BACKGROUND OF THE INVENTION
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The following patents or specifications disclose club heads containing face reinforcing elements:
British Patent Specification, No. 398,643, to Squire, issued Sep. 21, 1933;
United States Patents:
Clark, U.S. Pat. No. 769,939, issued Sep. 13, 1904
Palmer, U.S. Pat. No. 1,167,106, issued Jan. 4, 1916
Barnes, U.S. Pat. No. 1,546,612, issued Jul. 21, 1925
Drevitson, U.S. Pat. No. 1,678,637, issued Jul. 31, 1928
Weiskoff, U.S. Pat. No. 1,907,134, issued May 2, 1933
Schaffer, U.S. Pat. No. 2,460,435, issued Feb. 1, 1949
Chancellor, U.S. Pat. No. 3,589,731, issued Jun. 29, 1971
Glover, U.S. Pat. No. 3,692,306, issued Sep. 19, 1972
Zebelean, U.S. Pat. No. 4,214,754, issued Jul. 29, 1980
Schmidt, U.S. Pat. No. 4,511,145, issued Apr. 16, 1985
Yamada, U.S. Pat. No. 4,535,990, issued Aug. 20, 1985
Chen, et al., U.S. Pat. No. 4,681,321, issued Jul. 21, 1987
Kobayashi, U.S. Pat. No. 4,732,389, issued Mar. 22, 1988
Shearer, U.S. Pat. No. 4,944,515, issued Jul. 31, 1990
Shiotani, et al., U.S. Pat. No. 4,988,104, issued Jan. 29, 1991
Duclos, U.S. Pat. No. 5,176,383, issued Jan. 5, 1993
Atkins, U.S. Pat. No. 5,464,211, issued Nov. 7, 1995
Rigal, et al., U.S. Pat. No. 5,547,427, issued Aug. 20, 1996
Lu, U.S. Pat. No. Re. 35,955, reissued Nov. 10, 1998
Noble, et al., U.S. Pat. No. 5,954,596, issued Sep. 21, 1999
SUMMARY OF THE PRESENT INVENTION
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.
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.
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.
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.
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.
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.
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.
The cross sectional area of the face wall at incrementally increasing radii, r1, r2, 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.
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.
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+BX3)1, to a thickness in one embodiment of about 0.125 near the geometric center. (Note the rib height in the drawings are exaggerated).
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.
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.
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.
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.
Other objects and advantages will appear more clearly from the following detailed description.