TECHNICAL FIELD OF INVENTION
- BACKGROUND OF THE INVENTION
The present invention generally relates to golf balls, and more particularly to a low weight two piece golf ball for golfers with a low club head speed.
The flight of a golf ball is determined by many factors, but only three factors are typically controlled by the golfer. By impacting the ball with a golf club, the golfer controls the speed, the launch angle and the spin rate of the golf ball. The launch angle sets the initial trajectory of the golf ball's flight. The speed and spin of the ball give the ball lift which will define the ball's overall flight path along with the weight and drag of the golf ball. Where the ball stops after being struck by a golf club also depends greatly on the weather and the landing surface the ball contacts.
Many golfers have what is termed a “low swing speed.” This means that the club head speed at impact is relatively slow when compared to a professional golfer's. Typically, when driving a golf ball the average professional golf ball speed is approximately 234 ft/s (160 mph). A person having a low swing speed typically drives the ball at a speed less than 220 ft/s (150 mph). A person with a low swing speed has a low ball speed. Consequently, his or her ball does not fly very far because of the lack of speed and lift. A significant percentage of all golfers today use such low swing speeds and consequently produce drives of less than 210 yards.
Standard balls are optimized for distance at swing speeds generally greater than 90 mph. Standard balls weigh more than 45 grams, while lightweight balls generally weigh less than 44 grams. Typically, lightweight golf balls are designed for low swing speed golfers. These lightweight golf balls usually are two-piece solid balls made with a single-solid core, encased by a hard cover material. The resiliency of the core can be increased so that the compression is high, which in addition to making the balls stiffer, increases the initial velocity and decreases the ball's spin rate. This maximizes the distance achieved by low swing speed players. However, these balls tend to have a hard feel and are difficult to control around the greens. Additionally, these golf balls can have insufficient mass to provide good distance at the target audience.
Golf balls generally include a spherical outer surface with a plurality of dimples formed thereon. Conventional dimples are circular depressions that reduce drag and increase lift. Lightweight golf balls typically have a dimple package tuned for a standard weight golf ball, which results in a ball that flies too high and short.
- SUMMARY OF THE INVENTION
A need exists for a high performance golf ball designed for low swing speed players, particularly those with a club head speed of less than 90 mph that offers improved distance with superior feel.
The present invention is directed to a golf ball comprising a core and a cover layer surrounding the core. In addition, the golf ball has a weight between about 44.5 grams and 45 grams, a diameter of at least 1.68 inches and a coefficient of restitution of about at least 0.82 at a club head speed of about 100 ft/sec. The golf ball has a dimple pattern to provide optimal trajectory and overall distance.
In one preferred embodiment, the dimple pattern includes dimples having at least three different diameters. The dimples preferably cover at least 80% of the exterior surface. The dimples also preferably have an edge angle greater than 14 degrees to a phantom sphere concentric with and having a same diameter as the exterior surface of the cover.
According to one aspect of the invention, the exterior surface defines between about 200 and about 600 dimples.
According to another aspect of the invention, the plurality of dimples may comprise an aerodynamic coefficient magnitude defined by Cmag=√(CL 2+CD 2) and an aerodynamic force angle defined by Angle=tan−1(CL/CD), where CL is a lift coefficient and CD is a drag coefficient. Additionally, the golf ball may include an outer land surface, wherein the outer land surface comprises at least one first substantially constant width and at least one second substantially constant width, wherein said first and second widths separate the dimples. Additionally, the golf ball may have a first aerodynamic coefficient magnitude from about 0.24 to about 0.27 and a first aerodynamic force angle of about 31 degrees to about 35 degrees at a Reynolds Number of about 230000 and a spin ratio of about 0.085 and a second aerodynamic coefficient magnitude from about 0.25 to about 0.28 and a second aerodynamic force angle of about 34 degrees to about 38 degrees at a Reynolds Number of about 207000 and a spin ratio of about 0.095.
According to another aspect of the invention, the golf ball may have a third aerodynamic coefficient magnitude from about 0.26 to about 0.29 and a third aerodynamic force angle of about 35 degrees to about 39 degrees at a Reynolds Number of about 184000 and a spin ratio of about 0.106. Also, the golf ball may have a fourth aerodynamic coefficient magnitude from about 0.27 to about 0.30 and a fourth aerodynamic force angle of about 37 degrees to about 42 degrees at a Reynolds Number of about 161000 and a spin ratio of about 0.122.
