Golf ball

Abstract: A golf ball having a circular dimples and uncircular dimples arranged in a different percentages depending on spherical zones, whereby a favorable aerodynamic property is obtained by eliminating the difference in trajectories between line hitting and face hitting. In a spherical zone in the vicinity of the great circle uncircular dimples are arranged in a percentage higher than circular dimples, whilst in a spherical zone further from the great circle circular dimples are arranged in a higher percentage.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a golf ball, and more particularly, to the golf ball having an improved aerodynamic symmetrical property which can be accomplished by arranging dimples of different surface configurations on the surface thereof. Description of the Related Arts Normally, 280 to 540 dimples are formed on the surface of the golf ball. The function of dimples is to reduce pressure resistance to the golf ball and improve dynamic lift thereof. More specifically, in order to lift it high in air, the separation point between air and the upper surface thereof is required to be as back ward as possible compared with the separation point between air and the lower surface thereof so as to make air pressure existing above it smaller than that existing below it. In order to accelerate the separation of air existing above it from the upper surface thereof, it is necessary to make the air current in the periphery thereof turbulent. In this sense, a dimple which makes the air current around the golf ball turbulent is aerodynamically superior. Since the golf ball is molded by a pair of upper and lower semispherical molds having dimple patterns, dimples cannot be arranged on the parting line corresponding to the connecting face of the upper and lower molds. Therefore, one great circle path corresponding to the parting line and not intersecting any dimples is formed on the surface of the golf ball. As the surface configuration of the dimple, circular, elliptic, polygonal or the like forms are adopted. The golf ball may have dimples of the same surface configuration or various surface configurations formed on the surface thereof. In view of dimple effect, the surface of the golf ball may be divided into a spherical zone in the vicinity of a great circle not intersecting any dimples and a spherical zone remote from the great circle. According to conventional methods of arranging dimples of different surface configurations, both spherical zones have the same dimple arrangement, i.e., dimples are uniformly arranged throughout the surface of the golf ball. This is also the case with a golf ball according to the preamble of claim 1 known from FR-A-2 194 457. This prior art golf ball has 12 polygonal dimples uniformly distributed among a majority of circular dimples, the polygonal dimples forming the vestices of 20 regular spherical triangles on the surface of the ball. When dimples of different configurations are arranged on the surface of the golf ball uniformly in both spherical zones, the dimple effect in the spherical zone in the vicinity of the great circle is different from the other spherical zone due to the existence of the great circle. Consequently, the following problem occurs in the aerodynamic symmetrical property of the golf ball. It is preferable that the golf ball flies in the same trajectory each time it flies. That is, preferably, the trajectory height, flight time, and flight distance of the golf ball is the same, regardless whether or not its rotational axis in its backspin coincides with the great circle path. But actually, the dimple effect varies according to a rotational axis, namely, whether or not a circumference which rotates fastest in its backspin coincides with the great circle path. More specifically, in line hitting, i.e., when the golf ball rotates in its backspin such that the circumference which rotates fastest in its backspin coincides with the great circle path, the dimple effect of making the air current around the golf ball turbulent is smaller than the dimple effect obtained in face hitting, i.e., when the golf ball rotates in its backspin such that the circumference which rotates fastest in its backspin does not coincide with the great circle path. Thus the trajectory height of the golf ball is lower and consequently the flight time thereof in line hitting is shorter than those in face hitting. If the golf ball has a different flight performance according to a rotational axis, i.e., if the golf ball has an unfavorable aerodynamic property, a player's ability cannot be displayed. In order to solve the above-described problem, methods for manufacturing golf balls having no great circles are proposed, for example, in Japanese Patent Laid-Open Publication 64-8983 and Japanese Patent Laid-Open Publication No. 62-47379. However, due to various problems, these methods are incapable of putting golf balls on the market. Such being the case, golf balls commercially available have at least one great circle path. SUMMARY OF THE INVENTION It is an object of the present invention to provide a golf ball, having at least one great circle path formed on the surface thereof, in which a favorable aerodynamic property is obtained by eliminating the difference in trajectories between line hitting and face hitting. This object is achieved according to the invention with a golf ball as claimed in claim 1. According to the golf ball of the present invention, the dimple effect of (L) zone is increased by arranging non-circular dimples in (L) spherical zone in more than 60% of all dimples arranged in (L) spherical zone and circular dimples in (F) spherical zone