US 20060116218 A1
A metal wood golf club head is provided having a front face with an impact zone including a compliant area. Preferably, the compliant area is disposed in an upper portion of the front face. Preferably, a through-slit is provided in the front face to form the compliant area. The through-slit may be an elongated slot substantially parallel to a top of the front face and may include an elastomeric reinforcement. The compliant area creates an ultra-low center of gravity relative to the geometric face center, resulting in higher launch angles and spin rate ratios. The compliant area upwardly shifts the coefficient of restitution to the geometric center of the face and thereby increases the carry distance of a golf ball hit off the club head.
1. A golf club head comprising:
a first body having a front face interposed between a crown section and a sole section, the front face having a geometric face center and an impact zone comprising a compliant area.
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This application is a continuation-in-part of U.S. application Ser. No. 10/622,682, filed on Sep. 15, 2003, which is incorporated by reference herein in its entirety.
The present invention relates to an improved golf club head. More particularly, the present invention relates to a golf club head having an impact zone with a compliant area. Still more particularly, the present invention relates to a golf club head having a front face with a through-slit.
Golf clubs have achieved a remarkable transformation from persimmon wood clubs to the present day metal woods with their extremely large head sizes. This has been made possible by high strength metallic materials, which allow the golf ball to be hit farther and straighter because of increased club head inertia and coefficient of restitution.
Particularly, development of titanium alloys, which are light (specific gravity: 4.5 to 5.0) and strong, have allowed significant increases in the head size and subsequent practical shaft length of a golf club. Specifically, a large moment of inertia, resulting in an increased area of high speed on the club face can be achieved by use of a large club head. Thus there is a constant demand for club heads of greater size. However, enlarging the club head also increases its weight. Most of the metal wood golf clubs manufactured today have a shell thickness so thin that they border on practical manufacturing limits. This has resulted in the search for materials that are even less dense than titanium. Golf club manufacturers are looking for solutions wherein lighter and stronger materials may be employed. And, in some cases, for materials that will partially replace titanium, which is relatively costly and requires considerable care in forming and casting.
Among the more prominent considerations in club head design are loft, lie, face angle, horizontal face bulge, vertical face roll, center of gravity, inertia, material selection, and overall head weight. While this basic set of criteria is generally the focus of golf club engineering, several other design aspects must also be addressed. The interior design of the club head may be made to achieve particular performance characteristics, such as with the inclusion of hosel or shaft attachment means, or the use of weight members.
The United States Golf Association (USGA), the governing body for the rules of golf in the United States, has specifications for the performance of golf clubs and golf balls. Golf clubs are limited to a Coefficient of Restitution (COR) of 0.83. One USGA rule limits the golf ball's initial velocity after a prescribed impact to 250 feet per second ±2% (or 255 feet per second maximum initial velocity). To achieve greater golf ball travel distance, ball velocity after impact and the coefficient of restitution of the ball-club impact must be maximized while remaining within the rules.
A variety of techniques may be utilized to vary the deformation of the club face, including uniform face thinning, thinned faces with ribbed stiffeners and varying thickness, among others. These designs should have sufficient structural integrity to withstand repeated impacts without permanently deforming the club face. The thinner face maximizes the coefficient of restitution. The more a face rebounds upon impact, the more energy that may be imparted to the ball, thereby increasing distance. In order to make the faces thinner, manufacturers have moved to a forged or stamped metal face which are stronger than cast faces. Common practice is to attach the forged or stamped metal face by welding them to the body or sole. The thinner faces are more vulnerable to failure. Thus, there is a need for a golf club with a face that maximizes golf ball distance while maintaining accuracy due to a reduced sensitivity to face impact location.
The present invention provides a novel manner for providing the face of the club with the desired flex and rebound at impact thereby maximizing coefficient of restitution and golf ball distance, while maintaining accuracy.
The present invention relates to a multi-material, multi-component metal wood golf club head comprised of a front face having a geometric face center, wherein the center of gravity is at least 6 mm lower than the geometric face center, and the point of maximum Coefficient of Restitution (COR) is not lower than 2 mm below the geometric face center.
