WO2008102977A2

WO2008102977A2 - Golf ball

Info

Publication number: WO2008102977A2
Application number: PCT/KR2008/000985
Authority: WO
Inventors: Hae Cheon Choi; Jin Choi; Gwang Min Son
Original assignee: Seoul National University Industry Foundation
Priority date: 2007-02-22
Filing date: 2008-02-20
Publication date: 2008-08-28
Also published as: WO2008102977A3; EP2112948A2; EP2112948A4; KR100803528B1; EP2112948B1; US20120270683A1

Abstract

Disclosed herein is a golf ball which has not only an air resistance similar to or smaller than that of a dimpled golf ball, but also a significantly reduced area ratio of grooves (20) relative to the total surface area of the golf ball, thereby achieving an enhanced carry distance and high accuracy in the directionality of putting. The golf ball has net-shaped grooves (20) formed on an outer surface of a sphere (10).

Description

Description GOLF BALL

Technical Field

[1] The present invention is related to a golf ball, and more particularly, to a golf ball which has not only an air resistance similar to or smaller than that of a dimpled golf ball, but also a significantly reduced area ratio of grooves relative to the total surface area of the golf ball, thereby achieving an enhanced carry distance and high accuracy in the directionality of putting.

[2]

Background Art

[3] In general, a golf ball, which has a spherical surface divided into many spherical polygonal faces each being arranged with a circular dimple, has been used for a long time. Such a conventional dimpled golf ball is known to fulfill the symmetry of a spherical surface while achieving a reduced air resistance and consequently an increased carry distance thereof.

[4] Currently, examples of widely used divisional compositions of a sphere include a spherical icosahedron, a spherical icosi-dodecahedron, a spherical dodecahedron, a spherical octahedron, a spherical hexahedron, a spherical hexa-octahedron, or other further divided spherical polyhedrons having smaller faces. In golf balls having the same size as one another, the above mentioned spherical divisional compositions can be actually overlapped with one another except for specially deformed ones. Therefore, it can be concluded in a broad sense that the above mentioned spherical divisional compositions are identical to one another. If circular dimples of a golf ball are arranged on one of the above divisional compositions, it can be said that a carry distance of the golf ball is determined by the area ratio of the dimples relative to the total surface area of the golf ball.

[5] If a golfer hits a dimpled golf ball, the dimpled golf ball is subjected to strong repulsive elasticity by a force applied from the head of a golf club, and simultaneously has a back spin by a loft angle of the club head. In the case where the golf club is a driver, for example, the dimpled golf ball has an initial flying velocity of approximately 190 to 300 km/hr and an initial back spin of approximately 2200 to 4500 rpm. In this case, dimples of the golf ball act to create a turbulent flow on the surface of the golf ball and in turn, the turbulent flow acts to delay the separation of air streams around the golf ball, thereby reducing a pressure difference between front and rear portions of the dimpled golf ball, and resulting in a reduction of air resistance acting on the golf ball. [6] Although there is a known hypothesis related to a dimpled golf ball, in that air generates eddies inside dimples to thereby create a turbulent flow around a golf ball, the inventors of the present invention proved through an experiment that a turbulent flow around the golf ball is created through the shear layer instability as air separates at the dimple rather than entering into the dimple, as published in a professional journal "Physics of Fluids"(April, 2006).

[7]

Disclosure of Invention Technical Problem

[8] However, to reduce an air resistance acting on a dimpled golf ball, generally, the area ratio of dimples relative to the total surface area of the golf ball has to be more than 75%. This makes it impossible to achieve a high accuracy in the directionality of putting.

[9] As shown in FIGS. 1 and 2, in a conventional dimpled golf ball 1 in which dimples occupy a great area ratio, a putter 2 generally strikes irregular faces formed with the dimples of the dimpled golf ball 1 and this makes the golf ball 1 to move in a direction slightly different from the golfer's intension. In other words, the golf ball deviates from a hole cup even by an extremely small angular error occurred in putting.

