Optimally elastic golf club head

Abstract

A golf club head is composed of elastic substructures having moderate elasticity and consisting of a face, outer shell, and inner structure in which said elastic substructures that cooperate so as to provide larger impulses to the ball at impact, due to combined elastic properties of the club face for hits at all locations on the face. This allows better distance of shots when loft angle and other design details are appropriately chosen. The structure also minimizes variations of angular orientation of the face surface at the point of impact for all such hits. The elastic substructures can take several forms such as an internal elastic support around the periphery of the face structure, an internal support for the central part of the face structure, and an elastic structure attached to the front side of the face structure, an elastic outer shell, and their combinations. The structure also provides adequate strength, and minimum weight such that a maximum amount of concentrated mass can be located in advantageous places as far as practical from the center of gravity of the head so as to realize maximum moments of inertia about the center of gravity.

Description

[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.

BACKGROUND OF THE INVENTION

[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 1. Thin faces are prone to structural failure.

[0009] Defect 2. Hits that are somewhat away from the face center experience different stiffness (usually higher) than for center hits and the advantage of more distance is reduced or even lost.

[0010] Defect 3. Hits at or near the perimeter of the face structure experience much greater stiffness than for defect 2 and the error is magnified.

[0011] Defect 4. For off-center hits, the angular orientation of the face surface at the point of impact may be altered by the force of impact and as a result, the ball is launched in an unintended direction.

[0012] Defect 5. Defect 4 depends on the head speed of the club at impact.

[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 2, 3, 4, and/or 5. Formerly, club faces were so stiff and strong that they deformed a negligible amount upon impact and these defects did not appear.

[0014] The main purpose for the present invention is to reduce all 5 defects identified above. Various means are described for achieving this result.

[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 2 objects collide and the centers of gravity of both are traveling along the same line which is perpendicular to the impact surface. NCR is the ratio of the separation velocity of the center of gravity of one body relative to the center of gravity of the other after impact to the corresponding approach velocity before impact.

[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.

PRIOR ART

[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 '990 in that the structures are of composite materials and would be much too stiff according to the experience of the present inventors.

[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] FIG. 1 illustrates the most common prior art structure among woods designed with the spring effect. It represents a horizontal cross sectional view of a wood-type head made of metal. The head is almost always hollow. The basic face structure and shell are made of strong metal. Sometimes such hollow metal heads are filled with foam. Its purpose is to reduce the sound of impact. It is too soft and has too much internal vibration-damping behavior to be significant as a spring-effect element. Other details of the club head are of minor importance for the purposes of the present invention.

[0049] The rear portions of most prior art club heads are usually shaped somewhat differently from what is shown in FIG. 1. One feature of the prior art rear structure of minor significance is that the walls are generally able to bulge outward a small amount upon impact. This bulging slightly reduces the stiffness of such rear structures. The bulging is strongly opposed by the curved shape and hoop stresses of the rear portion. The result is substantially greater stiffness than what is described for the present invention, in spite of the curved walls of the rear portion.

[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 4 of FIG. 1 with that illustrated at numeral 5.

[0052] The structure of FIG. 1 has all 5 design defects (defects 1 through 5 described above).

[0053] In FIG. 1, there is an illustration of the nature of defects 2, 3, and 4. Face structure deformation (exaggerated for illustration) for a center hit is shown by dotted lines 5A and the location of the center hit is indicated by the heavy line 5B. Note that at the impact, the angular orientation of the deformed face is the same as for the undeformed face.

[0054] Deformation of the face structure for an offcenter hit is shown by the dotted lines 4A, with the impact location indicated by the heavy line 4B. Note that here, the angular orientation of the deformed face structure is changed from the angular orientation of the undeformed face. This causes the launch direction of flight of the ball to be altered. Also, the amount of rearward movement of this part of the face is less than for the center hit because this part of the structure is more stiff. This may cause many yards loss of distance. This illustrates defect 3 for moderately off-center hits and defect 4 for hits near the edge of the face (defect 4 is generally worse than defect 3). It is clear that the amount of the change of face angular orientation depends on the head speed of the golfer which illustrates defect 5. A strong hitter will have much greater changes in angular orientation of the face surface than a weak hitter. In turn, this makes it clear that change of angular orientation should be minimized for off-center hits, and that is a principal purpose of the present invention.

[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 1 through 5 and none provide means for reducing or eliminating all 5 defects.

SUMMARY OF THE INVENTION

[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 5 design defects. One such form includes one or more internal supports for the central part of the basic face structure. Another embodiment is a thick elastic structure having the desired moderately low stiffness by virtue of material having lower modulus of elasticity together with suitable structural shape. The stiffness is much lower as compared to solid metal or composites and it replaces the conventional face. The preferred embodiments include a structural shell supporting the face structure, which shell is made of elastic material having much lower stiffness than metals or composite plastics, such that said shell functions so as to provide a significant part of the elasticity. In the preferred designs, this shell is combined with some of the other novel structural features.

