Abstract:
A set of wood golf clubs have wood club heads with substantially the same external shape. The vertical centers of gravity of the wood club heads are varied by setting the weight within the respective soles and the crowns, while keeping the total weight of the wood club heads substantially constant. The wood club heads have no integral hosel. The wood club shafts are attached to the wood club heads by providing a bore in the wood club head sized to receive the wood club shaft therein, and a threaded fastener that engages the wood club shaft to the wood club head, when the wood club shaft is inserted into the bore. The wood club heads are desirably cast to shape, using casting cores that provide for the shifting of weight between the soles and the crowns within the set.

Description:
[0001]    This invention relates to wood golf clubs and, more particularly, to such wood golf clubs wherein the vertical center of gravity of the wood club head is selectable.  
         BACKGROUND OF THE INVENTION  
         [0002]    The golf clubs that are used to hit the golf ball the greatest distances are the “woods”. The woods originally were made of natural wood but today are made of metals or composite materials. However, they continue to be termed “wood golf clubs” or “woods”, and that terminology is used herein.  
           [0003]    The wood golf clubs have wood club heads with relatively large mass, and loft angles of the faces relative to the soles selected to achieve a long flight distance of the struck golf ball. A golf player typically carries up to five woods, which are distinct from each other in that the loft angle varies from about 7 to about 11 degrees for a driver wood golf club, and about 12 degrees and higher for other wood golf clubs. Of the golf clubs termed “woods”, the drivers, with relatively low loft angles, are designed to hit the golf ball the greatest distances. The golfer selects the required wood golf club from this group of wood golf clubs. A wood golf club, and normally a driver, is used for most long shots from the tee, and may be used on intermediate shots on some longer holes.  
           [0004]    As the game of golf has been studied analytically, it has become clear that the design of the wood golf club plays a part in the ability of the player to hit long, accurately directed shots. For example, the shapes of the wood club heads have been optimized. Large-sized wood club heads have been introduced. Wood club heads have been designed to allow the player to add weight to the wood club head.  
           [0005]    While these approaches yield benefits, the present inventors have observed that most players still cannot obtain wood golf clubs that are optimal for the individual. Players vary according to weight, height, strength, skill and other factors. Wood golf clubs may be purchased with varying shaft lengths, but the wood club heads themselves do not change, except as to the loft angle of the face and the ability to add weight to the wood club head in some designs. These approaches do not provide the required flexibility in selecting the wood club heads that are best suited to the individual player.  
           [0006]    There is a need for an improved approach to the design of wood club heads, which allows the player to obtain wood golf clubs that are optimized for the individual. The present invention fulfills this need, and further provides related advantages.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides a set of wood golf clubs and a method for selecting the wood golf clubs from this set that are best suited for the individual player. The set of wood golf clubs have different wood club heads with different vertical centers of gravity, while maintaining the other physical characteristics of the wood club heads unchanged. This variation permits the player to be tested with the different wood club heads and equipped with a wood club head of each loft angle that is best suited for the player. Additionally, the wood club heads are designed to allow different shafts to be used with the various wood club heads, so that the proper shaft may be matched to the proper wood club head.  
           [0008]    In accordance with the invention, a set of wood golf clubs comprises a first wood club head having a first-club-head sole weight, a first-club-head crown weight, and a first club head total weight, and a second wood club head having a second-club-head sole weight, a second-club-head crown weight, and a second club head total weight. An external shape of the first wood club head and an external shape of the second wood club head are substantially the same, and the first club head total weight and the second club head total weight are substantially the same. The first-club-head sole weight is greater than the second-club-head sole weight, and the first-club-head crown weight is less than the second-club-head crown weight. Preferably, each of the first wood club head and the second wood club head is formed of exactly two pieces, a wood club head body and a wood club head face with a joint therebetween.  
           [0009]    In one embodiment, each of the first wood club head and the second wood club head displaces substantially the same volume, preferably about 335 cubic centimeters. In another embodiment, each of the first wood club head and the second wood club head weighs from about 195 grams to about 205 grams.  
