CROSS REFERENCE TO A RELATED PATENT APPLICATION
FIELD OF INVENTION
This is a continuation-in-part of my co-pending U.S. patent application Ser. No. 11/975,556 filed on Oct. 22, 2007. Any patent issued hereon will date from Oct. 22, 2007, i.e. the filing date of the co-pending patent application.
- DESCRIPTION OF THE RELATED ART
This invention relates to golf balls and particularly to golf ball having reduced side spin. Side spin is a spin generated around the golf ball center in a plane oblique to the flight path of the ball. Side spin is produced when the face of the golf club strikes the ball at an oblique angle to the path of the club. The present invention relates to a golf ball that is constructed to oppose side spin forces generated by the oblique angle striking force of the club face.
Side spin of a golf ball is undesired because it causes the ball to take a curved path after it leaves the club face, so that the ball goes off course from the direction intended by the golfer. With a right-handed golfer a curvature to the right is termed a slice, and a curvature to the left is termed a hook.
- SUMMARY OF THE INVENTION
U.S. Pat. No. 7,041,011 issued to M. J. Sullivan et al on May 9, 2006 discloses a golf ball designed to have a relatively low spin rate, with an associated lowered tendency to hook or slice. The golf ball has an outer layer containing regions of weighting material that provides perimeter weighting for the ball. Such perimeter weighting increases the moment of inertia of the ball, which the patentees believe causes the ball to have a lower spin rate, compared to a conventional golf ball.
The present invention relates to a golf ball having one or more grooves in its spherical outer surface. Each groove has a sufficient width and depth dimension so that when the ball is airborne a ball-related laminar air flow is achieved in each groove, thereby generating resistance to side spin of the ball. Each groove acts as a miniature air vane that has a turbine-like resistance to the side spin force. The turbine-like resistance exerts a braking action to reduce the side spin and minimize the ball slice or hook (depending on the direction of the side spin).
BRIEF DESCRIPTION OF THE DRAWINGS
The action of the groove in the golf ball surface is somewhat similar to the action of the fletches or vanes on an in-flight arrow. In each case the vane reacts to a disturbing force to stabilize the in-flight object (golf ball or arrow). In the case of the arrow the vane reacts to the disturbing force to produce stabilizing spinning motion of the arrow around the arrow axis. In the case of the golf ball the vane (groove) reacts to the side spin force so as to absorb the side spin energy, thereby reducing the undesired side spin.
FIG. 1 is a sectional view of a conventional golf ball in flight after being struck by a golf club.
FIG. 2 is an enlarged fragmentary sectional view of the FIG. 1 golf ball, showing certain turbulence-producing dimples on the golf ball surface.
FIG. 3 is a plan view of a golf ball embodying the present invention. FIG. 3 includes two lines showing the air separating and then flowing around the ball surface as the ball moves in a left to right direction.
FIG. 4 is a sectional view taken on line 4-4 in FIG. 3.
FIG. 5 is a fragmentary enlarged sectional view of the FIG. 3 golf ball, showing in cross section a groove in the ball spherical surface. While the ball is in flight in the groove accommodates a laminar air flow that provides a resistance to side spin of the golf ball.
FIG. 6 is a fragmentary sectional view taken on line 6-6 in FIG. 5.
FIG. 7 shows the FIG. 3 golf ball while in-flight prior to alignment of an air flow groove with the main air stream flowing over the ball.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 8 shows the FIG. 7 golf ball after the air flow groove has been aligned with the air stream generated by the golf ball.
Referring to FIG. 1, there is shown a conventional golf ball 10 after being struck by a golf club, so that the ball is moving in a left to right direction in an ascending path, designated by numeral 12. The ball is shown in cross section to illustrate the ball internal structure. The ball includes an inner spherical core 12 having a center 16, and an outer cover 18 molded onto the core. The outer spherical surface 20 of the cover is covered with small dimples 21.
The ball can have a diameter of 1.68 inches, as required by the U.S. Golf Association. Each dimple 21 can typically be a circular depression having a diameter 23 of about 0.13 inch and a depth 25 of about 0.010 inch. Cover 18 may have a thickness on the order of 0.1 inch. The ball interacts with the stagnant air in the path of the ball to form an air separation point 22 in front of the ball, an air attachment zone 24 downstream from air separation point 22, and a turbulent wake area W downstream from air attachment zone 24.
The function of dimples 21 is to promote attachment of the air to the spherical surface of ball 10 so as to lengthen air attachment zone 24 (along path line 12).
In air attachment zone 24 dimples 21 generate localized boundary layer turbulence that interacts with the relative laminar flow of air spaced from the ball spherical surface 20, such that the laminar flow is attached to the ball surface.
The term “relative laminar air flow” is used herein to mean a flow relative to ball 10. In actual terms the air is relatively stagnant in the directions of ball movement; however the air is considered to move relative to the ball.
The present invention relates to a modification of the conventional golf ball (FIG. 1) that reduces the side spin of the ball that contributes to ball slice or ball hook (i.e. undesired curvature of the ball from a straight trajectory). As illustrated in FIG. 1, side spin can be a spinning motion of the ball around the ball center 16 (or a point near the center) in a direction generally transverse to the ball flight path, as indicated by arrow 26. Side spin is believed to be caused when the face of the club head strikes the ball at an oblique (non-normal) angle to the path of the club head. The present invention provides one or more elongated grooves in the ball surface that interact with air in air attachment zone 24 so as to resist the side spin force generated when the club head strikes the ball obliquely.
