[0002] 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 specified conditions. In addition to this specification, there is a tolerance of plus 4% and a 2% tolerance for test error.

[0003] 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.

[0004] 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 [0005] Numerous dimple configurations for use on golf balls are well- known in the patented prior art, including contoured dimples. For example, the White U. S. patent No. 1,418,220 discloses a golf ball having rectangular dimples formed in the surface thereof. Each rectangular dimple includes in its bottom surface a small circular recess. Such a dimple configuration prolongs the life of the golf ball as well as improves the flight of the ball when struck. Golf balls having dimples with different configurations are also known in the patented prior art as shown by the U. S. patents to Nomura et al No. 4,869,512 and Oka et al No.

5,143,377, No. 5,174,578, and No. 5,338,039. Patent No. 5,174,578 for example discloses a golf ball having both circular and polygonal dimples. While the dimple combinations of the prior art increase the turbulence of the air flow across the surface of the golf ball during flight, there is still room for improvement in this regard as a function of dimple designs.

[0006] The present invention was developed in order to improve the aerodynamic efficiency of the dimples on a golf ball so that the ball will travel a straighter and a greater distance than conventional golf balls having circular dimples and golf balls with combinations of dimples as shown in the prior art.

SUMMARY OF THE INVENTION [0007] Accordingly, it is a primary object of the present invention to provide a golf ball having a spherical surface including a plurality of dimples arranged in the surface. A first group of dimples in the ball surface has a circular

configuration and a second group of dimples has a compound configuration including a first circular dimple portion and a second circular dimple portion arranged in a bottom surface of the first circular dimple portion. The second circular dimple portion has a diameter less than that of the first circular dimple portion, whereby the circular and compound dimples increase the turbulence of the air flow across the golf ball surface to improve the flight characteristics of the ball.

[0008] According to another object of the invention, there are a greater number of compound dimples than circular dimples, and the compound dimples are arranged around a circular dimple.

[0009] According to a further object of the invention, the diameter of the circular dimples and the diameter of the first circular portion of the compound dimples is equal.

BRIEF DESCRIPTION OF THE FIGURES [0010] These and other objects according to the invention will become apparent from a study of the following specification when viewed in the light of the accompanying drawing, in which: [0011] Fig. 1 is plan view of a golf ball including a plurality of compound and circular dimples according to the invention; [0012] Fig. 2 is a sectional view of a circular dimple according to the invention; and [0013] Fig. 3 is a sectional view of a compound dimple according to the invention.

DETAILED DESCRIPTION

[0014] In Fig. 1, there is shown a golf ball 2 having a spherical surface which'contains a plurality of circular dimples 4, the circle being defined where the dimple intersects with the surface of the ball. The dimples may all be of the same diameter, or different diameter dimples may be provided. Each dimple includes an outer edge 6 having a circular geometric configuration and a concave bottom surface 8 in the golf ball as shown in Fig. 2. The circular dimples 4 have a depth d extending from the surface of the golf ball to the lowermost portion of the bottom surface.

[0015] The golf ball 2 further contains a second plurality or group of compound dimples 10. As used herein, a compound dimple is essentially a dimple within a dimple. As best shown in Fig. 3, the compound dimple includes a first circular portion defined by the intersection of the outer edge 12 of the dimple with the golf ball surface. The first portion has a bottom surface 14 in which is arranged a second circular dimple portion 16 similar to the dimple 10 but having a lesser diameter. The diameter is defined as the distance across the dimple portion between its outer edge. Preferably, the second dimple portion 16 is concentrically arranged within the first dimple portion. The compound dimple has a depth d2 extending between the ball surface and the bottom surface of the second dimple portion 16.

[0016] Preferably, the diameters of the circular dimples 4 and the compound dimples 10 are equal, although they need not be. According to the preferred embodiment shown in Fig. 1, there are a greater number of compound dimples 10 than there are circular dimples 4, with the compound dimples surrounding the circular dimples. The dimples can be arranged in a geometric pattern on the ball to maximize the dimple coverage on the ball surface.

Depending on the geometric pattern, a total of 336,410,422 or 428 dimples (both

circular and compound) are provided on the ball surface. Other numbers of dimples are possible.

[0017] In an alternate embodiment, the circular and compound dimples are randomly arranged on the ball surface. In either embodiment, the combination of circular and compound dimples significantly alters the air flow across the surface of the ball as it travels through the air when struck by a golf club. The altered air flow has increased turbulence and serves to decrease the drag on the ball, thereby increasing the distance that it will travel.

[0018] While in accordance with the provisions of the patent statutes 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.