Abstract:
An internal vibration damper for hollow golf club heads is disclosed. Of particular concern is vibration of the club sole and crown when the face of the club impacts a golf ball. At least one column extends from the sole to the crown, approximately perpendicular to the surfaces of the sole and crown. The column construction or its mounting acts to dampen and reduce vibrations of the sole and crown toward and apart from each other upon ball impact on the face of the club head.

Description:
BACKGROUND OF THE INVENTION 
   The present disclosure relates to damping sound and vibration in large hollow golf club heads by providing a damper between the sole and top wall or crown of such golf clubs. 
   Currently, large, hollow metal driver-type golf club heads typically generate a strong and often objectionable, sharp ringing sound immediately after impact of a face of the club head on a ball. When hollow metal heads first became available, they were often filled with a vibration-damping foam material. This added unwanted weight. What was worse, because of its lack of rigidity, the added weight of the foam did not participate fully in the impact. This caused reduced driving distance. More recently with even larger heads of this type, the ringing sound was allowed by club head designers, even with the objection of some golfers. 
   Test have shown that the impact of a ball on the club face of a typical modern hollow golf club head produces an amplitude of vibration of the crown (top wall) and sole (bottom wall) of the head such that the crown-sole distance expands about 0.02 inch during and immediately following impact. This causes a predominately crown-sole oscillation that persists for the order of one second and emits a sharp sound in the range of about 1000 to 5000 thousand cycles per second. This is in the general frequency range of maximum audible sensation to the ears of typical humans. The stiffness for a force tending to reduce the crown-sole distance was found to be about 2000 pounds of force per inch of deformation. Because peak forces on the club face at impact are in the range of 2500 pounds, the club head must be designed to have far greater stiffness for face-rear vibrations than the 2000 pounds per inch of crown-sole stiffness. For this reason, oscillations in the face-rear direction are far smaller, higher frequency, and emit much less audible sound. 
   Thus, reducing vibrations in the crown-sole direction is important for overall sound reduction. Vibrations in the face-rear direction are relatively unimportant. The damping structure should add fewer than about 2 grams of mass, because such mass may not significantly participate in the impact. 
   PRIOR ART 
   Vibration damping methods are widely known in the field of mechanical vibrations. When there is no damping, vibrations are not diminished and continue indefinitely. When viscous damping (damping force proportional to deformation velocity) is present, it may be small, with vibrations dying out slowly, or if larger, dying more rapidly. There is an amount of viscous damping called critical damping, which causes the vibrations to cease. More damping simply causes initial motion to cease more slowly but with no vibration. To reduce sound, damping is preferably in the range of about five times critical damping to one fifth of critical damping. The latter case allows vibrations but they diminish rapidly. 
   Viscous damping may be provided by liquids or semi-liquids that experience shear deformation. Many somewhat flexible solids may be deformed, but do not return quickly to their original shapes and approximate viscous damping in some respects. 
   As an alternate to the viscous damping discussed above, dry sliding friction may be used. That is the drag force when 2 flat surfaces of solids that are pressed together are caused to slide relatively to one another. This can effectively suppress continued vibrations when the drag force is suitable. 
   Finally, it is to be noted that all solids provide a degree of internal damping when stressed, ranging from extremely slight (hard steel for example) to quite large (some types of rubber for example). Thus in principle all structures stressed in tension, compression or shear have at least a slight degree of damping. In the present disclosure, damping materials include viscous liquids, those solids having large damping properties such as for some kinds of rubber, certain elastomeric plastics, and dry sliding friction. 
   U.S. Pat. No. 5,429,365 (McKeigen) shows a post member that joins a club head crown to its sole. This changes the fundamental (i.e. lowest) mode of vibration frequency to become much higher. That effect could eliminate sound only by raising the lowest vibration mode to a frequency above the audible range, which is unlikely. The purpose of the post is to join parts of the club head together.  FIG. 1  of this disclosure was taken from that patent to illustrate the structure. Significant damping was not suggested. 