           [0010]    In one preferred form, each of the first wood club head and the second wood club head has no integral hosel. Each of the wood golf clubs further comprises a bore in the respective wood club head sized to receive a wood club shaft therein, and a threaded fastener that engages the respective wood club shaft to the respective wood club head, when the wood club shaft is inserted into the bore. At least one of the wood club heads has a wood club shaft affixed thereto by this approach.  
           [0011]    The wood club heads are preferably “metal woods”, wherein each of the first wood club head and the second wood club head is made of a metal alloy such as a titanium alloy. The wood club heads are preferably cast by an approach such as lost wax casting or die casting, so that the wood club heads have an as-cast microstructure, as distinct from a forged or otherwise worked microstructure.  
           [0012]    In the approach of most interest, there is additionally a third wood club head having a third-club-head sole weight, a third-club-head crown weight, and a third club head total weight. The external shape of the first wood club head, the external shape of the second wood club head, and an external shape of the third wood club head are substantially the same. The first club head total weight, the second club head total weight, and the third club head total weight are substantially the same. The first-club-head sole weight is greater than the second-club-head sole weight, and the second-club-head sole weight is greater than the third-club-head sole weight. The first-club-head crown weight is less than the second-club-head crown weight, and the second-club-head crown weight is less than the third-club-head crown weight. The result of shifting the weight between the sole and the crown is to move the vertical center of gravity of the club head. This three-club-head set thus may be characterized as having a low center-of-gravity wood club head, a medium center-of-gravity wood club head, and a high center-of-gravity wood club head, where low, medium, and high are measured vertically in a direction generally perpendicular from the sole of the wood club head.  
           [0013]    A method for providing a wood golf club for a player comprises the steps of providing a first wood golf club for the player, the first wood golf club having a first wood club head with a first club head total weight and a first vertical center of gravity, analyzing the performance of the player using the first wood golf club, providing a second wood golf club for the player, the second wood golf club having a second wood club head with a second wood club head total weight substantially equal to the first wood club head total weight and a second vertical center of gravity different from first vertical center of gravity, and analyzing the performance of the player using the second wood golf club. These steps may be, and typically are, repeated for additional wood club heads and with a variety of wood club shafts. The wood club heads are preferably of the type described previously.  
           [0014]    The “set” of wood club heads described herein are of the same loft angle, weight, shape, and other physical characteristics. They provide a variation of the vertical center of gravity for a selected loft angle. There would be a different set of wood club heads for a different loft angle of the wood club head. Thus, for example, in the low, medium, and high vertical centers-of-gravity cases and for the five standard wood golf club loft angles, there would be three wood club heads for each loft angle, for a total of fifteen wood club heads over the five loft angles. These various wood club heads may be assembled with shafts of any of a variety of lengths, stiffnesses, materials of construction, and the like, using the feature of the selectability of the shaft. This variability allows the player to be provided with many combinations of wood club types in order to determine which combinations are optimal for the individual.  
           [0015]    Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a perspective view of a wood golf club according to the invention;  
         [0017]    FIGS.  2 - 4  are sectional views taken on line  2 - 2  of FIG. 1, illustrating a preferred technique for adjusting the center of gravity of the wood club head;  
         [0018]    FIGS.  5 - 7  are side sectional views, like those of FIGS.  2 - 4 , and taken on line  2 - 2  of FIG. 1, illustrating a second technique for adjusting the center of gravity of the wood club head;  
         [0019]    [0019]FIG. 8 is an enlarged, partially exploded, sectional view of the wood club head, taken on line  8 - 8  of FIG. 1; and  
         [0020]    [0020]FIG. 9 is a block diagram of a method of providing a wood golf club for a player. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    [0021]FIG. 1 depicts a wood golf club  20 . The wood golf club  20  is sometimes termed a “wood” club or a “wood”. The wood golf club  20  includes a wood club head  22  and a generally cylindrical wood club shaft  24  affixed to the wood club head  22 . The wood club shaft  24  may be of any operable material of construction, such as metal (e.g., titanium, aluminum), composite (e.g., graphite/epoxy), or even natural wood; produced by any operable method; of any operable diameter; of any operable length; and of any operable physical properties (e.g., elastic modulus, strength). One of the features of the present invention, as will be discussed subsequently in relation to FIG. 8, is that the wood club shaft  24  is readily interchangeable.  
