Abstract:
A metal wood golf club head adapted for attachment to a shaft, with a body comprising of a first body portion and a second body portion, each portion constructed of a different density material. Combining a high density material in the first body portion with a low density material in the second body portion, creates an ultra-low center of gravity relative to the geometric face center, resulting in higher launch angles and spin rate ratios. Thickening the lower area of the front face lowers the center of gravity and upwardly shifts the coefficient of restitution to the geometric center of the face.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/192,112, filed Jul. 29, 2005, now pending, which is a continuation-in-part of U.S. patent application Ser. No. 10/662,682 filed on Sep. 15, 2003, now pending, which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a multi-material, multi-component metal wood golf club head. 
         [0004]    2. Description of the Related Art 
         [0005]    Golf clubs have achieved a remarkable transformation from persimmon wood clubs to the present day metal woods with their extremely large head sizes. This has been made possible by high strength metallic materials, which allow the golf ball to be hit farther and straighter because of increased club head inertia and coefficient of restitution. 
         [0006]    Particularly, development of titanium alloys, which are light (specific gravity: 4.5 to 5.0) and strong, have allowed significant increases in the head size and subsequent practical shaft length of a golf club. Specifically, a large moment of inertia, resulting in an increased area of high speed on the club face can be achieved by use of a large club head. Thus there is a constant demand for club heads of greater size. However, enlarging the club head also increases its weight. Most of the metal wood golf clubs manufactured today have a shell thickness so thin that they border on practical manufacturing limits. This has resulted in the search for materials that are even less dense than titanium. Golf club manufacturers are looking for solutions wherein lighter and stronger materials may be employed. And, in some cases, for materials that will partially replace titanium, which is relatively costly and requires considerable care in forming and casting. 
         [0007]    Among the more prominent considerations in club head design are loft, lie, face angle, horizontal face bulge, vertical face roll, center of gravity, inertia, material selection, and overall head weight. While this basic set of criteria is generally the focus of golf club engineering, several other design aspects must also be addressed. The interior design of the club head may be made to achieve particular performance characteristics, such as with the inclusion of hosel or shaft attachment means, or the use of weight members. 
         [0008]    The United States Golf Association (USGA), the governing body for the rules of golf in the United States, has specifications for the performance of golf clubs and golf balls. Golf clubs are limited to a Coefficient of Restitution (COR) of 0.83. One USGA rule limits the golf ball&#39;s initial velocity after a prescribed impact to 250 feet per second±2% (or 255 feet per second maximum initial velocity). To achieve greater golf ball travel distance, ball velocity after impact and the coefficient of restitution of the ball-club impact must be maximized while remaining within the rules. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention relates to a multi-material, multi-component metal wood golf club head comprised of a front face having a geometric face center, wherein the center of gravity is at least 6 mm lower than the geometric face center, and the point of maximum Coefficient of Restitution (COR) is not lower than 2 mm below the geometric face center. 
         [0010]    An embodiment of the invention, designated as club head, comprises a first body portion, a second body portion, and a hosel member. The first body portion  20  comprises a cup-like face section, a sole section, and a bore-thru hosel tube. The second body portion comprises at least a crown section and a substantial portion of a skirt section, and is of a lower density than the first body portion. The density of the second body portion may be between about 0.1 g/cc to 4.0 g/cc. 
         [0011]    The material of construction for the first body portion may be a stainless steel alloy, but preferably is a titanium alloy. While magnesium is preferred for the second body portion, composite, or other lightweight metal such as aluminum, or a thermoplastic may be substituted for the magnesium, but with different performance characteristics. The third body portion is a hosel section formed from a lightweight metal or a thermoplastic, including nylon, composite or aluminum materials. 
         [0012]    The club head of the present invention has a coefficient of restitution (COR) greater than 0.80, with a COR gradient created in the front face. The thickness of the face is preferably progressively greater in a direction from the crown section to the sole section. This is a beneficial design consideration, since the club head has a lowered center of gravity, the greater face thickness at the sole section refocuses the COR towards the center of the face. 
