Patent Application
20090280926
The present invention relates to a golf club head, more particularly to a large-sized hollow head comprising a face member and a main member made of different titanium alloys.
In recent years, based on the progress of manufacturing technology, various golf club heads having very large volumes are offered in the marketplace, such a large-sized golf club heads can provide a larger sweet spot area and larger moment of inertia, therefore, it has an advantage such that the directionality of the hit balls are improved, in other words, even if ball hitting positions are varied around the sweet spot, variations of the initial directions of the balls become small.
The large-sized golf club heads however, have a problem with the design freedom. In order to prevent the swing balance of a golf club from deteriorating, the weight of the club head has to be limited not to go beyond a certain value. Accordingly, the club head has to be increased in the size within a weight limit. As a result, a weight margin is decreased, which margin can be utilized to deepen the center of gravity of the head, for example as the weight of a separate weight member. The use of a magnesium alloy having a smaller specific gravity might be conceived. But, it is difficulty to obtain a sufficient durability because of the relatively low strength of a magnesium alloy.
It is therefore, an object of the present invention to provide a golf club head, in which a weight margin is increased to increase the degree of design freedom, and the depth of the center of gravity and moment of inertia of the head are improved.
According to the present invention, a golf club head has a hollow structure comprising: a face member made of a first titanium alloy having a specific gravity G1 of less than 4.42; and a main member made of a second titanium alloy having a specific gravity G2 of less than 4.42 and being different in the composition from the first titanium alloy.
According to the present invention, the different titanium alloys are used in the face member and main member. Therefore, it becomes possible to improve the characteristics of the face member and main member by using alloys' compositions suitable for obtaining the characteristics required for the respective members. Both of the first titanium alloy and second titanium alloy have specific gravities of less than 4.42. Therefore, it becomes possible to reduce the weights of the face member and main member, and thereby a large weight margin capable of utilizing for adjusting the position of the center of gravity can be obtained. Thus, the present invention can provide a golf club head in which the design freedom of the weight distribution is high.
In this specification, sizes, positions, directions and the like relating to the club head refer to those under a standard state of the club head unless otherwise noted.
Here, the standard state of the club head 1 is such that the club head is set on a horizontal plane HP so that the center line CL of the club shaft (not shown) is inclined at the lie angle while keeping the club shaft center line CL on a vertical plane VP, and the club face 2 forms its loft angle with respect to the horizontal plane HP. Incidentally, in the case of the club head alone, the center line of the shaft inserting hole 7a can be used instead of the center line of the club shaft.
“Sweet spot SS” is the point of intersection between the club face and a straight line N drawn normally to the club face 2 passing the center of gravity GH of the head.
“Front-back direction” is a direction parallel with the straight line N projected on the horizontal plane HP.
“Toe-heel direction” is a direction parallel with the horizontal plane HP and perpendicular to the front-back direction.
“Leading edge Le” is a contact point between the club face 2 and a vertical plane parallel with the vertical plane VP.
“Depth LG of the center of gravity GH” is the horizontal distance between the center of gravity GH and the leading edge Le.
“Lateral moment of inertia” is the moment of inertia of the head around a vertical axis passing through the center of gravity GH.
“Vertical moment of inertia” is the moment of inertia of the head around a horizontal axis passing through the center of gravity GH in parallel to the toe-heel direction of the head.
“Elastic modulus”: In this application, the elastic moduli of the titanium alloys refer to the values determined as follows. Firstly, the stress-strain curve of the alloy was obtained according to JIS Z 2201 “Test pieces for tensile test for metallic materials” and JIS Z 2241 “Method of tensile test for metallic materials”. Then, from the elastic deformation region of the curve, the elastic modulus was determined. The speed of the crosshead of the tensile tester was 1.0 mm/min.
Embodiments of the present invention will now be described in detail in conjunction with accompanying drawings.
In the drawings, golf club head 1 according to the present invention is a hollow head for a wood-type golf club such as driver (#1) or fairway wood.
