GOLF CLUB HEAD

Abstract

A hollow golf club head according to this invention includes a face portion, a crown portion, and a sole/side portion which includes a sole portion and a side portion. This golf club head includes a rib which extends from the toe side to the heel side in the sole portion, and a weight portion which is provided in the sole portion on the back side with respect to the rib, and increases the amplitude of vibration of the sole portion. The natural frequency of the first-order vibration mode of the sole portion is 2,500 Hz or more. A mass m (g) of the weight portion satisfies 1≦m<6. The rib has a quadrangular cross-sectional shape with a width b (mm) and a height h (mm), and 0.20≦b·h3/m4<8.00.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a golf club head and, more particularly, to a technique for improving an impact sound.

2. Description of the Related Art

In hollow golf club heads typified by a driver head, techniques for improving an impact sound by appropriately designing the hollow body construction have been proposed. For example, Japanese Patent Laid-Open Nos. 11-155982 and 2003-275345 disclose techniques for improving an impact sound by partially varying the thickness of a sole portion. Also, Japanese Patent Laid-Open Nos. 2002-186691 and 2003-102877 disclose techniques for improving an impact sound by providing a rib in a sole portion.

The volume of a hollow golf club head is increasing every year, so its crown portion and sole portion are getting thinner, and their areas are increasing along with this trend. Therefore, a low-pitched impact sound is more likely to be generated at the time of striking a golf ball. Under the circumstance, golfers who prefer high-pitched impact sounds want golf club heads which generate higher-pitched impact sounds. Partially varying the thickness of a sole portion produces a certain effect of increasing the pitch of an impact sound, as disclosed in Japanese Patent Laid-Open Nos. 11-155982 and 2003-275345. Providing a rib in a sole portion also produces a certain effect of increasing the pitch of an impact sound, as disclosed in Japanese Patent Laid-Open Nos. 2002-186691 and 2003-102877. These techniques increase the pitch of an impact sound by increasing the degree of constraint of the sole portion. However, as the degree of constraint of the sole portion increases, an impact sound is more likely to have low loudness and poor resonance.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a golf club head which generates a higher-pitched, louder impact sound even when its head volume increases.

According to the present invention, there is provided a hollow golf club head including a face portion, a crown portion, and a sole/side portion which includes a sole portion and a side portion, the head comprising: a rib which extends from a toe side to a heel side in the sole portion; and a weight portion which is provided in the sole portion on a back side with respect to the rib, and increases an amplitude of vibration of the sole portion, wherein a natural frequency of a first-order vibration mode of the sole portion is not less than 2,500 Hz, a mass m (g) of the weight portion satisfies 1≦m<6, the rib has a quadrangular cross-sectional shape with a width b (mm) and a height h (mm), and 0.20≦b·h³/m⁴<8.00.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 2A is a sectional view taken along a line X-X in FIG. 1;

FIG. 2B is a view of the golf club head when viewed from the side of a sole portion;

FIG. 3 is a front view of the golf club head when viewed from the side of a face portion;

FIG. 4 is a view for explaining the middle region; and

FIGS. 5A to 5C are views showing the vibration analysis results.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a perspective view of a golf club head 10 according to an embodiment of the present invention when a rib 20 and a weight portion 21 provided inside it are seen through, FIG. 2A is a sectional view taken along a line X-X in FIG. 1, and FIG. 2B is a view of the golf club head 10 when viewed from the side of a sole portion 131.

The golf club head 10 takes the form of a hollow body, and its peripheral wall forms a face portion 11 which forms a face surface (striking surface), a crown portion 12 which forms the upper portion of the golf club head 10, and a sole/side portion 13. The sole/side portion 13 forms the sole portion 131 which forms the bottom portion of the golf club head 10, and a side portion 132 between the crown portion 12 and the sole portion 131. The side portion 132 forms the side portion of the golf club head 10, and includes a toe-side side portion 132a, heel-side side portion 132b, and back-side side portion 132c. The golf club head 10 also includes a hosel portion 15 in which a shaft is mounted.