[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.

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] FIG. 1 shows a typical basic prior art face structure;

[0060] FIG. 2 is a horizontal cross sectional view of a club head made according to a first form of the present invention, taken as on line 2-2 in FIG. 3;

[0061] FIG. 3 is a sectional view taken as on line 3-3 in FIG. 2;

[0062] FIG. 4 is a schematic mechanical dynamic model of a club head-ball impact, using combined or “lumped” constants for masses, springs, and damping;

[0063] FIG. 5 is a graphic representation of the effect on NCR of varying some of the parameters shown in FIG. 4;

[0064] FIG. 6 is a horizontal cross sectional view of a club head made according to a second form of the present invention;

[0065] FIG. 7 is a cross sectional view taken as on line 7-7 in FIG. 6;

[0066] FIG. 8 is a horizontal cross sectional view of a club head, showing a third form of the supplemental elastic structure of the present invention;

[0067] FIG. 9 is a horizontal cross sectional view of a club head showing a fourth form of the supplemental elastic structure of the present invention;

[0068] FIG. 10 is an enlarged sectional view of a fifth form of the elastic head structure, showing a portion of the face structure circled at D in FIG. 8 and at E in FIG. 9, showing an alternate configuration for an elastomeric material layer;

[0069] FIG. 11 is an enlarged sectional view of sixth form showing a portion circled at D in FIG. 8 and at E in FIG. 9 showing a modified configuration for an elastomeric material layer;

[0070] FIG. 12 is a view of FIG. 10 and FIG. 11 in the direction 12-12 in each of the Figures;

[0071] FIG. 13 is a view of FIGS. 10 and 11 taken on the same line 12-12 showing formation of ribs instead of holes as an alternate construction of the elastic material layer;

[0072] FIG. 14 is a cross sectional view taken on a sight line similar to FIG. 10 shown as an alternate design of a supplemental elastic structure form in a layer of a club face;

[0073] FIG. 15 is a front view of seventh form of the invention showing a club head made of elastic material with the face partially broken away to show the internal structure;

[0074] FIG. 16 is a sectional view as indicated at 16-16 in FIG. 15, showing more details of the internal structure;

[0075] FIG. 17 is an eighth form of the invention showing a horizontal sectional view of a wood-type head illustrating location of elastic internal parts and including an elastic shell;

[0076] FIG. 18 is a sectional view as shown at 18-18 in FIG. 17, showing one form of the internal elastic part;

[0077] FIG. 19 is an enlarged sectional view in the position on a club head indicated at G in FIG. 18, but showing an alternative form of the internal elastic parts;

[0078] FIG. 20 is an enlarged sectional view in the position on a club head indicated at G in FIG. 18, showing a further alternative form of the internal elastic part in which support against column buckling is indicated; and

[0079] FIG. 21 illustrates an internal elastic structure that is an alternate to FIG. 18 and viewed along lines 18-18 in FIG. 17.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

[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 FIG. 4 for center hits. This is like a model described by Johnson and Hubble, page 495 of the book, SCIENCE AND GOLF III, © 1999, The World Scientific Congress of Golf Trust, except for the addition of damper c3. Provision was made by the inventors for all three springs to be linear or nonlinear as desired and as was done in this reference. This model is also similar to models used by Cochran, page 488 and by Yamaguchi et al, page 501 in the same book; and by Lieberman and Johnson in the book SCIENCE AND GOLF II, © 1994. Elastic and damping constants for the ball were the same as used in an article by Lieberman and Johnson on page 307 of that book.

[0083] FIG. 5 illustrates some of the results of the analysis conducted by computer with the model of FIG. 4. It shows how the NCR varies for various values of k3, at approach speed of 160 feet per second (109 miles per hour). It is for the case where c3=0 and the spring k3 is linear. The three curves are for three values of the parameter R. Parameter R is the ratio of mass of the front part of the model, Mhf, which moves with the ball surface, to the total mass of the head, Mt, where Mt is the sum of Mhf and Mhb in FIG. 4. That is, R=Mhf/Mt. The curve, R=0.005 is essentially the same as for R=0 and shows how NCR varies with stiffness k3 when R is nearly zero, which means the mass Mhf is relatively near to zero. For k3 less than about 1 million pounds per foot, when R=0.10, there are marked changes, and when R=0.20, there is a profound change. The horizontal dashed line represents an NCR=0.83 which is the upper limit as specified by the United States Golf Association rules. This graph shows that for these conditions, stiffness k3 should be between about 0.4 million and 0.7 million pounds per foot (33,333 and 58,333 pounds per inch) if the NCR is to be near to 0.83, and shows that R should not be much greater than 0.10.

[0084] Other values for nonlinearity of k3 and for damping c3 alter results, but FIG. 4 gives a useful general picture.

