Golf club head with face wall flexure control system

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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS It should be understood that the drawings (except FIGS. 18 and 19 ) of the present club head are to scale 1″&equals;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. 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. 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. 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. 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 ΔMAX = PL 3 48 &it; E &it; &it; I &it; &NewLine; &it; where &it; &it; P = &it; force , L = &it; Length E = &it; Modulus &it; &it; of &it; &it; Elasticity Eq . &it; ( 1 ) 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 ΔMAX = PL 3 192 &it; E &it; &it; I Eq . &it; ( 2 ) 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 . 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. In FIG. 16 (analogous to FIGS. 9, 10 and 13 ), the maximum deflection is: 3 ΔMAX = 693 &it; &it; Pr 2 400 &it; &it; Et 3 &it; &NewLine; &it; where &it; &it; E = &it; Modulus &it; &it; of &it; &it; Elasticity P = &it; Force r = &it; plate &it; &it; radius t = &it; plate &it; &it; thickness Eq . &it; ( 3 ) In FIG. 17 analogous to FIGS. 11, 12 , and 14 , the maximum deflection is: 4 ΔMAX = 273 &it; W &it; &it; Pr 2 400 &it; &it; Et 3 Same constants as above. 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. 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 . 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. 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. 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. 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. 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. 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. 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. 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. The face wall 12 , according to the present invention, has a uniform thickness between 0.045 inches and 0.070 inches. 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 . 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 . 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. 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. 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. 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. 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. 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. 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. 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. 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. 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 .