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[0001] This application refers to and priority is claimed from the United States Provisional Patent Application Ser. No. 60/309,888 filed Aug. 3, 2001 and from United States Provisional Application Ser. No. 60/348,921 filed Oct. 23, 2001, the contents of both of which applications are incorporated by reference in their entirety.
[0002] This invention relates to golf club heads and principally to, but not limited to, wood-type clubs. The principles and designs described can be applied to irons but the need is small since an iron with less loft can always be chosen where extra distance is desired.
[0003] Presently, woods are nearly always made with rather stiff materials, using structurally strong and stiff basic face and shell structures and are hollow. Recent designs of woods use a relatively thin metal face such that they have a spring effect giving added shot distance for hits, provided such hits are near the face center. Strong metals are the usual materials of construction of such hollow woods. Strong, stiff “composite” materials are sometimes used in place of metal, such as plastic reinforced with glass fibers or carbon fibers. It is essential for the basic face structure and supporting structure to be sufficiently strong to withstand the impact between the club head and ball.
[0004] In the following, this basic face structure will usually be referred to as the “basic face structure” or “face structure” and the supplemental structure as the “elastic structure,” which may take various forms and be composed of various “substructures” such as an elastic shell and an elastic central part.
[0005] “Off-center” hits refer to hits that are on the face but are away from the ideal spot which is often called the sweet spot and is at or near the center of the face.
[0006] In 1985 or earlier (referenced in U.S. Pat. No. 4,928,965) it was recognized that there is an important advantage if the effective stiffness of the basic face structure is reduced so as to deform appreciably toward the rear of the club head upon impact of club head and ball. In recent years, this is widely referred to as a “spring effect.” The result was that the normal coefficient of restitution was increased with corresponding increase of launch velocity and greater distance for the shot. This is usually accomplished in modern metal woods by making the basic face structure thinner so as to be less stiff for deforming in the fore-aft direction and to have less mass which moves with the surface of the ball during impact.
[0007] Five serious design and performance defects for current wood designs having the spring effect may be described as follows.
[0008] Defect
[0009] Defect
[0010] Defect
[0011] Defect
[0012] Defect
[0013] A commonly heard complaint about the so-called spring-effect drivers is that they are good for hits at or very near the center and poor for off-center hits. This is a result of defects
[0014] The main purpose for the present invention is to reduce all
[0015] The “normal coefficient of restitution” is abbreviated herein as NCR to distinguish it from the shear coefficient of restitution which is sometimes abbreviated as SCR. What is herein called NCR is also commonly called the “coefficient of restitution” or COR or e. Its formal definition is for the so-called “central collision” or in our usage, “center hit” in which
[0016] The term “elastic” refers to the ability of a material or a structure to be deformed and to nearly return to its original shape after being deformed. When applied to a material, “elastic” is usually defined by the modulus of elasticity (E) and may be very low, such as for rubber, or high as for metals, for which E is nearly always many millions of pounds per square inch. When applied to a structure, elastic properties are very strongly dependent on the structural configuration as well as the value of E for the material of which it is made. The term “stiffness” refers to how easy or difficult it is to cause the deformation of a structure. Stiffness is governed by a structure's shape, location and nature of forces applied, and the modulus of elasticity (E) of the material. The term “composite” as used here refers to plastic material reinforced by fibers such as glass, graphite, or other strong fibers, with the result of much increased stiffness and strength.
[0017] The following are U.S. patents which represent prior art and which are at least somewhat related to what is claimed as novel herein.
[0018] Allen U.S. Pat. No. 6,354,961
[0019] Krumme et al 5,807,190
[0020] Rigal et al U.S. Pat. No. 5,547,427
[0021] Chen U.S. Pat. No. 5,494,281
[0022] Duclos U.S. Pat. No. 5,176,383
[0023] Shiotani U.S. Pat. No. 4,988,104
[0024] Allen U.S. Pat. No. 4,930,781
[0025] Chen et al U.S. Pat. No. 4,681,321
[0026] Yamada U.S. Pat. No. 4,535,990
[0027] Doong U.S. Pat. No. 6,354,956
[0028] Chern U.S. Pat. No. 6,007,435
[0029] Mick U.S. Pat. No. 5,586,948
[0030] Allen U.S. Pat. No. 5,301,941
[0031] Allen U.S. Pat. No. 5,060,951
[0032] Shearer U.S. Pat. No. 4,944,515
[0033] Yamaguchi et al U.S. Pat. No. 4,928,965
[0034] Curtis et al U.S. Pat. No. 4,614,627
[0035] U.S. Pat. No. 4,535,990 describes a wood-type driver club head made of fiber-reinforced plastic (composite) and having an internal column also of composite for the purpose of mechanical support of the face upon impact. The structure has much higher stiffness than what is claimed herein.