[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, k3, and c3 causes maximum rearward deflection of the k3 spring to be typically 0.05 to 0.08 inch and may be even more in some good designs. For the novel present designs off-center hits even as far as the edge of the face, cause deflections of 0.02 to as much as 0.10 inch. Such deflections are much lower at or near the edge for conventional spring effect designs. Lower speed reduces such deflection and higher speed increases them.

[0086] Other characteristics are easily found from the computer based calculation using the model of FIG. 4.

[0087] It is clear that for k3 below about 1 million pounds per foot, large changes can appear if the value of R is much more than 0.10. This is because of a tendency for resonance effects and attendant phase shifts. Another effect becomes significant for k3 less than about 300,000 pounds per foot: Analysis shows that the front of the face may bounce away from the ball, then return so that there are actually two hits very closely separated in time and more than two hits are possible.

[0088] When k3 is nonlinear, and when c3 is not zero, the curves differ considerably from those of FIG. 4, if k3 is less than about 1 million pounds per foot. For larger k3 values, the differences are generally smaller.

[0089] A workable conclusion is that R should be less than 0.10, stiffness k3 should be well below 1 million pounds per foot, and damping c3 should be small.

[0090] This model of FIG. 4 is not sufficiently detailed to replace the need to do testing of actual samples, but provides useful general guidance for the trends of changes in the parameters. More detail and other conclusions regarding club head design are given in 2 books written by the inventors, “HOW GOLF CLUBS REALLY WORK AND HOW TO OPTIMIZE THEIR DESIGNS” © 2000 and “BETTER GOLF FROM NEW RESEARCH” © 2001, available from Origin Inc of Jackson Wyoming.

[0091] FIG. 2 and 3 illustrate one embodiment of the invention wherein the elastic structure 6 is in the form of an elastic ring, preferably an elastomeric ring, having the same outline shape as the perimeter of the basic face plate structure. The face plate 7 is joined near its periphery to the edges of a shell 7A, only by elastic ring 6. At impact on the face plate, this ring can compress, giving less stiffness for rearward movement of the basic face plate structure. There is a small gap 8 between the basic face plate structure and the rear body of the club head, to allow rearward movement of the basic face plate structure upon impact with a ball.

[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 FIG. 6 of patent '453, numeral 58 of patent '453 is the face plate structure and numeral 60 of patent '453 is part of stiff shell 20 of patent '453. Thus, the structure of patent '453 suffers from defects 2 and 3 (defined above) because a hit near the perimeter of the face structure encounters the stiff shell.

[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 FIG. 2 in that the ratio R tends to be high unless the face is thin and then the face is weak and stiffness is very low. As indicated above, R=[mass of the face which moves with the ball surface] divided by [total mass of the head].

[0094] FIG. 6 and the cross sectional view in FIG. 7 show a modified elastic structure of the present invention which is preferred over that of FIG. 2 and FIG. 3. In FIGS. 6 and 7 there is a central rod 17 which is firmly joined to the rear surface of the basic face plate structure 3, for example, by a weldment 23. The basic face plate structure is supported at its periphery by a hollow shell in a conventional manner and such shell has moderate stiffness as discussed later, wherein such shell allows significant deformation for hits at or near the edge of the face. When rod 17 is loaded in compression upon impact it slightly compresses or reduces in length and has a defined spring constant (meaning the ratio of force divided by deflection). It thus forms a spring member. When made of most metals, in order to achieve the values desired for stiffness, such a central compression rod must be 10 or more inches long. For a shorter configuration, it may be joined at 20 (welded or brazed) to a concentric tube 18 which will be in tension at impact, and will elongate. In turn, tube 18 is joined to tube 19 at 22 and tube 19 is in compression. Tube 19 is joined to the rear end of the shell at 21. Plug 25 may be used to fill the hole.

[0095] The spring member shown in cross section in FIG. 7 need not be round. Square or other cross sectional shapes can be used. Furthermore, more than the 3 concentric spring elements shown in FIGS. 6 and 7 may be used when more deflection is needed without exceeding desired material stresses.

[0096] In a specific example for 17-4 ph stainless steel construction, the concentric cylinders or members 17, 18, and 19 may be of equal cross sectional area of 0.0163 square inches (which means that central rod 17 is 0.144 inch in diameter). The sum of the lengths of 17, 18, and 19 may be about 11 inches but the actual length is only about 4 inches because of the telescoping of the members. In this case, the combination of 17, 18, and 19 has a stiffness resisting rearward movement of the face plate 3 of 533,000 pounds per foot. If the face plate 3 is relatively much less stiff, the center of the face plate 3 may exhibit a combined stiffness in the vicinity of 600,000 to 700,000 pounds per foot. Reference to FIG. 5 shows that this is in the range desired to give an NCR of about .82 provided R is in the range of 0.1 or less.

[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 3.

