Patent Publication Number: US-7591735-B2

Title: Golf club head

Description:
FIELD OF THE INVENTION 
     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. 
     BACKGROUND OF THE INVENTION 
     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&#39;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. 
     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. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in order to overcome the deficits of prior art. 
     According to the aspects of the present invention, there is provided a 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 the temperature dependences of which are different. 
     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. 
     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. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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. 
         FIG. 1  is an exploded perspective view of a golf club head A according to one embodiment of the present invention; 
         FIG. 2A  is a sectional view of the golf club head A in an exploded state taken along the line X-X of  FIG. 1 ; 
         FIG. 2B  is a sectional view of the golf club head A in an assembled state taken along the line X-X of  FIG. 1 ; 
         FIG. 3  is a sectional view taken along the line Y-Y of  FIG. 2A ; 
         FIG. 4A  is a graph showing the temperature dependences of the loss coefficients of the respective viscoelastic materials used in comparative experiments; and 
         FIG. 4B  is a graph showing the result of the vibration measurement experiment for golf club heads according to the example and Comparative Examples 1 and 2. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. 
       FIG. 1  is an exploded perspective view of a golf club head A according to one embodiment of the present invention,  FIG. 2A  is a sectional view of the golf club head A in an exploded state taken along the line X-X of  FIG. 1 ,  FIG. 2B  is a sectional view of the golf club head A in an assembled state taken along the line X-X of  FIG. 1 , and  FIG. 3  is a sectional view taken along the line Y-Y of  FIG. 2A . 
     The golf club head A is an iron type golf club head and includes a head main body  10  and a face plate  20  which is fixed to the front surface side of the head main body  10  to form a face surface  20   a . Although this embodiment is exemplified by an iron type golf club head, the present invention can also be applied to another type of golf club head. 
     The head main body  10  integrally has a hosel portion  10   a  to be connected to a shaft, a sole portion  10   b , and a back portion  10   c , and is made of, e.g., stainless steel or soft iron. An opening  10   d  is formed in the upper portion of the head main body  10  to extend from the front surface side to the rear surface side, thus decreasing the weight and lowering the barycenter of the head main body  10 . A rib  10   e  which defines the space where the face plate  20  is to be fixed and a contacting portion  10   f  with which the rear surface of the face plate  20  is to contact is formed on the front surface of the head main body  10 . 
     The face plate  20  is formed with the face surface  20   a  on its front surface and a stepped portion  20   b  formed at its circumference. The rear surface of the face plate  20  forms a flat surface. For example, the face plate  20  is made of stainless steel, maraging steel, brass, a copper alloy (e.g., beryllium copper or bronze), titanium, a titanium alloy, duralumin, an amorphous metal, an FRM, or the like. 
     A cavity portion  11  is formed in the head main body  10  to open to the face plate  20  side and be closed on the back portion  10   c  side. The cavity portion  11  is defined by circumferential walls  12  to  14  integrally formed with the head main body  10 . Of the end faces on the face plate  20  side of the circumferential walls  12  to  14 , that end face of the circumferential wall  12  which is above cavity portion  11  has an contacting portion  12   a  which is flush with the contacting portion  10   f  and contacts with the rear surface of the face plate  20 , and a non-contacting portion  12   b  which is spaced apart from the rear surface of the face plate  20  inside the contacting portion  12   a . The end face of the circumferential wall  14  which is at the bottom of the cavity portion  11  comprises only an contacting portion  14   a  which is flush with the contacting portion  10   f  and contacts with the rear surface of the face plate  20 . Those end faces of the circumferential wall  13  which are on the two sides of the cavity portion  11  have non-contacting portions  13   a  which are spaced apart from the rear surface of the face plate  20  and flush with the non-contacting portion  12   b . Unlike the non-contacting portion  12   b , the non-contacting portions  13   a  are formed throughout the entire range in the direction of thickness of the circumferential wall  13 . 
