Golf clubhead
BACKGROUND 
     This invention relates to a wood type of golf clubhead. More particularly the invention relates to a golf clubhead which has a recessed or inverted hosel portion, an alignment groove for aligning the clubhead, a flat sole portion, and an aerodynamic shape. 
     Golf clubs of the wood type are no longer made only from wood. Such clubs are now commonly made from metal such as stainless steel, titanium, and aluminum and from composite material such as fibers of graphite, Kevlar™, or boron and resin. 
     Many golf clubheads include a hosel which extends upwardly above the face of the clubhead for attaching the shaft of the clubhead. However, a conventional hosel increases weight in the high heel area. It is becoming increasingly common for golf club designers to redistribute the weight of the clubhead to the high toe and low heel areas as taught, for example, by U.S. Pat. Nos. 4,471,961 and 5,120,062. 
     Some clubheads have used a shorter hosel to reduce weight in the high heel area. For example, U.S. Pat. Nos. 5,042,806 and 5,240,252 describe clubheads in which the hosel does not extend above the face. However, such a clubhead does not provide the same support for the shaft as does a clubhead with a traditional hosel. 
     Another problem with wood type clubheads is properly aligning the face of the clubhead. With iron type clubheads many golfers use the bottom groove of the face to align the clubhead square, i.e., perpendicular, to the intended line of flight. The top line of an iron clubhead cannot be used to align the clubhead because the top line is not perpendicular to the intended line of flight as viewed by a golfer at address. 
     However, the face of a wood type golf club has a low loft angle, and the grooves of the face are not easily apparent and usable for alignment at address. Using the face grooves for alignment is also complicated by the fact that the face of most wood type clubheads is provided with bulge and roll curvature, as explained, for example, in U.S. Pat. No. 4,471,961. 
     Many wood type golf clubs therefore include some alignment indicator such as a line or arrow on the top of the clubhead which indicates the intended line of flight. However, some golfers prefer to use the face for aligning the clubhead square rather than relying on an indicator on top of the clubhead. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, a clubhead is provided with an inverted or recessed hosel area. The inverted hosel area includes a generally concave wall which curves toward the sole of the clubhead and reduces the weight in the high heel area. The shaft is reinforced by a hosel tube which extends upwardly from the inverted hosel area. The hosel tube is formed from a light yet strong material, such as titanium, to minimize the weight in the hosel area. 
     The clubhead is also provided with an alignment groove at the intersection of the face and the crown of the clubhead. A portion of the alignment groove lies in a vertical plane which is perpendicular to the midplane of the clubhead and allows a golfer to align the clubhead square to the line of flight. 
     The sole includes a flat portion which supports the clubhead in the address position. The toe portion and rear portion of the club extend upwardly from the flat portion to merge with the crown in a generally V-shaped aerodynamic profile. 
    
    
     DESCRIPTION OF THE DRAWING 
     The invention will be explained in conjunction with an illustrative embodiment shown in the accompanying drawing, in which 
     FIG. 1 is a fragmentary perspective view of a golf club formed in accordance with the invention; 
     FIG. 2 is a front elevational view of the clubhead; 
     FIG. 3 is a top view of the clubhead; 
     FIG. 4 is a toe end view of the clubhead taken along the line 4--4 of FIG. 2; 
     FIG. 5 is a heel end view of the clubhead taken along the line 5--5 of FIG. 2; 
     FIG. 6 is a sectional view taken along the line 6--6 of FIG. 3; 
     FIG. 7 is an enlarged fragmentary view of a portion of FIG. 7; 
     FIG. 8 is a bottom view of the clubhead; 
     FIG. 9 is a fragmentary sectional view taking the line 9--9 of FIG. 3; 
     FIG. 10 is a fragmentary sectional view taken along the line 10--10 of FIG. 9; and 
     FIG. 11 is a fragmentary sectional view taken along the line 11--11 of FIG. 3. 
    
    
     DESCRIPTION OF SPECIFIC EMBODIMENTS 
     FIG. 1 illustrates a wood type of golf club 15 which includes a clubhead 16 and a shaft 17. The particular clubhead illustrated is formed from metal, but the clubhead can also be formed from other material such as wood and composites. 
