Golf club head

[0001] The present invention relates to a golf club head and, more particularly, to a technique for controlling vibration of a golf club head by a viscoelastic body.

[0002] A golf club head having a viscoelastic body has been proposed to improve the hitting impression or adjust the hitting sound on impact. When the viscoelastic body is attached, the vibration on impact is absorbed by the viscoelastic body to improve the hitting impression and decrease the hitting sound that is offensive to the player's ear. Japanese Utility Model Registration No. 3112038 discloses a golf club head having a plurality of types of elastic weights having different specific gravities and elasticities. Japanese Patent Laid-Open No. 2004-313777 discloses a golf club head having a plurality of types of elastic bodies having different hardnesses.

[0003] The present inventors inspected the resonance frequency of a golf club head alone. A plurality of resonance frequencies were confirmed in a range of approximately 4,000 Hz to 10,000 Hz. Therefore, to reduce the vibration of the golf club head effectively, it is desired to attach a viscoelastic body that can reduce the vibration within a wide frequency range to the golf club head. In general, however, there is a limit to the frequency range of a viscoelastic material that is effective to reduce vibration depending on the material. The present inventors also inspected the resonance frequency of the golf club as a whole. A plurality of resonance frequencies were confirmed in a range of approximately 2,000 Hz or less. Therefore, to reduce the vibration of the golf club as a whole, the vibration is preferably reduced within a wider frequency range.

[0004] The present invention has been made in order to overcome the deficits of prior art.

[0005] According to the aspects of the present invention, there is provided a hollow golf club head having a viscoelastic body, wherein the viscoelastic body is made by mixing a plurality of types of viscoelastic materials with loss coefficients temperature dependences of which are different.

[0006] The temperature dependence of the loss coefficient (so-called tan δ) of a viscoelastic material represents the degree of the vibration attenuating effect of the viscoelastic material at any given temperature, and is related to the degree of the vibration attenuating effect of the viscoelastic material at any given frequency. More specifically, relatively, whereas a viscoelastic material with a large loss coefficient at a low temperature provides a high vibration attenuating effect in a high frequency band, a viscoelastic material with a large loss coefficient at a high temperature provides a high vibration attenuating effect in a low frequency band.

[0007] Therefore, when a plurality of types of viscoelastic materials with loss coefficients the temperature dependences of which are different are mixed, a viscoelastic body which can reduce vibration in a wider frequency range can be obtained. Such a viscoelastic body cannot be obtained from a single viscoelastic material. When the mixed viscoelastic body is mounted in a golf club, variation in a wider frequency range can be reduced.

[0008] Other features and advantages of the present invention will be apparent from the following descriptions taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.

[0009] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0010] FIG. 1 includes a sectional view showing the structure of a golf club head A according to an embodiment of the present invention, and an enlarged view of the main part of the same;

[0011] FIG. 2 is an exploded perspective view of the fixing structure of viscoelastic bodies;

[0012] FIG. 3A is a sectional view showing the structure of a golf club head B according to another embodiment of the present invention;

[0013] FIG. 3B is a view showing an example of the viscoelastic body; and

[0014] FIG. 4 is a graph showing the temperature dependences of the loss coefficients of the respective viscoelastic materials forming viscoelastic bodies and that of the loss coefficient of the viscoelastic body obtained by mixing the materials.

[0015] Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.

[0016] FIG. 1 includes a sectional view showing the structure of a golf club head A according to an embodiment of the present invention, and an enlarged view of the main part of the same. The golf club head A forms a hollow body, and its circumferential wall constitutes a face portion 10 which forms a golf ball hitting surface, a crown portion 20 which forms the upper surface of the golf club head A, a side portion 30 (only the back side is shown) which forms the toe-side, heel-side, and back-side side surfaces of the golf club head A, and a sole portion 40 which forms the bottom surface of the golf club head A. The golf club head A is also provided with a hosel portion 80 to which a shaft is to be fixed. The golf club head A is desirably made of, e.g., a titanium-based metal material.

[0017] Although the golf club head A is a golf club head that is to be used as a driver, the present invention can be applied to a wood type golf club head including a fairway wood or the like other than the driver as well, a utility type golf club head, and other hollow golf club heads.

[0018] A recess portion 41 extending into the golf club head A is integrally formed in the sole portion 40, and a viscoelastic body 60 is disposed in the recess portion 41. The recess portion 41 forms a fixing portion of the viscoelastic body 60. Although the outline of the side wall of the recess portion 41 forms a circle in this embodiment, the shape of the recess portion 41 is not limited to this, but the outline of the side wall of the recess portion 41 can form an ellipse or a shape having corners. A screw hole 41b is formed in a bottom portion 41a of the recess portion 41. The screw hole 41b is located substantially at the center of the bottom portion 41a.