   U.S. Pat. No. 5,890,973 (Gamble) shows various face-rear members to influence behavior of the face upon impact. In one form shown in  FIG. 2  of this disclosure, there is a structure  72  and  74  that may be filled with fluid. It is stated that this structure and at least some of its variations may provide damping and reduce the tinny sound of impact. 
   Those skilled in the field of vibrations will recognize that the configurations illustrated in the &#39;973 patent may provide a degree of damping of face-rear vibrations, but are much less effective for reducing vibrations in the crown-sole direction than the configurations defined in this invention. The basic reason is that the present invention provides vibration damping effects directly on the important parts that cause most of the sound generation, namely the crown and sole. 
   U.S. Pat. Nos. 5,316,298 (Hutin et al.) and 5,586,947 (Hutin) show means for damping vibrations in golf club heads in which a visco-elastic layer is applied to the vibrating surface with an outer layer of more rigid material. While damping is obtained in this manner, the layered wall structure is very distinct from the present disclosure. 
   SUMMARY 
   The present disclosure provides damping coupling structure between the crown or top wall of a hollow metal golf club head and the sole or bottom wall. 
   The vibrations of a club head mostly make sound when the larger surfaces vibrate, principally when there is motion in the crown-sole mode (the crown bulging upward while the sole bulges downward and the reverse). This generates sound due to the broad surface areas of the crown wall and sole, because this is normally the lowest-frequency mode of vibration of a club head, and is excited by the transient forces of impact of the ball on the club head face. Small areas generate less sound than large areas. 
   In various embodiments shown, physical damping connections are provided between the crown and sole, which have the large surfaces of the hollow golf club head that are the source of most vibration and noise. 
   Damping structures disclosed include viscous liquids, solids having large damping properties, such as some kinds of rubber; certain elastomeric plastics and dry sliding friction. 
   Structural elements having such damping properties provide damping directly between the walls that cause the most sound generation, namely the crown and the sole. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a drawing of a prior art club head taken from U.S. Pat. No. 5,429,365 showing a rigid, substantially non-damping crown-sole structural member for head strength. 
       FIG. 2  is a drawing of a prior art club head taken from U.S. Pat. No. 5,890,973 showing a face-rear internal member that is said to be capable of providing damping of vibration of the face and rear walls of a club head. 
       FIG. 3  is a hollow club head illustrating the nature of the vibrations of the crown and sole, which cause sound. 
       FIG. 4  shows one form of the damping structure of the present disclosure. 
       FIG. 5  shows another form of damping structure of this disclosure. 
       FIG. 6  shows a form of damping structure of the present disclosure that may use deformation of a solid or liquid or may use dry sliding damping. 
       FIG. 7  is a cross sectional view taken as on line  7 - 7  in  FIG. 6 . 
       FIG. 8  is a cross sectional view similar to  FIG. 7  but illustrates how a controlled dry friction lining layer may be used for less wear than the  FIG. 7  showing. 
       FIG. 9  is a cross sectional view similar to  FIG. 7 , but including a thick, viscous liquid or semi soft material between telescoping tubular cylinders to provide damping. 
       FIG. 10  is a fragmentary sectional view showing a crown-sole tubular damping structure attached to the crown of a golf club, with a rubber attachment layer used to provide damping. 
       FIG. 11  is a fragmentary cross sectional view showing an attachment structure for attaching a tube of damping material to a wall of the golf club head. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 3  is a drawing of a typical large hollow metal golf club head  1  having a face  7  held at edges  6  and  8  to a crown wall  4  and a sole wall  9 , respectively. The face is conventionally welded in place. The club head is thus enclosed around the perimeter of the face, as is well known, leaving a hollow interior. The rear  2  of the club head joins the sole  9  and crown  4  and is spaced from the face. 
   The dotted lines  5  illustrate the basic mode of crown-sole vibration of the hollow driver head  1 , immediately after impact by a ball on the face  7 . These vibrations and deflections of the crown and sole cause a sound that can be heard by a golfer. Relatively slight face-rear movement (not shown) accompanies this vibration. 