[0099] The type of spring of FIGS. 6 and 7 is unusual in that essentially all of the material is uniformly stressed in tension or compression, causing it to have less mass than a coil spring or leaf spring having the same stiffness and same maximum load capability. In the latter types of springs, the fibers near the neutral axis are lightly stressed and contribute extra mass but little strength or stiffness. Minimum mass which moves with the golf ball at impact with the face (Mhf in FIG. 4) tends to be an important consideration for good spring effect club head designs. Minimal mass of the springs helps to achieve this.

[0100] The basic face plate structure 3 may be thickened in an annular location spaced toward the periphery from the elastic structure as shown at 24 in FIG. 6. This allows the basic face plate structure 3 to have less weight and may also be designed to broaden the central area where desired values of NCR are obtained. A disadvantage for FIG. 6 in the form described is that impacts near the edge have little or no advantageous spring effect when shell 3A is made of metal or composites (defect 3). This may be avoided by making shell 3A of less stiff design such as using polycarbonate, and joining face structure 3 to said shell.

[0101] FIG. 8 is a horizontal cross section of a club head 26 showing a different form of elastic structure 27 comprising a layer which is bonded to the front side of a relatively stiff basic face plate structure 26A. The basic face plate structure is supported at its periphery by a shell 26B.

[0102] The elastic structure 27 is preferably made of rubber or other elastomer such as polyurethane, PPDI, TPE, EPDM, or ECH. Here, “elastomer” refers to an elastic material which is rubber-like in its nature and has a very low value of E. In this case, most of the deformation upon impact takes place in the elastic structure 27. That part of the mass of the outer face surface 27 which moves (deflects) with the surface of the ball at impact is quite small. This means that the mass ratio R is very small, corresponding approximately to the curve in FIG. 5 labeled R=0.005. This curve is well removed from the area of large R for stiffness in the vicinity of 400,000 pounds per foot (in this region, large R values correspond to low NCR values.) To serve well, most elastomers have too much internal damping when stressed. Though not shown in FIG. 5, when damping constant c3 is not small, the NCR value tends to be lower than desired.

[0103] FIG. 9 is a horizontal cross section of a club head 28 having a shell 28B and a basic face plate structure 28A. The basic face plate structure 28A is supported at its periphery by the shell 28B in a normal manner. An elastomeric layer 30, corresponding to the elastomeric layer 27 in FIG. 8 is bonded to the outer surface of face plate 28A. A thin metal layer 31 is bonded to the outer face of elastomeric layer 30, and thus the outer surface of thin metal layer 31 forms the ball strike face. (It is also possible to use other materials such as composite materials or polycarbonate for such face layer 31). Upon impact, the metal layer 31 deforms under the ball and is subject to tensile and bending stresses which may advantageously be designed to provide an important part of the stiffness of the club head 28. In that case, since the elastomeric layer 30 need not supply the bulk of the stiffness, its internal damping characteristics are less important. For an elastic structure made in this way, the part of the mass or weight of the club head which moves (deflects) with the ball during impact is slightly higher than for FIG. 8, but is still quite small compared with prior art basic face plate structures which have been designed to increase NCR.

[0104] Shell structures 26B in FIG. 8 and 28B in FIG. 9 may be made of material such as polycarbonate, which is much less stiff than metal or composites, to provide more spring effect for hits at or near the edge of the face structure as was discussed above in connection with FIGS. 2 and 3. In the design of FIGS. 8 and 9 layers 27 or 30 also provide a spring effect near the edge of the face structure.

[0105] An advantage for the embodiments of FIGS. 8 and 9 is that most of the mass of the head is far from the center of gravity and this causes the moment of inertia of the head about all axes to be large. In turn, that causes the head to have less rotation for an off-center hit with the result of more distance and less scatter for said off-center hits. Large inertia values are quite important for all designs.

[0106] FIG. 10 is an enlarged cross sectional view of a portion circled at D in FIG. 8 or at E in FIG. 9. It shows a useful variation for the elastic or elastomeric layer 27 in FIG. 8 and/or elastomeric layer 30 in FIG. 9. When elastomeric layer 27 or elastomeric layer 30 is solid, at impact it may behave as if it is rather stiff because the elastomeric material cannot easily deform away from the center of impact. In FIG. 10, there is shown a plurality of holes 32 created in the elastomeric material, also shown as 34 in FIG. 12 which is a view in the direction 12-12 in FIG. 10. In this case, at impact, the elastomeric material layer may move toward the central axes of holes 32 and thus allow the face to deform (so as to reduce its thickness) more easily under the ball at impact.

[0107] FIG. 11 is essentially identical with FIG. 10 except that the holes 33 extend completely through the elastomer layer. Accordingly, FIG. 11 is more suitable for use with the construction of FIG. 9, which has the metal layer 31 on the outer face.

