG. 22. Each intermediate portion
preferably has different flexural stiffness to vary the launch and
lateral angle of the golf ball. Furthermore, the ratio of flexural
stiffness between the central region and each of the intermediate
portions is greater than or equal to about 3.0, and more preferably
between about 6.0 and about 12.0.
[0144] While various descriptions of the present invention are
described above, it should be understood that the various features
of each embodiment can be used alone or in any combination thereof.
Therefore, this invention is not to be limited to only the
specifically preferred embodiments depicted herein. Further, it
should be understood that variations and modifications within the
spirit and scope of the invention may occur to those skilled in the
art to which the invention pertains. For example, the face and/or
individual portions can have thickness variations in a step-wise or
continuous fashion. Other modifications include a perimeter portion
that has a thickness that is greater than or less than the
adjacent, intermediate portion. In addition, the shapes of the
central, intermediate, and perimeter portions are not limited to
those disclosed herein. Accordingly, all expedient modifications
readily attainable by one versed in the art from the disclosure set
forth herein that are within the scope and spirit of the present
invention are to be included as further embodiments of the present
invention. The scope of the present invention is accordingly
defined as set forth in the appended claims.
* * * * *