Abstract:
A wood-type golf club head has a hollow shell structure having a head length L (mm), a head-depth W (mm) and a sweet spot height H (mm) which satisfy: 0.80≦W/L≦1.0 and H≦76×(W/L)−31. The head length L is the distance between the clubshaft axis CL and a point T farthest from the clubshaft axis CL. The head depth W is the distance between a plane FP tangent to the sweet spot SS and a point B farthest from the plane FP.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a golf club head, more particularly to a wood-type golf club head having a hollow structure configured to increase the carry distance. 
         [0002]    Wood-type hollow golf club heads having various shapes have been proposed. 
         [0003]    With respect to the position of the center of gravity of the head, there is a tendency that, when the size of the golf club head in the back-and-forth direction is increased, the distance of the center of gravity from the club face is also increased. Since the club face is usually provided with a loft angle larger than 0 degree, the sweet spot height increases with the increase in the distance of the center of gravity. This will increase the likelihood that the golf ball hits a lower part of the club face under the sweet spot, and the backspin is increased due to the gear effect. As a result, the ball flight tends to become so called “ballooning” or “rising” trajectory due to too much backspin and a relatively low launching angle. Thus, the carry distance becomes short. 
         [0004]    When the size of the head in the toe-heel direction is increased, the distance between the center of gravity and the axis of the club shaft tends to increase accordingly. Therefor, there is a tendency that even at the time of impact the head can not return to the right address position where the club face is at right angle to the target line (trajectory) of the ball, and so called “ball gripping” or “ball holding” on the club face becomes insufficient. As a result, the ball flight tends to become slice. Thus, the directionality of flying of the ball is not good. Further, as the air resistance of the head becomes increased, the drag during swing increases to decrease the head speed. Thus, the carry distance becomes short. 
       SUMMARY OF THE INVENTION 
       [0005]    It is therefore, an object of the present invention to provide a golf club head in which, by optimizing the head shape in relation to the position of the sweat spot, an optimum trajectory can be obtained to increase the carry distance and the ball holding can be improved to improve the directionality of flying of the ball. 
         [0006]    According to the present invention, a wood-type golf club head having a hollow structure having a head length L (mm), a head depth W (mm) and a sweet spot height H (mm) which satisfy 
         [0000]      0.80 ≦W/L≦ 1.0 and 
         [0000]        H≦ 76×( W/L )−31. 
         [0007]    Definitions 
         [0008]    In this application, the dimensions refer to the values measured under the standard state of the club head unless otherwise noted. 
         [0009]    The standard state of the club head is such that the club head is set on a horizontal plane HP so that the axis CL of the clubshaft is inclined at the lie angle beta while keeping the axis CL on a vertical plane VP 1 , and the club face  2  forms its loft angle alpha with respect to the horizontal plane HP. Incidentally, in the case of the club head alone, the center line of the shaft inserting hole  7  can be used as the clubshaft axis CL. 
         [0010]    The sweet spot SS is the point of intersection between the club face  2  and a straight line N drawn normally to the club face  2  passing the center G of gravity of the head. 
         [0011]    The sweet spot height H is the height of the sweet spot measured vertically from the horizontal plane HP. 
         [0012]    The back-and-forth direction is a direction parallel with the straight line N projected on the horizontal plane HP. 
         [0013]    The heel-and-toe direction is a direction parallel with the horizontal plane HP and perpendicular to the back-and-forth direction. 
         [0014]    The head length L is the distance of a point T measured perpendicularly to and from the clubshaft axis CL of the shaft inserting hole  7 , and the point T is on the surface of the head on the toe-side and farthest from the axis CL. 
         [0015]    The head depth W is the distance of a point B measured perpendicularly to and from a plane FP, and the plane FP is defined as being tangent to the club face  2  at the sweet spot SS, and the point B is on the surface of the head on the backside and farthest from the plane FP. 
         [0016]    The distance GL of the center G of gravity is the distance of the center G of gravity measured perpendicularly to and from the clubshaft axis CL. 
         [0017]    The term “wood-type golf club” used in this application is meant for at least number 1 to 5 woods having a loft angle of not less than 7.0 degrees, but not more than 20 degrees. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a front view of a wood-type golf club head according to the present invention. 
           [0019]      FIG. 2  is a top view thereof. 
           [0020]      FIG. 3  is a cross sectional view taken along line A-A of  FIG. 2  showing an embodiment of the present invention. 
           [0021]      FIG. 4  is a cross sectional view similar to  FIG. 3  showing another embodiment of the present invention. 
           [0022]      FIG. 5  is a cross sectional view similar to  FIG. 3  showing still another embodiment of the present invention. 