         [0022]    [0022]FIG. 2 is a sectional view through the wood club head  22 . In the preferred form, the basic structure of the wood club head  22  preferably includes two pieces, a one-piece wood head body  26  and a one-piece wood head face plate  28  affixed to the wood head body  26  by a weldment  30 , by an adhesive, or by other means for affixing. The wood head body  26  may be described in terms of two regions pertinent to the present discussion, a generally planar sole  32  that rests upon the ground  34 , and a crown  36  that is visible to the eye of the player when the player holds the wood golf club  20  and looks downwardly toward the wood club head  22 . The wood head body  26  is preferably hollow, and the crown  36  is convexly (outwardly) curved relative to the interior of the wood head body  26 . The crown  36  is the convexly, outwardly curved portion of the wood head body  26  that is uppermost in FIG. 2. The sole  32  is the lowermost portion of the wood head body  26  in FIG. 2, which is flat over most of its area and slightly upwardly curved toward the left hand side of FIG. 2 (remote from the wood head face plate  28 ). The sole  32  meets and is contiguous with the crown  36  on the left hand side of FIG. 2.  
         [0023]    The wood head body  26  may be made of any operable material, but is preferably made of a metal alloy such as a titanium alloy. The wood head body  26  may be made by any operable manufacturing process, but is preferably made by a casting technique such as lost wax casting or die casting. It may also be forged or machined. The wood head face plate  28  is made separately from the wood head body  26 . The wood head face plate  28  is preferably also a metal alloy such as a titanium alloy, but a different alloy composition than used in the wood head body  26 . The wood head face plate  28  is preferably forged. After the wood head body  26  and the wood head face plate  28  are fabricated separately, they are joined by fitting the wood head face plate  28  into a recess formed on the wood head body  26  and then welded, adhesively bonded, or otherwise attached in place by the weldment  30  that extends around the periphery of the wood head face plate  28 .  
         [0024]    The inventors have determined that an important performance characteristic of the wood golf club  20  is a vertical location of a center of gravity  38  of the wood head body  26 . The “vertical location” is a distance D CG  from an external surface  40  of the sole  32  toward the crown  36  measured along a line  42  perpendicular to the planar portion of the sole  32 .  
         [0025]    FIGS.  2 - 4  illustrate three wood club heads  22  for a set of wood golf clubs  20 . These three wood club heads  22  of FIGS.  2 - 4  have substantially the same external shapes and volumes. The three wood club heads  22  also have substantially the same total weights. The shapes, volumes, and weights of the three wood club heads  22  in this set of wood golf clubs  20  are substantially the same in order to allow optimization of the selection of the vertical location of the center of gravity  38 , without simultaneously varying other parameters such as shape, loft angle, and total weight of the wood club head  22 .  