According to yet another aspect of the invention, the golf ball may have a fifth aerodynamic coefficient magnitude from about 0.29 to about 0.32 and a fifth aerodynamic force angle of about 39 degrees to about 43 degrees at a Reynolds Number of about 138000 and a spin ratio of about 0.142 and a sixth aerodynamic coefficient magnitude from about 0.32 to about 0.35 and a sixth aerodynamic force angle of about 40 degrees to about 44 degrees at a Reynolds Number of about 115000 and a spin ratio of about 0.170.
According to yet another aspect of the invention, the golf ball may have a seventh aerodynamic coefficient magnitude from about 0.36 to about 0.40 and a seventh aerodynamic force angle of about 41 degrees to about 45 degrees at a Reynolds Number of about 92000 and a spin ratio of about 0.213 and an eighth aerodynamic coefficient magnitude from about 0.40 to about 0.45 and an eighth aerodynamic force angle of about 40 degrees to about 44 degrees at a Reynolds Number of about 69000 and a spin ratio of about 0.284.
According to another aspect of the invention, a 100 kg load on the golf ball has a deflection of about 3.0 mm to about 4.0 mm.
According to another aspect of the invention, the golf ball preferably has a coefficient of restitution of about 0.83 to about 0.87 at a club speed of about 100 ft/sec, and more preferably a coefficient of restitution of about 0.83 to about 0.85 at a club speed of about 100 ft/sec. According to another aspect of the invention, the golf ball has a coefficient of restitution of about at least 0.82 at a club head speed of about 125 ft/sec.
Preferably, the surface of the core has a Shore C material hardness of between about 50 and about 80.
The cover layer preferably has a thickness less than or equal to about 0.08 inch.
In one embodiment, the cover layer may be formed of a thermoplastic material, and the thermoplastic material may be selected from the group including: partially or fully neutralized ionomers, thermoplastic polyurethane, metallocene, thermoplastic urethane, fusabond, or other single site catalyzed polymer, or blends thereof.
In yet another embodiment, the cover layer is formed of a thermoset material, and the thermoset material may be selected from the group including: aromatic urethane, light stable urethane, light stable polyurea, polyurethane-ionomer or blends thereof.
The cover layer may have a Shore D material hardness of between about 30 and about 75. In another embodiment, the cover layer may have a Shore D material hardness of less than about 60.
- BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is also directed to a golf ball comprising a core, a cover layer surrounding the core. In addition, the golf ball has a weight between about 44.5 grams and about 45 grams, a deflection at 100 kg of about 3.0 mm to about 4.0 mm, a diameter of at least 1.68 inches, and a coefficient of restitution of about 0.82 to about 0.87 at a club head speed of 100 ft/sec. The golf ball has a plurality of dimples provided on an exterior surface of the cover layer to provide an optimal trajectory and overall distance for the golf ball.
The advantages and features of this invention will be more clearly appreciated from the following detailed description, when taken in conjunction with the accompanying drawings, wherein like numbers are used for like features, in which:
FIG. 1 is a perspective view of a first embodiment of a golf ball of the present invention;
FIG. 2 is a cross-sectional view of the golf ball of FIG. 1; and
- DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 3 is an illustration of the forces acting on a golf ball.
The distance that a golf ball would travel upon impact is a function of the coefficient of restitution (CoR) and the aerodynamic characteristics of the ball. The CoR is defined as the ratio of the relative velocity of two colliding objects after the collision to the relative velocity of the two colliding objects prior to the collision. The CoR varies from 0 to 1.0. A CoR value of 1.0 is equivalent to a perfectly elastic collision, and a CoR value of 0.0 is equivalent to a perfectly inelastic collision. For golf balls, CoR has been approximated as a ratio of the velocity of the golf ball after impact to the velocity of the golf ball prior to impact.
CoR is an important measurement of the collision between the ball and a large mass. One conventional technique for measuring CoR uses a golf ball or golf ball subassembly, air cannon, and a stationary vertical steel plate. The steel plate provides an impact surface weighing about 100 pounds or about 45 kilograms. A pair of ballistic light screens, which measure ball velocity, are spaced apart and located between the air cannon and the steel plate. The ball is fired from the air cannon toward the steel plate over a range of test velocities from 50 ft/sec to 180 ft/sec. Unless noted otherwise, all CoR data presented in this application are measured using a speed of 100 ft/sec. As the ball travels toward the steel plate, it activates each light screen so that the time at each light screen is measured. This provides an incoming time period proportional to the ball's incoming velocity. The ball impacts the steel plate and rebounds though the light screens, which again measure the time period required to transit between the light screens. This provides an outgoing transit time period proportional to the ball's outgoing velocity. The CoR can be calculated by the ratio of the outgoing transit time period to the incoming transit time period.
