Patent Grant
8465379
This application claims priority from Japanese Patent Application No. 2010-029998 filed Feb. 15, 2010, which is incorporated herein by reference in its entirety.
The present invention relates to a golf club head, and specifically relates to a golf club head having an improvement in the thickness of a back surface of a face portion.
Most recent wood clubs have heads, at least the face portions, made of a metal material. A face portion needs to have a sufficiently large thickness to have strength sufficient to withstand impact with a ball. Although the size of heads has been increasing, the size must be less than a volume of 460 cm3 with a tolerance of +10 cm3 by rule. Thus, most drivers now have 460-cm3 large heads extremely close to the upper limit.
Such increase in head size accordingly increases the weight of a face portion. To reduce the weight of a face portion and to retain the strength of the face portion also, the thickness of the face portion is reduced while a rib is provided to a back surface of the face portion. For example, Japanese Patent Application Publication No. 2006-141806 describes a face portion in which six ribs extend from a central portion of the face to circumferential portions of the face.
Meanwhile, if ribs are provided in an X-shaped arrangement on a central portion of a back surface of a face portion, the face portion provides a considerably lower restitution performance when a ball is hit at a sole side or crown side of the face than when at the center of the face. To solve this problem, Japanese Patent Application Publication No. 2008-36050 describes a face portion whose back surface is divided into four segments by such ribs in such a manner that the thicknesses of sole-side and crown-side segments are smaller than those of toe-side and heel-side segments.
Conventionally, a number of high-restitution heads with a remarkably increased coefficient of restitution (hereinafter, COR), have been developed. However, high-restitution heads having a COR of 0.830 or higher cannot be used in competitions after 2008. For this reason, a golf club head having a COR that is not increased at the center of a face portion is currently under development. It has been found, however, that if the COR at the center of a face portion is not increased, the restitution performance at a surface of the face other than the center is reduced; in particular, the performance at a sole side of the face is reduced more than that of a crown side thereof.
In view of the above-described problems, an object of the present invention is to provide a golf club head that includes a face portion having a reduced weight while retaining the strength and having a low restitution performance at a level that conforms to a COR rule, and that is capable of demonstrating a substantially uniform restitution performance, even when a ball is hit off the center of the face.
In order to achieve the above object, a golf club head according to the present invention has a hollow structure, and includes: a face portion having a ball hitting surface; and at least four main ribs disposed on an inner surface of the face portion. In the golf club head, among the four main ribs, a first main rib extends from a center portion of the face portion toward a crown, a second main rib extends from the center portion toward a sole, and the other two main ribs also extend from the center portion toward the outside of the face portion, and the face portion is formed to have such a thickness that the center portion, the first main rib, and the second main rib become thinner in this order.
It is preferable that, among the four main ribs, a third main rib extend from the center portion toward a hosel, a fourth main rib extend from the center portion toward a portion, closer to a toe, of the sole, and the face portion be formed to have such a thickness that the center portion, the third main rib, and the fourth main rib become thinner, in this order.
It is preferable that the face portion be divided by the first to fourth main ribs into four regions: a region on a toe and crown side of the face portion; a region on a toe and sole side thereof; a region on a heel and crown side thereof; and a region on a heel and sole side thereof, and the face portion in the region on the toe and sole side be formed to have a thickness smaller than a thickness in the region on the heel and crown side.
The golf club head according to the present invention preferably includes, at the center portion where the first to fourth main ribs intersect, a center of gravity of the golf club head, which is projected on the surface of the face portion. Furthermore, the golf club head according to the present invention preferably further includes a reinforcement rib disposed on the inner surface of the face portion and extending toward the outside of the face portion from the center portion where the first to fourth main ribs intersect. Furthermore, it is preferable that the reinforcement rib have a thickness gradually reduced from the intersecting portion in the outward direction, and be formed to extend to a position between the center portion and an end portion of the face portion.
In the present invention as described above, at least four main ribs are provided, including the first main rib extending from the center portion toward the crown and the second main rib extending from the center portion toward the sole. Additionally, the face portion is formed to have such a thickness that the center portion, the first main rib, and the second main rib become thinner, in this order. Accordingly, the face portion has a reduced weight while retaining the strength, and the restitution performance of the face portion is reduced to such a level that conforms to a COR rule; furthermore, even when a ball is hit off the center of the face, a substantially uniform restitution performance can be demonstrated.