As shown in
In the case of a wood-type club head for a driver (#1), it is preferable that the head volume is set in a range of not less than 400 cc, more preferably not less than 425 cc, still more preferably not less than 450 cc in order to increase the moment of inertia of the club head 1 to thereby minimize the undesirable rotational motion of the club head at the time of mishit and to improve the directionality of the hit ball. If the volume of the club head 1 is too large, on the other hand, since the club head weight is increased, for example, the swing balance is liable to deteriorate and the head speed decreases. Further, there is a possibility that the wall thickness of the shell structure is forced to decrease in order to control the weight of the head and the durability is decreased. Therefore, the head volume is preferably not more than 470 cc, more preferably not more than 460 cc.
As to the weight of the club head 1, in order to avoide significant deterioration of the swing balance, the weight is preferably set in a range of not less than 175 grams, more preferably not less than 180 grams, still more preferably not less than 185 grams, but not more than 210 grams, more preferably not more than 205 grams.
In this embodiment, the main member 1B comprises the above-mentioned crown portion 4, sole portion 5, side portion 6 and hosel portion 7 which are integrally formed, and an opening o closed by the face member is formed in the front thereof.
The face member 1A is not provided with the undermentioned turnback 9 and is made up of a face plate 8 only. The face plate 8 or face member 1A has a shape similar but slightly smaller than the shape of the club face 2 defined by the edge (2a-2e). The area of the face plate is at least 60%, preferably at least 70%, more preferably at least 80% of the area of the club face 2.
Preferably, the weight W1 of the face member 1A is set in a range of from 35 to 60 grams. The weight W2 of the main member 1B is preferably set in a range of from 120 to 165 grams.
In this embodiment, the face member 1A comprises a face plate 8 whose front surface defines the club face 2, and a turnback 9 extending backwards from the edge of the face plate 8.
The face member 1A is formed by press molding, forging or the like so as to include the face plate 8 and turnback 9 integrally. In other words, the face member 1A is not formed by assembling two or more parts.
The face plate 8 forms a major part of the face portion 3 including the sweet spot. In this example, the entirety of the face portion 3 is formed.
The turnback 9 is formed along at least part of the peripheral edge (2a-2d) of the club face 2. In this example, the turnback 9 is formed along almost entire length of the peripheral edge (2a-2d), excepting a part corresponding to the hosel portion 7. Thus, the turnback 9 includes a crown-side turnback 9a forming a front part of the crown portion 4, a sole-side turnback 9b forming a front part of the sole portion 5, a toe-side turnback 9c forming a front part of the side portion 5 on the toe-side, and a heel-side turnback 9d forming a front part of the side portion 5 on the heel-side.
The main member 1B accordingly comprises a major part 4a of the crown portion 4, a major part 5a of the sole portion 5, a major part 6a of the side portion 6 and the above-mentioned hosel portion 7 which are integrally formed, and in the front thereof, an opening O closed by the face member is formed.
This three-piece structure is a modification of the structure shown in
In the case of the two-piece structures, the face member 1A is made of a first titanium alloy, and the main member 1B is made of a second titanium alloy which is different in the composition from the first titanium alloy.
In the case of the three-piece structures, the face member 1A, main member 1B and crown member 1C are made of a first, second and third titanium alloys, respectively, which are different from each other in the composition.
Preferably, the specific gravity G3 of the third titanium alloy is set to be larger than the specific gravity G1 of the first titanium alloy and the specific gravity G2 of the second titanium alloy in order to deepen the center of gravity of the head.
In each case, the specific gravity G1 of the first titanium alloy and the specific gravity G2 of the second titanium alloy are set in a range of less than 4.42, preferably less than 4.40, more preferably less than 4.39.