The golf club head 10 is a driver golf club head. However, the present invention is applicable to wood type golf club heads including not only a driver golf club head but also, for example, a fairway wood type golf club head, utility (hybrid) golf club heads, and other hollow golf club heads. The golf club head 10 can be made of a metal material such as a titanium-based metal (for example, Ti-6Al-4V titanium alloy), stainless steel, or a copper alloy such as beryllium copper.

The golf club head 10 can be assembled by bonding a plurality of parts. The golf club head 10 can be formed from, for example, a main body member and a face member. The main body member forms the peripheral portions of the crown portion 12, sole portion 131, side portion 132, and face portion 11, and has an opening partially formed in a portion corresponding to the face portion 11. The face member is bonded in the opening in the main body member.

Referring to FIGS. 1, 2A, and 2B, the elongated rib 20 and the point-like weight portion 21 are formed on the inner upper surface of the sole portion 131. The rib 20 adjusts the natural frequency of the golf club head 10. The weight portion 21 increases the amplitude of vibration of the sole portion 131 at the time of impact.

In this embodiment, the rib 20 traverses the sole portion 131 in the toe-to-heel direction, and has its one end 20a connected to the toe-side side portion 132a, and its other end 20b connected to the heel-side side portion 132b. Although the rib 20 is formed integrally with the sole portion 131 and side portions 132a and 132b in this embodiment, it may be provided as a separate member and firmly fixed on the sole portion 131 and side portions 132a and 132b. The rib 20 has a quadrangular cross-sectional shape with a width b (mm) and a height h (mm), as shown in FIG. 2A. The height h of the rib 20 is that from the upper surface of the sole portion 131 (thin region S2).

The weight portion 21 increases the amplitude of vibration of its vicinity to adjust the resonance and loudness of an impact sound. The weight portion 21 is positioned on the back side with respect to the rib 20. As the position of the rib 20 is closer to the face portion 11 than the weight portion 21, it is easier to increase the eigenvalue (natural frequency) of the first-order vibration mode (primary vibration mode) of the sole portion 131. To increase the amplitude of vibration of the sole portion 131, the weight portion 21 is preferably disposed at the position of an antinode of vibration of the sole portion 131 or in its vicinity. The position of an antinode of vibration of the sole portion 131 generally falls within the middle region in both the toe-to-heel direction and the face-to-back direction of the golf club head when viewed from the bottom side. Hence, the weight portion 21 is preferably disposed in the middle region.

The middle region can be specified in the following way. First, as shown in FIG. 3, when the golf club head 10 is grounded so that an angle θ1 (lie angle) formed between a shaft axis line L0 and the grounding surface is a specific lie angle defined for the golf club head 10, and the loft angle is a specific loft angle (this grounding state will be referred to as specific grounding hereinafter), a grounding point C of the sole portion 131 is determined as a point on the center line of the dimension of the golf club head 10 in the toe-to-heel direction. Note that when the sole portion 131 is grounded in a plane defined on the grounding surface, its grounding point C is determined as the center in the widthwise direction.

Next, as shown in FIG. 4, an intersection point PF between the face portion 11 and a face parallel to the center line defined by the grounding point C, and an intersection point PB between the back end and this face, both when the golf club head 10 is viewed from the bottom side while being kept in a specific grounding state, are defined. A position CP one half of a distance L1 between the intersection points PF and PB is defined as the center point. Also, the dimension of the golf club head 10 in the toe-to-heel direction is defined as L2.

The middle region R can be defined by a dimension W1 in the face-to-back direction (flight trajectory direction) and a dimension W2 in the toe-to-heel direction upon defining the position CP as its center. The dimension W1 can be, for example, 0.4×L1 to 0.6L×1, and the dimension W2 can be, for example, 0.4×L2 to 0.6×L2.