           [0023]      FIG. 6  is a partial cross sectional view of the sole portion for explaining a structure and a way of setting a separate weight member. 
           [0024]      FIGS. 7 and 8  are a schematic top view and a schematic right side view of the head for explaining a way of setting another example of the separate weight member. 
           [0025]      FIG. 9  is a perspective view of a face plate. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    Embodiments of the present invention will now be described in detail in conjunction with the accompanying drawings. 
         [0027]    Wood-type golf club head according to the present invention has a hollow shell structure  1   a.    
         [0028]    The hollow shell structure  1   a  comprises: a face portion  3  whose front face defines a club face  2  for striking a ball; a crown portion  4  intersecting the club face  2  at the upper edge  2   a  thereof; a sole portion  5  intersecting the club face  2  at the lower edge  2   b  thereof; and a side portion  6  between the crown portion  4  and sole portion  5  which extends from a toe-side edge  2   c  to a heel-side edge  2   d  of the club face  2  through the back face BF of the club head. 
         [0029]    At the heel side end of the crown portion  4 , there is formed a hosel portion  1   b  be attached to an end of a club shaft (not shown) inserted into the shaft inserting circular hole  7 . 
         [0030]    In the case of a wood-type club head for number  1  wood, it is preferable that the head volume is set in a range of not less than 350 cc, more preferably not less than 360 cc still more preferably not less than 380 cc in order to increase the moment of inertia and the depth of the center of gravity. However, to prevent an excessive increase in the club head weight and deteriorations of swing balance and durability and further in view of golf rules or regulations, the head volume is preferably set in a range of not more than 470 cc, more preferably not more than 460 cc. 
         [0031]    The mass of the club head  1  is preferably set in a range of not less than 180 grams, more preferably not less than 185 grams in view of the swing balance and rebound performance, but not more than 220 grams, more preferably not more than 215 grams in view of the shot directionality and traveling distance of the ball. 
         [0032]    The loft angle alpha is set in a range of from not less than 7.0 degrees, preferably not less than 7.5 degrees, more preferably not less than 8.0 degrees, but not more than 20 degrees, preferably not more than 19.0 degrees, more preferably not more than 18.0 degrees. 
         [0033]    As to the materials for the head, it is possible that the club head  1  partially includes nonmetallic materials, e.g. fiber reinforced resins, ionomer resins and the like. In this embodiment, however, the club head  1  is made of one or more metal materials. For example, stainless steels, maraging steels, pure titanium, titanium alloys, aluminum alloys and the like can be used. 
         [0034]    According to the present invention, the ratio (W/L) of the head depth W (mm) to the head length L (mm) is set in a range of from 0.80 to 1.0. 
         [0035]    Through experimental tests conducted by the inventor, it was found that: when the ratio (W/L) is less than 0.80, as the head length L becomes long for the head depth W, it becomes difficult to rotate the head back to the accurate address position during swing, and as a result, miss shots such as slice shot are induced. Further, the distance GL of the center G of gravity increases and the ball holding becomes insufficient, which further induce a slice shot. Thus, the directionality is deteriorated. Moreover, there is a tendency that the user feels the head as being undersized, therefore, the head can not give the user a sense of ease when addressed to the ball. 
         [0036]    In the present invention, since the ratio (W/L) is not less than 0.80, the club head can rotate and return to the accurate address position at impact, and as a result, the directionality can be improved. From this point of view, it is desirable that, by relatively decreasing the head length L, the ratio (W/L) is set in a range of not less than 0.82, more preferably not less than 0.85. 
         [0037]    Contrary, when the ratio (W/L) is over 1.00, as the head length L becomes short for the head depth W, there is a tendency that the head rotates beyond the accurate address position during swing, and as a result, hook shots are induced. Therefore, the ratio (W/L) is not more than 1.0, preferably not more than 0.98, more preferably not more than 0.95, still more preferably not more than 0.93. 
         [0038]    In this embodiment, it is preferable that the distance GL is set in a range of from 36 to 41 mm. 
         [0039]    By setting the ratio (W/L) as above, it becomes possible to proved the club head  1  with an appropriate weight distribution, which makes it easy to achieve the preferable range (36 to 41 mm) for the distance GL 
         [0040]    If the absolute value of the head length L is too small, as the distance GL becomes decreased, a hook shot is liable to occur. Further, the head can not provide a sense of easy when addressed to the ball and it becomes difficult to meet the ball. Contrary if the head length L is too large, the ball holding is liable to be deteriorated. Therefore, the head length L is set in a range of not less than 95 mm, preferably not less than 100 mm, more preferably not less than 105 mm, but not more than 140 mm, preferably not more than 135 mm, more preferably not more than 130 mm. 
