Abstract:
A hollow golf club bead includes a sole, a crown, a skirt, and a striking face. The golf club includes a junction interconnecting the sole, crown, and skirt to the striking face, the junction including at least one stiffening member.

Description:
RELATED U.S. APPLICATION DATA 
     Continuation of application Ser. No. 12/789,117, filed on May 27, 2010, which is a continuation of application Ser. No. 12/476,945, filed on Jun. 2, 2009, which is a continuation of application Ser. No. 11/441,244, filed on May 26, 2006, now U.S. Pat. No. 7,585,233. 
    
    
     BACKGROUND 
     With the advent of thin walled metalwood golf club heads, the performance of metalwood clubs has improved considerably. By increasing the surface area of the striking face, using high strength alloys for its construction, and reducing its thickness to introduce a “trampoline” effect, club head designers have increased the efficiency of energy transfer from a metalwood club to a golf ball. As a result, the United States Golf Association (USGA) has imposed regulations to limit energy transferred from drivers to a golf ball by defining a maximum “characteristic time” (CT) that the clubface may remain in contact with a suspended steel weight impacting it. The maximum CT corresponds to a maximum “coefficient of restitution” (COR) for metalwood clubs. Currently, the maximum COR permissible by the USGA is 0.830. 
     SUMMARY 
     For golf club striking faces of a fixed size and substantially constant thickness, there exists a thickness below which the CT value will be outside the range allowable by the USGA, but that may still be structurally feasible for use on a club head. Limiting the amount of material used to construct a club&#39;s face is desirable for cost savings and improved mass properties. 
     Various metalwood designs have been proposed utilizing variable face thickness profiles that both meet the USGA&#39;s CT limitation and minimize face mass. However, such faces are typically expensive to produce. Other designs have incorporated thin faces with protracted rib or support structures appended to or formed integrally with the striking face, and these too have proven costly to manufacture, and increase complexity of the club head design. 
     A need exists for improved USGA conforming metalwood golf club heads which minimize the amount of material used to construct the club face, as well as for hollow golf club heads which maximize average energy transfer efficiency of the striking face. 
     Various implementations of the broad principles described herein provide a golf club head which may be manufactured with a face that utilizes less material than a conventional design, and that may conform to USGA rules and regulations for metal woods. Further, features are proposed which may improve performance characteristics of hollow club heads, and increase the average energy transfer efficiency such heads&#39; striking faces. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various implementations will now be described, by way of example only, with reference to the following drawings in which: 
         FIG. 1  is a perspective view of an exemplary club head. 
         FIG. 2  is a cross-sectional view of the club head of  FIG. 1  taken at line II-II. 
         FIG. 3  ( a ) is an enlarged view of an exemplary configuration for detail III of  FIG. 2 . 
         FIG. 3  ( b ) is a further enlarged view of an exemplary configuration for detail III of  FIG. 2 . 
         FIG. 3  ( c ) is a further enlarged view of an exemplary configuration for detail III of  FIG. 2 . 
         FIG. 3  ( d ) is a further enlarged view of an exemplary configuration for detail III of  FIG. 2 . 
         FIG. 4  ( a ) is a heel view of the club head of  FIG. 1 . 
         FIG. 4  ( b ) is a close up view of detail IV of  FIG. 4  ( a ). 
         FIG. 5  is a front view of the club head of  FIG. 1 . 
         FIG. 6  is a perspective view of the club head of  FIG. 1  showing exemplary aspects thereof. 
         FIG. 7  is a perspective view of the club head of  FIG. 1  showing exemplary aspects thereof. 
         FIG. 8  ( a ) is a cut-away perspective view of the club head of  FIG. 1  showing an exemplary internal feature thereof. 
         FIG. 8  ( b ) is an enlarged view of an exemplary detail VIII of  FIG. 8  ( a ). 
         FIG. 8  ( c ) is an enlarged view of an exemplary detail VIII of  FIG. 8  ( a ). 
         FIG. 8  ( d ) is an enlarged view of an exemplary detail VIII of  FIG. 8  ( a ). 
