WO1997028852A1

WO1997028852A1 - Golf club head controlling golf ball movement

Info

Publication number: WO1997028852A1
Application number: PCT/US1997/002106
Authority: WO
Inventors: Christian Paul Marlowe; James Robert Cope
Original assignee: Copex Corporation
Priority date: 1996-02-07
Filing date: 1997-02-07
Publication date: 1997-08-14
Also published as: AU2526597A

Abstract

The present invention provides a more stable golf club than existing club designs. The club can have heel (20) and butt weights (96) to move the head center of gravity (32), and head and club centers of percussion (48) to desired locations to yield superior ball control, a wood insert (160) on the face of the club head to provide improved head wear, a joint (208) between the shaft and head having both adhesive for high strength bonding and metal to metal contact (220, 224) for increased energy transfer, and a lightweight shaft (44) having a relatively high strength. These features, singly or collectively, provide a club that is more stable during a golfer's swing, and therefore yields a greater degree of ball control relative to existing club designs.

Description

GOLF CLUB HEAD CONTROLLING GOLF BALL MOVEMEN-T

FIELD OF THE INVENTION The present invention relates generally to golf clubs and specifically to weighted golf clubs.

BACKGROUND OF THE INVENTION

Golf is a popular sport world-wide. Golf clubs are typically sold in sets including a number of drivers and irons and a pitching wedge and putter. A key consideration in using the golf clubs, especially the drivers and irons, is ball control (e.g., the distance of the drive and accuracy of the placement of the golf ball) .

Existing golf clubs suffer from a number of ball control problems. By way of example, golfers often "slice" the golf ball which causes the ball trajectory to be significantly offset from the intended trajectory. The golfer can also experience a sharp vibration when the golf club head strikes the golf ball, which not only creates ball control problems but also causes golfer discomfort and even physical ailments such as tennis elbow. To overcome such problems, golf clubs have been modified to position a "sweet spot" on the face of the head at the probable location where the golf ball contacts the head. Contacting the golf ball with the "sweet spot" is believed to maximize the amount of energy transferred from the golfer to the golf ball via the golf club. Even if this belief were true, the "sweet spot" is assumed to be a point location on the face of the golf club head and is therefore easily missed by the ball. Moreover, the toe and heel weighting of the head required to enlarge the size of a "sweet spot" and thereby increase the probability of the "sweet spot" contacting the golf ball can cause the golf club to be too heavy, which can detract from the effectiveness of the golfer's swing.

SUMMARY OF THE INVENTION It is an objective of the present invention to provide a golf club enabling a golfer to have a high degree of ball control. Related objectives include providing a golf club that maximizes the amount of energy transferred from the golfer to the golf ball via the golf club; that minimizes the rotation and/or translation of the golf club during use; that inhibits vibration of the golf club upon impact with the golf ball; that maximizes the size of the true "sweet spot" on the face of the head; and/or that has a relatively light weight.

These and other objectives are addressed by the various inventions set forth herein. In a first invention, a golf club includes: (i) a club shaft; (ii) a club head attached to a lower end of the club shaft; and (iii) a heel weight, at least a portion of which is located between (a) the side of the club shaft closest to the toe end and (b) the heel end. The weight of the first portion is sufficient to cause (i) the center of gravity of the club head to be located between the heel end and a line formed by a side of the club shaft and (ii) the center of percussion of the club head relative to the club shaft to be located at a distance from the club head, with the center of percussion being located closer to the toe end than the heel end to substantially stabilize the golf club upon contact of the club head with a golf ball. To comply with USGA regulations for woods and drivers, the longitudinal axis of the club shaft is located at a distance of no more than about 0.625 inches from the heel end.

The effect of moving the club head center of percussion relative to the club shaft to a distance from the toe end of the head and the club head center of gravity to the area between the club shaft and the heel end is to make the entire face of the club head a "sweet spot." This feature provides the golfer with a higher degree of ball control and drive distance relative to existing club heads.

In one embodiment, the first portion represents at least about 25% of the total weight of the club head. More preferably, the first portion represents from about one- third to about one-half of the total weight of the club head. Typically, the first portion is at least about 50 grams (for a driver club) and more typically ranges from about 70 to about 105 grams. In another embodiment, the center of gravity is substantially collinear with the club shaft. Preferably, this translates into the center of gravity being located within about 0.18 inches of the club shaft longitudinal axis and more preferably within about 0.10 inches of the club shaft longitudinal axis. Most preferably, the center of gravity is substantially collinear with the centerline of the club shaft.