     The clubhead includes a face 19, a generally convex top portion or crown 20, and a generally convex bottom portion 21. The top and bottom portions merge to form a curved peripheral edge 22 which is relatively sharp or streamlined (FIGS. 2, 4, 5, and 6). 
     The bottom portion of the clubhead includes a sole 24, a toe wall 25 (FIG. 2) which merges with the edge 22, a rear wall 26 (FIGS. 4 and 5) which merges with the edge 22, and a heel wall 27 (FIG. 2) which merges with the edge 22. The toe wall 25 forms a relatively sharp included angle with the crown 20 at the edge 22, i.e. an angle which is no greater than about 90°. The rear wall 26 also forms a relatively sharp included angle with the crown 20 at the edge 22. The angle formed by the rear wall 26 and crown 20 is substantially the same as the angle formed by the toe wall 25 and the crown 20, i.e. it is also a relatively sharp angle which is no greater than about 90°. 
     The sole 24 includes a flat portion or pad 29 (FIGS. 2, 6, and 8). The flat portion is designed to support the clubhead on the ground at address in the proper loft and lie orientation. Although individual golfers might hold a particular clubhead differently at address, clubheads are designed with specific loft and lie angles which are measured with respect to one orientation of the club. See, for example, the discussion in U.S. Pat. No. 5,150,550. 
     Referring to FIG. 2, the angle A between the centerline CL of the shaft and a horizontal ground plane G determines the lie of the clubhead. Referring to FIG. 4, the angle B between the face 19 and a vertical plane V determines the loft of the clubhead. If the face includes bulge and/or roll curvature and is not planar, the loft angle is determined by a plane which is tangent to the center of the face. The tangent plane extends perpendicularly to a vertical midplane MP which extends through the center of the face perpendicular to the ground plane G and the vertical plane V. The flat portion 19 of the sole is coplanar with the ground plane G at address, and the size of the flat portion is preferably sufficient to provide tactile feedback to the golfer to enable the golfer to be aware of the correct address position. 
     A groove 30 (FIG. 8) is provided in the sole pad 29 to facilitate moving the flat portion through turf, soil, or sand as the clubhead impacts the ball, the groove is aligned with the midplane MP and terminates in a flared rear end 31. 
     The rear wall 26 is slightly convex in FIGS. 4-6 and curves upwardly and rearwardly from the sole pad 29 to the edge 22. The toe wall 25 and heel wall 27 are also generally convex and curve outwardly and upwardly to the edge 22. The toe portion 32 of the face (FIG. 2) is relative sharp and V-shaped, and the included angle of the V-shaped toe portion 32 of the face is about 90°. A continuous curved outer periphery is formed at the edge 22 of the clubhead by the intersections of the crown with the toe wall, the rear wall, and the heel wall. 
     A hosel portion 33 is located at the juncture between the crown 20 and the heel portion 34 of the face. The hosel portion includes an inverted or recessed portion 35 which is provided by a generally arcuate or concave wall 36. Referring to FIGS. 2 and 9, the concave wall 36 curves inwardly from the edge 22 toward the toe and upwardly toward the crown. The concave wall is generally channel-shaped and extends along an axis 37 (FIGS. 3 and 5) which is preferably substantially perpendicular to the vertical plane V at address. 
     In one specific embodiment of the invention, the concave wall was circular and had a radius of about 1/2 inch. The wall extended over an arc of about 90°. The maximum depth of the recess measured from a line extending across the recess from the shoulder 38 at the crown to the shoulder 39 at the heel was about 0.15 inch. 
     A hosel tube 41 extends upwardly from the center of the inverted portion 35 beyond the top of the crown 20. The shaft 17 is secured within the hosel tube by epoxy or adhesive. The hosel tube is preferably formed from titanium which is strong yet lightweight. The titanium tube reinforces the shaft without contributing excessive weight to the high heel area. However, the hosel tube can also be made of the same material as the clubhead, such as stainless steel and can also be formed integrally with the clubhead during the casting process. 