[0019] A fixing member 50 threadably engages with a screw hole 41b. The fixing member 50 and an interposed member 70 fix the viscoelastic body 60. FIG. 2 is an exploded perspective view of the fixing structure of the viscoelastic bodies, showing the viscoelastic body 60, interposed member 70, and fixing member 50. In FIG. 2, the interposed member 70 is partially cutaway.

[0020] The fixing member 50 has a shaft body 52 formed with a threaded portion at its one end to threadably engage with the screw hole 41b, and a head portion 51 integrally connected to the other end of the shaft body 52. The viscoelastic body 60 forms a circular flat plate, and an opening 60′ where the shaft body 52 is to extend is formed at the central portion of the viscoelastic body 60. Although the opening 60′ is circular through hole, the present invention is not limited to this, and, e.g., a notch 60′ may be formed as in a viscoelastic body 60c shown in FIG. 3B. Although the viscoelastic bodies 60 and 60c are circular, their shapes can be elliptic or have corners.

[0021] The viscoelastic body 60 is made by mixing a plurality of types of viscoelastic materials with loss coefficients (so-called tan δ) the temperature dependences of which are different. The temperature dependence of the loss coefficient of a viscoelastic material represents the degree of the vibration attenuating effect of the viscoelastic material at any given temperature, and is related to the degree of the vibration attenuating effect of the viscoelastic material at any given frequency. More specifically, relatively, whereas a viscoelastic material with a large loss coefficient at a low temperature provides a large vibration attenuating effect in a high frequency band, a viscoelastic material with a large loss coefficient at a high temperature provides a high vibration attenuating effect in a low frequency band.

[0022] Therefore, when a plurality of types of viscoelastic materials with loss coefficients the temperature dependences of which are different are mixed, a viscoelastic body which can reduce vibration in a wider frequency range can be obtained. Such a viscoelastic body cannot be obtained from a single viscoelastic material. When the mixed viscoelastic body is mounted in the golf club A, variation in a wider frequency range can be reduced.

[0023] Examples of viscoelastic materials that are mixed to form the viscoelastic body 60 include IIR (butyl bromide composition), NBR (acrylonitrile-butadiene rubber), natural rubber, silicone rubber, styrene-based rubber, and the like. The viscoelastic body 60 can also be formed by mixing a metal powder or the like in a mixture of the viscoelastic materials described above to adjust their specific gravities.

[0024] An example of a method of mixing a plurality of types of viscoelastic materials with loss coefficients the temperature dependences of which are different is heating the respective viscoelastic materials to soften them, and then kneading the softened materials. Desirably, the viscoelastic materials are uniformly kneaded without changing their respective compositions.

[0025] Desirably, the viscoelastic body 60 is made of a plurality of types of viscoelastic materials with loss coefficients the peak value temperatures of which are different. In general, the loss coefficient of a viscoelastic material gradually decreases at each temperature with respect to the peak value temperature as a peak. Therefore, when a plurality of types of viscoelastic materials with loss coefficients the peak value temperatures of which are different are mixed, the viscoelastic body 60 which can reduce vibration in a wider frequency range can be obtained.

[0026] A plurality of types of viscoelastic materials to be mixed desirably include two types of viscoelastic materials whose peak value temperatures of the loss coefficients have a difference of 15° C. and more. The viscoelastic body 60 which can reduce vibration in a wider frequency range can be obtained by mixing such viscoelastic materials. However, if the difference between the peak value temperatures of the loss coefficients of a plurality of types of viscoelastic materials is too large, the loss coefficient of the viscoelastic body obtained by mixing the materials may largely decrease at an intermediate temperature between the respective peak value temperatures. Therefore, a plurality of types of viscoelastic materials to be mixed desirably include two types of viscoelastic materials whose peak value temperatures of the loss coefficients have a difference of 15° C. to 60° C. (both inclusive), and more desirably from 15° C. to 35° C. (both inclusive).

[0027] Desirably, a plurality of types of viscoelastic materials to be mixed include viscoelastic materials with the loss coefficient the peak value temperature of which are respectively less than −30° C. and −30° C. or more. The viscoelastic material with the loss coefficient the peak value temperature of which is less than −30° C. provides a relatively high vibration attenuating effect in the high frequency band, and the viscoelastic material with the loss coefficient the peak value temperature of which is −30° C. or more provides a relatively high vibration attenuating effect in the low frequency band. Therefore, vibration in a wider frequency range can be reduced.

[0028] The loss coefficient of the viscoelastic body 60 obtained by mixing a plurality of types of viscoelastic materials is desirably 0.3 or more in the range from −40° C. to −10° C. (both inclusive). If the loss coefficient is 0.3 or more, a higher vibration attenuating effect can be obtained.