In another embodiment, the center of percussion of the entire golf club relative to a rotational axis located near the point of contact of the golfer's hands with the club shaft (i.e., the grip) is located at substantially the same location as the club head's center of gravity. In a preferred configuration, the distance between the center of gravity and center of percussion is no more than about 0.50 inches. This result is realized by including a butt weight at the upper end of the club shaft, which causes the golf club's center of percussion to move towards the club head so that the center of percussion is preferably no more than about 0.2 inches from the club shaft longitudinal axis. To yield this result, the butt weight is typically located at a distance of no more than about 0.5 inches from the club shaft longitudinal axis and in the upper 10% of the length of the club shaft, which translates into the center of gravity of the butt weight being located at a distance of no more than about 2.0 inches from the upper end of the club shaft, and the butt weight typically ranges from about 10 to about 25% and more typically from about 10 to about 22% of the total weight of the golf club or from about 39 to about 82 grams. The various features of this invention combine to provide a more stable golf club that provides for significantly increased ball control and drive distances relative to existing golf clubs. Compared to existing clubs, the features reduce the amplitude and frequency of club vibrations and the rotation and/or translation of the golf club caused by impact of the head with the golf ball. As a consequence, the amount of energy transferred from the golfer to the golf ball via the golf club is significantly increased.

In another invention, a method is provided for moving the center of gravity of the club head and centers of percussion to the desired locations. To position the head's center of gravity as desired, the steps include: (i) determining whether the center of gravity of the club head is at a desired location, the desired location being in the club head along the club shaft, and (ii) when the center of gravity is not at the desired location, placing the heel weight between the heel end of the club and a portion of the club shaft that is sufficient to cause the center of gravity to be located between the heel end and an edge of the club shaft and a center of percussion of the club head relative to the club shaft to be located at a distance from the club head. To locate the center of gravity, the club head is suspended from a first point on the club head to identify a first line along which the center of gravity is located and the club head is suspended from a second point on the club head that is different from the first point to identify a second line along which the club head center of gravity is located. The center of gravity is located at the intersection of the two lines. To position the golf club's center of percussion relative to the rotational axis located near the grip as desired, the steps include: (i) determining whether the center of percussion of the golf club is at a desired location, the desired location being substantially the same location as the center of gravity of the club head and substantially collinear with the club shaft, and (ii) when the center of percussion location is not substantially the same location as the desired location, placing a butt weight in a butt end of the club shaft that is sufficient to move the center of percussion to the desired location. To determine if the first location is the desired location, the distance from a pivot point on the golf club (i.e., the pivot point resulting from the contact of the golf club with the golf ball) to the desired location is measured and a predetermined period of oscillation of the golf club about the pivot point is determined based on the distance. The predetermined period of oscillation permits the butt weight to be progressively increased until the period of oscillation of the golf club about the pivot point is substantially the same as the predetermined period of oscillation. In another invention, the golf club includes a club shaft, an insert composed of phenolic/linen, wood, solid graphite, or composites thereof, and a club head attached to the lower end of the shaft. The head includes metal shell having a face for contacting the golf ball. The insert is mounted on the face to contact the golf ball to substantially inhibit deformation of the face therefrom.

The wood insert can be persimmon wood, hickory, maple or composites thereof. The preferred wood insert is composed of persimmon wood to replicate the aesthetically pleasing contact sound of the conventional persimmon wood drivers with a golf ball.

To amplify the contact sound, the metal shell can be substantially hollow. Preferably, at least about 85% of the metal shell is occupied by a space.

The insert not only yields an attractive sound when the insert contacts a golf ball but also is resistant to deformation from repeated contact with golf balls. The unattractive metal clang that is produced by conventional metal-faced heads is eliminated by the wood insert. Compared to metal-faced heads, the insert has significantly greater resistance to deformation or warpage caused by repeated contact with golf balls.

In another invention, the golf club includes a club shaft, a club head attached to the club shaft, and a specially designed joint between the head and shaft. In a first portion of the joint, the shaft has a smaller diameter than a hole in the club head for receiving the shaft, thereby forming a gap between the shaft and the head for receiving an adhesive therein to adhere the head to the shaft. In a second portion of the joint, portions of the shaft contact portions of the head. The contact of the head and shaft substantially inhibits the movement of the head relative to the shaft when the club contacts the golf ball.

The length of the second portion is preferably at least about 25% of the total length of the joint. More preferably the length of the second portion ranges from about 33 to about 50% of the total length of the joint.

The second portion of the joint can include a grooved surface and/or a projection received in the grooved surface in at least one of the lower club shaft and head. A tapered member can be included in the lower end of the shaft to force the grooved surface against the projection.

The joint provides a strong bond between the head and shaft due to the presence of the adhesive without the attendant drawbacks of the adhesive. The tendency of the adhesive to absorb part of the force when the head impacts the golf ball is reduced by the metal-to-metal contact of the shaft and head in the second portion of the joint. The metal-to-metal contact enhances the transfer of energy from the golfer to the golf ball and provides the golfer with a solid feel when the head strikes the golf ball. Finally, in another invention the golf club includes a lightweight club shaft attached to the head. The shaft is primarily composed of a beryllium alloy containing aluminum to provide a shaft that is not only relatively light weight, but also has a high strength.