         [0026]    The vertical locating of the center of gravity  38  of the three wood club heads  22 , while maintaining the limitation of substantially constant external shape, volume, and total weight, may be accomplished by any operable approach. FIGS.  2 - 4  illustrate a preferred approach, changing the thicknesses of the sole  32  and the crown  36  to redistribute weight and move the center of gravity  38  vertically. The thickness changes and the movement of the center of gravity  38  are quite small and may be difficult to discern in precisely scaled drawings, so in FIGS.  2 - 4  the thickness variations and the vertical displacement of the center of gravity  38  are exaggerated. In the wood club head  22  of FIG. 2, a thickness t S  of the sole  32  is relatively large, and a thickness t C  of the crown  36  is relatively small, so that the weight of the sole is relatively large and the weight of the crown is relatively small. Consequently, the center of gravity  38  is relatively low (i.e., near to the sole  32 ). (The exact locations where the thickness of the sole and the thickness of the crown are measured is not critical, as long as they are generally in the centers of the respective regions and are consistently positioned from wood club head to wood club head within a set.) The weight of a region such as the crown or the sole generally correlates with its thickness within this set of club heads, so that the thicker the region, the greater its weight. In the wood club head  22  of FIG. 3, the thickness t S  of the sole  32  is smaller than that of the wood club head  22  of FIG. 2, and the thickness t C  of the crown  36  is greater than that of the wood club head  22  of FIG. 2. The result is that the center of gravity  38  of the wood club head  22  of FIG. 3 is higher (i.e., further from the sole  32 ) than the center of gravity  38  of the wood club head  22  of FIG. 2. In the wood club head  22  of FIG. 4, the thickness t S  of the sole  32  is smaller than that of the wood club head  22  of FIG.  3 , and the thickness t C  of the crown  36  is greater than that of the wood club head  22  of FIG. 3. The result is that the center of gravity  38  of the wood club head  22  of FIG. 4 is higher (i.e., further from the sole  32 ) than the center of gravity  38  of the wood club head  22  of FIG. 3. The wood club head  22  of FIG. 2 is termed the “L” (low) center of gravity variation, the wood club head  22  of FIG. 3 is termed the “M” (medium) center of gravity variation, and the wood club head  22  of FIG. 4 is termed the “H” (high) center of gravity variation. More variations in the vertical location of the center of gravity  38  may be provided than the three illustrated, but initial testing indicates that three variations are sufficient for most applications. The changes in thickness of the sole  32  and of the crown  36  in each case are selected so that the total weight of the wood club head  22  remains the same. The changes in thickness are accommodated by varying the position of an inner wall  44  of the wood club head  22 , so that the shape of an outer wall  46  remains unchanging.  
         [0027]    The wood head bodies  22  of FIGS.  2 - 4  are preferably manufactured by a lost wax casting approach. This technique is known generally for the manufacture of hollow golf club head bodies of other designs, see for example U.S. Pat. No. 5,429,365. Generally, there is an outer casting shell that defines the position, shape, and size of the outer wall  46 , and a casting core that defines the position, shape, and size of the inner wall  44 . In the present case, the outer casting shell used for the three wood club heads  22  of FIGS.  2 - 4  is the same, so that the wood head bodies  22  have the same external shape, loft angle, and volume, about 335 cubic centimeters in the preferred approach. The casting cores used to cast the three wood head bodies  26  have a constant volume, so that the total amount of metal (and thence the weight) in each of the wood head bodies  26  is a constant amount, preferably in the range of from about 195 to about 205 grams in the preferred approach wherein the wood head bodies  26  are cast from the titanium alloy titanium-6 weight percent aluminum-4 weight percent vanadium. The casting cores are differently positioned, so as to define the thicknesses of the sole  32  and the crown  36  in the manner discussed previously to produce the three different types of wood club heads  22  of FIGS.  2 - 4 .  
         [0028]    Once the outer casting shell and the casting core are positioned, molten metal is poured into the space therebetween and cooled to solidify and to form each of the wood head bodies  22 . Any operable castable material may be used, but a titanium alloy such as titanium-6 weight percent aluminum-4 weight percent vanadium is preferred. After the cast metal has solidified, the outer casting shell and the casting core are removed, leaving the final hollow cast wood club head  22  having a cast microstructure. In alternative fabrication techniques, such as a forged or a machined microstructure, the final wood club head  22  has a corresponding microstructure such as a forged or a machined microstructure, respectively.  