Hereinafter, a golf club head of an embodiment according to the present invention will be described with reference to the attached drawings.
As shown in
In
As shown in
The first to fourth main ribs 12 to 15 are preferably formed to extend to end portions of the face portion 11 or to the vicinity of the end portions. The intersecting portion 17 of the face portion 11 is surrounded by a substantially flat peripheral portion 19. The peripheral portion 19 is divided by the first to fourth main ribs 12 to 15 into four regions: a toe-crown region 19a, a toe-sole region 19b, a heel-crown region 19c, and a heel-sole region 19d.
All of the first to fourth main ribs 12 to 15 are each formed to have a thickness which is largest at its center and is reduced toward the adjacent substantially flat peripheral portions. For instance, as shown in
Moreover, a thickest portion of at least one of the first to fourth main ribs 12 to 15 is formed to differ in thickness from corresponding portions of the other main ribs. For example, as shown in
The thicknesses of the thickest portions of the main ribs on the crown side and those on the sole side differ from each other by preferably approximately 0.2 mm or larger, more preferably approximately 0.3 mm or larger. Meanwhile, the upper limit of this difference in thickness is preferably approximately 0.7 mm or less, more preferably approximately 0.6 mm or less. Moreover, the thickness of a thickest portion of a thinnest main rib among the first to fourth main ribs 12 to 15 needs to differ from the thickness of the adjacent peripheral portion 19 by at least approximately 0.3 mm or more, preferably approximately 0.5 mm or more, more preferably approximately 0.6 mm or more. Meanwhile, the upper limit of this difference in thickness is preferably approximately 2.0 mm or less, more preferably approximately 1.8 mm or less.
The first to fourth main ribs 12 to 15 are preferably formed to have a substantially equal width. The widths of the first to fourth main ribs 12 to 15 at portions in contact with the back surface of the face portion are preferably approximately 2 mm or more, more preferably approximately 3 mm or more. Meanwhile, the upper limit of the widths of the first to fourth main ribs 12 to 15 are preferably approximately 12 mm or less, more preferably approximately 10 mm or less.
On the back surface of the face portion 11, a reinforcement rib may be formed. As the reinforcement rib, a toe-side reinforcement rib 16a extending from the intersecting portion 17 to the toe-crown region 19a and a heel-side reinforcement rib 16b extending from the intersecting portion 17 to the heel-sole region 19d are formed as shown in
Each reinforcement rib 16 is also formed to have a thickness which is largest at its center and is reduced toward the peripheral portion, as in the case of the main ribs. Meanwhile, the reinforcement rib 16 is formed to have the thickness gradually reduced from the intersecting portion 17 toward the outer edge of the face portion 11 as shown in
The reinforcement rib 16 can be formed from the center portion of the face portion to a position between the central portion and the outer edge. The length of the reinforcement rib 16 is preferably approximately 45% or more, more preferably approximately 50% or more, of the length from the center portion to the outer edge of the face portion 11. Meanwhile, the upper limit of the length of the reinforcement rib 16 is preferably approximately 90% or less, more preferably approximately 85% or less of the above length. The length of the reinforcement rib 16 on the toe side and that of the reinforcement rib 16 on the heel side may be the same or different from each other.
A thickest portion of the reinforcement rib 16 may be as thick as, thicker, or thinner than the thickest portion of a thickest main rib among the first to fourth main ribs 12 to 15. When the thickest portion of the reinforcement rib 16 is thinner or thicker, the difference between the two is preferably approximately 0.1 mm or more but approximately 0.5 mm or less. The width of the thickest portion of the reinforcement rib 16 is preferably approximately 2 mm or more, more preferably approximately 3 mm or more. Meanwhile, the upper limit of the width of the reinforcement rib 16 is preferably approximately 12 mm or less, more preferably approximately 10 mm or less.
