Golf ball

A golf ball has dimples arranged in eight spherical equilateral triangles obtained by projecting, on the imaginary spherical surface of the golf ball, the ridge lines of a regular octahedron inscribing the imaginary spherical surface. Three great circles corresponding to the ridge lines being projected on the spherical surface. One great circle coinciding with a mold seam is formed as the sole great circle unintersecting dimples and the other two great circles intersect dimples. Between 300 to 550 dimples are formed in the golf ball with the dimples being equivalently arranged in each of the eight spherical equilateral triangles.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a golf ball, and more particularly, to the 
golf ball having an octahedral dimple arrangement which improves the 
flight performance of the golf ball. 
2. Description of the Related Arts 
Normally, 300 to 550 dimples are formed on the surface of a golf ball so as 
to increase the flight distance thereof by improving the aerodynamic 
characteristic thereof. Of various proposals regarding dimple 
arrangements, regular octahedral arrangement is most widely adopted 
because dimples are arranged symmetrically and regularly. 
As shown in FIGS. 10, 11 and 12, according to the regular octahedral 
arrangement, the spherical surface of a golf ball 1 is divided into eight 
spherical equilateral triangles by projecting, on the spherical surface of 
the golf ball 1, the ridge lines 2a of a regular octahedron 2 inscribing 
the spherical surface of the golf ball 1 and dimples are equivalently 
arranged in each spherical triangle as shown in FIG. 12. The ridge lines 
2a projected on the spherical surface of the golf ball 1 form three great 
circles 3, 4, and 5 on which dimples 6 are not arranged. That is, the golf 
balls 1 has on the surface thereof three great circles which do not 
intersect the dimples 6. 
Normally, since the golf ball is molded by a pair of upper and lower 
semispherical molds, dimples are not arranged on the seam between the 
upper and lower molds so as to facilitate the removal of a burr formed 
when the golf ball is molded. Therefore, in the regular octahedral dimple 
arrangement, the great circle 3 coincides with the seam. 
The main object of the dimple is to accelerate the transition of the 
turbulent flow of a boundary layer and increase the aerodynamic 
characteristic of the golf ball in order to increase the flight distance 
of the golf ball. Therefore, it is well known to those skilled in the art 
to effectively arrange dimples to accelerate the transition of the 
turbulent flow of the boundary layer. From this point of view, various 
proposals have hitherto been made to improve the regular octahedral dimple 
arrangement on the surface of the golf ball. According to the dimple 
arrangement proposed by Japanese Patent Laid-Open Publication No. 62-79072 
(unexamined), dimples of large and small diameters are arranged on the 
surface of the golf ball. According to the dimple arrangement proposed by 
Japanese Patent Laid-Open Publication No. 2-152476 (unexamined), dimples 
of more than three different diameters are arranged on the surface of the 
golf ball. 
The regular octahedral dimple arrangements proposed by these prior patent 
applications are capable of improving the flight performance of the golf 
ball to some extent, however, there is still a problem due to three great 
circles being formed on the golf ball. 
Namely, when the golf ball flies with backspin, dimples arranged on a 
circumference which rotates fastest in its backspin have the most affect 
on the flight distance of the golf ball. When the circumference which 
rotates fastest in its backspin coincides or approximately coincides with 
a great circle having no dimples arranged thereon, dimple effect is 
reduced, so that the flight distance of the golf ball becomes shorter. In 
the octahedral dimple arrangement, there is a great possibility that the 
circumference which rotates fastest in its backspin coincides or 
approximately coincides with one of the three great circles because the 
golf ball has three great circles unintersecting dimples. Therefore, the 
flight distance of the golf ball is varied due to one of the great circles 
formed thereon. 
SUMMARY OF THE INVENTION 
It is therefore the object of the present invention to provide a golf ball 
having a regular octahedral dimple arrangement and a favorable aerodynamic 
symmetrical property so as to increase the flight distance thereof by 
providing only one great circle unintersecting dimples. 