[0036] U.S. Pat. No. 4,614,627 describes a club head composed of strong, stiff plastic materials but there is no indication that the structural parts were or could be designed to serve the functions claimed in the present patent. If the dimensions of the drawings are approximately to scale, experience of the present inventors indicates that the structure would be too stiff and would not be able to exhibit the desired stiffness.
[0037] U.S. Pat. No. 4,681,321 is similar to patent '
[0038] U.S. Pat. No. 4,928,965 shows use of materials of lower elasticity than metals to increase the coefficient of restitution by use of a face layer from 8 to 40 millimeters (0.315 to 1.575 inches) thick, but what is called the coefficient of restitution is not as generally understood and is largely meaningless since head velocity after impact is not given. U.S. Pat. No. 4,930,781 shows a metallic honeycomb structure attached to the rear of the face and having thickness of ⅝ to {fraction (15/16)} inch, is designed for high strength and stiffness, and clearly has much greater stiffness than desirable for best NCR.
[0039] U.S. Pat. Nos. 4,944,515, 4,988,104, 5,060,951, 5,176,383 and 5,301,941 are concerned with making the face more stiff, rather than less stiff.
[0040] U.S. Pat. No. 5,494,281 shows an elastic face supported around its periphery by a relatively stiff metal rear shell.
[0041] U.S. Pat. No. 5,505,453 shows a relatively stiff face supported around its perimeter by numerous belleville washers intended to provide a controllable spring effect. Hits near the face perimeter would engage the front edge of the shell and have poor performance.
[0042] U.S. Pat. No. 5,547,427 has a relatively stiff metal face called a “sealing element” which is supported by plastic rear structure(s). The specification states that such rear structure is intended to be stiff and may be made of fiber reinforced plastic.
[0043] U.S. Pat. Nos. 5,586,948, 5,807,190, and 6,077,435 show unusual elastic structures for control of face elasticity for ball impacts that are near the center of the face, '435 differing by having an unusually hard structure attached to the back of the face. All have relatively stiff structure for hits near the perimeter of the face.
[0044] U.S. Pat. No. 6,348,015 provides mathematical analysis for design of a flexible face, but does not provide adequate flexibility for off-center hits, particularly those near the perimeter of the face.
[0045] U.S. Pat. No. 6,354,956 shows a moveable face structure which is illustrated as stiff (the language is unclear) having support from a resilient member which is not described. Hits near the perimeter of the face would involve the front edge of the shell and such hits would not have the desired benefit of spring effect.
[0046] U.S. Pat. No. 6,354,961 uses an elastic face together with a stiff shell structure and an inner support column which contacts and supports the face only for impacts of sufficient force, thus allowing relatively better performance for weak hits than for strong hits. Off-center hits do not have the full benefit and near the edge, almost no benefit because the spring effect is absent.
[0047] In all of these examples of prior art, the angular orientation of the face surface for offcenter hits is altered upon impact and that alters the launch direction of such golf shots.
[0048]
[0049] The rear portions of most prior art club heads are usually shaped somewhat differently from what is shown in
[0050] In some prior art cases, the basic face structure has approximately uniform thickness.
[0051] When the face structure is sufficiently thin for the desired elastic properties, structural failure of the face caused by strong hits is a serious problem, especially for woods having uniform face thickness. Most commercially available driver heads having spring effect reduce this problem by making the face thicker near the central area for greater strength there, but such failure is still common. This is illustrated by comparison of the face thickness numeral
[0052] The structure of
[0053] In
[0054] Deformation of the face structure for an offcenter hit is shown by the dotted lines
[0055] A pending patent application, published as No. US2001/0001773A1 by T. Naruo et al shows a version of the spring-effect face structure wherein the face plate thickness is varied in special ways. Emphasis is given to use of inserted patches in the basic face structure, the patch being of any of various materials such as aluminum, titanium, or stainless steel. It is essential (though the joining method is not specifically explained in the application) that these various materials must be strongly joined to, and made part of, the basic face structure. The joining is essential because stresses are quite high. Presumably, such inserts are to be welded or brazed into the face so as to become an integral part of the face.
