# Patent

## Title
Golf ball

## Abstract

A golf ball has a large number of dimples (A to D) on a surface thereof. A surface area occupation ratio Y of the dimples is 0.80 to 0.90. A total volume V of the dimples is 300 mm3 to 700 mm3. A mean volume Va to be a value obtained by dividing the total volume V by a total number N of the dimples is 1.30 mm3 or more. A mean curvature R to be a mean value of a curvature r in the sectional shape of the dimple is 16 mm or more. A mean occupation ratio y to be a value obtained by dividing the surface area occupation ratio Y by the total number N of the dimples is 0.0022 or more. A sum X of a contour length x of the dimple and the surface area occupation ratio Y satisfy a relationship indicated by an expression (I):

X≦3882·Y+1495.  (I)

## Background
This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2002-009077 filed in JAPAN on Jan. 17, 2002, which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a golf ball. More particularly, the present invention relates to an improvement in a dimple of the golf ball.
2. Description of the Related Art
A golf ball has approximately 200 to 550 dimples on a surface thereof. The role of the dimples resides in one aspect that such dimples disturb an air stream around the golf ball during the flight to accelerate the transition of a turbulent flow at a boundary layer, thereby causing a turbulent flow separation (which will be hereinafter referred to as a “dimple effect”). The acceleration of the transition of the turbulent flow causes a separating point of air from the golf ball to be shifted backward so that a drag coefficient (Cd) is reduced, resulting in an increase in the flight distance of the golf ball. In addition, the acceleration of the transition of the turbulent flow increases a differentia between upper and lower separating points of the golf ball which is caused by a back spin. Consequently, a lift acting on the golf ball is increased.
One element to greatly influence the flight performance of a golf ball include a total volume of dimples. The trajectory of a golf ball having a total volume which is too small tends to hop, and the trajectory of a golf ball having a total volume which is too large tends to drop. In any case, a sufficient flight distance cannot be obtained. In order to obtain a proper trajectory and a great flight distance, the total volume of the dimples is to be set within a predetermined range.
Various proposals for the density of a dimple have also been made. For example, Japanese Patent Publication No. Sho 58-50744 (U.S. Pat. No. 5,080,367) has disclosed a golf ball in which dimples are densely provided such that a pitch between the dimples is set to 1.62 mm or less if possible. Japanese Laid-Open Patent Publication No. Sho 62-192181 (U.S. Pat. No. 4,813,677) has disclosed a golf ball in which dimples are densely provided so as not to form a new dimple having an area which is equal to or larger than a mean area in a land portion. Japanese Laid-Open Patent Publication No. Hei 4-347177 (U.S. Pat. No. 5,292,132) has disclosed a golf ball in which dimples are provided very densely such that the number of land portions in which a rectangle having a predetermined dimension can be drawn is 40 or less. All the golf balls disclosed in the known publications have dimples provided densely, in other words, the surface area occupation ratio of the dimples is increased. The skilled in the art have recognized that the surface area occupation ratio is one of the important specifications to influence a dimple effect.
A golf player is very interested in making a good score and causing a golf ball to fly to a distance. A large number of golf players desire a golf ball which is excellent in a flight performance. As described above, various improvements have been made in relation to the total volume and surface area occupation ratio of the dimples. However, a golf ball to meet the demand of the golf player has not been obtained.
SUMMARY OF THE INVENTION
The present inventors have taken note of a mean volume Va as an important element to influence the dimple effect. The present inventors have found that an existing golf ball having a greater mean volume Va tends to be more excellent in a flight performance if a surface area occupation ratio Y and a total volume V are equal. By setting the relationship between the surface area occupation ratio Y, the total volume V and the mean volume Va to a range which cannot be obtained by the existing golf ball, the flight performance could be enhanced.
A golf ball according to the present invention has a large number of dimples on a surface thereof. A surface area occupation ratio Y of the dimples is 0.80 to 0.90. A total volume V of the dimples is 300 mm3 to 700 mm3. A mean volume Va to be a value obtained by dividing the total volume V by a total number N of the dimples is 1.30 mm3 or more.
In a golf ball in which the surface area occupation ratio Y, the total volume V and the mean volume Va satisfy the range, the ratio of the number of dimples having large sizes to the total number N of the dimples is high. The reason why the flight performance of the golf ball is excellent is not clear in detail. It is guessed that a dimple having a large size contributes to a reduction in a drag coefficient (Cd), particularly, a reduction in the drag coefficient (Cd) in a high-speed region immediately after hitting.
It is preferable that a mean curvature R to be a mean value of a curvature r in a sectional shape of the dimple should be 16 mm or more. Such a golf ball presents a more excellent flight performance.
It is preferable that a mean occupation ratio y to be a value obtained by dividing the surface area occupation ratio Y by the total number N of the dimples should be 0.0022 or more. In such a golf ball, the ratio of the occupation of dimples having comparatively large areas is high. The golf ball presents a more excellent flight performance.
It is preferable that a sum X of a contour length x of the dimple and the surface area occupation ratio Y should satisfy a relationship indicated by an expression (I):

