Patent Application
20090075752
The present invention relates to a golf club head capable of reducing the variation in the carry distance of a struck ball and thereby increasing the carry distances in totality.
The directional stability of a struck ball is an important factor for stabilizing the carry distance. If the ball is struck off-center, the club head is moved or rotates around the center of gravity of the head more or less. If such a rotational movement of the club head at the time of off-center shot is reduced, then the lunching direction of the struck ball is stabilized.
In recent years, on the other hand, large-sized various wood-type golf club heads have been proposed. Usually, the large-sized golf club heads are increased in the lateral moment of inertia and vertical moment of inertia.
If the vertical moment of inertia is increased, then the vertical gear effect becomes reduced, therefore, if the ball hitting position is off the sweet spot upward or downward, the carry distance tends to decrease.
AS well known in the art, the vertical gear effect is as follows. If the ball hitting position is off the sweet spot SS upwards or downwards, then as shown in
Due to the frictional engagement between the golf ball and the club face (f), the contact surface of the golf ball receives a force in the reverse direction to the rotational direction of the club head like a gear. As a result, the backspin of the struck ball is decreased in the case of an upper hitting position or increased in the case of a lower hitting position.
In consequence, in the case of the golf club heads whose vertical moment of inertia is large where the rotational movement is decreased as explained above, if the ball hitting position is off the sweet spot upward, the backspin can not be fully decreased.
On the other hand, due to the face roll having a radius of curvature Y, in the case of the upper hitting position, when compared with the sweet spot SS, the loft angle becomes increased and the launch angle of the struck ball is also increased. As a result, the ballistic course is very liable to become a rising trajectory and thereby the carry distance is decreased.
Contrary, in the case of the lower hitting position, the backspin can not be fully increased, and the launch angle of the ball is decreased. As a result, the ball tends to drop quickly and thereby the carry distance is decreased.
Thus, in the case of a large-sized golf club head, due to the relatively large vertical moment of inertia, there is a tendency that the carry distance varies wide depending of the ball hitting position.
It is therefore, an object of the present invention to provide a golf club head in which, by increasing the lateral moment of inertia and decreasing the thickness of the club head, the vertical moment of inertia is decreased on the whole, and thereby the variation in the carry distance can be reduced.
According to the present invention, a hollow golf club head has a head volume of not less than 430 cc, a lateral moment of inertia of from 5000 to 5900 g sq·cm, and a club head thickness of from 45 to 58 mm.
Therefore, the vertical moment of inertia is decreased. As a result, even if the ball hitting position is off the sweet spot upward or downward, the struck ball benefits from the vertical gear effect and the decrease in the carry distance is controlled.
Further, since the lateral moment of inertia is very large, even if the ball hitting position is off the sweet spot toward the toe or heel, the lateral movement of the club head becomes very small, and the directional stability of the struck ball is improved, therefore, the decrease in the carry distance is controlled.
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 (alpha) while keeping the club shaft center line CL on a vertical plane VP1, and the club face 2 forms its loft angle (beta) with respect to the horizontal plane HP. Incidentally, in the case of the club head alone, the center line of the shaft inserting hole (h) can be used instead of the center line of the club shaft.
Lateral moment of inertia Ma is the moment of inertia around a vertical axis A1 passing through the center of gravity G in the standard state.
Vertical moment of inertia Mb is the moment of inertia around a horizontal axis A2 passing through the center of gravity G in the heel-and-toe direction of the head in the standard state.
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 G of the head.
Back-and-forth direction is a direction parallel with the above-mentioned straight line N projected on the horizontal plane HP.
Heel-and-toe direction is a direction TH parallel with the horizontal plane HP and perpendicular to the back-and-forth direction.
Club head thickness H is the height measured from the horizontal plane HP to the highest point (m) on the crown portion of the club head, namely, the highest point of the head excluding the upwardly protruding hosel portion if any.
Sweet spot height GH is a height of the sweet spot Ss measured from the horizontal plane HP.
Face progression FP is the horizontal distance between the leading edge Le of the club head and the vertical plane VP1 including the club shaft center line CL, measured in a vertical plane VP3 including the sweet spot SS and the center of gravity G.
Leading edge Le is a contact point between the club face 2 and a vertical plane VP2 parallel with the vertical plane VP1.
Gravity point depth GL is the horizontal distance between the center of gravity G and the vertical plane VP2.
Wood-type golf club is meant for at least number 1 to 5 woods, and clubs comprising heads having similar shapes may be included.