     FIG. 4  fragmentarily shows a rear portion of a hollow golf club head having a sole wall  14  and crown wall  15 , with a damping structure between the two walls. The damping structure comprises a screw  19  or other column that has rubber or elastomeric washers  16  and  13  under a conical head  19 A of the screw and anchor nut  17 , respectively. The screw or column  19  is thus connected to the crown and sole through damping structure. When the screw  19  is in tension, the rubber material of the washers  16  and  13  tends to flow outward from its rest position and thus provides damping effect. Rather than rubber, other moderately soft material may be used provided it has much internal damping and can return to shape after being loaded. The rubber washers  16  and  13  need not be at both ends of the screw or column  19  since only one washer, under the head  19 A or nut  17  provides damping for the crown and sole. 
     FIG. 5  shows a structure similar to  FIG. 4 , but using a flat-headed screw  20  with damping material  16 A under its head  20 A. The screw  20  is threaded at  20 B into a threaded bore in the sole  14 . The washer  16 A dampens vibration of the crown wall  15  and sole  14 . 
     FIG. 6  shows a damping structure between crown wall  15  and sole wall  14  comprising a tube  24  and an internal telescoping rod  26  that slides in the bore of the tube  24 . The friction of relative sliding of the rod and tube provides damping. A lining of material  25  slides on either the inner surface of the tube  24  or rod  26  to provide controlled friction. More details of this construction are provided in  FIGS. 7 ,  8 , and  9 . 
     FIG. 7  shows how the outer tube  24  of  FIG. 6  may be modified by having slits  30  in one or both sides. It may have an inside diameter slightly smaller than internal rod  26 , with the result that dry sliding friction is provided when the crown  15  and sole  14  move relative to each other as they vibrate, thus providing the damping of the vibrations. 
     FIG. 8  shows how a lining material  37  may be interposed between tube  24  and rod  26  of  FIG. 6  wherein the material can be selected to provide controlled sliding friction, with little wear. A material such as automobile brake lining material may be used. 
     FIG. 9  is similar to  FIG. 8  but without slits in the tube  24 A and there is a viscous liquid filling  41  in the space between the inner surface of the tube  24 A and the rod  26 A, without need of clamping action. The viscous liquid is best chosen from highly viscous liquids. To avoid the liquid from moving out from the tube  24 A, the liquids may be replaced by semi-liquids that behave as solids but begin to flow when only slight stress is applied, such as heavy grease. Another possibility is use of rubber or other semi-solid damping material. 
   Either the tube  24  or rod  26  may extend from crown to sole and may be attached to the sole or crown  15  by anchoring by bonding or otherwise on the inner surface of the crown wall or sole wall or in a hole in the wall as in  FIG. 6 . The tube or rod may be of vibration absorbing material having Young&#39;s modulus stiffness in the range of 50,000 up to 5,000,000 pounds per square inch, density less than 1.5 grams per cubic centimeter, and good internal damping characteristics. Some polyurethane formulations are suitable. 
     FIG. 10  is an enlarged view of a modified junction in the region between a tube such as tube  24  and the crown shown at dotted circle  28   FIG. 6 . The modified junction shows a tubular member  50 , preferably with ends somewhat deformed inward as shown at  55  to provide end surface area and with a patch or layer of rubber-like (elastomeric) damping material  51  that is firmly bonded to the end of the tubular member  50 . While the crown  15  of a club is illustrated, a similar structure may be at the sole end of tube  50  instead. Alternately both ends of tubular member  50  can be similarity attached to both the sole and crown by the damping material  51 . 
   A small amount of bonding material shown at  53  may be used at the periphery or edge of material layer  51 , to secure the material  51  to the inner surfaces of the crown (or sole). The other portions of the damping material  51  may separate momentarily from the inner surface of crown  15  during a vibration, as indicated at dotted line  56 , but the bonding attachment at  53  keeps the tubular member  50  and material  51  in place. The layer or patch  51  is selected in size to provide some movement in the center during vibration, but yet hold the tube  50  in place. As shown, the patch  51  may be round or square and with a diameter or side length in face to rear wall direction about 2 times the diameter of tube  50 . 
