Abstract:
A golf club set consisting of a plurality of golf clubs having a series of continuous club numbers, characterized in that an angle of centroid defined as an angle described between an extension line of a face of a club head and a perpendicular passing through a center axis of a club shaft when the club shaft of each of the golf clubs is placed on a horizontal table with the club head thereof being suspended freely, is smaller for the golf clubs having higher club numbers and progressively larger in the order of decreasing club numbers among a plurality of the golf clubs.

Description:
This application is a continuation of application Ser. No. 07/996,641 filed Dec. 24, 1992, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to golf club sets. More in particular, it relates to golf club sets in which any golf club has a substantially equal level of hitting easiness irrespective of its club number, and which can make equal in directivity of a hit ball golf clubs having lower club numbers which are difficult to handle particularly for amateur golf players, to golf clubs having higher club numbers. 
     Generally, a golf club set comprises the combination of a series of golf clubs ranging from the club numbers of 1 to 5 in the case of a wood type golf club set and the combination of a series of golf clubs ranging from the club numbers 1 to 9, PW (pitching wedge) and 5 W (sand wedge) in the case of an iron type golf club set. The lower the golf club number, the longer becomes a club shaft and the smaller a loft angle of the face of the club head. Therefore, the lower the golf club number, the more difficult becomes the golf club for an amateur golf player to handle, so that a miss shot is likely to occur and a ball is likely to slice to the right at the time of hitting. Accordingly, the amateur golf players in general seldom use the golf clubs having lower club numbers, and these clubs are mostly kept stored in a golf bag as decorative items. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide golf club sets which enable particularly amateur golf players, who mostly fail to swing at a high head speed, to obtain substantially equal directivity of a ball hit by any golf club irrespective of a club number. 
     It is another object of the present invention to provide golf club sets which allow a player to swing golf clubs having lower club numbers with the same ease as with golf clubs having higher club numbers. 
     To accomplish the objects described above, the golf club set according to the present invention employs the structure wherein an angle of centroid θ defined as an angle described between an extension line of a face of a club head and a line perpendicularly passing through a center axis of a club shaft when the club shaft of each of the golf clubs is placed on a horizontal table with the club head thereof being suspended freely, is so changed as to increase progressively in the order of decreasing club numbers, or is set to a substantially equal one for all the golf clubs. 
     As described above, the angle of centroid θ of the golf club having each club number is set so that the club shaft of the golf club having a greater club shaft length and lower club number is brought closer to the centroid of the club head. Therefore, a golf player can catch correctly a ball even with a club having a lower club number in the same way as with a golf club having a small club shaft length and a higher club number. This also holds true of the golf club set in which the angle of centroid θ of each golf club is set to a substantially equal one for all the golf clubs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1a and 1b are respectively a front view and a side view of a wood type golf club constituting a golf club set according to the present invention; 
     FIGS. 2a and 2b are respectively a front view and a side view of an iron type golf club constituting a golf club set according to the present invention; 
     FIG. 3 is an explanatory graph showing the relation between club numbers and angles of centroid of a gold club set according to an embodiment of the present invention; 
     FIG. 4 is an explanatory graph showing the relation between club numbers and angles of centroid of a golf club set according to another embodiment of the invention; 
     FIG. 5 is an explanatory graph showing the relation between club numbers and angles of centroid of a golf club set according to still another embodiment of the invention; 
     FIG. 6a is an explanatory view showing a method of measuring the angle of centroid of a golf club; 
     FIG. 6b is a view when viewed from a direction of arrow VIb of FIG. 6a; 
     FIG. 7 is an explanatory view showing a method of measuring the angle of centroid of an iron type golf club and corresponding to FIG. 6b; and 
     FIG. 8 is an explanatory graph showing the relation between club numbers and angles of centroid of a golf club set according to a pair art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Golf clubs having lower club numbers have a greater club shaft length and are therefore difficult to handle. As a result of intensive studies on the search for means for making these golf clubs having lower club numbers easily handleable or operable in the same way as the golf clubs having higher club numbers and smaller club shaft length, the inventors of the present invention have found out that this handleability is closely associated with an angle of centroid, and that in the golf clubs having greater club shaft length and lower club numbers, the centroid of the club head can be brought closer to a connecting portion of the club shaft as its angle of centroid is increased and in this way, a golf player can more correctly hit a ball. 
     In the present invention, the term &#34;angle of centroid&#34; means the angle measured as shown in FIGS. 6a and 6b. In other words, a club shaft 2 of a golf club G is placed on a horizontal table 7 with its club head 1 being suspended freely outside the horizontal table 7. Then, the club head 1 comes to a halt with its centroid lying on a vertical plane Y--Y containing the center axis of the club shaft 2. An angle θ between a toe-heel line X--X at the bottom of a striking face 1a of the club head 1 and the vertical plane Y--Y passing through the center axis of the club shaft 2 under this state is defined as the &#34;angle of centroid&#34; as shown in FIG. 6b. Though FIGS. 6a and 6b show the case of a wood type golf club, the angle of centroid θ of an iron type golf club can be measured similarly as shown in FIG. 7. 
     When the angles of centroid θ are examined for golf clubs constituting conventional golf club sets, the angles of centroid are smaller for golf clubs having lower club numbers, and are greater for golf clubs having higher club numbers as shown in FIG. 8. Table below represents a definite example of the relation between the club numbers and the angles of centroid in the conventional golf club set. 
     