         [0013]    The weight reduction, due to the use of lower density materials in the second body portion and hosel member, allows for that weight to be relocated in the club head. The present invention provides for a weight member, having a generally horseshoe shape, to be positioned on the inside surface of the sole section, at a point near the sole/skirt junction. This further lowers the club head center of gravity and moves it farther from the face, and preferably at least 12 mm from the centerline of the shaft axis. 
         [0014]    Another embodiment of the invention utilizes only two body portions, the light weight second portion incorporating both the crown section and the hosel member. 
         [0015]    In another aspect of the present invention, an insert is placed on the club face on a surface opposite the striking surface. The insert, which is light-weight and can be made of a variety of materials, stiffens the portion of the club face on and around the attachment location. This increased face stiffness lowers the coefficient of restitution of the affected area of the club face. As a result, the compliant area or “sweet spot” of the club head is shifted upward, preferably above the geometric center of the club face. Providing a face that is stiffer near the sole and progressively less stiff approaching the crown produces a higher launching, lower spinning trajectory of a struck golf ball, adding distance to the golf shot. The acoustics and feel of the golf club may also be improved. The insert may be a tapered patch, thicker near the sole than the crown, that is adhered or otherwise attached to the inner surface of the club face. The increased thickness of the insert near the sole imparts more stiffness to that portion of the club face, and a greater decrease in the local coefficient of restitution. The tapered form of the insert approaching the crown imparts less stiffness and results in a lesser decrease in the local coefficients of restitution. The insert may be provided as one or more ribs that can be oriented vertically, horizontally, or both on the club face. Again, the ribs are provided with more mass toward the sole and decreasing mass as the ribs approach the crown. Rather than having a face of varying thickness to produce a COR gradient, the insert allows the face to be of uniform thickness. This reduces the weight of the face, which weight the club head designer can apply elsewhere in locations that increase the forgiveness and playability of the resulting golf club. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0016]    The present invention is described with reference to the accompanying drawings, in which like reference characters reference like elements, and wherein: 
           [0017]      FIG. 1  is a front schematic of a golf club with the face square and the club head soled in the address position for depicting the face center and center of gravity based on test data. 
           [0018]      FIG. 2  is a top schematic of  FIG. 1 . 
           [0019]      FIG. 3  is an expanded pictorial view of an embodiment of the invention, having three body portions. 
           [0020]      FIG. 4  is a top view of  FIG. 3  thereof. 
           [0021]      FIG. 5  is a cut out top view taken along line A-A of  FIG. 8 . 
           [0022]      FIG. 6  is a partial cross-sectional view showing the bore-thru hosel tube and weight member. 
           [0023]      FIG. 7  is a toe view of  FIG. 3  thereof. 
           [0024]      FIG. 8  is a front view of  FIG. 3  thereof. 
           [0025]      FIG. 9  is an expanded pictorial view of another embodiment of the invention. having two body portions. 
           [0026]      FIG. 10  is a top view of  FIG. 9  thereof. 
           [0027]      FIG. 11  is a toe view of  FIG. 9  thereof. 
           [0028]      FIG. 12  is a front view of  FIG. 9  thereof 
           [0029]      FIG. 13   a  is a side view of the variable thickness front face of the present invention. 
           [0030]      FIG. 13   b  is a side view of the variable thickness front face of an alternate embodiment. 
           [0031]      FIG. 14  is a graph illustrating the relationship of launch angles to the face center for the prior art Titleist® 983K driver. 
           [0032]      FIG. 15  is a graph illustrating the relationship of launch angles to the front face for the present invention. 
           [0033]      FIG. 16  is a graph depicting the relationship of backspin to the front face for the prior art Titleist® 983 K. 
           [0034]      FIG. 17  is a graph depicting the relationship of backspin to the front face for the present invention. 
           [0035]      FIG. 18  is a graph relating ball speed to front face for the prior art 983K. 
           [0036]      FIG. 19  is a graph relating ball speed to front face for the present invention. 
           [0037]      FIG. 20  is a graph showing ball distance at positions on the front face of the prior art 983K. 
           [0038]      FIG. 21  is a graph showing ball distance at positions on the front face of the present invention. 
           [0039]      FIG. 22  shows a front view of another embodiment of a golf club head of the present invention including a stiffening insert. 
           [0040]      FIG. 23  shows a side view of the golf club head of  FIG. 22 . 
