1. Field of the Invention
The present invention relates to a golf club head designed with optimized inertial properties and center of mass relative through the center of gravity.
2. Description of the Related Art
As driver golf club heads have increased in volume (>300 cubic centimeters) their moments of inertia have also increased, providing greater forgiveness for off-center hits. The conventional method for enlargement of golf club heads was to maximize the spatial distribution of mass in all three orthogonal orientations. Although this approach was effective in increasing the moments of inertia of the golf club heads, it also resulted in the center of gravity of the golf club head being positioned substantially rearward from the front face of the golf club head.
As the center of gravity is positioned further rearward from the front face, deleterious effects result for shots struck off-center from the sweet spot of the golf club head. Increased gear effect is the main cause of the deleterious effects. For heel-ward or toe-ward off-center hits, the increased gear effect can cause increased side-spin, which increases dispersion, reduces distance and reduces robustness of ball flight. For off-center hits above the sweet spot, the increased gear effect causes reduced backspin, which can cause an undesirable trajectory having insufficient carry length or time of flight, which in turn can result in reduced distance and reduced robustness.
In addition, the same conventional golf club head designs are limited with regard to the maximum face area, both physical and practical limitations. The physical limitation is due to the golf club head having insufficient mass to both increase the length and width of the golf club head and also to increase the face size without exceeding the upper range of the preferred total golf club head mass. Such mass distributions are dependent on minimum wall thickness values required to achieve acceptable in-service durability.
The practical limitation is that as the face size is increased, hit locations in certain regions around the face perimeter will yield an unsatisfactory ball flight due to the aforementioned deleterious effects, which are accentuated for larger faces. The deleterious effects increase in a non-linear manner as the distance from the face center increases. Thus the incremental face area gained by increasing face size will be subject to more extreme deleterious effects. This limits the practical length of the club, because probable hit distribution across the surface of the face broadens as the club length increases. As a result a longer club will yield a larger percentage of hits in the perimeter regions of the face where the deleterious effects occur. This offsets the otherwise beneficial effect of increased head speed. As club length increases, head speed increases up to a length of approximately 52 inches, at which point aerodynamic and biomechanical effects offset the length effect.
Further, conventional head designs having a center of gravity positioned substantially rearward from the face are subject to significant dynamic loft effects, which can be undesirable. Dynamic loft increases with head speed, so that golfers with higher head speeds experience more dynamic loft than those with slower swing speeds. This is opposite of what is desired as higher head speeds generally require less loft, otherwise excess backspin will be generated, which negatively affects trajectory and performance.
One invention that addresses center of gravity depth is set forth in U.S. Pat. No. 6,344,002 to Kajita for a Wood Club Head. The Kajita invention discloses a golf club head with a center of gravity not more than 30 mm (1.18 inches) from the face. However, the Kajita invention does not address a high moment of inertia about the horizontal axis.
U.S. Pat. No. 6,146,571 to Vincent, et. al., discloses a method of manufacturing a golf club head wherein the walls are obtained by injecting a material such as plastic over an insert affixed to a meltable core. The core has a melt point lower than that of the injectable plastic material so that once the core is removed, an inner volume is maintained to form the inner cavity. The insert may comprise a resistance element for reinforcing the internal portion of the front wall of the shell upon removal of the core where the reinforcement element is comprised of aluminum with a laterally extending portion comprised of steel.
U.S. Pat. No. 6,149,534 to Peters, et al., discloses a golf club head having upper and lower metal engagement surfaces formed along a single plane interface wherein the metal of the lower surface is heavier and more dense than the metal of the upper surface.
U.S. Pat. Nos. 5,570,886 and 5,547,427 to Rigal, et al., disclose a golf club head of molded thermoplastic having a striking face defined by an impact-resistant metallic sealing element. The sealing element defines a front wall of the striking surface of the club head and extends upward and along the side of the impact surface to form a neck for attachment of the shaft to the club head. The sealing element preferably being between 2.5 mm and 5 mm in thickness.
U.S. Pat. No. 5,425,538 to Vincent, et al., discloses a hollow golf club head having a steel shell and a composite striking surface composed of a number of stacked woven webs of fiber.
U.S. Pat. No. 5,377,986 to Viollaz, et al., discloses a golf club head having a body composed of a series of metal plates and a hitting plate comprised of plastic or composite material wherein the hitting plate is imparted with a forwardly convex shape. Additionally, U.S. Pat. No. 5,310,185 to Viollaz, et al., discloses a hollow golf club head having a body composed of a series of metal plates, a metal support plate being located on the front hitting surface to which a hitting plate comprised of plastic or composite is attached. The metal support plate has a forwardly convex front plate associated with a forwardly convex rear plate of the hitting plate thereby forming a forwardly convex hitting surface.
U.S. Pat. No. 5,106,094 to Desboilles, et al., discloses a golf club head having a metal striking face plate wherein the striking face plate is a separate unit attached to the golf club head with a quantity of filler material in the interior portion of the club head.
U.S. Pat. No. 4,568,088 to Kurahashi discloses a wooden golf club head body reinforced by a mixture of wood-plastic composite material. The wood-plastic composite material being unevenly distributed such that a higher density in the range of between 5 mm and 15 mm lies adjacent to and extends substantially parallel with the front face of the club head.
U.S. Pat. No. 4,021,047 to Mader discloses a golf club wherein the sole plate, face plate, heel, toe and hosel portions are formed as a unitary cast metal piece and wherein a wood or composite crown is attached to this unitary piece thereby forming a hollow chamber in the club head.
