Title:

Golf club head with face wall flexure control system

Document Type and Number:

United States Patent Application 20020183134

Kind Code:

Abstract:

A metal club head designed for increased flexure at ball impact including a face wall reinforcing network that increases in thickness from the perimeter wall to a point near the face wall geometric center.

Representative Image:

Golf club head with face wall flexure control system

Inventors:

Allen, Dillis V. (Elgin, IL, US)
Raymont, William R. (Las Vegas, NV, US)

Plaque It!

RELATED APPLICATION

[0001] This application is a Continuation in Part of U.S. application Ser. No. 09/344,172, Filed: Jun. 24, 1999, entitled “GOLF CLUB FACE FLEXURE CONTROL SYSTEM” filed in the name of Dillis V. Allen, and is related to U.S. application Ser. No. ______, Filed: ______, entitled “IMPROVED GOLF CLUB HEAD WITH FACE WALL FLEXURE CONTROL SYSTEM”.

BACKGROUND OF THE INVENTION

[0002] In the last several years, the USGA has struggled with attempting to devise a fair test to limit the trampoline effect of the face wall at ball impact. Recent innovation in titanium alloys, and particularly the Beta titanium alloys has enabled the golf club head designer to dramatically reduce face thickness and achieve greater face flexure without face failure. Faced with the politics of golf integrity, which pits the golf traditionalists against those seeking enhanced performance from new technology, the USGA has devised a rebound test where a ball is fired at a test sample club and inlet and outlet velocities are measured. If ball exit velocities exceed the inlet velocity by a predetermined fractional multiplica (<.90) not relevant to this discussion, the club fails the test. There is also a great debate as to whether such USGA testing is in the best interest of golf, particularly for amateur players, who Arnold Palmer characterizes as a group that should not be bound by these strict USGA rules, but should be permitted use of clubs that do not conform to the present (July 2001) USGA testing rules.

[0003] In any event, the USGA rules and the concomitant colossal debate over which clubs are legal and which are not has created a large market for both clubs that marginally pass the USGA rules and those that are illegal under the USGA rules. The latter market is enhanced because the USGA rules are not applicable outside North America.

[0004] In this environment, the present invention is directed toward a plurality of techniques for increasing the flexure of the face wall of a golf club without exceeding the elastic limit anywhere across the face wall. Conventional techniques for varying face wall flexure are: (1) face wall material selection; (2) face wall shape variation; (3) face wall area control; (4) face wall heat treatment, and, of course; (5) face wall thickness changes.

[0005] By using trial and error techniques, many golf club head designers have combined these factors to achieve what is now termed a “non-conforming” club head. Several manufacturers including Callaway Golf and Ping Golf, as well as many of their imitators, have a variable thickness face wall where the face is thicker near the point of ball impact and thins as it approaches the perimeter wall. The problem with this technique is the thickness of the face must be over 0.125 inches over a major portion of the face wall to prevent face wall failure, and face thickness variation is limited to 2× because of club head weight limitations. The present invention solves these problems.

[0006] Investment casting techniques innovated in the late 1960s have revolutionized the design, construction and performance of golf club heads up to the present time. Initially only novelty putters and irons were investment cast, and it was only until the early years of the 1980s that investment cast metal woods achieved any degree of commercial success. The initial iron club heads that were investment cast in the very late 1960s and early 1970s innovated the cavity backed club heads made possible by investment casting which enabled the molder and tool designer to form rather severe surface changes in the tooling that were not possible in prior manufacturing techniques for irons which were predominantly at that time forgings. The forging technology was expensive because of the repetition of forging impacts and the necessity for progressive tooling that rendered the forging process considerably more expensive than the investment casting process and that distinction is true today although there have been recent techniques in forging technology to increase the severity of surface contours albeit them at considerable expense.

[0007] The investment casting process, sometimes known as the lost wax process, permits the casting of complex shapes found beneficial in golf club technology, because the ceramic material of the mold is formed by dipping a wax master impression repeatedly into a ceramic slurry with drying periods in-between and with a silica coating that permits undercutting and abrupt surface changes almost without limitation since the wax is melted from the interior of the ceramic mold after complete hardening.