The first main rib 12 preferably inclines toward the toe with respect to the vertical direction. The second main rib 13 preferably inclines toward the heel with respect to the vertical direction. The first and second main ribs 12, 13 inclined in this manner allow the restitution performance to be demonstrated to the maximum in an upper portion of the toe and a lower portion of the heel at which amateur golfers are most likely to hit balls. Specifically, as shown in
The third main rib 14 preferably inclines toward the crown or hosel with respect to the horizontal direction. The fourth main rib 15 preferably inclines toward the sole with respect to the horizontal direction. The third and fourth main ribs 14, 15 inclined in this manner allow the restitution performance to be demonstrated to the maximum in an upper portion of the toe. Specifically, an inclination θb of a central line 32 of the third and fourth main ribs 14, 15 with respect to the horizontal line 30 is preferably approximately 5° or more, more preferably approximately 10° or higher. Meanwhile, the upper limit of the inclination θb is preferably approximately 80° or less, more preferably approximately 70° or less. A central axis 33 of the reinforcement rib 16 preferably bisects an angle formed between the central axis 31 of the first and second main ribs 12, 13 and the central axis 32 of the third and fourth main ribs 14, 15 (i.e., the central axis 33 forms an angle θc with each of the central axes 31, 32).
The first and second main ribs 12, 13 may be smoothly curved into an S shape or Z shape instead of extending straight along the central axis 31. The third and fourth main ribs 14, 15 may also be smoothly curved into an S shape or Z shape instead of extending straight along the central axis 32. The main ribs smoothly curved in this manner allow increase in the area of both regions of the toe-crown region 19a and the heel-sole region 19d.
The thickness of the peripheral portion 19 of the face portion 11 is substantially uniform in each region of the toe-crown region 19a, the toe-sole region 19b, the heel-crown region 19c, and the heel-sole region 19d. The thicknesses in the toe-crown region 19a, the toe-sole region 19b, the heel-crown region 19c, and the heel-sole region 19d may be the same or different from one another. Preferably, to make uniform the COR at the peripheral portions of the toe-sole region 19b and the toe-sole region 19c, it is possible to form the toe-sole region 19b thinner than the toe-sole region 19c. This difference in thickness is preferably approximately 0.025 mm or larger, more preferably approximately 0.05 mm or more, and further preferably approximately 0.1 mm or more. Meanwhile, if the difference in thickness is too large, uniform restitution performance may not be obtained in some cases. Accordingly, the upper limit of the difference in thickness is preferably approximately 0.5 mm or less, more preferably approximately 0.4 mm or less.
The thickness of the toe-crown region 19a and the thickness of the toe-sole region 19b may be the same or different from each other. Nevertheless, to make more uniform the COR at portions on the crown side and on the sole side of the face portion, the toe-sole region 19b is preferably thinner than the toe-crown region 19a. This difference in thickness is preferably approximately 0.025 mm or more, more preferably approximately 0.05 mm or more, and further preferably approximately 0.1 mm or more. Meanwhile, if the difference in thickness is too large, uniform restitution performance may not be obtained in some cases. Accordingly, the upper limit of the difference in thickness is preferably approximately 0.5 mm or less, more preferably approximately 0.4 mm or less.
The thickness of the heel-crown region 19c and the thickness of the heel-sole region 19d may be the same or different from each other. When the heel-crown region 19c and the heel-sole region 19d differ in thickness, the difference in thickness is preferably approximately 0.05 mm or more but approximately 0.5 mm or less.
As shown in
The center portion 18 is thicker than the thickest portion of the thickest main rib among the first to fourth main ribs 12 to 15. This difference in thickness is preferably approximately 0.1 mm or more but approximately 0.5 mm or less. In addition, the center portion 18 preferably has a flat circular shape as shown in
The thickest portions of the first to fourth main ribs 12 to 15 are made different in thickness from each other and from the peripheral portion 19 as described above. The thicknesses of the thickest portions of the first to fourth main ribs 12 to 15 are preferably approximately 3.0 mm or larger, more preferably approximately 3.2 mm or larger. Meanwhile, the upper limit of the thicknesses of the first to fourth main ribs 12 to 15 is preferably approximately 4.2 mm or less, more preferably approximately 4.0 mm or less. The thickness of the thickest portion of the reinforcement rib 16 is preferably approximately 3.0 mm or more, more preferably approximately 3.2 mm or more. Meanwhile, the upper limit of the thickness of the reinforcement rib 16 is preferably approximately 4.2 mm or less, more preferably approximately 4.0 mm or less.