U.S. Pat. No. 5,624,331 to Lo, et al. discloses a hollow metal golf club head where the metal casing of the head is composed of at least two openings. The head also contains a composite material disposed within the head where a portion of the composite material is located in the openings of the golf club head casing.
U.S. Pat. No. 1,167,387 to Daniel discloses a hollow golf club head wherein the shell body is comprised of metal such as aluminum alloy and the face plate is comprised of a hard wood such as beech, persimmon or the like. The face plate is aligned such that the wood grain presents endwise at the striking plate.
U.S. Pat. No. 3,692,306 to Glover discloses a golf club head having a bracket with sole and striking plates formed integrally thereon. At least one of the plates has an embedded elongate tube for securing a removably adjustable weight means.
U.S. Pat. No. 5,410,798 to Lo discloses a method of manufacturing a composite golf club head using a metal casing to which a laminated member is inserted. A sheet of composite material is subsequently layered over the openings of the laminated member and metal casing to close off the openings in the top of both. An expansible pocket is then inserted into the hollow laminated member comprising sodium nitrite, ammonium chloride and water causing the member to attach integrally to the metal casing when the head is placed into a mold and heated.
U.S. Pat. No. 4,877,249 to Thompson discloses a wood golf club head embodying a laminated upper surface and metallic sole surface having a keel. In order to reinforce the laminations and to keep the body from delaminating upon impact with an unusually hard object, a bolt is inserted through the crown of the club head where it is connected to the sole plate at the keel and tightened to compress the laminations.
U.S. Pat. No. 3,897,066 to Belmont discloses a wooden golf club head having removably inserted weight adjustment members. The members are parallel to a central vertical axis running from the face section to the rear section of the club head and perpendicular to the crown to toe axis. The weight adjustment members may be held in place by the use of capsules filled with polyurethane resin, which can also be used to form the faceplate. The capsules have openings on a rear surface of the club head with covers to provide access to adjust the weight means.
U.S. Pat. No. 2,750,194 to Clark discloses a wooden golf club head with weight adjustment means. The golf club head includes a tray member with sides and bottom for holding the weight adjustment preferably cast or formed integrally with the heel plate. The heel plate with attached weight member is inserted into the head of the golf club via an opening.
U.S. Pat. No. 5,193,811 to Okumoto, et al., discloses a wood type club head body comprised primarily of a synthetic resin and a metallic sole plate. The metallic sole plate has on its surface for bonding with the head body integrally formed members comprising a hosel on the heel side, weights on the toe and rear sides and a beam connecting the weights and hosel. Additionally, U.S. Pat. No. 5,516,107 to Okumoto, et al., discloses a golf club head having an outer shell, preferably comprised of synthetic resin, and metal weight member/s located on the interior of the club head. A foamable material is injected into the hollow interior of the club to form the core. Once the foamable material has been injected and the sole plate is attached, the club head is heated to cause the foamable material to expand thus holding the weight member/s in position in recess/es located in toe, heel and/or back side regions by pushing the weight member into the inner surface of the outer shell.
U.S. Pat. No. 4,872,685 to Sun discloses a wood type golf club head wherein a female unit is mated with a male unit to form a unitary golf club head. The female unit comprises the upper portion of the golf club head and is preferably composed of plastic, alloy, or wood. The male unit includes the structural portions of sole plate; a face insert consists of the striking plate and weighting elements. The male unit has a substantially greater weight being preferably composed of a light metal alloy. The units are mated or held together by bonding and or mechanical means.
U.S. Pat. No. 5,398,935 to Katayama discloses a wood golf club head having a striking face wherein the height of the striking face at a toe end of the golf club head is nearly equal to or greater than the height of the striking face at the center of the club head.
U.S. Pat. No. 1,780,625 to Mattern discloses a club head with a rear portion composed of a light-weight metal such as magnesium. U.S. Pat. No. 1,638,916 to Butchart discloses a golf club with a balancing member composed of persimmon or a similar wood material, and a shell-like body composed of aluminum attached to the balancing member.
Anderson, U.S. Pat. Nos. 5,024,437, 5,094,383, 5,255,918, 5,261,663 and 5,261,664 disclose a golf club head having a full body composed of a cast metal material and a face insert composed of a hot forged metal material.
Viste, U.S. Pat. No. 5,282,624 discloses a golf club head with a cast metal body and a forged steel face insert with grooves on the exterior surface and the interior surface of the face insert and having a thickness of 3 mm.
Rogers, U.S. Pat. No. 3,970,236, discloses an iron club head with a formed metal face plate insert fusion bonded to a cast iron body.
Aizawa, U.S. Pat. No. 5,242,168 discloses a golf club head having a fiber reinforced resin body with a thin metallic film layer.
Yamada, U.S. Pat. No. 4,535,990 discloses a golf club head having a fiber reinforced resin body with a face insert composed of a polycarbonate or like material.
Aizawa et al., U.S. Pat. No. 5,465,968 discloses a golf club head having a fiber reinforced resin body with a beryllium face plate.
The Rules of Golf, established and interpreted by the United States Golf Association (“USGA”) and The Royal and Ancient Golf Club of Saint Andrews, set forth certain requirements for a golf club head. The requirements for a golf club head are found in Rule 4 and Appendix II. Complete descriptions of the Rules of Golf are available on the USGA web page at www.usga.org. Although the Rules of Golf do not expressly state specific parameters for a golf club face, Rule 4-1e prohibits the face from having the effect at impact of a spring with a golf ball. In 1998, the USGA adopted a test procedure pursuant to Rule 4-1e, which measures club face COR. This USGA test procedure, as well as procedures like it, may be used to measure club face COR.