[0108] FIG. 12 is a view in direction 12-12 of FIG. 10 or FIG. 11. At 34, FIG. 12 shows the holes or cavities 32 and 33. They need not be round as shown, but could be square, rectangular, or even triangular if desired, and may be tapered to help realize the desired elastic characteristics. Further, their centers may be located at apexes of a hexagonal pattern rather than of a square pattern as shown or may be otherwise distributed.

[0109] The relief areas of removed material or cavities of FIGS. 10 and 11 may take the form of grooves or slots rather than holes. This configuration is shown in FIG. 13 which shows a view of FIG. 10 or 11 in direction 12-12, for the case where grooves or slots 35 are formed, rather than holes. The grooves or slots leave elastomeric ribs 40 for support of metal layer 31 of FIG. 9. This is simply another option for causing the elastomer layer to have the desired elastic properties at impact.

[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 32 or 33 may be more or less widely spaced, be larger or smaller holes, or even be omitted. Stated otherwise, in case a different stiffness is desired, no matter where on the face, the holes may be made larger or more closely spaced or smaller and more widely spaced. In the case where slots 35 or ribs 40 are used rather than holes, they may be varied as desired by being wider or narrower or may be positioned at narrower or wider spacing or may be absent. In either case, the thickness of the elastomeric layer may also be varied to achieve the stiffness variation desired.

[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 31 in FIG. 9 can be varied to provide control of local values of stiffness for the same purpose as discussed in connection with varying the stiffness of the layers 27 or 30. Furthermore, a combination of such changes in the metal layer and the elastomeric layer may be used.

[0112] FIG. 14 is a further embodiment in which coil springs are made to function as elastic members in place of the use of the above described elastomeric material. A long spring wire is wrapped in a spiral to form a coil spring to support the strike face or cover sheet 38. The coil springs may be wound of flat wire rather than round, which will result in less weight for the same spring performance. The coils 37 are bonded to the basic face plate structure 36 and to the face sheet 38 across the diameter of the spring by bonding material indicated at 39. The bonding material may be epoxy or other adhesives, brazing, solder or other selected bonding materials.

[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] FIGS. 15 and 16 show an embodiment basically like those described above, but markedly different in appearance.

[0115] In FIGS. 15 and 16, 41 is a shell structure. There is a basic face structure 40 which is joined around its perimeter to shell 41 and there are one or more internal supports shown at 42 which serve to provide compression spring characteristics. Thicknesses of sections 41 and 42 are preferably less than what is suggested by the drawings of FIGS. 15 and 16. These parts have much less stiffness than typical wood-type clubs of current designs, primarily by being made of material having much lower modulus of elasticity, E. Whereas E is typically 10 to 30 million pounds per square inch (psi) for metals, and composites are 1 to 40 million psi, materials for items 40, 41, and 42 preferably have values of E less than 0.5 million psi and consequently, tend to be much less stiff. Polycarbonate plastic is a favored material for these parts and has a value, E=0.34 million psi.

[0116] Shell 41 may have a cavity or other provision to which concentrated weights such as 44 may be bonded wherever desired in or on said shell. A shaft socket 43 is provided for the shaft. The parts are joined by bonding, plastic welding or the like.

[0117] The face structure's thickness may be varied as shown at 45 and 46 to help maintain the desired NCR for off-center hits and reduce the mass R which moves with the impact.

[0118] While only one internal support is shown in FIGS. 15 and 16, a number of similar supports are possible. One possibility is to have a plurality of tubular supports that are similar in construction to internal support 42, of varying dimensions such that they can be bonded in place with one inside another. They may also be smaller tubes like 42 but located side-by-side rather than concentric. They may also be simple posts, plates, or columns spaced as desired. These embodiments will be discussed below in a somewhat different form in connection with FIGS. 17 through 21.

[0119] This embodiment makes it possible to minimize all 5 of the defects which were defined above.

[0120] FIG. 17 shows the general nature of a preferred embodiment in which all or most of the structure concerned with elasticity and spring effect at impact is of moderate stiffness such that in addition to center hits on the face, off-center hits and hits at or near the perimeter of the face have benefits of the spring effect. Such benefits are present for prior art designs only for hits at or near the center of the face. While the other novel embodiments previously described also have this characteristic, the embodiment of FIGS. 17 through 21 represents a preferred form and combines features from the earlier embodiments.

[0121] In FIG. 17, 50 is the shell structure made of material of suitable stiffness and strength and having low internal damping. Polycarbonate plastic is satisfactory. Polyester and other strong, resilient plastics are possibilities.

[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 50A. If preferred, it may be located more forwardly or more rearwardly or may be absent if one material is used for the entire shell structure.

