Abstract:
A metal wood golf club head adapted for attachment to a shaft, having a stiff lower front face and a compliant upper front face. An insert serves as an impact face. The lower front face has a substantially greater thickness providing a stiffer face area. A cavity behind the lower front face removes undesired weight from the front face and allowing for weight to be redistributed to more desirable locations.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     The present application is a continuation-in-part of co-pending U.S. patent application Ser. No. 10/662,682, filed on Sep. 15, 2003, wherein the disclosure of the parent application is incorporated herein in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a multi-material, multi-component metal wood golf club head having an improved face design.  
       BACKGROUND OF THE INVENTION  
       [0003]     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.  
         [0004]     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. Golf club manufacturers are looking for solutions wherein lighter and stronger materials may be employed to achieve results such as lower ball spin and higher launch angles.  
         [0005]     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 club design may be improved to yield longer ball flight, and maximize ball velocity after impact while remaining within the rules.  
         [0006]     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).  
       SUMMARY OF THE INVENTION  
       [0007]     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.  
         [0008]     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 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.  
         [0009]     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.  
         [0010]     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.  
         [0011]     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.  
         [0012]     Another embodiment of the invention utilizes only two body portions, the light weight second portion incorporating both the crown section and the hosel member.  
         [0013]     One embodiment of the invention discloses a metal wood with a face having an impact zone comprising a stiff lower area and a compliant upper area, with a cavity defined in the lower area which can be filled by either a lightweight material such as plastic, ceramic, or even air. The cavity has a cover that is either welded or held on by an epoxy. The body of the club is cast and he casting includes the cavity. The impact face is a welded insert. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      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.  
         [0015]      FIG. 2  is a top schematic of  FIG. 1 .  
         [0016]      FIG. 3  is an expanded pictorial view of an embodiment of the invention, having three body portions.  
         [0017]      FIG. 4  is a top view of  FIG. 3  thereof.  
         [0018]      FIG. 5  is a cut out top view taken along line A-A of  FIG. 8 .  
         [0019]      FIG. 6  is a partial cross-sectional view showing the bore-thru hosel tube and weight member.  
         [0020]      FIG. 7  is a toe view of  FIG. 3  thereof.  
         [0021]      FIG. 8  is a front view of  FIG. 3  thereof.  
         [0022]      FIG. 9  is an expanded pictorial view of another embodiment of the invention. having two body portions.  
         [0023]      FIG. 10  is a top view of  FIG. 9  thereof.  
         [0024]      FIG. 11  is a toe view of  FIG. 9  thereof.  
         [0025]      FIG. 12  is a front view of  FIG. 9  thereof  
         [0026]      FIG. 13   a  is a side view of the variable thickness front face of the present invention.  
         [0027]      FIG. 13   b  is a side view of the variable thickness front face of an alternate embodiment.  
         [0028]      FIG. 13   c  is a side view of a variable thickness front face with a hollow cavity in the cast body.  
         [0029]      FIG. 14  is a graph illustrating the relationship of launch angles to the face center for the prior art Titleist® 983K driver.  
         [0030]      FIG. 15  is a graph illustrating the relationship of launch angles to the front face for the present invention.  
         [0031]      FIG. 16  is a graph depicting the relationship of backspin to the front face for the prior art Titleist® 983 K.  
         [0032]      FIG. 17  is a graph depicting the relationship of backspin to the front face for the present invention.  
         [0033]      FIG. 18  is a graph relating ball speed to front face for the prior art 983K.  
         [0034]      FIG. 19  is a graph relating ball speed to front face for the present invention.  
         [0035]      FIG. 20  is a graph showing ball distance at positions on the front face of the prior art 983K.  
         [0036]      FIG. 21  is a graph showing ball distance at positions on the front face of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0037]     The golf club head according to preferred embodiments of the present invention, is a multi-material and multi-component hollow club head.  
         [0038]     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 .  
         [0039]     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 .  
         [0040]     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.  
         [0041]     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 is 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 critical design concept for 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.  
         [0042]     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 .  
         [0043]     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.  
                                     TABLE I                       (Clubhead Mass Properties)                                    Titleist ®   Embodiment   Embodiment   Embodiment       From    983K   A   B   C           (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.             
 
         [0044]     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&#39;s center of gravity was 2.29 mm above its geometric face center. Comparable shifts in the center of gravity C are seen in the test data for embodiments B and C. 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 .  
         [0045]      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°).  
         [0046]      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.  
         [0047]     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”.  
         [0048]     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.  
         [0049]     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 monitors 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.  
         [0050]     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.  
         [0051]     An alternate embodiment for the front face section  37  is shown in  FIG. 7   b,  wherein the face insert is of a constant thickness in the T 2  area and varied T 1  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.  
         [0052]     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: 
 
(v club-post −v ball-post )/(v ball-pre −v club-pre ) 
 
 where, v club-post  represents the velocity of the club after impact; 
        v ball-post  represents the velocity of the ball after impact;     v club-pre  represents the velocity of the club before impact (a value of zero for USGA COR conditions); and     v ball-post  represents the velocity of the ball before impact.        
 
         [0056]     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.  
         [0057]     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.  
         [0058]     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.  
         [0059]     An embodiment of the invention is shown on  FIG. 13   c,  wherein a cast metal wood body  61  has a face perimeter  69  defining an opening  62  that is filled by an insert  63  which is welded to the face perimeter  69  to serve as an impact face. The insert  63  can be forged, sheet metal formed or cast. The cast metal wood body  61  combines with the insert  63  to create a variable front face which is thicker at a lower area  65  and gradually thinner towards an upper area  68 . There is a cavity defined in the lower area  65  of the cast body  61  rearward of the front face. This cavity  66  may be filled with a lightweight material  67  such as plastic, a ceramic, or air. The cavity  66  is sealed by a cover  68  which may be welded or sealed by an epoxy or similar bonding agent. The greater thickness of the lower area  65  makes the face of the club much stiffer in that area while the thinner upper area  68  is more compliant. This type of design results in a ball launch which after impact has a lower spin and higher launch angle, and therein a longer ball flight while maintaining a Coefficient of Restitution greater than 80. While the stiffer lower area  65  and compliant upper area  68  create a desirable metal wood design, having a large amount of mass towards the front of the club head is not desirable. The creation of the cavity  66  allows a substantial amount of weight to be removed from the front, possibly to be moved to a more desirable location in the club head. It is well known in the design of metal woods, that moving weight away from the front face and placing it low in the club head, helps create a preferred club head center of gravity. The present design allows for the club head to be thicker and therefore stiffer in the lower area of the face, but without the extra mass. The cavity  66  allows for weight to be shifted to more desirable areas of the club head.  
         [0060]     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.  
         [0061]     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.