GOLF CLUB HEAD

Abstract

A golf club head has a face portion with a thick-walled portion located in the center of the face portion and an outer peripheral portion located on an outer periphery of the thick-walled portion. The thick-walled portion has a central portion of the face portion having a largest thickness, a first ridge which surrounds the central portion and has a smaller thickness than the central portion, and a first valley which is located between the central portion and the first ridge and has a smaller thickness than the first ridge. The golf club head maintains a low weight of a face portion and suppresses dispersion of CT values at each hitting point so that the CT values at hitting points other than a sweet spot are substantially equal to the CT value at the sweet spot.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a golf club head, and more particularly, relates to a golf club head having a thick-walled portion of which the thickness varies depending on positions thereof, provided on the back surface of a face member.

2. Description of Related Art

Most recent wood club heads are configured so that at least a face portion is formed of a metallic material. The wall thickness of the face portion must be increased so as to maintain a strength capable of withstanding a shock of impact by a ball. The increase in head size continues, but on the other hand, the rules specify that the volume of a club head must be less than 460 cm³ plus an allowable error of 10 cm³. Therefore, the head volumes of most drivers are very close to the upper 460 cm³ limit. When the head size is increased, the sweet area expands, the peripheral weight distribution is emphasized, and the transverse and vertical moment of inertia increases, so that an error at the time of off-center hitting can be alleviated. However, if the head size is increased and thereby the head weight is also increased, the swing balance increases and the head speed drops, by which the carry may be decreased. To solve this problem, measures have been taken: the whole of the head may be formed of titanium or an alloy thereof (unless specially mentioned, hereinafter, “titanium or an alloy thereof” is referred to as “titanium”) having a low specific gravity and a high strength, or a composite head of carbon and titanium.

Also, many types of highly resilient heads having not only a large head size, but also a high restitution coefficient of the head, have been developed. From the year 2008, a highly resilient head having a restitution coefficient of 0.830 or more cannot be used in competition. So far, a thick-walled face material having an increased restitution coefficient has been used positively along with the increase in head size. However, even if a highly resilient head is used, when a ball is hit by a face portion other than the sweet area, that is, at the time of off-center hitting, a spring effect cannot be anticipated, and the carry tends to decrease extremely.

To solve such a problem, there has been developed such a golf club head which is provided with a thick-walled portion surrounding the center of the back surface of a face member so as to decrease the thickness at the center of the face so that when a ball is hit at a position off the sweet spot, a high initial velocity can be imparted to the ball. Refer to U.S. Pat. No. 6,824,475, FIG. 5A.

Additionally, there has been developed a golf club head which is provided with a protruding block in the center of the back surface of a face and two annular ribs surrounding this protruded block, thereby increasing the strength of the golf club head and further enabling a stabilized hitting. Refer to U.S. Pat. No. 7,448,961, FIG. 1.

However, in the golf club heads described in U.S. Pat. Nos. 6,824,475 and 7,448,961 above, because the back surface of the face is provided with an intensified thickness, the weight of an entire head is increased as compared to a case in which the back surface is provided with no increased thickness. Furthermore, there is another problem in that a value indicating the resilience performance of a ball, called the CT value (Contact Time Value), may vary depending on a hitting point of the ball.

SUMMARY OF THE INVENTION

In view of the above-described problems, an object of the present invention is to provide a golf club head maintaining a low weight of the face member and suppressing dispersion of CT values of the face member so that the CT values at hitting points other than a sweet spot are substantially equal to the CT value at the sweet spot.

To achieve the above-described object, a golf club head of the present invention has a face portion formed of metallic material, in which the face portion includes a thick-walled portion located in the center of the face portion and an outer peripheral portion located on an outer periphery of the thick-walled portion, and in which the thick-walled portion includes a central portion of the face portion having a largest thickness, a first ridge which surrounds the central portion and has a smaller thickness than the central portion, and a first valley which is located between the central portion and the first ridge and has a smaller thickness than the first ridge.