Another CoR measuring method uses a titanium disk. This method is described in U.S. Pat. No. 6,688,991, and is assigned to the same assignee as the present invention.
The CoR of the golf ball is affected by a number of factors including the composition the core and the composition of the cover. The core may be single layer core or multi-layer core. It may also be solid or fluid filled. It may also be wound or foamed, or it may contain fillers. The cover may also be single layer cover or multi-layer cover. The cover may be thin or thick. The cover may have a high hardness or low hardness to control the spin and feel of the ball. Any of the above factors can contribute to the CoR of the ball.
Hardness is preferably measured pursuant to ASTM D-2240 in either button or slab form on the Shore D scale. More specifically, Shore D scale measures the indentation hardness of a polymer. The higher Shore D value indicates higher hardness of the polymer. The Shore D material hardness is measured on the ball according to ASTM D-2240 in either button or slab form.
Specific gravity as used in this application is defined in terms of test ASTM D-297.
The flexural modulus is preferably measured according to ASTM D6272-02. These tests may be carried out using a 0.5 in/min crosshead speed and a 2 inch span length in the four point bending mode. Test samples may be conditioned at 23° C., 50% RH for 2 weeks and then the tests performed.
Deflection is measured by applying loads of 10 kg, 100 kg and 130 kg to either the core or golf ball. Typically tests measure the deflection under a 100 kg load, or the deflection at 130 kg minus the deflection at 10 kg (the 130-10 kg test). Different apparatus may be used, such as a compression/tensile tester manufactured by Stable Micro Systems in Surrey, UK, Model MT-LQ. A cross-head speed of 2.5 cm/min is preferably used.
Compression is measured by applying a spring-loaded force to the golf ball center, golf ball core or the golf ball to be examined, with a manual instrument (an “Atti gauge”) manufactured by the Atti Engineering Company of Union City, N.J. This machine, equipped with a Federal Dial Gauge, Model D81-C, employs a calibrated spring under a known load. The sphere to be tested is forced a distance of 0.2 inch (5 mm) against this spring. If the spring, in turn, compresses 0.2 inch, the compression is rated at 100; if the spring compresses 0.1 inch, the compression value is rated as 0. Thus more compressible, softer materials will have lower Atti gauge values than harder, less compressible materials. Compression measured with this instrument is also referred to as PGA compression. The approximate relationship that exists between Atti or PGA compression and Riehle compression can be expressed as:
(Atti or PGA compression)=(160-Riehle Compression).
In accordance with one aspect of the present invention, when golf balls with larger diameter cores and a thin ionomeric cover layer are made with less weight, i.e., less than 45.93 grams and preferably between about 44.5 grams and about 45 grams, the balls fly longer when struck with lower swing speed clubs. The clubs can launch the balls on to higher flight trajectories and therefore longer distance. A dimple pattern specifically tuned for a low weight ball may be provided. The specifically tuned dimple pattern assists in providing a higher flight trajectory and longer distance for the ball.
Additionally, with lower overall ball deflection in the range of 3.0 mm to 4.0 mm, the ball spin rate is sufficiently high to improve greenside play.
Hence, a high performance ball, i.e., long distance with good greenside play, for low swing speed players is achieved, as described below.
Referring to FIGS. 1 and 2, a golf ball 10 comprises a core 12 and at least one cover layer 14 surrounding the core. Cover layer 14 preferably includes a plurality of dimples 16.
Preferably, core 12 has an outer diameter greater than 1.50 inches and the ball 10 has a weight of between about 44.5 grams and about 45 grams, thereby forming a low weight golf ball with a large core.
In addition, golf ball 10 preferably has a deflection of between about 3.0 mm to 4.0 mm at 100 kg, a coefficient of restitution (CoR) at 100 ft/s of greater than 0.820, and a ball diameter of at least 1.68 inches. More preferably, the ball has a CoR at 100 ft/sec between about 0.83 and about 0.87, and still more preferably between about 0.83 and about 0.84. In another embodiment, the ball has a CoR at 125 ft/sec of at least 0.82. Preferably, the ball has a diameter between about 1.68 inches and 1.685 inches and the cover has a thickness of about 0.08 inches or less.
