Patent Abstract:
A golf club head having a hollow construction produces a characteristic low ball hitting sound to accommodate the diversity of golfers&#39; preferences for ball hitting sounds even if the volume of the golf club head is increased to 430 to 500 cc and the weight thereof is decreased to 160 to 220 g. In a golf club head having a hollow construction and including a face part, a sole part, a crown part, and a side part, in which the head volume is 430 to 500 cc, and the head weight is 160 to 220 g, the area of the sole part is increased so that the primary natural frequency of the sole part is 2400 Hz or less, and a weight is formed at a position of the center of vibration in the sole part on the inner surface on the hollow construction side of the sole part.

Full Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a golf club head having a hollow construction. 
     Recently, large golf club heads having a head volume exceeding 430 cc have been developed. Since the large head has an enlarged sweet area on the head, it has become possible to manufacture an easy-to-use golf club that is less likely to cause a decrease in carry even in an off-center shot. However, if a head having a hollow construction is made large, the thicknesses of members forming a crown part and a sole part must be decreased. Therefore, a ball hitting sound at the time a ball hits tends to be low. 
     Generally, a high ball hitting sound peculiar to a metal head is to the golfer&#39;s liking. Therefore, various ways and means have been devised to control the ball hitting sound of such a large-size and light-weight head. For example, Japanese Patent Application Publication No. 2003-339922 describes a technique in which, to produce a high and clear ball hitting sound, a metallic thin small piece is fixed on the inner surface of a golf club head on the toe side of a sole part in a state in which one plate surface of the small piece adheres closely to the sole part. Also, Japanese Patent Application Publication No. 2006-204604 describes a technique in which, to improve the low ball hitting sound, at least one rib extending from the toe side to the heel side is arranged in the sole part, and this rib is extended curvedly so that the toe-side end and the heel-side end of the rib are nearer to the face side than the central area of the rib. 
     On the other hand, not all golfers like a metallic and high-pitched sound. Japanese Patent Application Publication No. 2008-200319 and Japanese Patent Application Publication No. 2008-200339 describe a technique in which, to make the ball hitting sound of golf club head loud and to make the reverberation long, the radius of curvature of the sole part, crown part, or side part is made larger than the minimum radius of curvature of the face surface of golf club head, and a rib or a flat plate shaped member is provided in a portion having a larger radius of curvature so that the value of resonance frequency of this portion is within ±10% of the value of resonance frequency of the face surface. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a golf club head having a hollow construction, which produces a characteristic low ball hitting sound to accommodate the diversity of golfers&#39; preferences for ball hitting sounds even if the volume of the golf club head is increased to 430 to 500 cc and the weight thereof is decreased to 160 to 220 g. 
     To achieve the above object, as one aspect of the present invention, a golf club head in accordance with the present invention has a hollow construction, includes a face part, a sole part, a crown part, and a side part, and is characterized in that the head has a volume in the range of 430 to 500 cc and a weight in the range of 160 to 220 g; and the area of the sole part is in the range such that the primary natural frequency of the sole part is 2400 Hz or lower. 
     As another aspect of the present invention, a golf club head in accordance with the present invention has a hollow construction, including a face part, a sole part, a crown part, and a side part, and is characterized in that the head has a volume in the range of 430 to 500 cc and a weight in the range of 160 to 220 g; and a weight is formed on the inner surface of the sole part so that the primary natural frequency of the sole part is 2400 Hz or lower. 
     As still another aspect of the present invention, a golf club head in accordance with the present invention has a hollow construction, including a face part, a sole part, a crown part, and a side part, and is characterized in that the head has a volume in the range of 430 to 500 cc and a weight in the range of 160 to 220 g; and the radius of curvature of the outer surface of the sole part in the toe-to-heel direction is 230 mm or larger so that the primary natural frequency of the sole part is 2400 Hz or lower. 
     In the above-described second and third aspects, the area of the sole part is preferably in the range of 3000 to 14,000 mm 2 . Also, in the first and third aspects, a weight is preferably formed in a portion of the center of vibration in the sole part on the inner surface of the sole part. Furthermore, in the first and second aspects, the radius of curvature of the outer surface of the sole part in the toe-to-heel direction is 230 mm or greater. 
     As described above, according to the present invention, even for a large-size and light-weight golf club head having a volume of 430 to 500 cc and a weight of 160 to 220 g, the primary natural frequency of the sole part can be made 2400 Hz or lower by increasing the area of the sole part, by forming a weight on the inner surface on the hollow construction side of the sole part, or by making the radius of curvature of the outer surface of the sole part in the toe-to-heel direction 230 mm or larger. Thereby, a characteristic low ball hitting sound can be obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a bottom plan view showing a first embodiment of a golf club head in accordance with the present invention; 
         FIG. 1B  is a front view of the golf club head shown in  FIG. 1A ; 
         FIG. 2A  is a bottom plan view showing a second embodiment of a golf club head in accordance with the present invention; 
