Patent Grant
10420987
The present invention relates to a golf club head capable of improving a carry distance of a stuck ball and a method for predicting the carry distance performance thereof.
There has been known a golf club head which is, in order to improve the average carry distance of stuck balls, increased in the moment of inertia Ix around a vertical axis passing through the center of gravity of the head in a standard state in which the head is set on a horizontal plane so that the shaft center line is inclined at the lie angle within a vertical plane and the club face lies at the loft angle.
In such golf club head, even if a ball is struck off the sweet spot of the club face, since the rotation of the club head around the vertical axis is inhibited, a decrease in the initial speed of the struck ball is lessened.
Consequently, it has an advantage such that the carry distance loss is reduced.
The recent golf rules, however, limit a maximum value of the moment of inertia around the vertical axis. Therefore, it is required to develop a new technique being able to further improve the carry distance.
It is therefore, an object of the present invention to provide a golf club head which can increase carry distances of average golfers whose probability of off-center shot is relatively high.
Ball hitting test was made by average golfers whose club head speed ranges from 38 to 45 m/s in order to obtain the distribution of the hitting positions on the club face.
From the test results, it was discovered that hitting positions of average golfers are distributed along a straight line h passing through the sweet spot SS and inclining downwardly towards the heel from the toe at an angle of about 28 degrees with respect to the horizontal plane HP.
From this, it was fond that, for further improving the carry distance, it is effective to control the rotation of the club head on off-center shots by increasing a moment of inertia Iy around an inclined axis passing through the center of gravity of the head and placed within a plane parallel with the above-mentioned vertical plane within which the shaft center line is placed and inclined downwardly toward the toe from the heel at angle θ1 of 62 degrees with respect to the horizontal plane.
Based on this finding, the present invention was made.
According to the present invention, a golf club head has a hollow structure and
under a standard state in which the head is set on a horizontal plane so that a shaft center line is placed within a vertical plane and inclined at a fixed lie angle of 60 degrees with respect to the horizontal plane and the club face lies at the loft angle of the club head,
a moment of inertia Ix of the club head around a vertical axis passing through the center of gravity of the head is 4500 to 5900 g sq·cm,
a moment of inertia Iy of the club head around an inclined axis passing through the center of gravity of the head and inclined downwardly toward the toe from the heel at an angle θ of 62 degrees with respect to the horizontal plane within a plane parallel with the vertical plane within which the center line of the shaft is placed is 5300 to 6800 g sq·cm, and
the moment of inertia Iy in g sq·cm and the moment of inertia Ix in g sq·cm satisfy
Iy=<1.071×Ix+482.
Preferably, the moment of inertia Iy around the inclined axis is more than the moment of inertia Ix around the vertical axis. Preferably, the volume of the head is 420 to 470 cc.
Further, according to the present invention, a method for predicting carry distance performance of a golf club head comprises:
a step of measuring a moment of inertia Iy of the club head around an inclined axis,
wherein under a standard state in which the head is set on a horizontal plane so that a center line of a shaft is placed within a vertical plane and inclined at a fixed lie angle of 60 degrees with respect to the horizontal plane and the club face lies at the loft angle of the club head,
the inclined axis is defined as passing through the center of gravity of the head and inclined downwardly toward the toe from the heel at an angle θ of 62 degrees with respect to a horizontal plane within a plane parallel with a vertical plane within which the center line of the shaft is placed; and
a step of predicting a carry distance by the golf club head based on the measured value of the moment of inertia Iy around the inclined axis.
As explained, the moment of inertia Iy is that around the axis perpendicular to the above-mentioned straight line (h) shown in
As the moment of inertia Ix around the vertical axis is limited within a range of from 4500 to 5900 g sq·cm, the head comes into compliance with the golf rules.
Further, the following conditional relationship
Iy=<1.071×Ix+482 g sq·cm
is satisfied. As a result, a wall thickness of the golf club head can not be excessively decreased, and the club head can be provided with durability.
Thus, in the golf club head according to the present invention, the moment of inertia around the inclined axis is increased while the moment of inertia around the vertical axis is limited to meet the golf rules. Therefor, even when off-center shot is made, the kinetic energy of the club head is effectively transferred to the ball so that the carry distance can be improved, while providing durability for the head.
In this application including the description and claims, positions, dimensions, directions and like of the club head refer to those under the standard state of the head unless otherwise noted.
The standard state of the head is such that, as shown in
The sweet spot SS is an intersecting point of a normal line (n) to the club face 2A drawn from the center of gravity G of the head with the club face 2A.
The edge of the club face 2A is defined by a virtual edge line (Pe) if the edge is unclear due to smooth change in the curvature. As shown in
Embodiments of present invention will now be described in detail in conjunction with accompanying drawings.