     Second cavity portions  15  are formed on the two sides of the cavity portion  11 . The cavity portions  15  serve to decrease the weight of the head main body  10 . Although the cavity portions  15  are formed on the two sides of the cavity portion  11  in this embodiment, the cavity portion  15  can be formed on only one side of the cavity portion  11 . Although the cavity portions  15  are left hollow in this embodiment, weights or the like to adjust the barycentric position of the golf club head A can be inserted in the cavity portions  15 . 
     A viscoelastic body  30  is loaded in a compressed state in the space formed by the cavity portion  11  and face plate  20 . A front surface  30   a  of the viscoelastic body  30  is in tight contact with the rear surface of the face plate  20 . 
     The viscoelastic body  30  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. 
     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. 
     Examples of viscoelastic materials that are mixed to form the viscoelastic body  30  include IIR (butyl bromide composition), NBR (acrylonitrile-butadiene rubber), natural rubber, silicone rubber, styrene-based rubber, and the like. The viscoelastic body  30  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. 
     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. 
     Desirably, the viscoelastic body  30  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  30  which can reduce vibration in a wider frequency range can be obtained. 
     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  30  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 from 15° C. to 60° C. (both inclusive), and more desirably from 15° C. to 35° C. (both inclusive). 
     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. 
     The loss coefficient of the viscoelastic body  30  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. 
     When assembling the golf club head A having the above structure, first, the viscoelastic body  30  is inserted in the cavity portion  11  of the head main body  10 . Then, as shown in  FIG. 2B , the face plate  20  is inserted in the space of the head main body  10  defined by the rib  10   e  such that the rear surface of the face plate  20  tightly contacts with the contacting portion  10   f  of the head main body  10 . After that, the rib  10   e  is caulked with the stepped portion  20   b  of the face plate  20  to fix the face plate  20  to the head main body  10 . The viscoelastic body  30  is designed in size such that it is compressed in the cavity portion  11 . 
     In the golf club head A according to this embodiment, the viscoelastic body  30  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. Since the viscoelastic body  30  can reduce vibration in a wider frequency range, the single viscoelastic body  30  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  30  are loaded. Naturally, a plurality of viscoelastic bodies  30  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. 
     As the viscoelastic body  30  is disposed within the golf club head A in this embodiment, it does not expose outside. As the viscoelastic body  30  is protected by the head main body  10  and face plate  20 , it will not be damaged. As the viscoelastic body  30  is inserted in a compressed state in the space defined by the cavity portion  11  and face plate  20 , the viscoelastic body  30  comes into tight contact with the golf club head A to enhance the vibration reducing effect. 
     When the non-contacting portions  12   b  and  13   a  are formed on the end faces of the circumferential walls  12  and  13  that define the cavity portion  11 , a gap communicating with the cavity portion  11  is formed in the end faces of the circumferential walls  12  and  13 . Thus, part of the viscoelastic body  30  in a compressed state is allowed to extend into the gap. 
       FIG. 2B  shows a state wherein part of the viscoelastic body  30  extends into the gap between the non-contacting portion  12   b  and face plate  20 . Even if the compression margin of the viscoelastic body  30  is increased, when fixing the face plate  20  to the head main body  10 , the head main body  10  and face plate  20  can be prevented from biting into the viscoelastic body  30 . Particularly, in this embodiment, as the gap formed by the non-contacting portions  13   a  communicates not only with the cavity portion  11  but also with the cavity portions  15 , the allowable extension amount of the viscoelastic body  30  increases, so that the head main body  10  and face plate  20  can be more prevented from biting into the viscoelastic body  30 . Since part of the viscoelastic body  30  extends into the gap between the non-contacting portions  12   b  and  13   a  and face plate  20 , the tight contact area between the viscoelastic body  30  and face plate  20  also increases more. 