         FIG. 8  ( e ) is an enlarged view of an exemplary detail VIII of  FIG. 8  ( a ). 
         FIG. 8  ( f ) is an enlarged view of an exemplary detail VIII of  FIG. 8  ( a ). 
         FIG. 8  ( g ) is an enlarged view of an exemplary detail VIII of  FIG. 8  ( a ). 
         FIG. 8  ( h ) is an enlarged view of an exemplary detail VIII of  FIG. 8  ( a ). 
         FIG. 8  ( i ) is cross sectional view of an exemplary detail VIII of  FIG. 8  ( h ) taken at line VIII(i)-VIII(i). 
         FIG. 9  ( a ) is an enlarged view of an exemplary detail VIII of  FIG. 8  ( a ). 
         FIG. 9  ( b ) is an enlarged view of an exemplary detail VIII of  FIG. 8  ( a ). 
         FIG. 9  ( c ) is an enlarged view of an exemplary detail VIII of  FIG. 8  ( a ). 
         FIG. 10  is an enlarged side view of detail VIII of  FIG. 8  ( a ). 
         FIG. 11  is a top view of the detail of  FIG. 10 . 
         FIG. 12  is a graph comparing ball speed at various horizontal face positions on a golf club with and a golf club without features in accordance with the present invention. 
         FIG. 13  is a graph comparing COR at various horizontal face positions on a golf club with and a golf club without features in accordance with the present invention. 
         FIG. 14  ( a ) is a cut-away perspective view of the club head of  FIG. 1  showing exemplary aspects thereof. 
         FIG. 14  ( b ) is an enlarged view of an exemplary detail XI of  FIG. 14  ( a ). 
         FIG. 15  ( a ) is an enlarged view of an exemplary detail XI of  FIG. 14  ( a ). 
         FIG. 15  ( b ) is an enlarged view of an exemplary detail XI of  FIG. 14  ( a ). 
         FIG. 15  ( c ) is an enlarged view of an exemplary detail XI of  FIG. 14  ( c ). 
     
    
    
     For the purposes of illustration these figures are not necessarily drawn to scale. In all of the figures, like components are designated by like reference numerals. 
     DETAILED DESCRIPTION 
     Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the broad inventive principles discussed herein. However, these broad principles may be practiced without these particulars and thus these details need not be limiting. In other instances, well known elements have not been shown or described to avoid unnecessarily obscuring the invention. Accordingly, the detailed description and drawings are to be regarded in an illustrative rather than a restrictive sense. 
     With reference to  FIG. 1 , a golf club head  200  is shown having four primary surfaces, each defining a portion of the head: a front surface generally defining a striking face  202  generally bounded by a face perimeter edge  205 , a bottom surface generally defining a sole  204  (shown in  FIG. 2 ), a side surface generally defining a skirt  206 , and a top surface generally defining a crown  208 . The sole, the crown, the strike surface, and a rear portion of the club head may at least partially delimit a substantially enclosed interior cavity. Optionally, a hosel  210  may be provided for receiving a shaft (not shown) to which the head  200  may be attached. The face  202  is connected to the sole, skirt and crown via a junction  212 . 
       FIG. 2  shows section II-II of head  200  from  FIG. 1 , with junction  212  generally connecting the striking face  202  to the crown  208 , and to the sole  206  at detail III. 
       FIGS. 3(   a )- 3 ( d ) show several enlarged views of detail III from  FIG. 2 , each demonstrating a unique example of a possible configuration for the junction  212 . It should be appreciated that while the junction configurations of  FIGS. 3(   a )- 3 ( d ) are shown generally connecting the face  202  to the sole  204 , each configuration may be used to connect the face to the crown  208 , and/or the skirt  206 . A single junction configuration may be used to connect the face  202  to each of the sole, the crown, and the skirt. Alternatively, the various junction configurations may be used interchangeably and in any combination. 
     As in  FIG. 3(   a ), the junction may generally comprise a convex, or outwardly radiused or contoured corner. The radius, or contour, may vary along the generally annular extent of the junction, and may or may not be a constant radius at any single location. 
