Golf ball

Abstract: A golf ball dimple (A), formed on the spherical surface of a golf ball, being polygonal in the surface configuration thereof and having a double slope (c,d) in the sectional configuration thereof. The gradient (ϑ1) of one slope (c) disposed in the vicinity of an edge of the dimple is greater than that (ϑ2) of the other slope (d) disposed in the vicinity of the bottom thereof so that the dimple has a plane having a large angle with respect to an air flow in the periphery of the golf ball.

Description: The present invention relates to a golf ball and more particularly to an improved shape of the dimples to make the flow of air in the periphery of the golf ball turbulent during the flight thereof so as to improve the aerodynamic performance of the golf ball. Description of the Related Arts A golf ball has normally 280 to 540 dimples formed on its spherical surface which are depressed radially inwardly from the spherical surface. The role of the dimples is to reduce pressure drag to the golf ball and improve the dynamic lift thereof. More specifically, in order to lift the golf ball high in the air during the flight of the golf ball, it is necessary to shift the separation point between the air and the upper surface of the golf ball more to rearward than the separation point between the air and the lower surface thereof. Thus, the air pressure above the golf ball can be made to be smaller than that below it. In order to accelerate the separation of the air existing above the golf ball from the upper surface thereof, it is necessary to make the air current around the golf ball turbulent. In this sense, it can be said that dimples capable of making the air flow in the periphery of the golf ball very turbulent are aerodynamically superior. In view of the role of the dimples, there have been made proposals regarding the combination of dimples in various configurations formed on the surface of the golf ball to make the flow of air at the periphery of the golf ball turbulent. For example, Japanese Patent Laid-Open Publication No. 48-19325 discloses dimples having pentagonal or hexagonal surface configuration. According to examined Japanese Patent Publication No. 3-23184, a dimple has two different curvatures (double radius) in its sectional configuration. According to Japanese Patent Laid-Open Publication No. 64-8982, dimples comprise circular dimples and non-circular dimples. US-A-1 418 220 discloses a golf ball as defined in the preamble of claim 1. The dimples of this prior art golf ball are rectangular depression having sloped side walls and a flat bottom and a small sperical recess in the center of the bottom. The dimples of the above-described proposals do not have the effect of making the air flow in the periphery of the golf ball turbulent to a great extent. Thus, the flight distance of the golf balls having the dimples according to the proposals is not as desired. It is an object of the present invention to provide a golf ball having configuration improved dimples to make the air flow in the periphery of the golf ball very turbulent so as to improve the flight distance of the golf ball. In accomplishing these and other objects of the present invention, there is provided a golf ball according to claim 1. The above-described "surface configuration" of the dimple means the configuration of the dimple viewed in the direction from a normal line on the spherical surface of the golf ball. The dimples have a "double slope" as shown by a solid line of Fig. 1, which means a sectional configuration of the dimple from a dimple edge (a) to the center (b) of the dimple which is composed of two straight lines (c) and (d) having gradient or angle of slope different from each other. The straight line (c) near the dimple edge (a) is referred to as a first slope and the straight line (d) near the dimple bottom is referred to as a second slope. Within the limited range of the dimple volume, the configuration of the double slope of the dimple is preferably set to satisfy the following three conditions to increase the effect of sweeping air away from the periphery of the golf ball. Firstly, as defined in claim 1, if the gradient of the first slope (c) is 1 and the gradient of the second slope (d) is 2, 1 > 2. Secondly, supposing that the horizontal length between the vertex (a) of a polygonal dimple and the center (b) thereof is L1; and the horizontal length between the intersection (e) of the first slope (c) with the second slope (d) and the center (b) of the regular pentagon is L2; L2/L1 ≥ 0.6 Thirdly, supposing that the distance between the imaginary spherical surface of the golf ball and the deepest point of the dimple is F1; the vertical length between the imaginary spherical surface of the