An embodiment of the invention, designated as club head, comprises a first body portion, a second body portion, and a hosel member. The first body portion comprises a cup-like face section, a sole section, and a bore-thru hosel tube. The second body portion comprises at least a crown section and a substantial portion of a skirt section, and is of a lower density than the first body portion. The density of the second body portion may be between about 0.1 g/cc to 4.0 g/cc.
The material of construction for the first body portion may be a stainless steel alloy, but preferably is a titanium alloy. While magnesium is preferred for the second body portion, composite, or other lightweight metal such as aluminum, or a thermoplastic may be substituted for the magnesium, but with different performance characteristics. The third body portion is a hosel section formed from a lightweight metal or a thermoplastic, including nylon, composite or aluminum materials.
The club head of the present invention has a coefficient of restitution (COR) greater than 0.80, with a COR gradient created in the front face. The thickness of the face is preferably progressively greater in a direction from the crown section to the sole section. This is a beneficial design consideration, since the club head has a lowered center of gravity, the greater face thickness at the sole section refocuses the COR towards the center of the face.
The weight reduction, due to the use of lower density materials in the second body portion and hosel member, allows for that weight to be relocated in the club head. The present invention provides for a weight member, having a generally horseshoe shape, to be positioned on the inside surface of the sole section, at a point near the sole/skirt junction. This further lowers the club head center of gravity and moves it farther from the face, and preferably at least 12 mm from the centerline of the shaft axis.
Another embodiment of the invention utilizes only two body portions, the light weight second portion incorporating both the crown section and the hosel member.
In another embodiment of the invention, a golf club head comprises a first body having a front face interposed between a crown section and a sole section, the front face having a geometric face center and an impact zone comprising a compliant area.
The club head may have a center of gravity below the geometric face center, and the center of gravity may be at least 6 mm lower than the geometric face center.
The compliant area may be disposed above the geometric face center. Additionally, a stiff area may be disposed on the front face at or below the geometric face center. The front face may have a substantially constant thickness; alternatively the front face may gradually increase in thickness in a gradient from the crown section to the sole section. Additionally, the compliant area may be more compliant than the remainder of the front face.
In one embodiment, a through-slit may be provided in the front face comprising the compliant area. The through-slit may be elongated and substantially parallel to the crown section of the club head. The through-slit may have a width less than 4 mm and may have a length greater than 30 mm. The through-slit may comprise two opposing ends, the ends having expanded portions. The through-slit may be substantially C-shaped. Additionally, a reinforcement may be disposed behind the front face to reinforce the through-slit. The reinforcement may comprise an elastomeric material.
In one embodiment, the front face has an increase in deflection to the front face of the club head as compared to a substantially similar golf club head without a compliant area under substantially similar robot testing conditions. The club head may have a decrease in the spin rate of a golf ball leaving the front face of the club head as compared with a substantially similar club head without a compliant area under substantially similar robot test conditions. The club head may have an increase in the launch angle of a golf ball leaving the front face after impact with the club head as compared with a substantially similar club head without a compliant area under substantially similar robot test conditions. The club head may have an increase in the carry distance of a ball hit with the club head as compared with a substantially similar club head without a compliant area under substantially similar robot test conditions.
In one embodiment, the spin rate to launch angle ratio is less than 275 under robot test conditions. In another embodiment, the spin rate to launch angle ratio is less than 250. In yet another embodiment, the club head has a maximum coefficient of restitution greater than 0.80.
Preferred features of the present invention are disclosed in the accompanying drawings, wherein similar reference characters denote similar elements throughout the several views, and wherein:
The golf club head according to preferred embodiments of the present invention, is a multi-material and multi-component hollow club head.
As shown is
The density range for second body portion 32 and hosel member 33, is from about 0.1 g/cc to 4.0 g/cc. Both may be formed from materials such as aluminum, graphite composite, a thermoplastic, but the preferred material for the second body portion 32 is magnesium, and the preferred material for the hosel member 33 is nylon. The method of manufacturing the portions 32 and 33, may be casting, injection molding, machining, prepreg sheet formed, and the like. Preferably, the second body portion 32 has a thickness in the range of about 0.5 mm to about 1.5 mm, and more preferably less than about 1.0 mm. An advantage of injection molding is that it may provide the second body portion 32 with a geometrically complex shape that includes the crown section 34 and a substantial part of the skirt section 35.
