Abstract:
A device for selectively damping golf club vibrations by controlling their frequencies through optimal positioning at the point of maximum deformation energy for the vibration modes excited after impact. The device may be located at either or both of upper and lower intermediate sections of the club shaft, and is constituted by at least one layer of rigid material joined to the shaft surface by an intermediate layer of resilient material.

Description:
FIELD OF THE INVENTION 
     The invention relates to an improvement designed to damp vibratory phenomena in a golf club, and, more specifically, in its shaft. The invention concerns the golf club shaft, as well as the club itself. 
     BACKGROUND OF THE INVENTION 
     During the game of golf, the golfer strikes the ball to move it instrument termed a golf club, which is constituted by a shaft, and which incorporates a head at its lower end, and, at its upper end, is equipped with a handle or grip. 
     To drive the ball into the hole, the golfer uses several types of clubs distinguished by the shapes of their heads used to strike the ball and by the length of their shafts. The impact of the ball on the hitting surface of the club head generates, on the shaft, vibratory phenomena which prove especially unpleasant for the golfer, who, after the impact of the ball, feels discomfort which causes him to lose confidence in his club for the next hit. 
     An analysis of vibratory phenomena has shown that vibrations in a golf club represent the sum of several elementary vibratory phenomena, or modes, whose frequencies range between 0 and 200 Hertz; i.e., a first, vibratory mode in the plane of the swing, of the &#34;free embedded flection&#34; type for which the frequency is approximately 5 Hertz; a second mode of vibration, of the &#34;supported-embedded flection&#34; type, having a frequency of approximately 50 Hertz; a third, torsional mode of vibration whose frequency is approximately 75 Hertz; and a fourth mode of vibration of the first, harmonic flection type, having a frequency of approximately 130 Hertz. The frequency values depend on the properties of the shaft and head, and on the nature of the boundary conditions (site and gripping intensity). All of these vibrations are felt by the golfer as a disagreeable sensation upon impact, and they thus lessen the confidence the golfer has in the equipment, since he anticipates these unpleasant sensations before hitting the ball. It must be noted that the vibration amplitudes are particularly strong because the speed of the club head at the moment of impact is high and because the strokes are off-center. 
     Different means for reducing vibration amplitudes are known in the art. Complete elimination or attenuation of bad vibrations deprives the golfer of information feedback. In fact, some manufacturers have incorporated, along the entire length of the shaft and in the structure, fibers, e.g., made of Kelvar, which in the context of use, exhibit well-known damping properties so as to reduce energy and thus the amplitudes of the vibrations; however, damping is not selective and, accordingly, the club damps all modes. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to solve the problems of golf clubs according to prior art, by proposing a device designed to damp vibrations selectively in the golf club, by controlling the frequency, or frequencies, to be damped and the amount of damping of each mode of vibration by optimal positioning of the device, i.e., at the point where the energy of deformation is at a maximum for the modes excited after impact. 
     According to the invention, the damping means are positioned in proximity to the lower end of the club grip and above the neck of the club head. 
     To this end, the golf club shaft comprising a tubular profile incorporates several parts, i.e., an upper part designed to receive the club grip and extended downward by an upper intermediate section, followed by a central section, then a lower intermediate section, and finally, a lower part designed to be fitted into the club head, and this shaft comprises at least one damping device positioned in the area of at least of these intermediate sections. 
     According to one embodiment, the golf club shaft comprises a damping device located in the upper intermediate section, and, according to another embodiment, this device is located in the lower intermediate section. 
     According to another arrangement, the shaft according to the invention incorporates an upper damping device positioned in the upper intermediate section and a lower damping device in the lower intermediate section. 
     According to one variant, the damping device is positioned on the outer surface of the shaft structure, while, according to another variant, the damping device is placed on the internal surface of the shaft. 