golf ball and the intersection (e) of the first slope (c) with the second slope (d) is F2; and the radius of golf ball is R, the following equation is established: {F2-R+(R 2 -L1 2 ) 1/2 }/{F1-R+(R 2 -L1 2 ) 1/2 } ≥ 0.6 The sides of the polygonal dimple are curved because the surface of the golf ball is curved and hence the surface configuration of the dimple is not polygonal in a strict sense. According to the present invention, such a surface configuration is regarded as approximately polygonal and called a polygonal dimple. As described above, the dimple according to the present invention is polygonal in its surface configuration and has a double slope. The polygonal configuration has the effect of making the air flow turbulent. The double-slope configuration of the dimple allows the gradient of its first slope to be larger than the gradient of the single-slope configuration conventionally adopted, as shown by a broken line (g) of Fig. 1, supposing that the dimple volume of the double slope configuration is equal to that of the single-slope configuration. That is, the plane (surface of first slope) having a great angle with respect to an air flow can be formed in continuity with the dimple edge. Thus, the double-slope configuration has the effect of sweeping air away from the periphery of the golf ball. That is, the air in the periphery of the golf is made to be turbulent by the polygonal configuration of the dimple and swept away from the golf ball by the double-slope configuration. Thus, the dimple polygonal and doubly sloped increases the aerodynamic characteristic of the golf ball. According to the golf ball of the present invention, the dimples having the above-described configuration comprises more than 40% of all dimples. Therefore, the golf ball has an improved flight performance and hence a long flight distance. Experimental researches have indicated that a golf ball having polygonal and doubly sloped dimples which are less than 40% of all dimples formed on the surface thereof does not have an improved flight performance and thus does not fly as long as a golf ball having more than 40% of all dimples formed as polygonal and doubly sloped dimples. These and other objects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: Fig. 1 is an explanatory view for describing the double slope of a polygonal dimple according to the present invention; Fig. 2 is a front view showing dimples according to a first embodiment of the present invention; Fig. 3 is a plan view showing the dimples according to the first embodiment; Fig. 4 is a plan view showing a dimple (A) according to the first embodiment; Fig. 5 is a sectional view showing the dimple (A); Fig. 6 is a perspective view showing the dimple (A); Fig. 7 is a front view showing dimples according to a second embodiment; Fig. 8 is a plan view showing the dimples according to the second embodiment; Fig. 9 is a plan view showing a dimple (E) according to the second embodiment; Fig. 10 is a sectional view showing the dimple (E); Fig. 11 is a front view showing dimples according to a third embodiment; Fig. 12 is a plan view showing the dimples according to the third embodiment; Fig. 13 is a plan view showing a dimple (C) according to the third embodiment of the present invention; Fig. 14 is a sectional view showing the dimple (C); Fig. 15 is a perspective view showing the dimple (C); Fig. 16 is a front view showing dimples according to a fourth embodiment; Fig. 17 is a plan view showing the dimples according to the fourth embodiment; Fig. 18 is a plan view showing a dimple (B) according to the fourth embodiment; Fig. 19 is a sectional view showing the dimple (C); Fig. 20 is a perspective view showing the dimple (B); Fig. 21 is a front view showing dimples according to a fifth embodiment; Fig. 22 is a plan view showing the dimples according to the fifth embodiment; Fig. 23 is a front view showing dimples according to a sixth embodiment; Fig. 24 is a plan view showing the dimples according to the sixth embodiment; Fig. 25 is a plan view showing a dimple (D) according to the sixth embodiment; Fig. 26 is a sectional view showing the dimple (D); Fig. 27 is a perspective view showing the dimple (D); Fig. 28 is a front view showing dimples according to a first comparison example; Fig. 29 is a plan view showing the dimples according to the first comparison example; Fig. 30 is a front view showing dimples according to a second comparison example; Fig. 31 is a plan view showing the dimples according to the second comparison example; Fig. 32 is a front view showing dimples according to a third comparison example; and Fig. 33 is a plan view showing the dimples according to the third comparison example. DETAILED DESCRIPTION OF THE