[0008] This process was adopted in the 1980s to manufacture “wooden” club heads and was found particularly successful because the construction of these heads requires interior undercuts and thin walls because of their stainless steel construction. The metal wood club head, in order to conform to commonly acceptable club head weights on the order of 195 to 210 gms. when constructed of stainless steel, must have extremely thin wall thicknesses on the order of 0.020 to 0.070 inches on the perimeter walls to a maximum of 0.125 inches on the forward wall which is the ball striking surface. This ball striking surface, even utilizing a high strength stainless steel such as 17-4, without reinforcement, must have a thickness of at least 0.125 inches to maintain its structural integrity for the high club head speed player of today who not uncommonly has speeds in the range of 100 to 150 feet per second at ball impact.

[0009] Faced with this dilemma of manufacturing a club head of adequate strength while limiting the weight of the club head in a driving metal wood in the range of 195 to 210 gms., designers have found it difficult to increase the perimeter weighting effect of the club head.

[0010] Metal woods by definition are perimeter weighted because in order to achieve the weight limitation of the club head described above with stainless steel materials, it is necessary to construct the walls of the club head very thin which necessarily produces a shell-type construction where the rearwardly extending wall extends from the perimeter of the forward ball striking wall, and this results in an inherently perimeter weighted club, not by design but by a logical requirement.

[0011] Prior attempts to manufacture very large stainless steel metal club heads with larger than normal faces has proved exceedingly difficult because of the 195 to 210 gm. weight requirements for driving club heads to achieve the most desirable club swing weights. Thus, to the present date stainless steel “jumbo” club heads have been manufactured with standard sized face walls, deeply descending top walls from the front to the rear of the club head, and angular faceted sole plates all designed to decrease the gross enclosed volume of the head but which do not detract from the apparent, not actual, volumetric size of the head. This has led to many manufacturers switching from stainless steel to aluminum and titanium alloys, which are of course lighter, to enlarge the head as well as the face.

[0012] A further problem in the prior art references which suggest utilizing these rigidifying elements, is that they are completely silent on how these reinforcing elements, when not cast into the face wall, are attached into the club head. And the method of attachment, as will be seen from the present invention, is critical to the benefits of increasing resonant frequency and rebound of the face wall in accordance with the present invention. Presently known bonding techniques are not sufficient to yield these benefits.

[0013] Still another of these prior references suggests making the head of synthetic material and the support rod of a similar material, but these low modulus and soft materials cannot significantly raise the resonant frequency or rebound time of the ball striking face wall.

[0014] The following patents or specifications disclose club heads containing face reinforcing elements:

[0015] Foreign Patents:

[0016] British Patent Specification, No. 398,643, to Squire, issued Sep. 21, 1933;

[0017] United States Patents:

[0018] Clark, U.S. Pat. No. 769,939, issued Sep. 13, 1904

[0019] Palmer, U.S. Pat. No. 1,167,106, issued Jan. 4, 1916

[0020] Barnes, U.S. Pat. No. 1,546,612, issued Jul. 21, 1925

[0021] Drevitson, U.S. Pat. No. 1,678,637, issued Jul. 31, 1928

[0022] Weiskoff, U.S. Pat. No. 1,907,134, issued May 2, 1933

[0023] Schaffer, U.S. Pat. No. 2,460,435, issued Feb. 1, 1949

[0024] Chancellor, U.S. Pat. No. 3,589,731, issued Jun. 29, 1971

[0025] Glover, U.S. Pat. No. 3,692,306, issued Sep. 19, 1972

[0026] Zebelean, U.S. Pat. No. 4,214,754, issued Jul. 29, 1980

[0027] Schmidt, U.S. Pat. No. 4,511,145, issued Apr. 16, 1985

[0028] Yamada, U.S. Pat. No. 4,535,990, issued Aug. 20, 1985

[0029] Chen, et al., U.S. Pat. No. 4,681,321, issued Jul. 21, 1987

[0030] Kobayashi, U.S. Pat. No. 4,732,389, issued Mar. 22, 1988

[0031] Shearer, U.S. Pat. No. 4,944,515, issued Jul. 31, 1990

[0032] Shiotani, et al., U.S. Pat. No. 4,988,104, issued Jan. 29, 1991

[0033] Duclos, U.S. Pat. No. 5,176,383, issued Jan. 5, 1993

[0034] Atkins, U.S. Pat. No. 5,464,211, issued Nov. 7, 1995

[0035] Rigal, et al., U.S. Pat. No. 5,547,427, issued Aug. 20, 1996

[0036] Lu, U.S. Pat. No. Re. 35,955, reissued Nov. 10, 1998

[0037] Noble, et al., U.S. Pat. No. 5,954,596, issued Sep. 21, 1999

SUMMARY OF THE PRESENT INVENTION

[0038] In accordance with the present invention, a metal club head is designed for increased flexure at ball impact including a pleat or alternatively a tongue and groove connection in the perimeter wall that provide reduced resistance to face wall expansion at ball impact, and more energy transfer to the ball, and a face wall reinforcing network that increases in height from the perimeter wall to a point near the face wall geometric center.