If the edge (2a and 2b) of the club face 2 is unclear due to smooth change in the curvature, as shown in
a) and
In the drawings, golf club head 1 according to the present invention is a wood-type hollow golf club head. The head 1 comprises a face portion 3 whose front face defines a club face 2 for striking a ball; a crown portion 4 intersecting the club face 2 at the upper edge 2a thereof; a sole portion 5 intersecting the club face 2 at the lower edge 2b thereof; a side portion 6 between the crown portion 4 and sole portion 5; and a hosel portion 7 disposed at the heel-side end to be attached to an end of a club shaft inserted into a shaft inserting hole (h). The club head 1 is provided a shell structure with thin walls having a closed hollow (i).
The club face 2 is provided with a face roll (a curvature from crown to sole) of a radius of curvature PR, and a face bulge (a curvature from heel to toe) of a radius of curvature RB.
The outer surface of the crown portion 4 is convexly curved. Thus, apart from the hosel portion 7, the highest point (m) is positioned within the outer surface of the crown portion 4.
The hosel portion 7 has a tubular portion protruding upwardly from the crown portion 4 and defining the shaft inserting hole (h).
The outer surface of the hosel portion 7 is connected to the outer surface of the crown portion 4 through a transitional concave curve.
The side portion 6 can be formed to extend continuously from the toe to the heel through the rear of the head. But, in this embodiment, the side portion 6 is formed discontinuously.
In this embodiment, the club head 1 is made of metal materials. But, in order to reduce the club head weight and/or to adjust the position of the center of gravity G of the head, a fiber reinforced resin can be used together with the metal materials. Preferably used are metal materials having a large specific tensile strength, for example, stainless steels, maraging steels, pure titanium, titanium alloys, magnesium alloys aluminum alloys and the like are. In the case of the titanium alloys, for example Ti-6Al-4V, Ti-15V-3Cr-3Al-3Sn, Ti-15Mo-5Zr-3Al, Ti-13V-11Cr-3Al and the like are be preferably used.
The club head 1 is manufactured by assembling a plurality of parts (usually 2 to 5 parts) each prepared by an appropriate method, for example, casting, rolling, forging, pressure molding or the like.
The volume of the club head 1 is set in a range of not less than 430 cc, preferably not less than 440 cc, more preferably not less than 450 cc.
Such a large head volume can give the user easy feelings at the time of addressing the ball and can increase the gravity point depth GL and the lateral moment of inertia Ma so as to improve the directional stability of the struck ball.
If the volume is less than 430 cc, it becomes difficult to improve the directional stability of the struck ball.
If the volume is too large, on the other hand, problems arise such as increase in the club head weight, deterioration of swing balance, decrease in the durability and the like, therefore, it is preferable that the volume is set to be not more than 600 cc, preferably not more than 550 cc. If golf rules are considered, the volume should be not more than 460 cc.
If the mass of the club head 1 is too small, then the lateral moment of inertia is decreased, and also the kinetic energy during swing is decreased, therefore, the improvement in the carry distance can not be expected. If the mass of the club head 1 is too large, on the other hand, it becomes difficult to swing the golf club through the ball, and there is a possibility that the directional stability of the struck ball is deteriorated and the carry distance is decreased. In this light, the mass of the club head is preferably not less than 180 g, more preferably not less than 185 g, but preferably not more than 210 g, more preferably not more than 205 g.
In the case that the club head is provided with a relatively large volume of more than 430 cc and the area of the club face 2 is relatively large as a necessary consequence, when the ball hitting position is off the sweet spot towards the heel or toe, there is possibility that the distance in the heel-and-toe direction between the hitting position and the sweet spot becomes very large. Even in such a condition, in order that the rotational movement (head movement) of the club head 1 around the vertical axis A1 is surely reduces to thereby stabilize the direction of the struck ball, the lateral moment of inertia Ma should be large enough.
Therefore, the lateral moment of inertia Ma has to be increased up to 5000 g sq·cm at least. Preferably, the lateral moment of inertia Ma is not less than 5300 g sq·cm, more preferably not less than 5500 g sq·cm. However, if the lateral moment of inertia Ma is too large, there is a possibility that the club head weight becomes excessively heavy, and the shape of the club head becomes extraordinary. Therefore, the lateral moment of inertia Ma is at most 5900 g sq·cm.
The present inventor discovered that the club head thickness H and the vertical moment of inertia Mb have a certain correlation and that the vertical moment of inertia Mb can be kept at small values by reducing the club head thickness H.
