Abstract:
A metal wood-type golf club includes a weight member disposed along the interior surface of the bottom wall. The weight member is sized and distributed so as to increase the moment of inertia of the golf club about a vertical axis extending through the center of gravity as well as lowering the center of gravity of the club head itself. The longitudinal position of the weight member is selected as a function of the loft angle of the club face. The weight member is moved forward for a club having a small loft angle and moved rearward for a club having a high loft angle so that the vertical gear effect about the center of gravity partially offsets the natural backspin of the club to a greater or lesser degree depending on the loft angle of the club.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to golf clubs and, in particular, to so-called metal wood-type golf clubs. 
     Golf clubs known as “woods” traditionally have a head made of a suitable wooden material such as maple or persimmon attached to one end of an elongated shaft. These wooden club heads are usually solid and are shaped with their weight properly distributed about their center of gravity to maximize performance. Golf club “wood” heads have also been formed of suitable metals such as stainless steel and titanium. Metal heads are usually hollow. Various attempts have been made to distribute weight in metal heads with respect to their center of gravity so that the performance is maximized. Such attempts have included placing different types and numbers of weight members at different locations inside the metal heads. Examples of such attempts are disclosed in prior U.S. Pat. No. 4,869,507 to Sahm; U.S. Pat. No. 5,058,895 to Igarashi; U.S. Pat. No. 5,141,230 to Antonious; and, U.S. Pat. No. 5,219,408 to Sun. 
     The Sahm patent teaches that lowering the center of gravity of a club head would tend to add more loft to a golf shot. Igarashi teaches that perimeter weighting increases the moment of inertia of a wood type club. The increased moment of inertia causes the club to resist twisting when a ball is not struck at the “sweet spot”, that is, the point on the club face at which a line normal to the face passes through the club head&#39;s center of gravity. Reducing the twisting causes the ball to travel with less loss of directional control. None of the aforementioned prior art patents, however, teach use of a weight member to tailor gear effect-induced topspin to partially offset the natural loft angle induced backspin of a metal wood-type club. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a metal wood-type golf club comprising a hollow body with a face disposed at a predetermined loft angle adapted for impacting a golf ball. In a preferred embodiment of a golf club, a weight member is disposed along the interior surface of the bottom wall. The weight member is sized and distributed so as to increase the moment of inertia of the golf club about a vertical axis extending through the center of gravity as well as lowering the center of gravity of the club head itself. Additionally, the longitudinal position of the weight member is selected as a function of the loft angle of the club face so that the gear effect about the center of gravity partially offsets the natural backspin of the club. The weight pad is moved forward for a club having a small loft angle and moved rearward for a club having a high loft angle. 
     Moving the center of gravity fore and aft as a function of loft angle permits clubs to be designed to take advantage of vertical gear effect to tailor the amount of backspin imparted to a golf ball for a given loft angle, thereby enabling the club to deliver the ideal trajectory without over spinning or under spinning the ball. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawing figures in which like references designate like elements and, in which: 
     FIG. 1 is a top plan view of a prior art golf club head; 
     FIG. 2 is a top plan view of a golf club head incorporating features of the present invention; 
     FIG. 3 is a sectional view taken along lines  3 — 3  of FIG. 2; 
     FIG. 4 is a sectional view of a golf club head incorporating features of the present invention having an increased loft angle; 
     FIG. 5 is a sectional view of a golf club head incorporating features of the present invention having a still further increased loft angle; 
     FIG. 6 is a top sectional view of the golf club head of FIG. 4; and 
     FIG. 7 is a sectional view of the golf club head of FIG.  5 . 
    
    
     DETAILED DESCRIPTION 
     The drawing figures are intended to illustrate the general manner of construction and are not necessary to scale. In the detailed description and in the drawing figures, specific illustrative examples are shown and herein described in detail. It should be understood, however, that the drawing figures and the detailed description are not intended to limit the invention to the particular form disclosed but are merely illustrative and intended to teach one of ordinary skill how to make and/or use the invention claimed herein and for setting forth the best mode for carrying out the invention. 
     FIG. 1 depicts a prior art golf club  10  such as that disclosed in U.S. Pat. No. 5,954,596 to Noble and assigned to the assignee of the present invention. Golf club  10  has a hosel  12 , a center of gravity  14 , and a face  16 . As is well-known in the art, upon impact with a golf ball  20  at a location  22  that is offset from center of gravity  14 , club  10  will tend to rotate in the direction of arrow “a” as a result of the torque couple induced by line of action  24  being offset a distance “1” from center of gravity  14 . The rotation of club head  10  about center of gravity  14  in the direction of arrow “a” will cause the face  16  of club  10  to open, which will tend to cause ball  20  to fly off of face  16  in direction indicated by arrow  26 , which results in a slice type of hit. 