According to one aspect of the present invention the golf ball core is formulated so that the golf ball core has a compression of between about 30 and about 90 or a deflection of about 3.0 to about 5.0 at 100 kg. A representative base composition for forming golf ball core 12 comprises polybutadiene rubber (PBD) that has a mid to high Mooney viscosity. Preferably, the core has a Mooney viscosity greater than about 35, more preferably greater than about 40, even more preferably greater than about 45, and most preferably in the range from about 50 to about 52 Mooney. PBD with higher Mooney viscosity may also be used, so long as the viscosity of the PBD does not reach a level where the high viscosity PBD clogs or otherwise adversely interferes with the manufacturing machinery. It is contemplated that PBD with viscosity less than 65 Mooney can be used with the present invention. A “Mooney” unit is a unit used to measure the plasticity of raw or unvulcanized rubber. The plasticity in a “Mooney” unit is equal to the torque, measured on an arbitrary scale, on a disk in a vessel that contains rubber at a temperature of 100° C. and rotates at two revolutions per minute. The measurement of Mooney viscosity is defined according to ASTM D-1646.
Golf ball cores made with mid to high Mooney viscosity PBD material exhibit increased resiliency, hence distance, without increasing the hardness of the ball. Commercial sources of suitable mid to high Mooney PBD include Bayer AG. “CB 23”, which has a Mooney viscosity of about 51 and is a highly linear polybutadiene, is a preferred PBD. If desired, the polybutadiene can also be mixed with other elastomers known in the art, such as natural rubber, styrene butadiene, and/or isoprene in order to further modify the properties of the core. When a mixture of elastomers is used, the amounts of other constituents in the core composition are typically based on 100 parts by weight of the total elastomer mixture.
Preferably, the core has a surface hardness of between about 40 JIS C and about 100 JIS C. More preferably, the core has a surface hardness of between about 45 JIS C and about 90 JIS C. Most preferably, the core has a surface hardness of between about 50 JIS C and about 80 JIS C. The surface is at least 5 Shore C harder than the center of the core (as measured on the core).
In accordance with another aspect of the invention, the addition of sulfur compound to the core further increases the resiliency and the CoR of the ball. Preferred sulfur compounds include, but are not limited to, pentachlorothiophenol (PCTP) and a salt of PCTP. A preferred salt of PCTP is ZnPCTP. The utilization of PCTP and ZnPCTP in golf ball cores to produce soft and fast cores is disclosed in U.S. Pat. No. 6,635,716, which is incorporated by reference herein, in its entirety. A suitable PCTP is sold by the Structol Company under the tradename A95. ZnPCTP is commercially available from EchinaChem.
Metal salt diacrylates, dimethacrylates, and monomethacrylates suitable for use in this invention include those wherein the metal is magnesium, calcium, zinc, aluminum, sodium, lithium or nickel. Zinc diacrylate (ZDA) is preferred, but the present invention is not limited thereto. ZDA provides golf balls with a high initial velocity. The ZDA can be of various grades of purity. For the purposes of this invention, lower quantity of zinc stearate in the ZDA indicates higher ZDA purity. ZDA containing less than about 10% zinc stearate is preferable. More preferable is ZDA containing about 4-8% zinc stearate. Suitable, commercially available zinc diacrylates include those from Sartomer Co. The preferred concentrations of ZDA that can be used are about 15 pph to about 40 pph based upon 100 pph of polybutadiene or alternately, polybutadiene with a mixture of other elastomers that equal 100 pph. Advantageously, the PCTP organic sulfur reacts with the ZDA used in the core to further increase the initial velocity of golf balls.
Free radical initiators are used to promote cross-linking of the metal salt diacrylate, dimethacrylate, or monomethacrylate and the polybutadiene. Suitable free radical initiators for use in the invention include, but are not limited to peroxide compounds, such as dicumyl peroxide, 1,1 -di(t-butylperoxy) 3,3,5-trimethyl cyclohexane, a-a bis(t-butylperoxy) diisopropylbenzene, 2,5-dimethyl-2,5di(t-butylperoxy) hexane, or di-t-butyl peroxide, and mixtures thereof. Other useful initiators would be readily apparent to one of ordinary skill in the art without any need for experimentation. The initiator(s) at about 70% to about 100% activity are preferably added in an amount ranging between about 0.05 pph and about 2.5 pph based upon 100 parts of butadiene, or butadiene mixed with one or more other elastomers. More preferably, the amount of initiator added ranges between about 0.15 pph and about 2 pph and most preferably between about 0.25 pph and about 1.5 pph. Suitable commercially available dicumyl peroxides include Perkadox BC, which is >90% active dicumyl peroxide, and DCP 70, which is >70% active dicumyl peroxide.
