Abstract:
A golf club is provided having improved playing characteristics based upon a multiple material construction. This construction involves a club body in combination with a face insert that defines a hollow channel therebetween. This hollow channel is substantially filled with a heterogeneous viscoelastic material, such as urethane containing tungsten powder. The heterogeneous material is formulated such that the density of the material is varied based upon the location of that material within the hollow channel of the golf club head. In particular, lower density portions of the material are located near the top of the club head, and higher density portions are located near the bottom or sole of the club head. This moves the center of gravity of the club head downward and rearward, yielding improved feel and improved weight distribution and enhancing performance of the club.

Description:
FIELD OF THE INVENTION 
     The present invention relates to golf clubs and more specifically to golf clubs with improved mass properties and vibration damping. 
     BACKGROUND OF THE INVENTION 
     Perimeter weighting in iron-type golf clubs distributes non-essential mass of the iron towards the perimeter, reducing the effects that off-center hits have on the golf club and producing more accurate and consistent golf ball trajectories. Perimeter weighting is achieved by creating a cavity in the back of the golf club opposite the face or hitting surface. The material weight removed to create this cavity is redistributed around the perimeter of the golf club head. In general, larger cavity volumes correspond to increased amounts of mass distributed around the perimeter. 
     Removing material from the rear of the club head, however, reduces the thickness of the club face. Since the club face is the hitting surface, the club face cannot be so thin that the strength of the club face surface is not sufficient to withstand the stress resulting from a golf ball striking the club face. Reducing the thickness of the club face may also increase vibrations upon impact. These vibrations may cause bad feel to the user. 
     There are various examples of secondary material incorporation into iron golf club heads for vibration damping. Some of these examples have provided the additional benefit of displacing weight to the perimeter of the club head so as to increase the club head&#39;s rotational moment or inertia (MOI). These vibration dampers, however, have involved multiple materials such as in constrained layer damping, or they have been positioned across the entire face or isolated to the lower area of the club head. In addition, most conventional club heads are made of one homogenous material and the secondary damping materials incorporated into the golf club head are also homogenous. This type of construction, however, imposes design constraints on the bead configuration, thus limiting the opportunity to produce an iron with forgiving play characteristics while at the same time maintaining a traditional sized head. The use of one homogenous material also may limit the placement of the head&#39;s center of gravity. 
     Therefore, a golf club head is desired that utilizes a secondary material to improve vibration damping while improving the placement of the center of gravity and MOI of the club head to improve golf ball launch conditions and to improve the feel of the club to the user. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a golf club having improved playing characteristics based upon a multiple material construction. This construction involves a club body portion having a face insert. There is a hollow area or channel between the face insert and the body portion after the insertion of the face insert. This hollow channel is substantially filled with a heterogeneous viscoelastic material, such as urethane or natural or synthetic rubber containing additives or fillers to modify the material&#39;s density. Suitable fillers include high density fillers and low density fillers. High density fillers include, but are not limited to, metal powders such as tungsten powder. Low density fillers include, but are not limited to, micro-spheres or voids created by foaming agents. The fillers are partially incorporated into the viscoelastic material so that a lower density portion of the material is located near the top or crown of the club head and a higher density portion is located near the bottom or sole of the club head. This moves the center of gravity of the club head downward and rearward while providing vibration damping. The shape and volume of the channel can also be varied to further modify the weight distribution in the golf club head. The incorporation of this secondary or damping material provides improved feel, improved weight distribution, and enhanced club performance. 
     For example, in one embodiment, the heterogeneous composite material has at least a first region having a first density and disposed in the channel toward the top line of the golf club body and a second region having a second density and disposed in the channel toward the sole of the body. The second density is greater than the first density, thereby lowering the center of gravity while providing vibration damping. When the channel is in the shape of a generally annular or elliptical ring running substantially parallel to the perimeter of the body of the golf club head, the first region of the composite material is disposed in a first portion of the channel adjacent the top line, and the second region of the composite material is disposed in a second portion of the channel adjacent the sole. This annular or elliptical ring can be arranged with uniform dimensions, or the dimensions can be varied to further affect weight distribution. For example, the annular channel can have a first width disposed adjacent the top line and a second width disposed adjacent the sole, such that the second width is greater than the first width. Similarly, the annular channel further can have a first depth in the first width area and a second depth in the second width area, such that the second depth is greater than the first depth. Therefore, a greater amount or volume of heterogeneous composite material can be placed toward the sole and rearward in the club head. 
