According to the United States Golf Association (U. S. G. A.) Rules, a golf ball may not have a weight in excess of 1.620 ounces or a diameter smaller than 1.680 inches. The initial velocity of balls conforming to U. S. G. A. regulations may not exceed 250 feet per second with a maximum tolerance of 2%. Initial velocity is measured on a standard machine kept by the U. S. G. A. A projection on a wheel rotating at a defined speed hits the test ball, and the length of time it takes the ball to traverse a set distance after impact is measured. U. S. G. A. regulations also require that a ball not travel a distance greater than 280 yards when hit by the U. S. G. A. outdoor driving machine under specifies conditions. In addition to this specification, there is a tolerance of plus 4% and a 2% tolerance for test error.

These specifications limit how far a struck golf ball will travel in several ways. Increasing the weight of a golf ball tends to increase the distance it will travel and lower the trajectory. A ball having greater momentum is better able to overcome drag. Reducing the diameter of the ball also has the effect of increasing the distance it will travel when hit. This is believed to occur primarily because a smaller ball has a smaller projected area and thus, a lower drag when traveling through the air. Increasing initial velocity increases the distance the ball will travel.

Drag on a golf ball is also reduced by forming a plurality of dimples, often circular, in the outer surface of the ball. The dimples serve to reduce the pressure

differential between the front and rear of the ball as it travels through the air.

BRIEF DESCRIPTION OF THE PRIOR ART Current golf ball patterns use various numbers of dimples having specific widths, usually laid out with the goal of maximizing surface coverage as long as symmetry in flight is maintained. Dimple depth is manipulated slightly to achieve a higher or lower trajectory, but the ratioi f d h to width is constant on a golf ball at about 7%. V It is known in the patented prior art to provide a golf ball with two groups of dimples having the same diameter but two different depths as disclosed in the U. S. patent to Moriyama No. 5,518,246. It is also known in the patented prior art to provide a golf ball having at least three sets of dimples wherein each of the sets of dimples has a different diameter and depth as disclosed in the Yamagishi U. S. patent No. 5,033,750. The ratio of the diameter to depth of the dimples of a particular set is approximately equal to the diameter to depth ratios of the other two sets.

The present invention was developed in order to provide a golf ball having a plurality of dimples of different depths wherein the different-depth dimples are arranged in a particular geometry having a dimple depth progression to improve the aerodynamic characteristics of the ball.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of the invention to provide a golf ball having a spherical surface and including a geometric pattern defined on the golf

ball surface. Within the geometries of the pattern are provided a plurality of dimples comprising at least two groups. The first group of dimples has a first depth and the dimples thereof are arranged adjacent to a portion of the perimeter of the each geometry, and the second group of dimples has a second depth different from the first depth. The dimples of the second group are arranged within the first group of dimples. The first and second depths are independent of the widths of the dimples of the first and second groups. Owing to this arrangement of different depth dimples, the golf ball has improved aerodynamic properties.

According to another object of the invention, the golf ball includes a third group of dimples having a third depth different from the second depth and independent of the width of the third group of dimples. The third group of dimples is arranged within the second group of dimples so that a depth progression of dimples is provided within each geometry. In one embodiment, the first group of outer dimples has a greater depth than the second group which in turn has a greater depth than the innermost third group of dimples. In an alternative embodiment, the third group of innermost dimples has a greater depth than the second group which in turn has a greater depth than the outermost first group of dimples. In still another embodiment, the first and third groups of dimples have the same depth which is different from that of the second group of dimples.

It is yet another object of the invention to provide a number of great circles on the surface of the golf ball to define the geometric pattern which comprises a plurality of generally equal triangles. One of the great circles defines the equator of the ball and divides the ball into two hemispheres. The same number of triangles is thus provided in each hemisphere.