Although the weight portion 21 has a circular cylindrical shape in this embodiment, it may have other shapes. Although the weight portion 21 is formed integrally with the sole portion 131 by locally increasing the thickness of the sole portion 131 in this embodiment, it may be attached to the sole portion 131 as a separate member. If the weight portion 21 is provided as a separate member, it preferably uses a member (for example, a screw) having a specific gravity higher than a material which forms the sole portion 131. Again, if the weight portion 21 is provided as a separate member, it may be detachable from the sole portion 131 so as to be replaced with another weight portion 21 having a different weight. With this arrangement, the user can perform impact sound adjustment.

Referring to FIG. 2B, in this embodiment, the sole/side portion 13 includes a thick region S1 on the side of the face portion 11, a thin region S2, and a thick region S3 on the back side in turn from the side of the face portion 11 to the back side. In this embodiment, the rib 20 and weight portion 21 are disposed in the thin region S2. A plurality of lines BL indicate the boundary lines between the regions S1 to S3.

The thicknesses of the peripheral wall in the regions S1 to S3 satisfy S1>S2 and S3>S2. The thin region S2 has a thickness of, for example, 0.8 mm, the thick region S1 has a thickness of, for example, 1.4 mm, and the thick region S3 has a thickness of, for example, 1.3 mm. Also, the face portion 11 has a thickness of, for example, 3 mm, and the crown portion 12 has a thickness of, for example, 0.6 mm (inclusive) to 0.7 mm (inclusive).

The thin region S2 is formed to traverse at least the sole portion 131 from the toe side to the heel side. Although the thin region S2 extends even to the side portions 132a and 132b in this embodiment, it may be formed only in the sole portion 131.

The thick region S1 is formed on the side of the face portion 11 with respect to the thin region S2 to be adjacent to the thin region S2. In this embodiment, the thick region S1 starts from a boundary portion BD between the sole portion 131 and the face portion 11, and extends up to the thin region S2. Although the thick region S1 extends even to the side portions 132a and 132b in this embodiment, it may be formed only in the sole portion 131. In this case, the thick region S1 may be formed only in part of the sole portion 131.

The thick region S3 is formed on the back side (on the side of the back-side side portion 132c) with respect to the thin region S2 to be adjacent to the thin region S2. Although the thick region S3 extends even to the side portions 132a and 132b and back-side side portion 132c in this embodiment, it may be formed only in the sole portion 131, only in the sole portion 131 and back-side side portion 132c, or only in the sole portion 131 and side portions 132a and 132b.

The principle of improving an impact sound in this embodiment will be described next. In general, with an increase in head volume, the head peripheral wall needs to be thinner and the area of each portion increases, so the eigenvalue of the entire head decreases, and the eigenvalue (natural frequency) of the first-order vibration mode of the sole portion 131, in turn, decreases. Therefore, a low-pitched impact sound is more likely to be generated at the time of striking a golf ball in that case. In this embodiment, the sole portion 131 is constrained by providing the rib 20, so the eigenvalue of its first-order vibration mode increases. This makes it possible to increase the pitch of an impact sound.

Also, in this embodiment, because the thick region S1, the thin region S2, and the thick region S3 are formed in the sole/side portion 13 in turn from the face side to the back side, the thin region S2 is more likely to vibrate at the time of striking a golf ball. By providing the rib 20 in the thin region S2, the thin region S2 is constrained by the rib 20, thus making it possible to further increase the pitch of an impact sound. Further, providing the weight portion 21 in the thin region S2 that is more likely to vibrate makes it possible to further increase the amplitude of vibration of the sole portion 131, thus improving the loudness and resonance of an impact sound.

As the degree of constraint of the sole portion 131 is increased using the rib 20, an impact sound can have a higher pitch but still has low loudness and poor resonance. However, in this embodiment, because the weight portion 21 is provided, the amplitude of vibration of the sole portion 131 at the time of impact increases. Therefore, a higher-pitched, louder impact sound can be generated even when the head volume increases. The head volume is, for example, 400 cc (inclusive) to 460 cc (inclusive).