The materials for forming first body portion 31 may be stainless steel, pure titanium or a titanium alloy. The more preferred material comprises titanium alloys, such as titanium 6-4 alloy, which comprises 6% aluminum and 4% vanadium, or SP-700 titanium alloy, which comprises 4.7% aluminum, 2.9% vanadium, 2.0% molybdenum and 2.1% iron and is commercially available from NKK (Japan) and RTI International Metals (Niles, Ohio). First body portion 31 may be manufactured through casting with a face insert that is made by forming, or forging with a stamped sole, or forming a wrapped face with a stamped sole, or powdered metal forming, or metal-injection-molding and the like.
By using magnesium for the second body portion 32, a certain amount of weight may be reassigned to the weight member 40, which is integral with the sole section 36. The horseshoe shaped weight member 40 has a specified density is the range from about 4 g/cc to 20 g/cc, and may be selected from such materials as tungsten, molybdenum or another like metal in a like density range. Weight member 40 may be cast, injection molded, machined or formed by a powdered metal process. Weight member 40 is positioned away from the face section 37, a critical design concept for the lowering of the center of gravity C. The methods for determining the positioning of the center of gravity C and the calculation of the geometric face center X are shown on schematic
Three embodiments of the club head 30 design of the present invention were tested against a prior art club (Titleist® 983K driver) which is very similar in appearance, size and shape of the embodiments of the present invention. The three embodiments were all generally identical to each other except for the materials of construction of the second and third body portions 32, 33.
Test results for determining the position of the center of gravity C as it relates to the geometric face center are presented below in Table I, for three different embodiments of the present invention. Test data is also presented for the prior art club head Titleist® 983K, for comparison purposes.
Embodiment A of the present invention provides for a shift in the center of gravity C to a position at least 6 mm below the geometric face center X. The actual test results show the center of gravity C to be 7.88 mm below its geometric face center X, while tests for the Titleist®983K (having a titanium crown and skirt) provided data indicating that the 983K's center of gravity was 2.29 mm above its geometric face center. Comparable shifts in the center of gravity C are seen in the test data for embodiments B and C.
The Titleist® 983K has a volume of 363 cubic centimeters, and a titanium SP700 stamped hitting face with a thickness of about 0.122 inch. Unlike the present invention, the 983K does not have a thickness gradient in the hitting face 48 (discussed below). And, while the second body portion 32 of the present invention is formed from magnesium, and the hosel member 33 is formed of nylon, these portions of the 983K are formed from the heavier titanium alloys. Other than these differences, the embodiments of the present invention and the 983K are very comparable in size and dimension. Test results are shown in
A significant improvement in ball speed of the present invention over the prior art 983K can be best described by
The final results are culminated in
These figures depict the initial ball speeds when the clubs traveling at about 110 mph impact Titleist PRO V1 balls. The angle of attack is about 2°, and the effective loft angle is about 12°. The clubs are mounted on a robot, which is driven to impact the balls at the desired club speed. Robots are commercially available from the True Temper Corporation or the Wilson® Sporting Goods Co. The locations of ball impacts are distributed over a rectangular area of 0.50 inch in the vertical direction and about 1.0 inch in the horizontal direction. The mechanical driver has the ability to repeatedly hit the balls at any desirable location on the hitting face. The ball speeds are measured by launch monitors. Any suitable launch monitors can be used. Examples of launch monitors include those described in commonly owned U.S. Pat. Nos. 6,533,674, 6,500,073, 6,488,591, 6,285,445, 6,241,622, 5,803,823 and 5,471,383, among others.
Preferably, the front face section 37 of the present invention has a gradient thickness in the hitting face 48 ranging from the thinnest thickness about the crown section 34 to the thickest at the sole section 36.
