Patent Grant
9586107
The present application claims priority on Patent Application No. 2014-184672 filed in Japan on Sep. 10, 2014, the entire contents of which are hereby incorporated by reference.
Field of the Invention
The present invention relates to a golf club.
Description of the Related Art
It is a flight distance that is an important item to evaluate a golf club.
Japanese Patent Application Laid-Open No. 2004-201911 discloses a wood club in which the mass ratio of a head occupied in the total mass of the golf club is 73% or greater and 81% or less. The kinetic energy of the head can be increased due to a large mass of the head. The initial velocity of a ball can be increased due to the collision against the head having a large kinetic energy. In Japanese Patent Publication No. 5546673 (US2015/0087435), the concept of a moment of inertia about a swing axis is introduced. The concept can contribute to an improvement in a flight distance performance.
The moment of inertia about the swing axis is considered, and thereby the ease of a swing can be improved while a head weight can be increased. Demand for an increase in a flight distance has more and more increased. The present invention enables a further increase in a flight distance based on new technical ideas.
It is an object of the present invention to provide a golf club excellent in a flight distance performance.
A golf club according to a preferred aspect of the present invention includes a head, a shaft, and a grip. A club inertia moment about a swing axis is defined as Isw (kg·cm2). A club inertia moment about a grip end is defined as Ige (kg·cm2). Preferably, the inertia moment Ige is 2820 (kg·cm2) or greater and less than 2870 (kg·cm2). Preferably, Isw/Ige is equal to or less than 2.42.
A club weight is defined as Wc (kg), an axial direction distance from the grip end to a center of gravity of the club is defined as Lc (cm), and a club inertia moment about the center of gravity of the club is defined as Ic (kg·cm2). The inertia moment Isw (kg·cm2) is calculated by Equation (1) below. The inertia moment Ige (kg·cm2) is calculated by Equation (2) below.
Isw=Wc×(Lc+60)2+Ic (1)
Ige=Wc×(Lc)2+Ic (2)
Preferably, a grip weight Wg is equal to or less than 0.037 Kg. Preferably, a head weight Wh is equal to or greater than 0.194 kg.
Preferably, Wh/Wc is equal to or greater than 0.72.
In the following, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.
It is noted that in the present application, the term “axial direction” means the axial direction of a shaft.
The golf club 2 has an excellent flight distance performance. The golf club 2 is a driver (a number 1 wood).
Preferably, a club length is equal to or greater than 43 inches. Preferably, the golf club 2 is a wood type golf club. Preferably, the head 4 is a wood type golf club head.
The shaft 6 is formed of a laminate of fiber reinforced resin layers. The shaft 6 is a tubular body. The shaft 6 has a hollow structure. As shown in
In
The shaft 6 is a so-called carbon shaft. Preferably, the shaft 6 is formed by curing prepreg sheets. In the prepreg sheet, fibers are aligned substantially in one direction. The prepreg in which fibers are aligned substantially in one direction is also referred to as a UD prepreg. “UD” stands for a uni-direction. It may be fine to use a prepreg other than the UD prepreg. For example, the prepreg sheet may include woven fiber.
The prepreg sheet includes fiber and a resin. The resin is also referred to as a matrix resin. Typically, the fiber is carbon fiber. Typically, the matrix resin is a thermosetting resin.
The shaft 6 is manufactured by a so-called sheetwinding method. In the prepreg, the matrix resin is in a semi-cured state. The shaft 6 is formed by winding and curing prepreg sheets.
The matrix resin used for the prepreg sheet can be an epoxy resin, or a thermosetting resin or thermoplastic resin other than epoxy resins. From the viewpoint of shaft strength, epoxy resins are preferably the matrix resin.
A method for manufacturing the shaft 6 is not limited. From the viewpoint of weight reduction and the degree of freedom for design, a shaft manufactured by a sheetwinding method is preferable. The material of the shaft 6 is not limited. The shaft 6 may be a steel shaft, for example.
The shaft 6 is configured of a plurality of sheets. The shaft 6 is configured of eleven sheets from a first sheet s1 to an eleventh sheet s11. The development view illustrated in
In
The development view illustrates the order of winding the sheets as well as the disposition of the sheets in the axial direction of the shaft (shaft axial direction). For example in
In the present application, the term “layer” and the term “sheet” are used. The “layer” is wound, and the term “sheet” is not wound. A “layer” is formed by winding a “sheet”. That is, a wound “sheet” forms a “layer”. Moreover, in the present application, the same reference numerals and signs are used for the layer and the sheet. For example, a layer formed of the sheet s1 is a layer s1.