The eigenvalue (natural frequency) of the first-order vibration mode of the sole portion 131 may decrease upon providing the weight portion 21. However, the natural frequency of the first-order vibration mode of the sole portion 131 is kept as high as 2,500 Hz or more using the rib 20 or using the rib 20 and the thick/thin regions together, as in this embodiment.

The rib 20 advantageously increases the pitch of an impact sound but disadvantageously decreases its loudness, while the weight portion 21 advantageously increases the amplitude of vibration of the sole portion 131 so as to increase the loudness of an impact sound but disadvantageously decreases its pitch, as described above. Accordingly, it is important not only to individually adjust the rib 20 and weight portion 21 but also to optimize their balance.

The weight portion 21 has a mass m (g) that satisfies 1≦m<6. The amplitude increasing effect is poor if the mass m is smaller than 1 g, while it is difficult to increase the pitch of an impact sound if the mass m is 6 g or more.

The second moment of area (b·h³/12) of the rib 20 is one factor which influences the degree of constraint of the sole portion 131 by the rib 20. Hence, b·h³ can be used as an index for the degree of constraint. To keep the eigenvalue (natural frequency) of the first-order vibration mode of the sole portion 131 as high as 2,500 Hz or more, b·h³ is preferably 50 or more. b·h³ is more preferably 100 or more. If the degree of constraint is too high, the loudness of an impact sound may not increase even when the weight portion 21 is provided. Accordingly, b·h³ is preferably 700 or less and more preferably 650 or less. When the width b and height h are individually defined, they preferably satisfy 0.5<b<3 and 2<h<7, respectively.

To evaluate the balance between the rib 20 and the weight portion 21, b·h³/m⁴ is used as an index for this balance. The denominator m⁴ is a parameter associated with the mass of the weight portion 21, and is the fourth power of this mass in correspondence with the order of b·h³. The numerator b·h³ is a parameter associated with the second moment of area of the rib 20.

If the b·h³/m⁴ value is relatively large, the second moment of area of the rib 20 is large relative to the mass of the weight portion 21, that is, an impact sound with a relatively high pitch but low loudness is generated. However, if the b·h³/m⁴ value is relatively small, an impact sound with a relatively low pitch is generated. When 0.20≦b·h³/m⁴<8.00, it is possible to generate an impact sound having both a high pitch and loudness.

EXAMPLE

Models of a plurality of golf club heads were designed on a computer, and vibration analysis was performed for each model on the computer. All these models are driver heads with the same shape and the same volume of 460 cc, and are different only in the specifications of a rib 20 and a weight portion 21. Note that these golf club heads are made of a titanium alloy (Ti-6Al-4V).

Each model has the same arrangement as the golf club head 10 shown in FIGS. 1, 2A, and 2B, and includes a rib 20, a weight portion 21, and a sole/side portion 13 which includes a thick region S1 on the side of a face portion 11, a thin region S2, and a thick region S3 on the back side in turn from the side of the face portion 11 to the back side. The thin region S2 has a dimension of 65 mm in the face-to-back direction, and a thickness of 0.6 mm. A distance LW of the weight portion 21 from an intersection point PF is 50 mm, and a distance LR of the rib 20 from the intersection point PF is 35 mm.

A width b (mm) and a height h (mm) of the rib 20 were set so that the b·h³ value changes for each model within the range of 50 to 650. Also, a mass m (g) of the weight portion 21 was set so as to change for each model within the range of 0 (without a weight portion) to 8(g).

In vibration analysis, the pitch (frequency), resonance (vibration time), and loudness (amplitude) of an impact sound were calculated.