In accomplishing these and other objects, the present invention provides a 
golf ball having dimples arranged in eight spherical equilateral triangles 
obtained by projecting, on the imaginary spherical surface of the golf 
ball, the ridge lines of a regular octahedron inscribing the imaginary 
spherical surface. Of three great circles corresponding to the ridge lines 
projected on the spherical surface, one great circle coinciding with a 
seam between a pair of molds is formed as the sole great circle 
unintersecting dimples and the other two great circles intersect dimples. 
According to the preferred golf ball, dimples are arranged equivalently in 
each of the eight spherical equilateral triangles. 
Preferably, each dimple intersecting the two great circles corresponding to 
the ridge lines projected on the spherical triangle protrudes from one 
spherical equilateral triangle to an adjacent spherical equilateral 
triangle in the length of more than 0.3 mm. 
In order to equalize to each other the aerodynamic characteristic of the 
vicinity of the seam corresponding to the great circle is formed and 
unintersecting dimples and the vicinity of the poles having dimples 
densely arranged, the surface of the golf ball is divided into an S 
spherical zone in the vicinity of the seam and a P spherical zone in the 
vicinity of the poles P. The dimple specification of S and P zones are set 
so that assuming that RS is a value obtained by dividing the total volume 
of all dimples arranged in S zone by the surface area of S zone of the 
imaginary spherical surface and RP is a value obtained by dividing the 
total volume of all dimples arranged in P zone by the surface area of P 
zone of the imaginary spherical surface, RS/RP is set in the range: 
EQU 0.95.ltoreq.RS/RP.ltoreq.1.20 
According to the above construction, since the golf ball has only one great 
circle corresponding to the seam not intersecting dimples, the possibility 
that a circumference which rotates fastest in its backspin coincides or 
approximately coincides with the great circle can be reduced, so that the 
flight distance of the golf ball can be increased by improving the 
aerodynamic characteristic thereof. 
In addition, dimples of larger volumes are arranged in S zone in the 
vicinity of the seam on which the great circle unintersecting dimples is 
formed. Dimples of smaller volumes are arranged in P zone, in the vicinity 
of the poles, in which dimples are densely arranged. Therefore, the 
aerodynamic symmetrical property of the golf ball can be improved. That 
is, the aerodynamic characteristic of the golf ball is equalized between a 
case where a circumference which rotates fastest in its backspin coincides 
with the seam and a case where a circumference which rotates fastest in 
its backspin coincides with the pole. 
Further scope of applicability of the present invention will become 
apparent from the detailed description given hereinafter. However, it 
should be understood that the detailed description and specific examples, 
while indicating preferred embodiments of the invention, are given by way 
of illustration only, since various changes and modifications within the 
spirit and scope of the invention will become apparent to those skilled in 
the art from the detailed description.

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. 
FIG. 1A is a plan view, showing a golf ball 10 according to the present 
invention, viewed with the pole P of the golf ball 10 placed uppermost. 
FIG. 1B is a front view showing the golf ball 10 shown in FIG. 1A. 
Based on a regular octahedron as shown in FIG. 11, dimples 11 are arranged 
on the golf ball 10. That is, the seam coincides with one of three great 
circles 12, 13, and 14 corresponding to the ridge lines, of a regular 
octahedron which inscribes the imaginary spherical surface of the golf 
ball 10, projected on the spherical surface of the golf ball 10. That is, 
the great circle 12 does not intersect the dimples 11 while the great 
circles 13 and 14 intersect the dimples 11. 
Since the golf ball 10 has a regular octahedron on, the golf ball 10 has on 
the surface thereof eight spherical equilateral triangles I through VIII. 
According to this embodiment, dimples 11 are arranged equivalently in each 
eight triangles I through VIII. The dimples 11 consist of eight kinds A 
through H as shown in Table 1. The diameter of the dimple A is identical 
to that of the dimple B. The diameter of the dimple C is identical to that 
of the dimple D; the diameter of the dimple E is identical to that of the 
dimple F; and the diameter of the dimple G is identical to that of the 
dimple H. But the depths, curvatures, and volumes of the dimples A and B 
are different from each other; those of the dimple C are different from 
those of the dimple D; those of the dimple E are different from those of 
the dimple F; and those of the dimple G are different from those of the 
dimple H. 
