Golf club head

Abstract

A golf club having an increased moment of inertia and improved ball-hitting directionality is provided. A metal hollow golf club head comprises: a face portion; a crown portion; and a sole portion, and when the golf club has a lie angle of 60° with its club head volume being within 470 cm 3 , a moment of inertia about the axial line centered on the plumb line passing through the golf club head center of gravity is 5000 to 6000 g-cm 2 . In order to increase the moment of inertia, the thickness of the center portion of the crown portion is reduced by chemical etching, and a mass, including the portion of mass reduction, is positioned in the sole portion on the side of the toe portion; moreover, the separation distance from the center of gravity to the mass is increased.

1 . A golf club, comprising: a face portion positioned on a front surface of a metal hollow golf club head and having a striking face to strike a golf ball; a crown portion forming an upper surface of the club, and a sole portion forming a lower surface of the club, wherein
 the mass of the metal hollow golf club head is 210 g or less,   characteristic time (CT value) of the metal hollow golf club head, relating to a restitution characteristic, is 257 μs or less; and   when a lie angle of the metal hollow golf club head is 60°, volume of the metal hollow golf club head is 470 cm 3  or less, and moment of inertia about an axial line which is the center of a plumb line passing through the center of gravity of the metal hollow golf club head, is in the range 5000 to 6000 g-cm 2 .   
   
   
       2 . The golf club according to  claim 1 , wherein the metal is a titanium alloy sheet member, and a substantial center portion and an outer peripheral portion including sites of the plumb line within the curved surface of the crown portion and/or the sole portion constituting the body differ in thickness. 
   
   
       3 . The golf club according to  claim 1  or  claim 2 , wherein the metal hollow golf club head is formed by joining, by welding, the face portion, the sole portion, the crown portion, and a hosel portion to which the shaft is connected. 
   
   
       4 . The golf club according to  claim 2 , wherein a weight of 20 g or more is positioned at the position of a rotation radius most distant from the plumb line and at the crown portion and/or the sole portion. 
   
   
       5 . The golf club according to  claim 4 , wherein the weight is positioned on a back side of the toe portion. 
   
   
       6 . The golf club according to  claim 5 , wherein toe-side and back-side sites of the sole portion are formed in shapes protruding outward relative to the crown portion, and the weight is positioned in this protruding sole portion. 
   
   
       7 . The golf club according to  claim 1 , wherein
 the metal hollow golf club head has:   a length (X) from the heel portion to the toe portion longer than a length (Y) from the face portion to the rear surface;   a length from the heel to the toe of 127 mm (5 inches) or less;   a length from the sole to the crown of 71.12 mm (2.8 inches) or less; and   a moment of inertia (MOI) within a range calculated using the following approximating equation (1):
   MOI=( aY   2   +bY+c )×( dX+e )/ f   (1) 
   where X is the length from the heel portion to the toe portion, Y is the length from the face portion to the rear surface, and a, b, c, d, e, and f are constants.   
   
   
       8 . The golf club according to  claim 1 , wherein
 the metal hollow golf club head has:   a length (X) from the heel portion to the toe portion longer than a length (Y) from the face portion to the rear surface;   a length from the heel to the toe of 127 mm (5 inches) or less;   a length from the sole to the crown of 71.12 mm (2.8 inches) or less; and   a position of the center of gravity, as seen from the plumb direction, existing within a range encompassed by the following two equations:
     Y=−gX   2   +hX   2   +i   (2) 
     Y=−jX   2   +k   (3) 
   where X is the position in the direction from the heel portion to the toe portion, Y is the position in the direction from the face portion to the rear surface, g, h, j, and k are constants, the X has an origin at the center of the distance from the heel portion to the toe portion, and the Y has an origin in the face surface.