As discussed above, when ZDA or another metal salt of diacrylates, dimethacrylates, and monomethacrylates are used in the core, about 1 pph to about 20 pph of zinc oxide (or a smaller amount of calcium oxide and higher amount of peroxide) is preferably added to the core composition to react and neutralize any acrylic acid that may be present. More preferably, about 1.5 pph to about 12 pph of zinc oxide is added and most preferably about 2 pph to about 8 pph of zinc oxide is added.
Antioxidants may also be included. Antioxidants are compounds, which prevent the breakdown of the elastomer. Antioxidants useful in the present invention include, but are not limited to, quinoline type antioxidants, amine type antioxidants, and phenolic type antioxidants.
Other ingredients such as accelerators, e.g., tetra methylthiuram, processing aids, processing oils, dyes and pigments, as well as other additives well known to the skilled artisan may also be used in the present invention in amounts sufficient to achieve the purpose for which they are typically used.
Preferably about 1 pph to about 25 pph of regrind may be used. Most preferably, about 5 pph to about 20 pph of regrind may be used.
Low density fillers can also be added to the core formulation. Preferably about 1 pph to about 15 pph of low density fillers may be used. Most preferably, about 5 pph to about 10 pph of low density fillers may be used. Low density fillers can be used to reduce the weight of the ball. Suitable low density fillers may include hollow spheres or microspheres that can be incorporated into the core material including, for example polybutadiene.
High density fillers can also be added to the core formulation. Preferably about 0 pph to about 15 pph of high density fillers may be used. More preferably, about 3 pph to about 12 pph of high density fillers may be used. Most preferably, about 5 pph to about 10 pph of high density fillers may be used. Depending on the weight of the core, high density fillers can be added to the cover to improve the moment of inertia of the ball. High density fillers can be used, so long as the ball has the preferred weight, discussed above. High moment of inertia balls are fully discussed in U.S. Pat. No. 6,494,795, which is incorporated by reference herein, in its entirety.
Suitable high density fillers may have specific gravity in the range from about 2 to about 19, and include, for example, metal (or metal alloy) powder, metal oxide, metal searates, particulates, carbonaceous materials, and the like or blends thereof. Examples of useful metal (or metal alloy) powders include, but are not limited to, bismuth powder, boron powder, brass powder, bronze powder, cobalt powder, copper powder, inconel metal powder, iron metal powder, molybdenum powder, nickel powder, stainless steel powder, titanium metal powder, zirconium oxide powder, aluminum flakes, tungsten metal powder, beryllium metal powder, zinc metal powder, or tin metal powder. Examples of metal oxides include but are not limited to zinc oxide, iron oxide, aluminum oxide, titanium dioxide, magnesium oxide, zirconium oxide, and tungsten trioxide. Examples of particulate carbonaceous materials include but are not limited to graphite and carbon black. A more preferred high density filler is tungsten, tungsten oxide or tungsten metal powder due to its particularly high specific gravity of about 19.
Examples of other useful fillers include but are not limited to graphite fibers, precipitated hydrated silica, clay, talc, glass fibers, aramid fibers, mica, calcium metasilicate, barium sulfate, zinc sulfide, silicates, diatomaceous earth, calcium carbonate, magnesium carbonate, regrind (which is recycled uncured center material mixed and ground to 30 mesh particle size), manganese powder, and magnesium powder.
In accordance to another aspect of the present invention, the cover layer 14 thickness is minimized. To that end, the thickness of cover layer 14 (as shown in FIG. 2) is equal to or less than about 0.08 inches. Most preferably, the thickness of the cover layer is equal to or less than 0.07 inches. Preferably, the cover layer 14 is made of one layer, although it will be appreciated that multiple layers may form the cover layer 14. The thinness of the cover layer provides more volume for the core 12, and thereby more resilient polymeric core materials can be included in the core layer. Preferred compositions and properties of the cover layer in accordance to the present invention are described below.
Preferably, the cover layer is formed as a single layer of a thermoplastic material. In another embodiment, the cover layer is formed as a single layer of thermoset material.