[0123] A shaft socket 51 is provided on the shell. The illustrated elements 54 may be much more closely spaced than shown in FIG. 17 (and also in FIGS. 18-21). In such case, the internal central part elastic structure 54 may have a ball strike surface 53 at a forward end of the internal central elastic structure. The central elastic support for the ball impact is primarily supplied by the central structure 54 consisting of various forms of elastic structural elements that are described in detail below in connection with FIGS. 18 through 21. As shown, the internal central elastic structure is supported by a plate 55. In turn, plate 55 is supported by shell 50, using a shoulder or ledge 57. Central structure 54 may alternatively be supported at its rear end on the shell in which case plate 55 is not used. Internal masses may be added as desired, and bonded in place, as shown at 56 or in other places in or on the head.

[0124] An alternate layer 52 forming a ball strike or impact surface can be supported on the internal central elastic structure for providing a ball striking surface. This is a preferred arrangement.

[0125] FIG. 18 is a cross sectional view in the direction indicated by 18-18 in FIG. 17. It shows one form for central part structure or member 54. This form for central part structure or member 54 has walls 58 which are compressible in the fore-aft direction upon impact on the ball impact surface. Such walls are joined as at 59 and may also be joined to the shell so as to form a one-piece honeycomb structure having square open elements. Alternately, the walls of the honeycomb may be free of the shell, depending on the needs for stiffness of the structure. The open elements need not be square and could be circular, triangular, hexagonal, or other shape as desired.

[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 58 spreads outwardly toward the shell 50 along a distance rearward from the face. The result is that the wall structure 58 shows greater stiffness in compression than would be the case if only the wall portion 58 directly rearward of the impact carried the entire compression load. This spreading of the stress tends to make it desirable for walls 58 to be thicker toward the front and thinner toward the rear when the compressive stiffness under an impact has suitable value for the usual case where there is also a desire for minimum mass of central member 54.

[0127] For such cases which involve spreading of the stress, plate 55 may be eliminated so that the stress is caused to spread to the shell walls 50. Alternately, plate 55 can be made less thick such that it provides a part of the elastic behavior.

[0128] FIG. 19 shows how the honeycomb structure of FIG. 18 could be replaced by an assembly of individual columns 60 forming the central part structure and extending along the length “L” in FIG. 17. Such columns may have a cross sectional shape which is rectangular, circular, triangular, X-shaped, or other shape or they could be hollow tubes. Because they are individual, independent columns, they act to keep the stress of the impact load from spreading to such neighboring columns as are located outside of the impact area (toward the toe, heel, up, or down, relative to the impact area). This allows more flexible design control over compressive stiffness at various parts of the face.

[0129] If very long, the columns of FIG. 19 have a tendency to buckle as Euler columns. FIG. 20 shows how columns 60 may be replaced by columns 61 at least selected ones of which have a means of support against buckling which support being provided by thin walls 62 that connect columns 61 from one to another. Some columns 61 can be left unconnected. The result is that the center part structure can be designed so as to behave very nearly as individual columns with respect to stress spreading, or very nearly as a homogeneous structure as approximated by the honeycomb of FIG. 18.

[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 FIG. 17 of about 1.6 to 2. If shorter, A when designed for the desired compressive stiffness, the columns must have less cross sectional area, which raises the maximum compressive stress and thus provides a minimum length L for such materials. That is, under these conditions the compressive strain at impact exceeds the failure limit for such materials if such columns are too short.

[0132] The columns, honeycomb elements, or plates of FIGS. 18 through 21 may be varied in thickness and proximity to each other as desired, so as to optimize compressive stiffness over the face which may be needed to minimize distance variations of off-center hits. Such variations of stiffness over the face are of great concern for current designs for off-center hits. Variation of the shell thickness and material also provides an important degree of design control over said variations of stiffness. In the case of FIG. 20, the thin walls 62 may be varied in thickness or even eliminated in some areas as further means to allow design control over compressive stiffness at various locations of off-center hits.

[0133] There is another alternate for central part structure or member 54 in FIG. 17. This is to use elastomers. They have the ability to survive far greater strain and have far lower values of E as compared to the plastic materials discussed above. In turn, this means that that dimension L in FIG. 17 will be shorter. Candidate elastomers are the elastomeric compounds used for the interior of so-called “solid” golf balls; natural rubber; and perhaps a few others. Most synthetic rubbers have excessive internal damping. That means that they do not return promptly and nearly completely to their original shape after being loaded in compression or tension and would not be suitable for this use.

[0134] With such elastomers, a solid form can be considered for central part structure or member 54, having no holes or fewer and smaller holes. With very low values for E, and particularly if there are holes, length L in FIG. 17 may be much shorter, such as 0.3 or less. If fore-aft holes are chosen they allow a degree of design control over the coefficient of restitution at various locations on the face. In this case the elastic structure 54 can become essentially the same as was described at D and E in FIGS. 8 and 9 and in detail in FIGS. 10-14.

[0135] FIG. 21 is another variation of the honeycomb center part structure of FIG. 18. In this form, the honeycomb structure 58 is replaced by spaced walls or plates 65 that extend along the length L in FIG. 17. Design and performance characteristics are similar. The advantage is that molding and assembly of this design is easier than for FIG. 18.