The shaft 6 includes a straight layer, a bias layer, and a hoop layer. In the development view of the present application, an orientation angle Af of fiber is denoted in the sheets. The orientation angle Af is an angle with respect to the shaft axial direction.
The sheet having the notation “0 degree” configures the straight layer. The sheet for the straight layer is also referred tows a straight sheet in the present application.
The straight layer is a layer that the fiber orientation is substantially at an angle of 0 degree with respect to the shaft axial direction. Because of errors, for example, in winding, the fiber orientation may not be 0 degree perfectly with respect to the shaft axial direction. Generally, in the straight layer, an absolute angle θa is equal to or less than 10 degrees.
It is noted that the absolute angle θa means the absolute value of the orientation angle Af. For example, the phrase that the absolute angle θa is equal to or less than 10 degrees means that the angle Af is −10 degrees or greater and +10 degrees or less.
In the embodiment in
The bias layer has high correlations with the torsional rigidity and torsional strength of the shaft. Preferably, the bias sheet includes a pair of two sheets that the fiber orientations are inclined in the opposite directions with each other. From the viewpoint of torsional rigidity, the absolute angle θa of the bias layer is preferably equal to or greater than 15 degrees, more preferably equal to or greater than 25 degrees, and still more preferably equal to or greater than 40 degrees. From the viewpoint of torsional rigidity and flexural rigidity, the absolute angle θa of the bias layer is preferably equal to or less than 60 degrees, and more preferably equal to or less than 50 degrees.
In the shaft 6, the sheets configuring the bias layer are the second sheet s2 and the third sheet s3. As discussed above, in
In
In the shaft 6, the sheet configuring the hoop layer is the eighth sheet s8. Preferably, the absolute angle θa in the hoop layer is set substantially at 90 degrees with respect to the shaft axis. However, because of errors, for example, in winding, the fiber orientation may not be 90 degrees perfectly with respect to the shaft axial direction. Generally, in the hoop layer, the absolute angle θa is 80 degrees or greater and 90 degrees or less. In the present application, the prepreg sheet for the hoop layer is also referred to as a hoop sheet.
The number of layers formed of a single sheet is not limited. For example, if the number of sheet ply is 1, this sheet is wound once in the circumferential direction. If the number of sheet ply is 1, this sheet forms a single layer at all the positions in the circumferential direction of the shaft.
For example, if the number of sheet ply is 2, this sheet is wound twice in the circumferential direction. If the number of sheet ply is 2, this sheet forms two layers at all the positions in the circumferential direction of the shaft.
For example, if the number of sheet ply is 1.5, this sheet is wound 1.5 times in the circumferential direction. If the number of sheet ply is 1.5, this sheet forms a single layer at positions in the circumferential direction at angles of 0 to 180 degrees and forms two layers at positions in the circumferential direction at angles of 180 degrees to 360 degrees.
As described above, in the present application, the sheets and the layers are classified based on the orientation angle of fiber. Moreover, in the present application, the sheets and the layers are classified based on the length in the shaft axial direction.
In the present application, the layer disposed over the entire length in the shaft axial direction is referred to as a full length layer. In the present application, the sheet disposed over the entire length in the shaft axial direction is referred to as a full length sheet. A wound full length sheet forms a full length layer.
In the present application, the layer partially disposed in the shaft axial direction is referred to as a partial layer.
In the present application, the sheet partially disposed in the shaft axial direction is referred to as a partial sheet. A wound partial sheet forms a partial layer.
In the present application, the full length layer that is a straight layer is referred to as a full length straight layer. In the embodiment in
In the present application, the full length layer that is a hoop layer is referred to as a full length hoop layer. In the embodiment in
In the present application, the partial layer that is a straight layer is referred to as a partial straight layer. In the embodiment in
The partial straight sheets are the sheet s1, the sheet s4, the sheet s5, the sheet s10, and the sheet s11.
In the present application, the partial layer that is a hoop layer is referred to as a partial hoop layer. The embodiment in
In the present application, the term “butt partial layer” is used. Preferably, the butt partial layer is a layer which reaches the butt end Bt, but does not reach the tip end Tp. Examples of the butt partial layer include a butt straight layer and a butt hoop layer. In the embodiment in
In the present application, the term “tip partial layer” is used. Preferably, the tip partial layer is a layer which reaches the tip end Tp, but does not reach the butt end Bt. Examples of the tip partial layer include a tip straight layer. In the embodiment in
The shaft 6 is prepared by the sheetwinding method using the sheets illustrated in
The sheetwinding method is excellent in the degree of freedom for design. By the method, weight distribution of the shaft 6 can be easily adjusted. By the method, the inertia moments Isw, Ige, Ic, and the like can be adjusted.