According to the present invention, a club head 1 can be formed as a wood-type head. e.g. driver (#1), fairway wood and the like having a hollow structure with a hollow (i) therein.
In the case of such wood-type head 1, it is preferable that the club head 1 has a volume of about 420 cc to about 470 cc. If the volume v is less than 420 cc, the club head 1 looks smaller and fails to give a sense of assurance at address, and there is a possibility that a sweet area becomes small. If the volume V exceeds 470 cc, since the mass of the club head increases, it becomes difficult to swing through the ball, and the head speed decreases. Further, it goes against the golf rules. In this light, the volume v is preferably not less than 425 cc, more preferably not less than 430 cc.
If the mass of the club head 1 is too small, there is a tendency that the kinetic energy of the club head decreases, and the carry distance can not be improved. If the mass is too large, there is a tendency that it becomes difficult to swing through the ball, and the carry distance and directional stability of the ball are deteriorated. In this light, the mass of the club head 1 is preferably set in a range of not less than 160 g, more preferably not less than 180 g, but not more than 240 g, more preferably not more than 220 g.
According to the present invention, the following conditions (I), (II) and (II) are satisfied:
If the moment of inertia Iy around the inclined axis becomes more than the value of 1.071×Ix+482 g sq·cm, then there is a possibility that the wall thickness of the club head 1 is decreased to deteriorate the durability.
As explained above, the club head 1 according to the present invention is provided with a larger moment of inertia Iy around the inclined axis while complying with the golf rules. Therefore, the restitution coefficient is increased in the off-center shot area, and the kinetic energy of the club head can be effectively transferred to the ball even on off-center shot, and the carry distance can be improved and the golf club head can be provided with durability.
In order to bring out the above function more steady, the moment of inertia Iy around the inclined axis is preferably set to be more than the moment of inertia Ix around the vertical axis.
The club head 1 having such moment of inertia Ix and Iy can be obtained by allocating more weight to positions distant from the inclined axis K.
In this application, the restitution coefficient is meant for the coefficient of rebound of the golf ball calculated by the following experimental method.
In particular, by the use of a ball launcher, a golf ball is let off to hit the sweet spot SS of the club face of the club head placed on a pedestal at rest without being fixed thereto, and the collision velocity Vi of the golf ball and the rebound velocity Vo immediate after the collision are measured.
The restitution coefficient e is given by
(Vo/Vi)=(e*M−m)/(M+m)
where
M is the mass of the club head, and
m is the mass of the golf ball.
The distance from the mouth of the ball launcher to the club face is set at 55 inches. The ball is launched to hit the club face perpendicularly thereto at a distance less than 5 mm from the sweet spot. The initial velocity of the ball is set at 160+/−0.5 feet/sec (48.768+/−0.1524 meter/sec). As to the golf balls, Titleist's PINNACLE GOLD is used.
In the following embodiments, each club head 1 comprises: a face portion 3 having the club face 2A for hitting a ball; a crown portion 4 defining the top surface of the club head extending to the upper edge 2a of the club face 2A; a sole portion 5 defining the bottom face of the club head extending to the lower edge 2b of the club face 2A; a side portion 6 extending between the crown portion 4 and the sole portion 5 and extending from the toe-side edge 2c of the club face 2A to the heel-side edge 2d of the club face 2A through the back face 2B of the club head; and a hosel portion 7 provided in a heel-side part of the crown portion 4 and having a shaft inserting hole 7e into which the tip end of the club shaft (not shown) is inserted. The head has a hollow structure with a relatively thin wall.
The club head 1 can be formed by assembling a head main body 1A provided in a crown portion side with an opening O, and a crown member 1B fixed to the head main body 1A so as to close the opening O.
It is preferable that the head main body 1A is made of one or more kinds of metal materials including a metal material having a relatively large specific gravity, and the crown member 1B is made of a material having a specific gravity less than the metal material of the head main body 1A having a relatively large specific gravity. This helps to reduce the weight of the club head in its upper part to thereby increase the moment of inertia 1y around the inclined axis.
As to the materials for the head main body 1A, stainless steel, maraging steel, titanium alloy and the like are preferred. The head main body 1A can be manufactured through a technique of forging or casting. Further, it is also possible to manufacture the head main body by assembling two or more parts prepared for example by bending rolled materials and the like. Preferably, the head main body is formed as a single casting integrally molded.
As to the materials for the crown member 1B, fiber reinforced resin, titanium alloy, aluminum alloy, magnesium alloy and the like are preferred.
Further, a fiber reinforced resin material may be used to form a part of the head main body 1A excepting the face portion 3.