in more than 60% of all dimples arranged in (F) spherical zone. Thus, the dimple effect reduced in (L) zone by the great circle is compensated so that the dimple effect of (L) spherical zone is equal to that of (F) spherical zone. The reason why the dimple effect in (L) spherical zone is increased is that a non-circular dimple has effect of making air current more turbulent than a circular dimple as described above. That is, the air current in the periphery of the circular dimple, for example, d-1 as shown in Fig. 1 is smooth while the air current in the periphery of the non-circular dimples, for example, d-2, d-3, and d-4 as shown in Fig. 2, 3, and 4, respectively makes air current turbulent when air current runs against the edge of the non-circular dimple. According to the above construction, when the golf ball is line-hit, i.e., when it rotates about a rotational axis, the circumference of which coincides with the great circle, dimple effect of (L) spherical zone can be improved because non-circular dimples are arranged in the vicinity of the great circle in more than 60% of all dimples arranged therein. Thus, the trajectory height, flight time, and flight distance of the golf ball in line hitting are similar to those in face hitting. That is, the golf ball has an equal flight performance wherever it is hit, namely, irrespective of a rotational axis in its backspin. The central angle made by a circumference which divides the golf ball into (L) spherical zone and (F) spherical zone is not limited to 15°, but determined by the number of great circles. If one to two great circles are formed on the surface of the golf ball, preferably, the central angle of the circumference is 20° while if three great circles are formed on the surface thereof, the line connecting the circumference and the center of the golf ball with each other makes 10° with the line connecting the center of the golf ball and each great circle with each other. Since the area of (L) spherical zone increases with the increase of the number of great circles, it is favorable to reduce the area of each (L) spherical zone so that the golf ball has a favorable aerodynamic property. Accordingly, the central angle of each circumference is decreased from 20° to 10° with the increase of the number of great circle paths. The dimple arranged in (L) spherical zone means that the center of the dimple is positioned in (L) spherical zone and similarly, the dimple arranged in (F) spherical zone means that the center of the dimple is positioned in (F) spherical zone. The center of an uncircular dimple as shown in Fig. 4 is the center of gravity of the surface configuration thereof. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: Fig. 1 is a schematic view showing air current on a circular dimple; Fig. 2 is a schematic view showing air current on a non-circular dimple; Fig. 3 is a schematic view showing air current on a non-circular dimple; Fig. 4 is a schematic view showing air current on a non-circular dimple; Fig. 5 is a front view showing a golf ball according to a first embodiment of the present invention; Fig. 6 is a plan view of the golf ball shown in Fig. 5; Fig. 7 is a front view showing an L spherical zone and an F spherical zone of the golf ball according to the first embodiment of the present invention; Fig. 8 is a descriptive view for describing the boundary line between L spherical zone and F spherical zone; Fig. 9 is a front view showing a golf ball according to a second embodiment of the present invention; Figs. 10 is a plan view of the golf ball shown in Fig. 9; Fig. 11 is a front view showing L spherical zone and F spherical zone of a golf ball according to the second embodiment of the present invention; Fig. 12 is a front view showing a golf ball according to a first comparative example; Fig. 13 is a plan view of the golf ball shown in Fig. 12; Fig. 14 is a front view showing L spherical zone and F spherical zone of the golf ball according to the first comparative example; Fig. 15 is a front view showing a golf ball according to a second comparative example; Fig. 16 is a plan view showing the golf ball according to the second comparative example; and Fig. 17 is a front view showing L spherical zone and F spherical zone of the golf ball according to the second comparative 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. Referring to Figs. 5, 6, and 7 showing a golf ball G1 in accordance with a first embodiment of the present invention, dimples of the golf ball G1 are arranged based on regular octahedral arrangement, i.e., the spherical surface of the golf ball G1 is divided into areas corresponding to the faces of a regular octahedron to form eight identical spherical equilateral triangles. The golf ball G1 has three great circle paths 1, 2, and 3 not intersecting any dimples. Since the golf ball G1 has three great circles, the central angle of each boundary circumference (X) dividing the surface of the golf ball into two zones, an (L) spherical zone and an (F) spherical zone is set to ϑ = 10° as shown in Fig. 8 for the reason described previously. More specifically, the line connecting each boundary circumference (X) with the center of the golf ball makes 10° with the line connecting each great circle path 1, 2, and 3 with the center of the golf ball G1. (L) zone ranges from each great circle path 1, 2, and 3 to each boundary circumference (X). (F) zone is the region other than (L) zone. As shown in Fig. 7, dimples D1 arranged in (L) zone are black while dimples D2 arranged in (F) zone are white. The number of dimples D1 arranged in (L) zone is 168 and that of dimples D2 arranged in (F) zone is also 168, totalling 336 as shown in