X≦3882·Y+1495  (I).

Such a golf ball includes a dimple pattern having a smaller total contour length X for the surface area occupation ratio Y. The golf ball presents a more excellent flight performance.

It is preferable that a ratio of the number of dimples having a contour length x of 10.5 mm or more to a total number N of the dimples should be 91% or more. Such a golf ball presents a particularly excellent flight performance.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view showing a golf ball according to an embodiment of the present invention,
FIG. 2 is a front view showing the golf ball in FIG. 1,
FIG. 3 is a typical enlarged sectional view showing a part of the golf ball in FIG. 1,
FIG. 4 is a plan view showing a golf ball according to an example 2 of the present invention,
FIG. 5 is a front view showing the golf ball in FIG. 4,
FIG. 6 is a plan view showing a golf ball according to an example 3 of the present invention,
FIG. 7 is a front view showing the golf ball in FIG. 6,
FIG. 8 is a plan view showing a golf ball according to a comparative example 1 of the present invention,
FIG. 9 is a front view showing the golf ball in FIG. 8,
FIG. 10 is a plan view showing a golf ball according to a comparative example 2 of the present invention,
FIG. 11 is a front view showing the golf ball in FIG. 10,
FIG. 12 is a plan view showing a golf ball according to a comparative example 3 of the present invention, and
FIG. 13 is a front view showing the golf ball in FIG. 12.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described below in detail based on a preferred embodiment with reference to the drawings.
A golf ball shown in FIGS. 1 and 2 has a diameter of 40 mm to 45 mm, and furthermore, 42 mm to 44 mm. From the viewpoint of the fact that an air resistance is reduced within such a range as to satisfy the standards of the United States Golf Association (USGA), it is particularly preferable that the diameter should be set to 42.67 mm to 42.80 mm. The golf ball has a weight of 40 g to 50 g, and furthermore, 44 g to 47 g. From the viewpoint of the fact that an inertia is increased within such a range as to satisfy the standards of the United States Golf Association, it is particularly preferable that the weight should be set to 45.00 g to 45.93 g.
The golf ball includes an A dimple having a circular plane shape and a diameter of 4.5 mm, a B dimple having a circular plane shape and a diameter of 4.1 mm, a C dimple having a circular plane shape and a diameter of 3.5 mm, and a D dimple having a circular plane shape and a diameter of 2.7 mm. In this specification, the term of “plane shape” implies a shape of a contour line to be a boundary between a virtual spherical surface and a dimple as seen at infinity. The number of the A dimples is 130, that of the B dimples is 150, that of the C dimples is 60 and that of the D dimples is 32. The total number of the dimples of the golf ball is 372.
FIG. 3 is a typical enlarged sectional view showing a part of the golf ball in FIG. 1. FIG. 3 shows a planar section taken along a center of gravity of the plane shape of the dimple and a center of the golf ball. As is apparent from FIG. 3, the dimple takes the sectional shape of an almost circular arc. In other words, the surface of the dimple constitutes apart of a spherical surface. In FIG. 3, a virtual sphere (on the assumption that the dimples are not present) is shown in a two-dotted chain line.
In this specification, a “total volume V” implies the sum of volumes v of all the dimples. The “volume v of the dimple” implies the volume of a portion surrounded by the virtual sphere and the surface of the dimple. A mean volume Va implies a value (V/N) obtained by dividing the total volume V by the total number N of the dimples. In the golf ball shown in FIGS. 1 and 2, the A dimple has a volume v of 1.788 mm3, the B dimple has a volume v of 1.351 mm3, the C dimple has a volume v of 0.855 mm3 and the D dimple has a volume v of 0.426 mm3. Accordingly, the golf ball has a total volume V of 500.0 mm3 and a mean volume Va of 1.344 mm3.
In FIG. 3, a curvature of a circular arc constituting the sectional shape is shown in an arrow r. In the case of a dimple taking a sectional shape which is not the circular arc and a dimple having a non-circular plane shape, the curvature r is varied depending on a measuring portion. In such a case, it is possible to suppose a circular dimple taking a circular arc-shaped section which has the same area as that of the plane shape of the dimple and the same volume v as that of the dimple. Based on the sectional shape of the dimple thus supposed, the curvature r is calculated.
In this specification, the term of “mean curvature R” implies a mean value of the curvatures r of all the dimples. For example, in the case of a golf ball including n1 dimples having a curvature r1, n2 dimples having a curvature r2 and n3 dimples having a curvature r3, the mean curvature R is calculated by the following equation.