The low weight and high strength of the shaft permit a club to strike the optimal balance between club head speed and club momentum at contact with the golf ball. As will be appreciated, lighter weight clubs produce higher club head speeds during a swing while heavier weight clubs produce higher club momentums during the swing. The lightweight shaft also permits smaller heel and butt weights relative to conventional shafts to yield the features of the first invention. Even with the heel and butt weights of the first invention, the total weight of a driver golf club using the lightweight shaft is only about 13.0 ounces. Surprisingly, the combined weights of the butt weight and the lightweight shaft is less than the normal weight of conventional steel shafts without a butt weight.

BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A-L depict a first invention which utilizes heel and butt weights, with Fig. IF being a cross-sectional view taken along line A-A of Fig. IE, Fig. IH a cross- sectional view taken along line B-B of Fig. IG, Fig. 1J a cross-sectional view taken along line A-A of Fig. il, and Fig. IL a cross-sectional view taken along line B-B of Fig. IK;

Figs. 2A and B depict the invention during a golfer's swing and the various axes of rotation; Fig. 2C depicts a prior art club during a golfer's swing;

Fig. 2D depicts another view of a golf club according to the present invention;

Fig. 3A and B depict a methodology used to locate the center of gravity of the head;

Fig. 4 depicts a methodology used to locate the center of percussion of the club;

Figs. 5A is a cross-sectional view and 5B is a front view depicting the wood insert of another invention; Figs. 5C-F are views of a golf club head according to another embodiment of the present invention, with Fig. 5D being a cross-sectional view taken along line A-A of Fig. 5C and Fig. 5F a cross-sectional view taken along line B-B of Fig. 5E; Figs. 6A-C are cross-sectional views depicting the hosel and club shaft according to another invention of the present invention wherein Fig. 6B is a section along line A-A and Fig. 6C along line B-B;

Fig. 7 is a cross-sectional view depicting the interior of the hosel before assembly; Figs. 8A-B depict the club shaft; Fig. 9 depicts the tapered plug when received by the club shaft; and

Fig. 10 is a plot of beryllium/aluminum content versus modulus.

DETAILED DESCRIPTION

The various inventions of golf clubs according to the present invention represent significant enhancements over existing golf clubs. Relative to existing golf clubs, the inventions not only significantly enhance the ability of the golfer to control a golf ball but also substantially increase the amount of energy transferred from the golfer to the golf ball. The inventions therefore permit better ball placement and/or longer drives. As discussed in detail below, the various inventions employ one or more of a heel weight, butt weight, wood insert, modified joint between the hosel and shaft and/or lightweight shaft to yield these results.

The Heel Weight Referring to Figs. 1A-L, a first invention uses a heel weight 20 adjacent to the heel end 24 of the club head 28 to cause the center of gravity 32 of the club head to be located between the heel end 24 and a line 36 formed by a side 40 of the club shaft 44 and the club head center of percussion 48 relative to the club shaft 44 to be located at a distance from the club head. As shown in Fig. IC, this configuration causes virtually the entire club head to be located between the club head center of gravity and center of percussion which has been found to provide a stabilizing effect on the club head upon impact with the golf ball. The center of percussion can be explained by relatively simple physics. For a body that rotates about a fixed axis, such as the club head 28 about the club shaft 44, the resultant of all of the forces acting on the body passes through the center of percussion. The center of percussion lies along a line drawn through the body's center of gravity. The distance from the axis of rotation to the center of percussion can be calculated from the equation q = K₀ ² + r, in which q = distance from the axis of rotation to the center of percussion, K₀ = the radius of gyration of the body with respect to the axis of rotation, and r = the distance from the axis of rotation to the body's center of gravity. The radius of gyration of the body with respect to the axis of rotation can be calculated from the equation K₀ ² = I/m, where I is the total moment of inertia of the body about the axis of rotation and m is the body's total mass.

While not wishing to be bound by any theory, it is believed that the improved performance of clubs according to the present invention is based upon the recognition that a golf club at the moment of impacting a golf ball is a percussive and not an inertial system as commonly believed. Unlike a percussive system, the resultant of all of the forces acting on a body in an inertial system passes through the body's center of gravity, because the body in an inertial system does not rotate in response to the forces applied to the body. Prior art golf clubs use toe and heel weighting in the head to move the club head center of gravity to the probable point of impact of the club head with the golf ball based on the erroneous belief that the club is an inertial system. In this manner, it is erroneously believed that all of the resultant forces acting on the head will be transferred to the golf ball upon impact. The present invention, in contrast, positions the probable point of impact between the center of percussion and the center of gravity which provides a more stable system. Referring to Figs. IC and 2B, it has been determined that the tendency of the club head 28 to rotate about the shaft axis 52 (i.e., axis Y-Y) is significantly reduced by positioning the club head center of gravity 32 at the heel end 24 and the club head center of percussion 48 relative to the shaft axis 52 at a distance from the toe end 56. The primary difference between Figs. IC and 2B are the relative positions of the centers of gravity 32a,b. Center of gravity 32a is on the axis Y-Y and center of gravity 32b is located a distance "r" from the axis Y-Y. As shown in Fig. 2B, when the club head 28 impacts the golf ball 60 during a golfer's swing, the club head 28 will attempt to rotate clockwise about the club shaft axis in response to the force of the impact as shown in Fig. 2B. The effect of positioning the club head center of percussion relative to the shaft axis and center of gravity on either side of the point of impact between the club head and golf ball is to make the rectangular area of the club head bounded by the axes X-X and Y-Y and lines A-A and B-B equivalent to a sweet spot (e.g., the sweet spot is depicted as the thatched portion of the club head in Fig. IC) . The line A-A intersects the axis Y-Y and the line B-B intersects the axis X-X at the centers of percussion of the club head about the axes of rotation X-X and Y-Y, respectively. As noted above, the center of percussion 48 is taken relative to the rotational axis Y-Y due to the tendency of the head to rotate sideways about the Y-Y axis when contacting the golf ball, and the center of percussion 49 relative to the rotational axis X-X due to the tendency of the head to bend backwards about the X-X axis when contacting the ball. As shown in Figs. IC and 2B, lines X-X and A-A are parallel to one another and both are orthogonal to the mutually parallel lines B-B and Y-Y.

