Iron type golf club head

1. An iron-type golf club head comprising:

a heel,

a toe,

a sole,

a top-line of the iron-type club head,

a striking face having a forward-facing ball-striking surface, a rearward-facing surface, and an ideal striking location; and

a perimeter weight surrounding the striking face;

wherein the striking face has a supported region supported by the perimeter weight and an unsupported region, with the ideal striking location lying within the unsupported region, the unsupported region having a thickness that varies in a heel-toe direction;

wherein a heel portion of the unsupported region of the striking face is located on a heel side of an imaginary vertical plane that extends perpendicularly to the ground plane and that contains an imaginary line that extends in a direction normal to the striking face at the ideal striking location when the clubhead is in the normal address position, and wherein a toe portion of the unsupported region of the face is located on a toe side of the imaginary plane;

wherein the clubhead has a relative coefficient of restitution of at least −0.030; and

wherein the following two inequalities are satisfied:

SA TOE >SA HEEL ,  (1)

and

[(Σ n=1 N E n t n 3 )÷ N ]÷[(Σ m=1 M E m t m 3 )÷ M ]>1.1;  (2)

wherein:

SA TOE is defined as the surface area of the toe portion of the unsupported region,

SA HEEL is defined as the surface area of the heel portion of the unsupported region,

E n and t n are the effective Young's Modulus value and the thickness, respectively, for the n th cross-section of the toe portion of the unsupported region of the striking face,

E m and t m are the effective Young's Modulus value and the thickness, respectively, for the m th cross-section of the heel portion of the unsupported region of the striking face,

and N and M have values determined by discretizing SA TOE and SA HEEL , respectively, into 1 mm×1 mm sections;

wherein the golf club head has a hollow construction defining an interior cavity;

wherein a hitting region of the unsupported region of the striking face lies within an imaginary circle drawn on the ball-striking surface, with the imaginary circle having a radius of 20 mm and having a center located at the ideal striking location.

2. The club head of claim 1 wherein the interior cavity is at least substantially filled with a filler material.

3. The club head of claim 2 wherein the filler material is an expandable foam.

4. The club head of claim 3 wherein the filler material has a density between about 0.03 and 0.19 g/cm 3 .

5. The club head of claim 2 wherein the filler material is selected from the group of foamed polymers, ionomers and visoelastic elastomers.

6. An iron-type golf club head comprising:

a heel,

a toe,

a sole,

a top-line of the iron-type club head,

a striking face having a forward-facing ball-striking surface, a rearward-facing surface, and an ideal striking location; and

a perimeter weight surrounding the striking face;

wherein the striking face has a supported region supported by the perimeter weight and an unsupported region, with the ideal striking location lying within the unsupported region, the unsupported region having a thickness that varies in a heel-toe direction;

wherein a heel portion of the unsupported region of the striking face is located on a heel side of an imaginary vertical plane that extends perpendicularly to the ground plane and that contains an imaginary line that extends in a direction normal to the striking face at the ideal striking location when the clubhead is in the normal address position, and wherein a toe portion of the unsupported region of the face is located on a toe side of the imaginary plane;

wherein the clubhead has a relative coefficient of restitution of at least −0.030; and

wherein the following two inequalities are satisfied:

SA TOE >SA HEEL ,  (1)

and

[(Σ n=1 N E n t n 3 )÷ N ]÷[(Σ m=1 M E m t m 3 )÷ M ]>1.1;  (2)

wherein:

SA TOE is defined as the surface area of the toe portion of the unsupported region,

SA HEEL is defined as the surface area of the heel portion of the unsupported region,

E n and t n are the effective Young's Modulus value and the thickness, respectively, for the n th cross-section of the toe portion of the unsupported region of the striking face,

E m and t m are the effective Young's Modulus value and the thickness, respectively, for the m th cross-section of the heel portion of the unsupported region of the striking face,

and N and M have values determined by discretizing SA TOE and SA HEEL , respectively, into 1 mm×1 mm sections;

wherein the golf club head has a hollow construction defining an interior cavity;

wherein the interior cavity is at least substantially filled with a filler material;

wherein the striking face includes a separate striking plate attached to the perimeter weight.