     As shown in  FIG. 3(   b ), the junction may generally comprise a concave, or inwardly radiused or contoured corner. The radius, or contour, may vary along the generally annular extent of the junction, and may or may not be a constant radius at any single location. 
       FIG. 3(   c ) demonstrates the junction having a generally beveled configuration. 
       FIG. 3(   d ) shows the junction generally embodied as a corner. 
     In the following examples, the junction may comprise any adjacent portions of the face  202 , sole  204 , skirt  206 , and crown  208 . Generally, the junction is defined as a portion of the head which interconnects the face  202  to at least a portion of the remainder of the head  200 . Since there are a variety of possible configurations for the junction  212 , including those presented above and others, it may be beneficial to define the junction as shown in  FIG. 4  ( a ). With the sole  206  resting on a substantially planar surface  300  and a hosel axis  211  positioned at a designated lie angle, a, (see  FIG. 5 ) typically between about 45 to about 65 degrees, an imaginary line  302  (see  FIG. 4  ( b )), tangent to the strike face at a geometric center, C, may be located in an imaginary vertical plane perpendicular to the strike face and passing through the geometric center. In this example, the face  202  is shown having vertical roll curvature. The imaginary line  302  and the planar surface  300  intersect at a first reference point  304 , which may serve as a point of origin from which junction  212  may generally be represented dimensionally by a height, H, and a length, L. H may be measured along the direction of the imaginary line  302 , from the first reference point  304  to a second reference point  306 . Further, L may be measured along the direction of the surface  300 , from the first reference point  304  to a third reference point  308 . The second reference point  306  and the third reference point  308  may be projected onto the head  200 , to define junction points  310  on the exterior surface of the head  200 . The second reference point  306  is projected onto the strike face  202  in a direction normal to the imaginary line  302 , and the third reference point  308  is projected onto the sole  204  in a direction normal to the planar surface, as shown in  FIG. 4  ( b ). 
     H and L may thus dimensionally represent the junction  212  on the head  200  at a generally vertical planar location substantially perpendicular to the striking face  202 , and delimited by the points  304 ,  306  and  308 . To define the junction  212  in other areas of the head, a set of imaginary junction bounding lines  312  (on the face  202 ) and  314  (on the sole  204 , the skirt  206  and the crown  208 ) may be traced on the head  200  to form a closed loop, passing through the junction points  310  and maintaining a substantially constant distance (d′, d″) from a reference feature, for example, each imaginary junction bounding line  312  may be parallel to the face perimeter edge  205 , as shown in  FIGS. 4  ( b ) and  5 . 
     As an example, for a metalwood driver having a volume of, e.g., 300-600 cm 3 , both H and L may have values of up to about 20 mm. More preferably, both H and L may have values up to about 14 mm. More preferably still, H may have a value of up to about 12 mm, and L may have a value of up to about 10 mm. 
     The junction  212  may be locally stiffened to improve the performance of the head  200 . In particular, certain performance advantages may be gained by introducing local stiffening at selected locations. 
     For example, at least one stiffening member  400  (see  FIGS. 8  ( a ),  15  ( a ), and  15  ( b )) may be generally positioned so as to be proximate the intersection of the junction  212  and a vertical plane  600  and/or a horizontal plane  602  that pass through center C of the striking face  202 , as shown in  FIG. 6 . Since the junction  212  generally extends annularly about the center of the striking face  202 , four locations are defined proximate to which at least one stiffening member may be located to obtain beneficial results, and may be represented by the points  604 ,  606 ,  608  and  610 . The points  604 ,  606 ,  608  and  610  define a top location, a bottom location, a heel location, and a toe location, respectively, and are intended only as a general indication of approximate locations for at least one stiffening member  400 . 