According to another embodiment of the golf club head, the thick-walled portion has a shape depressed substantially circularly toward the center of the face portion on two sides opposing each other of a substantially circular shape or a substantially elliptical shape.

According to another embodiment of the golf club head, the substantially circular depressions are so configured that the depression on the toe side is directed obliquely with respect to the sole direction and the depression on the heel side is directed obliquely with respect to the crown direction.

According to another embodiment of the golf club head, the length from the upper side to the lower side of the first valley is 30 to 50% the height of the face portion passing through the center of the face portion.

According to another embodiment of the golf club head, the length from the upper side to the lower side of the first ridge is 40 to 60% the height of the face portion passing through the center of the face portion.

According to another embodiment of the golf club head, a difference between the thickness of the central portion and the thickness of the first ridge is 0.05 to 0.5 mm, and a difference between the thickness of the first ridge and the thickness of the first valley is 0.05 to 0.3 mm.

According to another embodiment of the present invention, the thick-walled portion further includes a second ridge which surrounds the first ridge and has a smaller thickness than the first ridge, and a second valley which is located between the first ridge and the second ridge and has a smaller thickness than the second ridge.

The golf club head of the present invention has a face portion formed of metallic material, and the face portion includes a thick-walled portion located in the center of the face portion and an outer peripheral portion located on an outer periphery of the thick-walled portion. The thick-walled portion has a shape depressed substantially circularly toward the center of the face portion on two sides opposing each other of a substantially circular shape or a substantially elliptical shape. The thick-walled portion includes a central portion of the face portion having a largest thickness, a first ridge which surrounds the central portion and has a smaller thickness than the central portion, and a first valley which is located between the central portion and the first ridge and has a smaller thickness than the first ridge. Consequently, a low weight of the face portion is maintained and dispersion of the CT values at each hitting point is suppressed, so that the CT values at hitting points other than a sweet spot are substantially equal to the CT value at the sweet spot. Thus, even if a ball is hit at a position off the sweet spot, the carry can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an embodiment of a golf club head according to the present invention;

FIG. 2 is a schematic sectional view of the golf club head taken along the line II-II of FIG. 1;

FIG. 3 is a rear side view of a face portion constituting the golf club head shown in FIG. 1.

FIG. 4 is a schematic sectional view of the face portion taken along the line III-III of FIG. 3;

FIG. 5 is a rear side view indicating the heights of the face portion, a first valley and a first ridge of the face portion shown in FIG. 3;

FIG. 6 is a rear side view showing the angle of an ellipse in the face portion shown in FIG. 3;

FIG. 7 is a rear side view of a face portion according to a second embodiment;

FIG. 8 is a schematic sectional view of a face portion according to a third embodiment;

FIG. 9 is a schematic sectional view of a face portion according to a fourth embodiment;

FIG. 10 is a rear side view of a face portion according to a fifth embodiment;

FIG. 11 is a rear side view showing hitting points in a simulation of an Example;

FIG. 12 is a schematic sectional view of a face portion according to a comparative example; and

FIG. 13 is a graph showing a simulation result of CT values of the example and the comparative example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the golf club head according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a front view showing an embodiment of the golf club head according to the present invention and FIG. 2 is a schematic sectional view of the golf club head taken along the line II-II of FIG. 1.

As shown in FIGS. 1 and 2, a golf club head 1 is constituted of a face member 10 having a face portion and a main body member 30. The main body member 30 includes a crown portion 4, a sole portion 5, a hosel portion 6, and a side portion 7, and these portions are formed integrally. This face member 10 and the main body member 30 are joined together by welding, so that a hollow structure is formed in the interior of the golf club head 1. In the meantime, the surface of the hollow structure side of the face member 10, that is, a structure appearing on the back surface is indicated by dotted lines. On the back surface of the face member 10, an asperity is formed to vary the thickness of the face member 10. The back surface of the face member 10 will be described.