         [0041]    If the absolute value of the head depth W is too small, as the depth of the center G of gravity (namely, the length of the straight N) becomes decreased, the directionality is liable to deteriorate. Further, the head can not provide a sense of easy when addressed. Contrary, if the absolute value of the head depth W is too large, the sweet spot height tends to be increased, and as a result, the backspin increases and the ball flight becomes a ballooning trajectory to decrease the carry distance. Therefore, the head depth W is set in a range of not less than 80 mm, preferably not less than 85 mm, more preferably not less than 90 mm, but not more than 130 mm, preferably not more than 125 mm, more preferably not more than 120 mm. 
         [0042]    From the results of experimentally tests carried out by the inventor, it was also found that, by specifically limiting the sweet spot height H in relation to the above-mentioned ratio (W/L), a ballooning trajectory is prevented and therefore, the carry distance can be increased. 
       According thereto, it is desirable to determine the sweet spot height H (mm) so as to satisfy the following conditional expression (1), preferably expression (2), more preferably expression (3): 
       [0043]        H≦ 76×( W/L )−31  (1) 
         [0000]        H≦ 76×( W/L )−34  (2) 
         [0000]        H≦ 76×( W/L )−39  (3) 
         [0000]    It is preferable that the sweet spot height H is as low as possible in view of the prevention of the ballooning trajectory. But, if the sweet spot SS becomes distant from the average impact points of the average golfers (pints ranging from the center of the club face to 3 mm above), the rebound performance is liable to deteriorate. In this embodiment, therefore, it is preferable that the sweet spot height H is not less than 25 mm, but, not more than 45.0 mm, preferably not more than 40.0 mm, more preferably not more than 39.0 mm, still more preferably not more than 38.0 mm. 
         [0044]    If the distance in the back-and-forth direction between the sweet spot SS and the clubshaft axis CL is too small, the distance in the back-and-forth direction between the center G of gravity and the axis CL (and the angle delta between line z and plane VP 1  in  FIG. 2 ) becomes increased. Therefore, there is a tendency that the head turns over the right address position at impact and a hook shot is liable occur. Further, the head  1  also becomes easy to rotate around a horizontal axis extending in the toe-heel direction, and as a result, the ball is liable to hit a lower part of the club face  2 , which increases the backspin. 
         [0000]    Therefore, the distance Q of the sweet spot SS measured perpendicularly to and from the above-mentioned vertical plane VP 1  including the axis CL is preferably set in a range of from not less than 0.060 times, more preferably not less than 0.070 times, still more preferably not less than 0.080 times the head depth W. 
         [0045]    However, if the distance Q is more than 0.25, the air resistance of the head increases because the position of the club shaft shifts backward as the distance Q increases and the air resistance increases as the club shaft shifts backward. Therefore, the distance Q is preferably set in a range of from not more than 0.25 times, more preferably not more than 0.22 times, still more preferably not more than 0.20 times the head depth W. 
         [0046]    In this embodiment, the absolute value of the distance Q is preferably set in a range of from not less than 5.0 mm, more preferably not less than 7.0 mm, still more preferably not less than 9.0 mm, but, not more than 25 mm, more preferably not more than 22 mm, still more preferably not more than 20 mm. 
         [0047]      FIGS. 3 ,  4  and  5  each show an example of the configuration to decrease the sweet spot height H while increasing the (W/L). 
         [0048]    In  FIG. 3 , the crown portion  4  is relatively flattened by providing a large radius Rc of curvature, and the maximum thickness D (or height) of the head is decreased. 
         [0049]    In the vertical plane VP 2  including the straight N, the radius Rc of curvature of the outer surface of the crown portion  4  is preferably set in a range of from not less than 150 mm, more preferably not less than 180 mm, still more preferably not less than 200 mm, but, preferably not more than 500 mm, more preferably not more than 450 mm. 
         [0050]    Further, the maximum thickness D of the club head is preferably set in a range of from not more than 65 mm, more preferably not more than 63 mm, still more preferably not more than 60 mm, but, not less than 45 mm, more preferably not less than 50 mm. 
         [0051]    In  FIG. 4 , the side portion  6  is gradually decreased in the vertical height from the front to the back, and the height h at the extreme rear end point B is set in a range of not more than 45% but not less than 20% of the maximum thickness D of the club head. The crown portion  4  is provided with a convex curvature. 
         [0052]    In  FIG. 5 , the crown portion  4  is provided with a concave curvature. 
         [0053]    In addition to these designs shown in  FIGS. 3-5 , 
         [0054]    to reduce the weight of the head in the crown portion  4  and/or side portion  6  by using light weight materials having a relatively low specific gravity, e.g. metal materials such as magnesium alloys and aluminum alloys, resins such as engineering plastics and fiber reinforced resins; 
         [0055]    to reduce the weight of the head in the crown portion  4  and/or side portion  6  by decreasing the wall thickness thereof; 
         [0056]    to provide one or more unclosed openings in the crown portion  4 ; 