         FIG. 2B  is a front view of the golf club head shown in  FIG. 2A ; 
         FIG. 3A  is a bottom plan view showing a third embodiment of a golf club head in accordance with the present invention; 
         FIG. 3B  is a front view of the golf club head shown in  FIG. 3A ; 
         FIG. 4A  is a bottom plan view showing a fourth embodiment of a golf club head in accordance with the present invention; 
         FIG. 4B  is a front view of the golf club head shown in  FIG. 4A ; 
         FIG. 5A  is a bottom plan view of a golf club head of comparative example; 
         FIG. 5B  is a front view of the golf club head shown in  FIG. 5A . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of a golf club head in accordance with the present invention will now be described with reference to the accompanying drawings.  FIG. 1A  is a bottom plan view showing a first embodiment of the golf club head in accordance with the present invention, and  FIG. 1B  is a front view of the golf club head shown in  FIG. 1A . 
     As shown in  FIGS. 1A and 1B , a golf club head  10  of this embodiment includes a face part  11 , a sole part  12 , a crown part  13 , a side part  14 , and a hosel part  15 . The side part  14  wraps around the head  10  from the toe side  14   a  to the heal side  14   b  via the back side. Also, the face part  11  and the sole part  12  are formed so as to be adjacent to each other. Although not shown in particular, the head  10  has a hollow construction, and the inner surfaces on the hollow construction side of the parts of head are formed so as to be almost smooth like the outer surface thereof. 
     In the present invention, a large golf club head having a volume of 430 cc or greater is taken up. A further preferred head volume is 435 cc or greater. On the other hand, the upper limit of the head volume is 500 cc, preferably 470 cc. Also, in the present invention, a lightweight golf club head having a weight of 220 g or less is taken up. A preferred club weight is 195 g or less. On the other hand, the lower limit of head weight is 160 g, preferably 165 g. 
     In this embodiment, the area of the sole part  12  is designed so as to be large so that the primary natural frequency of vibrations of the sole part  12  caused when a ball is hit by the golf club head  10  is 2400 Hz or less. For example, the area of the sole part  12  is preferably 4000 mm 2  or greater, more preferably 6000 mm 2  or greater. By remarkably increasing the area of the sole part  12  with respect to the head volume in this manner, the amplitude of the sole part  12  is increased, so that the primary natural frequency of the sole part  12  can be made 2400 Hz or less. 
     The primary natural frequency is preferably 2200 Hz or less, more preferably 2000 Hz or less. The lower limit of the primary natural frequency is preferably 1300 Hz because too large a head volume is not to a golfer&#39;s liking. On the other hand, if the area of the sole part  12  is too large, swing is hindered. Therefore, the area of the sole part  12  is preferably 14,000 mm 2  or less, more preferably 13,000 mm 2  or less. 
     The radius of curvature R of the outer surface of the sole part  12  in the direction directed from the toe side  14   a  to the heel side  14   b  is preferably 150 mm or greater, further preferably 160 mm or greater. On the other hand, if the radius of curvature R is too large, it is difficult for the golfer to set up the head  10 , which poses a problem of difficulty in assuming a posture. Therefore, the radius of curvature R is preferably 500 mm or less, further preferably 450 mm or less. 
     To maintain a fixed strength, the wall thickness of the sole part  12  is preferably 0.6 mm or greater, further preferably 0.7 mm or greater. On the other hand, if the wall thickness is too large, the weight increases. Therefore, the wall thickness of the sole part  12  is preferably 1.5 mm or less, further preferably 1.2 mm or less. 
     In this specification, the “sole part” means a part having a wall thickness different from that of the adjacent side part or face part. In the case in which the wall thickness of the sole part is the same as that of the side part or the face part, a portion in which the radius of curvature R of the outer surface of the sole part changes greatly is made a boundary with the side part or the face part. Also, the “area of the sole part” means an area of the outer surface of the sole part. 
       FIGS. 2A and 2B  show a second embodiment of the golf club head in accordance with the present invention,  FIG. 2A  being a bottom plan view of the golf club head, and  FIG. 2B  being a front view thereof. As shown in  FIGS. 2A and 2B , a golf club head  20  of this embodiment also includes a face part  21 , a sole part  22 , a crown part  23 , a side part  24 , and a hosel part  25 . In this embodiment, the side part  24  is formed between the face part  21  and the sole part  22 . 
     In this embodiment, the radius of curvature R of the outer surface of the sole part  22  in the direction directed from the toe side  24   a  to the heel side  24   b  is designed so as to be large, being 230 mm or greater, so that the primary natural frequency of the sole part  22  is 2400 Hz or less. This radius of curvature R is preferably 350 mm or greater, further preferably 400 mm or greater. By remarkably increasing the radius of curvature R of the sole part  22  in this manner, the shape of the sole part  22  is made flat, so that the primary natural frequency of the sole part  22  can be made 2400 Hz or less. On the other hand, if the radius of curvature R is too large, the above-described problem arises. Therefore, the radius of curvature R is preferably 500 mm or less, further preferably 450 mm or less. 
     In this embodiment, the area of the sole part  22  need not necessarily be increased, and is preferably 3000 mm 2  or greater, more preferably 4000 mm 2  or greater, and still more preferably 6000 mm 2  or greater. To maintain a fixed strength, the wall thickness of the sole part  22  is preferably 0.6 mm or greater, more preferably 0.7 mm or greater. On the other, if the wall thickness of the sole part  22  is too large, the weight increases. Therefore, the wall thickness of the sole part  22  is preferably 1.5 mm or less, further preferably 1.2 mm or less. 
