DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0031] Parent patent application Ser. No. 09/551,771, which has been incorporated herein in its entirety, discloses an improved golf club that also produces a relatively large “sweet spot” or zone of substantially uniform high initial velocity or high coefficient of restitution (COR).

[0032] COR or coefficient of restitution is one way of measuring ball resiliency. 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_club-post−v_ball-post)/(v_ball-pre−v_club-pre)

[0033] where,

[0034] v_club-post represents the velocity of the club after impact;

[0035] v_ball-post represents the velocity of the ball after impact;

[0036] v_club-pre represents the velocity of the club before impact (a value of zero for USGA COR conditions); and

[0037] v_ball-post represents the velocity of the ball before impact.

[0038] 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 distance.

[0039] As shown in FIGS. 1, 1A and 1B (which are designated as FIGS. 3, 3A and 3B in the parent application), the accuracy of the club and the club's large zone of uniform high initial velocity are produced by hitting face 2, having central portion 4 and a surrounding intermediate portion 6. The central portion is 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 undeformed so that the ball flies on-target. Thus, upon ball impact the deformation of intermediate portion 6 allows central region 4 to move into and out of the club head as a unit. Surrounding intermediate portion 6 may be located adjacent to central portion 4 or another portion may be interposed therebetween. As a result, the head exhibits a coefficient of restitution greater than about 0.81.

[0040] The above is accomplished by providing central portion 4 with a first flexural stiffness and intermediate portion 6 with a second flexural stiffness. Flexural stiffness (FS) is defined as each portion's average Elastic modulus (E) times each portion's average thickness (t) cubed or (FS=Et³). The calculation of averages of modulus and thickness is fully disclosed in the parent application, which has already been incorporated by reference in its entirety. The flexural stiffness of central portion 4 is substantially different from the flexural stiffness of surrounding intermediate portion 6. As a result, upon ball impact, intermediate portion 6 exhibits substantial deformation so that central portion 4 moves into the club head, and the central portion exhibits minimal deformation. In one embodiment, the flexural stiffness of the central portion is at least three times the flexural stiffness of the surrounding intermediate portion. In other embodiments, the flexural stiffness of the central portion is preferably at least six to at least twelve times the flexural stiffness of the surrounding intermediate portion. More preferably, the flexural stiffness of the central portion is greater than about 25,000 lb-in. Most preferably, the flexural stiffness of the central portion is greater than about 55,000 lb-in. Preferably, the flexural stiffness of the surrounding intermediate portion is less than about 16,000 lb-in. More preferably, the flexural stiffness of the surrounding intermediate portion is less than about 10,000 lb-in.

[0041] Since the flexural stiffness is a function of material and thickness, the following techniques can be used to achieve the substantial difference between the flexural stiffness of central portion 4 and intermediate portion 6: 1) different materials can be used for each portion, 2) different thicknesses can be used for each portion, or 3) different materials and thickness can be used for each portion. For example, in a preferred 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.

[0042] The golf club head may further include a perimeter portion 8 disposed between the intermediate portion and the body of the club head. In one embodiment, perimeter portion 8 has a third flexural stiffness that is at least two times greater than the flexural stiffness of intermediate portion 6. Preferably, the area of central portion comprises about 15% to about 60% of the total area of the club head face, and more preferably about 20% to about 50%.

[0043] Hitting face 2, thus, has the highest FS portion in the middle of the hitting face and the FS decreases toward the edge of the hitting face. The hitting face may comprise a face insert, which is welded onto a cavity defined on the face. Face insert is disclosed in commonly owned pending patent application bearing Ser. No. 10/038,235.

[0044] In accordance to one aspect of the present invention, the thickness of intermediate portion 6 or optional perimeter portion 8 on hitting face 2 can be thinly manufactured by removing the weld lines from the hitting face to the crown and sole of the club head. Club head 10 in accordance to an embodiment of the present invention is shown in FIGS. 2-4, and is attachable to a hosel, a shaft and a grip member. Club head 10 preferably comprises three parts, which include a face cup 12, a crown plate 14 and a cast member 16. The face cup, the crown plate and the cast member are welded together at weld lines 20 and 22. Face cup 22 comprises hitting face 2, partial crown portion 24 and partial sole/toe portion 26. Partial crown portion 24 and partial sole/toe portion 26 form sidewalls around hitting face 2. As illustrated in FIG. 2, weld line 20 is set back away from the perimeter of hitting face 2 or back away from the parting lines. Accordingly, surrounding intermediate portion 6 and/or perimeter portion 8 of hitting face 2, as shown in FIG. 4, can be made as thin as necessary. Preferably, face cup is made by forging. In the forging process, a malleable metal suitable for use as a hitting face, such as titanium, titanium alloy, carbon steel, stainless steel, beryllium copper, and other forgeable metals, is heated and then hammered into the desired shape of the face cup. The more preferred metal is titanium 6-4 alloy, which comprises 6% aluminum and 4% vanadium, or SP700 titanium alloy, which comprises 4.7% aluminum, 2.9% vanadium, 2.0% molybdenum and 2.1% iron and is commercially available from NKK (Japan) and RTI International Metals (Niles, Ohio).