As shown in FIG. 2, according to the dimple specification of Table 1, 
diameter is the length of a common tangent to both end points (a) and (b) 
of the dimple 11; depth is the length longest of perpendiculars dropped 
from the above tangent to the surface of the dimple 11, namely, the length 
from point (c) to (d); curvature is the radius (R) of a sphere, part of 
which forms the surface of the dimple 11; and volume is indicated by 
diagonal lines of FIG. 2. 
TABLE 1 
__________________________________________________________________________ 
dimple specifications between golf balls of 
the present invention and the comparison examples 
total 
number kind 
number 
diame- curva- 
of of of ter depth 
ture 
volume 
total volume (mm.sup.3) 
RS RP RS/ 
dimples dimple 
dimples 
(mm) 
(mm) 
(mm) 
(mm) 
S zone 
P zone 
whole 
mm.sup.3 /mm.sup.2 
mm.sup.3 /mm.sup.2 
RP 
__________________________________________________________________________ 
embodi- 
410 A 96 4.10 
0.16 
13.1 
1.07 
165.9 
174.4 
340.3 
0.123 0.116 1.06 
ment B 138 4.10 
0.14 
14.8 
0.95 
C 16 3.70 
0.16 
10.6 
0.88 
D 32 3.70 
0.14 
12.0 
0.78 
E 48 3.20 
0.16 
8.3 0.63 
F 16 3.20 
0.14 
9.4 0.55 
G 40 2.80 
0.16 
6.3 0.49 
H 24 2.80 
0.14 
7.1 0.43 
compari- 
416 A 200 3.95 
0.17 
11.6 
1.04 
170.6 
167.0 
337.6 
0.109 0.128 0.85 
son B 216 3.00 
0.17 
6.7 0.60 
__________________________________________________________________________ 
According to the golf ball 10, as shown in FIG. 1A, eight kinds of dimples 
11 are arranged equivalently in each of the eight spherical equilateral 
triangles I through VIII so that the dimples 11 are symmetrical with 
respect to each of the great circles 12, 13, and 14 corresponding to the 
ridge lines of a regular octahedron inscribing the imaginary spherical 
surface of the golf ball 10 on which the ridge lines are projected. More 
specifically, each of the great circles 13 and 14 bisects dimples 11-1. 
That is, each of the dimples 11-1 on the great circles 13 and 14 is 
divided equivalently into two portions by the great circles 13 and 14 
respectively and is arranged in adjacent equilateral triangles. While the 
dimples 11 which are adjacent to the great circle 12 and are not arranged 
on the great circle 12 are symmetrical with respect thereto as shown in 
FIG. 1B. 
As shown in FIG. 3A, dimples are arranged equivalently in each of the eight 
equilateral triangles as follows: First, each of the eight equilateral 
triangles formed according to a regular octahedron is divided into six 
congruent spherical triangles, so that the spherical surface of the golf 
ball is divided into 48 congruent triangles. Then, assuming that one of 
the 48 triangles is a unit triangle X, dimples 11 are arranged on each 
side X-1, X-2, and X-3 of the triangle X so that they intersect each side 
X-1, X-2, and X-3. As shown in FIG. 3B, the dimples 11 are arranged in 
each of the 48 unit triangles so that each triangle has the same dimple 
arrangement as that of triangle X. According to this design, the golf ball 
10 has dimples arranged equivalently in each of the eight spherical 
equilateral triangles and no great circles unintersecting dimples. 
However, as described above, dimples cannot be arranged on the seam 
because it is necessary to remove a burr formed on the seam between a pair 
of semispherical upper and lower molds. Therefore, dimples which are to be 
formed on the great circle corresponding to the seam are removed as shown 
in FIG. 4A or moved as shown in FIG. 4B or a dimple arrangement is 
redesigned to form only one seam corresponding to the great circle 12 
unintersecting dimples in combination of dimple movement and removal. The 
movement or removal of dimples which are to be formed on the seam great 
circle corresponding to the seam results in intersections of dimples and 
the formation of bald areas. In order to overcome this problem, fine 
adjustments such as movements of dimples inside each of the eight 
spherical equilateral triangles, size alterations and additions of dimples 
are carried out so that dimples are equivalently arranged in each 
spherical equilateral triangle. 