By using the titanium alloys having the specific gravities G1 and G2 of which values are very small in comparison with conventional values for the face member and main member, the weight reduction of the large-sized golf club head becomes readily possible. Accordingly, the club head 1 can produce a large weight margin to move the center of gravity of the head to a desired position, and the design freedom of the weight distribution is increased.
If the specific gravities are increased over 4.42, it becomes difficult to obtain a large weight margin while maintaining the large head volume. The lower limit of the specific gravity is conceptually not need to be defined, but, practically values more than 4.30 are preferred.
It is possible that the specific gravity G1 is the same as or different from the specific gravity G2.
Preferably, the ratio (G1/G2) is set in a range of from about 0.98 to about 1.02.
In the case of a large-sized golf club head, generally, there is a tendency that the spring-like effect becomes high and not in compliance with the Rules of Golf. To increase the thickness of the face portion is effectual for decreasing the spring-like effect, but it lessens the design freedom of the weight distribution since the club head weight is also increased. Therefore, the first titanium alloy of the face member 1A is increased in the elastic modulus more than the second titanium alloy of the main member 1B. Thereby, the deflection of the face portion at impact can be decreased so that the spring-like effect becomes in compliance with the Rules of Golf without increasing the thickness or weight of the face portion 3. Further, the use of such high modulus first titanium alloy is also preferable in view of the durability of the face portion 3. In this light, the ratio (E1/E2) of the elastic modulus E1 of the first titanium alloy to the elastic modulus E2 of the second titanium alloy is preferably not less than 1.05, more preferably not less than 1.07, still more preferably not less than 1.10. However, if the elastic modulus ratio (E1/E2) is excessively increased, then the spring-like effect is also decreased excessively or the durability of the main member 1B becomes insufficient. Further, there is a possibility that stress concentrates on the boundary between the first titanium alloy and second titanium alloy. Therefore, the elastic modulus ratio (E1/E2) is preferably not more than 1.40, more preferably less than 1.37, still more preferably less than 1.35.
More specifically, the elastic modulus E1 of the first titanium alloy is preferably not less than 110 GPa, more preferably not less than 115 GPa, still more preferably not less than 118 GPa, but not more than 140 GPa, more preferably not more than 137 GPa, still more preferably not more than 135 GPa.
If less than 110 GPa, the spring-like effect tends to increase against the Rules of Golf. If more than 140 GPa, the spring-like effect largely decreases and the carry distance is accordingly decreased.
Further, in view of the durability of the club head, preferably the elastic modulus E2 of the second titanium alloy of the main member 1B is set to be not less than 95 GPa, more preferably not less than 100 GPa, still more preferably not less than 105 GPa. on the other hand, if the elastic modulus E2 is excessively increased, the spring-like effect of the club head is also decreased and the carry distance decreases. Therefore, the elastic modulus E2 of the second titanium alloy is preferably not more than 120 GPa, more preferably not more than 117 GPa, still more preferably not more than 115 GPa.
The elastic modulus (E1/G1) of the first titanium alloy divided by the specific gravity G1 (no unit) thereof, namely, the ratio of the elastic modulus (E1) to the specific gravity G1 is preferably not less than 27.0 GPa, more preferably not less than 27.5 GPa, still more preferably not less than 28.0 GPa, but not more than 32.0 GPa, more preferably not more than 31.5 GPa, still more preferably not more than 31.0 GPa.
If the ratio (E1/G1) is less than 27.0 GPa, it becomes difficult to reduce the weight of the face member 1A while maintaining the necessary strength. If more than 32.0 GPa, the titanium alloy becomes embrittled, and the durability is decreased.
For the similar reasons, the elastic modulus (E2/G2) of the second titanium alloy divided by the specific gravity G2 (no unut) thereof, namely, the ratio of the elastic modulus (E2) to the specific gravity G2 is preferably not less than 23.0 GPa, more preferably not less than 23.5 GPa, still more preferably not less than 24.0 GPa, but preferably not more than 27.5 GPa, more preferably not more than 27.0 GPa, still more preferably less than 27.0 GPa, most preferably not more than 26.5 GPa.