[0045] The preferred forging process is die or billet forging, in which a pre-measured rod of forgeable metal is heated and placed between a die, which contains the desire shape of the face cup, and a hammer. The heated metal is then hammered into the desired face cup. An advantage of forging the face cup is that the thickness of the face can be as thin as about 0.060 inch (or about 1.5 mm) around the perimeter or edge of the hitting face. Referring to FIG. 1, the thickness, T₂, of surrounding intermediate portion 6 can be as thin as about 0.060 inch (1.5 mm), and the thickness, T₁, of central portion 4 is preferably between about 0.08 inch (2.0 mm) and about 0.20 inch (5.0 mm), and more preferably between about 0.12 inch (3.0 mm) to about 0.16 inch (4 mm).

[0046] The thickness of partial crown portion 24 on face cup 12 is preferably between about 0.020 inch (0.50 mm) and 0.080 inch (2.0 mm) and more preferably about 0.060 inch (1.5 mm). The thickness of partial sole/toe portion 26 of face cup 12 is preferably between about 0.020 inch (0.50 mm) and 0.080 inch (2.0 mm) and more preferably about 0.060 inch (1.5 mm). Furthermore, weld lines 20 is preferably set back at least about 0.5 inch (12 mm) from edge 28 of hitting face 2. The set back can be as much as 1.0 inch (25.4 mm) or more.

[0047] Crown plate 14 is preferably stamped from sheet metal. Preferably, crown plate 14 is made from titanium or titanium alloy or one of the suitable materials for face cup 12 listed above. Stamping is the preferred method of making the crown plate, because it can be made from very thin sheet metal with oriented grain structure. Moreover, it can be made thinner than casting or forging, which reduces the weight and stiffness of the crown. A cast titanium crown plate can be made as thin as about 1.1 mm, due to manufacturing limitations. A stamped titanium crown plate in accordance to one aspect of the present invention can be as thin as 0.7 mm. Preferably, crown plate 14 has a thickness in the range of about 0.5 mm to about 1.5 mm, and more preferably less than about 1.0 mm. Alternatively, the sheet metal can be cold rolled or cold worked to reduce the thickness and weight of the metal and/or to cause the grain structures of the metal to flow. Stamped crown plate 14 may be oriented with the direction of its grain flow substantially parallel to hitting face 2, or substantially perpendicular to hitting face 2. Depending on the orientation, stamped crown may be more ductile or stiffer. This feature provides designers with more flexibility in club design. More preferably, the grain structure is oriented substantially perpendicular to the hitting face to increase ductility.

[0048] Member 16 is preferably cast. An advantage of casting is that it provides member 16 with geometrically complex shape. As shown in FIGS. 3 and 4, cast member 16 comprises hosel 30, which may extend to the bottom of the club, one or more decorative member 32 and pocket 34 adapted to receive a predetermined weight (not shown) to add weight to the club or to balance the club. Cast member 16 is preferably sufficiently large to include toe 36, back portion 40, heel 42 and sole 44 of club head 10. Face cup 12, crown plate 14 and cast member 16 are preferably welded together to form club head 10. Any conventional welding techniques can be used. A high quality plasma welding technique, similar to the welding technique used in Titleist® 983 driver club, is preferred.

[0049] Another advantage of casting member 16 is that the hosel can be made integral therewith. Conventional clubs typically include a hosel welded on to the body of the club, which requires more manufacturing time and increases the complexity of manufacturing. Another advantage is that when the hosel is cast with casting member, its weight is not concentrated near the striking face. Also, since the hosel is not directly welded to the hitting face, it cannot negatively affect the flexibility of the hitting face. The hosel is a structurally rigid member, and when it is welded to the face it can reduce the flexibility of the hitting face.

[0050] In another embodiment, crown plate 14 is integrally cast with member 16, and cast member 16 is welded to a separately formed sole plate 46 along lines 44 shown in FIGS. 7-9. Cast member 16 and sole plate 46 are sized and dimensioned to be welded to forged face cup 12, as described above. Sole plate 46 may have pocket 34 welded thereon to receive additional weights, or sole plate may be made from high density metal or with relatively high thickness to add weight or to balance the club. In this embodiment, member 16 is preferably manufactured by casting, as discussed above and sole plate 46 is preferably manufactured by stamping sheet metal. As discussed above with respect to crown plate 14 above, sole plate 46 may be stamped from a rolled sheet that has a grain flow pattern, and the sole plate can be welded to cast member 16 with the grain flow pattern substantially parallel or substantially perpendicular to hitting face 2. Preferably, the grain flow pattern is oriented substantially perpendicular to hitting face 2 for increased ductility.