     As shown in  FIG. 7 , the imaginary planes  612  and  614  may be oriented about +45 and −45 degrees to horizontal. Said planes may intersect the head  200  proximate center C of the striking face  202 , so as to generally divide the head  200  into a toe region  616 , a heel region  618 , a top region  620  and a bottom region  622 . The top region  620  and the bottom region  622  have a heel-to-toe length dimension. Preferably, multiple stiffening members may be located on the junction  212  in any or all of the above regions, in any combination. More preferably, stiffening members may be provided at the junction  212  in both regions  616  and  618 , or in both regions  620  and  622 . Even more preferably, a single stiffening member may be provided at the junction  212  in the region  622  and/or at the junction  212  in the region  620 . 
     Generally, the stiffening member  400  may comprise a mass provided within the junction  212 . The mass may be formed integrally with at least a portion of the junction  212 , and may have a variety of configurations. For example, as shown in  FIG. 8  ( a ), the stiffening member  400  may be a contoured mass  402 . The mass  402  may have at least one peak  404 , where the true thickness, T, (shown in  FIG. 10 ) of the stiffening member is a maximum and decreases away from the peak  404 . While the contoured mass  402  is shown as a single, mound-shaped mass in this embodiment, it should be appreciated that such a mass may have a variety of shapes. 
     Alternatively, the stiffening member  400  may be a geometrically shaped mass, examples of which are shown in  FIGS. 8  ( b )-(e).  FIG. 8  ( b ) shows a substantially pyramid-shaped mass  410 , having a peak  412 , where T (shown in  FIG. 10 ) decreases away from the peak. 
       FIG. 8  ( c ) shows a prism-shaped mass  420  substantially longitudinally disposed in the front-to-rear direction of the club head. The mass has a spine  422 , where T (shown in  FIG. 10 ) decreases away from the spine in the heel and toe (lateral) directions. In one example, T may also decrease away from a point of maximum true thickness  424 , located on the spine  422  in the longitudinal direction. 
       FIG. 8  ( d ) shows a substantially trapezoid-shaped mass  430 , having a plateau  432  and sides  434 , which slope away from the plateau. Generally, at least one point  436  may exist on the plateau  432  where T is a maximum. 
       FIG. 8  ( e ) shows a mass  430 ′ having additional sides  438  which may also slope away from a plateau  432 ′. 
       FIG. 8  ( f ) shows a substantially rectangle-shaped mass  440  having a plateau  442 , and sides  444 , which may slope away from the plateau. Generally, at least one point  446  may exist on plateau  442  where T is a maximum. 
       FIG. 8  ( g ) shows a mass  440 ′ having additional sides  448  which may also slope away from a plateau  442 ′. 
     In addition, the stiffening member  400  may comprise at least one pleat or corrugation  450  in the wall portion forming the junction  212 , as shown in  FIG. 8  ( h ). For added clarity, a cross section of the corrugation  450  is shown in  FIG. 8  ( i ). Although the corrugation  450  is shown here as not extending into the striking face  202  so as to conform to USGA rules which prohibit channels from extending into the striking face, it should be appreciated that should a non-conforming club head design be desired, the corrugation  450  may extend into the face  202 . Further, it may be desirable for the corrugation  450  to extend outside of the junction  212  into the sole  204 , for added reinforcement and/or cosmetic appeal (not shown). Should a single corrugation provide insufficient stiffness to the junction  212 , a plurality of corrugations may be provided (not shown). 
     The preceding description recites several exemplary embodiments for the stiffening member  400 . It should be appreciated in particular that a variety of other embodiments may be adapted for use as the mass portion of the stiffening member  400 . 
     In all applicable configurations, the maximum thickness T of the mass member should generally be selected to impart sufficient stiffness to the junction  212  to provide the desired effects. For example, the maximum value of T may generally be greater than the average wall thickness of the junction  212 . For example, the junction may have wall thicknesses ranging from about 0.4 mm to about 4 mm, and the maximum value of T may be between about 1 mm and about 8 mm. More preferably, the maximum value of T may be between about 3 mm and about 7 mm. Most preferably, the maximum value of T may be between about 4 mm and about 6 mm. 
     Further, as illustrated in  FIG. 11 , the stiffening member  400  may have a width, W, that may range from about 2 mm to about 15 mm. More preferably, the width may generally be from about 3 mm to about 7 mm. 