R=(r1·n1+r2·n2+r3·n3)/(n1+n2+n3)

In the golf ball shown in FIGS. 1 and 2, the A dimple has a curvature r of 23.98 mm, the B dimple has a curvature r of 19.91 mm, the C dimple has a curvature r of 14.53 mm, and the D dimple has a curvature r of 8.67 mm. Accordingly, the mean curvature R of the golf ball is 19.5 mm.
In FIG. 3, a diameter of the dimple is shown in an arrow d. The diameter d represents a distance between both contacts in the case in which a common tangent line is drawn on both ends of the dimple. The contact continues to form a contour line.
In this specification, the term of “surface area occupation ratio Y” implies a value obtained by dividing the sum of the areas of all the dimples by the surface area of a virtual sphere. The “area of the dimple” implies the area of the plane shape of the dimple. In the case of a circular dimple, an area s is calculated by the following equation.

s=(d/2)2·π

In the golf ball shown in FIGS. 1 and 2, the A dimple has an area S of 15.9 mm2, the B dimple has an area s of 13.2 mm2, the C dimple has an area s of 9.6 mm2, and the D dimple has an area s of 5.7 mm2. Accordingly, a sum S of the dimple areas is 4805.4 mm2. The total area S is divided by the surface area of the virtual sphere so that a surface area occupation ratio Y is calculated. In the golf ball, the surface area occupation ratio Y is 0.840. By dividing the surface area occupation ratio Y by the total number N of the dimples, a mean occupation ratio y is calculated. In the golf ball, the mean occupation ratio y is 0.00226.
In this specification, the term of “total contour length X” implies the sum of contour lengths x of all the dimples. The “contour length x” implies a distance measured actually along the contour line of the dimple. For example, in the case in which the dimple has a triangular plane shape, the total length of three sides is represented by the contour length x. Since these sides are present on a spherical surface, they are not straight lines but circular arcs in a strict sense. The length of the circular arc is set to be the length of the side. In the case of a circular dimple, the contour length x is calculated by the following equation.