Thermoplastic materials include for example, partially or fully neutralized ionomers, thermoplastic polyurethane, metallocene, thermoplastic urethane, fusabond or other single site catalyzed polymer, or blends thereof. Thermoset materials include polyurethane, polyurea, aromatic material, aliphatic material, or blends thereof. Exemplary preferable forms of such materials include aromatic urethane, light stable urethane, polyurethane-ionomer, and light stable polyurea. The cover layer can be cast or reaction-injection molded as known by those of ordinary skill in the art. If a urethane or urea cover layer is used, the ball preferably has a moisture barrier between core 12 and cover layer 14. The use of moisture barriers is described in U.S. Pat. No. 6,632,147, which is incorporated by reference herein in its entirety. As discussed above, an ionomer such as Surlyn can be included between core 12 and a urethane urea cover 14 to be the moisture barrier layer.
If the cover layer is formed of thermoplastic material, the cover layer preferably has a flexural modulus of between about 500 psi and about 80,000 psi. More preferably, the flexural modulus is between about 20,000 psi and about 80,000 psi and most preferably, the flexural modulus is between about 25,000 psi and about 70,000 psi.
If the cover layer is formed of thermoset material, the cover layer preferably has a flexural modulus of between about 500 psi and about 80,000 psi. More preferably, the flexural modulus is between about 500 psi and about 45,000 psi and most preferably, the flexural modulus is between about 1000 psi and about 40,000 psi.
If the cover layer is formed of thermoplastic material, the cover layer preferably has a Shore D hardness of between about 30 and about 75. More preferably, the Shore D hardness is between about 40 and about 70, and most preferably, the Shore D hardness is between about 45 and about 68.
If the cover layer is formed of thermoset material, the cover layer preferably has a Shore D material hardness of between about 30 and about 75. More preferably, the Shore D material hardness is between about 35 and about 65, and most preferably, the Shore D material hardness is between about 40 and about 65.
In another embodiment, the cover layer has a Shore D material hardness of less than about 60, and preferably less than about 55.
The core 12 and cover layer 14, as described above, are formed according to methods well known by those of ordinary skill in the art.
With respect to FIGS. 1 and 2, the cover layer 14 preferably has between about 200 and about 600 dimples 16. More preferably, the cover layer 14 has between 300 and 450 dimples 16. Preferably, the dimples are spherical or circular. Any suitable dimple pattern may be used on the golf ball 10.
In accordance with one aspect of the present invention, a modified dimple pattern is provided to adjust incrementally the distance that the ball would travel without affecting the other qualities of the ball. This modified dimples pattern is discussed below and is disclosed in more detail in co-pending U.S. application Ser. No. 10/980,203 filed on Nov. 11, 2004, and is assigned to the same assignee as the present invention. This co-pending application is incorporated by reference herein in its entirety.
As shown generally in FIG. 1, the golf ball 10 has a spherical surface. The spherical surface is defined by points lying on at least a 1.68 inch diameter of golf ball 10 for USGA regulation golf balls. For non-regulation golf balls, the spherical surface may instead be considered an inner-sphere which is covered by an outer surface, such as is described in the U.S. Pat. No. 6,290,615 patent ('615 patent), incorporated herein by reference in its entirety. In the '615 patent, the spherical surface is covered by a raised tubular lattice. Either concept for the spherical surface applies to the present invention.
The plurality of dimples 16 separated by outer un-dimpled or land surfaces, designated generally as 18, is provided on an outer surface of golf ball 10. As shown, dimples 16 are circular. Suitable dimples for use with this invention include dimples of any shape, including triangular, square, rectangular, pentagon, hexagon, heptagon, octagon, any other polygons, circular, hemispherical, elliptical, spherical or any other shape.
Preferably, dimples 16 are depressions extending into the cover of golf ball 10. Alternatively, dimples 16 may be raised projections extending beyond the spherical surface of golf ball 10. In one preferred embodiment, the golf ball 10 has dimples with at least three different diameters, more preferably five different diameters. The dimples preferably cover at least 80% of the surface of the golf ball and have an overall edge angle of greater than 14 degrees.
The dimple pattern is preferably arranged into identifiable sections or regions that form an overall pattern on the surface of golf ball 10. Preferably, dimples 16 are generally arranged in an icosahedron pattern, i.e., comprising twenty (20) identifiable triangular sections. Other suitable patterns include tetrahedron, octahedron, hexahedron and dodecahedron, among other polyhedrons, or any other discernable grouping of dimples.