           [0041]      FIG. 24  shows a front view of another embodiment of a golf club head of the present invention including a stiffening insert. 
           [0042]      FIG. 25  shows a side view of the golf club head of  FIG. 24 . 
           [0043]      FIG. 26  shows a front view of another embodiment of a golf club head of the present invention including a stiffening insert. 
           [0044]      FIG. 27  shows a side view of the golf club head of  FIG. 26 . 
           [0045]      FIG. 28  shows a front view of another embodiment of a golf club head of the present invention including a stiffening insert. 
           [0046]      FIG. 29  shows a side view of the golf club head of  FIG. 28 . 
           [0047]      FIG. 30  shows a side view of another embodiment of a golf club head of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0048]    The golf club head according to preferred embodiments of the present invention, is a multi-material and multi-component hollow club head. 
         [0049]    As shown is  FIGS. 3-8 , a club head  30  is generally composed of three components, which includes a first body portion  31 , a second body portion  32  and a hosel member  33 . First body portion  31  is substantially comprised of: a cup-shaped front face section  37 ; a sole section  36  that includes a horseshoe shaped high density weight member  40  that is positioned on the inner surface of the sole section  36  at a predetermined distance from the front face section  37 ; and, a bore-thru-hosel tube  42 . Second body portion  32  is of a lower density than the first body portion  31  and comprises at least a crown section  34 , and a substantial portion of a skirt section  35 . Hosel member  33  is also of a low density material having one end  45  for connection to a shaft (not shown) and the opposing end  46  for connection to the bore-thru-hosel tube  42 . 
         [0050]    The density range for second body portion  32  and hosel member  33 , is from about 0.1 g/cc to 4.0 g/cc. Both may be formed from materials such as aluminum, graphite composite, a thermoplastic, but the preferred material for the second body portion  32  is magnesium, and the preferred material for the hosel member  33  is nylon. The method of manufacturing the portions  32  and  33 , may be casting, injection molded, machining, prepreg sheet formed, and the like. Preferably, the second body portion  32  has a thickness in the range of about 0.5 mm to about 1.5 mm, and more preferably less than about 1.0 mm. An advantage of injection molding is that it may provide the second body portion  32  with a geometrically complex shape that includes the crown section  34  and a substantial part of the skirt section  35 . 
         [0051]    The materials for forming first body portion  31  may be stainless steel, pure titanium or a titanium alloy. The more preferred material comprises titanium alloys, such as titanium 6-4 alloy, which comprises 6% aluminum and 4% vanadium, or SP-700 titanium alloy, which comprises 4.7% aluminum, 2.9% vanadium, 2.0% molybdenum and 2.1% iron and is commercially available from NKK (Japan) and RTI International Metals (Niles, Ohio). First body portion  31  may be manufactured through casting with a face insert that is made by forming, or forging with a stamped sole, or forming a wrapped face with a stamped sole, or powdered metal forming, or metal-injection-molding and the like. 
         [0052]    By using magnesium for the second body portion  32 , a certain amount of weight may be reassigned to the weight member  40 , which is integral with the sole section  36 . The horseshoe shaped weight member  40  has a specified density in the range from about 4 g/cc to 20 g/cc, and may be selected from such materials as tungsten, molybdenum or another like metal in a like density range. Weight member  40  may be cast, injection molded, machined or formed by a powdered metal process. Weight member  40  is positioned away from the face section  37 , a design concept that facilitates the lowering of the center of gravity C. The methods for determining the positioning of the center of gravity C and the calculation of the geometric face center X are shown on schematic  FIGS. 1 and 2 . Dimensions were measured with the club head face square and the club soled in the address position. 
         [0053]    Three embodiments of the club head  30  design of the present invention were tested against a prior art club (Titleist® 983K driver) which is very similar in appearance, size and shape of the embodiments of the present invention. The three embodiments were all generally identical to each other except for the materials of construction of the second and third body portions  32 ,  33 . 
         [0054]    Test results for determining the position of the center of gravity C as it relates to the geometric face center are presented below in Table I, for three different embodiments of the present invention. Test data is also presented for the prior art club head Titleist® 983K, for comparison purposes. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                 (Club Head Mass Properties) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Titleist ® 983K 
                 Embodiment A 
                 Embodiment B 
                 Embodiment C 
               