The most desired location for the rotational axis X-X is the position of the axis X'-X' as shown in Fig. IC. The latter axis is located at the intersection of the club shaft 44 and club head 28, which is the point of intersection of the club shaft with the hosel. The placement of the rotational axis X-X at this location 45 would significantly reduce breakage of golf clubs. As will be appreciated, the location 45 represents the weakest point on the golf club. Relative to existing clubs, there would be significantly reduced rotational forces and percussive oscillations at the location 45 if the axis X-X were placed at this location. To move the axis X-X to this location 45, the center of gravity 32a must be moved closer to the location by appropriate configuration of the heel weight. The axis X-X intersects the axis Y-Y at the head center of gravity 32a. As will be appreciated, there is a limit as to how close the center of gravity 32a can be moved to location 45. In a preferred embodiment, the distance L' from the location 45 to the axis X-X is no more than about 0.5 inches.

To provide the increased stability of the club head, the heel weight (and therefore the center of gravity of the heel weight) is located between the outer edge 36 of the club shaft 44 and heel end 24 and has a sufficient weight to cause the head center of gravity and various centers of percussion to be located at the positions noted above. Preferably, the club head center of gravity 32 is located at a distance of no more than about 0.18, more preferably 0.10, and most preferably 0.05 inches from the club shaft's longitudinal axis 64. For clubs other than putters, USGA regulations require the club shaft's longitudinal axis 64 to be located at a distance of no more than about 0.625 inches from the heel end 24. Accordingly, the club head center of gravity 32 is preferably located at a distance of no more than about 0.625, and more preferably from about 0.500 to about 0.625 inches from the heel end 24.

The total weight of the heel weight combined with the weight of the club head between the outside edge 36 of the club shaft 44 and the heel end 24 (including the heel weight) is preferably substantially equal to the total weight of the club head between the toe end 56 and the outside edge 36 of the club shaft 44. Preferably, the heel weight is at least about 25% of the total weight of the club head and more preferably ranges from about one-third to about one-half of the total club head weight. In a typical application, the heel weight is at least about 50 grams, and more preferably ranges from about 70 to about 105 grams. A preferred material for the heel weight has a density ranging from about 16.5 to 18.5 g/cm³.

In most applications, the positioning of the club head center of gravity 32 inside of the outer edge 36 of the club shaft 44 will necessarily cause the club head center of percussion 48 to be located at a distance from the toe end 56. Put more simply, the moment of inertia of the club head 28 about the club shaft 44 when the club head center of gravity 32 is located along the club shaft 44 will generally yield a radius of gyration that is sufficient to move the club head center of percussion 48 to the desired location outside the head.

Referring to Figs. 3A and B, the process to locate the center of gravity will now be described. The process requires the club head to be sequentially suspended from a number of different locations on the club head with the relative orientations of the club head and the suspension line being related to the location of the club head center of gravity. By way of example, the club head 28 is disconnected from the club shaft and is suspended by a first suspension line 68 from a first point 72 on the club head. A first extension line 76 of the first suspension line is marked on the head using an erasable marker such as chalk. The club head is next suspended by a second suspension line 80 from a second point 84 on the club head. The second point 84 is located at a distance from the first point 72. A second extension line 88 of the second suspension line is marked on the club head. The club head center of gravity is located at the intersection 92 of the first and second extension lines 76, 88.

The methodology to move the head center of gravity to the desired location typically requires the above-described steps to be repeated several times. The steps are initially used without heel weights being placed in the club head to locate the club head center of gravity. An estimate is made of the amount of heel weight required to move the club head center of gravity to the desired location and the heel weight is added to the club head. The steps are repeated to locate the club head center of gravity at a first location after addition of the heel weight. If the first location is not the desired location, additional heel weight is added to the club head and the steps again repeated. Additional heel weight is sequentially added and the steps repeated until the club head center of gravity is at the desired location.

