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The present application is a continuation-in-part of co-pending U.S. patent application Ser. No. 10/606,317, filed on Jun. 25, 2003,
This invention relates to a hybrid golf club having a hollow golf club head with a composite core.
The desire for perimeter weighting in a golf club iron is well known in the art. This desire stems from the fact that as the mass of the club is distributed towards the perimeter, the trajectory of the hit ball becomes more accurate, despite off-center hits away from the sweet spot of the golf club face or hitting surface. Consequently, many modern golf club irons have a rear cavity that extends towards the rear side of the face surface of the iron. The weight saved, by creating a rear cavity in the club, is re-distributed to the perimeter of the golf club head, and the greater the volume of the cavity, the greater the amount of mass of metal that can be redistributed to the perimeter of the golf club head.
Conventionally, golf club heads were made from a single material, usually stainless steel for some metal woods and iron type clubs, and recently a large shift in the use of titanium for metal woods. Carbon fiber composite materials have been introduced in an effort to decrease the weight of the golf club head while subsequently increasing the club head's volume. Composite materials have been used widely to reinforce thin club faces, while providing ‘feel” and in some instances vibration dampening.
Typically, in an iron club head, composite inserts are used to support the rear surface of the front face. They are generally sheets of composite attached with an adhesive. The lightweight composite allows for the face to be thin and therefore a larger face and bigger sweet spot.
It is desirable to provide a golf club that optimizes the moment of inertia (MOI) and also normalizes the ball speed over a large area of the face. Thus the ball is launched at similar speeds over a large region to create a larger sweet zone.
The present invention is directed to a golf club having a metal body with a hollow composite core structure. The body is made of a first material having a front face of variable stiffness and a rear cavity. The composite core is of a lower density than the body and includes a portion juxtaposed with the front face for support.
In one embodiment of the invention, a composite core and metallic body are combined to form a hollow golf club head. The composite is used to structurally support a thin front face, and for increased Coefficient of Restitution (COR). Preferably, the front face is of a higher density and lower Young's Modulus than the composite core.
In an embodiment of the invention the front face has a first stiffness at the center of gravity (near the center of the face) and becomes progressively more flexible away from the center of gravity. Preferably, the club is designed such that the face provides substantially uniform ball speed from hits at various locations, i.e., an enlarged sweet zone. The COR across the front face varies from about 0.8 to about 0.9 across the front face. The variation in flexibility across the face may be a result of the front face structure alone, or it may result from a combination of the front face and composite core structures or the front face and composite core materials. The internal volume of the golf club iron head is about 35 cc to 50 cc.
An embodiment of the invention is comprised of a metal body member that may be cast, forged, stamped or made by metal injection molding. The body member is placed in a mold and a composite core is biasly inflated and expanded against the metal body and mold by a bladder method. Preferably, the composite core is located such that the composite material is juxtaposed against portions of the metal body and mold. The mold is used as a boundary for specific regions of the club head where the metal body has an opening(s) such that the exterior of the club is partially metal and partially composite. Embodiments of the invention may be provided in both hollow irons as well as metal woods.
The composite core is made up of a plurality of carbon fiber layers, preferably six, each layer is unidirectional, and horizontal oriented layers alternate with vertical oriented layers to provide strength.
The club has a port in the sole for the introduction and removal of a bladder material. This port houses a plug, preferably a heavy material such as tungsten which has a density greater than 14 g/cc3. The extra weight in the sole is allowed by the removal of weight in the body, especially in the front face which may be very thin because of the lightweight composite core backing. The weight placed in the sole provides for increased peak trajectory.
FIG. 1 is a rear view of the hybrid club of the present invention showing the exposed bladder molded composite core.
FIG. 2 is a sole view showing the plug position.
FIG. 3 is schematic toe view showing the center of gravity for a Titleist® Model 503-H 22° of the present invention in relationship to a conventional 3 iron, such as a Titleist® Model 804.