               
                 From FIGS. 1 &amp; 2 
                 (mm) 
                 (mm) 
                 (mm) 
                 (mm) 
               
               
                   
               
             
          
           
               
                 CG-Xfc 
                 4.37 
                 −2.05 
                 −0.4 
                 −0.88 
               
               
                 CG-Yfc 
                 2.29 
                 −7.88 
                 −6.61 
                 −8.19 
               
               
                 CG-Zfc 
                 31.89 
                 31.08 
                 30.30 
                 31.12 
               
               
                 CG-B 
                 35.76 
                 31.44 
                 32.30 
                 31.34 
               
               
                 CG-C 
                 −15.47 
                 −15.26 
                 −14.92 
                 −14.86 
               
               
                 FC-X 
                 −27.79 
                 −21.18 
                 −23.27 
                 −22.59 
               
               
                 FC-Y 
                 27.29 
                 29.85 
                 29.46 
                 29.59 
               
               
                 FC-Z 
                 16.42 
                 15.82 
                 15.38 
                 16.27 
               
               
                   
               
               
                 MOI IMPACTS 
                 (kg-mm 2 ) 
                 (kg-mm 2 ) 
                 (kg-mm 2 ) 
                 (kg-mm 2 ) 
               
               
                   
               
               
                 High-low - x 
                 231.2 
                 217.6 
                 225.2 
                 218.9 
               
               
                 Heel-toe - y 
                 358.6 
                 370.3 
                 414.5 
                 355.7 
               
               
                 Lofted - z 
                 351.3 
                 255.4 
                 293.0 
                 251.9 
               
               
                 About shaft 
                 653.9 
                 563.5 
                 582.3 
                 557.9 
               
               
                   
               
               
                 (a) Embodiment A comprises magnesium second body portion 32 and a nylon hosel member 33. 
               
               
                 (b) Embodiment B comprises a composite second body portion 32 and an aluminum hosel member 33. 
               
               
                 (c) Embodiment C comprises a composite second body portion 32 and a nylon hosel member 33. 
               
             
          
         
       