     In addition, the stiffening member  400  may comprise at least one rib  500  provided on the junction  212 , as shown in  FIGS. 9  ( a )- 9  ( c ) and  15  ( a )- 15  ( c ). Preferably, rib(s)  500  may be provided in addition to, e.g., mass  402 . It may also be preferable that rib(s)  500  be formed integrally with either the junction  212  or the mass  402 , or both. Preferably, several ribs  500  may be provided on the junction  212  proximate to and/or or integrally with the mass  402 . More preferably, rib(s)  500  may be formed on the mass  402 .  FIGS. 9  ( a ) and  15  ( a ) show one rib  500  generally intersecting the mass  402 . In  FIGS. 9  ( b ) and  15  ( b ), two ribs  500  are shown on either side of the mass  402 . In  FIGS. 9  ( c ) and  15  ( c ), three ribs  500  are shown distributed across the width of the mass  402 . The number, size, and location of the ribs may depend on the overall configuration of the stiffening member  400  and an analysis of the effect a mass member alone has on the impact efficiency of the head  200 . The mass  402  is shown above as an example only, and it should be appreciated that the use of ribs may complement any mass member configuration. 
     Generally, if rib(s)  500  are incorporated, they may have a maximum true height, H MAX , from about 2 mm to about 12 mm, as shown in  FIG. 10 . Optionally, H MAX  may be selected such that rib(s)  500  extend a distance D beyond the maximum true thickness, T, of the mass member, e.g. mass member  402 . D may generally have values between about 0.1 mm and about 10 mm. 
     Generally, the introduction of the stiffening member  400  at the junction  212  may allow a reduction in thickness of the striking face  202  while maintaining a maximum COR of 0.830 or less per USGA rules as well as the structural integrity of the head  200 . The stiffening member  400  may further allow for a COR of substantially 0.830 to be achieved over a greater percentage of surface area of the face  202 . Alternatively, the stiffening member  400  may allow for a maximum COR that is higher than the USGA mandated maximum over a greater percentage of surface area of the face  202 . More generally, the stiffening member  400  may increase COR values on the face  202 , resulting in a higher average COR value for the face  202 . 
     For identical club heads of a given face thickness, or thickness profile, it was found that the stiffening member  400  increases ball speed values across face  202 . Two heads similar to that shown in  FIG. 1  were comparison tested to demonstrate the results. In the first head, a single stiffening member  400 , such as one shown in  FIG. 9  ( c ), was provided in the junction  212  at a location generally corresponding to location  606  of  FIG. 6 , and ball speed values and COR values were recorded at various locations laterally along the face  202 . The same measurements were recorded for a second head which was not provided with a stiffening member, but which was otherwise substantially identical. The results are shown graphically in  FIGS. 12 and 13 .  FIG. 12  shows ball speed values measured at various locations horizontally across the face, demonstrating increased ball speed values overall for the head provided with the stiffening member  400 .  FIG. 13  shows COR values measured at various locations horizontally across the face  202 , demonstrating increased COR across the face of the head provided with the stiffening member  400 . Similar results were obtained when applying the same principles to optimize striking face performance vertically along the face. 
     Further, the introduction of the stiffening member  400  may also enable the point of maximum COR to be repositioned to an area that may be more desirable without altering external head geometry and shape. For example, it may be believed that, on average, golfers strike the ball towards the toe of the club more frequently than at the geometric center of the face. In such an example, strategically placing the stiffening member  400  on the junction  212  to reposition the point of maximum COR towards the toe side of the face  202  may yield a club head that drives the ball longer, on average. 
     It should be noted that, although examples are given only showing the stiffening member  400  located internally within the head  200 , the stiffening member may be equally effective when positioned on the exterior of the head on the junction  212 . This may be particularly true when the junction  212  has an inwardly curved or concave configuration as shown in  FIG. 3  ( b ). 
     The above-described implementations of the broad principles described herein are given only as examples. Therefore, the scope of the invention should be determined not by the exemplary illustrations given, but by the furthest extent of the broad principles on which the above examples are based. Aspects of the broad principles are reflected in appended claims and their equivalents.