     The inverted portion 35 of the hosel reduces the amount of material and the weight in the hosel area. The reduction in weight in the hosel area enables weight to be redistributed to other areas of the clubhead, for example the high toe and low heel areas. The inverted portion also lowers the center of gravity of the clubhead and reduces drag or air resistance as the clubhead is swung. The combination of the inverted portion and the streamlined or tear drop shaped profile provided by the sharp peripheral edge 22 improves the aerodynamic features of the clubhead. 
     The inverted hosel portion also positions the shaft centerline farther from the heel and closer to the center of gravity CG (FIG. 2) of the clubhead. Since the hosel tube 41 and the shaft extend through the center of the concave wall 36, the shaft is spaced away from the shoulder 39 on the heel. 
     The particular clubhead illustrated in FIGS. 1-11 is formed from 17-4 stainless steel by investment casting. As is well known in clubhead manufacturing, the investment casting process forms a hollow clubhead with an open bottom. The opening in the bottom is closed by a soleplate which is welded to the periphery of the opening. 
     Referring to FIGS. 9-11, a generally cylindrical boss or lug 44 is formed integrally with the rear surface 45 of the face. A portion of the boss advantageously extends to the heel wall 27 along the inside surface of the face to form an internal casting gate 46 for the molten metal which forms the clubhead. 
     As described in U.S. Pat. No. 5,346,218, a mold for casting a metal clubhead conventionally includes an external gate through which the molten metal is poured. However, molds for large clubheads advantageously also include internal gates to facilitate flow of molten metal throughout the mold cavity. The boss 44 is formed by an internal gate in the mold which communicates with the conventional external gate at the heel portion of the mold. The internal gate facilitates the casting of the boss, the face, and the crown and also provides weight in the low heel area of the clubhead. 
     The boss is cast with an internal cylindrical bore 47 (FIG. 9) for the hosel tube 41. The hosel is permanently secured within the bore by epoxy. The hosel can also be additionally or alternately secured by screw threads, mechanical force fit, interlock mechanism, etc. The bore terminates in a bottom wall 48 which supports the bottom of the hosel tube and the shaft. The bottom wall is provided with an opening 49 to permit the clubhead to be filled with polyurethane foam if desired. 
     The clubhead can also be cast from titanium or other suitable metal. Titanium is lighter than stainless steel and a titanium clubhead can be larger than a steel clubhead of the same weight. Since molten titanium flows more easily than molten steel, a titanium clubhead does not need an internal gate for the boss 44. The boss of a titanium clubhead can be formed integrally with the rear surface of the face 52 of the clubhead but does not need to extend to the heel wall. 
     Referring to FIGS. 1 and 2, the front surface of the face 19 of the clubhead 16 is provided with conventional grooves 55 which are substantially parallel to the ground plane G. The specific embodiment of the clubhead which is illustrated in the drawing included bulge and roll curvatures which were oriented about axes 45° from the ground plane as described in U.S. Pat. No. 4,471,961. 
     An alignment groove, cut, or recess 56 is provided at the intersection between the face 19 and the crown 20. The alignment groove curves upwardly between the toe portion and the heel portion of the edge 22 and forms the top edge of the face and the front edge of the crown. Referring to FIGS. 3, 4, and 7, the alignment groove includes a rear surface 57 which lies in a plane which is parallel to or substantially parallel to the vertical plane V. 
     The alignment groove is readily visible to the golfer at address and enables the golfer to align the clubhead by squaring the alignment groove to the intended line of flight. Even though the alignment groove follows the curvature of the crown 20, it appears straight or substantially straight to the golfer when viewed at address, particularly because the rear surface of the groove lies in a substantially vertical plane and is therefore substantially straight. 
     If desired, the plane of the alignment groove can be angled with respect to the face to provide an open or closed face when the alignment groove is squared in order to compensate for a hook or a slice. 
     In the preferred embodiment the alignment groove is located at the intersection of the face and crown. However, the alignment groove could also be located on the crown behind the face or on the face below the crown. The alignment groove is preferably formed during the casting process. 
     Alternatively, alignment means could be provided by a painted or cut line or other indicia which extended substantially parallel to the vertical plane V. 
     While in the foregoing specification a detailed description of specific embodiments of the invention was set forth for the purpose of illustration, it will be understood that many of the details herein given can be varied considerably by those skilled in the art without departing from the spirit and scope of the invention.