As used herein, “inter-dimple spacing” is the width of land area 18 between any two adjacent dimples 16, as shown in FIG. 1. An inter-dimple spacing may have a circular or other non-polygonal configuration, such as spacing 20. Preferably, the inter-dimple spacings between any two adjacent polygonal dimples are substantially constant. In other words, the sides of adjacent polygonal dimples are substantially parallel to each other forming constant spacing between them. The aggregate of all inter-dimple spacings forms land area 18. Preferably, the surface area of land area 18 is not more than about 40% of the total surface area of the spherical surface of golf ball 10. More preferably, less than about 30% of the total surface area of golf ball 10 is land area. Even more preferably, less than about 20% of the total surface area of golf ball 10 is land area.
The present invention is further described herein in terms of aerodynamic criteria that are defined by the magnitude and direction of the aerodynamic forces, for the range of Spin Ratios and Reynolds Numbers that encompass the flight regime for typical golf ball trajectories. These aerodynamic criteria and forces are described below.
The forces acting on a golf ball in flight are enumerated in Equation 1 and illustrated in FIG. 3:
F=F L +F D +F G (Eq. 1)
Where F=total force vector acting on the ball
FL=lift force vector
FD=drag force vector
FG=gravity force vector
The lift force vector (FL) acts in a direction dictated by the cross product of the spin vector and the velocity vector. The drag force vector (FD) acts in a direction that is directly opposite the velocity vector. The magnitudes of the lift and drag forces of Equation 1 are calculated in Equations 2 and 3, respectively:
FL=0.5CLρAV2 (Eq. 2)
FD=0.5CDρAV2 (Eq. 3)
where ρ=density of air (slugs/ft3)
A=projected area of the ball (ft2) ((π/4)D2)
D=ball diameter (ft)
V=ball speed (ft/s)
CL=dimensionless lift coefficient
CD=dimensionless drag coefficient
Lift and drag coefficients are typically used to quantify the force imparted to a ball in flight and are dependent on air density, air viscosity, ball speed, and spin rate. The influence of all these parameters may be captured by two dimensionless parameters: Spin Ratio (SR) and Reynolds Number (NRe). Spin Ratio is the rotational surface speed of the ball divided by ball speed. Reynolds Number quantifies the ratio of inertial to viscous forces acting on the golf ball moving through air. SR and NRe are calculated in Equations 4 and 5 below:
SR=ω(D/2)/V (Eq. 4)
N Re =DVρ/μ (Eq. 5)
where ω=ball rotation rate (radians/s) (2π(RPS))
RPS=ball rotation rate (revolution/s)
V=ball speed (ft/s)
D=ball diameter (ft)
ρ=air density (slugs/ft3)
μ=absolute viscosity of air (lb/ft-s)
There are a number of suitable methods for determining the lift and drag coefficients for a given range of SR and NRe, which include the use of indoor test ranges with ballistic screen technology. U.S. Pat. No. 5,682,230, the entire disclosure of which is incorporated by reference herein in its entirety, teaches the use of a series of ballistic screens to acquire lift and drag coefficients. U.S. Pat. Nos. 6,186,002 and 6,285,445, also incorporated by reference herein in their entirety, disclose methods for determining lift and drag coefficients for a given range of velocities and spin rates using an indoor test range, wherein the values for CL and CD are related to SR and NRe for each shot. One skilled in the art of golf ball aerodynamics testing could readily determine the lift and drag coefficients through the use of an indoor test range, or alternatively in a wind tunnel.
The aerodynamic property of a golf ball can be quantified by two parameters that account for both lift and drag simultaneously: (1) the magnitude of aerodynamic force (Cmag), and (2) the direction of the aerodynamic force (Angle). It has now been discovered that flight performance improvements are attained when the dimple pattern and dimple profiles are selected to satisfy preferred magnitude and direction criteria. The magnitude and angle of the aerodynamic force are related to the lift and drag coefficients and, therefore, the magnitude and angle of the aerodynamic coefficients are used to establish the preferred criteria. The magnitude and the angle of the aerodynamic coefficients are defined in Equations 6 and 7 below:
C mag=√(C L 2 +C D 2) (Eq. 6)
Angle=tan−1(C L /C D) (Eq. 7)
To ensure consistent flight performance regardless of ball orientation, the percent deviation of Cmag for each SR and NRe plays an important role. The percent deviation of Cmag may be calculated in accordance with Equation 8, wherein the ratio of the absolute value of the difference between the Cmag for any two orientations to the average of the Cmag for these two orientations is multiplied by 100.