According to the above method, the golf ball 10 has the great circle 12 
corresponding to the seam which does not intersect the dimples 11, two 
great circles 13 and 14 intersecting the dimples 11, and the dimples 11 
equivalently arranged in each of the eight spherical equilateral 
triangles. 
As shown in FIG. 5, the length L of the dimple 11 intersecting the great 
circles 13 and 14 and protruding from the spherical equilateral triangle I 
to the adjacent spherical equilateral triangle II is favorably, more than 
0.3 mm, and more favorably, 0.8 mm. In this embodiment, the length L of 
the dimple 11 is more than 1.4 mm. 
The number of dimples 11-1 which intersect the great circles 13 and 14 
respectively is at least two, favorably eight or more, and more favorably, 
30 or more. According to this embodiment, 34 dimples 11-1 intersect both 
the great circles 13 and 14, respectively. 
In addition to the embodiment as shown in FIGS. 1 and 5, dimples may 
intersect the great circle 13 and 14 as shown in FIGS. 6A, 6B, FIGS. 7A, 
7B, and 7C in which one-quarter of the great circle 13 between the seam 12 
and the pole P is shown. 
Referring to FIG. 6A, two dimples intersect the great circles 13 and 14, 
respectively. In FIG. 6B, eight dimples intersect the great circles 13 and 
14, respectively. FIGS. 6A and 6B show an example in which the dimples 11 
are equivalently arranged in each of the eight spherical equilateral 
triangles. 
Referring to FIGS. 7A, 7B, and 7C, the dimples 11-1 are not equivalently 
arranged in each of the eight spherical equilateral triangles. FIG. 7A 
shows an example in which four dimples 11-1 intersect the great circles 13 
and 14, respectively. FIG. 7B shows an example in which the dimples 11-1 
intersect the great circles 13 and 14 in three patterns (i), (ii), and 
(iii). In pattern (i), the great circle 13 passes through the center of 
the dimple 11-1. In pattern (ii), the dimples at the right and left sides 
with respect to the great circle intersects the great circles 13 and 14, 
respectively, thus projecting from one spherical equilateral triangle to 
the adjacent triangle and overlapping with another dimple protruding 
similarly. In pattern (iii), the dimple 11-1 projects from one triangle to 
the adjacent triangle in a manner similar to the pattern (ii), but the 
patter (iii) differs from pattern (ii) in that the dimple 11-1 protrudes 
from only one triangle to the other triangle and the projecting length 
thereof is less than one-half of the radius thereof. In this embodiment of 
FIG. 7B, the great circles 13 and 14 intersect 36 dimples, respectively. 
Referring to FIG. 7C, the great circles 13 and 14 intersect 16 dimples, 
respectively. 
In the golf ball having the great circle 12 formed thereon, when the great 
circle 12 coincides or approximately coincides with a circumference which 
rotates fastest in its backspin, the dimple effect is reduced and as such, 
the trajectory becomes low and the flight distance becomes short. In order 
to solve this problem, the following construction is provided: The surface 
of the golf ball 10 is divided into two zones, namely, an S spherical zone 
in the vicinity of the poles P as shown in FIG. 8. The volume of the 
dimple in S zone is greater than that of the dimple in P zone while the 
diameters of both dimples are equal to each other. More specifically, as 
shown by one-dot chain lines, S zone ranges from the great circle 12 to 
each of circumferences formed in correspondence with a central angle 
.theta. (10.degree..ltoreq..theta.&lt;60.degree.) with respect to the seam. 
As shown by two-dot chain lines, P zone ranges from each of the 
circumferences corresponding to the central angle .theta. to the poles P. 