According thereto, by limiting the club head thickness H within a range of not more than 58 mm, preferably not more than 56 mm, more preferably not more than 55 mm, still more preferably not more than 55 mm, the increase in the vertical moment of inertia Mb can be restrained even when the head volume is increased up to 430 cc at least and also the lateral moment of inertia Ma is increased up to 5000 g sq·cm at least.
If the club head thickness H is too small, the sweet spot area becomes narrow, and as a result, the carry distances are liable to decrease. Therefore, the club head thickness H is preferably set in a range of from not less than 45 mm, more preferably not less than 47 mm, still more preferably not less than 49 mm.
In order to improve the carry distance stably, the vertical moment of inertia Mb is preferably set in a range of not more than 5000 g sq·cm, more preferably not more than 4500 g sq·cm, still more preferably not more than 4000 g sq·cm.
If the vertical moment of inertia Mb becomes excessively small, on the other hand, there is a tendency that the head movement at impact increases, and the carry distance is decreased, therefore, the vertical moment of inertia Mb is preferably not less than 2500 g sq·cm, more preferably not less than 2700 g sq·cm, still more preferably not less than 3000 g sq·cm.
In the case of a golf club head having a large head volume and a small club head thickness H, there is a tendency that the center of gravity G of the head comes far away from the club shaft center line CL, namely, as shown in
Accordingly, during swing, due to the centrifugal force, the club head 1 is subjected to a rotational movement as indicated in broken line such that the center of gravity G approaches the extension of the club shaft center line CL when viewed from the heel side of the head.
Such rotational movement is increased in proportion to the increase in the head speed during swing and as a result, the dynamic loft angle at impact is increased.
In other words, the loft angle is varied depending on the swing speed, thus, it is difficult for the user to control the ballistic course and carry distance of the ball.
In order to solve this problem, the club head 1 in this example has a streamline shape, and the crown surface length LC is set to be longer than the sole surface length LS.
As shown in
the sole surface length LS is defined as the length measured along the outer surface of the sole portion 5 from the lower edge 2b of the club face 2 to the rearmost point BP.
Thus, at least at the rearmost point BP, the side portion 6 is interrupted, and the head has a streamline shape.
Accordingly, during swing, the velocity of air flow along the surface of the crown portion becomes faster than the velocity of air flow along the surface of the sole portion, and the air pressure to the crown portion becomes lower than the air pressure to the sole portion, and the club head 1, in particular its rear part, obtains lift. Therefore, the above-mentioned rotational movement of the head is reduced, and the resultant increase of the loft angle can be avoided, and thereby the carry distances become stable.
If the ratio (LC/LS) of the crown surface length LC to the sole surface length LS is less than 1.02, the lifting is still insufficient. But, if the ratio (LC/LS) is more than 1.20, there is a tendency that the lifting and the restraint of the increase in the loft angle become excess. Therefore, the ratio (LC/LS) is preferably not less than 1.02, more preferably not less than 1.05, but preferably not more than 1.20, more preferably not more than 1.10, still more preferably not more than 1.09.
The crown surface length LC is preferably not less than 105 mm, more preferably not less than 108 mm, still more preferably not less than 110 mm, but not more than 125 mm, more preferably not more than 122 mm, still more preferably not more than 120 mm.
The sole surface length LS preferably not less than 100 mm, more preferably not less than 103 mm, still more preferably not less than 105 mm, but not more than 120 mm, more preferably not more than 117 mm, still more preferably not more than 115 mm.
Incidentally, the ratio (LC/LS) can be changed for example by setting the radius of curvature of the contour of the crown portion 4 at smaller values than that of the sole portion 5 and by decreasing the height BH of the rearmost point BP.
To decrease the height BH is preferable because the height of the center of gravity G is also decreased thereby. In this light, the height BH is preferably not more than 30 mm, more preferably not more than 28 mm, still more preferably not more than 25 mm.
If the sweet spot height GH is too large, the backspin tends to increase excessively. If the sweet spot height GH is too small contrary, the backspin is decreased which tends to result in a drop ball. In either case, the carry distance is decreased. Therefore, the sweet spot height GH is preferably set in a range of not more than 38 mm, more preferably not more than 36 mm, still more preferably not more than 34 mm, but not less than 25 mm, more preferably not less than 27 mm, still more preferably not less than 29 mm.
The face progression FP has influence upon the returning motion of the club head from swing and upon the timing of impacting the ball. By setting the face progression FP in a range of not less than 17 mm, preferably not less than 19 mm, but not more than 28 mm, preferably not more than 26 mm, more preferably not more than 25 mm, the directional stability of the struck ball can be improved to stabilize the carry distance.
