Patent Application
20090203467
The present invention relates to an improved metal wood or driver golf club. More particularly, the present invention relates to a hollow golf club head with a lower center of gravity and a higher moment of inertia.
The complexities of golf club design are known. The specifications for each component of the club (i.e., the club head, shaft, 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.
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, center of gravity, rotational moment of inertia, material selection, and overall head weight. While this basic set of criteria is generally the focus of golf club designers, 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 a hosel or a shaft attachment means, perimeter weights on the club head, and fillers within the hollow club heads.
Golf club heads must also be strong to withstand the repeated impacts that occur during collisions between the golf club and the golf balls. The loading that occurs during this transient event can create a peak force of over 2,000 lbs. Thus, a major challenge is to design the club face and club body to resist permanent deformation or failure by material yield or fracture. Conventional hollow metal wood drivers made from titanium typically have a uniform face thickness exceeding 2.5 mm or 0.10 inch to ensure structural integrity of the club head.
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 initial 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 designers. 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 and club face flexibility.
Concerned that improvements to golf equipment may render the game less challenging, 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 equipment. These performance specifications dictate the size and weight of a conforming golf ball or a conforming golf club. USGA rules limit a number of parameters for drivers. For example, the volume of drivers has been limited to 460±10 cubic centimeters. The length of the shaft, except for putter, has been capped at 48 inches. The driver clubs have to fit inside a 5-inch square and the height from the sole to the crown cannot exceed 2.8 inches. The USGA has further limited the coefficient of restitution of the impact between a driver and a golf ball to 0.830.
The USGA has also observed that the rotational moment of inertia of drivers, or the club's resistance to twisting on off-center hits, has tripled from about 1990 to 2005, which coincides with the introduction of oversize drivers. Since drivers with higher rotational moment of inertia are more forgiving on off-center hits, the USGA was concerned that further increases in the club head's inertia may reduce the challenge of the game, albeit that only mid and high handicap players would benefit from drivers with high moment of inertia due to their tendencies for off-center hits. In 2006, the USGA promulgated a limit on the moment of inertia for drivers at 5900 g·cm2±100 g·cm2 or 32.259 oz·in2±0.547 oz·in2. The limit on the moment of inertia is to be measured around a vertical axis, the y-axis as used herein, through the center of gravity of the club head.
A number of patent references have disclosed driver clubs with high moment of inertia, such as U.S. Pat. Nos. 6,607,452 and 6,425,832. These driver clubs use a circular weight strip disposed around the perimeter of the club body away from the hitting face to obtain a moment of inertia from 2800 to 5000 g·cm2 about the vertical axis. U.S. Pat. App. Pub. No. 2006/0148586 A1 discloses driver clubs with moment of inertia in the vertical direction from 3500 to 6000 g·cm2. However, the '586 application limits the shape of the driver club to be substantially square when viewed from the top, and the moment of inertia in the horizontal direction through the center of gravity is significantly lower than the moment of inertia in the vertical direction.
However, most oversize drivers on the market at this time have moments of inertia in the range of about 4,000 to 4,300 g·cm2. Hence, there remains a need for more forgiving drivers or metal wood clubs for mid to high handicap players to take advantage of the higher limit on moment of inertia in both the vertical and horizontal directions.
The present invention includes more efficient shapes for hollow club heads, such as metal woods, drivers, fairway woods, putters or utility clubs. These shapes include, but are not limited to, triangles, truncated triangles or trapezoids. These shapes use less surface area, and more weight can be re-positioned to improve the rotational moments of inertia and the location of the center of gravity.
The present invention also includes hollow golf club heads that have a lightweight midsection so that more weight can be redistributed to improve the rotational moments of inertia and the location of the center of gravity.
The foregoing and other features and advantages of the invention will be apparent from the following description of the invention as illustrated in the accompanying drawings. The accompanying drawings, which are incorporated herein and form a part of the specification, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.
a-2d are the top, perspective, side and front views, respectively, of an idealized triangular inventive club head;
a-3d are the top, perspective, side and front views, respectively, of another idealized club head;
Rotational moment of inertia (“MOI” or “Inertia”) in golf clubs is well known in the art, and is fully discussed in many references, including U.S. Pat. No. 4,420,156, which is incorporated herein by reference in its entirety. When the inertia is too low, the club head tends to rotate excessively from off-center hits. Higher inertia indicates higher rotational mass and less rotation from off-center hits, thereby allowing off-center hits to fly farther and closer to the intended path. Inertia can be measured about a vertical axis going through the center of gravity of the club head (Iyy), and about a horizontal axis through the center of gravity (c.g.) of the club head (Ixx), as shown in
Inertia is also measured about the shaft axis (Isa), also shown in
In general, to increase the sweet spot, the center of gravity of the club head is moved toward the bottom and back of the club head. This permits an average golfer to launch the ball up in the air faster and hit the ball farther. In addition, the moment of inertia of the club head is increased to minimize the distance and accuracy penalties associated with off-center hits. In order to move the weight down and back without increasing the overall weight of the club head, material or mass is taken from one area of the club head and moved to another. Materials can be taken from the face of the club, creating a thin club face, the crown and/or the sole and placed toward the back of the club.