[0029] The interposed member 70 is a member interposed between the viscoelastic body 60 and the head portion 51 of the fixing member 50, and serves to press the viscoelastic body 60 against the bottom portion 41a of the recess portion 41 substantially evenly. The interposed member 70 has a flat surface 70a with the same shape as the outer shape of the viscoelastic body 60, and an opening 70b where the shaft body 52 is to extend is formed at the center of the interposed member 70. Although the opening 70b is a circular through hole, the present invention is not limited to this, and the opening 70b can be a notch in the same manner as in the viscoelastic body (FIG. 3B). The central portion of the interposed member 70 is thinner-walled than its circumferential portion. Thus, when the fixing member 50 is attached to the recess portion 41, the head portion 51 of the fixing member 50 is partly buried in the interposed member 70.

[0030] In the golf club head A having the above structure, the shaft body 52 of the fixing member 50 is inserted in the openings 70b and 60′ of the interposed member 70 and viscoelastic body 60, and the threaded portion at the distal end of the shaft body 52 is threadably engaged with the screw hole 41b. Thus, the viscoelastic body 60 is fixed as it is sandwiched between the head portion 51 and bottom portion 41a.

[0031] In the golf club head A according to this embodiment, the viscoelastic body 60 which is made by mixing a plurality of types of viscoelastic materials with loss coefficients the temperature dependences of which are different from each other is loaded to reduce vibration in a wider frequency range.

[0032] As the viscoelastic body 60 forms a structure through which the shaft body 52 of the fixing member 50 extends, the depth of the recess portion 41 can be made shallower, so that the viscoelastic body 60 can be fixed at a position closer to the circumferential wall (sole portion 40). Accordingly, the vibration damping effect of the viscoelastic body 60 can improve.

[0033] According to this embodiment, since the interposed member 70 is interposed between the head portion 51 and the viscoelastic body 60, the viscoelastic body 60 can be pressed against the bottom portion 41a substantially evenly regardless of the size of the head portion 51, so that tight contact between the viscoelastic body 60 and bottom portion 41a can be ensured. This further improves the vibration damping effect. Due to the presence of the interposed member 70, the viscoelastic body 60 does not expose outside but are protected. Thus, the viscoelastic body 60 can be prevented from being damaged.

[0034] The fixing member 50 and interposed member 70 can also be used as members to adjust the barycentric position of the golf club head A. For example, the fixing member 50 and interposed member 70 can be made of a material having a specific gravity that is different from that of the circumferential wall of the golf club head A. When the circumferential wall of the golf club head A is made of a titanium alloy (specific gravity: about 4.5), if the fixing member 50 and interposed member 70 are made of stainless steel (specific gravity: about 7.8) or a tungsten alloy (specific gravity: about 13.0), the fixing member 50 and interposed member 70 can serve as weights as well, and the barycentric position of the golf club head A is closer to the portions of the fixing member 50 and interposed member 70. Conversely, if the fixing member 50 and interposed member 70 are made of an aluminum alloy (specific gravity: about 2.7), the barycentric position of the golf club head A is farther away from the portions of the fixing member 50 and interposed member 70.

[0035] Examples of the portion to fix the viscoelastic body 60 can include the side portion 30 and crown portion 20 in addition to the sole portion 40. If the viscoelastic bodies are fixed to sole portion 40, as in this embodiment, the center of gravity the golf club head A can be lowered. When a viscoelastic body is fixed to the back-side side portion 30, the center of gravity of the golf club head A can be deepened.

[0036] According to the golf club head A of this embodiment, since the viscoelastic body 60 can reduce vibration in a wider frequency range, the single viscoelastic body 60 can implement sufficient vibration deduction. This makes it possible to reduce the number of components of the golf club head A and to simplify assembly operation, compared to a case in which a plurality of viscoelastic bodies 60 are loaded. Naturally, a plurality of viscoelastic bodies 60 can be loaded in different parts. In this case, viscoelastic bodies with loss coefficients the temperature dependences of which are different from each other can be used.

[0037] FIG. 3A is a sectional view showing the structure of a golf club head B in which a plurality of viscoelastic bodies are fixed at a plurality of portions. In FIG. 3A, the same members as those of the golf club head A are denoted by the same reference numerals, and a description thereof will be omitted. In the golf club head B, a viscoelastic body 61a is fixed to a sole portion 40, and a viscoelastic body 61b is fixed to a back-side side portion 30. In the same manner as in the golf club head A, the viscoelastic bodies 61a and 61b are made by mixing a plurality of types of viscoelastic materials with loss coefficients the temperature dependences of which are different. If the temperature dependence of the loss coefficient of the viscoelastic body 61a is different from that of the loss coefficient of the viscoelastic body 61b after the viscoelastic bodies 61a and 61b are formed by mixing the materials, vibration in a wider frequency range can be reduced.