[0039] The golf club head at ball impact has been extremely difficult to analyze from a design standpoint because of the peculiar traditional shape, particularly of the metal wood, the singular point of attachment of the shaft at the hosel which has no analogy to a vise holding the head during testing, the bulge and roll of the club face, and the peculiar effect of the perimeter wall on the face dynamics. The present invention does not solve these design problems, but focuses on a system for increasing face flexure and energy transfer to the ball.

[0040] This invention or inventions, bifurcates the present solution into two parts; the first is a face reinforcing network that increases in thickness from the perimeter wall to a point near the geometric center of the club face according to sound mathematical approximations. The face wall thinning techniques in the prior art, while helpful, do not have face wall thickness variations that optimize face wall flexure. In the present design face wall thickness, or more accurately effective thickness, increases from the perimeter wall to near the face wall geometric center by a factor in the range of 3.0 to 7.0 times and does so geometrically in its more specific definition.

[0041] Effective thickness, as used herein, is the flexure characteristic of the present rib reinforcement face compared to a solid face wall of varying thickness without any reinforcing ribs. Thus, using the present technique, the present rib design can achieve the same face flexure pattern as a solid faced club having a face wall thickness variation of up to seven fold, without adding the excessive weight of that solid face wall.

[0042] In its broadest aspects, some of these principles can be utilized in solid faced clubs with variable face thickness, such as shown in the Kubica, et al., U.S. Pat. Nos. 5,906,549 and 5,954,596. However, the narrow rib reinforcing network of the present invention permits a far greater increase in effective face thickness than solid faced club heads, because it provides greater reinforcement without the trade-off of increased face weight. That is, if in a solid face wall club with face thickness thinning near the perimeter wall, the thickness at the face center were seven times the thickness at the perimeter wall, the thickness at the center would be about 0.434 inches and the club head would be far overweight. The present invention solves this problem.

[0043] Thus, according to the present invention, the face wall can be very thin and light, as thin as 0.062 inches when made of a high quality beta titanium such as 15 Mo 3-3 hardened. Yet, the ribbing network gives the same effect as face increase variation of 3 to 7 times in a solid faced head.

[0044] These principles are based upon the mathematical premise that face wall stress at ball impact is concentrated in a very small area surrounding and behind the ball. This is due in part to the outward and inward moments on the face caused by the perimeter wall and the thickness and size of the face wall itself.

[0045] The cross sectional area of the face wall at incrementally increasing radii, r ₁ , r ₂ , etc. from the center to the perimeter increases more significantly than previously thought. These areas define the face wall's ability to resist stress at these radii and thus the largest sectional area, at the perimeter wall, is capable of handling the greatest load. And this is what leads to the conclusion the face wall needs to be dramatically thinner at the perimeter wall than at the face wall center to achieve not only maximum deflection at the face wall center, but uniform deflection from the geometric center out to the perimeter wall. This also maximizes the spring effect of the face wall and energy transfer to the ball.

[0046] Simple beam theory, discussed below, while helpful, does not properly analyze club face wall stress because of (1) the torque applied to the face wall by the perimeter wall and (2) the increasing cross-sectional area of the face wall as the radius about the geometric center increases. And while simple calculations indicate the cross sectional area (the area cut by a hole saw around the geometric center) increases linearly; i.e. Kr, as the radius r around the center increases, this ignores the moments or torque applied to the perimeter of the face wall by the perimeter wall at ball impact.

