This present invention relates to a hollow golf club head comprising a face portion whose front face defines a club face for hitting a ball, wherein said face portion comprises a center portion forming an area having a sweet spot, and a peripheral portion surrounding the center portion and having the thickness smaller than the thickness of said center portion, wherein the thickness of the peripheral portion is reduced from the sole portion side of the head toward the crown portion side.
1. A hollow golf club head comprising
a face portion whose front face defines a club face for hitting a ball,
a crown portion intersecting the club face at the upper edge thereof, and
a sole portion intersecting the club face at the lower edge thereof, wherein
said face portion comprises a center portion forming an area having a sweet spot, and
a peripheral portion surrounding the center portion and having the thickness smaller than the thickness of said center portion, wherein
the peripheral portion comprises a crown side portion provided between said center portion of the face portion and the crown portion, and a sole side portion provided between said center portion of the face portion and the sole portion,
the thickness of said peripheral portion is reduced from the sole portion side toward the crown portion side, and
a ratio (t 3 /t 2 ) between the thickness t 3 of the sole side peripheral portion and the thickness t 2 of the crown side peripheral portion being in a range of from 1.2 to 2.0, in a vertical cross section passing through a centroid of the club face under a standard condition in which the club head is placed on a horizontal surface at its lie angle and its loft angle.
2. The golf club head according to claim 1 , wherein the thickness of the center portion is substantially fixed.
3. The golf club head according to claim 1 or 2 , wherein the thickness of the center portion is largest in the face portion.
4. A golf club head according to claim 1 , wherein the thickness of the center portion is gradually increased toward a center.
5. The golf club head according to claim 1 , wherein the thickness of the center portion is in a range of from 2.5 to 3.8 mm.
6. The club head according to claim 1 , wherein the profile shape of the center portion is similar to a shape drawn by the edge of the club face.
7. The club head according to claim 1 , wherein the peripheral portion is completely continuous around the center portion.
8. The golf club head according to claim 7 , wherein
the peripheral portion comprises a toe side portion provided between the center portion of the face portion and a toe of the club head and
a heel side portion provided between the center portion of the face portion and a heel of the club head, and
each of the toe and heel side portions has substantially the same thickness at the same height from the horizontal surface.
9. A golf club head according to claim 1 , wherein the peripheral portion is intermittent in the sole portion side.
10. The golf club head according to claim 1 , wherein the thickness of the peripheral portion is smoothly reduced from the sole portion side toward the crown portion side.
11. The golf club head according to claim 1 , wherein
the ratio (t 3 /t 2 ) is in a range of from 1.4 to 2.0.
12. The golf club head according to claim 1 , wherein
the difference (t 1 -t 2 ) between the maximum thickness t 1 of the center portion and the thickness t 2 of the crown side portion in the crown portion side is in a range of from 0.5 to 2.0 mm,
in a vertical cross section passing through a centroid of the club face under a standard condition in which the head is brought into contact with the horizontal surface at prescribed lie angle and loft angle.
13. The golf club head according to claim 1 , wherein in the face portion, the ratio (f/F) between the distance F from a centroid of the club face to an edge of the club face, and the distance f from said centroid to an edge of the center portion is in a range of from 0.4 to 0.8, in an optional straight line K extending from the centroid to the edge of the club face.
14. The golf club head according to claim 1 , wherein the thickness t 3 of the sole side portion is in a range of from 2.0 to 3.5 mm.