Examples of methods for adjusting the inertia moments include (A1) to (A9) below.
In the present application, the club weight is defined as Wc (kg), the head weight is defined as Wh (kg), the shaft weight is defined as Ws (kg), and the grip weight is defined as Wg (kg).
In the embodiment, the inertia moments (the moments of inertia) below are considered. The unit of these inertia moments is “kg·cm2”.
The club inertia moment Isw is an inertia moment about a swing axis Zx.
The club inertia moment Ige is a moment of inertia about a grip end. In more detail, the club inertia moment Ige is a moment of inertia about an axis Zy passed through the grip end.
In order to calculate the inertia moments using the parallel axis theorem, the inertia moments (the moments of inertia) below are used.
The following is the detail of the inertia moments (a) and (b).
[Club Inertia Moment Isw]
Isw is the inertia moment of the golf club 2. Isw is the inertia moment about the swing axis Zx.
As illustrated in
The inertia moment Isw (kg·cm2) is calculated by Equation (1) below. Equation (1) is based on the parallel axis theorem.
Isw=Wc×(Lc+60)2+Ic (1)
As illustrated in
The axis Zx is intersected at right angles with the axis Z1.
[Club Inertia Moment Ige]
Ige is the moment of inertia of the golf club 2. Ige is the moment of inertia about the grip end.
Ige is the moment of inertia about the axis Zy. The axis Zy is passed through the grip end of the golf club 2. The axis Zy is parallel to the axis Zx and the axis Zc. The axis Zy is perpendicular to the shaft axis Z1. The axis Zy is intersected at right angles with the axis Z1.
The inertia moment Ige (kg·cm2) is calculated by Equation (2) below. Equation (2) is based on the parallel axis theorem.
Ige=Wc×(Lc)2+Ic (2)
Conventionally, a swing balance (a club balance) is known as an index of the ease of a swing. However, the swing balance is a static moment, and not a dynamic index.
A swing is dynamic. A dynamic index can accurately reflect the ease of a swing. For the dynamic index of the ease of a swing, the inertia moment Isw about the swing axis can be used.
Furthermore, in the present embodiment, the inertia moment Ige is used in addition to the inertia moment Isw.
In actual swings, a wrist cock occurs. The wrist cock is maintained in the early stage of a downswing. The wrist cock is gradually released as an impact approaches.
In the actual swings, the rotation center of the swing is the body of a golf player. When the wrist cock is kept, the golf club 2 is passed close to the body. In other words, when the wrist cock is kept, the golf club 2 is passed close to the rotation center. An effective club inertia moment about the swing axis can depend on the degree of the wrist cock. In order to maximize a head speed, it is preferable to consider the influence of the wrist cock.
A swing simulation was used in order to confirm the influence of the wrist cock. A two-link rigid body model was used for the simulation.
The two-link model includes a first link L1, a second link L2, a joint J1, and a joint J2. The first link L1 is a rigid body. The second link L2 is a rigid body.
One end of the first link L1 is connected to the joint J1. The other end of the first link L1 is connected to the joint J2. One end of the second link L2 is connected to the joint J2. The other end of the second link L2 is a free end.
The first link L1 corresponds to an arm. The second link L2 corresponds to a golf club. The joint J1 corresponds to a shoulder joint. The joint J2 corresponds to a wrist joint. The speed of the free end of the second link L2 is a head speed.
An angle θ1 between the first link L1 and the second link L2 corresponds to the angle of the wrist cock. In a state where the wrist cock is kept, the angle θ1 is small. The release of the wrist cock is started before the impact.
The angle θ1 is gradually increased by the release of the wrist cock. Usually, in the impact, the angle θ1 is close to 180 degrees.
The degree of the wrist cock depends on the golf player. For example, the degree of the wrist cock in a golf player having great strength is greatly different from the degree of the wrist cock in a golf player having small strength. The capability of the release (release capability) of the wrist cock also depends on the golf player. From these viewpoints, the golf player is classified into four types. The four types are types 1 to 4. The golf player of the type 1 has a very low head speed.
The golf player of the type 2 has a low head speed. The golf player of the type 3 has a slightly high head speed. The golf player of the type 4 has a high head speed.