The process to locate the club head center of percussion is the same as that discussed below in connection with locating the golf club center of percussion. The Butt Weight

Referring to Figs. IA and 2D, the first invention can include a butt weight 96 at the butt end 100 of the club shaft 44 to cause the center of percussion of the entire golf club 104 about an axis Z-Z that is substantially orthogonal to the club head shaft longitudinal axis (and not the center of percussion of the head as in the case of the heel weight) to be located at substantially the same point as the club head center of gravity to substantially stabilize the golf club upon contact of the club head with the golf ball. Preferably, the golf club center of percussion 104 is collinear with the club shaft 44. More preferably, the golf club center of percussion is located at a distance of no more than about 0.5 inches from the shaft longitudinal axis 64 and most preferably within about 0.2 inches of the shaft longitudinal axis 64.

The golf club center of percussion and club head center of gravity are at substantially the same points because the collocation of the center of percussion and golf club center of percussion at substantially the same point essentially anchors the heel end of the sweet spot in space. By way of example, when the golf ball contacts the sweet spot away from the point of collocation of the golf club center of percussion and center of gravity, the anti- rotation characteristics provided by the sweet spot provide a solid contact with the golf ball. Preferably, the distance between the golf club center of percussion and club head center of gravity is no more than about 0.50, more preferably 0.25, and most preferably 0.10 inches.

While not wishing to be bound by any theory, as shown in Figs. 2A and B the invention is based upon the recognition that, when the club head 28 contacts the golf ball 60 during a golfer's swing, not only will the club head 28 attempt to rotate about the X-X and Y-Y axes as described above but also will the golf club 110 attempt to rotate about the axis Z-Z at the point of intersection 108 of the golfer's hands and the club shaft 44. The golf club 110 will normally attempt to rotate about the point under the right-handed golfer's left thumb, or approximately 4 inches from the butt end 100 of the club shaft 44. As illustrated in Fig. 2A, the existence of an axis of rotation Z-Z for the golf club creates a center of percussion (which is the node about which the golf club oscillates) . As illustrated in Fig. 2C, the sharp oscillations in the shaft 308 experienced by golfers at the location 312 of the Z-Z axis when the head 316 of an existing club 300 contacts the golf ball 60 are believed to be caused by the impact of the ball 60 at a significant distance from the center of percussion 304. This distance magnifies the wavelengths of the oscillations about the center of percussion.

Returning to Fig. 2A, the tendency of the golf club 110 to rotate about the axis of rotation at the intersection of the golfer's hands and the club shaft and the wavelengths of the oscillations are significantly reduced by positioning the golf club center of percussion 104 at substantially the same point as the club head center of gravity 32. As will be appreciated, positioning the center of percussion (i.e., node) closer to the point of impact between the club head and golf ball will significantly reduce the magnitude of the resulting oscillations about the golf club center of percussion 104 due to the diminished distance between the golf club center of percussion and the point of impact of the head 28 with the ball 60.

The butt weight 96 is preferably located adjacent to the butt end 100 of the club shaft 44. Preferably, the butt weight is located in the upper 10% and more preferably 5% of the length of the club shaft. The center of gravity of the butt weight is preferably located at a distance of no more than about 2 inches and most preferably within about 0.5 to about 1.5 inches of the butt end 100. The butt weight 96 preferably represents at least about 10% and more preferably ranges from about 10 to about 25% of the total weight of the golf club. Because the driver golf club preferably weighs from about 350 to about 370 grams, the butt weight 96 has a preferred weight of at least about 39 grams and more preferably ranges from about 39 to about 82 grams. The butt weight is preferably composed of the same material as the heel weight.

Referring to Fig. 4, the process to locate the golf club center of percussion will be described. The following equations permit the golf club center of percussion to be located by a series of empirical measurements: I = T² x mrg/4π² and q = I/m x r and q = T² x g/4π², where I is the moment of inertia about the axis of rotation, T is the time constant (seconds per oscillation) measured by counting the number of oscillations n of the golf club when suspended from the axis of rotation over a given time period t (T = t/n) , m is the total mass of the golf club, r is the distance from the center of gravity of the golf club to the axis of rotation, g is the gravitational constant (i.e., 386.4 inches/sec.²) , and q is the distance from the axis of rotation to the golf club center of percussion. The location process requires a series of repetitive measurements to be taken to identify the average period T of a number of oscillations n of the golf club when suspended from the point of intersection of the axis of rotation and the club shaft (i.e., the point where the golfer's left thumb contacts the shaft) . The average period is compared with a predetermined value for T that would be measured if the golf club center of percussion was in the desired location and, based on the difference, an appropriate amount of butt weight is added. The predetermined value is computed based upon the distance from the desired location of the golf club center of percussion to the axis of rotation (i.e., q) because of the equation:

rp2 _ 9

4π²q

By way of example, the golf club 110 is suspended by a freely rotated pivot axis 114 from the point at which the axis of rotation 108 intersects the club shaft 44. The suspended club is caused to oscillate and the time t, measured for a fixed number of oscillations n to determine the first average period T.,. Based upon the difference between the first average period and the predetermined value, an appropriate amount of butt weight 96 is added to the butt end 100 of the golf club 44. The suspended club is again caused to oscillate and the time t₂ measured for the fixed number of oscillations n to determine a second average period T₂. The steps are repeated until the average period measured for the club is substantially equivalent to the predetermined value. As will be appreciated, the same process can be used to locate the head center of percussion from any axis pivot location in connection with the selection of a heel weight.