The thickness of the peripheral portion 19 may differ among the toe-crown region 19a, the toe-sole region 19b, the heel-crown region 19c, and the heel-sole region 19d as described above. The thickness of the peripheral portion 19 is preferably approximately 1.0 mm or more, more preferably approximately 1.5 mm or more. Meanwhile, the upper limit of the thickness of the peripheral portion 19 is preferably approximately 3.0 mm or less, more preferably approximately 2.5 mm or less. The thickness of the center portion 18 differs from the thicknesses of the main ribs 12 to 15 as described above, and is preferably approximately 2.5 mm or more, more preferably approximately 2.7 mm or more. Meanwhile, the upper limit of the thickness of the center portion 18 is preferably approximately 4.0 mm or less, more preferably approximately 3.8 mm or less.
The face member 10 can be formed by any one of forging and casting. As the material of the face member 10, titanium, titanium alloy, stainless steel, or the like can be used. The volume of the golf club head 1 is preferably approximately 100 cc or larger, more preferably approximately 150 cc or larger. Meanwhile, the volume of the golf club head 1 is preferably approximately 500 cc or less, more preferably approximately 460 cc or less. The weight of the golf club head 1 is preferably approximately 170 g or more, more preferably approximately 175 g or more. Meanwhile, the weight of the golf club head 1 is preferably approximately 250 g or less, more preferably approximately 245 g or less.
Note that, in the above-described embodiment, the reinforcement ribs 16 are provided as shown in
Golf club heads according to the present invention were prepared, and the coefficients of restitution (CORs) at face portions were evaluated. In the present examples, instead of actually measuring the COR values, the characteristic times (CTs) were measured. The CT value is a quantitative value and can be used to measure easily with high accuracy the spring effect of a face, which is adopted by the United States Golf Association (USGA) and Royal and Ancient Golf Club of St Andrews (R&A). The CT value can be measured with a portable pendulum machine (portable pendulum tester) approved by R&A Rules Limited. Generally, a face that flexes well causes a small loss in energy, and accordingly allows a high initial speed of the ball. For this reason, the CT value expresses such flexure with a contact time between a ball and a face. Now, by the rule, the uppermost limit is set at 257 (specified 239 with a tolerance of 18) μsec.
The golf club head of Example 1 was provided with the first to fourth main ribs and the reinforcement ribs as shown in
Note that the common conditions for the face portion were as follows. The width of the face portion was 75 mm; the height thereof was 43 mm; the first to fourth main ribs were inclined, as in
In each of Examples and Comparative Example, the CT values at ball-hitting points were measured. The CT values were measured with the ball-hitting points set at 15 hitting points which were different from one another in the vertical and horizontal directions as shown in
Under these conditions, the CT values were measured at the hitting points in Examples 1 to 3 and Comparative Example. Tables 2 to 5 show the results. Note that, in Tables 2 to 5, the position of the central hitting point 40c was set at 0 mm. The distance toward the crown or heel was expressed as a positive value, while the distance toward the sole or toe was expressed as a negative value.
As shown in Table 5, in the golf club head of Comparative Example in which the center portion, the main ribs, and the reinforcement ribs were all formed to have the same thickness, the CT values at the four hitting points 40bH, 40bL, 40dH, 40dL which were away from the central hitting point 40c in the crown-heel direction and in the toe-heel direction by ±10 mm were smaller than the CT values at the central hitting point 40c by 10 to 27 μsec. Meanwhile, in the golf club head of Example 1 in which the thicknesses of the first and third main ribs on the crown side were smaller than the thickness of the center portion by 0.2 mm and the thicknesses of the second and fourth main ribs on the sole side were smaller than the thicknesses of the first and third main rib on the crown side by 0.3 mm, the CT values at the four hitting points 40bH, 40bL, 40dH, 40dL were smaller than the CT value at the central hitting point 40c only by 5 to 14 μsec, indicating that the CT values of the face portion were more uniform than those in Comparative Example.
In the golf club head of Example 2 in which the thickness of the peripheral portion in the toe-sole region was smaller than the thickness thereof in the heel-crown region by 0.5 mm, the difference in CT value between the four hitting points 40bH, 40bL, 40dH, 40dL and the central hitting point 40c was 1 to 10 μsec, indicating that the CT values of the face portion were further uniform. In the golf club head of Example 3 in which no reinforcement rib was provided, the difference in CT value between the four hitting points 40bH, 40bL, 40dH, 40dL and the central hitting point 40c was 1 to 10 μsec, indicating that the CT values of the face portion was uniform as those in Example 2.
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