     
         [0055]    Embodiment A of the present invention provides for a shift in the center of gravity C to a position at least 6 mm below the geometric face center X. The actual test results show the center of gravity C to be 7.88 mm below its geometric face center X, while tests for the Titleist® 983K (having a titanium crown and skirt) provided data indicating that the 983K′s center of gravity was 2.29 mm above its 15 geometric face center. Comparable shifts in the center of gravity C are seen in the test data for embodiments B and C. 
         [0056]    The Titleist® 983K has a volume of 363 cubic centimeters, and a titanium SP700 stamped hitting face with a thickness of about 0.122 inch. Unlike the present invention, the 983K does not have a thickness gradient in the hitting face  48  (discussed below). And, while the second body portion  32  of the present invention is formed from magnesium, and the hosel member  33  is formed of nylon, these portions of the 983K are formed from the heavier titanium alloys. Other than these differences, the embodiments of the present invention and the 983K are very comparable in size and dimension. Test results are shown in  FIGS. 14-21 . 
         [0057]      FIGS. 14 and 15 , depict data indicating launch angles of the prior art Titleist® 983K and Embodiment A (with the magnesium second body portion  32 ) respectively. The low center of gravity C, of Embodiment A, creates a launch angle of about 1.5° higher than that achieved with the prior art 983K club head (13° versus)11.5°. 
         [0058]      FIG. 16  graphically details the spin rate performance of the prior art 983K club head versus the magnesium crown of Embodiment A, as shown in  FIG. 17 . At the geometric face center of each club head (shown as 0.00 on the X-Y coordinates), the present invention produces a backspin of almost 500 rpm lower than the prior art 983K. 
         [0059]    A significant improvement in ball speed of the present invention over the prior art 983K can be best described by  FIGS. 18 and 19 . The maximum ball speed of the prior art club head is achieved at a position about 0.20 inches above the geometric face center ( FIG. 18 ) while the maximum ball speed of the magnesium crown present invention is maintained at about the geometric center or lower. This point of maximum ball speed is the point of maximum coefficient of restitution, which is often referred to by golfers as the “sweet spot.” 
         [0060]    The final results are culminated in  FIGS. 20 and 21 . With data taken at the geometric center for both club heads,  FIG. 21  shows the club head of the present invention achieving an increase of almost 7.5 yards over that of the prior art. 
         [0061]    These figures depict the initial ball speeds when the clubs traveling at about 110 mph impact Titleist PRO V1 ® balls. The angle of attack is about 2°, and the effective loft angle is about 12°. The clubs are mounted on a robot, which is driven to impact the balls at the desired club speed. Robots are commercially available from the True Temper Corporation or the Wilson® Sporting Goods Co. The locations of ball impacts are distributed over a rectangular area of 0.50 inch in the vertical direction and about 1.0 inch in the horizontal direction. The mechanical driver has the ability to repeatedly hit the balls at any desirable location on the hitting face. The ball speeds are measured by launch monitors. Any suitable launch monitor can be used. Examples of launch monitors include those described in commonly owned U.S. Pat. Nos. 6,533,674, 6,500,073, 6,488,591, 6,285,445, 6,241,622, 5,803,823 and 5,471,383, among others. 
         [0062]    Preferably, the front face section  37  of the present invention has a gradient thickness in the hitting face  48  ranging from the thinnest thickness about the crown section  34  to the thickest at the sole section  36 .  FIG. 13   a  depicts the preferred front face section  37 , as including a machined face insert, and wherein T 1 , of the upper portion near the crown section  34  can be as thin as about 0.08 inch (2.03 mm), the thickness T 2 , at the middle section is about 3 mm, and the lower portion nearer to the sole section  36  has a thickness T 3  of about 0.20 inch (5.0 mm). This thickening of the lower region of the hitting face  48  causes an upward shift of the point of maximum coefficient of restitution (COR) to a position not lower than 2 mm below the geometric face center X and preferably about equal to the face center X. The club head  30  has a COR of at least 0.80 under test conditions, such as those specified by the USGA. 
         [0063]    An alternate embodiment for the front face section  37  is shown in  FIGS. 7   b ,  5  wherein the face insert is of a constant thickness in the T 2  area and varied T i  and T 3  areas, with the thinnest thickness at the crown area. Not shown is another alternative front face section wherein the insert area thickness T 2  is varied and the thickness of sections depicted by T 1  and T 3  are constant. 
         [0064]    The standard USGA conditions for measuring the coefficient of restitution is set forth in the USGA  Procedure for measuring the Velocity Ration of a Club Head for Conformance to Rule  4-1 e , Appendix II. Revision I, Aug. 4, 1998 and Revision 0, Jul. 6, 1998, available from the USGA. Such tests measure COR by measuring ball resiliency. COR is the ratio of the velocity of separation to the velocity of approach. In this model, therefore, COR was determined using the following formula: 
         [0000]      (V club-post -V ball-post )/(V ball-pre -V club-pre ) 
         [0000]    where: 
         [0065]    V club-post  represents the velocity of the club after impact; 