FIG. 3 shows the back surface of the face member 10 which constitutes the golf club head 1 shown in FIG. 1. FIG. 4 is a schematic sectional view taken along the line III-III of FIG. 3. The sectional view of FIG. 4 is intended to make the structure of the present invention understood easily, but it is not depicted faithfully according to a scale.

As shown in FIG. 3, a thick-walled portion 16 is formed within an ellipse shown by line 13 on an outer peripheral portion 12 having a flat surface of the back surface of the face member 10. In both end portions of the long axis of the ellipse, depressions 15a and 15b are formed in the thick-walled portion 16, so that they are depressed circularly toward the center thereof. That is, the thick-walled portion 16 is surrounded by the depressions 15 and the elliptical line 13 on both side portions of the short axis of the ellipse.

As shown in FIGS. 3 and 4, a substantially trapezoidal central portion 17 having a largest thickness T₁ in the face member 10 and having a flat surface is formed in the center of the thick-walled portion 16. The thickness is decreased gradually toward the elliptical line 13 from this central portion 17 and after that, is increased gradually. That is, a first valley 19 is formed to surround the central portion 17.

The thickness is increased gradually again toward the elliptical line 13 from the first valley 19 and after that, is decreased gradually again. That is, a first ridge 18 is formed to surround the first valley 19.

Furthermore, the thickness is decreased gradually from the first ridge 18 toward the elliptical line 13 or the depressions 15. As shown in FIG. 4, the thickness from the elliptical line 13 or the depressions 15 up to an outer edge of the face member 10, that is, the thickness of the outer peripheral portion 12, is constant.

The thickness T₁ of the central portion 17 is preferred to be 2.0 to 3.8 mm. Preferably, a thickness T₂ of the first ridge 18 is smaller than the thickness T₁ of the central portion 17 and 2.0 to 3.6 mm. Preferably, a difference between T₁ and T₂ is 0.05 mm and more preferably, 0.1 or more. Furthermore, this difference is preferably not more than 0.5 mm and more preferably not more than 0.4 mm.

Preferably, the thickness T₃ of the first valley 19 is less than the thickness T₂ of the first ridge 18 and 0.03 to 0.3 mm. A difference between T₂ and T₃ is preferably at least 0.05 mm and more preferably at least 0.2 mm. Furthermore, this difference is preferably not more than 0.3 mm and more preferably not more than 0.2 mm.

Preferably, the thickness T₄ of the outer peripheral portion 12 is smaller than the thickness T₃ of the first valley 19 and 1.5 to 2.5 mm. A difference between T₃ and T₄ is preferably at least 0.1 mm and more preferably at least 0.3 mm. Furthermore, this difference is preferably not more than 1.5 mm and more preferably not more than 1.0 mm. Setting the thickness of the outer peripheral portion 12 in this range enables the weight of the face portion to be decreased.

As described above, the thick-walled portion 16 is so constructed that the thickness is decreased gradually from T₁ to T₃ from an edge of the central portion 17 toward the first valley 19, then increased gradually from T₃ to T₂ from the first valley 19 toward the first ridge 18 and decreased again gradually from T₂ to T₄ from the first ridge 18 toward the depressions 15. The thickness T₄ of a region outside the depressions 15, that is, the outer peripheral portion 12, is constant.

The central portion 17 contains a sweet spot of the golf club head 1. This central portion 17 also contains an intersection of the long axis and the short axis of the ellipse shown by the line 13, namely the center of the ellipse. The intersection and the sweet spot may be identical to each other or different from each other.

Referring to FIG. 5, the height of the face member 10 passing through the center of the face member 10 is H₁. A length from the upper side to the lower side of the first ridge 18 in a height direction of the face member 10 is H₂. Likewise, a length from the upper side to the lower side of the first valley 19 is H₃, and a length from the upper side to the lower side of the edge of the central portion 17 is H₄. Preferably, H₂ is 40 to 60% H₁. H₃ is preferably 30 to 50% H₁. H₄ is preferably 10 to 40% H₁.