         [0057]    to decrease the amount of protrusion of the hosel portion  1   b ; can be also employed. 
         [0058]    In the case that the crown portion  5  and/or side portion  6  is decreased in the thickness, it is desirable to reduce the thickness to a small range of 0.3 to 0.5 mm by press molding a rolled metal sheet since it is difficult to reduce the thickness less than 0.6 or 0.7 mm by casting the meta material. 
         [0000]    In order to weld such thin metal plates, plasma welding, especially laser welding is preferred. Further, soldering, adhesive bonding and the like can be used. 
         [0059]    Furthermore, the following designs to lower the mass distribution of the head can be used: 
         [0060]    to flatten the sole portion  5  by providing the outer surface with a large radius Rs of curvature ( FIG. 1 ); 
         [0061]    to increase the thickness of the sole portion  5  wholly or partially; and 
         [0062]    to provide a separate weight member  10 . 
         [0063]      FIG. 6  shows a way of setting a weight member  10  in the hollow shell structure  1   a.    
         [0064]      FIGS. 7 and 8  show a way of setting a weight member  10  outside the hollow shell structure  1   a.    
         [0065]    The weight member  10  is made from a material having a larger specific gravity than that of the hollow shell structure  1   a , especially the material of the sole portion  5 . For example, stainless steels, brass, tungsten, tungsten alloys and the like can be used. 
         [0066]    In  FIG. 6 , a weight member  10  is fixed to the sole portion  5 . By placing the weight member  10  near the club face  2 , the sweet spot height H can be effectively reduced. 
         [0067]    In this example, to mount the weight member  10 , the sole portion  5  is provided with a socket protruding into the hollow shell, and the weight member  10  is put in the socket. To fix the weight member, caulking, adhesive agent and the like can be utilized. 
         [0068]    In  FIGS. 7 and 8 , the weight member  10  is an arched round bar extending from the toe to the heel along the side portion  6 , leaving a space therebetween. The ends  10   a  and  10   b  are fixed to the side portion  6  at the toe and heel. Such weight member  10  can increase the depth of the center of gravity, while decreasing the sweet spot height. 
       Comparative Tests: 
       [0069]    Golf club heads having a head volume of 460 cc and a loft angle of 10 degrees were made based on the structure shown in  FIGS. 1-3 , and tested as follows. 
         [0070]    Each of the heads is composed of a hollow main body (m) having a front opening, and a face plate (f) attached to the hollow main body so as to cover the front opening. 
         [0071]    As shown in  FIG. 9 , the face plate (f) defines the face portion  3  and a turnback  11  is provide around the face portion  3  so as to extend backward from the edge of the club face  2 . The amount of the backward extension F of the turnback was 10 mm excepting a part near the hosel portion. 
         [0000]    The face plate (f) was a casting of a titanium alloy Ti-5.5Al-1Fe (“Super Ti—X 51AF” Nippon steel corporation). The hollow main body (m) was a casting of a titanium alloy Ti-6Al-4v. The hollow main body (m) was fixed to the face plate (f) by laser welding. 
         [0072]    In the sole portion, as shown in  FIG. 6 , a weight member  10  made of sintered compact of a tungsten nickel alloy having a specific gravity of 12 was fixed thereto. The weight member put in a socket was fixed to the sole portion by means of caulking and an adhesive. 
         [0073]    The total weight of the club head was 205 grams. 
         [0074]    The sweet spot height H was varied by changing the thicknesses of the sole portion and side portion and the position and mass of the weight member. 
         [0075]    The specifications are shown in Table 1. 
         [0076]    In the comparison tests, the club heads were attached to identical shafts to make wood clubs having a total length of 44.75 inches. 
         [0077]    Using each club, ten right-handed golfers having handicap ranging from 5 to 20 hit golf balls six times per person. 
         [0078]    The average carry distance was computed for each club from the sixty shots. 
         [0079]    Further, the deviation (yard) of the point of fall of the struck ball from the target line of the ball was measured, providing that the value is −(minus) when the point of fall is right of the target line, and +(plus) when left of the target line. And the average deviation was computed for each club from the sixty shots. Usually, it is required that the absolute value of the average is at most 10 yards. When the absolute value is less than 5, the directionality of the head is regarded as very good. 
         [0080]    As to easiness of swing the club, and sense of ease when addressed to the ball, each head was evaluated into five ranks (5: very good, 4: Good, 3: Average, 2: Baddish, 1: Bad) by the ten golfers. The average value was computed for each club from the evaluations by the ten golfers. 
         [0081]    The test results are shown in Table 1. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Ex. 1 
                 Ex. 2 
                 Ex. 3 
                 Ex. 4 
                 Ex. 5 
                 Ex. 6 
                 Ref. 1 
                 Ref. 2 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Head 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Head depth W (mm) 
                 102 
                 107 
                 112 
                 107 
                 112 
                 112 
                 100 
                 121 
               