Percent deviation C mag=|(C mag1 −C mag2)|/((C mag1 +C mag2)/2)*100 (Eq. 8)
where Cmag1=Cmag for orientation 1, and
Cmag2=Cmag for orientation 2.
To achieve the consistent flight performance, the percent deviation is preferably about 6 percent or less. More preferably, the deviation of Cmag is about 3 percent or less.
Aerodynamic asymmetry typically arises from parting lines inherent in the dimple arrangement or from parting lines associated with the manufacturing process. The percent Cmag deviation is preferably obtained using Cmag values measured with the axis of rotation normal to the parting line plane, commonly referred to as a poles horizontal, “PH” orientation and Cmag values measured in an orientation orthogonal to PH, commonly referred to as a pole over pole, “PP” orientation. The maximum aerodynamic asymmetry is generally measured between the PP and PH orientation.
The percent deviation of Cmag as outlined above applies to the orientations, PH and PP, as well as any other two orientations. For example, if a particular dimple pattern is used having a great circle of shallow dimples, different orientations should be measured. The axis of rotation to be used for measurement of symmetry in the above example scenario would be normal to the plane described by the great circle and coincident to the plane of the great circle.
It has also been discovered that the Cmag and Angle criteria for golf balls with a nominal diameter of 1.68 and a nominal weight of 1.62 ounces may be advantageously scaled to obtain the similar optimized criteria for golf balls of any size and weight. Any preferred aerodynamic criteria may be adjusted to obtain the Cmag and angle for golf balls of any size and weight in accordance with Equations 9 and 10.
C mag(ball) =C mag(nominal)√(sin(Angle(nominal))*(W ball/1.62)*(1.68/D ball)2)2+(cos(Angle(nominal))2) (Eq. 9)
Angle(ball)=tan−1(tan(Angle(nominal))*(W ball/1.62)*(1.68/D ball)2) (Eq. 10)
It is believed that a golf ball made in accordance with the present invention will share similar characteristics with the golf balls discussed in U.S. Pat. No. 6,729,976 ('976 patent), the disclosure of which is incorporated herein in its entirety. Table 1 illustrates the anticipated aerodynamic criteria for a golf ball of the present invention that results in increased flight distances. The criteria are specified as low, median, and high Cmag
and Angle for eight specific combinations of SR and NRe
. Golf balls with Cmag
and Angle values between the low and the high number are preferred. More preferably, the golf balls of the invention have Cmag
and Angle values between the low and the median numbers delineated in Table 1. The Cmag
values delineated in Table 1 are intended for golf balls that conform to USGA size and weight regulations. The size and weight of the golf balls used with the aerodynamic criteria of Table 1 are 1.68 inches and 44.8 grams, respectively.
|TABLE 1 |
|Aerodynamic Characteristics For |
|Ball Diameter = 1.68″, Ball Weight = 44.8 grams |
| ||Magnitude ||Angle |
|NRe ||SR ||Low ||Median ||High ||Low ||Median ||High |
|230000 ||0.085 ||0.24 ||0.26 ||0.27 ||30 ||32 ||34 |
|207000 ||0.095 ||0.25 ||0.27 ||0.28 ||33 ||35 ||37 |
|184000 ||0.106 ||0.26 ||0.28 ||0.29 ||34 ||37 ||38 |
|161000 ||0.122 ||0.27 ||0.29 ||0.30 ||36 ||39 ||41 |
|138000 ||0.142 ||0.29 ||0.31 ||0.32 ||37 ||40 ||42 |
|115000 ||0.170 ||0.32 ||0.34 ||0.35 ||39 ||41 ||43 |
|92000 ||0.213 ||0.36 ||0.39 ||0.40 ||40 ||42 ||44 |
|69000 ||0.284 ||0.40 ||0.43 ||0.44 ||39 ||41 ||43 |
Other anticipated aerodynamic characteristics of the golf ball are described and discussed in greater detail in the '976 patent.
While the above invention has been described with reference to certain preferred embodiments, it should be kept in mind that the scope of the present invention is not limited to these embodiments. One skilled in the art may find variations of these preferred embodiments which, nevertheless, fall within the spirit of the present invention, whose scope is defined by the claims set forth below.