       FIGS. 3A and 3B  show a third embodiment of the golf club head in accordance with the present invention,  FIG. 3A  being a bottom plan view of the golf club head, and  FIG. 3B  being a front view thereof. As shown in  FIGS. 3A and 3B , a golf club head  30  of this embodiment also includes a face part  31 , a sole part  32 , a crown part  33 , a side part  34 , and a hosel part  35 . 
     In this embodiment, a weight  36  is formed on the inner surface on the hollow construction side of the sole part  32  so that the primary natural frequency of the sole part  32  is 2400 Hz or less. Since the weight  36  is formed within the head  30 , the weight  36  is shown by a broken line in  FIGS. 3A and 3B . The weight  36  is preferably formed at a position of the center of vibration caused in the sole part  32  at the time of hitting a ball. By forming the weight  36  at the position of the center of vibration in this manner, the primary natural frequency of the sole part  32  can be decreased to 2400 Hz or less. The center of vibration of the sole part  32  usually takes place at a position of the centroid of the sole part  32  if the wall thickness of the sole part  32  is uniform. 
     The weight of the weight  36  is preferably 3 g or greater, further preferably 4 g or greater. If the weight is too large, an influence is exerted on swing balance, or the whole of head becomes heavy, so that there arises a problem in that the head volume must be decreased. Therefore, the weight of the weight  36  is preferably 10 g or less, further preferably 9 g or less. Also, to control the vibrations of the sole part  32  properly, the area of the weight  36  that is in contact with the inner surface of the sole part  32  is preferably 200 mm 2  or less, further preferably 150 mm 2  or less. The lower limit of this area is preferably 20 mm 2 . 
       FIGS. 3A and 3B  show the case in which the shape of the weight  36  is a rectangular prism. However, the shape of the weight  36  is not limited to this, and a rectangular prismatic, spherical, ellipsoidal, cylindrical, conical, or truncated conical shape, or other polyhedral shapes may be used. Also, the weight  36  may be joined to the sole part  32 , for example, by welding by adhering one surface thereof closely to the inner surface of the sole part  32 , or may be formed integrally, for example, by casting. 
     In this embodiment as well, as in the second embodiment, the area of the sole part  32  need not necessarily be increased, and is preferably 3000 mm 2  or greater, more preferably 4000 mm 2  or greater, and still more preferably 6000 mm 2  or greater. The wall thickness of the sole part  32  is preferably 0.6 mm or greater, more preferably 0.7 mm or greater as in the second embodiment. Also, the wall thickness of the sole part  32  is preferably 1.5 mm or less, more preferably 1.2 mm or less. 
       FIGS. 4A and 4B  show a fourth embodiment of the golf club head in accordance with the present invention,  FIG. 4A  being a bottom plan view of the golf club head, and  FIG. 4B  being a front view thereof. As shown in  FIGS. 4A and 4B , this embodiment is a combination of the first embodiment and the third embodiment. That is to say, the area of a sole part  42  is designed so as to be large, and a weight  46  is formed on the inner surface of the sole part  42 . 
     In this embodiment, the area of the sole part  42  is preferably 4000 mm 2  or greater, further preferably 6000 mm 2  or greater. By making the area of the sole part  42  large and by forming the weight  46  on the inner surface of the sole part  42  as described above, the primary natural frequency of the sole part  42  can be made 2200 Hz or less, further 2000 Hz or less. The upper limit of the area is preferably 14,000 mm 2 , more preferably 13,000 mm 2 . The weight  46  is preferably formed at a position at the center of vibration of the sole part  42 . Although  FIGS. 4A and 4B  show one weight  46 , since the area of the sole part  42  is large, a plurality of weights  46  can be formed when the center of vibration takes place at a plurality of positions of the sole part  42 . 
     As described above, in the present invention, the first through third embodiments can be combined. The area and the radius of curvature of the sole part are increased by combining the first and second embodiments, a weight is formed on the inner surface of the sole part having an increased radius of curvature by combining the second and third embodiments, or a weight is formed on the inner surface of the sole part having an increased area and an increased radius of curvature by combining the first through third embodiments. Thereby, the primary natural frequency of the sole part can be made 2200 Hz or less, or more preferably 2000 Hz or less. 
     In any of these embodiments, the face part, the sole part, the crown part, the side part, the hosel part, and the weight can be made of a metallic material having the same or different composition. These elements are preferably made of, for example, a titanium alloy or an aluminum alloy. For example, a titanium alloy (Ti-6Al-4V) having a composition of 5.5 to 6.75 wt % Al, 3.5 to 4.5 wt % V, the balance being Ti and unavoidable impurities can be used. 
     EXAMPLES 
     Golf club heads of examples 1 to 4 and a comparative example having specifications given in Table 1 were manufactured. The “length” in Table 1 means a distance between the toe and the heel of the sole part, and the “depth” in Table 1 means a distance between the face and the back of the sole part. The appearances of examples 1 to 4 and comparative example correspond to  FIGS. 1A to 5B . In all of the examples and the comparative example, the Ti-6AL-4V alloy was used, and the head had a volume of 450 cc. The primary natural frequencies of the sole parts of the examples 1 to 4 and the comparative example were determined by FEM analysis. The results are given in Table 1. 
     