7. The club head of claim 6 wherein the striking plate is attached by welding.

8. An iron-type golf club head comprising:

a heel,

a toe,

a sole,

a top-line of the iron-type club head,

a striking face having a forward-facing ball-striking surface, a rearward-facing surface, and an ideal striking location; and

a perimeter weight surrounding the striking face;

wherein the striking face has a supported region supported by the perimeter weight and an unsupported region, with the ideal striking location lying within the unsupported region, the unsupported region having a thickness that varies in a heel-toe direction;

wherein a heel portion of the unsupported region of the striking face is located on a heel side of an imaginary vertical plane that extends perpendicularly to the ground plane and that contains an imaginary line that extends in a direction normal to the striking face at the ideal striking location when the clubhead is in the normal address position, and wherein a toe portion of the unsupported region of the face is located on a toe side of the imaginary plane;

wherein the clubhead has a relative coefficient of restitution of at least −0.030; and

wherein the following two inequalities are satisfied:

SA TOE >SA HEEL ,  (1)

and

[(Σ n=1 N E n t n 3 )÷ N ]÷[(Σ m=1 M E m t m 3 )÷ M ]>1.1;  (2)

wherein:

SA TOE is defined as the surface area of the toe portion of the unsupported region,

SA HEEL is defined as the surface area of the heel portion of the unsupported region,

E n and t n are the effective Young's Modulus value and the thickness, respectively, for the n th cross-section of the toe portion of the unsupported region of the striking face,

E m and t m are the effective Young's Modulus value and the thickness, respectively, for the m th cross-section of the heel portion of the unsupported region of the striking face,

and N and M have values determined by discretizing SA TOE and SA HEEL , respectively, into 1 mm×1 mm sections;

wherein the golf club head has a hollow construction defining an interior cavity;

wherein the interior cavity is at least substantially filled with a filler material;

further including at least one weighting element located on the club head to adjust a center of gravity of the clubhead.

9. A clubhead for an iron-type golf club comprising:

a heel,

a toe,

a sole,

a top-line of the iron-type golf club clubhead,

a striking face having a forward-facing ball-striking surface, a rearward-facing surface, and an ideal striking location; and

a perimeter weight surrounding the striking face;

wherein the striking face has a supported region supported by the perimeter weight and an unsupported region, with the ideal striking location lying within the unsupported region, the unsupported region having a thickness that varies in a heel-toe direction;

wherein a heel portion of the unsupported region of the striking face is located on a heel side of an imaginary center vertical plane that extends perpendicularly to the ground plane and that contains an imaginary line that extends in a direction normal to the striking face at the ideal striking location when the clubhead is in the normal address position, and wherein a toe portion of the unsupported region of the face is located on a toe side of the imaginary plane;

wherein a hitting region of the unsupported region of the striking face lies between an imaginary heel side vertical plane and an imaginary toe side vertical plane, where the heel side vertical plane is spaced 20 mm to the heel side and is parallel to the center vertical plane, and the toe side vertical plane is spaced 20 mm to the toe side and is parallel to the center vertical plane;

wherein the club head has a hollow construction defining an interior cavity;

wherein the interior cavity is at least substantially filled with an expandable foam;

wherein a mean point-wise cross sectional bending stiffness of the toe portion of the unsupported region is larger than the mean point-wise cross sectional bending stiffness of the heel portion of the unsupported region; and

wherein the striking face has an ideal striking location and the club head has a localized stiffened region toward of the ideal striking location.

10. The club head of claim 9 wherein the localized stiffened region has a geometric shape selected from one of an inverted cone, triangle, square, trapezoid or irregular shape.

11. The club head of claim 9 wherein the filler material has a density between about 0.03 and 0.19 g/cm 3 .

12. The club head of claim 9 wherein the striking face includes a separate striking plate attached to the perimeter weight.

13. The club head of claim 12 wherein at least a portion of the striking plate has a thickness of about 1.8 to 2.0 mm.

14. The club head of claim 12 wherein at least a portion of the striking plate has a thickness of about 1.7 to 2.5 mm.

15. The club head of claim 12 wherein the striking plate is attached by welding.

16. The club head of claim 9 wherein at least one weighting element located on the club head to adjust a center of gravity of the clubhead.

17. The club head of claim 9 wherein the clubhead has a relative coefficient of restitution of at least −0.030; and

wherein the following two inequalities are satisfied:

SA TOE HR >SA HEEL HR ,  (1)

and

[(Σ n=1 N E n t n 3 )÷ N ]÷[(Σ m=1 M E m t m 3 )÷ M ]>1.4;  (2)

wherein:

SA TOE HR is defined as the surface area of the toe portion of the hitting region,

SA HEEL HR is defined as the surface area of the heel portion of the hitting region,

E n and t n are the effective Young's Modulus value and the thickness, respectively, for the n th cross-section of the toe portion of the hitting region of the striking face,

E m and t m are the effective Young's Modulus value and the thickness, respectively, for the m th cross-section of the heel portion of the hitting region of the striking face,

and N and M have values determined by discretizing SA TOE HR and SA HEEL HR , respectively, into 1 mm×1 mm sections.

18. The club head of claim 9 wherein the localized stiffened region is an inverted cone having a symmetrical donut shaped area of increased thickness with a center located toward of the ideal striking location.