x=d·π

In the golf ball shown in FIGS. 1 and 2, the A dimple has a contour length x of 14.1 mm, the B dimple has a contour length x of 12.9 mm, the C dimple has a contour length x of 11.0 mm and the D dimple has a contour length x of 8.5 mm. In the golf ball, a total contour length X is 4701.1 mm.
In the present invention, the surface area occupation ratio Y is set to 0.80 to 0.90. If the surface area occupation ratio Y is less than the range, the lift of the golf ball might become insufficient during a flight. In this respect, the surface area occupation ratio Y is more preferably 0.81 or more and particularly preferably 0.83 or more. If the surface area occupation ratio Y exceeds the range, the trajectory of the golf ball might be too high. In this respect, it is particularly preferable that the surface area occupation ratio Y should be 0.87 or less.
In the present invention, the total volume V is set to 300 mm3 to 700 mm3. If the total volume V is less than the range, a trajectory might hop. From this viewpoint, it is more preferable that the total volume V should be 400 mm3 or more, and it is particularly preferable that the total volume V should be 460 mm3 or more. If the total volume V exceeds the range, the trajectory might drop. From this viewpoint, it is more preferable that the total volume V should be 600 mm3 or less, and it is particularly preferable that the total volume V should be 540 mm3 or less.
In the case in which a designer is to design a golf ball having a predetermined total volume V and a high surface area occupation ratio Y, he (she) can use means for increasing the number of the dimples to achieve the surface area occupation ratio Y and means for increasing the size of the dimple to achieve the surface area occupation ratio Y. The golf ball according to the present invention has a mean volume Va of 1.30 mm3 or more. In other words, in the golf ball according to the present invention, the size of the dimple is set to be large so that a predetermined surface area occupation ratio Y can be achieved. It is guessed that a dimple having a large size contributes to a reduction in a drag coefficient (Cd) in a stage immediately after hitting (that is, a stage in which the golf ball flies at a high speed).
In respect of the flight performance, the mean volume Va is more preferably 1.35 mm3 or more, and particularly preferably 1.50 mm3 or more. If the mean volume Va is too large, the surface of the golf ball is not smooth. For this reason, the mean volume Va is preferably 3.00 mm3 or less, and particularly preferably 2.50 mm3 or less.
While the volume v of each dimple is not particularly restricted, it is usually set to 0.2 mm3 to 4.5 mm3. A ratio of the number of dimples having a volume v of 1.35 mm3 or more to a total number N is preferably 20% or more, and particularly preferably 30% or more.
In respect of the flight performance, the mean curvature R is preferably 16 mm or more, more preferably 18 mm or more, and particularly preferably 20 mm or more. If the mean curvature R is too great, the surface of the golf ball is not smooth. For this reason, the mean curvature R is preferably 30 mm or less, and particularly preferably 25 mm or less.
While the curvature r of each dimple is not particularly restricted, it is usually set to 5 mm to 50 mm. A ratio of the number of dimples having a curvature r of 16 mm or more to a total number N is preferably 60% or more, more preferably 70% or more, and particularly preferably 80% or more. The ratio is ideally 100%.
It is preferable that the mean occupation ratio y should be 0.0022 or more. If the mean occupation ratio y is less than the range, the drag coefficient (Cd) might be increased in a stage in which a flight speed is high, resulting in an insufficient flight distance of the golf ball. In this respect, the mean occupation ratio y is more preferably 0.00225 or more, further preferably 0.00230 or more, and particularly preferably 0.00250 or more. If the mean occupation ratio y is too high, the surface of the golf ball is not smooth. For this reason, it is preferable that the mean occupation ratio y should be 0.00400 or less.
It is preferable that the surface area occupation ratio Y and the total contour length X should satisfy the relationship indicated by the following expression (I).

X≦3882·Y+1495  (I)

The golf ball has a smaller total contour length X for the surface area occupation ratio Y. The golf ball has a small drag coefficient (Cd) during a flight and presents an excellent flight performance. As long as the present inventors know, there has not been a golf ball satisfying the expression (I).

In respect of a reduction in the drag coefficient (Cd), it is more preferable that the total contour length X and the surface area occupation ratio Y should satisfy the following expression (II), further preferably the following expression (III), and particularly preferably the following expression (IV).

X≦3882·Y+1445  (II)

X≦3882·Y+1335  (III)

X≦3882·Y+1085  (IV)

In order to maintain the original feature of the golf ball to be an almost sphere, the total contour length X and the surface area occupation ratio Y are to satisfy the relationship in the following expression (V).

X≧3882·Y+95  (V)