As shown in FIG. 6, the long axis of the ellipse represented by the line 13 is inclined toward the crown side on the side of the toe 3 and toward the sole side on the side of the heel 2. This inclination is designed to correspond to a fact that generally, hitting points attained by golfers are distributed eccentrically in the crown side on the side of the toe 3 and in the sole side on the side of the heel 2. More specifically, preferably, the ellipse is arranged such that the inclination θ of the long axis 42 thereof is approximately 5° or more with respect to a horizontal line 40 when a golf club head is placed at an ordinary address position and more preferably so that the inclination θ is approximately 10° or more. Furthermore, the inclination θ of the long axis 42 of the ellipse is preferably not more than approximately 40° and more preferably not more than approximately 30°.

A ratio between the length of the long axis and the length of the short axis of the ellipse shown by the line 13 is preferably in a range of 100:50 to 50:50 and more preferably in a range of 95:50 to 70:50 (Of course, if the long axis and the short axis are equal in length, not an ellipse but a circle is formed). Preferably, a ratio between the length of the long axis on the thick-walled portion 16 (that is, a length between the depressions 15a and 15b) and the length of the short axis of the ellipse is in a range of 5:4 to 5:6. The curvature radius of the depression 15a on the side of the sole is preferably at least approximately 12 mm and more preferably at least approximately 13 mm. The curvature radius of the depression 15a on the side of the sole is preferably not more than approximately 25 mm and more preferably not more than approximately 20 mm.

The face member 10 may be formed either by forging or casting. As the material of the face member 10, titanium, titanium alloy or stainless steel may be used. The volume of the golf club head 1 is preferably at least approximately 160 cc and more preferably as large as at least approximately 350 cc. On the other hand, the volume of the golf club head 1 is preferably not more than approximately 500 cc and more preferably not more than approximately 480 cc. Furthermore, the weight of the golf club head 1 is preferably at least approximately 150 g and more preferably at least approximately 160 g. On the other hand, the weight of the golf club head 1 is preferably not more than approximately 250 g and more preferably as light as not more than approximately 200 g.

Although FIG. 4 shows the surface of the hitting side of the face member 10 in a flat shape in order to make the structure of the present invention understood easily, a bulge having a curvature radius of 250 to 800 mm may be formed on the hitting surface of the face member 10. Likewise, a roll having a curvature radius of 250 mm to 800 mm may be formed on the hitting surface of the face member.

As shown in FIG. 1, the present invention has been described for a case in which an entire face portion of the golf club head 1 is made of the face member 10. However, the present invention is not limited to this embodiment, but for example, it is permissible to form a central portion of the face portion with a face member while a remaining portion on both ends of the face portion may be formed integrally with a head main body.

FIG. 7 shows a second embodiment of the face member 10. Unlike FIG. 3, the thick-walled portion 16 is in an elliptical shape surrounded by the elliptical line 13. The central portion 17 is also in an elliptical shape and the center of this central portion 17 is equal to the center of the elliptical line 13. Then, the first valley 19 and the first ridge 18 are formed sequentially to surround this central portion 17. That is, the central portion 17, the first valley 19, the first ridge 18 and the elliptical line 13 form a concentric ellipse.

FIG. 8 is a schematic sectional view of a third embodiment of the face portion 10. Unlike in FIG. 4, the first valley 19 having a thickness T₃ has a certain area. Furthermore, the first ridge 18 having a thickness T₂ has a certain area.

FIG. 9 is a schematic sectional view of a fourth embodiment of the face portion 10. Unlike in FIG. 4, the thickness is not decreased gradually from an edge of the central portion 17 toward the first valley 19; the first valley 19 is located just below the edge of the central portion 17. Furthermore, the thickness is not decreased gradually from the first ridge 18 toward the depressions 15; the first ridge 18 is located just above the depressions 15.

FIG. 10 is a rear side view of a fifth embodiment of the face portion 10. According to this embodiment, a second valley 22 and a second ridge 21 are formed sequentially in the face portion 10 to surround the first ridge 18.