     The channel between the club body portion and the face insert may comprise discrete portions, with at least one portion containing lower density viscoelastic material and at least another portion containing a higher density viscoelastic material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a first perspective rear view of an embodiment of the golf club heads of the present invention; 
         FIG. 2  is a perspective front view of the club body portion without the hitting face; and 
         FIG. 3  is a cross-sectional view through line  3 - 3  of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the accompanying figures, exemplary embodiments of the golf club head  10  in accordance with the present invention include body portion  20  ( FIGS. 1 and 2 ) connected to hosel  22 . Hosel  22  is adapted to receive a shaft (not shown). The club head  20  is preferably cast or forged from suitable material such as stainless steel, carbon steel or titanium. Body portion  20  includes crown  24 , toe  26 , sole  28  and heel  30  that form the perimeter of body portion  20 . Hosel  22  extends generally from heel  30  of body portion  20 . Club head  10  is preferably a cavity back club; therefore, body portion  20  includes rear perimeter  32  extending from the back of the club head and running along its perimeter. The portion of perimeter weight  32  along sole  28  is larger/thicker to move the center of gravity downward and rearward. Arrangements for perimeter weighting are generally known in the art. 
     As is shown in  FIG. 3 , club head  10  also includes face insert  38  attached to the front  36  of body portion  20 . Suitable materials for face insert  38  include, but are not limited to, stainless steel, preferably a high-strength steel material, and non-steel materials such as titanium and metal matrix composites (MMC). Face insert  38  forms the club face or hitting surface of club head  10 . Suitable methods for attaching face insert  38  to body portion  20  include, but are not limited to, welding, swaging, press fitting, hot isostatic pressing and attachment using bonding agents or adhesives. In one embodiment, face insert  38  is attached to body portion  20  by laser-welding face insert  38  to cast body portion  20  of the golf club. Face insert  38  is in contact with and supported by body portion  20  at one or more support  40 . In other areas, face insert  38  is spaced from body portion  20  to define channel  42  disposed between at least a portion of face insert  38  and body portion  20 . In one embodiment, channel  42  can be completely enclosed between body portion  20  and face insert  38 . Channel  42  is adapted to receive a secondary or damping material. 
     In one embodiment, hollow or channel  42  is not completely enclosed but is arranged to have one or more open areas or openings  44  to the back cavity. Openings  44  can be positioned near to line  24  or sole  28 , and can be an elongated channel or circular shape. These open areas or openings allow any secondary material disposed in the channel to be visible to the user. Channel  42  can be formed as a uniform channel or can vary in size and shape. In one embodiment, channel  42  forms a generally annular shape running substantially parallel to rear perimeter  32 . In one embodiment, channel  42  between face insert  38  and cast body  20  extends from about 45° to about 360° around the perimeter of the face of the golf club. Channel  42  may comprise several discrete portions. In one embodiment, the width of this annular channel is varied. For example, annular channel  42  can have first width  46  disposed adjacent top line  24  and second width  48  disposed adjacent sole  28 . In one embodiment, second width  48  is greater than first width  46 . In addition, the depth of the annular channel can be varied. For example, channel  42  can include first depth  50  and areas of second depth  53 , such as at openings  44  as shown in the cross-sectional view of  FIG. 3 , in first width  46  or other areas disposed toward top line  24  and second depth  53  in the second width  48  area. Second depth  53  is greater than first depth  50 . Varying the depth and width of channel  42  varies the volume of channel  42  and the amount of channel  42  in contact with face insert  38 . 
     In order to damp vibration and improve weight distribution, heterogeneous composite material  52  is disposed in at least a portion of channel  42 . Composite material  52  is heterogeneous in that the composition and density of composite material  52  is varied depending on its location within channel  42 . In one embodiment, heterogeneous composite material  52  is disposed in the entire channel  42 . In general, the composition, e.g., the density, of composite material  52  is varied in order to shift more weight downward and rearward, thereby moving the center of gravity of golf club head  10  downward and rearward as well. Therefore, the portion of composite material  52  located toward crown  24  is formulated to have lower density, and the portion of composite material located toward sole  28  is formulated to have higher density. The volume and configuration of channel  42  can also be used to improve the weight distribution. For example, the channel is arranged to be larger or to extend farther rearward in areas located near the sole of the club head. In one embodiment, heterogeneous composite material  52  contains first region  54  having a first density and disposed in channel  42  toward crown  24  of body portion  20 . The composite material also includes second region  56  containing second density and disposed in channel  42  toward sole  28  of body portion  20 . The second density is greater than the first density. 
     Suitable methods for introducing or attaching the composite damping material to the channel include, but are not limited to, pouring or injecting the damping material into the hollow area after face insert  42  is welded to the body, for example through openings in the back of the body portion. The face insert can also be crimped into place, allowing the heterogenous composite material to be molded separately and placed into the cast body before crimping, providing the benefit of ease of manufacture. The molded material can be press fit or attached using a bonding agent such as glues or epoxies. Alternatively, the composite material can be poured or injected into the hollow area before face insert  42  is installed, as with laser-welded attachments. 