     As is also well-known in the art, it is possible to design a club head so that the undesirable initial trajectory caused by an off center hit will be at least partially compensated by the so-called “gear effect,” which imparts a counteracting spin to the golf ball. As can be seen from FIG. 1, because the rotation of golf club  10  in the direction indicated by arrow “a” is dynamic, for so long as golf ball  20  is in contact with face  16 , friction between face  16  and golf ball  20  will cause the surfaces to tend to move together like meshing gears (hence the name gear effect). This coupled movement of surfaces will impart a corresponding spin in the direction indicated by arrow “b” to ball  20 . Thus, as can be seen from FIG. 1, in the case of a toe hit, which results in an initial trajectory to the right of the target (for a right handed golfer), the gear effect will impart a hook type spin to the golf ball  20 . This spin will tend to cause golf ball  20  to correct somewhat for the initial incorrect trajectory. Similarly, an impact on the hosel side of center of gravity  14  will tend to cause an initial trajectory to the left of the target, with a slice type of spin on golf ball  20  that will correct somewhat for the initial incorrect trajectory. It should be noted that the foregoing discussion takes into account only forces acting in the horizontal plane which tend to open or close the face about a vertical axis extending through center of gravity  14  and imparting spin to golf ball  20  about a vertical axis, which affects the horizontal trajectory of the golf ball. Accordingly, for the sake of clarity, the forces and reactions discussed with reference to FIG. 1 will be referred to hereinafter as “horizontal gear effect” as opposed to vertical gear effect, which will be discussed in detail hereinafter. 
     Referring to FIGS. 2 and 3, a golf club head  200  incorporating features of the present invention includes a hollow body  210  formed of a suitable metal material such as stainless steel or a titanium alloy having a heel portion  212 , a toe portion  214 , a top wall  216 , a bottom wall  236 , a rear wall  218 , and a front wall  220  including a face  222  arranged for contacting a golf ball. Club head  200  further includes a weight member  224  composed of individual weight pads  226  and  228  (shown in broken lines in FIG.  2 ). 
     Club head  200  has an initial center of gravity  230  which is the center of gravity of the club head without taking into account the mass of weight member  224 . Club head  200  also includes a final center of gravity  232  which is the center of gravity of club head  200  taking into account weight member  224 . As can be seen from an inspection of FIGS. 2 and 3 the effect of the addition of weight member  224  to club head  200  is to move the center of gravity lower and further forward. Weight pads  226  and  228  each comprise trapezoidal parallelepipeds formed at a suitable metal material such as stainless steel, zirconium titanium or alloys of zirconium or titanium extending upward from inner surface  234  of bottom wall  236  of club head  200 . The shape and orientation of weight pads and  226  and  228  (trapezoidal parallelepipeds having a long axis parallel to the longitudinal axis  240 , and having their respective short parallel sides  242  and  244  nearest center of gravity  232 ) is dictated by a desire to maximize the moment of inertia of weight member  224  about a vertical axis extending through center gravity  232  while still moving the center of gravity downward and forward in accordance with the present invention. 
     With reference to FIG. 3, face  222  of club head  200  is inclined at a loft angle  246  with respect to a first vertical plane  248  containing the longitudinal axis of shaft  238  and parallel to a horizontal line “h,” which is tangent to face  222  at its center and thus defines an idealized “plane” of face  222  (face  222  in reality having both bulge and roll rending it less than a pure planar surface). Accordingly as used herein in connection with defining the angular orientation of the vertical plane containing the longitudinal axis of the shaft relative to the face, the “plane” of the club face means the vertical plane containing line “h.” As face  222  strikes golf ball  320 , loft angle  246  causes golf ball  320  to be launched at an initial upward trajectory  250 . Simultaneously, the inertial effect of golf ball  320  striking the inclined face  222  imparts a backspin (opposite the direction of arrow b′) on golf ball  320 . What the inventors of the present invention discovered, however, is that simultaneously, the dynamic forces acting on club head  200  striking golf ball  320  cause club head  200  to rotate about its center of gravity  232  in a face-up direction as indicated in arrow a′ in FIG.  3 . It was determined that this dynamic face-up rotation could be utilized to moderate the backspin imparted to golf ball  320  by adding a topspin component to the club-ball interaction, and that this effect could be tailored by moving the center of gravity of the club head  200  laterally forward and backward as a function of loft angle  246 . 
     As illustrated in FIG. 3, as club head  200  rotates about its center of gravity in the direction a′, for so long as golf ball  320  is in contact with face  222 , friction between the contacting surfaces of face  222  and golf ball  320  causes the surfaces to move together. Accordingly, rotation of golf club head  200  about its center of gravity  232  imparts an opposite rotation in the direction of arrow b′ to golf ball  320 . This is a similar mechanism to the horizontal gear effect discussed with reference to FIG. 1, however, the rotation of club head  200  is about a horizontal axis passing through center of gravity  232  and the rotation of golf ball  320  is about a horizontal axis passing through its center of gravity. The spin thus imparted to golf ball  320  affects the vertical trajectory of golf ball  320 . Accordingly, the interaction between face  222  and golf ball  320  is referred to herein as the “vertical gear effect” to distinguish it from the horizontal gear effect previously discussed. 