INVENTION Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. A first embodiment of the present invention will be described below with reference to Figs. 1 and 6. In the first embodiment, a golf ball has dimples being regular pentagonal and having a double slope. More specifically, as shown in Figs. 4, 5, and 6, the golf ball has 332 dimples (A) regular pentagonal in the surface configuration thereof and doubly sloped in the sectional configuration thereof. The specification of the dimple (A) is shown in Table 1. L1, L2, F1, F2, 1, and 2 in Table 1 show the length of each portion described previously with reference to Fig. 1. That is, as shown in Fig. 5, L1 is the horizontal length between the vertex (a) of a regular polygon and the center (b) thereof. L2 is the horizontal length between the intersection (e) of a first slope (c) with a second slope (d) and the center (b) of the regular pentagon. F1 is the depth between the imaginary spherical surface of the golf ball and the deepest point of the dimple. F2 is the vertical length between the imaginary spherical surface of the golf ball and the intersection (e) of the first slope (c) with the second slope (d). specification of dimple of embodiments and comparison examples dimple surface section L1 L2 F1 F2 r1 r2 A reg-pen d-slope 2.00 1.48 0.28 0.23 - - B reg-hex d-slope 1.90 1.39 0.29 0.23 - - C reg-pen s-slope 2.00 - 0.24 - - - D reg-hex s-slope 1.90 - 0.24 - - - E circular d-radius 1.85 - 0.19 - 14.0 3.0 In the Table 1, L1, L2, F1, F2, r1, and r2 are shown in millimeters; surface configuration is abbreviated as surface; sectional configuration is abbreviated as section; regular pentagon is abbreviated as reg-pen; regular hexagon is abbreviated as reg-hex; double slope is abbreviated as d-slope; single slope is abbreviated as s-slope; and double radius is abbreviated as d-radius. The configuration of the double slope of the dimple (A) satisfies the following three conditions: Firstly, L2/L1 ≥ 0.6 Secondly, {F2-R+(R 2 -L1 2 ) 1/2 }/{F1-R+(R 2 -L1 2 ) 1/2 } ≥ 0.6 where R is the radius of golf ball. Thirdly, 1 > 2. The third condition is automatically satisfied if the first and second conditions are satisfied. In the dimple (A), the gradient of the first slope (c) is greater than that of the second slope (d) so as to improve the effect of sweeping air away from the periphery of the golf ball. A second embodiment of the present invention is described below with reference to Figs. 7 through 10. The golf ball of the second embodiment has two kinds of dimples, namely, dimples regular pentagonal in the surface configuration thereof and doubly sloped in the sectional configuration thereof and dimples being circular in the surface configuration thereof and having a double radius. That is, the golf ball has 152 dimples (A) similar to those of the first embodiment and 180 dimples (E) being circular in the surface configuration thereof and having the double radius as shown in Figs. 9 and 10, thus having 332 dimples in total. The specification of the dimple (E) is shown in Table 1. L1 in Table 1 shows the radius of the circular dimple (E) as shown in Fig. 10; r1 shows the curvature of the curved surface of the bottom portion of the dimple (E); and r2 shows the curvature of the curved surface in the vicinity of the edge (a) of the dimple (E). In the dimple (E), the curvature r2 is smaller than the curvature r1. That is, the curved surface near the dimple edge (a) forms a large angle (gradient) with respect to the flow of air in the periphery of the golf ball so as to improve the aerodynamic characteristic of the golf ball. A third embodiment of the present invention is described below with reference to Figs. 11 through 15. The golf ball of the third embodiment has dimples regular pentagonal and doubly sloped and dimples regular pentagonal and singly sloped. That is, the golf ball has 152 dimples (A) similar to the first and second embodiments and 180 dimples (C) pentagonal in the surface configuration thereof and having a single slope as shown in Figs. 13 through 15, thus having 332 dimples in total. The single slope configuration is sectionally straight in the line (f) connecting an edge (a) thereof and its center (b) with each other as shown in Fig. 14. The specification of the dimple (C) is shown in the above Table 1. A fourth embodiment of the present invention will be described below with reference to Figs. 16 and 20. A golf ball according to the fourth embodiment has dimples regular hexagonal and doubly sloped. That is, as shown in Figs. 18 through 20, the golf ball has 332 dimples (B) regular hexagonal in the surface configuration thereof and doubly sloped in the sectional configuration thereof. The specification of the dimple (A) is shown in the above Table 1. The dimple (B) satisfies the above-described three conditions similarly to the dimple (A). That is, the gradient of a first slope (c) is greater than that of a second slope (d) so as to obtain the effect of sweeping air away from the periphery of the golf ball. A fifth embodiment of the present invention is described below with reference to Figs. 21 and 22. The golf ball of the fifth embodiment has two kinds of dimples, namely, 152 dimples (B) regular hexagonal in the surface configuration thereof and doubly sloped in the sectional configuration thereof similarly to the fourth embodiment and 180 dimples (E) being circular in the surface configuration thereof and having a double radius similarly to the second embodiment, thus having 332 dimples in total. A sixth embodiment of the present invention is described below with reference to Figs. 23 through 27. The golf ball according to the sixth embodiment has dimples regular hexagonal in the surface configuration thereof and doubly sloped in the sectional configuration thereof and dimples regular hexagonal in the surface configuration thereof and singly sloped in the sectional configuration thereof. That is, the golf ball has 152 dimples (B) regular hexagonal in the surface configuration thereof and doubly sloped in the sectional configuration thereof similarly to the fourth and fifth embodiments and 180 dimples (D) regular hexagonal in the surface configuration thereof and singly sloped (shown by (f) in Fig. 26) as shown in Figs. 25, 26, and 27, thus having 332 dimples in total. The specification of the dimple (D) is shown in Table 1. Golf balls of first through third comparison examples were prepared to examine the effect of the dimple (A) through the dimple (E) of the first through sixth embodiment. Figs. 28 and 29 show the golf ball of the first comparison example. The golf ball has 332 dimples (E) being circular in the surface configuration thereof and having a double radius similarly to the dimples of the second and fifth embodiments. Figs. 30 and 31 show the golf ball of the second comparison example. The golf ball has 332 dimples (C) regular pentagonal in the surface configuration thereof and singly sloped in the sectional configuration thereof similarly to the dimple of the third embodiment. Figs. 32 and 33 show the golf ball of the third comparison example. The golf ball has 332 dimples (D) regular hexagonal in the surface configuration thereof and singly sloped in the sectional configuration thereof similarly to the dimple of the sixth embodiment. The golf balls of the first through sixth embodiment and those of the first through third comparison example were all thread-wound and had a balata cover and a liquid center, respectively. They had the same construction and composition. The outer diameters thereof were all 42.70 ± 0.03mm and the compression thereof were all 95 ± 2. Every golf balls had an icosahedral arrangement which has been widely adopted as a dimple-arranging pattern, and 332 dimples. The experimental results of the first through sixth embodiment and those of the first through third comparison example are described below. Using a swing robot manufactured by "True Temper Corp., the golf balls of the first through sixth embodiment and those of the first through the third comparison example were shot by a driver (W1) at a head speed of 45m/sec to measure the flight distance of each golf ball. The spin was 3500 ± 300rpm and the ball-shotting angle was 10 ± 0.5°. The golf balls were kept 23 ± 1°C in an oven until they were shot. Wind blew at a speed of 1.1 to 2.8m/sec in the direction from the right. Table 2 shows the average of the test result of 20 golf balls used for each of the first through sixth embodiment and the first through third comparison example. dimple of embodiments and comparison examples and test result of flight distance dimple test result of flight distance carry (yard) run (yard) total (yard) trajectory height(DEG) 1E A(reg.pen.)(d.sl.)332 227.4 12.5 239.9 13.3 2E A(reg.pen.)(d.sl.)152 222.5 12.9 235.4 12.7 B(c.)(d.r.) 180 3E A(reg.pen.)(d.sl.)152 223.0 13.5 236.5 13.0 C(reg.pen.)(s.sl.)180 4E B(reg.hex.)(d.sl.)332 226.9 12.4 239.3 13.2 5E B(reg.hex.)(d.sl.)152 222.0 13.1 235.1 12.5 E(c.)(d.r.) 180 6E B(reg.hex.)(d.sl.)152 222.2 13.6 235.8 13.1 D(reg.hex.)(s.sl.)180 1C E(c.)(d.r.) 332 216.3 13.2 229.5 12.2 2C C(reg.pen.)(s.sl.)332 218.2 14.7 232.9 11.9 3C D(reg.pen.)