     The viscoelastic body  30  and cavity portion  11  are designed in shape such that the front surface  30   a  is parallel to the rear surface of the face plate  20 . With this structure, the front surface  30   a  of the viscoelastic body  30  comes into tight contact with the rear surface of the face plate  20  with a substantially uniform pressure, thus improving the tight contact state. 
     In this embodiment, the cavity portion  11  is formed in the lower side of the head main body  10 , and the viscoelastic body  30  inserted in the cavity portion  11  is located in the lower side of the head main body  10 . This structure can lower the barycentric position of the golf club head A, thus achieving a low barycenter. An iron type golf club hits a golf ball with its point close to the lower portion of the face surface  20   a . Thus, the viscoelastic body  30  is located substantially behind the position of the golf ball hitting point, so that the vibration damping effect of the viscoelastic body  30  can improve. 
     In this embodiment, the width (d in  FIG. 1 ) in a direction along the face plate  20  of the viscoelastic body  30  increases downward from its upper portion, and the cavity portion  11  has a shape to match this. Hence, the barycentric position of the viscoelastic body  30  is low. This can lower the barycentric position of the golf club head A, thus further achieving a low barycenter. 
     In this embodiment, the viscoelastic body  30  is disposed behind the face plate  20 . However, the position to dispose the viscoelastic body  30  is not limited to this, but the viscoelastic body  30  can be adhered at various portions. 
     EXAMPLE &amp; COMPARATIVE EXAMPLES 
     The golf club head A shown in  FIG. 1  was subjected to comparison tests. The viscoelastic materials of the viscoelastic body  30  used in the example of the present invention and its comparative examples are as follows. 
     Example 
     Mixture of acrylonitrile-butadiene rubber and butyl bromide composition 
     Comparative Example 1 
     Butyl bromide composition alone used in the example 
     Comparative Example 2 
     Acrylonitrile-butadiene rubber alone used in the example 
     Note that, in the example, 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. 
       FIG. 4A  is a graph showing the temperature dependences of the loss coefficients of the respective viscoelastic materials used in the experiment, and shows the temperature dependences at the vibration of 1 Hz. Referring to  FIG. 4A , a line a represents the temperature dependence of the loss coefficient of the viscoelastic material (butyl bromide composition alone) used to form the viscoelastic body  30  of Comparative Example 1. A line b represents the temperature dependence of the loss coefficient of the viscoelastic material (acrylonitrile-butadiene rubber alone) used to form the viscoelastic body  30  of Comparative Example 2. A line c represents the temperature dependence of the loss coefficient of the viscoelastic material (mixture of acrylonitrile-butadiene rubber used in Comparative Example 2 and butyl bromide composition used in Comparative Example 1) used to form the viscoelastic body  30  of the example. 
     As indicated by the lines a and b of  FIG. 4A , the respective viscoelastic materials used to form the viscoelastic material (mixture) of the example 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). 
     The viscoelastic material of the example represented by the line c of  FIG. 4A  shows the characteristics such as a combination of the temperature dependences of the loss coefficients of the respective viscoelastic materials used in Comparative Examples 1 and 2. The line c indicates large loss coefficients in a wider temperature range. As indicated by the line c of  FIG. 4A , the loss coefficient of the viscoelastic material (mixture) of the example is 0.3 or more in the range from −40° C. to −10° C. (both inclusive). 
       FIG. 4B  is a graph showing the result of the vibration measurement experiment for golf club heads according to the example and Comparative Examples 1 and 2. In  FIG. 4B , the attenuation ratios are calculated by modal analysis. The plots in  FIG. 4B  indicate the attenuation ratios of the resonance frequencies of the respective golf club heads. Square plots indicate the example, blank circle plots indicate Comparative Example 1, and triangular plots indicate Comparative Example 2. In the example, a high attenuation ratio is obtained in a wide frequency range. 
     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. 
     This application claims the benefit of Japanese Application No. 2005-351281, filed Dec. 5, 2005, which is hereby incorporated by reference herein in its entirety.