The inventors of the present invention have discovered a unique and efficient shape for a club head that can provide high rotational moments of inertia in both the vertical and horizontal axis through the c.g. Such a club head is illustrated in an idealized form in
Idealized club head 10 meets all of the USGA size limits. More particularly, the volume of the club head is set at 460 cc and its weight is limited to 200 grams. As best shown in
The thickness of hitting face 14 is set at 0.122 inch to imitate an actual hitting face and the side wall of the rest of the club is set at about 0.026 inch. While keeping the weight of the club head at 200 grams, due to the efficient use of surface area, i.e., minimizing the surface area of the club head to reduce the weight of the club head, a weight of about 19 grams can be saved and can be positioned proximate to aft 16 to maximize the location of the c.g. and to maximize the rotational inertias of the club head. The mass properties of idealized club head 10 are shown in Table 1.
As shown in Table 1, Iyy or the vertical rotational inertia through c.g. is at the USGA limit and Ixx or the horizontal rotational inertia through c.g. is also substantial. A relatively high Ixx is more forgiving on high or low impacts with the golf balls relative to the c.g. and reduces the tendency to alter the trajectory of the ball's flight. The inertias shown in Tables 1, 2 and 3 are calculated using a commercially available CAD (computer aided design) system.
Another idealized club head shape, shown in
The thickness of hitting face 24 is also set at 0.122 inch to imitate an actual hitting face and the side wall of the rest of the club is set at about 0.026 inch. While keeping the weight of the club head at 200 grams, due to the higher surface area caused by the rectangular shape, a weight of only 3.7 grams can be saved and positioned proximate to aft 26. The mass properties of idealized club head 20 are shown and compared to those of idealized club head 10 in Table 2.
The advantages of the triangular shape for the driver club head are clearly shown in Table 2. While the weight, volume and Iyy are the same or substantially the same for both shapes, the more efficient triangular shape allows significantly more weight to be placed aft of the hitting face to improve c.g. and Ixx.
Club head 30, as shown in
The volume of club head 30 is about 450 cc or higher and its weight is about 194 grams to about 200 grams. Its height is about 2.4 inches or less. The entire club head can fit into a 5-inch square with about 5 mm of clearance. Hosel 38 is preferably made from a low density material, such as aluminum, and is located substantially above a plane located at a peak of crown 32. This triangular/trapezoidal shape has less than about 8% by volume behind the c.g. than a traditional pear shaped driver. The club has a titanium hitting face with a thickness of about 0.130 inch. The rest of the club is made from titanium with a thickness of about 0.024 inch for the crown and skirt and about 0.030 inch for the sole. The mass properties of inventive, non-idealized club head 30 are shown in TABLE 3.
In accordance with another aspect of the present invention, weight from the crown, sole and skirt/side of the club head is moved aft or to the perimeter of the club head to increase rotational inertia of the club head. Additionally, a mid-section of the club head is made from a lightweight material, such as carbon fiber composites, aluminum, magnesium, thermoplastic or thermoset polymers, so that additional weights can be re-deployed from the midsection to the aft section and/or along the perimeter.
As shown in
In one embodiment, midsection 50 is attached to front hitting cup 42 and aft cup 48 by adhesives, such as DP420NS or DP460NS, which are two-part epoxies available from 3M, among other known adhesives.
In Table 4 below, the mass properties calculated by a CAD program of an all titanium version of club head 30 and of composite club head 40 are shown. In this example, club head 40 is made out of titanium, which has a density of about 4.43 g/cc, and has carbon fiber tube midsection, which has a density of about 1.2 g/cc. The density of the midsection should be equal to or less than about half as much as and preferably equal to or less than about a third as much as the density of front hitting cup and/or the density of the aft cup.
The results from Table 4 show that using the lightweight midsection allows 43.3 grams of weight (instead of 21 grams) to be utilized aft or around the perimeter to increase rotational inertias. The c.g. is lowered by about 0.035 inch. Iyy is increased by about 11.9% and Ixx is increased by about 25.7%.
Other embodiments of the triangular/trapezoidal club head with lightweight midsections are shown in
Club head 70, shown in
Club head 80, shown in
Club head 90, shown in
Club head 100, shown in
Club head 110, shown in
Additionally, club head 120, shown in
The mass properties of various composite club heads with a lightweight midsection and those of other club heads of various geometries were estimated using a CAD program to ascertain the optimal shape(s), c.g. locations and rotational inertias. The results are summarized in Table 5. For reference purpose, the mass properties of club heads 30 and 40 from Table 4 are repeated in Table 5 as Assemblies #3b and #3b-cf1, respectively.
All the club heads in Table 5 weigh 197 grams, and have a sole thickness of about 0.030 inch and crown/side wall thickness of about 0.024 inch, except that Assembly #3 has a crown/side wall thickness of 0.030 inch and Assemblies #3b-cf1 and #3b-cf2 have Ti sidewalls of about 0.030 inch and carbon fiber midsection sidewalls of about 0.035 inch. Additionally, the “Maximum Dimensions” column indicates the dimensions of a rectangular prism that the club head would fit within. The maximum rectangular prism allowed by the USGA is 5″×5″×2.8″.
The results in Table 5 show that the club heads that contain a lightweight midsection, i.e., Assemblies #3b-cf1 and #3b-cf2, have the highest combination of Ixx and Iyy. Additionally, the results from Assemblies #1 and #2 show that for triangular club head, such as those shown in
The club heads of the present invention can also be used with other types of hollow golf clubs, such as fairway woods, hybrid clubs or putters.
While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of illustration and example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the appended claims and their equivalents. It will also be understood that each feature of each embodiment discussed herein, and of each reference cited herein, can be used in combination with the features of any other embodiment. All patents and publications discussed herein are incorporated by reference herein in their entirety.
The present application is a continuation of pending U.S. patent application Ser. No. 11/552,729, filed Oct. 25, 2006, the disclosure of which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11552729 | Oct 2006 | US |
| Child | 12193110 | US |