The thickness of the second valley 22 is less than the thickness T₃ of the first valley 19 and greater than or equal to the thickness T₄ of the outer peripheral portion 12. A difference between the thickness of the second valley 22 and the thickness T₃ of the first valley 19 is preferably at least 0.1 mm and more preferably at least 0.3 mm. This difference is preferably not more than 1.0 mm and more preferably not more than 0.8 mm.

The thickness of the second ridge 21 is less than the thickness T₂ of the first ridge 18 and greater than the thickness of the second valley 22. A difference between the thickness of the second ridge 21 and the thickness T₂ of the first ridge 18 is preferably at least 0.1 mm and more preferably at least 0.3 mm. Furthermore, this difference is preferably not more than 1.5 mm and more preferably not more than 1.0 mm.

As shown in FIG. 10, thin-walled portions 14a and 14b each having a smaller thickness than the outer peripheral portion 12 may be provided in regions surrounded by the elliptical lines 13 on both end portions of the long axis of the ellipse and by depressions 15a and 15b. A difference in the thickness between the thin-walled portion 14 and the outer peripheral portion 14 is preferably at least approximately 0.1 mm and more preferably at least approximately 0.2 mm. The thickness of the thin-walled portion 14 is preferably at least approximately 1.8 mm and more preferably at least approximately 1.9 mm. On the other hand, the thickness of the thin-walled portion 14 is preferably not more than approximately 2.2 mm and more preferably not more than approximately 2.1 mm. Setting the thickness of the thin-walled portion 14 within this range enables improvement of resilience performance on the toe side and the heel side normally having a low resilience property.

Examples

A CT value (Contact Time Value) of a face member of the present invention was calculated through a simulation using a computer (Example 1). The face member was constructed in the structure shown in FIG. 3 and FIG. 4. As a design condition of the face member, the thickness T₁ of the central portion 17 was set to 3.7 mm, the thickness T₂ of the first ridge 18 was set to 3.5 mm, the thickness T₃ of the first valley 19 was set to 3.0 mm and the thickness T₄ of the outer peripheral portion 12 was set to 2.4 mm. The height H₁ of the face member 10 was set to 50 mm, the length H₂ from the upper side to the lower side of the first ridge 18 was set to 30 mm, the height H₃ from the upper side to the lower side of the first valley 19 was set to 20 mm and the length H₄ from the upper side to the lower side of the central portion 17 was set to 14 mm. Furthermore, the length of the long axis of the ellipse was set to 64 mm, the length of the short axis was set to 40 mm and an angle θ of the ellipse was set to 15°. The curvature radius of the depression 15b on the side of the toe 3 was set to 32 mm and the curvature radius of the depression 15a on the side of the heel 2 was set to 12 mm. A ratio of the area between the outer peripheral portion 12 and the thick-walled portion 16 which occupy the entire face portion was set to 7:5. This ratio was calculated with the central portion 17 included in the thick-walled portion 16, and the central portion 17 was approximately 3% of the entire face portion.

The face member 10 was supposed to be made of titanium alloy, so that the Young's modulus thereof was 108 GPa and the Poisson ratio thereof was 0.30.

As shown in FIG. 11, five different hitting points in a horizontal direction were investigated. A hitting point 50c in the center was assumed to be a hitting point on the sweet spot and within the central portion 17 of the face member. Four other hitting points were assumed to be hitting points apart from the sweet spot. The hitting points 10 mm apart from the hitting point 50c in the center to the sides of the toe 3 and the heel 2 within the thick-walled portion 16 were designated as hitting points 50b and 50d, whereas the hitting points 20 mm apart from the hitting point 50c to the sides of the toe 3 and the heel 2 within the thick-walled portion 16 were designated as hitting points 50a and 50e.

The hitting point 50a and the hitting point 50e are located substantially between the first ridge 18 and the depressions 15. Furthermore, the hitting point 50b and the hitting point 50d are located substantially between an edge of the central portion 17 and the first valley 19.