In order to achieve the above-mentioned relationship between the moment of inertia Ix and the moment of inertia Iy, for example, it is possible that the wall thickness of the club head 1 in any part is reduced as far as possible, and the reduced weight is assigned to a weight member 1C made of a high specific gravity material, then the weight member is disposed in a peripheral region of the club head 1.
Preferably, the weight member 1C has a specific gravity of not less than 7.0, more preferably not less than 10.0, still more preferably not less than 13.0, and
the weight member 1C is made of a material having a relatively large specific gravity for example, an alloy comprising one or two or more of tungsten, nickelic, stainless steel and the like.
The weight member 1C is fixed directly to the surface of the hollow (i). But it is also possible to fix it to the club head 1 by the use of an attachment (not shown).
Further, the club head 1 can be provided in the club face 2A with score lines SL which extend straight and become parallel with the horizontal direction in the front view of the head under the standard state as shown in
Incidentally, the above-mentioned loft angle is more than zero degree.
The club head 1 in this embodiment is composed of a fore part 10 including the face portion 3, and an aft part 11 connected to the fore part 10 forming a stepped part j in the crown portion 4, sole portion 5 and side portion 6.
The fore part 10 includes, in addition to the face portion 3, a face turnback 13 extending for a short distance from the edge of the face portion 3 toward the back face 2B.
The face turnback 13 includes:
a crown front part 13a extending backward from the upper edge 2a of the club face 2A;
a sole front part 13b extending backward from the lower edge 2 of the club face 2A;
a toe front part 13c extending backward from the toe-side edge 2c of the club face 2A; and
a heel front part 13d extending backward from the heel-side edge 2d of the club face 2A.
As to the dimensions of the front parts 13a-13c in the front-back direction of the head, as shown in
The aft part 11 includes:
a crown rear part 4b connected to the crown front part 13a through a stepped part j having a front face substantially parallel with the club face 2A;
a sole rear part 5b connected to the sole front part 13b through a stepped part j having a rear face substantially parallel with the club face 2A; and
a side rear part 6b connected to the toe front part 13c through a stepped part j having a rear face substantially parallel with the club face 2A.
As is clear from the front view of the head under the standard state shown in
As shown in
As shown in
Accordingly, the club head 1 in this embodiment has a peculiar shape such that only a part of the aft part 11 positioned on the toe-side of the center of gravity G of the head is bent upwardly. In other words, the aft part 11 is twisted around an axis extending in the front-back direction of the head relatively to the fore part 10 such that the toe-side of the aft part 11 goes upward of the toe-side of the fore part 10 thereby forming the stepped parts j.
The outer surface of a part of the aft part 11 on the heel-side of the center of gravity G of the head is smoothly connected to the outer surface of the fore part 10.
As a results, it becomes possible for the club head 1 to have a mass distribution suitable for achieving the moment of inertia Iy around the inclined axis and the moment of inertia Ix around the vertical axis within the above-mentioned ranges.
In the club head 1 in this embodiment, the moment of inertia 1y (g sq·cm) around the inclined axis and the moment of inertia Ix (g sq·cm) around the vertical axis satisfy
Iy<1.071×Ix+482 g sq·cm
and further
Iy=<1.111×Ix−255 g sq·cm.
Therefore, the head can be easily manufactured while securing a necessary wall thickness for the head.
It is possible to use a single weight member 1c, but it is also possible dispose two or more weight members 1C as shown in
In
For example, the crown member 1B is made of a fiber reinforced resin material. In particular, it is preferred that the crown member 1B is made by laminating prepreg sheets.
The rest, namely the head main body 1A is made of a metal material, such as a titanium alloy or the like
In the club head 1 in this embodiment, the club face 2A has a contour shape such that, in the front view of the head under the standard state, a straight line (th), which is defined as extending between a toe-side point (tm) on the edge of the club face 2A at the toe-side extreme end and a heel-side point (hm) on the edge of the club face 2A at the heel-side extreme end, is inclined at an angle δ of not less than 15 degrees with respect to the horizontal plane HP.
The club head 1 in this embodiment has a shape belonging to the conventional wood-type than the peculiar twisted shape of the first embodiment.
Even so, in such club head 1, it becomes possible to effectively distribute the mass to positions distant from the inclined axis K, therefore, it is possible for the club head 1 to have a mass distribution suitable for achieving the moment of inertia Iy and Ix within the above-mentioned ranges.
In this embodiment too, one or more weight members 1C can be disposed as described in conjunction with the first embodiment.
The club head 1 in this the embodiment is provided in the hollow (i) with a ring-shaped weight member 1C surrounding the inclined axis K or a plurality of circular arc weight members 1C arranged circularly to surround the inclined axis K.