Table 1. The number of non-circular dimples, namely, square dimples D1-1 or regular octagonal dimples D1-2 is 120 which is 71% of dimples D1 arranged in (L) zone while the number of circular dimples D1-3 arranged in (L) zone is 48 which is 29% of dimples D1. The number of non-circular dimples, namely, square dimples D2-1 or regular octagonal dimples D2-2 is 48 which is 29% of dimples D2 arranged in (F) zone while the number of circular dimples D2-3 in (F) zone is 120 which is 71% of dimples D2. As apparent from the above description, according to the golf ball G1 of the first embodiment, in (L) zone the non-circular dimples are more than the circular dimples while in (F) zone the number of non-circular dimples is less than that of circular dimples so that air current in the periphery of (L) zone is more turbulent than that in the periphery of (F) zone. Referring to Figs. 9, 10, and 11, a golf ball according to a second embodiment of the present invention is described below. Dimples of a golf ball G2 is arranged on the surface thereof based on regular icosahedral arrangement conventionally used, i.e., the spherical surface of the golf ball G2 is divided into areas corresponding to the faces of a regular icosahedron to form 20 identical spherical equilateral triangles. The golf ball G2 has one great circle path 1 corresponding to the parting line. For the reason described previously, the central angle of each boundary circumference (X) dividing the surface of the golf ball into two zones, (L) spherical zone and (F) spherical zone is set to ϑ = 20°. More specifically, the line connecting each boundary circumference (X) with the center of the golf ball G2 makes 20° with the line connecting the great circle path 1 with the center of the golf ball. As shown in Fig. 11, dimples D1' arranged in (L) zone are black while dimples D2' arranged in (F) zone are white. The number of dimples D1' arranged in (L) zone is 120 and that of dimples D2' arranged in (F) zone is 212, totalling 332 as shown in Table 1. The dimples D1' arranged in (L) zone are all non-circular dimples, namely, regular hexagonal dimples. The number of the non-circular dimples, namely regular hexagonal dimples, is 80 which is 38% of dimples D2' arranged in (F) zone. The number of circular dimples is 132 which is 62% of the dimples D2' arranged in (F) zone. As apparent from the above description, according to the golf ball G2 of the second embodiment, only non-circular dimples are arranged in (L) zone while more circular dimples than non-circular dimples are arranged in (F) zone so that air current in the periphery of (L) zone is more turbulent than that in the periphery of (F) zone. According to the first and second embodiments, polygonal dimples such as square, regular octagonal or regular hexagonal dimples are used as non-circular dimples. This is because these regular polygonal dimples have more favorable symmetrical properties than dimples of other non-circular configurations and act on air current irrespective of the direction thereof. Since dimples are formed on the spherical surface of the golf ball, the sides of a regular polygonal dimple are all spherical. But according to the present invention, a dimple which is a regular polygon when viewed along the normal line to the curve of the golf ball at a given point is regarded as a regular polygonal dimple. In order to examine the operation and effect of the aerodynamic property of the golf ball according to the present invention, a first comparative example golf balls corresponding to the first embodiment and a second comparative example golf balls corresponding to the second embodiment were prepared. Referring to Figs. 12, 13, and 14 showing a golf ball G3 according to a first comparative example, dimples of the golf ball G3 are arranged based on regular octahedral arrangement, and there are three great circle paths 1, 2, and 3 not intersecting dimples, similar to the first embodiment. Therefore, the central angle of each boundary circumference dividing the surface of the golf ball G3 into two zones, (L) spherical zone and (F) spherical zone is set to ϑ = 10° similarly to the first embodiment. In Fig. 14, dimples D1 arranged in (L) zone are represented black while dimples D2 arranged in (F) zone are represented white. As shown in Table 1, 168 dimples are arranged in (L) zone and (F) zone of the first comparative example the golf ball G3, respectively, totalling 336 similar to the first embodiment. The number of non-circular dimples, namely square dimples D1-1 arranged in (L) zone is 72 which is 43% of dimples D1 arranged therein while the number of circular dimples D1-3 arranged in (L) zone is 96 which is 57% of dimples D1 arranged therein. The number of non-circular dimples, namely square dimples D2-1 or regular octagonal dimples D2-2 arranged in (F) zone is 48 which is 29% of dimples D2 arranged therein while the number of circular dimples D2-3 arranged in (F) zone is 120 which is 71% of dimples D2 arranged therein. In the golf ball G3 of the first comparative example, circular dimples having a smaller effect of making air current turbulent are more numerous than non-circular dimples both in (L) and (F) zones. Referring to Figs. 15, 16, and 17, second comparative example golf balls G4 are described below. Dimples are arranged on the surface thereof based on regular icosahedral arrangement. The golf ball G4 has one great circle path corresponding to the parting line similarly to the second embodiment. The central angle of each boundary circumference dividing the surface of the golf ball into two zones, (L) spherical zone and (F) spherical zone, is set to ϑ = 20°. In Fig. 17, dimples D1' arranged