Furthermore, as a comparison, the same simulation as described above was implemented about a face member in which the thick-walled portion of the Example 1 had a section shown in FIG. 12 (Comparative Example 1). The face member is so constructed that a thickness T₁₁ of the central portion was 3.7 mm at maximum such that the thickness is decreased gradually from the central portion toward the edge of the thick-walled portion. A thickness T₁₂ of an edge of the thick-walled portion was 2.4 mm.

A simulation result of the above-described Example 1 and Comparative Example 1 is shown in FIG. 13 and Table 1. In the meantime, in the graph shown in FIG. 13, the position of the hitting point 50c in the center was assumed to be 0 mm and a distance toward the heel side was represented by a positive value, whereas a distance toward the toe side was represented by a negative value.

TABLE 1
Expected CT Values of each Hitting Point
Expected	Hitting	Hitting	Hitting	Hitting	Hitting
CT value	point 50a	point 50b	point 50c	point 50d	point 50e
(μsec)	(−20 mm)	(−10 mm)	(0 mm)	(10 mm)	(20 mm)
Comparative	234	241	238	243	246
example 1
Example 1	239	241	238	241	241

In the Comparative Example 1 in which the thickness is decreased gradually from T₁₁ to T₁₂ from the central portion toward the periphery of the thick-walled portion as shown in FIG. 13 and Table 1, the CT value at the hitting point 50a (20 mm to the toe side) was 234 microseconds and the CT value at the hitting point 50e (20 mm to the heel side) was 246 microseconds. That is, there was a large dispersion in the CT value depending on the hitting point.

In contrast, in the Example 1 using the face portion of the present invention, the CT value at the hitting point 50a (20 mm to the toe side) was 239 microseconds and the CT value at the hitting point 50e (20 mm to the heel side) was 241 microseconds. That is, as compared to the Comparative Example 1, the dispersion in the CT value of each hitting point was decreased so that the CT values were substantially equal. In view of this result, it is evident that even if a ball is hit at a position apart from the sweet spot, resilience performance near when the ball is hit at the sweet spot can be exerted.

The weight of the face member of the Comparative Example 1 was 32.8 g whereas the weight of the face member 10 of the Example 1 was 32.0 g. That is, reduction of the weight by 0.8 g was achieved.

Claims

1. A golf club head comprising a face portion formed of metallic material, the face portion comprising a thick-walled portion located in the center of the face portion and an outer peripheral portion located on an outer periphery of the thick-walled portion, and the thick-walled portion comprising a central portion of the face portion having a largest thickness, a first ridge which surrounds the central portion and has a smaller thickness than the central portion, and a first valley which is located between the central portion and the first ridge and has a smaller thickness than the first ridge.

2. A golf club head according to claim 1, wherein the thick-walled portion has a shape depressed substantially circularly toward the center of the face portion on two sides opposing each other of a substantially circular shape or a substantially elliptical shape.

3. A golf club head according to claim 2, wherein the substantially circular depressions are so configured that the depression on the toe side is directed obliquely with respect to the sole direction and the depression on the heel side is directed obliquely with respect to the crown direction.

4. A golf club head according to claim 1, wherein the length from the upper side to the lower side of the first valley is 30 to 50% the height of the face portion passing through the center of the face portion.

5. A golf club head according to claim 1, wherein the length from the upper side to the lower side of the first ridge is 40 to 60% the height of the face portion passing through the center of the face portion.

6. A golf club head according to claim 1, wherein a difference between the thickness of the central portion and the thickness of the first ridge is 0.05 to 0.5 mm, and a difference between the thickness of the first ridge and the thickness of the first valley is 0.05 to 0.3 mm.

7. A golf club head according to claim 1, wherein the thick-walled portion further comprises a second ridge which surrounds the first ridge and has a smaller thickness than the first ridge, and a second valley which is located between the first ridge and the second ridge and has a smaller thickness than the second ridge.