       
         
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Sole 
                   
                 Primary 
               
             
          
           
               
                   
                   
                   
                   
                 Wall 
                   
                   
                   
                 Head 
                 natural 
               
               
                   
                   
                 Area 
                 R 
                 thickness 
                 Length 
                 Depth 
                 Weight 
                 weight 
                 frequency 
               
               
                   
                 Appearance 
                 [mm 2 ] 
                 [mm] 
                 [mm] 
                 [mm] 
                 [mm] 
                 [g] 
                 [g] 
                 [Hz] 
               
               
                   
                   
               
             
          
           
               
                 Example 1 
                 FIGS. 1A 
                 7113 
                 234 
                 0.8 
                 119 
                 94 
                 — 
                 180 
                 2150 
               
               
                   
                 and 1B 
               
               
                 Example 2 
                 FIGS. 2A 
                 7090 
                 425 
                 1.0 
                 91 
                 93 
                 — 
                 182 
                 1919 
               
               
                   
                 and 2B 
               
               
                 Example 3 
                 FIGS. 3A 
                 4466 
                 165 
                 0.8 
                 63 
                 76 
                 5 
                 183 
                 2112 
               
               
                   
                 and 3B 
               
               
                 Example 4 
                 FIGS.4A 
                 7113 
                 234 
                 0.8 
                 119 
                 94 
                 5 
                 182 
                 1830 
               
               
                   
                 and 4B 
               
               
                 Comparative 
                 FIGS. 5A 
                 4466 
                 165 
                 0.8 
                 63 
                 76 
                 — 
                 175 
                 2686 
               
               
                 Example 
                 and 5B 
               
               
                   
               
             
          
         
       
     
     As shown in Table 1, for the comparative example having a sole area of about 4500 mm 2 , the primary natural frequency of sole part was very high, being about 2700 Hz. On the other hand, for example 1 having a large sole area of about 7100 mm 2 , the primary natural frequency of the sole part was able to be decreased significantly to about 2200 Hz. Also, for example 2 having a large sole area of about 7100 mm 2  and a large radius of curvature of sole of about 400 mm, the primary natural frequency of sole part was able to be decreased to about 1900 Hz. For example 3 having the same sole area as that of the comparative example and provided with a 5-gram weight in the center of vibration of sole part, the primary natural frequency of sole part was able to be decreased significantly to about 2100 Hz. Furthermore, for example 4 having a large sole area of about 7100 mm 2  and provided with a 5-gram weight in the center of vibration of sole part, the primary natural frequency of sole part was able to be decreased to about 1800 Hz.

Technology Classification (CPC): 0