     In a preferred embodiment, channel  42  is arranged with a generally annular shape that runs substantially parallel to the perimeter of body portion  20 . In this arrangement, first region  54  of composite material  52  is disposed in a first portion of channel  42  disposed adjacent top line  24 , and second region  56  of composite material  52  is disposed in a second portion of channel  42  adjacent sole  28 . In this embodiment, composite material  52  substantially fills the entire channel  42 , providing contact with face insert  38  throughout the channel area. 
     The heterogeneous material is selected to enhance weight distribution and vibration damping. In one embodiment, the heterogeneous composite material includes a viscoelastic material. Suitable viscoelastic materials include, but are not limited to, polyurethane, natural or synthetic rubbers, other elastomers, epoxies, and combinations thereof. Preferably, the heterogeneous composite material includes a polyurethane made from a polyol and a polyisocyanate. In general, any viscoelastic material can be used. If the heterogeneous material is to be poured or injected, the material should have a low viscosity, minimal shrinkage rate and quick set-up time to allow for ease of manufacturing. Suitable materials include silicone rubbers such as RTV-627, which is commercially available from MG Chemicals of Surrey, B.C., Canada. 
     Changes in the weight or density of the heterogeneous composite material to achieve heterogeneity are achieved by adding fillers to the viscoelastic materials. These fillers can either decrease, e.g., glass beads, micro-spheres or voids created by foaming agents, or increase, e.g., metal powders, the density of the composite material. Suitable fillers include, but are not limited to, carbon graphite, metal fibers, zinc oxide, barium sulfate, calcium oxide, calcium carbonate and silica, as well as the other well known corresponding salts and oxides thereof, foaming agents, glass spheres, metals and combinations thereof. Preferably the additive or filler is a metal powder. Suitable metal powders include, but are not limited to, tungsten, magnesium, titanium and aluminum. Preferably, the metal powder has high density such as tungsten powder, producing, for example, a tungsten-filled silicone rubber. The amount of filler is selected based upon the desired density distribution requirements. In one embodiment, upper portion  54  contains un-filled viscoelastic material and lower portion  56  contains high density metal-filled viscoelastic material. 
     Additional components or additives that can be added to the heterogeneous composite material include UV stabilizers and other dyes, as well as optical brighteners and fluorescent pigments and dyes. Such additional ingredients may be added in any amounts that will achieve their desired purpose. 
     As shown in the figures, club body portion  20  also includes central opening  58  having perimeter  59  that generally parallels the perimeter of body portion  20 . Opening  58  exposes back surface  60  of face insert  38  to the back of the club head. Adjacent perimeter  59  of opening  58  is contact surface  40  that is in contact with face insert  38 . In one embodiment, step or space  62  runs along perimeter  59  and is spaced from contact surface  40 , as shown in  FIG. 3 . This provides a gap that can be used to inject the heterogeneous composite materials  52 . 
     Exemplary embodiments of golf clubs having the face insert, cast body and heterogeneous viscoelastic material in accordance with the present invention provide improved feel due to the damping provided by viscoelastic material  52  confined in channel  42  disposed between body portion  20  and face insert  38 . The damping material is in contact with and is located directly behind the hitting area, as well as around the perimeter of the face, where significant vibration could occur. By removing weight from the topline and upper perimeter and replacing it with lighter viscoelastic material and by adding high density filler to the viscoelastic material near the sole, the center of gravity is lowered. Arrangements in accordance with the present invention can be used with various types of golf clubs includes irons, putters and wedges. 
     Golf clubs in accordance with exemplary embodiments of the present invention allow for damping material to be placed around the entire perimeter of the face, if desired, or to be isolated to specific areas of the club head such as only the topline or only the high or low toe area. In addition to the mass property and vibration damping benefits, the channel may have a unique cosmetic appearance if part of the channel is left exposed. The exposed area would create a window or series of windows through which the viscoelastic material can be seen. 
     Alternatively, the density of the damping material remains substantially the same throughout, and the damping material is made from a composite material, such as a viscoelastic material with fillers, as described in details above. In one example, the viscoelastic material comprises polyurethane and the filler comprises low density micro-spheres or high density metal powders. The option of using low density or high density fillers provides golf club designers with additional degrees of freedom to locate the center of gravity at desired locations, to size the sweet spot of the golf clubs, and to adjust MOI as desired. 
     While it is apparent that the illustrative embodiments of the invention disclosed herein fulfill the objectives of the present invention, it is appreciated that numerous modifications and other embodiments may be devised by those skilled in the art. Additionally, feature(s) and/or element(s) from any embodiment may be used singly or in combination with other embodiment(s) and steps or elements from methods in accordance with the present invention can be executed or performed in any suitable order. Therefore, it will be understood that the appended claims are intended to cover all such modifications and embodiments, which would come within the spirit and scope of the present invention.