         ______________________________________Club No.   #1    #2    #3   #4  #5   #6  #7   #8  #9   PW______________________________________Angle of   4°         6°               8°                    10°                        12°                             14°                                 16°                                      18°                                          20°                                               22°centroid θ______________________________________ 
    
     In other words, in the conventional golf club set, the connecting position of the club shaft to the club head is much more spaced from the centroid of the club head with a golf club of a lower club number. Since the distance between the club shaft and the centroid of the club head is great and the club shaft length is great as described above, such a golf club is particularly difficult to handle for an amateur golf player who can produce only a low head speed. 
     In the golf club sets according to the present invention, the club numbers of a plurality of golf clubs constituting the golf club set have the relation with the angles of centroid θ as shown in FIG. 3. For example, the angle of centroid is greater in the golf club #1 having a low club number and is smaller with PW (#10) having a high club number. In other words, the connecting position of the club shaft to the club head is closer to the centroid of the club head in the golf club having a greater club shaft length and a lower club number, and according to this arrangement, even an amateur golf player whose fails to get a high head speed can handle easily the golf clubs having lower club numbers in the same way as the golf clubs having higher club numbers. In the present invention, the angle of centroid of PW having a higher club number is preferably set to about 22° and the angle of centroid may be incremented by 1° to 3° as the club number is decremented by one. Needless to say, the angles of centroid may be changed in accordance with the desire of the golf player. 
     In the golf club set having the construction shown in FIG. 3, the difference of the angles of centroid between the golf clubs having the adjacent club numbers is preferably the same. If the difference of the angles of centroid θ between the golf clubs having adjacent club numbers is the same across all the golf clubs constituting the golf club set, feeling at the time of hitting a ball can be changed continuously between the golf clubs, and the golf club set becomes easier for the player to swing and hit the ball. 
     The present invention employs the structure in which the angles of centroid are increased for the golf clubs having lower club numbers and are decreased for the golf clubs having higher club numbers. In comparison with the continuous change of the angles of centroid as shown in FIG. 3, the angles of centroid may be changed step-wise as shown in FIG. 4 and the angles of centroid of all the golf clubs constituting the golf club set may be set to an equal one as shown in FIG. 5. In either case, substantially the same effect can be obtained. 
     The angles of centroid can be changed stepwise in the following way as shown in FIG. 4. For example, a group of long iron type golf clubs of the club numbers #1 to #3 are provided with the same angle of centroid, a group of middle iron type golf clubs of the club numbers #4 to #6 are provided by the same angle of centroid which is smaller than that of the long iron type golf clubs, and finally, a group of golf clubs having the club numbers #7 to #10 (PW) are provided with the same angle of centroid, which is smaller than that of the middle iron type golf clubs. 
     As the golf clubs constituting the golf club sets described above, wood type golf clubs preferably have the structure such as shown in FIGS. 1a and 1b and iron type golf clubs preferably have the structure shown in FIGS. 2a and 2b. 
     In the wood type golf club Ga shown in FIG. 1a, 1b and the iron type golf club Gb shown in FIGS. 2a, 2b, a hosel 4 bent in a crank shape is fixed to a neck 3 on the heel side of the club head 1, and the club shaft 2 is connected and fixed through this hosel 4. The crank shape of the hosel 4 is offset in a direction extending from the neck 3 to the face 1a towards the toe side. In other words, the center axis R--R of the hosel on the side of the club shaft 2 is offset inward by a distance L relative to the center axis S--S of the hosel on the side of the neck 3 of the club head 1. The angle of centroid θ can be adjusted easily by adjusting the offset distance L between the center axis S--S of the hosel on the club head side and the center axis R--R of the hosel on the club shaft side. 
     The angle of centroid θ can be increased by increasing the offset distance L and bringing the center axis R--R of the hosel on the side of the club shaft 2 closer to the centroid of the club head 1. However, the fitting position of the club shaft 2 is stipulated to be within 16 mm from the heel by the regulation. Therefore, this offset distance L must be changed within the distance of 16 mm from the heel side. 
     The golf club set according to the present invention that has the construction described above may comprise the iron type golf clubs alone, or the wood type golf clubs alone, or the combination of the iron type golf clubs and the wood type golf clubs. 
     The iron type golf club set may comprise the combination of non-metallic golf club made of a resin with the exception of a sole plate and metallic golf clubs. In the case of a golf club set comprising the combination of a plurality of wood type golf clubs and iron type golf clubs, the angles of centroid θ are changed in such a way that a group of the iron type golf clubs follow a group of the wood type golf clubs: For instance, if the group of the wood type has club numbers 1 to 4 and the group of the iron type has club numbers 3 to 9, the angles of centroid θ decrease like this; the club number 1 to 4 of the wood type and the club number 3 to 9 of the iron type. 
     As described above, in the golf club set according to the present invention, an angle of centroid θ of a golf club is so changed as to increase progressively in the order of decreasing club numbers. Therefore, the club shaft of the golf club having a greater club shaft length and a lower club number is brought closer to the centroid of the club head. Accordingly, even an amateur golf player who cannot produce a high head speed can hit easily and correctly the ball with the golf club having a lower club number. For this reason, the golf player can swing and hit the ball with a substantially equal ease for all the golf clubs from the golf clubs having lower club numbers to the golf clubs having higher club numbers.