The Insert A second invention includes an insert attached to the face of the club head at the probable point of impact between the face and the golf ball. The insert substantially inhibits deformation of the face from repeated contact with the golf ball and eliminates the annoying clanging or ringing sound generated by existing clubs upon impact with the golf ball.

It has been found that a solid piece of persimmon (and a number of other wood species) are not strong enough to withstand the forces generated when the golf ball is hit with a driver. The energy to be absorbed for an average golfer is about 814 in-lb/sec based on a club head weight of 210 grams and a club head speed of 100 mph. Better golfers swing faster than 100 mph but this is the range of energy the insert must absorb. Further work in developing a laminated, impact resistant structure with proper adhesive attachment to the metal housing, and/or use of structural foam has resulted in an insert for a club head that assists in the absorbtion of the above energy with an added safety factor. The insert can be composed of phenolic/linen, solid graphite, wood, or composites thereof. The foam gives the club head an added ability to distribute throughout the club head energy imparted to the head upon contact with the golf ball.

Referring to Figs. 5A and B, the insert 160 is attached to the face 164 of a metal shell 168 to form the club head 28. One or more flanges 172 hold the insert 160 in position on the flange. The wood insert can be any wood, such as persimmon wood, hickory, or maple, but persimmon wood is preferred. It has been discovered that persimmon wood not only eliminates the clanging or ringing sound but also produces a desirable and distinctive sound similar to that produced by older clubs using persimmon heads.

To amplify the unique sound of the persimmon wood contacting the golf ball, the metal shell 168 is substantially hollow. Preferably, at least about 85% and more preferably from about 50 to about 85% by volume of the metal shell 168 is occupied by a space. The sound can be dampened, if desired, by placing a rigid and/or flexible foam inside of the metal shell 168. The insert 160 is cut in a wedge-shape for strength and stability on the face 164. The wedge-shape prevents the wood insert 160 from moving up relative to the face 164 when the wood insert 160 contacts the golf ball.

Figs. 5C-F depict another embodiment of the present invention that attaches the insert 160 to the face of the club head 28 by a different technique. The club head 28 includes upper flanges 300a,b on the upper interior surface of the head and a lower flange 304 on the lower interior surface of the head for engaging (and supporting) the rear 308 of the insert. The step 308 on the insert 160 extends around the periphery of the club head 28 and engages the peripheral edge 312 of the front face of the head. This configuration has been found to provide superior support for the insert, which translates into a lower incidence of club damage.

The Modified Joint Between the Hosel and Shaft In a third invention the golf club has a joint between the hosel and shaft that significantly increases, relative to existing clubs, the amount of force transferred from the golfer to the golf ball. In a first portion of the joint, a gap exists between the club shaft and the interior walls of the hosel to receive an epoxy adhesive to provide high impact bonding strength, and, in a second portion, the club shaft is sized to contact the interior walls of the hosel to inhibit movement of the club head relative to the club shaft during impact of the head with the golf ball. While not wishing to be bound by any theory, it is believed that existing joints between the club shaft and hosel, which use an epoxy resin for high strength bonding, give the golf club a "soft" feel upon impact with the golf ball because the resin acts like a torsion spring or cushion during impact between the golf club and golf ball. The "spring" reduces the amount of force transferred from the golfer to the golf ball. The present invention overcomes this problem by using the second portion of the joint, which behaves like a pressed joint when the golf ball contacts the club head. The invention thereby provides the benefits of the high strength epoxy resin bonding without its attendant detriments. Unlike the "soft" feel of conventional golf clubs, the pressed joint of the present invention (i.e., second portion) provides a solid feel to the golfer when the head impacts the golf ball. Referring to Figs. 6 through 9, the first portion 204 of the shaft 44 has a smaller diameter to form the gap 208 between the interior walls 212 of the hosel hole 200 and the club shaft 44 and a length "L^*. Preferably, the gap 208 is at least about 0.005 inches and more preferably ranges from about 0.005 to about 0.010 inches in width. An adhesive, such as a high strength epoxy resin, is received within the gap 208 for high bonding strength between the club shaft 44 and hosel hole 200.