         [0066]    V ball-post  represents the velocity of the ball after impact; 
         [0067]    V club-pre  represents the velocity of the club before impact (a value of zero for USGA COR conditions); and 
         [0068]    V ball-pre  represents the velocity of the ball before impact. 
         [0069]    The COR, in general, depends on the shape and material properties of the colliding bodies. A perfectly elastic impact has a COR of one (1.0), indicating that no energy is lost, while a perfectly inelastic or perfectly plastic impact has a COR of zero (0.0), indicating that the colliding bodies did not separate after impact resulting in a maximum loss of energy. Consequently, high COR values are indicative of greater ball velocity and distance. 
         [0070]    First and second body portions,  31 ,  32  and hosel member  33 , are sized and dimensioned to be attached together by any conventional methods used to join dissimilar materials, such as brazing and structural adhesives. A high quality plasma welding technique, similar to the welding technique used in Titleist® 983 driver club, is preferred. 
         [0071]    An alternate embodiment, depicted by  FIGS. 9-12 , and referred to as club head  50 , illustrates the advantage of injection molding the second body portion, wherein a hosel section  51  and bore-thru-hosel tube  52  are integrated with a crown section  53  to form a crown portion  54 . The advantage is that even more of the “high section” of the club head is made from a low density material (compared to the club head of embodiment  30  where bore-thru is made of higher density material). This allows for further lowering of the center of gravity C. The challenge is that the hosel is typically less rigid when made of low density material. Conventional golf clubs typically include a hosel welded on to the body of the club, which requires more manufacturing time and increases the complexity of manufacturing. 
         [0072]    Alternatively, the club head of the present invention may also be used with the smaller fairway woods, which can have volume as low as about 150 cubic centimeters. Preferably, the mass of the inventive club head is greater than 150 grams but less than 300 grams. It is anticipated that a fairway wood may be made from the design concepts of the present invention. Such a wood may have a first body portion made of a metal such as stainless steel, a second body portion (substantially the crown and skirt) made from a lower density metal such as titanium, and a hosel member having a density no greater than the second body portion. 
         [0073]    Another feature of the present invention includes the use of an insert positioned on an inner surface of the face opposite the strike surface. The insert may be used to stiffen the lower portion (that is, a portion located at or towards the sole) of the strike face, lowering the face COR. Restricting the COR of the lower portion of the strike face beneficially shifts the “compliant zone” or “sweet zone” of the face upward toward the crown. In other words, the point of maximum COR on the strike face is shifted upward such that it is between the crown and the geometric center of the face. The face has a COR between the sole and the geometric center (of the face) that is substantially less than the COR between the crown and the geometric center. Providing a face that is stiffer near the sole and progressively less stiff approaching the crown produces a higher launching, lower spinning trajectory of a struck golf ball, producing additional distance to the golf shot. The acoustics and feel of the golf club may also be improved. The insert creates a preferred striking zone located on the upper half of the face, the zone having a greater COR range than the rest of the face. 
         [0074]    Forming the COR lowering insert of a light-weight material allows the face to be selectively reinforced and stiffened without adding significant weight to the club head. Similarly, the face can be of substantially uniform thickness rather than the gradient design discussed previously, freeing up additional weight. As used herein, “of substantially uniform thickness” means of uniform thickness within typical manufacturing and machining tolerances. This weight savings can be used advantageously by the club designer to optimize the center of gravity location, such as by adding weight members, without altering the overall weight of the club head. The club will thus not feel abnormally heavy to the golfer. Preferred exemplary materials contemplated for forming the insert include composites, resin systems, thermoset materials, thermoplastic materials, pitch based carbon fibers, PAN based carbon fibers, Kevlar® fibers, fiberglass fibers, spectra fibers, or combinations thereof. Similar light-weight materials may also be used. Composite materials have a lower density when compared to homogeneous materials such as titanium, steel, and other alloys, yet can stiffen the face due to their higher tensile modulus. 
         [0075]      FIG. 22  shows a face view of a first embodiment of a club head  100  with a stiffening insert  105 , and  FIG. 23  shows a toe-side view of this embodiment. The club head  100  includes a face, a crown, a sole, and a skirt coupled together to form a club head body having an interior volume. In this embodiment, the insert  105  is provided in the form of ribs. The ribs are attached to the inner surface of the face, within the interior volume. The ribs are spaced apart, preferably at regular intervals, and are oriented vertically in a sole-to-crown direction. While five ribs are shown in the illustrated embodiment, any number of ribs may be used. Three to seven ribs are preferred. Each of the ribs is wider at the sole end than at the crown end, thereby imparting more stiffness to the sole end of the face than the crown end. It should be noted that the ribs can extend from the sole all the way to the crown, or they may extend only partially up the face and not reach the crown. The ribs are wider at a sole end than at a crown end. The width of the ribs preferably may be from approximately 0.1 inch to approximately 0.15 inch wide at the sole end and gradually reduce in width approaching the crown end. 