     According to one advantageous embodiment the damping device comprises a ring made of a rigid material and connected to the golf club shaft by a flexible connector, such as an intermediate layer of a viscoelastic material, which is bonded adhesively both to the rigid ring and to the club shaft. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the invention will emerge from the following description provided with reference to the attached drawings, supplied solely by way of example. 
     FIG. 1 is a view of a golf club shaft. 
     FIGS. 2 and 3 represent a first embodiment of the invention. 
     FIG. 3 is a lateral view as seen from F in FIG. 2. 
     FIG. 4 is an enlarged transverse cross-section along line T--T in FIG. 2. 
     FIG. 5 is a longitudinal cross-section along line V--V in FIG. 4. 
     FIG. 6 is a perspective view, partly cut away showing the damping device in greater detail. 
     FIGS. 7 and 8 are views similar to those in FIGS. 2 and 3, showing a second embodiment of the invention. 
     FIGS. 9 and 10 are views similar to those in FIGS. 2 and 3, showing a third embodiment of the invention. 
     FIGS. 11, 12, and 13 illustrate a variant of the damping device. 
     FIG. 11 is a view similar to FIG. 4. 
     FIG. 12 is a view similar to FIG. 5. 
     FIG. 13 is a view similar to FIG. 6. 
     FIG. 14 illustrates another variant, in a view similar to FIG. 12. 
     FIG. 15 is a view similar to FIG. 4, illustrating a variant. 
     FIG. 16 is another variant of the view in FIG. 15. 
     FIG. 17 is a view similar to FIG. 5, showing a variant. 
     FIG. 18 is a partial view of a variant. 
     FIGS. 19 and 20 illustrate a variant of the damping device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a golf club shaft 1 constituted by a slightly conical tube larger at its upper end 7 than at its lower end 6, having a length L and made of steel or a composite material. The shaft comprises a lower part 60 having a length L1 and designed to be fitted into the neck 5 of the club head 2, and an upper part 70 inserted in the grip 3 and having a length L2. The central portion 100, having a length L5, is extended downward by a lower intermediate section 16 having a length L3, and upward by an upper intermediate section 15. The lower intermediate section 16 having a length L4 is located just above the flush-fitted lower part 60. 
     More especially, the upper intermediate section 15 may be specified as having a length L4 measuring approximately 0.2 L, and can be positioned at a distance L2 from the upper end 7 of approximately 0.2 L. Similarly, the lower part 60 and the lower intermediate section 16 have a length L1+L3 of approximately 0.2 L. 
     According to one of the inventive features, the shaft comprises at least one damping device, which is positioned in one of the intermediate sections. 
     FIGS. 2 and 3 illustrate a golf club according to one embodiment of the invention. This golf club comprises, in conventional fashion, a shaft 1 which incorporates a head 2 at its lower end, while it comprises a grip 3 at its upper end. These three basic, well-known components will not be described in detail; it will be mentioned only that the head 2 has a hitting surface 4 designed to strike the ball in order to drive it, and a neck 5 in which the lower portion 60 of the shaft 1 is embedded. It should be noted, in addition, that the head may have different shapes depending on the type of golf club, each manufacturer offering similar, but not identical, general shapes for a given type of club. FIGS. 2 and 3 illustrate a type of golf club called a &#34;wood,&#34; it being understood that the invention can also be applied to clubs called &#34;irons&#34; and &#34;putters.&#34; 
     According to the invention, the shaft comprises at least one damping device 8 constituted by an outer ring 9 made of a rigid material and joined to the upper surface 10 of the shaft 1 by means of an intermediate layer 11 made of a flexible material, advantageously of the viscoelastic type. 
     The outer ring 9 is, for example, cylindrical and produced from a metal tube made of aluminum or a Zycral aluminum alloy, or of a composite material, whose draping ensures maximum rigidity and a thickness &#34;e1&#34; ranging from approximately 0.3 to several millimeters, and whose length L1 is, for example, between 1 and 20% of the total length L of the shaft 1, and, advantageously, between 7 and 10%. Accordingly, the length L1 of the ring may be between 70 and 100 millimeters. 