     As shown in FIGS. 2 and 3, placement of weight member  224  comprising weight pads  226  and  228  causes the center of gravity of club head  200  to move from the location indicated by initial center of gravity  230  to the position indicated by final center of gravity  232 . In the illustrative embodiment, loft angle  246  is about 14° and the final center of gravity  232  is about 0.040 inches forward and 0.025 inches below initial center of gravity  230 . Since the moment arm  252  from final center of gravity  232  to impact point  254  is shorter than the moment arm from initial center of gravity  230  to impact point  254 , for a given rate of angular velocity ω the surface speed at impact point  254  is less with the center of gravity located at final center of gravity  232  than with initial center of gravity  230 . Accordingly, relocating the center of gravity further forward reduces the vertical gear effect induced topspin component to the rotation of golf ball  320  leaving face  222 . Accordingly, golf ball  320  has more backspin then it would if the center of gravity were located at initial center of gravity  230 . This is appropriate for clubs having relatively modest loft such as a three wood having a loft angle of between 11° and 16° as shown in FIG.  3 . 
     With reference to FIGS. 4 and 6, club head  400  comprises a hollow body  410  having a top wall  416 , bottom wall  436 , rear wall  418 , and front wall  420  including a face  422  for impacting a golf ball. Face  422  is inclined at a loft angle  446  with respect to a vertical plane  448  parallel to face  422  and containing the longitudinal axis of golf club shaft  248 . Loft angle  446  is greater than loft angle  246  of club head  200 . Weight member  424  comprising weight pads  426  and  428  is disposed on inner surface  434  of bottom wall  436 . Weight member  424  is sized and positioned so as to move the center of gravity of club head  400  from a position indicated by initial center of gravity  430  to a position indicated by final center of gravity  432 . In the illustrative embodiment of FIG. 4, loft angle  446  is approximately 17° and the final center of gravity  432  is approximately 0.020 inches forward of initial center of gravity  430  and approximately 0.026 inches below initial center of gravity  430 . As with the embodiment of FIG. 3, loft angle  446  of club head  400  imparts an initial trajectory and an initial backspin to golf ball  420  upon impact. The dynamic forces acting on club head  400  cause it to rotate in a direction indicated by arrow a″ about final center of gravity  432 . The frictional contact between the contacting surfaces of golf ball  420  and club head  400  at impact point  454  causes the surfaces to move together thus imparting a vertical gear effect topspin component indicated by arrow b″ in golf ball  420 . Because the moment arm  452  between final center of gravity  432  and impact point  454  is slightly shorter then the moment arm from initial center of gravity  430  to impact point  454 , for a given angular velocity ω, the vertical gear effect induced top spin component is slightly less than if the center of gravity were located at initial center of gravity  430 . Accordingly, the backspin imparted to golf ball  420  will be slightly less then if weight member  424  were not present. This is appropriate for a golf club having moderate loft such as a five wood having a loft angle of from 16° to 18°. 
     With reference to FIGS. 5 and 7, a golf club head  500  comprises a hollow body  510  having a top wall  516 , a bottom wall  536 , a rear wall  518 , and a front wall  520  including a face  522 . Face  522  is inclined at a loft angle  546  with respect to a vertical plane  548  parallel to face  522  and containing the longitudinal axis of golf club shaft  238 . Loft angle  546  is greater than either loft angle  446  or loft angle  246 . Upon impact between club head  500  and golf ball  520 , inclined face  522  imparts an initial trajectory and backspin to golf ball  520 . The dynamic forces of impact also cause club head  500  to rotate in a direction indicated by arrow a′″ about final center of gravity  532 . For so long as golf ball  520  is in contact with face  522 , the contacting surfaces move together and the vertical gear effect induces a corresponding rotational component indicated by arrow b′″ which tends to counteract the face-induced backspin in golf ball  520 . Weight member  524 , composed of weight pads  526  and  528  is attached to inner surface  534  of bottom wall  536  and is sized and positioned so as to move the center of gravity of club head  500  from the position indicated by initial center of gravity  530  to the position indicated by final center of gravity  532 . In an illustrative embodiment, loft angle  546  is approximately 20° and weight member  524  is sized and positioned so as to move the center of gravity of club head  500  rearward approximately 0.020 inches and downward approximately 0.01 inches. Because moment arm  552  from final center of gravity  532  to impact point  554  is longer than the moment arm from initial center of gravity  530  to impact point  554 , for a given angular velocity ω, the surface speed at impact  554  is greater with the center of gravity of club head  500  at final center of gravity  532  then with the center of gravity at initial center of gravity  530 . Accordingly, the vertical gear effect induced topspin component is greater with weight member  524  present than without. Accordingly, club head  500  produces less back spin with weight member  524  present and the center of gravity located at final center of gravity  532  than with weight member  524  absent and center of gravity located at initial center of gravity  530 . This is appropriate for clubs having substantial loft such as a 7 wood having a loft angle of from 18° to 22°. 
     By tailoring the location of the center of gravity in the fore and aft direction as a function of the loft angle of the club, a hollow metal wood-type club incorporating features of the present invention is capable of delivering the ideal trajectory without overspinning or under spinning the ball. 
     Although certain illustrative embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from spirit and scope of the invention. Accordingly, it is intended that the invention should be limited only to the extent required by the appended claims and the rules and principals of applicable law.