[0136] While all of the center part structure elements described in FIGS. 10, 11, and 17 through 21 are discussed and illustrated as being generally perpendicular to the face, they may advantageously be as much as 45 degrees from perpendicular. This allows them to provide reduced stiffness for impacts on the face, while not becoming too short.

[0137] There are preferred dimensional ranges for the designs of FIGS. 17 through 21 which are subject to variation, depending strongly on the modulus of elasticity E for the material chosen. The following dimensional ranges are for polycarbonate material and similar materials such as polyester. Shell thickness 50B in FIGS. 17, 18, and 21 may range from .04 to 0.10 inch and may vary at various locations on the shell as desired for best performance. Dimension 50C in FIG. 18, 63 in FIG. 20, and 68 in FIG. 21 represent the spacing of elastic elements and may range from 0.05 or less to about 0.50 inch and may vary in various locations. In FIG. 20, dimensions 63 and 64 may vary from 0.1 to 0.6 inch and this also applies to the corresponding dimensions of FIG. 19 and dimensions 63 and 64 need not be equal. Dimension 50D in FIG. 18 and dimension 67 in FIG. 21 may vary from 20% to 60% of dimension 50C or dimension 68. In FIGS. 19 and 20, the cross sectional area of columns may be large or small compared to the open areas, and may range from 20% to 80% of the total area.

[0138] It should be noted that FIGS. 17 through 21 are an extension of the form and concepts described in connection with FIGS. 8 to 13 and if elastomeric material is used, the similarity is close.

[0139] At the hitting surface, the front end of the central elastic member 54 of FIG. 17 may need no face cover if its elements (58, 60, 61 or 65) are closely spaced. The surface serves best with a face cover 52 such as shown in dash lines. Where durability and abrasion resistance is important polyurethane rubber or thin polycarbonate are good choices for thin cover 52, contributing negligibly to stiffness, mass, and internal damping while still serving as a durable face hitting surface. Various other plastic materials are suitable.

[0140] Face cover 52 may be made of thin metal. In that case, the thin face cover may be a significant part of the stiffness of the club face and of the mass which moves at impact. Such cover may also cause the load to spread more broadly over the central elastic member 54 and alter its optimum design.

[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.

Claims

1. A golf club head composed of parts which include an elastic shell, a face, and a central part located behind said face and said central part being inside of said elastic shell, elasticity of said head being defined by said shell in cooperation with at least one other member, said at least one other member being chosen from a group having elements consisting of said face, said face being elastic, said central part, said central part being elastic, and combinations of said elements of the group.

2. The golf club head of claim 1 wherein said face deforms between 0.02 and 0.10 inch for impact with a golf ball with approach velocity of 109 miles per hour, said impact being at any location on said face.

3. The golf club head of claim 1, wherein said elastic central part comprises a layer of elastic material attached to the back side of a said face and to said elastic shell.

4. The golf head of claim 3, wherein the said layer of elastic material has cavities therein that extend at least partially through said layer of elastic material for adjusting elastic properties.

5. The golf club head of claim 4, wherein the cavities comprise holes through said layer of elastic material.

6. The golf club head of claim 4, wherein said cavities comprise holes at least partially through said layer of elastic material.

7. The golf club head of claim 1, wherein said central part is chosen to be an internal support having a ball striking surface exposed to the front side of said shell, said shell supporting said internal support, said internal support having suitable elastic properties so as to provide a desired normal coefficient of restitution for golf club and striking surface impact.

8. The golf club head of claim 7, wherein said shell has a cross plate supported thereon spaced from the ball striking surface, said internal support being at least partially supported on said plate.

9. The golf club head of claim 3, wherein said face comprises a sheet of material and the elastic properties of said layer of elastic material and said sheet of material joined thereto are varied by altering at least one of the factors chosen from the group consisting of thickness of the elastic layer, cavities formed in the elastic layer, and variation of thickness of the sheet of material, to control the local values of elastic and mass properties as measured at the face.

10. The golf club head of claim 2 wherein said elastic center part comprises a coil spring joined to the face, a front plate joined to an outer side of the coil spring, the coil spring comprising a series of coils with a coil diameter spacing the face and front plate.

11. A golf club head comprising a shell having a ball striking face side and an opposite rear side, said shell defining a perimeter of the ball striking face side, said ball striking face side comprising a ball strike surface of a non-metallic member supported on said shell to at least partially carry loads from impact of a golf ball striking said ball striking surface and causing deflection of the said ball striking surface relative to said shell.

12. The golf club head of claim 11 wherein said member extends to the perimeter of the shell.

13. The golf club head of claim 11 wherein said non-metallic member comprises a plurality of deformable columns having first ends supported on a rear side of said shell, and second ends forming said ball strike surface.