If the gravity point depth GL is decreased, there is a possibility that the lateral moment of inertia Ma becomes decreased, therefore, the gravity point depth GL is preferably not less than 30 mm, more preferably not less than 32 mm, still more preferably not less than 33 mm. If the depth GL is too large, on the other hand, the head tends to become insensitive to the impact feeling. Further, the position of the sweet spot SS tends to become high, and potential for off-center hit (lower hit) increases. It is therefore preferable that the gravity point depth GL is set to be not more than 60 mm, more preferably not more than 57 mm, still more preferably not more than 55 mm.
In order to secure the lateral moment of inertia Ma and the gravity point depth GL, the size HL of the club head 1 measured in the back-and-forth direction from the leading edge Le to the rearmost point BP, is preferably set in a range of not less than 110 mm, more preferably not less than 115 mm, but not more than 127 mm, more preferably not more than 125 mm.
Although the club head 1 is decreased in the club head thickness H and the vertical moment of inertia Mb as explained above, the vertical gear effect occurs more or less.
In this embodiment, the face roll is provided throughout the club face 2 and the radius of curvature PR is set in a range of not less than 12 inches, preferably not less than 14 inches, more preferably not less than 16 inches, but not more than 25 inches, preferably not more than 23 inches, more preferably not more than 21 inches. These specific values of the radius of curvature RR are measured in the above-mentioned vertical plane VP3 for the part between a point Pu 10 mm downward from the upper edge 2a along the club face 2 and a point Pd 10 mm upward from the lower edge 2b along the club face 2, as shown in
In this embodiment, because of the relatively large lateral moment of inertia Ma, even if the ball hitting position is off the sweet spot towards the toe or heel, the sidespin of the struck ball is not so increased. Therefore, it is preferable that the radius of curvature RB of the face bulge is increased. Preferably, the radius of curvature RB is set in a range of not less than 15 inches, more preferably not less than 17 inches, still more preferably not less than 20 inches, but not more than 50 inches, more preferably not more than 45 inches, still more preferably not more than 40 inches.
In the plan view of the club head under the standard state, the overall area of the club head is preferably set in a range of not less than 115 sq·cm, more preferably not less than 117 sq·cm, still more preferably not less than 120 sq·cm. In other words, the projected area of the head on the horizontal plane HP is so limited. As a result, the lateral moment of inertia Ma can be effectively increased, and it is possible to give the user easy fillings when addressing the ball. If the projected area is too large, on the other hand, violation of the golf rules or regulations and an undesirable increase in the club head weight are resulted, therefore, the projected area is preferably not more than 140 sq·cm, more preferably not more than 137 sq·cm, still more preferably not more than 135 sq·cm.
Wood-type hollow golf club heads were prepared and tested for the carry distance and the directional stability of the struck ball. All of the club heads had same structures and same specifications except for the specifications shown in Table 1. The volume, mass, lie angle and loft angle of the heads were 460 cc, 195 grams, 59 degrees and 11.5 degrees, respectively. The heads were each made from a main part formed by casting a molten titanium alloy Ti-6Al-4V, a face plate formed by forging a titanium alloy Ti-5.5Al-1Fe, and a crown plate formed by forging a titanium alloy Ti-15V-3Cr-3Al-3sn.
The main part was provided with a front opening and a top opening. The face plate and crown plate were laser welded to the main part so as to cover the front opening and the top opening, respectively.
The moments of inertia Ma and Mb were adjusted by changing the wall thicknesses of the sole portion, side portion and/or crown portion.
Carry Distance Test:
Each head was attached to an FRP shaft (MP400, flex R, manufactured by SRI Sports Limited) to make a wood club.
The club was mounted on a swing robot and hit three-piece balls five times par each of the following three positions at a head speed of 40 m/s.
Center: the sweet spot sS
upper: 5 mm above the sweet spot
Lower: 5 mm below the sweet spot
with respect to each of the three positions, the average carry distance was calculated. Further, the average of all of the positions was calculated. The results are shown in Table 1.
Variation in Carry Distance Test:
Using the above-mentioned golf clubs, each of ten golfers having handicaps of 10 to 20 hit three-piece balls ten times par a club.
With respect to each of the golfers, the difference between the maximum carry distance and minimum carry distance was obtained. Then, the average of the differences of the ten golfers was calculated. The results are shown in Table 1, wherein the smaller the value, the smaller the variation.
From the test results, it was confirmed that the decrease in the carry distance at the time of upward or downward off-center shot can be significantly controlled, and the stable carry distances can be achieved.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-239679 | Sep 2007 | JP | national |