               
                 Head length L (mm) 
                 128 
                 122 
                 118 
                 122 
                 118 
                 118 
                 133 
                 110 
               
               
                 ratio(W/L) 
                 0.80 
                 0.88 
                 0.95 
                 0.88 
                 0.95 
                 0.95 
                 0.75 
                 1.10 
               
               
                 Sweet spot height H (mm) 
                 29.0 
                 35.0 
                 40.0 
                 31.0 
                 37.0 
                 33.0 
                 29.0 
                 45.0 
               
               
                 Distance GL (mm) 
                 41 
                 39 
                 37 
                 39 
                 37 
                 36 
                 43 
                 38 
               
               
                 Distance Q (mm) 
                 18 
                 18 
                 18 
                 18 
                 18 
                 18 
                 18 
                 18 
               
               
                 Ratio(Q/W) 
                 0.18 
                 0.17 
                 0.16 
                 0.17 
                 0.16 
                 0.16 
                 0.18 
                 0.15 
               
               
                 Test results 
               
               
                 Carry distance (yard) 
                 240 
                 239 
                 236 
                 247 
                 241 
                 249 
                 236 
                 232 
               
               
                 Deviation (yars) 
                 −4.2 
                 +1.8 
                 +3.1 
                 +2.4 
                 +3.8 
                 +4.6 
                 −12.3 
                 +18.6 
               
               
                 Sense of ease 
                 3.1 
                 4.0 
                 4.4 
                 4.1 
                 4.5 
                 4.4 
                 1.8 
                 4.2 
               
               
                 Easiness of swing 
                 2.9 
                 3.6 
                 4.2 
                 3.7 
                 4.3 
                 4.3 
                 2.7 
                 4.0 
               
               
                   
               
             
          
         
       
     
         [0082]    From the test results, it was confirmed that the heads according to the present invention can be improved in the carry distance, deviation (directionality), easiness of swing, and sense of ease when addressed from a comprehensive standpoint.