         [0029]    Other operable techniques for changing the vertical location of the center of gravity  38  may be used, and FIGS.  5 - 7  illustrate one such alternative approach. The pertinent parts of the prior discussion of the embodiments of FIGS.  2 - 4  are incorporated here. In the embodiment of FIGS.  5 - 7 , a sole fitting  48  is formed in the sole  32 , and a crown fitting  50  is formed in the crown  36 . These fittings  48  and  50  are externally accessible. A corresponding sole weight insert  52  and a crown weight insert  54  are inserted into the respective sole fitting  48  and crown fitting  50 . In a preferred version of this embodiment, the fittings  48  and  50  are female-threaded fittings, and the weight inserts  52  and  54  are matching male-threaded weights. The weight inserts  52  and  54  may be readily installed, removed, and moved in various combinations. The total weight of the sole weight insert  52  and the crown weight insert  54  is maintained constant, so that the total weight of the wood club heads  22  of FIGS.  5 - 7  remains constant.  
         [0030]    The approach of FIGS.  2 - 4  has the advantage that the weight change is distributed broadly over the sole and the crown. The approach of FIGS.  5 - 7  has the advantage that the weight inserts  52  and  54  may be readily changed. The approach of FIGS.  5 - 7  has the additional advantage that the total of the weight inserts  52  and  54  may be readily changed, if desired.  
         [0031]    The wood club heads of FIGS.  2 - 4  and  5 - 7  are illustrated as being conventional in configuration, except for the ability to change the vertical location of the center of gravity. Other modifications that have been found or may be found useful in wood club heads, such as changes in external shape or total weight, or material of construction, may be utilized in conjunction with the present approach.  
         [0032]    The approaches of FIGS.  2 - 4  and FIGS.  5 - 7  are used to change the vertical location of the center of gravity  38 . Another factor that significantly influences the performance of the wood golf club  20  is the nature of the wood club shaft  24 . FIG. 8 illustrates an embodiment of the present approach that allows various types of wood club shafts  24  to be used with the variations of FIGS.  2 - 4  and FIGS.  5 - 7 . The preferred wood club head  22  of the present approach has no integral hosel, which is a tubular portion that extends upwardly from the crown  36  of the conventional wood club head. The wood club shaft of the conventional wood club is inserted into the hosel and affixed to the hosel with an adhesive such as an epoxy.  
         [0033]    In the present approach as seen in FIG. 8, the wood club head  22  has no hosel, but instead has a bore  60  fabricated into the wood head body  26 . The bore  60  has a base  62  that defines the bottom of the bore  60 . An aperture  64  extends through the base  62 . The bore  60  is sized to receive a hosel fitting  66  affixed to an end  68  of the wood club shaft  24 . (The hosel fitting  66  is not integral with the wood club head  22 .) The bore  60  is oriented in the wood club head  22  so that the wood club shaft  24  has the proper orientation to the wood club head  22  and to the wood head face plate  28 . A fastener, preferably a male-threaded fastener  70  such as the illustrated bolt, extends through the aperture  64  of the base  62  to engage the female-threaded hosel fitting  66 , and thence the wood club shaft  24 , to the respective wood club head  22 , when the hosel fitting  66  is inserted into the bore  60 . The sole  32  is locally recessed at recess  72  so that the head of the fastener  70  does not strike the ground  34  when the wood golf club  20  is swung. With this approach, the wood club shaft  24  may be readily changed so that different shafts may be tested and possibly used with the various wood club heads  22 . Shafts of different lengths, diameters, materials of constructions, elastic properties, and other characteristics may thence be utilized.  
         [0034]    An important application of the present approach is to maximize the performance of the golf player for the wood golf clubs, by providing the optimal wood golf club equipment for the individual player. FIG. 9 illustrates this approach. A wood golf club of a test configuration is provided, numeral  80 . The performance of the wood golf club test configuration when used by the particular player is analyzed, numeral  82 . The steps  80 ,  82  are repeated, numeral  84 , for a new test configuration, and may be repeated as many times as necessary to determine the optimum performance of the player as a function of the several variables that may be evaluated. Variables that may be included in the evaluation include the wood club head  22  and particularly the vertical location of the center of gravity of the wood club head, as discussed above, the type of drive club shaft  24  that is installed to the wood club head  22 , and the type of golf ball being hit. This procedure would be used for a first set of wood golf clubs with a constant selected loft angle, and then may be used for additional sets of wood golf clubs with a different (but constant within any one set) loft angle. The present procedure is expected to yield the most benefits for the wood golf clubs with the lowest loft angles, termed the “drivers”, but it may be used as well for other wood golf clubs.  
