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.”
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.
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.
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.
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.
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, IZZ, which is at least about 4400 g·cm2. The face further includes a bulge curvature and a roll curvature, and the bulge curvature is between about 0 cm−1 and about 0.027 cm−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, IXX, is at least about 2500 g·cm2, and in another embodiment IXX is at least about 3000 g·cm2. In certain embodiments, IZZ is greater than IXX. In another embodiment, the face includes a front side and a back side that define a variable face thickness.
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−1 and about 0.066 cm−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 IZZ is between about 4400 g·cm2 and about 5000 g·cm2. 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 IZZ is between about 5000 g·cm2 and about 5500 g·cm2. 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 IZZ is between about 5500 g·cm2 and about 6000 g·cm2. 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 IZZ is about 6000 g·cm2.
In certain described embodiments, the bulge curvature is between about 0.016 cm−1 and about 0.027 cm−1. In other embodiments, the roll curvature is between about 0.033 cm−1 and about 0.066 cm−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−1. In some embodiments, the bulge curvature and the roll curvature are constant over the face of the golf club head.
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, IZZ, is at least about 4400 g·cm2, and the moment of inertia about the CG X axis, IXX, is at least about 2500 g·cm2 and IZZ is greater than IXX. Further, the ratio of the bulge curvature divided by the roll curvature, RC, satisfies the following equation:
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.
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, IZZ, is at least about 4400 g·cm2, and the moment of inertia about the CG X axis, IXX, is at least about 2500 g·cm2 and IZZ is greater than IXX. The ratio of the bulge curvature divided by the roll curvature, RC, satisfies the following equation:
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.
As shown in
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.
The method used to obtain the values in the present disclosure is the optical comparator method. Referring back to
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.
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−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.
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
A moment of inertia about a golf club head CG X-axis such as that shown in
I
XX=∫(y2+z2)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
Similarly, a moment of inertia about the golf club head CG Z-axis is calculated by the following equation:
I
ZZ=∫(x2+y2)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.
According to the present disclosure, the MOI about the CG X axis IXX is at least about 2500 g·cm2 and can be as high as about 5000 g·cm2. The MOI about the CG Z axis IZZ is greater than IXX and is at least about 4400 g·cm2 and can be as high as about 6000 g·cm2. It is understood that the MOI about the CG Z axis can be higher than 6000 g·cm2.
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 IXX and the CG Z-axis IZZ.
If the MOI around the CG Z axis IZZ 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 Θ relative to the centerline of the swing 20, compensating for the reduced gear effect associated with a club having a relatively high MOI.
Making reference to elements described in
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, IXX, 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, IXX, 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.
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.
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.
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−1 and about 0.027 cm−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, Kb (cm), and roll curvature, Kr (cm) satisfy the equation:
Computer simulations were performed with a variety of different testing parameters.
Computer simulations were performed to determine bulge radii for a variety of MOIs about the CG Z axis, IZZ. 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, IZZ values ranged from 4000 g·cm2 to 6000 g·cm2. 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. RBulge is the bulge radius, in centimeters.
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:
As can be seen from Table 3, the bulge radius, RBulge, (in centimeters) for a golf club swung with a headspeed of 70 mph, according to the computer simulation, is RBulge=0.00517*IZZ+20.8. Similarly, the bulge radius, RBulge, (in centimeters) for a golf club swung with a headspeed of 90 mph is 0.00522*IZZ+12.7. Similar results are obtained for the other headspeeds by referring to Table 3.
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, IZZ, can be determined by the equation RBulge=0.00505*IZZ+13.95.
As described above, the preferred MOI about the CG Z axis IZZ is between about 4400 g·cm2 and about 6000 g·cm2. Thus the preferred RBulge is between about 36.17 cm and about 44.25 cm, respectively corresponding to a preferred bulge curvature range between about 0.023 cm−1 and about 0.028 cm−1. In other embodiments, the bulge curvature may be even lower, such as 0.016 cm−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−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.
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 RRoll of 20.3 centimeters, this produces the following bulge radius to roll radius equations:
For a range of MOI about the CG Z axis IZZ between about 3500 g·cm2 and about 6000 g·cm2, these equations give the following range of bulge radius to roll radius ratios for each head speed:
In the preferred embodiment, using the ideal RBulge equation RBulge=0.00505*IZZ+13.95, the ratio of the bulge radius to the roll radius becomes:
Using a range of MOIs about the CG Z axis, IZZ, between about 4400 g·cm2 and about 6000 g·cm2, this equation produces a range for the ratio of the bulge radius to the roll radius between 1.78:1-2.13:1.
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:
Using a range of MOIs about the CG Z axis, IZZ, between about 4400 g·cm2 and about 6000 g·cm2, this equation produces a range for the ratio of the bulge radius to the roll radius between 1.42:1-1.74:1
Because the curvature is defined as 1/RBulge or 1/RRoll, the ratio of the bulge curvature to the roll curvature can be defined as 1/(RBulge/RRoll). Useful bounding equations can then be defined according to the computer simulation for the ratio of the bulge curvature to the roll curvature, RC, in the preferred embodiment as:
A broader ratio of curvatures RC can also be defined using the broader range of roll radii between 15.24 centimeters and 30.48 centimeters as follows:
Experimental testing of varying bulge radii and MOI about the CG Z axis IZZ was conducted, and the bulge for each IZZ was found for a plurality of IZZ. The results are summarized as follows:
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, IZZ. 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, IZZ can be found using the equation RBulge=0.0085*IZZ+3.387 where R is the bulge radius, in centimeters.
These experimental results further indicate a range for the ratio of the bulge curvature divided by roll curvature, indicated by the variable RC. This range can be expressed by the equation:
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 (RC) for a range of MOIs about the CG Z axis, IZZ. For example, the overall range for RC for IZZ between about 4400 g·cm2 and about 6000 g·cm2 is between 0.28 and 0.75. The range for RC for IZZ between about 4400 g·cm2 and about 5000 g·cm2 is between about 0.33 and 0.75. The other ranges for RC for this embodiment of the golf club can be found by reference to Table 1, above.
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 IZZ golf club heads.
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.
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.
Thus, the present invention discloses the most preferred and effective bulge to roll curvature ratio. Therefore, straighter and longer golf shots are possible.
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.
This application is a continuation of U.S. patent application Ser. No. 12/316,921, filed Dec. 16, 2008, which claims the benefit of U.S. Provisional Application Nos. 61/008,690, filed Dec. 21, 2007, and 61/080,203, filed Jul. 11, 2008, all of which applications are incorporated herein by reference.
Number | Date | Country | |
---|---|---|---|
61008690 | Dec 2007 | US | |
61080203 | Jul 2008 | US |
Number | Date | Country | |
---|---|---|---|
Parent | 12316921 | Dec 2008 | US |
Child | 13204487 | US |