         [0076]      FIG. 24  shows a face view of another embodiment of a club head  100  with a stiffening insert  105 , and  FIG. 25  shows a toe-side view of this embodiment. Similarly to the previous embodiment, the stiffening insert takes the form of ribs attached to the inner surface of the face, oriented vertically in a sole-to-crown direction. Here, however, the ribs vary in thickness, rather than in width, from the sole to the crown. In these FIGURES, the ribs are illustrated as extending from the sole all the way to the crown, though they could also extend only partially up the face. 
         [0077]    The ribs are thickest toward the sole and thinnest toward the crown. In a preferred design, each of the ribs is from approximately 0.1 inch to approximately 0.15 inch thick at the sole end and gradually reduce in thickness to the crown end. Five ribs are illustrated merely for exemplary purposes. Ribs that decrease in both width and thickness from the sole towards the crown may also be used to stiffen selective portions of the face. 
         [0078]      FIG. 26  shows a face view of another embodiment of a club head  100  with a stiffening insert  105 , and  FIG. 27  shows a toe-side view of this embodiment. Here, again, the stiffening insert takes the form of ribs attached to the inner surface of the face. This time, however, the ribs are oriented horizontally in a toe-to-heel direction. As shown, the ribs decrease in thickness from the sole towards the crown. The rib nearest the sole has the greatest thickness, and the rib nearest the crown has the least thickness. Exemplary dimensions include from approximately 0.22 inch to approximately 0.18 inch thick for the rib nearest the sole and from approximately 0.022 inch to approximately 0.018 inch thick for the rib nearest the crown. The ribs can extend completely across the face from the toe to the heel, or, alternatively, only across a portion of the inner face surface. 
         [0079]    Vertical ribs and horizontal ribs may be used in combination within a single club head. More mass, whether by being thicker or wider or both, is provided at the sole, and less is provided toward the crown. More mass yields greater stiffening forces applied to the face, and greater stiffness means less COR. The maximum COR is thus shifted upward towards the crown. For example, the lower (stiffer) half of a club head incorporating this aspect of the invention may have an average COR of 0.82 or less, while the upper (more compliant) half of the face has the maximum COR allowed by the governing bodies of golf. Currently, this limit is 0.83. 
         [0080]      FIG. 28  shows a face view of another embodiment of a club head  100  with a stiffening insert  105 , and  FIG. 29  shows a toe-side view of this embodiment. Rather than being in the form of ribs, here the stiffening insert is provided in the form of a patch coupled to the inner surface of the face. The patch is coupled adjacent the sole and extends upward toward the crown. In the embodiment illustrated in  FIGS. 28 and 29 , the patch does not extend all the way to the crown.  FIG. 30  shows a toe-side view of a similar embodiment, but with the patch extending all the way to the crown. The patch has a tapered thickness, being thickest at a lower portion adjacent the sole and thinnest at an upper portion toward the crown and away from the sole. As previously discussed, the increased mass and thickness towards the sole imparts more stiffening to the lower portion of the club face and shifts the compliant or sweet zone upward, preferably above the geometric center of the face. Providing the stiffening means in the form of a patch facilitates attaching the insert to the inner surface of the club head. 
         [0081]    The stiffening insert, regardless of its form, may be attached to the face prior to its attachment to the club head body. Alternatively, the face may first be coupled to the body and then the insert attached thereto, such as through an opening in the crown over which a crown insert is later attached. Bonding or adhering are preferred for attaching the insert to the face. The stiffening insert creates a face having a non-uniform COR to achieve more desired ball performance in use. The insert is attached to a portion of the face inner surface, stiffens the face in and around the area of attachment, lowering the COR thereof below a predetermined value, and shifting the compliant portion upward, preferably above the geometric center of the face. 
         [0082]    While various descriptions of the present invention are described above, it should be understood that the various features of each embodiment could be used alone or in any combination thereof. Therefore, this invention is not to be limited to only the specifically preferred embodiments depicted herein. Further, it should be understood that variations and modifications within the spirit and scope of the invention might occur to those skilled in the art to which the invention pertains. The scope of the present invention is accordingly defined as set forth in the appended claims.