In the front view of the head under the standard state, the circle, along which the weight member or members 1CR are arranged, is inclined downwardly toward the heel from the toe preferably at an angle of 56 degrees with respect to the horizontal plane HP.
The club head 1 in this embodiment also has a shape belonging to the conventional wood-type than the peculiar twisted shape of the first embodiment.
Such continuous ring-shaped weight member 1C or the circularly-arranged circular arc weight members 1C can be used in the above-mentioned first and second embodiments instead of a plurality of the weight members 1C having a shape like a block or button as shown in
[Maximum Second-Order Moment Axis R of Club Face]
Here, a maximum second-order moment axis R is defined as an axis, which extends straight passing through the centroid z of a two-dimensional shape and about which the second-order moment z becomes maximum. The second-order moment z about an axis is the integration of the product of the area dA of a micro region in the 2-D shape and the square of the distance y thereto from the axis. Namely, I=∫y2 dA.
In the second embodiment, as shown in
In the first embodiment, the angle ω is in a range of from 75 to 90 degrees.
In the third embodiment, the angle ω is in a range of from 75 to 90 degrees.
[Method for Predicting Carry Distance Performance of Club Head]
Next, a method for predicting carry distance performance of a club head is described.
Firstly, plural kinds of club heads, which are different from each other in respect of at least one of the shape of the head, the mass of weight member(s) 1C and the position(s) of weight member(s) 1C, are prepared, and
the club heads are each measured for the moment of inertia Iy around the inclined axis and the moment of inertia Ix around the vertical axis.
The moment of inertia can be measured, for example, by the use of a measurement instrument such as Moment of Inertia Measuring Instrument manufactured by INERTIA DYNAMICS Inc.
Then, the plural kinds of the club heads are attached to club shafts to make golf clubs. Using the golf clubs, actual ball hitting tests are made by average golfers in order to obtain the average carry distance of each club. From the average carry distance and the moment of inertia Iy and Ix, a correlation table (not shown) of these parameters is prepared.
In order to predict carry distance performance of an object club head, the head is measured for the moment of inertia Iy around the inclined axis K and the moment of inertia Ix around the vertical axis.
Using the measured value of the moment of inertia Iy around the inclined axis K, the correlation table is looked up to obtain the corresponding average carry distance as the predicted or estimated carry distance performance of the object club head.
Therefore, by employing this method for predicting carry distance performance, the carry distance performance of a club head can be easily predicted without making an actual test by golfers.
Comparison Tests
In order to confirm the effects of the invention, a computer simulation was made.
Wood-type golf club heads (driver) having a conventional shape (Ref. 1), the structure shown in
By simulating the above-mentioned experimental method, the restitution coefficient was determined, and the restitution coefficient ratio was obtained therefrom, wherein the restitution coefficient ratio is the ratio (e2/e1) of the restitution coefficient e2 at any point in the club face to the restitution coefficient e1 at the sweet spot SS.
Further, the minimum wall thickness occurring in the crown portion or sole portion was obtained.
Each head was composed of the head main body made of a titanium alloy having a specific gravity of 4.42 and the crown member made of a fiber reinforced resin material having a specific gravity of 1.40. Except for the specifications shown in Table 1, all of the heads had the same specifications some of which are as follows.
lie angle alpha: 60 degrees
loft angle beta: 9.6 degrees
head volume: 460 cc
mass of club head: 210 g
angle θ1 of inclined axis: 62 degrees
wall thickness of face portion: 2.8 mm
(a): 0.995 to 1.000
(b): 0.990 to 0.995
(c): 0.985 to 0.990
From the simulation results, it was confirmed that, in contrast to the contour plot of Comparative example Ref. 1 not satisfying the above-mentioned conditions (I), (II) and (II), the contour plot of embodiment Ex. 5 satisfying the conditions (I), (II) and (II) is inclined corresponding to the distribution of hitting positions of average golfers shown in
Also in the case of other embodiments satisfying the conditions (I), (II) and (II), contour plots similar to
Further, for each head, the restitution coefficient ratio at a position apart from the sweet spot SS by 30 mm toward the heel-side and 15 mm toward the sole-side was obtained. The results are shown in Table 1.
The value of the restitution coefficient ratio at this position will give an indication of the rebound performance of the club head when the hitting position is distributed as shown in
From the simulation results, it was confirmed that, in comparison with the comparative example golf club heads, the embodiment golf club heads was significantly improved in the rebound performance while the durability was maintained as a substantial wall thickness could be secured.
While preferred embodiments of the present invention have been described in conjunction with the accompanying drawings, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.
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