Games using tangible projectile – Golf – Ball
Reexamination Certificate
1999-04-20
2002-05-07
Vo, Peter (Department: 3729)
Games using tangible projectile
Golf
Ball
C473S370000, C473S373000, C473S374000, C473S376000, C473S377000, C473S378000, C273S348100, C273S280000, C273S237000, C273S237000, C264S328100
Reexamination Certificate
active
06383091
ABSTRACT:
This invention relates to a golf ball comprising a core, an intermediate layer, and a cover, and more particularly, to such a golf ball in which the core or the cover is provided with protrusions penetrating into the intermediate layer.
BACKGROUND OF THE INVENTION
A variety of studies and proposals have been made to find a good compromise between flight distance and “feel” of golf balls. For solid golf balls comprising a solid core and a cover, one common approach is to construct the core and the cover into multilayer structures for adjusting their hardness and dimensions (including diameter and gage).
For example, U.S. Pat. No. 5,439,227 discloses a three-piece golf ball comprising a core, a cover inner layer and a cover outer layer, the cover outer layer being harder than the cover inner layer. U.S. Pat. No. 5,490,674 discloses a three-piece golf ball comprising a solid core of inner and outer layers and a cover, the core inner layer being harder than the core outer layer.
While the respective layers of most golf balls define smooth spherical surfaces, the golf balls disclosed in U.S. Pat. Nos. 2,376,085 and 5,692,973 have a core which is provided with outwardly extending protrusions for preventing the core from being offset during injection molding of the cover therearound. The protrusions in these golf balls are substitutes for the support pins used during injection molding. These patents do not attempt to positively utilize the shape effect of support pin-substituting protrusions, but rather intend to avoid incorporation of a distinct material in the cover by forming the protrusions from the same material as the cover.
SUMMARY OF THE INVENTION
An object of the invention is to provide a golf ball comprising a core, an intermediate layer and a cover wherein the core or cover is provided with a plurality of protrusions penetrating into the intermediate layer, thereby achieving a good compromise between flight distance and control, which has never been achieved in prior art golf balls.
The shape effect of respective layers of a golf ball was investigated. It is well known from the study of strength of materials that a beam supporting an axial compressive load gives rise to the buckling phenomenon that as the load increases, uniform compression becomes unstable and is shifted laterally whereby the beam is bent. The invention has been devised by applying the buckling phenomenon to a golf ball. Specifically, in a golf ball comprising a core, an intermediate layer, and a cover, the core or the cover is integrally provided with a plurality of protrusions penetrating into the intermediate layer, and the material of which the protrusions are made is harder than the material of which the intermediate layer is made. The protrusions each satisfy the applicable range of Euler's buckling formula:
L
>&pgr;(
EI/A&sgr;
b
)
½
wherein L is the length (mm) of the protrusion, E is the Young's modulus (MPa) of the material of the protrusion, I is the geometrical moment of inertia (mm
4
) of the protrusion, A is the cross-sectional area (mm
2
) of the protrusion, and &sgr;
b
is the yield stress (MPa) of the material of the protrusion. Then the buckling phenomenon is applicable to the core or cover protrusions embedded in the intermediate layer.
When the ball is struck at a relatively high head speed, typically with a driver, the protrusions embedded within the intermediate layer give rise to a buckling phenomenon so that the ball is substantially deformed, which provides a reduced spin rate and an increased launch angle, resulting in an increased carry. When the ball is struck at a relatively low head speed, typically with a short iron, the protrusions within the intermediate layer does not give rise to a buckling phenomenon and the ball undergoes small deformation, which provides an increased backspin rate and maintains ease of control. With respect to the “feel” of the ball when hit, the ball gives a soft pleasant feel on driver shots and a tight full-body feel on short iron shots.
More particularly, when the ball is struck at a relatively high head speed as with a driver so that ball is given a large impact force, that force acts to cause the protrusions to buckle. On the other hand, when the ball is struck at a relatively low head speed as with a short iron so that the ball is given a small impact force, the protrusions do not buckle. In the former case of large impact force, the protrusions buckle so that the strength of the protrusions embedded in the intermediate layer does not substantially act and only the strength of the intermediate layer formed softer than the protrusions contributes. This results in a reduced spin rate and an increased carry. In the latter case of small impact force, the protrusions do not buckle so that the strength of the intermediate layer in a substantial sense is a combination of the strength of the intermediate layer in itself and the strength of the protrusions embedded therein, that is, higher than the strength of the intermediate layer in itself by a value attributable to the protrusions of higher hardness. Then the intermediate layer exhibits a harder behavior, leading to an increased spin rate. Therefore, in the golf ball having protrusions of higher hardness penetrating in the intermediate layer according to the invention, the intermediate layer with protrusions embedded therein exhibits a different behavior depending on the magnitude of impact force, that is, the number of golf club.
Accordingly, the present invention provides a golf ball comprising a core, an intermediate layer around the core, and a cover around the intermediate layer. The core or the cover is integrally provided with a plurality of protrusions penetrating into the intermediate layer. The material of which the protrusions are made has a Shore D hardness which is at least 8 units higher than the Shore D hardness of the material of which the intermediate layer is made. The protrusions satisfy the applicable range of Euler's buckling formula. Preferably, the protrusions each have a rounded planar shape at its top.
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Maruko Takashi
Masutani Yutaka
Bridgestone Sports Co. Ltd.
Kim Paul
Sughrue & Mion, PLLC
Vo Peter
LandOfFree
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