FIG. 4 is a cross-sectional view along line A-A of the invention of FIG. 1 showing the bladder molded composite core
FIG. 5 is a schematic showing the six layers of carbon fiber that forms the composite core.
FIG. 6 is a bar chart indicating potential carry distance.
FIG. 7 is a bar chart indicating peak trajectory height and roll distance.
An embodiment of an iron golf club head 10 of the present invention is shown on FIGS. 1 to 5. The body 12 of the golf club head 10 has a metal portion having a front face 16 for striking golf balls, a top section 15, a sole 17 having an open port 19, a hosel 21, and a rear opening 25. A sole plug 26 is inserted within the port 19, as discussed later. The body 12 has a cavity 22 that is defined rearward of the face section 14. A lightweight composite core 20 is biasly placed within the cavity 22, juxtaposed against a rear surface 18 of the body 12, to internally reinforce the body 12, and also support the front face 16. The composite core 20 preferably has a composite structure made-up of a plurality of unidirectional carbon fiber layers, preferably six layers, with the horizontal direction fibers alternated with the vertical direction fibers for optimum strength. The metal body 12 may be cast, forged, stamped or made by a metal injection molding method, preferably the head is cast from 431 stainless steel. Reinforcing the body 12 with the lightweight composite core 20 allows for the body 12 to be thinned down in select regions. The thinned down regions permit the mass distribution optimization (Center of Gravity and Moment of Inertia) of the club head 10, and also stiffening the front face 16 that may be relatively flexible due to the thin structure, and therein allows for weight distribution and also dampening of vibrations which helps to create solid feel.
The front face 16 can be made relatively thin because of the reinforcement of the composite core 20. The thickness (t1) of the front face 16 is preferably in a range between about 0.04 inch to 0.12 inch, and more preferably, between about 0.06 inch to 0.1 inch, while the thickness (t2) of the composite core 20 is preferably between about 0.02 inch to about 0.1 inch. The composite reinforced front face 16 can be designed to provide face flexibility characteristics that yield maximum Coefficient of Restitution (COR) values from about 0.8 to about 0.9. The COR of the club head 10 may vary across the front face 16 to normalize ball speed and provide an enlarged sweet zone for added forgiveness. Therein the COR of the club 10 of the present invention may be about 0.8 at the face center and greater than 0.8 away from the face center. Generally, the stiffness of the front face 16 is greatest at the face center, and becomes progressively more flexible away from the face center. The coefficient of restitution is obtained under test conditions, such as those specified by the USGA. The standard USGA conditions for measuring the coefficient of restitution is set forth in the USGA Procedure for Measuring the Velocity Ratio of a Club Head for Conformance to Rule 4-1e, Appendix II available from the U.S.G.A.
The club head 10 forms a hollow style club 10 with thin walls in select regions, especially the upper 14a and lower 14b regions of the face side 16. The composite core 20 may be made of plastic, carbon graphite or any lightweight material with a density less than 4.5 gm/cc, and may be inserted into the hollow golf club 10 in a variety of methods. While the method of inserting the composite core 20 may vary, the bladder method is preferred. In this method, a composite core 20 composed of a carbon fiber pre-preg material that is cut into face, body and rear lay-up pieces are pressurized by a bladder (not shown) that is inserted into the cavity 22 through a port 19. The bladder is preferably made from latex, silicone, or similar materials. Preferably, the composite core 20 is located such that the composite material is juxtaposed against portions of the metal body 12 and the mold. The assembly comprises, the metal golf club body 12, composite core 20, and bladder. When positioned in a mold, which is not shown, the composite core 20 is used as a boundary for specific regions of the club head 10 where the metal body 12 has an opening, such as the rear opening 25. Thus, the exterior of the resultant club head 10 is partially metal and partially composite. A source of pressurized gas, usually air, (source not shown) is introduced through the port 19 to inflate and expand the bladder, and thereby cause plies of the composite core 20 to biasly expand against the inner walls of the golf club 10 and against the internal walls of the mold. The internal walls of the tool are used as a boundary for a region of composite or plastic that is visible to the outside of the golf club 10. Heat may be provided at a predetermined temperature for a selected period of time, i.e., a time sufficient to allow proper curing of the composite material, which for an embodiment of the invention is maintaining the club head 10 in a mold for about 30 minutes, at a pressure of about 50 psi and a temperature of about 275° F. After depressurizing, the bladder may be removed through the port 19, and the golf club head 10 may be removed from the mold. The exterior of the resultant club head 10 is partially metal body 12 and partially composite core material 20 with an internal volume between about 35 cc to 50 cc. Upon removal from the mold, the head 10 has molding residue removed and the perimeter of the club head 10 is sanded smooth and the polished for a final scratch finish. The rear piece of the composite core 20 has a clear coat applied and artwork is performed with a laser alignment fixture prior to a lacquer applied to the face and a sole number painted thereon to finish the head.