The second portion 216 of the club shaft 44 has one or more grooves 220 that are received within matching ribs 224 in the hosel walls 212 to provide metal-to-metal contact between the club shaft 44 and hosel 200. The second portion has a length "L₂". Preferably, the length of the second portion 216 is at least about 25% and more preferably ranges from about 33 to about 50% of the total length "L-"of the joint (i.e., the sum of L₁ and L₂) . The lengths of the grooves 220 and matching ribs 224 are at least about 0.25 inches and more preferably range from about 0.33 to about 0.50 inches.

The depth ("D") of the grooves 220 must be sufficient to accommodate the ribs 224. Preferably, the grooves 220 have a depth ranging from about 0.002 to about 0.025 inches. Due to the gap, the ribs 224 have a greater depth, preferably ranging from about 0.004 to about 0.030 inches. The joint can include a tapered plug 228. The upper end 232 of the tapered plug has a smaller diameter than the interior shaft diameter and the lower end 236 of the tapered plug has a larger diameter than the interior shaft diameter. The tapered plug 228 forces the grooves 220 into the ribs 224 for a more rigid contact between the club shaft 44 and hosel 200. The tapered plug 228 preferably has an angular shape. As shown in Fig. 7B, the tapered plug 228 most preferably has a hexagonal shape. As shown in Fig. 9, the hexagonal tapered plug 228 causes the circular interior of the shaft 44 to deform plastically in an attempt to conform to the hexagonal shape of the plug 228. This deformation causes the interior and therefore exterior of the shaft to have a larger effective diameter. This larger effective diameter causes the grooves 220 to be wedged against the ribs 224 in the hosel wall.

The Lightweight Shaft In a fourth invention the golf club has a high strength yet lightweight club shaft. The club shaft preferably comprises at least about 50% by weight beryllium. The most preferred shaft composition is 100% beryllium. The shaft composition can also be a beryllium alloy containing aluminum. The beryllium alloy preferably contains at least about 50% by weight and more preferably from about 62 to about 66% by weight beryllium.

Accordingly, the density of the club shaft ranges from about 0.070 to about 0.095 lb/in³.

Because the modulus of the beryllium/aluminum alloy is substantially the same as that of steel, the strength of the shaft of the present invention is no less than that of conventional steel club shafts. Aluminum has a Youngs modulus of about 10x10° psi and a density of about 0.10 lb/in³. Beryllium has a Youngs modulus of about 42x10° psi and a density of 0.067 lb/in³. In the preferred compositional ranges above, the alloy has a Youngs modulus of at least about 20xl0⁶ psi and more preferably at least about 30x10° psi. Preferably, the club shaft has a shear modulus of at least about 10x10° psi and more preferably at least about 15x10° psi. Preferably, the club shaft has a spring constant of about 1.0 lb/in (when properly supported) and more preferably ranging from about 0.9 to about 1.1 lb/in.

As can be seen from Fig. 10, a linear relationship exists between the effective modulus of the alloy and the relative percentages of aluminum and beryllium in the alloy. By way of example, an alloy containing 63% by weight beryllium and 37% by weight aluminum will have an effective modulus of about 30x10° psi.

The weight of the club shaft of the present invention is considerably less than that of conventional steel club shaft on similar wall thicknesses. Preferably, the weight of the driver club shaft is no more than about 70 grams and more preferably ranges from about 30 grams to about 70 grams. The total weight of the driver golf club preferably is no more than about 370 grams and more preferably ranges from about 350 to about 370 grams. Accordingly, the driver club shaft is no more than about 20% by weight of the driver golf club.

The fourth invention has numerous unexpected advantages relative to other lightweight shafts, particularly graphite shafts. Unlike other lightweight shafts, torsional deflection and side loading torque of shafts according to the fourth invention are similar to conventional steel shafts. As will be appreciated, conventional lightweight graphite-based shafts have relatively high torsional deflection and side loading torque and are therefore more unstable and fragile. Although torsional stiffness can be improved by adding special components (e.g., boron) to the graphite matrix, such components significantly increase the weight of the shaft to that of steel. Consequently, addition of the butt weight can cause the shaft to be too heavy. Several modifications can be made to each of the four inventions shown in Figs. 1 through 10. By way of example, the first invention shown in Figs. 1-2B can include the wood insert on the face of the club head, the modified joint between the club head and club shaft and/or the lightweight club shaft. The lightweight club shaft can reduce the amount of the butt weight required to position the golf club center of percussion at the desired location. With the lightweight club shaft, for example, the preferred butt weight only weighs from about 39 to about 82 grams. The second invention shown in Figs. 5A and B can include the butt and heel weights, the modified joint between the club head and the club shaft, and/or the lightweight club shaft. The third invention shown in Figs. 6 through 9 can include the butt and heel weights, the wood insert, and/or the lightweight club shaft. Finally, the fourth invention can include the butt and heel weights, the wood insert, and the modified joint between the club shaft and club head.

While various inventions have been described in detail, it is apparent that modifications and adaptations of those inventions will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the scope of these inventions, as set forth in the following claims.