Assuming that a value RS is obtained by dividing the total volume of all 
dimples arranged in S zone by the surface area of S zone of the imaginary 
sphere and that a value RP is obtained by dividing the total volume of all 
dimples arranged in P zone by the surface area of P zone of the imaginary 
sphere, RS/RP is set as follows: 
EQU 0.95.ltoreq.RS/RP.ltoreq.1.20 
For example, supposing that the dimple A and the dimple B have the same 
diameter of 4.1 mm, the greater volume dimple A is arranged in S zone and 
the smaller volume dimple B is arranged in P zone. 
In this embodiment, the spherical surface of the golf ball is divided into 
S zone and P zone at an angle of 30.degree. and the total volume of all 
dimples arranged in S zone is 165.9 mm.sup.3. The value RS obtained by 
dividing the dimple volume 165.9 mm.sup.3 by the surface area of S zone of 
the imaginary sphere is 0.123 mm.sup.3 /mm.sup.2. The total volume of all 
dimples arranged in P zone is 174.4 mm.sup.3. The value RP obtained by 
dividing the dimple volume 174.4 mm.sup.3 by the surface area of P zone of 
the imaginary sphere is 0.116 mm.sup.3 /mm.sup.2. Therefore, RS/RP is 1.06 
which satisfies the range between 0.95 and 1.20 as described above. If 
RS/RP is less than 0.95, the trajectory of the golf ball becomes low when 
the great circle 12 coincides or approximately coincides with a 
circumference which rotates fastest in its backspin. If RS/RP is more than 
1.20, the trajectory of the golf ball becomes too high. 
The reason the central angle .theta. which divides the surface of the golf 
ball into S zone and P zone is 10.degree. or more and less than 60.degree. 
is as follows: If the central angle .theta. is less than 10.degree., 
dimples are arranged in an extremely small number in S zone. Consequently, 
the division of the surface of the golf ball into S zone and P zone has no 
meaning and the differentiation of dimple volume has no effect either. If 
the central angle .theta. is more than 60.degree., the dimple effect of S 
zone is greater than that of P zone, and consequently, the aerodynamic 
symmetrical property cannot be improved. Accordingly, the central angle 
.theta. is appropriately set at the angle of 10.degree. or more than 
10.degree. and less than 60.degree. in consideration of the dimple 
arrangement, the construction of the golf ball, and mixing proportion of 
materials of the golf ball. 
EXPERIMENT 1 
The flight performance tests of the golf ball according to the present 
invention and comparison golf ball, or conventional golf ball were 
conducted. 
Comparison golf balls 1 having a dimple specification as shown in Table 1 
and FIGS. 9A, 9B, and 9C were prepared. The comparison golf balls 1 have 
regular octahedral arrangement and three great circles 3, 4, and 5 not 
intersecting dimples. The volume of dimples of the comparison golf balls 1 
arranged in S and P zones are not differentiated. Accordingly, RS/RP is as 
small as 0.85. 
Each of the golf balls according to the present invention as shown in FIG. 
1 and comparison golf balls as shown in FIG. 9 has a liquid center wound 
with thread covered with a balata cover. Both golf balls have the same 
construction and mixing proportion of materials. The outer diameter is 
each 42.70.+-.0.03 mm and compression is each 95.+-.2. 
Flight test of the balls according to the present invention and comparison 
golf balls were conducted using a swing robot manufactured by True Temper 
Corp. Balls were hit by a driver (No. 1 wood) at a head speed of 45 m/s. 
Spin was 3500.+-.300 rpm and a ball launching angle was 10.+-.0.5.degree.. 
Wind was fair at a speed of 0.6.about.2.8 m/s. 
The number of the golf balls of the embodiment and the comparison golf 
balls prepared was 20, respectively. The temperature thereof was kept at 
23.degree..+-.1.degree. C. The golf balls of the embodiment and the 
comparison golf balls were alternately hit. 
The carry, total, and duration of flight of the golf balls of the 
embodiment and comparison golf balls shown in Table 2 are the average of 
those of 20 golf balls. 