[10]

Technical Solution

[11] Therefore, the present invention has been made in view of the above problems, and the objective of the present invention is to provide a golf ball which has not only an air resistance similar to or smaller than that of a dimpled golf ball by virtue of net-shaped grooves formed in a spherical surface thereof, but also a significantly reduced area ratio of the grooves relative to the total surface area of the golf ball, thereby achieving an enhanced carry distance and high accuracy in the directionality of putting.

Advantageous Effects

[12] According to the present invention, a golf ball has net-shaped grooves formed throughout a sphere. With this configuration, an air resistance acting on the golf ball is similar to or smaller than that acting on a dimpled golf ball, thus resulting in an improvement in the carry distance of the golf ball.

[13] Further, according to the present invention, as a result of considerably reducing the area ratio of the grooves relative to the surface area of the golf ball, it is possible to reduce the occurrence of putting errors due to the curvature of the grooves, resulting in accurate putting of the golf ball.

[14]

Brief Description of the Drawings [15] The above and other objective, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[16] FIG. 1 is a perspective view illustrating a dimpled golf ball in a putting position;

[17] FIG. 2 is a sectional view taken along the line A-A of FIG. 1;

[18] FIG. 3 is a plan view illustrating a golf ball formed with grooves according to an embodiment of the present invention; [19] FIG. 4 is a schematic diagram of the grooves according to one embodiment of the present invention; [20] FIG. 5 is a schematic diagram of the grooves according to another embodiment of the present invention; [21] FIG. 6 is a schematic diagram of the grooves according to yet another embodiment of the present invention; [22] FIG. 7 is a photograph illustrating laboratory equipment having a model of a golf ball according to the present invention; [23] FIG. 8 is a schematic diagram illustrating grooves formed in the surface of the model of the golf ball according to the present invention; [24] FIG. 9 is a photograph illustrating a model of a golf ball according to the present invention, which has grooves and protrusions formed at intervals along the grooves; [25] FIGS. 10 and 13 are graphs illustrating the relationship between the Reynolds number and the air resistance coefficient; [26] FIGS. 11 and 14 are graphs illustrating the relationship between the velocity of a golf ball and the air resistance; [27] FIG. 12 is a photograph illustrating another model of a golf ball according to the present invention, which has grooves and protrusions continuously formed along the grooves; and [28] FIG. 15 is a partial sectional view of a golf ball having grooves and protrusions formed along the grooves according to the present invention. [29]

Best Mode for Carrying Out the Invention [30] To accomplish the above objective, the present invention provides a golf ball in which net-shaped grooves are formed on the outer surface of a sphere. [31] Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, a detailed description related to known configurations or functions will be omitted if it is determined to make the subject matter of the present invention unclear. [32] As shown in FIG. 3, the golf ball in accordance with a preferred embodiment of the present invention includes net-shaped grooves 20 formed on the outer surface of a sphere 10. The net-shaped grooves 20 may be connected to or separated from one another.

[33] The shape of each groove 20 can be freely selected among a variety of different shapes so long as all the grooves 20 have a net shape. In one embodiment of the present invention for forming the net-shaped grooves 20, as shown in FIG. 4, first, a spherical regular polyhedron is inscribed in the sphere 10 such that vertexes 31 of spherical regular polygons constituting the spherical regular polyhedron touch on the sphere 10. Then, certain specific points 33a on a spherical surface of the sphere 10 are determined such that an included angle θ between a straight line 32 connecting one of the vertexes 31 to a center 11 of the sphere 10 and a straight line 34 connecting the center 11 of the sphere 10 to one of the specific points 33a has a predetermined value. When the specific points 33a are determined, circular paths 35 are defined on the surface of the sphere 10 by connecting the specific points 33a to one another. The grooves 20 can be formed along the circular paths 35. Here, each edge of the regular polyhedron is defined by connecting every two adjacent vertexes 31 to each other via the shortest path on the surface of the sphere 10.