Claims

What is claimed is:

1. A golf club, comprising: a club shaft; a club head attached to a lower end of said club shaft, said club head having a toe end and a heel end with said heel end being located closer to said club shaft than said toe end, wherein the longitudinal axis of said club shaft is located at a distance of no more than about 0.625 inches from said heel end; and a heel weight, at least a first portion of which is located between (a) the side of said club shaft closest to said toe end and (b) said heel end, wherein the weight of said first portion is sufficient to cause (i) the center of gravity of said club head to be located between said heel end and a line formed by a side of said club shaft and (ii) the center of percussion of said club head relative to said club shaft to be located at a distance from said club head, with the center of percussion being located closer to said toe end than said heel end to substantially stabilize said golf club upon contact of said club head with a golf ball.

2. The golf club of Claim 1, wherein said first portion represents at least about 25% of the total weight of said club head.

3. The golf club of Claim 1, wherein said first portion represents from about one-third to about one-half of the total weight of said club head.

4. The golf club of Claim 1, wherein said first portion is at least about 50 grams.

5. The golf club of Claim 1, wherein said first portion ranges from about 70 to about 105 grams.

6. The golf club of Claim 1, wherein said center of gravity is collinear with said club shaft.

7. The golf club of Claim 1, wherein said center of gravity is located no more than about 0.18 inches from said club shaft longitudinal axis.

8. The golf club of Claim 1, wherein said golf club has a center of percussion relative to an axis orthogonal to said club shaft and said center of percussion is located at substantially the same location as said center of gravity.

9. The golf club of Claim 1, wherein: said club shaft (i) comprises a butt weight located at an upper end of said club shaft, whereby said butt weight causes the center of percussion of said golf club to be located at a distance of no more than about 0.5 inches from said club shaft longitudinal axis and at substantially the same point as the center of gravity of said club head to substantially stabilize said golf club upon contact of said club head with a golf ball.

10. The golf club of Claim 1, wherein said club shaft includes at least about 50% by weight beryllium.

11. The golf club of Claim 1, wherein said club head includes a metal shell having a face for contacting a golf ball, an insert being mounted on said face to contact said golf ball, said insert comprising at least one of wood, phenolic/linen, graphite, and composites thereof.

12. The golf club of Claim 1, wherein said club head forms a joint with a lower end of said club shaft, such that in a first portion of said joint said club shaft has a smaller diameter than a hole in said club head for receiving said club shaft, thereby forming a gap between said club shaft and said club head for receiving an adhesive therein, and in a second portion of said joint said club shaft contacts said club head, whereby the contact of said club head and club shaft in said second portion substantially inhibits the movement of said club head relative to said club shaft when said club head contacts a golf ball.

13. A golf club, comprising: a club shaft; a club head attached to a lower end of said club shaft, said club head having a toe end and a heel end with said heel end being located closer to said club shaft than said toe end, wherein the longitudinal axis of said club shaft is located at a distance of no more than about 0.625 inches from said heel end; and a butt weight located at an upper end of said club shaft, whereby said butt weight causes the center of percussion of said golf club relative to an axis orthogonal to said club shaft to be located at substantially the same point as the center of gravity of said club head to substantially stabilize said golf club upon contact of said club head with a golf ball.

14. The golf club of Claim 13, wherein said center of percussion of said golf club is located at a point that is substantially collinear with said club shaft.

15. The golf club of Claim 13, wherein said butt weight is located at a distance of no more than about 0.5 inches from said club shaft longitudinal axis.

16. The golf club of Claim 13, wherein said butt weight ranges from about 39 to about 82 grams.

17. The golf club of Claim 13, wherein said butt weight is at least about 10% of the total weight of said golf club.

18. The golf club of Claim 13, wherein said butt weight ranges from about 10 to about 25% of the total weight of said golf club.

19. The golf club of Claim 13, wherein said butt weight is located in the upper 10% of the length of said club shaft.

20. The golf club of Claim 13, wherein said butt weight has a center of gravity located no more than about 2.0 inches from the upper end of said club shaft.

21. The golf club of Claim 13, wherein said center of percussion is located at a distance of no more than about

0.2 inches from said club shaft longitudinal axis.

22. The golf club of Claim 13, wherein said center of gravity is located at a first location and said center of percussion is located at a second location and wherein said first location is no more than about 0.5 inches from said second location.

23. The golf club of Claim 13, wherein: said club head includes a metal shell having a face for contacting a golf ball, an insert being mounted on said face to contact said golf ball to substantially inhibit deformation of said face therefrom, said insert comprising at least one phenolic/linen, graphite, wood, and composites thereof.

24. A golf club, comprising: a club shaft; an insert comprising at least one of phenolic/linen, graphite, wood, and composites thereof; and a club head attached to a lower end of said club shaft, said club head including a metal shell having a face for contacting a golf ball, wherein said wood insert is mounted on said face to contact said golf ball to substantially inhibit deformation of said face therefrom.

25. The golf club of Claim 24, wherein said insert comprises at least one of persimmon wood, hickory, or maple.