Generally, as the head weight Wh is larger, an increase in a ball speed is anticipated. Meanwhile, as the head weight Wh is larger, the center of gravity Gc moves to the head 4 side; the inertia moment Ige is increased; and it becomes difficult to swing the golf club. For this reason, generally, a golf club having a small inertia moment Ige is suitable for the golf player having small strength, and a golf club having a large inertia moment Ige is suitable for the golf player having great strength. That is, the skill of the golf player can be defined based on the size of a suitable inertia moment Ige. The golf player of the type 2 is a golf player suitable for a golf club having an inertia moment Ige of 2820 (kg·cm2) or greater and less than 2870 (kg·cm2), and corresponds to the golf player having the low head speed.
Before the simulation, seven golf players belonging to the type 2 executed a trial hit. In the trial hit, a test club suitable for the test golf player of the type 2 was used. A sensor was attached to the grip end of the test club. The sensor included a three-dimensional acceleration sensor and a three-dimensional angular velocity sensor. Information from the sensor (sensor information) was obtained by the trial hit.
In the simulation, inverse dynamics analysis was performed using the sensor information and the specifications of the test club (weight, position of the center of gravity, moment of inertia, club length). A shoulder torque T1 and a wrist torque T2 were calculated by the inverse dynamics analysis. The shoulder torque T1 is a torque exhibited about the shoulder in the trial hit. The wrist torque T2 is a torque exhibited about the wrist in the trial hit.
Next, forward dynamics analysis was performed using the specifications of the club to be verified, the shoulder torque T1, and the wrist torque T2. In the forward dynamics analysis, the specifications of the club to be verified were applied to the second link L2. In the forward dynamics analysis, the shoulder torque T1 was applied to the joint J1, and the wrist torque T2 was applied to the joint J2. As a result of the forward dynamics analysis, a swing model of the golf player of the type 2 was obtained. A head speed in the impact was calculated by the swing model.
Next, the head speed was verified using the swing model. In order to perform the verification, a plurality of club specifications were set. A head speed in each of the club specifications was calculated by the simulation.
In
In the simulation of
A head speed in each of the club specifications was calculated for each of swing data of the seven golf players.
A contour drawing of the obtained head speeds is shown in
A contour line as a reference value is shown by a thick solid line. The contour lines are drawn at intervals of every 0.1 m/s. The upper-left-most contour line has a head speed smaller by 0.5 m/s than the reference value. The lower-right-most contour line has a head speed greater by 0.4 m/s than the reference value. As shown in the contour drawing, the head speed is increased toward the lower right.
In other words, as the inertia moment Ige is larger and the inertia moment Isw is smaller, the head speed is larger.
This shows the effectiveness of setting Isw/Ige to be equal to or less than a predetermined value.
The result shown in
The result shown in
In
In the actual swings, the golf club is not rotated about the grip end. The golf club is rotated about the body of a golf player together with the arms of the golf player. In the present application, the swing axis Zx is set in consideration of the actual swings. The swing axis is apart from the grip end. In order to evaluate the ease of a dynamic swing, a spacing Dx between the swing axis Zx and the grip end is set (see
A swing is dynamic. As compared with the static index, the dynamic index tends to reflect the ease of a swing. Moreover, as described above, the actual conditions of swings are considered for the inertia moment Isw. Therefore, the inertia moment Isw accurately reflects the ease of a swing.
Meanwhile, in the actual swings, the wrist cock occurs. The wrist cock is rotation of the club about the grip end. Therefore, the wrist cock has a high correlation with the club inertia moment Ige.
As described above, in the actual swings, the club is passed closer to the body as the wrist cock is kept. That is, the club is passed closer to the body as the angle θ1 is smaller. Therefore, in the actual swings, the effective club inertia moment tends to be smaller as the wrist cock is kept. The moment of inertia about the swing axis considering the wrist cock is also referred to as the effective swing MI.
As described above, in a state where the wrist cock is maintained, the effective swing MI is small. Therefore, in this case, the head speed is likely to be increased. However, in order to achieve a square impact, it is necessary to release the wrist cock. This is because the face is opened in the impact while the wrist cock is maintained. Release timing affects the head speed.