The total contour length X is properly determined based on the relationship with the surface area occupation ratio Y within the range to satisfy the expression (I), and is usually set to 2800 mm to 5000 mm, and particularly 3100 mm to 4800 mm.
In respect of a reduction in the drag coefficient (Cd), the ratio of the number of the dimples having a contour length x of 10.5 mm or more to the total number of the dimples is set to 91% or more, and particularly preferably 95% or more. The ratio is ideally 100%.
While the size of each dimple is not particularly restricted, the circular dimple usually has a diameter d of 2.0 mm to 8.0 mm, and particularly 3.0 mm to 7.0 mm. It is possible to form dimples of a simple kind or plural kinds. Anon-circular dimple (a dimple having a non-circular plane shape) maybe formed in place of the circular dimple or together with the circular dimple. In the case in which the non-circular dimple is to be formed, a contour length x is usually set to 6 mm to 25 mm, and particularly 9 mm to 22 mm. In respect of the easiness of manufacture of a mold for a golf ball, the non-circular dimple is not formed but only the circular dimple is preferably formed. In particular, a circular dimple having a circular arc-shaped section is preferable.
The total number of the dimples is preferably 200 to 500. If the total number is less than the range, there is a possibility that the original feature of the golf ball to be an almost sphere cannot be maintained. From this viewpoint, it is particularly preferable that the total number should be 250 or more. If the total number exceeds the range, there is a possibility that the drag coefficient (Cd) might be increased, resulting in an insufficient flight distance. From this viewpoint, it is particularly preferable that the total number should be 400 or less.
The diameter d, the curvature r, the volume v and the like are obtained by actually measuring the golf ball. In general, the golf ball has a coated layer provided on a surface thereof and dimensions are precisely measured actually with difficulty by the influence of the coated layer in some cases. In the present invention, for convenience, it is also possible to actually measure a golf ball which has not been coated or to actually measure the dimension of a mold.
The structure of the golf ball is not particularly restricted and a so-called wound golf ball or a solid golf ball (a one-piece golf ball, a two-pieces golf ball, a three-pieces golf ball or the like) may be used. Moreover, a material is not particularly restricted and a well-known material can be used.
EXAMPLES
Example 1
A core formed of a solid rubber was put in a mold and an ionomer resin composition was injected to form a cover around the core. The surface of the cover was coated so that a golf ball according to an example 1 which has a dimple pattern shown in a plan view of FIG. 1 and a front view of FIG. 2 was obtained. The golf ball has an outside diameter of 42.70±0.03 mm, a weight of approximately 45.4 g, and a compression of 93±2 (by an ATTI compression tester produced by Atti Engineering Co., Ltd.).
The golf ball includes 130 A dimples having a circular plane shape, a diameter of 4.5 mm and a volume v of 1.788 mm3, 150 B dimples having a circular plane shape, a diameter of 4.1 mm and a volume v of 1.351 mm3, 60 C dimples having a circular plane shape, a diameter of 3.5 mm and a volume v of 0.855 mm3, and 32 D dimples having a circular plane shape, a diameter of 2.7 mm and a volume v of 0.426 mm3. In the golf ball, a mean curvature R is 19.5 mm, a total contour length X is 4701.1 mm, a total volume V is 500.0 mm3, a mean volume Va is 1.344 mm3, a surface area occupation ratio Y is 0.840, and a mean occupation ratio y is 0.00226.
Example 2
A golf ball according to an example 2 which has a dimple pattern shown in a plan view of FIG. 4 and a front view of FIG. 5 was obtained in the same manner as in the example 1 except that the mold was changed. The golf ball includes 170 A dimples having a circular plane shape, a diameter of 4.4 mm and a volume v of 1.718 mm3, 120 B dimples having a circular plane shape, a diameter of 4.0 mm and a volume v of 1.295 mm3, 60 C dimples having a circular plane shape, a diameter of 3.4 mm and a volume v of 0.818 mm3, and 12 D dimples having a circular plane shape, a diameter of 2.3 mm and a volume v of 0.298 mm3. In the golf ball, a mean curvature R is 18.4 mm, a total contour length X is 4585.5 mm, a total volume V is 500.1 mm3, a mean volume Va is 1.382 mm3, a surface area occupation ratio Y is 0.818, and a mean occupation ratio y is 0.00226.