[0056] All prior art designs suffer from the defects described above, most having defects
[0057] The present invention relates to a structure of moderate elasticity, separate from such elasticity as is inherent in the basic face structure, that is used for current designs of faces for wood-type golf clubs. This elastic structure can take any of several forms, all of which reduce or eliminate most or all of the
[0058] The present invention uses an elastic structure or structures to supplement the stiffness of the basic face structure or may replace an elastic face structure entirely.
[0059]
[0060]
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[0065]
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[0075]
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[0077]
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[0079]
[0080] When stiffness, mass, and internal damping characteristics of the face have suitable values, the result is commonly called the “spring effect” or the “trampoline effect”, and this can add 5 to 20 yards to a golfer's hit.
[0081] Off-center hits have basic differences from center hits. They must be studied by much more complicated analysis and/or evaluated experimentally. Off-center hits ordinarily give much less distance and altered launch direction of the ball for drives as compared to center hits. The design problem is generally to minimize this change of launch direction and this loss of distance. The stiffness, moment of inertia of the head, its face curvature, the amount of the off-center distance, the shear coefficient of restitution (or an equivalent), and other factors must be considered in addition to the concept of NCR.
[0082] The present inventors used computer-based analysis to study the face stiffness problem with a model of club head-ball impact which is illustrated in
[0083]
[0084] Other values for nonlinearity of k
[0085] For ideally designed club heads, and with head-ball approach speed for center hits at 109 miles per hour (160 feet per second); with a club head weighing about 200 grams; and with appropriate values for R, k
[0086] Other characteristics are easily found from the computer based calculation using the model of
[0087] It is clear that for k
[0088] When k
[0089] A workable conclusion is that R should be less than 0.10, stiffness k
[0090] This model of
[0091]
[0092] This alternate has an advantage over prior art clubs in that there is a useful degree of control over the elasticity near the edge of the club face plate. Note that in U.S. Pat. No. 5,505,453, belville washers provided a similar edge support, but as seen in
[0093] As was pointed out earlier, most prior art basic face plate structures give little or no control over the stiffness at or near the perimeter of the face. There is a disadvantage for the embodiment of
[0094]
[0095] The spring member shown in cross section in
[0096] In a specific example for 17-4 ph stainless steel construction, the concentric cylinders or members
[0097] Long, slender columns may buckle to one side and fail as a long column, as is well known in structural theory. The three concentric cylinders providing the elastic structure in this example provide mutual lateral support and buckling failure is not likely. In cases where buckling may be of concern, the central part of the column can easily be supported against significant lateral deformation by use of light weight support members.
[0098] Instead of one such multi-element column, two or more such columns may be used, suitably distributed over the basic face plate structure
[0099] The type of spring of
[0100] The basic face plate structure
[0101]
[0102] The elastic structure
[0103]
[0104] Shell structures
[0105] An advantage for the embodiments of
[0106]
[0107]
[0108]
[0109] The relief areas of removed material or cavities of
[0110] A further refinement is to vary the cavity hole or slot size and/or spacing so as to permit design control over the local values of stiffness in compression. For example, a hit at (or near) the edge of the face may give best results if the local stiffness is changed. In this vicinity holes
[0111] In addition to varying the nature of the cavities formed as holes, ribs, or slots, the thickness and/or modulus of elasticity of metal layer
[0112]
[0113] It is also possible to combine one or more of the various disclosed elastic structures with a shell structure having small or moderate stiffness to modify the elastic properties of the club head.
[0114]
[0115] In
[0116] Shell
[0117] The face structure's thickness may be varied as shown at
[0118] While only one internal support is shown in
[0119] This embodiment makes it possible to minimize all 5 of the defects which were defined above.
[0120]
[0121] In
[0122] This shell structure may have a rear portion of greater strength and/or stiffness if desired. The location of such transition, if used, is shown as a bonded joint at
[0123] A shaft socket
[0124] An alternate layer
[0125]
[0126] When a compressive force is applied by impact of the ball on the ball impact surface of the face structure, the stress in walls
[0127] For such cases which involve spreading of the stress, plate
[0128]
[0129] If very long, the columns of
[0130] The inventors have found that suitable materials for the honeycomb and shell include polycarbonate plastic, ABS, and polyester resin plastic and similar materials.
[0131] These materials dictate a minimum column length L indicated in
[0132] The columns, honeycomb elements, or plates of
[0133] There is another alternate for central part structure or member
[0134] With such elastomers, a solid form can be considered for central part structure or member
[0135]
[0136] While all of the center part structure elements described in
[0137] There are preferred dimensional ranges for the designs of
[0138] It should be noted that
[0139] At the hitting surface, the front end of the central elastic member
[0140] Face cover
[0141] Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.