[0047] The net effect of these moments caused by the perimeter wall on the face wall is to strengthen the face wall particularly near the perimeter wall. To compensate for this effect, the present rib network increases from zero or near zero near or at the perimeter wall, geometrically at K(X+BX ³ ) ¹ , to a thickness in one embodiment of about 0.125 near the geometric center. (Note the rib height in the drawings are exaggerated). 1. K and B are constants

[0048] The second design feature of the present invention, claimed in the above “Related Application”, is a pleat or alternatively tongue and groove connections between the perimeter wall and the face wall that each permit the face wall to more easily expand radially (flatten) in the plane of the face wall. These features are independent of and can be used without the above face wall ribbing. Metal woods normally have face walls curved in orthogonal planes, the curve in a horizontal plane being formed on a radius called “bulge”, and the curve in a vertical plane being found is a radius referred to as “roll”. Face curvature by itself reduces face wall flexure more than flat faces. Also, the moments created by the perimeter wall, which exist in both flat and curved face walls, resist uniform face deflection and contribute to localized face wall distortion around the ball at impact. If the face wall is permitted to more easily flatten at impact, stresses in the face wall are spread more uniformly across the face wall and the face wall deflects more uniformly from the geometric center to the perimeter wall upon impact.

[0049] It should be understood at this point that effective face thickness variation and pleat or tongue and groove connectors at the perimeter wall are all designed to achieve similar ends; i.e., maximize face wall deflection. Thus, they can be utilized in club head design independent of one another, or together, as shown in the drawings embodiments where they have a cumulative effect toward those ends.

[0050] The perimeter wall pleat or the tongue and groove connections are in fact separate embodiments. In the pleat embodiment, the face wall and a short portion of the perimeter wall are cast in one piece and hardened. The perimeter wall portion has a concave perimeter pleat that acts as a pair of opposed Bellville springs. As these springs compress on impact, the outer diameter of the springs increases and thus lessens the resistance the perimeter wall has to face wall expansion. And the Bellville springs, upon recovery after compression, deliver energy back to the ball as it leaves the club face wall.

[0051] In the other embodiment, the tongue and groove connection, the face wall floats slightly in the perimeter wall in all directions, permitting face wall expansion and reducing resistance to face wall deflection.

[0052] Other objects and advantages will appear more clearly from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] FIG. 1 is a front view of the club head according to the present invention;

[0054] FIG. 2 is a top view of the club head according to the present invention;

[0055] FIG. 3 is a right side view of the club head according to the present invention;

[0056] FIG. 4 is a left side view of the club head according to the present invention;

[0057] FIG. 5 is a horizontal mid-section of the front piece of the club head;

[0058] FIG. 6 is a vertical mid-section of the front piece of the club head;

[0059] FIG. 7 is a rear view of the front of the front piece of the club head illustrated in FIGS. 5 and 6 ;

[0060] FIG. 8 is a left side view of the rear piece of the club head according to the present invention;

[0061] FIGS. 9, 10 , 11 and 12 are beam theory drawings;

[0062] FIGS. 13 and 14 are beam theory drawings illustrating shear and moments;

[0063] FIGS. 15 and 16 are disk theory analysis drawings;

[0064] FIGS. 17 and 18 are fragmentary sections illustrating a tongue and groove embodiment of the present invention, and;

[0065] FIG. 19 is a fragmentary section of a still further tongue and groove connection embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0066] It should be understood that the drawings (except FIGS. 18 and 19 ) of the present club head are to scale 1″=1″, within of course the limits of the patent draftsman, and therefore, dimensions that are not specifically set forth either as single dimensions, or ranges, may be measured on the drawings and as such are within the disclosure of the present invention and these dimensions may after the filing of the present invention, be added to the disclosure, specification or claims with the modifier “substantially” without constituting new matter.

[0067] As noted above, both simple single beam technology and circular disc technology do not have exact analogy to the dynamics of metal golf clubs and particularly metal woods, but do provide a useful comparison for experimentation. The bulge and roll of the club face is simulated in FIGS. 9 to 12 . In FIGS. 9 and 10 , the convex face wall 10 easily flattens upon impact force P to the flat or concave positions shown in FIG. 10 . This occurs when reaction forces F ₁ and F ₂ act only in a vertical direction. What actually happens is depicted in FIGS. 11 and 12 . The perimeter wall creates moments on the face depicted as M ₁ and M ₂ that resist wall flattening.

[0068] So long as the face wall is convex as shown in both FIGS. 11 and 12 , the perimeter wall will also exert inward forces F ₃ and F ₄ on the face wall, resisting flattening to the FIG. 10 position. The result of these forces creates the localized depression of the face wall around the golf ball illustrated in FIG. 12 that is responsible for face wall failure if the designer simply attempts to uniformly thin the face wall. This localized depression represents the condition the present invention eliminates.