"Carry" shown in Table 2 is the distance from a hitting point to a falling 
point; "total" is the distance from the hitting point to the point at 
which each golf ball stopped; and "trajectory height" is an angle of 
elevation viewed from the launching point of each golf ball to the highest 
point thereof in trajectory. 
TABLE 2 
______________________________________ 
Flight distance test 
trajectory flight 
carry total height duration 
(yard) (yard) (DEG) (SEC) 
______________________________________ 
embodiment 
228.5 245.3 13.30 5.30 
comparison 
224.2 242.0 13.18 5.21 
______________________________________ 
TABLE 3 
______________________________________ 
Symmetrical property test 
trajectory 
flight 
kind of carry total height duration 
hitting (yard) (yard) (DEG) (SEC) 
______________________________________ 
embodi- 
pole 245.5 260.2 13.72 5.87 
ment seam 244.9 260.5 13.67 5.87 
compar- 
pole 242.6 254.6 13.57 5.79 
ison seam 238.8 256.0 13.20 5.46 
______________________________________ 
As shown in Table 2, the golf ball of the embodiment traveled further than 
the golf ball of the comparison golf ball by 4.3 yards in carry and by 3.3 
yards in "total". It was confirmed from this result that in flight 
distance, the golf ball of the embodiment having one great circle formed 
thereon is superior to the comparison golf ball having three great 
circles. 
EXPERIMENT 2 
Symmetrical test was conducted on the golf balls according to the 
embodiment and the comparison golf balls used in example 1, employing a 
swing robot manufactured by True Temper Corp. The golf balls were hit by a 
driver at a head speed of 48.8 m/s. Spin was 3500.+-.300 rpm; ball 
launching angle was 9.degree..+-.0.5.degree.. Wind was fair at a speed of 
0.3.about.2.2 m/s. The number of the embodiment golf balls and the 
comparison golf balls was 40 respectively, 20 ball were used each for pole 
hitting and seam hitting. The temperature thereof was kept at 23.degree. 
C..+-.1.degree. C. 
According to seam hitting, a rotational axis is selected so that a 
circumference which rotates fastest in its backspin coincides with the 
seam. According to pole hitting, a circumference perpendicular to the 
rotational axis in seam-hitting functions as the rotational axis of the 
backspin. 
As shown in Table 3 indicating the result of the symmetrical property test, 
the golf balls of the embodiment had little difference in carry, total, 
trajectory height, and duration of flight between seam hitting and pole 
hitting. On the other hand, according to the comparison golf balls, the 
trajectory height in seam hitting was lower than that in pole hitting, and 
the duration of flight and carry in seam hitting were shorter than those 
in pole hitting. 
It was confirmed from the above result that dimple effect is not reduced 
even in seam hitting and a golf ball having a favorable symmetrical 
property can be obtained owing to the differentiation of dimple volumes in 
S zone and P zone as described previously. 
That is: 
EQU 0.95.ltoreq.RS/RP.ltoreq.1.20 
As apparent from the foregoing description, without damaging a favorable 
symmetrical property and fine view of regular octahedral dimple 
arrangement, the golf ball in accordance with the present invention is 
capable of achieving a flight performance more favorable than that of the 
conventional golf ball. That is, since the golf ball has only one great 
circle corresponding to the seam not intersecting dimples, the possibility 
that a circumference which rotates fastest in its backspin coincides or 
approximately coincides with the great circle is reduced, so that the 
flight distance of the golf ball can be increased. 
In addition, the surface of the golf ball is divided into two zones. One is 
in the vicinity of the great circle unintersecting dimples and the other 
is in the vicinity of the poles. The volumes of dimples are differentiated 
according to each zone so as to improve the difference in the aerodynamic 
symmetrical property of the golf ball between seam hitting and pole 
hitting. Accordingly, the trajectory of the golf ball is not varied so 
much even though the golf ball spins about a varied rotational axis. As 
such, the golf ball is capable of faithfully display a player's ability, 
thus contributing to the improvement of player's skill. Further, since the 
golf ball has only one great circle corresponding to the seam, an upper 
mold is rotated with respect to a lower mold so as to design various 
dimple arrangement without affecting the flight performance thereof. 
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.