[34] The spherical regular polyhedron may be a spherical regular hexahedron or regular icosahedron, and the included angle θ may be 45 to 80 degrees. The spherical regular hexahedron has six spherical squares and eight vertexes 31, and the spherical regular icosahedron has twenty spherical regular triangles and twelve vertexes 31. Therefore, when each groove is formed along one associated circular path 35 defined about each vertex 31 and consequently, eight or twelve grooves are formed in the surface of the sphere 10 such that they are connected to one another, all the grooves 20 occupy only a small area ratio relative to the surface area of the golf ball. This assists in putting of the golf ball in a desired accurate direction. Assuming that a vertex 31 is the stagnation point and the sphere 10 has a smooth surface, separation of air streams occurs at the angle θ of approximately 80 degrees. Accordingly, when eddies are generated by use of the grooves 20 before the separation occurs, the separation point is shifted to the angle θ of 120 degrees. This can greatly reduce an air resistance acting on the golf ball. In conclusion, it is preferable that the groove be formed on the basis of the included angle θ of 45 to 80 degrees.

[35] In another embodiment of the present invention as shown in FIG. 5, a spherical regular polyhedron, which consists of spherical regular polygons each having a center of gravity 36, is inscribed in the sphere 10, and specific points 33b on the surface of the sphere 10 are determined such that an included angle θ between a straight line 37 connecting one of the centers of gravity 36 to the center 11 of the sphere 10 and a straight line 38 connecting the center 11 of the sphere 10 to one of the specific points 33b has a predetermined value. If the specific points 33b are determined, circular paths 39 connecting the specific points 33b to one another are defined on the surface of the sphere 10. The grooves 20 can be formed along the circular paths 39.

[36] Preferably, the spherical regular polyhedron is a spherical regular octahedron or regular dodecahedron, and the included angle θ is 45 to 80 degrees. The spherical regular octahedron has eight spherical regular triangles and six vertexes 31, and the spherical regular dodecahedron has twelve spherical regular pentagons and twenty vertexes 31. Therefore, when each groove is formed about each vertex 31 and consequently, six or twenty grooves are formed along the circular paths 39 such that they are connected to one another. In this case, however, there is a problem in that the area ratio of the grooves relative to the surface area of the golf ball may be too small to reduce an air resistance acting on the golf ball down to a desired level, or may be too large to improve the directionality of putting.

[37] The shape of each groove can be changed into a variety of different shapes other than the above described shapes, so long as all the grooves maintain a net shape and fulfill the symmetry of a spherical surface, and the surface area of the grooves occupies 14 to 69 % of the surface area of the golf ball.

[38] In yet another embodiment of the present invention showing another different shape of the grooves, the sphere 10 has a divisional composition of a spherical polyhedron, and grooves are formed along edges 41 of the spherical polyhedron. The spherical polyhedron may be a spherical regular icosahedron, or may be a spherical icosahedron consisting of eight spherical regular pentagons and twelve spherical regular hexagons as shown in FIG. 6. Even in the case where the outer surface of the sphere 10 is divided into spherical polygons fulfilling the symmetry of a spherical surface for arrangement of dimples, the present invention is applicable in such a manner that grooves are formed along the edges 41 of the spherical polyhedron. The grooves, formed along the edges 41 of the spherical polyhedron, may be connected to or separated from one another.

[39] Referring to FIG. 7 illustrating laboratory equipment used in an experiment of the present invention, an experimental model of a golf ball was installed in a wind tunnel, to measure an air resistance acting on the experimental model while increasing the velocity of wind from 5m/s to 30m/s by lm/s. On the basis of dimensional analysis and similarity, if a golf ball has the same Reynolds number as that of the experimental model, the golf ball and the experimental model also have the same air resistance coefficient as each other. Accordingly, an air resistance actually acting on the golf ball could be calculated based on experimental values.

[40] A method for forming grooves in the surface of the model used in the above experiment will now be described in detail with reference to FIG. 8. First, a regular hexahedron is inscribed in the model such that the model has a divisional composition of a spherical regular hexahedron. Then, a circular path 35a is defined about one vertex 31a of a spherical square constituting the spherical regular hexahedron by connecting three vertexes (only two vertexes 31b and 31c are visible from FIG. 8) closest to the vertex 31a to one another. In this case, the included angle θ is approximately 70 degrees. In the case of the remaining vertexes 31b, 31c, 3 Id, ..., similarly, circular paths 35b to 35h thereof can be defined, and grooves can be formed along all the circular paths 35a to 35h. When the outer surface of the sphere 10 is divided, by the circular paths 35a to 35h, into a plurality of cells, grooves can be additionally formed along shorter diagonal lines 42a, 42b, 42c, 42d, ... of some cells containing the edges 41 of the spherical regular hexahedron.