An alternate embodiment for the front face section 37 is shown in
The standard USGA conditions for measuring the coefficient of restitution is set forth in the USGA Procedure for measuring the Velocity Ration of a Club Headfor Conformance to Rule 4-1e, Appendix II. Revision I, Aug. 4, 1998 and Revision 0, Jul. 6, 1998, available from the USGA. Such tests measure COR by measuring ball resiliency. COR is the ratio of the velocity of separation to the velocity of approach. In this model, therefore, COR was determined using the following formula:
The COR, in general, depends on the shape and material properties of the colliding bodies. A perfectly elastic impact has a COR of one (1.0), indicating that no energy is lost, while a perfectly inelastic or perfectly plastic impact has a COR of zero (0.0), indicating that the colliding bodies did not separate after impact resulting in a maximum loss of energy. Consequently, high COR values are indicative of greater ball velocity and distance.
First and second body portions, 31, 32 and hosel member 33, are sized and dimensioned to be attached together by any conventional methods used to join dissimilar materials, such as brazing and structural adhesives. A high quality plasma welding technique, similar to the welding technique used in Titleist® 983 driver club, is preferred.
An alternate embodiment, depicted by
Alternatively, the club head of the present invention may also be used with the smaller fairway woods, which can have volume as low as about 150 cubic centimeters. Preferably, the mass of the inventive club head is greater than 150 grams but less than 300 grams. It is anticipated that a fairway wood may be made from the design concepts of the present invention. Such a wood may have a first body portion made of a metal such as stainless steel, a second body portion (substantially the crown and skirt) made from a lower density metal such as titanium, and a hosel member having a density no greater than the second body portion.
In another embodiment, the front face section 56 of a club head 58 may include an impact zone 60 having a compliant area 62. Generally, the compliant area 62 causes a portion of the impact zone 60 to be more compliant than the remainder of the impact zone 60 of the front face section 56. Thus, the front face section 56 has an increase in deflection at the compliant area 62 as compared to a substantially similar golf club head without a compliant area. The compliant area may be disposed on any desired portion of the impact zone. In one embodiment, the compliant area is found on the upper portion of the hitting area, preferably above the geometric face center X of the front face section of the golf club. The compliant area 62 of the front face section 56 causes the golf ball after impact to have a lower spin rate and a higher launch angle. This results in longer golf ball flight. As discussed above, the club head provides a shift in the center of gravity C to below the geometric face center X. Preferably, the center of gravity C is shifted to a position at least 6 mm below the geometric face center X. It will be appreciated that the compliant area 62 may be made with numerous different constructions. One example of such a construction is illustrated in
As illustrated in
As illustrated in
It will be appreciated that the through-slit 70 may have any desired shape. As illustrated in
In another embodiment, the impact zone may include a stiff area 78 in addition to the compliant area 62. For example, as illustrated in
The club head 58 having the compliant area 62 has a decrease in the spin rate of a golf ball leaving the front face section of the club head as compared with a substantially similar club head without a compliant area under similar test conditions. Additionally, the club head has an increase in the launch angle of a golf ball leaving the front face after impact with the club head as compared with a substantially similar club head without a compliant area under substantially similar test conditions. The decreased spin rate and increased launch angle result in a club head that has an increase in the carry distance of a ball hit with the club head as compared with a substantially similar club head without a compliant area. Preferably, the spin rate to launch angle ratio is less than 275 under robot test conditions. More preferably, the spin rate to launch angle ratio is less than 250. The club head has a maximum coefficient of restitution of greater than 0.80.
It will be appreciated that the embodiments of
The through-slit 70 may be formed in the club head by machining. Alternatively, the through-slit 70 may be formed from the process of making the first body by sheet metal stamping, casting or forging. In yet another embodiment, the through-slit 70 is formed by two portions that form the club head, such that the two portions are not welded together on at least a part of the intersection between the portions. Thus, the through-slit 70 is formed by the unwelded adjacent portions.
While various descriptions of the present invention are described above, it should be understood that the various features of each embodiment could be used alone or in any combination thereof. Therefore, this invention is not to be limited to only the specifically preferred embodiments depicted herein. Further, it should be understood that variations and modifications within the spirit and scope of the invention might occur to those skilled in the art to which the invention pertains. The scope of the present invention is accordingly defined as set forth in the appended claims.