For the first titanium alloy and second titanium alloy having relatively low specific gravities, preferably used are
In the case of the face member 1A provided with the turnback 9 as shown in
In the case of the main member 1B used in combination with the face member 1A with the turnback 9, the weight W2 thereof of is preferably not less than 110 grams, more preferably not less than 115 grams, still more preferably not less than 120 grams to provide durability necessary for the club head. But, the weight W2 is preferably not more than 155 grams, more preferably less than 150 grams, still more preferably less than 145 grams to prevent the swing balance from deteriorating and to obtain a large weight margin.
The face member 1A and crown member 1C are formed by plastic forming such as forging and press molding. The main member 1B is integrally formed by casting such as lost-wax precision casting. These members are welded each other.
In the above-mentioned embodiments show in
As best depicted in
Preferably, the thickness t1 of the central thick region 3A is set in a range of not less than 2.90 mm, more preferably not less than 2.95 mm, still more preferably not less than 3.00 mm, but not more than 3.50 mm, more preferably not more than 3.40 mm, still more preferably not more than 3.3 mm.
If the thickness t1 is less than 2.90 mm, there is a possibility that the coefficient of restitution of the club head is increased over the limit provided by the Rules of Golf. If more than 3.50 mm, since the weight of the face portion 3 increases, it becomes difficult to increase the depth of the center of gravity.
In order to maintain the durability, the thickness t2 of the annular thinner region 3B is set in a range of not less than 2.35 mm, preferably not less than 2.40 mm, more preferably not less than 2.50 mm, but not more than 2.70 mm, preferably not more than 2.60 mm in order to provide a desirable degree of the spring-like effect.
In order to prevent a stress concentration on the boundary between the central thick region 3A and annular thinner region 3B, a transitional part 3C whose thickness continuously changes from t1 to t2 is formed along the boundary.
The thickness t3 of the crown portion 4, crown major part 4a and crown member 1C; the thickness t4 of the sole portion 5 and sole major part 5a; the thickness t5 of the side portion 6 and side major part 6a are preferably not less than 0.65 mm, more preferably not less than 0.70 mm, but not more than 1.2 mm, more preferably not more than 1.1 mm.
If less than 0.65 mm, it becomes difficult to provide necessary durability. If more than 1.2 mm, the club head weight increases, and the design freedom of the weight distribution is liable to be restricted.
The above-mentioned turnback 9 is preferably provided with a length D (measurement in the front-back direction) of not more than 30 mm, more preferably not more than 28 mm, still more preferably not more than 25 mm. If the length D is more than 30 mm, it becomes difficult to form the face member 1A through plastic forming such as forging and press molding, and the production efficiency decreases. However, it is preferable that the length D of the turnback 9 is not less than 7 mm, more preferably not less than 10 mm, still more preferably not less than 15 mm.
The face member 1A is welded to the main member 1B. Therefore, by setting the length D more than 7 mm, a possible adverse effect of the heat during welding on the face portion can be minimized. Further, the stress at impact decreases and the durability can be improved. Further, as shown in
The weight margin obtained as above can be utilized to provide a separate weight member 20. In this case, the weight member 20 can be fixed to the back part of the main member 1B in the sole portion 5 and/or side portion 5 as shown in
Wood-type golf club heads (volume 460 cc, lie 57.5 degrees, loft 12.0 degrees) were made, changing the wall thickness of the face member and main member and the weight and position of the weight member (made of a tungsten alloy having a specific gravity of 19.0), but not changing the total weight of the head inclusive of the weight member as far as possible. And the depth of the center of gravity and moment of inertia were measured. The measurement values are shown in Table 1 together with the specifications of the heads.
From the test results, it was confirmed that, according to the present invention, the weight margine and degree of design freedom can be increased, therefore, it is possible to increase the depth of the center of gravity and moment of inertia.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-125011 | May 2008 | JP | national |