[0069] The perimeter wall, of course, has a positive dynamic effect on the face wall and energy transfer to the ball. Thus, the appropriate design approach is to balance the effects of a FIGS. 9 and 10 design with the too restrictive effect of the FIGS. 11 and 12 design and to that end the present inventions are directed.

[0070] A review of beam and disc technology confirms these principles. FIG. 13 shows a single simple beam, centrally loaded that in part analogizes FIGS. 9 and 10 . The shear forces across the beam are constant and the moments at the ends of the beam are zero. The maximum deflection at the center of beam under a concentrated load at midspan are: 1 $\begin{matrix} ΔMAX = \frac{{PL}^{3}}{48 E I} where \begin{matrix} P = force, \\ L = Length \\ E = Modulus of Elasticity \end{matrix} & Eq . (1) \end{matrix}$ embedded image

[0071] Compare this relationship to FIG. 14 , which illustrates the same force P applied to a single beam centrally when the beam is fixed at both ends. Note in FIG. 14 the reverse moments M applied to beam. This simulates the effect of the perimeter wall on the face wall, although not precisely. The maximum deflection of the beam in this system under the same load P is defined as: 2 $\begin{matrix} ΔMAX = \frac{{PL}^{3}}{192 E I} & Eq . (2) \end{matrix}$ embedded image

[0072] Somewhat over-simplified, cancelling out the common factors in equations (1) and (2), the non-restrictive system in FIG. 13 has four times the maximum deflection under the same load as the system in FIG. 14 .

[0073] FIGS. 15 and 16 illustrate circular disc systems that somewhat complicate the analysis of simple single beam review. In a single beam the cross section of the beam stays constant, while in the disc system, the cross sections of the disc, defined at circles around any radius, increase as one moves outwardly from the center or point of theoretical ball impact. This is why the disc analogy is closer to a club head than the beam.

[0074] In FIG. 16 (analogous to FIGS. 9, 10 and 13 ), the maximum deflection is: 3 $\begin{matrix} ΔMAX = \frac{693 \Pr^{2}}{400 {Et}^{3}} where \begin{matrix} E = Modulus of Elasticity \\ P = Force \\ r = plate radius \\ t = plate thickness \end{matrix} & Eq . (3) \end{matrix}$ embedded image

[0075] In FIG. 17 analogous to FIGS. 11, 12 , and 14 , the maximum deflection is: 4 $ΔMAX = \frac{273 W \Pr^{2}}{400 {Et}^{3}}$ embedded image

[0076] Same constants as above.

[0077] Thus, the disc unrestrained in all directions at its perimeter has a maximum deflection 2.54 times the maximum deflection of the disc fixed from movement in all directions at its perimeter. This in part explains the significant resistive effect of the perimeter wall.

[0078] Referring to the drawings and particularly FIGS. 1 to 8 and 17 , 18 , and 19 , a “jumbo” club head 10 is illustrated, preferably entirely constructed of a high performance forged or cast beta titanium material such as 15Mo3-3. In the embodiment disclosed in FIGS. 1 to 8 , the head is constructed of a forward piece 11 including a face wall 12 , and a short perimeter wall 13 , welded to a rear piece 15 illustrated in FIG. 8 including a sole plate portion 17 , a side and rear wall portion 18 , and a crown portion 19 . Note that the forward portion 11 carries an integral hosel 20 having a standard shaft receiving bore 21 therein that also extends through hosel upper portion 22 .

[0079] As noted above, the drawings, as filed, are substantially to scale and the dimensions in some aspects of the present invention are important to the performance of the golf club head.

[0080] Firstly, with respect to the size and shape of the face wall 12 , and particularly as depicted in FIG. 1 , the face wall has a horizontal length F of 4.344 inches, and a vertical height E of 2.344 inches.

[0081] It should be understood that the geometry of the face 12 is designed to provide more uniform deflection across the face upon ball impact, and while the vertical height E in the specific embodiment is 2.344 inches, the advantages of the face geometry can be achieved in face walls having a height greater than 1.9 inches. One important aspect of achieving more uniform face wall deflection, according to the present invention, is to provide a more circular face which enhances uniform face wall deflection.

[0082] Toward that end the central upper edge 25 and the lower central edge 26 each have a radius of 3.25 inches although the benefits of the present invention can be achieved with these radii in the range of 2.75 to 3.50 inches. The upper edges 28 and 29 adjacent central edge portion 25 and the lower edge portions 31 and 32 adjacent the lower edge central portion 26 are tangent to the central portions 25 and 26 and are substantially straight to increase the face height at toe portion 33 and heel portion 34 of the face wall.