Example 3
A golf ball according to an example 3 which has a dimple pattern shown in a plan view of FIG. 6 and a front view of FIG. 7 was obtained in the same manner as in the example 1 except that the mold was changed. The golf ball includes 72 A dimples having a circular plane shape, a diameter of 5.9 mm and a volume v of 3.836 mm3, 24 B dimples having a circular plane shape, a diameter of 4.5 mm and a volume v of 1.566 mm3, 88 C dimples having a circular plane shape, a diameter of 3.8 mm and a volume v of 1.004 mm3, 112 D dimples having a circular plane shape, a diameter of 3.6 mm and a volume v of 0.790 mm3, and 24 E dimples having a circular plane shape, a diameter of 2.7 mm and a volume v of 0.387 mm3. In the golf ball, a mean curvature R is 24.9 mm, a total contour length X is 4194.7 mm, a total volume V is 500.0 mm3, a mean volume Va is 1.562 mm3, a surface area occupation ratio Y is 0.808, and a mean occupation ratio y is 0.00252.
Comparative Example 1
A golf ball according to a comparative example 1 which has a dimple pattern shown in a plan view of FIG. 8 and a front view of FIG. 9 was obtained in the same manner as in the example 1 except that the mold was changed. The golf ball includes 30 A dimples having a circular plane shape, a diameter of 4.3 mm and a volume v of 1.702 mm3, 130 B dimples having a circular plane shape, a diameter of 4.0 mm and a volume v of 1.381 mm3, 180 C dimples having a circular plane shape, a diameter of 3.7 mm and a volume v of 1.109 mm3, 60 D dimples having a circular plane shape, a diameter of 3.4 mm and a volume v of 0.880 mm3, and 32 E dimples having a circular plane shape, a diameter of 2.8 mm and a volume v of 0.530 mm3. In the golf ball, a mean curvature R is 14.0 mm, a total contour length X is 5053.6 mm, a total volume V is 499.9 mm3, a mean volume Va is 1.157 mm3, a surface area occupation ratio Y is 0.829, and a mean occupation ratio y is 0.00192.
Comparative Example 2
A golf ball according to a comparative example 2 which has a dimple pattern shown in a plan view of FIG. 10 and a front view of FIG. 11 was obtained in the same manner as in the example 1 except that the mold was changed. The golf ball includes 30 A dimples having a circular plane shape, a diameter of 4.3 mm and a volume v of 1.722 mm3, 130 B dimples having a circular plane shape, a diameter of 4.0 mm and a volume v of 1.398 mm3, 180 C dimples having a circular plane shape, a diameter of 3.7 mm and a volume v of 1.123 mm3, 60 D dimples having a circular plane shape, a diameter of 3.4 mm and a volume v of 0.892 mm3, and 20 E dimples having a circular plane shape, a diameter of 2.8 mm and a volume v of 0.538 mm3. In the golf ball, a mean curvature R is 13.9 mm, a total contour length X is 4948.0 mm, a total volume V is 499.9 mm3, a mean volume Va is 1.190 mm3, a surface area occupation ratio Y is 0.816, and a mean occupation ratio y is 0.00194.
Comparative Example 3
A golf ball according to a comparative example 3 which has a dimple pattern shown in a plan view of FIG. 12 and a front view of FIG. 13 was obtained in the same manner as in the example 1 except that the mold was changed. The golf ball includes 132 A dimples having a circular plane shape, a diameter of 4.4 mm and a volume v of 2.047 mm3, 60 B dimples having a circular plane shape, a diameter of 4.2 mm and a volume v of 1.796 mm3, 60 C dimples having a circular plane shape, a diameter of 3.5 mm and a volume v of 1.095 mm3, and 60 D dimples having a circular plane shape, a diameter of 3.3 mm and a volume v of 0.939 mm3. In the golf ball, a mean curvature R is 13.0 mm, a total contour length X is 3898.1 mm, a total volume V is 500.0 mm3, a mean volume Va is 1.603 mm3, a surface area occupation ratio Y is 0.686, and a mean occupation ratio y is 0.00220.
[Flight Distance Test]
20 golf balls according to each of the examples and the comparative examples were prepared and were maintained at 23° C. On the other hand, a driver comprising a metal head (trade name of “XXIOW#1” produced by Sumitomo Rubber Industries, Ltd., loft: 8 degrees, shaft hardness: X) was attached to a swing machine (produced by Golf Lab Co., Ltd.). Machine conditions were set to have a head speed of 50 m/sec, a back spin speed of approximately 2000 rpm obtained immediately after hitting and a launch angle of approximately 10 degrees, and the golf ball was hit and a flight distance (a distance between a launch point and a stationary point) was measured. The following Tables 1 and 2 show the mean value of the results of measurement for the 20 golf balls.







