Patent Application
20070149311
This invention relates generally to golf equipment and, in particular, to golf club heads.
As is well known to golf manufacturers and many golfers, the “sweet spot” of a golf club head is the point on the front face at which a line drawn normal to the front face passes through the center of gravity of the golf club head. If a golfer swings a golf club so that the club head impacts the golf ball at the sweet spot, few if any harmonic vibrations are excited within the golf club head and shaft system. Consequently, the maximum amount of energy from the golfer's swing is available for momentum transfer to the golf ball. Conversely, if the golfer swings the golf club so that it impacts the golf ball away from the sweet spot, the impact frequently excites various torsional and bending oscillations. Such a mis-hit has two deleterious consequences. The harmonic oscillations are felt as unpleasant vibrations transmitted to the golfer's hands and the energy lost through the harmonic oscillations is not available for momentum transfer to the golf ball thus resulting in a shorter distance of travel for the golf ball for the same swing speed. This effect is compounded by the fact that in many cases the sweet spot on the front face is at or near the point of the front face which has the highest compliance and therefore, the highest effective coefficient of restitution. Thus, a golf ball hit at the sweet spot will travel substantially further than a golf ball hit at a point on the front face away from the sweet spot. Accordingly, it would be advantageous to provide a golf club head having a lower resilience toward the center of the club head and a higher resiliency toward heel and toe ends of the club head so that the energy transferred to the golf ball would be uniform across the front face irrespective of where the impact occurs.
U.S. Pat. No. 5,807,190 to Krumme, et al. discloses a club head in which the face insert is composed of many small rods arranged in a closely packed array. According to the Krumme patent, use of individual rod segments to form the front face allows the properties of the front face to vary in any pattern over the impact area, simply by varying the materials out of which the individual rods are made. Use of multiple materials within the array of rods could render a front face having the desired distribution of resiliency. Such use of multiple materials would, however, render the club hard non-conforming, for Rule 5(b) of Appendix II of the United States Golf Association requires that the whole of the impact area of a club head be of the same material. Accordingly, what is needed is a golf club head in which the resiliency of the face may be varied across the front face without varying the rod material.
The present invention comprises a golf club head having a face insert the effective resiliency of which varies across a striking surface on a front face of the club head body. According to an illustrative embodiment, the club head body has a cavity for receiving a face insert. The face insert, which is disposed in the cavity, is supported from beneath by a substrate sandwiched between a back surface of the face insert and a bottom surface of the cavity. The substrate is formed of one or more materials to provide the substrate with low resiliency near a central region of the cavity and higher resiliency near either a heel region or a toe region of the cavity. By varying the substrate, the effective resiliency, which is a composite of the face insert and substrate, may be manipulated so that the effective coefficient of restitution between the club head and a golf ball may be made uniform across the entire front face.
The present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawings figures in which like references designate like elements and, in which:
The drawing figures are intended to illustrate the general manner of construction and are not necessarily to scale. In the detailed description and in the drawing figures, specific illustrative examples are shown and herein described in detail. It should be understood, however, that the drawing figures and the detailed description are not intended to limit the invention to the particular form disclosed but are merely illustrative and intended to teach one of ordinary skill how to make and/or use the invention claimed herein and for setting forth the best mode for carrying out the invention.
With reference to
As shown most clearly in
Face insert 40, which is positioned in a central region 62 of cavity 28 is preferably made from an elastomer such as polyurethane having a resiliency of between 0.5 and 0.85. Face inserts 42 and 44 may be made of a metal alloy, ceramic or elastomer having a resiliency greater than that of face insert 40. The material choices for face inserts 40, 42 and 44 will vary from club head to club head depending on the location of the vibrational nodes and anti-nodes of the golf club head.
Where a principal node of the club head is located in the central region 62 of cavity 28, little energy is lost due to the excitation of harmonic vibrations within the club head 10. Accordingly, a golf ball will travel a greater distance for a given club head speed. Conversely, if a golf ball is struck in a heel region 64 of cavity 28 proximal face insert 42, energy will be lost due to the excitation of harmonic vibrations in club 10 and the ball will not travel as far. Similarly, if a golf ball is struck in a toe region 66 of cavity 28 proximal face insert 44, energy will be lost due to the excitation of harmonic vibrations in club head 10. The energy lost in a “toe hit” versus a “heel hit” may or may not be the same. Therefore, in order to compensate separately for a “toe hit” or “heel hit”, the material chosen for face inserts 42 and 44 may be of different resiliencies so as to dissipate different amounts of energy.
The effective coefficient of restitution, as used herein, is the ratio of the velocity of a golf ball struck by the golf club head at various locations on the front face as compared to the velocity of the golf ball in a perfectly elastic collision. The apparent coefficient of restitution C for a golf club of mass M1 travelling at a velocity V1 and striking a stationary golf ball of mass M2 may be described by the following equation:
C=(V2b−V2c)/(V1c−V1b)
Where V1c is the the club head velocity before impact, V1b is the ball velocity before impact, V2c is the club head velocity after impact, and V2b is the ball velocity after impact.
The effective coefficient of restitution will be a function of not only the composite resiliency of face insert 36 and any one of face inserts 40, 42 and 44 but also the energy lost due to the aforementioned excitation of vibrations within the club head. Since the material of face insert 36 must be the same across the entirety of striking surface 34, and since the losses introduced as a result of exciting harmonic vibrations within golf club head 10 are difficult to control, the effective coefficient of restitution can be made uniform across the striking surface 34 most effectively by reducing the resiliency of face insert 40 relative to face inserts 42 and 44 so that the sum of the energy lost due to the resiliency of the face inserts 42, 44, 46 plus the energy lost due to the excitation of harmonic vibrations is equal across the front face 16 of the body 12. Although the resiliency of face insert 36 has some effect on the overall resiliency, the overall resiliency of striking surface 34 is dominated by the resiliency of substrate 38. Therefore, the overall resiliency of striking surface 34 can be manipulated by altering the resiliency of substrate 38 notwithstanding the presence of face insert 36. The result is that, for a given club head velocity, the golf club head will impart the same initial velocity to a golf ball irrespective of where on the front face the golf ball is hit.
With reference to
Although certain illustrative embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the spirit and scope of the invention. For example, first face insert may be a solid insert or a veneer rather than a plurality of rod elements. Accordingly, it is intended that the invention should be limited only to extent required by the appended claims and the rules and principals of applicable law.