[41] Considering now the detailed conditions of the above experiment, the diameter of the model was 150 mm. In Example 1, the outer surface of the model was formed with grooves having a width of 5 mm and a depth of 0.5 mm. In Example 2, protrusions having a height of 0.5 mm were additionally formed in the grooves. In Example 3, the protrusions were partially cut and removed at intervals as shown in FIG. 9.

[42] [43] Table 1 [Table 1] [Table ]

[44] [45] Values in Table 1 represent reduced values of the models and should be considered as actual numerical values of the golf ball having grooves formed in the surface thereof on the basis of dimensional analysis and similarity.

[46] FIG. 10 is a graph illustrating the relationship between the Reynolds number and the air resistance coefficient, and FIG. 11 is a graph illustrating the relationship between the velocity of a golf ball and the air resistance. These graphs are for the comparison of an air resistance acting on the grooved golf ball of the present invention with that acting on a conventional dimpled golf ball.

[47] In the case of Example 1, an air resistance acting on the grooved golf ball begins to be smaller than that acting on the dimpled golf ball from the critical point where the Reynolds number is approximately 190,000 (the velocity of the golf ball is 240 km/hr). Since the initial velocity of a drive shot is 190 to 300 km/hr, the overall air resistance acting on the grooved golf ball is larger than that acting on the dimpled golf ball, thus suffering from a reduction of a carry distance and consequently, being unsuitable for use as a golf ball. In conclusion, when the width of the grooves is smaller than 2 mm and no protrusions are formed in the grooves, the air resistance acting on the grooved golf ball exceeds that acting on the dimpled golf ball, resulting in a reduced carry distance of the golf ball. Therefore, in this case, it is preferable that the number of the grooves, having the width of 2 mm or less, be increased as compared to that of Example 1, so as to increase the area ratio of the grooves relative to the surface area of the golf ball, for the sake of reducing the air resistance acting on the golf ball.

[48] In Example 2 in which protrusions are formed in the grooves, it is seen from FIGS. 10 and 11 that the air resistance acting on the grooved golf ball is smaller than that acting on the dimpled golf ball except for a region where the Reynolds number is 50,000(80 km/hr) to 110,000(140 km/hr). As compared to the dimpled golf ball in which the area ratio of dimples relative to the surface area of the dimpled golf ball is approximately 75 to 84%, the area ratio of the grooves relative to the surface area of the grooved golf ball is only approximately 23%. Therefore, the grooved golf ball of Example 2 could achieve a remarkable reduction in the occurrence of putting errors due to the curvature of the grooves, thus enabling accurate putting of the golf ball.

[49] Example 3 has the same experimental conditions as those of Example 2 except for the fact that the protrusions formed in the grooves are partially cut and removed at intervals, rather than being continuously connected to one another. Similar to Example 2, the air resistance acting on the golf ball of Example 3 is smaller than that acting on the dimpled golf ball.

[50] In the experiment of the present invention, also, other models having a diameter of 150 mm are considered. In Example 4, the outer surface of the model is formed with grooves having a width of 10 mm and a depth of 1 mm. In Example 5, continuous protrusions having a height of 1 mm are formed in the grooves as shown in FIG. 12.

[51] [52] Table 2 [Table 2] [Table ]

[53]

[54] Values in Table 2 represent reduced values of the models and should be considered as actual numerical values of the golf ball having grooves formed in the surface thereof on the basis of dimensional analysis and similarity.

[55] FIG. 13 is a graph illustrating the relationship between the Reynolds number and the air resistance coefficient, and FIG. 14 is a graph illustrating the relationship between the velocity of a golf ball and the air resistance. These graphs are for the comparison of an air resistance acting on the grooved golf ball of the present invention with that acting on a conventional dimpled golf ball.