TABLE 1







Dimple Specification and Evaluation Result











Example 1
Example 2
Example 3




















Type
A
B
C
D
A
B
C
D
A
B
C
D
E























Diameter
4.5
4.1
3.5
2.7
4.4
4.0
3.4
2.3
5.9
4.5
3.8
3.6
2.7


d (mm)


Curvature
23.98
19.91
14.53
8.67
21.64
17.90
12.95
5.95
48.92
28.36
19.19
16.21
11.01


r (mm)


Contour length
14.1
12.9
11.0
8.5
13.8
12.6
10.7
7.2
18.5
14.1
11.9
11.3
8.5


x (mm)


Volume
1.788
1.351
0.855
0.426
1.718
1.295
0.818
0.298
3.836
1.566
1.004
0.790
0.387


v (mm3)


Number
130
150
60
32
170
120
60
12
72
24
88
112
24


Number ratio
34.9
40.3
16.1
8.6
47.0
33.1
16.6
3.3
22.5
7.5
27.5
35.0
7.5


(%)










Total number
372
362
320


N


Mean curvature
19.5
18.4
24.9


R (mm)


Total contour length
4701.1
4585.5
4194.7


X (mm)


Total volume
500.0
500.1
500.0


V (mm3)


Mean volume
1.344
1.382
1.562


Va (mm3)


Occupation ratio
0.840
0.818
0.808


Y


Mean occupation ratio
0.00226
0.00226
0.00252


y


Flight distance
254.5
256.4
258.3


(m)
















TABLE 2







Dimple Specification and Evaluation Result











Comparative Example 1
Comparative Example 2
Comparative Example 3





















Type
A
B
C
D
E
A
B
C
D
E
A
B
C
D
























Diameter
4.3
4.0
3.7
3.4
2.8
4.3
4.0
3.7
3.4
2.8
4.4
4.2
3.5
3.3


d (mm)


Curvature
18.45
15.97
13.68
11.56
7.86
18.06
15.64
13.39
11.32
7.70
15.66
14.28
9.94
8.84


r (mm)


Contour length
13.5
12.6
11.6
10.7
8.8
13.5
12.6
11.6
10.7
8.8
13.8
13.2
11.0
10.4


x (mm)


Volume
1.702
1.381
1.109
0.880
0.530
1.722
1.398
1.123
0.892
0.538
2.047
1.796
1.095
0.939


v (mm3)


Number
30
130
180
60
32
30
130
180
60
20
132
60
60
60


Number ratio
6.9
30.1
41.7
13.9
7.4
7.1
31.0
42.9
14.3
4.8
42.3
19.2
19.2
19.2


(%)










Total number
432
420
312


N


Mean curvature
14.0
13.9
13.0


R (mm)


Total contour
5053.6
4948.0
3898.1


length X (mm)


Total volume
499.9
499.9
500.0


V (mm3)


Mean volume
1.157
1.190
1.603


Va (mm3)


Occupation
0.829
0.816
0.686


ratio


Y


Mean
0.00192
0.00194
0.00220


occupation


ratio


y


Flight distance
248.2
247.3
242.3


(m)









As is apparent from the Tables 1 and 2, the golf balls according to the examples have greater flight distances than those of the golf balls according to the comparative examples. From the results of evaluation, the advantage of the present invention is obvious.
The above description is only illustrative and can be variously changed without departing from the scope of the present invention.

## Claims

1. A golf ball having a large number of dimples on a surface thereof,
wherein a surface area occupation ratio Y of the dimples is 0.80 to 0.90,
a total volume V of the dimples is 300 mm3 to 700 mm3, and
a mean volume Va to be a value obtained by dividing the total volume V by a total number N of the dimples is 1.30 mm3 or more, wherein a sum X of a contour length x of the dimple and the surface area occupation ratio Y satisfy a relationship indicated by an expression (I):


X≦3882·Y+1495  (I).

2. The golf ball according to claim 1, wherein a mean occupation ratio y to be a value obtained by dividing the surface area occupation ratio Y by the total number N of the dimples is 0.0022 or more.

3. The golf ball according to claim 1, wherein said golf ball comprises at least four types of said dimples, wherein each of said type of dimple differs in diameter and volume from each other.

4. A golf ball having a large number of dimples on a surface thereof,
wherein a surface area occupation ratio Y of the dimples is 0.80 to 0.90;
a total volume V of the dimples is 300 mm3 to 700 mm3; and
a mean volume Va to be a value obtained by dividing the total volume V by a total number N of the dimples is 1.30mm3 or more; and
wherein a mean curvature R to be a mean value of a curvature r in a sectional shape of the dimple is 16 mm or more.

5. The golf ball according to claim 4, wherein a mean occupation ratio y to be a value obtained by dividing the surface area occupation ratio Y by the total number N of the dimples is 0.0022 or more.

6. The golf ball according to claim 4, wherein a sum X of a contour length x of the dimple and the surface area occupation ratio Y satisfy a relationship indicated by an expression (I):


X≦3882·Y+1495  (I).

7. The golf ball according to claim 5, wherein a sum X of a contour length x of the dimple and the surface area occupation ratio Y satisfy a relationship indicated by an expression (I):


X≦3882·Y+1495  (I).

8. The golf ball according to claim 1, 2, 4, 5 or 7, wherein a ratio of the number of dimples having a contour length x of 10.5 mm or more to the total number N of the dimples is 91% or more.