   The bond for the patch of material  51  is applied only in selected locations, as shown only at  53 , so that if the crown moves away from the vibration damper tube, the patch of material  51  can flex as indicated by dotted lines  56 , without breaking the bond. While only one bond location  53  is shown, there may be more than one and if the patch of damping material  51  has adequate diameter or size, and low enough stiffness, the bonding to the crown (or sole) could be in the form of a peripheral bond along the outer edge of the patch of material  51 . 
   The lowest resonant frequency of the internal crown-sole column or member disclosed for vibrations in the face-rear direction, which is the direction transverse to the long axis of the column or member, and which is called the transverse mode of vibration, should be above 2000 Hz. Preferably the lowest resonant frequency in the transverse mode is well above 2000 Hz, for example 4000 Hz or more, so that ball-face impact does not cause excessive vibration of the internal crown-sole column or member in the face-rear direction relative to the club head. 
   The cross sectional shape of tubes or columns shown does not have to be circular, but may be of other shapes. A rectangular shape or I-beam shape could be used so that the stiffness in the face-rear direction is high enough to minimize face-rear deformation of member  50  during the short time of ball-face impact. 
   In the embodiment shown in  FIG. 11 , a vibration absorbing or damping tube  60  is of size to be fitted onto a plug or short post  62  that is fixed to the crown  15 . If the fit is free, so the tube  60  can slide on the plug or post  62 , the vibration damping occurs when the tube  60  is compressed against the inner surface of crown  15 . The tube is cut to length so it abuts the inner surface of crown  15  at rest. If the tube fits with some friction between the plug and the tube, but is still movable, slippage of the tube  60  on the plug of post  62  add damping when the parts slip. If the tube is force fitted on the plug  62 , so the fit is very tight, the tube  60  will provide damping in both tension and compression as the crown  15  vibrates as shown in  FIG. 3 . The plug or post  62  can be used for mounting the tube  60  to the club head sole, if desired. All of the listed variations of fit between the tube  60  and plug  62  are usable. 
   A calculated example, for a tube  60  of durometer about 55 A polyurethane with Young&#39;s modulus of 100,000 pounds per square inch, density of 1.2 grams/cubic centimeter, outside diameter of ⅜ inch, inside diameter of 5/16 inch and length of 1.5 inches, indicates the tube has a lowest resonant frequency of 2500 to 5000 Hz. The resonant frequency depends in part on how firmly the ends of the tube  60  are attached to the sole and crown. This range of lowest resonant frequencies would be satisfactory, but a lowest resonant frequency higher than this range is desirable. If the lowest resonant frequency in bending is much below this range, tube  60  is subject to excessive transverse vibrations at ball impact in the face-rear direction that would cause its mass to not fully participate in the impact, resulting in slightly less distance of a golf shot, and the damping capability of the tube  60  may be diminished. The above example of ⅜ inch outside diameter tubing weighs about 1.0. gram. The tubular configuration is thus preferable to a solid cylinder. The tube need not have a round cross section. 
   It is noted that use of 2 or more of the various damping structures described above may be positioned approximately as desired for best damping. 
   The embodiment of  FIG. 10  is easily constructed. The reason is that for many cases, the face structure is welded to the rear shell, and use of the  FIG. 10  design allows the damping device to be positioned and bonded as required inside the shell between the crown and sole before the face is in place. The face is welded on to the hollow head after this mounting step. The use of a rod or tube of suitable damping characteristics such as polyurethane may also be desirable, as described above. Other of the forms described may be preferred to facilitate other methods of manufacture of the hollow club head. 
   In any case, suitable damping can be satisfactorily estimated by analytical methods, but experiments are generally necessary to make sure that suitable damping and durability are achieved. Fortunately, the level of damping may vary substantially with acceptable results. 
   Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.