The release of the wrist cock increases the relative speed of the head to the wrist. The suitable release can contribute to an improvement in the head speed. Ideally, it is preferable that the wrist cock is sufficiently kept, and the wrist cock is released at once just before the impact. For example, from the viewpoint of the improvement in the head speed in two swings shown by a solid line and a dashed line in
Thus, the degree of the wrist cock and the release timing of the wrist cock affect the head speed. As described above, the degree of the wrist cock and the degree of the release depend on the golf player. Conditions for optimizing the head speed are set for every type of the golf player. In the golf player of the type 2 suitable for the club satisfying (B) below, the head speed can be improved when (A) and (B) below are satisfied. In the golf player of the type 2, the wrist cock can be kept and the suitable release can also be achieved when (A) and (B) are satisfied. Therefore, the head speed is increased.
Isw/Ige≦2.42 (A)
2820≦Ige<2870 (B)
A region S1 satisfying the above conditions (A) and (B) in the Ige-Isw plane can be expressed as shown in
The region S2 is a region satisfying a condition of (C) below in addition to (A) and (B) above. The region S3 is a region satisfying a condition of (D) below in addition to (B) above.
Isw≧6824.4 (C)
Isw<6824.4 (D)
Even if Isw is the same or larger in the region S2, the cock causes a decrease in the effective swing MI. In the region S3, Isw is decreased, and the cock causes a decrease in the effective swing MI.
Since an effect provided by the decrease in the effective swing MI is large in the region S2, the head speed can be improved even if Isw is large. In the region S3, the head speed can be further improved.
Thus, even if both Ige and Isw are increased by an increase in the head weight, a swing keeping the cock can be achieved. Therefore, the effective swing MI can be decreased, and the head speed can be improved.
When the head weight is increased, a rebound performance can be improved. However, the head speed may be reduced. In the present embodiment, by the increase in the head weight, the inertia moment Ige is increased, and the wrist cock is likely to be maintained. The effective swing MI can be reduced by maintaining the wrist cock. Therefore, even if the head weight is increased, the head speed can be improved. By appropriately setting the ratio between Isw and Ige, the head speed can be improved while the head weight can be increased.
The axis Zc shown in
The axis Zy shown in
In the present application, a reference state (not illustrated) is defined. The reference state is a state in which the club 2 is placed on a horizontal plane at a specified lie angle and a real loft angle. In the reference state, the shaft axis Z1 is included in a plane VP1 perpendicular to the horizontal plane. The plane VP1 is defined as a reference vertical plane. The specified lie angle and real loft angle are described on product catalogs, for example. As apparent from
The axis Zy is included in the reference vertical plane. That is, in the measurement of the inertia moment Ige, the swing axis Zy is included in the reference vertical plane.
It is assumed that the center of gravity Gc of the club is located on the shaft axis Z1. Because of the position of the center of gravity of the head, the real center of gravity of the club is slightly deviated from the shaft axis Z1. The real center of gravity of the club can be located in a space, for example. In the present application, it is assumed that a point on the axis Z1 closest to the real center of gravity of the club is the center of gravity Gc of the club described above. In other words, the center of gravity Gc of the club in the present application is an intersection point between the axis Z1 and a perpendicular line from the real center of gravity of the club to the axis Z1. The approximation of the position of the center of gravity of the club gives a slight difference to the value of Isw and Ige. However, the difference is so small that the difference does not affect the effects described in the present application.
From the viewpoint of the ease of a swing, the inertia moment Isw is preferably equal to or less than 6950 (kg·cm2), more preferably equal to or less than 6900 (kg·cm2), still more preferably equal to or less than 6890 (kg·cm2), yet still more preferably equal to or less than 6880 (kg·cm2), yet still more preferably equal to or less than 6870 (kg·cm2), yet still more preferably equal to or less than 6860 (kg·cm2), and yet still more preferably equal to or less than 6850 (kg·cm2). From the viewpoint of suppressing an excessively small head weight Wh, the inertia moment Isw is preferably equal to or greater than 6300 (kg·cm2), and more preferably equal to or greater than 6350 (kg·cm2).
As described above, in the golf player of the type 2, the inertia moment Ige is preferably equal to or greater than 2820 (kg·cm2). From the viewpoint of promoting the wrist cock to reduce the effective swing MI, the inertia moment Ige is equal to or greater than 2830 (kg·cm2). As described above, the inertia moment Ige for the golf player of the type 2 is preferably less than 2870 (kg·cm2). From the viewpoint of suitable release of the wrist cock, the inertia moment Ige is preferably equal to or less than 2865 (kg·cm2), and more preferably equal to or less than 2860 (kg·cm2).