     As has been previously stated, the intermediate ring 11 is an interface, advantageously made of a viscoelastic material and produced as a layer having a thickness &#34;e2&#34; of between 1 and 4 millimeters. 
     Thus, the inner surface 12 of the intermediate damping layer 1 is bonded or welded to the outer surface 10 of the shaft, while the outer surface 13 of this intermediate layer is bonded or welded to the inner surface 14 of the outer ring 9. 
     As shown in FIGS. 2 and 3, the damping device 8 is, according to an additional feature of the invention, positioned on the top part of the shaft in the upper intermediate section 15 located in proximity to the lower end of the grip 3. 
     FIGS. 7 and 8 illustrate a variant in which a lower damping device 8&#39;, identical to that in FIGS. 2 to 6, is positioned on the bottom of the shaft, in the lower intermediate section 16 located just above the flush-fitting of the shaft in the club head, and, more specifically, just above the neck 5 of this head. In the case of FIG. 7, the length L2 of the damping device is between 1 and 20% of the total length &#34;L&#34; of the shaft, and preferably between 1 and 10%. 
     FIGS. 9 and 10 illustrate another possible variant, in which the shaft incorporates two damping devices 8&#34;i, 8&#34;s, i.e., a first, upper damping device 8&#34;s positioned at the top of the shaft in the upper intermediate section 15 and a second, lower damping device 8&#34;i positioned at the bottom of the shaft in the lower intermediate section 16, so as to leave the median section of the shaft free. 
     FIGS. 1 to 10 show a &#34;wood,&#34; but the damping device can, of course, be used on other types of clubs, such as irons and putters, while remaining within the scope of the invention. Only the vibration-frequency values are changed for these other types of clubs, but not the form of the modes of vibration. As a consequence, placement of the damping devices remains identical. 
     According to the embodiments described hereinabove, the damping device 8, 8&#39;, 8&#34; is placed on the outer surface 10 of shaft but it could, while remaining on the outside of its structure, be, for example, positioned on the inner surface of the shaft, on the inside of the tube which forms it, as shown in FIGS. 11, 12, and 13: or else, it may be located within the shaft structure, as shown in FIG. 14. According to the variant in which the damping device 8 lies in the shaft structure itself, it is advantageously made of a composite material, and this damping device is placed, for example, between two layers of material 100, 101 during the manufacturing process, the device being such that the ring 9 made of rigid material is replaced by the upper layer 101. 
     FIGS. 15 illustrates one variant of the flexible connector 11 composed of several intermediate elements 110, 111, 112, 113, while the layer is tubular in the other embodiments. 
     FIG. 16 illustrates another variant, in which the elastic connector is produced from a series of several intermediate damping layers 114, 115 separated by a separation layer 102 made of a rigid material, thus forming a sandwich-shaped damping stack. 
     In all of the examples described above, the damping material may be of a different type, in particular of a rubber- or thermoplastic-type viscoelastic material, or of a fiber-based composite material having damping properties, such as aramid fiber-based composite materials. 
     FIG. 17 is a view similar to FIG. 5 showing a damping device according to a variant, in which the device comprises only the elastic material layer 11 produced as a ring, the rigid ring 9 in the preceding embodiments having been eliminated. 
     In FIG. 19, the outer rigid ring 19 is composed of several adjacent portions 190, 191, 192, 193 separated by a space, or spaces, extending longitudinally along the generating line. The number of portions may vary from approximately 2 to 6. The elastic material layer 11 arranged beneath the ring 19 is continuous and covers the upper surface of the shaft 1 around its entire circumference (FIG. 20). 
     Of course, the damping device may be positioned, not just below the grip and in contact with it, but moved away from it, as shown in FIG. 18, so as to leave a space &#34;e.&#34; This arrangement may be adopted when the damping device is located at the bottom, below the neck of the head.