The introduction of the plug 26 in the port 19 causes the center of gravity of the club head to be lowered. Plugs 26 of varying weight can adjust the swing weight of the club to match a golfer's specifications. An embodiment of the invention used a plug 26 made from tungsten with a density of about 14 g/cm3.
FIG. 3 illustrates the relationship of the center of gravity of a Titleist® Model 503-H, 22° loft hybrid iron of the present invention, and a Titleist® Model 804, 3 iron, which would be the iron closest in specification to the hybrid club. The center of gravity of the hybrid Model 503-H is lower and further rearward than the 3 iron. This will mean greater distance and greater peak trajectory which translates into a better “drop and stop”™ performance. The Model 503-H with about a 22° loft will yield a ball backspin of less than 5000 rpm at a ball speed of about 126 mph at a launch angle of about 14°.
Performance test data utilizing the swing characteristics of the “Average Tour Player” is available for the Model 503-H hybrid irons against conventional iron clubs. FIG. 6 is a chart depicting the carry distance of the average tour player for various irons and fairway woods. The Model 503-H hybrid with a 22° loft would fall between the 3 and 2 irons with a carry distance of 221 yards versus the 217 yards expected with the 3 iron and 224 yards with the 2 iron. The Model 503-H hybrid with a 19° loft will deliver 229 yards versus 224 yards for a 2 iron and 234 yards with a 19° fairway wood. FIG. 7 correlates the data from FIG. 6 and what it means as to peak trajectory height and roll distance.
The hybrid design offers a hollow construction, wide and low bounce sole for a more forgiving club than a traditional long iron, thin front face supported by the composite core, a lowered and further back center of gravity improves launch angle and spin, all of which makes for an easier to hit golf club than the traditionally designed long irons. These hybrid clubs are designed as an easier hitting alternative to the 2, 3 and 4 irons and/or 3, 4, 5 and 7 fairway woods depending on individual preferences.
The construction of the club head 10 can comprise a variation in the thickness of the front face 16, in which the front face 16 is preferably partitioned into oval regions, each having a progressively lower stiffness. Thus, moving away from the face center, the front face 16 decreases in stiffness and thus increases in flexibility, therein increasing the COR in that area. This design normalizes ball speed over a large range, thus improving the golf club's “forgiveness” or enlarged sweet spot. The front face 16 may be made such that it's flexibility in the face center (proximate the location of the CG) is generally stiffer than the area around the face center. The increase in COR in combination with the energy loss, that occurs from missing a direct central hit on the front face 16, balances out to thereby give the same ball speed as a shot hit directly in line with the face center. While it is known that variable face flexibility can be achieved by making adjustments in the thickness of the front face 16, an example of the invention accomplishes the varying of flexibility by incorporating a varying composite stiffness (via geometry or material variations).
It is believed that those skilled in the pertinent art will recognize the improved inventive concepts of this invention. And they will readily understand that while the present invention has been described in association with a preferred embodiment thereof, and other embodiments illustrated in the accompanying drawings, numerous changes, modifications and substitutions of equivalents may be made therein without departing from the spirit and scope of this invention.