As described above, by considering a ratio (Isw/Ige), the ease of a swing is achieved, and an appropriate wrist cock is achieved. The appropriate wrist cock can decrease the effective swing MI and increase the head speed. The increase in the head weight increases Ige. The appropriate increase in Ige promotes the wrist cock, and increases the head speed. By considering the wrist cock and the effective swing MI, the increase in the head speed can be achieved even if the head weight is increased. From this viewpoint, Isw/Ige is preferably equal to or less than 2.42.
Excessive Ige may cause insufficient release of the wrist cock. From this viewpoint, Isw/Ige is equal to or greater than 2.40. The contour drawing (Isw/Ige) shown in
In the present embodiment, the inertia moment Isw is considered. The inertia moment Isw is a dynamic index. The substance of a swing is reflected in the inertia moment Isw.
Furthermore, in the present embodiment, Isw/Ige is set to be equal to or less than a predetermined value. The inertia moment Ige increases the wrist cock. The inertia moment Isw is a dynamic index which can optimize the ease of a swing. To a greater or lesser extent, the actual swings involve the wrist cock. The characteristic of the swing is more correctly reflected by considering both the inertia moment Isw and the inertia moment Ige. The wrist cock is promoted by increasing the inertia moment Ige, and the inertia moment Isw is suppressed, and thereby the ease of a swing can be increased while the effective swing MI can be decreased.
A swing weight (club balance) is generally used as the index of the ease of a swing. When the head weight Wh is increased, the swing weight tends to be increased. For this reason, a reduction in the swing weight has been considered as in a reduction in the head weight Wh. There has been known a technical thought that the ease of a swing and the reduction in the head weight Wh are linked. The technical thought has been common for the person skilled in the art.
Meanwhile, in the present embodiment, even if the head weight Wh is increased, the head speed can be increased. This is achieved by the optimization of the wrist cock. When the head weight is increased, the swing weight is increased, but the wrist cock is promoted. The effective swing MI is decreased by maintaining the wrist cock, and the head speed can be increased. In the present embodiment, Isw/Ige is optimized. The degree of the wrist cock intercorrelates with the inertia moment Ige. The suitable wrist cock is obtained by making Isw/Ige proper, and the head speed can be improved.
[Head Weight Wh]
Even if the head weight Wh is increased, the head speed can be improved by considering Isw/Ige as described above. The optimization of Isw/Ige is achieved by not only the increase in the head weight Wh but also the reduction in the shaft weight Ws or grip weight Wg described later, for example.
The initial velocity of a ball is increased by the increase in the head weight Wh. From these viewpoints, the head weight Wh is preferably equal to or greater than 194 g (0.194 kg), more preferably equal to or greater than 195 g (0.195 kg), and still more preferably equal to or greater than 196 g (0.196 kg). From the viewpoint of the release capability of the golf player of the type 2, the head weight Wh is preferably equal to or less than 210 g (0.210 kg), more preferably equal to or less than 205 g (0.205 kg), and still more preferably equal to or less than 200 g (0.200 kg).
[Shaft Weight Ws]
From the viewpoint of the strength and durability of the shaft, the shaft weight Ws is preferably equal to or greater than 30 g (0.030 kg), more preferably equal to or greater than 32 g (0.032 kg), and still more preferably equal to or greater than 34 g (0.034 kg). From the viewpoint of the ease of a swing, the shaft weight Ws is preferably equal to or less than 50 g (0.050 kg), more preferably equal to or less than 48 g (0.048 kg), and still more preferably equal to or less than 46 g (0.046 kg).
[Grip Weight Wg]
From the viewpoint of achieving appropriate Isw, the grip weight is preferably equal to or less than 37 g (0.037 kg), more preferably equal to or less than 36 g (0.036 kg), still more preferably equal to or less than 35 g (0.035 kg), yet still more preferably equal to or less than 34 g (0.034 kg), yet still more preferably equal to or less than 33 g (0.033 kg), yet still more preferably equal to or less than 32 g (0.032 kg), yet still more preferably equal to or less than 31 g (0.031 kg), yet still more preferably equal to or less than 30 g (0.030 kg), yet still more preferably equal to or less than 29 g (0.029 kg), yet still more preferably equal to or less than 28 g (0.028 kg), yet still more preferably equal to or less than 27 g (0.027 kg), yet still more preferably equal to or less than 26 g (0.026 kg), and yet still more preferably equal to or less than 25 g (0.025 kg).
From the viewpoint of the strength and durability of the grip, the grip weight Wg is preferably equal to or greater than 15 g (0.015 kg), more preferably equal to or greater than 18 g (0.018 kg), and still more preferably equal to or greater than 20 g (0.020 kg).
