Games using tangible projectile – Golf – Club or club support
Reexamination Certificate
2002-11-12
2004-10-19
Blau, Stephen (Department: 3711)
Games using tangible projectile
Golf
Club or club support
C473S321000, C473S323000
Reexamination Certificate
active
06805642
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to golf clubs and, more particularly, to a hybrid shaft for improving the performance of golf clubs.
BACKGROUND OF THE INVENTION
A modern golf club typically comprises a shaft, a head connected to the shaft's tip end, and a grip disposed at the shaft's butt end. Perhaps more than any other component, the shaft affects overall club performance. It is generally accepted that the optimal golf club shaft should have lightweight, high torsional stiffness, configurable bending stiffness, and provide moderately high swing weight and vibration-damping property.
A lightweight club generates greater acceleration, which in turn yields a higher swing velocity, than a heavy club does for the same amount of applied force. For clubs of similar weight and mass distribution, the greater the swing velocity, the farther the ball will travel when driven by the clubs. Torsional stiffness is preferred to limit unwanted angular deflection of the head about the shaft. This allows the face of the club head to impact the ball squarely so that the ball's flight will follow a straight path. The torsional stiffness may be enhanced by enlarging the shaft's diameter to increase polar moment of inertia, as well as by using materials having high Young's modulus such as steel.
Skilled golfers who generate high swing velocity prefer clubs having a high bending stiffness. Average golfers, on the other hand, like clubs with low bending stiffness to take advantage of the “kick” resulting from shaft flexing during early part of swing and subsequent release as the golf club head impacts the ball. But golfers of all levels want a set of clubs having essentially the same swing weights to achieve consistent play. Swing weight is a measure of how the mass is distributed on a club and equates to the dynamic characteristics or “feel” of the club. Tip-weighted shafts and/or heavy club heads tend to increase the clubs' swing weights, while butt-weighted shafts and/or light club heads tend to decrease the clubs' swing weights. A desirable club should also incorporate vibration-damping materials to absorb tactile shock and reduce acoustic propagation caused by the head striking the ball and/or ground.
There are essentially three existing club shaft designs, including metal shafts, composite shafts, and hybrid shaft of metal and composite material. Conventional shafts often optimize some of the characteristics mentioned above while compromising others.
The metal shaft, typically formed from steel, has long been the mainstay of golf club design. Steel has a high shear modulus, giving the shafts an inherently high torsional stiffness. Shafts of various bending stiffness and swing weights can be obtained by manipulating the thickness and lengths of the flexible tip portion and the rigid butt portion. Steel is also durable, strong, inexpensive, and provides great consistency of characteristics from one shaft to another. Unfortunately, steel is dense, and clubs having steel shafts are heavy, have relatively poor acceleration and consequently a lower swing velocity. Additionally, The conventional heavy rubber grip used with the steel shaft, comprising about 15% or more of the total mass of a typical driver or any fairway woods, further compounds the weight and weight distribution problems. Steel shafts are also very poor in absorbing shocks or damping vibrations.
Club shafts comprising composite materials such as graphite are commonly preferred over steel shafts because they can be made extremely lightweight and conform to desired flexural characteristics. The light graphite shaft affords the club with high swing velocity, which produces long drives. Primary drawbacks of the composite graphite designs are their high bending stiffness and low torsional stiffness. To provide a composite shaft with the same torsional stiffness as a metal shaft, particularly in the tip end where the torsional stress is great, many plies of high modulus fibers oriented at ±45 degree angle to the longitudinal axis of the shaft must be incorporated. Unfortunately, these fibers add significant bulk and weight in a particularly undesirable location on the shaft. Additionally, graphite composite shafts are more likely to break, particularly at the tip portion, the part of the shaft with the smallest diameter. Nonetheless, most golfers prefer composite shafts because they are lightweight and have a more pleasant “feel” at impact than steel shafts. Composite shafts are also less sensitive to resonance phenomena since graphite composites are good vibration damping materials.
Hybrid shaft designs typically incorporate both metal and composite materials. U.S. Pat. Nos. 4,836,545 and 5,253,867 both disclose two-piece hybrid shafts that join together a lower metal tip portion with an upper composite butt portion. U.S. Pat. No. 5,028,464 discloses a golf club shaft having a laminated composite tube on the inside, a resin coat on the outside, and a transparent metallic layer disposed between the laminated tube and the resin coat. The transparent metallic layer is formed by depositing or plating a very thin layer of a metallic element onto a transparent cloth of organic and/or organic fibers impregnated with a thermosetting or thermoplastic resin. U.S. Pat. No. 5,083,780 discloses a tubular metal shaft having a short shell of reinforced composite molded over a predetermined location on the metal shaft to control the bending point of the shaft. U.S. Pat. No. 5,259,614 discloses a golf club shaft having a hollow steel tubular core and a composite filament spirally wound about the core to form a seamless jacket thereabout. U.S. Pat. No. 5,607,364 discloses a golf club shaft including a damping layer coated to the inner diameter of the shaft, and the damping layer is formed from a viscoelastic material. U.S. Pat. No. 5,904,628 discloses, among others, a lightweight hollow metal golf club shaft with an inflatable and flexible bladder which is pressurized by a gas to rigidify, reinforce and enhance the performance of the shaft. U.S. Pat. No. 6,139,444 discloses a hollow composite shaft having a preformed sheath metal tube surround the tip portion of the composite shaft as an external stiffener. U.S. Pat. No. 6,302,806 discloses a composite shaft having steel filaments aligned longitudinally in the tip portion for weighting, and steel filaments aligned longitudinally in the butt portion for reinforcement, thereby adjusting center of gravity and bending point of the shaft. U.S. patent application Ser. No. 09/248,569 discloses a hybrid shaft having a steel tip portion and a composite butt portion joined together, and the steel tip has a vibration damping member embedded therein. U.S. patent application Ser. No. 09/813,608 discloses a steel golf shaft having a steel tip portion and a steel butt portion joined by a composite pivot portion via connectors of various configurations.
There remains a need, however, for an improved golf club shaft that is light weight and provides the improved feel and vibration damping of fiber/resin composite shafts, as well as increased torsional stiffness and resistance to breakage of metal shafts.
SUMMARY OF THE INVENTION
The present invention is directed to a hollow golf club shaft of circular cross section having a tubular cover layer and a tubular core layer. The cover layer and the core layer are conjoined and coextend substantially the entire length of the shaft. Preferably, the cover layer has a thickness of less than about 0.2 inches, and the core layer has a thickness of less than about 0.3 inches. The cover layer is formed from an isotropic material such as metal matrix composites, metals and alloys thereof, including titanium, steel, stainless steel, aluminum, tungsten, nickel, copper, zinc, brass, bronze, magnesium, tin, gold, or silver. Preferably, the cover layer is a solid, continuous and non-porous metallic sheath.
The core layer is formed from a non-isotropic material, such as a reinforcement material, preferably impregnated with a vi
Acushnet Company
Blau Stephen
LandOfFree
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