         [0035]    The following performance tables for golfers A, B and C, employees of the assignee, were developed by the procedure of FIG. 9 during the initial testing of the present approach. Each entry in the tables represents the average of multiple hits of a single commercial brand of golf ball. Performance was evaluated using a standard Launch Monitor device for analyzing golf ball movement. In each case, the golfer used three wood golf clubs  20 . The wood club head  22  in each case was a 335 cubic centimeter, 200 gram, 7.5 degree loft angle club. The variation between the wood golf clubs was a low (L), medium (M), or high (H) vertical position of the center of gravity  38 . The following table gives the approximate thicknesses, measured in inches, of the sole  32  and the crown  36  at the same respective point on each wood club head, and the resulting vertical position of the center of gravity in millimeters  
                                           Club Ident.   Sole Thickness   Crown Thickness   Center of Gravity                   H   0.040   0.060   32       M   0.050   0.050   30       L   0.060   0.040   28                  
 
         [0036]    In the following performance tables, the table entries are, from left to right, the wood club head identification (L, M, or H), the initial launch speed (Vo) of the ball in miles per hour, the spin rate (SR) of the ball in revolutions per minute, the launch angle (LA) of the ball in degrees, the carry distance (CD) on the fly of the golf ball in yards, and the total distance (TD) of the golf ball on the fly and rolling, in yards.  
                                                                                                               Club Ident   Vo   SR   LA   CD   TD                                        Golfer A                    H   160.5   2066   8.6   228.7   265.4           M   160.3   2163   9.4   237.9   268.2           L   161.2   2436   9.7   239.0   271.9           Golfer B           H   158.9   1992   9.9   229.8   266.2           M   158.8   2263   10.0   233.7   267.8           L   159.7   2745   10.2   240.5   271.1           Golfer C           H   161.4   3169   14.8   250.9   276.7           M   159.5   3400   15.3   247.8   272.2           L   160.1   3384   16.3   248.7   272.8                      
 
         [0037]    The results set forth in these tables are not to be interpreted as good or bad, consistent or inconsistent. These results simply reflect the performance of each individual player using various types of wood club combinations and for a single type of golf ball.  
         [0038]    In these data, Golfers A and B each achieves the greatest carry distance and total distance with the low center of gravity wood club head. Golfer C, on the other hand, achieves the greatest carry distance and total distance with the high center of gravity wood club head. Based on this data, the selection of wood club heads for Golfers A and B would be different than for Golfer C. These extremely limited data are presented to illustrate the operation of the present approach. In practice, much more data would be gathered for each player, including the effects of variations in the shape and volume of the wood club head, the weight of the wood club head, the loft angle of the wood club head, the type of wood club shaft, the materials of construction of the wood club shaft and the wood club head, the golf ball played, and even other features available in wood club heads.  
         [0039]    This approach may be used in a custom-fitting procedure to find a single wood golf club that is optimal for that player, taking into account all of the variables discussed above. Once that single wood golf club is identified, then the illustrated version with the removable shaft (FIG. 8) may be used by the player. To make the illustrated embodiment into a permanent wood golf club, the hosel fitting  66  may be fixed in place with a permanent adhesive, and a cap may be fitted over the head of the fastener  70  and fixed in place with the permanent adhesive. In other cases, other variables may be considered: wind conditions, launch angle, heel/toe properties, side spin, accuracy relative to an axis, distance accuracy, face mapping, and the like. Thus, for example, a number of golf clubs may be identified for use by the player, such as a wood golf club driver for use in still air conditions, a wood golf club driver for use in headwinds, a wood golf club driver for use in tailwinds, and the like.  
         [0040]    Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.