14. The golf club head of claim 13 wherein said columns comprise a plurality of said columns at least some of which are joined by walls extending perpendicular to said ball strike surface.

15. The golf club head of claim 11, wherein said non metallic member comprises a plurality of deformable walls formed into a honeycomb, the walls extending generally perpendicular to the ball strike surface.

16. The golf club head of claim 13, wherein the said plurality of deformable columns are held by walls formed as a honeycomb structure.

17. The golf club head of claim 11, wherein said non metallic member comprises a plurality of spaced apart walls generally perpendicular to said ball strike surface.

18. A method of providing a desired coefficient of restitution for impact of a golf ball on a strike face of a golf club head after deflection caused by impact of a said golf ball on any location on said strike face comprising providing an elastic material between the strike face and a golf club head shell to transfer deflection loads from the strike face to said shell.

19. The method of claim 18 including forming said elastic material as an elastomeric layer having a strike face structure forming an outer portion of a face plate structure, providing a plate member carrying the elastomeric layer to the golf club head shell, and securing said plate member to said shell.

20. The method of claim 18 including supporting a plate member at a perimeter of the golf club head shell, adhering an elastomeric material layer on an outer surface of the plate member, and adhering a thin metal plate to an outer surface of the elastomeric material layer.

21. The method of claim 18, wherein a striking face is on a plate member, and providing the elastic material between the plate member and the golf club shell.

22. The method of claim 18 wherein the strike face is formed on an end of the elastic material.

23. A golf club head having a face structure, a ball impact surface on said face structure, a central part structure and a shell structure in which said face structure, central part structure, and shell structure have material and structural design such that said ball impact surface is able to deform elastically in a rearward direction at least 0.02 inch from impact of said ball at approach speed perpendicular to said ball impact surface of 109 miles per hour, at substantially any point on said face structure, the design and materials of said structures selected to thereby allow said face structure to deform and return elastically to increase the momentum transferred to a golf ball when struck by said golf club head with impacts normal to said ball impact surface at substantially all locations of impact of the ball on said ball impact surface and minimize changes in angular orientation of said ball impact surface during all such impacts, as compared with known designs of golf club heads having flexible features, which cannot so deform and return elastically.

24. The golf club head of claim 23 wherein said central part structure is composed of columns having long axes within 45 degrees of perpendicular to the center of said face structure ball impact surface.

25. The golf club head of claim 24 wherein said columns are generally perpendicular to the center of said face structure ball impact surface.

26. The golf club head of claim 25 wherein at least some of said columns are joined by flexible walls so as to transmit low force between adjacent columns in the direction of the long axes of such columns, and to transmit significant force from one column to an adjacent column to reduce the tendency of the columns to buckle.

27. The golf club head of claim 26 wherein said flexible walls are adjoined to selected ones of the plurality of columns forming the center part structure.

28. The golf club head of claim 23 wherein the material of said center part structure is one of the materials chosen from a group consisting of polycarbonate plastic, polyester plastic, ABS plastic and elastomeric materials.

29. The golf club head of claim 23 wherein said face structure is formed as a ball impact surface on a face end of said center part structure.

30. The golf club head of claim 23 wherein said shell structure is composed of a material chosen from a group consisting of polycarbonate plastic, polyester plastic, ABS plastic, and elastomeric materials.

31. The golf club head of claim 23 wherein said central part structure comprises a honeycomb cross section structure and is composed of material having Young's modulus of elasticity less than 500,000 pounds per square inch.

32. The golf club head of claim 31 wherein said honeycomb cross section has a cross sectional shape having open space defined by intersecting walls forming a geometric pattern.

33. The golf club head of claim 23 wherein there is a stiff and strong support plate behind the said central part structure, the said central part structure is made of elastomeric material, and said central part structure has a length in a direction substantially perpendicular to the ball impact surface of less than 0.3 inch.

34. The golf club head of claim 23 wherein there is a face structure between said central part structure and the ball impact surface, said central part structure comprising a tubular column of a selected cross sectional shape, said tubular column being disposed against the face structure so as to elastically support said face structure with respect to rearward movement of said face structure.

35. The golf club head of claim 34 in which said tubular column is in the form of a plurality of concentric telescoping metal tubes such that an innermost tube supports said face structure and is in compression during impact from a golf ball, and the inner most tube being joined to the next outer tube at rearward ends thereof, said next outer tube being in tension and being joined to a third outer tube at forward ends, an outermost one of said concentric telescoping tubes being joined to a rear portion of said shell structure of said golf club head.

36. The golf club head of claim 35 in which a plurality of said concentric telescoping tubes is disposed in selected locations on the face structure to provide support and stiffness of the face structure in desired locations to approximate desired strength and elasticity at substantially all locations of said face structure.

37. The golf club head of claim 25 wherein said central structure extends for a length L rearwardly from the face structure and the length L being at least 1.6 inches and within the shell structure.