FIGS. 3 and 4 show a golf ball embodying the invention. The illustrated ball has three elongated grooves 28 spaced equidistantly around the ball circumference, as shown best in FIG. 4. When the ball is airborne the three grooves interact with the air surrounding the ball so as to be aligned with the stream of air attached to the ball spherical surface. The term “aligned” is herein used to mean generally that each groove extends parallel to the air stream, such that laminar flow velocity air in air attachment zone 24 can move through each groove while remaining generally parallel to the ball flight path 12. Each groove has a circumferential component (as indicated by the curved dashed lines in FIG. 3) so that laminar air flowing through each groove remains contiguous with and attached to the main air stream surrounding the ball. The “air flow” mentioned herein is flow relative to the moving ball, not flow in the absolute sense.
One of the side surfaces of each groove 28 functions as a miniature turbine blade (or arrow vane) to oppose the side spin forces designated by arrow 26. Each groove 28 absorbs some of the side spin force so that during the course of ball travel the side spin rate decreases appreciably, thereby eliminating or reducing the undesired slicing or hooking action. In this context, a slice is associated with side spin in one direction, whereas a hook is associated with side spin in the opposite direction. Grooves 28 resist side spin in either direction. The grooves act cumulatively.
As the air in the air attachment zone 24 enters each groove 28 it has zero velocity in the arrow 26 direction. Spinning movement of the golf ball in the arrow 26 direction causes one side wall of each groove 28 to accelerate the air in the arrow 26 direction from a zero velocity condition up to the side spins velocity of the golf ball. The acceleration energy is absorbed by the golf ball so that eventually the side spins is eliminated or substantially reduced, as noted above.
When the ball is struck by the club head, grooves 28 can have a random orientation (not necessarily aligned with the ball flight path or air movement direction). During the initial stage of the ball travel grooves 28 interact with the air in air attachment zone 24 to turn the ball to a position where the grooves are aligned with the air stream in zone 24. Again, “air stream” means flow relative to the moving golf ball.
FIGS. 7 and 8 illustrate generally how the ball can be turned to align grooves 28 with the air stream in air attachment zone 24. In FIG. 7, groove 28 is at some random angle to flight path 12 and the associated reversely flowing air stream. Laminar air surrounding the ball flows through groove 28, as shown by arrows 30. The flowing air interacts with side surfaces of each groove 28 to turn the ball into a position wherein the grooves are aligned with the ball flight path (and direction of laminar air flow). In the FIG. 8 ball position grooves 28 are enabled to resist undesired side spin of the ball, while offering minimal resistance to forward ball movement.
It will be seen from FIG. 3 that each groove 28 has a length that is approximately the same as the length of air attachment zone 24. The grooves are long enough to interact with the laminar air flow in zone 24 without being directly exposed to the turbulent air generated at separation point 22 or the turbulent air in wake area W. Flow through each groove 28 is essentially high rate non-turbulent laminar flow, which is preferable for absorption of side spin energy. Each groove has a length that is a major portion of the distance between imaginary points 32 and 33, measured along the ball surface (i.e. more than fifty percent of the distance between points 32 and 33).
Grooves 28 are of similar length, as shown in FIG. 3. The grooves terminate at a common distance from two imaginary points 32 and 33 located on a diametrical line 35 passing through golf ball center 16. The grooves interact with air in air attachment zone 24 to oppose side spin rotation of the ball, without introducing any significant adverse disturbing force onto the ball.
Each groove 28 has sufficient depth and width to accommodate a desired volume of laminar velocity air in zone 24. FIG. 5 shows one cross section that each groove can have. Preferrably the groove depth is on the order of about 0.05 inch. Similarly, the groove width is about 0.05 inch. Typically, the golf ball cover 18 has a thickness of about 0.1 inch. Each dimple 21 has a diameter 23 of about 0.13 inch, and a depth dimension 25 measuring about 0.01 inch, which is conventional in golf ball construction practice.
The width and depth dimensions for each groove 28 are several times the depth dimension of each dimple, whereby the groove has sufficient cross sectional area to accommodate laminar air flow. The turbulent boundary layer on the groove side walls and groove bottom wall is insufficient to choke off laminar air flow through the groove. As noted above, FIG. 5 shows groove 28 having a depth of about 0.05 inch and a width of about 0.05 inch. The depth of each associated dimple is about 0.01 inch. With such dimensions the groove depth (or width) is about five times the dimple depth. In preferred practice of the invention the groove depth (and width) is at least five times the dimple depth so that air in each groove has a laminar flow relative to the ball.
Dimples 21 are not shown in FIGS. 3 and 4. However, it will be appreciated that, in practice, the non-grooved area of the golf ball spherical surface can be covered turbulence-generating dimples. The present invention is concerned particularly with the provision of one or more air interaction grooves 28 in the golf ball spherical surface. The golf ball can be dimpled per conventional practice.
End areas of each groove merge gradually with the spherical surface of the golf ball, as shown in FIG. 6. The bottom wall of each groove has a ramp like continuation 37 that merges with surface 20 of the ball at a relatively small angle. The aim is to minimize turbulence that might interfere with a smooth flow of air into or out of each groove 28.