FIG. 5A is a view showing the mass m of the weight portion 21, the b·h³ value of the rib 20, and the calculation result of the eigenvalue (natural frequency) of the first-order vibration mode of each model. The tolerance of the eigenvalue of the first-order vibration mode is 2,500 Hz or more, and calculation results that fall within this tolerance are indicated by shaded portions. If the mass m of the weight portion 21 is 6 g or more, a natural frequency of 2,500 Hz or more cannot be achieved. Accordingly, the mass m of the weight portion 21 must be smaller than 6 g. If the b·h³ value is 50 or more, a natural frequency of 2,500 Hz or more can be achieved. Accordingly, the width b and height h must be set so that the b·h³ value is 50 or more.

FIG. 5B is a view showing the mass m of the weight portion 21, the b·h³ value of the rib 20, and the evaluation result of the resonance and loudness of an impact sound generated by each model. The resonance and loudness were evaluated using four grades (A to D). Grade A is the best, and grades A and B fall within the tolerance (shaded portions). The larger the mass m, and the smaller the b·h³ value of the rib 20, the better the resonance and loudness of an impact sound become. Conversely, the smaller the mass m, and the larger the b·h³ value of the rib 20, the poorer the resonance and loudness of an impact sound become. When the weight portion 21 is provided (mass m≠0), there is a model that has a b·h³ value of 650 and is evaluated as grade D, and this means that the evaluation result degrades as the b·h³ value increases. Hence, b·h³ is preferably 700 or less and more preferably 650 or less.

FIG. 5C is a view showing the mass m of the weight portion 21, the b·h³ value of the rib 20, and the b·h³/m⁴ value of each model. Each shaded portion shown in FIG. 5C is a portion in which the shaded portions shown in FIGS. 5A and 5B overlap each other, that is, indicates a model in which the eigenvalue (natural frequency) of the first-order vibration mode is 2,500 Hz or more and the evaluation result of the resonance and loudness of an impact sound is A or B, so it generates a satisfactory impact sound. As can be seen from FIG. 5C, no model having a b·h³/m⁴ value less than 0.20 generates a satisfactory impact sound. Hence, the b·h³/m⁴ value must be 0.20 or more.

The upper limit of b·h³/m⁴ has a maximum value of 3.13 in a model in which the weight portion 21 has a mass of 2 g and the rib 20 has a b·h³ value of 50 among models which generate satisfactory impact sounds. However, the upper limit is expected to have a larger value in consideration of the relationships between changes in b·h³/m⁴ of the five models in which the weight portion 21 has a mass of 2 g, and changes in the natural frequency shown in FIG. 5A and the evaluation result of the resonance and loudness of an impact sound shown in FIG. 5B. In a model in which the weight portion 21 has a mass of 2 g and the rib 20 has a b·h³ value of 200, the b·h³/m⁴ value is 12.50 and the natural frequency falls within the tolerance but the evaluation result of the resonance and loudness of an impact sound is grade C. Hence, a satisfactory impact sound is expected to be produced when the b·h³/m⁴ value is the average between 3.13 and 12.50, that is, less than 8.00.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2011-133523, filed Jun. 15, 2011, which is hereby incorporated by reference herein in its entirety.

Claims

1. A hollow golf club head including a face portion, a crown portion, and a sole/side portion which includes a sole portion and a side portion, the head comprising: a rib which extends from a toe side to a heel side in the sole portion; anda weight portion which is provided in the sole portion on a back side with respect to said rib, and increases an amplitude of vibration of the sole portion,wherein a natural frequency of a first-order vibration mode of the sole portion is not less than 2,500 Hz,a mass m (g) of said weight portion satisfies 1≦m<6,said rib has a quadrangular cross-sectional shape with a width b (mm) and a height h (mm), and0.20≦b·h3/m4<8.00.

2. The head according to claim 1, wherein the sole/side portion includes a thick region on a side of the face portion, a thin region, and a thick region on the back side in turn from the side of the face portion to the back side, andsaid rib and said weight portion are disposed in the thin region.

3. The head according to claim 1, wherein a head volume is not less than 400 cc.