[0083] The overall volume of the club head 10 is in the range of 370 cc., noting that is conventional to quantify club head volume in metric units even though the dimensions set forth in this specification are in inches. Toward this specific volume, and referring to FIG. 1 , the overall horizontal length of the club head 10 viewed from the front from the furthest extent of the toe wall 35 from the heel wall 36 identified by the letter G is 4.94 inches, and the overall height of the club from the sole portion 17 to the uppermost portion of the crown wall 15 identified by the letter D in FIG. 1 is 2.62 inches. Overall club head length L is 4.156. The hosel 22 has a substantial inset as seen by the ratio of A/B.

[0084] As seen in FIGS. 5, 6 , and 7 , the face wall 12 has a ribbed reinforcing network 38 that promotes the uniform deflection of the face wall from the geometric center to the perimeter wall portion 13 . That is, the network 38 is designed so there will be a straight line deflection of the face wall 12 from the geometric center G.C. to the perimeter wall 13 in a fashion similar to the straight line deflection of the strings in a tennis racket upon ball impact. Note in the plane of FIG. 5 , which is a horizontal plane extending through the geometric axis of the face wall, that the face 12 is curved indicating it has “bulge”, and in the plane of FIG. 6 , which is a vertical plane taken through the geometric center of the face wall, the face wall 12 is also curved indicating the face wall has “roll”. The curvature of the face wall in these two orthogonal planes may, for example, be on the order of 15 inches. Note also in FIG. 6 that the face wall has a “loft” of 10 degrees, and typically loft will vary in the driver club from 6 degrees to about 11 degrees.

[0085] It should be understood at this point that certain aspects of the present invention can be applied to fairway woods and iron-type clubs as well. Irons, however, have no roll or bulge curvatures and hence have less resistance to face wall deflection assuming equal face thicknesses and size.

[0086] The network 38 is designed to provide a far greater stiffness variation from the geometric center to the perimeter wall 13 than can be achieved with variable solid (ribless) face thickness. In variable face thickness designs, which are ribless, face thickness variation can only vary by approximately 2.0. That is, the thickness of the face wall near the perimeter wall can only be about half the thickness of the face wall at the geometric center G.C. without resulting in excessive face wall weight and excessive overall club head weight. In the present invention, effective face wall thickness with the rib network 38 can compare to face thickness variations of 3.0 to 7.0 in ribless designs without adding excessive weight to the head. It should be understood, however, that in the range of 7.0, the network 38 will begin to have excessive face stiffness, which is contrary to the purpose of the present invention so that the preferable operating range for the network 38 is closer to 3.0 to achieve maximum face deflection.

[0087] The face wall 12 , according to the present invention, has a uniform thickness between 0.045 inches and 0.070 inches.

[0088] The network 38 is seen to include an annular rib 42 integral with and extending rearwardly from the face wall 12 . The annular rib 42 has a depth of between 0.100 to 0.200 inches and a thickness of 0.062 inches, and the rib 42 has a diameter of approximately 0.750 inches. Extending radially outwardly and integral with both the annular rib 42 and the face wall 12 are eight ribs 43 , 44 , 45 , 46 , 47 , 48 , 49 and 50 , spaced apart approximately 45 degrees in the plane of FIG. 7 , which is a rear view of the club head body forward piece 11 .

[0089] The ribs 45 and 49 ( FIG. 6 ) meet the side of the rib 42 about 0.030 inches below the top of the rib 42 and ribs 44 , 46 , 50 and 48 join the side of the rib 42 about 0.020 inches below the top of rib 42 .

[0090] Note particularly that near the perimeter wall the ribs 43 to 50 have a height of 0 to promote flexure of the face wall, and they have their maximum thickness where the ribs join the annular rib 42 . The effective thickness variation has been determined by comparing the present face and network 38 to a plurality of ribless faces having face thickness variations from 3.0 to 7.0. This effective thickness variation, defined as the thickness t _a at point A near the perimeter wall, and a thickness at a point B near the geometric center, where t _b /t _a is at least 3.0 and in the range of 3.0 to 4.0.

[0091] The annular rib 42 may also be elliptical with the major axis of the ellipse extending horizontally across the face. The ribs 43 and 50 would then be more equal in length and provide more uniform deflection of the face in both horizontal and vertical directions.