[0038] The fixing structure of the viscoelastic body 61a is the same as that of the golf club head A described above. The fixing structure of the viscoelastic body 61b is also the same as that of the golf club head A. A brief description will be made. A recess portion 31 extending into the golf club head B is integrally formed in the back-side side portion 30, and the viscoelastic body 61b is disposed in the recess portion 31. The recess portion 31 forms a fixing portion that is different from that of a recess portion 41. A screw hole 31b is formed in a bottom portion 31a of the recess portion 31. A fixing member 50′ similar to a fixing member 50 threadably engages with the screw hole 31b. The fixing member 50′ and an interposed member 70′ which is similar to an interposed member 70 fix the viscoelastic body 61b. The fixing member 50′ has a shaft body 52′ formed with a threaded portion at its one end to threadably engage with the screw hole 31b, and a head portion 51′ integrally connected to the other end of the shaft body 52′.

[0039] The shaft body 52′ of the fixing member 50′ is inserted in openings 70b′ and 61b′ of the interposed member 70′ and viscoelastic body 61b, respectively, and the threaded portion at the distal end of the shaft body 52′ is threadably engaged with the screw hole 31b. Thus, the viscoelastic body 61b is fixed as it is sandwiched between the head portion 51′ and bottom portion 31a.

[0040] In the golf club head B with the above structure, separate vibration damping effects can be enhanced for the vibration occurring in the sole portion 40 and that in the side portion 30. As the viscoelastic body 61b and its fixing structure are disposed in the back-side side portion 30, the back side of the golf club head B becomes heavy to deepen the center of gravity. As the viscoelastic body 61a and its fixing structure are disposed in the sole portion 40, the sole portion 40 side of the golf club head B becomes heavy to lower the center of gravity. Therefore, with the golf club head B, in addition to the vibration damping effect, the center of gravity can be lowered and deepened. The materials of the respective fixing members 50 and 50′ and interposed members 70 and 70′ of the two sets of the fixing structures may be the same or different. If the materials of the respective fixing members 50 and 50′ and interposed members 70 and 70′ are different, the barycentric position described above can be adjusted.

[0041] Viscoelastic bodies (60, 60c, 61a, 61b) will be described below. In this example, a case in which each viscoelastic body is formed by mixing acrylonitrile-butadiene rubber and a butyl bromide composition.

[0042] FIG. 4 is a graph showing the temperature dependences of the loss coefficients of the respective viscoelastic materials forming the viscoelastic bodies and that of the loss coefficient of the viscoelastic body obtained by mixing the materials, and shows the temperature dependences at the vibration of 1 Hz. Referring to FIG. 4, a line a represents temperature dependence of the loss coefficient of the butyl bromide composition alone. A line b represents the temperature dependence of the loss coefficient of the acrylonitrile-butadiene rubber alone. A line c represents the temperature dependence of the loss coefficient of the viscoelastic material (mixture) obtained by mixing the acrylonitrile-butadiene rubber and butyl bromide composition. Note that, in the mixture, the mixing ratio of the acrylonitrile-butadiene rubber to the butyl bromide composition is 3:7. The mixture was heated at about 170° C. to be softened, and then uniformly kneaded.

[0043] As indicated by the lines a and b of FIG. 4, the respective viscoelastic materials used in the mixture have loss coefficients the peak value temperatures of which are different. The difference between the peak value temperatures of the loss coefficients of the respective viscoelastic materials is about 20° C., which is higher than 15° C. The peak value temperature of the loss coefficient of one viscoelastic material is less than −30° C. (line a), and the peak value temperature of the loss coefficient of the other viscoelastic material is −30° C. or more (line b)

[0044] As indicated by the line c of FIG. 4, the mixture shows the characteristics such as a combination of the temperature dependence of the loss coefficient of the acrylonitrile-butadiene rubber alone and that of the loss coefficient of butyl bromide composition alone, and large loss coefficients are shown in a wider temperature range. That is, a viscoelastic body which can reduce vibration in a wider frequency range can be obtained. Such a viscoelastic body cannot be obtained from a single viscoelastic material. As indicated by the line c of FIG. 4, the loss coefficient of the mixture is 0.3 or more in the range from −40° C. to −10° C. (both inclusive).

[0045] As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

[0046] This application claims the benefit of Japanese Patent Application No. 2005-351282 filed on Dec. 5, 2005, which is hereby incorporated by reference herein in its entirety.