The grip weight Wg can be adjusted by the volume of the grip, the specific gravity of rubber, the use of foamed rubber, and so on. The grip weight Wg may be adjusted by combining foamed rubber with non-foamed rubber.
[Shaft Length Lf2]
From the viewpoint of improving the head speed by increasing the rotation radius of a swing, the shaft length Lf2 is preferably equal to or greater than 99 cm, more preferably equal to or greater than 105 cm, still more preferably equal to or greater than 107 cm, and yet more preferably equal to or greater than 110 cm. From the viewpoint of suppressing variation in points to hit, the shaft length Lf2 is preferably equal to or less than 120 cm, more preferably equal to or less than 118 cm, and still more preferably equal to or less than 116 cm.
[Distance Lf1]
The center of gravity Gs of the shaft comes close to the butt end Bt, and a more weight can be distributed to the head. From this viewpoint, the distance Lf1 (see
[Lf1/Lf2]
From the viewpoint of increasing weight distribution to the head to promote the wrist cock, Lf1/Lf2 is preferably equal to or greater than 0.53, more preferably equal to or greater than 0.55, still more preferably equal to or greater than 0.56, and yet still more preferably equal to or greater than 0.57. From the viewpoint of improving the strength of the tip end part of the shaft, Lf1/Lf2 is preferably equal to or less than 0.67, more preferably equal to or less than 0.66, and still more preferably equal to or less than 0.65.
[Club Length L]
From the viewpoint of improving the head speed, the club length L is preferably equal to or greater than 43 inches, more preferably equal to or greater than 44 inches, still more preferably equal to or greater than 45 inches, yet still more preferably equal to or greater than 45.2 inches, yet still more preferably equal to or greater than 45.3 inches, and yet still more preferably equal to or greater than 45.4 inches. From the viewpoint of suppressing variation in points to hit, the club length L is preferably equal to or less than 48 inches, more preferably equal to or less than 47 inches, still more preferably equal to or less than 46.5 inches, and yet still more preferably equal to or less than 46 inches.
The club length L in the present application is measured based on the golf rule of “1c. Length” in “1. Clubs” of “Appendix II. Design of Clubs”, defined by R&A (Royal and Ancient Golf Club of Saint Andrews).
It is a driver that particular importance is placed on the flight distance performance. From this viewpoint, preferably, the club 2 is a driver. From the viewpoint of the flight distance performance, the real loft is preferably equal to or greater than 7 degrees, and preferably equal to or less than 15 degrees. From the viewpoint of enlarging a high restitution area, the volume of the head is preferably equal to or greater than 350 cc, more preferably equal to or greater than 380 cc, still more preferably equal to or greater than 400 cc, and yet still more preferably equal to or greater than 420 cc. From the viewpoint of the strength of the head, the volume of the head is preferably equal to or less than 470 cc.
[Club Weight Wc]
From the viewpoint of the ease of a swing, the club weight Wc is preferably equal to or less than 300 g (0.300 kg), more preferably equal to or less than 295 g (0.295 kg), still more preferably equal to or less than 290 g (0.290 kg), yet more preferably equal to or less than 285 g (0.285 kg), still yet more preferably equal to or less than 280 g (0.280 kg), and still more preferably equal to or less than 275 g (0.275 kg). In consideration of the strength of the grip, the shaft, and the head, the club weight We is preferably equal to or greater than 230 g (0.230 kg), more preferably equal to or greater than 240 g (0.240 kg), still more preferably equal to or greater than 245 g (0.245 kg), and yet more preferably equal to or greater than 250 g (0.250 kg).
[Wh/Wc]
From the viewpoint of the promotion of the wrist cock, a ratio (Wh/Wc) is preferably greater. A rebound performance is improved by the increase in the head weight Wh. From the viewpoint of the promotion of the wrist cock and the rebound performance, Wh/Wc is preferably equal to or greater than 0.72, and more preferably equal to or greater than 0.725. In consideration of the strength of the shaft and the like, the head weight is preferably equal to or less than a predetermined value. From this viewpoint, Wh/Wc is equal to or less than 0.80.
In order to increase the flight distance, the increase in the ball speed is important. To achieve this, it is effective to improve the head speed and also increase the head weight. It is considered to decrease the inertia moments Isw and Ige in order to achieve the former. However, to achieve decreasing the inertia moments Isw and Ige, the head weight is preferably smaller. Therefore, the two approaches for increasing the flight distance are generally in a trade-off relation. Conventionally, it was difficult to achieve both the approaches.