[0092] As noted above, in uniform thickness face walls the cross sectional area of the face about any radius around the geometric center G.C. increases as the radius about the geometric center increases. It is this cross sectional area that is proportional to the ability of the face at any given point on the face to resist ball impact stresses on the face so that at the geometric center G.C., where the radius is 0 and the section O, the face wall (absent the network 38 ) is at its weakest point in resisting ball impact forces, and at the perimeter wall at 40 the section is the greatest and has its greatest resistance to ball impact and thus the network 38 seeks to weaken the face wall at 40 and to strengthen the face wall strength at the geometric center G.C., utilizing the network 38 . These cross sectional areas, which are effectively the areas scribed by hole saws centered about the geometric center G.C., increase linearly from the geometric center to near the perimeter wall. However, this analysis neglects the effect of the perimeter wall on the face wall, which is, to provide moments on the face wall tending to maintain the curvature of the face wall 12 . To compensate for the effect of the perimeter wall on the face wall, the ribs 43 to 50 , rather than being straight in configuration to match the linear variation in face wall cross sections moving outwardly from the geometric center G.C., are instead curved to further weaken the face wall moving radially outwardly from the geometric center to compensate for the moments acting on the face wall by the perimeter walls around the face wall.

[0093] Face wall deflection, according to the present invention, is further enhanced by a pleat 54 illustrated in FIGS. 1 to 7 , and an elastomeric tongue and groove section illustrated in FIGS. 17, 18 and 19 . As noted above, the ability of the face wall to flatten upon ball impact is impeded by the perimeter wall, which in accordance with the analysis in FIGS. 11, 12 , 14 , and 16 , provides inward forces on the face wall 12 that inhibit the flattening of the face wall upon ball impact. The pleat 54 and the tongue and groove connection 55 reduce the inward forces acting on the face wall by the perimeter walls.

[0094] The pleat 54 , as seen in FIGS. 2 to 8 , is formed in the forward part 13 illustrated in FIG. 7 , and extends completely around the face wall except at the hosel 22 . The perimeter wall at the hosel 22 , as seen in FIG. 2 , has a slot 56 that connects pleat portion 54 a and pleat portion 54 b.

[0095] As seen in FIGS. 5 and 6 , the pleat 54 is defined by perimeter wall portion 59 and perimeter wall portion 60 that are generally V-shaped in configuration. Wall portion 59 has an angle of approximately 55 to 60 degrees with respect to a vertical plane noted in FIG. 5 , while wall portion 60 has an angle of about 5 to 10 degrees with respect to that same parallel plane. It should be understood, however, that the angles of wall portions 59 and 60 vary to accommodate the unique geometry of the crown wall, side walls, and sole plate of the particular club head under consideration.

[0096] The walls 59 and 60 are in effect Bellville springs that collapse slightly upon ball impact and permit face wall perimeter edge in the plane 61 to move outwardly upon ball impact as the pleat 54 collapses slightly in accordance with well known Bellville spring geometry. It should also be noted that the pleat 54 as it expands as the ball leaves the face 12 , releases its stored energy to the ball enhancing ball exit velocity.

[0097] The slot 56 weakens the face slightly at the hosel 22 to prevent the hosel from rigidifying the face excessively at this point. The pleat may be covered by rings coplanar with the outer walls of the club head for aesthetics.

[0098] As seen in FIGS. 17 and 18 , the elastomeric tongue and groove connection 55 includes a rectangular perimeter recess 66 in the perimeter of the face wall 12 a , and a perimeter tongue 67 integrally formed on an annular bezel 68 welded to an annular recess 69 in the forward edge of perimeter wall 70 . A U-shaped elastomeric ring 72 is mounted in recess 66 and around the tongue 67 . Ring 72 has a durometer in the range of 50 to 90 Shore A. This elastomeric connection permits the face wall to flatten more easily upon impact as the face wall 12 a twists about the tongue 67 in the plane of FIG. 18 . In addition to facilitating the twisting of the face wall 12 a as it flattens, the elastomeric connection 55 also permits radial expansion of the face wall 12 a , which of course tends to occur as the face wall flattens from its roll and bulge unloaded configuration.

[0099] An alternative elastomeric connection 76 is illustrated in FIG. 19 where tongue 77 is formed on the face wall and groove 78 is formed on bezel 79 .

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