BRIEF DESCRIPTION OF THE FIGURES Other objects and advantages of the invention will become apparent from a study of the following specification when viewed in the light of the accompanying drawing, in which: Figs. 1 and 2 are plan views, respectively, of a spherical golf ball illustrating the manner of defining a geometric pattern on the surface of the ball; Fig. 3 is a plan view of a golf ball according to the invention including a first dimple pattern comprising three groups of dimples having a progressive depth; Fig. 4 is a plan view of a golf ball according to the invention including a second dimple pattern comprising three groups of dimples having a progressive depth; and Fig. 5 is a sectional view of a dimple showing its diameter and depth.

DETAILED DESCRIPTION Referring to Figs. 1 and 2, the golf ball 2 according to the invention has a spherical configuration formed by injection molding the ball in a cavity defined between two separable molding plates. Each plate has a hemispherical cavity, the cavities being adapted to mate when the plates are brought together. Thus, the golf ball has an equator E at the juncture of the molding plates which divides the ball into two identical hemispheres, each of which contains a pole P. Imaginary great circles are arranged on the surface of the ball and pass through the poles to divide the ball surface into a geometric pattern of equal sections or geometries. In Fig. 2, two circles 4,6 are shown which divide each hemisphere into four equal

triangles T. Other geometric patterns can be defined on the surface of the ball in accordance with the invention. For example, a third great circle through the poles would divide each hemisphere into six triangular geometries.

Each of the triangles T is filled with a plurality of non-overlapping dimples 8 as shown in Figs. 3 and 4. In Fig. 3, a first pattern of dimples within the triangle is shown, and in Fig. 4, a second pattern of dimples within the triangle is shown.

The dimples are all circular and may have the same diameter. The diameter D is measured across the dimple between where the edges thereof intersect the surface of the ball as shown in Fig 5. Alternatively, two or more groups of dimples may be provided with different diameters.

In conventional golf balls, the ratio of depth to width of a dimple is constant for all dimples on the ball. The depth d is defined as the maximum difference between the radius of the ball at the surface and the radius at the bottom of the dimple as shown in Fig. 5. The depth to width ratio in conventional golf balls is generally 7% or 1: 14.3. In the golf ball according to the invention, the ratio is not constant. Rather a progression of the depth of the dimples within each triangle is provided.

In the embodiment of Fig. 3, there are shown two groups of dimples. The first group of dimples X all have a first depth and are arranged about the periphery of the triangle T. The second group of dimples Y all have a second depth different from the first depth. The depths of the first and second groups of dimples are independent of the dimple widths. The second dimples Y are arranged within the first group of dimples X. The first depth may be greater than the second depth, whereby the innermost dimples are shallower than the outermost dimples, resulting in an"outside-in"depth progression within each triangle. Conversely, the first depth may be less than the second depth, whereby the outermost dimples

are shallower than the innermost dimples, resulting in an"inside-out"depth progression within each triangle.

In the embodiment of Fig. 4, there are shown three groups of dimples arranged within the triangle T. The dimples X of the first group all have a first depth, the dimples Y of the second group all have a second depth different from the first depth, and the dimples Z of the third group all have a third depth different from the second depth. The depths of the first, second, and third groups of dimples are all independent of the dimple widths. The first group of dimples X is arranged about a portion of the perimeter of the triangle T, the second group of dimples Y is arranged within the first group of dimples, and the third group of dimples Z is arranged within the second group of dimples Y. The first depth of the dimples X is greater than the second depth of the dimples Y which in turn is greater than the third depth of the dimples Z to define an"outside-in"depth progression within the triangle. Conversely, the first depth of the dimples X may be less than the second depth of the dimples Y which in turn may be less than the third depth of the dimples Z to define an"inside-out"depth progression. Alternatively, the first and third depths of the dimples X and Z may be equal but different from the second depth of the dimples Y to define an undulating depth progression within the each triangle.

With the dimple depth progression within a repetitive geometry across the surface of a golf ball, the ball is provided with superior aerodynamic properties.

Depending on the depth progression selected, golf balls can be designed to achieve higher or lower trajectories.

While in accordance with the provisions of the patent statute the preferred forms and embodiments of the invention have been illustrated and described, it will be apparent to those of ordinary skill in the art that various changes and modifications may be made without deviating from the inventive concepts set forth above.