(s.sl.)332 218.5 14.5 233.0 12.2 In the Table 2, embodiment is abbreviated as E, 1E is first embodiment, 2E is second embodiment, 3E is third embodiment, 4E is fourth embodiment, 5E is fifth embodiment and 6E is sixth embodiment; comparison example is abbreviated as c, 1C is first comparison, 2C is second comparison and 3C is third comparison; regular pentagonal is abbreviated as (reg.pen.); double slope is abbreviated as (d.sl.); circular is abbreviated as (c.); single slope is abbreviated as (s.sl.); regular hexagonal is abbreviated as (reg.hex.); double radius is abbreviated as (d.r.). Further, in the Table 2, carry is the distance from the shot point to the drop point; total is the distance from the shot point to the stop point; run is the difference between total and carry; and trajectory height is an angle of elevation formed between the horizontal line and the straight line connecting the ball-hitting point with the highest point of the golf ball in trajectory. As shown in Table 2, the golf balls of the first and fourth embodiments having dimples of only double-slope configuration had a longest carry. The golf balls of the second, third, fifth, and sixth embodiments having 152 dimples (46% of all dimples) of the double-slope configuration had a second longest carry. The golf balls of the first to third comparison example on which dimple of double-slope configuration were not formed had a shortest carry. The test results indicate that the double-slope configuration causes the golf ball to have a favorable aerodynamic characteristic. The advantage of the double-slope configuration is that as described previously, a plane having a large angle with respect to the flow of air in the periphery of the golf ball is formed in the vicinity of an edge of a polygonal dimple. The greater the angle of the plane, namely, the gradient of the plane is, the greater is the effect of sweeping air away from the periphery of the golf ball. In view of the fact that the diameter and volume of the dimple are limited to a certain range, the gradient in the vicinity of the dimple edge cannot be made to be large in the case of the single-slope configuration while the gradient in the vicinity of the dimple edge can be made to be great in the case of the double-slope configuration. The characteristic configuration of the dimple according to the present invention is polygonal in the surface configuration thereof, but the dimple of a regular polygonal configuration is more favorable than that of a polygonal configuration. This is because the regular polygonal dimple has the effect of sweeping air away from the golf ball equally in every spin direction of the golf ball. As apparent from the foregoing description, the dimple is polygonal in the surface configuration thereof and has a double slope in the sectional configuration thereof. Therefore, the dimple has a striking effect of sweeping air away from the periphery of the golf ball and making the air flow very turbulent. Thus, the dimple improves the aerodynamic characteristic of the golf ball. The golf ball according to the present invention has dimples in the above-described configuration at more than 40% of all dimples thereof. Therefore, the golf ball has an improved flight performance and hence a long flight distance. Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.

Claims: A golf ball having a plurality of dimples (A, B, C, D, E) on its surface, wherein more than 40% of all dimples are dimples (A, B) of polygonal shape each comprising an outer portion (c) adjacent the edge of the dimple and having its surface inclined towards the center (b) of the dimple with a first angle of slope ( 1 ), and an inner portion (d) continuing from said first portion (c) to the center (b) of the dimple, characterized in that said inner portion (d) of the dimple has its surface inclined towards the center (b) of the dimple with a second angle of slope ( 2 ) which is smaller than said first angle of slope ( 1 ). A golf ball as claimed in claim 1, wherein said polygonal shape is regular polygonal. A golf ball as claimed in claim 2, wherein said regular polygonal shape is regular pentagonal or regular hexagonal. A golf ball as claimed in claim 1, wherein the ratio between the horizontal length L1 from the vertex of said dimple to the center thereof and the horizontal length L2 from the intersection of said first slope with said second slope in said double slope to the center of the dimple is L2/L1 ≥ 0.6. A golf ball as claimed in claim 1, wherein the following equation is established, in which F1 is the distance between the imaginary spherical surface of said golf ball and the deepest point of the dimple, F2 is the vertical length between the imaginary spherical surface of said golf ball and the intersection of the first slope with the second slope and R is the radius of the golf ball: {F2-R+(R 2 -L1 2 ) 1/2 }/{F1-R+(R 2 -L1 2 ) 1/2 } ≥ 0.6

Inventors: OHSHIMA SHINJI, OKA KENGO, OHSHIMA, SHINJI, OKA, KENGO
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LIMITED
Application year: 1992
Main classification: A63B37
IPC codes: A63B37