As is apparent from Equations (1) and (2) above, when the inertia moment Ige is increased, the inertia moment Isw is also inevitably increased along with the increase in the inertia moment Ige. However, even if the inertia moment Ige is increased, the present inventors have found that the head speed can be rather improved if the increment of the inertia moment Isw to the increment of the inertia moment Ige is equal to or less than a predetermined value, as a result of the simulation shown in
Isw/Ige≦2.42 may be set for the golf player of the type 2 suitable for 2820 (kg·cm2)≦Ige<2870 (kg·cm2). The combination of the inertia moments Isw and Ige satisfying the above conditions is selected, and thereby the head speed can be improved while the head weight can be maintained. Therefore, from the viewpoints of both the head weight and the head speed, it is possible to apply a large kinetic energy to the ball. Therefore, the flight distance can be increased.
In the following, the effects of the present invention will be clarified by examples. However, the present invention should not be interpreted in a limited way based on the description of the examples.
Table 1 shows examples of prepregs usable for the shaft according to the present invention,
A shaft in a stack configuration the same as the configuration of the shaft 6 was prepared. That is, a shaft in the configuration of the sheets illustrated in
The obtained shaft was attached with a commercially available driver head (XXIO 8 made by DUNLOP SPORTS CO. LTD.: a loft angle of 10.5 degrees) and a grip, and a golf club according to example 1 was obtained. Table 2 shows the specifications and evaluation result of example 1.
Shafts and golf clubs according to examples and comparative examples were obtained in the same way as example 1 except the specifications shown in Table 2 below.
In these examples and comparative examples, the head weight Wh was adjusted by polishing the outer surface of the head and using an adhesive. The adhesive was applied to the inner surface of the head. The adhesive is a thermoplastic adhesive, fixed to a predetermined position on the inner surface of the head at room temperature, and flows at high temperature. While the temperature of the adhesive was set at high temperature, the adhesive was poured into the head, and then cooled at ambient temperature for fixing. The adhesive was disposed so as not to change the position of the center of gravity of the head.
In the examples and comparative examples, the grip weight Wg was adjusted by the material and volume of the grip. Foamed rubber was used for the grip. The specific gravity of the grip was adjusted by a foaming rate.
In order to obtain a desired inertia moment Isw and inertia moment Ige, the specifications of the shaft were adjusted by the above-mentioned items (A1) to (A9) if needed.
[Evaluation Method]
[Moments of Inertia]
The inertia moment Isw was calculated by Equation (1) described above. The inertia moment Ige was calculated by Equation (2) described above. The club inertia moment Ic was measured using MODEL NUMBER RK/005-002 made by INERTIA DYNAMICS Inc. The calculated values are shown in Table 2.
[Head Speed, Ball Initial Velocity]
Five testers belonging to the type 2 conducted the evaluation. Each tester hit a ball with each club for ten times. Therefore, hits were made for 50 times for each of the clubs in total. In the hits, the head speed in impact and the ball initial velocity were measured. The mean values of 50 items of data are shown in Table 2 above.
An angle θ1 when cock is released is a cock angle θ1 when the release of the cook is started. The values shown in Table 2 are differences with comparative example 1. It is shown that as the value is smaller, the cock is greater.
For example, the values in examples 1 and 2 are smaller than the value in comparative example 1. It is found that the cock is greater in examples 1 and 2 as compared with comparative example 1.
The head speeds and ball speeds in examples 1 to 3 were greater than the head speeds and ball speeds in comparative examples 1 and 2. As shown in the evaluated results, the superiority of the present invention is apparent.
The method described above is applicable to golf clubs.
The description above is merely an example, and can be variously modified within the scope not deviating from the principles of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-184672 | Sep 2014 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 7326125 | Moriyama | Feb 2008 | B2 |
| 8241139 | Brekke | Aug 2012 | B2 |
| 8328656 | Rice | Dec 2012 | B2 |
| 20020142855 | Cook | Oct 2002 | A1 |
| 20130095945 | Nakamura | Apr 2013 | A1 |
| 20140155190 | Nakamura | Jun 2014 | A1 |
| 20150018114 | Stokke | Jan 2015 | A1 |
| 20150087435 | Nakamura | Mar 2015 | A1 |
| Number | Date | Country |
|---|---|---|
| 2004-201911 | Jul 2004 | JP |
| 2014-131624 | Jul 2014 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20160067564 A1 | Mar 2016 | US |