[56] Although Examples 4 and 5 show the air resistances acting on the grooved golf ball similar to that acting on the dimpled golf ball, it could be appreciated that the area ratios of grooves relative to the surface area of the respective golf balls of Examples 4 and 5 are only approximately 46%, thereby enabling accurate putting of the golf ball as compared to the dimpled golf ball.

[57] When no protrusions are formed in the grooves, it is preferable that the groove 20 have a width W below 4 mm and a depth GH of 0.1 to 0.4 mm in consideration of the air resistance acting on the golf ball and the accurate directionality of putting. If the depth GH of the groove 20 is smaller than 0.1 mm, RPM of the backspin of the grooved golf ball decreases as compared to that of the dimpled golf ball, thus resulting in a reduced lift force.

[58] As shown in FIG. 15, when a protrusion 21 is formed in the groove 20, the width W of the groove 20 is preferably 1 to 5 mm, and the depth GH of the groove 20 is preferably 0.1 to 0.5 mm. Also, in consideration of the accurate directionality of putting, the height H of the protrusion 21 is preferably smaller than the depth GH of the groove 20. Similar to the grooves 20, the protrusion 21 may be connected to or separated from other protrusions.

[59] Here, it can be appreciated that the width W and the depth GH of the groove 20 and the height H of the protrusion 21, formed in the surface of the sphere 10, may be changed per their locations such that a variety of different sizes of grooves 20 or protrusions 21 exist together in the single sphere 10.

[60]

Industrial Applicability

[61] As apparent from the above description, according to the present invention, a golf ball has net-shaped grooves formed throughout a sphere. With this configuration, an air resistance acting on the golf ball is similar to or smaller than that acting on a dimpled golf ball, thus resulting in an improvement in the carry distance of the golf ball.

[62] Further, according to the present invention, as a result of considerably reducing the area ratio of the grooves relative to the surface area of the golf ball, it is possible to reduce the occurrence of putting errors due to the curvature of the grooves, resulting in accurate putting of the golf ball.

[63] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

[1] A golf ball wherein net-shaped grooves are formed on an outer surface of a sphere, and the net-shaped grooves are connected to or separated from one another.

[2] The golf ball according to claim 1, wherein the area of the grooves is 14 to 69% of the total surface area of the golf ball.

[3] The golf ball according to claim 2, wherein each groove has a width below 4 mm and a depth of 0.1 to 0.4 mm.

[4] The golf ball according to claim 2, wherein each groove has a width of 1 to 5 mm and a depth of 0.1 to 0.5 mm, and the groove is formed with a protrusion merely having a height smaller than the depth of the groove, and the protrusion is connected to or separated from other protrusions.

[5] The golf ball according to any one of claims 1 to 4, wherein the sphere has a divisional composition of a spherical regular polyhedron, and each groove is formed along a circular path drawn by connecting specific points on the surface of the sphere, each specific point being determined such that an included angle between a straight line connecting one of vertexes of spherical regular polygons constituting the spherical regular polyhedron to a center of the sphere and a straight line connecting the specific point to the center of the sphere has a predetermined value.

[6] The golf ball according to claim 5, wherein the spherical regular polyhedron is a spherical regular hexahedron or regular icosahedron, and the included angle is 45 to 80 degrees.

[7] The golf ball according to any one of claims 1 to 4, wherein the sphere has a divisional composition of a spherical regular polyhedron, and each groove is formed along a circular path drawn by connecting specific points on the surface of the sphere, each specific point being determined such that an included angle between a straight line connecting one of centers of gravity of spherical regular polygons constituting the spherical regular polyhedron to a center of the sphere and a straight line connecting the specific point to the center of the sphere has a predetermined value.

[8] The golf ball according to claim 7, wherein the spherical regular polyhedron is a spherical regular octahedron or regular dodecahedron, and the included angle is 45 to 80 degrees.

[9] The golf ball according to any one of claims 1 to 4, wherein the sphere has a divisional composition of a spherical polyhedron, and the grooves are formed along edges of the spherical polyhedron. [10] The golf ball according to claim 9, wherein the spherical polyhedron is a spherical regular icosahedron, or a spherical icosahedron consisting of eight spherical regular pentagons and twelve spherical regular hexagons.