[0051] The inner cavity 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 has a volume greater than 250 cubic centimeters, and more preferably greater than 275 cubic centimeters, and most preferably 350 cubic centimeters or more. Alternatively, the club head of the present invention may also be used with the smaller fairway woods, which can have volume as low as about 150 cubic centimeters. Preferably, the mass of the inventive club head is greater than 150 grams but less than 220 grams.

[0052] Club head 10 in accordance to an embodiment of the present invention was tested against a convention club, which has a constant thickness hitting face. The results are shown in FIGS. 10 and 11. These figures illustrate the initial ball speeds when the clubs traveling at about 100 mph impact the balls. The angle of attack is about 2.5°, and the effective loft angle is about 13°. The clubs are mounted on a robot, which is driven to impact the balls at the desired club speed. Robots are commercially available from the True Temper Corporation or the Wilson® Sporting Goods Co. The locations of ball impacts are distributed over a rectangular area of 0.50 inch in the vertical direction and about 1.0 inch in the horizontal direction. (The vertical and horizontal scales in FIGS. 10 and 11 are not the same). The mechanical driver has the ability to repeatedly hit the balls at any desirable location on the hitting face. The ball speeds are measured by launch monitors. Any suitable launch monitors can be used. Examples of launch monitors include those described in commonly owned U.S. Pat. Nos. 6,533,674, 6,500,073, 6,488,591, 6,285,445, 6,241,622, 5,803,823 and 5,471,383, among others.

[0053] The hitting face includes a vertical centerline VCL and a horizontal centerline HCL perpendicular thereto. The VCL can be defined as an imaginary vertical line drawn substantially down the middle of the hitting face, and the HCL can be defined as an imaginary horizontal line drawn substantially across the middle of the hitting face. The geometric center (GC) of hitting face 16 is located at the intersection of centerlines VCL and HCL. In the tests, the geometric center is within the 0.50 inch by 1.0 inch rectangle, and more preferably coincides with the center of the rectangle. The center of the rectangle is the intersection of the two lines connecting opposite corners of the rectangle.

[0054] The conventional club is the Titleist 983E club, which has a volume of 350 cubic centimeters, titanium SP700 stamped hitting face with a thickness of about 0.122 inch. The inventive club, which has a volume of 400 cubic centimeters, has central region 4 with a thickness of about 0.180 inch, and intermediate region 6 with a thickness of about 0.060 inch, as illustrated in FIG. 4, to give a FS ratio of about 27. Central portion 4 occupies about 15% of the total area of the hitting face. The hitting face of the inventive club is forged from SP700 titanium alloy.

[0055] As illustrated in FIGS. 10 and 11, the prior art club, while possessing slightly higher initial ball speeds and good “sweet spot” or area of high COR or initial ball speeds, the inventive club head has a significantly larger sweet spot. As shown, the initial ball speeds generated by the inventive club varies from a peak of about 145.81 feet per second to about 144 feet per second inside the tested 0.5 inch by 1.0 inch rectangle, or within a range of less than 2 feet per second. Hence, within this tested rectangle the variation of initial ball velocity is less than 2% of the peak initial ball velocity, more preferably less than 1.5%. The conventional club produced initial ball speeds in the range of about 147.77 feet per second at its peak to about 143 feet per second, or within a range of more than 4.5 feet per second. In other words, the initial ball speed contour lines generated by the conventional club, as shown in FIG. 10, has more speed variations, as indicated by the multiple contour lines, than those of the inventive club, as illustrated in FIG. 11. In practical terms, the inventive club in accordance to an embodiment of the invention provides more predictable distance that the balls fly after impact, or in other words the distance that the balls fly after impact is less dependent on striking the ball at the center of the hitting face. In FIGS. 10 and 11, the left side corresponds to the side closer to the heel of the club head, and the right side corresponds to the side closer to the toe of the club head.

[0056] While various descriptions of the present invention are described above, it should be understood that the various features of each embodiment could 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 might occur to those skilled in the art to which the invention pertains. For example, the face and/or individual zones can have thickness variations in a step-wise or continuous fashion. Other modifications include a perimeter zone that has a thickness that is greater than or less than the adjacent, intermediate zone. In addition, the shapes of the central, intermediate, and perimeter zones 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.