in (L) zone are represented black while dimples D2' arranged in (F) zone are represented white. As shown in Table 1, 120 dimples are arranged in (L) zone and 212 dimples are arranged in (F) zone of the golf ball G3, totalling 332 similarly to the second embodiment. All of 120 dimples arranged in (L) zone are non-circular, namely regular hexagonal. Similarly, all of 212 dimples arranged in (F) zone are also non-circular, namely regular hexagonal. That is, only non-circular dimples having the effect of making air current strongly turbulent are arranged both in (L) zone and (F) zones of the golf ball G4 of the second comparative example. The golf balls of the first and second embodiments and the first and second comparative examples are each thread-wound and have a liquid center and a balata cover. They have the same composition and construction. The outer diameter thereof is all 42.70 ± 0.03mm and the compression thereof is all 95 ± 2. Experimental results of the first and second embodiments and the first and second comparative examples are described below. Using a swing robot manufactured by True Temper Corp., tests for examining symmetrical property thereof were conducted. The test conditions were as follows: Club used: driver (W1) Head speed: 48.8 m/sec Spin: 3500 ± 300 rpm Angle of elevation: 9° ± 0.5° Wind: against, 0.9 ∼ 2.7m/s Temperature of golf balls: 23° ± 1°C The number of golf balls prepared for each embodiment and comparative example was 40. Under this condition, 20 balls were line-hit and 20 balls were face-hit. The averages of carries, trajectory heights (trajectory height means an angle of elevation viewed from a launching point of a golf ball to the highest point thereof in flight) and flight time were measured. The results are shown in Table 2 below. Symmetrical Characteristic Test way of hitting carry (yard) trajectory height (DEG) flight time (SEC) first embodiment line hitting 237.4 13.72 6.10 face hitting 238.4 13.76 6.10 second embodiment line hitting 235.0 13.91 6.22 face hitting 235.6 13.84 6.25 first comparative example line hitting 231.1 13.29 5.77 face hitting 237.4 13.70 6.05 second comparative example line hitting 234.7 13.99 6.20 face hitting 228.5 14.38 6.54 As clear from Table 2, according to the golf balls of the first and second embodiments, the carry, the trajectory height, and the flight time in line hitting were almost equal to those in face hitting. As compared with the golf ball of the embodiments, according to the first comparative example golf balls, the trajectory height in line hitting was lower than that in face hitting and the flight time and the carry in line hitting were shorter than those in face hitting. This is because the percentage of non-circular dimples arranged in (L) zone of the first comparative example golf balls is lower than that of non-circular dimples arranged in (L) zone of the golf ball according to the first embodiment and consequently, in line hitting, the dimple effect of the first comparative example golf balls is smaller than that of the golf balls of the first embodiment. Similarly, according to the second comparative example golf balls, the trajectory height in line hitting was lower than that in face hitting and the flight time in line hitting was shorter than those in face hitting. This is because the percentage of non-circular dimples arranged in (F) zone of the second comparative example golf balls is much greater than that of non-circular dimples arranged in (F) zone of the golf ball according to the first embodiment and consequently, in face hitting, the dimple effect of the second comparative example golf balls is too great. Non-circular dimples have effect of making the air current in the vicinity of the golf ball strongly turbulent, but if they are arranged inappropriately on the surface of the golf ball as exemplified in the second comparative example golf balls, the golf ball has an unfavorable symmetrical property and consequently, its flight distance is short. As apparent from the foregoing description, the golf balls according to the first and second embodiments have a more favorable aerodynamic property than the first and second comparative example golf balls and have a small difference of the trajectory irrespective of whether the golf ball rotates in back spin on a rotational axis which coincides with that of the great circle path or a rotational axis which does not coincide with that of the great circle path. 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.

Claims: A golf ball having dimples on its spherical surface, the dimples comprising circular dimples and non-circular dimples and being arranged so that at least one great circle (1) on the golf ball surface does not intersect any dimples, characterized in that in a zone (L) which is defined by said great circle (1) and a boundary circle spaced from said great circle by a central angle (ϑ) of less than approximately 20° on both sides thereof, more than 60% of the dimples are non-circular dimples and in the surface aera (F) outside said zone (L) more than 60% of the dimples are circular dimples. A golf ball as claimed in claim 1, wherein there are three mutually orthogonal great circles (1, 2, 3) not intersecting any dimples, and the central angle (ϑ) of the boundary circles defining said zones (L) on both sides of each of said great circles (1, 2, 3) is less than approximately 15°. A golf ball as claimed in claim 2, wherein said central angle (ϑ) is approximately 10°.

Inventors: OHSHIMA SHINJI, OKA KENGO, OHSHIMA, SHINJI, OKA, KENGO
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LIMITED
Application year: 1991
Main classification: A63B37
IPC codes: A63B37